Sample records for characteristic diffusion length

  1. Characteristic length of glass transition

    NASA Astrophysics Data System (ADS)

    Donth, E.

    1996-03-01

    The characteristic length of the glass transition (? _? ) is based on the concept of cooperatively rearranging regions (CRR's) by Adam & Gibbs (1965): ? _? is the diameter of one CRR. In the theoretical part of the talk a formula is derived how this length can be calculated from calorimetric data of the transformation interval. The approach is based on fluctuations in natural functional subsystems. The corresponding thermodynamics is represented e.g. in a book of the author (E. Donth, Relaxation and Thermodynamics in Polymers. Glass Transition, Akademie-Verlag, Berlin 1992). A typical value for this length is 3 nanometers. In the experimental part several examples are reported to enlarge the experimental evidence for such a length: Squeezing the glass transition in the amorphous layers of partially crystallized PET (C. Schick, Rostock), glass transition of small-molecule glass formers in a series of nanoscaled pores of porous glasses (F. Kremer, Leipzig), comparison with a concentration fluctuation model in homogeneous polymer mixtures (E.W. Fischer, Mainz), and, from our laboratory, backscaling to ? _? across the main transition from the entanglement spacing in several amorphous polymers such as PVAC, PS, NR, and some polymer networks. Rouse backscaling was possible in the ? ? splitting region of several poly(n alkyl methacrylates) resulting in small characteristic lengths of order 1 nanometer near the onset of ? cooperativity. In a speculative outlook a dynamic density pattern is presented, having a cellular structure with higher density and lower mobility of the cell walls. It will be explained, with the aid of different thermal expansion of wall and clusters, how the clusters within the cells maintain a certain mobility far below the glass temperature.

  2. 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

  3. Diffusion lengths in amphoteric GaAs heteroface solar cells

    NASA Technical Reports Server (NTRS)

    Ashley, K. L.; Beal, S. W.

    1978-01-01

    Minority-carrier diffusion lengths in amphoteric GaAs:Si were investigated. Electron and hole diffusion lengths in p- and n-type, respectively, were determined to be 13 microns and 7 microns. Preliminary efficiency measurements on heteroface structures based on amphoteric GaAs:Si p-n junctions indicated that these devices should make excellent solar cells.

  4. 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 ?m 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.

  5. Diffusion lengths of silicon solar cells from luminescence images

    SciTech Connect

    Wuerfel, P.; Trupke, T.; Puzzer, T.; Schaeffer, E.; Warta, W.; Glunz, S. W. [Centre of Excellence for Advanced Silicon Photovoltaics and Photonics, University of New South Wales, Sydney, NSW 2052 (Australia); Fraunhofer Institut fuer Solare Energiesysteme, Heidenhofstrasse 2, Freiburg 79110 (Germany)

    2007-06-15

    A method for spatially resolved measurement of the minority carrier diffusion length in silicon wafers and in silicon solar cells is introduced. The method, which is based on measuring the ratio of two luminescence images taken with two different spectral filters, is applicable, in principle, to both photoluminescence and electroluminescence measurements and is demonstrated experimentally by electroluminescence measurements on a multicrystalline silicon solar cell. Good agreement is observed with the diffusion length distribution obtained from a spectrally resolved light beam induced current map. In contrast to the determination of diffusion lengths from one single luminescence image, the method proposed here gives absolute values of the diffusion length and, in comparison, it is much less sensitive to lateral voltage variations across the cell area as caused by local variations of the series resistance. It is also shown that measuring the ratio of two luminescence images allows distinguishing shunts or surface defects from bulk defects.

  6. Measuring spin diffusion length using spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Kannan, Harsha; Fan, Xin; Xiao, John

    2014-03-01

    Ever since its discovery, spin Seebeck effect (SSE) has attracted plenty of attention. The conversion from thermal gradient to spin current has shown great potential in thermal energy harvesting. SSE can also be utilized as a source to generate pure spin current to unveil new physics. Here we show that it is possible to measure spin diffusion length of a heavy metal Pt by studying the SSE as a function of Pt layer thickness. The SSE signal first increases, peaks, and then decreases with increasing Pt layer thickness. By fitting with a drift-diffusion model, we obtain the spin diffusion length of Pt to be about 2nm, close to that obtained from other techniques. Moreover, we can insert a thin layer of Cu in order to remove the possible proximity effect. Similar spin-diffusion length is obtained from this measurement.

  7. Dynamic, In Situ Measurement of Sea-Ice Characteristic Length

    E-print Network

    Fox, Colin

    1 Dynamic, In Situ Measurement of Sea-Ice Characteristic Length Colin Fox Mathematics Department, Auckland, New Zealand Abstract­ We present a method for measuring the char- acteristic length of sea ice a range of localized measurements. The method is used to detemine the characteristic length of the sea ice

  8. Measurement of Micrometer Diffusion Lengths by Nuclear Spectrometry

    SciTech Connect

    Strokan, N.B.; Ivanov, A.M.; Lebedev, A.A. [Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 (Russian Federation); Syvaejaervi, M.; Yakimova, R. [Linkoeping University, S-581 83 Linkoeping (Sweden)

    2005-12-15

    A method for determination of diffusion lengths in the range 0.5-50 {mu}m, which corresponds to carrier lifetimes in the nanosecond range, is suggested A calibrated nonequilibrium charge is injected into the base of the reverse-biased diode structure. The injection is provided by alpha particles generated by natural decay in the single-particle counting mode. The nuclear spectrometry technique is used to measure the amount of charge that diffused across the base to the boundary of the electric-field region. The loss of charge during the diffusion is calculated as a function of the depth of alpha particle penetration beyond the electric-field region. The derived power-law functions make it possible to relate the diffusion length with the exponent and numerical factor that describes the loss of charge. The experiment is performed with lightly doped 4H-SiC epitaxial films.

  9. Spin Hall angle in Pd below the spin diffusion length

    NASA Astrophysics Data System (ADS)

    Vlaminck, V.; Schultheiss, H.; Pearson, J.; Fradin, F.; Bader, S.; Hoffmann, A.; Mosendz, O.

    2011-03-01

    The spin-orbit coupling gives rise to an inter-conversion of spin and charge currents. A pure spin current is accompanied by a charge accumulation perpendicular to both the spin polarization and spin current, so-called inverse spin Hall effect (ISHE). We report measurements of the ISHE in a permalloy/palladium (Py/Pd) bilayer integrated with a coplanar wave-guide by pumping a pure spin current via ferromagnetic resonance (FMR). The magnetization precession creates a spin accumulation at the Py/Pd interface that diffuses into the normal metal and partially scatters back into the permalloy when the Pd thickness is smaller than the spin diffusion length. We observe an increasing broadening of the FMR linewidth with increasing thickness of Pd from which we extract the spin diffusion length in Pd and an average spin mixing conductance. The resultant pure spin current induces, in turn, a spin Hall voltage that is measured across the metallic layer. The spin Hall angle obtained from fitting the dc voltage remains fairly constant even for thickness smaller than the spin diffusion length. U.S. Department of Energy, contract No. DE-ACOZ-06CH11357.

  10. Beta Irradiation of Silicon Junction Devices: Effects on Diffusion Length

    Microsoft Academic Search

    L. C. Olsen

    1972-01-01

    The effects of electron irradiation on the minority carrier diffusion length in silicon devices has been studied by utilizing Pm-147 and Kr-85 beta sources. The beta spectra of Pm-147 and Kr-85 are characterized by maximum beta-particle energies of 230 and 670 kev, respectively. Short-circuit current for Li-doped p+n and n+p cells has been measured while the devices are continually irradiated.

  11. Enhanced exciton diffusion length via cooperative quantum transport

    NASA Astrophysics Data System (ADS)

    Mohseni, Masoud; Abasto, Damian; Lloyd, Seth; Zanardi, Paolo

    2011-03-01

    The energy transfer rate in biomolecular systems is typically calculated from the transition probability of an excitation hopping from one molecule to another using Förster energy transfer based on dipole-dipole interaction of individual molecules in the perturbative regime. However, due to strong interactions of among a group of molecules the excitation can become highly delocalized leading to an effective large dipole moment with an enhanced oscillator strength. Under certain symmetries, this could lead to an enhancement in exicton transfer rate via cooperative donation or acceptance of an excitation. Here, we explore this phenomenon in various multichromophoric geometries, under different symmetries, initial conditions, and dynamics. We study the behavior of the exciton diffusion length under the effects of disorders and environmental fluctuations and quantify the crossover from ballistic to diffusive regimes. Specifically, for a quasi-1 D array of rings containing N chromophores interacting with a bosonic bath, an interplay of time scales dictates the exciton dynamics. In the ``far-field'' regime, environmental interactions are dominating and the system properties are approaching those of the incoherent equilibrium Gibbs state. However, in the ``near-field'' the coherent interactions among dipole aggregates dominate other time scales and exciton diffusion length is enhanced by a factor of ?{ N } .

  12. Performance Characteristics of Plane-Wall Two-Dimensional Diffusers

    NASA Technical Reports Server (NTRS)

    Reid, Elliott G

    1953-01-01

    Experiments have been made at Stanford University to determine the performance characteristics of plane-wall, two-dimensional diffusers which were so proportioned as to insure reasonable approximation of two-dimensional flow. All of the diffusers had identical entrance cross sections and discharged directly into a large plenum chamber; the test program included wide variations of divergence angle and length. During all tests a dynamic pressure of 60 pounds per square foOt was maintained at the diffuser entrance and the boundary layer there was thin and fully turbulent. The most interesting flow characteristics observed were the occasional appearance of steady, unseparated, asymmetric flow - which was correlated with the boundary-layer coalescence - and the rapid deterioration of flow steadiness - which occurred as soon as the divergence angle for maximum static pressure recovery was exceeded. Pressure efficiency was found to be controlled almost exclusively by divergence angle, whereas static pressure recovery was markedly influenced by area ratio (or length) as well as divergence angle. Volumetric efficiency. diminished as area ratio increased, and at a greater rate with small lengths than with large ones. Large values of the static-pressure-recovery coefficient were attained only with long diffusers of large area ratio; under these conditions pressure efficiency was high and. volumetric efficiency low. Auxiliary tests with asymmetric diffusers demonstrated that longitudinal pressure gradient, rather than wall divergence angle, controlled flow separation. Others showed that the addition of even a short exit duct of uniform section augmented pressure recovery. Finally, it was found that the installation of a thin, central, longitudinal partition suppressed flow separation in short diffusers and thereby improved pressure recovery

  13. Study of minority carrier diffusion lengths in photoactive layers of multijunction solar cells

    SciTech Connect

    Mintairov, S. A., E-mail: mintairov@scell.ioffe.ru; Andreev, V. M.; Emelyanov, V. M.; Kalyuzhnyy, N. A.; Timoshina, N. K.; Shvarts, M. Z.; Lantratov, V. M. [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation)

    2010-08-15

    A technique for determining a minority carrier's diffusion length in photoactive III-V layers of solar cells by approximating their spectral characteristics is presented. Single-junction GaAs, Ge and multi-junction GaAs/Ge, GaInP/GaAs, and GaInP/GaInAs/Ge solar cells fabricated by hydride metal-organic vapor-phase epitaxy (H-MOVPE) have been studied. The dependences of the minority carrier diffusion length on the doping level of p-Ge and n-GaAs are determined. It is shown that the parameters of solid-state diffusion of phosphorus atoms to the p-Ge substrate from the n-GaInP nucleation layer are independent of the thickness of the latter within 35-300 nm. It is found that the diffusion length of subcells of multijunction structures in Ga(In)As layers is smaller in comparison with that of single-junction structures.

  14. 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., E-mail: ahny@ajou.ac.kr [Department of Physics and Division of Energy Systems Research, Ajou University, Suwon 443-749 (Korea, Republic of)

    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 ?m as compared to that of visible illumination measured at 90 ?m. 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.

  15. Effect of outlet diffusers on vortex amplifier characteristics

    Microsoft Academic Search

    S. A. MacGregor; N. Syred

    1982-01-01

    The outlet diffuser is shown to have a considerable effect on both the performance and characteristics of vortex amplifiers. The effect of conical and plate diffusers is compared. Vortex amplifiers fitted with conical diffusers exhibit characteristics with large amplitude oscillations and often large discontinuities, which makes them unacceptable for many applications. The use of plate diffusers tends to suppress the

  16. Vibration Modes and Characteristic Length Scales in Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Tanguy, Anne

    2015-06-01

    The numerical study of the mechanical responses of amorphous materials at the nanometer scale shows characteristic length scales that are larger than the intrinsic length of the microstructure. In this article, we review the different scales appearing upon athermal elastoplastic mechanical load and we relate it to a detailed study of the vibrational response. We compare different materials with different microstructures and different bond directionality (from Lennard-Jones model materials to amorphous silicon and silicate glasses). This work suggests experimental measurements that could help to understand and, if possible, to predict plastic deformation in glasses.

  17. Effects of venturi length on combustion characteristics on inshot burners

    SciTech Connect

    Rao, A.V.; Gollahalli, S.R. [Univ. of Oklahoma, Norman, OK (United States). School of Aerospace and Mechanical Engineering

    1996-12-31

    An experimental study of the changes caused in the flame structure and pollutant emission characteristics by the modifications of the primary-air venturi of an inshot burner used in residential natural gas furnaces is presented. The venturi modification examined in this study are the shape of the venturi inlet, and the venturi length. Modified venturi with curved inlets produce higher primary-air entrainment and slightly smaller (by 5 to 10%) emission indices of NOx and CO than the standard parallel side venturi. However, the changes in the venturi length for the modified geometry do not result in significant further changes.

  18. Gate control of the electron spin-diffusion length in semiconductor quantum wells

    PubMed Central

    Wang, G.; Liu, B. L.; Balocchi, A.; Renucci, P.; Zhu, C. R.; Amand, T.; Fontaine, C.; Marie, X.

    2013-01-01

    The spin diffusion length is a key parameter to describe the transport properties of spin polarized electrons in solids. Electrical spin injection in semiconductor structures, a major issue in spintronics, critically depends on this spin diffusion length. Gate control of the spin diffusion length could be of great importance for the operation of devices based on the electric field manipulation and transport of electron spin. Here we demonstrate that the spin diffusion length in a GaAs quantum well can be electrically controlled. Through the measurement of the spin diffusion coefficient by spin grating spectroscopy and of the spin relaxation time by time-resolved optical orientation experiments, we show that the diffusion length can be increased by more than 200% with an applied gate voltage of 5?V. These experiments allow at the same time the direct simultaneous measurements of both the Rashba and Dresselhaus spin-orbit splittings. PMID:24052071

  19. Controlled Ambipolar Doping and Gate Voltage Dependent Carrier Diffusion Length in Lead Sulfide Nanowires

    E-print Network

    Yu, Dong

    Controlled Ambipolar Doping and Gate Voltage Dependent Carrier Diffusion Length in Lead Sulfide observed a strong dependence of minority carrier diffusion length on gate voltage, which can be understood of high quality PbS NWs opens up exciting avenues for their applications in photodetectors

  20. Photographic surveying of minority carrier diffusion length in polycrystalline silicon solar cells by electroluminescence

    Microsoft Academic Search

    Takashi Fuyuki; Hayato Kondo; Tsutomu Yamazaki; Yu Takahashi; Yukiharu Uraoka

    2005-01-01

    Photographic surveying of the minority carrier diffusion length distribution in polycrystalline silicon solar cells was proposed. Light emission from the cell under the forward bias was captured by a charge coupled device camera. We have found that the intensity distribution of light emission clearly agreed with the mapping of minority carrier diffusion length in polycrystalline silicon active layers. The emission

  1. Diffusion Correction to Slow Invariant Manifolds in a Short Length Scale Limit

    E-print Network

    Diffusion Correction to Slow Invariant Manifolds in a Short Length Scale Limit Joshua D. Mengers Abstract-- Slow Invariant Manifolds (SIM) are calculated for isothermal closed reaction-diffusion systems as a model reduction technique. Diffusion effects are examined using a Galerkin projection that rigorously

  2. Effect of Orifice Length-Diameter Ratio on Spray Characteristics

    NASA Technical Reports Server (NTRS)

    Gellales, A G

    1930-01-01

    The effect of variations of orifice length to diameter ratio on spray characteristics was determined for a 0.014-inch and a 0.040-inch orifice for ratio of 0.5 to 4.0. The nozzles containing the orifices were mounted in an injection valve and tested with a plan stem and with a helically grooved stem. The injection pressure was varied from 4000 to 8000 pounds per square inch. The air density into which the fuel was sprayed was varied from the density obtained with a pressure of 60 pounds per square inch to the density obtained with a pressure of 250 pounds per square inch at room temperature. The tests showed that increasing the orifice length to diameter ratio with a plain stem in the injection valve causes the spray tip penetration first to decrease, reaching a minimum between a ratio of 1.5 and 2.5, and then to increase, reaching a maximum at a ratio greater than 3.5. The spray cone angle showed little change with variation of the ratio. With a helically grooved stem and small ratio of orifice area to groove area, the penetration at first shows little tendency towards a minimum; but as the time of injection is increased to 0.004 second, the penetration becomes a minimum at a ratio between 0.5 and 2.0.

  3. 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.

  4. 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. [comp.] [comp.

    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.

  5. Diffusion length measurements using the scanning electron microscope. [in semiconductor devices

    NASA Technical Reports Server (NTRS)

    Weizer, V. G.

    1975-01-01

    A measurement technique employing the scanning electron microscope is described in which values of the true bulk diffusion length are obtained. It is shown that surface recombination effects can be eliminated through the application of highly doped surface field layers. The influence of high injection level effects and low-high junction current generation on the resulting measurement was investigated. Close agreement is found between the diffusion lengths measured by this method and those obtained using a penetrating radiation technique.

  6. Effective diffusion lengths for minority carriers in solar cells as determined from internal quantum efficiency analysis

    Microsoft Academic Search

    Rolf Brendel; Uwe Rau

    1999-01-01

    We introduce a general relationship between the effective diffusion length LQ of solar cells derived from spectral quantum efficiency Q and the effective diffusion length LJ that determines the saturation current j0=qn0D\\/LJ of the diode in the dark. The general relation LQ>=LJ holds in the presence of grain boundaries and of spatially nonhomogeneous doping profiles. We find the relation LQ=LJ

  7. Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber.

    PubMed

    Stranks, Samuel D; Eperon, Giles E; Grancini, Giulia; Menelaou, Christopher; Alcocer, Marcelo J P; Leijtens, Tomas; Herz, Laura M; Petrozza, Annamaria; Snaith, Henry J

    2013-10-18

    Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI(3-x)Cl(x)) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development. PMID:24136964

  8. Characteristic lengths for evaporation suppression from patchy porous surfaces

    NASA Astrophysics Data System (ADS)

    Lehmann, Peter; Or, Dani

    2014-05-01

    For non-uniformly wet porous surfaces, evaporation rates vary nonlinearly with mean surface water content and with the areal fraction of wet patches. The nonlinearity stems from the complex vapor field forming over individual pores and patches that could enhance vapor fluxes from pores surrounded by dry area (relative to fluxes from the same area of free water surface). The resulting evaporation rates from such a surface are similar to free water surface evaporation despite considerably lower evaporating area (low surface water content). Theoretically, such flux compensation could be suppressed by lumping isolated pores into clusters with equal mean water content. The resulting arrangement in wet patches ensures nearly 1D conditions within the patch and some flux enhancement at the periphery. The interplay between patch water content, patch size, and mean surface water content within a prescribed air flow boundary layer was modeled analytically using single pore diffusion as a building block. Results show existence of a characteristic cluster size that yields the largest evaporation suppression for a given boundary layer thickness and spacing between patches. For patches larger than this size, the relative evaporation rate from patchy surface (relative to free water surface evaporation) reaches a predictable rate equal to the fractional area of clusters. Model predictions for the relation between pore cluster size and evaporation suppression were evaluated numerically and in a series of wind tunnel experiments using porous surfaces with different pore clusters. The findings could be used for the design of optimal porous covers for suppressing evaporation losses from water reservoirs, or for controlling evaporative drying from engineered porous surfaces.

  9. Estimation of minority carrier diffusion lengths in InP/GaAs solar cells

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    Minority carrier diffusion length is one of the most important parameters affecting the solar cell performance. An attempt is made to estimate the minority carrier diffusion lengths is the emitter and base of InP/GaAs heteroepitaxial solar cells. The PC-1D computer model was used to simulate the experimental cell results measured at NASA Lewis under AMO (air mass zero) spectrum at 25 C. A 16 nm hole diffusion length in the emitter and a 0.42 micron electron diffusion length in the base gave very good agreement with the I-V curve. The effect of varying minority carrier diffusion lengths on cell short current, open circuit voltage, and efficiency was studied. It is also observed that the front surface recombination velocity has very little influence on the cell performance. The poor output of heteroepitaxial cells is caused primarily by the large number of dislocations generated at the interfaces that propagate through the bulk indium phosphide layers. Cell efficiency as a function of dislocation density was calculated and the effect of improved emitter bulk properties on cell efficiency is presented. It is found that cells with over 16 percent efficiencies should be possible, provided the dislocation density is below 10(exp 6)/sq cm.

  10. Determination of the Pt spin diffusion length by spin-pumping and spin Hall effect

    SciTech Connect

    Zhang, Wei; Pearson, John E.; Hoffmann, Axel [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Vlaminck, Vincent [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States) [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Colegio de Ciencias e Ingenería, Universidad San Fransciso de Quito, Quito (Ecuador); Divan, Ralu [Center for Nanoscale Materials, Argonne National Laboratory, Illinois 60439 (United States)] [Center for Nanoscale Materials, Argonne National Laboratory, Illinois 60439 (United States); Bader, Samuel D. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States) [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Center for Nanoscale Materials, Argonne National Laboratory, Illinois 60439 (United States)

    2013-12-09

    The spin diffusion length of Pt at room temperature and at 8 K is experimentally determined via spin pumping and spin Hall effect in permalloy/Pt bilayers. Voltages generated during excitation of ferromagnetic resonance from the inverse spin Hall effect and anisotropic magnetoresistance effect were investigated with a broadband approach. Varying the Pt layer thickness gives rise to an evolution of the voltage line shape due to the superposition of the above two effects. By studying the ratio of the two voltage components with the Pt layer thickness, the spin diffusion length of Pt can be directly extracted. We obtain a spin diffusion length of ?1.2 nm at room temperature and ?1.6 nm at 8 K.

  11. 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.

  12. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber

    NASA Astrophysics Data System (ADS)

    Stranks, Samuel; Eperon, Giles; Grancini, Giulia; Menelaou, Christopher; Alcocer, Marcelo; Leijtens, Tomas; Herz, Laura; Petrozza, Annamaria; Snaith, Henry

    2014-03-01

    Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI3-xClx) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of order 100 nanometers. Finally, we fabricated solution-processed thin-film planar heterojunction devices, achieving power conversion efficiencies of over 12% using the mixed halide absorber but only 4% with the triiodide perovskite. Our results show that the long diffusion lengths justify the high efficiency of planar heterojunction perovskite solar cells, and identify a critical parameter to optimize for future perovskite absorber development.

  13. Interpretation of scanning electron microscope measurements of minority carrier diffusion lengths in semiconductors

    NASA Technical Reports Server (NTRS)

    Flat, A.; Milnes, A. G.

    1978-01-01

    In scanning electron microscope (SEM) injection measurements of minority carrier diffusion lengths some uncertainties of interpretation exist when the response current is nonlinear with distance. This is significant in epitaxial layers where the layer thickness is not large in relation to the diffusion length, and where there are large surface recombination velocities on the incident and contact surfaces. An image method of analysis is presented for such specimens. A method of using the results to correct the observed response in a simple convenient way is presented. The technique is illustrated with reference to measurements in epitaxial layers of GaAs. Average beam penetration depth may also be estimated from the curve shape.

  14. Direct simulation of pumping characteristics for a model diffusion pump

    Microsoft Academic Search

    YK Lee; JW Lee

    1996-01-01

    The pumping characteristics of a single\\/multi-stage diffusion pump were simulated using the Direct Simulation Monte Carlo (DSMC) method. The hard sphere model is used as a molecular model and the No Time Counter (NTC) scheme is employed as a collision sampling technique. Steady state flow characteristics such as velocity, temperature, density distributions of the pumped gas and oil vapor are

  15. Characteristics of transitional and turbulent jet diffusion flames in microgravity

    NASA Technical Reports Server (NTRS)

    Bahadori, Yousef M.; Small, James F., Jr.; Hegde, Uday G.; Zhou, Liming; Stocker, Dennis P.

    1995-01-01

    This paper presents the ground-based results obtained to date in preparation of a proposed space experiment to study the role of large-scale structures in microgravity transitional and turbulent gas-jet diffusion flames by investigating the dynamics of vortex/flame interactions and their influence on flame characteristics. The overall objective is to gain an understanding of the fundamental characteristics of transitional and turbulent gas-jet diffusion flames. Understanding of the role of large-scale structures on the characteristics of microgravity transitional and turbulent flames will ultimately lead to improved understanding of normal-gravity turbulent combustion.

  16. Temporal scaling characteristics of diffusion as a new MRI contrast: Findings in rat hippocampus

    PubMed Central

    Özarslan, Evren; Shepherd, Timothy M.; Koay, Cheng Guan; Blackband, Stephen J.; Basser, Peter J.

    2012-01-01

    Features of the diffusion-time dependence of the diffusion-weighted magnetic resonance imaging (MRI) signal provide a new contrast that could be altered by numerous biological processes and pathologies in tissue at microscopic length scales. An anomalous diffusion model, based on the theory of Brownian motion in fractal and disordered media, is used to characterize the temporal scaling (TS) characteristics of diffusion-related quantities, such as moments of the displacement and zero-displacement probabilities, in excised rat hippocampus specimens. To reduce the effect of noise in magnitude-valued MRI data, a novel numerical procedure was employed to yield accurate estimation of these quantities even when the signal falls below the noise floor. The power-law dependencies characterize the TS behavior in all regions of the rat hippocampus, providing unique information about its microscopic architecture. The relationship between the TS characteristics and diffusion anisotropy is investigated by examining the anisotropy of TS, and conversely, the TS of anisotropy. The findings suggest the robustness of the technique as well as the reproducibility of estimates. TS characteristics of the diffusion-weighted signals could be used as a new and useful marker of tissue microstructure. PMID:22306798

  17. Surface preparation for determining diffusion length by the surface photovoltage method

    Microsoft Academic Search

    1985-01-01

    A method of treating the surface of a sample of n-type silicon material in preparation for measurements for determining the minority carrier diffusion length of the material by the surface photovoltage method comprises applying a strong oxidizing agent to an appropriately prepared surface of a semiconductor material such as silicon. The oxidizing agent is taken from the group consisting of

  18. SIMULATION OF SOLIDIFICATION GRAIN STRUCTURES WITH A MULTIPLE DIFFUSION LENGTH SCALES MODEL

    E-print Network

    Paris-Sud XI, Université de

    an isolated dendritic grain. For instance, single crystal production of nickel-base superalloys by directional for the prediction of micro- and macrosegregation based on solute diffusion. On the one hand an open microsegregation expressions for two length scales based on the primary and secondary dendrite arm spacing and assuming

  19. Effect of fiber volume fraction and length on the wear characteristics of glass fiber-reinforced

    E-print Network

    Vaziri, Ashkan

    Effect of fiber volume fraction and length on the wear characteristics of glass fiber the fiber weight percent added to the matrix as well as fiber length. Methods. Dental specimens with glass fiber content of 2, 5.1, 5.7, and 7.6 wt% with fiber length of either 1.5 or 3 mm, were prepared

  20. Characteristic Length Scale of Bicontinuous Nanoporous Structure by Fast Fourier Transform

    Microsoft Academic Search

    Takeshi Fujita; Ming Wei Chen

    2008-01-01

    We propose a method derived from fast Fourier transform (FFT) process to measure the characteristic length scale of bicontinuous nanoporous structures. By rotationally averaging the FFT power spectrum of a nanoporous micrograph from scanning electron microscope (SEM) or transmission electron microscope (TEM), a significant peak in the power spectrum can be obtained, which reflects the characteristic length scale of the

  1. The Effect of Laminate Configuration on Characteristic Lengths and Rail Shear Strength

    Microsoft Academic Search

    Fu-Kuo Chang; Richard A. Scott; George S. Springer

    1984-01-01

    Tests were performed measuring the characteristic lengths in tension and in com pression and the rail shear strength of Fiberite T300\\/1034-C graphite epoxy com posites. The results show the effects of geometry on the characteristic lengths. The results also indicate the variability of rail shear strength with the volume fraction of zero degree plies in the laminate.

  2. Flow characteristics in the downstream region of a conical diffuser

    Microsoft Academic Search

    P. Prinos; A. Goulas

    1992-01-01

    Using the Navier-Stokes equations in conjunction with the k-epsilon model of turbulence, the characteristics of flow in the region downstream of a conical diffuser with 5 deg angle of inclination are calculated. Two representative stations 1D sub 2 and 10D sub 2 after the diffuser exit are selected for comparison against experimental results. The calculations indicate an underestimation of mean

  3. 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. PMID:23066756

  4. Surface preparation for determining diffusion length by the surface photovoltage method

    SciTech Connect

    Goodman, A.M.

    1985-03-26

    A method of treating the surface of a sample of n-type silicon material in preparation for measurements for determining the minority carrier diffusion length of the material by the surface photovoltage method comprises applying a strong oxidizing agent to an appropriately prepared surface of a semiconductor material such as silicon. The oxidizing agent is taken from the group consisting of potassium permanganate (KMnO/sub 4/), potassium dichromate (K/sub 2/Cr/sub 2/O/sub 7/), and ammonium dichromate ((NH/sub 4/)/sub 2/Cr/sub 2/O/sub 7/). The surface preparation assures a consistently large surface photovoltage that is stable during the surface photovoltage measurement for minority carrier diffusion length.

  5. Moderate Reynolds number axisymmetric jet development downstream an extended conical diffuser: Influence of extension length

    Microsoft Academic Search

    A. Van Hirtum; X. Grandchamp; X. Pelorson

    2009-01-01

    Low-velocity (bulk velocity of 4.4m\\/s) and moderate Reynolds (7350) axisymmetrical jet development is studied by hot-film single sensor anemometry. The jet issues from a conical convergent-divergent diffuser with uniform extension (diameter 25mm). Decreasing the length-to-diameter ratio of the extension tube from 20 down to 0.4 is shown to alter severely the mean velocity profile at the tube outlet from Blasius

  6. Charge collection microscopy on p-WSe2 - Recombination sites and minority carrier diffusion length

    NASA Astrophysics Data System (ADS)

    Lewerenz, H. J.; Ferris, S. D.; Doherty, C. J.; Leamy, H. J.

    1982-02-01

    Charge collection microscopy of the layered semiconductor WSe2 is reported. Steps on the surfaces of layered material, bulk dislocations, and growth irregularities are identified as recombination sites. The minority carrier diffusion length perpendicular to the layer structure is determined to be 1.6 + or - 0.2 microns on a smooth surface. The results demonstrate a correlation between step-like surface structures and loss of current collection efficiency in solar energy-converting devices made from layered semiconductors.

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

    DOEpatents

    Goldstein, Bernard (Princeton, NJ); Dresner, Joseph (Princeton, NJ); Szostak, Daniel J. (Mercerville, NJ)

    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.

  8. Control design that respects characteristic length scales in smart systems and smart structures

    Microsoft Academic Search

    John Baillieul

    1999-01-01

    Although there is a mature and continually growing body of knowledge concerning the ways in which the dynamics of fluids and solids depend on characteristic length scales, current theories governing control design do not take explicit account of length scales. Recent research has demonstrated the need to take such considerations into account in designing control systems for smart materials and

  9. Characteristics of donkey spermatozoa along the length of the epididymis.

    PubMed

    Contri, A; Gloria, A; Robbe, D; De Amicis, I; Carluccio, A

    2012-01-01

    In mammals, the epididymis has numerous interrelated functions including absorptive and secretory activity that affect luminal environment and cell membrane, and the maturation and storage of sperm. Spermatozoa acquire their motility and fertilizing ability during their passage through the epididymis and the motility of epididymal spermatozoa should be a balance between the maturation of flagellum and the inhibition of the flagellar machinery. In this study maturational change in sperm characteristics were evaluated in the epididymis of donkey. Spermatozoa collected from four portions of the epididymis (head, cranial corpus, caudal corpus, tail) were compared before and after ejaculation for viability, mitochondrial activity, kinetic parameters, and morphology. A significant increase in the mitochondrial activity along the epididymis was reported, suggesting a possible involvement in the motion mechanism. This should be corroborated by the significant correlation between mitochondrial activity and the total and progressive motility and the increase in velocities of spermatozoa recorded by computer-assisted sperm analysis. The percentage of most of the abnormal spermatozoa were similar in all tracts, with a great variability between jackasses. Only the bent midpiece percentage decreased significantly along epididymis. A significant increase in the percentage of distal cytoplasmic droplets (DCD), and a simultaneous decrease in the proximal cytoplasmic droplets (PCD), was found. The DCD fell down after ejaculation suggesting the late loss of the cytoplasmic residual (DCD) in the donkey, as hypothesized in the stallion. Because the prevalence of PCD were similar in both tail epididymal and ejaculated spermatozoa, a defect of the maturative process in the PCD sperm should be speculated. PMID:21872312

  10. 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. PMID:25531034

  11. 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.

  12. Flow characteristics in the downstream region of a conical diffuser

    NASA Astrophysics Data System (ADS)

    Prinos, P.; Goulas, A.

    1992-08-01

    Using the Navier-Stokes equations in conjunction with the k-epsilon model of turbulence, the characteristics of flow in the region downstream of a conical diffuser with 5 deg angle of inclination are calculated. Two representative stations 1D sub 2 and 10D sub 2 after the diffuser exit are selected for comparison against experimental results. The calculations indicate an underestimation of mean velocity and turbulence kinetic energy at the first station, while satisfactory agreement is obtained for the mean velocity at the second station. The use of a modified k-epsilon model sensitive to adverse pressure conditions improves the predictions considerably. The effect of inlet properties and Reynolds number on the flow characteristics at the above stations is studied using various inlet profiles and a range of Reynolds numbers based on the inlet diameter from 50,000 to 280,000.

  13. Diffusion characteristics of ethylene glycol in skeletal muscle.

    PubMed

    Oliveira, Luís M; Carvalho, Maria Inês; Nogueira, Elisabete M; Tuchin, Valery V

    2015-05-01

    Part of the optical clearing study in biological tissues concerns the determination of the diffusion characteristics of water and optical clearing agents in the subject tissue. Such information is sufficient to characterize the time dependence of the optical clearing mechanisms—tissue dehydration and refractive index (RI) matching. We have used a simple method based on collimated optical transmittance measurements made from muscle samples under treatment with aqueous solutions containing different concentrations of ethylene glycol (EG), to determine the diffusion time values of water and EG in skeletal muscle. By representing the estimated mean diffusion time values from each treatment as a function of agent concentration in solution, we could identify the real diffusion times for water and agent. These values allowed for the calculation of the correspondent diffusion coefficients for those fluids. With these results, we have demonstrated that the dehydration mechanism is the one that dominates optical clearing in the first minute of treatment, while the RI matching takes over the optical clearing operations after that and remains for a longer time of treatment up to about 10 min, as we could see for EG and thin tissue samples of 0.5 mm. PMID:25525766

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

    NASA Astrophysics Data System (ADS)

    Leon, R. P.

    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.

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

    NASA Astrophysics Data System (ADS)

    Leon, R. P.

    1987-05-01

    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.

  16. 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.

  17. 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.

  18. Quantifying the effect of metal-rich precipitates on minority carrier diffusion length in multicrystalline silicon using synchrotron-based

    E-print Network

    in semiconductor devices. Equivalence with well-established diffusion length measurement techniques is demonstrated correlation between local concentrations of copper and nickel silicide precipitates and a decrease of minority

  19. Diffusion lengths in irradiated N/P InP-on-Si solar cells

    NASA Technical Reports Server (NTRS)

    Wojtczuk, Steven; Colerico, Claudia; Summers, Geoffrey P.; Walters, Robert J.; Burke, Edward A.

    1996-01-01

    Indium phosphide (InP) solar cells were made on silicon (Si) wafers (InP/Si) by to take advantage of both the radiation-hardness properties of the InP solar cell and the light weight and low cost of Si wafers. The InP/Si cell application is for long duration and/or high radiation orbit space missions. Spire has made N/P InP/Si cells of sizes up to 2 cm by 4 cm with beginning-of-life (BOL) AM0 efficiencies over 13% (one-sun, 28C). These InP/Si cells have higher absolute efficiency and power density after a high radiation dose than gallium arsenide (GaAs) or silicon (Si) solar cells after a fluence of about 2e15 1 MeV electrons/sq. cm. In this work, we investigate the minority carrier (electron) base diffusion lengths in the N/P InP/Si cells. A quantum efficiency model was constructed for a 12% BOL AM0 N/P InP/Si cell which agreed well with the absolutely measured quantum efficiency and the sun-simulator measured AM0 photocurrent (30.1 mA/sq. cm). This model was then used to generate a table of AM0 photocurrents for a range of base diffusion lengths. AM0 photocurrents were then measured for irradiations up to 7.7e16 1 MeV electrons/sq. cm (the 12% BOL cell was 8% after the final irradiation). By comparing the measured photocurrents with the predicted photocurrents, base diffusion lengths were assigned at each fluence level. A damage coefficient K of 4e-8 and a starting (unirradiated) base electron diffusion length of 0.8 microns fits the data well. The quantum efficiency was measured again at the end of the experiment to verify that the photocurrent predicted by the model (25.5 mA/sq. cm) agreed with the simulator-measured photocurrent after irradiation (25.7 mA/sq. cm).

  20. Diffusion length measurement using the scanning electron microscope. [for silicon solar cell

    NASA Technical Reports Server (NTRS)

    Weizer, V. G.

    1975-01-01

    The present work describes a measuring technique employing the scanning electron microscope in which values of the true bulk diffusion length are obtained. It is shown that surface recombination effects can be eliminated through application of highly doped surface field layers. The effects of high injection level and low-high junction current generation are investigated. Results obtained with this technique are compared to those obtained by a penetrating radiation (X-ray) method, and a close agreement is found. The SEM technique is limited to cells that contain a back surface field layer.

  1. Cross-field diffusion in low-temperature plasma discharges of finite length

    NASA Astrophysics Data System (ADS)

    Curreli, Davide; Chen, Francis F.

    2014-12-01

    The long-standing problem of plasma diffusion across a magnetic field (B-field) is reviewed, with emphasis on low-temperature linear devices of finite length with the magnetic field aligned along an axis of symmetry. In these partially ionized plasmas, cross-field transport is dominated by ion–neutral collisions and can be treated simply with fluid equations. Nonetheless, electron confinement is complicated by sheath effects at the endplates, and these must be accounted for to get agreement with experiment. ).

  2. 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.

  3. Absolute standard of diffusion length and lifetime of minority charge carriers in single-crystal silicon

    NASA Astrophysics Data System (ADS)

    Skidanov, V. A.

    2014-11-01

    A substantial difference in electron recombination cross sections on Fe-B complexes (?1) and on activated iron ions (?2) in boron-doped single-crystal silicon is used to independently determine the lifetime of electrons in the standard T st using the surface photo-emf method. Pairs of values of the lifetime T 1 and T 2 before and after the decomposition of the Fe-B complexes were measured for each of 600 ingots at arbitrary diffusion length L cal for the calibrating specimen and were placed on the plane ( T 1, T 2). At the boundary of the region filled with the points, ingots are presented that are only contaminated with iron ions, so that T 2/ T 1 = ?1/?2. The true values of L st and T st of the calibrating specimen and the ratio ?1/?2 = 12.5 ± 0.5 are determined by selecting a new value of the diffusion length for the calibrating specimen, which straightens the boundary of the region filled with the points after the recalculation of the values of T 1 and T 2.

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

    DOEpatents

    Moore, Arnold R. (Princeton, NJ)

    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.

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

    DOEpatents

    Moore, Arnold R. (Princeton, NJ)

    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.

  6. Diffusion lengths in irradiated N/P InP-on-Si solar cells

    NASA Technical Reports Server (NTRS)

    Wojtczuk, Steven; Colerico, Claudia; Summers, Geoffrey P.; Walters, Robert J.; Burke, Edward A.

    1995-01-01

    Indium phosphide (InP) solar cells are being made on silicon (Si) wafers (InP/Si) to take advantage of both the radiation-hardness properties of the InP solar cell and the light weight and low cost of Si wafers compared to InP or germanium (Ge) wafers. The InP/Si cell application is for long duration and/or high radiation orbit space missions. InP/Si cells have higher absolute efficiency after a high radiation dose than gallium arsenide (GaAs) or silicon (Si) solar cells. In this work, base electron diffusion lengths in the N/P cell are extracted from measured AM0 short-circuit photocurrent at various irradiation levels out to an equivalent 1 MeV fluence of 1017 1 MeV electrons/sq cm for a 1 sq cm 12% BOL InP/Si cell. These values are then checked for consistency by comparing measured Voc data with a theoretical Voc model that includes a dark current term that depends on the extracted diffusion lengths.

  7. Relationship between carrier diffusion lengths and defect density in hydrogenated amorphous silicon

    SciTech Connect

    Sakata, I.; Yamanaka, M.; Sekigawa, T. [Electron Devices Division, Electrotechnical Laboratory, Umezono 1-1-4, Tsukuba, Ibaraki 305 (Japan)] [Electron Devices Division, Electrotechnical Laboratory, Umezono 1-1-4, Tsukuba, Ibaraki 305 (Japan)

    1997-02-01

    Experimental studies and numerical analysis have been carried out to clarify the relationship between carrier diffusion lengths and defect density in undoped a-Si:H. It has been confirmed that in device quality plasma-deposited a-Si:H, the diffusion lengths of both electrons and holes under steady-state illumination of the intensity equivalent to normal solar cell operating conditions are determined by the density of Si dangling-bond defects ranging between 3{times}10{sup 15} and 8{times}10{sup 16} cm{sup {minus}3}. This rather trivial result, however, has not been obtained in previous studies in which the carrier transport data obtained by the steady-state photocarrier grating method were treated incorrectly. The ratio of the drift mobility of electrons to that of holes and the ratio of electron lifetime to the hole lifetime in a-Si:H under illumination have been determined and their implications discussed. {copyright} {ital 1997 American Institute of Physics.}

  8. Diffusion current characteristics of defect-limited nBn mid-wave infrared detectors

    NASA Astrophysics Data System (ADS)

    Savich, G. R.; Sidor, D. E.; Du, X.; Morath, C. P.; Cowan, V. M.; Wicks, G. W.

    2015-04-01

    Mid-wave infrared, nBn detectors remain limited by diffusion current generated in the absorber region even when defect concentrations are elevated. In contrast, defect-limited conventional pn-junction based photodiodes are subject to Shockley-Read-Hall generation in the depletion region and subsequent carrier drift. Ideal nBn-architecture devices would be limited by Auger 1 generation; however, typical nBn detectors exhibit defect-dominated performance associated with Shockley-Read-Hall generation in the quasi-neutral absorbing region. Reverse saturation current density characteristics for defect-limited devices depend on the minority carrier diffusion length, absorbing layer thickness, and the dominant minority carrier generation mechanism. Unlike pn-based photodiodes, changes in nBn dark current due to elevated defect concentrations do not manifest at small biases, thus, the zero bias resistance area product, RoA, is not a useful parameter for characterizing nBn-architecture photodetector performance.

  9. Moisture diffusion parameter characteristics for epoxy composites and neat resins

    NASA Technical Reports Server (NTRS)

    Long, E. R., Jr.

    1979-01-01

    The moisture absorption characteristics of two graphite/epoxy composites and their corresponding cured neat resins were studied in high humidity and water immersion environments at elevated temperatures. Moisture absorption parameters, such as equilibrium moisture content and diffusion coefficient derived from data taken on samples exposed to high humidity and water soak environments, were compared. Composite swelling in a water immersion environment was measured. Tensile strengths of cured neat resin were measured as a function of their equilibrium moisture content after exposure to different moisture environments. The effects of intermittent moderate tensile loads on the moisture absorption parameters of composite and cured neat resin samples were determined.

  10. Tilt Beam Characteristic by Changing Length of Finite-Sized Square Dielectric Substrate of One Arm Rectangular Spiral Antenna

    E-print Network

    De Flaviis, Franco

    Tilt Beam Characteristic by Changing Length of Finite-Sized Square Dielectric Substrate of One Arm by changing the length of finite-sized square dielectric substrate of one arm rectangular spiral antenna has). Horizontal spiral arm length (HL) is varied from HL=0.8o to HL=5.2o to choose the length that yields

  11. CHARACTERISTIC LENGTH OF ENERGY-CONTAINING STRUCTURES AT THE BASE OF A CORONAL HOLE

    SciTech Connect

    Abramenko, V. I.; Yurchyshyn, V. B.; Goode, P. R.; Ahn, K.; Cao, W. [Big Bear Solar Observatory, 40386 N. Shore Lane, Big Bear City, CA 92314 (United States); Zank, G. P.; Dosch, A. [CSPAR, University of Alabama in Huntsville, Huntsville, AL (United States)

    2013-08-20

    An essential parameter for models of coronal heating and fast solar wind acceleration that rely on the dissipation of MHD turbulence is the characteristic energy-containing length {lambda} of the squared velocity and magnetic field fluctuations (u{sup 2} and b{sup 2}) transverse to the mean magnetic field inside a coronal hole (CH) at the base of the corona. The characteristic length scale directly defines the heating rate. We use a time series analysis of solar granulation and magnetic field measurements inside two CHs obtained with the New Solar Telescope at Big Bear Solar Observatory. A data set for transverse magnetic fields obtained with the Solar Optical Telescope/Spectro-Polarimeter on board the Hinode spacecraft was utilized to analyze the squared transverse magnetic field fluctuations b{sub t}{sup 2}. Local correlation tracking was applied to derive the squared transverse velocity fluctuations u {sup 2}. We find that for u {sup 2} structures, the Batchelor integral scale {lambda} varies in a range of 1800-2100 km, whereas the correlation length sigmav and the e-folding length L vary between 660 and 1460 km. Structures for b{sub t}{sup 2} yield {lambda} Almost-Equal-To 1600 km, sigmav Almost-Equal-To 640 km, and L Almost-Equal-To 620 km. An averaged (over {lambda}, sigmav, and L) value of the characteristic length of u {sup 2} fluctuations is 1260 {+-} 500 km, and that of b{sub t}{sup 2} is 950 {+-} 560 km. The characteristic length scale in the photosphere is approximately 1.5-50 times smaller than that adopted in previous models (3-30 Multiplication-Sign 10{sup 3} km). Our results provide a critical input parameter for current models of coronal heating and should yield an improved understanding of fast solar wind acceleration.

  12. Relation Between Discharge Length and Laser Pulse Characteristics in Longitudinally Excited CO2 Laser

    NASA Astrophysics Data System (ADS)

    Uno, Kazuyuki; Dobashi, Kazuma; Akitsu, Tetsuya; Jitsuno, Takahisa

    2013-04-01

    A longitudinally excited CO2 laser pumped by a fast discharge emits a short laser pulse, similarly to TEA and Q-switched CO2 lasers. We investigated the relation between the discharge length and the laser pulse characteristics to develop a longitudinally excited CO2 laser producing a high spike laser pulse. We examined discharge lengths of 30, 45, and 60 cm, using the same mirrors and the same excitation circuit with the same input energy. A longer discharge length increased the discharge volume and improved the laser output energy. However, the longer discharge length caused a long discharge formation time (a slow fall time of the discharge voltage) due to the higher discharge impedance, which resulted in a long laser pulse tail. Therefore, the longitudinally excited CO2 laser had optimum conditions for obtaining a high spike laser pulse effectively.

  13. Length-force characteristics of in vivo human muscle reflected by supersonic shear imaging.

    PubMed

    Sasaki, Kazushige; Toyama, Sho; Ishii, Naokata

    2014-07-15

    Recently, an ultrasound-based elastography technique has been used to measure stiffness (shear modulus) of an active human muscle along the axis of contraction. Using this technique, we explored 1) whether muscle shear modulus, like muscle force, is length dependent; and 2) whether the length dependence of muscle shear modulus is consistent between electrically elicited and voluntary contractions. From nine healthy participants, ankle joint torque and shear modulus of the tibialis anterior muscle were measured at five different ankle joint angles during tetanic contractions and during maximal voluntary contractions. Fascicle length, pennation angle, and tendon moment arm length of the tetanized tibialis anterior calculated from ultrasound images were used to reveal the length-dependent changes in muscle force and shear modulus. Over the range of joint angles examined, both force and shear modulus of the tetanized muscle increased with increasing fascicle length. Regression analysis of normalized data revealed a significant linear relationship between force and shear modulus (R(2) = 0.52, n = 45, P < 0.001). Although the length dependence of shear modulus was consistent, irrespective of contraction mode, the slope of length-shear modulus relationship was steeper during maximal voluntary contractions than during tetanic contractions. These results provide novel evidence that length-force relationship, one of the most fundamental characteristics of muscle, can be inferred from in vivo imaging of shear modulus in the tibialis anterior muscle. Furthermore, the estimation of length-force relationship may be applicable to voluntary contractions in which neural and mechanical interactions of multiple muscles are involved. PMID:24876360

  14. 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.

  15. Air entry-based characteristic length for estimation of permeability of variably compacted earth materials

    NASA Astrophysics Data System (ADS)

    Assouline, S.; Or, D.

    2008-11-01

    The permeability k of a porous medium is a geometrical pore space attribute required for quantifying fluid flows and transport processes for hydrological, civil, agriculture, and petroleum engineering applications. Permeability is often expressed as proportional to a characteristic length squared and inversely proportional to factors accounting for porosity, pore shape, and tortuosity effects. Compaction and diagenesis reduce porosity, mean pore size, and connectivity, resulting in decrease in k. Permeability prediction relies on suitable selection of a characteristic length that may vary from simple hydraulic radius approximation of Kozeny-Carman to more complex critical path analysis to identify flow-limiting pore size. For porous media undergoing significant changes in pore space (e.g., compaction due to anthropogenic activities), the proper choice of a robust characteristic length is particularly challenging. We propose using the air entry pressure, a natural characteristic length that gauges the largest drainable pore size. This choice of a characteristic length is compatible with the Aissen formula that provides robust estimates of k for complex pore shapes. Additionally, the model considers geometrical (tortuosity) factors and links relative changes in porosity to concurrent changes in k. The model was tested against experimental data for sands, sandstones with different cementing agents, and unconsolidated soils. For unconsolidated sands and soils the model provides reasonable predictions of permeability for the entire range of porosities determined in laboratory or field experiments. However, for sandstones, and especially those containing cementing agents such as clay, the model is valid up to a critical porosity where hydraulic connectivity is lost, resulting in drastic reduction in k. The geometrical factor for soils was influenced by silt-to-clay ratio, while for sands, it was correlated with mean grain diameter. The model offers improvement in predicting k and provides a means for incorporating critical pore size and connectivity information in addition to porosity.

  16. Characteristics of Gaseous Diffusion Flames with High Temperature Combustion Air in Microgravity

    NASA Technical Reports Server (NTRS)

    Ghaderi, M.; Gupta, A. K.

    2003-01-01

    The characteristics of gaseous diffusion flames have been obtained using high temperature combustion air under microgravity conditions. The time resolved flame images under free fall microgravity conditions were obtained from the video images obtained. The tests results reported here were conducted using propane as the fuel and about 1000 C combustion air. The burner included a 0.686 mm diameter central fuel jet injected into the surrounding high temperature combustion air. The fuel jet exit Reynolds number was 63. Several measurements were taken at different air preheats and fuel jet exit Reynolds number. The resulting hybrid color flame was found to be blue at the base of the flame followed by a yellow color flame. The length and width of flame during the entire free fall conditions has been examined. Also the relative flame length and width for blue and yellow portion of the flame has been examined under microgravity conditions. The results show that the flame length decreases and width increases with high air preheats in microgravity condition. In microgravity conditions the flame length is larger with normal temperature combustion air than high temperature air.

  17. The Narrow Pulse Approximation and long length scale determination in xenon gas diffusion NMR studies of model porous media

    E-print Network

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

    2002-11-10

    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 (~ 1 - 1.5 bead diameters). The Pade approximation can be used as a reference for expected xenon D(t) data between the short and long time limits, allowing us to explore deviations from the expected behaviour at intermediate times as a result of finite sample size effects. Finally, the application of the Pade interpolation between the long and short time asymptotic limits yields a fitted length scale (the "Pade length"), which is found to be ~ 0.13b for all bead packs, where b is the bead diameter.

  18. Renal Water Molecular Diffusion Characteristics in Healthy Native Kidneys: Assessment with Diffusion Tensor MR Imaging

    PubMed Central

    Zheng, Zhenfeng; Shi, Huilan; Zhang, Jing; Zhang, Yunting

    2014-01-01

    Background To explore the characteristics of diffusion tensor imaging (DTI) and magnetic resonance (MR) imaging in healthy native kidneys. Methods Seventy-three patients without chronic kidney disease underwent DTI-MRI with spin echo-echo planar (SE-EPI) sequences accompanied by an array spatial sensitivity encoding technique (ASSET). Cortical and medullary mean, axial and radial diffusivity (MD, AD and RD), fractional anisotropy (FA) and primary, secondary and tertiary eigenvalues (?1, ?2, ?3) were analysed in both kidneys and in different genders. Results Cortical MD, ?2, ?3, and RD values were higher than corresponding medullary values. The cortical FA value was lower than the medullary FA value. Medullary ?1 and RD values in the left kidney were lower than in the right kidney. Medullary ?2, and ?3 values in women were higher than those in men. Medullary FA values in women were lower than those in men. Medullary FA (r?=?0.351, P?=?0.002) and ?1 (r?=?0.277, P?=?0.018) positively correlated with eGFR. Medullary FA (r?=??0.25, P?=?0.033) negatively correlated with age. Conclusions Renal water molecular diffusion differences exist in human kidneys and genders. Age and eGFR correlate with medullary FA and primary eigenvalue. PMID:25470776

  19. Identifying local characteristic lengths governing sound wave properties in solid foams

    NASA Astrophysics Data System (ADS)

    Tan Hoang, Minh; Perrot, Camille

    2013-02-01

    Identifying microscopic geometric properties and fluid flow through opened-cell and partially closed-cell solid structures is a challenge for material science, in particular, for the design of porous media used as sound absorbers in building and transportation industries. We revisit recent literature data to identify the local characteristic lengths dominating the transport properties and sound absorbing behavior of polyurethane foam samples by performing numerical homogenization simulations. To determine the characteristic sizes of the model, we need porosity and permeability measurements in conjunction with ligament lengths estimates from available scanning electron microscope images. We demonstrate that this description of the porous material, consistent with the critical path picture following from the percolation arguments, is widely applicable. This is an important step towards tuning sound proofing properties of complex materials.

  20. Factors affecting gestation length and estrus cycle characteristics in Spanish donkey breeds reared in southern Spain.

    PubMed

    Galisteo, J; Perez-Marin, C C

    2010-08-01

    This paper investigated gestation length and estrus cycle characteristics in three different Spanish donkey breeds (Andalusian, Zamorano-Leones, and Catalonian) kept on farm conditions in southern Spain, using data for ten consecutive breeding seasons. Gestation length was measured in 58 pregnancies. Ovarian ultrasonography was used to detect the ovulation, in order to ascertain true gestation length (ovulation-parturition). Pregnancy was diagnosed approximately 14-18 d after ovulation and confirmed on approximately day 60. Average gestation length was 362 +/-15.3 (SD) d, and no significant differences were observed between the three different breeds. Breeding season had a significant effect (P < 0.01), with longer gestation lengths when jennies were covered during the early period. Breed, age of jenny, year of birth, foal gender, month of breeding, and type of gestation had no significant effect on gestation length. After parturition, foal-heat was detected in 53.8% of the postpartum cycles studied (n = 78), and ovulation occurred on day 13.2 +/- 2.7. The duration of foal-heat was 4.7 +/-1.7 d, with a pregnancy rate of 40.5%. When subsequent estrus cycles were analyzed, the interovulatory interval (n = 68) and estrus duration (n = 258) were extended to a mean 23.8 +/- 3.5 and 5.7 +/- 2.2 d, respectively. Both variables were influenced by the year of study (P < 0.03 and P < 0.001), whereas month and season of ovulation (P < 0.005 and P < 0.009, respectively) affected only interovulatory intervals. Estrus duration was significantly longer than that observed at the foal-heat (P < 0.006), and the pregnancy rate was 65.8%. This study provides reference values for true gestation length and estrus cycle characteristics in Spanish jennies. Breeding season affected gestation length in farm conditions. Also, seasonal influence was observed on the length of the estrus cycle (i.e., interovulatory interval), although foal-heat was not affected by environmental factors. PMID:20451997

  1. Path-length-resolved dynamic light scattering in highly scattering random media: The transition to diffusing wave spectroscopy

    E-print Network

    Path-length-resolved dynamic light scattering in highly scattering random media: The transition diffusive light. Our experimental analysis provides details on the transition from single scattering.80. s Dynamic light scattering DLS has been used extensively during the past few decades for characterization

  2. 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.

  3. Record Charge Carrier Diffusion Length in Colloidal Quantum Dot Solids via Mutual Dot-To-Dot Surface Passivation.

    PubMed

    Carey, Graham H; Levina, Larissa; Comin, Riccardo; Voznyy, Oleksandr; Sargent, Edward H

    2015-06-01

    Through a combination of chemical and mutual dot-to-dot surface passivation, high-quality colloidal quantum dot solids are fabricated. The joint passivation techniques lead to a record diffusion length for colloidal quantum dots of 230 ± 20 nm. The technique is applied to create thick photovoltaic devices that exhibit high current density without losing fill factor. PMID:25899173

  4. Potential fluctuations, diffusion length and lateral photovoltage in hydrogenated amorphous silicon and silicon–germanium thin films

    Microsoft Academic Search

    Alok Srivastava; S. C. Agarwal

    2002-01-01

    The lateral photovoltage (LPV) has been measured between coplanar electrodes by illuminating hydrogenated amorphous silicon samples at various positions with a red laser spot. We find that the LPV decreases at higher temperatures and increases upon light soaking. Similar results are obtained for hydrogenated amorphous silicon–germanium alloys. The diffusion length of carriers in our samples is measured by the steady-state

  5. Length scale of heterogeneities in glassy propylene carbonate probed by oxygen diffusion

    NASA Astrophysics Data System (ADS)

    Syutkin, V. M.; Vyazovkin, V. L.; Korolev, V. V.; Grebenkin, S. Yu.

    2010-08-01

    A new method using the quenching of guest molecule phosphorescence by molecular oxygen is proposed for determination of heterogeneity size in glassy matrixes. The method is based on the high sensitivity of the diffusion of oxygen molecules to spatial density fluctuations. Phenanthrene phosphorescence decay was monitored at different concentrations of molecular oxygen in propylene carbonate below Tg. An unusual dependence of the phosphorescence decay on oxygen concentration was observed: an increase in the concentration leads to anomalously large increase in the quenching rate at short times. This dependence is considered to be caused by matrix heterogeneity. To describe the phosphorescence decay, we use a model of glass as a heterogeneous medium where oxygen jump rates are spatially correlated. The length of spatial correlation for the jump rates is taken as heterogeneity size. Using the model, the value of 1.5±0.5 nm was obtained for the size of structural heterogeneities in glassy propylene carbonate. The dispersion of barriers for oxygen jumps is estimated to be 4±1 kJ/mole and the average barrier energy is found to be 50 kJ/mole.

  6. Length scale of heterogeneities in glassy propylene carbonate probed by oxygen diffusion.

    PubMed

    Syutkin, V M; Vyazovkin, V L; Korolev, V V; Grebenkin, S Yu

    2010-08-21

    A new method using the quenching of guest molecule phosphorescence by molecular oxygen is proposed for determination of heterogeneity size in glassy matrixes. The method is based on the high sensitivity of the diffusion of oxygen molecules to spatial density fluctuations. Phenanthrene phosphorescence decay was monitored at different concentrations of molecular oxygen in propylene carbonate below T(g). An unusual dependence of the phosphorescence decay on oxygen concentration was observed: an increase in the concentration leads to anomalously large increase in the quenching rate at short times. This dependence is considered to be caused by matrix heterogeneity. To describe the phosphorescence decay, we use a model of glass as a heterogeneous medium where oxygen jump rates are spatially correlated. The length of spatial correlation for the jump rates is taken as heterogeneity size. Using the model, the value of 1.5+/-0.5 nm was obtained for the size of structural heterogeneities in glassy propylene carbonate. The dispersion of barriers for oxygen jumps is estimated to be 4+/-1 kJ/mole and the average barrier energy is found to be 50 kJ/mole. PMID:20726646

  7. 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.

  8. Characteristic length scales for vortex detachment on plunging profiles with varying leading-edge geometry

    NASA Astrophysics Data System (ADS)

    Rival, David E.; Kriegseis, Jochen; Schaub, Pascal; Widmann, Alexander; Tropea, Cameron

    2014-01-01

    Experiments on leading-edge vortex (LEV) growth and detachment from a plunging profile have been conducted in a free-surface water tunnel. Direct-force and velocity-field measurements have been performed at a Reynolds number of Re = 10,000, a reduced frequency of k = 0.25, and a Strouhal number of St = 0.16, for three varying leading-edge geometries. The leading-edge shape is shown to influence the shear layer feeding the LEV, and thus to some extent the development of the LEV and associated flow topology. This effect in turn influences the arrival time of the rear (LEV) stagnation point at the trailing edge, which, once breached, constitutes a detachment of the LEV. It is found that despite minor phase changes in LEV detachment through leading-edge shape, the position of the trailing edge (chord length) should be chosen as the characteristic length scale for the vortex separation process.

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

    PubMed

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

    2008-07-01

    Diffusion characteristics of chlorferon and diethylthiophosphate (DETP) in Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients for chlorferon and DETP in Ca-alginate gel beads determined at conditions suitable for biodegradation studies were 2.70 x 10(-11) m(2)/s and 4.28 x 10(-11) m(2)/s, respectively. Diffusivities of chlorferon and DETP were influenced by several factors, including viscosity of the bulk solution, agitation speed, and the concentrations of diffusing substrate and immobilized cells. Diffusion coefficients increased with increasing agitation speed, probably due to poor mixing at low speed and some attrition of beads at high speeds. Diffusion coefficients also increased with decreasing substrate concentration. Increased cell concentration in the gel beads caused lower diffusivity. Theoretical models to predict diffusivities as a function of cell weight fraction overestimated the effective diffusivities for both chlorferon and DETP, but linear relations between effective diffusivity and cell weight fraction were derived from experimental data. Calcium-alginate gel beads with radii of 1.65-1.70 mm used in this study were not subject to diffusional limitations: external mass transfer resistances were negligible based on Biot number calculations and effectiveness factors indicated that internal mass transfer resistance was negligible. Therefore, the degradation rates of chlorferon and DETP inside Ca-alginate gel beads were reaction-limited. PMID:18080347

  10. 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.

  11. Moisture Diffusivity Characteristics of Rough Rice Under Infrared Radiation Heating

    Technology Transfer Automated Retrieval System (TEKTRAN)

    To design an efficient infrared (IR) dryer for rough rice, it is important to understand the drying behavior of rice grains under infrared heating. The objective of this study was to determine the moisture diffusivity and moisture diffusivity coefficient of rough rice under IR heating and cooling. ...

  12. Characteristic length scale of input data in distributed models: implications for modeling grain size

    USGS Publications Warehouse

    Artan, Guleid A.; Neale, C. M. U.; Tarboton, D. G.

    2000-01-01

    The appropriate spatial scale for a distributed energy balance model was investigated by: (a) determining the scale of variability associated with the remotely sensed and GIS-generated model input data; and (b) examining the effects of input data spatial aggregation on model response. The semi-variogram and the characteristic length calculated from the spatial autocorrelation were used to determine the scale of variability of the remotely sensed and GIS-generated model input data. The data were collected from two hillsides at Upper Sheep Creek, a sub-basin of the Reynolds Creek Experimental Watershed, in southwest Idaho. The data were analyzed in terms of the semivariance and the integral of the autocorrelation. The minimum characteristic length associated with the variability of the data used in the analysis was 15 m. Simulated and observed radiometric surface temperature fields at different spatial resolutions were compared. The correlation between agreement simulated and observed fields sharply declined after a 10×10 m2 modeling grid size. A modeling grid size of about 10×10 m2 was deemed to be the best compromise to achieve: (a) reduction of computation time and the size of the support data; and (b) a reproduction of the observed radiometric surface temperature.

  13. 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., E-mail: hfding@nju.edu.cn [Department of Physics, National Laboratory of Solid State Microstructures, Nanjing University, 22 Hankou Road, Nanjing 210093 (China)

    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.

  14. Edge effects on the characteristics of li diffusion in graphene.

    PubMed

    Uthaisar, Chananate; Barone, Veronica

    2010-08-11

    We study the adsorption and diffusion of Li atoms on the surface of planar graphenes by means of density functional theory. When the dimensionality of graphene is reduced to a quasi-one-dimension, armchair and zigzag edges appear. We show that the presence of these edges affects not only the reactivity of the carbon material toward the adsorption of Li adatoms but also their diffusion properties. These properties strongly depend on the specific morphology of the edges. Our results indicate that Li adatoms will diffuse toward the edges while Li diffusion channels appear along the ribbon axis. For most of the diffusion paths studied here, energy barriers are lower than those in graphene. This effect is significantly more pronounced toward the edges, where energy barriers can be up to 0.15 eV smaller than those in in graphene, producing an increase of up to 2 orders of magnitude in the diffusion coefficient at room temperature. Our results indicate that electrodes fabricated with these materials should increase the power of Li-ion batteries. PMID:20698596

  15. 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.

  16. On the characteristic length scales associated with plastic deformation in metallic glasses

    SciTech Connect

    Murali, P.; Zhang, Y. W. [Institute of High Performance Computing, Singapore 138632 (Singapore); Gao, H. J. [School of Engineering, Brown University, Rhode Island 02912 (United States)

    2012-05-14

    Atomistic simulations revealed that the spatial correlations of plastic displacements in three metallic glasses, FeP, MgAl, and CuZr, follow an exponential law with a characteristic length scale l{sub c} that governs Poisson's ratio {nu}, shear band thickness t{sub SB}, and fracture mode in these materials. Among the three glasses, FeP exhibits smallest l{sub c}, thinnest t{sub SB}, lowest {nu}, and brittle fracture; CuZr exhibits largest l{sub c}, thickest t{sub SB}, highest {nu}, and ductile fracture, while properties of MgAl lie in between those of FeP and CuZr. These findings corroborate well with existing experimental observations and suggest l{sub c} as a fundamental measure of the shear transformation zone size in metallic glasses.

  17. On the characteristic length scales associated with plastic deformation in metallic glasses

    NASA Astrophysics Data System (ADS)

    Murali, P.; Zhang, Y. W.; Gao, H. J.

    2012-05-01

    Atomistic simulations revealed that the spatial correlations of plastic displacements in three metallic glasses, FeP, MgAl, and CuZr, follow an exponential law with a characteristic length scale ?c that governs Poisson's ratio ?, shear band thickness tSB, and fracture mode in these materials. Among the three glasses, FeP exhibits smallest ?c, thinnest tSB, lowest ?, and brittle fracture; CuZr exhibits largest ?c, thickest tSB, highest ?, and ductile fracture, while properties of MgAl lie in between those of FeP and CuZr. These findings corroborate well with existing experimental observations and suggest ?c as a fundamental measure of the shear transformation zone size in metallic glasses.

  18. Effect on fan flow characteristics of length and axial location of a cascade thrust reverser

    NASA Technical Reports Server (NTRS)

    Dietrich, D. A.

    1975-01-01

    A series of static tests were conducted on a model fan with a diameter of 14.0 cm to determine the fan operating characteristics, the inlet static pressure contours, the fan-exit total and static pressure contours, and the fan-exit pressure distortion parameters associated with the installation of a partial-circumferential-emission cascade thrust reverser. The tests variables included the cascade axial length, the axial location of the reverser, and the type of fan inlet. It was shown that significant total and static pressure distortions were produced in the fan aft duct, and that some configurations induced a static pressure distortion at the fan face. The amount of flow passed by the fan and the level of the flow distortions were dependent upon all the variables tested.

  19. NOx emission characteristics of counterflow syngas diffusion flames with airstream dilution

    E-print Network

    Aggarwal, Suresh K.

    NOx emission characteristics of counterflow syngas diffusion flames with airstream dilution Daniel Abstract Syngas is produced through a gasification process using variety of fossil fuels, including coal, biomass, organic waste, and refinery residual. Although, its composition may vary significantly

  20. The impact of network characteristics on the diffusion of innovations

    NASA Astrophysics Data System (ADS)

    Peres, Renana

    2014-05-01

    This paper studies the influence of network topology on the speed and reach of new product diffusion. While previous research has focused on comparing network types, this paper explores explicitly the relationship between topology and measurements of diffusion effectiveness. We study simultaneously the effect of three network metrics: the average degree, the relative degree of social hubs (i.e., the ratio of the average degree of highly-connected individuals to the average degree of the entire population), and the clustering coefficient. A novel network-generation procedure based on random graphs with a planted partition is used to generate 160 networks with a wide range of values for these topological metrics. Using an agent-based model, we simulate diffusion on these networks and check the dependence of the net present value (NPV) of the number of adopters over time on the network metrics. We find that the average degree and the relative degree of social hubs have a positive influence on diffusion. This result emphasizes the importance of high network connectivity and strong hubs. The clustering coefficient has a negative impact on diffusion, a finding that contributes to the ongoing controversy on the benefits and disadvantages of transitivity. These results hold for both monopolistic and duopolistic markets, and were also tested on a sample of 12 real networks.

  1. Information technology innovations: general diffusion patterns and its relationships to innovation characteristics

    Microsoft Academic Search

    James T. C. Teng; Varun Grover; Wolfgang Güttler

    2002-01-01

    While many scholars of organizational innovations have examined characteristics of innovations such as relative advantage and complexity and how they facilitate the adoption of an innovation by organizations, others have used mathematical models to fit diffusion patterns. In this study, the authors attempt to integrate these two areas of inquiry and explore the possibilities to predict diffusion patterns based on

  2. Ballistic versus diffusive base transport in the high-frequency characteristics of bipolar transistors

    E-print Network

    Luryi, Serge

    Ballistic versus diffusive base transport in the high-frequency characteristics of bipolar a universal character both in the diffusion limit ( W)Z,,) and the ballistic limit (I,,. IV). In the latter ("ballistic") limit Z& W, the second term in Eqs. (4) and (5) is negligible 2770 Appl. Phys. Lett. 60 (22), 1

  3. 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.

  4. 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.

  5. An investigation on the incompressible turbulent mean swirling flow characteristics change along straight conical diffuser

    Microsoft Academic Search

    M. Benisek; M. Nedeljkovic; S. Cantrak

    1990-01-01

    Energy loss in the swirling flow of an incompressible fluid in a straight conical diffuser is investigated experimentally. The diffuser apparatus has length 1.8 m, inlet diameter 0.4 m, and outlet diameter 0.730 m, and the measurements are obtained at Reynolds numbers between 60,000 and 550,000 and at values of the swirl parameter Omega0 between 0.09 and 2.07. The results

  6. Effective diffusivities and pore-transport characteristics of washcoated ceramic monolith for automotive catalytic converter

    Microsoft Academic Search

    Tomáš Starý; Olga Šolcová; Petr Schneider; Miloš Marek

    2006-01-01

    Using the chromatographic technique (carrier-gas: N2; tracer-gases: He, Ar) the effective diffusivity in single-pellet string columns (SPSC) packed with porous slab particles was studied. Dispersion due to extra-column effects was eliminated via convolution of column responses for two lengths. The measurements were done for cordierite particles and for cordierite coated with alumina-based washcoat. The effective diffusion coefficients for two tracer–carrier

  7. Hydraulic characteristics of straight conical diffusers of hydropower plants

    Microsoft Academic Search

    V. Ya. Karelin; N. V. Gromik; V. V. Volshanik

    1987-01-01

    This article constructs a parametric model for the hydraulic behavior of diffusers used in the intake and turbine regions of hydroelectric plants with the aim of optimizing their design efficiency, hydraulic throughput, and dimensions according to the various demands placed on them by different regions of the plant as well as by the overall size and output of the plant

  8. JOURNAL DE PHYSIQUE Colloque C6,suppl6ment au no 11-12, Tome 34, Novembre-Dtcembre 1973,page C6-65 THE MEASUREMENT OF ELECTRON DIFFUSION LENGTHS IN GaAs

    E-print Network

    Boyer, Edmond

    -65 THE MEASUREMENT OF ELECTRON DIFFUSION LENGTHS IN GaAs J. P. GOWERS Mullard Research Laboratories, Redhill, Surrey variables, the escape probability P and the electron diffusion length L. The measurement of L is therefore

  9. 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

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

    SciTech Connect

    Nogues, Gilles, E-mail: gilles.nogues@neel.cnrs.fr; Den Hertog, Martien [Inst. NEEL, Univ. Grenoble Alpes, F-38042 Grenoble (France); Inst. NEEL, CNRS, F-38042 Grenoble (France); Auzelle, Thomas; Gayral, Bruno; Daudin, Bruno [INAC, CEA, F-38054 Grenoble (France)

    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.

  11. Diffusion-coupled molecular assembly: structuring of coordination polymers across multiple length scales.

    PubMed

    Hirai, Kenji; Reboul, Julien; Morone, Nobuhiro; Heuser, John E; Furukawa, Shuhei; Kitagawa, Susumu

    2014-10-22

    Porous coordination polymers (PCPs) are an intriguing class of molecular-based materials because of the designability of framework scaffolds, pore sizes and pore surface functionalities. Besides the structural designability at the molecular scale, the structuring of PCPs into mesoscopic/macroscopic morphologies has attracted much attention due to the significance for the practical applications. The structuring of PCPs at the mesoscopic/macroscopic scale has been so far demonstrated by the spatial localization of coordination reactions on the surface of templates or at the phase boundaries. However, these methodologies have never been applied to the fabrication of solid-solution or multivariate metal-organic frameworks (MOFs), in which multiple components are homogeneously mixed. Herein, we demonstrate the structuring of a box-type superstructure comprising of a solid-solution PCP by integrating a bidirectional diffusion of multiple organic ligands into molecular assembly. The parent crystals of [Zn2(ndc)2(bpy)]n were placed in the DMF solution of additional organic component of H2bdc, and the temperature was rapidly elevated up to 80 °C (ndc = 1,4-naphthalenedicarboxylate, bpy = 4,4'-bipyridyl, bdc = 1,4-benzenedicarboxylate). The dissolution of the parent crystals induced the outward diffusion of components; contrariwise, the accumulation of the other organic ligand of H2bdc induced the inward diffusion toward the surface of the parent crystals. This bidirectional diffusion of multiple components spatially localized the recrystallization at the surface of cuboid parent crystals; therefore, the nanocrystals of a solid-solution PCP ([Zn2(bdc)1.5(ndc)0.5(bpy)]n) were organized into a mesoscopic box superstructure. Furthermore, we demonstrated that the box superstructures enhanced the mass transfer kinetics for the separation of hydrocarbons. PMID:25254320

  12. Chemical diffusion characteristics of Al-Si alloy melts under a transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Bian, Xiufang; Li, Yumin; Liu, Yang; Yang, Chuncheng; Zhao, Xiaolin

    2015-07-01

    Effect of a transverse magnetic field on the chemical diffusion (interdiffusion) characteristics between Al-10 at.% Si metallic melts and pure Al melts has been investigated experimentally. Results show that the application of a weak transverse magnetic field has evidently decreased the diffusivity of solute atoms and retarded the interdiffusion process. This effect can be attributed to the combined suppression action of interior Hall Effect and Lorentz force on the atoms mobility.

  13. 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

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

    NASA Astrophysics Data System (ADS)

    Placidi, E.; Arciprete, F.; Latini, V.; Latini, S.; Magri, R.; Scuderi, M.; Nicotra, G.; Patella, F.

    2014-09-01

    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.

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

    SciTech Connect

    Placidi, E., E-mail: ernesto.placidi@ism.cnr.it; Arciprete, F. [Istituto di Struttura della Materia, CNR, Via del Fosso del Cavaliere 100, 00133 Rome (Italy); Università di Roma “Tor Vergata”, Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Rome (Italy); Latini, V.; Latini, S.; Patella, F. [Università di Roma “Tor Vergata”, Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Rome (Italy); Magri, R. [Dipartimento di Scienze Fisiche, Informatiche e Matematiche (FIM), Università di Modena e Reggio Emilia, and Centro S3 CNR-Istituto Nanoscienze, Via Campi 213/A, 4100 Modena (Italy); Scuderi, M.; Nicotra, G. [CNR-IMM, Strada VIII, 5, 95121 Catania (Italy)

    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.

  16. Morphologic characteristics and immunohistochemical profile of diffuse intrinsic pontine gliomas.

    PubMed

    Ballester, Leomar Y; Wang, Zengfeng; Shandilya, Shaefali; Miettinen, Markku; Burger, Peter C; Eberhart, Charles G; Rodriguez, Fausto J; Raabe, Eric; Nazarian, Javad; Warren, Katherine; Quezado, Martha M

    2013-09-01

    Tumors of the central nervous system are the second most common malignancy in children. In particular, diffuse intrinsic pontine gliomas (DIPGs) are aggressive tumors with poor prognosis and account for 10% to 25% of pediatric brain tumors. The majority of DIPGs are astrocytic, infiltrative, and localized to the pons. Studies have shown median survival times of less than a year, with 90% of children dying within 2 years. We built multitissue arrays with 24 postmortem DIPG samples and analyzed the morphology and expression of several proteins (p53, EGFR, GFAP, MIB1, BMI1, ?-catenin, p16, Nanog, Nestin, OCT4, OLIG2, SOX2) with the goal of identifying potential treatment targets and improving our understanding of the biology of these tumors. The majority of DIPGs were high-grade gliomas (22), with 18 cases having features of glioblastoma (World Health Organization [WHO] grade IV) and 4 cases with high-grade features consistent with anaplastic astrocytoma (WHO grade III). One case was low grade (WHO grade II), and 1 case showed intermediate features between a grade II and grade III glioma (low mitotic rate but increased cellularity and cell atypia), being difficult to grade precisely. The majority of the tumors were positive for GFAP (24/24), MIB1 (23/24), OLIG2 (22/24), p16 (20/24), p53 (20/24), SOX2 (19/24), EGFR (16/24), and BMI1 (9/24). Our results suggest that dysregulation of EGFR and p53 may play an important role in the development of DIPGs. The majority of DIPGs express stem cell markers such as SOX2 and OLIG2, consistent with a role for tumor stem cells in the origin and maintenance of these tumors. Targeted therapies against these proteins could be beneficial in treatment. PMID:24076776

  17. The effects of inlet temperature and turbulence characteristics on the flow development inside a gas turbine exhaust diffuser

    NASA Astrophysics Data System (ADS)

    Bomela, Christian Loangola

    The overall industrial gas turbine efficiency is known to be influenced by the pressure recovery in the exhaust system. The design and, subsequently, the performance of an industrial gas turbine exhaust diffuser largely depend on its inflow conditions dictated by the turbine last stage exit flow state and the restraints of the diffuser internal geometry. Recent advances in Computational Fluid Dynamics (CFD) tools and the availability of computer hardware at an affordable cost made the virtual tool a very attractive one for the analysis of fluid flow through devices like a diffuser. In this backdrop, CFD analyses of a typical industrial gas turbine hybrid exhaust diffuser, consisting of an annular diffuser followed by a conical portion, have been carried out with the purpose of improving the performance of these thermal devices using an open-source CFD code "OpenFOAM". The first phase in the research involved the validation of the CFD approach using OpenFOAM by comparing CFD results against published benchmark experimental data. The numerical results closely captured the flow reversal and the separated boundary layer at the shroud wall where a steep velocity gradient has been observed. The standard k --epsilon turbulence model slightly over-predicted the mean velocity profile in the casing boundary layer while slightly under-predicted it in the reversed flow region. A reliable prediction of flow characteristics in this region is very important as the presence of the annular diffuser inclined wall has the most dominant effect on the downstream flow development. The core flow region and the presence of the hub wall have only a minor influence as reported by earlier experimental studies. Additional simulations were carried out in the second phase to test the veracity of other turbulence models; these include RNG k--epsilon, the SST k--o, and the Spalart-Allmaras turbulence models. It was found that a high resolution case with 47.5 million cells using the SST k--o turbulence model produced a mean flow velocity profile at the middle of the annular diffuser portion that had the best overall match with the experiment. The RNG k --epsilon, however, better predicted the diffuser performance along the exhaust diffuser length by means of the pressure recovery coefficient. These results were obtained using uniform inflow conditions and steady-state simulations. As such, the last phase of our investigations involved varying the inflow parameters like the turbulence intensity, the inlet flow temperature, and the flow angularity, which constitute important characteristics of the turbine blade wake, to investigate their impact on the diffuser design and performance. These isothermal CFD simulations revealed that by changing the flow temperature from 15 to 427°C, the pressure recovery coefficient significantly increased. However, it has been shown that the increase of temperature had no effects on the size of the reversed flow region and the thickness of the separated casing boundary layer, although the flow appears to be more turbulent. Furthermore, it has been established that an optimum turbulence intensity of about 4% produced comparable diffuser performance as the experiment. We also found that a velocity angle of about 2.5° at the last turbine stage will ensure a better exhaust diffuser performance.

  18. Optimization of hybrid blue organic light-emitting diodes based on singlet and triplet exciton diffusion length

    NASA Astrophysics Data System (ADS)

    Lee, Song Eun; Lee, Ho Won; Lee, Jae Woo; Hwang, Kyo Min; Park, Soo Na; Yoon, Seung Soo; Kim, Young Kwan

    2015-06-01

    The hybrid blue organic light-emitting diodes (HB OLEDs) with triplet harvesting (TH) structures within an emitting layer (EML) are fabricated with fluorescent and phosphorescent EMLs. The TH is to transfer triplet excitons from fluorescence to phosphorescence, where they can decay radiatively. Remarkably, the half-decay lifetime of a hybrid blue device with fluorescent and phosphorescent EML thickness of 5 and 25 nm, measured at an initial luminance of 500 cd/m2, has improved twice than that of using a conventional structure. Additionally, the blue device’s efficiency improved. We attribute this improvement to the efficient triplet excitons energy transfer and the optimized distribution of the EML which depends on singlet and triplet excitons diffusion length that occurs within each the EML.

  19. Performance characteristics of two annular dump diffusers using suction-stabilized vortex flow control

    NASA Technical Reports Server (NTRS)

    Juhasz, A. J.; Smith, J. M.

    1978-01-01

    The two diffusers employed in the investigation had the same overall area ratio but different prediffuser area ratios and suction slot geometries. Velocity profile and diffuser pressure recovery performance data were obtained at ambient pressure and temperature, with inlet Mach numbers ranging from 0.18 to 0.41 and suction rate varying from zero to 18% of total inlet mass flow rate. On the basis of the reported investigation it is concluded that suction stabilized vortex flow diffusers show promise for application in combustors because of relatively high static pressure recovery and low total pressure loss obtained in a short length. Performance obtained using a narrow angle (7 degree) prediffuser was superior to that obtained with a prediffuser having a 14 degree included angle.

  20. 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., E-mail: stuchin@isp.nsc.ru; Brunev, D. V.; Zverev, A. V.; Dvoretsky, S. A. [Institute of Semiconductor Physics, Russian Academy of Science, Siberian Division, 13, Acad. Lavrent'ev Avenue, Novosibirsk 630090 (Russian Federation)

    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.

  1. Ceruminal diffusion activities and ceruminolytic characteristics of otic preparations – an in-vitro study

    PubMed Central

    2013-01-01

    Background An in-vitro setup was established in order to determine a) the diffusion activities of eight otic preparations (Aurizon®, Eas Otic®, Epi Otic®, Otifree®, Otomax®, Panolog®, Posatex®, Surolan®) through synthetic cerumen, and b) the ceruminolytic capacity and impregnation effects of these products. The main lipid classes of canine cerumen produced with moderate, non-purulent otitis externa were determined by thin layer chromatography and were subsequently used to produce a standardised synthetic cerumen (SCC). SCC was filled into capillary tubes, all of which were loaded with six commercially available multipurpose otic medications and two ear cleaners, each mixed with two markers in two experimental setups. These two marker compounds (Oil red O and marbofloxacin) were chosen, since they exhibit different physicochemical drug characteristics by which it is possible to determine and verify the diffusion activity of different types of liquids (i.e. the otic preparations). A synthetic cerumen described in the literature (JSL) was also used for comparison as its lipid composition was different to SCC. The diffusion activities of the otic preparations through both types of synthetic cerumen were studied over 24 hours. A second in-vitro experiment determined both the ceruminolytic activity and impregnation effect of the otic preparations by comparing the weight loss or weight gain after repeated incubation of JSL. Results Canine cerumen is mainly composed of triglycerides, sterol esters, fatty acid esters and squalene. The diffusion experiments showed a high diffusion efficacy along with a high impregnation effect for one test product. All the other products exhibited a lower diffusion activity with a mild to moderate impregnation effect. A mild ceruminolytic activity was observed for the two ear cleaners but not for any of the otic medications. Conclusions The present study demonstrates that there are significant differences in the diffusion characteristics and ceruminolytic properties of the eight tested otic preparations. PMID:23574753

  2. Channel characteristics analysis of diffuse indoor cellular optical wireless communication systems

    NASA Astrophysics Data System (ADS)

    Wu, D.; Ghassemlooy, Z.; Le-Minh, H.; Rajbhandari, S.; Chao, L.

    2011-12-01

    In this paper, two models for diffuse indoor cellular optical wireless communication (OWC) systems with and without a holographic light shaping diffuser (LSD) are presented. For both models, the power distribution, the impulse response of the channels and root mean square (RMS) delay are described and analyzed. We perform a computer simulation to compare the channel characteristics of the typical indoor cellular OWC systems with that employing the holographic LSD. The results show that the system with the holographic LSD provides a more uniform power distribution and a less RMS delay spread for the same divergence angles.

  3. Flow field and performance characteristics of combustor diffusers: A basic study

    SciTech Connect

    Hestermann, R.; Kim, S.; Ben Khaled, A.; Wittig, S. [Univ. Karlsruhe (Germany). Lehrstuhl und Inst. fuer Thermische Stroemungsmaschinen

    1995-10-01

    Results of a detailed study concerning the influence of geometric as well as fluid mechanic parameters o the performance of a plane model combustor diffuser in cold flow are presented. For a qualitative insight into the complex flow field inside the prediffuser, the sudden expansion region, and the flow field around the flame tube dome, results of a flow visualization study with the hydrogen bubble method as well as with the ink jet method are presented for different opening angles of the prediffuser and for different flame tube distances. Also, quantitative data from detailed measurements with LDV and conventional pressure probes in a geometrically similar air-driven setup are presented. These data clearly demonstrate the effect of boundary layer thickness as well as the influence of different turbulence levels at the entry of the prediffuser on the performance characteristics of combustor diffusers. The possibility of getting an unseparated flow field inside the prediffuser even at large opening angles by appropriately matching the diffuser`s opening angle and the flame tube distance is demonstrated. Also, for flows with an increased turbulence level at the entrance--all other conditions held constant--an increased opening angle can be realized without experiencing flow separation. The comparison of the experimental data with predictions utilizing a finite-volume-code based on a body-fitted coordinate system for diffusers with an included total opening angle less than 18 deg demonstrates the capability of describing the flow field in combustor diffusers with reasonable accuracy.

  4. Enhanced performance of an AlGaN/GaN high electron mobility transistor on Si by means of improved adatom diffusion length during MOCVD epitaxy

    NASA Astrophysics Data System (ADS)

    Shahedipour-Sandvik, F.; Leathersich, J.; Tompkins, R. P.; Suvarna, P.; Tungare, M.; Walsh, T. A.; Kirchner, K. W.; Zhou, S.; Jones, K. A.

    2013-07-01

    Four types of AlGaN/GaN high electron mobility transistor (HEMT) structures have been epitaxially grown on Si substrates by metalorganic chemical vapor deposition (MOCVD) and fabricated into devices. To achieve crack-free device structures, various stress-engineering methods have been employed including the use of AlGaN/AlGaN-graded layers, insertion of low-temperature AlN layers and ion implantation of the AlN/Si substrate. To improve material quality, pulsed MOCVD is used to enhance adatom diffusion length during (Al) GaN epitaxy of various layers in the HEMT structure. A comparison between structural and morphological characteristics of the HEMTs shows improvement in the (0 0 0 2) symmetric rocking curve value to 837.9 s-1 and the surface roughness of 0.21 nm for HEMT structures grown using pulsed epitaxy. An OFF-state breakdown voltage of 217 V at a drain current of 1 mA mm-1 at Vg = -8 V was measured for the structure with enhanced material quality.

  5. Diffusion in the vicinity of standard-design nuclear power plants--I. Wind-tunnel evaluation of diffusive characteristics of a simulated suburban neutral atmospheric boundary layer.

    PubMed

    Payne, A W; Snyder, W H; Binkowski, F S; Watson, J E

    1982-12-01

    A large meteorological wind tunnel was used to simulate a suburban atmospheric boundary layer. The model-prototype scale was 1:300 and the roughness length was approximately 1.0 m full scale. The model boundary layer simulated full scale dispersion from ground-level and elevated release points over surfaces of comparable roughness length. This information should prove useful in a variety of transport and diffusion studies over short to moderate downwind distances. It will be used in Part II as the baseline data set with which to compare diffusion downwind of standard-design nuclear power plants. PMID:7152946

  6. Strength characteristics of the self-sustained wave in grooved channels with different groove length

    NASA Astrophysics Data System (ADS)

    Sun, Faming; Bian, Yongning; Arima, Hirofumi; Ikegami, Yasuyuki; Xu, Xinsheng

    2010-12-01

    The self-sustained oscillations arising in a series of grooved channels are investigated experimentally. Pressure drop, time-averaged and time-various local pressure in the grooved channels with six kinds of groove length are measured with the differential transducer and the pressure sensor, respectively, and the flow structures are visualized using the aluminum dust method. The local pressure signal shows that the self-sustained wave appears in the first or second frequency, and the Strouhal number, based on the nature frequency of the self-sustained wave, is almost equivalent for the first or second frequency in the same channel. Meanwhile, the Strouhal number for each channel decreases monotonously with the groove length. Furthermore, it is found that increasing pressure will result in higher amplitude of the self-sustained wave, this behavior is significant for the efficient heat transfer in practical engineering.

  7. The dependence of the latency relaxation on sarcomere length and other characteristics of isolated muscle fibres

    PubMed Central

    Mulieri, Louis A.

    1972-01-01

    1. The latency relaxation has been examined in single fibres from frog striated muscle with particular attention given to its possible relation to Ca2+ release during excitation—contraction coupling. 2. Latency relaxations were recorded at 19-23° C from massively stimulated (0·2 msec pulses) single fibres using two selected RCA 5734 transducer tubes in a bridge circuit. 3. The depth of the latency relaxation has its full value when stimulus strength is between 40 and 400% above twitch threshold. Stronger stimuli reversibly diminish the latency relaxation. 4. The variation in depth of latency relaxation with sarcomere length was found similar to that reported previously for multifibre preparations but in single fibres the peak of the curve consists of a plateau between sarcomere lengths of 2·8 ? and 3·2 ?. 5. Sucrose hypertonicity increases the depth of the latency relaxation at sarcomere lengths below 2·8 ? but above this length it has either no effect or a depressant effect depending on the degree of hypertonicity. 6. The maximal depth of the latency relaxation (measured at 3 ?) averaged 0·23% of the maximal tetanus tension (measured at 2·2 ?) and was strongly correlated (r = 0·87) with the latter in forty-five single fibres. 7. The maximal depth of the latency relaxation is not correlated with the number of sarcomeres in series in a fibre. 8. The results of this study are shown to fully support and extend Sandow's (1966) hypothesis that the latency relaxation is caused by release of activator Ca2+ from the sarcoplasmic reticulum. PMID:4537709

  8. Diffusion characteristics and molecular size of DOM in plant and soil extracts

    NASA Astrophysics Data System (ADS)

    Fuß, Roland; Zsolnay, Ádám.; Munch, Jean Charles

    2010-05-01

    The main sources of dissolved organic matter (DOM) in soil are plant litter, root exudates, soil fauna, and the un-dissolved soil organic matter pool. A strong spatial heterogeneity of these sources, even on the microscale, is observed in soil. Consequently diffusion of DOM is an important transport process, which connects "hot-spots" of microbial activity and substrates. Therefore an experiment was conducted in order to measure diffusion constants of DOM and 2 inorganic nutrients. Furthermore, hydrodynamic diameters were calculated from these constants, which give an approximation of molecular size. The diffusion characteristics of several parameters in aqueous extracts of two soils and of barley were investigated. They were: Ammonium, nitrate, dissolved organic nitrogen (DON), dissolved inorganic carbon, dissolved organic carbon (DOC), and 3 different fluorophore groups associated with DOM. The fluorophore groups were identified and quantified from fluorescence excitation emission spectra with the PARAFAC model. Two of the groups resembled groups, which have been used to imply the presence of humic substances (HS). Our results give reason to believe these groups can be regarded as indicators of dissolved HS in aqueous extracts only with caution. The other group, enriched in the barley extract, was the "tryptophan" group. However, its diffusion constant differed markedly between the soil and barley extracts, indicating that compounds other than tryptophan contributed to this fluorophore in soil extracts. When the Stokes-Einstein equation was applied to the diffusion coefficients of DOC (in all extracts about 0.27 x 10-5 cm2 s-1 at 4 °C), a mean hydrodynamic diameter of 1.0 nm for the DOC was calculated. The diffusion constants for the other DOM parameters were also similar, regardless of source, with the exception of the "tryptophan" fluorophore group from barley, which diffused about 1.5 times faster than that from the soils and was in good agreement with the theoretical diffusion coefficient of tryptophan. There was no evidence of macromolecules in DOM. The diffusion of the inorganic nitrogen species was up to 4 times as rapid as that for DOC. Therefore, where in situ metabolism is fuelled by diffusion, diffusion rates of dissolved nitrogen are not likely to be the limiting factor.

  9. Determination of the minority carrier diffusion length in compositionally graded Cu,,In,Ga...Se2 solar cells using electron beam induced

    E-print Network

    Wu, Junqiao

    and compared with external quantum efficiency measurements. © 2010 American Institute of Physics. doi:10 for the accurate determination of the carrier collection efficiency and minority carrier diffusion length in Cu In across the film thickness introduce quasielectric fields that are found to improve collection efficiency

  10. 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.

  11. Characteristics of Gas Emission at Super-Length Fully-Mechanized Top Coal Caving Face

    Microsoft Academic Search

    Jia-lin XU; Bei-jian YU; Jin-fu LOU; Dong-ping WANG

    2007-01-01

    Characteristics of gas emission at the K8206 working face in the Third mine of the Yangquan Coal Group were investigated. The effects of strata movement, advancing velocity of working face, production capacity of working face and gas extraction capability of strike high-level entry on gas emission at K8206 working face were analyzed. A regression equation, reflecting the relationship between relative

  12. Night and Day in the VA: Associations between Night Shift Staffing, Nurse Workforce Characteristics, and Length of Stay

    PubMed Central

    de Cordova, Pamela B.; Phibbs, Ciaran S.; Schmitt, Susan; Stone, Patricia W.

    2014-01-01

    In hospitals, nurses provide patient care around the clock, but the impact of night staff characteristics on patient outcomes is not well understood. The aim of this study was to examine the association between night nurse staffing and workforce characteristics and the length of stay (LOS) in 138 Veterans Affairs (VA) hospitals using panel data from 2002 through 2006. Staffing in hours per patient day was higher during the day than at night. The day nurse workforce had more educational preparation than the night workforce. Nurses’ years of experience at the unit, facility, and VA level were greater at night. In multivariate analyses controlling for confounding variables, higher night staffing and a higher skill mix were associated with reduced LOS. PMID:24403000

  13. Determination of carrier lifetime and diffusion length in Al-doped 4H–SiC epilayers by time-resolved optical techniques

    NASA Astrophysics Data System (ADS)

    Liaugaudas, Gediminas; Dargis, Donatas; Kwasnicki, Pawel; Arvinte, Roxana; Zielinski, Marcin; Jaraši?nas, K?stutis

    2015-01-01

    A series of p-type 4H–SiC epilayers with aluminium concentration ranging from 2? × ?1016 to 8? × ?1019?cm?3 were investigated by time-resolved optical techniques in order to determine the effect of aluminium doping on high-injection carrier lifetime at room temperature and the diffusion coefficient at different injections (from ?3? × ?1018 to ?5? × ?1019?cm?3) and temperatures (from 78 to 730?K). We find that the defect limited carrier lifetime ?SRH decreases from 20?ns in the low-doped samples down to ?0.6?ns in the heavily doped epilayers. Accordingly, the ambipolar diffusion coefficient decreases from Da = 3.5?cm2?s?1 down to ?0.6?cm2?s?1, corresponding to the hole mobility of µh = 70?cm2?Vs?1 and 12?cm2?Vs?1, respectively. In the highly doped epilayers, the injection-induced decrease of the diffusion coefficient, due to the transition from the minority carrier diffusion to the ambipolar diffusion, provided the electron diffusion coefficient of De ? 3?cm2?s?1. The Al-doping resulted in the gradual decrease of the ambipolar diffusion length, from LD = 2.7?µm down to LD = 0.25?µm in the epilayers with the lowest and highest aluminium concentrations.

  14. Multiscaling for systems with a broad continuum of characteristic lengths and times: Structural transitions in nanocomposites.

    PubMed

    Pankavich, S; Ortoleva, P

    2010-06-01

    The multiscale approach to N-body systems is generalized to address the broad continuum of long time and length scales associated with collective behaviors. A technique is developed based on the concept of an uncountable set of time variables and of order parameters (OPs) specifying major features of the system. We adopt this perspective as a natural extension of the commonly used discrete set of time scales and OPs which is practical when only a few, widely separated scales exist. The existence of a gap in the spectrum of time scales for such a system (under quasiequilibrium conditions) is used to introduce a continuous scaling and perform a multiscale analysis of the Liouville equation. A functional-differential Smoluchowski equation is derived for the stochastic dynamics of the continuum of Fourier component OPs. A continuum of spatially nonlocal Langevin equations for the OPs is also derived. The theory is demonstrated via the analysis of structural transitions in a composite material, as occurs for viral capsids and molecular circuits. PMID:20661319

  15. Multiscaling for systems with a broad continuum of characteristic lengths and times: Structural transitions in nanocomposites

    PubMed Central

    Pankavich, S.; Ortoleva, P.

    2010-01-01

    The multiscale approach to N-body systems is generalized to address the broad continuum of long time and length scales associated with collective behaviors. A technique is developed based on the concept of an uncountable set of time variables and of order parameters (OPs) specifying major features of the system. We adopt this perspective as a natural extension of the commonly used discrete set of time scales and OPs which is practical when only a few, widely separated scales exist. The existence of a gap in the spectrum of time scales for such a system (under quasiequilibrium conditions) is used to introduce a continuous scaling and perform a multiscale analysis of the Liouville equation. A functional-differential Smoluchowski equation is derived for the stochastic dynamics of the continuum of Fourier component OPs. A continuum of spatially nonlocal Langevin equations for the OPs is also derived. The theory is demonstrated via the analysis of structural transitions in a composite material, as occurs for viral capsids and molecular circuits. PMID:20661319

  16. Multiscaling for systems with a broad continuum of characteristic lengths and times: Structural transitions in nanocomposites

    NASA Astrophysics Data System (ADS)

    Pankavich, S.; Ortoleva, P.

    2010-06-01

    The multiscale approach to N-body systems is generalized to address the broad continuum of long time and length scales associated with collective behaviors. A technique is developed based on the concept of an uncountable set of time variables and of order parameters (OPs) specifying major features of the system. We adopt this perspective as a natural extension of the commonly used discrete set of time scales and OPs which is practical when only a few, widely separated scales exist. The existence of a gap in the spectrum of time scales for such a system (under quasiequilibrium conditions) is used to introduce a continuous scaling and perform a multiscale analysis of the Liouville equation. A functional-differential Smoluchowski equation is derived for the stochastic dynamics of the continuum of Fourier component OPs. A continuum of spatially nonlocal Langevin equations for the OPs is also derived. The theory is demonstrated via the analysis of structural transitions in a composite material, as occurs for viral capsids and molecular circuits.

  17. Effects of Characteristic Length Scales on the Exciton Dynamics in Rubrene Single Crystals

    E-print Network

    Gieseking, Björn; Müller, Benjamin; Deibel, Carsten; Engels, Bernd; Dyakonov, Vladimir; Pflaum, Jens

    2013-01-01

    As for its inorganic counterparts the future developments in organic electronics are driven by an advanced device miniaturization. Therefore, the opto-electronic behavior of up-to-date devices is progressively governed by the local structural environment. However, there is a lack of organic semiconductor materials providing access to the fundamental structure-functionality relation, either due to limitations by their inherent growth or their optical characteristics. In this work we present a systematic investigation of the optical states, so-called excitons, and their temporal evolution in the prototypical organic semiconductor rubrene by means of time and temperature dependent photoluminescence studies. This material offers the unique possibility of preparing well-defined morphologies with adjustable degree of confinement. By this approach we are able to confirm the direct influence on the temperature dependent optical processes with picosecond resolution already for a spatial localization of excitation on t...

  18. Poroelastic response of articular cartilage by nanoindentation creep tests at different characteristic lengths.

    PubMed

    Taffetani, M; Gottardi, R; Gastaldi, D; Raiteri, R; Vena, P

    2014-07-01

    Nanoindentation is an experimental technique which is attracting increasing interests for the mechanical characterization of articular cartilage. In particular, time dependent mechanical responses due to fluid flow through the porous matrix can be quantitatively investigated by nanoindentation experiments at different penetration depths and/or by using different probe sizes. The aim of this paper is to provide a framework for the quantitative interpretation of the poroelastic response of articular cartilage subjected to creep nanoindentation tests. To this purpose, multiload creep tests using spherical indenters have been carried out on saturated samples of mature bovine articular cartilage achieving two main quantitative results. First, the dependence of indentation modulus in the drained state (at equilibrium) on the tip radius: a value of 500 kPa has been found using the large tip (400 ?m radius) and of 1.7 MPa using the smaller one (25 ?m). Secon, the permeability at microscopic scale was estimated at values ranging from 4.5×10(-16) m(4)/N s to 0.1×10(-16) m(4)/N s, from low to high equivalent deformation. Consistently with a poroelastic behavior, the size-dependent response of the indenter displacement disappears when characteristic size and permeability are accounted for. For comparison purposes, the same protocol was applied to intrinsically viscoelastic homogeneous samples of polydimethylsiloxane (PDMS): both indentation modulus and time response have been found size-independent. PMID:24814573

  19. Thermal-wave resonant-cavity measurements of the thermal diffusivity of air: A comparison between cavity-length and modulation-frequency scans

    Microsoft Academic Search

    J. Shen; A. Mandelis; B. D. Aloysius

    1996-01-01

    The application of a thermal-wave resonant cavity to thermal-diffusivity measurements of gases has been investigated. The cavity was constructed using a thin aluminum foil wall as the intensitv-modulated laser-beam oscillator source opposite a pyroclectric polyvilidene fluoride wall acting as a signal transducer. Theoretically, cavity-length and modulation-frequency scans both produce resonance-like extrema in lock-in in-phase and quadrature curses. These extrema can

  20. Effect of Photon Recycling on Diffusion Length and Internal Quantum Efficiency in AlxGa1-xAs-GaAs Heterostructures

    Microsoft Academic Search

    Toshihide Kuriyama; Takeshi Kamiya; Hisayoshi Yanai

    1977-01-01

    The photon recycling process, i.e., the excitation of electron-hole pairs by the reabsorption of luminescent light, has large effects on the determination of the minority carrier diffusion length L and the internal quantum efficiency etain GaAs with a high quantum efficiency. In this report, we show that the separate treatments of L and etain cause the erroneous results for materials

  1. Use of electron beam induced current to determine diffusion lengths and radiation damage coefficients in GaAs space solar cells

    Microsoft Academic Search

    C. Hardingham

    1997-01-01

    A novel technique for determining minority carrier diffusion lengths in solar cell devices is described. The technique comprises electron beam induced current measurements together with modelling based on the use of carrier generation distribution functions derived by Monte Carlo techniques. The technique is applied to various GaAs solar cells, as-made and irradiated with high-energy protons or electrons, in order to

  2. Pore-size dependence and characteristics of water diffusion in slit-like micropores

    E-print Network

    S. O. Diallo

    2015-04-10

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

  3. A study of damage zones or characteristic lengths as related to the fracture behavior of graphite/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Yeow, Y. T.; Brinson, H. F.

    1977-01-01

    Uniaxial tensile tests conducted on a variety of graphite/epoxy laminates, containing narrow rectangular slits, square or circular holes with various aspect ratios are discussed. The techniques used to study stable crack or damage zone growth--namely, birefringence coatings, COD gages, and microscopic observations are discussed. Initial and final fracture modes are discussed as well as the effect of notch size and shape, and laminate type on the fracture process. Characteristic lengths are calculated and compared to each other using the point, average and inherent flaw theories. Fracture toughnesses are calculated by the same theories and compared to a boundary integral equation technique. Finite width K-calibration factors are also discussed.

  4. Characteristic length scales and time-averaged transport velocities of suspended sediment in the mid-Atlantic Region, USA

    USGS Publications Warehouse

    Pizzuto, James; Schenk, Edward R.; Hupp, Cliff R.; Gellis, Allen; Noe, Greg; Williamson, Elyse; Karwan, Diana L.; O'Neal, Michael; Marquard, Julia; Aalto, Rolf; Newbold, Denis

    2014-01-01

    Watershed Best Management Practices (BMPs) are often designed to reduce loading from particle-borne contaminants, but the temporal lag between BMP implementation and improvement in receiving water quality is difficult to assess because particles are only moved downstream episodically, resting for long periods in storage between transport events. A theory is developed that describes the downstream movement of suspended sediment particles accounting for the time particles spend in storage given sediment budget data (by grain size fraction) and information on particle transit times through storage reservoirs. The theory is used to define a suspended sediment transport length scale that describes how far particles are carried during transport events, and to estimate a downstream particle velocity that includes time spent in storage. At 5 upland watersheds of the mid-Atlantic region, transport length scales for silt-clay range from 4 to 60 km, while those for sand range from 0.4 to 113 km. Mean sediment velocities for silt-clay range from 0.0072 km/yr to 0.12 km/yr, while those for sand range from 0.0008 km/yr to 0.20 km/yr, 4–6 orders of magnitude slower than the velocity of water in the channel. These results suggest lag times of 100–1000 years between BMP implementation and effectiveness in receiving waters such as the Chesapeake Bay (where BMPs are located upstream of the characteristic transport length scale). Many particles likely travel much faster than these average values, so further research is needed to determine the complete distribution of suspended sediment velocities in real watersheds.

  5. Characteristic length scales and time-averaged transport velocities of suspended sediment in the mid-Atlantic Region, USA

    NASA Astrophysics Data System (ADS)

    Pizzuto, James; Schenk, Edward R.; Hupp, Cliff R.; Gellis, Allen; Noe, Greg; Williamson, Elyse; Karwan, Diana L.; O'Neal, Michael; Marquard, Julia; Aalto, Rolf; Newbold, Denis

    2014-02-01

    Watershed Best Management Practices (BMPs) are often designed to reduce loading from particle-borne contaminants, but the temporal lag between BMP implementation and improvement in receiving water quality is difficult to assess because particles are only moved downstream episodically, resting for long periods in storage between transport events. A theory is developed that describes the downstream movement of suspended sediment particles accounting for the time particles spend in storage given sediment budget data (by grain size fraction) and information on particle transit times through storage reservoirs. The theory is used to define a suspended sediment transport length scale that describes how far particles are carried during transport events, and to estimate a downstream particle velocity that includes time spent in storage. At 5 upland watersheds of the mid-Atlantic region, transport length scales for silt-clay range from 4 to 60 km, while those for sand range from 0.4 to 113 km. Mean sediment velocities for silt-clay range from 0.0072 km/yr to 0.12 km/yr, while those for sand range from 0.0008 km/yr to 0.20 km/yr, 4-6 orders of magnitude slower than the velocity of water in the channel. These results suggest lag times of 100-1000 years between BMP implementation and effectiveness in receiving waters such as the Chesapeake Bay (where BMPs are located upstream of the characteristic transport length scale). Many particles likely travel much faster than these average values, so further research is needed to determine the complete distribution of suspended sediment velocities in real watersheds.

  6. Characteristics of Diffusion in the Corticospinal Tract of Patients with Early Stage of Schizophrenia: Diffusion Tensor Magnetic Resonance Imaging.

    PubMed

    Ublinskii, M V; Semenova, N A; Lukovkina, O V; Sidorin, S V; Lebedeva, I S; Kaleda, V G; Barkhatova, A N; Akhadov, T A

    2015-05-01

    Specific features of diffusion in the cerebral corticospinal tract of patients with early stages of schizophrenia were studied using methods of diffusion tensor magnetic-resonance imaging and magnetic resonance spectroscopy. A decrease in the coefficient of fractional anisotropy in the posterior limb of the internal capsule and an increase in diffusion coefficient in the radiate crown and motor cortex were observed. The results reflect different mechanisms of changes in water diffusion in various areas of the corticospinal tract: changes in nerve fiber microstructure in the internal capsule of the left hemisphere and a decrease in their density in the motor cortex and radiate crown. PMID:26033583

  7. Length of stay and costs for asthma patients by hospital characteristics--a five-year population-based analysis.

    PubMed

    Lin, Herng-Ching; Kao, Senyeong; Wen, Hsyien-Chia; Wu, Chuan-Song; Chung, Chi-Li

    2005-09-01

    This study sets out to explore the relationship between hospital characteristics, asthma length of stay (LOS), and costs per discharge. The study adopts hospitalization data from the Taiwan National Health Insurance Research Database covering the period from 1997 to 2001. Study subjects were identified from the database by principal diagnosis of asthma or asthmatic bronchitis, with a total of 139,630 cases being included in the study. Multiple-regression analyses were performed to explore the relationship between LOS, costs per discharge and hospital characteristics, adjusting for age, gender, and discharge status of patients, as well as complications or comorbidities. The regression analyses showed that, compared with district hospitals, medical centers and regional hospitals have longer and more statistically significant LOS, as well as higher costs. Hospitals operating on a for-profit basis have shorter LOS and lower costs than public and not-for-profit hospitals. This study shows the existence of wide variations in LOS and costs per discharge for asthma hospitalizations, between the various types of hospitals in Taiwan. PMID:16169785

  8. Characteristics of the probability function for three random-walk models of reaction-diffusion processes

    NASA Astrophysics Data System (ADS)

    Musho, Matthew K.; Kozak, John J.

    1984-10-01

    A method is presented for calculating exactly the relative width (?2)1/2/, the skewness ?1, and the kurtosis ?2 characterizing the probability distribution function for three random-walk models of diffusion-controlled processes. For processes in which a diffusing coreactant A reacts irreversibly with a target molecule B situated at a reaction center, three models are considered. The first is the traditional one of an unbiased, nearest-neighbor random walk on a d-dimensional periodic/confining lattice with traps; the second involves the consideration of unbiased, non-nearest-neigh bor (i.e., variable-step length) walks on the same d-dimensional lattice; and, the third deals with the case of a biased, nearest-neighbor walk on a d-dimensional lattice (wherein a walker experiences a potential centered at the deep trap site of the lattice). Our method, which has been described in detail elsewhere [P.A. Politowicz and J. J. Kozak, Phys. Rev. B 28, 5549 (1983)] is based on the use of group theoretic arguments within the framework of the theory of finite Markov processes. The approach allows the separate effects of geometry (system size N, dimensionality d, and valency ?), of the governing potential and of the medium temperature to be assessed and their respective influence on (?2)1/2/, ?1, and ?2 to be studied quantitatively. We determine the classes of potential functions and the regimes of temperature for which allowing variable-length jumps or admitting a bias in the site-to-site trajectory of the walker produces results which are significantly different (both quantitatively and qualitatively) from those calculated assuming only unbiased, nearest-neighbor random walks. Finally, we demonstrate that the approach provides a method for determining a continuous probability (density) distribution function consistent with the numerical data on (?2)1/2/, ?1, and ?2 for the processes described above. In particular we show that the first of the above reaction-diffusion models (and probability the second) can be described quantitatively by an exponential distribution function in d=2,3 and by a Pearson type III distribution in d=1.

  9. Experimental study and analytical modeling of the channel length influence on the electrical characteristics of small-molecule thin-film transistors

    NASA Astrophysics Data System (ADS)

    Boukhili, W.; Mahdouani, M.; Bourguiga, R.; Puigdollers, J.

    2015-07-01

    Bottom-contact p-type small-molecule copper phthalocyanine (CuPc) thin film transistors (TFTs) with different channel lengths have been fabricated by thermal evaporation. The influence of the channel length on the current-voltage characteristics of the fabricated transistors were investigated in the linear and saturation regimes. The devices exhibit excellent p-type operation characteristics. Results show that devices with smaller channel length (L = 2.5 ?m and 5 ?m) present the best electrical performance, in terms of drain current value, field effect mobility and subthreshold slope. Saturation field-effect mobilities of 1.7 × 10-3 cm2 V-1 s-1 and 1 × 10-3 cm2 V-1 s-1 were obtained for TFTs with channel lengths of L = 2.5 ?m and L = 5 ?m, respectively. Transmission line method was used to study the dependence of the contact resistance with the channel length. Contact resistance becomes dominant with respect to the channel resistance only in the case of short channel devices (L = 2.5 ?m and 5 ?m). It was also found that the field effect mobility is extremely dependent on the channel length dimension. Finally, an analytical model has been developed to reproduce the dependence of the transfer characteristics with the channel length and the obtained data are in good agreement with the experimental results for all fabricated devices.

  10. High-pressure soot formation and diffusion flame extinction characteristics of gaseous and liquid fuels

    NASA Astrophysics Data System (ADS)

    Karatas, Ahmet Emre

    High-pressure soot formation and flame stability characteristics were studied experimentally in laminar diffusion flames. For the former, radially resolved soot volume fraction and temperature profiles were measured in axisymmetric co-flow laminar diffusion flames of pre-vaporized n-heptane-air, undiluted ethylene-air, and nitrogen and carbon dioxide diluted ethylene-air at elevated pressures. Abel inversion was used to re-construct radially resolved data from the line-of-sight spectral soot emission measurements. For the latter, flame extinction strain rate was measured in counterflow laminar diffusion flames of C1-4 alcohols and hydrocarbon fuels of n-heptane, n-octane, iso-octane, toluene, Jet-A, and biodiesel. The luminous flame height, as marked by visible soot radiation, of the nitrogen- and helium-diluted n-heptane and nitrogen- and carbon dioxide-diluted ethylene flames stayed constant at all pressures. In pure ethylene flames, flame heights initially increased with pressure, but changed little above 5 atm. The maximum soot yield as a function of pressure in nitrogen-diluted n-heptane diffusion flames indicate that n-heptane flames are slightly more sensitive to pressure than gaseous alkane hydrocarbon flames at least up to 7 atm. Ethylene's maximum soot volume fractions were much higher than those of ethane and n-heptane diluted with nitrogen (fuel to nitrogen mass flow ratio is about 0.5). Pressure dependence of the peak carbon conversion to soot, defined as the percentage of fuel's carbon content converted to soot, was assessed and compared to previous measurements with other gaseous fuels. Maximum soot volume fractions were consistently lower in carbon dioxide-diluted flames between 5 and 15 atm but approached similar values to those in nitrogen-diluted flames at 20 atm. This observation implies that the chemical soot suppression effect of carbon dioxide, previously demonstrated at atmospheric pressure, is also present at elevated pressures up to 15 atm, but fades off beyond 15 atm. In flame stability experiments, the extinction strain rates increased with decreasing dilution. In general, the fuels with higher carbon number and fuels with more compact structures were found to be more prone to extinction. Counterflow laminar diffusion flames established at the impingement of reactants with a top-hat (axially uniform) velocity profile were found to be more resistant to extinction than those with a parabolic exit velocity profile. Multiple solutions to the flame stability were observed for certain hydrocarbons.

  11. Oxygen sensing characteristics of limiting current-type sensors with microstructural and structural variations in diffusion barrier

    Microsoft Academic Search

    Jong-Heun Lee; Hoin Kim; Byung Ki Kim

    1996-01-01

    Several compositional mixtures of Al2O3 (mean diameter = 1.0 ?m)-YSZ (yttria stabilized zirconia, mean diameter = 0.05 ?m) porous layers were used to study the oxygen sensing characteristics and mechanisms of the limiting current-type sensors with various microstructures of the diffusion barriers. The pore size, the porosity, the limiting current, and the degree of the normal diffusion increased with Al2O3

  12. [Analysis of the molecular characteristics and cloning of full-length coding sequence of interleukin-2 in tree shrews].

    PubMed

    Huang, Xiao-Yan; Li, Ming-Li; Xu, Juan; Gao, Yue-Dong; Wang, Wen-Guang; Yin, An-Guo; Li, Xiao-Fei; Sun, Xiao-Mei; Xia, Xue-Shan; Dai, Jie-Jie

    2013-04-01

    While the tree shrew (Tupaia belangeri chinensis) is an excellent animal model for studying the mechanisms of human diseases, but few studies examine interleukin-2 (IL-2), an important immune factor in disease model evaluation. In this study, a 465 bp of the full-length IL-2 cDNA encoding sequence was cloned from the RNA of tree shrew spleen lymphocytes, which were then cultivated and stimulated with ConA (concanavalin). Clustal W 2.0 was used to compare and analyze the sequence and molecular characteristics, and establish the similarity of the overall structure of IL-2 between tree shrews and other mammals. The homology of the IL-2 nucleotide sequence between tree shrews and humans was 93%, and the amino acid homology was 80%. The phylogenetic tree results, derived through the Neighbour-Joining method using MEGA5.0, indicated a close genetic relationship between tree shrews, Homo sapiens, and Macaca mulatta. The three-dimensional structure analysis showed that the surface charges in most regions of tree shrew IL-2 were similar to between tree shrews and humans; however, the N-glycosylation sites and local structures were different, which may affect antibody binding. These results provide a fundamental basis for the future study of IL-2 monoclonal antibody in tree shrews, thereby improving their utility as a model. PMID:23572362

  13. [Cloning of full-length coding sequence of tree shrew CD4 and prediction of its molecular characteristics].

    PubMed

    Tian, Wei-Wei; Gao, Yue-Dong; Guo, Yan; Huang, Jing-Fei; Xiao, Chang; Li, Zuo-Sheng; Zhang, Hua-Tang

    2012-02-01

    The tree shrews, as an ideal animal model receiving extensive attentions to human disease research, demands essential research tools, in particular cellular markers and monoclonal antibodies for immunological studies. In this paper, a 1 365 bp of the full-length CD4 cDNA encoding sequence was cloned from total RNA in peripheral blood of tree shrews, the sequence completes two unknown fragment gaps of tree shrews predicted CD4 cDNA in the GenBank database, and its molecular characteristics were analyzed compared with other mammals by using biology software such as Clustal W2.0 and so forth. The results showed that the extracellular and intracellular domains of tree shrews CD4 amino acid sequence are conserved. The tree shrews CD4 amino acid sequence showed a close genetic relationship with Homo sapiens and Macaca mulatta. Most regions of the tree shrews CD4 molecule surface showed positive charges as humans. However, compared with CD4 extracellular domain D1 of human, CD4 D1 surface of tree shrews showed more negative charges, and more two N-glycosylation sites, which may affect antibody binding. This study provides a theoretical basis for the preparation and functional studies of CD4 monoclonal antibody. PMID:22345010

  14. Microstructural characteristics of HIP-bonded monolithic nuclear fuels with a diffusion barrier

    NASA Astrophysics Data System (ADS)

    Jue, Jan-Fong; Keiser, Dennis D.; Breckenridge, Cynthia R.; Moore, Glenn A.; Meyer, Mitchell K.

    2014-05-01

    Due to the limitation of maximum uranium load achievable by dispersion fuel type, the Global Threat Reduction Initiative is developing an advanced monolithic fuel to convert US high-performance research reactors to low-enriched uranium. Hot-isostatic-press (HIP) bonding was the single process down-selected to bond monolithic U-Mo fuel meat to aluminum alloy cladding. A diffusion barrier was applied to the U-Mo fuel meat by roll-bonding process to prevent extensive interaction between fuel meat and aluminum-alloy cladding. Microstructural characterization was performed on fresh fuel plates fabricated at Idaho National Laboratory. Interfaces between the fuel meat, the cladding, and the diffusion barrier, as well as between the U-10Mo fuel meat and the Al-6061 cladding, were characterized by scanning electron microscopy. Preliminary results indicate that the interfaces contain many different phases while decomposition, second phases, and chemical banding were also observed in the fuel meat. The important attributes of the HIP-bonded monolithic fuel are: diffusion barrier with a thickness of 25 ?m. A transverse cross section that exhibits relatively equiaxed grains with an average grain diameter of 10 ?m. Chemical banding, in some areas more than 100 ?m in length, that is very pronounced in longitudinal (i.e., rolling) direction with Mo concentration varying from 7-13 wt.%. Decomposed areas containing plate-shaped low-Mo phase. A typical Zr/cladding interaction layer with a thickness of 1-2 ?m. A visible UZr2 bearing layer with a thickness of 1-2 ?m. Mo-rich precipitates (mainly Mo2Zr, forming a layer in some areas) followed by a Mo-depleted sub-layer between the visible UZr2-bearing layer and the U-Mo matrix. No excessive interaction between cladding and the uncoated fuel edge. Cladding-to-cladding bonding that exhibits no cracks or porosity with second phases high in Mg, Si, and O decorating the bond line. Some of these attributes might be critical to the irradiation performance of monolithic U-10Mo nuclear fuel. There are several issues or concerns that warrant more detailed study, such as precipitation along the cladding-to-cladding bond line, chemical banding, uncovered fuel-zone edge, and the interaction layer between the U-Mo fuel meat and zirconium. Future post-irradiation examination results will focus, among other things, on identifying in-reactor failure mechanisms and, eventually, directing further fresh fuel characterization efforts.

  15. Microstructural Characteristics of HIP-bonded Monolithic Nuclear Fuels with a Diffusion Barrier

    SciTech Connect

    Jan-Fong Jue; Dennis D. Keiser, Jr.; Cynthia R. Breckenridge; Glenn A. Moore; Mitchell K. Meyer

    2014-05-01

    Due to the limitation of maximum uranium load achievable by dispersion fuel type, the Global Threat Reduction Initiative (GTRI) is developing an advanced monolithic fuel to convert US high performance research reactors to low-enriched uranium. Hot-isostatic-press bonding was the single process down-selected to bond monolithic U-Mo fuel meat to aluminum alloy cladding. A diffusion barrier was applied to the U–Mo fuel meat by roll-bonding process to prevent extensive interaction between fuel meat and aluminum-alloy cladding. Microstructural characterization was performed on fresh fuel plates fabricated at Idaho National Laboratory. Interfaces between fuel meat, cladding, and diffusion barrier, as well as U–10Mo fuel meat and Al–6061 cladding were characterized by scanning electron microscopy. Preliminary results indicate that the interfaces contain many different phases while decomposition, second phases, and chemical banding were also observed in the fuel meat. The important attributes of the HIP-bonded monolithic fuel are • A typical Zr diffusion barrier of thickness 25 µm • Transverse cross section that exhibits relatively equiaxed grains with an average grain diameter of 10 µm • Chemical banding, in some areas more than 100 µm in length, that is very pronounced in longitudinal (i.e., rolling) direction with Mo concentration varying from 7–13 wt% • Decomposed areas containing plate-shaped low-Mo phase • A typical Zr/cladding interaction layer of thickness 1-2 µm • A visible UZr2 bearing layer of thickness 1-2 µm • Mo-rich precipitates (mainly Mo2Zr, forming a layer in some areas) followed by a Mo-depleted sub-layer between the visible UZr2-bearing layer and the U–Mo matrix • No excessive interaction between cladding and the uncoated fuel edge • Cladding-to-cladding bonding that exhibits no cracks or porosity with second phases high in Mg, Si, and O decorating the bond line. • Some of these attributes might be critical to the irradiation performance of monolithic U-10Mo nuclear fuel. There are several issues or concerns that warrant more detailed study, such as precipitation along cladding-to-cladding bond line, chemical banding, uncovered fuel-zone edge, and interaction layer between U–Mo fuel meat and zirconium. Future post-irradiation examination results will focus, among other things, on identifying in-reactor failure mechanisms and, eventually, directing further fresh fuel characterization efforts.

  16. Characteristic distributions of intracerebral hemorrhage–associated diffusion-weighted lesions

    PubMed Central

    Auriel, Eitan; Gurol, Mahmut Edip; Ayres, Alison; Dumas, Andrew P.; Schwab, Kristin M.; Vashkevich, Anastasia; Martinez-Ramirez, Sergi; Rosand, Jonathan; Viswanathan, Anand

    2012-01-01

    Objectives: To determine whether small diffusion-weighted imaging (DWI) lesions occur beyond the acute posthemorrhage time window in patients with intracerebral hemorrhage (ICH) and to characterize their spatial distribution in patients with lobar and deep cerebral hemorrhages. Methods: In this cross-sectional study, we retrospectively analyzed 458 MRI scans obtained in the acute (?7 days after ICH) or nonacute (>14 days after ICH) phases from 392 subjects with strictly lobar (n = 276) and deep (n = 116) ICH (48.7% women; mean age 72.8 ± 11.7 years). DWI, apparent diffusion coefficient maps, fluid-attenuated inversion recovery, and T2* MRIs were reviewed for the presence and location of DWI lesions. Results: We identified 103 DWI hyperintense lesions on scans from 62 subjects, located mostly in lobar brain regions (90 of 103, 87.4%). The lesions were not uniformly distributed throughout the brain lobes; patients with strictly lobar ICH had relative overrepresentation of lesions in frontal lobe, and patients with deep ICH in parietal lobe (p = 0.002). Although the frequency of DWI lesions tended to be greater on scans performed within 7 days after ICH (39 of 214, 18.2%), they continued at high frequency in the nonacute period as well (23 of 178, 12.9%, odds ratio 1.5, 95% confidence interval 0.86–2.6 for acute vs nonacute). There was also no difference in frequency of lesions on acute and nonacute scans among 66 subjects with MRIs in both time periods (8 of 66 acute, 10 of 66 nonacute, odds ratio 0.77, 95% confidence interval 0.25–2.4). Conclusions: The high frequency of DWI lesions beyond the acute post-ICH period and their characteristic distributions suggest that they are products of the small vessel diseases that underlie ICH. PMID:23197745

  17. An Estimate of the Integral of the Modulus for a Generalized-Poisson-Distribution Characteristic Function over an Interval of Small Length

    Microsoft Academic Search

    L. V. Rozovsky

    2002-01-01

    In this note, we obtain new estimates for integrals of a generalized-Poisson-distribution characteristic function over intervals of sufficiently small length. Typical applications of such estimates are the following ones: evaluation of the convergence rate of moments in the CLT, estimates of concentration functions, and local limit theorems. Bibliography: 8 titles.

  18. Diffusion

    NSDL National Science Digital Library

    Christopher Thomas (None; )

    2006-11-09

    Diffusion is the movement of particles from an area of high concentration to an area of low concentration. The molecules move until equilibrium is reached. If a perfume is sprayed on one side of the room, the perfume molecules will eventually spread out all over the room until there are equal concentrations of the molecules throughout the space.

  19. Performance characteristics of two annular dump diffusers using suction-stabilized vortex flow control

    NASA Technical Reports Server (NTRS)

    Juhasz, A. J.; Smith, J. M.

    1978-01-01

    Test results are described for two abrupt area change annular diffusers with provisions for maintaining suction stabilized toroidal vortices at the area discontinuity. Both diffusers had an overall area ratio of 4.0 with the prediffuser area ratio being 1.18 for diffuser A and 1.4 for diffuser B. Performance was evaluated at near atmospheric pressure and temperature for a range of inlet Mach numbers from 0.18 to 0.41 and suction rates from 0 to 18%. Static pressure recovery improved significantly as the suction rate was increased to approximately 11%. Results obtained with diffuser A were superior to that obtained with diffuser B. Flat radial profiles of exit velocity were not obtained since the flow showed preferential hub or tip attachment at moderate suction rates. At high suction rates the diffuser exit flow became circumferentially nonuniform and unstable.

  20. Diffusion

    NSDL National Science Digital Library

    Since the advent of the internet, a number of artists and related organizations have become interested in utilizing the web to promulgate new forms of artistic creation and their subsequent dissemination. Supported by the Arts Council of England, these Diffusion eBooks are essentially pdf files that readers can download, print out and make into booklets. As the site suggests, "the Diffusion format challenges conventions of interactivity-blending the physical and the virtual and breaking the dominance of mouse and screen as the primary forms of human computer interaction...the format's aim is to take the reader away from the screen and computer and engage them in the process of production." There are a number of creative booklets available here for visitors, complete with instruction on how to assemble them for the desired effect. For anyone with even a remote interest in the possibilities afforded by this rather curious new form of expression, this website is worth a look.

  1. Moisture diffusion and permeability characteristics of hydroxypropylmethylcellulose and hard gelatin capsules.

    PubMed

    Barham, Ahmad S; Tewes, Frederic; Healy, Anne Marie

    2015-01-30

    The primary objective of this paper is to compare the sorption characteristics of hydroxypropylmethylcellulose (HPMC) and hard gelatin (HG) capsules and their ability to protect capsule contents. Moisture sorption and desorption isotherms for empty HPMC and HG capsules have been investigated using dynamic vapour sorption (DVS) at 25°C. All sorption studies were analysed using the Young-Nelson model equations which distinguishes three moisture sorption types: monolayer adsorption moisture, condensation and absorption. Water vapour diffusion coefficients (D), solubility (S) and permeability (P) parameters of the capsule shells were calculated. ANOVA was performed with the Tukey comparison test to analyse the effect of %RH and capsule type on S, P, and D parameters. The moisture uptake of HG capsules were higher than HPMC capsules at all %RH conditions studied. It was found that values of D and P across HPMC capsules were greater than for HG capsules at 0-40 %RH; whereas over the same %RH range S values were higher for HG than for HPMC capsules. S values decreased gradually as the %RH was increased up to 60% RH. To probe the effect of moisture ingress, spray dried lactose was loaded into capsules. Phase evolution was characterised by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and differential scanning calorimetry (DSC). The capsules under investigation are not capable of protecting spray dried lactose from induced solid state changes as a result of moisture uptake. For somewhat less moisture sensitive formulations, HPMC would appear to be a better choice than HG in terms of protection of moisture induced deterioration. PMID:25526672

  2. High-Subsonic Performance Characteristics and Boundary-Layer Investigations of a 12 10-Inch-Inlet-Diameter Conical Diffuser

    NASA Technical Reports Server (NTRS)

    Little, B. H., Jr.; Wilbur, Stafford W.

    1950-01-01

    Performance and boundary-layer data were taken in a 12 degree 10-inch inlet-diameter conical diffuser of 2:1 exit- to inlet-area ratio. These data were taken for two inlet-boundary-layer conditions. The first condition was that of a thinner inlet boundary later (boundary-layer displacement thickness, delta* approximately equal to 0.034) produced by an inlet section approximately 1 inlet diameter in length between the entrance bell and the diffuser. The second condition was a thicker inlet boundary layer (delta* approximately equal to 0.120) produced by an additional inlet section length of approximately 6 diameters. Longitudinal static-pressure distributions were measured fro wall static orifices. Transverse total- and static-pressure surveys were made at the inlet and exit stations. Boundary-layer velocity distributions were measured at seven stations between the inlet and exit. These data were obtained for a Reynolds number (based on inlet diameter) range of 1 x 10(exp 6) to 3.9 x 10(exp 6). The corresponding Mach number range was from M = 0.2 to choking. At the maximum-power-available condition supersonic flow was obtained as far as 4.5 inches downstream from the diffuser inlet with a maximum Mach number of M approximately equal to 1.5. The total-pressure loss through the diffuser in percentage of inlet dynamic pressure was approximately 2.5 percent for the thinner inlet boundary later and 5.5 percent for the thicker inlet boundary later over the lower subsonic range. These valued increased with increasing flow rate- the values for the thicker inlet boundary later more than those for the thinner inlet boundary layer. The diffuser effectiveness, expressed as the ratio of the actual static-pressure rise to the ideal static-pressure rise, was about 85 percent for the thinner inlet boundary layer and about 67 percent for the thicker inlet boundary later in the lower subsonic range. These values decrease with increasing flow rate. Separated flow was observed for both inlet-boundary-layer conditions in the region of adverse pressure gradient just downstream of the transition curvature from inlet section to diffuser. The flow for the thinner-inlet-boundary-layer condition did not fully re-establish itself along the diffuser walls. The thicker inlet-boundary-layer flow, while not completely re-establishing the normal flow pattern downstream of the separated region, did re-establish more successfully than the thinner inlet boundary layer.

  3. Aerodynamic performance and noise characteristics of a centrifugal compressor with modified vaned diffusers

    NASA Astrophysics Data System (ADS)

    Ohta, Yutaka; Okutsu, Yasuhiko; Goto, Takashi; Outa, Eisuke

    2006-12-01

    Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressor with vaned diffusers are discussed by experiments and visualization techniques using a colored oil-film method. The focus of the research is concentrated on the leading edge shape of diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise. The compressor-radiated noise can be reduced by more than ten decibels by using modified diffuser vanes which have 3-D tapered shapes on both pressure and suction surfaces of the leading edge. Furthermore, by adopting the proposed modified diffuser vanes, the secondary flow which is considered to be an obstruction of diffuser pressure recovery can be suppressed, and also the pressure decrease observed in the throat part of the diffuser flow passage is reducible. Thus, the proposed diffuser vanes show a favorable result for both noise and the aerodynamic performance of the centrifugal compressor, and offer a few basic guidelines for the diffuser vane design.

  4. Characteristics and pathological mechanism on magnetic resonance diffusion-weighted imaging after chemoembolization in rabbit liver VX-2 tumor model

    Microsoft Academic Search

    You-Hong Yuan; En-Hua Xiao; Jian-Bin Liu; Zhong He; Ke Jin; Cong Ma; Jun Xiang; Jian-Hua Xiao; Wei-Jian Chen

    AIM: To investigate dynamic characteristics and pathological mechanism of signal in rabbit VX-2 tumor model on diffusion-weighted imaging (DWI) after chemoembolization. METHODS: Forty New Zealand rabbits were included in the study and forty-seven rabbit VX-2 tumor models were raised by implanting directly and intrahepatically after abdominal cavity opened. Forty VX-2 tumor models from them were divided into four groups. DWI

  5. 0.15 ?m gate length InAlAs\\/InGaAs power metamorphic HEMT on GaAs substrate with extremely low noise characteristics

    Microsoft Academic Search

    Hyung Sup Yoon; Jin Hee Lee; Jae Yeob Shim; Ju Yeon Hong; Dong Min Kang; Woo Jin Chang; Hae Cheon Kim; Kyoung Ik Cho

    2003-01-01

    The 0.15 ?m gate-length power metamorphic HEMTs (MHEMT) with wide head T-shaped gate has been fabricated and the DC, microwave, and noise performance of the device were characterized. The MHEMT device shows the DC output characteristics having an extrinsic transconductance of 740 mS\\/mm and a threshold voltage of -0.75 V. The fT and fmax obtained for the 0.15 ?m ×

  6. Modeling and Natural Frequency Characteristics of Coupled Vibration with Varying Length of Hoisting Rope in Drum Winding System

    Microsoft Academic Search

    Guohua Cao; Zhencai Zhu; Weihong Peng; Xianbiao Mao

    2010-01-01

    In order to avoid resonance and enhance safety during designing hoist control method for mine hoisting system, the model of drum winding system guided by a head heave with varying length of hosting rope was established by the method of moving frame approach. According to Hamilton principle, the extensional, torsional and lateral coupled mathematical model with the effect of a

  7. Aerodynamic performance and noise characteristics of a centrifugal compressor with modified vaned diffusers

    Microsoft Academic Search

    Yutaka Ohta; Yasuhiko Okutsu; Takashi Goto; Eisuke Outa

    2006-01-01

    Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressor with vaned diffusers\\u000a are discussed by experiments and visualization techniques using a colored oil-film method. The focus of the research is concentrated\\u000a on the leading edge shape of diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise.\\u000a The compressor-radiated noise

  8. Magnetic resonance diffusion characteristics of histologically defined prostate cancer in humans.

    PubMed

    Xu, Junqian; Humphrey, Peter A; Kibel, Adam S; Snyder, Abraham Z; Narra, Vamsidhar R; Ackerman, Joseph J H; Song, Sheng-Kwei

    2009-04-01

    The contrast provided by diffusion-sensitive magnetic resonance offers the promise of improved tumor localization in organ-confined human prostate cancer (PCa). Diffusion tensor imaging (DTI) measurements of PCa were performed in vivo, in patients undergoing radical prostatectomy, and later, ex vivo, in the same patients' prostatectomy specimens. The imaging data were coregistered to histological sections of the prostatectomy specimens, thereby enabling unambiguous characterization of diffusion parameters in cancerous and benign tissues. Increased cellularity, and hence decreased luminal spaces, in peripheral zone PCa led to approximately 40% and 50% apparent diffusion policy (ADC) decrease compared with benign peripheral zone tissues in vivo and ex vivo, respectively. In contrast, no significant diffusion anisotropy differences were observed between the cancerous and noncancerous peripheral zone tissues. However, the dense fibromuscular tissues in prostate, such as stromal tissues in benign prostatic hyperplasia in central gland, exhibited high diffusion anisotropy. A tissue classification method is proposed to combine DTI and T2-weighted image contrasts that may provide improved specificity of PCa detection over T2-weighted imaging alone. PCa identified in volume rendered MR images qualitatively correlates well with histologically determined PCa foci. PMID:19215051

  9. Effects of Maternal and Infant Characteristics on Birth Weight and Gestation Length in a Colony of Rhesus Macaques (Macaca mulatta)

    PubMed Central

    Hopper, Kelly J; Capozzi, Denise K; Newsome, Joseph T

    2008-01-01

    A retrospective study using maternal and birth statistics from an open, captive rhesus macaque colony was done to determine the effects of parity, exposure to simian retrovirus (SRV), housing, maternal parity, and maternal birth weight on infant birth weight, viability and gestation length. Retrospective colony statistics for a 23-y period indicated that birth weight, but not gestation length, differed between genders. Adjusted mean birth weights were higher in nonviable infants. Mothers positive for SRV had shorter gestations, but SRV exposure did not affect neonatal birth weights or viability. Infants born in cages had longer gestations than did those born in pens, but neither birth weight nor viability differed between these groups. Maternal birth weight did not correlate with infant birth weight but positively correlated with gestation length. Parity was correlated with birth weight and decreased viability. Increased parity of the mother was associated with higher birth weight of the infant. A transgenerational trend toward increasing birth weight was noted. The birth statistics of this colony were consistent with those of other macaque colonies. Unlike findings for humans, maternal birth weight had little predictive value for infant outcomes in rhesus macaques. Nonviable rhesus infants had higher birth weights, unlike their human counterparts, perhaps due to gestational diabetes occurring in a sedentary caged population. Similar to the situation for humans, multiparity had a protective effect on infant viability in rhesus macaques. PMID:19149417

  10. Numerical simulation of gas diffusion effects on charge/discharge characteristics of a solid oxide redox flow battery

    NASA Astrophysics Data System (ADS)

    Ohmori, Hiroko; Uratani, Syoichi; Iwai, Hiroshi

    2012-06-01

    Fundamental characteristics of a solid oxide redox flow battery consisting of solid oxide electrochemical cell (SOEC) and redox metal were studied by a gas-diffusion based time-dependent 1-D numerical simulation taking both the electrochemical and redox reactions into account. Close attention was paid to the distributions of the participating gas species and their effects on the charge/discharge performance. The volume expansion/reduction of the porous metal associated with the redox reaction was modeled as decrease/increase in local porosity. The numerical results for charge/discharge operation qualitatively showed the time-dependent distributions of the related physical quantities such as the gas concentrations, the active reaction region in the redox metal, and its local porosity. It was found that, to ensure effective redox reaction throughout the operation, the gas diffusion in the redox metal should be carefully designed.

  11. Characteristics of Copper-to-Silicon diffusion in copper wire bonding

    Microsoft Academic Search

    Shawn X. Zhang; S. W. Ricky Lee

    2007-01-01

    The replacement of Au and Al wires with Cu wires in wire bonding has become an emerging trend in IC packaging nowadays. Although some research works have been carried out for the applications of Cu wire bonding, they are mainly focused on the processing and material issues of Cu wire bonds. However, the Cu in the wire bonds may diffuse

  12. Noise Characteristics and Optimum Fiber Length of Spectral Inversion Using Four-Wave Mixing in a Dispersion-Shifted Fiber

    Microsoft Academic Search

    Xiupu Zhang; Bo. F. Jørgensen

    1997-01-01

    An analysis of noise characteristics, described by an effective noise figure, of polarization-sensitive and polarization-insensitive spectral inverters based on four-wave mixing in a dispersion-shifted fiber is given considering the influence of optical filters on noise. It is found that inserting optical filters in the input signal channel and\\/or in the pump channel can reduce effective noise figure of the spectral

  13. Effects of grooves and openings in the roofs of elbow draft tube diffusers on the power characteristics of Kaplan turbines

    Microsoft Academic Search

    I. E. Mikhailov; E. L. Mityurev; V. V. Kazennov; V. V. Volshanik; V. B. Bondarenko

    1973-01-01

    Conclusions  \\u000a \\u000a \\u000a \\u000a 1. \\u000a \\u000a The presence of grooves for installation of the maintenance gates in the lateral walls and pier of an elbow draft tube diffuser,\\u000a with the roof opening tightly closed by means of a special plug which ensures a plane surface, practically does not affect\\u000a the power characteristics of the turbine.\\u000a \\u000a \\u000a \\u000a \\u000a 2. \\u000a \\u000a The presence of an uncovered opening leads to

  14. Microstructural White Matter Tissue Characteristics Are Modulated by Homocysteine: A Diffusion Tensor Imaging Study

    PubMed Central

    Hsu, Jung-Lung; Chen, Wei-Hung; Bai, Chyi-Huey; Leu, Jyu-Gang; Hsu, Chien-Yeh; Viergever, Max A.; Leemans, Alexander

    2015-01-01

    Homocysteine level can lead to adverse effects on the brain white matter through endothelial dysfunction, microstructural inflammation, and neurotoxin effects. Despite previously observed associations between elevated homocysteine and macroscopic structural brain changes, it is still unknown whether microstructural associations of homocysteine on brain tissue properties can be observed in healthy subjects with routine MRI. To this end, we investigated potential relationships between homocysteine levels and microstructural measures computed with diffusion tensor imaging (DTI) in a cohort of 338 healthy participants. Significant positive correlations were observed between homocysteine levels and diffusivity measures in the bilateral temporal WM, the brainstem, and the bilateral cerebellar peduncle. This is the first study demonstrating that DTI is sufficiently sensitive to relate microstructural WM properties to homocysteine levels in healthy subjects. PMID:25693199

  15. Microstructural white matter tissue characteristics are modulated by homocysteine: a diffusion tensor imaging study.

    PubMed

    Hsu, Jung-Lung; Chen, Wei-Hung; Bai, Chyi-Huey; Leu, Jyu-Gang; Hsu, Chien-Yeh; Viergever, Max A; Leemans, Alexander

    2015-01-01

    Homocysteine level can lead to adverse effects on the brain white matter through endothelial dysfunction, microstructural inflammation, and neurotoxin effects. Despite previously observed associations between elevated homocysteine and macroscopic structural brain changes, it is still unknown whether microstructural associations of homocysteine on brain tissue properties can be observed in healthy subjects with routine MRI. To this end, we investigated potential relationships between homocysteine levels and microstructural measures computed with diffusion tensor imaging (DTI) in a cohort of 338 healthy participants. Significant positive correlations were observed between homocysteine levels and diffusivity measures in the bilateral temporal WM, the brainstem, and the bilateral cerebellar peduncle. This is the first study demonstrating that DTI is sufficiently sensitive to relate microstructural WM properties to homocysteine levels in healthy subjects. PMID:25693199

  16. MRI of diffuse liver disease: characteristics of acute and chronic diseases

    PubMed Central

    Chundru, Surya; Kalb, Bobby; Arif-Tiwari, Hina; Sharma, Puneet; Costello, James; Martin, Diego R.

    2014-01-01

    Diffuse liver disease, including chronic liver disease, affects tens of millions of people worldwide, and there is a growing need for diagnostic evaluation as treatments become more readily available, particularly for viral liver diseases. Magnetic resonance imaging (MRI) provides unique capabilities for noninvasive characterization of the liver tissue that rival or surpass the diagnostic utility of liver biopsies. There has been incremental improvement in the use of standardized MRI sequences, acquired before and after administration of a contrast agent, for the evaluation of diffuse liver disease and the study of the liver parenchyma and blood supply. More recent developments have led to methods for quantifying important liver metabolites, including lipids and iron, and liver fibrosis, the hallmark of chronic liver disease. Here, we review the MRI techniques and diagnostic features associated with acute and chronic liver disease. PMID:24808418

  17. Gas permeability, diffusivity, solubility, and aging characteristics of 6FDA-durene polyimide membranes

    Microsoft Academic Search

    Wen-Hui Lin; Tai-Shung Chung

    2001-01-01

    We have determined the intrinsic gas transport properties of He, H2, O2, N2, CH4, and CO2 for a 6FDA-durene polyimide as a function of pressure, temperature and aging time. The permeability coefficients of O2, N2, CH4, and CO2 decrease slightly with increasing pressure. The pressure-dependent diffusion coefficients and solubility coefficients are consistent with the dual-sorption model and partial immobilization. All

  18. Electron diffusion in intense high frequency electromagnetic fields

    Microsoft Academic Search

    S. Bhattacharjee; I. Dey; S. Jain; H. Amemiya

    The phenomenon of electron diffusion in a background gas, in the presence of high frequency electromagnetic fields is investigated. Monte-Carlo simulation procedures were applied to determine the number of collisions N. The dependence of N on the externally controllable parameters like the electron-neutral mean free path ? and the characteristic diffusion length ? (determined by the geometry) were studied. It

  19. Diffusion regions of magnetic reconnection at the magnetopause, Cluster observations

    Microsoft Academic Search

    A. Vaivads

    2004-01-01

    We present cases during which Cluster spacecraft cross diffusion regions of reconnection at the magnetopause. During the events the distance between spacecraft is comparable to the ion inertial length (100km). We show that spacecraft observations of the diffusion regions are in many aspects consistent with numerical simulations of fast reconnection. We aim to explore how the main observational characteristics of

  20. Specific features of the current-voltage characteristics of diffuse glow discharges in Ar:N{sub 2} mixtures

    SciTech Connect

    Dyatko, N. A. [Troitsk Institute for Innovation and Fusion Research (Russian Federation); Ionikh, Yu. Z.; Meshchanov, A. V. [St. Petersburg State University (Russian Federation); Napartovich, A. P. [Troitsk Institute for Innovation and Fusion Research (Russian Federation); Barzilovich, K. A. [St. Petersburg State University (Russian Federation)

    2010-12-15

    The characteristics of diffuse glow discharges in pure argon and the Ar + 1%N{sub 2} mixture at pressures of 2-80 Torr were studied experimentally and numerically. The discharge operated in a molybdenumglass tube with an inner diameter of 2.8 cm and interelectrode distance of 75 cm. The current-voltage characteristic of the discharge and the populations of the N{sub 2}(B{sup 3{Gamma}}{sub g}) and N{sub 2}(C{sup 3{Gamma}}{sub u}) states were measured. It is shown that, at relatively low pressures (P < 10 Torr), the current-voltage characteristic of a discharge in the argon-nitrogen mixture lies higher than that in pure argon. In contrast, at higher pressures (P > 15 Torr), the current-voltage characteristic of a discharge in the mixture lies lower than that in pure argon. As the pressure increases, the effect of the reduction in the discharge voltage becomes more pronounced. A self-consistent zero-dimensional kinetic model is developed that allows one to calculate the characteristics of the positive column of a discharge in pure argon and Ar:N{sub 2} mixtures under the conditions of high vibrational excitation of nitrogen. A detailed description of the model is presented, and the calculated results are compared with experimental data. The model adequately reproduces the observed change in the current-voltage characteristic in Ar and the Ar + 1%N{sub 2} mixture with increasing gas pressure. It is shown that the main ionization mechanism in the Ar + 1%N{sub 2} mixture at moderate pressures is the associative ionization of excited nitrogen atoms.

  1. Elevated-temperature flow strength, creep resistance and diffusion welding characteristics of Ti-gAl-2Nb-1Ta-0.8Mo

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Moore, T. J.

    1977-01-01

    A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo was conducted. Two mill-processed forms of this alloy were examined. The forged material was essentially processed above the beta transus while the rolled form was subjected to considerable work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

  2. Elevated temperature flow strength, creep resistance and diffusion welding characteristics of Ti-6Al-2Nb-1Ta-0.8Mo

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Moore, T. J.

    1979-01-01

    A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo has been conducted. Two mill-processed forms of this alloy were examined. The forged material had been processed above the beta transus (approximately 1275 K) while the rolled form had been subjected to work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

  3. Diffuse mesenterial sclerosis: a characteristic feature of chronic small-bowel allograft rejection.

    PubMed

    Klaus, Alexander; Margreiter, Raimund; Pernthaler, Heinz; Klima, Günther; Offner, Felix A

    2003-01-01

    Chronic rejection is the major cause of late intestinal allograft dysfunction. The aim of this study was to analyze in detail the histopathological features of chronic rejection in the ACI-to-Lewis rat model of intestinal transplantation. Chronic rejection was achieved in orthotopic small-bowel allografts (ACI-Lewis) by limited immunosuppression with cyclosporin A (CyA). Isogeneic transplants (ACI-ACI) as well as native bowels (ACI) with and without immunosuppression served as controls. Bowels were removed together with the mesenteries 90 days postoperatively and analyzed using sections stained with hematoxylin and eosin as well as Masson's trichrome. The slides were coded, randomized and analyzed by grading of histological abnormalities. The most striking alterations of the allografts were noticed in the mesenteries exhibiting an extensive infiltration by mononuclear cells accompanied by a progressive diffuse fibrosis with shrinking of the mesenteries. These changes were most pronounced in the perivascular areas of the mesenteric arteriae and venae rectae. Three of five allografts showed vasculitis with myointimal proliferation of the arteriae rectae. Focally, there was spill-over of the inflammatory cells onto the intestinal muscularis propria. The mucosa of the allografts showed mild blunting, lymphocytic infiltration of the crypt epithelium and increased crypt cell apoptoses. The submucosa was unaffected, and there were no detectable abnormalities of the enteric ganglion cells. The present data support the view that chronic rejection of intestinal allografts is characterized by a diffuse sclerosing mesenteritis which may significantly contribute to late graft dysfunction. The present model may be useful to study the pathomechanisms of this inflammatory fibrosing process. PMID:12536314

  4. An invariance property of diffusive random walks

    NASA Astrophysics Data System (ADS)

    Blanco, S.; Fournier, R.

    2003-01-01

    Starting from a simple animal-biology example, a general, somewhat counter-intuitive property of diffusion random walks is presented. It is shown that for any (non-homogeneous) purely diffusing system, under any isotropic uniform incidence, the average length of trajectories through the system (the average length of the random walk trajectories from entry point to first exit point) is independent of the characteristics of the diffusion process and therefore depends only on the geometry of the system. This exact invariance property may be seen as a generalization to diffusion of the well-known mean-chord-length property (Case K. M. and Zweifel P. F., Linear Transport Theory (Addison-Wesley) 1967), leading to broad physics and biology applications.

  5. Brillouin Lasing with a Reduced Self-Pulsing Characteristic Using a Short-Length Erbium-Doped Fiber as the Nonlinear Gain Medium

    NASA Astrophysics Data System (ADS)

    Zarei, A.; Z. R. R. Rosdin, R.; M. Ali, N.; H., Ahmad; W. Harun, S.

    2014-05-01

    A single-wavelength Brillouin laser is demonstrated by using a 3-m-long erbium doped fiber (EDF) in a ring cavity. The EDF is used to provide both nonlinear and linear gains to generate a stimulated Brillouin scattering (SBS) and to amplify the generated SBS, respectively. The Brillouin erbium fiber laser (BEFL) operates at 1561.5 nm, where the operating wavelength is up-shifted by 0.08nm from the Brillouin pump. The operation wavelength is also tunable within 1560.6-1562.6 nm. The BEFL also shows a self-pulsing characteristic with repetition of 66.7 kHz when the BP is set around the threshold pump power of 13mW. Compared to the conventional Brillouin fiber laser with a long cavity length, the proposed BEFL exhibits a significantly lower amplitude of pulse. This laser has many potential applications, such as in optical communication and sensors.

  6. Measuring Length

    NSDL National Science Digital Library

    This article focuses on young students encountering the measurement of length. The article cites examples of key concepts in recognizing length as an attribute and in proper and improper ways to measure length. Conservation and additivity of length, standard and non-standard units, iteration, and the zero point are among the topics presented.

  7. "Smoking-Gun" Observables of Magnetic Reconnection: Spatiotemporal Evolution of Electron Characteristics Throughout the Diffusion Region

    NASA Astrophysics Data System (ADS)

    Shuster, J. R.; Chen, L. J.; Bessho, N.; Li, G.; Torbert, R. B.; Wang, S.; Argall, M. R.; Daughton, W. S.

    2014-12-01

    Electron distribution functions can provide "smoking-gun" evidence for the detection of electron diffusion regions in collisionless magnetic reconnection. Knowledge of the spatiotemporal evolution of electron distributions during reconnection is significantly lacking, and will further elucidate the outstanding questions of how, where, and when electrons are energized during reconnection. Based on spacecraft observations and PIC simulations of symmetric reconnection, electrons in the inflow region are known to exhibit a temperature anisotropy Te// > Te?. Studies of exhaust electrons have reported hot and isotropic electrons, while others have reported anisotropic exhaust structures. Electron distributions in the vicinity of the X-line have a triangular, 3D velocity space structure with distinct striations corresponding to the number of times electrons reflect within the electron current layer. Here, we report the spatial and temporal evolution of electron distributions from the vicinity of the X-line to the end of the electron outflow jet, with the discovery that the discrete striations swirl and rotate as electrons re-magnetize, forming arc and ring structures. Highly structured, time-dependent electron anisotropy develops in the exhaust distributions only near or after the peak reconnection rate, explaining the previous discrepancy concerning the degree of electron anisotropy in the exhaust, and suggesting a technique to infer the evolution stage of reconnection using spacecraft measurements. We also present a theory for predicting the spacing of the striations of electron distributions in the vicinity of the X-line based on local measurements, which could be directly tested by spacecraft observations. Electron data from Cluster magnetotail reconnection inflows and exhausts exhibit many anisotropic structures as predicted by simulation. Observed distributions near the reconnection mid-plane (Bx ~ 0 nT) are often highly structured with populations exhibiting Te? > Te// in addition to lower energy field-aligned beams. Our work advances the understanding of electron distribution evolution, setting a foundation to successfully interpret the high resolution electron data anticipated from NASA's upcoming Magnetospheric Multi-Scale Mission.

  8. PS-b-PEO/Silica Films with Regular and Reverse Mesostructures of Large Characteristic Length Scales Prepared by Solvent Evaporation-Induced Self-Assembly

    SciTech Connect

    YU,KUI; BRINKER,C. JEFFREY; HURD,ALAN J.; EISENBERG,ADI

    2000-11-22

    Since the discovery of surfactant-templated silica by Mobil scientists in 1992, mesostructured silica has been synthesized in various forms including thin films, powders, particles, and fibers. In general, mesostructured silica has potential applications, such as in separation, catalysis, sensors, and fluidic microsystems. In respect to these potential applications, mesostructured silica in the form of thin films is perhaps one of the most promising candidates. The preparation of mesostructured silica films through preferential solvent evaporation-induced self-assembly (EISA) has recently received much attention in the laboratories. However, no amphiphile/silica films with reverse mesophases have ever been made through this EISA procedure. Furthermore, templates employed to date have been either surfactants or poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers, such as pluronic P-123, both of which are water-soluble and alcohol-soluble. Due to their relatively low molecular weight, the templated silica films with mesoscopic order have been limited to relatively small characteristic length scales. In the present communication, the authors report a novel synthetic method to prepare mesostructured amphiphilic/silica films with regular and reverse mesophases of large characteristic length scales. This method involves evaporation-induced self-assembly (EISA) of amphiphilic polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers. In the present study, the PS-b-PEO diblocks are denoted as, for example, PS(215)-b-PEO(100), showing that this particular sample contains 215 S repeat units and 100 EO repeat units. This PS(215)-b-PEO(100) diblock possesses high molecular weight and does not directly mix with water or alcohol. To the authors knowledge, no studies have reported the use of water-insoluble and alcohol-insoluble amphiphilic diblocks as structure-directing agents in the synthesis of mesostructured silica films through EISA. It is believed that the present system is the first to yield amphiphile/silica films with regular and reverse mesophases, as well as curved multi-bilayer mesostructures, through EISA. The ready formation of the diblock/silica films with multi-bilayer vesicular mesostructures is discussed.

  9. Characteristics of hydrogen–hydrocarbon composite fuel turbulent jet flames

    Microsoft Academic Search

    Ahsan R. Choudhuri; S. R. Gollahalli

    2003-01-01

    The characteristics (flame length, pollutant emission, radiative heat loss fraction, and volumetric soot concentration) of hydrogen–hydrocarbon composite fuel turbulent jet diffusion flames are presented. A correlation of flame length with hydrogen concentration in the fuel mixture is shown. The reactivity of fuel mixture increases with the increase of hydrogen concentration, which ultimately shortens the combustion time, and thereby reduces the

  10. Anomalous output characteristic shift for the n-type lateral diffused metal-oxide-semiconductor transistor with floating P-top layer

    SciTech Connect

    Liu, Siyang; Zhang, Chunwei; Sun, Weifeng, E-mail: swffrog@seu.edu.cn [National ASIC System Engineering Research Center, Southeast University, Nanjing 210096 (China); Su, Wei; Wang, Shaorong; Ma, Shulang; Huang, Yu [CSMC Technologies Corporation, Wuxi 214061 (China)

    2014-04-14

    Anomalous output characteristic shift of the n-type lateral diffused metal-oxide-semiconductor transistor with floating P-top layer is investigated. It shows that the linear drain current has obvious decrease when the output characteristic of fresh device is measured for two consecutive times. The charge pumping experiments demonstrate that the decrease is not from hot-carrier degradation. The reduction of cross section area for the current flowing, which results from the squeezing of the depletion region surrounding the P-top layer, is responsible for the shift. Consequently, the current capability of this special device should be evaluated by the second measured output characteristic.

  11. Ballistic-Diffusive Heat-Conduction Equations

    Microsoft Academic Search

    Gang Chen; Gang

    2001-01-01

    We present new heat-conduction equations, named ballistic-diffusive equations, which are derived from the Boltzmann equation. We show that the new equations are a better approximation than the Fourier law and the Cattaneo equation for heat conduction at the scales when the device characteristic length, such as film thickness, is comparable to the heat-carrier mean free path and\\/or the characteristic time,

  12. Decay Lengths for Diffusive Transport Activated by Andreev Reflections in Al\\/n-GaAs\\/Al Superconductor-Semiconductor-Superconductor Junctions

    Microsoft Academic Search

    J. Kutchinsky; R. Taboryski; T. Clausen; C. B. Sørensen; A. Kristensen; P. E. Lindelof; J. Bindslev Hansen; C. Schelde Jacobsen; J. L. Skov

    1997-01-01

    In a highly doped GaAs semiconductor with superconducting contacts of Al, clear conductance peaks are observed at zero voltage bias and at V = +\\/-2Delta\\/e, +\\/-Delta\\/e. The subharmonic energy gap structure originates from Andreev scattering with diffusive, but energy conserving, transport in the GaAs. The zero bias excess conductance is due to phase-coherent transport. Both effects are suppressed when the

  13. Boundary-layer analysis of subsonic inlet diffuser geometries for engines nacelles

    NASA Technical Reports Server (NTRS)

    Albers, J. A.; Felderman, E. J.

    1974-01-01

    Theoretical Mach number distributions and boundary-layer parameters are presented for subsonic nacelle inlet diffuser geometries with length to exit diameter ratios ranging from 0.4 to 1.6 and diffuser exit area to throat area ratios ranging from 1.1 to 2.0. The major portion of the study was done with a cubic diffuser contour with the inflection point at the midpoint of the diffuser, a diffuser throat Mach number of 0.6, and a free-stream Mach number of 0.12. Calculations were performed at both model (diffuser exit diameter, 30.5 cm) and full-scale (diffuser exit diameter, 183 cm) sizes. Separation limits were defined by establishing a separation boundary on plots of diffuser area ratio as a function of diffuser length to diameter ratio. The effects of diffuser contour, inlet lip geometry, and throat Mach number on the boundary-layer characteristics are illustrated. The major results of the study indicate that the separation boundary is shifted to greater area ratios by (1) increasing the diffuser length, (2) increasing the scale of the diffuser and, (3) moving the inflection point of the diffuser contour to or ahead of the midpoint of the diffuser.

  14. 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.

  15. Ladybug Lengths

    NSDL National Science Digital Library

    2012-01-01

    This lesson introduces students to the measurable attribute of length and provides practice in measuring length using non-standard units. The lesson is launched using the story Ladybug on the Move by Richard Fowler. Lesson objectives, teaching ideas, and handouts are included.

  16. DIFFUSION IN THE VICINITY OF STANDARD-DESIGN NUCLEAR POWER PLANTS-I. WIND-TUNNEL EVALUATION OF DIFFUSIVE CHARACTERISTICS OF A SIMULATED SUBURBAN NEUTRAL ATMOSPHERIC BOUNDARY LAYER

    EPA Science Inventory

    A large meteorological wind tunnel was used to simulate a suburban atmospheric boundary layer. The model-prototype scale was 1:300 and the roughness length was approximately 1.0 m full scale. The model boundary layer simulated full scale dispersion from ground-level and elevated ...

  17. Diffusive Transport in Hydroxypropylcellulose:Water

    NASA Astrophysics Data System (ADS)

    Streletzky, Kiril A.; Phillies, George D. J.; O'Connell, Robert; Whitford, Paul; Hanson, Helen

    2005-03-01

    A systematic analysis of mode structure of diffusive relaxations in solutions of neutral polymer of 1MDa hydroxypropylcellulose (HPC) is presented. Experimental techniques that have been applied in our studies include static light scattering, dynamic light scattering, optical probe diffusion, and viscometry. In the optical probe diffusion method we monitor the translational diffusion of dilute monodisperse spheres through aqueous polymer solutions over a range of temperatures, distances, and time scales. Based on the data from these extensive studies we conclude that: 1) HPC solutions have a characteristic length of 50-70nm that matches the polymer’s hydrodynamic radius; 2) the diffusion rate of optical probes through aqueous polymer solutions is not determined by the macroscopic viscosity of the solutions; 3) probe and polymer relaxations are not generally the same; 4) the apparent viscometric crossover near 6g/L is confirmed by the optical probe behavior.

  18. Characteristics of the circadian rhythm in diffusive resistance of Abutilon theophrasti leaves in humid and dry environments.

    PubMed

    Fuhrman, M H; Koukkari, W L

    1982-01-01

    Diffusive resistance of the upper and lower leaf surfaces of Abutilon theophrasti Medic, was measured with an automatic diffusive resistance meter. Plants were maintained in growth chambers under 4 different environments: 1. high humidity, well-watered, 2. high humidity, dry, 3. low humidity, well-watered, 4. low humidity, dry. Diffusive resistance measurements were obtained every 4 h for up to 3 days when the plants were subjected to either daily regimes consisting of 15 h of light followed by 9 h of darkness or to continuous illumination. Leaf movements were also monitored. Diffusive resistance was rhythmic (circadian) under all the environmental conditions examined. The pattern of diffusive resistance was the same regardless of whether the humidity and/or soil moisture were high or low. The rhythms of diffusive resistance of the upper and lower leaf surfaces differed, however, in amplitude and in the phase at which the minimum value was reached. Diffusive resistance of the leaf was highest (peak of the rhythm) when the leaf blade was in a nearly horizontal position. PMID:7140475

  19. Diffusive-Compression Acceleration and Turbulent Diffusion of Cosmic Rays in Quasi-periodic and Turbulent Flows

    Microsoft Academic Search

    G. M. Webb; C. M. Ko; G. P. Zank; J. R. Jokipii

    2003-01-01

    Multiple scale perturbation methods are used to study the transport and acceleration of energetic charged particles in quasi-periodic, fluid velocity structures in one, two, or three space dimensions, with spatial period lu, where lu is much less than the diffusion scale length ld=kappa0\\/u0 and kappa0 and u0 are characteristic values of the energetic particle diffusion coefficients and fluid speed, respectively.

  20. Effect of Introducing ?-FeSi2 Template Layers on Defect Density and Minority Carrier Diffusion Length in Si Region near p-?-FeSi2/n-Si Heterointerface

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

    The electrical properties of defects in a p-?-FeSi2/n-Si heterostructures were investigated by deep level transient spectroscopy (DLTS) and the electron-beam-induced current (EBIC) technique. DLTS revealed the presence of trap levels for holes, caused by defects in the n-Si layer near the interface during the ?-FeSi2 film fabrication. The defect density became small when a 20-nm-thick ?-FeSi2 template layer was grown on the n-Si prior to molecular beam epitaxy (MBE) of a 700-nm-thick ?-FeSi2 layer. The diffusion length of minority carriers in the n-Si was found to be approximately 15 µm by EBIC. This is much larger than the value of approximately 3 µm for the n-Si obtained when the template layer was not inserted.

  1. Analysis of EIS characteristics of CO2 corrosion of well tube steels with corrosion scales

    Microsoft Academic Search

    Z. Q. Bai; C. F. Chen; M. X. Lu; J. B. Li

    2006-01-01

    The electrochemical impedance spectroscopy (EIS) was used to study the characteristics of CO2 corrosion of N80 and 4Cr steels with corrosion scales. The results indicated that CO2 corrosion scale on tube steel could prevent the rate of mass transfer remarkably, corrosion rate was controlled by ions diffusion in corrosion scale, which led to finite length diffusion impedance occurred in electrochemical

  2. Analysis of EIS characteristics of CO 2 corrosion of well tube steels with corrosion scales

    Microsoft Academic Search

    Z. Q. Bai; C. F. Chen; M. X. Lu; J. B. Li

    2006-01-01

    The electrochemical impedance spectroscopy (EIS) was used to study the characteristics of CO2 corrosion of N80 and 4Cr steels with corrosion scales. The results indicated that CO2 corrosion scale on tube steel could prevent the rate of mass transfer remarkably, corrosion rate was controlled by ions diffusion in corrosion scale, which led to finite length diffusion impedance occurred in electrochemical

  3. SPECIAL ISSUE DEVOTED TO MULTIPLE RADIATION SCATTERING IN RANDOM MEDIA: Time-domain diffuse optical tomography using analytic statistical characteristics of photon trajectories

    NASA Astrophysics Data System (ADS)

    Konovalov, Aleksandr B.; Vlasov, V. V.; Kalintsev, A. G.; Kravtsenyuk, Olga V.; Lyubimov, Vladimir V.

    2006-11-01

    The inverse problem of diffuse optical tomography (DOT) is reduced by the method of photon average trajectories (PAT) to the solution of the integral equation integrated along the conditional mean statistical photon trajectory. The PAT bending near the flat boundary of a scattering medium is estimated analytically. These estimates are used to determine the analytic statistical characteristics of photon trajectories for the flat layer geometry. The inverse DOT problem is solved by using the multiplicative algebraic algorithm modified to improve the convergence of the iteration reconstruction process. The numerical experiment shows that the modified PAT method permits the reconstruction of near-surface optical inhomogeneities virtually without distortions.

  4. Finger Length

    NSDL National Science Digital Library

    American Association for the Advancement of Science (; )

    2005-03-28

    This Science Update explores male agression patterns and their correlation to pre-natal testosterone exposure. Although life experience plays a huge role in shaping who we are, the foundations of our personality begin in the womb. One recent study looks to finger length for signs of a man's pre-natal exposure to testosterone.n women, the index and ring finger are roughly equal in length. But in most men, the ring finger is longer. That's a result of fetal exposure to testosterone. Psychologists Alison Bailey and Pete Hurd, of the University of Alberta in Canada, studied these finger ratios in male college students. And they found that men with more dramatic differences tended to be more aggressive. Additional links to resources are given for further inquiry.

  5. Experimental study of the potential use of diffusing wave spectroscopy to investigate the structural characteristics of blood under multiple scattering

    Microsoft Academic Search

    Alexander N. Korolevich; Igor V. Meglinsky

    2000-01-01

    The extension of the photon correlation spectroscopy (PCS) in multiple scattering regime, so-called diffusing wave spectroscopy (DWS) was employed to the study of blood samples. Multiple scattered light from a helium–neon (He–Ne) laser beam incident on the blood samples was detected by a photomultiplier, and both the temporal autocorrelation intensity functions g2(?) and power spectra S(?) were measured by a

  6. Outer membrane and porin characteristics of Serratia marcescens grown in vitro and in rat intraperitoneal diffusion chambers.

    PubMed Central

    Malouin, F; Campbell, G D; Halpenny, M; Becker, G W; Parr, T R

    1990-01-01

    The composition and antibiotic permeability barrier of the outer membrane of Serratia marcescens were assessed in cells grown in vivo and in vitro. Intraperitoneal diffusion chambers implanted in rats were used for the in vivo cultivation of bacteria. Outer membranes isolated from log-phase bacterial cells recovered from these chambers were compared with membranes isolated from cells grown in vitro. Analysis revealed that the suspected 41-kilodalton porin and the OmpA protein were recovered on sodium dodecyl sulfate-polyacrylamide gels in equal quantities. Several high-molecular-weight proteins, thought to be iron starvation induced, appeared in the diffusion chamber-grown cells. The outer membrane permeability barriers to cephaloridine were similar in in vivo- and in vitro-grown cells based on permeability coefficient calculations. The permeability coefficient of cephaloridine in S. marcescens cells (30.3 x 10(-5) to 38.9 x 10(-5) cm s-1) was greater than that obtained for an Escherichia coli strain expressing only porin OmpC but smaller than those obtained for the E. coli wild type and a strain expressing only porin OmpF. Functional characterization of the suspected porin was performed by using the planar lipid bilayer technology. The sodium dodecyl sulfate-0.4 M NaCl-soluble porin from both in vitro- and in vivo-grown cells showed an average single-channel conductance in 1 M KCl of 1.6. A partial amino acid sequence (19 residues) was obtained for the S. marcescens porin. The sequence showed a very high homology to the E. coli OmpC porin. These data identified the S. marcescens outer membrane 41-kilodalton protein as a porin by both functional and amino acid analyses. Also, the methodology used allowed for efficient growth and recovery of diffusion chamber-grown bacterial cells and permitted identification of specific in vivo-induced changes in bacterial cell membrane composition. Images PMID:2157667

  7. Spatiotemporal evolution of electron characteristics in the electron diffusion region of magnetic reconnection: Implications for acceleration and heating

    NASA Astrophysics Data System (ADS)

    Shuster, J. R.; Chen, L.-J.; Hesse, M.; Argall, M. R.; Daughton, W.; Torbert, R. B.; Bessho, N.

    2015-04-01

    Based on particle-in-cell simulations of collisionless magnetic reconnection, the spatiotemporal evolution of electron velocity distributions in the electron diffusion region (EDR) is reported to illustrate how electrons are accelerated and heated. Approximately when the reconnection rate maximizes, electron distributions in the vicinity of the X line exhibit triangular structures with discrete striations and a temperature (Te) twice that of the inflow region. Te increases as the meandering EDR populations mix with inflowing electrons. As the distance from the X line increases within the electron outflow jet, the discrete populations swirl into arcs and gyrotropize by the end of the jet with Te about 3 times that of the X line. Two dominant processes increase Te and produce the spatially and temporally evolving EDR distributions: (1) electric field acceleration preferential to electrons which meander in the EDR for longer times and (2) cyclotron turning by the magnetic field normal to the reconnection layer.

  8. A study of the influence of boron diffusion sources on the material and electrical characteristics of silicon p-n junctions

    E-print Network

    Huang, Kuan-Chun Andrew

    1976-01-01

    'ers on Boat / To Vent B, H I N t O I + Ar Quartz Diffusion Tube Valves and Flowmeter Fig. 2. 3. B H6 deposition system. Although previous researchers (15-18) had reported the doping characteristics of B2H6, it is found in this experiment... AFTER DRIVE-IN, n/D DEPTH, ~m. atoms/cm3 DOWN VOLTAGE, v. CITANCE, ni. BN (M) B2H6 BBr BN (A) B2H6 BBr BN (A) B2H~ BBr 27+1 27 + 1 27 + 135 + 15 135 + 15 135 + 15 550 + 50 5/0 + $0 550 + 50 3. 8 2, ll, 2. ll. 2. 2 19 4x10 19 ll x...

  9. Diffusion loading and drug delivery characteristics of alginate gel microparticles produced by a novel impinging aerosols method.

    PubMed

    Hariyadi, Dewi M; Lin, Sharon Chien-Yu; Wang, Yiwei; Bostrom, Thor; Turner, Mark S; Bhandari, Bhesh; Coombes, Allan G A

    2010-12-01

    Microencapsulation of a hydrophilic active (gentamicin sulphate (GS)) and a hydrophobic non-steroidal anti-inflammatory drug (ibuprofen) in alginate gel microparticles was accomplished by molecular diffusion of the drug species into microparticles produced by impinging aerosols of alginate solution and CaCl(2) cross-linking solution. A mean particle size in the range of 30-50 µm was measured using laser light scattering and high drug loadings of around 35 and 29% weight/dry microparticle weight were obtained for GS and ibuprofen respectively. GS release was similar in simulated intestinal fluid (phosphate buffer saline (PBS), pH 7.4, 37°C) and simulated gastric fluid (SGF) (HCl, pH 1.2, 37°C) but was accelerated in PBS following incubation of microparticles in HCl. Ibuprofen release was restricted in SGF but occurred freely on transfer of microparticles into PBS with almost 100% efficiency. GS released in PBS over 7?h, following incubation of microparticles in HCl for 2?h was found to retain at least 80% activity against Staphylococcus epidermidis while Ibuprofen retained around 50% activity against Candida albicans. The impinging aerosols technique shows potential for producing alginate gel microparticles of utility for protection and controlled delivery of a range of therapeutic molecules. PMID:20958098

  10. Correlations between PAH bioavailability, degrading bacteria, and soil characteristics during PAH biodegradation in five diffusely contaminated dissimilar soils.

    PubMed

    Crampon, M; Bureau, F; Akpa-Vinceslas, M; Bodilis, J; Machour, N; Le Derf, F; Portet-Koltalo, F

    2014-01-01

    The natural biodegradation of seven polycyclic aromatic hydrocarbons (PAHs) by native microorganisms was studied in five soils from Normandy (France) from diffusely polluted areas, which can also pose a problem in terms of surfaces and amounts of contaminated soils. Bioavailability tests using cyclodextrin-based extractions were performed. The natural degradation of low molecular weight (LMW) PAHs was not strongly correlated to their bioavailability due to their sorption to geosorbents. Conversely, the very low degradation of high molecular weight (HMW) PAHs was partly correlated to their poor availability, due to their sorption on complexes of organic matter and kaolinites or smectites. A principal component analysis allowed us to distinguish between the respective degradation behaviors of LMW and HMW PAHs. LMW PAHs were degraded in less than 2-3 months and were strongly influenced by the relative percentage of phenanthrene-degrading bacteria over total bacteria in soils. HMW PAHs were not significantly degraded, not only because they were less bioavailable but also because of a lack of degrading microorganisms. Benzo[a]pyrene stood apart since it was partly degraded in acidic soils, probably because of a catabolic cooperation between bacteria and fungi. PMID:24671402

  11. ESTIMATION OF TURBULENT DIFFUSIVITY WITH DIRECT NUMERICAL SIMULATION OF STELLAR CONVECTION

    SciTech Connect

    Hotta, H.; Iida, Y.; Yokoyama, T., E-mail: hotta.h@eps.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2012-05-20

    We investigate the value of horizontal turbulent diffusivity {eta} by numerical calculation of thermal convection. In this study, we introduce a new method whereby the turbulent diffusivity is estimated by monitoring the time development of the passive scalar, which is initially distributed in a given Gaussian function with a spatial scale d{sub 0}. Our conclusions are as follows: (1) assuming the relation {eta} = L{sub c} v{sub rms}/3, where v{sub rms} is the root-mean-square (rms) velocity, the characteristic length L{sub c} is restricted by the shortest one among the pressure (density) scale height and the region depth. (2) The value of turbulent diffusivity becomes greater with the larger initial distribution scale d{sub 0}. (3) The approximation of turbulent diffusion holds better when the ratio of the initial distribution scale d{sub 0} to the characteristic length L{sub c} is larger.

  12. 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. PMID:18851009

  13. Diffusion Geometry Diffusion Geometry

    E-print Network

    Hirn, Matthew

    Diffusion Geometry Diffusion Geometry for High Dimensional Data Matthew J. Hirn July 3, 2013 #12;Diffusion Geometry Introduction Embedding of closed curve Figure: Left: A closed, non-self-intersecting curve in 3 dimensions. Right: Its embedding as a circle. #12;Diffusion Geometry Introduction Cartoon

  14. Performance of conical diffusers

    Microsoft Academic Search

    P. C. Sharma

    1979-01-01

    An experimental study of the effect of the entrance length and the inlet Reynolds number on the performance of a straight walled conical diffuser with thin, turbulent boundary layer and subsonic inlet flow is reported. The experimental measurements included pressure distributions along the diffuser and velocity traverses at six stations. Area ratio was found to be the major geometric parameter

  15. Length measurement in accelerated systems

    E-print Network

    Bahram Mashhoon; Uwe Muench

    2002-06-27

    We investigate the limitations of length measurements by accelerated observers in Minkowski spacetime brought about via the hypothesis of locality, namely, the assumption that an accelerated observer at each instant is equivalent to an otherwise identical momentarily comoving inertial observer. We find that consistency can be achieved only in a rather limited neighborhood around the observer with linear dimensions that are negligibly small compared to the characteristic acceleration length of the observer.

  16. Hole diffusion at the recombination junction of thin film tandem solar cells and its effect on the illuminated current-voltage characteristic

    NASA Astrophysics Data System (ADS)

    Palit, N.; Dasgupta, A.; Ray, S.; Chatterjee, P.

    2000-09-01

    Computer simulation of experimental current density-voltage (J-V) and quantum efficiency characteristics of thin film p1-i1-n1-p2 structures and of double junction solar cells (p1-i1-n1-p2-i2-n2), has been used to understand the hole transport mechanisms near the np "tunnel" junction between two subcells of a multijunction structure. Two different types of p layers at the junction have been studied: (i) hydrogenated microcrystalline silicon (?c-Si:H) and (ii) hydrogenated amorphous silicon carbide (a-SiC:H). There is a striking difference between the experimental J-V characteristics for the p1-i1-n1-p2 structures, with case (i) having a fairly high fill factor (FF) and conversion efficiency (?), as against a very low FF and ? in case (ii). Although the difference is much smaller for double junction cells employing these two types of materials as the p layer at the junction, the fill factor of the cell employing ?c-Si:H is about 8% higher. Analysis of transport properties as a function of position by computer modeling reveals that the main difference in behavior between the two cases is due to the much higher free hole population in the p layer at the junction when it is microcrystalline; which in turn, is a direct consequence of the lower activation energy for this case. We also learn that not only tunneling and the electric field in the bottom subcell, but also diffusion, plays a major role in pushing the holes produced in it by the incident light towards the recombination layer at the junction; and thereby helps improve cell performance, especially its fill factor. We conclude that the p layer at the junction should have a high free hole density (low activation energy in the device), to attain an overall high fill factor and conversion efficiency. Another interesting inference is the fact that tunneling as transport mechanism for holes towards the junction is more important when the p layer at the junction is a-SiC:H than when it is microcrystalline, while diffusion plays a more prominent role in propelling holes towards the junction in the latter case.

  17. Characteristic oscillatory motion of a camphor boat sensitive to physicochemical environment

    NASA Astrophysics Data System (ADS)

    Nakata, S.; Yoshii, M.; Matsuda, Y.; Suematsu, N. J.

    2015-06-01

    A self-propelled camphor boat on water was investigated from the viewpoint of characteristic features of motion and mode-bifurcation depending on the diffusion length of camphor molecules. When a camphor disk was connected to the bottom of a larger plastic plate and then was placed on water, either oscillatory motion (repetition between rest and motion) or continuous motion was observed. In this paper, we report the novel features of this motion and mode-bifurcation as a function of the diffusion length of camphor molecules, e.g., multiple accelerations during oscillation, period-2 or irregular oscillatory motion, and reciprocating oscillation. These characteristic motion and mode-bifurcation are discussed in relation to the diffusion length of camphor molecules under the camphor boat and the development of camphor molecules from the camphor boat on water.

  18. The Diffusion Process

    NSDL National Science Digital Library

    This is a description for a learning module from Maricopa Advanced Technology Education Center. This PDF describes the module; access may be purchased by visiting the MATEC website. In an orderly and comprehensive set of lectures, lessons, and laboratory activities, MATEC explicates for your learners the complex process of diffusion. Beginning with an overview of diffusion's purpose in altering a wafer's electrical characteristics, the module then drills down to specifics: process parameters, different techniques of diffusion, the use of a hot probe to evaluate diffusion, and wafer handling. Your learners demonstrate their new knowledge by diffusing selected dopants into a silicon wafer.

  19. A microscopic model of ballistic-diffusive crossover

    NASA Astrophysics Data System (ADS)

    Bagchi, Debarshee; Mohanty, P. K.

    2014-11-01

    Several low-dimensional systems show a crossover from diffusive to ballistic heat transport when system size is decreased. Although there is some phenomenological understanding of this crossover phenomenon at the coarse-grained level, a microscopic picture that consistently describes both the ballistic and the diffusive transport regimes has been lacking. In this work we derive a scaling form for the thermal current in a class of one dimensional systems attached to heat baths at boundaries and rigorously show that the crossover occurs when the characteristic length scale of the system competes with the system size.

  20. Pharmacologically induced erect penile length and stretched penile length are both good predictors of post-inflatable prosthesis penile length.

    PubMed

    Osterberg, E C; Maganty, A; Ramasamy, R; Eid, J F

    2014-01-01

    Inflatable penile prosthesis (IPP) remains the gold standard for the surgical treatment of refractory erectile dysfunction; however, current literature to aid surgeons on how best to counsel patients on their postoperative inflated penile length is lacking. The aim of this study was to identify preoperative parameters that could better predict postoperative penile length following insertion of an IPP. Twenty men were enrolled in a prospective study examining penile lengths before and after IPP surgery. Patients with Peyronie's disease were excluded from this analysis. Baseline preoperative characteristics, including body mass index, history of hypertension, diabetes, Sexual Health Inventory for Men scores and/or prior radical prostatectomy were recorded. All patients underwent implantation with a three-piece inflatable Coloplast penile prosthesis. We compared stretched penile length to pharmacologically induced erect lengths. Postoperatively, we measured inflated penile lengths at 6 weeks and assessed patients' perception of penile size at 12 weeks. The median (±interquartile range) stretched penile length and pharmacologically induced erect penile length was 15 (±3) and 14.25 (±2)?cm, respectively (P=0.5). Median post-prosthesis penile length (13.5±2.13?cm) was smaller than preoperative pharmacologically induced length (P=0.02) and preoperative stretched penile length (P=0.01). The majority of patients (70%) had a decrease in penile length (median loss 0.5±1.5?cm); however, this loss was perceptible by 43% of men. Stretched penile length and pharmacologically induced erect penile length were equally good predictors of postoperative inflated length (Spearman's correlation 0.8 and 0.9, respectively). Pharmacologically induced erect penile length and stretched penile lengths are equal predictors of post-prosthesis penile length. The majority of men will experience some decrease in penile length following prosthesis implantation; however <50% report a subjective loss of penile length. PMID:24430278

  1. Diffused junction p(+)-n solar cells in bulk GaAs. II - Device characterization and modelling

    NASA Technical Reports Server (NTRS)

    Keeney, R.; Sundaram, L. M. G.; Rode, H.; Bhat, I.; Ghandhi, S. K.; Borrego, J. M.

    1984-01-01

    The photovoltaic characteristics of p(+)-n junction solar cells fabricated on bulk GaAs by an open tube diffusion technique are presented in detail. Quantum efficiency measurements were analyzed and compared to computer simulations of the cell structure in order to determine material parameters such as diffusion length, surface recombination velocity and junction depth. From the results obtained it is projected that proper optimization of the cell parameters can increase the efficiency of the cells to close to 20 percent.

  2. How wall properties control diffusion in grooved nanochannels: a molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Sofos, Filippos; Karakasidis, Theodoros E.; Liakopoulos, Antonios

    2013-08-01

    The effect of a geometrically-rough wall, amplified by its degree of wettability and stiffness on diffusion coefficient in cases of fluid flow in nanochannels is studied by non-equilibrium molecular dynamics. Diffusion coefficient values, either inside the grooves or as average channel values are affected by the rough wall characteristics. A significant anisotropy along the directions parallel and normal to the flow is observed inside the grooves, while a critical value of groove length below which this anisotropy is enhanced exists. Wall wettability is the property that affects diffusion the most and could be a means of controlling its behavior.

  3. Investigation of High-Subsonic Performance Characteristics of a 12 Degree 21-Inch Conical Diffuser, Including the Effects of Change in Inlet-Boundary-Layer Thickness

    NASA Technical Reports Server (NTRS)

    Copp, Martin R.; Klevatt, Paul L.

    1950-01-01

    Investigations were conducted of a 12 degree 21-inch conical diffuser of 2:l area ratio to determine the interrelation of boundary layer growth and performance characteristics. surveys were made of inlet and exit from, longitudinal static pressures were recorded, and velocity profiles were obtained through an inlet Reynolds number range, determined From mass flows and based on inlet diameter of 1.45 x 10(exp 6) to 7.45 x 10(exp 6) and a Mach number range of 0.11 to approximately choking. These investigations were made to two thicknesses of inlet boundary layer. The mean value, over the entire range of inlet velocities, of the displacement thickness of the thinner inlet boundary layer was approximately 0.035 inch and that of the thicker inlet boundary layer was approximately six times this value. The loss coefficient in the case of the thinner inlet boundary layer had a value between 2 to 3 percent of the inlet impact pressure over most of the air-flow range. The loss coefficient with the thicker inlet boundary layer was of the order of twice that of the thinner inlet boundary layer at low speeds and approximately three times at high speeds. In both cases the values were substantially less than those given in the literature for fully developed pipe flow. The static-pressure rise for the thinner inlet boundary layer was of the order of 95 percent of that theoretically possible over the entire speed range. For the thicker inlet boundary layer the static pressure rise, as a percentage of that theoretically possible, ranged from 82 percent at low speeds to 68 percent at high speeds.

  4. Characteristics of SiO x N y films deposited by inductively coupled plasma enhanced chemical vapor deposition using HMDS\\/NH 3\\/O 2\\/Ar for water vapor diffusion barrier

    Microsoft Academic Search

    J. H. Lee; C. H. Jeong; H. B. Kim; J. T. Lim; S. J. Kyung; G. Y. Yeom

    2006-01-01

    SiOxNy thin films were deposited by inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) using hexamethyldisilazane (HMDS, 99.9%)\\/NH3\\/O2\\/Ar at a low temperature, and examined for use as a water vapor diffusion barrier. The film characteristics were investigated as a function of the O2:NH3 ratio. An increase in the O2:NH3 ratio decreased the level of impurities such as –CHx, N–H in

  5. Influence of chain length in nonylphenol ethoxylate surfactants on the film formation behaviour of methylmethacrylate-2-ethylhexyl acrylate copolymer latexes: part 1. Differential scanning calorimetry and atomic force microscopy

    Microsoft Academic Search

    Lynda A Cannon; Richard A Pethrick

    2002-01-01

    A comparison of the film forming characteristics of methylmethacrylate-2-ethylhexyl acrylate latex copolymers stabilised with nonyl-phenol ethoxylate molecules of varying chain lengths is presented. The ability of the stabiliser to segregate and diffuse from the interfacial layer into the surrounding media influences both the rate of coalescence process and structure of the film formed. Dynamic mechanical analysis, minimum film formation temperature

  6. Combustion characteristics of hydrogen–hydrocarbon hybrid fuels

    Microsoft Academic Search

    Ahsan R Choudhuri; S. R Gollahalli

    2000-01-01

    A comparative study of the flame structure and characteristics of diffusion flames of the mixture of hydrogen–hydrocarbon (natural gas and propane) hybrid fuel in a slow co-flowing stream of air is presented. The volumetric content of natural gas and propane in the mixture was varied from 0–35%. The burner exit Reynolds number was varied from 150–3000. Measurements include flame length,

  7. A continuous time random walk model with multiple characteristic times

    NASA Astrophysics Data System (ADS)

    Sau Fa, Kwok; Mendes, R. S.

    2010-04-01

    In this paper we consider a continuous time random walk (CTRW) model with a decoupled jump pdf. Further, we consider an approximate jump length pdf; for the waiting time pdf we do not use any approximation and we employ a function which depends on multiple characteristic times given by a sum of exponential functions. This waiting time pdf can reproduce power-law behavior for intermediate times. Using this specific waiting time probability density, we analyze the behavior of the second moment generated by the CTRW model. It is known that the waiting time pdf given by an exponential function generates a normal diffusion process, but for our waiting time pdf the second moment can give an anomalous diffusion process for intermediate times, and the normal diffusion process is maintained for the long-time limit. We note that systems which present subdiffusive behavior for intermediate times but reach normal diffusion at large times have been observed in biology.

  8. Microviscometric studies on thermal diffusion 

    E-print Network

    Reyna, Eddie

    1959-01-01

    . The main interest of 6 tais work was the molecular weight dependence of the thermal diffusion coefficient and the suitability of thermal diffusion as a method of frac- tionation of polymers. Since the work of Debye and Bueche, applications of thermal.... a monot& nic function, zn this c~ e of time rathez thau length. From these conszuoratiom , it was seen -24- that a diffusion coefficient dependent only on concentration was inadequate in explaining the observed effects. Another consideration...

  9. Arc Length Gone Global

    ERIC Educational Resources Information Center

    Boudreaux, Gregory M.; Wells, M. Scott

    2007-01-01

    Everyone with a thorough knowledge of single variable calculus knows that integration can be used to find the length of a curve on a given interval, called its arc length. Fortunately, if one endeavors to pose and solve more interesting problems than simply computing lengths of various curves, there are techniques available that do not require an…

  10. Diffusion /Osmosis

    NSDL National Science Digital Library

    Jensen

    2007-11-26

    This project is use to review the concepts of diffusion and osmosis 1. Watch the tutorials on diffusion and osmosis. Take the online quiz at the end of each one. Diffusion Animation Osmosis Animation 2. Do the interactive lab on diffusion. Stop when you get to the calculating water potential section. Diffusion/Osmosis Interactive Demo 3. Play the Quia review games. Quia Games- matching/concetration Quia Jeopardy 4. Check out the Elodea leaf cells. Be able to ...

  11. Soluble intercellular adhesion molecule-1 (s-ICAM-1\\/s-CD54) in diffuse large B-cell lymphoma: association with clinical characteristics and outcome

    Microsoft Academic Search

    M. J. Terol; M. Tormo; J. A. Martinez-Climent; I. Marugan; I. Benet; A. Ferrandez; A. Teruel; R. Ferrer; J. García-Conde

    2003-01-01

    Background: High serum levels of soluble intercellular adhesion molecule-1(s-ICAM-1\\/s-CD54) have been associated with adverse clinical features and poor outcome in chronic lymphocytic leukemia, Hodgkin's disease and non-Hodgkin's lymphoma, but their value in the different subtypes of non-Hodgkin's lymphoma has not been well addressed. Patients and methods: Our aim was to study the serum levels of s-ICAM-1 in diffuse large B-cell

  12. Force and Pressure Recovery Characteristics at Supersonic Speeds of a Conical Spike Inlet with a Bypass Discharging from the Top or Bottom of the Diffuser in an Axial Direction

    NASA Technical Reports Server (NTRS)

    Allen, J L; Beke, Andrew

    1953-01-01

    Force and pressure-recovery characteristics of a nacelle-type conical-spike inlet with a fixed-area bypass located in the top or bottom of the diffuser are presented for flight Mach numbers of 1.6, 1.8, and 2.0 for angles of attack from 0 degrees to 9 degrees. Top or bottom location of the bypass did not have significant effects on diffuser pressure-recovery, bypass mass-flow ratio, or drag coefficient over the range of angles of attack, flight Mach numbers, and stable engine mass-flow ratios investigated. A larger stable subcritical operating range was obtained with the bypass on the bottom at angles of attack from 3 degrees to 9 degrees at a flight Mach number of 2.0. At a flight Mach number of 2.0, the discharge of 14 percent of the critical mass flow of the inlet by means of a bypass increased the drag only one-fifth of the additive drag that would result for equivalent spillage behind an inlet normal shock without significant reductions in diffuser pressure recovery.

  13. Performance characteristics of diffusive gradients in thin films equipped with a binding gel layer containing precipitated ferrihydrite for measuring arsenic(V), selenium(VI), vanadium(V), and antimony(V).

    PubMed

    Luo, Jun; Zhang, Hao; Santner, Jakob; Davison, William

    2010-11-01

    Measurements at high spatial resolution by DGT (diffusive gradients in thin films) require a binding agent that is homogeneously distributed in the binding layer. Formation of ferrihydrite by in situ precipitation within a hydrogel has been previously shown to meet these requirements for the measurement of oxyanions by DGT. Here, we report for the first time detailed performance characteristics of the binding gel and associated DGT devices obtained by deployment in known solutions. To allow comparison of measured and theoretical accumulation of As(V), Se(VI), V(V), and Sb(V), their diffusion coefficients were determined using an independent diffusion cell. Theoretical responses were obtained irrespective of ionic strength (1-100 mmol L(-1)) and pH (3-8), except for Se above pH 7.8 and V below pH 5. Calculated detection limits, based on deployment times of 1 day, were lower than those for devices made with a binding gel cast with a ferrihydrite slurry, and the measured capacity of the binding layer was also superior. There was no evidence for interference from other oxyanions, but binding performance showed some deterioration after 38 days of storage. The potential capability for measuring labile forms of these oxyanions in acidic to neutral, fresh to brackish waters was demonstrated. PMID:20936784

  14. On collisional diffusion in a stochastic magnetic field

    SciTech Connect

    Abdullaev, S. S. [Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung - Plasmaphysik, EURATOM Association, 52425 Jülich (Germany)] [Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung - Plasmaphysik, EURATOM Association, 52425 Jülich (Germany)

    2013-08-15

    The effect of particle collisions on the transport in a stochastic magnetic field in tokamaks is investigated. The model of resonant magnetic perturbations generated by external coils at the plasma edge is used for the stochastic magnetic field. The particle collisions are simulated by a random walk process along the magnetic field lines and the jumps across the field lines at the collision instants. The dependencies of the local diffusion coefficients on the mean free path ?{sub mfp}, the diffusion coefficients of field lines D{sub FL}, and the collisional diffusion coefficients, ?{sub ?} are studied. Based on these numerical data and the heuristic arguments, the empirical formula, D{sub r}=?{sub ?}+v{sub ||}D{sub FL}/(1+L{sub c}/?{sub mfp}), for the local diffusion coefficient is proposed, where L{sub c} is the characteristic length of order of the connection length l{sub c}=?qR{sub 0}, q is the safety factor, R{sub 0} is the major radius. The formula quite well describes the results of numerical simulations. In the limiting cases, the formula describes the Rechester-Rosenbluth and Laval scalings.

  15. Dynamic Frame Length ALOHA

    Microsoft Academic Search

    F. Schoute

    1983-01-01

    Adding frame structure to slotted ALOHA makes it very convenient to control the ALOHA channel and eliminate instability. The frame length is adjusted dynamically according to the number of garbled, successful, and empty timeslots in the past. Each terminal that has a packet to transmit selects at random one of thentimeslots of a frame. Dynamic frame length ALOHA achieves a

  16. Length of Quantum Trajectories

    Microsoft Academic Search

    Jean-Claude Zambrini; Kunio Yasue

    1984-01-01

    A notion of length for quantum mechanical trajectories is introduced within the realm of stochastic mechanics. Using a stochastic calculus of variation, one shows that the geodesic dynamics is not the free one, but the quantum evolution in the time-dependent quadratic potential associated with the Wiener process in stochastic mechanics. The length for the free evolution is also examined.

  17. Neandertal clavicle length.

    PubMed

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

    2014-03-25

    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

  18. Characteristics of Signals Originating near the Lithium-Diffused N+ Contact of High Purity Germanium P-Type Point Contact Detectors

    SciTech Connect

    Aguayo, E. [Pacific Northwest National Laboratory (PNNL); Amman, M. [Lawrence Berkeley National Laboratory (LBNL); Avignone, F. T. [University of South Carolina/ORNL; Barabash, A.S. [Institute of Theoretical & Experimental Physics, Moscow, Russia; Barton, P. J. [Lawrence Berkeley National Laboratory (LBNL); Beene, James R [ORNL; Bertrand Jr, Fred E [ORNL; Boswell, M. [Los Alamos National Laboratory (LANL); Brudanin, V. [Joint Institute for Nuclear Research, Dubna, Russia; Busch, M. [Duke University; Chan, Y-D [Lawrence Berkeley National Laboratory (LBNL); Christofferson, C. D. [South Dakota School of Mines & Technology, Rapid City, SD; Collar, Juan I. [University of Chicago; Combs, D. C. [University of North Carolina / Triangle Universities Nuclear Lababoratory, Durham; Cooper, Reynold J [ORNL; Detwiler, J.A. [Lawrence Berkeley National Laboratory (LBNL); Doe, P. J. [University of Washington; Efremenko, Yuri [University of Tennessee (UTK) and Oak Ridge National Laboratory (ORNL); Egorov, V. [Joint Institute for Nuclear Research, Dubna, Russia; Ejiri, H. [Osaka University; Elliott, S. R. [Los Alamos National Laboratory (LANL); Esterline, J. [Duke University; Fast, J.E. [Pacific Northwest National Laboratory (PNNL); Fields, N. [University of Chicago; Finnerty, P. [University of North Carolina / Triangle Universities Nuclear Lababoratory, Durham; Fraenkle, F. M. [University of North Carolina / Triangle Universities Nuclear Lababoratory, Durham; Galindo-Uribarri, Alfredo {nmn} [ORNL; Gehman, V. M. [Los Alamos National Laboratory (LANL); Giovanetti, G. K. [Univ, of North Carolina & Triangle Universities Nucl. Lab - Durham, NC; Green, M. P. [University of North Carolina / Triangle Universities Nuclear Lababoratory, Durham; Guiseppe, V.E. [University of South Dakota; Gusey, K. [Joint Institute for Nuclear Research, Dubna, Russia; Hallin, A. L. [University of Alberta, Edmonton, Canada; Hazama, R. [Osaka University; Henning, R. [Univ, of North Carolina & Triangle Universities Nucl. Lab - Durham, NC; Hoppe, E.W. [Pacific Northwest National Laboratory (PNNL); Horton, M. [South Dakota School of Mines & Technology, Rapid City, SD; Howard, S. [South Dakota School of Mines and Technology; Howe, M. A. [University of North Carolina / Triangle Universities Nuclear Lababoratory, Durham; Johnson, R. A. [University of Washington, Seattle; Keeter, K.J. [Black Hills State University, Spearfish, SD; Kidd, M. F. [Los Alamos National Laboratory (LANL); Knecht, A. [University of Washington, Seattle; Kochetov, O. [Joint Institute for Nuclear Research, Dubna, Russia; Konovalov, S.I. [Institute of Theoretical & Experimental Physics, Moscow, Russia; Kouzes, R. T. [Pacific Northwest National Laboratory (PNNL); LaFerriere, B. D. [Pacific Northwest National Laboratory (PNNL); Leon, J. [University of Washington, Seattle; Leviner, L. E. [University of North Carolina / Triangle Universities Nuclear Lababoratory, Durham; Loach, J.C. [Lawrence Berkeley National Laboratory (LBNL); Looker, Q. [Lawrence Berkeley National Laboratory (LBNL); Luke, P.N. [Lawrence Berkeley National Laboratory (LBNL); MacMullin, S. [University of North Carolina / Triangle Universities Nuclear Lababoratory, Durham; Marino, M. G. [University of Washington, Seattle; Martin, R.D. [Lawrence Berkeley National Laboratory (LBNL); Merriman, J. H. [Pacific Northwest National Laboratory (PNNL); Miller, M. L. [University of Washington, Seattle; Mizouni, L. [PPNL/Univ. of South Carolina; Nomachi, M. [Osaka University; Orrell, John L. [Pacific Northwest National Laboratory (PNNL); Overman, N. R. [Pacific Northwest National Laboratory (PNNL); Perumpilly, G. [University of South Dakota; Phillips II, D. G. [University of North Carolina / Triangle Universities Nuclear Lababoratory, Durham; Poon, A.W.P. [Lawrence Berkeley National Laboratory (LBNL); et al.

    2013-01-01

    A study of signals originating near the lithium-diffused n+ contact of p-type point contact (PPC) high purity germanium detectors (HPGe) is presented. The transition region between the active germanium and the fully dead layer of the n+ contact is examined. Energy depositions in this transition region are shown to result in partial charge collection. This provides a mechanism for events with a well defined energy to contribute to the continuum of the energy spectrum at lower energies. A novel technique to quantify the contribution from this source of background is introduced. Experiments that operate germanium detectors with a very low energy threshold may benefit from the methods presented herein.

  19. Anomalous Diffusion: In diffusion-weighted magnetic resonance imaging (MRI) of neural tissue, classical models

    E-print Network

    McQuade, D. Tyler

    Anomalous Diffusion: In diffusion-weighted magnetic resonance imaging (MRI) of neural tissue modeled diffusion in neural tissue from the perspective of a continuous time random walk. Here, the characteristic diffusion decay is represented by the Mittag- Leffler function (see figure), which relaxes

  20. Compressor and fan wake characteristics

    NASA Technical Reports Server (NTRS)

    Lakshminarayana, B.

    1975-01-01

    Approaches for developing an analytical model capable of determining the effects of rotor flow and blade parameters and turbulence properties (i.e. energy, velocity correlations, and length scale) on the rotor wake characteristics and its diffusion properties are discussed. The three-dimensional model will employ experimental measurements, instantaneous velocities, and turbulence properties at various stations downstream from a rotor. A triaxial probe and a rotating conventional probe, which is mounted on a traverse gear operated by two step motors, are to be used for these measurements. The final rotor wake model will be capable of predicting the discrete and broadband noise generated in a fan rotor and of evaluating the aerodynamic losses, efficiency and optimum spacing between a rotor and stator in turbomachinery.

  1. Optical properties of real photonic crystals: anomalous diffuse transmission

    Microsoft Academic Search

    A. Femius Koenderink; Willem L. Vos

    2005-01-01

    Unavoidable structural disorder in photonic crystals causes multiple scattering of light, resulting in extinction of coherent beams and generation of diffuse light. We demonstrate experimentally that the diffusely transmitted intensity is distributed over exit angles in a strikingly non-Lambertian manner, depending strongly on frequency. The angular redistribution of diffuse light reveals both photonic gaps and the diffuse extrapolation length, as

  2. The Diffusion Process

    NSDL National Science Digital Library

    This website includes an animation which illustrates the diffusion process. The two models that have been developed to explain the mechanism for the diffusion of dopants into silicon are the Vacancy model and the Interstitial model. It is the different bonding characteristics of the dopants with silicon that determine the diffusion mechanism. Although each model is based on these differences, they are not mutually exclusive. Objective: Explain the difference between the Vacancy and Interstitial diffusion models. You can find this animation under the heading "Process & Equipment III." This simulation is from Module 019 of the Process & Equipment III Cluster of the MATEC Module Library (MML). To view other clusters or for more information about the MML visit http://matec.org/ps/library3/process_I.shtmlKey

  3. Hole diffusion at the recombination junction of thin film tandem solar cells and its effect on the illuminated current-voltage characteristic

    Microsoft Academic Search

    N. Palit; A. Dasgupta; S. Ray; P. Chatterjee

    2000-01-01

    Computer simulation of experimental current density-voltage (J-V) and quantum efficiency characteristics of thin film p1-i1-n1-p2 structures and of double junction solar cells (p1-i1-n1-p2-i2-n2), has been used to understand the hole transport mechanisms near the np ``tunnel'' junction between two subcells of a multijunction structure. Two different types of p layers at the junction have been studied: (i) hydrogenated microcrystalline silicon

  4. Bonding characteristics and diffusion barrier effect of the TiC phase formed at the bonding interface in an explosively welded titanium\\/high- carbon steel clad

    Microsoft Academic Search

    A. Chiba; M. Nishida; Y. Morizono; K. Imamura

    1995-01-01

    Microstructural aspects and bonding characteristics of the explosively welded titanium\\/high-carbon steel clad of the as-welded\\u000a and postannealed states were investigated. Amorphous and ?Ti phases were observed at the interface in the as-welded clad.\\u000a These were considered to be the trace of melting and subsequently rapid solidification of thin layers along the contact surface\\u000a of both the parent materials. The melting

  5. Interrelationships of Watershed Characteristics

    Microsoft Academic Search

    Don M. Gray

    1961-01-01

    The application of the principles of dimensional analysis to obtain the relationships between characteristics of the unit hydrograph and topographic and morphometric properties of a watershed is not possible unless careful consideration is given to the selection of variables. Evidence is presented which shows that, in small watersheds, drainage-area size A, length of the main stream L, and length to

  6. Relativistic Length Agony Continued

    NASA Astrophysics Data System (ADS)

    Redzic, D. V.

    2014-06-01

    We made an attempt to remedy recent confusing treatments of some basic relativistic concepts and results. Following the argument presented in an earlier paper (Redzic 2008b), we discussed the misconceptions that are recurrent points in the literature devoted to teaching relativity such as: there is no change in the object in Special Relativity, illusory character of relativistic length contraction, stresses and strains induced by Lorentz contraction, and related issues. We gave several examples of the traps of everyday language that lurk in Special Relativity. To remove a possible conceptual and terminological muddle, we made a distinction between the relativistic length reduction and relativistic FitzGerald-Lorentz contraction, corresponding to a passive and an active aspect of length contraction, respectively; we pointed out that both aspects have fundamental dynamical contents. As an illustration of our considerations, we discussed briefly the Dewan-Beran-Bell spaceship paradox and the 'pole in a barn' paradox.

  7. Identifying anomalous diffusion and melting in dusty plasmas

    SciTech Connect

    Feng Yan; Goree, J.; Liu Bin [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)

    2010-09-15

    Anomalous diffusion in liquids and the solid-liquid phase transition (melting) are studied in two-dimensional Yukawa systems. The self-intermediate scattering function (self-ISF), calculated from simulation data, exhibits a temporal decay, or relaxation, with a characteristic relaxation time. This decay is found to be useful for distinguishing normal and anomalous diffusion in a liquid, and for identifying the solid-liquid phase transition. For liquids, a scaling of the relaxation time with length scale is found. For the solid-liquid phase transition, the shape of the self-ISF curve is found to be a sensitive indicator of phase. Friction has a significant effect on the timing of relaxation, but not the melting point.

  8. Rotational diffusion of magnetic nickel nanorods in colloidal dispersions.

    PubMed

    Günther, A; Bender, P; Tschöpe, A; Birringer, R

    2011-08-17

    Colloidal dispersions of Ni nanorods were synthesized by pulsed electrodeposition of Ni into nanoporous aluminum oxide layers followed by dissolution of the templates. Geometrical characterization of the nanorods by transmission electron microscopy and scanning electron microscopy allowed us to determine the average length (100-250 nm) and diameter (20-40 nm) of the rods and to estimate the thickness of the polyvinylpyrrolidone surfactant layer. Due to their acicular shape, nanorods of the given size are uniaxial ferromagnetic single domain particles and exhibit a distinct anisotropic polarizability. These two characteristic properties are the physical basis for magnetic field-dependent optical transmission and allow us to investigate the rotational diffusion of the nanorods in liquid dispersion. In the present study, we employed AC magnetization measurements, dynamical light scattering and optical transmission measurements in a rotating magnetic field to determine the rotational diffusion coefficient. The results from all three methods were consistent and agree with theory within a factor of 2. PMID:21757802

  9. The characteristics of atmospheric ice nuclei measured at the top of Huangshan (the Yellow Mountains) in Southeast China using a newly built static vacuum water vapor diffusion chamber

    NASA Astrophysics Data System (ADS)

    Jiang, Hui; Yin, Yan; Su, Hang; Shan, Yunpeng; Gao, Renjie

    2015-02-01

    A newly built static vacuum water vapor diffusion chamber was built to measure the concentration of ice nuclei (INs) at the top of Huangshan (the Yellow Mountains) in Southeast China. The experiments were conducted under temperatures between - 15 °C and - 23 °C and supersaturations with respect to ice between 4% and 25%. The results show that the average IN concentration was in the range of 0.27 to 7.02 L- 1, when the temperature was varied from - 15 °C to - 23 °C. The changes in IN concentrations with time were correlated with the change of number concentration of the aerosol particles of 0.5-20 ?m in diameter. The square correlation coefficients (R2) between IN and coarse aerosol particles (0.5-20 ?m in diameter) were all higher than 0.60, much higher than that (0.10) between IN and smaller particles (0.01-0.5 ?m). The concentration of ice nuclei at 14:00 LST was significantly higher than that at 08:00 LST, which is correlated with the diurnal variation of the concentration of aerosol particles. A parametric equation was developed based on measurements to represent the variations of IN concentration with temperature and supersaturation.

  10. Variable focal length microlenses

    NASA Astrophysics Data System (ADS)

    L. G., Commander; Day, S. E.; Selviah, D. R.

    2000-04-01

    Refractive surface relief microlenses (150 ?m diameter) are immersed in nematic liquid crystal in a cell. Application of a variable voltage across the cell effectively varies the refractive index of the liquid crystal and results in a change of the focal length by the lensmakers formula (E. Hecht, Optics, 2nd edn., Addison-Wesley, Reading, Massachusetts, 1987, p. 138). We describe the cell design and construction and demonstrate a range of focal lengths from +490 to +1000 ?m for 2 to 12 V applied. A diverging lens results when the voltage is lower. Theoretical models are developed to account for some of the observed aberrations.

  11. Precision structural diagnostics of layered superconductor/ferromagnet nanosystems V/Fe by reflectometry and diffuse scattering of synchrotron radiation

    SciTech Connect

    Nikitin, A. M., E-mail: am.nikitin@physics.msu.ru [Moscow State University (Russian Federation); Borisov, M. M.; Mukhamedzhanov, E. Kh.; Kovalchuk, M. V. [National Research Center Kurchatov Institute (Russian Federation); Sajti, S.; Tancziko, F.; Deak, L.; Bottyan, L. [Hungarian Academy of Sciences, KFKI Research Institute for Particle and Nuclear Physics (Hungary); Khaydukov, Yu. N.; Aksenov, V. L. [Moscow State University (Russian Federation)

    2011-09-15

    Layered superconducting ferromagnetic nanosystems Cu(32 nm)/V(40-80 nm)/Fe(0.5-4 nm)/MgO(001) have been investigated by reflectometry and the diffuse scattering of synchrotron radiation. The data obtained make it possible to determine the important characteristics of samples such as the layer thickness and the rms heights and lateral correlation lengths of roughness at the interfaces.

  12. Lengths of Ladybugs

    NSDL National Science Digital Library

    Utah LessonPlans

    2012-09-18

    In this math lesson, learners explore the concept of using units to measure length. Learners first read "Ladybug on the Move" by Richard Fowler and measure the distance the ladybug travels on each page using yarn. Next, learners make their own "Go Ladybug Go!" books and use lima beans and a ladybug ruler to make and record measurements.

  13. Document Length Normalization.

    ERIC Educational Resources Information Center

    Singhal, Amit; And Others

    1996-01-01

    Describes a study that investigated document retrieval relevance based on document length in an experimental text collection. Topics include term weighting and document ranking, retrieval strategies such as the vector-space cosine match, and a modified technique called the pivoted cosine normalization. (LRW)

  14. Reversible variable length codes

    Microsoft Academic Search

    Y. Takishima; M. Wada; H. Murakami

    1995-01-01

    Proposes some reversible variable length codes (RVLCs) which can be decoded instantaneously both in the forward and backward directions and have high transmission efficiency. These codes can be used, for example, in the backward reconstruction of video signals from the data last received when some signal is lost midway in the transmission. Schemes for a symmetrical RVLC requiring only a

  15. 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

  16. Rat medial gastrocnemius muscles produce maximal power at a length lower than the isometric optimum length

    Microsoft Academic Search

    A. de Haan; P. A. Huijing; M. R. van der Vliet

    2003-01-01

    The interaction of relative muscle length and force-velocity characteristics was investigated in the fully activated rat medial gastrocnemius muscle in situ. Average maximal isometric force (as a percentage of the of the maximal isometric force at Lo,iso) at relative lengths measured below isometric optimum (Lo,iso) was 96% at Lo,isoф mm, 88% at Lo,isoц mm and 58% at Lo,isoш mm. Force-velocity

  17. Analysis of EIS characteristics of CO 2 corrosion of well tube steels with corrosion scales

    NASA Astrophysics Data System (ADS)

    Bai, Z. Q.; Chen, C. F.; Lu, M. X.; Li, J. B.

    2006-08-01

    The electrochemical impedance spectroscopy (EIS) was used to study the characteristics of CO 2 corrosion of N80 and 4Cr steels with corrosion scales. The results indicated that CO 2 corrosion scale on tube steel could prevent the rate of mass transfer remarkably, corrosion rate was controlled by ions diffusion in corrosion scale, which led to finite length diffusion impedance occurred in electrochemical impedance spectra. Additionally, pitting of N80 steel could lead to additional capacitive reactance in impedance spectrum. The ion diffusion coefficient in corrosion scale and porosity of corrosion scale could be calculated by Warburg impedance coefficient, the results shown that the value of H + diffusion coefficient in N80 and 4Cr corrosion scale is (3.46 and 1.76) × 10 -10 m 2 s -1, respectively. The protective ability of 4Cr corrosion scale was better than that of N80 corrosion scale.

  18. Diffusive Compression Acceleration and Turbulent Diffusion of Cosmic Rays

    Microsoft Academic Search

    G. M. Webb; C. M. Ko; G. P. Zank; R. Jokipii

    2002-01-01

    Multiple scales perturbation methods are used to study the transport and acceleration of energetic charged particles in a quasi-periodic, fluid velocity structures in one, two or three space dimensions, for cases where the spatial period of the velocity structure is much less than the diffusion-convection scale length of the background flow. The large scale transport equation obtained by averaging over

  19. Protein self-diffusion in crowded solutions

    PubMed Central

    Roosen-Runge, Felix; Hennig, Marcus; Zhang, Fajun; Jacobs, Robert M. J.; Sztucki, Michael; Schober, Helmut; Seydel, Tilo; Schreiber, Frank

    2011-01-01

    Macromolecular crowding in biological media is an essential factor for cellular function. The interplay of intermolecular interactions at multiple time and length scales governs a fine-tuned system of reaction and transport processes, including particularly protein diffusion as a limiting or driving factor. Using quasielastic neutron backscattering, we probe the protein self-diffusion in crowded aqueous solutions of bovine serum albumin on nanosecond time and nanometer length scales employing the same protein as crowding agent. The measured diffusion coefficient D(?) strongly decreases with increasing protein volume fraction ? explored within 7% ? ? ? 30%. With an ellipsoidal protein model and an analytical framework involving colloid diffusion theory, we separate the rotational Dr(?) and translational Dt(?) contributions to D(?). The resulting Dt(?) is described by short-time self-diffusion of effective spheres. Protein self-diffusion at biological volume fractions is found to be slowed down to 20% of the dilute limit solely due to hydrodynamic interactions. PMID:21730176

  20. Fokker-Planck . . . Diffusion . . .

    E-print Network

    Fokker-Planck . . . Diffusion . . . Diffusion- . . . Application: . . . Summary and . . . First #12;Fokker-Planck . . . Diffusion . . . Diffusion- . . . Application: . . . Summary and . . . Topics: 1. Fokker-Planck transport equation 2. Diffusion approximation 3. Diffusion-convection transport

  1. Introduction Diffusion Tensor Imaging

    E-print Network

    Zhang, Shuzhong

    Introduction Diffusion Tensor Imaging Diffusion Kurtosis Imaging D-Eigenvalues and . . . Further ·Full Screen ·Close ·Quit Diffusion Tensor and Diffusion Kurtosis Tensor in Biomedical Engineering Diffusion Tensor Imaging Diffusion Kurtosis Imaging D-Eigenvalues and . . . Further Discussion Home Page

  2. Effects of vaned diffuser pressure recovery on centrifugal compressor stage performance 

    E-print Network

    Eason, Robyn Monique

    1985-01-01

    Diffuser, ?l 19(b) S~se Pressure Distribution at 100% N for Diffuser ?2 54 55 20(a) Static Pressure Recovery Coefficients for Diffuser ?1 20(b) Static P~ Recovery Coefficients for Diffuser ?2 57 58 21(a) Perf~ Characteristics for Diffuser ?1... ? ? ? 64 21(b) Performance Characteristics for Diffuser ?2 ? ? 65 22 Experimental Perfounance Canpariscn Between Diffusers ?1 and ?2 69 A ? flow area A/A* ? critical area ratio B ? blockage factor C ? static pressure recovery coefficient P c...

  3. Relativistic diffusion

    E-print Network

    Haba, Z

    2008-01-01

    We define a relativistic diffusion equation on the phase space. We consider stochastic Ito (Langevin) differential equation on the phase space as a perturbation by noise of relativistic dynamics. The motion in an electromagnetic field is treated as an example. Transport equations and equilibrium probability distributions are investigated. A relation to diffusions appearing in heavy ion collisions is briefly discussed.

  4. Hillslope diffusion

    NSDL National Science Digital Library

    Jeni McDermott

    This lab is designed to help students apply hillslope diffusion equations (derived in class prior to the lab) to understand real-world hillslopes. The major goal is a deeper understanding of hillslope processes and the equations used to describe hillslope diffusion by observing the same factors described in the equations on real-world hillslopes.

  5. Diffusion in supersonic, turbulent, compressible flows

    E-print Network

    Ralf S. Klessen; Doug N. C. Lin

    2003-02-25

    We investigate diffusion in supersonic, turbulent, compressible flows. Supersonic turbulence can be characterized as network of interacting shocks. We consider flows with different rms Mach numbers and where energy necessary to maintain dynamical equilibrium is inserted at different spatial scales. We find that turbulent transport exhibits super-diffusive behavior due to induced bulk motions. In a comoving reference frame, however, diffusion behaves normal and can be described by mixing length theory extended into the supersonic regime.

  6. Diffusive Compression Acceleration of Charged Particles

    Microsoft Academic Search

    Jack R. Jokipii; J. Giacalone; J. Kota

    2003-01-01

    We consider the acceleration of fast charged particles by smo oth compressions and expansions in a collisionless fluid, using the diffusion approximation. If the diffusion length kappa\\/U is of the order of the fluid scale or larger, efficient acceleration occurs which has similarities with both 2nd-order Fermi acceleration and diffusive shock acceleration, but is different from both. A simple, one-dimensional

  7. Scale Length of Mantle Heterogeneities: Helium Diffusion Constraints

    Microsoft Academic Search

    S. Hart; M. Kurz; Z. Wang

    2007-01-01

    While Earth's mantle is unequivocally heterogeneous, the size, formation and distribution of these geochemical heterogeneities remain enigmatic. Following the veined mantle proposals of Hanson (1977) and Wood (1979), various postulates of mesoscale lithologic heterogeneities (veins, pods, layers, plums) have been advanced. However, the issue remains contentious, and no smoking gun has survived scrutiny. Do the heterogeneities reflect large scale (tens

  8. Spin Hall angle in Pd below the spin diffusion length

    Microsoft Academic Search

    V. Vlaminck; H. Schultheiss; J. Pearson; F. Fradin; S. Bader; A. Hoffmann; O. Mosendz

    2011-01-01

    The spin-orbit coupling gives rise to an inter-conversion of spin and charge currents. A pure spin current is accompanied by a charge accumulation perpendicular to both the spin polarization and spin current, so-called inverse spin Hall effect (ISHE). We report measurements of the ISHE in a permalloy\\/palladium (Py\\/Pd) bilayer integrated with a coplanar wave-guide by pumping a pure spin current

  9. Three-dimensional analysis of MHD generators and diffusers

    SciTech Connect

    Vanka, S P; Ahluwalia, R K; Doss, E D

    1982-03-01

    The three-dimensional flow and heat transfer phenomena in MHD channels and diffusers are analyzed by solving the governing partial differential equations for flow and electrical fields. The equation set consists of the mass continuity equation, the three momentum equations, the equations for enthalpy, turbulence kinetic energy and its dissipation rate, and the Maxwell equations. This set of coupled equations is solved by the use of a finite-difference calculation procedure. The turbulence is represented by a two-equation model of turbulence in which partial differential equations are solved for the turbulence kinetic energy and its dissipation rate. Calculations have been performed for Faraday and diagonally-connected channels. Specifically, the AEDC (Faraday) and the UTSI (diagonal) channels have been analyzed, and the results are compared with experimental data. The agreement is fairly good for all the measured quantities. The effects of channel loading on the three-dimensional flow characteristics of Faraday and diagonally-connected generators have been also analyzed. A simple argument is presented to show qualitatively the role of MHD body forces in generating axial vorticity and hence secondary flows in the cross-stream. Calculations have also been made to study the flow evolution in MHD diffusers. The calculations show that the velocity overshoots and secondary flows decay along the diffusers length. Plots of velocity, skin friction and pressure recovery are presented to illustrate the flow development in MHD diffusers.

  10. The long and short of food-chain length

    Microsoft Academic Search

    David M. Post

    2002-01-01

    Food-chain length is a central characteristic of ecological communities that has attracted considerable attention for over 75 years because it strongly affects community structure, ecosystem processes and contaminant concentrations. Conventional wisdom holds that either resource availability or dynamical stability limit food-chain length; however, new studies and new techniques challenge the conventional wisdom and broaden the discourse on food-chain length. Recent

  11. Diffusion in potato during far infrared radiation drying

    Microsoft Academic Search

    T. M. Afzal; T. Abe

    1998-01-01

    The effect of radiation intensity and thickness of slab on the moisture diffusion characteristics of potato during FIR drying is investigated. The standard solution to the non-stationary state diffusion equation was used as a mathematical tool. A model fitting procedure was applied to the experimental drying data to determine the diffusion coefficients. The diffusivity was found to vary with radiation

  12. Measures of dispersion as constraints for length-frequency analysis

    E-print Network

    Length-frequency analysis (LFA) methods are widely used in popu- lation dynamics studies, particu- larly growth rings on hard parts. LFA is characteristically subjective, and numerous authors have warned peaks. Only data sets that were not based on LFA, composite samples, orback-calculated lengths at age

  13. SELECTION FOR LENGTH OF LIFE IN THE HONEYBEE (APIS MELLIFERA)

    E-print Network

    Paris-Sud XI, Université de

    SELECTION FOR LENGTH OF LIFE IN THE HONEYBEE (APIS MELLIFERA) Jovan M. KULIN Two-way selection in the honeybee for long and short length of life in laboratory cages was carried characteristics in honeybees has attracted the interest of several investigators of this beneficial insect. O. W

  14. Length of the Day

    NSDL National Science Digital Library

    2012-08-03

    In this activity, students measure the length of the day using the rotation of the Earth, and discover that the Sun is not exactly in the same place at the same clock time every day, understand that the changes are due to motions of the Earth, and lead to differences in solar, star, and sidereal time. This resource is from PUMAS - Practical Uses of Math and Science - a collection of brief examples created by scientists and engineers showing how math and science topics taught in K-12 classes have real world applications.

  15. Effect of Increasing Diffusion Gradient Direction Number on Diffusion Tensor Imaging Fiber Tracking in the Human Brain

    PubMed Central

    Yao, Xufeng; Yu, Tonggang; Liang, Beibei; Xia, Tian; Huang, Qinming

    2015-01-01

    Objective To assess the effects of varying the number of diffusion gradient directions (NDGDs) on diffusion tensor fiber tracking (FT) in human brain white matter using tract characteristics. Materials and Methods Twelve normal volunteers underwent diffusion tensor imaging (DTI) scanning with NDGDs of 6, 11, 15, 21, and 31 orientations. Three fiber tract groups, including the splenium of the corpus callosum (CC), the entire CC, and the full brain tract, were reconstructed by deterministic DTI-FT. Tract architecture was first qualitatively evaluated by visual observation. Six quantitative tract characteristics, including the number of fibers (NF), average length (AL), fractional anisotropy (FA), relative anisotropy (RA), mean diffusivity (MD), and volume ratio (VR) were measured for the splenium of the CC at the tract branch level, for the entire CC at tract level, and for the full brain tract at the whole brain level. Visual results and those of NF, AL, FA, RA, MD, and VR were compared among the five different NDGDs. Results The DTI-FT with NDGD of 11, 15, 21, and 31 orientations gave better tracking results compared with NDGD of 6 after the visual evaluation. NF, FA, RA, MD, and VR values with NDGD of six were significantly greater (smallest p = 0.001 to largest p = 0.042) than those with four other NDGDs (11, 15, 21, or 31 orientations), whereas AL measured with NDGD of six was significantly smaller (smallest p = 0.001 to largest p = 0.041) than with four other NDGDs (11, 15, 21, or 31 orientations). No significant differences were observed in the results among the four NDGD groups of 11, 15, 21, and 31 directions (smallest p = 0.059 to largest p = 1.000). Conclusion The main fiber tracts were detected with NDGD of six orientations; however, the use of larger NDGD (? 11 orientations) could provide improved tract characteristics at the expense of longer scanning time. PMID:25741203

  16. 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.

  17. 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.

  18. Feg-EPMA and Nanosims Profiles of Zoned Crystals for Diffusion Chronometry

    NASA Astrophysics Data System (ADS)

    Saunders, K.; Buse, B.; Kilburn, M.; Kearns, S.; Blundy, J. D.

    2014-12-01

    Diffusion chronometry is an alternative method that can be used to assess timescales of magmatic events. It relies on the chemical relaxation of chemical zoning within magmatic crystals. By studying a range of elements within a single crystal we can probe a range of magmatic processes and interrogate timescales of processes from days to millennia. Diffusion modifies the elemental concentrations of adjacent crystal zones. The timescales that can be investigated are limited not only by the diffusivity of an element and the available diffusion coefficients but also the resolution of the measured chemical profile and hence the analytical technique used to acquire these profiles. To obtained reliable diffusion timescales the analytical length scale must be shorter than the characteristic diffusion length. In addition sufficient analytical points must be present on the profile to ensure that the profile is 'real' and not a convolution artefact. Thus in some cases, sub-micron spatial resolution is required. Two such possible techniques that can achieve nanoscale resolution are field emission gun electron probe micro analyser (FEG-EPMA) and NanoSIMS. Plagioclase and pyroxene crystals were analysed by FEG-EPMA and NanoSIMS to investigate the achievable spatial resolution that could be attained. For quantitative analyses, analytical protocols for FEG-EPMA for plagioclase and pyroxene have been developed that can achieve spot analyses of down to 300 nm diameters with 300 nm spacing for major and trace elements. NanoSIMS can achieve a 200 nm spot diameter, but currently the chemical profiles are only qualitative. This increase in spatial resolution of analytical techniques has demonstrated that compositional boundaries within zoned crystals are relatively sharp (< 2 microns). Thus assuming step-profiles as an initial condition in simple 1D diffusion models is appropriate in many cases.

  19. Tortuosity Measurement and the Effects of Finite Pulse Widths on Xenon Gas Diffusion NMR Studies of Porous Media

    E-print Network

    R. W. Mair; M. D. Hurlimann; P. N. Sen; L. M. Schwartz; S. Patz; R. L. Walsworth

    2002-11-10

    We have extended the utility of NMR as a technique to probe porous media structure over length scales of ~ 100 - 2000 micron by using the spin 1/2 noble gas 129Xe imbibed into the system's pore space. Such length scales are much greater than can be probed with NMR diffusion studies of water-saturated porous media. We utilized Pulsed Gradient Spin Echo NMR measurements of the time-dependent diffusion coefficient, D(t) of the xenon gas filling the pore space to study further the measurements of both the surface area-pore volume ratio, S/Vp, and the tortuosity (pore connectivity) of the medium. In uniform-size glass bead packs, we observed D(t) decreasing with increasing t, reaching an observed asymptote of ~ 0.62 - 0.65D0, that could be measured over diffusion distances extending over multiple bead diameters. Measurements of D(t)/D0 at differing gas pressures showed this tortuosity limit was not affected by changing the characteristic diffusion length of the spins during the diffusion encoding gradient pulse. This was not the case at the short time limit, where D(t)/D0 was noticeably affected by the gas pressure in the sample. Increasing the gas pressure, and hence reducing D0 and the diffusion during the gradient pulse served to reduce the previously observed deviation of D(t)/D0 from the S/Vp relation. The Pade approximation is used to interpolate between the long and short time limits in D(t). While the short time D(t) point lay above the interpolation line in the case of small beads, due to diffusion during the gradient pulse on the order of the pore size, it was also noted that the experimental D(t) data fell below the Pade line in the case of large beads, most likely due to finite size effects.

  20. Odd Length Contraction

    NASA Astrophysics Data System (ADS)

    Smarandache, Florentin

    2013-09-01

    Let's denote by VE the speed of the Earth and byVR the speed of the rocket. Both travel in the same direction on parallel trajectories. We consider the Earth as a moving (at a constant speed VE -VR) spacecraft of almost spherical form, whose radius is r and thus the diameter 2r, and the rocket as standing still. The non-proper length of Earth's diameter, as measured by the astronaut is: L = 2 r?{ 1 -|/VE -VR|2 c2 } < 2 r . Therefore Earth's diameter shrinks in the direction of motion, thus Earth becomes an ellipsoid - which is untrue. Planet Earth may increase or decrease its diameter (volume), but this would be for other natural reasons, not because of a...flying rocket! Also, let's assume that the astronaut is laying down in the direction of motion. Therefore, he would also shrink, or he would die!

  1. Exploratory laboratory study of lateral turbulent diffusion at the surface of an alluvial channel

    USGS Publications Warehouse

    Sayre, William W.; Chamberlain, A.R.

    1964-01-01

    In natural streams turbulent diffusion is one of the principal mechanisms by which liquid and suspended-particulate contaminants are dispersed in the flow. A knowledge of turbulence characteristics is therefore essential in predicting the dispersal rates of contaminants in streams. In this study the theory of diffusion by continuous movements for homogeneous turbulence is applied to lateral diffusion at the surface of an open channel in which there is uniform flow. An exploratory-laboratory investigation was conducted in which the lateral dispersion at the water surface of a sand-Led flume was studied by measuring the lateral spread from a point source of small floating polyethylene articles. The experiment was restricted to a single set of low and channel geometry conditions. The results of the study indicate that with certain restrictions lateral dispersion in alluvial channels may be successfully described by the theory of diffusion by continuous movements. The experiment demonstrates a means for evaluating the lateral diffusion coefficient and also methods for quantitatively estimating fundamental turbulence properties, such as the intensity and the Lagrangian integral scale of turbulence in an alluvial channel. The experimental results show that with increasing distance from the source the coefficient of lateral turbulent diffusion increases initially but tends toward a constant limiting value. This result is in accordance with turbulent diffusion theory. Indications are that the distance downstream from the source required for the diffusion coefficient to reach its limiting value is actually very small when compared to the length scale of most diffusion phenomena in natural streams which are of practical interest.

  2. Riemann equation for prime number diffusion

    NASA Astrophysics Data System (ADS)

    Chen, Wen; Liang, Yingjie

    2015-05-01

    This study makes the first attempt to propose the Riemann diffusion equation to describe in a manner of partial differential equation and interpret in physics of diffusion the classical Riemann method for prime number distribution. The analytical solution of this equation is the well-known Riemann representation. The diffusion coefficient is dependent on natural number, a kind of position-dependent diffusivity diffusion. We find that the diffusion coefficient of the Riemann diffusion equation is nearly a straight line having a slope 0.99734 in the double-logarithmic axis. Consequently, an approximate solution of the Riemann diffusion equation is obtained, which agrees well with the Riemann representation in predicting the prime number distribution. Moreover, we interpret the scale-free property of prime number distribution via a power law function with 1.0169 the scale-free exponent in respect to logarithmic transform of the natural number, and then the fractal characteristic of prime number distribution is disclosed.

  3. Length control of microtubules by depolymerizing molecular motors

    E-print Network

    Govindan, Bindu S; Chowdhury, Debashish

    2007-01-01

    Microtubules (MTs), nano-tubes which act as struts in the scaffolding of eucaryotic cells, also serve as tracks for intracellular molecular motor transport in eucaryotic cells. In many biological processes, the length distribution of the MTs is controlled by a class of motor proteins called depolymerases (DPs). A DP diffuses or walks along a MT to reach one of the tips of the MT and then begins depolymerizing the MT itself. We develop a quantitative model that captures both these processes within a single theoretical framework. We show that the action of both diffusing and walking DPs leads to a length-dependent depolymerization of the MT; however, their effects on the length distribution are different. Under experimental conditions, the diffusing DP produces a non-monotonic distribution of lengths as opposed to a nearly exponential distribution in the case of the walking DP. The former also shows a minimum in the r.m.s fluctuation to mean ratio of the length against the DP concentration, while the latter doe...

  4. Computer simulation of a wind tunnel test section with discrete finite-length wall slots

    NASA Technical Reports Server (NTRS)

    Kemp, W. B., Jr.

    1986-01-01

    A computer simulation of a slotted wind tunnel test section which includes a discrete, finite-length wall slot representation with plenum chamber constraints and accounts for the nonlinear effects of the dynamic pressure of the slot outflow jet and of the low energy of slot inflow air was developed. The simulation features were selected to be those appropriate for the intended subsequent use of the simulation in a wall interference assessment procedure using sparsely located wall pressure measurements. It is demonstrated that accounting for slot discreteness is important in interpreting wall pressure measured between slots, and that accounting for nonlinear slot flow effects produces significant changes in tunnel-induced velocity distributions and, in particular, produces a longitudinal component of tunnel-induced velocity due to model lift. A characteristic mode of tunnel flow interaction with constraints imposed by the plenum chamber and diffuser entrance is apparent in simulation results and is derived analytically through a simplified analysis.

  5. FILAMENT LENGTHS IN STRIATED MUSCLE

    Microsoft Academic Search

    SALLY G. PAGE; H. E. HUXLEY

    1963-01-01

    Filament lengths in resting and excited frog muscles have been measured in the electron microscope, and investigations made of the changes in length that are found under different conditions, to distinguish between those changes which arise during preparation and the actual differences in the living muscles. It is concluded that all the measured differences in filament length are caused by

  6. Critical Waves and the Length Problem of Biology

    E-print Network

    Laughlin, R 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 substances. Min oscillations in E. coli are cited as precedent resonant length measurement using chemical potential waves analogous to laser detection. Mitotic structures in eucaryotes 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. PNAS Significance Statement: This paper invokes physical principles to address the question of how living things might use reaction-diffusion to measure out and regulate the many thou...

  7. Diffusion across characteristic boundaries with critical points

    Microsoft Academic Search

    B. J. Matkowsky; Z. Schuss; C. Tier

    1983-01-01

    The problems of the effect of small white noise perturbations on a deterministic dynamical system in the plane with an asymptotically stable equilibrium point or limit cycle and an equilibrium point surrounded by closed trajectories are considered. The mean exit time and the distribution of exit points for each problem is determined by solving singularly perturbed elliptic boundary value problems

  8. A model for the effective diffusion of gas or the vapor phase in a fractured media unsaturated zone driven by periodic atmospheric pressure fluctuations

    SciTech Connect

    Vold, E.L.

    1997-03-01

    There is evidence for migration of tritiated water vapor through the tuff in the unsaturated zone from the buried disposal shafts located on a narrow mesa top at Area G, Los Alamos, NM. Field data are consistent with an effective in-situ vapor phase diffusion coefficient of 1.5x10{sup {minus}3} m{sup s}/s, or a factor of 60 greater than the binary diffusion coefficient for water vapor in air. A model is derived to explain this observation of anomolously large diffusion, which relates an effective vapor or gas phase diffusion coefficient in the fractured porous media to the subsurface propagation of atmospheric pressure fluctuations (barometric pumping). The near surface (unattenuated) diffusion coefficient is independent of mode period under the simplified assumptions of a complete {open_quote}mixing mechanism{close_quote} for the effective diffusion process. The unattenuated effective diffusion driven by this barometric pumping is proportional to an average media permeability times the sum of the square of pressure mode amplitudes, while the attenuation length is proportional to the squarer root of the product of permeability times mode period. There is evidence that the permeability needed to evaluate the pressure attenuation length is the in-situ value, approximately that of the matrix. The diffusion which results using Area G parameter values is negligible in the matrix but becomes large at the effective permeability of the fractured tuff matrix. The effective diffusion coefficient predicted by this model, due to pressure fluctuations and the observed fracture characteristics, is in good agreement with the observed in-situ diffusion coefficient for tritium field measurements. It is concluded that barometric pumping in combination with the enhanced permeability of the fractured media is a likely candidate to account for the observed in-field migration of vapor in the near surface unsaturated zone at Area G.

  9. Mode structure of diffusive transport in hydroxypropylcellulose:water

    NASA Astrophysics Data System (ADS)

    Phillies, George D. J.; O'Connell, Robert; Whitford, Paul; Streletzky, Kiril A.

    2003-11-01

    A systematic analysis of the mode structure of diffusive relaxations in 1 MDa hydroxypropylcellulose(HPC):water is presented. New methods and data include (1) use of integral spectral moments to characterize nonexponential decays, (2) spectra of small probes in concentrated HPC solutions, (3) temperature dependence of the mode structure, and (4) comparison of optical probe spectra and spectra of probe-free polymer solutions. We find that (1) probe and polymer relaxations are in general not the same; (2) the apparent viscometric crossover near ct?6 g/l is echoed by probe behavior; (3) our HPC solutions have a characteristic dynamic length, namely the 50 nm length that matches the polymer's hydrodynamic radius; (4) characterization of spectral modes with their mean relaxation time affords simplifications relative to other characterizations; and (5) contrary to some expectations, Stokes-Einsteinian behavior (diffusion rate determined by the macroscopic viscosity) is not observed, even for large probes in relatively concentrated solutions. We propose that the viscometric and light scattering effects found in HPC solutions at elevated concentrations reflect the incipient formation of a generalized Kivelson [S. A. Kivelson et al., J. Chem. Phys. 101, 2391 (1994)] glass.

  10. 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. PMID:19391727

  11. Relativistic diffusion

    E-print Network

    Z. Haba

    2009-02-26

    We discuss a relativistic diffusion in the proper time in an approach of Schay and Dudley. 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 Juettner 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. Relativistic diffusion

    Microsoft Academic Search

    Z. Haba

    2009-01-01

    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

  13. Diffusion Models

    NSDL National Science Digital Library

    Alexei Sharov

    Web-based intructional material describing the use of diffusion models in population ecology. This page is part of a set of on-line lectures on Quantitative Population Ecology produced by Alexei Sharov in the Department of Entomology at Virginia Tech.

  14. 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.

  15. Universality of modulation length and time exponents

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Saurish; Dobrosavljevi?, Vladimir; Seidel, Alexander; Nussinov, Zohar

    2012-10-01

    We study systems with a crossover parameter ?, such as the temperature T, which has a threshold value ?* across which the correlation function changes from exhibiting fixed wavelength (or time period) modulations to continuously varying modulation lengths (or times). We introduce a hitherto unknown exponent ?L characterizing the universal nature of this crossover and compute its value in general instances. This exponent, similar to standard correlation length exponents, is obtained from motion of the poles of the momentum (or frequency) space correlation functions in the complex k-plane (or ?-plane) as the parameter ? is varied. Near the crossover (i.e., for ???*), the characteristic modulation wave vector KR in the variable modulation length “phase” is related to that in the fixed modulation length “phase” q via |KR-q|?|T-T*|?L. We find, in general, that ?L=1/2. In some special instances, ?L may attain other rational values. We extend this result to general problems in which the eigenvalue of an operator or a pole characterizing general response functions may attain a constant real (or imaginary) part beyond a particular threshold value ?*. We discuss extensions of this result to multiple other arenas. These include the axial next-nearest-neighbor Ising (ANNNI) model. By extending our considerations, we comment on relations pertaining not only to the modulation lengths (or times), but also to the standard correlation lengths (or times). We introduce the notion of a Josephson time scale. We comment on the presence of aperiodic “chaotic” modulations in “soft-spin” and other systems. These relate to glass-type features. We discuss applications to Fermi systems, with particular application to metal to band insulator transitions, change of Fermi surface topology, divergent effective masses, Dirac systems, and topological insulators. Both regular periodic and glassy (and spatially chaotic behavior) may be found in strongly correlated electronic systems.

  16. Linear study of Rayleigh-Taylor instability in a diffusive quantum plasma

    SciTech Connect

    Momeni, Mahdi [Faculty of Physics, Shahrood University, Shahrood (Iran, Islamic Republic of)] [Faculty of Physics, Shahrood University, Shahrood (Iran, Islamic Republic of)

    2013-08-15

    The linear Rayleigh-Taylor (RT) instability in an incompressible quantum plasma is investigated on the basis of quantum magnetohydrodynamic model. It is shown that the occurrence of RT instability depends on density-temperature inhomogeneity (characteristic lengths) on one hand, and the system layer size on the other. It is also observed that the combined effects of external magnetic field, diffusivity, and quantum pressure significantly modify the dispersion properties of system in both the parallel and perpendicular directions. For any case, the imaginary and real parts of dispersion relation are presented and the possibility and conditions for the instability growth rate are discussed.

  17. Discrete Wavelet Diffusion for Image Denoising

    Microsoft Academic Search

    Kashif Rajpoot; Nasir Rajpoot; J. Alison Noble

    2008-01-01

    \\u000a Nonlinear diffusion, proposed by Perona-Malik, is a well-known method for image denoising with edge preserving characteristics.\\u000a Recently, nonlinear diffusion has been shown to be equivalent to iterative wavelet shrinkage, but only for (1) Mallat-Zhong\\u000a dyadic wavelet transform and (2) Haar wavelet transform. In this paper, we generalize the equivalence of nonlinear diffusion\\u000a to non-linear shrinkage in the standard discrete wavelet

  18. Sub-100 nm channel length graphene transistors

    PubMed Central

    Liao, Lei; Bai, Jingwei; Cheng, Rui; Lin, Yungchen; Jiang, Shan; Qu, Yongquan; Huang, Yu; Duan, Xiangfeng

    2010-01-01

    Here we report high performance sub-100 nm channel length grapheme transistors fabricated using a self-aligned approach. The graphene transistors are fabricated using a highly-doped GaN nanowire as the local gate, with the source and drain electrodes defined through a self-aligned process and the channel length defined by the nanowire size. This fabrication approach allows the preservation of the high carrier mobility in graphene, and ensures nearly perfect alignment between source, drain, and gate electrodes. It therefore affords transistor performance not previously possible. Graphene transistors with 45–100 nm channel lengths have been fabricated with the scaled transconductance exceeding 2 mS/µm, comparable to the best performed high electron mobility transistors with similar channel lengths. Analysis of and the device characteristics gives a transit time of 120–220 fs and the projected intrinsic cutoff transit frequency (fT) reaching 700–1400 GHz. This study demonstrates the exciting potential of graphene based electronics in terahertz electronics. PMID:20815334

  19. Mapping the exciton diffusion in semiconductor nanocrystal solids.

    PubMed

    Kholmicheva, Natalia; Moroz, Pavel; Bastola, Ebin; Razgoniaeva, Natalia; Bocanegra, Jesus; Shaughnessy, Martin; Porach, Zack; Khon, Dmitriy; Zamkov, Mikhail

    2015-03-24

    Colloidal nanocrystal solids represent an emerging class of functional materials that hold strong promise for device applications. The macroscopic properties of these disordered assemblies are determined by complex trajectories of exciton diffusion processes, which are still poorly understood. Owing to the lack of theoretical insight, experimental strategies for probing the exciton dynamics in quantum dot solids are in great demand. Here, we develop an experimental technique for mapping the motion of excitons in semiconductor nanocrystal films with a subdiffraction spatial sensitivity and a picosecond temporal resolution. This was accomplished by doping PbS nanocrystal solids with metal nanoparticles that force the exciton dissociation at known distances from their birth. The optical signature of the exciton motion was then inferred from the changes in the emission lifetime, which was mapped to the location of exciton quenching sites. By correlating the metal-metal interparticle distance in the film with corresponding changes in the emission lifetime, we could obtain important transport characteristics, including the exciton diffusion length, the number of predissociation hops, the rate of interparticle energy transfer, and the exciton diffusivity. The benefits of this approach to device applications were demonstrated through the use of two representative film morphologies featuring weak and strong interparticle coupling. PMID:25682881

  20. Turbulence reduces magnetic diffusivity in DTS liquid sodium experiment

    NASA Astrophysics Data System (ADS)

    Cabanes, S.; Schaeffer, N.; Nataf, H. C.

    2014-12-01

    Earth, Sun and many other astrophysical bodies produce their own magnetic field by dynamo action, where induction of magnetic field by fluid motion overcomes the Joule dissipation when the magnetic Reynolds number Rm = UL/? is large enough (U and L are characteristic velocity and length-scale and ? the magnetic diffusivity). Large scale motion of a conducting medium shearing pre-existing magnetic field lines is a well known process to produce large scale magnetic field by omega-effect. However, such a process cannot sustain a self-excited dynamo and small-scale turbulent motions are usually invoked as the appropriate mechanism to dynamo action. The contribution of turbulent fluctuations to the induction of mean magnetic field is investigated in our liquid sodium spherical Couette experiment, with an imposed magnetic field. Many measurements are used through an inversion technique to obtain a radial profile of alpha and beta effects together with the mean flow at magnetic Reynolds number Rm = 100. It appears that the small scale turbulent fluctuations can be modeled as a strong contribution to the magnetic diffusivity which is negative in the interior region and positive close to the outer shell.Direct numerical simulations of our experiment support these results. The lowering of the effective magnetic diffusivity by small scale fluctuations implies that turbulence can actually help to achieve self-generation of large scale magnetic fields.

  1. Relations between Some Characteristic Lengths in a Triangle

    ERIC Educational Resources Information Center

    Koepf, Wolfram; Brede, Markus

    2005-01-01

    The paper's aim is to note a remarkable (and apparently unknown) relation for right triangles, its generalisation to arbitrary triangles and the possibility to derive these and some related relations by elimination using Groebner basis computations with a modern computer algebra system. (Contains 9 figures.)

  2. Diffusion of bed load particles subject to different flow conditions

    NASA Astrophysics Data System (ADS)

    Cecchetto, Martina; Cotterle, Luca; Tregnaghi, Matteo; Tait, Simon; Marion, Andrea

    2015-04-01

    An in-depth understanding of sediment motion in rivers has acquired increasing importance lately in order to plan restoration activities that provide ecological benefit. River beds constitute the interfacial environment where several species live and mass exchange of sediments/nutrients/pollutants can take place. Moving grains interacting with the bed deposit and can locally change the bed surface topography they can also act as carriers for contaminants associated with the grains. Study the motion of grains on the bed, in particular the extent and variability of their travel distance with regards to the flow conditions can provide information on the transport of grain associated contaminants. The results of a series of experimental tests, in which increasing levels of boundary shear stress were applied over a bed deposit of natural river gravel, are reported. Image databases consisted of a series of bed images acquired at a frequency of 45 Hz were collected. Analysis of the images has provided time and position data to plot the trajectories of more than 200 moving grains for each test. This data enables the derivation of the statistics of the un-truncated probability distribution of the detected particles' step length, which is consider as the distance moved by a particle from the moment it is entrained to the instant it stops on the bed. In recent studies the movement of bed load material has been indicated as diffusive, but little is known about the spatial and temporal scales of this diffusion. The analysis of the longitudinal and transverse trajectories for the tracked particles has here revealed three regimes of diffusion: a ballistic diffusion which takes place at the very beginning of particles motion, an anomalous intermediate regime, and a normal subdiffusion which occurs for larger times. Characteristic time scales separate these three diffusive regimes. Results show that in experiments with higher shear stresses the time scale separating the ballistic from the intermediate regime decreases, whereas an opposite trend is observed for the boundary between the intermediate and the final subdiffusion regime. This suggests that flow intensity influences the particle traveling time depending on the diffusive regime. An equivalent pattern emerges for the transversal diffusion, even if it is characterized by much smaller time scales. The simultaneous measurement of the 3D near bed flow field via a PIV system has allowed the grain velocity to be linked to the spatial averaged fluid velocity. Understanding the type of advective and diffusive process along with its mechanics can potentially allow for derivation of bed-load transport rate equations, able to replicate this behaviour, without the need of experimental measurements.

  3. Multiport Diffuser as Line Source of Momentum in Shallow Water

    NASA Astrophysics Data System (ADS)

    Lee, Joseph H.; Jirka, Gerhard H.

    1980-08-01

    Multiport diffusers are linear structures consisting of many closely spaced nozzles which inject a series of high-velocity jets into an ambient fluid. The discharge of heated water into the shallow coastal zone is considered herein as a typical practice for cooling water disposal from steam electric power generation. The flow and temperature fields, induced in the otherwise stagnant and homogeneous fluid layer, are analyzed by representing the diffuser as a line source of fluid momentum in a two-dimensional coordinate system, thus neglecting the initial momentum transfer zone in which the three-dimensional jets merge to produce a vertically fully mixed flow. A scaling argument which considers the effect of pressure deviations, turbulent bottom friction, and lateral turbulent diffusion shows that the flow field can be divided into the near field, of order of the diffuser length, and into the far field, at longer distances. The near field is characterized by a predominantly inviscid behavior and gives rise to a contracting slipstream motion, qualitatively similar to the slipstream produced by an airscrew. The shape of the slip streamline is found by mapping the complex potential of the flow into the log hodograph plane. The boundary conditions at the diffuser line are assumed to be a uniform normal velocity and a uniform longitudinal acceleration. The interior velocity and pressure distribution are determined through a finite difference solution using the known geometry of the slipstream. Results indicate a strong separation angle (60°) of the slipstream at the diffuser and a rapid approach to the asymptotic contraction value (½). An integral model is developed for the depth-averaged temperature and velocity in the far field of the `diffuser plume' (i.e., a localized current with elevated temperatures with weaker velocities and a uniform temperature outside). The model includes the effect of turbulent friction at the plume bottom, described by a quadratic friction law, and of lateral turbulent entrainment, described by the entrainment hypothesis of Morton et al. (1956). The far-field model is combined with the inviscid near-field solution, thus superimposing the real fluid effects onto the properties of the contracting slipstream. Two distinctive features characterize the diffuser plume. First, it experiences an exponential loss of fluid momentum through turbulent bottom friction which leads to an ultimate plume stagnation at a characteristic distance ƒ0LD/(16H), where ƒ0 is a quadratic friction coefficient, LD the diffuser length, and H the water depth, and also puts a limit on the total lateral entrainment flow. Second, the initial plume characteristics, and thus its rate of entrainment, are controlled by the accelerating high-velocity slipstream in the vicinity of the line source. Experiments in a shallow laboratory basin corroborate the theoretical results, both as regards the qualitative features of the contracting slipstream and the quantitative observations of induced velocities and flow rates.

  4. Design of plane diffusers in turbulent flow

    Microsoft Academic Search

    Jianhong Zhang; C. K. Chu; Vijay Modi

    1995-01-01

    Optimal control theory for shape design has been applied in this paper to design a plane diffuser operating under turbulent flow conditions. The design objective is to maximize the diffuser pressure rise for a prescribed inlet width and length. The flow description is provided by the two-dimensional Reynolds-Averaged-Navier-Stokes (RANS) equations with a Baldwin-Lomax (1978) algebraic turbulence model. A set of

  5. Optimum plane diffusers in laminar flow

    Microsoft Academic Search

    Hayri Cabuk; Vijay Modi

    1992-01-01

    The paper considers an optimum design of an internal flow component such as a diffuser in laminar flow. The problem of determining the profile of a plane diffuser of given upstream width and length that provides the maximum static pressure rise is solved for 2D incompressible laminar flow governed by the steady-state Navier-Stokes equations. A set of 'adjoint' equations is

  6. SLOW DIFFUSIVE GRAVITATIONAL INSTABILITY BEFORE DECOUPLING

    SciTech Connect

    Thompson, Todd A., E-mail: thompson@astronomy.ohio-state.ed [Department of Astronomy and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210 (United States)

    2010-02-01

    Radiative diffusion damps acoustic modes at large comoving wavenumber (k) before decoupling ('Silk damping'). In a simple WKB analysis, neglecting moments of the temperature distribution beyond the quadrupole (the tight-coupling limit), damping appears in the acoustic mode as a term of order ik{sup 2}tau-dot{sup -1}, where tau-dot is the scattering rate per unit conformal time. Although the Jeans instability is stabilized on scales smaller than the adiabatic Jeans length, I show that the medium is linearly unstable to first order in tau-dot{sup -1} to a slow diffusive mode. At large comoving wavenumber, the characteristic growth rate becomes independent of spatial scale and constant: (t{sub KH} a){sup -1} approx (128piG/9kappa{sub T} c)(rho{sub m}/rho{sub b}), where a is the scale factor, rho{sub m} and rho{sub b} are the matter and baryon energy density, respectively, and kappa{sub T} is the Thomson opacity. This is the characteristic timescale for a fluid parcel to radiate away its total thermal energy content at the Eddington limit, analogous to the Kelvin-Helmholz (KH) timescale for a radiation pressure-dominated massive star or the Salpeter timescale for black hole growth. Although this mode grows at all times prior to decoupling and on scales smaller than roughly the horizon, the growth time is long, about 100 times the age of the universe at decoupling. Thus, it modifies the density and temperature perturbations on small scales only at the percent level. The physics of this mode in the tight-coupling limit is already accounted for in the popular codes CMBFAST and CAMB, but is typically neglected in analytic studies of the growth of primordial perturbations. The goal of this work is to clarify the physics of this diffusive instability in the epoch before decoupling, and to emphasize that the universe is formally unstable on scales below the horizon, even in the limit of very large tau-dot. Analogous instabilities that might operate at yet earlier epochs are also mentioned.

  7. Laminar Diffusion Flame Studies (Ground- and Space-Based Studies)

    NASA Technical Reports Server (NTRS)

    Dai, Z.; El-Leathy, A. M.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    Laminar diffusion flames are of interest because they provide model flame systems that are far more tractable for analysis and experiments than more practical turbulent diffusion flames. Certainly, understanding flame processes within laminar diffusion flames must precede understanding these processes in more complex turbulent diffusion flames. In addition, many properties of laminar diffusion flames are directly relevant to turbulent diffusion flames using laminar flamelet concepts. Laminar jet diffusion flame shapes (luminous flame boundaries) have been of particular interest since the classical study of Burke and Schumann because they are a simple nonintrusive measurement that is convenient for evaluating flame structure predictions. Thus, consideration of laminar flame shapes is undertaken in the following, emphasizing conditions where effects of gravity are small, due to the importance of such conditions to practical applications. Another class of interesting properties of laminar diffusion flames are their laminar soot and smoke point properties (i.e., the flame length, fuel flow rate, characteristic residence time, etc., at the onset of soot appearance in the flame (the soot point) and the onset of soot emissions from the flame (the smoke point)). These are useful observable soot properties of nonpremixed flames because they provide a convenient means to rate several aspects of flame sooting properties: the relative propensity of various fuels to produce soot in flames; the relative effects of fuel structure, fuel dilution, flame temperature and ambient pressure on the soot appearance and emission properties of flames; the relative levels of continuum radiation from soot in flames; and effects of the intrusion of gravity (or buoyant motion) on emissions of soot from flames. An important motivation to define conditions for soot emissions is that observations of laminar jet diffusion flames in critical environments, e.g., space shuttle and space station facilities, cannot involve soot emitting flames in order to ensure that test chamber windows used for experimental observations are not blocked by soot deposits, thereby compromising unusually valuable experimental results. Another important motivation to define conditions where soot is present in diffusion flames is that flame chemistry, transport and radiation properties are vastly simplified when soot is absent, making such flames far more tractable for detailed numerical simulations than corresponding soot-containing flames. Motivated by these observations, the objectives of this phase of the investigation were as follows: (1) Observe flame-sheet shapes (the location of the reaction zone near phi=1) of nonluminous (soot free) laminar jet diffusion flames in both still and coflowing air and use these results to develop simplified models of flame-sheet shapes for these conditions; (2) Observe luminous flame boundaries of luminous (soot-containing) laminar jet diffusion flames in both still and coflowing air and use these results to develop simplified models of luminous flame boundaries for these conditions. In order to fix ideas here, maximum luminous flame boundaries at the laminar smoke point conditions were sought, i.e., luminous flame boundaries at the laminar smoke point; (3) Observe effects of coflow on laminar soot- and smoke-point conditions because coflow has been proposed as a means to control soot emissions and minimize the presence of soot in diffusion flames.

  8. Trajectory Length Distribution (TLD), a novel concept to characterize mixing in flow systems

    Microsoft Academic Search

    J. Villermaux

    1996-01-01

    A novel function is introduced to characterize mixing in flow systems, the Trajectory Length Distribution (TLD) representing the distribution of distances covered by fluid elements (or particles) in the system. This allows to define a macromixing index comparing the mean trajectory length to a characteristic dimension of the vessel. As an illustration, preliminary results are presented, showing Return Length Distributions

  9. Hydrogeomorphology and river impoundment affect food-chain length of diverse Neotropical food webs

    E-print Network

    Hoeinghaus, David J.

    Hydrogeomorphology and river impoundment affect food-chain length of diverse Neotropical food webs-900 Parana´, Brasil. Food-chain length is a central characteristic of ecological communities that affects community structure and ecosystem function. What determines the length of food chains is not well resolved

  10. The word-length effect in reading: a review.

    PubMed

    Barton, Jason J S; Hanif, Hashim M; Eklinder Björnström, Laura; Hills, Charlotte

    2014-01-01

    The finding that visual processing of a word correlates with the number of its letters has an extensive history. In healthy subjects, a variety of methods, including perceptual thresholds, naming and lexical decision times, and ocular motor parameters, show modest effects that interact with high-order effects like frequency. Whether this indicates serial processing of letters under some conditions or indexes low-level visual factors related to word length is unclear. Word-length effects are larger in pure alexia, where they probably reflect a serial letter-by-letter strategy, due to failure of lexical whole-word processing and variable dysfunction in letter encoding. In pure alexia, the word-length effect is systematically related to mean naming latency, with the word-length effect becoming proportionally greater as naming latency becomes more delayed in severe cases. Other conditions may also generate enhanced word-length effects. This occurs in right hemianopia: Computer simulations suggest a criterion of 160?ms/letter to distinguish hemianopic dyslexia from pure alexia. Normal reading development is accompanied by a decrease in word-length effects, whereas persistently elevated word-length effects are characteristic of developmental dyslexia. Little is known about word-length effects in other reading disorders. We conclude that the word-length effect captures the efficiency of the perceptual reading process in development, normal reading, and a number of reading disorders, even if its mechanistic implications are not always clear. PMID:24665973

  11. Experimental evidence for two thermodynamic length scales in neutralized polyacrylate gels

    NASA Astrophysics Data System (ADS)

    Horkay, Ferenc; Hecht, Anne-Marie; Grillo, Isabelle; Basser, Peter J.; Geissler, Erik

    2002-11-01

    The small angle neutron scattering (SANS) behavior of fully neutralized sodium polyacrylate gels is investigated in the presence of calcium ions. Analysis of the SANS response reveals the existence of three characteristic length scales, two of which are of thermodynamic origin, while the third length is associated with the frozen-in structural inhomogeneities. This latter contribution exhibits power law behavior with a slope of about -3.6, reflecting the presence of interfaces. The osmotically active component of the scattering signal is defined by two characteristic length scales, a correlation length ? and a persistence length L.

  12. The influence of a voltage ramp on the measurement of I-V characteristics of a solar cell

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1980-01-01

    For efficiency and convenience the voltage applied to a Si solar cell is often fairly rapidly driven from zero to the open circuit value typically at a common rate of 1 V per millisecond. During this time the values of current are determined as a function of the instantaneous voltage thus producing an I-V characteristic. The present paper shows that the customary expressions for the current as a function of cell parameters still remain valid provided that the diffusion length in the expression for the dark current is changed from its steady state value L to the effective diffusion length L1 given by L1 = L(1 + qV/kT.tau) to the -1/2, where V is the ramp rate considered constant and tau is the lifetime of minority carriers. This result is true to a very good approximation provided that low level injection prevails.

  13. Diffusion in High-Temperature Ferrochrome Alloy Oxidation

    Microsoft Academic Search

    Petr M. Vasilyuk

    2003-01-01

    Simulation has been applied to the diffusion characteristics such as the effective component diffusion coefficients in Fe ? 35 mass% Cr ? (0.5-3.0) mass% Al bearing surface oxides at the time of peeling. The simulation results are in agreement with experimental data on the layerwise phase compositions of the oxides. The model is described for the diffusion in a three-layer

  14. Whirling motion of swirl center in a conical diffuser

    Microsoft Academic Search

    O. Kitoh; E. Kamiya

    1986-01-01

    Experiments have been carried out in order to investigate the physical characteristics of a swirling flow in a conical diffuser. Changes in the shape of the swirling flow were determined from the spectra of pressure fluctuations at the diffuser wall. Some statistical relations between the geometry of the diffuser wall and swirl parameters (swirl intensity and swirl Reynolds number) are

  15. Predictors in geriatric psychiatry hospital length of stay.

    PubMed

    DiNapoli, Elizabeth A; Regier, Natalie; McPherron, Jesse; Mundy, Michael J; Sabastian, Sabin; Doss, Jerry; Parmelee, Patricia A

    2015-06-01

    This paper examined predictors of length of stay in a freestanding geriatric psychiatry hospital. Data on patient and treatment characteristics of geriatric inpatients (N = 1,593) were extracted from an archival administrative tracking database from Mary Starke Geriatric Harper Center. Five independent variables (length of time between last discharge and most recent admission, number of previous admissions, number of assaults, co-morbid medical condition, and admitting psychiatric diagnosis) were entered into a hierarchical regression model as potential predictors of length of stay in a geriatric psychiatry hospital. Number of assaults committed by the patient was the only significant predictor of length of stay, such that patients that had a greater number of assaults were more likely to have longer lengths of stay than those with fewer assaults. These findings highlight the importance of identifying patients at risk for assaultive behavior and developing effective interventions for aggression in geriatric psychiatry hospitals. PMID:25355603

  16. HYDRODYNAMIC CLASSIFICATION OF SUBMERGED MULTIPORT-DIFFUSER DISCHARGES

    EPA Science Inventory

    Discharges into water bodies from submerged multiport diffusers are characterized by a variety of possible flow configurations, ranging from internally trapped layers in deep stratified environments to vertically fully mixed plumes under shallow. conditions. he length-scale class...

  17. Mach-Zehnder Modulator Arm-Length-Mismatch Measurement Technique

    NASA Astrophysics Data System (ADS)

    Geary, Kevin; Kim, Seong-Ku; Seo, Byoung-Joon; Fetterman, Harold R.

    2005-03-01

    This paper describes a robust measurement technique for determining the effective length mismatch of the two arms of a Mach-Zehnder modulator (MZM), based on its broad-band filter characteristics. The proposed method involves measuring the Vpi (lambda), n(lambda), and transfer function of a modulator at various externally applied bias points. This mismatch measurement technique is applied to a packaged polymer rib waveguide MZM, and it is shown that it has an arm-length mismatch of 1.9 ?m. Poling-induced writing is then proposed as a fabrication technique that can consistently produce polymer MZMs with arm-length-mismatch values less than 2 ?m.

  18. Using two-photon standing waves and patterned photobleaching to measure diffusion from nanometers to microns in biological systems

    NASA Astrophysics Data System (ADS)

    Davis, Sara K.; Bardeen, Christopher J.

    2002-05-01

    A method of measuring molecular diffusion rates in microscopic sample volumes is described. This method utilizes the standing wave interference created by colliding two counterpropagating laser beams at the focus of two opposing microscope objectives, creating a periodic light distribution in a volume on the order of 1 fl. By using a Pockels cell to vary the laser intensity with a time resolution of milliseconds, we show how this experimental geometry can be used to perform ultrahigh resolution fluorescence recovery after patterned photobleaching (FRAPP) experiments. A mathematical treatment of the experiment shows that the laser excitation profile has two characteristic length scales, the width of the focal spot and the period of the standing wave, which permits the simultaneous measurement of dynamics on two separate length scales. This feature may be used to determine whether the measured diffusion is anomalous. We present experimental results using a femtosecond Ti:sapphire laser to create a two-photon excitation profile with a fringe visibility on the order of 100. This standing wave is used to demonstrate FRAPP in both model dye/polymer systems and in more complex systems like living cells stained with a fluorescent dye. By combining the advantages of standing wave microscopy and two-photon fluorescence recovery after photobleaching, this technique permits the measurement of very short length motions in localized sample volumes, which should be useful in both biology and the study of diffusion in microscopically heterogeneous systems.

  19. Diffusive Shock Acceleration

    NASA Astrophysics Data System (ADS)

    Baring, Matthew

    2003-04-01

    The process of diffusive acceleration of charged particles in shocked plasmas is widely invoked in astrophysics to account for the ubiquitous presence of signatures of non-thermal relativistic electrons and ions in the universe. This statistical energization mechanism, manifested in turbulent media, was first posited by Enrico Fermi in 1949 to explain the observed cosmic ray population, which exhibits an almost power-law distribution in rigidity. The absence of a momentum scale is a key characteristic of diffusive shock acceleration, and astrophysical systems generally only impose scales at the injection (low energy) and loss (high energy) ends of the particle spectrum. The existence of structure in the cosmic ray spectrum (the "knee") at around 3000 TeV has promoted contentions that there are at least two origins for cosmic rays, a galactic one supplying those up to the knee, and perhaps an extragalactic one that can explain even the ultra-high energy cosmic rays (UHECRs) seen at 1-300 EeV. Accounting for the UHECRs with familiar astrophysical sites of acceleration has historically proven difficult due to the need to assume high magnetic fields in order to reduce the shortest diffusive acceleration timescale, the ion gyroperiod, to meaningful values. Yet active galaxies and gamma-ray bursts remain strong and interesting candidate sources for UHECRs, turning the theoretical focus to relativistic shocks. This review summarizes properties of diffusive shock acceleration that are salient to the issue of UHECR generation. These include spectral indices, anisotropies, acceleration efficencies and timescales, as functions of the shock speed and mean field orientation, and also the degree of field turbulence. Astrophysical sites for UHECR production are also critiqued.

  20. Strain-Rate-Free Diffusion Flames: Initiation, Properties, and Quenching

    NASA Technical Reports Server (NTRS)

    Fendell, Francis; Rungaldier, Harald; Gokoglu, Suleyman; Schultz, Donald

    1997-01-01

    For about a half century, the stabilization of a steady planar deflagration on a heat-sink-type flat-flame burner has been of extraordinary service for the theoretical modeling and diagnostic probing of combusting gaseous mixtures. However, most engineering devices and most unwanted fire involve the burning of initially unmixed reactants. The most vigorous burning of initially separated gaseous fuel and oxidizer is the diffusion flame. In this useful idealization (limiting case), the reactants are converted to product at a mathematically thin interface, so no interpenetration of fuel and oxidizer occurs. This limit is of practical importance because it often characterizes the condition of optimal performance (and sometimes environmentally objectionable operation) of a combustor. A steady planar diffusion flame is most closely approached in the laboratory in the counterflow apparatus. The utility of this simple-strain-rate flow for the modeling and probing of diffusion flames was noted by Pandya and Weinberg 35 years ago, though only in the last decade or so has its use become internationally common place. However, typically, as the strain rate a is reduced below about 20 cm(exp -1), and the diffusion-flame limit (reaction rate much faster than the flow rate) is approached, the burning is observed to become unstable in earth gravity. The advantageous steady planar flow is not available in the diffusion-flame limit in earth gravity. This is unfortunate because the typical spatial scale in a counterflow is (k/a)(sup 1/2), where k denotes a characteristic diffusion coefficient; thus, the length scale becomes large, and the reacting flow is particularly amenable to diagnostic probing, as the diffusion-flame limit is approached. The disruption of planar symmetry is owing the fact that, as the strain rate a decreases, the residence time (l/a) of the throughput in the counterflow burner increases. Observationally, when the residence time exceeds about 50 msec, the inevitably present convective (Rayleigh-Benard) instabilities, associated with hot-under-cold (flame-under-fresh-reactant) stratification of fluid in a gravitational field, have time to grow to finite amplitude during transit of the burner.

  1. Experiments on integral length scale control in atmospheric boundary layer wind tunnel

    Microsoft Academic Search

    Kapil Varshney; Kamal Poddar

    Accurate predictions of turbulent characteristics in the atmospheric boundary layer (ABL) depends on understanding the effects\\u000a of surface roughness on the spatial distribution of velocity, turbulence intensity, and turbulence length scales. Simulation\\u000a of the ABL characteristics have been performed in a short test section length wind tunnel to determine the appropriate length\\u000a scale factor for modeling, which ensures correct aeroelastic

  2. The effect of cavitation on the hydrofoil dynamic characteristics

    NASA Astrophysics Data System (ADS)

    Yang, J.; Zhou, L. J.; Wang, Z. W.; Zhi, F. L.

    2013-12-01

    Cavitation in hydraulic machinery usually causes a change of fluid dynamic characteristics. In order to predict the effect of cavitation on hydrofoil characteristics, the cavitation around a hydrofoil was studied numerically. The full cavitation model and a modified RNG k ?-turbulence model were used. The finite volume method with the SIMPLEC scheme was used to discretize the time-dependent equations. The second-order upwind scheme was used for the convection terms with the central difference scheme used for the diffusion terms. Fluid dynamic characteristics including cavity's length, shedding frequency, pressure coefficient and lift and drag force coefficients features in a range of cavitation number were analyzed. Computations were made on the three-dimensional flow field around a NACA66 hydrofoil at 8° angle of attack. The recording force signals exhibit periodic behaviours with the time. And the cavity shedding frequency increases with the cavitation number, however the length of cavity decreases with the cavitation number, which result in changing of lift-drag ratio. Especially for larger cavitation numbers, the lift drag ratio of cavitation field is getting closer and closer to that of non-cavitation field.

  3. Experimental Evaluation of Rocket Exhaust Diffusers for Altitude Simulation

    NASA Technical Reports Server (NTRS)

    Sivo, Joseph N.; Meyer, Carl L.; Peters, Daniel J.

    1960-01-01

    An experimental investigation of exhaust diffusers has been conducted to evaluate various methods of minimizing the overall pressure ratio (from chamber to ambient pressure) required to establish and maintain full expansion of the nozzle flow (altitude simulation). Exhaust-diffuser configurations investigated were (1) cylindrical diffusers, (2) diffusers with contraction, and (3) diffusers including a right-angle turn. Cylindrical diffusers were evaluated with primary nozzles of various area ratios and types, as well as two clustered configurations; the other diffusers were evaluated with individual nozzles of constant area ratio and varied type. Air was the working fluid, except for two check points obtained with JP-4 fuel and liquid-oxygen rocket engines and cylindrical diffusers. The minimum length-diameter ratio of cylindrical diffusers was about 6 for minimum pressure-ratio requirements. With cylindrical diffusers of adequate length, the pressure-ratio requirements were primarily a function of the ratio of diffuser to nozzle-throat areas and were essentially independent of primary-nozzle type (including two clustered configurations) or area ratio. The two check points obtained with rocket engines indicated the pressure-ratio requirements at given ratios of diffuser to nozzle-throat areas were lowered, as compared with the requirements with air, as a result of the reduced ratio of specific heats. The minimum length-diameter ratio of the contraction throat of convergent-divergent diffusers was also about 6 for minimum pressure-ratio requirements. With adequate contraction-throat length, the pressure-ratio requirements of such diffusers were appreciably below those of comparable cylindrical diffusers when used with conical and cutoff-isentropic nozzles, but not when used with a bell nozzle. Minimum pressure-ratio requirements of a diffuser including a simple long-radius right-angle turn at maximum diffuser area, obtained with the center of radius of the turn a minimum of 2 diffuser diameters downstream of the nozzle exit, were not appreciably above those of a comparable optimum cylindrical diffuser. A diffuser including a long-radius right-angle turn at a contraction minimum area had somewhat lower pressure-ratio requirements than the aforementioned simple turn.

  4. Scale Length of Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Fathi, K.; Allen, M.; Gonzalez-Solares, E.; Hatziminaoglou, E.; Peletier, R.

    2009-07-01

    As a part of a Euro-VO research initiative, we have undertaken a programme aimed at studying the scale length of 54909 Sa-Sd spiral galaxies from the SDSS DR6 catalogue. We have retrieved u, g, r, i, z-band images for all galaxies in order to derive the light profiles. We also calculate asymmetry parameters to select non-disturbed disks for which we will derive exponential disk scale lengths. As images in different bands probe different optical depths and stellar populations, it is likely that a derived scale length value should depend on waveband, and our goal is to use the scale length variations with band pass, inclination, galaxy type, redshift, and surface brightness, in order to better understand the nature of spiral galaxies.

  5. AMBIPOLAR DIFFUSION HEATING IN TURBULENT SYSTEMS

    SciTech Connect

    Li, Pak Shing [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Myers, Andrew [Physics Department, University of California, Berkeley, CA 94720 (United States); McKee, Christopher F., E-mail: psli@astron.berkeley.edu, E-mail: atmyers@berkeley.edu, E-mail: cmckee@berkeley.edu [Physics Department and Astronomy Department, University of California, Berkeley, CA 94720 (United States)

    2012-11-20

    The temperature of the gas in molecular clouds is a key determinant of the characteristic mass of star formation. Ambipolar diffusion (AD) is considered one of the most important heating mechanisms in weakly ionized molecular clouds. In this work, we study the AD heating rate using two-fluid turbulence simulations and compare it with the overall heating rate due to turbulent dissipation. We find that for observed molecular clouds, which typically have Alfven Mach numbers of {approx}1 and AD Reynolds numbers of {approx}20, about 70% of the total turbulent dissipation is in the form of AD heating. AD has an important effect on the length scale where energy is dissipated: when AD heating is strong, most of the energy in the cascade is removed by ion-neutral drift, with a comparatively small amount of energy making it down to small scales. We derive a relation for the AD heating rate that describes the results of our simulations to within a factor of two. Turbulent dissipation, including AD heating, is generally less important than cosmic-ray heating in molecular clouds, although there is substantial scatter in both.

  6. Cylindrical diffuser performance using a truncated plug nozzle

    NASA Technical Reports Server (NTRS)

    Galanga, F. L.; Mueller, T. J.

    1976-01-01

    Cylindrical diffuser performance for a truncated plug nozzle without external flow was tested in a blowdown wind tunnel. The nozzle was designed for an exit Mach number of 1.9 and the plug was conical in shape from the throat and converged to the axis of symmetry at an angle of 10 degrees. The diffuser section was fashioned into two 13.97 cm lengths to facilitate boring of the duct diameter and to allow for testing of two different duct lengths. A slotted hypotube was installed in the base of the diffuser to measure pressure distribution down the centerline of the diffuser. The data obtained included: the typical centerline and sidewall pressure ratio variation along the diffuser, cell pressure ratio vs overall pressure ratio for long and short diffusers and a comparison of minimum experimental cell pressure ratio vs area ratio.

  7. LINEAR DIFFUSION Erkut Erdem

    E-print Network

    Erdem, Erkut

    LINEAR DIFFUSION Erkut Erdem Hacettepe University February 24th, 2012 CONTENTS 1 Linear Diffusion 1 2 Appendix - The Calculus of Variations 5 References 6 1 LINEAR DIFFUSION The linear diffusion (heat (noisy) input image and u(x, t) be initialized with u(x, 0) = u0(x) = f (x). Then, the linear diffusion

  8. NONLINEAR DIFFUSION Erkut Erdem

    E-print Network

    Erdem, Erkut

    NONLINEAR DIFFUSION Erkut Erdem Hacettepe University March 9th, 2013 CONTENTS 1 Perona-Malik Type Nonlinear Diffusion 1 2 Total Variation (TV) Regularization 5 3 Edge Enhancing Diffusion 8 References 11 1 PERONA-MALIK TYPE NONLINEAR DIFFUSION The main theory behind nonlinear diffusion models is to use

  9. Statistical mechanics derivation of hydrodynamic boundary conditions: the diffusion equation

    Microsoft Academic Search

    M. Fuchs; K. Kroy

    2002-01-01

    Considering the example of interacting Brownian particles we present a linear response derivation of the boundary condition for the corresponding hydrodynamic description (the diffusion equation). This requires us to identify a non-analytic structure in a microscopic relaxation kernel connected to the frequency-dependent penetration length familiar for diffusive processes, and leads to a microscopic definition of the position where the hydrodynamic

  10. The diffusive dynamics of water confined in ganglioside micelles

    NASA Astrophysics Data System (ADS)

    Cantù, L.; Cavatorta, F.; Corti, M.; Del Favero, E.; Deriu, A.

    1997-02-01

    We have investigated by QENS the dynamics of water associated to gangliosides. The dependence of the QENS line-broadening versus Q indicates that proton diffusion is restricted when investigated over scale lengths of about 6-8 Å; at smaller distances the diffusivity parameters are similar to those of pure water at a lower temperature.

  11. Measurement of gas diffusion coefficient using photonic crystal fiber

    Microsoft Academic Search

    Y. L. Hoo; W. Jin; H. L. Ho; D. N. Wang

    2003-01-01

    We report the use of photonic crystal fiber (PCF) for the measurement of gas diffusion constant. PCF has uniform airhole columns along the fiber length that provide the basis for the study of gas diffusion based on the capillary method. The gas concentration within the airhole columns is monitored by measuring the attenuation of light through the PCF caused by

  12. Diffusion of physisorbed layers and their connection to MEMS effectiveness

    Microsoft Academic Search

    Brendan Paul Miller

    2009-01-01

    The aim of this work is to connect the physics of surface diffusion of a lubricant to Micro-Electro-Mechanical System (MEMS) lubrication. Some hurdles must be overcome in order to make this connection. One must have a way to experimentally measure surface diffusivity. Length scales must be taken into account since the mechanism of lubrication varies from the macro scale to

  13. Influence of interface compounds on interface bonding characteristics of aluminium and silicon carbide

    SciTech Connect

    Sozhamannan, G.G., E-mail: sozhan30@yahoo.co.in [Department of Mechanical Engineering, College of Engineering, Anna University Chennai, Chennai-600025 (India); Prabu, S. Balasivanandha [Department of Mechanical Engineering, College of Engineering, Anna University Chennai, Chennai-600025 (India)

    2009-09-15

    The interface plays an important role in improving the mechanical properties of metal matrix composites. Hence, it is essential to evaluate interface bonding of Aluminium/Silicon carbide. The interface bonding of Aluminum/Silicon carbide samples were prepared by various processing temperatures at constant holding time. The interface compounds at the interface were evaluated by an energy dispersive spectroscope and diffusion length of compounds was calculated by Arrhenius equation. The interface structure was analyzed by a scanning electron microscope. The interface characteristics were evaluated by tensile test and microhardness test.

  14. On the Physics of Jet Diffusion Flames

    Microsoft Academic Search

    EMMANUEL VILLERMAUX; DANIEL DUROX

    1992-01-01

    A physical model for the laminar jet diffusion flame including chemical kinetics effects is provided. We produce the appropriate set of dimensionless groups needed to discuss the role of buoyancy and jet outlet velocity Uo on such flames. We are particularly interested in flame lengths L\\\\ the behaviour of the flame is shown to split in two regimes. The regime

  15. Diffusion of Singlet Excitons in Tetracene Crystals

    Microsoft Academic Search

    G. Vaubel; H. Baessler

    1970-01-01

    The diffusion length ls of singlet excitons in crystalline tetracene was measured in the temperature range 293 to 160 °K utilizing the quenching effect exerted on the crystal fluorescence by exciton traps located at the crystal surface. It is found that ls = 120 ± 10 Å at room temperature. It increases exponentially with decreasing temperature until it approaches a

  16. The correlation length for interplanetary magnetic field fluctuations

    NASA Technical Reports Server (NTRS)

    Fisk, L. A.; Sari, J. W.

    1972-01-01

    It is argued that it is appropriate to consider two correlation lengths for interplanetary magnetic field fluctuations. For particles with gyro-radii large enough to encounter and be scattered by large-scale tangential discontinuities in the field (particles with energies greater than or approximately equal to several GeV/nucleon) the appropriate correlation length is simply the mean spatial separation between the discontinuities, L approximately 2 x 10 to the 11th power. Particles with gyro-radii much less than this mean separation (energies less than or approximately equal to 100 MeV/nucleon) appear to be unaffected by the discontinuities and respond only to smaller-scale field fluctuations. For these particles the correlation length is shown to be L approximately 10 to the 10th power cm. With this system of two correlation lengths the cosmic-ray diffusion tensor may be altered from what was predicted by, for example, Jokipii and Coleman, and the objections raised recently by Klimas and Sandri to the diffusion analysis of Jokipii may apply only at relatively low energies (approximately 50 MeV/nucleon).

  17. Length-weight and length-length relationships of fish species from the Aegean Sea (Greece)

    Microsoft Academic Search

    D. K. Moutopoulos; K. I. Stergiou

    2002-01-01

    Summary We present the relationships between total (TL), fork(FL) and standard (SL) length for 37 fish species and the relationships between TL and wet weight for 40 fish species from the Aegean Sea (Cyclades; Greece). The relationships between TL, FL and SL were all linear (for all cases: r2 > 0.928). The values of the exponent b of the length-weight

  18. Comparison of diffusion- and pumped-sampling methods to monitor volatile organic compounds in ground water, Massachusetts Military Reservation, Cape Cod, Massachusetts, July 1999-December 2002

    USGS Publications Warehouse

    Archfield, Stacey A.; LeBlanc, Denis R.

    2005-01-01

    To evaluate diffusion sampling as an alternative method to monitor volatile organic compound (VOC) concentrations in ground water, concentrations in samples collected by traditional pumped-sampling methods were compared to concentrations in samples collected by diffusion-sampling methods for 89 monitoring wells at or near the Massachusetts Military Reservation, Cape Cod. Samples were analyzed for 36 VOCs. There was no substantial difference between the utility of diffusion and pumped samples to detect the presence or absence of a VOC. In wells where VOCs were detected, diffusion-sample concentrations of tetrachloroethene (PCE) and trichloroethene (TCE) were significantly lower than pumped-sample concentrations. Because PCE and TCE concentrations detected in the wells dominated the calculation of many of the total VOC concentrations, when VOC concentrations were summed and compared by sampling method, visual inspection also showed a downward concentration bias in the diffusion-sample concentration. The degree to which pumped- and diffusion-sample concentrations agreed was not a result of variability inherent within the sampling methods or the diffusion process itself. A comparison of the degree of agreement in the results from the two methods to 13 quantifiable characteristics external to the sampling methods offered only well-screen length as being related to the degree of agreement between the methods; however, there is also evidence to indicate that the flushing rate of water through the well screen affected the agreement between the sampling methods. Despite poor agreement between the concentrations obtained by the two methods at some wells, the degree to which the concentrations agree at a given well is repeatable. A one-time, well-bywell comparison between diffusion- and pumped-sampling methods could determine which wells are good candidates for the use of diffusion samplers. For wells with good method agreement, the diffusion-sampling method is a time-saving and cost-effective alternative to pumped-sampling methods in a long-term monitoring program, such as at the Massachusetts Military Reservation.

  19. Native-oxide-based selective area growth of InP nanowires via metal-organic molecular beam epitaxy mediated by surface diffusion

    NASA Astrophysics Data System (ADS)

    Calahorra, Yonatan; Greenberg, Yaakov; Cohen, Shimon; Ritter, Dan

    2012-06-01

    The growth of InP nanowires on an InP(111) B substrate is reported. The substrate native oxide was not removed from the surface prior to growth. Nanowires were grown at 400?°C from gold catalysts in a selective area manner, without bulk growth. Unlike SiO2-based metal-organic molecular beam epitaxy selective area growth, the growth reported here is mediated by surface diffusion with a characteristic diffusion length of 4 ?m, about an order of magnitude larger than values for diffusion on bare substrates. A pre-growth heating treatment at 450?°C was found to increase the yield of nanowire nucleation from the gold catalysts.

  20. 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.

  1. Parallel flow diffusion battery

    DOEpatents

    Yeh, Hsu-Chi (Albuquerque, NM); Cheng, Yung-Sung (Albuquerque, NM)

    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.

  2. Buoyancy Effects on Flow Transition in Hydrogen Gas Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Albers, Burt W.; Agrawal, Ajay K.; Griffin, DeVon (Technical Monitor)

    2000-01-01

    Experiments were performed in earth-gravity to determine how buoyancy affected transition from laminar to turbulent flow in hydrogen gas jet diffusion flames. The jet exit Froude number characterizing buoyancy in the flame was varied from 1.65 x 10(exp 5) to 1.14 x 10(exp 8) by varying the operating pressure and/or burner inside diameter. Laminar fuel jet was discharged vertically into ambient air flowing through a combustion chamber. Flame characteristics were observed using rainbow schlieren deflectometry, a line-of-site optical diagnostic technique. Results show that the breakpoint length for a given jet exit Reynolds number increased with increasing Froude number. Data suggest that buoyant transitional flames might become laminar in the absence of gravity. The schlieren technique was shown as effective in quantifying the flame characteristics.

  3. Filtering spams using the minimum description length principle

    Microsoft Academic Search

    Tiago A. Almeida; Akebo Yamakami; Jurandy Almeida

    2010-01-01

    Spam has become an increasingly important problem with a big economic impact in society. Spam filtering poses a special problem in text categorization, of which the defining characteristic is that filters face an active adversary, which constantly attempts to evade filtering. In this paper, we present a novel approach to spam filtering based on the minimum description length principle. The

  4. Human Factor Analysis of Long Cane Design: Weight and Length

    ERIC Educational Resources Information Center

    Rodgers, Mark D.; Emerson, Robert Wall

    2005-01-01

    In a series of experiments, canes of different lengths, weights, and weight distributions were assessed to determine the effect of these characteristics on various performance measures. The results indicate that the overall weight of a cane and the distribution of weight along a cane's shaft do not affect a person's performance, but accuracy does…

  5. Length of occupational noise exposure and blood pressure

    Microsoft Academic Search

    Thierry Lang; Christiane Fouriaud; Marie-Christine Jacquinet-Salord

    1992-01-01

    Summary A cross-sectional study was performed in the Paris area, with a total of 7901 subjects; 432 of them were exposed to occupational noise = 85 dBA. Noise was measured by the worksite physicians, and length of exposure was collected through interview. The subjects exposed to noise were mainly workers, their body mass index was higher and their job characteristics

  6. Altered Anatomical Network in Early Blindness Revealed by Diffusion Tensor Tractography

    PubMed Central

    Li, Jun; Li, Yonghui; Yu, Chunshui; Jiang, Tianzi

    2009-01-01

    The topological architecture of the cerebral anatomical network reflects the structural organization of the human brain. Recently, topological measures based on graph theory have provided new approaches for quantifying large-scale anatomical networks. Diffusion MRI studies have revealed the efficient small-world properties and modular structure of the anatomical network in normal subjects. However, no previous study has used diffusion MRI to reveal changes in the brain anatomical network in early blindness. Here, we utilized diffusion tensor imaging to construct binary anatomical networks for 17 early blind subjects and 17 age- and gender-matched sighted controls. We established the existence of structural connections between any pair of the 90 cortical and sub-cortical regions using deterministic tractography. Compared with controls, early blind subjects showed a decreased degree of connectivity, a reduced global efficiency, and an increased characteristic path length in their brain anatomical network, especially in the visual cortex. Moreover, we revealed some regions with motor or somatosensory function have increased connections with other brain regions in the early blind, which suggested experience-dependent compensatory plasticity. This study is the first to show alterations in the topological properties of the anatomical network in early blindness. From the results, we suggest that analyzing the brain's anatomical network obtained using diffusion MRI data provides new insights into the understanding of the brain's re-organization in the specific population with early visual deprivation. PMID:19784379

  7. Simplified model for mass diffusivity estimation based on dynamic pendant drop volume analysis

    NASA Astrophysics Data System (ADS)

    Pedro, Vargas; Junior, Guerrero; Maria, Jiménez; Damelys, Zabala

    2012-01-01

    We present a simplified correlation for calculating the dissolved gas moles in a pendant drop during the diffusion time, for several drop shapes. After this correlation is determined, the Yang and Gu (Ind Eng Chem Res 44:4474-4483, 2005) dynamic pendant drop volume analysis (DPDVA) method for calculation of mass diffusivity from the pendant drop volume variation against time can be used. We solved the differential equation in cylindrical coordinates for the mass transfer model of the gas diffusion into the liquid inside the pendant drop, using a different characteristic length (LC), instead of the outer radius of the syringe needle (rn) used in Yang and Gu (Ind Eng Chem Res 44:4474-4483, 2005) for defining the dimensionless variables. LC is the relationship between the pendant drop volume and its mass transfer surface area at the initial conditions. The generalized correlation saves time, simplifies the method application and the deviations in the diffusion coefficient calculation respect to the complete Yang and Gu model are below 6%.

  8. Modeling Suomi-NPP VIIRS Solar Diffuser Degradation due to Space Radiation

    NASA Astrophysics Data System (ADS)

    Shao, X.; Cao, C.

    2014-12-01

    The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard Suomi-NPP uses a solar diffuser (SD) as on-board radiometric calibrator for the reflective solar band (RSB) calibration. Solar diffuser is made of Spectralon (one type of fluoropolymer) and was chosen because of its controlled reflectance in the VIS-NIR-SWIR region and its near-Lambertian reflectance profile. Spectralon is known to degrade in reflectance at the blue end of the spectrum due to exposure to space radiations such as solar UV radiation and energetic protons. These space radiations can modify the Spectralon surface through breaking C-C and C-F bonds and scissioning or cross linking the polymer, which causes the surface roughness and degrades its reflectance. VIIRS uses a SDSM (Solar Diffuser Stability Monitor) to monitor the change in the Solar Diffuser reflectance in the 0.4 - 0.94 um wavelength range and provide a correction to the calibration constants. The H factor derived from SDSM reveals that reflectance of 0.4 to 0.6um channels of VIIRS degrades faster than the reflectance of longer wavelength RSB channels. A model is developed to derive characteristic parameters such as mean SD surface roughness height and autocovariance length of SD surface roughness from the long term spectral degradation of SD reflectance as monitored by SDSM. These two parameters are trended to assess development of surface roughness of the SD over the operation period of VIIRS.

  9. Laser glass marking: influence of pulse characteristics

    NASA Astrophysics Data System (ADS)

    Rolo, Ana; Coelho, João; Pires, Margarida

    2005-09-01

    Laser glass marking is currently used in several glass materials for different purposes, such as bar codes for product tracking, brand logos or just decoration. Systems with a variety of different laser sources, with inherent power ranges, wavelengths and pulse regimes have been used, namely CO2, Nd:YAG, Excimer, Ti-Sapphire lasers. CO2 Lasers systems, although being a reliable tool for materials processing, and very compact in the case of sealed low power lasers, are usually associated with a localized thermal loading on the material, causing brittle materials like glass to crack around the irradiated area. In this experimental study a pulsed CO2 laser was used to direct marking the glass surface. The temporal characteristics of the laser pulse--pulse length, period and duty cycle were varied, and glass materials with different thermal properties were used in order to correlate the marking process--cracking or softening with or without material removal with the laser and material characteristics. Glass materials with major industrial application, such as soda-lima, borosilicate (PYREX) glasses and crystal have been investigated. Laser marked areas have been characterized in terms of surface optical properties, like diffuse and direct reflectance and transmittance for white light, directly related with marked surface quality.

  10. 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…

  11. IMF Length Scales and Predictability: The Two Length Scale Medium

    NASA Technical Reports Server (NTRS)

    Collier, Michael R.; Szabo, Adam; Slavin, James A.; Lepping, R. P.; Kokubun, S.

    1999-01-01

    We present preliminary results from a systematic study using simultaneous data from three spacecraft, Wind, IMP 8 (Interplanetary Monitoring Platform) and Geotail to examine interplanetary length scales and their implications on predictability for magnetic field parcels in the typical solar wind. Time periods were selected when the plane formed by the three spacecraft included the GSE (Ground Support Equipment) x-direction so that if the parcel fronts were strictly planar, the two adjacent spacecraft pairs would determine the same phase front angles. After correcting for the motion of the Earth relative to the interplanetary medium and deviations in the solar wind flow from radial, we used differences in the measured front angle between the two spacecraft pairs to determine structure radius of curvature. Results indicate that the typical radius of curvature for these IMF parcels is of the order of 100 R (Sub E). This implies that there are two important IMF (Interplanetary Magnetic Field) scale lengths relevant to predictability: (1) the well-established scale length over which correlations observed by two spacecraft decay along a given IMF parcel, of the order of a few tens of Earth radii and (2) the scale length over which two spacecraft are unlikely to even observe the same parcel because of its curvature, of the order of a hundred Earth radii.

  12. 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.

  13. Screening length in plasma winds

    E-print Network

    Elena Caceres; Makoto Natsuume; Takashi Okamura

    2007-06-04

    We study the screening length L_s of a heavy quark-antiquark pair in strongly coupled gauge theory plasmas flowing at velocity v. Using the AdS/CFT correspondence we investigate, analytically, the screening length in the ultra-relativistic limit. We develop a procedure that allows us to find the scaling exponent for a large class of backgrounds. We find that for conformal theories the screening length is (boosted energy density)^{-1/d}. As examples of conformal backgrounds we study R-charged black holes and Schwarzschild-anti-deSitter black holes in (d+1)-dimensions. For non-conformal theories, we find that the exponent deviates from -1/d and as examples we study the non-extremal Klebanov-Tseytlin and Dp-brane geometries. We find an interesting relation between the deviation of the scaling exponent from the conformal value and the speed of sound.

  14. 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.

  15. Experimental investigation of flow through an asymmetric plane diffuser

    NASA Astrophysics Data System (ADS)

    Buice, Carl U.

    There is a need for measurements in complex turbulent flows that originate from very well-defined initial conditions. Testing of large-eddy simulations and other higher-order computation schemes requires inlet boundary condition data that are not normally measured. The use of fully developed upstream conditions offers a solution to this dilemma in that the upstream conditions can be adequately computed at any level of sophistication. The asymmetric plane diffuser geometry consists of a 2-D channel of height H entering a one-sided diffuser (one straight wall and one oblique wall) 21H in length, giving a divergence angle of 10 degrees. The diffuser discharges into a 2-D channel with a separation distance of 4.7H. The flow is characterized by an inlet with fully developed 2-D channel flow, a smooth wall separation, and downstream reattachment and redevelopment of the wall boundary layer. Accurately calculating a flow with these characteristics provides significant challenges for most computational models. The two-dimensionality of the flow through an asymmetric plane diffuser has been documented with special attention to spanwise uniformity, conservation of mass, and conservation of momentum. The inlet conditions for the diffuser were shown to match the results of Hussain and Reynolds' fully-developed turbulent channel flow experiment at Resb{H,cl}=20,000. Mean velocity and turbulence profiles have been measured throughout the domain using a variety of anemometry techniques with the exception of the shear and wall normal stresses within the recirculation region. The static pressure and wall shear stress distributions have been measured along both walls. Turbulent dispersion of a passive scalar, temperature, has been measured in the recovering channel flow and is compared with measurements made in a fully-developed turbulent channel. The results of this experiment are compared to the results of two different calculations made for the same diffuser geometry and Reynolds number. One of the calculations is a Large Eddy Simulation (LES) conducted by Massimiliano Fatica of the Center for Turbulence Research (CTR). The other is a Reynolds Averaged Navier Stokes (RANS) calculation using Paul Durbins vsp2-f turbulence model. Both calculations captured the major features of the flow including separation and reattachment.

  16. Double-diffusive layer formation

    NASA Astrophysics Data System (ADS)

    Zaussinger, Florian; Kupka, Friedrich; Hücker, Sebastian; Egbers, Christoph

    2015-04-01

    Double-diffusive convection plays an important role in geo- and astrophysical applications. The special case, where a destabilising temperature gradient counteracts a stabilising solute gradient leads to layering phenomena under certain conditions. Convectively mixed layers sandwiched in diffusive interfaces form a so-called stack. Well-known double-diffusive systems are observed in rift lakes in Africa and even from the coffee drink Latte Macciatto. Stacks of layers are also predicted to occur inside massive stars and inside giant planets. Their dynamics depend on the thermal, the solute and the momentum diffusivities, as well on the ratio of the gradients of the opposing stratifications. Since the layering process cannot be derived from linear stability analysis, the full nonlinear set of equations has to be investigated. Numerical simulations have become feasible for this task, despite the physical processes operate on a vast range of length and time scales, which is challenging for numerical hydrodynamical modelling. The oceanographically relevant case of fresh and salty water is investigated here in further details. The heat and mass transfer is compared with theoretical results and experimental measurements. Additionally, the initial dynamic of layering, the transient behaviour of a stack and the long time evolution are presented using the example of Lake Kivu and the interior of a giant planet.

  17. Nanoparticle Diffusion in Polymer Nanocomposites

    SciTech Connect

    Kalathi, Jagannathan [Columbia University, New York] [Columbia University, New York; Yamamoto, Umi [University of Illinois, Urbana-Champaign] [University of Illinois, Urbana-Champaign; Schweizer, Kenneth [University of Illinois] [University of Illinois; Grest, Gary S. [Sandia National Laboratories (SNL)] [Sandia National Laboratories (SNL); Kumar, Sanat [Columbia University, New York] [Columbia University, New York

    2014-01-01

    Large-scale molecular dynamics simulations show that nanoparticle (NP) diffusivity in weakly interacting mixtures of NPs and polymer melts has two very different classes of behavior depending on their size. NP relaxation times and their diffusivities are completely described by the local, Rouse dynamics of the polymer chains for NPs smaller than the polymer entanglement mesh size. The motion of larger NPs, which are comparable to the entanglement mesh size, is significantly slowed by chain entanglements, and is not describable by the Stokes-Einstein relationship. Our results are in essentially quantitative agreement with a force-level generalized Langevin equation theory for all the NP sizes and chain lengths explored, and imply that for these lightly entangled systems, activated NP hopping is not important.

  18. Low Reynolds number flow through nozzle-diffuser elements in valveless micropumps

    Microsoft Academic Search

    Vishal Singhal; Suresh V. Garimella; Jayathi Y. Murthy

    2004-01-01

    Flow characteristics of low Reynolds number laminar flow through gradually expanding conical and planar diffusers were investigated. Such diffusers are used in valveless micropumps to effect flow rectification and thus lead to pumping action in one preferential direction. Four different types of diffuser flows are considered: fully developed and thin inlet boundary layer flows through conical and planar diffusers. The

  19. Exactly Solvable Dynamical Models with a Minimal Length Uncertainty

    NASA Astrophysics Data System (ADS)

    Bernardo, Reginald Christian S.; Esguerra, Jose Perico H.

    2015-05-01

    We present exact analytical solutions to the classical equations of motion and analyze the dynamical consequences of the existence of a minimal length for the free particle, particle in a linear potential, anti-symmetric constant force oscillator, harmonic oscillator, vertical harmonic oscillator, linear diatomic chain, and linear triatomic chain. It turns out that the speed of a free particle and the magnitude of the acceleration of a particle in a linear potential have larger values compared to the non-minimal length counterparts - the increase in magnitudes come from multiplicative factors proportional to what is known as the generalized uncertainty principle parameter. Our analysis of oscillator systems suggests that the characteristic frequencies of systems also have larger values than the non-minimal length counterparts. In connection with this, we discuss a kind of experimental test with which the existence of a minimal length may be detected on a classical level.

  20. Aeolian sand transport: Length and height distributions of saltation trajectories

    NASA Astrophysics Data System (ADS)

    Ho, T. D.; Valance, A.; Dupont, P.; Ould El Moctar, A.

    2014-03-01

    We report wind-tunnel measurements on aeolian sand transport aiming at characterizing the distribution of the length and height of trajectories of the saltating particles. We employ a simple horizontal sand trap device to assess the distribution of saltation length while the distribution of saltation height is inferred from the measurements of the particle lift-off velocity by means of particle velocimetry tracking techniques. Our measurements reveal that the saltation length and height present a continuum distribution which decreases monotonously and exhibits a long tail that can be well described by a lognormal law. Interestingly, these distributions are found almost invariant with the flow strength. As a consequence, the mean saltation length (l¯) and height (h¯) are independent of the flow strength confirming previous indirect measurements. The influence of the flow strength is only seen through the tail of the saltation length distribution: the higher the Shields number, the flatter the distribution tail. Finally, experiments carried out with sand of different sizes show that the mean saltation length and height are not related to the sand grain size through a simple manner but depend instead linearly with the height zf of the Bagnold focus point: l??6zf and h??0.6zf. This last result emphasizes that the focus height is an important characteristic length scale of the saltation transport.

  1. Control of arc length during gas metal arc welding

    SciTech Connect

    Madigan, R.B.; Quinn, T.P.

    1994-12-31

    An arc-length control system has been developed for gas metal arc welding (GMAW) under spray transfer welding conditions. The ability to monitor and control arc length during arc welding allows consistent weld characteristics to be maintained and therefore improves weld quality. Arc length control has only been implemented for gas tungsten arc welding (GTAW), where an automatic voltage control (AVC) unit adjusts torch-to-work distance. The system developed here compliments the voltage- and current-sensing techniques commonly used for control of GMAW. The system consists of an arc light intensity sensor (photodiode), a Hall-effect current sensor, a personal computer and software implementing a data interpretation and control algorithms. Arc length was measured using both arc light and arc current signals. Welding current was adjusted to maintain constant arc length. A proportional-integral-derivative (PID) controller was used. Gains were automatically selected based on the desired welding conditions. In performance evaluation welds, arc length varied from 2.5 to 6.5 mm while welding up a sloped workpiece (ramp in CTWD) without the control. Arc length was maintained within 1 mm of the desired (5 mm ) with the control.

  2. Microscopic Diffusion and Hydrodynamic Interactions of Hemoglobin in Red Blood Cells

    PubMed Central

    Doster, Wolfgang; Longeville, Stéphane

    2007-01-01

    The cytoplasm of red blood cells is congested with the oxygen storage protein hemoglobin occupying a quarter of the cell volume. The high protein concentration leads to a reduced mobility; the self-diffusion coefficient of hemoglobin in blood cells is six times lower than in dilute solution. This effect is generally assigned to excluded volume effects in crowded media. However, the collective or gradient diffusion coefficient of hemoglobin is only weakly dependent on concentration, suggesting the compensation of osmotic and friction forces. This would exclude hydrodynamic interactions, which are of dynamic origin and do not contribute to the osmotic pressure. Hydrodynamic coupling between protein molecules is dominant at short time- and length scales before direct interactions are fully established. Employing neutron spin-echo-spectroscopy, we study hemoglobin diffusion on a nanosecond timescale and protein displacements on the scale of a few nanometers. A time- and wave-vector dependent diffusion coefficient is found, suggesting the crossover of self- and collective diffusion. Moreover, a wave-vector dependent friction function is derived, which is a characteristic feature of hydrodynamic interactions. The wave-vector and concentration dependence of the long-time self-diffusion coefficient of hemoglobin agree qualitatively with theoretical results on hydrodynamics in hard spheres suspensions. Quantitative agreement requires us to adjust the volume fraction by including part of the hydration shell: Proteins exhibit a larger surface/volume ratio compared to standard colloids of much larger size. It is concluded that hydrodynamic and not direct interactions dominate long-range molecular transport at high concentration. PMID:17513357

  3. Gas diffusion and microstructural properties of ordered mesoporous silica fibers.

    PubMed

    Alsyouri, Hatem M; Lin, Jerry Y S

    2005-07-21

    Pore and surface diffusion of carbon dioxide (CO(2)) and ethylene (C(2)H(4)) in the nanopores of ordered mesoporous silica fibers about 200 microm in length was measured by the transient gravimetric method. The experimentally determined pore diffusivity data, coupled with the porosity, pore size, and fiber length, are used to obtain the actual length of the nanopores in silica fibers. These measurements reveal a structure of the ordered nanopores whirling helically around the fiber axis with a spiral diameter of about 15 microm and a pitch value of 1.6 microm. At room temperature the surface diffusion contributes about 10% to the total diffusional flux for these two gases in the nanopores of the ordered mesoporous silica fibers. The surface diffusion coefficients for the ordered mesoporous silica fibers are about 1 order of magnitude larger than the non-ordered mesoporous alumina or silica with similar pore size. PMID:16852707

  4. Molecular Dynamics of Diffusive-Ballistic Heat Conduction in Single-Walled Carbon Nanotubes

    E-print Network

    Maruyama, Shigeo

    Molecular Dynamics of Diffusive-Ballistic Heat Conduction in Single-Walled Carbon Nanotubes-3-1 Hongo, Bunkyo-ku Tokyo 113-8656, Japan Diffusive-ballistic heat conduction of finite-length single. A gradual transition from nearly pure ballistic to diffusive-ballistic heat conduction was identified from

  5. Diffusive-Ballistic Heat Conduction of Carbon Nanotubes and Nanographene Junichiro Shiomi and Shigeo Maruyama*

    E-print Network

    Maruyama, Shigeo

    Diffusive-Ballistic Heat Conduction of Carbon Nanotubes and Nanographene Ribbons Junichiro Shiomi-3-5800-6983 Abstract Investigations of diffusive-ballistic heat conduction of finite-length single-walled carbon of the balance between ballistic and diffusive heat conduction. For both systems, the profile indicates

  6. Internode Length in Pisum1

    PubMed Central

    Reid, James B.

    1983-01-01

    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

  7. The Minimum Description Length Principle

    Microsoft Academic Search

    Peter D. Grünwald

    2007-01-01

    The minimum description length (MDL) principle is a powerful method of inductive inference, the basis of statistical modeling, pattern recognition, and machine learning. It holds that the best explanation, given a limited set of observed data, is the one that permits the greatest compression of the data. MDL methods are particularly well-suited for dealing with model selection, prediction, and estimation

  8. Electron localization length in polyaniline

    Microsoft Academic Search

    P. K. Kahol; R. P. Perera; K. K. Satheesh Kumar; S. Geetha; D. C. Trivedi

    2003-01-01

    Electrical DC conductivity, magnetic susceptibility, and EPR measurements are used to investigate the electron localization behavior of polyaniline as a function of the dopant type using seven sulfonic acid based doping acids. In spite of differences in the magnitude and the temperature dependences of DC conductivity and magnetic susceptibility data, the experiments reveal a localization length of approximately 30Å for

  9. 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.

  10. FIBONACCI LENGTH AND EFFICIENCY IN GROUP PRESENTATIONS

    E-print Network

    St Andrews, University of

    FIBONACCI LENGTH AND EFFICIENCY IN GROUP PRESENTATIONS Peter Philip Campbell Ph.D. Thesis . . . . . . . . . . . . . 14 2 Introduction to Fibonacci length and generalizations 19 1 Introduction and apology considerations . . . . . . . . . . . . . . . . . 47 3.1 Fibonacci length

  11. Diffusion, dimensionality and noise in transcriptional regulation

    E-print Network

    Gasper Tkacik; William Bialek

    2007-12-12

    The precision of biochemical signaling is limited by randomness in the diffusive arrival of molecules at their targets. For proteins binding to the specific sites on the DNA and regulating transcription, the ability of the proteins to diffuse in one dimension by sliding along the length of the DNA, in addition to their diffusion in bulk solution, would seem to generate a larger target for DNA binding, consequently reducing the noise in the occupancy of the regulatory site. Here we show that this effect is largely cancelled by the enhanced temporal correlations in one dimensional diffusion. With realistic parameters, sliding along DNA has surprisingly little effect on the physical limits to the precision of transcriptional regulation.

  12. The Effect of Upstream Vane Wakes on Annular Diffuser Flows

    NASA Astrophysics Data System (ADS)

    Cherry, Erica; Padilla, Angelina; Elkins, Christopher; Eaton, John

    2008-11-01

    Experiments were performed to determine the sensitivity to inlet conditions of the flow in two annular diffusers. One of the diffusers was a conservative design typical of a diffuser directly upstream of the combustor in a jet engine. The other had the same length and inlet shape as the first diffuser but a larger area ratio and was meant to operate on the verge of separation. Each diffuser was connected to two different inlets, one containing a fully-developed channel flow, the other containing wakes from a row of airfoils. Three-component velocity measurements were taken on the flow in each inlet/diffuser combination using Magnetic Resonance Velocimetry. Results will be presented on the 3D velocity fields in the two diffusers and the effect of the airfoil wakes on separation and secondary flows.

  13. Bunch Length Measurements using Coherent Radiation

    SciTech Connect

    Ischebeck, Rasmus; Barnes, Christopher; Blumenfeld, Ian; Decker, Franz-Josef; Hogan, Mark; Iverson, Richard H.; Krejcik, Patrick; Siemann, Robert H.; Walz, Dieter; /SLAC; Kirby, Neil; /Stanford U., Phys. Dept.; Clayton, Chris; Huang, Chengkun; Johnson, Devon K.; Lu, Wei; Marsh, Ken; /UCLA; Deng, Suzhi; Oz, Erdem; /Southern California U.

    2005-06-24

    The accelerating field that can be obtained in a beam-driven plasma wakefield accelerator depends on the current of the electron beam that excites the wake. In the E-167 experiment, a peak current above 10 kA will be delivered at a particle energy of 28 GeV. The bunch has a length of a few ten micrometers and several methods are used to measure its longitudinal profile. Among these, autocorrelation of coherent transition radiation (CTR) is employed. The beam passes a thin metallic foil, where it emits transition radiation. For wavelengths greater than the bunch length, this transition radiation is emitted coherently. This amplifies the long-wavelength part of the spectrum. A scanning Michelson interferometer is used to autocorrelate the CTR. However, this method requires the contribution of many bunches to build an autocorrelation trace. The measurement is influenced by the transmission characteristics of the vacuum window and beam splitter. We present here an analysis of materials, as well as possible layouts for a single shot CTR autocorrelator.

  14. Electrostatic Microinstabilities within the Electron Diffusion Layer

    NASA Astrophysics Data System (ADS)

    Jara-Almonte, J.; Daughton, W.; Ji, H.; Yamada, M.

    2013-10-01

    Both numerical simulations and laboratory experiments have extensively studied the electron skin-depth scale structure of the electron diffusion layer, but neither have fully resolved both the scale-seperation and physics on scales between the Debye length and the skin-depth. Here, the first fully kinetic 2D simulations of anti-parallel magnetic reconnection at realistic electron temperatures (c /vthe = 64 and ?pe /?e = 32) are presented. Macroscopic features such as the reconnection rate or layer width are found to be insensitive to the electron temperature. When the electron temperature becomes sufficiently low, the electron diffusion layer becomes unstable to electrostatic instabilities involving multiple streaming populations near the X-line. This leads to multiple electron holes within the electron diffusion layer which interact non-linearly to generate turbulence which may be important in understanding the electron heating within the diffusion layer observed in experiments. Both numerical simulations and laboratory experiments have extensively studied the electron skin-depth scale structure of the electron diffusion layer, but neither have fully resolved both the scale-seperation and physics on scales between the Debye length and the skin-depth. Here, the first fully kinetic 2D simulations of anti-parallel magnetic reconnection at realistic electron temperatures (c /vthe = 64 and ?pe /?e = 32) are presented. Macroscopic features such as the reconnection rate or layer width are found to be insensitive to the electron temperature. When the electron temperature becomes sufficiently low, the electron diffusion layer becomes unstable to electrostatic instabilities involving multiple streaming populations near the X-line. This leads to multiple electron holes within the electron diffusion layer which interact non-linearly to generate turbulence which may be important in understanding the electron heating within the diffusion layer observed in experiments. This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the Center for Magnetic Self-Organization (CMSO).

  15. Design and construction of instruments for exciton diffusion characterization and for patterning of thin films

    E-print Network

    Mendoza, Hiroshi Antonio

    2012-01-01

    In this thesis the instruments explore two main aspects of organic optoelectronic devices. One instrument characterizes exciton diffusion and the other patterns organic thin films. Exciton diffusion characteristics are ...

  16. RIS-M-2361 DESCRIPTION OF THE RIS PUFF DIFFUSION MODEL

    E-print Network

    EMISSION MODEL; COMPUTERIZED SIMULATION; DIFFUSION; EARTH ATMOSPHERE; HEAT FLUX; METEOROLOGY; PLUMES modeled by a standard Guassian plume model which computes one- hour average plume characteristics for prediction and simulation of atmospheric pollutant diffusion. The model considers individual puffs

  17. Reaction-diffusion textures

    Microsoft Academic Search

    Andrew P. Witkin; Michael Kass

    1991-01-01

    We present a method for texture synthesis based on the simulation of a process of local nonlinear interaction, called reaction-diffusion, which has been proposed as a model of biological pattern formation. We extend traditional reaction-diffusion systems by allowing anisotropic and spatially non-uniform diffusion, as well as multiple competing directions of diffusion. We adapt reaction-diffusion system to the needs of computer

  18. Ultrastructural Characteristics of the Testis, Spermatogenesis and Taxonomic Values of Sperm Morphology in Male Ruditapes philippinarum in Western Korea

    PubMed Central

    Kim, Jin Hee; Chung, Jae Seung; Lee, Ki-Young

    2013-01-01

    Ultrastructural characteristics of the germ cells and accessory cells in testis during spermatogenesis and taxonomic values of mature sperm morphology of Ruditapes philippinarum were investigated by the transmission electron microscope and scanning electron microscope observations. The testis is the diffuse organ that consists of branching acini containing developing germ cells and accessory cells associated with spermatogenesis. The morphology of the spermatozoon is of the primitive type and is somewhat different to those of other bivalves. The morphologies of the sperm nucleus type and the acrosome shape of this species have a cylinderical type and a modified cone shape, respectively. As some ultrastructural characteristics of the acrosomal vesicle, the peripheral parts of two basal rings show electron opaque part, while the apex part of the acrosome shows electron lucent part. These characteristics of sperm belong to the family Veneridae in the subclass Heterodonta, unlike a characteristic of the subclass Pteriomorphia showing all part of the acrosome being composed of electron opaque part. In particular, a cylinder-like nucleus of the sperm is curved. The spermatozoon is approximately 48-51 ?m in length, including a long acrosome (about 2.40 ?m in length), a curved sperm nucleus (about 3.40 ?m in length), and a tail flagellum. The axoneme of the sperm tail shows a 9+2 structure. PMID:25949128

  19. Radon Diffusion Measurement in Polyethylene based on Alpha Detection

    SciTech Connect

    Rau, Wolfgang [Department of Physics, Queen's University Kingston, ON, K7L 3N6 (Canada)

    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.

  20. Variable focal length deformable mirror

    DOEpatents

    Headley, Daniel (Albuquerque, NM); Ramsey, Marc (Albuquerque, NM); Schwarz, Jens (Albuquerque, NM)

    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.

  1. Restricted diffusion in annular geometrical pores

    NASA Astrophysics Data System (ADS)

    Ghadirian, Bahman; Torres, Allan M.; Yadav, Nirbhay N.; Price, William S.

    2013-03-01

    Nuclear magnetic resonance (NMR) diffusion (including diffusion MRI) experiments are only as powerful as the models used to analyse the NMR diffusion data. A major problem, especially with measurements on biological systems, is that the existing models are only very poor approximations of cellular shape. Here, diffusion propagators and pulsed gradient spin-echo attenuation equations are derived in the short gradient pulse limit for diffusion within the annular region of a concentric cylinder of finite length and, similarly, within the annular region of a concentric sphere. The models include the possibility of relaxation at the boundaries and, in the case of the concentric cylinder, having the cylinder arbitrarily oriented with respect to the direction of the applied field gradient. The two models are also of interest due to their direct analogy to optical double slit diffraction. Also expressions for the mean square displacements, which are very useful information for determining the diffusion coefficient within these complex geometries, are obtained as well as for the limiting cases of diffusion on cylindrical and spherical shells and in a ring.

  2. Interferometric measurements of a dendritic growth front solutal diffusion layer

    NASA Technical Reports Server (NTRS)

    Hopkins, John A.; Mccay, T. D.; Mccay, Mary H.

    1991-01-01

    An experimental study was undertaken to measure solutal distributions in the diffusion layer produced during the vertical directional solidification (VDS) of an ammonium chloride - water (NH4Cl-H2O) solution. Interferometry was used to obtain concentration measurements in the 1-2 millimeter region defining the diffusion layer. These measurements were fitted to an exponential form to extract the characteristic diffusion parameter for various times after the start of solidification. The diffusion parameters are within the limits predicted by steady state theory and suggest that the effective solutal diffusivity is increasing as solidification progresses.

  3. Critical Length Limiting Superlow Friction

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Benassi, Andrea; Vanossi, Andrea; Urbakh, Michael

    2015-02-01

    Since the demonstration of superlow friction (superlubricity) in graphite at nanoscale, one of the main challenges in the field of nano- and micromechanics was to scale this phenomenon up. A key question to be addressed is to what extent superlubricity could persist, and what mechanisms could lead to its failure. Here, using an edge-driven Frenkel-Kontorova model, we establish a connection between the critical length above which superlubricity disappears and both intrinsic material properties and experimental parameters. A striking boost in dissipated energy with chain length emerges abruptly due to a high-friction stick-slip mechanism caused by deformation of the slider leading to a local commensuration with the substrate lattice. We derived a parameter-free analytical model for the critical length that is in excellent agreement with our numerical simulations. Our results provide a new perspective on friction and nanomanipulation and can serve as a theoretical basis for designing nanodevices with superlow friction, such as carbon nanotubes.

  4. Critical length limiting superlow friction.

    PubMed

    Ma, Ming; Benassi, Andrea; Vanossi, Andrea; Urbakh, Michael

    2015-02-01

    Since the demonstration of superlow friction (superlubricity) in graphite at nanoscale, one of the main challenges in the field of nano- and micromechanics was to scale this phenomenon up. A key question to be addressed is to what extent superlubricity could persist, and what mechanisms could lead to its failure. Here, using an edge-driven Frenkel-Kontorova model, we establish a connection between the critical length above which superlubricity disappears and both intrinsic material properties and experimental parameters. A striking boost in dissipated energy with chain length emerges abruptly due to a high-friction stick-slip mechanism caused by deformation of the slider leading to a local commensuration with the substrate lattice. We derived a parameter-free analytical model for the critical length that is in excellent agreement with our numerical simulations. Our results provide a new perspective on friction and nanomanipulation and can serve as a theoretical basis for designing nanodevices with superlow friction, such as carbon nanotubes. PMID:25699452

  5. 60 nm gate-length Si/SiGe HEMT

    NASA Astrophysics Data System (ADS)

    Kasamatsu, A.; Kasai, K.; Hikosaka, K.; Matsui, T.; Mimura, T.

    2004-03-01

    We fabricated n-channel Si/SiGe high electron mobility transistors (HEMTs) with a T-shaped Schottky-metal gate whose length was down to 60 nm. dc measurements showed that the 60 nm gate device had good pinch-off behavior, and its maximum transconductance was 156 mS/mm. RF measurements of the 60 nm gate device showed a current gain cutoff frequency of 52 GHz and a maximum oscillation frequency of 112 GHz. The gate-length dependence of the device characteristics was also discussed. The 60 nm gate is the shortest one ever reported so far for Si/SiGe HEMT.

  6. Self-aligned submicron gate length gallium arsenide MESFET

    E-print Network

    Huang, Hsien-Ching

    1987-01-01

    -type 4& Ohmic contact for n-type 4 Drii't velocity dependence on electric field for silicon and GaAs Central and satellite valleys in the conduction band of GaAs I-V characteristic snd electric field behavior in silicon MESFET. Sohd lines: no gate... reverse bias GaAs long gate length MESFET behavior in n-channel of electric field, electron drift velocity, carrier concentration, and mobility . GaAs short gate length MESFET behavior in n-channel of electron drift velocity for 40 KV/cm step Electron...

  7. Self-Diffusion of Symmetric Star Polymers

    NASA Astrophysics Data System (ADS)

    Frischknecht, Amalie; Milner, Scott T.

    2000-03-01

    We use a recent theory of arm retraction in star polymers, which successfully describes their distinctive rheology, to calculate the self-diffusion constant of symmetric stars. Star polymers can only take a diffusive step when an arm fully retracts to the center. Due to the wide separation of relaxation times along the star arms, star polymers obey dynamic dilution, in which the effective entanglement network dilutes as portions of the star arms relax. This implies a picture of self-diffusion in which the junction point hops a distance of order the dilated tube diameter ad associated with the diluted network, rather than a distance of order the original ``skinny'' tube diameter a0 defined by the entanglement molecular weight. The difference is substantial, since ad scales with arm length N as a_0N^2/7. However, comparing our results to self-diffusion data of Bartels et. al.,(C. R. Bartels, B. Crist, Jr., L. J. Fetters, and W. W. Graessley, Macromolecules 19), 785, 1986. we find that the data is more consistent with diffusive hops of a length scale a0 rather than a_d.

  8. Development of Yttrium Stabilized Zirconia (YSZ) diffusion barrier coatings for mitigation of Fuel-Cladding Chemical Interactions

    NASA Astrophysics Data System (ADS)

    Firouzdor, Vahid; Brechtl, Jamieson; Wilson, Lucas; Semerau, Brandon; Sridharan, Kumar; Allen, Todd R.

    2013-07-01

    Fuel-Cladding Chemical Interactions (FCCIs) in a nuclear reactor occurs due to thermal and radiation enhanced inter-diffusion between the cladding and fuel materials. This can have the detrimental effects of reducing the effective cladding wall thickness and the formation of low melting point eutectic compounds. Deposition of thin diffusion barrier coatings in the inner surface of the cladding can potentially reduce or delay the onset of FCCI. This study examines the feasibility of using nanofluid-based electrophoretic deposition (EPD) process to deposit coatings of Yttrium Stabilized Zirconia (YSZ) as the diffusion barrier coating. The deposition parameters, including the nanofluid solvent, additive, particle size, current, and voltage were optimized using test flat substrates of T91 ferritic-martensitic steel. A post deposition sintering step was also conducted and optimized to improve the bonding and mechanical integrity of the coating. Diffusion characteristics of the coatings were investigated by diffusion couple experiments using cerium as a fuel fission product responsible for solid state FCCI. These diffusion couple studies performed at 575 °C for 100 h showed that the YSZ coatings significantly reduced the solid state inter-diffusion between cerium and steel. A heat transfer model was developed to simulate the changes in temperature profile inside the fuel cladding by addition of YSZ coating. It was found that even though the temperature can increase in the coated cladding, the temperature falls below the melting point of uranium and eutectic temperature in Fe-U phase diagram. Using a co-axial configuration in conjunction with the EPD process, YSZ was successfully deposited uniformly on the inner surfaces of 12? length sections of cladding with 4 mm inner diameter. Such a coating is extremely hard to make by conventional coating technologies like thermal spray or vapor deposition.

  9. Diffusion Confusion 8 4 Problem set #4: Fun with diffusion

    E-print Network

    Spiegelman, Marc W.

    Diffusion Confusion 8 4 Problem set #4: Fun with diffusion Today's thrill packed exercise will be to deal with diffusion and advection-diffusion in one dimension. All exercises here will be in Matlab-nicolson diffusion of a gaussian initial condition with dirichlet boundary conditions (Diffusion/diffusion cn

  10. Temperature dependence of the length scale for cooperative motion in glass-forming liquids

    NASA Astrophysics Data System (ADS)

    Erwin, Brian M.

    When considered in the framework of a dynamic scaling model, the length scale of cooperative motion of all glass-forming liquids appears to have a universal temperature dependence. This model also predicts relaxation times with a system specific temperature dependence, as the product of the universal cooperative length scale raised to the sixth power and a non-universal thermally activated process. This model was successfully applied to over 49 glass-forming liquids, including 14 novel indane-based glasses. Rotational dynamics and translational diffusion of small anisotropic molecular probes are used to estimate the length scale of cooperative motion in a model-independent manner for five glass-formers. This length scale agrees quantitatively with the length scale obtained in 4-D NMR experiments which is known to measure the size of the slow relaxing regions. Temperature dependence of self-diffusion, dielectric alpha-relaxation time and viscosity each provide model-dependent length scales that are proportional to the cooperative length scale utilized by the dynamic scaling model. Each of these methods are self consistent and collectively prove that the cooperative length grows as temperature is lowered below the "caging" temperature TA, below which dynamics are cooperative in nature. This length appears to diverge at a temperature 10-20 K below the glass transition temperature T g for fragile glass-formers. Employing the tested framework of dynamic scaling, the cooperative lengths at Tg and TA are estimated for three molecular glass-formers and three polymeric glass-formers. At TA, the cooperative length for molecular glass-formers is found to be approximately the van der Waals radius of the molecule. Assuming this result to be general, the cooperative length at Tg for fifteen other glass-forming liquids is estimated, resulting in the conclusion that 2 nm ? xi(Tg) ? 10 nm.

  11. Length-dependent dynamics of microtubules

    E-print Network

    Vandana Yadav; Sutapa Mukherji

    2012-04-02

    Certain regulatory proteins influence the polymerization dynamics of microtubules by inducing catastrophe with a rate that depends on the microtubule length. Using a discrete formulation, here we show that, for a catastrophe rate proportional to the microtubule length, the steady-state probability distributions of length decay much faster with length than an exponential decay as seen in the absence of these proteins.

  12. Length-dependent dynamics of microtubules

    E-print Network

    Yadav, Vandana

    2012-01-01

    Certain regulatory proteins influence the polymerization dynamics of microtubules by inducing catastrophe with a rate that depends on the microtubule length. Using a discrete formulation, here we show that, for a catastrophe rate proportional to the microtubule length, the steady-state probability distributions of length decay much faster with length than an exponential decay as seen in the absence of these proteins.

  13. Collision avoidance analysis for transition taper length

    Microsoft Academic Search

    Jinxian Weng

    2011-01-01

    Transition taper length plays a vitally important role in work zone safety operations because too short a transition taper length will result in higher accident risks and too long a transition taper length could increase traffic delay. This paper evaluates transition taper length under various traffic conditions and road geometries using collision avoidance analysis. The longitudinal distances for lane changing

  14. Real-Valued Semigroups and (Causal) Diffusion

    SciTech Connect

    Kowar, Richard [Department of Mathematics, University of Innsbruck, Technikerstrasse 21a/2, A-6020, Innsbruck (Austria)

    2011-09-22

    It can be shown that a process modeled by a strongly continuous real-valued semigroup (that has a space convolution operator as infinitesimal generator) cannot satisfy causality. By causality we mean that a characteristic feature of a process like an interface or a front must propagate with a finite speed. We present and discuss a causal model of diffusion that satisfies the semigroup property at a discrete set of time instants M:={l_brace}m{tau}|m is an element of N{sub 0}{r_brace} and that in contrast to the classical diffusion model is not smooth. More precisely, if v denotes the concentration of a substance diffusing with constant speed, then v is continuous but its time derivative is discontinuous at the discrete set M of time instants. It is this property of (causal) diffusion that forbids the classical limit procedure {tau}{yields}0 that leads to the noncausal diffusion model in Stochastics. Finally, we give two explanations why in some cases the discretization of the noncausal diffusion model can be considered as an approximation of the causal diffusion model. In particular, we present an inhomogeneous wave equation with a time dependent coefficient that is satisfied by causal diffusion.

  15. Riemann equation for prime number diffusion.

    PubMed

    Chen, Wen; Liang, Yingjie

    2015-05-01

    This study makes the first attempt to propose the Riemann diffusion equation to describe in a manner of partial differential equation and interpret in physics of diffusion the classical Riemann method for prime number distribution. The analytical solution of this equation is the well-known Riemann representation. The diffusion coefficient is dependent on natural number, a kind of position-dependent diffusivity diffusion. We find that the diffusion coefficient of the Riemann diffusion equation is nearly a straight line having a slope 0.99734 in the double-logarithmic axis. Consequently, an approximate solution of the Riemann diffusion equation is obtained, which agrees well with the Riemann representation in predicting the prime number distribution. Moreover, we interpret the scale-free property of prime number distribution via a power law function with 1.0169 the scale-free exponent in respect to logarithmic transform of the natural number, and then the fractal characteristic of prime number distribution is disclosed. PMID:26026319

  16. Sex Ratio, Fecundity, and Models Predicting Length at Sexual Maturity of Redband Trout in Idaho Desert Streams

    Microsoft Academic Search

    Daniel J. Schill; George W. LaBar; Elizabeth R. J. M. Mamer; Kevin A. Meyer

    2010-01-01

    Factors affecting length at maturity and other important reproductive characteristics have not been investigated for Idaho redband trout Oncorhynchus mykiss gairdneri residing in desert streams. Prespawning redband trout were collected from nine streams, and estimates of length at sexual maturity, median age at maturity, sex ratio, and fecundity were developed along with models predicting length at maturity from physical stream

  17. Measurement of Diffusion in Entangled Rod-Coil Triblock Copolymers

    NASA Astrophysics Data System (ADS)

    Olsen, B. D.; Wang, M.

    2012-02-01

    Although rod-coil block copolymers have attracted increasing attention for functional nanomaterials, their dynamics relevant to self-assembly and processing have not been widely investigated. Because the rod and coil blocks have different reptation behavior and persistence lengths, the mechanism by which block copolymers will diffuse is unclear. In order to understand the effect of the rigid block on reptation, tracer diffusion of a coil-rod-coil block copolymer through an entangled coil polymer matrix was experimentally measured. A monodisperse, high molecular weight coil-rod-coil triblock was synthesized using artificial protein engineering to prepare the helical rod and bioconjugaiton of poly(ethylene glycol) coils to produce the final triblock. Diffusion measurements were performed using Forced Rayleigh scattering (FRS), at varying ratios of the rod length to entanglement length, where genetic engineering is used to control the protein rod length and the polymer matrix concentration controls the entanglement length. As compared to PEO homopolymer tracers, the coil-rod-coil triblocks show markedly slower diffusion, suggesting that the mismatch between rod and coil reptation mechanisms results in hindered diffusion of these molecules in the entangled state.

  18. Simulating dislocation loop internal dynamics and collective diffusion using stochastic differential equations

    SciTech Connect

    Derlet, P. M.; Gilbert, M. R.; Dudarev, S. L. [Condensed Matter Theory Group, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); EURATOM/CCFE Fusion Association, Culham Centre for Fusion Energy, Oxfordshire OX14 3DB (United Kingdom)

    2011-10-01

    Nanoscale prismatic loops are modeled via a partial stochastic differential equation that describes an overdamped continuum elastic string, with a view to describing both the internal and collective dynamics of the loop as a function of temperature. Within the framework of the Langevin equation, expressions are derived that relate the empirical parameters of the model, the friction per unit length, and the elastic stiffness per unit length, to observables that can be obtained directly via molecular-dynamics simulations of interstitial or vacancy prismatic loop mobility. The resulting expressions naturally exhibit the properties that the collective diffusion coefficient of the loop (i) scales inversely with the square root of the number of interstitials, a feature that has been observed in both atomistic simulation and in situ TEM investigations of loop mobility, and (ii) the collective diffusion coefficient is not at all dependent on the internal interactions within the loop, thus qualitatively rationalizing past simulation results showing that the characteristic migration energy barrier is comparable to that of a single interstitial, and cluster migration is a result of individual (but correlated) interstitial activity.

  19. Microfabricated diffusion source

    DOEpatents

    Oborny, Michael C. (Albuquerque, NM); Frye-Mason, Gregory C. (Cedar Crest, NM); Manginell, Ronald P. (Albuquerque, NM)

    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.

  20. Effect of ion-chelating chain lengths in thiophene-based monomers on in situ photoelectrochemical polymerization and photovoltaic performances.

    PubMed

    Song, In Young; Kim, Minjun; Park, Taiho

    2015-06-01

    We synthesized thiophene-based monomers (bis-EDOTs) with different ethylene glycol oligomer (EGO) lengths (TBO3, TBO4, and TBO5) and investigated their polymerization characteristics during photoelectrochemical polymerization (PEP) at the surfaces of dye (D205)-sensitized TiO2 nanocrystalline particles. During the PEP reaction, monomers were expected to diffuse toward neighboring dyes through the growing polymer layers to enable continuous chain growth. We found that the less bulky monomer (TBO3) formed a more compact polymer layer with a high molecular weight. Its diffusion to the active sites through the resulting growing polymer layer was, therefore, limited. We deployed layers of the polymers (PTBO3, PTBO4, and PTBO5) in iodine-free solid-state hybrid solar cells to investigate the lithium ion chelating properties of the polymers as a function of the number of oxygen atoms present in the EGOs. PTBO4 and PTBO5 were capable of chelating lithium ions, yielding a photovoltaic performance that was 142% of the performance obtained without the polymer layers (3.0 ? 5.2%). PMID:25977990

  1. Transport relaxation time and length scales in turbulent suspensions

    E-print Network

    P. Claudin; F. Charru; B. Andreotti

    2010-11-03

    We show that in a turbulent flow transporting suspended sediment, the unsaturated sediment flux $q(x,t)$ can be described by a first-order relaxation equation. From a mode analysis of the advection-diffusion equation for the particle concentration, the relaxation length and time scales of the dominant mode are shown to be the deposition length $H U/V_{\\rm fall}$ and deposition time $H/V_{\\rm fall}$, where $H$ is the flow depth, $U$ the mean flow velocity and $V_{\\rm fall}$ the sediment settling velocity. This result is expected to be particularly relevant for the case of sediment transport in slowly varying flows, where the flux is never far from saturation. Predictions are shown to be in quantitative agreement with flume experiments, for both net erosion and net deposition situations.

  2. 7—THE CSIRO STAPLE STRENGTH\\/LENGTH SYSTEM PART I: DESIGN AND PERFORMANCE

    Microsoft Academic Search

    R. N. Caffin

    1980-01-01

    A description is given of the CSIRO Staple Strength\\/Length system, developed to provide measurements of staple strength and length as an aid to predicting processing performance from greasy-wool characteristics. The general design principles are presented, together with a discussion ot the system performance and some typical results.

  3. SOME GOOD ORTHOGONAL BIPOLAR SPREADING SEQUENCES OF LENGTHS 12 AND 20

    E-print Network

    Seberry, Jennifer

    SOME GOOD ORTHOGONAL BIPOLAR SPREADING SEQUENCES OF LENGTHS 12 AND 20 Jennifer Seberry, Beata J characteristics of the orthogonal bipolar spreading sequences of lengths 12 and 20. The orthogonal bipolar In [4], Lipski and Marek indicated that there is a common expectation that bipolar orthogonal (Hadamard

  4. Measurement of MODIS optics effective focal length, distortion, and modulation transfer function

    NASA Astrophysics Data System (ADS)

    Thurlow, Paul E.; Cline, Richard W.

    1993-08-01

    A combination MODIS optics characteristics, short back focal length, and relatively distorting optics, has required major revisions in techniques used earlier to characterize effective focal length (EFL) and modulation transfer function (MTF) in the thematic mapper (TM) project. This paper compares measurement approaches used to characterize TM optics and revised methodology intended to characterize MODIS optics at an integration and assembly level.

  5. Thermal Diffusivity of Quartz and its Relation to Structure

    NASA Astrophysics Data System (ADS)

    Hoefer, M.; Schilling, F. R.

    2001-12-01

    Thermal transport properties of minerals are fundamental for an understanding of heat transport in rocks and they are a prerequisite to model temperature distribution within the Earth. Besides its significance for crustal rocks, quartz and its physical properties are of interest in material science. Beyond that, quartz is of elementary importance due to its unique physical behavior, especially during low to high transformation. Quartz is characterized by a high anisotropy in thermal expansion, sound velocity, and thermal diffusivity. During the phase transition from low to high quartz the physical properties vary non-linearly, whereas sound velocity shows a distingued minimum, and average Poisson's ratio becomes negative. Moreover, quartz shows the highest thermal diffusivity and strongest temperature dependence of all silicates. Thermal diffusivity a and thermal conductivity l are interrelated by {l = cP ? a}. Thermal diffusivity can be expressed by mean phonon (sound) velocity v and mean free path length l by a = 1/3 v l. By combining measured phononic velocity and thermal diffusivity the structure dependent mean free path length can be revealed. To determine thermal diffusivity of quartz especially during the low to high transition in the a- and c-direction we used a high precision transient technique (Schilling 1999) with high temperature resolution up to 800\\deg C. For temperatures below 500 \\deg C a pronounced 1/T dependence of thermal diffusivity is observed and is highest in the c-direction. A minimum in thermal diffusivity is observed during the phase transition. Above the transition thermal diffusivity increases and the highest diffusivity is observed in the a-direction. A similar cross over is observed for the maximum phononic velocity. Between 500\\deg and 800\\deg C velocity and thermal diffusivity show similar behavior. No significant contribution of radiative heat transport is detectable over the examined temperature range. The thermal diffusivity behavior up to 500\\deg C is dominated by an increase in phonon-phonon-interactions. Above 500\\deg C the mean free path length of phonons remains nearly constant. All three, the maximum mean free path length, the maximum in velocity, and the maximum in thermal diffusivity are observed in the same direction. A model will be presented, which interrelates sound velocity and mean free path length, describing the observed behavior. Financial support from the DFG is gratefully acknowledged. Schilling F.R., (1999) EJM, 11, 1115-1124

  6. Diffusion on spatial network

    NASA Astrophysics Data System (ADS)

    Hui, Zi; Tang, Xiaoyue; Li, Wei; Greneche, Jean-Marc; Wang, Qiuping A.

    2015-04-01

    In this work, we study the problem of diffusing a product (idea, opinion, disease etc.) among agents on spatial network. The network is constructed by random addition of nodes on the planar. The probability for a previous node to be connected to the new one is inversely proportional to their spatial distance to the power of ?. The diffusion rate between two connected nodes is inversely proportional to their spatial distance to the power of ? as well. Inspired from the Fick's first law, we introduce the diffusion coefficient to measure the diffusion ability of the spatial network. Using both theoretical analysis and Monte Carlo simulation, we get the fact that the diffusion coefficient always decreases with the increasing of parameter ? and ?, and the diffusion sub-coefficient follows the power-law of the spatial distance with exponent equals to -?-?+2. Since both short-range diffusion and long-range diffusion exist, we use anomalous diffusion method in diffusion process. We get the fact that the slope index ? in anomalous diffusion is always smaller that 1. The diffusion process in our model is sub-diffusion.

  7. Tracer diffusion inside fibrinogen layers

    NASA Astrophysics Data System (ADS)

    Cie?la, Micha?; Gudowska-Nowak, Ewa; Sagués, Francesc; Sokolov, Igor M.

    2014-01-01

    We investigate the obstructed motion of tracer (test) particles in crowded environments by carrying simulations of two-dimensional Gaussian random walk in model fibrinogen monolayers of different orientational ordering. The fibrinogen molecules are significantly anisotropic and therefore they can form structures where orientational ordering, similar to the one observed in nematic liquid crystals, appears. The work focuses on the dependence between level of the orientational order (degree of environmental crowding) of fibrinogen molecules inside a layer and non-Fickian character of the diffusion process of spherical tracer particles moving within the domain. It is shown that in general particles motion is subdiffusive and strongly anisotropic, and its characteristic features significantly change with the orientational order parameter, concentration of fibrinogens, and radius of a diffusing probe.

  8. Anomalous diffusion dynamics of associating artificial proteins in hydrogels

    NASA Astrophysics Data System (ADS)

    Tang, Shengchang; Wang, Muzhou; Olsen, Bradley

    2015-03-01

    Associative polymer gels have attracted a great deal of interest as responsive materials and biomaterials; while a great deal is known about their mechanical properties, knowledge about self-diffusion in these materials is still limited. Using coiled-coil proteins as a model associative polymer system where the number of stickers per polymer and molar mass of chains between stickers are exactly defined, we investigate self-diffusion in associative polymer hydrogels using forced Rayleigh scattering on the length scales ranging from 0.3 to 50 ?m. Although the presence of associative groups reduces the rate of diffusion, ``superdiffusive'' scaling is observed for the first time up to a length scale of 10 ?m. Fickian diffusion is recovered at larger length scales. The anomalous diffusion strongly depends on the temperature and the hydrogel concentration. We propose a simple two state model to capture the interplay between the diffusion of the proteins and the association of the coiled-coil segments. The model is able to capture both the anomalous regime and the Fickian regime, and provides estimation of the apparent diffusivities and the dissociation rates of the coiled-coil domains.

  9. Dependence of Ion Dynamics on the Polymer Chain Length in Poly(ethylene oxide)-Based Polymer Electrolytes.

    PubMed

    Chattoraj, Joyjit; Knappe, Marisa; Heuer, Andreas

    2015-06-01

    It is known from experiments that in the polymer electrolyte system, which contains poly(ethylene oxide) chains (PEO), lithium-cations (Li(+)), and bis(trifluoromethanesulfonyl)imide-anions (TFSI(-)), the cation and the anion diffusion and the ionic conductivity exhibit a similar chain-length dependence: with increasing chain length, they start dropping steadily, and later, they saturate to constant values. These results are surprising because Li-cations are strongly correlated with the polymer chains, whereas TFSI-anions do not have such bonding. To understand this phenomenon, we perform molecular dynamics simulations of this system for four different polymer chain lengths. The diffusion results obtained from our simulations display excellent agreement with the experimental data. The cation transport model based on the Rouse dynamics can successfully quantify the Li-diffusion results, which correlates Li diffusion with the polymer center-of-mass motion and the polymer segmental motion. The ionic conductivity as a function of the chain length is then estimated based on the chain-length-dependent ion diffusion, which shows a temperature-dependent deviation for short chain lengths. We argue that in the first regime, counterion correlations modify the conductivity, whereas for the long chains, the system behaves as a strong electrolyte. PMID:25965904

  10. Critical Waves and the Length Problem of Biology

    E-print Network

    R. B. Laughlin

    2015-04-17

    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 substances. Min oscillations in E. coli are cited as precedent resonant length measurement using chemical potential waves analogous to laser detection. Mitotic structures in eucaryotes 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. PNAS Significance Statement: This paper invokes physical principles to address the question of how living things might use reaction-diffusion to measure out and regulate the many thousands of lengths required to make their body parts and internal organs. It argues that two ideas have been missing. One is that oscillation is necessary to achieve the necessary design stability and plasticity. The other is that the system must be tuned to criticality to stabilize the propagation velocity, thus enabling clocks to function as meter sticks. The broader significance is twofold: First, a fundamental piece of the machinery of life is probably invisible to present-day biochemical methods because they are too slow. Second, the simplicity of growth and form identified a century ago by D'Arcy Thompson is probably a symptom of biological engineering strategies, not primitive law.

  11. Length-Controlled Elasticity in 3D Fiber Networks

    E-print Network

    C. P. Broedersz; M. Sheinman; F. C. MacKintosh

    2011-08-22

    We present a model for disordered 3D fiber networks to study their linear and nonlinear elasticity over a wide range of network densities and fiber lengths. In contrast to previous 2D models, these 3D networks with binary cross-links are under-constrained with respect to fiber stretching elasticity, suggesting that bending may dominate their response. We find that such networks exhibit a fiber length-controlled bending regime and a crossover to a stretch-dominated regime for lengths beyond a characteristic scale that depends on the fiber's elastic properties. Finally, by extending the model to the nonlinear regime, we show that these networks become intrinsically nonlinear with a vanishing linear response regime in the limit of floppy or long filaments.

  12. Length control of microtubules by depolymerizing motor proteins

    E-print Network

    Bindu S. Govindan; Manoj Gopalakrishnan; Debashish Chowdhury

    2008-07-08

    In many intracellular processes, the length distribution of microtubules is controlled by depolymerizing motor proteins. Experiments have shown that, following non-specific binding to the surface of a microtubule, depolymerizers are transported to the microtubule tip(s) by diffusion or directed walk and, then, depolymerize the microtubule from the tip(s) after accumulating there. We develop a quantitative model to study the depolymerizing action of such a generic motor protein, and its possible effects on the length distribution of microtubules. We show that, when the motor protein concentration in solution exceeds a critical value, a steady state is reached where the length distribution is, in general, non-monotonic with a single peak. However, for highly processive motors and large motor densities, this distribution effectively becomes an exponential decay. Our findings suggest that such motor proteins may be selectively used by the cell to ensure precise control of MT lengths. The model is also used to analyze experimental observations of motor-induced depolymerization.

  13. Characteristics of Yerevan High Transparency Scintillators

    SciTech Connect

    Zorn, Carl; Asryan, Gegham; Egiyan, Kim; Tarverdyan, M.; Amaryan, Moscov; Amaryan, Moskov; Demirchyan, Raphael; Stepanyan, Stepan; Burkert, Volker; Sharabian, Youri

    1992-08-01

    Optical transmission, light output and time characteristics are given for long scintillator strips fabricated at the Yerevan Physics Institute using the extrusion method. It is shown that at 45% relative (to anthracene) light output, good transmission (2.5/2.9 m attenuation length with photomultiplier direct readout and 3/3.5 m attenuation length fiber readout) and time characteristics (average decay time 2.8 nsec) were obtained.

  14. 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)

  15. Abstract--Hybrid diffusion imaging (HYDI) is a new diffusion MRI method for characterizing complex diffusion.

    E-print Network

    Bucci, David J.

    Abstract-- Hybrid diffusion imaging (HYDI) is a new diffusion MRI method for characterizing complex diffusion. Diffusion-weighted measurements are obtained on multiple `shells' of constant diffusion weighting. This diffusion encoding approach is amenable to multiple types of diffusion imaging analysis. The inner shells

  16. Characteristics of the Martian atmosphere surface layer

    NASA Technical Reports Server (NTRS)

    Clow, G. D.; Haberle, R. M.

    1990-01-01

    Elements of various terrestrial boundary layer models are extended to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian atmospheric surface ('constant flux') layer. The atmospheric surface layer consists of an interfacial sublayer immediately adjacent to the ground and an overlying fully turbulent surface sublayer where wind-shear production of turbulence dominates buoyancy production. Within the interfacial sublayer, sensible and latent heat are transported by non-steady molecular diffusion into small-scale eddies which intermittently burst through this zone. Both the thickness of the interfacial sublayer and the characteristics of the turbulent eddies penetrating through it depend on whether airflow is aerodynamically smooth or aerodynamically rough, as determined by the Roughness Reynold's number. Within the overlying surface sublayer, similarity theory can be used to express the mean vertical windspeed, temperature, and water vapor profiles in terms of a single parameter, the Monin-Obukhov stability parameter. To estimate the molecular viscosity and thermal conductivity of a CO2-H2O gas mixture under Martian conditions, parameterizations were developed using data from the TPRC Data Series and the first-order Chapman-Cowling expressions; the required collision integrals were approximated using the Lenard-Jones potential. Parameterizations for specific heat and binary diffusivity were also determined. The Brutsart model for sensible and latent heat transport within the interfacial sublayer for both aerodynamically smooth and rough airflow was experimentally tested under similar conditions, validating its application to Martian conditions. For the surface sublayer, the definition of the Monin-Obukhov length was modified to properly account for the buoyancy forces arising from water vapor gradients in the Martian atmospheric boundary layer. It was found that under most Martian conditions, the interfacial and surface sublayers offer roughly comparable resistance to sensible heat and water vapor transport and are thus both important in determining the associated fluxes.

  17. Narrow groove welding gas diffuser assembly and welding torch

    DOEpatents

    Rooney, Stephen J. (East Berne, NY)

    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.

  18. UPDATING APPLIED DIFFUSION MODELS

    EPA Science Inventory

    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 Socie...

  19. Quantifying transport within a porous medium over a hierarchy of length scales

    NASA Astrophysics Data System (ADS)

    Holland, D. J.; Scheven, U. M.; Middelberg, A. P. J.; Gladden, L. F.

    2006-03-01

    Magnetic resonance techniques are used to probe transport within a porous medium over length scales of microns to centimeters. In particular, the apparent discrepancy between estimates of dispersion within porous media determined by pulsed field gradient magnetic resonance techniques and a conventional elution analysis is addressed. The model porous medium considered is a packed bed of height and internal diameter 22.5 and 16.8mm, respectively, packed with highly porous cross-linked dextran particles approximately 50?m in diameter. Experiments were performed for Peclet numbers in the range 1diffusion coefficient [(2.8±0.2)×10-10m2s-1], and characteristic time, Te, for exchange between the intra- and interparticle pore space (˜300ms). The value of porosity was in excellent agreement with that obtained by elution analysis. However, values of the axial dispersion coefficient obtained using the two approaches did not agree well. For example, at Pe =1.1, the dispersion coefficients measured by APGTSE NMR and elution analysis were (1.6±0.1)×10-9m2s-1 and (1.8±0.2)×10-8m2s-1, respectively. These results suggest that whilst the micro-/mesolength scale properties of the porous medium are well characterized using the APGSTE NMR measurement, the technique is unable to probe the millimeter length scales in the bed over which heterogeneities in the flow may exist and therefore contribute significantly to the macroscopic dispersion characteristic of the bed, as determined by elution analysis. This is confirmed by demonstrating that the contribution of mechanical mixing to dispersion within the porous medium extends to the longest time scales studied (>6Te). To identify the dominant influences on the macroscopic dispersion characteristics of the porous medium, magnetic resonance flow velocity images within the packed bed were acquired. Numerical reconstructions of the residence time distribution of the fluid within the bed using these data yielded a value of the dispersion coefficient of (0.8±0.4)×10-8m2s-1, in far better agreement with the elution analysis, thereby demonstrating that it is the millimeter-scale heterogeneity in the flow field within the bed that is the dominant contribution to the macroscopic dispersion. Extension of the model to incorporate the effect of maldistribution of the input pulse further improves agreement with the elution analysis.

  20. 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.

  1. Pb diffusion in zircon

    Microsoft Academic Search

    D. J Cherniak; E. B Watson

    2001-01-01

    Diffusion of Pb was characterized in natural and synthetic zircon under a range of conditions. In most experiments, mixtures of Pb sulfate and ground zircon were used as the sources of diffusant, with Pb depth profiles measured with Rutherford Backscattering Spectrometry (RBS). As complement to these “in-diffusion” experiments, “out-diffusion” experiments were run on both synthetic Pb-doped and natural zircon with

  2. Polymer Diffusion in the Presence of Nanoparticles

    NASA Astrophysics Data System (ADS)

    Winey, Karen

    2014-03-01

    The center-of-mass diffusion of polymers within a polymer melt proceeds by the mechanism of reptation wherein the polymer is confined to a tube that is defined by neighboring entanglements and moves along its contour. Polymer diffusion is perturbed when the melt contains nanoparticles that are comparable in size to the radius of gyration (Rg) of the polymers. Within this talk, we will present tracer diffusion coefficients (D) results for three types of nanocomposite: spherical nanoparticles with surface functionalization, spherical nanoparticles with brushes, and cylindrical nanoparticles (aspect ratio = 5 to 50). When functionalized spherical nanoparticles have neutral or attractive interactions with the polymer matrix, a monotonic decrease in the diffusion coefficient is observed across a wide range of polymer molecular weight, nanoparticle size, and nanoparticle concentration. These data collapse onto a master curve when plotted as D normalized by the diffusion coefficient into a neat homopolymer (D/Do) versus our confinement parameter defined as the interparticle distance divided by 2Rg (ID/2Rg). Polymer diffusion in systems with grafted spherical nanoparticles exhibit the same D/Do versus ID/2Rg, when ID accounts for the extent to which the tracer polymer penetrates the polymer brush. For various cylindrical nanoparticles D/Do versus nanoparticle concentration exhibits a minimum when 2Rg is both larger than the nanoparticle diameter and smaller than the nanoparticle length. Complimentary molecular dynamics simulations and neutron scattering results will also be presented.

  3. Crystalline Bis-urea Nanochannel Architectures Tailored for Single-File Diffusion Studies.

    PubMed

    Bowers, Clifford R; Dvoyashkin, Muslim; Salpage, Sahan R; Akel, Christopher; Bhase, Hrishi; Geer, Michael F; Shimizu, Linda S

    2015-06-23

    Urea is a versatile building block that can be modified to self-assemble into a multitude of structures. One-dimensional nanochannels with zigzag architecture and cross-sectional dimensions of only ?3.7 Å × 4.8 Å are formed by the columnar assembly of phenyl ether bis-urea macrocycles. Nanochannels formed by phenylethynylene bis-urea macrocycles have a round cross-section with a diameter of ?9.0 Å. This work compares the Xe atom packing and diffusion inside the crystalline channels of these two bis-ureas using hyperpolarized Xe-129 NMR. The elliptical channel structure of the phenyl ether bis-urea macrocycle produces a Xe-129 powder pattern line shape characteristic of an asymmetric chemical shift tensor with shifts extending to well over 300 ppm with respect to the bulk gas, reflecting extreme confinement of the Xe atom. The wider channels formed by phenylethynylene bis-urea, in contrast, present an isotropic dynamically average electronic environment. Completely different diffusion dynamics are revealed in the two bis-ureas using hyperpolarized spin-tracer exchange NMR. Thus, a simple replacement of phenyl ether with phenylethynylene as the rigid linker unit results in a transition from single-file to Fickian diffusion dynamics. Self-assembled bis-urea macrocycles are found to be highly suitable materials for fundamental molecular transport studies on micrometer length scales. PMID:26035000

  4. An Autocatalytic Model for the - Diffusion of Educational Innovations

    Microsoft Academic Search

    Stephen B. Lawton; William H. Lawton

    1979-01-01

    The spread of educational innovations is a topic that has been investi gated from a multitude of viewpoints. Some individuals have been interested in dissemination of particular practices or products; others have studied the diffusion process itself; and still others have focused on the adopters, their characteristics and motivations. This paper is in the tradition of diffusion research, but it

  5. 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)

  6. CT and MRI of diffuse liver disease

    Microsoft Academic Search

    Neil M Rofsky; Haskel Fleishaker

    1995-01-01

    CT and MRI contribute important information to the clinical evaluation of diffuse liver disease. In some cases, these modalities can establish a diagnosis that was not ascertained histologically, which is often the case when sampling errors prevent a definitive tissue diagnosis. Characteristic alterations of liver attenuation on CT, signal changes on MRI, and morphological changes appreciated with both modalities can

  7. Roll diffusion bonding of titanium alloy panels

    NASA Technical Reports Server (NTRS)

    Bennett, J.; De Witt, T. E.; Jones, A. G.; Koeller, F.; Muser, C.

    1968-01-01

    Roll diffusion bonding technique is used for fabricating T-stiffened panel assemblies from titanium alloy. The single unit fabrication exhibits excellent strength characteristics under tensile and compressive loads. This program is applied to structures in which weight/strength ratio and integral construction are important considerations.

  8. Diffusing-wave spectroscopy of flows

    Microsoft Academic Search

    Serguei E. Skipetrov; Sergei S. Chesnokov; Igor V. Meglinsky; Valery V. Tuchin

    1999-01-01

    The technique of diffusing-wave spectroscopy (DWS) consists in deriving properties of random multiple-scattering media from measurements of the temporal autocorrelation function of scattered intensity. Both the characteristics of light- scattering particles (size, absorption and scattering coefficients, etc.) and the macroscopic dynamic structure of the sample may be studied by means of DWS. The technique has a considerable potential for application

  9. Mechanisms of countergradient diffusion in turbulent combustion

    NASA Astrophysics Data System (ADS)

    Yoshizawa, Akira; Fujiwara, Hitoshi; Abe, Hiroyuki; Matsuo, Yuichi

    2009-01-01

    The mechanism of countergradient diffusion of chemical species and heat in turbulent combustion is sought with the aid of the results by the two-scale direct-interaction approximation. The deviation of the Reynolds stress and the turbulent fluxes of chemical species, heat, and mass from their gradient-diffusion representations is related to the Lagrange derivatives of mean velocity and scalars. Their relative magnitude to the gradient-diffusion parts paves the way for explaining the countergradient diffusion. Towards engineering applications, these theoretical findings are converted to a Reynolds-averaged model. It consists of a closed system of equations for the mean density, the mean velocity, the mean internal energy, and the mean scalar, with the turbulence equations for the kinetic energy and its dissipation rate supplemented. This system is tested in a turbulent premixed flame and is shown to reproduce some of the characteristics pointed out by the direct numerical simulation.

  10. Free path lengths in quasicrystals

    E-print Network

    Jens Marklof; Andreas Strömbergsson

    2013-04-07

    Previous studies of kinetic transport in the Lorentz gas have been limited to cases where the scatterers are distributed at random (e.g. at the points of a spatial Poisson process) or at the vertices of a Euclidean lattice. In the present paper we investigate quasicrystalline scatterer configurations, which are non-periodic, yet strongly correlated. A famous example is the vertex set of the Penrose tiling. Our main result proves the existence of a limit distribution of the free path length, which answers a question of Wennberg. The limit distribution is characterised by a certain random variable on the space of higher dimensional lattices, and is distinctly different from the exponential distribution observed for random scatterer configurations. The key ingredients in the proofs are equidistribution theorems on homogeneous spaces, which follow from Ratner's measure classification.

  11. 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.

  12. Thermoacoustic optical path length stabilization in a single-mode optical fiber.

    PubMed

    Lewoczko-Adamczyk, Wojciech; Schiemangk, Max; Müller, Holger; Peters, Achim

    2009-02-01

    We present a simple technique to actively stabilize the optical path length in an optical fiber. A part of the fiber is coated with a thin, electrically conductive layer, which acts as a heater. The optical path length is thus modified by temperature-dependent changes in the refractive index and the mechanical length of the fiber. For the first time, we measure the dynamic response of the optical path length to the periodic changes of temperature and find it to be in agreement with our former theoretical prediction. The fiber's response to the temperature changes is determined by the speed of sound in quartz rather than by slow thermal diffusion. Making use of this fact, we succeeded in actively stabilizing the optical path length with a closed-loop bandwidth of 3.8 kHz. PMID:19183596

  13. Diffusion in heterogeneous media

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Liu, L.

    2012-12-01

    Diffusion in heterogeneous media has been investigated for over forty years. However, the fundamental equations for bulk (effective) diffusivity in multi-phase systems were incorrect because of the use of an inappropriate similarity between diffusion and other physical properties such as thermal conductivity. The mistake has permeated through the literature and textbooks. Specifically, the role of concentration partitioning between different phases in diffusion was not considered in such similarity relations. In this work, we present the correct method to derive such relations in heterogeneous media. Barrer [1] used the similarity between diffusivity and thermal conductivity to derive the relation between the bulk (effective) diffusivity and the individual-phase diffusivities. The approach was followed by many others [2-4]. Unfortunately the similarity approach by Barrer [1] is incorrect because there is also dissimilarity. The key difference is that, even though heat conduction and mass diffusion are characterized by a similar flux equation, in heat conduction, T is continuous across phase boundaries, whereas in diffusion, C is usually not continuous across phase boundaries. The concentration in each phase plays a major role in controlling the contribution by the phase to the bulk diffusive flux and hence the bulk diffusivity. For example, if the concentration of a component in a phase is very low, even if the diffusivity in the phase is high, the contribution of diffusion in that phase to the bulk diffusion flux can still be negligible. Hence, previous models for diffusivity in composite materials or multi-mineral rocks, no matter how sophisticated, are fundamentally wrong because the foundation is a mistake. Correcting the mistake is straightforward. The mass flux can be written in terms of chemical potential and mobility [5,6]. Because chemical potential is continuous across phase boundaries, the relation between bulk mobility and individual-phase mobilities is the same as that between bulk heat conductivity and individual-phase heat conductivities. That is, all previous relations for diffusion cannot be directly applied to diffusivities, but can be applied to mobilities. Then, from the relation between diffusivity and mobility, the correct equations can be obtained, as will be shown in the presentation. [1] Barrer (1968) Diffusion in Polymers, Academic Press, 165. [2] Crank (1975) The Mathematics of Diffusion, Clarendon Press. [3] Brady (1983) Am. J. Sci. 283A, 181. [4] Torquato et al. (1999) J. Appl. Phys. 85, 1560. [5] Lesher (1994) J Geophys. Res. 99, 9585. [6] Zhang (1993) J Geophys. Res. 98, 11901.

  14. Titanium diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, Daniele J.; Liang, Yan

    2014-12-01

    Diffusion of Ti has been characterized in natural olivine and synthetic forsterite. Experiments on the natural olivines were run under buffered conditions (IW and NNO), and those on synthetic forsterite were run in air. Titanium diffusion appears relatively insensitive to crystallographic orientation and oxygen fugacity under the range of investigated conditions, and diffusivities are similar for Fe-bearing olivine and forsterite. For Ti diffusion in synthetic forsterite, we obtain the following Arrhenius relation for diffusion over the temperature range 900-1400 °C:

  15. Fission track length distributions in multi-system thermochronology (Invited)

    NASA Astrophysics Data System (ADS)

    Gleadow, A. J.; Seiler, C.

    2013-12-01

    Fission track length distributions contain a unique record of past temperature variations and therefore play a key role in low-temperature thermochronology, for which there is no exact equivalent in any other method. Confined track lengths closely approximate the true etchable ranges of latent fission tracks [1] and are therefore favoured for fission track studies, but they still have a number of practical limitations. These include small numbers of suitable tracks, especially when only horizontal confined tracks are measured. Using only track-in-track events for measurement further limits the sample size. These restrictions become acute for low track-density samples, where length measurements may be impossible. Irradiating the surface with 252Cf tracks [2] can substantially increase the number of confined tracks, but many researchers do not have access to a Cf source. An even more significant issue has emerged from inter-laboratory comparison experiments that demonstrate a disturbingly poor reproducibility of length measurements between observers [3], a problem compounded by a lack of standardisation in measurement techniques. As a result, individual observers may measure different positions for the end of a track, contributing significantly to variability, and consequently blurring the thermal histories obtained. New digital microscopes open up important opportunities for improved track length measurements by reducing restrictions on sample size, and eliminating some sources of inter-observer bias. We have developed a track length measurement system that enables precise determination of vertical as well as horizontal track dimensions, allowing 3D lengths to be obtained. Lengths are measured on captured image stacks that can be analysed easily and may also be shared, for greater standardisation between laboratories. Length measurements are highly reproducible between different observers using this system, suggesting that at least one source of variability can be eliminated. The selection of lengths for imaging, however, still remains a source of potential bias between observers. The new measurement system also enables measurement of 3D lengths of surface-intersecting ';semi-tracks', the distributions of which have been well understood theoretically [1,4], but have not been used in practice because of difficulties of measuring vertical dimensions on older microscopes. Semi-track lengths are, of course, a degraded measure compared to confined tracks because they are randomly truncated. However, this is more than compensated by their very much greater abundance, by a factor of >60, compared to confined tracks. They are also more amenable to semi- or fully-automated measurement techniques than confined tracks. Moreover the distribution characteristics of semi-track lengths relative to confined track lengths are well understood so that in principle the two types could be used together in modelling thermal histories. The implementation of these new approaches for track length measurement should significantly improve the precision and standardisation of track length measurements at every stage of their utilisation, from annealing studies to thermal history modelling of unknowns. [1] Galbraith (2003) Statistics for FT Analysis, Chapman & Hall [2] Donelick et al. (2005) Rev Min Geochem 58, 49-94 [3] Ketcham et al. (2009) Ear Planet Sci Lett 284, 504-515 [4] Jonckheere & Van den haute (1999) Rad Meas 30, 155-179

  16. Teacher Characteristics.

    ERIC Educational Resources Information Center

    Darr, Ralph F., Jr.

    This paper focuses primarily on the more prominent teacher characteristics research published in the latter half of the 1980s. Literature on the characteristics of elementary, secondary, and college-level teachers is reviewed. Demographic data suggest that today's public school teachers are older and more experienced, and have more years of…

  17. 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.

  18. Classical momentum diffusion in double- ? -kicked particles

    NASA Astrophysics Data System (ADS)

    Stocklin, M. M. A.; Monteiro, T. S.

    2006-08-01

    We investigate the classical chaotic diffusion of atoms subjected to pairs of closely spaced pulses (“kicks”) from standing waves of light (the 2?-KP ). Recent experimental studies with cold atoms implied an underlying classical diffusion of a type very different from the well-known paradigm of Hamiltonian chaos, the standard map. The kicks in each pair are separated by a small time interval ??1 , which together with the kick strength K , characterizes the transport. Phase space for the 2?-KP is partitioned into momentum “cells” partially separated by momentum-trapping regions where diffusion is slow. We present here an analytical derivation of the classical diffusion for a 2?-KP including all important correlations which were used to analyze the experimental data. We find an asymptotic (t??) regime of “hindered” diffusion: while for the standard map the diffusion rate, for K?1 , D˜K2/2[1-2J2(K)⋯] oscillates about the uncorrelated rate D0=K2/2 , we find analytically, that the 2?-KP can equal, but never diffuses faster than, a random walk rate. We argue this is due to the destruction of the important classical “accelerator modes” of the standard map. We analyze the experimental regime 0.1?K??1 , where quantum localization lengths L˜?-0.75 are affected by fractal cell boundaries. We find an approximate asymptotic diffusion rate D?K3? , in correspondence to a D?K3 regime in the standard map associated with the “golden-ratio” cantori.

  19. Dinosaur Skull and Body Length Predictions

    NSDL National Science Digital Library

    2012-06-26

    In this activity (located on page 2 of PDF), learners will look for a relationship between skull size and body length among various dinosaurs. Starting from a list of dinosaur measurements, learners will compare dinosaur sizes to common objects and create a chart that plots body length against skull length to see if the data predicts other dinosaurs' length from skull size. Relates to the linked video, DragonflyTV GPS: Baby Dinosaurs.

  20. Continuous time anomalous diffusion in a composite medium

    Microsoft Academic Search

    B. A. Stickler; E. Schachinger

    2011-01-01

    The one-dimensional continuous time anomalous diffusion in composite media consisting of a finite number of layers in immediate contact is investigated. The diffusion process itself is described with the help of two probability density functions (PDFs), one of which is an arbitrary jump-length PDF, and the other is a long-tailed waiting-time PDF characterized by the waiting-time index beta?(0,1). The former

  1. Exact curvilinear diffusion coefficients in the repton model.

    PubMed

    Buhot, A

    2005-10-01

    The Rubinstein-Duke or repton model is one of the simplest lattice model of reptation for the diffusion of a polymer in a gel or a melt. Recently, a slightly modified model with hardcore interactions between the reptons has been introduced. The curvilinear diffusion coefficients of both models are exactly determined for all chain lengths. The case of periodic boundary conditions is also considered. PMID:16235000

  2. Diffusion of circular DNA in two-dimensional cavity arrays.

    PubMed

    Nykypanchuk, Dmytro; Hoagland, David A; Strey, Helmut H

    2009-11-01

    Through a two-dimensional cavity array with connecting pores of submolecular size, diffusion of relaxed circular and linear DNA molecules is visualized by fluorescence microscopy. Across the entropic barriers transport regime, associated with spatially heterogeneous confinement of flexible polymers, circular DNA diffuses slower than linear DNA of the same length, a trend indicating that linear DNA preferably moves through connecting pores by the threading of an end rather than the looping of a midsection. PMID:19821478

  3. Search techniques, Fibonacci lengths and centropolyhedral groups

    E-print Network

    St Andrews, University of

    Search techniques, Fibonacci lengths and centro­polyhedral groups C. M. Campbell and P. P. Campbell the Fibonacci orbit of G with respect to the generating set A, denoted FA (G). If FA (G) is periodic, we call the length of the period of the sequence the Fibonacci length of G with respect to A, written LENA (G). We

  4. Largemouth Bass Fishery Responses to Length Limits

    E-print Network

    Wilde, Gene

    MANAGEMENT Largemouth Bass Fishery Responses to Length Limits By Gene R. Wilde ABSTRACT I compiled quantitative information from published and unpublished studies that evaluated large- mouth bass fishery hypotheses about largemouth bass fishery responses to minimum-length and slot-length limits. Minimum

  5. TRAFFIC STREAM CHARACTERISTICS BY FRED L. HALL4

    E-print Network

    Bertini, Robert L.

    TRAFFIC STREAM CHARACTERISTICS BY FRED L. HALL4 Professor, McMaster University, Department of Civil;CHAPTER 2 - Frequently used Symbols k density of a traffic stream in a specified length of road L length Stream Characteristics Author's note: This material has benefited greatly from the assistance of Michael

  6. Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals

    NASA Astrophysics Data System (ADS)

    Shi, Dong; Adinolfi, Valerio; Comin, Riccardo; Yuan, Mingjian; Alarousu, Erkki; Buin, Andrei; Chen, Yin; Hoogland, Sjoerd; Rothenberger, Alexander; Katsiev, Khabiboulakh; Losovyj, Yaroslav; Zhang, Xin; Dowben, Peter A.; Mohammed, Omar F.; Sargent, Edward H.; Bakr, Osman M.

    2015-01-01

    The fundamental properties and ultimate performance limits of organolead trihalide MAPbX3 (MA = CH3NH3+; X = Br– or I–) perovskites remain obscured by extensive disorder in polycrystalline MAPbX3 films. We report an antisolvent vapor-assisted crystallization approach that enables us to create sizable crack-free MAPbX3 single crystals with volumes exceeding 100 cubic millimeters. These large single crystals enabled a detailed characterization of their optical and charge transport characteristics. We observed exceptionally low trap-state densities on the order of 109 to 1010 per cubic centimeter in MAPbX3 single crystals (comparable to the best photovoltaic-quality silicon) and charge carrier diffusion lengths exceeding 10 micrometers. These results were validated with density functional theory calculations.

  7. Two dimensional turbulent diffusion calculations for application to atmospheric laser propagation

    NASA Astrophysics Data System (ADS)

    Yee, Charles L.

    1990-05-01

    High power laser propagation through the turbulent atmospheric is difficult due to thermal blooming effects. Current atmospheric turbulence models assume that the turbulent structure is transported across the laser beam diameter at the mean wind speed. This frozen turbulence model is valid if the laser length is short compared to the characteristic time scale associated with the evolution of the turbulence. However, for laser systems with very long inter-pulse spacing, the turbulent structure may have sufficient time to evolve dynamically between laser pulses. The turbulent structure early in the pulse train may be quite different from the turbulent structure late in the pulse train. In this study, the results from a two dimensional code used to model the time evolution of atmospheric turbulence are presented. Calculations of the turbulent diffusion and the auto-correlation time of the turbulence as a function of eddy size and velocity structure constant are also given.

  8. Diffusion laws in dendritic spines

    PubMed Central

    2011-01-01

    Dendritic spines are small protrusions on a neuronal dendrite that are the main locus of excitatory synaptic connections. Although their geometry is variable over time and along the dendrite, they typically consist of a relatively large head connected to the dendritic shaft by a narrow cylindrical neck. The surface of the head is connected smoothly by a funnel or non-smoothly to the narrow neck, whose end absorbs the particles at the dendrite. We demonstrate here how the geometry of the neuronal spine can control diffusion and ultimately synaptic processes. We show that the mean residence time of a Brownian particle, such as an ion or molecule inside the spine, and of a receptor on its membrane, prior to absorption at the dendritic shaft depends strongly on the curvature of the connection of the spine head to the neck and on the neck's length. The analytical results solve the narrow escape problem for domains with long narrow necks. PMID:22655862

  9. Diffusion in confined geometries.

    PubMed

    Burada, P Sekhar; Hänggi, Peter; Marchesoni, Fabio; Schmid, Gerhard; Talkner, Peter

    2009-01-12

    Diffusive transport of particles or, more generally, small objects, is a ubiquitous feature of physical and chemical reaction systems. In configurations containing confining walls or constrictions, transport is controlled both by the fluctuation statistics of the jittering objects and the phase space available to their dynamics. Consequently, the study of transport at the macro- and nanoscales must address both Brownian motion and entropic effects. Herein we report on recent advances in the theoretical and numerical investigation of stochastic transport occurring either in microsized geometries of varying cross sections or in narrow channels wherein the diffusing particles are hindered from passing each other (single-file diffusion). For particles undergoing biased diffusion in static suspension media enclosed by confining geometries, transport exhibits intriguing features such as 1) a decrease in nonlinear mobility with increasing temperature or also 2) a broad excess peak of the effective diffusion above the free diffusion limit. These paradoxical aspects can be understood in terms of entropic contributions resulting from the restricted dynamics in phase space. If, in addition, the suspension medium is subjected to external, time-dependent forcing, rectification or segregation of the diffusing Brownian particles becomes possible. Likewise, the diffusion in very narrow, spatially modulated channels is modified via contact particle-particle interactions, which induce anomalous sub-diffusion. The effective sub-diffusion constant for a driven single file also develops a resonance-like structure as a function of the confining coupling constant. PMID:19025741

  10. Diffusion of iron, cobalt, and nickel in liquid germanium

    SciTech Connect

    Denisov, V.M.; Beletskii, V.V.

    1988-03-01

    To improve the processes employed for preparing single crystals with fixed electrophysical properties it is necessary to have information about the coefficients of diffusion of the impurities present in the melts. In this paper data on the diffusion of Fe, Co, and Ni in liquid germanium, starting from its melting point up to 1380/degree/K, are presented. The coefficients of diffusion of Fe, Co, and Ni in liquid Ge were determined by the capillary method. It was established that the change in the structure of liquid helium as a function of the temperature is responsible for the characteristic features of diffusion in the systems studied.

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

    E-print Network

    Kazuhiko Seki; Sanoop Ramachandran; Shigeyuki Komura

    2011-07-22

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

  12. On Quasilinear Perpendicular Diffusion

    E-print Network

    O. Stawicki

    2005-03-26

    Quasilinear perpendicular diffusion of charged particles in fluctuating electromagnetic fields is the focus of this paper. A general transport parameter for perpendicular diffusion is presented being valid for an arbitrary turbulence geometry and a plasma wave dispersion relation varying arbitrarily in wavevector. The new diffusion coefficient is evaluated in detail for slab turbulence geometry for two special cases: (1) Alfv\\'enic turbulence and (2) dynamical magnetic turbulence. Furthermore, perpendicular diffusion in 2D geometry is considered for a purely dynamical magnetic turbulence. The derivations and numerical calculations presented here cast serious doubts on the applicability of quasilinear theory for perpendicular diffusion. Furthermore, they emphasize that nonlinear effects play a crucial role in the context of perpendicular diffusion.

  13. Clustering method for estimating principal diffusion directions.

    PubMed

    Nazem-Zadeh, Mohammad-Reza; Jafari-Khouzani, Kourosh; Davoodi-Bojd, Esmaeil; Jiang, Quan; Soltanian-Zadeh, Hamid

    2011-08-01

    Diffusion tensor magnetic resonance imaging (DTMRI) is a non-invasive tool for the investigation of white matter structure within the brain. However, the traditional tensor model is unable to characterize anisotropies of orders higher than two in heterogeneous areas containing more than one fiber population. To resolve this issue, high angular resolution diffusion imaging (HARDI) with a large number of diffusion encoding gradients is used along with reconstruction methods such as Q-ball. Using HARDI data, the fiber orientation distribution function (ODF) on the unit sphere is calculated and used to extract the principal diffusion directions (PDDs). Fast and accurate estimation of PDDs is a prerequisite for tracking algorithms that deal with fiber crossings. In this paper, the PDDs are defined as the directions around which the ODF data is concentrated. Estimates of the PDDs based on this definition are less sensitive to noise in comparison with the previous approaches. A clustering approach to estimate the PDDs is proposed which is an extension of fuzzy c-means clustering developed for orientation of points on a sphere. MDL (Minimum description length) principle is proposed to estimate the number of PDDs. Using both simulated and real diffusion data, the proposed method has been evaluated and compared with some previous protocols. Experimental results show that the proposed clustering algorithm is more accurate, more resistant to noise, and faster than some of techniques currently being utilized. PMID:21642005

  14. Clustering method for estimating principal diffusion directions

    PubMed Central

    Nazem-Zadeh, Mohammad-Reza; Jafari-Khouzani, Kourosh; Davoodi-Bojd, Esmaeil; Jiang, Quan; Soltanian-Zadeh, Hamid

    2012-01-01

    Diffusion tensor magnetic resonance imaging (DTMRI) is a non-invasive tool for the investigation of white matter structure within the brain. However, the traditional tensor model is unable to characterize anisotropies of orders higher than two in heterogeneous areas containing more than one fiber population. To resolve this issue, high angular resolution diffusion imaging (HARDI) with a large number of diffusion encoding gradients is used along with reconstruction methods such as Q-ball. Using HARDI data, the fiber orientation distribution function (ODF) on the unit sphere is calculated and used to extract the principal diffusion directions (PDDs). Fast and accurate estimation of PDDs is a prerequisite for tracking algorithms that deal with fiber crossings. In this paper, the PDDs are defined as the directions around which the ODF data is concentrated. Estimates of the PDDs based on this definition are less sensitive to noise in comparison with the previous approaches. A clustering approach to estimate the PDDs is proposed which is an extension of fuzzy c-means clustering developed for orientation of points on a sphere. MDL (Minimum description length) principle is proposed to estimate the number of PDDs. Using both simulated and real diffusion data, the proposed method has been evaluated and compared with some previous protocols. Experimental results show that the proposed clustering algorithm is more accurate, more resistant to noise, and faster than some of techniques currently being utilized. PMID:21642005

  15. Multinomial diffusion equation

    SciTech Connect

    Balter, Ariel I.; Tartakovsky, Alexandre M.

    2011-06-24

    We describe a new, microscopic model for diffusion that captures diffusion induced fluctuations at scales where the concept of concentration gives way to discrete particles. We show that in the limit as the number of particles N {yields} {infinity}, our model is equivalent to the classical stochastic diffusion equation (SDE). We test our new model and the SDE against Langevin dynamics in numerical simulations, and show that our model successfully reproduces the correct ensemble statistics, while the classical model fails.

  16. Diffusion, Osmosis, and Dialysis

    NSDL National Science Digital Library

    Molecular Literacy Project

    Materials such as water, nutrients, dissolved gases, ions and waste are constantly moving across a cell's membrane. In this activity, students interact with models of diffusion and osmosis and observe the net flow of molecules in air, in cells, and across a cell's semi-permeable membrane. Students will be able to: Determine that diffusion results from random motion and/or collisions of particles; learn that particles diffuse from high concentration to low concentration; explore simple diffusion across a semi-permeable membrane; connect the process to dialysis.

  17. Inheritance of Telomere Length in a Bird

    PubMed Central

    Horn, Thorsten; Robertson, Bruce C.; Will, Margaret; Eason, Daryl K.; Elliott, Graeme P.; Gemmell, Neil J.

    2011-01-01

    Telomere dynamics are intensively studied in human ageing research and epidemiology, with many correlations reported between telomere length and age-related diseases, cancer and death. While telomere length is influenced by environmental factors there is also good evidence for a strong heritable component. In human, the mode of telomere length inheritance appears to be paternal and telomere length differs between sexes, with females having longer telomeres than males. Genetic factors, e.g. sex chromosomal inactivation, and non-genetic factors, e.g. antioxidant properties of oestrogen, have been suggested as possible explanations for these sex-specific telomere inheritance and telomere length differences. To test the influence of sex chromosomes on telomere length, we investigated inheritance and sex-specificity of telomere length in a bird species, the kakapo (Strigops habroptilus), in which females are the heterogametic sex (ZW) and males are the homogametic (ZZ) sex. We found that, contrary to findings in humans, telomere length was maternally inherited and also longer in males. These results argue against an effect of sex hormones on telomere length and suggest that factors associated with heterogamy may play a role in telomere inheritance and sex-specific differences in telomere length. PMID:21364951

  18. Experimental studies of non-Fickian moisture diffusion in plastic packages

    Microsoft Academic Search

    Shaohua Yang; Hailong Liu

    2011-01-01

    Moisture penetrating into the polymer and subsequent hygroswelling stress play an important role in the integrity and reliability of plastic electronic packages. In this paper, moisture absorption experiments of four types of plastic encapsulated microcircuits (PEMs) were conducted. Moisture diffusion characteristics of PEMs available by experiments were measured and typical moisture diffusion characteristics were calculated. Fickian second law controls distribution

  19. Analysis of Reaction-Diffusion Systems with Anomalous Subdiffusion

    PubMed Central

    Haugh, Jason M.

    2009-01-01

    Abstract 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. PMID:19619457

  20. 13.3 Arc Length and Speed 1. Arc Length in R2

    E-print Network

    Anderson, Douglas R.

    13.3 Arc Length and Speed 1. Arc Length in R2 : 2. Arc Length in R3 : 3. Arc Length in R3 for the intersection of the cone z = x2 + y2 and the plane y + z = 2 and find the length of the arc in the first octant vector pointing in the direction of the orientation of the curve. Speed: s (t) = r (t) = v(t) Velocity: v

  1. Buoyancy Effects in Fully-Modulated, Turbulent Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Hermanson, J. C.; Johari, H.; Ghaem-Maghami, E.; Stocker, D. P.; Hegde, U. G.; Page, K. L.

    2003-01-01

    Pulsed combustion appears to have the potential to provide for rapid fuel/air mixing, compact and economical combustors, and reduced exhaust emissions. The objective of this experiment (PuFF, for Pulsed-Fully Flames) is to increase the fundamental understanding of the fuel/air mixing and combustion behavior of pulsed, turbulent diffusion flames by conducting experiments in microgravity. In this research the fuel jet is fully-modulated (i.e., completely shut off between pulses) by an externally controlled valve system. This gives rise to drastic modification of the combustion and flow characteristics of flames, leading to enhanced fuel/air mixing compared to acoustically excited or partially-modulated jets. Normal-gravity experiments suggest that the fully-modulated technique also has the potential for producing turbulent jet flames significantly more compact than steady flames with no increase in exhaust emissions. The technique also simplifies the combustion process by avoiding the acoustic forcing generally present in pulsed combustors. Fundamental issues addressed in this experiment include the impact of buoyancy on the structure and flame length, temperatures, radiation, and emissions of fully-modulated flames.

  2. Diffusion-weighted imaging of the brain in infants and children

    Microsoft Academic Search

    Richard L. Robertson; Charles M. Glasier

    2007-01-01

    During the last decade, diffusion-weighted imaging (DWI) has become an important tool in the evaluation of a variety of disorders\\u000a of the central nervous system in children. DWI relies on variability in the diffusivity of water molecules in the presence\\u000a of a supplemental diffusion-sensitizing gradient to produce image contrast. Pathologic states alter the diffusion characteristics\\u000a of brain water in a

  3. 16 Diffusion Tensor MRI Visualization

    E-print Network

    Utah, University of

    16 Diffusion Tensor MRI Visualization 16.1 Introduction Diffusion Tensor Magnetic Resonance Imaging the diffusion of water molecules. The direction of fastest diffusion is aligned with fiber orientation in a pattern that can be numerically modeled by a diffusion tensor. DTI is the only modality for noninva

  4. NONLINEAR DIFFUSION PDES Erkut Erdem

    E-print Network

    Erdem, Erkut

    NONLINEAR DIFFUSION PDES Erkut Erdem Hacettepe University March 5th, 2012 CONTENTS 1 Perona-Malik Type Nonlinear Diffusion 1 2 Edge Enhancing Diffusion 5 References 7 1 PERONA-MALIK TYPE NONLINEAR DIFFUSION The main theory behind nonlinear diffusion models is to use nonlinear PDEs to create a scale space

  5. Effective path length corrections in beam-beam scattering experiments

    NASA Technical Reports Server (NTRS)

    Brinkmann, R. T.; Trajmar, S.

    1981-01-01

    The effect of the change of scattering geometry with scattering angle in beam-beam experiments is investigated. Atomic (molecular) target distributions associated with static gas, orifice, tube, capillary array (with and without further collimation), and jet sources have been considered in model calculations for a number of commonly used electron scattering geometries. The relationship between scattering intensity, cross section, and the geometrical integral called 'effective path length' is derived. Volume correction factors (the reciprocal of effective path length) have been calculated for sample cases to illustrate the effect of various beam and scattering geometry characteristics. The validity of the model calculation has been experimentally verified. Most of the commonly used scattering geometries require significant correction of the scattering intensity distributions, but with proper planning scattering geometries can be designed such that the intensity and the cross section angular distribution are identical within 1%.

  6. Biomechanical implications of mild leg length inequality.

    PubMed Central

    McCaw, S T; Bates, B T

    1991-01-01

    The effect of mild leg length inequality (lower extremity length difference less than 3 cm) on posture and gait has been the source of much controversy. Many opinions have been expressed both for and against the need for intervention to reduce the magnitude of the discrepancy. This paper emphasizes the need for accurate and reliable assessment of leg length differences using a clinically functional radiographic technique, and reviews the biomechanical implications of leg length inequality as related to the development of stress fractures, low back pain and osteoarthritis. PMID:1913023

  7. Statistical analysis of knee ligament lengths.

    PubMed

    Clément, B; Drouin, G; Shorrock, G; Gely, P

    1989-01-01

    Absolute locations of the main knee ligamentous structures' insertion sites on the femur, the tibia and the patella have been obtained for 30 knees originating from 18 fresh human cadavers. For each knee, the length of ten selected structures was deduced. These length data form the input of the statistical analysis presented in the paper. The correlations between the ligament lengths are presented. A comparison of the lengths from the left and right (laterality) knees of the same specimen is also done and shows no significant difference. The sex difference is also studied and does not seem to be a determinant parameter for the sample investigated. Prediction equations are proposed to estimate the ligament lengths for the knee in extension with respect to the three external parameters: height, weight and femoral condyle width. The menisco-femoral length, the patellar tendon length and the patellar length are not related to the external parameters and predictions are based on mean values. For the other six ligament lengths, the square multiple correlation coefficient with the external parameters ranges between 0.22 and 0.43. The condylar width is the most often used external parameter in these equations while the weight parameter is never present. PMID:2613711

  8. Microtubule Length-Regulation by Molecular Motors

    E-print Network

    Melbinger, Anna; Frey, Erwin

    2012-01-01

    Length-regulation of microtubules (MTs) is essential for many cellular processes. Molecular motors like kinesin 8, which move along MTs and also act as depolymerases, are known as key players in MT dynamics. However, the regulatory mechanisms of length control remain elusive. Here, we investigate a stochastic model accounting for the interplay between polymerization kinetics and motor-induced depolymerization. We determine the dependence of MT length and variance on rate constants and motor concentration. Moreover, our analyses reveal how collective phenomena lead to a well-defined MT length.

  9. Microtubule Length-Regulation by Molecular Motors

    E-print Network

    Anna Melbinger; Louis Reese; Erwin Frey

    2012-04-25

    Length-regulation of microtubules (MTs) is essential for many cellular processes. Molecular motors like kinesin 8, which move along MTs and also act as depolymerases, are known as key players in MT dynamics. However, the regulatory mechanisms of length control remain elusive. Here, we investigate a stochastic model accounting for the interplay between polymerization kinetics and motor-induced depolymerization. We determine the dependence of MT length and variance on rate constants and motor concentration. Moreover, our analyses reveal how collective phenomena lead to a well-defined MT length.

  10. 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)

  11. DCT-Based Characterization of Milk Products Using Diffuse Reflectance Images

    E-print Network

    DCT-Based Characterization of Milk Products Using Diffuse Reflectance Images Sara Sharifzadeh of diffuse reflectance images of laser illumination on milk products in different wave lengths. Based and discriminate eight different milk products. Comparing this result with the current characteriza tion method

  12. Current–voltage characteristics of manganite–titanite perovskite junctions

    PubMed Central

    Ifland, Benedikt; Peretzki, Patrick; Kressdorf, Birte; Saring, Philipp; Kelling, Andreas; Seibt, Michael

    2015-01-01

    Summary After a general introduction into the Shockley theory of current voltage (J–V) characteristics of inorganic and organic semiconductor junctions of different bandwidth, we apply the Shockley theory-based, one diode model to a new type of perovskite junctions with polaronic charge carriers. In particular, we studied manganite–titanate p–n heterojunctions made of n-doped SrTi1? yNbyO3, y = 0.002 and p-doped Pr1? xCaxMnO3, x = 0.34 having a strongly correlated electron system. The diffusion length of the polaron carriers was analyzed by electron beam-induced current (EBIC) in a thin cross plane lamella of the junction. In the J–V characteristics, the polaronic nature of the charge carriers is exhibited mainly by the temperature dependence of the microscopic parameters, such as the hopping mobility of the series resistance and a colossal electro-resistance (CER) effect in the parallel resistance. We conclude that a modification of the Shockley equation incorporating voltage-dependent microscopic polaron parameters is required. Specifically, the voltage dependence of the reverse saturation current density is analyzed and interpreted as a voltage-dependent electron–polaron hole–polaron pair generation and separation at the interface. PMID:26199851

  13. Cosmology with matter diffusion

    NASA Astrophysics Data System (ADS)

    Calogero, Simone; Velten, Hermano

    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 phi 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 ?. The standard ?CDM model can be recovered by setting ? = 0. If diffusion takes place (? > 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.

  14. Diffusive neural network

    Microsoft Academic Search

    Gaetano L. Aiello

    2002-01-01

    A non-connectionist model of a neuronal network based on passive diffusion of neurotransmitters is presented as an alternative to hard-wired artificial neural networks. Classic thermodynamical approach shows that the diffusive network is capable of exhibiting asymptotic stability and a dynamics resembling that of a chaotic system. Basic computational capabilities of the net are discussed based on the equivalence with a

  15. Hydrogen diffusion in aluminum

    Microsoft Academic Search

    R MCLELLAN

    1983-01-01

    Although the diffusivity of hydrogen in aluminum has been measured by several different authors, there is essentially no mutual agreement and the sets of data are separated by orders of magnitude. There is little doubt these mass-flow determinations of the H-diffusivity are subject to great uncertainties connected with the presence of the surface oxide layer, as has been discussed recently

  16. Robust anisotropic diffusion

    Microsoft Academic Search

    Michael J. Black; Guillermo Sapiro; David H. Marimont; David Heeger

    1998-01-01

    Relations between anisotropic diffusion and robust statis tics are described in this pa- per. Specifically, we show that anisotropic diffusion can be seen as a robust estimation procedure that estimates a piecewise smooth image from a noi sy input image. The \\

  17. 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…

  18. International Technology Diffusion

    Microsoft Academic Search

    Wolfgang Keller

    2004-01-01

    This paper surveys what is known about the extent of international technology diffusion and channels through which technology spreads. Productivity differences explain much of the variation in incomes across countries, and technology plays a key role in determining productivity. The pattern of worldwide technical change is determined largely by international technology diffusion because a few rich countries account for most

  19. International Technology Diffusion

    Microsoft Academic Search

    Wolfgang Keller

    2001-01-01

    I discuss the concept and empirical importance of international technology diffusion from the point of view of recent work on endogenous technological change. In this literature, technology is viewed as technological knowledge. I first review the major concepts, and how international technology diffusion relates to other factors affecting economic growth in open economies. The following main section of the paper

  20. Diffusion in Semiconductors

    Microsoft Academic Search

    Derek Shaw

    2007-01-01

    Atomic diffusion in semiconductors refers to the migration of atoms, including host, dopant and impurities. Diffusion occurs in all thermodynamic phases, but the solid phase is the most important in semiconductors. There are two types of semiconductor solid phase: amorphous (including organic) and crystalline. In this chapter we consider crystalline semiconductors and describe the processes by which atoms and defects

  1. Zero-flux planes, flux reversals and diffusion paths in ternary and quaternary diffusion

    SciTech Connect

    Dayananda, M.A.

    1986-05-23

    During isothermal multicomponent diffusion, interdiffusion fluxes of individual components can go to zero at zero-flux planes (ZFP) and exhibit flux reversals from one side to the other of such planes. Interdiffusion fluxes as well as the locations and compositions of ZFPs for components are determined directly from the concentration profiles of diffusion couples without the need for prior knowledge of interdiffusion coefficients. The development and identification of ZFPs is reviewed with the aid of single phase and two-phase diffusion couples investigated in the Cu-Ni-Zn system at 775/sup 0/C. ZFP locations in the diffusion zone nearly correspond to sections where the activity of a component is the same as its activity in either of the terminal alloys of a couple. Path slopes at ZFPs are uniquely dictated by the atomic mobility and thermodynamic data for the components. Discontinuous flux reversals for the components can also occur at interfaces in multiphase couples. Identification of ZFPs is also presented for diffusion in the Cu-Ni-Zn-Mn quaternary system. Analytical representation of diffusion paths for both ternary and quaternary diffusion couples is presented with the aid of characteristic path parameters.

  2. Turbulent flow in a conical diffuser - Overview and implications

    Microsoft Academic Search

    R. S. Azad; S. Z. Kassab

    1989-01-01

    Turbulent flow in a conical diffuser has been examined through determination of the mean pressures, mean strain rates, energy, shear stress, triple products, length scale, and balances of energy and shear stress. Some quantities are more revealing than others in pointing out the complexity of a flow subjected to an adverse pressure gradient. Sudden application of extra strain rate to

  3. Further investigation of conical diffusers with annular injection

    Microsoft Academic Search

    R. K. Duggins; D. Lampard; A. T. Sanders

    1978-01-01

    A comprehensive investigation is made, for a wide range of incompressible flows, into the merits of annular injection as a means of obtaining a high-performance diffuser with short axial length. Results show that injection yields considerable improvements in both the quality of the discharging flow and the magnitude of the pressure recovery. Accordingly, the technique is strongly recommended when a

  4. Turbulent flow in a conical diffuser: Overview and implications

    Microsoft Academic Search

    R. S. Azad; S. Z. Kassab

    1989-01-01

    Turbulent flow in a conical diffuser has been examined through determination of the mean pressures, mean strain rates, energy, shear stress, triple products, length scale, and balances of energy and shear stress. Some quantities are more revealing than others in pointing out the complexity of a flow subjected to an adverse pressure gradient. Sudden application of extra strain rate to

  5. Enigma of H3 in diffuse interstellar clouds

    E-print Network

    Oka, Takeshi

    1 Enigma of H3 + in diffuse interstellar clouds Benjamin J. McCall1,2 and Takeshi Oka1 1 Department + in dense (molecular) clouds is now well understood,1 and observations of H3 + in these environments now permit measurements of the path lengths, number densities, and kinetic temperatures of dense clouds

  6. 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 ?=175 to Coulomb parameters up to ?=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

  7. Diffusion in Coulomb crystals

    SciTech Connect

    Hughto, J.; Schneider, A. S.; Horowitz, C. J.; Berry, D. K. [Department of Physics and Nuclear Theory Center, Indiana University, Bloomington, Indiana 47405 (United States); University Information Technology Services, Indiana University, Bloomington, Indiana 47408 (United States)

    2011-07-15

    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 {Gamma}=175 to Coulomb parameters up to {Gamma}=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.

  8. Self-diffusion of Rod-like Viruses Through Smectic Layer

    E-print Network

    M. Paul Lettinga; Eric Grelet

    2007-10-31

    We report the direct visualization at the scale of single particles of mass transport between smectic layers, also called permeation, in a suspension of rod-like viruses. Self-diffusion takes place preferentially in the direction normal to the smectic layers, and occurs by quasi-quantized steps of one rod length. The diffusion rate corresponds with the rate calculated from the diffusion in the nematic state with a lamellar periodic ordering potential that is obtained experimentally.

  9. Lossy radial diffusion of relativistic Jovian electrons

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.; Coroniti, F. V.

    1976-01-01

    The radial diffusion equation with synchrotron losses is solved by the Laplace-transform method for near equatorially mirroring relativistic electrons. The evolution of a power-law distribution function is found, and the characteristics of synchrotron burnoff are stated in terms of explicit parameters for an arbitrary diffusion coefficient of a specific form. The peaking of the 10.4-cm volume emissivity from Jupiter at an L shell of about 1.8 provides an estimate of the diffusion coefficient in the radiation belts; one value is suggested as the appropriate modification, for an equatorial field strength of 4.2 G, of the Birmingham et al. (1974) result. Nonsynchrotron losses are included phenomenologically; from the phase-space densities reported by McIlwain and Fillius (1975), the particle lifetime is estimated. Asymptotic forms for the distribution in the strong synchrotron loss regime are provided.

  10. Oxygen diffusion in titanite: Lattice diffusion and fast-path diffusion in single crystals

    E-print Network

    Watson, E. Bruce

    Oxygen diffusion in titanite: Lattice diffusion and fast-path diffusion in single crystals X June 2006 Editor: P. Deines Abstract Oxygen diffusion in natural and synthetic single-crystal titanite cold-seal pressure vessels for durations of 1 day to several weeks. Diffusive uptake profiles of 18 O

  11. Helium diffusion in carbonates

    NASA Astrophysics Data System (ADS)

    Amidon, W. H.; Cherniak, D. J.; Watson, E. B.; Hobbs, D.

    2013-12-01

    The abundance and large grain size of carbonate minerals make them a potentially attractive target for 4He thermochronology and 3He cosmogenic dating, although the diffusive properties of helium in carbonates remain poorly understood. This work characterizes helium diffusion in calcite and dolomite to better understand the crystal-chemical factors controlling He transport and retentivity. Slabs of cleaved natural calcite and dolomite, and polished sections of calcite cut parallel or normal to c, were implanted with 3He at 3 MeV with a dose of 5x1015/cm2. Implanted carbonates were heated in 1-atm furnaces, and 3He distributions following diffusion anneals were profiled with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. For 3He transport normal to cleavage surfaces in calcite, we obtain the following Arrhenius relation over the temperature range 78-300°C: Dcalcite = 9.0x10-9exp(-55 × 6 kJ mol-1/RT) m2sec-1. Diffusion in calcite exhibits marked anisotropy, with diffusion parallel to c about two orders of magnitude slower than diffusion normal to cleavage faces. He diffusivities for transport normal to the c-axis are similar in value to those normal to cleavage surfaces. Our findings are broadly consistent with helium diffusivities from step-heating measurements of calcite by Copeland et al. (2007); these bulk degassing data may reflect varying effects of diffusional anisotropy. Helium diffusion normal to cleavage surfaces in dolomite is significantly slower than diffusion in calcite, and has a much higher activation energy for diffusion. For dolomite, we obtain the following Arrhenius relation for He diffusion over the temperature range 150-400°C: Ddolomite = 9.0x10-8exp(-92 × 9 kJ mol-1/RT) m2sec-1. The role of crystallographic structure in influencing these differences among diffusivities was evaluated using the maximum aperture approach of Cherniak and Watson (2011), in which crystallographic structures are sectioned along possible diffusion directions and the maximum interstitial apertures in each 'slice' in the structure are identified. Preliminary results show that observed differences in diffusivities are consistent with the size of the smallest maximum aperture along each diffusion direction. In calcite, the smallest maximum apertures are ~0.92 and ~0.66 angstroms for cleavage-normal and c-axis parallel directions respectively. In dolomite, the smallest maximum aperture is ~0.78 angstroms for the cleavage normal direction. Work is in progress on characterizing helium diffusion for other orientations in dolomite, and in other carbonates, including aragonite and magnesite, and in implementing these diffusion findings in the interpretation and modeling of bulk volume diffusion in heterogeneous calcite crystals common in many geologic applications. Copeland et al. (2007) GCA 71, 4488-4511 Cherniak and Watson, (2011) Chem. Geo. 288, 149-161

  12. Characteristics of Interdiffusion between 17-4 PH Steel and Nickel

    NASA Astrophysics Data System (ADS)

    Laik, A.; Gawde, P. S.; Bhanumurthy, K.; Kale, G. B.

    2008-04-01

    The characteristics of interdiffusion between precipitation-hardened 17-4 PH grade stainless steel and nickel were studied in the temperature range of 900 °C to 1100 °C, using diffusion couples of these two materials. The diffusion coefficients of the major diffusing elements Fe, Ni, Cr, and Cu were evaluated for this multicomponent system. The diffusion paths plotted on the Fe-Ni-Cr isotherm showed a flat “S” shape, suggesting insignificant interaction among the diffusing species. The temperature dependence of the diffusion coefficients for each element was evaluated, and the activation energies for diffusion were determined. The asymmetric nature of concentration variation of the elements at the diffusion zone was observed and was explained by the difference in diffusivities of the diffusing species. The activation energy for diffusion of Ni was found to be lower than that of Fe and Cr.

  13. Eddy current correction in diffusion-weighted imaging using pairs of images acquired with opposite diffusion gradient polarity.

    PubMed

    Bodammer, Nils; Kaufmann, Jörn; Kanowski, Martin; Tempelmann, Claus

    2004-01-01

    In echo-planar-based diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI), the evaluation of diffusion parameters such as apparent diffusion coefficients and anisotropy indices is affected by image distortions that arise from residual eddy currents produced by the diffusion-sensitizing gradients. Correction methods that coregister diffusion-weighted and non-diffusion-weighted images suffer from the different contrast properties inherent in these image types. Here, a postprocessing correction scheme is introduced that makes use of the inverse characteristics of distortions generated by gradients with reversed polarity. In this approach, only diffusion-weighted images with identical contrast are included for correction. That is, non-diffusion-weighted images are not needed as a reference for registration. Furthermore, the acquisition of an additional dataset with moderate diffusion-weighting as suggested by Haselgrove and Moore (Magn Reson Med 1996;36:960-964) is not required. With phantom data it is shown that the theoretically expected symmetry of distortions is preserved in the images to a very high degree, demonstrating the practicality of the new method. Results from human brain images are also presented. PMID:14705060

  14. Thorium Diffusion in Monazite

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    2006-05-01

    Diffusion of thorium has been characterized in synthetic monazite under dry conditions. The synthetic monazites (either pure CePO4, NdPO4, or a mixed LREE phosphate containing Ce, Nd, and Sm) were grown via a Na2CO3-MoO3 flux method. The source of diffusant for the experiments were either synthesized ThSiO4 or CaTh(PO4)2 powders. Experiments were performed by placing source and monazite in Pt capsules and annealing capsules in 1 atm furnaces for times ranging from 10 days to a few hours, at temperatures from 1400 to 1550C. The Th distributions in the monazite were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation was obtained for diffusion in monazite: DSm = 7.2x103 exp(-814 kJ mol-1/RT) m2sec-1 The diffusivity of Th was similar for monazites containing a single REE and the mixed LREE phosphates. Th diffusion was also similar for experiments run using the Th silicate and Ca-Th phosphate sources, suggesting that the substitutional mechanism for Th in monazite, i.e, Th+4 + Si+4 for REE+3 + P+5 with the ThSiO4 source, and Th+4 + Ca+2 for 2REE+3 with the CaTh(PO4)2 source, does not significantly affect Th diffusivities, and that Th is likely the rate-limiting species. Th diffusion in monazite is about 4 orders of magnitude slower than Pb diffusion (Cherniak et al., 2004). This contrasts with findings of Gardes et al. (2005) who determined that Pb, Th and REE diffusivities in monazite are similar. Th diffusion in zircon (Cherniak et al., 1997) is about an order of magnitude slower than in monazite, but with similar activation energy for diffusion. The smaller diffusivities in zircon may be a consequence of the larger disparity in size between Th and the Zr site in zircon as compared with Th and the REE site in monazite. Nonetheless, Th is essentially immobile in monazite with respect to exchange by volume diffusion under most geologic conditions; these findings may have implications for containment of high- level actinide-based nuclear waste in monazite ceramic waste forms. Cherniak et al. (1997) Chem. Geol. 134, 289-301; Cherniak et al. (2004) GCA 68, 829-840; Gardes et al.(2005)abstract, EUG General Assembly

  15. Simple, accurate, and precise measurements of thermal diffusivity in liquids using a thermal-wave cavity

    E-print Network

    Mandelis, Andreas

    -wave phase and cavity length. Measurement precision is directly related to the corresponding precision to the precision with which the relevant cavity lengths can be measured. The methodology was appliedSimple, accurate, and precise measurements of thermal diffusivity in liquids using a thermal

  16. Global Optimization by Adapted Diffusion

    E-print Network

    Poliannikov, Oleg V.

    In this paper, we study a diffusion stochastic dynamics with a general diffusion coefficient. The main result is that adapting the diffusion coefficient to the Hamiltonian allows to escape local wide minima and to speed ...

  17. Macromolecule diffusion into muscle tissue

    NSDL National Science Digital Library

    Powell, Adam C., IV

    2004-07-08

    Diffusion in spherical coordinates from a small device into fibrous muscle tissue, with discussion of something like a boundary layer, mass transfer coefficient, anisotropic diffusion, and biological complications to diffusion.

  18. Matching and indexing sequences of different lengths

    Microsoft Academic Search

    Tolga Bozkaya; Nasser Yazdani; Meral Özsoyo?lu

    1997-01-01

    In this paper, we consider the problem of efficient matching and retrieval of sequences of different lengths. Most of the previous research is concentrated on similarity matching and retrieval of sequences of the same length using Euclidean distance metric. For similarity matching of sequences, we use a modified version of the edit distance function, and consider two sequences matching if

  19. Glass Fiber Length Degradation in Thermoplastics Rocessing

    Microsoft Academic Search

    Robert A. Schweizer

    1982-01-01

    Glass fiber length is of great concern to both the compounder and molder of fiberglass reinforced thermoplastics. We know that the fiber attrition is considerable, but how short is it and where in the process does it occur? Can it be affected by using the longer length chopped strands? These are the types of questions that have gone unanswered because

  20. Global patterns of aquatic food chain length

    Microsoft Academic Search

    M. Jake Vander Zanden; William W. Fetzer

    2007-01-01

    Food chain length is a fundamental ecosystem property, and plays a central role in determining ecosystem functioning. Recent advances in the field of stable isotope ecology allow the estimation of food chain length (FCL) from stable nitrogen isotope (d15N) data. We conducted a global literature synthesis and estimated FCL for 219 lake, stream, and marine ecosystems. Streams had shorter food