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1

Effective diffusion length of multicrystalline solar cells  

NASA Astrophysics Data System (ADS)

Previous definitions of effective diffusion length 0268-1242/13/7/021/img1 of a multicrystalline semiconductor are reviewed. A new definition is proposed, which is based on the comparison of the current collected from the base of a multicrystalline solar cell and a single-crystal cell for uniform carrier generation, and holds for any sample thickness. An analytical expression for 0268-1242/13/7/021/img1 is obtained from the solution of the three-dimensional equation for the charge collection probability 0268-1242/13/7/021/img3 inside a grain with square cross section. This expression is used to numerically study the dependence of 0268-1242/13/7/021/img1 on the bulk diffusion length, grain size and grain boundary recombination velocity, and to make a comparison with previous specifications of 0268-1242/13/7/021/img1. The results indicate, in particular, that 0268-1242/13/7/021/img1 is the value that would be determined by the surface photovoltage method. The case of a cell with grains of different properties is briefly discussed and an average 0268-1242/13/7/021/img1 is defined. It is also shown that 0268-1242/13/7/021/img3 can be used to calculate the contribution of the base to the reverse saturation current of the cell.

Donolato, C.

1998-07-01

2

Connecting molecular structure and exciton diffusion length in rubrene derivatives.  

PubMed

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

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

2013-06-10

3

Characteristic Length in a Linear Acceleration  

NASA Astrophysics Data System (ADS)

The role of the characteristic length that characterizes linear acceleration is studied, in order to find how does this length determine the characteristic wavelength of the radiation created by the accelerated charge. Unruh equation for the temperature observed by a detector accelerated relative to the vacuum is used to determine the wavelength distribution of the radiation emitted by a linearly accelerated charge, and it is found that this distribution is peaked close to the characteristic length that characterizes the linear acceleration, which is the radius of curvature of the curved electric field created by the acelerated charge.

Harpaz, Amos

2007-03-01

4

The lateral ambipolar diffusion length in quantum dot lasers  

Microsoft Academic Search

Using the segmented contact technique we determine the lateral out-diffusion current in shallow etched quantum dot ridges of different width and by fitting this out-diffusion data we obtain the ambipolar diffusion length as a function of the intrinsic carrier injection level. The measured data reveals two regimes of reduced diffusion that can be explained by a mechanism involving the thermal

A. Sobiesierski; D. Naidu; P. M. Smowton

2011-01-01

5

Pulsed ion beam measurement of defect diffusion lengths in irradiated solids  

NASA Astrophysics Data System (ADS)

Radiation-generated point defects in solids often experience dynamic annealing—diffusion and interaction processes after the thermalization of collision cascades. The length scale of dynamic annealing can be described in terms of the characteristic defect diffusion length (Ld). Here, we propose to measure Ld by a pulsed beam method. Our approach is based on the observation of enhanced defect production when, for individual ion pulses, the average separation between adjacent damage regions is smaller than Ld. We obtain a value for Ld of ˜30 nm for float-zone Si crystals bombarded at room temperature with 500 keV Ar ions.

Charnvanichborikarn, S.; Myers, M. T.; Shao, L.; Kucheyev, S. O.

2013-04-01

6

Spin flip diffusion length and giant magnetoresistance at low temperatures  

Microsoft Academic Search

Measurements at 4.2 K of the magnetoresistance of Co\\/AgMn, Co\\/CuMn, Co\\/AgPt, and Co\\/CuPt multilayers with the current perpendicular to the layer planes (CPP-MR) show effects of reduced spin diffusion lengths due to alloying of the nonmagnetic metal with impurities that produce spin-spin (Mn) or spin-orbit (Pt) scattering. Combining the data with a theory by Valet and Fert gives the spin

Q. Yang; P. Holody; S.-F. Lee; L. L. Henry; R. Loloee; P. A. Schroeder; W. P. Pratt Jr.; J. Bass

1994-01-01

7

Diffusion characteristics of alginate membranes.  

PubMed

The diffusive properties of alginate membranes prepared by the interfacial reaction of sodium alginate solution with gypsum substrates were studied. The penetrants of primary importance for the above study were methyl methacrylate (MMA) and water, since alginate membranes are used as mould release agents, during the casting of poly(methyl methacrylate) (PMMA) in gypsum moulds in a water bath. Vapour sorption measurements were carried out at various temperatures. The effect of temperature and the combined action of water and MMA on the swelling behaviour of the membrane was also investigated. The results indicate that the water sorption of alginate membranes is non-Fickian, in spite of the linearity of the curves obtained by plotting Mt/M infinity versus t 1/2, at least for a short time period. The membrane treatment with methyl methacrylate, leads to considerably lower equilibrium sorption, possibly because of the formation of a thin film of poly(methyl methacrylate) on the membrane surface. PMID:3676427

Andreopoulos, A G

1987-09-01

8

Characteristic Lengths of Magnetic Field in Magnetohydrodynamic Turbulence  

Microsoft Academic Search

In the framework of turbulence dynamo, flow motions amplify a weak seed magnetic field through the stretching of field lines. Although the amplification process has been a topic of active research, less attention has been paid to the length scales of magnetic field. In this Letter, we describe a numerical study on characteristic lengths of magnetic field in magnetohydrodynamic turbulence.

Jungyeon Cho; Dongsu Ryu

2009-01-01

9

Correlation of ion dynamics with characteristic length scales and network structural units in bismuth borate glasses  

NASA Astrophysics Data System (ADS)

Ion dynamics in lithium bismuth borate conducting glasses have been reported in wide composition and temperature ranges. The activation energy for the dc conduction has been analysed using Anderson-Stuart model and a correlation between the dc conductivity and the doorway radius has been predicted. The characteristic length scales for ion dynamics, such as mean square displacement and spatial extent of sub-diffusive motion of lithium ions have been determined from the ac conductivity and dielectric spectra, respectively. A direct connection between the ion dynamics and the characteristic length scales and the network structural units have been established.

Shaw, A.; Ghosh, A.

2013-09-01

10

Correlation of ion dynamics with characteristic length scales and network structural units in bismuth borate glasses.  

PubMed

Ion dynamics in lithium bismuth borate conducting glasses have been reported in wide composition and temperature ranges. The activation energy for the dc conduction has been analysed using Anderson-Stuart model and a correlation between the dc conductivity and the doorway radius has been predicted. The characteristic length scales for ion dynamics, such as mean square displacement and spatial extent of sub-diffusive motion of lithium ions have been determined from the ac conductivity and dielectric spectra, respectively. A direct connection between the ion dynamics and the characteristic length scales and the network structural units have been established. PMID:24070293

Shaw, A; Ghosh, A

2013-09-21

11

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

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

12

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

PubMed Central

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.

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

2013-01-01

13

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

PubMed

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

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

2013-09-20

14

Evidence of a characteristic ignition length of a flame  

NASA Astrophysics Data System (ADS)

Ignition process of vegetation from a cylindrical flame radiation is examined using Koo and Pagni [1] model. The radiation flux is power-law decreasing with distance [2], while the ignition time increases exponentially. This last behavior yields a characteristic length of fuel ignition from a flame, inducing a percolation type phase transition.

Baara, Y.; Khalloufi, K.; Zekri, N.

2013-03-01

15

Atomic jump lengths in surface diffusion: experiment and theory  

Microsoft Academic Search

One-dimensional diffusion by long jumps has recently been found for Pd on W(211). The frequency of long jumps is derived from measurements of the distribution of displacements of a single adatom. The data, corrected for the effect of finite plane size, reveal that 15% of the jumps cover two nearest-neighbor distances and 10% cover three nearest-neighbor distances at 133 K.

Donna Cowell Senft

1996-01-01

16

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

SciTech Connect

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.

Cudzinovic, M.; Sopori, B. [comp.

1995-11-01

17

EFFECT OF CRYSTAL DEFECTS ON MINORITY CARRIER DIFFUSION LENGTHS IN 6H Sic  

Microsoft Academic Search

Minority-carrier diffusion lengths in n-type 6H-SIC were measured using the planar electron-beam induced current (EBIC) technique. Experimental values of electron beam current, EBIC, and beam voltage were obtained for n-type SIC with a carrier concentration of 1.7E17 ~m-~. This data was fit to theoretically calculated diode efficiency curves, and the diffusion length and metal layer thickness extracted. The extracted hole

S. M. Hubbard; M. Tabib-Azar; S. Bailey; G. Rybicki; P. Neudeck; R. Raffaelle

18

Measuring minority-carrier diffusion length using a Kelvin probe force microscope  

Microsoft Academic Search

A method based on Kelvin probe force microscopy for measuring minority-carrier diffusion length in semiconductors is described. The method is based on measuring the surface photovoltage between the tip of an atomic force microscope and the surface of an illuminated semiconductor junction. The photogenerated carriers diffuse to the junction and change the contact potential difference between the tip and the

R. Shikler; N. Fried; T. Meoded; Y. Rosenwaks

2000-01-01

19

Direct measurement of minority carriers diffusion length using Kelvin probe force microscopy  

Microsoft Academic Search

We report on the use of Kelvin force microscopy as a method for measuring very short minority carrier diffusion length in semiconductors. The method is based on measuring the surface photovoltage between the tip of an atomic force microscope and the surface of an illuminated semiconductor junction. The photogenerated carriers diffuse to the junction, and change the contact potential difference

T. Meoded; R. Shikler; N. Fried; Y. Rosenwaks

1999-01-01

20

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

PubMed

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

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

21

CHARACTERISTIC LENGTHS OF MAGNETIC FIELD IN MAGNETOHYDRODYNAMIC TURBULENCE  

SciTech Connect

In the framework of turbulence dynamo, flow motions amplify a weak seed magnetic field through the stretching of field lines. Although the amplification process has been a topic of active research, less attention has been paid to the length scales of magnetic field. In this Letter, we describe a numerical study on characteristic lengths of magnetic field in magnetohydrodynamic turbulence. We considered the case of very weak or zero mean magnetic field, which is applicable to the turbulence in the intergalactic space. Our findings are as follows. (1) At saturation, the peak of magnetic field spectrum occurs at approxL{sub 0}/2, where L{sub 0} is the energy injection scale, while the most energy containing scale is approxL{sub 0}/5. The peak scale of spectrum of projected, two-dimensional field is approxL{sub 0}. (2) During the stage of magnetic field amplification, the energy equipartition scale shows a power law increase of approxt {sup 1.5}, while the integral and curvature scales show a linear increase. The equipartition, integral, and curvature scales saturate at approxL{sub 0}, approx0.3L{sub 0}, and approx0.15L{sub 0}, respectively. (3) The coherence length of magnetic field defined in the Faraday rotation measure (RM) due to the intergalactic magnetic field (IGMF) is related to the integral scale. We present a formula that expresses the standard deviation of RM, sigma{sub RM}, in terms of the integral scale and rms strength of the IGMF, and estimate that sigma{sub RM} would be approx100 and approx a few rad m{sup -2} for clusters and filaments, respectively.

Cho, Jungyeon [Department of Astronomy and Space Science, Chungnam National University, Daejeon (Korea, Republic of); Ryu, Dongsu, E-mail: cho@canopus.cnu.ac.k, E-mail: ryu@canopus.cnu.ac.k

2009-11-01

22

Exciton diffusion length analysis of mixed donor materials in organic solar cells by doping with phosphorescent iridium complex  

NASA Astrophysics Data System (ADS)

In this paper, the photovoltaic characteristics of ITO/(t-bt)2Ir(acac):CuPc (mixed ratio R by weight)/C60/BCP/Ag organic solar cells (OSCs) are analyzed in detail. The intrinsic properties of a (t-bt)2Ir(acac):CuPc doped layer on device performance are discussed based on theoretical analysis of the experimental OSCs. By studying the photoluminescence densities of pure (t-bt)2Ir(acac) film and mixed films with R=0.75, 0.9, the key exciton diffusion lengths LD were calculated to be 28.3+/-5.0 nm, 31.7+/-5.0 nm, and 33.0+/-2.0 nm, respectively. A new method is then proposed to calculate LD for films with R<0.75. The analysis gives an exciton diffusion length of LD=17.4+/-2.5 nm for a mixed film with R=0.25, an improvement of 74% in comparison to a pure CuPc layer. Moreover, the exciton diffusion efficiency ?ED of an OSC with R=0.25 is obviously improved with the assistance of an increased exciton diffusion length. Finally, to reveal the influence of the dopant (t-bt)2Ir(acac) on charge carrier collection H(V), device energy loss is analyzed and discussed.

Yu, Junsheng; Huang, Jiang; Lin, Hui; Jiang, Yadong

2010-12-01

23

Effective optical path length investigation for cubic diffuse cavity as gas absorption cell  

NASA Astrophysics Data System (ADS)

A simple cubic-shaped cavity with a high-diffuse-reflectivity inner coating as a novel gas detection cell was developed. The effective optical path length (EOPL) was evaluated by comparing the oxygen absorption signal in the cavity and in air based on tunable diode laser absorption spectroscopy. The law for a spherical cavity was applied and modified to a cubic cavity as a function of reflectivity ?, port fraction f, and the side length. Single-pass average path length of the cubic cavity was 0.723(7) times the side length. EOPL can be modified conveniently by adjusting the parameters of the cavity.

Yu, Jia; Zheng, Fu; Gao, Qiang; Li, Yinjie; Zhang, Yungang; Zhang, Zhiguo; Wu, Shaohua

2013-10-01

24

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

NASA Astrophysics Data System (ADS)

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.

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

2009-05-01

25

Characteristic length scales in dense and sparse canopy  

NASA Astrophysics Data System (ADS)

Atmospheric flows near the land surface resemble a rough-wall boundary layer in the absence of a canopy. However, for a dense and extensive canopy, the flow becomes analogous to a mixing layer. For these two extreme cases, a basic framework exists for quantifying critical attributes of the flow dynamics relevant to scalar transport. What is currently lacking is an analogous theory for intermediate canopy densities in which the flow is neither clearly a rough-wall boundary layer nor a mixing layer. Our objective is to examine the inter-connection between canopy density and key flow statistics within and just above the canopy as needed for quantifying momentum and scalar transport. Towards this end, a flume experiment in which a model canopy consisting of a regular array of vertical cylinders having different densities is used. Our analysis suggests that sparse canopies resemble boundary layers while dense canopies share many attributes with perturbed mixing layers. For intermediate canopy densities, the flow near the canopy-atmopshere interface is a superposition of boundary layers and mixing layers with the relative importance of each flow type being dependent on the canopy density. Furthermore, deeper inside the canopy the flow field is primarily dominated by vorticity linked to von Karman vortex streets. We further develop this hypothesis via characteristic length scales derived from our previous analysis and investigate its formulation in the context of the mean momentum balance and closure models.

Poggi, D.; Porporato, A.; Ridolfi, L.; Albertson, J. D.; Katul, G. G.

2003-04-01

26

On the diffusion length and grain size homogeneity requirements for efficient thin-film polycrystalline silicon solar cells  

NASA Astrophysics Data System (ADS)

We examine the influence of intragrain defects and grain boundaries on the macroscopic performance of a thin film polycrystalline silicon solar cell. In addition, we evaluate the effect of grain size inhomogeneity on the cell performance via circuit simulations. From an analytical study of charge transport in individual grains and homogeneous grain systems, we obtain the grain size and intragrain diffusion length requirements for a desired efficiency. We identify the conditions under which the grain size and the intragrain diffusion length dominate the cell characteristics. In devices with intragrain effective diffusion length Lmono ? 100 µm and grain boundary recombination velocity SGB ? 104 cm s-1, achieving a larger grain size beyond several µm is not crucial. The inhomogeneous distribution circuit simulations show that grain size inhomogeneity is not the main limiting factor in polycrystalline silicon solar cells. This is so even in thin polycrystalline silicon films with a broad grain size distribution such as those made with aluminum-induced crystallization at low annealing temperature. The main reason is that the optimum bias point for grains of different sizes only differ by about ˜50 mV over a fairly wide grain diameter range 0.5-50 µm even when Lmono = 100 µm and SGB = 105 cm s-1.

Abass, A.; Van Gestel, D.; Van Wichelen, K.; Maes, B.; Burgelman, M.

2013-01-01

27

Calculation of radon diffusion coefficient and diffusion length for different building construction materials  

Microsoft Academic Search

The diffusion of radon in dwellings is a process determined by the radon concentration gradient across the building material\\u000a structure between the radon source and the surrounding air, and can be a significant contributor to indoor radon inflow. Radon\\u000a can originate from the deeply buried deposit beneath homes and can migrate to the surface of earth. Radon emanates to the

A. K. Narula; S. K. Goyal; Savita Saini; R. P. Chauhan; S. K. Chakarvarti

2009-01-01

28

Twitch characteristics in relation to muscle architecture and actual muscle length  

Microsoft Academic Search

The length dependence of twitch time characteristics is quantified for several skeletal muscles of the rat: lateral gastrocnemius, medial gastrocnemius, plantaris, soleus and semimembranosus. It is shown that muscle architecture influences the length dependent behaviour of twitch time characteristics of muscles. Twitch contraction time is less susceptible to length changes of the muscles than the twitch relaxation time. With the

R. D. Woittiez; P. A. Huijing; R. H. Rozendal

1984-01-01

29

Structure and characteristic length scales in cluster-cluster aggregation simulation  

NASA Astrophysics Data System (ADS)

The structure of a system of aggregating particles is studied by simulation, in both two and three dimensions, using the on-lattice diffusion-limited cluster aggregation model. We calculate static structure factors S(Q) and pair distribution functions for the aggregating system as a whole. The peak in the scattering function, reported for many experimental aggregating colloidal systems and observed in the simulated structures, is shown to correspond to the characteristic outer radius of a `depletion zone' around clusters. The time-scaling properties of S(Q) are examined. A scaling of the structure factor analogous to the case of spinodal decomposition has been observed in experiments; we find reasonable structure factor scaling at intermediate densities and intermediate times but, due to the relatively small systems studied here, we must be cautious in either confirming or denying the presence of similar structure factor scaling for the simulation model throughout the aggregation, especially at early time and at high density. We examine various `characteristic' length scales in the model system, such as the average radius of gyration of clusters, the radius of the largest cluster, the length scale equivalent to the position of the structure factor peak, and so on, in a more general attempt to determine whether the system can be characterised by a single important length scale. From this there is reasonable indication that approximate scaling is demonstrated over a limited region of time. This is consistent with results from light-scattering experiments. Lastly, an examination of the total perimeter length of the ensemble of clusters in the simulation indicates that we may divide the aggregation into three distinct time regimes, corresponding to a pre-aggregation, a pre-fractal, and a fractal regime.

Haw, M. D.; Sievwright, M.; Poon, W. C. K.; Pusey, P. N.

1995-02-01

30

Direct simulation of pumping characteristics for a model diffusion pump  

Microsoft Academic Search

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

YK Lee; JW Lee

1996-01-01

31

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

Microsoft Academic Search

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

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

2009-01-01

32

Structure and Flame Length of Fully-Modulated, Turbulent Diffusion Flames  

Microsoft Academic Search

The turbulent flame structure and flame length of fully-modulated diffusion flames was examined over a range of pulsing frequencies, injection flow rates, and duty-cycles. An injection system employing an electronically-controlled solenoid value was used to discharge puffs of unhealed natural gas and ethylene fuel into still air at one atmosphere pressure. Video imaging of the luminosity from the sooting regions

J. C. HERMANSON; R. DUGNANI; H. JOHARI

2000-01-01

33

Lift-off Heights and Visible Lengths of Vertical Turbulent Jet Diffusion Flames in Still Air  

Microsoft Academic Search

The lift-off heights and visible-flame lengths of jet diffusion flames in still air have been determined for hydrogen, propane, methane and ethylene.The flame lift-off height varies linearly with the jet exit velocity and is independent of the burner diameter for a given gas. The results support the assumption that if the burner exit flow is choked the burner can be

T. Gautam

1984-01-01

34

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

SciTech Connect

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

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

2007-10-01

35

Diffusion of Nanoparticles in Semidilute Polymer Solutions: The Effect of Different Length Scales.  

NASA Astrophysics Data System (ADS)

Gold nanoparticles (Au NPs) were used to investigate the length-scale dependent dynamics in semidilute poly(ethylene glycol) (PEG)-water solutions. Fluctuation correlation spectroscopy was used to measure the diffusion coefficients (D) of the NPs as a function of their radius, Ro (2.5-10 nm), PEG volume fraction, ? (0-0.37) and molecular weight, Mw (5 kg/mol and 35 kg/mol). Our results indicate that the radius of gyration, Rg of the polymer chain is the crossover length scale for the NPs experiencing nanoviscosity or macroviscosity. The reduced diffusivity can be plotted on a single master curve as Do/D= exp (?(Ro/?)^?) for Rg > Ro and as Do/D= exp (?(Rg/?)^?) for Rg <= Ro, where Do is diffusion coefficient in the neat solvent, ? is the correlation length, ? = 1.63 and ? = 0.89. In the intermediate size regime, ? < Ro < a(?), where `a(?)' is the tube diameter for entangled polymer liquid, we found that D ˜ ?-1.45 and independent of Mw. For Ro > a(?), D˜?-4 was obtained. The results were compared with currently available theories.

Kohli, Indermeet; Mukhopadhyay, Ashis

2012-10-01

36

Effect of silicon nitride layers on the minority carrier diffusion length in c-Si wafers  

SciTech Connect

Silicon nitride layers prepared from silane and ammonia based gases by microwave assisted plasma enhanced chemical vapor deposition (PECVD) and by low pressure chemical vapor deposition (LPCVD) techniques on p-type c-silicon substrates were studied via the methods of surface photovoltage (SPV), Fourier transform infrared (FTIR), and secondary-ion-mass spectroscopy (SIMS). The effective diffusion length in silicon was evaluated by the SPV method, and it was strongly influenced by the deposited SiN{sub x} layer. The FTIR spectra show the form of chemical bond of hydrogen in the layer. Two absorption bands belonging to Si-H and N-H groups and their modification after temperature treatment were found in the spectra of PECVD samples, while in the spectra of LPCVD samples only N-H bonds were recognized. Transport of H from PECVD silicon nitride into Si subsurface layer during the annealing process is shown by SIMS profiles of hydrogen. Positive influence of the penetrated H manifests in passivation of defects in the subsurface Si layer and, consequently, in better operation of the space charge region below the nitride and in longer effective diffusion length of minority carriers in the Si bulk. The average value of the diffusion length in the Si samples with the LPCVD nitride was shorter and dependent on the location of wafers in the reactor.

Tousek, Jiri; Touskova, Jana; Poruba, Ales; Hlidek, Pavel; Loerincik, Jan [Faculty of Mathematics and Physics, Department of Macromolecular Physics, Charles University, Ke Karlovu 5, 121 16 Prague (Czech Republic); Solartec s.r.o., Televizni 2618, 756 61 Roznov pod Radhostem (Czech Republic); Institute of Physics, Charles University, Ke Karlovu 5, 121 16 Prague (Czech Republic); Institute of Radioengineering and Electronics, Academy of Sciences of the Czech Republic, Chaberska 57, 18251 Prague (Czech Republic) and Department of Physics, Faculty of Science, J.E. Purkyne University, Ceske Mladeze 8, 40096 Usti nad Labem (Czech Republic)

2006-12-01

37

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

38

Method and apparatus for determining minority carrier diffusion length in semiconductors  

DOEpatents

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.

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

1983-07-12

39

Acid Diffusion Length Corresponding to Post Exposure Bake Time and Temperature  

NASA Astrophysics Data System (ADS)

The post exposure bake (PEB) step in lithography is important for fabricating good patterns when a chemically amplified resist is used. Hydrogen ions or acid is generated by a photoacid generator through light exposure. The generated acid diffuses and acts as a catalyst for chemical amplification during the PEB step. Acid diffusion length (ADL) affects the deprotection of a resist polymer, such that linewidth is affected by ADL. The common parameter that determines ADL is the acid diffusion coefficient D; thus, we must determine D accurately in order to obtain the actual linewidth. However, D cannot be unambiguously determined for the actual PEB temperature and time. ADL has become a critical factor for 100 nm patterns and below. Thus, the accurate ADL determination becomes an important issue for better linewidth prediction by simulation. To match ADL and PEB time and temperature, we attempted to determine the relationship between the PEB parameters and ADL. As a result, we obtained a reasonable ADL.

Park, Jin-Back; Kim, Sung-Hyuck; Kim, Sung-Jin; Cho, Jung-Hyuk; Oh, Hye-Keun

2007-01-01

40

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

PubMed Central

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.

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

2012-01-01

41

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

PubMed

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

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

2012-01-26

42

Length dependence of the saturation characteristics in 1.5-?m multiple quantum well optical amplifiers  

Microsoft Academic Search

The dependence on amplifier length of gain and gain saturation characteristics in 1.5-?m multiple-quantum-well optical amplifiers is reported. Gain measurements are presented for amplifiers with lengths of 200 ?m to 1 mm, and a simple model is introduced which relates gain and saturation characteristics to the amplifier length. The 1-mm-long device has superb properties, with a gain of 25.2 dB

G. Eisenstein; N. Tessler; U. Koren; J. M. Wiesenfeld; G. Raybon; C. A. Burrus

1990-01-01

43

Thermal diffusion of oligosaccharide solutions: the role of chain length and structure.  

PubMed

We investigated the chain length dependence of the thermodiffusion behavior of oligosaccharides by the infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS) technique. Three disaccharides, sucrose, cellobiose and maltose, two trisaccharides, melezitose and raffinose, and a tetrasaccharide, stachyose, have been studied. We determined the thermal diffusion (D(T)), mass diffusion (D), and Soret (S(T)) coefficient as a function of temperature and concentration. While monosaccharides in water accumulate at the cold side in the investigated temperature (20-50 degrees C) and concentration (0.2-0.6667 wt) range, oligosaccharides enrich on the warm side with decreasing temperature or increasing sugar concentration. Additionally, we determined the kinematic viscosity (nu), the density (rho), and the thermal expansion coefficient (alpha) of the mixtures in order to check the linear correlation between D(T) and the ratio alpha/nu, which has been recently found for aqueous solutions of monosaccharides and for alkane mixtures. Finally, we found that D(T) and D decay with increasing chain length of the oligosaccharides in the whole studied range of temperatures, in contradiction with experimental results for nonpolar mixtures and theoretical predictions. PMID:20684655

Blanco, Pablo; Kriegs, Hartmut; Arlt, Bastian; Wiegand, Simone

2010-08-26

44

Method and apparatus for determining minority carrier diffusion length in semiconductors  

DOEpatents

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.

Moore, Arnold R. (Princeton, NJ)

1984-01-01

45

Method and apparatus for determining minority carrier diffusion length in semiconductors  

DOEpatents

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.

Moore, Arnold R. (Princeton, NJ)

1984-02-21

46

A diffusion accelerated solution method for the nonlinear characteristic scheme  

SciTech Connect

Recently the nonlinear characteristic scheme for spatially discretizing the discrete-ordinate equations was introduced. This scheme is accurate for both optically thin and optically thick spatial meshes and produces strictly positive angular and scalar fluxes. The nonlinear characteristic discrete-ordinate equations can be solved using the source iteration method; however, it is well known that the this method converges prohibitively slowly for optically thick problems with scattering ratios at or near unity. In this paper we describe a diffusion accelerated solution method for solving the nonlinear characteristic equations in slab geometry.

Wareing, T.A.; Walters, W.F.; Morel, J.E.

1995-02-01

47

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

NASA Astrophysics Data System (ADS)

Magnetic braking is essential for cloud contraction and star formation. Ambipolar diffusion is unavoidable in self-gravitating, magnetic clouds and leads to single-stage (as opposed to hierarchical) fragmentation (or core formation) and protostar formation. Magnetic forces dominate thermal-pressure and centrifugal forces over scales comparable to molecular cloud radii. Magnetic support of molecular clouds and the imperfect collisional coupling between charged and neutral particles introduce a critical magnetic length scale (?M,cr = 0.62?A?ff) and an Alfvén length scale ((?A = ??A?ni), respectively, in the problem which together with a critical thermal length scale (?T,cr = 1.09Ca?ff) explain naturally the formation of fragments (or cores) in otherwise quiescent clouds and determine the sizes and masses of these fragments during the subsequent stages of contraction. (The quantity ?A is the Alfvén speed, ?ni the mean neutral-ion collision time, Ca the adiabatic speed of sound, and ?ff the free4all time scale.) Numerical calculations based on new adaptive-grid techniques follow the formation of fragments by ambipolar diffusion and their subsequent collapse up to an enhancement in central density above its initial equilibrium value by a factor ?106 with excellent spatial resolution. The results confirm the existence and relevance of the three length scales and extend the analytical understanding of fragmentation and star formation derived from them. The ultimately bimodal opposition to gravity (by magnetic forces in the envelope and by thermal-pressure forces in the core) introduces a break in the slope of the log pn -log r profile. The relation Bc ? pkc between the magnetic field strength and the gas density in cloud cores holds with K = 0.4 - 0.5 even in the presence of ambipolar diffusion up to densities ˜109 cm-3 for a wide variety of clouds. The value K ? ½ is fairly typical. At the late stages of evolution, for example, at a central density of about 3 × 108 cm-3, a typical core is relatively uniform, contains 0.1 Msun and a magnetic field ? 3 mG, and is surrounded by a spatially rapidly decreasing, highly nonspherical (disklike) density distribution. The amount of mass available for accretion onto the compact core is limited by magnetic forces, and is typically ?1 Msun. These results are built into the detailed scenario for star formation described recently elsewhere.

Mouschovias, Telemachos Ch.

1991-05-01

48

Minority carrier diffusion length extraction in Cu2ZnSn(Se,S)4 solar cells  

NASA Astrophysics Data System (ADS)

We report measurement of minority carrier diffusion length (Ld) for high performance Cu2ZnSn(S,Se)4 (CZTSSe) solar cells in comparison with analogous Cu(In,Ga)(S,Se)2 (CIGSSe) devices. Our Ld extraction method involves performing systematic measurements of the internal quantum efficiency combined with separate capacitance-voltage measurement. This method also enables the measurement of the absorption coefficient of the absorber material as a function of wavelength in a finished device. The extracted values of Ld for CZTSSe samples are at least factor of 2 smaller than those for CIGSSe samples. Combined with minority carrier lifetime (?) data measured by time-resolved photoluminescence, we deduce the minority carrier mobility (?e), which is also relatively low for the CZTSSe samples.

Gokmen, Tayfun; Gunawan, Oki; Mitzi, David B.

2013-09-01

49

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

NASA Astrophysics Data System (ADS)

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.

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

1983-03-01

50

Non-dimensional scaling of turbulence characteristics and turbulent diffusivity  

Microsoft Academic Search

Plasma turbulence characteristics, including radial correlation lengths, decorrelation times, amplitude profile and flow velocity, have been measured during a rho* scan on DIII-D while all other transport relevant dimensionless quantities (e.g., beta, nu*, kappa, q, Te\\/Ti) are held nearly constant. The turbulence is measured by examining the correlation properties of the local long wavelength (k?rhoi <= 1) density fluctuations, measured

G. R. McKee; C. C. Petty; R. E. Waltz; C. Fenzi; R. J. Fonck; J. E. Kinsey; T. C. Luce; K. H. Burrell; D. R. Baker; E. J. Doyle; X. Garbet; R. A. Moyer; C. L. Rettig; T. L. Rhodes; D. W. Ross; G. M. Staebler; R. Sydora; M. R. Wade

2001-01-01

51

Characteristics of acoustic-gravity waves in a diffusively separated atmosphere  

Microsoft Academic Search

The effects of wave-induced diffusion on the characteristics of plane acoustic gravity waves in the earth's thermosphere are investigated by means of a two fluid model atmosphere in diffusive equilibrium. At wave periods greater than the shortest characteristic diffusion time for the minor gas, diffusion induced by the wave is considered to act to eliminate amplitude and phase differences between

A. D. del Genio; G. Schubert; J. M. Straus

1979-01-01

52

MAGNETIC QUENCHING OF TURBULENT DIFFUSIVITY: RECONCILING MIXING-LENGTH THEORY ESTIMATES WITH KINEMATIC DYNAMO MODELS OF THE SOLAR CYCLE  

SciTech Connect

The turbulent magnetic diffusivity in the solar convection zone is one of the most poorly constrained ingredients of mean-field dynamo models. This lack of constraint has previously led to controversy regarding the most appropriate set of parameters, as different assumptions on the value of turbulent diffusivity lead to radically different solar cycle predictions. Typically, the dynamo community uses double-step diffusivity profiles characterized by low values of diffusivity in the bulk of the convection zone. However, these low diffusivity values are not consistent with theoretical estimates based on mixing-length theory, which suggest much higher values for turbulent diffusivity. To make matters worse, kinematic dynamo simulations cannot yield sustainable magnetic cycles using these theoretical estimates. In this work, we show that magnetic cycles become viable if we combine the theoretically estimated diffusivity profile with magnetic quenching of the diffusivity. Furthermore, we find that the main features of this solution can be reproduced by a dynamo simulation using a prescribed (kinematic) diffusivity profile that is based on the spatiotemporal geometric average of the dynamically quenched diffusivity. This bridges the gap between dynamically quenched and kinematic dynamo models, supporting their usage as viable tools for understanding the solar magnetic cycle.

Munoz-Jaramillo, Andres; Martens, Petrus C. H. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States); Nandy, Dibyendu, E-mail: martens@solar.physics.montana.edu, E-mail: amunoz@cfa.harvard.edu, E-mail: dnandi@iiserkol.ac.in [Indian Institute for Science Education and Research, Kolkata, Mohampur 741252, West Bengal (India)

2011-01-20

53

Existence of optimum intermolecular spacing for maximum exciton diffusion length in tris(2-phenylpyridine) iridium(III)  

Microsoft Academic Search

A study of one-dimensional exciton diffusion in tris(2-phenylpyridine) iridium(III) molecules as a function of intermolecular spacing is reported. We show for the first time the existence of an optimum intermolecular spacing that gives the longest diffusion length in [Ir(ppy)3] molecules. When the intermolecular spacing is too short, the long-range excitonic quenching becomes dominant; on the other hand, when it is

Y. Divayana; X. W. Sun

2010-01-01

54

Bifurcation characteristics of fractional reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

Anomalous behavior of many complex heterogeneous systems is known to be adequate modeled with the fractional differential equations and in particular with the fractional reaction-diffusion systems (FRDS). In this article, a generalized reaction-diffusion model in form of a system of nonlinear fractional partial differential equations is considered. It is shown that orders of the fractional derivatives contained in the FRDS are new bifurcation parameters that can change stability both of the spatially-homogeneous and of the spatially-nonhomogeneous stationary solutions. A general principle of linear stability for FRDS is formulated. The results of linear stability analysis are confirmed by computer simulations of some basic FRDS with classical nonlinearities. It is shown that stability of steady state solutions of FRDS and their evolution are mainly determined by the orders of the fractional derivatives and the eigenvalue spectrum of the linearized systems. Moreover, new types of spatiotemporal solutions and new mechanisms of pattern formation can be observed in FRDS because of new bifurcation types. Characteristic plots of evolution of steady state solutions for basic time-fractional reaction-diffusion systems are presented.

Datsko, Bohdan; Gafiychuk, Vasyl; Luchko, Yuri

2012-11-01

55

Spin wave mode transition induced by surface anisotropy and characteristic length in magnetic nanoparticles  

Microsoft Academic Search

In magnetic nanoparticles with cylindrical symmetry of the magnetization configurations, spin wave mode transition (SWMT) is predicted for the case of a surface anisotropy parallel to the uniform magnetization. Theoretical investigation has shown that a characteristic length can be determined to evaluate the spatial influence of the spin wave mode excited by surface anisotropy. This knowledge implies SWMT occurs as

Peiheng Zhou; Li Zhang; Longjiang Deng

2010-01-01

56

Three-dimensional transport imaging for the spatially resolved determination of carrier diffusion length in bulk materials.  

PubMed

A contact-free optical technique is developed to enable a spatially resolved measurement of minority carrier diffusion length and the associated mobility-lifetime (??) product in bulk semiconductor materials. A scanning electron microscope is used in combination with an internal optical microscope and imaging charge-coupled device (CCD) to image the bulk luminescence from minority carrier recombination associated with one-dimensional excess carrier generation. Using a Green's function to model steady-state minority carrier diffusion in a three-dimensional half space, non-linear least squares analysis is then applied to extract values of carrier diffusion length and surface recombination velocity. The approach enables measurement of spatial variations in the ?? product with a high degree of spatial resolution. PMID:22559534

Blaine, K E; Phillips, D J; Frenzen, C L; Scandrett, C; Haegel, N M

2012-04-01

57

Levitation effect: role of symmetry and dependence of diffusivity on the bond length of homonuclear and heteronuclear diatomic species.  

PubMed

Molecular dynamics investigation of model diatomic species confined to the ?-cages of zeolite NaY is reported. The dependence of self-diffusivity on the bond length of the diatomic species has been investigated. Three different sets of runs have been carried out. In the first set, the two atoms of the diatomic molecule interact with the zeolite atoms with equal strength (example, O(2), the symmetric case). In the second and third sets which correspond to asymmetric cases, the two atoms of the diatomic molecule interact with unequal strengths (example, CO). The result for the symmetric case exhibits a well-defined maximum in self-diffusivity for an intermediate bond length. In contrast to this, the intermediate asymmetry leads to a less pronounced maximum. For the large asymmetric case, the maximum is completely absent. These findings are analyzed by computing a number of related properties. These results provide a direct confirmation at the microscopic level of the suggestion by Derouane that the supermobility observed experimentally by Kemball has its origin in the mutual cancellation of forces. The maximum in diffusivity from molecular dynamics is seen at the value predicted by the levitation effect. Further, these findings suggest a role for symmetry in the existence of a diffusivity maximum as a function of diameter of the diffusant often referred to as the levitation effect. The nature of the required symmetry for the existence of anomalous diffusivity is interaction symmetry which is different from that normally encountered in crystallography. PMID:21401037

Sharma, Manju; Yashonath, S

2011-03-14

58

On the anomalous diffusion characteristics of membrane-bound proteins  

Microsoft Academic Search

It is shown how the transitions from sub-diffusion to super-diffusion and from sub-diffusion to normal diffusion of individual (independent) proteins within plasma membranes [S. Khan et al., Phys. Rev. E 71 (2005) 041915] can be understood within the framework of a Levy-flight model.

A. M. Reynolds

2005-01-01

59

Identifying local characteristic lengths governing sound wave properties in solid foams  

NASA Astrophysics Data System (ADS)

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.

Tan Hoang, Minh; Perrot, Camille

2013-02-01

60

Transistor characteristics of 14-nm-gate-length EJ-MOSFETs  

Microsoft Academic Search

We have fabricated electrically variable shallow junction metal-oxide-silicon field-effect transistors (EJ-MOSFETs) to investigate transport characteristics of ultrafine gate MOSFETs. By using EB direct writing on an ultrahigh-resolution negative resist (calixarene), we could achieved a gate length of only 14 nm. Despite such an ultrafine gate, the device exhibited transistor operation at room temperature. From studying the devices with the gate

H. Kawaura; T. Sakamoto; T. Baba; Y. Ochiai; J. Fujita; J. Sone

2000-01-01

61

Characteristic length scales governing plasticity\\/brittleness of bulk metallic glasses at ambient temperature  

Microsoft Academic Search

In this letter, we propose a unified theory for the size-dependent plasticity of bulk metallic glasses (BMGs) at room temperature. Based on the principle of energy balance and the shear-banding kinetics, two characteristic length scales are derived. One is a sample-geometry dependent variable related to the elastic energy released to drive shear-band propagation and the other is a material-dependent constant

Y. Yang; J. C. Ye; J. Lu; P. K. Liaw; C. T. Liu

2010-01-01

62

Direct determination of minority carrier diffusion lengths at axial GaAs nanowire p-n junctions.  

PubMed

Axial GaAs nanowire p-n diodes, possibly one of the core elements of future nanowire solar cells and light emitters, were grown via the Au-assisted vapor-liquid-solid mode, contacted by electron beam lithography, and investigated using electron beam induced current measurements. The minority carrier diffusion lengths and dynamics of both, electrons and holes, were determined directly at the vicinity of the p-n junction. The generated photocurrent shows an exponential decay on both sides of the junction and the extracted diffusion lengths are about 1 order of magnitude lower compared to bulk material due to surface recombination. Moreover, the observed strong diameter-dependence is well in line with the surface-to-volume ratio of semiconductor nanowires. Estimating the surface recombination velocities clearly indicates a nonabrupt p-n junction, which is in essential agreement with the model of delayed dopant incorporation in the Au-assisted vapor-liquid-solid mechanism. Surface passivation using ammonium sulfide effectively reduces the surface recombination and thus leads to higher minority carrier diffusion lengths. PMID:22364406

Gutsche, Christoph; Niepelt, Raphael; Gnauck, Martin; Lysov, Andrey; Prost, Werner; Ronning, Carsten; Tegude, Franz-Josef

2012-02-29

63

Modeling tip zones to predict the throw and length characteristics of faults  

SciTech Connect

A map of faults in a 60 km{sup 2} area of the southern North Sea has been produced from three-dimensional seismic data. The faults shown on the map obey power-law cumulative-frequency distributions for throw (power-law exponent, D, {approx} 2.7) and length (D {approx} 1.1). Simulations have been carried out to correct for sampling biases in the data and to make predictions of the throw the data and to make predictions of the throw and length scaling characteristics of the faults. The most important bias is caused by poor resolution of the small displacement tip zones of faults. The raw data show considerable scatter in their length: throw ratios, but they more closely fit a linar relationship if a length of 500 m is added to each fault, thereby making up for the zones near the fault tips with throws ({approx} 15 m) below seismic resolution. Further variability in the data may be caused by such geological factors as fault interaction. Tip lengths have been extended to simulate the actual fault pattern in the study area. Maps produced by this procedure can be used to estimate the true connectivity of the fault network. Extending the faults results in greater connectivity than shown by the raw data, which may cause greater compartmentalization of the rock mass. This greater compartmentalization has implications for hydrocarbon exploitation if the faults are sealing. A problem with the model, however, is that it does not deal effectively with the interaction of subparallel, noncoplanar faults. To test the reliability of the procedure, we analyzed exposure-scale faults in Somerset, United Kingdom, where the tips are well constrained. Both length-throw relationships and map-pattern connectivity for the simulated fault networks agree closely with the actual data.

Pickering, G.; Sanderson, D.J.; Bull, J.M. [Univ. of Southampton (United Kingdom)] [and others

1997-01-01

64

Characteristics of Cluster Implantation and Low Diffusion Annealing  

SciTech Connect

Beyond 45 nm device fabrication, it is recognized that the ultra-shallow junction (USJ) formation is required, which is achieved by the ultra-low energy ion implantation and ultra-low diffusion annealing. For this purpose, Cluster ion implantation (CII) and the Flash lamp annealing (FLA) activation processes have been developed. In this paper, we introduce characteristics of activation using B{sub 18}Hx{sup +} implantation with FLA, which are applied to a source drain extension (SDE) for pMOSFET in Hgh-k/metal process. We will prove that the combined process of B{sub 18}Hx{sup +} and FLA can make the low sheet resistance and the fine crystal recovery for USJ formation such a SDE. Moreover, the combined process of C{sub 7}Hx{sup +} implantation and FLA can make the high stress region for nMOSFET by the high substitutional Carbon. If both of B{sub 18}Hx{sup +} implantation and C{sub 7}Hx{sup +} implantation with FLA are applied to High-k/metal process, it will give the highest performance. The combination of FLA and cluster ion implanter ''CLARIS'' which is developed for IC fabrication, will promise the most powerful performance beyond 45 nm node device.

Nagayama, Tsutomu; Hamamoto, Nariaki; Umisedo, Sei; Tanjyo, Masayasu [Nissin Ion Equipment Co., Ltd., 575 Kuze-Tonoshiro-cho, Minami-ku, Kyoto, 601-8205 (Japan); Ootsuka, Fumio [Semiconductor Leading Edge Technologies, Inc, (Selete), 16-1 Onogawa, Tsukuba-shi, 305-8569 (Japan); Renesas Technology Corp. (Japan); Aoyama, Takayuki [Semiconductor Leading Edge Technologies, Inc, (Selete), 16-1 Onogawa, Tsukuba-shi, 305-8569 (Japan)

2008-11-03

65

Fiber length and pulping characteristics of switchgrass, alfalfa stems, hybrid poplar and willow biomasses.  

PubMed

Switchgrass (Panicum virgatum), alfalfa stems (Medicago sativa), second year growth hybrid poplar (Populus) and willow (Salix spp.) were examined to determine fiber characteristics, pulping behavior and paper properties. Alfalfa stems and switchgrass both showed length weighted average fiber length (LWW) of 0.78 mm, a very narrow fiber length distribution and high fines content. Willow and hybrid poplar have lower fines content but a very low average fiber length (0.42 and 0.48 mm LWW). In addition, the four biomass species showed distinctly different chemical compositions. Switchgrass was defibered successfully using Soda and Soda Anthraquinone (AQ) pulping and demonstrated good paper properties. Both fast-growing wood species pulped well using the Kraft process, and showed acceptable tensile strength, but low tear strength. Alfalfa stems reacted very poorly to Soda and Soda AQ pulping but responded well to Kraft and Kraft AQ. Pulps with tensile and tear strength considerably higher than those found for commercial aspen pulps were observed for alfalfa. All four biomass species examined demonstrated low pulp yield. The highest yields were obtained with poplar and switchgrass (around 43%). Considering the short fibers and low yields, all four biomass types will likely only be used in paper manufacturing if they offer considerable economic advantage over traditional pulp wood. PMID:19720527

Ai, Jun; Tschirner, Ulrike

2009-08-31

66

Permeability models of porous media: Characteristic length scales, scaling constants and time-dependent electrokinetic coupling  

NASA Astrophysics Data System (ADS)

Four important models that describe the fluid permeability of geological porous media and that are derived from different physical approaches have been rewritten in a generic form that implies a characteristic scale length and scaling constant for each model. The four models have been compared theoretically and using experimental data from 22 bead packs and 188 rock cores from a sand-shale sequence in the UK sector of the North Sea. The Kozeny-Carman model did not perform well because it takes no account of the connectedness of the pore network, and should no longer be used. The other three models (Schwartz, Sen and Johnson (SSJ), Katz and Thompson (KT) and the so-called RGPZ) all performed well when used with their respective length scales and scaling constants. Surprisingly, we have found that the SSJ and KT models are extremely similar, such that their characteristic scale lengths and scaling constants are almost identical even though they are derived using extremely different approaches; the SSJ model by weighting the Kozeny-Carman model using the local electric field, the KT model using entry radii from fluid imbibition measurements. The experimentally determined scaling constants for each model were found to be cSSJ ? cKT ? 8/3 ? cRGPZ/3. Use of these models with AC electrokinetic theory has also allowed us to show that these scaling constants are also related to the a value in the RGPZ model and the m* value in time-dependent electrokinetic theory, and then derive a relationship between the electrokinetic transition frequency and the RGPZ scale length, which we have validated using experimental data. The practical implication of this work for permeability prediction is that the Katz and Thompson model should be used when fluid imbibition data is available, while the RGPZ model should be used when electrical data is available.

Glover, Paul; Walker, Emile

2010-05-01

67

The characteristics of hydrogen diffusion and concentration around a crack tip concerned with hydrogen embrittlement  

Microsoft Academic Search

Previously, we proposed a physical model for hydrogen diffusion and accumulation around the crack tip and performed accurate numerical analysis which takes account of the effects of both hydrogen diffusion and accumulation due to the stress gradient. Based on this analysis, the characteristics of hydrogen accumulation around the crack tip were clarified.Since the characteristics of stress corrosion cracking and corrosion

A. Toshimitsu Yokobori; Yasrou Chinda; Takenao Nemoto; Koji Satoh; Tetsuya Yamada

2002-01-01

68

Diffusion characteristics of water vapor in some keratins  

Microsoft Academic Search

Summary A detailed examination of the diffusion behavior of water vapor in stratum corneum samples obtained from humans, guinea pig and neonatal rat, a well as in human air fibers, was carried out. It has been found that, as with most polymeric films above the glass transition temperature, diffusion of water vapor into stratum corneum and hair is characterized by

A. F. El-Shimi; H. M. Princen

1978-01-01

69

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. ...

70

Characteristic length scales of spatial models in ecology via fluctuation analysis  

PubMed Central

A technique of fluctuation analysis is introduced for the identification of characteristic length scales in spatial models, with similarities to the recently introduced methods using correlations. The identified length scale provides the optimal size to extract non-trivial large-scale behaviour in such models. The method is demonstrated for three biological models: genetic selection, plant competition and a complex marine system; the first two are coupled map lattices and the last one is a cellular automaton. These cover the three possibilities for asymptotic (long time) dynamics: fixation (the system converges to a fixed point); statistical fixation (the spatial statistics converge to fixed values); and complex statistical structure (the statistics do not converge to fixed values). The technique is shown to have an additional use in the identification of aggregation or dispersal at various scales. The method is rigorously justifiable in the cases when the system under analysis satisfies the FKG (Fortuin-Kasteleyn-Ginibre) property and has a fast decay of correlations. We also discuss the connection between the fluctuation analysis length scale and hydrodynamic limits methods to derive large scale equations for ecological models.

Keeling, M. J.; Mezic, I.; Hendry, R. J.; McGlade, J.; Rand, D. A.

1997-01-01

71

Water-like solvation thermodynamics in a spherically symmetric solvent model with two characteristic lengths  

PubMed Central

We examine by molecular dynamics simulation the solubility of small apolar solutes in a solvent whose particles interact via the Jagla potential, a spherically symmetric ramp potential with two characteristic lengths: an impenetrable hard core and a penetrable soft core. The Jagla fluid has been recently shown to possess water-like structural, dynamic, and thermodynamic anomalies. We find that the solubility exhibits a minimum with respect to temperature at fixed pressure and thereby show that the Jagla fluid also displays water-like solvation thermodynamics. We further find low-temperature swelling of a hard-sphere chain dissolved in the Jagla fluid and relate this phenomenon to cold unfolding of globular proteins. Our results are consistent with the possibility that the presence of two characteristic lengths in the Jagla potential is a key feature of water-like solvation thermodynamics. The penetrable core becomes increasingly important at low temperatures, which favors the formation of low-density, open structures in the Jagla solvent.

Buldyrev, Sergey V.; Kumar, Pradeep; Debenedetti, Pablo G.; Rossky, Peter J.; Stanley, H. Eugene

2007-01-01

72

New sequentially etched quantum-yield technique for measuring surface recombination velocity and diffusion lengths of solar cells  

SciTech Connect

We have developed a new technique to characterize the individual layers of high-efficiency solar cells. In general, the technique allows one to set lower bounds for diffusion lengths and upper and lower bounds for interface recombination velocity. This is sufficient to determine which parameter limits performance, and often the actual parameter values are also determined accurately. We obtain this information by fitting a theoretical model to quantum-yield spectra measured on a sample in its initial state, and after its window passivation and top active layers are sequentially etched away. With such data on two p on n GaAs solar cells with Al/sub x/Ga/sub 1-//sub x/As passivation, we determined minority-carrier hole diffusion lengths of 1.0 +- 0.2 and 0.2 +- 0.05 ..mu.. in the Te-doped n layers for first and second samples, respectively. We found lower limits for the minority-carrier electron diffusion lengths in the top p layers of 2.0 ..mu.. in the carbon-doped first sample and 4.0 ..mu.. in the Mg-doped second sample. We determined interface recombination velocities of 4.0 +- 0.5 (10/sup 5/) cm/s at the carbon-doped p layer's interface with its Al/sub 0.45/Ga/sub 0.55/As passivation layer, and between 500 and 10/sup 4/ cm/s for the Mg-doped layer's interface with its Al/sub 0.9/Ga/sub 0.1/As passivation layer. After stripping the Al/sub x/Ga/sub 1-//sub x/As layer away, we measured surface recombination velocities of 8.0 +- 2.0 (10/sup 6/) cm/s on the carbon-doped sample, and 1.0 +- 0.2 (10/sup 7/) cm/s on the Mg-doped sample.

Partain, L.D.; Kuryla, M.S.; Fraas, L.M.; McLeod, P.S.; Cape, J.A.

1987-06-01

73

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

Microsoft Academic Search

Opposing views exist as to how unesterified fatty acids (FA) enter and leave cells. It is commonly believed that for short- and medium-chain FA free diffusion suffices whereas it is questioned whether proteins are required to facilitate transport of long-chain fatty acid (LCFA). Furthermore, it is unclear whether these proteins facilitate binding to the plasma membrane, trans-membrane movement, dissociation into

Frits Kamp; James A. Hamilton

2006-01-01

74

Current-perpendicular-to-plane spin transport properties of CoFe alloys: Spin diffusion length and scattering asymmetry  

Microsoft Academic Search

From measurements of the current-perpendicular-to-plane magnetoresistance of magnetic multilayers and exchange-biased spin-valves combining the ferromagnetic (F) alloys Co50Fe50 and Co70Fe30 with the nonmagnetic metal Cu, we extract values of the bulk scattering asymmetry, betaF, the spin-diffusion length, lsfF, the interface scattering asymmetry, gammaF\\/Cu, and twice the enhanced specific resistance, 2ARF\\/Cu*. The parameters of the two alloys lie within mutual uncertainties

C. Ahn; K.-H. Shin; R. Loloee; J. Bass; W. P. Pratt

2010-01-01

75

Stability Characteristics of Turbulent Hydrogen Dilute Diffusion Flames  

Microsoft Academic Search

Diffusion flame combustion of high-hydrogen fuels in land-based gas turbine combustors may include dilution of the fuel with inert gases and high velocity fuel injection to reduce NOx emissions. Stability regimes of such combustors are investigated in this study by examining turbulent dilute diffusion flames of hydrogen\\/nitrogen mixtures, issuing into a quiescent environment from a thin-lipped tube. This study has

Nathan T. Weiland; Peter A. Strakey

2009-01-01

76

Moisture Diffusion Inside Paper Materials in the Hygroscopic Range and Characteristics of Diffusivity Parameters  

Microsoft Academic Search

Some current models for moisture diffusion in paper in the hygroscopic range are analyzed. In general, two types of diffusion models can be recognized. Models of the first type treat paper as a homogeneous medium with moisture flux that is proportional to the gradient in moisture content. Although useful in some instances this approach fails frequently because it homogenizes the

B. V. Ramarao; A. Massoquete; S. Lavrykov; S. Ramaswamy

2003-01-01

77

Hole diffusion length in n-TiO2 single crystals and sintered electrodes - Photoelectrochemical determination and comparative analysis  

NASA Astrophysics Data System (ADS)

The photoelectrochemical behavior of an n-TiO2 (rutile) single crystal under different treatments (mechanical polishing and chemical and photoelectrochemical etching) is analyzed, and the conditions under which Gaertner's model can be applied are determined. The hole diffusion length Lp obtained from the photoelectrochemical data is about 10 to the -6th cm for the etched single crystal and seems to be governed by electron-hole recombination at centers associated with impurities introduced in the lattice during the manufacturing process. This value of the hole diffusion length determines the minimum value of the donor concentration Nd for an efficient separation of carriers within the semiconductor depletion layer. This explains the existence of a maximum of the quantum efficiency for Nd of about 6 x 10 to the 18th per cu cm, which has been found to be a value common to n-TiO2 single crystals of different origin. Lattice defects introduced near the crystal surface by mechanical polishing behave as recombination centers which reduce Lp to values of the order of 10 to the -7th cm. A comparison with Lp values of n-TiO2 sintered electrodes is made.

Salvador, P.

1984-04-01

78

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

SciTech Connect

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.

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

79

PREDICTION OF CHARACTERISTIC LENGTH AND FRACTURE TOUGHNESS IN DUCTILE-BRITTLE TRANSITION  

SciTech Connect

Finite element method was used to analyze the three-point bend experimental data of A533B-1 pressure vessel steel obtained by Sherry, Lidbury, and Beardsmore [1] from -160 to -45 C within the ductile-brittle transition regime. As many researchers have shown, the failure stress ({sigma}{sub f}) of the material could be approximated as a constant. The characteristic length, or the critical distance (r{sub c}) from the crack tip, at which {sigma}{sub f} is reached, is shown to be temperature dependent based on the crack tip stress field calculated by the finite element method. With the J-A{sub 2} two-parameter constraint theory in fracture mechanics, the fracture toughness (J{sub C} or K{sub JC}) can be expressed as a function of the constraint level (A{sub 2}) and the critical distance r{sub c}. This relationship is used to predict the fracture toughness of A533B-1 in the ductile-brittle transition regime with a constant {sigma}{sub f} and a set of temperature-dependent r{sub c}. It can be shown that the prediction agrees well with the test data for wide range of constraint levels from shallow cracks (a/W= 0.075) to deep cracks (a/W= 0.5), where a is the crack length and W is the specimen width.

Lam, P

2008-04-15

80

Characteristic length of dynamic glass transition near T{sub g} for a wide assortment of glass-forming substances  

SciTech Connect

Dynamic heterogeneity is an active field of glass-transition research. the length scale of this heterogeneity is called the characteristic length. It can be calculated from complex heat capacity curves in the equilibrium liquid or from dynamic calorimetry curves corrected with regard to nonequilibrium. No molecular parameters or microscopic models are necessary for obtaining the length. The authors report the characteristic length near glass temperature for about 30 glass formers including small-molecule liquids, polymers, silicate glasses, a metallic glass, a liquid crystal, and a plastic crystal. The lengths are between 1.0 and 3.5 nm with certain accumulations between 1.0 and 2.0 nm and between 2.5 and 3.5 nm. To try a correlation to other properties, the authors find that at least two should be included, e.g., Angell's fragility and the distance of T{sub g} from the crossover temperature, T{sub c}.

Hempel, E.; Hempel, G.; Hensel, A.; Schick, C.; Donth, E.

2000-03-23

81

Effects of Diffusion Pump Oil Contamination on the Reflectance Characteristics of Various Surfaces.  

National Technical Information Service (NTIS)

During thermal testing in a space simulation chamber, the extent of diffusion pump oil contamination on all important surfaces should be determined. This information and an understanding of the reflectance characteristics of the oil contaminated surfaces ...

E. C. Pinion

1966-01-01

82

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

National Technical Information Service (NTIS)

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. Th...

A. K. Gupta M. Ghaderi

2004-01-01

83

Electron beam-induced increase of electron diffusion length in p-type GaN and AlGaN\\/GaN superlattices  

Microsoft Academic Search

The diffusion length, L, of electrons in Mg-doped p-GaN grown by metal-organic chemical vapor deposition was found to increase linearly from 0.55 to 2.0 mum during 1500 s of electron beam irradiation. Similar trends were observed for p-type Mg-doped GaN and AlGaN\\/GaN superlattices grown by molecular-beam epitaxy. While the electron diffusion length in p-(Al)GaN depends on irradiation time, the diffusion

Leonid Chernyak; Andrei Osinsky; Vladimir Fuflyigin; E. F. Schubert

2000-01-01

84

Characteristics of TiN barrier layer against Cu diffusion  

Microsoft Academic Search

Thin films of TiN interposed between Cu and SiO2 layers have been examined as a diffusion barrier as well as an adhesion-promoting layer for Cu metallization. Reliability of TiN barrier layer has been investigated by studying the penetration of copper into thermal oxide as a function of temperature. We have used X-ray diffraction, Auger electron spectroscopy and capacitance-voltage(C–V) measurements in

M. Y. Kwak; D. H. Shin; T. W. Kang; K. N. Kim

1999-01-01

85

Carrier diffusion lengths in (In,Ga)(As,N)/GaAs quantum wells studied by spatially resolved cathodoluminescence  

NASA Astrophysics Data System (ADS)

We have directly measured the carrier diffusion length Ld of dilute nitride single quantum wells (QWs) by means of spatially resolved cathodoluminescence (CL) spectroscopy as a function of the CL detection energy (E ) for different temperatures. While Ld (E ) of a GaAs/(Al,Ga)As reference sample does not vary with E , Ld (E ) of (In,Ga)(As,N)/GaAs QWs is significantly reduced with increasing E . The qualitative difference of Ld (E ) between the binary and quaternary QWs is explained in terms of different transport mechanisms (hopping versus tunnelling, respectively) in conjunction with the presence of localized states. Ld of (In,Ga)(As,N) QWs decreases rapidly with increasing temperature. Ld can be significantly reduced by the presence of extended defects even at low temperatures.

Jahn, U.; Miguel-Sánchez, J.; Flissikowski, T.; Grahn, H. T.; Hey, R.; Guzmán, A.

2006-03-01

86

Moisture Diffusion Parameter Characteristics for Epoxy Composites and Neat Resins.  

National Technical Information Service (NTIS)

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...

E. R. Long

1979-01-01

87

Flow Characteristics in Compact Thermal Spray Coating Systems with Minimum Length Nozzle  

NASA Astrophysics Data System (ADS)

In this study, numerical analysis is performed to adopt the equivalence ratio on the high velocity oxygen fuel (HVOF) thermal spray coating systems equipped with a minimum length nozzle. The analysis is applied to investigate the axisymmetric, steady-state, turbulent, and chemically combusting flow both within the torch and in a free jet region between the torch and the substrate to be coated. The combustion is modeled using a single-step and eddy-dissipation model which assumes that the reaction rate is limited by the turbulent mixing rate of the fuel and oxidant. As the diameter of the nozzle throat is increased, the location of the Mach shock disc moves backward from the nozzle exit. As the throat diameter and the divergent portion are 6 mm and 8 mm, respectively, the pressure in the HVOF system is the lowest at the chamber and the expanding gas is steadily maintained with both high velocity and high temperature for different equivalence ratios. Thus, relatively minor amendments of the equivalence ratio and the geometry of HVOF can lead to improved control over coating characteristics.

Seung-Hyun, Kim; Youn-Jea, Kim

2009-10-01

88

Prognostic factors in diffuse malignant pleural mesothelioma: effects of pretreatment clinical and laboratory characteristics  

Microsoft Academic Search

The aim of this study was to investigate the effects of various pretreatment clinical and laboratory characteristics on the survival of patients with diffuse malignant pleural mesothelioma (DMPM). One hundred histopathologically confirmed DMPM patients were evaluated. Fifty-nine were treated with chemoimmunotherapy, while 41 who had refused chemoimmunotherapy received supportive therapy alone. The following pretreatment characteristics were evaluated in both univariate

M. METINTAS; S. METINTAS; I. UCGUN; A. R. GIBBS; E. HARMANCI; F. ALATAS; S. ERGINEL; N. TEL; O. PASAOGLU

2001-01-01

89

Diffuse Shock-Aurora: the Characteristics, Evolution and Cause (Invited)  

NASA Astrophysics Data System (ADS)

The magnetospheric compression and magnetic reconnection are enhanced in the local noon sector when interplanetary shocks impinge on the subsolar magnetopause. Auroras in the dayside high latitude ionosphere light up within seconds to few minutes indicating causes of the aurora in the outer magnetosphere and/or on the magnetopause ~10 RE away from the ionosphere. Consistent observation results from space and the ground revealed that the equatorward expanding and anti-sunward propagating shock aurora first seen from space is primarily diffuse aurora. The aurora is generated by hard electrons with energies near or greater than 1 keV at FAST. The electrons have an isotropic pitch angle distribution and an evident enhancement in the energy and number fluxes during the shock compression. These precipitated electrons penetrate to lower ionosphere at ~150 km altitude than the soft electrons and excite green auroral emissions of 557.7 nm that have been identified by the ground all-sky imager (ASI) and the meridian-scanning photometer (MSP). The diffuse auroral intensity can exceed the red arcs (which is a rare situation in auroral emissions) and can be brighter than 5 kR. Theoretically, the speculated cause in the outer magnetosphere is the temperature anisotropy near equator where the most intense compression develops. The temperature anisotropy provides a possible source of free energy for different plasma instabilities that lead to the wave-particle scattering enhancement. Consequently, isotropic electrons flourish, so do those in the loss cone, which explains what have been measured at FAST and the ground. Although near-equator in situ measurements of the temperature anisotropy have not been widely reported, relevant observations are documented and will be reviewed in this paper to examine the theory.

Zhou, X.

2010-12-01

90

The Influence of Operating Temperature on Mass Transfer Characteristics during a Diffusion Process in Bilimbi Fruit  

Microsoft Academic Search

The effects of operating temperature on an osmotic sucrose solution with a selected concentration pattern (30-50-70 °Brix) on mass transfer characteristics during the diffusion process in bilimbi fruits in a dehydration system were investigated. Half-ripe bilimbi fruits were used. In the pretreatment step, all fruits were blanched in boiling water for 1 min to soften the fruit for better diffusion.

Chairat SIRIPATANA

91

The characteristic behavior of finite length line sources of heat in a crossflow  

Microsoft Academic Search

A modified simple integral model for plume behavior from finite length line sources of heat and momentum is presented that identifies observed trends in plume trajectory data. Experiments on several finite length line sources of heat and momentum in the form of elevated (rows of stacks) and surface (slot) releases were conducted in a water tunnel. Plume behavior was documented

P. R. Slawson; G. J. Hitchman; L. E. Hawker

1990-01-01

92

The Narrow Pulse Approximation and Long Length Scale Determination in Xenon Gas Diffusion NMR Studies of Model Porous Media  

Microsoft Academic Search

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

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

2002-01-01

93

Morphologic characteristics and immunohistochemical profile of diffuse intrinsic pontine gliomas.  

PubMed

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

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

94

Length-dependent thermoelectric characteristics of silicon nanowires on plastics in a relatively low temperature regime in ambient air  

NASA Astrophysics Data System (ADS)

We report on the thermoelectric characteristics of p-type silicon nanowires (NWs) on plastics in the relatively low temperature regime below 47?° C, and for temperature differences of less than 10 K in ambient air. Thermal profile images are utilized to directly determine the temperature difference in the NWs generated by Joule heating in air. The Seebeck coefficient of the NWs increases from 294 to 414 ?V K?1 as the NW length varies from 40 to 280 ?m. For a temperature difference of 7 K, the maximal Seebeck voltage can be estimated to be 2.7 mV for NWs with a length of 280 ?m. In contrast, the output power is maximized for NWs length of 240 ?m. The maximized output power obtained experimentally in this study is 2.1 pW at a temperature difference of 6 K. The thermoelectric characteristics are analyzed and discussed.

Choi, Jinyong; Cho, Kyoungah; Kim, Sangsig

2013-11-01

95

Length-dependent thermoelectric characteristics of silicon nanowires on plastics in a relatively low temperature regime in ambient air.  

PubMed

We report on the thermoelectric characteristics of p-type silicon nanowires (NWs) on plastics in the relatively low temperature regime below 47?° C, and for temperature differences of less than 10 K in ambient air. Thermal profile images are utilized to directly determine the temperature difference in the NWs generated by Joule heating in air. The Seebeck coefficient of the NWs increases from 294 to 414 ?V K(-1) as the NW length varies from 40 to 280 ?m. For a temperature difference of 7 K, the maximal Seebeck voltage can be estimated to be 2.7 mV for NWs with a length of 280 ?m. In contrast, the output power is maximized for NWs length of 240 ?m. The maximized output power obtained experimentally in this study is 2.1 pW at a temperature difference of 6 K. The thermoelectric characteristics are analyzed and discussed. PMID:24141226

Choi, Jinyong; Cho, Kyoungah; Kim, Sangsig

2013-10-18

96

Channel-length-dependent transport and photovoltaic characteristics of carbon-nanotube-based, barrier-free bipolar diode.  

PubMed

Carbon nanotube (CNT) diodes with different channel length between L = 0.6 ?m to 3.5 ?m are fabricated on the same tube, and the electric and photovoltaic characteristics are investigated. It is found that although the open voltage of the diode increases rapidly for channel length L less than 1.0 ?m, it saturates for longer channel devices. On the other hand, the short circuit current of the diode exhibites a clear peak at intermediate channel length of about 1.5 ?m, a large leakage current via tunneling for short channel device and significantly decreased current for long channel device due to the increased recombination and channel resistance. The optimal channel length for a CNT diode in photovoltaic application is thus determined to be about 1.5 ?m. PMID:22324635

Yang, Leijing; Wang, Sheng; Zeng, Qingsheng; Zhang, Zhiyong; Li, Yan; Zhou, Weiwei; Liu, Jie; Peng, Lian-Mao

2012-02-15

97

Evidence for a large, thermal-activated characteristic length scale in unstable homoepitaxial growth on GaAs(001)  

NASA Astrophysics Data System (ADS)

We report on observations of unstable growth on GaAs(001) surfaces nanopatterned with grooves of varying length/width aspect ratios. For homoepitaxial growth at temperatures near 500 °C, we find that ridges build up at the upper long edges of grooves oriented along [110]. No ridges form at the long edges of grooves oriented [110]; instead cusps form at the bottoms of such grooves. Most interestingly, we find that the evolution of ridge heights during growth breaks into two distinct branches, with the separation occurring at a groove length of 7.5+2.5 µm for growth at 525 °C, and at a length which is an order of magnitude smaller than this for growth at 460 °C. These observations indicate the presence of very large, thermally-activated characteristic lengths which governs the evolution of the topography during growth.

Lin, Chuan-Fu; Kan, Hung-Chih; Kanakaraju, S.; Richardson, C. J.; Phaneuf, R. J.

2013-10-01

98

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

PubMed Central

Diffusion imaging has shown promise as a predictive and prognostic biomarker in glioma. We assessed the ability of graded functional diffusion maps (fDMs) and apparent diffusion coefficient (ADC) characteristics to predict overall survival (OS) in recurrent glioblastoma multiforme (GBM) patients treated with bevacizumab. Seventy-seven patients with recurrent GBMs were retrospectively examined. MRI scans were obtained before and approximately 6 weeks after treatment with bevacizumab. Graded fDMs were created by registering datasets to each patient's pretreatment scan and then performing voxel-wise subtraction between post- and pretreatment ADC maps. Voxels were categorized according to the degree of change in ADC within pretreatment fluid-attenuated inversion recovery (FLAIR) and contrast-enhancing regions of interest (ROIs). We found that the volume of tissue showing decreased ADC within both FLAIR and contrast-enhancing regions stratified OS (log-rank, P < .05). fDMs applied to contrast-enhancing ROIs more accurately predicted OS compared with fDMs applied to FLAIR ROIs. Graded fDMs (showing voxels with decreased ADC between 0.25 and 0.4 µm2/ms) were more predictive of OS than traditional (single threshold) fDMs, and the predictive ability of graded fDMs could be enhanced even further by adding the ADC characteristics from the fDM-classified voxels to the analysis (log-rank, P < .001). These results demonstrate that spatially resolved diffusion-based tumor metrics are a powerful imaging biomarker of survival in patients with recurrent GBM treated with bevacizumab.

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

2011-01-01

99

An in-situ method to measure a soil`s undisturbed pore gas radon concentration, diffusion length for radon and air filled porosity  

SciTech Connect

Previous work has shown that for soils of insignificant permeability (soils with permeability less than about 10{sup {minus}12} m{sup 2}) the important soil parameters for characterizing radon mobility in the soil`s steady-state pore gas radon concentration at depth (C{sub s}), the soil`s bulk diffusion length for radon (L) and the soil`s air filled porosity (p{sub a}). Existing methods to measure these parameters have been based wholly or in part on measurements of soil samples taken to a laboratory for analysis. The drawbacks of this approach are twofold: (1) since soil structure can be quite heterogeneous, the sample may not have characteristics indicative of the site as a whole, and (2) since the parameters are dependent on soil structure and the soil structure of the sample may be changed in the process of acquiring the sample, one may be changing the parameters that one is trying to measure. These problems can be avoided by using a totally in-situ method to measure C{sub s}, L, and p{sub a}. This paper describes a totally in-situ method for simultaneously measuring the important soil parameters, based on measurements of the radon concentration as a function of time for the gas in a cavity in the soil. 7 refs., 3 figs., 3 tabs.

Jarzemba, M.S.; Blue, T.E. [Ohio State Univ., Columbus, OH (United States)

1996-04-01

100

Path length distributions for solar photons under cloudy skies: Comparison of measured first and second moments with predictions from classical and anomalous diffusion theories  

NASA Astrophysics Data System (ADS)

Using high-resolution oxygen A band spectrometry (?/?? = 60000) in the 767.7-770.7 nm wavelength range, we investigate the first and second moments of the distributions of path lengths of photons in transmitted skylight for different cloud conditions. Our observations are supported by measurements of column liquid water path by multichannel microwave radiometry, cloud structure by millimeter cloud radar observations, and cloud base by a laser ceilometer. For the investigated multilayer cloud covers (decks of stratus, cumulus, altostratus, and cirrus), our measurements indicate that the photon path statistics are mostly governed by anomalous diffusion, whereby classical diffusion occurs in the limiting case of a single compact (plane parallel) cloud layer. The ratio for the inferred second and first moments of the path lengths confirms the relation recently derived by Davis and Marshak (2002) for photon diffusion in single optically thick cloud layers and extends it to more complex cloud geometry.

Scholl, T.; Pfeilsticker, K.; Davis, A. B.; Klein Baltink, H.; Crewell, S.; LöHnert, U.; Simmer, C.; Meywerk, J.; Quante, M.

2006-06-01

101

SURFACTANT ADSORPTION TO SPHERICAL PARTICLES: THE INTRINSIC LENGTH SCALE GOVERNING THE SHIFT FROM DIFFUSION TO KINETIC-CONTROLLED MASS TRANSFER  

Microsoft Academic Search

When a drop or bubble of radius b is formed in surfactant solution, surfactant adsorbs, diffuses from solution, and desorbs to establish the equilibrium surface concentration. The transport coefficients for diffusion, adsorption, and desorption are fundamental parameters. However, the transport mechanisms that control the interface far from equilibrium are highly context dependent. Thus, no surfactant has universal “diffusion-controlled” transport. Here

Fang Jin; R. Balasubramaniam; Kathleen J. Stebe

2004-01-01

102

Burning Characteristics of Non-Spread Diffusion Flames of Liquid Fuel Soaked in Porous Beds  

Microsoft Academic Search

An experimental study was conducted to investigate the effects of sand size and sand layer depth on the burning characteristics of non spread diffusion flames of liquid fuel soaked in porous beds. Sand beds with sand sizes from 0.12 to 3.18 mm and sand layer depths from 50 to 80 mm were chosen as the porous beds. Pure methanol was

Wenjun Kong; Christopher Y. H. Chao; Jinghong Wang

2002-01-01

103

Combustion characteristics of a swirling inverse diffusion flame upon oxygen content variation  

Microsoft Academic Search

The combustion characteristics of a swirling inverse diffusion flame (IDF) upon variation of the oxygen content in the oxidizer were experimentally studied. The oxidizer jet was a mixture mainly composed of oxygen and nitrogen gases, with a volumetric oxygen fraction of 20%, 21% and 26%, and liquefied petroleum gas (LPG) was used as the fuel. Each set of experiment was

H. S. Zhen; C. W. Leung; C. S. Cheung

2011-01-01

104

National Seminar on the Diffusion of New Instructional Materials and Practices. 5.0 Characteristics of the Communications Network: What are the Mechanisms Within the Diffusion System That Encourage or Discourage the Diffusion of Innovation?  

ERIC Educational Resources Information Center

|In this document conference participants consider characteristics of the communications network for diffusion of new instructional materials and practices. Responses to these questions are presented: What are the communication mechanisms within the diffusion system that encourage or discourage the diffusion of innovation? What role do journal…

Social Science Education Consortium, Inc., Boulder, CO.

105

Chain Length Dependence of Two-Dimensional Infrared Spectral Pattern Characteristic to 310-Helix Peptides  

NASA Astrophysics Data System (ADS)

Two-dimensional infrared spectra of Z-(Aib)n-OtBu (n = 3, 5, 8 and 10) were measured to investigate how they depend on the peptide chain length. The onset of the 310-helical spectral signature appears to occur at the pentapeptide.

Maekawa, Hiroaki; Formaggio, Fernando; Toniolo, Claudio; Ge, Nien-Hui

106

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

PubMed

BACKGROUND: An in-vitro setup was established in order to determine a) the diffusion activities of eight otic preparations (Aurizon(R), Eas Otic(R), Epi Otic(R), Otifree(R), Otomax(R), Panolog(R), Posatex(R), Surolan(R)) 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

Stahl, Jessica; Mielke, Stefanie; Pankow, Wolf-Rüdiger; Kietzmann, Manfred

2013-04-10

107

Characteristic length of a holographic superconductor with d-wave gap  

NASA Astrophysics Data System (ADS)

After the discovery of the s-wave and p-wave holographic superconductors, holographic models of the d-wave superconductor have also been constructed recently. We study analytically the perturbation of the dual gravity theory to calculate the superconducting coherence length ? of the d-wave holographic superconductor near the superconducting phase transition point. The superconducting coherence length ? diverges as (1-T/Tc)-1/2 near the critical temperature Tc. We also obtain the magnetic penetration depth ??(Tc-T)-1/2 by adding a small external homogeneous magnetic field. The results agree with the s-wave and p-wave models, which are also the same as the Ginzburg-Landau theory.

Zeng, Hua-Bi; Jiang, Yu; Fan, Zhe-Yong; Zong, Hong-Shi

2010-12-01

108

Coherence Length Characteristics from Broadband Semiconductor Emitters: Superluminescent Diodes versus Broadband Laser Diodes  

Microsoft Academic Search

This paper reports on the measurement and analysis of the coherence function for broadband emitters such as superluminescent diodes (SLDs) and novel broadband laser diodes (BLDs) from self-assembled InGaAs\\/GaAs quantum- dot (QD) and InAs\\/InP quantum-dash (Qdash) structures that emit at center wavelengths of 1150nm and 1650nm, respectively. Using the fiber-based spectral interferometry system, coherence lengths in fiber of 23 µm

C. E. Dimas; C. L. Tan; B. S. Ooi

109

Diffusion Characteristics and Waveguiding Properties of Lithium-Metaniobate Optical Waveguides and Devices  

NASA Astrophysics Data System (ADS)

Diffusion characteristics and optical waveguiding properties of proton exchanged (PE) and annealed LiNbO _3 waveguides, prepared under a variety of diffusion conditions, are investigated experimentally and a phenomenological model describing the diffusion characteristics is derived. The study begins with an experimental investigation of the effects of finite melt volume on the PE process. It has been found that repeated use of the benzoic acid melt for performing PE in LiNbO_3, results in the dilution of the melt due to lithium outdiffusion from the LiNbO_3 crystal. An empirical model describing the effect and its consequences is developed. The concentration profiles of H and Li in PE LiNbO _3 are measured using Secondary Ion Mass Spectroscopy (SIMS). The measured rectangular (step -like) concentration profiles are modeled by considering concentration dependent self-diffusion coefficients in the ion exchange equations. The concentration profiles of H and Li in annealed PE LiNbO_3 shows that it can be modeled by the standard thermal diffusion theory. Matching the measured profiles to the calculated profiles has resulted in the derivation of the diffusion coefficient for H and Li during annealing. Channel waveguides prepared under a variety of diffusion conditions have been characterized for their mode shape/size. The near-field profiles generated from the parameter space study are compared to the profiles calculated by the effective index method using the PE phenomenological model. Results from diffusion parameter space study have been used to fabricate switched optical directional couplers in PE LiNbO_3. The proton exchange phenomenological diffusion model can be used to predict the characteristics of complicated waveguiding geometries. The parameter space study carried out on channel waveguides has demonstrated that the PE process allows easy tailoring of the mode shape/size and can be used as a tool to design novel devices. Finally, the lessons learned from this study should be applicable in fabricating proton exchanged devices in LiTaO _3.

Vohra, Sandeep Tushar

110

Characteristic length scale of the intermediate structure in zero-pressure-gradient boundary layer flow.  

PubMed

In a turbulent boundary layer over a smooth flat plate with zero pressure gradient, the intermediate structure between the viscous sublayer and the free stream consists of two layers: one adjacent to the viscous sublayer and one adjacent to the free stream. When the level of turbulence in the free stream is low, the boundary between the two layers is sharp, and both have a self-similar structure described by Reynolds-number-dependent scaling (power) laws. This structure introduces two length scales: one-the wall-region thickness-determined by the sharp boundary between the two intermediate layers and the second determined by the condition that the velocity distribution in the first intermediate layer be the one common to all wall-bounded flows and in particular coincide with the scaling law previously determined for pipe flows. Using recent experimental data, we determine both these length scales and show that they are close. Our results disagree with the classical model of the "wake region." PMID:10760253

Barenblatt, G I; Chorin, A J; Prostokishin, V M

2000-04-11

111

First-principles thermodynamic calculations of diffusion characteristics of impurities in ?-iron  

NASA Astrophysics Data System (ADS)

Because solute impurities have an effect on embrittlement through segregation under irradiation, solute stability and the influence of irradiation on the diffusion characteristics of impurities become prominent due to several acceleration effects of high irradiance circumstances in irradiated materials. In this study, the diffusion characteristics of several impurities in non-magnetic fcc iron are investigated using first-principles density functional theory (DFT) calculations. In accordance with classical diffusion and transition state theories, we nonempirically evaluated the contribution to properties of the binding energy between vacancy and each impurity and the migration enthalpy. The migration energy was calculated using the nudged elastic band method with DFT. The vacancy formation energy, including the entropic contributions to free energies in ?-iron, was evaluated by considering vibrational phonon frequencies based on frozen phonons employing the harmonic approximation for the lattice dynamics. Consequently, we confirmed that the binding energy between large-radius impurities and vacancies is larger than that with an equivalent size of the solvent element, and that the migration enthalpies of these impurities are quite small compared with self diffusion. This finding may indicate that the electronic binding states at the saddle point have a large influence on the migration of impurities.

Tsuru, T.; Kaji, Y.

2013-11-01

112

Element diffusion ability in metasomatic agents and its effect on chemical characteristics of metasomatized peridotites  

NASA Astrophysics Data System (ADS)

Detailed in situ LM-ICPMS researches on the composite xenoliths from Yingfengling volcano of Leizhou Peninsula, South China, indicate that most incompatible trace elements of clinopyroxenes in composite xenoliths decrease spatially from pyroxenites to distal lherzolites, and compatible elements and HREE increase steeply. The increasing and decreasing rate is distinct for different trace elements, which give rise to element chromatographic fractionation within metasomatized lherzolites. The element chromatographic fractionation result actually from the difference in element diffusive rate in melts or fluids percolating through wallrock lherzolites. Based on element variation profiles in composite xenoliths this study indicates that Sr, Nb, La and Ce have the highest diffusive mobility, MREE-HREE are moderate, and Zr, Hf, Ti, Ga and Sc are very low in most cases. Higher diffusive rates of LREE than HREE would enlarge the REE fractionation of metasomatized peridotites, and lower diffusive rate of Zr, Hf and Ti relative to neighbor REEs with similar incompatibility would cause the relative depletion of these elements in metasomatized peridotites. Trace elements commonly have a higher diffusive rate in fluid-rich infiltrating melt, which will weaken element chromatographic fractionation during the metasomatism. The range of mantle metasomatism caused by silicate melt intrusion is very limited, generally within tens of centimeters wide. The width of metasomatized wallrock peridotites near the pyroxenite or horblendite veins was strictly controlled by both melt volume and chemical characteristics.

Yu, J.; O'Reilly, S. Y.

2010-12-01

113

Distinct Clusterings and Characteristic Path Lengths in Dynamic Small-World Networks with Identical Limit Degree Distribution  

NASA Astrophysics Data System (ADS)

Many real-world networks belong to a particular class of structures, known as small-world networks, that display short distance between pair of nodes. In this paper, we introduce a simple family of growing small-world networks where both addition and deletion of edges are possible. By tuning the deletion probability q t , the model undergoes a transition from large worlds to small worlds. By making use of analytical or numerical means we determine the degree distribution, clustering coefficient and average path length of our networks. Surprisingly, we find that two similar evolving mechanisms, which provide identical degree distribution under a reciprocal scaling as t goes to infinity, can lead to quite different clustering behaviors and characteristic path lengths. It is also worth noting that Farey graphs constitute the extreme case q t ?0 of our random construction.

Shang, Yilun

2012-11-01

114

The role of mesopores in intracrystalline transport in USY zeolite: PFG NMR diffusion study on various length scales.  

PubMed

PFG NMR has been applied to study intracrystalline diffusion in USY zeolite as well as in the parent ammonium-ion exchanged zeolite Y used to produce the USY by zeolite steaming. The diffusion studies have been performed for a broad range of molecular displacements and with two different types of probe molecules (n-octane and 1,3,5-triisopropylbenzene) having critical molecular diameters smaller and larger than the openings of the zeolite micropores. Our experimental data unambiguously show that, in contrast to what is usually assumed in the literature, the intracrystalline mesopores do not significantly affect intracrystalline diffusion in USY. This result indicates that the intracrystalline mesopores of USY zeolite do not form a connected network, which would allow diffusion through crystals only via mesopores. PMID:16159301

Kortunov, P; Vasenkov, S; Kärger, J; Valiullin, R; Gottschalk, P; Elía, M Fé; Perez, M; Stöcker, M; Drescher, B; McElhiney, G; Berger, C; Gläser, R; Weitkamp, J

2005-09-21

115

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

PubMed Central

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.

Pankavich, S.; Ortoleva, P.

2010-01-01

116

Evaluation of a multimode fiber optic low coherence interferometer for path length resolved Doppler measurements of diffuse light.  

PubMed

The performance of a graded index multimode fiber optic low coherence Mach-Zehnder interferometer with phase modulation is analyzed. Investigated aspects were its ability to measure path length distributions and to perform path length resolved Doppler measurements of multiple scattered photons in a turbid suspension of particles undergoing Brownian and translational motion. The path length resolution of this instrument is compared with a system using single mode fibers for illumination and detection. The optical path lengths are determined from the zero order moment of the phase modulation peak in the power spectrum. The weighted first moment, which is equal to the average Doppler shift, shows a linear response for different mean flow velocities within the physiological range. PMID:18163752

Varghese, Babu; Rajan, Vinayakrishnan; Van Leeuwen, Ton G; Steenbergen, Wiendelt

2007-12-01

117

National Seminar on the Diffusion of New Instructional Materials and Practices. 3.0 Product Characteristics: What Are the Characteristics of Educational Products That Make Them More or Less Likely To Be Diffused?  

ERIC Educational Resources Information Center

|In this working paper of the National Seminar on the Diffusion of New Instructional Materials and Practices individual conference participants answer this question: What are the characteristics of educational products that make them more or less likely to be diffused? Responses focus on considerations related to size of the product, cost,…

Social Science Education Consortium, Inc., Boulder, CO.

118

Investigation of doped calcium aluminosilicate glass: A coupling between thermal-expansion and thermal-diffusion models for assessment of nonradiative relaxation time and characteristic diffusion time  

Microsoft Academic Search

This paper discusses the use of photoacoustic models to obtain the nonradiative relaxation time (?) and characteristic diffusion time (??) for a sample showing visible absorption bands from fluorescent ion-doped low-silica calcium aluminosilicate glass. Two models allowing phase shift analyses, the thermal-expansion and thermal-diffusion models, are briefly reviewed. These models have limitations when the photoacoustic signal depends on both factors,

N. E. Souza Filho; A. C. Nogueira; J. H. Rohling; M. L. Baesso; A. N. Medina; A. P. L. Siqueira; J. A. Sampaio; H. Vargas; A. C. Bento

2009-01-01

119

Investigation of doped calcium aluminosilicate glass: A coupling between thermal-expansion and thermal-diffusion models for assessment of nonradiative relaxation time and characteristic diffusion time  

Microsoft Academic Search

This paper discusses the use of photoacoustic models to obtain the nonradiative relaxation time (tau) and characteristic diffusion time (taubeta) for a sample showing visible absorption bands from fluorescent ion-doped low-silica calcium aluminosilicate glass. Two models allowing phase shift analyses, the thermal-expansion and thermal-diffusion models, are briefly reviewed. These models have limitations when the photoacoustic signal depends on both factors,

N. E. Souza Filho; A. C. Nogueira; J. H. Rohling; M. L. Baesso; A. N. Medina; A. P. L. Siqueira; J. A. Sampaio; H. Vargas; A. C. Bento

2009-01-01

120

Experimental investigation of the length of a free diffusion jet of fuel gases diluted with inert gases  

NASA Astrophysics Data System (ADS)

Experimental investigation of the length of single burning jets of methane and hydrogen previously diluted with an inert gas (nitrogen or helium) was carried out. Efflux of fuel gases into the atmosphere occurred through cylindrical extension pieces 4 and 8 mm in diameter. The Reynolds numbers at the cut of a piece varied in the range from 400 to 12,000. A clearly defined dependence of the jet length on the quality of the added inert gas is obtained. The correlation of experimental data made it possible to recommend formulas for engineering calculations of free laminar and turbulent jets.

Polezhaev, Yu. V.; Vorob'ev, B. A.; Korovin, G. K.; Lamden, D. I.; Mostinskii, I. L.; Shigin, R. L.

2010-05-01

121

Diffusive capacitance in space charge limited organic diodes: Analysis of peak in capacitance-voltage characteristics  

NASA Astrophysics Data System (ADS)

One of the significant features of capacitance-voltage (C-V) characteristics of organic diodes is the occurrence of a peak near the built-in voltage due to competition between diffusion and drift of carriers. The voltage dependence of the rise in small signal capacitance prior to the peak is modulated by the transit time of the carriers and leads to a linear 1/C2/3 vs V dependence, which has been demonstrated both through simulation, and experiments using small molecule (m-MTDATA) based diodes. The utility of such analysis in obtaining threshold voltages significant for characterization of organic diodes has been demonstrated.

Tripathi, Durgesh C.; Mohapatra, Y. N.

2013-06-01

122

Investigation of Three-Dimensional Unsteady Flow Characteristics in Transonic Diffusers  

NASA Astrophysics Data System (ADS)

Three-dimensional characteristics of unsteady flow in supercritical transonic diffuser are investigated. For various pressure ratios three-dimensional flow containing a normal shock/turbulent boundary layer interaction regions with shockwave and pseudo-shockwaves fluctuating in longitudinal and spanwise directions is observed. Experimental and numerical investigations show details of the flowfield in the vicinity of terminal shock, interaction regions and downstream turbulent unsteady flow. Spectral analysis of pressure fluctuations reveals existence of two characteristic frequencies attributed to the shockwave fluctuation in longitudinal direction for the lower frequency case and acoustic resonance in spanwise direction for the higher one. Vortices appear at each corner in transversal sections modifying the core flow. As a result, size and depth of longitudinal and vertical penetration of separation regions impelled by the terminal shock is either increased or decreased.

Proshchanka, Dzianis; Yonezawa, Koichi; Tsujimoto, Yoshinobu

123

Breakdown characteristics of high-side lateral double-diffused metal oxide semiconductor devices.  

PubMed

In this paper, we discuss the breakdown characteristics of an LDMOSFET (Lateral Double-diffused Metal Oxide Semiconductor Field Effect Transistor) structure for the optimization of engineering parameters such as the gap between the DEEP N-WELL and the source region and the doping concentration of the N(ADJUST)-layer. The fabricated device exhibits the breakdown voltage (BVdss) over 110 V and the specific on-resistance as low as 2.20 mOmega cm2. The robust breakdown characteristics seem to be due to the migration of the location wherein maximum impact ionization occurs from the gate region to the drain side, which was confirmed by the numerical simulation which verifies that the maximum impact ionization rate of the proposed structure is 2.44 x 10(16) cm(-3) s(-1), while that of the conventional structure being 6.69 x 10(19) cm(-3) s(-1). PMID:22966560

Sung, Kunsik; Kim, Kwangsik; Won, Taeyoung

2012-07-01

124

The length dependence of translational diffusion, free solution electrophoretic mobility, and electrophoretic tether force of rigid rod-like model duplex DNA.  

PubMed Central

In this work, boundary element modeling is used to study the transport of highly charged rod-like model polyions of various length under a variety of different aqueous salt conditions. Transport properties considered include free solution electrophoretic mobility, translational diffusion, and the components of the "tether force" tensor. The model parameters are chosen to coincide with transport measurements of duplex DNA carried out under six different salt/temperature conditions. The focus of the analysis is on the length dependence of the free solution electrophoretic mobility. In a solution containing 0.04 M Tris-acetate buffer at 25 degrees C, calculated mobilities using straight rod models show a stronger dependence on fragment length than that observed experimentally. By carrying out model studies on curved rod models, it is concluded that the "leveling off" of mobility with fragment length is due, in part at least, to the finite curvature of DNA. Experimental mobilities of long duplex DNA in monovalent alkali salts are reasonably well explained once account is taken of long-range bending and the simplifying assumptions of the model studies.

Allison, S; Chen, C; Stigter, D

2001-01-01

125

Effects of phenotypic characteristics on the length of stay of dogs at two no kill animal shelters.  

PubMed

Adoption records from 2 no kill shelters in New York State were examined to determine how age, sex, size, breed group, and coat color influenced the length of stay (LOS) of dogs at these shelters. Young puppies had the shortest length of stay; LOS among dogs increased linearly as age increased. Neither coat color nor sex influenced LOS. Considering only size classifications, medium-size dogs had the greatest LOS, and extra small dogs and puppies remained in shelters for the least amount of time. Considering only breed groupings, dogs in the guard group had the greatest LOS and those in the giant group had the shortest LOS. The lack of effect of coat color was not expected, nor was the shorter LOS among "fighting" breeds compared with other breed groups. Coat color and breed may have only local effects on LOS that do not generalize to all shelters, including traditional shelters. Understanding the traits of dogs in a specific shelter and the characteristics of these nonhuman animals desired by adopters are critical to improving the welfare of animals served by that shelter. PMID:23282290

Brown, William P; Davidson, Janelle P; Zuefle, Marion E

2013-01-01

126

The anatomical characteristics of superior longitudinal fasciculus I in human brain: Diffusion tensor tractography study.  

PubMed

The superior longitudinal fasciculus (SLF) I is known to be involved in regulation of higher aspects of motor function. Using diffusion tensor imaging (DTI), we attempted to identify the SLF I and to investigate the anatomical characteristics of the SLF I in the human brain. We recruited 30 healthy subjects for this study. The SLF I was obtained using the FMRIB Software Library. The seed region of interest (ROI) was given at the superior parietal lobule (SPL) and the target ROI was the supplementary motor area (SMA) along with the dorsal part of the premotor area (PMA). Values of fractional anisotropy (FA), mean diffusivity (MD), and tract volume were measured. The SLF I originated from the SPL and medial parietal cortex, passed through the white matter of the SPL and superior frontal gyrus, and then terminated in the SMA and dorsal PMA. There were no significant differences between hemispheres in terms of the FA, MD, and tract volume. We present with the anatomical characteristics of the SLF I in the human brain using DTI. We think that the methodology and results of this study would be helpful to researchers in this field. PMID:22085696

Jang, Sung Ho; Hong, Ji Heon

2011-11-06

127

Extra-thermodynamic study on surface diffusion in reversed-phase liquid chromatography using silica gels bonded with alkyl ligands of different chain lengths  

SciTech Connect

Surface diffusion on adsorbents made of silica gels bonded to C{sub 1}, C{sub 4}, C{sub 8}, and C{sub 18} alkyl ligands was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships: enthalpy-entropy compensation (EEC) and linear free-energy relationship (LFER). First, the values of the surface diffusion coefficient (D{sub s}), normalized by the density of the alkyl ligands, were analyzed with the modified Arrhenius equation, following the four approaches proposed in earlier research. This showed that an actual EEC resulting from substantial physicochemical effects occurs for surface diffusion and suggested a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length. Second, a new model based on EEC was derived to explain the LFER between the logarithms of D{sub s} measured under different RPLC conditions. This showed that the changes of free energy, enthalpy, and entropy of surface diffusion are linearly correlated with the carbon number in the alkyl ligands of the bonded phases and that the contribution of the C{sub 18} ligand to the changes of the thermodynamic parameters corresponds to that of the C{sub 10} ligand. The new LFER model correlates the slope and intercept of the LFER to the compensation temperatures derived from the EEC analyses and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy. Finally, the new model was used to estimate D{sub s} under various RPLC conditions. The values of D{sub s} that were estimated from only two original experimental D{sub s} data were in agreement with corresponding experimental D{sub s} values, with relative errors of {approx}20%, irrespective of some RPLC conditions.

Miyabe, Kanji [Toyama University, Japan; Guiochon, Georges A [ORNL

2005-06-01

128

Extrathermodynamic study of surface diffusion in reversed-phase liquid chromatography with silica gels bonded with alkyl ligands of different chain lengths.  

PubMed

Surface diffusion on adsorbents made of silica gels bonded to C1, C4, C8, and C18 alkyl ligands was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships: enthalpy-entropy compensation (EEC) and linear free-energy relationship (LFER). First, the values of the surface diffusion coefficient (D(s)), normalized by the density of the alkyl ligands, were analyzed with the modified Arrhenius equation, following the four approaches proposed in earlier research. This showed that an actual EEC resulting from substantial physicochemical effects occurs for surface diffusion and suggested a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length. Second, a new model based on EEC was derived to explain the LFER between the logarithms of D(s) measured under different RPLC conditions. This showed that the changes of free energy, enthalpy, and entropy of surface diffusion are linearly correlated with the carbon number in the alkyl ligands of the bonded phases and that the contribution of the C18 ligand to the changes of the thermodynamic parameters corresponds to that of the C10 ligand. The new LFER model correlates the slope and intercept of the LFER to the compensation temperatures derived from the EEC analyses and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy. Finally, the new model was used to estimate D(s) under various RPLC conditions. The values of D(s) that were estimated from only two original experimental D(s) data were in agreement with corresponding experimental D(s) values, with relative errors of approximately 20%, irrespective of some RPLC conditions. PMID:16852485

Miyabe, Kanji; Guiochon, Georges

2005-06-23

129

Diffusion  

NSDL National Science Digital Library

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.

Christopher Thomas (None;)

2006-11-09

130

Patient and Hospital Characteristics Associated With Length of Stay and Hospital Charges for Pediatric Sports-Related Injury Hospitalizations in the United States, 2000-2003  

Microsoft Academic Search

OBJECTIVES.The objectives of this study were to describe the patient and hospital characteristics of pediatric sports injury hospitalization and to determine the hospital characteristics that are associated with length of stay and total hospital charges (per discharge). METHODS.Children who were aged 5 to 18 years and had a diagnosis of a sports injury in the Nationwide Inpatient Sample between 2000

Jingzhen Yang; Corinne Peek-Asa; Veerasathpurush Allareddy; George Phillips; Ying Zhang; Gang Cheng; Lucille A. Carver

2010-01-01

131

Time-domain diffuse optical tomography using analytic statistical characteristics of photon trajectories  

SciTech Connect

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. (special issue devoted to multiple radiation scattering in random media)

Konovalov, Aleksandr B; Vlasov, V V [E.I. Zababakhin All-Russian Scientific-Research Institute of Technical Physics, Russian Federal Nuclear Centre, Snezhinsk, Chelyabinsk region (Russian Federation); Kalintsev, A G; Lyubimov, Vladimir V [Research Institute for Laser Physics, St. Petersburg (Russian Federation); Kravtsenyuk, Olga V [Foundation for Research and Technology-Hellas (IESL-FORTH), Institute of Electronic Structure and Lasers, Crete (Greece)

2006-11-30

132

Effects of Space Shuttle flight on the reflectance characteristics of diffusers in the near-infrared, visible, and ultraviolet regions  

NASA Astrophysics Data System (ADS)

Many remote sensing instruments employ diffuse targets for calibration. These targets usually consist of diffusers with high Lambertian characteristics illuminated by a calibrated irradiance source. There is increasing interest in conducting in-orbit radiance calibration checks of remote sensing instruments using sunlight reflected off a diffuser. We report on the effects of space flight on the reflectance properties of polytetrafluoroethylene and aluminum diffuser samples flown on three Space Shuttle flights. These experiments showed good stability of both diffuser types in the visible and near infrared but experienced measurable degradation in the ultraviolet. Degradation varied from flight to flight and seemed to be related to different levels of contamination experienced on the three flights.

Hilsenrath, Ernest; Herzig, Howard H.; Williams, Donald E.; Bruegge, Carol J.; Stiegman, Albert E.

1994-11-01

133

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

Microsoft Academic Search

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

Jong-Heun Lee; Hoin Kim; Byung Ki Kim

1996-01-01

134

Fundamental Characteristics of Moisture Transport, Diffusion, and the Moisture-Induced Damages in Polymeric Materials in Electronic Packaging  

Microsoft Academic Search

\\u000a In this chapter, the fundamental characteristics of moisture transport, diffusion, and the moisture-induced damages in polymeric\\u000a materials and along interfaces in electronic packaging is reviewed. Both Fickian and non-Fickian diffusion behaviors are discussed.\\u000a It has been found that saturated moisture concentration does not depend on temperature but relative humidity only as long\\u000a as the temperature is far below the glass

X. J. Fan; S. W. R. Lee

135

Investigation of doped calcium aluminosilicate glass: A coupling between thermal-expansion and thermal-diffusion models for assessment of nonradiative relaxation time and characteristic diffusion time  

NASA Astrophysics Data System (ADS)

This paper discusses the use of photoacoustic models to obtain the nonradiative relaxation time (?) and characteristic diffusion time (??) for a sample showing visible absorption bands from fluorescent ion-doped low-silica calcium aluminosilicate glass. Two models allowing phase shift analyses, the thermal-expansion and thermal-diffusion models, are briefly reviewed. These models have limitations when the photoacoustic signal depends on both factors, in a coupling mechanism. An alternative model is proposed to take both thermal expansion and thermal diffusion into account with a single temperature solution for the heat-coupled differential equation. This model is simulated for absorbing samples near the thermally thick region. The model is applied to Eu-V codoped glass showing intermediate signal dependence from ?-1.0 to ?-3/2. The nonradiative time and characteristic diffusion time are derived with 33

Souza Filho, N. E.; Nogueira, A. C.; Rohling, J. H.; Baesso, M. L.; Medina, A. N.; Siqueira, A. P. L.; Sampaio, J. A.; Vargas, H.; Bento, A. C.

2009-11-01

136

LABORATORY ASSESSMENT OF THE PERMEABILITY AND DIFFUSION CHARACTERISTICS OF FLORIDA CONCRETES - PHASE I. METHODS DEVELOPMENT AND TESTING  

EPA Science Inventory

The report gives results of Phase I of a laboratory assessment of the permeability and diffusion characteristics of Florida concretes. (NOTE: The ability of concrete to permit air flow under pressure (permeability) and the passage of radon gas without any pressure difference (dif...

137

LABORATORY ASSESSMENT OF THE PERMEABILITY AND DIFFUSION CHARACTERISTICS OF FLORIDA CONCRETES - PHASE I - METHODS DEVELOPMENT AND TESTING  

EPA Science Inventory

The report gives results of Phase I of a laboratory assessment of the permeability and diffusion characteristics of Florida concretes. (NOTE: The ability of concrete to permit air flow under pressure (permeability) and the passage of radon gas without any pressure difference (dif...

138

Assessment of nonradiative relaxation time and characteristic diffusion time of neodymium, erbium and cobalt doped low silica calcium aluminosilicate glasses  

Microsoft Academic Search

Nonradiative relaxation time (?) and characteristic diffusion time (??) of Nd, Er and Co doped low silica calcium aluminosilicate (LSCA) glasses were assessed by means of photoacoustic spectroscopy. The results are interpreted in terms of frequency dependence predicted by the theory of Rosencwaig and Gersho. Whereas ? varied between 7.2ms and 36ms, the values of ?? lied between 0.25ms and

L. Mota; J. A. Sampaio; M. G. da Silva; H. Vargas

2011-01-01

139

Effect of Alkyl Chain Length on the Rotational Diffusion of Nonpolar and Ionic Solutes in 1-Alkyl-3-Methylimidazolium-bis(trifluoromethylsulfonyl)imides.  

PubMed

Rotational diffusion of a nonpolar solute 9-phenylanthracene (9-PA) and a cationic solute rhodamine 110 (R110) has been examined in a series of 1-alkyl-3-methylimidazolium (alkyl = octyl, decyl, dodecyl, tetradecyl, hexadecyl, and octadecyl) bis(trifluoromethylsulfonyl)imides to understand the influence of alkyl chain length on solute rotation. In this study, reorientation times (?r) have been measured as a function of viscosity (?) by varying the temperature (T) of the solvents. These results have been analyzed using the Stokes-Einstein-Debye (SED) hydrodynamic theory along with the ones obtained for the same solutes in 1-alkyl-3-methylimidazolium (alkyl = methyl, ethyl, propyl, butyl, and hexyl) bis(trifluoromethylsulfonyl)imides (Gangamallaiah and Dutt, J. Phys. Chem. B 2012, 116, 12819-12825). It has been noticed that the data for 9-PA and R110 follows the relation ?r = A(?/T)(n) with A being the ratio of hydrodynamic volume of the solute to the Boltzmann constant and n = 1 as envisaged by the SED theory. However, upon increasing the alkyl chain length from methyl to octadecyl significant deviations from the SED theory have been observed especially from the octyl derivative onward. From methyl to octadecyl derivatives, the value of A decreases by a factor of 3 for both the solutes and n by a factor of 1.4 and 1.6 for 9-PA and R110, respectively. These observations have been rationalized by taking into consideration the organized structure of the ionic liquids, whose influence appears to be pronounced when the number of carbon atoms in the alkyl chain attached to the imidazolium cation exceeds eight. PMID:24070127

Gangamallaiah, V; Dutt, G B

2013-09-26

140

Clinico-radiologic characteristics of long-term survivors of diffuse intrinsic pontine glioma.  

PubMed

Diffuse intrinsic pontine glioma (DIPG) is the deadliest central nervous system tumor in children. The survival of affected children has remained poor despite treatment with radiation therapy (RT) with or without chemotherapy. We reviewed the medical records of all surviving patients with DIPG treated at our institution between October 1, 1992 and May 31, 2011. Blinded central radiologic review of the magnetic resonance imaging at diagnosis of all surviving patients and 15 controls with DIPG was performed. All surviving patients underwent neurocognitive assessment during follow-up. Five (2.6 %) of 191 patients treated during the study period were surviving at a median of 9.3 years from their diagnosis (range 5.3-13.2 years). Two patients were younger than 3 years, one lacked signs of pontine cranial nerve involvement, and three had longer duration of symptoms at diagnosis. One patient had a radiologically atypical tumor and one had a tumor originating in the medulla. All five patients received RT. Chemotherapy was variable among these patients. Neurocognitive assessments were obtained after a median interval of 7.1 years. Three of four patients who underwent a detailed evaluation showed cognitive function in the borderline or mental retardation range. Two patients experienced disease progression at 8.8 and 13 years after diagnosis. A minority of children with DIPG experienced long-term survival with currently available therapies. These patients remained at high risk for tumor progression even after long follow-ups. Four of our long-term survivors had clinical and radiologic characteristics at diagnosis associated with improved outcome. PMID:23813229

Jackson, Sadhana; Patay, Zoltan; Howarth, Robyn; Pai Panandiker, Atmaram S; Onar-Thomas, Arzu; Gajjar, Amar; Broniscer, Alberto

2013-06-29

141

Effects of MRTI sampling characteristics on estimation of HIFU SAR and tissue thermal diffusivity  

NASA Astrophysics Data System (ADS)

While the non-invasive and three-dimensional nature of magnetic-resonance temperature imaging (MRTI) makes it a valuable tool for high-intensity focused ultrasound (HIFU) treatments, random and systematic errors in MRTI measurements may propagate into temperature-based parameter estimates used for pretreatment planning. This study assesses the MRTI effects of zero-mean Gaussian noise (SD = 0.0-2.0 °C), temporal sampling (tacq = 1.0-8.0 s), and spatial averaging (Res = 0.5-2.0 mm isotropic) on HIFU temperature measurements and temperature-based estimates of the amplitude and full width half maximum (FWHM) of the HIFU specific absorption rate and of tissue thermal diffusivity. The ultrasound beam used in simulations and ex vivo pork loin experiments has lateral and axial FWHM dimensions of 1.4 mm and 7.9 mm respectively. For spatial averaging simulations, beams with lateral FWHM varying from 1.2-2.2 mm are also assessed. Under noisy conditions, parameter estimates are improved by fitting to data from larger voxel regions. Varying the temporal sampling results in minimal changes in measured temperatures (<2% change) and parameter estimates (<5% change). For the HIFU beams studied, a spatial resolution of 1 × 1 × 3 mm3 or smaller is required to keep errors in temperature and all estimated parameters less than 10%. By quantifying the errors associated with these sampling characteristics, this work provides researchers with appropriate MRTI conditions for obtaining estimates of parameters essential to pretreatment modeling of HIFU thermal therapies.

Dillon, C. R.; Todd, N.; Payne, A.; Parker, D. L.; Christensen, D. A.; Roemer, R. B.

2013-10-01

142

Effects of MRTI sampling characteristics on estimation of HIFU SAR and tissue thermal diffusivity.  

PubMed

While the non-invasive and three-dimensional nature of magnetic-resonance temperature imaging (MRTI) makes it a valuable tool for high-intensity focused ultrasound (HIFU) treatments, random and systematic errors in MRTI measurements may propagate into temperature-based parameter estimates used for pretreatment planning. This study assesses the MRTI effects of zero-mean Gaussian noise (SD = 0.0-2.0 °C), temporal sampling (tacq = 1.0-8.0 s), and spatial averaging (Res = 0.5-2.0 mm isotropic) on HIFU temperature measurements and temperature-based estimates of the amplitude and full width half maximum (FWHM) of the HIFU specific absorption rate and of tissue thermal diffusivity. The ultrasound beam used in simulations and ex vivo pork loin experiments has lateral and axial FWHM dimensions of 1.4 mm and 7.9 mm respectively. For spatial averaging simulations, beams with lateral FWHM varying from 1.2-2.2 mm are also assessed. Under noisy conditions, parameter estimates are improved by fitting to data from larger voxel regions. Varying the temporal sampling results in minimal changes in measured temperatures (<2% change) and parameter estimates (<5% change). For the HIFU beams studied, a spatial resolution of 1 × 1 × 3 mm(3) or smaller is required to keep errors in temperature and all estimated parameters less than 10%. By quantifying the errors associated with these sampling characteristics, this work provides researchers with appropriate MRTI conditions for obtaining estimates of parameters essential to pretreatment modeling of HIFU thermal therapies. PMID:24077026

Dillon, C R; Todd, N; Payne, A; Parker, D L; Christensen, D A; Roemer, R B

2013-09-27

143

Modeling of output characteristics in erbium-doped fiber ring lasers for effective active fiber lengths and input pump powers  

NASA Astrophysics Data System (ADS)

Erbium-doped fiber lasers (EDFL) are attracting a great deal of attention in the optical communications industry. This is due mainly to the fact that the gain spectrums of these lasers are well matched to the output spectrum of erbium doper fiber amplifiers (EDFA) in the 1550 nm operating window. Many different configurations for the fiber lasers have been developed in recent years. The two most popular are ring and linear cavity lasers. Ring lasers can be designed to have a large tuning range when consideration is given to active fiber length and output coupling ratios. Here an erbium-doped fiber ring laser is modeled for comparison of input pump powers and active fiber lengths. Theoretical analysis is given based on values of optical component losses for couplers, isolators, and tuning elements. We will present the laser output powers that are dependent on the output couplers reflectivity for a range of optical pump powers and various active fiber lengths.

Todd, Shawn; Matin, M.

2005-08-01

144

Analysis of Temperature Effects on High-Frequency Characteristics of RF Lateral-Diffused MetalOxideSemiconductor Transistors  

Microsoft Academic Search

In this work, the effects of temperature on the DC and RF characteristics of lateral-diffused metal-oxide-semiconductor (LDMOS) transistors were studied. Devices with different layout structures were fabricated using a 40 V LDMOS process. The temperature coefficients of the threshold voltage and channel mobility are negative and their values are similar for devices with fishbone and ring structures. In addition, we

Hsin-Hui Hu; Kun-Ming Chen; Guo-Wei Huang; Alex Chien; Eric Cheng; Yu-Chi Yang; Chun-Yen Chang

2008-01-01

145

Highlighting a variety of unusual characteristics of adsorption and diffusion in microporous materials induced by clustering of guest molecules  

Microsoft Academic Search

In this work, we highlight several unusual characteristics of adsorption and diffusion of a variety of guest molecules, such as linear and branched alkalies with a number of C atoms in the 1-6 range, CO2, and Ar in microporous structures such as zeolites (FAU, NaY) and metal organic frameworks (IRMOF-1, CuBTC, MIL-47, MIL-53 (Cr)-1p, PCN-6') that have channel or cavity

Rajamani Krishna; Baten van J. M

2010-01-01

146

Restricted Diffusion in Biophysical Systems  

PubMed Central

The pulsed-gradient spin echo nuclear magnetic resonance (PGSENMR) technique was used to measure restricted diffusion of water in three types of animal tissue: human blood plasma and red cells; rat and rabbit heart; rat and rabbit liver. Characteristic lengths (L) for restriction of diffusion are estimated from dependence on the measuring time. Limitations on the range of observable restrictive lengths (1.5-15 ?m) are discussed. The decrease in diffusivity due to 1 ?m alumina powder (volume fraction = 0.18) in glycerin/water mixtures agrees with the Wang theory assuming spherical particles and no hydration. The characteristic length (L ? 4 ?m) is larger than the particle size (1 ?m) or separation (1.8 ?m). Comparison of the diffusivities in tissues at short diffusion times with the Wang theory indicates some bound or trapped water. For packed red blood cells, a restriction (L ? 2.3 ?m) was attributed tothe red cell membrane. A permeability p ? 0.014 cm/s may be estimated from the decrease in diffusivity. Average values of diffusivity ratio in heart were: 0.36 ± 0.02 for rat; and 0.26 ± 0.03 for rabbit; and in liver: 0.25 ± 0.01 for rat; 0.25 ± .04 for 10-day old rabbit; and 0.195 ± 0.03 for 2-yr old rabbit. A restriction (L ? 2.7 ?m) in rat liver probably results from the mitochondria.

Cooper, Robert L.; Chang, David B.; Young, Allan C.; Martin, Carroll J.; Ancker-Johnson, Betsy

1974-01-01

147

Characteristics of reactively sputtered niobium nitride thin films as diffusion barriers for Cu metallization  

NASA Astrophysics Data System (ADS)

NbN films were prepared by radio frequency reactive magnetron sputtering and then employed as diffusion barriers between Cu and Si. The microstructure of the NbN films was an assembly of very small columnar crystallites with a cubic structure. To investigate the properties as diffusion barriers, we performed metallurgical reactions of Cu/NbN0.8/Si, Cu/Nb/Si and Cu/TaN0.7/Si for comparisons. The sheet resistance increased dramatically after annealing above 750°C for Cu/NbN0.80/Si, and above 500°C for both Cu/Nb/Si and Cu/TaN0.7/Si. The interfaces were deteriorated seriously and formation of Cu3Si was observed when the sheet resistance was significantly increased. The diffusion coefficient of Cu in NbN barrier films was estimated by using the change of resistance (? R s / R s %). Compared with TaN0.7, NbN0.8 films possess larger grain size and lower Cu diffusion coefficient. Our results suggest that the NbN film can be used as a diffusion barrier for Cu metallization as compared to the well-known TaN film.

Huang, Cheng-Lin; Lai, Chih-Huang; Tsai, Po-Hao; Huang, Hsing-An; Lin, Jing-Cheng; Lee, Chiapyng

2013-09-01

148

Materials evaluation of diffusion bonded steel bar and its impact characteristics  

Microsoft Academic Search

When we apply non-destructive test for evaluating the soundness of weld joints it is necessary to know the mechanical properties of the joints by destructive test. In this paper we tried to obtain the correlation between the data by ultrasonic C-scope method and the absorbed energy by Charpy impact test for diffusion bonded steel bars. The surface roughness of specimens

Mitsuaki Katoh; Kazumasa Nishio; Tomiko Yamaguchi

2002-01-01

149

Clinical characteristics and prognostic analysis of Chinese patients with diffuse large B-cell lymphoma  

Microsoft Academic Search

Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma in adults. As it is a highly heterogenous disease, many studies have focused on finding useful prognostic factors to help guide therapy. In this report, we examine several biological markers in 83 patients with DLBCL enrolled in our hospital, including cell origin, serum lactate dehydrogenase (LDH) levels, and

Xiaoyan Ke; Jing Wang; Zifen Gao; Lingzhi Zhao; Min Li; Hongmei Jing; Jijun Wang; Wei Zhao; Heather Gilbert; Xiao-Feng Yang

2010-01-01

150

Pulsed electric fields and their impact on the diffusion characteristics of potato slices  

Microsoft Academic Search

Mass transfer in potato slices and strips after Pulsed Electric Fields (PEF) treatment was examined to evaluate potential application of PEF in potato processing. PEF treatment on cell material leads to pore formation in cell membrane and thus modifies diffusion of intra- and extracellular media. Results showed enhanced release of intracellular molecules from permeabilized tissue as well as improved uptake

A. Janositz; A.-K. Noack; D. Knorr

2011-01-01

151

A Poisson model for identifying characteristic size effects in frequency data: Application to frequency-size distributions for global earthquakes, "starquakes", and fault lengths  

NASA Astrophysics Data System (ADS)

The standard Gaussian distribution for incremental frequency data requires a constant variance which is independent of the mean. We develop a more general and appropriate method based on the Poisson distribution, which assumes different unknown variances for the frequencies, equal to the means. We explicitly include "empty bins", and our method is quite insensitive to the choice of bin width. We develop a maximum likelihood technique that minimizes bias in the curve fits, and penalizes additional free parameters by objective information criteria. Various data sets are used to test three different physical models that have been suggested for the density distribution: the power law; the double power law; and the "gamma" distribution. For the CMT catalog of global earthquakes, two peaks in the posterior distribution are observed at moment magnitudes m* = 6.4 and 6.9 implying a bimodal distribution of seismogenic depth at around 15 and 30 km, respectively. A similar break at a characteristic length of 60 km or so is observed in moment-length data, but this does not outperform the simpler power law model. For the earthquake frequency-moment data the gamma distribution provides the best overall fit to the data, implying a finite correlation length and a system near but below the critical point. In contrast, data from soft gamma ray repeaters show that the power law is the best fit, implying infinite correlation length and a system that is precisely critical. For the fault break data a significant break of slope is found instead at characteristic scale of 44 km, implying a typical seismogenic thickness of up to 22 km or so in west central Nevada. The exponent changes from 1.5 to -2.1, too large to be accounted for by changes in sampling for an ideal, isotropic fractal set.

Leonard, Thomas; Papasouliotis, Orestis; Main, Ian G.

2001-01-01

152

Assessment of nonradiative relaxation time and characteristic diffusion time of neodymium, erbium and cobalt doped low silica calcium aluminosilicate glasses  

NASA Astrophysics Data System (ADS)

Nonradiative relaxation time ( ?) and characteristic diffusion time (??) of Nd, Er and Co doped low silica calcium aluminosilicate (LSCA) glasses were assessed by means of photoacoustic spectroscopy. The results are interpreted in terms of frequency dependence predicted by the theory of Rosencwaig and Gersho. Whereas ? varied between 7.2 ms and 36 ms, the values of ?? lied between 0.25 ms and 0.7 ms. For the neodymium doped LSCA glass, a decrease in ?? was observed as the ion concentration was increased. The results indicates that rare earth ion acts as network modifier, disrupting the glass lattice.

Mota, L.; Sampaio, J. A.; da Silva, M. G.; Vargas, H.

2011-01-01

153

First-passage characteristics of biased diffusion in a planar wedge  

NASA Astrophysics Data System (ADS)

We obtain compact, exact, analytical expressions for the first-passage-time distribution for a particle undergoing biased diffusion in a planar wedge for wedge angles ?/p, where p is a positive integer. We then provide the long-time limit of the first-passage time and found it to be dependent on the drift direction and wedge angle. We finally provide exact expressions for the mean first-passage time for specific cases.

Dy, Diandrew Lexter; Esguerra, Jose Perico

2013-07-01

154

First-passage characteristics of biased diffusion in a planar wedge.  

PubMed

We obtain compact, exact, analytical expressions for the first-passage-time distribution for a particle undergoing biased diffusion in a planar wedge for wedge angles ?/p, where p is a positive integer. We then provide the long-time limit of the first-passage time and found it to be dependent on the drift direction and wedge angle. We finally provide exact expressions for the mean first-passage time for specific cases. PMID:23944428

Dy, Diandrew Lexter; Esguerra, Jose Perico

2013-07-17

155

The Stationary Current-Voltage Characteristics of the Quantum Drift-Diffusion Model  

Microsoft Academic Search

This paper is concerned with numerical algorithms for the bipolar quantumdrift diffusion model. For the thermal equilibrium case a quasi-gradientmethod minimizing the energy functional is introduced and strong convergenceis proven. The computation of current--voltage characteristicsis performed by means of an extended Gummel--iteration. It is shownthat the involved fixed point mapping is a contraction for small appliedvoltages. In this case the

Andreas Unterreiter

1999-01-01

156

The Magnesium Diffused Layer Characteristics of a Lithium Niobate Single Crystal with Magnesium-Ion Indiffusion  

Microsoft Academic Search

A Mg-ion indiffusion process was applied to lithium niobate single crystal substrates with a deposited magnesium oxide thin film. By means of electron probe microanalysis and X-ray diffraction analysis, the Mg concentration distribution along the depth of the magnesium diffused layer was obtained and the activation energy for Mg-ion indiffusion was determined to be 288 KJ\\/mol. It was also determined

Wenxiu Que; Siakpiang Lim; Liangying Zhang; Xi Yao

1998-01-01

157

Improving the tribological characteristics of powder steel parts via multicomponent diffusion saturation of working surfaces  

Microsoft Academic Search

This paper discusses a new method for chemical heat treatment – multicomponent diffusion saturation of the surface of powder-steel\\u000a products with chromium, silicon, and manganese in order to improve product performance, especially with respect to tribological\\u000a properties. The samples to be saturated were fabricated from powdered iron, and powdered 40, 60, and 40N2M steel. The control\\u000a samples consisted of hot-stamped

A. B. Korostelev; D. A. Chumak-Zhun

2008-01-01

158

Extra-thermodynamic study on surface diffusion in reversed-phase liquid chromatography using silica gels bonded with alkyl ligands of different chain lengths  

Microsoft Academic Search

Surface diffusion on adsorbents made of silica gels bonded to C, C, C, and C alkyl ligands was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships: enthalpy-entropy compensation (EEC) and linear free-energy relationship (LFER). First, the values of the surface diffusion coefficient (D{sub s}), normalized by the density of the alkyl ligands, were analyzed with

Kanji Miyabe; Georges A Guiochon

2005-01-01

159

Characteristics of diffusion-weighted stimulated echo pulse sequence in human skeletal muscle.  

PubMed

The aim of our study was to simulate an effective diffusion-weighted imaging (DWI) pulse sequence and to evaluate the best b value in skeletal muscle. The evaluated pulse sequences were spin echo (SE), stimulated echo (STE), and gradient-recalled echo (GRE). The signal intensity changed in some DWI pulse sequences when the b value was changed. Moreover, the static magnetic field of 1.5 T was compared with that of 3.0 T. Next, diffusion tensor imaging of the human skeletal muscle was measured. The experimental subjects were healthy male volunteers (n = 7; age 21.8 ± 1.1 years). We changed the b value in steps of 100 s/mm(2) from 0 to 2000 s/mm(2), and the diffusion values [fractional anisotropy (FA), ?(1), ?(2), and ?(3)] were calculated based on the data. The STE method could maintain signals up to b values of 1300 s/mm(2), but the SE and GRE methods suffered from high noise. In the human study, the mean FA (±SD) was 0.41 ± 0.02 in the tibialis anterior muscle (TA) and 0.31 ± 0.02 in the soleus muscle (SOL) at a b value of 1000 s/mm(2). The correlation of the FA with the b value coefficient and the P value by Student's t test were r = 0.981 and P < 0.001 for the TA and r = 0.982, P < 0.001 for the SOL. However, the FA became high with a low b value. In conclusion, STE was very useful for DWI in a short T (2)-value tissue. Moreover, a minimum b value of 800 s/mm(2) was necessary for evaluation of human skeletal muscle. PMID:22893182

Hata, Junichi; Yagi, Kazuo; Hikishima, Keigo; Numano, Tomokazu; Goto, Masami; Yano, Keichi

2012-08-15

160

Cavity length and temperature dependent characteristics of compressively strained InGaAsP MQW BH lasers with a two-step compositional SCH structure  

NASA Astrophysics Data System (ADS)

We investigated the cavity length and temperature dependence of the device characteristics for 1.5 µm InGaAsP/InGaAsP multiple quantum well lasers with a two-step compositional separate confinement heterostructure by eptiaxial regrowth. The device parameters, such as internal optical loss, internal quantum efficiency, transparency current density and modal differential gain, were estimated by fittings to experimental values of threshold current density and slope efficiency as a function of cavity length. Under continuous wave (CW) mode at 25 °C, the uncoated 600 µm long laser emitted a maximum output power of 22 mW with a threshold current of 9.3 mA and a slope efficiency of 0.17 mW mA-1, and it operated up to 97 °C. The full-width at half-maximum values of far-field patterns with a single lobe remained almost constant, indicating ~18.7° (horizontal) × 24° (vertical) at 25 °C over a wide range of injection current. In terms of maximum CW operating temperature, the optimum cavity length is governed by the trade off between emitting volume and internal temperature of lasers, leading to a temperature of 116 °C at a cavity length of 900 µm. By applying a high-reflectivity coating, based on an Au/Ti metallic mirror with an insulation layer of SiO2, on the rear facet of lasers, the device performance was significantly improved due to the reduced mirror loss without degradation of electrical properties, resulting in a high output power of 36 mW and a low threshold current of 7.8 mA and with a slope efficiency of 0.263 mW mA-1 under CW mode at 25 °C for the 600 µm long cavity.

Ko, Y. H.; Park, S. W.; Yu, J. S.

2008-09-01

161

Characteristics of red-emitting broad area stripe laser diodes with zinc diffused window structures  

NASA Astrophysics Data System (ADS)

We have applied zinc diffused window structures to 640 nm broad area stripe laser diodes (BALDs) for the first time. A solid-phase zinc diffusion technique was used for a thick single quantum well (SQW) in GaInP employing the short wavelength and disordered active layer possessed a blue shift of 58 nm in photoluminescence spectrum. We fabricated 10 mm arrays including twenty-five BALDs and each BALD consists of a 60 ?m ridge stripe and a 1000 ?m cavity. An initial catastrophic optical damage (COD) level of the window laser was increased by four times of a conventional none-window laser. A long-term reliability under automatic current control was investigated for initial output powers of 13W and 15W which overcome a previous demonstration of 7.2 W. Measured degradations within a period of 1000-hours were 5 % or less, in contrast a half-life period of our conventional none-window laser with an initial output power of 10 W was only 120-hours. Therefore the window structure improved the BALD in terms of the COD level and the long-term reliability.

Ohno, Tomoki; Takiguchi, Mikio; Wakabayashi, Kazuya; Uchida, Hiroyuki; Naganuma, Kaori; Ohara, Maho; Ito, Satoshi; Hirata, Shoji

2010-02-01

162

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

SciTech Connect

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.

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

163

Characteristics of Diffuse X-Ray Line Emission within 20 Parsecs of the Galactic Center  

NASA Astrophysics Data System (ADS)

Over the last three years, the Galactic center region has been monitored with the Chandra X-Ray Observatory. Besides the X-ray emission from the target object, Sgr A*, diffuse X-ray emission was detected throughout most of the 17'×17' field of view. With 11 Chandra observations through 2002 June, the total effective exposure reaches ~590 ks, providing significant photon statistics on much of the detailed structure within the faint, often filamentary, diffuse X-ray emission. The true-color X-ray image and the equivalent-width images for the detected elemental species of the Galactic center region demonstrate that the diffuse X-ray features have a broad range of spatiospectral properties. Enhancements of the low ionization state Fe line emission (E~6.4 keV) to the northeast of Sgr A* can be interpreted as fluorescence within the dense interstellar medium resulting from irradiation by hard, external X-ray sources. They may also be explained by emission induced by the bombardments by high-energy particles on the ambient medium, such as may accompany unresolved supernova ejecta intruding into dense interstellar medium. The detection of molecular cloud counterparts to the 6.4 keV Fe line-emitting features indicates that these Fe line features are associated with dense Galactic center clouds and/or active star-forming regions, which strongly supports the proposed origins of the X-ray reflection and/or supernova ejecta for the Fe line emission. We detect highly ionized S and Si lines that are generally coincident with the low ionization state Fe line emission and the dense molecular clouds in the northeast of Sgr A*. These hot plasmas are then most likely produced by massive star-forming activities and/or supernova remnants in the Galactic center. In contrast, we find that highly ionized He-like Fe line emission (E~6.7 keV) is primarily distributed along the plane instead of being concentrated in the northeast of Sgr A*. The implied high temperature and the relatively uniform, but strong, alignment along the plane are consistent with the magnetic-confinement model, suggesting that this hot gas component has been reheated by the strong interstellar magnetic fields in the Galactic center to produce the observed He-like Fe line emission.

Park, Sangwook; Muno, Michael P.; Baganoff, Frederick K.; Maeda, Yoshitomo; Morris, Mark; Howard, Christian; Bautz, Mark W.; Garmire, Gordon P.

2004-03-01

164

NO x emission characteristics of counterflow syngas diffusion flames with airstream dilution  

Microsoft Academic Search

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, it generally contains CO and H2 as the dominant fuel components with varying amount of methane and diluents. Due to its wide flexibility in fuel sources and superior pollutants characteristics, the syngas is being

Daniel E. Giles; Sibendu Som; Suresh K. Aggarwal

2006-01-01

165

In-vivo estimates of axonal characteristics using optimized diffusion MRI protocols for single fibre orientation.  

PubMed

This work presents diffusion MR protocols that allow estimation of axonal parameters like diameter and density in the live human brain. Previous approaches demand very high field experimental systems or suffer from long acquisition times and are therefore impractical for use in clinical studies. We propose a method that significantly reduces scan time by making use of the a-priori known fibre orientation in structures with well defined single fibre (SF) organisation like the corpus callosum (CC) and produces protocols that can be performed in under 25 minutes on a standard clinical system. Results from a computer simulation experiment show that our SF protocols can generate parameter estimates with similar precision to previously proposed orientation invariant (OI) protocols. Furthermore, we acquire the 20 minute long SF protocol and the 1 hour long OI protocol in a scan/rescan study on two healthy subjects and compare the axonal parameter maps from both protocols. PMID:20879283

Schneider, Torben; Wheeler-Kingshott, Claudia A M; Alexander, Daniel C

2010-01-01

166

Effective medium approach for heterogeneous reaction-diffusion media  

NASA Astrophysics Data System (ADS)

An effective medium theory that can be used to calculate effective diffusion and reaction rate coefficients in random heterogeneous reaction-diffusion systems is described. The predictions of the theory are compared with simulations of spatially distributed media with different types of heterogeneity. The magnitude of the front velocity in bistable media is used to gauge the accuracy of the theoretical predictions. Quantitative agreement is found if the diffusion length in the heterogeneities is large compared to the characteristic width of the front. However, for small diffusion lengths the agreement depends on the type of heterogeneity. The effective medium predictions are also compared with simulations on systems with regular or temporal disorder.

Alonso, Sergio; Bär, Markus; Kapral, Raymond

2009-12-01

167

Non-scaling behavior in Fractional Diffusion  

NASA Astrophysics Data System (ADS)

It is well known that Brownian diffusion is characterized by a mean squared displacement which varies linearly in time, ˜t and that anomalous diffusion is characterized by a mean square displacement which is nonlinear in time, ˜t^?. It is generally accepted that fractional diffusion, which is used to describe anomalous diffusion is also characterized by the same scaling behavior in the second moment. It is shown that this is not always so and that inward radial fractional diffusion in one, two, and three dimensions does not exhibit this scaling. However, the outward radial fractional diffusion does exhibit this scaling. The reason for this unexpected behavior in inward fractional diffusion is the existence of a characteristic length, and the separation of variables which occurs because of the boundary conditions.

Narahari Achar, B. N.; Hanneken, John W.

2003-03-01

168

Experimental investigation of characteristics of a diffusion flame established over liquid ethanol surface under opposed air flow  

SciTech Connect

A preliminary study of the shape and the extinction characteristics of a diffusion flame established over a circular liquid fuel surface under the influence of an opposed air flow, is presented. Renewable liquid fuel such as ethanol is employed. A simple heterogeneous combustion setup, which consists of a cylindrical tube containing ethanol located at the bottom, is exposed to an opposed air flow from a coaxial circular pipe of same size located at the top at a fixed separation distance. Axial and radial extents of flame for different air flow rates are qualitatively analyzed. Burning rates of ethanol for different separation distances and air flow rates are recorded. For a fixed separation distance, at a particular air flow rate the flame extinction takes place. Extinction air flow rates and corresponding strain rates for different separation distances are presented. (author)

Sen, Anirudh; Raghavan, Vasudevan; Shet, U.S.P. [Department of Mechanical Engineering, Indian Institute of Technology Madras, 206A TDCE Lab., Chennai 600036 (India)

2009-03-15

169

Analysis of Temperature Effects on High-Frequency Characteristics of RF Lateral-Diffused Metal-Oxide-Semiconductor Transistors  

NASA Astrophysics Data System (ADS)

In this work, the effects of temperature on the DC and RF characteristics of lateral-diffused metal-oxide-semiconductor (LDMOS) transistors were studied. Devices with different layout structures were fabricated using a 40 V LDMOS process. The temperature coefficients of the threshold voltage and channel mobility are negative and their values are similar for devices with fishbone and ring structures. In addition, we found that both the cutoff frequency ( fT) and the maximum oscillation frequency ( fmax) decrease with increasing temperature. The variations of fT with different temperatures are not only affected by the change in transconductance but also affected by the drain resistance. Finally, the temperature behaviors of S-parameters were measured, and the ring structure showed less S22 variation with different temperatures than the fishbone structure. We extracted the model parameters of the devices to explain this observation.

Hu, Hsin-Hui; Chen, Kun-Ming; Huang, Guo-Wei; Chien, Alex; Cheng, Eric; Yang, Yu-Chi; Chang, Chun-Yen

2008-04-01

170

Steady-state characteristics of a laser utilizing transmission gratings in crystals with a diffusion nonlinearity  

SciTech Connect

A theory of a frequency-degenerate four-wave interaction in media with a nonlocal nonlinearity is used to calculate the steady-state energy characteristics of a laser utilizing transmission gratings, which are then compared with the results of a qualitative analysis of a system based on the holographic approach. It is shown that a suitable selection of the transparency of the resonator mirrors can ensure either highly efficient conversion of a pump beam into an output beam or into a beam with a reversed wave front.

Odulov, S.G.; Sukhoverkhova, L.G.

1984-03-01

171

AN INVESTIGATION OF DIFFUSION PROCESSES IN SEVERAL POLYMERS. III. IRREVERSIBLE CHANGES IN DIFFUSION CHARACTERISTICS RESULTING FROM Co⁶° $gamma$IRRADIATION OF THE POLYMER  

Microsoft Academic Search

The action of gamma radiation on the diffusion of He and Ar through ; irradiated polymers (polyethylene, polyamide 54\\/10, methanolpolyaraide 2\\/10, ; polytetrafluoroethylene, polyvinyl chloride, and SKS 30) was investigated. ; Results showed that an increase in the absorbed energy (dose) produced (a) a ; decrease in the diffusion rate of gases through polyethylene, polyaraides, and ; SKS-30 which is

N. S. Tikhomirova; Yu. M. Malinskii; V. L. Karpov

1960-01-01

172

Design and Characteristics of Mode-Coupling LiNbO3 Ultrasonic Motor Depended on Width-to-Length Ratio of the Stator Vibrator  

NASA Astrophysics Data System (ADS)

A miniature ultrasonic motor fabricated from a LiNbO3 rectangular plate was studied to improve its rotation characteristics. In this motor, the coupling modes of in-plane longitudinal and flexural modes caused by crystal anisotropy are used to realize a single-phase drive motor. The mode coupling vibrator is designed to have crystal cut angles and the width-to-length ratio W/L of the vibrator shape. In this study, we noted the new coupling condition of W/L? 0.84 compared with the conventional ratio of W/L=0.255. We considered the mechanism of the mode coupling and the design of the stator vibrator by finite element method analysis and experiments. From the results, we fabricated and investigated prototype motors of the vibrator with dimensions of 10× 2.55× 0.5 and 4.10× 3.48× 0.5 mm3. The newly designed motor with the vibrator of W/L=0.849 improved the motor characteristics for the equalization of rotation in both directions.

Hideki Tamura,; Takanori Morooka,; Yasuhiro Yamayoshi,; Manabu Aoyagi,; Takehiro Takano,; Seiji Hirose,

2010-07-01

173

Ladybug Lengths  

NSDL National Science Digital Library

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.

2012-01-01

174

Ladybug Lengths  

NSDL National Science Digital Library

This experience focuses studentâs attention on the attributes of length and gives students the opportunity to develop knowledge of and skills in using nonstandard units of measurement. The lesson begins with a connection to children's literature. As students practice measuring length, they do so using nonstandard units.

Math, Illuminations N.

2009-01-28

175

Heavy-Metal Concentrations in Small Mammals from a Diffusely Polluted Floodplain: Importance of Species- and Location-Specific Characteristics  

PubMed Central

The soil of several floodplain areas along large European rivers shows increased levels of heavy metals as a relict from past sedimentation of contaminants. These levels may pose risks of accumulation in food webs and toxicologic effects on flora and fauna. However, for floodplains, data on heavy-metal concentrations in vertebrates are scarce. Moreover, these environments are characterised by periodical flooding cycles influencing ecologic processes and patterns. To investigate whether the suggested differences in accumulation risks for insectivores and carnivores, omnivores, and herbivores are reflected in the actual heavy-metal concentrations in the species, we measured the current levels of Zn, Cu, Pb, and Cd in 199 specimens of 7 small mammal species (voles, mice, and shrews) and in their habitats in a diffusely polluted floodplain. The highest metal concentrations were found in the insectivorous and carnivorous shrew, Sorex araneus. Significant differences between the other shrew species, Crocidura russula, and the vole and mouse species was only found for Cd. The Cu concentration in Clethrionomys glareolus, however, was significantly higher than in several other vole and mouse species. To explain the metal concentrations found in the specimens, we related them to environmental variables at the trapping locations and to certain characteristics of the mammals. Variables taken into account were soil total and CaCl2-extractable metal concentrations at the trapping locations; whether locations were flooded or nonflooded; the trapping season; and the life stage; sex; and fresh weight of the specimens. Correlations between body and soil concentrations and location or specimen characteristics were weak. Therefore; we assumed that exposure of small mammals to heavy-metal contamination in floodplains is significantly influenced by exposure time, which is age related, as well as by dispersal and changes in foraging and feeding patterns under influence of periodic flooding.

Leuven, R. S. E. W.; van der Velde, G.; Jungheim, G.; Koelemij, E. I.; de Vries, F. T.; Eijsackers, H. J. P.; Smits, A. J. M.

2007-01-01

176

Ballistic-Diffusive Heat-Conduction Equations  

Microsoft Academic Search

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,

Gang Chen; Gang

2001-01-01

177

Effective diffusivity of passive scalars in rotating turbulence.  

PubMed

We use direct numerical simulations to compute turbulent transport coefficients for passive scalars in turbulent rotating flows. Effective diffusion coefficients in the directions parallel and perpendicular to the rotation axis are obtained by studying the diffusion of an imposed initial profile for the passive scalar, and calculated by measuring the scalar average concentration and average spatial flux as a function of time. The Rossby and Schmidt numbers are varied to quantify their effect on the effective diffusion. It is found that rotation reduces scalar diffusivity in the perpendicular direction. The perpendicular diffusion can be estimated from mixing length arguments using the characteristic velocities and lengths perpendicular to the rotation axis. Deviations are observed for small Schmidt numbers, for which turbulent transport decreases and molecular diffusion becomes more significant. PMID:23496621

Imazio, P Rodriguez; Mininni, P D

2013-02-25

178

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 ...

179

Finger Length  

NSDL National Science Digital Library

Although life experience plays a huge role in shaping who we are, the foundations of our personality begin in the womb. This Science Update describes a recent study that looks to finger length for signs of a man's pre-natal exposure to testosterone.

Science Update;

2005-03-28

180

Binding of SecB to ribosome-bound polypeptides has the same characteristics as binding to full-length, denatured proteins  

PubMed Central

The interaction of the chaperone SecB with ribosome-bound polypeptides that are in the process of elongation has been studied using an in vitro protein synthesis system. The binding is characterized by the same properties as those demonstrated for the binding of SecB to full-length proteins that are in nonnative conformation: it is readily reversible and has no specificity for the leader peptide. In addition, it is shown that the growing polypeptide chains must achieve a critical length to bind tightly enough to allow their isolation in complex with SecB. This explains the longstanding observation that, even when export is cotranslational, it begins late in synthesis. Furthermore, the required length is approximately the same as the length that defines the binding frame within denatured, full-length proteins bound to SecB.

Randall, Linda L.; Topping, Traci B.; Hardy, Simon J. S.; Pavlov, Michael Y.; Freistroffer, David V.; Ehrenberg, Mans

1997-01-01

181

Characteristics of hydrogen–hydrocarbon composite fuel turbulent jet flames  

Microsoft Academic Search

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

Ahsan R. Choudhuri; S. R. Gollahalli

2003-01-01

182

Noise characteristics of centrifugal blower with low solidity cascade diffuser (Noise reduction by means of small groove located at LSD blade leading tip)  

Microsoft Academic Search

This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blower characteristic\\u000a and the noise generated by the LSD. The small grooves were set up at the root and\\/or tip near the leading edge of the LSD\\u000a blade. In order to clarify the mechanism of noise increase due to LSD and

Tengen Murakami; Masahiro Ishida; Daisaku Sakaguchi; Yu Koba

2009-01-01

183

Characteristic signal changes in the pontine base on T2- and multishot diffusion-weighted images in spinocerebellar ataxia type 1  

Microsoft Academic Search

The aim of the present study was to demonstrate characteristic signal changes of the pontine base on T2-weighted images of\\u000a patients with SCA 1, and to elucidate the relationship between abnormal high-intensities of the pontine base on T2-weighted\\u000a images and the findings on multishot diffusion-weighted images. We assessed abnormal signals of the pontine base on T2-weighted\\u000a images from 50 controls

M. Adachi; T. Kawanami; H. Ohshima; T. Hosoya

2006-01-01

184

Spatial characteristics of newly diagnosed grade 3 glioma assessed by magnetic resonance metabolic and diffusion tensor imaging.  

PubMed

The spatial heterogeneity in magnetic resonance (MR) metabolic and diffusion parameters and their relationship were studied for patients with treatment-naive grade 3 gliomas. MR data were evaluated from 51 patients with newly diagnosed grade 3 gliomas. Anatomic, diffusion, and metabolic imaging data were considered. Variations in metabolite levels, apparent diffusion coefficient (ADC), and fractional anisotropy (FA) were evaluated in regions of gadolinium enhancement and T2 hyperintensity as well as regions with abnormal metabolic signatures. Contrast enhancement was present in only 21 of the 51 patients. When present, the enhancing component of the lesion had higher choline-to-N-acetylaspartate index (CNI), higher choline, lower N-acetylaspartate, similar creatine, similar ADC and FA, and higher lactate/lipid than the nonenhancing lesion. Regions with CNI ? 4 had higher choline, lower N-acetylaspartate, higher lactate/lipid, higher ADC, and lower FA than normal-appearing white matter and regions with intermediate CNI values. For lesions that exhibited gadolinium enhancement, the metabolite levels and diffusion parameters in the region of enhancement were consistent with it corresponding to the most abnormal portion of the tumor. For nonenhancing lesions, areas with CNI ? 4 were the most abnormal in metabolic and diffusion parameters. This suggests that the region with the highest CNI might provide a good target for biopsies for nonenhancing lesions to obtain a representative histologic diagnosis of its degree of malignancy. Metabolic and diffusion parameter levels may be of interest not only for directing tissue sampling but also for defining the targets for focal therapy and assessing response to therapy. PMID:22348171

Ozturk-Isik, Esin; Pirzkall, Andrea; Lamborn, Kathleen R; Cha, Soonmee; Chang, Susan M; Nelson, Sarah J

2012-02-01

185

Spatial Characteristics of Newly Diagnosed Grade 3 Glioma Assessed by Magnetic Resonance Metabolic and Diffusion Tensor Imaging1  

PubMed Central

The spatial heterogeneity in magnetic resonance (MR) metabolic and diffusion parameters and their relationship were studied for patients with treatment-naive grade 3 gliomas. MR data were evaluated from 51 patients with newly diagnosed grade 3 gliomas. Anatomic, diffusion, and metabolic imaging data were considered. Variations in metabolite levels, apparent diffusion coefficient (ADC), and fractional anisotropy (FA) were evaluated in regions of gadolinium enhancement and T2 hyperintensity as well as regions with abnormal metabolic signatures. Contrast enhancement was present in only 21 of the 51 patients. When present, the enhancing component of the lesion had higher choline-to-N-acetylaspartate index (CNI), higher choline, lower N-acetylaspartate, similar creatine, similar ADC and FA, and higher lactate/lipid than the nonenhancing lesion. Regions with CNI ? 4 had higher choline, lower N-acetylaspartate, higher lactate/lipid, higher ADC, and lower FA than normal-appearing white matter and regions with intermediate CNI values. For lesions that exhibited gadolinium enhancement, the metabolite levels and diffusion parameters in the region of enhancement were consistent with it corresponding to the most abnormal portion of the tumor. For nonenhancing lesions, areas with CNI ? 4 were the most abnormal in metabolic and diffusion parameters. This suggests that the region with the highest CNI might provide a good target for biopsies for nonenhancing lesions to obtain a representative histologic diagnosis of its degree of malignancy. Metabolic and diffusion parameter levels may be of interest not only for directing tissue sampling but also for defining the targets for focal therapy and assessing response to therapy.

Ozturk-Isik, Esin; Pirzkall, Andrea; Lamborn, Kathleen R; Cha, Soonmee; Chang, Susan M; Nelson, Sarah J

2012-01-01

186

Effect of the column length on the characteristics of the packed bed and the column efficiency in a dynamic axial compression column  

Microsoft Academic Search

The axial homogeneity of preparative-scale chromatography columns was studied by measuring the overall properties of similar columns differing only by their lengths. The properties investigated were the packing density, the external porosity, the permeability and the column efficiency. Two different materials were used, one made of large, irregular silica particles compressed under either a high or a low degree of

Joon-Ho Koh; Georges Guiochon

1998-01-01

187

A characteristic-based finite analytic method for solving the two-dimensional steady state advection-diffusion equation  

Microsoft Academic Search

This paper develops an improved finite analytic (FA) solution method to the advection-diffusion equation (ADE) for solving advection-dominated steady state transport problems. The FA method solves the ADE analytically in localized, discrete elements, with each element linked through local boundary conditions. Previous FA methods have suffered from complex solution formulations as well as from numerical dispersion stemming from inaccuracies in

Thomas Lowry; Shu-Guang Li

2002-01-01

188

Binary and ternary gas mixtures with temperature enhanced diffuse glow discharge characteristics for use in closing switches  

DOEpatents

An improvement to the gas mixture used in diffuse glow discharge closing switches is disclosed which includes binary and ternary gas mixtures which are formulated to exhibit decreasing electron attachment with increasing temperature. This increases the efficiency of the conductance of the glow discharge and further inhibits the formation of an arc. 11 figs.

Christophorou, L.G.; Hunter, S.R.

1990-06-26

189

Binary and ternary gas mixtures with temperature enhanced diffuse glow discharge characteristics for use in closing switches  

DOEpatents

An improvement to the gas mixture used in diffuse glow discharge closing switches is disclosed which includes binary and ternary gas mixtures which are formulated to exhibit decreasing electron attachment with increasing temperature. This increases the efficiency of the conductance of the glow discharge and further inhibits the formation of an arc.

Christophorou, Loucas G. (Oak Ridge, TN); Hunter, Scott R. (Oak Ridge, TN)

1990-01-01

190

LABORATORY ASSESSMENT OF THE PERMEABILITY AND DIFFUSION CHARACTERISTICS OF FLORIDA CONCRETES: PHASE II. FIELD SAMPLES AND ANALYSES  

EPA Science Inventory

The report gives results of a study to: (1) establish the capability of measuring concrete's permeability and diffusivity, (2) measure these parameters in a small sampling of the typical types of Florida concrete, and (3) if possible, correlate the physical parameters of the conc...

191

Vaneless diffusers  

NASA Astrophysics Data System (ADS)

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

Senoo, Y.

192

On Indexation and Contract Length.  

National Technical Information Service (NTIS)

This paper investigates the effects of wage indexation on macroeconomic fluctuations in a model which highlights the joint determination of two contract characteristics: contract length and an indexing parameter. Within the framework developed by this ana...

J. A. Gray

1976-01-01

193

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)

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.

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

2006-11-01

194

On the characteristic features of the magnetic field diffusion in an inhomogeneous plasma in the EMHD approximation  

SciTech Connect

The magnetic field transport in a spatially inhomogeneous plasma is studied theoretically in the electron MHD approximation. A model problem with a given periodic plasma density profile is considered in plane geometry. In this case, the magnetic field is transported diffusively and the effective diffusion coefficient is determined by the geometric and time parameters of the perturbed density, as well as by the magnetization parameter. It is found that, under certain relationships between the parameters of the problem, there is a kind of resonant effect-a decrease in the plasma conductivity. The problem under consideration does not refer solely to plasma physics: the results obtained here can also be used to describe transport processes in other branches of physics.

Tolstik, D. A. [Russian Research Centre Kurchatov Institute (Russian Federation)

2008-06-15

195

[Hormone-dependent characteristics of the myocyte cell surface in the human myoma and myometrium cultured in diffusion chambers].  

PubMed

The normal and the pathologically changed human myometrium was cultured in the diffusion chamber implanted in the subcutaneous cellular tissue of the rat. In the absence of hormonal influence the growth of myometrium culture is only insignificant, while no myoma cell growth was found at all. Estradiol stimulates the growth and development of the myometrium culture and the myoma. A combined action of estradiol and progesterone stimulates the collagen formation. PMID:3282373

Skopichev, V G; Arutiunian, N A; Pro?mina, F I; Savitski?, G A

1988-01-01

196

Generalized Drift-Diffusion Model In Semiconductors  

SciTech Connect

A new drift-diffusion model is proposed based on the computation of the stationary nonlocal current density. The semi classical Boltzmann equation is solved keeping all the anisotropies of the distribution function with the use of the continued fractions. The conductivity is calculated in the linear approximation and for arbitrary collision frequency with respect to Kv{sub t} where K{sup -1} is the characteristic length scale of the system and V{sub t} is the thermal velocity. The nonlocal conductivity can be used to close the generalized drift-diffusion equations valid for arbitrary collisionality.

Mesbah, S.; Bendib-Kalache, K.; Bendib, A. [Laboratoire d'Electronique Quantique, Faculte de Physique, USTHB, El Allia, BP 32, Bab Ezzouar 16111, Algiers (Algeria)

2008-09-23

197

Diffusion characteristics associated with neuronal injury and glial activation following hypoxia-ischemia in the immature brain  

PubMed Central

To identify quantitative MRI indices of injury in the brain following neonatal hypoxic-ischemic brain injury (HI), we subjected mouse pups to HI on postnatal day 7 and obtained conventional and diffusion weighted in vivo images of the brain 24 hours later followed by histological assessment. T2-weighted images showed increased signal intensity in the CA1 and CA2 regions of the hippocampus ipsilateral to the injury and adjacent white matter (WM). In contrast, diffusion imaging showed reduced apparent diffusion coefficient (ADC) values in CA1 and CA2, but increased values in the adjacent WM. Histological analysis showed widespread gliosis with degenerating oligodendrocytes in the ipsilateral hippocampus. In addition, WM areas that were abnormal by MRI showed an increase in the number of activated microglia (CD45 positive cells). Activated caspase-3 immunostaining showed a marked increase in neurons in the hippocampal regions corresponding to those with reduced ADC, and a quantitative measure of staining showed a statistically significant correlation with the ADC. In contrast, ADC was higher in adjacent white matter, where histology showed activation of microglia and reactive oligodendrocytes but not caspase-3 activation. These results suggest that the ADC response differs between areas of neuronal injury as compared with those showing glial changes without marked cell death.

Lodygensky, Gregory A.; West, Tim; Moravec, Matthew D.; Back, Stephen A.; Dikranian, Krikor; Holtzman, David M.; Neil, Jeffrey J.

2011-01-01

198

Patient age at diagnosis is associated with the molecular characteristics of diffuse large B-cell lymphoma.  

PubMed

Diffuse large B-cell lymphoma is the most frequent type of B-cell lymphoma in adult patients but also occurs in children. Patients are currently assigned to therapy regimens based on arbitrarily chosen age limits only (eg, 18 or 60 years) and not biologically justified limits. A total of 364 diffuse large B-cell lymphomas and related mature aggressive B-cell lymphomas other than Burkitt lymphoma from all age groups were analyzed by comprehensive molecular profiling. The probability of several biologic features previously reported to be associated with poor prognosis in diffuse large B-cell lymphoma, such as ABC subtype, BCL2 expression, or cytogenetic complexity, increases with age at diagnosis. Similarly, various genetic features, such as IRF4 translocations, gains in 1q21, 18q21, 7p22, and 7q21, as well as changes in 3q27, including gains and translocations affecting the BCL6 locus, are significantly associated with patient age, but no cut-offs between age groups could be defined. If age was incorporated in multivariate analyses, genetic complexity lost its prognostic significance, whereas the prognostic impact of ABC subtype and age were additive. Our data indicate that aging is a major determinant of lymphoma biology. They challenge current concepts regarding both prognostic biomarkers and treatment stratification based on strict age cut-offs. PMID:22238326

Klapper, Wolfram; Kreuz, Markus; Kohler, Christian W; Burkhardt, Birgit; Szczepanowski, Monika; Salaverria, Itziar; Hummel, Michael; Loeffler, Markus; Pellissery, Shoji; Woessmann, Wilhelm; Schwänen, Carsten; Trümper, Lorenz; Wessendorf, Swen; Spang, Rainer; Hasenclever, Dirk; Siebert, Reiner

2012-01-11

199

Surprising non-scaling behavior in fractional diffusion  

NASA Astrophysics Data System (ADS)

It is well known that Brownian diffusion is characterized by a mean-squared displacement which varies linearly in time, ~t and that anomalous diffusion, by a mean-square displacement which is nonlinear in time, ~t?. It is generally accepted that fractional diffusion, which is used to describe anomalous diffusion, is also characterized by the same scaling behavior in the second moment, ~t?. It is shown in this paper that this is not always so and that inward radial fractional diffusion in one, two and three dimensions does not exhibit this scaling, where as outward radial fractional diffusion in these cases does exhibit the scaling. The reason for this unexpected behavior is the existence of a characteristic length, and the separation of variables, which occurs because of the boundary conditions.

Achar, B. N. Narahari; Hanneken, John W.

2003-05-01

200

Biofouling of Polymer Hydrogel Materials and its Effect on Diffusion and Enzyme-Based Luminescent Glucose Sensor Functional Characteristics  

PubMed Central

Background Continuous glucose monitoring is crucial to developing a successful artificial pancreas. However, biofouling and host response make in vivo sensor performance difficult to predict. We investigated changes in glucose diffusivity and sensor response of optical enzymatic glucose sensors due to biological exposure. Method Three hydrogel materials, poly(2-hydroxyethyl methacrylate) (pHEMA), poly(acrylamide) (pAM), and poly(2-hydroxyethyl methacrylate)-co-poly(acrylamide) (p(HEMA-co-AM)), were tested for glucose diffusivity before and after exposure to serum or implantation in rats for 1 month. Luminescent sensors based on these materials were measured to compare the response to glucose before and after serum exposure. Results Glucose diffusivity through the pHEMA [(8.1 ± 0.38) × 10-8 cm2/s] slabs was much lower than diffusivity through pAM [(2.7 ± 0.15) × 10-6 cm2/s] and p(HEMA-co-AM) [(2.5 ± 0.08) × 10-6]. As expected from these differences, sensor response was highly dependent on material type. The pHEMA sensors had a maximum sensitivity of 2.5%/(mg/dl) and an analytical range of 4.2–356 mg/dl, while the p(HEMA-co-AM) sensors had a higher sensitivity [14.9%/(mg/dl)] and a narrower analytical range (17.6–70.5 mg/dl). After serum exposure, the pHEMA sensors were unaffected, whereas the p(HEMA-co-AM) sensors exhibited significantly decreased sensitivity and increased analytical range. Conclusions Decreases in glucose diffusivity in the polymers resulting from in vitro serum exposure and residence in vivo were shown to be similar, suggesting that serum incubation was a reasonable approximation of in vivo fouling. While biofouling is expected to affect the response of flux-based sensors, we have shown that this depended on the type of sensor and matrix used. Therefore, proper design and materials selection may minimize response alterations occurring upon implantation.

Roberts, Jason R.; Park, Jaebum; Helton, Kristen; Wisniewski, Natalie; McShane, Michael J.

2012-01-01

201

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

NASA Astrophysics Data System (ADS)

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

Seki, Kazuhiko; Ramachandran, Sanoop; Komura, Shigeyuki

2011-08-01

202

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

PubMed

The diffusion coefficient of an inclusion in a liquid membrane is investigated by taking into account the interaction between membranes and bulk solvents of arbitrary thickness. As illustrative examples, the diffusion coefficients of two types of inclusions, a circular domain composed of fluid with the same viscosity as the host membrane and that of a polymer chain embedded in the membrane, are studied. The diffusion coefficients are expressed in terms of the hydrodynamic screening lengths, which vary according to the solvent thickness. When the membrane fluid is dragged by the solvent of finite thickness, via stick boundary conditions, multiple hydrodynamic screening lengths together with the weight factors to the diffusion coefficients are obtained from the characteristic equation. The conditions for which the diffusion coefficients can be approximated by the expression including only a single hydrodynamic screening length are also shown. PMID:21929018

Seki, Kazuhiko; Ramachandran, Sanoop; Komura, Shigeyuki

2011-08-04

203

Diffusion barrier and electrical characteristics of a self-aligned MgO layer obtained from a Cu(Mg) alloy film  

NASA Astrophysics Data System (ADS)

Diffusion barrier characteristics and electrical properties of self-aligned MgO layers obtained from a Cu(Mg) alloy film have been investigated. Self-aligned surface and interfacial MgO layers were formed upon annealing a Cu(Mg) film in an oxygen ambient and prevented interdiffusion of Cu in SiO2 up to 700 °C. The thermal stability of a pure Cu/TiN/Si multilayer system has been significantly enhanced up to 800 °C by the MgO layers by forming a MgO/Cu/MgO/TiN/Si multilayer system. A combined structure of Si3N4(500 Å)/MgO(100 Å) increased the breakdown voltage up to 20 V from 15 V and reduced the leakage current density down to 3×10-9 A/cm2 from 1×10-8 A/cm2 compared to a pure copper system. Consequently, the deposition of Cu(Mg) alloy followed by annealing in an oxygen ambient gives rise to the formation of a self-aligned MgO layer with excellent diffusion barrier and electrical characteristics and the film can be applied as a gate electrode in thin-film transistor/liquid-crystal displays, resulting in a reduction of process steps.

Lee, W. H.; Cho, H. L.; Cho, B. S.; Kim, J. Y.; Nam, W. J.; Kim, Y.-S.; Jung, W. G.; Kwon, H.; Lee, J. H.; Lee, J. G.; Reucroft, P. J.; Lee, C. M.; Lee, E. G.

2000-10-01

204

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

Microsoft Academic Search

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

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

2006-01-01

205

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

Microsoft Academic Search

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

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

2006-01-01

206

A Physical Understanding of RF Noise in Bulk nMOSFETs With Channel Lengths in the Nanometer Regime  

Microsoft Academic Search

Experimental and simulation results of high-frequency channel noise in MOSFETs with 40-, 80-, and 110- nm gate lengths are presented. The measured dc $I$–$V$ characteristics can be matched using the drift–diffusion (DD) and hydrodynamic (HD) transport models, both incorporating velocity saturation. The DD model grossly underestimates the measured noise, demonstrating the inadequacy of channel-length modulation and impact ionization to explain

Vinayak M. Mahajan; Pradeep Rao Patalay; Renuka P. Jindal; Hisashi Shichijo; Sam Martin; Fan-Chi Hou; Charles Machala; Django E. Trombley

2012-01-01

207

Characteristics of Plasma-Treated Amorphous Ta-Si-C Film as a Diffusion Barrier for Copper Metallization  

NASA Astrophysics Data System (ADS)

Ta-Si-C film was prepared by magnetron sputtering, and the thermal stability of the plasma-treated film as a copper diffusion barrier was evaluated. The barrier properties and failure behaviors of the studied films were elucidated using a four-point probe, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The as-deposited Ta-Si-C film had an amorphous structure, and the structure remained stable at an elevated temperature, allowing the film to be adopted as a barrier to inhibit Cu diffusion. The Cu/Ta26Si41C32/Si stacked structure had a failure temperature of 750°C/1 min when the 5-nm-thick Ta26Si41C32 film was treated by exposure to Ar/H2 plasma mixture, while the stacked film failed at 800°C/1 min when treated by exposure to Ar/N2 plasma mixture. Using the Ar/N2 plasma treatment favorably enhanced the thermal stability of the Ta26Si41C32 thin film as a barrier for Cu interconnections. When the Ta-Si-C film thickness was further reduced to 2 nm, the film retained the barrier effect at 650°C, 700°C, and 750°C for Ta34Si47C18, Ta30Si44C25, and Ta26Si41C32 compositions, respectively.

Fang, Jau-Shiung; Su, Wu-Jia; Huang, Meng-Shuo; Chiu, Chin-Fu; Chin, Tsung-Shune

2013-09-01

208

Influence of Geometrical Characteristics and Operating Conditions on the Effectiveness of Ozone Contacting in Fine-Bubbles Conventional Diffusion Reactors  

Microsoft Academic Search

Ozone contactor hydrodynamics are strongly dependent on the geometry and the operating conditions of the system. In this paper results obtained on a pilot scale reactor showing the relationship between the geometrical characteristics of an ozonation reactor and its hydrodynamic behavior are presented. The validity of the proposed models has been checked on several full-scale reactors for which data were

Zdravka Do-Quang; Clementina Cortina Ramirez; Michel Roustan

2000-01-01

209

Random diffusion model.  

PubMed

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

Mazenko, Gene F

2008-09-18

210

Exciton Diffusion in Air-Suspended Single-Walled Carbon Nanotubes  

Microsoft Academic Search

Direct measurements of the diffusion length of excitons in air-suspended single-walled carbon nanotubes are reported. Photoluminescence microscopy is used to identify individual nanotubes and to determine their lengths and chiral indices. Exciton diffusion length is obtained by comparing the dependence of photoluminescence intensity on the nanotube length to numerical solutions of diffusion equations. We find that the diffusion length in

S. Moritsubo; T. Murai; T. Shimada; Y. Murakami; S. Chiashi; S. Maruyama; Y. K. Kato

2010-01-01

211

Discharge characteristics of He-Ne-Xe gas mixture with varying Xe contents and at varying sustain electrode gap lengths in the plasma display panel  

SciTech Connect

The discharge characteristics of He-Ne-Xe gas mixture in the plasma display panel were investigated using a two-dimensional numerical simulation to understand the effects of adding He and varying the Xe contents in the gas mixture, and also varying sustain electrode gap. With 5% Xe content and 60 mum sustain electrode gap, decreased ionization led to the improvement of the vacuum ultraviolet (vuv) efficacy at increasing He mixing ratios. However, at 20% Xe content and 60 mum sustain electrode gap, increased electron heating improved the vuv efficacy until the He mixing ratio reached 0.7, but the efficacy decreased beyond the ratio of 0.7 due to the increased ionization of Xe atoms. At 5% Xe content and 200 mum sustain electrode gap, the vuv efficacy increased as a result of increased electron heating at the gap space at increasing He mixing ratios.

Kwon, Ohyung; Whang, Ki-Woong [Plasma Laboratory, Inter-University Semiconductor Research Center, Department of Electrical and Computer Engineering, College of Engineering, Seoul National University, Seoul 151-742 (Korea, Republic of); Bae, Hyun Sook [Information and Electronics Research Institute, School of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology, Daejon 305-701 (Korea, Republic of)

2009-09-15

212

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

PubMed

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

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

2010-10-19

213

Characteristics and Results of the Management of Diffuse Large B-Cell Lymphomas: The Experience of C?te d'Ivoire  

PubMed Central

Diffuse large B-cell lymphomas have been little studied in black Africans. The purpose of our study was to determine the characteristics and results of the management of these lymphomas. Patients and Methods. In a descriptive and analytic retrospective study we studied the medical records of 63 patients with diffuse large B-cell lymphoma hospitalized during the period from 1991 to 2007. The diagnosis was made after lymph node or organ biopsy. Response to treatment, OS, PFS, and toxicity were studied. The complete response has been analyzed univariate and multivariate analysis. Results. The median age was 42 years. The sex ratio was 2. The HIV serology was positive in 11 cases, and 8 patients had antiretroviral therapy. In 71% the lymphoma was at stages III and IV of Ann Arbor. IPI was ?3 in 65%. Complete remission was achieved in 43%. Only 43% of patients had had a good compliance. Progression-free survival at 3 years was 32%, and overall survival at 3 years was 50%. 13% of patients were lost to follow up, and 51% of them died. In terms of analysis the complete remission rate was influenced by the stage of Ann Arbor (P < 0.0001), biological b symptoms (P < 0.01), the IPI (P < 0.0001), and the socioeconomic standing (P = 0.001). In multivariate analysis, only IPI and stage of Ann Arbor influence the complete remission.

Tolo Diebkile, Aissata; Kouakou, Boidy; N'dhatz, Emeraude; Nanho, Clotaire D.; Meite, N'Dogomo; Ayemou, Romeo; Sekongo, Mamadou Y.; Kouehion, Paul; Konan, Mozart; Koffi, Gustave K.; Sanogo, Ibrahima

2012-01-01

214

ESTIMATION OF TURBULENT DIFFUSIVITY WITH DIRECT NUMERICAL SIMULATION OF STELLAR CONVECTION  

SciTech Connect

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.

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

215

Correlation of microscopic length scales of ion dynamics with network structure in lithium-iodide-doped lithium metaphosphate glasses  

NASA Astrophysics Data System (ADS)

In this paper we have studied the correlation of microscopic length scales of ion dynamics with the network structure in lithium-iodide-doped lithium metaphosphate glasses. We have obtained microscopic length scales for ion dynamics, such as the characteristic mean square displacement and the spatial extent of sub-diffusive motion of the lithium ions. We have observed that the lithium ions have to travel a smaller distance to overcome the nearest percolation barriers in order to perform long-range diffusion. The phosphate chain lengths shorten with the addition of lithium iodide to metaphosphate glasses. We have also studied the network structure of these glasses, and a correlation between the length scales of ion dynamics and the network structure has been obtained.

Shaw, A.; Ghosh, A.

2012-12-01

216

Diffusion and reverse diffusion processes in social networks: Analysis using the degree of Diffusion ?  

Microsoft Academic Search

Diffusion of information in a social network is characterized by introducing a new parameter, “Degree of Diffusion ?.” It relates the ratio of adopters to non-adopters, with the penetration depth in a diffusion process over a social network. Each social network model is found to have on average a different degree of diffusion characteristic value: Random ? =148, Small-World ?

Khaled Mahdi; Sadegh Torabi; Maytham Safar

2010-01-01

217

The extensibility of Aplysia nerve and the determination of true axon length.  

PubMed Central

1. Characteristics of Aplysia nerves in response to extension were examined in comparison with nerves of the cat, frog and lobster. 2. Only the Aplysia nerve was easily elongated up to about 5 times its resting or relaxing length without impairing propagation of the action potential along the axon in the nerve. 3. The conduction velocity along the elongated nerve increased linearly in proportion to the nerve length in the range from the relaxing length to about 1.2-1.5 times extension (the first phase). However, upon further extension it stayed constant regardless of the nerve length (the second phase). 4. In the relaxed nerve bundle the course of the axons was zigzagging and the axon membrane had numerous foldings or wrinklings. 5. The true length of the zigzagging axon was measured by analysing the length of intra-axonal diffusion following intracellular injection of radioactive acetylcholine ([3H]ACh) whose diffusion kinetics in the axoplasm have been studied in detail (Koike & Nagata, 1979). The length of the axon coincided with the nerve length at which the first phase shifted to the second phase. 6. Cat and frog nerves shrank after dissecting out from the body. When extended, they showed the first phase from the shortened length to their original length in the body. These nerves lacked the second phase. The lobster nerve did not shrink and lacked both phases. 7. Thus the zigzagging course of the axon is suggested to be responsible for the first phase during which the axon length did not change but took a straight course upon nerve extension. 8. On the other hand, the second phase appears to be caused by actual extension of the axon itself and could be explained by reduction of the wrinklings of the membrane. Images Fig. 1 Fig. 3 Fig. 4 Fig. 9

Koike, H

1987-01-01

218

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.

2012-12-05

219

Lateral diffusion in sphingomyelin bilayers.  

PubMed

Sphingomyelin (SM) is an important lipid of eukaryotic cellular membranes and neuronal tissues. We studied lateral diffusion in macroscopically oriented bilayers of synthetic palmitoylsphingomyelin (PSM) and natural sphingomyelins of egg yolk (eSM), bovine brain (bSM) and bovine milk (mSM) by pulsed field gradient NMR (PFG NMR) in the temperature range 45-60 °C. We found that the mean values of lateral diffusion coefficients (LDCs) of SMs are 1.9-fold lower compared with those of dipalmitoylphosphatidylcholine (DPPC), which is similar in molecular structure. This discrepancy could be explained by the characteristics of intermolecular SM interactions. The LDCs of different SMs differ: egg SM is most similar to PSM; both of them have a 10% higher LDC value compared with the other two natural SMs. Besides, all natural SMs show a complicated form of the spin-echo diffusion decay (DD), which is an indicator of a distribution of LDC values in bilayers. This peculiarity is explained by the broad distributions of hydrocarbon chain lengths of the natural SMs studied here, especially mSM and bSM. We confirmed the relationship between chain length and LDC in the bilayers by computer analysis of a set of (1)H NMR spectra obtained by scanning the value of the pulsed field gradient. There is a correlation between lower LDC values and SM molecules with longer acyl chains. The most probable mechanisms by which long-chain SM molecules decrease their lateral diffusion relative to the average value are protrusion into the other side of the bilayer or lateral separation into areas that diverge with their LDCs. PMID:21031608

Filippov, A V; Rudakova, M A; Munavirov, B V

2010-12-01

220

Limb Length Discrepancy  

MedlinePLUS

... area. This procedure will not cause an immediate correction in length. Instead, the limb length discrepancy will ... this option include the possibility of slight over-correction or under-correction of the limb length discrepancy. ...

221

A nonlinear equation for ionic diffusion in a strong binary electrolyte  

PubMed Central

The problem of the one dimensional electro-diffusion of ions in a strong binary electrolyte is considered. The mathematical description, known as the Poisson-Nerst-Planck (PNP) system, consists of a diffusion equation for each species augmented by transport due to a self consistent electrostatic field determined by the Poisson equation. This description is also relevant to other important problems in physics such as electron and hole diffusion across semi-conductor junctions and the diffusion of ions in plasmas. If concentrations do not vary appreciably over distances of the order of the Debye length, the Poisson equation can be replaced by the condition of local charge neutrality first introduced by Planck. It can then be shown that both species diffuse at the same rate with a common diffusivity that is intermediate between that of the slow and fast species (ambipolar diffusion). Here we derive a more general theory by exploiting the ratio of Debye length to a characteristic length scale as a small asymptotic parameter. It is shown that the concentration of either species may be described by a nonlinear partial differential equation which provides a better approximation than the classical linear equation for ambipolar diffusion but reduces to it in the appropriate limit.

Ghosal, Sandip; Chen, Zhen

2011-01-01

222

Diffusion in correlated random potentials, with applications to DNA  

NASA Astrophysics Data System (ADS)

Many biological processes involve one-dimensional diffusion over a correlated inhomogeneous energy landscape with a correlation length ?c . Typical examples are specific protein target location on DNA, nucleosome repositioning, or DNA translocation through a nanopore, in all cases with ?c ?10 nm . We investigate such transport processes by the mean first passage time (MFPT) formalism, and find diffusion times which exhibit strong sample to sample fluctuations. For a displacement N , the average MFPT is diffusive, while its standard deviation over the ensemble of energy profiles scales as N3/2 with a large prefactor. Fluctuations are thus dominant for displacements smaller than a characteristic Nc ?c : typical values are much less than the mean, and governed by an anomalous diffusion rule. Potential biological consequences of such random walks, composed of rapid scans in the vicinity of favorable energy valleys and occasional jumps to further valleys, is discussed.

Slutsky, Michael; Kardar, Mehran; Mirny, Leonid A.

2004-06-01

223

Diffusion characteristics of collagen film  

Microsoft Academic Search

Collagen films prepared by treating collagen gel solutions with different concentrations of glutaraldehyde were evaluated as a biodegradable and biocompatible drug carrier for cosmetically effective agents in this study. The influences of concentration of glutaraldehyde (0, 0.05, 0.075, 0.1, 0.2, 0.25, and 0.3%, v\\/w) with a fixed concentration (1%, w\\/w) of collagen on the crosslinking rate of collagen gel solutions

Hsiu-O Ho; Cheng-Wen Lin; Ming-Thau Sheu

2001-01-01

224

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

PubMed

Measurement of the kinetics of extraction of copper(II) by 19 different 5-alkyl-2-hydroxybenzaldoximes (alkyl is C7H15 and C9H19) from acidic (hydrogen sulfate buffer) aqueous solution in the range pH 3.4-2.0, into 20% v/v toluene in n-hexane is reported. The lowering of the interfacial tension has been measured in some cases. The solubility of the extractants in water has been measured spectrophotometrically. A modified Taylor-Aris dispersion technique has been used to measure the diffusion coefficients in n-hexane and Orfom SX7 of some of the extractants and of the copper(II) complexes which they form. At low initial bulk concentrations (<10 mol m-3) of the extractants, the rate of extraction is controlled by the rate of diffusion of the extractant from the bulk to the organic-aqueous interface. The diffusion coefficient is related to the steric bulk of the alkyl substituent. At higher initial bulk concentrations (200 mol m-3) of the extractants, when the interface is saturated, the rate of extraction is inversely related to the apparent steric bulk of the alkyl substituent. Copyright 1999 Academic Press. PMID:10191010

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

1999-05-01

225

Diffusion in Dense Inhomogeneous Colloid Suspensions in Narrow Channels  

NASA Astrophysics Data System (ADS)

We report the results of a study of single particle diffusion in dense colloid fluids confined in a ribbon channel geometry that is intermediate between quasi-one-dimensional (q1D) and quasi-two-dimensional (q2D). In all of the systems studied the colloid density distribution transverse to the ribbon channel is stratified with peak amplitudes that depend on the colloid density. Although the virtual walls that confine a stratum are structured with a scale length of the colloid diameter, that structure does not have an apparent influence on the single particle diffusion, which shows the characteristic features of diffusion in a q1D channel with smooth walls. We find that for all channel widths and packing fractions studied the single particle transverse diffusion coefficient in a stratum is smaller than the single particle longitudinal diffusion coefficient in the same stratum, and that the single particle longitudinal diffusion coefficient varies very little from stratum to stratum, being only slightly smaller in the dense strata next to the walls than in central strata. The lack of variation of the longitudinal diffusion coefficient with apparent stratum density is explained by application of the Fischer-Methfessel approximation to the local density in an inhomogeneous liquid. The ratio of the transverse to longitudinal diffusion coefficients varies very slowly with ribbon width, implying a very slow transition from q1D to q2D behavior.

Lin, Binhua; Wonder, Emily; Rice, Stuart A.

2012-02-01

226

Correlating anomalous diffusion with lipid bilayer membrane structure using single molecule tracking and atomic force microscopy  

NASA Astrophysics Data System (ADS)

Anomalous diffusion has been observed abundantly in the plasma membrane of biological cells, but the underlying mechanisms are still unclear. In general, it has not been possible to directly image the obstacles to diffusion in membranes, which are thought to be skeleton bound proteins, protein aggregates, and lipid domains, so the dynamics of diffusing particles is used to deduce the obstacle characteristics. We present a supported lipid bilayer system in which we characterized the anomalous diffusion of lipid molecules using single molecule tracking, while at the same time imaging the obstacles to diffusion with atomic force microscopy. To explain our experimental results, we performed lattice Monte Carlo simulations of tracer diffusion in the presence of the experimentally determined obstacle configurations. We correlate the observed anomalous diffusion with obstacle area fraction, fractal dimension, and correlation length. To accurately measure an anomalous diffusion exponent, we derived an expression to account for the time-averaging inherent to all single molecule tracking experiments. We show that the length of the single molecule trajectories is critical to the determination of the anomalous diffusion exponent. We further discuss our results in the context of confinement models and the generating stochastic process.

Skaug, Michael J.; Faller, Roland; Longo, Marjorie L.

2011-06-01

227

Arc Length Gone Global  

ERIC Educational Resources Information Center

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…

Boudreaux, Gregory M.; Wells, M. Scott

2007-01-01

228

Measuring Thermodynamic Length  

SciTech Connect

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

Crooks, Gavin E

2007-09-07

229

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

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

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

2006-01-01

230

Effective Jump Length of Coupled Continuous Time Random Walk  

NASA Astrophysics Data System (ADS)

The concept effective jump length is proposed. Due to the joint probability density function of jump length and waiting time, it is complicated to distinguish the diffusion types. However, we calculate the probability density function of effective jump length for the coupled continuous time random walk model we proposed previously. The mean square displacements deduced are coincident with the known results. More importantly, we find that the anomalous diffusion induced by the coupled model is equivalent to the competition between long jump length and long waiting time.

Liu, Jian; Bao, Jing-Dong

2013-02-01

231

Diffusion /Osmosis  

NSDL National Science Digital Library

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 ...

Jensen

2007-11-26

232

Planck Length and Cosmology  

NASA Astrophysics Data System (ADS)

We show that an unification of quantum mechanics and general relativity implies that there is a fundamental length in Nature in the sense that no operational procedure would be able to measure distances shorter than the Planck length. Furthermore we give an explicit realization of an old proposal by Anderson and Finkelstein who argued that a fundamental length in nature implies unimodular gravity. Finally, using hand waving arguments we show that a minimal length might be related to the cosmological constant which, if this scenario is realized, is time dependent.

Calmet, Xavier

233

Characteristics of a new type of Mie scattering volume diffuser and its use as a spectral albedo calibration standard for the solar reflective wavelength region  

NASA Astrophysics Data System (ADS)

Emerging instrumental requirements for remotely sensing tropospheric trace species have led to a rethinking by some of the paradigm for Système International d'Unités (SI) traceability of the spectral irradiance and radiance radiometric calibrations to spectral albedo (sr-1) which is not a SI unit. In the solar reflective wavelength region the spectral albedo calibrations are tied often to either the spectral albedo of a solar diffuser or the Moon. This new type of Mie scattering diffuser (MSD) is capable of withstanding high temperatures, and is more Lambertian than SpectralonTM. It has the potential of covering the entire solar reflective wavelength region. Laboratory measurements have shown that the specular reflectance component is negligible, and indicate that internal absorption by multiple scattering is small. This MSD, a true volume diffuser, exhibits a high degree of radiometric stability which suggests that measurements at the National Institute of Standards and Technology (NIST) could provide a spectral albedo standard. Measurements are currently in progress of its radiometric stability under a simulated space environment of high energy ionizing and ultraviolet (UV) solar radiation for its eventual use in space as a solar diffuser.

Heath, Donald F.; Georgiev, Georgi

2011-09-01

234

Holographic diffusers  

NASA Astrophysics Data System (ADS)

Holographic diffusers are prepared using silver halide (Agfa 8E75 and Kodak 649F) and photopolymer (Polaroid DMP 128 and DuPont 600, 705, and 150 series) media. It is possible to control the diffusion angle in three ways: by selection of the properties of the source diffuser, by control of its subtended angle, and by selection of the holographic medium. Several conventional diffusers based on refraction or scattering of light are examined for comparison.

Wadle, Stephen; Wuest, Daniel; Cantalupo, John; Lakes, Roderic S.

1994-01-01

235

Diffusion MRI  

NASA Astrophysics Data System (ADS)

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

Fukuyama, Hidenao

236

Coefficients of Effective Length.  

ERIC Educational Resources Information Center

Under certain conditions, a validity Coefficient of Effective Length (CEL) can produce highly misleading results. A modified coefficent is suggested for use when empirical studies indicate that underlying assumptions have been violated. (Author/BW)

Edwards, Roger H.

1981-01-01

237

Length of Stay  

PubMed Central

Five methodologies for predicting hospital length of stay were developed and compared. Two—a subjective Bayesian forecaster and a regression forecaster—also measured the relative importance of the symptomatic and demographic factors in predicting length of stay. The performance of the methodologies was evaluated with several criteria of effectiveness and one of cost. The results should provide encouragement for those interested in computer applications to utilization review and to scheduling inpatient admissions.

Gustafson, David H.

1968-01-01

238

Editorial: Redefining Length  

SciTech Connect

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

Sprouse, Gene D. [American Physical Society (United States)

2011-07-15

239

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

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

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

240

The dynamics of unsteady detonation with diffusion  

SciTech Connect

Here we consider an unsteady detonation with diffusion included. This introduces an interaction between the reaction length scales and diffusion length scales. Detailed kinetics introduce multiple length scales as shown though the spatial eigenvalue analysis of hydrogen-oxygen system; the smallest length scale is {approx} 10{sup 7} m and the largest {approx} 10{sup -2} m; away from equilibrium, the breadth can be larger. In this paper, we consider a simpler set of model equations, similar to the inviscid reactive compressible fluid equations, but include diffusion (in the form of thermal/energy, momentum, and mass diffusion). We will seek to reveal how the complex dynamics already discovered in one-step systems in the inviscid limit changes with the addition of diffusion.

Aslam, Tariq Dennis [Los Alamos National Laboratory; Romick, Christopher [NOTRE DAME; Powers, Joseph [NOTRE DAME

2010-01-01

241

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

2012-11-22

242

On collisional diffusion in a stochastic magnetic field  

NASA Astrophysics Data System (ADS)

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 ?mfp, the diffusion coefficients of field lines DFL, and the collisional diffusion coefficients, ?? are studied. Based on these numerical data and the heuristic arguments, the empirical formula, Dr=??+v||DFL/(1+Lc/?mfp), for the local diffusion coefficient is proposed, where Lc is the characteristic length of order of the connection length lc=?qR0, q is the safety factor, R0 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.

Abdullaev, S. S.

2013-08-01

243

An investigation on parallel, divergent and convergent acetylene dual jet diffusion flames  

SciTech Connect

Turbulent jet diffusion flames are quite common in industrial applications. Because of the large flow rates involved, usually the fuel gas is discharged through multiple burners and the mutual interaction between the jets determines flame shape, length, and general characteristics. Results are presented and discussed of an experimental investigation on acetylene turbulent dual jet diffusion flames. The study includes parameters of flames in parallel, divergent and convergent configurations. Tests with two parallel jets with addition of helium in the fuel stream were also performed and analyzed. The variation of overall flame length and of other flame physical characteristics, such as width, volume and conditions for lifting, are presented as functions of burner tip Reynolds number, jet distance from each other and inclination angle. The effects of diluent concentration in the fuel gas stream are presented for single and two parallel jets.

Abdalla, V.R.; Carvalho, J.A. Jr.; Ferreira, M.A.

1999-11-01

244

Combustion characteristics of hydrogen–hydrocarbon hybrid fuels  

Microsoft Academic Search

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,

Ahsan R Choudhuri; S. R Gollahalli

2000-01-01

245

Element diffusion in novae  

Microsoft Academic Search

Enhanced abundances of heavy elements are characteristic of all nova ejecta, their source being material dredged up from the progenitor white dwarf's core. The degree of mixing between core and accreted material may be inferred from the observed abundances. The authors consider diffusion during the accretion phase, followed by convection at the onset of the thermonuclear runaway as the mixing

D. Prialnik; A. Kovetz

1997-01-01

246

Variable focal length microlenses  

NASA Astrophysics Data System (ADS)

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.

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

2000-04-01

247

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

SciTech Connect

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.

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

248

Effective medium theory for reaction rates and diffusion coefficients of heterogeneous systems.  

PubMed

A simple effective medium theory is derived for spatially heterogeneous nonlinear reaction-diffusion media. Its validity is tested through comparisons with simulations of front and pulse propagation in systems with spatially varying diffusion coefficients and reaction rates. The theory is able to predict wave speeds if the characteristic front width is much larger than the length scale of the heterogeneities. This condition is violated in media with isolated or weakly connected sites. However, the theory nevertheless provides good results in cases where it correctly predicts the percolation threshold of the medium. PMID:19658977

Alonso, Sergio; Kapral, Raymond; Bär, Markus

2009-06-12

249

Effective Medium Theory for Reaction Rates and Diffusion Coefficients of Heterogeneous Systems  

NASA Astrophysics Data System (ADS)

A simple effective medium theory is derived for spatially heterogeneous nonlinear reaction-diffusion media. Its validity is tested through comparisons with simulations of front and pulse propagation in systems with spatially varying diffusion coefficients and reaction rates. The theory is able to predict wave speeds if the characteristic front width is much larger than the length scale of the heterogeneities. This condition is violated in media with isolated or weakly connected sites. However, the theory nevertheless provides good results in cases where it correctly predicts the percolation threshold of the medium.

Alonso, Sergio; Kapral, Raymond; Bär, Markus

2009-06-01

250

Drift and diffusion in periodic potentials: Upstream and downstream step times are distributed identically  

PubMed Central

This note deals with particles diffusing in one dimension in the presence of a periodic potential and a uniform driving force. We show that (i) the probabilities for the particle to make a step of the length L, where L is the period, in the upstream and downstream directions are independent of the periodic potential, and (ii) the distributions of the step time are independent of the step direction. These two characteristics are used to derive expressions for the effective drift velocity and diffusion coefficient.

Dagdug, Leonardo; Berezhkovskii, Alexander M.

2009-01-01

251

Sampling by Length.  

ERIC Educational Resources Information Center

Discussion of sampling methods used in information science research focuses on Fussler's method for sampling catalog cards and on sampling by length. Highlights include simple random sampling, sampling with probability equal to size without replacement, sampling with replacement, and examples of estimating the number of books on shelves in certain…

Handley, John C.

1991-01-01

252

Reversible variable length codes  

Microsoft Academic Search

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

Y. Takishima; M. Wada; H. Murakami

1995-01-01

253

Sampling by Length.  

ERIC Educational Resources Information Center

|Discussion of sampling methods used in information science research focuses on Fussler's method for sampling catalog cards and on sampling by length. Highlights include simple random sampling, sampling with probability equal to size without replacement, sampling with replacement, and examples of estimating the number of books on shelves in…

Handley, John C.

1991-01-01

254

Slow-release of methanogenic inhibitors derived from encapsulated calcium carbide using paraffin wax and/or rosin: matrix optimization and diffusion characteristics.  

PubMed

Acetylene has been found to significantly inhibit biological activity of methanogens and thus might be applicable for reducing the generation and emission of methane from municipal solid waste landfills. However, acetylene is gaseous and so it is considered physically infeasible to directly apply this gas to waste in landfill conditions. In the present study, a novel acetylene release mechanism was tested, using a matrix of acetylene entrapped in high hydrophobic paraffin wax and/or rosin and calcium carbide capsules with a ratio of 1.0?g?g(-1) matrix and a diameter of 10?mm to facilitate the gradual release of acetylene. A diffusion mechanism model (Q = &b.gamma; × t (0.5)) for the matrix was derived based on the T. Higuchi equation, and the effective diffusion coefficients (D(e)) were acquired by linear fitting. Additionally, it was found that D(e) remained constant when the rosin content was up to more than 20% g?g(-1) matrix. PMID:21172951

Tiantao, Zhao; Youcai, Zhao; Lijie, Zhang; Haoquan, Chen; Feng, Shi; Haiyan, Zhou

2010-12-20

255

Food-chain length and adaptive foraging  

PubMed Central

Food-chain length, the number of feeding links from the basal species to the top predator, is a key characteristic of biological communities. However, the determinants of food-chain length still remain controversial. While classical theory predicts that food-chain length should increase with increasing resource availability, empirical supports of this prediction are limited to those from simple, artificial microcosms. A positive resource availability–chain length relationship has seldom been observed in natural ecosystems. Here, using a theoretical model, we show that those correlations, or no relationships, may be explained by considering the dynamic food-web reconstruction induced by predator's adaptive foraging. More specifically, with foraging adaptation, the food-chain length becomes relatively invariant, or even decreases with increasing resource availability, in contrast to a non-adaptive counterpart where chain length increases with increasing resource availability; and that maximum chain length more sharply decreases with resource availability either when species richness is higher or potential link number is larger. The interactive effects of resource availability, adaptability and community complexity may explain the contradictory effects of resource availability in simple microcosms and larger ecosystems. The model also explains the recently reported positive effect of habitat size on food-chain length as a result of increased species richness and/or decreased connectance owing to interspecific spatial segregation.

Kondoh, Michio; Ninomiya, Kunihiko

2009-01-01

256

Anisotropic diffusion in a finite cylinder, with geochemical applications  

Microsoft Academic Search

Atomic diffusion in minerals may not be well represented by solutions to the diffusion equation for a sphere with a single-valued diffusivity, either because they have platy or elongated habits or because the energetics of diffusion is sensitive to crystallographic direction. In many cases, a cylinder having characteristic radial and axial diffusivities is arguably a better model, but rigorous solutions

E. Bruce Watson; Keith H. Wanser; Kenneth A. Farley

2010-01-01

257

Imaging characteristics of diffuse large cell extra nodal non-Hodgkin's lymphoma involving the palate and maxillary sinus: a case report  

PubMed Central

Non-Hodgkin's lymphomas are a group of highly diverse malignancies and have a strong tendency to affect organs and tissues that do not ordinarily contain lymphoid cells. Primary extra nodal lymphoma of the hard palate is rare. Here, we present a case of diffuse large B cell lymphoma in a 60-year-old male patient that manifested as slightly painful ulcerated growth on the edentulous right maxillary alveolar ridge extending onto the palate, closely resembling carcinoma of the alveolar ridge. Computed tomography images showed the involvement of the maxillary sinus and right nasal cavity, along with destruction of hard palate, superiorly extending into the orbit. This case report highlights the importance of imaging to evaluate the exact extent of such large malignant lesions, which is essential for treatment planning.

Meduri, Venkateswarlu; Paramkusam, Geetha

2012-01-01

258

Critical line length determination  

Microsoft Academic Search

One of the most severe faults for a circuit breaker to interrupt is the short-line fault (SLF). In this paper, digital testing is applied to determine the critical line length, i.e. the short-line fault percentage that stresses the circuit breaker most, for three different circuit breakers. Three arc models have been used for the calculations and three indicators have been

P. H. Schavemaker; L. van der Sluis; A. J. P. de Lange

2000-01-01

259

Variable-focal-length microelectromechanical lens  

Microsoft Academic Search

We discuss the characteristics of a novel microelectromechanical cylindrical focusing mirror having a focal length which is controlled by active and intrinsic stresses in the thin films composing it. The unactuated mechanical state of the mirror is determined by intrinsic stress levels in a SiN structural layer and a piezoelectric PZT actuator layer which are part of a doubly clamped

Mark J. Mescher; Michael L. Reed; Tuviah E. Schlesinger

1998-01-01

260

The back-diffusion effect of air on the discharge characteristics of atmospheric-pressure radio-frequency glow discharges using bare metal electrodes  

Microsoft Academic Search

Radio-frequency (RF), atmospheric-pressure glow discharge (APGD) plasmas using bare metal electrodes have promising prospects in the fields of plasma-aided etching, deposition, surface treatment, disinfection, sterilization, etc. In this paper, the discharge characteristics, including the breakdown voltage and the discharge voltage for sustaining a stable and uniform alpha mode discharge of the RF APGD plasmas are presented. The experiments are conducted

Wen-Ting Sun; Tian-Ran Liang; Hua-Bo Wang; He-Ping Li; Cheng-Yu Bao

2007-01-01

261

Lengthy Relationships: Foot Length, Stride, Leg Length, Height  

NSDL National Science Digital Library

Paleontologists occasionally find ancient tracks and footprints preserved in the rocks. This lesson opens the door to analysing those footprints, and gleaning information about body size and activities of the extinct animals that made the tracks. Students will learn that patterns can reveal much about the past, in light of the present; and that bipedalism has appeared several times. Relationships will be found between foot length and leg length; foot length and height; leg length and height; stride length and leg length; and stride length and speed.

Johnson, Jennifer

262

Puzzle of the Electrostatic Persistence Length  

NASA Astrophysics Data System (ADS)

Electrostatic interactions play an important role in controlling properties of synthetic and biological polyelectrolytes. The change in the ionic environment in such systems can significantly influence their conformational properties. For semiflexible polyelectrolyte chains with ionic groups interacting via the screened Debye-Huckel potential the electrostatic contribution to the chain persistence length scales quadratically with the Debye screening length (OSF model). However, recent computer simulations of flexible polyelectrolyte chains with explicit counterions and salt ions show that in the wide interval of the solution ionic strengths the electrostatic contribution to chain persistence length is proportional to the Debye screening length, rD. To understand the crossover between flexible and semiflexible chain behavior and elucidate the effect of explicit ions on chain conformations we performed molecular dynamics of polyelectrolyte chains with degree of polymerization N=300 and different values of the chain bending rigidity varying between K=1 and K=160. Our simulations have shown that the bond-bond correlation function describing chain's orientational memory can be approximated by a sum of two exponential functions manifesting the existence of the two characteristic length scales. One describes the chain's bending rigidity at the distances along the polymer backbone shorter than rD while another controls the long-length scale chain's orientational correlations. The long-length scale bending rigidity is proportional to rD for chains with bending rigidity smaller than a crossover bending rigidity K*.

Dobrynin, A. V.; Carrillo, J.-M. Y.

2013-03-01

263

Theoretical and experimental study of the influence of nitrogen admixture on characteristics of dc diffuse glow discharge in rare gases at intermediate pressures  

NASA Astrophysics Data System (ADS)

An effect of nitrogen admixture on the electric field in positive column of diffuse glow discharge in various rare gases at intermediate pressures is studied both experimentally and theoretically. The discharge is maintained in a cylindrical glass tube. Earlier it was observed and reproduced in calculations that addition of N2 (1%) to Ar at pressure 40 Torr led to noticeable decrease in the electric field strength at a fixed discharge current. In the present work there are results for pure Ne and Ne + 1%N2 gas mixtures at pressure 40 Torr. It is found that the addition of N2 to Ne leads to the increase in the electric field strength; the observed effect is reproduced in calculations. The explanation of differences in the impact of N2 addition on the electric field strength in Ar and Ne discharges is given. On the basis of the performed analysis it is predicted that the addition of N2 to He leads to the increase in the electric field in the discharge and the addition of N2 to Xe leads to the decrease in the electric field. For the case of He, the prediction is experimentally confirmed in this work, while for the case of Xe, it is corroborated by literature data.

Dyatko, N. A.; Ionikh, Y. Z.; Meshchanov, A. V.; Napartovich, A. P.

2013-09-01

264

Tracer diffusion in silica inverse opals.  

PubMed

We employed fluorescence correlation spectroscopy (FCS) to study the diffusion of small fluorescence tracers in liquid filled silica inverse opals. The inverse opals consisted of a nanoporous silica scaffold spanning a hexagonal crystal of spherical voids of 360 nm diameter connected by circular pores of 70 nm diameter. The diffusion of Alexa Fluor 488 in water and of perylene-3,4,9,10-tetracarboxylic diimide (PDI) in toluene was studied. Three diffusion modes could be distinguished: (1) Free diffusion limited by the geometric constraints given by the inverse opal, where, as compared to the free solution, this diffusion is slowed down by a factor of 3-4, (2) slow diffusion inside the nanoporous matrix of the silica scaffold, and (3) diffusion limited by adsorption. On the length scale of the focus of a confocal microscope of roughly 400 nm diffusion was non-Fickian in all cases. PMID:20232884

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

2010-06-15

265

Wound complications and stitch length  

Microsoft Academic Search

The effect of suturing with a very short stitch on the development of wound complications in midline incisions was investigated. Three hundred sixty-eight patients were analysed. The suture length to wound length ratio and mean stitch length were calculated. Wound infection occurred in 4% (four of 103) of patients sutured with a mean stitch length of less than 4 cm, in

D. Millbourn; L. A. Israelsson

2004-01-01

266

Identifying anomalous diffusion and melting in dusty plasmas  

SciTech Connect

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.

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

2010-09-15

267

Stain length passive dosimeters  

SciTech Connect

Passive dosimeters with instant readout capability have been devised by combining the principles of a gas indicator tube with membrane control of mass transfer. The membrane controls the diffusion of the gas or vapour to the reagent-impregnated support where it reacts to produce a stain. Results with H/sub 2/S and benzene monitors demonstrate that time-weighted average concentration of ambient gas or vapour can be measured accurately and precisely by following the movement of the coloured stain in the specially prepared and calibrated indicator tube. The 95% confidence interval of such measurements at the ThV is +/-20% for H/sub 2/S and +/-15% for benzene, well within NI0SH limits of acceptability.

Sefton, M.V.

1982-11-01

268

Stain length passive dosimeters  

SciTech Connect

Passive dosimeters with instant readout capability have been devised by combining the principles of a gas indicator tube with membrane control of mass transfer. The membrane controls the diffusion of the gas or vapor to the reagent impregnanted support where it reacts to produce a stain. Results with H/sub 2/S and benzene monitors demonstrated that time weighted average concentration of ambient gas or vapor can be measured accurately and precisely by following the movement of the colored stain in the specially prepared and calibrated indicator tube. The 95% confidence interval of such measurements at the TLV (80 ppm-hrs) is +/- 20% for H/sub 2/S and +/- 15% for benzene, well within NIOSH limits of acceptability.

Sefton, M.V.; Kostas, A.V.; Lombardi, C.

1982-11-01

269

Role of long jumps in surface diffusion  

Microsoft Academic Search

We analyze a probability of atomic jumps for more than one lattice spacing in activated surface diffusion. First, we studied a role of coupling between the x and y degrees of freedom for the diffusion in a two-dimensional substrate potential. Simulation results show that in the underdamped limit the average jump length scales with the damping coefficient eta as ~eta-sigmalambda

O. M. Braun; R. Ferrando

2002-01-01

270

Sandstones of unexpectedly high diffusibility.  

PubMed

Measurements have been made of diffusion coefficients (D(i)=-mass flux/concentration gradient) using a double reservoir, steady-state method with two tracers, CaBr(2) and amino-G-acid, on intact samples of Triassic red-bed sandstone from northwest England. Diffusibility (D'=D(i)/diffusion coefficient in water) averages 0.124, ranging between 0.075 and 0.215 (porosity 0.1 to 0.24), very similar for the two tracers. Implied tortuosities (actual path length/straight line length) average 1.21 (range 1.06 to 1.47), with constrictivities close to 1. In comparison with limited red-bed sandstone data from elsewhere, these D' values are up to 4 times greater, and tortuosity correspondingly lower. Re-interpretation of formation factor data from previous studies on shallow sandstone samples also from northwest England confirms that diffusibility is significantly higher in these sandstones than others from similar palaeoenvironment/stratigraphic units. The lower tortuosities appear to result from the relatively high permeability, open fabric of the rock, properties likely to be present in shallow sandstone systems used for water supply. It is concluded that diffusion rates may, in some shallow freshwater-containing continental sandstone systems, be significantly greater than is implied by estimates of sandstone diffusibility current in the literature. PMID:21146250

Bashar, Khairul; Tellam, John H

2010-11-23

271

Diffuse unilateral subacute neuroretinitis.  

PubMed

Diffuse unilateral subacute neuroretinitis (DUSN) is a usually unilateral inflammatory disease characterized by an insidious, usually severe loss of peripheral and central vision. Clinical characteristics are manifested in early and late stages. Parasites of different sizes and several species of nematodes have been reported as the etiology of DUSN without conclusive evidence about the specific agent. Because serologic testing has been variable, the definitive diagnosis is made when the clinical characteristics of DUSN are found in conjunction with an intraocular worm. Laser photocoagulation, pars plana vitrectomy, thiabendazole, and albendazole have been used to treat DUSN with variable success. PMID:23244243

Arevalo, J Fernando; Arevalo, Fernando A; Garcia, Reinaldo A; de Amorim Garcia Filho, Carlos Alexandre; de Amorim Garcia, Carlos Alexandre

2012-12-18

272

Approximate sample sizes required to estimate length distributions  

USGS Publications Warehouse

The sample sizes required to estimate fish length were determined by bootstrapping from reference length distributions. Depending on population characteristics and species-specific maximum lengths, 1-cm length-frequency histograms required 375-1,200 fish to estimate within 10% with 80% confidence, 2.5-cm histograms required 150-425 fish, proportional stock density required 75-140 fish, and mean length required 75-160 fish. In general, smaller species, smaller populations, populations with higher mortality, and simpler length statistics required fewer samples. Indices that require low sample sizes may be suitable for monitoring population status, and when large changes in length are evident, additional sampling effort may be allocated to more precisely define length status with more informative estimators. ?? Copyright by the American Fisheries Society 2007.

Miranda, L. E.

2007-01-01

273

The role of diffusion in broadband infrared absorption in chalcogen-doped silicon  

NASA Astrophysics Data System (ADS)

Sulfur doping of silicon beyond the solubility limit by femtosecond laser irradiation leads to near-unity broadband absorption of visible and infrared light and the realization of silicon-based infrared photodetectors. The nature of the infrared absorption is not yet well understood. Here we present a study on the reduction of infrared absorptance after various anneals of different temperatures and durations for three chalcogens (sulfur, selenium, and tellurium) dissolved into silicon by femtosecond laser irradiation. For sulfur doping, we irradiate silicon in SF6 gas; for selenium and tellurium, we evaporate a film onto the silicon and irradiate in N2 gas; lastly, as a control, we irradiated untreated silicon in N2 gas. Our analysis shows that the deactivation of infrared absorption after thermal annealing is likely caused by dopant diffusion. We observe that a characteristic diffusion length—common to all three dopants—leads to the reduction of infrared absorption. Using diffusion theory, we suggest a model in which grain size of the resolidified surface layer can account for this characteristic diffusion length, indicating that deactivation of infrared absorptance may be caused by precipitation of the dopant at the grain boundaries.

Tull, Brian R.; Winkler, Mark T.; Mazur, Eric

2009-08-01

274

Holographic diffusers  

NASA Astrophysics Data System (ADS)

Diffusers are playing an increasingly important role in optics as a means to either improve uniformity of light applied for illumination of an object, or to improve visibility of an image created by an optical system from a wider range of angles. Probably the most popular applications of the first kind are milky light bulbs commonly used as light sources in our houses or flat panel displays with backlight illumination used in portable computers. The best known application of the second kind is an ordinary wall used as a screen for slide or film projector. Other examples of this type are diffusers in the view finding systems of some photographic and film cameras and in a variety of rear image projection systems (like microfiche readers or rear TV projection systems, for example). It is obvious, in this context, that demand for diffusers will increase with expansion of such systems.

Pawluczyk, Romuald

1994-01-01

275

Edge effects in crystal growth under intermediate diffusive-kinetic control  

NASA Astrophysics Data System (ADS)

Crystal growth on a semiinfinite surface is considered. The remaining semiinfinite part of the plane is covered with a mask on which no crystal growth can occur. The mass-transfer coefficient, which measures the rate at which the surface reaction proceeds, is considered to be finite. Together with the diffusion coefficient D this parameter defines a characteristic time tau and length lambda. A solution valid for large tau is derived. It is shown that crystal-growth conditions change markedly within a neighborhood of the mask edge whose length is of the order of lambda. Outside this region crystal growth is almost fully diffusion-controlled. Within the region surface control exerts its influence, but the grown layer is much thicker there than elsewhere. As long as the grown layer is much thinner than lambda, growth at the mask edge is kinetically controlled.

Kuiken, H. K.

1985-09-01

276

Electrical Characteristics of High Mobility Si/Si0.5Ge0.5/SOI Quantum-Well p-MOSFETs with a Gate Length of 100 nm and an Equivalent Oxide Thickness of 1.1 nm  

NASA Astrophysics Data System (ADS)

Short-channel high-mobility Si/Si0.5Ge0.5/silicon-on-insulator (SOI) quantum-well p-type metal-oxide-semiconductor field effect transistors (p-MOSFETs) were fabricated and electrically characterized. The transistors show good transfer and output characteristics with Ion/Ioff ratio up to 105 and sub-threshold slope down to 100mV/dec. HfO2/TiN gate stack is employed and the equivalent oxide thickness of 1.1 nm is achieved. The effective hole mobility of the transistors reaches 200cm2/V·s, which is 2.12 times the Si universal hole mobility.

Mu, Zhi-Qiang; Yu, Wen-Jie; Zhang, Bo; Xue, Zhong-Ying; Chen, Ming

2013-10-01

277

Demonstrating Diffusion  

ERIC Educational Resources Information Center

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

Foy, Barry G.

1977-01-01

278

Coaxial atomizer liquid intact lengths  

Microsoft Academic Search

Average intact lengths of round liquid jets generated by airblast coaxial atomizer were measured from over 1500 photographs. The intact lengths were studied over a jet Reynolds number range of 18,000 and Weber number range of 260. Results are presented for two different nozzle geometries. The intact lengths were found to be strongly dependent on Re and We numbers. An

Hasan Eroglu; Norman Chigier; Zoltan Farago

1991-01-01

279

Hydrogen diffusion on silicon surfaces  

NASA Astrophysics Data System (ADS)

Diffusion of atomic hydrogen on silicon serves as a model system for the investigation of thermally activated diffusion processes of covalently bound adsorbates on semiconductor surfaces. Over the past two decades, a detailed understanding of the hopping mechanisms for H/Si(0 0 1) and H/Si(1 1 1) has been obtained using a variety of experimental and theoretical methods. Hydrogen diffusion on silicon is in general characterized by energy barriers that are substantially larger than for adsorbate diffusion on metal surfaces, by the occurrence of different pathways on one surface, as well as by a strong participation of the underlying lattice in the hopping process.In the case of the flat Si(0 0 1) surface, three diffusion pathways were identified: site exchange within one Si dimer, hopping along dimer rows, and hopping across dimer rows, with barriers of 1.4, 1.7 and 2.4 eV, respectively. These barriers correlate with the distances of the involved adsorption sites of 2.4, 3.8 and 5.2 Å. While hydrogen diffusion on Si(0 0 1) is strongly anisotropic at surface temperatures below 700 K, the measurement of high hopping rates by means of a combination of pulsed laser heating and scanning tunneling microscopy reveals similar jump frequencies around 108 s-1 at 1400 K. Diffusion across steps is found to occur with similar speed as diffusion along dimer rows.Hydrogen diffusion on Si(1 1 1) 7 × 7 involves 4.4-Å-long jumps between restatom and adatom sites, accompanied by strong distortions of the adatom backbonds. Crossing the unit-cell boundaries via a 6.7-Å-long migration pathway between two adatoms is the rate limiting process for diffusion on macroscopic length scales, which has an activation energy of 1.5 eV.

Dürr, M.; Höfer, U.

2013-02-01

280

Finite element simulation of diffusion into polycrystalline materials  

Microsoft Academic Search

Diffusion in polycrystalline materials is investigated by means of numerical finite element simulations for constant source conditions. The grain boundaries are assumed to provide fast diffusion paths. Main emphasis is put on situations that typically occur for nanocrystals, viz. on situations in which (i) the diffusion length is significant compared with grain size, (ii) the influence of boundaries that are

D. Gryaznov; J. Fleig; J. Maier

2008-01-01

281

The long and short of food-chain length  

Microsoft Academic Search

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

David M. Post

2002-01-01

282

Diffusion in potato during far infrared radiation drying  

Microsoft Academic Search

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

T. M. Afzal; T. Abe

1998-01-01

283

Conditional Length of Stay.  

PubMed Central

OBJECTIVE: To develop and test a new outcome measure, Conditional Length of Stay (CLOS), to assess hospital performance when deaths are rare and complication data are not available. DATA SOURCES: The 1991 and 1992 MedisGroups National Comparative Data Base. STUDY DESIGN: We use engineering reliability theory traditionally applied to estimate mechanical failure rates to construct a CLOS measure. Specifically, we use the Hollander-Proschan statistic to test if LOS distributions display an "extended" pattern of decreasing hazards after a transition point, suggesting that "the longer a patient has stayed in the hospital, the longer a patient will likely stay in the hospital" versus an alternative possibility that "the longer a patient has stayed in the hospital, the faster a patient will likely be discharged from the hospital." DATA COLLECTION/EXTRACTION METHODS: Abstracted records from 7,777 pediatric pneumonia cases and 3,413 pediatric appendectomy cases were available for analysis. PRINCIPAL FINDINGS: For both conditions, the Hollander-Proschan statistic strongly displays an "extended" pattern of LOS by day 3 (p<.0001) associated with declining rates of discharge. This extended pattern coincides with increasing patient complication rates. Worse admission severity and chronic disease contribute to lower rates of discharge after day 3. CONCLUSIONS: Patient stays tend to become prolonged after complications. By studying CLOS, one can determine when the rate of hospital discharge begins to diminish--without the need to directly observe complications. Policymakers looking for an objective outcome measure may find that CLOS aids in the analysis of a hospital's management of complicated patients without requiring complication data, thereby facilitating analyses concerning the management of patients whose care has become complicated.

Silber, J H; Rosenbaum, P R; Koziol, L F; Sutaria, N; Marsh, R R; Even-Shoshan, O

1999-01-01

284

Development of a General Descriptive Model for Diffusion Adsorption Reactive Systems . Entwicklung Eines Modells Zur Allgemeinen Beschreibung von Diffusions-Adsorptions-Reaktions-Systemen.  

National Technical Information Service (NTIS)

The characteristics of diffusion, adsorption, and reaction type chemical processes are presented. Two experimental methods for determining the diffusion coefficients are described. A numerical analysis of diffusion controlled adsorption processes is expla...

R. Ott

1971-01-01

285

Axial Length of Eyes with Rhegmatogenous Retinal Detachment  

Microsoft Academic Search

We conducted a prospective study of 226 eyes with nontraumatic rhegmatogenous retinal detachment; we examined patient characteristics as well as changes in axial length and corneal curvature induced by scleral buckling surgery. Eyes with a round hole in lattice degeneration were characterized by axial length that was longer than that of eyes with retinal tears with and without lattice degeneration.

Hidenobu Tanihara; Akira Negi; Shinichiro Kawano; Hitoshi Ishigouoka; Yoshiki Ueda; Satomi Yoshida-Suzuki; Hiroyuki Amano; Emiko Satou; Yoshihito Honda

1993-01-01

286

700 Å Gate length buried channel Silicon MOSFET's  

Microsoft Academic Search

Buried channel silicon MOSFETs with gate lengths as small as 700 Å have been fabricated using high-resolution electron-beam lithography, multilayer resists, reactive-ion etching, and low temperature processing. In this paper we describe the variations of I-V characteristic, transconductance, pinch-off voltage, and output resistance as a function of gate length.

R. G. Swartz; R. E. Howard; L. D. Jackel; P. Grabbe; R. W. Epworth; D. M. Tennant; V. D. Archer

1982-01-01

287

The Improvement of Length Scaling in the Hyperdynamics Method  

Microsoft Academic Search

Many important physical phenomena, such as film growth, bulk diffusion, radiation damage annealing, dislocation climb and catalysis, require both long time scale and large length scale molecular dynamics, where conventional molecular dynamics methods are not applicable due to the computational costs. The hyperdynamics method has enabled us to perform molecular dynamics for a longer time scale. However, this method is

Soo Young Kim; Arthur Voter

2007-01-01

288

Influence of axial length on IOL constants.  

PubMed

In IOL formulas, the lens itself is represented by specific constants. Usually, these are given by the manufacturers as averages that need customization to allow for individual measurement setups. Apart from the instrumentation, patient characteristics such as axial length distribution may influence IOL constants, as demonstrated in this study. The effect of axial length on different IOL constants was studied on model calculations in theoretical ametropic eyes derived from the standard Gullstrand eye as well as in clinical results obtained for different surgical centers within the ULIB project in optical biometry. The model calculations showed definite dependence of IOL constants of different formulas on axial length, which was strongest for the SRK II A-constant. Clinical results are in good qualitative and quantitative agreement with SRK/T A-constants varying within 0.4 D for axial length averages of 23.2 to 24.2 mm. Even if the same instrumentation is used, different IOL constants may be necessary due to different axial length means in the respective patient populations. Thus, for best refractive results, constant individualization should be done at the surgeon level. Published constants like ULIB constants are nevertheless a good starting point. PMID:23431726

Haigis, Wolfgang

2012-12-01

289

Chromosome-length polymorphism in fungi.  

PubMed Central

The examination of fungal chromosomes by pulsed-field gel electrophoresis has revealed that length polymorphism is widespread in both sexual and asexual species. This review summarizes characteristics of fungal chromosome-length polymorphism and possible mitotic and meiotic mechanisms of chromosome length change. Most fungal chromosome-length polymorphisms are currently uncharacterized with respect to content and origin. However, it is clear that long tandem repeats, such as tracts of rRNA genes, are frequently variable in length and that other chromosomal rearrangements are suppressed during normal mitotic growth. Dispensable chromosomes and dispensable chromosome regions, which have been well documented for some fungi, also contribute to the variability of the fungal karyotype. For sexual species, meiotic recombination increases the overall karyotypic variability in a population while suppressing genetic translocations. The range of karyotypes observed in fungi indicates that many karyotypic changes may be genetically neutral, at least under some conditions. In addition, new linkage combinations of genes may also be advantageous in allowing adaptation of fungi to new environments.

Zolan, M E

1995-01-01

290

Steric effects on diffusion into bituminous coals  

SciTech Connect

The reactions of maleic anhydride, cis-maleate esters, and acetylenedicarboxylate esters with Pittsburgh No. 8 or Illinois No. 6 coal using o-xylene or o-dichlorobenzene solvent are diffusion controlled. Diffusion is Fickian in all cases. The measured activation energies are between 5.4 and 7.6 kcal/mol. Diffusion rates decrease slowly with increasing alkyl chain length and sharply with branching. Diffusion rates are slightly faster with o-xylene than when o-dichlorobenzene is used. 40 refs., 5 figs., 4 tabs.

John W. Larsen; Doyoung Lee [Pennsylvania State University, University Park, PA (United States). Energy Institute

2006-02-01

291

Black-hole entropy and minimal diffusion  

NASA Astrophysics Data System (ADS)

The density of states reproducing the Bekenstein-Hawking entropy-area scaling can be modeled via a nonlocal field theory. We define a diffusion process based on the kinematics of this theory and find a spectral dimension whose flow exhibits surprising properties. While it asymptotes four from above in the infrared, in the ultraviolet the spectral dimension diverges at a finite (Planckian) value of the diffusion length, signaling a breakdown of the notion of diffusion on a continuum spacetime below that scale. We comment on the implications of this minimal diffusion scale for the entropy bound in a holographic and field-theoretic context.

Arzano, Michele; Calcagni, Gianluca

2013-10-01

292

Diffusion bonding  

DOEpatents

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

Anderson, Robert C. (Oak Ridge, TN)

1976-06-22

293

Reconstruction of brain neuronal pathways in brain from the diffusion tensor MRI data  

NASA Astrophysics Data System (ADS)

MRI based fiber tracking is a diagnostic method based on the diffusion tensor MRI data, which allows to find pathways of neuronal bundles in brain in vivo. In this work we propose a method of neuronal pathways reconstruction using A-star algorithm, with the possibility to assess its the effectiveness. One of the criteria is the probabilistic search parameter G, defined by a set of diffusion coefficients in a given volume element. The parameter G obtained trajectory correlated to its length has the meaning of entropy and allows to assess reliability of the found path. The proposed method was tested on simulated data with the characteristic behavior of trajectories of the complex variations, different cases of intersection of the beams passing through the intersection without a common voxels, and obtained characteristics of the corresponding probability.

Nasretdinov, A. R.; Il'yasov, K. A.; Nedopekin, O. V.

2012-11-01

294

Effective medium theory of a diffusion-weighted signal.  

PubMed

Living tissues and other heterogeneous media generally consist of structural units with different diffusion coefficients and NMR properties. These blocks, such as cells or clusters of cells, can be much smaller than the imaging voxel, and are often comparable with the diffusion length. We have developed a general approach to quantify the medium heterogeneity when it is much finer than the sample size or the imaging resolution. The approach is based on the treatment of the medium statistically in terms of the correlation functions of the local parameters. The diffusion-weighted signal is explicity found for the case in which the local diffusivity varies in space, in the lowest order in the diffusivity variance. We demonstrate how the correlation length and the variance of the local diffusivity contribute to the time-dependent diffusion coefficient and the time-dependent kurtosis. Our results are corroborated by Monte Carlo simulations of diffusion in a two-dimensional heterogeneous medium. PMID:20886563

Novikov, Dmitry S; Kiselev, Valerij G

2010-08-01

295

Persistence length in polyelectrolyte systems  

NASA Astrophysics Data System (ADS)

Conformation of flexible polyelectrolytes in solution is considered theoretically. The first point is that these polymers cannot be characterized by one persistence length. The persistence length is scale-dependent (starting from ''bare'' persistence length at smallest length scales and up to the Odijk value at scales larger than the Debye radius). Another point is that the chains in real experimental situations (and in simulations) cannot be considered as infinite; also excluded volume interactions (originating from short-scale part of Coulomb repulsion potential) can neither be neglected. These two effects leads to strong deviations from Odijk predictions causing a decrease of the apparent exponent for the dependence of persistence length on ionic strength. We also demonstrate that the apparent exponent obtained with Khokhlov-Khachaturian (1982) and Li-Witten (1995) approaches is about or below 1 for realistic chain lengths.

Semenov, Alexander; Nyrkova, Irina

1998-03-01

296

Unified drift-diffusion theory for transverse spin currents in spin valves, domain walls, and other textured magnets.  

PubMed

Spins transverse to the magnetization of a ferromagnet only survive over a short distance. We develop a drift-diffusion approach that captures the main features of transverse spin effects in systems with arbitrary spin textures (e.g., vortices and domain walls) and generalizes the Valet-Fert theory. In addition to the standard characteristic lengths (mean free path for majority and minority electrons, and spin diffusion length), the theory introduces two length scales, the transverse spin coherence length ?(?) and the (Larmor) spin precession length ?(L). We show how ?(L) and ?(?) can be extracted from ab initio calculations or measured with giant magnetoresistance experiments. In long (adiabatic) domain walls, we provide an analytic formula that expresses the so-called "nonadiabatic" (or fieldlike) torque in terms of these length scales. However, this nonadiabatic torque is no longer a simple material parameter but depends on the actual spin texture: in thin (<10??nm) domain walls, we observe very significant deviations from the adiabatic limit. PMID:23005670

Petitjean, Cyril; Luc, David; Waintal, Xavier

2012-09-13

297

Comments on Electrostatic Persistence Length  

NASA Astrophysics Data System (ADS)

I have shown that the quadratic dependence of the electrostatic persistence length on the Debye screening length obtained in the classical Odijk-Skolnick-Fixman (OSF) theory is a result of incorrect assumption made about the energetic penalty for chain deformation. By including chain elasticity the linear dependence of the electrostatic persistence length on the Debye screening length is obtained. This result is derived by applying simple scaling analysis of the angle fluctuations and Gaussian variational principle to the system of strongly and weakly charged polymer chains.

Dobrynin, Andrey

2005-03-01

298

Length control of He atmospheric plasma jet plumes: Effects of discharge parameters and ambient air  

SciTech Connect

The effects of various discharge parameters and ambient gas on the length of He atmospheric plasma jet plumes expanding into the open air are studied. It is found that the voltage and width of the discharge-sustaining pulses exert significantly stronger effects on the plume length than the pulse frequency, gas flow rate, and nozzle diameter. This result is explained through detailed analysis of the I-V characteristics of the primary and secondary discharges which reveals the major role of the integrated total charges of the primary discharge in the plasma dynamics. The length of the jet plume can be significantly increased by guiding the propagating plume into a glass tube attached to the nozzle. This increase is attributed to elimination of the diffusion of surrounding air into the plasma plume, an absence which facilitates the propagation of the ionization front. These results are important for establishing a good level of understanding of the expansion dynamics and for enabling a high degree of control of atmospheric pressure plasmas in biomedical, materials synthesis and processing, environmental and other existing and emerging industrial applications.

Xiong, Q.; Xiong, Z.; Xian, Y.; Zhou, F.; Zou, C.; Hu, J.; Gong, W.; Jiang, Z. [College of Electrical and Electronic Engineering, HuaZhong University of Science and Technology, WuHan, Hubei 430074 (China); Lu, X.; Ostrikov, K. [Plasma Nanoscience Centre Australia (PNCA), CSIRO Materials Science and Engineering, P. O. Box 218, Lindfield, New South Wales 2070 (Australia)

2009-04-15

299

Universality of modulation length and time exponents.  

PubMed

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 K(R) in the variable modulation length "phase" is related to that in the fixed modulation length "phase" q via |K(R)-q|[proportionality]|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. PMID:23214554

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

2012-10-18

300

Revisiting surface diffusion in random deposition  

NASA Astrophysics Data System (ADS)

An investigation of the effect of surface diffusion in random deposition model is made by analytical methods and reasoning. For any given site, the extent to which a particle can diffuse is decided by the morphology in the immediate neighbourhood of the site. An analytical expression is derived to calculate the probability of a particle at any chosen site to diffuse to a given length, from first principles. This method may become particularly important in cases where obtaining the continuum limit and solving the corresponding differential equation may not be feasible. Numerical simulation of surface diffusion in random deposition model with varying extents of diffusion are performed and their results are interpreted in the light of the analytical calculations. Systems with surface diffusion show an initial random deposition-like growth upto monolayer deposition, then a deviation due to correlation effects and eventual saturation. An explanation for this behaviour is discussed and the point of departure from the linear form is estimated analytically.

Mal, Baisakhi; Ray, Subhankar; Shamanna, J.

2011-08-01

301

Quantum diffusion  

SciTech Connect

We consider a simple quantum system subjected to a classical random force. Under certain conditions it is shown that the noise-averaged Wigner function of the system follows an integro-differential stochastic Liouville equation. In the simple case of polynomial noise-couplings this equation reduces to a generalized Fokker-Planck form. With nonlinear noise injection new ``quantum diffusion`` terms rise that have no counterpart in the classical case. Two special examples that are not of a Fokker-Planck form are discussed: the first with a localized noise source and the other with a spatially modulated noise source.

Habib, S.

1994-10-01

302

DIFFUSION PUMP  

DOEpatents

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

Levenson, L.

1963-09-01

303

Unconventional diffusion of light in strongly localized open absorbing media  

NASA Astrophysics Data System (ADS)

Very recent experiments have discovered that localized light in strongly absorbing media displays intriguing diffusive phenomena. Here we develop a first-principles theory of light propagation in open media with arbitrary absorption strength and sample length. We show analytically that waves in localized open absorbing media exhibit highly unconventional diffusion. Specifically, wave energy transport follows the diffusion equation with the diffusion coefficient exhibiting spatial resolution. Most strikingly, despite that the system is controlled by two parameters—the ratio of the localization (absorption) length to the sample length—the spatially resolved diffusion coefficient displays novel single parameter scaling: It depends on the position in the sample via the returning probability. Our analytic predictions for this diffusion coefficient are confirmed by numerical simulations. In the strong absorption limit they agree well with the experimental results.

Zhao, Li-Yi; Tian, Chu-Shun; Zhang, Zhao-Qing; Zhang, Xiang-Dong

2013-10-01

304

Sub-100 nm channel length graphene transistors.  

PubMed

Here we report high-performance sub-100 nm channel length graphene 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/?m, 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 frequency (f(T)) reaching 700-1400 GHz. This study demonstrates the exciting potential of graphene based electronics in terahertz electronics. PMID:20815334

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

2010-10-13

305

Predicting psychiatric length of stay  

Microsoft Academic Search

This study sought to determine to what extent a multivariate model could predict psychiatric inpatient length of stay. Data were collected from psychiatric service discharges at the Jewish Hospital of Cincinnati during 10 months in 1992 and 1993. Descriptive and multivariate analysis were completed using twelve variables to predict length of stay. The results of this investigation indicated a statistically

Holly S. Bezold; Martin MacDowell; Robert Kunkel

1996-01-01

306

Distribution of bubble lengths in DNA.  

PubMed

The distribution of bubble lengths in double-stranded DNA is presented for segments of varying guanine-cytosine (GC) content, obtained with Monte Carlo simulations using the Peyrard-Bishop-Dauxois model at 310 K. An analytical description of the obtained distribution in the whole regime investigated, i.e., up to bubble widths of the order of tens of nanometers, is available. We find that the decay lengths and characteristic exponents of this distribution show two distinct regimes as a function of GC content. The observed distribution is attributed to the anharmonic interactions within base pairs. The results are discussed in the framework of the Poland-Scheraga and the Peyrard-Bishop (with linear instead of nonlinear stacking interaction) models. PMID:17243750

Ares, S; Kalosakas, G

2007-01-23

307

Dispersion length scales within the urban canopy  

NASA Astrophysics Data System (ADS)

We discuss the results of lab experiments on three model urban canopies with small, medium and large building aspect ratios to examine the physics of dispersion within the urban canopy from a near-ground continuous point source of passive scalar. The model urban canopies had aspect ratios of building height to width (H/w) = 0.25, 1, 3. Measurements were taken of the turbulent velocity and scalar fields. Plume spreads, concentrations and distance from the source were non-dimensionalized using urban canopy length, time and velocity scales based on the geometry of the buildings. The scaling collapses the data for all three aspect ratios. A model to describe the results is developed. The model is based on a simple Gaussian formulation where the diffusion coefficients are determined by the theories of Taylor (1921) in the horizontal plane, and Hunt and Weber (1979) to account for the vertically inhomogeneous turbulence.

Huq, Pablo; Franzese, Pasquale

2011-11-01

308

Cosmic Ray Diffusion Tensor Throughout the Heliosphere  

Microsoft Academic Search

We calculate the cosmic ray diffusion tensor based on a recently developed model of magnetohydrodynamic (MHD) turbulence in the expanding solar wind [Breech et al., 2008.]. Parameters of this MHD model are tuned by using published observations from Helios, Voyager 2, and Ulysses. We present solutions of two turbulence parameter sets and derive the characteristics of the cosmic ray diffusion

C. Pei; J. W. Bieber; B. Breech; R. A. Burger; J. Clem; W. H. Matthaeus

2008-01-01

309

Positron diffusion in solid and liquid Ga and Bi  

SciTech Connect

The diffusion length of positrons in Ga and Bi was measured using a positron beam. For Ga, there is a drop from 1200(100) to 60(5) A upon melting; this is interpreted in terms of creation of centers that trap the positron. As the temperature of the liquid is increased, the diffusion length increases, suggesting that the size of the traps changes. For Bi, the diffusion length decreases from 500(30) to 190(10) A upon melting, and increases slightly as the temperature is increased. This drop is interpreted as increased positron-ion scattering, and not positron trapping as in Ga.

Gramsch, E.; Lynn, K.G.; Throwe, J.; Kanazawa, I. (Brookhaven National Laboratory, Upton, New York (USA))

1991-09-02

310

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

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.

Vold, E.L.

1997-03-01

311

Atmospheric Diffusion and Air Pollution: Abstracts.  

National Technical Information Service (NTIS)

The abstracts cover a variety of areas in pollution. Included are diffusion of these pollutants, sampling, tall emission sources, the factor of wind direction, and characteristics of the change in pH in atmospheric precipitation in urban areas.

M. E. Berlyand

1971-01-01

312

Diffusion of 40Ar in muscovite  

Microsoft Academic Search

Hydrothermal treatment of closely sized muscovite aggregates in a piston-cylinder apparatus induced 40Ar? loss that is revealed in 40Ar\\/39Ar step heating spectra. Age spectra and Arrhenius data, however, differ from that expected from a single diffusion length scale. A numerical model of episodic loss assuming the presence of multiple diffusion domains yields excellent fits between synthetic and actual degassing spectra.

T. Mark Harrison; Julien Célérier; Amos B. Aikman; Joerg Hermann; Matthew T. Heizler

2009-01-01

313

The Perpendicular Diffusion Coefficient for Charged Particles of Arbitrary Energy  

NASA Astrophysics Data System (ADS)

The problem of perpendicular diffusion by a particle in a turbulent plasma is a problem of enduring interest, and one that has yet to be fully solved. Analytic models do not agree with either observations or numerical simulations. Recently, a nonlinear theory was developed by Matthaeus et al. [2003] which, for the first time, appears to be consistent with numerical simulations in both the high- and low-energy particle regimes. Their approach is to assume that perpendicular transport is governed by the velocity of gyrocenters that follow magnetic field lines. Qin et al. [2002a,b] showed using numerical simulations that perpendicular diffusion could occur only in the presence of a transverse complex magnetic field. Flux surfaces with high transverse complexity are characterized by the rapid separation of nearby magnetic field lines and are therefore important to perpendicular diffusion. In particular, it appears that the combination of slab and 2D turbulence (a ``two-component'' model) is necessary to produce transverse complexity, and that slab turbulence alone, for example, is insufficient. The nonlinear theory is expressed through the solution of an integral equation. While the numerical solution of the integral equation in the appropriate parameter regime shows excellent agreement with numerical simulations for both high- and low-energy particles, the physical content is difficult to evaluate, nor is it evident how ? xx scales with parameters such as the energy density in magnetic fluctuations, mean field strength, particle gyroradius, MHD turbulence correlation length scales, parallel diffusion coefficient, etc. Furthermore, the integral equation formulation is not readily amenable to inclusion in models and numerical codes that require the perpendicular diffusion coefficient explicitly, such as heliospheric cosmic ray modulation models. We therefore introduce an explicit model for turbulence in the solar wind and solve the integral equation approximately for ? xx. We show that our approximate solution agrees very well with the numerical solution of the fully nonlinear integral equation. The approximate solution reveals the dependence of ? xx on the characteristics of the turbulent magnetofluid and particle energy (through the particle gyroradius). We conclude by using the perpendicular diffusion coefficient to evaluate 1) the particle acceleration timescale for diffusive shock acceleration at perpendicular shocks, and 2) the diffusion coefficient for cosmic ray modulation throughout the heliosphere.

Zank, G. P.; Li, G.; Florinski, V.; Webb, G. M.; Le Roux, J. A.; Matthaeus, W. H.

2003-12-01

314

Length Distributions in Loop Soups  

NASA Astrophysics Data System (ADS)

Statistical lattice ensembles of loops in three or more dimensions typically have phases in which the longest loops fill a finite fraction of the system. In such phases it is natural to ask about the distribution of loop lengths. We show how to calculate moments of these distributions using CPn-1 or RPn-1 and O(n) ? models together with replica techniques. The resulting joint length distribution for macroscopic loops is Poisson-Dirichlet with a parameter ? fixed by the loop fugacity and by symmetries of the ensemble. We also discuss features of the length distribution for shorter loops, and use numerical simulations to test and illustrate our conclusions.

Nahum, Adam; Chalker, J. T.; Serna, P.; Ortuño, M.; Somoza, A. M.

2013-09-01

315

Optimal Patent Length and Breadth  

Microsoft Academic Search

In providing rewards to innovators, there is a tradeoff between patent length and breadth. This article provides conditions under which the optimal patent policy involves infinitely-lived patents, with patent breadth adjusting to provide the required reward for innovation.

Richard Gilbert; Carl Shapiro

1990-01-01

316

Full Length Donor History Questionnaire  

Center for Biologics Evaluation and Research (CBER)

Text VersionPage 1. This document is one component of the donor history questionnaire documents (Version No. ... Full-Length Donor History Questionnaire ... More results from www.fda.gov/downloads/biologicsbloodvaccines/bloodbloodproducts

317

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

NASA Astrophysics Data System (ADS)

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.

Momeni, Mahdi

2013-08-01

318

Diffusion Path Theorems for Ternary Diffusion Couples  

NASA Astrophysics Data System (ADS)

A review is given of 17 theorems concerning diffusion paths in ternary diffusion couples published by Kirkaldy and Brown in 1963. An additional 11 theorems are given herein that were taken from work published on diffusion paths after that time. The new theorems are concerned primarily with diffusion paths that result from crossing multiple-phase regions in an interdiffusion zone. The theorems describe a method for classifying microstructural boundaries between the regions and a catalog of diffusion path features that are unique to each type of boundary. In addition, a proposal is given for how to plot diffusion paths in quaternary and higher order systems.

Morral, John E.

2012-10-01

319

SLOW DIFFUSIVE GRAVITATIONAL INSTABILITY BEFORE DECOUPLING  

SciTech Connect

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.

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

320

Numerical analysis of a vortex controlled diffuser  

NASA Astrophysics Data System (ADS)

A numerical study of a prototypical vortex controlled diffuser is performed. The basic diffuser geometry consists of a step expansion in a pipe of area ratio 2.25:1. The incompressible Reynolds averaged Navier-Stokes equations, employing the K-epsilon turbulence model, are solved. Results are presented for bleed rates ranging from 1 to 7 percent. Diffuser efficiencies in excess of 80 percent are obtained. Reattachment lengths are reduced by a factor of up to 3. These results are in qualitative agreement with previous experimental work. However, differences in some basic details of experimentally observed and the present numerically generated flowfields exist. The effect of swirl is also investigated.

Spall, Robert E.

1993-11-01

321

What determines drying rates at the onset of diffusion controlled stage-2 evaporation from porous media?  

NASA Astrophysics Data System (ADS)

Early stages of evaporation from porous media are marked by relatively high evaporation rates supplied by capillary liquid flow from a receding drying front to vaporization surface. At a characteristic drying front depth, hydraulic continuity to the surface is disrupted marking the onset of stage-2 evaporation where a lower evaporative flux is supported by vapor diffusion. Observations suggest that in some cases the transition is accompanied by a jump in the vaporization plane from the surface to a certain depth below. The resulting range of evaporation rates at the onset of stage-2 is relatively narrow (0.5-2.5 mm d-1). The objective is to estimate the depth of the vaporization plane that defines vapor diffusion length at the onset of stage-2. The working hypothesis is that the jump length is determined by a characteristic length of connected clusters at the secondary drying front that obeys a power law with the system's Bond number. We conducted evaporation experiments using sands and glass beads of different particle size distributions and extracted experimental data from the literature for model comparison. Results indicate the jump length at the end of stage-1 was affected primarily by porous media properties and less so by boundary conditions. Results show power law relationships between the length of the vaporization plane jump and Bond number with an exponent of -0.48 in good agreement with the percolation theory theoretical exponent of -0.47. The results explain the origins of a relatively narrow range of evaporation rates at the onset of stage-2, and provide a means for estimating these rates.

Shokri, N.; Or, D.

2011-09-01

322

Channel Length Scaling Effects in Graphene Field-Effect Transistor  

NASA Astrophysics Data System (ADS)

We present measurement and analysis of the current-voltage characteristics in the high-bias regime of graphene field-effect transistors of different channel lengths. The devices are fabricated with a gate dielectric process based on a polyvinyl alcohol adsorption layer, enabling reliable top-gates with the highest reported efficiency. Device characteristics are strongly determined by velocity saturation of the carriers, the zero-bandgap density-of states, contact doping, and tunneling. Contact doping strongly reduces the effective channel length in the absence of ``spacer'' between the gated channel region and the contacts. Surface polar optical phonon scattering determines saturation velocities down to short channel lengths. At the shortest channel lengths, band-to-band tunneling degrades device output conductance and transconductance.

Meric, Inanc; Chauhan, Jyotsna; Han, Melinda; Kim, Philip; Guo, Jing; Shepard, Kenneth L.

2010-03-01

323

Design Optimization of Mixed-flow Pump Impellers and Diffusers in a Fixed Meridional Shape  

NASA Astrophysics Data System (ADS)

In this paper, design optimization for mixed-flow pump impellers and diffusers has been studied by using a commercial CFD code and DOE(design of experiments). We also discussed how to improve the performance of the mixed-flow pump by designing the impeller and diffuser in the mixed-flow pump. Geometric design variables were defined by the vane plane development which indicates the blade-angle distributions and length of the impeller and the diffusers. The vane plane development was controlled by using blade-angle in a fixed meridional shape. First the design optimization of the defined impeller geometric variables was done, and then the flow characteristics were analyzed in the point of incidence angle at the diffuser leading edge for the optimized impeller. Then design optimizations of the defined diffuser shape variables were performed. The importance of the geometric design variables was analyzed by using 2k factorial designs, and the design optimization of the geometric variables were determined using the response surface method. The objective functions are defined as the total head and the total efficiency at the design flow-rate. From the comparison of CFD results between optimized pump and base design model, the reason for the performance improvement was discussed.

Kim, Sung; Choi, Young-Seok; Lee, Kyoung-Yong

2010-06-01

324

Multiple Scattering in Clouds: Insights from Three-Dimensional Diffusion/P{sub 1} Theory  

SciTech Connect

In the atmosphere, multiple scattering matters nowhere more than in clouds, and being a product of its turbulence, clouds are highly variable environments. This challenges three-dimensional (3D) radiative transfer theory in a way that easily swamps any available computational resources. Fortunately, the far simpler diffusion (or P{sub 1}) theory becomes more accurate as the scattering intensifies, and allows for some analytical progress as well as computational efficiency. After surveying current approaches to 3D solar cloud-radiation problems from the diffusion standpoint, a general 3D result in steady-state diffusive transport is derived relating the variability-induced change in domain-average flux (i.e., diffuse transmittance) to the one-point covariance of internal fluctuations in particle density and in radiative flux. These flux variations follow specific spatial patterns in deliberately hydrodynamical language: radiative channeling. The P{sub 1} theory proves even more powerful when the photon diffusion process unfolds in time as well as space. For slab geometry, characteristic times and lengths that describe normal and transverse transport phenomena are derived. This phenomenology is used to (a) explain persistent features in satellite images of dense stratocumulus as radiative channeling, (b) set limits on current cloud remote-sensing techniques, and (c) propose new ones both active and passive.

Davis, Anthony B. [Los Alamos National Laboratory (United States); Marshak, Alexander [NASA's Goddard Space Flight Center (United States)

2001-03-15

325

The evolution of size in variable length representations  

Microsoft Academic Search

In many cases, a program's length increases during artificial evolution. This is known as “bloat”, “fluff” or “increasing structural complexity”. We show that bloat is not specific to genetic programming and suggest it is inherent in search techniques with discrete variable-length representations using simple static evaluation functions. We investigate the bloating characteristics of three non-population-based and one population-based search technique

W. B. Langdon; Simulated Annealing

1998-01-01

326

Strength versus gauge length in ceramic-matrix composites  

Microsoft Academic Search

The strength of ceramic-matrix composites as a function of sample gauge length is derived as a function of the composite constituent material properties. Within the context of a global load-sharing assumption for how load is transferred from broken to unbroken fibers, the analysis shows that, for samples shorter than 0.8[delta][sub c] (where [delta][sub c] is the characteristic slip length determining

William A. Curtin

1994-01-01

327

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...

328

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

Microsoft Academic Search

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

D. K. Moutopoulos; K. I. Stergiou

2002-01-01

329

Continuous time random walk with jump length correlated with waiting time  

NASA Astrophysics Data System (ADS)

A coupled continuous time random walk (CTRW) model is proposed, in which the jump length of a walker is correlated with waiting time. The power law distribution is chosen as the probability density function of waiting time and the Gaussian-like distribution as the probability density function of jump length. Normal diffusion, subdiffusion and superdiffusion can be realized within the present model. It is shown that the competition between long-tailed distribution and correlation of jump length and waiting time will lead to different diffusive behavior.

Liu, Jian; Bao, Jing-Dong

2013-02-01

330

Parallel flow diffusion battery  

DOEpatents

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.

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

1984-08-07

331

Parallel flow diffusion battery  

DOEpatents

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.

Yeh, H.C.; Cheng, Y.S.

1984-01-01

332

Scale Length of Disk Galaxies  

NASA Astrophysics Data System (ADS)

Disk scale length rd and central surface brightness ?0 for a sample of 29955 bright disk galaxies from the Sloan Digital Sky Survey have been analyzed. Cross correlation of the SDSS sample with the LEDA catalogue allowed us to investigate the variation of the scale lengths for different types of disk/spiral galaxies and present distributions and typical trends of scale lengths all the SDSS bands with linear relations that indicate the relation that connect scale lengths in one passband to another. We use the volume corrected results in the r-band and revisit the relation between these parameters and the galaxy morphology, and find the average values = 3.8 +/- 2.1 kpc and = 20.2 +/- 0.7 mag arcsec-2. The derived scale lengths presented here are representative for a typical galaxy mass of 1010.8 M?, and the RMS dispersion is larger for more massive galaxies. We analyse the rd-?0 plane and further investigate the Freeman Law and confirm that it indeed defines an upper limit for ?0 in bright disks (rmag < 17.0), and that disks in late type spirals (T >= 6) have fainter central surface brightness. Our results are based on a sample of galaxies in the local universe (z < 0.3) that is two orders of magnitudes larger than any sample previously studied, and deliver statistically significant results that provide a comprehensive test bed for future theoretical studies and numerical simulations of galaxy formation and evolution.

Fathi, Kambiz

2011-12-01

333

Do grammars minimize dependency length?  

PubMed

A well-established principle of language is that there is a preference for closely related words to be close together in the sentence. This can be expressed as a preference for dependency length minimization (DLM). In this study, we explore quantitatively the degree to which natural languages reflect DLM. We extract the dependencies from natural language text and reorder the words in such a way as to minimize dependency length. Comparing the original text with these optimal linearizations (and also with random linearizations) reveals the degree to which natural language minimizes dependency length. Tests on English data show that English shows a strong effect of DLM, with dependency length much closer to optimal than to random; the optimal English grammar also has many specific features in common with English. In German, too, dependency length is significantly less than random, but the effect is much weaker than in English. We conclude by speculating about some possible reasons for this difference between English and German. PMID:21564213

Gildea, Daniel; Temperley, David

2009-10-27

334

Persistence Length of Stable Microtubules  

NASA Astrophysics Data System (ADS)

Microtubules are a vital component of the cytoskeleton. As the most rigid of the cytoskeleton filaments, they give shape and support to the cell. They are also essential for intracellular traffic by providing the roadways onto which organelles are transported, and they are required to reorganize during cellular division. To perform its function in the cell, the microtubule must be rigid yet dynamic. We are interested in how the mechanical properties of stable microtubules change over time. Some "stable" microtubules of the cell are recycled after days, such as in the axons of neurons or the cilia and flagella. We measured the persistence length of freely fluctuating taxol-stabilized microtubules over the span of a week and analyzed them via Fourier decomposition. As measured on a daily basis, the persistence length is independent of the contour length. Although measured over the span of the week, the accuracy of the measurement and the persistence length varies. We also studied how fluorescently-labeling the microtubule affects the persistence length and observed that a higher labeling ratio corresponded to greater flexibility.

Hawkins, Taviare; Mirigian, Matthew; Selcuk Yasar, M.; Ross, Jennifer

2011-03-01

335

Cultural Diffusion of Chinese Opera Based on Replicator Dynamics Model  

Microsoft Academic Search

Chinese opera has become a part of Chinese culture, and but faces the challenge of the existence today. Chinese opera culture needs the effective diffusion and protection. The paper shows that the diffusion process is very complicated. According to the complicated characteristics of cultural evolution, this paper establishes an evolutionary game model to simulate the diffusion process of Chinese opera

Han Zhou

2010-01-01

336

Comparison between computer simulation of transport and diffusion of cloud seeding material within stratiform cloud and the NOAA-14 satellite cloud track  

NASA Astrophysics Data System (ADS)

A precipitation enhancement operation using an aircraft was conducted from 1415 to 1549 LST 14 March 2000 in Shaanxi Province. The NOAA-14 satellite data received at 1535 LST soon after the cloud seeding shows that a vivid cloud track appears on the satellite image. The length, average width and maximum width of the cloud track are 301 km, 8.3 and 11 km, respectively. Using a three-dimensional numerical model of transport and diffusion of seeding material within stratiform clouds, the spatial concentration distribution characteristics of seeding material at different times, especially at the satellite receiving time, are simulated. The model results at the satellite receiving time are compared with the features of the cloud track. The transported position of the cloud seeding material coincides with the position of the track. The width, shape and extent of diffusion of the cloud seeding material axe similar to that of the cloud track. The spatial variation of width is consistent with that of the track. The simulated length of each segment of the seeding line accords with the length of every segment of the track. Each segment of the cloud track corresponds to the transport and diffusion of each segment of the seeding line. These results suggest that the cloud track is the direct physical reflection of cloud seeding at the cloud top. The comparison demonstrates that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulated results are sound and trustworthy. The area, volume, width, depth, and lateral diffusive rate corresponding to concentrations 1, 4, and 10 L-1 are simulated in order to understand the variations of influencing range.

Yu, X.; Dai, J.; Lei, H. C.; Fan, P.

2005-01-01

337

Mach-Zehnder Modulator Arm-Length-Mismatch Measurement Technique  

NASA Astrophysics Data System (ADS)

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.

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

2005-03-01

338

Current-Induced Exchange Length and Geometrically Constrained Magnetic Wall  

NASA Astrophysics Data System (ADS)

We analyzed stable magnetic structures of a geometrically constrained magnetic wall under direct current (dc) and found that there exists a characteristic length induced by the competition between the spin transfer torque and the torque due to exchange interaction. This current-induced exchange length is inversely proportional to the applied dc, and the magnetic ripple structure appears when the current-induced exchange length is smaller than the nanoscale constriction. We also found that the amplitude of the magnetic ripple structure oscillates as a function of the applied dc, which can be observed as an oscillation of the resistance against the applied dc.

Matsushita, Katsuyoshi; Sato, Jun; Imamura, Hiroshi

2010-03-01

339

Screening length in plasma winds  

NASA Astrophysics Data System (ADS)

We study the screening length Ls 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. 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.

Cáceres, Elena; Natsuume, Makoto; Okamura, Takashi

2006-10-01

340

The Soret effect in dilute polymer solutions: Influence of chain length, chain stiffness, and solvent quality  

NASA Astrophysics Data System (ADS)

Thermal diffusion in dilute polymer solutions is studied by reverse nonequilibrium molecular dynamics. The polymers are represented by a generic bead-spring model. The influence of the solvent quality on the Soret coefficient is investigated. At constant temperature and monomer fraction, a better solvent quality causes a higher affinity for the polymer to the cold region. This may even go to thermal-diffusion-induced phase separation. The sign of the Soret coefficient changes in a symmetric nonideal binary Lennard-Jones solution when the solvent quality switches from good to poor. The known independence of the thermal diffusion coefficients of the molecular weight is reproduced for three groups of polymers with different chain stiffnesses. The thermal diffusion coefficients reach constant values at chain lengths of around two to three times the persistence length. Moreover, rigid polymers have higher Soret coefficients and thermal diffusion coefficients than more flexible polymers.

Zhang, Meimei; Müller-Plathe, Florian

2006-09-01

341

Overview of bunch length measurements.  

SciTech Connect

An overview of particle and photon beam bunch length measurements is presented in the context of free-electron laser (FEL) challenges. Particle-beam peak current is a critical factor in obtaining adequate FEL gain for both oscillators and self-amplified spontaneous emission (SASE) devices. Since measurement of charge is a standard measurement, the bunch length becomes the key issue for ultrashort bunches. Both time-domain and frequency-domain techniques are presented in the context of using electromagnetic radiation over eight orders of magnitude in wavelength. In addition, the measurement of microbunching in a micropulse is addressed.

Lumpkin, A. H.

1999-02-19

342

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

Microsoft Academic Search

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

J. Villermaux

1996-01-01

343

Nonlinear scaling of surface water diffusion with bulk water viscosity of crowded solutions.  

PubMed

The translational hydration dynamics within 0.5-1.5 nm of the surface of a DPPC liposome, a model biomacromolecular surface, is analyzed by the recently developed Overhauser dynamic nuclear polarization (ODNP) technique. We find that dramatic changes to the bulk solvent cause only weak changes in the surface hydration dynamics. Specifically, both a >10-fold increase in bulk viscosity and the restriction of diffusion by confinement on a multiple nm length-scale change the local translational diffusion coefficient of the surface water surrounding the lipid bilayer by <2.5-fold. By contrast, previous ODNP studies have shown that changes to the biomacromolecular surface induced by folding, binding, or aggregation can cause local hydration dynamics to vary by factors of up to 30. We suggest that the surface topology and chemistry at the ?1.5 nm scale, rather than the characteristics of the solvent, nearly exclusively determine the macromolecule's surface hydration dynamics. PMID:23347324

Franck, John M; Scott, John A; Han, Songi

2013-03-11

344

Separated diffuser flow analysis, volume 1  

Microsoft Academic Search

This report describes a finite difference computer program TASED (Turbulent Annular Sudden-Expansion Diffuser), which predicts flow properties in an axisymmetric annular duct of arbitrary shape which contains an arbitrarily shaped axisymmetric annular centerbody in the duct exit. The centerbody may contain openings through which air is allowed to flow. A two-equation TKL (Turbulent Kinetic Energy and Length Scale) turbulence model

H. L. Stocker; T. E. Scott; C. F. Shieh; J. E. Caruthers

1981-01-01

345

AMBIPOLAR DIFFUSION HEATING IN TURBULENT SYSTEMS  

SciTech Connect

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.

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

346

Ambipolar Diffusion Heating in Turbulent Systems  

NASA Astrophysics Data System (ADS)

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 Alfvén Mach numbers of ~1 and AD Reynolds numbers of ~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.

Li, Pak Shing; Myers, Andrew; McKee, Christopher F.

2012-11-01

347

Appearance of Meningiomas on Diffusion-weighted Images: Correlating Diffusion Constants with Histopathologic Findings  

Microsoft Academic Search

BACKGROUND AND PURPOSE: Malignant and atypical meningiomas are prone to recur- rence and aggressive growth, which affects treatment planning and prognostication. Investi- gators have used diffusion-weighted imaging and apparent diffusion coefficient (ADC) maps to compare tumor grade and cellularity with the histopathologic findings of intraaxial primary brain neoplasms. The purpose of this study was to determine whether the signal characteristics

Christopher G. Filippi; Mark A. Edgar; Aziz M. Ulug; Joan C. Prowda; Linda A. Heier; Robert D. Zimmerman

2001-01-01

348

Comments on 'Intermolecular Forces: Thermal Diffusion and Diffusion in He-Kr and H2-Kr'.  

National Technical Information Service (NTIS)

In the paper by Annis, Humphreys, and Mason, deviations from the geometric mean combining rule for the characteristic energy parameter were suggested as the major cause of disagreement between theoretical and experimental diffusion properties. These devia...

M. J. Hiza A. G. Duncan

1968-01-01

349

Slip Diffusion and Lévy Flights of an Adsorbed Gold Nanocluster  

Microsoft Academic Search

Anomalous diffusion of a gold nanocrystal Au140, adsorbed on the basal plane of graphite, exhibiting Lévy-type power-law flight-length and sticking-time distributions, is predicted through extensive molecular dynamics simulations. An atomistic collective slip-diffusion mechanism is proposed and analyzed.

W. D. Luedtke; Uzi Landman

1999-01-01

350

Retrapping and velocity inversion in jump diffusion  

SciTech Connect

A method for the solution of the Kramers problem in periodic potentials is proposed in the general case of a tilted periodic potential. The method is then applied to the Fokker-Planck equation with a cosine potential without tilt, and the results for the jump-length probability distribution are compared to simulation data concerning the lengths crossed by a hopping particle before its first velocity inversion. It is shown that, at high dissipation, the diffusing particle thermalizes in most cases in the cell where it inverts the velocity for the first time. On the contrary, at low dissipation the actual length of the jump and the length crossed before the first velocity inversion display significant differences, showing that the first velocity inversion is not a good criterion for the length of the jump, just in the case where long jumps are more important.

Ferrando, R.; Spadacini, R.; Tommei, G.E. (Centro di Fisica delle Superfici e delle Basse Temperature del Consiglio Nazionale delle Ricerche, Unita dell'Istituto Nazionale di Fisica della Materia, Dipartimento di Fisica, via Dodecaneso 33, 16146 Genova (Italy))

1995-01-01

351

Fractional baud-length coding  

NASA Astrophysics Data System (ADS)

We present a novel approach for modulating radar transmissions in order to improve target range and Doppler estimation accuracy. This is achieved by using non-uniform baud lengths. With this method it is possible to increase sub-baud range-resolution of phase coded radar measurements while maintaining a narrow transmission bandwidth. We first derive target backscatter amplitude estimation error covariance matrix for arbitrary targets when estimating backscatter in amplitude domain. We define target optimality and discuss different search strategies that can be used to find well performing transmission envelopes. We give several simulated examples of the method showing that fractional baud-length coding results in smaller estimation errors than conventional uniform baud length transmission codes when estimating the target backscatter amplitude at sub-baud range resolution. We also demonstrate the method in practice by analyzing the range resolved power of a low-altitude meteor trail echo that was measured using a fractional baud-length experiment with the EISCAT UHF system.

Vierinen, J.

2011-06-01

352

Detecting messages of unknown length  

NASA Astrophysics Data System (ADS)

This work focuses on the problem of developing a blind steganalyzer (a steganalyzer relying on machine learning algorithm and steganalytic features) for detecting stego images with different payload. This problem is highly relevant for practical forensic analysis, since in practice, the knowledge about the steganographic channel is very limited, and the length of hidden message is generally unknown. This paper demonstrates that the discrepancy between payload in training and testing / application images can significantly decrease the accuracy of the steganalysis. Two fundamentally different approaches to mitigate this problem are then proposed. The first solution relies on quantitative steganalyzer. The second solution transforms one-sided hypothesis test (unknown message length) to simple hypothesis test by assuming a probability distribution on length of messages, which can be efficiently solved by many machine-learning tools, e.g. by Support Vector Machines. The experimental section of the paper (a) compares both solutions on steganalysis of F5 algorithm with shrinkage removed by wet paper codes for JPEG images and LSB matching for raw (uncompressed) images, (b) investigates the effect of the assumed distribution of the message length on the accuracy of the steganalyzer, and (c) shows how the accuracy of steganalysis depends on Eve's knowledge about details of steganographic channel.

Pevny, Tomas

2011-02-01

353

Ballistic to Diffusive Crossover in III–V Nanowire Transistors  

Microsoft Academic Search

In this paper, the authors examine the crossover between ballistic and diffusive transport in III-V nanowire transistors. The authors find that at lower drain voltages the ballistic-to-diffusive crossover occurs at channel lengths of approximately 2.3 nm at room temperature. However, when increasing the drain voltage, the ballistic-to-diffusive crossover can be more than nine times as long at room temperature. As

M. J. Gilbert; Sanjay K. Banerjee

2007-01-01

354

Diffusion in porous building materials with high internal magnetic field gradients.  

PubMed

Measuring the water diffusivity in porous building materials with NMR is hindered by the presence of large internal magnetic field gradients originating from magnetic impurities (Fe). To investigate the diffusion of water in these materials, a stimulated echo NMR technique is applied. A new analytical equation for the long-time signal decay in the presence of spatially varying internal field gradients is derived. This equation is experimentally confirmed by measurements on representative materials with large internal gradients (fired-clay brick and sintered crushed glass) and a material with very small internal gradients (glass filter). The diffusivity is determined in the long time limit, where it is constant and limited by the tortuosity of the pore structure. Tortuosities of different samples derived from the NMR data show an excellent agreement with the macroscopic tortuosities measured by electrochemical impedance spectroscopy. The developed technique can also be applied in unsaturated media, during e.g., drying, water absorption, and concentration changes. The characteristic length scales of the internal field fluctuations estimated from the model are compared with the structural length scales, whereas the magnitude of these fluctuations is compared with results of macroscopic magnetization measurements. PMID:14987603

Petkovi?, J; Huinink, H P; Pel, L; Kopinga, K

2004-03-01

355

Measurement of radon diffusion in polyethylene based on alpha detection  

NASA Astrophysics Data System (ADS)

Radon diffusion in different materials has been measured in the past. Usually the diffusion measurements are based on a direct determination of the amount of radon that diffuses through a thin layer of material. Here we present a method based on the measurement of the radon daughter products which are deposited inside the material. Looking at the decay of 210Po allows us to directly measure the exponential diffusion profile characterized by the diffusion length. In addition we can determine the solubility of radon in PE. We also describe a second method to determine the diffusion constant based on the short-lived radon daughter products 218Po and 214Po, using the identical experimental setup.Measurements for regular polyethylene (PE) and High Molecular Weight Polyethylene (HMWPE) yielded diffusion lengths of (1.3±0.3) mm and (0.8±0.2) mm and solubilities of 0.5±0.1 and 0.7±0.2, respectively, for the first method; the diffusion lengths extracted from the second method are noticeably larger which may be caused by different experimental conditions during diffusion.

Rau, Wolfgang

2012-02-01

356

Length, time, and energy scales of photosystems.  

PubMed

The design of photosynthetic systems reflects the length scales of the fundamental physical processes. Energy transfer is rapid at the few angstrom scale and continues to be rapid even at the 50-A scale of the membrane thickness. Electron tunneling is nearly as rapid at the shortest distances, but becomes physiologically too slow well before 20 A. Diffusion, which starts out at a relatively slow nanosecond time scale, has the most modest slowing with distance and is physiologically competent at all biologically relevant distances. Proton transfer always operates on the shortest angstrom scale. The structural consequences of these distance dependencies are that energy transfer networks can extend over large, multisubunit and multicomplex distances and take leaps of 20 A before entering the domain of charge separating centers. Electron transfer systems are effectively limited to individual distances of 15 A or less and span the 50 A dimensions of the bioenergetic membrane by use of redox chains. Diffusion processes are generally used to cover the intercomplex electron transfer distances of 50 A and greater and tend to compensate for the lack of directionality by restricting the diffusional space to the membrane or the membrane surface, and by multiplying the diffusing species through the use of pools. Proton transfer reactions act over distances larger than a few angstroms through the use of clusters or relays, which sometimes rely on water molecules and which may only be dynamically assembled. Proteins appear to place a premium on robustness of design, which is relatively easily achieved in the long-distance physical processes of energy transfer and electron tunneling. By placing cofactors close enough, the physical process is relatively rapid compared to decay processes. Thus suboptimal conditions such as cofactor orientation, energy level, or redox potential level can be tolerated and generally do not have to be finely tuned. The most fragile regions of design tend to come in areas of complex formation and catalysis involving proton management, where relatively small changes in distance or mutations can lead to a dramatic decrease in turnover, which may already be limiting the overall speed of energy conversion in these proteins. Light-activated systems also face a challenge to robust function from the ever-present dangers of high redox potential chemistry. This can turn the protein matrix and wandering oxygen molecules into unintentional redox partners, which in the case of PSII requires the frequent, costly replacement of protein subunits. PMID:12629967

Moser, Christopher C; Page, Christopher C; Cogdell, Richard J; Barber, James; Wraight, Colin A; Dutton, P Leslie

2003-01-01

357

Quasineutral Limit of a Nonlinear Drift Diffusion Model for Semiconductors  

Microsoft Academic Search

The limit of vanishing Debye length (charge neutral limit ) in a nonlinear bipolar drift-diffusion model for semiconductors without pn-junction (i.e. with a unipolar background charge ) is studied. The quasineutral limit (zero-Debye-length limit) is performed rigorously by using the so-called entropy functional which yields appropriate uniform estimates.

Ingenuin Gasser; Ling Hsiao; Peter A. Markowich; Shu Wang

2000-01-01

358

A shear lag analysis predicts the strong size effect on the persistence length of microtubules  

NASA Astrophysics Data System (ADS)

As one essential component in cytoskeleton, the persistence length of a microtubule was reported to strongly depend on its contour length. To understand this intriguing size effect, here we develop a composite model for a microtubule with an adapted shear lag analysis. A characteristic length is identified, over which the persistence length of a microtubule monotonously increases with its contour length until it saturates, in consistency with the experimental data. This work clearly shows that shear lag between neighboring protofilaments due to the highly anisotropy leads to the strong size effect on the persistence lengths of microtubules.

Chen, Bin

2012-08-01

359

Robustness of compound Dirichlet priors for Bayesian inference of branch lengths.  

PubMed

We modified the phylogenetic program MrBayes 3.1.2 to incorporate the compound Dirichlet priors for branch lengths proposed recently by Rannala, Zhu, and Yang (2012. Tail paradox, partial identifiability and influential priors in Bayesian branch length inference. Mol. Biol. Evol. 29:325-335.) as a solution to the problem of branch-length overestimation in Bayesian phylogenetic inference. The compound Dirichlet prior specifies a fairly diffuse prior on the tree length (the sum of branch lengths) and uses a Dirichlet distribution to partition the tree length into branch lengths. Six problematic data sets originally analyzed by Brown, Hedtke, Lemmon, and Lemmon (2010. When trees grow too long: investigating the causes of highly inaccurate Bayesian branch-length estimates. Syst. Biol. 59:145-161) are reanalyzed using the modified version of MrBayes to investigate properties of Bayesian branch-length estimation using the new priors. While the default exponential priors for branch lengths produced extremely long trees, the compound Dirichlet priors produced posterior estimates that are much closer to the maximum likelihood estimates. Furthermore, the posterior tree lengths were quite robust to changes in the parameter values in the compound Dirichlet priors, for example, when the prior mean of tree length changed over several orders of magnitude. Our results suggest that the compound Dirichlet priors may be useful for correcting branch-length overestimation in phylogenetic analyses of empirical data sets. PMID:22328570

Zhang, Chi; Rannala, Bruce; Yang, Ziheng

2012-02-10

360

Reaction-diffusion textures  

Microsoft Academic Search

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

Andrew P. Witkin; Michael Kass

1991-01-01

361

Variable focal length deformable mirror  

DOEpatents

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.

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

2007-06-12

362

Design improvements increase run length  

SciTech Connect

The Hawaiian Independent Refinery (HIRI) visbreaker recently completed 843 stream days of operation before its first heater decoke and major turnaround and inspection. This is believed to be a record and shows that, with proper design criteria, longer run lengths and lower maintenance and operating costs can be achieved than previously thought possible. From this commercial experience it can be seen that it is feasible to design coil-type visbreakers to achieve very long run lengths, and because the coke formation that does occur can be quickly and easily removed, better on-stream time and lower maintenance costs can be achieved. The capital and other costs associated with soaker drums and the difficulty and expense of removing and disposing of the coke are well known, as are the problems of fuel oil degradation with soaker drums without complex internals. This demonstrated improvement in run length and on-stream time, together with other improvements made in the past 10 years, gives modern coil design a definite advantage in most visbreaking applications. Many of the concepts employed are applicable to existing units and other processes where undesirable coke formation is normally a problem.

Wood, J.R. (Petroleum Refining Consultants, Christiansted, St. Croix, VI (US)); Marino, C.K. (Hawaiian Independent Refining, Inc., Ewa Beach, HI (US))

1991-02-25

363

Effect of CFRP plate length strengthening continuous steel beam  

Microsoft Academic Search

This paper focused on behavior of beam strengthened with CFRP plate and effect of strengthening length. The simply supported steel beam tested in previous work was modeled using ANSYS finite element software, The same parameters as the experimental data were used to model the steel beam in FEA. Characteristic points on the load–deflection response curve predicted using finite element analysis

Majid Mohammed Ali Kadhim

364

Cooperative Length Scale and Fragility of Polystyrene under Confinement  

NASA Astrophysics Data System (ADS)

While thin films are an attractive model system to investigate the impact of confinement on glassy behavior, extending studies beyond thin films to geometries of higher dimensionalities is vital from both scientific and technological viewpoints. In this talk, we present the impact of confinement on the characteristic length at the glass transition as well as the fragility for confined polystyrene (PS) nanoparticles under isochoric conditions. We measure the glass transition temperature (Tg), fictive temperature (Tf) and isochoric heat capacity of silica-capped PS nanoparticles as a function of diameter via differential scanning calorimetry. From the measurement of Tf, we obtain the isochoric fragility, and via the fluctuation formula, the characteristic length at the glass transition. We illustrate that confinement under isochoric conditions for PS nanoparticles leads to a significant increase in the isochoric fragility while the characteristic length is reduced with size. At the minimum the results demonstrate a relationship between fragility and the characteristics length of isochorically-confined polymer that is not intuitive from the Adam-Gibbs theory.

Zhang, Chuan; Guo, Yunlong; Priestley, Rodney

2012-02-01

365

Human Factor Analysis of Long Cane Design: Weight and Length  

ERIC Educational Resources Information Center

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…

Rodgers, Mark D.; Emerson, Robert Wall

2005-01-01

366

Bunch Length Measurements using Coherent Radiation  

SciTech Connect

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.

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

367

Diffusive-Ballistic Heat Conduction of Carbon Nanotubes and Nanographene Ribbons  

NASA Astrophysics Data System (ADS)

Investigations of diffusive-ballistic heat conduction of finite-length single- walled carbon nanotubes and nanographene ribbons at room temperature have been carried out by using non-equilibrium molecular dynamics simulations. The length dependences of the thermal conductivity reveal the variation of the balance between ballistic and diffusive heat conductions. For both systems, the profile indicates a significant contribution of the ballistic phonon transport even with a length of about a micrometer. Comparison of the length effects of single-walled carbon nanotubes and nanographene ribbons highlights the roles of phonon dispersions and the extent of phonon scattering on diffusive-ballistic heat conduction.

Shiomi, Junichiro; Maruyama, Shigeo

2010-10-01

368

Enhancing phosphorylation cascades by anomalous diffusion  

NASA Astrophysics Data System (ADS)

A key event in many cellular signaling cascades is the multiple phosphorylation of proteins by specialized kinases. A prototypical example is the mitogen-activated protein kinase (MAPK) that alters the cell's gene transcription after having been phosphorylated twice by the same kinase. Here, we show that anomalous diffusion, induced, for example, by cytoplasmic crowding, can significantly improve the activation of MAPK. Our results on anomalous diffusion with the characteristics of fractional Brownian motion and obstructed diffusion compare favorably to very recent biochemical data on MAPK activation at varying degrees of cytoplasmic crowding. Our results predict any Michaelis-Menten scheme in which a substrate is modified by the same enzyme several times to show an increased performance due to anomalous diffusion when dissociation rates of the intermediate enzyme-substrate complexes are high while the irreversible catalytic step is slow. Thus, crowding-induced anomalous diffusion can strongly alter the behavior of many cellular signaling pathways.

Hellmann, M.; Heermann, D. W.; Weiss, M.

2012-03-01

369

Quantifying GFP Diffusion in Escherichia coli by Using Continuous Photobleaching with Evanescent Illumination  

PubMed Central

Fluorescence recovery after photobleaching and fluorescence correlation spectroscopy are the primary means for studying translational diffusion in biological systems. Both techniques, however, present numerous obstacles for measuring translational mobility in structures only slightly larger than optical resolution. We report a new method using through-prism total internal reflection fluorescence microscopy with continuous photobleaching (TIR-CP) to overcome these obstacles. Small structures, such as prokaryotic cells or isolated eukaryotic organelles, containing fluorescent molecules are adhered to a surface. This surface is continuously illuminated by an evanescent wave created by total internal reflection. The characteristic length describing the decay of the evanescent intensity with distance from the surface is smaller than the structures. The fluorescence decay rate resulting from continuous evanescent illumination is monitored as a function of the excitation intensity. The data at higher excitation intensities provide apparent translational diffusion coefficients for the fluorescent molecules within the structures because the decay results from two competing processes (the intrinsic photobleaching propensity and diffusion in the small structures). We present the theoretical basis for the technique and demonstrate its applicability by measuring the diffusion coefficient, 6.3 ± 1.1 µm2/sec, of green fluorescent protein (GFP) in Escherichia coli cells.

Slade, Kristin M.; Steele, Bridgett L.; Pielak, Gary J.; Thompson, Nancy L.

2009-01-01

370

Delta-doping in diffusion studies  

NASA Astrophysics Data System (ADS)

The ?-doping where the dopant is confined on the length-scale of the lattice constant provides perfectly ideal conditions to study the atomic transport processes. We have studied MBE-grown GaAs samples ?-doped with Si and Al layers. Long time diffusion anneals have been performed in the temperature range 550 800 °C. The distribution profiles are examined by SIMS-profiling. We obtain Si diffusion coefficients in good agreement with the other recent studies using different techniques (rapid thermal annealing, capacitance-voltage profiling, sandwiched diffusion source). This contrasts with the earlier measurements based on diffusion of implanted dopants which were much more widely spread. We conclude that the more accurate data allowed with the ?-doping show that the diffusion coefficient is an intrinsic parameter provided that the amount of dopant and the dislocation density are kept sufficiently small. Le dopage-delta, où le dopant est confiné à l'échelle du paramètre du réseau, fournit les conditions parfaitement idéales pour étudier les processus de transport atomique. Nous avons étudié des échantillons de GaAs obtenus par épitaxie par jet moléculaire dopés par des couches-delta de Si et Al. Des traitements de diffusion de longue durée ont été réalisés dans l'intervalle de température 550 à 800°C. Les profils de distribution sont examinés par spectrométrie d'émission d'ions secondaires. Nous obtenons des coefficients de diffusion de Si en bon accord avec les autres études récentes utilisant des techniques différentes (traitement thermique ultrarapide, profil de distribution par la méthode capacité-voltage, diffusion d'une couche “ sandwich ”). Ceci diffère des mesures antérieures qui, basées sur la diffusion de dopants implantés, étaient beaucoup plus dispersées. Nous concluons que les données plus précises rendues possibles par le dopage-delta montrent que le coefficient de diffusion est un paramètre intrinsèque à la condition que la quantité de dopant et la densité de dislocation demeurent assez faibles.

Bénière, François; Chaplain, René; Gauneau, Marcel; Reddy, Viswanatha; Régrény, André

1993-12-01

371

Microfabricated diffusion source  

DOEpatents

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.

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

2008-07-15

372

Diffusion in solids studied by nuclear resonant X-ray and neutron scattering.  

PubMed

Nuclear resonant scattering of synchrotron radiation and quasielastic neutron scattering allow the measurement of frequencies, directions and lengths of jumps of diffusing atoms. Both methods have been successfully applied to diffusion in solids. Synergies and respective advantages of these two techniques as well as recent developments are discussed on the basis of an example: diffusion in intermetallic alloys. PMID:12091728

Kaisermayr, Martin; Sepiol, Bogdan; Combet, Jerome; Rüffer, Rudolf; Pappas, Catherine; Vogl, Gero

2002-06-30

373

Restricted diffusion in annular geometrical pores  

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

374

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

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

375

The Length of Time's Arrow  

SciTech Connect

An unresolved problem in physics is how the thermodynamic arrow of time arises from an underlying time reversible dynamics. We contribute to this issue by developing a measure of time-symmetry breaking, and by using the work fluctuation relations, we determine the time asymmetry of recent single molecule RNA unfolding experiments. We define time asymmetry as the Jensen-Shannon divergencebetween trajectory probability distributions of an experiment and its time-reversed conjugate. Among other interesting properties, the length of time's arrow bounds the average dissipation and determines the difficulty of accurately estimating free energy differences in nonequilibrium experiments.

Feng, Edward H.; Crooks, Gavin E.

2008-08-21

376

Oxygen diffusion in basalt and andesite melts: experimental results and discussion of chemical versus tracer diffusion  

NASA Astrophysics Data System (ADS)

Chemical diffusion coefficients for oxygen in melts of Columbia River basalt (Ice Harbor Dam flow) and Mt. Hood andesite have been determined at 1 atm. The diffusion model is that of sorption or desorption of oxygen into a sphere of uniform initial concentration from a constant and semi-infinite atmosphere. The experimental design utilizes a thermogravimetric balance to monitor the rate of weight change arising from the response of the sample redox state to an imposed fO2. Oxygen diffusion coefficients are approximately an order-ofmagnitude greater for basaltic melt than for andesitic melt. At 1260° C, the oxygen diffusion coefficients are: D=1.65×10-6cm2/s and D=1.43×10-7cm2/s for the basalt and andesite melts, respectively. The high oxygen diffusivity in basaltic melt correlates with a high ratio of nonbridging oxygen/tetrahedrally coordinated cations, low melt viscosity, and high contents of network-modifying cations. The dependence of the oxygen diffusion coefficient on temperature is: D=36.4exp(-51,600±3200/ RT)cm2/s for the basalt and D=52.5exp(-60,060±4900/ RT)cm2/s for the andesite ( R in cal/deg-mol; T in Kelvin). Diffusion coefficients are independent of the direction of oxygen diffusion (equilibrium can be approached from extremely oxidizing or reducing conditions) and thus, melt redox state. Characteristic diffusion distances for oxygen at 1260° C vary from 10-2 to 102 m over the time interval of 1 to 106 years. A compensation diagram shows two distinct trends for oxygen chemical diffusion and oxygen tracer diffusion. These different linear relationships are interpreted as supporting distinct oxygen transport mechanisms. Because oxygen chemical diffusivities are generally greater than tracer diffusivities and their Arrhenius activation energies are less, transport mechanisms involving either molecular oxygen or vacancy diffusion are favored.

Wendlandt, Richard F.

1991-10-01

377

Scaling of Avian Primary Feather Length  

Microsoft Academic Search

The evolution of the avian wing has long fascinated biologists, yet almost no work includes the length of primary feathers in consideration of overall wing length variation. Here we show that the length of the longest primary feather () contributing to overall wing length scales with negative allometry against total arm (ta = humerus+ulna+manus). The scaling exponent varied slightly, although

Robert L. Nudds; Gary W. Kaiser; Gareth J. Dyke; Andrew Farke

2011-01-01

378

Length-dependent dynamics of microtubules  

NASA Astrophysics Data System (ADS)

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.

Yadav, Vandana; Mukherji, Sutapa

2011-12-01

379

Characteristics of thermosiphon reboilers  

Microsoft Academic Search

The paper describes the operational characteristics of thermosiphon reboilers on the basis of an experimental and theoretical study. The operational responses to a variation of the driving temperature difference, the operating pressure and the liquid head in the inlet line are discussed in detail. Furthermore, the influence of several design parameters as length and diameter of the pipes is presented.

Stephan Arneth; Johann Stichlmair

2001-01-01

380

Fibreoptic diffuse-light irradiators of biological tissues  

SciTech Connect

We report techniques for the fabrication of laser radiation diffusers for interstitial photodynamic therapy. Using chemical etching of the distal end of silica fibre with a core diameter of 200 - 600 {mu}m, we have obtained long (up to 40 mm) diffusers with good scattering uniformity. Laser ablation has been used to produce cylindrical diffusers with high emission contrast and a scattering uniformity no worse than {approx}10 % in their middle part. The maximum length of the diffusers produced by this method is 20 - 25 mm. (laser applications and other topics in quantum electronics)

Volkov, Vladimir V; Loshchenov, V B; Konov, Vitalii I; Kononenko, Vitalii V [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2010-10-15

381

Radon Diffusion Measurement in Polyethylene based on Alpha Detection  

SciTech Connect

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.

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

2011-04-27

382

Self-diffusion in random-tiling quasicrystals  

NASA Astrophysics Data System (ADS)

The first explicit realization of the conjecture that phason dynamics leads to self-diffusion in quasicrystals is presented for the icosahedral Ammann tilings. On short time scales, the transport is found to be subdiffusive with the exponent ?~=0.57(1), while on long time scales it is consistent with normal diffusion that is up to an order of magnitude larger than in the typical room temperature vacancy-assisted self-diffusion. No simple finite-size scaling is found, suggesting anomalous corrections to normal diffusion, or existence of at least two independent length scales. A connection with transport in membranes is also noted.

Jari?, Marko Vukobrat; Sørensen, Erik S.

1994-10-01

383

Updating Applied Diffusion Models.  

National Technical Information Service (NTIS)

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 Amer...

J. C. Weil

1985-01-01

384

Dynamic Diffuser Loudspeakers.  

National Technical Information Service (NTIS)

Government standards for dynamic diffuser loudspeakers (GOST 9010-67) include those with round or oval diffusers, with simple or complex portable systems. They are designed for use in radio, television, and various types of sound recording instruments. Th...

1969-01-01

385

Unbiased diffusion in tubes with corrugated walls  

NASA Astrophysics Data System (ADS)

This study is devoted to unbiased motion of a point Brownian particle in a tube with corrugated walls made of conical sections of a varying length. Effective one-dimensional description in terms of the generalized Fick-Jacobs equation is used to derive a formula which gives the effective diffusion coefficient of the particle as a function of the geometric parameters of the tube. Comparison with the results of Brownian dynamics simulations allows us to establish the domain of applicability of both the one-dimensional description and the formula for the effective diffusion coefficient.

Dagdug, Leonardo; Vazquez, Marco-Vinicio; Berezhkovskii, Alexander M.; Bezrukov, Sergey M.

2010-07-01

386

Pb diffusion in zircon  

Microsoft Academic Search

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

D. J Cherniak; E. B Watson

2001-01-01

387

Thermo-Quantum Diffusion  

NASA Astrophysics Data System (ADS)

A new approach to the thermo-quantum diffusion is proposed and a nonlinear quantum Smoluchowski equation is derived, which describes classical diffusion in the field of the Bohm quantum potential. A nonlinear thermo-quantum expression for the diffusion front is obtained, being a quantum generalization of the classical Einstein law. The quantum diffusion at zero temperature is also described and a new dependence of the position dispersion on time is derived. A stochastic Bohm-Langevin equation is also proposed.

Tsekov, Roumen

2009-03-01

388

Real-Valued Semigroups and (Causal) Diffusion  

SciTech Connect

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.

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

2011-09-22

389

Handbook on atmospheric diffusion  

SciTech Connect

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)

Hanna, S.R.; Briggs, G.A.; Hosker, R.P. Jr.

1982-01-01

390

Diffusion Strategy Guide.  

ERIC Educational Resources Information Center

|A methodology is presented for planning and managing the spread of educational innovations. The first portion of the guide develops a theoretical framework for diffusion which summarizes and capitalizes on the latest marketing and on the latest marketing and diffusion research findings. Major stages in the diffusion paradigm discussed include…

McCutcheon, James R.; Sanders, John R.

391

Natural convection within a vertical finite-length channel in free space  

SciTech Connect

Natural convection within a vertical finite length channel in free space is studied in this article to remove assumptions that need to be made on velocity and temperature profiles at the channel entrance. For small channel aspect ratios and low Rayleigh numbers, significant deviations of the Nusselt number and temperature distributions exist due to the effects of vertical thermal diffusion and free space stratification in the channel. A new correlation was proposed on induced Reynolds number for vertical finite length channel. 8 refs.

Lin, S.C.; Chang, K.P.; Hung, Y.H. (National Tsing Hua Univ., Hsinchu (Taiwan, Province of China))

1994-04-01

392

Numerical Modelling of the Sound Fields in Urban Streets with Diffusely Reflecting Boundaries  

NASA Astrophysics Data System (ADS)

A radiosity-based theoretical/computer model has been developed to study the fundamental characteristics of the sound fields in urban streets resulting from diffusely reflecting boundaries, and to investigate the effectiveness of architectural changes and urban design options on noise reduction. Comparison between the theoretical prediction and the measurement in a scale model of an urban street shows very good agreement. Computations using the model in hypothetical rectangular streets demonstrate that though the boundaries are diffusely reflective, the sound attenuation along the length is significant, typically at 20-30 dB/100 m. The sound distribution in a cross-section is generally even unless the cross-section is very close to the source. In terms of the effectiveness of architectural changes and urban design options, it has been shown that over 2-4 dB extra attenuation can be obtained either by increasing boundary absorption evenly or by adding absorbent patches on the fac&?t;/DA>ades or the ground. Reducing building height has a similar effect. A gap between buildings can provide about 2-3 dB extra sound attenuation, especially in the vicinity of the gap. The effectiveness of air absorption on increasing sound attenuation along the length could be 3-9 dB at high frequencies. If a treatment is effective with a single source, it is also effective with multiple sources. In addition, it has been demonstrated that if the fac&?t;/DA>ades in a street are diffusely reflective, the sound field of the street does not change significantly whether the ground is diffusely or geometrically reflective.

Kang, J.

2002-12-01

393

Ink diffusion in water  

NASA Astrophysics Data System (ADS)

The diffusion of ink in water was investigated. Both stamp ink and Quink blue ink were chosen for the analysis. The displacement of the diffused ink front was measured at temperatures of 10-30 °C. The experimental data of the ink front were in good agreement with the theory of diffusion. The diffusion coefficients satisfy the Arrhenius plot, and the activation energy is smaller for the Quink blue ink than for the stamp ink. The mechanism of the ink diffusion is explained by the kinetics of viscous flow.

Lee, Sanboh; Lee, H.-Y.; Lee, I.-F.; Tseng, C.-Y.

2004-03-01

394

Measurement of Diffusion in Entangled Rod-Coil Triblock Copolymers  

NASA Astrophysics Data System (ADS)

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.

Olsen, B. D.; Wang, M.

2012-02-01

395

Signal characteristics of focal bone marrow lesions in patients with multiple myeloma using whole body T1w-TSE, T2w-STIR and diffusion-weighted imaging with background suppression  

Microsoft Academic Search

Objective  This study analyses the diagnostic potential of Diffusion-Weighted Imaging with Background Suppression (DWIBS) in the detection\\u000a of focal bone marrow lesions from multiple myeloma. The signal and contrast properties of DWIBS are evaluated in correlation\\u000a with the serum concentration of M-component (MC) and compared with established T1- and T2-weighted sequences.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  Data from 103 consecutive studies in 81 patients are analysed

Gregor Sommer; Markus Klarhöfer; Claudia Lenz; Klaus Scheffler; Georg Bongartz; Leopold Winter

2011-01-01

396

Reaction-diffusion processes with nonlinear diffusion.  

PubMed

We study reaction-diffusion processes with concentration-dependent diffusivity. First, the decay of the concentration in the single-species and two-species diffusion-controlled annihilation processes is determined. We then consider two natural inhomogeneous realizations. The two-species annihilation process is investigated in the situation when the reactants are initially separated, namely each species occupies a half space. In particular, we establish the growth law of the width of the reaction zone. The single-species annihilation process is studied in the situation when the spatially localized source drives the system toward the nonequilibrium steady state. Finally, we investigate a dissolution process with a localized source of diffusing atoms which react with the initially present immobile atoms forming immobile molecules. PMID:23214535

Krapivsky, P L

2012-10-09

397

Analysis of fluorophore diffusion by continuous distributions of diffusion coefficients: application to photobleaching measurements of multicomponent and anomalous diffusion.  

PubMed Central

Fluorescence recovery after photobleaching (FRAP) is widely used to measure fluorophore diffusion in artificial solutions and cellular compartments. Two new strategies to analyze FRAP data were investigated theoretically and applied to complex systems with anomalous diffusion or multiple diffusing species: 1) continuous distributions of diffusion coefficients, alpha(D), and 2) time-dependent diffusion coefficients, D(t). A regression procedure utilizing the maximum entropy method was developed to resolve alpha(D) from fluorescence recovery curves, F(t). The recovery of multi-component alpha(D) from simulated F(t) with random noise was demonstrated and limitations of the method were defined. Single narrow Gaussian alpha(D) were recovered for FRAP measurements of thin films of fluorescein and size-fractionated FITC-dextrans and Ficolls, and multi-component alpha(D) were recovered for defined fluorophore mixtures. Single Gaussian alpha(D) were also recovered for solute diffusion in viscous media containing high dextran concentrations. To identify anomalous diffusion from FRAP data, a theory was developed to compute F(t) and alpha(D) for anomalous diffusion models defined by arbitrary nonlinear mean-squared displacement versus time relations. Several characteristic alpha(D) profiles for anomalous diffusion were found, including broad alpha(D) for subdiffusion, and alpha(D) with negative amplitudes for superdiffusion. A method to deduce apparent D(t) from F(t) was also developed and shown to provide useful complementary information to alpha(D). alpha(D) and D(t) were determined from photobleaching measurements of systems with apparent anomalous subdiffusion (nonuniform solution layer) and superdiffusion (moving fluid layer). The results establish a practical strategy to characterize complex diffusive phenomena from photobleaching recovery measurements.

Periasamy, N; Verkman, A S

1998-01-01

398

Direct Measurement of Diffusion in Olfactory Cilia Using a Modified FRAP Approach  

PubMed Central

The diffusion coefficient of fluorescein in detached cilia of Xenopus laevis olfactory receptor neurons was measured using spatially-resolved FRAP, where the dye along half of the ciliary length was photobleached and its spatiotemporal fluorescence redistribution recorded. Fitting a one-dimensional numerical simulation of diffusion and photobleaching for 35 cilia resulted in a mean value of the diffusion coefficient and thus a reduction by a factor of compared to free diffusion in aqueous solution.

Alevra, Mihai; Schwartz, Peter; Schild, Detlev

2012-01-01

399

Li diffusion in zircon  

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

400

Dynamics of desorption with lateral diffusion  

NASA Astrophysics Data System (ADS)

The dynamics of desorption from a submonolayer of adsorbed atoms or ions are significantly influenced by the absence or presence of lateral diffusion of the adsorbed particles. When diffusion is present, the adsorbate configuration is simultaneously changed by two distinct processes, proceeding in parallel: adsorption/desorption, which changes the total adsorbate coverage, and lateral diffusion, which is coverage conserving. Inspired by experimental results, we here study the effects of these competing processes by kinetic Monte Carlo simulations of a simple lattice-gas model. In order to untangle the various effects, we perform large-scale simulations, in which we monitor coverage, correlation length, and cluster-size distributions, as well as the behavior of representative individual clusters, during desorption. For each initial adsorbate configuration, we perform multiple, independent simulations, without and with diffusion, respectively. We find that, compared to desorption without diffusion, the coverage-conserving diffusion process produces two competing effects: a retardation of the desorption rate, which is associated with a coarsening of the adsorbate configuration, and an acceleration due to desorption of monomers ``evaporated'' from the cluster perimeters. The balance between these two effects is governed by the structure of the adsorbate layer at the beginning of the desorption process. Deceleration and coarsening are predominant for configurations dominated by monomers and small clusters, while acceleration is predominant for configurations dominated by large clusters.

Juwono, Tjipto; Rikvold, Per Arne

2013-09-01

401

Polarization characteristics of a linearly polarized laser beam after hollow light pipe in projectors  

NASA Astrophysics Data System (ADS)

In this work, a multilayered dielectric film and metallic film are used as reflecting surface to fabricate light pipe. Linearly polarized laser beam with wave length of 532nm enters into the light pipe. After multi-reflection process, laser beam come out from the light pipe. We have found that the polarization state of linearly polarized incident light after reflection are different for the light pipe coated with metal and multilayered dielectric film. We also found a distributed polarization characteristic in the output optical field. The polarization degree has been simulated by using ZEMAX software. Laser speckle contrast from a glass diffuser is measured to exam the simulated result.

Zhao, PengFei; Zhang, Shengtao; Wang, Yanhong; Shi, Yunbo; Chen, XuYuan

2012-11-01

402

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

SciTech Connect

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.

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

403

Turbulence generation and diffusion in coastal breaking waves  

NASA Astrophysics Data System (ADS)

Turbulence in the surf zone is a complex topic of study, of importance for both hydromorphodynamic and environmental studies. In this paper experimental results of turbulent flows for field tests in the Spanish Mediterranean coast are presented. The spatail and temporal resolution of measurements were limited by the ElectroMagnetic Sensors wich result in "filtering" out the small scales and observing; thus only macroturbulence due to breaking waves has been measured. The experimental field-results have been obtained during DELTA`93 and DELTA`96 largescale surf zone experiments in the Ebro Delta, (Spain), under Spilling/plungeing breaking waves (Rodriguez, 1997, PhD Thesis UPC, Barcelona). The field works include several measurements as topo-bathymetric surveys, water levels, 2DH and 2DV velocities, suspended sediment concentrations, sediment properties, meteorological conditions, etc. Several test across the surf zone with high vertical resolution were obtained, covering low, medium and high energy levels. Macroturbulence has been splitted from oscillatory für irregular waves with a recent technique and then turbulent characteristics have been obtained. This turbulent properties are compared with state-of-art macroturbulence characteristics and a new semi-empirical length-scale formulation is proposed. Further measurements on structure functions of the velocity turbulent fluctuations are compared with the distributions of effective surface diffusivity.

Rodriguez, A.; Mosso, C.; Serra, P.; Diez, M.

2009-04-01

404

A Simple Single Step diffusion and Emitter Etching Process for High Efficiency Gallium Antimonide Thermophotovoltaic Devices  

SciTech Connect

A single step diffusion followed by precise etching of the diffused layer has been developed to obtain a diffusion profile appropriate for high efficiency GaSb thermophotovoltaic cells. The junction depth was controlled through monitoring of light current-voltage (I-V) curves (photovoltaic response) during the post diffusion emitter etching process. The measured photoresponses (prior to device fabrication) have been correlated with the quantum efficiencies and the open circuit voltages in the fabricated devices. An optimum junction depth for obtaining highest quantum efficiency and open circuit voltage is presented based on diffusion lengths (or monitoring carrier lifetimes), carrier mobility and typical diffused impurity profile in GaSb.

G. Rajagopalan; N.S. Reddy; E. Ehsani; I.B. Bhat; P.S. Dutta; R.J. Gutmann; G. Nichols; G.W. Charache; O. Sulima

2003-08-29

405

7 CFR 51.610 - Midrib length.  

Code of Federal Regulations, 2013 CFR

...INSPECTION ACT FRESH FRUITS, VEGETABLES AND OTHER PRODUCTS 1,2 (INSPECTION, CERTIFICATION, AND STANDARDS) United States Consumer Standards for Celery Stalks Definitions § 51.610 Midrib length. Midrib length of a branch...

2013-01-01

406

Lognormality of the Distribution of Japanese Sentence Lengths  

NASA Astrophysics Data System (ADS)

The lengths of sentences in written texts have been reported to exhibit characteristic distributions that resemble lognormal distributions. However, the mechanism responsible for such lognormality is unclear. In this quantitative study, we analyze over 10,000 Japanese sentences from out-of-copyright Japanese texts stored on Aozora Bunko. We first confirm that sentence length distributions can be better represented by the lognormal function than by other functions (e.g., the gamma distribution). Next, under the assumption that each sentence is generated by a hierarchical branching process in terms of dependency trees, we test whether the composition of sentences can be explained by a simple multiplicative process by utilizing the Japanese dependency analyzer CaboCha. The results imply that the lognormality of sentence length distributions originates from the dependency tree depth and that a simple multiplicative model cannot accurately model the processes involved in generating sentences.

Furuhashi, Sho; Hayakawa, Yoshinori

2012-03-01

407

Atomistic Simulation of Polymer Crystallization at Realistic Length Scales  

SciTech Connect

Understanding the dynamics of polymer crystallization during the induction period prior to crystal growth is a key goal in polymer physics. Here we present the first study of primary crystallization of polymer melts via molecular dynamics simulations at physically realistic (about 46 nm) length scales. Our results show that the crystallization mechanism involves a spinodal decomposition microphase separation caused by an increase in the average length of rigid trans segments along the polymer backbone during the induction period. Further, the characteristic length of the growing dense domains during the induction period is longer than predicted by classical nucleation theory. These results indicate a new 'coexistence period' in the crystallization, where nucleation and growth mechanisms coexist with a phase separation mechanism. Our results provide an atomistic verification of the fringed micelle model.

Gee, R H; Fried, L E

2005-01-28

408

Monte Carlo Simulation of Diffusion Process on Quasi-Lattice  

NASA Astrophysics Data System (ADS)

The characteristics of the diffusion process of quasicrystals are studied for one-dimensional and two-dimensional models by the conventional Monte Carlo simulation. For the one-dimensional model, the tracer diffusion coefficients of an isolated particle are calculated for the three types of lattice models, i.e., single crystal, binary solid solution and quasicrystal. The characteristics of diffusivity of the one-dimensional quasicrystal model are derived from comparisons among the three types of models. For the two-dimensional model, the characteristics of diffusivity of a quasicrystal are discussed in comparison with those of the honeycomb lattice. In particular, the concentration dependence of diffusivity on the two-dimensional Penrose lattice is calculated and the effects of interatomic potential are discussed.

Sasajima, Yasushi; Sakayori, Kazuhiko; Ichimura, Minoru; Imabayashi, Mamoru

1992-05-01

409

Effect of morphology of polyaniline on its discharge characteristics in nonaqueous electrolyte  

SciTech Connect

Various conducting organic polymers, such as polyaniline, polypyrrole, and polyacetylene have been investigated as functional materials for many kinds of electrochemical applications. For example, polyaniline has been used as a cathode material in rechargeable nonaqueous batteries. The discharge and charge performance of polyaniline which has a fibrous morphology was investigated from microscopic current density and anion diffusion time constant measurements. The microscopic discharge current density is calculated from the radius of the polyaniline fibril, assuming the true electrode surface area corresponds to the surface area of the long polyaniline fibril (2 Al, L:the sum of the length of the polyaniline fibril). The time constant for the diffusion of anions in the polyaniline fibril was calculated from a{sup 2}/D, where D is the diffusion coefficient and a is the polyaniline fibril radius. The diffusion coefficient was measured using an impedance method, and the a{sup 2}/D parameter was calculated. Galvanostatic discharge and charge cycle tests were carried out to decide the performance of polyaniline cathodes with different fibril radii. From these experiments, it can be seen that the dependence of the discharge characteristics on the fibril radius is diminished by the positive dependencies of the diffusion coefficient and roughness of the polyaniline fibril on the fibril radius.

Kanamura, Kiyoshi; Kawai, Yasunori; Yonezawa, Susumu; Takehara, Zenichiro [Kyoto Univ. (Japan)

1995-09-01

410

Dinosaur Skull and Body Length Predictions  

NSDL National Science Digital Library

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.

Twin Cities Public Television, Inc.

2007-01-01

411

Confinement effects on diffusion in polymer multilayers  

NASA Astrophysics Data System (ADS)

We have measured the collective diffusion coefficient of polystyrene and deuterated polystyrene on length scales approaching and less than the radius of gyration of the polymer chains. This has been achieved by preparing multilayers of alternating thin films of polystyrene and deuterated polystyrene; neutron reflectivity is used to follow the decay, on annealling, of the Bragg peaks corresponding to the fundamental and harmonic spatial frequencies of this artificially created composition modulation. The decay of the composition modulation is not well described by a single exponential relaxation, and the collective diffusion coefficient extracted from the long time limit of the decay is smaller than the bulk diffusion coefficient, and decreases with increasing wave-vector.

Jones, R. A. L.; Sivaniah, E.; Sferrazza, M.; Penfold, J.

1997-03-01

412

Differential eddy diffusion of biogeochemical tracers  

NASA Astrophysics Data System (ADS)

The marine ecosystem dynamics in the subtropical regions is controlled by the availability of nutrients. Their supply depends on lateral transport from higher latitudes, which is affected by the characteristics of the oceanic mesoscale turbulence. In many cases turbulent transport is parameterized in terms of eddy diffusion. We here test the validity of this approach in a mesoscale turbulence model coupled to a simple ecosystem model. We show that the parameterization can be profitably used, provided that an effective eddy diffusion coefficient that depends on the reaction time scale of the transported tracers is used. If the diffusion coefficient valid for conservative tracers is used to express diffusion of nutrients and plankton, turbulent transport and biological productivity can be significantly overestimated.

Pasquero, C.

2005-09-01

413

Characteristic Time Scales of Characteristic Magmatic Processes and Systems  

NASA Astrophysics Data System (ADS)

Every specific magmatic process, regardless of spatial scale, has an associated characteristic time scale. Time scales associated with crystals alone are rates of growth, dissolution, settling, aggregation, annealing, and nucleation, among others. At the other extreme are the time scales associated with the dynamics of the entire magmatic system. These can be separated into two groups: those associated with system genetics (e.g., the production and transport of magma, establishment of the magmatic system) and those due to physical characteristics of the established system (e.g., wall rock failure, solidification front propagation and instability, porous flow). The detailed geometry of a specific magmatic system is particularly important to appreciate; although generic systems are useful, care must be taken to make model systems as absolutely realistic as possible. Fuzzy models produce fuzzy science. Knowledge of specific time scales is not necessarily useful or meaningful unless the hierarchical context of the time scales for a realistic magmatic system is appreciated. The age of a specific phenocryst or ensemble of phenocrysts, as determined from isotopic or CSD studies, is not meaningful unless something can be ascertained of the provenance of the crystals. For example, crystal size multiplied by growth rate gives a meaningful crystal age only if it is from a part of the system that has experienced semi-monotonic cooling prior to chilling; crystals entrained from a long-standing cumulate bed that were mechanically sorted in ascending magma may not reveal this history. Ragged old crystals rolling about in the system for untold numbers of flushing times record specious process times, telling more about the noise in the system than the life of typical, first generation crystallization processes. The most helpful process-related time scales are those that are known well and that bound or define the temporal style of the system. Perhaps the most valuable of these times comes from the observed durations and rates of volcanism. There can be little doubt that the temporal styles of volcanism are the same as those of magmatism in general. Volcano repose times, periodicity, eruptive fluxes, acoustic emission structures, lava volumes, longevity, etc. must also be characteristic of pluton-dominated systems. We must therefore give up some classical concepts (e.g., instantaneous injection of crystal-free magma as an initial condition) for any plutonic/chambered system and move towards an integrated concept of magmatism. Among the host of process-related time scales, probably the three most fundamental of any magmatic system are (1) the time scale associated with crystal nucleation (J) and growth (G) (tx}=C{1(G3 J)-{1}/4; Zieg & Marsh, J. Pet. 02') along with the associated scales for mean crystal size (L) and population (N), (2) the time scale associated with conductive cooling controlled by a local length scale (d) (tc}=C{2 d2/K; K is thermal diffusivity), and (3) the time scale associated with intra-crystal diffusion (td}=C{3 L2/D; D is chemical diffusivity). It is the subtle, clever, and insightful application of time scales, dovetailed with realistic system geometry and attention paid to the analogous time scales of volcanism, that promises to reveal the true dynamic integration of magmatic systems.

Marsh, B. D.

2004-05-01

414

Focal length tunable fluidic adaptive lens  

Microsoft Academic Search

In this presentation, we demonstrate a fluidic adaptive lens inspired by animal eye's crystalline lens that can be deformed by muscles to adjust its focal length. Fluidic adaptive lenses, which can adjust their focal length by changing the shape or index without moving parts, are attractive. In summary, we have demonstrated a fluidic lens with an adjustable focal length over

Deying Zhang; Yu-Hwa Lo

2003-01-01

415

Word Length Analysis of Jane Austen's Letters  

Microsoft Academic Search

This paper deals with word length in twenty of Jane Austen's letters and is part of a research project performed in Göttingen. Word length in English has so far only been studied in the context of contemporary texts (Hasse & Weinbrenner, 1995; Riedemann, 1994) and in the English dictionary (Rothschild, 1986). It has been ascertained that word length in texts

Jutta Frischen

1996-01-01

416

LENGTH MUTATIONS IN HUMAN MITOCHONDRIAL DNA  

Microsoft Academic Search

By high-resolution, restriction mapping of mitochondrial DNAs purified from 112 human individuals, we have identified 14 length variants caused by small additions and deletions (from about 6 to 14 base pairs in length). Three of the 14 length differences are due to mutations at two locations within the D loop, whereas the remaining 11 occur at seven sites that are

R. L. CA; A. C. WILSON

1983-01-01

417

28 CFR 551.4 - Hair length.  

Code of Federal Regulations, 2013 CFR

... 2013-07-01 2013-07-01 false Hair length. 551.4 Section 551.4 Judicial...MANAGEMENT MISCELLANEOUS Grooming § 551.4 Hair length. (a) The Warden may not restrict hair length if the inmate keeps it neat and...

2013-07-01

418

Quantifying diffusive mass transfer in rocks undergoing recrystallization: diffusion regime maps  

NASA Astrophysics Data System (ADS)

Recrystallization is a powerful mechanism for homogenizing chemical signatures in rocks because grain boundaries, which form pathways for rapid diffusion, sweep through the grain interiors. Diffusion in static grain boundaries is classically described in terms of Harrison's A- B- and C-regimes. In the A-regime, diffusion occurs both in grain boundaries and grain interiors, and can be described by a combined effective diffusion coefficient. In the B-regime, diffusion occurs in grain boundaries and margins, but the interior of grains are unaffected, while in the C-regime, diffusion occurs only in the grain boundaries. When boundaries are mobile, the A-regime is reached much more quickly for a given grain size and temperature. The location of this boundary in temperature-time space has not generally been quantified, since this requires knowledge both of volume and grain boundary diffusion parameters, and grain boundary velocities. The existence of these data for calcite means that we can present, for the first time, quantitative diffusion regime maps for conditions of normal grain growth driven by surface energy, and for dynamic recrystallization. This in turn allows characteristic diffusion distances to be calculated in the A-regime. The method can easily be generalized to situations where diffusion occurs via a grain boundary fluid or melt phase. We apply the maps to experimental data on 44Ca diffusion in recrystallizing calcite, where an independent method of analysis has shown that in the mobile boundaries, grain boundary diffusion rates were enhanced by at least 5 orders of magnitude compared with published values for static boundaries. The maps confirm that enhanced rates of grain boundary diffusion are required to explain the overall distance of mass transfer. We also apply the maps to mass-transfer in the Gavarnie Thrust mylonite in the Pyrenees, where microzoning patterns in dynamically recrystallized calcite suggest that pervasive grain boundary diffusion on a scale of metres occurred, but grain interiors were not homogenized. The maps indicate that grain boundary diffusion is unlikely to have been sufficient to produce the mass-transfer observed at 300°C, but that diffusion in a grain boundary fluid phase can explain both the scale of mass-transfer and the rapid grain boundary migration required. There are many potential applications for the maps once data on diffusion and grain boundary migration rates becomes available. Examples are spreading of climate signals in ice cores, isotopic homogenization in the mantle, and the reliability of metamorphic P-T data in recrystallized rocks.

McCaig, A. M.; Covey-Crump, S. J.; Ben Ismail, W.; Lloyd, G. E.

2006-12-01

419

Classical momentum diffusion in double- ? -kicked particles  

NASA Astrophysics Data System (ADS)

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.

Stocklin, M. M. A.; Monteiro, T. S.

2006-08-01

420

Elasticity of fluctuating charged membranes probed by X-ray grazing-incidence diffuse scattering  

NASA Astrophysics Data System (ADS)

We have investigated the structure, fluctuations and elasticity parameters of charged fluid membranes composed of didodecyldimethylammonium halide bilayers (DDAX) with different counterions (X = Cl- or Br-) by non-specular (diffuse) X-ray scattering. The samples have been prepared as highly aligned thick stacks on silicon support and have been swollen at controlled osmotic pressures. From line-shape analysis of the diffuse scattering, we can determine the fluctuation amplitudes of the membranes in the L? phase and the characteristic correlation lengths. According to the Caillé model, the measured structural parameters have been expressed in terms of the exponent ? and smectic penetration length ?, from which the smectic compression modulus B (J/m3) and the bending modulus K (J/m) have been determined, as a function of the swelling state. We show that the results are in quantitative agreement with the mean-field electrostatic Poisson-Boltzmann calculations, controlled by the bilayers surface charge density (surfactant head groups with free or condensed counterions).

Brotons, G.; Belloni, L.; Zemb, Th.; Salditt, T.

2006-09-01

421

Fractality in the neuron axonal topography of the human brain based on 3-D diffusion MRI  

NASA Astrophysics Data System (ADS)

In this work the fractal architecture of the neuron axonal topography of the human brain is evaluated, as derived from 3-D diffusion MRI (dMRI) acquisitions. This is a 3D extension of work performed previously in 2D regions of interest (ROIs), where the fractal dimension of the neuron axonal topography was computed from dMRI data. A group study with 18 subjects is here conducted and the fractal dimensions D f of the entire 3-D volume of the brains is estimated via the box counting, the correlation dimension and the fractal mass dimension methods. The neuron axon data is obtained using tractography algorithms on diffusion tensor imaging of the brain. We find that all three calculations of D f give consistent results across subjects, namely, they demonstrate fractal characteristics in the short and medium length scales: different fractal exponents prevail at different length scales, an indication of multifractality. We surmise that this complexity stems as a collective property emerging when many local brain units, performing different functional tasks and having different local topologies, are recorded together.

Katsaloulis, P.; Ghosh, A.; Philippe, A. C.; Provata, A.; Deriche, R.

2012-05-01

422

Curved and diffuse interface effects on the nuclear surface tension  

NASA Astrophysics Data System (ADS)

We redefine the surface tension coefficient for a nuclear Fermi-liquid drop with a finite diffuse layer. Following the Gibbs-Tolman concept, we introduce the equimolar radius Re of the droplet surface at which the surface tension is applied and the radius of tension surface Rs which provides the minimum of the surface tension coefficient ?. This procedure allows us to derive both the surface tension and the corresponding curvature correction (Tolman length) correctly for the curved and diffuse interface. We point out that the curvature correction depends significantly on the finite diffuse interface. We show that Tolman's length ? is negative for a nuclear Fermi-liquid drop. The value of the Tolman length is only slightly sensitive to the Skyrme force parametrization and equals ?=-0.36 fm.

Kolomietz, V. M.; Lukyanov, S. V.; Sanzhur, A. I.

2012-08-01

423

Sexual harassment: Organizational context and diffuse status  

Microsoft Academic Search

Data from a large survey of federal employees is utilized to compare three broad competing perspectives that suggest effects on sexual harassment within organizations. Three different viewpoints stress power differentials, minority status, and diffuse master status characteristics. Results of the study indicate that intraorganizational theories emphasizing either power inequalities or work group compositional heterogeneities are unable to account for the

Terri C. Fain; Douglas L. Anderton

1987-01-01

424

Intrinsic shortest path length: a new, accurate a priori wirelength estimator  

Microsoft Academic Search

A priori wirelength estimation is concerned with predicting various wirelength characteristics before placement. In this work we propose a novel, accurate estimator of net lengths. We observe that in \\

Andrew B. Kahng; Sherief Reda

2005-01-01

425

Nonlocal models and length scale effects on metal forming processes  

Microsoft Academic Search

The classical theories of plasticity or continuum damage mechanics do not include scale effects associated to a characteristic\\u000a length of the material, which is often present in deformation processes, and which results in a limitation of the localization\\u000a of the plastic deformation or damage in narrow bands. The numerical models based in these theories suffer from size and orientation\\u000a pathological

José M. A. César Sá; Cai Zheng

426

National Seminar on the Diffusion of New Instructional Materials and Practices. 1.0 Are There Characteristics of Particular Subject Matters That Make Products Which Are Based on Them More or Less Likely to be Adopted? and 2.0 Are There Characteristics of Developers That Tend to Inhibit or Encourage Use of Their Ideas and Products?  

ERIC Educational Resources Information Center

|Participants in a National Seminar on the Diffusion of New Instructional Materials and Practices included scientists and educators in the natural and social sciences and mathematics from universities, curriculum projects, and school districts throughout the United States. This document is the first of a series of working papers which were…

Social Science Education Consortium, Inc., Boulder, CO.

427

Correction for external mass transfer resistance in diffusive sampling  

SciTech Connect

An important source of error inherent in diffusive sampling is depletion of the analyte in the region around the open end of the sampler. Error due to depletion occurs when external mass transfer resistance is significant compared with the sampler's internal mass transfer resistance. A simple method to correct this error is presented. Multiple diffusive samplers of differing lengths are exposed simultaneously. A plot of calculated concentration of the analyte at the open end of the samplers vs. diffusive flux is extrapolated to a sampler of infinite length, yielding an estimate of concentration in the bulk atmosphere. This method was demonstrated with a diffusive sampler for water vapor by comparing extrapolated concentrations of water vapor with concentrations measured with a dew-point hygrometer.

Persoff, P.; Hodgson, A.T.

1985-11-01

428

Diffusion laws in dendritic spines  

PubMed Central

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.

2011-01-01

429

Multinomial diffusion equation.  

PubMed

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??, 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. PMID:21797338

Balter, Ariel; Tartakovsky, Alexandre M

2011-06-24

430

Gaseous diffusion system  

DOEpatents

1. A gaseous diffusion system comprising a plurality of diffusers connected in cascade to form a series of stages, each of said diffusers having a porous partition dividing it into a high pressure chamber and a low pressure chamber, and means for combining a portion of the enriched gas from a succeeding stage with a portion of the enriched gas from the low pressure chamber of each stage and feeding it into one extremity of the high pressure chamber thereof.

Garrett, George A. (Oak Ridge, TN); Shacter, John (Stamford, CT)

1978-01-01

431

Multinomial diffusion equation  

NASA Astrophysics Data System (ADS)

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??, 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.

Balter, Ariel; Tartakovsky, Alexandre M.

2011-06-01

432

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

Microsoft Academic Search

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

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

2010-01-01

433

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

NASA Astrophysics Data System (ADS)

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.

Thurlow, Paul E.; Cline, Richard W.

1993-08-01

434

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

Microsoft Academic Search

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.

R. N. Caffin

1980-01-01

435

Correlation Length Scales of Isotopic Variations Along Mid-Ocean Ridges and Upper Mantle Dynamics  

Microsoft Academic Search

How isotopic variations in basalts erupted at the Earth's surface are linked to convective mixing in the underlying mantle is a central problem in geodynamics. The objective of this study is to quantify the length scales of upper mantle heterogeneity through spatial statistical analysis of MORB. We define a characteristic length scale, the scale of segregation L, computed from the

D. W. Graham; F. J. Spera

2003-01-01

436

Trait Attribution as a Function of Hair Length and Correlates of Subjects' Preferences for Hair Style  

Microsoft Academic Search

The study was designed to examine the trait attribution process of American female college students to male stimulus targets differing in hair length and to explore the relationship between differences in preferences for hair length and differences in S characteristics of the perceiver. In a between Ss design, groups of females (N = 90) rated male stimulus targets of various

Kevin Peterson; James P. Curran

1976-01-01

437

Diffusion, Osmosis, and Dialysis  

NSDL National Science Digital Library

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.

Project, Molecular L.

438

Microwave enhanced diffusion  

SciTech Connect

The observation of more rapid reaction and/or sintering during microwave processing of ceramics has lead to speculation that microwave processing results in enhanced diffusion.'' The loss mechanisms by which microwaves interact with a crystal lattice have been reviewed. These mechanisms were evaluated with regard to the atomic theory of diffusion. The potential for these loss mechanisms to influence atomic diffusion, and thus produce enhancement will be discussed. Existing evidence, both direct and indirect, regarding microwave enhanced diffusion has been reviewed and will be discussed along with recent experimental data. 15 refs., 5 figs.

Katz, J.D.; Blake, R.D. (Los Alamos National Lab., NM (USA)); Kenkre, V.M. (New Mexico Univ., Albuquerque, NM (USA))

1991-01-01

439

Length-dependent self-assembly of oligothiophene derivatives in thin films  

Microsoft Academic Search

Thin-film aggregation characteristics of a series of oligothiophenes with a central thieno[3,4-b]thiophene ester unit and 4 (M5), 8 (M9), and 16 (M17) regioregular hexylthiophene units were investigated. These oligomers exhibited length-dependent self-assembly characteristics upon spin coating. M9 formed long fibers, while M5 and M17 formed random domains. Grazing incidence x-ray diffraction was performed to understand the reason for this length

Brian S. Rolczynski; Jodi M. Szarko; Byeongdu Lee; Joseph Strzalka; Jianchang Guo; Yongye Liang; Luping Yu; Lin X. Chen

2011-01-01

440

Ergodic versus diffusive decoherence in mesoscopic devices  

NASA Astrophysics Data System (ADS)

We report on the measurement of phase coherence length in a high-mobility two-dimensional electron gas patterned in two different geometries, a wire and a ring. The phase coherence length is extracted both from the weak localization correction in long wires and from the amplitude of the Aharonov-Bohm oscillations in a single ring, in a low-temperature regime when decoherence is dominated by electronic interactions. We show that these two measurements lead to different phase coherence lengths, namely L?wire?T-1/3 and L?ring?T-1/2. This difference reflects the fact that the electrons winding around the ring necessarily explore the whole sample (ergodic trajectories), while in a long wire the electrons lose their phase coherence before reaching the edges of the sample (diffusive regime).

Capron, Thibaut; Texier, Christophe; Montambaux, Gilles; Mailly, Dominique; Wieck, Andreas D.; Saminadayar, Laurent

2013-01-01

441

Mean-Field Theory for Diffusion-Limited Cluster Formation  

Microsoft Academic Search

A mean-field theory for the diffusion-controlled cluster formation is presented by considering the competition among the different portions of a growing cluster for the incoming diffusive particles. This competition is shown to introduce a screening length which depends inversely on the density of the cluster. The Hausdorff dimensionality D of these clusters is shown to be (d2+1)(d+1) where d is

M. Muthukumar

1983-01-01

442

Long Jumps in the Surface Diffusion of Large Molecules  

Microsoft Academic Search

We have studied the diffusion of the two organic molecules DC and HtBDC on the Cu(110) surface by scanning tunneling microscopy. Surprisingly, we find that long jumps, spanning multiple lattice spacings, play a dominating role in the diffusion of these molecules-the root-mean-square jump lengths are as large as 3.9 and 6.8 lattice spacings, respectively. The presence of long jumps is

M. Schunack; T. R. Linderoth; F. Rosei; E. Lægsgaard; I. Stensgaard; F. Besenbacher

2002-01-01

443

Coarse grained model of diffusion in entangled bidisperse polymer melts.  

PubMed

Chain diffusion is studied in mixtures of bidisperse linear polymers of same chemical identity by means of simulations. The two subpopulations are moderately to highly entangled, with the shorter chain length N(S), fulfilling N(S)N(e)> or =5. To this end, a coarse grained model calibrated to reproduce both the structure and dynamics of chains in monodisperse entangled melts is used [A. Rakshit and R. C. Picu, J. Chem. Phys. 125, 164907 (2006)]. Its performance in reproducing chain dynamics in a polydisperse melt is tested by extensively comparing the results with those obtained from an equivalent fine scale representation of the same system (a bead-spring model). The coarse grained model is used further to investigate the scaling of the diffusion coefficient with the length of the two types of chains and its dependence on the respective fractions. The model reproduces many features observed experimentally. For example, the diffusion coefficient of one of the chain types decreases with increasing the length of the other type chains. It is shown that, in this model, this effect is not linked to constraint release. When the matrix chains become sufficiently long, their length does not influence the diffusion coefficient of the short chains anymore. The diffusion coefficient of the short chains scales with their weight fraction in a manner consistent with experimental observations. In mixtures, the dynamics of the short chains is slower and that of the long chains is marginally faster than in their respective monodisperse melts. PMID:17935441

Picu, R C; Rakshit, A

2007-10-14

444

Coarse grained model of diffusion in entangled bidisperse polymer melts  

NASA Astrophysics Data System (ADS)

Chain diffusion is studied in mixtures of bidisperse linear polymers of same chemical identity by means of simulations. The two subpopulations are moderately to highly entangled, with the shorter chain length NS, fulfilling NS/Ne>=5. To this end, a coarse grained model calibrated to reproduce both the structure and dynamics of chains in monodisperse entangled melts is used [A. Rakshit and R. C. Picu, J. Chem. Phys. 125, 164907 (2006)]. Its performance in reproducing chain dynamics in a polydisperse melt is tested by extensively comparing the results with those obtained from an equivalent fine scale representation of the same system (a bead-spring model). The coarse grained model is used further to investigate the scaling of the diffusion coefficient with the length of the two types of chains and its dependence on the respective fractions. The model reproduces many features observed experimentally. For example, the diffusion coefficient of one of the chain types decreases with increasing the length of the other type chains. It is shown that, in this model, this effect is not linked to constraint release. When the matrix chains become sufficiently long, their length does not influence the diffusion coefficient of the short chains anymore. The diffusion coefficient of the short chains scales with their weight fraction in a manner consistent with experimental observations. In mixtures, the dynamics of the short chains is slower and that of the long chains is marginally faster than in their respective monodisperse melts.

Picu, R. C.; Rakshit, A.

2007-10-01

445

Diffusion-controlled first-order surface reaction in turbulent flow  

SciTech Connect

The effect of advective diffusion on the rate of reactant consumption by a first-order surface reaction is analyzed in the fast-reaction limit. The decay of reactant concentration is described by the function n(t) {approx} exp(-{lambda}t). In the limit of well-developed turbulence, the scaling estimates {lambda} {approx} L{sup -1}{kappa}{sup 3/4}{mu}{sup 1/4} and {lambda} {approx} f{kappa}{sup 3/4}{mu}{sup 1/4} are obtained,