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1

Large spin diffusion length in an amorphous organic semiconductor.  

PubMed

We directly measured a spin diffusion length (lambdas) of 13.3 nm in amorphous organic semiconductor (OS) rubrene (C42H28) by spin polarized tunneling. In comparison, no spin-conserved transport has been reported in amorphous Si or Ge. Absence of dangling bond defects can explain the spin transport behavior in amorphous OS. Furthermore, when rubrene barriers were grown on a seed layer, the elastic tunneling characteristics were greatly enhanced. Based on our findings, lambdas in single-crystalline rubrene can be expected to reach even millimeters, showing the potential for organic spintronics development. PMID:18643439

Shim, J H; Raman, K V; Park, Y J; Santos, T S; Miao, G X; Satpati, B; Moodera, J S

2008-06-01

2

Diffusion lengths in amphoteric GaAs heteroface solar cells  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

3

Diffusion lengths of silicon solar cells from luminescence images  

Microsoft Academic Search

A method for spatially resolved measurement of the minority carrier diffusion length in silicon wafers and in silicon solar cells is introduced. The method, which is based on measuring the ratio of two luminescence images taken with two different spectral filters, is applicable, in principle, to both photoluminescence and electroluminescence measurements and is demonstrated experimentally by electroluminescence measurements on a

P. Wuerfel; T. Trupke; T. Puzzer; E. Schaeffer; W. Warta; S. W. Glunz

2007-01-01

4

Pulsed ion beam measurement of defect diffusion lengths in irradiated solids.  

PubMed

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. PMID:23524408

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

2013-04-24

5

Measurement of radon diffusion length in thin membranes.  

PubMed

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

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

2012-07-01

6

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

7

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

8

Scale length of mantle heterogeneities: Constraints from helium diffusion  

NASA Astrophysics Data System (ADS)

A model of coupled He production/diffusion is used to constrain the question of whether Earth's peridotitic mantle contains ubiquitous mesoscale veins or slabs of other lithologies. The high diffusion rates of helium preclude survival of He isotope heterogeneities on scales smaller than a few tens of meters, especially if they represent long term in-growth of 4He in the mantle. For 1.5 Gyr residence times, and a diffusion coefficient of 10 - 10 m 2/s, 0.5 km slabs or 2 km cylinders will lose > 90% of in-grown 4He. However, substantial 3He/ 4He variations may persist in slabs or be induced in adjacent mantle, depending on initial He, U and Th contents. We have modeled three cases of 3He/ 4He equilibration between mantle domains: an ocean crust (OC) slab in depleted upper mantle (DMM) or in enriched mantle (BSE), and a BSE slab in DMM. For a 1 km OC slab in DMM (8 Ra today), the slab today will have 3He/ 4He of only 3 Ra, and will have influenced the surrounding mantle with 4He for > 7 km on either side. The average 3He/ 4He of this mixed zone will be < 7 Ra, even when sampled by melts over a total width of 20-50 km. For the case of a 1 km BSE slab in DMM (8 Ra today), the slab will be 37 Ra today, and will have infected a mantle domain > 16 km wide. Even with a 60 km melt sampling width, the average 3He/ 4He will be > 15 Ra. Slabs may lose their He signature by diffusion, but their presence will be recorded in the surrounding mantle. We have evaluated 3 along-axis N-MORB ridge-crest data sets in this context (MAR 25.7-26.5°S; EPR 19-23°S; SWIR 16-24° E), with a view to defining scale-lengths of He isotope variability. The average 3He/ 4He variability for these 3 areas is very small, and independent of spreading rate: 0.13, 0.19 and 0.21 Ra (± 1 ?). Since these ridges range from ultra-slow to very fast-spreading, the variability in size of along-axis magma chambers will lead inevitably to various scales of melt averaging. We conclude that these ridge areas are not sampling mantle that contains enriched veins or recycled oceanic crust slabs of significant size (> tens of meters). It appears difficult to sustain a view of the upper mantle as a ubiquitous mixture of veins and depleted matrix, with MORB always representing an averaging of this mixture.

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

2008-05-01

9

Thermal Diffusivity and Conductivity Measurements: Effect of Sample Length and Radiation  

NASA Astrophysics Data System (ADS)

Measurements of thermal diffusivity D and conductivity ? commonly show an upturn as a function of temperature. The upturn is very apparent in semi-transparent materials such as upper mantle minerals at absolute temperatures T of the order of 600-700 K. Although the effect is readily attributed to a radiative component, it shows a temperature dependence that is more characteristic of a black body (e.g., T3) than that expected from actual optical absorption spectra at high temperature for very large dimensions. When radiative conductivity ?r is obtained from optical methods, it tends begin at lower temperatures and to level off as absorption increases with T. Part of the discrepancy can be assigned to the fact that photon mean free path mfp( T) is usually comparable with sample dimensions. However, the problem is worsened in portions of the spectra by spectral path lengths (reciprocal absorption coefficients) substantially longer than sample lengths, an effect manifested in length-dependent radiative diffusion. For olivine (Mg0.91,Fe0.09)2SiO4 we have used a model of 1-dimensional spectral absorption and emission between volume elements to demonstrate that as sample length increases, ?r approaches that expected from spectral methods.

Shankland, T. J.; Schilling, F. R.; Gibert, B.; Gratz, K.

2005-12-01

10

Changes in diffusion path length with old age in diffuse optical tomography  

NASA Astrophysics Data System (ADS)

Diffuse, optical near infrared imaging is increasingly being used in various neurocognitive contexts where changes in optical signals are interpreted through activation maps. Statistical population comparison of different age or clinical groups rely on the relative homogeneous distribution of measurements across subjects in order to infer changes in brain function. In the context of an increasing use of diffuse optical imaging with older adult populations, changes in tissue properties and anatomy with age adds additional confounds. Few studies investigated these changes with age. Duncan et al. measured the so-called diffusion path length factor (DPF) in a large population but did not explore beyond the age of 51 after which physiological and anatomical changes are expected to occur [Pediatr. Res. 39(5), 889-894 (1996)]. With increasing interest in studying the geriatric population with optical imaging, we studied changes in tissue properties in young and old subjects using both magnetic resonance imaging (MRI)-guided Monte-Carlo simulations and time-domain diffuse optical imaging. Our results, measured in the frontal cortex, show changes in DPF that are smaller than previously measured by Duncan et al. in a younger population. The origin of these changes are studied using simulations and experimental measures.

Bonnéry, Clément; Leclerc, Paul-Olivier; Desjardins, Michèle; Hoge, Rick; Bherer, Louis; Pouliot, Philippe; Lesage, Frédéric

2012-05-01

11

Scale Length of Mantle Heterogeneities: Helium Diffusion Constraints  

NASA Astrophysics Data System (ADS)

While Earth's mantle is unequivocally heterogeneous, the size, formation and distribution of these geochemical heterogeneities remain enigmatic. Following the veined mantle proposals of Hanson (1977) and Wood (1979), various postulates of mesoscale lithologic heterogeneities (veins, pods, layers, plums) have been advanced. However, the issue remains contentious, and no smoking gun has survived scrutiny. Do the heterogeneities reflect large scale (tens of km) chemical variability in a lithologically homogeneous (peridotitic) mantle, or smaller mesoscale (less than a few kms) mafic layers or veins embedded in a peridotitic matrix (or both)? We argue that the high diffusion rates of helium preclude survival of He isotope heterogeneities on scales smaller than a few hundred meters, especially if they represent long term in-growth of 4He in the convecting mantle. Using a coupled He diffusion-production model, 1.5 Gy residence times, and a diffusion coefficient of 10-10 m2/sec (olivine, mid-upper mantle), 1 km slabs or 2.3 km cylinders will lose >80% of in-grown 4He. However, substantial 3/4He signatures may persist in slabs or be induced in adjacent mantle, depending on initial He, U and Th contents. We have modeled three cases of 1.5 Gy 3/4He equilibration between mantle domains: an ocean crust (OC) slab in depleted upper mantle (DMM) or in enriched mantle (BSE), and a BSE slab in DMM. For a 1 km OC slab in DMM (8 Ra today), the slab today will have 3/4He of only 3 Ra, and will have infected the surrounding mantle with 4He for >5 km on each side. The average 3/4He of this mixed zone will be <6 Ra even when sampled by melts over a total width of 20 km. For the case of a 1 km OC slab in BSE (50 Ra today), the slab will be 47 Ra today, almost fully equilibrated with ambient mantle. For the case of a 1 km BSE slab in DMM (8 Ra today), the slab will be 37 Ra today, and will have infected a mantle domain >16 km wide. Even with a 50 km melt sampling width, the average 3/4He will be >20 Ra. In essence, slabs may lose their He signature by diffusion, but it will remain recorded in the surrounding mantle; i.e. veins may run but they can't hide! For both enriched and depleted upper mantle slabs, sampled along a spreading ridge, the 3/4He variability on 10-20 km scale lengths would be easily observed; even massive along-axis melt mixing (50-100 km) would not hide these signatures. We have evaluated 3 extant ridge-crest data sets in this context (MAR 0-47S; EPR 19-23S; SWIR 16- 24E), with a view to defining scale-lengths of He isotope variability. The average 3/4He variability for these 3 areas is 0.47, 0.19 and 0.21 Ra (±1 sigma); a well-sampled sub-area on the MAR (25.7-26.5S) is 0.13 Ra. There is a monotonic variation along the SWIR, from 6.6 to 7.3 Ra; variability about a best fit line is 0.09 Ra (maximum deviation is only 0.20 Ra). At the smallest scale, a single 20 km EPR flow field shows similar variability (0.29 Ra) to the above examples. Since these ridges range from slow to very fast-spreading, the variability in size of along- axis magma chambers will lead inevitably to various scales of melt averaging. We conclude that these ridge areas are not sampling mantle that contains enriched veins or recycled oceanic crust slabs of any significant size. This is especially clear for the 500 km domain on the SWIR, where very small He variability is observed, superimposed on a large scale He gradient. In particular, the view of the upper mantle as a ubiquitous mixture of veins and depleted matrix, with MORB always representing an averaging of this mixture, appears untenable.

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

2007-12-01

12

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

2013-01-01

13

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

14

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

15

Microrheology and characteristic lengths in wormlike micelles made of a zwitterionic surfactant and SDS in brine.  

PubMed

We study the Brownian motion of probe particles embedded in a wormlike micellar fluid made of a zwitterionic surfactant N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (TDPS), sodium dodecyl sulfate (SDS), and salty water to get structural and dynamical information of the micellar network. The motion of the probe particles was tracked with diffusing wave spectroscopy, and the mean square displacement as a function of time for the particles was obtained. This allowed us to obtain the long-time diffusion coefficient for microspheres moving in the micellar network and the cage size where each particle is harmonically bound at short times in that network. The bulk mechanical susceptibility of the fluid determines the response of the probe particles excited by the thermal stochastic forces. As a consequence, the mean square displacement curves allowed us to calculate the elastic (storage) and the viscous (loss) moduli as a function of the frequency. From these curves, spanning a wide frequency range, we estimated the characteristic lengths as the mesh size, the entanglement length, the persistence length, and the contour length for micellar solutions of different zwitterionic surfactant concentration, surfactant ratio ([SDS]/[TDPS]), salt concentration, and temperature. Mesh size, entanglement length, and persistence length are almost insensitive to the change of these variables. In contrast, the contour length changes in an important way. The contour length becomes shorter as the temperature increases, and it presents a peak at a surfactant ratio of ?0.50-0.55. When salt is added to the solution, the contour length presents a peak at a salt concentration of ?0.225 M, and in some solutions, this length can reach values of ?12 ?m. Scission energies help us to understand why the contour length first increases and then decreases when salt is added. PMID:20825212

Sarmiento-Gomez, Erick; Lopez-Diaz, David; Castillo, Rolando

2010-09-30

16

Determination of diffusion lengths in silicon by an X-ray method  

NASA Technical Reports Server (NTRS)

By calibrating X-ray machine with cells of known diffusion lengths, measurements on test cells can be madeate rate of one every two minutes with standard deviation of less than two percent. test cells are compared with calibration cells whose diffusion lengths have been measured by an electron beam method.

Lamneck, J. H., Jr.

1970-01-01

17

Acid Diffusion Length in Line-and-Space Resist Patterns Fabricated by Extreme Ultraviolet Lithography  

NASA Astrophysics Data System (ADS)

Acids generated upon exposure to radiation induce the polarity change of the polymer through catalytic chain reactions in chemically amplified resists. With the reduction of feature size, the acid diffusion length increasingly becomes an important issue. In this study, we investigated the acid diffusion length in line-and-space patterns fabricated using a small field exposure tool for extreme ultraviolet (EUV) lithography and the EIDEC standard resist to clarify the acid diffusion length in a state-of-the-art resist. The acid diffusion length depended on the nominal line width and exposure dose. Upon exposure to EUV radiation with an exposure dose of 16 mJ cm-2, the acid diffusion length (three-dimensional) in a line-and-space pattern with 21 nm nominal line width was 9.5 nm.

Kozawa, Takahiro; Santillan, Julius Joseph; Itani, Toshiro

2013-07-01

18

Time and length scales for diffusion in liquids.  

PubMed

The first six even moments of the displacement of a molecule in water and an atom in liquid argon are found by molecular dynamics simulations and compared with the moments predicted by diffusion theory. We find a noticeable difference between the moments higher than the second. The ratio between predicted and calculated moments approaches unity as 1/t for times larger than 10 ps. Continuous time random walk is used to explain this slow approach of the moments to their diffusion limit. PMID:12188692

Berezhkovskii, A M; Sutmann, G

2002-06-01

19

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.] [comp.

1995-11-01

20

Diffusion length damage coefficient and annealing studies in proton-irradiated InP  

NASA Technical Reports Server (NTRS)

We report on the measurement of the diffusion length damage coefficient (K(sub L)) and the annealing characteristics of the minority carrier diffusion length (L(sub n)) in Czochralski-grown zinc-doped indium phosphide (InP), with a carrier concentration of 1 x 10(exp l8) cm(exp -3). In measuring K(sub L) irradiations were made with 0.5 MeV protons with fluences ranging from 1 x 10(exp 11) to 3 x 10(exp 13) cm(exp -2). Pre- and post-irradiation electron-beam induced current (EBIC) measurements allowed for the extraction of L(sub n) from which K(sub L) was determined. In studying the annealing characteristics of L(sub n) irradiations were made with 2 MeV protons with fluence of 5 x 10(exp 13) cm(exp -2). Post-irradiation studies of L(sub n) with time at room temperature, and with minority carrier photoinjection and forward-bias injection were carried out. The results showed that recovery under Air Mass Zero (AMO) photoinjection was complete. L(sub n) was also found to recover under forward-bias injection, where recovery was found to depend on the value of the injection current. However, no recovery of L(sub n) after proton irradiation was observed with time at room temperature, in contrast to the behavior of 1 MeV electron-irradiated InP solar cells reported previously.

Hakimzadeh, Roshanak; Vargas-Aburto, Carlos; Bailey, Sheila G.; Williams, Wendell

1993-01-01

21

Estimating the differential diffusion length of the stable water isotope signals obtained from ice core records.  

NASA Astrophysics Data System (ADS)

Stable water isotope signals retrieved from polar ice core records are smoothed by diffusion in the firn stage. The total amount of diffusion a layer has experienced can be quantified in terms of the diffusion length, which is the average displacement of a molecule due to diffusion. This length is a function of the firn temperature and the accumulation rate which makes it a valuable proxy for past local temperatures (Johnsen et al, 2000, Simonsen et al, 2011). In principle this proxy can be derived from either of the individual isotope signals (Oxygen-18 or Deuterium), but it is much better constrained when the difference in diffusion length between the two isotopes is used. The individual diffusion lengths and the differential diffusion lengths are commonly calculated using the power spectral densities (PSD) of the isotope data. The Maximum Entropy Method (MEM) is often used for the calculation of the PSD, but other methods such as the fast fourier transform or ones based on the autocorrelation series of the isotope data can also be used. However, in all these methods a parameter has to be chosen, for example the auto regression order in the MEM. Additionally, it is necessary to define a cut off frequency in order to use only the red part of the power spectrum. These choices can significantly influence diffusion length obtained with these methods. We present a new method which circumvents these issues, based on the correlation between the Oxygen-18 and Deuterium records. The measured Deuterium record is numerically diffused, after which the correlation between this record and the measured Oxygen-18 record is calculated. The correlation reaches a maximum when the diffusion lengths of the two records are equal. This allows us to reconstruct the differential diffusion length. A large number of synthetic data sets were created to (1) test this correlation method and (2), for the MEM, find the optimum values for the parameters in this method. The values found by the correlation method need to be corrected for offsets resulting from the finite sampling resolution and measurement uncertainty. The two methods yield results with comparable precision. References: Johnsen, S. et al, 2000. Diffusion of stable isotopes in polar firn and ice: the isotope effect in diffusion. In: Physics of Ice Core Records, Ed: Hondoh, T., p.121-140, Hokkaido Press, Sapporo. Simonsen, S.B. et al, 2011. Past surface temperatures at the NorthGRIP drill site from the difference in firn diffusion of water isotopes. Climate of the Past 7, 1327-1335.

van der Wel, Gerko; Fischer, Hubertus; Meijer, Harro A. J.

2013-04-01

22

Turbulent diffusion of momentum and suspended particles: A finite-mixing-length theory  

Microsoft Academic Search

A finite-mixing-length theory is presented for turbulent mixing. This theory contains Fickian diffusion as the limiting case for lm\\/L-->0, where lm is the mixing length and L is the scale of the distribution under consideration. The new model is of similar generality to that of Taylor (1921), ``Diffusion by continuous movements.'' However, while Taylor's model, being strictly Lagrangian, is difficult

Peter Nielsen; Ian A. L. Teakle

2004-01-01

23

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

24

Drift-diffusion crossover and the intrinsic spin diffusion lengths in semiconductors  

Microsoft Academic Search

We study the propagation of electron spin density polarization and spin currents in n-doped semiconductors within the two-component drift-diffusion model in an applied electric field (E). The drift and diffusion contributions to the spin currents are examined, which shows how the spin current could be enhanced. We find that there is a crossover field (Ex), where the drift and diffusion

M. Idrish Miah

2008-01-01

25

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

26

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

2014-07-01

27

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

NASA Astrophysics Data System (ADS)

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

Zhang, Wei; Vlaminck, Vincent; Pearson, John E.; Divan, Ralu; Bader, Samuel D.; Hoffmann, Axel

2013-12-01

28

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

SciTech Connect

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

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

2013-12-09

29

Lifetime and diffusion length measurements on silicon material and solar cells  

NASA Technical Reports Server (NTRS)

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

Othmer, S.; Chen, S. C.

1978-01-01

30

Characteristic lengths for evaporation suppression from patchy porous surfaces  

NASA Astrophysics Data System (ADS)

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

Lehmann, Peter; Or, Dani

2014-05-01

31

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

NASA Astrophysics Data System (ADS)

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

Bjorgaard, Josiah A.; Köse, Muhammet E.

2013-05-01

32

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

NASA Technical Reports Server (NTRS)

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

Flat, A.; Milnes, A. G.

1978-01-01

33

Minority carrier diffusion lengths and absorption coefficients in silicon sheet material  

SciTech Connect

One of the indicators which determine a material's potential for use as a solar cell is the minority carrier diffusion length (L/sub D/) of the material. To determine L/sub D/ a surface photovoltage (SPV) technique is used. This method is dependent upon an accurate knowledge of the optical absorption coefficient as function of wavelength. The results for the absorption coefficients for various types of silicon sheet material are compared to those previously used in the two models. The resultant effect upon the diffusion length is also discussed in detail. 7 refs.

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

1980-01-01

34

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

NASA Astrophysics Data System (ADS)

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

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

1985-03-01

35

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

36

Electron-beam induced current measurements of diffusion length in Si doped MOCVD grown GaN  

Microsoft Academic Search

This paper reports on the electron-beam induced current (EBIC) measurement of minority carrier diffusion length as a function of electron beam acceleration voltage in Si-doped, MOCVD grown, gallium nitride. The measured diffusion length varied from 160nm at 8kV to 220nm at 15kV. Possible reasons for the observed diffusion length dependence on voltage are discussed.

D. Wee; G. Parish; B. D. Nener

2010-01-01

37

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

38

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

PubMed

We report a simple, controlled doping method for achieving n-type, intrinsic, and p-type lead sulfide (PbS) nanowires (NWs) grown by chemical vapor deposition without introducing any impurities. A wide range of carrier concentrations is realized by adjusting the ratio between the Pb and S precursors. The field effect electron mobility of n-type PbS NWs is up to 660 cm(2)/(V s) at room temperature, in agreement with a long minority carrier diffusion length measured by scanning photocurrent microscopy (SPCM). Interestingly, we have observed a strong dependence of minority carrier diffusion length on gate voltage, which can be understood by considering a carrier concentration dependent recombination lifetime. The demonstrated ambipolar doping of high quality PbS NWs opens up exciting avenues for their applications in photodetectors and photovoltaics. PMID:23066756

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

2012-11-14

39

Diffusion length measurements of thin GaAs solar cells by means of energetic electrons  

NASA Technical Reports Server (NTRS)

A calculation of the short circuit current density (j sub sc) of a thin GaAs solar cell induced by fast electrons is presented. It is shown that in spite of the disparity in thickness between the N-type portion of the junction and the P-type portion of the junction, the measurement of the bulk diffusion length L sub p of the N-type part of the junction is seriously hampered due to the presence of a sizable contribution to the j sub sc from the P-type region of the junction. Corrections of up to 50% had to be made in order to interpret the data correctly. Since these corrections were not amenable to direct measurements it is concluded that the electron beam method for the determination of the bulk minority carrier diffusion length, which works so well for Si solar cells, is a poor method when applied to thin GaAs cells.

Vonross, O.

1980-01-01

40

Study of the Correlation Between Dislocations and Diffusion Length in In(49)Ga(51)P Solar Cells.  

National Technical Information Service (NTIS)

A quantitative, contact-free method for extracting minority carrier diffusion length is used to measure the relatively small variations in diffusion length associated with dislocation bands in mismatched epitaxy in the p-type region of a two dimensional h...

S. E. Williams

2008-01-01

41

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

NASA Technical Reports Server (NTRS)

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

Hakimzadeh, Roshanak; Bailey, Sheila G.

1993-01-01

42

Measurement of the coherence length of diffusely scattered laser beams with adaptive photodetectors  

NASA Astrophysics Data System (ADS)

Original experiments on measurements of the coherence length of diffusely scattered CW laser beams using GaAs adaptive photodetectors based on the photo-EMF effect are presented. Simplicity of the configuration, capability to detect aberrated speckle-like wavefronts with high signal-to-noise ratio, and potentially high speed of operation make this configuration potentially useful for Optical Coherence Tomography and Laser Ranging.

Carrasco, M. L. Arroyo; Montero, P. Rodr?´guez; Stepanov, S.

1998-12-01

43

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

NASA Astrophysics Data System (ADS)

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 SiNx 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.

Toušek, Ji?í; Toušková, Jana; Poruba, Aleš; Hlídek, Pavel; Lörin?ík, Jan

2006-12-01

44

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

45

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

46

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

PubMed

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. PMID:23968156

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

2013-01-01

47

Determination of carrier diffusion length in p- and n-type GaN  

NASA Astrophysics Data System (ADS)

Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active layer capped with either 500 nm p- GaN or 1300 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a function of the top GaN thickness upon photogeneration near the surface region by above bandgap excitation. Taking into consideration the absorption in the active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be about 92 ± 7 nm and 68 ± 7 nm for Mg-doped p-type GaN and 432 ± 30 nm and 316 ± 30 nm for unintentionally doped n-type GaN, respectively. Cross-sectional cathodoluminescence line-scan measurement was performed on a separate sample and the diffusion length in n-type GaN was measured to be 280 nm.

Hafiz, Shopan; Metzner, Sebastian; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Karbaum, Christopher; Bertram, Frank; Christen, Jürgen; Gil, Bernard; Özgür, Ümit

2014-03-01

48

Influence of Different Diffuser Angle on Sedan's Aerodynamic Characteristics  

NASA Astrophysics Data System (ADS)

The aerodynamic characteristics have a great influence on the fuel economics and the steering stability of a high speed vehicle. The underbody rear diffuser is one of important aerodynamic add-on devices. The parameters of the diffuser, including the diffuser angle, the number and the shape of separators, the shape of the end plate and etc, will affect the underbody flow and the wake. Here, just the influence of the diffuser angle was investigated without separator and the end plate. The method of Computational Fluid Dynamics was adopted to study the aerodynamic characteristics of a simplified sedan with a different diffuser angle respectively. The diffuser angle was set to 0°, 3°, 6°, 9.8° and 12° respectively. The diffuser angle of the original model is 9.8°. The conclusions were drawn that when the diffuser angle increases, the underbody flow and especially the wake change greatly and the pressure change correspondingly; as a result, the total aerodynamic drag coefficients of car first decrease and then increases, while the total aerodynamic lift coefficients decrease.

Hu, Xingjun; Zhang, Rui; Ye, Jian; Yan, Xu; Zhao, Zhiming

49

Quantifying Characteristic Length Scales and Patterns in Topography  

NASA Astrophysics Data System (ADS)

The geometry of mountain topography depends on climate, tectonic, and biologic processes that operate on different temporal and spatial scales. Quantitative measures of landscape geometry are of interest for a) identifying potential correlations with the different types of processes, and b) for comparing observed topography with calibrated landscape evolution models of different regions. Over the years, several of these geomorphic metrics have been developed and used. Most of these metrics are regional values, i.e. they are calculated over an area of specific extent. Usually a region's typical horizontal length scale, like the average ridge-to-valley-distance, is used for this. However, this value is often chosen arbitrarily from a visual assessment of the landscape. In this study we aim to develop a quantitative measure of landscape properties that identifies dominant trends in drainage spacing and orientation. This is done by taking into account variations in topographic relief on different wavelenghts. More specifically, we use an autocorrelation function that is evaluated for different directions, thereby identifying prevalent orientation of features. The area of interest is then subdivided into parts of the thus obtained size and the process repeated, so that higher order structures are revealed. The results not only provides a size for the area over which other geomorphic metrics can be calculated such as the mean slope or the hypsometric integral, but may also be used as an additional measure for the form of the landscape itself. The method is applied to three regions along the South American Pacific coastal areas between latitudes of 26°S and 40°S. The study areas have distinctly different climate and vegetation conditions, showing the effect of different landscape forms on the values obtained. Results indicate a systematic variation between the three investigated regions. In the northern drier part of the coast results indicate large variations in the obtained correlation lengths depending on orientation and distinct higher order features. This is in stark contrast to the southern most region where little variation in correlation length and only weak secondary structures can be seen.

Schmiddunser, Matthias; Ehlers, Todd A.

2014-05-01

50

Characteristic length of an AdS/CFT superconductor  

SciTech Connect

We investigate in more detail the holographic model of a superconductor recently found by Hartnoll, Herzog, and Horowitz [Phys. Rev. Lett. 101, 031601 (2008)], which is constructed from a condensate of a charged scalar field in AdS{sub 4}-Schwarzschild background. By analytically studying the perturbation of the gravitational system near the critical temperature T{sub c}, we obtain the superconducting coherence length proportional to 1/{radical}(1-T/T{sub c}) via AdS/CFT (anti-de Sitter/conformal field theory) correspondence. By adding a small external homogeneous magnetic field to the system, we find that a stationary diamagnetic current proportional to the square of the order parameter is induced by the magnetic field. These results agree with Ginzburg-Landau theory and strongly support the idea that a superconductor can be described by a charged scalar field on a black hole via AdS/CFT duality.

Maeda, Kengo [Department of Engineering, Shibaura Institute of Technology, Saitama, 330-8570 (Japan); Okamura, Takashi [Department of Physics, Kwansei Gakuin University, Sanda, 669-1337 (Japan)

2008-11-15

51

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

52

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

53

Characteristics of donkey spermatozoa along the length of the epididymis.  

PubMed

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

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

2012-01-01

54

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

NASA Technical Reports Server (NTRS)

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

Leon, R. P.

1987-01-01

55

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

NASA Technical Reports Server (NTRS)

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

Leon, R. P.

1987-01-01

56

Temperature dependence of diffusion length, lifetime and minority electron mobility in GaInP  

SciTech Connect

The mobility of electrons in double heterostructures of p-type Ga{sub 0.50}In{sub 0.50}P has been determined by measuring minority carrier diffusion length and lifetime. The minority electron mobility increases monotonically from 300?K to 5?K, limited primarily by optical phonon and alloy scattering. Comparison to majority electron mobility over the same temperature range in comparably doped samples shows a significant reduction in ionized impurity scattering at lower temperatures, due to differences in interaction of repulsive versus attractive carriers with ionized dopant sites. These results should be useful in modeling and optimization for multi-junction solar cells and other optoelectronic devices.

Schultes, F. J.; Haegel, N. M., E-mail: nmhaegel@nps.edu [Physics Department, Naval Postgraduate School, Monterey, California 93943 (United States); Christian, T.; Alberi, K.; Fluegel, B. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Jones-Albertus, R.; Pickett, E.; Liu, T.; Misra, P.; Sukiasyan, A.; Yuen, H. [Solar Junction, Inc., San Jose, California 95131 (United States)] [Solar Junction, Inc., San Jose, California 95131 (United States)

2013-12-09

57

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

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

58

Measurement of diffusion length, lifetime, and surface recombination velocity in thin semiconductor layers  

NASA Astrophysics Data System (ADS)

A small-signal admittance method is developed for the determination of two important parameters affecting the performance of several semiconductor devices with thin layers such as integrated-injection-logic and MOS transistors, OCHI-HLE, BSF and TJ solar cells. These parameters, the minority-carrier diffusion length (or the minority-carrier lifetime) and the surface recombination velocity, are found using a combination of low-frequency and high-frequency admittance measurements. The theoretical base of the method and experimental results showing its application and usefulness are presented.

Gonzalez, F. N.; Neugroschel, A.

1984-04-01

59

Temperature dependence of diffusion length, lifetime and minority electron mobility in GaInP  

NASA Astrophysics Data System (ADS)

The mobility of electrons in double heterostructures of p-type Ga0.50In0.50P has been determined by measuring minority carrier diffusion length and lifetime. The minority electron mobility increases monotonically from 300 K to 5 K, limited primarily by optical phonon and alloy scattering. Comparison to majority electron mobility over the same temperature range in comparably doped samples shows a significant reduction in ionized impurity scattering at lower temperatures, due to differences in interaction of repulsive versus attractive carriers with ionized dopant sites. These results should be useful in modeling and optimization for multi-junction solar cells and other optoelectronic devices.

Schultes, F. J.; Christian, T.; Jones-Albertus, R.; Pickett, E.; Alberi, K.; Fluegel, B.; Liu, T.; Misra, P.; Sukiasyan, A.; Yuen, H.; Haegel, N. M.

2013-12-01

60

Investigation of the accuracy of the spectral photocurrent method for the determination of minority carrier diffusion length  

NASA Astrophysics Data System (ADS)

The non-scanning, junction-based photocurrent method is one of many techniques that have been devised to determine the minority carrier diffusion length in semiconductor materials. The accuracy of this method is the subject of this paper and the investigation focuses on the theoretical equation that relates the diffusion length to the measured photocurrent produced by a Schottky barrier diode. Specifically, the investigation concentrates on a commonly used assumption in the derivation of this equation, which is that carriers arriving at the edge of the depletion region are swept away from the depletion edge toward the surface barrier at a velocity that is much greater than the diffusion velocity. The subsequent analysis and the results presented in this paper are based on experiments using p-type GaN. The results obtained from numerical simulations show that both velocities have comparable magnitude and the assumption in question is technically incorrect, especially when the diffusion length is very short, as is common for p-type GaN. However, further analysis also shows that in practice this does not adversely affect the accuracy of the diffusion values calculated. In fact, when the diffusion length is very short, the common equation results in calculated diffusion length values that are more accurate compared to those derived from the more detailed equation. This is an indirect consequence of the choice of the effective depletion width and hence, the relative proportion of the drift and diffusion currents.

Wee, D.; Parish, G.; Nener, B.

2012-04-01

61

Measurement of Minority Charge Carrier Diffusion Length in Gallium Nitride Nanowires Using Electron Beam Induced Current (EBIC).  

National Technical Information Service (NTIS)

Electron Beam Induced Current (EBIC) measurements were performed on GaN nanowires to determine minority charge carrier diffusion length, Ld. Although EBIC has been used to characterize bulk and thin film materials, very little is known about near contact ...

C. P. Ong

2009-01-01

62

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

63

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

64

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

65

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

66

Depth profiling of the minority-carrier diffusion length in intrinsically gettered silicon by electron-beam-induced current  

Microsoft Academic Search

A new electron-beam-induced current method is proposed for the depth profiling of nonuniform minority-carrier diffusion lengths in semiconductors. An induced current scan is obtained on a Schottky diode formed on the surface of a beveled sample and converted into a collection efficiency profile &eegr;(z). From this profile the depth distribution of the diffusion length L(z) is deduced using a direct

C. Donolato; M. Kittler

1988-01-01

67

Turbulent transport, characteristic length and time scales above and within the BEMA forest site at Castelporziano  

NASA Astrophysics Data System (ADS)

Turbulent transport characteristics were determined above and inside the BEMA-forest to estimate the time and length scales for the diffusive transport of trace constituents like VOCs between the canopy and the atmosphere. The Eulerian ( ?T) and Lagrangian ( ?L) time scales for turbulent transport in the crown region during neutral to unstable conditions are found to be less than 10 2 s. Inside the canopy for heights below z/ hc = 0.9 during free convective conditions with small u ? (and u ? < w ?), ?T and ?L increased up to 2 × 10 2-6 × 10 2 s. When mechanical turbulence caused more intensive mixing ( u ? > w ?) also down to the trunk space atmosphere, values of about ?T ? 2 × 10 2 were determined for z/ hc < 0.9. Time scales ?crt for chemical reactions of VOC with radicals (OH, NO 3) mostly fulfil the relation ?crt > ?T, ?L for compounds emitted from the crown. Only for ?T > 2 × 10 2 the relation ?crt ? ?T holds for some compounds in the lower canopy and an influence of chemical reactions on the net VOC flux to the atmosphere can be expected.

Zelger, Michael; Schween, Jan; Reuder, Jochen; Gori, Tullio; Simmerl, Karin; Dlugi, Ralph

68

Unambiguous distinction between diffusion length and surface recombination velocity of solar cells at different excitation levels  

NASA Astrophysics Data System (ADS)

In this work we present a conclusive separation of bulk and surface recombination properties of solar cells. For this purpose, bifacial silicon solar cells were fabricated. The backside differential spectral response of the cells has been measured in the presence of bias light, both with and without backside passivation by means of corona charging on top of a thermal oxide. Employing the common one-dimensional Shockley model, the measurement curves have been simulated. This enables the base diffusion length to be distinguished from the backside surface recombination velocity. As such, their values have been determined individually. Repeating this procedure for different intensities of bias light has yielded the nonlinear behavior of the recombination mechanisms. By applying the Schockley-Read-Hall recombination theory, it was deduced that Fe interstitials presumably are the predominant bulk recombination centers.

Wawer, P.; Rochel, M.; Wagemann, H.-G.

1999-06-01

69

Minority carrier diffusion lengths and absorption coefficients in silicon sheet material  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

70

Metal content of multicrystalline silicon for solar cells and its impact on minority carrier diffusion length  

NASA Astrophysics Data System (ADS)

Instrumental neutron activation analysis was performed to determine the transition metal content in three types of silicon material for cost-efficient solar cells: Astropower silicon-film sheet material, Baysix cast material, and edge-defined film-fed growth (EFG) multicrystalline silicon ribbon. The dominant metal impurities were found to be Fe (6×1014 cm-3 to 1.5×1016 cm-3, depending on the material), Ni (up to 1.8×1015 cm-3), Co (1.7×1012 cm-3 to 9.7×1013 cm-3), Mo (6.4×1012 cm-3 to 4.6×1013 cm-3), and Cr (1.7×1012 cm-3 to 1.8×1015 cm-3). Copper was also detected (less than 2.4×1014 cm-3), but its concentration could not be accurately determined because of a very short decay time of the corresponding radioactive isotope. In all samples, the metal contamination level would be sufficient to degrade the minority carrier diffusion length to less than a micron, if all metals were in an interstitial or substitutional state. This is a much lower value than the actual measured diffusion length of these samples. Therefore, most likely, the metals either formed clusters or precipitates with relatively low recombination activity or are very inhomogeneously distributed within the samples. No significant difference was observed between the metal content of the high and low lifetime areas of each material. X-ray microprobe fluorescence spectrometry mapping of Astropower mc-Si samples confirmed that transition metals formed agglomerates both at grain boundaries and within the grains. It is concluded that the impact of metals on solar cell efficiency is determined not only by the total metal concentration, but also by the distribution of metals within the grains and the chemical composition of the clusters formed by the metals.

Istratov, A. A.; Buonassisi, T.; McDonald, R. J.; Smith, A. R.; Schindler, R.; Rand, J. A.; Kalejs, J. P.; Weber, E. R.

2003-11-01

71

Studies on the starting transient of a straight cylindrical supersonic exhaust diffuser: Effects of diffuser length and pre-evacuation state  

Microsoft Academic Search

Effects of essential performance parameters on the starting transient of a straight cylindrical supersonic exhaust diffuser (SED) are numerically investigated. Diffuser starting and evacuation transients are examined in terms of SED lengths and pre-evacuation configuration. Preconditioned Favre-averaged Navier–Stokes equations incorporated with a low Reynolds number turbulence model and Sakar’s method to treat turbulence compressibility is solved for strongly turbulent all-Mach

Byung Hoon Park; Ji Hyung Lee; Woongsup Yoon

2008-01-01

72

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

73

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

74

An electron beam induced current method of determining minority carrier diffusion lengths in thin film solar cells  

Microsoft Academic Search

Minority carrier diffusion lengths were determined on both sides of the Cu(x)S\\/CdS heterojunction in polycrystalline thin film solar cells by an electron beam induced current (EBIC) method. This method uses a beam of electrons about 250 A in diameter to generate excess electron-hole pairs (EHP) in local regions of the cell. The average diffusion distance of the carriers is characterized

J. J. Oakes; I. G. Greenfield; L. D. Partain

1975-01-01

75

Characteristic length scale of critical ventilation velocity in tunnel smoke control  

Microsoft Academic Search

This paper investigates the characteristic length scale in an analytical correlation of critical ventilation velocity. The critical ventilation velocity is defined as the minimum airflow velocity to prevent smoke backlayering and is often used for smoke control in tunnels. Using a one-dimensional assumption of uniform mixing, the correlation of critical ventilation velocity was derived from the Froude number, which considered

Kai Kang

2010-01-01

76

Predicting orbital debris shape and orientation effects on spacecraft shield ballistic limits based on characteristic length  

Microsoft Academic Search

We propose the use of “characteristic length,” based on radar cross section, as a metric for comparing the performance of orbital debris impactors of differing shapes, and the use of NASA's standard breakup model (SBM) “flake” shape as the representative particle for predicting orbital debris penetration effects. We also propose the use of a 26-view methodology for examining non-spherical particles

J. E. Williamsen; S. W. Evans

2006-01-01

77

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

PubMed

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

Sasaki, Kazushige; Toyama, Sho; Ishii, Naokata

2014-07-15

78

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

79

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

SciTech Connect

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

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

2013-08-20

80

Characteristic Length of Energy-containing Structures at the Base of a Coronal Hole  

NASA Astrophysics Data System (ADS)

An essential parameter for models of coronal heating and fast solar wind acceleration that rely on the dissipation of MHD turbulence is the characteristic energy-containing length ? of the squared velocity and magnetic field fluctuations (u 2 and b 2) transverse to the mean magnetic field inside a coronal hole (CH) at the base of the corona. The characteristic length scale directly defines the heating rate. We use a time series analysis of solar granulation and magnetic field measurements inside two CHs obtained with the New Solar Telescope at Big Bear Solar Observatory. A data set for transverse magnetic fields obtained with the Solar Optical Telescope/Spectro-Polarimeter on board the Hinode spacecraft was utilized to analyze the squared transverse magnetic field fluctuations b_t^2. Local correlation tracking was applied to derive the squared transverse velocity fluctuations u 2. We find that for u 2 structures, the Batchelor integral scale ? varies in a range of 1800-2100 km, whereas the correlation length sigmav and the e-folding length L vary between 660 and 1460 km. Structures for b_t^2 yield ? ? 1600 km, sigmav ? 640 km, and L ? 620 km. An averaged (over ?, sigmav, and L) value of the characteristic length of u 2 fluctuations is 1260 ± 500 km, and that of b_t^2 is 950 ± 560 km. The characteristic length scale in the photosphere is approximately 1.5-50 times smaller than that adopted in previous models (3-30 × 103 km). Our results provide a critical input parameter for current models of coronal heating and should yield an improved understanding of fast solar wind acceleration.

Abramenko, V. I.; Zank, G. P.; Dosch, A.; Yurchyshyn, V. B.; Goode, P. R.; Ahn, K.; Cao, W.

2013-08-01

81

Spin-Diffusion Lengths in Ag(4%Sn) and Cu(2%Ge) alloys  

NASA Astrophysics Data System (ADS)

Alloying Ag with a little Sn, or Cu with a little Ge, greatly increases elastic scattering of electrons---i.e., greatly decreases the electron mean-free-path (mfp), but does not produce much spin-flipping---i.e., leaves the electron spin-diffusion length, l, relatively long. Thus, dilute AgSn and CuGe alloys were used to study effects of changing the mfp on current-perpendicular-to-plane (CPP) magnetoresistance [1] and current-induced magnetization switching (CIMS) [2], while leaving spin-flipping weak. Published transport data in dilute AgSn and CuGe alloys give only lower bounds for l [3-5]. We find l = 34 ± 4 nm for Ag(4%Sn) and l = 125 ± 10 nm for Cu(2%Ge). [1] K. Eid et al., J. Magn. Magn. Mat. 224, L205 (2001). [2] N. Theodoropoulou et al., Phys. Rev. B (rapid comm.) in press. [3] S.-F.Lee et al., J. Magn. Magn. Mat. 118, L1 (993). [4] J. Bass et al, Mat. Sci. and Eng. B31, 77 (1995). [5] J. Bass and W.P. Pratt Jr., J. Phys. Cond. Matt. 19, 183201 (2007).

Sharma, Amit; Richard, Brandon; Fowler, Quinton; Loloee, Reza; Pratt, William, Jr.; Bass, Jack

2008-03-01

82

Diffusion characteristics of a T-type microchannel with different configurations and inlet angles.  

PubMed

A series of symmetrical and asymmetrical microfluidic T-sensors with different inlet angles were fabricated to study the mixing characteristics of a T-type microstructure for generating concentration gradient. Computational fluid dynamics (CFD) simulations showed that the concentration gradient, transition zone and diffusion length were different for various configurations and inlet angles. Quick mix and sharp concentration gradient occurred in the asymmetrical structure with large inlet angle. The observed concentration gradients in the fabricated microchannel were consistent with the theoretical prediction. In this microstructure, stagnant zone and z-direction diffusion also affected the concentration gradient. Based on the simulation results, the microfluidic structure was optimized to generate desired concentration gradient for a cell-based study. PMID:17575354

Yang, Jun; Pi, Xitian; Zhang, Liguo; Liu, Xiangshao; Yang, Jing; Cao, Yi; Zhang, Wenxian; Zheng, Xiaolin

2007-06-01

83

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

84

Neighborhood characteristics and leukocyte telomere length: The Multi-Ethnic Study of Atherosclerosis.  

PubMed

Telomeres are the protective caps at the ends of eukaryotic chromosomes. Telomeres get shorter each time a cell divides, and critically shortened telomeres trigger cellular senescence. Thus, telomere length is hypothesized to be a biological marker of aging. The purpose of this study was to examine the association between neighborhood characteristics and leukocyte telomere length. Using data from a subsample (n=978) of the Multi-Ethnic Study of Atherosclerosis, a population-based study of women and men aged 45-84, we found that neighborhood social environment (but not neighborhood socioeconomic disadvantage) was associated with telomere length. Respondents who lived in neighborhoods characterized by lower aesthetic quality, safety, and social cohesion had shorter telomeres than those who lived in neighborhoods with a more salutary social environment, even after adjusting for individual-level socioeconomic status and biomedical and lifestyle factors related to telomere length. Telomere length may be one biological mechanism by which neighborhood characteristics influence an individual?s risk of disease and death. PMID:24859373

Needham, Belinda L; Carroll, Judith E; Diez Roux, Ana V; Fitzpatrick, Annette L; Moore, Kari; Seeman, Teresa E

2014-07-01

85

Potential fluctuations, diffusion length and lateral photovoltage in hydrogenated amorphous silicon and silicon-germanium thin films  

Microsoft Academic Search

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

Alok Srivastava; S. C. Agarwal

2002-01-01

86

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

NASA Technical Reports Server (NTRS)

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

Leon, R. P.

1987-01-01

87

Flow development and turbulence length scales within an annular gas turbine exhaust diffuser  

Microsoft Academic Search

This paper presents the experimental investigation of a scaled down model of a PGT10 gas turbine diffuser by Nuovo Pignone S.p.A. The model was designed to operate in geometric and Reynolds number similarity with the GT diffuser, and 24 guide vanes are mounted at inlet to reproduce typical inlet conditions of an industrial gas turbine diffuser. The PGT10 diffuser has

Stefano Ubertini; Umberto Desideri

2000-01-01

88

Method to extract diffusion length from solar cell parameters-Application to polycrystalline silicon  

NASA Astrophysics Data System (ADS)

A closed form, analytical expression for the interdependence of the effective diffusion length Leff and the open-circuit voltage of solar cells is derived for the parallel connection of recombination in the space-charge region and in the neutral base region. This expression allows for the calculation of Leff from the open-circuit voltage, the short-circuit current, and the base doping of the solar cell as the only quantities that need to be determined experimentally. Values of Leff calculated with our method match with an accuracy of 35% values that are determined experimentally by quantum-efficiency measurements of silicon solar cells. The agreement holds in a range 0.3 ?m

Taretto, K.; Rau, U.; Werner, J. H.

2003-05-01

89

Probing the role of chain length on the diffusion dynamics of ?-conjugated polymers by fluorescence correlation spectroscopy.  

PubMed

We investigate the role of the chain length and molecular weight distribution on the diffusion dynamics of freshly synthesized MEH-PPV polymer chains. For the above purpose, a new technique based on combination of size exclusion chromatography (SEC) with fluorescence correlation spectroscopy (FCS) is developed to probe the diffusion dynamics of a narrow molecular weight distribution of fractionated samples of 20-500 kDa. The narrow dispersed samples were characterized by absorbance, emission, and time-resolved fluorescence decay techniques. The results revealed that the properties of fractionated samples were almost uniform for a wide range of molecular weights. A maximum entropy based method for FCS data analysis is employed to obtain the correct diffusion coefficients of the polymer chains with heterogeneous dynamics. The FCS experiment on the unfractionated broad molecular weight sample is not enough to establish the correlation between the molecular weight of the chains with diffusion dynamics and emphasized the need for relatively monodispersed ?-conjugated polymers. FCS results show that higher molecular weight chains diffuse much faster than shorter ones. Atomic force microscopy revealed that 300 kDa polymers produced 130 nm particles, whereas 50 kDa polymer chains formed micrometer size aggregates. At higher molecular weights, the strong chain interactions promote the formation of globular (or tightly packed) particles which diffuse faster in solution. The low molecular weight chains experience strong interparticle interaction; as a consequence, the diffusion of chains becomes slower. In the present investigation, we demonstrate the need for the narrow polydisperse sample for establishing the correlation between diffusion dynamics and chain length (or molecular weights) of ?-conjugated polymers using a single molecule spectroscopy technique such as FCS. PMID:21842892

Murthy, A V R; Goel, Mahima; Patil, Shivprasad; Jayakannan, M

2011-09-22

90

Fracture characteristics of TMCP and QT steel weldments with respect to crack length  

Microsoft Academic Search

This experimental investigation focuses on an evaluation of fracture characteristics of API 2W Gr.50 (TMCP) and 580MPa class high-strength steel (QT) weldments with respect to crack length to width ratio. Crack tip opening displacement (CTOD) values from single edge notched bending (SENB) specimen are associated with the Charpy toughness of root weld located at the middle of the specimen thickness

Y. T. Shin; S. W. Kang; H. W. Lee

2006-01-01

91

Discharge characteristics of magnetron cells with different lengths in ultrahigh vacuum  

Microsoft Academic Search

Discharge characteristics of several magnetron cells have been measured at different experimental conditions. The cell diameter was always 27mm, while the length was between 13 and 50mm. The voltage was varied between 1 and 8kV. The magnetic field and pressure were constant at 0.13T and 1×10?8mbar, respectively. The maximum current through the cell was found to be a strong function

Alenka Vesel; Miran Mozeti?; Anton Zalar

2003-01-01

92

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

NASA Technical Reports Server (NTRS)

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

Ghaderi, M.; Gupta, A. K.

2003-01-01

93

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

PubMed Central

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

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

2011-01-01

94

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

95

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

96

Penetration and lateral diffusion characteristics of polycrystalline graphene barriers.  

PubMed

We report penetration and lateral diffusion behavior of environmental molecules on synthesized polycrystalline graphene. Penetration occurs through graphene grain boundaries resulting in local oxidation. However, when the penetrated molecules diffuse laterally, the oxidation region will expand. Therefore, we measured the lateral diffusion rate along the graphene-copper interface for the first time by the environment-assisted crack growth test. It is clearly shown that the lateral diffusion is suppressed due to the high van der Waals interaction. Finally, we employed bilayer graphene for a perfect diffusion barrier facilitated by decreased defect density and increased lateral diffusion path. PMID:24213805

Yoon, Taeshik; Mun, Jeong Hun; Cho, Byung Jin; Kim, Taek-Soo

2014-01-01

97

Measurement of carrier lifetime, effective recombination velocity, and diffusion length near the grain boundary using the time-dependent electron-beam-induced current  

Microsoft Academic Search

The apparatus is described that has been used to determine the lifetime, the effective recombination velocity, and the diffusion length near the grain boundary in a polycrystalline silicon solar cell. The lifetime has been estimated from rise of the electron-beam-induced current after switching on the incident electron beam; the diffusion length and the effective recombination velocity have been determined from

A. Romanowski; D. B. Wittry

1986-01-01

98

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

Microsoft Academic Search

The near-field electron beam induced current technique is used to study the minority carrier effective diffusion length versus electron beam energy on structures containing spherical Ge nanocrystals (NCs) with diameters of 50 nm and 70 nm formed by a two step dewetting\\/nucleation process. For both nanocrystal sizes, the effective diffusion length increases with the electron beam energy and then decreases

Quang-Tri Doan; Abdelillah El Hdiy; Michel Troyon

2011-01-01

99

Determination of carrier diffusion length in MOCVD-grown GaN epilayers on sapphire by optical techniques  

Microsoft Academic Search

Two optical techniques for the determination of a bipolar diffusion length LD of optically excited carriers in GaN epitaxial layers, namely a time-resolved picosecond four-wave mixing (FWM) on free carrier grating and time-integrated photoluminescence (PL) are presented and examined. The PL technique is based on time-integrated photoluminescence (PL) spectra measurements from the front and back sides of the sample under

E. V. Lutsenko; A. L. Gurskii; V. N. Pavlovskii; G. P. Yablonskii; T. Malinauskas; K. Jaraši?nas; B. Schineller; M. Heuken

2006-01-01

100

Fluorescence Correlation Spectroscopy Measurements of the Membrane Protein TetA in Escherichia coli Suggest Rapid Diffusion at Short Length Scales  

PubMed Central

Structural inhomogeneities in biomembranes can lead to complex diffusive behavior of membrane proteins that depend on the length or time scales that are probed. This effect is well studied in eukaryotic cells, but has been explored only recently in bacteria. Here we used fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS) to study diffusion of the membrane protein TetA-YFP in E. coli. We find that the diffusion constant determined from FRAP is comparable to other reports of inner membrane protein diffusion constants in E. coli. However, FCS, which probes diffusion on shorter length scales, gives a value that is almost two orders of magnitude higher and is comparable to lipid diffusion constants. These results suggest there is a population of TetA-YFP molecules in the membrane that move rapidly over short length scales (? 400 nm) but move significantly more slowly over the longer length scales probed by FRAP.

Chow, David; Guo, Lin; Gai, Feng; Goulian, Mark

2012-01-01

101

Characteristics of Cluster Implantation and Low Diffusion Annealing  

NASA Astrophysics Data System (ADS)

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 B18Hx+ 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 B18Hx+ and FLA can make the low sheet resistance and the fine crystal recovery for USJ formation such a SDE. Moreover, the combined process of C7Hx+ implantation and FLA can make the high stress region for nMOSFET by the high substitutional Carbon. If both of B18Hx+ implantation and C7Hx+ 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; Ootsuka, Fumio; Aoyama, Takayuki

2008-11-01

102

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

103

Measurement of diffusion lengths in quaternary semiconducting thin layers by spectrum imaging  

NASA Astrophysics Data System (ADS)

A method is described to detect and measure diffusion in complex layer systems. The technique of spectrum imaging is a combination of electron energy-loss spectroscopy and imaging in a transmission electron microscope with imaging energy filter. It allows to extract chemical profiles with a spatial resolution of about 1 nm at a compositional sensitivity better than 1 at% for most elements. This has been applied to multilayers of quaternary semiconductors, where simple electron microscopy based imaging techniques cannot distinguish between the diffusion of different atomic species. The diffusivities of sulphur in ZnMgSSe/ZnSe quantum well laser structures and of magnesium and manganese across interfaces in CdMnTe/CdTe/CdMgTe quantum wells have been determined.

Walther, T.

2001-12-01

104

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

105

Growth characteristics of polycyclic aromatic hydrocarbons in dimethyl ether diffusion flame  

Microsoft Academic Search

The growth characteristics of polycyclic aromatic hydrocarbons (PAHs) in laminar dimethyl ether (DME) diffusion flame were investigated experimentally, and we assumed that the growth of PAHs within the flame was predominantly due to methyl addition\\/cyclization (MAC) mechanism. Methane and propane laminar diffusion flames were also investigated for comparison, and their PAHs growth characteristics had been explained by reactions concerning acetylene

Kazuhiro Hayashida; Toshio Mogi; Kenji Amagai; Masataka Arai

2011-01-01

106

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

NASA Technical Reports Server (NTRS)

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

Tabib-Azar, Massood

1997-01-01

107

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

108

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

109

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

NASA Technical Reports Server (NTRS)

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

Bailey, Sheila G.; Hakimzadeh, Roshanak

1993-01-01

110

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

111

Cow characteristics and their association with production performance with different dry period lengths.  

PubMed

Shortening or omitting the dry period (DP) has been proposed as a management strategy to improve energy balance of dairy cows in early lactation. Both shortening and complete omission of the DP reduces milk production in the subsequent lactation compared with a conventional DP length of 60d. Some cows have less milk production loss than other cows after applying no DP or a short DP. The aim of this study is to evaluate which cow characteristics are associated with the amount of milk production losses following no DP or a short DP (30d). Daily production information from the lactation before and after the DP was available from 161 dairy cows (54 cows with a 0-d DP, 51 cows with a 30-d DP, and 56 cows with a 60-d DP) from a research herd. Daily production (milk, fat, and protein) until 305d in milk was estimated for all cows. Subsequently, total fat- and protein-corrected milk yield from 60d before the expected calving date until 305d in the following lactation (FPCMtotal) was estimated. A statistical analysis was performed to evaluate which cow characteristics were associated with limited or no production losses following no DP or a short DP, compared with a conventional DP length of 60d. Average FPCMtotal was 9,341, 10,499, and 10,795kg for cows with no DP, a 30-d DP, and a 60-d DP, respectively. The cow characteristics parity, daily milk production at 12wk before the expected calving date, and reduction in daily milk production between 16 and 12wk before the expected calving date were associated with production loss due to a short (30d) or no DP. Compared with 60d DP, multiparous cows had less production loss (987kg) following no DP than primiparous cows (2,132kg). The difference in FPCMtotal between the 3DP groups was largest for cows with a low milk production (e.g., 10kg/d) at 12wk before the expected calving date. The greater the reduction in milk production between 16 and 12wk before the expected calving date, the larger the difference in FPCMtotal between the 3DP groups. The difference in FPCMtotal between cows with no DP and 60d DP at a reduction in milk production between 16 and 12wk of 10% was 665kg, whereas this difference was 1,138kg at a reduction of 70%. The cow characteristics found can be used to select cows for specific DP lengths in a decision-support model to support the farmer on the economic optimal DP length for each individual cow. Output of such a decision-support model can be, for instance, to advise a 30-d DP for multiparous cows with high milk production (e.g., 25kg/d) at 12wk before the expected calving date. PMID:24952774

Steeneveld, W; van Knegsel, A T M; Remmelink, G J; Kemp, B; Vernooij, J C M; Hogeveen, H

2014-08-01

112

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

113

Edge effects on the characteristics of li diffusion in graphene.  

PubMed

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

Uthaisar, Chananate; Barone, Veronica

2010-08-11

114

Optical absorption coefficient and minority carrier diffusion length measurements in low-cost silicon solar cell material  

SciTech Connect

The optical absorption coefficient of silicon solar cell material grown by three low-cost growth methods was measured in the wavelength interval 0.8< or =lambda< or =1.0 ..mu..m, the wavelength region of interest in surface photovoltage measurements of the minority carrier diffusion length. The square root of the absorption coefficient was found to vary linearly with photon energy over the wavelengths studied, and the measured data agree with a linear empirical fit to within 0.5% RMS. The absorption coefficients obtained are slightly lower than those reported by Runyan, with the greatest disagreement at long wavelengths. Minority carrier diffusion lengths computed using the present absorption coefficients are approximately 16% greater than those calculated using Runyan's data. Excellent sample-to-sample agreement within and between lots indicates that for two of the growth methods studied, material quality as judged by optical properties has not been sacrificed by the use of low-cost growth methods. Samples grown by the third growth method studied showed measurably poorer optical quality.

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

1982-11-01

115

Effect of Nose Length, Fuselage Length, and Nose Fineness Ratio on the Longitudinal Aerodynamic Characteristics of Two Complete Models at High Subsonic Speeds  

NASA Technical Reports Server (NTRS)

An investigation has been made of the effects of nose length, fuselage length, and nose fineness ratio on the static longitudinal aerodynamic characteristics of an airplane model with a swept wing and low tail and of a second model with a highly tapered wing of moderate sweep and a T-tail. The tests were conducted in the Langley high-speed 7- by 10-foot tunnel at Mach numbers from 0.60 to 0.92. The nose and body cross sections were circular. For either the model with the swept wing and low tail or the model with the highly tapered wing of moderate sweep and the T-tail, the effects of forebody changes amounted primarily to rotations of the pitching-moment curves (changes in static margin) over the test ranges of angle of attack and Mach number. For the range of body shapes investigated the longitudinal stability at low lift is decreased by an increase in nose length or in fuselage length or by a reduction in nose fineness ratio when the fuselage length is held constant. In general, the stability for all model configurations showed substantially the same variation with changes in forebody area moment. The forebody changes did not alter the angle of attack at which an unstable break occurred in the moment contribution of the T-tail but did alter somewhat the magnitude of the instability.

Goodson, Kenneth W.

1958-01-01

116

Electron-beam-induced current determination of minority-carrier diffusion length and surface recombination velocity in mercury-cadmium-telluride  

Microsoft Academic Search

A method is presented for determining the minority-carrier diffusion length and surface recombination velocity in passivated, shallow junction semiconductor devices. The method is particularly useful with devices where the minority-carrier diffusion length is comparable to the diameter of the electron beam interaction volume. A gaussian beam profile is convoluted with a theoretical model for electron-beam-induced current and the results used

B. E. Artz

1985-01-01

117

Molecular dynamic simulation of dicationic ionic liquids: effects of anions and alkyl chain length on liquid structure and diffusion.  

PubMed

Structures and dynamics of nine geminal dicationic ionic liquids (DILs) Cn(mim)2X2, where n = 3, 6, and 9 and X = PF6(-), BF4(-), and Br(-), were studied by molecular dynamic simulations (J. Phys. Chem.B2004, 108, 2038-2047). A force field with a minor modification for C3(mim)2 × 2 was adopted for the simulations. Densities, detailed microscopic structures, mean-square displacements (MSD), and self-diffusivities for various ion pairs from MD simulations have been presented. The calculated densities for C9(mim)2X2 (X = Br(-) and BF4(-)) agreed well with the experimental values. The calculated RDFs show that anions are well organized around the imidazolium rings. The calculated RDFs indicate that, unlike the mono cationic ILs, the anions and cations in DILs distribute homogeneously. Enthalpies of vaporization were calculated and correlated with the structural features of DILs. The local structure of C9(mim)2X2 (X = Br, PF6) was examined by the spatial distribution function (SDF). The calculated SDFs show that similar trends were found by other groups for mono cationic ionic liquids (ILs). The highest probability densities are located around the imidazolium ring hydrogens. The calculated diffusion coefficients show that the ion diffusivities are 1 order of magnitude smaller than that of the mono cationic ionic liquids. The effects of alkyl chain length and anion type on the diffusion coefficient were also studied. The dynamics of the imidazolium rings and the alkyl chain in different time scales have also discussed. The calculated transference numbers show that the anions have the major role in carrying the electric current in a DIL. PMID:22897217

Yeganegi, Saeid; Soltanabadi, Azim; Farmanzadeh, Davood

2012-09-20

118

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

119

Characteristics of the nonelderly with selected sources of health insurance and lengths of uninsured spells.  

PubMed

This Issue Brief examines the characteristics of individuals with selected sources of coverage and combinations of sources of coverage over a 12-month period. In addition, it examines the characteristics of individuals who experience spells without health insurance and the lengths of these spells. It uses the most recent 12-month period from the Survey of Income and Program Participation and builds on previous research on the lengths of spells with and without health insurance. Analysis of individuals' health insurance coverage from October 1994 to September 1995 showed that approximately 77.6 percent of the nonelderly had health insurance coverage during this entire period. In addition, 22.4 percent of the nonelderly were uninsured for at least one month during this period, and 7.4 percent of the nonelderly were uninsured for the entire period. Of those with health insurance coverage for the entire year, approximately 83 percent were covered by private health insurance, with at least 81 percent of this group receiving the coverage from employment-based sources. Eighty-five percent of the spells without health insurance with an observed beginning and end lasted for 4 months or less, and 99 percent lasted for 8 months or less. When examining the spells with either an observed beginning or end, 55 percent of these spells were found to last for 4 months or less, and 87 percent were found to last for 8 months or less. However, investigation of all spells without health insurance showed that approximately one-half of all spells without health insurance coverage lasted for 8 months or longer. This report found that two-thirds of spells without health insurance last for less than one year, confirming previous research that a majority of these spells are for less than a year. However, this report also confirms the existence of a significant number--approximately one-third of all individuals with a spell of noncoverage--of chronically uninsured individuals. These individuals are the most likely to delay seeking treatment for illnesses and to use the emergency room as their only site of care. Because they are in poverty or near poverty, much of this care is uncompensated. Thus, to the extent that providers can shift these costs onto other payers, all individuals and employers share in these costs through higher health insurance premiums or higher taxes to finance public hospitals and public insurance programs. Recent major health insurance legislation has addressed access to health insurance, and in many cases focused solely on continued access to employment-based coverage, but has done very little to address the affordability of coverage. However, as this report demonstrates, many individuals experiencing spells without health insurance have low incomes. Thus, to obtain coverage, individuals need not only increased access to health insurance but also the ability to afford this health insurance. PMID:10179854

Copeland, C

1998-06-01

120

Aerodynamic Characteristics of a Flying-Boat Hull Having a Length-Beam Ratio of 15, TED No. NACA 2206  

NASA Technical Reports Server (NTRS)

An investigation was made in the Langley 300 MPH 7- by 10-foot tunnel to determine the aerodynamic characteristics of a flying-boat hull of a length-beam ratio of 15 in the presence of a wing. The investigation was an extension of previous tests made on hulls of length-beam ratios of 6, 9, and 12; these hulls were designed to have approximately the same hydrodynamic performance with respect to spray and resistance characteristics. Comparison with the previous investigation at lower length-beam ratios indicated a reduction in minimum drag coefficients of 0.0006 (10 peroent)with fixed transition when the length-beam ratio was extended from 12 to 15. As with the hulls of lower length-beam ratio, the drag reduction with a length-beam ratio of 15 occurred throughout the range of angle of attack tested and the angle of attack for minimum drag was in the range from 2deg to 3deg. Increasing the length-beam ratio from 12 to 15 reduced the hull longitudinal instability by an mount corresponding to an aerodynamic-center shift of about 1/2 percent of the mean aerodynamic chord of the hypothetical flying boat. At an angle of attack of 2deg, the value of the variation of yawing-moment coefficient with angle of yaw for a length-beam ratio of 15 was 0.00144, which was 0.00007 larger than the value for a length-beam ratio of 12.

Riebe, John M.; Naeseth, Rodger L.

1951-01-01

121

Anatomical characteristics of roots of citrus rootstocks that vary in specific root length  

Microsoft Academic Search

summary Among citrus rootstocks, higher specific root length (SRL, root length}d. wt) has been linked to several specific morphological and physiological traits, including smaller average root diameter, higher root hydraulic conductivity and higher rates of root proliferation. In this study, thickness of the outer tangential exodermal (hypodermal) wall and its suberin layer, number of passage cells, presence of epidermis, and

D. M. E ISSENSTAT; D. S. A CHOR

1999-01-01

122

Effect of Length-Beam Ratio on the Aerodynamic Characteristics of Flying-Boat Hulls without Wing Interference  

NASA Technical Reports Server (NTRS)

Contains experimental results of an investigation of the aerodynamic characteristics of a family of flying boat hulls of length beam ratios 6, 9, 12, and 15 without wing interference. The results are compared with those taken on the same family of hulls in the presence of a wing.

Lowry, John G.; Riebe, John M.

1948-01-01

123

The Effects of Display Characteristics on the Bias of Estimates of Whisker Length of Regular and Notched Boxplots.  

ERIC Educational Resources Information Center

Effects of display characteristics on bias of estimates of whisker length of 2 types of box-and-whisker plots were studied in 2 studies involving 347 college students. Bias seems to be the product of a three-way interaction between spatial orientation, interquartile spread, and whisker/spread ratio. (SLD)

Wells, James B.; Layne, Ben H.

1996-01-01

124

The relations between sarcomere length and characteristics of isometric twitch contractions of frog sartorius muscle  

PubMed Central

1. Relations between sarcomere length, tension and time course of isometric twitches at 20° C were determined for thirty-two sartorius muscles from Rana temporaria. 2. The maximum isometric twitch tension per unit cross-sectional area of muscle ranged from 0·56 to 2·2 kg/cm2 at 20° C and initial sarcomere length about 2·1 ?. This variation was not correlated with the corresponding measure of tetanic tension. 3. The maximum isometric twitch tension per unit cross-sectional area of muscle at 2·1 ? sarcomere length was directly correlated with twitch contraction time and inversely correlated with the cross-sectional area of the muscle. 4. The isometric twitch contraction was potentiated with increase in initial sarcomere length from about 2·1 to about 2·8 ? at 20° C, and the degree of potentiation was inversely correlated with the maximum isometric twitch tension per unit cross-sectional area of muscle at 2·1 ? sarcomere length. 5. The sarcomere length: twitch tension relation is labile and may be altered by changes in temperature and the after-effects of repetitive stimulation. 6. Variation in twitch contractions at different sarcomere lengths are discussed in connexion with excitation—contraction coupling and the degree of activation of muscle fibres during twitch contractions at 20° C.

Close, R. I.

1972-01-01

125

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

126

Molecular beam epitaxy of ?- FeSi films on Si(111) substrates and its influence on minority-carrier diffusion length of Si measured by EBIC  

NASA Astrophysics Data System (ADS)

We have studied the influence of molecular beam epitaxy (MBE) of ?- FeSi films on minority-carrier diffusion length of an n-type Si(111) substrate. It was found from electron beam induced current technique that the diffusion length was less influenced in sample formed with a ?- FeSi template prior to the MBE growth than that in sample grown without the template. The size of ?- FeSi grains measured by electron back-scatter diffraction was also discussed.

Kawakami, H.; Suzuno, M.; Akutsu, K.; Chen, J.; Fuxing, Y.; Sekiguchi, T.; Suemasu, T.

127

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

NASA Technical Reports Server (NTRS)

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

Vonroos, O.

1978-01-01

128

Effect of nose shape and tail length on supersonic stability characteristics of a projectile  

NASA Technical Reports Server (NTRS)

The effect of nose shape and tail length on the static stability of a fin-stabilized projectile has been investigated in the Langley Unitary Plan with tunnel at angles of attack to about 12 deg for a Mach number range from 1.5 to 2.5. The tests were made at a constant Reynolds number of 6.56 x 1,000,000 per meter. The results of the investigation showed that nose shape had no effect on the static stability. Increasing the tail length resulted in a progressively stabilizing tendency. However, only the 1.5-caliber-tail-length configuration was stable over the test angle-of-attack range at Mach number 1.5. This configuration was marginally stable or unstable at the higher Mach numbers, and the shorter configurations were unstable at all Mach numbers for either part of or the entire test angle-of-attack range.

Sawyer, W. C.; Collins, I. K.

1973-01-01

129

Supersonic and hypersonic aerodynamic characteristics of two shuttle-orbiter configurations designed for reduced length  

NASA Technical Reports Server (NTRS)

Performance, stability, and control tests at supersonic and hypersonic speeds have been performed on two versions of a shuttle orbiter configuration designed for reduced length. One of the test configurations had twin dorsal fins rolled out 15 deg the other a centerline single dorsal fin. Effects of elevon and body deg flap deflection, rudder flare, planform fillet, and aileron deflection were examined. The supersonic tests were over the Mach number range from 1.6 to 4.63 at a Reynolds number based on model length of 4,300,000. The hypersonic tests were conducted at a Mach number of 10.3 and Reynolds number of 670,000.

Stone, H. W.

1974-01-01

130

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

131

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

132

Effect of Nose Shape and Tail Length on Supersonic Stability Characteristics of a Projectile.  

National Technical Information Service (NTIS)

The effect of nose shape and tail length on the static stability of a fin-stabilized projectile has been investigated in the Langley Unitary Plan with tunnel at angles of attack to about 12 deg for a Mach number range from 1.5 to 2.5. The tests were made ...

W. C. Sawyer I. K. Collins

1973-01-01

133

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

134

Quantitative analysis along the pyramidal tract by length-normalized parameterization based on diffusion tensor tractography: Application to patients with relapsing neuromyelitis optica  

Microsoft Academic Search

In this study, we introduced a length-normalized parameterization method to establish anatomical correspondence of white matter fiber tracts across subjects and applied this method to investigate the presence of abnormal diffusion along the pyramidal tract (PYT) of relapsing neuromyelitis optica (RNMO) patients without visible brain lesions. In this approach, the part of the PYT between the lowest slice of the

Fuchun Lin; Chunshui Yu; Tianzi Jiang; Kuncheng Li; Xiaobo Li; Wen Qin; Hong Sun; Piu Chan

2006-01-01

135

Denoising of Chinese calligraphy tablet images based on run-length statistics and structure characteristic of character strokes  

Microsoft Academic Search

In this paper, a novel approach is proposed for denoising of Chinese calligraphy tablet documents. The method includes two\\u000a phases: First, a partial differential equations (PDE) based the total variation model and Otsu thresholding method are used\\u000a to preprocess the calligraphy document image. Second, a new method based on run-length statistics and structure characteristics\\u000a of Chinese characters is proposed to

Jun-song Zhang; Jin-hui Yu; Guo-hong Mao; Xiu-zi Ye

2006-01-01

136

Cavity-length effects of high-temperature high-power continuous-wave characteristics in quantum-cascade lasers  

Microsoft Academic Search

We report the cavity-length dependent high-temperature high-power cw characteristics in lambda=6 mum quantum-cascade lasers with a thick electroplated Au top contact layer. For a high-reflectivity (HR) coated 15 mum wide and 3 mm long laser, the cw operation is achieved up to 313 K (40 °C) with an output power of 17 mW. At 298 K, a very high cw

J. S. Yu; A. Evans; J. David; L. Doris; S. Slivken; M. Razeghi

2003-01-01

137

Experimental investigation of characteristic length scale in periodic heterogeneous porous media  

Microsoft Academic Search

An experimental investigation of scale-dependent dispersion in periodic heterogeneous porous media was conducted. Models with two-, three- and four-layer periodic heterogeneities were constructed to investigate the effect of heterogeneity size on the scale-dependence of dispersion. Longitudinal dispersion coefficients were determined as a function of column length by measuring the breakthrough of a continuous injection of potassium chloride tracer solution. Chloride

N. C. Irwin; M. M. Botz; R. A. Greenkorn

1996-01-01

138

Characteristics of ZnO/Si prepared by Zn 3P 2 diffusion  

NASA Astrophysics Data System (ADS)

p-ZnO thin film formation on Si substrate is investigated using rf magnetron sputtering followed by Zn 3P 2 diffusion process. In order to form p-ZnO thin film, n-ZnO thin film is initially deposited on Si substrate using rf magnetron sputtering. Then, Zn 3P 2 source diffusion by closed ampoule technique is performed on ZnO/Si test structure. The electrical and optical characteristics of the ZnO thin films are investigated and the effect of Zn 3P 2 diffusion on the properties of ZnO thin films are examined. From the analysis results, it is verified that p-type ZnO thin film on p-Si substrate is formed by dopants diffusion.

Ko, Young-Don; Jung, Jihoun; Bang, Kyu-Hyun; Park, Min-Chul; Huh, Kwang-Soo; Myoung, Jae-Min; Yun, Ilgu

2002-12-01

139

Flow, conduction, and a characteristic length in periodic bicontinuous porous media  

NASA Astrophysics Data System (ADS)

The Stokes equation system and Ohm's law were solved within periodic bicontinuous porous media of simple-cubic (sc) symmetry. The results were used to test the permeability scaling law proposed by Johnson, Koplik, and Schwartz [Phys. Rev. Lett. 57, 2564 (1986)], which uses a length parameter ? to relate the Darcy permeability k and formation factor F. We found that the scaling law M==8Fk/?2~=1 was obeyed by many bicontinuous porous media within the sc crystallographic family. However, this is not valid when the constrictions in the porous media approach an orificelike aspect: The scaling law is not universal.

Saeger, R. B.; Scriven, L. E.; Davis, H. T.

1991-10-01

140

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

Microsoft Academic Search

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

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

2007-01-01

141

Study of the damping characteristics of sectional flight vehicles of different length  

Microsoft Academic Search

The dependence of the damping characteristics of axisymmetric tri-sectional flight vehicles executing plane oscillations about the zero angle of attack on their geometric parameters is investigated on the supersonic range of uniform oncoming air flow Mach numbers. Systematic data are obtained using the least laborious approach, namely, by calculating the steady-state inviscid flow past equivalent bodies determined from the principle

A. V. Antonets; V. N. Shmanenkov

2004-01-01

142

Channel characteristics analysis of diffuse indoor cellular optical wireless communication systems  

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

143

The influences of thermodynamic characteristics on aerodynamic roughness length over land surface  

NASA Astrophysics Data System (ADS)

It has previously been shown that aerodynamic roughness length changes significantly along with nearsurface atmospheric thermodynamic state; however, at present, this phenomenon remains poorly understood, and very little research concerning this topic has been conducted. In this paper, by using the data of different underlying surfaces provided by the Experimental Co-observation and Integral Research in Semi-arid and Arid Regions over North China, aerodynamic roughness length ( z 0) values in stable, neutral, and unstable atmospheric stratifications are compared with one another, and the relationship between z 0 and atmospheric thermodynamic stability ( ?) is analyzed. It is found that z 0 shows great differences among the stable, neutral, and unstable atmospheric thermodynamic states, with the difference in z 0 values between the fully thermodynamic stable condition and the neutral condition reaching 60% of the mean z 0. Furthermore, for the wind speed range in which the wind data are less sensitive to z 0, the surface z 0 changes more significantly with ?, and is highly correlated with both the Monin-Obukhov stability ( ? 0) and the overall Richardson number ( R ib), with both of their correlation coefficients greater than 0.71 and 0.47 in the stable and unstable atmospheric stratification, respectively. The empirical relation fitted with the experimental observations is quite consistent with the Zilitinkevich theoretical relation in the stable atmosphere, but the two are quite distinct and even show opposite variation tendencies in the unstable atmosphere. In application, however, verification of the empirical fitted relations by using the experimental data finds that the fitted relation is slightly more applicable than the Zilitinkevich theoretical relation in stable atmospheric stratification, but it is much more suitable than the Zilitinkevich relation in unstable atmospheric stratification.

Zhang, Qiang; Yao, Tong; Yue, Ping; Zhangf, Liyang; Zeng, Jian

2013-04-01

144

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

PubMed

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

Pankavich, S; Ortoleva, P

2010-06-01

145

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

146

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

Microsoft Academic Search

Previous work has shown that for soils of insignificant permeability (soils with permeability less than about 10⁻¹² m²) 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

M. S. Jarzemba; T. E. Blue

1996-01-01

147

Estimating the spin diffusion length of semiconducting Indium Tin Oxide using Co/Indium Tin Oxide/Co spin valve junctions  

NASA Astrophysics Data System (ADS)

We have measured the transport behavior of Co/Indium Tin Oxide (ITO)/Co current-perpendicular-to-plane submicron spin-valve devices with ITO spacer thickness up to 20 nm, fabricated directly using a three-dimensional focused-ion beam etching technique. Using a simplified Valet-Fert model, we have determined a spin asymmetry ratio for Co of 0.55 and spin diffusion length of 6+/-1 nm in semiconducting ITO at room temperature.

Hakimi, A. M. H. R.; Banerjee, N.; Aziz, A.; Robinson, J. W. A.; Blamire, M. G.

2010-03-01

148

Measurement of diffusion length in CuInSe2 and CdS by the electron beam induced current method  

Microsoft Academic Search

The minority-carrier diffusion length L(e) for electrons in p-CuInSe2 was determined by analyzing the magnitude of the electron beam induced current as a function of distance from the p\\/n junction in an n-CdS\\/p-CuInSe2 solar cell whose solar energy conversion efficiency was about 8%. Data obtained for electron beam energies of 10, 20, and 30 keV showed that L(e) was at

J. Piekoszewski; J. J. Loferski; J. Beall; W. Giriat; L. Castaner

1980-01-01

149

Diffusion  

NSDL National Science Digital Library

Diffusion is the net movement of particles from areas of high concentration (number of particles per unit area) to low concentration. In this activity, students use a molecular dynamics model to view the behavior of diffusion in gases and liquids.

Consortium, The C.

2011-12-11

150

Interactions between a fractal tree-like object and hydrodynamic turbulence: flow structure and characteristic mixing length  

NASA Astrophysics Data System (ADS)

The vegetation canopy has a significant impact on various physical and biological processes such as forest microclimate, rainfall evaporation distribution and climate change. Most scaled laboratory experimental studies have used canopy element models that consist of rigid vertical strips or cylindrical rods that can be typically represented through only one or a few characteristic length scales, for example the diameter and height for cylindrical rods. However, most natural canopies and vegetation are highly multi-scale with branches and sub-branches, covering a wide range of length scales. Fractals provide a convenient idealization of multi-scale objects, since their multi-scale properties can be described in simple ways (Mandelbrot 1982). While fractal aspects of turbulence have been studied in several works in the past decades, research on turbulence generated by fractal objects started more recently. We present an experimental study of boundary layer flow over fractal tree-like objects. Detailed Particle-Image-Velocimetry (PIV) measurements are carried out in the near-wake of a fractal-like tree. The tree is a pre-fractal with five generations, with three branches and a scale reduction factor 1/2 at each generation. Its similarity fractal dimension (Mandelbrot 1982) is D ~ 1.58. Detailed mean velocity and turbulence stress profiles are documented, as well as their downstream development. We then turn attention to the turbulence mixing properties of the flow, specifically to the question whether a mixing length-scale can be identified in this flow, and if so, how it relates to the geometric length-scales in the pre-fractal object. Scatter plots of mean velocity gradient (shear) and Reynolds shear stress exhibit good linear relation at all locations in the flow. Therefore, in the transverse direction of the wake evolution, the Boussinesq eddy viscosity concept is appropriate to describe the mixing. We find that the measured mixing length increases with increasing streamwise locations. Conversely, the measured eddy viscosity and mixing length decrease with increasing elevation, which differs from eddy viscosity and mixing length behaviors of traditional boundary layers or canopies studied before. In order to find an appropriate length for the flow, several models based on the notion of superposition of scales are proposed and examined. One approach is based on spectral distributions. Another more practical approach is based on length-scale distributions evaluated using fractal geometry tools. These proposed models agree well with the measured mixing length. The results indicate that information about multi-scale clustering of branches as it occurs in fractals has to be incorporated into models of the mixing length for flows through canopies with multiple scales. The research is supported by National Science Foundation grant ATM-0621396 and AGS-1047550.

Meneveau, C. V.; Bai, K.; Katz, J.

2011-12-01

151

Night and day in the VA: associations between night shift staffing, nurse workforce characteristics, and length of stay.  

PubMed

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

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

2014-04-01

152

Photovoltaic characteristics of diffused P/+N bulk GaAs solar cells  

NASA Technical Reports Server (NTRS)

The photovoltaic characteristics of P(+)N junction solar cells fabricated on bulk GaAs by an open tube diffusion technique are described in this paper.Spectral response measurements were analyzed in detail and compared to a computer simulation in order to determine important material parameters. It is projected that proper optimization of the cell parameters can increase the efficiency of the cells from 12.2 percent to close to 20 percent.

Borrego, J. M.; Keeney, R. P.; Bhat, I. B.; Bhat, K. N.; Sundaram, L. G.; Ghandhi, S. K.

1982-01-01

153

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

PubMed

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

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

2014-07-01

154

Improved current and power density with a micro-scale microbial fuel cell due to a small characteristic length.  

PubMed

A microbial fuel cell (MFC) is a bio-electrochemical converter that can extract electricity from biomass by the catabolic reaction of microorganisms. This work demonstrates the impact of a small characteristic length in a Geobacteraceae-enriched, micro-scale microbial fuel cell (MFC) that achieved a high power density. The small characteristic length increased the surface-area-to-volume ratio (SAV) and the mass transfer coefficient. Together, these factors made it possible for the 100-µL MFC to achieve among the highest areal and volumetric power densities - 83?W/cm(2) and 3300?W/cm(3), respectively - among all micro-scale MFCs to date. Furthermore, the measured Coulombic efficiency (CE) was at least 79%, which is 2.5-fold greater than the previously reported maximum CE in micro-scale MFCs. The ability to improve these performance metrics may make micro-scale MFCs attractive for supplying power in sub-100µW applications, especially in remote or hazardous conditions, where conventional powering units are hard to establish. PMID:24956566

Ren, Hao; Torres, César I; Parameswaran, Prathap; Rittmann, Bruce E; Chae, Junseok

2014-11-15

155

Quantification of Neocortical Slice Diffusion Characteristics Using Pharmacokinetic and Pharmacodynamic Modelling  

PubMed Central

Pharmacological brain slice experiments are complicated by the need to ensure adequate drug delivery deep into the healthy layers of the tissue. Because tissue slices have no blood supply, this is achieved solely by passive drug diffusion. The aim of this study was to determine whether pharmacokinetic/pharmacodynamic (PKPD) modeling could be adapted to estimate drug diffusion times in neocortical brain slices. No-magnesium seizure-like event (SLE) activity was generated in 41 slices (400??m). Two anesthetic agents, etomidate (24??M, n = 14) and thiopental (250??M, n = 14), and magnesium ions (n = 13) were delivered to effect reversible reductions in SLE frequency. Concentration-effect hysteresis loops were collapsed using a first order rate constant model and equilibrium half-lives (t1/2Ke0) derived. The t1/2Ke0 values obtained were consistent with expectations. The median (range) t1/2Ke0 of 83.1 (19.4–330.1)?min for etomidate is in keeping with its known slow diffusion into brain slice tissue. Values for etomidate and thiopental (111.8 (27.8–198.0)?min) were similar, while magnesium had a significantly faster equilibration rate (t1/2Ke0 of 26.1 (8.6–77.0)?min) compared to the anesthetics, as expected for a simple ion. In conclusion, PKPD modeling is a simple and practical method that can be applied to brain slice experiments for investigating drug diffusion characteristics.

Voss, Logan J.; van Kan, Claudia; Sleigh, James W.

2013-01-01

156

Experimental investigation of the effect of vertical-tail size and length and of fuselage shape and length on the static lateral stability characteristics of a model with 45 degree sweptback wing and tail surfaces  

NASA Technical Reports Server (NTRS)

An investigation was made to determine the effects of vertical-tail size and length and of fuselage shape and length on the static lateral stability characteristics of a model with wing and vertical tails having the quarter-chord lines swept back 45 degrees. The results indicate that the directional instability of the various isolated fuselages was about two-thirds as large as that predicted by classical theory.

Queijo, M J; Wolhart, Walter D

1951-01-01

157

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

USGS Publications Warehouse

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

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

2014-01-01

158

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

159

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

Microsoft Academic Search

Indium phosphide (InP) solar cells are more radiation resistant than gallium arsenide (GaAs) and silicon (Si) solar cells, and their growth by heteroepitaxy offers additional advantages leading to the development of light weight, mechanically strong, and cost-effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5- and 3-MeV proton irradiations have been explained by the variation in the minority-carrier diffusion

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

1993-01-01

160

The effect of zinc concentration on vacancies jump rate, diffusion coefficient and jump length in Cu–Zn ferrite  

Microsoft Academic Search

Samples with the chemical formula Cu1?xZnxFe2O4 (x=0.2, 0.4, 0.6, 0.8 and 1) were prepared by the standard ceramic method. The dielectric constant and dielectric loss tangent were studied as a function of vacancy jump rate. The results show that the dielectric constant and dielectric loss tangent decrease with increasing vacancy jump rate. In addition, the electron jump length in the

H. M. Zaki

2009-01-01

161

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

162

Thermal Characteristics and Structure of Fully-Modulated, Turbulent Diffusion Flames in Microgravity  

NASA Technical Reports Server (NTRS)

Turbulent jet diffusion flames are studied in microgravity and normal gravity under fully-modulated conditions for a range of injection times and a 50% duty cycle. Diluted ethylene was injected through a 2-mm nozzle at a Reynolds number of 5,000 into an open duct, with a slow oxidizer co-flow. Microgravity tests are conducted in NASA's 2.2 Second Drop Tower. Flames with short injection times and high duty cycle exhibit a marked increase in the ensemble-averaged flame length due to the removal of buoyancy. The cycle-averaged centerline temperature profile reveals higher temperatures in the microgravity flames, especially at the flame tip where the difference is about 200 K. In addition, the cycle-averaged measurements of flame radiation were about 30% to 60% greater in microgravity than in normal gravity.

Hermanson, J. C.; Johari, H.; Stocker, D. P.; Hegde, U. G.

2003-01-01

163

Diffusion, diffusion creep and grain growth characteristics of nanocrystalline and fine-grained monoclinic, tetragonal and cubic zirconia  

Microsoft Academic Search

The experimentally measured grain size compensated diffusion creep rates are essentially identical in cubic, tetragonal and monoclinic zirconia, suggesting a similarity in the absolute magnitudes of their grain boundary diffusion coefficients. However, grain growth is substantially slower in tetragonal zirconia due to significant grain boundary segregation.

Atul H. Chokshi

2003-01-01

164

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

SciTech Connect

A method is presented for calculating exactly the relative width (sigma/sup 2/)/sup 1/2//, the skewness ..gamma../sub 1/, and the kurtosis ..gamma../sub 2/ characterizing the probability distribution function for three random-walk models of diffusion-controlled processes. For processes in which a diffusing coreactant A reacts irreversibly with a target molecule B situated at a reaction center, three models are considered. The first is the traditional one of an unbiased, nearest-neighbor random walk on a d-dimensional periodic/confining lattice with traps; the second involves the consideration of unbiased, non-nearest-neigh bor (i.e., variable-step length) walks on the same d-dimensional lattice; and, the third deals with the case of a biased, nearest-neighbor walk on a d-dimensional lattice (wherein a walker experiences a potential centered at the deep trap site of the lattice). Our method, which has been described in detail elsewhere (P.A. Politowicz and J. J. Kozak, Phys. Rev. B 28, 5549 (1983)) is based on the use of group theoretic arguments within the framework of the theory of finite Markov processes.

Musho, M.K.; Kozak, J.J.

1984-10-01

165

Evaluation of the minority carrier diffusion length by means of electron beam induced current and Monte Carlo simulation in AlGaAs and GaAs p-i-n solar cells  

Microsoft Academic Search

A new method of determining the minority carrier diffusion length in multilayer solar cells is described. Electron beam-induced current (EBIC) gain measurements, performed in a scanning electron microscope in the planar sample configuration, are compared with values obtained by calculations using a Monte Carlo simulation program of electron trajectories. Values for diffusion lengths obtained by this method from five AlGaAs

E. Grunbaum; E. Napchan; Z. Barkay; K. Barnham; J. Nelson; C. T. Foxon; J. S. Roberts; D. B. Holt

1995-01-01

166

Complex Experimental Evaluation of the Characteristics of Propagation of HF Signals Along Midlatitude Paths of Different Length and Orientation  

NASA Astrophysics Data System (ADS)

We outline a complex approach for measuring distance-frequency, angular, spectral, and statistical characteristics of HF signals and present the results of experimental studies of the turbidity coefficient, frequency-spread bandwidth, variations in the Doppler frequency shift, bearing, and elevation angle in a wide frequency range for the Khabarovsk-Rostov-on-Don, Moscow-Rostov-on-Don, and Cyprus-Rostov-on-Don sounding paths under various geophysical conditions. It is shown that the most probable values of the turbidity coefficient for one-hop paths in the afternoon range from 2 to 4. The turbidity coefficient decreases to about 0.6 in the twilight hours. The turbidity coefficient tends to decrease with the path length. The average frequency-spread bandwidth at the 95% level of the received signal power is found to be minimal for illuminated path and does not exceed a value from 0.1 to 0.3 Hz. The frequency-spread bandwidth increases in the sunset hours or under nonuniform illumination, but does not exceed 4 Hz. We estimated the range of Doppler frequency shift variations which are due mainly to the influence of medium-scale traveling ionospheric disturbances and do not exceed 2 Hz in the experiments. The method of one-position location of a radiation source is tested by the results of angular measurements on the basis of the IRI-2001 ionospheric model.

Vertogradov, G. G.; Myatezhnikov, Yu. P.; Uryadov, V. P.; Rozanov, S. V.

2004-01-01

167

Influences of carrier diffusion and radial mode field pattern on high speed characteristics for microring lasers  

NASA Astrophysics Data System (ADS)

High-speed directly modulated microlasers are potential light sources for on-chip optical interconnection and photonic integrated circuits. In this Letter, dynamic characteristics are studied for microring lasers by rate equation analysis considering radial carrier hole burning and diffusion and experimentally. The coupled modes with a wide radial field pattern and the injection current focused in the edge area of microring resonator can greatly improve the high speed response curve due to the less carrier hole burning. The small-signal response curves of a microring laser connected with an output waveguide exhibit a larger 3 dB bandwidth and smaller roll-off at low frequency than that of the microdisk laser with the same radius of 15 ?m, which accords with the simulation results.

Lv, Xiao-Meng; Huang, Yong-Zhen; Yang, Yue-De; Zou, Ling-Xiu; Long, Heng; Liu, Bo-Wen; Xiao, Jin-Long; Du, Yun

2014-04-01

168

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

169

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

170

Box, Line, and Midgap Plots: Effects of Display Characteristics on the Accuracy and Bias of Estimates of Whisker Length.  

ERIC Educational Resources Information Center

The accuracy and bias of estimates of whisker length based on box, line, and midgap plots were examined. For each type of graph, 20 different undergraduates (n=60) viewed 48 single-plot graphs. Whisker-length estimates for box and line plots were more accurate and less biased than those for midgap plots. (TJH)

Stock, William A.; Behrens, John T.

1991-01-01

171

Quantifying the effect of metal-rich precipitates on minority carrier diffusion length in multicrystalline silicon using synchrotron-based spectrally resolved x-ray beam-induced current  

NASA Astrophysics Data System (ADS)

Synchrotron-based, spectrally resolved x-ray beam-induced current (SR-XBIC) is introduced as a technique to locally measure the minority carrier diffusion length in semiconductor devices. Equivalence with well-established diffusion length measurement techniques is demonstrated. The strength of SR-XBIC is that it can be combined in situ with other synchrotron-based analytical techniques, such as x-ray fluorescence microscopy (?-XRF) and x-ray absorption microspectroscopy (?-XAS), yielding information about the distribution, elemental composition, chemical nature, and effect on minority carrier diffusion length of individual transition metal species in multicrystalline silicon. SR-XBIC, ?-XRF, and ?-XAS measurements were performed on intentionally contaminated multicrystalline silicon, revealing a strong correlation between local concentrations of copper and nickel silicide precipitates and a decrease of minority carrier diffusion length. In addition, the reduction of minority carrier diffusion length due to submicron-sized Cu3Si and NiSi2 precipitates could be decoupled from the influence of homogeneously distributed nanoprecipitates and point defects.

Buonassisi, T.; Istratov, A. A.; Pickett, M. D.; Marcus, M. A.; Hahn, G.; Riepe, S.; Isenberg, J.; Warta, W.; Willeke, G.; Ciszek, T. F.; Weber, E. R.

2005-07-01

172

Mechanical principles of effects of botulinum toxin on muscle length-force characteristics: An assessment by finite element modeling.  

PubMed

Recent experiments involving muscle force measurements over a range of muscle lengths show that effects of botulinum toxin (BTX) are complex e.g., force reduction varies as a function of muscle length. We hypothesized that altered conditions of sarcomeres within active parts of partially paralyzed muscle is responsible for this effect. Using finite element modeling, the aim was to test this hypothesis and to study principles of how partial activation as a consequence of BTX affects muscle mechanics. In order to model the paralyzing effect of BTX, only 50% of the fascicles (most proximal, or middle, or most distal) of the modeled muscle were activated. For all muscle lengths, a vast majority of sarcomeres of these BTX-cases were at higher lengths than identical sarcomeres of the BTX-free muscle. Due to such "longer sarcomere effect", activated muscle parts show an enhanced potential of active force exertion (up to 14.5%). Therefore, a muscle force reduction originating exclusively from the paralyzed muscle fiber populations, is compromised by the changes of active sarcomeres leading to a smaller net force reduction. Moreover, such "compromise to force reduction" varies as a function of muscle length and is a key determinant of muscle length dependence of force reduction caused by BTX. Due to longer sarcomere effect, muscle optimum length tends to shift to a lower muscle length. Muscle fiber-extracellular matrix interactions occurring via their mutual connections along full peripheral fiber lengths (i.e., myofascial force transmission) are central to these effects. Our results may help improving our understanding of mechanisms of how the toxin secondarily affects the muscle mechanically. PMID:24704169

Turkoglu, Ahu N; Huijing, Peter A; Yucesoy, Can A

2014-05-01

173

Characteristic distributions of intracerebral hemorrhage-associated diffusion-weighted lesions  

PubMed Central

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

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

2012-01-01

174

AN EVALUATION OF THE DIFFUSION-BONDING CHARACTERISTICS OF ZIRCALOY2  

Microsoft Academic Search

Ten promising diffuser elements were used in experiments aimed at ; joining Zircaloy-2 components by a diffusion-bonding technique. Copper, nickel, ; nickel-phosphorus, manganese, and silicon appear most favorable for this purpose. ; (auth);

Feduska

1959-01-01

175

Analyzing the Effect of Diffusion Bonding Process Parameters on Bond Characteristics of Mg-Al Dissimilar Joints  

NASA Astrophysics Data System (ADS)

The principle difficulty when joining magnesium (Mg)-aluminium (Al) lies in the existence of formation of oxide films and brittle intermetallic in the bond region. However, diffusion bonding can be used to join these alloys without much difficulty. Temperature, pressure, and holding time are the three main variables which govern the integrity of a diffusion bond. This paper focuses on the effect of these parameters on diffusion layer thickness, hardness and strength of AZ31B magnesium-AA2024 aluminium dissimilar joints. The experiments were conducted based on three factors, five-level, and central composite rotatable design with full replications technique. Empirical relationships were developed to predict diffusion layer thickness, hardness and strength using response surface methodology. From this investigation, it is found that bonding temperature has predominant effect on bond characteristics.

Mahendran, G.; Babu, S.; Balasubramanian, V.

2010-07-01

176

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...

177

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...

178

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

179

Solute Diffusion Characteristics of a Rapid Hardening Al-Cu-Mg Alloy during the Early Stages of Age Hardening  

NASA Astrophysics Data System (ADS)

The heat-transfer characteristics of a rapid hardening Al-1.1Cu-1.7Mg at. pct alloy during the early stages of age hardening have been tested, both by experiment and finite element modeling, for a typical laboratory-scale sample, and subsequently a maximum diffusion distance by random walk has been calculated for the solute atom species. It is found that due to small diffusion distances compared to the average dislocation loop interspacing, the dislocation-locking hardness mechanism is not likely, and rather, the cluster hardening model is more accurate.

Marceau, R. K. W.; Tsafnat, N.; Haley, D.; Ringer, S. P.

2010-08-01

180

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

181

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

SciTech Connect

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

Akutsu, Keiichi; Kawakami, Hideki; Suzuno, Mitsushi; Yaguchi, Takashi [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Jiptner, Karolin; Chen, Jun; Sekiguchi, Takashi [National Institute for Materials Science, Tsukuba, Ibaraki 305-0044 (Japan); Ootsuka, Teruhisa [National Institute of Advanced Industrial Science and Technology, Ibaraki 305-8568 (Japan); Suemasu, Takashi [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Japan Science and Technology Agency, CREST, Chiyoda-ku, Tokyo 102-0075 (Japan)

2011-06-15

182

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

2013-10-21

183

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

184

Theoretical and experimental analyses of atom diffusion characteristics on wire bonding interfaces  

NASA Astrophysics Data System (ADS)

The features of ultrasonic bonding interface were inspected by using a high resolution transmission electron microscope. Stress of ultrasonic bonding interface was analysed by the finite elements simulation. Results show that the high stress of bonding interface was caused by ultrasonic vibration, which increased the dislocation density inside the metal crystalline lattice which provides the fast diffusion channels, and provided driving force for atom inter-diffusion. 'Short-circuit diffusion' during ultrasonic bonding is more prominent than crystal diffusion. For the given ultrasonic bonding parameters, depth of atom diffusion at Au/Al interface of ultrasonic bonding was about 100-300 nm in several ten milliseconds, which forms the bonding strength of 0.65 N, and it is an inter-metallic compound of AuAl2. These will be helpful for further analysis.

Li, Junhui; Fuliang, Wang; Han, Lei; Zhong, Jue

2008-07-01

185

Altering length and velocity feedback during a neuro-musculoskeletal simulation of normal gait contributes to hemiparetic gait characteristics  

PubMed Central

Background Spasticity is an important complication after stroke, especially in the anti-gravity muscles, i.e. lower limb extensors. However the contribution of hyperexcitable muscle spindle reflex loops to gait impairments after stroke is often disputed. In this study a neuro-musculoskeletal model was developed to investigate the contribution of an increased length and velocity feedback and altered reflex modulation patterns to hemiparetic gait deficits. Methods A musculoskeletal model was extended with a muscle spindle model providing real-time length and velocity feedback of gastrocnemius, soleus, vasti and rectus femoris during a forward dynamic simulation (neural control model). By using a healthy subject’s base muscle excitations, in combination with increased feedback gains and altered reflex modulation patterns, the effect on kinematics was simulated. A foot-ground contact model was added to account for the interaction effect between the changed kinematics and the ground. The qualitative effect i.e. the directional effect and the specific gait phases where the effect is present, on the joint kinematics was then compared with hemiparetic gait deviations reported in the literature. Results Our results show that increased feedback in combination with altered reflex modulation patterns of soleus, vasti and rectus femoris muscle can contribute to excessive ankle plantarflexion/inadequate dorsiflexion, knee hyperextension/inadequate flexion and increased hip extension/inadequate flexion during dedicated gait cycle phases. Increased feedback of gastrocnemius can also contribute to excessive plantarflexion/inadequate dorsiflexion, however in combination with excessive knee and hip flexion. Increased length/velocity feedback can therefore contribute to two types of gait deviations, which are both in accordance with previously reported gait deviations in hemiparetic patients. Furthermore altered modulation patterns, in particular the reduced suppression of the muscle spindle feedback during swing, can contribute largely to an increased plantarflexion and knee extension during the swing phase and consequently to hampered toe clearance. Conclusions Our results support the idea that hyperexcitability of length and velocity feedback pathways, especially in combination with altered reflex modulation patterns, can contribute to deviations in hemiparetic gait. Surprisingly, our results showed only subtle temporal differences between length and velocity feedback. Therefore, we cannot attribute the effects seen in kinematics to one specific type of feedback.

2014-01-01

186

Electrical and optical characteristics of diffuse nanosecond pulsed discharge plasma using a needle-array electrode in atmospheric air  

NASA Astrophysics Data System (ADS)

In this paper, a stable and diffuse dielectric barrier discharge plasma excited by bipolar nanosecond pulse is obtained under a needle-array electrode at atmospheric pressure in air. The images of the diffuse discharge, electric characteristics, and the optical emission spectra emitted from the diffuse discharge are investigated under mono and multi needle electrodes configuration. The peak value of discharge current, the average power, the power density, the emission intensity of N2 (C3?u ?B3?g, 0-0), and the gas temperature of the diffuse dielectric barrier discharge plasmas are investigated under different needle electrode numbers based on the waveforms of pulse voltage-current and the optical emission spectra. Moreover, the plasma area is obviously enlarged in the transverse direction when the needle electrode number is increased from 1 to 13. An area approximately 65 × 45 mm2 diffuse discharge plasma region under 13 needle electrodes can be obtained and the discharge plasma still keeps good uniformity, which could be used for large-area surface processing in several fields spanning from biological sterilization and plasma medicine to surface modification of materials and synthesis of functional materials.

Liu, Zhi-jie; Wang, Wen-chun; Zhang, Li; Wang, Sen; Yang, De-zheng; Zhang, Shuai; Tang, Kai

2014-05-01

187

Numerical Investigation of Characteristics of Vapor-Droplet Flow under Nonuniform Heat Release Along the Tube Length.  

National Technical Information Service (NTIS)

Numerical study of the effect of non-uniform energy release of the type 'hot', 'cold' spot in a vertical heated tube on mass-heat-exchange characteristics of vapour-drop non-equilibrium flow is carried out. The calculations are conducted for P=15.6 MPa pr...

V. M. Kashcheev Y. V. Muranov Y. S. Yur'ev

1986-01-01

188

Parametric dispersion and amplification characteristics of hot electron driven diffusive semiconductor plasmas*  

NASA Astrophysics Data System (ADS)

In this paper, an analytical expression for hot electron driven diffusion induced second-order susceptibility is obtained under non-resonant laser irradiation in magnetised semiconductor plasma. The hot electron effect due to intense pump modifies the momentum transfer collision frequency and diffusion coefficient which in turns enhances the dispersion as well as gain of the medium. The analysis deals with the qualitative behaviour of the anomalous parametric dispersion and the gain profile of the n-InSb semiconductor plasma.

Nimje, Nilesh; Ghosh, S.

2013-06-01

189

Magnetic Resonance Diffusion Characteristics of Histologically Defined Prostate Cancer in Humans  

PubMed Central

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

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

2010-01-01

190

A study on the characteristics of the diffusion layer thickness and porosity of the PEMFC  

NASA Astrophysics Data System (ADS)

In the preparation of electrodes for the proton exchange membrane (PEMFC), the effect of the fabrication method and the thickness of the gas diffusion layer and the impregnation method of Nafion solution on the cell performance was investigated, and unit cell tests were performed. The gas diffusion layer was prepared by rolling, spraying, and screen printing methods, and Nafion solution was impregnated using spraying and brushing methods. The diffusion layer in a PEMFC consists of a thin layer of carbon black mixed with polytetrafluoroethylene (PTFE) that is coated onto a sheet of macro-porous carbon backing cloth. The effects of different fabrication methods and thicknesses of gas diffusion layer are discussed in the light of porosimetry and I- V polarization curves and variables related to the electrode analyzed by numerical simulation. The spraying method proved to be more profitable for cell performance than the brushing method for the impregnation of Nafion solution because it reduced the charge transfer resistance and extended the three-phase region. The goals of this work are to find the optimum thickness of the gas diffusion layer and to undertake an analysis of the system.

Lee, Han-Kyu; Park, Jong-Ho; Kim, Do-Young; Lee, Tae-Hee

191

Study of the Interface Characteristic of Be/HR-1 Stainless Steel Following Diffusion Bonding  

NASA Astrophysics Data System (ADS)

The interface structure of Be/HR-1 stainless steel (SS) joint following diffusion bonding was investigated. Metallurgical observation, electron scanning microscopy, X-ray diffraction and scanning Auger microspectroscopy were performed for basic evaluation of bonded joints. There are intermetallic compounds such as Be11Fe and Be12Cr in the interface region of Be/SS joints, which drastically reduce the mechanical strength of the joints. Cu, Ag and Al barriers can block effective inter-diffusion of Be and HR-1 stainless steel, then forming brittle phases.

Zhang, Peng-Cheng; Bai, Bin; Yang, Jiang-Rong; Zou, Jue-Sheng; Zhou, Shou-Qi

192

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

193

Diffusion characteristics dissociate ouabain binding from inotropic effect in guinea-pig myocardium.  

PubMed Central

1. [3H]-ouabain uptake in resting guinea-pig papillary muscles depended directly on incubation time and inversely with muscle radius. The equivalence of both parameters support the relevance of diffusion. A particular mechanism of receptor-controlled diffusion was implicated by the saturation of initial rates of uptake with increasing ouabain concentrations. Saturation of initial uptake indicates an inhomogeneity of receptor occupancy with ouabain-equilibrated receptors in the superficial areas of the preparation and free receptors in the muscle core. 2. For comparison [3H]-ouabain diffusion was evaluated in a non-cellular preparation i.e. glass fibre filters soaked with modified Krebs-Henseleit solution. Diffusion was approximately 3 orders of magnitude faster when compared with the papillary muscles. 3. The time course of the inotropic effect of ouabain on rested-state contractions dissociated from the tissue content of ouabain with an increased steroid concentration. This dissociation appears to be associated with the inhomogeneity of receptor occupancy, since equal amounts of the steroid correspond to different concentration profiles in the tissue when the bath concentration is changed. Functional coupling between different muscle areas may have modulated the influence of inhomogeneous receptor occupancy.

Ebner, F.; Siegl, H.

1988-01-01

194

The statistical characteristics of diffuse multipath radiation and its effect on antenna performance  

Microsoft Academic Search

Diffuse multipath is a random phenomenon that arises out of the diffraction of waves from rough surfaces. This form of multipath can, in turn, affect the angle estimation performance of monopulse antenna systems. In order to evaluate its effect, it is necessary to obtain the channel spread function that results. This function is basically the wave number spectrum of the

T. P. McGarty

1975-01-01

195

Statistical Characteristics of Diffuse Multipath Radiation and Its Effect on Antenna Performance.  

National Technical Information Service (NTIS)

Diffuse multipath is a random phenomenon that arises out of the diffraction of waves from rough surfaces. This form of multipath can, in turn, affect the angle estimation performance of monopulse antenna systems. In order to evaluate its effect, it is nec...

T. P. McGarty

1975-01-01

196

Characteristics of Full and Partial Multipart Diffusers Discharging Thermal Wastes in Open Channel Flow.  

National Technical Information Service (NTIS)

Of the two system types which transfer condenser waste heat to the atmosphere, once-through cooling systems are significantly less costly than closed-cycle cooling systems. For once-through cooling, disposal methods using multiport diffuser-pipes provide ...

B. A. Christensen J. G. Melville A. D. Parr

1980-01-01

197

Measurement of ZnO Nanoparticles Using Diffusive Gradients in Thin Films: Binding and Diffusional Characteristics.  

PubMed

Rapid growth in finding new applications for manufactured nanomaterials (MNM) has recently been accompanied by awareness about their related adverse toxicological and environmental impacts. Due to their intrinsic nature, measuring available concentrations of MNMs in the environment is a major challenge. This research is a launching point toward filling this gap, as it presents the potential of the well-established diffusive gradients in thin films (DGT) technique to determine MNMs concentrations in situ. Two binding layers commonly used in DGT devices were shown to be able to bind ZnO nanoparticles (ZnO NPs). The use of different types of diffusive layers demonstrated the critical role of their pore size for selective function of the DGT devices. The ZnO NPs can pass through the open pore diffusive layer used in standard DGT devices and be retained by the binding resin layer. However, the diffusion of ZnO NPs can be prevented when a 1000 MWCO (molecular weight cut off) dialysis membrane is placed in the front of the diffusive gel layer. A combination of two or more DGT devices with known diffusive layer properties should enable deduction of concentrations of available ZnO NPs in the environment. Unlike metal ions, determining diffusion coefficient values for ZnO NPs is challenging and greatly affected by shape, morphology, and solution-induced changes of the particles. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) demonstrated that retention of ZnO NPs by Chelex and Metsorb binding layers occurs through chemisorption. The superior uptake kinetic for Chelex indicates that it is a better candidate for further development of DGT devices to measure ZnO NPs. These initial results are promising and important for further developing the DGT technique to measure available concentrations of manufactured nanomaterials in the different environmental media (waters, soils, and sediments). Further experiments investigating the effects of pH, ionic strength, and solution chemistry on the performance of DGT for measuring MNM concentrations are needed. PMID:24831848

Pouran, Hamid M; Martin, Francis L; Zhang, Hao

2014-06-17

198

A factor analysis approach to examining relationships among ovarian steroid concentrations, gonadotrophin concentrations and menstrual cycle length characteristics in healthy, cycling women  

PubMed Central

STUDY QUESTION How are ovarian steroid concentrations, gonadotrophins and menstrual cycle characteristics inter-related within normal menstrual cycles? SUMMARY ANSWER Within cycles, measures of estradiol production are highly related to one another, as are measures of progesterone production; however, the two hormones also show some independence from one another, and measures of cycle length and gonadotrophin concentrations show even greater independence, indicating minimal integration within cycles. WHAT IS KNOWN ALREADY The menstrual cycle is typically conceptualized as a cohesive unit, with hormone levels, follicular development and ovulation all closely inter-related within a single cycle. Empirical support for this idea is limited, however, and to our knowledge, no analysis has examined the relationships among all of these components simultaneously. STUDY DESIGN, SIZE, DURATION A total of 206 healthy, cycling Norwegian women participated in a prospective cohort study (EBBA-I) over the duration of a single menstrual cycle. Of these, 192 contributed hormonal and cycle data to the current analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS Subjects provided daily saliva samples throughout the menstrual cycle from which estradiol and progesterone concentrations were measured. FSH and LH concentrations were measured in serum samples from three points in the same menstrual cycle and cycle length characteristics were calculated based on hormonal data and menstrual records. A factor analysis was conducted to examine the underlying relationships among 22 variables derived from the hormonal data and menstrual cycle characteristics. MAIN RESULTS AND THE ROLE OF CHANCE Six rotated factors emerged, explaining 80% of the variance in the data. Of these, factors representing estradiol and progesterone concentrations accounted for 37 and 13% of the variance, respectively. There was some association between measures of estradiol and progesterone production within cycles; however, cycle length characteristics and gonadotrophin concentrations showed little association with any measure of ovarian hormone concentrations. LIMITATIONS, REASONS FOR CAUTION Our summary measures of ovarian hormones may be imprecise in women with extremely long or short cycles, which could affect the patterns emerging in the factor analysis. Given that we only had data from one cycle on each woman, we cannot address how cycle characteristics may covary within individual women across multiple cycles. WIDER IMPLICATIONS OF THE FINDINGS Our findings are generalizable to other healthy populations with typical cycles, however, may not be applicable to cycles that are anovulatory, extreme in length or otherwise atypical. The results support previous findings that measures of estradiol production are highly correlated across the cycle, as are measures of progesterone production. Estradiol and progesterone concentrations are associated with one another, furthermore. However factor analysis also revealed more complex underlying patterns in the menstrual cycle, highlighting the fact that gonadotrophin concentrations and cycle length characteristics are virtually independent of ovarian hormones. These results suggest that despite integration of follicular and luteal ovarian steroid production across the cycle, cycle quality is a multi-faceted construct, rather than a single dimension. STUDY FUNDING/COMPETING INTEREST(S) The EBBA-I study was supported by a grant from the Norwegian Cancer Society (49 258, 05087); Foundation for the Norwegian Health and Rehabilitation Organizations (59010-2000/2001/2002); Aakre Foundation (5695-2000, 5754-2002) and Health Region East. The current analyses were completed under funding from the National Institutes of Health (K12 ES019852). No competing interests declared.

Barrett, E.S.; Thune, I.; Lipson, S.F.; Furberg, A.-S.; Ellison, P.T.

2013-01-01

199

Measuring Length  

NSDL National Science Digital Library

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

2009-08-01

200

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

201

Performance characteristics for the measurement of Cs and Sr by diffusive gradients in thin films (DGT)  

Microsoft Academic Search

The new technique of diffusive gradients in thin films (DGT) has been used for the first time with a general cation exchange resin (AG50W-X8) as the binding agent. Its use for the measurement of Cs and Sr has been systematically investigated. Individual experiments showed that resin embedded in polyacrylamide gel efficiently removed Cs and Sr from solution. Cs and Sr

Ling-Yun Chang; William Davison; Hao Zhang; Mike Kelly

1998-01-01

202

Branch structure of IV-characteristics in the capacitively coupled Josephson junctions model with the diffusion current  

NASA Astrophysics Data System (ADS)

We have solved numerically a system of dynamical equations for the gauge-invariant phase differences between superconducting layers for a stack of N intrinsic junctions and obtained a total branch structure in the current-voltage characteristics (IVC) of the stack. The coupling dependence of the branch’s slopes is investigated and demonstrated that the equidistance of the branch structure in capacitively coupled Josephson junctions (CCJJ) model is broken at small values of coupling parameter. Changes in the parameters of the boundary conditions and the use of periodic boundary conditions do not affect this result. In the framework of the CCJJ model with the diffusion current we simulate an experiment and obtain the IV-characteristic with equidistant branch structure at different values of model parameters.

Shukrinov, Yu. M.; Mahfouzi, F.; Seidel, P.

2007-09-01

203

Content characteristics driving the diffusion of antismoking messages: implications for cancer prevention in the emerging public communication environment.  

PubMed

This study examined how content characteristics of antitobacco messages affect smokers' selective exposure to and social sharing of those messages. Results from an experiment revealed that content features predicting smokers' selection of antismoking messages are different from those predicting whether those messages are shared. Antismoking messages smokers tend to select are characterized by strong arguments (odds ratio = 2.02, P = .02) and positive sentiments (odds ratio = 3.08, P = .03). Once selected, the messages more likely to be retransmitted by smokers were those with novel arguments (B = .83, P = .002) and positive sentiments (B = 1.65, P = .005). This research adds to the literature about the content characteristics driving the social diffusion of antitobacco messages and contributes to our understanding of the role of persuasive messages about smoking cessation in the emerging public communication environment. PMID:24395989

Kim, Hyun Suk; Lee, Sungkyoung; Cappella, Joseph N; Vera, Lisa; Emery, Sherry

2013-12-01

204

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

2013-01-01

205

Probing surface characteristics of diffusion-limited-aggregation clusters with particles of variable size.  

PubMed

We develop a technique for probing the harmonic measure of a diffusion-limited-aggregation (DLA) cluster surface with variable-size particles and generate 1000 clusters with 50 x 10(6) particles using an original off-lattice killing-free algorithm. Taking, in sequence, the limit of the vanishing size of the probing particles and then sending the growing cluster size to infinity, we achieve unprecedented accuracy in determining the fractal dimension D=1.7100(2) crucial to the characterization of the geometric properties of DLA clusters. PMID:17358103

Menshutin, A Yu; Shchur, L N; Vinokur, V M

2007-01-01

206

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

207

The effect of rhythmic auditory stimulation (RAS) on gait characteristics of cadence, velocity, and stride length in persons with late stage dementia.  

PubMed

Persons (N = 28) diagnosed with dementia in late stage who had locomotion Functional Independence Measure (FIM) ratings of l, total assistance required, and 2, maximal assistance required, participated as subjects. All participants were enrolled in a restorative ambulation program which was implemented in this study under 3 conditions: Rhythmic auditory stimulation in which metronomic beats were imbedded in music, rhythmic auditory stimulation which consisted of metronomic beats without music, and no auditory stimulus. Gait characteristics of cadence, velocity, and stride length were compared across the 3 conditions. No statistically significant differences were found, however, observation showed that assistive burden seemed less when both forms of rhythmic auditory stimulation were used. Further research is recommended to study the effects of RAS on care burden and continued ambulation throughout the disease trajectory. PMID:16897907

Clair, Alicia Ann; O'Konski, Marjorie

2006-01-01

208

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

209

Investigation of high-intensity laser-plasma interaction and fast electron source characteristics from 1-10 ps pulse length  

NASA Astrophysics Data System (ADS)

Efficient conversion of laser energy to hot electrons is extremely important for the success of Fast Ignition (FI), where a drive laser pulse with duration of 10ps and energy 100's of kJ is required. Here we report the first theoretical and numerical study on the characteristics of laser-plasma interaction (LPI) and fast electron source production from 1-10 ps pulse drive. It is found that due to a significant hydrodynamic plasma expansion in picoseconds, the fast electron acceleration mechanism strongly relies on the laser leading edge depletion [1] in near critical plasma and the electrostatic potential [2] caused by low-density plasmas. Both the fast electron average temperature and the laser-electron conversion efficiency increase more than 2 times by extending the laser pulse length from 1ps to 10 ps. Their dependences on the preplasma scale length are also analyzed. [4pt] [1] A. P. L. Robinson et al., PPCF 53, 065019 (2011).[0pt] [2] B. S. Paradkar et al., PRE 83 046401 (2011).

Sorokovikova, A.; Qiao, B.; Wei, M. S.; Stephens, R. B.; Patel, P.; McLean, H.; Beg, F. N.

2012-10-01

210

Correlation between lithium storage and diffusion properties and electrochromic characteristics of WO3 thin films  

NASA Astrophysics Data System (ADS)

As essential electrochromic (EC) materials are related to energy savings in fenestration technology, tungsten oxide (WO3) films have been intensively studied recently. In order to achieve better understanding of the mechanism of EC properties, and thus facilitate optimization of device performance, clarification of the correlation between cation storage and transfer properties and the coloration performance is needed. In this study, transparent polycrystalline and amorphous WO3 thin films were deposited on SnO2:F-coated glass substrates by the pulsed laser deposition technique. Investigation into optical transmittance in a wavelength range of 400-800 nm measured at a current density of 130 ?A · cm-2 with the applied potential ranging from 3.2 to 2.2 V indicates that polycrystalline films have a larger optical modulation of ~ 30% at 600 nm and a larger coloration switch time of 95 s in the whole wavelength range compared with amorphous films (~ 24% and 50 s). Meanwhile, under the same conditions, polycrystalline films show a larger lithium storage capacity corresponding to a Li/W ratio of 0.5, a smaller lithium diffusion coefficient (2×10-12 cm2·s-1 for Li/W=0.24) compared with the amorphous ones, which have a Li/W ratio of 0.29 and a coefficient of ~2.5×10-11 cm2·s-1 as Li/W=0.24. These results demonstrate that the large optical modulation relates to the large lithium storage capacity, and the fast coloration transition is associated with fast lithium diffusion.

Yu, Peng-Fei; Cui, Zhong-Hui; Fan, Wu-Gang; Guo, Xiang-Xin

2013-03-01

211

Full-length amyloid-beta (1-42(43)) and amino-terminally modified and truncated amyloid-beta 42(43) deposit in diffuse plaques.  

PubMed Central

The amino- and carboxyl-terminal properties of the amyloid-beta (A beta) peptides deposited in diffuse plaques, one of the earliest forms of A beta deposition, were examined in the brains of patients with Down's syndrome and Alzheimer's disease and in aged individuals without dementia by immunocytochemistry. This was done using a panel of antibodies that specifically discriminate the terminal structures and modifications at the amino and carboxyl termini of A beta. Diffuse plaques found in the cerebral and cerebellar cortex, neostriatum, and hypothalamus of Down's syndrome, Alzheimer's disease, and nondemented brains were strongly immunoreactive for A beta N1(L-Asp), A beta N1(L-isoAsp), A beta N1(D-Asp), and A beta N3(pyroGlu) and weakly positive for A beta N11(pyroGlu) and A beta N17(Leu). Diffuse plaques also were positive for A beta 42(43) but negative for A beta 40, using carboxyl-terminal-specific anti-A beta antibodies. These results suggest that the amino termini of the A beta species that initially deposit in diffuse plaques begin with A beta N1(Asp) with or without structural modifications (isomerization and racemization), as well as with A beta N3(pyroGlu), and terminate preferentially at A beta 42(43) rather than A beta 40. Images Figure 2 Figure 3

Iwatsubo, T.; Saido, T. C.; Mann, D. M.; Lee, V. M.; Trojanowski, J. Q.

1996-01-01

212

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

213

Diffusion and Perfusion Characteristics of MELAS (Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-Like Episode) in Thirteen Patients  

PubMed Central

Objective We analyzed the diffusion and perfusion characteristics of acute MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) lesions in a large series to investigate the controversial changes of the apparent diffusion coefficient (ADC) that were reported in prior studies. Materials and Methods We analyzed 44 newly appearing lesions during 28 stroke-like episodes in 13 patients with MELAS. We performed a visual assessment of the MR images including the ADC and perfusion maps, comparison of the ADC between the normal and abnormal areas, comparison of % ADC between the 44 MELAS lesions and the 30 acute ischemic infarcts. In addition, the patterns of evolution on follow-up MR images were analyzed. Results Decreased, increased, and normal ADCs were noted in 16 (36%), 16 (36%), and 12 (27%) lesions, respectively. The mean % ADC was 102 ± 40.9% in the MELAS and 64 ± 17.8% in the acute vascular infarcts (p < 0.001), while perfusion imaging demonstrated hyper-perfusion in six acute MELAS lesions. On follow-up images, resolution, progression, and tissue loss were noted in 10, 4, and 17 lesions, respectively. Conclusion The cytotoxic edema gradually evolves following an acute stroke-like episode in patients with MELAS, and this may overlap with hyper-perfusion and vasogenic edema. The edematous swelling may be reversible or it may evolve to encephalomalacia, suggesting irreversible damage.

Kim, Ji Hye; Jeon, Tae Yeon; Rha, Jung Ho; Eo, Hong; Yoo, So-Young; Shu, Chang Hae

2011-01-01

214

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

215

Immunohistochemical and Molecular Characteristics with Prognostic Significance in Diffuse Large B-Cell Lymphoma  

PubMed Central

Diffuse large B-cell lymphoma (DLBCL) is an aggressive non-Hodgkin lymphoma with marked biologic heterogeneity. We analyzed 100 cases of DLBCL to evaluate the prognostic value of immunohistochemical markers derived from the gene expression profiling-defined cell origin signature, including MYC, BCL2, BCL6, and FOXP1 protein expression. We also investigated genetic alterations in BCL2, BCL6, MYC and FOXP1 using fluorescence in situ hybridization and assessed their prognostic significance. BCL6 rearrangements were detected in 29% of cases, and BCL6 gene alteration (rearrangement and/or amplification) was associated with the non-germinal center B subtype (non-GCB). BCL2 translocation was associated with the GCB phenotype, and BCL2 protein expression was associated with the translocation and/or amplification of 18q21. MYC rearrangements were detected in 15% of cases, and MYC protein expression was observed in 29% of cases. FOXP1 expression, mainly of the non-GCB subtype, was demonstrated in 37% of cases. Co-expression of the MYC and BCL2 proteins, with non-GCB subtype predominance, was observed in 21% of cases. We detected an association between high FOXP1 expression and a high proliferation rate as well as a significant positive correlation between MYC overexpression and FOXP1 overexpression. MYC, BCL2 and FOXP1 expression were significant predictors of overall survival. The co-expression of MYC and BCL2 confers a poorer clinical outcome than MYC or BCL2 expression alone, whereas cases negative for both markers had the best outcomes. Our study confirms that DLBCL, characterized by the co-expression of MYC and BCL2 proteins, has a poor prognosis and establishes a significant positive correlation with MYC and FOXP1 over-expression in this entity.

Bellas, Carmen; Garcia, Diego; Vicente, Yolanda; Kilany, Linah; Abraira, Victor; Navarro, Belen; Provencio, Mariano; Martin, Paloma

2014-01-01

216

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

SciTech Connect

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

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

2000-11-22

217

Analysis of the impact of surface layer properties on evaporation from porous systems using column experiments and modified definition of characteristic length  

NASA Astrophysics Data System (ADS)

hydraulic properties of the layer at the vicinity of the soil surface have significant impact on evaporation and could be harnessed to reduce water losses. The effect of the properties of the upper layer on the evolution of phase distribution during the evaporation process is first illustrated from three-dimensional pore network simulations. This effect is then studied from experiments carried out on soil columns under laboratory conditions. Comparisons between homogeneous columns packed with coarse (sand) and fine (sandy loam) materials and heterogeneous columns packed with layers of fine overlying coarse material and coarse overlying fine material of different thicknesses are performed to assess the impact of upper layer properties on evaporation. Experiments are analyzed using the classical approach based on the numerical solution of Richards equation and semianalytical theoretical predictions. The theoretical analysis is based on the clear distinction between two drying regimes, namely, the capillary regime and the gravity-capillary regime, which are the prevailing regimes in our experiments. Simple relationships enabling to estimate the duration of stage 1 evaporation (S1) for both regimes are proposed. In particular, this led to defining the characteristic length for the gravity-capillary regime from the consideration of viscous effects at low water content differently from available expressions. The duration of S1, during which most of the water losses occur, for both the homogeneous and two-layer columns is presented and discussed. Finally, the impact of liquid films and its consequences on the soil hydraulic conductivity function are briefly discussed.

Assouline, Shmuel; Narkis, Kfir; Gherabli, Rivka; Lefort, Philippe; Prat, Marc

2014-05-01

218

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

NASA Astrophysics Data System (ADS)

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

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

1984-06-01

219

The spatial and temporal characteristics of the apparent-diffusion-coefficient-dependent fMRI signal changes during visual stimulation.  

PubMed

The blood oxygenation level dependent (BOLD) contrast has been commonly used to detect fMRI signal. The majority of the BOLD signals are believed to arise from the venous and capillary networks. However, only those from the capillaries are spatially close to the neuronal activities, while the signals from large veins could be distant, rendering the overall localization inaccurate. In recent years, an alternative contrast using arterial spin labeled (ASL) perfusion imaging techniques has been proposed for predominant capillary sensitivity. Such acquisition methods, however, are intrinsically limited in temporal resolution and spatial coverage. Another contrast mechanism, free of such constraints, is based on the apparent diffusion coefficient (ADC) changes during brain activation using isotropic diffusion weighting. It has been shown that these changes are synchronized with brain activation and that they, as a whole, temporally precede BOLD activation, suggesting significant upstream arterial contribution. Moreover, the spatial overlaps between the upstream ADC and downstream BOLD activations are shown to be more localized in the capillaries, which are the temporal and spatial middle ground. In this paper, we sought to further investigate the temporal and spatial characteristics of ADC contrast with additional arterial signal suppression. Also, a pixel-based evaluation was performed in conjunction with the averaged global assessment. It was found that in addition to the known spatial discrepancy and global timing advance compared to the BOLD signal, the ADC activation endured significant temporal heterogeneities. Such fine spatial and temporal assessment could help characterize the exact signal sources of ADC contrast, and ultimately achieve exclusive capillary sensitivity. PMID:15876620

Song, Allen W; Gangstead, Stacey L

2004-03-01

220

Rotational diffusion of nonpolar and ionic solutes in 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides: is solute rotation always influenced by the length of the alkyl chain on the imidazolium cation?  

PubMed

In an attempt to find out whether the length of the alkyl chain on the imidazolium cation has a bearing on solute rotation, temperature-dependent fluorescence anisotropies of three structurally similar solutes have been measured in a series of 1-alkyl-3-methylimidazolium (alkyl = methyl, ethyl, propyl, butyl, and hexyl) bis(trifluoromethylsulfonyl)imides. Solute-solvent coupling constants obtained from the experimentally measured reorientation times with the aid of Stokes-Einstein-Debye hydrodynamic theory indicate that there is no influence of the length of the alkyl chain on the rotation of nonpolar, anionic, and cationic solutes 9-phenylanthracene (9-PA), fluorescein (FL), and rhodamine 110 (R110), respectively. It has also been noticed that the rotational diffusion of 9-PA is closer to the predictions of slip hydrodynamics, whereas the rotation of negatively charged FL and positively charged R110 is almost identical and follows stick hydrodynamics in these ionic liquids. Despite having similar shape and size, ionic solutes rotate slower by a factor of 3-4 compared to the nonpolar solute. Interplay of specific and electrostatic interactions between FL and the imidazolium cation of the ionic liquids, and between R110 and the bis(trifluoromethylsulfonyl)imide anion, appear to be responsible for the observed behavior. These results are an indication that the length of the alkyl chain on the imidazolium cation does not alter their physical properties in a manner that has an effect on solute rotation. PMID:23013036

Gangamallaiah, V; Dutt, G B

2012-10-25

221

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

222

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

NASA Astrophysics Data System (ADS)

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

Liu, Siyang; Zhang, Chunwei; Sun, Weifeng; Su, Wei; Wang, Shaorong; Ma, Shulang; Huang, Yu

2014-04-01

223

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

224

Hydrogen bonding effects in adsorption of water-alcohol mixtures in zeolites and the consequences for the characteristics of the Maxwell-Stefan diffusivities.  

PubMed

This work highlights a variety of peculiar characteristics of adsorption and diffusion of polar molecules such as water, methanol and ethanol in zeolites. These peculiarities are investigated with the aid of configurational-bias Monte Carlo (CBMC) simulations of adsorption isotherms, and molecular dynamics (MD) simulations of diffusivities in FAU, MFI, DDR, and LTA zeolites. Because of strong hydrogen bonding, significant clustering of the guest molecules occurs in all investigated structures. Because of molecular clustering, the inverse thermodynamic factor 1/Gamma(i) identical with (d[ln c(i)])/(d[ln f(i)]) exceeds unity for a range molar concentrations c(i) within the micropores. The degree of clustering is lowered as the temperature is increased. For the concentration ranges for which 1/Gamma(i) > 1, the Fick diffusivity, D(i), for unary diffusion is often lower than both the Maxwell-Stefan, D(i), and the self-diffusivity, D(i,self). For water-alcohol mixtures, the hydrogen bonding between water and alcohol molecules is much more predominant than for water-water, and alcohol-alcohol molecule pairs. Consequently, the adsorption of water-alcohol mixtures shows significant deviations from the predictions of the ideal adsorbed solution theory (IAST). The water-alcohol bonding also leaves its imprint on the mixture diffusion characteristics. The Maxwell-Stefan diffusivity, D(i), of either component in water-alcohol mixtures is lower than the corresponding values of the pure components; this behavior is distinctly different from that for mixtures of nonpolar guest molecules. The binary exchange coefficient D(12) for water-alcohol mixtures is also significantly lower than either self-exchange coefficients D(11) and D(22) of the constituent species. This implies that correlation effects are significantly stronger in water-alcohol mixtures than for the constituent species. Correlation effects are found to be significant for water-alcohol mixture diffusion in DDR and LTA zeolites, even though such effects are negligible for the pure constituents. The major conclusion to emerge from this investigation is that, unlike mixtures of nonpolar molecules, it is not possible to estimate water-alcohol mixture adsorption and diffusion characteristics on the basis of pure component data. PMID:20411951

Krishna, Rajamani; van Baten, Jasper M

2010-07-01

225

Finger Length  

NSDL National Science Digital Library

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

American Association for the Advancement of Science (;)

2005-03-28

226

Damage and recovery characteristics of lithium-containing solar cells.  

NASA Technical Reports Server (NTRS)

Damage and recovery characteristics were measured on lithium-containing solar cells irradiated by 1-MeV electrons. Empirical expressions for cell recovery time, diffusion-length damage coefficient immediately after irradiation, and diffusion-length damage coefficient after recovery were derived using results of short-circuit current, diffusion-length, and reverse-bias capacitance measurements. The damage coefficients were expressed in terms of a single lithium density parameter, the lithium gradient. A fluence dependence was also established, this dependence being the same for both the immediate-post-irradiation and post-recovery cases. Cell recovery rates were found to increase linearly with lithium gradient.

Faith, T. J.

1971-01-01

227

Mixed finite element method for generalized convection-diffusion equations based on an implicit characteristic-based algorithm  

Microsoft Academic Search

Summary  A mixed finite element method for generalized convection-diffusion equations is proposed. The primitive variable with its\\u000a spatial gradient and the diffusion flux are interpolated as independent variables. The variational (weak) form of the governing\\u000a equations is given on the basis of the extended Hu-Washizu three-field variational principle. The mixed element is formulated\\u000a with stabilized one point quadrature scheme and particularly

W. Wu; X. Li

2007-01-01

228

Supersonic Axial-Force Characteristics of a Rectangular-Box Cavity with Various Length-to-Depth Ratios in a Flat Plate.  

National Technical Information Service (NTIS)

A wind-tunnel investigation has been conducted at Mach numbers of 1.50, 2.16, and 2.86 to obtain axial-force data on a metric rectangular-box cavity with various length-to-depth ratios. The model was tested at angles of attack from -4 deg to -2 deg. The r...

A. B. Blair R. L. Stallings

1986-01-01

229

Macro-meso two-scale model for predicting the VOC diffusion coefficients and emission characteristics of porous building materials  

NASA Astrophysics Data System (ADS)

Through the observation of the pore structure and mercury intruding porosimetry (MIP) experiments of some typical porous building materials, we found that the diffusion coefficient of the material can be expressed by that of a representative elementary volume (REV) in which the pore structure can be simplified as a connection in series of macro and meso pores. Based upon that, a macro-meso two-scale model for predicting the diffusion coefficient of porous building materials is proposed. In contrast to the traditional porous mass transfer model for determining the diffusion coefficient described in the literature [Blondeau, P., Tiffonnet, A.L., Damian, A., Amiri, O., Molina, J.L., 2003. Assessment of contaminant diffusivities in building materials from porosimetry tests. Indoor Air 13, 302-310; Seo, J., Kato, S., Ataka, Y., Zhu, Q., 2005. Evaluation of effective diffusion coefficient in various building materials and absorbents by mercury intrusion porosimetry. In Proceedings of the Indoor Air, Beijing, China, pp. 1854-1859], the proposed model relates the volatile organic compound (VOC) diffusion coefficient of building material not only to the porosity of the building material, but also to the pore size distribution and pore connection modes. To verify the model, a series of experiments of VOC emissions of three types of medium-density board were conducted. The comparison of the model and experimental results shows that the proposed model agrees much better with the experimental results than the traditional models in the literature. More validation for other building materials is needed. The proposed model is useful for predicting the VOC diffusion coefficient of porous building materials and for developing low VOC emission building materials.

Xiong, Jianyin; Zhang, Yinping; Wang, Xinke; Chang, Dongwu

230

Formation of PS-b-PEO/Silica Films with Flat or Curved Multi-Bilayer Mesostructures of Large-Characteristic Length Scales Prepared by Solvent Evaporation-Induced Self-Assembly  

SciTech Connect

Diblock/silica films with multi-bilayer vesicular mesostructures of large characteristic length scales were synthesized through evaporation-induced self-assembly of PS-b-PEO. The present system is believed to be the first to yield diblock/silica films with multi-bilayer vesicular mesostructures through solvent evaporation-induced self-assembly (EISA). The ready formation in the present system is argued to be the polydispersity of polymer chains.

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

2000-11-22

231

Effects of airplane characteristics and takeoff noise and field length constraints on engine cycle selection for a Mach 2.32 cruise application  

NASA Technical Reports Server (NTRS)

Sideline noise and takeoff field length were varied for two types of Mach 2.32 cruise airplane to determine their effect on engine cycle selection. One of these airplanes was the NASA/Langley-LTV arrow wing while the other was a Boeing modified delta-plus-tail derived from the earlier 2707-300 concept. Advanced variable cycle engines were considered. A more conventional advanced low bypass turbofan engine was used as a baseline for comparison. Appropriate exhaust nozzle modifications were assumed, where needed, to allow all engines to receive either an inherent co-annular or annular jet noise suppression benefit. All the VCE's out-performed the baseline engine by substantial margins in a design range comparison, regardless of airplane choice or takeoff restrictions. The choice among the three VCE's considered, however, depends on the field length, noise level, and airplane selected.

Whitlow, J. B., Jr.

1976-01-01

232

Myofascial force transmission is increasingly important at lower forces: firing frequency-related length-force characteristics of rat extensor digitorum longus  

Microsoft Academic Search

Aim: Effects of submaximal stimulation frequencies on myofascial force transmission were investigated for rat anterior crural muscles with all motor units activated. -\\u000aMethods: Tibialis anterior and extensor hallucis longus (TAEHL) muscles were kept at constant muscle-tendon complex length, but extensor digitorum longus muscle (EDL) was lengthened distally. All muscles were activated simultaneously at 10, 20, 30 and 100 Hz

H. J. M. Meijer; G. C. Baan; P. A. Huijing

2006-01-01

233

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

234

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.

1988-06-28

235

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...

236

Ambipolar diffusion, cloud cores, and star formation: Two-dimensional, cylindrically symmetric contraction. II - Results and a length scale for protostellar cores. III - A further parameter study and magnetically controlled accretion rate  

NASA Astrophysics Data System (ADS)

Ambipolar diffusion initiates the formation and collapse of cores in self-gravitating, thermally supercritical model clouds which would be in exact equilibrium states if the magnetic field were frozen in the matter. We follow the contraction to an increase of the central density by a factor of 106 (e.g., from 3 × 103 to 3 × 109 cm-3). The results are interpreted in terms of the thermal (??,cr = 1.4C?ff) magnetic (?M = &?A?ff), and Alfvén (?A = ??A?ni) length scales, discussed recently elsewhere, where C, ?A, ?ff, and ?ni are, respectively, the isothermal sound speed, the Alfvén speed in the neutrals, the free-fall time, and the neutral-ion collision time. Typically, a nearly uniform-density core forms and shrinks in time, leaving behind a "tail" of infalling matter in which a power4aw density profile tends to be established. Magnetic forces (typically) remain the dominant opposition to gravity in the envelope and introduce a break in the slope of the log ?n-log r profile; at larger radii the structure of the cloud throughout the evolution is primarily determined by the physical conditions prevailing in the parent cloud. In the core and the innermost part of the tail, magnetic forces tend to relinquish to thermal-pressure forces the role of primary opposition to gravity, and a (second) break in the slope of log ?n-log r appears in the tail as well; it is more pronounced the more bimodal the opposition to gravity (by thermal-pressure forces in the core and magnetic forces in the envelope) becomes. As time progresses, the tail extends inward in radius because of the decreasing size of the uniform-density core. The mass infall (or accretion) rate from the envelope is controlled by (usually slow) ambipolar diffusion, whose time scale is typically 3-4 orders of magnitude longer in the envelope than in the core, as found analytically in 1979 by Mouschovias. The dependence of the results on the three free parameters present in the two-fluid equations is studied. For initially thermally supercritical, primarily magnetically supported clouds, the evolution of the cores is insensitive to the other (at most two) free parameters that enter through the boundary conditions the initial conditions introduce no new free parameters. In a following paper, we extend the parameter study and discuss further the two breaks in the slope of the log ?n-log r profile, the mass infall rate, and the dependence of the exponent ? in the relation Bc ? ??c between the magnetic field strength and the gas density in the core on the free parameters.

Mouschovias, Telemachos Ch.; Morton, Scott A.

1992-05-01

237

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.

238

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

239

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

240

Effect of Series Resistance on Field-Effect Mobility at Varying Channel Lengths and Investigation into the Enhancement of Source/Drain Metallized Thin-Film Transistor Characteristics  

NASA Astrophysics Data System (ADS)

The degradation in device performance due to parasitic resistance along the source and drain electrodes is a serious problem in thin-film transistor fabrication. The effect of this series resistance on the field-effect mobility has been discussed and solutions for the reduction of this unexpected resistance were studied in this work. From the derivation of the drain current, it was shown that the additional resistance had a greater influence on short-channel devices. The ratio of the series resistance to the channel resistance determined the amount of degradation to the field-effect mobility. A thin-film transistor using an aluminum-metallized source/drain was suggested; it showed an improvement in comparison with the conventional doped source/drain device, with a maximum mobility of 105 cm2 V-1 s-1. However, significant degradation of the mobility in the short-channel cases exposed the limitations of the structure. By employing doping for the source/drain metallized structure the maximum mobility reached a value of 150 cm2 V-1 s-1. The decrease in the mobility caused by the channel length decrease was also improved. This study clearly explained the problem of additional resistance on the field-effect mobility of thin-film transistors and the achievements of a device using a self-aligned fabrication process with metallized electrodes.

Duy, Nguyen Van; Baek, Kyunghyun; Son, Dang Ngoc; Lee, Wonbaek; Kim, Kwangryul; Choi, Byoungdeog; Chung, Hokyun; Yi, Junsin

2011-02-01

241

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

242

Experimental study of vortex diffusers  

SciTech Connect

This report documents experimental research performed on vortex diffusers used in ventilation and air-conditioning systems. The main objectives of the research were (1) to study the flow characteristics of isothermal jets issuing from vortex diffusers, (2) to compare the vortex diffuser`s performance with that of a conventional diffuser, and (3) to prepare a report that disseminates the results to the designers of ventilation and air-conditioning systems. The researchers considered three diffusers: a conventional round ceiling diffuser and two different styles of vortex diffusers. Overall, the vortex diffusers create slightly more induction of ambient air in comparison to the conventional diffuser.

Shakerin, S.; Miller, P.L. [National Renewable Energy Lab., Golden, CO (United States)

1995-11-01

243

The effect of diffusion induced lattice stress on the open-circuit voltage in silicon solar cells  

NASA Technical Reports Server (NTRS)

It is demonstrated that diffusion induced stresses in low resistivity silicon solar cells can significantly reduce both the open-circuit voltage and collection efficiency. The degradation mechanism involves stress induced changes in both the minority carrier mobility and the diffusion length. Thermal recovery characteristics indicate that the stresses are relieved at higher temperatures by divacancy flow (silicon self diffusion). The level of residual stress in as-fabricated cells was found to be negligible in the cells tested.

Weizer, V. G.; Godlewski, M. P.

1984-01-01

244

Role of electroless nickel diffusion barrier on the combinatorial plating characteristics of dense Pd/Ni/PSS composite membranes  

NASA Astrophysics Data System (ADS)

This work addresses the combinatorial plating characteristics of dense Pd/Ni/porous stainless steel (PSS) composite membranes in comparison with Pd/PSS membranes. While Pd/PSS membranes were fabricated using 0.1 ?m nominal pore size PSS supports, Pd/Ni/PSS membranes were fabricated using 0.5 and 0.1 ?m nominal pore size PSS supports. Both Ni and Pd films were deposited using an identified novel electroless plating process that characterizes the optimal utilization of surfactant, sonication and reducing agent contacting pattern in Pd electroless plating baths. It was observed that the combinatorial plating characteristics for Pd/Ni/PSS membranes were significantly different and poorer in comparison with those obtained for the Pd/PSS membranes. In summary, it has been inferred that the introduction of nickel interdiffusion barrier was not fruitful to reduce the critical thickness of dense Pd film without jeopardizing upon the pore densification.

Pujari, Murali; Agarwal, Amrita; Uppaluri, Ramgopal; Verma, Anil

2014-06-01

245

Performance characteristics of suspended particulate reagent-iminodiacetate as a binding agent for diffusive gradients in thin films  

Microsoft Academic Search

The performance characteristics of an alternative binding agent, suspended particulate reagent-iminodiacetate (SPR-IDA), for use with DGT methodology were investigated. The parameters investigated during this study included gel hydration, blank levels, elution factor (fe), capacity, the effects of pH on the binding of trace metals by DGT. The novel application of this resin for use as a quantitative standard for laser

Kent W. Warnken; Hao Zhang; William Davison

2004-01-01

246

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

PubMed

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

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

2014-07-01

247

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

2010-12-01

248

Comparison of Clinical and Radiographic Characteristics between Nodular Bronchiectatic Form of Nontuberculous Mycobacterial Lung Disease and Diffuse Panbronchiolitis  

PubMed Central

The nodular bronchiectatic form of nontuberculous mycobacterial (NTM) lung disease and diffuse panbronchiolits (DPB) show similar clinical and radiographic findings. The present study was performed to clarify the clinicoradiographic similarities as well as the differences between NTM lung disease and DPB. The initial clinicoradiographic features of 78 patients with the nodular bronchiectatic form of NTM lung disease (41 patients with Mycobacterium avium complex infection and 37 patients with Mycobacterium abscessus infection) were compared with those of 35 patients with DPB. Old age, female sex, a history of tuberculosis treatment, and hemoptysis were related to NTM lung disease while exertional dyspnea, coarse crackles, history of sinusitis, obstructive abnormalities in pulmonary function tests, and hypoxemia were related to DPB. The number of lobes involved with bronchiolitis and bronchiectasis on chest computed tomography were more numerous in DPB patients. There is considerable overlap in the clinical and radiographic appearances of the nodular bronchiectatic form of NTM lung disease and DPB, although some clinicoradiographic features differ between two diseases. The correct diagnosis, including aggressive microbiologic evaluation, should be made for the appropriate management of patients presenting with bilateral bronchiectasis and bronchiolitis.

Park, Hye Yun; Suh, Gee Young; Chung, Man Pyo; Kim, Hojoong; Kwon, O Jung; Chung, Myung Jin; Kim, Tae Sung; Lee, Kyung Soo

2009-01-01

249

Characteristics of the motions, turbulence intensity, diffusivity, flux of momentum and sensible heat in the upper atmosphere  

NASA Technical Reports Server (NTRS)

Analyses of the meteorological rocket data obtained from an experiment conducted at 3-hour intervals at 8 western meridional rocket stations are presented. Large variations in the meridional wind contribute substantially to overall turbulence in the tropical stratosphere. The solar semidiurnal component of wind oscillations in the tropics was observed to be much higher than predicted by theory, often exceeding the magnitude of the diurnal amplitude throughout the stratosphere. The observed value of the solar diurnal amplitude in the stratosphere was in line with theoretical prediction. The solar terdiurnal amplitudes for temperature, meridional and zonal winds were non-negligible and must be considered in any harmonic analysis. Phase angle variation with height was rapid for all harmonics; however, there was general agreement between predicted and observed phase angles. Because of large changes in the mean winds in the mesosphere with season, harmonic determinations are difficult. There appear to be large zonal wind changes even within the same season as mentioned previously. Turbulence diffusivity in the upper stratosphere is greater near the equator than in the mid-latitudes.

Kao, S. K.; Lordi, N. J.

1977-01-01

250

Binding and diffusion characteristics of 14C EDTA and 99mTc DTPA in respiratory tract mucus glycoprotein from patients with chronic bronchitis.  

PubMed Central

Measurement of pulmonary clearance of an inhaled aerosol of technetium-99m labelled diethylenetriaminepenta-acetate (DTPA) by external detection methods has been used widely as an index of permeability across alveolar epithelium and bronchial mucosa. To determine the applicability of the tracer to measurement of permeability in the airways the diffusion and binding characteristics of 99mTc DTPA and the chemically related ethylenediaminetetra-acetic acid labelled with carbon-14 (14C EDTA) was studied in purified respiratory tract mucus glycoprotein from patients with chronic bronchitis. The diffusion coefficients for 99mTc DTPA and 14C EDTA through mucus gels were significantly lower than those for tritiated water. Both molecules bound to the mucus gels with high affinity at two independent low capacity sites. Appreciable amounts of 99mTc DTPA or 14C EDTA are therefore unlikely to cross mucus layers of physiological thickness over periods of four or five hours. This suggests that when pulmonary clearance is determined by the 99mTc DTPA method the tracer retained in mucus lined airways will provide background activity. This study supports the assumption that pulmonary clearance measurements are mainly measuring alveolar epithelial permeability and should not be used to study bronchial epithelial permeability.

Cheema, M S; Groth, S; Marriott, C

1988-01-01

251

Augmentation of turbulent heat transfer on a flat plate with a three-dimensional protuberance. I - Local heat transfer characteristics and flow pattern around a finite length circular proturberance  

NASA Astrophysics Data System (ADS)

In order to obtain the fundamental data on the high performance roughened heating surface, the augmentative effects of a three-dimensional protuberance, whose height was the same order as boundary layer thickness, was investigated. In this paper, the local heat transfer characteristics and flow field around a single and finite length circular cylindrical protuberance have been investigated experimentally, under the condition of H/D = 0.5 to about 1.0, H/to about = 5 Theta 15, and Re(H) 5000 to about 30000. Consequently, the most effective shape parameter for the augmentation of heat transfer was indicated, and a wake flow structure was proposed. And an arrangement of maximum heat transfer coefficient was presented experimentally as a function of shape parameter.

Kawamura, T.; Hiwada, M.; Mabuchi, I.; Kumada, M.

1984-12-01

252

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

NASA Astrophysics Data System (ADS)

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 ? mode discharge of the RF APGD plasmas are presented. The experiments are conducted by placing the home-made planar-type plasma generator in ambient and in a vacuum chamber, respectively, with helium as the primary plasma-forming gas. When the discharge processes occur in ambient, particularly for the lower plasma-working gas flow rates, the experimental measurements show that it is the back-diffusion effect of air in atmosphere, instead of the flow rate of the gas, that results in the obvious decrease in the breakdown voltage with increasing plasma-working gas flow rate. Further studies on the discharge characteristics, e.g. the luminous structures, the concentrations and distributions of chemically active species in plasmas, with different plasma-working gases or gas mixtures need to be conducted in future work.

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

2007-05-01

253

Diffusing wave spectroscopy in Maxwellian fluids  

NASA Astrophysics Data System (ADS)

We present a critical assessment of the diffusing wave spectroscopy (DWS) technique for obtaining the characteristic lengths and for measuring the loss and storage moduli of a reasonable well-known wormlike micelle (WM) system. For this purpose, we tracked the Brownian motion of particles using DWS embedded in a Maxwellian fluid constituted by a wormlike micellar solution made of cetyltrimethylammonium bromide (CTAB), sodium salicylate (NaSal), and water. We found that the motion of particles was governed by the viscosity of the solvent at short times and by the stress relaxation mechanisms of the giant micelles at longer times. From the time evolution of the mean square displacement of particles, we could obtain for the WM solution the cage size where each particle is harmonically bound at short times, the long-time diffusion coefficient, and experimental values for the exponent that accounts for the broad spectrum of relaxation times at the plateau onset time found in the ensuremath < ? r2(t)> vs. time curves. In addition, from the ensuremath < ? r2(t)> vs. time curves, we obtained ensuremath Gprime(?) and ensuremath Gprime prime(?) for the WM solutions. All the DWS microreological information allowed us to estimate the characteristic lengths of the WM network. We compare our DWS microrheological results and characteristic lengths with those obtained with mechanical rheometers at different NaSal/CTAB concentration ratios and temperatures.

Galvan-Miyoshi, J.; Delgado, J.; Castillo, R.

2008-08-01

254

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

255

Gene expression profiling of Epstein-Barr virus-positive diffuse large B-cell lymphoma of the elderly reveals alterations of characteristic oncogenetic pathways.  

PubMed

Epstein-Barr virus (EBV)-positive diffuse large B-cell lymphoma (DLBCL) of the elderly (EBV[+]DLBCL-E) is classified as a subtype of DLBCL. Until now, its molecular pathogenesis has remained unknown. To identify pathways characteristic of EBV(+)DLBCL-E, gene expression profiling of five EBV(+)DLBCL-E and seven EBV-negative DLBCL (EBV[-]DLBCL) cases was undertaken using human oligonucleotide microarray analysis. Gene set enrichment analysis and gene ontology analysis showed that gene sets of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) and nuclear factor kappa B (NF-?B) pathways were enriched in EBV(+)DLBCL-E cases. To confirm the results of the expression profiles, in vitro analysis was performed. Expression profiling analysis showed that high activation of the JAK-STAT and NF-?B pathways was induced by EBV infection into DLBCL cell lines. Activation of the NF-?B pathway was confirmed in EBV-infected cell lines using an electrophoretic mobility shift assay. Western blot analysis revealed an increased protein expression level of phosphorylated signal transducer and activator of transcription 3 (STAT3) in an EBV-infected cell line. Protein expression of phosphorylated STAT3 was frequently observed in lymphoma cells of EBV(+)DLBCL-E clinical samples using immunohistochemistry (EBV[+]DLBCL-E: 80.0% [n = 20/25] versus EBV[-]DLBCL: 38.9% [n = 14/36]; P = 0.001). The results of the present study suggest that activation of the JAK-STAT and NF-?B pathways was characteristic of EBV(+)DLBCL-E, which may reflect the nature of EBV-positive tumor cells. Targeting these pathways as therapies might improve clinical outcomes of EBV(+)DLBCL-E. PMID:24581222

Kato, Harumi; Karube, Kennosuke; Yamamoto, Kazuhito; Takizawa, Jun; Tsuzuki, Shinobu; Yatabe, Yasushi; Kanda, Teru; Katayama, Miyuki; Ozawa, Yukiyasu; Ishitsuka, Kenji; Okamoto, Masataka; Kinoshita, Tomohiro; Ohshima, Koichi; Nakamura, Shigeo; Morishima, Yasuo; Seto, Masao

2014-05-01

256

An Investigation of Diffusion Barrier Characteristics of an Electroless Co(W,P) Layer to Lead-Free SnBi Solder  

NASA Astrophysics Data System (ADS)

Diffusion barrier characteristics for eutectic SnBi solder/electroless Co(W,P) couples were investigated via liquid-state aging at 250°C and solid-state aging at 120°C. At the couple interface, CoSn3 intermetallic compound (IMC) spallation was observed for the SnBi/amorphous Co(W,P) couple subjected to liquid-state aging. In contrast, no spallation of IMCs was observed for the SnBi/amorphous Co(W,P) couples subjected to solid-state aging. For the SnBi/polycrystalline Co(W,P) couple, a thick IMC layer was observed adjacent to a tungsten-enriched amorphous interfacial layer regardless of aging conditions. IMC formation in all samples indicated that Co(W,P) is essentially a sacrificial barrier to SnBi solder. However, amorphous Co(W,P) might also exhibit stuffed-type barrier behavior due to its relatively high phosphorus (P) content. Analytical results indicated that the P content in Co(W,P) is a crucial factor affecting the structural evolution at the SnBi/electroless Co(W,P) interface.

Pan, Hung-Chun; Hsieh, Tsung-Eong

2011-03-01

257

The diffusive idealization of charged particle transport in random magnetic fields  

NASA Technical Reports Server (NTRS)

The transport of charged particles diffusing in a random magnetic field parallel to a relatively large guiding field is presented. The same coefficient of diffusion is obtained by three methods. Two corrections must be added to the expression in which the diffusive flux is proportional to the gradient of the density. Explicit expressions are given for a characteristic time and a characteristic length which describe the corrections. The well known divergence of the coefficient of diffusion, which is implied by the quasilinear analysis of pitch angle scattering, does not occur if the scattering rate is finite at 90 deg pitch angle. This effect is illustrated by formulas which give the coefficient of diffusion when the quasilinear expression is perturbed by a variable amount of isotropic scattering.

Earl, J. A.

1974-01-01

258

A nonlinear equation for ionic diffusion in a strong binary electrolyte.  

PubMed

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. PMID:21818176

Ghosal, Sandip; Chen, Zhen

2010-07-01

259

Chapter 16: Image Restoration by Non-standard Diffusion  

Microsoft Academic Search

Many authors used different techniques for image restoration. Variational approaches are mainly used for this purpose. For example, the Mumfort-Shah is a model type for the free discontinuity in the restoration and segmentation of images. The main characteristic of this model is the isotropic diffusion, minimizing the length of the boundaries, while the classical models due to Rudin-Osher-Fatmi, minimize the

M. Maouni; F. Z. Nouri; D. Meskine

2008-01-01

260

Charged Particle Diffusion in Isotropic Random Static Magnetic Fields  

NASA Astrophysics Data System (ADS)

Study of the transport and diffusion of charged particles in a turbulent magnetic field remains a subject of considerable interest. Research has most frequently concentrated on determining the diffusion coefficient in the presence of a mean magnetic field. Here we consider Diffusion of charged particles in fully three dimensional statistically isotropic magnetic field turbulence with no mean field which is pertinent to many astrophysical situations. We classify different regions of particle energy depending upon the ratio of Larmor radius of the charged particle to the characteristic outer length scale of turbulence. We propose three different theoretical models to calculate the diffusion coefficient each applicable to a distinct range of particle energies. The theoretical results are compared with those from computer simulations, showing very good agreement.

Subedi, P.; Sonsrettee, W.; Matthaeus, W. H.; Ruffolo, D. J.; Wan, M.; Montgomery, D.

2013-12-01

261

Non-Gaussian Statistics and Anomalous Diffusion in Porous Media  

NASA Astrophysics Data System (ADS)

Two time displacement correlation functions grow linearly with time for ordinary diffusion, but for the case of anomalous diffusion it shows more complex time dependence. Anomalous diffusion is abundant in fluid dynamics with complex flow, generally chaotic and turbulent flow. In porous media this behavior is seen even in absence of flow, i.e. pure diffusion - as well as for hydrodynamic dispersion - molecular transport at low Reynold's number. These involve motion of molecules restricted by structures. We describe how transport of complex fluids contained within complex matrices can be used to explore the physics of complex porous media with their multiple characteristic time and length scales, varying over many orders of magnitude.

Sen, P. N.

262

Measuring Thermodynamic Length  

NASA Astrophysics Data System (ADS)

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 interest in understanding matter out of equilibrium. In this Letter, we will consider how to define thermodynamic 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.

2007-09-01

263

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

264

Nonlinear diffusion with linearly varying diffusivity  

NASA Astrophysics Data System (ADS)

An approximate analytical solution to the nonlinear diffusion equation is presented. The diffusivity is assumed to be linearly dependent on concentration. The one-dimensional problem is reduced to an ordinary differential equation through the Boltzmann transformation and a technique which is exploiting basic characteristics of the exact solution is developed. The technique presented here can be applied to problems of groundwater contamination, to problems of water absorption into unsaturated soils, as well as to various other engineering problems leading to the diffusion equation. A comparison of the numerical results with other methods concludes the paper.

Tolikas, Panagiotis K.; Sidiropoulos, Epaminondas

1984-03-01

265

Length, time, and energy scales of photosystems  

Microsoft Academic Search

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-Å scale of the membrane thickness. Electron tunneling is nearly as rapid at the shortest distances, but becomes physiologically too slow well before 20 Å. Diffusion, which starts out

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

2003-01-01

266

Circumference and Arc Length  

NSDL National Science Digital Library

This unit will introduce you to circumference of a circle, and how to find the measurement of the edge of a piece of pizza! (Arc length!) Ok. Let's make sure you remember circumference of a circle, you know, the distance around a circle? Click on the following link and take notes! Circle Circumference Now we can use that to find the arc length, or the length of the crust part of the edge of a pizza! Take notes: Arcs in Circles Now, let's ...

Neubert, Mrs.

2011-03-24

267

Leg Length Inequality  

PubMed Central

Leg length inequality, a common abnormality, can cause musculoskeletal pain, scoliosis, and osteoarthritis of the hip. Seven percent of the asymptomatic population has a leg length inequality greater than 12 mm; the incidence is considerably higher (13%-22%) in individuals complaining of low back pain. Correction can usually be accomplished by shoe modification, and can result in dramatic relief of pain. Leg length inequality of more than half an inch is considered clinically significant. Leg length measurement should be routine in all patients complaining of low back pain, hip pain, and atypical flank and lower quadrant pain. Correction might prove very cost-effective.

Sharpe, Colin R.

1983-01-01

268

Neandertal clavicle length.  

PubMed

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

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

2014-03-25

269

Simulation run length planning  

Microsoft Academic Search

To design a stochastic simulation experiment, it is helpful to have an estimate of the simulation run lengths required to achieve desired statistical precision. Preliminary estimates of required run lengths can be obtained by approximating the stochastic model of interest by a more elementary Markov model that can be analyzed analytically. When steady-state quantities are to be estimated by sample

Ward Whitt

1989-01-01

270

Microvessel length density, total length, and length per neuron in five subcortical regions in schizophrenia.  

PubMed

Recent studies (Prabakaran et al. in Mol Psychiat 9:684-697, 2004; Hanson and Gottesman in BMC Med Genet 6:7, 2005; Harris et al. in PLoS ONE 3:e3964, 2008) have suggested that microvascular abnormalities occur in the brains of patients with schizophrenia. To assess the integrity of the microvasculature in subcortical brain regions in schizophrenia, we investigated the microvessel length density, total microvessel length, and microvessel length per neuron using design-based stereologic methods in the caudate nucleus, putamen, nucleus accumbens, mediodorsal nucleus of the thalamus, and lateral nucleus of the amygdala in both hemispheres of 13 postmortem brains from male patients with schizophrenia and 13 age-matched male controls. A general linear model multivariate analysis of variance with diagnosis and hemisphere as fixed factors and illness duration (patients with schizophrenia) or age (controls), postmortem interval and fixation time as covariates showed no statistically significant differences in the brains from the patients with schizophrenia compared to the controls. These data extend our earlier findings in prefrontal cortex area 9 and anterior cingulate cortex area 24 from the same brains (Kreczmanski et al. in Acta Neuropathol 109:510-518, 2005), that alterations in microvessel length density, total length, and particularly length per neuron cannot be considered characteristic features of schizophrenia. As such, compromised brain metabolism and occurrence of oxidative stress in the brains of patients with schizophrenia are likely caused by other mechanisms such as functional disruption in the coupling of cerebral blood flow to neuronal metabolic needs. PMID:19198859

Kreczmanski, Pawel; Heinsen, Helmut; Mantua, Valentina; Woltersdorf, Fritz; Masson, Thorsten; Ulfig, Norbert; Schmidt-Kastner, Rainald; Korr, Hubert; Steinbusch, Harry W M; Hof, Patrick R; Schmitz, Christoph

2009-04-01

271

Welding arc length control system  

NASA Technical Reports Server (NTRS)

The present invention is a welding arc length control system. The system includes, in its broadest aspects, a power source for providing welding current, a power amplification system, a motorized welding torch assembly connected to the power amplification system, a computer, and current pick up means. The computer is connected to the power amplification system for storing and processing arc weld current parameters and non-linear voltage-ampere characteristics. The current pick up means is connected to the power source and to the welding torch assembly for providing weld current data to the computer. Thus, the desired arc length is maintained as the welding current is varied during operation, maintaining consistent weld penetration.

Iceland, William F. (Inventor)

1993-01-01

272

Determination of diffusion rates in acrylamide-based photopolymer material  

NASA Astrophysics Data System (ADS)

Holographic data storage systems, utilising photopolymer material as the recording medium, have recently been presented. Because of their relatively low cost and ease of use, due to their self-processing nature, photopolymers provide many potential advantages as the holographic recording material and data storage medium of choice. Photopolymers show promise, for example, for Write-Once Read-Many (WORM) storage systems. The photopolymer recording medium used in this study is an Acrylamide/Polyvinylalcohol (A/PVA) based dry layer. An important material characteristic, which determines the performance of any photopolymer medium, is the spatial frequency response of that material. Previously, applying our Non-local Photo-Polymerisation Driven Diffusion Model, (NPDD), we have discussed the effects on material behaviour of the length of the polymer chains and the rates of diffusion within the material. These parameters have been shown to be critically important in determining the response of the material. If the average length of the Polyacrylamide (photopolymerised Acrylamide monomer, PA), chains is shortened, an increase in the diffusion coefficient of these molecules might be observed. According to the NPDD shorter PA chains should then result in an increase in the materials spatial frequency response, and ultimately in an increase in holographic data storage capacity. In this paper we report on several experiments carried out (a) to determine the diffusion constant of the PA and (b) to also determine the diffusion constants of both water and Propanol in our material layers.

Close, C. E.; Gleeson, M. R.; Kelly, J. V.; O'Neill, F. T.; Mooney, D.; Sheridan, J. T.

2006-05-01

273

Length Paradox in Relativity  

ERIC Educational Resources Information Center

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

Martins, Roberto de A.

1978-01-01

274

Length and Elongation Sensor.  

National Technical Information Service (NTIS)

A length and elongation sensor includes an elastomeric optical wave guide and a time domain reflectometer. The elastomeric optical wave guide consists of a urethane outer cladding and an optical gel core. A transparent window is hermetically sealed to the...

L. E. Sansone

1996-01-01

275

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

276

W\\/O\\/W double emulsion technique using ethyl acetate as organic solvent: effects of its diffusion rate on the characteristics of microparticles  

Microsoft Academic Search

Monomethoxypoly(ethylene glycol)-b-poly(dl-lactide) copolymer (PELA) microparticles loading lysozyme were prepared through a modified W\\/O\\/W double emulsion-solvent diffusion method using ethyl acetate (EA) as organic solvent. The modified process was divided into five steps: (1) primary emulsification (W1\\/O), (2) re-emulsification (W1\\/O\\/W2), (3) pre-solidification, (4) solidification and (5) purification. The pre-solidification step was carried out in the modified process to control the diffusion

Fan Tao Meng; Guang Hui Ma; Wei Qiu; Zhi Guo Su

2003-01-01

277

Novel Diffusivity Measurement Technique  

NASA Technical Reports Server (NTRS)

A common-path interferometer (CPI) system was developed to measure the diffusivity of liquid pairs. The CPI is an optical technique that can be used to measure changes in the gradient of the refraction index of transparent materials. This system uses a shearing interferometer that shares the same optical path from a laser light source to the final imaging plane. Hence, the molecular diffusion coefficient of liquids can be determined using the physical relations between changes in the optical path length and the liquid phase properties. The data obtained with this interferometer were compared with similar results from other techniques and demonstrated that the instrument is superior in measuring the diffusivity of miscible liquids while keeping the system very compact and robust. CPI can also be used for studies in interface dynamics and other diffusion-dominated-process applications.

Rashidnia, Nasser

2001-01-01

278

On internodal length.  

PubMed Central

A study has been made of changes in internodal lengths in rat tibial nerves and human sural nerves with age. Myelinated fibre counts on these nerves showed that maximum numbers were reached at an early stage of development. The slope of regression lines relating internodal length to fibre diameter was relatively flat at this stage, but became steeper with increasing age. Maximum internodal length in rat tibial nerve was closely related to growth of the limb bones. Whilst this study confirms that the largest fibres are subjected to hind limb growth for the greatest period, and therefore have the longest internodes, it does not support the generally accepted view that short internodes are the consequence of the later myelination of small fibres, and hence shorter period of extension due to growth. Images Figs. 2-3

Jacobs, J M

1988-01-01

279

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

280

Data reduction problems using a 3-hole directional pressure probe to investigate mean flow characteristics in the vaneless gap between impeller and diffuser radial pump  

NASA Astrophysics Data System (ADS)

Among several different measurement techniques that have been already performed and presented in a radial impeller pump model including PIV, a directional pressure probe has been used to obtain mean velocity field and stagnation pressure between impeller outlet and the inlet vaned diffuser sections. These measurements are supposed to get more information not only about global pump head coefficient including vaned diffuser ones but also about impeller performances itself. Pressure probe information is affected by rotor-stator interactions and impeller rotation, and this paper presents a way to explain and correct pressure probe indications in order to achieve a better evaluation of overall impeller mean performances. The use of unsteady RANS calculation results is found to be a useful way to perform better data reduction analysis for this purpose.

Cherdieu, P.; Dupont, P.; Bayeul-Lainé, A. C.; Dazin, A.; Bois, G.

2013-12-01

281

Peculiarities of diffusion in gels  

NASA Astrophysics Data System (ADS)

An optical method was applied to study the peculiarities of diffusion in gel: this method provides real-time visualization of spreading of solutes brought into the gel. It was shown that spectral characteristics of reflected light give additional information about nature of diffusive spreading of solutes and about state of the gel. Gels with different densities and lifetime were studied. These parameters have strong influence on the velocity of diffusion. The study demonstrated critical differences for diffusion process in gels with true solutions and with solutions with nanoparticles. Experiments discovered the anisotropy in 3D diffusion of solutes in gels; physical explanation of this phenomenon was proposed.

Pokusaev, B. G.; Karlov, S. P.; Vyazmin, A. V.; Nekrasov, D. A.

2013-12-01

282

Peculiarities of diffusion in gels  

NASA Astrophysics Data System (ADS)

An optical method was applied to study the peculiarities of diffusion in gel: this method provides real-time visualization of spreading of solutes brought into the gel. It was shown that spectral characteristics of reflected light give additional information about nature of diffusive spreading of solutes and about state of the gel. Gels with different densities and lifetime were studied. These parameters have strong influence on the velocity of diffusion. The study demonstrated critical differences for diffusion process in gels with true solutions and with solutions with nanoparticles. Experiments discovered the anisotropy in 3D diffusion of solutes in gels; physical explanation of this phenomenon was proposed.

Pokusaev, B. G.; Karlov, S. P.; Vyazmin, A. V.; Nekrasov, D. A.

2014-12-01

283

Characteristics of a radon diffusion chamber with electrical collection using plastic nuclear track detectors. Open file report 31 August 1982-30 November 1983  

Microsoft Academic Search

A portable radon diffusion chamber was tested with electrical collection of radon daughter nuclei for enhancement of sensitivity. The detector was small enough to be worn suspended from a belt. With a battery-supplied high voltage, the sensitivity was found to be 1.43 tracks\\/sq cm per pCi-h\\/lambda of ambient radon at 50% relative humidity. The track densities on the surfaces of

A. L. Frank; E. V. Benton

1982-01-01

284

Macrokinetic analysis of polarisation characteristics of gas-diffusion electrodes in contact with liquid electrolytes, Part II: Oxygen reduction as example for a higher order reaction  

Microsoft Academic Search

Classical partial oxidation processes often suffer from low selectivities. Promising alternatives are electrochemical processes\\u000a where the oxidation takes place at a packed-bed anode while an oxygen-consuming gas–liquid membrane is used as cathode. As\\u000a a basis for the reliable design of such a process, the performance of oxygen-consuming gas-diffusion electrodes (GDE) is investigated\\u000a experimentally and is analysed based on a rigorous

Kai Sundmacher; Thorsten Schultz

2005-01-01

285

Lengths of Ladybugs  

NSDL National Science Digital Library

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

Lessonplans, Utah

2012-09-18

286

Extended Fuel Cycle Length.  

National Technical Information Service (NTIS)

Extended fuel cycle length and burnup are currently offered by Framatome and Fragema in order to satisfy the needs of the utilities in terms of fuel cycle cost and of overall systems cost optimization. We intend to point out the consequences of an increas...

M. Bruyere A. Vallee C. Collette

1986-01-01

287

Contact Diffusion Interaction of Materials with Cladding.  

National Technical Information Service (NTIS)

Consideration is given to problems arising from diffusion interaction between materials and their claddings and the film of condensate formed on their surfaces. Topics include: characteristics of diffusion in condensates formed on a hot cladding; diffusio...

A. A. Babad-Zakhryapina

1967-01-01

288

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

289

Diffusivity in turbulent fluid containing two dominant scales, and compressible shear layer according to a kinetic theory  

NASA Technical Reports Server (NTRS)

The solution of the two nonequilibrium-degree kinetic equation was first determined for the effective length scale and turbulence energy for a spatially homogeneous turbulence field with two characteristic length scales, where the source for one family of eddies exists. This solution was applied to the evaluation of the eddy diffusivity in the combustion chamber of an internal combustion engine. The result was compared with another existing solution. This was carried out to demonstrate the feasibility of obtaining an effective length-scale equation within the context of the kinetic theory. A formulation and partial solution of the compressible plane shear layer are also presented.

Chung, P. M.

1976-01-01

290

Simulation of current collapse in the 0.25 µm gate Length Al0.28Ga0.72N\\/GaN HEMT  

Microsoft Academic Search

A 2D drift-diffusion (DD) and Hydrodynamic (HD) transport models within ATLAS simulation toolbox by Silvaco have been calibrated against experimental I–V characteristics of the 0.25µm gate length GaN High Electron Mobility Transistor (HEMT). The simulations take into account both piezoelectric and spontaneous polarization effects at the interface of AlGaN and GaN. The simulations have been employed to investigate the current

S. Faramehr; K. Kalna; P. Igic

2012-01-01

291

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 Navarrete, Estanislao; Amman, M.; Avignone, F. T.; Barabash, A.; Barton, P. J.; Beene, Jim; Bertrand, F.; Boswell, M.; Brudanin, V.; Busch, Matthew; Chan, Yuen-Dat; Christofferson, Cabot-Ann; Collar, Juan; Combs, Dustin C.; Cooper, R. J.; Detwiler, Jason A.; Doe, Peter J.; Efremenko, Yuri; Egorov, Viatcheslav; Ejiri, H.; Elliott, S. R.; Esterline, James H.; Fast, James E.; Fields, N.; Finnerty, P.; Fraenkle, Florian; Galindo-Uribarri, A.; Gehman, Victor M.; Giovanetti, G. K.; Green, Matthew P.; Guiseppe, Vincente; Gusey, K.; Hallin, A. L.; Hazama, R.; Henning, Reyco; Hoppe, Eric W.; Horton, Mark; Howard, Stanley; Howe, Mark; Johnson, R. A.; Keeter, K.; Kidd, Mary; Knecht, A.; Kochetov, Oleg; Konovalov, S.; Kouzes, Richard T.; LaFerriere, Brian D.; Leon, Jonathan D.; Leviner, L.; Loach, J. C.; Looker, Ron L.; Luke, P.; MacMullin, S.; Marino, Michael G.; Martin, R. D.; Merriman, Jason H.; Miller, M. L.; Mizouni, Leila K.; Nomachi, Masaharu; Orrell, John L.; Overman, Nicole R.; Perumpilly, Gopakumar; Phillips, D.; Poon, Alan; Radford, Davis; Rielage, Keith; Robertson, R. G. H.; Ronquest, M. C.; Schubert, Alexis G.; Shima, T.; Shirchenko, M.; Snavely, Kyle J.; Steele, David; Strain, J.; Timkin, V.; Tornow, W.; Varner, R. L.; Vetter, Kai; Vorren, Kris R.; Wilkerson, J. F.; Yakushev, E.; Yaver, Harold; Young, A.; Yu, Chang-Hong; Yumatov, Vladimir

2013-02-11

292

Characteristics of signals originating near the lithium-diffused N+ contact of high purity germanium p-type point contact detectors  

NASA Astrophysics Data System (ADS)

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.; Amman, M.; Avignone, F. T.; Barabash, A. S.; Barton, P. J.; Beene, J. R.; Bertrand, F. E.; Boswell, M.; Brudanin, V.; Busch, M.; Chan, Y.-D.; Christofferson, C. D.; Collar, J. I.; Combs, D. C.; Cooper, R. J.; Detwiler, J. A.; Doe, P. J.; Efremenko, Yu.; Egorov, V.; Ejiri, H.; Elliott, S. R.; Esterline, J.; Fast, J. E.; Fields, N.; Finnerty, P.; Fraenkle, F. M.; Galindo-Uribarri, A.; Gehman, V. M.; Giovanetti, G. K.; Green, M. P.; Guiseppe, V. E.; Gusey, K.; Hallin, A. L.; Hazama, R.; Henning, R.; Hoppe, E. W.; Horton, M.; Howard, S.; Howe, M. A.; Johnson, R. A.; Keeter, K. J.; Kidd, M. F.; Knecht, A.; Kochetov, O.; Konovalov, S. I.; Kouzes, R. T.; Laferriere, B. D.; Leon, J.; Leviner, L. E.; Loach, J. C.; Looker, Q.; Luke, P. N.; Macmullin, S.; Marino, M. G.; Martin, R. D.; Merriman, J. H.; Miller, M. L.; Mizouni, L.; Nomachi, M.; Orrell, J. L.; Overman, N. R.; Perumpilly, G.; Phillips, D. G.; Poon, A. W. P.; Radford, D. C.; Rielage, K.; Robertson, R. G. H.; Ronquest, M. C.; Schubert, A. G.; Shima, T.; Shirchenko, M.; Snavely, K. J.; Steele, D.; Strain, J.; Timkin, V.; Tornow, W.; Varner, R. L.; Vetter, K.; Vorren, K.; Wilkerson, J. F.; Yakushev, E.; Yaver, H.; Young, A. R.; Yu, C.-H.; Yumatov, V.; Majorana Collaboration

293

Diffusion Path Representation for Two-Phase Ternary Diffusion Couples.  

National Technical Information Service (NTIS)

Several two-phase, solid-solid diffusion couples from diffusion studies in the ternary Cu-Ni-Zn, Fe-Ni-Al and Cu-Ag-Au systems were investigated for their analytical representation on the basis of characteristic path parameters. The concentration profiles...

M. A. Dayananda R. Venkatasubramanian

1986-01-01

294

On collisional diffusion in a stochastic magnetic field  

SciTech Connect

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

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

2013-08-15

295

Microphase separation at two length scales  

NASA Astrophysics Data System (ADS)

The possibility of microphase separation at two different length scales in monodisperse AB block copolymer melts consisting of a homopolymer A block and either a linear alternating AB copolymer block (poly(A)_m-block-poly(B-alt -A)_n) or an AB comb copolymer block poly(A)_m-block-poly(A- graft-B)_n, is investigated. An analysis of the structure factor reveals that in the parameter space of n and m three different cases can be distinguished: I) The structure factor has only one minimum corresponding to the short length scale (i.e. the characteristic length of the repeating unit of the alternating or comb block). II) The structure factor has only one minimum corresponding to the long length scale (the characteristic length of the blocks). III) Two minima are present leading to a competition between microphase separation at the short and the long length scale. Depending on the choice of n and m, one of these three possibilities will occur.

Nap, R. J.; Kok, C.; ten Brinke, G.; Kuchanov, S. I.

2001-04-01

296

Characteristic changes in T 2-value, apparent diffusion coefficient, and ultrastructure of substantia nigra evolving exofocal postischemic neuronal death in rats  

Microsoft Academic Search

To correlate the magnetic resonance (MR) imaging characteristics of exofocal postischemic neuronal death (EPND) in the substantia nigra (SN) with associated histologic changes, we occluded the left middle cerebral artery of rats for 1, 4, 7, or 12 days. Day 1 (post-occlusion) T2-weighted images revealed high signal intensity indicative of infarction in the ipsilateral caudate nucleus, putamen, and cortex but

Fengyu Zhao; Toshihiko Kuroiwa; Naoyuki Miyasaka; Tsukasa Nagaoka; Makoto Nakane; Akira Tamura; Hidehiro Mizusawa

2001-01-01

297

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

298

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

299

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

300

Spatial distribution and broad-band spectral characteristics of the diffuse X-ray background, 0.1 - 1.0 keV  

NASA Technical Reports Server (NTRS)

Preliminary maps covering more than 85 percent of the sky are presented for three energy bands: the B band, the C band, and the M band. The study was undertaken to find evidence that most of the diffuse X-ray background at energies less than 1 keV is local to the galaxy and that it is most probably due to thermal radiation from a low density plasma which fills a substantial fraction of interstellar space. A preliminary analysis of the data is provided including a report that most of the B and C band flux has a common origin, probably in a 10 to the 6th power K region surrounding the Sun, and that most of the M band flux does not originate from the same material.

Mccammon, D.; Kraushaar, W. L.; Sanders, W. T.; Burrows, D. N.

1979-01-01

301

Length of Time's Arrow  

NASA Astrophysics Data System (ADS)

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 divergence between 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.

2008-08-01

302

Length of the Day  

NSDL National Science Digital Library

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

303

Electrostatic persistence length.  

PubMed

The persistence length is calculated for polyelectrolyte chains with fixed bond lengths and bond angles (pi-theta), and a potential energy consisting of the screened Coulomb interaction between beads, potential wells alpha phi(i)2 for the dihedral angles phi(i), and coupling terms beta phi(i) phi(i+/-1). This model defines a librating chain that reduces in appropriate limits to the freely rotating or wormlike chains, it can accommodate local crumpling or extreme stiffness, and it is easy to simulate. A planar-quadratic (pq), analytic approximation is based on an expansion of the electrostatic energy in eigenfunctions of the quadratic form that describes the backbone energy, and on the assumption that the quadratic form not only is positive but also adequately confines the chain in an infinite phase space of dihedral angles to the physically unique part with all |phi(i)| < pi. The pq approximation is available under these weak constraints, but the simulations confirm its quantitative accuracy only under the expected condition that alpha is large, that is, for very stiff chains. Stiff chains can also be simulated with small alpha and small theta and compared to an OSF approximation suitably generalized to chains with finite rather than vanishing theta, and increasing agreement with OSF is found the smaller is theta. The two approximations, one becoming exact as alpha --> infinity with fixed theta, the other as theta --> 0 with fixed alpha, are quantitatively similar in behavior, both giving a persistence length P = P0 + aD2 for stiff chains, where D is the Debye length. However, the coefficient apq is about twice the value of aOSF. Under other conditions the simulations show that P may or not be linear in D2 at small or moderate D, depending on the magnitudes of alpha, beta, theta, and the charge density but always becomes linear at large D. Even at a moderately low charge density, corresponding to fewer than 20% of the beads being charged, and with strong crumpling induced by large beta, increasing D dissolves blobs and recovers a linear dependence of P on D2, although a lower power of D gives an adequate fit at moderate D. For the class of models considered, it is concluded that the only universal feature is the asymptotic linearity of P in D2, regardless of flexibility or stiffness. PMID:20148527

Fixman, Marshall

2010-03-11

304

Two-dimensional network simulation of diffusion driven coarsening of foam inside a porous medium  

SciTech Connect

In order to use foams in subsurface applications, it is necessary to understand their stability in porous media. Diffusion driven coarsening of a stationary or nonflowing foam in a porous medium results in changing gas pressures and a coarsening of the foam texture. A two-dimensional network simulation has been created that predicts the behavior of foam in a porous medium by physically specifying the locations of all the lamellae in the system and by solving the complete set of Young-Laplace and diffusion equations. An hourglass approximates the shape of the pores, and the pore walls are considered to be highly water wet. A singularity arises in the system of differential algebraic equations due to the curvature of the pore walls. This singularity is a signal that the system must undergo oscillations or sudden lamellar rearrangements before the diffusion process can continue. Newton-Raphson iteration is used along with Keller`s method of arc-length continuation and a new jump resolution technique to locate and resolve bifurcations in the system of coupled lamellae. Gas bubbles in pore throats are regions of encapsulated pressure. As gas is released from these bubbles during diffusion, the pressure of the bubbles in the pore bodies increases. When the pressure increase is scaled by the characteristic Young-Laplace pressure, the equilibrium time for the diffusion process is scaled by the ratio of the square of the characteristic length to the gas diffusivity and two dimensionless groups. One describes the ease with which gas can diffuse through a lamella, the second represents the amount of gas encapsulated within the pore throats initially. Given this scaling, the resulting plots of pressure versus time and normalized lamellae positions versus time are universal for all system sizes and characteristics. This is true as long as the initial lamella distribution is the same in each case.

Cohen, D.; Patzek, T.W.; Radke, C.J.

1996-04-01

305

Single molecule diffusion in critical lipid bilayers  

NASA Astrophysics Data System (ADS)

Time-dependent single molecule diffusion coefficients are discussed for a fluorescent probe molecule in lipid mixtures near a miscibility critical point. The calculations take advantage of the theoretical wave vector dependent composition diffusion coefficients obtained by Inaura and Fujitani [J. Phys. Soc. Jpn. 77, 114603 (2008)]. It is suggested that the diffusion of the probe molecule reflects in part the time-dependent composition diffusion near a critical point. The calculations show a striking biphasic time-dependent diffusion that switches from a faster diffusion at short times to a slower diffusion at a time approximately equal to ??2/D where ? is the correlation length and D is the composition diffusion coefficient at the switch time. This biphasic diffusion should be readily detectable experimentally.

McConnell, Harden

2012-12-01

306

Radon diffusion studies in some building materials using solid state nuclear track detectors  

Microsoft Academic Search

LR-115 plastic track detector has been used to study radon diffusion through some building materials, viz. cement, soil, marble chips, sand and lime as well as air. Diffusion constant and diffusion length is calculated for all these materials.

Surinder Singh; Jatinder Kumar; Baldev Singh; Jaspal Singh

1999-01-01

307

Length of stain dosimeter  

NASA Technical Reports Server (NTRS)

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

Lueck, Dale E. (inventor)

1994-01-01

308

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

Microsoft Academic Search

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

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

1995-01-01

309

Hillslope diffusion  

NSDL National Science Digital Library

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

Mcdermott, Jeni

310

Mixed-layer eddy diffusivity: effects of surface relaxation and turbulent mixing  

NASA Astrophysics Data System (ADS)

We present an analytical formula for eddy tracer diffusivity in the mixed layer where both air-sea interaction and turbulent mixing are relevant. The eddy diffusivity is given by the mixing length theory, which is proportional to the characteristic velocity of geostrophic eddies in the ocean interior multiplied by he mixing length that is governed by effects of nonlinear advection, eddy propagation, surface relaxation, and turbulent mixing. Due to the existence of eddy propagation, the diffusivity is enhanced for tracers subject to weak restoring, and suppressed when the relaxation is strong. Turbulent mixing acts to mitigate the suppression by strong relaxation on the diffusivity, so under strong restoring with time scales comparable or even shorter than that of the turbulent mixing, the diffusivity remains large and increases downward from the surface. The analytical solution compares reasonably well with outcome of a complex numerical model for tracers with differential surface restoring. The modeled mixed-layer eddy diffusivity varies by a factor of two with different tracers and depth, implying that effects of both air-sea interaction and mixed-layer dynamics are probably not negligible for eddy transfer in the real ocean.

Zhang, Y.; Ferrari, R. M.

2012-12-01

311

Tailoring diffusion in analog spacetimes.  

PubMed

Diffusive transport is characterized by the scaling law (length)^{2}?(time). In this paper we show that this relationship is significantly altered in curved analog spacetimes. This circumstance provides an opportunity to tailor diffusion: by a suitable design of the analog metric, it is possible to create materials where diffusion is either faster or slower than in normal media, as desired. This prediction can, in principle, be tested experimentally with optical analogs, curved graphene sheets, and so on (indeed with any analog spacetime). PMID:22680445

Smerlak, Matteo

2012-04-01

312

Spatiotemporal characteristics of postischemic hyperperfusion with respect to changes in T1, T2, diffusion, angiography, and blood-brain barrier permeability  

PubMed Central

The spatiotemporal dynamics of postischemic hyperperfusion (HP) remains incompletely understood. Diffusion, perfusion, T2, T1, angiographic, dynamic susceptibility-contrast magnetic resonance imaging (MRI) and magnetic resonance angiography were acquired longitudinally at multiple time points up to 7 days after stroke in rats subjected to 30-, 60-, and 90-minutes middle cerebral artery occlusion (MCAO). The spatiotemporal dynamics of postischemic HP was analyzed and compared with T1, T2 and blood–brain barrier (BBB) changes. No early HP within 3?hours after recanalization was observed. Late (?12?hours) HP was present in all animals of the 30-minute MCAO group (N=20), half of the animals in the 60-minute MCAO group (N=8), and absent in the 90-minute MCAO group (N=9). Dynamic susceptibility-contrast MRI and magnetic resonance angiography corroborated HP. Hyperperfusion preceded T2 increase in some animals, but HP and T2 changes temporally coincided in others. T2 peaked first at 24?hours whereas HP peaked at 48?hours after occlusion, and HP resolved by day 7 in most animals at which point the arteries became tortuous. Pixel-by-pixel tracking analysis showed that tissue did not infarct (migrated from core or mismatch at 30?minutes to normal at 48?hours) showed normal cerebral blood flow (CBF), whereas infarct tissue (migrated from core or mismatch at 30?minutes to infarct at 48?hours) showed exaggerated CBF, indicating that HP was associated with poor outcome.

Shen, Qiang; Du, Fang; Huang, Shiliang; Duong, Timothy Q

2011-01-01

313

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

PubMed

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

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

2014-07-01

314

Characteristics of 0.8- and 0.2-microns gate length In(x)Ga(1-x) As/In(0.52)Al(0.48)As/InP (0.53 less than or equal to x less than or equal to 0.70) modulation-doped field-effect transistors at cryogenic temperatures  

NASA Technical Reports Server (NTRS)

The performance characteristics of InP-based In(x)Ga(1-x)As/In(0.52)Al(0.48)As (0.53 is less than or equal to x is less than or equal to 0.70) pseudomorphic modulation-doped field-effect transistors (MODFET's) as a function of strain in the channel, gate, length, and temperature were investigated analytically and experimentally. The strain in the channel was varied by varying the In composition x. The temperature was varied in the range of 40-300 K and the devices have gate lengths L(sub g) of 0.8 and 0.2 microns. Analysis of the device was done using a one-dimensional self consistent solution of the Poisson and Schroedinger equations in the channel, a two-dimensional Poisson solver to obtain the channel electric field, and a Monte Carlo simulation to estimate the carrier transit times in the channel. An increase in the value of the cutoff frequency is predicted for an increase in In composition, a decrease in temperature, and a decrease in gate length. The improvements seen with decreasing temperature, decreasing gate length, and increased In composition were smaller than those predicted by analysis. The experimental results on pseudomorphic InGaAs/InAlAs MODFET's showed that there is a 15-30 percent improvement in cutoff frequency in both the 0.8- and 0.2-micron gate length devices when the temperature is lowered from 300 to 40 K.

Lai, Richard; Bhattacharya, Pallab K.; Yang, David; Brock, Timothy L.; Alterovitz, Samuel A.; Downey, Alan N.

1993-01-01

315

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

316

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

317

Rotational diffusion of magnetic nickel nanorods in colloidal dispersions  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

318

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

319

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

320

FILAMENT LENGTHS IN STRIATED MUSCLE  

Microsoft Academic Search

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

SALLY G. PAGE; H. E. HUXLEY

1963-01-01

321

Network Structure and Diffusion in Highly Crosslinked Ionizable Networks  

NASA Astrophysics Data System (ADS)

The structural features of novel ionizable polymer networks prepared from oligo(ethylene glycol) (OEG) multiacrylates and acrylic acid (AA) have been examined using diffusion and ^13C NMR relaxation studies. The experimental program was designed to probe (i) the composition-dependent network structure of the copolymer networks and (ii) the impact of varying the AA content and the OEG chain length on the polymer chain dynamics. Penetrant diffusion coefficients calculated according to a Fickian treatment of the swelling data indicate an increase in the network mesh size with increasing AA content or with increasing OEG chain length. The shapes of the penetrant uptake curves suggest a coupling of Fickian and relaxation-driven contributions to the overall swelling behavior. Significantly, the effect of increasing the AA content on the characteristic chain relaxation time (as indicated by the location of the inflection point in plots of the fractional penetrant uptake versus the square root of time) is reversed as the OEG chain length is varied, suggesting that chain relaxation is controlled by crosslinking considerations for shorter OEG chains and by compositional considerations for longer OEG chains. Measured compositional effects on solid state ^13C NMR relaxation times support our conclusions.

Scott, Robert; Peppas, Nicholas

1998-03-01

322

Coaxial atomizer liquid intact lengths  

NASA Technical Reports Server (NTRS)

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 empirical equation was derived as a function of these parameters. A comparison of the intact lengths for round jets and flat sheets shows that round jets generate shorter intact lengths.

Eroglu, Hasan; Chigier, Norman; Farago, Zoltan

1991-01-01

323

Shortened Estrous Cycle Length, Increased FSH Levels, FSH Variance, Oocyte Spindle Aberrations, and Early Declining Fertility in Aging Senescence-Accelerated Mouse Prone-8 (SAMP8) Mice: Concomitant Characteristics of Human Midlife Female Reproductive Aging.  

PubMed

Women experience a series of specific transitions in their reproductive function with age. Shortening of the menstrual cycle begins in the mid to late 30s and is regarded as the first sign of reproductive aging. Other early changes include elevation and increased variance of serum FSH levels, increased incidences of oocyte spindle aberrations and aneuploidy, and declining fertility. The goal of this study was to investigate whether the mouse strain senescence-accelerated mouse-prone-8 (SAMP8) is a suitable model for the study of these midlife reproductive aging characteristics. Midlife SAMP8 mice aged 6.5-7.85 months (midlife SAMP8) exhibited shortened estrous cycles compared with SAMP8 mice aged 2-3 months (young SAMP8, P = .0040). Midlife SAMP8 mice had high FSH levels compared with young SAMP8 mice, and mice with a single day of high FSH exhibited statistically elevated FSH throughout the cycle, ranging from 1.8- to 3.6-fold elevation on the days of proestrus, estrus, metestrus, and diestrus (P < .05). Midlife SAMP8 mice displayed more variance in FSH than young SAMP8 mice (P = .01). Midlife SAMP8 ovulated fewer oocytes (P = .0155). SAMP8 oocytes stained with fluorescently labeled antitubulin antibodies and scored in fluorescence microscopy exhibited increased incidence of meiotic spindle aberrations with age, from 2/126 (1.59%) in young SAMP8 to 38/139 (27.3%) in midlife SAMP8 (17.2-fold increase, P < .0001). Finally, SAMP8 exhibited declining fertility from 8.9 pups/litter in young SAMP8 to 3.5 pups/litter in midlife SAMP8 mice (P < .0001). The age at which these changes occur is younger than for most mouse strains, and their simultaneous occurrence within a single strain has not been described previously. We propose that SAMP8 mice are a model of midlife human female reproductive aging. PMID:24654787

Bernstein, Lori R; Mackenzie, Amelia C L; Kraemer, Duane C; Morley, John E; Farr, Susan; Chaffin, Charles L; Merchenthaler, István

2014-06-01

324

Geometric Optimization of Relative Link Lengths for Biomimetic Robotic Fish  

Microsoft Academic Search

This paper focuses on the design of fishlike underwater robots using an optimization approach to choose relative link lengths. Considering both ichthyologic characteristics and mechatronic constraints, the optimal link-length ratios are numerically calculated by an improved constrained cyclic variable method. Comparative results, before and after the optimization, demonstrate the enhanced performance

Junzhi Yu; Long Wang; Min Tan

2007-01-01

325

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

326

Kinetic transitions in diffusion-reaction space. II. Geometrical effects  

NASA Astrophysics Data System (ADS)

We extend the stochastic master equation approach described earlier [J. J. Kozak and R. Davidson, J. Chem. Phys. 101, 6101 (1994)] to examine the influence on reaction efficiency of multipolar correlations between a fixed target molecule and a diffusing coreactant, the latter constrained to move on the surface of a host medium (e.g., a colloidal catalyst or molecular organizate) modeled as a Cartesian shell [Euler characteristic, ?=2]. Our most comprehensive results are for processes involving ion pairs, and we find that there exists a transition between two qualitatively different types of behavior in diffusion-reaction space, viz., a regime where the coreactant's motion is totally correlated with respect to the target ion, and a regime where the coreactant's motion is effectively uncorrelated. This behavior emerges both in the situation where correlations between the ion pair are strictly confined to the surface of the host medium or where correlations can be propagated through the host medium. The effects of system size are also examined and comparisons with diffusion-reaction processes taking place on surfaces characterized by Euler characteristic ?=0 are made. In all cases studied, the most dramatic effects on the reaction efficiency are uncovered in the regime where the Onsager (thermalization) length is comparable to the mean displacement of the coreactant, a conclusion consistent with results reported in earlier work.

Kozak, John J.

1999-02-01

327

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

328

Nuclear-magnetic-resonance diffusion simulations in two phases in porous media  

NASA Astrophysics Data System (ADS)

Time-dependent diffusion simulations which can be measured by nuclear magnetic resonance (NMR) were numerically performed in consolidated reconstructed porous media saturated by two immobile fluids. The phase distributions were obtained by an immiscible lattice Boltzmann technique which incorporates interfacial tension and wetting. The apparent diffusion coefficient in each fluid was determined by a random walk algorithm. Permeability and conductivity tensors were calculated by finite-difference schemes. The major properties valid for a single phase could be generalized to two phases. First, the characteristic length ? introduced by Johnson [Phys. Rev. Lett. 57, 2564 (1986)] is of the order of twice the phase volume to surface ratio. Second, the apparent diffusion coefficients for all porosities, saturations, and phases can be represented by a single dimensionless curve.

Valfouskaya, A.; Adler, P. M.

2005-11-01

329

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

330

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

331

Hydrogen isotope effects on ITG scale length, pedestal and confinement in JT-60 H-mode plasmas  

NASA Astrophysics Data System (ADS)

The dependence of heat transport, edge pedestal and confinement on isotopic composition was investigated in conventional H-mode plasmas. Identical profiles for the electron density, electron temperature and ion temperature were obtained for hydrogen and deuterium plasmas, whereas the required power clearly increased for hydrogen, which resulted in a reduction in heat diffusivity for deuterium. The determination of identical temperature profiles, despite the different heating power, suggested that the characteristics of heat conduction essentially differ for hydrogen and deuterium, even at the same scale length of temperature gradient. The self-regulating physics mechanism determining the overall H-mode confinement was also addressed. The inverse of the ion temperature gradient (ITG) scale length, or ?Ti/Ti, which is required for a given ion heat diffusivity, increased by a factor of approximately 1.2 for deuterium compared with that for hydrogen. The relationship between edge pedestal pressure and global ?p holds true consistently regardless of the difference in the isotopic composition. A higher value of ?p was obtained for deuterium because of its smaller ITG scale length and because of the additional stored energy in the thermal and fast ion components, the latter due to an increase in the slowing down time with an increase in isotopic mass.

Urano, H.; Takizuka, T.; Aiba, N.; Kikuchi, M.; Nakano, T.; Fujita, T.; Oyama, N.; Kamada, Y.; Hayashi, N.; the JT-60 Team

2013-08-01

332

Diffusion (or conduction) along a slightly tapering tube, and its application to the determination of diffusion coefficients  

Microsoft Academic Search

The diffusion equation has been solved for the case of diffusion from a slightly tapering tube into an infinite medium of zero concentration. The theory provides a means of correcting results obtained for diffusion coefficients in the capillary tube method of Anderson and Saddington, when the tube is not of uniform bore throughout its length. This is frequently the case

A. Talbot; J. A. Kitchener

1956-01-01

333

Lateral diffusion in an archipelago. Distance dependence of the diffusion coefficient.  

PubMed Central

An understanding of the distance dependence of the lateral diffusion coefficient is useful in comparing the results of diffusion measurements made over different length scales, and in analyzing the kinetics of mobile redox carriers in organelles. A distance-dependent, concentration-dependent diffusion coefficient is defined, and it is evaluated by Monte Carlo calculations of a random walk by mobile point tracers in the presence of immobile obstacles on a triangular lattice, representing the diffusion of a lipid or a small protein in the presence of immobile membrane proteins. This work confirms and extends the milling crowd model of Eisinger, J., J. Flores, and W. P. Petersen (1986. Biophys J. 49:987-1001). Similar calculations for diffusion of mobile particles interacting by a hard-core repulsion yield the distance dependence of the self-diffusion coefficient. An expression for the range of short-range diffusion is obtained, and the distance scales for various diffusion measurements are summarized.

Saxton, M J

1989-01-01

334

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

335

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

336

Sub-100 nm channel length graphene transistors  

PubMed Central

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

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

2010-01-01

337

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

338

The Length of My Feet  

NSDL National Science Digital Library

This is Lesson 1 of a five lesson unit. "This lesson focuses students' attention on the attributes of length and develops their knowledge of and skill in using nonstandard units of measurement, their feet. It provides practice with and remediation of the measurable attributes of length." (from NCTM Illuminations)

Math, Illuminations N.

2009-01-28

339

Line Lengths and Starch Scores.  

ERIC Educational Resources Information Center

Investigates readability of different line lengths in advertising body copy, hypothesizing a normal curve with lower scores for shorter and longer lines, and scores above the mean for lines in the middle of the distribution. Finds support for lower scores for short lines and some evidence of two optimum line lengths rather than one. (SKC)

Moriarty, Sandra E.

1986-01-01

340

[Ultrasound determination of leg length].  

PubMed

A diagnostic method is presented for measuring the leg length and the difference in leg lengths with ultrasound. A special device for holding and moving the ultrasound transducer was constructed. The measuring points on the hip, knee, and upper ankle can be visualized with a 5- or 7.5-MHz linear scanner. The measuring device gives the distance of the points in centimeters so that the difference corresponds to the real length of the leg, femur, and tibia. Tests conducted on corpses and clinical examples show that ultrasound in combination with our special device is an ideal method for determining the exact length of the leg. Ultrasound measurement of the leg length offers a reliable, noninvasive, and easily performed method. Because ultrasound is not limited by radiation hazards, our technique can be used for clinical screening. PMID:12017860

Konermann, W; Gruber, G

2002-03-01

341

Amosphous diffusion barriers  

NASA Technical Reports Server (NTRS)

Amorphous W-Zr and W-N alloys were investigated as diffusion barriers in silicon metallization schemes. Data were presented showing that amorphous W-Zr crystallizes at 900 C, which is 200 C higher than amorphous W-Ni films, and that both films react with metallic overlayers at temperatures far below the crystllization temperature. Also, W-N alloys (crystalline temperature of 600 C) were successfully incorporated as a diffusion barrier in contact structures with both Al and Ag overlayers. The thermal stability of the electrical characteristics of shallow n(+)p junctions significantly improved by incorporating W-N layers in the contact system. One important fact demonstated was the critical influence of the deposition parameters during formation of these carriers.

Kolawa, E.; So, F. C. T.; Nicolet, M-A.

1986-01-01

342

Flux saturation length of sediment transport.  

PubMed

Sediment transport along the surface drives geophysical phenomena as diverse as wind erosion and dune formation. The main length scale controlling the dynamics of sediment erosion and deposition is the saturation length Ls, which characterizes the flux response to a change in transport conditions. Here we derive, for the first time, an expression predicting Ls as a function of the average sediment velocity under different physical environments. Our expression accounts for both the characteristics of sediment entrainment and the saturation of particle and fluid velocities, and has only two physical parameters which can be estimated directly from independent experiments. We show that our expression is consistent with measurements of Ls in both aeolian and subaqueous transport regimes over at least 5 orders of magnitude in the ratio of fluid and particle density, including on Mars. PMID:24313529

Pähtz, Thomas; Kok, Jasper F; Parteli, Eric J R; Herrmann, Hans J

2013-11-22

343

Study for noninvasive determination of optical properties of bio-tissue using spatially resolved diffuse reflectance  

NASA Astrophysics Data System (ADS)

The optical characteristics of absorption and scattering of irradiated tissue determine light spatial distribution and the subsequent biological effects, which could decide the dosimetry for laser medical applications. Studys have shown that the optical properties of bio-tissue could be determined through some fitting algorithms with spatially resolved diffuse reflectance theory based on the measurement of diffuse reflectance. The regression of reflectance data with by diffusion theory model was important for optical properties estimation. In the paper, the reflectance versus distance data acquired from Monte Carlo method was by fit to diffusion theory model by the nonliear least-squares fitting algorithm to study the produre and mothod of determination of optical properties. And attention was especially paid to the influence of the radial step width ?r, length of radial distance rL and start value of radial distance r0 on the regression results. Preliminary results indicated that the radial step width and length of radial distance rL both have little influence on the fitting. Nevertheless, the start value of radial distance r0 of reflectance data has great influence on the fitting. Fitting deviation would become little while the start value of radial distance r0 grow greater. and an appropriate r0 was important for data fitting. Study also showd a more accurate light diffuse reflectance theoretical model was need for estimate the optical parameters by fitting the diffuse reflectance data accurately. Our work maybe be helpful to the experiment measurement of light diffuse reflectance data for noninvasive optical properties determination.

Peng, Dong-qing; Li, Hui

2012-12-01

344

Unified Drift-Diffusion Theory for Transverse Spin Currents in Spin Valves, Domain Walls, and Other Textured Magnets  

NASA Astrophysics Data System (ADS)

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 (<10nm) domain walls, we observe very significant deviations from the adiabatic limit.

Petitjean, Cyril; Luc, David; Waintal, Xavier

2012-09-01

345

Diffusion orientation transform revisited.  

PubMed

Diffusion orientation transform (DOT) is a powerful imaging technique that allows the reconstruction of the microgeometry of fibrous tissues based on diffusion MRI data. The three main error sources involving this methodology are the finite sampling of the q-space, the practical truncation of the series of spherical harmonics and the use of a mono-exponential model for the attenuation of the measured signal. In this work, a detailed mathematical description that provides an extension to the DOT methodology is presented. In particular, the limitations implied by the use of measurements with a finite support in q-space are investigated and clarified as well as the impact of the harmonic series truncation. Near- and far-field analytical patterns for the diffusion propagator are examined. The near-field pattern makes available the direct computation of the probability of return to the origin. The far-field pattern allows probing the limitations of the mono-exponential model, which suggests the existence of a limit of validity for DOT. In the regimen from moderate to large displacement lengths the isosurfaces of the diffusion propagator reveal aberrations in form of artifactual peaks. Finally, the major contribution of this work is the derivation of analytical equations that facilitate the accurate reconstruction of some orientational distribution functions (ODFs) and skewness ODFs that are relatively immune to these artifacts. The new formalism was tested using synthetic and real data from a phantom of intersecting capillaries. The results support the hypothesis that the revisited DOT methodology could enhance the estimation of the microgeometry of fiber tissues. PMID:19815083

Canales-Rodríguez, Erick Jorge; Lin, Ching-Po; Iturria-Medina, Yasser; Yeh, Chun-Hung; Cho, Kuan-Hung; Melie-García, Lester

2010-01-15

346

Single-particle diffusion in dense inhomogeneous colloid suspensions in ribbon channels.  

PubMed

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 quasione dimensional (q1D) and quasitwo dimensional (q2D). This paper complements a previous paper about pair diffusion in the same system [Phys. Rev. E 82, 031403 (2010)]. 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 the central strata. The lack of variation in the longitudinal diffusion coefficient with apparent stratum density is explained by the 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. PMID:22181142

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

2011-10-01

347

Tortuosity measurement and the effects of finite pulse widths on xenon gas diffusion NMR studies of porous media  

NASA Technical Reports Server (NTRS)

We have extended the utility of NMR as a technique to probe porous media structure over length scales of approximately 100-2000 microm by using the spin 1/2 noble gas 129Xe imbibed into the system's pore space. Such length scales are much greater than can be probed with NMR diffusion studies of water-saturated porous media. We utilized Pulsed Gradient Spin Echo NMR measurements of the time-dependent diffusion coefficient, D(t), of the xenon gas filling the pore space to study further the measurements of both the pore surface-area-to-volume ratio, S/V(p), and the tortuosity (pore connectivity) of the medium. In uniform-size glass bead packs, we observed D(t) decreasing with increasing t, reaching an observed asymptote of approximately 0.62-0.65D(0), that could be measured over diffusion distances extending over multiple bead diameters. Measurements of D(t)/D(0) at differing gas pressures showed this tortuosity limit was not affected by changing the characteristic diffusion length of the spins during the diffusion encoding gradient pulse. This was not the case at the short time limit, where D(t)/D(0) was noticeably affected by the gas pressure in the sample. Increasing the gas pressure, and hence reducing D(0) and the diffusion during the gradient pulse served to reduce the previously observed deviation of D(t)/D(0) from the S/V(p) relation. The Pade approximation is used to interpolate between the long and short time limits in D(t). While the short time D(t) points lay above the interpolation line in the case of small beads, due to diffusion during the gradient pulse on the order of the pore size, it was also noted that the experimental D(t) data fell below the Pade line in the case of large beads, most likely due to finite size effects.

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

2001-01-01

348

Diffusion Processes in Metals.  

National Technical Information Service (NTIS)

This book consists of a collection of papers dealing with diffusion welding of metals, effect of irradiation on diffusion and diffusion-controlled processes, migration of particles in the stress-field of dislocation loops, diffusion in liquid metals, grai...

1969-01-01

349

Vertical turbulent diffusion in stably stratified flows  

NASA Astrophysics Data System (ADS)

Based on a Lagrangian description of fluid particle dispersion we suggest that there is a single expression for the vertical eddy diffusivity for all scalars following fluid particles in stably stratified flows. This expression is the same as the Osborn-Cox diffusivity for buoyancy. To test this hypothesis we carry out turbulence simulations with stable background stratification by solving the Boussinesq equations with random forcing together with the equation for a passive scalar with an initial vertical Gauss profile. The development of the mean scalar concentration is studied for three different values of the width of the profile, ?. It is found that the passive scalar diffuses in very good agreement with the classical diffusion equation if the ratio between ? and a turbulent length scale is large enough. The associated eddy diffusivity agrees exactly with the Osborn-Cox diffusivity for buoyancy.

Lindborg, Erik; Fedina, Ekaterina

2009-01-01

350

Scale Length of Disk Galaxies  

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

351

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

352

THE THEORY OF DIFFUSION IN CELL MODELS  

PubMed Central

The differential equations which describe the simultaneous diffusion of water and a salt in a cell model have been formulated and solved. The equations have been derived from the general laws which describe diffusion processes, thereby furnishing a physical interpretation for the constants which enter into the theory. The theoretical time curves for the two diffusing substances are in good agreement with the experimentally determined curves and accurately reproduce all of the essential characteristics of the experiment.

Longsworth, Lewis G.

1933-01-01

353

Ambipolar diffusion in complex plasma.  

PubMed

A self-consistent model of the ambipolar diffusion of electrons and ions in complex (dusty) plasmas accounting for the local electric fields, the dust grain charging process, and the interaction of the plasma particles with the dust grains and neutrals is presented. The dependence of the diffusion coefficient on the interaction of the electrons and ions with the dust grains as well as with the neutrals are investigated. It is shown that increase of the dust density leads to a reduction of the diffusion scale length, and this effect is enhanced at higher electron densities. The dependence of the diffusion scale length on the neutral gas pressure is found to be given by a power law, where the absolute value of the power exponent decreases with increase of the dust density. The electric field gradient and its effects are shown to be significant and should thus be taken into account in studies of complex plasmas with not very small dust densities. The possibility of observing localized coherent dissipative nonlinear dust ion-acoustic structures in an asymmetrically discharged double plasma is discussed. PMID:17501000

Losseva, T V; Popel, S I; Yu, M Y; Ma, J X

2007-04-01

354

Determining multiple length scales in rocks  

PubMed

Carbonate reservoirs in the Middle East are believed to contain about half of the world's oil. The processes of sedimentation and diagenesis produce in carbonate rocks microporous grains and a wide range of pore sizes, resulting in a complex spatial distribution of pores and pore connectivity. This heterogeneity makes it difficult to determine by conventional techniques the characteristic pore-length scales, which control fluid transport properties. Here we present a bulk-measurement technique that is nondestructive and capable of extracting multiple length scales from carbonate rocks. The technique uses nuclear magnetic resonance to exploit the spatially varying magnetic field inside the pore space itself--a 'fingerprint' of the pore structure. We found three primary length scales (1-100 microm) in the Middle-East carbonate rocks and determined that the pores are well connected and spatially mixed. Such information is critical for reliably estimating the amount of capillary-bound water in the rock, which is important for efficient oil production. This method might also be used to complement other techniques for the study of shaly sand reservoirs and compartmentalization in cells and tissues. PMID:10910355

Song; Ryu; Sen

2000-07-13

355

In situ experiment to determine advective-diffusive controls on solute transport in a clay-rich aquitard.  

PubMed

Solute transport in clay-rich aquitards is characterized as molecular diffusion- or advection-dominated based on the Péclet number (P(e)). However, few field-based measurements of the coefficient of molecular diffusion (D(e)) exist, and none with a range of advection- or diffusion-dominated conditions in the same aquitard. In this long-term field experiment, standing water in a recovering well was spiked with deuterium ((2)H), then water-level recovery and ?(2)H values were monitored as the well returned to static conditions over 1054 days. After a second (2)H spike, water levels and ?(2)H values were monitored to day 1644 while under near static conditions. Modeling of the second spike was used to define the D(e) of (2)H as (3-4)× 10(-10)m(2)s(-1) for an accessible porosity of 0.31. Reservoir concentrations from the initial spike were modeled to define the transition from advection- to diffusion-dominated transport. This occurred after 200 days, consistent with a transition in P(e) from <1 to >1 when the length term is taken as the radial extent of the tracer plume (normalized concentration <0.05). This study verifies plume extent as the characteristic length term in the calculation of P(e) and demonstrates the transition from advection- to diffusion-dominated transport as the value of P(e) decreases below unity. PMID:22343012

Barbour, S Lee; Hendry, M Jim; Wassenaar, Leonard I

2012-04-01

356

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

357

Determination of local diffusion properties in heterogeneous biomaterials.  

PubMed

The coupling between structure and diffusion properties is essential for the functionality of heterogeneous biomaterials. Structural heterogeneity is defined and its implications for time-dependent diffusion are discussed in detail. The effect of structural heterogeneity in biomaterials on diffusion and the relevance of length scales are exemplified with regard to different biomaterials such as gels, emulsions, phase separated biopolymer mixtures and chocolate. Different diffusion measurement techniques for determination of diffusion properties at different length and time scales are presented. The interplay between local and global diffusion is discussed. New measurement techniques have emerged that enable simultaneous determination of both structure and local diffusion properties. Special emphasis is given to fluorescence recovery after photobleaching (FRAP). The possibilities of FRAP at a conceptual level is presented. The method of FRAP is briefly reviewed and its use in heterogeneous biomaterials, at barriers and during dynamic changes of the structure is discussed. PMID:19481193

Lorén, Niklas; Nydén, Magnus; Hermansson, Anne-Marie

2009-08-30

358

When Does Length Cause the Word Length Effect?  

ERIC Educational Resources Information Center

The word length effect, the finding that lists of short words are better recalled than lists of long words, has been termed one of the benchmark findings that any theory of immediate memory must account for. Indeed, the effect led directly to the development of working memory and the phonological loop, and it is viewed as the best remaining…

Jalbert, Annie; Neath, Ian; Bireta, Tamra J.; Surprenant, Aimee M.

2011-01-01

359

IMF Length Scales and Predictability: The Two Length Scale Medium  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

360

Continuously variable focal length lens  

DOEpatents

A material preferably in crystal form having a low atomic number such as beryllium (Z=4) provides for the focusing of x-rays in a continuously variable manner. The material is provided with plural spaced curvilinear, optically matched slots and/or recesses through which an x-ray beam is directed. The focal length of the material may be decreased or increased by increasing or decreasing, respectively, the number of slots (or recesses) through which the x-ray beam is directed, while fine tuning of the focal length is accomplished by rotation of the material so as to change the path length of the x-ray beam through the aligned cylindrical slows. X-ray analysis of a fixed point in a solid material may be performed by scanning the energy of the x-ray beam while rotating the material to maintain the beam's focal point at a fixed point in the specimen undergoing analysis.

Adams, Bernhard W; Chollet, Matthieu C

2013-12-17

361

Continuous lengths of oxide superconductors  

DOEpatents

A layered oxide superconductor prepared by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon. A continuous length of a second substrate ribbon is overlaid on the first substrate ribbon. Sufficient pressure is applied to form a bound layered superconductor precursor powder between the first substrate ribbon and the second substrate ribbon. The layered superconductor precursor is then heat treated to establish the oxide superconducting phase. The layered oxide superconductor has a smooth interface between the substrate and the oxide superconductor.

Kroeger, Donald M. (Knoxville, TN); List, III, Frederick A. (Andersonville, TN)

2000-01-01

362

Coherence length of neutron superfluids  

SciTech Connect

The coherence length of superfluid neutron matter is calculated from the microscopic BCS wave function of a Cooper pair in momentum space making use of recent nucleon-nucleon potential models and including polarization (RPA) effects. We find as our main result that the coherence length is proportional to the Fermi momentum to pairing gap ratio, in good agreement with simple estimates used in the literature, with a nearly interaction independent constant of proportionality. Our calculations can be applied to the problem of inhomogeneous superfluidity of hadronic matter in the crust of a neutron star. {copyright} {ital 1997} {ital The American Physical Society}

De Blasio, F.V.; Hjorth-Jensen, M. [NORDITA, Blegdamsvej 17, DK-2100 Copenhagen O/ (Denmark)] [NORDITA, Blegdamsvej 17, DK-2100 Copenhagen O/ (Denmark); Elgaro/y, O.; Engvik, L. [Department of Physics, University of Oslo, N-0316 Oslo (Norway)] [Department of Physics, University of Oslo, N-0316 Oslo (Norway); Lazzari, G. [European Centre for Theoretical Studies in Nuclear Physics and Related Areas, Trento (Italy)] [European Centre for Theoretical Studies in Nuclear Physics and Related Areas, Trento (Italy); Baldo, M.; Schulze, H. [Dipartimento di Fisica, Universita di Catania and I.N.F.N., Sezione di Catania, corso Italia 57, I-95129 Catania (Italy)] [Dipartimento di Fisica, Universita di Catania and I.N.F.N., Sezione di Catania, corso Italia 57, I-95129 Catania (Italy)

1997-10-01

363

Coarsening of precipitation patterns in a moving reaction-diffusion front  

NASA Astrophysics Data System (ADS)

Precipitation patterns emerging in a two-dimensional moving front are investigated on the example of NaOH diffusing into a gel containing AlCl3 . The time evolution of the precipitate Al(OH)3 can be observed since the precipitate redissolves in the excess outer electrolyte NaOH and thus it exists only in a narrow optically accessible region of the reaction front. The patterns display self-similar coarsening with a characteristic length ? increasing with time as ?(t)˜t . A theory based on the Cahn-Hilliard phase-separation dynamics, including redissolution, is shown to yield agreement with the experiments.

Volford, A.; Lagzi, I.; Molnár, F., Jr.; Rácz, Z.

2009-11-01

364

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

SciTech Connect

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

2013-08-15

365

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

366

The finite length diocotron mode  

Microsoft Academic Search

A simple model is presented of a finite length electron plasma column supporting a small amplitude diocotron wave with mode number m=1. The electrons are contained inside conducting cylinders in an axial magnetic field, with negative voltages on end cylinders providing axial containment. The m=1 diocotron mode is the E×B drift orbit of an offset electron column around the cylinder

K. S. Fine; C. F. Driscoll

1998-01-01

367

Telomere length in human blastocysts.  

PubMed

This is a retrospective study aiming to assess telomere length in human embryos 4 days post fertilization and to determine whether it is correlated to chromosomal ploidy, embryo developmental rate and patient age. Embryos were donated from patients undergoing treatment in the assisted conception unit. Seven couples took part, generating 35 embryos consisting of 1130 cells. Quantitative fluorescent in-situ hybridization (FISH) measured the telomere length of every cell using a pan-telomeric probe. Conventional FISH on six chromosomes was used to assess aneuploidy in the same cells. Maternal and paternal age, referral reason, embryo developmental rate and type of chromosomal error were taken into account. Chromosomally abnormal cells were associated with shorter telomeres than normal cells for embryos that were developmentally slow. Cells produced by women of advanced maternal age and those with a history of repeated miscarriage tended to have substantially shorter telomeres. There was no significant difference in telomere length with respect to the rate of embryo development 5 days post fertilization. Telomeres play an important role in cell division and shorter telomeres may affect embryonic ploidy. Reduced telomere length was associated with aneuploid cells and embryos from women of advanced maternal age. PMID:24581987

Mania, Anastasia; Mantzouratou, Anna; Delhanty, Joy D A; Baio, Gianluca; Serhal, Paul; Sengupta, Sioban B

2014-05-01

368

Why Reevaluate Dry Period Length?  

Microsoft Academic Search

Possible advantages of reducing length of dry period include increased income from milk production, simpli- fied dry cow management, decreased metabolic disor- ders, and alleviation of overcrowded dry cow facilities. There is abundant data to support a 60-d dry period to maximize milk yield the next lactation. The great majority of data is from studies using farm records (e.g., DHI

R. R. Grummer; R. R. Rastani

2004-01-01

369

Diffuse scattering from the icosahedral phase alloys  

NASA Astrophysics Data System (ADS)

Neutron and X-ray measurements of the diffuse scattering from single-grain samples of the icosahedral phase of Al-Li-Cu are presented. The X-ray measurements were analyzed to determine the integrated intensity of the diffuse scattering relative to the sharp diffraction peaks, as well as the length scale of the correlations which produce the diffuse scattering. The neutron data show that these correlations are static rather than dynamic in nature. A simple model based on the disordered packing of icosahedral clusters of atoms reproduces the unusual ringlike nature of this scattering. Quantitatively, this model overestimates the degree of disorder present in these alloys.

Goldman, A. I.; Guryan, C. A.; Stephens, P. W.; Parsey, J. M., Jr.; Aeppli, G.

1988-10-01

370

Numerical analysis of a vortex controlled diffuser  

NASA Technical Reports Server (NTRS)

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.

1993-01-01

371

Seismic Hazard and Fault Length  

NASA Astrophysics Data System (ADS)

If mx is the largest earthquake magnitude that can occur on a fault, then what is mp, the largest magnitude that should be expected during the planned lifetime of a particular structure? Most approaches to these questions rely on an estimate of the Maximum Credible Earthquake, obtained by regression (e.g. Wells and Coppersmith, 1994) of fault length (or area) and magnitude. Our work differs in two ways. First, we modify the traditional approach to measuring fault length, to allow for hidden fault complexity and multi-fault rupture. Second, we use a magnitude-frequency relationship to calculate the largest magnitude expected to occur within a given time interval. Often fault length is poorly defined and multiple faults rupture together in a single event. Therefore, we need to expand the definition of a mapped fault length to obtain a more accurate estimate of the maximum magnitude. In previous work, we compared fault length vs. rupture length for post-1975 earthquakes in Southern California. In this study, we found that mapped fault length and rupture length are often unequal, and in several cases rupture broke beyond the previously mapped fault traces. To expand the geologic definition of fault length we outlined several guidelines: 1) if a fault truncates at young Quaternary alluvium, the fault line should be inferred underneath the younger sediments 2) faults striking within 45° of one another should be treated as a continuous fault line and 3) a step-over can link together faults at least 5 km apart. These definitions were applied to fault lines in Southern California. For example, many of the along-strike faults lines in the Mojave Desert are treated as a single fault trending from the Pinto Mountain to the Garlock fault. In addition, the Rose Canyon and Newport-Inglewood faults are treated as a single fault line. We used these more generous fault lengths, and the Wells and Coppersmith regression, to estimate the maximum magnitude (mx) for the major faults in southern California. Then we compared our mx values with those proposed by CALTRANS, and those assumed in the 2002 USGS/CGS hazard model. To calculate the planning magnitude mp we assumed a truncated Gutenberg-Richter magnitude distribution with parameters a, b, and mx. We fixed b and solved for the a-value in terms of mx, b, and the tectonic moment rate. For many faults mp is relatively insensitive to mx and typically falls off at higher magnitudes because the a-value decreases with increasing mx when the moment rate is constrained. Furthermore, we find that by increasing mx the cumulative earthquake rate actually decreases for smaller magnitude (5 and 6) events. This suggests that fewer magnitude 5 and 6 earthquakes are required to balance the moment budget if larger, but highly infrequent, earthquakes are allowed to occur.

Black, N. M.; Jackson, D. D.; Mualchin, L.

2005-12-01

372

Experimental evidence for two thermodynamic length scales in neutralized polyacrylate gels  

NASA Astrophysics Data System (ADS)

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

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

2002-11-01

373

The correlation length for interplanetary magnetic field fluctuations  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

374

Fractional diffusion models of anomalous diffusion  

NASA Astrophysics Data System (ADS)

Perturbative transport experiments, and numerical simulations have provided evidence of non-Gaussian, anomalous diffusive transport in magnetically confined plasmas. These results are incompatible with the standard diffusive, local transport paradigm, and there is the need to develop alternative models. Here we explore the idea of constructing non-Gaussian diffusion models using fractional diffusion operators. In particular, we study the role of non-Gaussian diffusion in the propagation of fronts in the L-H transition, and show that fractional diffusion leads to the exponential acceleration of the front and the algebraic decay of the front's tail [1]. We also present a fractional in space and time diffusion model describing the non-Gaussian diffusion of test particles in pressure driven plasma turbulence. [1] D. del-Castillo-Negrete, B.A. Carreras, and V.E. Lynch, Phys Rev Lett, 91, 018302-1, (2003).

del-Castillo-Negrete, Diego; Carreras, B. A.; Lynch, V. E.

2003-10-01

375

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

376

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

377

Hospital Staff Nurses' Shift Length Associated With Safety and Quality of Care  

PubMed Central

The objective of this study was to analyze hospital staff nurses’ shift length, scheduling characteristics, and nurse reported safety and quality. A secondary analysis of a large nurse survey linked with hospital administrative data was conducted. More than 22 000 registered nurses’ reports of shift length and scheduling characteristics were examined. Extended shift lengths were associated with higher odds of reporting poor quality and safety. Policies aimed at reducing the use of extended shifts may be advisable.

Stimpfel, Amy Witkoski; Aiken, Linda H.

2013-01-01

378

FRACTIONAL PEARSON DIFFUSIONS  

PubMed Central

Pearson diffusions are governed by diffusion equations with polynomial coefficients. Fractional Pearson diffusions are governed by the corresponding time-fractional diffusion equation. They are useful for modeling sub-diffusive phenomena, caused by particle sticking and trapping. This paper provides explicit strong solutions for fractional Pearson diffusions, using spectral methods. It also presents stochastic solutions, using a non-Markovian inverse stable time change.

Leonenko, Nikolai N.; Meerschaert, Mark M.

2013-01-01

379

The finite length diocotron mode  

NASA Astrophysics Data System (ADS)

A simple model is presented of a finite length electron plasma column supporting a small amplitude diocotron wave with mode number m=1. The electrons are contained inside conducting cylinders in an axial magnetic field, with negative voltages on end cylinders providing axial containment. The m=1 diocotron mode is the E×B drift orbit of an offset electron column around the cylinder axis, due to radial electric fields from image charges on the wall. The model predicts that the mode frequency will be higher than that of an infinitely long column due to ?-drifts from the radial containment fields at the plasma ends. The predicted dependencies on plasma length, radius, and temperature agree well with experiments, where frequency increases up to 2.5× are observed. For very short plasmas, these containment fields predominate over the image charge fields, and the plasma orbit is called the ``magnetron'' mode. The shift in the magnetron frequency due to image charges is also calculated.

Fine, K. S.; Driscoll, C. F.

1998-03-01

380

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

381

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

382

Surface self-diffusion of an organic glass.  

PubMed

Surface self-diffusion has been measured for an organic glass for the first time. The flattening of 1000 nm surface gratings of liquid indomethacin occurs by viscous flow at 12 K or more above the glass transition temperature and by surface diffusion at lower temperatures. Surface diffusion is at least 10(6) times faster than bulk diffusion, indicating a highly mobile surface. Our data suggest that surface diffusion is the leading mechanism of surface evolution for organic glasses at micrometer to nanometer length scales. PMID:21770657

Zhu, L; Brian, C W; Swallen, S F; Straus, P T; Ediger, M D; Yu, L

2011-06-24

383

An asynchronous instruction length decoder  

Microsoft Academic Search

This paper describes an investigation of potential ad- vantages and pitfalls of applying an asynchronous design methodology to an advanced microprocessor architecture. A prototype complex instruction set length decoding and steering unit1 was implemented using self-timed circuits. The prototype chip was fabricated on a 0.25µ CMOS pro- cess and tested successfully. Results show significant ad- vantages - in particular, performance

Ken Stevens; Shai Rotem; Ran Ginosar; Peter Beerel; Chris Myers; Kenneth Yun; Rakefet Kol; Charles Dike; Marly Roncken

2001-01-01

384

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

385

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

386

Some Experimental Aspects of Diffusion in Metals.  

National Technical Information Service (NTIS)

Diffusion is present whenever there is a change in the local composition in solids. When solid A and solid B are brought into contact and this couple is brought to a high temperature, it is found that after a certain length of time, the atoms of solid A n...

C. T. Tomizuka

1967-01-01

387

Comprehensive management of diffuse malignant peritoneal mesothelioma  

Microsoft Academic Search

AimsIn the past, diffuse malignant peritoneal mesothelioma (DMPM) has been regarded as a terminal condition. The length of the survival was dependent upon the aggressive versus indolent biology of the neoplasm, nevertheless cure was not considered as a reasonable expectation and the overall median survival was approximately one year.

P. H. Sugarbaker; T. D. Yan; O. A. Stuart; D. Yoo

2006-01-01

388

WORKSPACE GENERATION AS A DIFFUSION PROCESS  

Microsoft Academic Search

In this paper we show that the workspace of a highly artic- ulated manipulator can be found by solving a partial differential equation. This diffusion-type equation describes the evolution of the workspace density function depending on manipulator length and kinematic properties. The support of the workspace density function is the workspace of the manipulator. The PDE govern- ing workspace density

Yunfeng Wang; Gregory S. Chirikjian

2000-01-01

389

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

390

The estimate of the Venus magnetotail length  

NASA Astrophysics Data System (ADS)

We consider the process of flux tubes straightening in the Venus magnetotail on the basis of MHD model. We estimate the distance x t, where flux tubes are fully straightened due to the magnetic tension and the magnetotail with the characteristic geometry of field lines ("slingshot" geometry) ends. We investigate the influence of the transversal current sheet scale on the process of flux tubes straightening. The assumption of a thin current sheet allows to obtain a lower estimate of the magnetotail length, x t > 31 R V ( R V is the Venus radius), while the assumption of a broad current sheet allows to obtain an upper estimate, x t < 44 R V. We show that kinetic effects associated with the losses of particles with small pitch angles from the flux tube and the influx of magnetosheath plasma into the flux tube do not significantly affect the estimate of the magnetotail length. The model predicts the existence of energetic fluxes of protons H+ (2-5 keV) and oxygen ions O+ (35-80 keV) in the distant tail. We discuss the magnetotail structure at x > x t.

Vasko, I. Yu.; Zelenyi, L. M.; Popov, V. Yu.

2014-03-01

391

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

392

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

393

Significance of tumor length as prognostic factor for esophageal cancer.  

PubMed

Abstract Our study indicated the relationship between tumor length and clinicopathologic characteristics as well as long-term survival in esophageal cancer. A total of 116 patients who underwent curative surgery for thoracic esophageal cancer with standard lymphadenectomy in 2 fields between 2000 and 2010 were included in the study. The medical records of these patients were retrospectively reviewed. The patients with tumor length ?3 cm had a highly significant difference in the involvement of adventitia and lymph node stations. The patients with tumor length ?3 cm had significantly lower rates of involvement of the adventitia and lymph node stations. Tumor length could have a significant impact on both the overall survival and disease-free survival of patients with resected esophageal carcinomas and may provide additional prognostic value to the current tumor, node, and metastasis staging system before patients receive any cancer-specific treatment. PMID:23971777

Zeybek, Arife; Erdo?an, Abdullah; Gülkesen, Kemal Hakan; Ergin, Makbule; Sarper, Alpay; Dertsiz, Levent; Demircan, Abid

2013-01-01

394

Interfacial effects on nanoconfined diffusive mass transport regimes  

PubMed Central

A hierarchical multiscale modeling approach, incorporating Molecular Dynamics and Finite Element techniques, was used to study parametrically diffusion regimes through nanoconfined fluid. Novel parameters which determine the character of the diffusion regime and diffusion kinetics within the nanoscale confined fluids were established by exploring diffusion where the interface effects at the solid surface are important. New diffusion transport characteristics are established when nanochannel confining dimension approaches 3–4 sizes of diffusing molecules, which also marks peripheries of the non-Fickian transport regime.

Kojic, M.; Milosevic, M.; Ferrari, M.

2013-01-01

395

(VDA) Vapor Diffusion Apparatus Tray  

NASA Technical Reports Server (NTRS)

These Vapor Diffusion Apparatus (VDA) trays were first flown in the Thermal Enclosure System (TES) during the USMP-2 (STS-62) mission. Each tray can hold 20 protein crystal growth chambers. Each chamber contains a double-barrel syringe; one barrel holds protein crystal solution and the other holds precipitant agent solution. During the microgravity mission, a torque device is used to simultaneously retract the plugs in all 20 syringes. The two solutions in each chamber are then mixed. After mixing, droplets of the combined solutions are moved onto the syringe tips so vapor diffusion can begin. During the length of the mission, protein crystals are grown in the droplets. Shortly before the Shuttle's return to Earth, the experiment is deactivated by retracting the droplets containing protein crystals, back into the syringes.

1994-01-01

396

Length dependence of carbon nanotube thermal conductivity and the "problem of long waves"  

NASA Technical Reports Server (NTRS)

We present the first calculations of finite length carbon nanotube thermal conductivity that extend from the ballistic to the diffusive regime, throughout a very wide range of lengths and temperatures. The long standing problem of vanishing scattering of the "long wavelength phonf dramatically here, making the thermal conductivity diverge as the nanotube length increases. We show that the divergence disappears if 3-phonon scattering processes are considered to second or higher order. Nevertheless, for defect free nanotubes, the thermal conductivity keeps increasing up to very large lengths (10 gm at 300 K). Defects in the nanotube are also able to remove the long wavelength divergence.

Mingo, N.; Broido, D. A.

2005-01-01

397

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

398

The response of the upper atmosphere to perturbations from diffusive equilibrium  

NASA Technical Reports Server (NTRS)

It is generally assumed that, in the atmosphere above 120 km, the deviations from diffusive equilibrium are small, though a minor constituent may show some deviation. The response of such a constituent to perturbations from diffusive equilibrium was analyzed qualitatively. It is shown that the magnitude of these deviations is mainly determined by the characteristic diffusion time. For a time-dependent perturbation, the ratio of the characteristic time of the perturbation to the characteristics diffusion time is an important parameter.

Blum, P. W.

1972-01-01

399

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

400

NMR Measures of Heterogeneity Length  

NASA Astrophysics Data System (ADS)

Advanced solid state NMR spectroscopy provides a wealth of information about structure and dynamics of complex systems. On a local scale, multidimensional solid state NMR has elucidated the geometry and the time scale of segmental motions at the glass transition. The higher order correlation functions which are provided by this technique led to the notion of dynamic heterogeneities, which have been characterized in detail with respect to their rate memory and length scale. In polymeric and low molar mass glass formers of different fragility, length scales in the range 2 to 4 nm are observed. In polymeric systems, incompatibility of backbone and side groups as in polyalkylmethacrylates leads to heteogeneities on the nm scale, which manifest themselves in unusual chain dynamics at the glass transition involving extended chain conformations. References: K. Schmidt-Rohr and H.W. Spiess, Multidimensional Solid-State NMR and Polymers,Academic Press, London (1994). U. Tracht, M. Wilhelm, A. Heuer, H. Feng, K. Schmidt-Rohr, H.W. Spiess, Phys. Rev. Lett. 81, 2727 (1998). S.A. Reinsberg, X.H. Qiu, M. Wilhelm, M.D. Ediger, H.W. Spiess, J.Chem.Phys. 114, 7299 (2001). S.A. Reinsberg, A. Heuer, B. Doliwa, H. Zimmermann, H.W. Spiess, J. Non-Crystal. Solids, in press (2002)

Spiess, Hans W.

2002-03-01

401

Dependence on chain length of NMR relaxation times in mixtures of alkanes  

NASA Astrophysics Data System (ADS)

Many naturally occurring fluids, such as crude oils, consist of a very large number of components. It is often of interest to determine the composition of the fluids in situ. Diffusion coefficients and nuclear magnetic resonance (NMR) relaxation times can be measured in situ and depend on the size of the molecules. It has been shown [D. E. Freed et al., Phys. Rev. Lett. 94, 067602 (2005)] that the diffusion coefficient of each component in a mixture of alkanes follows a scaling law in the chain length of that molecule and in the mean chain length of the mixture, and these relations were used to determine the chain length distribution of crude oils from NMR diffusion measurements. In this paper, the behavior of NMR relaxation times in mixtures of chain molecules is addressed. The author explains why one would expect scaling laws for the transverse and longitudinal relaxation times of mixtures of short chain molecules and mixtures of alkanes, in particular. It is shown how the power law dependence on the chain length can be calculated from the scaling laws for the translational diffusion coefficients. The author fits the literature data for NMR relaxation in binary mixtures of alkanes and finds that its dependence on chain length agrees with the theory. Lastly, it is shown how the scaling laws in the chain length and the mean chain length can be used to determine the chain length distribution in crude oils that are high in saturates. A good fit is obtained between the NMR-derived chain length distributions and the ones from gas chromatography.

Freed, Denise E.

2007-05-01

402

Free Path Lengths in Quasicrystals  

NASA Astrophysics Data System (ADS)

Previous studies of kinetic transport in the Lorentz gas have been limited to cases where the scatterers are distributed at random (e.g., at the points of a spatial Poisson process) or at the vertices of a Euclidean lattice. In the present paper we investigate quasicrystalline scatterer configurations, which are non-periodic, yet strongly correlated. A famous example is the vertex set of a Penrose tiling. Our main result proves the existence of a limit distribution for the free path length, which answers a question of Wennberg. The limit distribution is characterised by a certain random variable on the space of higher dimensional lattices, and is distinctly different from the exponential distribution observed for random scatterer configurations. The key ingredients in the proofs are equidistribution theorems on homogeneous spaces, which follow from Ratner's measure classification.

Marklof, Jens; Strömbergsson, Andreas

2014-03-01

403

Ligand chain length conveys thermochromism.  

PubMed

Thermochromic properties of a series of non-ionic copper compounds have been reported. Herein, we demonstrate that Cu(ii) ion with straight-chain primary amine (A) and alpha-linolenic (fatty acid, AL) co-jointly exhibit thermochromic properties. In the current case, we determined that thermochromism becomes ligand chain length-dependent and at least one of the ligands (A or AL) must be long chain. Thermochromism is attributed to a balanced competition between the fatty acids and amines for the copper(ii) centre. The structure-property relationship of the non-ionic copper compounds Cu(AL)2(A)2 has been substantiated by various physical measurements along with detailed theoretical studies based on time-dependent density functional theory. It is presumed from our results that the compound would be a useful material for temperature-sensor applications. PMID:24943491

Ganguly, Mainak; Panigrahi, Sudipa; Chandrakumar, K R S; Sasmal, Anup Kumar; Pal, Anjali; Pal, Tarasankar

2014-08-14

404

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

NASA Technical Reports Server (NTRS)

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

Von Roos, O.

1980-01-01

405

Correlated diffusion of colloidal particles near a liquid-liquid interface.  

PubMed

Optical microscopy and multi-particle tracking are used to investigate the cross-correlated diffusion of quasi two-dimensional colloidal particles near an oil-water interface. The behaviors of the correlated diffusion along longitudinal and transverse direction are asymmetric. It is shown that the characteristic length for longitudinal and transverse correlated diffusion are particle diameter d and the distance z from particle center to the interface, respectively, for large particle separation z. The longitudinal and transverse correlated diffusion coefficient D||(r) and D[perpendicular](r) are independent of the colloidal area fraction n when n < 0.3, which indicates that the hydrodynamic interactions(HIs) among the particles are dominated by HIs through the surrounding fluid for small n. For high area fraction n > 0.4 the power law exponent for the spatial decay of [Formula: see text] begins to decrease, which suggests the HIs are more contributed from the 2D particle monolayer self for large n. PMID:24465498

Zhang, Wei; Chen, Song; Li, Na; Zhang, Jia Zheng; Chen, Wei

2014-01-01

406

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

407

The scaling and shift of morphogen gene expression boundary in a nonlinear reaction diffusion system.  

PubMed

The scaling and shift of the gene expression boundary in a developing embryo are two key problems with regard to morphogen gradient formation in developmental biology. In this study, a bigradient model was applied to a nonlinear reaction diffusion system (NRDS) to investigate the location of morphogen gene expression boundary. In contrast to the traditional synthesis-diffusion-degradation model, the introduction of NRDS in this study contributes to the precise gene expression boundary at arbitrary location along the anterior-posterior axis other than simply midembryo even when the linear characteristic lengths of two morphogens are equal. The scaling location depends on the ratio of two morphogen influxes ([Formula: see text]) and concentrations ([Formula: see text]) as well as the nonlinear reaction diffusion parameters ([Formula: see text]). We also formulate a direct relationship between the shift in the gene expression boundary and the influx of morphogen and find that enhancing the morphogen influx is helpful to build up a robust gene expression boundary. By analyzing the robustness of the morphogen gene expression boundary and comparing with the relevant results in linear reaction diffusion system, we determine the precise range of the ratio of the two morphogen influxes with a lower shift in the morphogen gene expression boundary and increased system robustness. PMID:24824850

Li, Wei-Shen; Shao, Yuan-Zhi

2014-06-01

408

Altered Anatomical Network in Early Blindness Revealed by Diffusion Tensor Tractography  

PubMed Central

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

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

2009-01-01

409

Measuring charge carrier diffusion in coupled colloidal quantum dot solids.  

PubMed

Colloidal quantum dots (CQDs) are attractive materials for inexpensive, room-temperature-, and solution-processed optoelectronic devices. A high carrier diffusion length is desirable for many CQD device applications. In this work we develop two new experimental methods to investigate charge carrier diffusion in coupled CQD solids under charge-neutral, i.e., undepleted, conditions. The methods take advantage of the quantum-size-effect tunability of our materials, utilizing a smaller-bandgap population of quantum dots as a reporter system. We develop analytical models of diffusion in 1D and 3D structures that allow direct extraction of diffusion length from convenient parametric plots and purely optical measurements. We measure several CQD solids fabricated using a number of distinct methods and having significantly different doping and surface ligand treatments. We find that CQD materials recently reported to achieve a certified power conversion efficiency of 7% with hybrid organic-inorganic passivation have a diffusion length of 80 ± 10 nm. The model further allows us to extract the lifetime, trap density, mobility, and diffusion coefficient independently in each material system. This work will facilitate further progress in extending the diffusion length, ultimately leading to high-quality CQD solid semiconducting materials and improved CQD optoelectronic devices, including CQD solar cells. PMID:23701285

Zhitomirsky, David; Voznyy, Oleksandr; Hoogland, Sjoerd; Sargent, Edward H

2013-06-25

410

An Efficient Variable-Length Data-Compression Scheme  

NASA Technical Reports Server (NTRS)

Adaptive variable-length coding scheme for compression of stream of independent and identically distributed source data involves either Huffman code or alternating run-length Huffman (ARH) code, depending on characteristics of data. Enables efficient compression of output of lossless or lossy precompression process, with speed and simplicity greater than those of older coding schemes developed for same purpose. In addition, scheme suitable for parallel implementation on hardware with modular structure, provides for rapid adaptation to changing data source, compatible with block orientation to alleviate memory requirements, ensures efficiency over wide range of entropy, and easily combined with such other communication schemes as those for containment of errors and for packetization.

Cheung, Kar-Ming; Kiely, Aaron B.

1996-01-01

411

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

412

Phase-Length Optical Phase-Locked-Loop Sensor (PLOPS)  

NASA Technical Reports Server (NTRS)

PLOPS system designed to provide high-resolution measurement of change in optical length from optical-system source to any optical reflector, including diffuse reflector. Serves as adjustable optical ruler, providing high resolution in measurements of small and large changes in distance to target. Use is broad and includes most measurement situations requiring information on length, vibration, and their derivatives. Applications include building dynamics, remote sensing of vibrations in such systems as turbine-based machinery, monitoring of structural dynamics, noncontacting sensing of surface contours, measurement of large strains as in earthquake monitoring, measurement of atmospheric dynamics and turbulence, high-resolution sensing of humidity, detection of surface acoustic waves by optical microscopy, and related areas.

Heyman, Joseph S.; Rogawski, Robert S.

1988-01-01

413

Tau Protein Diffuses along the Microtubule Lattice*  

PubMed Central

Current models for the intracellular transport of Tau protein suggest motor protein-dependent co-transport with microtubule fragments and diffusion of Tau in the cytoplasm, whereas Tau is believed to be stationary while bound to microtubules and in equilibrium with free diffusion in the cytosol. Observations that members of the microtubule-dependent kinesin family show Brownian motion along microtubules led us to hypothesize that diffusion along microtubules could also be relevant in the case of Tau. We used single-molecule total internal reflection fluorescence microscopy to probe for diffusion of individual fluorescently labeled Tau molecules along microtubules. This allowed us to avoid the problem that microtubule-dependent diffusion could be masked by excess of labeled Tau in solution that might occur in in vivo overexpression experiments. We found that approximately half of the individually detected Tau molecules moved bidirectionally along microtubules over distances up to several micrometers. Diffusion parameters such as diffusion coefficient, interaction time, and scanned microtubule length did not change with Tau concentration. Tau binding and diffusion along the microtubule lattice, however, were sensitive to ionic strength and pH and drastically reduced upon enzymatic removal of the negatively charged C termini of tubulin. We propose one-dimensional Tau diffusion guided by the microtubule lattice as one possible additional mechanism for Tau distribution. By such one-dimensional microtubule lattice diffusion, Tau could be guided to both microtubule ends, i.e. the sites where Tau is needed during microtubule polymerization, independently of directed motor-dependent transport. This could be important in conditions where active transport along microtubules might be compromised.

Hinrichs, Maike H.; Jalal, Avesta; Brenner, Bernhard; Mandelkow, Eckhard; Kumar, Satish; Scholz, Tim

2012-01-01

414

Buoyancy Effects on Flow Transition in Hydrogen Gas Jet Diffusion Flames  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

415

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

2008-07-15

416

Developments in diffusion weighted magnetic resonance imaging (MRI) with applications to neural tissue  

Microsoft Academic Search

Translational diffusion of water within biological tissue can be measured noninvasively using magnetic resonance imaging techniques. Diffusion imaging of neural tissue can provide very valuable information about the tissue microstructure because of its sensitivity to the molecular motion in length scales much smaller than the resolution of the images and similar to the dimensions of the cells. Diffusion attenuated multidirectional

Evren Ozarslan

2004-01-01

417

Study of the diffusion of trace elements and radionuclides in soils  

Microsoft Academic Search

Thin layer method of measuring diffusion processes was modified to shorten time and to increase efficiency of experiments. For this purpose small and fine glass capillaries of 20 mm length and inner diameter of several millimeters were used as diffusion cells. The diffusion of trace amounts of137Cs, its dependence on soil moisture and interaction with the soil have been studied.

A. Gosman; J. Blaží?ek

1994-01-01

418

Analytical model of susceptibility-induced MR signal dephasing: Effect of diffusion in a microvascular network  

Microsoft Academic Search

A deterministic analytical model that describes the time course of magnetic resonance signal relaxation due to magnetic field inhomogeneity induced by a vascular network is developed. Both static and diffusion dephasing are taken into account. The contribution of the diffusion dephasing is calculated for rela- tively large vessels (R G 10µm) or short measurement times when the diffusion length is

V. G. Kiselev; S. Posse

1999-01-01

419

Radiative diffusion in stellar atmospheres: diffusion velocities  

Microsoft Academic Search

Aims.The present paper addresses some of the problems in the buildup of element stratification in stellar magnetic atmospheres due to microscopic diffusion, in particular the redistribution of momentum among the various ionisation stages of a given element and the calculation of diffusion velocities in the presence of inclined magnetic fields. Methods: .We have considerably modified and extended our CARAT code

G. Alecian; M. J. Stift

2006-01-01

420

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

421

Structural and Environmental Characteristics of Stereotyped Behaviors.  

ERIC Educational Resources Information Center

This study examined structural characteristics and environmental variables in the stereotypic behaviors of eight individuals with developmental disabilities. Findings indicated that structural characteristics (percentage of time, bout length, and bout length variability) were highly correlated. Also, stereotyped behaviors were more likely to occur…

Hall, Scott; Thorns, Tracy; Oliver, Chris

2003-01-01

422

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

423

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

424

Radon Diffusion Measurement in Polyethylene based on Alpha Detection  

NASA Astrophysics Data System (ADS)

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 s