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1

Complete suppression of boron transient-enhanced diffusion and oxidation-enhanced diffusion in silicon using localized substitutional carbon incorporation  

NASA Astrophysics Data System (ADS)

In this letter, we show the ability, through introduction of a thin Si1-x-yGexCy layer, to eliminate the enhancement of enhanced boron diffusion in silicon due to an oxidizing surface or ion implant damage. This reduction of diffusion is accomplished through a low-temperature-grown thin epitaxial Si1-x-yGexCy layer which completely filters out excess interstitials introduced by oxidation or ion implant damage. We also quantify the oxidation-enhanced diffusion (OED) and transient-enhanced diffusion (TED) dependence on substitutional carbon level, and further report both the observation of carbon TED and OED, and its dependence on carbon levels.

Carroll, M. S.; Chang, C.-L.; Sturm, J. C.; Büyüklimanli, T.

1998-12-01

2

Species, dose and energy dependence of implant induced transient enhanced diffusion  

Microsoft Academic Search

Special test structures which separate implant damage from a buried monitor boron layer were used to observe the transient diffusion associated with implant annealing. The large anomalous diffusion length is independent of implant species but strongly dependent on implant energy. This is modeled by enhanced Frenkel pair recombination along dense cascade damage tracks associated with heavier ions. The enhancement in

P. B. Griffin; R. F. Lever; R. Y. S. Huang; H. W. Kennel; P. A. Packan; J. D. Plummer

1993-01-01

3

Phosphorous transient enhanced diffusion suppression and activation enhancement with cluster carbon co-implantation  

SciTech Connect

Carbon co-implantation is well known as an effective method for suppressing boron/phosphorous transient enhanced diffusion (TED). Germanium pre-amorphization implantation (PAI) is usually applied prior to carbon co-implantation for suppressing channeling tail of dopants. In this study, cluster carbon was applied instead of the combination of germanium PAI and monomer carbon co-implantation prior to phosphorous implantation. Dependence of phosphorous activation and TED on amorphous layer thickness, carbon dose, carbon distribution and substrate temperature have been investigated. Cluster carbon implantation enables thick amorphous layer formation and TED suppression at the same time and low temperature implantation enhances the ability of amorphous layer formation so that shallow junction and low Rs can be achieved without Ge implantation.

Nakashima, Yoshiki; Hamamoto, Nariaki; Nagayama, Tsutomu; Koga, Yuji; Umisedo, Sei; Kawamura, Yasunori; Hashimoto, Masahiro; Onoda, Hiroshi [Nissin Ion Equipment Co., Ltd., 575 Kuze Tonoshiro-cho, Minami-ku, Kyoto, 601-8205 (Japan)

2012-11-06

4

Simulation of Dopant Redistribution During Gate Oxidation Including Transient-Enhanced Diffusion Caused by Implantation Damage  

NASA Astrophysics Data System (ADS)

Dopant redistribution during gate oxidation in metal-oxide-semiconductor (MOS) fabrication processes has been studied by secondary-ion mass spectrometry (SIMS). In the first set of experiments, dopant profiles after gate oxidation are measured and compared to those after N2 annealing. From the measured profiles, the contribution of oxidation-enhanced diffusion (OED) to the entire dopant redistribution is determined and an OED model parameter is calibrated. In the second set of experiments, samples which are subjected only to wafer loading and unloading steps are prepared and dopant profiles are measured. From the measured profiles, the magnitude of transient-enhanced diffusion (TED) which occurs during the wafer loading step is estimated and an interstitial-clustering parameter is calibrated. The parameters calibrated in this study are combined with the point-defect parameters taken from the literature, and dopant redistribution during the entire gate oxidation cycle is simulated. Calculated dopant profiles agree well with the measured SIMS profiles and show correct time dependence of TED and OED, as observed in the present experiments. In the simulations, interstitial concentration at the oxidizing Si/SiO2 interface is found to be 40 times the equilibrium concentration. The supersaturation caused by surface oxidation is small and the contribution of OED is negligible under typical gate oxidation conditions where oxide thickness is less than 100 \\AA@. Dopant profiles after gate oxidation are mainly dominated by TED@. However, as oxidation proceeds, the contribution of OED increases because it continues while TED almost ends in the wafer loading step of gate oxidation. Segregation of boron in the channel region is also studied. It is found that a greater amount of boron is lost in oxidation than in N2 annealing. The effect of segregation on device characteristics is not negligible for buried-channel PMOS devices, because the threshold voltage of the devices is sensitive to the change in the amount of boron.

Uchida, Tetsuya; Eikyu, Katsumi; Tsukuda, Eiji; Fujinaga, Masato; Teramoto, Akinobu; Yamashita, Tomohiro; Kunikiyo, Tatsuya; Ishikawa, Kiyoshi; Kotani, Norihiko; Kawazu, Satoru; Hamaguchi, Chihiro; Nishimura, Tadashi

2000-05-01

5

Effective diffusivity in transient state  

NASA Astrophysics Data System (ADS)

The effective diffusivity in a polymer matrix modified with inclusions is usually calculated based on Kalnin-Kotomin's model [J. R. Kalnin, E. A. Kotomin, and J. Maier, J. Phys. Chem. Solids 63, 449-456 (2002)], which extends the well known Maxwell-Garnett formula. Kalnin-Kotomin's model correctly predicts effective diffusivity for stationary diffusion or for infinite media. In the present paper diffusion in composite media is studied for finite systems under transient conditions. The process of diffusion is modeled numerically and effective diffusion coefficient in the transient state is estimated, which, under certain conditions, is different from the predictions of the Kalnin-Kotomin's model. An analytical model is proposed to explain deviations of the transient effective coefficient of diffusion from the stationary case.

Tabor, Zbis?aw; Nowak, Pawe?; Krzak, Ma?gorzata; Warszy?ski, Piotr

2013-08-01

6

Effective diffusivity in transient state.  

PubMed

The effective diffusivity in a polymer matrix modified with inclusions is usually calculated based on Kalnin-Kotomin's model [J. R. Kalnin, E. A. Kotomin, and J. Maier, J. Phys. Chem. Solids 63, 449-456 (2002)], which extends the well known Maxwell-Garnett formula. Kalnin-Kotomin's model correctly predicts effective diffusivity for stationary diffusion or for infinite media. In the present paper diffusion in composite media is studied for finite systems under transient conditions. The process of diffusion is modeled numerically and effective diffusion coefficient in the transient state is estimated, which, under certain conditions, is different from the predictions of the Kalnin-Kotomin's model. An analytical model is proposed to explain deviations of the transient effective coefficient of diffusion from the stationary case. PMID:23968111

Tabor, Zbis?aw; Nowak, Pawe?; Krzak, Ma?gorzata; Warszy?ski, Piotr

2013-08-21

7

Microwave enhanced diffusion  

SciTech Connect

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

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

1991-01-01

8

Damage calibration concept and novel B cluster reaction model for B transient enhanced diffusion over thermal process range from 600°C (839 h) to 1100°C (5 s) with various ion implantation doses and energies  

Microsoft Academic Search

We propose to use a fixed damage factor combined with an effective dose to generate an initial interstitial silicon concentration profile at a given B ion implantation conditions and demonstrate that this methodology can readily explain transient enhanced diffusion (TED) in almost all relevant cases of practical VLSI processing. We also developed a B cluster reaction model which enables us

K. Suzuki; T. Miyashita; Y. Tada; A. Hoefler; N. Strecker; W. Fichtner

1997-01-01

9

Transient moisture diffusion through paperboard materials  

Microsoft Academic Search

The performance of many products such as those made of containerboard or other paperboards is sensitive to moisture. Transient moisture profiles result in heterogeneities in mechanical properties and can often lead to catastrophic failure. Viewed as a composite porous medium the system comprises hygroscopic fibers and void spaces both of which are continuous. Furthermore, both phases conduct moisture by diffusion

A Bandyopadhyay; B. V Ramarao; Shri Ramaswamy

2002-01-01

10

CHEMISTRY IN DIFFUSE CLOUDS WITH TRANSIENT MICROSTRUCTURE  

SciTech Connect

Microstructure is observed on many lines of sight in the diffuse interstellar medium, mainly through variations in atomic line absorptions on timescales of a decade or less. This timescale implies that microstructure exists on a size scale comparable with that of the solar system; it is overpressured and transient. Both observations and theory confirm that a specific chemistry occurs in microstructure. We therefore explore a model of diffuse interstellar gas in which the chemistry in diffuse clouds is supplemented by chemistry in many transient and tiny perturbations. These perturbations are here assumed to be of unidentified origin, but it is assumed that ambipolar diffusion occurs within them. For plausible physical parameters, we find that this model can account for the range of molecular column densities observed in diffuse clouds, including species not usually accounted for by conventional models. Some molecular ions, predicted to be generated in the microstructure (including HS{sup +}, CH{sup +} {sub 2}, CH{sup +} {sub 3}, H{sub 2}O{sup +}, and H{sub 3}O{sup +}) but not yet observed in diffuse clouds, should be present at levels that may allow their detection.

Cecchi-Pestellini, C.; Casu, S. [INAF-Osservatorio Astronomico di Cagliari, Strada n.54, Loc. Poggio dei Pini, I-09012 Capoterra (Italy); Williams, D. A.; Viti, S. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)

2009-12-01

11

Nonlocal diffusivity: Impact on transient transport studies  

SciTech Connect

Nonlocal effects are observed in a number of transient transport studies in tokamaks and stellarators. In this paper some consequences of nonlocality are discussed on the basis of a heuristic model for the electron heat diffusivity ({chi}{sub {ital e}}). The main consequence is the presence of an additional (``missing``) heating power term ({ital {tilde p}}{sub {chi}}) in the heat transport equation. Suitable combinations of {ital {tilde p}}{sub {chi}} and modulated power profiles should give rise to detectable effects in modulated heating experiments such as those planned on the Frascati Tokamak Upgrade (FTU) [R. Andreani {ital et} {ital al}., in {ital Fusion} {ital Technology}, Proceedings of the 16th Symposium, London, 1990, edited by B. E. Keen, M. Huguet, and R. Hemsworth (Elsevier Science, Amsterdam, 1991), Vol. 1, p. 218]. Failure to properly include {ital {tilde p}}{sub {chi}} effects (if present) can lead to an overestimate of {chi}{sub {ital e}} from heat wave propagation analysis. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Jacchia, A.; Mantica, P. [Istituto di Fisica del Plasma, Associazione EURATOM-ENEA-CNR, I-20133 Milano (Italy); De Luca, F.; Galli, P.; Gorini, G. [Dipartimento di Fisica, Universita degli Studi di Milano, I-20133 Milano (Italy)

1995-12-01

12

ICTS of MOS Interface States Enhanced by Gold Diffusion  

Microsoft Academic Search

An enhancement of interface states of Si MOS diode by gold diffusion is observed by the isothermal capacitance transient spectroscopy (ICTS) measurement. The observed ICTS spectra are identified as the interface states with the help of numerical simulation. Although the gold diffusion is accompanied by thermal annealing, the effect of the thermal annealing on the interface states is eliminated with

Haruhiko Yoshida; Hirohiko Niu; Seigô Kishino

1991-01-01

13

TACS enhancements for the electromagnetic transient program  

SciTech Connect

Transient Analysis of Control Systems (TACS) of the Electromagnetic Transient Program (EMTP) has been enhanced in many ways. There are major changes in methods of ordering components to minimize the introduction of time step and history term errors. Initialization algorithms have been greatly enhanced to allow multiple frequency initialization. An IF THEN ELSE'' control structure and the use of user written FORTRAN routines are among the important new features available to users of TACS.

Lasseter, R.H.; Zhou, J. (Univ. of Wisconsin, Madison, WI (United States))

1994-05-01

14

Analytical solutions for transient diffusion problems in infinite media  

Microsoft Academic Search

In this paper, analytical solutions for transient diffusion problems in one-dimensional, two-dimensional and three-dimensional infinite\\/semi-infinite media with the locally prescribed field variable have been derived. Since the locally prescribed field variable forms the boundary condition of the diffusion problem, its distribution is considered to be either linear or quadratic in a local area of the problem domain so that it

Chongbin Zhao; G. P. Steven

1996-01-01

15

Thermal Diffusivity Measurements in Edible Oils using Transient Thermal Lens  

NASA Astrophysics Data System (ADS)

Time resolved thermal lens (TL) spectrometry is applied to the study of the thermal diffusivity of edible oils such as olive, and refined and thermally treated avocado oils. A two laser mismatched-mode experimental configuration was used, with a He Ne laser as a probe beam and an Ar+ laser as the excitation one. The characteristic time constant of the transient thermal lens was obtained by fitting the experimental data to the theoretical expression for a transient thermal lens. The results showed that virgin olive oil has a higher thermal diffusivity than for refined and thermally treated avocado oils. This measured thermal property may contribute to a better understanding of the quality of edible oils, which is very important in the food industry. The thermal diffusivity results for virgin olive oil, obtained from this technique, agree with those reported in the literature.

Valdez, R. Carbajal.; Pérez, J. L. Jiménez.; Cruz-Orea, A.; Martín-Martínez, E. San.

2006-11-01

16

Pore-scale modeling of transient and steady-state vapor diffusion in partially-saturated porous media  

SciTech Connect

Vapor diffusion in porous media in the presence of its own liquid may be enhanced due to pore-scale processes, such as condensation and evaporation across isolated liquid islands. Webb and Ho (1997) developed a mechanistic pore-scale model of these processes under steady-state conditions in which condensation and evaporation on the liquid island were equal. The vapor diffusion rate was significantly enhanced by these liquid island processes by up to an order of magnitude compared to a dry porous media. However, vapor transport by diffusion is often complicated by transient effects, such as in drying applications, in which net evaporation of liquid may further augment the vapor flux from diffusion. The influence of transient effects on the enhancement factors for vapor diffusion is evaluated in this paper. In addition, the effect of vapor pressure lowering on the enhancement factor and on porescale vapor fluxes is shown.

Webb, S.W.

1998-05-01

17

Comparison of radon diffusion coefficients measured by transient-diffusion and steady-state laboratory methods  

SciTech Connect

A method was developed and used to determine radon diffusion coefficients in compacted soils by transient-diffusion measurements. A relative standard deviation of 12% was observed in repeated measurements with a dry soil by the transient-diffusion method, and a 40% uncertainty was determined for moistures exceeding 50% of saturation. Excellent agreement was also obtained between values of the diffusion coefficient for radon in air, as measured by the transient-diffusion method, and those in the published literature. Good agreement was also obtained with diffusion coefficients measured by a steady-state method on the same soils. The agreement was best at low moistures, averaging less than ten percent difference, but differences of up to a factor of two were observed at high moistures. The comparison of the transient-diffusion and steady-state methods at low moistures provides an excellent verification of the theoretical validity and technical accuracy of these approaches, which are based on completely independent experimental conditions, measurement methods and mathematical interpretations.

Kalwarf, D.R.; Nielson, K.K.; Rich, D.C.; Rogers, V.C.

1982-11-01

18

Transient behavior of diffusion-induced creep and creep rupture  

Microsoft Academic Search

Steady state solutions to three types of diffusion problems: creep, grain boundary sliding and intergranular crack growth,\\u000a have been published in the literature. This paper considers, in detail, the events which occur between the time when the external\\u000a stress is applied and the time when the steady state is eventually reached. The time constant of the transient has been calculated.

Rishi Raj

1975-01-01

19

Enhancing rotational diffusion using oscillatory shear.  

PubMed

Taylor dispersion--shear-induced enhancement of translational diffusion--is an important phenomenon with applications ranging from pharmacology to geology. Through experiments and simulations, we show that rotational diffusion is also enhanced for anisotropic particles in oscillatory shear. This enhancement arises from variations in the particle's rotation (Jeffery orbit) and depends on the strain amplitude, rate, and particle aspect ratio in a manner that is distinct from the translational diffusion. This separate tunability of translational and rotational diffusion opens the door to new techniques for controlling positions and orientations of suspended anisotropic colloids. PMID:23767752

Leahy, Brian D; Cheng, Xiang; Ong, Desmond C; Liddell-Watson, Chekesha; Cohen, Itai

2013-05-29

20

Transient Hydrothermal Stresses in Composites: Coupling of Moisture and Heat with Temperature Varying Diffusivity.  

National Technical Information Service (NTIS)

The influence of coupled diffusion of heat and moisture on the transient stresses in a composite is investigated analytically where the moisture diffusion coefficient is taken to be temperature dependent while the thermal diffusion coefficient is kept con...

G. C. Sih M. T. Shih

1979-01-01

21

Diffusion modeling of ion implanted boron in Si during RTA: Correlation of extended defect formation and annealing with the enhanced diffusion of boron. [Rapid Thermal Annealing  

SciTech Connect

Accurate modeling of the enhanced diffusion of boron during rapid thermal annealing has been accomplished by incorporating the effects of extended defect formation and annealing on enhanced diffusion into a multizone, semiempirical model. The multizone model divides the implant profile into three zones defining regions of different defects and diffusion enhancements. The model also contains the initial enhanced diffusion and the transient diffusion effects associated with the dissolution of defect clusters and the annealing of extended defects, respectively. The saturation time for transient-enhanced diffusion contains an exponential function of implant dose in order to model the increase in point defect generated with higher implant dose. As a result, the model accurately simulates the boron diffusion profile over a wide range of implant doses and also shows the immobile boron peak of precipitated dopants produced during high dose implantation.

Kinoshita, H.; Lo, G.Q.; Kwong, D.L. (Univ. of Texas, Austin (United States)); Novak, S. (Evans East, Inc., Plainsboro, NJ (United States))

1993-01-01

22

AMBIPOLAR DIFFUSION IN ACTION: TRANSIENT C SHOCK STRUCTURE AND PRESTELLAR CORE FORMATION  

SciTech Connect

We analyze the properties of steady and time-dependent C shocks under conditions prevailing in giant molecular clouds. For steady C shocks, we show that ionization equilibrium holds and uses numerical integration to obtain a fitting formula for the shock thickness mediated by ambipolar diffusion, L{sub shock}{proportional_to}n{sub 0}{sup -3/4} v{sub 0}{sup 1/2} B{sub 0}{sup 1/2}{chi}{sub i0}{sup -1}. Our formula also agrees with an analytic estimate based on ion-neutral momentum exchange. Using time-dependent numerical simulations, we show that C shocks have a transient stage when the neutrals are compressed much more strongly than the magnetic field. The transient stage has a duration set by the neutral-ion collision time, t{sub AD} {approx} L{sub shock}/v{sub drift} {approx} 0.1-1 Myr. This transient creates a strong enhancement in the mass-to-magnetic flux ratio. Under favorable conditions, supercritical prestellar cores may form and collapse promptly as a result of magnetic flux loss during the transient stage of C shocks.

Chen Cheyu; Ostriker, Eve C., E-mail: cychen@astro.umd.edu, E-mail: ostriker@astro.umd.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

2012-01-10

23

GUI enhances electromagnetic transients simulation tools  

SciTech Connect

For more than two decades, power systems engineers have been using electromagnetic transients simulation programs (generically designated herein as emtp) for planning, designing, and operating power systems. While several of these programs are already known for their technical competence, their user interfaces are severely lacking compared to the advanced interfaces used in other fields. Although user-friendliness is the most apparent advantage of a graphical user interface (GUI), there are other benefits of a more essential nature. Currently, some graphical user interfaces are available, but many are still in infant stages of development and are not viable for commercial studies. This article describes a revolutionary graphical user interface, PSCAD[trademark]. The description of this GUI includes a discussion of the capabilities, scope, and reliability of the simulation program it was designed for. The simulation results obtained using a GUI are only as good as and limited by the simulation program it uses. At present, the interface fully support two electromagnetic transients simulation tools: EMTDC[trademark], a general-purpose, high-performance emtp (EMTDC is described briefly in this article); RTDS[trademark], a general purpose, real-time electromagnetic-transients digital simulator.

Nayak, O.; Irwin, G.; Neufeld, A. (Manitoba HVDC Research Centre, Winnipeg, Manitoba (Canada))

1995-01-01

24

New insight into transient contrast enhancement on computed tomography after endovascular treatment of stroke.  

PubMed

Transient contrast enhancement on computed tomography following endovascular treatment of stroke is a recognized entity that has been previously reported. Technological advances in brain imaging now have the potential to explore and refine its proposed etiology. We describe three patients in whom the location of contrast enhancement correlates with decreased cerebral blood volume on pre-therapeutic CT perfusion studies and with restricted diffusion on MRI. In this regard, contrast enhancement demarcated areas of completed cerebral infarction. The diagnostic and etiological implications are discussed. PMID:22958769

Antonucci, M U; Mocco, J; Bennett, J A

2012-09-10

25

Enhancing photocurrent transient spectroscopy by electromagnetic modeling  

NASA Astrophysics Data System (ADS)

The shape and duration of photocurrent transients generated by a photoconductive switch depend on both the intrinsic response of the active material and the geometry of the transmission line structure. The present electromagnetic model decouples both shape forming contributions. In contrast to previously published work, it accounts for the particular operating mode of transient spectroscopy. The objective is to increase the time resolution by two approaches, by optimizing structural response and by deconvolving it from experimental data. The switch structure is represented by an effective transimpedance onto which the active material acts as current generator. As proof of concept, the response of a standard microstrip switch is modeled and deconvolved from experimental data acquired in GaAs, yielding a single exponential material response and hence supporting the validity of the approach. Beyond compensating for the response deterioration by the structure, switch architectures can be a priori optimized with respect to frequency response. As an example, it is shown that a microstrip gap that can be deposited on materials incompatible with standard lithography reduces pulse broadening by an order of magnitude if it is provided with transitions to coplanar access lines.

Diesinger, H.; Panahandeh-Fard, M.; Wang, Z.; Baillargeat, D.; Soci, C.

2012-05-01

26

Assessing one-dimensional diffusion in nanoporous materials from transient concentration profiles  

Microsoft Academic Search

The use of interference microscopy has enabled the direct observation of transient concentration profiles generated by intracrystalline transport diffusion in nanoporous materials. The thus accessible intracrystalline concentration profiles contain a wealth of information which cannot be deduced by any macroscopic method. In this paper, we illustrate five different ways for determining the concentration-dependent diffusivity in one-dimensional systems and two for

Lars Heinke; Jörg Kärger

2008-01-01

27

Thermal diffusivity measurement by the transient hot-wire technique: A reappraisal  

Microsoft Academic Search

The theory of the transient hot-wire technique for thermal conductivity measurements is reassessed in the special context of thermal diffusivity measurements. A careful examination of the working equation and an error analysis are employed to identify the principal sources of error. Notwithstanding earlier claims to the contrary, the best precision that can be attained in thermal diffusivity measurements is of

C. A. Nieto de Castro; B. Taxis; H. M. Roder; W. A. Wakeham

1988-01-01

28

Anisotropic enhanced backscattering induced by anisotropic diffusion.  

PubMed

The enhanced backscattering cone displaying a strong anisotropy from a material with anisotropic diffusion is reported. The constructive interference of the wave is preserved in the helicity preserving polarization channel and completely lost in the nonpreserving one. The internal reflectivity at the interface modifies the width of the backscatter cone. The reflectivity coefficient is measured by angular-resolved transmission. This interface property is found to be isotropic, simplifying the backscatter cone analysis. The material used is a macroporous semiconductor, gallium phosphide, in which pores are etched in a disordered position but with a preferential direction. PMID:15524650

Bret, B P J; Lagendijk, A

2004-09-03

29

Evaluation of the Effect of Gravity Force on Transient Mass Diffusion Fields  

NASA Astrophysics Data System (ADS)

In this study, the relationship between gravitational force and diffusion phenomena in aque-ous solutions is discussed. The microgravity environment gives a high quality crystal growth condition which produces high quality medicines or foods. In this condition, a natural con-vection can be neglected and diffusion phenomenon without convection is observed. The mass diffusion coefficient is one of the most important thermophysical properties to investigate that mass transport system. However, the available experimental data of mass diffusion coefficients in microgravity conditions is not enough. Because it is quite a few opportunity that exper-iments can be conducted using facilities which produce microgravity environment for a long time. Then we have developed an observation system of small transient diffusion fields within 20 seconds. The experimental apparatus is composed of phase shifting interferometer, special designed signal processing unit and recorder. The mechanism of test cell used in this study has a unique performance that the transient diffusion fields can be produced continuously with no change of solutions and cell. Therefore this system can be applied to short-time microgravity experiment which is generated by the parabolic flight of an airplane. By using this system, the transient diffusion field of Sodium Chloride (NaCl) solution in microgravity conditions could be clearly observed and the mass diffusion coefficient was estimated from the obtained data. In microgravity condition, the transient diffusion fields have different appearances from the normal gravity condition. A slight acceleration governs the transient diffusion fields because of no density difference, so vibrations applied the apparatus disturb the transient diffusion fields. The measured mass diffusion coefficient has been estimated as a smaller value compared with ones under normal gravity condition. Using the airplane as a facility, not only microgravity condition but also 0.8G, 1.5G or varied gravity level conditions can be generated during flight experiments. On the sudden change of gravity level from microgravity to 1.5G, different ap-pearances in the transient diffusion fields could be observed. The mass diffusion coefficient depends on measurement time. From this phenomenon, it is possible to guess that the dynamic re-clustering process may occur in the solutions.

Komiya, Atsuki; Maruyama, Shigenao

30

Research on Transient Liquid Phase Diffusion Bonding of Steel Sandwich Panels Under Small Plastic Deformation  

Microsoft Academic Search

Plastic deformation was newly introduced in transient liquid phase (TLP) diffusion bonding of steel sandwich panels. The effect\\u000a of plastic deformation on bonding strength was investigated through lab experiments. It was assumed that three factors, including\\u000a newly generated metal surface area, deformation heat, and lattice distortion, contribute to the acceleration of interface\\u000a atoms diffusion and increase of diffusion coefficients. A

H. Li; Z. X. Li

2008-01-01

31

Fracture-Flow-Enhanced Solute Diffusion into Fractured Rock  

SciTech Connect

We propose a new conceptual model of fracture-flow-enhanced matrix diffusion, which correlates with fracture-flow velocity, i.e., matrix diffusion enhancement induced by rapid fluid flow within fractures. According to the boundary-layer or film theory, fracture flow enhanced matrix diffusion may dominate mass-transfer processes at fracture-matrix interfaces, because rapid flow along fractures results in large velocity and concentration gradients at and near fracture-matrix interfaces, enhancing matrix diffusion at matrix surfaces. In this paper, we present a new formulation of the conceptual model for enhanced fracture-matrix diffusion, and its implementation is discussed using existing analytical solutions and numerical models. In addition, we use the enhanced matrix diffusion concept to analyze laboratory experimental results from nonreactive and reactive tracer breakthrough tests, in an effort to validate the new conceptual model.

Wu, Yu-Shu; Ye, Ming; Sudicky, E.A.

2007-12-15

32

Boron-enhanced-diffusion of boron: The limiting factor for ultra-shallow junctions  

SciTech Connect

Reducing implant energy is an effective way to eliminate transient enhanced diffusion (TED) due to excess interstitials from the implant. It is shown that TED from a fixed Si dose implanted at energies from 0.5 to 20 keV into boron doping-superlattices decreases linearly with decreasing Si ion range, virtually disappearing at sub-keV energies. However, for sub-keV B implants diffusion remains enhanced and x{sub j} is limited to {ge} 100 nm at 1,050 C. The authors term this enhancement, which arises in the presence of B atomic concentrations at the surface of {approx} 6%, Boron-Enhanced-Diffusion (BED).

Agarwal, A. [Lucent Technologies, Murray Hill, NJ (United States). Bell Labs.]|[Oak Ridge National Lab., TN (United States). Solid State Div.; Eaglesham, D.J.; Gossmann, H.J.; Pelaz, L.; Herner, S.B.; Jacobson, D.C. [Lucent Technologies, Murray Hill, NJ (United States). Bell Labs.; Haynes, T.E. [Oak Ridge National Lab., TN (United States); Erokhin, Y.; Simonton, R. [Eaton Corp., Beverly, MA (United States). Semiconductor Equipment Operations

1997-12-01

33

Transient model of an intermediate surge system for the Paducah Gaseous Diffusion Plant  

SciTech Connect

Engineering design work (Reference 1) is underway for intermediate surge systems to be added to the Paducah Gaseous Diffusion Plant (PGDP) cascade as part of the Process Inventory Control System (PICS) project. These systems would be located between 000 buildings and lower half 00 buildings and would remove or add inventory during cascade transients in order to protect cascade compressors from overload and surge. Similar systems were operated in the Oak Ridge Gaseous Diffusion Plant cascade and are operated in the Portsmouth Gaseous Diffusion Plant cascade. A steady state flow analysis of the system to be installed at the PGDP has been made. The flow analysis did not address response of the surge system to the cascade transients, nor did it address automatic control of the system. The need to address these issues prompted development of the transient model described in this report. 2 refs., 8 figs., 2 tabs.

Beard, B.; Blankenship, J.G.; McGrady, P.W.

1989-09-01

34

Transient Localized Patterns in Noise-Driven Reaction-Diffusion Systems  

PubMed Central

Noise can induce excitable systems to make transient transitions between quiescent and active states. Here we investigate the possibility that these transitions occur locally in a spatially-extended medium, leading to the occurrence of spatiotemporal patches of activation. We show that this can in fact occur in a parameter range such that there exist (in general unstable) localized solutions of the governing deterministic reaction-diffusion equations. Our work is motivated by a recent biological example showing transiently excited cell membrane regions.

Hecht, Inbal; Kessler, David A.; Levine, Herbert

2010-01-01

35

Induced nuclear fission viewed as a diffusion process: Transients  

Microsoft Academic Search

Induced nuclear fission is viewed as a diffusion process of the fission degree of freedom over the fission barrier. We describe this process in terms of a Fokker-Planck equation which contains the fission variable and its canonically conjugate momentum. We solve this equation numerically for several energies (temperatures) of the fissioning nucleus neglecting changes of the fission barrier due to

P. Grangé; Li Jun-Qing; H. A. Weidenmueller

1983-01-01

36

Picomolar Amyloid-? Peptides Enhance Spontaneous Astrocyte Calcium Transients.  

PubMed

Amyloid-? (A?) peptides are constitutively produced in the brain throughout life via mechanisms that can be regulated by synaptic activity. Although A? has been extensively studied as the pathological plaque-forming protein species in Alzheimer's disease (AD), little is known about the normal physiological function(s) and signaling pathway(s). We previously discovered that physiologically-relevant, low picomolar amounts of A? can enhance synaptic plasticity and hippocampal-dependent cognition in mice. In this study, we demonstrated that astrocytes are cellular candidates for participating in this type of A? signaling. Using calcium imaging of primary astrocyte cultures, we observed that picomolar amounts of A? peptides can enhance spontaneous intracellular calcium transient signaling. After application of 200 pM A?42 peptides, the frequency and amplitude averages of spontaneous cytosolic calcium transients were significantly increased. These effects were dependent on ?7 nicotinic acetylcholine receptors (?7-nAChRs), as the enhancement effects were blocked by a pharmacological ?7-nAChR inhibitor and in astrocytes from an ?7 deficient mouse strain. We additionally examined evoked intercellular calcium wave signaling but did not detect significant picomolar A?-induced alterations in propagation parameters. Overall, these results indicate that at a physiologically-relevant low picomolar concentration, A? peptides can enhance spontaneous astrocyte calcium transient signaling via ?7-nAChRs. Since astrocyte-mediated gliotransmission has been previously found to have neuromodulatory roles, A? peptides may have a normal physiological function in regulating neuron-glia signaling. Dysfunction of this signaling process may underlie glia-based aspects of AD pathogenesis. PMID:23948929

Lee, Linda; Kosuri, Pallav; Arancio, Ottavio

2014-01-01

37

Transient couple heat transfer in an absorbing rectangular medium with one semitransparent diffuse boundary  

NASA Astrophysics Data System (ADS)

This paper studies 2-D transient coupled radiative and conductive heat transfer in an absorbing non-scattering rectangular medium. The medium have one diffuse semitransparent boundary, and the other three boundaries are black. The reflectivity of the diffuse semitransparent boundary is determined by integrating the reflected energy over the whole hemispherical space according to the Fresnel’s reflective law and Snell’s refractive law based on assuming each bit of the rough surface to be optically smooth.

Luo, Jian-Feng; Yi, Hong-Liang; Tan, He-Ping

2010-10-01

38

Stratification of heterogeneous diffusion MRI ischemic lesion with kurtosis imaging - Evaluation of mean diffusion and kurtosis MRI mismatch in an animal model of transient focal ischemia  

PubMed Central

Background and Purpose Ischemic tissue damage is heterogeneous, resulting in complex patterns in the widely used diffusion-weighted MRI (DWI). Our study examined the spatiotemporal characteristics of diffusion kurtosis imaging (DKI) in an animal model of transient middle cerebral artery occlusion (MCAO). Methods Adult male Wistar rats (N = 18) were subjected to 90min MCAO. Multi-parametric MRI were obtained during MCAO and 20 min after reperfusion, with DWI obtained using eight b-values from 250 to 3000 s/mm2 in six diffusion gradient directions. Diffusion and kurtosis lesions were outlined in shuffled images by two investigators independently. T2 MRI was obtained 24 hr after MCAO to evaluate stroke outcome. Results Mean diffusion (MD) lesion (23.5±8.1%, percentage of the brain slice) was significantly larger than mean kurtosis (MK) lesion (13.2±2.0%) during MCAO. MD lesion decreased significantly after reperfusion (13.8±4.3%) while MK lesion showed little change (13.0±2.5%), with their lesion size difference being insignificant. Conclusions We demonstrated that MD/MK mismatch recovered reasonably well upon reperfusion while regions with concurrent MD and MK deficits showed poor recovery. DKI may help stratify heterogeneous DWI lesion for enhanced characterization of ischemic tissue injury.

Cheung, Jerry S.; Wang, Enfeng; Lo, Eng H; Sun, Phillip Zhe

2012-01-01

39

Numerical studies on transient double-diffusive and mixed convection in cylindrical enclosures  

Microsoft Academic Search

Numerical studies on transient convection phenomena are introduced. The studies are related to computation and description of time dependent flow, temperature and concentration fields. Two topics related with convection phenomena in cylindrical enclosures are presented, the first being double diffusive natural convection in cylindrical vessels. The subject of research is concerned with the liquid-liquid interface stability and its relationship with

Jose Raul Rujano Maldonado

1999-01-01

40

Exciton diffusion in semiconducting single-wall carbon nanotubes studied by transient absorption microscopy  

NASA Astrophysics Data System (ADS)

We report a spatially resolved transient absorption study of exciton diffusion in a thin films of isolated semiconducting single-wall carbon nanotubes. Spatiotemporal dynamics of excitons injected by a tightly focused pump pulse are studied by measuring differential reflection and differential transmission of a time-delayed and spatially scanned probe pulse. We observe a bi-exponentially decaying signal with a fast time constant of 0.66 ps and a slower time constant of 2.8 ps. Both constants are independent of the pump fluence. The squared width of the exciton density profile increases linearly with time, as expected for a diffusion process. We measured a diffusion coefficient of 200 ± 10 cm^2/s at room temperature, which is independent of the pump fluence. We additionally investigated the diffusion coefficient at temperatures of 10 and 150 K and found diffusion coefficients of approximately 300 ± 10 cm^2/s at both.

Ruzicka, Brian; Wang, Rui; Lohrman, Jessica; Ren, Shenqiang; Zhao, Hui

2013-03-01

41

Enhancing phosphorylation cascades by anomalous diffusion  

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

42

Enhancement of Ambipolar Diffusion Rates through Field Fluctuations  

NASA Astrophysics Data System (ADS)

Previous treatments of ambipolar diffusion in star-forming molecular clouds do not consider the effects of fluctuations in the fluid fields about their mean values. This work generalizes the ambipolar diffusion problem in molecular cloud layers to include such fluctuations. Because magnetic diffusion is a nonlinear process, fluctuations can lead to an enhancement of the ambipolar diffusion rate. In addition, the stochastic nature of the process makes the ambipolar diffusion time take on a distribution of different values. In this poster, we focus on the case of long wavelength fluctuations and find that the rate of ambipolar diffusion increases by a significant factor ? ~ 1 - 10. The corresponding decrease in the magnetic diffusion time helps make ambipolar diffusion more consistent with observations.

Fatuzzo, M.; Adams, F. C.

2002-05-01

43

Enhancement of Ambipolar Diffusion Rates through Field Fluctuations  

NASA Astrophysics Data System (ADS)

Previous treatments of ambipolar diffusion in star-forming molecular clouds do not consider the effects of fluctuations in the fluid fields about their mean values. This paper generalizes the ambipolar diffusion problem in molecular cloud layers to include such fluctuations. Because magnetic diffusion is a nonlinear process, fluctuations can lead to an enhancement of the ambipolar diffusion rate. In addition, the stochastic nature of the process makes the ambipolar diffusion time take on a distribution of different values. In this paper, we focus on the case of long-wavelength fluctuations and find that the rate of ambipolar diffusion increases by a significant factor ?~1-10. The corresponding decrease in the magnetic diffusion time helps make ambipolar diffusion more consistent with observations.

Fatuzzo, Marco; Adams, Fred C.

2002-05-01

44

Benchmarking report for WIGGLE: A one-dimensional transient diffusion theory code  

SciTech Connect

WIGGLE is a static/transient one-dimensional diffusion theory calculation written to estimate the axial power profile while safety rods are falling during a scram. The code is used in the LOCA Limits Analysis Package (LLAP), a part of the SRS system for calculating thermal-hydraulic limits. Since WIGGLE was designed to be implemented through LLAP and not as a stand-alone code, it consists entirely of subroutines; the problem data must be passed to it from a driver routine. This project concerned the verification of WIGGLE, which limited it to the determination that WIGGLE is correctly implementing the transient 1D diffusion equation. The approach was to compare the results of the code with three analytic solutions: a static homogeneous calculation of the pre-accident power profile (without end-fittings); a static heterogeneous calculation of the pre-accident power profile (includes end-fittings); and a transient calculation designed to test the time-dependent calculational ability. The results of all three calculations were essentially identical to the analytical solutions, thus giving us confidence that WIGGLE is correctly solving the one-dimensional time-dependent diffusion equation.

Pevey, R.E.

1990-11-01

45

Carrier-diffusion measurements in silicon with a Fourier-transient-grating method  

NASA Astrophysics Data System (ADS)

Carrier-diffusion measurements in silicon using a newly developed Fourier-transient-grating technique is presented. The method uses a laser light pulse projected through a semitransparent grid pattern to excite a sinusoidal excess carrier grating within the sample. The interdiffusion of carriers is monitored by free-carrier absorption of a focused infrared probe beam. The grating is scanned across the probe beam and the spatial Fourier transform is calculated at each sampling time following the excitation pulse. The resulting Fourier spectrum shows a peak for a frequency corresponding to the grating period and the decay of the amplitude of this spatial-frequency component represents a characteristic grating erasure time, which is related to the carrier diffusivity. This Fourier-transient-grating method allows sensitive measurements of the carrier diffusivity over a broad range of injection levels, both in the minority carrier regime as well as for high-injection conditions including the transition between the two regimes. Here, measurement data are presented for silicon samples of various doping concentration and types for excess carrier injections in the range ~1012-1017 cm-3. At low densities of injected carriers, our measurement data are in agreement with generally accepted low-injection lattice-scattering mobility values showing the transition to the high-injection range according to ambipolar theory. However, at excess carrier concentrations exceeding 1015 cm-3, the diffusion coefficient is clearly reduced with respect to the ambipolar diffusivity (using constant electron and hole diffusivities) due to carrier-carrier scattering effects. This reduction is stronger above an injected carrier density of 1016 cm-3 than that predicted by many-body quantum theory [J. F. Young and H. M. van Driel, Phys. Rev. B 26, 2147 (1982)]. The diffusivity data, converted to mobilities using Einstein's relation, have also been compared to recent semiempiric drift-mobility models used for semiconductor device simulation.

Linnros, Jan; Grivickas, Vytautas

1994-12-01

46

Transients.  

National Technical Information Service (NTIS)

The lecture includes typical transients to be analyzed, the requirements put on computer codes and a description of the computer codes as well as results obtained with these codes. Transients analysis is necessary within the licensing of reactors, in risk...

W. Frisch

1980-01-01

47

{l_brace}311{r_brace} Defects in ion-implanted silicon: The cause of transient diffusion, and a mechanism for dislocation formation  

SciTech Connect

Ion implantation is used at several critical stages of Si integrated circuit manufacturing. The authors show how {l_brace}311{r_brace} defects arising after implantation are responsible for both enhanced dopant diffusion during annealing, and stable dislocations post-anneal. They observe {l_brace}311{r_brace} defects in the earliest stages of an anneal. They subsequently undergo rapid Ostwald ripening and evaporation. At low implant doses evaporation dominates, and they can quantitatively relate the interstitials emitted from these defects to the transient enhancement in diffusivity of dopants such as B and P. At higher doses Ostwald ripening is significant, and they observe the defects to undergo a series of unfaulting reactions to form both Frank loops and perfect dislocations. They demonstrate the ability to control both diffusion and dislocations by the addition of small amounts of carbon impurities.

Eaglesham, D.J.; Stolk, P.A.; Cheng, J.Y.; Gossmann, H.J.; Poate, J.M. [AT and T Bell Labs., Murray Hill, NJ (United States); Haynes, T.E. [Oak Ridge National Lab., TN (United States). Solid State Div.

1995-04-01

48

Dynamics of surface thermal expansion and diffusivity using two-color reflection transient gratings  

SciTech Connect

We report ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(100) samples at several temperatures. Using a 75 fs ultraviolet probe with visible excitation beams, the electronic effects that dominate single color experiments become negligible; thus surface expansion due to heating and the subsequent contraction caused by cooling provide the dominant influence on the diffracted probe. The diffracted signal was composed of two components, thermal expansion of the surface and heat flow away from the surface, allowing the determination of the rate of expansion as well as the surface thermal diffusivity. At room temperature a signal rise due to thermal expansion was observed, corresponding to a maximum average displacement of {approx} 1 {angstrom} at 32 ps. Large fringe spacings were used, thus the dominant contributions to the signal were expansion and diffusion perpendicular to the surface. Values for the surface thermal diffusivity of GaAs were measured and found to be in reasonable agreement with bulk values above 50{degrees}K. Below 50{degrees}K, the diffusivity at the surface was more than an order of magnitude slower than in the bulk due to increased phonon boundary scattering. Comparison of the results with a straightforward thermal model yields good agreement over a range of temperatures (12--300{degrees}K). The applicability and advantages of the transient grating technique for studying photothermal and photoacoustic phenomena are discussed.

Pennington, D.M.; Harris, C.B. [California Univ., Berkeley, CA (United States). Dept. of Chemistry

1993-02-01

49

Modeling the reversible, diffusive sink effect in response to transient contaminant sources.  

PubMed

A physically based diffusion model is used to evaluate the sink effect of diffusion-controlled indoor materials and to predict the transient contaminant concentration in indoor air in response to several time-varying contaminant sources. For simplicity, it is assumed the predominant indoor material is a homogeneous slab, initially free of contaminant, and the air within the room is well mixed. The model enables transient volatile organic compound (VOC) concentrations to be predicted based on the material/air partition coefficient (K) and the material-phase diffusion coefficient (D) of the sink. Model predictions are made for three scenarios, each mimicking a realistic situation in a building. Styrene, phenol, and naphthalene are used as representative VOCs. A styrene butadiene rubber (SBR) backed carpet, vinyl flooring (VF), and a polyurethane foam (PUF) carpet cushion are considered as typical indoor sinks. In scenarios involving a sinusoidal VOC input and a double exponential decaying input, the model predicts the sink has a modest impact for SBR/styrene, but the effect increases for VF/phenol and PUF/naphthalene. In contrast, for an episodic chemical spill, SBR is predicted to reduce the peak styrene concentration considerably. A parametric study reveals for systems involving a large equilibrium constant (K), the kinetic constant (D) will govern the shape of the resulting gasphase concentration profile. On the other hand, for systems with a relaxed mass transfer resistance, K will dominate the profile. PMID:12244748

Zhao, D; Little, J C; Hodgson, A T

2002-09-01

50

Interstitial Air Pressure Dependence of Effective Thermal Conductivity and Diffusivity of Rajasthan Desert Sand Using Transient Hot-Strip Method  

Microsoft Academic Search

The transient hot strip (T H S) method used for the simultaneous measurement of effective thermal conductivity and diffusivity of loose granular two-phase materials at normal pressure and room temperature is now used for the measurement of effective thermal conductivity and diffusivity of Rajasthan Desert sand at different interstitial air pressure and room temperature. Experimental values of effective thermal conductivities

N. S. Saxena; M. A. Chohan; S. E. Gustafsson

1987-01-01

51

Hole diffusivity in GaAsBi alloys measured by a picosecond transient grating technique  

NASA Astrophysics Data System (ADS)

We applied a time-resolved transient grating technique for investigation of nonequilibrium carrier dynamics in GaAs1-xBix alloys with x=0.025-0.063. The observed decrease in carrier bipolar diffusivity with lowering temperature and its saturation below 80 K revealed a strong localization of nonequilibrium holes. Thermal activation energy ?Ea=46 meV of diffusivity and low hole mobility value ?h=10-20 cm2/V s at room temperature confirmed the hybridization model of the localized Bi states with the valence band of GaAs. Nonlinear increase in carrier recombination rate with the Bi content, 1/?R~Bi(x)3.2 indicated an increasing structural disorder in the alloy.

Nargelas, S.; Jarašiunas, K.; Bertulis, K.; Pa?ebutas, V.

2011-02-01

52

Transient cerebral hypoperfusion enhances intraarterial carmustine deposition into brain tissue  

Microsoft Academic Search

We hypothesized that bolus injections of lipid soluble chemotherapeutic drugs during transient cerebral hypoperfusion could\\u000a significantly boost regional drug delivery. In the first two groups of New Zealand White rabbits we measured brain tissue\\u000a carmustine concentrations after intravenous infusion, intraarterial infusion with normal perfusion, and after intraarterial\\u000a injections during transient cerebral hypoperfusion. In the third group of animals we assessed

Shailendra Joshi; Mei Wang; Joshua J. Etu; Raymond F. Suckow; Thomas B. Cooper; Steven J. Feinmark; Jeffrey N. Bruce; Robert L. Fine

2008-01-01

53

The initial transient period of gravitationally unstable diffusive boundary layers developing in porous media  

NASA Astrophysics Data System (ADS)

Gravitationally unstable, transient, diffusive boundary layers play an important role in carbon dioxide sequestration. Though the linear stability of these layers has been studied extensively, there is wide disagreement in the results, and it is not clear which methodology best reflects the physics of the instability. We demonstrate that this disagreement stems from an inherent sensitivity of the problem to how perturbation growth is measured. During an initial transient period, the concentration and velocity fields exhibit different growth rates and these rates depend on the norm used to measure perturbation amplitude. This sensitivity decreases at late times as perturbations converge to dominant quasi-steady eigenmodes. Therefore, we characterize the linear regime by measuring the duration of the initial transient period, and we interpret the convergence process by examining the growth rates and non-orthogonality of the quasi-steady eigenmodes. To judge the relevance of various methodologies and perturbation structures to physical systems, we demonstrate that every perturbation has a maximum allowable initial amplitude above which the sum of the base-state and perturbation produces unphysical negative concentrations. We then perform direct numerical simulations to demonstrate that optimal perturbations considered in previous studies cannot support finite initial amplitudes. Consequently, convection in physical systems is more likely triggered by ``sub-optimal'' perturbations that support finite initial amplitudes.

Tilton, Nils; Daniel, Don; Riaz, Amir

2013-09-01

54

Numerical studies on transient double-diffusive and mixed convection in cylindrical enclosures  

NASA Astrophysics Data System (ADS)

Numerical studies on transient convection phenomena are introduced. The studies are related to computation and description of time dependent flow, temperature and concentration fields. Two topics related with convection phenomena in cylindrical enclosures are presented, the first being double diffusive natural convection in cylindrical vessels. The subject of research is concerned with the liquid-liquid interface stability and its relationship with the different flow and mixing characteristics observed in the system. Interface penetration phenomena during transient double diffusive convection in a vertical cylinder is analyzed through direct numerical simulation. The fluid is initially motionless with a pre-existent two-layers density stratification featuring a diffusion-like interface. The flow is initiated when a uniform heat flux is applied from the sidewall. The influence of relevant parameters on velocity of interface penetration and intensity of mixing are analyzed. Two regimes of interface penetration were identified and characterized namely: convective and diffusive-convective regimes of interface penetration. The second topic is mixed natural and forced convection. In this case the investigation is focused on transient oscillatory convection and its suppression in the Czochralski growth melt. A numerical analysis assuming axisymmetric flow and temperature fields in a cylindrical enclosure was performed in which the swirl component of velocity is included in the computation to account for rotational effects. Temperature and flow field oscillations were computed for natural and forced convection dominant flow regimes. Numerical predictions are in excellent agreement with previously reported experimental results. Computational results are presented which disclose relevant features of oscillatory thermal and flow fields. Parametric studies were carried out to evaluate the effect of crystal radius and melt depth variations on the oscillatory flows. It was shown that non-oscillatory striation free conditions can be attained, for both natural convection dominant or forced convection dominant flow modes by reducing the radius fraction rc/Rc, and increasing the crucible aspect ratio Rc/H. The effect of a circular flat plate immersed in the melt was also evaluated for different vertical positions of the baffle. It was found that inserting a baffle with a radius slightly larger than the crystal radius at an appropriate vertical position can effectively attenuate thermal fluctuations.

Rujano Maldonado, Jose Raul

1999-10-01

55

Non-diffusive relaxation of a transient thermal grating analyzed with the Boltzmann transport equation  

NASA Astrophysics Data System (ADS)

The relaxation of an one-dimensional transient thermal grating (TTG) in a medium with phonon-mediated thermal transport is analyzed within the framework of the Boltzmann transport equation (BTE), with the goal of extracting phonon mean free path (MFP) information from TTG measurements of non-diffusive phonon transport. Both gray-medium (constant MFP) and spectrally dependent MFP models are considered. In the gray-medium approximation, an analytical solution is derived. For large TTG periods compared to the MFP, the model yields an exponential decay of grating amplitude with time in agreement with Fourier's heat diffusion equation, and at shorter periods, phonon transport transitions to the ballistic regime, with the decay becoming strongly non-exponential. Spectral solutions are obtained for Si and PbSe at 300 K using phonon dispersion and lifetime data from density functional theory calculations. The spectral decay behaviors are compared to several approximate models: a single MFP solution, a frequency-integrated gray-medium model, and a ``two-fluid'' BTE solution. We investigate the utility of using the approximate models for the reconstruction of phonon MFP distributions from non-diffusive TTG measurements.

Collins, Kimberlee C.; Maznev, Alexei A.; Tian, Zhiting; Esfarjani, Keivan; Nelson, Keith A.; Chen, Gang

2013-09-01

56

Enhancing the Sensitivity of HAWC to sub-Tev Transients  

NASA Astrophysics Data System (ADS)

The High Altitude Water Cherenkov (HAWC) Observatory, currently being built 4100 meters above sea level near Pico de Orizaba, Mexico, is well-suited for observing transient phenomena above 1 TeV due to its large field of view (2 sr) and high uptime (˜100%). However, sub-TeV transient events are also of physical interest due to the overlap in energy with satellite experiments such as the Fermi gamma-ray space telescope. This presents a challenge since the sub-TeV primary particles observed with HAWC tend to be difficult to distinguish from noise. To address this problem, we propose a method in which particle arrival directions are fit to triplets of triggered PMTs in a short sliding trigger window (100 ns). The resulting arrival directions are then summed in a coarsely binned significance map of the sky with a time window of one to several seconds. This algorithm is simple enough to be applied online, and can localize the positions of transient sources to within 8 degrees. We run the method over HAWC30 detector data to estimate the noise rate and use simulated events to calculate the sensitivity to transients.

Wisher, Ian

2013-04-01

57

Molecular diffusion and DNP enhancement in aqueous char suspensions.  

PubMed

The heterogeneous 1H dynamic nuclear polarization (DNP) effect is studied at low magnetic fields for a system consisting of several newly synthesized carbon chars suspended in water. By using Fourier Transform pulsed-field-gradient spin-echo NMR spectroscopy, several different self-diffusion coefficients have been observed in aqueous char suspensions, corresponding to regions of differing water mobility in the porous structure. Proton spin-lattice relaxation data generally confirm the results of molecular diffusion measurements. Through utilization of the Torrey model, the influence of "cage effects" on DNP enhancement in porous media is discussed. Results suggest that short-range nuclear-electronic interactions in pores have a dominant effect on DNP enhancement in char suspensions. PMID:9878471

Odintsov, B M; Belford, R L; Ceroke, P J; Idiyatullin, Z S; Kashaev, R S; Kuriashkin, I V; Rukhlov, V S; Temnikov, A N; Clarkson, R B

1998-12-01

58

Enhanced Diffusion Weighting Generated by Selective Adiabatic Pulse Trains  

PubMed Central

A theoretical description and experimental validation of the enhanced diffusion weighting generated by selective adiabatic full passage (AFP) pulse trains is provided. Six phantoms (Ph-1 to Ph-6) were studied on a 4T Varian/Siemens whole body MRI system. Phantoms consisted of 2.8 cm diameter plastic tubes containing a mixture of 10 ?m ORGASOL polymer beads and 2 mM Gd-DTPA dissolved in 5% agar (Ph-1) or nickel(II) ammonium sulphate hexahydrate doped (56.3 mM – 0.8 mM) water solutions (Ph-2 to Ph-6). A customized localization by adiabatic selective refocusing (LASER) sequence containing slice selective AFP pulse trains and pulsed diffusion gradients applied in the phase encoding direction was used to measure 1H2O diffusion. The b-value associated with the LASER sequence was derived using the Bloch-Torrey equation. The apparent diffusion coefficients measured by LASER were comparable to those measured by a conventional pulsed gradient spin-echo (PGSE) sequence for all phantoms. Image signal intensity increased in Ph-1 and decreased in Ph-2 – Ph-6 as AFP pulse train length increased while maintaining a constant echo-time. These experimental results suggest that such AFP pulse trains can enhance contrast between regions containing microscopic magnetic susceptibility variations and homogeneous regions in which dynamic dephasing relaxation mechanisms are dominant.

Sun, Ziqi; Bartha, Robert

2007-01-01

59

Enhanced photocoagulation with catheter-based diffusing optical device.  

PubMed

A novel balloon catheter-based diffusing optical device was designed and evaluated to assist in treating excessive menstrual bleeding. A synthetic fused-silica fiber was micro-machined precisely to create scattering segments on a 25 mm long fiber tip for uniform light distribution. A visible wavelength (?=532??nm) was used to specifically target the endometrium due to the high vascularity of the uterine wall. Optical simulation presented 30% wider distribution of photons along with approximately 40% higher irradiance induced by addition of a glass cap to the diffuser tip. Incorporation of the optical diffuser with a polyurethane balloon catheter considerably enhanced coagulation depth and area (i.e., 3.5 mm and 18.9??cm2 at 1 min irradiation) in tissue in vitro. The prototype device demonstrated the coagulation necrosis of 2.8±1.2??mm (n=18) and no thermal damage to myometrium in in vivo caprine models. A prototype 5 cm long balloon catheter-assisted optical diffuser was also evaluated with a cadaveric human uterus to confirm the coagulative response of the uterine tissue as well as to identify the further design improvement and clinical applicability. The proposed catheter-based diffusing optical device can be a feasible therapeutic tool to photocoagulate endometrial cell layers in an efficient and safe manner. PMID:23154817

Kang, Hyun Wook; Kim, Jeehyun; Oh, Jungwhan

2012-11-01

60

Temperature dependent normal and anomalous electron diffusion in porous Ti O2 studied by transient surface photovoltage  

NASA Astrophysics Data System (ADS)

A model system of nanoporous TiO2 sensitized with dye molecules at the outer surface is investigated by time resolved surface photovoltage (SPV) at temperatures between -120°C and 270°C to get information about electron diffusion over more than 10 orders of magnitude in time. The SPV transients increase in time due to independent electron diffusion and reach a maximum at a certain peak time due to reaching the screening length. The increasing parts of the SPV transients are characterized by a power law while the SPV power coefficient amounts to half of the dispersion parameter of anomalous diffusion. Anomalous diffusion is observed for times down to the duration time of the laser pulse (150ps) . With increasing temperature, the SPV power coefficient increases to its saturation value of 0.5 corresponding to normal diffusion. At lower temperatures, the SPV power coefficients decrease with increasing intensity of the exciting laser pulses. The decay of the SPV transients is determined by thermally activated normal diffusion. The minimal charge transfer time of an electron back to the positively charged dye molecule amounts to 2ps which is obtained from thermally activated logarithmic decays.

Dittrich, Thomas; Mora-Seró, Iván; García-Belmonte, Germà; Bisquert, Juan

2006-01-01

61

Enhancing the ABAQUS thermomechanics code to simulate multipellet steady and transient LWR fuel rod behavior  

Microsoft Academic Search

A powerful multidimensional fuels performance analysis capability, applicable to both steady and transient fuel behavior, is developed based on enhancements to the commercially available ABAQUS general-purpose thermomechanics code. Enhanced capabilities are described, including: UO2 temperature and burnup dependent thermal properties, solid and gaseous fission product swelling, fuel densification, fission gas release, cladding thermal and irradiation creep, cladding irradiation growth, gap

R. L. Williamson

2011-01-01

62

Enhancing the ABAQUS Thermomechanics Code to Simulate Steady and Transient Fuel Rod Behavior  

Microsoft Academic Search

A powerful multidimensional fuels performance capability, applicable to both steady and transient fuel behavior, is developed based on enhancements to the commercially available ABAQUS general-purpose thermomechanics code. Enhanced capabilities are described, including: UO2 temperature and burnup dependent thermal properties, solid and gaseous fission product swelling, fuel densification, fission gas release, cladding thermal and irradiation creep, cladding irradiation growth , gap

R. L. Williamson; D. A. Knoll

2009-01-01

63

Verification, validation, and benchmarking report for TRIMHX: A three dimensional hexagonal transient diffusion theory code  

SciTech Connect

TRIMHX is a fundamental Reactor Analysis tool in use at the Savannah River Site (SRS) and is an integral part of the Generalized Reactor Analysis Subsystem (GRASS). TRIMHX solves the time dependent multigroup neutron diffusion equation in two and three dimensional hexagonal geometry by standard and coarse mesh finite difference methods. The TRIMHX implementation assumes the solution to this equation can be discretized in space, energy, and time. These are industry accepted approaches which can be found in many nuclear engineering books. This report concerns the verification and validation of TRIMHX, a transient two and three dimensional hex-z diffusion theory code. The validation was performed to determine the accuracy of the code, and the verification was performed to determine if the code was correctly using the correct theory and that all the subroutines function as required. For TRIMHX, the validation requirement was satisfied by comparing the results of the code with experiments and benchmarking the code against other standard or validated code results. The verification requirement for TRIMHX was performed indirectly since it is impossible and not necessary to reverify a large code like TRIMHX line by line. The extensive operations history of TRIMHX in conjunction with the comparisons against many numerical experiments (exact solutions) and other diffusion theory codes is sufficient to establish that the code is functioning as intended and therefore it is verified. This report summarizes four sets of experiments performed in 1974, 1977, and 1988, two DIF3D/TRIMHX comparison problems performed in 1991, a DIF3D/FX2-TH/TRIMHX comparison problem produced for this report, and the comparison of TRIMHX/GRIMHX initial static calculations. The results of these experiments show that TRIMHX was correctly implemented and is ready to submit into SCMS production mode.

Le, T.L.

1992-03-01

64

Simultaneous measurement of the thermal conductivity and thermal diffusivity of unconsolidated materials by the transient hot wire method  

Microsoft Academic Search

This paper describes a new design for the transient hot wire method that can obtain the thermal conductivity and thermal diffusivity of unconsolidated materials. In this method, the thermal conductivity is determined from the slope of the temperature rise versus time of an electrically heated wire. The temperature rise is detected as the unbalanced voltage of a precision Wheatstone bridge.

Greg C. Glatzmaier; W. Fred Ramirez

1985-01-01

65

Simultaneous measurement of the thermal conductivity and the thermal diffusivity of liquids by the transient hot-wire method  

Microsoft Academic Search

The paper describes a method and an instrument to measure the thermal conductivity and the thermal diffusivity of liquids simultaneously by the transient hot-wire method. Though the principle of this method has formerly been known, the practical application to fluids has been enabled only by high-precision measurement. In the present method, the thermal conductivity can be determined from the slope

Y. Nagasaka; A. Nagashima

1981-01-01

66

Time-independent hybrid enrichment for finite element solution of transient conduction–radiation in diffusive grey media  

NASA Astrophysics Data System (ADS)

We investigate the effectiveness of the partition-of-unity finite element method for transient conduction–radiation problems in diffusive grey media. The governing equations consist of a semi-linear transient heat equation for the temperature field and a stationary diffusion approximation to the radiation in grey media. The coupled equations are integrated in time using a semi-implicit method in the finite element framework. We show that for the considered problems, a combination of hyperbolic and exponential enrichment functions based on an approximation of the boundary layer leads to improved accuracy compared to the conventional finite element method. It is illustrated that this approach can be more efficient than using h adaptivity to increase the accuracy of the finite element method near the boundary walls. The performance of the proposed partition-of-unity method is analyzed on several test examples for transient conduction–radiation problems in two space dimensions.

Mohamed, M. Shadi; Seaid, Mohammed; Trevelyan, Jon; Laghrouche, Omar

2013-10-01

67

Radiation enhanced diffusion of Ti in Al2O3  

NASA Astrophysics Data System (ADS)

Titanium bulk and dislocation diffusion coefficients at 1000 °C have been determined for Ti in single crystal ?-Al2O3(0001) for three types of samples: (i) Ti evaporated onto Al2O3, (ii) 48Ti+at 100 eV deposited onto Al2O3, and (iii) 48Ti+ at 100 eV deposited onto radiation damaged Al2O3 (damage inflected by implantation of 46Ti+ at 7 keV). Diffusion penetration profiles were obtained by using secondary ion mass spectrometry depth profiling techniques. For the deposited and implanted Ti+ samples, the bulk diffusion coefficients (D) are 5.4×10-21 and 5.6×10-17 m2 s-1, respectively, and dislocation diffusion coefficients are 3.6×10-17 and 1.4×10-12 m2 s-1, respectively. Comparing the D's for Ti in the undamaged and damaged Al2O3, the D's for the latter samples are higher by a factor of 104-105, reflecting the radiation enhanced diffusion due to the defect structure inflected by the implanted 7 keV 46Ti+. Comparing the D's for Ti deposited onto Al2O3 (both the evaporated and 100 eV 48Ti+ samples) with those for Cr deposited onto Al2O3, the Ti D's are larger by a factor of 10, reflecting the influence of the valence state of the cation. These results show that cationic diffusion coefficients in Al2O3 can be controlled by varying the level of defects in the crystal.

Weiss, M.; Lu, M.; van der Heide, P.; Lee, S. M.; Ada, E.; Lee, H. S.; Rabalais, J. W.

2000-09-01

68

A hybrid superconducting fault current limiter for enhancing transient stability in Korean power systems  

NASA Astrophysics Data System (ADS)

Additional power generation sites have been limited in Korea, despite the fact load demands are gradually increasing. In order to meet these increasing demands, Korea's power system company has begun constructing new generators at existing sites. Thus, multi-unit plants can create problems in terms of transient stability when a large disturbance occurs. This paper proposes a hybrid superconducting fault current limiter (SFCL) application to enhance the transient stability of multi-unit power plants. SFCLs reduce fault currents, and limitation currents decrease the imbalance of the mechanical and electrical torque of the generators, resulting in an improvement in transient stability.

Seo, Sangsoo; Kim, Seog-Joo; Moon, Young-Hwan; Lee, Byongjun

2013-11-01

69

Enhancing chemical identification efficiency by SAW sensor transients through a data enrichment and information fusion strategy—a simulation study  

NASA Astrophysics Data System (ADS)

The paper proposes a new approach for improving the odor recognition efficiency of a surface acoustic wave (SAW) transient sensor system based on a single polymer coating. The vapor identity information is hidden in transient response shapes through dependences on specific vapor solvation and diffusion parameters in the polymer coating. The variations in the vapor exposure and purge durations and the sensor operating frequency have been used to create diversity in transient shapes via termination of the vapor-polymer equilibration process up to different stages. The transient signals were analyzed by the discrete wavelet transform using Daubechies-4 mother wavelet basis. The wavelet approximation coefficients were then processed by principal component analysis for creating feature space. The set of principal components define the vapor identity information. In an attempt to enhance vapor class separability we analyze two types of information fusion methods. In one, the sensor operation frequency is fixed and the sensing and purge durations are varied, and in the second, the sensing and purge durations are fixed and the sensor operating frequency is varied. The fusion is achieved by concatenation of discrete wavelet coefficients corresponding to various transients prior to the principal component analysis. The simulation experiments with polyisobutylene SAW sensor coating for operation frequencies over [55-160] MHz and sensing durations over [5-60] s were analyzed. The target vapors are seven volatile organics: chloroform, chlorobenzene, o-dichlorobenzene, n-heptane, toluene, n-hexane and n-octane whose concentrations were varied over [10-100] ppm. The simulation data were generated using a SAW sensor transient response model that incorporates the viscoelastic effects due to polymer coating and an additive noise source in the output. The analysis reveals that: (i) in single transient analysis the class separability increases with sensing duration for a given frequency of operation, and also with frequency for a given sensing duration, and (ii) the information fusion based on both the multiple sensing cycles and the multiple sensing frequencies enhances the class separability by nearly an order of magnitude.

Singh, Prashant; Yadava, R. D. S.

2013-05-01

70

A review of porous media enhanced vapor-phase diffusion mechanisms, models, and data: Does enhanced vapor-phase diffusion exist?  

SciTech Connect

A review of mechanisms, models, and data relevant to the postulated phenomenon of enhanced vapor-phase diffusion in porous media is presented. Information is obtained from literature spanning two different disciplines (soil science and engineering) to gain a diverse perspective on this topic. Findings indicate that while enhanced vapor diffusion tends to correct the discrepancies observed between past theory and experiments, no direct evidence exists to support the postulated processes causing enhanced vapor diffusion. Numerical modeling analyses of experiments representative of the two disciplines are presented in this paper to assess the sensitivity of different systems to enhanced vapor diffusion. Pore-scale modeling is also performed to evaluate the relative significance of enhanced vapor diffusion mechanisms when compared to Fickian diffusion. The results demonstrate the need for additional experiments so that more discerning analyses can be performed.

Ho, C.K.; Webb, S.W.

1996-05-01

71

Enhanced translational diffusion of confined water under electric field  

NASA Astrophysics Data System (ADS)

High resolution quasielastic neutron scattering measurements have been used to study the effects of applied electric field on the dynamics of water molecules confined in the pores of folded silica sheet material FSM-12 with an average pore diameter (apd) of 16 Å. In the absence of field, there is a significant slowing down of the water molecule diffusion as the temperature is lowered, in agreement with previous observations. The application of a moderate electric field of 2.5 kV/mm remarkably enhances the translational diffusion of water molecules. We interpret this as being due to a disruption of the hydrogen bonding by the electric field. This new observation suggests that existing theories valid at large electric field strengths may have to be corrected at moderate fields.

Diallo, S. O.; Mamontov, E.; Nobuo, W.; Inagaki, S.; Fukushima, Y.

2012-08-01

72

Enhanced diffusion in shock activated Be-Al interfaces  

SciTech Connect

Enhanced diffusion of aluminum in shock activated beryllium has been observed. Cylindrical samples of aluminum coated beryllium rods were axisymetrically loaded up to 40 GPa and a total residual strain of up to 6.7%. The defect microstructure produced by both the shock wave and strain enabled the transport of aluminum in beryllium to exceed its equilibrium solid state saturation. This {open_quotes}super saturated{close_quotes} aluminum, upon heating exsolves out at relatively low temperatures and forms very strong interfaces with pressure mated components.

Staudhammer, K.P.

1997-05-01

73

Inversion of diffusive transient electromagnetic data by a conjugate-gradient method  

NASA Astrophysics Data System (ADS)

Inversion of three-dimensional transient electromagnetic (TEM) data to obtain electrical conductivity and permeability can be done by a time-domain algorithm that extends to diffusive electromagnetic (EM) fields the imaging methods originally developed for seismic wavefields (Claerbout, 1971; Tarantola, 1984). The algorithm uses a conjugate-gradient search for the minimum of an error functional involving EM measurements governed by Maxwell's equations without displacement currents. The connection with wavefield imaging comes from showing that the gradient of the error functional can be computed by propagating the errors back into the model in reverse time and correlating the field generated by the backpropagation with the incident field at each point. These two steps (backpropagation and cross correlation) are the same ones used in seismic migration. The backpropagated TEM fields satisfy the adjoint Maxwell's equations, which are stable in reverse time. With magnetic field measurements the gradient of the error functional with respect to conductivity is the cross correlation of the backpropagated electric field with the incident electric field, whereas the gradient with respect to permeability is the cross correlation of the backpropagated magnetic field with the time derivative of the incident magnetic field. Tests on two-dimensional models simulating crosswell TEM surveys produce good images of a conductive block scatterer, with both exact and noisy data, and of a dipping conductive layer. Convergence, however, is slow.

Wang, Tsili; Oristaglio, Michael; Tripp, Alan; Hohmann, Gerald

1994-07-01

74

Enhanced detection in CT colonography using adaptive diffusion filtering  

NASA Astrophysics Data System (ADS)

Computer-aided detection (CAD) is a computerized procedure in medical science that supports the medical team's interpretations and decisions. CAD often uses information from a medical imaging modality such as Computed Tomography to detect suspicious lesions. Algorithms to detect these lesions are based on geometric models which can describe the local structures and thus provide potential region candidates. Geometrical descriptive models are very dependent on the data quality which may affect the false positive rates in CAD. In this paper we propose an efficient adaptive diffusion technique that adaptively controls the diffusion flux of the local structures in the data using robust statistics. The proposed method acts isotropically in the homogeneous regions and anisotropically in the vicinity of jump discontinuities. This method structurally enhances the data and makes the geometrical descriptive models robust. For the iterative solver, we use an efficient gradient descent flow solver based on a PDE formulation of the problem. The whole proposed strategy, which makes use of adaptive diffusion filter coupled with gradient descent flows has been developed and evaluated on clinical data in the application to colonic polyp detection in Computed Tomography Colonography.

Douiri, Abdel; Siddique, Musib; Ye, Xujiong; Beddoe, Gareth; Slabaugh, Greg

2009-02-01

75

Enhancing the ABAQUS Thermomechanics Code to Simulate Steady and Transient Fuel Rod Behavior  

SciTech Connect

A powerful multidimensional fuels performance capability, applicable to both steady and transient fuel behavior, is developed based on enhancements to the commercially available ABAQUS general-purpose thermomechanics code. Enhanced capabilities are described, including: UO2 temperature and burnup dependent thermal properties, solid and gaseous fission product swelling, fuel densification, fission gas release, cladding thermal and irradiation creep, cladding irradiation growth , gap heat transfer, and gap/plenum gas behavior during irradiation. The various modeling capabilities are demonstrated using a 2D axisymmetric analysis of the upper section of a simplified multi-pellet fuel rod, during both steady and transient operation. Computational results demonstrate the importance of a multidimensional fully-coupled thermomechanics treatment. Interestingly, many of the inherent deficiencies in existing fuel performance codes (e.g., 1D thermomechanics, loose thermo-mechanical coupling, separate steady and transient analysis, cumbersome pre- and post-processing) are, in fact, ABAQUS strengths.

R. L. Williamson; D. A. Knoll

2009-09-01

76

Transient enhancement of high-order harmonic generation in expanding molecules  

SciTech Connect

High-order harmonic generation (HHG) is limited by the probability of recombination of the returning electron with the parent ion. We show here that the internuclear distance of simplest diatomic molecules, determining differently delocalized initial electronic states, can be used to enhance the HHG conversion efficiency exceeding the atomic one. We propose an experiment based on a double-pulse pump-drive scheme where a strong transient enhancement of the HHG yield is predicted.

Pfeifer, T.; Walter, D.; Gerber, G.; Emelin, M.Yu.; Ryabikin, M.Yu.; Chernobrovtseva, M.D.; Sergeev, A.M. [Physikalisches Institut, Universitaet Wuerzburg, Am Hubland, D-97074 Wuerzburg (Germany); Institute of Applied Physics, Russian Academy of Sciences, ul. Ul'yanova 46, Nizhni Novgorod, 603950 (Russian Federation)

2004-07-01

77

Transient stability enhancement in power system with distributed static series compensator (DSSC)  

Microsoft Academic Search

Long distance AC transmission system is often subjected to stability problems which limit the transmission capability. Large power systems often suffer from weakly damped swings between synchronous generators. This paper aims to enhance the transient stability of the power system with the use of distributed static series compensator (DSSC). First of all, a detailed simulation model of the DSSC has

S. Golshannavaz; M. Mokhtari; M. Khalilian; D. Nazarpour

2011-01-01

78

Enhancement of Transient Stability of an Industrial Cogeneration System with Superconducting Magnetic Energy Storage Unit  

Microsoft Academic Search

This paper has developed the coordination of load shedding scheme and superconducting magnetic energy storage (SMES) unit to enhance the transient stability of a large industry cogeneration facility. The load-shedding scheme and the tie-line tripping strategy by using the frequency relays have been designed to prevent the power system from collapse when an extemal fault of utility power system occurs.

C. T. Hsu

2002-01-01

79

Transient splenial lesion of corpus callosum associated with antiepileptic drug: conventional and diffusion-weighted magnetic resonance images.  

PubMed

Transient focal lesions of splenium of corpus callosum can be seen as a component of many central nervous system diseases, including antiepileptic drug toxicity. The conventional magnetic resonance (MR) findings of the disease are characteristic and include ovoid lesions with high signal intensity at T2-weighted MRI. Limited information exists about the diffusion-weighted MRI characteristics of these lesions vanishing completely after a period of time. We examined the conventional, FLAIR, and diffusion-weighted MR images of a patient complaining of depressive mood and anxiety disorder after 1 year receiving antiepileptic medication. PMID:16372694

Hakyemez, B; Erdogan, C; Yildirim, N; Gokalp, G; Parlak, M

2005-11-01

80

Positional enhancer-blocking activity of the chicken ?-globin insulator in transiently transfected cells  

PubMed Central

It is thought that insulators demarcate transcriptionally and structurally independent chromatin domains. Insulators are detected by their ability to block enhancer–promoter interactions in a directional manner, and protect a transgene from position effects. Most studies are performed in stably transformed cells or organisms. Here we analyze the enhancer-blocking activity of the chicken ?-globin insulator in transient transfection experiments in both erythroid and nonerythroid cell lines. We show that four tandem copies of a 90-bp fragment of this insulator were able to block an enhancer in these experiments. In circular plasmids, placement on either side of the enhancer reduced activity, but when the plasmid was linearized, the enhancer-blocking activity was observed only when the insulator was placed between the promoter and the enhancer. These observations are consistent with the position-dependent enhancer-blocking activity of the insulator observed in stable transformation experiments.

Recillas-Targa, Felix; Bell, Adam C.; Felsenfeld, Gary

1999-01-01

81

Interactive effect of oxygen diffusion and volatiles advection on transient thermal degradation of poly methyl methacrylate (PMMA)  

Microsoft Academic Search

A transient, one-dimensional model has been presented to formulate the substantial role of polymer gasification in the early\\u000a stages of fire growth. The present model comprises the interaction between the oxygen diffusion and the released volatiles\\u000a on the rate of polymer gasification, when the polymeric sample is subjected to an external radiative source. The model also\\u000a includes different mechanisms affecting

Arash Kashani; Javad Abolfazli Esfahani

2008-01-01

82

Transient Stability Enhancement of Wind Generator by a New Logical Pitch Controller  

NASA Astrophysics Data System (ADS)

In order to investigate the impacts of the integration of wind farms into utilities networks, transient stability should be analyzed before connecting wind turbine generator system (WTGS) to the power system. In this paper, a new logical pitch controller equipped with fuzzy logic controller (FLC) has been proposed, which can enhance the transient performance of WTGS during severe network disturbances. Moreover, it can maintain the output power at rated level when wind speed is over the rated speed. Before transient stability analysis, it is necessary to determine initial values of WTGS connected to the external network. In this paper, the initial value calculation method of WTGS is discussed at different wind conditions. Finally, in order to evaluate the effectiveness of the proposed controller in improving the transient stability, simulations have been carried out for severe network disturbances and windy conditions, considering mechanical dead zone of the pitch actuation system. Simulation results clearly indicate that the proposed controller can enhance the transient stability of wind generator at any network, fault or windy condition, and maintain output power of wind generator at rated level when wind speed is over the rated speed.

Muyeen, S. M.; Ali, Mohd. Hasan; Takahashi, Rion; Murata, Toshiaki; Tamura, Junji

83

Fluorine-enhanced boron diffusion in germanium-preamorphized silicon  

SciTech Connect

Silicon wafers were preamorphized with 60 keV Ge{sup +} or 70 keV Si{sup +} at a dose of 1x10{sup 15} atoms/cm{sup 2}. F{sup +} was then implanted into some samples at 6 keV at doses ranging from 1x10{sup 14} to 5x10{sup 15} atoms/cm{sup 2}, followed by {sup 11}B{sup +} implants at 500 eV, 1x10{sup 15} atoms/cm{sup 2}. Secondary-ion-mass spectrometry confirmed that fluorine enhances boron motion in germanium-preamorphized materials in the absence of annealing. The magnitude of boron diffusion scales with increasing fluorine dose. Boron motion in as-implanted samples occurs when fluorine is concentrated above 1x10{sup 20} atoms/cm{sup 3}. Boron atoms are mobile in as-implanted, amorphous material at concentrations up to 1x10{sup 19} atoms/cm{sup 3}. Fluorine directly influences boron motion only prior to activation annealing. During the solid-phase epitaxial regrowth process, fluorine does not directly influence boron motion, it simply alters the recrystallization rate of the silicon substrate. Boron atoms can diffuse in germanium-amorphized silicon during recrystallization at elevated temperatures without the assistance of additional dopants. Mobile boron concentrations up to 1x10{sup 20} atoms/cm{sup 3} are observed during annealing of germanium-preamorphized wafers.

Jacques, J.M.; Jones, K.S.; Robertson, L.S.; Li-Fatou, A.; Hazelton, C.M.; Napolitani, E.; Rubin, L.M. [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Texas Instruments Inc., Dallas, Texas 75243 (United States); Istituto Nazionale per la Fisica della Materia-Materials and Technologies for Information and Communication Science (INFM-MATIS) and Dipartimento di Fisica, via Marzolo 8, I-35131 Padova (Italy); Axcelis Technologies, Beverly, Massachusetts 01915 (United States)

2005-10-01

84

Large enhancement of transient photovoltage induced by the absorption of the metal Al  

NASA Astrophysics Data System (ADS)

The transient photovoltage of ITO/CuPc/Al is studied. The transient photovoltage under the Al side illumination is much greater than that under ITO side illumination. It is not negligible while light is almost completely absorbed by the Al layer. It seems that the light absorption of the Al layer could enhance the generation of the photoinduced carriers in the organic layer, which is further shown by the transient photovoltage study of ITO/Al/NPB/Au. A possible mechanism proposed is that the holes generated in the Al are because of light absorption that is injected from the Al to organic materials. This results in further charge separation by the internal built-in electric field.

Wu, Bo; Sun, XiaoYu; Sun, ZhengYi; You, YinTao; Lu, Min; Ding, XunMin; Hou, XiaoYuan

2012-07-01

85

Ex vivo and in vivo diffusion of ropivacaine through spinal meninges: influence of absorption enhancers.  

PubMed

Following epidural administration, cerebrospinal fluid bioavailability of local anesthetics is low, one major limiting factor being diffusion across the arachnoid mater barrier. The aim of this study was to evaluate the influence of absorption enhancers on the meningeal permeability of epidurally administered ropivacaine. Five enhancers known for their ability to increase drug permeability via transcellular and/or paracellular pathways, i.e. palmitoyl carnitine, ethylenediaminetetraacetic acid, sodium caprate, dodecylphosphocholine and pentylglycerol, were tested ex vivo on fresh specimen of meninges removed from cervical to lumbar level of rabbit spine following laminectomy and placed in diffusion chambers. Among them, sodium caprate lead to the best permeability improvement for both marker and drug (440% and 112% for mannitol and ropivacaine, respectively) and was therefore selected for in vivo study in a sheep model using microdialysis technique to evaluate epidural and intrathecal ropivacaine concentrations following epidural administration. Resulting dialysate and plasma concentrations were used to calculate pharmacokinetic parameters. Following sodium caprate pre-treatment, ropivacaine intrathecal maximal concentration (Cmax) was 1.6 times higher (78 ± 16 ?g ml(-1) vs 129 ± 26 ?g ml(-1), p<0.05) but the influence of the absorption enhancer was only effective the first 30 min following ropivacaine injection, as seen with the significantly increase of intrathecal AUC(0-30 min) (1629 ± 437 ?g min ml(-1) vs 2477 ± 559 ?g min ml(-1), p<0.05) resulting in a bioavailable fraction 130% higher 30 min after ropivavaine administration. Co-administration of local anesthetics with sodium caprate seems to allow a transient and reversible improvement of transmeningeal passage into intrathecal space. PMID:21056096

Brandhonneur, Nolwenn; Dollo, Gilles; Ratajczak-Enselme, Maja; Deniau, Anne Laure; Chevanne, François; Estèbe, Jean Pierre; Legrand, Alain; Le Corre, Pascal

2010-11-04

86

Comparison of homogenized and enhanced diffusion solutions of model PWR problems  

SciTech Connect

Model problem comparisons in slab geometry are made between two forms of homogenized diffusion theory and enhanced diffusion theory. The pin-cell discontinuity factors for homogenized diffusion calculations are derived from homogenized variational nodal P1 response matrices and from standard finite differencing. Enhanced diffusion theory consists of applying quasi-reflected interface conditions to reduce variational nodal Pn response matrices to one degree of freedom per interface, without homogenization within the cell. As expected both homogenized diffusion methods preserve reaction rates exactly if the discontinuity factors are derived from the P 11 reference solutions. If no reference lattice solution is available, discontinuity factors may be approximated from single cells with reflected boundary conditions; the computational effort is then comparable to calculating the enhanced diffusion response matrices. In this situation enhanced diffusion theory gives the most accurate results and finite difference discontinuity factors the least accurate. (authors)

Lewis, E. E. [Dept. of Mechanical Engineering, Northwestern Univ., 2145 Sheridan Rd., Evanston, IL 60208 (United States); Smith, M. A. [Nuclear Engineering Div., Argonne National Laboratory, 9700 S. Cass Ave, Argonne, IL 60439 (United States)

2012-07-01

87

Transient decrease in nociceptor GRK2 expression produces long-term enhancement in inflammatory pain  

PubMed Central

In heterozygous mice, attenuation of G-protein-coupled receptor kinase 2 (GRK2) level in nociceptors is associated with enhanced and prolonged inflammatory hyperalgesia. To further elucidate the role of GRK2 in nociceptor function we reversibly decreased GRK2 expression using intrathecal antisense oligodeoxynucleotide (AS-ODN). GRK2 AS-ODN administration led to an enhanced and prolonged hyperalgesia induced by prostaglandin E 2, epinephrine and carrageenan. Morover, this effect persisted unattenuated 2 weeks after the last dose of antisense, well after GRK2 protein recovered, suggesting that transient attenuation of GRK2 produced neuroplastic changes in nociceptor function. Unlike hyperalgesic priming induced by transient attenuation of GRK2 produced neuroplastic changes in nociceptor function. Unlike hyperalgesic priming induced by transient activation of protein kinase C epsilon (PKC?), (Aley et al., 2000, Parada et al., 2003b), the enhanced and prolonged hyperalgesia following attenuation of GRK2 is PKC?- and cytoplasmic polyadenylation element binding protein (CPEB)-independent and is protein kinase A (PKA)- and Src tyrosine kinase (Src)-dependent. Finally, rats treated with GRK2 AS-ODN exhibited enhanced and prolonged hyperalgesia induced by direct activation of second messengers, adenyl cyclase, Epac or PKA, suggesting changes downstream of G-protein-coupled receptors. Because inflammation can produce a decrease in GRK2, such a mechanism could help explain a predilection to develop chronic pain, after resolution of acute inflammation.

Ferrari, Luiz F.; Bogen, Oliver; Alessandri-Haber, Nicole; Levine, Emma; Gear, Robert W.; Levine, Jon D.

2012-01-01

88

Real-time speckle reduction and coherence enhancement in ultrasound imaging via nonlinear anisotropic diffusion  

Microsoft Academic Search

This paper presents a novel approach for speckle reduction and coherence enhancement of ultrasound images based on nonlinear coherent diffusion (NCD) model. The proposed NCD model combines three different models. According to speckle extent and image anisotropy, the NCD model changes progressively from isotropic diffusion through anisotropic coherent diffusion to, finally, mean curvature motion. This structure maximally low-pass filters those

Khaled Z. Abd-Elmoniem; Abou-Bakr M. Youssef; Yasser M. Kadah

2002-01-01

89

Enhanced diffusion of liquid-coated gas bubbles in solids  

Microsoft Academic Search

Gas bubble diffusion in solids is typically due to surface diffusion of matrix atoms along the gas-solid interface. Insoluble impurities that segregate to the interface tend to suppress surface diffusion by chemically combining with the surface atoms, as in the creation of a metal oxide layer, or by simply presenting a physical barrier to the kinetic jump process. We propose

C. De W. Van Siclen; R. N. Wright

1993-01-01

90

Current-pulse-induced enhancement of transient photodetective effect in tilted manganite film.  

PubMed

A current-pulse-induced enhancement effect of transient photovoltage has been discovered in tilted manganite La(2/3)Ca(1/3)MnO(3) film at room temperature. Here, by applying a pulsed current stimulus before pulse laser irradiation, we observed a significant enhancement of more than 50% in photovoltaic sensitivity. The current-pulse-induced photovoltaic enhancement can be tuned not only by the stimulating current value but also by the stimulating time. Such enhancement is time-sensitive and reproducible. This electrically induced effect, observed at room temperature, has both the benefit of a discovery in materials properties and the promise of applications for thin film manganites in photodetectors. PMID:23263085

Ni, H; Zhao, K; Xi, J F; Feng, X; Xiang, W F; Zhao, S Q; Kong, Y-C; Wong, H K

2012-12-17

91

Enhanced Lipid Diffusion and Mixing in Accelerated Molecular Dynamics  

PubMed Central

Accelerated molecular dynamics (aMD) is an enhanced sampling technique that expedites conformational space sampling by reducing the barriers separating various low-energy states of a system. Here, we present the first application of the aMD method on lipid membranes. Altogether, ?1.5 ?s simulations were performed on three systems: a pure POPC bilayer, a pure DMPC bilayer, and a mixed POPC:DMPC bilayer. Overall, the aMD simulations are found to produce significant speedup in trans–gauche isomerization and lipid lateral diffusion versus those in conventional MD (cMD) simulations. Further comparison of a 70-ns aMD run and a 300-ns cMD run of the mixed POPC:DMPC bilayer shows that the two simulations yield similar lipid mixing behaviors, with aMD generating a 2–3-fold speedup compared to cMD. Our results demonstrate that the aMD method is an efficient approach for the study of bilayer structural and dynamic properties. On the basis of simulations of the three bilayer systems, we also discuss the impact of aMD parameters on various lipid properties, which can be used as a guideline for future aMD simulations of membrane systems.

2011-01-01

92

Flux expansion nodal method for solving static and transient neutron diffusion equations, in hexagonal-z geometry  

SciTech Connect

An intra-nodal flux expansion nodal method (FENM) for solving static and transient neutron diffusion equations in hexagonal-z geometry has been developed, in which the flux distributions are expanded into a set of analytic basis functions and orthogonal second-order polynomials. In order to improve the nodal coupling relations, a new type of nodal boundary conditions is proposed, which requires the continuity of both the zero- and first-order moments of partial currents across the nodal surfaces. The numerical results for a series of benchmark problems demonstrate that FENM exhibits good accuracy and convergence. (authors)

Bangyang, X.; Zhongsheng, X. [Dept. of Nuclear Engineering, Xi'An Jiaotong Univ., Xi'an, Shaanxi 710049 (China); Chunyu, X.; Dong, Y. [National Key Laboratory of Reactor System Design Technology, Chengdu, Sichuan 610041 (China)

2006-07-01

93

Transient splenial lesion of the corpus callosum associated with antiepileptic drugs: evaluation by diffusion-weighted MR imaging  

Microsoft Academic Search

.  \\u000a Transient focal lesions in the splenium of the corpus callosum have been reported in epileptic patients receiving antiepileptic\\u000a drugs. The characteristic imaging features included an oval high signal lesion on T2-weighted images in the central part of\\u000a the splenium, no enhancement on post-contrast MR images, and complete reversibility without specific treatment. We report\\u000a identical MR imaging findings in a

Masayuki Maeda; Takashi Shiroyama; Hirokazu Tsukahara; Taro Shimono; Shigeki Aoki; Kan Takeda

2003-01-01

94

Numerical Analysis of Effect of Backplate Diffusivity on the Transient Temperature in Friction Stir Welding  

NASA Astrophysics Data System (ADS)

It is still not clearly known as to what extent the temperature field of friction stir welding joint is influenced by backplate diffusivity owing to the limitation of temperature measuring points. In the present study, therefore, the effect of backplate diffusivity on the temperature field of the workpiece was systematically investigated based on the numerical analysis. Simulated results show that the backplate diffusivity has a significant influence on not only the peak temperature but the final temperature distribution. More heat is dissipated by using a high thermal conductivity backplate during FSW. With increasing the backplate diffusivity, the peak temperature decreases gradually and the average cooling rate increases first and then slightly decreases. In addition, the time spent above 195 °C presents a nearly linear decrease with increasing the backplate diffusivity. Moreover, the width of temperature region higher than 195 °C in the transverse direction is remarkably diminished by using the backplate of a high conductivity, and changes little during the entire process.

Zhang, Zhihan; Li, Wenya; Li, Jinglong; Chao, Y. J.

2013-09-01

95

Pore-scale modeling of enhanced vapor diffusion in porous media  

SciTech Connect

Vapor diffusion in porous media in the presence of its liquid has often been analyzed like air diffusion. The diffusion rate is much lower than in free space due to the presence of the porous medium and any liquid present. However, enhanced vapor diffusion has also been postulated such that the diffusion rate may approach free-space values. The mechanisms postulated to lead to this enhancement include condensation/evaporation across isolated liquid islands in the porous media and an increased temperature gradient in the gas phase. In order to try to understand the mechanisms involved in such an enhancement, pore-scale models have been developed. Vapor diffusion in the presence of liquid islands has been evaluated for a one-dimensional pore network under a concentration gradient. The simulations show that significant enhancement of vapor diffusion is indeed possible in the presence of liquid islands, while air diffusion decreases slightly. While the present pore-scale model indicates that enhanced vapor diffusion is possible, only experimental data can confirm the relevant processes.

Webb, S.W.; Ho, C.K.

1997-10-01

96

Transient Evolution of a Planar Diffusion Flame Aft of a Translating Flat Plate.  

National Technical Information Service (NTIS)

The high degree of spatial symmetry of a planar diffusion flame affords great simplifications for experimental and modeling studies of gaseous fuel combustion. Particularly, in a microgravity environment, where buoyancy effects are negligible, an effectiv...

S. A. Gokoglu

2003-01-01

97

Multiple transient point heat sources identification in heat diffusion: application to experimental 2D problems  

Microsoft Academic Search

This paper deals with an inverse problem, which consists of the experimental identification of line heat sources in a homogeneous solid in transient heat conduction. The location and strength of the line heat sources are both unknown. For a single source we examine the case of a source which moves in the system during the experiment. The identification procedure is

Frédéric Lefèvre; Christophe Le Niliot

2002-01-01

98

Measurement and modeling of the transient adsorption, desorption and diffusion processes in microporous materials  

Microsoft Academic Search

Using pulse-response experiments the adsorption and diffusion behavior of a number of gases in microporous materials was measured in the temperature range 300–773K. By modeling these pulse responses it is possible to simultaneously determine the equilibrium constant for adsorption, the absolute rate constants for adsorption and desorption, as well as the diffusivity inside micropores. The pulse-response measurements are very reproducible

T. A. Nijhuis; L. J. P. van den Broeke; M. J. G. Linders; J. M. van de Graaf; F. Kapteijn; M. Makkee; J. A. Moulijn

1999-01-01

99

Enhancement of diffusion through foods using alternating electric fields  

Microsoft Academic Search

This work describes a procedure and equipment to study molecular diffusion in model foods under conditions of elevated temperatures and in the presence of alternating electrical fields by the uptake of indicator dyes. A series of experimental rigs have been built which allow diffusion to be studied over a range of temperatures. A technique, based on image analysis and optical

M. R. Kemp; P. J. Fryer

2007-01-01

100

Enhancement of diffuse reflectance using air tunnel structure.  

PubMed

Submicrometer air gap structure has formed on diffuse reflection structure to improve light reflectance. Covering polymer or liquid on a diffuse reflector to make optical components induces the severe decrease of the total reflectance, since the diffuse reflected angle of some light rays is larger than the critical angle and the rays travel to the medium until meeting a proper small incident angle. The reflectance drops to 68% of the original value with just a polymer coating on the diffuse reflector. The formation of an air tunnel structure between the polymer layer and the diffuse reflector makes a symmetrical reflective index matching state and recovers 95% of the original reflectance. Due to the simple fabrication process and the chemical stability, the structure can be applied to various optical components and reflective display devices. PMID:23381414

Jang, Jae Eun; Lee, Gae Hwang; Song, Byoung Gwon; Cha, Seung Nam; Jung, Jae Eun

2013-02-01

101

WEE1 kinase inhibition enhances the radiation response of diffuse intrinsic pontine gliomas.  

PubMed

Diffuse intrinsic pontine glioma (DIPG) is a fatal pediatric disease. Thus far, no therapeutic agent has proven beneficial in the treatment of this malignancy. Therefore, conventional DNA-damaging radiotherapy remains the standard treatment, providing transient neurologic improvement without improving the probability of overall survival. During radiotherapy, WEE1 kinase controls the G(2) cell-cycle checkpoint, allowing for repair of irradiation (IR)-induced DNA damage. Here, we show that WEE1 kinase is one of the highest overexpressed kinases in primary DIPG tissues compared with matching non-neoplastic brain tissues. Inhibition of WEE1 by MK-1775 treatment of DIPG cells inhibited the IR-induced WEE1-mediated phosphorylation of CDC2, resulting in reduced G(2)-M arrest and decreased cell viability. Finally, we show that MK-1775 enhances the radiation response of E98-Fluc-mCherry DIPG mouse xenografts. Altogether, these results show that inhibition of WEE1 kinase in conjunction with radiotherapy holds potential as a therapeutic approach for the treatment of DIPG. PMID:23270927

Caretti, Viola; Hiddingh, Lotte; Lagerweij, Tonny; Schellen, Pepijn; Koken, Phil W; Hulleman, Esther; van Vuurden, Dannis G; Vandertop, W Peter; Kaspers, Gertjan J L; Noske, David P; Wurdinger, Thomas

2012-12-27

102

DNA replication facilitates the action of transcriptional enhancers in transient expression assays.  

PubMed Central

We demonstrate a general role for DNA replication in the activation of gene transcription in transient transfection assays. The effect is observed for a wide range of genes and cell types, transfected by a number of protocols and is independent of increased template copy number. Replication does not stimulate transcription driven by proximal promoter elements alone but requires a functional enhancer element. This synergy between an active replication origin and an enhancer is not confined to elements from viruses such as SV40, which undergo an early to late switch in gene expression that is tightly coupled to replication, since the enhancer-containing long terminal repeats from retroviruses are strongly stimulated by replication. Furthermore, synthetic enhancers consisting of multimerised binding sites for one or two factors are also subject to replication-activation. The diversity of synthetic and natural enhancers used in this study suggests that replication and transcription do not share a common protein factor. We propose that replication leads to chromatin modifications that facilitate enhancer action. Images

Wilson, A C; Patient, R K

1993-01-01

103

Changes in diffusion parameters, energy-related metabolites and glutamate in the rat cortex after transient hypoxia/ischemia.  

PubMed

It has been shown that global anoxia leads to dramatic changes in the diffusion properties of the extracellular space (ECS). In this study, we investigated how changes in ECS volume and geometry in the rat somatosensory cortex during and after transient hypoxia/ischemia correlate with extracellular concentrations of energy-related metabolites and glutamate. Adult male Wistar rats (n = 12) were anesthetized and subjected to hypoxia/ischemia for 30 min (ventilation with 10% oxygen and unilateral carotid artery occlusion). The ECS diffusion parameters, volume fraction and tortuosity, were determined from concentration-time profiles of tetramethylammonium applied by iontophoresis. Concentrations of lactate, glucose, pyruvate and glutamate in the extracellular fluid (ECF) were monitored by microdialysis (n = 9). During hypoxia/ischemia, the ECS volume fraction decreased from initial values of 0.19 +/- 0.03 (mean +/- S.E.M.) to 0.07 +/- 0.01 and tortuosity increased from 1.57 +/- 0.01 to 1.88 +/- 0.03. During reperfusion the volume fraction returned to control values within 20 min and then increased to 0.23 +/- 0.01, while tortuosity only returned to original values (1.53 +/- 0.06). The concentrations of lactate and glutamate, and the lactate/pyruvate ratio, substantially increased during hypoxia/ischemia, followed by continuous recovery during reperfusion. The glucose concentration decreased rapidly during hypoxia/ischemia with a subsequent return to control values within 20 min of reperfusion. We conclude that transient hypoxia/ischemia causes similar changes in ECS diffusion parameters as does global anoxia and that the time course of the reduction in ECS volume fraction correlates with the increase of extracellular concentration of glutamate. The decrease in the ECS volume fraction can therefore contribute to an increased accumulation of toxic metabolites, which may aggravate functional deficits and lead to damage of the central nervous system (CNS). PMID:16759801

Homola, Ales; Zoremba, Norbert; Slais, Karel; Kuhlen, Ralf; Syková, Eva

2006-06-06

104

Electric Field Enhanced Diffusion of Salicylic Acid through Polyacrylamide Hydrogels  

NASA Astrophysics Data System (ADS)

The release mechanisms and the diffusion coefficients of salicylic acid -loaded polyacrylamide hydrogels were investigated experimentally by using a modified Franz-diffusion cell at 37 ^oC to determine the effects of crosslinking ratio and electric field strength. A significant amount of salicylic acid is released within 48 hours from the hydrogels of various crosslinking ratios, with and without electric field. The release characteristic follows the Q vs. t^1/2 linear relationship. Diffusion coefficient initially increases with increasing electric field strength and reaches the maximum value at electric field strength of 0.1 V; beyond that it decreases with electric field strength and becomes saturated at electric field strength of 5 V. The diffusion coefficient increases at low electric field strength (less 0.1 V) as a result of the electrophoresis of the salicylic acid, the expansion of pore size, and the induced pathway in pigskin. For electric field strength higher than 0.1 V, the decrease in the diffusion coefficient is due to the reduction of the polyacrylamide pore size. The diffusion coefficient obeys the scaling behavior D/Do=(drug size/pore size)^m, with the scaling exponent m equal to 0.93 and 0.42 at electric fields of 0 and 0.1 V, respectively.

Niamlang, Sumonman; Sirivat, Anuvat

2008-03-01

105

NESTLE: Few-group neutron diffusion equation solver utilizing the nodal expansion method for eigenvalue, adjoint, fixed-source steady-state and transient problems  

Microsoft Academic Search

NESTLE is a FORTRAN77 code that solves the few-group neutron diffusion equation utilizing the Nodal Expansion Method (NEM). NESTLE can solve the eigenvalue (criticality); eigenvalue adjoint; external fixed-source steady-state; or external fixed-source. or eigenvalue initiated transient problems. The code name NESTLE originates from the multi-problem solution capability, abbreviating Nodal Eigenvalue, Steady-state, Transient, Le core Evaluator. The eigenvalue problem allows criticality

P. J. Turinsky; R. M. K. Al-Chalabi; P. Engrand; H. N. Sarsour; F. X. Faure; W. Guo

1994-01-01

106

Enhancement of gas-phase diffusion in the presence of liquid  

NASA Astrophysics Data System (ADS)

Gas diffusion in porous media occurs in both the gas and liquid phases. In many instances, gas diffusion in the liquid phase is ignored. However, under many conditions, gas diffusion in the liquid phase may be more important than gas diffusion in the gas phase. Two different cases will be examined in this work. The first case is a continuous liquid path between the gas concentrations of interest modeled after Jury et al. (1984). The second case is the situation at low liquid saturation where liquid islands exist. For the first case, Jury's model can be rewritten as a ratio of the total gas diffusion in the gas and liquid phases to that just in the gas phase. The liquid diffusion coefficient is approximately 10-4 times the gas diffusion coefficient consistent with Jury et al. (1984). The ratio of total diffusion to gas-phase diffusion is then only a function of Henry's constant and the liquid saturation. For higher values of Henry's constant, such as for CO2 and O2, the effect of diffusion in the liquid phase is small except at high liquid saturations. For small values of Henry's constant, such as for some VOCs and explosive compounds, diffusion in the liquid phase dominates for low and moderate liquid saturation values. The second case is the enhancement of diffusion caused by liquid islands at low liquid saturation. Enhanced vapor diffusion across liquid islands has been observed and modeled by Webb and Ho (1999), where condensation and evaporation occur on opposite ends of the liquid island. Vapor diffusion enhancement of up to a factor of 10 has been observed. Similarly, gas can diffuse through the liquid island. For high values of Henry's constant, gas diffusion through liquid islands is negligible and can be ignored. For small values of Henry's constant, diffusion through liquid islands may be much greater than diffusion through gas, so the rate is enhanced. The work was sponsored by the Geneva International Center for Humanitarian Demining (GICHD) under the direction of Havard Bach. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

Webb, S.; Angert, A.

2003-04-01

107

Enhancement of inhibitory synaptic transmission in large aspiny neurons after transient cerebral ischemia  

PubMed Central

Large aspiny neurons and most of the GABAergic interneurons survive transient cerebral ischemia while medium spiny neurons degenerate in 24 h. Expression of a long-term enhancement of excitatory transmission in medium spiny neurons but not in large aspiny neurons has been indicated to contribute to this selective vulnerability. Because neuronal excitability is determined by the counterbalance of excitation and inhibition, the present study examined inhibitory synaptic transmission in large aspiny neurons after ischemia in rats. Transient cerebral ischemia was induced for 22 minutes using the four-vessel occlusion method and whole-cell voltage-clamp recording was performed on striatal slices. The amplitudes of evoked inhibitory postsynaptic currents in large aspiny neurons were significantly increased at 3 h and 24 h after ischemia, which was mediated by the increase of presynaptic release. Postsynaptic responses were depressed at 24 h after ischemia. Inhibitory postsynaptic currents could be evoked in large aspiny neurons at 24 h after ischemia, suggesting that they receive GABAergic inputs from the survived GABAergic interneurons. Muscimol, a GABAA receptor agonist, presynaptically facilitated inhibitory synaptic transmission at 24 h after ischemia. Such facilitation was dependent on the extracellular calcium and voltage-gated sodium channels. The present study demonstrates an enhancement of inhibitory synaptic transmission in large aspiny neurons after ischemia, which might reduce excitotoxicity and contribute, at least in part, to the survival of large aspiny neurons. Our data also suggests that large aspiny neurons might receive inhibitory inputs from GABAergic interneurons.

Li, Yan; Lei, Zhigang; Xu, Zao C.

2009-01-01

108

Enhanced Vapor-Phase Diffusion in Porous Media - LDRD Final Report.  

National Technical Information Service (NTIS)

As part of the Laboratory-Directed Research and Development (LDRD) Program at Sandia National Laboratories, an investigation into the existence of enhanced vapor-phase diffusion (EVD) in porous media has been conducted. A thorough literature review was in...

C. K. Ho S. W. Webb

1999-01-01

109

Developments in Fish Culture: Enhanced Diffusion of Calcein into Rainbow Trout Fry Using Cavitation Level Ultrasound.  

National Technical Information Service (NTIS)

Enhanced diffusion of calcein into rainbow trout, Oncorhynchus mykiss, fry was achieved using cavitation level ultrasound for the purpose of mass marking. Three variables, consisting of two voltage amplitudes, two calcein concentrations, and two treatment...

A. N. Bart G. A. Kindschi H. Ahmed J. Clark J. Young R. S. Langer Y. Zohar

1999-01-01

110

Persistent wind-induced enhancement of diffusive CO2 transport in a mountain forest snowpack  

NASA Astrophysics Data System (ADS)

Diffusion dominates the transport of trace gases between soil and the atmosphere. Pressure gradients induced by atmospheric flow and wind interacting with topographical features cause a small but persistent bulk flow of air within soil or snow. This forcing, called pressure pumping or wind pumping, leads to a poorly quantified enhancement of gas transport beyond the rate of molecular diffusion. This study was conducted to quantify the role of pressure pumping in enhancement of CO2 transport through a mountain forest seasonal snowpack. Observations of 12CO2 and 13CO2 within the snowpack, soil, and air of a subalpine forest were made over three winters in the Rocky Mountains, USA. These molecules differ in their rates of diffusion, providing a means to quantify the relative importance of diffusion and advection. An empirical model was developed to describe the transport of these gases through the snowpack, assuming that isotopic variability was caused solely by wind. We found that advection was a persistent phenomenon within the snowpack. Under calm conditions, isotopic patterns followed those associated with diffusion. In the presence of wind, the 4.4‰ isotopic effect of diffusion was diminished, and transport was enhanced beyond the diffusive rate for a given mole fraction gradient. Pressure pumping in our forest snowpack enhanced transport of CO2 beyond molecular diffusion by up to 40% in the short term (hours) but by at most 8%-11% when integrated over a winter. These results should be applicable to trace gas transport in a variety of biogeochemical applications.

Bowling, D. R.; Massman, W. J.

2011-12-01

111

On the Maxwell-Stefan approach to diffusion: a general resolution in the transient regime for one-dimensional systems.  

PubMed

The diffusion process in a multicomponent system can be formulated in a general form by the generalized Maxwell-Stefan equations. This formulation is able to describe the diffusion process in different systems, such as, for instance, bulk diffusion (in the gas, liquid, and solid phase) and diffusion in microporous materials (membranes, zeolites, nanotubes, etc.). The Maxwell-Stefan equations can be solved analytically (only in special cases) or by numerical approaches. Different numerical strategies have been previously presented, but the number of diffusing species is normally restricted, with only few exceptions, to three in bulk diffusion and to two in microporous systems, unless simplifications of the Maxwell-Stefan equations are considered. In the literature, a large effort has been devoted to the derivation of the analytic expression of the elements of the Fick-like diffusion matrix and therefore to the symbolic inversion of a square matrix with dimensions n x n (n being the number of independent components). This step, which can be easily performed for n = 2 and remains reasonable for n = 3, becomes rapidly very complex in problems with a large number of components. This paper addresses the problem of the numerical resolution of the Maxwell-Stefan equations in the transient regime for a one-dimensional system with a generic number of components, avoiding the definition of the analytic expression of the elements of the Fick-like diffusion matrix. To this aim, two approaches have been implemented in a computational code; the first is the simple finite difference second-order accurate in time Crank-Nicolson scheme for which the full mathematical derivation and the relevant final equations are reported. The second is based on the more accurate backward differentiation formulas, BDF, or Gear's method (Shampine, L. F. ; Gear, C. W. SIAM Rev. 1979, 21, 1.), as implemented in the Livermore solver for ordinary differential equations, LSODE (Hindmarsh, A. C. Serial Fortran Solvers for ODE Initial Value Problems, Technical Report; https://computation.llnl.gov/casc/odepack/odepack_ home.html (2006).). Both methods have been applied to a series of specific problems, such as bulk diffusion of acetone and methanol through stagnant air, uptake of two components on a microporous material in a model system, and permeation across a microporous membrane in model systems, both with the aim to validate the method and to add new information to the comprehension of the peculiar behavior of these systems. The approach is validated by comparison with different published results and with analytic expressions for the steady-state concentration profiles or fluxes in particular systems. The possibility to treat a generic number of components (the limitation being essentially the computational power) is also tested, and results are reported on the permeation of a five component mixture through a membrane in a model system. It is worth noticing that the algorithm here reported can be applied also to the Fick formulation of the diffusion problem with concentration-dependent diffusion coefficients. PMID:20000727

Leonardi, Erminia; Angeli, Celestino

2010-01-14

112

Multiple copies of virG enhance the transient transformation of celery, carrot and rice tissues by Agrobacterium tumefaciens  

Microsoft Academic Search

In an effort to improve the T-DNA-mediated transformation frequency of economically important crops, we investigated the possible enhancement effect of multiple copies of virG genes contained in Agrobacterium tumefaciens strains upon the transient transformation of celery, carrot and rice tissues. Four days after A. tumefaciens infection, we performed histochemical ß-glucuronidase (GUS) assays to determine the frequency of transient transformation of

Chang-Nong Liu; Xiu-Qing Li; Stanton B. Gelvin

1992-01-01

113

Transient Enhancement of Inhibitory Synaptic Transmission in Hippocampal CA1 Pyramidal Neurons after Cerebral Ischemia  

PubMed Central

Pyramidal neurons in hippocampal CA1 regions are highly sensitive to cerebral ischemia. Alterations of excitatory and inhibitory synaptic transmission may contribute to the ischemia-induced neuronal degeneration. However, little is known about the changes of GABAergic synaptic transmission in the hippocampus following reperfusion. We examined the GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) in CA1 pyramidal neurons 12 hours and 24 hours after transient forebrain ischemia. The amplitudes of evoked IPSCs (eIPSCs) were increased significantly 12 hours after ischemia and returned to control levels 24 hours following reperfusion. The potentiation of eIPSCs was accompanied by an increase of miniature IPSCs (mIPSCs) amplitude, and an enhanced response to exogenous application of GABA, indicating the involvement of postsynaptic mechanisms. Furthermore, there was no obvious change of the paired-pulse ratio (PPR) of eIPSCs and the frequency of mIPSCs, suggesting that the potentiation of eIPSCs might not be due to the increased presynaptic release. Blockade of adenosine A1 receptors led to a decrease of eIPSCs amplitude in post-ischemic neurons but not in control neurons, without affecting the frequency of mIPSCs and the PPR of eIPSCs. Thus, tonic activation of adenosine A1 receptors might, at least in part, contribute to the enhancement of inhibitory synaptic transmission in CA1 neurons after forebrain ischemia. The transient enhancement of inhibitory neurotransmission might temporarily protect CA1 pyramidal neurons, and delay the process of neuronal death after cerebral ischemia.

Liang, Rui; Pang, Zhi-Ping; Deng, Ping; Xu, Zao C.

2009-01-01

114

A review of radiation enhanced diffusion in perspective materials  

Microsoft Academic Search

In this paper, lattice defects and vacancy diffusion coefficients for a variety of materials and temperatures have been calculated on the basis of a modified procedure in [V.A. Starostin, Phys. Chem. Mater. Treat. 5 (1999) 104 (in Russian)] of the model of Beloshitsky [V.V. Beloshitsky, Rad. Eff. 88 (1986) 249]. Arrhenius low enthalpies were defined as linear functions from the

V. A. Starostin

2006-01-01

115

Performance enhancement of PV solar system by diffused reflection  

Microsoft Academic Search

Various methods are being adopted to enhance the performance of a solar panel. The most common method is to track the sun for performance enhancement. Such method needs complicated control and drive circuits for implementation. Also, the power required for the tracking motor has to be provided by the solar panel and the battery system. Although better performance is achievable

Rizwan ur Rahman; Dewan Ishtiaque Ahmed; Mufrad Ahmed Fahmi; Tithi Tasnuva; M. Fayyaz Khan

2009-01-01

116

Boron-enhanced diffusion of boron from ultralow-energy boron implantation  

SciTech Connect

The authors have investigated the diffusion enhancement mechanism of BED (boron enhanced diffusion), wherein the boron diffusivity is enhanced three to four times over the equilibrium diffusivity at 1,050 C in the proximity of a silicon layer containing a high boron concentration. It is shown that BED is associated with the formation of a fine-grain polycrystalline silicon boride phase within an initially amorphous Si layer having a high B concentration. For 0.5 keV B{sup +}, the threshold implantation dose which leads to BED lies between 3 {times} 10{sup 14} and of 1 {times} 10{sup 15}/cm{sup {minus}2}. Formation of the shallowest possible junctions by 0.5 keV B{sup +} requires that the implant dose be kept lower than this threshold.

Agarwal, A.; Eaglesham, D.J.; Gossmann, H.J.; Pelaz, L.; Herner, S.B.; Jacobson, D.C. [Lucent Technologies, Murray Hill, NJ (United States). Bell Labs.; Haynes, T.E. [Oak Ridge National Lab., TN (United States). Solid State Div.; Erokhin, Y.E. [Eaton Corp., Beverly, MA (United States)

1998-05-03

117

Enhanced lifetime hybrid-diffuser cesium reservoir photocathode  

NASA Astrophysics Data System (ADS)

A novel self-healing hybrid-diffuser cesium reservoir photocathode is demonstrated. The model-driven design optimizes operating temperature to match diffusion and evaporation rates and maximize quantum efficiency of the cesiated tungsten surface. A sintered-wire tungsten emitter promotes surface uniformity. Cesium loss is less than 0.023 µg/cm2/hr at 125ºC, and conservatively extrapolated reservoir lifetime exceeds 30,000 hours. Contamination robustness to a direct atmospheric leak with room-temperature contamination by over 200 Langmuirs of oxidizing gases is excellent, with 90% of maximum QE repeatedly restored via in situ self-healing recesiation under gentle 90ºC heating.

Montgomery, Eric J.; Pan, Zhigang; Riddick, Blake C.; O'Shea, Patrick G.; Feldman, Donald W.; Jensen, Kevin L.; Ives, R. Lawrence; Falce, Louis R.

2013-01-01

118

A review of radiation enhanced diffusion in perspective materials  

NASA Astrophysics Data System (ADS)

In this paper, lattice defects and vacancy diffusion coefficients for a variety of materials and temperatures have been calculated on the basis of a modified procedure in [V.A. Starostin, Phys. Chem. Mater. Treat. 5 (1999) 104 (in Russian)] of the model of Beloshitsky [V.V. Beloshitsky, Rad. Eff. 88 (1986) 249]. Arrhenius low enthalpies were defined as linear functions from the temperature for metals, insulators and semiconductors. The anomalous behavior of high temperature superconductors is discussed.

Starostin, V. A.

2006-01-01

119

Persistent wind-induced enhancement of diffusive CO2 transport in a mountain forest snowpack  

Microsoft Academic Search

Pressure pumping causes ventilation of trace gases from a seasonal snowpackPressure pumping enhances trace gas transport beyond the rate of molecular diffusionEnhanced transport is 40% higher in the short term but 8%–11% higher over a winter

D. R. Bowling; W. J. Massman

2011-01-01

120

Glibenclamide enhances neurogenesis and improves long-term functional recovery after transient focal cerebral ischemia.  

PubMed

Glibenclamide is neuroprotective against cerebral ischemia in rats. We studied whether glibenclamide enhances long-term brain repair and improves behavioral recovery after stroke. Adult male Wistar rats were subjected to transient middle cerebral artery occlusion (MCAO) for 90?minutes. A low dose of glibenclamide (total 0.6??g) was administered intravenously 6, 12, and 24?hours after reperfusion. We assessed behavioral outcome during a 30-day follow-up and animals were perfused for histological evaluation. In vitro specific binding of glibenclamide to microglia increased after pro-inflammatory stimuli. In vivo glibenclamide was associated with increased migration of doublecortin-positive cells in the striatum toward the ischemic lesion 72?hours after MCAO, and reactive microglia expressed sulfonylurea receptor 1 (SUR1) and Kir6.2 in the medial striatum. One month after MCAO, glibenclamide was also associated with increased number of NeuN-positive and 5-bromo-2-deoxyuridine-positive neurons in the cortex and hippocampus, and enhanced angiogenesis in the hippocampus. Consequently, glibenclamide-treated MCAO rats showed improved performance in the limb-placing test on postoperative days 22 to 29, and in the cylinder and water-maze test on postoperative day 29. Therefore, acute blockade of SUR1 by glibenclamide enhanced long-term brain repair in MCAO rats, which was associated with improved behavioral outcome. PMID:23149556

Ortega, Francisco J; Jolkkonen, Jukka; Mahy, Nicole; Rodríguez, Manuel J

2012-11-14

121

Cardiac Amyloidosis: Typical Imaging Findings and Diffuse Myocardial Damage Demonstrated by Delayed Contrast-Enhanced MRI  

SciTech Connect

Amyloidosis is a rare systemic disease. However, involvement of the heart is a common finding and is the most frequent cause of death in amyloidosis. We report the sonographic, scintigraphic, and MRI features of a pathologically proven case of cardiac amyloidosis. Delayed contrast-enhanced MR images, using an inversion recovery prepped gradient-echo sequence, revealed diffuse enhancement in the wall of both left and right ventricles. This enhancement suggested expansion of the extracellular space of the myocardium caused by diffuse myocardial necrosis secondary to deposition of amyloid.

Sueyoshi, Eijun, E-mail: EijunSueyoshi@aol.com; Sakamoto, Ichiro; Okimoto, Tomoaki; Hayashi, Kuniaki [Nagasaki University School of Medicine, Department of Radiology (Japan); Tanaka, Kyouei; Toda, Genji [Nagasaki University School of Medicine, Department of Cardiology (Japan)

2006-08-15

122

Experimental demonstration of diffusion signal enhancement in 2D DESIRE images.  

PubMed

In magnetic resonance microscopy based on conventional Fourier encoding techniques, molecular self-diffusion leads to a loss in signal to noise ratio while also limiting the spatial resolution. As opposed to standard diffusion-weighted sequences, the DESIRE (Diffusion Enhancement of SIgnal and REsolution) method gains signal through diffusion via a signal difference measurement, corresponding to the total number of spins saturated by a localized pulse applied for a given amount of time. The higher the diffusion coefficient at that location, the larger the number of spins effectively saturated and thus the higher the difference in signal. While the method has been previously demonstrated in 1D, the availability of higher magnetic fields and gradient strengths has recently brought its development within reach in 2D. Here we report the implementation of 2D DESIRE and the first experimental evaluation of enhancements in water and thin silicone oil. Enhancement levels obtained by saturating a 60 ?m diameter region (effectively ~140 ?m) and allowing diffusion lengths of 28 ?m or 7 ?m, respectively, are consistent with theoretical predictions. The typical enhancement values are 100% in water and 20% in silicone oil. PMID:22578554

Jelescu, Ileana O; Boulant, Nicolas; Le Bihan, Denis; Ciobanu, Luisa

2012-03-20

123

Experimental demonstration of diffusion signal enhancement in 2D DESIRE images  

NASA Astrophysics Data System (ADS)

In magnetic resonance microscopy based on conventional Fourier encoding techniques, molecular self-diffusion leads to a loss in signal to noise ratio while also limiting the spatial resolution. As opposed to standard diffusion-weighted sequences, the DESIRE (Diffusion Enhancement of SIgnal and REsolution) method gains signal through diffusion via a signal difference measurement, corresponding to the total number of spins saturated by a localized pulse applied for a given amount of time. The higher the diffusion coefficient at that location, the larger the number of spins effectively saturated and thus the higher the difference in signal. While the method has been previously demonstrated in 1D, the availability of higher magnetic fields and gradient strengths has recently brought its development within reach in 2D. Here we report the implementation of 2D DESIRE and the first experimental evaluation of enhancements in water and thin silicone oil. Enhancement levels obtained by saturating a 60 ?m diameter region (effectively ˜140 ?m) and allowing diffusion lengths of 28 ?m or 7 ?m, respectively, are consistent with theoretical predictions. The typical enhancement values are 100% in water and 20% in silicone oil.

Jelescu, Ileana O.; Boulant, Nicolas; Le Bihan, Denis; Ciobanu, Luisa

2012-05-01

124

A hybrid preprocessing method using geometry based diffusion and elective enhancement filtering for pulmonary nodule detection  

NASA Astrophysics Data System (ADS)

The computer aided diagnostic (CAD) system has been developed to assist radiologist for early detection and analysis of lung nodules. For pulmonary nodule detection, image preprocessing is required to remove the anatomical structure of lung parenchyma and to enhance the visibility of pulmonary nodules. In this paper a hybrid preprocessing technique using geometry based diffusion and selective enhancement filtering have been proposed. This technique provides a unified preprocessing framework for solid nodule as well as ground glass opacity (GGO) nodules. Geometry based diffusion is applied to smooth the images by preserving the boundary. In order to improve the sensitivity of pulmonary nodule detection, selective enhancement filter is used to highlight blob like structure. But selective enhancement filter sometimes enhances the structures like blood vessel and airways other than nodule and results in large number of false positive. In first step, geometry based diffusion (GBD) is applied for reduction of false positive and in second step, selective enhancement filtering is used for further reduction of false negative. Geometry based diffusion and selective enhancement filtering has been used as preprocessing step separately but their combined effect was not investigated earlier. This hybrid preprocessing approach is suitable for accurate calculation of voxel based features. The proposed method has been validated on one public database named Lung Image Database Consortium (LIDC) containing 50 nodules (30 solid and 20 GGO nodule) from 30 subjects and one private database containing 40 nodules (25 solid and 15 GGO nodule) from 30 subjects.

Dhara, Ashis K.; Mukhopadhyay, Sudipta

2012-02-01

125

Transiently enhanced LPS-induced fever following hyperthermic stress in rabbits  

NASA Astrophysics Data System (ADS)

Hyperthermia has been shown to induce an enhanced febrile response to the bacterial-derived endotoxin lipopolysaccharide (LPS). The aim of the present study was to test the hypothesis that the enhanced LPS-induced fever seen in heat stressed (HS) animals is caused by leakage of intestinal bacterial LPS into the circulation. Male rabbits were rendered transiently hyperthermic (a maximum rectal temperature of 43°C) and divided into three groups. They were then allowed to recover in a room at 24°C for 1, 2 or 3 days post-HS. One day after injection with LPS, the post-HS rabbits exhibited significantly higher fevers than the controls, though this was not seen in rabbits at either 2 or 3 days post-HS. The plasma levels of endogenous LPS were significantly increased during the HS as compared to those seen in normothermic rabbits prior to HS. LPS fevers were not induced in these animals. One day post-HS, rabbits that had been pretreated with oral antibiotics exhibited significantly attenuated LPS levels. When challenged with human recombinant interleukin-1? instead of LPS, the 1-day post-HS rabbits did not respond with enhanced fevers. The plasma levels of TNF? increased similarly during LPS-induced fevers in both the control and 1-day post-HS rabbits, while the plasma levels of corticosterone and the osmolality of the 1-day post-HS rabbits showed no significant differences to those seen prior to the HS. These results suggest that the enhanced fever in the 1-day post-HS rabbits is LPS specific, and may be caused by increased leakage of intestinal endotoxin into blood circulation.

Shibata, Masaaki; Uno, Tadashi; Riedel, Walter; Nishimaki, Michiyo; Watanabe, Kaori

2005-11-01

126

A Multigroup diffusion solver using pseudo transient continuation for a radiation-hydrodynamic code with patch-based AMR  

SciTech Connect

We present a scheme to solve the nonlinear multigroup radiation diffusion (MGD) equations. The method is incorporated into a massively parallel, multidimensional, Eulerian radiation-hydrodynamic code with adaptive mesh refinement (AMR). The patch-based AMR algorithm refines in both space and time creating a hierarchy of levels, coarsest to finest. The physics modules are time-advanced using operator splitting. On each level, separate 'level-solve' packages advance the modules. Our multigroup level-solve adapts an implicit procedure which leads to a two-step iterative scheme that alternates between elliptic solves for each group with intra-cell group coupling. For robustness, we introduce pseudo transient continuation ({Psi}tc). We analyze the magnitude of the {Psi}tc parameter to ensure positivity of the resulting linear system, diagonal dominance and convergence of the two-step scheme. For AMR, a level defines a subdomain for refinement. For diffusive processes such as MGD, the refined level uses Dirichet boundary data at the coarse-fine interface and the data is derived from the coarse level solution. After advancing on the fine level, an additional procedure, the sync-solve (SS), is required in order to enforce conservation. The MGD SS reduces to an elliptic solve on a combined grid for a system of G equations, where G is the number of groups. We adapt the 'partial temperature' scheme for the SS; hence, we reuse the infrastructure developed for scalar equations. Results are presented. We consider a multigroup test problem with a known analytic solution. We demonstrate utility of {Psi}tc by running with increasingly larger timesteps. Lastly, we simulate the sudden release of energy Y inside an Al sphere (r = 15 cm) suspended in air at STP. For Y = 11 kT, we find that gray radiation diffusion and MGD produce similar results. However, if Y = 1 MT, the two packages yield different results. Our large Y simulation contradicts a long-standing theory and demonstrates the inadequacy of gray diffusion.

Shestakov, A I; Offner, S R

2006-09-21

127

A Multigroup diffusion Solver Using Pseudo Transient Continuation for a Radiaiton-Hydrodynamic Code with Patch-Based AMR  

SciTech Connect

We present a scheme to solve the nonlinear multigroup radiation diffusion (MGD) equations. The method is incorporated into a massively parallel, multidimensional, Eulerian radiation-hydrodynamic code with adaptive mesh refinement (AMR). The patch-based AMR algorithm refines in both space and time creating a hierarchy of levels, coarsest to finest. The physics modules are time-advanced using operator splitting. On each level, separate 'level-solve' packages advance the modules. Our multigroup level-solve adapts an implicit procedure which leads to a two-step iterative scheme that alternates between elliptic solves for each group with intra-cell group coupling. For robustness, we introduce pseudo transient continuation ({Psi}tc). We analyze the magnitude of the {Psi}tc parameter to ensure positivity of the resulting linear system, diagonal dominance and convergence of the two-step scheme. For AMR, a level defines a subdomain for refinement. For diffusive processes such as MGD, the refined level uses Dirichet boundary data at the coarse-fine interface and the data is derived from the coarse level solution. After advancing on the fine level, an additional procedure, the sync-solve (SS), is required in order to enforce conservation. The MGD SS reduces to an elliptic solve on a combined grid for a system of G equations, where G is the number of groups. We adapt the 'partial temperature' scheme for the SS; hence, we reuse the infrastructure developed for scalar equations. Results are presented. We consider a multigroup test problem with a known analytic solution. We demonstrate utility of {Psi}tc by running with increasingly larger timesteps. Lastly, we simulate the sudden release of energy Y inside an Al sphere (r = 15 cm) suspended in air at STP. For Y = 11 kT, we find that gray radiation diffusion and MGD produce similar results. However, if Y = 1 MT, the two packages yield different results. Our large Y simulation contradicts a long-standing theory and demonstrates the inadequacy of gray diffusion.

Shestakov, A I; Offner, S R

2007-03-02

128

Molecular Dynamics Study of Superlattice Superionic Conductor: Enhancement of Oxygen Ion Diffusion in YSZ  

Microsoft Academic Search

A constant-volume molecular dynamics calculation has been performed for a cubic yttria-stabilized zirconia (Y2O3)c(ZrO2)1-c, where Y layers and Zr layers are alternately accumulated to form a superlattice. A considerable enhancement of the diffusion of oxygen ions was observed at the composition c=0.33, at which the diffusion coefficient in the superlattice is about three times larger than the case of a

Hideo Okazaki; Hisashi Suzuki; Katsuyoshi Ihata

1994-01-01

129

Enhanced ICBM Diffusion Tensor Template of the Human Brain  

PubMed Central

Development of a diffusion tensor (DT) template that is representative of the micro-architecture of the human brain is crucial for comparisons of neuronal structural integrity and brain connectivity across populations, as well as for the generation of a detailed white matter atlas. Furthermore, a DT template in ICBM space may simplify consolidation of information from DT, anatomical and functional MRI studies. The previously developed “IIT DT brain template” was produced in ICBM-152 space, based on a large number of subjects from a limited age-range, using data with minimal image artifacts, and non-linear registration. That template was characterized by higher image sharpness, provided the ability to distinguish smaller white matter fiber structures, and contained fewer image artifacts, than several previously published DT templates. However, low-dimensional registration was used in the development of that template, which led to a mismatch of DT information across subjects, eventually manifested as loss of local diffusion information and errors in the final tensors. Also, low-dimensional registration led to a mismatch of the anatomy in the IIT and ICBM-152 templates. In this work, a significantly improved DT brain template in ICBM-152 space was developed, using high-dimensional non-linear registration and the raw data collected for the purposes of the IIT template. The accuracy of inter-subject DT matching was significantly increased compared to that achieved for the development of the IIT template. Consequently, the new template contained DT information that was more representative of single-subject human brain data, and was characterized by higher image sharpness than the IIT template. Furthermore, a bootstrap approach demonstrated that the variance of tensor characteristics was lower in the new template. Additionally, compared to the IIT template, brain anatomy in the new template more accurately matched ICBM-152 space. Finally, spatial normalization of a number of DT datasets through registration to the new and existing IIT templates was improved when using the new template.

Zhang, Shengwei; Peng, Huiling; Dawe, Robert J.; Arfanakis, Konstantinos

2010-01-01

130

Temporal evolution and spatial distribution of the diffusion constant of water in rat brain after transient middle cerebral artery occlusion.  

PubMed

The regional distribution and temporal evolution of the diffusion coefficient (Dw) of water in rat brain was measured during and after transient middle cerebral artery (MCA) occlusion. Male Wistar rats (n = 14) were subjected to 2 h of middle cerebral artery occlusion, induced by intracarotid insertion of a filament. Diffusion (n = 14) and perfusion (n = 7) weighted magnetic resonance imaging were performed before, and at various time points after MCA occlusion, ranging from 30 min up to 7 days. Our data demonstrate that the temporal profiles of Dw differ between the severely and the least damaged regions of tissue. In the core of the lesion, where the tissue evolved to necrosis, Dw declined significantly (P < 0.001) within 0.5 h after onset of ischemia, and remained depressed until 24 h after withdrawal of the suture. However, no statistically significant decline in Dw was found in the perifocal regions containing morphologically intact cells. Perfusion MRI qualitatively exhibited a hypoperfusion and reperfusion during, and after 2 h MCA occlusion, respectively. A significant (r > or = 0.71, P < 0.01) correlation was found between delta Dw (the difference in Dw between the ipsilateral ischemic and homologous contralateral control regions) obtained immediately before withdrawal of the suture (2 h of ischemia) and at specific early time points after withdrawal of the suture, and the degree of ischemic cell damage. No significant (P > 0.01) correlation was detected at an early time points of ischemia or at other time points after withdrawal of the suture.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8138799

Jiang, Q; Zhang, Z G; Chopp, M; Helpern, J A; Ordidge, R J; Garcia, J H; Marchese, B A; Qing, Z X; Knight, R A

1993-12-15

131

Region-based adaptive anisotropic diffusion for image enhancement and denoising  

NASA Astrophysics Data System (ADS)

A novel region-based adaptive anisotropic diffusion (RAAD) is presented for image enhancement and denoising. The main idea of this algorithm is to perform the region-based adaptive segmentation. To this end, we use the eigenvalue difference of the structure tensor of each pixel to classify an image into homogeneous detail, and edge regions. According to the different types of regions, a variable weight is incorporated into the anisotropic diffusion partial differential equation for compromising the forward and backward diffusion, so that our algorithm can adaptively encourage strong smoothing in homogeneous regions and suitable sharpening in detail and edge regions. Furthermore, we present an adaptive gradient threshold selection strategy. We suggest that the optimal gradient threshold should be estimated as the mean of local intensity differences on the homogeneous regions. In addition, we modify the anisotropic diffusion discrete scheme by taking into account edge orientations. We believe our algorithm to be a novel mechanism for image enhancement and denoising. Qualitative experiments, based on various general digital images and several T1- and T2-weighted magnetic resonance simulated images, show significant improvements when the RAAD algorithm is used versus the existing anisotropic diffusion and the previous forward and backward diffusion algorithms for enhancing edge features and improving image contrast. Quantitative analyses, based on peak signal-to-noise ratio, the universal image quality index, and the structural similarity confirm the superiority of the proposed algorithm.

Wang, Yi; Niu, Ruiqing; Zhang, Liangpei; Shen, Huanfeng

2010-11-01

132

Study of the translational diffusion of the benzophenone ketyl radical in comparison with stable molecules in room temperature ionic liquids by transient grating spectroscopy  

SciTech Connect

Transient grating (TG) spectroscopy has been applied to the photoinduced hydrogen-abstraction reaction of benzophenone (BP) in various kinds of room temperature ionic liquids (RTILs). After the photoexcitation of BP in RTILs, the formation of a benzophenone ketyl radical (BPK) was confirmed by the transient absorption method, and the TG signal was analyzed to determine the diffusion coefficients of BPK and BP. For comparison, diffusion coefficients of carbon monoxide (CO), diphenylacetylene (DPA), and diphenylcyclopropenone (DPCP) in various RTILs were determined by the TG method using the photodissociation reaction of DPCP. While the diffusion coefficients of the stable molecules BP, DPA, and DPCP were always larger than those predicted by the Stokes-Einstein (SE) relation in RTILs, that of BPK was much smaller than those of the stable molecules and relatively close to that predicted by the SE relation in all solvents. For the smallest molecule CO, the deviation from the SE relation was evident. The diffusion coefficients of stable molecules are better represented by a power law of the inverse of the viscosity when the exponent was less than unity. The ratios of the diffusion coefficient of BP to that of BPK were larger in RTILs (2.7-4.0) than those (1.4-2.3) in conventional organic solvents. The slow diffusion of BPK in RTILs was discussed in terms of the fluctuation of the local electric field produced by the surrounding solvent ions.

Nishiyama, Y.; Fukuda, M.; Terazima, M.; Kimura, Y. [Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan)

2008-04-28

133

Numerical simulation of multicomponent gas diffusion and flow in coals for CO 2 enhanced coalbed methane recovery  

Microsoft Academic Search

This paper presents an alternative model of multicomponent gas diffusion and flow in bulk coals, focusing on CH4–CO2 counter-diffusion associated with CO2-sequestration enhanced coalbed methane (CO2-ECBM) recovery. The model was developed based on the bidisperse diffusion mechanism and the Maxwell–Stefan (MS) diffusion theory, which provides an improved simulation of multicomponent gas diffusion dynamics. The model was firstly validated under the

X. R. Wei; G. X. Wang; P. Massarotto; S. D. Golding; V. Rudolph

2007-01-01

134

Molecular dynamics simulation of enhanced oxygen ion diffusion in strained yttria-stabilized zirconia  

Microsoft Academic Search

The application of strain to yttria-stabilized zirconia (YSZ), which can be realized by sandwiching a thin YSZ film epitaxially between layers of a material with larger lattice constants, is proposed as a means to enhance oxygen ion mobility. The possible mechanism of such an enhancement was investigated by molecular dynamics using a CeO2-YSZ superlattice. The calculated diffusion coefficient of oxygen

Ken Suzuki; Momoji Kubo; Yasunori Oumi; Ryuji Miura; Hiromitsu Takaba; Adil Fahmi; Abhijit Chatterjee; Kazuo Teraishi; Akira Miyamoto

1998-01-01

135

FSH enhances the proliferation of ovarian cancer cells by activating transient receptor potential channel C3.  

PubMed

Recent studies have suggested that FSH plays an important role in ovarian epithelial carcinogenesis. We demonstrated that FSH stimulates the proliferation and invasion of ovarian cancer cells, inhibits apoptosis and facilitates neovascularisation. Our previous work has shown that transient receptor potential channel C3 (TRPC3) contributes to the progression of human ovarian cancer. In this study, we further investigated the interaction between FSH and TRPC3. We found that FSH stimulation enhanced the expression of TRPC3 at both the mRNA and protein levels. siRNA-mediated silencing of TRPC3 expression inhibited the ability of FSH to stimulate proliferation and blocked apoptosis in ovarian cancer cell lines. FSH stimulation was associated with the up-regulation of TRPC3, while also facilitating the influx of Ca(2)(+) after treatment with a TRPC-specific agonist. Knockdown of TRPC3 abrogated FSH-stimulated Akt/PKB phosphorylation, leading to decreased expression of downstream effectors including survivin, HIF1-? and VEGF. Ovarian cancer specimens were analysed for TRPC3 expression; higher TRPC3 expression levels correlated with early relapse and worse prognosis. Association with poor disease-free survival and overall survival remained after adjusting for clinical stage and grade. In conclusion, TRPC3 plays a significant role in the stimulating activity of FSH and could be a potential therapeutic target for the treatment of ovarian cancer, particularly in postmenopausal women with elevated FSH levels. PMID:23580589

Tao, Xiang; Zhao, Naiqing; Jin, Hongyan; Zhang, Zhenbo; Liu, Yintao; Wu, Jian; Bast, Robert C; Yu, Yinhua; Feng, Youji

2013-05-30

136

Transients of the electromagnetically-induced-transparency-enhanced refractive Kerr nonlinearity: Theory  

SciTech Connect

We present a theory describing the transients and rise times of the refractive Kerr nonlinearity which is enhanced using electromagnetically induced transparency (EIT). We restrict our analysis to the case of a pulsed signal field with continuous-wave EIT fields, and all fields are well below saturation. These restrictions enable the reduction of an EIT Kerr, four-level, density-matrix equation to a two-level Bloch-vector equation which has a simple and physically intuitive algebraic solution. The physically intuitive picture of a two-level Bloch vector provides insights that are easily generalized to more complex and experimentally realistic models. We consider generalization to the cases of Doppler broadening, many-level EIT systems (we consider the D1 line of {sup 87}Rb), and optically thick media. For the case of optically thick media we find that the rise time of the refractive EIT Kerr effect is proportional to the optical thickness. The rise time of the refractive EIT Kerr effect sets important limitations for potential few-photon applications.

Pack, M. V.; Camacho, R. M.; Howell, J. C. [Department of Physics, University of Rochester, Rochester, New York 14627 (United States)

2006-07-15

137

Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame.  

PubMed

The off-resonance rotating frame technique based on the spin relaxation properties of off-resonance T1rho can significantly increase the sensitivity of detecting paramagnetic labeling at high magnetic fields by MRI. However, the in vivo detectable dimension for labeled cell clusters/tissues in T1rho-weighted images is limited by the water diffusion-exchange between mesoscopic scale compartments. An experimental investigation of the effect of water diffusion-exchange between compartments on the paramagnetic relaxation enhancement of paramagnetic agent compartment is presented for in vitro/in vivo models. In these models, the size of paramagnetic agent compartment is comparable to the mean diffusion displacement of water molecules during the long RF pulses that are used to generate the off-resonance rotating frame. The three main objectives of this study were: (1) to qualitatively correlate the effect of water diffusion-exchange with the RF parameters of the long pulse and the rates of water diffusion, (2) to explore the effect of water diffusion-exchange on the paramagnetic relaxation enhancement in vitro, and (3) to demonstrate the paramagnetic relaxation enhancement in vivo. The in vitro models include the water permeable dialysis tubes or water permeable hollow fibers embedded in cross-linked proteins gels. The MWCO of the dialysis tubes was chosen from 0.1 to 15 kDa to control the water diffusion rate. Thin hollow fibers were chosen to provide sub-millimeter scale compartments for the paramagnetic agents. The in vivo model utilized the rat cerebral vasculatures as a paramagnetic agent compartment, and intravascular agents (Gd-DTPA)30-BSA were administrated into the compartment via bolus injections. Both in vitro and in vivo results demonstrate that the paramagnetic relaxation enhancement is predominant in the T1rho-weighted image in the presence of water diffusion-exchange. The T1rho contrast has substantially higher sensitivity than the conventional T1 contrast in detecting paramagnetic agents, especially at low paramagnetic agent volumetric fractions, low paramagnetic agent concentrations, and low RF amplitudes. Short pulse duration, short pulse recycle delay and efficient paramagnetic relaxation can reduce the influence of water diffusion-exchange on the paramagnetic enhancement. This study paves the way for the design of off-resonance rotating experiments to detect labeled cell clusters/tissue compartments in vivo at a sub-millimeter scale. PMID:17412624

Zhang, Huiming; Xie, Yang; Ji, Tongyu

2007-03-16

138

Effect of water vapor diffusion enhancement on soil moisture/temperature and evaporation - A numerical study  

NASA Astrophysics Data System (ADS)

Experimental and numerical studies concerning the coupled flow of liquid water and water vapor in porous media have shown differences in observed and Fickian diffusion-based modeled water vapor fluxes. Early studies explain these differences with evaporation-condensation effects in liquid islands in the variably saturated zone and enhanced water vapor flux due to local thermal gradients which differ between the different phases (air, water and solid) due to non-equilibrium effects at the pore scale. Consequently, an "enhancement factor" was introduced to correct for differences between model simulations and observations. Although widely used, recent studies question the existence of enhanced vapor diffusion because enhanced vapor-phase diffusion has never been measured or observed directly. In this contribution, we present results from numerical experiments in which we simulate coupled water and heat flow. The impact of the enhancement factor was evaluated by including or excluding it in the parameterization of the systems' properties. We designed three different model scenarios: one scenario with boundary conditions that represent field conditions and two scenarios representing different kinds of laboratory soil column experiments, to investigate under which conditions the impact of the enhancement factor could be observed in experiments. Finally, we tested with model simulations whether liquid water flow in films, which is not considered in the classical Mualem- van Genuchten parameterization of the hydraulic conductivity curve, can be an alternative explanation for larger than expected evaporation fluxes.

Steenpass, Christian; Vanderborght, Jan; Huisman, Johan Alexander

2010-05-01

139

Defect Enhanced Diffusion Process and Hydrogen Delayed Fracture in High Strength Steels.  

National Technical Information Service (NTIS)

A defect enhanced diffusion model for hydrogen delayed fracture in high strength steels is suggested. It is shown that the rate of crack growth is dependent on the square or higher power of the stress intensity factor which is consistent with recent exper...

C. W. Lung Mu Zaiqin

1985-01-01

140

Enhanced Vapor-Phase Diffusion in Porous Media - LDRD Final Report  

Microsoft Academic Search

As part of the Laboratory-Directed Research and Development (LDRD) Program at Sandia National Laboratories, an investigation into the existence of enhanced vapor-phase diffusion (EVD) in porous media has been conducted. A thorough literature review was initially performed across multiple disciplines (soil science and engineering), and based on this review, the existence of EVD was found to be questionable. As a

C. K. Ho; S. W. Webb

1999-01-01

141

Effect of water vapor diffusion enhancement on soil moisture\\/temperature and evaporation - A numerical study  

Microsoft Academic Search

Experimental and numerical studies concerning the coupled flow of liquid water and water vapor in porous media have shown differences in observed and Fickian diffusion-based modeled water vapor fluxes. Early studies explain these differences with evaporation-condensation effects in liquid islands in the variably saturated zone and enhanced water vapor flux due to local thermal gradients which differ between the different

Christian Steenpass; Jan Vanderborght; Johan Alexander Huisman

2010-01-01

142

Diffusivity measurement of semi-transparent media: model of the coupled transient heat transfer and experiments on glass, silica glass and zinc selenide  

Microsoft Academic Search

The aim of this theoretical and experimental study is to provide a complete methodology to estimate the intrinsic diffusivity of semi-transparent media from flash method experiments. A semi-analytical model describes the coupled conductive–radiative transient heat transfer in a slab. The relevance of the model used for the inversion is then investigated. Experimental results are presented for several semi-transparent samples: float

M Lazard; S André; D Maillet

2004-01-01

143

Cosolute Paramagnetic Relaxation Enhancements Detect Transient Conformations of Human Uracil DNA Glycosylase (hUNG)  

PubMed Central

The human DNA repair enzyme uracil DNA glycosylase (hUNG) locates and excises rare uracil bases that arise in DNA from cytosine deamination or through dUTP incorporation by DNA polymerases. Previous NMR studies of hUNG have revealed millisecond time scale dynamic transitions in the enzyme-nonspecific DNA complex, but not the free enzyme, that were ascribed to a reversible clamping motion of the enzyme as it scans along short regions of duplex DNA in its search for uracil. Here we further probe the properties of the nonspecific DNA binding surface of {2H12C}{15N}-labeled hUNG using a neutral chelate of a paramagnetic Gd3+ cosolute (Gd(HP-DO3A)). Overall, the measured paramagnetic relaxation enhancements (PREs) on R2 of the backbone amide protons for free hUNG and its DNA complex were in good agreement with those calculated based on their relative exposure observed in the crystal structures of both enzyme forms. However, the calculated PREs systematically underestimated the experimental PREs by large amounts in discrete regions implicated in DNA recognition and catalysis: active site loops involved in DNA recognition (268–274, 246–250), the uracil binding pocket (143–148, 169–170), a transient extrahelical base binding site (214–216), and a remote hinge region (129–132) implicated in dynamic clamping. These reactive hot spots were not correlated with electrostatic, structural or hydrophobic properties that might be common to these regions, leaving the possibility that the effects arise from dynamic sampling of exposed conformations that are distinct from the static structures. Consistent with this suggestion, the above regions have been previously shown to be flexible based on relaxation dispersion measurements and course-grained normal mode analysis. A model is suggested where the intrinsic dynamic properties of these regions allows sampling of transient conformations where the backbone amide groups have greater average exposure to solvent as compared to the static structures. We conclude that PREs derived from the paramagnetic cosolute reveal dynamic hot spots in hUNG and that these regions are highly correlated with substrate binding and recognition.

Sun, Yan; Friedman, Joshua I.; Stivers, James T.

2011-01-01

144

Control of grid-connected fuel cell power plant for transient stability enhancement  

Microsoft Academic Search

This paper describes a dynamic model of a SOFC fuel cell, which can be used in transient stability studies. The model is applied to a distributed utility grid that uses a fuel cell and a gas turbine as distributed generators (DGs). Transient stability of the system is investigated for different DGs power outputs using a software developed based on the

K. Sedghisigarchi; A. Feliachi

2002-01-01

145

Can Enhanced Diffusion Improve Helioseismic Agreement for Solar Models with Revised Abundances?  

NASA Astrophysics Data System (ADS)

Recent solar photospheric abundance analyses (by Asplund et al. and Lodders) revise the C, N, O, Ne, and Ar abundances downward by 0.15-0.2 dex compared to previous determinations by Grevesse & Sauval. The abundances of Fe and other elements are reduced by smaller amounts, 0.05-0.1 dex. With these revisions, the photospheric Z/X decreases to 0.0165 (or 0.0177, according to Lodders), and Z decreases to ~0.0122 (or 0.0133, according to Lodders). A number of papers (by, e.g., Basu & Antia, Montalban et al., Bahcall & Pinsonneault, Turck-Chièze et al., and Antia & Basu) report that solar models evolved with standard opacities and diffusion treatment using these new abundances give poor agreement with helioseismic inferences for sound-speed and density profile, convection-zone helium abundance, and convection-zone depth. These authors also considered a limited set of models with increased opacities, enhanced diffusion, or abundance variations to improve agreement, finding no entirely satisfactory solution. Here we explore evolved solar models with varying diffusion treatments, including enhanced diffusion with separate multipliers for helium and other elements, to reduce the photospheric abundances, while keeping the interior abundances about the same as earlier standard models. While enhanced diffusion improves agreement with some helioseismic constraints compared to a solar model evolved with the new abundances using nominal input physics, the required increases in thermal diffusion rates are unphysically large, and none of the variations tried completely restores the good agreement attained using the earlier abundances. A combination of modest opacity increases, diffusion enhancements, and abundance increases near the level of the uncertainties, while somewhat contrived, remains the most physically plausible means to restore agreement with helioseismology. The case for enhanced diffusion would be improved if the inferred convection-zone helium abundance could be reduced; we recommend reconsidering this derivation in light of new equations of state with modified abundances and other improvements. We also recommend considering, as a last resort, diluting the convection zone, which contains only 2.5% of the Sun's mass, by accretion of material depleted in the more volatile elements C, N, O, Ne, and Ar after the Sun arrived on the main sequence.

Guzik, Joyce A.; Watson, L. Scott; Cox, Arthur N.

2005-07-01

146

Monitoring Response to Convection-enhanced Taxol Delivery in Brain Tumor Patients Using Diffusion-weighted Magnetic Resonance Imaging1  

Microsoft Academic Search

Convection-enhanced drug delivery (CEDD) is a novel approach to enhance the delivery of drugs directly into brain tumors. We have used diffusion-weighted MRI (DWMRI) to monitor the effects of intratumoral CEDD in three brain tumor patients treated with Taxol. Clear changes in the images and the water diffusion parameters were observed shortly after the initiation of treatment. Initially, a bright

Yael Mardor; Yiftach Roth; Zvi Lidar; Tali Jonas; Raphael Pfeffer; Stephan E. Maier; Meir Faibel; Dvora Nass; Moshe Hadani; Arie Orenstein; Jack S. Cohen; Zvi Ram

147

Quartz veins deformed by diffusion creep-accommodated grain boundary sliding during a transient, high strain-rate event in the Southern Alps, New Zealand  

NASA Astrophysics Data System (ADS)

The crystallographic preferred orientations (CPOs) and microstructures of deformed quartz veins were measured for four samples in the hanging-wall of the Alpine Fault in the Southern Alps, New Zealand. Their deformation and exhumation has occurred since 4 Ma. The quartz veins have been ductilely sheared to finite shear-strains of 5 15 in late Cenozoic shear zones at 450±50 °C, 310±90 MPa and strain-rates between 2×10-11 and 2×10-9 s-1. The sheared veins have a polygonal microstructure with few subgrains and an average grain-size of ˜100 ?m. The CPO of the veins is random to very weak within the shear zones. We suggest that dislocation creep accommodated initial shear deformation, at high stresses and strain-rates. The deformation must have created a strong CPO and concomitant dynamic recrystallization reduced the grain-size significantly. Dissipation of stresses during initial deformation lead to a stress and strain-rate drop required for a switch to diffusion creep-accommodated grain boundary sliding (GBS). Continued shearing accommodated by GBS destroyed the CPO. Post-deformational grain growth gave rise to a final polygonal microstructure with a similar grain size in veins and in the wall rocks. Analysis of existing experimental data suggest that this sequence of events is possible in the time available. Rates of all processes may have been enhanced by the presence of a water-rich fluid within the shear zones. These observations of naturally deformed rocks provide a model for the processes that may occur during short-lived deformation at transiently-high stresses at mid-crustal depths or deeper.

Wightman, Ruth H.; Prior, David J.; Little, Timothy A.

2006-05-01

148

The Range of Diffusion Enhancement of B and P in Si during Thermal Oxidation  

NASA Astrophysics Data System (ADS)

The lateral range of oxidation enhanced diffusion (OED) of B and P in Si is investigated using selective oxidation at 1100°C with directly formed Si3N4 films as oxidation resistant masks and FZ Si crystals as substrates. It is found that this OED range of B agrees well with that of P and that the range increases with oxidation time. The value of the range is found to be much larger than previously. The results can be explained using a model in which the range is determined by interstitial diffusion.

Mizuo, Shoichi; Higuchi, Hisayuki

1982-02-01

149

Enhanced diffusion of solute metals forming complexes with radiation defects in silica  

NASA Astrophysics Data System (ADS)

The mixing kinetics of Cu, Ag, W, Pt, and Au single layers embedded in silica when irradiated with heavy ions at temperatures (T) of 110 and 300K was investigated by means of in situ RBS analyses in alternation with irradiations. The spreading of peaks related to the metallic species is generally anisotropic and obeys either a quadratic or a linear dependence on the ion dose according to the increasing T. The quadratic law is attributed to a control of the diffusion by the coupling of the large impurity atoms M with matrix defects, and a classical regime of radiation enhanced diffusion is observed when this coupling is made easier (higher T or mass of M). Other factors such as internal stresses affect the rates of M dissolution and diffusion.

Pivin, J. C.; Garrido, E.; Rizza, G.; Thome, L.

1998-05-01

150

Biopsy-Controlled Liver Fibrosis Staging Using the Enhanced Liver Fibrosis (ELF) Score Compared to Transient Elastography  

PubMed Central

Background and Aims Chronic liver diseases are characterized by inflammatory and fibrotic liver injuries that often result in liver cirrhosis with its associated complications such as portal hypertension and hepatocellular carcinoma. Liver biopsy still represents the reference standard for fibrosis staging, although transient elastography is increasingly used for non-invasive monitoring of fibrosis progression. However, this method is not generally available and is associated with technical limitations emphasizing the need for serological biomarkers staging of liver fibrosis. The enhanced liver fibrosis (ELF) score was shown to accurately predict significant liver fibrosis in different liver diseases, although extracellular matrix components detected by this score may not only mirror the extent of liver fibrosis but also inflammatory processes. Methods In this prospective biopsy-controlled study we evaluated the utility of the ELF score in comparison to transient elastography to predict different stages of fibrosis in 102 patients with chronic liver diseases. Results Both techniques revealed similar area under receiver operating characteristic curve values for prediction of advanced fibrosis stages. Compared to transient elastography, the ELF score showed a broader overlap between low and moderate fibrosis stages and a stronger correlation with inflammatory liver injury. Conclusions Both the ELF score as well as transient elastography allowed for high quality fibrosis staging. However, the ELF score was less discriminative in low and moderate fibrosis stages and appeared more strongly influenced by inflammatory liver injury. This should be considered when making clinical interpretations on the basis of ELF score values.

Wahl, Kristin; Rosenberg, William; Vaske, Bernhard; Manns, Michael P.; Schulze-Osthoff, Klaus; Bahr, Matthias J.; Bantel, Heike

2012-01-01

151

Enhancement of hyperspectral imagery using spectrally weighted tensor anisotropic nonlinear diffusion for classification  

NASA Astrophysics Data System (ADS)

Tensor Anisotropic Nonlinear Diffusion (TAND) is a divergence PDE-based diffusion technique that is "guided" by an edge descriptor, such as the structure tensor, to stir the diffusion. The structure tensor for vector valued images such as HSI is most often defined as the average of the scalar structure tensors for each band. The problem with this definition is the assumption that all bands provide the same amount of edge information giving them the same weights. As a result non-edge pixels can be reinforced and edges can be weakened resulting in poor performance by processes that depend on the structure tensor. Iterative processes such as TAND, in particular, are vulnerable to this phenomenon. Recently a weighted structure tensor based on the heat operator has been proposed [1]. The weights are based on the heat operator. This tensor takes advantage of the fact that, in HSI, neighboring spectral bands are highly correlated, as are the bands of its gradient. By taking advantage of local spectral information, the proposed scheme gives higher weighting to local spectral features that could be related to edge information allowing the diffusion process to better enhance edges while smoothing out uniform regions facilitating the process of classification. This article present how classification results are affected by using TAND based on the heat weighted structure tensor as an image enhancement step in a classification system.

Marin-Mcgee, Maider J.; Velez-Reyes, Miguel

2013-05-01

152

Heavy ion irradiation of glasses: Enhanced diffusion and preferential sputtering of alkali elements  

Microsoft Academic Search

Soda-lime glasses have been irradiated by using different ions (H, N, O, Ne, Ar, Kr) in 20–300 keV energy range. The observed modifications in the alkali depth distribution have been analyzed on the basis of a phenomenological model, which takes into account for an enhanced diffusion and a surface preferential sputtering. A correlation between the alkali sputtering cross-section and the

G. Battaglin; A. Boscoletto; G. Della Mea; G. De Marchi; P. Mazzoldi; A. Miotello; B. Tiveron

1986-01-01

153

Oxygen diffusion in minihemoglobin from Cerebratulus lacteus : a locally enhanced sampling study  

Microsoft Academic Search

Heme proteins serve as a source of oxygen in nervous tissue during anoxia. The functional routes of a dioxygen (O\\u000a 2) diffusion in a novel structure of a minihemoglobin (CerHb) molecule present in worm Cerebratulus lacteus are not known. In this paper, the results of 1ns molecular dynamics simulations of this process are presented. The locally\\u000a enhanced sampling method (LES)

Slawomir Orlowski; Wieslaw Nowak

2007-01-01

154

Concurrent MRI and diffuse optical tomography of breast after indocyanine green enhancement  

PubMed Central

We present quantitative optical images of human breast in vivo. The images were obtained by using near-infrared diffuse optical tomography (DOT) after the administration of indocyanine green (ICG) for contrast enhancement. The optical examination was performed concurrently with a magnetic resonance imaging (MRI) exam on patients scheduled for excisional biopsy or surgery so that accurate image coregistration and histopathological information of the suspicious lesions was available. The ICG-enhanced optical images coregistered accurately with Gadolinium-enhanced magnetic resonance images validating the ability of DOT to image breast tissue. In contrast to simple transillumination, we found that DOT provides for localization and quantification of exogenous tissue chromophore concentrations. Additionally our use of ICG, an albumin bound absorbing dye in plasma, demonstrates the potential to differentiate disease based on the quantified enhancement of suspicious lesions.

Ntziachristos, Vasilis; Yodh, A. G.; Schnall, Mitchell; Chance, Britton

2000-01-01

155

Cooperative enhancement of TPA in cruciform double-chain DSB derivation: a femtosecond transient absorption spectra study  

NASA Astrophysics Data System (ADS)

Femtosecond time-resolved transient absorption (TA) spectra study was adopted to study the mechanism of the cooperative enhancement of two-photon absorption (TPA) cross section from the linear structure 1,4-di(4'-N,N-diphenylaminostyryl)benzene (DPA-DSB) to its cruciform double-chain dimer DPA-TSB. The results suggested that a non-emissive intramolecular charge-transfer (ICT) state, ICT’, was present upon excitation in the dimer, which was absent in the monomer. The existence of this non-emissive state, indicating the enhancement of the intramolecular charge-transfer of the dimer, should be the reason for the cooperative enhancement of the TPA cross section of the dimer compared to the monomer.

He, X.; Wang, Y.; Yang, Z.; Ma, Y.; Yang, Y.

2010-09-01

156

Effects of Pulse Current on Transient Liquid Phase (TLP) Diffusion Bonding of SiCp/2024Al Composites Sheet Using Mixed Al, Cu, and Ti Powder Interlayer  

NASA Astrophysics Data System (ADS)

The effects of pulse current on transient liquid phase (TLP) diffusion bonding of SiCp/2024Al composites sheet were investigated at 853 K (580 °C) using a mixed slurry of Al, Cu, and Ti powder interlayer. The process parameters were as follows: the pulse current density of 1.15 × 102 A/mm2, the original pressure of 0.5 MPa, the vacuum of 1.3 × 10-3 Pa, and the bonding time from 15 to 60 minutes. Moreover, the bonding mechanism in correlation with the microstructural and mechanical properties variation was analyzed.

Wang, Bo; Jiang, Shaosong; Zhang, Kaifeng

2012-09-01

157

Enhanced Vapor-Phase Diffusion in Porous Media - LDRD Final Report  

SciTech Connect

As part of the Laboratory-Directed Research and Development (LDRD) Program at Sandia National Laboratories, an investigation into the existence of enhanced vapor-phase diffusion (EVD) in porous media has been conducted. A thorough literature review was initially performed across multiple disciplines (soil science and engineering), and based on this review, the existence of EVD was found to be questionable. As a result, modeling and experiments were initiated to investigate the existence of EVD. In this LDRD, the first mechanistic model of EVD was developed which demonstrated the mechanisms responsible for EVD. The first direct measurements of EVD have also been conducted at multiple scales. Measurements have been made at the pore scale, in a two- dimensional network as represented by a fracture aperture, and in a porous medium. Significant enhancement of vapor-phase transport relative to Fickian diffusion was measured in all cases. The modeling and experimental results provide additional mechanisms for EVD beyond those presented by the generally accepted model of Philip and deVries (1957), which required a thermal gradient for EVD to exist. Modeling and experimental results show significant enhancement under isothermal conditions. Application of EVD to vapor transport in the near-surface vadose zone show a significant variation between no enhancement, the model of Philip and deVries, and the present results. Based on this information, the model of Philip and deVries may need to be modified, and additional studies are recommended.

Ho, C.K.; Webb, S.W.

1999-01-01

158

Transient Enhancement and Detuning of Laser-Driven Parametric Instabilities by Particle Trapping  

Microsoft Academic Search

Kinetic simulations of backward stimulated Raman scattering (BSRS), where the Langmuir wave coherence time is greater than the bounce time for trapped electrons, yield transient reflectivity levels far above those predicted by fluidlike models. Electron trapping reduces the Langmuir wave damping and lowers the Langmuir wave frequency, and leads to a secular phase shift between the Langmuir wave and the

H. X. Vu; D. F. Dubois; B. Bezzerides

2001-01-01

159

Voltage regulation and transient stability enhancement of a radial AC transmission system using UPFC  

Microsoft Academic Search

The unified power flow controller (UPFC) is a typical FACTS (flexible AC transmission systems) device that is capable of the instantaneous control of transmission line parameters. This paper presents the transient model and control system of UPFC. The presented control system enables the UPFC to following the exchanges of line active and reactive power reference values, regulating the DC link

S. H. Hosseini; A. Ajami

2004-01-01

160

OBSERVATION OF LARGE TRANSIENT FIELD ENHANCEMENTS IN PHOTOCONDUCTIVE ZnSe SWITCHES  

Microsoft Academic Search

Photoconductive switching using polycrystalline ZnSe with transparent liquid electrolytic electrode under pulsed bias was investigated. Nonlinear optical transmission which is due to high internal electric fields of this switch under moderate biases was observed. The temporal behavior of the optical transmission shows large transient field-induced optical absorption followed by an increase of optical trunsmission. From the optical transmission measurements, large

Pak S. Cho; Julius Goldhar; Chi H. Lee

1993-01-01

161

Diffusion  

NSDL National Science Digital Library

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

Christopher Thomas (None;)

2006-11-09

162

Enhanced Carbon Diffusion in Austenitic Stainless Steel Carburized at Low Temperature  

NASA Astrophysics Data System (ADS)

Austenitic stainless steel AISI 316L was carburized by a novel, low-temperature gas-phase process. Using a calibrated scanning Auger microprobe (SAM) analysis of cross-sectional specimens under dynamic sputtering, we determined the fraction-depth profile of carbon. The profile is concave—very different from the shape expected for concentration-independent diffusion—and indicates a carbide-free solid solution with carbon levels up to 15 at. pct and a case depth of ?30 ?m. A Boltzmann-Matano analysis with a careful evaluation of the stochastic and potential systematic errors indicates that increasing levels of carbon significantly enhance carbon diffusion. For the highest carbon level observed (15 at. pct), the carbon diffusion coefficient is more than two orders of magnitude larger than in dilute solution. The most likely explanation for this strong increase is that carbon-induced local expansion of metal-metal atom distances, observed as an expansion of the lattice parameter, reduces the activation energy for carbon diffusion.

Ernst, F.; Avishai, A.; Kahn, H.; Gu, X.; Michal, G. M.; Heuer, A. H.

2009-08-01

163

Field enhanced diffusion of nitrogen and boron in 4H-silicon carbide  

NASA Astrophysics Data System (ADS)

A field enhanced diffusion (FED) model is proposed for the observed phenomenon of dopant migration within 4H silicon carbide (4H-SiC) during high temperature annealing. The proposed FED model is based on the combined effects of both dopant diffusion and the in-built p-n junction electric field gradients found within the doped substrate resulting from the presence of the substrate dopants. Measured as-implanted dopant concentration profile data prior to high temperature annealing are utilized as input data for the proposed FED model. The resultant FED profile predictions of the proposed model during annealing are shown to be in excellent agreement with experimental findings. Parameters are extracted using the FED model simulation for the high temperature ionic diffusivity and ionic field mobility for nitrogen dopant in boron co-doped 4H-SiC. The extracted values for the ionic diffusivity and the ionic mobility of the nitrogen donor in boron co-doped 4H-SiC found using the model are 7.2×10-15 cm2 s-1 and 1.6×10-13 cm2 V-1 s-1, respectively.

Phelps, G. J.; Chester, E. G.; Johnson, C. M.; Wright, N. G.

2003-10-01

164

An extended convection diffusion model for red blood cell-enhanced transport of thrombocytes and leukocytes  

NASA Astrophysics Data System (ADS)

Transport phenomena of platelets and white blood cells (WBCs) are fundamental to the processes of vascular disease and thrombosis. Unfortunately, the dilute volume occupied by these cells is not amenable to fluid-continuum modeling, and yet the cell count is large enough that modeling each individual cell is impractical for most applications. The most feasible option is to treat them as dilute species governed by convection and diffusion; however, this is further complicated by the role of the red blood cell (RBC) phase on the transport of these cells. We therefore propose an extended convection-diffusion (ECD) model based on the diffusive balance of a fictitious field potential, ?, that accounts for the gradients of both the dilute phase and the local hematocrit. The ECD model was applied to the flow of blood in a tube and between parallel plates in which a profile for the RBC concentration field was imposed and the resulting platelet concentration field predicted. Compared to prevailing enhanced-diffusion models that dispersed the platelet concentration field, the ECD model was able to simulate a near-wall platelet excess, as observed experimentally. The extension of the ECD model depends only on the ability to prescribe the hematocrit distribution, and therefore may be applied to a wide variety of geometries to investigate platelet-mediated vascular disease and device-related thrombosis.

Hund, S. J.; Antaki, J. F.

2009-10-01

165

Determination of Reduced Number and Suitable Locations of Fuzzy Logic Controlled Braking Resistors for Transient Stability Enhancement  

NASA Astrophysics Data System (ADS)

Braking resistor is known to be a very powerful tool for transient stability improvement in electric power systems. Usually, in a large power system braking resistors are placed at each generator terminal bus which requires a high installation as well as operation cost. Also, heavy computation is required for the controllers used for the switching of the resistors. From these viewpoints, this paper directs to the study of installation of reduced number of fuzzy logic controlled braking resistors at suitable locations for transient stability enhancement. Groups of coherent generators in the power system are determined. Then one braking resistor is installed in each of the coherent group and at each of the remaining generator terminal bus. Thus, the number of braking resistors is reduced and hence the installation and operation cost as well as computational burden for the controllers are minimized. The suitable location for the braking resistor in each coherent group of generators is determined according to the values of the transient stability index as calculated for a 3LG (Three-phase-to-ground) fault at the points near the generators of the coherent group without considering the braking resistors in the system. The effectiveness of the proposed method is demonstrated through EMTP simulations for the IEEJ West-10 machine model system.

Ali, Mohd. Hasan; Murata, Toshiaki; Tamura, Junji

166

Analysis of Oxidation-Enhanced/Retarded Diffusions of Substitutional Impurities in Silicon  

NASA Astrophysics Data System (ADS)

Oxidation-enhanced/retarded diffusions of substitutional impurities in Si(OED/ORD) are generally expressed by well-known equations consisting of self-interstitial and vacancy concentrations (I and V). From the asymptotic forms of the formal solutions of those equations, an approximate relation between I and V was obtained in the time range of interest. Identifying this approximate relation with that of local equilibrium between I and V gave a simple method by which to obtain mathematically self-consistent solutions of OED and ORD equations. Consequently, I and V were obtained as functions of the diffusion time. The fractional components of the interstitialcy mechanism for OED of P and ORD of Sb (d1P and d1Sb) were obtained, with the first results being independent of time, i.e., d1P{=}0.93 and d1Sb{=}0.029 at 1100°C.

Okino, Takahisa

1992-04-01

167

Enhancement in Diffusion of Electrolyte through Membrane Using Ultrasonic Dialysis Equipment with Plane Membrane  

NASA Astrophysics Data System (ADS)

Application of ultrasound to accelerate the dialysis separation of electrolytes through a membrane was studied with ultrasonic dialysis equipment. The experiments were conducted with cellophane membrane and KCl solution, CH3COONa solution, and a mixture of KCl and saponin solutions. It was found that the diffusion velocity of electrolyte through a membrane with ultrasonic irradiation is faster than that without ultrasonic irradiation, and it increases with acoustic pressure. It has become clear that the reasons for enhancement caused by ultrasound are increase in liquid particle velocity and diffusion coefficient due to ultrasonic vibration. It was confirmed that the permeability of the membrane was not degraded by ultrasound in the ranges of acoustic pressure and irradiation time in this study.

Li, Hui; Ohdaira, Etsuzo; Ide, Masao

1995-05-01

168

Self-assembled subnanolayers as interfacial adhesion enhancers and diffusion barriers for integrated circuits  

NASA Astrophysics Data System (ADS)

Preserving the structural and functional integrity of interfaces and inhibiting deleterious chemical interactions are critical for realizing devices with sub-50 nm thin films and nanoscale units. Here, we demonstrate that ~0.7-nm-thick self-assembled monolayers (SAMs) comprising mercapto-propyl-tri-methoxy-silane (MPTMS) molecules enhance adhesion and inhibit Cu diffusion at Cu/SiO2 structures used in device metallization. Cu/SAM/SiO2/Si(001) structures show three times higher interface debond energy compared to Cu/SiO2 interfaces due to a strong chemical interaction between Cu and S termini of the MPTMS SAMs. This interaction immobilizes Cu at the Cu/SAM interface and results in a factor-of-4 increase in Cu-diffusion-induced failure times compared with that for structures without SAMs.

Ramanath, G.; Cui, G.; Ganesan, P. G.; Guo, X.; Ellis, A. V.; Stukowski, M.; Vijayamohanan, K.; Doppelt, P.; Lane, M.

2003-07-01

169

Heat transport in the XXZ spin chain: from ballistic to diffusive regimes and dephasing enhancement  

NASA Astrophysics Data System (ADS)

In this work we study the heat transport in an XXZ spin-1/2 Heisenberg chain with homogeneous magnetic field, incoherently driven out of equilibrium by reservoirs at the boundaries. We focus on the effect of bulk dephasing (energy-dissipative) processes in different parameter regimes of the system. The non-equilibrium steady state of the chain is obtained by simulating its evolution under the corresponding Lindblad master equation, using the time evolving block decimation method. In the absence of dephasing, the heat transport is ballistic for weak interactions, while being diffusive in the strongly interacting regime, as evidenced by the heat current scaling with the system size. When bulk dephasing takes place in the system, diffusive transport is induced in the weakly interacting regime, with the heat current monotonically decreasing with the dephasing rate. In contrast, in the strongly interacting regime, the heat current can be significantly enhanced by dephasing for systems of small size.

Mendoza-Arenas, J. J.; Al-Assam, S.; Clark, S. R.; Jaksch, D.

2013-07-01

170

Multispecies diffusion models: A study of uranyl species diffusion  

SciTech Connect

Rigorous numerical description of multi-species diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication for imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multi-species diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multi-species diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multi-species U(VI) diffusion under steady-state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that a fully coupled diffusion model can be well approximated by a component-based diffusion model, which considers difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be rigorously enforced, if necessary, by adding an artificial kinetic reaction term induced by the charge separation. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from US Department of Energy's Hanford 300A where intragrain diffusion is a rate-limiting process controlling U(VI) adsorption and desorption. The grain-scale reactive diffusion model was able to describe U(VI) adsorption/desorption kinetics that has been described using a semi-empirical, multi-rate model. Compared with the multi-rate model, the diffusion models have the advantage to provide spatiotemporal speciation evolution within the diffusion domains.

Liu, Chongxuan; Shang, Jianying; Zachara, John M.

2011-12-14

171

Inflammatory acidic pH enhances hydrogen sulfide-induced transient receptor potential ankyrin 1 activation in RIN-14B cells.  

PubMed

Hydrogen sulfide (H2 S), a toxic volcanic gas, functions as a gaseous physiological and pathophysiological molecule. Recently we have shown that H2 S elicits acute pain through the activation of transient receptor potential ankyrin 1 (TRPA1), which is expressed mainly in primary nociceptive neurons. We also demonstrated enhancement of H2 S-induced TRPA1 activation and pain under inflammatory acidic conditions, but the underlying mechanism has not been elucidated. Here, we attempted to clarify this mechanism by using endogenously TRPA1-expressing RIN-14B, a rat pancreatic islet cell line. For this purpose, the intracellular Ca(2+) concentration ([Ca(2+) ]i )], reactive oxygen species (ROS), and intracellular pH (pHi ) were measured with fluorescent imaging techniques. The intracellular H2 S concentration was assayed by the methylene blue method. To clarify the cellular function of H2 S, 5-hydroxytryptamine (5-HT) secretion was analyzed. In RIN-14B, the increase of [Ca(2+) ]i and the release of 5-HT induced by NaHS, an H2 S donor, were enhanced under inflammatory acidic conditions. Transition of H2 S into cells was enhanced at pH 6.8. H2 S failed to increase the intracellular ROS level and only slightly decreased pHi . These results suggest that H2 S directly activates TRPA1 and that its increment of diffusion into cells may be involved in the potentiation of TRPA1 activation under external acidic conditions. Thus, our study supports the pathophysiological functions of H2 S in inflammatory pain. © 2013 Wiley Periodicals, Inc. PMID:23873754

Takahashi, Kenji; Ohta, Toshio

2013-07-19

172

The Galactic Central Diffuse X-Ray Enhancement: A Differential Absorption/Emission Analysis  

NASA Astrophysics Data System (ADS)

The soft X-ray background shows a general enhancement toward the inner region of the Galaxy. But whether this enhancement is a local feature (e.g., a superbubble within a distance of <~200 pc) and/or a phenomenon related to energetic outflows from the Galactic center/bulge remains unclear. Here we report a comparative X-ray emission and absorption study of diffuse hot gas along the sight lines toward 3C 273 and Mrk 421, on and off the enhancement, but at similar Galactic latitudes. The diffuse 3/4 keV emission intensity, as estimated from the ROSAT All Sky Survey, is about 3 times higher toward 3C 273 than toward Mrk 421. Based on archival Chandra grating observations of these two AGNs, we detect X-ray absorption lines (e.g., O VII K?, K?, and O VIII K? transitions at z~0) and find that the mean hot gas thermal and kinematic properties along the two sight lines are significantly different. By subtracting the foreground and background contribution, as determined along the Mrk 421 sight line, we isolate the net X-ray absorption and emission produced by the hot gas associated with the enhancement in the direction of 3C 273. From a joint analysis of these differential data sets, we obtain the temperature, dispersion velocity, and hydrogen column density as 2.0(1.6,2.3)×106 K, 216(104, 480) km s-1, and 2.2(1.4,4.1)×1019 cm-2, respectively (90% confidence intervals), assuming that the gas is approximately isothermal, solar in metal abundances, and equilibrium in collisional ionization. We also constrain the effective line-of-sight extent of the gas to be 3.4(1.0, 10.1) kpc, strongly suggesting that the enhancement most likely represents a Galactic central phenomenon.

Yao, Yangsen; Wang, Q. Daniel

2007-09-01

173

A Differential Absorption/Emission Analysis of the Galactic Central Diffuse X-ray Enhancement  

NASA Astrophysics Data System (ADS)

The soft X-ray background shows a general enhancement toward the inner region of the Galaxy. But whether this enhancement is a local feature (e.g., a superbubble within a distance of 200 pc or a phenomenon related to energetic outflows from the Galactic center/bulge remains unclear. Here we report a comparative X-ray emission and absorption study of diffuse hot gas along the sight lines toward 3C 273 and Mrk 421, on and off the enhancement, but at similar Galactic latitudes. The diffuse 3/4-keV emission intensity, as estimated from the ROSAT All Sky Survey, is about three times higher toward 3C 273 than toward Mrk 421. Based on archival Chandra grating observations of these two AGNs, we detect z 0 X-ray absorption lines (e.g., OVII Kalpha, Kbeta, and OVIII Kalpha transitions) and find that the mean hot gas thermal and kinematic properties along the two sight lines are significantly different. By subtracting the background contribution, as determined along the Mrk 421 sight line, we isolate the net X-ray absorption and emission produced by the hot gas associated with the enhancement in the direction of 3C 273. From a joint analysis of these differential data sets, we obtain the temperature, dispersion velocity, and hydrogen column density as 2.0E6 K, 200 km/s, and 2E19 cm^{-2}, respectively, assuming that the gas is approximately isothermal, solar in metal abundances, and in collisional ionization equilibrium. We also constrain the effective extent of the gas to be 3.4 kpc, strongly suggesting that the enhancement most likely represents a Galactic central phenomenon.

Yao, Yangsen; Wang, Q.

2007-05-01

174

Transient Three-Phase Three-Component Flow. Pt. 3. 3D Three-Fluid Diffusion Model.  

National Technical Information Service (NTIS)

A mathematical model of a transient three-dimensional three-phase three-component flow described by three-velocity fields in porous body is presented. A combination of separated mass and energy equations together with mixture momentum equations for the fl...

N. I. Kolev

1986-01-01

175

Transient MR Signal Changes in Patients with Generalized Tonicoclonic Seizure or Status Epilepticus: Periictal Diffusion-weighted Imaging  

Microsoft Academic Search

BACKGROUND AND PURPOSE:Our purpose was to investigate transient MR signal chang- es on periictal MR images of patients with generalized tonicoclonic seizure or status epilepticus and to evaluate the clinical significance of these findings for differential diagnosis and under- standing of the pathophysiology of seizure-induced brain changes. METHODS: Eight patients with MR images that were obtained within 3 days after

Jeong-Ah Kim; Jin Il Chung; Pyeong Ho Yoon; Dong Ik Kim; Tae-Sub Chung; Eun-Ju Kim; Eun-Kee Jeong

176

Electrochemical transient investigations on the diffusion of minority charge carriers in YSZ doped by transition metal oxides  

Microsoft Academic Search

The voltage relaxation of galvanic cells with zirconia based electrolytes polarised between an inert Pt electrode and a Pt\\/air\\u000a electrode is analysed to obtain the diffusion coefficients of holes and electrons. The hole diffusion coefficient can be reduced\\u000a by replacing zirconium with guest ions of different size, e.g. Nb5+ and Ti4+. The TZP phase with 3 mol% Y2O3 of dopant

X. J. Huang; W. Weppner

1999-01-01

177

Comparison between the Predictions of Diffusion-Reaction Models and Localized Ca 2+ Transients in Amphibian Skeletal Muscle Fibers  

Microsoft Academic Search

We developed a three-dimensional cylindrical diffusion-reaction model of a single amphibian myofibril in which Ca2+ release occurred only at the Z-line. The model incorporated diffusion of Ca2+, Mg2+, and all relevant buffer species, as well as the kinetic binding reactions between the buffers and appropriate ions. Model data was blurred according to a Gaussian approximation of the point spread function

David Novo; Marino DiFranco; Julio L. Vergara

2003-01-01

178

Single file diffusion enhancement in a fluctuating modulated quasi-1D channel  

NASA Astrophysics Data System (ADS)

We show that the diffusion of a single file of particles moving in a fluctuating modulated quasi-1D channel is enhanced with respect to the one in a bald pipe. This effect, induced by the fluctuations of the modulation, is favoured by the incommensurability between the channel potential modulation and the moving file periodicity. This phenomenon could be of importance in order to optimize the critical current in superconductors, in particular in the case where mobile vortices move in 1D channels designed by patterns of pinning sites.

Coupier, G.; Saint Jean, M.; Guthmann, C.

2007-03-01

179

Dynamic contrast-enhanced diffuse optical tomography (DCE-DOT): experimental validation with a dynamic phantom  

NASA Astrophysics Data System (ADS)

Dynamic contrast-enhanced diffuse optical tomography (DCE-DOT) can provide spatially resolved enhancement kinetics of an optical contrast agent. We undertook a systematic phantom study to evaluate the effects of the geometrical parameters such as the depth and size of the inclusion as well as the optical parameters of the background on the recovered enhancement kinetics of the most commonly used optical contrast agent, indocyanine green (ICG). For this purpose a computer-controlled dynamic phantom was constructed. An ICG-intralipid-water mixture was circulated through the inclusions while the DCE-DOT measurements were acquired with a temporal resolution of 16 s. The same dynamic study was repeated using inclusions of different sizes located at different depths. In addition to this, the effect of non-scattering regions was investigated by placing a second inclusion filled with water in the background. The phantom studies confirmed that although the peak enhancement varied substantially for each case, the recovered injection and dilution rates obtained from the percentage enhancement maps agreed within 15% independent of not only the depth and the size of the inclusion but also the presence of a non-scattering region in the background. Although no internal structural information was used in these phantom studies, it may be necessary to use it for small objects buried deep in tissue. However, the different contrast mechanisms of optical and other imaging modalities as well as imperfect co-registration between both modalities may lead to potential errors in the structural a priori. Therefore, the effect of erroneous selection of structural priors was investigated as the final step. Again, the injection and dilution rates obtained from the percentage enhancement maps were also immune to the systematic errors introduced by erroneous selection of the structural priors, e.g. choosing the diameter of the inclusion 20% smaller increased the peak enhancement 60% but changed the injection and dilution rates only less than 10%.

Burcin Unlu, Mehmet; Lin, Yuting; Gulsen, Gultekin

2009-11-01

180

Impact of chemically enhanced diffusion on dissolved inorganic carbon stable isotopes in a fertilized lake  

NASA Astrophysics Data System (ADS)

At high pH the chemical reaction of CO2 with OH- can significantly increase the mass transfer of CO2 between air and water. The reaction of CO2 with OH- strongly fractionates carbon isotopes in comparison to simple diffusion. These processes, chemically enhanced diffusion (CED) and chemically enhanced fractionation (CEF), greatly influence the carbon budgets and carbon isotope ratios for water bodies with high pH. Using floating chambers, we estimated mass transfer coefficients for CO2 and a nonreactive gas, CH4, in an experimentally eutrophied lake. The mass transfer coefficient estimated from CH4 flux did not vary greatly between measurements (k600 = 1.83 ± 0.33 cm h-1; mean ±1 SD) and agreed well with other independent estimates of mass transfer. The mass transfer coefficient of CO2, however, was chemically enhanced by 3.5- to 7.5-fold. This enhancement was related to pH and temperature but was slightly higher than predictions from an existing model. We determined the role of CEF by modifying a model of CED to include both carbon isotopes (12C and 13C). A whole-lake addition of inorganic 13C to Peter Lake created dynamics in ?13C-dissolved inorganic carbon (DIC) and provided a test of the new model. The value of ?13C-DIC decreased from approximately -9‰ to -21‰, a result that was well predicted by the model including CEF but could not be duplicated when CEF was omitted. Thus CED and CEF influenced the mass balance of air-water CO2 exchange and had isotopic consequences for DIC. Although CEF is considered inconsequential for mean oceanic conditions, this model could be applied to marine systems for inorganic carbon modeling in areas where pH is elevated or physical mass transfer is limited because of low turbulence.

Bade, Darren L.; Cole, Jonathan J.

2006-01-01

181

Analysis of Oxidation Enhanced and Retarded Diffusions and Growth of Oxidation Stacking Fault in Silicon  

NASA Astrophysics Data System (ADS)

In order to determine the fractional components of the interstitialcy mechanism for Sb, P and self-diffusions, dISb, dIP and dIsd, and the supersaturation ratios of vacancies and self-interstitials, sV and sI, from the experimental results of the oxidation-enhanced diffusion (OED) of P, oxidation-retarded diffusion (ORD) of Sb and growth of the interstitial-type stacking fault by oxidation (OSF), the equations of OED, ORD and OSF and of the special relation between sV and sI were solved simultaneously. The effect of the stacking fault energy upon growth of the OSF was taken into account in the OSF equation. As the experimental results of OED, ORD and OSF did not satisfy their equations exactly, nine kinds of solutions were obtained and three of them were shown. The errors caused by the lack of exact satisfaction were shown. A dIsd much smaller than 0.5 was obtained.

Yoshida, Masayuki

1988-06-01

182

On the Enhanced Cosmic-Ray Ionization Rate in the Diffuse Cloud toward ? Persei  

NASA Astrophysics Data System (ADS)

The spatial distribution of the cosmic-ray flux is important in understanding the interstellar medium (ISM) of the Galaxy. This distribution can be analyzed by studying different molecular species along different sight lines whose abundances are sensitive to the cosmic-ray ionization rate. Recently several groups have reported an enhanced cosmic-ray ionization rate (?=?CR?standard) in diffuse clouds compared to the standard value, ?standard (=2.5×10-17 s-1), measured toward dense molecular clouds. In an earlier work we reported an enhancement ?CR=20 toward HD 185418. McCall et al. have reported ?CR=48 toward ? Persei based on the observed abundance of H+3, while Le Petit et al. found ?CR~10 to be consistent with their models for this same sight line. Here we revisit ? Persei and perform a detailed calculation using a self-consistent treatment of the hydrogen chemistry, grain physics, energy and ionization balance, and excitation physics. We show that the value of ?CR deduced from the H+3 column density, N(H+3), in the diffuse region of the sight line depends strongly on the properties of the grains because they remove free electrons and change the hydrogen chemistry. The observations are largely consistent with ?CR~40, with several diagnostics indicating higher values. This underscores the importance of a full treatment of grain physics in studies of interstellar chemistry.

Shaw, Gargi; Ferland, G. J.; Srianand, R.; Abel, N. P.; van Hoof, P. A. M.; Stancil, P. C.

2008-03-01

183

Monitoring radiation belt particle precipitation - automatic detection of enhanced transient ionisation in the lower plasmasphere using subionospheric narrow band VLF signals  

Microsoft Academic Search

Signals of naval VLF transmitters, propagating long distances along the Earth-ionosphere waveguide (EIWG) have been widely applied as effective tools for monitoring transient ionization at mesospheric altitudes. Perturbations in recorded amplitude and\\/or phase data series of stable frequency signals may refer to the effect of transient enhanced ionization in the EIWG, due to e.g. loss-cone precipitation of trapped energetic electrons

P. Steinbach; J. Lichtenberger; Cs. Ferencz

2009-01-01

184

Electron donor limitations reduce microbial enhanced trichloroethene DNAPL dissolution: a flux-based analysis using diffusion-cells.  

PubMed

Electron donor limitations likely reduce microbial enhanced trichloroethene (TCE) dense non-aqueous phase liquid (DNAPL) dissolution. This study quantitatively examined the relation between the DNAPL dissolution enhancement and the electron donor supply rate. An experiment used diffusion-cells with a 5.5 cm central sand layer, separating a DNAPL layer from an aqueous top layer. Top layers were amended with different concentrations of formate (0-16 mM). The TCE DNAPL dissolution rate increased from no enhancement compared to abiotic dissolution without formate, to a 2.4 times dissolution enhancement with 16 mM formate amended to the top layer. With 2, 4 and 8 mM formate amended the top layer, the TCE diffusion flux out of the DNAPL layer equaled the formate diffusion flux out of the top layer, which illustrates their stoichiometric interdependence under electron donor limiting conditions. In contrast, with 16 mM formate amended to the top layer, the TCE diffusion flux was lower than the formate diffusion flux, demonstrating that the dechlorination kinetics limited the DNAPL dissolution enhancement. The DNAPL dissolution flux under electron donor limiting conditions was readily predicted from the electron donor concentration in the top layer. PMID:23228910

Philips, Jo; Van Muylder, Roeland; Springael, Dirk; Smolders, Erik

2012-12-08

185

AAV-Mediated Gene Targeting Is Significantly Enhanced by Transient Inhibition of Nonhomologous End Joining or the Proteasome In Vivo  

PubMed Central

Abstract Recombinant adeno-associated virus (rAAV) vectors have clear potential for use in gene targeting but low correction efficiencies remain the primary drawback. One approach to enhancing efficiency is a block of undesired repair pathways like nonhomologous end joining (NHEJ) to promote the use of homologous recombination. The natural product vanillin acts as a potent inhibitor of NHEJ by inhibiting DNA-dependent protein kinase (DNA-PK). Using a homology containing rAAV vector, we previously demonstrated in vivo gene repair frequencies of up to 0.1% in a model of liver disease hereditary tyrosinemia type I. To increase targeting frequencies, we administered vanillin in combination with rAAV. Gene targeting frequencies increased up to 10-fold over AAV alone, approaching 1%. Fah?/?Ku70?/? double knockout mice also had increased gene repair frequencies, genetically confirming the beneficial effects of blocking NHEJ. A second strategy, transient proteasomal inhibition, also increased gene-targeting frequencies but was not additive to NHEJ inhibition. This study establishes the benefit of transient NHEJ inhibition with vanillin, or proteasome blockage with bortezomib, for increasing hepatic gene targeting with rAAV. Functional metabolic correction of a clinically relevant disease model was demonstrated and provided evidence for the feasibility of gene targeting as a therapeutic strategy.

Paulk, Nicole K.; Loza, Laura Marquez; Finegold, Milton J.

2012-01-01

186

Lack of transient receptor potential melastatin 8 activation by phthalate esters that enhance contact hypersensitivity in mice.  

PubMed

We studied the involvement of sensory neurons in skin sensitization to allergens using a mouse model in which the T-helper type 2 response is essential. Skin sensitization to fluorescein isothiocyanate (FITC) has been shown to be enhanced by several phthalate esters, including dibutyl phthalate (DBP). For different types of phthalate esters, we found a correlation between the ability of transient receptor potential (TRP) A1 activation and that of enhancing skin sensitization. A TRPA1-specific antagonist, HC-030031, was shown to suppress skin sensitization in the presence of DBP. However, since phthalate esters also activate TRPV1, phthalate esters could activate other types of TRP channels non-selectively. Furthermore, sensitization to FITC is also enhanced by menthol, which activates TRPA1 and TRPM8. Here we established an in vitro system for measuring TRPM8 activation. The selectivity for TRPM8 was established by the fact that two TRPM8 agonists (menthol and icilin) induced calcium mobilization, whereas agonists of TRPA1 and TRPV1 did not. We demonstrated that phthalate esters do not activate TRPM8. TRPA1-antagonist HC-030031 did not inhibit TRPM8 activation induced by menthol or icilin. These results show that phthalate esters activate TRPA1 and TRPV1 with selectivity. TRPM8 activation is not likely to be involved in the sensitization to FITC. PMID:23296101

Kurohane, Kohta; Sahara, Yurina; Kimura, Ayako; Narukawa, Masataka; Watanabe, Tatsuo; Daimon, Takashi; Imai, Yasuyuki

2013-01-04

187

Enhancing the Social Capital of Learning Communities by Using an Ad Hoc Transient Communities Service  

Microsoft Academic Search

In online learning, communities can help to enhance learning. However, because of the dynamic nature of communities, attaining and sustaining these communities can be difficult. One aspect that has an influence on, and is influenced by these dynamics is the social capital of a community. Features of social capital are the social network structure, the sense of belonging and, the

Sibren Fetter; Adriana J. Berlanga; Peter B. Sloep

2009-01-01

188

Stabilizing effect of diffusion in enhanced oil recovery and three-layer Hele-Shaw flows with viscosity gradient  

Microsoft Academic Search

In the presence of diffusion, stability of three-layer Hele-Shaw flows which models enhanced oil recovery processes by polymer\\u000a flooding is studied for the case of variable viscosity in the middle layer. This leads to the coupling of the momentum equation\\u000a and the species advection-diffusion equation the hydrodynamic stability study of which is presented in this paper.\\u000a \\u000a Linear stability analysis of

Prabir Daripa; G. Pa?a

2007-01-01

189

Transient regulatory T cell ablation deters oncogene-driven breast cancer and enhances radiotherapy.  

PubMed

Rational combinatorial therapeutic strategies have proven beneficial for the management of cancer. Recent success of checkpoint blockade in highly immunogenic tumors has renewed interest in immunotherapy. Regulatory T (T reg) cells densely populate solid tumors, which may promote progression through suppressing anti-tumor immune responses. We investigated the role of T reg cells in murine mammary carcinogenesis using an orthotopic, polyoma middle-T antigen-driven model in Foxp3(DTR) knockin mice. T reg cell ablation resulted in significant determent of primary and metastatic tumor progression. Importantly, short-term ablation of T reg cells in advanced spontaneous tumors led to extensive apoptotic tumor cell death. This anti-tumor activity was dependent on IFN-? and CD4(+) T cells but not on NK or CD8(+) T cells. Combination of T reg cell ablation with CTLA-4 or PD-1/PD-L1 blockade did not affect tumor growth or improve the therapeutic effect attained by T reg cell ablation alone. However, T reg cell targeting jointly with tumor irradiation significantly reduced tumor burden and improved overall survival. Together, our results demonstrate a major tumor-promoting role of T reg cells in an autochthonous model of tumorigenesis, and they reveal the potential therapeutic value of combining transient T reg cell ablation with radiotherapy for the management of poorly immunogenic, aggressive malignancies. PMID:24127486

Bos, Paula D; Plitas, George; Rudra, Dipayan; Lee, Sue Y; Rudensky, Alexander Y

2013-10-14

190

Measurement of Large Spiral and Target Waves in Chemical Reaction-Diffusion-Advection Systems: Turbulent Diffusion Enhances Pattern Formation  

NASA Astrophysics Data System (ADS)

In the absence of advection, reaction-diffusion systems are able to organize into spatiotemporal patterns, in particular spiral and target waves. Whenever advection is present that can be parametrized in terms of effective or turbulent diffusion D*, these patterns should be attainable on a much greater, boosted length scale. However, so far, experimental evidence of these boosted patterns in a turbulent flow was lacking. Here, we report the first experimental observation of boosted target and spiral patterns in an excitable chemical reaction in a quasi-two-dimensional turbulent flow. The wave patterns observed are ˜50 times larger than in the case of molecular diffusion only. We vary the turbulent diffusion coefficient D* of the flow and find that the fundamental Fisher-Kolmogorov-Petrovsky-Piskunov equation, vf?D*, for the asymptotic speed of a reactive wave remains valid. However, not all measures of the boosted wave scale with D* as expected from molecular diffusion, since the wave fronts turn out to be highly filamentous.

von Kameke, A.; Huhn, F.; Muñuzuri, A. P.; Pérez-Muñuzuri, V.

2013-02-01

191

Suppressed indium diffusion and enhanced absorption in InGaAs/GaAsP stepped quantum well solar cell  

NASA Astrophysics Data System (ADS)

A multiple stepped quantum well (MSQW) structure, in which GaAs step layers are sandwiched between strain-balanced InGaAs wells and GaAsP barriers, has been proposed and improvements in sub-GaAs-bandgap QE have been demonstrated. We have studied the effect of indium diffusion on the optical properties in quantum well solar cell by measuring the absorptance and photoluminescence spectra. Theoretical calculations indicate that the transition energy level and the absorption magnitude are sensitive to indium diffusion. The MSQW structure with GaAs step layer is a feasible way to suppress indium diffusion and enhance the absorption.

Wen, Yu; Wang, Yunpeng; Nakano, Yoshiaki

2012-01-01

192

Enhanced preliminary group classification of a class of generalized diffusion equations  

NASA Astrophysics Data System (ADS)

The method of preliminary group classification is rigorously defined, enhanced and related to the theory of group classification of differential equations. Typical weaknesses in papers on this method are discussed and strategies to overcome them are presented. The preliminary group classification of the class of generalized diffusion equations of the form ut=f(x,u)ux2+g(x,u)uxx is carried out. This includes a justification for applying this method to the given class, the simultaneous computation of the equivalence algebra and equivalence (pseudo) group, as well as the classification of inequivalent appropriate subalgebras of the whole infinite-dimensional equivalence algebra. The extensions of the kernel algebra, which are induced by such subalgebras, are exhaustively described. These results improve those recently published in Commun Nonlinear Sci Numer Simul.

Dos Santos Cardoso-Bihlo, Elsa; Bihlo, Alexander; Popovych, Roman O.

2011-09-01

193

Improving Surface Geostrophic Current from a GOCE derived Mean Dynamic Topography using Edge Enhancing Diffusion filtering  

NASA Astrophysics Data System (ADS)

With the increase in the geoid resolution provided by the Gravity and steady-state Ocean Circulation Explorer (GOCE) mission, the ocean's Mean Dynamic Topography (MDT) can be now estimated with an accuracy that has not been seen before using geodetic methods. Nevertheless, it still needs to be filtered in order to remove the noise in the signal. Here we deal with the capabilities of the Edge Enhancing Diffusion (EED) filters for filtering the MDT in order to improve the computation of the surface geostrophic currents (SGC). It is proved how this method conserves all the advantages that the non-linear isotropic filters have over the standard linear isotropic Gaussian filters. Moreover, the EED is shown to be more stable and almost independent of the local errors. This fact makes this filtering strategy preferred when filtering noisy surfaces.

Sánchez Reales, J. M.; Andersen, O. B.; Vigo, M. I.

2012-04-01

194

Solutions of Simultaneous Equations for Oxidation Enhanced and Retarded Diffusions and Oxidation Stacking Fault in Silicon  

NASA Astrophysics Data System (ADS)

Equations for oxidation enhanced and retarded diffusions (OED and ORD) and oxidation stacking faults (OSF) in silicon have been solved simultaneously, using experimental results at 1100°C for 1.0× 104--2.4× 105 s. A simple relation between the concentrations of self-interstitials and vacancies was assumed in order to obtain the solutions. It is concluded that the product of the concentrations of the self-interstitials and vacancies, CICV, is nearly equal to the value for thermal equilibrium, CI0CV0, and that the fractional components of the interstitialcy mechanism for self-, Sb and P diffusions are smaller than 0.5, smaller than 0.5 and larger than 0.5, respectively. This shows that the growth of OSF is caused mainly by the undersaturation of a vacancy, and that the ORD of Sb and the OED of P occur. The time dependences of the supersaturation ratios of the self-interstitials and vacancies were also obtained.

Yoshida, Masayuki; Matsumoto, Satoru; Ishikawa, Yutaka

1986-07-01

195

Diffusion-Temperature-Dependent Formation of Cu Centers in Cu-Saturated Silicon Crystals Studied by Photoluminescence and Deep-Level Transient Spectroscopy  

NASA Astrophysics Data System (ADS)

Using photoluminescence (PL) and deep-level transient spectroscopy (DLTS) we observed the concentration changes of Cu-related centers in silicon crystals saturated with Cu at various temperatures (600-1000 °C), in which each sample was measured at the same location for both methods. The DLTS peak assigned to have the same origin as the 1.014 eV PL center (CuPL center) was by far the strongest component among the DLTS peaks, and no DLTS peak due to isolated substitutional Cu (Cus) was observed for any of the diffusion temperatures used. The PL and DLTS intensities of the CuPL center increased with increasing diffusion temperature of Cu from 600 to 700 °C, reached a maximum between 700 and 800 °C, then sharply decreased at higher temperatures than 800 °C. This behavior was reasonably explained by considering the outdiffusion and precipitation of Cu in addition to the solubility of Cu. The maximum DLTS concentration of the CuPL center (˜1014 cm-3) observed in the present study far exceeded the estimated concentration of Cus formed through a vacancy-mediated reaction. From this finding we concluded that a model containing Cus was invalid for the CuPL center and that another model containing unique Cu atom at the center of the Si-Si bond was realistic.

Nakamura, Minoru; Murakami, Susumu; Kawai, Naoyuki J.; Saito, Shigeaki; Arie, Hiroyuki

2008-06-01

196

Ciclopirox delivery into the human nail plate using novel lipid diffusion enhancers.  

PubMed

Abstract Context: Onychomycosis is a common fungal infection of the nail plate and bed that affects up to 14% of the population and can have a substantial impact on the quality of life of those affected. Objective: This study compared the onychopharmacokinetics, nail absorption, nail distribution, and nail penetration of [(14)C]-ciclopirox dissolved in novel lipid diffusion enhancers with that of a commercial ciclopirox nail lacquer using the in vitro finite dose model. Materials and methods: The penetration rate of ciclopirox was determined by applying doses of topical formulation twice daily to human nail plates for 11?d. Drug absorption was then measured by monitoring its rate of appearance in each nail layer and in the cotton pad/nail supporting bed. Results: After a multiple day treatment, cumulative concentrations of ciclopirox formulated with lipid enhancers in the deep nail layer and the nail bed were significantly greater than cumulative concentrations of the commercial ciclopirox lacquer (p?enhancers, the amount of ciclopirox in the ventral/intermediate layer and supporting bed dramatically exceed the inhibitory concentration of ciclopirox for the most common onychomycosis organisms. These results suggest that topical ciclopirox with lipid enhancers has the potential to be an effective topical treatment for onychomycosis, and the lipidic pathway of the nail can be utilized as a means of effective transungual delivery. PMID:23600655

Hafeez, Farhaan; Hui, Xiaoying; Selner, Marc; Rosenthal, Bert; Maibach, Howard

2013-04-19

197

Selective-diffusion regularization for enhancement of microcalcifications in digital breast tomosynthesis reconstruction  

SciTech Connect

Purpose: Digital breast tomosynthesis (DBT) has been shown to improve mass detection. Detection of microcalcifications is more challenging because of the large breast volume to be searched for subtle signals. The simultaneous algebraic reconstruction technique (SART) was found to provide good image quality for DBT, but the image noise is amplified with an increasing number of iterations. In this study, the authors developed a selective-diffusion (SD) method for noise regularization with SART to improve the contrast-to-noise ratio (CNR) of microcalcifications in the DBT slices for human or machine detection. Methods: The SD method regularizes SART reconstruction during updating with each projection view. Potential microcalcifications are differentiated from the noisy background by estimating the local gradient information. Different degrees of regularization are applied to the signal or noise classes, such that the microcalcifications will be enhanced while the noise is suppressed. The new SD method was compared to several current methods, including the quadratic Laplacian (QL) method, the total variation (TV) method, and the nonconvex total p-variation (TpV) method for noise regularization with SART. A GE GEN2 prototype DBT system with a stationary digital detector was used for the acquisition of DBT scans at 21 angles in 3 deg. increments over a {+-}30 deg. range. The reconstruction image quality without regularization and that with the different regularization methods were compared using the DBT scans of an American College of Radiology phantom and a human subject. The CNR and the full width at half maximum (FWHM) of the line profiles of microcalcifications within the in-focus DBT slices were used as image quality measures. Results: For the comparison of large microcalcifications in the DBT data of the subject, the SD method resulted in comparable CNR to the nonconvex TpV method. Both of them performed better than the other two methods. For subtle microcalcifications, the SD method was superior to other methods in terms of CNR. In both the subject and phantom DBT data, for large microcalcifications, the FWHM of the SD method was comparable to that without regularization, which was wider than that of the TV type methods. For subtle microcalcifications, the SD method had comparable FWHM values to the TV type methods. All three regularization methods were superior to the QL method in terms of FWHM. Conclusions: The SART regularized by the selective-diffusion method enhanced the CNR and preserved the sharpness of microcalcifications. In comparison with three existing regularization methods, the selective-diffusion regularization was superior to the other methods for subtle microcalcifications.

Lu Yao; Chan, Heang-Ping; Wei Jun; Hadjiiski, Lubomir M. [Department of Radiology, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2010-11-15

198

Structure enhancement diffusion and contour extraction for electron tomography of mitochondria  

PubMed Central

The interpretation and measurement of the architectural organization of mitochondria depend heavily upon the availability of good software tools for filtering, segmenting, extracting, measuring, and classifying the features of interest. Images of mitochondria contain many flow-like patterns and they are usually corrupted by large amounts of noise. Thus, it is necessary to enhance them by denoising and closing interrupted structures. We introduce a new approach based on anisotropic nonlinear diffusion and bilateral filtering for electron tomography of mitochondria. It allows noise removal and structure closure at certain scales, while preserving both the orientation and magnitude of discontinuities without the need for threshold switches. This technique facilitates image enhancement for subsequent segmentation, contour extraction, and improved visualization of the complex and intricate mitochondrial morphology. We perform the extraction of the structure-defining contours by employing a variational level set formulation. The propagating front for this approach is an approximate signed distance function which does not require expensive re-initialization. The behavior of the combined approach is tested for visualizing the structure of a HeLa cell mitochondrion and the results we obtain are very promising.

Miller, Michelle; Blomgren, Peter

2009-01-01

199

Transient activation of the PI3K-AKT pathway by hepatitis C virus to enhance viral entry.  

PubMed

The PI3K-AKT signaling pathway plays an important role in cell growth and metabolism. Here we report that hepatitis C virus (HCV) transiently activates the PI3K-AKT pathway. This activation was observed as early as 15 min postinfection, peaked by 30 min, and became undetectable at 24 h postinfection. The activation of AKT could also be mediated by UV-inactivated HCV, HCV pseudoparticle, and the ectodomain of the HCV E2 envelope protein. Because antibodies directed against CD81 and claudin-1, but not antibodies directed against scavenger receptor class B type I or occludin, could also activate AKT, the interaction between HCV E2 and its two co-receptors CD81 and claudin-1 probably triggered the activation of AKT. This activation of AKT by HCV was important for HCV infectivity, because the silencing of AKT by siRNA or the treatment of cells with its inhibitors or with the inhibitor of its upstream regulator PI3K significantly inhibited HCV infection, whereas the expression of constitutively active AKT enhanced HCV infection. The PI3K-AKT pathway is probably involved in HCV entry, because the inhibition of this pathway could inhibit the entry of HCV pseudoparticle but not the VSV pseudoparticle into cells. Furthermore, the treatment of cells with the AKT inhibitor AKT-V prior to HCV infection inhibited HCV infection, whereas the treatment after HCV infection had no obvious effect. Taken together, our studies indicated that HCV transiently activates the PI3K-AKT pathway to facilitate its entry. These results provide important information for understanding HCV replication and pathogenesis and raised the possibility of targeting this cellular pathway to treat HCV patients. PMID:23095753

Liu, Zhe; Tian, Yongjun; Machida, Keigo; Lai, Michael M C; Luo, Guangxiang; Foung, Steven K H; Ou, Jing-hsiung James

2012-10-24

200

Transient enhanced expression of Cdk5 activator p25 after acute and chronic d-amphetamine administration.  

PubMed

The cellular and molecular mechanisms of sensitization in the addictive process are still unclear. Recently, chronic treatment with cocaine has been shown to upregulate the expression of cyclin-dependent kinase 5 (cdk5) and its specific activator, p35, in the striatum, as a downstream target gene of DeltaFosB, and has been implicated in compensatory adaptive changes associated with psychostimulants. Cdk5 is a serine/threonine kinase and its activation is achieved through association with a regulatory subunit, either p35 or p39. P35 is cleaved by the protease calpain, which results in the generation of a truncated product termed p25, which contains all elements necessary for cdk5 activation. The cdk5/p35 complex plays an essential role in neuronal development and survival. It has also been involved in neuronal trafficking and transport and in dopaminergic transmission, indicating its role either in presynaptic and postsynaptic signaling. In this study we report that the cdk5/p35 complex participates in acute and chronic d-amphetamine (AMPH)-evoked behavioral events, and we show a surprisingly transient enhanced expression of p25 and a lasting increased expression of p35 in dorsal striatal synaptosomes after acute and chronic AMPH administration. Pak1, a substrate for cdk5, is also enriched in the synaptosomal fraction of acute AMPH-treated rats. Our data suggest that the transient upregulation of p25 may regulate the activity of cdk5 in phosphorylating particular substrates, such as Pak1, implicated in the compensatory adaptive morphophysiologic changes associated with the process of behavioral sensitization to psychostimulants. PMID:18991853

Mlewski, Estela Cecilia; Krapacher, Favio Ariel; Ferreras, Soledad; Paglini, Gabriela

2008-10-01

201

Change in the microscopic diffusion mechanisms of boron implanted into silicon with increase in the annealing temperature  

Microsoft Academic Search

A two stream model of boron diffusion in silicon has been developed. The model is intended for simulation of transient enhanced diffusion including redistribution of ion-implanted boron during low temperature annealing. The following mechanisms of boron diffusion were proposed, namely: the mechanism of a long-range migration of nonequilibrium boron interstitials and the mechanism due to the formation, migration, and dissolution

O. I. Velichko; A. A. Hundorina

2011-01-01

202

Transient Domain Interactions Enhance the Affinity of the Mitotic Regulator Pin1 toward Phosphorylated Peptide Ligands.  

PubMed

The mitotic regulator Pin1 plays an important role in protein quality control and age-related medical conditions such as Alzheimer disease and Parkinson disease. Although its cellular role has been thoroughly investigated during the past decade, the molecular mechanisms underlying its function remain elusive. We provide evidence for interactions between the two domains of Pin1. Several residues displayed unequivocal peak splits in nuclear magnetic resonance spectra, indicative of two different conformational states in equilibrium. Pareto analysis of paramagnetic relaxation enhancement data demonstrates that the two domains approach each other upon addition of a nonpeptidic ligand. Titration experiments with phosphorylated peptides monitored by fluorescence anisotropy and chemical shift perturbation indicate that domain interactions increase Pin1's affinity toward peptide ligands. We propose this interplay of the domains and ligands to be a general mechanism for a large class of two-domain proteins. PMID:23972472

Matena, Anja; Sinnen, Christian; van den Boom, Johannes; Wilms, Christoph; Dybowski, J Nikolaj; Maltaner, Ricarda; Mueller, Jonathan W; Link, Nina M; Hoffmann, Daniel; Bayer, Peter

2013-08-22

203

Comparative Analysis of Percutaneous Absorption Enhancement by d Limonene and Oleic Acid Based on a Skin Diffusion Model  

Microsoft Academic Search

Percutaneous absorption-enhancing effects of d-limonene and oleic acid were investigated using three model drugs with different lipophilicities in in vitro diffusion experiments with guinea pig skin. Pretreatment of the skin with d-limonene resulted in a large penetration enhancement for the lipophilic butylparaben (BP) and amphiphilic 6-mercaptopurine (6-MP) but had little effect on the hydrophilic mannitol (MT). Oleic acid caused a

Yasuo Koyama; Hiroto Bando; Fumiyoshi Yamashita; Yoshinobu Takakura; Hitoshi Sezaki; Mitsuru Hashida

1994-01-01

204

Optomechanical Shutter Modulated Broad-Band Cavity–Enhanced Absorption Spectroscopy of Molecular Transients of Astrophysical Interest  

NASA Astrophysics Data System (ADS)

We describe a sensitive spectroscopic instrument capable of measuring broad-band absorption spectra through supersonically expanding planar plasma pulses. The instrument utilizes incoherent broad-band cavity-enhanced absorption spectroscopy (IBBCEAS) and incorporates an optomechanical shutter to modulate light from a continuous incoherent light source, enabling measurements of durations as low as -400 -s. The plasma expansion is used to mimic conditions in translucent interstellar clouds. The new setup is particularly applicable to test proposed carriers of the diffuse interstellar bands, as it permits swift measurements over a broad spectral range with a resolution comparable to astronomical observations. The sensitivity is estimated to be better than 10 ppm/pass, measured with an effective exposure time of only 1 s.

Walsh, Anton; Zhao, Dongfeng; Ubachs, Wim; Linnartz, Harold

2013-10-01

205

Surface enhancement effect on the diffuse reflectance infrared Fourier transform spectra of compounds having a pyridine ring  

Microsoft Academic Search

A surface enhancement effect was examined for the diffuse reflectance infrared spectra of structurally related compounds having a pyridine ring when a silver colloidal solution was used as the medium which induced the effect. Filter paper, which was considered to provide a favorable state of aggregation of the silver colloidal particles, was used for the preparation of the samples to

Seiichiro Higuchi; Kazumi Takayama; Yohichi Gohshi; Keiichi Furuya

1999-01-01

206

Nicotinic Acetylcholine Receptor Channel Electrostatics Determined by Diffusion-Enhanced Luminescence Energy Transfer  

PubMed Central

The electrostatic potentials within the pore of the nicotinic acetylcholine receptor (nAChR) were determined using lanthanide-based diffusion-enhanced fluorescence energy transfer experiments. Freely diffusing Tb3+-chelates of varying charge constituted a set of energy transfer donors to the acceptor, crystal violet, a noncompetitive antagonist of the nAChR. Energy transfer from a neutral Tb3+-chelate to nAChR-bound crystal violet was reduced 95% relative to the energy transfer to free crystal violet. This result indicated that crystal violet was strongly shielded from solvent when bound to the nAChR. Comparison of energy transfer from positively and negatively charged chelates indicate negative electrostatic potentials of ?25 mV in the channel, measured in low ionic strength, and ?10 mV measured in physiological ionic strength. Debye-Hückel analyses of potentials determined at various ionic strengths were consistent with 1–2 negative charges within 8 Å of the crystal violet binding site. To complement the energy transfer experiments, the influence of pH and ionic strength on the binding of [3H]phencyclidine were determined. The ionic strength dependence of binding affinity was consistent with ?3.3 charges within 8 Å of the binding site, according to Debye-Hückel analysis. The pH dependence of binding had an apparent pKa of 7.2, a value indicative of a potential near ?170 mV if the titratable residues are constituted of aspartates and glutamates. It is concluded that long-range potentials are small and likely contribute little to selectivity or conductance whereas close interactions are more likely to contribute to electrostatic stabilization of ions and binding of noncompetitive antagonists within the channel.

Meltzer, Robert H.; Lurtz, Monica M.; Wensel, Theodore G.; Pedersen, Steen E.

2006-01-01

207

Saikosaponin a Enhances Transient Inactivating Potassium Current in Rat Hippocampal CA1 Neurons.  

PubMed

Saikosaponin a (SSa), a main constituent of the Chinese herb Bupleurum chinense DC., has been demonstrated to have antiepileptic activity. Recent studies have shown that SSa could inhibit NMDA receptor current and persistent sodium current. However, the effects of SSa on potassium (K(+)) currents remain unclear. In this study, we tested the effect of SSa on 4AP-induced epileptiform discharges and K(+) currents in CA1 neurons of rat hippocampal slices. We found that SSa significantly inhibited epileptiform discharges frequency and duration in hippocampal CA1 neurons in the 4AP seizure model in a dose-dependent manner with an IC 50 of 0.7? ? M. SSa effectively increased the amplitude of I Total and I A , significantly negative-shifted the activation curve, and positive-shifted steady-state curve of I A . However, SSa induced no significant changes in the amplitude and activation curve of I K . In addition, SSa significantly increased the amplitude of 4AP-sensitive K(+) current, while there was no significant change in the amplitude of TEA-sensitive K(+) current. Together, our data indicate that SSa inhibits epileptiform discharges induced by 4AP in a dose-dependent manner and that SSa exerts selectively enhancing effects on I A . These increases in I A may contribute to the anticonvulsant mechanisms of SSa. PMID:23554830

Xie, Wei; Yu, Yun Hong; Du, Yong Ping; Zhao, Yun Yan; Li, Chang Zheng; Yu, Lin; Duan, Jian Hong; Xing, Jun Ling

2013-02-21

208

Hepatic Cavernous Hemangiomas: Relationship between Speed of Intratumoral Enhancement during Dynamic MRI and Apparent Diffusion Coefficient on Diffusion-Weighted Imaging  

PubMed Central

Objective To investigate the relationships between the apparent diffusion coefficients (ADCs) on diffusion-weighted imaging (DWI) and the speed of contrast-enhancement in hepatic hemangiomas. Materials and Methods Sixty-nine hepatic hemangiomas (? 1 cm) were evaluated with DWI, by using multiple b values (b = 50, 400, 800 s/mm2), followed by a gadolinium-enhanced dynamic MRI. The lesions were classified into three groups, according to the speed of contrast-enhancement on the portal phase. ADCs were measured on the ADC map automatically, and were calculated by using the two different b values (mADC50-400 with b values = 50 and 400; mADC400-800 with b values = 400 and 800 s/mm2). Results The mean ADCs (× 10-3 mm2/s) were significantly higher in the rapid group (1.9 ± 0.44) than in the intermediate (1.7 ± 0.35, p = 0.046) or the slow groups (1.4 ± 0.34, p = 0.002). There were significant differences between the rapid and the slow groups in mADC50-400 (2.12 vs. 1.48; p = 0.008) and mADC400-800 (1.68 vs. 1.22, p = 0.010), and between the rapid and the intermediate groups in mADC50-400 (2.12 vs. 1.79, p = 0.049). Comparing mADC50-400 with mADC400-800, there was a significant difference only in the rapid group (p = 0.001). Conclusion Higher ADCs of rapidly-enhancing hemangiomas may be related to richer intralesional vascular perfusion. Also, the restricted diffusion may be attributed to the difference of structural characteristics of hemangioma.

Nam, Se Jin; Park, Kae Young; Chung, Jae-Joon; Kim, Joo Hee; Kim, Ki Whang

2012-01-01

209

A finite element simulation on transient large deformation and mass diffusion in electrodes for lithium ion batteries  

NASA Astrophysics Data System (ADS)

Lithium-ion batteries have attracted great deal of attention recently. Silicon is one of the most promising anode materials for high-performance lithium-ion batteries, due to its highest theoretical specific capacity. However, the short lifetime confined by mechanical failure in the silicon anode is now considered to be the biggest challenge in desired applications. High stress induced by the huge volume change due to lithium insertion/extraction is the main reason underlying this problem. Some theoretical models have been developed to address this issue. In order to properly implement these models, we develop a finite element based numerical method using a commercial software package, ABAQUS, as a platform at the continuum level to study fully coupled large deformation and mass diffusion problem. Using this method, large deformation, elasticity–plasticity of the electrodes, various spatial and temporal conditions, arbitrary geometry and dimension could be fulfilled. The interaction between anode and other components of the lithium ion batteries can also be studied as an integrated system. Several specific examples are presented to demonstrate the capability of this numerical platform.

An, Yonghao; Jiang, Hanqing

2013-10-01

210

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

PubMed

Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an axisymmetric diffusion experiment coupled with tracer profiling may be a promising approach to estimate of diffusion anisotropy of sedimentary rocks. PMID:21288593

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

2011-01-09

211

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

SciTech Connect

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

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

2011-02-01

212

Delayed marrow infusion in mice enhances hematopoietic and osteopoietic engraftment by facilitating transient expansion of the osteoblastic niche.  

PubMed

Transplantation of bone marrow cells leads to engraftment of osteopoietic and hematopoietic progenitors. We sought to determine whether the recently described transient expansion of the host osteoblastic niche after marrow radioablation promotes engraftment of both osteopoietic and hematopoietic progenitor cells. Mice infused with marrow cells 24 hours after total body irradiation (TBI) demonstrated significantly greater osteopoietic and hematopoietic progenitor chimerism than did mice infused at 30 minutes or 6 hours. Irradiated mice with a lead shield over 1 hind limb showed greater hematopoietic chimerism in the irradiated limb than in the shielded limb at both the 6- and 24-hour intervals. By contrast, the osteopoietic chimerism was essentially equal in the 2 limbs at each of these intervals, although it significantly increased when cells were infused 24 hours compared with 6 hours after TBI. Similarly, the number of donor phenotypic long-term hematopoietic stem cells was equivalent in the irradiated and shielded limbs after each irradiation-to-infusion interval but was significantly increased at the 24-hour interval. Our findings indicate that a 24-hour delay in marrow cell infusion after TBI facilitates expansion of the endosteal osteoblastic niche, leading to enhanced osteopoietic and hematopoietic engraftment. PMID:23916672

Marino, Roberta; Otsuru, Satoru; Hofmann, Ted J; Olson, Timothy S; Rasini, Valeria; Veronesi, Elena; Boyd, Kelli; Gaber, Mostafa Waleed; Martinez, Caridad; Paolucci, Paolo; Dominici, Massimo; Horwitz, Edwin M

2013-08-02

213

Turboprop+: enhanced Turboprop diffusion-weighted imaging with a new phase correction.  

PubMed

Faster periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) diffusion-weighted imaging acquisitions, such as Turboprop and X-prop, remain subject to phase errors inherent to a gradient echo readout, which ultimately limits the applied turbo factor (number of gradient echoes between each pair of radiofrequency refocusing pulses) and, thus, scan time reductions. This study introduces a new phase correction to Turboprop, called Turboprop+. This technique employs calibration blades, which generate 2-D phase error maps and are rotated in accordance with the data blades, to correct phase errors arising from off-resonance and system imperfections. The results demonstrate that with a small increase in scan time for collecting calibration blades, Turboprop+ had a superior immunity to the off-resonance-related artifacts when compared to standard Turboprop and recently proposed X-prop with the high turbo factor (turbo factor = 7). Thus, low specific absorption rate and short scan time can be achieved in Turboprop+ using a high turbo factor, whereas off-resonance related artifacts are minimized. PMID:23023533

Lee, Chu-Yu; Li, Zhiqiang; Pipe, James G; Debbins, Josef P

2012-09-28

214

Radiation enhanced diffusion of hydrogen in perovskite-type oxide ceramics under reactor irradiation  

NASA Astrophysics Data System (ADS)

Electrical conductivity of yttrium-doped perovskite-type barium-cerium oxide ceramics (BaCe0.9Y0.1O3-?), implanted with 10 keV H2+ ions, was measured in situ under fission reactor irradiation. An increment of the electrical conductivity, called radiation induced conductivity (RIC), was observed with increasing ionizing dose rate. The RIC for the specimen with implanted H at 1.1 kGy/s and irradiation temperatures 473 673 K was higher by about four orders of magnitude than the base conductivity without radiation at 0 Gy/s, and was about two orders of magnitude higher than that without H. The RIC is attributed to electronic excitation as well as hydrogen enhanced diffusion. The RIC greatly depended on the irradiation temperature, but was insensitive to the fast neutron fluence in the range 3.3 7.4 × 1023 n/m2. The results show that the radiation induced defects, produced by neutron collisions, and radiolysis have no influence on the electronic and protonic conduction.

Tsuchiya, B.; Shikama, T.; Nagata, S.; Toh, K.; Narui, M.; Yamazaki, M.

2007-08-01

215

Improving the Prediction of Stroke or Death After Transient Ischemic Attack (TIA) by Adding Diffusion-weighted Imaging Lesions and TIA Etiology to the ABCD2 Score.  

PubMed

The present study investigated the addition of transient ischemic attack (TIA) etiology and diffusion-weighted imaging (DWI) to the ABCD2 score, creating the ABCDE+ score, to improve the predictive ability of stroke risk or death at 6 months after TIA. We performed a cohort study of 150 consecutive patients with TIA. All patients underwent DWI and all had an etiologic workup and were followed up for 6 months. The area under the receiver operating characteristic curve (AUC) was used to compare the scores' ability to predict the outcome of stroke or death. Multivariate Cox regression analysis was performed to evaluate the association between the measured variables and subsequent stroke or death. Thirty patients (20%) experienced future stroke, and 12 patients (8%) died within the 6-month follow-up. A comparison of AUCs demonstrated the superiority of the ABCDE+ score over the ABCD2 score for predicting stroke (0.64 vs 0.60) and for predicting death (0.62 vs 0.56). ABCD2 score >4, ABCDE+ score >6, large-artery disease, and lesions detected on DWI were found to be independent predictors of future stroke, and ABCDE+ score >6, age, and heart disease were independent predictors of death. We conclude that incorporating DWI positivity and etiology of TIA into the ABCD2 score can improve the ability to predict stroke and death within 6 months after TIA. PMID:22609319

Arhami Dolatabadi, Ali; Meisami, Amirhosein; Hatamabadi, Hamidreza; Mansori, Behnam; Shahrami, Ali; Amini, Afshin; Jamali, Kazem

2012-05-18

216

Lévy diffusion in a force field, Huber relaxation kinetics, and nonequilibrium thermodynamics: H theorem for enhanced diffusion with Lévy white noise  

NASA Astrophysics Data System (ADS)

A characteristic functional approach is suggested for Lévy diffusion in disordered systems with external force fields. We study the overdamped motion of an ensemble of independent particles and assume that the force acting upon one particle is made up of two additive components: a linear term generated by a harmonic potential and a second term generated by the interaction with the disordered system. The stochastic properties of the second term are evaluated by using Huber's approach to complex relaxation [Phys. Rev. B 31, 6070 (1985)]. We assume that the interaction between a moving particle and the environment can be expressed by the contribution of a large number of relaxation channels, each channel having a very small probability of being open and obeying Poisson statistics. Two types of processes are investigated: (a) Lévy diffusion with static disorder for which the fluctuations of the random force are frozen and last forever and (b) diffusion with strong dynamic disorder and independent Lévy fluctuations (Lévy white noise). In both cases we show that the probability distribution of the position of a diffusing particle tends towards a stationary nonequilibrium form. The characteristic functional of concentration fluctuations is evaluated in both cases by using the theory of random point processes. For large times the fluctuations of the concentration field are stationary and the corresponding probability density functional can be evaluated analytically. In this limit the fluctuations depend on the distribution of the total number of particles but are independent of the initial positions of the particles. We show that the logarithm of the stationary probability functional plays the role of a nonequilibrium thermodynamic potential, which has a structure similar to the Helmholtz free energy in equilibrium thermodynamics: it is made up of the sum of an energetic component, depending on the external mechanical potential, and of an entropic component, depending on the concentration field. We show that the conditions for the existence and stability of the nonequilibrium steady state, which emerges for large times, can be expressed in terms of the stochastic potential. For Lévy white noise the average concentration field can be expressed as the solution of a fractional Fokker-Planck equation. We show that the stochastic potential is a Lyapunov function of the fractional Fokker-Planck equation, which ensures that all transient solutions for the average concentration field tend towards a unique stationary form.

Vlad, Marcel O.; Ross, John; Schneider, Friedemann W.

2000-08-01

217

Levy diffusion in a force field, Huber relaxation kinetics, and nonequilibrium thermodynamics: H theorem for enhanced diffusion with Levy white noise  

SciTech Connect

A characteristic functional approach is suggested for Levy diffusion in disordered systems with external force fields. We study the overdamped motion of an ensemble of independent particles and assume that the force acting upon one particle is made up of two additive components: a linear term generated by a harmonic potential and a second term generated by the interaction with the disordered system. The stochastic properties of the second term are evaluated by using Huber's approach to complex relaxation [Phys. Rev. B 31, 6070 (1985)]. We assume that the interaction between a moving particle and the environment can be expressed by the contribution of a large number of relaxation channels, each channel having a very small probability of being open and obeying Poisson statistics. Two types of processes are investigated: (a) Levy diffusion with static disorder for which the fluctuations of the random force are frozen and last forever and (b) diffusion with strong dynamic disorder and independent Levy fluctuations (Levy white noise). In both cases we show that the probability distribution of the position of a diffusing particle tends towards a stationary nonequilibrium form. The characteristic functional of concentration fluctuations is evaluated in both cases by using the theory of random point processes. For large times the fluctuations of the concentration field are stationary and the corresponding probability density functional can be evaluated analytically. In this limit the fluctuations depend on the distribution of the total number of particles but are independent of the initial positions of the particles. We show that the logarithm of the stationary probability functional plays the role of a nonequilibrium thermodynamic potential, which has a structure similar to the Helmholtz free energy in equilibrium thermodynamics: it is made up of the sum of an energetic component, depending on the external mechanical potential, and of an entropic component, depending on the concentration field. We show that the conditions for the existence and stability of the nonequilibrium steady state, which emerges for large times, can be expressed in terms of the stochastic potential. For Levy white noise the average concentration field can be expressed as the solution of a fractional Fokker-Planck equation. We show that the stochastic potential is a Lyapunov function of the fractional Fokker-Planck equation, which ensures that all transient solutions for the average concentration field tend towards a unique stationary form. (c) 2000 The American Physical Society.

Vlad, Marcel O. [Department of Chemistry, Stanford University, Stanford, California 94305-5080 (United States); Center of Mathematical Statistics, Casa Academiei Romane, Calea Septembrie 13, Bucharest 5, (Romania); Ross, John [Department of Chemistry, Stanford University, Stanford, California 94305-5080 (United States); Schneider, Friedemann W. [University of Wuerzburg, Institute of Physical Chemistry, Am Hubland, D-97074 Wuerzburg, (Germany)

2000-08-01

218

Enhanced diffusion of uranium and thorium linked to crystal plasticity in zircon.  

PubMed

The effects of crystal-plasticity on the U-Th-Pb system in zircon is studied by quantitative microstructural and microchemical analysis of a large zircon grain collected from pyroxenite of the Lewisian Complex, Scotland. Electron backscatter diffraction (EBSD) mapping reveals a c.18 degree variation in crystallographic orientation that comprises both a gradual change in orientation and a series of discrete low-angle (<4 degrees) boundaries. These microstructural data are consistent with crystal-plastic deformation of zircon associated with the formation and migration of dislocations. A heterogeneous pattern of dark cathodoluminescence, with the darkest domains coinciding with low-angle boundaries, mimics the deformation microstructure identified by EBSD. Geochemical data collected using the Sensitive High Resolution Ion MicroProbe (SHRIMP) shows a positive correlation between concentrations of the elements U, Th and Pb (ranging from 20-60 ppm, 30-110 ppm, and 14-36 ppm, respectively) and Th/U ratio (1.13-1.8) with the deformation microstructure. The highest measured concentrations and Th/U coincide with low-angle boundaries. This enrichment is interpreted to reflect enhanced bulk diffusion of U and Th due to the formation and migration of high-diffusivity dislocations. 207Pb/206Pb ages for individual analyses show no significant variation across the grain, and define a concordant, combined mean age of 2451 +/- 14 Ma. This indicates that the grain was deformed shortly after initial crystallization, most probably during retrograde Inverian metamorphism at amphibolite facies conditions. The elevated Th over U and consistent 207Pb/206Pb ages indicates that deformation most likely occurred in the presence of a late-stage magmatic fluid that drove an increase in the Th/U during deformation. The relative enrichment of Th over U implies that Th/U ratio may not always be a robust indicator of crystallization environment. This study provides the first evidence of deformation-related modification of the U-Th system in zircon and has fundamental implications for the application and interpretation of zircon trace element data. PMID:17181855

Timms, Nicholas E; Kinny, Peter D; Reddy, Steven M

2006-12-20

219

Azide treatment enhances cell-to-cell diffusion in staminal hairs of Setcreasea purpurea  

Microsoft Academic Search

Summary The effect of azide on the diffusion of fluorescent molecular probes was examined in staminal hairs ofSetcreasea purpurea. Staminal hairs were treated with azide before being microinjected with fluorescent molecular probes of different size, charge, and structure. The cell-to-cell movement of these fluorescent molecules was videotaped, analyzed, and coefficients of diffusion through plasmodesmata (D) and coefficients of diffusion across

E. B. Tucker

1993-01-01

220

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO2·Y2O3  

Microsoft Academic Search

First measurements of oxygen grain boundary diffusion coefficients in nanocrystalline yttria-doped ZrO2 (n-ZrO2·6.9 mol % Y2O3) are presented. The 18O diffusion profiles measured by secondary ion mass spectroscopy are much deeper in the nanocrystalline specimens than in single crystals. An oxygen diffusivity, DB, in the grain boundaries can be deduced, which is 3 orders of magnitude higher than in single

Gregor Knöner; Klaus Reimann; Ralf Röwer; Ulf Södervall; Hans-Eckhardt Schaefer

2003-01-01

221

Modeling stress development and hydrogen diffusion in plasma enhanced chemical vapor deposition silicon nitride films submitted to thermal cycles  

NASA Astrophysics Data System (ADS)

We conducted isochronal stress hysteresis measurements coupled with thermal desorption spectroscopy on silicon nitride thin films obtained by performing plasma enhanced chemical vapor deposition on (001) silicon wafers. Above the deposition temperature, we observed irreversible stress build-up in parallel to substantial hydrogen effusion out of the films. We confirmed that the hydrogen dissociation and stress build-up can be modeled with similar kinetic equations. The hydrogen dissociation and stress development activation energies as well as the hydrogen diffusion coefficients were determined by fitting the experimental data with solutions to the kinetics and Fickian diffusion equations obtained with the finite difference method. A first order correlation was found between the hydrogen diffusion coefficients calculated between 400 and 800 °C and the silicon nitride film density.

Morin, Pierre Francois; Pelletier, Bertrand; Laffosse, Elise; Plantier, Lise

2013-10-01

222

Greatly enhanced eccentricity oscillations in quadruple systems composed of two binaries: implications for stars, planets and transients  

NASA Astrophysics Data System (ADS)

We study the orbital evolution of hierarchical quadruple systems composed of two binaries on a long mutual orbit, where each binary acts as a Kozai-Lidov (KL) perturber on the other. We find that the coupling between the two binaries qualitatively changes the behaviour of their KL cycles. The binaries can experience coherent eccentricity oscillations as well as excursions to very high eccentricity that occur over a much larger fraction of the parameter space than in triple systems. For a ratio of outer to inner semimajor axes of 10-20, about 30-50 per cent of equal-mass quadruples reach eccentricity 1 - e < 10-3 in one of the binaries. This is about 4-12 times more than for triples with equivalent parameters. Orbital `flips' and collisions without previous tidal interaction are similarly enhanced in quadruples relative to triples. We argue that the frequency of evolutionary paths influenced by KL cycles is comparable in the triple and quadruple populations even though field quadruples are a factor of ˜5 less frequent than triples. Additionally, quadruples might be a non-negligible source of triples and provide fundamentally new evolutionary outcomes involving close binaries, mergers, collisions and associated transients, which occur without any fine tuning of parameters. Finally, we study the perturbations to a planetary orbit due to a distant binary and we find that the fraction of orbital flips is a factor of 3-4 higher than for the corresponding triple system given our fiducial parameters with implications for hot Jupiters and star-planet collisions.

Pejcha, Ond?ej; Antognini, Joe M.; Shappee, Benjamin J.; Thompson, Todd A.

2013-10-01

223

Coercivity enhancement of anisotropic die-upset Nd-Fe-B powders by Pr-Cu alloy diffusion  

NASA Astrophysics Data System (ADS)

The grain boundary diffusion treatment using the low melting point Pr-Cu eutectic alloy was applied to enhance the coercivity of anisotropic die-upset Nd-Fe-B powders. It was found that the room temperature coercivity of the powders increases from 13 kOe to 24 kOe. The thickness of the grain boundary layer was increased and the Fe and Co content in the grain boundary phases was decreased. The modified boundary layers may thus increase the domain wall nucleation field, leading to an enhancement in the coercivity. The diffusion of Pr-Cu alloy prevents the loss of continuity of the Nd-rich grain boundary phase and retains the crystal texture in the initial grains.

Wan, Fangming; Han, Jingzhi; Zhang, Yinfeng; Zhang, Xiaodong; Yang, Jinbo; Yang, Yingchang; Hu, Boping; Rao, Xiaolei; Cai, Daoyan; Chen, Zhian; Chen, Renjie; Yan, Aru

2013-05-01

224

Diffuser System Modeling and Design for Dissolved Oxygen Enhancement of Reservoirs and Releases  

Microsoft Academic Search

In support of the Tennessee Valley Authority's Lake Improvement Program, a line diffuser system was developed that was applied and proven effective at six TVA hydropower projects. To be effective, the placement of the diffusers and distribution of the oxygen input must be optimized for site-specific water quality and water flow conditions. Most TVA applications were relatively straightforward designs with

Mark H. Mobley; Gary E. Hauser; Dan F. McGinnis; R. Jim Ruane

225

Theoretical model and computer simulation results of enhanced diffusion of high-temperature implanted aluminum in silicon carbide  

Microsoft Academic Search

Wide application of silicon carbide (SiC) films in microelectronics devices makes especially important predictions of the doping profiles during and\\/or after thermal treatment. A macroscopic kinetic model of enhanced diffusion of aluminum in SiC films during ion bombardment at high temperature has been considered. The set of equations describing the kinetic model takes into account generation of Si and C

G. V. Gadiyak

1997-01-01

226

Theoretical model and computer simulation results of enhanced diffusion of high-temperature implanted aluminum in silicon carbide  

Microsoft Academic Search

The wide-spread use of silicon carbide (SiC) films in the production of microelectronic devices make predictions of the doping profiles during and\\/or after thermal treatment especially important. A macroscopic kinetic model of enhanced diffusion of aluminum in SiC films during ion bombardment at high temperatures has been considered. The set of equations describing the kinetic model takes into account the

G. V. Gadiyak

1998-01-01

227

Theory of enhanced proximity effect by midgap Andreev resonant state in diffusive normal-metal\\/triplet superconductor junctions  

Microsoft Academic Search

Enhanced proximity effect by the midgap Andreev resonant state (MARS) in a diffusive normal-metal\\/insulator\\/triplet superconductor (DN\\/TS) junction is studied based on the Keldysh-Nambu quasiclassical Green's-function formalism. By choosing a p -wave superconductor as a typical example of the TS, conductance of the junction and the spatial variation of the quasiparticle local density of states (LDOS) in the DN are calculated

Y. Tanaka; S. Kashiwaya; T. Yokoyama

2005-01-01

228

Evidence of recombination enhanced diffusion of impurities at low temperature into high-k dielectric with tantalum oxide as an example  

NASA Astrophysics Data System (ADS)

For ordinary diffusion of Si into Ta2O5 on a Si substrate, there should be no difference for n-type or p-type substrate; however, experimentally, we noticed that Si can diffuse rapidly and this diffusion process tended to be faster for n-type Si substrate than for p-type Si substrate under an oxygen plasma at 350 °C. This can only be explained by the mechanism of recombination enhanced diffusion. Beside Si, B, and Sb were shown to be able to diffuse into tantalum oxide under an oxygen plasma or nitrous oxide plasma at a temperature below 400 °C.

Lau, W. S.; Chandima Perera, M. T.; Chu, P. K.

2010-02-01

229

Theory of isotope diffusion in a material with multiple species and its implications for hydrogen-enhanced electrical conductivity in olivine  

NASA Astrophysics Data System (ADS)

The relationship between isotope diffusion coefficient and electrical conductivity is examined for a material where a dominant charge-carrying atomic species (e.g., hydrogen) is present as various forms with different diffusion coefficients (e.g., two protons trapped at M-site vacancy, one proton trapped at M-site vacancy etc.). It is shown that the isotopic diffusion occurs keeping the concentration ratio of each species fixed as determined by the thermo-chemical environment. Consequently, the isotope diffusion coefficient is the harmonic average of diffusion coefficients of individual species and is dominated by the slowest diffusing species. In contrast, when electric current is carried by charged species, the concentrations of individual species do not change. Therefore, electrical conductivity is related to the arithmetic average of individual diffusion coefficients dominated by the fastest diffusing species. The difference between these two cases can be large when different species have largely different diffusion coefficients. This model provides an explanation for the observed differences between experimental observations on isotopic diffusion (of H-D) and hydrogen-enhanced electrical conductivity and supports a hybrid model of hydrogen-enhanced electrical conduction where electrical conductivity is dominated by the fast moving hydrogen-related species. The species with the largest mobility may change with temperature leading to a change in anisotropy of conductivity. The degree of enhancement of electrical conductivity by hydrogen is high enough to explain most of the geophysically observed electrical conductivity of Earth's upper mantle.

Karato, Shun-ichiro

2013-06-01

230

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO2.Y2O3.  

PubMed

First measurements of oxygen grain boundary diffusion coefficients in nanocrystalline yttria-doped ZrO(2) (n-ZrO(2).6.9 mol % Y(2)O(3)) are presented. The (18)O diffusion profiles measured by secondary ion mass spectroscopy are much deeper in the nanocrystalline specimens than in single crystals. An oxygen diffusivity, D(B), in the grain boundaries can be deduced, which is approximately 3 orders of magnitude higher than in single crystals. From the present data the temperature variation of the oxygen grain boundary diffusivity, D(B) = 2.0 x 10(-5) exp (-0.91 eVk(B)T) m(2)s, and the oxygen surface exchange coefficient, k = 1.4 x 10(-2) exp (-1.13 eVk(B)T) ms, are derived. PMID:12655074

Knoner, Gregor; Reimann, Klaus; Rower, Ralf; Sodervall, Ulf; Schaefer, Hans-Eckhardt

2003-03-24

231

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO2?Y2O3  

PubMed Central

First measurements of oxygen grain boundary diffusion coefficients in nanocrystalline yttria-doped ZrO2 (n-ZrO2?6.9 mol % Y2O3) are presented. The 18O diffusion profiles measured by secondary ion mass spectroscopy are much deeper in the nanocrystalline specimens than in single crystals. An oxygen diffusivity, DB, in the grain boundaries can be deduced, which is ?3 orders of magnitude higher than in single crystals. From the present data the temperature variation of the oxygen grain boundary diffusivity, DB = 2.0 × 10?5 exp (?0.91 eV/kBT) m2/s, and the oxygen surface exchange coefficient, k = 1.4 × 10?2 exp (?1.13 eV/kBT) m/s, are derived.

Knoner, Gregor; Reimann, Klaus; Rower, Ralf; Sodervall, Ulf; Schaefer, Hans-Eckhardt

2003-01-01

232

Understanding and Enhancing Hydrogen Diffusion in MgH2 and NaMgH3  

NASA Astrophysics Data System (ADS)

The transport properties of hydrogen in metal hydrides are crucial to the kinetics of H2 storage in these materials. We use first-principles calculations to identify the defects that are relevant for H transport in MgH2 and NaMgH3. In both materials, the physically relevant defects are charged and H diffusion is dominated by mobility of negatively charged interstitial H. Interestingly, the diffusion of these species occurs via concerted mechanisms with low energy barriers. To improve the charged interstitial H diffusivity, a series of transition-metal additives are screened to lower the formation energy of mobile defects. Our results provide a practical way to examine and alter H diffusion in light metal hydrides.

Sholl, David; Hao, Shiqiang

2009-03-01

233

Multiphoton microscopy guides neurotrophin modification with poly(ethylene glycol) to enhance interstitial diffusion  

NASA Astrophysics Data System (ADS)

Brain-derived neurotrophic factor (BDNF) is a promising therapeutic agent for the treatment of neurodegenerative diseases. However, the limited distribution of this molecule after administration into the brain tissue considerably hampers its efficacy. Here, we show how multiphoton microscopy of fluorescently tagged BDNF in brain-tissue slices provides a useful and rapid screening method for examining the diffusion of large molecules in tissues, and for studying the effects of chemical modifications-for example, conjugating with polyethylene glycol (PEG)-on the diffusion constant. This single variable, obtained by monitoring short-term diffusion in real time, can be effectively used for rational drug design. In this study on fluorescently tagged BDNF and BDNF-PEG, we identify slow diffusion as a major contributing factor to the limited penetration of BDNF, and demonstrate how chemical modification can be used to overcome this barrier.

Stroh, Mark; Zipfel, Warren R.; Williams, Rebecca M.; Ma, Shu Chin; Webb, Watt W.; Saltzman, W. Mark

2004-07-01

234

Thaumatin crystallization aboard the International Space Station using liquid-liquid diffusion in the Enhanced Gaseous Nitrogen Dewar (EGN).  

PubMed

This paper reports results from the first biological crystal-growth experiment on the International Space Station (ISS). Crystals of thaumatin were grown using liquid-liquid diffusion in Tygon tubing transported in the Enhanced Gaseous Nitrogen Dewar (EGN). Different volume ratios and concentrations of protein and precipitant were used to test different adaptations of the vapor-diffusion crystallization recipe to the liquid-liquid diffusion method. The EGN warmed up from 77 to 273 K in about 4 d, about the same time it took to warm from 273 to 293 K. The temperature within the EGN was 293-297 K for the majority of the experiment. Air gaps that blocked liquid-liquid diffusion formed in the tubes. Nonetheless, crystals were grown. Synchrotron diffraction data collected from the best space-grown crystal extended to 1.28 A, comparable to previous studies of space-grown thaumatin crystals. The resolution of the best ground-control crystal was only 1.47 A. It is not clear if the difference in diffraction limit arises from factors other than crystal size. Improvements in temperature control and the elimination of air gaps are needed, but the results show that the EGN on the ISS can be used to produce space-grown crystals that diffract to high resolution. PMID:11976485

Barnes, Cindy L; Snell, Edward H; Kundrot, Craig E

2002-04-26

235

Diffusion kurtosis imaging and log-normal distribution function imaging enhance the visualisation of lesions in animal stroke models.  

PubMed

In this work, we report a case study of a stroke model in animals using two methods of quantification of the deviations from Gaussian behaviour: diffusion kurtosis imaging (DKI) and log-normal distribution function imaging (LNDFI). The affected regions were predominantly in grey rather than in white matter. The parameter maps were constructed for metrics quantifying the apparent diffusivity (evaluated from conventional diffusion tensor imaging, DKI and LNDFI) and for those quantifying the degree of deviations (mean kurtosis and a parameter ? characterising the width of the distribution). We showed that both DKI and LNDFI were able to dramatically enhance the visualisation of ischaemic lesions in comparison with conventional methods. The largest relative change in the affected versus healthy regions was observed in the mean kurtosis values. The average changes in the mean kurtosis and ? values in the lesions were a factor of two to three larger than the relative changes observed in the mean diffusivity. In conclusion, the applied methods promise valuable perspectives in the assessment of stroke. PMID:22461260

Grinberg, Farida; Ciobanu, Luisa; Farrher, Ezequiel; Shah, N Jon

2012-03-27

236

Gas sensing enhancement of aluminum-doped ZnO nanovase structure with many gas facile diffusivity paths  

NASA Astrophysics Data System (ADS)

Al-doped ZnO nanovase structures were synthesized by thermal evaporation method with a fast temperature rise speed. It was found that there were a good amount of nanovase structures with a large aperture on the top of it and many short nanorods grew from their surface to generate many holes or channels enough for gas to quickly diffuse from surface to the inside of nanovase. Gas sensors were fabricated using the Al-doped ZnO nanostructures to examine the responses to 500 ppm C2H5OH, CO, NH3, and CH4 gases. The Al-doped ZnO nanovases exhibited a better response and selectivity toward ethanol as high as 34.1 at 300 °C. These results showed that Al-doped ZnO nanovases are highly promising for ethanol sensor applications, as the gas diffusion and mass transportation in sensing materials are significantly enhanced by their unique structures.

Lingmin, Yu; Xinhui, Fan; Lei, Cao; Lijun, Qi; Wen, Yan

2013-01-01

237

Selection of dopants to enhance hydrogen diffusion rates in MgH2 and NaMgH3  

NASA Astrophysics Data System (ADS)

The transport properties of hydrogen in metal hydrides are crucial to the kinetics of H2 storage in these materials. Previous first-principles calculations and experiments have shown that H transport in MgH2 and NaMgH3 is dominated by charged defects. This creates the possibility of enhancing hydrogen diffusion in these materials by adding dopants that alter the population of the relevant charged defects. We describe a comprehensive set of first-principles calculations examining dopants in MgH2 and NaMgH3 for this purpose. Only a small number of elemental dopants are found to have favorable properties, but these dopants could increase the diffusivity of H by two to three orders of magnitude relative to the undoped materials.

Hao, Shiqiang; Sholl, David S.

2009-04-01

238

Enhanced Thermal Diffusion of Li in Graphite by Alternating Vertical Electric Field: A Hybrid Quantum-Classical Simulation Study  

NASA Astrophysics Data System (ADS)

Enhancing the diffusivity of the Li ion in a Li-graphite intercalation compound that has been used as a negative electrode in the Li-ion rechargeable battery, is important in improving both the recharging speed and power of the battery. In the compound, the Li ion creates a long-range stress field around itself by expanding the interlayer spacing of graphite. We advance the hybrid quantum-classical simulation code to include the external electric field in addition to the long-range stress field by first-principles simulation. In the hybrid code, the quantum region selected adaptively around the Li ion is treated using the real-space density-functional theory for electrons. The rest of the system is described with an empirical interatomic potential that includes the term relating to the dispersion force between the C atoms in different layers. Hybrid simulation runs for Li dynamics in graphite are performed at 423 K under various settings of the amplitude and frequency of alternating electric fields perpendicular to C-layers. We find that the in-plane diffusivity of the Li ion is enhanced significantly by the electric field if the amplitude is larger than 0.2 V/Å within its order and the frequency is as high as 1.7 THz. The microscopic mechanisms of the enhancement are explained.

Ohba, Nobuko; Ogata, Shuji; Tamura, Tomoyuki; Kobayashi, Ryo; Yamakawa, Shunsuke; Asahi, Ryoji

2012-02-01

239

Diffuse cauda equina enhancement in a middle aged male with Susac syndrome and symptomatic cauda equina syndrome.  

PubMed

Susac syndrome is a rare neurologic disorder first described by Susac et al. in 1979. Clinically, Susac syndrome consists of a triad including encephalopathy, branch retinal artery occlusions and sensorineural hearing loss. All three components of the triad usually do not present at the same time, thus delaying time to diagnosis. MRI studies often show characteristic punched out lesions of the central fibers of the corpus callosum. Intracranial leptomeningeal enhancement may be seen, however, cauda equina involvement has not been described to our knowledge. We present a case of Susac syndrome in a middle-aged male with symptoms of cauda equina syndrome, and spinal MRI showing diffuse enhancement of the nerve roots of the cauda equina. PMID:23845898

Allmendinger, Andrew M; Viswanadhan, Narayan; Klufas, Roman A; Hsu, Liangge

2013-07-09

240

Depth Profiles of Cu Centers in Silicon Crystals Deposited with Cu and Diffused between 400 and 1000 °C Measured by Deep-Level Transient Spectroscopy  

NASA Astrophysics Data System (ADS)

For Cu-deposited Si crystals, we observed markedly different formation behavior of Cu-related species between samples that diffused below and above the eutectic temperature (EUT; 802 °C) of the Si-Cu system. The Cu center denoted as the CuDLB center was the dominant species under the Cu silicide layer and was almost homogenously distributed in the bulk of the samples that diffused below the EUT. For the samples that diffused above the EUT, the center concentration was markedly low near the surface due to the out-diffusion of Cu and gradually increased before forming a plateau in the region deeper than 30 ?m from the surface.

Nakamura, Minoru; Murakami, Susumu

2010-09-01

241

Diffusion-enhanced lanthanide energy transfer studies of protein prosthetic groups  

SciTech Connect

A long-lived luminescent solute in aqueous solution (e.g., /sup 5/D/sub 4/ terbium, tau approx. =10/sup -3/s) can donate its excitation energy to a chromophore such as a protein prosthetic group by, e.g., the radiationless dipolar mechanism of Foerster. However, in contrast to the usual energy-transfer experiment, a donor with a 10/sup -3/s lifetime can diffuse extensively through the solution and, in a time scale short compared to its excited lifetime, sample all permitted locations with respect to chromophoric acceptors. As recently indicated by Thomas et al. energy transfer in this rapid-diffusion limit can permit direct measurement of the allowed distance of closest approach of small solute molecules to chromophores which may be buried within proteins or membranes.

Meares, C.F.; Yeh, S.M.; Rice, L.S.

1980-10-01

242

Transient Stability Enhancement by Fuzzy Logic-Controlled SMES Considering Coordination With Optimal Reclosing of Circuit Breakers  

Microsoft Academic Search

This paper aims at investigating the effect of the coordination of fuzzy logic-controlled superconducting magnetic energy storage (SMES) and optimal reclosing on the transient stability in a simulated multi-machine power system during unsuccessful reclosing of circuit breakers. The performance of the coordinated operation of fuzzy logic-controlled SMES and optimal reclosing is compared to that of the coordinated operation of fuzzy

Mohd. Hasan Ali; Toshiaki Murata; Junji Tamura

2008-01-01

243

Thermal Management of a Soft Starter: Transient Thermal Impedance Model and Performance Enhancements Using Phase Change Materials  

Microsoft Academic Search

Adverse effects of starting-torque transients and high in-rush currents in induction motors are typically mitigated by employing electronically controlled soft starting voltages through silicon-controlled rectifiers (SCRs). However, the heat dissipation in the soft starter must be carefully managed in the design of motor drives. The objective of this study is both to address the heat dissipation in the soft starter

Fabien Volle; Suresh V. Garimella; Mark A. Juds

2010-01-01

244

A possibility of the oxygen diffusion enhancement in YSZ: a molecular dynamics study  

Microsoft Academic Search

A constant volume molecular dynamics calculation has been carried out for an yttria stabilized zirconia (YSZ) with composition (ZrO2)0.8(Y2O3)0.2, in which Y ions are artificially arranged in layers. The oxygen ion diffusion coefficient in the artificial YSZ is larger than that in YSZ with a random distribution of Y ions. A way of synthesizing YSZ with a larger value of

Hideo Okazaki; Hisashi Suzuki; Katsuyoshi Ihata

1994-01-01

245

Diffusion Limitation and Hyperoxic Enhancement of Oxygen Consumption in Zooxanthellate Sea Anemones, Zoanthids, and Corals  

Microsoft Academic Search

Absfract. Depending on their size and morphology, anthozoan polyps and colonies may be diffusion-limited in their oxygen consumption, even under well-stirred, air-saturated conditions. This is indicated by an en hancement of oxygen consumption under steady-state hyperoxic conditions that simulate the levels of 02 pro duced photosynthetically by zooxanthellae in the hosts' tissues. Such hyperoxia in the tissues of zooxanthellate species

J. MALCOLM SHICK

1990-01-01

246

Enhanced iron self-diffusion in the near-surface region investigated by nuclear resonant scattering  

Microsoft Academic Search

The access to X-rays of third generation synchrotron radiation sources enables studies of dynamics in metallic systems in grazing incidence geometry. Combining grazing incidence reflection of X-rays with nuclear resonant scattering of synchrotron radiation allows depth-selective investigations of hyperfine parameters and diffusion phenomena of iron and iron compounds. The unique feature of this method is its sensitivity to near-surface motions

M. Sladecek; B. Sepiol; M. Kaisermayr; J. Korecki; B. Handke; H. Thiess; O. Leupold; R. Rüffer; G. Vogl

2002-01-01

247

The Monitoring Population Density of Pests Based on Edge-enhancing Diffusion Filtering and Image Processing  

Microsoft Academic Search

As is known, agriculture is very important in China, but the problem about pests has hampered the further development of Chinese\\u000a agriculture. Digital image-processing technology and mathematical morphology are referred to as the main research methods,\\u000a and tiny pets like aphids among field are referred to as the research objects. Image processing technology such as edgeenhancing\\u000a diffusion filtering, mathematical morphology

Yuehuan Wang; Guirong Weng

2007-01-01

248

Depth progression of dissociation reaction of the 1.014-eV photoluminescence copper center in copper-diffused silicon crystal measured by deep-level transient spectroscopy  

NASA Astrophysics Data System (ADS)

Changes in the concentration depth profiles of the 1.014-eV photoluminescence (PL) copper center and its dissociation product by annealing were measured by deep-level transient spectroscopy (DLTS). The transformation reaction between these centers by annealing was not homogeneous throughout; it started at the sample surface and extended deeper with increasing annealing time. From this finding, the precipitation of interstitial copper in the surface region and its out-diffusion in the bulk are analyzed as the underlying processes to dissociate the center. The origin of the difference in the dissociation energies of the center obtained by DLTS and PL measurements is discussed.

Nakamura, Minoru; Murakami, Susumu

2011-04-01

249

Monitoring radiation belt particle precipitation - automatic detection of enhanced transient ionisation in the lower plasmasphere using subionospheric narrow band VLF signals  

NASA Astrophysics Data System (ADS)

Signals of naval VLF transmitters, propagating long distances along the Earth-ionosphere waveguide (EIWG) have been widely applied as effective tools for monitoring transient ionization at mesospheric altitudes. Perturbations in recorded amplitude and/or phase data series of stable frequency signals may refer to the effect of transient enhanced ionization in the EIWG, due to e.g. loss-cone precipitation of trapped energetic electrons (Carpenter et al., 1984, Dowden and Adams, 1990), burst of solar plasma particles (Clilverd et al., 2001). The contribution of precipitating particles are thought to be substantial in certain Sun-to-Earth energy flow processes in the upper atmosphere (Rodger et al., 2005). Narrow band VLF measuring network has been set up, developed and operated in Hungary, running in the last decade almost continuously, dedicated to monitor ionization enhancement regions along numerous transmitter-receiver paths. This setup is based on Omnipal and Ultra-MSK equipment, logging amplitude and phase data of received signals, sampled at frequencies of selected VLF transmitters. Signal trajectories, selected for recording represent proper configuration to survey transient ionization caused by energetic particles in the sub-polar region, such as effect of scattered particles of the inner radiation belt. Reprocessing of the mass archived recordings has been started using a newly developed signal processing code, detecting and classifying different sort of perturbations automatically on narrow band VLF series. Occurrence rates, daily and seasonal variation, statistics of transient ionization enhancements, their geographic distribution within the surveyed range and time period, and correlation with intense geomagnetic and/or Solar event is yielded by this analysis. References: Carpenter, D.L., Inan, U.S., Trimpi, M.L., Helliwell, R.A., and Katsufrakis, J.P.: Perturbations of subionospheric LF and MF signals due to whistler-induced electron precipitation burst, J.Geophys.Res., 89, A11, 9837-9862, 1984. Clilverd, M. A., Seppälä, A., Rodger, C.J., Thomson, N.R., Verronen, P.T., Turunen, E., Ulich, Th., Lichtenberger, J., and Steinbach, P.: Modelling polar ionospheric effects during the October-November 2003 solar proton events, Radio Sci., 41, RS2001, doi:10.1029/2005RS003290. Dowden, R.L., and Adams, C.D.D.: Lightning-induced perturbations on VLF subionospheric transmissions, J. Atmos. Terr. Phys., 52, 5, 357-363, 1990. Rodger, C.J., Clilverd, M.A., Thomson,N.R., Nunn, D., and Lichtenberger, J.: Lightning driven inner radiation belt energy deposition into the atmosphere: regional and global estimates, Ann. Geophys., 23, 3419-3430, 2005.

Steinbach, P.; Lichtenberger, J.; Ferencz, Cs.

2009-04-01

250

Stroma cell-derived factor-1? signaling enhances calcium transients and beating frequency in rat neonatal cardiomyocytes.  

PubMed

Stroma cell-derived factor-1? (SDF-1?) is a cardioprotective chemokine, acting through its G-protein coupled receptor CXCR4. In experimental acute myocardial infarction, administration of SDF-1? induces an early improvement of systolic function which is difficult to explain solely by an anti-apoptotic and angiogenic effect. We wondered whether SDF-1? signaling might have direct effects on calcium transients and beating frequency.Primary rat neonatal cardiomyocytes were culture-expanded and characterized by immunofluorescence staining. Calcium sparks were studied by fluorescence microscopy after calcium loading with the Fluo-4 acetoxymethyl ester sensor. The cardiomyocyte enriched cellular suspension expressed troponin I and CXCR4 but was vimentin negative. Addition of SDF-1? in the medium increased cytoplasmic calcium release. The calcium response was completely abolished by using a neutralizing anti-CXCR4 antibody and partially suppressed and delayed by preincubation with an inositol triphosphate receptor (IP3R) blocker, but not with a ryanodine receptor (RyR) antagonist. Calcium fluxes induced by caffeine, a RyR agonist, were decreased by an IP3R blocker. Treatment with forskolin or SDF-1? increased cardiomyocyte beating frequency and their effects were additive. In vivo, treatment with SDF-1? increased left ventricular dP/dtmax.These results suggest that in rat neonatal cardiomyocytes, the SDF-1?/CXCR4 signaling increases calcium transients in an IP3-gated fashion leading to a positive chronotropic and inotropic effect. PMID:23460790

Hadad, Ielham; Veithen, Alex; Springael, Jean-Yves; Sotiropoulou, Panagiota A; Mendes Da Costa, Agnès; Miot, Françoise; Naeije, Robert; De Deken, Xavier; Entee, Kathleen Mc

2013-02-27

251

Electrolyte diffusion in compacted montmorillonite engineered barriers  

SciTech Connect

The bentonite-based engineered barrier or packing is a proposed component of several designs conceived to dispose of high-level nuclear waste in geologic repositories. Once radionuclides escape the waste package, they must first diffuse through the highly impermeable clay-rich barrier before they reach the host repository. To determine the effectiveness of the packing as a sorption barrier in the transient release period and as a mass-transfer barrier in the steady release period over the geologic time scales involved in nuclear waste disposal, a fundamental understanding of the diffusion of electrolytes in compacted clays is required. We present, and compare with laboratory data, a model quantifying the diffusion rates of cationic cesium and uncharged tritium in compacted montmorillonite clay. Neutral tritium characterizes the geometry (i.e., tortuosity) of the particulate gel. After accounting for cation exchange, we find that surface diffusion is the dominant mechanism of cation transport, with an approximate surface diffusion coefficient of 2 x 10 W cmS/s for cesium. This value increases slightly with increasing background ionic strength. The implications of this work for the packing as a migration barrier are twofold. During the transient release period, K/sub d/ values are of little importance in retarding ion migration. This is because sorption also gives rise to a surface diffusion path, and it is surface diffusion which controls the diffusion rate of highly sorbing cations in compacted montmorillonite. During the steady release period, the presence of surface diffusion leads to a flux through the packing which is greatly enhanced. In either case, if surface diffusion is neglected, the appropriate diffusion coefficient of ions in compacted packing will be in considerable error relative to current design recommendations. 11 refs., 4 figs., 1 tab.

Jahnke, F.M.; Radke, C.J.

1985-09-01

252

Contrast-enhanced diffuse optical tomography of brain perfusion in humans using ICG  

NASA Astrophysics Data System (ADS)

Regular monitoring of brain perfusion at the bedside in neurointensive care is desirable. Currently used imaging modalities are not suited for constant monitoring and often require a transport of the patient. Noninvasive near infrared spectroscopy (NIRS) in combination with an injection of a safe dye (indocyanine green, ICG) could serve as a quasi-continuous brain perfusion monitor. In this work, we evaluate prerequisites for the development of a brain perfusion monitor using continuous wave (cw) NIRS technique. We present results from a high-resolution diffuse optical tomography (HR-DOT) experiment in humans demonstrating the separation of signals from skin from the brain. This technique can help to monitor neurointensive care patients on a regular basis, detecting changes in cortical perfusion in time.

Habermehl, Christina; Schmitz, Christoph; Steinbrink, Jens

2012-02-01

253

Quantitative Diffusion Weighted Imaging and Dynamic Susceptibility-weighted Contrast-enhanced Perfusion MRI Analysis of T2-hypointense Lesion Components in Pediatric Diffuse Intrinsic Pontine Glioma  

PubMed Central

Background and Purpose Focal anaplasia in cerebral neoplasm has been found to be characterized by T2 hypointensity, signal enhancement on post-contrast T1-weighted images and restricted water diffusion.. We identified T2HOFs with these MRI characteristics in children with DIPG and hypothesized that those represent areas of focal anaplasia, hence may also exhibitid increased perfusion properties, therefore we used dynamic susceptibility-weighted perfusion MRI to support our hypothesis,. Materials and Methods We retrospectively reviewed the baseline MRI scans of 86 patients (48 girls, 37 boys, median age 6.1 years, range 1.1–17.6 years) treated for DIPG at our hospital (2004–2009). T2HOFs with the described MRI characteristics were identified in 10 patients. We used an ROI-based, quantitative multiparametric (ADC, FA, rCBV, rCBF, and rMTT) approach to compare the MRI properties of T2HOFs with those of the typical T2HRT. Results ADC was significantly lower in T2HOFswith the specified MRI characteristics compared to T2HRTs (range, 0.71 to 1.95 ?m2/ms vs. 1.36 to 2.13 ?m2/ms, P < .01) and FA (range, 0.12 to 0.34 vs. 0.07 to 0.24, P=.03) and rCBV (range, 0.4 to 2.62 vs. 0.23 to 1.57, P=.01) were significantly higher. Neither rCBF nor rMTT was significantly different between T2HOFs and T2HRTs. Conclusion Our data suggest that T2HOFs in DIPG may represent areas of focal anaplasia and underline the importance of regional, rather than global tumor field analysis in the diagnostic imaging workup of cerebral neoplasms and guidance for biopsy in particular.

Lobel, U.; Sedlacik, J.; Reddick, W.E.; Kocak, M.; Ji, Q.; Broniscer, A.; Hillenbrand, C.M.; Patay, Z.

2012-01-01

254

Facilitated diffusion of glucosamine-6-phosphate synthase inhibitors enhances their antifungal activity  

Microsoft Academic Search

N3-(4-Methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP) and 2-amino-2- deoxy-D-glucitol-6-phosphate (ADGP) are strong inhibitors of the essential fungal en- zyme, glucosamine-6-phosphate synthase, but their antifungal activity is poor, due to slow penetration of these agents through the cytoplasmic membrane. In the present studies we have exploited the possibility of enhancement of ADGP and FMDP antifungal activity by improving their transport properties. It has been

Agnieszka Janiak; Barbara Cybulska; Joanna Szlinder-Richert; Edward Borowski

2002-01-01

255

Mapping of the mouse olfactory system with manganese-enhanced magnetic resonance imaging and diffusion tensor imaging.  

PubMed

As the power of studying mouse genetics and behavior advances, research tools to examine systems level connectivity in the mouse are critically needed. In this study, we compared statistical mapping of the olfactory system in adult mice using manganese-enhanced MRI (MEMRI) and diffusion tensor imaging (DTI) with probabilistic tractography. The primary goal was to determine whether these complementary techniques can determine mouse olfactory bulb (OB) connectivity consistent with known anatomical connections. For MEMRI, 3D T1-weighted images were acquired before and after bilateral nasal administration of MnCl(2) solution. Concomitantly, high-resolution diffusion-tensor images were obtained ex vivo from a second group of mice and processed with a probabilistic tractography algorithm originating in the OB. Incidence maps were created by co-registering and overlaying data from the two scan modalities. The resulting maps clearly show pathways between the OB and amygdala, piriform cortex, caudate putamen, and olfactory cortex in both the DTI and MEMRI techniques that are consistent with the known anatomical connections. These data demonstrate that MEMRI and DTI are complementary, high-resolution neuroimaging tools that can be applied to mouse genetic models of olfactory and limbic system connectivity. PMID:22527121

Gutman, David A; Magnuson, Matthew; Majeed, Waqas; Keifer, Orion P; Davis, Michael; Ressler, Kerry J; Keilholz, Shella

2012-04-24

256

MRI edge enhancement as a diffusive discord of spin phase structure.  

PubMed

The enhancement of magnetic resonance image intensity near impermeable boundaries can be nicely described by a new approach where the diffusional spin echo attenuation is linked to the correlation function of molecular motion. In this method the spin phase structure created by the applied gradient is considered to be a composition of plane waves with the wave vectors representing feasible momentum states of a particle in confinement. The enhancement of edges on the magnetic resonance images (MRI) comes out as a discord of plane waves due to particle motion. It results from the average of the wave phase by using the cumulant expansion in the Gaussian approximation. The acquired analytical expression describes the MRI signal space distribution where the enhancement of edges depends on the intensity and the duration of gradient sequence as well as on the length of the mean squared particle displacement in restricted geometry. This new method works well with gradients of general waveform and is, therefore, suitable for imaging sequences where finite or even modulated gradients are usually used. PMID:10053144

Stepisnik, J; Duh, A; Mohoric, A; Sersa, I

1999-03-01

257

Enhanced neurogenesis in organotypic cultures of rat hippocampus after transient subfield-selective excitotoxic insult induced by domoic acid.  

PubMed

New neurons are continuously generated in the hippocampus and may play an important role in many physiological and pathological conditions. Here we present evidence of cell proliferation and neurogenesis after a selective and transient excitotoxic injury to the hippocampal cornu ammonis 1 (CA1) area induced by low concentrations of domoic acid (DOM) in rat organotypic hippocampal slice cultures (OHSC). DOM is an excitatory amino acid analog to kainic acid that acts through glutamate receptors to elicit a rapid and potent excitotoxic response. Exposure of slice cultures to varying concentrations of DOM for 24 h induced dose-dependent neuronal toxicity that was independent of activation of classic apoptotic markers. Treatment with 2 ?M DOM for 24 h caused a selective yet transient neurotoxic injury in the CA1 subfield of the hippocampus that appeared recovered after 7 days of incubation in a DOM-free medium and showed significant microgliosis but no sign of astrogliosis. The DOM insult (2 ?M, 24 h) resulted in a significant upregulation of cell proliferation, as assessed by 5-bromo-2-deoxyuridine (BrdU) incorporation, and a concurrent increase of the neuronal precursor cell marker doublecortin (DCX) within the subgranular zone of the dentate gyrus and area CA1. Neurogenesis occurred primarily during the first week after termination of the DOM exposure. Our study shows that exposure of OHSC to concentrations of DOM below those required to induce permanent neurotoxicity can induce proliferation and differentiation of neural progenitor cells that may contribute to recovery from mild injury and to develop abnormal circuits relevant to disease. PMID:22366222

Pérez-Gómez, A; Tasker, R A

2012-02-08

258

Site-selective transient photoluminescence enhancement of impurity-trapped excitons in NaMgF3:Yb2+  

NASA Astrophysics Data System (ADS)

The excited-state structure of impurity-trapped excitons are measured in a multisite system. We use a two-color (UV-IR) pulsed photoluminescence enhancement technique, which probes the interlevel transitions and dynamics of impurity-trapped excitons in doped insulating phosphor materials. The technique is applied to NaMgF3:Yb2+, which exhibits emission from two charge-compensation centers with peaks at 22300 cm-1 (448 nm) and 24000 cm-1 (417 nm). The observed photoluminescence enhancement is caused by a combination of intraexcitonic excitation and electron trap liberation. The electron traps are inferred to have a depth of approximately 800 cm-1.

Hughes-Currie, Rosa B.; Senanayake, Pubudu S.; Wells, Jon-Paul R.; Reid, Michael F.; Berden, Giel; Reeves, Roger J.; Meijerink, Andries

2013-09-01

259

Transient receptor potential ankyrin 1 activation enhances hapten sensitization in a T-helper type 2-driven fluorescein isothiocyanate-induced contact hypersensitivity mouse model.  

PubMed

Some chemicals contribute to the development of allergies by increasing the immunogenicity of other allergens. We have demonstrated that several phthalate esters, including dibutyl phthalate (DBP), enhance skin sensitization to fluorescein isothiocyanate (FITC) in a mouse contact hypersensitivity model, in which the T-helper type 2 (Th2) response is essential. On the other hand, some phthalate esters were found to activate transient receptor potential ankyrin 1 (TRPA1) cation channels on sensory neurons. We then found a positive correlation between the enhancing effects of several types of phthalate esters on skin sensitization to FITC and their ability to activate TRPA1. Here we examined the involvement of TRPA1 in sensitization to FITC by using TRPA1 agonists other than phthalate esters. During skin sensitization to FITC, the TRPA1 agonists (menthol, carvacrol, cinnamaldehyde and DBP) augmented the ear-swelling response as well as trafficking of FITC-presenting dendritic cells to draining lymph nodes. We confirmed that these TRPA1 agonists induced calcium influx into TRPA1-expressing Chinese hamster ovary (CHO) cells. We also found that TRPA1 antagonist HC-030031 inhibited DBP-induced calcium influx into TRPA1-expressing CHO cells. After pretreatment with this antagonist upon skin sensitization to FITC, the enhancing effect of DBP on sensitization was suppressed. These results suggest that TRPA1 activation will become a useful marker to find chemicals that facilitate sensitization in combination with other immunogenic haptens. PMID:22935519

Shiba, Takahiro; Tamai, Takuma; Sahara, Yurina; Kurohane, Kohta; Watanabe, Tatsuo; Imai, Yasuyuki

2012-08-23

260

Exposure of nondividing populations of primary human fibroblasts to UV (254 nm) radiation induces a transient enhancement in capacity to repair potentially lethal cellular damage  

SciTech Connect

Nondividing (arrested) populations of primary human fibroblasts from normal individuals exposed to an intial dose (1.5 or 3 Jm/sup -2/) of far-UV (254 nm) radiation and then incubated in medium containing low (0.5%) serum develop enhanced resistance to inactivation of cloning efficiency by a second (challenge) dose of UV. The resistance develops within 2-4 days, after which there is a decline. Resistance develops to a higher degree and more rapidly (1-2 days) in cells derived from patients with the variant form of xeroderma pigmentosum. Excision-deficient cells from xeroderma pigmentosum complementation group A individuals also develop UV resistance after a lower (0.2 Jm/sup -2/) exposure to UV. Enhanced UV resistance does not develop in UV-irradiated cell populations incubated with the protein synthesis inhibitor cycloheximide (5 ..mu..M). These observations are consistent with the interpretation that exposure of human fibroblasts to low doses of UV induces synthesis of a protein involved in a metabolic pathway that transiently enhances the capacity of cells to repair potentially lethal damage resulting from a subsequent dose of UV.

Tyrrell, R.M.

1984-02-01

261

Tailored exciton diffusion in organic photovoltaic cells for enhanced power conversion efficiency.  

PubMed

Photoconversion in planar-heterojunction organic photovoltaic cells (OPVs) is limited by a short exciton diffusion length (L(D)) that restricts migration to the dissociating electron donor/acceptor interface. Consequently, bulk heterojunctions are often used to realize high efficiency as these structures reduce the distance an exciton must travel to be dissociated. Here, we present an alternative approach that seeks to directly engineer L(D) by optimizing the intermolecular separation and consequently, the photophysical parameters responsible for excitonic energy transfer. By diluting the electron donor boron subphthalocyanine chloride into a wide-energy-gap host material, we optimize the degree of interaction between donor molecules and observe a ~50% increase in L(D). Using this approach, we construct planar-heterojunction OPVs with a power conversion efficiency of (4.4 ± 0.3)%, > 30% larger than the case of optimized devices containing an undiluted donor layer. The underlying correlation between L(D) and the degree of molecular interaction has wide implications for the design of both OPV active materials and device architectures. PMID:23142837

Menke, S Matthew; Luhman, Wade A; Holmes, Russell J

2012-11-11

262

Sparsity enhanced spatial resolution and depth localization in diffuse optical tomography  

PubMed Central

Abstract: In diffuse optical tomography (DOT), researchers often face challenges to accurately recover the depth and size of the reconstructed objects. Recent development of the Depth Compensation Algorithm (DCA) solves the depth localization problem, but the reconstructed images commonly exhibit over-smoothed boundaries, leading to fuzzy images with low spatial resolution. While conventional DOT solves a linear inverse model by minimizing least squares errors using L2 norm regularization, L1 regularization promotes sparse solutions. The latter may be used to reduce the over-smoothing effect on reconstructed images. In this study, we combined DCA with L1 regularization, and also with L2 regularization, to examine which combined approach provided us with an improved spatial resolution and depth localization for DOT. Laboratory tissue phantoms were utilized for the measurement with a fiber-based and a camera-based DOT imaging system. The results from both systems showed that L1 regularization clearly outperformed L2 regularization in both spatial resolution and depth localization of DOT. An example of functional brain imaging taken from human in vivo measurements was further obtained to support the conclusion of the study.

Kavuri, Venkaiah C.; Lin, Zi-Jing; Tian, Fenghua; Liu, Hanli

2012-01-01

263

Enhanced characterization of oilfield emulsions via NMR diffusion and transverse relaxation experiments.  

PubMed

The procedure proposed by Packer and Rees (J. Colloid Interface Sci. 40 (1972) 206) to interpret pulsed field gradient spin-echo (PGSE) experiments on emulsions is commonly used to resolve for the distribution of droplet sizes via nuclear magnetic resonance (NMR). Nevertheless, such procedure is based on several assumptions that may restrict its applicability in many practical cases. Among such constrains, (a) the amplitude of the spin-echo (signal) must be influenced solely by the drop phase, and not by the continuous phase; and (b) the shape of the drop size distribution must be assumed a priori. This article discusses new theory to interpret results from PGSE experiments and a novel procedure that couples diffusion measurements (PGSE) with transverse relaxation rate experiments (the so-called CPMG sequence) to overcome the above limitations. Results from experiments on emulsions of water dispersed in several crude oils are reported to demonstrate that the combined CPMG-PGSE method renders drop size distributions with arbitrary shape, the water/oil ratio of the emulsion and the rate of decay of magnetization at the interfaces, i.e. the surface relaxivity. It is also shown that the procedure allows screening if the dispersion is oil-in-water (o/w) or water-in-oil (w/o) in a straightforward manner and that it is suitable to evaluate stability of emulsions. PMID:12969643

Peña, Alejandro A; Hirasaki, George J

2003-09-18

264

Identifying Knowledge-Attitude-Practice Gaps to Enhance HPV Vaccine Diffusion.  

PubMed

To examine differences in knowledge, attitudes, and related practices among adopters and nonadopters of the human papillomavirus (HPV) vaccine, the researchers conducted 83 in-depth interviews with 18- to 26-year-old women. The study identified knowledge-attitude-practice gaps in the context of the HPV vaccine to explain why diffusion of a preventive innovation (such as the HPV vaccine) requires targeted risk communication strategies in order to increase demand. Salient findings included similarities between vaccinated and unvaccinated women's lack of knowledge and uncertainties about HPV and cervical cancer. Vaccinated women who had no knowledge of HPV or no-risk/low-risk perceptions of HPV reported receiving vaccination, indicating HPV risk protection behavior could precede knowledge acquisition for vaccinated women. These vaccinated women identified an interpersonal network supportive of vaccination and reported supportive social influences. Among unvaccinated women, unsupportive vaccination attitudes included low perceived personal risk of HPV. In contrast, unvaccinated women often cited erroneous beliefs that HPV could be avoided by abstinence, monogamy, and knowledge of their partners' sexual history as reasons that the vaccine was not personally relevant. Unvaccinated women cited interpersonal influences that activated short- and long-term vaccination safety and efficacy concerns. Different levels of fear regarding the HPV vaccine may underlie (a) attitudinal differences between vaccinated and unvaccinated women in perceived vaccination value and (b) attitude-practice gaps. PMID:23767775

Cohen, Elisia L; Head, Katharine J

2013-06-14

265

Stress-induced switch in Numb isoforms enhances Notch-dependent expression of subtype-specific transient receptor potential channel.  

PubMed

The Notch signaling pathway plays an essential role in the regulation of cell specification by controlling differentiation, proliferation, and apoptosis. Numb is an intrinsic regulator of the Notch pathway and exists in four alternative splice variants that differ in the length of their phosphotyrosine-binding domain (PTB) and proline-rich region domains. The physiological relevance of the existence of the Numb splice variants and their exact regulation are still poorly understood. We previously reported that Numb switches from isoforms containing the insertion in PTB to isoforms lacking this insertion in neuronal cells subjected to trophic factor withdrawal (TFW). The functional relevance of the TFW-induced switch in Numb isoforms is not known. Here we provide evidence that the TFW-induced switch in Numb isoforms regulates Notch signaling strength and Notch target gene expression. PC12 cells stably overexpressing Numb isoforms lacking the PTB insertion exhibited higher basal Notch activity and Notch-dependent transcription of the transient receptor potential channel 6 (TRPC6) when compared with those overexpressing Numb isoforms with the PTB insertion. The differential regulation of TRPC6 expression is correlated with perturbed calcium signaling and increased neuronal vulnerability to TFW-induced death. Pharmacological inhibition of the Notch pathway or knockdown of TRPC6 function ameliorates the adverse effects caused by the TFW-induced switch in Numb isoforms. Taken together, our results indicate that Notch and Numb interaction may influence the sensitivity of neuronal cells to injurious stimuli by modulating calcium-dependent apoptotic signaling cascades. PMID:20038578

Kyriazis, George A; Belal, Cherine; Madan, Meenu; Taylor, David G; Wang, Jang; Wei, Zelan; Pattisapu, Jogi V; Chan, Sic L

2009-12-28

266

Transient photoreceptor deconstruction by CNTF enhances rAAV-mediated cone functional rescue in late stage CNGB3-achromatopsia.  

PubMed

Achromatopsia is a genetic disorder of cones, and one of the most common forms is a channelopathy caused by mutations in the ?-subunit, CNGB3, of the cone cyclic nucleotide-gated (CNG) channel. Recombinant adeno-associated virus of serotype 5 (rAAV5)-mediated gene transfer of human CNGB3 cDNA to mutant dog cones results in functional and structural rescue in dogs <0.5 years of age, but treatment is minimally effective in dogs >1 year. We now test a new therapeutic concept by combining gene therapy with the administration of ciliary neurotrophic factor (CNTF). Intravitreal CNTF causes transient dedifferentiation of photoreceptors, a process called deconstruction, whereby visual cells become immature with short outer segments, and decreased retinal function and gene expression that subsequently return to normal. Cone function was successfully rescued in all mutant dogs treated between 14 and 42 months of age with this strategy. CNTF-mediated deconstruction and regeneration of the photoreceptor outer segments prepares the mutant cones optimally for gene augmentation therapy. PMID:23568263

Komáromy, András M; Rowlan, Jessica S; Corr, Amanda T Parton; Reinstein, Shelby L; Boye, Sanford L; Cooper, Ann E; Gonzalez, Amaliris; Levy, Britt; Wen, Rong; Hauswirth, William W; Beltran, William A; Aguirre, Gustavo D

2013-04-09

267

NESTLE: Few-group neutron diffusion equation solver utilizing the nodal expansion method for eigenvalue, adjoint, fixed-source steady-state and transient problems.  

National Technical Information Service (NTIS)

NESTLE is a FORTRAN 77 code that solves the few-group neutron diffusion equation utilizing the Nodal Expansion Method (NEM). NESTLE can solve the eigenvalue (criticality); eigenvalue adjoint; external fixed-source steady-state; or external fixed-source. o...

P. J. Turinsky R. M. K. Al-Chalabi P. Engrand H. N. Sarsour F. X. Faure

1994-01-01

268

Selective cavity-enhanced trace gas detection via diffusion time-of-fight  

NASA Astrophysics Data System (ADS)

A novel approach to optical detection of airborne explosive vapor using a combination of cavity enhanced ab- sorption spectroscopy (CEAS) and diusion time of ight (DiTOF) is reported. The direct optical detection of explosive vapors by absorption presents a number of unique challenges due to low vapor pressures of explosive compounds, a lack of resolved spectral features, and the presence of interfering species with overlapping absorp- tion spectra. By recording the changing optical absorption as sampled atmosphere diuses into an explosive-free buer gas, the concentration of explosive molecules may be determined using a Bayesian statistical signal process- ing technique. This technique avoids the need for laser wavelength scans while simultaneously providing robust background rejection. The use of xed laser wavelengths allows for the use of cavity-locked cavity ring-down or cavity-locked direct cavity transmission absorption measurements with high data acquisition rates and signi- cantly reduces the complexity of the laser system by eliminating the need for precision wavelength monitoring. This allows for the development of compact, eld deployable sensors based on this technique. Experimental demonstration of the simultaneous detection of multiple species of hydrocarbon tracer molecules at 4295 cm-1 will be reported. The results of the current work will be applied to the detection of TNT vapor to show a projected sensitivity of 2 pptv in a diesel exhaust background.

Miller, Anthony; Richman, Bruce; Viteri, C. Ricardo; McKeever, Jason

2012-05-01

269

In vivo evaluation of retinal and callosal projections in early postnatal development and plasticity using manganese-enhanced MRI and diffusion tensor imaging  

Microsoft Academic Search

The rodents are an excellent model for understanding the development and plasticity of the visual system. In this study, we explored the feasibility of Mn-enhanced MRI (MEMRI) and diffusion tensor imaging (DTI) at 7T for in vivo and longitudinal assessments of the retinal and callosal pathways in normal neonatal rodent brains and after early postnatal visual impairments. Along the retinal

Kevin C. Chan; Joe S. Cheng; Shujuan Fan; Iris Y. Zhou; Jian Yang; Ed X. Wu

270

Dense fully 111-textured TiN diffusion barriers: Enhanced lifetime through microstructure control during layer growth  

NASA Astrophysics Data System (ADS)

Low-temperature deposition of TiN by reactive evaporation or sputter deposition onto amorphous substrates leads to highly underdense layers which develop mixed 111/002 orientations through competitive growth. In contrast, we demonstrate here the growth of low-temperature (450 °C) fully dense polycrystalline TiN layers with complete 111 texture. This was achieved by reactive magnetron sputter deposition using a combination of: (1) highly oriented 25-nm-thick 0002 Ti underlayers to provide 111 TiN orientation through texture inheritance (local epitaxy) and (2) high flux (JN2+/JTi=14), low-energy (EN2+~=20 eV), N2+ ion irradiation in a magnetically unbalanced mode to provide enhanced adatom diffusion leading to densification during TiN deposition. The Ti underlayers were also grown in a magnetically unbalanced mode, in this case with an incident Ar+/Ti flux ratio of 2 and EAr+~=11 eV. All TiN films were slightly overstoichiometric with a N/Ti ratio of 1.02+/-0.03. In order to assess the diffusion-barrier properties of dense 111-textured TiN, Al overlayers were deposited without breaking vacuum at 100 °C. Al/TiN bilayers were then annealed at a constant ramp rate of 3 °C s-1 to 650 °C s-1 and the interfacial reaction between Al and TiN was monitored by in situ synchrotron x-ray diffraction measurements. As a reference point, we find that interfacial Al3Ti formation is observed at 450 °C in Al/TiN bilayers in which the TiN layer is deposited directly on SiO2 in a conventional magnetically balanced mode and, hence, is underdense with a mixed 111/002 orientation. However, the onset temperature for interfacial reaction was increased to 610 °C in bilayers with fully dense TiN exhibiting complete 111 preferred orientation.

Chun, J.-S.; Petrov, I.; Greene, J. E.

1999-10-01

271

Early Detection of Lewis Lung Carcinoma Tumor Control by Irradiation Using Diffusion-Weighted and Dynamic Contrast-Enhanced MRI  

PubMed Central

Purpose To investigate the correlation between diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) derived parameters and radioresponsiveness of Lewis lung carcinoma (LLC) tumor. Materials and Methods LLC tumor growth in C57BL/6 mouse limb was used for the experiment. The tumors were irradiated with 10 Gy×5, or 30 Gy×2 vs. sham irradiation. Fourteen tumors were subjected to DW-MRI and DCE-MRI pre-radiotherapy and weekly imaging after radiotherapy. The temporal changes in apparent diffusion coefficient (ADC) and DCE-MRI derived parameters (Ktrans, kep, ve, and vp) were correlated with tumor size, and were histologically compared with CD31 staining of resected tumors. Results The 10 Gy×5 dose inhibited tumor growth for a week, while 30 Gy×2 controlled tumor growth for a 3-week observation period. One week after radiotherapy (week 2), irradiated tumors showed significantly higher values of ADC than untreated ones (10 Gy×5, p?=?0.004; 30 Gy×2, p?=?0.01). Significantly higher values of ve were shown earlier by 30 Gy×2 vs. sham (p?=?0.01) and 10 Gy×5 vs. sham irradiation (p?=?0.05). Sustained higher ve from 10 Gy×5 compared to sham irradiated tumors was evident at week 3 (p?=?0.016) and week 4 (p?=?0.046). A 13.8% early increase in ADC for 30 Gy×2 tumor group (p?=?0.002) and a 16.5% increase for 10 Gy×5 group were noted (p?=?0.01) vs. sham irradiation (which showed a 2.2% decrease). No differences were found for Ktrans, kep, or vp. Both radiotherapy groups demonstrated significant reduction in microvessel counts. Conclusion Early increase in ADC and ve correlated with tumor control by irradiation.

Cheng, Jason Chia-Hsien; Yuan, Ang; Chen, Jyh-Horng; Lu, Yi-Chien; Cho, Kuan-Hung; Wu, Jian-Kuen; Wu, Chien-Jang; Chang, Yeun-Chung; Yang, Pan-Chyr

2013-01-01

272

EAAC1 gene deletion alters zinc homeostasis and enhances cortical neuronal injury after transient cerebral ischemia in mice.  

PubMed

The excitatory amino acids glutamate and cysteine are actively transported into neurons from the extracellular space by the high affinity glutamate transporter EAAC1. The astrocyte glutamate transporters, GLT1 and GLAST, are the primary mediators of glutamate clearance. EAAC1 has a limited role in this function. However, uptake of cysteine into neurons via EAAC1 contributes to neuronal antioxidant function by providing cysteine substrate for glutathione synthesis. Mice in which the EAAC1 gene has been deleted were seen to have enhanced susceptibility to neuronal oxidative stress and developed brain atrophy and cognitive function decline with aging. The aim of the current study was to evaluate if EAAC1 confers protection against ischemic events. Young adult CD-1 wild-type or EAAC1(-/-) mice were subjected to 30 min of bilateral common carotid artery occlusion and evaluated for neuronal death and zinc translocation. The intensity of TSQ fluorescence in the cytoplasm of cortical neurons in the EAAC1(-/-) mice was significantly higher than wild-type mice, indicating that the cortical neurons of EAAC1(-/-) mice contain higher cytoplasmic concentrations of labile (or free) zinc. Zinc translocation into cortical neurons was also enhanced in EAAC1(-/-) mice. Three days after ischemia, Fluoro-Jade B staining revealed that EAAC1(-/-) mice had more than twice as many degenerating neurons as wild-type mice. N-acetylcysteine, a membrane-permeant cysteine pro-drug, normalized basal zinc levels, reduced TSQ (+) neurons and reduced ischemic neuronal death in the EAAC1(-/-) mice when delivered in a pre-treatment fashion. Taken together, this study implicates EAAC1-dependent cysteine uptake as an endogenous source of enhancing antioxidant function and zinc homeostasis in neurons in the ischemic brain. PMID:22575539

Jang, Bong Geom; Won, Seok Joon; Kim, Jin Hee; Choi, Bo Young; Lee, Min Woo; Sohn, Min; Song, Hong Ki; Suh, Sang Won

2012-05-08

273

Structure, stability, and diffusion of arsenic-silicon interstitial pairs  

NASA Astrophysics Data System (ADS)

Recent experimental studies [A. Ural, P. B. Griffin, and J. D. Plummer, J. Appl. Phys. 85, 6440 (1999); R. Kim, T. Hirose, T. Shano, H. Tsuji, and K. Taniguchi, Jpn. J. Appl. Phys. 41, 227 (2002); S. Solmi, M. Ferri, M. Bersani, D. Giubertoni, and V. Soncini, J. Appl. Phys. 94, 4950 (2003)] have suggested the importance of Si interstitials in As transient enhanced diffusion during pn junction formation in silicon. Using density functional theory calculations within the generalized gradient approximation, we have examined the structure, stability and diffusion of As-Sii pairs. For the negatively charged As-Sii pair, we find a minimum energy structure in which the As atom bridges two approximate lattice Si atoms, while for the neutral and positively charged As-Sii we find the lowest energy structure is comprised of an As and Sii pair that is aligned in the [110] direction while sharing a lattice site. Our results suggest that in n-type extrinsic regions the diffusion of -1 charged As-Sii pairs will be prevailing with an overall activation energy of 3.1-3.4 eV, while under intrinsic conditions the neutral and -1 charged pairs will both contribute to arsenic diffusion. The predicted activation energies are similar to experimental observations for As diffusion and previous calculations for As-vacancy complex diffusion. These results clearly support that interstitials can contribute significantly to As transient enhanced diffusion, particularly in the region where interstitials exist in excess.

Harrison, Scott A.; Edgar, Thomas F.; Hwang, Gyeong S.

2005-12-01

274

An Analytical Solution for the Transient Two-Dimensional Advection–Diffusion Equation with Non-Fickian Closure in Cartesian Geometry by the Generalized Integral Transform Technique  

Microsoft Academic Search

Analytical solutions of equations are of fundamental importance in understanding and describing physical phenomena, since\\u000a they are able to take into account all the parameters of a problem and investigate their influence. In a recent work, [Bus07]\\u000a reported an analytical solution for the stationary two-dimensional advection–diffusion equation with Fickian closure by the\\u000a Generalized Integral Laplace Transform Technique (GILTT). The main

D. Buske; M. T. Vilhena; D. Moreira; T. Tirabassi

275

Enhanced performance of bio-cathode microbial fuel cells with the applying of transient-state operation modes.  

PubMed

To enhance the MFC's denitrification performance, this study investigated three different external circuits/operation modes of the MFC: alternative charging and discharging (ACD), intermittent charging (IC) and constant external resistance (R). Results showed that the ACD and IC modes offered larger output currents as well as higher nitrate and COD removal rates than the steady R mode. The best performance was achieved with the ACD mode. At the initial [COD]=?1200mg/L and [NO3(-)]=?140mg/L, the ACD mode delivered an average power density of 0.91W/m(3), an average nitrate removal rate of 15.5mg/(Ld) and an average COD removal rate of 137mg/(Ld), 268%, 207% and 168% respectively greater than those by the R mode. The enhancement by the ACD and IC modes was more pronounced at lower nitrate and COD concentrations and/or with the lack of stirring of electrolyte solutions. PMID:23994964

Liang, Peng; Yuan, Lulu; Wu, Wenlong; Yang, Xufei; Huang, Xia

2013-08-09

276

Diameter-dependent boron diffusion in silicon nanowire-based transistors  

NASA Astrophysics Data System (ADS)

We analyzed the carrier profile in silicon nanowire-based tunnel-FETs as a function of nanowire diameter using scanning spreading resistance microscopy. The nanowires were etched into an epitaxially grown stack, of which the top layer was in situ boron doped and the top contact was implanted. We revealed a significantly reduced boron diffusion inside narrower nanowires and a nonuniform diffusion depth in wider nanowires. Using process simulations, we attribute the latter to a reduced transient enhanced diffusion close to the nanowire sidewall caused by the recombination of excess interstitials. The shallower profile in narrower nanowires is related to an enhanced interstitial annihilation.

Schulze, Andreas; Florakis, Antonios; Hantschel, Thomas; Eyben, Pierre; Verhulst, Anne S.; Rooyackers, Rita; Vandooren, Anne; Vandervorst, W.

2013-02-01

277

Theory of enhanced proximity effect by midgap Andreev resonant state in diffusive normal-metal/triplet superconductor junctions  

NASA Astrophysics Data System (ADS)

Enhanced proximity effect by the midgap Andreev resonant state (MARS) in a diffusive normal-metal/insulator/triplet superconductor (DN/TS) junction is studied based on the Keldysh-Nambu quasiclassical Green’s-function formalism. By choosing a p -wave superconductor as a typical example of the TS, conductance of the junction and the spatial variation of the quasiparticle local density of states (LDOS) in the DN are calculated as the function of the magnitudes of the resistance Rd , Thouless energy in the DN, and the transparency of the insulating barrier. The resulting conductance spectrum has a zero-bias conductance peak (ZBCP) and the LDOS has a zero energy peak (ZEP) except for ?=?/2 (0????/2) , where ? denotes the angle between the lobe direction of the p -wave pair potential and the normal to the interface. The widths of the ZBCP and the ZEP are reduced with the increase of Rd while their heights are drastically enhanced. These peaks are revealed to be suppressed by applying a magnetic field. When the magnitude of Rd / R0 is sufficiently large, the total zero voltage resistance of the junction is almost independent of the Rd for ???/2 . The extreme case is ?=0 , where total zero voltage resistance is always R0 /2 . We also studied the charge transport in px +i py -wave junctions, where only the quasiparticles with perpendicular injection feel the MARS. Even in this case, the resulting LDOS in the DN has a ZEP. Thus the existence of the ZEP in the LDOS of the DN region is a remarkable feature for DN/TS junctions which have never been expected for the DN/singlet superconductor junctions where the MARS and proximity effect compete with each other. Based on these results, a crucial test to identify triplet pairing superconductors based on tunneling experiments is proposed.

Tanaka, Y.; Kashiwaya, S.; Yokoyama, T.

2005-03-01

278

Sub-Alfvénic Non-ideal Magnetohydrodynamic Turbulence Simulations with Ambipolar Diffusion. III. Implications for Observations and Turbulent Enhancement  

NASA Astrophysics Data System (ADS)

Ambipolar diffusion (AD) is believed to be a crucial process for redistributing magnetic flux in the dense molecular gas that occurs in regions of star formation. We carry out numerical simulations of this process in regions of low ionization using the heavy-ion approximation. The simulations are for regions of strong field (plasma ? = 0.1) and mildly supersonic turbulence ({\\cal M}=3, corresponding to an Alfvén Mach number of 0.67). The velocity power spectrum of the neutral gas changes from an Iroshnikov-Kraichnan spectrum in the case of ideal MHD to a Burgers spectrum in the case of a shock-dominated hydrodynamic system. The magnetic power spectrum shows a similar behavior. We use a one-dimensional radiative transfer code to post-process our simulation results; the simulated emission from the CS J = 2-1 and H13CO+ J = 1-0 lines shows that the effects of AD are observable in principle. Linewidths of ions are observed to be less than those of neutrals, and we confirm previous suggestions that this is due to AD. We show that AD is unlikely to affect the Chandrasekhar-Fermi method for inferring field strengths unless the AD is stronger than generally observed. Finally, we present a study of the enhancement of AD by turbulence, finding that AD is accelerated by factor 2-4.5 for non-self-gravitating systems with the level of turbulence we consider.

Li, Pak Shing; McKee, Christopher F.; Klein, Richard I.

2012-01-01

279

SUB-ALFVENIC NON-IDEAL MAGNETOHYDRODYNAMIC TURBULENCE SIMULATIONS WITH AMBIPOLAR DIFFUSION. III. IMPLICATIONS FOR OBSERVATIONS AND TURBULENT ENHANCEMENT  

SciTech Connect

Ambipolar diffusion (AD) is believed to be a crucial process for redistributing magnetic flux in the dense molecular gas that occurs in regions of star formation. We carry out numerical simulations of this process in regions of low ionization using the heavy-ion approximation. The simulations are for regions of strong field (plasma {beta} = 0.1) and mildly supersonic turbulence (M=3, corresponding to an Alfven Mach number of 0.67). The velocity power spectrum of the neutral gas changes from an Iroshnikov-Kraichnan spectrum in the case of ideal MHD to a Burgers spectrum in the case of a shock-dominated hydrodynamic system. The magnetic power spectrum shows a similar behavior. We use a one-dimensional radiative transfer code to post-process our simulation results; the simulated emission from the CS J = 2-1 and H{sup 13}CO{sup +} J = 1-0 lines shows that the effects of AD are observable in principle. Linewidths of ions are observed to be less than those of neutrals, and we confirm previous suggestions that this is due to AD. We show that AD is unlikely to affect the Chandrasekhar-Fermi method for inferring field strengths unless the AD is stronger than generally observed. Finally, we present a study of the enhancement of AD by turbulence, finding that AD is accelerated by factor 2-4.5 for non-self-gravitating systems with the level of turbulence we consider.

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

2012-01-01

280

Transient phase-space localization  

Microsoft Academic Search

We show that dynamics can, in general, be used to enhance the coherence of a Hamiltonian ensemble and we analyze the transient coherence using the coarse-grained entropy. We illustrate this concept using a Rydberg atom subject to an impulsive momentum transfer or ``kick.'' Classical simulations predict that the wave packet generated by the kick undergoes strong transient phase-space localization, which

C. L. Stokely; F. B. Dunning; C. O. Reinhold; A. K. Pattanayak

2002-01-01

281

Transient shifts in frontal and parietal circuits scale with enhanced visual feedback and changes in force variability and error.  

PubMed

When subjects perform a learned motor task with increased visual gain, error and variability are reduced. Neuroimaging studies have identified a corresponding increase in activity in parietal cortex, premotor cortex, primary motor cortex, and extrastriate visual cortex. Much less is understood about the neural processes that underlie the immediate transition from low to high visual gain within a trial. This study used 128-channel electroencephalography to measure cortical activity during a visually guided precision grip task, in which the gain of the visual display was changed during the task. Force variability during the transition from low to high visual gain was characterized by an inverted U-shape, whereas force error decreased from low to high gain. Source analysis identified cortical activity in the same structures previously identified using functional magnetic resonance imaging. Source analysis also identified a time-varying shift in the strongest source activity. Superior regions of the motor and parietal cortex had stronger source activity from 300 to 600 ms after the transition, whereas inferior regions of the extrastriate visual cortex had stronger source activity from 500 to 700 ms after the transition. Force variability and electrical activity were linearly related, with a positive relation in the parietal cortex and a negative relation in the frontal cortex. Force error was nonlinearly related to electrical activity in the parietal cortex and frontal cortex by a quadratic function. This is the first evidence that force variability and force error are systematically related to a time-varying shift in cortical activity in frontal and parietal cortex in response to enhanced visual gain. PMID:23365186

Poon, Cynthia; Coombes, Stephen A; Corcos, Daniel M; Christou, Evangelos A; Vaillancourt, David E

2013-01-30

282

Solid state chemistry and non-steady state radiation enhanced diffusion (NSRED): Part I. Synthesis and characterization of some lithium-tin and lithium-silver-tin polar intermetallics. Part II. Titanium diffusion in ion-modified magnesium oxide surfaces  

NASA Astrophysics Data System (ADS)

Part I of this thesis centers on the investigation of the structural, electronic and physical properties of Li-Sn based novel polar intermetallic compounds. In spite of both scientific and technological interests, the understanding of structure-property relationships of polar intermetallics based on Li-Sn system have not been extensively studied. Our exploratory studies focus on the chemistry of the Li-richest binary phase, Li4.4Sn, as well as on the discovery of new ternary Li-rich phases. Careful phase analyses coupled with X-ray and neutron diffraction studies resulted in the reformulation of Li4.4Sn as Li17Sn4. Exploratory synthesis in the Li-rich side of the ternary Li-Ag-Sn system also led to the discovery of two novel ternary lithium silver stannides phases: Li32.54Ag 9.46Sn10 and Li17Ag3Sn6. The new ternary compounds represent examples of two new crystal structure-types. Li32.54Ag9.46Sn10 exhibits high Li content, and a structure with covalent Ag-Sn framework with significant Li/Ag defects indicating its potential as an anode material for Li-ion batteries. Li 17Ag3Sn6 represents the first example of a quasi-2-dimensional polar intermetallic of the Li-Ag-Sn system. Its high lithium content also suggests it is a viable candidate for Li-battery anode applications. Part II of this thesis focuses on the investigation of defect production upon inert and chemically reactive energetic ion irradiated single crystals of MgO (100). Ti diffusion in ion pre-irradiated (low-energy ion beams of Ar+, Cl+ and Cr+ of 7keV) MgO (100) surfaces was selected as a model system in this work. The annealing process followed ion-irradiation treatment. Diffusion was conducted in an inert atmosphere. In these conditions, non-steady state concentration defects were created and a new type of diffusion termed as Non-Steady State Radiation Enhanced Diffusion (NSRED) was developed. NSRED is obtained by using the following: ion irradiation in the keV range followed by annealing; the diffusion range overlaps heavily with the central region of the collision cascade; the diffusing species are evaporated on the pre-irradiated surfaces. Secondary Ion Mass Spectrometry was used to measure the diffusion coefficients versus ion irradiation conditions as well as their time dependence. A theoretical model was formulated to calculate the depth-dependent bulk diffusion coefficients and the following order was obtained: DTi/Cr/MgO > DTi/Ar/MgO > DTi/Cl/MgO (where D stands for the depth-dependent diffusion coefficient of samples bombarded with Cr, Ar and Cl, respectively). Monte-Carlo (TRIM) simulations, lattice deformation effects, electrical neutrality requirements as well as nature of vacancies were used to explain the observed trend. Additional kinetic studies and HRXRD experiments were performed to further explain the DTi/Ar/MgO > DTi/Cl/MgO trend. A modified Kapinos-Platonov model was used to include the chemical effect observed. Larger vacancies cluster are assumed to form after relaxation processes under Cl+ bombardment versus Ar+ bombardment. The model accounts for: (1) enhanced diffusion obtained due to the vacancy cluster dissociation during the annealing process, the so-called post-irradiation annealing effect; (2) enhanced diffusion obtained due to the chemical properties of the ions, the so-called chemical effect.

Lupu, Corina

283

Developmental programming of eNOS uncoupling and enhanced vascular oxidative stress in adult rats after transient neonatal oxygen exposure.  

PubMed

The authors have previously shown that neonatal hyperoxic stress leads to high blood pressure, impaired endothelium-mediated vasodilatation, and increased vascular production of superoxide anion by NAD(P)H oxidase in adulthood. However, it is unknown whether changes in nitric oxide (NO) production and/or bioinactivation prevail and whether NO synthase (NOS) is also a source of superoxide. The purpose of this study was to evaluate whether adult animals exposed to neonatal hyperoxic stress have impaired vascular NO production associated with NOS uncoupling participating to vascular superoxide production and vascular dysfunction. In adult male rats exposed to 80% oxygen from day 3 to 10 of life (H, n = 6) versus room air controls (CTRL, n = 6), vascular (aorta) NO production is decreased at baseline (CTRL: 21 ± 1 vs. H: 16 ± 2 4,5-diaminofluorescein diacetate fluorescence intensity arbitrary units; P < 0.05) and after carbachol stimulation (acetylcholine analog; CTRL: 26 ± 2 vs. H: 18±2; P < 0.05). Pretreatment with L-arginine (CTRL: 32 ± 4 vs. H: 31 ± 5) and L-sepiapterine [analog of key NOS cofactor tetrahydro-L-biopterin (BH4)] (CTRL: 30 ± 3 vs. H: 29 ± 3) normalizes NO production after carbachol. L-Sepiapterine also normalizes impaired vasodilatation to carbachol. Vascular endothelial NO synthase (eNOS) immunostaining is reduced, whereas total eNOS protein expression is increased in H (CTRL: 0.76 ± 0.08 vs. H: 1.76± 0.21; P < 0.01). The significantly higher superoxide generation (CTRL: 20 ± 2 vs. H: 28 ± 3 hydroethidine fluorescence intensity arbitrary units; P < 0.05) is prevented by pretreatment with the eNOS inhibitor N-nitro-L-arginine methyl ester (CTRL: 21 ± 4 vs. H: 22 ± 4). Taken together, the current data indicate a role for eNOS uncoupling in enhanced vascular superoxide, impaired endothelium-mediated vasodilatation, and decreased NO production in adult animals with programmed elevated blood pressure after a brief neonatal oxygen exposure. PMID:23011469

Yzydorczyk, Catherine; Comte, Blandine; Huyard, Fanny; Cloutier, Anik; Germain, Nathalie; Bertagnolli, Mariane; Nuyt, Anne Monique

2013-01-01

284

Enhanced heat conductivity in stochastic magnetic field of tokomak affected by the ratio of the parallel to the perpendicular heat diffusivity  

NASA Astrophysics Data System (ADS)

Electron heat transport across stochastic magnetic fields is studied numerically in order to find out how the ratio of the parallel to the perpendicular heat diffusivity affects the enhanced heat conductivity and its radial profile in tokomak plasma physics. To find out the details of profile, non-local stochastic magnetic fields, in which the perturbed magnetic islands are separated with each other but very close to in the minor radius of tokomak, are chosen as research objects in our simulation work. Our numerical results indicate that the ratio of the parallel to the perpendicular heat diffusivity is a very important effective factor, which dominate how far the enhanced conductivity contributed by a perturbed magnetic field approach to zero from the rational surface in minor radius. Besides that, a theoretical analysis was provided and compared with the numerical results in this article.

Gao, H.

2012-11-01

285

Enhanced macromolecular diffusion in brain extracellular space in mouse models of vasogenic edema measured by cortical surface photobleaching  

Microsoft Academic Search

Diffusion of solutes and macromolecules in brain extracellular space (ECS) is important for normal brain function and efficient drug delivery, and is thought to be impaired in edematous brain. Here we measured the diffusion of an inert macromolecular fluorescent marker (FITC- dextran, 70 kDa) in the ECS by fluorescence recovery after photobleaching after staining the exposed cerebral cortex in vivo.

Marios C. Papadopoulos; Devin K. Binder; A. S. Verkman

2004-01-01

286

Suppression of oxidation-enhanced boron diffusion in silicon by carbon implantation and characterization of MOSFETs with carbon-implanted channels  

Microsoft Academic Search

In NMOS transistors with boron-doped channels, Oxdation-Enhanced Diffusion (OED) is a key contributor to boron profile broadening. Starting with the arguments presented in several recent reports on the role of carbon in silicon as a sink for self-interstitials, we have explored the feasibility of using carbon in the Metal Oxide Silicon Field Effect Transistor (MOSFET) active region to retard boron

Ibrahim Ban; M. C. Ozturk; E. K. Demirlioglu

1997-01-01

287

Dynamic Contrast-Enhanced and Diffusion MRI Show Rapid and Dramatic Changes in Tumor Microenvironment in Response to Inhibition of HIF-1? Using PX478  

Microsoft Academic Search

PX-478 is a new agent known to inhibit the hypoxia- responsivetranscriptionfactor,HIF-1A,inexperimental tumors. The current study was undertaken in prepa- ration for clinical trials to determine which noninvasive imaging endpoint(s) is sensitive to this drug's actions. Dynamic contrast-enhanced (DCE) and diffusion- weighted (DW) magnetic resonance imaging (MRI) were used to monitor acute effects on tumor hemo- dynamics and cellularity, respectively. Mice

Bénédicte F. Jordan; Matthew Runquist; Natarajan Raghunand; Amanda Baker; Ryan Williams; Lynn Kirkpatrickb; Garth Powis; Robert J. Gillies

2005-01-01

288

Diagnosis of cirrhosis with intravoxel incoherent motion diffusion MRI and dynamic contrast-enhanced MRI alone and in combination: preliminary experience  

Microsoft Academic Search

PURPOSE: To report our preliminary experience with the use of intravoxel incoherent motion (IVIM) diffusion-weighted magnetic resonance imaging (DW-MRI) and dynamic contrast-enhanced (DCE)-MRI alone and in combination for the diagnosis of liver cirrhosis. MATERIALS AND METHODS: Thirty subjects (16 with noncirrhotic liver, 14 with cirrhosis) were prospectively assessed with IVIM DW-MRI (n = 27) and DCE-MRI (n = 20). IVIM

Jignesh Patel; Eric E. Sigmund; Henry Rusinek; Marcel Oei; James S. Babb; Bachir Taouli

2010-01-01

289

Pulse mitigation and heat transfer enhancement techniques. Volume 3: Liquid sodium heat transfer facility and transient response of sodium heat pipe to pulse forward and reverse heat load  

Microsoft Academic Search

This report presents the description of a liquid sodium heat transfer facility (sodium loop) constructed to support the study of transient response of heat pipes. The facility, consisting of the loop itself, a safety system, and a data acquisition system, can be safely operated over a wide range of temperature and sodium flow rate. The transient response of a heat

L. C. Chow; O. J. Hahn; H. X. Nguyen

1992-01-01

290

Hyperglycemia Delays Terminal Depolarization and Enhances Repolarization after Peri-Infarct Spreading Depression as Measured by Serial Diffusion MR Mapping  

Microsoft Academic Search

We investigated the effect of hyperglycemia on the initiation and propagation of spreading depression-like peri-infarct ischemic depolarization (SD) induced by focal cerebral ischemia in rats. Peri-infarct SD were monitored during the initial 15 minutes after remotely induced middle cerebral artery occlusion (MCAO) using serial diffusion weighted magnetic resonance imaging. Maps of the apparent diffusion coefficient (ADC) were calculated and ADC

Thomas Els; Joachim Röther; Christian Beaulieu; Alexander de Crespigny; Michael Moseley

1997-01-01

291

An enhanced transient expression system in plants based on suppression of gene silencing by the p19 protein of tomato bushy stunt virus  

Microsoft Academic Search

Summary Transient gene expression is a fast, flexible and reproducible approach to high-level expression of useful proteins. In plants, recombinant strains of Agrobacterium tumefaciens can be used for transient expression of genes that have been inserted into the T-DNA region of the bacterial Ti plasmid. A bacterial culture is vacuum-infiltrated into leaves, and upon T-DNA transfer, there is ectopic expression

Olivier Voinnet; Susana Rivas; Pere Mestre; David Baulcombe

2003-01-01

292

Presynaptic enhancement by eugenol of spontaneous excitatory transmission in rat spinal substantia gelatinosa neurons is mediated by transient receptor potential A1 channels.  

PubMed

Eugenol, which is contained in several plants including clove, has been widely used as an analgesic and anti-inflammatory drug in the dental clinic. Eugenol also has anesthetic effects and produces sedation and the reduction of convulsion threshold. These benefits have been partly attributed to the effects of eugenol on neural tissues, such as inhibition of voltage-gated ion channels. As expected from the fact that eugenol is a vanilloid compound, this drug activates transient receptor potential (TRP) V1 channels in the peripheral nervous system (PNS). Although eugenol affects synaptic transmission in the central nervous system (CNS), this has not yet been fully examined. We investigated how eugenol affects spontaneous glutamatergic excitatory transmission in substantia gelatinosa (SG; lamina II of Rexed) neurons of adult rat spinal cord slices by use of the blind whole-cell patch-clamp technique. Bath-applied eugenol reversibly enhanced spontaneous excitatory transmission and produced an outward current at -70 mV in SG neurons. The former action was due to a large increase in the frequency of spontaneous excitatory postsynaptic current (sEPSC) with a small increase in the amplitude. These actions of eugenol were seen by its repeated application and resistant to a voltage-gated Na(+) channel blocker tetrodotoxin. The effect of eugenol on sEPSC frequency was concentration-dependent with an EC(50) value of 3.8 mM and unaffected by a TRPV1 antagonist capsazepine, whereas inhibited by a nonspecific TRP antagonist ruthenium red and a TRPA1 antagonist HC-030031. On the other hand, the eugenol-induced outward current was not affected by these TRP antagonists. It is concluded that eugenol activates TRPA1 channels in the SG, leading to an increase in the spontaneous release of L-glutamate to SG neurons, and that eugenol also produces a membrane hyperpolarization that is not mediated by TRP channels. Eugenol is suggested to activate different types of TRP channel between the PNS and CNS. PMID:22426238

Inoue, M; Fujita, T; Goto, M; Kumamoto, E

2012-02-28

293

Physics and modeling of dopant diffusion for advanced device applications  

NASA Astrophysics Data System (ADS)

Physically based diffusion models have been developed to simulate dopant diffusion for advanced semiconductor device technology. Based on extensive experimental results and fundamental defect related kinetics, the diffusion models has been developed to include various diffusion species and defect reactions in order to simulate the complex dopant redistribution due to transient enhanced diffusion (TED). For next generation channel doping technology, the experiment and modeling of indium diffusion during high temperature rapid thermal annealing (RTA) was carried out. The diffusion of implanted indium is a combined effect of TED and thermal equilibrium diffusion. The implanted indium cannot be fully activated after RTA due to carrier freeze-out. A diffusion model was developed to describe the indium redistribution during RTA. The TED induced by ion implantation was extensively investigated for the phosphorus diffusion during low temperature furnace annealing. The TED of implanted phosphorus shows an initial decay at the early stage of annealing, and increases with increasing implant energy and dose. Dose loss of phosphorus was found during the TED period due to interface segregation. TED was shown to dominate the dose loss process. The Hybrid diffusion model including defect clustering and interface segregation effects was developed. The model accurately simulates the TED and dose loss of implanted phosphorus during low temperature annealing. The co-diffusion study for arsenic and boron was performed to understand the boron redistribution in the channel region due to the TED caused by the arsenic source/drain implant. The boron segregation in the arsenic profile is induced by the combined effects of junction electric field and TED during annealing. The segregation is driven by the TED caused by either ion implantation or arsenic deactivation. To simulate the co-diffusion phenomenon, dislocation and arsenic clustering kinetics and their interactions with point defects are included. Results show that arsenic deactivation causes additional boron segregation which affects channel doping profile greatly and degrades the device performance.

Chang, Ruey-Dar

294

IMAGE SEGMENTATION AND EDGE DETECTION VIA CONSTRAINED DIFFUSION AND ADAPTIVE MORPHOLOGY: A CNN APPROACH TO BUBBLE-DEBRIS IMAGE ENHANCEMENT  

Microsoft Academic Search

In this paper, a cellular neural network (CNN) based locally adaptive scheme is presented for image segmentation and edge detection. It is shown that combining a constrained (linear or nonlinear) diffusion approach with adaptive morphology leads to a robust segmentation algorithm for an important class of image models. These images comprise of simple geometrical objects, each having a homogeneous gray-scale

Csaba Rekeczky; Abraham Schultz; István Szatmári; Tamás Roska; Leon O. Chua

295

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

296

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

DOEpatents

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

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

1990-01-01

297

Note: the role of external electric fields in enhancing ion mobility, drift velocity, and drift-diffusion rates in aqueous electrolyte solutions [J. Chem. Phys. 134, 114504 (2011)].  

PubMed

The effect of external electric fields on enhancing ion mobility, drift velocity, and drift diffusion as a function of solution concentration has been investigated using molecular dynamics simulations. Our results show that the unusual nonlinear behavior observed when the solution concentration matches seawater is also observed when the concentration is reduced to half of that value. These results are of significance in designing processes for desalinating seawater using electro-deionization in which the concentration would decrease during salt removal, and for purification of brackish waters which also have lower salt content. PMID:22360264

Murad, Sohail

2012-02-21

298

Label-free in situ detection of individual macromolecular assemblies by surface enhanced Raman scattering.  

PubMed

We demonstrate label-free detection of lipid vesicles and polystyrene beads freely diffusing in aqueous solution using surface enhanced Raman scattering (SERS). The signals observed enable real-time identification and monitoring of individual particles interacting with the SERS substrate. SERS is demonstrated as a label-free method capable of monitoring transient species in solution on the millisecond time scale. PMID:23103901

Asiala, Steven M; Schultz, Zachary D

2012-10-29

299

Transient analysis of water transport in PEM fuel cells  

Microsoft Academic Search

This paper theoretically studies the water transport phenomena in PEM fuel cells, mainly investigating the transient behavior in the gas diffusion layer (GDL), catalyst layer (CL) and proton exchange membrane (PEM). In the PEM, both diffusion and electro-osmosis processes are considered, while in the GDL and CL, only diffusion process is taken into account. The process of water uptake is

Wei-Mon Yan; Hsin-Sen Chu; Jian-Yao Chen; Chyi-Yeou Soong; Falin Chen

2006-01-01

300

Enhanced diffusion through surface excursion: A master-equation approach to the narrow-escape-time problem  

NASA Astrophysics Data System (ADS)

We present a master-equation approach to the narrow-escape-time (NET) problem, i.e., the time needed for a particle contained in a confining domain with a single small or narrow opening to exit the domain. In this paper we introduce an alternative type of confining domain (to the usually spherical one) and we consider the diffusion process on a lattice rather than in continuous space. We have obtained analytic results for the basic quantity studied in the NET problem, the mean first-passage time, and we have studied its dependence in terms of the transition (desorption) probability over (from) the surface boundary and the confining domain dimensions. In addition to our analytical approach, we have implemented Monte Carlo simulations, finding excellent agreement between the theoretical results and simulations.

Rojo, Félix; Budde, Carlos E.

2011-08-01

301

Transient Ischemic Attack  

MedlinePLUS

NINDS Transient Ischemic Attack Information Page Synonym(s): Mini Stroke Table of Contents (click to jump to sections) What is Transient Ischemic ... Trials Organizations Additional resources from MedlinePlus What is Transient Ischemic Attack? A transient ischemic attack (TIA) is a transient ...

302

Modeling of ion implantation and diffusion in Si  

SciTech Connect

Classical molecular dynamics simulations are used to study damage produced during implantation of semiconductors with different ion masses and energies between 1-25 keV. The time scale for these simulations is only on the order of ns, and therefore problems like transient enhanced diffusion of dopants or formation of extended defects can not be studied with these models. Monte Carlo simulations, including as input the results obtained from molecular dynamics calculations, are used to extend the simulation time, and in particular, to study processes like ion implantation and defects diffusion in semiconductors. As an example, we show results for diffusion of the damage produced by implantation of Si with 5 keV Xe ions at low doses. Results of the simulations are compared with experiments in order to validate the model.

Caturla, M-J; Diaz de la Rubia, T.; Bedrossian, P.J.

1996-09-01

303

Transient droplet heating at high Peclet number  

Microsoft Academic Search

The transient heating of a spherical liquid particle at high Peclet number has been calculated with the use of adaptive grids for low Reynolds numbers. The use of adaptive grids greatly enhances the efficiency of the calculations and allows for the large Peclet numbers to be studied. The results of the calculations show that the transient period of internal isotherm

H. A. Dwyer; R. J. Kee; P. K. Barr; B. R. Sanders

1981-01-01

304

Two-Time Three-Equation Method for Analysis of Oxidation-Enhanced and -Retarded Diffusions and Growth of Oxidation Stacking Faults in Silicon  

NASA Astrophysics Data System (ADS)

For analysis of oxidation-enhanced and -retarded diffusion (OED and ORD) and oxidation stacking faults (OSF) in Si, two out of the three equations for OED, ORD and OSF were used. The equation for a local equilibrium between self-interstitials and vacancies was also used. Thus three equations were used. Two time values were taken in these three equations. In the previous paper (Jpn. J. Appl. Phys. 27 (1988) 967), the experimental results were modified in order to obtain physically reasonable solutions. But this is not good. In the present work, therefore, the equations were simultaneously solved without modifying experimental results. It was concluded that the equation of OSF should not be used.

Okino, Takahisa; Yoshida, Masayuki

1990-01-01

305

Dynamic Contrast-Enhanced and Diffusion MRI Show Rapid and Dramatic Changes in Tumor Microenvironment in Response to Inhibition of HIF-1? Using PX-4781  

PubMed Central

Abstract PX-478 is a new agent known to inhibit the hypoxia-responsive transcription factor, HIF-1?, in experimental tumors. The current study was undertaken in preparation for clinical trials to determine which noninvasive imaging endpoint(s) is sensitive to this drug's actions. Dynamic contrast-enhanced (DCE) and diffusion-weighted (DW) magnetic resonance imaging (MRI) were used to monitor acute effects on tumor hemodynamics and cellularity, respectively. Mice bearing human xenografts were treated either with PX-478 or vehicle, and imaged over time. DW imaging was performed at three b values to generate apparent diffusion coefficient of water (ADCw) maps. For DCE-MRI, a macromolecular contrast reagent, BSA-Gd-DTPA, was used to determine vascular permeability and vascular volume fractions. PX-478 induced a dramatic reduction in tumor blood vessel permeability within 2 hours after treatment, which returned to baseline by 48 hours. The anti-VEGF antibody, Avastin, reduced both the permeability and vascular volume. PX-478 had no effect on the perfusion behavior of a drug-resistant tumor system, A-549. Tumor cellularity, estimated from ADCw, was significantly decreased 24 and 36 hours after treatment. This is the earliest significant response of ADC to therapy yet reported. Based on these preclinical findings, both of these imaging endpoints will be included in the clinical trial of PX-478.

Jordan, Benedicte F; Runquist, Matthew; Raghunand, Natarajan; Baker, Amanda; Williams, Ryan; Kirkpatrick, Lynn; Powis, Garth; Gillies, Robert J

2005-01-01

306

Dynamic contrast-enhanced and diffusion MRI show rapid and dramatic changes in tumor microenvironment in response to inhibition of HIF-1alpha using PX-478.  

PubMed

PX-478 is a new agent known to inhibit the hypoxia-responsive transcription factor, HIF-1alpha, in experimental tumors. The current study was undertaken in preparation for clinical trials to determine which noninvasive imaging endpoint(s) is sensitive to this drug's actions. Dynamic contrast-enhanced (DCE) and diffusion-weighted (DW) magnetic resonance imaging (MRI) were used to monitor acute effects on tumor hemodynamics and cellularity, respectively. Mice bearing human xenografts were treated either with PX-478 or vehicle, and imaged over time. DW imaging was performed at three b values to generate apparent diffusion coefficient of water (ADCw) maps. For DCE-MRI, a macromolecular contrast reagent, BSA-Gd-DTPA, was used to determine vascular permeability and vascular volume fractions. PX-478 induced a dramatic reduction in tumor blood vessel permeability within 2 hours after treatment, which returned to baseline by 48 hours. The anti-VEGF antibody, Avastin, reduced both the permeability and vascular volume. PX-478 had no effect on the perfusion behavior of a drug-resistant tumor system, A-549. Tumor cellularity, estimated from ADCw, was significantly decreased 24 and 36 hours after treatment. This is the earliest significant response of ADC to therapy yet reported. Based on these preclinical findings, both of these imaging endpoints will be included in the clinical trial of PX-478. PMID:15967100

Jordan, Bénédicte F; Runquist, Matthew; Raghunand, Natarajan; Baker, Amanda; Williams, Ryan; Kirkpatrick, Lynn; Powis, Garth; Gillies, Robert J

2005-05-01

307

Pressure Transient Analysis of Fractal Reservoirs  

Microsoft Academic Search

The authors present a formulation for a fractal fracture network embedded into a Euclidean matrix. Single-phase flow in the fractal object is described by an appropriate modification of the diffusivity equation. The system's pressure-transient response is then analyzed in the absence of matrix participation and when both the fracture network and the matrix participate. The results obtained extend previous pressure-transient

Jincai Chang; Yanis Yortsos

1990-01-01

308

DIFFUSION PUMP  

DOEpatents

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

Levenson, L.

1963-09-01

309

Dopant and self-diffusion in extrinsic n-type silicon isotopically controlled heterostructures  

SciTech Connect

We present experimental results of dopant- and self-diffusion in extrinsic silicon doped with As. Multilayers of isotopically controlled {sup 28}Si and natural silicon enable simultaneous analysis of {sup 30}Si diffusion into the {sup 28}Si enriched layers and dopant diffusion throughout the multilayer structure. In order to suppress transient enhanced self- and dopant diffusion caused by ion implantation, we adopted a special approach to dopant introduction. First, an amorphous 250-nm thick Si layer was deposited on top of the Si isotope heterostructure. Then the dopant ions were implanted to a depth such that all the radiation damage resided inside this amorphous cap layer. These samples were annealed for various times and temperatures to study the impact of As diffusion and doping on Si self-diffusion. The Si self-diffusion coefficient and the dopant diffusivity for various extrinsic n-type conditions were determined over a wide temperature range. We observed increased diffusivities that we attribute to the increase in the concentration of the native defect promoting the diffusion.

Silvestri, Hughes H.; Sharp, Ian D.; Bracht, Hartmut A.; Nicols, Sam P.; Beeman, Jeff W.; Hansen, John; Nylandsted-Larsen, Arme; Haller, Eugene E.

2002-04-01

310

Enhanced functional brain imaging by using adaptive filtering and a depth compensation algorithm in diffuse optical tomography.  

PubMed

Reflectance diffuse optical tomography (rDOT) of brain function is limited by its high sensitivity to the superficial tissues (i.e., the scalp and skull) and by its severe decrease in measurement sensitivity with increased depth. Significant interference in rDOT results from spontaneous fluctuations that are embedded in both the superficial tissues and brain, such as arterial pulsation and vasomotion. In this study, first we investigate coherence and phase shift of the spontaneous fluctuations in the resting state, within the superficial tissues and at various depths of the brain, respectively. We demonstrate that the spontaneous fluctuations originating from arterial pulsations ( ? 1 Hz) are spatially global and temporally coherent, while the fluctuations originating from vasomotion ( ? 0.1 Hz) tend to have less coherence with increased depth. Second, adaptive cancellation of spontaneous fluctuations with a frequency-specific strategy is utilized and validated in both resting and activation (evoked by a finger-tapping task) states. Third, improved depth localization of motor activation in reconstructed rDOT images is achieved by combining adaptive cancellation with a depth compensation algorithm that we recently reported. PMID:21296704

Tian, Fenghua; Niu, Haijing; Khan, Bilal; Alexandrakis, George; Behbehani, Khosrow; Liu, Hanli

2011-02-04

311

Transient plasma physics and applications  

NASA Astrophysics Data System (ADS)

The focus of this dissertation is to investigate the physics and technology of transient plasma discharges, wherein the generation of nanosecond pulsed electrical discharges ignite quiescent and flowing fuel/air mixtures. The purpose is to develop a fundamental understanding of the combustion initiated by the transient plasmas and the gas discharge physics (streamer structures and their evolution), and apply the physics to the improvement of ignition in various engine systems. In this study, significant improvements, by factors as great as 10 times, were achieved in the delay to ignition of pulse detonation engines. These improvements lead to the solution of a major problem in the development of the engines. In this work, we endeavor to understand the dynamics of chemistry occurring in engine ignition, related pulsed power, and characteristics of transient plasma generation and evolution. This study included the design and construction of transient plasma generation system based on pulsed power science, measurement of ignition delay for quiescence combustion chamber and air/fuel mixture with various flow rate from 25 to 300 g/s, measurement of OH* emission during transient plasma ignition process, and sub-nanosecond imaging of transient plasma generation and evolution. Knowledge obtained through this comprehensive study is applied to deflagration initiation and the enhancement of deflagration to detonation transitions in pulsed detonation engines, and for improved ignition for applications of these engines.

Wang, Fei

312

Modeling Transient Eruptive Processes  

NASA Astrophysics Data System (ADS)

Computer models of volcanic eruptions are essential for understanding the physical processes occurring within a volcanic conduit. We are building upon previous modeling efforts in order to simulate two-phase homogeneous flow prior to fragmentation. Our code is designed to track changing pressure, velocity, density, and volatile concentrations within the conduit. Its primary emphasis is the efficient numerical modeling of transient eruptive events. As such, it is possible to model eruption triggers associated with sudden decompression, more gradual diffusive bubble growth, and injection of volatile-rich magma. We alter initial conditions, including volatile distribution, conduit geometry, and magma recharge to quantify how these parameters affect eruption evolution. Our model complements existing numerical approaches for eruption dynamics and incorporates results from experimentalists and observational volcanologists. This enables us to assess the relative impact of various solubility laws, diffusion rates, as well as nucleation and fragmentation criteria. In the process, we address other important questions within the modeling community, such as: When and where does nucleation occur? What kind of boundary conditions should be imposed at the fragmentation front / gas-particle-jet boundary? How do turbulent flow, wall friction, and erosion affect flow? Modeling results are to be compared with observations from contemporaneous eruptions at Colima, Mexico, Santiaguito, Guatemala, and Tungurahua, Ecuador.

Johnson, J. B.; Proussevitch, A.; Sahagian, D.

2004-05-01

313

Experimental Investigation of Radio-Turbulence Induced Diffusion -- Final Report  

SciTech Connect

The outcome of this research project suggests that the transport of radon in water is significantly greater than that predicted solely by molecular diffusion. The original study was related to the long term storage of {sup 226}Ra-bearing sand at the DOE Fernald site and determining whether a barrier of water covering the sand would be effective in reducing the emanation of {sup 222}Rn from the sand. Initial observations before this study found the transport of radon in water to be greater than that predicted solely by molecular diffusion. Fick's law on diffusion was used to model the transport of radon in water including the impact associated with radioactive decay. Initial measurements suggested that the deposition of energy in water associated with the radioactive decay process influences diffusion and enhances transport of radon. A multi-region, one-dimensional, steady-state transport model was used to analyze the movement of radon through a sequential column of air, water and air. An effective diffusion coefficient was determined by varying the thickness of the water column and measuring the time for transport of {sup 222}Rn through of the water barrier. A one-region, one-dimensional transient diffusion equation was developed to investigate the build up of radon at the end of the water column to the time when a steady-state, equilibrium condition was achieved. This build up with time is characteristic of the transport rate of radon in water and established the basis for estimating the effective diffusion coefficient for {sup 222}Rn in water. Several experiments were conducted using different types and physical arrangements of water barriers to examine how radon transport is influenced by the water barrier. Results of our measurements confirm our theoretical analyses which suggest that convective forces other than pure molecular diffusion impact the transport of {sup 222}Rn through the water barrier. An effective diffusion coefficient is defined that includes effects of molecular diffusion and convection to describe the transport of radon in water. The effective diffusion coefficients measured in these experiments are 6.8 x 10{sup -4} {+-} 28% and 3.5 x 10{sup -4} {+-} 34% cm{sup 2} sec{sup -1} for the steady-state and transient diffusion conditions, respectively. Water barriers ranging in thickness from 30-50 cm reduce the amount of radon released from the radium-bearing source material by a factor of 0.3-0.1, respectively.

Spitz, H. B.; Usman, S.

2005-07-07

314

Crossover from Normal to Anomalous Diffusion in Systems of Field-Aligned Dipolar Particles  

NASA Astrophysics Data System (ADS)

Using molecular dynamics simulations we investigate the translational dynamics of particles with dipolar interactions in homogenous external fields. For a broad range of concentrations, we find that the anisotropic, yet normal diffusive behavior characterizing weakly coupled systems becomes anomalous both parallel and perpendicular to the field at sufficiently high dipolar coupling and field strength. After the ballistic regime, chain formation first yields cagelike motion in all directions, followed by transient, mixed diffusive-superdiffusive behavior resulting from cooperative motion of the chains. The enhanced dynamics disappears only at higher densities close to crystallization.

Jordanovic, Jelena; Jäger, Sebastian; Klapp, Sabine H. L.

2011-01-01

315

{ital Ab Initio} Pseudopotential calculations of dopant diffusion in Si  

SciTech Connect

The ab initio pseudopotential method is used to study transient-enhanced-diffusion (TED) related processes. The electronic degrees of freedom are included explicitly, together with the fully self-consistent treatment of the electron charge density. A large supercell and a fine k-point mesh are used to ensure numerical convergence. Such method has been demonstrated to give quantitative description of defect energetic. We will show that boron diffusion is significantly enhanced in the presence of the Si interstitial due to the substantial lowering of the migrational barrier through a kick-out mechanism. The resulting mobile boron can also be trapped by another substitutional boron, forming an immobile and elect rically inactive two-boron pair. Similarly, carbon diffusion is also enhanced significantly due to the pairing with Si interstitial. However, carbon binds to Si interstitial much more strongly than boron does, taking away most Si interstitial from boron at sufficiently large carbon concentration, which causes the suppression of the boron TED. We will also show that Fermi level effect plays an important role in both Si interstitial and boron diffusion.

Zhu, J., LLNL

1997-04-28

316

Time Dependent Resistance Increase in Poly-Si Load Resistor due to Hydrogen Diffusion from Plasma-Enhanced Chemical Vapor Deposition Silicon Nitride Film in High Density Static Random Access Memories  

Microsoft Academic Search

A study has been done on hydrogen diffusion into poly-Si load resistors in high density static random access memories (SRAMs) from plasma-enhanced chemical vapor deposition (CVD) silicon nitride film. For the first time, it was found that the resistance of load resistors in 1 Mbit SRAMs increases in proportion to the time during high temperature duration testing, resulting in time

Hideki Shibata; Kazuhiko Hashimoto

1994-01-01

317

Differential microstructure and physiology of brain and bone metastases in a rat breast cancer model by diffusion and dynamic contrast enhanced MRI.  

PubMed

Pharmacological approaches to treat breast cancer metastases in the brain have been met with limited success. In part, the impermeability of the blood brain barrier (BBB) has hindered delivery of chemotherapeutic agents to metastatic tumors in the brain. BBB-permeable chemotherapeutic drugs are being developed, and noninvasively assessing the efficacy of these agents will be important in both preclinical and clinical settings. In this regard, dynamic contrast enhanced (DCE) and diffusion weighted imaging (DWI) are magnetic resonance imaging (MRI) techniques to monitor tumor vascular permeability and cellularity, respectively. In a rat model of metastatic breast cancer, we demonstrate that brain and bone metastases develop with distinct physiological characteristics as measured with MRI. Specifically, brain metastases have limited permeability of the BBB as assessed with DCE and an increased apparent diffusion coefficient (ADC) measured with DWI compared to the surrounding brain. Microscopically, brain metastases were highly infiltrative, grew through vessel co-option, and caused extensive edema and injury to the surrounding neurons and their dendrites. By comparison, metastases situated in the leptomenengies or in the bone had high vascular permeability and significantly lower ADC values suggestive of hypercellularity. On histological examination, tumors in the bone and leptomenengies were solid masses with distinct tumor margins. The different characteristics of these tissue sites highlight the influence of the microenvironment on metastatic tumor growth. In light of these results, the suitability of DWI and DCE to evaluate the response of chemotherapeutic and anti-angiogenic agents used to treat co-opted brain metastases, respectively, remains a formidable challenge. PMID:22042553

Budde, Matthew D; Gold, Eric; Jordan, E Kay; Frank, Joseph A

2011-11-01

318

Pretreatment Diffusion-Weighted and Dynamic Contrast-Enhanced MRI for Prediction of Local Treatment Response in Squamous Cell Carcinomas of the Head and Neck  

PubMed Central

OBJECTIVE The objective of our study was to predict response to chemoradiation therapy in patients with head and neck squamous cell carcinoma (HNSCC) by combined use of diffusion-weighted imaging (DWI) and high-spatial-resolution, high-temporal-resolution dynamic contrast-enhanced MRI (DCE-MRI) parameters from primary tumors and metastatic nodes. SUBJECTS AND METHODS Thirty-two patients underwent pretreatment DWI and DCE-MRI using a modified radial imaging sequence. Postprocessing of data included motion-correction algorithms to reduce motion artifacts. The median apparent diffusion coefficient (ADC), volume transfer constant (Ktrans), extracellular extravascular volume fraction (ve), and plasma volume fraction (vp) were computed from primary tumors and nodal masses. The quality of the DCE-MRI maps was estimated using a threshold median chi-square value of 0.10 or less. Multivariate logistic regression and receiver operating characteristic curve analyses were used to determine the best model to discriminate responders from nonresponders. RESULTS Acceptable ?2 values were observed from 84% of primary tumors and 100% of nodal masses. Five patients with unsatisfactory DCE-MRI data were excluded and DCEMRI data for three patients who died of unrelated causes were censored from analysis. The median follow-up for the remaining patients (n = 24) was 23.72 months. When ADC and DCE-MRI parameters (Ktrans, ve, vp) from both primary tumors and nodal masses were incorporated into multivariate logistic regression analyses, a considerably higher discriminative accuracy (area under the curve [AUC] = 0.85) with a sensitivity of 81.3% and specificity of 75% was observed in differentiating responders (n = 16) from nonresponders (n = 8). CONCLUSION The combined use of DWI and DCE-MRI parameters from both primary tumors and nodal masses may aid in prediction of response to chemoradiation therapy in patients with HNSCC.

Chawla, Sanjeev; Kim, Sungheon; Dougherty, Lawrence; Wang, Sumei; Loevner, Laurie A.; Quon, Harry; Poptani, Harish

2013-01-01

319

Magnetization exchange in capillaries by microcirculation affects diffusion-controlled spin-relaxation: a model which describes the effect of perfusion on relaxation enhancement by intravascular contrast agents.  

PubMed

The effect of perfusion on relaxation time in tissue has only been considered for first-pass kinetics of NMR-signal after application of contrast agents. The importance of perfusion on relaxation has not yet been studied for steady state conditions, i.e., when the intravascular relaxation rate is constant in time. The aim of this study is to develop a model in which T1 relaxation is derived as a function of perfusion and intracapillary volume fraction (regional blood volume). Tissue is considered to be two-compartment system, which consists of intracapillary and extravascular space. Intracapillary relaxation differs from relaxation in the arterial system due to diffusion-exchange of magnetization from extravascular to intracapillary space. Perfusion tends to attenuate this difference and thus counteracts the effect on intracapillary relaxation. Relaxation in the extravascular and intracapillary magnetization are linked by diffusion. This dependence is presented in analytical form and a generic equation is derived. AT1 experiment is considered in which all spins of tissue and blood are inverted at the beginning. Calculations are performed for the fast exchange model of tissue. Perfusion increases relaxation enhancement of intravascular contrast agents. This effect is considerable in highly perfused tissue like myocardium. The dependence of relaxation on perfusion implies an overestimation of the regional blood volume when the calculation of the latter is based on tissue models that neglect perfusion. The model presented here is applied to predict the effect of perfusion on T1 imaging with FLASH-pulse sequences because this technique has been proven to be a powerful method to obtain T1 maps within a short time interval. For the fast exchange model, two algorithms are suggested that determine perfusion and regional blood volume from T1 imaging in the presence and absence of intravascular contrast agents. PMID:8771021

Bauer, W R; Hiller, K H; Roder, F; Rommel, E; Ertl, G; Haase, A

1996-01-01

320

Transient heat flux shielding using thermal metamaterials  

NASA Astrophysics Data System (ADS)

We have developed a heat shield based on a metamaterial engineering approach to shield a region from transient diffusive heat flow. The shield is designed with a multilayered structure to prescribe the appropriate spatial profile for heat capacity, density, and thermal conductivity of the effective medium. The heat shield was experimentally compared to other isotropic materials.

Narayana, Supradeep; Savo, Salvatore; Sato, Yuki

2013-05-01

321

Thermophysical Analysis of Sandstone by Pulse Transient Method  

Microsoft Academic Search

Stones belong to porous materials where water in pores plays an important role during the freeze–thaw process. A thermophysical analysis based on the pulse transient method has been used to study an ageing cycle, namely the freeze–thaw cycle. Thermophysical analysis is based on measuring the thermophysical properties under specific thermodynamic conditions. The transient method determines the specific heat, thermal diffusivity,

L.' Kubicár; V. Vretenár; V. Bohá?; P. Tiano

2006-01-01

322

Diffusion-controlled detection of trinitrotoluene: interior nanoporous structure and low highest occupied molecular orbital level of building blocks enhance selectivity and sensitivity.  

PubMed

Development of simple, cost-effective, and sensitive fluorescence-based sensors for explosives implies broad applications in homeland security, military operations, and environmental and industrial safety control. However, the reported fluorescence sensory materials (e.g., polymers) usually respond to a class of analytes (e.g., nitroaromatics), rather than a single specific target. Hence, the selective detection of trace amounts of trinitrotoluene (TNT) still remains a big challenge for fluorescence-based sensors. Here we report the selective detection of TNT vapor using the nanoporous fibers fabricated by self-assembly of carbazole-based macrocyclic molecules. The nanoporosity allows for time-dependent diffusion of TNT molecules inside the material, resulting in further fluorescence quenching of the material after removal from the TNT vapor source. Under the same testing conditions, other common nitroaromatic explosives and oxidizing reagents did not demonstrate this postexposure fluorescence quenching; rather, a recovery of fluorescence was observed. The postexposure fluorescence quenching as well as the sensitivity is further enhanced by lowering the highest occupied molecular orbital (HOMO) level of the nanofiber building blocks. This in turn reduces the affinity for oxygen, thus allocating more interaction sites for TNT. Our results present a simple and novel way to achieve detection selectivity for TNT by creating nanoporosity and tuning molecular electronic structure, which when combined may be applied to other fluorescence sensor materials for selective detection of vapor analytes. PMID:22339204

Che, Yanke; Gross, Dustin E; Huang, Helin; Yang, Dongjiang; Yang, Xiaomei; Discekici, Emre; Xue, Zheng; Zhao, Huijun; Moore, Jeffrey S; Zang, Ling

2012-03-01

323

In vivo evaluation of retinal and callosal projections in early postnatal development and plasticity using manganese-enhanced MRI and diffusion tensor imaging.  

PubMed

The rodents are an excellent model for understanding the development and plasticity of the visual system. In this study, we explored the feasibility of Mn-enhanced MRI (MEMRI) and diffusion tensor imaging (DTI) at 7 T for in vivo and longitudinal assessments of the retinal and callosal pathways in normal neonatal rodent brains and after early postnatal visual impairments. Along the retinal pathways, unilateral intravitreal Mn2+ injection resulted in Mn2+ uptake and transport in normal neonatal visual brains at postnatal days (P) 1, 5 and 10 with faster Mn2+ clearance than the adult brains at P60. The reorganization of retinocollicular projections was also detected by significant Mn2+ enhancement by 2%-10% in the ipsilateral superior colliculus (SC) of normal neonatal rats, normal adult mice and adult rats after neonatal monocular enucleation (ME) but not in normal adult rats or adult rats after monocular deprivation (MD). DTI showed a significantly higher fractional anisotropy (FA) by 21% in the optic nerve projected from the remaining eye of ME rats compared to normal rats at 6 weeks old, likely as a result of the retention of axons from the ipsilaterally uncrossed retinal ganglion cells, whereas the anterior and posterior retinal pathways projected from the enucleated or deprived eyes possessed lower FA after neonatal binocular enucleation (BE), ME and MD by 22%-56%, 18%-46% and 11%-15% respectively compared to normal rats, indicative of neurodegeneration or immaturity of white matter tracts. Along the visual callosal pathways, intracortical Mn2+ injection to the visual cortex of BE rats enhanced a larger projection volume by about 74% in the V1/V2 transition zone of the contralateral hemisphere compared to normal rats, without apparent DTI parametric changes in the splenium of corpus callosum. This suggested an adaptive change in interhemispheric connections and spatial specificity in the visual cortex upon early blindness. The results of this study may help determine the mechanisms of axonal uptake and transport, microstructural reorganization and functional activities in the living visual brains during development, diseases, plasticity and early interventions in a global and longitudinal setting. PMID:21985904

Chan, Kevin C; Cheng, Joe S; Fan, Shujuan; Zhou, Iris Y; Yang, Jian; Wu, Ed X

2011-10-01

324

Secondary porosity in a transient vadose zone  

SciTech Connect

The Western New York Nuclear Service Center is the site of low and high level radioactive waster buried in a series of trenches excavated in a 28 m thick, Lavery-age silty clay diamicton that exhibits a 6 meter thick transient vadoes zone where exposed at the surface. Hydrostratigraphy of this till includes a 0.25 m thick poorly developed macroporous soil, a 3.5 m thick weathered zone of densely spaced and randomly orientated horizontal and vertical fractures, a 2 m thick unweathered zone of intermittently spaced fractures exhibiting east-west orientations, and a massive 23 m thick unweathered till zone that exhibits isolated, east-west orientated fractures. Bulk hydraulic conductivity of this active flow zone decreases with depth from 10[sup [minus]5] to 10[sup [minus]8] cm/s. The specific discharge of vertically flowing groundwater in the massive till zone is 1.25 cm/yr. A water surplus in the recharge season saturates the fractured zone to grade with up to 7.37 cm/yr of net infiltration. Tritium and radionuclides from the waste trenches and surrounding soil matrix hydrodynamically disperse into the field-saturated fracture network that contains meteoric recharge water. A soil moisture deficit in discharge season produces a vadose zone of widened fractures that via capillarity enhances the diffusion of contaminants into the soil matrix. These enlarged connecting conduits laterally channel the excess infiltration from the recharge season and diffused contaminants to local lowlands and incised streams that truncate the unweathered till. The current vadose and phreatic zone flow study will be used in numeric simulations that will delineate the areal extend and temporal duration of these seepage faces and the time frame of possible surfaces water contamination.

Frederick, W.T.; Grasso, T.X. Jr. (Dames and Moore, West Valley, NY (United States))

1993-03-01

325

Diffusion /Osmosis  

NSDL National Science Digital Library

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

Jensen

2007-11-26

326

Transient drainage summary report  

SciTech Connect

This report summarizes the history of transient drainage issues on the Uranium Mill Tailings Remedial Action (UMTRA) Project. It defines and describes the UMTRA Project disposal cell transient drainage process and chronicles UMTRA Project treatment of the transient drainage phenomenon. Section 4.0 includes a conceptual cross section of each UMTRA Project disposal site and summarizes design and construction information, the ground water protection strategy, and the potential for transient drainage.

NONE

1996-09-01

327

Gas diffusion ultrabarriers on polymer substrates using Al{sub 2}O{sub 3} atomic layer deposition and SiN plasma-enhanced chemical vapor deposition  

SciTech Connect

Thin films grown by Al{sub 2}O{sub 3} atomic layer deposition (ALD) and SiN plasma-enhanced chemical vapor deposition (PECVD) have been tested as gas diffusion barriers either individually or as bilayers on polymer substrates. Single films of Al{sub 2}O{sub 3} ALD with thicknesses of >=10 nm had a water vapor transmission rate (WVTR) of <=5x10{sup -5} g/m{sup 2} day at 38 deg. C/85% relative humidity (RH), as measured by the Ca test. This WVTR value was limited by H{sub 2}O permeability through the epoxy seal, as determined by the Ca test for the glass lid control. In comparison, SiN PECVD films with a thickness of 100 nm had a WVTR of approx7x10{sup -3} g/m{sup 2} day at 38 deg. C/85% RH. Significant improvements resulted when the SiN PECVD film was coated with an Al{sub 2}O{sub 3} ALD film. An Al{sub 2}O{sub 3} ALD film with a thickness of only 5 nm on a SiN PECVD film with a thickness of 100 nm reduced the WVTR from approx7x10{sup -3} to <=5x10{sup -5} g/m{sup 2} day at 38 deg. C/85% RH. The reduction in the permeability for Al{sub 2}O{sub 3} ALD on the SiN PECVD films was attributed to either Al{sub 2}O{sub 3} ALD sealing defects in the SiN PECVD film or improved nucleation of Al{sub 2}O{sub 3} ALD on SiN.

Carcia, P. F.; McLean, R. S. [DuPont Central Research and Development, Wilmington, Delaware 19880 (United States); Groner, M. D.; Dameron, A. A. [Deparment of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (United States); George, S. M. [Deparment of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (United States); Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309 (United States)

2009-07-15

328

Analysis of coupled bimolecular reaction kinetics and diffusion by two-color fluorescence correlation spectroscopy: enhanced resolution of kinetics by resonance energy transfer.  

PubMed Central

In two-color fluorescence correlation spectroscopy (TCFCS), the fluorescence intensities of two fluorescently-labeled species are cross-correlated over time and can be used to identify static and dynamic interactions. Generally, fluorophore labels are chosen that do not undergo Förster resonance energy transfer (FRET). Here, a general TCFCS theory is presented that accounts for the possibility of FRET between reactants in the reversible bimolecular reaction, [reaction: see text] where k(f) and k(b) are forward and reverse rate constants, respectively (dissociation constant K(d) = k(b)/k(f)). Using this theory, we systematically investigated the influence on the correlation function of FRET, reaction rates, reactant concentrations, diffusion, and component visibility. For reactants of comparable size and an energy-transfer efficiency of approximately 90%, experimentally measurable cross-correlation functions should be sensitive to reaction kinetics for K(d) > 10(-8) M and k(f) >or= approximately 10(7) M(-1)s(-1). Measured auto-correlation functions corresponding to donor and acceptor labels are generally less sensitive to reaction kinetics, although for the acceptor, this sensitivity increases as the visibility of the donor increases relative to the acceptor. In the absence of FRET or a significant hydrodynamic difference between reactant species, there is little effect of reaction kinetics on the shape of auto- and cross-correlation functions. Our results suggest that a subset of biologically relevant association-dissociation kinetics can be measured by TCFCS and that FRET can be advantageous in enhancing these effects.

Hom, Erik F Y; Verkman, A S

2002-01-01

329

Usefulness of a Combined Approach of T1-Weighted, T2-Weighted, Dynamic Contrast-Enhanced, and Diffusion-Weighted Imaging in Prostate Cancer  

PubMed Central

Purpose We evaluated the value of a combined approach of T1-weighted (T1W) imaging, T2-weighted (T2W) imaging, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), and diffusion-weighted imaging (DWI) for the detection of prostate cancer and extracapsular extension (ECE) in patients with prostate cancer by using pathologic data after radical prostatectomy. Materials and Methods From April 2009 to December 2011, 126 patients who underwent radical prostatectomy and prostate MRI for prostate cancer were analyzed retrospectively. The MRI findings were compared with the pathologic findings of the radical prostatectomy specimens in each patient. The sensitivity, specificity, and accuracy of the detection of prostate cancer and extracapsular extension were analyzed. Results The prostate cancer detection rate by use of T1W and T2W imaging, DCE-MRI, and their combination was 65.1%, 69.0%, and 80.2%, respectively (p=0.023). The detection rate using T1W and T2W imaging, DCE-MRI, DWI, and their combination was 57.7%, 65.4%, 67.3%, and 80.8%, respectively (p=0.086). The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of combination MRI (T1W, T2W, and DCE-MRI) for ECE were 46.4%, 91.4%, 83.9%, and 68.1%, respectively. The sensitivity of combination MRI (T1W, T2W, and DCE-MRI) for ECE tended to increase as the prostate-specific antigen level rose (p=0.010). The sensitivity, specificity, PPV, and NPV of combination MRI (T1W, T2W, DCE-MRI, and DWI) for ECE were 65.0%, 87.5%, 76.5%, and 80.0%, respectively. Conclusions A combined approach of T1W, T2W, and DCE-MRI with DWI demonstrated an accurate detection rate of prostate cancer. Also, combination approaches showed a high specificity for predicting ECE, although sensitivity was relatively lower. Therefore, these methods are reliable for predicting prostate cancer. However, a new protocol is necessary to enhance the sensitivity for predicting ECE.

Min, Byung Dal; Cho, Bum Sang; Kim, Yong-June; Yun, Seok Joong; Lee, Sang-Cheol; Kim, Wun-Jae

2012-01-01

330

ON THE X-RAY OUTBURSTS OF TRANSIENT ANOMALOUS X-RAY PULSARS AND SOFT GAMMA-RAY REPEATERS  

SciTech Connect

We show that the X-ray outburst light curves of four transient anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), namely, XTE J1810-197, SGR 0501+4516, SGR 1627-41, and CXOU J164710.2-455216, can be produced by the fallback disk model that was also applied to the outburst light curves of persistent AXPs and SGRs in our earlier work. The model solves the diffusion equation for the relaxation of a disk that has been pushed back by a soft gamma-ray burst. The sets of main disk parameters used for these transient sources are very similar to each other and to those employed in our earlier models of persistent AXPs and SGRs. There is a characteristic difference between the X-ray outburst light curves of transient and persistent sources. This can be explained by the differences in the disk surface density profiles of the transient and persistent sources in quiescence indicated by their quiescent X-ray luminosities. Our results imply that a viscous disk instability operating at a critical temperature in the range of {approx}1300-2800 K is a common property of all fallback disks around AXPs and SGRs. The effect of the instability is more pronounced and starts earlier for the sources with lower quiescent luminosities, which leads to the observable differences in the X-ray enhancement light curves of transient and persistent sources. A single active disk model with the same basic disk parameters can account for the enhancement phases of both transient and persistent AXPs and SGRs. We also present a detailed parameter study to show the effects of disk parameters on the evolution of the X-ray luminosity of AXPs and SGRs in the X-ray enhancement phases.

Cal Latin-Small-Letter-Dotless-I skan, Sirin; Ertan, Uenal [Sabanc Latin-Small-Letter-Dotless-I University, Orhanl Latin-Small-Letter-Dotless-I -Tuzla, Istanbul, 34956 (Turkey)

2012-10-20

331

Universal scaling in transient creep  

NASA Astrophysics Data System (ADS)

When aggregates of small grains are pressed together in the presence of small amounts of solvent the aggregate compacts and the grains tend to stick together. This happens to salt and sugar in humid air, and to sediments when buried in the Earths crust. Stress concentration at the grain contacts cause local dissolution, diffusion of the dissolved material out of the interface and deposition on the less stressed faces of the grains. This process, in geology known as pressure solution creep, plays a central role during compaction of sedimentary basins during tectonic deformation of the Earth's crust in strengthening of active fault gouges following earthquakes and in ceramics. Experimental data on pressure solution creep has so far not been sufficiently accurate to understand the transient processes at the grain scale. Here we present experimental evidence that pressure solution creep does not establish a steady state interface microstructure as previously thought. Conversely, pressure solution creep strain and the characteristic size of interface microstructures grow as the cubic root of time. Transient creep with the same scaling is known in metallurgy (Andrade creep). The apparent universal scaling of pressure solution transient creep is explained here using an analogy with spinodal dewetting.

Dysthe, D. K.; Podladchikov, Y.; Renard, F.; Feder, J.; Jamtveit, B.

2002-12-01

332

Geometry Changes Transient Transport in Plasmas  

NASA Astrophysics Data System (ADS)

Role of ballooning effect in toroidal plasmas on the transient transport problems is investigated. Due to the mode localization along the magnetic field line, a meso scale appears in a radial correlation length of fluctuating fields. This scale length introduces the interference of the gradient and flux in different radial locations. For the fluctuation which gives the gyro-Bohm-like diffusion in a stationary state, this long radial correlation of the fluctuating field causes a fast propagation of response against a rapid transient perturbation. Upper bound of transient thermal diffusivity is derived. This analysis suggests an important role of plasma geometrical configuration on the transient transport. A case of Heliotron configurations is discussed for illustration. In a hill case, the interchange mode turbulence can dominate, which has short radial correlation length. In the magnetic well geometry, the ballooning effect becomes strong and a toroidal localization further increases the radial extent of the eigenmode. It is predicted that the fast transient response against high frequency modulation is much stronger for Heliotron plasmas in magnetic well configuration and is much weaker for those in magnetic hill configurations, in comparison with equivalent tokamaks.

Itoh, Kimitaka; Itoh, Sanae-I.

2001-10-01

333

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

Microsoft Academic Search

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

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

2006-01-01

334

COMPLEX DIFFUSION ON IMAGE GRAPHS  

PubMed Central

Complex diffusion was introduced in image processing literature as a means to achieve simultaneous denoising and enhancement of scalar valued images. In this paper, we present a novel geometric framework for achieving complex diffusion on color images expressed as image graphs. In this framework, we develop a new variational formulation for achieving complex diffusion. This formulation involves a modified harmonic map functional and is quite distinct from the Polyakov action described in earlier work by Sochen et al. Our formulation provides a framework for simultaneous (feature preserving) denoising and enhancement. We present results of comparison between the complex diffusion, and Beltrami flow all in the image graph framework.

Seo, Dohyung; Vemuri, Baba C

2009-01-01

335

Portable vapor diffusion coefficient meter  

DOEpatents

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

Ho, Clifford K. (Albuquerque, NM)

2007-06-12

336

Holographic diffusers  

NASA Astrophysics Data System (ADS)

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

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

1994-01-01

337

Diffusion MRI  

NASA Astrophysics Data System (ADS)

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

Fukuyama, Hidenao

338

Research on zinc diffusion in undoped InP  

NASA Astrophysics Data System (ADS)

When Zinc diffuses into undoped InP, the diffusion profiles are severely influenced by the process parameters, such as the diffusion temperature, the diffusion time, etc. In order to reduce the surface damage and enhance reproducibility, the diffusion temperature and the diffusion time are optimized. Under optimized. diffusion temperature, curve of diffusion depth versus the square root of the diffusion time is achieved. From this curve, the diffusion coefficient for zinc under the optimized temperature is calculated. The zinc profile was determined by electrochemical capacitance-voltage profiling (ECV), according to which zinc diffusion mechanism was explained.

Zhuang, ChunQuan; Lv, YanQiu; Gong, HaiMei

2005-10-01

339

Radiological examinations of transient ischemic attack.  

PubMed

Neuroimaging is critical in the evaluation of patients with TIA. CT and MRI are the two available options for imaging. Head CT is more widely available and commonly used. Diffusion MRI is the recommended modality to image an ischemic lesion. The presence of a diffusion lesion in a patient with transient neurological symptoms is an indicator of a high risk of recurrent stroke. Perfusion imaging with perfusion MRI or CT perfusion may improve the detection of ischemic lesions. Noninvasive vessel imaging may detect a symptomatic vessel lesion associated with an increased risk of stroke. PMID:24157560

Tung, Christie E; Olivot, Jean Marc; Albers, Gregory W

2013-10-11

340

Long Jump Rates in Surface Diffusion: W on W(110)  

Microsoft Academic Search

We have reexamined the diffusion of W adatoms on W(110) using the field ion microscope. The diffusivity is in good agreement with previous results and reveals no unusual features, but from observations of the distribution of displacements, corrected for diffusion during temperature transients, we have for the first time been able to measure the temperature dependence of rates for nearest-neighbor

Grazyna Antczak; Gert Ehrlich

2004-01-01

341

Diffusion-weighted MR imaging of acute stroke: Correlation with T2-weighted and magnetic susceptibility-enhanced MR imaging in cats  

SciTech Connect

We evaluated the temporal and anatomic relationships between changes in diffusion-weighted MR image signal intensity, induced by unilateral occlusion of the middle cerebral artery in cats, and tissue perfusion deficits observed in the same animals on T2-weighted MR images after administration of a nonionic intravascular T2 shortening agent. Diffusion-weighted images obtained with strong diffusion-sensitizing gradient strengths (5.6 gauss/cm, corresponding to gradient attenuation factor, b, values of 1413 sec/mm2) displayed increased signal intensity in the ischemic middle cerebral artery territory less than 1 hr after occlusion, whereas T2-weighted images without contrast usually failed to detect injury for 2-3 hr after stroke. After contrast administration (0.5-1.0 mmol/kg by Dy-DTPA-BMA, IV), however, T2-weighted images revealed perfusion deficits (relative hyperintensity) within 1 hr after middle cerebral artery occlusion that corresponded closely to the anatomic regions of ischemic injury shown on diffusion-weighted MR images. Close correlations were also found between early increases in diffusion-weighted MR image signal intensity and disrupted phosphorus-31 and proton metabolite levels evaluated with surface coil MR spectroscopy, as well as with postmortem histopathology. These data indicate that diffusion-weighted MR images more accurately reflect early-onset pathophysiologic changes induced by acute cerebral ischemia than do T2-weighted spin-echo images.

Moseley, M.E.; Kucharczyk, J.; Mintorovitch, J.; Cohen, Y.; Kurhanewicz, J.; Derugin, N.; Asgari, H.; Norman, D. (Univ. of California, San Francisco (USA))

1990-05-01

342

Osmosis and Diffusion  

ERIC Educational Resources Information Center

|OsmoBeaker is a CD-ROM designed to enhance the learning of diffusion and osmosis by presenting interactive experimentation to the student. The software provides several computer simulations that take the student through different scenarios with cells, having different concentrations of solutes in them.|

Sack, Jeff

2005-01-01

343

Element diffusion in novae  

Microsoft Academic Search

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

D. Prialnik; A. Kovetz

1997-01-01

344

Analysis of skin penetration enhancement based on a two-layer skin diffusion model with polar and nonpolar routes in the stratum corneum: dose-dependent effect of 1-geranylazacycloheptan-2-one on drugs with different lipophilicities.  

PubMed

The effects of 1-geranylazacycloheptan-2-one (GACH) on the in vitro skin penetration of seven drugs with various lipophilicities were studied. The penetration of drugs from aqueous vehicle through the guinea pig skin was increased depending on the pretreatment dose of GACH. The largest enhancement was observed for 5-fluorouracil (5-FU) and a bell-shaped relationship was obtained between enhancement ratio and the octanol/water partition coefficients of drugs. Further, Laplace transformed equations for percutaneous absorption of drug were derived from Fick's second law based on a two-layer skin diffusion model with polar and nonpolar routes in the stratum corneum. Through curve-fitting of their equations to penetration profiles using a nonlinear regression program MULTI(FILT) combined with a fast inverse Laplace transform (FILT) algorithm, the action mechanism of GACH was discussed in terms of its effect on the partitioning and diffusivity of drugs in each domain. With an increase in pretreatment dose of GACH, the estimated partition parameters of drugs into the nonpolar route increased but their diffusivities were little affected. The analysis based on a linear free-energy relationship suggested that the increase in partitioning of drugs into the nonpolar route was explained by its increasing polarity with GACH pretreatment. PMID:8401404

Yamashita, F; Yoshioka, T; Koyama, Y; Okamoto, H; Sezaki, H; Hashida, M

1993-07-01

345

Symptoms of transient ischemic attack.  

PubMed

Transient ischemic attack (TIA) is a cerebrovascular disease with temporary (<24 h) neurological symptoms. The symptoms of TIA patients are largely similar to those of ischemic stroke patients and include unilateral limb weakness, speech disturbances, sensory symptoms, visual disturbances, and gait difficulties. As these symptoms are transient, they are frequently evaluated based on patients' subjective reports, which are less precise than those of patients with stroke whose longer-lasting symptoms and signs can be reliably assessed by physicians. Some symptoms, such as monocular blindness, are much more common in TIA than in stroke, and limb shaking occurs almost exclusively in TIA patients. On the other hand, symptoms like hemivisual field defects or limb ataxia are underappreciated in TIA patients. These transient neurological symptoms are not necessarily caused by cerebrovascular diseases, but can be produced by a variety of non-vascular diseases. Careful history taking, examination, and appropriate imaging tests are needed to differentiate these TIA mimics from TIA. Each TIA symptom has a different specificity and sensitivity, and there has been an effort to assess the outcome of the patients through the use of specific clinical features. On top of this, recent developments in imaging techniques have greatly enhanced our ability to predict the outcomes of TIA patients. Perception or recognition of TIA symptoms may differ according to the race, sex, education, and specialty of physicians. Appropriate education of both the general population and physicians with regard to TIA symptoms is important as TIAs need emergent evaluation and treatment. PMID:24157558

Kim, Jong S

2013-10-11

346

Perception of acoustic transients  

NASA Astrophysics Data System (ADS)

The research investigates the role of knowledge based or top-down processing in the perception of nonlinguistic, transient signals. The experiments address issues in transient pattern classification, target observation, attentional focusing, auditory induction, and computer based performance aids. The theoretical significance and naval relevance of the research is considered.

Howard, J. H., Jr.

1984-01-01

347

Electromagnetic Transients Program (EMTP) Primer. Final Report.  

National Technical Information Service (NTIS)

This document is an outgrowth of a survey and analysis of Electromagnetic Transients Program (EMTP) user needs, in which improved user's documentation was determined to by the single most important enhancement to the EMTP. The Primer is an EMTP training m...

S. F. Mauser T. E. McDermott

1985-01-01

348

Online assessment and control of transient oscillations damping  

Microsoft Academic Search

A new approach to online assessment and control of transient oscillations is proposed. It relies on coupling Prony analysis and the SIME transient stability method, with the twofold objective: on one hand, to improve Prony's applicability and reliability, and on the other hand, to design generation rescheduling patterns able to enhance the damping of poorly damped oscillations and\\/or stabilize them.

Daniel Ruiz-Vega; Arturo R. Messina; Mania Pavella

2004-01-01

349

Connecting molecular structure and exciton diffusion length in rubrene derivatives.  

PubMed

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

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

2013-06-10

350

Intrinsic electric fields and proton diffusion in immobilized protein membranes. Effects of electrolytes and buffers.  

PubMed Central

We present a theory for proton diffusion through an immobilized protein membrane perfused with an electrolyte and a buffer. Using a Nernst-Planck equation for each species and assuming local charge neutrality, we obtain two coupled nonlinear diffusion equations with new diffusion coefficients dependent on the concentration of all species, the diffusion constants or mobilities of the buffers and salts, the pH-derivative of the titration curves of the mobile buffer and the immobilized protein, and the derivative with respect to ionic strength of the protein titration curve. Transient time scales are locally pH-dependent because of protonation-deprotonation reactions with the fixed protein and are ionic strength-dependent because salts provide charge carriers to shield internal electric fields. Intrinsic electric fields arise proportional to the gradient of an "effective" charge concentration. The field may reverse locally if buffer concentrations are large (greater to or equal to 0.1 M) and if the diffusivity of the electrolyte species is sufficiently small. The "ideal" electrolyte case (where each species has the same diffusivity) reduces to a simple form. We apply these theoretical considerations to membranes composed of papain and bovine serum albumin (BSA) and show that intrinsic electric fields greatly enhance the mobility of protons when the ionic strength of the salts is smaller than 0.1 M. These results are consistent with experiments where pH changes are observed to depend strongly on buffer, salt, and proton concentrations in baths adjacent to the membranes.

Zabusky, N J; Deem, G S

1979-01-01

351

Coherent interactions in femtosecond transient grating.  

PubMed

Transient grating of a dye in liquid has been measured as a function of the electronic coherence period. A diffractive beam splitter and a pair of wedge prisms are implemented to achieve precise spatial phase overlap and interferometrically accurate control of the time delay between the pump pulses. As the electronic coherence period is varied, coherent interactions lead to an enhancement or loss of the sharp feature in the transient grating signal near time zero, which is usually called coherent spike. Sensitivity of the transient grating signal to the solvation process also changes by the coherence time delay. All the features can be accounted for by invoking third-order nonlinear response functions. Numerical simulations have been performed to corroborate our description. This work identifies a major source of the coherent spike in the transient grating and transient absorption experiments. In addition, it allows us to propose a method that measures the solvation function more efficiently than conventional transient grating technique does. PMID:15267398

Park, June-Sik; Joo, Taiha

2004-03-15

352

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.

353

Transient Global Amnesia  

MedlinePLUS

... global amnesia is a sudden, temporary episode of memory loss that can't be attributed to a ... know well, but that doesn't make your memory loss less disturbing. Fortunately, transient global amnesia is ...

354

Transient Ischemic Attack  

MedlinePLUS

A transient ischemic attack (TIA) is a stroke that comes and goes quickly. It happens when the blood supply to part of the brain stops briefly. Symptoms of a TIA are like other stroke symptoms, but do not ...

355

Enhancing the durability of multi-walled carbon nanotube supported by Pt and Pt–Pd nanoparticles in gas diffusion electrodes  

Microsoft Academic Search

This work tries to improve the durability of electrocatalysts of gas diffusion electrodes (GDEs) by using multi-walled carbon nanotube supported Pt–Pd bimetallic (Pt–Pd\\/MWCNT). The durability investigation of multi-walled carbon nanotube supported metals was evaluated by a repetitive potential cycling (RPC) corrosion test and by extended constant potential (ECP) experiments. Potential cycling tests were performed from ?0.3 to 1.2 V at 50 mV s?1

Ahmad Nozad Golikand; Elaheh Lohrasbi; Mehdi Asgari

2010-01-01

356

Transient combustion in hybrid rockets  

NASA Astrophysics Data System (ADS)

Hybrid rockets regained interest recently as an alternative chemical propulsion system due to their advantages over the solid and liquid systems that are currently in use. Development efforts on hybrids revealed two important problem areas: (1) low frequency instabilities and (2) slow transient response. Both of these are closely related to the transient behavior which is a poorly understood aspect of hybrid operation. This thesis is mainly involved with a theoretical study of transient combustion in hybrid rockets. We follow the methodology of identifying and modeling the subsystems of the motor such as the thermal lags in the solid, boundary layer combustion and chamber gasdynamics from a dynamic point of view. We begin with the thermal lag in the solid which yield the regression rate for any given wall heat flux variation. Interesting phenomena such as overshooting during throttling and the amplification and phase lead regions in the frequency domain are discovered. Later we develop a quasi-steady transient hybrid combustion model supported with time delays for the boundary layer processes. This is integrated with the thermal lag system to obtain the thermal combustion (TC) coupled response. The TC coupled system with positive delays generated low frequency instabilities. The scaling of the instabilities are in good agreement with actual motor test data. Finally, we formulate a gasdynamic model for the hybrid chamber which successfully resolves the filling/emptying and longitudinal acoustic behavior of the motor. The TC coupled system is later integrated to the gasdynamic model to obtain the overall response (TCG coupled system) of gaseous oxidizer motors with stiff feed systems. Low frequency instabilities were also encountered for the TCG coupled system. Apart from the transient investigations, the regression rate behavior of liquefying hybrid propellants such as solid cryogenic materials are also studied. The theory is based on the possibility of enhancement of regression rate by the entrainment mass transfer from a liquid layer formed on the fuel surface. The predicted regression rates are in good agreement with the cryogenic experimental findings obtained recently at Edwards Airforce Base with a frozen pentane and gaseous oxygen system.

Karabeyoglu, Mustafa Arif

1998-09-01

357

Investigation Of A Transient Energetic Charge Exchange Fux Enhancement (?spike-on-tail?) Observed In Neutral-beam-heated H-mode Discharges In The National Spherical Torus Experiment  

SciTech Connect

In the National Spherical Torus Experiment (NSTX), a large increase in the charge exchange neutral flux localized at the Neutral Beam (NB) injection full energy is measured by the E||B (superimposed parallel electric and magnetic fields) Neutral Particle Analyzer (NPA). Termed the High-Energy Feature (HEF), it appears on the NB-injected energetic ion spectrum only in discharges where tearing or kink-type modes (f < 50 kHz) are absent, Toroidal Alfvén Eigenmode (TAE) activity (f ~ 50 - 150 kHz) is weak and Global Alfvén Eigenmode (GAE) activity (f ~ 400 – 1000 kHz) is robust. Compressional Alfvén eigenmode (CAE) activity (f > 1000 kHz) is usually sporadic or absent during the HEF event. The HEF exhibits growth times of ?t ~ 20 - 80 ms, durations of ~ 100 – 600 ms and peak-to-base flux ratios up to H = Fmax /Fmin ~ 10. In infrequent cases, a slowing down distribution below the HEF energy can develop that continues to evolve over periods > 100 ms, a time scale long compared with the typical fast ion equilibration times. HEFs are Transient energetic charge exchange flux enhancement (?spike-on-tail?) 2 observed only in H-mode (not L-mode) discharges with injected power Pb ? 4 MW and in the pitch range ? = vll /v ~ 0.7 – 0.9; i.e. only for passing particles. Increases of ~ 10 - 30 % in the measured neutron yield and total stored energy that are observed to coincide with the feature appear to be driven by concomitant broadening of measured Te(r), Ti(r) and ne(r) profiles and not the HEF itself. While the HEF has minimal impact on plasma performance, it nevertheless poses a challenging wave-particle interaction phenomenon to understand. Candidate mechanisms for HEF formation are developed based on quasilinear theory of wave-particle interaction. The only mechanism found to lead to the large NPA flux ratios, H = Fmax /Fmin , observed in NSTX is the quasilinear evolution of the energetic ion distribution, Fb(E,?,r), in phase space and the concomitant loss of some particles, which occurs due to the cyclotron interaction of the particles with destabilized modes having sufficiently high frequencies, F ~ 700 - 1000 kHz, in the plasma frame that are tentatively identified as Global Alfvén Eigenmodes.

S.S. Medley et. al.

2011-08-04

358

Diffusion in silicon isotope heterostructures  

SciTech Connect

The simultaneous diffusion of Si and the dopants B, P, and As has been studied by the use of a multilayer structure of isotopically enriched Si. This structure, consisting of 5 pairs of 120 nm thick natural Si and {sup 28}Si enriched layers, enables the observation of {sup 30}Si self-diffusion from the natural layers into the {sup 28}Si enriched layers, as well as dopant diffusion from an implanted source in an amorphous Si cap layer, via Secondary Ion Mass Spectrometry (SIMS). The dopant diffusion created regions of the multilayer structure that were extrinsic at the diffusion temperatures. In these regions, the Fermi level shift due to the extrinsic condition altered the concentration and charge state of the native defects involved in the diffusion process, which affected the dopant and self-diffusion. The simultaneously recorded diffusion profiles enabled the modeling of the coupled dopant and self-diffusion. From the modeling of the simultaneous diffusion, the dopant diffusion mechanisms, the native defect charge states, and the self- and dopant diffusion coefficients can be determined. This information is necessary to enhance the physical modeling of dopant diffusion in Si. It is of particular interest to the modeling of future electronic Si devices, where the nanometer-scale features have created the need for precise physical models of atomic diffusion in Si. The modeling of the experimental profiles of simultaneous diffusion of B and Si under p-type extrinsic conditions revealed that both species are mediated by neutral and singly, positively charged Si self-interstitials. The diffusion of As and Si under extrinsic n-type conditions yielded a model consisting of the interstitialcy and vacancy mechanisms of diffusion via singly negatively charged self-interstitials and neutral vacancies. The simultaneous diffusion of P and Si has been modeled on the basis of neutral and singly negatively charged self-interstitials and neutral and singly positively charged P species. Additionally, the temperature dependence of the diffusion coefficient of Si in Ge was measured over the temperature range of 550 C to 900 C using a buried Si layer in an epitaxially grown Ge layer.

Silvestri, Hughes Howland

2004-05-14

359

Diffusion in silicon isotope heterostructures  

NASA Astrophysics Data System (ADS)

The simultaneous diffusion of Si and the dopants B, P, and As has been studied by the use of a multilayer structure of isotopically enriched Si. This structure, consisting of 5 pairs of 120 nm thick natural Si and 28Si enriched layers, enables the observation of 30Si self-diffusion from the natural layers into the 28Si enriched layers, as well as dopant diffusion from an implanted source in an amorphous Si cap layer, via Secondary Ion Mass Spectrometry (SIMS). The dopant diffusion created regions of the multilayer structure that were extrinsic at the diffusion temperatures. In these regions, the Fermi level shift due to the extrinsic condition altered the concentration and charge state of the native defects involved in the diffusion process, which affected the dopant and self-diffusion. The simultaneously recorded diffusion profiles enabled the modeling of the coupled dopant and self-diffusion. From the modeling of the simultaneous diffusion, the dopant diffusion mechanisms, the native defect charge states, and the self- and dopant diffusion coefficients can be determined. This information is necessary to enhance the physical modeling of dopant diffusion in Si. It is of particular interest to the modeling of future electronic Si devices, where the nanometer-scale features have created the need for precise physical models of atomic diffusion in Si. The modeling of the experimental profiles of simultaneous diffusion of B and Si under p-type extrinsic conditions revealed that both species are mediated by neutral and singly, positively charged Si self-interstitials. The diffusion of As and Si under extrinsic n-type conditions yielded a model consisting of the interstitialcy and vacancy mechanisms of diffusion via singly negatively charged self-interstitials and neutral vacancies. The simultaneous diffusion of P and Si has been modeled on the basis of neutral and singly negatively charged self-interstitials and neutral and singly positively charged P species. Additionally, the temperature dependence of the diffusion coefficient of Si in Ge was measured over the temperature range of 550°C to 900°C using a buried Si layer in an epitaxially grown Ge layer.

Silvestri, Hughes Howland

360

Enhancement of the thermal transport in a culture medium with Au nanoparticles  

NASA Astrophysics Data System (ADS)

In this work, it is reported the gold nanoparticles synthesis, their characterization, and their application to the enhancement of the thermal transport in a cellular culture medium. The Au nanoparticles (NPs), with average size of 10 nm, contained into a culture medium (DMEM (1)/F12(1)) (CM) increased considerably the heat transfer in the medium. Thermal lens spectrometry (TLS) was used to measure the thermal diffusivity of the nanofluids. The characteristic time constant of the transient thermal lens was obtained by fitting the theoretical expression, for transient thermal lens, to the experimental data. Our results show that the thermal diffusivity of the culture medium is highly sensitive to the Au nanoparticle concentration and size. The ability to modify the thermal properties to nanometer scale becomes very important in medical applications as in the case of cancer treatment by using photodynamic therapy (PDT). A complementary study with UV-vis and TEM techniques was performed to characterize the Au nanoparticles.

Jiménez-Pérez, J. L.; Fuentes, R. Gutierrez; Alvarado, E. Maldonado; Ramón-Gallegos, E.; Cruz-Orea, A.; Tánori-Cordova, J.; Mendoza-Alvarez, J. G.

2008-11-01

361

Tailoring of electron diffusion through TiO2 nanowires  

NASA Astrophysics Data System (ADS)

Charge transport through a random network of onedimensional TiO2 nanostructures such as nanorods, nanowires, and nanofibers developed by electrospinning technique has been studied in the presence of an electrolyte by electrochemical impedance spectroscopy and transient photocurrent measurements. The results have been compared with the charge transport parameters of random TiO2 nanoparticle (25 nm) network. The charge transport was discussed under the framework of hopping transport. Continuous nanofibers had longer charge collecting times and short nanorods have enhanced scattering losses. The TiO2 films containing random network of nanowires of aspect ratio 10:1 can have an order of magnitude higher diffusion coefficient than other morphologies. Furthermore, charge transport through Nb-doped anatase TiO2 nanofibers was studied. It was observed that the Fermi level of TiO2 rise close to its conduction band and result in a band-edge type diffusion mechanism even at low bias voltages when 2 wt% Nb atoms replaces the Ti atoms in the anatase lattice. The Nb-doped anatase electrospun nanofibers showed high chemical capacitance, high effective diffusion coefficient, and lower transport resistance compared to the undoped samples and conventional nanoparticles.

Jose, R.; Yusoff, M. M.

2012-11-01

362

New advances in three dimensional transient electromagnetic inversion  

Microsoft Academic Search

Inversion of transient electromagnetic (TEM) data sets to image the subsurface three-dimensional (3-D) electrical conductivity and magnetic permeability properties can be done directly in the time domain. The technique, first introduced by Wang et al. for causal and diffusive electromagnetic (EM) fields and subsequently implemented by Zhdanov & Portniaguine in the framework of iterative migration, is based upon imaging methods

Gregory A. Newman; Michael Commer

2005-01-01

363

Model of Transient Response of Semiconductor Gas Sensors  

Microsoft Academic Search

The model of transient response of semiconductor gas sensor under modulation heating has been constructed successfully. The model consists of the heat conduction process from heater to the sensor surface, the reaction process on the sensor surface and diffusion process near the sensor surface to supply the inflammable gas. The calculated sensor response agreed well with experimental result under step

Akira Fujimoto; Takashi Kuwahara

2008-01-01

364

Transient Electric Dichroism of Rod-Like DNA Molecules  

Microsoft Academic Search

We report transient electric dichroism studies on monodisperse rod-like DNA molecules. By using restriction fragments and DNAs of known length, it is shown that the orientation time is accurately predicted by the theoretically calculated rotational diffusion coefficient. The field dependence of the steady-state dichroism values is not consistent with the induced electric dipole orientation mechanism, and the time dependence is

M. Hogan; N. Dattagupta; D. M. Crothers

1978-01-01

365

Trawling Transients with LOFAR  

NASA Astrophysics Data System (ADS)

The LOFAR radio telescope is a wide-field radio interferometer operating in the 10-240 MHz range, with baselines from 50m to 1000km. It will be a multi-purpose fully open observatory, which will however devote significant time and effort to completing key science projects that drove its design. It has started commissioning operations and is expected to start its first all-sky shallow survey near the end of 2010. The Transients Key Science Project aims to monitor all LOFAR imaging data streams for transient and variable sources down to 1-sec timescales, and beam-formed (pulsar) data for even shorter events. A special extension to the project, the AARTFAAC experiment, will use the inner 350-m area for all-time all-sky imaging of the radio sky, down to sub-Jy levels. I will report on the current status and first results of LOFAR, and especially the Transients KSP.

Wijers, Ralph A. M. J.

2011-01-01

366

Equivalent Isotropic Scattering Formulation for Transient Short-Pulse Radiative Transfer in Anisotropic Scattering Planar Media  

Microsoft Academic Search

An isotropic scaling formulation is evaluated for transient radiative transfer in a one-dimensional planar slab subject to collimated and or diffuse irradiation. The Monte Carlo method is used to implement the equivalent scattering and exact simulations of the transient short-pulse radiation transport through forward and backward anisotropic scattering planar media. The scaled equivalent isotropic scattering results are compared with predictions

Zhixiong Guo; Sunil Kumar

2000-01-01

367

Transient hardened power FETs  

SciTech Connect

N-channel power FETs offer significant advantages in power conditioning circuits. Similiarily to all MOS technologies, power FET devices are vulnerable to ionizing radiation, and are particularily susceptible to burn-out in high dose rate irradiations (>1E10 rads(Si)/sec.), which precludes their use in many military environments. This paper will summarize the physical mechanisms responsible for burn-out, and discuss various fabrication techniques designed to improve the transient hardness of power FETs. Power FET devices were fabricated with several of these techniques, and data will be presented which demonstrates that transient hardness levels in excess of 1E12 rads(Si)/sec. are easily achievable.

Dawes, W.R. Jr.; Fischer, T.A.; Huang, C.C.C.; Meyer, W.J.; Smith, C.S.; Blanchard, R.A.; Fortier, T.J.

1986-01-01

368

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

369

Methods to determine slow diffusion coefficients of biomolecules: applications to Engrailed 2, a partially disordered protein.  

PubMed

We present new NMR methods to measure slow translational diffusion coefficients of biomolecules. Like the heteronuclear stimulated echo experiment (XSTE), these new methods rely on the storage of information about spatial localization during the diffusion delay as longitudinal polarization of nuclei with long T(1) such as nitrogen-15. The new BEST-XSTE sequence combines features of Band-selective Excitation Short-Transient (BEST) and XSTE methods. By avoiding the saturation of all protons except those of amide groups, one can increase the sensitivity by 45% in small proteins. The new experiment which combines band-Selective Optimized Flip-Angle Short-Transient with XSTE (SOFAST-XSTE) offers an alternative when very short recovery delays are desired. A modification of the HSQC-edited version of the XSTE experiment offers enhanced sensitivity and access to higher resolution in the indirect dimension. These new methods have been applied to detect changes in diffusion coefficients due to dimerization or proteolysis of Engrailed 2, a partially disordered protein. PMID:21603954

Augustyniak, Rafal; Ferrage, Fabien; Paquin, Raphaël; Lequin, Olivier; Bodenhausen, Geoffrey

2011-05-21

370

The effect of excimer laser pretreatment on diffusion and activation of boron implanted in silicon  

SciTech Connect

We have investigated the effect of excimer laser annealing (ELA) on transient enhanced diffusion (TED) and activation of boron implanted in Si during subsequent rapid thermal annealing (RTA). It is observed that ELA with partial melting of the implanted region causes reduction of TED in the region that remains solid during ELA, where the diffusion length of boron is reduced by a factor of {approx}4 as compared to the as-implanted sample. This is attributed to several mechanisms such as liquid-state annealing of a fraction of the implantation induced defects, introduction of excess vacancies during ELA, and solid-state annealing of the defects beyond the maximum melting depth by the heat wave propagating into the Si wafer. The ELA pretreatment provides a substantially improved electrical activation of boron during subsequent RTA.

Monakhov, E.V.; Svensson, B.G.; Linnarsson, M.K.; La Magna, A.; Italia, M.; Privitera, V.; Fortunato, G.; Cuscuna, M.; Mariucci, L. [Department of Physics, Physical Electronics, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo (Norway); Royal Institute of Technology, Lab of Materials and Semiconductor Physics, P.O. Box Electrum 229, SE-164 40 Kista (Sweden); CNR-IMM Sezione Catania, Stradale Primosole 50, 95121 Catania (Italy); IFN-CNR, Via Cineto Romano 42, 00156 Rome (Italy)

2005-11-07

371

Lateral diffusion of nerve growth factor receptor: modulation by ligand-binding and cell-associated factors.  

PubMed Central

We compared the properties in human melanoma cell line A875 and rat pheochromocytoma cell line PC12 of nerve growth factor receptor (NGFr). We also analyzed NGFr and a truncated NGFR lacking the cytoplasmic domain, which were transiently expressed in COS cells. The full-length NGFR expressed in COS cells bound nerve growth factor (NGF) with positive cooperativity, but A875 NGFr and truncated NGFr in COS cells did not display positive cooperativity. The anti-human NGFr monoclonal antibody NGFR5 was characterized and found not to compete with NGF for binding to NGFr. Fabs were prepared from NGFR5 and 192, an anti-rat NGFR monoclonal antibody that was previously shown not to compete with NGF for binding. Fluorescein-labeled Fabs were used to measure the distribution and lateral diffusion of the NGFr. NGFr expressed on COS and A875 cells are diffusely distributed, but NGFr on the surface of PC12 cells appeared, for some cells, to be patched. In A875 cells, 51% of the NGFr was free to diffuse with diffusion coefficient (D) approximately 7 X 10(-10) cm2/s. In COS cells, 43% diffused with D approximately 5 X 10(-10) cm2/s. There was no significant difference in diffusibility between the full-length NGFr and the truncated NGFr. We compared NGFr diffusion on PC12 cells in suspension or adherent to collagen-coated coverslips. For suspension cells, we obtained 32% recovery with D approximately 2.5 X 10(-9) cm2/s. On adherent cells, we obtained 17% recovery with 6 X 10(-9) cm2/s. Binding of NGF enhanced lateral diffusion of NGFr in A875 cells and in PC12 cells in suspension but did not alter lateral diffusion of NGFr in COS cells or in adherent PC12 cells. NGF had no effect on the diffusing fraction or the distribution of NGFR for any cell line. Images

Venkatakrishnan, G; McKinnon, C A; Ross, A H; Wolf, D E

1990-01-01

372

Large enhancement of the effective lifetime of n-type multicrystalline silicon by two step spin-on phosphorus diffusion and SiO2 passivation  

NASA Astrophysics Data System (ADS)

A large improvement of the effective lifetime of n-type phosphorus doped multicrystalline silicon to reach 950 ?s has been realized by combining both two step phosphorus treatments and surface oxidation. The average lifetime increases after the phosphorus diffusion process is mainly attributed to the remove of killer impurities which induces impurity gettering effects at the external surfaces. But an evident decrease of the electrical activity of some grain boundaries after that process was also observed due to the formation of heavily n+-type front layer of a floating junction and tunneling oxide along them. Moreover, low quality n-type substrates with an oxide passivated emitter are shown to suppress the effect of light induced degradation.

Ben Jaballah, A.; Moumni, B.; Dhamrin, M.; Saitoh, T.; Kamisako, K.; Bessais, B.

2011-09-01

373

[Subtle focal diffusion abnormality in the hippocampus].  

PubMed

A 53-year-old female patient presented with sudden onset confusion and disorientation. Further neurological examination was unremarkable and the patient showed a complete recovery after several hours. A magnetic resonance imaging (MRI) examination performed 2 days later revealed a tiny focal lesion in the lateral hippocampus in the diffusion weighted images consistent with transient global amnesia. PMID:22710991

Macht, S; Hellen, F; Wenzel, D; Turowski, B

2012-07-01

374

Semiclassical limit for bipolar quantum drift-diffusion model  

Microsoft Academic Search

Semiclassical limit to the solution of transient bipolar quantum drift-diffusion model in semiconductor simulation is discussed. It is proved that the semiclassical limit of this solution satisfies the classical bipolar drift-diffusion model. In addition, the authors also prove the existence of weak solution.

Ju Qiangchang; Chen Li

2009-01-01

375

Transient Catalytic Combustion.  

National Technical Information Service (NTIS)

Results of an experimental study of the catalytic ignition of lean propane-air mixtures on platinum in a stacked-plate catalytic combustor are presented. The effects of inlet temperature, equivalence ratio and gas velocity on the ignition transient were i...

D. A. Santavicca

1986-01-01

376

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

377

Global transient stability and voltage regulation for multimachine power systems  

Microsoft Academic Search

This paper addresses simultaneously the major fundamental and difficult issues of nonlinearity, uncertainty, dimensionality and globality to derive performance enhancing power system stability control. The main focus is on simultaneous enhancement of transient stability and voltage regulation of power systems. This problem arises from the practical concern that both frequency and voltage control are important indices of power system control

Mark Gordon; David J. Hill

2008-01-01

378

Anomalous anisotropic diffusion dynamics of hydration water at lipid membranes.  

PubMed

The diffusional water dynamics in the hydration layer of a dipalmitoylphosphatidylcholine bilayer is studied using molecular dynamics simulations. By mapping the perpendicular water motion on the ordinary diffusion equation, we disentangle free energetic and friction effects and show that perpendicular diffusion is strongly reduced. The lateral water motion exhibits anomalous diffusion up to several nanoseconds and is characterized by even further decreased diffusion coefficients, which by comparison with coarse-grained simulations are explained by the transient corrugated effective free energy landscape imposed by the lipids. This is in contrast to homogenous surfaces, where boundary hydrodynamic theory quantitatively predicts the anisotropy of water diffusion. PMID:24074121

von Hansen, Yann; Gekle, Stephan; Netz, Roland R

2013-09-11

379

Moisture diffusion and vapour pressure modeling of IC packaging  

Microsoft Academic Search

A new physical quantity-wetness fraction-has been introduced to overcome the concentration discontinuity in the application of Fick's diffusion equation to multi-material systems such as in plastic IC packaging. This enables the use of commercial thermal diffusion software to model the transient moisture diffusion phenomenon in IC packaging. More significantly, the wetness fraction provides a simple means of computing the vapour

Ee Hua Wong; Yong Chua Teo; Thiam Beng Lim

1998-01-01

380

Diffusion bonding  

DOEpatents

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

Anderson, Robert C. (Oak Ridge, TN)

1976-06-22

381

The Transient Global Amnesia Syndrome  

Microsoft Academic Search

On basis of 35 patients who have suffered from transient global amnesia the pathophysiological mechanisms of this syndrome are discussed. Our impression is that the primary cause of this syndrome is a transient ischemia of the hippocampus, an opinion common with most earlier authors. The possibility of a unilateral hippocampal disturbance resulting in transient global amnesia is discussed. We are

R. Fogelholm; E. Kivalo; L. Bergström

1975-01-01

382

Tolerating transient faults in MARS  

Microsoft Academic Search

The concepts of transient fault handling in the MARS architecture are discussed. After an overview of the MARS architecture, the mechanisms for the detection of transient faults are discussed in detail. In addition to extensive checks in the hardware and in the operating system, time-redundant execution of application tasks is proposed for the detection of transient faults. The time difference

H. Kopetz; H. Kantz; G. Grunsteidl; P. Puschner; J. Reisinger

1990-01-01

383

Transient characteristics of rocket turbopumps  

Microsoft Academic Search

Transient characteristics of high-speed, high-pressure cryogenic turbopumps for rocket engines were examined experimentally by starting and stopping several rocket turbopumps rapidly by gas turbine drive. Aspects of transient characteristics studied were instantaneous pump head coefficient and pump efficiency, cavitation growth in the inducer during rapid acceleration, effects of the starting mode related to the propulsion system mission, and transient behavior

Takashi Shimura; Mitsuo Watanabe

1990-01-01

384

Synthesized light transients.  

PubMed

Manipulation of electron dynamics calls for electromagnetic forces that can be confined to and controlled over sub-femtosecond time intervals. Tailored transients of light fields can provide these forces. We report on the generation of subcycle field transients spanning the infrared, visible, and ultraviolet frequency regimes with a 1.5-octave three-channel optical field synthesizer and their attosecond sampling. To demonstrate applicability, we field-ionized krypton atoms within a single wave crest and launched a valence-shell electron wavepacket with a well-defined initial phase. Half-cycle field excitation and attosecond probing revealed fine details of atomic-scale electron motion, such as the instantaneous rate of tunneling, the initial charge distribution of a valence-shell wavepacket, the attosecond dynamic shift (instantaneous ac Stark shift) of its energy levels, and its few-femtosecond coherent oscillations. PMID:21903778

Wirth, A; Hassan, M Th; Grguras, I; Gagnon, J; Moulet, A; Luu, T T; Pabst, S; Santra, R; Alahmed, Z A; Azzeer, A M; Yakovlev, V S; Pervak, V; Krausz, F; Goulielmakis, E

2011-09-08

385

Lunar transient phenomena  

NASA Astrophysics Data System (ADS)

Lunar transient phenomena (LTP) sightings are classified into five categories: brightenings, darkenings, reddish colorations, bluish colorations, and obscurations. There is evidence that the remaining LTP's are of lunar origin. A substantial number of sightings are independently confirmed. They have been recorded on film and spectrograms, as well as with photoelectric photometers and polarization equipment. It suggested that the LTP's may be gentle outgassings of less-than-volcanic proportions.

Cameron, W. S.

1991-03-01

386

Searches for radio transients  

NASA Astrophysics Data System (ADS)

Exploration of the transient Universe is an exciting and fast-emerging area within radio astronomy. Known transient phenomena range in time scales from sub-nanoseconds to years or longer, thus spanning a huge range in time domain and hinting a rich diversity in their underlying physical processes. Transient phenomena are likely locations of explosive or dynamic events and they offer tremendous potential to uncover new physics and astrophysics. A number of upcoming next-generation radio facilities and recent advances in computing and instrumentation have provided a much needed impetus for this field which has remained a relatively uncharted territory for the past several decades. In this paper we focus mainly on the class of phenomena that occur on very short time scales (i.e. from ˜milliseconds to ˜nanoseconds), known as {it fast transients}, the detections of which involve considerable signal processing and data management challenges, given the high time and frequency resolutions required in their explorations, the role of propagation effects to be considered and a multitude of deleterious effects due to radio frequency interference. We will describe the techniques, strategies and challenges involved in their detections and review the world-wide efforts currently under way, both through scientific discoveries enabled by the ongoing large-scale surveys at Parkes and Arecibo, as well as technical developments involving the exploratory use of multi-element array instruments such as VLBA and GMRT. Such developments will undoubtedly provide valuable inputs as next-generation arrays such as LOFAR and ASKAP are designed and commissioned. With their wider fields of view and higher sensitivities, these instruments, and eventually the SKA, hold great potential to revolutionise this relatively nascent field, thereby opening up exciting new science avenues in astrophysics.

Bhat, N. D. R.

2011-09-01

387

Atomic transient recorder  

Microsoft Academic Search

In Bohr's model of the hydrogen atom, the electron takes about 150 attoseconds (1 as = 10-18s) to orbit around the proton, defining the characteristic timescale for dynamics in the electronic shell of atoms. Recording atomic transients in real time requires excitation and probing on this scale. The recent observation of single sub-femtosecond (1fs = 10-15s) extreme ultraviolet (XUV) light

R. Kienberger; E. Goulielmakis; M. Uiberacker; A. Baltuska; V. Yakovlev; F. Bammer; A. Scrinzi; Th. Westerwalbesloh; U. Kleineberg; U. Heinzmann; M. Drescher; F. Krausz

2004-01-01

388

Rheothermodynamics of transient networks  

Microsoft Academic Search

The transient network model of Green-Tobolsky [1946], Yamamoto [1956] and\\u000aTanaka-Edwards [1992] is formulated within the frame of thermodynamics of\\u000airreversible processes, using as a fundamental quantity the chemical potential\\u000aassociated to the connection of strands to the network and treating these\\u000aconnections as chemical-like reactions. All thermodynamic quantities are thus\\u000anaturally defined in and out of equilibrium. Constitutive equations

Jean-François Palierne

2000-01-01

389

Rheothermodynamics of transient networks  

Microsoft Academic Search

The transient network model of Green-Tobolsky [1946], Yamamoto [1956] and Tanaka-Edwards [1992] is formulated within the frame of thermodynamics of irreversible processes, using as a fundamental quantity the chemical potential associated to the connection of strands to the network and treating these connections as chemical-like reactions. All thermodynamic quantities are thus naturally defined in and out of equilibrium. Constitutive equations

J. F. Palierne

2000-01-01

390

Advanced PFBC transient analysis  

SciTech Connect

Transient modeling and analysis of Advanced Pressurized Fluidized Bed Combustion (PFBC) systems is a research area that is currently under investigative study by the United States Department of Energy`s Morgantown Energy Technology Center (METC). The object of the effort is to identify key operating parameters affecting plant performance and then quantify the basic response of major sub-systems to changes in operating conditions. PC-TRAX, a commercially available dynamic software program, was chosen and applied in this modeling and analysis effort. This paper summarizes and describes the development of a series of TRAX-based transient models of Advanced PFBC power plants. These power plants generate a high temperature flue gas by burning coal or other suitable fuel in a PFBC. The high temperature flue gas supports low-Btu fuel gas or natural gas combustion in a gas turbine topping combustor. When utilized, low-Btu fuel gas is produced in a bubbling bed carbonizer. High temperature, high pressure combustion products exiting the topping combustor are expanded in a modified gas turbine to generate electrical power. Waste heat from the system is used to generate and superheat steam for a reheat steam turbine bottoming cycle that generates additional electrical power. Basic control/instrumentation models were developed and modeled in PC-TRAX and used to investigate off-design plant performance. System performance for various transient conditions and control philosophies was studied.

White, J.S. [Parsons Power Group, Inc., Reading, PA (United States); Bonk, D.L.; Rogers, L. [USDOE Morgantown Energy Technology Center, WV (United States)

1996-12-31

391

Advanced PFBC transient analysis  

SciTech Connect

Transient modeling and analysis of advanced Pressurized Fluidized Bed Combustion (PFBC) systems is a research area that is currently under investigation by the US Department of Energy`s Federal Energy Technology Center (FETC). The object of the effort is to identify key operating parameters that affect plant performance and then quantify the basic response of major sub-systems to changes in operating conditions. PC-TRAX{trademark}, a commercially available dynamic software program, was chosen and applied in this modeling and analysis effort. This paper describes the development of a series of TRAX-based transient models of advanced PFBC power plants. These power plants burn coal or other suitable fuel in a PFBC, and the high temperature flue gas supports low-Btu fuel gas or natural gas combustion in a gas turbine topping combustor. When it is utilized, the low-Btu fuel gas is produced in a bubbling bed carbonizer. High temperature, high pressure combustion products exiting the topping combustor are expanded in a modified gas turbine to generate electrical power. Waste heat from the system is used to raise and superheat steam for a reheat steam turbine bottoming cycle that generates additional electrical power. Basic control/instrumentation models were developed and modeled in PC-TRAX and used to investigate off-design plant performance. System performance for various transient conditions and control philosophies was studied.

White, J.S. [Parsons Power Group, Inc., Reading, PA (United States); Bonk, D.L. [USDOE Federal Energy Technology Center, Morgantown, WV (United States)

1997-05-01

392

Transient critical heat flux  

SciTech Connect

The term Critical Heat Flux (CHF) is used in boiling heat transfer to describe the local value of the heat flux at which a characteristic reduction in the heat transfer coefficient first occurs. A major limitation on the thermal design of a light-water reactor (LWR) is the necessity to maintain an adequate safety margin between the CHF and the local heat flux. Extended operations at local power levels in excess of the CHF can lead to high-temperature oxidation and embrittlement or melting of the zircaloy cladding, thus jeopardizing the fuel rod's integrity. In nuclear reactors, the CHF level is more likely to be reached during abnormal (transient) operating conditions, rather than during normal (steady) operations. For accurate nuclear reactor modeling, the accurate prediction of CHF as a function of time-dependent, thermal-hydraulic conditions is essential. This research was a two-fold study. In the first part, the quasi-steady approach in predicting the CHF is defined and analyzed. Data from blowdown experiments are compared to commonly used steady-state correlations on a local-instantaneous basis. In the second part, faster transients, where the quasi-steady approach is unable to predict the CHF, are considered. A new theory is developed to predict the CHF in power transients, which are typical of Reactivity Initiated Accidents (RIA) in LWRs.

Pasamehmetoglu, K.O.

1986-01-01

393

Finite Volume Scheme for Double Convection-Diffusion Exchange of Solutes in Bicarbonate High-Flux Hollow-Fiber Dialyzer Therapy  

PubMed Central

The efficiency of a high-flux dialyzer in terms of buffering and toxic solute removal largely depends on the ability to use convection-diffusion mechanism inside the membrane. A two-dimensional transient convection-diffusion model coupled with acid-base correction term was developed. A finite volume technique was used to discretize the model and to numerically simulate it using MATLAB software tool. We observed that small solute concentration gradients peaked and were large enough to activate solute diffusion process in the membrane. While CO2 concentration gradients diminished from their maxima and shifted toward the end of the membrane, HCO3 ? concentration gradients peaked at the same position. Also, CO2 concentration decreased rapidly within the first 47 minutes while optimal HCO3 ? concentration was achieved within 30 minutes of the therapy. Abnormally high diffusion fluxes were observed near the blood-membrane interface that increased diffusion driving force and enhanced the overall diffusive process. While convective flux dominated total flux during the dialysis session, there was a continuous interference between convection and diffusion fluxes that call for the need to seek minimal interference between these two mechanisms. This is critical for the effective design and operation of high-flux dialyzers.

Annan, Kodwo

2012-01-01

394

Finite volume scheme for double convection-diffusion exchange of solutes in bicarbonate high-flux hollow-fiber dialyzer therapy.  

PubMed

The efficiency of a high-flux dialyzer in terms of buffering and toxic solute removal largely depends on the ability to use convection-diffusion mechanism inside the membrane. A two-dimensional transient convection-diffusion model coupled with acid-base correction term was developed. A finite volume technique was used to discretize the model and to numerically simulate it using MATLAB software tool. We observed that small solute concentration gradients peaked and were large enough to activate solute diffusion process in the membrane. While CO(2) concentration gradients diminished from their maxima and shifted toward the end of the membrane, HCO(3)(-) concentration gradients peaked at the same position. Also, CO(2) concentration decreased rapidly within the first 47 minutes while optimal HCO(3)(-) concentration was achieved within 30 minutes of the therapy. Abnormally high diffusion fluxes were observed near the blood-membrane interface that increased diffusion driving force and enhanced the overall diffusive process. While convective flux dominated total flux during the dialysis session, there was a continuous interference between convection and diffusion fluxes that call for the need to seek minimal interference between these two mechanisms. This is critical for the effective design and operation of high-flux dialyzers. PMID:23197994

Annan, Kodwo

2012-10-31

395

Modeling diffusion in foamed polymer nanocomposites.  

PubMed

Two-way multicomponent diffusion processes in polymeric nanocomposite foams, where the condensed phase is nanoscopically reinforced with impermeable fillers, are investigated. The diffusion process involves simultaneous outward permeation of the components of the dispersed gas phase and inward diffusion of atmospheric air. The transient variation in thermal conductivity of foam is used as the macroscopic property to track the compositional variations of the dispersed gases due to the diffusion process. In the continuum approach adopted, the unsteady-state diffusion process is combined with tortuosity theory. The simulations conducted at ambient temperature reveal distinct regimes of diffusion processes in the nanocomposite foams owing to the reduction in the gas-transport rate induced by nanofillers. Simulations at a higher temperature are also conducted and the predictions are compared with experimentally determined thermal conductivities under accelerated diffusion conditions for polyurethane foams reinforced with clay nanoplatelets of varying individual lamellar dimensions. Intermittent measurements of foam thermal conductivity are performed while the accelerated diffusion proceeded. The predictions under accelerated diffusion conditions show good agreement with experimentally measured thermal conductivities for nanocomposite foams reinforced with low and medium aspect-ratios fillers. The model shows higher deviations for foams with fillers that have a high aspect ratio. PMID:23463718

Ippalapalli, Sandeep; Ranaprathapan, A Dileep; Singh, Sachchida N; Harikrishnan, G

2013-03-05

396

Water Solubility and Diffusivity in BCB Resins used in Microelectronic Packaging and Sensor Applications  

Microsoft Academic Search

This paper presents a simple measurement method to estimate water solubility and diffusivity in dielectric polymers which have low sorption rates and high diffusivities. The polymer dielectric is sandwiched between electrodes to create a specific capacitive structure. It is then exposed to step-like humid air stimuli. The resulting transient capacitance increase is recorded and the sorption rate and the diffusivity

A. Tetelin; A. Achen; V. Pouget; C. Pellet; M. Topper; J.-L. Lachaud

2005-01-01

397

Diffusion-weighted and perfusion MRI demonstrates parenchymal changes in complex partial status epilepticus  

Microsoft Academic Search

Summary Diffusion-weighted MRI (DWI) and perfusion MRI (PI) have been mainly applied in acute stroke, but may provide information in the peri-ictal phase in epilepsy patients. Both transient reductions of brain water diffusion, namely a low apparent diffusion coefficient (ADC), and signs of hyperperfusion have been reported in experimental and human epilepsy case studies. We studied 10 patients with complex

Kristina Szabo; Annkathrin Poepel; Bernd Pohlmann-Eden; Jochen Hirsch; Tobias Back; Oliver Sedlaczek; Michael Hennerici; Achim Gass

2005-01-01

398

Anisotropic effective diffusion of torqued swimmers  

NASA Astrophysics Data System (ADS)

External torques affect the trajectories of swimming microorganisms. We calculate analytically the effective three-dimensional diffusivity of a spherical active particle subject to both a constant external torque and thermal noise. We find that the presence of a torque renders the effective diffusive behavior anisotropic. The analytical results are compared with Brownian dynamics simulations and we obtain excellent agreement. For steady swimmers an external torque always decreases the effective swimmer diffusivity whereas it may be enhanced for time-reversible swimmers.

Sandoval, M.

2013-03-01

399

Quantum diffusion  

SciTech Connect

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

Habib, S.

1994-10-01

400

Exercise-triggered transient R-wave enhancement and ST-segment elevation in II, III, and aVF ECG leads: a testament to the "plasticity" of the QRS complex during ischemia.  

PubMed

We describe a patient with coronary artery disease who showed transiently augmented R-waves in his electrocardiogram (ECG) during the course of an exercise treadmill test (ETT), an ECG pattern occasionally associated with the hyperacute phase of myocardial infarction and variant angina. This change in the R-waves was noted in II, III, and aVF ECG leads and was associated with ST-segment elevation; both changed gradually and were normalized during the recovery period. Cardiac enzymes after ETT were negative, and arteriography revealed 3-vessel coronary artery disease, with a completely occluded right coronary artery. The ventriculogram showed very mild hypokinesis of the inferior left ventricular wall, while the global ejection fraction was 75%. These ECG changes, noted previously during ETT in precordial ECG leads, are herein reported to occur also in II, III, and aVF ECG leads. The generation of these ECG changes, which hinges upon a late unopposed depolarization occurring in the course and at the site of severe ischemic injury, constitutes a transient focal ventricular conduction abnormality. PMID:15127379

Madias, John E; Attari, Mehran

2004-04-01

401

Cytoplasmic hydrogen ion diffusion coefficient.  

PubMed Central

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

al-Baldawi, N F; Abercrombie, R F

1992-01-01

402

Two-stage diffusion and nanoparticle formation in heavily implanted polycrystalline Al2O3  

NASA Astrophysics Data System (ADS)

Two-stage diffusion was experimentally observed for the first time in polycrystalline alumina. Samples were heavily implanted by Ti ions and the concentration depth profiles were determined by Rutherford backscattering spectrometry (RBS) with 2 MeV He+ ions. The Arrhenius-plot, derived from the RBS spectra, shows two different diffusion mechanisms for the implanted Ti ions between RT and 900°C: (i) radiation enhanced diffusion (RED) up to 730°C (ii) transient thermal-like diffusion between 730°C and 900°C. The extrapolation to zero-value at 710°C agrees well with the temperature, reported in (G.P. Pells, J. Am. Ceram. Soc. 77 (2) (1994) 368). At this temperature the annealing of F-centres is already completed. High resolution scanning electron microscopy (HSEM) with energy dispersive X-ray analysis (EDX) showed Ti-enriched nanoparticles with a typical diameter of about 10-15 nm on samples, implanted at RT. The nanoparticles agglomerate into larger particles at an implantation temperature of about 830°C. Combining RBS, HSEM, X-ray photoelectron spectroscopy (XPS) measurements with TRIM simulations (J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon, New York, 1985), more detailed information on depth and lateral distribution of Ti atoms was obtained.

Duvanov, S. M.; Balogh, A. G.

2000-12-01

403

Transient expression assays in tobacco protoplasts.  

PubMed

The sequence information generated through genome and transcriptome analysis from plant tissues has reached unprecedented sizes. Sequence homology-based annotations may provide hints for the possible function and roles of particular plant genes, but the functional annotation remains nonexistent or incomplete for many of them. To discover gene functions, transient expression assays are a valuable tool because they can be done more rapidly and at a higher scale than generating stably transformed tissues. Here, we describe a transient expression assay in protoplasts derived from suspension cells of tobacco (Nicotiana tabacum) for the study of the transactivation capacities of transcription factors. To enhance throughput and reproducibility, this method can be automated, allowing medium-throughput screening of interactions between large compendia of potential transcription factors and gene promoters. PMID:23616000

Vanden Bossche, Robin; Demedts, Brecht; Vanderhaeghen, Rudy; Goossens, Alain

2013-01-01

404

Familial Transient Global Amnesia  

PubMed Central

Following an episode of typical transient global amnesia (TGA), a female patient reported similar clinical attacks in 2 maternal aunts. Prior reports of familial TGA are few, and no previous account of affected relatives more distant than siblings or parents was discovered in a literature survey. The aetiology of familial TGA is unknown. A pathophysiological mechanism akin to that in migraine attacks, comorbidity reported in a number of the examples of familial TGA, is one possibility. The study of familial TGA cases might facilitate the understanding of TGA aetiology.

Davies, R. Rhys; Larner, A.J.

2012-01-01

405

Workshop on Radio Transients  

NASA Astrophysics Data System (ADS)

abstract-type="normal">SummaryWe are entering a new era in the study of variable and transient radio sources. This workshop discussed the instruments and the strategies employed to study those sources, how they are identified and classified, how results from different surveys can be compared, and how radio observations tie in with those at other wavelengths. The emphasis was on learning what common ground there is between the plethora of on-going projects, how methods and code can be shared, and how best practices regarding survey strategy could be adopted. The workshop featured the four topics below. Each topic commenced with a fairly brief introductory talk, which then developed into discussion. By way of preparation, participants had been invited to upload and discuss one slide per topic to a wiki ahead of the workshop. 1. Telescopes, instrumentation and survey strategy. New radio facilities and on-going projects (including upgrades) are both studying the variability of the radio sky, and searching for transients. The discussion first centred on the status of those facilities, and on projects with a time-domain focus, both ongoing and planned, before turning to factors driving choices of instrumentation, such as phased array versus single pixel feeds, the field of view, spatial and time resolution, frequency and bandwidth, depth, area, and cadence of the surveys. 2. Detection, pipelines, and classification. The workshop debated (a) the factors that influence decisions to study variability in the (u,v) plane, in images, or in catalogues, (b) whether, and how much, pipeline code could potentially be shared between one project and another, and which software packages are best for different approaches, (c) how data are stored and later accessed, and (d) how transients and variables are defined and classified. 3. Statistics, interpretation, and synthesis. It then discussed how (i) the choice of facility and strategy and (ii) detection and classification schemes influence what is seen (in terms of types of object and rates) by different surveys, (iii) how results from different surveys could be compared, and (iv) how what we know from existing surveys drives choices (i) and (ii), particularly as regards finding new classes of object. 4. Multiwavelength approaches. The workshop concluded by discussing what information is needed from wavelengths other than radio in order to classify transients and variables adequately and predict their rates as a function of topics (1), (2) and (3). It asked what the constraints are on responding to, and issuing triggers for, follow-up observations, and how that might feed back into considerations for designing our telescopes and surveys.

Croft, Steve; Gaensler, Bryan

2012-04-01

406

Interstitial-Mediated Diffusion in Germanium under Proton Irradiation  

SciTech Connect

We report experiments on the impact of 2.5 MeV proton irradiation on self-diffusion and dopant diffusion in germanium (Ge). Self-diffusion under irradiation reveals an unusual depth independent broadening of the Ge isotope multilayer structure. This behavior and the observed enhanced diffusion of B and retarded diffusion of P demonstrates that an interstitial-mediated diffusion process dominates in Ge under irradiation. This fundamental finding opens up unique ways to suppress vacancy-mediated diffusion in Ge and to solve the donor deactivation problem that hinders the fabrication of Ge-based nanoelectronic devices.

Bracht, H.; Schneider, S. [Institute of Materials Physics, University of Muenster, Wilhelm-Klemm-Strasse 10, D-48149 Muenster (Germany); Klug, J. N. [RUBION, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44780 Bochum (Germany); Liao, C. Y.; Haller, E. E. [MS and E Department, University of California at Berkeley, and Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Hansen, J. Lundsgaard; Larsen, A. Nylandsted [Department of Physics and Astronomy, Aarhus University, Ny Munkegade, DK-8000 Aarhus (Denmark); Bougeard, D. [Walter Schottky Institute, Technical University of Munich, Am Coulombwall 3, D-85748 Garching (Germany); Posselt, M.; Wuendisch, C. [Forschungszentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, D-01314 Dresden (Germany)

2009-12-18

407

Transient "cerebellar" mutism.  

PubMed

The term "cerebellar mutism" refers to a specific disorder in which a complete but transient loss of speech, followed by dysarthria, occurs following resection of intrinsic posterior cranial fossa tumors or cerebellar hemorrhages, or upon trauma. Although it is well known that the lack of long-tract findings and cranial nerve (CN) involvement is the rule, the pathophysiology of cerebellar mutism has not been clearly elucidated. A review of the relevant literature disclosed 93 patients with this condition, the majority of these being in the pediatric age group. The neuropathological findings were as follows: 57 primitive neuroectodermal tumors (PNET), 19 astrocytomas, 10 ependymomas, 5 vascular malformations, 1 metastatic tumor, and 1 traumatic injury. The interval before the onset of mutism ranged from 0 to 168 h (mean 40.9 h). The mutism lasted from 1 to 168 days (mean 37.6 days). Subsequent dysarthria was present in 75 (80%) of the 93 patients. In this article, some specific recent illustrative reports are presented, and the concept of the role of the cerebellum in language and cognition is discussed. With these data as our point of departure, various hypotheses that have been advanced to explain the pathogenesis of this transient speech disorder are analyzed. The findings of the study suggest that the cause of the cerebellar mutism is the ischemia caused by vasospasm, as it usually developed after a latent period. PMID:9660116

Turgut, M

408

Atomic transient recorder.  

PubMed

In Bohr's model of the hydrogen atom, the electron takes about 150 attoseconds (1 as = 10(-18) s) to orbit around the proton, defining the characteristic timescale for dynamics in the electronic shell of atoms. Recording atomic transients in real time requires excitation and probing on this scale. The recent observation of single sub-femtosecond (1 fs = 10(-15) s) extreme ultraviolet (XUV) light pulses has stimulated the extension of techniques of femtochemistry into the attosecond regime. Here we demonstrate the generation and measurement of single 250-attosecond XUV pulses. We use these pulses to excite atoms, which in turn emit electrons. An intense, waveform-controlled, few cycle laser pulse obtains 'tomographic images' of the time-momentum distribution of the ejected electrons. Tomographic images of primary (photo)electrons yield accurate information of the duration and frequency sweep of the excitation pulse, whereas the same measurements on secondary (Auger) electrons will provide insight into the relaxation dynamics of the electronic shell following excitation. With the current approximately 750-nm laser probe and approximately 100-eV excitation, our transient recorder is capable of resolving atomic electron dynamics within the Bohr orbit time. PMID:14985755

Kienberger, R; Goulielmakis, E; Uiberacker, M; Baltuska, A; Yakovlev, V; Bammer, F; Scrinzi, A; Westerwalbesloh, Th; Kleineberg, U; Heinzmann, U; Drescher, M; Krausz, F

2004-02-26

409

Mechanism for transient migration of xenon in UO2  

NASA Astrophysics Data System (ADS)

In this letter, we report recent work on atomistic modeling of diffusion migration events of the fission gas product xenon in UO2 nuclear fuel. Under nonequilibrium conditions, Xe atoms can occupy the octahedral interstitial site, in contrast to the thermodynamically most stable uranium substitutional site. A transient migration mechanism involving Xe and two oxygen atoms is identified using basin constrained molecular dynamics employing a Buckingham type interatomic potential. This mechanism is then validated using density functional theory calculations using the nudged elastic band method. An overall reduction in the migration barrier of 1.6-2.7 eV is obtained compared to vacancy-mediated diffusion on the uranium sublattice.

Liu, X.-Y.; Uberuaga, B. P.; Andersson, D. A.; Stanek, C. R.; Sickafus, K. E.

2011-04-01

410

Discrimination of hydrothermal mound structures using transient electromagnetic methods  

NASA Astrophysics Data System (ADS)

We present numerical modeling results to support the use of seafloor transient electromagnetic (EM) techniques in characterizing the buried component of active hydrothermal mounds. We construct 2-D electrical models of a volcanic-hosted sulphide mound and compute the EM fields created by a transient electric dipole source deployed on the seafloor. The time it takes for fields to diffuse between the source and receivers is diagnostic of the intervening electrical conductivity. In the case considered, the highly conductive, outcropping sulphide mound is essentially invisible to the EM probe, exposing the moderately conducting alteration and upflow zone below. Transient EM responses are measurably different for the model featuring concentrated upflow compared to the model containing a spatially broad fluid supply beneath the mound.

Evans, Rob L.; Everett, Mark E.

1994-03-01

411

Two-Phase Transients of Polymer Electrolyte Fuel Cells  

Microsoft Academic Search

A three-dimensional transient model fully coupling the two-phase flow, species transport, heat transfer, and electrochemical processes was developed to study the dynamics of gas-diffusion layer GDL dewetting and its impact on polymer electrolyte fuel cell performance. It was found that the dewetting of fuel cells by dry gas is characterized by several regimes of different time constants. These regimes can

Yun Wang; Chao-Yang Wang

2007-01-01

412

Effect of transient model of arrester on transient recovery voltage  

Microsoft Academic Search

Circuit breakers can fail to interrupt fault current when the power system has transient recovery voltage (TRV) characteristics that exceed the rating of circuit breaker. TRV is the voltage across the opening contacts of a fault interrupting circuit breaker immediately after the arc is extinguished. The actual shape of the transient is determined by the connected lumped and distributed inductive

B. Vahidi; E. Goodarzi; S. H. Hosseinian; M. R. B. Tavakoli

2007-01-01

413

Transient complex peroxisomal interactions  

PubMed Central

Mitochondria and peroxisomes are ubiquitous subcellular organelles that fulfill essential metabolic functions, rendering them indispensable for human development and health. Both are highly dynamic organelles that can undergo remarkable changes in morphology and number to accomplish cellular needs. While mitochondrial dynamics are also regulated by frequent fusion events, the fusion of mature peroxisomes in mammalian cells remained a matter of debate. In our recent study, we clarified systematically that there is no complete fusion of mature peroxisomes analogous to mitochondria. Moreover, in contrast to key division components such as DLP1, Fis1 or Mff, mitochondrial fusion proteins were not localized to peroxisomes. However, we discovered and characterized novel transient, complex interactions between individual peroxisomes which may contribute to the homogenization of the often heterogeneous peroxisomal compartment, e.g., by distribution of metabolites, signals or other “molecular information” via interperoxisomal contact sites.

Bonekamp, Nina A.; Schrader, Michael

2012-01-01