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1

Time scales of transient enhanced diffusion: Free and clustered interstitials  

NASA Astrophysics Data System (ADS)

Transient enhanced diffusion (TED) and electrical activation after nonamorphizing Si implantations into lightly B-doped Si multilayers shows two distinct timescales, each related to a different class of interstitial defect. At 700°C, ultrafast TED occurs within the first 15 s with a B diffusivity enhancement of > 2 × 10 5. Immobile clustered B is present at low concentration levels after the ultrafast transient and persists for an extended period (˜ 10 2-10 3 s). The later phase of TED exhibits a near-constant diffusivity enhancement of ? 1 × 10 4, consistent with interstitial injection controlled by dissolving {113} interstitial clusters. The relative contributions of the ultrafast and regular TED regimes to the final diffusive broadening of the B profile depends on the proportion of interstitials that escape capture by {113} clusters growing within the implant damage region upon annealing. Our results explain the ultrafast TED recently observed after medium-dose B implantation. In that case there are enough B atoms to trap a large proportion of interstitials in Si?B clusters, and the remaining interstitials contribute to TED without passing through an intermediate {113} defect stage. The data on the ultrafast TED pulse allows us to extract lower limits for the diffusivities of the Si interstitial ( DI > 2 × 10 -10 cm 2s -1) and the B interstitial(cy) defect ( DBi > 2 × 10 -13 cm 2s -1) at 700°C.

Cowern, N. E. B.; Huizing, H. G. A.; Stolk, P. A.; Visser, C. C. G.; de Kruif, R. C. M.; Kyllesbech Larsen, K.; Privitera, V.; Nanver, L. K.; Crans, W.

1996-12-01

2

Transient enhanced diffusion and deactivation of ion-implanted As in strained Si  

Microsoft Academic Search

First results on the effects of strain on transient enhanced diffusion and deactivation of As-implanted ultrashallow junctions are presented. A significant effect of strain on the magnitude and timescale of transient enhanced diffusion is observed, which is consistent with the stabilization of interstitial-type defects by tensile strain. Our results show no significant impact of strain on As electrical activity during

G. D. M. Dilliway; A. J. Smith; J. J. Hamilton; J. Benson; Lu Xu; P. J. McNally; G. Cooke; H. Kheyrandish; N. E. B. Cowern

2005-01-01

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

Effects of end-of-range dislocation loops on transient enhanced diffusion of indium implanted in silicon  

NASA Astrophysics Data System (ADS)

Transient enhanced diffusion of indium implanted in silicon is studied in the presence of the end-of-range (EOR) damage layer. To investigate the effect of EOR defects on the indium diffusion, the samples that were implanted with indium at a high dose (1×1013-5×1014/cm2) sufficient to produce the amorphous layer were prepared. Transmission electron microscopy measurements and Rutherford backscattering spectrometry reveal the amorphization threshold of indium implantation is around 5×1013/cm2 for 200 keV, 115In+ implanted with 100 ?A/cm2 beam current density at room temperature. These results are consistent with Monte Carlo simulation of implantation. Monte Carlo simulations indicate the deviation from the plus one model due to the mass effect of indium. After amorphization, following both RTA at 1000 °C and furnace anneal at low temperature (650 and 850 °C) in nitrogen ambient showed the formation of extrinsic EOR dislocation loops below the original amorphous/crystalline interface. During this process, strong segregation of indium toward the EOR dislocation loops is clearly observed. The profile shift of indium at a concentration of 1×1017 atoms/cm3 is not proportional to the implanted dose. Since most interstitials condense into EOR dislocation loops, diffusivity enhancement of indium is not proportional to the implant dose above amorphization threshold.

Noda, T.; Odanaka, S.; Umimoto, H.

2000-11-01

5

Linking ab initio energetics to experiment: kinetic Monte Carlo simulation of transient enhanced diffusion of B in Si  

SciTech Connect

We have developed a kinetic Monte Carlo (kMC) simulator that links atomic migration and binding energies determined primarily from first principles calculations to macroscopic phenomena and laboratory time scales. Input for the kMC simulation is obtained from a combination of ab initio planewave pseudopotential calculations, molecular dynamics simulations, and experimental data. The simulator is validated against an extensive series of experimental studies of the diffusion of B spikes in self-implanted Si. The implant energy, dose, and dose rate, as well as the detailed thermal history of the sample, are included. Good agreement is obtained with the experimental data for temperatures between 750 and 950 C and times from 15 to 255 s. At 1050o C we predict too little diffusion after 105 s compared to experiment: apparently, some mechanism which is not adequately represented by our model becomes important at this temperature. Below 1050o C, the kMC simulation produces a complete description over macroscopic time scales of the atomic level diffusion and defect reaction phenomena that operate during the anneals. This simulator provides a practical method for predicting technologically interesting phenomena, such as transient enhanced diffusion of B, over a wide range of conditions, using energetics determined from first-principles approaches.

Caturla, M. J.; Diaz de la Rubia, T.; Griffin, P. B.; Johnson, M. C.; Theiss, S.; Ural, A.

1998-12-16

6

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

7

Comparison of Radon Diffusion Coefficients Measured by Transient-Diffusion and Steady-State Laboratory Methods.  

National Technical Information Service (NTIS)

A method was developed and used to determine radon diffusion coefficients in compacted soils by transient-diffusion measurements. A relative standard deviation of 12 percent was observed in repeated measurements with a dry soil by the transient-diffusion ...

D. R. Kalkwarf K. K. Nielson D. C. Rich V. C. Rogers

1982-01-01

8

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

Microsoft Academic Search

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

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

1982-01-01

9

Enhanced diffusion welding  

NASA Technical Reports Server (NTRS)

Surfaces of unrecrystallized alloys are sanded and polished. This is followed by a two-step welding process by which the strength of the parent metal is retained at the weld joint. The first step forces the surfaces into intimate contact at a temperature where the metal still has good ductility. The second step causes diffusion, recrystallization, and grain growth across the original weld interface.

Holko, K. H.; Moore, T. J. (inventors)

1973-01-01

10

Diffusion enhances spontaneous electroweak baryogenesis.  

National Technical Information Service (NTIS)

We include the effects of diffusion in the electroweak spontaneous baryogeneis scenario and show that it can greatly enhance the resultant baryon density, by as much as a factor of 1/(alpha)(sub w)(sup 4) (approximately) 10(sup 6) over previous estimates....

A. G. Cohen D. B. Kaplan A. E. Nelson

1994-01-01

11

Tempered fractional model for transient anomalous diffusion  

NASA Astrophysics Data System (ADS)

Passive tracers in heterogeneous media experience preasymptotic transport with scale-dependent anomalous diffusion, before eventually converging to the asymptotic diffusion limit. We propose a novel tempered fractional model to capture the slow convergence of sub-diffusion to a diffusion limit for passive tracers in heterogeneous media. Previous research used power-law waiting times to capture the time-nonlocal transport process. Here those waiting times are exponentially tempered, to capture the natural cutoff of retention times. The model is validated against particle concentrations from detailed numerical simulations and field measurements, at various scales and geological environments. Applications to tempered anomalous super-diffusion will also be discussed. In that case, fast particle movements are exponentially cooled, resulting in a transition from fractional advection-dispersion at early time to classical behavior at late time.

Meerschaert, M. M.; Zhang, Y.; Baeumer, B.

2008-12-01

12

Transient radon diffusion through radon-proof membranes: A new technique for more precise determination of the radon diffusion coefficient  

Microsoft Academic Search

The following paper is focused on the numerical modelling of the transient radon diffusion through radon-proof membranes during the measurement of their radon diffusion coefficient. The major aim of such numerical modelling is to increase the accuracy of radon diffusion coefficients derived from the measured data sets. The developed complex “transient” numerical model is able to calculate the radon diffusion

Martin Jiranek; Zbynek Svoboda

2009-01-01

13

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

14

Enhancing Rotational Diffusion Using Oscillatory Shear  

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

15

Enhanced diffusion of phosphorus at grain boundaries  

NASA Technical Reports Server (NTRS)

Enhanced diffusion of phosphorus at grain boundaries in cast polycrystalline photovoltaic materials (Wacker, HEM, and Semix) was studied. It was found that the enhancements for the three materials were the same, indicating that the properties of boundaries are similar, even though they were grown by different techniques. In addition, it was observed that grain boundaries capable of enhancing the diffusion always have strong recombination activities. Both phenomena could be related to dangling bonds existing at the boundaries. The present study gives the first evidence that incoherent second order twins of 111/115-plane type are diffusion-active.

Cheng, L. J.; Shyu, C. M.; Stika, K. M.; Daud, T.; Crotty, G. T.

1982-01-01

16

Diffusion enhancement in on/off ratchets  

NASA Astrophysics Data System (ADS)

We show a diffusion enhancement of suspended polystyrene particles in an electrical on/off ratchet. The enhancement can be described by a simple master equation model. Furthermore, we find that the diffusion enhancement can be described by a general curve whose shape is only determined by the asymmetry of the ratchet repeat unit. The scaling of this curve can be explained from an analytical expression valid for small off-times. Finally, we demonstrate how the master equation model can be used to find the driving parameters for optimal particle separation.

Chr. Germs, W.; Roeling, E. M.; van IJzendoorn, L. J.; Janssen, R. A. J.; Kemerink, M.

2013-02-01

17

Anomalous diffusion and enhancement of diffusion in a vibrational motor  

NASA Astrophysics Data System (ADS)

The diffusion properties of a vibrational motor, in which an additional time-dependent driving brings the system out of equilibrium and the other time-periodic driving fills the role usually played by noise, are investigated. Within the tailored parameter regime, the diffusion coefficient evolving after a considerably long time develops a sharp peak closely related to the inflection points of the mean velocity upon an increase of the damping constant. The diffusion peak here depends on the superdiffusion motion of the particle. Also, negative velocity (for a positive bias) depending on the subdiffusive motion, i.e. dispersionless transport in the asymptotic long time limit, is obtained. Moreover, an enhancement of diffusion phenomenon can be observed. These results may be helpful for separating particles under some conditions by adjusting the external forces applied.

Guo, Wei; Du, Lu-Chun; Mei, Dong-Cheng

2014-04-01

18

Transient-Diffusion Measurements of Radon: Practical Interpretation of Measured Data  

Microsoft Academic Search

The mathematical calculation to obtain a radon diffusion coefficient from measured radon transient-diffusion data is usually done by fitting a difference equation to the data. The difference equation is obtained through transformation of the time-dependent diffusion equation based on Fick's law. But, actual measured transient-diffusion data often have much scatter. Therefore just fitting over the whole range of the measured

Tomozo SASAKI; Yasuyoshi GUNJI; Takao IIDA

2007-01-01

19

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

20

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

21

Enhancing photocurrent transient spectroscopy by electromagnetic modeling.  

PubMed

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. PMID:22667598

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

2012-05-01

22

Transient-Diffusion Measurement of Radon in Japanese Soils from a Mathematical Viewpoint  

Microsoft Academic Search

A transient-diffusion measurement method for radon diffusion coefficients in porous materials was first developed in the U.S.A. To get a correct interpretation of measured data by the transient-diffusion method, more attention needs to be put on mathematical treatment which has been somewhat neglected perhaps because of the inherent mathematical difficulty. Strictly speaking, the measured radon concentrations have to be interpreted

Tomozo SASAKI; Yasuyoshi GUNJI; Takeshi OKUDA

2006-01-01

23

Induced nuclear fission viewed as a diffusion process: Transients  

NASA Astrophysics Data System (ADS)

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 the temperature dependence of nuclear shell effects. We pay particular attention to the time ? needed for the system to build up the quasistationary probability flow over the fission barrier. The rate of the latter is approximated in terms of the Bohr-Wheeler formula or Kramer's transition state expression; the precise value of the quasistationary current depends on the nuclear friction constant ?. Our results for ? are consistent with those obtained earlier in the framework of a simplified model: As long as ?<=?0, the time ? is proportional to ?-1. This relationship exhibits the fact that with increasing friction ?, the diffusion process is accelerated, so that it takes the system increasingly less time to attain the quasistationary distribution. The constant ?0 is roughly given by 2?1, where ?1 is the frequency of a harmonic oscillator potential which osculates the potential at the minimum corresponding to the initial configuration of the fissioning nucleus. The condition ?<=?0 is roughly equivalent with the motion in that minimum being underdamped. The converse relationship-? increases with ?-is found for ?>?0. We ascribe this to the fact that now the fission variable executes an overdamped motion. Generalizing Kramers's original derivation, we obtain an analytical expression for the time dependence of the probability current over the fission barrier. For ?<~?0, this expression agrees well with our numerical results. We use it to calculate the energy dependence of the fission probability Pf and find that Pf grows much less rapidly with increasing excitation energy than would be predicted by the Bohr-Wheeler formula. This is in qualitative agreement with recent experimental findings and suggests that the energy dependence of Pf deserves further investigation and can be used to determine ? experimentally. Our analysis does not yet include the additional time delay incurred by the system on its way from the saddle to the scission point: Clearly the time needed to establish the quasistationary situation at the scission point will be larger than ?. This would probably lead to additional modifications of the energy dependence of Pf. NUCLEAR REACTIONS, FISSION Diffusion over a potential barrier; transients; deviation from Bohr-Wheeler formula.

Grangé, P.; Jun-Qing, Li; Weidenmüller, H. A.

1983-05-01

24

Transient airglow enhancement by lightning observed by satellite  

NASA Astrophysics Data System (ADS)

Transient airglow produced by lightning has been observed in many space missions. The ISUAL instrument on board the FORMOSAT 2 satellite has observed numerous cases of lightning events including sprite, ELVE, halo, and the enhancement in airglow layers for both OH and O2 airglow. The lightning events can produce excited states which react with background atmosphere to produce enhanced airglow. A mechanism involving O(1D) is discussed here.

Nee, J. B.; Dalgarno, A.

2008-12-01

25

Radiation enhanced diffusion in MgO  

NASA Astrophysics Data System (ADS)

Radiation enhanced diffusion and ion beam mixing of 18O, Ca, and Zn buried tracer layers in MgO, grown by molecular beam epitaxy, have been measured following irradiation with 2.0 MeV Kr+ and 1.0 MeV Ne+, He+, and H+ from 30 to 1500 °C. The ion beam mixing parameter varied between 1.0 and 5.0 Å5 eV-1 for the different tracers at 30 °C and increased slowly with increasing temperature. These results are consistent with ballistic mixing. In the highest temperature range investigated, 1350-1500 °C, the radiation enhanced diffusion coefficient for 18O was proportional to the square root of the irradiation flux and displayed an apparent activation enthalpy of 1.2 eV. These dependencies on flux and temperature are indicative of recombination-limited kinetics, with the measured activation enthalpy representing one-half the migration enthalpy of anion vacancies. From 1150 to 1350 °C an activation enthalpy of 4.1 eV was obtained. The unexpectedly high value is attributed to the dissociation energy of small vacancy clusters. Measurements on the cation sublattice were limited to temperatures below 900 °C owing to the excessive thermal diffusion associated with extrinsic vacancies, which are present for trivalent impurity charge compensation.

van Sambeek, A. I.; Averback, R. S.; Flynn, C. P.; Yang, M. H.; Jäger, W.

1998-06-01

26

A Comparison of Implicit Numerical Methods for Solving the Transient Spherical Diffusion Equation.  

National Technical Information Service (NTIS)

Comparative numerical temperature results obtained by using two implicit finite difference procedures for the solution of the transient diffusion equation in spherical coordinates are presented. The validity and accuracy of these solutions are demonstrate...

D. M. Curry

1977-01-01

27

Tempered stable Lévy motion and transient super-diffusion  

NASA Astrophysics Data System (ADS)

The space-fractional diffusion equation models anomalous super-diffusion. Its solutions are transition densities of a stable Lévy motion, representing the accumulation of power-law jumps. The tempered stable Lévy motion uses exponential tempering to cool these jumps. A tempered fractional diffusion equation governs the transition densities, which progress from super-diffusive early-time to diffusive late-time behavior. This article provides finite difference and particle tracking methods for solving the tempered fractional diffusion equation with drift. A temporal and spatial second-order Crank-Nicolson method is developed, based on a finite difference formula for tempered fractional derivatives. A new exponential rejection method for simulating tempered Lévy stables is presented to facilitate particle tracking codes.

Baeumer, Boris; Meerschaert, Mark M.

2010-03-01

28

THE EFFECT OF TURBULENT DIFFUSION ON TEMPERATURE TRANSIENTS IN LIQUID METAL FUEL REACTOR PIPELINES  

Microsoft Academic Search

A diffusion coefficient was calculated for a description of the ; turbulent dlffusion of heated fluid in cylindrical pipes of diameters appropriate ; to liquid metal fuel reactors utilizing Bi. From the transfer function resulting ; from the solution of the diffusion equation, the attenuation of sharp edged ; transients and the damping of oscillations were calculated to illustrate the

Thompson

1957-01-01

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

Electrostatic Rate Enhancement and Transient Complex of Protein-Protein Association  

PubMed Central

The association of two proteins is bounded by the rate at which they, via diffusion, find each other while in appropriate relative orientations. Orientational constraints restrict this rate to ~105 – 106 M?1s?1. Proteins with higher association rates generally have complementary electrostatic surfaces; proteins with lower association rates generally are slowed down by conformational changes upon complex formation. Previous studies (Zhou, Biophys. J. 1997;73:2441–2445) have shown that electrostatic enhancement of the diffusion-limited association rate can be accurately modeled by kD = kD0 exp(?*/ kBT), where kD and kD0 are the rates in the presence and absence of electrostatic interactions, respectively, * is the average electrostatic interaction energy in a “transient-complex” ensemble, and kBT is thermal energy. The transient-complex ensemble separates the bound state from the unbound state. Predictions of the transient-complex theory on four protein complexes were found to agree well with experiment when the electrostatic interaction energy was calculated with the linearized Poisson-Boltzmann (PB) equation (Alsallaq and Zhou, Structure 2007, 15:215–224). Here we show that the agreement is further improved when the nonlinear PB equation is used. These predictions are obtained with the dielectric boundary defined as the protein van der Waals surface. When the dielectric boundary is instead specified as the molecular surface, electrostatic interactions in the transient complex become repulsive and are thus predicted to retard association. Together these results demonstrate that the transient-complex theory is predictive of electrostatic rate enhancement and can help parameterize PB calculations.

Alsallaq, Ramzi; Zhou, Huan-Xiang

2012-01-01

31

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

32

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

33

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

34

Picomolar Amyloid-? Peptides Enhance Spontaneous Astrocyte Calcium Transients  

PubMed Central

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.

Lee, Linda; Kosuri, Pallav; Arancio, Ottavio

2014-01-01

35

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

36

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

37

Mass Transport in Salt Repositories: Transient Diffusion into Interbeds.  

National Technical Information Service (NTIS)

To estimate possible radioactive releases from a waste package to the near-field environment, we analyzed pressure-driven brine migration movement and release rates of low-solubility and readily soluble nuclides by diffusion. A possible pathway for radioa...

Y. Hwang W. W. L. Lee P. L. Chambre T. H. Pigford

1989-01-01

38

Enhanced diffusion of Zn in Al under Ne irradiation  

Microsoft Academic Search

The diffusion rate of Zn in Al has been enhanced by factors ; approximately 10²¹°sup 4$ under 80 keV Ne irradiation at 130°C. ; Diffusion couples were formed by ion implantation of Zn, and the concentration ; profiles were determined by ion backscattering. The data are analyzed by ; numerically solving the coupled diffusion equations for vacancies, interstitials ; and

1975-01-01

39

Gamma-Ray Enhanced Diffusion in alpha-Brass.  

National Technical Information Service (NTIS)

Enhanced diffusion in alpha-brass was studied under gamma irradiation. The parameters varied were the flux, the temperature, and the dislocation content of the alloy. It was found that the diffusion enhancement is highly sensitive to the state of cold wor...

R. E. Larsen A. C. Damask

1964-01-01

40

Superconvergence of Discontinuous Finite Element Solutions for Transient Convection-diffusion Problems  

Microsoft Academic Search

We present a study of the local discontinuous Galerkin method for transient convection–diffusion problems in one dimension. We show that p-degree piecewise polynomial discontinuous finite element solutions of convection-dominated problems are O(?xp+2) superconvergent at Radau points. For diffusion- dominated problems, the solution’s derivative is O(?xp+2) superconvergent at the roots of the derivative of Radau polynomial of degree p+1. Using these

Slimane Adjerid; Andreas Klauser

2005-01-01

41

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

42

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

Microsoft Academic Search

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

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

1989-01-01

43

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

National Technical Information Service (NTIS)

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(1...

D. M. Pennington C. B. Harris

1993-01-01

44

Partial transient liquid phase diffusion bonding of Zircaloy4 to stabilized austenitic stainless steel 321  

Microsoft Academic Search

An innovative method was applied for bonding Zircaloy-4 to stabilized austenitic stainless steel 321 using an active titanium interlayer. Specimens were joined by a partial transient liquid phase diffusion bonding method in a vacuum furnace at different temperatures under 1MPa dynamic pressure of contact. The influence of different bonding temperatures on the microstructure, microindentation hardness, joint strength and interlayer thickness

M. Mazar Atabaki; A. Talebi Hanzaei

2010-01-01

45

Transient liquid phase diffusion bonding of Udimet 720 for Stirling power converter applications  

Microsoft Academic Search

Udimet 720 has been selected for use on Stirling power converters for space applications. Because Udimet 720 is generally considered susceptible to strain age cracking if traditional fusion welding is used, other joining methods are being considered. A process for transient liquid phase diffusion bonding of Udimet 720 has been theoretically developed in an effort to eliminate the strain age

Donald L. Mittendorf; William G. Baggenstoss

1992-01-01

46

Transient Anomalous Diffusion of Telomeres in the Nucleus of Mammalian Cells  

NASA Astrophysics Data System (ADS)

We measured individual trajectories of fluorescently labeled telomeres in the nucleus of eukaryotic cells in the time range of 10-2-104sec? by combining a few acquisition methods. At short times the motion is subdiffusive with ?r2?˜t? and it changes to normal diffusion at longer times. The short times diffusion may be explained by the reptation model and the transient diffusion is consistent with a model of telomeres that are subject to a local binding mechanism with a wide but finite distribution of waiting times. These findings have important biological implications with respect to the genome organization in the nucleus.

Bronstein, I.; Israel, Y.; Kepten, E.; Mai, S.; Shav-Tal, Y.; Barkai, E.; Garini, Y.

2009-07-01

47

Coherence enhancing diffusion filtering based on the Phase Congruency Tensor  

Microsoft Academic Search

Many biomedical applications require the enhancement of coherent flow-like curvilinear structures in images. This can be accomplished in a natural way by adopting anisotropic diffusion filtering to local texture analysis by means of the structure tensor. Here we propose a contrast independent anisotropic diffusion filtering of curvilinear structures based on a novel concept: the Phase Congruency Tensor (PCT). The phase

Boguslaw Obara; Mark Fricker; Vicente Grau

2012-01-01

48

Enhanced Diffusion of Zn in Al under Ne Irradiation.  

National Technical Information Service (NTIS)

The diffusion rate of Zn in Al has been enhanced by factors approximately 10 exp 2 --10 exp 4 under 80 keV Ne irradiation at 130 exp 0 C. Diffusion couples were formed by ion implantation of Zn, and the concentration profiles were determined by ion backsc...

S. M. Myers

1975-01-01

49

Measurements of the transient velocity field in a strongly curved diffusing bend with periodic inflow unsteadiness  

NASA Astrophysics Data System (ADS)

This study examined the effects of periodic inflow unsteadiness on the flow development through fishtail-shaped diffusers utilized on small gas turbine engines. The periodic unsteadiness is due to the distortion of the flow in the peripheral direction at the exit of the centrifugal compressor impeller, caused by the jet-wake type of flow discharging from each impeller passage. Measurements of the transient velocity field were performed throughout the diffuser using a miniature 4-wire probe, at frequencies of inflow unsteadiness corresponding to design and off-design operating conditions in gas turbine installations. At the low end of the tested inflow unsteadiness frequencies, significant effects of inflow unsteadiness were observed on the time-averaged flow distortion throughout the diffuser. At these frequencies, the time variation of flow distortion was found to remain at comparable magnitudes throughout the diffuser.

Yaras, M. I.; Orsi, P.

50

Evidence for Enhanced Matrix Diffusion in Geological Environment  

NASA Astrophysics Data System (ADS)

Molecular diffusion in rock matrix, called as matrix diffusion, has been appreciated as a static process for elemental migration in geological environment that has been acknowledged in the context of geological disposal of radioactive waste. However, incomprehensible enhancement of matrix diffusion has been reported at a number of field test sites. Here, the matrix diffusion of saline water at Horonobe, Hokkaido, Japan is highlighted directly probing angstrom-scale pores on a field scale up to 1 km by positron--positronium annihilation spectroscopy. The first application of positron--positronium annihilation spectroscopy to field-scale geophysical research reveals the slight variation of angstrom-scale pores influenced by saline water diffusion with complete accuracy. We found widely interconnected 3 Å pores, which offer the pathway of saline water diffusion with the highly enhanced effective matrix diffusion coefficient of 4× 10-6 cm2 s-1. The present findings provide unambiguous evidence that the angstrom-scale pores enhance effective matrix diffusion on a field scale in geological environment.

Sato, Kiminori; Fujimoto, Koichiro; Nakata, Masataka; Shikazono, Naotatsu

2013-01-01

51

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

Microsoft Academic Search

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

Byung Hoon Park; Ji Hyung Lee; Woongsup Yoon

2008-01-01

52

Color Histogram Diffusion for Image Enhancement  

NASA Technical Reports Server (NTRS)

Various color histogram equalization (CHE) methods have been proposed to extend grayscale histogram equalization (GHE) for color images. In this paper a new method called histogram diffusion that extends the GHE method to arbitrary dimensions is proposed. Ranges in a histogram are specified as overlapping bars of uniform heights and variable widths which are proportional to their frequencies. This diagram is called the vistogram. As an alternative approach to GHE, the squared error of the vistogram from the uniform distribution is minimized. Each bar in the vistogram is approximated by a Gaussian function. Gaussian particles in the vistoram diffuse as a nonlinear autonomous system of ordinary differential equations. CHE results of color images showed that the approach is effective.

Kim, Taemin

2011-01-01

53

Level Set Diffusion for MRE Image Enhancement  

Microsoft Academic Search

\\u000a Magnetic resonance elastography (MRE) is an emerging technique for noninvasive imaging of tissue elasticity. Proprietary algorithms\\u000a are used to reconstruct tissue elasticity from the images of wave propagation within soft tissue. Elasticity reconstruction\\u000a suffers from interfering noise and outliers. The interference causes biased elasticity and undesired artifacts in the reconstructed\\u000a elasticity map. Anisotropic geometric diffusion is able to suppress image

Bing Nan Li; Chee-Kong Chui; Sim Heng Ong; Stephen Chang; Etsuko Kobayashi

2010-01-01

54

{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

55

Evolving Wallerian Degeneration after Transient Retinal Ischemia in Mice Characterized by Diffusion Tensor Imaging  

PubMed Central

Wallerian degeneration plays a significant role in many central nervous system (CNS) diseases. Tracking the progression of Wallerian degeneration may provide better understanding of the evolution of many CNS diseases. In this study, a 28-day longitudinal in vivo DTI of optic nerve (ON) and optic tract (OT) was conducted to evaluate the temporal and spatial evolution of Wallerian degeneration resulting from the transient retinal ischemia. At 3 ? 28 days after ischemia, ipsilateral ON and contralateral OT showed significant reduction in axial diffusivity (32 ? 40% and 21 ? 29% respectively) suggestive of axonal damage. Both ON and OT showed significant increase in radial diffusivity, 200 ? 290% and 58 ? 65% in ON and OT respectively, at 9 ? 28 days suggestive of myelin damage. Immuohistochmistry of phosphorylated neurofilament (pNF) and myelin basic protein (MBP) was performed to assess axonal and myelin integrities validating the DTI findings. Both DTI and immunohistochemistry detected that transient retinal ischemia caused more severe damage to ON than to OT. The current results suggest that axial and radial diffusivities are capable of reflecting the severity of axonal and myelin damage in mice as assessed using immunohistochemistry.

Sun, Shu-Wei; Liang, Hsiao-Fang; Cross, Anne H.; Song, Sheng-Kwei

2008-01-01

56

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

57

Transient phenomena, self-diffusion, and orientational effects in vibrated powders  

NASA Astrophysics Data System (ADS)

We explore the rich behavior of vibrated powders, focusing on the relaxation of transients between vibrational steady states, on the diffusion of independent particles, and on ``global'' and ``local'' angular distributions of contacting particles. When examined as a function of vibrational intensity, these are shown to be explicable in terms of a model of independent-particle and collective excitations. Our data provide a wealth of information about topics as diverse as consolidation under packing, the roughness of granular piles, and the local structure of bridges and arches in shaken packings.

Barker, G. C.; Mehta, Anita

1993-01-01

58

Transient liquid phase diffusion bonding of Udimet 720 for Stirling power converter applications  

NASA Astrophysics Data System (ADS)

Udimet 720 has been selected for use on Stirling power converters for space applications. Because Udimet 720 is generally considered susceptible to strain age cracking if traditional fusion welding is used, other joining methods are being considered. A process for transient liquid phase diffusion bonding of Udimet 720 has been theoretically developed in an effort to eliminate the strain age crack concern. This development has taken into account such variables as final grain size, joint homogenization, joint efficiency related to bonding aid material, bonding aid material application method, and thermal cycle.

Mittendorf, Donald L.; Baggenstoss, William G.

59

Transient liquid phase diffusion bonding of Udimet 720 for Stirling power converter applications  

NASA Technical Reports Server (NTRS)

Udimet 720 has been selected for use on Stirling power converters for space applications. Because Udimet 720 is generally considered susceptible to strain age cracking if traditional fusion welding is used, other joining methods are being considered. A process for transient liquid phase diffusion bonding of Udimet 720 has been theoretically developed in an effort to eliminate the strain age crack concern. This development has taken into account such variables as final grain size, joint homogenization, joint efficiency related to bonding aid material, bonding aid material application method, and thermal cycle.

Mittendorf, Donald L.; Baggenstoss, William G.

1992-01-01

60

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

Microsoft Academic Search

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.

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

2006-01-01

61

Radiation-enhanced self- and boron diffusion in germanium  

NASA Astrophysics Data System (ADS)

We report experiments on proton radiation-enhanced self- and boron (B) diffusion in germanium (Ge) for temperatures between 515 ?C and 720 ?C. Modeling of the experimental diffusion profiles measured by means of secondary ion mass spectrometry is achieved on the basis of the Frenkel pair reaction and the interstitialcy and dissociative diffusion mechanisms. The numerical simulations ascertain concentrations of Ge interstitials and B-interstitial pairs that deviate by several orders of magnitude from their thermal equilibrium values. The dominance of self-interstitial related defects under irradiation leads to an enhanced self- and B diffusion in Ge. Analysis of the experimental profiles yields data for the diffusion of self-interstitials (I) and the thermal equilibrium concentration of BI pairs in Ge. The temperature dependence of these quantities provides the migration enthalpy of I and formation enthalpy of BI that are compared with recent results of atomistic calculations. The behavior of self- and B diffusion in Ge under concurrent annealing and irradiation is strongly affected by the property of the Ge surface to hinder the annihilation of self-interstitials. The limited annihilation efficiency of the Ge surface can be caused by donor-type surface states favored under vacuum annealing, but the physical origin remains unsolved.

Schneider, S.; Bracht, H.; Klug, J. N.; Hansen, J. Lundsgaard; Larsen, A. Nylandsted; Bougeard, D.; Haller, E. E.

2013-03-01

62

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

63

Improved Diffusion Imaging through SNR-Enhancing Joint Reconstruction  

PubMed Central

Quantitative diffusion imaging is a powerful technique for the characterization of complex tissue microarchitecture. However, long acquisition times and limited signal-to-noise ratio (SNR) represent significant hurdles for many in vivo applications. This paper presents a new approach to reduce noise while largely maintaining resolution in diffusion weighted images, using a statistical reconstruction method that takes advantage of the high level of structural correlation observed in typical datasets. Compared to existing denoising methods, the proposed method performs reconstruction directly from the measured complex k-space data, allowing for Gaussian noise modeling and theoretical characterizations of the resolution and SNR of the reconstructed images. In addition, the proposed method is compatible with many different models of the diffusion signal (e.g., diffusion tensor modeling, q-space modeling, etc.). The joint reconstruction method can provide significant improvements in SNR relative to conventional reconstruction techniques, with a relatively minor corresponding loss in image resolution. Results are shown in the context of diffusion spectrum imaging tractography and diffusion tensor imaging, illustrating the potential of this SNR-enhancing joint reconstruction approach for a range of different diffusion imaging experiments.

Haldar, Justin P.; Wedeen, Van J.; Nezamzadeh, Marzieh; Dai, Guangping; Weiner, Michael W.; Schuff, Norbert; Liang, Zhi-Pei

2012-01-01

64

Thermal Diffusivities of Bilayer Films Deposited on Substrates Characterized Simultaneously by Transient Reflecting Grating Technique  

NASA Astrophysics Data System (ADS)

The transient reflecting grating (TRG) technique has been applied to characterize the thermal diffusivities of thin films in trilayered structures. Based on the TRG behavior in the trilayered structures of opaque film/transparent film/substrate, a two-dimensional theoretical model describing the thermal diffusion processes in the trilayed structures is presented and calculated by the finite-element method. The normalized TRG signals decayed with time can be expressed as a triple-exponential function with different time-dependent coefficients. The influences of the thermal properties of the first and second layer films on the TRG signals are calculated and discussed separately. By fitting the theoretical decay curves to the experimental measured data of a series of trilayered structures (Au/ZnO/Si and Al/ZnO/Si with different film thicknesses), the thermal diffusivities of both films in the trilayered structures can be evaluated simultaneously. The results show that the thermal diffusivities of the thin films are strongly dependent on the thickness of the thin films and significantly lower than the corresponding bulk materials, and decay with the decreasing thickness of the films.

Wu, Su-zhen; Zhang, Shu-yi; Sun, Hong-xiang

2013-09-01

65

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

66

Drift-diffusion modeling of photocurrent transients in bulk heterojunction solar cells  

NASA Astrophysics Data System (ADS)

We utilize a time-dependent drift-diffusion model incorporating electron trapping and field-dependent charge separation to explore the device physics of organic bulk-heterojunction solar cells based on blends of poly(3-hexylthiophene) (P3HT) with a red polyfluorene copolymer. The model is used to reproduce experimental photocurrent transients measured in response to a step-function excitation of light of varied intensity. The experimental photocurrent transients are characterized by (i) a fast rise of order 1 ?s followed by (ii) a slow rise of order 10-100 ?s that evolves into a transient peak at high intensity, (iii) a fast decay component after turn-off and (iv) a long-lived tail with magnitude that does not scale linearly with light intensity or steady-state photocurrent. The fast rise and decay components are explained by the transport of mobile carriers while the slow rise and decay components are explained by slower electron trapping and detrapping processes. The transient photocurrent peak at high intensities with subsequent decay to the steady-state value is explained by trap-mediated space-charge effects. The build-up of trapped electrons in the device produces reduction in the strength of the electric field near the transparent anode that increases the likelihood of bimolecular recombination, and lowers the overall efficiency of charge dissociation in the device. Notably the model demonstrates that a reduction in free charge generation rate by space-charge effects is as significant as bimolecular recombination in this device assuming Langevin-type bimolecular recombination. The model is also used to explore the dynamics of charge separation with an upper bound of 50 ns set for the lifetime of electron-hole pairs, and to provide an estimate of the trap density of 1.3×1022 m-3.

Hwang, Inchan; McNeill, Christopher R.; Greenham, Neil C.

2009-11-01

67

Recoverable creep deformation and transient local stress concentration due to heterogeneous grain-boundary diffusion and sliding in polycrystalline solids  

NASA Astrophysics Data System (ADS)

Numerical simulations are used to investigate the influence of heterogeneity in grain-boundary diffusivity and sliding resistance on the creep response of a polycrystal. We model a polycrystal as a two-dimensional assembly of elastic grains, separated by sharp grain boundaries. The crystal deforms plastically by stress driven mass transport along the grain boundaries, together with grain-boundary sliding. Heterogeneity is idealized by assigning each grain boundary one of two possible values of diffusivity and sliding viscosity. We compute steady state and transient creep rates as functions of the diffusivity mismatch and relative fractions of grain boundaries with fast and slow diffusion. In addition, our results show that under transient conditions, flux divergences develop at the intersection between grain boundaries with fast and slow diffusivity, which generate high local stress concentrations. The stress concentrations develop at a rate determined by the fast diffusion coefficient, and subsequently relax at a rate determined by the slow diffusion coefficient. The influence of the mismatch in diffusion coefficient, loading conditions, and material properties on the magnitude of this stress concentration is investigated in detail using a simple model problem with a planar grain boundary. The strain energy associated with these stress concentrations also makes a small fraction of the plastic strain due to diffusion and sliding recoverable on unloading. We discuss the implications of these results for conventional polycrystalline solids at high temperatures and for nanostructured materials where grain-boundary diffusion becomes one of the primary inelastic deformation mechanisms even at room temperature.

Wei, Yujie; Bower, Allan F.; Gao, Huajian

68

Partial transient liquid phase diffusion bonding of Zircaloy-4 to stabilized austenitic stainless steel 321  

SciTech Connect

An innovative method was applied for bonding Zircaloy-4 to stabilized austenitic stainless steel 321 using an active titanium interlayer. Specimens were joined by a partial transient liquid phase diffusion bonding method in a vacuum furnace at different temperatures under 1 MPa dynamic pressure of contact. The influence of different bonding temperatures on the microstructure, microindentation hardness, joint strength and interlayer thickness has been studied. The diffusion of Fe, Cr, Ni and Zr has been investigated by scanning electron microscopy and energy dispersive spectroscopy elemental analyses. Results showed that control of the heating and cooling rate and 20 min soaking at 1223 K produces a perfect joint. However, solid-state diffusion of the melting point depressant elements into the joint metal causes the solid/liquid interface to advance until the joint is solidified. The tensile strength of all the bonded specimens was found around 480-670 MPa. Energy dispersive spectroscopy studies indicated that the melting occurred along the interface of the bonded specimens as a result of the transfer of atoms between the interlayer and the matrix during bonding. This technique provides a reliable method of bonding zirconium alloy to stainless steel.

Atabaki, M. Mazar, E-mail: m.mazaratabaki@gmail.com [Department of Materials Engineering, Faculty of Mechanical Engineering, University Technology Malaysia, 81310 (Malaysia); Hanzaei, A. Talebi [Department of Metallurgy and Materials Engineering, Faculty of Engineering, University of Tehran (Iran, Islamic Republic of)

2010-10-15

69

Sustained and transient covert attention enhance the signal via different contrast response functions  

PubMed Central

We investigated the mechanisms underlying the effects of sustained and transient covert attention on contrast sensitivity. The aim of this study was twofold: (1) Using a zero-noise display, we assessed whether sustained (endogenous) attention enhances contrast sensitivity via signal enhancement, and compared the magnitude of the effect with that of transient (exogenous) attention. (2) We compared the contrast psychometric functions for both sustained and transient attention and evaluated them in terms of contrast gain and response gain models. Observers performed a 2AFC orientation discrimination task on a tilted target Gabor, presented alone at 1 of 8 iso-eccentric locations. Either a neutral (baseline), peripheral (to manipulate transient attention), or a central cue (to manipulate sustained attention) preceded the target. Even in the absence of external noise, and using suprathreshold stimuli, observers showed an attentional effect, evidence in support of signal enhancement underlying both sustained and transient attention. Moreover, sustained attention caused a strictly leftward threshold shift in the psychometric function, supporting a contrast gain model. Interestingly, with transient attention we observed a change in asymptote in addition to a threshold shift. These findings suggest that whereas sustained attention operates strictly via contrast gain, transient attention may be better described by a mixture of response gain and contrast gain

Ling, Sam; Carrasco, Marisa

2006-01-01

70

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

71

Enhanced diffusion weighting generated by selective adiabatic pulse trains  

NASA Astrophysics Data System (ADS)

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-Ph-6) were studied on a 4 T 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 (56.3-0.8 mM) water solutions (Ph-2-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 1H 2O 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

2007-09-01

72

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

73

Enhancement of the ultrasound images by modified anisotropic diffusion method.  

PubMed

Speckle is a primary factor which degrades the contrast resolution and masks the meaningful texture information present in an ultrasound image. Its presence severely hampers the interpretation and analysis of ultrasound images. When speckle reduction technique is applied for visual enhancement of ultrasound images, it is to be kept in mind that blurring associated with speckle reduction should be less and fine details are properly enhanced. With these points in consideration, the modified speckle reduction anisotropic diffusion (MSRAD) method is proposed in the present study to improve the visual quality of the ultrasound images. In the proposed MSRAD method, the four neighboring pixel template in speckle reduction anisotropic diffusion (SRAD) method of Yu and Acton (IEEE Trans Image Process 11:1260-1270, 2002) have been replaced by a new template of larger number of neighboring pixels to calculate the diffusion term. To enhance visual quality of ultrasound images, nonquadratic regularization (Yu and Yadegar, Proceedings of the IEEE international conference on image processing, 2006) is incorporated with MSRAD method and accordingly changes in parameter settings have been made. The performance of MSRAD method was evaluated using clinical ultrasound images, interpretation by the medical experts and results of MSRAD method by subjective and objective criteria. PMID:20574722

Mittal, Deepti; Kumar, Vinod; Saxena, Suresh Chandra; Khandelwal, Niranjan; Kalra, Naveen

2010-12-01

74

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

75

Transient Ischemic Attack and Stroke Can Be Differentiated by Analyzing the Diffusion Tensor Imaging  

PubMed Central

Objective We wanted to differentiate between transient ischemic attack (TIA) and minor stroke using fractional anisotropy and three-dimensional (3D) fiber tractography. Materials and Methods The clinical data, conventional magnetic resonance imaging (MRI), diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) were obtained for 45 TIA patients and 33 minor stroke patients. The fractional anisotrophy ratio (rFA) between the lesion and the mirrored corresponding contralateral normal tissue was calculated and analyzed. The spatial relationship between the lesion and the corticospinal tract (CST) was analyzed and the lesion sizes in the minor stroke patients and TIA patients were compared. Results Twenty-two of the 45 TIA patients (49%) revealed focal abnormalities following DWI. The rFA was significantly lower (p < 0.05) in the stroke patients (0.71 ± 0.29) compared to that of the TIA patients (1.05 ± 0.37). The CST was involved in almost all stroke lesions, but it was not involved in 68% of the TIA lesions. The TIA patients had significantly lower CST injury scores (3.25 ± 1.75) than did the stroke patients (8.80 ± 2.39) (p = 0.004). Conclusion Our data indicate that TIA and minor stroke can be identified by analyzing the rFA and the degree of CST involvement, and this may also allow more accurate prediction of a patient's long-term recovery or disability.

Zhenwei, Yao; Xiaoyuan, Feng

2011-01-01

76

Trap-controlled hydrogen diffusion and the mechanism of light-enhanced diffusion in [ital a]-Si:H  

SciTech Connect

We review our recent high-depth-resolution secondary ion mass spectrometry studies of hydrogen diffusion in amorphous silicon. We describe the trap-controlled H diffusion model supported by the experiments. Recent results on light enhancement of H diffusion in [ital a]-Si:H are also discussed.

Branz, H.M.; Asher, S.E.; Nelson, B.P. (National Renewable Energy Laboratory, Golden, Colorado (United States))

1992-12-01

77

Gas cloud infrared image enhancement based on anisotropic diffusion  

NASA Astrophysics Data System (ADS)

Leakage of dangerous gases will not only pollute the environment, but also seriously threat public safety. Thermal infrared imaging has been proved to be an efficient method to qualitatively detect the gas leakage. But some problems are remained, especially when monitoring the leakage in a passive way. For example, the signal is weak and the edge of gas cloud in the infrared image is not obvious enough. However, we notice some important characteristics of the gas plume and therefore propose a gas cloud infrared image enhancement method based on anisotropic diffusion. As the gas plume presents a large gas cloud in the image and the gray value is even inside the cloud, strong forward diffusion will be used to reduce the noise and to expand the range of the gas cloud. Frames subtraction and K-means cluttering pop out the gas cloud area. Forward-and-Backward diffusion is to protect background details. Additionally, the best iteration times and the time step parameters are researched. Results show that the gas cloud can be marked correctly and enhanced by black or false color, and so potentially increase the possibility of gas leakage detection.

Li, Jiakun; Wang, Lingxue; Zhang, Changxing; Long, Yunting; Zhang, Bei

2011-05-01

78

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

SciTech Connect

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, E-mail: m.s.mohamed@durham.ac.uk [School of Engineering and Computing Sciences, University of Durham, South Road, Durham DH1 3LE (United Kingdom); Seaid, Mohammed; Trevelyan, Jon [School of Engineering and Computing Sciences, University of Durham, South Road, Durham DH1 3LE (United Kingdom)] [School of Engineering and Computing Sciences, University of Durham, South Road, Durham DH1 3LE (United Kingdom); Laghrouche, Omar [Institute for Infrastructure and Environment, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom)] [Institute for Infrastructure and Environment, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom)

2013-10-15

79

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion  

PubMed Central

We observed interfacial chemical sharpening due to uphill diffusion in post annealed ultrathin multilayer stack of Co and Pt, which leads to enhanced interfacial perpendicular magnetic anisotropy (PMA). This is surprising as these elements are considered as perfectly miscible. This chemical sharpening was confirmed through quantitative energy dispersive x-ray (EDX) spectroscopy and intensity distribution of images taken on high angle annular dark field (HAADF) detector in Scanning Transmission Electron Microscopic (STEM) mode. This observation demonstrates an evidence of miscibility gap in ultrathin coherent Co/Pt multilayer stacks.

Das, Tanmay; Kulkarni, Prabhanjan D.; Purandare, S. C.; Barshilia, Harish C.; Bhattacharyya, Somnath; Chowdhury, Prasanta

2014-01-01

80

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion.  

PubMed

We observed interfacial chemical sharpening due to uphill diffusion in post annealed ultrathin multilayer stack of Co and Pt, which leads to enhanced interfacial perpendicular magnetic anisotropy (PMA). This is surprising as these elements are considered as perfectly miscible. This chemical sharpening was confirmed through quantitative energy dispersive x-ray (EDX) spectroscopy and intensity distribution of images taken on high angle annular dark field (HAADF) detector in Scanning Transmission Electron Microscopic (STEM) mode. This observation demonstrates an evidence of miscibility gap in ultrathin coherent Co/Pt multilayer stacks. PMID:24937637

Das, Tanmay; Kulkarni, Prabhanjan D; Purandare, S C; Barshilia, Harish C; Bhattacharyya, Somnath; Chowdhury, Prasanta

2014-01-01

81

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

NASA Astrophysics Data System (ADS)

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: UO 2 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. This new capability is demonstrated using a 2D axisymmetric analysis of the upper section of a simplified multipellet fuel rod, during both steady and transient operation. Comparisons are made between discrete and smeared-pellet simulations. Computational results demonstrate the importance of a multidimensional, multipellet, fully-coupled thermomechanical approach. Interestingly, many of the inherent deficiencies in existing fuel performance codes (e.g., 1D thermomechanics, loose thermomechanical coupling, separate steady and transient analysis, cumbersome pre- and post-processing) are, in fact, ABAQUS strengths.

Williamson, R. L.

2011-08-01

82

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

83

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

84

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

85

Transient Expression of the Cytochrome p450 CYP78A2 Enhances Anthocyanin Production in Flowers  

Microsoft Academic Search

Transient expression of a cytochrome P450 gene (CYP78A2) cloned from Phalaenopsis was shown to enhance the anthocyanin contents in the petals of transformed Phalaenopsis. In this study, it was characterized further to understand the relationship between this P450 and the anthocyanin biosynthesis\\u000a in flowers. The enhancement effect exerted by the P450 gene exhibits the following characteristics. First, its product seems

Vincent Su; Ban-Dar Hsu

2010-01-01

86

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

87

Performance enhancement of scan converter-based transient digitizers by digital image processing  

Microsoft Academic Search

A method for the enhancement of dynamic performance of scan converter-based transient digitizers is proposed. First, a technique for discriminating the best diode target region is illustrated. Then, by considering the digitized charge distribution on the target as a digital image, a filtering algorithm capable of recovering trace discontinuities is shown. Results of tests carried out on an actual digitizer

Pasquale Arpaia; Felice Cennamo; Pasquale Daponte; P. D'Apuzzo

1996-01-01

88

Transient stability enhancement of power systems by robust adaptive control with saturation constraint  

Microsoft Academic Search

Proposes a backstepping technique for designing a discrete-time adaptive excitation controller to enhance the transient stability of power systems under large sudden faults. This approach can be applied directly to a nonlinear model of the power system and it allows for abrupt changes in the power system parameters caused by three phase short circuit faults. It is shown that the

Ying Zhang; Changyun Wen; Yeng Chai Soh

1999-01-01

89

Transient double-diffusive convection in an axisymmetric wavy-walled enclosure  

NASA Astrophysics Data System (ADS)

Transient double-diffusive convection within a vertical wavy-wall cylinder was numerically studied. The enclosure is filled with a saturated porous medium, the fluid is Newtonian and the Boussinesq approach was applied. The cavity is heated from below while the lateral wavy wall is thermally insulated. The saturation concentration of a passive tracer is assumed to exist at the top. The initial condition considers the fluid is at rest with zero concentration. An analytical coordinate transformation was used to change the computational domain into a square. Heat and mass transfer were analyzed using non-dimensional parameters which include the cavity aspect ratio, dimensionless wavelength and amplitude of the wavy-wall, the Rayleigh-Darcy, effective Prandtl and Schmidt numbers. The average Nusselt and Sherwood numbers were evaluated while the transport phenomena evolve within the cavity. After a large dimensionless time the concentration gradients become weak and thermal stratification arises promoting low heat transfer, specially when the wave amplitude is large.

Sanchez, Fausto; Martinez, Simon; Ramirez, Hugo; Chavez, Jesus; Medina, Abraham

2011-11-01

90

Nanostructure Particle-Reinforced Transient Liquid Phase Diffusion Bonding: a Comparative Study  

NASA Astrophysics Data System (ADS)

Particle-reinforced aluminum-metal matrix composites (Al-MMCs) are used in many engineering applications, because they provide significant advantages when compared to monolithic aluminum alloys. However, there still exists the need to identify a suitable joining process for these materials, which minimizes particulate disruption and retains the strength of the MMC within the joint region. This study presents a comparison between joint qualities achieved when a monolithic interlayer is used vs when a nanoparticle-reinforced composite interlayer is used during transient liquid phase diffusion bonding of Al-6061 alloy containing 15 vol pct of Al2O3 particles. Examination of the joint region using scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS), and X-ray diffraction (XRD) showed the formation of eutectic phases such as Al3Ni, Al9FeNi, and Ni3Si within the joint zone. The results indicate that the addition of nanoparticle reinforcements into the interlayer can be used to improve joint strength and minimize particle segregation.

Cooke, Kavian O.; Khan, Tahir I.; Oliver, Gossett D.

2011-08-01

91

Clustering and suppression of transient noise in speech signals using diffusion maps  

Microsoft Academic Search

Recently we have presented a novel approach for transient noise reduction that relies on non-local (NL) filtering. In this paper, we modify and extend our approach to support clustering and suppression of a few transient noise types simultaneously, by introducing two novel concepts. We observe that voiced speech spectral components are slowly varying compared to transient noise. Thus, by applying

Ronen Talmon; Israel Cohen; Sharon Gannot

2011-01-01

92

Comparison of transient performance predictions of a solar-operated diffusion-type still with a roof-type still  

SciTech Connect

A new type of solar-operated diffusion still is proposed. The still is powered directly by solar radiation and is easy to operate and maintain. Analyses of the proposed diffusion still and the conventional roof-type still are carried out to predict the transient performance of both stills at various operating and design conditions. Comparison of the performance of both stills on four sample days through the year is considered. The comparison shows that, although the diffusion still has a higher cover temperature, (i.e., larger heat loss to ambient) than the roof-type still, the diffusion still is superior to the roof-type still in both production rate and operation efficiency. The results also show that an increase in ambient temperature improves the performance of both stills.

Elsayed, M.M.

1982-02-01

93

ATC Enhancement Considering Transient Stability by Optimal Power Flow Control Using UPFC  

NASA Astrophysics Data System (ADS)

With recent development of power electronics technology, power system stability enhancement and optimal power flow control by using Flexible AC Transmission System (FACTS) devices have so far been studied. The FACTS devices to relieve multiple constraints can also make it possible to enhance Available Transfer Capability (ATC) without construction of new transmission lines. In this paper, a new method for improving transient stability by Unified Power Flow Controller (UPFC) is proposed. Then the proposed method is applied to an OPF control method by using UPFC for relieving multiple constraints. The new OPF method is used for enhancement of ATC taking into account Transient stability constraints as well as overload and steady-state stability constraints. The OPF problem is formulated to minimize total capacity of inverters of UPFC. Effectiveness of the proposed method is shown by numerical examples for IEEJ East-10-machine test system.

Masuta, Taisuke; Motoki, Hiroaki; Yokoyama, Akihiko

94

Transient liquid-phase diffusion bonding of two-dimensional carbon–carbon composites to niobium alloy  

Microsoft Academic Search

Two-dimensional carbon–carbon composites (C\\/C) were successfully bonded to Nb alloy with a Ti\\/Cu interlayer by transient liquid-phase diffusion bonding (TLP-DB) in vacuum condition. The joining process consisted of two stages: solid diffusion bonding at 780°C under joining pressure of 4MPa for 30min, and TLP-DB at 1050°C for 30min under 0 or 0.03MPa. The results show that the eutectic Ti–Cu liquid,

J.-L. Li; J.-T. Xiong; F.-S. Zhang

2008-01-01

95

Giant Enhancement of Colloidal diffusion in a Corrugated Optical Vortex  

NASA Astrophysics Data System (ADS)

We experimentally study thermally driven velocity fluctuations of a Brownian particle in a tilted washboard potential. Our system consists of a single fluid-borne colloidal sphere driven by a holographically projected superposition of optical vortices. A single optical vortex is a ring-like optical trap created by focusing a helical mode of laser light. Torque exerted by an optical vortex's orbital angular momentum flux drives a trapped colloidal particle around its circumference. Superposing two optical vortices with opposite helicities and different amplitudes creates a corrugated optical vortex with sinusoidal intensity variations around its circumference. The resulting tilted washboard potential admits both static trapped states and dynamic running states. Digital video microscopy measurements of the resulting particle trajectories reveal a hundred-fold enhancement of the effective self-diffusion coefficient near the static-to-running transition.

Lee, Sang-Hyuk; Grier, David G.

2006-03-01

96

High-resolution photoinduced transient spectroscopy of defect centres in semi-insulating InP obtained by iron diffusion  

Microsoft Academic Search

High-resolution photoinduced transient spectroscopy (HRPITS) has been applied to study electronic properties of point defects in semi-insulating (SI) InP obtained by iron diffusion during the high-temperature annealing in iron-phosphide (IP) ambience. A two-dimensional approach to the spectral analysis of the photocurrent decays recorded in a wide range of temperatures and a neural network method to extracting the parameters of defect

P. Kami?ski; R. Koz?owski; S. Strzelecka; M. Paw?owski; E. Wegner; M. Piersa

2006-01-01

97

Doping-Enhanced Lithium Diffusion in Lithium-Ion Batteries  

NASA Astrophysics Data System (ADS)

We disclose a distortion-assisted diffusion mechanism in Li3N and Li2.5Co0.5N by first-principles simulations. A B2g soft mode at the ? point is found in ?-Li3N, and a more stable ?'-Li3N (P3¯m1) structure, which is 0.71 meV lower in energy, is further derived. The same soft mode is inherited into Li2.5Co0.5N and is enhanced due to Co doping. Consequently, unlike the usual Peierls spin instability along Co-N chains, large lithium-ion displacements on the Li-N plane are induced by a set of soft modes. Such a distortion is expected to offer Li atoms a route to bypass the high diffusion barrier and promote Li-ion conductivity. In addition, we further illustrate abnormal Born effective charges along Co-N chains which result from the competition between the motions of electrons and ion cores. Our results provide future opportunities in both fundamental understanding and structural modifications of Li-ion battery materials.

Wu, Gang; Wu, Shunnian; Wu, Ping

2011-09-01

98

A Nonlinear Excitation Controller Design Method for Terminal Voltage Regulation and Transient Stability Enhancement  

NASA Astrophysics Data System (ADS)

This paper proposes a cascade control method to design a nonlinear excitation controller to guarantee the terminal voltage regulation and the transient stability. Firstly, a nonlinear automatic voltage regulator (NAVR) in the inner loop is designed to control the terminal voltage exactly. Secondly, the generator model including the NAVR is transformed to be a reduced one. Subsequently, based on the reduced generator model, the nonlinear power system stabilizer in the external loop is designed to enhance the transient stability of the power systems. Furthermore, a coordination strategy is presented to improve the performances of the terminal voltage regulation in the steady state and the stability in the transient state. Finally, the proposed method is verified by numerous simulation results.

Huang, Chongxin; Zhang, Kaifeng; Dai, Xianzhong; Zang, Qiang

2014-06-01

99

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

100

Improved antibiotic-free plasmid vector design by incorporation of transient expression enhancers.  

PubMed

Methods to improve plasmid-mediated transgene expression are needed for gene medicine and gene vaccination applications. To maintain a low risk of insertional mutagenesis-mediated gene activation, expression-augmenting sequences would ideally function to improve transgene expression from transiently transfected intact plasmid, but not from spurious genomically integrated vectors. We report herein the development of potent minimal, antibiotic-free, high-manufacturing-yield mammalian expression vectors incorporating rationally designed additive combinations of expression enhancers. The SV40 72?bp enhancer incorporated upstream of the cytomegalovirus (CMV) enhancer selectively improved extrachromosomal transgene expression. The human T-lymphotropic virus type I (HTLV-I) R region, incorporated downstream of the CMV promoter, dramatically increased mRNA translation efficiency, but not overall mRNA levels, after transient transfection. A similar mRNA translation efficiency increase was observed with plasmid vectors incorporating and expressing the protein kinase R-inhibiting adenoviral viral associated (VA)1 RNA. Strikingly, HTLV-I R and VA1 did not increase transgene expression or mRNA translation efficiency from plasmid DNA after genomic integration. The vector platform, when combined with electroporation delivery, further increased transgene expression and improved HIV-1 gp120 DNA vaccine-induced neutralizing antibody titers in rabbits. These antibiotic-free vectors incorporating transient expression enhancers are safer, more potent alternatives to improve transgene expression for DNA therapy or vaccination. PMID:21107439

Luke, J M; Vincent, J M; Du, S X; Gerdemann, U; Leen, A M; Whalen, R G; Hodgson, C P; Williams, J A

2011-04-01

101

Incorporating Diffusion-Weighted Magnetic Resonance Imaging into an Observation Unit Transient Ischemic Attack Pathway  

PubMed Central

Background and Purpose: National guidelines advocate for early, aggressive transient ischemic attack (TIA) evaluations and recommend diffusion-weighted magnetic resonance imaging (MRI) for brain imaging. The purpose of this study is to examine clinician compliance, the yield of MRI, and patient-centered clinical outcomes following implementation of an emergency department observation unit (EDOU) clinical pathway incorporating routine MRI into the acute evaluation of patients with TIA. Methods: This is a prospective observational study of patients with TIA admitted from the ED. Patients with low-risk TIA were transferred to an EDOU for diagnostic testing including MRI; high-risk patients were directed to hospital admission. Clinical variables, diagnostic tests, and treatment were recorded for all patients. The primary clinical outcome was the rate of stroke or recurrent TIA, determined through telephone follow-up and medical record review at 7 and 30 days. Results: A total of 116 patients with TIA were enrolled. In all, 92 (79.3%) patients were transferred to the EDOU, of whom 69 (59.5%) were discharged without hospitalization. Compliance with the EDOU pathway was 83 (91.2%) of 92. Magnetic resonance imaging demonstrated acute infarct in 16 (15.7%) of 102 patients. Stroke (n = 2) or TIA (n = 3) occurred in 5 patients with TIA (4.3%, 95% confidence interval: 1.6%-10.0%) within 30 days; no strokes occurred after discharge. Conclusions: Implementation of a TIA clinical pathway incorporating MRI effectively encouraged guideline-compliant diagnostic testing; however, patient-important outcomes appear similar to diagnostic protocols without routine MRI. Further study is needed to assess the benefits and costs associated with routinely incorporating MRI into TIA evaluation.

Oostema, J. Adam; DeLano, Mark; Bhatt, Archit; Brown, Michael D.

2014-01-01

102

Transient stability enhancement of power systems via optimal nonlinear state feedback control  

Microsoft Academic Search

In this paper, the transient stabilization of power systems will be enhanced using optimal nonlinear feedback control. To\\u000a this end, a partial differential equation called Hamilton-Jacobi-Belman (HJB), should be solved, which does not have a closed\\u000a form solution in general. Nevertheless, there are some approximate solutions to solve HJB equations. In this paper, by using\\u000a a Taylor Series expansion, a

M. Jalili; M. J. Yazdanpanah

2006-01-01

103

Transient cold shock enhances zinc-finger nuclease-mediated gene disruption.  

PubMed

Zinc-finger nucleases (ZFNs) are powerful tools for editing the genomes of cell lines and model organisms. Given the breadth of their potential application, simple methods that increase ZFN activity, thus ensuring genome modification, are highly attractive. Here we show that transient hypothermia generally and robustly increased the level of stable, ZFN-induced gene disruption, thereby providing a simple technique to enhance the experimental efficacy of ZFNs. PMID:20436476

Doyon, Yannick; Choi, Vivian M; Xia, Danny F; Vo, Thuy D; Gregory, Philip D; Holmes, Michael C

2010-06-01

104

Transient enhancement and spectral narrowing of the photothermal effect of plasmonic nanoparticles under pulsed excitation.  

PubMed

The transient 100-fold enhancement and spectral narrowing to 2 nm of the photothermal conversion by solid gold nanospheres under near-infrared excitation with a short laser pulse is reported. This non-stationary effect was observed for a wide range of optical fluences starting from 10 mJ cm(-2) for single nanospheres, their ensembles and aggregated clusters in water, in vitro and in vivo. PMID:23161793

Lukianova-Hleb, Ekaterina Y; Volkov, Alexey N; Wu, Xiangwei; Lapotko, Dmitri O

2013-02-01

105

Copper centers in copper-diffused n-type silicon measured by photoluminescence and deep-level transient spectroscopy  

NASA Astrophysics Data System (ADS)

While photoluminescence observed the continuous change of the 1.014-eV copper center (CuPL center) intensity with diffusion temperature, deep-level transient spectroscopy (DLTS) measured a considerable number of independent copper-related peaks in silicon samples copper-diffused at different temperatures. There was no DLTS peak whose intensity showed the same diffusion-temperature dependence as that of the CuPL center intensity, which led the conclusion that the CuPL center has no electrically active energy level in the upper-half of the band-gap in silicon. All the DLTS peaks observed were attributed to originate from the variety of copper clusters or small copper precipitates.

Nakamura, Minoru; Murakami, Susumu; Udono, Haruhiko

2012-07-01

106

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

107

Diffuse dispersive delay and the time convolution/attenuation of transients  

NASA Astrophysics Data System (ADS)

Test data and analytic evaluations are presented to show that relatively poor 100 KHz shielding of 12 Db can effectively provide an electromagnetic pulse transient reduction of 100 Db. More importantly, several techniques are shown for lightning surge attenuation as an alternative to crowbar, spark gap, or power zener type clipping which simply reflects the surge. A time delay test method is shown which allows CW testing, along with a convolution program to define transient shielding effectivity where the Fourier phase characteristics of the transient are known or can be broadly estimated.

Bittner, Burt J.

1991-08-01

108

Radiation Enhanced Silicon Self-Diffusion and the Silicon Vacancy at High Temperatures  

Microsoft Academic Search

We report proton radiation enhanced self-diffusion (RESD) studies on Si-isotope heterostructures. Self-diffusion experiments under irradiation were performed at temperatures between 780 °C and 872 °C for various times and proton fluxes. Detailed modeling of RESD provides direct evidence that vacancies at high temperatures diffuse with a migration enthalpy of HmV=(1.8±0.5) eV significantly more slowly than expected from their diffusion at

H. Bracht; J. Fage Pedersen; N. Zangenberg; A. Nylandsted Larsen; E. E. Haller; G. Lulli; M. Posselt

2003-01-01

109

Transmission-grating-photomasked transient spin grating and its application to measurement of electron-spin ambipolar diffusion in (110) GaAs quantum wells.  

PubMed

A circular dichromatic transient absorption difference spectroscopy of transmission-grating-photomasked transient spin grating is developed and formularized. It is very simple in experimental setup and operation, and has high detection sensitivity. It is applied to measure spin diffusion dynamics and excited electron density dependence of spin ambipolar diffusion coefficient in (110) GaAs quantum wells. It is found that the spin ambipolar diffusion coefficient of (110) and (001) GaAs quantum wells is close to each other, but has an opposite dependence tendency on excited electron density. This spectroscopy is expected to have extensive applicability in the measurement of spin transport. PMID:22453489

Chen, Ke; Wang, Wenfang; Wu, Jingda; Schuh, D; Wegscheider, W; Korn, T; Lai, Tianshu

2012-03-26

110

Optical Transient-Grating Measurements of Spin Diffusion andRelaxation in a Two-Dimensional Electron Gas  

SciTech Connect

Spin diffusion in n-GaAs quantum wells, as measured by our optical transient-grating technique, is strongly suppressed relative to that of charge. Over a broad range of temperatures and dopings, the suppression of Ds relative to Dc agrees quantitatively with the prediction of ''spin Coulomb dra'' theory, which takes into account the exchange of spin in electron-electron collisions. Moreover, the spin-diffusion length, Ls, is a nearly constant 1 micrometer over the same range of T and n, despite Ds's varying by nearly two orders of magnitude. This constancy supports the D'yakonov-Perel'-Kachorovskii model of spin relaxation through interrupted precessional dephasing in the spin-orbit field.

Weber, Christopher P.

2005-12-15

111

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

112

Students' Misconceptions about Diffusion: How Can They Be Enhanced.  

ERIC Educational Resources Information Center

Although the concept of diffusion is thought to be simple and easily understood by most students, research studies revealed that many misconceptions regarding diffusion exist among secondary education students as well as college freshmen. Describes a study designed to seek out the causes for these misconceptions and to find ways to eliminate them.…

Merek, Edmund A.; And Others

1994-01-01

113

Fractional diffusion analysis of the electromagnetic fields generated by a transient straight current source over a porous geological media  

NASA Astrophysics Data System (ADS)

An interpretation based on the Continuous Time Random Walk theory (CTRW) to the diffusion of electromagnetic fields generated by a transient straight current source over a porous geological media is presented here. The CTRW theory is demonstrated to be a powerful tool to concisely and more accurately model a transport process in a fractal medium with complex structures, comparing to the classical transport theory. In the controlled-source electromagnetic (EM) induction setting, the time dependent evolution of the EM field of some sources over a rough medium are governed by the fractional diffusion EM equation in a CTRW sense. The master equation can be solved for a uniform conducting half-space in the Laplace domain semi-analytically. We use 2D finite difference method to calculate the solution numerically for the assigned space and transform to time domain with Gaver-Stehfest algorithm. Here we adopt a spatially uniform roughness parameter ? in the solution to characterize the complexity of the geoelectrical structure of the geological medium. To introduce the heterogeneity to our model, we set up the space as several 2 D blocks with different conductivities and ?s. Then we compare our results with the synthetic data we got from the high resolution numerical simulations. We are able to show that by introducing the heterogeneity to the fractional diffusion perspective, our approach is competent for tracing the diffusion process with less model parameters.

Ge, J.; Everett, M. E.; Weiss, C. J.

2010-12-01

114

Deciphering mechanisms of enhanced-retarded oxygen diffusion in doped Si  

NASA Astrophysics Data System (ADS)

We study enhanced/retarded diffusion of oxygen in doped silicon by means of first principle calculations. We evidence that the migration energy of oxygen dimers cannot be significantly affected by strain, doping type, or concentration. We attribute the enhanced oxygen diffusion in p-doped silicon to reduced monomer migration energy and the retarded oxygen diffusion in Sb-doped to monomer trapping close to a dopant site. These two mechanisms can appear simultaneously for a given dopant leading to contradictory experimental results. More generally, our findings cast a new light on phenomena involving oxygen diffusion: precipitation, thermal donors formation, and light induced degradation.

Timerkaeva, Dilyara; Caliste, Damien; Pochet, Pascal

2013-12-01

115

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

2013-02-01

116

Nonlinear pressure diffusion in a porous medium: Approximate solutions with applications to permeability measurements using transient pulse decay method  

NASA Astrophysics Data System (ADS)

Transient pulse decay has been widely used to measure permeability of tight rocks and synthetic materials. When the pore fluid is a gas (e.g., dry air, Ar, or N2) as used in a gas permeameter, the pressure diffusion equation governing the pulse decay problem is nonlinear due to a pressure-dependent gas compressibility and molecular slippage effect (also known as the Klinkenberg effect). To simplify data analysis in permeability measurement using a gas permeameter, an approximate solution to the nonlinear diffusion equation was obtained using a regular perturbation method. This solution, which is similar to the original exponential solution of Brace et al. [1968] for a case when the compressibility of the pore fluid is a constant, is valid in the limit when the volume of the interconnected pore fluid is much smaller than the volume of the upstream reservoir. Applications of the approximate solution to laboratory measured pulse decay data show that the estimated sample permeability can be overestimated by as much as a factor of two if the transient gas pressure decay experiment is conducted at low pressures and if molecular slippage is not taken into account. The molecular slippage can be effectively eliminated if the pulse decay measurement is conducted at a mean pressure at least 5 times higher than the Klinkenberg slip factor, which is on the order of 1 bar for texturally equilibrated marble and quartzite used in the permeability study of Wark and Watson [1998].

Liang, Yan; Price, Jonathan D.; Wark, David A.; Watson, E. Bruce

2001-01-01

117

Transient liquid phase diffusion bonding and associated recrystallization phenomenon when joining ODS ferritic superalloys  

Microsoft Academic Search

Oxide dispersion strengthened (ODS) ferritic superalloys attribute their excellent intermediate and high temperature creep resistant properties to the distribution of an inert oxide, Y2O3 within highly directional and elongated grains. Careful selection of joining techniques is, therefore, of utmost importance so that the parent metal microstructure is not disrupted and is continuous across the bond line. Transient liquid phase (TLP)

T. I. Khan; E. R. Wallach

1996-01-01

118

Effect of diffusion layer structure on the determination of corrosion rates from DC transient measurements  

Microsoft Academic Search

The boundary conditions usually used for solving the differential equations in the theory of electrochemical transient measurements are not applicable to measurements with corroding metals. In an electrode kinetic investigation the measurement starts from equilibrium, where no net current is flowing and no net chemical change is taking place before the application of the measuring signal. The situation is completely

Z. Nagy; P. J. Hernes; M. Minkoff; G. K. Leaf; R. H. Land

1989-01-01

119

Zinc diffusion enhanced Ga diffusion in GaAs isotope heterostructures  

Microsoft Academic Search

We have investigated the simultaneous diffusion of Zn and Ga in a 69GaAs\\/71GaAs isotope multilayer structure at temperatures between 618°C and 714°C. Diffusion profiles of Zn, 69Ga, and 71Ga were measured with secondary ion mass spectrometry. Accurate modeling of the simultaneous diffusion of Zn and Ga is achieved on the basis of a Ga vacancy and Ga interstitial controlled mode

H. Bracht; M. S. Norseng; E. E. Haller; K. Eberl

2001-01-01

120

Power Supply Reliability Assessment in UPFC-installed Transmission System for ATC Enhancement Considering Transient Stability  

NASA Astrophysics Data System (ADS)

With recent development of power electronics technology, power system stability enhancement and optimal power flow control by using Flexible AC Transmission System (FACTS) devices have so far been studied. The FACTS devices to relieve multiple constraints can also make it possible to enhance Available Transfer Capability (ATC) without construction of new transmission lines. The previous research revealed that ATC is expanded by avoiding multiple constraints in OPF using Unified Power Flow Controller (UPFC). For long-term operation of such ATC-expanded power system, it is necessary to evaluate power system reliability. In this paper, the evaluation method of supply reliability for UPFC-installed power system is proposed. Both thermal capacity and transient stability constraints are considered. The effectiveness of the proposed method is shown by numerical examples for IEEJ East10-machine test system.

Masuta, Taisuke; Yokoyama, Akihiko

121

Evolution Nonlinear Diffusion-Convection PDE Models for Spectrogram Enhancement  

NASA Astrophysics Data System (ADS)

In previous works we studied the application of PDE-based image processing techniques applied to the spectrogram of audio signals in order to improve the readability of the signal. In particular we considered the implementation of the nonlinear diffusive model proposed by Álvarez, Lions and Morel [1](ALM) combined with a convective term inspired by the differential reassignment proposed by Chassandre-Mottin, Daubechies, Auger and Flandrin [2]-[3]. In this work we consider the possibility of replacing the diffusive model of ALM by diffusive terms in divergence form. In particular we implement finite element approximations of nonlinear diffusive terms studied by Chen, Levine, Rao [4] and Antontsev, Shmarev [5]-[8] with a convective term.

Dugnol, B.; Fernández, C.; Galiano, G.; Velasco, J.

2008-09-01

122

Surface textured molybdenum zinc oxide for light diffusion enhancement  

Microsoft Academic Search

Surface textures have been fabricated on a molybdenum doped zinc oxide (MZO) film using a shadow mask in a co-sputter process. The surface textures yielded 5.3% and 10.1% of light diffusion in the visible light region for MZO films with a thickness of 100 nm and 200 nm, respectively. Light diffusion in the near infra-red region was slightly less with 4.5% for

Ching-Ming Hsu; Hon-Bin Lin; Wen-Tuan Wu

2009-01-01

123

Transient plane source (tps) sensors for simultaneous measurements of thermal conductivity and thermal diffusivity of insulators, fluids and conductors  

NASA Astrophysics Data System (ADS)

Thermal conductivity and thermal diffusivity are two important physical properties for designing any food engineering processes1. The knowledge of thermal properties of the elements, compounds and different materials in many industrial applications is a requirement for their final functionality. Transient plane source (tps) sensors are reported2 to be useful for the simultaneous measurement of thermal conductivity, thermal diffusivity and volumetric heat capacity of insulators, conductor liquids3 and high-TC superconductors4. The tps-sensor consists of a resistive element in the shape of double spiral made of 10 micrometer thick Ni-foils covered on both sides with 25 micrometer thick Kapton. This sensor acts both as a heat source and a resistance thermometer for recording the time dependent temperature increase. From the knowledge of the temperature co-efficient of the metal spiral, the temperature increase of the sensor can be determined precisely by placing the sensor in between two surfaces of the same material under test. This temperature increase is then related to the thermal conductivity, thermal diffusivity and volumetric heat capacity by simple relations2,5. The tps-sensor has been used to measure thermal conductivities from 0.001 Wm-1K-1to 600 Wm-1K-1 and temperature ranges covered from 77K- 1000K. This talk gives the design, advantages and limitations of the tpl-sensor along with its applications to the measurementof thermal properties in a variety of materials.

Maqsood, Asghari; Anis-ur-Rehman, M.

2013-12-01

124

Verification of high-order mixed finite-element solution of transient magnetic diffusion problems  

Microsoft Academic Search

We develop and present high-order mixed finite-element discretizations of the time-dependent electromagnetic diffusion equations for solving eddy-current problems on three-dimensional unstructured grids. The discretizations are based on high-order H(Grad), H(Curl), and H(Div) conforming finite-element spaces combined with an implicit and unconditionally stable generalized Crank-Nicholson time differencing method. We develop three separate electromagnetic diffusion formulations, namely the E (electric field), H(magnetic

Robert N. Rieben; Daniel A. White

2006-01-01

125

Fiber-driven resolution enhancement of diffusion-weighted images.  

PubMed

Diffusion-weighted imaging (DWI), while giving rich information about brain circuitry, is often limited by insufficient spatial resolution and low signal-to-noise ratio (SNR). This paper describes an algorithm that will increase the resolution of DW images beyond the scan resolution, allowing for a closer investigation of fiber structures and more accurate assessment of brain connectivity. The algorithm is capable of generating a dense vector-valued field, consisting of diffusion data associated with the full set of diffusion-sensitizing gradients. The fundamental premise is that, to best preserve information, interpolation should always be performed along axonal fibers. To achieve this, at each spatial location, we probe neighboring voxels in various directions to gather diffusion information for data interpolation. Based on the fiber orientation distribution function (ODF), directions that are more likely to be traversed by fibers will be given greater weights during interpolation and vice versa. This ensures that data interpolation is only contributed by diffusion data coming from fibers that are aligned with a specific direction. This approach respects local fiber structures and prevents blurring resulting from averaging of data from significantly misaligned fibers. Evaluations suggest that this algorithm yields results with significantly less blocking artifacts, greater smoothness in anatomical structures, and markedly improved structural visibility. PMID:24060317

Yap, Pew-Thian; An, Hongyu; Chen, Yasheng; Shen, Dinggang

2014-01-01

126

Transient diffusion of radionuclides from a cylindrical waste solid into fractured porous rock  

Microsoft Academic Search

This paper presents the numerical results of an analytical study for mass transfer and transport of radionuclides released from a cylindrical waste solid into water-saturated fractured porous rock. The purposes of this study are (1) to predict the diffusive mass flux from a cylindrical waste solid into a planar fracture and the surrounding rock matrix for the low-flow conditions wherein

J. Ahn; P. L. Chambre; T. H. Pigford

1990-01-01

127

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

128

Enhanced diffusion and the continuous spontaneous localization model  

NASA Astrophysics Data System (ADS)

We find an analogy between turbulence and the dynamics of the continuous spontaneous localization model (CSL) of the wave function. The use of a standard white noise in the localization process gives Richardson's t3 law for the turbulent diffusion, while the introduction of an affine noise in the CSL allows us to obtain the intermittency corrections to this law.

Santos, L. F.; Escobar, C. O.

1999-10-01

129

Isolated Diffusion Restriction Precedes the Development of Enhancing Tumor in a Subset of Patients with Glioblastoma  

PubMed Central

BACKGROUND AND PURPOSE Most response criteria for patients with glioblastoma rely on increases in the contrast enhancing abnormality to determine tumor progression. Our aim was to determine retrospectively in patients with glioblastoma whether diffusion restriction can predict the development of new enhancing mass lesions. MATERIALS AND METHODS We reviewed the brain MR imaging scans (including DWI and ADC maps) of 208 patients with glioblastoma. Patients with restricted diffusion in or adjacent to the tumor were identified, with further analysis only performed on those patients with low-ADC lesions without enhancement. These patients were followed to determine if new concordant enhancement developed at the site of the low-ADC lesion. A Wilcoxon signed rank test, competing risk analysis, and Kaplan-Meier curves were used to compare the mean drop in ADC values, assess enhancement-free survival, and determine overall survival, respectively. RESULTS In 67 of the 208 patients (32.2%), visibly detectable restricted diffusion was seen during treatment. The study cohort was formed by the 27 patients with low-ADC lesions and no corresponding enhancement. Twenty-three (85.2%) patients developed gadolinium-enhancing tumor at the site of restricted diffusion a median of 3.0 months later (95% CI, 2.6–4.1 months). The mean decrease in ADC was 22.9% from baseline (P < .001). The 3-month enhancement-free survival probability was 0.481 (95% CI, 0.288–0.675). The 12-month overall survival probability was 0.521 (95% CI, 0.345–0.788). Restricted diffusion predicted enhancement regardless of antiangiogenic therapy with bevacizumab. CONCLUSIONS In a subset of patients with glioblastoma, development of a new focus of restricted diffusion during treatment may precede the development of new enhancing tumor.

Karimi, S.; Sood, S.; Zhang, Z.; Mo, Q.; Gutin, P.H.

2014-01-01

130

Transient expression directed by homologous and heterologous promoter and enhancer sequences in fish cells.  

PubMed Central

In order to construct fish specific expression vectors for studies on gene regulation in vitro and in vivo a variety of heterologous enhancers and promoters from mammals and from viruses of higher vertebrate cells were tested for expression of the bacterial chloramphenicol acetyl transferase reporter gene in three teleost fish cell lines. Several viral enhancers were found to be constitutively active at high levels. The human metallothionein promoter showed inducible expression in the presence of heavy metal ions. A fish sequence was isolated that can be used as a homologous constitutively active promoter for expression of foreign genes. Using the human growth hormone gene with an active promoter in fish cells for transient expression insufficient splicing and lack of translation were observed, pointing to limitations in the use of heterologous genes in gene transfer experiments. On the contrary, some heterologous promoters and enhancers functioned in fish cells as well as in their cell type of origin, indicating that corresponding transcription factors are sufficiently conserved between fish and human over a period of 900 million years of independent evolution. Images

Friedenreich, H; Schartl, M

1990-01-01

131

CO-HP2-N2/Air Diffusion Flames: Thermal Radiation and Transient Effects  

NASA Astrophysics Data System (ADS)

Flames of CO/H2/N2 fuels have been investigated for various reasons. For instance, laminar, premixed flames were investigated experimentally by van Tiggelen and coworkers to determine the rate constant of the water-gas shift reaction [12.1] and the inhibition induced by CF3BR [12.2], [12.3], and numerically by Rogg and Williams [12.4] who derived a reduced kinetic mechanism for wet CO flames. Laminar, non-premixed flames were studied, for instance, by Drake and Blint [12.5], who investigated experimentally and numerically the structure of counterflow diffusion flames in the Tsuji geometry paying special attention to NO x formation. For the latter geometry, Chen et al [12.6] derived a reduced kinetic mechanism which they used in the numerical simulation of turbulent diffusion flames. For further information on work relevant to flames of CO/H2/N2 fuels the cited papers should be consulted.

Chen, J.-Y.; Liu, Y.; Rogg, B.

132

Solving the radiation diffusion and energy balance equations using pseudo-transient continuation  

Microsoft Academic Search

We develop a scheme for the system coupling the radiation diffusion and matter energy balance equations. The method is based on fully implicit, first-order, backward Euler differencing; Picard–Newton iterations solve the nonlinear system. We show that iterating on the radiation energy density and the emission source is more robust. Since the Picard–Newton scheme may not converge for all initial conditions

A. I. Shestakov; J. A. Greenough; L. H. Howell

2005-01-01

133

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

NASA Technical Reports Server (NTRS)

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 effectively strain-rate-free, vigorous flame may be obtained. Such a flame can also provide long residence times and large length scales for practical probing of flame structures and soot processes. This 2-D numerical study explores the feasibility of establishing such a planar diffusion flame in an enclosed container utilizing a realistic test protocol for a microgravity experiment. Fuel and oxygen mixtures, initially segregated into two half-volumes of a squat rectangular container by a thin separator, are ignited as soon as a flammable mixture is formed in the wake of the separator withdrawn in the centerplane. A triple-flame ensues that propagates behind the trailing edge of the separator. The results of calculations show that the mechanically- and thermally-induced convection decays in about two seconds. The establishment of a planar diffusion flame after this period seems feasible in the central region of the container with sufficient quantities of reactants left over for subsequent studies. An analysis of the flame initiation and formation process suggests how the feasibility of creating such a flame can be further improved.

Gokoglu, Suleyman A.

2003-01-01

134

Experimental correlations for transient soot measurement in diesel exhaust aerosol with light extinction, electrical mobility and diffusion charger sensor techniques  

NASA Astrophysics Data System (ADS)

A study of soot measurement deviation using a diffusion charger sensor with three dilution ratios was conducted in order to obtain an optimum setting that can be used to obtain accurate measurements in terms of soot mass emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement settings in steady-state operating conditions; evaluation of the proposed setting under the New European Driving Cycle; and a study of correlations for different measurement techniques. These correlations provide a reliable tool for estimating soot emission from light extinction measurement or from accumulation particle mode concentration. There are several methods and correlations to estimate soot concentration in the literature but most of them were assessed for steady-state operating points. In this case, the correlations are obtained by more than 4000 points measured in transient conditions. The results of the new two correlations, with less than 4% deviation from the reference measurement, are presented in this paper.

Bermúdez, Vicente; Pastor, José V.; López, J. Javier; Campos, Daniel

2014-06-01

135

Revisiting Taylor Dispersion: Differential enhancement of rotational and translational diffusion under oscillatory shear  

NASA Astrophysics Data System (ADS)

The idea of Taylor dispersion - enhancement of translational diffusion under shear - has found applications in fields from pharmacology to chemical engineering. Here, in a combination of experiment and simulations, we study the translational and rotational diffusion of colloidal dimers under triangle-wave oscillatory shear. We find that the rotational diffusion is enhanced, in addition to the enhanced translational diffusion. This ``rotational Taylor dispersion'' depends strongly on the strain rate (Peclet number), aspect ratio, and the shear strain, in contradistinction to translational Taylor dispersion in a shear flow, which depends only weakly on strain rate and aspect ratio. This separate tunability of translations and orientations promises important applications in mixing and self-assembly of solutions of anisometric colloids. We discuss the corresponding effect on the structure and rheology of denser suspensions of rod-like particles.

Leahy, Brian; Ong, Desmond; Cheng, Xiang; Cohen, Itai

2013-03-01

136

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

137

Intracranial dural fistula as a cause of diffuse MR enhancement of the cervical spinal cord  

Microsoft Academic Search

Spinal MR findings are reported in a patient with progressive myelopathy and intracranial dural arteriovenous fistula draining into spinal veins. Associated with previously reported abnormalities on T1 weighted and T2 weighted images, postcontrast T1 weighted images disclosed diffuse intense enhancement of the cervical cord itself. This enhancement decreased after endovascular treatment.

Valérie Bousson; Laurent Brunereau; Katayoun Vahedi; René Chapot

1999-01-01

138

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

139

2.5D Fractional Diffusion Analysis of The Electromagnetic Field Generated By A Transient Loop Source In Fractured Mediums  

NASA Astrophysics Data System (ADS)

A 2.5D finite difference (FD) frequency-domain modeling based on the Continuous Time Random Walk theory (CTRW) to the diffusion of electromagnetic fields generated by a transient loop source over a porous geological media is presented. The CTRW theory is demonstrated to be a powerful tool to concisely describe a transport process in fractal mediums with complex structures (Scher and Lax 1973, Metzler and Klafter 2000). In the controlled-source electromagnetic (CSEM) induction setting, the diffusion of Eddy currents in a rough medium is governed by the fractional differential EM equations in a CTRW sense (Everett 2009). We use staggered finite difference (FD) approach to discretize the equations in frequency domain. The biconjugate gradient iterative solver is implemented to solve sparse matrix equations. We compare the FD solutions with analytical solutions to a half space model to verify the accuracy of our code. Then FD solutions are calculated for a model with a 2D block fractured structures included in a homogeneous space. Via displaying the high sensitivity of the spatial variation of Ey fields to the geoelectrical properties and roughness of the block, we are able to show the potential of combination of CTRW theory with CSEM method in detecting unknown fractured targets in subsurface.

Ge, J.; Everett, M. E.; Weiss, C. J.

2011-12-01

140

Application of Monte Carlo techniques to transient thermal modeling of cavity radiometers having diffuse-specular surfaces  

NASA Technical Reports Server (NTRS)

A viable alternative to the net exchange method of radiative analysis which is equally applicable to diffuse and diffuse-specular enclosures is presented. It is particularly more advantageous to use than the net exchange method in the case of a transient thermal analysis involving conduction and storage of energy as well as radiative exchange. A new quantity, called the distribution factor is defined which replaces the angle factor and the configuration factor. Once obtained, the array of distribution factors for an ensemble of surface elements which define an enclosure permits the instantaneous net radiative heat fluxes to all of the surfaces to be computed directly in terms of the known surface temperatures at that instant. The formulation of the thermal model is described, as is the determination of distribution factors by application of a Monte Carlo analysis. The results show that when fewer than 10,000 packets are emitted, an unsatisfactory approximation for the distribution factors is obtained, but that 10,000 packets is sufficient.

Mahan, J. R.; Eskin, L. D.

1981-01-01

141

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

142

Interface- and diffusion-limited capillary rise of reactive melts with a transient contact angle  

NASA Astrophysics Data System (ADS)

The kinetics of unidirectional capillary penetration by a reactive fluid under the limiting cases of diffusion control and interface control has been derived for the reactive infiltration phenomenon characterized by a shrinking capillary radius due to interphase formation and an exponentially decaying contact angle. The computational outcomes for the reactive penetration of Si3N4 capillaries by AgCuTi brazes and of carbon capillaries by Si show that greater lengths are attained at lower values of the parabolic rate constant (under diffusion control), and the limiting length is reached earlier at larger values of the linear rate constant (under interface control). A capillary-driven flow analysis (Washburn equation) overestimates the infiltration kinetics, whereas an analysis that considers pore shrinkage but assumes the contact angle and the capillary pressure to be constant during flow underestimates the kinetics. The penetration lengths predicted by the analysis at pore closure due to reaction choking exhibit a slightly better agreement with the recent measurements in the Si/C system than the models of reactive flows currently in vogue.

Asthana, Rajiv

2002-07-01

143

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

144

Transient coherent anti-Stokes Raman scattering spectroscopy as a tool for measuring the diffusion coefficient and size of gas molecules  

SciTech Connect

Formulas are derived for evaluating the diffusion coefficient and size of gas molecules from transient coherent anti-Stokes Raman scattering measurements. Numerical estimates are presented for hydrogen. (special issue devoted to the 80th birthday of S.A. Akhmanov)

Nikitin, Sergei Yu [M. V. Lomonosov Moscow State University, Faculty of Physics, Moscow (Russian Federation)

2009-07-31

145

A universal law for high-temperature diffusion controlled transient creep  

NASA Astrophysics Data System (ADS)

IT IS suggested that transient creep at high temperatures arises principally as a result of the dispersal of entanglements by the climb mechanism. The dispersal of the entanglements is assumed to follow a unimolecular reaction kinetics with a rate constant that depends on stress and temperature in the same way as does the secondary creep rate. The analysis shows that the strain (?) versus time ( t) relation can be represented by ?=? 0+?. 3t+ {?-1}/{K}[1- exp(-K ??3t)] , where ?0 is the instantaneous strain on loading, ??3, the secondary creep rate, K ??3 the rate constant, and ? the ratio of initial to secondary creep rate. The experimental creep data on several b.c.c. and f.c.c. metals and alloys correlate quite well with the proposed mechanism. The constants ? and K were found to be independent of temperature and stress. The proposed formulation becomes inapplicable for correlating creep data in polycrystals at low stresses because of the significant contribution of grain-boundary sliding to the total creep at these stress levels.

Amin, K. E.; Mukherjee, A. K.; Dorn, J. E.

1970-12-01

146

Light-enhanced deep deuterium emission and the diffusion mechanism in amorphous silicon  

SciTech Connect

We demonstrate that hydrogen diffusion in hydrogenated amorphous silicon ([ital a]-Si:H) is trap controlled and measure a 1.4-eV barrier for deep deuterium emission to a transport level in D-doped [ital a]-Si:H. We show that light-enhanced diffusion in [ital a]-Si:H is caused by light-enhanced detrapping of H and not by heating of the sample. From our experiments, we obtain estimates of the free-H-diffusion coefficient (3[times]10[sup [minus]8] cm[sup 2] s[sup [minus]1]), the mean H displacement between deep trapping events (250 A), and the other parameters that determine the measured H-diffusion coefficient in [ital a]-Si:H.

Branz, H.M.; Asher, S.E.; Nelson, B.P. (National Renewable Energy Laboratory, Golden, Colorado 80401 (United States))

1993-03-15

147

Nonlinear multiscale wavelet diffusion for speckle suppression and edge enhancement in ultrasound images.  

PubMed

This paper introduces a novel nonlinear multiscale wavelet diffusion method for ultrasound speckle suppression and edge enhancement. This method is designed to utilize the favorable denoising properties of two frequently used techniques: the sparsity and multiresolution properties of the wavelet, and the iterative edge enhancement feature of nonlinear diffusion. With fully exploited knowledge of speckle image models, the edges of images are detected using normalized wavelet modulus. Relying on this feature, both the envelope-detected speckle image and the log-compressed ultrasonic image can be directly processed by the algorithm without need for additional preprocessing. Speckle is suppressed by employing the iterative multiscale diffusion on the wavelet coefficients. With a tuning diffusion threshold strategy, the proposed method can improve the image quality for both visualization and auto-segmentation applications. We validate our method using synthetic speckle images and real ultrasonic images. Performance improvement over other despeckling filters is quantified in terms of noise suppression and edge preservation indices. PMID:16524086

Yue, Yong; Croitoru, Mihai M; Bidani, Akhil; Zwischenberger, Joseph B; Clark, John W

2006-03-01

148

Zn diffusion enhancement of interdiffusion in a GaInAsP-InP heterostructure  

Microsoft Academic Search

The influence of concurrent Zn diffusion on the interdiffusion in a Gax In1?x Asy P1?y -InP heterostructure (x=0.28, y=0.61) was investigated using Auger electron spectroscopy and secondary-ion mass spectrometry. The measured profiles showed that the Zn diffusion (600 °C, 1–4 h) predominantly enhanced the cation (In-Ga) interdiffusion. The result could not be interpreted by the Zn-vacancy complex model. Under conditions

H.-H. Park; B. K. Kang; E. S. Nam; Y. T. Lee; J. H. Kim; O’D. Kwon

1989-01-01

149

First-principles calculation of self-diffusion, arsenic diffusion, and surface segregation in silicon  

Microsoft Academic Search

Integrated circuit device densities have increased more than 2000 times since Gordon Moore's observation of exponential growth in 1965. Modern devices are thus sensitive to minute variations in diffusion, such as the transient-enhanced diffusivity resulting from ion implantation, concentration-dependent diffusivity of dopants due to changes in the Fermi level, and the effects of high stresses and stress gradients (resulting from

Scott A. Centoni

2003-01-01

150

Enhancement of the quasilinear diffusion coefficient at the continuum limit.  

NASA Astrophysics Data System (ADS)

Recent analytic calculations(Laval, G. and D. Pesme, Phys. Lett. A) 80, 266, 1980; Laval, G. and D. Pesme, Phys. Fluids 26, 52, 1983. have questioned the validity of quasilinear theory in the regime where the linear growth time, ?_?, is longer than the resonance broadening time, ?_RB. The enhancement was observed both in test particle(Cary, J., D. Escande, and A. Verga, Phys. Rev. Lett.) 65, 3132, 1990. and in self-consistent simulations(Cary, J., I. Doxas, D. Escande and A. Verga, Phys. Fluids B) 4, 2062, 1992. for intermediate values of the overlap parameter A=?_r/? v_?, where ?r is the mode resonance width, and ? v_? the intermode separation. Simulations with high initial A, a regime more closely resembling the continuum, also show enhanced transport for ?_?/?_RB>~ 16, while for ?_?/?_RB<=ssim 3 the quasilinear result is recovered. Mode coupling is observed for ?_?/?_RB>~ 1, consistent with experiment(Tsunoda, S., F. Doveil and J. Malmberg, Phys. Fluids B) 3, 2747, 1991. and previous simulations(Theilhaber, K., G. Laval and D. Pesme, Phys. Fluids) 30, 3129, 1987. that observed mode coupling but no enhancement. Both experiment and previous simulations were in the regime ?_?/?_RB>1 but decidedly below ?_?/?_RB=16.

Doxas, Isidoros; Cary, John R.

1996-11-01

151

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

152

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

153

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 Dirichlet 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, Aleksei I. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore CA 94550 (United States)], E-mail: shestakov@llnl.gov; Offner, Stella S.R. [Physics Department, University of California, Berkeley CA 94720 (United States)], E-mail: soffner@berkely.edu

2008-01-10

154

Enhanced texture in die-upset nanocomposite magnets by Nd-Cu grain boundary diffusion  

NASA Astrophysics Data System (ADS)

Bulk anisotropic nanocomposite Nd2Fe14B/?-Fe magnets were prepared by hot pressing and die upsetting coupled with Nd-Cu grain boundary diffusion. The hot workability of nanocomposite magnets is enhanced dramatically by grain boundary diffusion of low melt point Nd-Cu alloy, resulting in a strong anisotropy by die upsetting. The microstructure of die-upset nanocomposite magnets is identical with that of the traditional die-upset rare earth-rich magnets. The coercivity, remanence, and squareness degree of demagnetization curves are optimized. The observation for microstructures and the analysis of magnetic properties suggest that the grain boundary diffusion mainly occurs in the hot deformation process.

Tang, Xin; Chen, Renjie; Yin, Wenzong; Wang, Jinzhi; Tang, Xu; Lee, Don; Yan, Aru

2013-02-01

155

The self-irradiation driven enhancement of diffusion processes in nuclear-safe ceramics  

NASA Astrophysics Data System (ADS)

The problem of long-term storage of nuclear-safe ceramics (NSC) supposedly containing plutonium, transition and rare-earth metals oxides is connected first with the necessity of the plutonium isotope enhanced diffusional release prognostication at storage temperatures. For lack of experimental features on diffusion processes in NSC, our estimations are based on the literature data for thermal-activated and radiation-enhanced diffusion (TAD and RED, respectively) of U and Pu in UO2 and (U, Pu)O2 oxides. .

Smirnov, E. A.; Timofeeva, L. F.

2000-07-01

156

Enhancement of microhomology-mediated genomic rearrangements by transient loss of mouse Bloom syndrome helicase  

PubMed Central

Bloom syndrome, an autosomal recessive disorder of the BLM gene, confers predisposition to a broad spectrum of early-onset cancers in multiple tissue types. Loss of genomic integrity is a primary hallmark of such human malignancies, but many studies using disease-affected specimens are limited in that they are retrospective and devoid of an appropriate experimental control. To overcome this, we devised an experimental system to recapitulate the early molecular events in genetically engineered mouse embryonic stem cells, in which cells undergoing loss of heterozygosity (LOH) can be enriched after inducible down-regulation of Blm expression, with or without site-directed DNA double-strand break (DSB) induction. Transient loss of BLM increased the rate of LOH, whose breakpoints were distributed along the chromosome. Combined with site-directed DSB induction, loss of BLM synergistically increased the rate of LOH and concentrated the breakpoints around the targeted chromosomal region. We characterized the LOH events using specifically tailored genomic tools, such as high-resolution array comparative genomic hybridization and high-density single nucleotide polymorphism genotyping, revealing that the combination of BLM suppression and DSB induction enhanced genomic rearrangements, including deletions and insertions, whose breakpoints were clustered in genomic inverted repeats and associated with junctional microhomologies. Our experimental approach successfully uncovered the detailed molecular mechanisms of as-yet-uncharacterized loss of heterozygosities and reveals the significant contribution of microhomology-mediated genomic rearrangements, which could be widely applicable to the early steps of cancer formation in general.

Yamanishi, Ayako; Yusa, Kosuke; Horie, Kyoji; Tokunaga, Masahiro; Kusano, Kohji; Kokubu, Chikara; Takeda, Junji

2013-01-01

157

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

2013-06-01

158

Transient Stability Enhancement of Power Systems by Lyapunov-Based Recurrent Neural Networks UPFC Controllers  

NASA Astrophysics Data System (ADS)

A Lyapunov-based recurrent neural networks unified power flow controller (UPFC) is developed for improving transient stability of power systems. First, a simple UPFC dynamical model, composed of a controllable shunt susceptance on the shunt side and an ideal complex transformer on the series side, is utilized to analyze UPFC dynamical characteristics. Secondly, we study the control configuration of the UPFC with two major blocks: the primary control, and the supplementary control. The primary control is implemented by standard PI techniques when the power system is operated in a normal condition. The supplementary control will be effective only when the power system is subjected by large disturbances. We propose a new Lyapunov-based UPFC controller of the classical single-machine-infinite-bus system for damping enhancement. In order to consider more complicated detailed generator models, we also propose a Lyapunov-based adaptive recurrent neural network controller to deal with such model uncertainties. This controller can be treated as neural network approximations of Lyapunov control actions. In addition, this controller also provides online learning ability to adjust the corresponding weights with the back propagation algorithm built in the hidden layer. The proposed control scheme has been tested on two simple power systems. Simulation results demonstrate that the proposed control strategy is very effective for suppressing power swing even under severe system conditions.

Chu, Chia-Chi; Tsai, Hung-Chi; Chang, Wei-Neng

159

Enhancement of an anti-tumor immune response by transient blockade of central T cell tolerance.  

PubMed

Thymic central tolerance is a critical process that prevents autoimmunity but also presents a challenge to the generation of anti-tumor immune responses. Medullary thymic epithelial cells (mTECs) eliminate self-reactive T cells by displaying a diverse repertoire of tissue-specific antigens (TSAs) that are also shared by tumors. Therefore, while protecting against autoimmunity, mTECs simultaneously limit the generation of tumor-specific effector T cells by expressing tumor self-antigens. This ectopic expression of TSAs largely depends on autoimmune regulator (Aire), which is expressed in mature mTECs. Thus, therapies to deplete Aire-expressing mTECs represent an attractive strategy to increase the pool of tumor-specific effector T cells. Recent work has implicated the TNF family members RANK and RANK-Ligand (RANKL) in the development of Aire-expressing mTECs. We show that in vivo RANKL blockade selectively and transiently depletes Aire and TSA expression in the thymus to create a window of defective negative selection. Furthermore, we demonstrate that RANKL blockade can rescue melanoma-specific T cells from thymic deletion and that persistence of these tumor-specific effector T cells promoted increased host survival in response to tumor challenge. These results indicate that modulating central tolerance through RANKL can alter thymic output and potentially provide therapeutic benefit by enhancing anti-tumor immunity. PMID:24752296

Khan, Imran S; Mouchess, Maria L; Zhu, Meng-Lei; Conley, Bridget; Fasano, Kayla J; Hou, Yafei; Fong, Lawrence; Su, Maureen A; Anderson, Mark S

2014-05-01

160

Enhancement of microhomology-mediated genomic rearrangements by transient loss of mouse Bloom syndrome helicase.  

PubMed

Bloom syndrome, an autosomal recessive disorder of the BLM gene, confers predisposition to a broad spectrum of early-onset cancers in multiple tissue types. Loss of genomic integrity is a primary hallmark of such human malignancies, but many studies using disease-affected specimens are limited in that they are retrospective and devoid of an appropriate experimental control. To overcome this, we devised an experimental system to recapitulate the early molecular events in genetically engineered mouse embryonic stem cells, in which cells undergoing loss of heterozygosity (LOH) can be enriched after inducible down-regulation of Blm expression, with or without site-directed DNA double-strand break (DSB) induction. Transient loss of BLM increased the rate of LOH, whose breakpoints were distributed along the chromosome. Combined with site-directed DSB induction, loss of BLM synergistically increased the rate of LOH and concentrated the breakpoints around the targeted chromosomal region. We characterized the LOH events using specifically tailored genomic tools, such as high-resolution array comparative genomic hybridization and high-density single nucleotide polymorphism genotyping, revealing that the combination of BLM suppression and DSB induction enhanced genomic rearrangements, including deletions and insertions, whose breakpoints were clustered in genomic inverted repeats and associated with junctional microhomologies. Our experimental approach successfully uncovered the detailed molecular mechanisms of as-yet-uncharacterized loss of heterozygosities and reveals the significant contribution of microhomology-mediated genomic rearrangements, which could be widely applicable to the early steps of cancer formation in general. PMID:23908384

Yamanishi, Ayako; Yusa, Kosuke; Horie, Kyoji; Tokunaga, Masahiro; Kusano, Kohji; Kokubu, Chikara; Takeda, Junji

2013-09-01

161

Canonical Wnt signaling transiently stimulates proliferation and enhances neurogenesis in neonatal neural progenitor cultures  

SciTech Connect

Canonical Wnt signaling triggers the formation of heterodimeric transcription factor complexes consisting of {beta}-catenin and T cell factors, and thereby controls the execution of specific genetic programs. During the expansion and neurogenic phases of embryonic neural development canonical Wnt signaling initially controls proliferation of neural progenitor cells, and later neuronal differentiation. Whether Wnt growth factors affect neural progenitor cells postnatally is not known. Therefore, we have analyzed the impact of Wnt signaling on neural progenitors isolated from cerebral cortices of newborn mice. Expression profiling of pathway components revealed that these cells are fully equipped to respond to Wnt signals. However, Wnt pathway activation affected only a subset of neonatal progenitors and elicited a limited increase in proliferation and neuronal differentiation in distinct subsets of cells. Moreover, Wnt pathway activation only transiently stimulated S-phase entry but did not support long-term proliferation of progenitor cultures. The dampened nature of the Wnt response correlates with the predominant expression of inhibitory pathway components and the rapid actuation of negative feedback mechanisms. Interestingly, in differentiating cell cultures activation of canonical Wnt signaling reduced Hes1 and Hes5 expression suggesting that during postnatal neural development, Wnt/{beta}-catenin signaling enhances neurogenesis from progenitor cells by interfering with Notch pathway activity.

Hirsch, Cordula [Institute of Molecular Medicine and Cell Research, Albert-Ludwigs-University Freiburg Stefan-Meier-Str. 17, D-79104 Freiburg (Germany); Campano, Louise M. [Institute of Molecular Medicine and Cell Research, Albert-Ludwigs-University Freiburg Stefan-Meier-Str. 17, D-79104 Freiburg (Germany); Woehrle, Simon [Institute of Molecular Medicine and Cell Research, Albert-Ludwigs-University Freiburg Stefan-Meier-Str. 17, D-79104 Freiburg (Germany); Hecht, Andreas [Institute of Molecular Medicine and Cell Research, Albert-Ludwigs-University Freiburg Stefan-Meier-Str. 17, D-79104 Freiburg (Germany)]. E-mail: andreas.hecht@mol-med.uni-freiburg.de

2007-02-01

162

Computer modeling of transient three-dimensional boiling-enhanced mixed convection  

SciTech Connect

A transient, three-dimensional, two-phase computational model for simulating boiling-enhanced mixed convection in free-surface flow is developed. General discrete-element analysis is used and equations of balance of momentum, conservation of energy, mass and vapor mass fraction are solved. The associated constitutive models for the kinetic (nonequilibrium) phase transport, thermophysical and transport properties are described. The computational model is first applied to study the three-dimensional hydrodynamic flow field around a protruding block in a channel filled with water. The numerical results show that the three-dimensional leading-edge horseshoe vortex and the downstream three-dimensional vortex are capable of strongly perturbing the flow structures and possibly modifying the heat-transfer characteristics. While three-dimensional simulation results agree qualitatively with two-dimensional ones in both the natural-convection and boiling-heat-transfer regimes, the flow is essentially three-dimensional and a two-dimensional model can not correctly capture the features of the flow. The outward heat flux in the boiling heat transfer regime is increased by ten-fold over the outward heat flux in the natural convection regime. The simulated heat fluxes are in good agreement with the available experimental data.

Elrais, K.A.

1988-01-01

163

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

NASA Astrophysics Data System (ADS)

The off-resonance rotating frame technique based on the spin relaxation properties of off-resonance T1 ? 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 T1 ?-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 T1 ?-weighted image in the presence of water diffusion-exchange. The T1 ? 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.

Zhang, Huiming; Xie, Yang; Ji, Tongyu

2007-06-01

164

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

2007-06-01

165

Rapid spectrophotometric determination of the exponential constant of ethanol-enhanced proton diffusion in yeasts  

Microsoft Academic Search

Summary  A rapid method for the determination of the exponential constant of ethanol-enhanced proton diffusion in yeasts has been developed.\\u000a This method was based on Bromophenol Blue to monitor the acidification by energized yeast cells suspensions. This method is\\u000a completely automated using a Beckman Biomek 1000 workstation.

J. C. Mauricio; J. M. Salmon

1992-01-01

166

A scale-based forward-and-backward diffusion process for adaptive image enhancement and denoising  

NASA Astrophysics Data System (ADS)

This work presents a scale-based forward-and-backward diffusion (SFABD) scheme. The main idea of this scheme is to perform local adaptive diffusion using local scale information. To this end, we propose a diffusivity function based on the Minimum Reliable Scale (MRS) of Elder and Zucker (IEEE Trans. Pattern Anal. Mach. Intell. 20(7), 699-716, 1998) to detect the details of local structures. The magnitude of the diffusion coefficient at each pixel is determined by taking into account the local property of the image through the scales. A scale-based variable weight is incorporated into the diffusivity function for balancing the forward and backward diffusion. Furthermore, as numerical scheme, we propose a modification of the Perona-Malik scheme (IEEE Trans. Pattern Anal. Mach. Intell. 12(7), 629-639, 1990) by incorporating edge orientations. The article describes the main principles of our method and illustrates image enhancement results on a set of standard images as well as simulated medical images, together with qualitative and quantitative comparisons with a variety of anisotropic diffusion schemes.

Wang, Yi; Niu, Ruiqing; Zhang, Liangpei; Wu, Ke; Sahli, Hichem

2011-12-01

167

Diffusion  

NSDL National Science Digital Library

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

Consortium, The C.

2011-12-11

168

Microstructural evolution in the partial transient liquid phase diffusion bonding of Zircaloy4 to stainless steel 321 using active titanium filler metal  

Microsoft Academic Search

Microstructural evolution of the partial transient liquid phase diffusion bonded Zircaloy-4 and stainless steel 321 using an active Ti-base interlayer were studied at different temperatures. Additionally, simple analytical models were developed to predict the evolution of the interlayer and intermetallics during the bonding operation. Bonds were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Precision measurement of the

M. Mazar Atabaki

2010-01-01

169

Cladding oxidation model development based on diffusion equations and a simulation of the monoclinic-tetragonal phase transformation of zirconia during transient oxidation  

NASA Astrophysics Data System (ADS)

Zircaloy cladding oxidation is mostly represented by parabolic rate correlation. But the correlation approach is not suitable for long-term isothermal oxidation [4] or oxidation occurs under steam starvation conditions [5] and cannot obtain the detailed oxygen distribution which impacts the detailed mechanical behavior. To obtain the detailed oxygen distribution, a multi-phase diffusion problem with moving boundaries was introduced to simulate the cladding oxidation [9,10]. However, the hysteresis phenomenon related to the coexistence of monoclinic-tetragonal phases of zirconia which are very important to model the cladding oxidation during a LOCA, is not analyzed. In this study, a cladding oxidation model based on diffusion equations in the temperature range from 923 K to 2098 K which contains ?-Zr, ?-Zr, monoclinic-ZrO2, tetragonal-ZrO2, and cubic-ZrO2 is developed and the detailed oxygen distribution in the cladding could be obtained. It showed that the simulations of short-term and long-term isothermal oxidation, transient oxidation, and oxidation under steam starvation conditions were reasonable through comparing with the experimental data. We found that our model can give a reasonable simulation of the hysteresis phenomenon of monoclinic-tetragonal phase transformation during transient oxidation as well as a much better simulation of the hypothetical LOCA transient oxidation experiments [11] in ORNL than that by the code based on the parabolic rate correlation. This indicates that the developed model can accurately simulate the cladding oxidation during a LOCA transient.

He, Xiaoqiang; Yu, Hongxing; Jiang, Guangming; Dang, Gaojian; Wu, Dan; Zhang, Yu

2014-08-01

170

Differentiation of Reactive and Tumor Metastatic Lymph Nodes with Diffusion-weighted and SPIO Enhanced MRI  

PubMed Central

Objectives Determination of lymphatic metastasis is of great importance for both treatment planning and patient prognosis. We aim to distinguish tumor metastatic lymph nodes (TLNs) and reactive lymph nodes (RLNs) with diffusion-weighted and superparamagnetic iron oxide (SPIO) enhanced magnetic resonance imaging (MRI). Materials and methods Ipsilateral popliteal lymph node metastasis or lymphadenitis model was established by hock injection of either luciferase-expressing 4T1 murine breast cancer cells or Complete Freund Adjuvant (CFA) in male Balb/C mice. At different time points after inoculation, bioluminescence imaging, T2-weighted, diffusion-weighted and SPIO enhanced MRI were performed. Imaging findings were confirmed by histopathological staining. Results Size enlargement was observed in both TLNs and RLNs. At day 28, TLNs showed strong bioluminescence signal and bigger size than RLNs (p < 0.01). At early stages up to day 21, both TLNs and RLNs appeared homogeneous on diffusion-weighted imaging (DWI). At day 28, TLNs showed heterogeneous apparent diffusion coefficient (ADC) map with significantly higher average ADC value of 0.41 ± 0.03 × 10?3 mm2/s than that of RLNs (0.34 ± 0.02 10?3 mm2/s, p < 0.05). On SPIO enhanced MRI, both TLNs and RLNs showed distinct T2 signal reduction at day 21 after inoculation. At day 28, TLNs demonstrated partial uptake of the iron oxide particles, which was confirmed by Prussian blue staining. Conclusions Both diffusion-weighted and SPIO enhanced MRI can distinguish tumor metastatic lymph nodes from reactive lymph nodes. However, neither method is able to detect tumor metastasis to the draining lymph nodes at early stages.

Zhang, Fan; Zhu, Lei; Huang, Xinglu; Niu, Gang; Chen, Siouan

2012-01-01

171

Combining Time Frequency Representation and Parametric Analysis for the Enhancement of Transients in Sleep EEG Signal.  

National Technical Information Service (NTIS)

The study of the electroencephalographic (EEG) signal contributes to sleep analysis. In the microstructure of the sleep EEG signal, transient patterns are characterized by their frequency content and their time duration. The Time-Frequency Representations...

E. Fortunato H. Rix G. Suisse O. Meste

2001-01-01

172

An evaluation of the contributions of diffusion and exchange in relaxation enhancement by MRI contrast agents  

NASA Astrophysics Data System (ADS)

Magnetic compounds are known to enhance water proton relaxation, either by diffusion or by proton exchange. An experimental procedure to distinguish both mechanisms is proposed and validated by relaxation measurements made in water-methanol solutions of Dy 3+, Ni 2+, Gd 3+, Tempo, and AMI-25. The test discriminates according to the character of the transverse relaxation in water-methanol solutions: a mono-exponential decay corresponds to diffusion, while a bi-exponential decay indicates the contribution of a proton exchange. The study of ferritin and akaganeite particle solutions confirms the occurrence of a proton exchange between protons belonging to hydroxyl groups of the particle surface and free water protons.

Gossuin, Yves; Roch, Alain; Muller, Robert N.; Gillis, Pierre

2002-09-01

173

Application of a combined superconducting fault current limiter and STATCOM to enhancement of power system transient stability  

NASA Astrophysics Data System (ADS)

Stable and reliable operation of the power system network is dependent on the dynamic equilibrium between energy production and power demand under large disturbance such as short circuit or important line tripping. This paper investigates the use of combined model based superconducting fault current limiter (SFCL) and shunt FACTS Controller (STATCOM) for assessing the transient stability of a power system considering the automatic voltage regulator. The combined model located at a specified branch based on voltage stability index using continuation power flow. The main role of the proposed combined model is to achieve simultaneously a flexible control of reactive power using STATCOM Controller and to reduce fault current using superconducting technology based SFCL. The proposed combined model has been successfully adapted within the transient stability program and applied to enhance the transient power system stability of the WSCC9-Bus system. Critical clearing time (CCT) has been used as an index to evaluate and validate the contribution of the proposed coordinated Controller. Simulation results confirm the effectiveness and perspective of this combined Controller to enhance the dynamic power system performances.

Mahdad, Belkacem; Srairi, K.

2013-12-01

174

Diffusion enhancement due to low-energy ion bombardment during sputter etching and deposition  

SciTech Connect

The effects of low-energy ion bombardment on enhancing elemental diffusion rates at both heterojunction interfaces during film deposition and over the compositionally altered layer created during sputter etching alloy targets have been considered. Depth dependent enhanced interdiffusion coefficients, expressed as D*(x)=D*(0) exp(-x/L/sub d/), where D*(0) is more than five orders of magnitude greater than thermal diffusion values, were measured in InSb/GaSb multilayer structures deposited by multitarget bias sputering. D*(0) was determined from the amplitude u of the compositional modulation in the multilayered films (layer thicknesses between 20 and 45 A) as measured by superlattice x-ray diffraction techniques. The value of D*(0) was found to increase from 3 x 10/sup -17/ to 1 x 10/sup -16/ cm/sup 2//sec as the applied substrate bias was increased from 0 to -75 V. However even at V/sub a/=0, the diffusion coefficient was enhanced owing to an induced substrate potential with respect to the positive space-charge region in the Ar discharge. The diffusion length of L/sub d/ of the ion bombardment created defects was approx.1000 A. Enhanced diffusion also has a significiant effect on the altered layer thickness x/sub e/ and the total sputtering time t/sub e/ (or ion dose) required to reach steady state during ion etching of multielement targets. The effects of using an exponentially depth dependent versus a constant value of the enhanced diffusion coefficient on calculated values of x/sub e/ and t/sub e/ in single-phase binary alloys were considered. The results show that both x/sub e/ and t/sub e/ are considerably larger using a depth dependent D*(x), when L/sub d/D*(0)/v, the usual case for most sputtering applications, the two solutions approach each other.

Eltoukhy, A.H.; Greene, J.E.

1980-08-01

175

Discovery and characterization of super-enhancer-associated dependencies in diffuse large B cell lymphoma.  

PubMed

Diffuse large B cell lymphoma (DLBCL) is a biologically heterogeneous and clinically aggressive disease. Here, we explore the role of bromodomain and extra-terminal domain (BET) proteins in DLBCL, using integrative chemical genetics and functional epigenomics. We observe highly asymmetric loading of bromodomain 4 (BRD4) at enhancers, with approximately 33% of all BRD4 localizing to enhancers at 1.6% of occupied genes. These super-enhancers prove particularly sensitive to bromodomain inhibition, explaining the selective effect of BET inhibitors on oncogenic and lineage-specific transcriptional circuits. Functional study of genes marked by super-enhancers identifies DLBCLs dependent on OCA-B and suggests a strategy for discovering unrecognized cancer dependencies. Translational studies performed on a comprehensive panel of DLBCLs establish a therapeutic rationale for evaluating BET inhibitors in this disease. PMID:24332044

Chapuy, Bjoern; McKeown, Michael R; Lin, Charles Y; Monti, Stefano; Roemer, Margaretha G M; Qi, Jun; Rahl, Peter B; Sun, Heather H; Yeda, Kelly T; Doench, John G; Reichert, Elaine; Kung, Andrew L; Rodig, Scott J; Young, Richard A; Shipp, Margaret A; Bradner, James E

2013-12-01

176

Enhanced surface diffusion through termination conversion during epitaxial SrRuO3 growth  

Microsoft Academic Search

During the initial growth of the ferromagnetic oxide SrRuO3 on TiO2-terminated SrTiO3, we observe a self-organized conversion of the terminating atomic layer from RuO2 to SrO. This conversion induces an abrupt change in growth mode from layer by layer to growth by step advancement, indicating a large enhancement of the surface diffusivity. This growth mode enables the growth of single-crystalline

Guus Rijnders; Dave H. A. Blank; Junghoon Choi; Chang-Beom Eom

2004-01-01

177

Blind signal extraction based speech enhancement in presence of diffuse background noise  

Microsoft Academic Search

This paper presents a new frequency domain blind signal extraction (FD-BSE) method for the extraction of a target speech in presence of diffuse background noise. This is a fast alternative to frequency domain blind signal separation (FD-BSS) for hands-free speech interface. Like the FD-BSS approach, the speech signal is enhanced by using a nonlinear filter to suppress the noise estimated

Jani Even; Hiroshi Saruwatari; Kiyohiro Shikano

2009-01-01

178

Stress enhanced self-diffusion in Si: Entropy effect in anisotropic elastic environment  

Microsoft Academic Search

We present a multiscale analysis on stress enhanced vacancy-mediated diffusion in strained Si that explicitly includes the Jahn–Teller structural distortion around vacancies. The resulting anisotropy combined with biaxial deformations applied to (100)-oriented films lead to an orientational dependency of the vacancy formation energy. At finite temperatures, it results in a strong entropy effect when thermal activation allows occupancy of high

Konstantin Z. Rushchanskii; Pascal Pochet

2008-01-01

179

Stress enhanced self-diffusion in Si: Entropy effect in anisotropic elastic environment  

Microsoft Academic Search

We present a multiscale analysis on stress enhanced vacancy-mediated diffusion in strained Si that explicitly includes the Jahn-Teller structural distortion around vacancies. The resulting anisotropy combined with biaxial deformations applied to (100)-oriented films lead to an orientational dependency of the vacancy formation energy. At finite temperatures, it results in a strong entropy effect when thermal activation allows occupancy of high

Konstantin Z. Rushchanskii; Pascal Pochet; Frédéric Lançon

2008-01-01

180

Curvature and singularity driven diffusion for oriented pattern enhancement with singular points  

Microsoft Academic Search

Oriented patterns, e.g. fingerprints, consist of smoothly varying flow-like patterns, together with important singular points (i.e. cores and deltas) where the orientation changes abruptly. Gabor filters and anisotropic diffusion methods have been widely used to enhance oriented patterns. How- ever, none of them can well cope with regions of varying curvatures or regions surrounding singular points. By in- corporating the

Qijun Zhao; Lei Zhang; David Zhang; Wenyi Huang; Jian Bai

2009-01-01

181

Curvature and singularity driven diffusion for oriented pattern enhancement with singular points  

Microsoft Academic Search

Oriented patterns, e.g. fingerprints, consist of smoothly varying flow-like patterns, together with important singular points (i.e. cores and deltas) where the orientation changes abruptly. Gabor filters and anisotropic diffusion methods have been widely used to enhance oriented patterns. However, none of them can well cope with regions of varying curvatures or regions surrounding singular points. By incorporating the ridge curvatures

Qijun Zhao; Lei Zhang; David Zhang; Wenyi Huang; Jian Bai

2009-01-01

182

Mechanism of the enhancement of self-diffusion on Cu(111) by trace amounts of S  

NASA Astrophysics Data System (ADS)

We find that <0.01 monolayer (ML) of S enhances surface diffusion on Cu(111) by several orders of magnitude. Using low-energy electron microscopy and scanning tunneling microscopy, we probe the mechanisms of this enhancement by monitoring the decay rate of island stacks and 2D island arrays as a function of S coverage and temperature. The decay rate of islands in stacks increases roughly as the S coverage cubed, consistent with the proposal that the enhanced surface diffusion is due to the formation of Cu_3S3 clusters^1. However, we also find a dramatic change in the mechanism of 2D island ripening as a function of S coverage. At higher S coverages (> ˜ 0.01 ML), large islands grow at the expense of nearby small islands, similar to clean Cu; with smaller amounts of S, this local ripening is not apparent: mass flows from islands to the steps bounding large terraces. We show that this phenomenon can be quantitatively understood if the Cu diffusion at low S coverages is limited by the rate of reaction of S and Cu to form clusters. [1] P.J. Feibelman, Phys. Rev. Lett. 85, 606 (2000).

Ling, W. L.; Bartelt, N. C.; Pohl, K.; de La Figuera, J.; McCarty, K. F.

2004-03-01

183

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

184

Thermal and radiation-enhanced diffusion in the bulk metallic glass Ni23Zr62Al15  

NASA Astrophysics Data System (ADS)

The temperature dependence of tracer diffusion in the three-component system NiZrAl was measured. For the composition Ni23Zr62Al15, it was possible to measure diffusion coefficients below and above the glass transition temperature. Similar to the binary metallic glass NiZr, the diffusion coefficient was strongly dependent on the atomic size of the tracer, varying by two orders of magnitude. The results are suggestive of a collective diffusion mechanism in bulk metallic glasses. Radiation-enhanced diffusion was also measured in this alloy and compared with measurements of radiation-induced viscous flow on similar alloys.

Flege, S.; Hahn, H.; Averback, R. S.

2004-01-01

185

Enhancing transient and small signal stability in power systems using a posicast excitation controller  

Microsoft Academic Search

In this paper a Posicast controller is designed to improve the power system stability containing the transient and the small signal stability. Unlike most of the recently published excitation control schemes, Posicast control is an unsophisticated and easy to implement control method that can effectively improve the stability of the system without increasing the complexity of the control system. The

M. R. Aghamohammadi; A. Ghorbani; S. Pourmohammad

2008-01-01

186

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

187

A total internal reflection fluorescence microscopy study of mass diffusion enhancement in water-based alumina nanofluids  

NASA Astrophysics Data System (ADS)

Mass diffusion of rhodamine 6G (R6G) in water-based alumina nanofluids is studied by means of total internal reflection fluorescence (TIRF) microscopy. We report a mass diffusivity enhancement that reaches an order of magnitude in a 2 vol % nanofluid when compared to the value in deionized water. Since experiments were performed with positively charged R6G, interfacial complexation between the dye and the nanoparticles was not observed. The effect of local density variations on mass diffusivity measurements is also addressed. An explanation for the enhancement of mass diffusion is presented using arguments based on dispersion, and it is shown that it correctly describes the order of magnitude differences between the thermal conductivity and mass diffusivity enhancements reported in the literature.

Veilleux, Jocelyn; Coulombe, Sylvain

2010-11-01

188

Tumor characterization in small animals using magnetic resonance-guided dynamic contrast enhanced diffuse optical tomography  

NASA Astrophysics Data System (ADS)

We present a magnetic resonance (MR)-guided near-infrared dynamic contrast enhanced diffuse optical tomography (DCE-DOT) system for characterization of tumors using an optical contrast agent (ICG) and a MR contrast agent [Gd-diethylenetriaminepentaacetic acid (DTPA)] in a rat model. Both ICG and Gd-DTPA are injected and monitored simultaneously using a combined MRI-DOT system, resulting in accurate co-registration between two imaging modalities. Fisher rats bearing R3230 breast tumor are imaged using this hybrid system. For the first time, enhancement kinetics of the exogenous contrast ICG is recovered from the DCE-DOT data using MR anatomical a priori information. As tumors grow, they undergo necrosis and the tissue transforms from viable to necrotic. The results show that the physiological changes between viable and necrotic tissue can be differentiated more accurately based on the ICG enhancement kinetics when MR anatomical information is utilized.

Lin, Yuting; Thayer, Dave; Nalcioglu, Orhan; Gulsen, Gultekin

2011-10-01

189

Oxidation-enhanced diffusion of boron in very low-energy N2+-implanted silicon  

NASA Astrophysics Data System (ADS)

In this article we study the interstitial injection during oxidation of very low-energy nitrogen-implanted silicon. Buried boron ? layers are used to monitor the interstitial supersaturation during the oxidation of nitrogen-implanted silicon. No difference in boron diffusivity enhancement was observed compared to dry oxidation of nonimplanted samples. This result is different from our experience from N2O oxynitridation study, during which a boron diffusivity enhancement of the order of 20% was observed, revealing the influence of interfacial nitrogen on interstitial kinetics. A possible explanation may be that implanted nitrogen acts as an excess interstitial sink in order to diffuse towards the surface via a non-Fickian mechanism. This work completes a wide study of oxidation of very low-energy nitrogen-implanted silicon related phenomena we performed within the last two years [D. Skarlatos, C. Tsamis, and D. Tsoukalas, J. Appl. Phys. 93, 1832 (2003); D. Skarlatos, E. Kapetanakis, P. Normand, C. Tsamis, M. Perego, S. Ferrari, M. Fanciulli, and D. Tsoukalas, J. Appl. Phys. 96, 300 (2004)].

Skarlatos, D.; Tsamis, C.; Perego, M.; Fanciulli, M.

2005-06-01

190

Frequency and amplitude enhancement of calcium transients by cyclic AMP in hepatocytes.  

PubMed

Interactions between signalling pathways such as the cyclic AMP and the Ca2+/phosphatidylinositol pathway may occur and be of major relevance in the regulation of cell function. We demonstrate here that cyclic-AMP-dependent mechanisms cause a marked increase in frequency and peak free Ca2+ of alpha 1-receptor-induced Ca2+ transients in single hepatocytes and lower the threshold for alpha 1-receptor agonists. Adrenaline at low physiological concentrations generates alpha 1-receptor-induced Ca2+ transients, which requires activation of the beta 2-receptor signalling pathway. We conclude that an interaction between the alpha 1-receptor signalling pathway and cyclic-AMP-dependent mechanisms activated by beta 2-receptor occupation is crucial to elicit a complete adrenergic response to adrenaline at physiological concentrations in rat hepatocytes. PMID:1847625

Schöfl, C; Sanchez-Bueno, A; Brabant, G; Cobbold, P H; Cuthbertson, K S

1991-02-01

191

Frequency and amplitude enhancement of calcium transients by cyclic AMP in hepatocytes.  

PubMed Central

Interactions between signalling pathways such as the cyclic AMP and the Ca2+/phosphatidylinositol pathway may occur and be of major relevance in the regulation of cell function. We demonstrate here that cyclic-AMP-dependent mechanisms cause a marked increase in frequency and peak free Ca2+ of alpha 1-receptor-induced Ca2+ transients in single hepatocytes and lower the threshold for alpha 1-receptor agonists. Adrenaline at low physiological concentrations generates alpha 1-receptor-induced Ca2+ transients, which requires activation of the beta 2-receptor signalling pathway. We conclude that an interaction between the alpha 1-receptor signalling pathway and cyclic-AMP-dependent mechanisms activated by beta 2-receptor occupation is crucial to elicit a complete adrenergic response to adrenaline at physiological concentrations in rat hepatocytes.

Schofl, C; Sanchez-Bueno, A; Brabant, G; Cobbold, P H; Cuthbertson, K S

1991-01-01

192

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

193

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

PubMed Central

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

2011-01-01

194

Diode laser frequency stabilization to transient spectral holes and spectral diffusion in Er 3+ : Y 2SiO 5 at 1536 nm  

Microsoft Academic Search

Diode laser frequency stabilization to 500Hz Allan deviation is demonstrated over 2ms integration times with drift reduced to 7kHz\\/min. This was achieved at 1536nm in the technologically important communications band by stabilizing external cavity diode lasers to regenerative transient spectral holes in the inhomogeneously broadened 4I15\\/2(1)?4I13\\/2(1) optical absorption of Er3+:Y2SiO5. Spectral diffusion, which currently limits the achievable stabilization performance, has

Thomas Böttger; Y. Sun; G. J. Pryde; G. Reinemer; R. L. Cone

2001-01-01

195

Enhanced visualization and quantification of magnetic resonance diffusion tensor imaging using the p:q tensor decomposition  

Microsoft Academic Search

Many scalar measures have been proposed to quantify magnetic resonance diffusion tensor imaging (MR DTI) data in the brain. However, only two parameters are commonly used in the literature: mean diffusion (D) and fractional anisotropy (FA). We introduce a visualization technique which permits the simultaneous analysis of an additional five scalar measures. This enhanced diversity is important, as it is

A Pena; H A L GREEN; T A CARPENTER; J D PICKARD; J H GILLARD

2006-01-01

196

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. PMID:23873754

Takahashi, Kenji; Ohta, Toshio

2013-10-01

197

Resolution enhancement in MRI of laser polarized 3He by control of diffusion  

NASA Astrophysics Data System (ADS)

Diffusion of atoms or molecules in presence of magnetic field gradients not only attenuates the NMR signal but also leads to distortions close to restricting boundaries. This phenomenon is most evident in imaging with laser polarized (LP) noble gases. Diffusion of gases can be manipulated, however, by admixing inert gases of different molecular weight. In this work we analyze the effect of mixing LP- 3He with SF 6 on the image quality of a phantom consisting of an arrangement of capillaries with different diameters. Admixing buffer gases of higher molecular weight changes the contrast and offers a means to record images with high spatial and time resolution. Additionally we demonstrate how distortions due to edge enhancement can be reduced even for long timed MRI-sequences.

Agulles-Pedrós, L.; Acosta, R. H.; Blümler, P.; Spiess, H. W.

2009-03-01

198

An evaluation of the contributions of diffusion and exchange in relaxation enhancement by MRI contrast agents.  

PubMed

Magnetic compounds are known to enhance water proton relaxation, either by diffusion or by proton exchange. An experimental procedure to distinguish both mechanisms is proposed and validated by relaxation measurements made in water-methanol solutions of Dy(3+), Ni(2+), Gd(3+), Tempo, and AMI-25. The test discriminates according to the character of the transverse relaxation in water-methanol solutions: a mono-exponential decay corresponds to diffusion, while a bi-exponential decay indicates the contribution of a proton exchange. The study of ferritin and akaganeite particle solutions confirms the occurrence of a proton exchange between protons belonging to hydroxyl groups of the particle surface and free water protons. PMID:12419669

Gossuin, Yves; Roch, Alain; Muller, Robert N; Gillis, Pierre

2002-01-01

199

Predicting diffuse light-enhancement of GPP from plant functional traits: A multi-site synthesis  

NASA Astrophysics Data System (ADS)

Diffuse light enhances canopy-scale photosynthesis because isotropic diffuse light penetrates deeper into the canopy, involves more leaf area in photosynthesis, and prevents the top of the canopy from becoming light saturated. However, the observational and modeling communities still have little understanding of how the 'Diffuse light Enhancement Effect' (DEE) varies across plant functional types or is constrained by factors such as nitrogen availability and plant structure. So far, variability in the strength of DEE across plant functional types (PFTs) remains poorly constrained, but canopy models indicate leaf area index (LAI) is a primary controller. While the very few existing multi-site, measurement-based syntheses of the DEE have provided valuable information on the variability of the DEE across a few plant functional types, no study has correlated measured metrics of DEE magnitude with direct measurements of canopy physical traits across a wide range of plant functional types. Here we report a new metric that is suitable for quantifying the DEE in both flux measurements and land surface models. We also present, for the first time, an examination of the relationship between the DEE metric and plant functional traits. Results from our 70+ site AmeriFlux and FLUXNET synthesis indicate that LAI is the strongest controller of the DEE across sites and PFTs, with less significant influences from foliar nitrogen, canopy height, and mean annual precipitation. Our results will enable direct evaluation and improvement of remote sensing algorithms and light use efficiency models (e.g. MODIS GPP), which to this point regard diffuse light fraction as a source of noise. Additionally, improving resolution of the DEE in prognostic land surface models, such as the Community Land Model (CLM), will greatly improve our ability to forecast future feedbacks to terrestrial carbon sequestration from changes in cloudiness and aerosol amount.

O'Halloran, T. L.; Barr, J. G.; Cook, B.; Goeckede, M.; Law, B. E.; Kueppers, L. M.; Riley, W. J.

2013-12-01

200

Intracochlear schwannoma presenting as diffuse cochlear enhancement: diagnostic challenges of a rare cause of deafness.  

PubMed

Intracochlear schwannoma is a rare, treatable, cause of unilateral hearing loss. Due to the small size, position, and variable clinical and imaging features, diagnosis presents a significant challenge and is often delayed. We present a case of a patient with an intracochlear schwannoma presenting as a diffuse enhancement of the cochlea, mimicking an infectious or inflammatory process. The absence of focal nodularity in this lesion on multiple high-resolution MRI examinations led to a delay of over 3 years from the patient's initial presentation to surgical diagnosis. Clinical history and examination, imaging features, pathologic findings, and surgical management options are described. PMID:20852964

Miller, M E; Moriarty, J M; Linetsky, M; Lai, C; Ishiyama, A

2012-03-01

201

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

202

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

SciTech Connect

We report observations of the dynamics of electromagnetically induced transparency (EIT) in a {lambda} system when the ground states are Stark shifted. Interactions of this type exhibit large optical nonlinearities called Kerr nonlinearities, and have numerous applications. The EIT Kerr nonlinearity is relatively slow, which is a limiting factor that may make many potential applications impossible. Using rubidium atoms, we observe the dynamics of the EIT Kerr nonlinearity using a Mach-Zehnder interferometer to measure phase modulation of the EIT fields resulting from a pulsed signal beam Stark shifting the ground state energy levels. The rise times and transients agree well with theory.

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

2007-09-15

203

Transient Three-Phase Three-Component Flow. Part 3: Three-Dimensional 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 a porous body is presented. A combination of separated mass and energy equations together with mixture momentum equations for the ...

N. I. Kolev

1986-01-01

204

1H relaxation enhancement induced by nanoparticles in solutions: influence of magnetic properties and diffusion.  

PubMed

Magnetic nanoparticles that induce nuclear relaxation are the most promising materials to enhance the sensitivity in Magnetic Resonance Imaging. In order to provide a comprehensive understanding of the magnetic field dependence of the relaxation enhancement in solutions, Nuclear Magnetic Resonance (1)H spin-lattice relaxation for decalin and toluene solutions of various Fe2O3 nanoparticles was investigated. The relaxation experiments were performed in a frequency range of 10 kHz-20 MHz by applying Field Cycling method, and in the temperature range of 257-298 K, using nanoparticles differing in size and shape: spherical--5 nm diameter, cubic--6.5 nm diameter, and cubic--9 nm diameter. The relaxation dispersion data were interpreted in terms of a theory of nuclear relaxation induced by magnetic crystals in solution. The approach was tested with respect to its applicability depending on the magnetic characteristics of the nanocrystals and the time-scale of translational diffusion of the solvent. The role of Curie relaxation and the contributions to the overall (1)H spin-lattice relaxation associated with the electronic spin-lattice and spin-spin relaxation was thoroughly discussed. It was demonstrated that the approach leads to consistent results providing information on the magnetic (electronic) properties of the nanocrystals, i.e., effective electron spin and relaxation times. In addition, features of the (1)H spin-lattice relaxation resulting from the electronic properties of the crystals and the solvent diffusion were explained. PMID:24811643

Kruk, D; Korpa?a, A; Taheri, S Mehdizadeh; Koz?owski, A; Förster, S; Rössler, E A

2014-05-01

205

1H relaxation enhancement induced by nanoparticles in solutions: Influence of magnetic properties and diffusion  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles that induce nuclear relaxation are the most promising materials to enhance the sensitivity in Magnetic Resonance Imaging. In order to provide a comprehensive understanding of the magnetic field dependence of the relaxation enhancement in solutions, Nuclear Magnetic Resonance 1H spin-lattice relaxation for decalin and toluene solutions of various Fe2O3 nanoparticles was investigated. The relaxation experiments were performed in a frequency range of 10 kHz-20 MHz by applying Field Cycling method, and in the temperature range of 257-298 K, using nanoparticles differing in size and shape: spherical - 5 nm diameter, cubic - 6.5 nm diameter, and cubic - 9 nm diameter. The relaxation dispersion data were interpreted in terms of a theory of nuclear relaxation induced by magnetic crystals in solution. The approach was tested with respect to its applicability depending on the magnetic characteristics of the nanocrystals and the time-scale of translational diffusion of the solvent. The role of Curie relaxation and the contributions to the overall 1H spin-lattice relaxation associated with the electronic spin-lattice and spin-spin relaxation was thoroughly discussed. It was demonstrated that the approach leads to consistent results providing information on the magnetic (electronic) properties of the nanocrystals, i.e., effective electron spin and relaxation times. In addition, features of the 1H spin-lattice relaxation resulting from the electronic properties of the crystals and the solvent diffusion were explained.

Kruk, D.; Korpa?a, A.; Taheri, S. Mehdizadeh; Koz?owski, A.; Förster, S.; Rössler, E. A.

2014-05-01

206

Force enhancement in lengthening contractions of cat soleus muscle in situ: transient and steady-state aspects.  

PubMed

Force enhancement (FE) associated with lengthening is a well-accepted phenomenon of active skeletal muscle, but the underlying mechanism(s) remain unknown. Similar to force depression (FD) following active shortening, the mechanism of FE may be attributed, at least in part, to cross-bridge kinetics. To examine this relationship, a post hoc analysis was performed on the transient force relaxation phase of previous in-situ FE experiments in soleus muscle-tendon units of anesthetized cats. For each muscle (n = 8), nine eccentric lengthenings (3 amplitudes, 3 velocities) were performed while tetanically stimulated (3T at 30 Hz, 3× ? motorneuron, 35 ± 1°C). To determine transient aspects of FE, the period immediately following stretching was fit with an exponential decay function (R (2) > 0.95). Statistical analyses revealed that total steady-state FE (FESS) increased with stretching amplitude and applied mechanical work. A positive relationship was observed between the active FESS and rate of force decay (k), indicating that a kinetic mechanism may explain active FE. However, for all muscles and stretch conditions, there was no correlation between the total amount of FESS and rate of decay. Therefore, FE cannot be explained solely by an active FE mechanism involving the interaction of actin and myosin. Rather, these findings suggest a combination of underlying mechanisms, including a kinetic mechanism for active FE, contributions of a passive elastic element, and possibly an activatable passive component operating outside of actin-myosin cross-bridging. Moreover, this transient analysis identifies that FE is not simply the opposite of FD, and its underlying mechanism(s) cannot simply be the opposite in nature. PMID:24303106

Koppes, Ryan A; Herzog, Walter; Corr, David T

2013-07-01

207

Force enhancement in lengthening contractions of cat soleus muscle in situ: transient and steady-state aspects  

PubMed Central

Force enhancement (FE) associated with lengthening is a well-accepted phenomenon of active skeletal muscle, but the underlying mechanism(s) remain unknown. Similar to force depression (FD) following active shortening, the mechanism of FE may be attributed, at least in part, to cross-bridge kinetics. To examine this relationship, a post hoc analysis was performed on the transient force relaxation phase of previous in-situ FE experiments in soleus muscle-tendon units of anesthetized cats. For each muscle (n = 8), nine eccentric lengthenings (3 amplitudes, 3 velocities) were performed while tetanically stimulated (3T at 30 Hz, 3× ? motorneuron, 35 ± 1°C). To determine transient aspects of FE, the period immediately following stretching was fit with an exponential decay function (R2 > 0.95). Statistical analyses revealed that total steady-state FE (FESS) increased with stretching amplitude and applied mechanical work. A positive relationship was observed between the active FESS and rate of force decay (k), indicating that a kinetic mechanism may explain active FE. However, for all muscles and stretch conditions, there was no correlation between the total amount of FESS and rate of decay. Therefore, FE cannot be explained solely by an active FE mechanism involving the interaction of actin and myosin. Rather, these findings suggest a combination of underlying mechanisms, including a kinetic mechanism for active FE, contributions of a passive elastic element, and possibly an activatable passive component operating outside of actin–myosin cross-bridging. Moreover, this transient analysis identifies that FE is not simply the opposite of FD, and its underlying mechanism(s) cannot simply be the opposite in nature.

Koppes, Ryan A; Herzog, Walter; Corr, David T

2013-01-01

208

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

209

Interfacial microstructure and properties of Ti(C, N)\\/Ni bonded by transient liquid-phase diffusion  

Microsoft Academic Search

Effects of the main process parameters(temperature and time) on microstructure and properties of Ti(C, N)\\/Ni interface bonded\\u000a by (Cu+Nb) interlayer in a vacuum diffusion bonding device were investigated. The interfacial microstructures consisted initially\\u000a of Ni3Nb metallic compound and eutectic of Ni3Nb+CuNiSS, and finally transformed to (Ti, Nb) (C, N)+Ni3Nb near Ti (C, N) and NiCuSS+Ni3Nb near Ni when diffusion bonding

Shiquan Zhou; Xiaogang Li; Weihao Xiong; Yunhong Zhou

2009-01-01

210

Photon enhanced diffusion model for ?-Si:H photo-degradation  

NASA Astrophysics Data System (ADS)

A photon enhanced diffusion (PED) model to describe hydrogenated amorphous silicon (?-Si:H) photo-degradation is proposed in this paper. The model utilizes the hydrogen content naturally incorporated into plasma-enhanced chemical vapour deposition (PECVD) silane (SiH4) produced ?-Si:H structures (or films) as an ionized diffusing dopant within the modelled structure. In this model, the mobile carrier charge state contribution of the electrically active included hydrogen at a given physical location is determined dynamically with respect to the position of the Fermi level. In this paper, hydrogenated ?-Si:H fabricated without additional doping is defined as h-type, to represent the hydrogen content of the ?-Si:H within the modelled structure. A modelled ?-Si:H structure (or device) consisting of n-type, h-type (included hydrogen dopant only) and p-type layers of widths 50 nm, 400 nm and 50 nm, respectively, having a 4 ? external series resistance is considered in this paper. The physical diffusion of the ionized included hydrogen across dopant boundaries with differing Fermi levels provides mobile dopant compensation for the charge carrier concentration within the simulated ?-Si:H structure. A hydrogen mobile charge state transition energy term for the diffusion of hydrogen across dopant boundaries within the deposited ?-Si:H structure is included in this model as a variable combination of the ?-Si:H structure's thermal and incident absorbed photon energy. In this model, the included hydrogen diffusion process and ionic charge state are directly related to the modelled dopant profile, temperature and cumulative adsorbed incident photon radiation. The total dopant charge distribution within the modelled ?-Si:H structure is used to dynamically calculate the internal electrostatic potential and field profiles within the structure, with the changing charge compensation effects of the diffusing electrically active included hydrogen. High electric fields calculated to be within the modelled ?-Si:H structure are used to enable incident photons to assist in a quantum-mechanical tunnelling mechanism, producing PED of the included hydrogen. The PED model calculates the open-circuit terminal potential (voltage) and resistance profile character across the modelled ?-Si:H structure to provide a representative output of the photo-degradation process in time, temperature and incident photon exposure. Results generated by the proposed PED model closely follow the character of observed photo-degradation effects in ?-Si:H photo-voltaic structures due to cumulative illumination, annealing and thermal cycling reported in the literature. Extracted values for the diffusion coefficient and proportion of electrically activated included hydrogen within the simulated ?-Si:H structure of 1.38 × 10-16 cm-2 s-1 and 2 × 10-8, respectively, were obtained from the PED model simulations.

Phelps, G. J.

2006-01-01

211

Multispecies diffusion models: A study of uranyl species diffusion  

NASA Astrophysics Data System (ADS)

Rigorous numerical description of multispecies diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication in imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multispecies diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multispecies diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multispecies U(VI) diffusion under a steady state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that for multispecies U(VI) diffusion under transient chemical conditions, a fully coupled diffusion model could be well approximated by a component-based diffusion model when the diffusion coefficient for each chemical component was properly selected. The component-based diffusion model considers the difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be enforced, if necessary, by adding a secondary migration term resulting from model simplification. The effect of ion activity coefficient gradients on multispecies diffusion is also discussed. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from U.S. Department of Energy's Hanford 300A, where intragranular 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 had been previously described using a semiempirical, multirate model. Compared with the multirate model, the diffusion models have the advantage to provide spatiotemporal speciation evolution within the diffusion domains.

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

2011-12-01

212

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

2013-03-01

213

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

NASA Astrophysics Data System (ADS)

Results are presented on kinetic regimes of backward stimulated Raman scattering [1] (BSRS) dominated by electron trapping in the primary daughter Langmuir wave (LW). This study is motivated by the need to understand the unexpectedly high BSRS reflectivities observed in experiments emulating the conditions of the National Ignition Facility (NIF) [2,3]. In the case of BSRS, it is found in our study that electron trapping can lead to much larger transient reflectivities than predicted by standard fluid-like Zakharov models (with fixed, linear, Landau damping)in regimes with high Landau damping of the primary Langmuir wave (LW)with large values of k_1?D [4]. It is also found that the LW frequency shift associated with trapped electrons [5] introduces a secular phase shift between the LW and the BSRS ponderomotive force. This phase shift detunes and saturates BSRS and a similar effect, due to ion trapping, is now understood to be the saturation mechanism for stimulated Brillouin scattering. [1] W.L. Kruer, The Physics of Laser-Plasma Interaction (Addison-Wesley, New York, 1988). [2] J.C. Fernandez et al., Observed Insensitivity of Stimulated Raman Scattering on Electron Density, Phys. Plasmas, accepted (2000). [3] D.S. Montgomery, private communication (1999). [4] D.A. Russell, D.F. DuBois, and H.A. Rose, Phys. Plasmas 6, 1294 (1999). [5] G.J. Morales and T.M. O'Neil, Phys. Rev. Lett. 28, 417 (1972).

Vu, Hoanh X.

2000-10-01

214

Diffusion of Paramagnetically Labeled Proteins in Cartilage: Enhancement of the 1-D NMR Imaging Technique  

NASA Astrophysics Data System (ADS)

Quantifying the diffusive transport of large molecules in avascular cartilage tissue is important both for planning potential pharamacological treatments and for gaining insight into the molecular-scale structure of cartilage. In this work, the diffusion coefficients of gadolinium-DTPA and Gd-labeled versions of four proteins—lysozyme, trypsinogen, ovalbumin, and bovine serum albumin (BSA) with molecular weights of 14,300, 24,000, 45,000, and 67,000, respectively—have been measured in healthy and degraded calf cartilage. The experimental technique relies on the effect of the paramagnetic on the relaxation properties of the surrounding water, combined with the time course of a 1-dimensional spatial profile of the water signal in the cartilage sample. The enhanced technique presented here does not require a prior measurement of the relaxivity of the paramagnetic compound in the sample of interest. The data are expressed as the ratio of the diffusion coefficient of a compound in cartilage to its diffusion coefficient in water. For healthy cartilage, this ratio was 0.34 ± 0.07 for Gd-DTPA, the smallest compound, and fell to 0.3 ± 0.1 for Gd-lysozyme, 0.08 ± 0.04 for Gd-trypsinogen, and 0.07 ± 0.04 for Gd-ovalbumin. Gd-BSA did not appear to enter healthy cartilage tissue beyond a surface layer. After the cartilage had been degraded by 24-h trypsinization, these ratios were 0.60 ± 0.03 for Gd-DTPA, 0.40 ± 0.08 for Gd-lysozyme, 0.42 ± 0.09 for Gd-trypsinogen, 0.16 ± 0.14 for Gd-ovalbumin, and 0.11 ± 0.05 for Gd-BSA. Thus, degradation of the cartilage led to increases in the diffusion coefficient of up to fivefold for the Gd-labeled proteins. These basic transport parameters yield insights on the nature of pore sizes and chemical-matrix interactions in the cartilage tissue and may prove diagnostically useful for identifying the degree and nature of damage to cartilage.

Foy, Brent D.; Blake, Joseph

2001-01-01

215

1,25 (OH)2D3 enhances PTH-induced Ca2+ transients in preosteoblasts by activating L-type Ca2+ channels  

NASA Technical Reports Server (NTRS)

We previously demonstrated electrophysiologically that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] shifts the activation threshold of L-type Ca2+ channels in osteoblasts toward the resting potential and prolongs mean open time. Presently, we used single-cell Ca2+ imaging to study the combined effects of 1,25(OH)2D3 and parathyroid hormone (PTH) during generation of Ca2+ transients in fura 2-loaded MC3T3-E1 cells. Pretreatment with 1,25(OH)2D3 concentrations, which alone did not produce Ca2+ transients, consistently enhanced Ca2+ responses to PTH. Enhancement was dose dependent over the range of 1 to 10 nM and was blocked by pretreatment with 5 microM nitrendipine during pretreatment. A 1,25(OH)2D3 analog that activates L-type channels and shifts their activation threshold also enhanced PTH responses. In contrast, an analog devoid of membrane Ca2+ effects did not enhance PTH-induced Ca2+ transients. The PTH-induced Ca2+ transient involved activation of a dihydropyridine-insensitive cation channel that was inhibited by Gd3+. Together, these data suggest that 1,25(OH)2D3 increases osteoblast responsiveness to PTH through rapid modification of L-type Ca2+ channel gating properties, whose activation enhances Ca2+ entry through other channels such as the PTH-responsive, Gd(3+)-sensitive cation channel.

Li, W.; Duncan, R. L.; Karin, N. J.; Farach-Carson, M. C.

1997-01-01

216

Recurrent transient apical cardiomyopathy (tako-tsubo-like left ventricular dysfunction) in a postmenopausal female with diffuse esophageal spasms.  

PubMed

Transient apical cardiomyopathy, also known as Takot-tsubo-like left ventricular dysfunction, is a clinical syndrome characterized by reversible left ventricular dysfunction at the apex with preserved basal contractility, in the setting of new ST and T wave changes suggestive of ischemia but no evidence of obstructive coronary artery disease on angiography. The main mechanism appears to be intense neuroadrenergic myocardial stimulation with endothelial dysfunction of the coronary vasculature. It has been noted that patients with esophageal spasms also have a tendency for coronary spasms. We present the case of a postmenopausal female with documented severe esophageal spasms who presented with atypical angina and recurrent Tako-tsubo cardiomyopathy. PMID:24695751

Brenes Salazar, Jorge A

2013-10-01

217

Enhanced and retarded Ga self-diffusion in Si and Be doped GaAs isotope heterostructures  

Microsoft Academic Search

Ga self-diffusion in undoped, Si- and Be-doped 71GaAs\\/natGaAs isotope heterostructures has been investigated at temperatures between 736°C and 1050°C. Concentration profiles of the Ga isotopes measured separately by secondary ion mass spectrometry reveal retarded (enhanced) self-diffusion when doped p-type (n-type), compared to intrinsic conditions. Electrochemical C–V profiling was performed to determine the free carrier concentrations before and after annealing. Detailed

H. Bracht; M. Norseng; E. E. Haller; K. Eberl; M. Cardona

1999-01-01

218

Transient enhancement of low-threshold calcium current in thalamic relay neurons after corticectomy.  

PubMed

1. The alterations of voltage-sensitive calcium currents produced in thalamic cells by injury were investigated under voltage clamp using patch-clamp recordings in the whole-cell configuration. 2. One day after unilateral cortical ablation in immature rats (postnatal day 7), low-threshold transient calcium (T) currents in acutely isolated thalamic relay neurons (RNs) were increased by 68% compared with contralateral controls (P < 0.001). Three days after the operation, T currents in injured neurons were at 44% of control levels (P < 0.001). On the other hand, high-threshold (L) calcium currents in RNs did not change over the same interval. 3. To investigate the mechanism for the increase of T current, both kinetics and voltage dependency of activation and inactivation were examined. At a test voltage of -40 mV, the activation time constant decreased from 4.1 to 3.2 ms (P < 0.05); however, this small change was insufficient to explain the large increase in T current. Time constants for both fast and slow inactivation did not change significantly, nor did voltage dependence of activation or inactivation of thalamic T currents. 4. Methyl-phenyl-succinimide (MPS, 1 mM), a compound known to block T currents, was used to examine possible alterations in the pharmacological properties of T channels after injury. MPS was more effective in reducing T currents in normal versus injured RNs (24 and 20% reductions, respectively; P < 0.05), suggesting that pharmacological properties of T channels in the injured RNs may be different from those of the normal RNs.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8395574

Chung, J M; Huguenard, J R; Prince, D A

1993-07-01

219

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

220

Development and in vitro evaluation of slippery nanoparticles for enhanced diffusion through native mucus.  

PubMed

Aim: The aim of this study was to investigate the mucus-penetrating properties of neutral nanoparticles comprising poly(acrylic acid) (PAA) and poly(allylamine) (PAM). Materials & methods: PAA and PAM nanoparticles were prepared on the basis of ionic interactions between the two polymers. Nanoparticles were characterized by particle size as well as surface charge. The cytotoxicity was examined via resazurin and lactate dehydrogenase assays. Using a modified Ussing chamber with mucus, the diffusion properties of obtained neutral nanoparticles were compared with control particles. Results: The obtained PAA-PAM nanoparticles demonstrated no significant cytotoxicity and displayed smooth and spherical surfaces, a particle size range of 200 nm and ?-potential of 0.9 mV. The diffusion efficiency of neutral nanoparticles was 2.5- and 1.8-fold higher than PAM and PAA nanoparticles, respectively. Conclusion: Taking enhanced mucus-penetrating properties into account, neutral nanoparticles were shown to be very promising in drug delivery via mucus membranes of different cavities. Original submitted 30 May 2012; Revised submitted 21 November 2012; Published online 23 April 2013. PMID:23611618

Laffleur, Flavia; Hintzen, Fabian; Shahnaz, Gul; Rahmat, Deni; Leithner, Katharina; Bernkop-Schnürch, Andreas

2014-03-01

221

Dramatic performance enhancement of evanescent-wave multimode fiber fluorometer using non-Lambertian light diffuser.  

PubMed

To enhance the performance of an evanescent-wave (EW) based sensor, efforts are usually made to modify the sensor architecture rather than the excitation source. In this paper, we theoretically examine the role of meridian and skew rays under total internal reflection (TIR) as well as tunneling rays with the emphasis on sensor performance. Our further investigation indicates that the intensity profile of the light source enormously influences the EW power, and thus the collectable fluorescent emission level as well. A non-Lambertian fiber-optic side-emitting diffuser (FOSED) is proposed and experimentally verified, revealing that a proper alignment of this FOSED can dramatically improve the signal quality and reduce the level of stray excitation light. In particular, the adoption of a FOSED or other light diffusers with similar output profiles will ensure that the excitation power is used more efficiently, suggesting a lower demand on the excitation source power level, and the performance of the stray light filter and detector. The superiority of this innovation is further addressed by comparing it with a long period grating (LPG) fiber-optic sensor, which claims highly efficient core to cladding mode coupling. This study presents a new concept for the construction of a high-performance and cost-effective EW-based sensor system. PMID:19550936

Ma, Jianjun; Bock, Wojtek J

2007-12-10

222

Co-Transport of Polycyclic Aromatic Hydrocarbons by Motile Microorganisms Leads to Enhanced Mass Transfer under Diffusive Conditions.  

PubMed

The environmental chemodynamics of hydrophobic organic chemicals (HOCs) are often rate-limited by diffusion in stagnant boundary layers. This study investigated whether motile microorganisms can act as microbial carriers that enhance mass transfer of HOCs through diffusive boundary layers. A new experimental system was developed that allows (1) generation of concentration gradients of HOCs under the microscope, (2) exposure and direct observation of microorganisms in such gradients, and (3) quantification of HOC mass transfer. Silicone O-rings were integrated into a Dunn chemotaxis chamber to serve as sink and source for polycyclic aromatic hydrocarbons (PAHs). This resulted in stable concentration gradients in water (>24 h). Adding the model organism Tetrahymena pyriformis to the experimental system enhanced PAH mass transfer up to hundred-fold (benzo[a]pyrene). Increasing mass transfer enhancement with hydrophobicity indicated PAH co-transport with the motile organisms. Fluorescence microscopy confirmed such transport. The effective diffusivity of T. pyriformis, determined by video imaging microscopy, was found to exceed molecular diffusivities of the PAHs up to four-fold. Cell-bound PAH fractions were determined to range from 28% (naphthalene) to 92% (pyrene). Motile microorganisms can therefore function as effective carriers for HOCs under diffusive conditions and might significantly enhance mobility and availability of HOCs. PMID:24625194

Gilbert, Dorothea; Jakobsen, Hans H; Winding, Anne; Mayer, Philipp

2014-04-15

223

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

2014-06-01

224

Enhanced Self-Diffusion on Cu(111) by Trace Amounts of S: Chemical-Reaction-Limited Kinetics  

NASA Astrophysics Data System (ADS)

We find that less than 0.01 monolayer of S can enhance surface self-diffusion on Cu(111) by several orders of magnitude. The measured dependence of two-dimensional island decay rates on S coverage (?S) is consistent with the proposal that Cu3S3 clusters are responsible for the enhancement. Unexpectedly, the decay and ripening are diffusion limited with very low and very high ?S but not for intermediate ?S. To explain this result we propose that surface mass transport in the intermediate region is limited by the rate of reaction to form Cu3S3 clusters on the terraces.

Ling, W. L.; Bartelt, N. C.; Pohl, K.; de La Figuera, J.; Hwang, R. Q.; McCarty, K. F.

2004-10-01

225

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

226

Calcium transient evoked by TRPV1 activators is enhanced by tumor necrosis factor-? in rat pulmonary sensory neurons  

PubMed Central

TNF?, a proinflammatory cytokine known to be involved in the pathogenesis of allergic asthma, has been shown to induce hyperalgesia in somatic tissue via a sensitizing effect on dorsal root ganglion neurons expressing transient receptor potential vanilloid type 1 receptor (TRPV1). Because TRPV1-expressing pulmonary sensory neurons play an important role in regulating airway function, this study was carried out to determine whether TNF? alters the sensitivity of these neurons to chemical activators. Responses of isolated nodose and jugular ganglion neurons innervating the rat lungs were determined by measuring the transient increase in intracellular Ca2+ concentration ([Ca2+]i). Our results showed the following. 1) A pretreatment with TNF? (50 ng/ml) for ?24 h increased significantly the peak ?[Ca2+]i evoked by capsaicin (Cap) in these neurons. A pretreatment with the same concentration of TNF? for a longer duration (?48 h) did not further increase the response, but pretreatment for a shorter duration (1 h) or with a lower concentration (25 ng/ml, 24 h) failed to enhance the Cap sensitivity. 2) The same TNF? pretreatment also induced similar but less pronounced and less uniform increases in the responses to acid (pH 6.5–5.5), 2-aminoethoxydiphenyl borate (2-APB), a common activator of TRPV1, V2, and V3 channels, and allyl isothiocyanate (AITC), a selective activator of TRPA1 channel. 3) In sharp contrast, the responses to ATP, ACh, and KCl were not affected by TNF?. 4) The TNF?-induced hypersensitivity to Cap was not prevented by pretreatment with indomethacin (30 ?M). 5) The immunoreactivity to both TNF receptor types 1 and 2 were detected in rat vagal pulmonary sensory neurons. In conclusion, prolonged treatment with TNF? induces a pronounced potentiating effect on the responses of isolated pulmonary sensory neurons to TRPV1 activators. This action of TNF? may contribute in part to the airway hyperresponsiveness induced by this cytokine.

Hu, Youmin; Gu, Qihai; Lin, Ruei-Lung; Kryscio, Richard

2010-01-01

227

Structure enhancement diffusion and contour extraction for electron tomography of mitochondria.  

PubMed

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. PMID:19254765

Bazán, Carlos; Miller, Michelle; Blomgren, Peter

2009-05-01

228

Microstructural evolution in the partial transient liquid phase diffusion bonding of Zircaloy-4 to stainless steel 321 using active titanium filler metal  

NASA Astrophysics Data System (ADS)

Microstructural evolution of the partial transient liquid phase diffusion bonded Zircaloy-4 and stainless steel 321 using an active Ti-base interlayer were studied at different temperatures. Additionally, simple analytical models were developed to predict the evolution of the interlayer and intermetallics during the bonding operation. Bonds were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Precision measurement of the interlayer width was made as a function of the bonding temperature. The liquid film migration occurred as a result of chemical solubility differences between the stable and metastable phases. The formation and growth model of the intermetallic compounds at the interfaces of Zircaloy-4/Ti-base interlayer and stainless steel 321/Ti-base interlayer for controlling the bonding process was studied considering the diffusion kinetics and the thermodynamics. The evolution of the interlayer thickness indicated a good agreement between the calculation and experimental measurement. It was also demonstrated that the low isothermal solidification kinetic was not only due to the enrichment of the liquid phase with the base alloying elements such as Ti and Zr, but also the reduction of solid solubility limit of Cu in the base alloys contributed to the reduction of isothermal solidification kinetic.

Atabaki, M. Mazar

229

Optomechanical shutter modulated broad-band cavity-enhanced absorption spectroscopy of molecular transients of astrophysical interest.  

PubMed

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. PMID:23240889

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

2013-10-01

230

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

231

Electrostatic enhancement of diffusion-controlled protein-protein association: comparison of theory and experiment on barnase and barstar1  

Microsoft Academic Search

The electrostatic enhancement of the association rate of barnase and bar- star is calculated using a transition-state theory like expression and atomic-detail modeling of the protein molecules. This expression predicts that the rate enhancement is simply the average Boltzmann factor in the region of configurational space where association occurs instantaneously in the diffusion-controlled limit. Based on experimental evidence, this ''transition

M. Vijayakumar; Kwan-Yin Wong; Gideon Schreiber; Alan R. Fersht; Attila Szabo; Huan-Xiang Zhou

1998-01-01

232

Characteristics of Enhanced and Low Amplitude Anisotropic Wave Trains and Interplanetary Transients  

NASA Astrophysics Data System (ADS)

The occurrence of a large number of high and low amplitude anisotropic wave train events over the years 1981 1994 has been examined along with the different solar features. The results indicate that the time of maximum of diurnal variation significantly remains in the 18-h direction for majority of the high and low amplitude wave trains. The amplitude of diurnal anisotropy remains significantly high and phase shifts towards earlier hours as compared to the quite day annual average values for majority of the HAEs. The diurnal amplitude remains significantly low and phase shifts towards earlier hours as compared to the quiet day annual average values for majority of the LAEs. The occurrence of these enhanced/low amplitude events is found to be dominant during the positive polarity of the Bz component of the interplanetary magnetic field. The amplitude of the diurnal anisotropy of these events is found to increase on the days of magnetic cloud as compared to the days prior to the event and it found to decrease during the later period of the event as the cloud passes the Earth. The high-speed solar wind streams do not play any significant role in causing these types of events. The interplanetary disturbances (magnetic clouds) are also effective in producing cosmic ray decreases.

Mishra, Rajesh K.; Mishra, Rekha Agarwal

2006-09-01

233

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

PubMed Central

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 IC50 of 0.7??M. SSa effectively increased the amplitude of ITotal and IA, significantly negative-shifted the activation curve, and positive-shifted steady-state curve of IA. However, SSa induced no significant changes in the amplitude and activation curve of IK. 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 IA. These increases in IA may contribute to the anticonvulsant mechanisms of SSa.

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

2013-01-01

234

A stochastic model for induced seismicity based on non-linear pressure diffusion and irreversible permeability enhancement  

NASA Astrophysics Data System (ADS)

During deep reservoir engineering projects, in which permeability is enhanced by high-pressure fluid injection, seismicity is invariably induced, posing nuisance to the local population and a potential hazard for structures. Hazard and risk assessment tools that can operate in real-time during reservoir stimulation depend on the ability to efficiently model induced seismicity. We here propose a novel modelling approach based on a combination of physical considerations and stochastic elements. It can model a large number of synthetic event catalogues, and at the same time is constrained by observations of hydraulic behaviour in the injection well. We model fluid flow using non-linear pressure diffusion equations, in which permeability increases irreversibly above a prescribed pressure threshold. The transient pressure field is used to trigger events at so-called `seed points' that are distributed randomly in space and represent potential earthquake hypocentres. We assign to each seed point a differential stress based on the mean estimates of the in situ stress field and add a normal distributed random value. Assuming a fault orientation with respect to the stress field and a Mohr-Coulomb failure criterion, we evaluate at each time step, if a seed point is triggered through a pressure increase. A negative proportional relationship between differential stress and b values is further assumed as observed from tectonic earthquakes and in laboratory experiments. As soon as an event is triggered, we draw a random magnitude from a power-law distribution with a b value corresponding to the differential stress at the triggered seed point. We thus obtain time-dependent catalogues of seismic events including magnitude. The strategy of modelling flow and seismicity in a decoupled manner ensures efficiency and flexibility of the model. The model parameters are calibrated using observations from the Basel deep geothermal experiment in 2006. We are able to reproduce the hydraulic behaviour, the space-time evolution of the seismicity and its frequency-magnitude distribution. A large number of simulations of the calibrated model are then used to capture the variability of the process, an important input to compute probabilistic seismic hazard. We also use the calibrated model to explore alternative injection scenarios by varying injection volume, pressure as well as depth, and show the possible effect of those parameters on seismic hazard.

Gischig, Valentin S.; Wiemer, Stefan

2013-08-01

235

Mannitol enhances intracellular calcium diffusion in the rat ileum--a hypothesis.  

PubMed

The addition of 92 or 136 mM mannitol to a modified saline solution that contained 1.25 mM Ca2+ led to a mannitol concentration-dependent increase in the amount of calcium absorbed in 1 h from 8 cm long ileal loops prepared from fasted male Sprague-Dawley rats, with body weights of 190 +/- 10 g. It is argued that this mannitol-enhanced movement of calcium out of the loop cannot have utilized the paracellular pathway, inasmuch as the luminal calcium concentration of the mannitol instillate decreased during the experiment, with a negative calcium gradient between luminal and body fluids. Instead it is proposed that uncomplexed mannitol and the uncharged calcium complex of mannitol entered the ileal cells. The uncomplexed intracellular mannitol would bind additional calcium that had crossed the brush border down its gradient. The increase in total intracellular calcium will raise the effective intracellular gradient and thereby amplify intracellular calcium diffusion. This in turn increases calcium absorption. PMID:10737546

Escoffier, L; Grishina, O; Pansu, D; Bronner, F

2000-01-01

236

Calcium mobilization is required for peroxynitrite-mediated enhancement of spontaneous transient outward currents in arteriolar smooth muscle cells  

Microsoft Academic Search

Transiently local release of Ca2+ from the sarcoplasmic reticulum (SR) activates nearby Ca2+-activated K+ channels to produce spontaneous transient outward currents (STOCs) in smooth muscle cells. The purpose of the present study was to investigate the possible effect of peroxynitrite (ONOO?) on STOCs in mesenteric arteriolar smooth muscle cells (ASMCs) and decide whether Ca2+ mobilization was involved in STOCs alteration

Bing-xing Pan; Gui-ling Zhao; Xu-liang Huang; Ke-Zhao

2004-01-01

237

Transient Overexpression of ?-Ca2+/Calmodulin-Dependent Protein Kinase II in the Nucleus Accumbens Shell Enhances Behavioral Responding to Amphetamine  

PubMed Central

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is known to contribute to the expression of psychostimulant sensitization by regulating dopamine (DA) overflow from DA neuron terminals in the nucleus accumbens (NAcc). The present experiments explored the contribution of CaMKII in NAcc neurons postsynaptic to these terminals where it is known to participate in a number of signaling pathways that regulate responding to psychostimulant drugs. Exposure to amphetamine transiently increased ?CaMKII levels in the shell but not the core of the NAcc. Thus, HSV (herpes simplex viral) vectors were used to transiently overexpress ?CaMKII in NAcc neurons in drug-naive rats, and behavioral responding to amphetamine was assessed. Transiently overexpressing ?CaMKII in the NAcc shell led to long-lasting enhancement of amphetamine-induced locomotion and self-administration manifested when ?CaMKII levels were elevated and persisting long after they had returned to baseline. Enhanced locomotion was not observed after infection in the NAcc core or sites adjacent to the NAcc. Transient elevation of NAcc shell ?CaMKII levels also enhanced locomotor responding to NAcc AMPA and increased phosphorylation levels of GluR1 (Ser831), a CaMKII site, both soon and long after infection. Similar increases in pGluR1 (Ser831) were observed both soon and long after exposure to amphetamine. These results indicate that the transient increase in ?CaMKII observed in neurons of the NAcc shell after viral-mediated gene transfer and likely exposure to amphetamine leads to neuroadaptations in AMPA receptor signaling in this site that may contribute to the long-lasting maintenance of behavioral and incentive sensitization by psychostimulant drugs like amphetamine.

Loweth, Jessica A.; Singer, Bryan F.; Baker, Lorinda K.; Wilke, Georgia; Inamine, Hidetoshi; Bubula, Nancy; Alexander, John K.; Carlezon, William A.; Neve, Rachael L.; Vezina, Paul

2010-01-01

238

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

239

Enhanced diffusion of Uranium and Thorium linked to crystal plasticity in zircon  

PubMed Central

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° variation in crystallographic orientation that comprises both a gradual change in orientation and a series of discrete low-angle (<4°) 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.

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

2006-01-01

240

Transformation reactions of copper centers in the space-charge region of a copper-diffused silicon crystal measured by deep-level transient spectroscopy  

NASA Astrophysics Data System (ADS)

The transformation reactions of copper centers by annealing in Schottky electrode-formed (EL-formed) silicon crystals diffused with copper were measured by deep-level transient spectroscopy (DLTS) and the results were compared with those measured in samples without electrode (EL-free). The dissociation speeds of the dominant center (denoted as the CuDLB center) to the dissociation product (denoted as the CuDLA center) in the EL-formed samples were more than two orders faster than those in EL-free samples at respective annealing temperatures, although the dissociation energy of the former center was identical in both samples. An extended copper center, which was never observed in EL-free samples, was formed in the EL-formed samples at the cost of the CuDLA center. The origins of these specialties in the EL-formed samples were attributed to the actions of the electric field on the copper species in the space-charge region of the samples. The easy dissociation of the CuDLA center in the EL-formed samples was explained by the change in the charge state of the center in the space-charge region of the samples. From this analysis, the positively charged copper bonded at the bond center (CuBC+) was proposed as the most probable model for the CuDLA center.

Nakamura, Minoru; Murakami, Susumu; Udono, Haruhiko

2012-09-01

241

An anisotropic diffusion method for denoising dynamic susceptibility contrast-enhanced magnetic resonance images  

NASA Astrophysics Data System (ADS)

The purpose of this study was to present an application of a novel denoising technique for improving the accuracy of cerebral blood flow (CBF) images generated from dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI). The method presented in this study was based on anisotropic diffusion (AD). The usefulness of this method was firstly investigated using computer simulations. We applied this method to patient data acquired using a 1.5 T MR system. After a bolus injection of Gd-DTPA, we obtained 40-50 dynamic images with a 1.32-2.08 s time resolution in 4-6 slices. The dynamic images were processed using the AD method, and then the CBF images were generated using pixel-by-pixel deconvolution analysis. For comparison, the CBF images were also generated with or without processing the dynamic images using a median or Gaussian filter. In simulation studies, the standard deviation of the CBF values obtained after processing by the AD method was smaller than that of the CBF values obtained without any processing, while the mean value agreed well with the true CBF value. Although the median and Gaussian filters also reduced image noise, the mean CBF values were considerably underestimated compared with the true values. Clinical studies also suggested that the AD method was capable of reducing the image noise while preserving the quantitative accuracy of CBF images. In conclusion, the AD method appears useful for denoising DSC-MRI, which will make the CBF images generated from DSC-MRI more reliable.

Murase, Kenya; Yamazaki, Youichi; Shinohara, Masaaki; Kawakami, Kazunori; Kikuchi, Keiichi; Miki, Hitoshi; Mochizuki, Teruhito; Ikezoe, Junpei

2001-10-01

242

Diffusion-enhanced Förster resonance energy transfer and the effects of external quenchers and the donor quantum yield.  

PubMed

The structural and dynamic properties of a flexible peptidic chain codetermine its biological activity. These properties are imprinted in intrachain site-to-site distances as well as in diffusion coefficients of mutual site-to-site motion. Both distance distribution and diffusion determine the extent of Förster resonance energy transfer (FRET) between two chain sites labeled with a FRET donor and acceptor. Both could be obtained from time-resolved FRET measurements if their individual contributions to the FRET efficiency could be systematically varied. Because the FRET diffusion enhancement (FDE) depends on the donor-fluorescence lifetime, it has been proposed that the FDE can be reduced by shortening the donor lifetime through an external quencher. Benefiting from the high diffusion sensitivity of short-distance FRET, we tested this concept experimentally on a (Gly-Ser)(6) segment labeled with the donor/acceptor pair naphthylalanine/2,3-diazabicyclo[2.2.2]oct-2-ene (NAla/Dbo). Surprisingly, the very effective quencher potassium iodide (KI) had no effect at all on the average donor-acceptor distance, although the donor lifetime was shortened from ca. 36 ns in the absence of KI to ca. 3 ns in the presence of 30 mM KI. We show that the proposed approach had to fail because it is not the experimentally observed but the radiative donor lifetime that controls the FDE. Because of that, any FRET ensemble measurement can easily underestimate diffusion and might be misleading even if it employs the Haas-Steinberg diffusion equation (HSE). An extension of traditional FRET analysis allowed us to evaluate HSE simulations and to corroborate as well as generalize the experimental results. We demonstrate that diffusion-enhanced FRET depends on the radiative donor lifetime as it depends on the diffusion coefficient, a useful symmetry that can directly be applied to distinguish dynamic and structural effects of viscous cosolvents on the polymer chain. We demonstrate that the effective FRET rate and the recovered donor-acceptor distance depend on the quantum yield, most strongly in the absence of diffusion, which has to be accounted for in the interpretation of distance trends monitored by FRET. PMID:23215358

Jacob, Maik H; Dsouza, Roy N; Ghosh, Indrajit; Norouzy, Amir; Schwarzlose, Thomas; Nau, Werner M

2013-01-10

243

Diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) for monitoring anticancer therapy  

Microsoft Academic Search

There is an increasing awareness that anatomical approaches based on measurements of tumor size have significant limitations\\u000a for assessing therapy response. Functional imaging techniques are increasing being used to monitor response to therapies with\\u000a novel mechanisms of action, often predicting the success of therapy before conventional measurements have changed. Dynamic\\u000a contrast-enhanced and diffusion magnetic resonance imaging (MRI) are the most

Anwar R. Padhani; Aftab Alam Khan

2010-01-01

244

Mechanisms of doping-enhanced superlattice disordering and of gallium self-diffusion in GaAs  

Microsoft Academic Search

Recently available Ga-Al interdiffusion results in GaAs\\/AlAs superlattices allow us to conclude that Ga self-diffusion in GaAs is carried by triply negatively charged Ga vacancies under intrinsic and n-doping conditions. The mechanism of the Si-enhanced superlattice disordering is the Fermi-level effect which increases the concentrations of the charged point defect species. For the effect of the p dopants Be and

T. Y. Tan

1988-01-01

245

Validation of Diffusion Tensor Magnetic Resonance Axonal Fiber Imaging with Registered Manganese-Enhanced Optic Tracts  

Microsoft Academic Search

Noninvasive mapping of white matter tracts using diffusion tensor magnetic resonance imaging (DTMRI) is potentially useful in revealing anatomical connectivity in the human brain. However, a gold standard for validating DTMRI in defining axonal fiber orientation is still lacking. This study presents the first validation of the principal eigenvector of the diffusion tensor in defining axonal fiber orientation by superimposing

Ching-Po Lin; Wen-Yih Isaac Tseng; Hui-Cheng Cheng; Jyh-Horng Chen

2001-01-01

246

Super-resolution imaging of diffusing analyte in surface-enhanced Raman scattering hot-spots  

NASA Astrophysics Data System (ADS)

This paper describes recent efforts to characterize the diffusion of single molecule SERS analytes adsorbed to the surface of aggregated silver nanoparticles. Using a two-dimensional Gaussian function to fit the point spread function of a single diffraction-limited SERS emission image, the centroid of the emission can be located with precision better than 5nm. Tracking the centroid over time allows a diffusion trajectory to be constructed. By calculating the mean-r-squared displacement as a function of time lag, the diffusion properties of the SERS centroid can be tracked. For the single molecule SERS centroids presented herein, the diffusion analysis shows signatures of subdiffusion, indicating barriers to Brownian diffusion on the nanoparticle surface.

Willets, Katherine A.; Stranahan, Sarah M.

2012-02-01

247

Major mouse placental compartments revealed by diffusion-weighted MRI, contrast-enhanced MRI, and fluorescence imaging  

PubMed Central

Mammalian models, and mouse studies in particular, play a central role in our understanding of placental development. Magnetic resonance imaging (MRI) could be a valuable tool to further these studies, providing both structural and functional information. As fluid dynamics throughout the placenta are driven by a variety of flow and diffusion processes, diffusion-weighted MRI could enhance our understanding of the exchange properties of maternal and fetal blood pools—and thereby of placental function. These studies, however, have so far been hindered by the small sizes, the unavoidable motions, and the challenging air/water/fat heterogeneities, associated with mouse placental environments. The present study demonstrates that emerging methods based on the spatiotemporal encoding (SPEN) of the MRI information can robustly overcome these obstacles. Using SPEN MRI in combination with albumin-based contrast agents, we analyzed the diffusion behavior of developing placentas in a cohort of mice. These studies successfully discriminated the maternal from the fetal blood flows; the two orders of magnitude differences measured in these fluids’ apparent diffusion coefficients suggest a nearly free diffusion behavior for the former and a strong flow-based component for the latter. An intermediate behavior was observed by these methods for a third compartment that, based on maternal albumin endocytosis, was associated with trophoblastic cells in the interphase labyrinth. Structural features associated with these dynamic measurements were consistent with independent intravital and ex vivo fluorescence microscopy studies and are discussed within the context of the anatomy of developing mouse placentas.

Solomon, Eddy; Avni, Reut; Hadas, Ron; Raz, Tal; Garbow, Joel Richard; Bendel, Peter; Frydman, Lucio; Neeman, Michal

2014-01-01

248

Major mouse placental compartments revealed by diffusion-weighted MRI, contrast-enhanced MRI, and fluorescence imaging.  

PubMed

Mammalian models, and mouse studies in particular, play a central role in our understanding of placental development. Magnetic resonance imaging (MRI) could be a valuable tool to further these studies, providing both structural and functional information. As fluid dynamics throughout the placenta are driven by a variety of flow and diffusion processes, diffusion-weighted MRI could enhance our understanding of the exchange properties of maternal and fetal blood pools-and thereby of placental function. These studies, however, have so far been hindered by the small sizes, the unavoidable motions, and the challenging air/water/fat heterogeneities, associated with mouse placental environments. The present study demonstrates that emerging methods based on the spatiotemporal encoding (SPEN) of the MRI information can robustly overcome these obstacles. Using SPEN MRI in combination with albumin-based contrast agents, we analyzed the diffusion behavior of developing placentas in a cohort of mice. These studies successfully discriminated the maternal from the fetal blood flows; the two orders of magnitude differences measured in these fluids' apparent diffusion coefficients suggest a nearly free diffusion behavior for the former and a strong flow-based component for the latter. An intermediate behavior was observed by these methods for a third compartment that, based on maternal albumin endocytosis, was associated with trophoblastic cells in the interphase labyrinth. Structural features associated with these dynamic measurements were consistent with independent intravital and ex vivo fluorescence microscopy studies and are discussed within the context of the anatomy of developing mouse placentas. PMID:24969421

Solomon, Eddy; Avni, Reut; Hadas, Ron; Raz, Tal; Garbow, Joel Richard; Bendel, Peter; Frydman, Lucio; Neeman, Michal

2014-07-15

249

Investigation of radiation enhanced diffusion of magnesium in substrates flown on the NASA genesis mission.  

SciTech Connect

The thermal diffusion of an Mg implant in Si has been measured with SIMS and compared to RIMS (resonant ionisation mass spectrometry) measurements of Mg implantation and diffusion in Si wafers exposed to solar wind irradiation in the NASA Genesis mission. The Genesis samples show much more surface segregation that the samples annealed in the laboratory, due to diffusion and segregation of the implanted Mg to the heavily damaged near surface regions of the Genesis wafers. This Mg transport has been modeled by solving a set of stiff differential equations and found to agree with RIMS measurements for a Mg interstitial migration energy of 0.7 eV.

King, B. V.; Pellin, M. J.; Burnett, D. S. (Materials Science Division); (Univ. of Newcastle); (California Inst. of Tech.)

2008-12-01

250

Convection-enhanced delivery of topotecan into diffuse intrinsic brainstem tumors in children.  

PubMed

Convection-enhanced delivery (CED) for the treatment of malignant gliomas is a technique that can deliver chemotherapeutic agents directly into the tumor and the surrounding interstitium through sustained, low-grade positive-pressure infusion. This allows for high local concentrations of drug within the tumor while minimizing systemic levels that often lead to dose-limiting toxicity. Diffuse intrinsic pontine gliomas (DIPGs) are universally fatal childhood tumors for which there is currently no effective treatment. In this report the authors describe CED of the topoisomerase inhibitor topotecan for the treatment of DIPG in 2 children. As part of a pilot feasibility study, the authors treated 2 pediatric patients with DIPG. Stereotactic biopsy with frozen section confirmation of glial tumor was followed by placement of bilateral catheters for CED of topotecan during the same procedure. The first patient underwent CED 210 days after initial diagnosis, after radiation therapy and at the time of tumor recurrence, with a total dose of 0.403 mg in 6.04 ml over 100 hours. Her Karnofsky Performance Status (KPS) score was 60 before CED and 50 posttreatment. Serial MRI initially demonstrated a modest reduction in tumor size and edema, but the tumor progressed and the patient died 49 days after treatment. The second patient was treated 24 days after the initial diagnosis prior to radiation with a total dose of 0.284 mg in 5.30 ml over 100 hours. Her KPS score was 70 before CED and 50 posttreatment. Serial MRI similarly demonstrated an initial modest reduction in tumor size. The patient subsequently underwent fractionated radiation therapy, but the tumor progressed and she died 120 days after treatment. Topotecan delivered by prolonged CED into the brainstem in children with DIPG is technically feasible. In both patients, high infusion rates (> 0.12 ml/hr) and high infusion volumes (> 2.8 ml) resulted in new neurological deficits and reduction in the KPS score, but lower infusion rates (< 0.04 ml/hr) were well tolerated. While serial MRI showed moderate treatment effect, CED did not prolong survival in these 2 patients. More studies are needed to improve patient selection and determine the optimal flow rates for CED of chemotherapeutic agents into DIPG to maximize safety and efficacy. Clinical trial registration no.: NCT00324844. PMID:23240851

Anderson, Richard C E; Kennedy, Benjamin; Yanes, Candix L; Garvin, James; Needle, Michael; Canoll, Peter; Feldstein, Neil A; Bruce, Jeffrey N

2013-03-01

251

Control of diffuser jet flow: turbulent kinetic energy and jet spreading enhancements assisted by a non-thermal plasma discharge  

NASA Astrophysics Data System (ADS)

An axisymmetric air jet exhausting from a 22-degree-angle diffuser is investigated experimentally by particle image velocimetry (PIV) and stereo-PIV measurements. Two opposite dielectric barrier discharge (DBD) actuators are placed along the lips of the diffuser in order to force the mixing by a co-flow actuation. The electrohydrodynamic forces generated by both actuators modify and excite the turbulent shear layer at the diffuser jet exit. Primary air jet velocities from 10 to 40 m/s are studied (Reynolds numbers ranging from 3.2 to 12.8 × 104), and baseline and forced flows are compared by analysing streamwise and cross-stream PIV fields. The mixing enhancement in the near field region is characterized by the potential core length, the centreline turbulent kinetic energy (TKE), the integrated value of the TKE over various slices along the jet, the turbulent Reynolds stresses and the vorticity fields. The time-averaged fields demonstrate that an effective increase in mixing is achieved by a forced flow reattachment along the wall of the diffuser at 10 m/s, whereas mixing enhancement is realized by excitation of the coherent structures for a primary velocity of 20 and 30 m/s. The actuation introduces two pairs of contra-rotating vortices above each actuator. These structures entrain the higher speed core fluid toward the ambient air. Unsteady actuations over Strouhal numbers ranging from 0.08 to 1 are also studied. The results suggest that the excitation at a Strouhal number around 0.3 is more effective to enhance the turbulence kinetic energy in the near-field region for primary jet velocity up to 30 m/s.

Benard, N.; Balcon, N.; Touchard, G.; Moreau, E.

2008-08-01

252

Kinetics of diffusion-mediated drug release enhanced by matrix degradation  

Microsoft Academic Search

Modified diffusion equations with a time-dependent diffusion coefficient were derived to formulate the kinetics of drug release from a quickly degradable matrix. To compare the theoretical equations with experimental observation, microspheres containing aclarubicin hydrochloride (ACR) were prepared by the solvent evaporation method using dl-lactic acid (LA) oligomers with different weight-average molecular weights ranging from 1,900 to 9,600. ACR release profiles

Ryoichi Wada; Suong-Hyu Hyon; Yoshito Ikada

1995-01-01

253

Enhancing the critical current properties of internal Mg diffusion-processed MgB2 wires by Mg addition  

NASA Astrophysics Data System (ADS)

The internal Mg diffusion (IMD) process produces a high-density MgB2 layer with high critical current properties, which makes it an attractive and promising method for fabricating MgB2 wires. We have obtained high critical current properties in our previous research. However, IMD-processed MgB2 wires can have unreacted B particles remain in the reacted layer due to the long Mg diffusion distance in the B layer during heat treatment. A reduction in the amount of unreacted B particles is expected to enhance the critical current properties. In this study, we attempted to disperse Mg powder in the B layer as an additive in order to decrease the Mg diffusion distance. We found that a 6 mol% Mg powder addition to a B layer drastically decreased the amount of unreacted B particles and enhanced the critical current density to twice the value for IMD-processed MgB2 wire with no Mg powder added. An analysis is presented that relates the microstructure to the critical current density.

Ye, S. J.; Song, M.; Matsumoto, A.; Togano, K.; Zhang, Y.; Kumakura, H.; Takeguchi, M.; Teranishi, R.; Kiyoshi, T.

2012-12-01

254

Thaumatin Crystallization Aboard the International Space Station Using Liquid-Liquid Diffusion in the Enhanced Gaseous Nitrogen Dewar (EGN)  

NASA Technical Reports Server (NTRS)

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 -196 C to 0 C in about four days, about the same time it took to warm from 0 C to 20 C. The temperature within the EGN was 20 - 24 C 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 Angstroms, comparable to previous studies of space-grown thaumatin crystals. The resolution of the best ground control crystal was only 1.47 Angstroms. It is not clear if the difference in diffraction limit is due to factors other than crystal size. Improvements in temperature control and the elimination of air gaps are needed, but the results show that EGN on the ISS can be used to produce space grown crystals that diffract to high resolution.

Kundrot, Craig; Barnes, Cindy L.; Snell, Edward H.; Stinson, Thomas N. (Technical Monitor)

2002-01-01

255

Determination of Si self-interstitial diffusivities from the oxidation-enhanced diffusion in B doping-superlattices: The influence of the marker layers  

Microsoft Academic Search

Si self-interstitial diffusivities can be extracted from the diffusive behavior of certain metals (e.g., Au) in an inert annealing ambient or from the diffusion of dopant markers (typically B) under oxidizing conditions. Each type of experiment yields fairly consistent results; however, interstitial diffusivities obtained in these two ways differ greatly. The marker layer experiments rely on the assumption that the

H.-J. Gossmann; G. H. Gilmer; C. S. Rafferty; F. C. Unterwald; T. Boone; J. M. Poate; H. S. Luftman; W. Frank

1995-01-01

256

Stator Diffusion Enhancement Using a Re-Circulating Co-Flowing Steady Jet (Postprint).  

National Technical Information Service (NTIS)

This paper outlines a steady flow control technique that augments the diffusion process within a stator passage via a continuous co-flowing secondary flow stream along the suction surface. The technique is similar to that used for flow vectoring in nozzle...

D. Carr G. Zha J. Estevadeordal N. J. Kuprowicz W. Copenhaver

2004-01-01

257

Study in Reservoir Conditions of Diffusion and Dispersion During Miscible Gas Injection for Enhanced Oil Recovery.  

National Technical Information Service (NTIS)

The experimental study on diffusion, in reservoir conditions was carried out both without a porous medium and with a porous medium. The approach was progressive;first binary mixtures (C/sub 1/ -C/sub 10/) to check our methods, then ternary mixtures (C/sub...

D. Hadiatno

1986-01-01

258

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

259

Diffusion-weighted and dynamic contrast-enhanced imaging as markers of clinical behavior in children with optic pathway glioma  

PubMed Central

Background Optic pathway gliomas (OPGs) are common pediatric brain tumors that pose significant clinical challenges with regard to predicting which tumors are likely to become symptomatic and require treatment. These tumors can arise sporadically or in the context of the inherited cancer predisposition syndrome, Neurofibromatosis type 1 (NF1). Few studies have suggested biological or imaging markers which predict the clinical course of this disease. Objective In this cross-sectional study, we hypothesize that the clinical behavior of OPGs in children can be differentiated by diffusion-weighted (DWI) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI). Methods 27 patients with OPG were studied using DWI and DCE MRI protocols. Diffusivity and permeability were calculated and correlated to OPG clinical behavior. Results Mean diffusivity values of 1.39 ?m2/ms and mean permeability values of 2.10 ml min?1 per 100 cc of tissue were measured. “Clinically-aggressive” OPGs had significantly higher mean permeability values (P=.05) than “clinically stable” tumors. In addition, there was a strong correlation between clinical aggressiveness and the absence of NF1 (P < 0.01). Conclusion These results suggest that DCE might be a useful biomarker for “clinically aggressive” OPG, which should be confirmed in larger prospective longitudinal studies.

Jost, Sarah C.; Ackerman, Joseph W.; Garbow, Joel R.; Manwaring, Linda P.; Gutmann, David H.; McKinstry, Robert C.

2013-01-01

260

Using high-Tc superconducting resonator for enhancement of diffusion tensor imaging  

Microsoft Academic Search

Here, a report on diffusion tensor imaging (DTI) using a 125.3 MHz high-temperature superconducting (HTS) surface resonator for magnetic resonance imaging (MRI) is presented. A 40 mm in diameter Bi2Sr2Ca2Cu3Ox (Bi-2223) tape surface resonator was built. Using a HTS surface resonator at 77 K than a similar copper surface resonator at 300 K, the capacity to save the accuracy of

In-Tsang Lin; Hong-Chang Yang; Jyh-Horng Chen

2011-01-01

261

Enhanced accuracy of single-molecule diffusion measurements with a photocleavable energy-transfer dyad.  

PubMed

A photocleavable energy-transfer dyad was synthesized, characterized, and applied to single-molecule fluorescence microscopy. After photocleavage, a combination of independent two-color single-molecule tracking and analysis of single-molecule energy-transfer efficiencies allows the determination of the temporal evolution of the relative distances between both fragments from the nm to the ?m scale. This gives access to a broad range of diffusion coefficients. PMID:24222580

Dill, Maren; Baier, Moritz C; Mecking, Stefan; Wöll, Dominik

2013-11-18

262

Enhanced structural correlations accelerate diffusion in charge-stabilized colloidal suspensions.  

PubMed

Theoretical calculations for colloidal charge-stabilized suspensions and hard-sphere suspensions show that hydrodynamic interactions yield a qualitatively different particle concentration dependence of the short-time self-diffusion coefficient. The effect, however, is numerically small and hardly accessible by conventional light-scattering experiments. By applying multiple-scattering decorrelation equipment and a careful data analysis we show that the theoretical prediction for charged particles is in agreement with our experimental results from aqueous polystyrene latex suspensions. PMID:11969984

Overbeck, E; Sinn, C; Watzlawek, M

1999-08-01

263

Vacancy enhancement of diffusion after quenching and during irradiation in silver-zinc alloys  

Microsoft Academic Search

Quenching and annealing experiments were performed on silver-zinc alloys with 8.14 and 30 at.%Zn. From the changes of the electrical resistivity due to an increase of the degree of short-range order, the activation energy of self-diffusion was determined to be QSD=1.60 and QSD=1.38 eV for both alloys, respectively. For the migration energy of vacancies, a value EVM=0.64 eV was found

W. Schule

1980-01-01

264

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

Microsoft Academic Search

The off-resonance rotating frame technique based on the spin relaxation properties of off-resonance T1? 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 T1?-weighted images is limited by the water diffusion-exchange between mesoscopic scale compartments. An experimental investigation of the effect of water

Huiming Zhang; Yang Xie; Tongyu Ji

2007-01-01

265

Experimental Assessment and Enhancement of Planar Laser-Induced Fluorescence Measurements of Nitric Oxide in an Inverse Diffusion Flame  

NASA Technical Reports Server (NTRS)

We have experimentally assessed the quantitative nature of planar laser-induced fluorescence (PLIF) measurements of NO concentration in a unique atmospheric pressure, laminar, axial inverse diffusion flame (IDF). The PLIF measurements were assessed relative to a two-dimensional array of separate laser saturated fluorescence (LSF) measurements. We demonstrated and evaluated several experimentally-based procedures for enhancing the quantitative nature of PLIF concentration images. Because these experimentally-based PLIF correction schemes require only the ability to make PLIF and LSF measurements, they produce a more broadly applicable PLIF diagnostic compared to numerically-based correction schemes. We experimentally assessed the influence of interferences on both narrow-band and broad-band fluorescence measurements at atmospheric and high pressures. Optimum excitation and detection schemes were determined for the LSF and PLIF measurements. Single-input and multiple-input, experimentally-based PLIF enhancement procedures were developed for application in test environments with both negligible and significant quench-dependent error gradients. Each experimentally-based procedure provides an enhancement of approximately 50% in the quantitative nature of the PLIF measurements, and results in concentration images nominally as quantitative as LSF point measurements. These correction procedures can be applied to other species, including radicals, for which no experimental data are available from which to implement numerically-based PLIF enhancement procedures.

Partridge, William P.; Laurendeau, Normand M.

1997-01-01

266

Enhanced near band edge luminescence of Ti/ZnO nanorod heterostructures due to the surface diffusion of Ti.  

PubMed

Information on the mechanistic differences in the luminescence properties of Ti/ZnO nanorods (NRs) has been obtained through the preparation of heterostructures by (a) varying the thickness of Ti from 1 nm to 20 nm keeping the substrate temperature at 400 °C, (b) varying the substrate temperature from room temperature (RT) to 500 °C while keeping the metal thickness constant at 10 nm and (c) annealing the RT Ti sputtered NRs at temperatures of 400 °C and 500 °C. The photoluminescence (PL) spectra show that the near band edge luminescence of ZnO in the ultraviolet (UV) region is enhanced as the thickness of Ti increases up to 5 nm and, thereafter, it falls. Sputtering of Ti on ZnO NRs at RT does not cause any UV enhancement but when sputtered at and above 400 °C, the UV intensity is enhanced. Annealing of RT Ti sputtered NRs at and above 400 °C also results in the enhancement of the UV peak, although with a lesser magnitude. Analysis of the PL results, supported by X-ray diffraction, field emission scanning electron microscopy, elemental mapping, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy and electrical I-V measurement results, show a clear indication that the surface diffusion of Ti causes a reduction in the surface defects. PMID:21931902

Mahanti, Moumita; Ghosh, Tushar; Basak, Durga

2011-10-01

267

New multiscale speckle suppression and edge enhancement with nonlinear diffusion and homomorphic filtering for medical ultrasound imaging  

NASA Astrophysics Data System (ADS)

Speckle, shown as a granular pattern, considerably degrades the image quality of ultrasound B-mode imaging and lowers the performance of image segmentation and registration techniques. Thus, speckle reduction while preserving the tissue structure (e.g., edges and boundaries of lesions) is important for ultrasound B-mode imaging. In this paper, a new approach for speckle reduction and edge enhancement based on laplacian pyramid nonlinear diffusion and homomorphic filtering (LPNDHF) is proposed for ultrasound B-mode imaging. In LPNDHF, nonlinear diffusion with a weighting factor is applied in multi-scale domain (i.e., laplacian pyramid) for effectively suppressing the speckle. In addition, in order to overcome the drawback from the previous LPND method, i.e., blurred edges, homomorphic filtering for edge and contrast enhancement is also applied from a finer scale to a coarser scale. From the simulation study, the proposed LPNDHF method showed the higher edge preservation and structure similarity values compared to the LPND and LPND with shock filtering (LPNDSF). Also, the LPNDHF provided the higher CNR values compared to LPND and LPNDSF, i.e., 5.02 vs. 3.66 and 2.91, respectively. From the tissue mimicking phantom study, the similar improvement in CNR was achieved from the LPNDHF over LPND and LPNDSF, i.e., 2.35 vs. 1.83 and 1.30. Moreover, the consistent results were obtained with the in vivo abdominal study. These preliminary results demonstrate that the proposed LPNDHF can improve the image quality of ultrasound B-mode imaging by increasing contrast and enhancing the specific signal details while effectively suppressing speckle.

Kang, Jinbum; Yoo, Yangmo

2014-03-01

268

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

SciTech Connect

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. -- Highlights: ? Role of TRPA1 activation was revealed in a mouse model of skin sensitization to FITC. ? TRPA1 agonists enhanced skin sensitization as well as dendritic cell trafficking. ? Dibutyl phthalate (DBP) has been shown to enhance skin sensitization to FITC. ? TRPA1 activation by DBP was inhibited by a selective antagonist, HC-030031. ? HC-030031 inhibited the enhancing effect of DBP on skin sensitization to FITC.

Shiba, Takahiro; Tamai, Takuma; Sahara, Yurina; Kurohane, Kohta [Laboratory of Microbiology and Immunology, School of Pharmaceutical Sciences, University of Shizuoka, 52?1 Yada, Suruga-ku, Shizuoka City, Shizuoka 422?8526 (Japan)] [Laboratory of Microbiology and Immunology, School of Pharmaceutical Sciences, University of Shizuoka, 52?1 Yada, Suruga-ku, Shizuoka City, Shizuoka 422?8526 (Japan); Watanabe, Tatsuo [Laboratory of Food Chemistry, School of Food and Nutritional Sciences, University of Shizuoka, 52?1 Yada, Suruga-ku, Shizuoka City, Shizuoka 422?8526 (Japan)] [Laboratory of Food Chemistry, School of Food and Nutritional Sciences, University of Shizuoka, 52?1 Yada, Suruga-ku, Shizuoka City, Shizuoka 422?8526 (Japan); Imai, Yasuyuki, E-mail: imai@u-shizuoka-ken.ac.jp [Laboratory of Microbiology and Immunology, School of Pharmaceutical Sciences, University of Shizuoka, 52?1 Yada, Suruga-ku, Shizuoka City, Shizuoka 422?8526 (Japan)] [Laboratory of Microbiology and Immunology, School of Pharmaceutical Sciences, University of Shizuoka, 52?1 Yada, Suruga-ku, Shizuoka City, Shizuoka 422?8526 (Japan)

2012-11-01

269

EXPERIMENTAL AND NUMERICAL STUDIES OF OPPOSED JET OXYGEN-ENHANCED METHANE DIFFUSION FLAMES  

Microsoft Academic Search

Planar oxygen-enhanced methane counterflow flames are investigated by optical diagnostics and numerical simulation. The major species concentrations and temperature measured from Raman scattering are compared to the detailed simulations of the flame formed between two opposed jets. The effect of stretch and the influence of oxygen concentration in the oxidizer on the flame structure are studied for nitrogen-diluted methane fuel

ZHONGXIAN CHENG; JOSEPH A. WEHRMEYER; ROBERT W. PITZ

2006-01-01

270

Using high-Tc superconducting resonator for enhancement of diffusion tensor imaging  

NASA Astrophysics Data System (ADS)

Here, a report on diffusion tensor imaging (DTI) using a 125.3 MHz high-temperature superconducting (HTS) surface resonator for magnetic resonance imaging (MRI) is presented. A 40 mm in diameter Bi2Sr2Ca2Cu3Ox (Bi-2223) tape surface resonator was built. Using a HTS surface resonator at 77 K than a similar copper surface resonator at 300 K, the capacity to save the accuracy of DTI in a reduced scan time (11 min) was demonstrated. The standard deviation of deviation angles of DTI fiber tracking was also improved by 2.5 gains. The use of HTS surface resonator may improve the reliability of fiber tracking experiments.

Lin, In-Tsang; Yang, Hong-Chang; Chen, Jyh-Horng

2011-06-01

271

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

272

Dislocation Enhancement of Seismic-Frequency Attenuation: Subgrain Boundary Diffusion and Triggered, Critical Emission of Dislocations  

NASA Astrophysics Data System (ADS)

Combined compressional creep and (Young's-modulus) attenuation experiments on polycrystalline ice-I (200 ? T[K] ? 260; 3 ? d[?m] ? 500; ?mean = 1MPa and ?? = 0.16MPa applied in a frequency range 10-4 ? ?[Hz] ? 10-1) demonstrate the attenuation behavior associated with the seismic attenuation band and the "high-temperature background," i.e., a power-law response Q-1 ? ?-m with m ~ 0.33. This response has, in general, been associated with grain boundary sliding rate-limited by atomic diffusion [e.g., 1-3], a mechanism that is very sensitive to grain size. In our experiments, however, with a grain size variation ~102, the attenuation response is independent of grain size, to first order. Scrutiny of the physics suggests that the attenuation is effected primarily by diffusive relaxation of subgrain boundaries [4, 5], the size of which, in materials deforming by a dislocation mechanism (as is the ice in our experiments), is set by the deviatoric stress [6, 7]. Applying the diffusion-effected physics to the subgrain size matches the universal scaling [e.g., 3] for materials that are linear-viscoelastic. Our ice specimens, however, demonstrate modest non-linearity, resulting in greater attenuation than that associated with the diffusion process [cf. 8] and yet retain the power-law form for attenuation, including the same slope m. The result is consistent with "self-organized critical" behavior in dislocation emission [9, 10] and the physics overall can be understood via models of self-similar scaling of crystalline (effective) viscosity [e.g., 11]. The potential application to seismic studies is profound: for example, if the upper mantle of Earth is convecting via a dislocation-creep or dislocation-accommodated grain-boundary-sliding mechanism, then the attenuation response is related not to the grain size, but rather to the subgrain structure associated with the creep of the rock. Thus, seismic attenuation measurements may well be useful for interpreting flow behavior in the mantle. [1] T.T. Gribb and R.F. Cooper, J. Geophys. Res. 103, doi:10.1029/98JB02786 (1998). [2] I. Jackson and U.H. Faul, Phys. Earth Planet. Inter. 183, doi:10.1016/j.pepi.2010.09.005 (2010). [3] C. McCarthy et al., J. Geophys. Res. 116, doi:10.1029/2011JB008384 (2011). [4] D.S. Stone et al., J. Geophys. Res. 109, doi:10.1029/2004JB003064 (2004). [5] Y. Gueguen et al., Phys. Earth Planet. Interior. 55, 254-258 (1989). [6] R.J. Twiss, Pure Appl. Geophys. 115, 227-244 (1977). [7] S.V. Raj and G.M. Pharr, Mater. Sci. Engr. 81, 217-237 (1986). [8] R.J.M. Farla et al., Science 336, 332-335 (2012). [9] T. Richeton et al., Nature Mater. 4, 465-469 (2005). [10] J. Puthoff, M.Sc. Thesis, University of Wisconsin-Madison (2005). [11] D.S. Stone, Acta Metall. Mater. 31, 599-608 (1991).

Cooper, R. F.; McCarthy, C.

2012-12-01

273

Coercivity enhancement of Nd-Fe-B sintered magnets by grain boundary modification via reduction-diffusion process  

NASA Astrophysics Data System (ADS)

The interface between the Nd2Fe14B particles and the grain boundary surrounding them in Nd-Fe-B sintered magnets was modified by diffusion Dy metal selectively through the grain boundary involving the reduction of Dy2O3 or DyF3 with CaH2 and the coercivity of them was effectively enhanced from 0.98 MA/m to 1.42 MA/m with keeping the high value of remanence. The resultant coercivity was higher than that of the magnets modified with Dy2O3 (HcJ = 1.10 MA/m) and DyF3 (HcJ = 1.24 MA/m) without using any reductant such as CaH2, respectively.

Li, D. S.; Nishimoto, M.; Suzuki, S.; Nishiyama, K.; Itoh, M.; Machida, K.

2009-02-01

274

Deposition of SiO2 by Plasma Enhanced Chemical Vapor Deposition as the Diffusion Barrier to Polymer Substrates  

NASA Astrophysics Data System (ADS)

SiO2 thin films were deposited at the temperatures <150°C by plasma enhanced chemical vapor deposition (PECVD) using a tetraethylorthosilicate (TEOS)/N2/O2 gas mixture, and the physical and chemical characteristics as well as the characteristics as a transparent diffusion barrier to H2O were investigated. Using a gas combination of TEOS(40 sccm)/O2(500 sccm)/N2(100 sccm) at source power of 500 W and dc bias voltage of -350 V, SiO2 with a stoichometric composition of SiO2 and a smooth surface similar to the substrate could be deposited. When a multilayer diffusion barrier composed of parylene(800 nm)/SiO2(100 nm)/parylene(800 nm)/SiO2(100 nm)/parylene(800 nm) was formed on a polyethersulfone (PES) substrate, the water vapor transmission rate (WVTR) of the substrate was decreased from 54.1 to 0.3 gm/(m2\\cdotday).

Jeong, Chang Hyun; Lee, June Hee; Lim, Jong Tae; Cho, Nam Gil; Moon, Cheol Hee; Yeom, Geun Young

2005-02-01

275

Fabrication and evaluation of enhanced diffusion bonded titanium honeycomb core sandwich panels with titanium aluminide face sheets  

NASA Technical Reports Server (NTRS)

A joining process was developed for fabricating lightweight, high temperature sandwich panels for aerospace applications using Ti-14Al-21Nb face sheets and Ti-3Al-2.5V honeycomb core. The process, termed Enhanced Diffusion Bonding (EDB), relies on the formation of a eutectic liquid through solid-state diffusion at elevated temperatures and isothermal solidification to produce joints in thin-gage titanium and titanium aluminide structural components. A technique employing a maskant on the honeycomb core was developed which permitted electroplating a controlled amount of EDB material only on the edges of the honeycomb core in order to minimize the structural weight and metallurgical interaction effects. Metallurgical analyses were conducted to determine the interaction effects between the EDB materials and the constituents of the sandwich structure following EDB processing. The initial mechanical evaluation was conducted with butt joint specimens tested at temperatures from 1400 - 1700 F. Further mechanical evaluation was conducted with EDB sandwich specimens using flatwise tension tests at temperatures from 70 - 1100 F and edgewise compression tests at ambient temperature.

Hoffmann, E. K.; Bird, R. K.; Bales, T. T.

1989-01-01

276

Evaluation of patients with diffuse unilateral subacute neuroretinitis by spectral domain optical coherence tomography with enhanced depth imaging  

PubMed Central

Background The purpose of this study was to determine the value of spectral domain optical coherence tomography (SD-OCT) in assessing patients with diffuse unilateral subacute neuroretinitis (DUSN). Methods This was an observational case series with clinical imaging correlation performed at the Retina and Vitreous Institute of Londrina and State University of Londrina, Paraná, Brazil. The series comprised ten consecutive patients with a confirmed diagnosis of DUSN, ie, seven patients with late-stage disease and three with early-stage disease, who were assessed by SD-OCT for mean macular, retinal nerve fiber layer, and choroidal thickness using enhanced depth imaging software. Results Comparing the affected eye with the healthy fellow eye, significant diffuse atrophy of the retinal layers with a decrease in mean macular (P=0.004) and retinal nerve fiber layer (P=0.002) thickness was found in all cases. There was no difference in choroidal thickness (P=0.262). Conclusion The correlation of SD-OCT results with central vision and funduscopic findings may explain the profound loss of visual function in patients with DUSN.

Berbel, Rodrigo F; Casella, Antonio Marcelo B; de Souza, Eduardo C; Farah, Michel E

2014-01-01

277

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

NASA Astrophysics Data System (ADS)

Organic photovoltaic cells (OPVs) have the potential to become a low-cost source of renewable energy due to their compatibility with high throughput processing techniques and the demonstration of power conversion efficiencies exceeding 10%. In the simplest planar heterojunction OPVs, photoconversion is limited by a short exciton diffusion length (LD) that restricts migration to the dissociating electron donor-acceptor (D-A) 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 alternate approach that seeks to directly engineer LD by optimizing the intermolecular separation and consequently, the photophysical parameters responsible for excitonic energy transfer. By diluting the electron donor boron subphthalocyanine chloride (SubPc) into a wide energy gap host material, we optimize the degree of interaction between donor molecules and observe a nearly 50% increase in LD. Using this approach, we construct planar heterojunction OPVs with a power conversion efficiency of 4.4%, 30% larger than the case of optimized devices containing an undiluted donor layer. It is worth noting that this efficiency also rivals those realized in optimized, bulk heterojunction OPVs based on SubPc and C60. The underlying correlation between LD and the degree of molecular interaction has wide implications for the design of both OPV active materials and device architectures.

Holmes, Russell J.

2013-03-01

278

Characterization of transferrin metal-binding sites by diffusion-enhanced energy transfer.  

PubMed

The distance from the protein surface to ferric or manganic ions in the two specific metal-binding sites of human serum transferrin has been estimated by measuring energy transfer from freely diffusing terbium chelaters in aqueous solution to transferrin-bound metal ions. In addition, both monoferric forms of the protein were studied, as well as the diferric complex formed by using oxalate instead of (bi)carbonate as the auxiliary anion in binding of iron(III) to transferrin. Second-order rate constants for energy transfer between electrically neutral terbium(III)--N-(2-hydroxy-ethyl)ethylenediaminetriacetate and the FeA, FeB, and Fe2 forms of transferrin were 0.9 X 10(5) M-1 S-1, 1.4 X 10(5) M-1 S-1, and 2.6 X 10(5) M-1 S-1, respectively (based on iron concentraton). For the Fe2 species, substitution of oxalate for (bi)carbonate has the effect of decreasing the accessibility of both electrically neutral and negatively charged terbium chelates to the protein-bound iron chromophores. Theoretical considerations of the effect of acceptor location in the protein on energy transfer suggest that the iron chromophores are not on the surface of the protein but are less than 1.7 nm below the surface. The use of diterbium transferrin as energy donor to a small cobalt chelate in solution or to diferric transferrin corroborates these results. PMID:6779862

Yeh, S M; Meares, C F

1980-10-28

279

Stress-induced Switch in Numb Isoforms Enhances Notch-dependent Expression of Subtype-specific Transient Receptor Potential Channel*  

PubMed Central

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.

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

2010-01-01

280

Transient Photoreceptor Deconstruction by CNTF Enhances rAAV-Mediated Cone Functional Rescue in Late Stage CNGB3-Achromatopsia  

PubMed Central

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.

Komaromy, Andras 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

2013-01-01

281

Interaction with Dopamine D2 Receptor Enhances Expression of Transient Receptor Potential Channel 1 at the Cell Surface  

PubMed Central

Receptor signaling is mediated by direct protein interaction with various types of cytoskeletal, adapter, effector, and additional receptor molecules. In brain tissue and in cultured neurons, activation of dopamine D2 receptors (D2Rs) has been found to impact cellular calcium signaling. Using a yeast two-hybrid approach, we have uncovered a direct physical interaction between the D2R and the transient receptor potential channel (TRPC) subtypes 1, 4 and 5. The TRPC/D2R interaction was further validated by GST-pulldown assays and coimmunoprecipitation from mammalian brain. Ultrastructural analysis of TRPC1 and D2R expression indicates colocalization of the two proteins within the cell body and dendrites of cortical neurons. In cultured cells, expression of D2Rs was found to increase expression of TRPC1 at the cell surface by 50%. These findings shed new light on the constituents of the D2R signalplex, and support the involvement of D2Rs in cellular calcium signaling pathways via a novel link to TRPC channels.

Hannan, Meredith A.; Kabbani, Nadine; Paspalas, Constantinos D.; Levenson, Robert

2008-01-01

282

Comparison of PDE-Based Nonlinear Diffusion Approaches for Image Enhancement and Denoising in Optical Coherence Tomography  

Microsoft Academic Search

A comparison between two nonlinear diffusion methods for denoising OCT images is performed. Specifically, we compare and contrast the performance of the traditional nonlinear Perona-Malik filter with a complex diffusion filter that has been recently introduced by Gilboa . The complex diffusion approach based on the generalization of the nonlinear scale space to the complex domain by combining the diffusion

Harry M. Salinas; Delia Cabrera Fernández

2007-01-01

283

Arctic canopy photosynthetic efficiency enhanced under diffuse light, linked to a reduction in the fraction of the canopy in deep shade.  

PubMed

We investigated how radiation conditions within a tundra canopy were linked to canopy photosynthesis, and how this linkage explained photosynthetic sensitivity to sky conditions, that is total radiation and its diffuse fraction. We measured within canopy radiation at leaf scales and net CO2 exchanges at canopy scales, under varied total irradiance and diffuse fraction, in Alaskan shrub tundra. Normalised mean radiation profiles within canopies showed no significant differences with varied diffuse fractions. However, radiation density distribution was non-normal, being more unimodal under diffuse conditions and distinctly bimodal under direct sunlight. There was a nearly three-fold increase in the proportion of the canopy in deep shade under direct illumination, compared to diffuse conditions. Under diffuse conditions the canopy had higher light-use efficiency (LUE), resulting in up to 17% greater photosynthesis. The enhancement in LUE under diffuse illumination was not related to differences in the mean light profiles, but instead was due to significant shifts in the density distribution of light at leaf scales, in particular a reduced fraction of the canopy in deep shade under diffuse illumination. These results provide unique information for testing radiative transfer schemes in canopy models, and for better understanding canopy structure and trait variation within plant canopies. PMID:24593320

Williams, Mathew; Rastetter, Edward B; Van der Pol, Laura; Shaver, Gaius R

2014-06-01

284

Phase synchronization of three locally coupled chaotic electrochemical oscillators: enhanced phase diffusion and identification of indirect coupling.  

PubMed

Experiments are carried out with three locally coupled phase coherent chaotic electrochemical oscillators (A-B-C) in nickel dissolution in sulfuric acid. As the interaction strength is increased among the electrodes, an onset of synchronization is observed where the frequencies become identical and the phase differences are bounded. The precision of the period of the oscillators is characterized by phase diffusion coefficients from phases and phase differences. The transition to synchronization with increase of coupling strength was found to be accompanied by enhanced phase fluctuations that cause the precision of the oscillations to deteriorate. A parallel synchrony analysis showed that the direct (between A and B and B and C) and the indirect (between A and C) couplings can be correctly identified with the use of a partial phase synchrony index; therefore, the network topology can be deduced from dynamical measurements. Numerical simulations with a locally coupled model for electrochemical chaos confirm the presence of enhanced phase fluctuations close to the transition to synchronization and the usefulness of the partial phase synchrony index for differentiation of direct from indirect interactions in a small network of oscillators. PMID:21405763

Wickramasinghe, Mahesh; Kiss, István Z

2011-01-01

285

Combining diffusion-weighted MRI with Gd-EOB-DTPA-enhanced MRI improves the detection of colorectal liver metastases  

PubMed Central

Objectives To compare the diagnostic accuracy of gadolinium-ethoxybenzyl-diethylenetriaminepentaacetic acid (Gd-EOB-DTPA)-enhanced MRI, diffusion-weighted MRI (DW-MRI) and a combination of both techniques for the detection of colorectal hepatic metastases. Methods 72 patients with suspected colorectal liver metastases underwent Gd-EOB-DTPA MRI and DW-MRI. Images were retrospectively reviewed with unenhanced T1 and T2 weighted images as Gd-EOB-DTPA image set, DW-MRI image set and combined image set by two independent radiologists. Each lesion detected was scored for size, location and likelihood of metastasis, and compared with surgery and follow-up imaging. Diagnostic accuracy was compared using receiver operating characteristics and interobserver agreement by kappa statistics. Results 417 lesions (310 metastases, 107 benign) were found in 72 patients. For both readers, diagnostic accuracy using the combined image set was higher [area under the curve (Az) = 0.96, 0.97] than Gd-EOB-DTPA image set (Az = 0.86, 0.89) or DW-MRI image set (Az = 0.93, 0.92). Using combined image set improved identification of liver metastases compared with Gd-EOB-DTPA image set (p<0.001) or DW-MRI image set (p<0.001). There was very good interobserver agreement for lesion classification (? = 0.81–0.88). Conclusions Combining DW-MRI with Gd-EOB-DTPA-enhanced T1 weighted MRI significantly improved the detection of colorectal liver metastases.

Koh, D-M; Collins, D J; Wallace, T; Chau, I; Riddell, A M

2012-01-01

286

Osmosensitivity of transient receptor potential vanilloid 1 is synergistically enhanced by distinct activating stimuli such as temperature and protons.  

PubMed

In animals, body-fluid osmolality is continuously monitored to keep it within a narrow range around a set point (?300 mOsm/kg). Transient receptor potential vanilloid 1 (TRPV1), a cation channel, has been implicated in body-fluid homeostasis in vivo based on studies with the TRPV1-knockout mouse. However, the response of TRPV1 to hypertonic stimuli has not been demonstrated with heterologous expression systems so far, despite intense efforts by several groups. Thus, the molecular entity of the hypertonic sensor in vivo still remains controversial. Here we found that the full-length form of TRPV1 is sensitive to an osmotic increase exclusively at around body temperature using HEK293 cells stably expressing rat TRPV1. At an ambient temperature of 24°C, a slight increase in the intracellular calcium concentration ([Ca(2+)](i)) was rarely observed in response to hypertonic stimuli. However, the magnitude of the osmosensitive response markedly increased with temperature, peaking at around 36°C. Importantly, the response at 36°C showed a robust increase over a hypertonic range, but a small decrease over a hypotonic range. A TRPV1 antagonist, capsazepine, and a nonspecific TRP channel inhibitor, ruthenium red, completely blocked the increase in [Ca(2+)](i). These results endorse the view that the full-length form of TRPV1 is able to function as a sensor of hypertonic stimuli in vivo. Furthermore, we found that protons and capsaicin likewise synergistically potentiated the response of TRPV1 to hypertonic stimuli. Of note, HgCl(2), which blocks aquaporins and inhibits cell-volume changes, significantly reduced the osmosensitive response. Our findings thus indicate that TRPV1 integrates multiple different types of activating stimuli, and that TRPV1 is sensitive to hypertonic stimuli under physiologically relevant conditions. PMID:21779403

Nishihara, Eri; Hiyama, Takeshi Y; Noda, Masaharu

2011-01-01

287

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]=~1200 mg/L and [NO3(-)]=~140 mg/L, the ACD mode delivered an average power density of 0.91 W/m(3), an average nitrate removal rate of 15.5mg/(Ld) and an average COD removal rate of 137 mg/(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

2013-11-01

288

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

289

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

290

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

291

A new multicompartmental reaction-diffusion modeling method links transient membrane attachment of E. coli MinE to E-ring formation  

Microsoft Academic Search

Many important cellular processes are regulated by reaction-diffusion (RD) of molecules that takes place both in the cytoplasm\\u000a and on the membrane. To model and analyze such multicompartmental processes, we developed a lattice-based Monte Carlo method,\\u000a Spatiocyte that supports RD in volume and surface compartments at single molecule resolution. Stochasticity in RD and the\\u000a excluded volume effect brought by intracellular

Satya Nanda Vel Arjunan; Masaru Tomita

2010-01-01

292

Combined prostate Diffusion Tensor Imaging and Dynamic Contrast Enhanced MRI at 3T - quantitative correlation with biopsy  

PubMed Central

The purpose of this work was to compare diagnostic accuracy of Diffusion Tensor Imaging (DTI), Dynamic Contrast Enhanced MRI (DCE MRI), and their combination in diagnosing prostate cancer. Twenty five patients with clinical suspicion of prostate cancer underwent MRI, prior to transrectal ultrasound (TRUS)-guided biopsies. MRI data were correlated to biopsy results. Logistic regression models were constructed for the DTI parameters, DCE MRI parameters, and their combination. The areas under the Receiver Operator Characteristic curves (AUC) were compared between the models. The nonparametric Wilcoxon signed rank test was used for statistical analysis. The sensitivity and specificity values were respectively 81% (74% – 87%) and 85% (79% – 90%) for DTI and 63% (55% – 70%) and 90% (85% – 94%) for DCE. The combination “DTI or DCE MRI” had 100% (97% – 100%) sensitivity and 77% (69% – 83%) specificity, while “DTI and DCE MRI” had 44% (37% – 52%) sensitivity and 98% (94% – 100%) specificity. The AUC for DTI + DCE parameters was significantly higher than that for either DTI (0.96 vs. 0.92, p = 0.0143) or DCE MRI parameters (0.96 vs. 0.87, p = 0.00187) alone. In conclusion, the combination of DTI and DCE MRI has significantly better accuracy in prostate cancer diagnosis than either technique alone.

Kozlowski, Piotr; Chang, Silvia D.; Meng, Ran; Madler, Burkhard; Bell, Robert; Jones, Edward C.; Goldenberg, S. Larry

2010-01-01

293

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

294

Analysis of model equations for stress-enhanced diffusion in coal layers. Part I: existence of a weak solution  

SciTech Connect

This paper is motivated by the study of the sorption processes in the coal. They are modeled by a nonlinear degenerate pseudoparabolic equation for stress-enhanced diffusion of carbon dioxide (CO{sub 2}) in coal. These types of equations arise in a number of cases when nonequilibrium thermodynamics or extended nonequilibrium thermodynamics is used to compute the flux. For the given equation, existence of the travelling wave-type solutions was extensively studied. Nevertheless, the existence seems to be known only for a sufficiently short time. We use the corresponding entropy functional in order to get existence, for any time interval, of an appropriate weak solution with square integrable first derivatives and satisfying uniform L-infinity-bounds. Due to the degeneracy, we obtain square integrability of the mixed second order derivative only in the region where the concentration phi is strictly positive. In obtaining the existence result it was crucial to have the regularized entropy as unknown for the approximate problem and not the original unknown (the concentration).

Mikelic, A.; Bruining, H. [University of Lyon, Lyon (France)

2008-07-01

295

A Transient Diffusion Model Yields Unitary Gap Junctional Permeabilities from Images of Cell-to-Cell Fluorescent Dye Transfer Between Xenopus Oocytes  

PubMed Central

As ubiquitous conduits for intercellular transport and communication, gap junctional pores have been the subject of numerous investigations aimed at elucidating the molecular mechanisms underlying permeability and selectivity. Dye transfer studies provide a broadly useful means of detecting coupling and assessing these properties. However, given evidence for selective permeability of gap junctions and some anomalous correlations between junctional electrical conductance and dye permeability by passive diffusion, the need exists to give such studies a more quantitative basis. This article develops a detailed diffusion model describing experiments (reported separately) involving transport of fluorescent dye from a “donor” region to an “acceptor” region within a pair of Xenopus oocytes coupled by gap junctions. Analysis of transport within a single oocyte is used to determine the diffusion and binding characteristics of the cellular cytoplasm. Subsequent double-cell calculations then yield the intercellular junction permeability, which is translated into a single-channel permeability using concomitant measurements of intercellular conductance, and known single-channel conductances of gap junctions made up of specific connexins, to count channels. The preceding strategy, combined with use of a graded size series of Alexa dyes, permits a determination of absolute values of gap junctional permeability as a function of dye size and connexin type. Interpretation of the results in terms of pore theory suggests significant levels of dye-pore affinity consistent with the expected order of magnitude of typical (e.g., van der Waals) intermolecular attractions.

Nitsche, Johannes M.; Chang, Hou-Chien; Weber, Paul A.; Nicholson, Bruce J.

2004-01-01

296

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

2013-04-01

297

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

PubMed Central

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.

Poon, Cynthia; Coombes, Stephen A.; Corcos, Daniel M.; Christou, Evangelos A.

2013-01-01

298

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

299

Chemically enhanced physical vapor deposition (CEPVD) of tantalum nitride-based films for diffusion barrier layers used in ULSI devices  

NASA Astrophysics Data System (ADS)

To address future ULSI barrier/liner deposition needs, we have investigated a hybrid approach to film deposition, referred to as chemically enhanced physical vapor deposition (CEPVD), attempting to provide Ionized Physical Vapor Deposition (IPVD)-like film quality and Chemical Vapor Deposition (CVD)-like step coverage. In CEPVD, a chemical precursor is introduced to the substrate during IPVD to provide a CVD component to the overall deposition process. The isotropic precursor flux is intended to provide film deposition on surfaces that are not impacted by the directional ions, such as the lower sidewall of a narrow via or trench. The kinetic energy delivered to the surface by the flux of ionized metal may serve to enhance chemical component deposition. We have focused on the Ta-N material system since Ta/TaN is widely used as a diffusion barrier in Cu damascene processing. CEPVD was carried out by introducing a Ta-containing, organometallic precursor (tert-butylimino tris(diethylamino) tantalum, or TBTDET) to the substrate during IPVD. Film thickness and step coverage were determined by cross-sectional SEM. Film atomic composition, molecular composition, chemical state, roughness, crystalline structure and resistivity were characterized using AES, SIMS, XPS, AFM, XRD and four-point-probe respectively. A zero-order semi-empirical model is established allowing the attachment of physical understanding and CEPVD experimental phenomena. The model stems from the knowledge of reactive sputtering and PECVD processes as well as the acquired CEPVD experiment results. It correlates the processing parameters with the target and film surface coverage by Ta, TaN and organic sites, from which one can predict the operation mode, either metallic or poison, and the film elemental composition. The organic by-products accounting for the detection of carbon on the substrate by AES analysis and poisoning of the target during the processing are categorized into non-volatile product (OR1) and volatile product (OR2) in a lump-sum assumption. Electron impact, H reducing and ion bombardment are considered as the enhancing mechanisms between the physical and chemical components and included as the reactants of the chemical reactions. Simulation results compare favorably with the experimental data.

Li, Ning

300

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

301

Performance of Enhanced Liver Fibrosis test and comparison with transient elastography in the identification of liver fibrosis in patients with chronic hepatitis B infection.  

PubMed

Assessment of liver fibrosis is important in determining prognosis, disease progression and need for treatment in patients with chronic hepatitis B (CHB). Limitations to the use of liver biopsy in assessing fibrosis are well recognized, and noninvasive tests are being increasingly evaluated including transient elastography (TE) and serum markers such as the Enhanced Liver Fibrosis (ELF) test. We assessed performance of ELF and TE in detecting liver fibrosis with reference to liver histology in a cohort of patients with CHB (n = 182), and compared the performance of these modalities. Median age was 46 and mean AST 70 IU/L. Cirrhosis was reported in 20% of liver biopsies. Both modalities performed well in assessing fibrosis at all stages. Area under receiver operator characteristic (AUROC) curves for detecting METAVIR fibrosis stages F ? 1, F ? 2, F ? 3 and F4 were 0.77, 0.82, 0.80 and 0.83 for ELF and 0.86, 0.86, 0.90 and 0.95 for TE. TE performed significantly better in the assessment of severe fibrosis (AUROC 0.80 for ELF and 0.90 for TE, P < 0.01) and cirrhosis (0.83 for ELF and 0.95 for TE, P < 0.01). This study demonstrates that ELF has good performance in detection of liver fibrosis in patients with CHB, and when compared, TE performs better in detection of severe fibrosis/cirrhosis. PMID:24750297

Trembling, P M; Lampertico, P; Parkes, J; Tanwar, S; Viganò, M; Facchetti, F; Colombo, M; Rosenberg, W M

2014-06-01

302

Transient osteoporosis of the knee  

Microsoft Academic Search

The MR findings in transient osteoporosis of the knee have been described as showing a diffuse area of decreased signal intensity\\u000a (relative to normal bone marrow) on T1-weighted images and increased signal intensity on T2-weighted images. We report a case\\u000a of transient osteoporosis, in which MRI showed a crescentic area of abnormal signal intensity in the posterior portion of\\u000a the

Russell K. Parker; Gerald J. Ross; James A. Urso

1997-01-01

303

Comparison of diffusion-weighted imaging and contrast-enhanced T1-weighted imaging on a single baseline MRI for demonstrating dissemination in time in multiple sclerosis  

PubMed Central

Background The 2010 Revisions to the McDonald Criteria have established that dissemination in time (DIT) of multiple sclerosis (MS) can be demonstrated by simultaneous presence of asymptomatic gadolinium-enhancing and nonenhancing lesions on a single magnetic resonance imaging (MRI). However, gadolinium-based contrast agents (GBCAs) have contraindications. Diffusion-weighted imaging (DWI) can detect diffusion alterations in active inflammatory lesions. The purpose of this study was to investigate if DWI can be an alternative to contrast-enhanced T1-weighted imaging (CE T1WI) for demonstrating DIT in MS. Methods We selected patients with clinically definite MS and evaluated their baseline brain MRI. Asymptomatic lesions were identified as either hyperintense or nonhyperintense on DWI and enhancing or nonenhancing on CE T1WI. Fisher’s exact test was performed to determine whether the hyperintensity on DWI was related to the enhancement on CE T1WI (P?enhancement were calculated. Results Twenty-two patients with 384 demyelinating lesions that were hyperintense on T2-weighted imaging and more than 3 mm in size were recruited. The diffusion hyperintensity and lesion enhancement were significantly correlated (P <0.001). The sensitivity, specificity, PPV, NPV and accuracy were 100%, 67.9%, 32.3%, 100% and 72.1%, respectively. Conclusions A hyperintense DWI finding does not necessarily overlap with contrast enhancement. There are many false positives, possibly representing other stages of lesion development. Although DWI may not replace CE T1WI imaging to demonstrate DIT due to the low PPV, it may serve as a screening MRI sequence where the use of GBCAs is a concern.

2014-01-01

304

Atomistic modeling of intrinsic and radiation-enhanced fission gas (Xe) diffusion in UO2±x: Implications for nuclear fuel performance modeling  

NASA Astrophysics Data System (ADS)

Based on density functional theory (DFT) and empirical potential calculations, the diffusivity of fission gas atoms (Xe) in UO2 nuclear fuel has been calculated for a range of non-stoichiometry (i.e. UO2±x), under both out-of-pile (no irradiation) and in-pile (irradiation) conditions. This was achieved by first deriving expressions for the activation energy that account for the type of trap site that the fission gas atoms occupy, which includes the corresponding type of mobile cluster, the charge state of these defects and the chemistry acting as boundary condition. In the next step DFT calculations were used to estimate migration barriers and internal energy contributions to the thermodynamic properties and calculations based on empirical potentials were used to estimate defect formation and migration entropies (i.e. pre-exponentials). The diffusivities calculated for out-of-pile conditions as function of the UO2±x non-stoichiometry were used to validate the accuracy of the diffusion models and the DFT calculations against available experimental data. The Xe diffusivity is predicted to depend strongly on the UO2±x non-stoichiometry due to a combination of changes in the preferred Xe trap site and in the concentration of uranium vacancies enabling Xe diffusion, which is consistent with experiments. After establishing the validity of the modeling approach, it was used for studying Xe diffusion under in-pile conditions, for which experimental data is very scarce. The radiation-enhanced Xe diffusivity is compared to existing empirical models. Finally, the predicted fission gas diffusion rates were implemented in the BISON fuel performance code and fission gas release from a Risø fuel rod irradiation experiment was simulated.

Andersson, D. A.; Garcia, P.; Liu, X.-Y.; Pastore, G.; Tonks, M.; Millett, P.; Dorado, B.; Gaston, D. R.; Andrs, D.; Williamson, R. L.; Martineau, R. C.; Uberuaga, B. P.; Stanek, C. R.

2014-08-01

305

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

306

Diffusion of antimony in silicon in the presence of point defects  

NASA Astrophysics Data System (ADS)

We have investigated the diffusion of Sb in Si in the presence of defects injected by high-energy implantation of Si ions at room temperature. MeV ion implantation increases the concentrations of vacancies, which induce transient-enhanced diffusion of Sb deposited in Si. We observed a significant enhancement of Sb diffusion. Secondary ions mass spectroscopy has been performed on the implanted samples before and after annealing. Rutherford-backscattering spectrometry has been used to characterize the high-energy implantation damage. By fitting diffusion profiles to a linear diffusive model, information about atomic scale diffusion of Sb, i.e. the generation rate of mobile state Sb and its mean migration length were extracted.

Yu, Xiangkun; Ma, K. B.; Chen, Q. Y.; Wang, Xuemei; Liu, Jiarui; Chu, Wei-Kan; Shao, Lin; Thompson, Phillip E.

2007-08-01

307

Coordination between the Rashba spin orbital interaction and space charge effect and enhanced spin injection into semiconductors in the diffusion region  

Microsoft Academic Search

We consider the effect of the Rashba spin-orbital interaction and space charge in a ferromagnet-insulator\\/semiconductor\\/insulator-ferromagnet junction where the spin current is severely affected by the doping, band structure and charge screening in the semiconductor. In the diffusion region, if the resistance of the tunnelling barriers is comparable to the semiconductor resistance, the magnetoresistance of this junction can be greatly enhanced

Wei Wu; Jinbin Li; Yue Yu; S. T. Chui

2004-01-01

308

Gas diffusion ultrabarriers on polymer substrates using Al2O3 atomic layer deposition and SiN plasma-enhanced chemical vapor deposition  

Microsoft Academic Search

Thin films grown by Al2O3 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 Al2O3 ALD with thicknesses of ?10 nm had a water vapor transmission rate (WVTR) of ?5×10?5 g\\/m2 day at 38 °C\\/85% relative humidity (RH), as measured

P. F. Carcia; R. S. McLean; M. D. Groner; A. A. Dameron; S. M. George

2009-01-01

309

Gas diffusion ultrabarriers on polymer substrates using Al2O3 atomic layer deposition and SiN plasma-enhanced chemical vapor deposition  

Microsoft Academic Search

Thin films grown by Al2O3 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 Al2O3 ALD with thicknesses of >=10 nm had a water vapor transmission rate (WVTR) of <=5×10-5 g\\/m2 day at 38 °C\\/85% relative humidity (RH), as measured

P. F. Carcia; R. S. McLean; M. D. Groner; A. A. Dameron; S. M. George

2009-01-01

310

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

311

Chemo-nociceptive signalling from the colon is enhanced by mild colitis and blocked by inhibition of transient receptor potential ankyrin 1 channels  

PubMed Central

Background and purpose: Transient receptor potential ankyrin 1 (TRPA1) channels are expressed by primary afferent neurones and activated by irritant chemicals including allyl isothiocyanate (AITC). Here we investigated whether intracolonic AITC causes afferent input to the spinal cord and whether this response is modified by mild colitis, morphine or a TRPA1 channel blocker. Experimental approach: One hour after intracolonic administration of AITC to female mice, afferent signalling was visualized by expression of c-Fos in laminae I–IIo of the spinal dorsal horn at sacral segment S1. Mild colitis was induced by dextran sulphate sodium (DSS) added to drinking water for 1 week. Key results: Relative to vehicle, AITC (2%) increased expression of c-Fos in the spinal cord. Following induction of mild colitis by DSS (2%), spinal c-Fos responses to AITC, but not vehicle, were augmented by 41%. Colonic inflammation was present (increased myeloperoxidase content and disease activity score), whereas colonic histology, locomotion, feeding and drinking remained unchanged. Morphine (10 mg·kg?1) or the TRPA1 channel blocker HC-030031 (300 mg·kg?1) inhibited the spinal c-Fos response to AITC, in control and DSS-pretreated animals, whereas the response to intracolonic capsaicin (5%) was blocked by morphine but not HC-030031. Conclusions and implications: Activation of colonic TRPA1 channels is signalled to the spinal cord. Mild colitis enhanced this afferent input that, as it is sensitive to morphine, is most likely of a chemonociceptive nature. As several irritant chemicals can be present in chyme, TRPA1 channels may mediate several gastrointestinal pain conditions.

Mitrovic, Martina; Shahbazian, Anaid; Bock, Elisabeth; Pabst, Maria A; Holzer, Peter

2010-01-01

312

On the transient solutions of three acoustic wave equations: van Wijngaarden's equation, Stokes' equation and the time-dependent diffusion equation.  

PubMed

Acoustic wave propagation in a dispersive medium may be described by a wave equation containing one or more dissipation terms. Three such equations are examined in this article: van Wijngaarden's equation (VWE) for sound propagating through a bubbly liquid; Stokes' equation for acoustic waves in a viscous fluid; and the time-dependent diffusion equation (TDDE) for waves in the interstitial gas in a porous solid. The impulse-response solution for each of the three equations is developed and all are shown to be strictly causal, with no arrivals prior to the activation of the source. However, the VWE is nonphysical in that it predicts instantaneous arrivals, which are associated with infinitely fast, propagating Fourier components in the Green's function. Stokes' equation and the TDDE are well behaved in that they do not predict instantaneous arrivals. Two of the equations, the VWE and Stokes' equation, satisfy the Kramers-Kronig dispersion relations, while the third, the TDDE, does not satisfy Kramers-Kronig, even though its impulse-response solution is causal and physically realizable. The Kramers-Kronig relations are predicated upon the (mathematical) existence of the complex compressibility, a condition which is not satisfied by the TDDE because the Fourier transform of the complex compressibility is not square-integrable. PMID:19062830

Buckingham, Michael J

2008-10-01

313

Chronoamperometric Transients at the Stationary Disk Microelectrode.  

National Technical Information Service (NTIS)

Chronoamperometric transients for diffusion controlled reactions at stationary platinum and gold microelectrodes have been examined. The results are compared with those predicted theoretically for hemispherical electrodes and for disk electrodes. The hemi...

T. Hepel J. Osteryoung

1981-01-01

314

Control of diffuser jet flow: turbulent kinetic energy and jet spreading enhancements assisted by a non-thermal plasma discharge  

Microsoft Academic Search

An axisymmetric air jet exhausting from a 22-degree-angle diffuser is investigated experimentally by particle image velocimetry\\u000a (PIV) and stereo-PIV measurements. Two opposite dielectric barrier discharge (DBD) actuators are placed along the lips of\\u000a the diffuser in order to force the mixing by a co-flow actuation. The electrohydrodynamic forces generated by both actuators\\u000a modify and excite the turbulent shear layer at

N. Benard; N. Balcon; G. Touchard; E. Moreau

2008-01-01

315

Transient analysis of polymer electrolyte fuel cells  

Microsoft Academic Search

A three-dimensional, transient model has been developed to study the transient dynamics of polymer electrolyte fuel cell (PEFC) operation. First, various time constants are estimated for important transient phenomena of electrochemical double-layer discharging, gas transport through the gas diffusion layer (GDL) and membrane hydration. It is found that membrane hydration occurs over a period of 10s, the gas transport of

Yun Wang; Chao-Yang Wang

2005-01-01

316

Hydrodynamic Enhancement of the Diffusion Rate in the Region between Two Fluctuating Membranes in Close Opposition: A Theoretical and Computational Study.  

PubMed

Periodic variation of the distance between two weakly adhering bodies gives rise to a huge tangential motions of the sandwiched solvent layer (squeezing flow). Oscillations either can be induced by an external applied field or can spontaneously arise from the coupling with the solvent heat bath. First we calculated by the Navier-Stokes equation the components of the fluid velocity near two oscillating juxtaposed plates. Then we evaluated the influence of plate oscillations on the transport properties of a trace diffusant dissolved at t = 0 in the outer medium for both deterministic and stochastic excitations. By employing both analytical (Fokker-Planck) and coarse-grained molecular dynamics (MD) simulations, we proved that the entry and migration rates of the diffusant sharply increases with the oscillation amplitudes. Enhancement was related to relevant parameters like oscillation frequency, fluid layer thickness, fluid viscosity, and temperature. An extension to the case of oscillating multistacked lamellae has been also made. Theoretical and MD results suggest a significant enhancement of the diffusant flux even in the worse situation of thermally excited small amplitude fluctuations. Excitation arising from other sources (e.g., microwave or ultrasound irradiation of solid-fluid layered systems) could have a dramatic effect on the transport phenomena. Possible implications to relevant biological problems have been discussed. PMID:24992344

Pannuzzo, Martina; Grassi, Antonio; Raudino, Antonio

2014-07-24

317

Self- and dopant diffusion in extrinsic boron doped isotopically controlled silicon multilayer structures  

SciTech Connect

Isotopically controlled silicon multilayer structures were used to measure the enhancement of self- and dopant diffusion in extrinsic boron doped silicon. {sup 30}Si was used as a tracer through a multilayer structure of alternating natural Si and enriched {sup 28}Si layers. Low energy, high resolution secondary ion mass spectrometry (SIMS) allowed for simultaneous measurement of self- and dopant diffusion profiles of samples annealed at temperatures between 850 C and 1100 C. A specially designed ion- implanted amorphous Si surface layer was used as a dopant source to suppress excess defects in the multilayer structure, thereby eliminating transient enhanced diffusion (TED) behavior. Self- and dopant diffusion coefficients, diffusion mechanisms, and native defect charge states were determined from computer-aided modeling, based on differential equations describing the diffusion processes. We present a quantitative description of B diffusion enhanced self-diffusion in silicon and conclude that the diffusion of both B and Si is mainly mediated by neutral and singly positively charged self-interstitials under p-type doping. No significant contribution of vacancies to either B or Si diffusion is observed.

Sharp, Ian D.; Bracht, Hartmut A.; Silvestri, Hughes H.; Nicols, Samuel P.; Beeman, Jeffrey W.; Hansen, John L.; Nylandsted Larsen, Arne; Haller, Eugene E.

2002-04-01

318

[Transient myopia].  

PubMed

Although transient myopia is an extremely rare symptom, systemic diseases which can also lead to a life-threatening condition should also be considered in cases of sudden deterioration of vision. Therefore, the initial diagnosis in an ophthalmological clinic or practice plays a decisive role. PMID:21590350

Borkenstein, A F; Hausberger, S; Mayer, C; Faschinger, C

2011-07-01

319

Aggressive Angiomyxoma with Diffusion-Weighted Magnetic Resonance Imaging and Dynamic Contrast Enhancement: A Case Report and Review of the Literature  

PubMed Central

Introduction Aggressive angiomyxoma (AA) is a rare benign soft tissue tumour usually affecting the pelvis and perineum of young women. Magnetic resonance imaging (MRI) is crucial in the management of AA patients for its diagnostic contribution and for the preoperative assessment of the actual tumour extension. Given the current development of less aggressive therapeutics associated with a higher risk of recurrence, close follow-up with MRI is fundamental after treatment. In this context, diffusion-weighted (DW) imaging has already shown high efficacy in the detection of early small relapses in prostate or rectal cancer. Case Report We report here a case of pelvic AA in a 51-year-old woman examined with dynamic contrast enhancement and DW-MRI, including apparent diffusion coefficient mapping and calculation. Conclusion To our knowledge, this is the first description of DW-MRI in AA reported in the literature. Here, knowledge about imaging features of AA will be reviewed and expanded.

Brunelle, S.; Bertucci, F.; Chetaille, B.; Lelong, B.; Piana, G.; Sarran, A.

2013-01-01

320

Dynamic Contrast-Enhanced and Diffusion-Weighted Magnetic Resonance Imaging Noninvasive Evaluation of Vascular Disrupting Treatment on Rabbit Liver Tumors  

PubMed Central

Evaluation of vascular disrupting treatment (VDT) is generally based on tumor size and enhancement on conventional magnetic resonance imaging (MRI) which, unfortunately, may be limited in providing satisfactory information. The purpose of the study is to evaluate consecutive changes of 20 rabbit VX2 liver tumors after VDT by dynamic contrast-enhanced MRI (DCE-MRI) and diffusion-weighted imaging (DWI) at a 3.0 T MR unit. Twenty four hours after intravenous injection of Combretastatin A-4-phosphate (CA4P) at 20 mg/kg, DCE-MRI derived Maximum Slope of Increase (MSI) and Positive Enhancement Integral (PEI) decreased sharply due to sudden shutting down of tumor feeding vessels. DWI derived Apparent Diffusion Coefficient (ADC) in tumor periphery decreased because of ischemic cell edema. On day 4, an increase of MSI was probably caused by the recovery of blood supply. A remarkable increase of ADC represented a large scale of necrosis among tumors. On day 8, the blood perfusion further decreased and the extent of necrosis further increased, reflected by lower MSI and PEI values and higher ADC value. On day 12, a second decrease of ADC was noticed because the re-growth of periphery tumor. The experimental data indicate that the therapeutic effects of VDT may be noninvasively monitored with DCE-MRI (reflecting tumor blood perfusion) and DWI (reflecting the changes of histology), which provide powerful measures for assessment of anticancer treatments.

Shao, Haibo; Ni, Yicheng; Zhang, Jian; Chen, Feng; Dai, Xu; Fan, Guoguang; Sun, Ziping; Xu, Ke

2013-01-01

321

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

322

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

DOEpatents

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

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

1988-06-28

323

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

324

Increased diffusivity in acute multiple sclerosis lesions predicts risk of black hole  

PubMed Central

Objective: Diffusion tensor imaging (DTI) quantifies Brownian motion of water within tissue. Inflammation leads to tissue injury, resulting in increased diffusivity and decreased directionality. We hypothesize that DTI can quantify the damage within acute multiple sclerosis (MS) white matter lesions to predict gadolinium (Gd)-enhancing lesions that will persist 12 months later as T1 hypointensities. Methods: A cohort of 22 individuals underwent 7 brain MRI scans over 15 months. DTI parameters were temporally quantified within regions of Gd enhancement. Comparison to the homologous region in the hemisphere contralateral to the Gd-enhancing lesion was also performed to standardize individual lesion DTI parameters. Results: After classifying each Gd-enhancing region as to black hole outcome, radial diffusivity, mean diffusivity, and fractional anisotropy, along with their standardized values, were significantly altered for persistent black holes (PBHs), and remained elevated throughout the study. A Gd-enhancing region with a 40% elevation in radial diffusivity had a 5.4-fold (95% confidence interval [CI]: 2.1, 13.8) increased risk of becoming a PBH, with 70% (95% CI: 51%, 85%) sensitivity and 69% (95% CI: 57%, 80%) specificity. A model of radial diffusivity, with volume and length of Gd enhancement, was associated with a risk of becoming a PBH of 5.0 (95% CI: 2.6, 9.9). Altered DTI parameters displayed a dose relationship to duration of black hole persistence. Conclusions: Elevated radial diffusivity during gadolinium enhancement was associated with increased risk for development of a persistent black hole, a surrogate of severe demyelination and axonal injury. An elevated radial diffusivity within active multiple sclerosis lesions may be indicative of more severe tissue injury. GLOSSARY ABH = acute black hole; CBH = chronic black hole; DTI = diffusion tensor imaging; FLAIR = fluid-attenuated inversion recovery; Gd = gadolinium; MS = multiple sclerosis; NAWM = normal-appearing white matter; PBH = persistent black hole; RD = radial diffusivity; ROI = region of interest; T1H = chronic T1 hypointensity; TBH = transient black hole.

Naismith, R.T.; Xu, J.; Tutlam, N.T.; Scully, P.T.; Trinkaus, K.; Snyder, A.Z.; Song, S.-K.; Cross, A.H.

2010-01-01

325

Transient response of the Atlantic Meridional Overturning Circulation to enhanced freshwater input to the Nordic Seas Arctic Ocean in the Bergen Climate Model  

Microsoft Academic Search

The transient response of the climate system to anomalously large freshwater input to the high latitude seas is examined using the newly developed Bergen Climate Model. A 150-yr twin-experiment has been carried out, consisting of a control and a freshwater integration. In the freshwater integration, the freshwater input to the Arctic Ocean and the Nordic Seas is artificially increased by

Odd Helge Otter; Helge Drange; Mats Bentsen; Nils Gunnar Kvamstø; Dabang Jiang

2004-01-01

326

Excision of a Ds -like maize transposable element ( Ac ?) in a transient assay in Petunia is enhanced by a truncated coding region of the transposable element Ac  

Microsoft Academic Search

Summary The excision of a Ds-like transposable element (Ac?) is mediated in trans by the transposable element Ac or its derivatives in Petunia protoplasts cotransfected with two plasmid DNAs. Excision restores the activity of the ?-glucuronidase (GUS) gene that is otherwise shut off by the presence of Ac? in its leader sequence. A transient expression assay (histochemical test) is used

Nicole Houba-Hérin; Detlef Becker; Astrid Post; Yvan Larondelle; Peter Starlinger

1990-01-01

327

Effects of Lewis Number on Temperatures of Spherical Diffusion Flames  

NASA Technical Reports Server (NTRS)

Spherical diffusion flames supported on a porous sphere were studied numerically and experimentally. Experiments were performed in 2.2 s and 5.2 s microgravity facilities. Numerical results were obtained from a Chemkin-based program. The program simulates flow from a porous sphere into a quiescent environment, yields both steady-state and transient results, and accounts for optically thick gas-phase radiation. The low flow velocities and long residence times in these diffusion flames lead to enhanced radiative and diffusive effects. Despite similar adiabatic flame temperatures, the measured and predicted temperatures varied by as much as 700 K. The temperature reduction correlates with flame size but characteristic flow times and, importantly, Lewis number also influence temperature. The numerical results show that the ambient gas Lewis number would have a strong effect on flame temperature if the flames were steady and nonradiating. For example, a 10% decrease in Lewis number would increase the steady-state flame temperature by 200 K. However, for these transient, radiating flames the effect of Lewis number is small. Transient predictions of flame sizes are larger than those observed in microgravity experiments. Close agreement could not be obtained without either increasing the model s thermal and mass diffusion properties by 30% or reducing mass flow rate by 25%.

Santa, K. J.; Sun, Z.; Chao, B. H.; Sunderland, P. B.; Axelbaum, R. I.; Urban, D. L.; Stocker, D. P.

2007-01-01

328

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

329

Stable isotope-enhanced two- and three-dimensional diffusion ordered 13C NMR spectroscopy (SIE-DOSY 13C NMR)  

NASA Astrophysics Data System (ADS)

The feasibility of obtaining high quality homonuclear or heteronuclear diffusion-ordered 13C NMR data is shown to be greatly improved by using 13C isotopically-enriched samples. Stable isotope-enhanced diffusion ordered (SIE-DOSY) 13C NMR has been applied to 13C-enriched carbohydrates, and has been used to determine diffusion coefficients for pentose and hexose monosaccharides, and a disaccharide and trisaccharide. These 2D spectra were obtained with as little as 8 min of acquisition time. Fully resolved 3D DOSY-HMQC NMR spectra of [U- 13C]xylose, [U- 13C]glucose, and [1- 13C gal]lactose were obtained in 5 h. Sample derivatization with [ carbonyl- 13C]acetate (peracetylation) extends the usefulness of the technique to included non-labeled sugars; the 13C-carbonyl - carbohydrate ring proton 1H- 13C correlations also provide additional structural information, as shown for the 3-D DOSY-HMQC analysis of a mixture of maltotriose and lactose per-[ carbonyl- 13C]acetates.

Vermillion, Karl; Price, Neil P. J.

2009-06-01

330

Plasma-Enhanced Atomic Layer Deposition of Ruthenium-Titanium Nitride Mixed-Phase Layers for Direct-Plate Liner and Copper Diffusion Barrier Applications  

NASA Astrophysics Data System (ADS)

Current interconnect networks in semiconductor processing utilize a sputtered TaN diffusion barrier, Ta liner, and Cu seed to improve the adhesion, microstructure, and electromigration resistance of electrochemically deposited copper that fills interconnect wires and vias. However, as wire/via widths shrink due to device scaling, it becomes increasingly difficult to have the volume of a wire/via be occupied with ECD Cu which increases line resistance and increases the delay in signal propagation in IC chips. A single layer that could serve the purpose of a Cu diffusion barrier and ECD Cu adhesion promoter could allow ECD Cu to occupy a larger volume of a wire/via, leading to a decrease in line resistance and decrease in signal delay. Previous work has shown RuTaN, RuWCN, and RuCo films can act as Cu diffusion barriers and be directly platable to thickness of 2-3nm. However, other material selections may prove as effective or possibly better. Mixed-phase films of ruthenium titanium nitride grown by atomic layer deposition (ALD) were investigated for their performance as a Cu diffusion barrier and as a surface for the direct plating of ECD Cu. All Ru was deposited by plasma-enhanced atomic layer deposition (PEALD) while TiN was deposited by either thermal ALD or PEALD. RuTiN, films with thermal ALD TiN and a Ru:Ti of 20:1 showed barrier performance comparable to PVD TaN at 3-4 nm thickness and 15 nm planar films were directly platable. Follow up work is certainly needed for this material set, yet initial results indicate RuTiN could serve as an effective direct plate liner for Cu interconnects.

Gildea, Adam James

331

Label-Free In Situ Detection of Individual Macromolecular Assemblies by Surface Enhanced Raman Scattering  

PubMed Central

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.

Asiala, Steven M.; Schultz, Zachary D.

2012-01-01

332

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

2013-05-14

333

Diffusion and relaxation in Hamiltonian chaos  

NASA Astrophysics Data System (ADS)

Chaos in Hamiltonian systems have great importance in fundamental physics as a basis of classical statistical mechanics, as well as in application to plasma physics and solid state physics. Some results are introduced on the properties of global diffusion for Hamiltonian systems with many degrees of freedom, through numerical studies on coupled map lattices. Many important facts were revealed for the chaos in area preserving mappings. The phase space of area preserved mapping is filled with self-similar structure of islands and cantori, which are related to dynamical properties such as anomalous diffusion and flicker noise. Such delicate structures are expected to smear out when the number of degrees of freedom increases. The main topic is whether making the system size large enhances the chaos and diffusion. The models are (1) standard map and (2) symplectic version of the coupled map lattices. The anomalous diffusion is observed both for area preserving mappings and for systems with many degrees of freedom, reflecting the self similar structures of phase spaces. In both cases, however, they are transients appearing only for a finite time. Crossover from anomalous to normal diffusion has its origin in array-like arrangement of equivalent hierarchies of island chains in phase space, and are common to low dimensional and high dimensional systems.

Konishi, Tetsuro

1991-04-01

334

Substrate and filter materials to enhance phosphorus removal in constructed wetlands treating diffuse farm runoff: a review  

Microsoft Academic Search

Constructed and restored wetlands have significant potential to reduce nutrient losses in drainage waters from New Zealand farms. While both types of wetland show reasonably good nitrogen (N) removal efficiencies, they are not always so effective at phosphorus (P) removal and their flooded topsoils can be net sources of P. Wetland P-removal efficiency could be enhanced, either by adding a

Deborah J. Ballantine; Chris C. Tanner

2010-01-01

335

ATMOSPHERIC DIFFUSION AND NATURAL RADON  

Microsoft Academic Search

A correction is made to Wilkening's analysis of the datly variation of ; eddy diffusivity of radon near tile ground. The term (- lambda N) added to the ; steady-state form of the diffusion equation, showing the phenomonon to be ; transient. In the above term, N (curve cm⁻³ is the radon content and ; lambda (= 2.1 x 10

J. R. Philip

1959-01-01

336

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

337

Low temperature plasma-enhanced atomic layer deposition of thin vanadium nitride layers for copper diffusion barriers  

SciTech Connect

Thin vanadium nitride (VN) layers were grown by atomic layer deposition using tetrakis(ethylmethylamino)vanadium and NH{sub 3} plasma at deposition temperatures between 70 Degree-Sign C and 150 Degree-Sign C on silicon substrates and polymer foil. X-ray photoelectron spectroscopy revealed a composition close to stoichiometric VN, while x-ray diffraction showed the {delta}-VN crystal structure. The resistivity was as low as 200 {mu}{Omega} cm for the as deposited films and further reduced to 143 {mu}{Omega} cm and 93 {mu}{Omega} cm by annealing in N{sub 2} and H{sub 2}/He/N{sub 2}, respectively. A 5 nm VN layer proved to be effective as a diffusion barrier for copper up to a temperature of 720 Degree-Sign C.

Rampelberg, Geert; Devloo-Casier, Kilian; Deduytsche, Davy; Detavernier, Christophe [Department of Solid State Sciences, Ghent University, Krijgslaan 281/S1, B-9000 Ghent (Belgium)] [Department of Solid State Sciences, Ghent University, Krijgslaan 281/S1, B-9000 Ghent (Belgium); Schaekers, Marc [IMEC, Kapeldreef 75, B-3001 Leuven (Belgium)] [IMEC, Kapeldreef 75, B-3001 Leuven (Belgium); Blasco, Nicolas [Air Liquide Electronics US, L.P., 46401 Landing Parkway, Fremont, California 94538 (United States)] [Air Liquide Electronics US, L.P., 46401 Landing Parkway, Fremont, California 94538 (United States)

2013-03-18

338

Enhanced performance of organic thin film solar cells using electrodes with nanoimprinted light-diffraction and light-diffusion structures.  

PubMed

An ITO substrate with periodic surface nanostructures was used to induce strong diffusion and diffraction of incident light. The nanostructures were fabricated using nanoimprint lithography on photoresist followed by coating of the ITO layer and organic materials with uniform morphology. The nanostructures embedded into the ITO layer were found to increase absorption in poly(3-hexylthiophene) : [6,6]-phenyl-C61-butyric acid methyl ester solar devices. The short-circuit current of the nanostructured organic solar cells improved from 7.07 to 10.76 mA/cm(2). This improvement was due to the increased effective optical path of absorbed light resulting from the trapping and scattering by the nanostructures. PMID:24735241

Chen, Jheng-Yuan; Yu, Ming-Hung; Chang, Chih-Yu; Chao, Yi-Hsiang; Sun, Kien Wen; Hsu, Chain-Shu

2014-05-14

339

Low temperature plasma-enhanced atomic layer deposition of thin vanadium nitride layers for copper diffusion barriers  

NASA Astrophysics Data System (ADS)

Thin vanadium nitride (VN) layers were grown by atomic layer deposition using tetrakis(ethylmethylamino)vanadium and NH3 plasma at deposition temperatures between 70 °C and 150 °C on silicon substrates and polymer foil. X-ray photoelectron spectroscopy revealed a composition close to stoichiometric VN, while x-ray diffraction showed the ?-VN crystal structure. The resistivity was as low as 200 ?? cm for the as deposited films and further reduced to 143 ?? cm and 93 ?? cm by annealing in N2 and H2/He/N2, respectively. A 5 nm VN layer proved to be effective as a diffusion barrier for copper up to a temperature of 720 °C.

Rampelberg, Geert; Devloo-Casier, Kilian; Deduytsche, Davy; Schaekers, Marc; Blasco, Nicolas; Detavernier, Christophe

2013-03-01

340

Advanced transient waveform digitizers  

NASA Astrophysics Data System (ADS)

A series of multi-channel transient waveform digitization integrated circuits with up to 5 GHz sample rates and parallel 10-bit digitization has been designed, tested, and fabricated in large quantities. The current CMOS circuit uses four arrays of 128 fast switched capacitors per channel to record four parallel analog transient inputs. Triggering and clocking is provided by a current-mode adjustable asynchronous active delay line that uses look-ahead to generate 128 4-way interleaved clocks without the need for external high-speed clocking. After transient capture, each channel is fed into 128 parallel 10-bit analog to digital converters for fast, channel-parallel digitization, followed by digital readout. The fast triggering and waveform capture, channel-parallel digitization and convenient word-parallel digital readout results in a responsive and low dead-time system. Acquisition sample rates range from ~50 kHz to ~3 GHz. Analog input bandwidth is approximately 350 MHz. Fixed-pattern spatial noise, after on-chip digitization, is equivalent to ~5 mV RMS. Temporal noise is typically equivalent to ~1 mV RMS, for a signal to noise ratio of ~2,500:1, RMS. This integrated circuit, the "Analog Transient Waveform Digitizer," has been successfully used to instrument the AMANDA and KamLAND neutrino physics experiments, and has been selected for use in the IceCube neutrino observatory. Current efforts to improve this technology will yield larger array sizes, sample rates in excess of 10 GHz, analog bandwidth exceeding 1 GHz, higher conversion rates, lower dead-time, greater uniformity and enhanced flexibility and ease of use.

Kleinfelder, Stuart

2003-02-01

341

Use of ambroxol and bromhexine as mucolytics for enhanced diffusion of furaltadone into tracheobronchial secretions in broilers.  

PubMed

1. Ambroxol and bromhexine were evaluated as mucolytics and to enhance the passage of furaltadone into tracheobronchial secretions (TBS) in chronic complicated respiratory disease-affected broilers. 2. Viscosity of TBS was noticeably increased in the ambroxol-treated birds and only slightly increased in the bromhexine groups; however, the physical (nature) of TBS was superior in the ambroxol-treated broilers. 3. There was a clear increase in the passage of furaltadone into tracheobronchial secretions only in the ambroxol-treated birds. 4. Everyday use of ambroxol in broilers is discussed. PMID:7583380

Sumano, H; Gracia, I; Capistrán, A; Meade, G; Rivero, A; Ruiz-Ramírez, L

1995-07-01

342

Depth-compensated diffuse optical tomography enhanced by general linear model analysis and an anatomical atlas of human head.  

PubMed

One of the main challenges in functional diffuse optical tomography (DOT) is to accurately recover the depth of brain activation, which is even more essential when differentiating true brain signals from task-evoked artifacts in the scalp. Recently, we developed a depth-compensated algorithm (DCA) to minimize the depth localization error in DOT. However, the semi-infinite model that was used in DCA deviated significantly from the realistic human head anatomy. In the present work, we incorporated depth-compensated DOT (DC-DOT) with a standard anatomical atlas of human head. Computer simulations and human measurements of sensorimotor activation were conducted to examine and prove the depth specificity and quantification accuracy of brain atlas-based DC-DOT. In addition, node-wise statistical analysis based on the general linear model (GLM) was also implemented and performed in this study, showing the robustness of DC-DOT that can accurately identify brain activation at the correct depth for functional brain imaging, even when co-existing with superficial artifacts. PMID:23859922

Tian, Fenghua; Liu, Hanli

2014-01-15

343

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

344

An enhanced International Prognostic Index (NCCN-IPI) for patients with diffuse large B-cell lymphoma treated in the rituximab era.  

PubMed

The International Prognostic Index (IPI) has been the basis for determining prognosis in patients with aggressive non-Hodgkin lymphoma (NHL) for the past 20 years. Using raw clinical data from the National Comprehensive Cancer Network (NCCN) database collected during the rituximab era, we built an enhanced IPI with the goal of improving risk stratification. Clinical features from 1650 adults with de novo diffuse large B-cell lymphoma (DLBCL) diagnosed from 2000-2010 at 7 NCCN cancer centers were assessed for their prognostic significance, with statistical efforts to further refine the categorization of age and normalized LDH. Five predictors (age, lactate dehydrogenase (LDH), sites of involvement, Ann Arbor stage, ECOG performance status) were identified and a maximum of 8 points assigned. Four risk groups were formed: low (0-1), low-intermediate (2-3), high-intermediate (4-5), and high (6-8). Compared with the IPI, the NCCN-IPI better discriminated low- and high-risk subgroups (5-year overall survival [OS]: 96% vs 33%) than the IPI (5 year OS: 90% vs 54%), respectively. When validated using an independent cohort from the British Columbia Cancer Agency (n = 1138), it also demonstrated enhanced discrimination for both low- and high-risk patients. The NCCN-IPI is easy to apply and more powerful than the IPI for predicting survival in the rituximab era. PMID:24264230

Zhou, Zheng; Sehn, Laurie H; Rademaker, Alfred W; Gordon, Leo I; Lacasce, Ann S; Crosby-Thompson, Allison; Vanderplas, Ann; Zelenetz, Andrew D; Abel, Gregory A; Rodriguez, Maria A; Nademanee, Auayporn; Kaminski, Mark S; Czuczman, Myron S; Millenson, Michael; Niland, Joyce; Gascoyne, Randy D; Connors, Joseph M; Friedberg, Jonathan W; Winter, Jane N

2014-02-01

345

Magnetic field enhanced convective diffusion of iron oxide nanoparticles in an osmotically disrupted cell culture model of the blood-brain barrier  

PubMed Central

Purpose The present study examines the use of an external magnetic field in combination with the disruption of tight junctions to enhance the permeability of iron oxide nanoparticles (IONPs) across an in vitro model of the blood–brain barrier (BBB). The feasibility of such an approach, termed magnetic field enhanced convective diffusion (MFECD), along with the effect of IONP surface charge on permeability, was examined. Methods The effect of magnetic field on the permeability of positively (aminosilane-coated [AmS]-IONPs) and negatively (N-(trimethoxysilylpropyl)ethylenediaminetriacetate [EDT]-IONPs) charged IONPs was evaluated in confluent monolayers of mouse brain endothelial cells under normal and osmotically disrupted conditions. Results Neither IONP formulation was permeable across an intact cell monolayer. However, when tight junctions were disrupted using D-mannitol, flux of EDT-IONPs across the bEnd.3 monolayers was 28%, increasing to 44% when a magnetic field was present. In contrast, the permeability of AmS-IONPs after osmotic disruption was less than 5%. The cellular uptake profile of both IONPs was not altered by the presence of mannitol. Conclusions MFECD improved the permeability of EDT-IONPs through the paracellular route. The MFECD approach favors negatively charged IONPs that have low affinity for the brain endothelial cells and high colloidal stability. This suggests that MFECD may improve IONP-based drug delivery to the brain.

Sun, Zhizhi; Worden, Matthew; Wroczynskyj, Yaroslav; Yathindranath, Vinith; van Lierop, Johan; Hegmann, Torsten; Miller, Donald W

2014-01-01

346

Response of HT29 colorectal xenograft model to cediranib assessed with 18 F-fluoromisonidazole positron emission tomography, dynamic contrast-enhanced and diffusion-weighted MRI.  

PubMed

Cediranib is a small-molecule pan-vascular endothelial growth factor receptor inhibitor. The tumor response to short-term cediranib treatment was studied using dynamic contrast-enhanced and diffusion-weighted MRI at 7 T, as well as (18) F-fluoromisonidazole positron emission tomography and histological markers. Rats bearing subcutaneous HT29 human colorectal tumors were imaged at baseline; they then received three doses of cediranib (3 mg/kg per dose daily) or vehicle (dosed daily), with follow-up imaging performed 2 h after the final cediranib or vehicle dose. Tumors were excised and evaluated for the perfusion marker Hoechst 33342, the endothelial cell marker CD31, smooth muscle actin, intercapillary distance and tumor necrosis. Dynamic contrast-enhanced MRI-derived parameters decreased significantly in cediranib-treated tumors relative to pretreatment values [the muscle-normalized initial area under the gadolinium concentration curve decreased by 48% (p=0.002), the enhancing fraction by 43% (p=0.003) and K(trans) by 57% (p=0.003)], but remained unchanged in controls. No change between the pre- and post-treatment tumor apparent diffusion coefficients in either the cediranib- or vehicle-treated group was observed over the course of this study. The (18) F-fluoromisonidazole mean standardized uptake value decreased by 33% (p=0.008) in the cediranib group, but showed no significant change in the control group. Histological analysis showed that the number of CD31-positive vessels (59 per mm(2) ), the fraction of smooth muscle actin-positive vessels (80-87%) and the intercapillary distance (0.17 mm) were similar in cediranib- and vehicle-treated groups. The fraction of perfused blood vessels in cediranib-treated tumors (81 ± 7%) was lower than that in vehicle controls (91 ± 3%, p=0.02). The necrotic fraction was slightly higher in cediranib-treated rats (34 ± 12%) than in controls (26 ± 10%, p=0.23). These findings suggest that short-term treatment with cediranib causes a decrease in tumor perfusion/permeability across the tumor cross-section, but changes in vascular morphology, vessel density or tumor cellularity are not manifested at this early time point. PMID:22777834

Bokacheva, Louisa; Kotedia, Khushali; Reese, Megan; Ricketts, Sally-Ann; Halliday, Jane; Le, Carl H; Koutcher, Jason A; Carlin, Sean

2013-02-01

347

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

348

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

2012-01-01

349

Concentration Dependence of Hydrogen Diffusion in Armco Iron.  

National Technical Information Service (NTIS)

The electrochemical permeation technique was used to determine diffusivity and solubility of hydrogen in annealed Armco iron. Analysis of permeation build-up transients showed that hydrogen diffusivity increased with increase in charging current density. ...

T. K. G. Namboodhiri L. Nanis

1972-01-01

350

Transient Faults in Computer Systems  

NASA Technical Reports Server (NTRS)

A powerful technique particularly appropriate for the detection of errors caused by transient faults in computer systems was developed. The technique can be implemented in either software or hardware; the research conducted thus far primarily considered software implementations. The error detection technique developed has the distinct advantage of having provably complete coverage of all errors caused by transient faults that affect the output produced by the execution of a program. In other words, the technique does not have to be tuned to a particular error model to enhance error coverage. Also, the correctness of the technique can be formally verified. The technique uses time and software redundancy. The foundation for an effective, low-overhead, software-based certification trail approach to real-time error detection resulting from transient fault phenomena was developed.

Masson, Gerald M.

1993-01-01

351

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

352

{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

353

Response of HT29 Colorectal Xenograft Model to Cediranib Assessed with 18F-FMISO PET, Dynamic Contrast-Enhanced and Diffusion-Weighted MRI  

PubMed Central

Cediranib (AZD2171, AstraZeneca, UK) is a small-molecule pan-VEGFR inhibitor. The tumor response to short-term cediranib treatment was studied using dynamic contrast-enhanced (DCE) and diffusion-weighted (DW) MRI at 7 T as well as 18F-fluoromisonidazle (18F-FMISO) PET and histological markers. Rats bearing subcutaneous HT29 human colorectal tumors were imaged at baseline, then received three doses of cediranib (3 mg/kg per dose daily) or vehicle (dosed daily), with follow up imaging performed 2 hours after the final cediranib or vehicle dose. Tumors were excised and evaluated for the perfusion marker Hoechst 33342, endothelial cell marker CD31, smooth muscle actin (SMA), intercapillary distance (ICD) and tumor necrosis. DCE-MRI-derived parameters decreased significantly in cediranib-treated tumors relative to pre-treatment values: the muscle-normalized initial area under the gadolinium concentration curve (nIAUC90) by 48% (p = 0.002), the enhancing fraction (EnF) by 43% (p = 0.003) and Ktrans by 57% (p = 0.003), but remained unchanged in controls. No change between pre- and post-treatment tumor apparent diffusion coefficient (ADC) in either cediranib- or vehicle-treated group was observed over the course of this study. 18F-FMISO SUVmean decreased by 33% (p = 0.008) in the cediranib group, but showed no significant change in the control group. Histological analysis showed that the number of CD31-positive vessels (59 per mm2), the fraction of SMA-positive vessels (80 to 87%) and ICD (0.17 mm) were similar in cediranib- and vehicle-treated groups. The fraction of perfused blood vessels in cediranib-treated tumors (81±7%) was lower than in vehicle controls (91±3%, p = 0.02). The necrotic fraction was slightly higher in cediranib-treated rats (34±12%) than in controls (26±10%, p = 0.23). These findings suggest that short-term treatment with cediranib causes a decrease of tumor perfusion/permeability across the tumor cross-section, but changes in vascular morphology, vessel density or tumor cellularity do not manifest at this early time point.

Bokacheva, Louisa; Kotedia, Khushali; Reese, Megan; Ricketts, Sally-Ann; Halliday, Jane; Le, Carl H.; Koutcher, Jason A.; Carlin, Sean

2012-01-01

354

Transient Dimers of Allergens  

PubMed Central

Background Allergen-mediated cross-linking of IgE antibodies bound to the Fc?RI receptors on the mast cell surface is the key feature of the type I allergy. If an allergen is a homodimer, its allergenicity is enhanced because it would only need one type of antibody, instead of two, for cross-linking. Methodology/Principal Findings An analysis of 55 crystal structures of allergens showed that 80% of them exist in symmetric dimers or oligomers in crystals. The majority are transient dimers that are formed at high protein concentrations that are reached in cells by colocalization. Native mass spectrometric analysis showed that native allergens do indeed form transient dimers in solution, while hypoallergenic variants of them exist almost solely in the monomeric form. We created a monomeric Bos d 5 allergen and show that it has a reduced capability to induce histamine release. Conclusions/Significance The results suggest that dimerization would be a very common and essential feature for allergens. Thus, the preparation of purely monomeric variants of allergens could open up novel possibilities for specific immunotherapy.

Rouvinen, Juha; Janis, Janne; Laukkanen, Marja-Leena; Jylha, Sirpa; Niemi, Merja; Paivinen, Tero; Makinen-Kiljunen, Soili; Haahtela, Tari; Soderlund, Hans; Takkinen, Kristiina

2010-01-01

355

Gas diffusion ultrabarriers on polymer substrates using Al2O3 atomic layer deposition and SiN plasma-enhanced chemical vapor deposition  

NASA Astrophysics Data System (ADS)

Thin films grown by Al2O3 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 Al2O3 ALD with thicknesses of >=10 nm had a water vapor transmission rate (WVTR) of <=5×10-5 g/m2 day at 38 °C/85% relative humidity (RH), as measured by the Ca test. This WVTR value was limited by H2O 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 ~7×10-3 g/m2 day at 38 °C/85% RH. Significant improvements resulted when the SiN PECVD film was coated with an Al2O3 ALD film. An Al2O3 ALD film with a thickness of only 5 nm on a SiN PECVD film with a thickness of 100 nm reduced the WVTR from ~7×10-3 to <=5×10-5 g/m2 day at 38 °C/85% RH. The reduction in the permeability for Al2O3 ALD on the SiN PECVD films was attributed to either Al2O3 ALD sealing defects in the SiN PECVD film or improved nucleation of Al2O3 ALD on SiN.

Carcia, P. F.; McLean, R. S.; Groner, M. D.; Dameron, A. A.; George, S. M.

2009-07-01

356

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

2012-03-14

357

Transient repetitive exposure to low level light therapy enhances collateral blood vessel growth in the ischemic hindlimb of the tight skin mouse.  

PubMed

The tight skin mouse (Tsk(-/+)) is a model of scleroderma characterized by impaired vasoreactivity, increased oxidative stress, attenuated angiogenic response to VEGF and production of the angiogenesis inhibitor angiostatin. Low-level light therapy (LLLT) stimulates angiogenesis in myocardial infarction and chemotherapy-induced mucositis. We hypothesize that repetitive LLLT restores vessel growth in the ischemic hindlimb of Tsk(-/+) mice by attenuating angiostatin and enhancing angiomotin effects in vivo. C57Bl/6J and Tsk(-/+) mice underwent ligation of the femoral artery. Relative blood flow to the foot was measured using a laser Doppler imager. Tsk(-/+) mice received LLLT (670 nm, 50 mW cm(-2), 30 J cm(-2)) for 10 min per day for 14 days. Vascular density was determined using lycopersicom lectin staining. Immunofluorescent labeling, Western blot analysis and immunoprecipitation were used to determine angiostatin and angiomotin expression. Recovery of blood flow to the ischemic limb was reduced in Tsk(-/+) compared with C57Bl/6 mice 2 weeks after surgery. LLLT treatment of Tsk(-/+) mice restored blood flow to levels observed in C57Bl/6 mice. Vascular density was decreased, angiostatin expression was enhanced and angiomotin depressed in the ischemic hindlimb of Tsk(-/+) mice. LLLT treatment reversed these abnormalities. LLLT stimulates angiogenesis by increasing angiomotin and decreasing angiostatin expression in the ischemic hindlimb of Tsk(-/+) mice. PMID:23231468

Zaidi, Maria; Krolikowki, John G; Jones, Deron W; Pritchard, Kirkwood A; Struve, Janine; Nandedkar, Sandhya D; Lohr, Nicole L; Pagel, Paul S; Weihrauch, Dorothée

2013-01-01

358

Transient Repetitive Exposure To Low Level Light Therapy Enhances Collateral Blood Vessel Growth In The Ischemic Hindlimb Of The Tight Skin Mouse  

PubMed Central

The tight skin mouse (Tsk?/+) is a model of scleroderma characterized by impaired vasoreactivity, increased oxidative stress, attenuated angiogenic response to VEGF, and production of the angiogenesis inhibitor angiostatin. Low level light therapy (LLLT) stimulates angiogenesis in myocardial infarction and chemotherapy-induced mucositis. We hypothesize repetitive LLLT restores vessel growth in the ischemic hindlimb of Tsk?/+ mice by attenuating angiostatin and enhancing angiomotin effects in vivo. C57Bl/6J and Tsk?/+ mice underwent ligation of the femoral artery. Relative blood flow to the foot was measured using a laser Doppler imager. Tsk?/+ mice received LLLT (670 nm, 50 mW cm2, 30 J/cm2) for 10 min/day for 14 days. Vascular density was determined using lycopersicom lectin staining. Immunofluorescent labeling, western blot analysis, and immunoprecipitation were used to determine angiostatin and angiomotin expression. Recovery of blood flow to the ischemic limb was reduced in Tsk?/+ compared with C57Bl/6 mice two weeks after surgery. LLLT treatment of Tsk?/+ mice restored blood flow to levels observed in C57Bl/6 mice. Vascular density was decreased, angiostatin expression was enhanced and angiomotin depressed in the ischemic hindlimb of Tsk?/+ mice. LLLT treatment reversed these abnormalities. LLLT stimulates angiogenesis by increasing angiomotin and decreasing angiostatin expression in the ischemic hindlimb of Tsk?/+ mice.

Zaidi, Maria; Krolikowki, John G.; Jones, Deron W.; Pritchard, Kirkwood A.; Struve, Janine; Nandedkar, Sandhya D.; Lohr, Nicole L.; Pagel, Paul S.; Weihrauch, Dorothee

2012-01-01

359

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

2012-02-01

360

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

361

An uncommon cause of transient neurological dysfunction.  

PubMed

Transient neurological dysfunction may be associated with uncommon disorders and should prompt consideration of a broad differential diagnosis when assessing patients with episodic symptoms. The most common causes of transient neurological dysfunction include transient ischemic attack (TIA), seizure disorder, and migraine and its variants. However, underlying unusual pathophysiological processes such as brain tumors can also cause transient neurological dysfunction. Here we present a case of a 68-year-old male with oligodendroglial gliomatosis cerebri (OGC) who presented with TIA-like symptoms. Brain magnetic resonance imaging revealed multiple diffuse T2 hyperintensities within the white and gray matter. Magnetic resonance spectroscopy was suggestive of gliomatosis cerebri and was particularly helpful in this case. The diagnosis of OGC was confirmed by histopathology and molecular genetic studies on brain biopsy tissue. In this report, we discuss the clinical and radiological characteristics of OGC and highlight the unusual presentation of this case. PMID:24982718

Farooq, Muhammad U; Bhatt, Archit; Chang, Howard T

2014-07-01

362

An Uncommon Cause of Transient Neurological Dysfunction  

PubMed Central

Transient neurological dysfunction may be associated with uncommon disorders and should prompt consideration of a broad differential diagnosis when assessing patients with episodic symptoms. The most common causes of transient neurological dysfunction include transient ischemic attack (TIA), seizure disorder, and migraine and its variants. However, underlying unusual pathophysiological processes such as brain tumors can also cause transient neurological dysfunction. Here we present a case of a 68-year-old male with oligodendroglial gliomatosis cerebri (OGC) who presented with TIA-like symptoms. Brain magnetic resonance imaging revealed multiple diffuse T2 hyperintensities within the white and gray matter. Magnetic resonance spectroscopy was suggestive of gliomatosis cerebri and was particularly helpful in this case. The diagnosis of OGC was confirmed by histopathology and molecular genetic studies on brain biopsy tissue. In this report, we discuss the clinical and radiological characteristics of OGC and highlight the unusual presentation of this case.

Bhatt, Archit; Chang, Howard T.

2014-01-01

363

Motion of a disordered polypeptide chain as studied by paramagnetic relaxation enhancements, 15N relaxation, and molecular dynamics simulations: how fast is segmental diffusion in denatured ubiquitin?  

PubMed

Molecular dynamics (MD) simulations have been widely used to analyze dynamic conformational equilibria of folded proteins, especially in relation to NMR observables. However, this approach found little use in the studies of disordered proteins, where the sampling of vast conformational space presents a serious problem. In this paper, we demonstrate that the latest advances in computation technology make it possible to overcome this limitation. The experimentally validated (calibrated) MD models allow for new insights into structure/dynamics of disordered proteins. As a test system, we have chosen denatured ubiquitin in solution with 8 M urea at pH 2. High-temperature MD simulations in implicit solvent have been carried out for the wild-type ubiquitin as well as MTSL-tagged Q2C, D32C, and R74C mutants. To recalibrate the MD data (500 K) in relation to the experimental conditions (278 K, 8 M urea), the time axes of the MD trajectories were rescaled. The scaling factor was adjusted such as to maximize the agreement between the simulated and experimental (15)N relaxation rates. The resulting effective length of the trajectories, 311 ?s, ensures good convergence properties of the MD model. The constructed MD model was validated against the array of experimental data, including additional (15)N relaxation parameters, multiple sets of paramagnetic relaxation enhancements (PREs), and the radius of gyration. In each case, a near-quantitative agreement has been obtained, suggesting that the model is successful. Of note, the MD-based approach rigorously predicts the quantities that are inherently dynamic, i.e., dependent on the motional correlation times. This cannot be accomplished, other than in empirical fashion, on the basis of static structural models (conformational ensembles). The MD model was further used to investigate the relative translational motion of the MTSL label and the individual H(N) atoms. The derived segmental diffusion coefficients proved to be nearly uniform along the peptide chain, averaging to D = 0.49-0.55 × 10(-6) cm(2)/s. This result was verified by direct analysis of the experimental PRE data using the recently proposed Ullman-Podkorytov model. In this model, MTSL and H(N) moieties are treated as two tethered spheres undergoing mutual diffusion in a harmonic potential. The fitting of the experimental data involving D as a single adjustable parameter leads to D = 0.45 × 10(-6) cm(2)/s, in good agreement with the MD-based analyses. This result can be compared with the range of estimates obtained from the resonance energy transfer experiments, D = 0.2-6.0 × 10(-6) cm(2)/s. PMID:21819149

Xue, Yi; Skrynnikov, Nikolai R

2011-09-21

364

Diffusion-induced modulational instability in magnetised semiconductor plasmas: effect of carrier heating  

NASA Astrophysics Data System (ADS)

The present paper is aimed to the exploration of modulational amplification in transversely magnetised diffusive semiconductors. By considering that the origin of modulational interaction lies in the third-order optical susceptibility ?^{(3)} arising from the nonlinear diffusion current density and using coupled mode theory, an analytical investigation of frequency modulational interaction between co-propagating laser beams and internally generated acoustic mode is presented. We have studied the steady state and transient amplification characteristics of modulated waves arising in the transversely magnetised semiconductor plasmas. The effect of carrier heating adds new dimensions to the present study. The heating effect reduces the required threshold amplitude of wave and enhances steady-state as well as transient gain of the generated acoustic mode.

Nimje, N.; Dubey, S.; Ghosh, S. K.

2010-08-01

365

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

366

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

367

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

368

Transient Voltage Recorder  

NASA Technical Reports Server (NTRS)

A voltage transient recorder can detect lightning induced transient voltages. The recorder detects a lightning induced transient voltage and adjusts input amplifiers to accurately record transient voltage magnitudes. The recorder stores voltage data from numerous monitored channels, or devices. The data is time stamped and can be output in real time, or stored for later retrieval. The transient recorder, in one embodiment, includes an analog-to-digital converter and a voltage threshold detector. When an input voltage exceeds a pre-determined voltage threshold, the recorder stores the incoming voltage magnitude and time of arrival. The recorder also determines if its input amplifier circuits clip the incoming signal or if the incoming signal is too low. If the input data is clipped or too low, the recorder adjusts the gain of the amplifier circuits to accurately acquire subsequent components of the lightning induced transients.

Medelius, Pedro J. (Inventor); Simpson, Howard J. (Inventor)

2002-01-01

369

High-energy transients.  

PubMed

We present an overview of high-energy transients in astrophysics, highlighting important advances over the past 50 years. We begin with early discoveries of ?-ray transients, and then delve into physical details associated with a variety of phenomena. We discuss some of the unexpected transients found by Fermi and Swift, many of which are not easily classifiable or in some way challenge conventional wisdom. These objects are important insofar as they underscore the necessity of future, more detailed studies. PMID:23630376

Gehrels, Neil; Cannizzo, John K

2013-06-13

370

Electromagnetic Transients Program (EMTP) primer  

NASA Astrophysics Data System (ADS)

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 be the single most important enhancement to the EMTP. The Primer is an EMTP training manual for new users. It includes introductory material and eleven sample studies so that the reader can learn by the case study method. The Primer is part of a series of new EMTP user manuals which covers program operation, theory, and application guide lines.

Mauser, S. F.; McDermott, T. E.

1985-09-01

371

Coronal transient--eruptive prominence of 1980 August 5  

SciTech Connect

A coronal transient was observed in association with an eruptive prominence event using the Mauna Loa experiment system. The transient, a rarefaction, formed before the acceleration of the eruptive prominence. Upward velocities of various features, as seen in the plane of the sky, show a marked difference as a function of time between the transient and the eruptive prominence. A region of enhanced electron density formed slowly in front of the rarefaction.

Fisher, R.; Garcia, C.J.; Seagraves, P.

1981-06-15

372

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

373

Effective diffusivity and tortuosity in a porous glass immobilization matrix  

Microsoft Academic Search

The effective diffusivity of glucose in porous glass beads was determined using a transient method. Predictions for the intraparticle and surface concentrations were made by an analytical solution of the mass balance. The value of the diffusivity was expected to be lower than the value of the corresponding diffusion coefficient in water, but the opposite was observed. This effect results

L. De Backer; G. Baron

1993-01-01

374

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

375

Transients in Power Systems  

Microsoft Academic Search

Power system engineering largely focuses on steady state analysis. The main areas of power system engineering are power flow studies and fault studies - both steady state technologies. But the world is largely transient, and power systems are always subject to time varying and short lived signals. This technical report concerns several important topics in transient analyses of power systems.

M. Belkhayat; J. Edwards; N. Hoonchareon; O. Marte; D. Stenberg; E. Walters

1995-01-01

376

A continuous time random walk approach to transient flow in heterogeneous porous media  

Microsoft Academic Search

We propose a new physical interpretation of the diffusion process for the piezometric head h(x, t) in heterogeneous aquifers based on the continuous time random walk (CTRW) theory. For the typical heterogeneities considered in this work, we find that a CTRW based diffusion equation for h(x, t) provides better fits to the transient flow simulations than the classical diffusion equation

Andrea Cortis; Christen Knudby

2006-01-01

377

The effects of neglecting displacement currents when studying transient wave propagation in the Earth  

Microsoft Academic Search

Diffusion approximations are often used to study the interaction of transient electromagnetic waves with the Earth. If a frequency-independent conductivity and permittivity are assumed, then neglecting the displacement currents in the Earth reduces the wave equation to the diffusion equation, which sometimes can be solved analytically using elementary special functions. We study the validity of the diffusion approximation for a

Hsueh-Yuan Pao; Steven L. Dvorak; D. G. Dudley

1996-01-01

378

Transient nucleation in glasses  

NASA Technical Reports Server (NTRS)

Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

Kelton, K. F.

1991-01-01

379

Nanosecond transient grating studies of jet-cooled NO2  

NASA Astrophysics Data System (ADS)

We report the application of nanosecond transient grating spectroscopy to probe the excited state level structure of NO2 near 487.9 nm. Intensity and polarization grating transients were obtained in one-color (DFWM) and two-color (TC-RFWM) configurations. Most grating transients exhibit pronounced beats, arising from coherences among excited state hyperfine levels, which are enhanced in polarization grating experiments. Analysis of these beats yields detailed information on the excited state hyperfine level structure at a resolution 100 times smaller than the bandwidth of the applied laser fields. The grating transients are compared to predictions of the grating decomposition method (GDM) using Fourier transform analysis.

Tang, Y.; Schmidt, J. P.; Reid, S. A.

1999-03-01

380

Transient tachypnea - newborn  

MedlinePLUS

TTN; Wet lungs - newborns; Retained fetal lung fluid; Transient RDS; Prolonged transition ... usually within 1 - 2 hours. Symptoms include: Bluish skin color (cyanosis) Rapid breathing, which may occur with ...

381

High energy transients  

NASA Technical Reports Server (NTRS)

A meeting was convened on the campus of the University of California at Santa Cruz during the two-week interval July 11 through July 22, 1983. Roughly 100 participants were chosen so as to give broad representation to all aspects of high energy transients. Ten morning review sessions were held in which invited speakers discussed the current status of observations and theory of the above subjects. Afternoon workshops were also held, usually more than one per day, to informally review various technical aspects of transients, confront shortcomings in theoretical models, and to propose productive courses for future research. Special attention was also given to the instrumentation used to study high energy transient and the characteristics and goals of a dedicated space mission to study transients in the next decade were determined. A listing of articles written by various members of the workshop is included.

Woosley, S. E.

1984-01-01

382

TIA (Transient Ischemic Attack)  

MedlinePLUS

... risk and understand your condition. TIA and Stroke: Medical Emergencies When someone has shown symptoms of a stroke or a TIA (transient ischemic attack), they require immediate medical attention. A doctor will gather information and make ...

383

Transient Response Analysis  

NASA Technical Reports Server (NTRS)

Transient Response Analysis Program, TRAP aids in analysis of frequency response of force-transmission and shock-damping devices. Devices analyzed with TRAP include hydraulic actuators, automotive shock absorbers and electromechanical actuators.

Blackman, L. D.

1985-01-01

384

Transient Ischemic Attack (TIA)  

MedlinePLUS

... Women and Stroke Fibromuscular Dysplasia Patent Foramen Ovale (PFO) Transient Ischemic Attack (TIA) TIA Risk Calculator Recurrent ... have someone take you to the hospital immediately. Treatment can be more helpful if given quickly. Stroke ...

385

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

386

Hillslope diffusion  

NSDL National Science Digital Library

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

Mcdermott, Jeni

387

Gamma ray transients  

NASA Technical Reports Server (NTRS)

The discovery of cosmic gamma ray bursts was made with systems designed at Los Alamos Laboratory for the detection of nuclear explosions beyond the atmosphere. HELIOS-2 was the first gamma ray burst instrument launched; its initial results in 1976, seemed to deepen the mystery around gamma ray transients. Interplanetary spacecraft data were reviewed in terms of explaining the behavior and source of the transients.

Cline, Thomas L.

1987-01-01

388

Penetration Enhancers for Human Skin: Mode of Action of 2Pyrrolidone and Dimethylformamide on Partition and Diffusion of Model Compounds Water, n-Alcohols, and Caffeine  

Microsoft Academic Search

Penetration-enhancing solvents may modify diffusional routes through the stratum corneum and the partitioning of drugs into these pathways. To investigate the mechanisms of action of enhancers, steady-state fluxes were measured in vitro for polar methanol, nonpolar octanol, and an intermediate compound, caffeine. selected as model penetrants; human stratum corneum conditioned on both sides with water or accelerants (2-pyrrolidone or dimethylformamide

Diane Southwell; Brian W. Barry

1983-01-01

389

On Asymmetric Diffusional Solidification During Transient Liquid Phase Bonding  

NASA Astrophysics Data System (ADS)

The underlying cause of asymmetric diffusion solidification which alters microstructure during transient liquid phase bonding under low temperature gradient was studied. A new solute-conserving asymmetric numerical model coupled with experimental verification showed that a transition from bi-directional to unidirectional solidification, under a constant temperature gradient, is controlled by competition between liquid and solid-state diffusion at one of the two liquid-solid interfaces. This mechanistic understanding would aid a more effective use of the process.

Ghobadi Bigvand, A.; Ojo, Olanrewaju A.

2014-04-01

390

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.

391

Inhomogeneous forcing and transient climate sensitivity  

NASA Astrophysics Data System (ADS)

Understanding climate sensitivity is critical to projecting climate change in response to a given forcing scenario. Recent analyses have suggested that transient climate sensitivity is at the low end of the present model range taking into account the reduced warming rates during the past 10-15 years during which forcing has increased markedly. In contrast, comparisons of modelled feedback processes with observations indicate that the most realistic models have higher sensitivities. Here I analyse results from recent climate modelling intercomparison projects to demonstrate that transient climate sensitivity to historical aerosols and ozone is substantially greater than the transient climate sensitivity to CO2. This enhanced sensitivity is primarily caused by more of the forcing being located at Northern Hemisphere middle to high latitudes where it triggers more rapid land responses and stronger feedbacks. I find that accounting for this enhancement largely reconciles the two sets of results, and I conclude that the lowest end of the range of transient climate response to CO2 in present models and assessments (<1.3 °C) is very unlikely.

Shindell, Drew T.

2014-04-01

392

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

393

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

394

Steady-state and transient results on insulation materials.  

National Technical Information Service (NTIS)

The Unguarded Thin-Heater Apparatus (UTHA, ASTM C 1114) was used to determine the thermal conductivity (k), specific heat (C), and thermal diffusivity ((alpha)) of selected building materials from 24 to 50(degree)C. Steady-state and transient measurements...

R. S. Graves D. W. Yarbrough D. L. McElroy H. A. Fine

1991-01-01

395

Transient osteoporosis of the femoral condyle: a case report  

Microsoft Academic Search

In this paper, we describe a patient with transient osteoporosis of the femoral condyle. A differential diagnosis should be made for osteonecrosis, infectious disorders, and infiltrative neoplasms based on the normal laboratory findings and diffuse bone edema pattern in MRI. Since this disorder is self-limiting, both the surgeon and clinician should be aware of this condition and must avoid unnecessary

Takeshi Komatsu; Yoshinori Kadoya; Yukihide Minoda; Toshiaki Masada; Yoshiki Yamano

2002-01-01

396

Bilateral Transient Osteoporosis of the Hip in a Young Man  

Microsoft Academic Search

Transient osteoporosis of the hip (TOH) is a rare disorder of unknown cause that is characterized by diffuse bone marrow edema of the femoral neck and head. A case of bilateral TOH occurring in a 32-yr-old man is reported and the radiological findings and bone densitometry that illustrate the natural history of this disorder are presented. The management of this

Mark J. Bolland

2008-01-01

397

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

398

Multiple transient nonobstructing intussusceptions in resolving intramural hemorrhage of the small intestine  

Microsoft Academic Search

Multiple transient intussuceptions of the small intestine may occur following diffuse intramural hemorrhage. Such intussusceptions have been reported in gastrointestinal allergy and sprue. A case is presented in which transient intussusceptions involved several different segments of the small bowel but produced no symptoms. A disordered motor function during the recovery from the intestinal hemorrhage may explain the intussusceptions.

Juan J. Cabrera; Talmadge R. Howell; William R. Fields

1972-01-01

399

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

400

Transient thermoreflectance imaging of active photonic crystals  

NASA Astrophysics Data System (ADS)

Transient thermoreflectance imaging is used to study the dynamics of the temperature inside active two-dimensional photonic crystals (PhCs). We developed a pump-probe setup suited for optically pumped devices that presents submicrosecond time resolution and submicrometer spatial resolution. Characteristic thermal dissipation times of 429 ns in a PhC Bloch mode cavity and of 999 ns in a PhC membrane are measured. This technique gives also access to the diffusivity of the suspended PhC.

Moreau, Virginie; Tessier, Gilles; Raineri, Fabrice; Brunstein, Maia; Yacomotti, Alejandro; Raj, Rama; Sagnes, Isabelle; Levenson, Ariel; de Wilde, Yannick

2010-03-01

401

Lightning-Transient Recorder  

NASA Technical Reports Server (NTRS)

Battery-powered system operates for more than one year. Recorder digitizes and records up to 146 current samples at selected intervals during lightning stroke. System continues to store time tags of lightning strokes even if transient current memory is full.

Grumm, R. L.

1984-01-01

402

Gestational transient thyrotoxicosis.  

PubMed

Gestational transient thyrotoxicosis refers to non-autoimmune hyperthyroidism in pregnant women and it is associated with hyperemesis gravidarum. During pregnancy, there are some alterations in thyroid gland, such as elevation of thyroxine binding globulin, increased iodium clearance in kidneys, and stimulation of thyroid gland by human chorionic gonadotropin. Hitherto, the pathophysiology underlying the development of gestational transient thyrotoxicosis has not been fully recognized. Studies showed that human chorionic gonadotropin, an agonist of thyroid stimulating hormone, may stimulate thyroid stimulating hormone receptor, leading to increased thyroid hormone. Diagnosis of gestational transient thyrotoxicosis is established based on inexistence history of previous hyperthyroidism, elevation of thyroid hormone, absence of hyperthyroid abnormalities signs on physical examination (such as: enlargement of thyroid gland, exophthalmia), and the absent of positive thyroid autoantibody. Generally, gestational transient thyrotoxicosis does not require medication, unless if hyperemesis gravidarum is present, thus the patient has to be hospitalized to receive intravenous rehydration, electrolyte correction and antiemetic medication. On cases with worsened or prolonged symptoms, anti-thyroid agents such as short term propiltiourasil is needed. PMID:19390130

Albaar, M Taha; Adam, John M F

2009-04-01

403

Partial transient osteoporosis  

Microsoft Academic Search

Regional transient osteoporosis (algodystrophie décalcifiante) has been recognised as a clinical and radiological syndrome in a number of reports published between 1947 and 1968 [16, 17, 23, 24, 11]. The condition is characterised clinically by the development of severe and often incapacitating pain around a major joint, usually the ankle, the knee, or the hip in middle-aged and elderly adults.

M. Lequesne; M. Kerboull; M. Bensasson; C. Perez; R. Dreiser; A. Forest

1977-01-01

404

Transient global ischemia enhances phosphorylation of the GluR1 subunit of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor in the hippocampal CA1 region in rats.  

PubMed

Phosphorylation of the GluR1 subunit of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor has been implicated in the regulation of the receptor channel. We investigated the effects of transient global ischemia in rats on phosphorylation of the GluR1 subunit in the hippocampal CA1 and CA3/dentate gyrus. Transient ischemia induced an increase in the phosphorylation of GluR1 at Ser831 in the CA1 at 1 h of reperfusion. In contrast, the phosphorylation of Ser845 in neither region was affected by the ischemia. The amounts of calcium/calmodulin-dependent kinase (CaMKII) and its activated form, but not cAMP-dependent protein kinase subunits, were increased in a crude membrane fraction after ischemia. The results suggest that an activated CaMKII may phosphorylate Ser831 of GluR1 and a consequent phosphorylation of GluR1 may be related to pathogenic events occurring in the vulnerable subfield of the hippocampus after transient global ischemia. PMID:12676337

Takagi, Yuko; Takagi, Norio; Besshoh, Shintaro; Miyake-Takagi, Keiko; Takeo, Satoshi

2003-04-24

405

Diagnostic assessment by dynamic contrast-enhanced and diffusion-weighted magnetic resonance in differentiation of breast lesions under different imaging protocols  

PubMed Central

Background The apparent diffusion coefficient (ADC) is a highly diagnostic factor in discriminating malignant and benign breast masses in diffusion-weighted magnetic resonance imaging (DW-MRI). The combination of ADC and other pictorial characteristics has improved lesion type identification accuracy. The objective of this study was to reassess the findings on an independent patient group by changing the magnetic field from 1.5-Tesla to 3.0-Tesla. Methods This retrospective study consisted of a training group of 234 female patients, including 85 benign and 149 malignant lesions, imaged using 1.5-Tesla MRI, and a test group of 95 female patients, including 19 benign and 85 malignant lesions, imaged using 3.0-Tesla MRI. The lesion of interest was segmented from the raw image and four sets of measurements describing the morphology, kinetics, DW-MRI, and texture of the pictorial properties of each lesion were obtained. Each lesion was characterized by 28 features in total. Three classical machine-learning algorithms were used to build prediction models on the training group, which evaluated the prognostic performance of the multi-sided features in three scenarios. To reduce information redundancy, five highly diagnostic factors were selected to obtain a compact yet informative characterization of the lesion status. Results Three classification models were built on the training of 1.5-Tesla patients and were tested on the independent 3.0-Tesla test group. The following results were found. i) Characterization of breast masses in a multi-sided way dramatically increased prediction performance. The usage of all features gave a higher performance in both sensitivity and specificity than any individual feature groups or their combinations. ii) ADC was a highly effective factor in improving the sensitivity in discriminating malignant from benign masses. iii) Five features, namely ADC, Sum Average, Entropy, Elongation, and Sum Variance, were selected to achieve the highest performance in diagnosis of the 3.0-Tesla patient group. Conclusions The combination of ADC and other multi-sided characteristics can increase the capability of discriminating malignant and benign breast lesions, even under different imaging protocols. The selected compact feature subsets achieved a high diagnostic performance and thus are promising in clinical applications for discriminating lesion type and for personalized treatment planning.

2014-01-01

406

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

407

[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

408

The role of external electric fields in enhancing ion mobility, drift velocity, and drift-diffusion rates in aqueous electrolyte solutions.  

PubMed

Molecular simulations have been carried out using the method of molecular dynamics to investigate the role of external electric fields on the ion mobility, drift velocity, and drift-diffusion rate of ions in aqueous electrolyte solutions. These properties are critical for a range of processes including electrodialysis, electro-deionization, electrophoresis, and electroosmosis. Our results show that external electric fields relax the hydrated ion structure at significantly larger time scales (between 300 and 800 ps), than most other relaxation processes in solutions (generally of the order of 1 ps). Previou