A role for chromosomal instability in the development of and selection for radioresistant cell variants

NASA Technical Reports Server (NTRS)

Limoli, C. L.; Corcoran, J. J.; Jordan, R.; Morgan, W. F.; Schwartz, J. L.

2001-01-01

Chromosome instability is a common occurrence in tumour cells. We examined the hypothesis that the elevated rate of mutation formation in unstable cells can lead to the development of clones of cells that are resistant to the cancer therapy. To test this hypothesis, we compared chromosome instability to radiation sensitivity in 30 independently isolated clones of GM10115 human-hamster hybrid cells. There was a broader distribution of radiosensitivity and a higher mean SF(2)in chromosomally unstable clones. Cytogenetic and DNA double-strand break rejoining assays suggest that sensitivity was a function of DNA repair efficiency. In the unstable population, the more radioresistant clones also had significantly lower plating efficiencies. These observations suggest that chromosome instability in GM10115 cells can lead to the development of cell variants that are more resistant to radiation. In addition, these results suggest that the process of chromosome breakage and recombination that accompanies chromosome instability might provide some selective pressure for more radioresistant variants. Copyright 2001 Cancer Research Campaign.

Strongly nonlinear dynamics of electrolytes in large ac voltages.

PubMed

Højgaard Olesen, Laurits; Bazant, Martin Z; Bruus, Henrik

2010-07-01

We study the response of a model microelectrochemical cell to a large ac voltage of frequency comparable to the inverse cell relaxation time. To bring out the basic physics, we consider the simplest possible model of a symmetric binary electrolyte confined between parallel-plate blocking electrodes, ignoring any transverse instability or fluid flow. We analyze the resulting one-dimensional problem by matched asymptotic expansions in the limit of thin double layers and extend previous work into the strongly nonlinear regime, which is characterized by two features--significant salt depletion in the electrolyte near the electrodes and, at very large voltage, the breakdown of the quasiequilibrium structure of the double layers. The former leads to the prediction of "ac capacitive desalination" since there is a time-averaged transfer of salt from the bulk to the double layers, via oscillating diffusion layers. The latter is associated with transient diffusion limitation, which drives the formation and collapse of space-charge layers, even in the absence of any net Faradaic current through the cell. We also predict that steric effects of finite ion sizes (going beyond dilute-solution theory) act to suppress the strongly nonlinear regime in the limit of concentrated electrolytes, ionic liquids, and molten salts. Beyond the model problem, our reduced equations for thin double layers, based on uniformly valid matched asymptotic expansions, provide a useful mathematical framework to describe additional nonlinear responses to large ac voltages, such as Faradaic reactions, electro-osmotic instabilities, and induced-charge electrokinetic phenomena.

On the parameterization of interleaving and turbulent mixing using CTD data from the Azores Frontal Zone

NASA Astrophysics Data System (ADS)

Kuzmina, N. P.

2000-01-01

CTD-data obtained in the Azores Frontal Zone using a towed undulating vehicle are analyzed to study the relationship between characteristics of intrusions and mean parameters of the thermohaline field. A self-similar dependence between intrusion intensity and hydrological parameters is obtained. The most well-founded interpretation of the empirical dependence is as follows: (a) the main source supporting intrusive layering is the salt finger convection; (b) the abrupt decrease of intrusion intensity with the reduction of geostrophic Richardson number obtained from the analysis is explained by the beginning of turbulence when salt fingers do not work any longer, so the "driving force" for intrusive motion disappears. These results are consistent with the conclusions of the paper [Kuzmina N.P., Rodionov V.B., 1992. About the influence of baroclinicity upon generation of the thermohaline intrusions in the oceanic frontal zones. Izvestiya Akad. Nauk SSSR, Atmosperic and Oceanic Physics 28 (10-11), 1077-1086]. These conclusions imply that there are three main mechanisms of intrusive layering at oceanic fronts, namely the 2D baroclinic instability of geostrophic flow, the vertical shear instability and the thermohaline instability where the driving source of intrusive motion is double diffusive convection. The baroclinic and thermohaline instabilities can generate intrusions of large vertical scale, while vertical shear instability usually gives rise to thin turbulent layers. Turbulence in these thin layers can prevent salt finger convection and thus destroy the energy source of the intrusive motion conditioned by thermoclinicity. Therefore, the baroclinicity plays two parts in the processes of the intrusive layering: (1) it prevents double-diffusion interleaving by means of turbulence, and (2) it generates intrusions due to the 2D baroclinic instability of geostrophic current. Using features of thermohaline interleaving as a specific tracer of turbulent mixing, we have estimated turbulent mixing coefficient as k t˜ Ri-0.8 ( Ri>1), where Ri is the geostrophic Richardson number. Application of the proposed approach to other frontal zones is discussed.

Ultrafast atomic layer-by-layer oxygen vacancy-exchange diffusion in double-perovskite LnBaCo2O5.5+δ thin films.

PubMed

Bao, Shanyong; Ma, Chunrui; Chen, Garry; Xu, Xing; Enriquez, Erik; Chen, Chonglin; Zhang, Yamei; Bettis, Jerry L; Whangbo, Myung-Hwan; Dong, Chuang; Zhang, Qingyu

2014-04-22

Surface exchange and oxygen vacancy diffusion dynamics were studied in double-perovskites LnBaCo2O5.5+δ (LnBCO) single-crystalline thin films (Ln = Er, Pr; -0.5 < δ < 0.5) by carefully monitoring the resistance changes under a switching flow of oxidizing gas (O2) and reducing gas (H2) in the temperature range of 250 ~ 800 °C. A giant resistance change ΔR by three to four orders of magnitude in less than 0.1 s was found with a fast oscillation behavior in the resistance change rates in the ΔR vs. t plots, suggesting that the oxygen vacancy exchange diffusion with oxygen/hydrogen atoms in the LnBCO thin films is taking the layer by layer oxygen-vacancy-exchange mechanism. The first principles density functional theory calculations indicate that hydrogen atoms are present in LnBCO as bound to oxygen forming O-H bonds. This unprecedented oscillation phenomenon provides the first direct experimental evidence of the layer by layer oxygen vacancy exchange diffusion mechanism.

Electro-convective versus electroosmotic instability in concentration polarization.

PubMed

Rubinstein, Isaak; Zaltzman, Boris

2007-10-31

Electro-convection is reviewed as a mechanism of mixing in the diffusion layer of a strong electrolyte adjacent to a charge-selective solid, such as an ion exchange (electrodialysis) membrane or an electrode. Two types of electro-convection in strong electrolytes may be distinguished: bulk electro-convection, due to the action of the electric field upon the residual space charge of a quasi-electro-neutral bulk solution, and convection induced by electroosmotic slip, due to electric forces acting in the thin electric double layer of either quasi-equilibrium or non-equilibrium type near the solid/liquid interface. According to recent studies, the latter appears to be the likely source of mixing in the diffusion layer, leading to 'over-limiting' conductance in electrodialysis. Electro-convection near a planar uniform charge selective solid/liquid interface sets on as a result of hydrodynamic instability of one-dimensional steady state electric conduction through such an interface. We compare the results of linear stability analysis obtained for instabilities of this kind appearing in the full electro-convective and limiting non-equilibrium electroosmotic formulations. The short- and long-wave aspects of these instabilities are discussed along with the wave number selection principles.

Observation of instability-induced current redistribution in a spherical-torus plasma.

PubMed

Menard, J E; Bell, R E; Gates, D A; Kaye, S M; LeBlanc, B P; Levinton, F M; Medley, S S; Sabbagh, S A; Stutman, D; Tritz, K; Yuh, H

2006-09-01

A motional Stark effect diagnostic has been utilized to reconstruct the parallel current density profile in a spherical-torus plasma for the first time. The measured current profile compares favorably with neoclassical theory when no large-scale magnetohydrodynamic instabilities are present in the plasma. However, a current profile anomaly is observed during saturated interchange-type instability activity. This apparent anomaly can be explained by redistribution of neutral beam injection current drive and represents the first observation of interchange-type instabilities causing such redistribution. The associated current profile modifications contribute to sustaining the central safety factor above unity for over five resistive diffusion times, and similar processes may contribute to improved operational scenarios proposed for ITER.

The Resistive-Wall Instability in Multipulse Linear Induction Accelerators

DOE PAGES

Ekdahl, Carl

2017-05-01

The resistive-wall instability results from the Lorentz force on the beam due to the beam image charge and current. If the beam pipe is perfectly conducting, the electric force due to the image charge attracts the beam to the pipe wall, and the magnetic force due to the image current repels the beam from the wall. For a relativistic beam, these forces almost cancel, leaving a slight attractive force, which is easily overcome by external magnetic focusing. However, if the beam pipe is not perfectly conducting, the magnetic field due to the image current decays on a magnetic-diffusion time scale.more » If the beam pulse is longer than the magnetic diffusion time, the repulsion of the beam tail will be weaker than the repulsion of the beam head. In the absence of an external focusing force, this causes a head-to-tail sweep of the beam toward the wall. This instability is usually thought to be a concern only for long-pulse relativistic electron beams. However, with the advent of multipulse, high current linear induction accelerators, the possibility of pulse-to-pulse coupling of this instability should be investigated. Lastly, we have explored pulse-to-pulse coupling using the linear accelerator model for Dual Axis Radiography for Hydrodynamic Testing beam dynamics code, and we present the results of this paper.« less

The Resistive-Wall Instability in Multipulse Linear Induction Accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ekdahl, Carl

The resistive-wall instability results from the Lorentz force on the beam due to the beam image charge and current. If the beam pipe is perfectly conducting, the electric force due to the image charge attracts the beam to the pipe wall, and the magnetic force due to the image current repels the beam from the wall. For a relativistic beam, these forces almost cancel, leaving a slight attractive force, which is easily overcome by external magnetic focusing. However, if the beam pipe is not perfectly conducting, the magnetic field due to the image current decays on a magnetic-diffusion time scale.more » If the beam pulse is longer than the magnetic diffusion time, the repulsion of the beam tail will be weaker than the repulsion of the beam head. In the absence of an external focusing force, this causes a head-to-tail sweep of the beam toward the wall. This instability is usually thought to be a concern only for long-pulse relativistic electron beams. However, with the advent of multipulse, high current linear induction accelerators, the possibility of pulse-to-pulse coupling of this instability should be investigated. Lastly, we have explored pulse-to-pulse coupling using the linear accelerator model for Dual Axis Radiography for Hydrodynamic Testing beam dynamics code, and we present the results of this paper.« less

Double-Diffusive Finger Convection: Flow Field Evolution in a Hele-Shaw Cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

COOPER,CLAY A.; GLASS JR.,ROBERT J.; TYLER,SCOTT W.

Double-diffusive finger convection is a hydrodynamic instability that can occur when two components with different diffusivities are oppositely stratified with respect to the fluid density gradient as a critical condition is exceeded. Laboratory experiments were designed using sodium chloride and sucrose solutions in a Hele-Shaw cell. A high resolution, full field, light transmission technique was used to study the development of the instability. The initial buoyancy ratio (R{sub p}), which is a ratio of fluid density contributions by the two solutes, was varied systematically in the experiments so that the range of parameter space spanned conditions that were nearly stablemore » (R{sub p} = 2.8) to those that were moderately unstable (R{sub p} = 1.4). In systems of low R{sub p}, fingers develop within several minutes, merge with adjacent fingers, form conduits, and stall before newer-generated fingers travel through the conduits and continue the process. Solute fluxes in low R{sub p} systems quickly reach steady state and are on the order of 10{sup {minus}6} m{sup 2} sec{sup {minus}1}. In the higher R{sub p} experiments, fingers are slower to evolve and do not interact as dynamically as in the lower R{sub p} systems. Our experiment with initial R{sub p} = 2.8 exhibited flux on the order of that expected for a similar diffusive system (i.e., 10{sup {minus}7} m{sup 2} sec{sup {minus}1}), although the structures were very different than the pattern of transport expected in a diffusing system. Mass flux decayed as t{sup 1/2} in two experiments each with initial R{sub p} = 2.4 and 2.8.« less

Droplet formation at the non-equilibrium water/water (w/w) interface

NASA Astrophysics Data System (ADS)

Chao, Youchuang; Mak, Sze Yi; Kong, Tiantian; Ding, Zijing; Shum, Ho Cheung

2017-11-01

The interfacial instability at liquid-liquid interfaces has been intensively studied in recent years due to their important role in nature and technology. Among them, two classic instabilities are Rayleigh-Taylor (RT) and double diffusive (DD) instabilities, which are practically relevant to many industrial processes, such as geologic CO2 sequestration. Most experimental and theoretical works have focused on RT or DD instability in binary systems. However, the study of such instability in complex systems, such as non-equilibrium ternary systems that involves mass-transfer-induced phase separation, has received less attention. Here, by using a ternary system known as the aqueous two-phase system (ATPS), we investigate experimentally the behavior of non-equilibrium water/water (w/w) interfaces in a vertically orientated Hele-Shaw cell. We observe that an array of fingers emerge at the w/w interface, and then break into droplets. We explore the instability using different concentrations of two aqueous phases. Our experimental findings are expected to inspire the mass production of all-aqueous emulsions in a simple setup.

Induction of virus resistance by exogenous application of double-stranded RNA.

PubMed

Mitter, Neena; Worrall, Elizabeth A; Robinson, Karl E; Xu, Zhi Ping; Carroll, Bernard J

2017-10-01

Exogenous application of double-stranded RNA (dsRNA) for virus resistance in plants represents a very attractive alternative to virus resistant transgenic crops or pesticides targeting virus vectors. However, the instability of dsRNA sprayed onto plants is a major challenge as spraying naked dsRNA onto plants provides protection against homologous viruses for only 5 days. Innovative approaches, such as the use of nanoparticles as carriers of dsRNA for improved stability and sustained release, are emerging as key disruptive technologies. Knowledge is still limited about the mechanism of entry, transport and processing of exogenously applied dsRNA in plants. Cost of dsRNA and regulatory framework will be key influencers towards practical adoption of this technology. Copyright © 2017 Elsevier B.V. All rights reserved.

‘Double cortex’ sign on FDG-PET/CT in diffuse band heterotopia

PubMed Central

Tripathi, Madhavi; Tripathi, Manjari; Kumar, Ganesh; Malhotra, Arun; Bal, Chandra Sekhar

2013-01-01

F-18 Fluorodeoxyglucose (FDG) Positron emission tomography/Computed Tomography (PET/CT) has come to play an increasingly important role for the pre-surgical evaluation of drug resistant epilepsy and complements Magnetic Resonance Imaging (MRI) in the evaluation of grey matter heterotopias. This case illustrates the characteristic pattern of metabolic abnormality in diffuse band heterotopia (DBH) which is otherwise called double cortex syndrome. The presence of metabolic activity in the heterotopic inner cortical band and in the overlying true cortex gives rise to the ‘double cortex’ sign on FDG-PET, concurrent CT provides a good anato-metabolic coregistration. PMID:24379541

Front fingering and complex dynamics driven by the interaction of buoyancy and diffusive instabilities.

PubMed

D'Hernoncourt, J; Merkin, J H; De Wit, A

2007-09-01

Traveling fronts can become transversally unstable either because of a diffusive instability arising when the key variables diffuse at sufficiently different rates or because of a buoyancy-driven Rayleigh-Taylor mechanism when the density jump across the front is statically unfavorable. The interaction between such diffusive and buoyancy instabilities of fronts is analyzed theoretically for a simple model system. Linear stability analysis and nonlinear simulations show that their interplay changes considerably the stability properties with regard to the pure Rayleigh-Taylor or diffusive instabilities of fronts. In particular, an instability scenario can arise which triggers convection around statically stable fronts as a result of differential diffusion. Moreover, spatiotemporal chaos can be observed when both buoyancy and diffusive effects cooperate to destabilize the front. Experimental conditions to test our predictions are suggested.

The Effect of Rotation on Oscillatory Double-diffusive Convection (Semiconvection)

NASA Astrophysics Data System (ADS)

Moll, Ryan; Garaud, Pascale

2017-01-01

Oscillatory double-diffusive convection (ODDC, more traditionally called semiconvection) is a form of linear double-diffusive instability that occurs in fluids that are unstably stratified in temperature (Schwarzschild unstable), but stably stratified in chemical composition (Ledoux stable). This scenario is thought to be quite common in the interiors of stars and giant planets, and understanding the transport of heat and chemical species by ODDC is of great importance to stellar and planetary evolution models. Fluids unstable to ODDC have a tendency to form convective thermocompositional layers that significantly enhance the fluxes of temperature and chemical composition compared with microscopic diffusion. Although a number of recent studies have focused on studying properties of both layered and nonlayered ODDC, few have addressed how additional physical processes such as global rotation affect its dynamics. In this work, we study first how rotation affects the linear stability properties of rotating ODDC. Using direct numerical simulations, we then analyze the effect of rotation on properties of layered and nonlayered ODDC, and we study how the angle of the rotation axis with respect to the direction of gravity affects layering. We find that rotating systems can be broadly grouped into two categories based on the strength of rotation. The qualitative behavior in the more weakly rotating group is similar to nonrotating ODDC, but strongly rotating systems become dominated by vortices that are invariant in the direction of the rotation vector and strongly influence transport. We find that whenever layers form, rotation always acts to reduce thermal and compositional transport.

Viscous, resistive MHD stability computed by spectral techniques

NASA Technical Reports Server (NTRS)

Dahlburg, R. B.; Zang, T. A.; Montgomery, D.; Hussaini, M. Y.

1983-01-01

Expansions in Chebyshev polynomials are used to study the linear stability of one dimensional magnetohydrodynamic (MHD) quasi-equilibria, in the presence of finite resistivity and viscosity. The method is modeled on the one used by Orszag in accurate computation of solutions of the Orr-Sommerfeld equation. Two Reynolds like numbers involving Alfven speeds, length scales, kinematic viscosity, and magnetic diffusivity govern the stability boundaries, which are determined by the geometric mean of the two Reynolds like numbers. Marginal stability curves, growth rates versus Reynolds like numbers, and growth rates versus parallel wave numbers are exhibited. A numerical result which appears general is that instability was found to be associated with inflection points in the current profile, though no general analytical proof has emerged. It is possible that nonlinear subcritical three dimensional instabilities may exist, similar to those in Poiseuille and Couette flow.

Diffusive instabilities in a hyperbolic activator-inhibitor system with superdiffusion

NASA Astrophysics Data System (ADS)

Mvogo, Alain; Macías-Díaz, Jorge E.; Kofané, Timoléon Crépin

2018-03-01

We investigate analytically and numerically the conditions for wave instabilities in a hyperbolic activator-inhibitor system with species undergoing anomalous superdiffusion. In the present work, anomalous superdiffusion is modeled using the two-dimensional Weyl fractional operator, with derivative orders α ∈ [1,2]. We perform a linear stability analysis and derive the conditions for diffusion-driven wave instabilities. Emphasis is placed on the effect of the superdiffusion exponent α , the diffusion ratio d , and the inertial time τ . As the superdiffusive exponent increases, so does the wave number of the Turing instability. Opposite to the requirement for Turing instability, the activator needs to diffuse sufficiently faster than the inhibitor in order for the wave instability to occur. The critical wave number for wave instability decreases with the superdiffusive exponent and increases with the inertial time. The maximum value of the inertial time for a wave instability to occur in the system is τmax=3.6 . As one of the main results of this work, we conclude that both anomalous diffusion and inertial time influence strongly the conditions for wave instabilities in hyperbolic fractional reaction-diffusion systems. Some numerical simulations are conducted as evidence of the analytical predictions derived in this work.

On the relationship between finger width, velocity, and fluxes in thermohaline convection

NASA Astrophysics Data System (ADS)

Sreenivas, K. R.; Singh, O. P.; Srinivasan, J.

2009-02-01

Double-diffusive finger convection occurs in many natural processes. The theories for double-diffusive phenomena that exist at present consider systems with linear stratification in temperature and salinity. The double-diffusive systems with step change in salinity and temperature are, however, not amenable to simple stability analysis. Hence factors that control the width of the finger, velocity, and fluxes in systems that have step change in temperature and salinity have not been understood so far. In this paper we provide new physical insight regarding factors that influence finger convection in two-layer double-diffusive system through two-dimensional numerical simulations. Simulations have been carried out for density stability ratios (Rρ) from 1.5 to 10. For each density stability ratio, the thermal Rayleigh number (RaT) has been systematically varied from 7×103 to 7×108. Results from these simulations show how finger width, velocity, and flux ratios in finger convection are interrelated and the influence of governing parameters such as density stability ratio and the thermal Rayleigh number. The width of the incipient fingers at the time of onset of instability has been shown to vary as RaT-1/3. Velocity in the finger varies as RaT1/3/Rρ. Results from simulation agree with the scale analysis presented in the paper. Our results demonstrate that wide fingers have lower velocities and flux ratios compared to those in narrow fingers. This result contradicts present notions about the relation between finger width and flux ratio. A counterflow heat-exchanger analogy is used in understanding the dependence of flux ratio on finger width and velocity.

Contributions of Microtubule Dynamic Instability and Rotational Diffusion to Kinetochore Capture.

PubMed

Blackwell, Robert; Sweezy-Schindler, Oliver; Edelmaier, Christopher; Gergely, Zachary R; Flynn, Patrick J; Montes, Salvador; Crapo, Ammon; Doostan, Alireza; McIntosh, J Richard; Glaser, Matthew A; Betterton, Meredith D

2017-02-07

Microtubule dynamic instability allows search and capture of kinetochores during spindle formation, an important process for accurate chromosome segregation during cell division. Recent work has found that microtubule rotational diffusion about minus-end attachment points contributes to kinetochore capture in fission yeast, but the relative contributions of dynamic instability and rotational diffusion are not well understood. We have developed a biophysical model of kinetochore capture in small fission-yeast nuclei using hybrid Brownian dynamics/kinetic Monte Carlo simulation techniques. With this model, we have studied the importance of dynamic instability and microtubule rotational diffusion for kinetochore capture, both to the lateral surface of a microtubule and at or near its end. Over a range of biologically relevant parameters, microtubule rotational diffusion decreased capture time, but made a relatively small contribution compared to dynamic instability. At most, rotational diffusion reduced capture time by 25%. Our results suggest that while microtubule rotational diffusion can speed up kinetochore capture, it is unlikely to be the dominant physical mechanism for typical conditions in fission yeast. In addition, we found that when microtubules undergo dynamic instability, lateral captures predominate even in the absence of rotational diffusion. Counterintuitively, adding rotational diffusion to a dynamic microtubule increases the probability of end-on capture. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Effect of toroidal rotation on resistive magnetohydrodynamic instability with a nonmonotonic q profile in cylindrical geometry

NASA Astrophysics Data System (ADS)

Xu, J. Q.; Peng, X. D.

2018-04-01

The effect of plasma rotation on the linear stability of the resistive magnetohydrodynamic (MHD) instabilities with a nonmonotonic q profile is investigated numerically in the cylindrical geometry. The results have shown that the plasma rotation has a stabilization effect on the double tearing modes (DTMs) depending on the magnitude of the velocity, while the velocity shear has a relatively weak effect. The effect of rotation on DTMs is determined by the velocity at each rational surface. A toroidal velocity imposed on the innermost rational surface has a weak effect on m > 1 DTMs. When the velocity is imposed on the outboard resonant surface, the growth rates of the DTMs are reduced for m > 1 modes; however, it has an obvious destabilizing effect on both m = 1 (with m the poloidal mode number) DTM and single tearing mode branches if the distance between the two rational surfaces is sufficiently small. It is shown that the effect of plasma rotation on the growth rates of the MHD instabilities is in phase with the integrated value of the coupling between potential fluctuation and magnetic flux perturbation.

Azimuthal magnetorotational instability with super-rotation

NASA Astrophysics Data System (ADS)

Rüdiger, G.; Schultz, M.; Gellert, M.; Stefani, F.

2018-02-01

It is demonstrated that the azimuthal magnetorotational instability (AMRI) also works with radially increasing rotation rates contrary to the standard magnetorotational instability for axial fields which requires negative shear. The stability against non-axisymmetric perturbations of a conducting Taylor-Couette flow with positive shear under the influence of a toroidal magnetic field is considered if the background field between the cylinders is current free. For small magnetic Prandtl number the curves of neutral stability converge in the (Hartmann number,Reynolds number) plane approximating the stability curve obtained in the inductionless limit . The numerical solutions for indicate the existence of a lower limit of the shear rate. For large the curves scale with the magnetic Reynolds number of the outer cylinder but the flow is always stable for magnetic Prandtl number unity as is typical for double-diffusive instabilities. We are particularly interested to know the minimum Hartmann number for neutral stability. For models with resting or almost resting inner cylinder and with perfectly conducting cylinder material the minimum Hartmann number occurs for a radius ratio of \\text{in}=0.9$ . The corresponding critical Reynolds numbers are smaller than 4$ .

An experimental study of the role of particle diffusive convection on the residence time of volcanic ash clouds

NASA Astrophysics Data System (ADS)

Deal, E.; Carazzo, G.; Jellinek, M.

2013-12-01

The longevity of volcanic ash clouds generated by explosive volcanic plumes is difficult to predict. Diffusive convective instabilities leading to the production of internal layering are known to affect the stability and longevity of these clouds, but the detailed mechanisms controlling particle dynamics and sedimentation are poorly understood. We present results from a series of analog experiments reproducing diffusive convection in a 2D (Hele-Shaw) geometry, which allow us to constrain conditions for layer formation, sedimentation regime and cloud residence time as a function of only the source conditions. We inject a turbulent particle-laden jet sideways into a tank containing a basal layer of salt water and an upper layer of fresh water, which ultimately spreads as a gravity current. After the injection is stopped, particles in suspension settle through the cloud to form particle boundary layers (PBL) at the cloud base. We vary the initial particle concentration of the plume and the injection velocity over a wide range of conditions to identify and characterize distinct regimes of sedimentation. Our experiments show that convective instabilities driven as a result of differing diffusivities of salt and particles lead to periodic layering over a wide range of conditions expected in nature. The flux of particles from layered clouds and the thicknesses of the layers are understood using classical theory for double diffusive convection adjusted for the hydrodynamic diffusion of particles. Although diffusive convection increases sedimentation rates for the smallest particles (<30 μm) its overall effect is to extend the cloud residence time to several hours by maintaining larger particles in suspension within the layers, which is several orders of magnitude longer than expected when considering individual settling rates.

Delay-induced wave instabilities in single-species reaction-diffusion systems

NASA Astrophysics Data System (ADS)

Otto, Andereas; Wang, Jian; Radons, Günter

2017-11-01

The Turing (wave) instability is only possible in reaction-diffusion systems with more than one (two) components. Motivated by the fact that a time delay increases the dimension of a system, we investigate the presence of diffusion-driven instabilities in single-species reaction-diffusion systems with delay. The stability of arbitrary one-component systems with a single discrete delay, with distributed delay, or with a variable delay is systematically analyzed. We show that a wave instability can appear from an equilibrium of single-species reaction-diffusion systems with fluctuating or distributed delay, which is not possible in similar systems with constant discrete delay or without delay. More precisely, we show by basic analytic arguments and by numerical simulations that fast asymmetric delay fluctuations or asymmetrically distributed delays can lead to wave instabilities in these systems. Examples, for the resulting traveling waves are shown for a Fisher-KPP equation with distributed delay in the reaction term. In addition, we have studied diffusion-induced instabilities from homogeneous periodic orbits in the same systems with variable delay, where the homogeneous periodic orbits are attracting resonant periodic solutions of the system without diffusion, i.e., periodic orbits of the Hutchinson equation with time-varying delay. If diffusion is introduced, standing waves can emerge whose temporal period is equal to the period of the variable delay.

Successful Surface Treatments for Reducing Instabilities in Advanced Nickel-base Superalloys for Turbine Blades

NASA Technical Reports Server (NTRS)

Locci, Ivan E.; MacKay, Rebecca A.; Garg, Anita; Ritzert, Frank J.

2004-01-01

An optimized carburization treatment has been developed to mitigate instabilities that form in the microstructures of advanced turbine airfoil materials. Current turbine airfoils consist of a single crystal superalloy base that provides the mechanical performance of the airfoil, a thermal barrier coating (TBC) that reduces the temperature of the base superalloy, and a bondcoat between the superalloy and the TBC, that improves the oxidation and corrosion resistance of the base superalloy and the spallation resistance of the TBC. Advanced nickel-base superalloys containing high levels of refractory metals have been observed to develop an instability called secondary reaction zone (SRZ), which can form beneath diffusion aluminide bondcoats. This instability between the superalloy and the bondcoat has the potential of reducing the mechanical properties of thin-wall turbine airfoils. Controlled gas carburization treatments combined with a prior stress relief heat treatment and adequate surface preparation have been utilized effectively to minimize the formation of SRZ. These additional processing steps are employed before the aluminide bondcoat is deposited and are believed to change the local chemistry and local stresses of the surface of the superalloy. This paper presents the detailed processing steps used to reduce SRZ between platinum aluminide bondcoats and advanced single crystal superalloys.

Explosive Magnetic Reconnection in Double-current Sheet Systems: Ideal versus Resistive Tearing Mode

NASA Astrophysics Data System (ADS)

Baty, Hubert

2017-03-01

Magnetic reconnection associated with the tearing instability occurring in double-current sheet systems is investigated within the framework of resistive magnetohydrodynamics (MHD) in a two-dimensional Cartesian geometry. A special emphasis on the existence of fast and explosive phases is taken. First, we extend the recent theory on the ideal tearing mode of a single-current sheet to a double-current layer configuration. A linear stability analysis shows that, in long and thin systems with (length to shear layer thickness) aspect ratios scaling as {S}L9/29 (S L being the Lundquist number based on the length scale L), tearing modes can develop on a fast Alfvénic timescale in the asymptotic limit {S}L\\to ∞ . The linear results are confirmed by means of compressible resistive MHD simulations at relatively high S L values (up to 3× {10}6) for different current sheet separations. Moreover, the nonlinear evolution of the ideal double tearing mode (IDTM) exhibits a richer dynamical behavior than its single-tearing counterpart, as a nonlinear explosive growth violently ends up with a disruption when the two current layers interact trough the merging of plasmoids. The final outcome of the system is a relaxation toward a new state, free of magnetic field reversal. The IDTM dynamics is also compared to the resistive double tearing mode dynamics, which develops in similar systems with smaller aspect ratios, ≳ 2π , and exhibits an explosive secondary reconnection, following an initial slow resistive growth phase. Finally, our results are used to discuss the flaring activity in astrophysical magnetically dominated plasmas, with a particular emphasis on pulsar systems.

Importance of fingering convection for accreting white dwarfs in the framework of full evolutionary calculations: the case of the hydrogen-rich white dwarfs GD 133 and G 29-38

NASA Astrophysics Data System (ADS)

Wachlin, F. C.; Vauclair, G.; Vauclair, S.; Althaus, L. G.

2017-05-01

Context. A large fraction of white dwarfs show photospheric chemical composition that is polluted by heavy elements accreted from a debris disk. Such debris disks result from the tidal disruption of rocky planetesimals that have survived to whole stellar evolution from the main sequence to the final white dwarf stage. Determining the accretion rate of this material is an important step toward estimating the mass of the planetesimals and understanding the ultimate fate of the planetary systems. Aims: The accretion of heavy material with a mean molecular weight, μ, higher than the mean molecular weight of the white dwarf outer layers, induces a double-diffusive instability producing the fingering convection and an extra-mixing. As a result, the accreted material is diluted deep into the star. We explore the effect of this extra-mixing on the abundance evolution of Mg, O, Ca, Fe and Si in the cases of the two well-studied polluted DAZ white dwarfs: GD 133 and G 29-38. Methods: We performed numerical simulations of the accretion of material that has a chemical composition similar to the bulk Earth composition. We assumed a continuous and uniform accretion and considered a range of accretion rates from 104 g/s to 1010 g/s. Two cases are simulated, one using the standard mixing length theory (MLT) and one including the double-diffusive instability (fingering convection). Results: The double-diffusive instability develops on a very short timescale. The surface abundance rapidly reaches a stationary value while the depth of the zone mixed by the fingering convection increases. In the case of GD 133, the accretion rate needed to reproduce the observed abundances exceeds by more than two orders of magnitude the rate estimated by neglecting the fingering convection. In the case of G 29-38 the needed accretion rate is increased by approximately 1.7 dex. Conclusions: Our numerical simulations of the accretion of heavy elements on the hydrogen-rich white dwarf GD 133 and G 29-38 show that fingering convection is an efficient mechanism to mix the accreted material deeply. We find that when fingering convection is taken into account, accretion rates higher by 1.7 to 2 dex than those inferred from the standard MLT are needed to reproduce the abundances observed in G 29-38 and GD 133.

Double Diffusive Convection in Materials Processing

NASA Technical Reports Server (NTRS)

Ramachandra, Narayanan; Leslie, Fred W.

1999-01-01

A great number of crystals grown in space are plagued by convective motions which contribute to structural flaws. The character of these instabilities is not well understood but is associated with density variations in the presence of residual gravity (g-jitter). As a specific example, past HgCdTe crystal growth space experiments by Lehoczky and co-workers indicate radial compositional asymmetry in the grown crystals. In the case of HgCdTe the rejected component into the melt upon solidification is HgTe which is denser than the melt. The space grown crystals indicate the presence of three dimensional flow with the heavier HgTe-rich material clearly aligned with the residual gravity (0.55-1.55 micro g) vector. This flow stems from double-diffusive convection, namely, thermal and solutal buoyancy driven flow in the melt. The study of double-diffusive convection is multi-faceted and rather vast. In our investigation, we seek to focus on one specific aspect of this discipline that is of direct relevance to materials processing especially crystal growth, namely, the side ways heating regime. This problem has been widely studied, both experimentally and numerically, in the context of solar ponds wherein the system is characterized by a linear salt (solutal) gradient with an imposed lateral temperature gradient. The induced flow instabilities arise from the wide disparity between the fluid thermal diffusivity and the solute diffusivity. The extension of the analysis to practical crystal growth applications has however not been rigorously made and understood. One subtle but important difference in crystal growth systems is the fact that die system solute gradient is non-linear (typically exponential). Besides, the crystal growth problem has the added complexities of solidification, both lateral and longitudinal thermal gradients and segregation phenomena in systems where binary and ternary compounds are being grown. This paper treats the side ways heating problem alone in a model fluid system. Results from detailed numerical calculations, mainly two dimensional are provided. The interactions between a non-linear solute gradient and an imposed transverse thermal gradient are investigated. The buoyancy effects are treated in the traditional Boussinesq approximation and also in a more complete density formulation to address recent concerns of the first approach especially in simulations of the system response in a reduced gravity environment. Detailed flow, temperature and solute field plots along with heat and mass transfer results are presented in the paper. Implications to practical crystal growth systems as discerned from the modeling results are also explored and reported.

Entrainment and mixing of shelf/slope waters in the near-surface Gulf Stream

NASA Astrophysics Data System (ADS)

Lillibridge, J. L., III; Hitchcock, G.; Rossby, T.; Lessard, E.; Mork, M.; Golmen, L.

1990-08-01

An interdisciplinary study of the entrainment of shelf and slope waters in the Gulf Stream front was undertaken in October 1985 northeast of Cape Hatteras. Fifteen hydrographic transects of the Gulf Stream front and of the shelf water intrusion known as Ford water were completed in 2 1/2 days with a towed undulating profiler, the SeaSoar, equipped with a conductivity-temperature-depth probe and a fluorometer. Upstream sections within 50 km of the shelf break show entrainment of surface and subsurface waters along the northern edge of the high-velocity Gulf Stream. The low-salinity core, first observed at 70 m, is subducted to >100 m. The subsurface Ford water is also at a maximum in chlorophyll, fluorescence, and dissolved oxygen and contains a distinct diatom assemblage of nearshore species. Productivity rates in the Ford water may be equivalent to those in slope waters. Expendable current profilers yield an estimated transport for subsurface shelf waters of 1 to 5×105 m3 s-1 and indicate that vertical shear at the depth of maximum static stability is typically 2×10-2 s-1. A bulk Richardson number is estimated over vertical scales of several meters by combining SeaSoar density profiles with velocity shear from concurrent expendable current profiler deployments. The minimum values are generally >1, and only infrequently are they at or below the 0.25 threshold for shear instability. The presence of double-diffusive processes around the low-salinity core of Ford water is indicated by elevated conductivity Cox numbers. The stability parameter "Turner angle" shows that low-salinity Ford water and its associated T-S property front are sites of double-diffusive mixing, given general agreement between the distributions of Turner angle and Cox number. We conclude that double-diffusive processes are more important than shear flow instability in governing cross-isopycnal mixing. However, downstream transit times are so swift that no measurable change or decay occurs in the Ford water. This explains the occurrence of distinct shelf water phytoplankton species within the low-salinity waters downstream of Cape Hatteras.

Stability and instability of hydromagnetic Taylor-Couette flows

NASA Astrophysics Data System (ADS)

Rüdiger, Günther; Gellert, Marcus; Hollerbach, Rainer; Schultz, Manfred; Stefani, Frank

2018-04-01

Decades ago S. Lundquist, S. Chandrasekhar, P. H. Roberts and R. J. Tayler first posed questions about the stability of Taylor-Couette flows of conducting material under the influence of large-scale magnetic fields. These and many new questions can now be answered numerically where the nonlinear simulations even provide the instability-induced values of several transport coefficients. The cylindrical containers are axially unbounded and penetrated by magnetic background fields with axial and/or azimuthal components. The influence of the magnetic Prandtl number Pm on the onset of the instabilities is shown to be substantial. The potential flow subject to axial fields becomes unstable against axisymmetric perturbations for a certain supercritical value of the averaged Reynolds number Rm bar =√{ Re ṡ Rm } (with Re the Reynolds number of rotation, Rm its magnetic Reynolds number). Rotation profiles as flat as the quasi-Keplerian rotation law scale similarly but only for Pm ≫ 1 while for Pm ≪ 1 the instability instead sets in for supercritical Rm at an optimal value of the magnetic field. Among the considered instabilities of azimuthal fields, those of the Chandrasekhar-type, where the background field and the background flow have identical radial profiles, are particularly interesting. They are unstable against nonaxisymmetric perturbations if at least one of the diffusivities is non-zero. For Pm ≪ 1 the onset of the instability scales with Re while it scales with Rm bar for Pm ≫ 1. Even superrotation can be destabilized by azimuthal and current-free magnetic fields; this recently discovered nonaxisymmetric instability is of a double-diffusive character, thus excluding Pm = 1. It scales with Re for Pm → 0 and with Rm for Pm → ∞. The presented results allow the construction of several new experiments with liquid metals as the conducting fluid. Some of them are described here and their results will be discussed together with relevant diversifications of the magnetic instability theory including nonlinear numerical studies of the kinetic and magnetic energies, the azimuthal spectra and the influence of the Hall effect.

Effect of concentration boundary layers on passive solute flows in a system of two polymeric membranes positioned in vertical planes.

PubMed

Slezak, Andrzej; Jasik-Slezak, Jolanta; Dworecki, Kazimierz

2003-01-01

The results of studies of influence of concentration boundary layers on passive diffusive transport in a double-membrane osmo-diffusive cell, containing a series of two (Ml and M(r)) vertically positioned, flat, microporous and symmetric polymer membranes (Nephrophane and Cellulose IMP-1) are presented in this paper. The membranes separated three compartments (l, m, r) containing binary, heterogeneous and non-ionic solutions (aqueous solutions of glucose or ethanol) or ternary non-electrolyte solutions (glucose solutions in 0.75 mol.l-1 solution of ethanol or ethanol solutions in 0.1 mol.l-1 aqueous solution of glucose). Solution concentrations fulfilled the condition C(k)l > C(k)m > C(k)r. The intermembrane compartment (m) was an infinitesimal solution layer. The volume of the m compartment and the volumes of the external (l and r) compartments fulfilled the condition Vl = Vr approximately 170 Vm. The tests were performed for configurations A and B of a double-membrane osmo-diffusive cell. In configuration A, the solution was located behind the M(r) membrane, and water was placed behind the Ml membrane, while in configuration B this sequence was reversed. The results obtained during experiment were interpreted in the categories of convective instability, which increased the value of diffusive permeability coefficient of the system: concentration boundary layer/membrane/concentration boundary layer.

A NEW MODEL FOR MIXING BY DOUBLE-DIFFUSIVE CONVECTION (SEMI-CONVECTION). III. THERMAL AND COMPOSITIONAL TRANSPORT THROUGH NON-LAYERED ODDC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moll, Ryan; Garaud, Pascale; Stellmach, Stephan, E-mail: rmoll@soe.ucsc.edu

2016-05-20

Oscillatory double-diffusive convection (ODDC; also known as semi-convection) refers to a type of double-diffusive instability that occurs in regions of planetary and stellar interiors that have a destabilizing thermal stratification and a stabilizing mean molecular weight stratification. In this series of papers, we use an extensive suite of three-dimensional (3D) numerical simulations to quantify the transport of heat and chemical species by ODDC. Rosenblum et al. first showed that ODDC can either spontaneously form layers that significantly enhance the transport of heat and chemical species compared to microscopic transport or remain in a state dominated by large-scale gravity waves, inmore » which there is a more modest enhancement of the turbulent transport rates. Subsequent studies in this series focused on identifying under what conditions layers form and quantifying transport through layered systems. Here we proceed to characterize transport through systems that are unstable to ODDC, but do not undergo spontaneous layer formation. We measure the thermal and compositional fluxes in non-layered ODDC from both two-dimensional (2D) and 3D numerical simulations, and show that 3D simulations are well approximated by similar simulations in a 2D domain. We find that the turbulent mixing rate in this regime is weak and can, to a first-level approximation, be neglected. We conclude by summarizing the findings of papers I through III into a single prescription for transport systems unstable to ODDC.« less

Instability of turing patterns in reaction-diffusion-ODE systems.

PubMed

Marciniak-Czochra, Anna; Karch, Grzegorz; Suzuki, Kanako

2017-02-01

The aim of this paper is to contribute to the understanding of the pattern formation phenomenon in reaction-diffusion equations coupled with ordinary differential equations. Such systems of equations arise, for example, from modeling of interactions between cellular processes such as cell growth, differentiation or transformation and diffusing signaling factors. We focus on stability analysis of solutions of a prototype model consisting of a single reaction-diffusion equation coupled to an ordinary differential equation. We show that such systems are very different from classical reaction-diffusion models. They exhibit diffusion-driven instability (turing instability) under a condition of autocatalysis of non-diffusing component. However, the same mechanism which destabilizes constant solutions of such models, destabilizes also all continuous spatially heterogeneous stationary solutions, and consequently, there exist no stable Turing patterns in such reaction-diffusion-ODE systems. We provide a rigorous result on the nonlinear instability, which involves the analysis of a continuous spectrum of a linear operator induced by the lack of diffusion in the destabilizing equation. These results are extended to discontinuous patterns for a class of nonlinearities.

Turing instability in reaction-diffusion systems with nonlinear diffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zemskov, E. P., E-mail: zemskov@ccas.ru

2013-10-15

The Turing instability is studied in two-component reaction-diffusion systems with nonlinear diffusion terms, and the regions in parametric space where Turing patterns can form are determined. The boundaries between super- and subcritical bifurcations are found. Calculations are performed for one-dimensional brusselator and oregonator models.

Stability diagrams for the surface patterns of GaN(0001bar) as a function of Schwoebel barrier height

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.

2017-01-01

Height and type of Schwoebel barriers (direct or inverse) decides about the character of the surface instability. Different surface morphologies are presented. Step bunches, double steps, meanders, mounds and irregular patterns emerge at the surface as a result of step (Schwoebel) barriers at some temperature or miscut values. The study was carried out on the two-component kinetic Monte Carlo (kMC) model of GaN(0001bar) surface grown in nitrogen rich conditions. Diffusion of gallium adatoms over N-polar surface is slow and nitrogen adatoms are almost immobile. We show that in such conditions surfaces remain smooth when gallium adatoms diffuse in the presence of low inverse Schwoebel barrier. It is illustrated by adequate stability diagrams for surface morphologies.

Upstream ionization instability associated with a current-free double layer.

PubMed

Aanesland, A; Charles, C; Lieberman, M A; Boswell, R W

2006-08-18

A low frequency instability has been observed using various electrostatic probes in a low-pressure expanding helicon plasma. The instability is associated with the presence of a current-free double layer (DL). The frequency of the instability increases linearly with the potential drop of the DL, and simultaneous measurements show their coexistence. A theory for an upstream ionization instability has been developed, which shows that electrons accelerated through the DL increase the ionization upstream and are responsible for the observed instability. The theory is in good agreement with the experimental results.

A new necessary condition for Turing instabilities.

PubMed

Elragig, Aiman; Townley, Stuart

2012-09-01

Reactivity (a.k.a initial growth) is necessary for diffusion driven instability (Turing instability). Using a notion of common Lyapunov function we show that this necessary condition is a special case of a more powerful (i.e. tighter) necessary condition. Specifically, we show that if the linearised reaction matrix and the diffusion matrix share a common Lyapunov function, then Turing instability is not possible. The existence of common Lyapunov functions is readily checked using semi-definite programming. We apply this result to the Gierer-Meinhardt system modelling regenerative properties of Hydra, the Oregonator, to a host-parasite-hyperparasite system with diffusion and to a reaction-diffusion-chemotaxis model for a multi-species host-parasitoid community. Copyright © 2012 Elsevier Inc. All rights reserved.

On flares, substorms, and the theory of impulsive flux transfer events

NASA Technical Reports Server (NTRS)

Bratenahl, A.; Baum, P. J.

1976-01-01

Solar flares and magnetospheric substorms are discussed in the context of a general theory of impulsive flux transfer events (IFTE). IFTE theory, derived from laboratory observations in the Double Inverse Pinch Device (DIPD), provides a quantitative extension of 'neutral sheet' theories to include nonsteady field line reconnection. Current flow along the reconnection line increases with magnetic flux storage. When flux build-up exceeds the level corresponding to a critical limit on the current, instabilities induce a sudden transition in the mode of conduction. The resulting IFTE, indifferent to the specific modes and instabilities involved, is the more energetic, the lower the initial resistivity. It is the more violent, the greater the resulting resistivity increase and the faster its growth. Violent events can develop very large voltage transients along the reconnection line. Persistent build-up promoting conditions produce relaxation oscillations in the quantity of flux and energy stored (build-up-IFTE cycles). It is difficult to avoid the conclusion: flares and substorms are examples of IFTE.

Distribution of Plasmoids in Post-Coronal Mass Ejection Current Sheets

NASA Astrophysics Data System (ADS)

Bhattacharjee, A.; Guo, L.; Huang, Y.

2013-12-01

Recently, the fragmentation of a current sheet in the high-Lundquist-number regime caused by the plasmoid instability has been proposed as a possible mechanism for fast reconnection. In this work, we investigate this scenario by comparing the distribution of plasmoids obtained from Large Angle and Spectrometric Coronagraph (LASCO) observational data of a coronal mass ejection event with a resistive magnetohydrodynamic simulation of a similar event. The LASCO/C2 data are analyzed using visual inspection, whereas the numerical data are analyzed using both visual inspection and a more precise topological method. Contrasting the observational data with numerical data analyzed with both methods, we identify a major limitation of the visual inspection method, due to the difficulty in resolving smaller plasmoids. This result raises questions about reports of log-normal distributions of plasmoids and other coherent features in the recent literature. Based on nonlinear scaling relations of the plasmoid instability, we infer a lower bound on the current sheet width, assuming the underlying mechanism of current sheet broadening is resistive diffusion.

Influence of toroidal rotation on resistive tearing modes in tokamaks

NASA Astrophysics Data System (ADS)

Wang, S.; Ma, Z. W.

2015-12-01

Influence of toroidal equilibrium plasma rotation on m/n = 2/1 resistive tearing modes is studied numerically using a 3D toroidal MHD code (CLT). It is found that the toroidal rotation with or without shear can suppress the tearing instability and the Coriolis effect in the toroidal geometry plays a dominant role on the rotation induced stabilization. For a high viscosity plasma (τR/τV ≫ 1, where τR and τV represent resistive and viscous diffusion time, respectively), the effect of the rotation shear combined with the viscosity appears to be stabilizing. For a low viscosity plasmas (τR/τV ≪ 1), the rotation shear shows a destabilizing effect when the rotation is large.

Effect of double layers on magnetosphere-ionosphere coupling

NASA Technical Reports Server (NTRS)

Lysak, Robert L.; Hudson, Mary K.

1987-01-01

The dynamic aspects of auroral current structures are reviewed with emphasis on consequences for models of microscopic turbulence (MT). A number of models of MT are introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. The effect of a double layer (DL) electric field which scales with the plasma temperature and the Debye length is compared with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is shown that the DL model is less diffusive than the resistive model, indicating the possibility of narrow intense current structures.

Control of transversal instabilities in reaction-diffusion systems

NASA Astrophysics Data System (ADS)

Totz, Sonja; Löber, Jakob; Totz, Jan Frederik; Engel, Harald

2018-05-01

In two-dimensional reaction-diffusion systems, local curvature perturbations on traveling waves are typically damped out and vanish. However, if the inhibitor diffuses much faster than the activator, transversal instabilities can arise, leading from flat to folded, spatio-temporally modulated waves and to spreading spiral turbulence. Here, we propose a scheme to induce or inhibit these instabilities via a spatio-temporal feedback loop. In a piecewise-linear version of the FitzHugh–Nagumo model, transversal instabilities and spiral turbulence in the uncontrolled system are shown to be suppressed in the presence of control, thereby stabilizing plane wave propagation. Conversely, in numerical simulations with the modified Oregonator model for the photosensitive Belousov–Zhabotinsky reaction, which does not exhibit transversal instabilities on its own, we demonstrate the feasibility of inducing transversal instabilities and study the emerging wave patterns in a well-controlled manner.

Spatiotemporal chaos in the dynamics of buoyantly and diffusively unstable chemical fronts

NASA Astrophysics Data System (ADS)

Baroni, M. P. M. A.; Guéron, E.; De Wit, A.

2012-03-01

Nonlinear dynamics resulting from the interplay between diffusive and buoyancy-driven Rayleigh-Taylor (RT) instabilities of autocatalytic traveling fronts are analyzed numerically for various values of the relevant parameters. These are the Rayleigh numbers of the reactant A and autocatalytic product B solutions as well as the ratio D =DB/DA between the diffusion coefficients of the two key chemical species. The interplay between the coarsening dynamics characteristic of the RT instability and the constant short wavelength modulation of the diffusive instability can lead in some regimes to complex dynamics dominated by irregular succession of birth and death of fingers. By using spectral entropy measurements, we characterize the transition between order and spatial disorder in this system. The analysis of the power spectrum and autocorrelation function, moreover, identifies similarities between the various spatial patterns. The contribution of the diffusive instability to the complex dynamics is discussed.

Closed-form breakdown voltage/specific on-resistance model using charge superposition technique for vertical power double-diffused metal–oxide–semiconductor device with high-κ insulator

NASA Astrophysics Data System (ADS)

Chen, Xue; Wang, Zhi-Gang; Wang, Xi; Kuo, James B.

2018-04-01

Not Available Project supported by the National Natural Science Foundation of China (Grant No. 61404110) and the National Higher-education Institution General Research and Development Project, China (Grant No. 2682014CX097).

Anisotropic diffusion in mesh-free numerical magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.

2017-04-01

We extend recently developed mesh-free Lagrangian methods for numerical magnetohydrodynamics (MHD) to arbitrary anisotropic diffusion equations, including: passive scalar diffusion, Spitzer-Braginskii conduction and viscosity, cosmic ray diffusion/streaming, anisotropic radiation transport, non-ideal MHD (Ohmic resistivity, ambipolar diffusion, the Hall effect) and turbulent 'eddy diffusion'. We study these as implemented in the code GIZMO for both new meshless finite-volume Godunov schemes (MFM/MFV). We show that the MFM/MFV methods are accurate and stable even with noisy fields and irregular particle arrangements, and recover the correct behaviour even in arbitrarily anisotropic cases. They are competitive with state-of-the-art AMR/moving-mesh methods, and can correctly treat anisotropic diffusion-driven instabilities (e.g. the MTI and HBI, Hall MRI). We also develop a new scheme for stabilizing anisotropic tensor-valued fluxes with high-order gradient estimators and non-linear flux limiters, which is trivially generalized to AMR/moving-mesh codes. We also present applications of some of these improvements for SPH, in the form of a new integral-Godunov SPH formulation that adopts a moving-least squares gradient estimator and introduces a flux-limited Riemann problem between particles.

Over-limiting Current and Control of Dendritic Growth by Surface Conduction in Nanopores

PubMed Central

Han, Ji-Hyung; Khoo, Edwin; Bai, Peng; Bazant, Martin Z.

2014-01-01

Understanding over-limiting current (faster than diffusion) is a long-standing challenge in electrochemistry with applications in desalination and energy storage. Known mechanisms involve either chemical or hydrodynamic instabilities in unconfined electrolytes. Here, it is shown that over-limiting current can be sustained by surface conduction in nanopores, without any such instabilities, and used to control dendritic growth during electrodeposition. Copper electrodeposits are grown in anodized aluminum oxide membranes with polyelectrolyte coatings to modify the surface charge. At low currents, uniform electroplating occurs, unaffected by surface modification due to thin electric double layers, but the morphology changes dramatically above the limiting current. With negative surface charge, growth is enhanced along the nanopore surfaces, forming surface dendrites and nanotubes behind a deionization shock. With positive surface charge, dendrites avoid the surfaces and are either guided along the nanopore centers or blocked from penetrating the membrane. PMID:25394685

Convective instability and boundary driven oscillations in a reaction-diffusion-advection model

NASA Astrophysics Data System (ADS)

Vidal-Henriquez, Estefania; Zykov, Vladimir; Bodenschatz, Eberhard; Gholami, Azam

2017-10-01

In a reaction-diffusion-advection system, with a convectively unstable regime, a perturbation creates a wave train that is advected downstream and eventually leaves the system. We show that the convective instability coexists with a local absolute instability when a fixed boundary condition upstream is imposed. This boundary induced instability acts as a continuous wave source, creating a local periodic excitation near the boundary, which initiates waves travelling both up and downstream. To confirm this, we performed analytical analysis and numerical simulations of a modified Martiel-Goldbeter reaction-diffusion model with the addition of an advection term. We provide a quantitative description of the wave packet appearing in the convectively unstable regime, which we found to be in excellent agreement with the numerical simulations. We characterize this new instability and show that in the limit of high advection speed, it is suppressed. This type of instability can be expected for reaction-diffusion systems that present both a convective instability and an excitable regime. In particular, it can be relevant to understand the signaling mechanism of the social amoeba Dictyostelium discoideum that may experience fluid flows in its natural habitat.

Seasonal variability of the diapycnal mixing in the Canary Islands channels

NASA Astrophysics Data System (ADS)

Rodríguez-Santana, Angel; Marrero-Díaz, Angeles; Machín, Francisco Jose; García-Weil, Luis; Sangrà, Pablo; Vélez-Belchí, Pedro; Fraile-Nuez, Eugenio; Estrada-Allis, Sheila

2014-05-01

Trimonthly surveys of XBT and XCTD (Expandable Bathytermograph and Conductivity-Temperature-Depth) crossing the whole Canary Islands channels were carried out (projects TRAMIC and PROMECA) from November 2012 until September 2013 using opportunity ships (Naviera Armas Ferries). With this data set and using salinity analytical relationships (Machín et al, 2010), vertical sections of temperature and potential density were obtained for each channel and season. In order to estimate the intensity of the diapycnal mixing in the first 500 m of the pycnocline, vertical sections of Thorpe length scale, Turner angle and gradient Richardson number (from the geostrophic vertical shear) were calculated for all the cases. The first results show how the diapycnal mixing due to the vertical shear instabilities is more intense close to the islands and in summer when the seasonal pycnocline is present. Mixing due to double diffusion processes (salt fingers) was found without sizable changes in the permanent pycnocline. Net turbulence diffusivities and diapycnal diffusive fluxes with their variability spatial and temporal will be estimate for each channel taking into account that processes of double diffusion and turbulence induced by vertical shear are present at the same time. Additionally the results obtained from hydrographic data from the cruise RAPROCAN-2013 (IEO) (October 2013) around Canary Islands will be used to compare them with the channels results. This work was co-funded by Canary Government (TRAMIC project: PROID20100092), European Union (FEDER) and Spanish Government (PROMECA: CTM2008-04057/MAR and CTM2009-06993-E/MAR)

Non-ideal magnetohydrodynamics on a moving mesh

NASA Astrophysics Data System (ADS)

Marinacci, Federico; Vogelsberger, Mark; Kannan, Rahul; Mocz, Philip; Pakmor, Rüdiger; Springel, Volker

2018-05-01

In certain astrophysical systems, the commonly employed ideal magnetohydrodynamics (MHD) approximation breaks down. Here, we introduce novel explicit and implicit numerical schemes of ohmic resistivity terms in the moving-mesh code AREPO. We include these non-ideal terms for two MHD techniques: the Powell 8-wave formalism and a constrained transport scheme, which evolves the cell-centred magnetic vector potential. We test our implementation against problems of increasing complexity, such as one- and two-dimensional diffusion problems, and the evolution of progressive and stationary Alfvén waves. On these test problems, our implementation recovers the analytic solutions to second-order accuracy. As first applications, we investigate the tearing instability in magnetized plasmas and the gravitational collapse of a rotating magnetized gas cloud. In both systems, resistivity plays a key role. In the former case, it allows for the development of the tearing instability through reconnection of the magnetic field lines. In the latter, the adopted (constant) value of ohmic resistivity has an impact on both the gas distribution around the emerging protostar and the mass loading of magnetically driven outflows. Our new non-ideal MHD implementation opens up the possibility to study magneto-hydrodynamical systems on a moving mesh beyond the ideal MHD approximation.

Sedimentation from flocculated suspensions in the presence of settling-driven gravitational interface instabilities

NASA Astrophysics Data System (ADS)

Rouhnia, Mohamad; Strom, Kyle

2015-09-01

We experimentally examine sedimentation from a freshwater suspension of clay flocs overlying saltwater in the presence of gravitational instabilities. The study seeks to determine: (1) if flocculation hampers or alters interface instability formation; (2) how the removal rates of sediment from the buoyant layer compare to those predicted by individual floc settling; and (3) whether or not it is possible to develop a model for effective settling velocity. The experiments were conducted in a tank at isothermal conditions. All experiments were initially stably stratified but later developed instabilities near the interface that grew into downward convecting plumes of fluid and sediment. Throughout, we measured sediment concentration in the upper and lower layers, floc size, and plume descent rates. The data showed that flocculation modifies the mixture settling velocity, and therefore shifts the mode of interface instability from double-diffusive (what one would expect from unflocculated clay) to settling-driven leaking and Rayleigh-Taylor instability formation. Removal rates of sediment from the upper layer in the presence of these instabilities were on the same order of magnitude as those predicted by individual floc settling. However, removal rates were found to better correlate with the speed of the interface plumes. A simple force-balance model was found to be capable of reasonably describing plume velocity based on concentration in the buoyant layer. This relation, coupled with a critical Grashof number and geometry relations, allowed us to develop a model for the effective settling velocity of the mixture based solely on integral values of the upper layer.

Double emulsions based on silicone-fluorocarbon-water and their skin penetration.

PubMed

Mahrhauser, Denise-Silvia; Fischer, Claudia; Valenta, Claudia

2016-02-10

Double emulsions have significant potential in pharmacy and cosmetics due to the feasibility of combining incompatible substances in one product and the protection of sensitive compounds by incorporating them into their innermost phase. However, a major drawback of double emulsions is their thermodynamic instability and their strong tendency to coalesce. In the present study, the physicochemical stability, the skin permeation and the skin penetration potential of modified semi-solid double emulsions was investigated. The double emulsions were prepared of the cosmetically applied perfluoropolyethers Fomblin HC/04 or Fomblin HC-OH, silicone, carbomer and water. Measurement of the droplet size and examination of the microscopic images confirmed their physicochemical stability over the observation period of eight weeks. Franz-type diffusion cell experiments revealed no increase in curcumin permeation due to the employed perfluoropolyethers compared to the respective control formulations. The formulations used as control were O/W macroemulsions with or without a Polysorbate 80/Sorbitane monooleate 80 surfactant combination. Likewise, tape stripping studies showed no penetration enhancing effect of the employed perfluoropolyethers which is desirable as both perfluoropolyethers are commonly applied components in human personal-care products. Copyright © 2015 Elsevier B.V. All rights reserved.

Processing of double-R-loops in (CAG)·(CTG) and C9orf72 (GGGGCC)·(GGCCCC) repeats causes instability

PubMed Central

Reddy, Kaalak; Schmidt, Monika H.M.; Geist, Jaimie M.; Thakkar, Neha P.; Panigrahi, Gagan B.; Wang, Yuh-Hwa; Pearson, Christopher E.

2014-01-01

R-loops, transcriptionally-induced RNA:DNA hybrids, occurring at repeat tracts (CTG)n, (CAG)n, (CGG)n, (CCG)n and (GAA)n, are associated with diseases including myotonic dystrophy, Huntington's disease, fragile X and Friedreich's ataxia. Many of these repeats are bidirectionally transcribed, allowing for single- and double-R-loop configurations, where either or both DNA strands may be RNA-bound. R-loops can trigger repeat instability at (CTG)·(CAG) repeats, but the mechanism of this is unclear. We demonstrate R-loop-mediated instability through processing of R-loops by HeLa and human neuron-like cell extracts. Double-R-loops induced greater instability than single-R-loops. Pre-treatment with RNase H only partially suppressed instability, supporting a model in which R-loops directly generate instability by aberrant processing, or via slipped-DNA formation upon RNA removal and its subsequent aberrant processing. Slipped-DNAs were observed to form following removal of the RNA from R-loops. Since transcriptionally-induced R-loops can occur in the absence of DNA replication, R-loop processing may be a source of repeat instability in the brain. Double-R-loop formation and processing to instability was extended to the expanded C9orf72 (GGGGCC)·(GGCCCC) repeats, known to cause amyotrophic lateral sclerosis and frontotemporal dementia, providing the first suggestion through which these repeats may become unstable. These findings provide a mechanistic basis for R-loop-mediated instability at disease-associated repeats. PMID:25147206

A method for polycrystalline silicon delineation applicable to a double-diffused MOS transistor

NASA Technical Reports Server (NTRS)

Halsor, J. L.; Lin, H. C.

1974-01-01

Method is simple and eliminates requirement for unreliable special etchants. Structure is graded in resistivity to prevent punch-through and has very narrow channel length to increase frequency response. Contacts are on top to permit planar integrated circuit structure. Polycrystalline shield will prevent creation of inversion layer in isolated region.

Determination of diffusion coefficients in polypyrrole thin films using a current pulse relaxation method

NASA Technical Reports Server (NTRS)

Penner, Reginald M.; Vandyke, Leon S.; Martin, Charles R.

1987-01-01

The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data.

Diapycnal Transport and Pattern Formation in Double-Diffusive Convection

DTIC Science & Technology

2015-12-01

of knowledge. The effects of turbulent-dominated and purely double-diffusive regimes are compared to dual turbulent/double-diffusive systems and...is presented to remedy this dearth of knowledge. The effects of turbulent-dominated and purely double-diffusive regimes are compared to dual...8 2. Double-Diffusion: The Constant Flux Ratio Model ..........................9 3. The Combined Effects of

Control of External Kink Instability

NASA Astrophysics Data System (ADS)

Navratil, Gerald

2004-11-01

A fundamental pressure and current limiting phenomenon in magnetically confined plasmas for fusion energy is the long wavelength ideal-MHD kink mode. These modes have been extensively studied in tokamak and reversed field pinch (RFP) devices. They are characterized by significant amplitude on the boundary of the confined plasma and can therefore be controlled by manipulation of the external boundary conditions. In the past ten years, the theoretically predicted stabilizing effect of a nearby conducting wall has been documented in experiments, which opens the possibility of a significant increase in maximum stable plasma pressure. While these modes are predicted to remain unstable when the stabilizing wall is resistive, their growth rates are greatly reduced from the hydrodynamic time scale to the time scale of magnetic diffusion through the resistive wall. These resistive wall slowed kink modes have been identified as limiting phenomena in tokamak (DIII-D, PBX-M, HBT-EP, JT-60U, JET, NSTX) and RFP (HBTX, Extrap, T2R) devices. The theoretical prediction of stabilization to nearly the ideal wall pressure limit by toroidal plasma rotation and/or active feedback control using coils has recently been realized experimentally. Sustained, stable operation at double the no-wall pressure limit has been achieved. Discovery of the phenomenon of resonant field amplification by marginally stable kink modes and its role in the momentum balance of rotationally stabilized plasmas has emerged as a key feature. A theoretical framework, based on an extension of the very successful treatment of the n=0 axisymmetric mode developed in the early 1990's, to understand the stabilization mechanisms and model the performance of active feedback control systems is now established. This allows design of kink control systems for burning plasma experiments like ITER.

Dynamical spike solutions in a nonlocal model of pattern formation

NASA Astrophysics Data System (ADS)

Marciniak-Czochra, Anna; Härting, Steffen; Karch, Grzegorz; Suzuki, Kanako

2018-05-01

Coupling a reaction-diffusion equation with ordinary differential equa- tions (ODE) may lead to diffusion-driven instability (DDI) which, in contrast to the classical reaction-diffusion models, causes destabilization of both, constant solutions and Turing patterns. Using a shadow-type limit of a reaction-diffusion-ODE model, we show that in such cases the instability driven by nonlocal terms (a counterpart of DDI) may lead to formation of unbounded spike patterns.

Patterns induced by super cross-diffusion in a predator-prey system with Michaelis-Menten type harvesting.

PubMed

Liu, Biao; Wu, Ranchao; Chen, Liping

2018-04-01

Turing instability and pattern formation in a super cross-diffusion predator-prey system with Michaelis-Menten type predator harvesting are investigated. Stability of equilibrium points is first explored with or without super cross-diffusion. It is found that cross-diffusion could induce instability of equilibria. To further derive the conditions of Turing instability, the linear stability analysis is carried out. From theoretical analysis, note that cross-diffusion is the key mechanism for the formation of spatial patterns. By taking cross-diffusion rate as bifurcation parameter, we derive amplitude equations near the Turing bifurcation point for the excited modes by means of weakly nonlinear theory. Dynamical analysis of the amplitude equations interprets the structural transitions and stability of various forms of Turing patterns. Furthermore, the theoretical results are illustrated via numerical simulations. Copyright © 2018. Published by Elsevier Inc.

Linear growth of the Kelvin-Helmholtz instability with an adiabatic cosmic-ray gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Akihiro; Takahashi, Hiroyuki R.; Kudoh, Takahiro

2014-06-01

We investigate effects of cosmic rays on the linear growth of the Kelvin-Helmholtz instability. Cosmic rays are treated as an adiabatic gas and allowed to diffuse along magnetic field lines. We calculated the dispersion relation of the instability for various sets of two free parameters, the ratio of the cosmic-ray pressure to the thermal gas pressure, and the diffusion coefficient. Including cosmic-ray effects, a shear layer is more destabilized and the growth rates can be enhanced in comparison with the ideal magnetohydrodynamical case. Whether the growth rate is effectively enhanced or not depends on the diffusion coefficient of cosmic rays.more » We obtain the criterion for effective enhancement by comparing the growing timescale of the instability with the diffusion timescale of cosmic rays. These results can be applied to various astrophysical phenomena where a velocity shear is present, such as outflows from star-forming galaxies, active galactic nucleus jet, channel flows resulting from the nonlinear development of the magnetorotational instability, and galactic disks.« less

Inhibition of ordinary and diffusive convection in the water condensation zone of the ice giants and implications for their thermal evolution

NASA Astrophysics Data System (ADS)

Friedson, A. James; Gonzales, Erica J.

2017-11-01

We explore the conditions under which ordinary and double-diffusive thermal convection may be inhibited by water condensation in the hydrogen atmospheres of the ice giants and examine the consequences. The saturation of vapor in the condensation layer induces a vertical gradient in the mean molecular weight that stabilizes the layer against convective instability when the abundance of vapor exceeds a critical value. In this instance, the layer temperature gradient can become superadiabatic and heat must be transported vertically by another mechanism. On Uranus and Neptune, water is inferred to be sufficiently abundant for inhibition of ordinary convection to take place in their respective condensation zones. We find that suppression of double-diffusive convection is sensitive to the ratio of the sedimentation time scale of the condensates to the buoyancy period in the condensation layer. In the limit of rapid sedimentation, the layer is found to be stable to diffusive convection. In the opposite limit, diffusive convection can occur. However, if the fluid remains saturated, then layered convection is generally suppressed and the motion is restricted in form to weak, homogeneous, oscillatory turbulence. This form of diffusive convection is a relatively inefficient mechanism for transporting heat, characterized by low Nusselt numbers. When both ordinary and layered convection are suppressed, the condensation zone acts effectively as a thermal insulator, with the heat flux transported across it only slightly greater than the small value that can be supported by radiative diffusion. This may allow a large superadiabatic temperature gradient to develop in the layer over time. Once the layer has formed, however, it is vulnerable to persistent erosion by entrainment of fluid into the overlying convective envelope of the cooling planet, potentially leading to its collapse. We discuss the implications of our results for thermal evolution models of the ice giants, for understanding Uranus' anomalously low intrinsic luminosity, and for inducing episodes of intense convection in the atmospheres of Saturn, Uranus, and Neptune.

Pattern formation in three-dimensional reaction-diffusion systems

NASA Astrophysics Data System (ADS)

Callahan, T. K.; Knobloch, E.

1999-08-01

Existing group theoretic analysis of pattern formation in three dimensions [T.K. Callahan, E. Knobloch, Symmetry-breaking bifurcations on cubic lattices, Nonlinearity 10 (1997) 1179-1216] is used to make specific predictions about the formation of three-dimensional patterns in two models of the Turing instability, the Brusselator model and the Lengyel-Epstein model. Spatially periodic patterns having the periodicity of the simple cubic (SC), face-centered cubic (FCC) or body-centered cubic (BCC) lattices are considered. An efficient center manifold reduction is described and used to identify parameter regimes permitting stable lamellæ, SC, FCC, double-diamond, hexagonal prism, BCC and BCCI states. Both models possess a special wavenumber k* at which the normal form coefficients take on fixed model-independent ratios and both are described by identical bifurcation diagrams. This property is generic for two-species chemical reaction-diffusion models with a single activator and inhibitor.

Low Mach number fluctuating hydrodynamics of multispecies liquid mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donev, Aleksandar, E-mail: donev@courant.nyu.edu; Bhattacharjee, Amit Kumar; Nonaka, Andy

We develop a low Mach number formulation of the hydrodynamic equations describing transport of mass and momentum in a multispecies mixture of incompressible miscible liquids at specified temperature and pressure, which generalizes our prior work on ideal mixtures of ideal gases [Balakrishnan et al., “Fluctuating hydrodynamics of multispecies nonreactive mixtures,” Phys. Rev. E 89 013017 (2014)] and binary liquid mixtures [Donev et al., “Low mach number fluctuating hydrodynamics of diffusively mixing fluids,” Commun. Appl. Math. Comput. Sci. 9(1), 47-105 (2014)]. In this formulation, we combine and extend a number of existing descriptions of multispecies transport available in the literature. Themore » formulation applies to non-ideal mixtures of arbitrary number of species, without the need to single out a “solvent” species, and includes contributions to the diffusive mass flux due to gradients of composition, temperature, and pressure. Momentum transport and advective mass transport are handled using a low Mach number approach that eliminates fast sound waves (pressure fluctuations) from the full compressible system of equations and leads to a quasi-incompressible formulation. Thermal fluctuations are included in our fluctuating hydrodynamics description following the principles of nonequilibrium thermodynamics. We extend the semi-implicit staggered-grid finite-volume numerical method developed in our prior work on binary liquid mixtures [Nonaka et al., “Low mach number fluctuating hydrodynamics of binary liquid mixtures,” http://arxiv.org/abs/1410.2300 (2015)] and use it to study the development of giant nonequilibrium concentration fluctuations in a ternary mixture subjected to a steady concentration gradient. We also numerically study the development of diffusion-driven gravitational instabilities in a ternary mixture and compare our numerical results to recent experimental measurements [Carballido-Landeira et al., “Mixed-mode instability of a miscible interface due to coupling between Rayleigh–Taylor and double-diffusive convective modes,” Phys. Fluids 25, 024107 (2013)] in a Hele-Shaw cell. We find that giant nonequilibrium fluctuations can trigger the instability but are eventually dominated by the deterministic growth of the unstable mode, in both quasi-two-dimensional (Hele-Shaw) and fully three-dimensional geometries used in typical shadowgraph experiments.« less

Experience of superheat of solutions: doubly metastable systems

NASA Astrophysics Data System (ADS)

Skripov, P. V.

2017-11-01

The phenomenon of attainable superheat of two-component mixtures has been studied experimentally by the method of pulse heating of a wire probe. Special attention was called to the appearance of double metastability in the course of heating. Besides the usual superheating with respect to the liquid-vapor equilibrium temperature, the objects under study turn out to be supersaturated with respect to the carbon dioxide content. Preliminary experiments were carried out in the region of instability located above the diffusion spinodal. The results obtained lead to the choice of the program of further research on doubly metastable and unstable systems with different degrees of component compatibility.

Effect of thermal diffusion on the stability of strongly tilted mantle plume tails

NASA Astrophysics Data System (ADS)

Kerr, R. C.; MéRiaux, C.; Lister, J. R.

2008-09-01

The effect of thermal diffusion on the stability of strongly tilted mantle plume tails is explored by investigating experimentally and numerically the gravitational instability of a rising horizontal cylindrical region of buoyant viscous fluid. At large viscosity ratios, we find that the instability is unaffected by diffusion when the Rayleigh number Ra is greater than about 300. When Ra is less than 300, diffusion significantly increases the time for instability, as the rising fluid region needs to grow substantially by entrainment before it becomes unstable. When Ra is less than about 140 and the rise height available H is less than about 40 times the cylinder radius, the rising region of fluid is unable to grow sufficiently and instability is prevented. When our results are applied to the Earth, we predict that thermal diffusion will stabilize plume tails in both the upper and lower mantle. We also predict that some of the buoyancy flux in mantle plumes is lost during ascent to form downstream thermal wakes in any larger-scale mantle flow.

Influence of toroidal rotation on resistive tearing modes in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, S.; Ma, Z. W., E-mail: zwma@zju.edu.cn

Influence of toroidal equilibrium plasma rotation on m/n = 2/1 resistive tearing modes is studied numerically using a 3D toroidal MHD code (CLT). It is found that the toroidal rotation with or without shear can suppress the tearing instability and the Coriolis effect in the toroidal geometry plays a dominant role on the rotation induced stabilization. For a high viscosity plasma (τ{sub R}/τ{sub V} ≫ 1, where τ{sub R} and τ{sub V} represent resistive and viscous diffusion time, respectively), the effect of the rotation shear combined with the viscosity appears to be stabilizing. For a low viscosity plasmas (τ{sub R}/τ{sub V} ≪ 1), the rotation shearmore » shows a destabilizing effect when the rotation is large.« less

Volume nanograting formation in laser-silica interaction as a result of the 1D plasma-resonance ionization instability

NASA Astrophysics Data System (ADS)

Gildenburg, V. B.; Pavlichenko, I. A.

2016-08-01

The initial stage of the small-scale ionization-induced instability developing inside the fused silica volume exposed to the femtosecond laser pulse is studied as a possible initial cause of the self-organized nanograting formation. We have calculated the spatial spectra of the instability with the electron-hole diffusion taken into account for the first time and have found that it results in the formation of some hybrid (diffusion-wave) 1D structure with the spatial period determined as the geometrical mean of the laser wavelength and characteristic diffusion length of the process considered. Near the threshold of the instability, this period occurs to be approximately equal to the laser half-wavelength in the silica, close to the one experimentally observed.

Long-time behavior and Turing instability induced by cross-diffusion in a three species food chain model with a Holling type-II functional response.

PubMed

Haile, Dawit; Xie, Zhifu

2015-09-01

In this paper, we study a strongly coupled reaction-diffusion system describing three interacting species in a food chain model, where the third species preys on the second one and simultaneously the second species preys on the first one. An intra-species competition b2 among the second predator is introduced to the food chain model. This parameter produces some very interesting result in linear stability and Turing instability. We first show that the unique positive equilibrium solution is locally asymptotically stable for the corresponding ODE system when the intra-species competition exists among the second predator. The positive equilibrium solution remains linearly stable for the reaction diffusion system without cross diffusion, hence it does not belong to the classical Turing instability scheme. But it becomes linearly unstable only when cross-diffusion also plays a role in the reaction-diffusion system, hence the instability is driven solely from the effect of cross diffusion. Our results also exhibit some interesting combining effects of cross-diffusion, intra-species competitions and inter-species interactions. Numerically, we conduct a one parameter analysis which illustrate how the interactions change the existence of stable equilibrium, limit cycle, and chaos. Some interesting dynamical phenomena occur when we perform analysis of interactions in terms of self-production of prey and intra-species competition of the middle predator. By numerical simulations, it illustrates the existence of nonuniform steady solutions and new patterns such as spot patterns, strip patterns and fluctuations due to the diffusion and cross diffusion in two-dimension. Published by Elsevier Inc.

Introduction to the Focus Issue: Chemo-Hydrodynamic Patterns and Instabilities

NASA Astrophysics Data System (ADS)

De Wit, A.; Eckert, K.; Kalliadasis, S.

2012-09-01

Pattern forming instabilities are often encountered in a wide variety of natural phenomena and technological applications, from self-organization in biological and chemical systems to oceanic or atmospheric circulation and heat and mass transport processes in engineering systems. Spatio-temporal structures are ubiquitous in hydrodynamics where numerous different convective instabilities generate pattern formation and complex spatiotemporal dynamics, which have been much studied both theoretically and experimentally. In parallel, reaction-diffusion processes provide another large family of pattern forming instabilities and spatio-temporal structures which have been analyzed for several decades. At the intersection of these two fields, "chemo-hydrodynamic patterns and instabilities" resulting from the coupling of hydrodynamic and reaction-diffusion processes have been less studied. The exploration of the new instability and symmetry-breaking scenarios emerging from the interplay between chemical reactions, diffusion and convective motions is a burgeoning field in which numerous exciting problems have emerged during the last few years. These problems range from fingering instabilities of chemical fronts and reactive fluid-fluid interfaces to the dynamics of reaction-diffusion systems in the presence of chaotic mixing. The questions to be addressed are at the interface of hydrodynamics, chemistry, engineering or environmental sciences to name a few and, as a consequence, they have started to draw the attention of several communities including both the nonlinear chemical dynamics and hydrodynamics communities. The collection of papers gathered in this Focus Issue sheds new light on a wide range of phenomena in the general area of chemo-hydrodynamic patterns and instabilities. It also serves as an overview of the current research and state-of-the-art in the field.

Phylogenetic study of metallo-β-lactamase producing multidrug resistant Pseudomonas aeruginosa isolates from burn patients.

PubMed

Jena, Jayanti; Debata, Nagen Kumar; Sahoo, Rajesh Kumar; Subudhi, Enketeswara

2015-12-01

The present study was carried out to understand the clonal relationship using enterobacteriaceae repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) among metallo-β-lactamase (MBL) producing multidrug resistant Pseudomonas aeruginosa isolates from burn victims and their susceptibility to commonly used anti-pseudomonal agents. In the present study 94 non-duplicate P. aeruginosa strains from the wound samples of burn patients were included. Identification of the isolates was done by biochemical methods and antibiotic sensitivity was done by disc diffusion method following CLSI (Clinical Laboratory Standard Institute) guidelines. By using imipenem (IPM)-EDTA disk diffusion/double disc synergy method carbapenem resistant organisms were tested for MBL. To define the clonal relationship ERIC-PCR was used. Of the 94 isolates, 18 (19.14%) were found resistant to IPM and MBL production was shown 11 (11.70%) by the IPM-EDTA disc diffusion method. From dendrogram of the ERIC-PCR profile four major clusters were obtained (A, B, C and D). Cluster B contained the majority of the isolates (6 strains 1, 4, 8, 9, 10 and 11). This study using ERIC-PCR of randomly collected isolates exhibits high genetic diversity which rules out cross contamination frequency. Copyright © 2015 Elsevier Ltd and ISBI. All rights reserved.

Investigation of the Flow Field and Performances of a Centrifugal Pump at Part Load

NASA Astrophysics Data System (ADS)

Prunières, R.; Inoue, Y.; Nagahara, T.

2016-11-01

Centrifugal pump performance curve instability, characterized by a local dent at part load, can be the consequence of flow instabilities in rotating or stationary parts. Such flow instabilities often result in abnormal operating conditions which can damage both the pump and the system. In order for the pump to have reliable operation over a wide flow rate range, it is necessary to achieve a design free of instability. The present paper focuses on performance curve instability of a centrifugal pump of mid specific speed (ωs = 0.65) for which instability was observed at part load during tests. The geometry used for this research consist of the first stage of a multi-stage centrifugal pump and is composed of a suction bend, a closed-type impeller, a vaned diffuser and return guide vanes. In order to analyse the instability phenomenon, PIV and CFD analysis were performed. Both methods qualitatively agree relatively well. It appears that the main difference before and after head drop is an increase of reverse flow rate at the diffuser passage inlet on the hub side. This reverse flow decreases the flow passing area at the diffuser passage inlet, disallowing effective flow deceleration and impairing static pressure recovery.

Ferroelectric behavior of Al substituted InP

NASA Astrophysics Data System (ADS)

Park, C. S.; Lee, S. J.; Kang, T. W.; Fu, D. J.

2006-12-01

InP:Al was grown by the liquid phase epitaxy method on InP (100)substrates. X-ray diffraction confirmed the epitaxial growth along (100) of AlInP. Photoluminescence spectra showed the evident effect of Al content. Ferroelectric characterization of the sample revealed a clear hysteresis in its polarization-voltage curves. The remnant polarization of InP:Al amounts to 1.99μC/cm2 at 300Hz, and it decreases with increasing temperature in a continuous and diffusive manner. Resistance measurement demonstrated a maximum resistance at 160°C, tentatively consistent with the transition temperature of remnant polarization. The ferroelectricity is accounted by the collective interaction between nuclei having the microscopic instability from the cation size difference in InP:Al.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moll, Ryan; Garaud, Pascale, E-mail: rmoll@soe.ucsc.edu

Oscillatory double-diffusive convection (ODDC, more traditionally called semiconvection) is a form of linear double-diffusive instability that occurs in fluids that are unstably stratified in temperature (Schwarzschild unstable), but stably stratified in chemical composition (Ledoux stable). This scenario is thought to be quite common in the interiors of stars and giant planets, and understanding the transport of heat and chemical species by ODDC is of great importance to stellar and planetary evolution models. Fluids unstable to ODDC have a tendency to form convective thermocompositional layers that significantly enhance the fluxes of temperature and chemical composition compared with microscopic diffusion. Although a numbermore » of recent studies have focused on studying properties of both layered and nonlayered ODDC, few have addressed how additional physical processes such as global rotation affect its dynamics. In this work, we study first how rotation affects the linear stability properties of rotating ODDC. Using direct numerical simulations, we then analyze the effect of rotation on properties of layered and nonlayered ODDC, and we study how the angle of the rotation axis with respect to the direction of gravity affects layering. We find that rotating systems can be broadly grouped into two categories based on the strength of rotation. The qualitative behavior in the more weakly rotating group is similar to nonrotating ODDC, but strongly rotating systems become dominated by vortices that are invariant in the direction of the rotation vector and strongly influence transport. We find that whenever layers form, rotation always acts to reduce thermal and compositional transport.« less

Nutrient chemotaxis suppression of a diffusive instability in bacterial colony dynamics

NASA Astrophysics Data System (ADS)

Arouh, Scott; Levine, Herbert

2000-07-01

Bacteria grown on a semisolid agar surface have been observed to form branching patterns as the colony envelope propagates outward. The fundamental cause of this instability relates to the need for limited nutrient to diffuse towards the colony. Here, we investigate the effect on this instability of allowing the bacteria to move chemotactically in response to the nutrient gradient. Our results show that this additional effect has a tendency to suppress the instability. Our calculations are done within the context of a simple ``cutoff'' model of colony dynamics, but presumably remain valid for more complex and hence more realistic approaches.

Volume nanograting formation in laser-silica interaction as a result of the 1D plasma-resonance ionization instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gildenburg, V. B., E-mail: gil@appl.sci-nnov.ru; Pavlichenko, I. A.; Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950

2016-08-15

The initial stage of the small-scale ionization-induced instability developing inside the fused silica volume exposed to the femtosecond laser pulse is studied as a possible initial cause of the self-organized nanograting formation. We have calculated the spatial spectra of the instability with the electron-hole diffusion taken into account for the first time and have found that it results in the formation of some hybrid (diffusion-wave) 1D structure with the spatial period determined as the geometrical mean of the laser wavelength and characteristic diffusion length of the process considered. Near the threshold of the instability, this period occurs to be approximatelymore » equal to the laser half-wavelength in the silica, close to the one experimentally observed.« less

Exploiting Tumor-Activated Testes Proteins to Enhance Efficacy of First-Line Chemotherapeutics in NSCLC

DTIC Science & Technology

2015-10-01

TERMS Cancer Testis Antigen (CTA), Fanconia- Anemia (FA), DNA Damage, Genomic Instability, DNA Double Strand Break (DSB) 16. SECURITY CLASSIFICATION OF...Cancer Testis Antigen (CTA) o Fanconia- Anemia (FA) o DNA Damage o Genomic Instability o DNA Double Strand Break (DSB) 3. Accomplishments • What

Wavenumber distribution in Hopf-wave instability: the reversible Selkov model of glycolytic oscillation.

PubMed

Dutt, Arun K

2005-09-22

We have investigated the short-wave instability due to Hopf bifurcation in a reaction-diffusion model of glycolytic oscillations. Very low values of the ratio d of the diffusion coefficient of the inhibitor (ATP) and that of the activator (ADP) do help to create short waves, whereas high values of the ratio d and the complexing reaction of the activator ADP reduces drastically the wave-instability domain, generating much longer wavelengths.

Control strategy on the double-diffusive convection in a nanofluid layer with internal heat generation

NASA Astrophysics Data System (ADS)

Mokhtar, N. F. M.; Khalid, I. K.; Siri, Z.; Ibrahim, Z. B.; Gani, S. S. A.

2017-10-01

The influences of feedback control and internal heat source on the onset of Rayleigh-Bénard convection in a horizontal nanofluid layer is studied analytically due to Soret and Dufour parameters. The confining boundaries of the nanofluid layer (bottom boundary-top boundary) are assumed to be free-free, rigid-free, and rigid-rigid, with a source of heat from below. Linear stability theory is applied, and the eigenvalue solution is obtained numerically using the Galerkin technique. Focusing on the stationary convection, it is shown that there is a positive thermal resistance in the presence of feedback control on the onset of double-diffusive convection, while there is a positive thermal efficiency in the existence of internal heat generation. The possibilities of suppress or augment of the Rayleigh-Bénard convection in a nanofluid layer are also discussed in detail.

The Effect of External Magnetic Fields on the MRT Instability in MagLIF

NASA Astrophysics Data System (ADS)

Hess, Mark; Peterson, Kyle; Weis, Matthew; Lau, Yue Ying

2014-10-01

Recent experiments on MagLIF which incorporate an external B-field suggest that the MRT instability within the liner has a different behavior than without the B-field. Previous work by Chandrasekhar and Harris have illustrated how the MRT growth rate, assuming fixed liner density and fixed acceleration, can change due to the presence of an external B-field. In this work, we show how the growth rate of the MRT instability is dynamically affected by the rapidly varying acceleration, liner density, and surface magnetic field, which is composed of the external B-field and the drive B-field of the liner in the MagLIF experiments. In addition, we also examine the effects of finite liner resistivity on MRT growth, which gives rise to an additional time scale corresponding to magnetic diffusion. We discuss the implications of this result for future MagLIF designs. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

Pull-in instability of paddle-type and double-sided NEMS sensors under the accelerating force

NASA Astrophysics Data System (ADS)

Keivani, M.; Khorsandi, J.; Mokhtari, J.; Kanani, A.; Abadian, N.; Abadyan, M.

2016-02-01

Paddle-type and double-sided nanostructures are potential for use as accelerometers in flying vehicles and aerospace applications. Herein the pull-in instability of the cantilever paddle-type and double-sided sensors in the Casimir regime are investigated under the acceleration. The D'Alembert principle is employed to transform the accelerating system into an equivalent static system by incorporating the accelerating force. Based on the couple stress theory (CST), the size-dependent constitutive equations of the sensors are derived. The governing nonlinear equations are solved by two approaches, i.e. modified variational iteration method and finite difference method. The influences of the Casimir force, geometrical parameters, acceleration and the size phenomenon on the instability performance have been demonstrated. The obtained results are beneficial to design and fabricate paddle-type and double-sided accelerometers.

Low-resistance noble metal contacts to high-temperature superconductors

NASA Technical Reports Server (NTRS)

Selim, R.; Caton, R.; Buoncristiani, A. M.; Byvik, C. E.; Edahl, R. A., Jr.

1990-01-01

Low-resistance contacts were made to both YBa2Cu3O(7-x) and Bi2BaSr2Cu2O8, and to related superconducting compounds by melting gold or silver pads onto the samples before the final oxygen treatment. Scanning electron microscope studies show that both gold and silver do not diffuse far from the contact area. The surface contact resistivity of the best contacts made by the melting technique has an upper limit value in the 10 to the -8th ohm sq cm range at 77 K. This contact resistivity shows no significant change in its value over a period of 17 months. Furthermore, an electron radiation dose of 5.7 x 10 to the 17th electron/sq cm only doubled the contact resistivity.

Moist, Double-diffusive convection

NASA Astrophysics Data System (ADS)

Oishi, Jeffrey; Burns, Keaton; Brown, Ben; Lecoanet, Daniel; Vasil, Geoffrey

2017-11-01

Double-diffusive convection occurs when the competition between stabilizing and a destabilizing buoyancy source is mediated by a difference in the diffusivity of each source. Such convection is important in a wide variety of astrophysical and geophysical flows. However, in giant planets, double-diffusive convection occurs in regions where condensation of important components of the atmosphere occurs. Here, we present preliminary calculations of moist, double-diffusive convection using the Dedalus pseudospectral framework. Using a simple model for phase change, we verify growth rates for moist double diffusive convection from linear calculations and report on preliminary relationships between the ability to form liquid phase and the resulting Nusselt number in nonlinear simulations.

Exploiting Tumor Activated Testes Proteins To Enhance Efficacy of First Line Chemotherapeutics in NSCLC

DTIC Science & Technology

2016-10-01

Antigen (CTA), Fanconia- Anemia (FA), DNA Damage, Genomic Instability, DNA Double Strand Break (DSB) 16. SECURITY CLASSIFICATION OF: 17. LIMITATION...Fanconia- Anemia (FA) o DNA Damage o Genomic Instability o DNA Double Strand Break (DSB) 3. Accomplishments • What were the major goals and objectives of

Contributions of microtubule rotation and dynamic instability to kinetochore capture

NASA Astrophysics Data System (ADS)

Sweezy-Schindler, Oliver; Edelmaier, Christopher; Blackwell, Robert; Glaser, Matt; Betterton, Meredith

2014-03-01

The capture of lost kinetochores (KCs) by microtubules (MTs) is a crucial part of prometaphase during mitosis. Microtubule dynamic instability has been considered the primary mechanism of KC capture, but recent work discovered that lateral KC attachment to pivoting MTs enabled rapid capture even with significantly reduced MT dynamics. We aim to understand the relative contributions of MT rotational diffusion and dynamic instability to KC capture, as well as KC capture through end-on and/or lateral attachment. Our model consists of rigid MTs and a spherical KC, which are allowed to diffuse inside a spherical nuclear envelope consistent with the geometry of fission yeast. For simplicity, we include a single spindle pole body, which is anchored to the nuclear membrane, and its associated polar MTs. Brownian dynamics treats the diffusion of the MTs and KC and kinetic Monte Carlo models stochastic processes such as dynamic instability. NSF 1546021.

Dynamics of Mesoscale Magnetic Field in Diffusive Shock Acceleration

NASA Astrophysics Data System (ADS)

Diamond, P. H.; Malkov, M. A.

2007-01-01

We present a theory for the generation of mesoscale (krg<<1, where rg is the cosmic-ray gyroradius) magnetic fields during diffusive shock acceleration. The decay or modulational instability of resonantly excited Alfvén waves scattering off ambient density perturbations in the shock environment naturally generates larger scale fields. For a broad spectrum of perturbations, the physical mechanism of energy transfer is random refraction, represented by the diffusion of Alfvén wave packets in k-space. The scattering field can be produced directly by the decay instability or by the Drury instability, a hydrodynamic instability driven by the cosmic-ray pressure gradient. This process is of interest to acceleration since it generates waves of longer wavelength, and so enables the confinement and acceleration of higher energy particles. This process also limits the intensity of resonantly generated turbulent magnetic fields on rg scales.

Sedimentation and gravitational instability of Escherichia coli Suspension

NASA Astrophysics Data System (ADS)

Salin, Dominique; Douarche, Carine

2017-11-01

The successive runs and tumbles of Escherichia coli bacteria provide an active matter suspension of rod-like particles with a large swimming, Brownian like, diffusion. As opposed to inactive elongated particles, this diffusion prevents clustering of the particles and hence instability in the gravity field. We measure the time dependent E . coli concentration profile during their sedimentation. After some hours, due to the dioxygen consumption, a motile / non-motile front forms leading to a Rayleigh-Taylor type gravitational instability. Analysing both sedimentation and instability in the framework of active particle suspensions, we can measure the relevant bacteria hydrodynamic characteristics such as its single particle sedimentation velocity and its hindrance volume. Comparing these quantities to the ones of equivalent passive particles (ellipsoid, rod) we tentatively infer the effective shape and size of the bacteria involved in its buoyancy induced advection and diffusion. Laboratoire FAST University Paris Saclay France.

Sedimentation and gravitational instability of Escherichia coli Suspension

NASA Astrophysics Data System (ADS)

Douarche, Carine; Salin, Dominique; Collaboration between Laboratory FAST; LPS Collaboration

2016-11-01

The successive run and tumble of Escherichia coli bacteria provides an active matter suspension of rod-like particles with a large swimming diffusion. As opposed to inactive elongated particles, this diffusion prevents clustering and instability in the gravity field. We measure the time dependent E . coli concentration profile during their sedimentation. After some hours, due to the dioxygen consumption, a motile / non-motile front forms leading to a Rayleigh-Taylor type gravitational instability. Analyzing both sedimentation and instability in the framework of active particle suspensions, we can measure the relevant bacteria hydrodynamic characteristics such as its single particle sedimentation velocity and its hindrance volume.

Homologous Recombination Repair Protects Against Particulate Chromate-induced Chromosome Instability in Chinese Hamster Cells

PubMed Central

Stackpole, Megan M.; Wise, Sandra S.; Duzevik, Eliza Grlickova; Munroe, Ray C.; Thompson, W. Douglas; Thacker, John; Thompson, Larry H.; Hinz, John M.; Wise, John Pierce

2008-01-01

Particulate hexavalent chromium [Cr(VI)] compounds are well-established human carcinogens. Cr(VI)-induced tumors are characterized by chromosomal instability (CIN); however, the mechanisms of this effect are unknown. We investigated the hypothesis that homologous recombination (HR) repair of DNA double strand breaks protect cells from Cr(VI)-induced CIN by focusing on the XRCC3 and RAD51C genes, which play an important role in cellular resistance to DNA double strand breaks. We used Chinese hamster cells defective in each HR gene (irs3 for RAD51C and irs1SF for XRCC3) and compared with their wildtype parental and cDNA-complemented controls. We found that the intracellular Cr ion levels varied among the cell lines after particulate chromate treatment. Importantly, accounting for differences in Cr ion levels, we discovered that XRCC3 and RAD51C cells treated with lead chromate had increased cytotoxicity and chromosomal aberrations, relative to wild-type and cDNA-complimented cells. We also observed the emergence of high levels of chromatid exchanges in the two mutant cell lines. For example, 1 ug/cm2 lead chromate induced 20 and 32 exchanges in XRCC3- and RAD51C-deficient cells, respectively, whereas no exchanges were detected in the wildtype and cDNA-complemented cells. These observations suggest that HR protects cells from Cr(VI)-induced CIN, consistent with the ability of particulate Cr(VI) to induce double strand breaks. PMID:17662313

On the Grain-modified Magnetic Diffusivities in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Xu, Rui; Bai, Xue-Ning

2016-03-01

Weakly ionized protoplanetary disks (PPDs) are subject to nonideal magnetohydrodynamic (MHD) effects, including ohmic resistivity, the Hall effect, and ambipolar diffusion (AD), and the resulting magnetic diffusivities ({η }{{O}},{η }{{H}}, and {η }{{A}}) largely control the disk gas dynamics. The presence of grains not only strongly reduces the disk ionization fraction, but also modifies the scalings of {η }{{H}} and {η }{{A}} with magnetic field strength. We analytically derive asymptotic expressions of {η }{{H}} and {η }{{A}} in both the strong and weak field limits and show that toward a strong field, {η }{{H}} can change sign (at a threshold field strength {B}{{th}}), mimicking a flip of field polarity, and AD is substantially reduced. Applied to PPDs, we find that when small ˜0.1 (0.01)μm grains are sufficiently abundant (mass ratio ˜0.01 (10-4)), {η }{{H}} can change sign up to ˜2-3 scale heights above the midplane at a modest field strength (plasma β ˜ 100) over a wide range of disk radii. The reduction of AD is also substantial toward the AD-dominated outer disk and may activate the magnetorotational instability. We further perform local nonideal MHD simulations of the inner disk (within 10 au) and show that, with sufficiently abundant small grains, the magnetic field amplification due to the Hall-shear instability saturates at a very low level near the threshold field strength {B}{{th}}. Together with previous studies, we conclude by discussing the grain-abundance-dependent phenomenology of PPD gas dynamics.

Double layers in contactor plasmas

NASA Technical Reports Server (NTRS)

Cooke, David L.

1990-01-01

The concept of using a hollow cathode to establish a low impedance contact between a spacecraft and the ambient plasma continues to gain in popularity, and is often then referred to as a plasma contactor. A growing number of studies indicate that large contact currents can be supported with small potential difference between the contactor and the ambient plasma. Results will be presented from a simple one-dimensional spherical model that obtains potentials from the solution of Poisson's equation, and particle densities from a turning point formalism that includes particle angular momentum. The neglect of collisions and magnetic field limits the realism. However, the results illustrate the effect of double layers that can form at the interface between contactor and ambient plasmas, when there is any voltage differential between the contactor and the ambient. The I-V characteristic of this model shows the usual space charge depends upon collection when the contactor flux is lower than some threshold; independence of I from variation in V when the flux is slightly greater than that threshold, and (numerical ?) instability for excessive flux suggesting the possibility of negative resistance. Even if a real I-V characteristic does not exhibit negative resistance, flat spots or high resistance regions may still be troublesome (or useful) to the total circuit.

Jet-front systems nearing strongly stratified region in differentially heated, rotating stratified annulus

NASA Astrophysics Data System (ADS)

Rolland, Joran; Achatz, Ulrich

2017-04-01

The differentially heated, rotating annulus configuration has been used for a long time as a model system of the earth troposphere. It can easily reproduce thermal wind and baroclinic waves in the laboratory. It has recently been shown numerically that provided the Rossby number, the rotation rate and the Brunt-Väisälä frequency were well chosen, this configuration also reproduces the spontaneous emission of gravity waves by jet front systems [1]. This offers a very practical configuration in which to study an important process of emission of atmospheric gravity waves. It has also been shown experimentally that this configuration can be modified in order to add the possibility for the emitted wave to reach a strongly stratified region [2]. It thus creates a system containing a model troposphere where gravity waves are spontaneously emitted and can propagate to a model stratosphere. For this matter a stratification was created using a salinity gradient in the experimental apparatus. Through double diffusion, this generates a strongly stratified layer in the middle of the flow (the model stratosphere) and two weakly stratified region in the top and bottom layers (the model troposphere). In this poster, we present simulations of this configuration displaying baroclinic waves in the top and bottom layers. We aim at creating jet front systems strong enough that gravity waves can be spontaneously emitted. This will thus offer the possibility of studying the wave characteristic and mechanisms in emission and propagation in details. References [1] S. Borchert, U. Achatz, M.D. Fruman, Spontaneous Gravity wave emission in the differentially heated annulus, J. Fluid Mech. 758, 287-311 (2014). [2] M. Vincze, I. Borcia, U. Harlander, P. Le Gal, Double-diffusive convection convection and baroclinic instability in a differentially heated and initially stratified rotating system: the barostrat instability, Fluid Dyn. Res. 48, 061414 (2016).

Absolute and convective instabilities and their roles in the forecasting of large frontal meanderings

NASA Astrophysics Data System (ADS)

Liang, X. San; Robinson, Allan R.

2013-10-01

Frontal meanderings are generally difficult to predict. In this study, we demonstrate through an exercise with the Iceland-Faeroe Front (IFF) that satisfactory predictions may be achieved with the aid of hydrodynamic instability analysis. As discovered earlier on, underlying the IFF meandering is a convective instability in the western boundary region followed by an absolute instability in the interior; correspondingly the disturbance growth reveals a switch of pattern from spatial amplification to temporal amplification. To successfully forecast the meandering, the two instability processes must be faithfully reproduced. This sets stringent constraints for the tunable model parameters, e.g., boundary relaxation, temporal relaxation, eddy diffusivity, etc. By analyzing the instability dispersion properties, these parameters can be rather accurately set and their respective ranges of sensitivity estimated. It is shown that too much relaxation inhibits the front from varying; on the other hand, too little relaxation may have the model completely skip the spatial growth phase, leading to a meandering way more upstream along the front. Generally speaking, dissipation/diffusion tends to stabilize the simulation, but unrealistically large dissipation/diffusion could trigger a spurious absolute instability, and hence a premature meandering intrusion. The belief that taking in more data will improve the forecast does not need to be true; it depends on whether the model setup admits the two instabilities. This study may help relieve modelers from the laborious and tedious work of parameter tuning; it also provides us criteria to distinguish a physically relevant forecast from numerical artifacts.

The platinum microelectrode/Nafion interface - An electrochemical impedance spectroscopic analysis of oxygen reduction kinetics and Nafion characteristics

NASA Technical Reports Server (NTRS)

Parthasarathy, Arvind; Dave, Bhasker; Srinivasan, Supramaniam; Appleby, John A.; Martin, Charles R.

1992-01-01

The objectives of this study were to use electrochemical impedance spectroscopy (EIS) to study the oxygen-reduction reaction under lower humidification conditions than previously studied. The EIS technique permits the discrimination of electrode kinetics of oxygen reduction, mass transport of O2 in the membrane, and the electrical characteristics of the membrane. Electrode-kinetic parameters for the oxygen-reduction reaction, corrosion current densities for Pt, and double-layer capacitances were calculated. The production of water due to electrochemical reduction of oxygen greatly influenced the EIS response and the electrode kinetics at the Pt/Nafion interface. From the finite-length Warburg behavior, a measure of the diffusion coefficient of oxygen in Nafion and diffusion-layer thickness was obtained. An analysis of the EIS data in the high-frequency domain yielded membrane and interfacial characteristics such as ionic conductivity of the membrane, membrane grain-boundary capacitance and resistance, and uncompensated resistance.

Nonlinear evolution of the Kelvin-Helmholtz instability in the double current sheet configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, Aohua; Li, Jiquan, E-mail: lijq@energy.kyoto-u.ac.jp; Kishimoto, Yasuaki

2016-03-15

The nonlinear evolution of the Kelvin-Helmholtz (KH) instability driven by a radially antisymmetric shear flow in the double current sheet configuration is numerically investigated based on a reduced magnetohydrodynamic model. Simulations reveal different nonlinear fate of the KH instability depending on the amplitude of the shear flow, which restricts the strength of the KH instability. For strong shear flows far above the KH instability threshold, the linear electrostatic-type KH instability saturates and achieves a vortex flow dominated quasi-steady state of the electromagnetic (EM) KH turbulence with large-amplitude zonal flows as well as zonal fields. The magnetic surfaces are twisted significantlymore » due to strong vortices but without the formation of magnetic islands. However, for the shear flow just over the KH instability threshold, a weak EM-type KH instability is saturated and remarkably damped by zonal flows through modifying the equilibrium shear flow. Interestingly, a secondary double tearing mode (DTM) is excited subsequently in highly damped KH turbulence, behaving as a pure DTM in a flowing plasma as described in Mao et al. [Phys. Plasmas 21, 052304 (2014)]. However, the explosive growth phenomenon is replaced by a gradually growing oscillation due to the extremely twisted islands. As a result, the release of the magnetic energy becomes slow and the global magnetic reconnection tends to be gentle. A complex nonlinear interaction between the EM KH turbulence and the DTMs occurs for the medium shear flows above the KH instability threshold, turbulent EM fluctuations experience oscillatory nonlinear growth of the DTMs, finally achieves a quasi-steady state with the interplay of the fluctuations between the DTMs and the EM KH instability.« less

Instabilities and turbulence in highly ionized plasmas in a magnetic field

NASA Technical Reports Server (NTRS)

Jennings, W. C.

1972-01-01

Physical mechanisms were considered which are responsible for plasma turbulence and the establishment of necessary conditions for energy exchange and transfer in the frequency spectrum. In addition, work was performed to better understand the drift instability in the highly inhomogeneous Rensselaer arc, and methods to suppress this instability using feedback stabilization techniques. Correlation techniques were refined to study plasma turbulence, the diffusion wave technique for monitoring cross-field diffusion was extended to include regimes of high turbulence levels, and a technique for coupling stabilizing RF power to the Rensselaer arc was developed.

Effect of double layers on magnetosphere-ionosphere coupling

NASA Technical Reports Server (NTRS)

Lysak, Robert L.; Hudson, Mary K.

1987-01-01

The Earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths. These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. A number of models of microscopic turbulence will be introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, the effects of a double layer electric field which scales with the plasma temperature and Debye length is compared with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than in the resistive model leading to the possibility of narrow, intense current structures.

Why Did the 2010 Eyjafjallajokull Volcanic Eruption Cloud Last So Long?

NASA Astrophysics Data System (ADS)

Jellinek, M.; Carazzo, G.

2013-12-01

The global economic consequences of the relatively small Eyjafjallajokull eruption in the spring of 2010 caught the world off guard. That the eruption cloud lasted for several months rather than weeks, efficiently disrupting air travel and the holiday plans of thousands of tourists, drew arguably more attention and a certainly garnered a highly emotional response. The longevity of this eruption cloud was touted to be "an anomaly". However, this anomaly nearly repeated itself the following year in the form of the 2011 Puyehue-Cordon Caulle eruption cloud. A major reason that the behavior of the 2010 Eyjafjallajokul cloud was surprising is that "standard" models for ash sedimentation (i.e., heavy particles fall out of the cloud faster than light particles) are incomplete. Observations of the 2010 Eyjafjallajokull, as well as the structure of atmospheric aerosol clouds from the 1991 Mt Pinatubo event, suggest that an additional key process in addition to particle settling is the production of internal layering. We use analog experiments on turbulent particle-laden umbrella clouds and simple models to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability leading to this layering. This 'particle diffusive convection' strongly influences cloud longevity where volcanic umbrella clouds are enriched in fine ash. More generally, volcanic cloud residence times will depend on ash fluxes related to both individual particle settling and diffusive convection. We discuss a new sedimentation model that includes both contributions to the particle flux and explains the the rate of change of particle concentration in the 1982 El Chichon, 1991 Mt Pinatubo and 1992 Mt Spurr ash-clouds. Examples of periodic layering in volcanic clouds compared with experiments in which periodic layering emerges as a result of buoyancy effects related to a particle-salt double diffusive instability.

Double-diffusive translation of Earth's inner core

NASA Astrophysics Data System (ADS)

Deguen, R.; Alboussiére, T.; Labrosse, S.

2018-03-01

The hemispherical asymmetry of the inner core has been interpreted as resulting form a high-viscosity mode of inner core convection, consisting in a translation of the inner core. A thermally driven translation, as originally proposed, is unlikely if the currently favoured high values of the thermal conductivity of iron at core conditions are correct. We consider here the possibility that inner core translation results from an unstable compositional gradient, which would develop either because the light elements present in the core become increasingly incompatible as the inner core grows, or because of a possibly positive feedback of the development of the F-layer on inner core convection. Though the magnitude of the destabilising effect of the compositional field is predicted to be similar to or smaller than the stabilising effect of the thermal field, the huge difference between thermal and chemical diffusivities implies that double-diffusive instabilities can still arise even if the net buoyancy increases upward. Using linear stability analysis and numerical simulations, we demonstrate that a translation mode can indeed exist if the compositional field is destabilising, even if the temperature profile is subadiabatic, and irrespectively of the relative magnitudes of the composition and potential temperature gradients. The existence of this double diffusive mode of translation requires that the following conditions are met: (i) the compositional profile within the inner core is destabilising, and remains so for a duration longer than the destabilisation timescale (on the order of 200 My, but strongly dependent on the magnitude of the initial perturbation); and (ii) the inner core viscosity is sufficiently large, the required value being a strongly increasing function of the inner core size (e.g. 1017 Pa.s when the inner core was 200 km in radius, and ≃ 3 × 1021 Pa.s at the current inner core size). If these conditions are met, the predicted inner core translation rate is found to be similar to the inner core growth rate, which is more consistent with inferences from the geomagnetic field morphology and secular variation than the higher translation rate predicted for a thermally driven translation.

Simulation of plasma double-layer structures

NASA Technical Reports Server (NTRS)

Borovsky, J. E.; Joyce, G.

1982-01-01

Electrostatic plasma double layers are numerically simulated by means of a magnetized 2 1/2 dimensional particle in cell method. The investigation of planar double layers indicates that these one dimensional potential structures are susceptible to periodic disruption by instabilities in the low potential plasmas. Only a slight increase in the double layer thickness with an increase in its obliqueness to the magnetic field is observed. Weak magnetization results in the double layer electric field alignment of accelerated particles and strong magnetization results in their magnetic field alignment. The numerical simulations of spatially periodic two dimensional double layers also exhibit cyclical instability. A morphological invariance in two dimensional double layers with respect to the degree of magnetization implies that the potential structures scale with Debye lengths rather than with gyroradii. Electron beam excited electrostatic electron cyclotron waves and (ion beam driven) solitary waves are present in the plasmas adjacent to the double layers.

Double Arc Instability in the Solar Corona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishiguro, N.; Kusano, K., E-mail: n-ishiguro@isee.nagoya-u.ac.jp

The stability of the magnetic field in the solar corona is important for understanding the causes of solar eruptions. Although various scenarios have been suggested to date, the tether-cutting reconnection scenario proposed by Moore et al. is one of the widely accepted models to explain the onset process of solar eruptions. Although the tether-cutting reconnection scenario proposes that the sigmoidal field formed by internal reconnection is the magnetic field in the pre-eruptive state, the stability of the sigmoidal field has not yet been investigated quantitatively. In this paper, in order to elucidate the stability problem of the pre-eruptive state, wemore » developed a simple numerical analysis in which the sigmoidal field is modeled by a double arc electric current loop and its stability is analyzed. As a result, we found that the double arc loop is more easily destabilized than the axisymmetric torus, and it becomes unstable even if the external field does not decay with altitude, which is in contrast to the axisymmetric torus instability. This suggests that tether-cutting reconnection may well work as the onset mechanism of solar eruptions, and if so, the critical condition for eruption under a certain geometry may be determined by a new type of instability rather than by the torus instability. Based on them, we propose a new type of instability called double arc instability (DAI). We discuss the critical conditions for DAI and derive a new parameter κ , defined as the product of the magnetic twist and the normalized flux of the tether-cutting reconnection.« less

The dynamics of layered and non-layered oscillatory double-diffusive convection

NASA Astrophysics Data System (ADS)

Moll, Ryan D.

Oscillatory double diffusive convection (ODDC) is a double diffusive instability that occurs in fluids that are unstably stratified in temperature and stably stratified in chemical composition. Regions unstable to ODDC are common in the interiors of stars and giant planets, and knowing thermal and compositional transport through these regions is important for stellar and planetary evolution models. Using 3D direct numerical simulations, Rosenblum et al. 2011 first showed that ODDC can either lead to the spontaneous formation of convective layers, or remain in a state dominated by large scale gravity waves. Subsequent studies focused on identifying the conditions for layer formation (Mirouh et al. 2012), and quantifying transport through layered systems (Wood et al. 2013). This document includes 3 works that build on the results of these earlier studies. The subject of the first is transport through non-layered ODDC and shows that in the absence of layered convection, ODDC is dominated by large scale gravity waves that grow to the size of the domain. We find that while these gravity waves induce small amounts of turbulent mixing, turbulent transport through non-layered systems is not significant for the purposes of astrophysical modeling (unlike in layered convection). The second study pertains to ODDC in the presence of Coriolis forces, and shows that rotating systems can be categorized depending on the strength of the rotation. We find that in the slowly rotating regime, the presence of rotation does not significantly affect qualitative behavior, but leads to modest reductions in thermal and compositional transport, while in the fast rotation regime qualitative behaviors are radically different, and systems are dominated by vortices that affect thermal and compositional transport in complex ways. In the final work we study simulations of ODDC at non-layered parameters that are forced into a layered configuration by initial conditions. Our results show that measurements of thermal and compositional transport deviate from values predicted by oft-cited geophysical transport laws.

Anomalous plasma diffusion and the magnetopause boundary layer

NASA Technical Reports Server (NTRS)

Treumann, Rudolf A.; Labelle, James; Haerendel, Gerhard; Pottelette, Raymond

1992-01-01

An overview of the current state of anomalous diffusion research at the magnetopause and its role in the formation of the magnetopause boundary layer is presented. Plasma wave measurements in the boundary layer indicate that most of the relevant unstable wave modes contribute negligibly to the diffusion process at the magnetopause under magnetically undisturbed northward IMF conditions. The most promising instability is the lower hybrid drift instability, which may yield diffusion coefficients of the right order if the highest measured wave intensities are assumed. It is concluded that global stationary diffusion due to wave-particle interactions does not take place at the magnetopause. Microscopic wave-particle interaction and anomalous diffusion may contribute to locally break the MD frozen-in conditions and help in transporting large amounts of magnetosheath plasma across the magnetospheric boundary.

Investigation of natural circulation instability and transients in passively safe novel modular reactor

NASA Astrophysics Data System (ADS)

Shi, Shanbin

The Purdue Novel Modular Reactor (NMR) is a new type small modular reactor (SMR) that belongs to the design of boiling water reactor (BWR). Specifically, the NMR is one third the height and area of a conventional BWR reactor pressure vessel (RPV) with an electric output of 50 MWe. The fuel cycle length of the NMR-50 is extended up to 10 years due to optimized neutronics design. The NMR-50 is designed with double passive engineering safety system. However, natural circulation BWRs (NCBWR) could experience certain operational difficulties due to flow instabilities that occur at low pressure and low power conditions. Static instabilities (i.e. flow excursion (Ledinegg) instability and flow pattern transition instability) and dynamic instabilities (i.e. density wave instability and flashing/condensation instability) pose a significant challenge in two-phase natural circulation systems. In order to experimentally study the natural circulation flow instability, a proper scaling methodology is needed to build a reduced-size test facility. The scaling analysis of the NMR uses a three-level scaling method, which was developed and applied for the design of the Purdue Multi-dimensional Integral Test Assembly (PUMA). Scaling criteria is derived from dimensionless field equations and constitutive equations. The scaling process is validated by the RELAP5 analysis for both steady state and startup transients. A new well-scaled natural circulation test facility is designed and constructed based on the scaling analysis of the NMR-50. The experimental facility is installed with different equipment to measure various thermal-hydraulic parameters such as pressure, temperature, mass flow rate and void fraction. Characterization tests are performed before the startup transient tests and quasi-steady tests to determine the loop flow resistance. The controlling system and data acquisition system are programmed with LabVIEW to realize the real-time control and data storage. The thermal-hydraulic and nuclear coupled startup transients are performed to investigate the flow instabilities at low pressure and low power conditions. Two different power ramps are chosen to study the effect of power density on the flow instability. The experimental startup transient tests show the existence of three different flow instability mechanisms during the low pressure startup transients, i.e., flashing instability, condensation induced instability, and density wave oscillations. Flashing instability in the chimney section of the test loop and density wave oscillation are the main flow instabilities observed when the system pressure is below 0.5 MPa. They show completely different type of oscillations, i.e., intermittent oscillation and sinusoidal oscillation, in void fraction profile during the startup transients. In order to perform nuclear-coupled startup transients with void reactivity feedback, the Point Kinetics model is utilized to calculate the transient power during the startup transients. In addition, the differences between the electric resistance heaters and typical fuel element are taken into account. The reactor power calculated shows some oscillations due to flashing instability during the transients. However, the void reactivity feedback does not have significant influence on the flow instability during the startup procedure for the NMR-50. Further investigation of very small power ramp on the startup transients is carried out for the thermal-hydraulic startup transients. It is found that very small power density can eliminate the flashing oscillation in the single phase natural circulation and stabilize the flow oscillations in the phase of net vapor generation. Furthermore, initially pressurized startup procedure is investigated to eliminate the main flow instabilities. The results show that the pressurized startup procedure can suppress the flashing instability at low pressure and low power conditions. In order to have a deep understanding of natural circulation flow instability, the quasi-steady tests are performed using the test facility installed with preheater and subcooler. The effects of system pressure, core inlet subcooling, core power density, inlet flow resistance coefficient, and void reactivity feedback are investigated in the quasi-steady state tests. The stability boundaries are determined between unstable and stable flow conditions in the dimensionless stability plane of inlet subcooling number and Zuber number. In order to predict the stability boundary theoretically, linear stability analysis in the frequency domain is performed at four sections of the loop. The flashing in the chimney is considered as an axially uniform heat source. The dimensionless characteristic equation of the pressure drop perturbation is obtained by considering the void fraction effect and outlet flow resistance in the chimney section. The flashing boundary shows some discrepancies with previous experimental data from the quasi-steady state tests. In the future, thermal non-equilibrium is recommended to improve the accuracy of flashing instability boundary.

Hydrodynamic fingering instability induced by a precipitation reaction

NASA Astrophysics Data System (ADS)

De Wit, Anne; Nagatsu, Yuichiro

2014-05-01

We experimentally demonstrate that a precipitation reaction at the miscible interface between two reactive solutions can trigger a hydrodynamic instability due to the build-up of a locally adverse mobility gradient related to a decrease in permeability. The precipitate results from an A+B → C type of reaction when a solution containing one of the reactant is injected into a solution of the other reactant in a porous medium or a Hele-Shaw cell. Finger-like precipitation patterns are observed upon displacement, the properties of which depend on whether A displaces B or vice-versa. A mathematical modeling of the underlying mobility profile in the cell reconstructed on the basis of one-dimensional reaction-diffusion concentration profiles confirms that the instability originates from a local decrease in mobility driven by the precipitation. Nonlinear simulations of the related reaction-diffusion-convection model reproduce the properties of the instability observed experimentally. In particular, the simulations suggest that differences in diffusivity between A and B may contribute to the asymmetric characteristics of the fingering precipitation patterns.

Intrinsic Instability of Cs2In(I)M(III)X6 (M = Bi, Sb; X = Halogen) Double Perovskites: A Combined Density Functional Theory and Experimental Study.

PubMed

Xiao, Zewen; Du, Ke-Zhao; Meng, Weiwei; Wang, Jianbo; Mitzi, David B; Yan, Yanfa

2017-05-03

Recently, there has been substantial interest in developing double-B-cation halide perovskites, which hold the potential to overcome the toxicity and instability issues inherent within emerging lead halide-based solar absorber materials. Among all double perovskites investigated, In(I)-based Cs 2 InBiCl 6 and Cs 2 InSbCl 6 have been proposed as promising thin-film photovoltaic absorber candidates, with computational examination predicting suitable materials properties, including direct bandgap and small effective masses for both electrons and holes. In this study, we report the intrinsic instability of Cs 2 In(I)M(III)X 6 (M = Bi, Sb; X = halogen) double perovskites by a combination of density functional theory and experimental study. Our results suggest that the In(I)-based double perovskites are unstable against oxidation into In(III)-based compounds. Further, the results show the need to consider reduction-oxidation (redox) chemistry when predicting stability of new prospective electronic materials, especially when less common oxidation states are involved.

Wrinkling instabilities in soft bilayered systems

PubMed Central

Budday, Silvia; Andres, Sebastian; Walter, Bastian

2017-01-01

Wrinkling phenomena control the surface morphology of many technical and biological systems. While primary wrinkling has been extensively studied, experimentally, analytically and computationally, higher-order instabilities remain insufficiently understood, especially in systems with stiffness contrasts well below 100. Here, we use the model system of an elastomeric bilayer to experimentally characterize primary and secondary wrinkling at moderate stiffness contrasts. We systematically vary the film thickness and substrate prestretch to explore which parameters modulate the emergence of secondary instabilities, including period-doubling, period-tripling and wrinkle-to-fold transitions. Our experiments suggest that period-doubling is the favourable secondary instability mode and that period-tripling can emerge under disturbed boundary conditions. High substrate prestretch can suppress period-doubling and primary wrinkles immediately transform into folds. We combine analytical models with computational simulations to predict the onset of primary wrinkling, the post-buckling behaviour, secondary bifurcations and the wrinkle-to-fold transition. Understanding the mechanisms of pattern selection and identifying the critical control parameters of wrinkling will allow us to fabricate smart surfaces with tunable properties and to control undesired surface patterns like in the asthmatic airway. This article is part of the themed issue ‘Patterning through instabilities in complex media: theory and applications.’ PMID:28373385

Influence of temperature on linear stability in buoyancy-driven fingering of reaction-diffusion fronts.

PubMed

Levitán, D; D'Onofrio, A

2012-09-01

A vertical Hele-Shaw cell was used to study the influence of temperature on Rayleigh-Taylor instabilities on reaction-diffusion fronts. The propagation of the chemical front can thus be observed, and experimental results can be obtained via image treatment. A chemical front produced by the coupling between molecular diffusion and the auto-catalysis of the chlorite-tetrathionate reaction, descends through the cell, consuming the reactants below while the product is formed above. Buoyancy-driven instabilities are formed due to the density difference between reactants and products, and the front takes a fingering pattern, whose growth rate has temperature dependence. In this study, the effect of temperature on the linear regime of the instability (that is, when the effects of such instability start to appear) was analyzed. To measure the instability, Fourier transform analysis is performed, in order to obtain the different wave numbers and their power as a function of time. Thus, the growth rate for each wave number and the most unstable wave number is obtained for each of the temperatures under study. Based on repeated experiments, a decrease in the growth rate for the most unstable wave number can be observed with the increase of temperature.

"Squishy capacitor" model for electrical double layers and the stability of charged interfaces.

PubMed

Partenskii, Michael B; Jordan, Peter C

2009-07-01

Negative capacitance (NC), predicted by various electrical double layer (EDL) theories, is critically reviewed. Physically possible for individual components of the EDL, the compact or diffuse layer, it is strictly prohibited for the whole EDL or for an electrochemical cell with two electrodes. However, NC is allowed for the artificial conditions of sigma control, where an EDL is described by the equilibrium electric response of electrolyte to a field of fixed, and typically uniform, surface charge-density distributions, sigma. The contradiction is only apparent; in fact local sigma cannot be set independently, but is established by the equilibrium response to physically controllable variables, i.e., applied voltage phi (phi control) or total surface charge q (q control). NC predictions in studies based on sigma control signify potential instabilities and phase transitions for physically realizable conditions. Building on our previous study of phi control [M. B. Partenskii and P. C. Jordan, Phys. Rev. E 77, 061117 (2008)], here we analyze critical behavior under q control, clarifying the basic picture using an exactly solvable "squishy capacitor" toy model. We find that phi can change discontinuously in the presence of a lateral transition, specify stability conditions for an electrochemical cell, analyze the origin of the EDL's critical point in terms of compact and diffuse serial contributions, and discuss perspectives and challenges for theoretical studies not limited by sigma control.

Influence of driven current on resistive tearing mode in Tokamaks

NASA Astrophysics Data System (ADS)

Ma, Zhiwei; Wang, Sheng; Zhang, Wei

2016-10-01

Influence of driven current on the m / n = 2 / 1 resistive tearing mode is studied systematically using a three-dimensional toroidal MHD code (CLT). A uniform driven current with Gaussian distribution in the radial direction is imposed around the unperturbed rational surface. It is found that the driven current can locally modify the profiles of the current and safety factor, such that the tearing mode becomes linearly stable. The stabilizing effect increases with increase of the driven current Icd or decrease of its width δcd, unless an excessively large driven current reverses the magnetic shear near the rational surface and drives other instabilities such as double or triple tearing modes. The stabilizing effect can be negligible or becomes reversed if the maximum driven current density is not at the unperturbed rational surface. ITER-CN Program.

The effect of spin induced magnetization on Jeans instability of viscous and resistive quantum plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Prerana, E-mail: preranaiitd@rediffmail.com; Chhajlani, R. K.

2014-03-15

The effect of spin induced magnetization and electrical resistivity incorporating the viscosity of the medium is examined on the Jeans instability of quantum magnetoplasma. Formulation of the system is done by using the quantum magnetohydrodynamic model. The analysis of the problem is carried out by normal mode analysis theory. The general dispersion relation is derived from set of perturbed equations to analyse the growth rate and condition of self-gravitational Jeans instability. To discuss the influence of resistivity, magnetization, and viscosity parameters on Jeans instability, the general dispersion relation is reduced for both transverse and longitudinal mode of propagations. In themore » case of transverse propagation, the gravitating mode is found to be affected by the viscosity, magnetization, resistivity, and magnetic field strength whereas Jeans criterion of instability is modified by the magnetization and quantum parameter. In the longitudinal mode of propagation, the gravitating mode is found to be modified due to the viscosity and quantum correction in which the Jeans condition of instability is influenced only by quantum parameter. The other non-gravitating Alfven mode in this direction is affected by finite electrical resistivity, spin induced magnetization, and viscosity. The numerical study for the growth rate of Jeans instability is carried out for both in the transverse and longitudinal direction of propagation to the magnetic field. The effect of various parameters on the growth rate of Jeans instability in quantum plasma is analysed.« less

Large amplitude m=1 diocotron mode measurements in the Electron Diffusion Gauge experiment

NASA Astrophysics Data System (ADS)

Jenkins, Thomas G.; Morrison, Kyle A.; Davidson, Ronald C.; Paul, Stephen F.

2002-01-01

Smaller-diameter pure electron plasmas are generated in the Electron Diffusion Gauge (EDG) using a thoriated tungsten filament wound into a spiral shape with an outer diameter which is 1/4 of the trap wall diameter. The m=1 diocotron mode is excited in the plasma by means of the resistive-wall instability, using a resistor-relay circuit which allows the mode to be induced at various initial amplitudes. The dynamics of this mode may be predicted using linear theory when the amplitude is small. However, it has been observed [e.g., Fine et al., Phys. Rev. Lett. 63, 2232 (1989)] [1] that at larger amplitudes the frequency of this mode (relative to the small-amplitude frequency) exhibits a quadratic dependence on the mode amplitude. In this paper, the frequency shift and nonlinear dynamics of the m=1 diocotron mode in the EDG device are investigated.

Vortex/Flame Interactions in Microgravity Pulsed Jet Diffusion Flames

NASA Technical Reports Server (NTRS)

Bahadori, M. Y.; Hegde, U.; Stocker, D. P.

1999-01-01

The problem of vortex/flame interaction is of fundamental importance to turbulent combustion. These interactions have been studied in normal gravity. It was found that due to the interactions between the imposed disturbances and buoyancy induced instabilities, several overall length scales dominated the flame. The problem of multiple scales does not exist in microgravity for a pulsed laminar flame, since there are no buoyancy induced instabilities. The absence of buoyant convection therefore provides an environment to study the role of vortices interacting with flames in a controlled manner. There are strong similarities between imposed and naturally occurring perturbations, since both can be described by the same spatial instability theory. Hence, imposing a harmonic disturbance on a microgravity laminar flame creates effects similar to those occurring naturally in transitional/turbulent diffusion flames observed in microgravity. In this study, controlled, large-scale, axisymmetric vortices are imposed on a microgravity laminar diffusion flame. The experimental results and predictions from a numerical model of transient jet diffusion flames are presented and the characteristics of pulsed flame are described.

Outcomes of the modified Brostrom procedure using suture anchors for chronic lateral ankle instability--a prospective, randomized comparison between single and double suture anchors.

PubMed

Cho, Byung-Ki; Kim, Yong-Min; Kim, Dong-Soo; Choi, Eui-Sung; Shon, Hyun-Chul; Park, Kyoung-Jin

2013-01-01

The present prospective, randomized study was conducted to compare the clinical outcomes of the modified Brostrom procedure using single and double suture anchors for chronic lateral ankle instability. A total of 50 patients were followed up for more than 2 years after undergoing the modified Brostrom procedure. Of the 50 procedures, 25 each were performed using single and double suture anchors by 1 surgeon. The Karlsson scale had improved significantly to 89.8 points and 90.6 points in the single and double anchor groups, respectively. Using the Sefton grading system, 23 cases (92%) in the single anchor group and 22 (88%) in the double anchor group achieved satisfactory results. The talar tilt angle and anterior talar translation on stress radiographs using the Telos device had improved significantly to an average of 5.7° and 4.6 mm in the single anchor group and 4.5° and 4.3 mm in the double anchor group, respectively. The double anchor technique was superior with respect to the postoperative talar tilt. The single and double suture anchor techniques produced similar clinical and functional outcomes, with the exception of talar tilt as a reference of mechanical stability. The modified Brostrom procedure using both single and double suture anchors appears to be an effective treatment method for chronic lateral ankle instability. Copyright © 2013 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Kinetic-MHD simulations of gyroresonance instability driven by CR pressure anisotropy

NASA Astrophysics Data System (ADS)

Lebiga, O.; Santos-Lima, R.; Yan, H.

2018-05-01

The transport of cosmic rays (CRs) is crucial for the understanding of almost all high-energy phenomena. Both pre-existing large-scale magnetohydrodynamic (MHD) turbulence and locally generated turbulence through plasma instabilities are important for the CR propagation in astrophysical media. The potential role of the resonant instability triggered by CR pressure anisotropy to regulate the parallel spatial diffusion of low-energy CRs (≲100 GeV) in the interstellar and intracluster medium of galaxies has been shown in previous theoretical works. This work aims to study the gyroresonance instability via direct numerical simulations, in order to access quantitatively the wave-particle scattering rates. For this, we employ a 1D PIC-MHD code to follow the growth and saturation of the gyroresonance instability. We extract from the simulations the pitch-angle diffusion coefficient Dμμ produced by the instability during the linear and saturation phases, and a very good agreement (within a factor of 3) is found with the values predicted by the quasi-linear theory (QLT). Our results support the applicability of the QLT for modelling the scattering of low-energy CRs by the gyroresonance instability in the complex interplay between this instability and the large-scale MHD turbulence.

[Diffuse large B-cell lymphoma with concomitant c-MYC and BCL6 gene rearrangements with primary skin involvement: A case report and a review of literature].

PubMed

Gabeeva, N G; Koroleva, D A; Belyaeva, A V; Chernova, N G; Kuzmina, L A; Sudarikov, A B; Obukhova, T N; Kovrigina, A M; Zvonkov, E E; Savchenko, V G

Double-hit lymphoma (DHL) is a rare aggressive B-cell lymphoma with concomitant c-MYC, BCL2 or BCL6 gene rearrangements, which is characterized by the high frequency of extranodal lesions and by resistance to chemotherapy. The median survival does not exceed 18 months in patients with this disease. The majority of DHL is represented by с-MYC/BCL2 cases. The combination of c-MYC/BCL6 occurs rarely (5-8%). The paper describes a case of DHL with concomitant c-MYC and BCL6 gene rearrangements, which mimics diffuse large B-cell lymphoma, leg-type.

Non-Linear Dynamics and Emergence in Laboratory Fusion Plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hnat, B.

2011-09-22

Turbulent behaviour of laboratory fusion plasma system is modelled using extended Hasegawa-Wakatani equations. The model is solved numerically using finite difference techniques. We discuss non-linear effects in such a system in the presence of the micro-instabilities, specifically a drift wave instability. We explore particle dynamics in different range of parameters and show that the transport changes from diffusive to non-diffusive when large directional flows are developed.

Live Imaging to Study Microtubule Dynamic Instability in Taxane-resistant Breast Cancers.

PubMed

Wang, Richard; Wang, Harris; Wang, Zhixiang

2017-02-20

Taxanes such as docetaxel belong to a group of microtubule-targeting agents (MTAs) that are commonly relied upon to treat cancer. However, taxane resistance in cancerous cells drastically reduces the effectiveness of the drugs' long-term usage. Accumulated evidence suggests that the mechanisms underlying taxane resistance include both general mechanisms, such as the development of multidrug resistance due to the overexpression of drug-efflux proteins, and taxane-specific mechanisms, such as those that involve microtubule dynamics. Because taxanes target cell microtubules, measuring microtubule dynamic instability is an important step in determining the mechanisms of taxane resistance and provides insight into how to overcome this resistance. In the experiment, an in vivo method was used to measure microtubule dynamic instability. GFP-tagged α-tubulin was expressed and incorporated into microtubules in MCF-7 cells, allowing for the recording of the microtubule dynamics by time lapse using a sensitive camera. The results showed that, as opposed to the non-resistant parental MCF-7CC cells, the microtubule dynamics of docetaxel-resistant MCF-7TXT cells are insensitive to docetaxel treatment, which causes the resistance to docetaxel-induced mitotic arrest and apoptosis. This paper will outline this in vivo method of measuring microtubule dynamic instability.

Evans functions and bifurcations of nonlinear waves of some nonlinear reaction diffusion equations

NASA Astrophysics Data System (ADS)

Zhang, Linghai

2017-10-01

The main purposes of this paper are to accomplish the existence, stability, instability and bifurcation of the nonlinear waves of the nonlinear system of reaction diffusion equations ut =uxx + α [ βH (u - θ) - u ] - w, wt = ε (u - γw) and to establish the existence, stability, instability and bifurcation of the nonlinear waves of the nonlinear scalar reaction diffusion equation ut =uxx + α [ βH (u - θ) - u ], under different conditions on the model constants. To establish the bifurcation for the system, we will study the existence and instability of a standing pulse solution if 0 < 2 (1 + αγ) θ < αβγ; the existence and stability of two standing wave fronts if 2 (1 + αγ) θ = αβγ and γ2 ε > 1; the existence and instability of two standing wave fronts if 2 (1 + αγ) θ = αβγ and 0 <γ2 ε < 1; the existence and instability of an upside down standing pulse solution if 0 < (1 + αγ) θ < αβγ < 2 (1 + αγ) θ. To establish the bifurcation for the scalar equation, we will study the existence and stability of a traveling wave front as well as the existence and instability of a standing pulse solution if 0 < 2 θ < β; the existence and stability of two standing wave fronts if 2 θ = β; the existence and stability of a traveling wave front as well as the existence and instability of an upside down standing pulse solution if 0 < θ < β < 2 θ. By the way, we will also study the existence and stability of a traveling wave back of the nonlinear scalar reaction diffusion equation ut =uxx + α [ βH (u - θ) - u ] -w0, where w0 = α (β - 2 θ) > 0 is a positive constant, if 0 < 2 θ < β. To achieve the main goals, we will make complete use of the special structures of the model equations and we will construct Evans functions and apply them to study the eigenvalues and eigenfunctions of several eigenvalue problems associated with several linear differential operators. It turns out that a complex number λ0 is an eigenvalue of the linear differential operator, if and only if λ0 is a zero of the Evans function. The stability, instability and bifurcations of the nonlinear waves follow from the zeros of the Evans functions. A very important motivation to study the existence, stability, instability and bifurcations of the nonlinear waves is to study the existence and stability/instability of infinitely many fast/slow multiple traveling pulse solutions of the nonlinear system of reaction diffusion equations. The existence and stability of infinitely many fast multiple traveling pulse solutions are of great interests in mathematical neuroscience.

Mixing of a passive scalar by the instability of a differentially rotating axial pinch

NASA Astrophysics Data System (ADS)

Paredes, A.; Gellert, M.; Rüdiger, G.

2016-04-01

The mean-field diffusion of passive scalars such as lithium, beryllium or temperature dispersals due to the magnetic Tayler instability of a rotating axial pinch is considered. Our study is carried out within a Taylor-Couette setup for two rotation laws: solid-body quasi-Kepler rotation. The minimum magnetic Prandtl number used is 0.05, and the molecular Schmidt number Sc of the fluid varies between 0.1 and 2. An effective diffusivity coefficient for the mixing is numerically measured by the decay of a prescribed concentration peak located between both cylinder walls. We find that only models with Sc exceeding 0.1 basically provide finite instability-induced diffusivity values. We also find that for quasi-Kepler rotation at a magnetic Mach number Mm ≃ 2, the flow transits from the slow-rotation regime to the fast-rotation regime that is dominated by the Taylor-Proudman theorem. For fixed Reynolds number, the relation between the normalized turbulent diffusivity and the Schmidt number of the fluid is always linear so that also a linear relation between the instability-induced diffusivity and the molecular viscosity results, just in the sense proposed by Schatzman (1977, A&A, 573, 80). The numerical value of the coefficient in this relation reaches a maximum at Mm ≃ 2 and decreases for larger Mm, implying that only toroidal magnetic fields on the order of 1 kG can exist in the solar tachocline.

Turing pattern dynamics and adaptive discretization for a super-diffusive Lotka-Volterra model.

PubMed

Bendahmane, Mostafa; Ruiz-Baier, Ricardo; Tian, Canrong

2016-05-01

In this paper we analyze the effects of introducing the fractional-in-space operator into a Lotka-Volterra competitive model describing population super-diffusion. First, we study how cross super-diffusion influences the formation of spatial patterns: a linear stability analysis is carried out, showing that cross super-diffusion triggers Turing instabilities, whereas classical (self) super-diffusion does not. In addition we perform a weakly nonlinear analysis yielding a system of amplitude equations, whose study shows the stability of Turing steady states. A second goal of this contribution is to propose a fully adaptive multiresolution finite volume method that employs shifted Grünwald gradient approximations, and which is tailored for a larger class of systems involving fractional diffusion operators. The scheme is aimed at efficient dynamic mesh adaptation and substantial savings in computational burden. A numerical simulation of the model was performed near the instability boundaries, confirming the behavior predicted by our analysis.

Cyclic Deformation, Damage, and Effects of Environment in the Ni3Al Ordered Alloy at Elevated Temperature

DTIC Science & Technology

1991-03-29

restricts atomic mobility leading to slower diffusion and perhaps better creep resistance. Ordered intermetallics such as aluminides and silicides are...evaluation of the mechanical properties of these materials (specifically creep , oxidation and fatigue) must be evaluated before implementation in...rate by an order of magnitude (frcm 0.001/s to 0.01/s) doubled the fatigue life at a given plastic strain range. When tested in vacuum environments

A cosmic double helix in the archetypical quasar 3C273.

PubMed

Lobanov, A P; Zensus, J A

2001-10-05

Finding direct evidence for plasma instability in extragalactic jets is crucial for understanding the nature of relativistic outflows from active galactic nuclei. Our radio interferometric observations of the quasar 3C273 made with the orbiting radio telescope, HALCA, and an array of ground telescopes have yielded an image in which the emission across the jet is resolved, revealing two threadlike patterns that form a double helix inside the jet. This double helical structure is consistent with a Kelvin-Helmholtz instability, and at least five different instability modes can be identified and modeled by a light jet with a Lorentz factor of 2 and Mach number of 3.5. The model reproduces in detail the internal structure of the jet on scales of up to 30 milli-arc seconds ( approximately 300 parsecs) and is consistent with the general morphology of the jet on scales of up to 1 kiloparsec.

Diffusion-Driven Charge Transport in Light Emitting Devices

PubMed Central

Oksanen, Jani; Suihkonen, Sami

2017-01-01

Almost all modern inorganic light-emitting diode (LED) designs are based on double heterojunctions (DHJs) whose structure and current injection principle have remained essentially unchanged for decades. Although highly efficient devices based on the DHJ design have been developed and commercialized for energy-efficient general lighting, the conventional DHJ design requires burying the active region (AR) inside a pn-junction. This has hindered the development of emitters utilizing nanostructured ARs located close to device surfaces such as nanowires or surface quantum wells. Modern DHJ III-N LEDs also exhibit resistive losses that arise from the DHJ device geometry. The recently introduced diffusion-driven charge transport (DDCT) emitter design offers a novel way to transport charge carriers to unconventionally placed ARs. In a DDCT device, the AR is located apart from the pn-junction and the charge carriers are injected into the AR by bipolar diffusion. This device design allows the integration of surface ARs to semiconductor LEDs and offers a promising method to reduce resistive losses in high power devices. In this work, we present a review of the recent progress in gallium nitride (GaN) based DDCT devices, and an outlook of potential DDCT has for opto- and microelectronics. PMID:29231900

Differential diffusion effects on buoyancy-driven instabilities of acid-base fronts: the case of a color indicator.

PubMed

Kuster, S; Riolfo, L A; Zalts, A; El Hasi, C; Almarcha, C; Trevelyan, P M J; De Wit, A; D'Onofrio, A

2011-10-14

Buoyancy-driven hydrodynamic instabilities of acid-base fronts are studied both experimentally and theoretically in the case where an aqueous solution of a strong acid is put above a denser aqueous solution of a color indicator in the gravity field. The neutralization reaction between the acid and the color indicator as well as their differential diffusion modifies the initially stable density profile in the system and can trigger convective motions both above and below the initial contact line. The type of patterns observed as well as their wavelength and the speed of the reaction front are shown to depend on the value of the initial concentrations of the acid and of the color indicator and on their ratio. A reaction-diffusion model based on charge balances and ion pair mobility explains how the instability scenarios change when the concentration of the reactants are varied.

Turbulence in Three-Dimensional Simulations of Magnetopause Reconnection

NASA Astrophysics Data System (ADS)

Price, L.; Swisdak, M.; Drake, J. F.; Burch, J. L.; Cassak, P. A.; Ergun, R. E.

2017-11-01

We present detailed analysis of the turbulence observed in three-dimensional particle-in-cell simulations of magnetic reconnection at the magnetopause. The parameters are representative of an electron diffusion region encounter of the Magnetospheric Multiscale (MMS) mission. The turbulence is found to develop around both the magnetic X line and separatrices, is electromagnetic in nature, is characterized by a wave vector k given by kρe˜(meTe/miTi)0.25 with ρe the electron Larmor radius, and appears to have the ion pressure gradient as its source of free energy. Taken together, these results suggest the instability is a variant of the lower hybrid drift instability. The turbulence produces electric field fluctuations in the out-of-plane direction (the direction of the reconnection electric field) with an amplitude of around ±10 mV/m, which is much greater than the reconnection electric field of around 0.1 mV/m. Such large values of the out-of-plane electric field have been identified in the MMS data. The turbulence in the simulations controls the scale lengths of the density profile and current layers in asymmetric reconnection, driving them closer to √{ρeρi} than the ρe or de scalings seen in 2-D reconnection simulations, and produces significant anomalous resistivity and viscosity in the electron diffusion region.

Double-diffusive layers in the Adriatic Sea

NASA Astrophysics Data System (ADS)

Carniel, Sandro; Sclavo, Mauro; Kantha, Lakshmi; Prandke, Hartmut

2008-01-01

A microstructure profiler was deployed to make turbulence measurements in the upper layers of the southern Adriatic Sea in the Mediterranean during the Naval Research Laboratory (NRL) DART06A (Dynamics of the Adriatic in Real Time) winter cruise in March 2006. Measurements in the Po river plume along the Italian coast near the Gargano promontory displayed classic double-diffusive layers and staircase structures resulting from the relatively colder and fresher wintertime Po river outflow water masses overlying warmer and more saline water masses from the Adriatic Sea. We report here on the water mass and turbulence structure measurements made both in the double-diffusive interfaces and the adjoining mixed layers in the water columns undergoing double-diffusive convection (DDC). This dataset augments the relatively sparse observations available hitherto on the diffusive layer type of DDC. Measured turbulence diffusivities are consistent with those from earlier theoretical and experimental formulations, suggesting that the wintertime Po river plume is a convenient and easily accessible place to study double diffusive convective processes of importance to mixing in the interior of many regions of the global oceans.

Saturation of the lower-hybrid-drift instability by mode coupling

NASA Technical Reports Server (NTRS)

Drake, J. F.; Guzdar, P. N.; Huba, J. D.

1983-01-01

A nonlinear mode-coupling theory of the lower-hybrid-drift instability is presented. It is found that the instability saturates by transferring energy from the growing, long wavelength modes to the damped, short wavelength modes. The saturation energy, mean square of the potential fluctuations, and diffusion coefficient are calculated self-consistently.

Precision process calibration and CD predictions for low-k1 lithography

NASA Astrophysics Data System (ADS)

Chen, Ting; Park, Sangbong; Berger, Gabriel; Coskun, Tamer H.; de Vocht, Joep; Chen, Fung; Yu, Linda; Hsu, Stephen; van den Broeke, Doug; Socha, Robert; Park, Jungchul; Gronlund, Keith; Davis, Todd; Plachecki, Vince; Harris, Tom; Hansen, Steve; Lambson, Chuck

2005-06-01

Leading resist calibration for sub-0.3 k1 lithography demands accuracy <2nm for CD through pitch. An accurately calibrated resist process is the prerequisite for establishing production-worthy manufacturing under extreme low k1. From an integrated imaging point of view, the following key components must be simultaneously considered during the calibration - high numerical aperture (NA>0.8) imaging characteristics, customized illuminations (measured vs. modeled pupil profiles), resolution enhancement technology (RET) mask with OPC, reticle metrology, and resist thin film substrate. For imaging at NA approaching unity, polarized illumination can impact significantly the contrast formation in the resist film stack, and therefore it is an important factor to consider in the CD-based resist calibration. For aggressive DRAM memory core designs at k1<0.3, pattern-specific illumination optimization has proven to be critical for achieving the required imaging performance. Various optimization techniques from source profile optimization with fixed mask design to the combined source and mask optimization have been considered for customer designs and available imaging capabilities. For successful low-k1 process development, verification of the optimization results can only be made with a sufficiently tunable resist model that can predicate the wafer printing accurately under various optimized process settings. We have developed, for resist patterning under aggressive low-k1 conditions, a novel 3D diffusion model equipped with double-Gaussian convolution in each dimension. Resist calibration with the new diffusion model has demonstrated a fitness and CD predication accuracy that rival or outperform the traditional 3D physical resist models. In this work, we describe our empirical approach to achieving the nm-scale precision for advanced lithography process calibrations, using either measured 1D CD through-pitch or 2D memory core patterns. We show that for ArF imaging, the current resist development and diffusion modeling can readily achieve ~1-2nm max CD errors for common 1D through-pitch and aggressive 2D memory core resist patterns. Sensitivities of the calibrated models to various process parameters are analyzed, including the comparison between the measured and modeled (Gaussian or GRAIL) pupil profiles. We also report our preliminary calibration results under selected polarized illumination conditions.

Helical magnetorotational instability in magnetized Taylor-Couette flow.

PubMed

Liu, Wei; Goodman, Jeremy; Herron, Isom; Ji, Hantao

2006-11-01

Hollerbach and Rüdiger have reported a new type of magnetorotational instability (MRI) in magnetized Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields. The salient advantage of this "helical" MRI (HMRI) is that marginal instability occurs at arbitrarily low magnetic Reynolds and Lundquist numbers, suggesting that HMRI might be easier to realize than standard MRI (axial field only), and that it might be relevant to cooler astrophysical disks, especially those around protostars, which may be quite resistive. We confirm previous results for marginal stability and calculate HMRI growth rates. We show that in the resistive limit, HMRI is a weakly destabilized inertial oscillation propagating in a unique direction along the axis. But we report other features of HMRI that make it less attractive for experiments and for resistive astrophysical disks. Large axial currents are required. More fundamentally, instability of highly resistive flow is peculiar to infinitely long or periodic cylinders: finite cylinders with insulating endcaps are shown to be stable in this limit, at least if viscosity is neglected. Also, Keplerian rotation profiles are stable in the resistive limit regardless of axial boundary conditions. Nevertheless, the addition of a toroidal field lowers thresholds for instability even in finite cylinders.

Induction of instability in water-in-oil-in-water double emulsions by freeze-thaw cycling.

PubMed

Rojas, Edith C; Papadopoulos, Kyriakos D

2007-06-19

Individual water-in-oil-in-water (W1/O/W2) double-emulsion globules loaded with fluorescently labeled bovine serum albumin (FITC-BSA) were optically monitored within cylindrical capillaries during freeze-thaw cycling. Coalescence of internal aqueous droplets (W1) and external aqueous phase (W2), termed external coalescence, was not observed before or during freezing of the oil phase (O). On the other hand, this instability mechanism was readily promoted during thawing. This realization confirms the previously suggested potential of W1/O/W2 double emulsions to trigger release upon oil thawing and demonstrates that it is a direct result of globule breakage through external coalescence. The presented results also identified a threshold in the relative W1 droplet size above which instability occurred, while smaller droplets remained unperturbed and therefore indicate that optimization of the delivery can be achieved by tuning the size of W1 droplets. In addition, we propose a possible explanation for the occurrence of instability during oil thawing and its dependence on the size of W1 droplets. Because this alternative globule-breakage mechanism simply uses temperature increase (solid-to-liquid-phase transition) as external stimulus, W1/O/W2 double-emulsion delivery systems can be easily tailored by choosing an oil phase with the appropriate phase-transition temperature.

Belinostat and vincristine demonstrate mutually synergistic cytotoxicity associated with mitotic arrest and inhibition of polyploidy in a preclinical model of aggressive diffuse large B cell lymphoma.

PubMed

Havas, Aaron P; Rodrigues, Kameron B; Bhakta, Anvi; Demirjian, Joseph A; Hahn, Seongmin; Tran, Jack; Scavello, Margarethakay; Tula-Sanchez, Ana A; Zeng, Yi; Schmelz, Monika; Smith, Catharine L

2016-12-01

Diffuse Large B-cell lymphoma (DLBCL) is an aggressive malignancy that has a 60 percent 5-year survival rate, highlighting a need for new therapeutic approaches. Histone deacetylase inhibitors (HDACi) are novel therapeutics being clinically-evaluated in combination with a variety of other drugs. However, rational selection of companion therapeutics for HDACi is difficult due to their poorly-understood, cell-type specific mechanisms of action. To address this, we developed a pre-clinical model system of sensitivity and resistance to the HDACi belinostat using DLBCL cell lines. In the current study, we demonstrate that cell lines sensitive to the cytotoxic effects of HDACi undergo early mitotic arrest prior to apoptosis. In contrast, HDACi-resistant cell lines complete mitosis after a short delay and arrest in G1. To force mitotic arrest in HDACi-resistant cell lines, we used low dose vincristine or paclitaxel in combination with belinostat and observed synergistic cytotoxicity. Belinostat curtails vincristine-induced mitotic arrest and triggers a strong apoptotic response associated with downregulated MCL-1 expression and upregulated BIM expression. Resistance to microtubule targeting agents (MTAs) has been associated with their propensity to induce polyploidy and thereby increase the probability of genomic instability that enables cancer progression. Co-treatment with belinostat effectively eliminated a vincristine-induced, actively cycling polyploid cell population. Our study demonstrates that vincristine sensitizes DLBCL cells to the cytotoxic effects of belinostat and that belinostat prevents polyploidy that could cause vincristine resistance. Our findings provide a rationale for using low dose MTAs in conjunction with HDACi as a potential therapeutic strategy for treatment of aggressive DLBCL.

Acoustic instability driven by cosmic-ray streaming

NASA Technical Reports Server (NTRS)

Begelman, Mitchell C.; Zweibel, Ellen G.

1994-01-01

We study the linear stability of compressional waves in a medium through which cosmic rays stream at the Alfven speed due to strong coupling with Alfven waves. Acoustic waves can be driven unstable by the cosmic-ray drift, provided that the streaming speed is sufficiently large compared to the thermal sound speed. Two effects can cause instability: (1) the heating of the thermal gas due to the damping of Alfven waves driven unstable by cosmic-ray streaming; and (2) phase shifts in the cosmic-ray pressure perturbation caused by the combination of cosmic-ray streaming and diffusion. The instability does not depend on the magnitude of the background cosmic-ray pressure gradient, and occurs whether or not cosmic-ray diffusion is important relative to streaming. When the cosmic-ray pressure is small compared to the gas pressure, or cosmic-ray diffusion is strong, the instability manifests itself as a weak overstability of slow magnetosonic waves. Larger cosmic-ray pressure gives rise to new hybrid modes, which can be strongly unstable in the limits of both weak and strong cosmic-ray diffusion and in the presence of thermal conduction. Parts of our analysis parallel earlier work by McKenzie & Webb (which were brought to our attention after this paper was accepted for publication), but our treatment of diffusive effects, thermal conduction, and nonlinearities represent significant extensions. Although the linear growth rate of instability is independent of the background cosmic-ray pressure gradient, the onset of nonlinear eff ects does depend on absolute value of DEL (vector differential operator) P(sub c). At the onset of nonlinearity the fractional amplitude of cosmic-ray pressure perturbations is delta P(sub C)/P(sub C) approximately (kL) (exp -1) much less than 1, where k is the wavenumber and L is the pressure scale height of the unperturbed cosmic rays. We speculate that the instability may lead to a mode of cosmic-ray transport in which plateaus of uniform cosmic-ray pressure are separated by either laminar or turbulent jumps in which the thermal gas is subject to intense heating.

An elevated source/drain-on-insulator structure to maximize the intrinsic performance of extremely scaled MOSFETs

NASA Astrophysics Data System (ADS)

Zhang, Zhikuan; Zhang, Shengdong; Feng, Chuguang; Chan, Mansun

2003-10-01

In this paper, a source/drain structure separated from the silicon substrate by oxide isolation is fabricated and studied. The source/drain diffusion regions are connected to the shallow source/drain extension through a smaller opening defined by a double spacer process. Experimental results indicate that the source/drain on insulator significantly reduces the parasitic capacitance. Further optimization by simulation indicates a reduction of series resistance and band-to-band drain leakage at off-state can be achieved in extremely scaled devices. Compared with the conventional planner source/drain structure, the reduction of parasitic capacitance and series resistance can be as much as 80% and 30% respectively.

Numerical MHD study for plasmoid instability in uniform resistivity

NASA Astrophysics Data System (ADS)

Shimizu, Tohru; Kondoh, Koji; Zenitani, Seiji

2017-11-01

The plasmoid instability (PI) caused in uniform resistivity is numerically studied with a MHD numerical code of HLLD scheme. It is shown that the PI observed in numerical studies may often include numerical (non-physical) tearing instability caused by the numerical dissipations. By increasing the numerical resolutions, the numerical tearing instability gradually disappears and the physical tearing instability remains. Hence, the convergence of the numerical results is observed. Note that the reconnection rate observed in the numerical tearing instability can be higher than that of the physical tearing instability. On the other hand, regardless of the numerical and physical tearing instabilities, the tearing instability can be classified into symmetric and asymmetric tearing instability. The symmetric tearing instability tends to occur when the thinning of current sheet is stopped by the physical or numerical dissipations, often resulting in the drastic changes in plasmoid chain's structure and its activity. In this paper, by eliminating the numerical tearing instability, we could not specify the critical Lundquist number Sc beyond which PI is fully developed. It suggests that Sc does not exist, at least around S = 105.

Cross-diffusion-induced subharmonic spatial resonances in a predator-prey system

NASA Astrophysics Data System (ADS)

Gambino, G.; Lombardo, M. C.; Sammartino, M.

2018-01-01

In this paper we investigate the complex dynamics originated by a cross-diffusion-induced subharmonic destabilization of the fundamental subcritical Turing mode in a predator-prey reaction-diffusion system. The model we consider consists of a two-species Lotka-Volterra system with linear diffusion and a nonlinear cross-diffusion term in the predator equation. The taxis term in the search strategy of the predator is responsible for the onset of complex dynamics. In fact, our model does not exhibit any Hopf or wave instability, and on the basis of the linear analysis one should only expect stationary patterns; nevertheless, the presence of the nonlinear cross-diffusion term is able to induce a secondary instability: due to a subharmonic spatial resonance, the stationary primary branch bifurcates to an out-of-phase oscillating solution. Noticeably, the strong resonance between the harmonic and the subharmonic is able to generate the oscillating pattern albeit the subharmonic is below criticality. We show that, as the control parameter is varied, the oscillating solution (sub T mode) can undergo a sequence of secondary instabilities, generating a transition toward chaotic dynamics. Finally, we investigate the emergence of sub T -mode solutions on two-dimensional domains: when the fundamental mode describes a square pattern, subharmonic resonance originates oscillating square patterns. In the case of subcritical Turing hexagon solutions, the internal interactions with a subharmonic mode are able to generate the so-called "twinkling-eyes" pattern.

Semitendinosus Tendon Transfer Associated With Distal Alignment for Patella Alta in a Patient With Recurrent Dislocations.

PubMed

Calderazzi, Filippo; Pellegrini, Andrea; Coviello, Gianluca; Groppi, Giulia; Ceccarelli, Francesco

2015-10-01

Patellofemoral instability is characterized by pain during normal daily activities and frequent dislocation events. In the reported case, an adolescent girl, aged 15 years, affected by left patellofemoral instability, underwent surgery with a double technique comprising tibial tubercle distalization and medial patellofemoral ligament reconstruction. In case of patella alta associated with patellofemoral instability, surgical treatment should focus on medial patellofemoral ligament repair and on recurrent instability prevention.

Microstructure Instability of Candidate Fuel Cladding Alloys: Corrosion and Stress Corrosion Cracking Implications

NASA Astrophysics Data System (ADS)

Jiao, Yinan; Zheng, Wenyue; Guzonas, David; Kish, Joseph

2016-02-01

This paper addresses some of the overarching aspects of microstructure instability expected from both high temperature and radiation exposure that could affect the corrosion and stress corrosion cracking (SCC) resistance of the candidate austenitic Fe-Cr-Ni alloys being considered for the fuel cladding of the Canadian supercritical water-cooled reactor (SCWR) concept. An overview of the microstructure instability expected by both exposures is presented prior to turning the focus onto the implications of such instability on the corrosion and SCC resistance. Results from testing conducted using pre-treated (thermally-aged) Type 310S stainless steel to shed some light on this important issue are included to help identify the outstanding corrosion resistance assessment needs.

Computer simulation of the Farley-Buneman instability and anomalous electron heating in the auroral ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Machida, S.; Goertz, C.K.

1988-09-01

We study the nonlinear saturation of the Farley-Buneman instability in a collisional plasma by a 2 1/2 dimensional electrostatic particle simulation which includes inelastic and elastic collisions of electrons and elastic collision of ions with neutrals. In our simulation, a uniform convection electric field is applied externally so that the relative velocity between the electrons and ions is greater than the ion sound speed and destabilizes the instability. We find a nonlinear frequency shift from higher to lower frequencies and diffusion of the wave spectrum in two dimensional wave number space. We are especially interested in finding whether the saturatedmore » wave turbulence can account for the anomalous heating rates observed in the polar ionosphere by Schlegel and St.-Maurice (1981). We find that the dominant mechanism for electron heating is due to an enhanced effective electron collision frequency and hence enhanced resistive heating as suggested by Primdahl (1986) and Robinson (1986) and not due to the heating of electrons by the electric field of the waves parallel to the magnetic field. For the ionospheric conditions discussed by Schlegel and St.-Maurice (1981) we find an anomalous heating rate of about 4 x 10/sup -7/ W/m/sup 3/. copyright American Geophysical Union 1988« less

A double medium model for diffusion in fluid-bearing rock

NASA Astrophysics Data System (ADS)

Wang, H. F.

1993-09-01

The concept of a double porosity medium to model fluid flow in fractured rock has been applied to model diffusion in rock containing a small amount of a continuous fluid phase that surrounds small volume elements of the solid matrix. The model quantifies the relative role of diffusion in the fluid and solid phases of the rock. The fluid is the fast diffusion path, but the solid contains the volumetrically significant amount of the diffusing species. The double medium model consists of two coupled differential equations. One equation is the diffusion equation for the fluid concentration; it contains a source term for change in the average concentration of the diffusing species in the solid matrix. The second equation represents the assumption that the change in average concentration in a solid element is proportional to the difference between the average concentration in the solid and the concentration in the fluid times the solid-fluid partition coefficient. The double medium model is shown to apply to laboratory data on iron diffusion in fluid-bearing dunite and to measured oxygen isotope ratios at marble-metagranite contacts. In both examples, concentration profiles are calculated for diffusion taking place at constant temperature, where a boundary value changes suddenly and is subsequently held constant. Knowledge of solid diffusivities can set a lower bound to the length of time over which diffusion occurs, but only the product of effective fluid diffusivity and time is constrained for times longer than the characteristic solid diffusion time. The double medium results approach a local, grain-scale equilibrium model for times that are large relative to the time constant for solid diffusion.

Nonlinear Landau damping in the ionosphere

NASA Technical Reports Server (NTRS)

Kiwamoto, Y.; Benson, R. F.

1978-01-01

A model is presented to explain the non-resonant waves which give rise to the diffuse resonance observed near 3/2 f sub H by the Alouette and ISIS topside sounders, where f sub H is the ambient electron cyclotron frequency. In a strictly linear analysis, these instability driven waves will decay due to Landau damping on a time scale much shorter than the observed time duration of the diffuse resonance. Calculations of the nonlinear wave particle coupling coefficients, however, indicate that the diffuse resonance wave can be maintained by the nonlinear Landau damping of the sounder stimulated 2f sub H wave. The time duration of the diffuse resonance is determined by the transit time of the instability generated and nonlinearly maintained diffuse resonance wave from the remote short lived hot region back to the antenna. The model is consistent with the Alouette/ISIS observations, and clearly demonstrates the existence of nonlinear wave-particle interactions in the ionosphere.

Hydrocarbon double-stapling remedies the proteolytic instability of a lengthy peptide therapeutic

PubMed Central

Bird, Gregory H.; Madani, Navid; Perry, Alisa F.; Princiotto, Amy M.; Supko, Jeffrey G.; He, Xiaoying; Gavathiotis, Evripidis; Sodroski, Joseph G.; Walensky, Loren D.

2010-01-01

The pharmacologic utility of lengthy peptides can be hindered by loss of bioactive structure and rapid proteolysis, which limits bioavailability. For example, enfuvirtide (Fuzeon, T20, DP178), a 36-amino acid peptide that inhibits human immunodeficiency virus type 1 (HIV-1) infection by effectively targeting the viral fusion apparatus, has been relegated to a salvage treatment option mostly due to poor in vivo stability and lack of oral bioavailability. To overcome the proteolytic shortcomings of long peptides as therapeutics, we examined the biophysical, biological, and pharmacologic impact of inserting all-hydrocarbon staples into an HIV-1 fusion inhibitor. We find that peptide double-stapling confers striking protease resistance that translates into markedly improved pharmacokinetic properties, including oral absorption. We determined that the hydrocarbon staples create a proteolytic shield by combining reinforcement of overall α-helical structure, which slows the kinetics of proteolysis, with complete blockade of peptide cleavage at constrained sites in the immediate vicinity of the staple. Importantly, double-stapling also optimizes the antiviral activity of HIV-1 fusion peptides and the antiproteolytic feature extends to other therapeutic peptide templates, such as the diabetes drug exenatide (Byetta). Thus, hydrocarbon double-stapling may unlock the therapeutic potential of natural bioactive polypeptides by transforming them into structurally fortified agents with enhanced bioavailability. PMID:20660316

Hydrodynamic Fingering Instability Induced by a Precipitation Reaction

NASA Astrophysics Data System (ADS)

Nagatsu, Y.; Ishii, Y.; Tada, Y.; De Wit, A.

2014-07-01

We experimentally demonstrate that a precipitation reaction at the miscible interface between two reactive solutions can trigger a hydrodynamic instability due to the buildup of a locally adverse mobility gradient related to a decrease in permeability. The precipitate results from an A +B→C type of reaction when a solution containing one of the reactants is injected into a solution of the other reactant in a porous medium or a Hele-Shaw cell. Fingerlike precipitation patterns are observed upon displacement, the properties of which depend on whether A displaces B or vice versa. A mathematical modeling of the underlying mobility profile confirms that the instability originates from a local decrease in mobility driven by the localized precipitation. Nonlinear simulations of the related reaction-diffusion-convection model reproduce the properties of the instability observed experimentally. In particular, the simulations suggest that differences in diffusivity between A and B may contribute to the asymmetric characteristics of the fingering precipitation patterns.

Testing a one-dimensional prescription of dynamical shear mixing with a two-dimensional hydrodynamic simulation

NASA Astrophysics Data System (ADS)

Edelmann, P. V. F.; Röpke, F. K.; Hirschi, R.; Georgy, C.; Jones, S.

2017-07-01

Context. The treatment of mixing processes is still one of the major uncertainties in 1D stellar evolution models. This is mostly due to the need to parametrize and approximate aspects of hydrodynamics in hydrostatic codes. In particular, the effect of hydrodynamic instabilities in rotating stars, for example, dynamical shear instability, evades consistent description. Aims: We intend to study the accuracy of the diffusion approximation to dynamical shear in hydrostatic stellar evolution models by comparing 1D models to a first-principle hydrodynamics simulation starting from the same initial conditions. Methods: We chose an initial model calculated with the stellar evolution code GENEC that is just at the onset of a dynamical shear instability but does not show any other instabilities (e.g., convection). This was mapped to the hydrodynamics code SLH to perform a 2D simulation in the equatorial plane. We compare the resulting profiles in the two codes and compute an effective diffusion coefficient for the hydro simulation. Results: Shear instabilities develop in the 2D simulation in the regions predicted by linear theory to become unstable in the 1D stellar evolution model. Angular velocity and chemical composition is redistributed in the unstable region, thereby creating new unstable regions. After a period of time, the system settles in a symmetric, steady state, which is Richardson stable everywhere in the 2D simulation, whereas the instability remains for longer in the 1D model due to the limitations of the current implementation in the 1D code. A spatially resolved diffusion coefficient is extracted by comparing the initial and final profiles of mean atomic mass. Conclusions: The presented simulation gives a first insight on hydrodynamics of shear instabilities in a real stellar environment and even allows us to directly extract an effective diffusion coefficient. We see evidence for a critical Richardson number of 0.25 as regions above this threshold remain stable for the course of the simulation. The movie of the simulation is available at http://www.aanda.org

About the influence of phase mixing process and current neutralization on the resistive sausage instability dynamics of a relativistic electron beam

NASA Astrophysics Data System (ADS)

Kolesnikov, E. K.; Manuilov, A. S.; Petrov, V. S.; Zelensky, A. G.

2018-05-01

The resistive sausage instability of the relativistic electron beam in dense gas-plasma medium in the case of the generation of equilibrium return plasma current is investigated. In this situation the eigenvalue equation of this instability is obtained. The stabilizing and destabilizing effects of the phase mixing and generation of the return plasma current respectively have been shown.

Differential Activity-Driven Instabilities in Biphasic Active Matter

NASA Astrophysics Data System (ADS)

Weber, Christoph A.; Rycroft, Chris H.; Mahadevan, L.

2018-06-01

Active stresses can cause instabilities in contractile gels and living tissues. Here we provide a generic hydrodynamic theory that treats these systems as a mixture of two phases of varying activity and different mechanical properties. We find that differential activity between the phases causes a uniform mixture to undergo a demixing instability. We follow the nonlinear evolution of the instability and characterize a phase diagram of the resulting patterns. Our study complements other instability mechanisms in mixtures driven by differential adhesion, differential diffusion, differential growth, and differential motion.

On numerical instabilities of Godunov-type schemes for strong shocks

NASA Astrophysics Data System (ADS)

Xie, Wenjia; Li, Wei; Li, Hua; Tian, Zhengyu; Pan, Sha

2017-12-01

It is well known that low diffusion Riemann solvers with minimal smearing on contact and shear waves are vulnerable to shock instability problems, including the carbuncle phenomenon. In the present study, we concentrate on exploring where the instability grows out and how the dissipation inherent in Riemann solvers affects the unstable behaviors. With the help of numerical experiments and a linearized analysis method, it has been found that the shock instability is strongly related to the unstable modes of intermediate states inside the shock structure. The consistency of mass flux across the normal shock is needed for a Riemann solver to capture strong shocks stably. The famous carbuncle phenomenon is interpreted as the consequence of the inconsistency of mass flux across the normal shock for a low diffusion Riemann solver. Based on the results of numerical experiments and the linearized analysis, a robust Godunov-type scheme with a simple cure for the shock instability is suggested. With only the dissipation corresponding to shear waves introduced in the vicinity of strong shocks, the instability problem is circumvented. Numerical results of several carefully chosen strong shock wave problems are investigated to demonstrate the robustness of the proposed scheme.

Effect of dust on tilted electrostatic resistive instability in a Hall thruster

NASA Astrophysics Data System (ADS)

Tyagi, Jasvendra; Singh, Sukhmander; Malik, Hitendra K.

2018-03-01

Effect of negatively charged dust on resistive instability corresponding to the electrostatic wave is investigated in a Hall thruster plasma when this purely azimuthal wave is tilted and strong axial component of wave vector is developed. Analytical calculations are done to obtain the relevant dispersion equation, which is solved numerically to investigate the growth rate of the instability. The magnitude of the growth rate in the plasma having dust particles is found to be much smaller than the case of pure plasma. However, the instability grows faster for the increasing dust density and the higher charge on the dust particles. The higher magnetic field is also found to support the instability.

Ionization Chemistry and Role of Grains on Non-ideal MHD Effects in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Xu, Rui; Bai, Xue-Ning; Oberg, Karin I.

2015-01-01

Ionization in protoplanetary disks (PPDs) is one of the key elements for understanding disk chemistry. It also determines the coupling between gas and magnetic fields hence strongly affect PPD gas dynamics. We study the ionization chemistry in the presence of grains in the midplane region of PPDs and its impact on gas conductivity reflected in non-ideal MHD effects including Ohmic resistivity, Hall effect and ambipolar diffusion. We first develop a reduced chemical reaction network from the UMIST database. The reduced network contains much smaller number of species and reactions while yields reliable estimates of the disk ionization level compared with the full network. We further show that grains are likely the dominant charge carrier in the midplane regions of the inner disk, which significantly affects the gas conductivity. In particular, ambipolar diffusion is strongly reduced and the Hall coefficient changes sign in the presence of strong magnetic field. The latter provides a natural mechanism to the saturation of the Hall-shear instability.

Evidence for Secondary Flux Rope Generated by the Electron Kelvin-Helmholtz Instability in a Magnetic Reconnection Diffusion Region

NASA Astrophysics Data System (ADS)

Zhong, Z. H.; Tang, R. X.; Zhou, M.; Deng, X. H.; Pang, Y.; Paterson, W. R.; Giles, B. L.; Burch, J. L.; Tobert, R. B.; Ergun, R. E.; Khotyaintsev, Y. V.; Lindquist, P.-A.

2018-02-01

Secondary flux ropes are suggested to play important roles in energy dissipation and particle acceleration during magnetic reconnection. However, their generation mechanism is not fully understood. In this Letter, we present the first direct evidence that a secondary flux rope was generated due to the evolution of an electron vortex, which was driven by the electron Kelvin-Helmholtz instability in an ion diffusion region as observed by the Magnetospheric Multiscale mission. The subion scale (less than the ion inertial length) flux rope was embedded within the electron vortex, which contained a secondary electron diffusion region at the trailing edge of the flux rope. We propose that intense electron shear flow produced by reconnection generated the electron Kelvin-Helmholtz vortex, which induced a secondary reconnection in the exhaust of the primary X line and then led to the formation of the flux rope. This result strongly suggests that secondary electron Kelvin-Helmholtz instability is important for reconnection dynamics.

Evidence for Secondary Flux Rope Generated by the Electron Kelvin-Helmholtz Instability in a Magnetic Reconnection Diffusion Region.

PubMed

Zhong, Z H; Tang, R X; Zhou, M; Deng, X H; Pang, Y; Paterson, W R; Giles, B L; Burch, J L; Tobert, R B; Ergun, R E; Khotyaintsev, Y V; Lindquist, P-A

2018-02-16

Secondary flux ropes are suggested to play important roles in energy dissipation and particle acceleration during magnetic reconnection. However, their generation mechanism is not fully understood. In this Letter, we present the first direct evidence that a secondary flux rope was generated due to the evolution of an electron vortex, which was driven by the electron Kelvin-Helmholtz instability in an ion diffusion region as observed by the Magnetospheric Multiscale mission. The subion scale (less than the ion inertial length) flux rope was embedded within the electron vortex, which contained a secondary electron diffusion region at the trailing edge of the flux rope. We propose that intense electron shear flow produced by reconnection generated the electron Kelvin-Helmholtz vortex, which induced a secondary reconnection in the exhaust of the primary X line and then led to the formation of the flux rope. This result strongly suggests that secondary electron Kelvin-Helmholtz instability is important for reconnection dynamics.

Instability resistance training across the exercise continuum.

PubMed

Behm, David G; Colado, Juan C; Colado, Juan C

2013-11-01

Instability resistance training (IRT; unstable surfaces and devices to strengthen the core or trunk muscles) is popular in fitness training facilities. To examine contradictory IRT recommendations for health enthusiasts and rehabilitation. A literature search was performed using MEDLINE, SPORT Discus, ScienceDirect, Web of Science, and Google Scholar databases from 1990 to 2012. Databases were searched using key terms, including "balance," "stability," "instability," "resistance training," "core," "trunk," and "functional performance." Additionally, relevant articles were extracted from reference lists. To be included, research questions addressed the effect of balance or IRT on performance, healthy and active participants, and physiologic or performance outcome measures and had to be published in English in a peer-reviewed journal. There is a dichotomy of opinions on the effectiveness and application of instability devices and conditions for health and performance training. Balance training without resistance has been shown to improve not only balance but functional performance as well. IRT studies document similar training adaptations as stable resistance training programs with recreationally active individuals. Similar progressions with lower resistance may improve balance and stability, increase core activation, and improve motor control. IRT is highly recommended for youth, elderly, recreationally active individuals, and highly trained enthusiasts.

Oxidation behavior of Al/Cr coating on Ti2AlNb alloy at 900 °C

NASA Astrophysics Data System (ADS)

Yang, Zhengang; Liang, Wenping; Miao, Qiang; Chen, Bowen; Ding, Zheng; Roy, Nipon

2018-04-01

In this paper, the Al/Cr coating was fabricated on the surface of Ti2AlNb alloy via rf magnetron sputtering and double glow treatment to enhance oxidation resistance. The protective coating with an outer layer of Al and inner layer of Cr has great bonding strength due to the in-diffusion of Cr and the inter-diffusion between Al and Cr to form Al-Cr alloyed layer which has great hardness. Acoustic emission curve which was detected via WS-2005 scratch tester indicates the bonding strength between Al/Cr coating and substrate is great. Morphology of Ti2AlNb alloy with Al/Cr coating after scratch test shows that the scratch is smooth without disbanding, and the depth and breadth of scratch are changed uniformly. The mass change was reduced after oxidation test due to the Al/Cr protective coating. Isothermal oxidation test at 900 °C was researched. Results indicate that Al/Cr coating provided oxidation resistance of Ti2AlNb alloy with prolonged air exposure at 900 °C. Al2O3 was detected by XRD patterns and SEM images, and was formed on the surface of Ti2AlNb alloy to protect substrate during oxidation test. A certain content of Cr is beneficial for the formation of Al2O3. Besides, Cr2O3 was produced under Al2O3 by outward diffusion of Cr to protect substrate sequentially, no cracks were discovered on Al/Cr protective coating. The process of Ti outward diffusion into surface was suppressive due to integration of Cr-Ti and Al-Ti intermetallics. A steady, adherent and continuous coated layer of Al/Cr on Ti2AlNb alloy increases oxidation resistance.

THE THERMAL INSTABILITY OF SOLAR PROMINENCE THREADS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soler, R.; Goossens, M.; Ballester, J. L., E-mail: roberto.soler@wis.kuleuven.be

The fine structure of solar prominences and filaments appears as thin and long threads in high-resolution images. In H{alpha} observations of filaments, some threads can be observed for only 5-20 minutes before they seem to fade and eventually disappear, suggesting that these threads may have very short lifetimes. The presence of an instability might be the cause of this quick disappearance. Here, we study the thermal instability of prominence threads as an explanation of their sudden disappearance from H{alpha} observations. We model a prominence thread as a magnetic tube with prominence conditions embedded in a coronal environment. We assume amore » variation of the physical properties in the transverse direction so that the temperature and density continuously change from internal to external values in an inhomogeneous transitional layer representing the particular prominence-corona transition region (PCTR) of the thread. We use the nonadiabatic and resistive magnetohydrodynamic equations, which include terms due to thermal conduction parallel and perpendicular to the magnetic field, radiative losses, heating, and magnetic diffusion. We combine both analytical and numerical methods to study linear perturbations from the equilibrium state, focusing on unstable thermal solutions. We find that thermal modes are unstable in the PCTR for temperatures higher than 80,000 K, approximately. These modes are related to temperature disturbances that can lead to changes in the equilibrium due to rapid plasma heating or cooling. For typical prominence parameters, the instability timescale is of the order of a few minutes and is independent of the form of the temperature profile within the PCTR of the thread. This result indicates that thermal instability may play an important role for the short lifetimes of threads in the observations.« less

Zonal flow evolution and overstability in accretion discs

NASA Astrophysics Data System (ADS)

Vanon, R.; Ogilvie, G. I.

2017-04-01

This work presents a linear analytical calculation on the stability and evolution of a compressible, viscous self-gravitating (SG) Keplerian disc with both horizontal thermal diffusion and a constant cooling time-scale when an axisymmetric structure is present and freely evolving. The calculation makes use of the shearing sheet model and is carried out for a range of cooling times. Although the solutions to the inviscid problem with no cooling or diffusion are well known, it is non-trivial to predict the effect caused by the introduction of cooling and of small diffusivities; this work focuses on perturbations of intermediate wavelengths, therefore representing an extension to the classical stability analysis on thermal and viscous instabilities. For density wave modes, the analysis can be simplified by means of a regular perturbation analysis; considering both shear and thermal diffusivities, the system is found to be overstable for intermediate and long wavelengths for values of the Toomre parameter Q ≲ 2; a non-SG instability is also detected for wavelengths ≳18H, where H is the disc scale-height, as long as γ ≲ 1.305. The regular perturbation analysis does not, however, hold for the entropy and potential vorticity slow modes as their ideal growth rates are degenerate. To understand their evolution, equations for the axisymmetric structure's amplitudes in these two quantities are analytically derived and their instability regions obtained. The instability appears boosted by increasing the value of the adiabatic index and of the Prandtl number, while it is quenched by efficient cooling.

Collision-Driven Negative-Energy Waves and the Weibel Instability of a Relativistic Electron Beam in a Quasineutral Plasma

NASA Astrophysics Data System (ADS)

Karmakar, Anupam; Kumar, Naveen; Shvets, Gennady; Polomarov, Oleg; Pukhov, Alexander

2008-12-01

A new model describing the Weibel instability of a relativistic electron beam propagating through a resistive plasma is developed. For finite-temperature beams, a new class of negative-energy magnetosound waves is identified, whose growth due to collisional dissipation destabilizes the beam-plasma system even for high beam temperatures. We perform 2D and 3D particle-in-cell simulations and show that in 3D geometry the Weibel instability persists even for collisionless background plasma. The anomalous plasma resistivity in 3D is caused by the two-stream instability.

Extensions to the time lag models for practical application to rocket engine stability design

NASA Astrophysics Data System (ADS)

Casiano, Matthew J.

The combustion instability problem in liquid-propellant rocket engines (LREs) has remained a tremendous challenge since their discovery in the 1930s. Improvements are usually made in solving the combustion instability problem primarily using computational fluid dynamics (CFD) and also by testing demonstrator engines. Another approach is to use analytical models. Analytical models can be used such that design, redesign, or improvement of an engine system is feasible in a relatively short period of time. Improvements to the analytical models can greatly aid in design efforts. A thorough literature review is first conducted on liquid-propellant rocket engine (LRE) throttling. Throttling is usually studied in terms of vehicle descent or ballistic missile control however there are many other cases where throttling is important. It was found that combustion instabilities are one of a few major issues that occur during deep throttling (other major issues are heat transfer concerns, performance loss, and pump dynamics). In the past and again recently, gas injected into liquid propellants has shown to be a viable solution to throttle engines and to eliminate some forms of combustion instability. This review uncovered a clever solution that was used to eliminate a chug instability in the Common Extensible Cryogenic Engine (CECE), a modified RL10 engine. A separate review was also conducted on classic time lag combustion instability models. Several new stability models are developed by incorporating important features to the classic and contemporary models, which are commonly used in the aerospace rocket industry. The first two models are extensions of the original Crocco and Cheng concentrated combustion model with feed system contributions. A third new model is an extension to the Wenzel and Szuch double-time lag model also with feed system contributions. The first new model incorporates the appropriate injector acoustic boundary condition which is neglected in contemporary models. This new feature shows that the injector boundary can play a significant role for combustion stability, especially for gaseous injection systems or a system with an injector orifice on the order of the size of the chamber. The second new model additionally accounts for resistive effects. Advanced signal analysis techniques are used to extract frequency-dependent damping from a gas generator component data set. The damping values are then used in the new stability model to more accurately represent the chamber response of the component. The results show a more realistic representation of stability margin by incorporating the appropriate damping effects into the chamber response from data. The original Crocco model, a contemporary model, and the two new models are all compared and contrasted to a marginally stable test case showing their applicability. The model that incorporates resistive aspects shows the best comparison to the test data. Parametrics are also examined to show the influence of the new features and their applicability. The new features allow a more accurate representation of stability margin to be obtained. The third new model is an extension to the Wenzel and Szuch double-time lag chug model. The feed system chug model is extended to account for generic propellant flow rates. This model is also extended to incorporate aspects due to oxygen boiling and helium injection in the feed system. The solutions to the classic models, for the single-time lag and the double-time lag models, are often plotted on a practical engine operating map, however the models have presented some difficulties for numerical algorithms for several reasons. Closed-form solutions for use on these practical operating maps are formulated and developed. These models are incorporated in a graphical user interface tool and the new model is compared to an extensive data set. It correctly predicts the stability behavior at various operating conditions incorporating the influence of injected helium and boiling oxygen in the feed system.

PLANETESIMAL FORMATION IN MAGNETOROTATIONALLY DEAD ZONES: CRITICAL DEPENDENCE ON THE NET VERTICAL MAGNETIC FLUX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okuzumi, Satoshi; Hirose, Shigenobu, E-mail: okuzumi@nagoya-u.jp

Turbulence driven by magnetorotational instability (MRI) affects planetesimal formation by inducing diffusion and collisional fragmentation of dust particles. We examine conditions preferred for planetesimal formation in MRI-inactive 'dead zones' using an analytic dead-zone model based on our recent resistive MHD simulations. We argue that successful planetesimal formation requires not only a sufficiently large dead zone (which can be produced by tiny dust grains) but also a sufficiently small net vertical magnetic flux (NVF). Although often ignored, the latter condition is indeed important since the NVF strength determines the saturation level of turbulence in MRI-active layers. We show that direct collisionalmore » formation of icy planetesimal across the fragmentation barrier is possible when the NVF strength is lower than 10 mG (for the minimum-mass solar nebula model). Formation of rocky planetesimals via the secular gravitational instability is also possible within a similar range of the NVF strength. Our results indicate that the fate of planet formation largely depends on how the NVF is radially transported in the initial disk formation and subsequent disk accretion processes.« less

Stress-Induced Resistive Switching in Pt/HfO2/Ti Devices

NASA Astrophysics Data System (ADS)

Zeevi, Gilad; Katsman, Alexander; Yaish, Yuval E.

2018-02-01

In the present work, we study the initial SET mechanism of resistive switching (RS) in Pt/HfO2/Ti devices under a static electrical stress and the RS mechanism under a bias sweeping mode with rates of 100 mV/s-300 mV/s. We characterize the thin HfO2 dielectric layer by x-ray photoelectron spectroscopy and x-ray diffraction. These findings show that the layer structure is stoichiometric and nanocrystalline with a crystal diameter of ˜ 14 Å. We measure the temporal dependence of the conductive filament growth at different temperatures and for various biases. Furthermore, these devices present stable bipolar resistive switching with a high-to-low resistive state (HRS/LRS) ratio of more than three orders of magnitude. Activation energy E RS ≈ 0.56 eV and drift current parameter V 0 ≈ 0.07 V were determined from the temporal dependence of the initial `SET' process, first HRS to LRS transition [for static electrical stress of V DS = (4.7-5.0 V)]. We analyze the results according to our model suggesting generation of double-charge oxygen vacancies at the anode and their diffusion across the dielectric layer. The double-charge vacancies transform to a single charge and then to neutral vacancies by capturing hot electrons, and form a conductive filament as soon as a critical neutral-vacancy cluster is formed across the dielectric layer.

Plasma processes in inert gas thrusters

NASA Technical Reports Server (NTRS)

Kaufman, H. R.; Robinson, R. S.

1979-01-01

Inert gas thrusters, particularly with large diameters, have continued to be of interest for space propulsion applications. Two plasma processes are treated in this study: electron diffusion across magnetic fields and double ion production in inert-gas thrusters. A model is developed to describe electron diffusion across a magnetic field that is driven by both density and potential gradients, with Bohm diffusion used to predict the diffusion rate. This model has applications to conduction across magnetic fields inside a discharge chamber, as well as through a magnetic baffle region used to isolate a hollow cathode from the main chamber. A theory for double ion production is presented, which is not as complete as the electron diffusion theory described, but it should be a useful tool for predicting double ion sputter erosion. Correlations are developed that may be used, without experimental data, to predict double ion densities for the design of new and especially larger ion thrusters.

Effect of fast electrons on the stability of resistive interchange modes in the TJ-II stellarator

DOE Office of Scientific and Technical Information (OSTI.GOV)

García, L.; Ochando, M. A.; Hidalgo, C.

2016-06-15

In this paper, we report on electromagnetic phenomena in low-β plasmas at the TJ-II stellarator, controlled by external heating. To understand the observations qualitatively, we introduce a simple modification of the standard resistive MHD equations, to include the potential impact of fast electrons on instabilities. The dominant instabilities of the modeling regime are resistive interchange modes, and calculations are performed in a configuration with similar characteristics as the TJ-II stellarator. The main effect of the trapping of fast electrons by magnetic islands induced by MHD instabilities is to increase the magnetic component of the fluctuations, changing the character of themore » instability to tearing-like and modifying the frequency of the modes. These effects seem to be consistent with some of the experimental observations.« less

Impact of porosity on Jeans instability in viscous quantum magnetoplasma

NASA Astrophysics Data System (ADS)

Prajapat, V.; Sutar, D. L.; Pensia, R. K.

2018-05-01

This paper treats the Jeans instability improved at the theoretical investigation of the presence of viscosity and resistivity in the porous medium. Following the normal mode analysis using the QMHD model, the dispersion relation is discussed for wave propagation in longitudinal and transverse direction. The Jeans criteria of instability are affected by the presence of porosity. The graphical presentation shows that porosity has a stabilizing effect while resistivity has destabilizing effect in the system.

On an instability exhibited by the ballistic-diffusive heat conduction model of Xu and Hu

DOE PAGES

Christov, I. C.; Jordan, P. M.

2013-11-13

We show that the constitutive relation for the thermal flux proposed by Xu & Hu (2011) admits an unconditional instability. We also highlight the difference between mathematical models containing delay and those that include relaxation effects.

The use of instability to train the core musculature.

PubMed

Behm, David G; Drinkwater, Eric J; Willardson, Jeffrey M; Cowley, Patrick M

2010-02-01

Training of the trunk or core muscles for enhanced health, rehabilitation, and athletic performance has received renewed emphasis. Instability resistance exercises have become a popular means of training the core and improving balance. Whether instability resistance training is as, more, or less effective than traditional ground-based resistance training is not fully resolved. The purpose of this review is to address the effectiveness of instability resistance training for athletic, nonathletic, and rehabilitation conditioning. The anatomical core is defined as the axial skeleton and all soft tissues with a proximal attachment on the axial skeleton. Spinal stability is an interaction of passive and active muscle and neural subsystems. Training programs must prepare athletes for a wide variety of postures and external forces, and should include exercises with a destabilizing component. While unstable devices have been shown to be effective in decreasing the incidence of low back pain and increasing the sensory efficiency of soft tissues, they are not recommended as the primary exercises for hypertrophy, absolute strength, or power, especially in trained athletes. For athletes, ground-based free-weight exercises with moderate levels of instability should form the foundation of exercises to train the core musculature. Instability resistance exercises can play an important role in periodization and rehabilitation, and as alternative exercises for the recreationally active individual with less interest or access to ground-based free-weight exercises. Based on the relatively high proportion of type I fibers, the core musculature might respond well to multiple sets with high repetitions (e.g., >15 per set); however, a particular sport may necessitate fewer repetitions.

Extended-spectrum beta-lactamase-producing Enterobacteriaceae in hospital urinary tract infections: incidence and antibiotic susceptibility profile over 9 years.

PubMed

Toner, Liam; Papa, Nathan; Aliyu, Sani H; Dev, Harveer; Lawrentschuk, Nathan; Al-Hayek, Samih

2016-07-01

Extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae are an increasing concern regarding antibiotic resistance and their potential to cause serious infections which are difficult to treat. The purpose of this surveillance programme was to assess the incidence of ESBL in adults amongst urinary isolates, identify risk factors, and detail the antibiotic susceptibility profile in order to guide empirical treatment. From 2006 to 2014, we reviewed 21,414 positive urine cultures for E. coli and Klebsiella sp. from a University hospital in the UK and found 1420 ESBL-positive specimens. Susceptibility testing was performed by British Society of Antimicrobial Chemotherapy disc diffusion testing. ESBL screening was performed on samples resistant to cefpodoxime and confirmed by double disc diffusion (Oxoid Ltd, Basingstoke, UK). Patient gender, age, inpatient status, and catheterisation were assessed as risk factors. ESBL production amongst E. coli urine cultures increased 44 %, from 4.6 to 6.6 % of all E. coli isolates. ESBL-positive organisms were associated with increases in drug resistance, particularly amongst fluoroquinolones, trimethoprim, and cephalexin. Multidrug resistance was a feature with 75 % of ESBL+ Klebsiella sp.-resistant ≥6 antibiotic classes. ESBL producers remained largely susceptible to carbapenems. Male gender, urinary catheterisation, inpatient status, and increasing age were identified as risk factors for ESBL infection or colonisation. We demonstrate that the incidence of ESBL-producing E. coli in urine cultures is increasing and that such isolates are multidrug resistant. Carbapenems and nitrofurantoin for E. coli infections remain effective, which may guide empirical antibiotic therapy.

Stabilization of a spatially uniform steady state in two systems exhibiting Turing patterns

NASA Astrophysics Data System (ADS)

Konishi, Keiji; Hara, Naoyuki

2018-05-01

This paper deals with the stabilization of a spatially uniform steady state in two coupled one-dimensional reaction-diffusion systems with Turing instability. This stabilization corresponds to amplitude death that occurs in a coupled system with Turing instability. Stability analysis of the steady state shows that stabilization does not occur if the two reaction-diffusion systems are identical. We derive a sufficient condition for the steady state to be stable for any length of system and any boundary conditions. Our analytical results are supported with numerical examples.

De novo balanced complex chromosome rearrangements involving chromosomes 1B and 3B of wheat and 1R of rye.

PubMed

Ren, Tianheng; Li, Zhi; Yan, Benju; Tan, Feiquan; Tang, Zongxiang; Fu, Shulan; Yang, Manyu; Ren, Zhenglong

2016-12-01

Complex chromosome rearrangements (CCRs) are defined as structural abnormalities involving more than two chromosome breaks, coupled with exchanges of chromosomal segments. Information on CCRs in plants is limited. In the present study, a plant (26-4) harboring translocation chromosomes 1RS.1BL and 4RS.4DL was selected from a double monosomic (1R and 4R) addition line, which was derived from the hybrid between wheat cultivar MY11 and a Chinese local rye variety. The genome of the plant with double alien translocation chromosomes in the monosomic form showed more instability than that harboring a single translocation. The CCRs involving chromosomes 1RS.1BL and 3B, which were generated de novo in this plant, showed double monosomic translocation chromosomes. A new CCR line with balanced reciprocal translocations 1RS.3BL and 3BS.1BL was developed, which presented normal morphological traits of wheat and underwent rapid growth in the field. A new 1RS.1BL translocation line was also selected from the progeny of plant 26-4. The CCRs and simple 1RS.1BL translocation lines showed significant improvement in grain yield, number of spikes per square meter, kernel number per spike, and resistance to stripe rust and powdery mildew. The CCR line exhibited better agronomic traits and adult plant resistance in the field than its sister line, which harbored a simple 1RS.1BL translocation. The CCRs are remarkable genetic resources for crop improvement.

Studies of Resistive-Wall Instability with Space-Charge Dominated Electron Beams

NASA Astrophysics Data System (ADS)

Wang, J. G.; Suk, H.; Reiser, M.

1996-05-01

An experiment to study the resistive-wall instability with space-charge dominated electrom beams is underway at the University of Maryland. The beams with localized perturbations are launched from a gridded electron gun and are matched into a resistive channel focused by a uniform solenoid. The channel is made of a 1-m long glass tube coated with resistive material (ITO). Two different tubes with 5.4 kΩ and 10.1 kΩ resistance, respectively, have been employed. Two fast wall-current monitors at both the entrance and exit of the channel provide the information about the instability. Typical beam parameters are 3-8 keV in energy, 30-80 mA in current and 100 ns in duration. The experiment has shown the growth of localized slow waves and decay of fast waves. The results are presented and compared with theory. The status of the experiment and future work are also discussed.

FOKKER-PLANCK ANALYSIS OF TRANSVERSE COLLECTIVE INSTABILITIES IN ELECTRON STORAGE RINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindberg, R. R.

We analyze single bunch transverse instabilities due to wakefields using a Fokker-Planck model. We expand on the work of Suzuki [1], writing out the linear matrix equation including chromaticity, both dipolar and quadrupolar transverse wakefields, and the effects of damping and diffusion due to the synchrotron radiation. The eigenvalues and eigenvectors determine the collective stability of the beam, and we show that the predicted threshold current for transverse instability and the profile of the unstable agree well with tracking simulations. In particular, we find that predicting collective stability for high energy electron beams at moderate to large values of chromaticitymore » requires the full Fokker-Planck analysis to properly account for the effects of damping and diffusion due to synchrotron radiation.« less

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

NASA Astrophysics Data System (ADS)

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

2013-12-01

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.

Diffusivity in Alumina Scales Grown on Al-MAX Phases

NASA Technical Reports Server (NTRS)

Smialek, James L.

2014-01-01

Ti3AlC2, Ti2AlC, and Cr2AlC are oxidation resistant MAX phase compounds distinguished by the formation of protective Al2O3 scales with well controlled kinetics. A modified Wagner treatment was used to obtain interfacial grain boundary diffusivity, deltaD(sub gb,O,int.), from scale growth rates and corresponding grain size. It is based on the p(O2)(exp -1/6) dependency of the double charged oxygen vacancy and oxygen diffusivity, coupled with the effective diffusion constant for short circuit grain boundary paths. Data from the literature for MAX phases was analyzed accordingly, and deltaD(sub gb,O,int.) was found to nearly coincide with the Arrhenius line developed for Zr-doped FeCrAl, where: deltaD(sub gb,O,int.) = 1.8x10(exp -10) exp(-375 kJ/RT) cubic meters/s. Furthermore, this oxidation relation suggests the more general format applicable to bulk samples under ambient conditions: deltaD(sub gb,O) = 7.567x10(exp -8) exp(-544 kJ/RT) p(O2)(exp -1/6) cubic meters/[s x Pa(exp -1/6)]. Data from many other FeCrAl(X) studies were similarly assessed to show general agreement with the relation for deltaD(sub gb,O,int.). This analysis reinforces the view that protective alumina scales grow by similar mechanisms for these Al-MAX phases and oxidation resistant FeCrAl alloys.

Turing instability in reaction-diffusion models on complex networks

NASA Astrophysics Data System (ADS)

Ide, Yusuke; Izuhara, Hirofumi; Machida, Takuya

2016-09-01

In this paper, the Turing instability in reaction-diffusion models defined on complex networks is studied. Here, we focus on three types of models which generate complex networks, i.e. the Erdős-Rényi, the Watts-Strogatz, and the threshold network models. From analysis of the Laplacian matrices of graphs generated by these models, we numerically reveal that stable and unstable regions of a homogeneous steady state on the parameter space of two diffusion coefficients completely differ, depending on the network architecture. In addition, we theoretically discuss the stable and unstable regions in the cases of regular enhanced ring lattices which include regular circles, and networks generated by the threshold network model when the number of vertices is large enough.

Cutaneous double-hit B-cell lymphoma: an aggressive form of B-cell lymphoma with a propensity for cutaneous dissemination.

PubMed

Magro, Cynthia M; Wang, Xuan; Subramaniyam, Shivakumar; Darras, Natasha; Mathew, Susan

2014-04-01

Diffuse large cell B-cell lymphoma of the skin is most commonly represented by diffuse large cell variants of primary cutaneous follicle center cell lymphoma and the leg-type lymphoma. In a minority of cases, the infiltrates are an expression of stage 4 disease of established extracutaneous B-cell lymphoma. We describe 3 patients with an aggressive form of B-cell lymphoma secondarily involving the skin. Two of the patients were in the ninth decade of life, whereas 1 patient was 34 years of age. In the elderly patients, there was an antecedent and/or concurrent history of follicular lymphoma, whereas in the younger patient, the tumor was a de novo presentation of this aggressive form of lymphoma. The elderly patients succumbed to their disease within less than a year from the time of diagnosis, whereas 1 patient is alive but with persistent and progressive disease despite chemotherapeutic intervention. The infiltrates in all 3 cases were diffuse and composed of large malignant hematopoietic cells that exhibited a round nucleus with a finely dispersed chromatin. Phenotypically, the tumor cells were Bcl-2 and CD10 positive, whereas Bcl-6 and Mum-1 showed variable positivity. One case showed combined Mum-1 positivity along with an acute lymphoblastic lymphoma phenotype, including the absence of CD20 expression. In each case, there was a c-MYC and BCL2/IGH rearrangement diagnostic of double-hit lymphoma. In one case, there was an additional BCL6 rearrangement, defining what is in essence triple-hit lymphoma. In conclusion, double-hit lymphoma is an aggressive form of B-cell neoplasia resistant to standard chemotherapy regimens, which in many but not all cases represents tumor progression in the setting of a lower grade B-cell malignancy.

Double-hit lymphomas constitute a highly aggressive subgroup in diffuse large B-cell lymphomas in the era of rituximab.

PubMed

Kobayashi, Tsutomu; Tsutsumi, Yasuhiko; Sakamoto, Natsumi; Nagoshi, Hisao; Yamamoto-Sugitani, Mio; Shimura, Yuji; Mizutani, Shinsuke; Matsumoto, Yosuke; Nishida, Kazuhiro; Horiike, Shigeo; Asano, Naoko; Nakamura, Shigeo; Kuroda, Junya; Taniwaki, Masafumi

2012-11-01

The incorporation of rituximab in immunochemotherapy has improved treatment outcomes for diffuse large B-cell lymphoma, but the prognosis for some diffuse large B-cell lymphomas remains dismal. Identification of adverse prognostic subgroups is essential for the choice of appropriate therapeutic strategy. We retrospectively investigated the impact of so-called 'double-hit' cytogenetic abnormalities, i.e. cytogenetic abnormalities involving c-MYC co-existing with other poor prognostic cytogenetic abnormalities involving BCL2, BCL6 or BACH2, on treatment outcomes for 93 consecutive diffuse large B-cell lymphoma patients. According to the revised international prognostic index, no patients were cytogenetically diagnosed with double-hit lymphomas in the 'very good' risk group or in the 'good' risk group, while 5 of 33 patients had double-hit lymphomas in the 'poor' risk group. All the double-hit lymphoma patients possessed both nodal and extranodal involvement. The overall complete response rate was 89.3%, overall survival 87.1% and progression-free survival 75.8% over 2 years (median observation period: 644 days). The complete response rates were 93.2% for the non-double-hit lymphoma patients and 40.0% for the double-hit lymphoma patients. Significantly longer progression-free survival and overall survival were observed for the 'very good' and the 'good' risk patients than for the 'poor' risk patients. Moreover, the progression-free survival of double-hit lymphoma was significantly shorter than that of the non-double-hit lymphoma 'poor' risk patients (P = 0.016). In addition, the overall survival of the double-hit lymphoma patients also tended to be shorter than that of the non-double-hit lymphoma 'poor' risk group. The diagnosis of double-hit lymphoma can help discriminate a subgroup of highly aggressive diffuse large B-cell lymphomas and indicate the need for the development of novel therapeutic strategies for double-hit lymphoma.

Influence of bilayer resist processing on p-i-n OLEDs: towards multicolor photolithographic structuring of organic displays

NASA Astrophysics Data System (ADS)

Krotkus, Simonas; Nehm, Frederik; Janneck, Robby; Kalkura, Shrujan; Zakhidov, Alex A.; Schober, Matthias; Hild, Olaf R.; Kasemann, Daniel; Hofmann, Simone; Leo, Karl; Reineke, Sebastian

2015-03-01

Recently, bilayer resist processing combined with development in hydrofluoroether (HFE) solvents has been shown to enable single color structuring of vacuum-deposited state-of-the-art organic light-emitting diodes (OLED). In this work, we focus on further steps required to achieve multicolor structuring of p-i-n OLEDs using a bilayer resist approach. We show that the green phosphorescent OLED stack is undamaged after lift-off in HFEs, which is a necessary step in order to achieve RGB pixel array structured by means of photolithography. Furthermore, we investigate the influence of both, double resist processing on red OLEDs and exposure of the devices to ambient conditions, on the basis of the electrical, optical and lifetime parameters of the devices. Additionally, water vapor transmission rates of single and bilayer system are evaluated with thin Ca film conductance test. We conclude that diffusion of propylene glycol methyl ether acetate (PGMEA) through the fluoropolymer film is the main mechanism behind OLED degradation observed after bilayer processing.

A double barrier memristive device

PubMed Central

Hansen, M.; Ziegler, M.; Kolberg, L.; Soni, R.; Dirkmann, S.; Mussenbrock, T.; Kohlstedt, H.

2015-01-01

We present a quantum mechanical memristive Nb/Al/Al2O3/NbxOy/Au device which consists of an ultra-thin memristive layer (NbxOy) sandwiched between an Al2O3 tunnel barrier and a Schottky-like contact. A highly uniform current distribution for the LRS (low resistance state) and HRS (high resistance state) for areas ranging between 70 μm2 and 2300 μm2 were obtained, which indicates a non-filamentary based resistive switching mechanism. In a detailed experimental and theoretical analysis we show evidence that resistive switching originates from oxygen diffusion and modifications of the local electronic interface states within the NbxOy layer, which influences the interface properties of the Au (Schottky) contact and of the Al2O3 tunneling barrier, respectively. The presented device might offer several benefits like an intrinsic current compliance, improved retention and no need for an electric forming procedure, which is especially attractive for possible applications in highly dense random access memories or neuromorphic mixed signal circuits. PMID:26348823

Nonequilibrium electrokinetic effects in beds of ion-permselective particles.

PubMed

Leinweber, Felix C; Tallarek, Ulrich

2004-12-21

Electrokinetic transport of fluorescent tracer molecules in a bed of porous glass beads was investigated by confocal laser scanning microscopy. Refractive index matching between beads and the saturating fluid enabled a quantitative analysis of intraparticle and extraparticle fluid-side concentration profiles. Kinetic data were acquired for the uptake and release of electroneutral and counterionic tracer under devised conditions with respect to constant pressure-driven flow through the device and the effect of superimposed electrical fields. Transport of neutral tracer is controlled by intraparticle mass transfer resistance which can be strongly reduced by electroosmotic flow, while steady-state distributions and bead-averaged concentrations are unaffected by the externally applied fields. Electrolytes of low ionic strength caused the transport through the charged (mesoporous) beads to become highly ion-permselective, and concentration polarization is induced in the bulk solution due to the superimposed fields. The depleted concentration polarization zone comprises extraparticle fluid-side mass transfer resistance. Ionic concentrations in this diffusion boundary layer decrease at increasing field strength, and the flux densities approach an upper limit. Meanwhile, intraparticle transport of counterions by electromigration and electroosmosis continues to increase and finally exceeds the transport from bulk solution into the beads. A nonequilibrium electrical double layer is induced which consists of mobile and immobile space charge regions in the extraparticle bulk solution and inside a bead, respectively. These electrical field-induced space charges form the basis for nonequilibrium electrokinetic phenomena. Caused by the underlying transport discrimination (intraparticle electrokinetic vs extraparticle boundary-layer mass transfer), the dynamic adsorption capacity for counterions can be drastically reduced. Further, the extraparticle mobile space charge region leads to nonlinear electroosmosis. Flow patterns can become highly chaotic, and electrokinetic instability mixing is shown to increase lateral dispersion. Under these conditions, the overall axial dispersion of counterionic tracer can be reduced by more than 2 orders of magnitude, as demonstrated by pulse injections.

Rarefaction-driven Rayleigh–Taylor instability. Part 1. Diffuse-interface linear stability measurements and theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgan, R. V.; Likhachev, O. A.; Jacobs, J. W.

Theory and experiments are reported that explore the behaviour of the Rayleigh–Taylor instability initiated with a diffuse interface. Experiments are performed in which an interface between two gases of differing density is made unstable by acceleration generated by a rarefaction wave. Well-controlled, diffuse, two-dimensional and three-dimensional, single-mode perturbations are generated by oscillating the gases either side to side, or vertically for the three-dimensional perturbations. The puncturing of a diaphragm separating a vacuum tank beneath the test section generates a rarefaction wave that travels upwards and accelerates the interface downwards. This rarefaction wave generates a large, but non-constant, acceleration of the order ofmore » $$1000g_{0}$$, where$$g_{0}$$is the acceleration due to gravity. Initial interface thicknesses are measured using a Rayleigh scattering diagnostic and the instability is visualized using planar laser-induced Mie scattering. Growth rates agree well with theoretical values, and with the inviscid, dynamic diffusion model of Duffet al. (Phys. Fluids, vol. 5, 1962, pp. 417–425) when diffusion thickness is accounted for, and the acceleration is weighted using inviscid Rayleigh–Taylor theory. The linear stability formulation of Chandrasekhar (Proc. Camb. Phil. Soc., vol. 51, 1955, pp. 162–178) is solved numerically with an error function diffusion profile using the Riccati method. This technique exhibits good agreement with the dynamic diffusion model of Duffet al. for small wavenumbers, but produces larger growth rates for large-wavenumber perturbations. Asymptotic analysis shows a$$1/k^{2}$$decay in growth rates as$$k\\rightarrow \\infty$$for large-wavenumber perturbations.« less

Rarefaction-driven Rayleigh–Taylor instability. Part 1. Diffuse-interface linear stability measurements and theory

DOE PAGES

Morgan, R. V.; Likhachev, O. A.; Jacobs, J. W.

2016-02-15

Theory and experiments are reported that explore the behaviour of the Rayleigh–Taylor instability initiated with a diffuse interface. Experiments are performed in which an interface between two gases of differing density is made unstable by acceleration generated by a rarefaction wave. Well-controlled, diffuse, two-dimensional and three-dimensional, single-mode perturbations are generated by oscillating the gases either side to side, or vertically for the three-dimensional perturbations. The puncturing of a diaphragm separating a vacuum tank beneath the test section generates a rarefaction wave that travels upwards and accelerates the interface downwards. This rarefaction wave generates a large, but non-constant, acceleration of the order ofmore » $$1000g_{0}$$, where$$g_{0}$$is the acceleration due to gravity. Initial interface thicknesses are measured using a Rayleigh scattering diagnostic and the instability is visualized using planar laser-induced Mie scattering. Growth rates agree well with theoretical values, and with the inviscid, dynamic diffusion model of Duffet al. (Phys. Fluids, vol. 5, 1962, pp. 417–425) when diffusion thickness is accounted for, and the acceleration is weighted using inviscid Rayleigh–Taylor theory. The linear stability formulation of Chandrasekhar (Proc. Camb. Phil. Soc., vol. 51, 1955, pp. 162–178) is solved numerically with an error function diffusion profile using the Riccati method. This technique exhibits good agreement with the dynamic diffusion model of Duffet al. for small wavenumbers, but produces larger growth rates for large-wavenumber perturbations. Asymptotic analysis shows a$$1/k^{2}$$decay in growth rates as$$k\\rightarrow \\infty$$for large-wavenumber perturbations.« less

Elucidating the genomic architecture of Asian EGFR-mutant lung adenocarcinoma through multi-region exome sequencing.

PubMed

Nahar, Rahul; Zhai, Weiwei; Zhang, Tong; Takano, Angela; Khng, Alexis J; Lee, Yin Yeng; Liu, Xingliang; Lim, Chong Hee; Koh, Tina P T; Aung, Zaw Win; Lim, Tony Kiat Hon; Veeravalli, Lavanya; Yuan, Ju; Teo, Audrey S M; Chan, Cheryl X; Poh, Huay Mei; Chua, Ivan M L; Liew, Audrey Ann; Lau, Dawn Ping Xi; Kwang, Xue Lin; Toh, Chee Keong; Lim, Wan-Teck; Lim, Bing; Tam, Wai Leong; Tan, Eng-Huat; Hillmer, Axel M; Tan, Daniel S W

2018-01-15

EGFR-mutant lung adenocarcinomas (LUAD) display diverse clinical trajectories and are characterized by rapid but short-lived responses to EGFR tyrosine kinase inhibitors (TKIs). Through sequencing of 79 spatially distinct regions from 16 early stage tumors, we show that despite low mutation burdens, EGFR-mutant Asian LUADs unexpectedly exhibit a complex genomic landscape with frequent and early whole-genome doubling, aneuploidy, and high clonal diversity. Multiple truncal alterations, including TP53 mutations and loss of CDKN2A and RB1, converge on cell cycle dysregulation, with late sector-specific high-amplitude amplifications and deletions that potentially beget drug resistant clones. We highlight the association between genomic architecture and clinical phenotypes, such as co-occurring truncal drivers and primary TKI resistance. Through comparative analysis with published smoking-related LUAD, we postulate that the high intra-tumor heterogeneity observed in Asian EGFR-mutant LUAD may be contributed by an early dominant driver, genomic instability, and low background mutation rates.

Super-spiral structures of bi-stable spiral waves and a new instability of spiral waves

NASA Astrophysics Data System (ADS)

Gao, Jian; Wang, Qun; Lü, Huaping

2017-10-01

A new type of super-spiral structure and instability of spiral waves (in numerical simulation) are investigated. Before the period-doubling bifurcation of this system, the super-spiral structure occurs caused by phase trajectory selection. This type of super-spiral structure is totally different from the super-spiral structure observed early. Although the spiral rotates, the super-spiral structure is stationary. Observably, fully turbulence of the system occurs suddenly which has no process of instability. The forming principle of this instability may have applications in cardiology.

One-dimensional energetic particle quasilinear diffusion for realistic TAE instabilities

NASA Astrophysics Data System (ADS)

Duarte, Vinicius; Ghantous, Katy; Berk, Herbert; Gorelenkov, Nikolai

2014-10-01

Owing to the proximity of the characteristic phase (Alfvén) velocity and typical energetic particle (EP) superthermal velocities, toroidicity-induced Alfvén eigenmodes (TAEs) can be resonantly destabilized endangering the plasma performance. Thus, it is of ultimate importance to understand the deleterious effects on the confinement resulting from fast ion driven instabilities expected in fusion-grade plasmas. We propose to study the interaction of EPs and TAEs using a line broadened quasilinear model, which captures the interaction in both regimes of isolated and overlapping modes. The resonance particles diffuse in the phase space where the problem essentially reduces to one dimension with constant kinetic energy and the diffusion mainly along the canonical toroidal angular momentum. Mode structure and wave particle resonances are computed by the NOVA code and are used in a quasilinear diffusion code that is being written to study the evolution of the distribution function, under the assumption that they can be considered virtually unalterable during the diffusion. A new scheme for the resonant particle diffusion is being proposed that builds on the 1-D nature of the diffusion from a single mode, which leads to a momentum conserving difference scheme even when there is mode overlap.

Pattern formation, social forces, and diffusion instability in games with success-driven motion

NASA Astrophysics Data System (ADS)

Helbing, Dirk

2009-02-01

A local agglomeration of cooperators can support the survival or spreading of cooperation, even when cooperation is predicted to die out according to the replicator equation, which is often used in evolutionary game theory to study the spreading and disappearance of strategies. In this paper, it is shown that success-driven motion can trigger such local agglomeration and may, therefore, be used to supplement other mechanisms supporting cooperation, like reputation or punishment. Success-driven motion is formulated here as a function of the game-theoretical payoffs. It can change the outcome and dynamics of spatial games dramatically, in particular as it causes attractive or repulsive interaction forces. These forces act when the spatial distributions of strategies are inhomogeneous. However, even when starting with homogeneous initial conditions, small perturbations can trigger large inhomogeneities by a pattern-formation instability, when certain conditions are fulfilled. Here, these instability conditions are studied for the prisoner’s dilemma and the snowdrift game. Furthermore, it is demonstrated that asymmetrical diffusion can drive social, economic, and biological systems into the unstable regime, if these would be stable without diffusion.

Resistive tearing instability in electron MHD: application to neutron star crusts

NASA Astrophysics Data System (ADS)

Gourgouliatos, Konstantinos N.; Hollerbach, Rainer

2016-12-01

We study a resistive tearing instability developing in a system evolving through the combined effect of Hall drift in the electron magnetohydrodynamic limit and Ohmic dissipation. We explore first the exponential growth of the instability in the linear case and we find the fastest growing mode, the corresponding eigenvalues and dispersion relation. The instability growth rate scales as γ ∝ B2/3σ-1/3, where B is the magnetic field and σ the electrical conductivity. We confirm the development of the tearing resistive instability in the fully non-linear case, in a plane-parallel configuration where the magnetic field polarity reverses, through simulations of systems initiating in Hall equilibrium with some superimposed perturbation. Following a transient phase, during which there is some minor rearrangement of the magnetic field, the perturbation grows exponentially. Once the instability is fully developed, the magnetic field forms the characteristic islands and X-type reconnection points, where Ohmic decay is enhanced. We discuss the implications of this instability for the local magnetic field evolution in neutron stars' crusts, proposing that it can contribute to heating near the surface of the star, as suggested by models of magnetar post-burst cooling. In particular, we find that a current sheet a few metres thick, covering as little as 1 per cent of the total surface, can provide 1042 erg in thermal energy within a few days. We briefly discuss applications of this instability in other systems where the Hall effect operates such as protoplanetary discs and space plasmas.

Optimization of Vertical Double-Diffused Metal-Oxide Semiconductor (VDMOS) Power Transistor Structure for Use in High Frequencies and Medical Devices

PubMed Central

Farhadi, Rozita; Farhadi, Bita

2014-01-01

Power transistors, such as the vertical, double-diffused, metal-oxide semiconductor (VDMOS), are used extensively in the amplifier circuits of medical devices. The aim of this research was to construct a VDMOS power transistor with an optimized structure to enhance the operation of medical devices. First, boron was implanted in silicon by implanting unclamped inductive switching (UIS) and a Faraday shield. The Faraday shield was implanted in order to replace the gate-field parasitic capacitor on the entry part of the device. Also, implanting the UIS was used in order to decrease the effect of parasitic bipolar junction transistor (BJT) of the VDMOS power transistor. The research tool used in this study was Silvaco software. By decreasing the transistor entry resistance in the optimized VDMOS structure, power losses and noise at the entry of the transistor were decreased, and, by increasing the breakdown voltage, the lifetime of the VDMOS transistor lifetime was increased, which resulted in increasing drain flow and decreasing Ron. This consequently resulted in enhancing the operation of high-frequency medical devices that use transistors, such as Radio Frequency (RF) and electrocardiograph machines. PMID:25763152

Optimization of Vertical Double-Diffused Metal-Oxide Semiconductor (VDMOS) Power Transistor Structure for Use in High Frequencies and Medical Devices.

PubMed

Farhadi, Rozita; Farhadi, Bita

2014-01-01

Power transistors, such as the vertical, double-diffused, metal-oxide semiconductor (VDMOS), are used extensively in the amplifier circuits of medical devices. The aim of this research was to construct a VDMOS power transistor with an optimized structure to enhance the operation of medical devices. First, boron was implanted in silicon by implanting unclamped inductive switching (UIS) and a Faraday shield. The Faraday shield was implanted in order to replace the gate-field parasitic capacitor on the entry part of the device. Also, implanting the UIS was used in order to decrease the effect of parasitic bipolar junction transistor (BJT) of the VDMOS power transistor. The research tool used in this study was Silvaco software. By decreasing the transistor entry resistance in the optimized VDMOS structure, power losses and noise at the entry of the transistor were decreased, and, by increasing the breakdown voltage, the lifetime of the VDMOS transistor lifetime was increased, which resulted in increasing drain flow and decreasing Ron. This consequently resulted in enhancing the operation of high-frequency medical devices that use transistors, such as Radio Frequency (RF) and electrocardiograph machines.

Three-dimensional doubly diffusive convectons: instability and transition to complex dynamics

NASA Astrophysics Data System (ADS)

Knobloch, Edgar; Beaume, Cedric; Bergeon, Alain

2017-11-01

Doubly diffusive convection in a closed vertically extended 3D container driven by competing horizontal temperature and concentration gradients is studied. No-slip boundary conditions are imposed. The buoyancy number N = - 1 to ensure the presence of a conduction state. The primary instability is subcritical and generates two families of spatially localised steady states known as convectons. The convectons bifurcate directly from the conduction state and are organized in a pair of primary branches that snake within a well-defined range of Rayleigh numbers as the convectons grow in length. Secondary instabilities generating twist result in secondary snaking branches of twisted convectons. These destabilize the primary convectons and are responsible for the absence of stable steady states, localized or otherwise, in the subcritical regime. As a result, once the Rayleigh number for the primary instability of the conduction state is exceeded, the system exhibits an abrupt transition to large amplitude spatio-temporal chaos that arises whenever the twist instability leading to collapse is faster than the nucleation time for new rolls. These numerical results are confirmed by determining the stability properties of all convecton states as well as spatially extended convection. Supported in part by the National Science Foundation under Grant DMS-1613132.

Prolonged Particulate Hexavalent Chromium Exposure Suppresses Homologous Recombination Repair in Human Lung Cells

PubMed Central

Browning, Cynthia L.; Qin, Qin; Kelly, Deborah F.; Prakash, Rohit; Vanoli, Fabio; Jasin, Maria

2016-01-01

Abstract Genomic instability is one of the primary models of carcinogenesis and a feature of almost all cancers. Homologous recombination (HR) repair protects against genomic instability by maintaining high genomic fidelity during the repair of DNA double strand breaks. The defining step of HR repair is the formation of the Rad51 nucleofilament, which facilitates the search for a homologous sequence and invasion of the template DNA strand. Particulate hexavalent chromium (Cr(VI)), a human lung carcinogen, induces DNA double strand breaks and chromosome instability. Since the loss of HR repair increases Cr(VI)-induced chromosome instability, we investigated the effect of extended Cr(VI) exposure on HR repair. We show acute (24 h) Cr(VI) exposure induces a normal HR repair response. In contrast, prolonged (120 h) exposure to particulate Cr(VI) inhibited HR repair and Rad51 nucleofilament formation. Prolonged Cr(VI) exposure had a profound effect on Rad51, evidenced by reduced protein levels and Rad51 mislocalization to the cytoplasm. The response of proteins involved in Rad51 nuclear import and nucleofilament formation displayed varying responses to prolonged Cr(VI) exposure. BRCA2 formed nuclear foci after prolonged Cr(VI) exposure, while Rad51C foci formation was suppressed. These results suggest that particulate Cr(VI), a major chemical carcinogen, inhibits HR repair by targeting Rad51, causing DNA double strand breaks to be repaired by a low fidelity, Rad51-independent repair pathway. These results further enhance our understanding of the underlying mechanism of Cr(VI)-induced chromosome instability and thus, carcinogenesis. PMID:27449664

Plasma sheet density dependence on Interplanetary Magnetic Field and Solar Wind properties: statistical study using 9+ year of THEMIS data

NASA Astrophysics Data System (ADS)

Nykyri, K.; Chu, C.; Dimmock, A. P.

2017-12-01

Previous studies have shown that plasma sheet in tenuous and hot during southward IMF, whereas northward IMF conditions are associated with cold, dense plasma. The cold, dense plasma sheet (CDPS) has strong influence on magnetospheric dynamics. Closer to Earth, the CDPS could be formed via double high-latitude reconnection, while at increasing tailward distance reconnection, diffusion and kinetic Alfven waves in association with Kelvin-Helmholtz Instability are suggested as dominant source for cold-dense plasma sheet formation. In this paper we present statistical correlation study between Solar Wind, Magnetosheath and Plasma sheet properties using 9+ years of THEMIS data in aberrated GSM frame, and in a normalized coordinate system that takes into account the changes of the magnetopause and bow shock location with respect to changing solar wind conditions. We present statistical results of the plasma sheet density dependence on IMF orientation and other solar wind properties.

Families’ Experiences of Doubling Up After Homelessness

PubMed Central

Bush, Hannah; Shinn, Marybeth

2017-01-01

This study examined experiences of doubling up among families after episodes of homelessness. Doubling up refers to two or more adults or families residing in the same housing unit, which has been an increasing trend in the United States in recent decades. Within the past 14 years, the number of households containing more than one family, related or unrelated, has more than tripled. Although doubling up is increasingly common among families at all income levels, this study seeks to understand the experiences of doubling up among families who have been homeless. Through qualitative interviews with caregivers of 29 families, we analyzed advantages and disadvantages of doubling up with the caregiver’s parent, other family, and nonfamily. Experiences were rated on a four-point scale—(1) mostly negative, (2) negative mixed, (3) positive mixed, and (4) mostly positive—and coded for various positive and negative themes. Overall, we found that doubling up was a generally negative experience for families in our sample, regardless of their relationship to their hosts. Common themes included negative effects on children, undesirable environments, interpersonal tension, and feelings of impermanence and instability. For formerly sheltered families in this study, doubling up after shelter did not resolve their period of housing instability and may be only another stop in an ongoing cycle of homelessness. PMID:29326758

Double Current Sheet Instabilities and the Transition to Turbulence.

NASA Astrophysics Data System (ADS)

Pucci, F.; Velli, M.; Biferale, L.; Sahoo, G.

2016-12-01

The double tearing instability has often been studied as a proxy for the m=1 kink mode in cylindrical plasma. In this paper we describe the results of 3D simulations of an initially periodic double current sheet described by Harris equilibria with a guide field in two cases: 1) zero net helicity and an average magnetic field and 2) a well defined helicity (force free but non constant alpha). We study and contrast the de-stabilization and transition to turbulence for these two cases: we describe spectra, cascades, and possible application to heliospheric phenomena, in particular CME evolution and relaxation. The research leading to these results has received fund- ing from the European Union's Seventh Framework Pro- gramme (FP7/2007-2013) under grant agreement No. 339032

Hydrodynamical instabilities induced by atomic diffusion in F and A stars : Impact on the opacity profile and asteroseimic age determination

NASA Astrophysics Data System (ADS)

Deal, M.; Richard, O.; Vauclair, S.

2017-12-01

Atomic diffusion, including the effect of radiative accelerations on individual elements, leads to important variations of the chemical composition inside the stars. The accumulation in specific layers of the elements, which are the main contributors of the local opacity, leads to hydrodynamical instabilities that modify the internal stellar structure and surface abundances. The modification of the initial chemical composition has important effects on the internal stellar mixing and leads to different surface and internal abundances of the elements. These processes also modify the age determination by asteroseismology.

Diffusion for holographic lattices

NASA Astrophysics Data System (ADS)

Donos, Aristomenis; Gauntlett, Jerome P.; Ziogas, Vaios

2018-03-01

We consider black hole spacetimes that are holographically dual to strongly coupled field theories in which spatial translations are broken explicitly. We discuss how the quasinormal modes associated with diffusion of heat and charge can be systematically constructed in a long wavelength perturbative expansion. We show that the dispersion relation for these modes is given in terms of the thermoelectric DC conductivity and static susceptibilities of the dual field theory and thus we derive a generalised Einstein relation from Einstein's equations. A corollary of our results is that thermodynamic instabilities imply specific types of dynamical instabilities of the associated black hole solutions.

Parametric spatiotemporal oscillation in reaction-diffusion systems.

PubMed

Ghosh, Shyamolina; Ray, Deb Shankar

2016-03-01

We consider a reaction-diffusion system in a homogeneous stable steady state. On perturbation by a time-dependent sinusoidal forcing of a suitable scaling parameter the system exhibits parametric spatiotemporal instability beyond a critical threshold frequency. We have formulated a general scheme to calculate the threshold condition for oscillation and the range of unstable spatial modes lying within a V-shaped region reminiscent of Arnold's tongue. Full numerical simulations show that depending on the specificity of nonlinearity of the models, the instability may result in time-periodic stationary patterns in the form of standing clusters or spatially localized breathing patterns with characteristic wavelengths. Our theoretical analysis of the parametric oscillation in reaction-diffusion system is corroborated by full numerical simulation of two well-known chemical dynamical models: chlorite-iodine-malonic acid and Briggs-Rauscher reactions.

Parametric spatiotemporal oscillation in reaction-diffusion systems

NASA Astrophysics Data System (ADS)

Ghosh, Shyamolina; Ray, Deb Shankar

2016-03-01

We consider a reaction-diffusion system in a homogeneous stable steady state. On perturbation by a time-dependent sinusoidal forcing of a suitable scaling parameter the system exhibits parametric spatiotemporal instability beyond a critical threshold frequency. We have formulated a general scheme to calculate the threshold condition for oscillation and the range of unstable spatial modes lying within a V-shaped region reminiscent of Arnold's tongue. Full numerical simulations show that depending on the specificity of nonlinearity of the models, the instability may result in time-periodic stationary patterns in the form of standing clusters or spatially localized breathing patterns with characteristic wavelengths. Our theoretical analysis of the parametric oscillation in reaction-diffusion system is corroborated by full numerical simulation of two well-known chemical dynamical models: chlorite-iodine-malonic acid and Briggs-Rauscher reactions.

A novel SOI LDMOS with substrate field plate and variable-k dielectric buried layer

NASA Astrophysics Data System (ADS)

Li, Qi; Wen, Yi; Zhang, Fabi; Li, Haiou; Xiao, Gongli; Chen, Yonghe; Fu, Tao

2018-09-01

A novel silicon-on-insulator (SOI) lateral double-diffused metal-oxide-semiconductor (LDMOS) structure has been proposed. The new structure features a substrate field plate (SFP) and a variable-k dielectric buried layer (VKBL). The SFP and VKBL improve the breakdown voltage by introducing new electric field peaks in the surface electric field distribution. Moreover, the SFP reduces the specific ON-resistance through an enhanced auxiliary depletion effect on the drift region. The simulation results indicate that compared to the conventional SOI LDMOS structure, the breakdown voltage is improved from 118 V to 221 V, the specific ON-resistance is decreased from 7.15 mΩ·cm2 to 3.81 mΩ·cm2, the peak value of surface temperature is declined by 38 K.

Double-strand break repair-adox: Restoration of suppressed double-strand break repair during mitosis induces genomic instability

PubMed Central

Terasawa, Masahiro; Shinohara, Akira; Shinohara, Miki

2014-01-01

Double-strand breaks (DSBs) are one of the severest types of DNA damage. Unrepaired DSBs easily induce cell death and chromosome aberrations. To maintain genomic stability, cells have checkpoint and DSB repair systems to respond to DNA damage throughout most of the cell cycle. The failure of this process often results in apoptosis or genomic instability, such as aneuploidy, deletion, or translocation. Therefore, DSB repair is essential for maintenance of genomic stability. During mitosis, however, cells seem to suppress the DNA damage response and proceed to the next G1 phase, even if there are unrepaired DSBs. The biological significance of this suppression is not known. In this review, we summarize recent studies of mitotic DSB repair and discuss the mechanisms of suppression of DSB repair during mitosis. DSB repair, which maintains genomic integrity in other phases of the cell cycle, is rather toxic to cells during mitosis, often resulting in chromosome missegregation and aberration. Cells have multiple safeguards to prevent genomic instability during mitosis: inhibition of 53BP1 or BRCA1 localization to DSB sites, which is important to promote non-homologous end joining or homologous recombination, respectively, and also modulation of the non-homologous end joining core complex to inhibit DSB repair. We discuss how DSBs during mitosis are toxic and the multiple safeguard systems that suppress genomic instability. PMID:25287622

Microfluidic preparation and self diffusion PFG-NMR analysis of monodisperse water-in-oil-in-water double emulsions.

PubMed

Hughes, Eric; Maan, Abid Aslam; Acquistapace, Simone; Burbidge, Adam; Johns, Michael L; Gunes, Deniz Z; Clausen, Pascal; Syrbe, Axel; Hugo, Julien; Schroen, Karin; Miralles, Vincent; Atkins, Tim; Gray, Richard; Homewood, Philip; Zick, Klaus

2013-01-01

Monodisperse water-in-oil-in-water (WOW) double emulsions have been prepared using microfluidic glass devices designed and built primarily from off the shelf components. The systems were easy to assemble and use. They were capable of producing double emulsions with an outer droplet size from 100 to 40 μm. Depending on how the devices were operated, double emulsions containing either single or multiple water droplets could be produced. Pulsed-field gradient self-diffusion NMR experiments have been performed on the monodisperse water-in-oil-in-water double emulsions to obtain information on the inner water droplet diameter and the distribution of the water in the different phases of the double emulsion. This has been achieved by applying regularization methods to the self-diffusion data. Using these methods the stability of the double emulsions to osmotic pressure imbalance has been followed by observing the change in the size of the inner water droplets over time. Copyright © 2012 Elsevier Inc. All rights reserved.

Microbial contamination of mobile phones in a health care setting in Alexandria, Egypt.

PubMed

Selim, Heba Sayed; Abaza, Amani Farouk

2015-01-01

This study aimed at investigating the microbial contamination of mobile phones in a hospital setting. Swab samples were collected from 40 mobile phones of patients and health care workers at the Alexandria University Students' Hospital. They were tested for their bacterial contamination at the microbiology laboratory of the High Institute of Public Health. Quantification of bacteria was performed using both surface spread and pour plate methods. Isolated bacterial agents were identified using standard microbiological methods. Methicillin-resistant Staphylococcus aureus was identified by disk diffusion method described by Bauer and Kirby. Isolated Gram-negative bacilli were tested for being extended spectrum beta lactamase producers using the double disk diffusion method according to the Clinical and Laboratory Standards Institute recommendations. All of the tested mobile phones (100%) were contaminated with either single or mixed bacterial agents. The most prevalent bacterial contaminants were methicillin-resistant S. aureus and coagulase-negative staphylococci representing 53% and 50%, respectively. The mean bacterial count was 357 CFU/ml, while the median was 13 CFU/ml using the pour plate method. The corresponding figures were 2,192 and 1,720 organisms/phone using the surface spread method. Mobile phones usage in hospital settings poses a risk of transmission of a variety of bacterial agents including multidrug-resistant pathogens as methicillin-resistant S. aureus. The surface spread method is an easy and useful tool for detection and estimation of bacterial contamination of mobile phones.

Microbial contamination of mobile phones in a health care setting in Alexandria, Egypt

PubMed Central

Selim, Heba Sayed; Abaza, Amani Farouk

2015-01-01

Aim: This study aimed at investigating the microbial contamination of mobile phones in a hospital setting. Methods: Swab samples were collected from 40 mobile phones of patients and health care workers at the Alexandria University Students’ Hospital. They were tested for their bacterial contamination at the microbiology laboratory of the High Institute of Public Health. Quantification of bacteria was performed using both surface spread and pour plate methods. Isolated bacterial agents were identified using standard microbiological methods. Methicillin-resistant Staphylococcus aureus was identified by disk diffusion method described by Bauer and Kirby. Isolated Gram-negative bacilli were tested for being extended spectrum beta lactamase producers using the double disk diffusion method according to the Clinical and Laboratory Standards Institute recommendations. Results: All of the tested mobile phones (100%) were contaminated with either single or mixed bacterial agents. The most prevalent bacterial contaminants were methicillin-resistant S. aureus and coagulase-negative staphylococci representing 53% and 50%, respectively. The mean bacterial count was 357 CFU/ml, while the median was 13 CFU/ml using the pour plate method. The corresponding figures were 2,192 and 1,720 organisms/phone using the surface spread method. Conclusions: Mobile phones usage in hospital settings poses a risk of transmission of a variety of bacterial agents including multidrug-resistant pathogens as methicillin-resistant S. aureus. The surface spread method is an easy and useful tool for detection and estimation of bacterial contamination of mobile phones. PMID:25699226

Cross-Diffusion Driven Instability for a Lotka-Volterra Competitive Reaction-Diffusion System

NASA Astrophysics Data System (ADS)

Gambino, G.; Lombardo, M. C.; Sammartino, M.

2008-04-01

In this work we investigate the possibility of the pattern formation for a reaction-diffusion system with nonlinear diffusion terms. Through a linear stability analysis we find the conditions which allow a homogeneous steady state (stable for the kinetics) to become unstable through a Turing mechanism. In particular, we show how cross-diffusion effects are responsible for the initiation of spatial patterns. Finally, we find a Fisher amplitude equation which describes the weakly nonlinear dynamics of the system near the marginal stability.

DNA Double-Strand Break Repair as Determinant of Cellular Radiosensitivity to Killing and Target in Radiation Therapy

PubMed Central

Mladenov, Emil; Magin, Simon; Soni, Aashish; Iliakis, George

2013-01-01

Radiation therapy plays an important role in the management of a wide range of cancers. Besides innovations in the physical application of radiation dose, radiation therapy is likely to benefit from novel approaches exploiting differences in radiation response between normal and tumor cells. While ionizing radiation induces a variety of DNA lesions, including base damages and single-strand breaks, the DNA double-strand break (DSB) is widely considered as the lesion responsible not only for the aimed cell killing of tumor cells, but also for the general genomic instability that leads to the development of secondary cancers among normal cells. Homologous recombination repair (HRR), non-homologous end-joining (NHEJ), and alternative NHEJ, operating as a backup, are the major pathways utilized by cells for the processing of DSBs. Therefore, their function represents a major mechanism of radiation resistance in tumor cells. HRR is also required to overcome replication stress – a potent contributor to genomic instability that fuels cancer development. HRR and alternative NHEJ show strong cell-cycle dependency and are likely to benefit from radiation therapy mediated redistribution of tumor cells throughout the cell-cycle. Moreover, the synthetic lethality phenotype documented between HRR deficiency and PARP inhibition has opened new avenues for targeted therapies. These observations make HRR a particularly intriguing target for treatments aiming to improve the efficacy of radiation therapy. Here, we briefly describe the major pathways of DSB repair and review their possible contribution to cancer cell radioresistance. Finally, we discuss promising alternatives for targeting DSB repair to improve radiation therapy and cancer treatment. PMID:23675572

Experimental Observations on a Low Strain Counter-Flow Diffusion Flame: Flow and Bouyancy Effects

NASA Technical Reports Server (NTRS)

Sutula, J. A.; Torero, J. L.; Ezekoye, O. A.

1999-01-01

Diffusion flames are of great interest in fire safety and many industrial processes. The counter-flow configuration provides a constant strain flow, and therefore is ideal to study the structure of diffusion flames. Most studies have concentrated on the high velocity, high strain limit, since buoyantly induced instabilities will disintegrate the planar flame as the velocity decreases. Only recently, experimental studies in microgravity conditions have begun to explore the low strain regimes. Numerical work has shown the coupling between gas phase reaction rates, soot reaction rates, and radiation. For these programs, size, geometry and experimental conditions have been chosen to keep the flame unaffected by the physical boundaries. When the physical boundaries can not be considered infinitely far from the reaction zone discrepancies arise. A computational study that includes boundary effects and accounts for the deviations occurring when the major potential flow assumptions are relaxed was presented by Borlik et al. This development properly incorporates all heat loss terms and shows the possibility of extinction in the low strain regime. A major constraint of studying the low strain regime is buoyancy. Buoyant instabilities have been shown to have a significant effect on the nature of reactants and heat transport, and can introduce instabilities on the flow that result in phenomena such as flickering or fingering. The counter-flow configuration has been shown to provide a flame with no symmetry disrupting instabilities for inlet velocities greater than 50 mm/s. As the velocity approaches this limit, the characteristic length of the experiment has to be reduced to a few millimetres so as to keep the Rayleigh number (Ra(sub L) = (Beta)(g(sub 0))(L(exp 3) del T)/(alpha(v))) below 2000. In this work, a rectangular counter-flow burner was used to study a two-dimensional counter-flow diffusion flame. Flow visualisation and Particle Image Velocimetry served to describe the nature of the stagnation plane for strain rates smaller than 100 (1/s). These experiments were conducted with a non-reacting flow. Video images of a propane air diffusion flame were used to describe the behaviour of a diffusion flame in this regime. Flame geometry and pulsation frequency are described.

Plasma diffusion at the magnetopause - The case of lower hybrid drift waves

NASA Technical Reports Server (NTRS)

Treumann, R. A.; Labelle, J.; Pottelette, R.

1991-01-01

The diffusion expected from the quasi-linear theory of the lower hybrid drift instability at the earth's magnetopause is recalculated. The resulting diffusion coefficient is marginally large enough to explain the thickness of the boundary layer under quiet conditions, based on observational upper limits for the wave intensities. Thus, one possible model for the boundary layer could involve equilibrium between the diffusion arising from lower hybrid waves and various loss processes.

When transcription goes on Holliday: Double Holliday junctions block RNA polymerase II transcription in vitro.

PubMed

Pipathsouk, Anne; Belotserkovskii, Boris P; Hanawalt, Philip C

2017-02-01

Non-canonical DNA structures can obstruct transcription. This transcription blockage could have various biological consequences, including genomic instability and gratuitous transcription-coupled repair. Among potential structures causing transcription blockage are Holliday junctions (HJs), which can be generated as intermediates in homologous recombination or during processing of stalled replication forks. Of particular interest is the double Holliday junction (DHJ), which contains two HJs. Topological considerations impose the constraint that the total number of helical turns in the DNA duplexes between the junctions cannot be altered as long as the flanking DNA duplexes are intact. Thus, the DHJ structure should strongly resist transient unwinding during transcription; consequently, it is predicted to cause significantly stronger blockage than single HJ structures. The patterns of transcription blockage obtained for RNA polymerase II transcription in HeLa cell nuclear extracts were in accordance with this prediction. However, we did not detect transcription blockage with purified T7 phage RNA polymerase; we discuss a possible explanation for this difference. In general, our findings implicate naturally occurring Holliday junctions in transcription arrest. Copyright © 2016 Elsevier B.V. All rights reserved.

Influence of asymmetric magnetic perturbation on the nonlinear evolution of double tearing modes

NASA Astrophysics Data System (ADS)

Xiong, G. Z.; Wang, L.; Li, X. Q.; Liu, H. F.; Tang, C. J.; Huang, J.; Zhang, X.; Wang, X. Q.

2017-06-01

The effects of asymmetric magnetic perturbation on the triggering and evolution of double tearing modes (DTMs) are investigated using nonlinear magnetohydrodynamics simulations in a slab geometry. We find that for reversed magnetic shear plasmas the resistive reconnection process induced by the initial perturbation at one rational surface can drive a new island at the other rational surface with the same mode number. The four typical states of the mode for the time evolution are found, and include: (i) a linear growth stage; (ii) a linear/nonlinear stable stage; (iii) an interactively driving stage; and (iv) a symmetric DTM stage. These differ from previous simulation results. Moreover, nonlinear DTM growth is found to strongly depend on the asymmetric magnetic perturbation, particularly in the early nonlinear phase. The initial perturbation strength scale of island width suggests that the left island enters into a Sweet-Parker growth process when the right island is sufficiently large to effectively drive the other. These results predict that although externally applied magnetic perturbations can suppress the neoclassical tearing mode they can also trigger new instabilities such as asymmetric DTMs.

Ferroelectric and structural instability in double perovskites Me1+Bi3+Me3+Nb5+O6 (Me1+ = Na, K, Rb; Me3+ = Sc, Ga, In, Lu)

NASA Astrophysics Data System (ADS)

Zinenko, V. I.; Zamkova, N. G.; Zhandun, V. S.; Pavlovskii, M. S.

2012-06-01

Within the Gordon-Kim generalized model with regard to the polarizabilities of ions, the lattice constants, the high-frequency permittivity, the Born dynamic charges, and the vibration constants of the crystal lattice are calculated for cation-ordered double perovskites Me1+Bi3+Me3+Nb5+O6. The vibration spectra of all the compounds exhibit two types of instabilities: instability associated with the rotation of the oxygen octahedron and ferroelectric instability. Various combinations of distortions with respect to the rotation mode yield five energetically most favorable distorted phases. The symmetry and the energy characteristics of these phases are discussed. In four of the five phases, the distortions associated with the oxygen octahedron rotation lead to polar phases, thus allowing one to speak of improper ferroelectricity in these compounds. One phase turns out to be nonpolar; however, it contains unstable polar modes such that a displacement along the eigenvectors of these modes gives rise to polarization in the crystal.

Gene encoding the group B streptococcal protein R4, its presence in clinical reference laboratory isolates & R4 protein pepsin sensitivity.

PubMed

Smith, B L; Flores, A; Dechaine, J; Krepela, J; Bergdall, A; Ferrieri, P

2004-05-01

R proteins were first identified by Lancefield in group B Streptococcus (GBS) as resistant to trypsin at pH8 and sensitive to pepsin at pH2. The R4 protein found predominantly in type III and some type II and V invasive isolates conforms to these criteria. The Rib protein, although structurally and epidemiologically similar to R4, was reported as resistant to both proteases. We report here the gene encoding the R4 protein from a type III group B streptococcal isolate (76-043) well characterized in our laboratory. Trypsin extracted GBS proteins were assayed for protease sensitivities by double-diffusion Ouchterlony using varying conditions for the enzyme pepsin. Standard haemoglobin assay was used to examine pepsin enzymatic activity. Thirty clinical isolates of varying protein profiles identified by double-diffusion from our reference strain laboratory were screened by PCR and Southern technique. SDS-PAGE gel purified R4 amino acid sequences were determined and used to design oligonucleotide primers for screening a 76-043 genomic library. R4 was sensitive to pepsin at pH2 but appeared resistant at pH4, the reported pH used for Rib. By standard haemoglobin assay and trypsin extract studies of R4 protein, pepsin was shown to be active at pH2, yet easily inactivated; assays of GBS surface proteins are critical at pH2. Of the amino acids initially sequenced from R4, 88 per cent (61/69) showed identity to Rib; the r4 nucleotide sequence was identical to that of rib. All isolates with strong positive protein reactions for R4 were positive in both PCR and Southern technique, whereas isolates expressing alpha, beta, R1/R4, and R5 (BPS) protein profiles were not. Sequenced PCR products aligned with identity to the R4 and Rib nucleotide sequences and confirmed the identity of these proteins and their molecular sequences.

[Antibiotic susceptibility and occurrence of ESBL, IBL and MBL in Pseudomonas aeruginosa strains].

PubMed

Wolska, Katarzyna; Jakubczak, Antoni; Soszyńska, Agnieszka

2008-01-01

The aim of this study was to evaluate the drug susceptibility of P. aeruginosa strains and to detect strains producing inducible beta-lactamases (IBL), extended-spectrum beta-lactamases (ESBL), and metallo-beta-lactamases (MBL). During 6 month (October 2005 - March 2006), 66 strains of P. aeruginosa strains were cultured from clinical specimens obtained from patients of two of hospitals in Siedlce and from patients of outpatient clinics. All the strains were identified in the automatic ATB (bio Mérieux). The susceptibility of bacteria to antibiotics was tested by standard disc diffusion method. The majority of strains were susceptible to meropenem (89.4%), piperacillin combined with tazobactam (84.8%), ciprofloxacin (84.8%) and piperacillin (83.3%). Many of our strains were resistant to carbenicillin (69.7%), mezlocillin (45.5%), gentamicin (42.4%) and netylmicin (30.3%). 6 strains (9.1%) were multidrug-resistant (MDR). Inducible beta-lactamases were detected with the use double disc method according to Sanders and Sanders. ESBL-producing strains were detected with double disc test (DDST) according to Jarlier et al. These strains were identified as ESBL-positive on the basis of the DDST were also determined using a double disc (DD) test according to Appleton. Production of metallo-beta-lactamases (MBL) was examined with the use of Etest MBL (AB Biodisk, Sweden) and the double disc test according to Arakava et al. Sixty-five IBL-producing strains (98.5% of all strains) and three strains (4.5%) with MBL activity were detected. Strains producing extended beta-lactamases (ESBL) were not found.

Fingering instabilities in bacterial community phototaxis

NASA Astrophysics Data System (ADS)

Vps, Ritwika; Man Wah Chau, Rosanna; Casey Huang, Kerwyn; Gopinathan, Ajay

Synechocystis sp PCC 6803 is a phototactic cyanobacterium that moves directionally in response to a light source. During phototaxis, these bacterial communities show emergent spatial organisation resulting in the formation of finger-like projections at the propagating front. In this study, we propose an analytical model that elucidates the underlying physical mechanisms which give rise to these spatial patterns. We describe the migrating front during phototaxis as a one-dimensional curve by considering the effects of phototactic bias, diffusion and surface tension. By considering the propagating front as composed of perturbations to a flat solution and using linear stability analysis, we predict a critical bias above which the finger-like projections appear as instabilities. We also predict the wavelengths of the fastest growing mode and the critical mode above which the instabilities disappear. We validate our predictions through comparisons to experimental data obtained by analysing images of phototaxis in Synechocystis communities. Our model also predicts the observed loss of instabilities in taxd1 mutants (cells with inactive TaxD1, an important photoreceptor in finger formation), by considering diffusion in mutually perpendicular directions and a lower, negative bias.

Double-bundle ACL reconstruction can improve rotational stability.

PubMed

Yagi, Masayoshi; Kuroda, Ryosuke; Nagamune, Kouki; Yoshiya, Shinichi; Kurosaka, Masahiro

2007-01-01

Double-bundle anterior cruciate ligament (ACL) reconstruction reproduces anteromedial and posterolateral bundles, and thus has theoretical advantages over conventional single-bundle reconstruction in controlling rotational torque in vitro. However, its superiority in clinical practice has not been proven. We analyzed rotational stability with three reconstruction techniques in 60 consecutive patients who were randomly divided into three groups (double-bundle, anteromedial single-bundle, posterolateral single-bundle). In the reconstructive procedure, the hamstring tendon was harvested and used as a free tendon graft. Followup examinations were performed 1 year after surgery. Anteroposterior laxity of the knee was examined with a KT-1000 arthrometer, whereas rotatory instability, as elicited by the pivot shift test, was assessed using a new measurement system incorporating three-dimensional electromagnetic sensors. Routine clinical evaluations, including KT examination, demonstrated no differences among the three groups. However, using the new measurement system, patients with double-bundle ACL reconstruction showed better pivot shift control of complex instability than patients with anteromedial and posterolateral single-bundle reconstruction.

Fokker-Planck analysis of transverse collective instabilities in electron storage rings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindberg, Ryan R.

We analyze single bunch transverse instabilities due to wakefields using a Fokker-Planck model. We first expand on the work of T. Suzuki, Part. Accel. 12, 237 (1982) to derive the theoretical model including chromaticity, both dipolar and quadrupolar transverse wakefields, and the effects of damping and diffusion due to the synchrotron radiation. We reduce the problem to a linear matrix equation, whose eigenvalues and eigenvectors determine the collective stability of the beam. We then show that various predictions of the theory agree quite well with results from particle tracking simulations, including the threshold current for transverse instability and the profilemore » of the unstable mode. In particular, we find that predicting collective stability for high energy electron beams at moderate to large values of chromaticity requires the full Fokker-Planck analysis to properly account for the effects of damping and diffusion due to synchrotron radiation.« less

Instabilities in the Sun-Jupiter-Asteroid three body problem

NASA Astrophysics Data System (ADS)

Urschel, John C.; Galante, Joseph R.

2013-03-01

We consider dynamics of a Sun-Jupiter-Asteroid system, and, under some simplifying assumptions, show the existence of instabilities in the motions of an asteroid. In particular, we show that an asteroid whose initial orbit is far from the orbit of Mars can be gradually perturbed into one that crosses Mars' orbit. Properly formulated, the motion of the asteroid can be described as a Hamiltonian system with two degrees of freedom, with the dynamics restricted to a "large" open region of the phase space reduced to an exact area preserving map. Instabilities arise in regions where the map has no invariant curves. The method of MacKay and Percival is used to explicitly rule out the existence of these curves, and results of Mather abstractly guarantee the existence of diffusing orbits. We emphasize that finding such diffusing orbits numerically is quite difficult, and is outside the scope of this paper.

Low cost fuel cell diffusion layer configured for optimized anode water management

DOEpatents

Owejan, Jon P; Nicotera, Paul D; Mench, Matthew M; Evans, Robert E

2013-08-27

A fuel cell comprises a cathode gas diffusion layer, a cathode catalyst layer, an anode gas diffusion layer, an anode catalyst layer and an electrolyte. The diffusion resistance of the anode gas diffusion layer when operated with anode fuel is higher than the diffusion resistance of the cathode gas diffusion layer. The anode gas diffusion layer may comprise filler particles having in-plane platelet geometries and be made of lower cost materials and manufacturing processes than currently available commercial carbon fiber substrates. The diffusion resistance difference between the anode gas diffusion layer and the cathode gas diffusion layer may allow for passive water balance control.

Gravitational instability of filamentary molecular clouds, including ambipolar diffusion; non-isothermal filament

NASA Astrophysics Data System (ADS)

Hosseinirad, Mohammad; Abbassi, Shahram; Roshan, Mahmood; Naficy, Kazem

2018-04-01

Recent observations of the filamentary molecular clouds show that their properties deviate from the isothermal equation of state. Theoretical investigations proposed that the logatropic and the polytropic equations of state with negative indexes can provide a better description for these filamentary structures. Here, we aim to compare the effects of these softer non-isothermal equations of state with their isothermal counterpart on the global gravitational instability of a filamentary molecular cloud. By incorporating the ambipolar diffusion, we use the non-ideal magnetohydrodynamics framework for a filament that is threaded by a uniform axial magnetic field. We perturb the fluid and obtain the dispersion relation both for the logatropic and polytropic equations of state by taking the effects of magnetic field and ambipolar diffusion into account. Our results suggest that, in absence of the magnetic field, a softer equation of state makes the system more prone to gravitational instability. We also observed that a moderate magnetic field is able to enhance the stability of the filament in a way that is sensitive to the equation of state in general. However, when the magnetic field is strong, this effect is suppressed and all the equations of state have almost the same stability properties. Moreover, we find that for all the considered equations of state, the ambipolar diffusion has destabilizing effects on the filament.

Prolonged Particulate Hexavalent Chromium Exposure Suppresses Homologous Recombination Repair in Human Lung Cells.

PubMed

Browning, Cynthia L; Qin, Qin; Kelly, Deborah F; Prakash, Rohit; Vanoli, Fabio; Jasin, Maria; Wise, John Pierce

2016-09-01

Genomic instability is one of the primary models of carcinogenesis and a feature of almost all cancers. Homologous recombination (HR) repair protects against genomic instability by maintaining high genomic fidelity during the repair of DNA double strand breaks. The defining step of HR repair is the formation of the Rad51 nucleofilament, which facilitates the search for a homologous sequence and invasion of the template DNA strand. Particulate hexavalent chromium (Cr(VI)), a human lung carcinogen, induces DNA double strand breaks and chromosome instability. Since the loss of HR repair increases Cr(VI)-induced chromosome instability, we investigated the effect of extended Cr(VI) exposure on HR repair. We show acute (24 h) Cr(VI) exposure induces a normal HR repair response. In contrast, prolonged (120 h) exposure to particulate Cr(VI) inhibited HR repair and Rad51 nucleofilament formation. Prolonged Cr(VI) exposure had a profound effect on Rad51, evidenced by reduced protein levels and Rad51 mislocalization to the cytoplasm. The response of proteins involved in Rad51 nuclear import and nucleofilament formation displayed varying responses to prolonged Cr(VI) exposure. BRCA2 formed nuclear foci after prolonged Cr(VI) exposure, while Rad51C foci formation was suppressed. These results suggest that particulate Cr(VI), a major chemical carcinogen, inhibits HR repair by targeting Rad51, causing DNA double strand breaks to be repaired by a low fidelity, Rad51-independent repair pathway. These results further enhance our understanding of the underlying mechanism of Cr(VI)-induced chromosome instability and thus, carcinogenesis. © The Author 2016. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

The Effects of Self-Discharge on the Performance of Symmetric Electric Double-Layer Capacitors and Active Electrolyte-Enhanced Supercapacitors: Insights from Modeling and Simulation

NASA Astrophysics Data System (ADS)

Ike, Innocent S.; Sigalas, Iakovos; Iyuke, Sunny E.

2017-02-01

The effects of self-discharge on the performance of symmetric electric double-layer capacitors (EDLCs) and active electrolyte-enhanced supercapacitors were examined by incorporating self-discharge into electrochemical capacitor models during charging and discharging. The sources of self-discharge in capacitors were side reactions or redox reactions and several impurities and electric double-layer (EDL) instability. The effects of self-discharge during capacitor storage was negligible since it took a fully charged capacitor a minimum of 14.0 days to be entirely discharged by self-discharge in all conditions studied, hence self-discharge in storage condition can be ignored. The first and second charge-discharge cycle energy efficiencies η_{{{{E}}1}} and η_{{{{E}}2}} of a capacitor of electrode effective conductivity α1 = 0.05 S/cm with only EDL instability self-discharge with current density J_{{VR}} = 1.25 × 10-3 A/cm2 were 72.33% and 72.34%, respectively. Also, energy efficiencies η_{{{{E}}1}} and η_{{{{E}}2}} of a similar capacitor with both side reactions and redox reactions and EDL instability self-discharges with current densities J_{{VR}} = 0.00125 A/cm2 and J_{{{{VR}}1}} = 0.0032 A/cm2 were 38.13% and 38.14% respectively, compared with 84.24% and 84.25% in a similar capacitor without self-discharge. A capacitor with only EDL instability self-discharge and that with both side reactions and redox reactions and EDL instability self-discharge lost 9.73 Wh and 28.38 Wh of energy, respectively, through self-discharge during charging and discharging. Hence, EDLCs charging and discharging time is significantly dependent on the self-discharge rate which are too large to be ignored.

Parallel electric fields in extragalactic jets - Double layers and anomalous resistivity in symbiotic relationships

NASA Technical Reports Server (NTRS)

Borovsky, J. E.

1986-01-01

After examining the properties of Coulomb-collision resistivity, anomalous (collective) resistivity, and double layers, a hybrid anomalous-resistivity/double-layer model is introduced. In this model, beam-driven waves on both sides of a double layer provide electrostatic plasma-wave turbulence that greatly reduces the mobility of charged particles. These regions then act to hold open a density cavity within which the double layer resides. In the double layer, electrical energy is dissipated with 100 percent efficiency into high-energy particles, creating conditions optimal for the collective emission of polarized radio waves.

Modeling resistive wall modes and disruptive instabilities with M3D-C1

NASA Astrophysics Data System (ADS)

Ferraro, Nm; Jardin, Sc; Pfefferle, D.

2016-10-01

Disruptive instabilities pose a significant challenge to the tokamak approach to magnetic fusion energy, and must be reliably avoided in a successful reactor. These instabilities generally involve rapid, global changes to the magnetic field, and electromagnetic interaction with surrounding conducting structures. Here we apply the extended-MHD code M3D-C1 to calculate the stability and evolution of disruptive modes, including their interaction with external conducting structures. The M3D-C1 model includes the effects of resistivity, equilibrium rotation, and resistive walls of arbitrary thickness, each of which may play important roles in the stability and evolution of disruptive modes. The strong stabilizing effect of rotation on resistive wall modes is explored and compared with analytic theory. The nonlinear evolution of vertical displacement events is also considered, including the evolution of non-axisymmetric instabilities that may arise during the current-quench phase of the disruption. It is found that the non-axisymmetric stability of the plasma during a VDE depends strongly on the thermal history of the plasma. This work is supported by US DOE Grant DE-AC02-09CH11466 and the SciDAC Center for Extended MHD Modeling.

Delay-induced Turing-like waves for one-species reaction-diffusion model on a network

NASA Astrophysics Data System (ADS)

Petit, Julien; Carletti, Timoteo; Asllani, Malbor; Fanelli, Duccio

2015-09-01

A one-species time-delay reaction-diffusion system defined on a complex network is studied. Traveling waves are predicted to occur following a symmetry-breaking instability of a homogeneous stationary stable solution, subject to an external nonhomogeneous perturbation. These are generalized Turing-like waves that materialize in a single-species populations dynamics model, as the unexpected byproduct of the imposed delay in the diffusion part. Sufficient conditions for the onset of the instability are mathematically provided by performing a linear stability analysis adapted to time-delayed differential equations. The method here developed exploits the properties of the Lambert W-function. The prediction of the theory are confirmed by direct numerical simulation carried out for a modified version of the classical Fisher model, defined on a Watts-Strogatz network and with the inclusion of the delay.

Aeroelastic Flutter Behavior of Cantilever within a Nozzle-Diffuser Geometry

NASA Astrophysics Data System (ADS)

Tosi, Luis Phillipe; Colonius, Tim; Sherrit, Stewart; Lee, Hyeong Jae

2015-11-01

Aeroelastic flutter arises when the motion of a structure and its surrounding flowing fluid are coupled in a constructive manner, causing large amplitudes of vibration in the immersed solid. A cantilevered beam in axial flow within a nozzle-diffuser geometry exhibits interesting resonance behavior that presents good prospects for internal flow energy harvesting. Different modes can be excited as a function of throat velocity, nozzle geometry, fluid and cantilever material parameters. This work explores the relationship between the aeroelastic flutter instability boundaries and relevant non-dimensional parameters via experiments. Results suggest that for a linear expansion diffuser geometry, a non-dimensional stiffness, non-dimensional mass, and non-dimensional throat size are the critical parameters in mapping the instability. This map can serve as a guide to future work concerning possible electrical output and failure prediction in energy harvesters.

Coherent vs. incoherent pairing in 2D systems near magnetic instability

NASA Astrophysics Data System (ADS)

Abanov, Ar.; Chubukov, A. V.; Finkel'stein, A. M.

2001-05-01

We study the superconductivity in 2D fermionic systems near antiferromagnetic instability, assuming that the pairing is mediated by spin fluctuations. This pairing involves fully incoherent fermions and diffusive spin excitations. We show that the competition between fermionic incoherence and strong pairing interaction yields the pairing instability temperature Tins which increases and saturates as the magnetic correlation length ξ → ∞. We argue that in this quantum-critical regime the pairing problem is qualitatively different from the BCS one.

The influence of cosmic rays on the stability and large-scale dynamics of the interstellar medium

NASA Astrophysics Data System (ADS)

Kuznetsov, V. D.

1986-06-01

The diffusion-convection formulation is used to study the influence of galactic cosmic rays on the stability and dynamics of the interstellar medium which is supposedly kept in equilibrium by the gravitational field of stars. It is shown that the influence of cosmic rays on the growth rate of MHD instability depends largely on a dimensionless parameter expressing the ratio of the characteristic acoustic time scale to the cosmic-ray diffusion time. If this parameter is small, the cosmic rays will decelerate the build-up of instabilities, thereby stabilizing the system; in contrast, if the parameter is large, the system will be destabilized.

Effects of anisotropic turbulent thermal diffusion on spherical magnetoconvection in the Earth's core

NASA Astrophysics Data System (ADS)

Ivers, D. J.; Phillips, C. G.

2018-03-01

We re-consider the plate-like model of turbulence in the Earth's core, proposed by Braginsky and Meytlis (1990), and show that it is plausible for core parameters not only in polar regions but extends to mid- and low-latitudes where rotation and gravity are not parallel, except in a very thin equatorial layer. In this model the turbulence is highly anisotropic with preferred directions imposed by the Earth's rotation and the magnetic field. Current geodynamo computations effectively model sub-grid scale turbulence by using isotropic viscous and thermal diffusion values significantly greater than the molecular values of the Earth's core. We consider a local turbulent dynamo model for the Earth's core in which the mean magnetic field, velocity and temperature satisfy the Boussinesq induction, momentum and heat equations with an isotropic turbulent Ekman number and Roberts number. The anisotropy is modelled only in the thermal diffusion tensor with the Earth's rotation and magnetic field as preferred directions. Nonlocal organising effects of gravity and rotation (but not aspect ratio in the Earth's core) such as an inverse cascade and nonlocal transport are assumed to occur at longer length scales, which computations may accurately capture with sufficient resolution. To investigate the implications of this anisotropy for the proposed turbulent dynamo model we investigate the linear instability of turbulent magnetoconvection on length scales longer than the background turbulence in a rotating sphere with electrically insulating exterior for no-slip and isothermal boundary conditions. The equations are linearised about an axisymmetric basic state with a conductive temperature, azimuthal magnetic field and differential rotation. The basic state temperature is a function of the anisotropy and the spherical radius. Elsasser numbers in the range 1-20 and turbulent Roberts numbers 0.01-1 are considered for both equatorial symmetries of the magnetic basic state. It is found that anisotropic turbulent thermal diffusivity has a strong destabilising effect on magneto-convective instabilities, which may relax the tight energy budget constraining geodynamo models. The enhanced instability is not due to a reduction of the total diffusivity. The anisotropy also strengthens instabilities which break the symmetry of the underlying state, which may facilitate magnetic field reversal. Geostrophic flow appears to suppress the symmetry breaking modes and magnetic instabilities. Through symmetry breaking and the geostrophic flow the anisotropy may provide a mechanism of magnetic field reversal and its suppression in computational dynamo models.

Combinatorial BTK and MALT1 inhibition augments killing of CD79 mutant diffuse large B cell lymphoma

PubMed Central

Nagel, Daniel; Bognar, Miriam; Eitelhuber, Andrea C.; Kutzner, Kerstin; Vincendeau, Michelle; Krappmann, Daniel

2015-01-01

Survival of activated B cell-subtype (ABC) of diffuse large B cell lymphoma (DLBCL) is driven by chronic B cell receptor (BCR) signaling that activates the canonical NF-κB pathway. Inhibition of BTK by Ibrutinib has been shown to kill ABC DLBCL cells that carry activating mutations in the BCR adaptor CD79. However, mutations in BTK or in downstream components such as CARMA1/CARD11 can render lymphomas Ibrutinib resistant. Therefore, we assessed here the simultaneous inhibition of BTK and the protease MALT1 that acts downstream of CARMA1 and is essential for ABC DLBCL tumor growth. We show that in CD79 mutant cells BTK is a crucial upstream regulator of MALT1, but dispensable in CARMA1 mutant ABC DLBCL. Combined inhibition of BTK by Ibrutinib and MALT1 by S-Mepazine additively impaired MALT1 cleavage activity and expression of NF-κB pro-survival factors. Thereby, combinatorial Ibrutinib and S-Mepazine treatment enhanced killing of CD79 mutant ABC DLBCL cells. Moreover, while expression of oncogenic CARMA1 in CD79 mutant cells conferred Ibrutinib resistance, double mutant cells were still sensitive to MALT1 inhibition by S-Mepazine. Thus, based on the genetic background combinatorial BTK and MALT1 inhibition may improve effectiveness of therapeutic treatment and reduce the chances for the development of drug resistances. PMID:26540570

Anomalous resistivity and the origin of heavy mass in the two-band Hubbard model with one narrow band

NASA Astrophysics Data System (ADS)

Kagan, M. Yu.; Val'kov, V. V.

2011-07-01

We search for marginal Fermi-liquid behavior [1] in the two-band Hubbard model with one narrow band. We consider the limit of low electron densities in the bands and strong intraband and interband Hubbard interactions. We analyze the influence of electron polaron effect [2] and other mechanisms of mass enhancement (related to momentum dependence of the self-energies) on the effective mass and scattering times of light and heavy components in the clean case (electron-electron scattering and no impurities). We find the tendency towards phase separation (towards negative partial compressibility of heavy particles) in the 3D case for a large mismatch between the densities of heavy and light bands in the strong-coupling limit. We also observe that for low temperatures and equal densities, the homogeneous state resistivity R( T) ˜ T 2 behaves in a Fermi-liquid fashion in both 3D and 2D cases. For temperatures higher than the effective bandwidth for heavy electrons T > W {*/ h }, the coherent behavior of the heavy component is totally destroyed. The heavy particles move diffusively in the surrounding of light particles. At the same time, the light particles scatter on the heavy ones as if on immobile (static) impurities. In this regime, the heavy component is marginal, while the light one is not. The resistivity saturates for T > W {*/ h } in the 3D case. In 2D, the resistivity has a maximum and a localization tail due to weak-localization corrections of the Altshuler-Aronov type [3]. Such behavior of resistivity could be relevant for some uranium-based heavy-fermion compounds like UNi2Al3 in 3D and for some other mixed-valence compounds possibly including layered manganites in 2D. We also briefly consider the superconductive (SC) instability in the model. The leading instability is towards the p-wave pairing and is governed by the enhanced Kohn-Luttinger [4] mechanism of SC at low electron density. The critical temperature corresponds to the pairing of heavy electrons via polarization of the light ones in 2D.

Anomalous resistivity and superconductivity in the two-band Hubbard model with one narrow band (Review)

NASA Astrophysics Data System (ADS)

Kagan, M. Yu.; Valkov, V. V.

2011-01-01

We search for marginal Fermi-liquid behavior in the two-band Hubbard model with one narrow band. We consider the limit of low electron densities in the bands and strong intraband and interband Hubbard interactions. We analyze the influence of electron-polaron effects and other mechanisms for mass-enhancement (related to the momentum dependence of the self-energies) on the effective mass and scattering times of light and heavy components in the clean case (electron-electron scattering and no impurities). We find a tendency towards phase separation (towards negative partial compressibility of heavy particles) in the 3D case with a large mismatch between the densities of heavy and light bands in the strong coupling limit. We also find that for low temperatures and equal densities, the resistivity in a homogeneous state R(T )∝T2 behaves as a Fermi-liquid in both 3D and 2D. For temperatures greater than the effective bandwidth for heavy electrons T >Wh*, the coherence of the heavy component breaks down completely. The heavy particles move diffusively in the surrounding light particles. At the same time, light particles scatter on heavy particles as if on immobile (static) impurities. Under these conditions, the heavy component is marginal, while the light component is not. The resistivity approaches saturation for T >Wh* in the 3D case. In 2D the resistivity has a maximum and a localization tail owing to weak-localization corrections of the Altshuler-Aronov type. This behavior of resistivity in 3D could be relevant for some uranium-based heavy-fermion compounds such as UNi2Al3 and in 2D, for some other mixed-valence compounds, possibly including layered manganites. We also consider briefly the superconductive (SC) instability in this model. The leading instability tends to p-wave pairing and is governed by an enhanced Kohn-Luttinger mechanism for SC at low electron densities. The critical temperature corresponds to the pairing of heavy electrons via polarization of the light electrons in 2D.

Toroidal modelling of resistive internal kink and fishbone instabilities

NASA Astrophysics Data System (ADS)

Wu, Tingting; He, Hongda; Liu, Yueqiang; Liu, Yue; Hao, G. Z.; Zhu, Jinxia

2018-05-01

The influence of energetic particles and plasma resistivity on the n =1 ( n is the toroidal mode number) internal kink and fishbone modes in tokamak plasmas is numerically investigated, using the full toroidal, resistive magnetohydrodynamic-kinetic hybrid stability code MARS-K [Liu et al., Phys. Plasmas 15 112503 (2008)]. The results show that energetic particles can either stabilize or destabilize the ideal internal kink mode, depending on the radial profiles of the particles' density and pressure. Resistive fishbones with and without an ideal wall are investigated. It is found that, in the presence of energetic particles as well as plasma resistivity, two branches of unstable roots exist, for a plasma which is ideally stable to the internal kink instability. One is the resistive internal kink mode. The other is the resistive fishbone mode. These two-branch solutions show similar behaviors, independent of whether the initial ideal kink stability is due to an ideal wall stabilization for high-beta plasmas, or due to a stable equilibrium below the Bussac pressure limit. For a realistic toroidal plasma, the resistive internal kink is the dominant instability, which grows much faster than the resistive fishbone. The plasma resistivity destabilizes the resistive internal kink while stabilizes the resistive fishbone. Systematic comparison with an analytic model qualitatively confirms the MARS-K results. Compared to analytic models based on the perturbative approach, MARS-K offers an improved physics model via self-consistent treatment of coupling between the fluid and kinetic effects due to energetic particles.

Double-strand break repair-adox: Restoration of suppressed double-strand break repair during mitosis induces genomic instability.

PubMed

Terasawa, Masahiro; Shinohara, Akira; Shinohara, Miki

2014-12-01

Double-strand breaks (DSBs) are one of the severest types of DNA damage. Unrepaired DSBs easily induce cell death and chromosome aberrations. To maintain genomic stability, cells have checkpoint and DSB repair systems to respond to DNA damage throughout most of the cell cycle. The failure of this process often results in apoptosis or genomic instability, such as aneuploidy, deletion, or translocation. Therefore, DSB repair is essential for maintenance of genomic stability. During mitosis, however, cells seem to suppress the DNA damage response and proceed to the next G1 phase, even if there are unrepaired DSBs. The biological significance of this suppression is not known. In this review, we summarize recent studies of mitotic DSB repair and discuss the mechanisms of suppression of DSB repair during mitosis. DSB repair, which maintains genomic integrity in other phases of the cell cycle, is rather toxic to cells during mitosis, often resulting in chromosome missegregation and aberration. Cells have multiple safeguards to prevent genomic instability during mitosis: inhibition of 53BP1 or BRCA1 localization to DSB sites, which is important to promote non-homologous end joining or homologous recombination, respectively, and also modulation of the non-homologous end joining core complex to inhibit DSB repair. We discuss how DSBs during mitosis are toxic and the multiple safeguard systems that suppress genomic instability. © 2014 The Authors. Cancer Science published by Wiley Publishing Asia Pty Ltd on behalf of Japanese Cancer Association.

Bias stress instability of double-gate a-IGZO TFTs on polyimide substrate

NASA Astrophysics Data System (ADS)

Cho, Won-Ju; Ahn, Min-Ju

2017-09-01

In this study, flexible double-gate thin-film transistor (TFT)-based amorphous indium-galliumzinc- oxide (a-IGZO) was fabricated on a polyimide substrate. Double-gate operation with connected front and back gates was compared with a single-gate operation. As a result, the double-gate a- IGZO TFT exhibited enhanced electrical characteristics as well as improved long-term reliability. Under positive- and negative-bias temperature stress, the threshold voltage shift of the double-gate operation was much smaller than that of the single-gate operation.

Double plasma resonance instability as a source of solar zebra emission

NASA Astrophysics Data System (ADS)

Benáček, J.; Karlický, M.

2018-03-01

Context. The double plasma resonance (DPR) instability plays a basic role in the generation of solar radio zebras. In the plasma, consisting of the loss-cone type distribution of hot electrons and much denser and colder background plasma, this instability generates the upper-hybrid waves, which are then transformed into the electromagnetic waves and observed as radio zebras. Aims: In the present paper we numerically study the double plasma resonance instability from the point of view of the zebra interpretation. Methods: We use a 3-dimensional electromagnetic particle-in-cell (3D PIC) relativistic model. We use this model in two versions: (a) a spatially extended "multi-mode" model and (b) a spatially limited "specific-mode" model. While the multi-mode model is used for detailed computations and verifications of the results obtained by the "specific-mode" model, the specific-mode model is used for computations in a broad range of model parameters, which considerably save computational time. For an analysis of the computational results, we developed software tools in Python. Results: First using the multi-mode model, we study details of the double plasma resonance instability. We show how the distribution function of hot electrons changes during this instability. Then we show that there is a very good agreement between results obtained by the multi-mode and specific-mode models, which is caused by a dominance of the wave with the maximal growth rate. Therefore, for computations in a broad range of model parameters, we use the specific-mode model. We compute the maximal growth rates of the double plasma resonance instability with a dependence on the ratio between the upper-hybrid ωUH and electron-cyclotron ωce frequency. We vary temperatures of both the hot and background plasma components and study their effects on the resulting growth rates. The results are compared with the analytical ones. We find a very good agreement between numerical and analytical growth rates. We also compute saturation energies of the upper-hybrid waves in a very broad range of parameters. We find that the saturation energies of the upper-hybrid waves show maxima and minima at almost the same values of ωUH/ωce as the growth rates, but with a higher contrast between them than the growth rate maxima and minima. The contrast between saturation energy maxima and minima increases when the temperature of hot electrons increases. Furthermore, we find that the saturation energy of the upper-hybrid waves is proportional to the density of hot electrons. The maximum saturated energy can be up to one percent of the kinetic energy of hot electrons. Finally we find that the saturation energy maxima in the interval of ωUH/ωce = 3-18 decrease according to the exponential function. All these findings can be used in the interpretation of solar radio zebras.

Barotropic instability with divergence - Theory and applications to Venus

NASA Technical Reports Server (NTRS)

Dobrovolskis, Anthony R.; Diner, David J.

1990-01-01

IR images of Venus reveal a curious double-lobed hot spot in the polar region. Elson (1982) has suggested that this dipole represents a barotropic instability associated with a high-latitude jet. Unfortunately, the classical theory of barotropic instability cannot predict temperature variations. This paper generalizes the theory to include horizontal divergence, vertical motions, and temperature variations, and applies it to the stratosphere of Venus. The fastest-growing barotropic instability in the nominal model matches the observed dipole in period and horizontal temperature pattern. The accompanying wind variations are comparable to the speed of the mean jet, indicating strong nonlinear effects. It is concluded that the Venus dipole may represent the self-limited stage of a barotropic instability with divergence.

Photobleachable Diazonium Salt-Phenolic Resin Two-Layer Resist System

NASA Astrophysics Data System (ADS)

Uchino, Shou-ichi; Iwayanagi, Takao; Hashimoto, Michiaki

1988-01-01

This article describes a new negative two-layer photoresist system formed by a simple, successive spin-coating method. An aqueous acetic acid solution of diazonium salt and poly(N-vinylpyrrolidone) is deposited so as to contact a phenolic resin film spin-coated on a silicon wafer. The diazonium salt diffuses into the phenolic resin layer after standing for several minutes. The residual solution on the phenolic resin film doped with diazonium salt is spun to form the diazonium salt-poly(N-vinylpyrrolidone) top layer. This forms a uniform two-layer resist without phase separation or striation. Upon UV exposure, the diazonium salt in the top layer bleaches to act as a CEL dye, while the diazonium salt in the bottom layer decomposes to cause insolubilization. Half μm line-and-space patterns are obtained with an i-line stepper using 4-diazo-N,N-dimethylaniline chloride zinc chloride double salt as the diazonium salt and a cresol novolac resin for the bottom polymer layer. The resist formation processes, insolubilization mechanism, and the resolution capability of the new two-layer resist are discussed.

Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH 3NH 3PbI 3 : Implications on Solar Cell Degradation and Choice of Electrode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ming, Wenmei; Yang, Dongwen; Li, Tianshu

Solar cells based on methylammonium lead triiodide (MAPbI 3) have shown remarkable progress in recent years and have demonstrated efficiencies greater than 20%. However, the long-term stability of MAPbI 3-based solar cells has yet to be achieved. Besides the well-known chemical and thermal instabilities, significant native ion migration in lead halide perovskites leads to current–voltage hysteresis and photoinduced phase segregation. Recently, it is further revealed that, despite having excellent chemical stability, the Au electrode can cause serious solar cell degradation due to Au diffusion into MAPbI 3. In addition to Au, many other metals have been used as electrodes inmore » MAPbI 3 solar cells. However, how the external metal impurities introduced by electrodes affect the long-term stability of MAPbI 3 solar cells has rarely been studied. A comprehensive study of formation energetics and diffusion dynamics of a number of noble and transition metal impurities (Au, Ag, Cu, Cr, Mo, W, Co, Ni, Pd) in MAPbI 3 based on first-principles calculations is reported herein. The results uncover important general trends of impurity formation and diffusion in MAPbI 3 and provide useful guidance for identifying the optimal metal electrodes that do not introduce electrically active impurity defects in MAPbI 3 while having low resistivities and suitable work functions for carrier extraction.« less

Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH3NH3PbI3: Implications on Solar Cell Degradation and Choice of Electrode.

PubMed

Ming, Wenmei; Yang, Dongwen; Li, Tianshu; Zhang, Lijun; Du, Mao-Hua

2018-02-01

Solar cells based on methylammonium lead triiodide (MAPbI 3 ) have shown remarkable progress in recent years and have demonstrated efficiencies greater than 20%. However, the long-term stability of MAPbI 3 -based solar cells has yet to be achieved. Besides the well-known chemical and thermal instabilities, significant native ion migration in lead halide perovskites leads to current-voltage hysteresis and photoinduced phase segregation. Recently, it is further revealed that, despite having excellent chemical stability, the Au electrode can cause serious solar cell degradation due to Au diffusion into MAPbI 3 . In addition to Au, many other metals have been used as electrodes in MAPbI 3 solar cells. However, how the external metal impurities introduced by electrodes affect the long-term stability of MAPbI 3 solar cells has rarely been studied. A comprehensive study of formation energetics and diffusion dynamics of a number of noble and transition metal impurities (Au, Ag, Cu, Cr, Mo, W, Co, Ni, Pd) in MAPbI 3 based on first-principles calculations is reported herein. The results uncover important general trends of impurity formation and diffusion in MAPbI 3 and provide useful guidance for identifying the optimal metal electrodes that do not introduce electrically active impurity defects in MAPbI 3 while having low resistivities and suitable work functions for carrier extraction.

Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH 3NH 3PbI 3 : Implications on Solar Cell Degradation and Choice of Electrode

DOE PAGES

Ming, Wenmei; Yang, Dongwen; Li, Tianshu; ...

2017-12-27

Solar cells based on methylammonium lead triiodide (MAPbI 3) have shown remarkable progress in recent years and have demonstrated efficiencies greater than 20%. However, the long-term stability of MAPbI 3-based solar cells has yet to be achieved. Besides the well-known chemical and thermal instabilities, significant native ion migration in lead halide perovskites leads to current–voltage hysteresis and photoinduced phase segregation. Recently, it is further revealed that, despite having excellent chemical stability, the Au electrode can cause serious solar cell degradation due to Au diffusion into MAPbI 3. In addition to Au, many other metals have been used as electrodes inmore » MAPbI 3 solar cells. However, how the external metal impurities introduced by electrodes affect the long-term stability of MAPbI 3 solar cells has rarely been studied. A comprehensive study of formation energetics and diffusion dynamics of a number of noble and transition metal impurities (Au, Ag, Cu, Cr, Mo, W, Co, Ni, Pd) in MAPbI 3 based on first-principles calculations is reported herein. The results uncover important general trends of impurity formation and diffusion in MAPbI 3 and provide useful guidance for identifying the optimal metal electrodes that do not introduce electrically active impurity defects in MAPbI 3 while having low resistivities and suitable work functions for carrier extraction.« less

Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH3NH3PbI3: Implications on Solar Cell Degradation and Choice of Electrode

PubMed Central

Ming, Wenmei; Yang, Dongwen; Li, Tianshu

2017-01-01

Abstract Solar cells based on methylammonium lead triiodide (MAPbI3) have shown remarkable progress in recent years and have demonstrated efficiencies greater than 20%. However, the long‐term stability of MAPbI3‐based solar cells has yet to be achieved. Besides the well‐known chemical and thermal instabilities, significant native ion migration in lead halide perovskites leads to current–voltage hysteresis and photoinduced phase segregation. Recently, it is further revealed that, despite having excellent chemical stability, the Au electrode can cause serious solar cell degradation due to Au diffusion into MAPbI3. In addition to Au, many other metals have been used as electrodes in MAPbI3 solar cells. However, how the external metal impurities introduced by electrodes affect the long‐term stability of MAPbI3 solar cells has rarely been studied. A comprehensive study of formation energetics and diffusion dynamics of a number of noble and transition metal impurities (Au, Ag, Cu, Cr, Mo, W, Co, Ni, Pd) in MAPbI3 based on first‐principles calculations is reported herein. The results uncover important general trends of impurity formation and diffusion in MAPbI3 and provide useful guidance for identifying the optimal metal electrodes that do not introduce electrically active impurity defects in MAPbI3 while having low resistivities and suitable work functions for carrier extraction. PMID:29610728

Radiation-induced instability and its relation to radiation carcinogenesis

NASA Technical Reports Server (NTRS)

Ullrich, R. L.; Ponnaiya, B.

1998-01-01

PURPOSE: A model that identifies radiation-induced genetic instability as the earliest cellular event in the multi-step sequence leading to radiation-induced cancer was previously proposed. In this paper ongoing experiments are discussed which are designed to test this model and its predictions in mouse mammary epithelial cells. RESULTS: Several lines of evidence are presented that appear to support this model: first, the development of delayed mutations in p53 following irradiation in altered growth variants; secondly, the high frequencies for the induction of both instability and transformation following irradiation in mammary epithelial cells; and finally, the demonstration that susceptibility to the induction of cytogenetic instability is a heritable trait that correlates with susceptibility to transformation and radiation-induced mammary cancer. Mice resistant to transformation and mammary cancer development are also resistant to the development of instability after irradiation. In contrast, mice sensitive to transformation and cancer are also sensitive to the development of cytogenetic instability. CONCLUSIONS: Data from this laboratory and from the studies cited above suggest a specific, and perhaps unique, role for radiation-induced instability as a critical early event associated with initiation of the carcinogenic process.

Phenomenon of period-doubling in holographic periodic structures exposed to UV radiation

NASA Astrophysics Data System (ADS)

Gulyaev, Sergey N.; Isaev, Igor V.

2001-02-01

This paper presents the experimental study of the period- doubling phenomenon occurring during the multi-cycle processing procedure incorporating the exposure of Ag halide photoemulsion with the primary recorded holographic structure to the short-wave UV radiation, washing and drying. It is suggested that the simultaneous presence of two contrary photochemical processes -- photodecomposition and radiation hardening in the gelatin results in instability of the primary holographic structure and in the formation of the spatial subharmonic of the surface relief. The phenomenon may be considered as a process of the self-organization initiated by instability of the macrostructure on a rearrangement of the microstructure on the molecule level. The period-doubling phenomenon has been found to occur in the experiments with the UV sources of a various spectral composition -- the mercury- vapor lamp and the excimer lamps operating on the mixtures of Xe+Cl2 and Kr+Cl2.

Solution of the nonlinear Poisson-Boltzmann equation: Application to ionic diffusion in cementitious materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arnold, J.; Kosson, D.S., E-mail: david.s.kosson@vanderbilt.edu; Garrabrants, A.

2013-02-15

A robust numerical solution of the nonlinear Poisson-Boltzmann equation for asymmetric polyelectrolyte solutions in discrete pore geometries is presented. Comparisons to the linearized approximation of the Poisson-Boltzmann equation reveal that the assumptions leading to linearization may not be appropriate for the electrochemical regime in many cementitious materials. Implications of the electric double layer on both partitioning of species and on diffusive release are discussed. The influence of the electric double layer on anion diffusion relative to cation diffusion is examined.

A remarkable solvent effect on the nuclearity of neutral titanium(IV)-based helicate assemblies.

PubMed

Weekes, David Michael; Diebold, Carine; Mobian, Pierre; Huguenard, Clarisse; Allouche, Lionel; Henry, Marc

2014-04-22

The spontaneous self-assembly of a neutral circular trinuclear Ti(IV) -based helicate is described through the reaction of titanium(IV) isopropoxide with a rationally designed tetraphenolic ligand. The trimeric ring helicate was obtained after diffusion of n-pentane into a solution with dichloromethane. The circular helicate has been characterized by using single-crystal X-ray diffraction study, (13) C CP-MAS NMR and (1) H NMR DOSY solution spectroscopic, and positive electrospray ionization mass-spectrometric analysis. These analytical data were compared with those obtained from a previously reported double-stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double-stranded helicate. Thermodynamic analysis by means of the PACHA software revealed that formation of the double-stranded helicates was characterized by ΔH(toluene)=-30 kJ mol(-1) and ΔS(toluene)=+357 J K(-1)  mol(-1) , whereas these values were ΔH(CH2 Cl2 )=-75 kJ mol(-1) and ΔS(CH2 Cl2 )=-37 J K(-1)  mol(-1) for the ring helicate. The transformation of the ring helicate into the double-stranded helicate was a strongly endothermic process characterized by ΔH(CH2 Cl2 )=+127 kJ mol(-1) and ΔH(n-pentane)=+644 kJ mol(-1) associated with a large positive entropy change ΔS=+1115 J K(-1) ⋅mol(-1) . Consequently, the instability of the ring helicate in pure dichloromethane was attributed to the rather high dielectric constant and dipole moment of dichloromethane relative to n-pentane. Suggestions for increasing the stability of the ring helicate are given. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Turbulent patterns in wall-bounded flows: A Turing instability?

NASA Astrophysics Data System (ADS)

Manneville, Paul

2012-06-01

In their way to/from turbulence, plane wall-bounded flows display an interesting transitional regime where laminar and turbulent oblique bands alternate, the origin of which is still mysterious. In line with Barkley's recent work about the pipe flow transition involving reaction-diffusion concepts, we consider plane Couette flow in the same perspective and transform Waleffe's classical four-variable model of self-sustaining process into a reaction-diffusion model. We show that, upon fulfillment of a condition on the relative diffusivities of its variables, the featureless turbulent regime becomes unstable against patterning as the result of a Turing instability. A reduced two-variable model helps us to delineate the appropriate region of parameter space. An intrinsic status is therefore given to the pattern's wavelength for the first time. Virtues and limitations of the model are discussed, calling for a microscopic support of the phenomenological approach.

Temperature-Induced Protein Release from Water-in-Oil-in-Water Double Emulsions

PubMed Central

Rojas, Edith C.; Staton, Jennifer A.; John, Vijay T.; Papadopoulos, Kyriakos D.

2009-01-01

A model water-in-oil-in-water (W1/O/W2) double emulsion was prepared by a two-step emulsification procedure and subsequently subjected to temperature changes that caused the oil phase to freeze and thaw while the two aqueous phases remained liquid. Our previous work on individual double-emulsion globules1 demonstrated that crystallizing the oil phase (O) preserves stability, while subsequent thawing triggers coalescence of the droplets of the internal aqueous phase (W1) with the external aqueous phase (W2), termed external coalescence. Activation of this instability mechanism led to instant release of fluorescently tagged bovine serum albumin (fluorescein isothiocyanate (FITC)-BSA) from the W1 droplets and into W2. These results motivated us to apply the proposed temperature-induced globule-breakage mechanism to bulk double emulsions. As expected, no phase separation of the emulsion occurred if stored at temperatures below 18 °C (freezing point of the model oil n-hexadecane), whereas oil thawing readily caused instability. Crucial variables were identified during experimentation, and found to greatly influence the behavior of bulk double emulsions following freeze-thaw cycling. Adjustment of these variables accounted for a more efficient release of the encapsulated protein. PMID:18543998

Small airway obstruction in COPD: new insights based on micro-CT imaging and MRI imaging.

PubMed

Hogg, James C; McDonough, John E; Suzuki, Masaru

2013-05-01

The increase in total cross-sectional area in the distal airways of the human lung enhances the mixing of each tidal breath with end-expiratory gas volume by slowing bulk flow and increasing gas diffusion. However, this transition also favors the deposition of airborne particulates in this region because they diffuse 600 times slower than gases. Furthermore, the persistent deposition of toxic airborne particulates stimulates a chronic inflammatory immune cell infiltration and tissue repair and remodeling process that increases the resistance in airways <2 mm in diameter four to 40-fold in COPD. This increase was originally attributed to lumen narrowing because it increases resistance in proportion to the change in lumen radius raised to the fourth power. In contrast, removal of one-half the number of tubes arranged in parallel is required to double their resistance, and approximately 90% need to be removed to explain the increase in resistance measured in COPD. However, recent reexamination of this problem based on micro-CT imaging indicates that terminal bronchioles are both narrowed and reduced to 10% of the control values in the centrilobular and 25% in the panlobular emphysematous phenotype of very severe (GOLD [Global Initiative for Chronic Obstructive Lung Disease] grade IV) COPD. These new data indicate that both narrowing and reduction in numbers of terminal bronchioles contribute to the rapid decline in FEV₁ that leads to severe airway obstruction in COPD. Moreover, the observation that terminal bronchiolar loss precedes the onset of emphysematous destruction suggests this destruction begins in the very early stages of COPD.

Small Airway Obstruction in COPD

PubMed Central

McDonough, John E.; Suzuki, Masaru

2013-01-01

The increase in total cross-sectional area in the distal airways of the human lung enhances the mixing of each tidal breath with end-expiratory gas volume by slowing bulk flow and increasing gas diffusion. However, this transition also favors the deposition of airborne particulates in this region because they diffuse 600 times slower than gases. Furthermore, the persistent deposition of toxic airborne particulates stimulates a chronic inflammatory immune cell infiltration and tissue repair and remodeling process that increases the resistance in airways <2 mm in diameter four to 40-fold in COPD. This increase was originally attributed to lumen narrowing because it increases resistance in proportion to the change in lumen radius raised to the fourth power. In contrast, removal of one-half the number of tubes arranged in parallel is required to double their resistance, and approximately 90% need to be removed to explain the increase in resistance measured in COPD. However, recent reexamination of this problem based on micro-CT imaging indicates that terminal bronchioles are both narrowed and reduced to 10% of the control values in the centrilobular and 25% in the panlobular emphysematous phenotype of very severe (GOLD [Global Initiative for Chronic Obstructive Lung Disease] grade IV) COPD. These new data indicate that both narrowing and reduction in numbers of terminal bronchioles contribute to the rapid decline in FEV1 that leads to severe airway obstruction in COPD. Moreover, the observation that terminal bronchiolar loss precedes the onset of emphysematous destruction suggests this destruction begins in the very early stages of COPD. PMID:23648907

Evaluation of Metallo-β-Lactamase-Production and Carriage of bla-VIM Genes in Pseudomonas aeruginosa Isolated from Burn Wound Infections in Isfahan

PubMed Central

Saffari, Mahmood; Firoozeh, Farzaneh; Pourbabaee, Mohammad; Zibaei, Mohammad

2016-01-01

Background Metallo-β-lactamase-production among Gram-negative bacteria, including Pseudomonas aeruginosa, has become a challenge for treatment of infections due to these resistant bacteria. Objectives The aim of the current study was to evaluate the metallo-β-lactamase-production and carriage of bla-VIM genes among carbapenem-resistant P. aeruginosa isolated from burn wound infections. Patients and Methods A cross-sectional study was conducted from September 2014 to July 2015. One hundred and fifty P. aeruginosa isolates were recovered from 600 patients with burn wound infections treated at Imam-Musa-Kazem Hospital in Isfahan city, Iran. Carbapenem-resistant P. aeruginosa isolates were screened by disk diffusion using CLSI guidelines. Metallo-β-lactamase-producing P. aeruginosa isolates were identified using an imipenem-EDTA double disk synergy test (EDTA-IMP DDST). For detection of MBL genes including bla-VIM-1 and bla-VIM-2, polymerase chain reaction (PCR) methods and sequencing were used. Results Among the 150 P. aeruginosa isolates, 144 (96%) were resistant to imipenem by the disk diffusion method, all of which were identified as metallo-β-lactamase-producing P. aeruginosa isolates by EDTA-IMP DDST. Twenty-seven (18%) and 8 (5.5%) MBL-producing P. aeruginosa isolates harbored bla-VIM-1 and bla-VIM-2 genes, respectively. Conclusions Our findings showed a high occurrence of metallo-β-lactamase production among P. aeruginosa isolates in burn patient infections in our region. Also, there are P. aeruginosa isolates carrying the bla-VIM-1 and bla-VIM-2 genes in Isfahan province. PMID:28144604

Ferroelectric and structural instability in double perovskites Me{sup 1+}Bi{sup 3+}Me{sup 3+}Nb{sup 5+}O{sub 6} (Me{sup 1+} = Na, K, Rb; Me{sup 3+} = Sc, Ga, In, Lu)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zinenko, V. I., E-mail: zvi@iph.krasn.ru; Zamkova, N. G.; Zhandun, V. S.

2012-06-15

Within the Gordon-Kim generalized model with regard to the polarizabilities of ions, the lattice constants, the high-frequency permittivity, the Born dynamic charges, and the vibration constants of the crystal lattice are calculated for cation-ordered double perovskites Me{sup 1+}Bi{sup 3+}Me{sup 3+}Nb{sup 5+}O{sub 6}. The vibration spectra of all the compounds exhibit two types of instabilities: instability associated with the rotation of the oxygen octahedron and ferroelectric instability. Various combinations of distortions with respect to the rotation mode yield five energetically most favorable distorted phases. The symmetry and the energy characteristics of these phases are discussed. In four of the five phases,more » the distortions associated with the oxygen octahedron rotation lead to polar phases, thus allowing one to speak of improper ferroelectricity in these compounds. One phase turns out to be nonpolar; however, it contains unstable polar modes such that a displacement along the eigenvectors of these modes gives rise to polarization in the crystal.« less

A global ocean climatological atlas of the Turner angle: implications for double-diffusion and water-mass structure

NASA Astrophysics Data System (ADS)

You, Yuzhu

2002-11-01

The 1994 Levitus climatological atlas is used to calculate the Turner angle (named after J. Stewart Turner) to examine which oceanic water masses are favorable for double-diffusion in the form of diffusive convection or salt-fingering and which are doubly stable. This atlas complements the Levitus climatology. It reveals the major double-diffusive signals associated with large-scale water-mass structure. In total, about 44% of the oceans display double-diffusion, of which 30% is salt-fingering and 14% is diffusive double-diffusion. Results show that various central and deep waters are favorable for salt-fingering. The former is due to positive evaporation minus precipitation, and the latter is due to thermohaline circulation, i.e. the southward spreading of relatively warm, salty North Atlantic Deep Water (NADW) overlying cold, fresh Antarctic Bottom Water. In the northern Indian Ocean and eastern North Atlantic, favorable conditions for salt-fingering are found throughout the water column. The Red Sea (including the Persian Gulf) and Mediterranean Sea are the sources of warm, salty water for the ocean. As consequence, temperature and salinity in these outflow regions both decrease from the sea surface to the bottom. On the other hand, ocean currents are in general sluggish in these regions. In the polar and subpolar regions of Arctic and Antarctic, Okhotsk Sea, Gulf of Alaska, the subpolar gyre of the North Pacific, the Labrador Sea, and the Norwegian Sea, the upper layer water is favorable for diffusive convection because of high latitude surface cooling and ice melting. Weak and shallow diffusive convection is also found throughout tropical regions and the Bay of Bengal. The former is due to excessive precipitation over evaporation and rain cooling, and the latter is due to both precipitation and river runoff. Diffusive convection in the ocean's interior is unique to the South Atlantic between Antarctic Intermediate Water and upper NADW (uNADW). It is the consequence of the intrusive equatorward flow of upper Circumpolar Deep Water, which carries with it the minimum temperature and very low salinity overlying warm, salty uNADW.

Dynamic stability of electrodynamic maglev systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Y.; Chen, S.S.; Mulcahy, T.M.

1997-01-01

Because dynamic instabilities are not acceptable in any commercial maglev system, it is important to consider dynamic instability in the development of all maglev systems. This study considers the stability of maglev systems based on mathematical models and experimental data. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on a guideway consisting of double L-shaped aluminum segments. The theory and analysis for motion-dependent magnetic-force-induced instability developed in this study provides basic stability characteristics and identifies future research needs for maglev systems.

Trapping saturation of the bump-on-tail instability and electrostatic harmonic excitation in earth's foreshock

NASA Technical Reports Server (NTRS)

Klimas, Alexander J.

1990-01-01

The Vlasov simulation is used to examine the trapping saturation of the bump-on-tail instability both with and without mode-mode coupling and subsequent harmonic excitation. It is found that adding the pumped harmonic modes leads to a significant difference in the behavior of the phase-space distribution function near the unstable bump at the saturation time of the instability. The pumped modes permit rapid plateau formation on the space-averaged velocity distribution, in effect preventing the onset of the quasi-linear velocity-diffusion saturation mechanism.

Genetic analysis of mouse embryonic stem cells bearing Msh3 and Msh2 single and compound mutations.

PubMed

Abuin, A; Zhang, H; Bradley, A

2000-01-01

We have previously described the use of homologous recombination and CRE-loxP-mediated marker recycling to generate mouse embryonic stem (ES) cell lines homozygous for mutations at the Msh3, Msh2, and both Msh3 and Msh2 loci (2). In this study, we describe the analysis of these ES cells with respect to processes known to be affected by DNA mismatch repair. ES cells homozygous for the Msh2 mutation displayed increased resistance to killing by the cytotoxic drug 6-thioguanine (6TG), indicating that the 6TG cytotoxic mechanism is mediated by Msh2. The mutation rate of the herpes simplex virus thymidine kinase 1 (HSV-tk1) gene was unchanged in Msh3-deficient ES cell lines but markedly elevated in Msh2-deficient and Msh3 Msh2 double-mutant cells. Notably, the HSV-tk1 mutation rate was 11-fold higher, on average, than that of the hypoxanthine-guanine phosphoribosyl transferase (Hprt) locus in Msh2-deficient cells. Sequence analysis of HSV-tk1 mutants from these cells indicated the presence of a frameshift hotspot within the HSV-tk1 coding region. Msh3-deficient cells displayed a modest (16-fold) elevation in the instability of a dinucleotide repeat, whereas Msh2-deficient and Msh2 Msh3 double-mutant cells displayed markedly increased levels of repeat instability. Targeting frequencies of nonisogenic vectors were elevated in Msh2-deficient ES cell lines, confirming the role of Msh2 in blocking recombination between diverged sequences (homeologous recombination) in mammalian cells. These results are consistent with accumulating data from other laboratories and support the current model of DNA mismatch repair in mammalian cells.

Genetic Analysis of Mouse Embryonic Stem Cells Bearing Msh3 and Msh2 Single and Compound Mutations

PubMed Central

Abuin, Alejandro; Zhang, HeJu; Bradley, Allan

2000-01-01

We have previously described the use of homologous recombination and CRE-loxP-mediated marker recycling to generate mouse embryonic stem (ES) cell lines homozygous for mutations at the Msh3, Msh2, and both Msh3 and Msh2 loci (2). In this study, we describe the analysis of these ES cells with respect to processes known to be affected by DNA mismatch repair. ES cells homozygous for the Msh2 mutation displayed increased resistance to killing by the cytotoxic drug 6-thioguanine (6TG), indicating that the 6TG cytotoxic mechanism is mediated by Msh2. The mutation rate of the herpes simplex virus thymidine kinase 1 (HSV-tk1) gene was unchanged in Msh3-deficient ES cell lines but markedly elevated in Msh2-deficient and Msh3 Msh2 double-mutant cells. Notably, the HSV-tk1 mutation rate was 11-fold higher, on average, than that of the hypoxanthine-guanine phosphoribosyl transferase (Hprt) locus in Msh2-deficient cells. Sequence analysis of HSV-tk1 mutants from these cells indicated the presence of a frameshift hotspot within the HSV-tk1 coding region. Msh3-deficient cells displayed a modest (16-fold) elevation in the instability of a dinucleotide repeat, whereas Msh2-deficient and Msh2 Msh3 double-mutant cells displayed markedly increased levels of repeat instability. Targeting frequencies of nonisogenic vectors were elevated in Msh2-deficient ES cell lines, confirming the role of Msh2 in blocking recombination between diverged sequences (homeologous recombination) in mammalian cells. These results are consistent with accumulating data from other laboratories and support the current model of DNA mismatch repair in mammalian cells. PMID:10594017

Radiation-induced chromosomal instability in BALB/c and C57BL/6 mice: the difference is as clear as black and white

NASA Technical Reports Server (NTRS)

Ponnaiya, B.; Cornforth, M. N.; Ullrich, R. L.

1997-01-01

Genomic instability has been proposed to be the earliest step in radiation-induced tumorigenesis. It follows from this hypothesis that individuals highly susceptible to induction of tumors by radiation should exhibit enhanced radiation-induced instability. BALB/c white mice are considerably more sensitive to radiation-induced mammary cancer than C57BL/6 black mice. In this study, primary mammary epithelial cell cultures from these two strains were examined for the "delayed" appearance of chromosomal aberrations after exposure to 137Cs gamma radiation, as a measure of radiation-induced genomic instability. As expected, actively dividing cultures from both strains showed a rapid decline of initial asymmetrical aberrations with time postirradiation. However, after 16 population doublings, cells from BALB/c mice exhibited a marked increase in the frequency of chromatid-type breaks and gaps which remained elevated throughout the time course of the experiment (28 doublings). No such effect was observed for the cells of C57BL/6 mice; after the rapid clearance of initial aberrations, the frequency of chromatid-type aberrations in the irradiated population remained at or near those of nonirradiated controls. These results demonstrate a correlation between the latent expression of chromosomal damage in vitro and susceptibility for mammary tumors, and provide further support for the central role of radiation-induced instability in the process of tumorigenesis.

Toward validation of a 3-D plasma turbulence model using LAPD data

NASA Astrophysics Data System (ADS)

Umansky, M. V.

2010-11-01

Detailed results from a 3-D fluid simulation of plasma turbulence are compared with experimental data from the Large Plasma Device (LAPD) at UCLA. LAPD is a magnetized plasma column experiment with a high repetition rate, allowing detailed time-and-space resolved probe data on plasma turbulence and transport. The large amount of data allows a thorough comparison with the simulation results. For the observed drift-type modes, LAPD plasmas are strongly collisional (φ*/νei1 and λei/L1), providing justification for a fluid treatment. Accordingly, the model is based on reduced Braginskii equations and is implemented in the framework of the BOUT code, originally developed at LLNL for tokamak edge plasmas. Analysis of linear plasma instabilities shows that resistive drift modes, rotation-driven interchange modes, and Kelvin-Helmholtz modes can all be important in LAPD and have comparable frequencies and growth rates. In nonlinear simulations using measured LAPD density profiles, evolution of instabilities and self-generated zonal flows results in a saturated turbulent state. Comparisons of these simulations with measurements in LAPD plasmas reveal good agreement, in particular in the frequency spectrum, spatial correlation, and amplitude probability distribution function of density fluctuations. Also, consistent with the experiment, the simulations indicate a great deal of similarity between plasma turbulence in LAPD and some features of tokamak edge turbulence. Similar to tokamak edge plasmas, density transport appears to be predominantly carried by large particle-flux events. Despite the intermittent character of the calculated turbulence, as indicated by fluctuation statistics, the turbulent particle flux is consistent with a diffusive model with diffusion coefficient close to the Bohm value.

Analytical Solutions for Radiative Transfer: Implications for Giant Planet Formation by Disk Instability

NASA Astrophysics Data System (ADS)

Boss, Alan P.

2009-03-01

The disk instability mechanism for giant planet formation is based on the formation of clumps in a marginally gravitationally unstable protoplanetary disk, which must lose thermal energy through a combination of convection and radiative cooling if they are to survive and contract to become giant protoplanets. While there is good observational support for forming at least some giant planets by disk instability, the mechanism has become theoretically contentious, with different three-dimensional radiative hydrodynamics codes often yielding different results. Rigorous code testing is required to make further progress. Here we present two new analytical solutions for radiative transfer in spherical coordinates, suitable for testing the code employed in all of the Boss disk instability calculations. The testing shows that the Boss code radiative transfer routines do an excellent job of relaxing to and maintaining the analytical results for the radial temperature and radiative flux profiles for a spherical cloud with high or moderate optical depths, including the transition from optically thick to optically thin regions. These radial test results are independent of whether the Eddington approximation, diffusion approximation, or flux-limited diffusion approximation routines are employed. The Boss code does an equally excellent job of relaxing to and maintaining the analytical results for the vertical (θ) temperature and radiative flux profiles for a disk with a height proportional to the radial distance. These tests strongly support the disk instability mechanism for forming giant planets.

Interface instabilities during displacements of two miscible fluids in a vertical pipe

NASA Astrophysics Data System (ADS)

Scoffoni, J.; Lajeunesse, E.; Homsy, G. M.

2001-03-01

We study experimentally the downward vertical displacement of one miscible fluid by another in a vertical pipe at sufficiently high velocities for diffusive effects to be negligible. For certain viscosity ratios and flow rates, the interface between the two fluids can destabilize. We determine the dimensionless flow rate Uc above which the instability is triggered and its dependence on the viscous ratio M, resulting in a stability map Uc=Uc(M). Two different instability modes have been observed: an asymmetric "corkscrew" mode and an axisymmetric one. We remark that the latter is always eventually disturbed by "corkscrew" type instabilities. We speculate that these instabilities are driven by the viscosity stratification and are analogous to those already observed in core annular flows of immiscible fluids.

Convective Instability and Mass Transport of the Diffusion Layer in CO2 Sequestration

NASA Astrophysics Data System (ADS)

Backhaus, S.

2011-12-01

The long-term fate of supercritical (sc) CO2 in saline aquifers is critical to the security of carbon sequestration, an important option for eliminating or reducing the emissions of this most prevalent greenhouse gas. scCO2 is less dense than brine and floats to the top of the aquifer where it is trapped in a metastable state by a geologic feature such as a low permeability cap rock. Dissolution into the underlying brine creates a CO2-brine mixture that is denser than brine, eliminating buoyancy and removing the threat of CO2 escaping back to the atmosphere. If molecular diffusion were the only dissolution mechanism, the CO2 waste stream from a typical large coal-fired electrical power plant may take upward of 10,000 years to no longer pose a threat, however, a convective instability of the dense diffusion boundary layer between the scCO2 and the brine can dramatically increase the dissolution rates, shortening the lifetime of the scCO2 waste pool. We present results of 2D and 3D similitude-correct, laboratory-scale experiments using an analog fluid system. The experiments and flow visualization reveal the onset of the convective instability, the dynamics of the fluid flows during the convective processes, and the long-term mass transfer rates.

Observation of Rayleigh-Taylor-instability evolution in a plasma with magnetic and viscous effects

DOE PAGES

Adams, Colin S.; Moser, Auna L.; Hsu, Scott C.

2015-11-06

We present time-resolved observations of Rayleigh-Taylor-instability (RTI) evolution at the interface between an unmagnetized plasma jet colliding with a stagnated, magnetized plasma. The observed instability growth time (~10μs) is consistent with the estimated linear RTI growth rate calculated using experimentally inferred values of density (~10 14cm–3) and deceleration (~10 9 m/s 2). The observed mode wavelength (≳1 cm) nearly doubles within a linear growth time. Furthermore, theoretical estimates of magnetic and viscous stabilization and idealized magnetohydrodynamic simulations including a physical viscosity model both suggest that the observed instability evolution is subject to magnetic and/or viscous effects.

Obtaining the porewater composition of a clay rock by modeling the in- and out-diffusion of anions and cations from an in-situ experiment.

PubMed

Appelo, C A J; Vinsot, A; Mettler, S; Wechner, S

2008-10-23

A borehole in the Callovo-Oxfordian clay rock in ANDRA's underground research facility was sampled during 1 year and chemically analyzed. Diffusion between porewater and the borehole solution resulted in concentration changes which were modeled with PHREEQC's multicomponent diffusion module. In the model, the clay rock's pore space is divided in free porewater (electrically neutral) and diffuse double layer water (devoid of anions). Diffusion is calculated separately for the two domains, and individually for all the solute species while a zero-charge flux is maintained. We explain how the finite difference formulas for radial diffusion can be translated into mixing factors for solutions. Operator splitting is used to calculate advective flow and chemical reactions such as ion exchange and calcite dissolution and precipitation. The ion exchange reaction is formulated in the form of surface complexation, which allows distributing charge over the fixed sites and the diffuse double layer. The charge distribution affects pH when calcite dissolves, and modeling of the experimental data shows that about 7% of the cation exchange capacity resides in the diffuse double layer. The model calculates the observed concentration changes very well and provides an estimate of the pristine porewater composition in the clay rock.

The Onset of Double Diffusive Convection in a Viscoelastic Fluid-Saturated Porous Layer with Non-Equilibrium Model

PubMed Central

Yang, Zhixin; Wang, Shaowei; Zhao, Moli; Li, Shucai; Zhang, Qiangyong

2013-01-01

The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer is studied when the fluid and solid phase are not in local thermal equilibrium. The modified Darcy model is used for the momentum equation and a two-field model is used for energy equation each representing the fluid and solid phases separately. The effect of thermal non-equilibrium on the onset of double diffusive convection is discussed. The critical Rayleigh number and the corresponding wave number for the exchange of stability and over-stability are obtained, and the onset criterion for stationary and oscillatory convection is derived analytically and discussed numerically. PMID:24312193

The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer with non-equilibrium model.

PubMed

Yang, Zhixin; Wang, Shaowei; Zhao, Moli; Li, Shucai; Zhang, Qiangyong

2013-01-01

The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer is studied when the fluid and solid phase are not in local thermal equilibrium. The modified Darcy model is used for the momentum equation and a two-field model is used for energy equation each representing the fluid and solid phases separately. The effect of thermal non-equilibrium on the onset of double diffusive convection is discussed. The critical Rayleigh number and the corresponding wave number for the exchange of stability and over-stability are obtained, and the onset criterion for stationary and oscillatory convection is derived analytically and discussed numerically.

An enzyme-free homogenous electrochemical assay for sensitive detection of the plasmid-mediated colistin resistance gene mcr-1.

PubMed

Li, Bo; Chai, Zhixin; Yan, Xiaohui; Liu, Chunchen; Situ, Bo; Zhang, Ye; Pan, Weilun; Luo, Shihua; Liu, Jianhua; Zheng, Lei

2018-05-22

Antibiotic resistance associated with the mcr-1 gene of Gram-negative bacteria, which confers resistance to drugs of last resort and has the potential to spread via plasmids, is one of the most pressing issues facing global health today. Point-of-care testing for the mcr-1 gene is needed to aid in the identification of colistin resistance in the field and to control its horizontal transmission. Here, we report the successful development of an enzyme-free homogenous electrochemical strategy for sensitive detection of the antibiotic resistance gene mcr-1 using the hybridization chain reaction and mcr-1-specific toehold probe. The long double-stranded DNA polymer produced using this strategy could be detected by assessing the diffusion of methylene blue towards the surface of a screen-printed gold electrode. Under optimized conditions, a linear relationship was observed between the variation of peak current and the natural logarithm of the mcr-1 gene concentration in the range of 1 nM to 1 μM with a detection limit of 0.78 nM (S/N = 3). This enzyme-free, isothermal platform is a rapid, portable, disposable, and sensitive method for detection of plasmid-mediated colistin resistance.

Plasmids in Gram negatives: molecular typing of resistance plasmids.

PubMed

Carattoli, Alessandra

2011-12-01

A plasmid is defined as a double stranded, circular DNA molecule capable of autonomous replication. By definition, plasmids do not carry genes essential for the growth of host cells under non-stressed conditions but they have systems which guarantee their autonomous replication also controlling the copy number and ensuring stable inheritance during cell division. Most of the plasmids confer positively selectable phenotypes by the presence of antimicrobial resistance genes. Plasmids evolve as an integral part of the bacterial genome, providing resistance genes that can be easily exchanged among bacteria of different origin and source by conjugation. A multidisciplinary approach is currently applied to study the acquisition and spread of antimicrobial resistance in clinically relevant bacterial pathogens and the established surveillance can be implemented by replicon typing of plasmids. Particular plasmid families are more frequently detected among Enterobacteriaceae and play a major role in the diffusion of specific resistance genes. For instance, IncFII, IncA/C, IncL/M, IncN and IncI1 plasmids carrying extended-spectrum beta-lactamase genes and acquired AmpC genes are currently considered to be "epidemic resistance plasmids", being worldwide detected in Enterobacteriaceae of different origin and sources. The recognition of successful plasmids is an essential first step to design intervention strategies preventing their spread. Copyright © 2011 Elsevier GmbH. All rights reserved.

Modified Back Contact Interface of CZTSe Thin Film Solar Cells: Elimination of Double Layer Distribution in Absorber Layer.

PubMed

Zhang, Zhaojing; Yao, Liyong; Zhang, Yi; Ao, Jianping; Bi, Jinlian; Gao, Shoushuai; Gao, Qing; Jeng, Ming-Jer; Sun, Guozhong; Zhou, Zhiqiang; He, Qing; Sun, Yun

2018-02-01

Double layer distribution exists in Cu 2 SnZnSe 4 (CZTSe) thin films prepared by selenizing the metallic precursors, which will degrade the back contact of Mo substrate to absorber layer and thus suppressing the performance of solar cell. In this work, the double-layer distribution of CZTSe film is eliminated entirely and the formation of MoSe 2 interfacial layer is inhibited successfully. CZTSe film is prepared by selenizing the precursor deposited by electrodeposition method under Se and SnSe x mixed atmosphere. It is found that the insufficient reaction between ZnSe and Cu-Sn-Se phases in the bottom of the film is the reason why the double layer distribution of CZTSe film is formed. By increasing Sn content in the metallic precursor, thus making up the loss of Sn because of the decomposition of CZTSe and facilitate the diffusion of liquid Cu 2 Se, the double layer distribution is eliminated entirely. The crystallization of the formed thin film is dense and the grains go through the entire film without voids. And there is no obvious MoSe 2 layer formed between CZTSe and Mo. As a consequence, the series resistance of the solar cell reduces significantly to 0.14 Ω cm 2 and a CZTSe solar cell with efficiency of 7.2% is fabricated.

Hydrodynamically induced fluid transfer and non-convective double-diffusion in microgravity sliding solvent diffusion cells

NASA Technical Reports Server (NTRS)

Pollmann, Konrad W.; Stodieck, Louis S.; Luttges, Marvin W.

1994-01-01

Microgravity can provide a diffusion-dominated environment for double-diffusion and diffusion-reaction experiments otherwise disrupted by buoyant convection or sedimentation. In sliding solvent diffusion cells, a diffusion interface between two liquid columns is achieved by aligning two offset sliding wells. Fluid in contact with the sliding lid of the cavities is subjected to an applied shear stress. The momentum change by the start/stop action of the well creates an additional hydrodynamical force. In microgravity, these viscous and inertial forces are sufficiently large to deform the diffusion interface and induce hydrodynamic transfer between the wells. A series of KC-135 parabolic flight experiments were conducted to characterize these effects and establish baseline data for microgravity diffusion experiments. Flow visualizations show the diffusion interface to be deformed in a sinusoidal fashion following well alignment. After the wells were separated again in a second sliding movement, the total induced liquid transfer was determined and normalized by the well aspect ratio. The normalized transfer decreased linearly with Reynolds number from 3.3 to 4.0% (w/v) for Re = 0.4 (Stokes flow) to a minimum of 1.0% for Re = 23 to 30. Reynolds numbers that provide minimum induced transfers are characterized by an interface that is highly deformed and unsuitable for diffusion measurements. Flat diffusion interfaces acceptable for diffusion measurements are obtained with Reynolds numbers on the order of 7 to 10. Microgravity experiments aboard a sounding rocket flight verified counterdiffusion of different solutes to be diffusion dominated. Ground control experiments showed enhanced mixing by double-diffusive convection. Careful selection of experimental parameters improves initial conditions and minimizes induced transfer rates.

Thermal ripples in a resistive and radiative instability. [in solar corona

NASA Technical Reports Server (NTRS)

Steinolfson, R. S.

1984-01-01

The development of the resistive tearing instability in the case of sheared magnetic fields is considered, taking into account also the occurrence of a radiatively driven thermal instability. It is pointed out that thermal conduction has generally been neglected in theories similar to those discussed. The present investigation is concerned with a consideration of both parallel and perpendicular thermal conduction, in addition to finite resistivity and radiative loss. Attention is given to the equations and the model, the spatial singularity which arises with consideration of only the parallel heat conduction, the removal of this singularity and the formation of temperature oscillations (thermal ripples) by inclusion of the perpendicular heat-flux component, and details regarding the numerical procedure. A brief explanation is provided of the conditions required for the oscillations, and potential implications of the results with respect to the solar flare are discussed.

Concentration polarization-based nonlinear electrokinetics in porous media: induced-charge electroosmosis.

PubMed

Leinweber, Felix C; Tallarek, Ulrich

2005-11-24

We have investigated induced-charge electroosmotic flow in a fixed bed of ion-permselective glass beads by quantitative confocal laser scanning microscopy. Externally applied electrical fields induce concentration polarization (CP) in the porous medium due to coupled mass and charge transport normal to the charge-selective interfaces. These data reveal the generation of a nonequilibrium electrical double layer in the depleted CP zones and the adjoining anodic hemispheres of the (cation-selective) glass beads above a critical field strength. This initiates CP-based induced-charge electroosmosis along curved interfaces of the quasi-electroneutral macropore space between glass beads. Caused by mutual interference of resulting nonlinear flow with (flow-inducing) space charge regions, an electrohydrodynamic instability can appear locally and realize turbulent flow behavior at low Reynolds numbers. It is characterized by a local destruction of the CP zones and concomitant removal of diffusion-limited mass transfer. More efficient pore-scale lateral mixing also improves macroscopic transport, which is reflected in the significantly reduced axial dispersion of a passive tracer.

Low-gravity fluid dynamics and transport phenomena. Progress in Astronautics and Aeronautics. Vol. 130

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koster, J.N.; Sani, R.L.

1990-01-01

Various papers on low-gravity fluid dynamics and transport phenomena are presented. Individual topics addressed include: fluid management in low gravity, nucleate pool boiling in variable gravity, application of energy-stability theory to problems in crystal growth, thermosolutal convection in liquid HgCdTe near the liquidus temperature, capillary surfaces in microgravity, thermohydrodynamic instabilities and capillary flows, interfacial oscillators, effects of gravity jitter on typical fluid science experiments and on natural convection in a vertical cylinder. Also discussed are: double-diffusive convection and its effects under reduced gravity, segregation and convection in dendritic alloys, fluid flow and microstructure development, analysis of convective situations with themore » Soret effect, complex natural convection in low Prandtl number metals, separation physics, phase partitioning in reduced gravity, separation of binary alloys with miscibility gap in the melt, Ostwald ripening in liquids, particle cloud combustion in reduced gravity, opposed-flow flame spread with implications for combustion at microgravity.« less

Superplastic Forming/Diffusion Bonding Without Interlayer of 5A90 Al-Li Alloy Hollow Double-Layer Structure

NASA Astrophysics Data System (ADS)

Jiang, Shaosong; Jia, Yong; Lu, Zhen; Shi, Chengcheng; Zhang, Kaifeng

2017-09-01

The hollow double-layer structure of 5A90 Al-Li alloy was fabricated by SPF/DB process in this study. The characteristics and mechanism of 5A90 Al-Li alloy with respect to superplasticity and diffusion bonding were investigated. Tensile tests showed that the optimal elongation of tensile specimens was 243.97% at the temperature of 400 °C and the strain rate of 0.001 s-1. Effect of the surface roughness, bonding temperature and bonding time to determine the microstructure and mechanical properties of diffusion bonding joints was investigated, and the optimum bonding parameters were 540 °C/2.5 h/Ra18. Through the finite element simulation, it could be found that the SPF/DB process of hollow double-layer structure was feasible. The hollow double-layer structure of 5A90 Al-Li alloy was manufactured, showing that the thickness distribution of the bonding area was uniform and the thinnest part was the round corner. The SEM images of diffusion bonding joints showed that sound bonding interfaces were obtained in which no discontinuity existed.

Resistance to CO2 diffusion in cuticular membranes of amphibious plants and the implication for CO2 acquisition.

PubMed

Frost-Christensen, Henning; Floto, Franz

2007-01-01

Cuticular membranes (CMs) were isolated from leaves of amphibious and submerged plants and their CO2 resistances were determined as a contribution to establish quantitatively the series of resistances met by CO2 diffusing from bulk water to the chloroplasts of submerged leaves. The isolation was performed enzymatically; permeabilities were determined and converted to resistances. The range of permeance values was 3 to 43 x 10(-6) m s(-1) corresponding to resistance values of 23 to 295 x 10(3) s m(-1), i.e. of the same order of magnitude as boundary layer resistances. The sum of boundary layer, CM, leaf cell and carboxylation resistances could be contained within the total diffusion resistance as determined from the photosynthetic CO2 affinity of the leaf. From the same species, the aerial leaf CM resistance was always higher than the aquatic leaf CM resistance. In a terrestrial plant, the CM resistance to CO2 diffusion was found lower in leaves developed submerged.

Positional stability of field-reversed-configurations in the presence of resistive walls

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rath, N., E-mail: nrath@trialphanenergy.com; Onofri, M.; Barnes, D. C.

2016-06-15

We show that in a field-reversed-configuration, the plasma is unstable to either transverse or axial rigid displacement, but never to both. Driving forces are found to be parallel to the direction of displacement with no orthogonal components. Furthermore, we demonstrate that the properties of a resistive wall (geometry and resistivity) in the vicinity of the plasma do not affect whether the plasma is stable or unstable, but in the case of an unstable system determine the instability growth rate. Depending on the properties of the wall, the instability growth is dominated by plasma inertia (and not affected by wall resistivity)more » or dominated by ohmic dissipation of wall eddy currents (and thus proportional to the wall resistivity).« less

Effects of Hall current and electrical resistivity on the stability of gravitating anisotropic quantum plasma

NASA Astrophysics Data System (ADS)

Bhakta, S.; Prajapati, R. P.

2018-02-01

The effects of Hall current and finite electrical resistivity are studied on the stability of uniformly rotating and self-gravitating anisotropic quantum plasma. The generalized Ohm's law modified by Hall current and electrical resistivity is used along with the quantum magnetohydrodynamic fluid equations. The general dispersion relation is derived using normal mode analysis and discussed in the parallel and perpendicular propagations. In the parallel propagation, the Jeans instability criterion, expression of critical Jeans wavenumber, and Jeans length are found to be independent of non-ideal effects and uniform rotation but in perpendicular propagation only rotation affects the Jeans instability criterion. The unstable gravitating mode modified by Bohm potential and the stable Alfven mode modified by non-ideal effects are obtained separately. The criterion of firehose instability remains unaffected due to the presence of non-ideal effects. In the perpendicular propagation, finite electrical resistivity and quantum pressure anisotropy modify the dispersion relation, whereas no effect of Hall current was observed in the dispersion characteristics. The Hall current, finite electrical resistivity, rotation, and quantum corrections stabilize the growth rate. The stability of the dynamical system is analyzed using the Routh-Hurwitz criterion.

Time-delayed feedback control of diffusion in random walkers.

PubMed

Ando, Hiroyasu; Takehara, Kohta; Kobayashi, Miki U

2017-07-01

Time delay in general leads to instability in some systems, while specific feedback with delay can control fluctuated motion in nonlinear deterministic systems to a stable state. In this paper, we consider a stochastic process, i.e., a random walk, and observe its diffusion phenomenon with time-delayed feedback. As a result, the diffusion coefficient decreases with increasing delay time. We analytically illustrate this suppression of diffusion by using stochastic delay differential equations and justify the feasibility of this suppression by applying time-delayed feedback to a molecular dynamics model.

Discontinuous Galerkin method for multicomponent chemically reacting flows and combustion

NASA Astrophysics Data System (ADS)

Lv, Yu; Ihme, Matthias

2014-08-01

This paper presents the development of a discontinuous Galerkin (DG) method for application to chemically reacting flows in subsonic and supersonic regimes under the consideration of variable thermo-viscous-diffusive transport properties, detailed and stiff reaction chemistry, and shock capturing. A hybrid-flux formulation is developed for treatment of the convective fluxes, combining a conservative Riemann-solver and an extended double-flux scheme. A computationally efficient splitting scheme is proposed, in which advection and diffusion operators are solved in the weak form, and the chemically stiff substep is advanced in the strong form using a time-implicit scheme. The discretization of the viscous-diffusive transport terms follows the second form of Bassi and Rebay, and the WENO-based limiter due to Zhong and Shu is extended to multicomponent systems. Boundary conditions are developed for subsonic and supersonic flow conditions, and the algorithm is coupled to thermochemical libraries to account for detailed reaction chemistry and complex transport. The resulting DG method is applied to a series of test cases of increasing physico-chemical complexity. Beginning with one- and two-dimensional multispecies advection and shock-fluid interaction problems, computational efficiency, convergence, and conservation properties are demonstrated. This study is followed by considering a series of detonation and supersonic combustion problems to investigate the convergence-rate and the shock-capturing capability in the presence of one- and multistep reaction chemistry. The DG algorithm is then applied to diffusion-controlled deflagration problems. By examining convergence properties for polynomial order and spatial resolution, and comparing these with second-order finite-volume solutions, it is shown that optimal convergence is achieved and that polynomial refinement provides advantages in better resolving the localized flame structure and complex flow-field features associated with multidimensional and hydrodynamic/thermo-diffusive instabilities in deflagration and detonation systems. Comparisons with standard third- and fifth-order WENO schemes are presented to illustrate the benefit of the DG scheme for application to detonation and multispecies flow/shock-interaction problems.

Double-diffusive convection in geothermal systems: the salton sea, California, geothermal system as a likely candidate

USGS Publications Warehouse

Fournier, R.O.

1990-01-01

Much has been published about double-diffusive convection as a mechanism for explaining variations in composition and temperature within all-liquid natural systems. However, relatively little is known about the applicability of this phenomenon within the heterogeneous rocks of currently active geothermal systems where primary porosity may control fluid flow in some places and fractures may control it in others. The main appeal of double-diffusive convection within hydrothermal systems is-that it is a mechanism that may allow efficient transfer of heat mainly by convection, while at the same time maintaining vertical and lateral salinity gradients. The Salton Sea geothermal system exhibits the following reservoir characteristics: (1) decreasing salinity and temperature from bottom to top and center toward the sides, (2) a very high heat flow from the top of the system that seems to require a major component of convective transfer of heat within the chemically stratified main reservoir, and (3) a relatively uniform density of the reservoir fluid throughout the system at all combinations of subsurface temperature, pressure, and salinity. Double-diffusive convection can account for these characteristics very nicely whereas other previously suggested models appear to account either for the thermal structure or for the salinity variations, but not both. Hydrologists, reservoir engineers, and particularly geochemists should consider the possibility and consequences of double-diffusive convection when formulating models of hydrothermal processes, and of the response of reservoirs to testing and production. ?? 1990.

Antimicrobial Activity of Endodontic Medicaments and Vehicles using Agar Well Diffusion Method on Facultative and Obligate Anaerobes

PubMed Central

Bhat, Kishore G; Sogi, Suma

2016-01-01

Aims The aim of this study was to determine the relative antimicrobial effectiveness of these endodontic medicaments and various vehicles using an agar well diffusion assay. Materials and methods Double Antibiotic Paste(DAP), modified DAP, 2% Chlorhexidine gluconate and their combination with four vehicles namely Polyethylene glycol 400 (PEG), Propylene glycol (PG), combinations of PG with PEG and lastly Glycerine were tested using agar well diffusion assay. The minimum bactericidal concentration was noted against four standard strains of organisms ie Streptococcus mutans ATCC( American Type Culture Collection) 25175, Staphylococcus aureus ATCC 12598, Enterococcus faecalis ATCC 35550 and Eschericia coli ATCC 25922. Successful endodontic therapy depends upon thorough disinfection of root canals. In some refractory cases, routine endodontic therapy is not sufficient, so intracanal medicaments are used for proper disinfection of canals. Issues of resistance, limited spectrum of activity and lack of antifungal properties, the hunt for the ideal intracanal medicament continues. In this regard, the vehicles used to form the pastes play a supportive role by forming the appropriate consistency for placement and may dramatically influence their chemical characteristics like their solubility and diffusion. Thus, inorder to use safer and equally effective intracanal medicaments, Chlorhexidine gluconate is being unveiled in this study. Results The difference between the four vehicles when combined with the same endodontic medicament studied above is nonsignificant (NS) except against Porphyromonas gingivalis. Propylene glycol is significantly effective than Glycerine when used with DAP ie C+M medicament combination. (p = 0.029) Conclusion 2% chlorhexidine gluconate and modified DAP can definitely replace DAP and triple antibiotic paste as end-odontic medicaments with chlorhexidine having an added advantage of bactericidal action, substantivity, biocompatibility, low toxicity, and lesser chances of developing resistance. How to cite this article Nalawade TM, Bhat KG, Sogi S. Antimicrobial Activity of Endodontic Medicaments and Vehicles using Agar Well Diffusion Method on Facultative and Obligate Anaerobes. Int J Clin Pediatr Dent 2016;9(4):335-341. PMID:28127166

Cattaneo-Christov double-diffusion theory for three-dimensional flow of viscoelastic nanofluid with the effect of heat generation/absorption

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Qayyum, Sajid; Shehzad, Sabir Ali; Alsaedi, Ahmed

2018-03-01

The present research article focuses on three-dimensional flow of viscoelastic(second grade) nanofluid in the presence of Cattaneo-Christov double-diffusion theory. Flow caused is due to stretching sheet. Characteristics of heat transfer are interpreted by considering the heat generation/absorption. Nanofluid theory comprises of Brownian motion and thermophoresis. Cattaneo-Christov double-diffusion theory is introduced in the energy and concentration expressions. Such diffusions are developed as a part of formulating the thermal and solutal relaxation times framework. Suitable variables are implemented for the conversion of partial differential systems into a sets of ordinary differential equations. The transformed expressions have been explored through homotopic algorithm. Behavior of sundry variables on the velocities, temperature and concentration are scrutinized graphically. Numerical values of skin friction coefficients are also calculated and examined. Here thermal field enhances for heat generation parameter while reverse situation is noticed for heat absorption parameter.

Different magnesium release profiles from W/O/W emulsions based on crystallized oils.

PubMed

Herzi, Sameh; Essafi, Wafa

2018-01-01

Water-in-oil-in-water (W/O/W) double emulsions based on crystallized oils were prepared and the release kinetics of magnesium ions from the internal to the external aqueous phase was investigated at T=4°C, for different crystallized lipophilic matrices. All the emulsions were formulated using the same surface-active species, namely polyglycerol polyricinoleate (oil-soluble) and sodium caseinate (water-soluble). The external aqueous phase was a lactose or glucose solution at approximately the same osmotic pressure as that of the inner droplets, in order to avoid osmotic water transfer phenomena. We investigated two types of crystallized lipophilic systems: one based on blends of cocoa butter and miglyol oil, exploring a solid fat content from 0 to 90% and the other system based on milk fat fractions for which the solid fat content varies between 54 and 86%. For double emulsions based on cocoa butter/miglyol oil, the rate of magnesium release was gradually lowered by increasing the % of fat crystals i.e. cocoa butter, in agreement with a diffusion/permeation mechanism. However for double emulsions based on milk fat fractions, the rate of magnesium release was independent of the % of fat crystals and remains the one at t=0. This difference in diffusion patterns, although the solid content is of the same order, suggests a different distribution of fat crystals within the double globules: a continuous fat network acting as a physical barrier for the diffusion of magnesium for double emulsions based on cocoa butter/miglyol oil and double globule/water interfacial distribution for milk fat fractions based double emulsions, through the formation of a crystalline shell allowing an effective protection of the double globules against diffusion of magnesium to the external aqueous phase. Copyright © 2017 Elsevier Inc. All rights reserved.

Ammonia Diffusion through Nalophan Double Bags: Effect of Concentration Gradient Reduction

PubMed Central

Capelli, Laura; Boiardi, Emanuela; Del Rosso, Renato

2014-01-01

The ammonia loss through Nalophan bags has been studied. The losses observed for storage conditions and times as allowed by the reference standard for dynamic olfactometry (EN 13725:2003) indicate that odour concentration values due to the presence of small molecules may be significantly underestimated if samples are not analysed immediately after sampling. A diffusion model was used in order to study diffusion through the bag. The study discusses the effect of concentration gradient (ΔC) across the polymeric membrane of the analyte. The ΔC was controlled by using a setup bag called “double bags.” Experimental data show a reduction of ammonia percentage losses due to the effect of the external multibarrier. The expedient of the double bag loaded with the same gas mixture allows a reduced diffusion of ammonia into the inner bag. Comparing the inner bag losses with those of the single bag stored in the same conditions (T, P, u) and with equal geometrical characteristics (S/V, z), it was observed that the inner bag of the double bag displays a 16% loss while the single bag displays a 37% loss. Acting on the ΔC it is possible to achieve a gross reduction of 57% in the ammonia leakage due to diffusion. PMID:25506608

Experimental Investigation of the Electrothermal Instability on Planar Foil Ablation Experiments

NASA Astrophysics Data System (ADS)

Steiner, Adam; Patel, Sonal; Yager-Elorriaga, David; Jordan, Nicholas; Gilgenbach, Ronald; Lau, Y. Y.

2014-10-01

The electrothermal instability (ETI) is an important early-time physical effect on pulsed power foil ablation experiments due to its ability to seed the destructive magneto-Rayleigh-Taylor (MRT) instability. ETI occurs whenever electrical resistivity has temperature dependence; when resistivity increases with temperature, as with solid metal liners or foils, ETI forms striation structures perpendicular to current flow. These striations provide an initial perturbation for the MRT instability, which is the dominant late-time instability in planar foil ablations. The MAIZE linear transformer driver was used to drive current pulses of approximately 600 kA into 400 nm-thick aluminum foils in order to study ETI in planar geometry. Shadowgraph images of the aluminum plasmas were taken for multiple shots at various times within approximately 50 ns of current start. Fourier analysis extracted the approximate wavelengths of the instability structures on the plasma-vacuum interface. Surface metrology of pre-shot foils was performed to provide a comparison between surface roughness features and resulting plasma structure. This work was supported by US DoE. S.G. Patel and A.M. Steiner supported by NPSC funded by Sandia. D.A. Yager supported by NSF fellowship Grant # DGE 1256260.

Stellar Evolution with Rotation: Mixing Processes in AGB Stars

NASA Astrophysics Data System (ADS)

Driebe, T.; Blöcker, T.

We included diffusive angular momentum transport and rotationally induced mixing processes in our stellar evolution code and studied the influence of rotation on the evolution of intermediate mass stars (M*=2dots6 Msolar) towards and along the asymptotic giant branch (AGB). The calculations start in the fully convective pre-main sequence phase and the initial angular momentu m was adjusted such that on the zero-age main sequence vrot=200 km/ s is achieved. The diffusion coefficients for the five rotational instabilities considered (dynamical shear, secular shear, Eddington-Sweet (ES) circulation, Solberg-Høiland-instability and Goldreich-Schubert-Fricke (GSF) instability) were adopted from Heger et al. (2000, ApJ 528, 368). Mixing efficiency and sensitivity of these processes against molecular weight gradients have been determined by calibration of the main sequence width. In this study we focus on the abundance evolution of carbon. On the one hand, the surface abundance ratios of 12C/13C a nd 12C/16O at the base of the AGB were found to be ≈ 7dots 10 and ≈ 0.1, resp., being a factor of two lower than in non-rotating models. This results from the slow but continuously operating rotationally induced mixing due to the ES-circulation and the GSF-instability during the long main sequence phase. On the other hand, 13C serves as neutron source for interior s-process nucleosynthesis in AGB stars vi a 13C(α,n)16O. Herwig et al. (1997, A&A 324, L81) found that a 13C pocket is forme d in the intershell region of 3 Msolar AGB star if diffusive overshoot is considered. Our calculations show, that mixing processes due to rotation open an alternative channel for the formation of a 13C pocket as found by Langer et al. (1999, A&A 346, L37). Again, ES-circulation and GSF-instability are the predominant rotational mixing processes.

Nonlinear study of the parallel velocity/tearing instability using an implicit, nonlinear resistive MHD solver

NASA Astrophysics Data System (ADS)

Chacon, L.; Finn, J. M.; Knoll, D. A.

2000-10-01

Recently, a new parallel velocity instability has been found.(J. M. Finn, Phys. Plasmas), 2, 12 (1995) This mode is a tearing mode driven unstable by curvature effects and sound wave coupling in the presence of parallel velocity shear. Under such conditions, linear theory predicts that tearing instabilities will grow even in situations in which the classical tearing mode is stable. This could then be a viable seed mechanism for the neoclassical tearing mode, and hence a non-linear study is of interest. Here, the linear and non-linear stages of this instability are explored using a fully implicit, fully nonlinear 2D reduced resistive MHD code,(L. Chacon et al), ``Implicit, Jacobian-free Newton-Krylov 2D reduced resistive MHD nonlinear solver,'' submitted to J. Comput. Phys. (2000) including viscosity and particle transport effects. The nonlinear implicit time integration is performed using the Newton-Raphson iterative algorithm. Krylov iterative techniques are employed for the required algebraic matrix inversions, implemented Jacobian-free (i.e., without ever forming and storing the Jacobian matrix), and preconditioned with a ``physics-based'' preconditioner. Nonlinear results indicate that, for large total plasma beta and large parallel velocity shear, the instability results in the generation of large poloidal shear flows and large magnetic islands even in regimes when the classical tearing mode is absolutely stable. For small viscosity, the time asymptotic state can be turbulent.

Complex DNA Damage: A Route to Radiation-Induced Genomic Instability and Carcinogenesis

PubMed Central

Mavragani, Ifigeneia V.; Nikitaki, Zacharenia; Souli, Maria P.; Aziz, Asef; Nowsheen, Somaira; Aziz, Khaled; Rogakou, Emmy

2017-01-01

Cellular effects of ionizing radiation (IR) are of great variety and level, but they are mainly damaging since radiation can perturb all important components of the cell, from the membrane to the nucleus, due to alteration of different biological molecules ranging from lipids to proteins or DNA. Regarding DNA damage, which is the main focus of this review, as well as its repair, all current knowledge indicates that IR-induced DNA damage is always more complex than the corresponding endogenous damage resulting from endogenous oxidative stress. Specifically, it is expected that IR will create clusters of damage comprised of a diversity of DNA lesions like double strand breaks (DSBs), single strand breaks (SSBs) and base lesions within a short DNA region of up to 15–20 bp. Recent data from our groups and others support two main notions, that these damaged clusters are: (1) repair resistant, increasing genomic instability (GI) and malignant transformation and (2) can be considered as persistent “danger” signals promoting chronic inflammation and immune response, causing detrimental effects to the organism (like radiation toxicity). Last but not least, the paradigm shift for the role of radiation-induced systemic effects is also incorporated in this picture of IR-effects and consequences of complex DNA damage induction and its erroneous repair. PMID:28718816

Complex DNA Damage: A Route to Radiation-Induced Genomic Instability and Carcinogenesis.

PubMed

Mavragani, Ifigeneia V; Nikitaki, Zacharenia; Souli, Maria P; Aziz, Asef; Nowsheen, Somaira; Aziz, Khaled; Rogakou, Emmy; Georgakilas, Alexandros G

2017-07-18

Cellular effects of ionizing radiation (IR) are of great variety and level, but they are mainly damaging since radiation can perturb all important components of the cell, from the membrane to the nucleus, due to alteration of different biological molecules ranging from lipids to proteins or DNA. Regarding DNA damage, which is the main focus of this review, as well as its repair, all current knowledge indicates that IR-induced DNA damage is always more complex than the corresponding endogenous damage resulting from endogenous oxidative stress. Specifically, it is expected that IR will create clusters of damage comprised of a diversity of DNA lesions like double strand breaks (DSBs), single strand breaks (SSBs) and base lesions within a short DNA region of up to 15-20 bp. Recent data from our groups and others support two main notions, that these damaged clusters are: (1) repair resistant, increasing genomic instability (GI) and malignant transformation and (2) can be considered as persistent "danger" signals promoting chronic inflammation and immune response, causing detrimental effects to the organism (like radiation toxicity). Last but not least, the paradigm shift for the role of radiation-induced systemic effects is also incorporated in this picture of IR-effects and consequences of complex DNA damage induction and its erroneous repair.

When linear stability does not exclude nonlinear instability

DOE PAGES

Kevrekidis, P. G.; Pelinovsky, D. E.; Saxena, A.

2015-05-29

We describe a mechanism that results in the nonlinear instability of stationary states even in the case where the stationary states are linearly stable. In this study, this instability is due to the nonlinearity-induced coupling of the linearization’s internal modes of negative energy with the continuous spectrum. In a broad class of nonlinear Schrödinger equations considered, the presence of such internal modes guarantees the nonlinear instability of the stationary states in the evolution dynamics. To corroborate this idea, we explore three prototypical case examples: (a) an antisymmetric soliton in a double-well potential, (b) a twisted localized mode in a one-dimensionalmore » lattice with cubic nonlinearity, and (c) a discrete vortex in a two-dimensional saturable lattice. In all cases, we observe a weak nonlinear instability, despite the linear stability of the respective states.« less

Modelling and formation of spatiotemporal patterns of fractional predation system in subdiffusion and superdiffusion scenarios

NASA Astrophysics Data System (ADS)

Owolabi, Kolade M.; Atangana, Abdon

2018-02-01

This paper primarily focused on the question of how population diffusion can affect the formation of the spatial patterns in the spatial fraction predator-prey system by Turing mechanisms. Our numerical findings assert that modeling by fractional reaction-diffusion equations should be considered as an appropriate tool for studying the fundamental mechanisms of complex spatiotemporal dynamics. We observe that pure Hopf instability gives rise to the formation of spiral patterns in 2D and pure Turing instability destroys the spiral pattern and results to the formation of chaotic or spatiotemporal spatial patterns. Existence and permanence of the species is also guaranteed with the 3D simulations at some instances of time for subdiffusive and superdiffusive scenarios.

Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

NASA Astrophysics Data System (ADS)

Rudolf, Pavel; Litera, Jiří; Alejandro Ibarra Bolanos, Germán; Štefan, David

2018-06-01

Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga's idea were proposed. All modifications are driven by manipulation of the shear layer region, which is believed to play important role in swirling flow instability. While some of the methods provide results close to the original one, none of them works in such a wide range. Series of numerical experiments support the idea that the necessary condition for vortex rope pulsation mitigation is increasing the fluid momentum along the draft tube axis.

Numerical simulation of fiber and wire array Z-pinches with Trac-II

NASA Astrophysics Data System (ADS)

Reisman, David Barton

Trac-II is a two dimensional axisymmetric resistive MHD code. It simulates all three spatial components (r, z, φ) of the magnetic field and fluid velocity vectors, and the plasma is treated as a single fluid with two temperatures (Te,Ti). In addition, it can optionally include a self-consistent external circuit. Recent modifications to the code include the addition of the 3-T radiation model, a 4-phase (solid- liquid-vapor-plasma) equation of state model (QEOS), a 4- phase electrical/thermal conductivity model, and an implicit solution of poloidal (Bz,Br) magnetic field diffusion. These changes permit a detailed study of fiber and wire array Z-pinches. Specifically, Trac-II is used to study the wire array Z-pinch at the PBFA-Z pulse power generator at Sandia National Laboratory. First, in 1-D we examine the behavior of a single wire in the Z-pinch. Then, using these results as initial radial conditions in 2-D, we investigate the dynamics of wire array configurations in the r-z and r-θ plane. In the r- z plane we examine the growth of the m = 0 or ``sausage'' instability in single wires within the array. In the r-θ plane we examine the merging behavior between neighboring wires. Special emphasis is placed on trying to explain how instability growth affects the performance of the Z-pinch. Lastly, we introduce Trac-III, a 3-D MHD code, and illustrate the m = 1 or ``kink'' instability. We also discuss how Trac-III can be modified to simulate the wire array Z-pinch.

A nonlinear dynamical system for combustion instability in a pulse model combustor

NASA Astrophysics Data System (ADS)

Takagi, Kazushi; Gotoda, Hiroshi

2016-11-01

We theoretically and numerically study the bifurcation phenomena of nonlinear dynamical system describing combustion instability in a pulse model combustor on the basis of dynamical system theory and complex network theory. The dynamical behavior of pressure fluctuations undergoes a significant transition from steady-state to deterministic chaos via the period-doubling cascade process known as Feigenbaum scenario with decreasing the characteristic flow time. Recurrence plots and recurrence networks analysis we adopted in this study can quantify the significant changes in dynamic behavior of combustion instability that cannot be captured in the bifurcation diagram.

Resistive MHD Simulation of Quasi-Single-Helicity State on KTX

NASA Astrophysics Data System (ADS)

Luo, Bing; Zhu, Ping; Li, Hong; Liu, Wandong

2016-10-01

The potential formation of quasi-single-helicity (QSH) state on Keda Torus eXperiment (KTX) is evaluated in resistive MHD simulations using the NIMROD code. In this work, we focus on the effects of finite resistivity on the mode structure and characteristics of the dominant linear and nonlinear resistive tearing-mode instability in a finite β, cylindrical reversed field pinch model configuration for KTX. In the typical resistivity regimes of KTX where Lundquist number S =105 , the plasma reaches a steady QSH state after the initial transient phase of multiple helicities. The dominat mode of the QSH state is developed from the dominat linear tearing mode instability. The conditions for and the variations of the formation of QSH states in different resistivity regimes of KTX will be reported and discussed. Supported by National Magnetic Confinement Fusion Science Program of China Grant Nos. 2014GB124002, 2015GB101004, 2011GB106000, and 2011GB106003.

Time-dependent computational studies of flames in microgravity

NASA Technical Reports Server (NTRS)

Oran, Elaine S.; Kailasanath, K.

1989-01-01

The research performed at the Center for Reactive Flow and Dynamical Systems in the Laboratory for Computational Physics and Fluid Dynamics, at the Naval Research Laboratory, in support of the NASA Microgravity Science and Applications Program is described. The primary focus was on investigating fundamental questions concerning the propagation and extinction of premixed flames in Earth gravity and in microgravity environments. The approach was to use detailed time-dependent, multispecies, numerical models as tools to simulate flames in different gravity environments. The models include a detailed chemical kinetics mechanism consisting of elementary reactions among the eight reactive species involved in hydrogen combustion, coupled to algorithms for convection, thermal conduction, viscosity, molecular and thermal diffusion, and external forces. The external force, gravity, can be put in any direction relative to flame propagation and can have a range of values. A combination of one-dimensional and two-dimensional simulations was used to investigate the effects of curvature and dilution on ignition and propagation of flames, to help resolve fundamental questions on the existence of flammability limits when there are no external losses or buoyancy forces in the system, to understand the mechanism leading to cellular instability, and to study the effects of gravity on the transition to cellular structure. A flame in a microgravity environment can be extinguished without external losses, and the mechanism leading to cellular structure is not preferential diffusion but a thermo-diffusive instability. The simulations have also lead to a better understanding of the interactions between buoyancy forces and the processes leading to thermo-diffusive instability.

Overheating instability of a thin conductor with respect to stratification

NASA Astrophysics Data System (ADS)

Garanin, S. F.; Kuznetsov, S. D.

2018-04-01

We consider an overheating instability of a thin (compared to the skin depth) conductor with respect to stratification at the stage when its resistivity rises up to an electrical explosion. Temperature perturbations under such conditions are shown to grow in proportion to resistivity. In the model, when resistivity is proportional to temperature, perturbations grow in proportion to temperature and hence exhibit no relative growth. For a conductor with initial thickness perturbations, temperature perturbations grow in proportion to resistivity and current action integral, i.e., somewhat faster than perturbations in the problem of constant thickness conductors. Comparison of our results with simulations of the growth of stratification during electrical heating of foils in warm dense matter generation systems demonstrates their close agreement.

Service life of fence posts treated by double-diffusion methods

Treesearch

Donald C. Markstrom; Lee R. Gjovik

1999-01-01

Service-life tests indicate that Engelmann spruce, lodgepole pine, and Rocky Mountain Douglas-fir fence posts treated by double-diffusion methods performed excellently after field exposure of 30 years with no failures. The test site was located in the semiarid Central Plains near Nunn, Colorado. Although Engelmann spruce posts generally defy treatment by other treating...

Radiation hydrodynamics of triggered star formation: the effect of the diffuse radiation field

NASA Astrophysics Data System (ADS)

Haworth, Thomas J.; Harries, Tim J.

2012-02-01

We investigate the effect of including diffuse field radiation when modelling the radiatively driven implosion of a Bonnor-Ebert sphere (BES). Radiation-hydrodynamical calculations are performed by using operator splitting to combine Monte Carlo photoionization with grid-based Eulerian hydrodynamics that includes self-gravity. It is found that the diffuse field has a significant effect on the nature of radiatively driven collapse which is strongly coupled to the strength of the driving shock that is established before impacting the BES. This can result in either slower or more rapid star formation than expected using the on-the-spot approximation depending on the distance of the BES from the source object. As well as directly compressing the BES, stronger shocks increase the thickness and density in the shell of accumulated material, which leads to short, strong, photoevaporative ejections that reinforce the compression whenever it slows. This happens particularly effectively when the diffuse field is included as rocket motion is induced over a larger area of the shell surface. The formation and evolution of 'elephant trunks' via instability is also found to vary significantly when the diffuse field is included. Since the perturbations that seed instabilities are smeared out elephant trunks form less readily and, once formed, are exposed to enhanced thermal compression.

Performance improvements of the vertical, double-diffused power metal-oxide-silicon field-effect transistor

NASA Astrophysics Data System (ADS)

Zhu, Ronghua

An n-channel power vertical double-diffused metal-oxide-silicon field-effect transistor (VDMOSFET) with a new atomic-lattice-layout (ALL) has been designed and fabricated. The performance of the VDMOSFET with the ALL has been studied experimentally and comprehensively for the first time. The experimental results with the ALL are compared with the square (SQ), hexagonal (HEX) and stripe (STR) layouts for different applications. For high-frequency applications of VDMOSFET, the ALL is superior to the HEX and inferior to the STR. The optimum specific on-resistance and input capacitance product (Rsb{ON,SP} × Csb{iss,SP}) and optimum specific on-resistance and output capacitance product (Rsb{ON,SP} × Csb{oss,SP}) for the ALL are 44% and 36% lower than the HEX, and 10% and 13% higher than the STR, respectively. The ALL offers superior performance compared to the SQ for applications involving smart power feedback control using integrated current sensor. For a typical sense resistance of 100 Omega, the sense current drops 44% of its value at 0 Omega for the SQ, but only 11% for the ALL. For high-voltage and high-current applications, such as voltage-controlled current source, one observes that the ALL enters into quasi-saturation region at lower gate voltage (Vsb{G}). Typically, quasi-saturation occurs at Vsb{G} of 3V above the threshold voltage (Vsb{T}) for ALL, whereas this voltage is 5 and 6V for the STR and HEX, respectively. Minority carrier lifetime control by proton implantation has been successfully employed to improve the VDMOSFET built-in diode switching performance for the first time. A sevenfold reduction in reverse recovery charge has been achieved with a proton energy of 2.5 MeV and dose of 3 × 10sp{11}/cmsp2. The impact of proton implantation on diode forward voltage and the VDMOSFET characteristics, such as Vsb{T}, leakage current and on-resistance, has been found negligible. Proton implantation has also been found to significantly improve the device ruggedness. The peak reverse current of the built-in diode is reduced to 17.6 A for a proton energy of 1.5 MeV compared to 29.1 A for an un-implanted device at di/dt = 450 A/mus. The optimum location of the proton has been found at approximately middle of the epi-layer.

Visualizing repetitive diffusion activity of double-strand RNA binding proteins by single molecule fluorescence assays.

PubMed

Koh, Hye Ran; Wang, Xinlei; Myong, Sua

2016-08-01

TRBP, one of double strand RNA binding proteins (dsRBPs), is an essential cofactor of Dicer in the RNA interference pathway. Previously we reported that TRBP exhibits repetitive diffusion activity on double strand (ds)RNA in an ATP independent manner. In the TRBP-Dicer complex, the diffusion mobility of TRBP facilitates Dicer-mediated RNA cleavage. Such repetitive diffusion of dsRBPs on a nucleic acid at the nanometer scale can be appropriately captured by several single molecule detection techniques. Here, we provide a step-by-step guide to four different single molecule fluorescence assays by which the diffusion activity of dsRBPs on dsRNA can be detected. One color assay, termed protein induced fluorescence enhancement enables detection of unlabeled protein binding and diffusion on a singly labeled RNA. Two-color Fluorescence Resonance Energy Transfer (FRET) in which labeled dsRBPs is applied to labeled RNA, allows for probing the motion of protein along the RNA axis. Three color FRET reports on the diffusion movement of dsRBPs from one to the other end of RNA. The single molecule pull down assay provides an opportunity to collect dsRBPs from mammalian cells and examine the protein-RNA interaction at single molecule platform. Copyright © 2016 Elsevier Inc. All rights reserved.

Computational Analysis on Performance of Thermal Energy Storage (TES) Diffuser

NASA Astrophysics Data System (ADS)

Adib, M. A. H. M.; Adnan, F.; Ismail, A. R.; Kardigama, K.; Salaam, H. A.; Ahmad, Z.; Johari, N. H.; Anuar, Z.; Azmi, N. S. N.

2012-09-01

Application of thermal energy storage (TES) system reduces cost and energy consumption. The performance of the overall operation is affected by diffuser design. In this study, computational analysis is used to determine the thermocline thickness. Three dimensional simulations with different tank height-to-diameter ratio (HD), diffuser opening and the effect of difference number of diffuser holes are investigated. Medium HD tanks simulations with double ring octagonal diffuser show good thermocline behavior and clear distinction between warm and cold water. The result show, the best performance of thermocline thickness during 50% time charging occur in medium tank with height-to-diameter ratio of 4.0 and double ring octagonal diffuser with 48 holes (9mm opening ~ 60%) acceptable compared to diffuser with 6mm ~ 40% and 12mm ~ 80% opening. The conclusion is computational analysis method are very useful in the study on performance of thermal energy storage (TES).

Direct simulation Monte Carlo investigation of the Richtmyer-Meshkov instability

DOE PAGES

Gallis, Michail A.; Koehler, Timothy P.; Torczynski, John R.; ...

2015-08-14

The Rayleigh-Taylor instability (RTI) is investigated using the Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce all qualitative features of the RTI and are in reasonable quantitative agreement with existing theoretical and empirical models in the linear, nonlinear, and self-similar regimes. At late times, the instability is seen to exhibit a self-similar behavior, in agreement with experimental observations. Formore » the conditions simulated, diffusion can influence the initial instability growth significantly.« less

Two-dimensional dynamics of elasto-inertial turbulence and its role in polymer drag reduction

NASA Astrophysics Data System (ADS)

Sid, S.; Terrapon, V. E.; Dubief, Y.

2018-02-01

The goal of the present study is threefold: (i) to demonstrate the two-dimensional nature of the elasto-inertial instability in elasto-inertial turbulence (EIT), (ii) to identify the role of the bidimensional instability in three-dimensional EIT flows, and (iii) to establish the role of the small elastic scales in the mechanism of self-sustained EIT. Direct numerical simulations of viscoelastic fluid flows are performed in both two- and three-dimensional straight periodic channels using the Peterlin finitely extensible nonlinear elastic model (FENE-P). The Reynolds number is set to Reτ=85 , which is subcritical for two-dimensional flows but beyond the transition for three-dimensional ones. The polymer properties selected correspond to those of typical dilute polymer solutions, and two moderate Weissenberg numbers, Wiτ=40 ,100 , are considered. The simulation results show that sustained turbulence can be observed in two-dimensional subcritical flows, confirming the existence of a bidimensional elasto-inertial instability. The same type of instability is also observed in three-dimensional simulations where both Newtonian and elasto-inertial turbulent structures coexist. Depending on the Wi number, one type of structure can dominate and drive the flow. For large Wi values, the elasto-inertial instability tends to prevail over the Newtonian turbulence. This statement is supported by (i) the absence of typical Newtonian near-wall vortices and (ii) strong similarities between two- and three-dimensional flows when considering larger Wi numbers. The role of small elastic scales is investigated by introducing global artificial diffusion (GAD) in the hyperbolic transport equation for polymers. The aim is to measure how the flow reacts when the smallest elastic scales are progressively filtered out. The study results show that the introduction of large polymer diffusion in the system strongly damps a significant part of the elastic scales that are necessary to feed turbulence, eventually leading to flow laminarization. A sufficiently high Schmidt number (weakly diffusive polymers) is necessary to allow self-sustained turbulence to settle. Although EIT can withstand a low amount of diffusion and remains in a nonlaminar chaotic state, adding a finite amount of GAD in the system can have an impact on the dynamics and lead to important quantitative changes, even for Schmidt numbers as large as 102. The use of GAD should therefore be avoided in viscoelastic flow simulations.

Crawling and turning in a minimal reaction-diffusion cell motility model: Coupling cell shape and biochemistry

NASA Astrophysics Data System (ADS)

Camley, Brian A.; Zhao, Yanxiang; Li, Bo; Levine, Herbert; Rappel, Wouter-Jan

2017-01-01

We study a minimal model of a crawling eukaryotic cell with a chemical polarity controlled by a reaction-diffusion mechanism describing Rho GTPase dynamics. The size, shape, and speed of the cell emerge from the combination of the chemical polarity, which controls the locations where actin polymerization occurs, and the physical properties of the cell, including its membrane tension. We find in our model both highly persistent trajectories, in which the cell crawls in a straight line, and turning trajectories, where the cell transitions from crawling in a line to crawling in a circle. We discuss the controlling variables for this turning instability and argue that turning arises from a coupling between the reaction-diffusion mechanism and the shape of the cell. This emphasizes the surprising features that can arise from simple links between cell mechanics and biochemistry. Our results suggest that similar instabilities may be present in a broad class of biochemical descriptions of cell polarity.

Effects of eletron heating on the current driven electrostatic ion cyclotron instability and plasma transport processes along auroral field lines

NASA Technical Reports Server (NTRS)

Ganguli, Supriya B.; Mitchell, Horace G.; Palmadesso, Peter J.

1988-01-01

Fluid simulations of the plasma along auroral field lines in the return current region have been performed. It is shown that the onset of electrostatic ion cyclotron (EIC) related anomalous resistivity and the consequent heating of electrons leads to a transverse ion temperature that is much higher than that produced by the current driven EIC instability (CDICI) alone. Two processes are presented for the enhancement of ion heating by anomalous resistivity. The anomalous resistivity associated with the turbulence is limited by electron heating, so that CDICI saturates at transverse temperature that is substantially higher than in the absence of resistivity. It is suggested that this process demonstrates a positive feedback loop in the interaction between CDICI, anomalous resistivity, and parallel large-scale dynamics in the topside ionosphere.

Evaluation of diffuse-illumination holographic cinematography in a flutter cascade

NASA Technical Reports Server (NTRS)

Decker, A. J.

1986-01-01

Since 1979, the Lewis Research Center has examined holographic cinematography for three-dimensional flow visualization. The Nd:YAG lasers used were Q-switched, double-pulsed, and frequency-doubled, operating at 20 pulses per second. The primary subjects for flow visualization were the shock waves produced in two flutter cascades. Flow visualization was by diffuse-illumination, double-exposure, and holographic interferometry. The performances of the lasers, holography, and diffuse-illumination interferometry are evaluated in single-window wind tunnels. The fringe-contrast factor is used to evaluate the results. The effects of turbulence on shock-wave visualization in a transonic flow are discussed. The depth of field for visualization of a turbulent structure is demonstrated to be a measure of the relative density and scale of that structure. Other items discussed are the holographic emulsion, tests of coherence and polarization, effects of windows and diffusers, hologram bleaching, laser configurations, influence and handling of specular reflections, modes of fringe localization, noise sources, and coherence requirements as a function of the pulse energy. Holography and diffuse illumination interferometry are also reviewed.

Ultra-low specific on-resistance 700V LDMOS with a buried super junction layer

NASA Astrophysics Data System (ADS)

Wang, Hai-Shi; Li, Zhi-you; Li, Ke; Qiao, Ming

2018-01-01

An ultra-low specific on-resistance 700 V lateral double-diffused MOSFET (LDMOS) with a buried super junction (BSJ) layer is proposed. [1-9] Buried P-pillars in the LDMOS can be depleted by neighboring N-pillars, overlying and underlying N-drift regions simultaneously, thus allowing a higher doping concentration. Consequently, the doping concentration of either the N-drift regions or N-pillars, or both, may also be increased therewith to compensate the surplus charges in the P-pillars. Compared with conventional surface super junction (SSJ) LDMOS, in which the super junction layer is implemented at the upper surface of the drift region, and P-pillars can only be depleted by the adjacent N-pillars and the N-drift regions beneath, the proposed novel LDMOS structure may have a lower specific on-resistance (Ron,sp) while maintain the same breakdown voltage (BV). Simulation results indicate that the Ron,sp of the novel structure is only 80.5 mΩ cm2 with a high BV of 750 V, which is reduced by 17% in comparison with the Ron,sp of a conventional SSJ LDMOS.

Thickness effect of ultra-thin Ta2O5 resistance switching layer in 28 nm-diameter memory cell

NASA Astrophysics Data System (ADS)

Park, Tae Hyung; Song, Seul Ji; Kim, Hae Jin; Kim, Soo Gil; Chung, Suock; Kim, Beom Yong; Lee, Kee Jeung; Kim, Kyung Min; Choi, Byung Joon; Hwang, Cheol Seong

2015-11-01

Resistance switching (RS) devices with ultra-thin Ta2O5 switching layer (0.5-2.0 nm) with a cell diameter of 28 nm were fabricated. The performance of the devices was tested by voltage-driven current—voltage (I-V) sweep and closed-loop pulse switching (CLPS) tests. A Ta layer was placed beneath the Ta2O5 switching layer to act as an oxygen vacancy reservoir. The device with the smallest Ta2O5 thickness (0.5 nm) showed normal switching properties with gradual change in resistance in I-V sweep or CLPS and high reliability. By contrast, other devices with higher Ta2O5 thickness (1.0-2.0 nm) showed abrupt switching with several abnormal behaviours, degraded resistance distribution, especially in high resistance state, and much lower reliability performance. A single conical or hour-glass shaped double conical conducting filament shape was conceived to explain these behavioural differences that depended on the Ta2O5 switching layer thickness. Loss of oxygen via lateral diffusion to the encapsulating Si3N4/SiO2 layer was suggested as the main degradation mechanism for reliability, and a method to improve reliability was also proposed.

Elucidation of the active conformation of vancomycin dimers with antibacterial activity against vancomycin-resistant bacteria.

PubMed

Nakamura, Jun; Yamashiro, Hidenori; Hayashi, Sayaka; Yamamoto, Mami; Miura, Kenji; Xu, Shu; Doi, Takayuki; Maki, Hideki; Yoshida, Osamu; Arimoto, Hirokazu

2012-10-01

Covalently linked vancomycin dimers have attracted a great deal of attention among researchers because of their enhanced antibacterial activity against vancomycin-resistant strains. However, the lack of a clear insight into the mechanisms of action of these dimers hampers rational optimization of their antibacterial potency. Here, we describe the synthesis and antibacterial activity of novel vancomycin dimers with a constrained molecular conformation achieved by two tethers between vancomycin units. Conformational restriction is a useful strategy for studying the relationship between the molecular topology and biological activity of compounds. In this study, two vancomycin units were linked at three distinct positions of the glycopeptide (vancosamine residue (V), C terminus (C), and N terminus (N)) to form two types of novel vancomycin cyclic dimers. Active NC-VV-linked dimers with a stable conformation as indicated by molecular mechanics calculations selectively suppressed the peptidoglycan polymerization reaction of vancomycin-resistant Staphylococcus aureus in vitro. In addition, double-disk diffusion tests indicated that the antibacterial activity of these dimers against vancomycin-resistant enterococci might arise from the inhibition of enzymes responsible for peptidoglycan polymerization. These findings provide a new insight into the biological targets of vancomycin dimers and the conformational requirements for efficient antibacterial activity against vancomycin-resistant strains. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superconductivity at 33-37 K in A L n2Fe4As4O2 (A =Kand Cs;L n =lanthanides)

NASA Astrophysics Data System (ADS)

Wu, Si-Qi; Wang, Zhi-Cheng; He, Chao-Yang; Tang, Zhang-Tu; Liu, Yi; Cao, Guang-Han

2017-09-01

We have synthesized ten iron oxyarsenides, K L n2Fe4As4O2 (L n =Gd,Tb,Dy, and Ho) and Cs L n2Fe4As4O2 (L n =Nd,Sm,Gd,Tb,Dy, and Ho) , with the aid of the lattice-match approach. The resultant compounds possess hole-doped conducting double FeAs layers [AFe4As4] 2 - that are separated by the insulating [Ln2O2] 2 + slabs. Measurements of electrical resistivity and dc magnetic susceptibility demonstrate bulk superconductivity at Tc=33 -37 K. We find that Tc correlates with the axial ratio c /a for all 12442-type superconductors discovered. Also, Tc tends to increase with the lattice mismatch, implying that lattice instability plays a role in the enhancement of superconductivity.

Impact of Lateral Straggle on the Analog/RF Performance of Asymmetric Gate Stack Double Gate MOSFET

NASA Astrophysics Data System (ADS)

Sivaram, Gollamudi Sai; Chakraborty, Shramana; Das, Rahul; Dasgupta, Arpan; Kundu, Atanu; Sarkar, Chandan K.

2016-09-01

This paper presents a systematic comparative study of Analog and RF performances of an underlapped double gate (U-DG) NMOSFET with Gate Stack (GS) for varying straggle lengths. Asymmetric underlap devices (A-U-DG) have been proposed as one of the remedies for reducing Short Channel Effects (SCE's) with the underlap being present towards the source for sub 20 nm devices. However, the Source to Drain (S/D) implant lateral diffusion leads to a variation in the effective underlap length. This paper investigates the impact of variation of straggle length on the Analog and RF parameters of the device. The RF performance is analyzed by considering the intrinsic capacitances (Cgd, Cgs), intrinsic resistances (Rgd, Rgs), transport delay (τm), inductance (Lsd), cutoff frequency (fT), and the maximum frequency of oscillations (fmax). The circuit performance of the devices are also studied. It is seen that the Analog and RF performances of the devices are improved by optimizing the S/D lateral straggle.

Double exposure using 193nm negative tone photoresist

NASA Astrophysics Data System (ADS)

Kim, Ryoung-han; Wallow, Tom; Kye, Jongwook; Levinson, Harry J.; White, Dave

2007-03-01

Double exposure is one of the promising methods for extending lithographic patterning into the low k I regime. In this paper, we demonstrate double patterning of k 1-effective=0.25 with improved process window using a negative resist. Negative resist (TOK N- series) in combination with a bright field mask is proven to provide a large process window in generating 1:3 = trench:line resist features. By incorporating two etch transfer steps into the hard mask material, frequency doubled patterns could be obtained.

Resolving Overlimiting Current Mechanisms in Microchannel-Nanochannel Interface Devices

NASA Astrophysics Data System (ADS)

Yossifon, Gilad; Leibowitz, Neta; Liel, Uri; Schiffbauer, Jarrod; Park, Sinwook

2015-11-01

We present results demonstrating the space charge-mediated transition between classical, diffusion-limited current and surface-conduction dominant over-limiting currents in a shallow micro-nanochannel device. The extended space charge layer develops at the depleted micro-nanochannel entrance at high current and is correlated with a distinctive maximum in the dc resistance. Experimental results for a shallow surface-conduction dominated system are compared with theoretical models, allowing estimates of the effective surface charge at high voltage to be obtained. Further, we extend the study to microchannels of moderate to large depths where the role of various electro-convection mechanisms becomes dominant. In particular, electro-osmotic of the second kind and electro-osmotic instability (EOI) which competes each other at geometrically heterogeneous (e.g. undulated nanoslot interface, array of nanoslots) nanoslot devices. Also, these effects are also shown to be strongly modulated by the non-ideal permselectivity of the nanochannel.

Interaction of thermal and mechanical processes in steep permafrost rock walls: A conceptual approach

NASA Astrophysics Data System (ADS)

Draebing, D.; Krautblatter, M.; Dikau, R.

2014-12-01

Degradation of permafrost rock wall decreases stability and can initiate rock slope instability of all magnitudes. Rock instability is controlled by the balance of shear forces and shear resistances. The sensitivity of slope stability to warming results from a complex interplay of shear forces and resistances. Conductive, convective and advective heat transport processes act to warm, degrade and thaw permafrost in rock walls. On a seasonal scale, snow cover changes are a poorly understood key control of the timing and extent of thawing and permafrost degradation. We identified two potential critical time windows where shear forces might exceed shear resistances of the rock. In early summer combined hydrostatic and cryostatic pressure can cause a peak in shear force exceeding high frozen shear resistance and in autumn fast increasing shear forces can exceed slower increasing shear resistance. On a multiannual system scale, shear resistances change from predominantly rock-mechanically to ice-mechanically controlled. Progressive rock bridge failure results in an increase of sensitivity to warming. Climate change alters snow cover and duration and, hereby, thermal and mechanical processes in the rock wall. Amplified thawing of permafrost will result in higher rock slope instability and rock fall activity. We present a holistic conceptual approach connecting thermal and mechanical processes, validate parts of the model with geophysical and kinematic data and develop future scenarios to enhance understanding on system scale.

Effect of rotation on fingering convection in stellar and planetary interiors

NASA Astrophysics Data System (ADS)

Sengupta, Sutirtha; Garaud, Pascale

2018-01-01

We study the effects of global rotation on the growth and saturation of the fingering (double-diffusive) instability at low Prandtl numbers and estimate the compositional transport rates as a function of the relevant non-dimensional parameters - the Taylor number, Ta^* (defined in terms of the rotation rate, Ω, thermal diffusivity κ_T and associated finger length scale d) and density ratio through direct numerical simulations. Within our explored range of parameters, we find rotation to have very little effect on vertical transport apart for an exceptional case where a cyclonic large scale vortex (LSV) is observed at low density ratio and fairly high Taylor number. The LSV leads to significant enhancement in the fingering transport rates by concentrating high composition fluid at its core which moves downward. The formation of such LSVs is of particular interest for solving the missing mixing problem in the astrophysical context of RGB stars though the parameter regime in which we observe the emergence of this LSV seems to be quite far from the stellar scenario. However, understanding the basic mechanism driving such large scale structures as observed frequently in polar regions of planets (e.g. those seen by Juno near the poles of Jupiter) is important in general for studies of rotating turbulence and its applications to stellar and planetary interior studies, and will be investigated in further detail in a forthcoming work.

Evidence of locally enhanced target heating due to instabilities of counter-streaming fast electron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koester, Petra; Cecchetti, Carlo A.; Booth, Nicola

2015-02-15

The high-current fast electron beams generated in high-intensity laser-solid interactions require the onset of a balancing return current in order to propagate in the target material. Such a system of counter-streaming electron currents is unstable to a variety of instabilities such as the current-filamentation instability and the two-stream instability. An experimental study aimed at investigating the role of instabilities in a system of symmetrical counter-propagating fast electron beams is presented here for the first time. The fast electron beams are generated by double-sided laser-irradiation of a layered target foil at laser intensities above 10{sup 19 }W/cm{sup 2}. High-resolution X-ray spectroscopy ofmore » the emission from the central Ti layer shows that locally enhanced energy deposition is indeed achieved in the case of counter-propagating fast electron beams.« less

Assessment of anterior shoulder instability by CT arthrography.

PubMed

Yang, S O; Cho, K J; Kim, M J; Ro, I W

1987-09-01

Computed tomography (CT) immediately after double-contrast shoulder arthrography was taken in twenty-two young male patients with anterior shoulder instability including recurrent dislocation and subluxation. This recently developed technique called CT arthrography can provide significant information about patients with glenohumeral instability which is difficult to obtain by conventional arthrography. Information about glenoid labrum pathology is useful for proper management of the shoulder with instability. Lesions identified in this study include anterior labral defects (attenuation, tear, displacement), anterior capsular distension and/or detachment, Hill-Sachs lesion, anterior glenoid rim compression fracture, and fracture of scapula. This article describes the method used in CT arthrography of the glenohumeral joint, reviews the normal cross-sectional anatomy, and emphasizes the importance of the application of CT arthrography in the shoulder disorder with instability. CT arthrography of the glenohumeral joint is easy to perform, is accurate, and has lower radiation dose than arthrotomography.

Analytical expression for Risken-Nummedal-Graham-Haken instability threshold in quantum cascade lasers.

PubMed

Vukovic, N; Radovanovic, J; Milanovic, V; Boiko, D L

2016-11-14

We have obtained a closed-form expression for the threshold of Risken-Nummedal-Graham-Haken (RNGH) multimode instability in a Fabry-Pérot (FP) cavity quantum cascade laser (QCL). This simple analytical expression is a versatile tool that can easily be applied in practical situations which require analysis of QCL dynamic behavior and estimation of its RNGH multimode instability threshold. Our model for a FP cavity laser accounts for the carrier coherence grating and carrier population grating as well as their relaxation due to carrier diffusion. In the model, the RNGH instability threshold is analyzed using a second-order bi-orthogonal perturbation theory and we confirm our analytical solution by a comparison with the numerical simulations. In particular, the model predicts a low RNGH instability threshold in QCLs. This agrees very well with experimental data available in the literature.

On the generation of double layers from ion- and electron-acoustic instabilities

NASA Astrophysics Data System (ADS)

Fu, Xiangrong; Cowee, Misa M.; Gary, S. Peter; Winske, Dan

2016-03-01

A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric field structures traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs—electron acoustic DLs—generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e., the hypothetical electron acoustic DLs cannot be formed in a way similar to ion acoustic DLs. Linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric field structures that propagate at the electron thermal speed, suggesting another potential explanation for the observations.

Increase of β-Lactam-Resistant Invasive Haemophilus influenzae in Sweden, 1997 to 2010

PubMed Central

Resman, Fredrik; Ristovski, Mikael; Forsgren, Arne; Kaijser, Bertil; Kronvall, Göran; Medstrand, Patrik; Melander, Eva; Odenholt, Inga

2012-01-01

The proportions of Haemophilus influenzae resistant to ampicillin and other β-lactam antibiotics have been low in Sweden compared to other countries in the Western world. However, a near-doubled proportion of nasopharyngeal Swedish H. influenzae isolates with resistance to β-lactams has been observed in the last decade. In the present study, the epidemiology and mechanisms of antimicrobial resistance of H. influenzae isolates from blood and cerebrospinal fluid in southern Sweden from 1997 to 2010 (n = 465) were studied. Antimicrobial susceptibility testing was performed using disk diffusion, and isolates with resistance to any tested β-lactam were further analyzed in detail. We identified a significantly increased (P = 0.03) proportion of β-lactam-resistant invasive H. influenzae during the study period, which was mainly attributed to a significant recent increase of β-lactamase-negative β-lactam-resistant isolates (P = 0.04). Furthermore, invasive β-lactamase-negative β-lactam-resistant H. influenzae isolates from 2007 and onwards were found in higher proportions than the corresponding proportions of nasopharyngeal isolates in a national survey. Multiple-locus sequence typing (MLST) of this group of isolates did not completely separate isolates with different resistance phenotypes. However, one cluster of β-lactamase-negative ampicillin-resistant (BLNAR) isolates was identified, and it included isolates from all geographical areas. A truncated variant of a β-lactamase gene with a promoter deletion, blaTEM-1-PΔ dominated among the β-lactamase-positive H. influenzae isolates. Our results show that the proportions of β-lactam-resistant invasive H. influenzae have increased in Sweden in the last decade. PMID:22687505

A preliminary study of the electro-oxidation of L-ascorbic acid on polycrystalline silver in alkaline solution

NASA Astrophysics Data System (ADS)

Majari Kasmaee, L.; Gobal, F.

Electrochemical oxidation of L-ascorbic acid on polycrystalline silver in alkaline aqueous solutions is studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (IS). The anodic electro-oxidation starts at -500 mV versus SCE and shows continued anodic oxidation in the cathodic half cycle in the CV regime signifying slowly oxidizing adsorbates. Diffusion coefficient of ascorbate ion measured under both voltammetric regimes is around 1.4 × 10 -5 cm 2 s -1. Impedance spectroscopy measures the capacitances associated with double layer and adsorption around 50 μF cm -2 and 4 mF cm -2 as well as the adsorption and decomposition resistances (rates).

The influence of stripe width on the threshold current of double-heterojunction lasers

NASA Technical Reports Server (NTRS)

Ladany, I.

1977-01-01

Experimental measurements of the threshold current of oxide-isolated stripe laser as a function of stripe width and p-layer resistivity are presented. A calculation of the influence of carrier outdiffusion has been made, including the effect of current leakage beyond the stripe edges. The calculated threshold increase is in substantial agreement with experiment for stripe widths down to about 10 microns. The data also yield an effective diffusion length of about 7 microns for the lasers studied. Deviations between experimental and calculated thresholds occurring at stripe widths of 4-6 microns are represented by an empirical curve which is compared with previously published calculations of threshold gain.

Active unsteady aerodynamic suppression of rotating stall in an incompressible flow centrifugal compressor with vaned diffuser

NASA Technical Reports Server (NTRS)

Lawless, Patrick B.; Fleeter, Sanford

1991-01-01

A mathematical model is developed to analyze the suppression of rotating stall in an incompressible flow centrifugal compressor with a vaned diffuser, thereby addressing the important need for centrifugal compressor rotating stall and surge control. In this model, the precursor to to instability is a weak rotating potential velocity perturbation in the inlet flow field that eventually develops into a finite disturbance. To suppress the growth of this potential disturbance, a rotating control vortical velocity disturbance is introduced into the impeller inlet flow. The effectiveness of this control is analyzed by matching the perturbation pressure in the compressor inlet and exit flow fields with a model for the unsteady behavior of the compressor. To demonstrate instability control, this model is then used to predict the control effectiveness for centrifugal compressor geometries based on a low speed research centrifugal compressor. These results indicate that reductions of 10 to 15 percent in the mean inlet flow coefficient at instability are possible with control waveforms of half the magnitude of the total disturbance at the inlet.

Effect of gravity on the stability and structure of lean hydrogen-air flames

NASA Technical Reports Server (NTRS)

Patnaik, G.; Kailasanath, K.

1991-01-01

Detailed, time-dependent, 2D numerical simulations with full hydrogen-oxygen chemistry are used to investigate the effects of gravity on the stability and structure of laminar flames in lean, premixed hydrogen-air mixtures. The calculations show that the effects of gravity becomes more important as the lean flammability limit is approached. In a 12 percent hydrogen-air mixture, gravity plays only a secondary role in determining the multidimensional structure of the flame with the stability and structure of the flame controlled primarily by the thermo-diffusive instability mechanism. However, in leaner hydrogen-air mixtures gravity becomes more important. Upward-propagating flames are highly curved and evolve into a bubble rising upwards in the tube. Downward-propagating flames are flat or even oscillate between structures with concave and convex curvatures. The zero-gravity flame shows only cellular structures. Cellular structures which are present in zero gravity can be suppressed by the effect of buoyancy for mixtures leaner than 11 percent hydrogen. These observations are explained on the basis of an interaction between the processes leading to buoyancy-induced Rayleigh-Taylor instability and the thermo-diffusive instability.

On the role of the lower hybrid drift instability in substorm dynamics

NASA Technical Reports Server (NTRS)

Huba, J. D.; Gladd, N. T.; Drake, J. F.

1981-01-01

Recent studies of the lower hybrid drift instability have shed new light on the role of this mode in field-reversed plasmas. For substorm magnetotail conditions it is found that the lower hybrid drift instability can penetrate to the neutral line and can dissipate magnetic energy at a rate of approximately 4 x 10 to the 17th erg/s. Thus this instability is capable of playing a major role in the onset of substorms and providing resistivity for reconnection processes in the context of the neutral line substorm model.

Beam-plasma instability in the presence of low-frequency turbulence. [during type 3 solar emission

NASA Technical Reports Server (NTRS)

Goldman, M. V.; Dubois, D. F.

1982-01-01

General equations are derived for a linear beam-plasma instability in the presence of low-frequency turbulence. Within a 'quasi-linear' statistical approximation, these equations contain Langmuir wave scattering, diffusion, resonant and nonresonant anomalous absorption, and a 'plasma laser' effect. It is proposed that naturally occurring density irregularities in the solar wind may stabilize the beam-unstable Langmuir waves which occur during type III solar emissions.

Lateral carrier diffusion and current gain in terahertz InGaAs/InP double-heterojunction bipolar transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiang, Han-Wei; Rode, Johann C.; Choudhary, Prateek

2014-01-21

The DC current gain in In{sub 0.53}Ga{sub 0.47}As/InP double-heterojunction bipolar transistors is computed based on a drift-diffusion model, and is compared with experimental data. Even in the absence of other scaling effects, lateral diffusion of electrons to the base Ohmic contacts causes a rapid reduction in DC current gain as the emitter junction width and emitter-base contact spacing are reduced. The simulation and experimental data are compared in order to examine the effect of carrier lateral diffusion on current gain. The impact on current gain due to device scaling and approaches to increase current gain are discussed.

Gyrokinetic modelling of the quasilinear particle flux for plasmas with neutral-beam fuelling

NASA Astrophysics Data System (ADS)

Narita, E.; Honda, M.; Nakata, M.; Yoshida, M.; Takenaga, H.; Hayashi, N.

2018-02-01

A quasilinear particle flux is modelled based on gyrokinetic calculations. The particle flux is estimated by determining factors, namely, coefficients of off-diagonal terms and a particle diffusivity. In this paper, the methodology to estimate the factors is presented using a subset of JT-60U plasmas. First, the coefficients of off-diagonal terms are estimated by linear gyrokinetic calculations. Next, to obtain the particle diffusivity, a semi-empirical approach is taken. Most experimental analyses for particle transport have assumed that turbulent particle fluxes are zero in the core region. On the other hand, even in the stationary state, the plasmas in question have a finite turbulent particle flux due to neutral-beam fuelling. By combining estimates of the experimental turbulent particle flux and the coefficients of off-diagonal terms calculated earlier, the particle diffusivity is obtained. The particle diffusivity should reflect a saturation amplitude of instabilities. The particle diffusivity is investigated in terms of the effects of the linear instability and linear zonal flow response, and it is found that a formula including these effects roughly reproduces the particle diffusivity. The developed framework for prediction of the particle flux is flexible to add terms neglected in the current model. The methodology to estimate the quasilinear particle flux requires so low computational cost that a database consisting of the resultant coefficients of off-diagonal terms and particle diffusivity can be constructed to train a neural network. The development of the methodology is the first step towards a neural-network-based particle transport model for fast prediction of the particle flux.

The nucleus is the target for radiation-induced chromosomal instability

NASA Technical Reports Server (NTRS)

Kaplan, M. I.; Morgan, W. F.

1998-01-01

We have previously described chromosomal instability in cells of a human-hamster hybrid cell line after exposure to X rays. Chromosomal instability in these cells is characterized by the appearance of novel chromosomal rearrangements multiple generations after exposure to ionizing radiation. To identify the cellular target(s) for radiation-induced chromosomal instability, cells were treated with 125I-labeled compounds and frozen. Radioactive decays from 125I cause damage to the cell primarily at the site of their decay, and freezing the cells allows damage to accumulate in the absence of other cellular processes. We found that the decay of 125I-iododeoxyuridine, which is incorporated into the DNA, caused chromosomal instability. While cell killing and first-division chromosomal rearrangements increased with increasing numbers of 125I decays, the frequency of chromosomal instability was independent of dose. Chromosomal instability could also be induced from incorporation of 125I-iododeoxyuridine without freezing the cells for accumulation of decays. This indicates that DNA double-strand breaks in frozen cells resulting from 125I decays failed to lead to instability. Incorporation of an 125I-labeled protein (125I-succinyl-concanavalin A), which was internalized into the cell and/or bound to the plasma membrane, neither caused chromosomal instability nor potentiated chromosomal instability induced by 125I-iododeoxyuridine. These results show that the target for radiation-induced chromosomal instability in these cells is the nucleus.

Convective Electrokinetic Instability With Conductivity Gradients

NASA Astrophysics Data System (ADS)

Chen, Chuan-Hua; Lin, Hao; Lele, Sanjiva; Santiago, Juan

2003-11-01

Electrokinetic flow instability has been experimentally identified and quantified in a glass T-junction microchannel system with a cross section of 11 um x 155 um. In this system, buffers of different conductivities were electrokinetically driven into a common mixing channel by a DC electric field. A convective instability was observed with a threshold electric field of 0.45 kV/cm for a 10:1 conductivity ratio. A physical model has been developed which consists of a modified Ohmic model formulation for electrolyte solutions and the Navier-Stokes equations with an electric body force term. The model and experiments show that bulk charge accumulation in regions of conductivity gradients is the key mechanism of such instabilities. A linear stability analysis was performed in a convective framework, and Briggs-Bers criteria were applied to determine the nature of instability. The analysis shows the instability is governed by two key parameters: the ratio of molecular diffusion to electroviscous time scale which governs the onset of instability, and the ratio of electroviscous to electroosmotic velocity which governs whether the instability is convective or absolute. The model predicted critical electric field, growth rate, wavelength, and phase speed which were comparable to experimental data.

Direct simulation Monte Carlo investigation of the Rayleigh-Taylor instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gallis, M. A.; Koehler, T. P.; Torczynski, J. R.

In this paper, the Rayleigh-Taylor instability (RTI) is investigated using the direct simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce many qualitative features of the growth of the mixing layer and are in reasonable quantitative agreement with theoretical and empirical models in the linear, nonlinear, and self-similar regimes. In some of the simulations at late times, the instability enters themore » self-similar regime, in agreement with experimental observations. Finally, for the conditions simulated, diffusion can influence the initial instability growth significantly.« less

Direct simulation Monte Carlo investigation of the Rayleigh-Taylor instability

DOE PAGES

Gallis, M. A.; Koehler, T. P.; Torczynski, J. R.; ...

2016-08-31

In this paper, the Rayleigh-Taylor instability (RTI) is investigated using the direct simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce many qualitative features of the growth of the mixing layer and are in reasonable quantitative agreement with theoretical and empirical models in the linear, nonlinear, and self-similar regimes. In some of the simulations at late times, the instability enters themore » self-similar regime, in agreement with experimental observations. Finally, for the conditions simulated, diffusion can influence the initial instability growth significantly.« less

Fluctuations and instabilities of a holographic metal

NASA Astrophysics Data System (ADS)

Jokela, Niko; Järvinen, Matti; Lippert, Matthew

2013-02-01

We analyze the quasinormal modes of the D2-D8' model of 2+1-dimensional, strongly-coupled, charged fermions in a background magnetic field and at non-zero density. The model is known to include a quantum Hall phase with integer filling fraction. As expected, we find a hydrodynamical diffusion mode at small momentum and the nonzero-temperature holographic zero sound, which becomes massive above a critical magnetic field. We confirm the previously-known thermodynamic instability. In addition, we discover an instability at low temperature, large mass, and in a charge density and magnetic field range near the quantum Hall phase to an inhomogeneous striped phase.

Chemical instability leads to unusual chemical-potential-independent defect formation and diffusion in perovskite solar cell material CH 3 NH 3 PbI 3

DOE PAGES

Ming, Wenmei; Chen, Shiyou; East China Normal Univ.; ...

2016-10-13

Methylammonium (MA) lead triiodide (MAPbI 3) has recently emerged as a promising solar cell material. But, MAPbI3 is known to have chemical instability, i.e., MAPbI3 is prone to decomposition into MAI and PbI 2 even at moderate temperatures (e.g. 330 K). Here, we show that the chemical instability, as reflected by the calculated negligible enthalpy of formation of MAPbI 3 (with respect to MAI and PbI 2), has an unusual and important consequence for defect properties, i.e., defect formation energies in low-carrier-density MAPbI 3 are nearly independent of the chemical potentials of constituent elements and thus can be uniquely determined. This allows straightforward calculations of defect concentrations and the activation energy of ionic conductivity (the sum of the formation energy and the diffusion barrier of the charged mobile defect) in MAPbI 3. Furthermore, the calculated activation energy for ionic conductivity due to Vmore » $$+\\atop{1}$$ diffusion is in excellent agreement with the experimental values, which demonstrates unambiguously that V$$+\\atop{1}$$ is the dominant diffusing defect and is responsible for the observed ion migration and device polarization in MAPbI3 solar cells. The calculated low formation energy of a Frenkel pair (V$$+\\atop{1}$$ -I$$-\\atop{i}$$ and low diffusion barriers of V$$+\\atop{1}$$ and Image I$$-\\atop{i}$$ suggest that the iodine ion migration and the resulting device polarization may occur even in single-crystal devices and grain-boundary-passivated polycrystalline thin film devices (which were previously suggested to be free from ion-migration-induced device polarization), leading to device degradation. Moreover, the device polarization due to the Frenkel pair (which has a relatively low concentration) may take a long time to develop and thus may avoid the appearance of the current–voltage hysteresis at typical scan rates.« less

Turbulent mixing within the Kuroshio in the Tokara Strait

NASA Astrophysics Data System (ADS)

Tsutsumi, Eisuke; Matsuno, Takeshi; Lien, Ren-Chieh; Nakamura, Hirohiko; Senjyu, Tomoharu; Guo, Xinyu

2017-09-01

Turbulent mixing and background current were observed using a microstructure profiler and acoustic Doppler current profilers in the Tokara Strait, where many seamounts and small islands exist within the route of the Kuroshio in the East China Sea. Vertical structure and water properties of the Kuroshio were greatly modified downstream from shallow seamounts. In the lee of a seamount crest at 200 m depth, the modification made the flow tend to shear instability, and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site, to Kρ ˜ O(10-3)-O(10-2) m2 s-1. A one-dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature-salinity profile. However, the estimated diffusion time-scale is at least 10 times longer than the observed advection time-scale. This suggests that the eddy diffusivity reaches to O(10-1) m2 s-1 in the vicinity of the seamount. At a site away from the abrupt topography, eddy diffusivity was also elevated to O(10-3) m2 s-1, and was associated with shear instability presumably induced by the Kuroshio shear and near-inertial internal-wave shear. Our study suggests that a better prediction of current, water-mass properties, and nutrients within the Kuroshio requires accurate understanding and parameterization of flow-topography interaction such as internal hydraulics, the associated internal-wave processes, and turbulent mixing processes.

Double diffusivity model under stochastic forcing

NASA Astrophysics Data System (ADS)

Chattopadhyay, Amit K.; Aifantis, Elias C.

2017-05-01

The "double diffusivity" model was proposed in the late 1970s, and reworked in the early 1980s, as a continuum counterpart to existing discrete models of diffusion corresponding to high diffusivity paths, such as grain boundaries and dislocation lines. It was later rejuvenated in the 1990s to interpret experimental results on diffusion in polycrystalline and nanocrystalline specimens where grain boundaries and triple grain boundary junctions act as high diffusivity paths. Technically, the model pans out as a system of coupled Fick-type diffusion equations to represent "regular" and "high" diffusivity paths with "source terms" accounting for the mass exchange between the two paths. The model remit was extended by analogy to describe flow in porous media with double porosity, as well as to model heat conduction in media with two nonequilibrium local temperature baths, e.g., ion and electron baths. Uncoupling of the two partial differential equations leads to a higher-ordered diffusion equation, solutions of which could be obtained in terms of classical diffusion equation solutions. Similar equations could also be derived within an "internal length" gradient (ILG) mechanics formulation applied to diffusion problems, i.e., by introducing nonlocal effects, together with inertia and viscosity, in a mechanics based formulation of diffusion theory. While being remarkably successful in studies related to various aspects of transport in inhomogeneous media with deterministic microstructures and nanostructures, its implications in the presence of stochasticity have not yet been considered. This issue becomes particularly important in the case of diffusion in nanopolycrystals whose deterministic ILG-based theoretical calculations predict a relaxation time that is only about one-tenth of the actual experimentally verified time scale. This article provides the "missing link" in this estimation by adding a vital element in the ILG structure, that of stochasticity, that takes into account all boundary layer fluctuations. Our stochastic-ILG diffusion calculation confirms rapprochement between theory and experiment, thereby benchmarking a new generation of gradient-based continuum models that conform closer to real-life fluctuating environments.

Energy dynamics in stressed magnetic fields - The filamentation and flare instabilities

NASA Technical Reports Server (NTRS)

Van Hoven, G.; Steinolfson, R. S.; Tachi, T.

1983-01-01

The thermal and tearing instabilities are believed to be the two primary temperature modification mechanisms in sheared astrophysical magnetic fields. The former gives rise to the formation of cool filaments and the latter to the release of magnetic energy. It has long been known that these processes are interrelated, most conspicuously in the case of the solar corona where prominences often precede flares within the same magnetic structure. It is also clear, from first principles, that the energy transport underlying the thermal instability should have a strong effect on the resistivity which facilitates magnetic tearing, and that the energy release of the latter should affect the temperature drop of the former. This paper describes some results of the first calculations which attempt to unify the dynamic treatment of these two coexisting instabilities. Growth rates as a function of resistivity, and examples of the primary mode structures are provided, along with a discussion of some critical aspects of the interaction of these two astrophysical energy flux mechanisms.

Numerical simulation of immiscible viscous fingering using adaptive unstructured meshes

NASA Astrophysics Data System (ADS)

Adam, A.; Salinas, P.; Percival, J. R.; Pavlidis, D.; Pain, C.; Muggeridge, A. H.; Jackson, M.

2015-12-01

Displacement of one fluid by another in porous media occurs in various settings including hydrocarbon recovery, CO2 storage and water purification. When the invading fluid is of lower viscosity than the resident fluid, the displacement front is subject to a Saffman-Taylor instability and is unstable to transverse perturbations. These instabilities can grow, leading to fingering of the invading fluid. Numerical simulation of viscous fingering is challenging. The physics is controlled by a complex interplay of viscous and diffusive forces and it is necessary to ensure physical diffusion dominates numerical diffusion to obtain converged solutions. This typically requires the use of high mesh resolution and high order numerical methods. This is computationally expensive. We demonstrate here the use of a novel control volume - finite element (CVFE) method along with dynamic unstructured mesh adaptivity to simulate viscous fingering with higher accuracy and lower computational cost than conventional methods. Our CVFE method employs a discontinuous representation for both pressure and velocity, allowing the use of smaller control volumes (CVs). This yields higher resolution of the saturation field which is represented CV-wise. Moreover, dynamic mesh adaptivity allows high mesh resolution to be employed where it is required to resolve the fingers and lower resolution elsewhere. We use our results to re-examine the existing criteria that have been proposed to govern the onset of instability.Mesh adaptivity requires the mapping of data from one mesh to another. Conventional methods such as consistent interpolation do not readily generalise to discontinuous fields and are non-conservative. We further contribute a general framework for interpolation of CV fields by Galerkin projection. The method is conservative, higher order and yields improved results, particularly with higher order or discontinuous elements where existing approaches are often excessively diffusive.

TURBULENT TRANSPORT IN A STRONGLY STRATIFIED FORCED SHEAR LAYER WITH THERMAL DIFFUSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garaud, Pascale

2016-04-10

This work presents numerical results on the transport of heat and chemical species by shear-induced turbulence in strongly stratified, thermally diffusive environments. The shear instabilities driven in this regime are sometimes called “secular” shear instabilities, and can take place when the Richardson number of the flow is large, provided the Péclet number is small. We have identified a set of simple criteria to determine whether these instabilities can take place or not. Generally speaking, we find that they may be relevant whenever the thermal diffusivity of the fluid is very large (typically larger than 10{sup 14} cm{sup 2} s{sup −1}),more » which is the case in the outer layers of high-mass stars (M ≥ 10 M{sub ⊙}), for instance. Using a simple model setup in which the shear is forced by a spatially sinusoidal, constant-amplitude body-force, we have identified several regimes ranging from effectively unstratified to very strongly stratified, each with its own set of dynamical properties. Unless the system is in one of the two extreme regimes (effectively unstratified or completely stable), however, we find that (1) only about 10% of the input power is used toward heat transport, while the remaining 90% is viscously dissipated; (2) that the effective compositional mixing coefficient is well-approximated by the model of Zahn, with D ≃ 0.02κ{sub T}/J where κ{sub T} is the thermal diffusivity and J is the Richardson number. These results need to be confirmed, however, with simulations in different model setups and at higher effective Reynolds number.« less

Numerical simulations of short-mixing-time double-wave-vector diffusion-weighting experiments with multiple concatenations on whole-body MR systems

NASA Astrophysics Data System (ADS)

Finsterbusch, Jürgen

2010-12-01

Double- or two-wave-vector diffusion-weighting experiments with short mixing times in which two diffusion-weighting periods are applied in direct succession, are a promising tool to estimate cell sizes in the living tissue. However, the underlying effect, a signal difference between parallel and antiparallel wave vector orientations, is considerably reduced for the long gradient pulses required on whole-body MR systems. Recently, it has been shown that multiple concatenations of the two wave vectors in a single acquisition can double the modulation amplitude if short gradient pulses are used. In this study, numerical simulations of such experiments were performed with parameters achievable with whole-body MR systems. It is shown that the theoretical model yields a good approximation of the signal behavior if an additional term describing free diffusion is included. More importantly, it is demonstrated that the shorter gradient pulses sufficient to achieve the desired diffusion weighting for multiple concatenations, increase the signal modulation considerably, e.g. by a factor of about five for five concatenations. Even at identical echo times, achieved by a shortened diffusion time, a moderate number of concatenations significantly improves the signal modulation. Thus, experiments on whole-body MR systems may benefit from multiple concatenations.

On the abrupt growth dynamics of nonlinear resistive tearing mode and the viscosity effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, A.; Li, Jiquan, E-mail: lijq@energy.kyoto-u.ac.jp; Kishimoto, Y.

2014-05-15

The nonlinear evolution of the resistive tearing mode exhibits an abrupt growth after an X-point collapse once the magnetic island exceeds a certain critical width Δ′w{sub c} for large instability parameter Δ′, leading to a current sheet formation [N. F. Loureiro et al., Phys. Rev. Lett. 95, 235003 (2005)]. In this work, we investigate the underlying mechanism of the X-point collapse as well as the current sheet formation including the viscosity effects, based on a secondary instability analysis. The secondary instability is excited due to the quasilinear current modification by the zonal current. In particular, it is identified that themore » current peaking effect is plausibly responsible for the onset of the X-point collapse and the current sheet formation, leading to the explosive growth of reconnected flux. In the presence of finite viscosity, the Δ′w{sub c} scaling with the resistivity gets modified. A transition behavior is revealed at P{sub r}≈1 for the viscosity dependence of Δ′w{sub c} and the linear tearing instability. However, the explosive growth seems to be independent of the viscosity in the magnetic Prandtl number P{sub r}<1 regime, while large viscosity plays a strong dissipation role.« less

Characterization of resistance to selected antibiotics and Panton-Valentine leukocidin-positive Staphylococcus aureus in a healthy student population at a Malaysian University

PubMed Central

Suhaili, Zarizal; Rafee, Putri ’Amira; Mat Azis, Norhidayah; Yeo, Chew Chieng; Nordin, Syafinaz Amin; Abdul Rahim, Abdul Rachman; Al-Obaidi, Mazen M. Jamil; Mohd Desa, Mohd Nasir

2018-01-01

Abstract Introduction This study aims to assess the antimicrobial susceptibility profiles of Staphylococcus aureus strains isolated from university students and to determine the prevalence of constitutive and inducible clindamycin resistance, the latter being able to cause therapeutic failure due to false in vitro clindamycin susceptibility. Methods S. aureus strains were isolated from the nasal swabs of 200 health sciences students of a Malaysian university. Twelve classes of antibiotics were used to evaluate the antimicrobial susceptibility profiles with the macrolide-lincosamide-streptogramin B (MLSB) phenotype for inducible clindamycin resistance determined by the double-diffusion test (D-test). Carriage of resistance and virulence genes was performed by PCR on S. aureus isolates that were methicillin resistant, erythromycin resistant and/or positive for the leukocidin gene, pvl (n=15). Results Forty-nine isolates were viable and identified as S. aureus with four of the isolates characterized as methicillin-resistant S. aureus (MRSA; 2.0%). All isolates were susceptible to the antibiotics tested except for penicillin (resistance rate of 49%), erythromycin (16%), oxacillin (8%), cefoxitin (8%) and clindamycin (4%). Of the eight erythromycin-resistant isolates, iMLSB was identified in five isolates (three of which were also MRSA). The majority of the erythromycin-resistant isolates harbored the msrA gene (four iMLSB) with the remaining iMLSB isolate harboring the ermC gene. Conclusion The presence of MRSA isolates which are also iMLSB in healthy individuals suggests that nasal carriage may play a role as a potential reservoir for the transmission of these pathogens. PMID:29564245

Characterization of resistance to selected antibiotics and Panton-Valentine leukocidin-positive Staphylococcus aureus in a healthy student population at a Malaysian University.

PubMed

Suhaili, Zarizal; Rafee, Putri 'Amira; Mat Azis, Norhidayah; Yeo, Chew Chieng; Nordin, Syafinaz Amin; Abdul Rahim, Abdul Rachman; Al-Obaidi, Mazen M Jamil; Mohd Desa, Mohd Nasir

2018-03-01

This study aims to assess the antimicrobial susceptibility profiles of Staphylococcus aureus strains isolated from university students and to determine the prevalence of constitutive and inducible clindamycin resistance, the latter being able to cause therapeutic failure due to false in vitro clindamycin susceptibility. S. aureus strains were isolated from the nasal swabs of 200 health sciences students of a Malaysian university. Twelve classes of antibiotics were used to evaluate the antimicrobial susceptibility profiles with the macrolide-lincosamide-streptogramin B (MLS B ) phenotype for inducible clindamycin resistance determined by the double-diffusion test (D-test). Carriage of resistance and virulence genes was performed by PCR on S. aureus isolates that were methicillin resistant, erythromycin resistant and/or positive for the leukocidin gene, pvl (n=15). Forty-nine isolates were viable and identified as S. aureus with four of the isolates characterized as methicillin-resistant S. aureus (MRSA; 2.0%). All isolates were susceptible to the antibiotics tested except for penicillin (resistance rate of 49%), erythromycin (16%), oxacillin (8%), cefoxitin (8%) and clindamycin (4%). Of the eight erythromycin-resistant isolates, iMLS B was identified in five isolates (three of which were also MRSA). The majority of the erythromycin-resistant isolates harbored the msrA gene (four iMLS B ) with the remaining iMLS B isolate harboring the ermC gene. The presence of MRSA isolates which are also iMLS B in healthy individuals suggests that nasal carriage may play a role as a potential reservoir for the transmission of these pathogens.

Double-spin-echo diffusion weighting with a modified eddy current adjustment.

PubMed

Finsterbusch, Jürgen

2010-04-01

Magnetic field inhomogeneities like eddy current-related gradient fields cause geometric distortions in echo-planar imaging (EPI). This in particular affects diffusion-weighted imaging where these distortions vary with the direction of the diffusion weighting and hamper the accurate determination of diffusion parameters. The double-spin-echo preparation often used aims to reduce the cumulative eddy current effect by adjusting the diffusion-weighting gradient pulse durations to the time constant of the dominant eddy current contribution. However, eddy currents with a variety of time constants may be present and cause residual distortions. Here, a modification is proposed where the two bipolar gradient pairs of the preparation are adjusted independently to different time constants. At the expense of a slightly prolonged echo time, residual geometric distortions and correspondingly increased values of the diffusion anisotropy can be reduced as is demonstrated in phantoms and the human brain. Thus, it may help to improve the reliability of diffusion-weighted EPI. Copyright 2010 Elsevier Inc. All rights reserved.

Modified Back Contact Interface of CZTSe Thin Film Solar Cells: Elimination of Double Layer Distribution in Absorber Layer

PubMed Central

Zhang, Zhaojing; Yao, Liyong; Bi, Jinlian; Gao, Shoushuai; Gao, Qing; Jeng, Ming‐Jer; Sun, Guozhong; Zhou, Zhiqiang; He, Qing; Sun, Yun

2017-01-01

Abstract Double layer distribution exists in Cu2SnZnSe4 (CZTSe) thin films prepared by selenizing the metallic precursors, which will degrade the back contact of Mo substrate to absorber layer and thus suppressing the performance of solar cell. In this work, the double‐layer distribution of CZTSe film is eliminated entirely and the formation of MoSe2 interfacial layer is inhibited successfully. CZTSe film is prepared by selenizing the precursor deposited by electrodeposition method under Se and SnSex mixed atmosphere. It is found that the insufficient reaction between ZnSe and Cu‐Sn‐Se phases in the bottom of the film is the reason why the double layer distribution of CZTSe film is formed. By increasing Sn content in the metallic precursor, thus making up the loss of Sn because of the decomposition of CZTSe and facilitate the diffusion of liquid Cu2Se, the double layer distribution is eliminated entirely. The crystallization of the formed thin film is dense and the grains go through the entire film without voids. And there is no obvious MoSe2 layer formed between CZTSe and Mo. As a consequence, the series resistance of the solar cell reduces significantly to 0.14 Ω cm2 and a CZTSe solar cell with efficiency of 7.2% is fabricated. PMID:29610727

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

PubMed

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

2002-09-01

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.

Threshold of transverse mode coupling instability with arbitrary space charge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balbekov, V.

The threshold of the transverse mode coupling instability is calculated in framework of the square well model at arbitrary value of space charge tune shift. A new method of calculation is developed beyond the traditional expansion technique. The square, resistive, and exponential wakes are investigated. It is shown that the instability threshold goes up indefinitely when the tune shift increases. Finally, a comparison with conventional case of the parabolic potential well is performed.

Threshold of transverse mode coupling instability with arbitrary space charge

DOE PAGES

Balbekov, V.

2017-11-30

The threshold of the transverse mode coupling instability is calculated in framework of the square well model at arbitrary value of space charge tune shift. A new method of calculation is developed beyond the traditional expansion technique. The square, resistive, and exponential wakes are investigated. It is shown that the instability threshold goes up indefinitely when the tune shift increases. Finally, a comparison with conventional case of the parabolic potential well is performed.

Spontaneous symmetry breaking by double lithium adsorption in polyacenes

NASA Astrophysics Data System (ADS)

Ortiz, Yenni. P.; Seligman, Thomas H.

2010-12-01

We show that adsorption of one lithium atom to polyacenes, i.e. chains of linearly fused benzene rings, will cause such chains to be slightly deformed. If we adsorb a second identical atom on the opposite side of the same ring, this deformation is dramatically enhanced despite the fact that a symmetric configuration seems possible. We argue, that this may be due to an instability of the Jahn-Teller type possibly indeed to a Peierls instability.

Spontaneous symmetry breaking by double lithium adsorption in polyacenes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortiz, Yenni. P.; Seligman, Thomas H.; Centro Internacional de Ciencias, Cuernavaca, Morelos

2010-12-23

We show that adsorption of one lithium atom to polyacenes, i.e. chains of linearly fused benzene rings, will cause such chains to be slightly deformed. If we adsorb a second identical atom on the opposite side of the same ring, this deformation is dramatically enhanced despite the fact that a symmetric configuration seems possible. We argue, that this may be due to an instability of the Jahn-Teller type possibly indeed to a Peierls instability.

Transient and diffusion analysis of HgCdTe

NASA Technical Reports Server (NTRS)

Clayton, J. C.

1982-01-01

Solute redistribution during directional solidification of HgCdTe is addressed. Both one-dimensional and two-dimensional models for solute redistribution are treated and model results compared to experiment. The central problem studied is the cause of radial inhomogeneities found in directionally solidified HgCdTe. A large scale gravity-driven interface instability, termed shape instability, is postulated to be the cause of radial inhomogeneities. Recommendations for future work, along with appropriate computer programs, are included.

Clonality and antimicrobial resistance gene profiles of multidrug- resistant Salmonella enterica serovar infantis isolates from four public hospitals in Rio de Janeiro, Brazil.

PubMed

Fonseca, E L; Mykytczuk, O L; Asensi, M D; Reis, E M F; Ferraz, L R; Paula, F L; Ng, L K; Rodrigues, D P

2006-08-01

In Brazil, Salmonella enterica serovar Infantis resistant to various antimicrobials, including cephalosporins, has been identified as an etiological agent of severe gastroenteritis in hospitalized children since 1994. In this study, 35 serovar Infantis strains, isolated from children admitted to four different Rio de Janeiro, Brazil, hospitals between 1996 and 2001, were characterized by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing in order to determine their genetic relatedness and antimicrobial resistance profiles. Thirty-four serovar Infantis strains were resistant to at least two antibiotic classes, and all 35 strains were susceptible to fluoroquinolones, cephamycin, and carbapenem. Extended-spectrum beta-lactamase (ESBL) screening by double-disk diffusion indicated that 32 serovar Infantis strains (91.4%) produced beta-lactamases that were inhibited by clavulanic acid. Antimicrobial resistance gene profiles were determined by PCR for a subset of 11 multidrug-resistant serovar Infantis strains, and putative ESBLs were detected by isoelectric focusing. Ten serovar Infantis strains carried bla(TEM), catI, ant(3")Ia and/or ant(3")Ib, sulI and/or sulII, and tet(D) genes as well as an integron-associated aac(6')-Iq cassette. Eight strains possessed at least four different beta-lactamases with pI profiles that confirmed the presence of both ESBLs and non-ESBLs. Our PFGE profiles indicated that 33 serovar Infantis strains isolated from Rio de Janeiro hospitals came from the same genetic lineage.

Emergence of a Stern Layer from the Incorporation of Hydration Interactions into the Gouy-Chapman Model of the Electrical Double Layer.

PubMed

Brown, Matthew A; Bossa, Guilherme Volpe; May, Sylvio

2015-10-27

In one of the most commonly used phenomenological descriptions of the electrical double layer, a charged solid surface and a diffuse region of mobile ions are separated from each other by a thin charge-depleted Stern layer. The Stern layer acts as a capacitor that improves the classical Gouy-Chapman model by increasing the magnitude of the surface potential and limiting the maximal counterion concentration. We show that very similar Stern-like properties of the diffuse double layer emerge naturally from adding a nonelectrostatic hydration repulsion to the electrostatic Coulomb potential. The interplay of electrostatic attraction and hydration repulsion of the counterions and the surface leads to the formation of a diffuse counterion layer that remains well separated from the surface. In addition, hydration repulsions between the ions limit and control the maximal ion concentration and widen the width of the diffuse double layer. Our mean-field model, which we express in terms of electrostatic and hydration potentials, is physically consistent and conceptually similar to the classical Gouy-Chapman model. It allows the incorporation of ion specificity, accounts for hydration properties of charged surfaces, and predicts Stern layer properties, which we analyze in terms of the effective size of the hydrated counterions.

Conceptual model for transport processes in the Culebra Dolomite Member, Rustler Formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holt, R.M.

1997-08-01

The Culebra Dolomite Member of the Rustler Formation represents a possible pathway for contaminants from the Waste Isolation Pilot Plant underground repository to the accessible environment. The geologic character of the Culebra is consistent with a double-porosity, multiple-rate model for transport in which the medium is conceptualized as consisting of advective porosity, where solutes are carried by the groundwater flow, and fracture-bounded zones of diffusive porosity, where solutes move through slow advection or diffusion. As the advective travel length or travel time increases, the nature of transport within a double-porosity medium changes. This behavior is important for chemical sorption, becausemore » the specific surface area per unit mass of the diffusive porosity is much greater than in the advective porosity. Culebra transport experiments conducted at two different length scales show behavior consistent with a multiple-rate, double-porosity conceptual model for Culebra transport. Tracer tests conducted on intact core samples from the Culebra show no evidence of significant diffusion, suggesting that at the core scale the Culebra can be modeled as a single-porosity medium where only the advective porosity participates in transport. Field tracer tests conducted in the Culebra show strong double-porosity behavior that is best explained using a multiple-rate model.« less

Anti-Quorum Sensing Potential of Crude Kigelia africana Fruit Extracts

PubMed Central

Chenia, Hafizah Y.

2013-01-01

The increasing incidence of multidrug-resistant pathogens has stimulated the search for novel anti-virulence compounds. Although many phytochemicals show promising antimicrobial activity, their power lies in their anti-virulence properties. Thus the quorum sensing (QS) inhibitory activity of four crude Kigelia africana fruit extracts was assessed qualitatively and quantitatively using the Chromobacterium violaceum and Agrobacterium tumefaciens biosensor systems. Inhibition of QS-controlled violacein production in C. violaceum was assayed using the qualitative agar diffusion assay as well as by quantifying violacein inhibition using K. africana extracts ranging from 0.31–8.2 mg/mL. Qualitative modulation of QS activity was investigated using the agar diffusion double ring assay. All four extracts showed varying levels of anti-QS activity with zones of violacein inhibition ranging from 9–10 mm. The effect on violacein inhibition was significant in the following order: hexane > dichloromethane > ethyl acetate > methanol. Inhibition was concentration-dependent, with the ≥90% inhibition being obtained with ≥1.3 mg/mL of the hexane extract. Both LuxI and LuxR activity were affected by crude extracts suggesting that the phytochemicals target both QS signal and receptor. K. africana extracts with their anti-QS activity, have the potential to be novel therapeutic agents, which might be important in reducing virulence and pathogenicity of drug-resistant bacteria in vivo. PMID:23447012

Effects of stacked quantitative resistances to downy mildew in lettuce do not simply add up.

PubMed

den Boer, Erik; Pelgrom, Koen T B; Zhang, Ningwen W; Visser, Richard G F; Niks, Rients E; Jeuken, Marieke J W

2014-08-01

In a stacking study of eight resistance QTLs in lettuce against downy mildew, only three out of ten double combinations showed an increased resistance effect under field conditions. Complete race nonspecific resistance to lettuce downy mildew, as observed for the nonhost wild lettuce species Lactuca saligna, is desired in lettuce cultivation. Genetic dissection of L. saligna's complete resistance has revealed several quantitative loci (QTL) for resistance with field infection reductions of 30-50 %. To test the effect of stacking these QTL, we analyzed interactions between homozygous L. saligna CGN05271 chromosome segments introgressed into the genetic background of L. sativa cv. Olof. Eight different backcross inbred lines (BILs) with single introgressions of 30-70 cM and selected predominately for quantitative resistance in field situations were intercrossed. Ten developed homozygous lines with stacked introgression segments (double combinations) were evaluated for resistance in the field. Seven double combinations showed a similar infection as the individual most resistant parental BIL, revealing epistatic interactions with 'less-than-additive' effects. Three double combinations showed an increased resistance level compared to their parental BILs and their interactions were additive, 'less-than-additive' epistatic and 'more-than-additive' epistatic, respectively. The additive interaction reduced field infection by 73 %. The double combination with a 'more-than-additive' epistatic effect, derived from a combination between a susceptible and a resistant BIL with 0 and 30 % infection reduction, respectively, showed an average field infection reduction of 52 %. For the latter line, an attempt to genetically dissect its underlying epistatic loci by substitution mapping did not result in smaller mapping intervals as none of the 22 substitution lines reached a similar high resistance level. Implications for breeding and the inheritance of L. saligna's complete resistance are discussed.

Sawtooth Stabilization and Onset of Alfvenic Instabilities

NASA Astrophysics Data System (ADS)

Nishimura, Y.; Cheng, C. Z.

2011-10-01

Tokamak sawtooth instabilities can be stabilized by high energy particles as a consequence of conservation of the third adiabatic invariant.On the other hand, termination of the stabilized period is reported due to the onset of Alfvenic instabilities (and thus the absence of the stabilizing mechanism). In this work, employing a kinetic-fluid model, the interaction of m=1 resistive kink mode and high energy particles is investigated. The onset of Alfvenic instabilities is examined as a function of the inversion radius location. D.J. Campbell et al., Phys. Rev. Lett. 60, 2148 (1988); F. Porcelli, Plasma Phys. Controlled Fusion 33, 1601 (1991).

Resolving the evolutionary paradox of genetic instability: a cost-benefit analysis of DNA repair in changing environments.

PubMed

Breivik, Jarle; Gaudernack, Gustav

2004-04-09

Loss of genetic stability is a critical phenomenon in cancer and antibiotic resistance, and the prevailing dogma is that unstable cells survive because instability provides adaptive mutations. Challenging this view, we have argued that genetic instability arises because DNA repair may be a counterproductive strategy in mutagenic environments. This paradoxical relationship has also been confirmed by explicit experiments, but the underlying evolutionary principles remain controversial. This paper aims to clarify the issue, and presents a model that explains genetic instability from the basic perspective of molecular evolution and information processing.

Near-limit flame structures at low Lewis number

NASA Technical Reports Server (NTRS)

Ronney, Paul D.

1990-01-01

The characteristics of premixed gas flames in mixtures with low Lewis numbers near flammability limits were studied experimentally using a low-gravity environment to reduce buoyant convection. The behavior of such flames was found to be dominated by diffusive-thermal instabilities. For sufficiently reactive mixtures, cellular structures resulting from these instabilities were observed and found to spawn new cells in regular patterns. For less reactive mixtures, cells formed shortly after ignition but did not spawn new cells; instead these cells evolved into a flame structure composed of stationary, apparently stable spherical flamelets. Experimental observations are found to be in qualitative agreement with elementary analytical models based on the interaction of heat release due to chemical reaction, differential diffusion of thermal energy and mass, flame front curvature, and volumetric heat losses due to gas and/or soot radiation.

A study of the propagation, dynamics, and extinguishment of cellular flames using microgravity techniques

NASA Technical Reports Server (NTRS)

Ronney, Paul D.

1989-01-01

The characteristics of premixed gas flames in mixtures with low Lewis numbers, free of natural convection effects, were investigated and found to be dominated by diffusive-thermal instabilities. For sufficiently reactive mixtures, cellular structures resulting from these instabilities were observed and found to spawn new cells in regular patterns. For less reactive mixtures, cells formed shortly after ignition but did not spawn new cells; instead these cells evolved into a flame structure composed of stationary, apparently stable spherical flamelets. As a result of these phenomena, well-defined flammability limits were not observed. The experimental results are found to be in qualitative agreement with a simple analytical model based on the interaction of heat release due to chemical reaction, differential diffusion of thermal energy and mass, flame front curvature, and heat losses due to gas radiation.

[Doublehit lymphomas -  review of the literature and case report].

PubMed

Smardová, J; Moulis, M; Lišková, K; Koptíková, J; Hrabálková, R; Klusáková, J

2014-01-01

Blymphocytes are cells of the immune system responsible for the antibody  mediated immune response. As estimated, a human body can produce as much as 1011 specific antibodies. There are no specific genes coding for every individual antibody in the human genome. Discrepancy between the huge diversity of antibodies and limited coding capacity of the genome is solved by combination of unique arrangement of genetic information for immunoglobulin and unique genetic and somatic processes providing this wide spectrum of antibodies. On one side, these mechanisms represent a life protecting source of a wide spectrum of antibodies but at the same time, they can be life threatening by raising the risk of a serious tumor disease, the B cell lymphoma. Double hit lymphomas represent a specific group of B cell lymphomas often featuring concurrent rearrangements of BCL2 and MYC genes. Activation of the MYC oncogene, typical for Burkitt lymphoma (BL), causes strong stimulation of cell proliferation. High activity of BCL 2, typical for follicular lymphoma, induces resistance to apoptosis. Concurrent damage of regulation of apoptosis and proliferation is probably responsible for the typical clinical manifestation of double hit lymphomas - aggressive course, resistance to conventional chemotherapy, high-risk of early relapse, short overall survival, frequent extranodal and central nervous system involvement. Recently, these lymphomas have attracted a strong attention of researchers as they provide sharp insights into processes of lymphocytes maturing and lymphomas development and highlight the double edged nature of mechanisms allowing the antibody broad diversity. Fifty  three year  old man was diagnosed with B cell lymphoma unclassifiable with features intermediate between diffuse large B cell lymphoma (DLBCL) and BL, based on morphology and immunophenotype. Fluorescent in situ hybridization analysis revealed double hit lymphoma diagnosis as the tumor cells bear t(14;18) translocation concurrently with the MYC gene rearrangement. The patient died five months after dia-gnosis.

Understanding of carbon-based supercapacitors ageing mechanisms by electrochemical and analytical methods

NASA Astrophysics Data System (ADS)

Liu, Yinghui; Soucaze-Guillous, Benoît; Taberna, Pierre-Louis; Simon, Patrice

2017-10-01

In order to shed light on ageing mechanisms of Electrochemical Double Layer Capacitor (EDLC), two kinds of activated carbons are studied in tetraethyl ammonium tetrafluoroborate (Et4NBF4) in acetonitrile. In floating mode, it turns out that two different ageing mechanisms are observed, depending on the activated carbon electrode materials used. On one hand, carbon A exhibits a continuous capacitance and series resistance fall-off; on the other hand, for carbon B, only the series resistance degrades after ageing while the capacitance keeps unchanged. Additional electrochemical characterizations (Electrochemical Impedance Spectroscopy - EIS - and diffusion coefficient calculations) were carried out showing that carbon A's ageing behavior is suspected to be primarily related to the carbon degradation while for carbon B a passivation occurs leading to the formation of a Solid Electrolyte Interphase-Like (SEI-L) film. These hypotheses are supported by TG-IR and Raman spectroscopy analysis. The outcome forms the latter is an increase of carbon defects on carbon A on positive electrode.

Suspended sub-50 nm vanadium dioxide membrane transistors: fabrication and ionic liquid gating studies

NASA Astrophysics Data System (ADS)

Sim, Jai S.; Zhou, You; Ramanathan, Shriram

2012-10-01

We demonstrate a robust lithographic patterning method to fabricate self-supported sub-50 nm VO2 membranes that undergo a phase transition. Utilizing such self-supported membranes, we directly observed a shift in the metal-insulator transition temperature arising from stress relaxation and consistent opening of the hysteresis. Electric double layer transistors were then fabricated with the membranes and compared to thin film devices. The ionic liquid allowed reversible modulation of channel resistance and distinguishing bulk processes from the surface effects. From the shift in the metal-insulator transition temperature, the carrier density doped through electrolyte gating is estimated to be 1 × 1020 cm-3. Hydrogen annealing studies showed little difference in resistivity between the film and the membrane indicating rapid diffusion of hydrogen in the vanadium oxide rutile lattice consistent with previous observations. The ability to fabricate electrically-wired, suspended VO2 ultra-thin membranes creates new opportunities to study mesoscopic size effects on phase transitions and may also be of interest in sensor devices.

Arnold diffusion for a complete family of perturbations

NASA Astrophysics Data System (ADS)

Delshams, Amadeu; Schaefer, Rodrigo G.

2017-01-01

In this work we illustrate the Arnold diffusion in a concrete example — the a priori unstable Hamiltonian system of 2 + 1/2 degrees of freedom H( p, q, I, φ, s) = p 2/2+ cos q - 1 + I 2/2 + h( q, φ, s; ɛ) — proving that for any small periodic perturbation of the form h( q, φ, s; ɛ) = ɛ cos q ( a 00 + a 10 cos φ + a 01 cos s) ( a 10 a 01 ≠ 0) there is global instability for the action. For the proof we apply a geometrical mechanism based on the so-called scattering map. This work has the following structure: In the first stage, for a more restricted case ( I* π/2 μ, μ = a 10/ a 01), we use only one scattering map, with a special property: the existence of simple paths of diffusion called highways. Later, in the general case we combine a scattering map with the inner map (inner dynamics) to prove the more general result (the existence of instability for any μ). The bifurcations of the scattering map are also studied as a function of μ. Finally, we give an estimate for the time of diffusion, and we show that this time is primarily the time spent under the scattering map.

Controlling direct contact force for wet adhesion with different wedged film stabilities

NASA Astrophysics Data System (ADS)

Li, Meng; Xie, Jun; Shi, Liping; Huang, Wei; Wang, Xiaolei

2018-04-01

In solid–liquid–solid adhesive systems, wedged films often feature instability at microscopic thicknesses, which can easily disrupt the adhesive strength of their remarkable direct contact force. Here, sodium dodecyl sulfate (SDS) was employed to tune the instability of adhesion in wedged glass–water–rubber films, achieving controllable direct contact. Experimental results showed that the supplement of SDS molecules significantly weakened the direct contact force for wet adhesion and eliminated it at high concentrations. The underlying reason was suggested to be the repulsive double-layer force caused by SDS molecules, which lowers the instability of the wedged film and balances the preload, disrupting the direct contact in wet adhesion.

Study of mechanism of stress-induced threshold voltage shift and recovery in top-gate amorphous-InGaZnO4 thin-film transistors with source- and drain-offsets

NASA Astrophysics Data System (ADS)

Mativenga, Mallory; Kang, Dong Han; Lee, Ung Gi; Jang, Jin

2012-09-01

Bias instability of top-gate amorphous-indium-gallium-zinc-oxide thin-film transistors with source- and drain-offsets is reported. Positive and negative gate bias-stress (VG_STRESS) respectively induce reversible negative threshold-voltage shift (ΔVTH) and reduction in on-current. Migration of positive charges towards the offsets lowers the local resistance of the offsets, resulting in the abnormal negative ΔVTH under positive VG_STRESS. The reduction in on-current under negative VG_STRESS is due to increase in resistance of the offsets when positive charges migrate away from the offsets. Appropriate drain and source bias-stresses applied simultaneously with VG_STRESS either suppress or enhance the instability, verifying lateral ion migration to be the instability mechanism.

Centrifugally Driven Rayleigh-Taylor Instability

NASA Astrophysics Data System (ADS)

Scase, Matthew; Hill, Richard

2017-11-01

The instability that develops at the interface between two fluids of differing density due to the rapid rotation of the system may be considered as a limit of high-rotation rate Rayleigh-Taylor instability. Previously the authors have considered the effect of rotation on a gravitationally dominated Rayleigh-Taylor instability and have shown that some growth modes of instability may be suppressed completely by the stabilizing effect of rotation (Phys. Rev. Fluids 2:024801, Sci. Rep. 5:11706). Here we consider the case of very high rotation rates and a negligible gravitational field. The initial condition is of a dense inner cylinder of fluid surrounded by a lighter layer of fluid. As the system is rotated about the generating axis of the cylinder, the dense inner fluid moves away from the axis and the familiar bubbles and spikes of Rayleigh-Taylor instability develop at the interface. The system may be thought of as a ``fluid-fluid centrifuge''. By developing a model based on an Orr-Sommerfeld equation, we consider the effects of viscosity, surface tension and interface diffusion on the growth rate and modes of instability. We show that under particular circumstances some modes may be stabilized. School of Mathematical Sciences.

Spatiotemporal Patterns in a Predator-Prey Model with Cross-Diffusion Effect

NASA Astrophysics Data System (ADS)

Sambath, M.; Balachandran, K.; Guin, L. N.

The present research deals with the emergence of spatiotemporal patterns of a two-dimensional (2D) continuous predator-prey system with cross-diffusion effect. First, we work out the critical lines of Hopf and Turing bifurcations of the current model system in a 2D spatial domain by means of bifurcation theory. More specifically, the exact Turing region is specified in a two-parameter space. In effect, by choosing the cross-diffusion coefficient as one of the momentous parameter, we demonstrate that the model system undergoes a sequence of spatiotemporal patterns in a homogeneous environment through diffusion-driven instability. Our results via numerical simulation authenticate that cross-diffusion be able to create stationary patterns which enrich the findings of pattern formation in an ecosystem.

Dynamic stability of maglev systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Y.; Chen, S.S.; Mulcahy, T.M.

1994-05-01

Because dynamic instabilities are not acceptable in any commercial maglev system, it is important to consider dynamic instability in the development of all maglev systems. This study considers the stability of maglev systems based on experimental data, scoping calculations, and simple mathematical models. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on a guideway consisting of double L-shaped aluminum segments. The theory and analysis developed in this study provides basic stability characteristics and identifies future research needs for maglev systems.

Numerical Modeling of HgCdTe Solidification: Effects of Phase Diagram, Double-Diffusion Convection and Microgravity Level

NASA Technical Reports Server (NTRS)

Bune, Andris V.; Gillies, Donald C.; Lehoczky, Sandor L.

1997-01-01

Melt convection, along with species diffusion and segregation on the solidification interface are the primary factors responsible for species redistribution during HgCdTe crystal growth from the melt. As no direct information about convection velocity is available, numerical modeling is a logical approach to estimate convection. Furthermore influence of microgravity level, double-diffusion and material properties should be taken into account. In the present study, HgCdTe is considered as a binary alloy with melting temperature available from a phase diagram. The numerical model of convection and solidification of binary alloy is based on the general equations of heat and mass transfer in two-dimensional region. Mathematical modeling of binary alloy solidification is still a challenging numericial problem. A Rigorous mathematical approach to this problem is available only when convection is not considered at all. The proposed numerical model was developed using the finite element code FIDAP. In the present study, the numerical model is used to consider thermal, solutal convection and a double diffusion source of mass transport.

Radiation from Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Mizuno, Y.; Hardee, P.; Sol, H.; Medvedev, M.; Zhang, B.; Nordlund, A.; Frederiksen, J. T.; Fishman, G. J.; Preece, R.

2008-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations of relativistic electron-ion (electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In the presence of relativistic jets, instabilities such as the Buneman instability, other two-streaming instability, and the Weibel (filamentation) instability create collisionless shocks, which are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The 'jitter' radiation from deflected electrons in small-scale magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation, a case of diffusive synchrotron radiation, may be important to understand the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

On the generation of double layers from ion- and electron-acoustic instabilities

DOE PAGES

Fu, Xiangrong; Cowee, Misa M.; Gary, Stephen Peter; ...

2016-03-17

A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric fields traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs – electron acoustic DLs – generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e.more » the hypothetical electron acoustic DLs cannot be formed in a way similar to ion acoustic DLs. We find that linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric fields that propagate at the electron thermal speed, suggesting another potential explanation for the observations.« less

On the generation of double layers from ion- and electron-acoustic instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Xiangrong, E-mail: xrfu@lanl.gov; Cowee, Misa M.; Winske, Dan

2016-03-15

A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric field structures traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs—electron acoustic DLs—generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e., the hypothetical electronmore » acoustic DLs cannot be formed in a way similar to ion acoustic DLs. Linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric field structures that propagate at the electron thermal speed, suggesting another potential explanation for the observations.« less

High Prevalence of Extended-Spectrum β-Lactamase-Producing Enterobacteriaceae in Wild Fish from the Mediterranean Sea in Algeria.

PubMed

Brahmi, Soumia; Touati, Abdelaziz; Dunyach-Remy, Catherine; Sotto, Albert; Pantel, Alix; Lavigne, Jean-Philippe

2018-04-01

We investigated the prevalence of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae among wild fish from the coast of Bejaia (Algeria) in the Mediterranean Sea. From March 2012 to August 2013, gut and gill samples of wild fish were screened for the presence of ESBL-producing Enterobacteriaceae. Strains were characterized with regard to antibiotic resistance, β-lactamase content, plasmid-mediated quinolone resistance, aminoglycoside resistance genes, and clonality (repetitive sequence-based polymerase chain reaction profiles and multilocus sequence typing). Virulence traits were performed for Escherichia coli and Klebsiella pneumoniae isolates. Of the 300 fish studied, 64 (21.3%) isolates were screened as positive for ESBL producing by the double-disc method. The isolates corresponded to E. coli, K. pneumoniae, Enterobacter cloacae, Morganella morganii, Citrobacter freundii, and Proteus vulgaris. A predominance of bla CTX-M gene was observed with a prevalence of 60.5% (n = 46). Furthermore, our study describes the association of important coresistance and virulence factors in E. coli and K. pneumoniae. Twelve of the ESBL producers carried genes of the qnr family and oqxAB gene and six carried the aac(6')-Ib-cr gene. Our results highlight for the first time the diffusion of multidrug-resistant Enterobacteriaceae isolates carrying resistance and virulence genes in fish from the Mediterranean Sea in Algeria.

Multilayered nano-architecture of variable sized graphene nanosheets for enhanced supercapacitor electrode performance.

PubMed

Biswas, Sanjib; Drzal, Lawrence T

2010-08-01

The diverse physical and chemical aspects of graphene nanosheets such as particle size surface area and edge chemistry were combined to fabricate a new supercapacitor electrode architecture consisting of a highly aligned network of large-sized nanosheets as a series of current collectors within a multilayer configuration of bulk electrode. Capillary driven self-assembly of monolayers of graphene nanosheets was employed to create a flexible, multilayer, free-standing film of highly hydrophobic nanosheets over large macroscopic areas. This nanoarchitecture exhibits a high-frequency capacitative response and a nearly rectangular cyclic voltammogram at 1000 mV/s scanning rate and possesses a rapid current response, small equivalent series resistance (ESR), and fast ionic diffusion for high-power electrical double-layer capacitor (EDLC) application.

Local magnetohydrodynamic instabilities and the wave-driven dynamo in accretion disks

NASA Technical Reports Server (NTRS)

Vishniac, Ethan T.; Diamond, Patrick

1992-01-01

We consider the consequences of magnetic buoyancy and the magnetic shearing instability (MSI) on the strength and organization of the magnetic field in a thin accretion disk. We discuss a model in which the wave-driven dynamo growth rate is balanced by the dissipative effects of the MSI. As in earlier work, the net helicity is due to small advective motions driven by nonlinear interactions between internal waves. Assuming a simple model of the internal wave spectrum generated from the primary m = 1 internal waves, we find that the magnetic energy density saturates at about (H/r) exp 4/3 times the local pressure (where H is the disk thickness and r is its radius). On very small scales the shearing instability will produce an isotropic fluctuating field. For a stationary disk this is equivalent to a dimensionless 'viscosity' of about (H/r) exp 4/3. The vertical and radial diffusion coefficients will be comparable to each other. Magnetic buoyancy will be largely suppressed by the turbulence due to the MSI. We present a rough estimate of its effects and find that it removes magnetic flux from the disk at a rate comparable to that caused by turbulent diffusion.

Gravitomagnetic Instabilities in Anisotropically Expanding Fluids

NASA Astrophysics Data System (ADS)

Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos, Demetrios B.; Vlahos, Loukas

Gravitational instabilities in a magnetized Friedman-Robertson-Walker (FRW) universe, in which the magnetic field was assumed to be too weak to destroy the isotropy of the model, are known and have been studied in the past. Accordingly, it became evident that the external magnetic field disfavors the perturbations' growth, suppressing the corresponding rate by an amount proportional to its strength. However, the spatial isotropy of the FRW universe is not compatible with the presence of large-scale magnetic fields. Therefore, in this paper we use the general-relativistic version of the (linearized) perturbed magnetohydrodynamic equations with and without resistivity, to discuss a generalized Jeans criterion and the potential formation of density condensations within a class of homogeneous and anisotropically expanding, self-gravitating, magnetized fluids in curved space-time. We find that, for a wide variety of anisotropic cosmological models, gravitomagnetic instabilities can lead to subhorizontal, magnetized condensations. In the nonresistive case, the power spectrum of the unstable cosmological perturbations suggests that most of the power is concentrated on large scales (small k), very close to the horizon. On the other hand, in a resistive medium, the critical wave-numbers so obtained, exhibit a delicate dependence on resistivity, resulting in the reduction of the corresponding Jeans lengths to smaller scales (well bellow the horizon) than the nonresistive ones, while increasing the range of cosmological models which admit such an instability.

APC/C Dysfunction Limits Excessive Cancer Chromosomal Instability

PubMed Central

Sansregret, Laurent; López-García, Carlos; Koch, André; McGranahan, Nicholas; Chao, William Chong Hang; Barry, David J.; Rowan, Andrew; Instrell, Rachael; Horswell, Stuart; Way, Michael; Howell, Michael; Singleton, Martin R.; Medema, René H.; Nurse, Paul; Petronczki, Mark; Swanton, Charles

2017-01-01

Intercellular heterogeneity, exacerbated by chromosomal instability (CIN), fosters tumor heterogeneity and drug resistance. However, extreme CIN correlates with improved cancer outcome, suggesting that karyotypic diversity required to adapt to selection pressures might be balanced in tumors against the risk of excessive instability. Here, we used a functional genomics screen, genome editing, and pharmacologic approaches to identify CIN-survival factors in diploid cells. We find partial anaphase-promoting complex/cyclosome (APC/C) dysfunction lengthens mitosis, suppresses pharmacologically induced chromosome segregation errors, and reduces naturally occurring lagging chromosomes in cancer cell lines or following tetraploidization. APC/C impairment caused adaptation to MPS1 inhibitors, revealing a likely resistance mechanism to therapies targeting the spindle assembly checkpoint. Finally, CRISPR-mediated introduction of cancer somatic mutations in the APC/C subunit cancer driver gene CDC27 reduces chromosome segregation errors, whereas reversal of an APC/C subunit nonsense mutation increases CIN. Subtle variations in mitotic duration, determined by APC/C activity, influence the extent of CIN, allowing cancer cells to dynamically optimize fitness during tumor evolution. Significance We report a mechanism whereby cancers balance the evolutionary advantages associated with CIN against the fitness costs caused by excessive genome instability, providing insight into the consequence of CDC27 APC/C subunit driver mutations in cancer. Lengthening of mitosis through APC/C modulation may be a common mechanism of resistance to cancer therapeutics that increase chromosome segregation errors. PMID:28069571

Gene amplification and microsatellite instability induced in tumorigenic human bronchial epithelial cells by alpha particles and heavy ions

NASA Technical Reports Server (NTRS)

Piao, C. Q.; Hei, T. K.; Hall, E. J. (Principal Investigator)

2001-01-01

Gene amplification and microsatellite alteration are useful markers of genomic instability in tumor and transformed cell lines. It has been suggested that genomic instability contributes to the progression of tumorigenesis by accumulating genetic changes. In this study, amplification of the carbamyl-P-synthetase, aspartate transcarbamylase, dihydro-orotase (CAD) gene in transformed and tumorigenic human bronchial epithelial (BEP2D) cells induced by either alpha particles or (56)Fe ions was assessed by measuring resistance to N-(phosphonacetyl)-l-aspartate (PALA). In addition, alterations of microsatellite loci located on chromosomes 3p and 18q were analyzed in a series of primary and secondary tumor cell lines generated in nude mice. The frequency of PALA-resistant colonies was 1-3 x 10(-3) in tumor cell lines, 5-8 x 10(-5) in transformed cells prior to inoculation into nude mice, and less than 10(-7) in control BEP2D cells. Microsatellite alterations were detected in all 11 tumor cell lines examined at the following loci: D18S34, D18S363, D18S877, D3S1038 and D3S1607. No significant difference in either PALA resistance or microsatellite instability was found in tumor cell lines that were induced by alpha particles compared to those induced by (56)Fe ions.

Hall Effect–Mediated Magnetic Flux Transport in Protoplanetary Disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xue-Ning; Stone, James M.

2017-02-10

The global evolution of protoplanetary disks (PPDs) has recently been shown to be largely controlled by the amount of poloidal magnetic flux threading the disk. The amount of magnetic flux must also coevolve with the disk, as a result of magnetic flux transport, a process that is poorly understood. In weakly ionized gas as in PPDs, magnetic flux is largely frozen in the electron fluid, except when resistivity is large. When the disk is largely laminar, we show that the relative drift between the electrons and ions (the Hall drift), and the ions and neutral fluids (ambipolar drift) can playmore » a dominant role on the transport of magnetic flux. Using two-dimensional simulations that incorporate the Hall effect and ambipolar diffusion (AD) with prescribed diffusivities, we show that when large-scale poloidal field is aligned with disk rotation, the Hall effect rapidly drags magnetic flux inward at the midplane region, while it slowly pushes flux outward above/below the midplane. This leads to a highly radially elongated field configuration as a global manifestation of the Hall-shear instability. This field configuration further promotes rapid outward flux transport by AD at the midplane, leading to instability saturation. In quasi-steady state, magnetic flux is transported outward at approximately the same rate at all heights, and the rate is comparable to the Hall-free case. For anti-aligned field polarity, the Hall effect consistently transports magnetic flux outward, leading to a largely vertical field configuration in the midplane region. The field lines in the upper layer first bend radially inward and then outward to launch a disk wind. Overall, the net rate of outward flux transport is about twice as fast as that of the aligned case. In addition, the rate of flux transport increases with increasing disk magnetization. The absolute rate of transport is sensitive to disk microphysics, which remains to be explored in future studies.« less

Efficient repair of DNA double-strand breaks in malignant cells with structural instability

PubMed Central

Cheng, Yue; Zhang, Zhenhua; Keenan, Bridget; Roschke, Anna V.; Nakahara, Kenneth; Aplan, Peter D.

2009-01-01

Aberrant repair of DNA double strand breaks (DSBs) is thought to be important in the generation of gross chromosomal rearrangements (GCRs). To examine how DNA DSBs might lead to GCRs, we investigated the repair of a single DNA DSB in a structurally unstable cell line. An I-SceI recognition site was introduced into OVCAR-8 cells between a constitutive promoter (EF1α) and the Herpes simplex virus thymidine kinase (TK) gene, which confers sensitivity to gancyclovir (GCV). Expression of I-SceI in these cells caused a single DSB. Clones with aberrant repair could acquire resistance to GCV by separation of the EF1α promoter from the TK gene, or deletion of either the EF1α promoter or the TK gene. All mutations that we identified were interstitial deletions. Treatment of cells with etoposide or bleomycin, agents known to produce DNA DSBs following expression of I-SceI also did not generate GCRs. Because we identified solely interstitial deletions using the aforementioned negative selection system, we developed a positive selection system to produce GCR. A construct containing an I-SceI restriction site immediately followed by a hygromycin phosphotransferase cDNA, with no promoter, was stably integrated into OVCAR-8 cells. DNA DSBs were produced by an I-SceI expression vector. None of the hygromycin resistant clones recovered had linked the hygromycin phosphotransferase cDNA to an endogenous promoter, but had instead captured a portion of the I-SceI expression vector. These results indicate that even in a structurally unstable malignant cell line, the majority of DNA DSBs are repaired by religation of the two broken chromosome ends, without the introduction of a GCR. PMID:19909760

Efficient repair of DNA double-strand breaks in malignant cells with structural instability.

PubMed

Cheng, Yue; Zhang, Zhenhua; Keenan, Bridget; Roschke, Anna V; Nakahara, Kenneth; Aplan, Peter D

2010-01-05

Aberrant repair of DNA double-strand breaks (DSBs) is thought to be important in the generation of gross chromosomal rearrangements (GCRs). To examine how DNA DSBs might lead to GCRs, we investigated the repair of a single DNA DSB in a structurally unstable cell line. An I-SceI recognition site was introduced into OVCAR-8 cells between a constitutive promoter (EF1alpha) and the Herpes simplex virus thymidine kinase (TK) gene, which confers sensitivity to gancyclovir (GCV). Expression of I-SceI in these cells caused a single DSB. Clones with aberrant repair could acquire resistance to GCV by separation of the EF1alpha promoter from the TK gene, or deletion of either the EF1alpha promoter or the TK gene. All mutations that we identified were interstitial deletions. Treatment of cells with etoposide or bleomycin, agents known to produce DNA DSBs following expression of I-SceI also did not generate GCRs. Because we identified solely interstitial deletions using the aforementioned negative selection system, we developed a positive selection system to produce GCR. A construct containing an I-SceI restriction site immediately followed by a hygromycin phosphotransferase cDNA, with no promoter, was stably integrated into OVCAR-8 cells. DNA DSBs were produced by an I-SceI expression vector. None of the hygromycin resistant clones recovered had linked the hygromycin phosphotransferase cDNA to an endogenous promoter, but had instead captured a portion of the I-SceI expression vector. These results indicate that even in a structurally unstable malignant cell line, the majority of DNA DSBs are repaired by religation of the two broken chromosome ends, without the introduction of a GCR.

Analytical and numerical treatment of resistive drift instability in a plasma slab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mirnov, V. V., E-mail: vvmirnov@wisc.edu; Sauppe, J. P.; Hegna, C. C.

An analytic approach combining the effect of equilibrium diamagnetic flows and the finite ionsound gyroradius associated with electron−ion decoupling and kinetic Alfvén wave dispersion is derived to study resistive drift instabilities in a plasma slab. Linear numerical computations using the NIMROD code are performed with cold ions and hot electrons in a plasma slab with a doubly periodic box bounded by two perfectly conducting walls. A linearly unstable resistive drift mode is observed in computations with a growth rate that is consistent with the analytic dispersion relation. The resistive drift mode is expected to be suppressed by magnetic shear inmore » unbounded domains, but the mode is observed in numerical computations with and without magnetic shear. In the slab model, the finite slab thickness and the perfectly conducting boundary conditions are likely to account for the lack of suppression.« less

Multi-region approach to free-boundary three-dimensional tokamak equilibria and resistive wall instabilities

NASA Astrophysics Data System (ADS)

Ferraro, N. M.; Jardin, S. C.; Lao, L. L.; Shephard, M. S.; Zhang, F.

2016-05-01

Free-boundary 3D tokamak equilibria and resistive wall instabilities are calculated using a new resistive wall model in the two-fluid M3D-C1 code. In this model, the resistive wall and surrounding vacuum region are included within the computational domain. This implementation contrasts with the method typically used in fluid codes in which the resistive wall is treated as a boundary condition on the computational domain boundary and has the advantage of maintaining purely local coupling of mesh elements. This new capability is used to simulate perturbed, free-boundary non-axisymmetric equilibria; the linear evolution of resistive wall modes; and the linear and nonlinear evolution of axisymmetric vertical displacement events (VDEs). Calculated growth rates for a resistive wall mode with arbitrary wall thickness are shown to agree well with the analytic theory. Equilibrium and VDE calculations are performed in diverted tokamak geometry, at physically realistic values of dissipation, and with resistive walls of finite width. Simulations of a VDE disruption extend into the current-quench phase, in which the plasma becomes limited by the first wall, and strong currents are observed to flow in the wall, in the SOL, and from the plasma to the wall.

Double Carbon Nano Coating of LiFePO4 Cathode Material for High Performance of Lithium Ion Batteries.

PubMed

Ding, Yan-Hong; Huang, Guo-Long; Li, Huan-Huan; Xie, Hai-Ming; Sun, Hai-Zhu; Zhang, Jing-Ping

2015-12-01

Double carbon-coated LiFePO4 (D-LiFePO4/C) composite with sphere-like structure was synthesized through combination of co-precipitation and solid-state methods. Cetyl-trimethyl-ammonium bromide (CTAB) and citric acid served as two kinds of carbon sources in sequence. SEM images demonstrated that double carbon coating had certain influence on the morphology. The thickness of carbon coating on D-LiFePO4/C was about 1.7 nm and the content of carbon was 2.48 wt%, according to HRTEM and TG analysis. The electrochemical impedance spectroscopy analysis indicated that the D-LiFePO4/C composite presented the charge-transfer resistance of 68 Ω and Li ion diffusion coefficient of 2.68 x 10(-13) cm2 S(-1), while the single carbon-coated LiFePO4 (S-LiFePO4/C) exhibited 135.5Ω and 4.03 x 10(-14) cm2 S(-1). Especially, the prepared D-LiFePO4/C electrode showed discharge capacities of 102.9 (10C) and 87.1 (20C) mA h g(-1), respectively, with almost no capacity lost after 400 cycles at 10C, which were much better than those of S-LiFePO4/C composite.

Three-dimensional flow of Prandtl fluid with Cattaneo-Christov double diffusion

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Aziz, Arsalan; Muhammad, Taseer; Alsaedi, Ahmed

2018-06-01

This research paper intends to investigate the 3D flow of Prandtl liquid in the existence of improved heat conduction and mass diffusion models. Flow is created by considering linearly bidirectional stretchable sheet. Thermal and concentration diffusions are considered by employing Cattaneo-Christov double diffusion models. Boundary layer approach has been used to simplify the governing PDEs. Suitable nondimensional similarity variables correspond to strong nonlinear ODEs. Optimal homotopy analysis method (OHAM) is employed for solutions development. The role of various pertinent variables on temperature and concentration are analyzed through graphs. The physical quantities such as surface drag coefficients and heat and mass transfer rates at the wall are also plotted and discussed. Our results indicate that the temperature and concentration are decreasing functions of thermal and concentration relaxation parameters respectively.

Some effects of horizontal discretization on linear baroclinic and symmetric instabilities

NASA Astrophysics Data System (ADS)

Barham, William; Bachman, Scott; Grooms, Ian

2018-05-01

The effects of horizontal discretization on linear baroclinic and symmetric instabilities are investigated by analyzing the behavior of the hydrostatic Eady problem in ocean models on the B and C grids. On the C grid a spurious baroclinic instability appears at small wavelengths. This instability does not disappear as the grid scale decreases; instead, it simply moves to smaller horizontal scales. The peak growth rate of the spurious instability is independent of the grid scale as the latter decreases. It is equal to cf /√{Ri} where Ri is the balanced Richardson number, f is the Coriolis parameter, and c is a nondimensional constant that depends on the Richardson number. As the Richardson number increases c increases towards an upper bound of approximately 1/2; for large Richardson numbers the spurious instability is faster than the Eady instability. To suppress the spurious instability it is recommended to use fourth-order centered tracer advection along with biharmonic viscosity and diffusion with coefficients (Δx) 4 f /(32√{Ri}) or larger where Δx is the grid scale. On the B grid, the growth rates of baroclinic and symmetric instabilities are too small, and converge upwards towards the correct values as the grid scale decreases; no spurious instabilities are observed. In B grid models at eddy-permitting resolution, the reduced growth rate of baroclinic instability may contribute to partially-resolved eddies being too weak. On the C grid the growth rate of symmetric instability is better (larger) than on the B grid, and converges upwards towards the correct value as the grid scale decreases.

Filamentation instability of a fast electron beam in a dielectric target.

PubMed

Debayle, A; Tikhonchuk, V T

2008-12-01

High-intensity laser-matter interaction is an efficient method for high-current relativistic electron beam production. At current densities exceeding a several kA microm{-2} , the beam propagation is maintained by an almost complete current neutralization by the target electrons. In such a geometry of two oppositely directed flows, beam instabilities can develop, depending on the target and the beam parameters. The present paper proposes an analytical description of the filamentation instability of an electron beam propagating through an insulator target. It is shown that the collisionless and resistive instabilities enter into competition with the ionization instability. This latter process is dominant in insulator targets where the field ionization by the fast beam provides free electrons for the neutralization current.

ATP-independent diffusion of double-stranded RNA binding proteins

PubMed Central

Koh, Hye Ran; Kidwell, Mary Anne; Ragunathan, Kaushik; Doudna, Jennifer A.; Myong, Sua

2013-01-01

The proteins harboring double-stranded RNA binding domains (dsRBDs) play diverse functional roles such as RNA localization, splicing, editing, export, and translation, yet mechanistic basis and functional significance of dsRBDs remain unclear. To unravel this enigma, we investigated transactivation response RNA binding protein (TRBP) consisting of three dsRBDs, which functions in HIV replication, protein kinase R(PKR)–mediated immune response, and RNA silencing. Here we report an ATP-independent diffusion activity of TRBP exclusively on dsRNA in a length-dependent manner. The first two dsRBDs of TRBP are essential for diffusion, whereas the third dsRBD is dispensable. Two homologs of TRBP, PKR activator and R3D1-L, displayed the same diffusion, implying a universality of the diffusion activity among this protein family. Furthermore, a Dicer–TRBP complex on dsRNA exhibited dynamic diffusion, which was correlated with Dicer’s catalytic activity. These results implicate the dsRNA-specific diffusion activity of TRBP that contributes to enhancing siRNA and miRNA processing by Dicer. PMID:23251028

Single anterior portal: A better option for arthroscopic treatment of traumatic anterior shoulder instability?

PubMed

Çiçek, Hakan; Tuhanioğlu, Ümit; Oğur, Hasan Ulaş; Seyfettinoğlu, Fırat; Çiloğlu, Osman; Beyzadeoğlu, Tahsin

2017-07-01

The aim of this study was to compare single and double anterior portal techniques in the arthroscopic treatment of traumatic anterior shoulder instability. A total of 91 cases who underwent arthroscopic Bankart repair for anterior shoulder instability were reviewed. The patients were divided into 2 groups as Group 1 (47 male and 2 female; mean age: 25.8 ± 6.8) for arthroscopic single anterior portal approach and Group 2 (41 male and 1 female; mean age: 25.4 ± 6.6) for the classical anterior double portal approach. The groups were compared for clinical scores, range of motion, analgesia requirement, complications, duration of surgery, cost and learning curve according to a short questionnaire completed by the relevant healthcare professionals. No statistically significant difference was found between the 2 groups in terms of pre-operative and post-operative Constant and Rowe Shoulder Scores, range of motion and complications (p > 0.05). In Group 2 patients, the requirement for post-operative analgesics was significantly higher (p < 0.001), whereas the duration of surgery was statistically significantly shorter in Group 1 (p < 0.001). In the assessment of the questionnaire, it was seen that a single portal anterior approach was preferred at a higher ratio (p = 0.035). The cost analysis revealed that the cost was 5.7% less for patients with a single portal. In the arthroscopic treatment of traumatic anterior shoulder instability accompanied by a Bankart lesion, the anterior single portal technique is as successful in terms of clinical results as the conventional double portal approach. The single portal technique has advantages such as less postoperative pain, a shorter surgical learning curve and lower costs. Level III, Therapeutic study. Copyright © 2017 Turkish Association of Orthopaedics and Traumatology. Production and hosting by Elsevier B.V. All rights reserved.

Effects of BOSU ball(s) during sit-ups with body weight and added resistance on core muscle activation.

PubMed

Saeterbakken, Atle H; Andersen, Vidar; Jansson, June; Kvellestad, Ann C; Fimland, Marius S

2014-12-01

The objective of this study was to assess the electromyographic activity of the rectus abdominis (upper and lower part) and external oblique during sit-ups performed on BOSU ball(s). Twenty-four men participated in a familiarization session, and in the next session, they performed the experimental tests in randomized order. The sit-ups were performed with 10 repetitions with body weight and with 10 repetition maximum (10RM) using elastic bands as external resistance under 4 different conditions: (a) on a stable surface, (b) with the BOSU ball under their feet (dome side down, lower-body instability), (c) BOSU ball under the low back (dome side up, upper-body instability), and (d) with BOSU balls under both feet and the low back (dual instability). The feet were not attached to the surface. We observed that with body weight, external oblique activation was decreased by upper-body instability and dual instability by 22-24% (p = 0.002-0.006), whereas the rectus abdominis was not affected by the surface. Using 10RM loads, the upper and lower rectus abdominis activities were increased by upper body and dual instability by 21-24% compared with that for a stable surface (P ≤ 0.001-0.036). Further, lower-body instability did not affect muscle activities significantly with either load for any condition. Hence, BOSU balls under the low back can increase and decrease abdominal muscle activation depending on the load, whereas placing a BOSU ball under the feet with the dome side down had little impact.

A Self-Contained Mapping Closure Approximation for Scalar Mixing

NASA Technical Reports Server (NTRS)

He, Guo-Wei; Zhang, Zi-Fan

2003-01-01

Scalar turbulence exhibits interplays of coherent structures and random fluctuations over a broad range of spatial and temporal scales. This feature necessitates a probabilistic description of the scalar dynamics, which can be achieved comprehensively by using probability density functions (PDFs). Therefore, the challenge is to obtain the scalar PDFs (Lundgren 1967; Dopazo 1979). Generally, the evolution of a scalar is governed by three dynamical processes: advection, diffusion and reaction. In a PDF approach (Pope 1985), the advection and reaction can be treated exactly but the effect of molecular diffusion has to be modeled. It has been shown (Pope 1985) that the effect of molecular diffusion can be expressed as conditional dissipation rates or conditional diffusions. The currently used models for the conditional dissipation rates and conditional diffusions (Pope 1991) have resisted deduction from the fundamental equations and are unable to yield satisfactory results for the basic test cases of decaying scalars in isotropic turbulence, although they have achieved some success in a variety of individual cases. The recently developed mapping closure approach (Pope 1991; Chen, Chen & Kraichnan 1989; Kraichnan 1990; Klimenko & Pope 2003) provides a deductive method for conditional dissipation rates and conditional di usions, and the models obtained can successfully describe the shape relaxation of the scalar PDF from an initial double delta distribution to a Gaussian one. However, the mapping closure approach is not able to provide the rate at which the scalar evolves. The evolution rate has to be modeled. Therefore, the mapping closure approach is not closed. In this letter, we will address this problem.

Heterogeneity induces spatiotemporal oscillations in reaction-diffusion systems

NASA Astrophysics Data System (ADS)

Krause, Andrew L.; Klika, Václav; Woolley, Thomas E.; Gaffney, Eamonn A.

2018-05-01

We report on an instability arising in activator-inhibitor reaction-diffusion (RD) systems with a simple spatial heterogeneity. This instability gives rise to periodic creation, translation, and destruction of spike solutions that are commonly formed due to Turing instabilities. While this behavior is oscillatory in nature, it occurs purely within the Turing space such that no region of the domain would give rise to a Hopf bifurcation for the homogeneous equilibrium. We use the shadow limit of the Gierer-Meinhardt system to show that the speed of spike movement can be predicted from well-known asymptotic theory, but that this theory is unable to explain the emergence of these spatiotemporal oscillations. Instead, we numerically explore this system and show that the oscillatory behavior is caused by the destabilization of a steady spike pattern due to the creation of a new spike arising from endogeneous activator production. We demonstrate that on the edge of this instability, the period of the oscillations goes to infinity, although it does not fit the profile of any well-known bifurcation of a limit cycle. We show that nearby stationary states are either Turing unstable or undergo saddle-node bifurcations near the onset of the oscillatory instability, suggesting that the periodic motion does not emerge from a local equilibrium. We demonstrate the robustness of this spatiotemporal oscillation by exploring small localized heterogeneity and showing that this behavior also occurs in the Schnakenberg RD model. Our results suggest that this phenomenon is ubiquitous in spatially heterogeneous RD systems, but that current tools, such as stability of spike solutions and shadow-limit asymptotics, do not elucidate understanding. This opens several avenues for further mathematical analysis and highlights difficulties in explaining how robust patterning emerges from Turing's mechanism in the presence of even small spatial heterogeneity.

Design and Fabrication of a Hele-Shaw Apparatus for Observing Instabilities of Diffusion Flames

NASA Technical Reports Server (NTRS)

Wichman, I. S.; Oravecz-Simpkins, L.; Olson, S.

2001-01-01

Examinations of flame fronts spreading over solid fuels in an opposed flow of oxidizer have shown that the flame front fragments into smaller (cellular) flames. These 'flamelets' will oscillate, recombine, or extinguish, indicating that they are in the near extinction limit regime (i.e., to one side of the quenching branch of the flammability map). Onset of unstable cellular flamelet formation for flame spread over thin fuels occurs when a heat-sink substrate is placed a small distance from the underside of the fuel. This heat-sink substrate (or backing) displaces the quenching branch of the flammability map in a direction that causes the instabilities to occur at higher air velocities. Similar near-limit behavior has been observed in other works using different fuels, thus suggesting that these dynamic mechanisms are fuel-independent and therefore fundamental attributes of flames in this near-limit flame spread regime. The objective of this project is to determine the contributions of the hydrodynamic and thermodiffusive mechanisms to the observed formation of flame instabilities. From this, a model of diffusion flame instabilities shall be generated. Previously, experiments were conducted in NASA drop towers, thereby limiting observation time to O(1-5 sec). The NASA tests exhibited flamelet survival for the entire drop time, suggesting that flamelets (i.e., small cellular flames) might exist, if permitted, for longer time periods. By necessity, experiments were limited to thermally thin cellulose fuels (approximately 0.001 in thick): instabilities could form by virtue of faster spread rates over thin fuels. Unstable behavior was unlikely in the short drop time for thicker fuels. In the International Space Station (ISS), microgravity time is unlimited, so both thin and thick fuels can be tested.

Can Hall effect trigger Kelvin-Helmholtz instability in sub-Alfvénic flows?

NASA Astrophysics Data System (ADS)

Pandey, B. P.

2018-05-01

In the Hall magnetohydrodynamics, the onset condition of the Kelvin-Helmholtz instability is solely determined by the Hall effect and is independent of the nature of shear flows. In addition, the physical mechanism behind the super- and sub-Alfvénic flows becoming unstable is quite different: the high-frequency right circularly polarized whistler becomes unstable in the super-Alfvénic flows whereas low-frequency, left circularly polarized ion-cyclotron wave becomes unstable in the presence of sub-Alfvénic shear flows. The growth rate of the Kelvin-Helmholtz instability in the super-Alfvénic case is higher than the corresponding ideal magnetohydrodynamic rate. In the sub-Alfvénic case, the Hall effect opens up a new, hitherto inaccessible (to the magnetohydrodynamics) channel through which the partially or fully ionized fluid can become Kelvin-Helmholtz unstable. The instability growth rate in this case is smaller than the super-Alfvénic case owing to the smaller free shear energy content of the flow. When the Hall term is somewhat smaller than the advection term in the induction equation, the Hall effect is also responsible for the appearance of a new overstable mode whose growth rate is smaller than the purely growing Kelvin-Helmholtz mode. On the other hand, when the Hall diffusion dominates the advection term, the growth rate of the instability depends only on the Alfvén -Mach number and is independent of the Hall diffusion coefficient. Further, the growth rate in this case linearly increases with the Alfvén frequency with smaller slope for sub-Alfvénic flows.

A validated non-linear Kelvin-Helmholtz benchmark for numerical hydrodynamics

NASA Astrophysics Data System (ADS)

Lecoanet, D.; McCourt, M.; Quataert, E.; Burns, K. J.; Vasil, G. M.; Oishi, J. S.; Brown, B. P.; Stone, J. M.; O'Leary, R. M.

2016-02-01

The non-linear evolution of the Kelvin-Helmholtz instability is a popular test for code verification. To date, most Kelvin-Helmholtz problems discussed in the literature are ill-posed: they do not converge to any single solution with increasing resolution. This precludes comparisons among different codes and severely limits the utility of the Kelvin-Helmholtz instability as a test problem. The lack of a reference solution has led various authors to assert the accuracy of their simulations based on ad hoc proxies, e.g. the existence of small-scale structures. This paper proposes well-posed two-dimensional Kelvin-Helmholtz problems with smooth initial conditions and explicit diffusion. We show that in many cases numerical errors/noise can seed spurious small-scale structure in Kelvin-Helmholtz problems. We demonstrate convergence to a reference solution using both ATHENA, a Godunov code, and DEDALUS, a pseudo-spectral code. Problems with constant initial density throughout the domain are relatively straightforward for both codes. However, problems with an initial density jump (which are the norm in astrophysical systems) exhibit rich behaviour and are more computationally challenging. In the latter case, ATHENA simulations are prone to an instability of the inner rolled-up vortex; this instability is seeded by grid-scale errors introduced by the algorithm, and disappears as resolution increases. Both ATHENA and DEDALUS exhibit late-time chaos. Inviscid simulations are riddled with extremely vigorous secondary instabilities which induce more mixing than simulations with explicit diffusion. Our results highlight the importance of running well-posed test problems with demonstrated convergence to a reference solution. To facilitate future comparisons, we include as supplementary material the resolved, converged solutions to the Kelvin-Helmholtz problems in this paper in machine-readable form.

The Spiral Wave Instability Induced by a Giant Planet. I. Particle Stirring in the Inner Regions of Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bae, Jaehan; Nelson, Richard P.; Hartmann, Lee

2016-12-01

We have recently shown that spiral density waves propagating in accretion disks can undergo a parametric instability by resonantly coupling with and transferring energy into pairs of inertial waves (or inertial-gravity waves when buoyancy is important). In this paper, we perform inviscid three-dimensional global hydrodynamic simulations to examine the growth and consequence of this instability operating on the spiral waves driven by a Jupiter-mass planet in a protoplanetary disk. We find that the spiral waves are destabilized via the spiral wave instability (SWI), generating hydrodynamic turbulence and sustained radially alternating vertical flows that appear to be associated with long wavelength inertial modes. In the interval 0.3 {R}{{p}}≤slant R≤slant 0.7{R}{{p}}, where R p denotes the semimajor axis of the planetary orbit (assumed to be 5 au), the estimated vertical diffusion rate associated with the turbulence is characterized by {α }{diff}∼ (0.2{--}1.2)× {10}-2. For the disk model considered here, the diffusion rate is such that particles with sizes up to several centimeters are vertically mixed within the first pressure scale height. This suggests that the instability of spiral waves launched by a giant planet can significantly disperse solid particles and trace chemical species from the midplane. In planet formation models where the continuous local production of chondrules/pebbles occurs over Myr timescales to provide a feedstock for pebble accretion onto these bodies, this stirring of solid particles may add a time constraint: planetary embryos and large asteroids have to form before a gas giant forms in the outer disk, otherwise the SWI will significantly decrease the chondrule/pebble accretion efficiency.

Serotype distribution and antimicrobial susceptibility of group B streptococci in pregnant women: results from a Swiss tertiary centre.

PubMed

Fröhlicher, Simone; Reichen-Fahrni, Gabriela; Müller, Martin; Surbek, Daniel; Droz, Sara; Spellerberg, Barbara; Sendi, Parham

2014-03-20

To evaluate the rates of penicillin, clindamycin and erythromycin resistance and the serotype distribution among isolates of group B streptococcus (GBS) obtained from pregnant women at the University Hospital of Bern in Switzerland. We prospectively collected screening samples for GBS colonisation at the University Women's Hospital Bern, Switzerland, between March 2009 and August 2010. We included 364 GBS isolates collected from vaginal, cervical or vaginal-perianal swabs at any gestation time. The minimal inhibitory concentrations for penicillin, clindamycin and erythromycin were established using Etest with 24 hours of incubation, and inducible clindamycin resistance was tested with double disk diffusion tests. Serotyping was done with a rapid latex agglutination test or, if not conclusive, with polymerase chain-reaction (PCR) testing. We looked for significant associations between resistance patterns, age groups, serotype and ethnicity. All isolates were susceptible to penicillin. Resistance rates were 14.5% for erythromycin and 8.2% for clindamycin. Of 364 isolates, 5.8% were susceptible to clindamycin but not to erythromycin, although demonstrating inducible clindamycin resistance. Hence, the final reported clindamycin resistance rate was 14%. Serotype III was the most frequent serotype (29%), followed by V (25%) and Ia (19%). Serotype V was associated with erythromycin resistance (p = 0.0007). In comparison with all other ethnicities, patients from Asia showed a higher proportion of erythromycin and clindamycin resistance (p = 0.018). No significant association between resistance patterns and age groups was found. In pregnant women with GBS colonisation, penicillin is the antibiotic of choice for intrapartum prophylaxis to prevent neonatal early-onset GBS sepsis. In women with penicillin allergy and at high risk for anaphylactic reaction, clindamycin may be an alternative. The resistance rate for clindamycin at our institution was 14%; therefore, susceptibility must be tested before administration.

Molecular characterization of macrolide resistant Streptococcus pyogenes isolates from pharyngitis patients in Serbia.

PubMed

Opavski, Natasa; Gajic, Ina; Borek, Anna L; Obszańska, Katarzyna; Stanojevic, Maja; Lazarevic, Ivana; Ranin, Lazar; Sitkiewicz, Izabela; Mijac, Vera

2015-07-01

A steady increase in macrolide resistance in Streptococcus pyogenes, group A streptococci (GAS) was reported in Serbia during 2004-2009 (9.9%). However, there are no data on the molecular epidemiology of pharyngeal macrolide resistance GAS (MRGAS) isolates. Therefore, the aims of this first nationwide study were to examine the prevalence of macrolide resistance in Serbian GAS and to determine their resistance phenotypes, genotypes and clonal relationships. Overall 3893 non-duplicate pharyngeal S. pyogenes isolates from outpatients with GAS infection were collected throughout country during 2008 and 2009. Among 486 macrolide resistant pharyngeal isolates collected, 103 were further characterized. Macrolide resistance phenotypes and genotypes were determined by double-disk diffusion test and PCR, respectively. Strain relatedness was determined by emm typing, multilocus sequence typing (MLST), multilocus variable tandem repeat analysis (MLVA), phage profiling (PP) and virulence factor profiling (VFP). Overall, macrolide resistance among GAS isolates in Serbia was 12.5%. M phenotype was the most common (71.8%), followed by iMLS (18.4%) and cMLS (9.7%). Three clonal complexes--emm75/mefA/ST49, emm12/mefA/ST36 and emm77/ermA/tetO/ST63 comprised over 90% of the tested strains. Although MLVA, PP and VFP distinguished 10, 20 and 12 different patterns, respectively, cluster analysis disclosed only small differences between strains which belonged to the same emm/ST type. Our data indicate dominance of three major internationally widely disseminated macrolide resistant clones and a high genetic homogeneity among the Serbian MRGAS population. Continued surveillance of macrolide resistance and clonal composition in MRGAS in Serbia in future is necessary to determine stability of MRGAS clones and to guide therapy strategies. Copyright © 2015 Elsevier B.V. All rights reserved.

Coulomb double helical structure

NASA Astrophysics Data System (ADS)

Kamimura, Tetsuo; Ishihara, Osamu

2012-01-01

Structures of Coulomb clusters formed by dust particles in a plasma are studied by numerical simulation. Our study reveals the presence of various types of self-organized structures of a cluster confined in a prolate spheroidal electrostatic potential. The stable configurations depend on a prolateness parameter for the confining potential as well as on the number of dust particles in a cluster. One-dimensional string, two-dimensional zigzag structure and three-dimensional double helical structure are found as a result of the transition controlled by the prolateness parameter. The formation of stable double helical structures resulted from the transition associated with the instability of angular perturbations on double strings. Analytical perturbation study supports the findings of numerical simulations.

The instability of the spiral wave induced by the deformation of elastic excitable media

NASA Astrophysics Data System (ADS)

Ma, Jun; Jia, Ya; Wang, Chun-Ni; Li, Shi-Rong

2008-09-01

There are some similarities between the spiral wave in excitable media and in cardiac tissue. Much evidence shows that the appearance and instability of the spiral wave in cardiac tissue can be linked to one kind of heart disease. There are many models that can be used to investigate the formation and instability of the spiral wave. Cardiac tissue is excitable and elastic, and it is interesting to simulate the transition and instability of the spiral wave induced by media deformation. For simplicity, a class of the modified Fitzhugh-Nagumo (MFHN) model, which can generate a stable rotating spiral wave, meandering spiral wave and turbulence within appropriate parameter regions, will be used to simulate the instability of the spiral wave induced by the periodical deformation of media. In the two-dimensional case, the total acreage of elastic media is supposed to be invariable in the presence of deformation, and the problem is described with Lx × Ly = N × ΔxN × Δy = L'xL'y = N × Δx'N × Δy'. In our studies, elastic media are decentralized into N × N sites and the space of the adjacent sites is changed to simulate the deformation of elastic media. Based on the nonlinear dynamics theory, the deformation effect on media is simplified and simulated by perturbing the diffusion coefficients Dx and Dy with different periodical signals, but the perturbed diffusion coefficients are compensatory. The snapshots of our numerical results find that the spiral wave can coexist with the spiral turbulence, instability of the spiral wave and weak deformation of the spiral wave in different conditions. The ratio parameter ɛ and the frequency of deformation forcing play a deterministic role in inducing instability of the spiral wave. Extensive studies confirm that the instability of the spiral wave can be induced and developed only if an appropriate frequency for deformation is used. We analyze the power spectrum for the time series of the mean activator of four sampled sites which are selected symmetrically in different cases, such as the condition that the spiral wave coexists with the spiral turbulence, spiral wave without evident deformation, complete instability of the spiral wave (turbulence) and weak deformation of the spiral wave. It is found that more new peaks appear in the power spectrum and the distribution of frequency becomes sparser when the spiral wave encounters instability.

Cavitation instability in bulk metallic glasses

NASA Astrophysics Data System (ADS)

Dai, L. H.; Huang, X.; Ling, Z.

2015-09-01

Recent experiments have shown that fracture surfaces of bulk metallic glasses (BMGs) usually exhibit an intriguing nanoscale corrugation like fractographic feature mediated by nanoscale void formation. We attribute the onset of this nanoscale corrugation to TTZs (tension transformation zones) mediated cavitation. In our recent study, the spall experiments of Zr-based BMG using a single-stage light gas gun were performed. To uncover the mechanisms of the spallation damage nucleation and evolution, the samples were designed to be subjected to dynamic tensile loadings of identical amplitude but with different durations by making use of the multi-stress pulse and the double-flyer techniques. It is clearly revealed that the macroscopic spall fracture in BMGs originates from the nucleation, growth and coalescence of micro-voids. Then, a microvoid nucleation model of BMGs based on free volume theory is proposed, which indicates that the nucleation of microvoids at the early stage of spallation in BMGs is resulted from diffusion and coalescence of free volume. Furthermore, a theoretical model of void growth in BMGs undergoing remote dynamic hydrostatic tension is developed. The critical condition of cavitation instability is obtained. It is found that dynamic void growth in BMGs can be well controlled by a dimensionless inertial number characterizing the competition between intrinsic and extrinsic time scales. To unveil the atomic-level mechanism of cavitation, a systematic molecular dynamics (MD) simulation of spallation behaviour of a binary metallic glass with different impact velocities was performed. It is found that micro-void nucleation is determined TTZs while the growth is controlled by shear transformation zones (STZs) at atomic scale.

Spatial variability of the Arctic Ocean's double-diffusive staircase

NASA Astrophysics Data System (ADS)

Shibley, N. C.; Timmermans, M.-L.; Carpenter, J. R.; Toole, J. M.

2017-02-01

The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure overlying the Atlantic Water Layer that can be attributed to the diffusive form of double-diffusive convection. The staircase consists of multiple layers of O(1) m in thickness separated by sharp interfaces, across which temperature and salinity change abruptly. Through a detailed analysis of Ice-Tethered Profiler measurements from 2004 to 2013, the double-diffusive staircase structure is characterized across the entire Arctic Ocean. We demonstrate how the large-scale Arctic Ocean circulation influences the small-scale staircase properties. These staircase properties (layer thicknesses and temperature and salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio spanning the staircase stratification. We show that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (approximately 3-4) on the Eurasian side and higher density ratio (approximately 6-7) on the Canadian side. We find that the Eurasian Basin staircase is characterized by fewer, thinner layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin layers and the absence of a well-defined staircase. A double-diffusive 4/3 flux law parametrization is used to estimate vertical heat fluxes in the Canadian Basin to be O(0.1) W m-2. It is shown that the 4/3 flux law may not be an appropriate representation of heat fluxes through the Eurasian Basin staircase. Here molecular heat fluxes are estimated to be between O(0.01) and O(0.1) W m-2. However, many uncertainties remain about the exact nature of these fluxes.

Preconditioned wire array Z-pinches driven by a double pulse current generator

NASA Astrophysics Data System (ADS)

Wu, Jian; Lu, Yihan; Sun, Fengju; Li, Xingwen; Jiang, Xiaofeng; Wang, Zhiguo; Zhang, Daoyuan; Qiu, Aici; Lebedev, Sergey

2018-07-01

Suppression of the core-corona structure and wire ablation in wire array Z-pinches is investigated using a novel double pulse current generator ‘Qin-1’ facility. The ‘Qin-1’ facility allows coupling a ∼10 kA 20 ns prepulse generator with a ∼0.8 MA 160 ns main current generator. The tailored prepulse current preheats wires to a gaseous state and the time interval between the prepulse and the main current pulse allows formation of a more uniform mass distribution for the implosion. The implosion of a gasified two aluminum-wire array showed no ablation phase and allowed all array mass to participate in the implosion. The initial perturbations formed from the inhomogeneous ablation were suppressed, however, the magneto Rayleigh–Taylor (MRT) instability during the implosion was still significant and further researches on the generation and development of the MRT instabilities of this gasified wire array are needed.

Charge instability in double quantum dots in Ge/Si core/shell nanowires

NASA Astrophysics Data System (ADS)

Zarassi, Azarin; Su, Zhaoen; Schwenderling, Jens; Frolov, Sergey M.; Hocevar, Moïra; Nguyen, Binh-Minh; Yoo, Jinkyoung; Dayeh, Shadi A.

Controlling dephasing times are of great challenge in the studies of spin qubit. Reported long spin coherence time and predicted strong spin-orbit interaction of holes in Ge/Si core/shell nanowires, as well as their weak coupling to very few nuclear spins of these group IV semiconductors, persuade electrical spin control. We have established Pauli spin blockade in gate-tunable quantum dots formed in these nanowires. The g-factor has been measured and evidence of spin-orbit interaction has been observed in the presence of magnetic field. However, electrical control of spins requires considerable stability in the double dot configuration, and imperfectly these dots suffer from poor stability. We report on fabrication modifications on Ge/Si core/shell nanowires, as well as measurement techniques to suppress the charge instabilities and ease the way to study spin-orbit coupling and resolve electric dipole spin resonance.

Genetic instability of an oligomycin resistance mutation in yeast is associated with an amplification of a mitochondrial DNA segment.

PubMed Central

Ragnini, A; Fukuhara, H

1989-01-01

In the yeast Kluyveromyces lactis, mutations affecting mitochondrial functions are often highly unstable. In order to understand the basis of this genetic instability, we examined the case of an oligomycin resistant mutant. When the mutant was grown in the absence of the drug, the resistance was rapidly lost. This character showed a typical cytoplasmic inheritance. The unstable resistance was found to be associated with the presence of a repetitive DNA in which the repeating unit was a specific segment of the mitochondrial DNA. The amplified molecules were co-replicating with the wild type genome in the mutant cells. The spontaneous loss of the drug resistance was accompanied by the disappearance of the amplified DNA. The repetitive sequence came from a 405 base-pair segment immediately downstream of a cluster of two transfer RNA genes (threonyl 2 and glutamyl). Modified processing of these tRNAs was detected in the mutant. A possible mechanism by which these events could lead to drug resistance is discussed. Images PMID:2780315

An earthquake instability model based on faults containing high fluid-pressure compartments

USGS Publications Warehouse

Lockner, D.A.; Byerlee, J.D.

1995-01-01

It has been proposed that large strike-slip faults such as the San Andreas contain water in seal-bounded compartments. Arguments based on heat flow and stress orientation suggest that in most of the compartments, the water pressure is so high that the average shear strength of the fault is less than 20 MPa. We propose a variation of this basic model in which most of the shear stress on the fault is supported by a small number of compartments where the pore pressure is relatively low. As a result, the fault gouge in these compartments is compacted and lithified and has a high undisturbed strength. When one of these locked regions fails, the system made up of the neighboring high and low pressure compartments can become unstable. Material in the high fluid pressure compartments is initially underconsolidated since the low effective confining pressure has retarded compaction. As these compartments are deformed, fluid pressure remains nearly unchanged so that they offer little resistance to shear. The low pore pressure compartments, however, are overconsolidated and dilate as they are sheared. Decompression of the pore fluid in these compartments lowers fluid pressure, increasing effective normal stress and shear strength. While this effect tends to stabilize the fault, it can be shown that this dilatancy hardening can be more than offset by displacement weakening of the fault (i.e., the drop from peak to residual strength). If the surrounding rock mass is sufficiently compliant to produce an instability, slip will propagate along the fault until the shear fracture runs into a low-stress region. Frictional heating and the accompanying increase in fluid pressure that are suggested to occur during shearing of the fault zone will act as additional destabilizers. However, significant heating occurs only after a finite amount of slip and therefore is more likely to contribute to the energetics of rupture propagation than to the initiation of the instability. We present results of a one-dimensional dynamic Burridge-Knopoff-type model to demonstrate various aspects of the fluid-assisted fault instability described above. In the numerical model, the fault is represented by a series of blocks and springs, with fault rheology expressed by static and dynamic friction. In addition, the fault surface of each block has associated with it pore pressure, porosity and permeability. All of these variables are allowed to evolve with time, resulting in a wide range of phenomena related to fluid diffusion, dilatancy, compaction and heating. These phenomena include creep events, diffusion-controlled precursors, triggered earthquakes, foreshocks, aftershocks, and multiple earthquakes. While the simulations have limitations inherent to 1-D fault models, they demonstrate that the fluid compartment model can, in principle, provide the rich assortment of phenomena that have been associated with earthquakes. ?? 1995 Birkha??user Verlag.

SPOP mutation leads to genomic instability in prostate cancer

PubMed Central

Boysen, Gunther; Barbieri, Christopher E; Prandi, Davide; Blattner, Mirjam; Chae, Sung-Suk; Dahija, Arun; Nataraj, Srilakshmi; Huang, Dennis; Marotz, Clarisse; Xu, Limei; Huang, Julie; Lecca, Paola; Chhangawala, Sagar; Liu, Deli; Zhou, Pengbo; Sboner, Andrea; de Bono, Johann S

2015-01-01

Genomic instability is a fundamental feature of human cancer often resulting from impaired genome maintenance. In prostate cancer, structural genomic rearrangements are a common mechanism driving tumorigenesis. However, somatic alterations predisposing to chromosomal rearrangements in prostate cancer remain largely undefined. Here, we show that SPOP, the most commonly mutated gene in primary prostate cancer modulates DNA double strand break (DSB) repair, and that SPOP mutation is associated with genomic instability. In vivo, SPOP mutation results in a transcriptional response consistent with BRCA1 inactivation resulting in impaired homology-directed repair (HDR) of DSB. Furthermore, we found that SPOP mutation sensitizes to DNA damaging therapeutic agents such as PARP inhibitors. These results implicate SPOP as a novel participant in DSB repair, suggest that SPOP mutation drives prostate tumorigenesis in part through genomic instability, and indicate that mutant SPOP may increase response to DNA-damaging therapeutics. DOI: http://dx.doi.org/10.7554/eLife.09207.001 PMID:26374986

Radiation-induced chromosomal instability in human mammary epithelial cells

NASA Technical Reports Server (NTRS)

Durante, M.; Grossi, G. F.; Yang, T. C.

1996-01-01

Karyotypes of human cells surviving X- and alpha-irradiation have been studied. Human mammary epithelial cells of the immortal, non-tumorigenic cell line H184B5 F5-1 M/10 were irradiated and surviving clones isolated and expanded in culture. Cytogenetic analysis was performed using dedicated software with an image analyzer. We have found that both high- and low-LET radiation induced chromosomal instability in long-term cultures, but with different characteristics. Complex chromosomal rearrangements were observed after X-rays, while chromosome loss predominated after alpha-particles. Deletions were observed in both cases. In clones derived from cells exposed to alpha-particles, some cells showed extensive chromosome breaking and double minutes. Genomic instability was correlated to delayed reproductive death and neoplastic transformation. These results indicate that chromosomal instability is a radiation-quality-dependent effect which could determine late genetic effects, and should therefore be carefully considered in the evaluation of risk for space missions.

Radiation-induced chromosomal instability in human mammary epithelial cells

NASA Astrophysics Data System (ADS)

Durante, M.; Grossi, G. F.; Yang, T. C.

Karyotypes of human cells surviving X- and alpha-irradiation have been studied. Human mammary epithelial cells of the immortal, non-tumorigenic cell line H184B5 F5-1 M/10 were irradiated and surviving clones isolated and expanded in culture. Cytogenetic analysis was performed using dedicated software with an image analyzer. We have found that both high- and low-LET radiation induced chromosomal instability in long-term cultures, but with different characteristics. Complex chromosomal rearrangements were observed after X-rays, while chromosome loss predominated after alpha-particles. Deletions were observed in both cases. In clones derived from cells exposed to alpha-particles, some cells showed extensive chromosome breaking and double minutes. Genomic instability was correlated to delayed reproductive death and neoplastic transformation. These results indicate that chromosomal instability is a radiation-quality-dependent effect which could determine late genetic effects, and should therefore be carefully considered in the evaluation of risk for space missions.

Onset of density-driven instabilities in fractured aquifers

NASA Astrophysics Data System (ADS)

Jafari Raad, Seyed Mostafa; Hassanzadeh, Hassan

2018-04-01

Linear stability analysis is conducted to study the onset of density-driven convection involved in solubility trapping of C O2 in fractured aquifers. The effect of physical properties of a fracture network on the stability of a diffusive boundary layer in a saturated fractured porous media is investigated using the dual porosity concept. Linear stability analysis results show that both fracture interporosity flow and fracture storativity play an important role in the stability behavior of the system. It is shown that a diffusive boundary layer under the gravity field in fractured porous media with lower fracture storativity and/or higher fracture interporosity flow coefficient is more stable. We present scaling relations for the onset of convective instability in fractured aquifers with single and variable matrix block size distribution. These findings improve our understanding of density-driven flow in fractured aquifers and are important in the estimation of potential storage capacity, risk assessment, and storage site characterization and screening.

Mirror instability and origin of morningside auroral structure

NASA Technical Reports Server (NTRS)

Chiu, Y. T.; Schulz, M.; Fennell, J. F.; Kishi, A. M.

1983-01-01

Auroral optical imagery shows marked differences between auroral features of the evening and morning sectors: the separation between diffuse and discrete auroras in the evening sector is not distinct in the morning sector, which is dominated by auroral patches and multiple banded structures aligned along some direction. Plasma distribution function signatures also show marked differences: downward electron beams and inverted-V signatures prefer the evening sector, while the electron spectra on the morning sector are similar to the diffuse aurora. A theory of morningside auroras consistent with these features was constructed. The theory is based on modulation of the growth rates of electron cyclotron waves by the mirror instability, which is in turn driven by inward-convected ions that have become anisotropic. This modulation produces alternating bands of enhanced and reduced electron precipitation which approximate the observed multiple auroral bands and patches of the morning sector.

Dephasing Catastrophe in 4-ε Dimensions: A Possible Instability of the Ergodic (Many-Body-Delocalized) Phase.

PubMed

Liao, Yunxiang; Foster, Matthew S

2018-06-08

In two dimensions, dephasing by a bath cuts off Anderson localization that would otherwise occur at any energy density for fermions with disorder. For an isolated system with short-range interactions, the system can be its own bath, exhibiting diffusive (non-Markovian) thermal density fluctuations. We recast the dephasing of weak localization due to a diffusive bath as a self-interacting polymer loop. We investigate the critical behavior of the loop in d=4-ε dimensions, and find a nontrivial fixed point corresponding to a temperature T^{*}∼ε>0 where the dephasing time diverges. Assuming that this fixed point survives to ε=2, we associate it with a possible instability of the ergodic phase. Our approach may open a new line of attack against the problem of the ergodic to many-body-localized phase transition in d>1 spatial dimensions.

Dephasing Catastrophe in 4 -ɛ Dimensions: A Possible Instability of the Ergodic (Many-Body-Delocalized) Phase

NASA Astrophysics Data System (ADS)

Liao, Yunxiang; Foster, Matthew S.

2018-06-01

In two dimensions, dephasing by a bath cuts off Anderson localization that would otherwise occur at any energy density for fermions with disorder. For an isolated system with short-range interactions, the system can be its own bath, exhibiting diffusive (non-Markovian) thermal density fluctuations. We recast the dephasing of weak localization due to a diffusive bath as a self-interacting polymer loop. We investigate the critical behavior of the loop in d =4 -ɛ dimensions, and find a nontrivial fixed point corresponding to a temperature T*˜ɛ >0 where the dephasing time diverges. Assuming that this fixed point survives to ɛ =2 , we associate it with a possible instability of the ergodic phase. Our approach may open a new line of attack against the problem of the ergodic to many-body-localized phase transition in d >1 spatial dimensions.

Slip-activated surface creep with room-temperature super-elongation in metallic nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Li; Sansoz, Frederic; He, Yang

2016-11-28

Atom diffusion assisted by surfaces or interfaces (e.g. Coble creep) has been known to be the origin of large creep rates and superplastic softening in nanosized crystals at low temperature. By contrast, source-limited crystal slip in defect-free nanostructures engenders important strengths, but also premature plastic instability and low ductility. Here, using in-situ transmission electron microscopy, we report a slip-activated surface creep mechanism that suppresses the tendency towards plastic instability without compromising the strength, resulting in ultra-large room-temperature plasticity in face-centered-cubic silver nanocrystals. This phenomenon is shown experimentally and theoretically to prevail over a material-dependent range of diameters where surface dislocationmore » nucleation becomes a stimulus to diffusional creep. This work provides new fundamental insight into coupled diffusive-displacive deformation mechanisms maximizing ductility and strength simultaneously in nanoscale materials.« less

Enhanced oxygen vacancy diffusion in Ta2O5 resistive memory devices due to infinitely adaptive crystal structure

NASA Astrophysics Data System (ADS)

Jiang, Hao; Stewart, Derek A.

2016-04-01

Metal oxide resistive memory devices based on Ta2O5 have demonstrated high switching speed, long endurance, and low set voltage. However, the physical origin of this improved performance is still unclear. Ta2O5 is an important archetype of a class of materials that possess an adaptive crystal structure that can respond easily to the presence of defects. Using first principles nudged elastic band calculations, we show that this adaptive crystal structure leads to low energy barriers for in-plane diffusion of oxygen vacancies in λ phase Ta2O5. Identified diffusion paths are associated with collective motion of neighboring atoms. The overall vacancy diffusion is anisotropic with higher diffusion barriers found for oxygen vacancy movement between Ta-O planes. Coupled with the fact that oxygen vacancy formation energy in Ta2O5 is relatively small, our calculated low diffusion barriers can help explain the low set voltage in Ta2O5 based resistive memory devices. Our work shows that other oxides with adaptive crystal structures could serve as potential candidates for resistive random access memory devices. We also discuss some general characteristics for ideal resistive RAM oxides that could be used in future computational material searches.

Hamiltonian bifurcation perspective on two interacting vortex pairs: From symmetric to asymmetric leapfrogging, period doubling, and chaos

NASA Astrophysics Data System (ADS)

Whitchurch, Brandon; Kevrekidis, Panayotis G.; Koukouloyannis, Vassilis

2018-01-01

In this work we study the dynamical behavior of two interacting vortex pairs, each one of them consisting of two point vortices with opposite circulation in the two-dimensional plane. The vortices are considered as effective particles and their interaction can be described in classical mechanics terms. We first construct a Poincaré section, for a typical value of the energy, in order to acquire a picture of the structure of the phase space of the system. We divide the phase space in different regions which correspond to qualitatively distinct motions and we demonstrate its different temporal evolution in the "real" vortex space. Our main emphasis is on the leapfrogging periodic orbit, around which we identify a region that we term the "leapfrogging envelope" which involves mostly regular motions, such as higher order periodic and quasiperiodic solutions. We also identify the chaotic region of the phase plane surrounding the leapfrogging envelope as well as the so-called walkabout and braiding motions. Varying the energy as our control parameter, we construct a bifurcation tree of the main leapfrogging solution and its instabilities, as well as the instabilities of its daughter branches. We identify the symmetry-breaking instability of the leapfrogging solution (in line with earlier works), and also obtain the corresponding asymmetric branches of periodic solutions. We then characterize their own instabilities (including period doubling ones) and bifurcations in an effort to provide a more systematic perspective towards the types of motions available to this dynamical system.

Hyper-resistive forced magnetic reconnection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vekstein, G., E-mail: g.vekstein@manchester.ac.uk

We study Taylor's model of forced magnetic reconnection mediated by plasma hyper-resistivity. This includes both linear and nonlinear regimes of the process. It is shown how the onset of plasmoid instability occurs in the strongly nonlinear regime of forced reconnection.

The Time-Dependent Structure of the Electron Reconnection Layer

NASA Technical Reports Server (NTRS)

Hesse, Michael; Zenitani, Seiji; Kuznetsova, Masha; Klimas, Alex

2009-01-01

Collisionless magnetic reconnection is often associated with time-dependent behavior. Specifically, current layers in the diffusion region can become unstable to tearing-type instabilities on one hand, or to instabilities with current-aligned wave vectors on the other. In the former case, the growth of tearing instabilities typically leads to the production of magnetic islands, which potentially provide feedback on the reconnection process itself, as well as on the rate of reconnection. The second class of instabilities tend to modulate the current layer along the direction of the current flow, for instance generating kink-type perturbations, or smaller-scale turbulence with the potential to broaden the current layer. All of these processes contribute to rendering magnetic reconnection time-dependent. In this presentation, we will provide a summary of these effects, and a discussion of how much they contribute to the overall magnetic reconnection rate.

Effect of Surface Tension Anisotropy and Welding Parameters on Initial Instability Dynamics During Solidification: A Phase-Field Study

NASA Astrophysics Data System (ADS)

Yu, Fengyi; Wei, Yanhong

2018-05-01

The effects of surface tension anisotropy and welding parameters on initial instability dynamics during gas tungsten arc welding of an Al-alloy are investigated by a quantitative phase-field model. The results show that the surface tension anisotropy and welding parameters affect the initial instability dynamics in different ways during welding. The surface tension anisotropy does not influence the solute diffusion process but does affect the stability of the solid/liquid interface during solidification. The welding parameters affect the initial instability dynamics by varying the growth rate and thermal gradient. The incubation time decreases, and the initial wavelength remains stable as the welding speed increases. When welding power increases, the incubation time increases and the initial wavelength slightly increases. Experiments were performed for the same set of welding parameters used in modeling, and the results of the experiments and simulations were in good agreement.

A large-area diffuse air discharge plasma excited by nanosecond pulse under a double hexagon needle-array electrode.

PubMed

Liu, Zhi-Jie; Wang, Wen-Chun; Yang, De-Zheng; Wang, Sen; Zhang, Shuai; Tang, Kai; Jiang, Peng-Chao

2014-01-01

A large-area diffuse air discharge plasma excited by bipolar nanosecond pulse is generated under a double hexagon needle-array electrode at atmospheric pressure. The images of the diffuse discharge, electric characteristics, and the optical emission spectra emitted from the diffuse air discharge plasma are obtained. Based on the waveforms of pulse voltage and current, the power consumption, and the power density of the diffuse air discharge plasma are investigated under different pulse peak voltages. The electron density and the electron temperature of the diffuse plasma are estimated to be approximately 1.42×10(11) cm(-3) and 4.4 eV, respectively. The optical emission spectra are arranged to determine the rotational and vibrational temperatures by comparing experimental with simulated spectra. Meanwhile, the rotational and vibrational temperatures of the diffuse discharge plasma are also discussed under different pulse peak voltages and pulse repetition rates, respectively. In addition, the diffuse air discharge plasma can form an area of about 70×50 mm(2) on the surface of dielectric layer and can be scaled up to the required size. Crown Copyright © 2013. Published by Elsevier B.V. All rights reserved.

Instability of warped discs

NASA Astrophysics Data System (ADS)

Doǧan, S.; Nixon, C. J.; King, A. R.; Pringle, J. E.

2018-05-01

Accretion discs are generally warped. If a warp in a disc is too large, the disc can `break' apart into two or more distinct planes, with only tenuous connections between them. Further, if an initially planar disc is subject to a strong differential precession, then it can be torn apart into discrete annuli that precess effectively independently. In previous investigations, torque-balance formulae have been used to predict where and when the disc breaks into distinct parts. In this work, focusing on discs with Keplerian rotation and where the shearing motions driving the radial communication of the warp are damped locally by turbulence (the `diffusive' regime), we investigate the stability of warped discs to determine the precise criterion for an isolated warped disc to break. We find and solve the dispersion relation, which, in general, yields three roots. We provide a comprehensive analysis of this viscous-warp instability and the emergent growth rates and their dependence on disc parameters. The physics of the instability can be understood as a combination of (1) a term that would generally encapsulate the classical Lightman-Eardley instability in planar discs (given by ∂(νΣ)/∂Σ < 0) but is here modified by the warp to include ∂(ν1|ψ|)/∂|ψ| < 0, and (2) a similar condition acting on the diffusion of the warp amplitude given in simplified form by ∂(ν2|ψ|)/∂|ψ| < 0. We discuss our findings in the context of discs with an imposed precession, and comment on the implications for different astrophysical systems.

Detailed Multidimensional Simulations of the Structure and Dynamics of Flames

NASA Technical Reports Server (NTRS)

Patnaik, G.; Kailasanath, K.

1999-01-01

Numerical simulations in which the various physical and chemical processes can be independently controlled can significantly advance our understanding of the structure, stability, dynamics and extinction of flames. Therefore, our approach has been to use detailed time-dependent, multidimensional, multispecies numerical models to perform carefully designed computational experiments of flames on Earth and in microgravity environments. Some of these computational experiments are complementary to physical experiments performed under the Microgravity Program while others provide a fundamental understanding that cannot be obtained from physical experiments alone. In this report, we provide a brief summary of our recent research highlighting the contributions since the previous microgravity combustion workshop. There are a number of mechanisms that can cause flame instabilities and result in the formation of dynamic multidimensional structures. In the past, we have used numerical simulations to show that it is the thermo-diffusive instability rather than an instability due to preferential diffusion that is the dominant mechanism for the formation of cellular flames in lean hydrogen-air mixtures. Other studies have explored the role of gravity on flame dynamics and extinguishment, multi-step kinetics and radiative losses on flame instabilities in rich hydrogen-air flames, and heat losses on burner-stabilized flames in microgravity. The recent emphasis of our work has been on exploring flame-vortex interactions and further investigating the structure and dynamics of lean hydrogen-air flames in microgravity. These topics are briefly discussed after a brief discussion of our computational approach for solving these problems.

Improving tribological properties of Ti-5Zr-3Sn-5Mo-15Nb alloy by double glow plasma surface alloying

NASA Astrophysics Data System (ADS)

Guo, Lili; Qin, Lin; Kong, Fanyou; Yi, Hong; Tang, Bin

2016-12-01

Molybdenum, an alloying element, was deposited and diffused on Ti-5Zr-3Sn-5Mo-15Nb (TLM) substrate by double glow plasma surface alloying technology at 900, 950 and 1000 °C. The microstructure, composition distribution and micro-hardness of the Mo modified layers were analyzed. Contact angles on deionized water and wear behaviors of the samples against corundum balls in simulated human body fluids were investigated. Results show that the surface microhardness is significantly enhanced after alloying and increases with treated temperature rising, and the contact angles are lowered to some extent. More importantly, compared to as-received TLM alloy, the Mo modified samples, especially the one treated at 1000 °C, exhibit the significant improvement of tribological properties in reciprocating wear tests, with lower specific wear rate and friction coefficient. To conclude, Mo alloying treatment is an effective approach to obtain excellent comprehensive properties including optimal wear resistance and improved wettability, which ensure the lasting and safety application for titanium alloys as the biomedical implants.

Harmonic cavities and the transverse mode-coupling instability driven by a resistive wall

DOE Office of Scientific and Technical Information (OSTI.GOV)

Venturini, M.

The effect of rf harmonic cavities on the transverse mode-coupling instability (TMCI) is still not very well understood. We offer a fresh perspective on the problem by proposing a new numerical method for mode analysis and investigating a regime of potential interest to the new generation of light sources where resistive wall is the dominant source of transverse impedance. When the harmonic cavities are tuned for maximum flattening of the bunch profile we demonstrate that at vanishing chromaticities the transverse single-bunch motion is unstable at any current, with growth rate that in the relevant range scales as the 6th powermore » of the current. With these assumptions and radiation damping included, we find that for machine parameters typical of 4th-generation light sources the presence of harmonic cavities could reduce the instability current threshold by more than a factor two.« less

Harmonic cavities and the transverse mode-coupling instability driven by a resistive wall

DOE PAGES

Venturini, M.

2018-02-01

The effect of rf harmonic cavities on the transverse mode-coupling instability (TMCI) is still not very well understood. We offer a fresh perspective on the problem by proposing a new numerical method for mode analysis and investigating a regime of potential interest to the new generation of light sources where resistive wall is the dominant source of transverse impedance. When the harmonic cavities are tuned for maximum flattening of the bunch profile we demonstrate that at vanishing chromaticities the transverse single-bunch motion is unstable at any current, with growth rate that in the relevant range scales as the 6th powermore » of the current. With these assumptions and radiation damping included, we find that for machine parameters typical of 4th-generation light sources the presence of harmonic cavities could reduce the instability current threshold by more than a factor two.« less

Harmonic cavities and the transverse mode-coupling instability driven by a resistive wall

NASA Astrophysics Data System (ADS)

Venturini, M.

2018-02-01

The effect of rf harmonic cavities on the transverse mode-coupling instability (TMCI) is still not very well understood. We offer a fresh perspective on the problem by proposing a new numerical method for mode analysis and investigating a regime of potential interest to the new generation of light sources where resistive wall is the dominant source of transverse impedance. When the harmonic cavities are tuned for maximum flattening of the bunch profile we demonstrate that at vanishing chromaticities the transverse single-bunch motion is unstable at any current, with growth rate that in the relevant range scales as the 6th power of the current. With these assumptions and radiation damping included, we find that for machine parameters typical of 4th-generation light sources the presence of harmonic cavities could reduce the instability current threshold by more than a factor two.

Pectins filled with LDH-antimicrobial molecules: preparation, characterization and physical properties.

PubMed

Gorrasi, Giuliana; Bugatti, Valeria; Vittoria, Vittoria

2012-06-05

Nanohybrids of layered double hydroxide (LDH) with intercalated active molecules: benzoate, 2,4-dichlorobenzoate, para-hydroxybenzoate and ortho-hydroxybenzoate, were incorporated into pectins from apples through high energy ball milling in the presence of water. Cast films were obtained and analysed. X-ray diffraction analysis showed a complete destructuration of all nanohybrids in the pectin matrix. Thermogravimetric analysis showed a better thermal resistance of pectin in the presence of fillers, especially para-hydroxybenzoate and ortho-hydroxybenzoate. Mechanical properties showed an improvement of elastic modulus in particular for LDH-para-hydroxybenzoate nanohybrid, due probably to a better interaction between pectin matrix and nanohybrid layers. Barrier properties (sorption and diffusion) to water vapour showed improvement in the dependence on the intercalated active molecule, the best improvement was achieved for composites containing para-hydroxybenzoate molecules, suggesting that the interaction between the filler phase and the polymer plays an important role in sorption and diffusion phenomena. Incorporation of these active molecules gave antimicrobial properties to the composite films giving opportunities in the field of active packaging. Copyright © 2012 Elsevier Ltd. All rights reserved.

Double-hit or dual expression of MYC and BCL2 in primary cutaneous large B-cell lymphomas.

PubMed

Menguy, Sarah; Frison, Eric; Prochazkova-Carlotti, Martina; Dalle, Stephane; Dereure, Olivier; Boulinguez, Serge; Dalac, Sophie; Machet, Laurent; Ram-Wolff, Caroline; Verneuil, Laurence; Gros, Audrey; Vergier, Béatrice; Beylot-Barry, Marie; Merlio, Jean-Philippe; Pham-Ledard, Anne

2018-03-26

In nodal diffuse large B-cell lymphoma, the search for double-hit with MYC and BCL2 and/or BCL6 rearrangements or for dual expression of BCL2 and MYC defines subgroups of patients with altered prognosis that has not been evaluated in primary cutaneous large B-cell lymphoma. Our objectives were to assess the double-hit and dual expressor status in a cohort of 44 patients with primary cutaneous large B-cell lymphoma according to the histological subtype and to evaluate their prognosis relevance. The 44 cases defined by the presence of more than 80% of large B-cells in the dermis corresponded to 21 primary cutaneous follicle centre lymphoma with large cell morphology and 23 primary cutaneous diffuse large B-cell lymphoma, leg type. Thirty-one cases (70%) expressed BCL2 and 29 (66%) expressed MYC. Dual expressor profile was observed in 25 cases (57%) of either subtypes (n = 6 or n = 19, respectively). Only one primary cutaneous follicle centre lymphoma, large-cell case had a double-hit status (2%). Specific survival was significantly worse in primary cutaneous diffuse large B-cell lymphoma, leg type than in primary cutaneous follicle centre lymphoma, large cell (p = 0.021) and for the dual expressor primary cutaneous large B-cell lymphoma group (p = 0.030). Both overall survival and specific survival were worse for patients belonging to the dual expressor primary cutaneous diffuse large B-cell lymphoma, leg type subgroup (p = 0.001 and p = 0.046, respectively). Expression of either MYC and/or BCL2 negatively impacted overall survival (p = 0.017 and p = 0.018 respectively). As the differential diagnosis between primary cutaneous follicle centre lymphoma, large cell and primary cutaneous diffuse large B-cell lymphoma, leg type has a major impact on prognosis, dual-expression of BCL2 and MYC may represent a new diagnostic criterion for primary cutaneous diffuse large B-cell lymphoma, leg type subtype and further identifies patients with impaired survival. Finally, the double-hit assessment does not appear clinically relevant in primary cutaneous large B-cell lymphoma.

Transient electroosmotic flow induced by DC or AC electric fields in a curved microtube.

PubMed

Luo, W-J

2004-10-15

This study investigates transient electroosmotic flow in a rectangular curved microtube in which the fluid is driven by the application of an external DC or AC electric field. The resultant flow-field evolutions within the microtube are simulated using the backwards-Euler time-stepping numerical method to clarify the relationship between the changes in the axial-flow velocity and the intensity of the applied electric field. When the electric field is initially applied or varies, the fluid within the double layer responds virtually immediately, and the axial velocity within the double layer tends to follow the varying intensity of the applied electric field. The greatest net charge density exists at the corners of the microtube as a result of the overlapping electrical double layers of the two walls. It results in local maximum or minimum axial velocities in the corners during increasing or decreasing applied electric field intensity in either the positive or negative direction. As the fluid within the double layer starts to move, the bulk fluid is gradually dragged into motion through the diffusion of momentum from the double layer. A finite time is required for the full momentum of the double layer to diffuse to the bulk fluid; hence, a certain phase shift between the applied electric field and the flow response is inevitable. The patterns of the axial velocity contours during the transient evolution are investigated in this study. It is found that these patterns are determined by the efficiency of momentum diffusion from the double layer to the central region of the microtube.

Wavelet-based multiscale window transform and energy and vorticity analysis

NASA Astrophysics Data System (ADS)

Liang, Xiang San

A new methodology, Multiscale Energy and Vorticity Analysis (MS-EVA), is developed to investigate sub-mesoscale, meso-scale, and large-scale dynamical interactions in geophysical fluid flows which are intermittent in space and time. The development begins with the construction of a wavelet-based functional analysis tool, the multiscale window transform (MWT), which is local, orthonormal, self-similar, and windowed on scale. The MWT is first built over the real line then modified onto a finite domain. Properties are explored, the most important one being the property of marginalization which brings together a quadratic quantity in physical space with its phase space representation. Based on MWT the MS-EVA is developed. Energy and enstrophy equations for the large-, meso-, and sub-meso-scale windows are derived and their terms interpreted. The processes thus represented are classified into four categories: transport; transfer, conversion, and dissipation/diffusion. The separation of transport from transfer is made possible with the introduction of the concept of perfect transfer. By the property of marginalization, the classical energetic analysis proves to be a particular case of the MS-EVA. The MS-EVA developed is validated with classical instability problems. The validation is carried out through two steps. First, it is established that the barotropic and baroclinic instabilities are indicated by the spatial averages of certain transfer term interaction analyses. Then calculations of these indicators are made with an Eady model and a Kuo model. The results agree precisely with what is expected from their analytical solutions, and the energetics reproduced reveal a consistent and important aspect of the unknown dynamic structures of instability processes. As an application, the MS-EVA is used to investigate the Iceland-Faeroe frontal (IFF) variability. A MS-EVA-ready dataset is first generated, through a forecasting study with the Harvard Ocean Prediction System using the data gathered during the 1993 NRV Alliance cruise. The application starts with a determination of the scale window bounds, which characterize a double-peak structure in either the time wavelet spectrum or the space wavelet spectrum. The resulting energetics, when locally averaged, reveal that there is a clear baroclinic instability happening around the cold tongue intrusion observed in the forecast. Moreover, an interaction analysis shows that the energy released by the instability indeed goes to the meso-scale window and fuel the growth of the intrusion. The sensitivity study shows that, in this case, the key to a successful application is a correct decomposition of the large-scale window from the meso-scale window.

Disease severity in a mouse model of ataxia telangiectasia is modulated by the DNA damage checkpoint gene Hus1

PubMed Central

Balmus, Gabriel; Zhu, Min; Mukherjee, Sucheta; Lyndaker, Amy M.; Hume, Kelly R.; Lee, Jaesung; Riccio, Mark L.; Reeves, Anthony P.; Sutter, Nathan B.; Noden, Drew M.; Peters, Rachel M.; Weiss, Robert S.

2012-01-01

The human genomic instability syndrome ataxia telangiectasia (A-T), caused by mutations in the gene encoding the DNA damage checkpoint kinase ATM, is characterized by multisystem defects including neurodegeneration, immunodeficiency and increased cancer predisposition. ATM is central to a pathway that responds to double-strand DNA breaks, whereas the related kinase ATR leads a parallel signaling cascade that is activated by replication stress. To dissect the physiological relationship between the ATM and ATR pathways, we generated mice defective for both. Because complete ATR pathway inactivation causes embryonic lethality, we weakened the ATR mechanism to different degrees by impairing HUS1, a member of the 911 complex that is required for efficient ATR signaling. Notably, simultaneous ATM and HUS1 defects caused synthetic lethality. Atm/Hus1 double-mutant embryos showed widespread apoptosis and died mid-gestationally. Despite the underlying DNA damage checkpoint defects, increased DNA damage signaling was observed, as evidenced by H2AX phosphorylation and p53 accumulation. A less severe Hus1 defect together with Atm loss resulted in partial embryonic lethality, with the surviving double-mutant mice showing synergistic increases in genomic instability and specific developmental defects, including dwarfism, craniofacial abnormalities and brachymesophalangy, phenotypes that are observed in several human genomic instability disorders. In addition to identifying tissue-specific consequences of checkpoint dysfunction, these data highlight a robust, cooperative configuration for the mammalian DNA damage response network and further suggest HUS1 and related genes in the ATR pathway as candidate modifiers of disease severity in A-T patients. PMID:22575700

Viscous-resistive layer in Rayleigh-Taylor instability

NASA Astrophysics Data System (ADS)

Silveira, F. E. M.; Orlandi, H. I.

2017-03-01

In this work, new scaling laws of the time growth rate γ of the Rayleigh-Taylor instability with the plasma resistivity η, kinematic viscosity ν, and electron number density ne are derived. A viscosity scale is defined in terms of the time decay of the perturbative fluid flow perpendicular to the equilibrium magnetic field, at the quasi-static approximation. Such a scale provides the identification of a viscous layer that can be combined with the resistive layer to produce a viscous-resistive layer. The latter, in turn, is found to satisfy an algebraic biquadratic equation. When viscous effects are negligible, it is shown that the viscous-resistive layer is given by the resistive layer. Somewhat surprisingly, when viscous effects cannot be neglected, it is shown that the viscous-resistive layer is given by the geometric mean of the resistive and viscous layers. A dispersion relation for the time growth rate is derived in terms of the viscous-resistive layer. When viscous effects cannot be neglected, two new scaling laws are found. At the quasi-static approximation, it is shown that γ ˜ (ην)1/4. However, on account of a finite electron mass, it is shown that γ˜(ν/ne ) 1 /3 . Further developments of our formulation are addressed in connection with a finite compressibility in the perturbative flow.

Scaling Relations for Viscous and Gravitational Flow Instabilities in Multiphase Multicomponent Compressible Flow

NASA Astrophysics Data System (ADS)

Moortgat, J.; Amooie, M. A.; Soltanian, M. R.

2016-12-01

Problems in hydrogeology and hydrocarbon reservoirs generally involve the transport of solutes in a single solvent phase (e.g., contaminants or dissolved injection gas), or the flow of multiple phases that may or may not exchange mass (e.g., brine, NAPL, oil, gas). Often, flow is viscously and gravitationally unstable due to mobility and density contrasts within a phase or between phases. Such instabilities have been studied in detail for single-phase incompressible fluids and for two-phase immiscible flow, but to a lesser extent for multiphase multicomponent compressible flow. The latter is the subject of this presentation. Robust phase stability analyses and phase split calculations, based on equations of state, determine the mass exchange between phases and the resulting phase behavior, i.e., phase densities, viscosities, and volumes. Higher-order finite element methods and fine grids are used to capture the small-scale onset of flow instabilities. A full matrix of composition dependent coefficients is considered for each Fickian diffusive phase flux. Formation heterogeneity can have a profound impact and is represented by realistic geostatistical models. Qualitatively, fingering in multiphase compositional flow is different from single-phase problems because 1) phase mobilities depend on rock wettability through relative permeabilities, and 2) the initial density and viscosity ratios between phases may change due to species transfer. To quantify mixing rates in different flow regimes and for varying degrees of miscibility and medium heterogeneities, we define the spatial variance, scalar dissipation rate, dilution index, skewness, and kurtosis of the molar density of introduced species. Molar densities, unlike compositions, include compressibility effects. The temporal evolution of these measures shows that, while transport at the small-scale (cm) is described by the classical advection-diffusion-dispersion relations, scaling at the macro-scale (> 10 m) shows transitions between advective, diffusive, ballistic, sub-diffusive, and non-Fickian diffusive behavior. These scaling relations can be used to improve the predictive powers of field-scale reservoir simulations that cannot resolve the complexities of unstable flow and transport at cm-m scales.

Buoyancy-driven instabilities around miscible A+B→C reaction fronts: a general classification.

PubMed

Trevelyan, P M J; Almarcha, C; De Wit, A

2015-02-01

Upon contact between miscible solutions of reactants A and B along a horizontal interface in the gravity field, various buoyancy-driven instabilities can develop when an A+B→C reaction takes place and the density varies with the concentrations of the various chemicals. To classify the possible convective instability scenarios, we analyze the spatial dependence of the large time asymptotic density profiles as a function of the key parameters of the problem, which are the ratios of diffusion coefficients and of solutal expansion coefficients of species A, B, and C. We find that 62 different density profiles can develop in the reactive problem, whereas only 6 of them can be obtained in the nonreactive one.

Suppression of transverse ablative Rayleigh-Taylor-like instability in the hole-boring radiation pressure acceleration by using elliptically polarized laser pulses.

PubMed

Wu, D; Zheng, C Y; Qiao, B; Zhou, C T; Yan, X Q; Yu, M Y; He, X T

2014-08-01

It is shown that the transverse Rayleigh-Taylor-like (RT) instability in the hole-boring radiation pressure acceleration can be suppressed by using an elliptically polarized (EP) laser. A moderate J×B heating of the EP laser will thermalize the local electrons, which leads to the transverse diffusion of ions, suppressing the short wavelength perturbations of RT instability. A proper condition of polarization ratio is obtained analytically for the given laser intensity and plasma density. The idea is confirmed by two-dimensional particle-in-cell simulations, showing that the ion beam driven by the EP laser is more concentrated and intense compared with that of the circularly polarized laser.

Induction Inserts at the Los Alamos PSR

NASA Astrophysics Data System (ADS)

Ng, K. Y.

2002-12-01

Ferrite-loaded induction tuners installed in the Los Alamos Proton Storage Ring have been successful in compensating space-charge effects. However, the resistive part of the ferrite introduces unacceptable microwave instability and severe bunch lengthening. An effective cure was found by heating the ferrite cores up to ˜ 130°C. An understanding of the instability and cure is presented.

Performance of active feedforward control systems in non-ideal, synthesized diffuse sound fields.

PubMed

Misol, Malte; Bloch, Christian; Monner, Hans Peter; Sinapius, Michael

2014-04-01

The acoustic performance of passive or active panel structures is usually tested in sound transmission loss facilities. A reverberant sending room, equipped with one or a number of independent sound sources, is used to generate a diffuse sound field excitation which acts as a disturbance source on the structure under investigation. The spatial correlation and coherence of such a synthesized non-ideal diffuse-sound-field excitation, however, might deviate significantly from the ideal case. This has consequences for the operation of an active feedforward control system which heavily relies on the acquisition of coherent disturbance source information. This work, therefore, evaluates the spatial correlation and coherence of ideal and non-ideal diffuse sound fields and considers the implications on the performance of a feedforward control system. The system under consideration is an aircraft-typical double panel system, equipped with an active sidewall panel (lining), which is realized in a transmission loss facility. Experimental results for different numbers of sound sources in the reverberation room are compared to simulation results of a comparable generic double panel system excited by an ideal diffuse sound field. It is shown that the number of statistically independent noise sources acting on the primary structure of the double panel system depends not only on the type of diffuse sound field but also on the sample lengths of the processed signals. The experimental results show that the number of reference sensors required for a defined control performance exhibits an inverse relationship to control filter length.

MHD simulation of transition process from the magneto-rotational instability to magnetic turbulence by using a high-order MHD simulation scheme

NASA Astrophysics Data System (ADS)

Hirai, K.; Katoh, Y.; Terada, N.; Kawai, S.

2016-12-01

In accretion disks, magneto-rotational instability (MRI; Balbus & Hawley, 1991) makes the disk gas in the magnetic turbulent state and drives efficient mass accretion into a central star. MRI drives turbulence through the evolution of the parasitic instability (PI; Goodman & Xu, 1994), which is related to both Kelvin-Helmholtz (K-H) instability and magnetic reconnection. The wave number vector of PI is strongly affected by both magnetic diffusivity and fluid viscosity (Pessah, 2010). This fact makes MHD simulation of MRI difficult, because we need to employ the numerical diffusivity for treating discontinuities in compressible MHD simulation schemes. Therefore, it is necessary to use an MHD scheme that has both high-order accuracy so as to resolve MRI driven turbulence and small numerical diffusivity enough to treat discontinuities. We have originally developed an MHD code by employing the scheme proposed by Kawai (2013). This scheme focuses on resolving turbulence accurately by using a high-order compact difference scheme (Lele, 1992), and meanwhile, the scheme treats discontinuities by using the localized artificial diffusivity method (Kawai, 2013). Our code also employs the pipeline algorithm (Matsuura & Kato, 2007) for MPI parallelization without diminishing the accuracy of the compact difference scheme. We carry out a 3-dimensional ideal MHD simulation with a net vertical magnetic field in the local shearing box disk model. We use 256x256x128 grids. Simulation results show that the spatially averaged turbulent stress induced by MRI linearly grows until around 2.8 orbital periods, and decreases after the saturation. We confirm the strong enhancement of the K-H mode PI at a timing just before the saturation, identified by the enhancement of its anisotropic wavenumber spectra in the 2-dimensional wavenumber space. The wave number of the maximum growth of PI reproduced in the simulation result is larger than the linear analysis. This discrepancy is explained by the simulation result that a shear flow created by MRI locally becomes thinner and faster due to interactions between antiparallel vortices induced by K-H mode PI, and this structure induces small scale waves which break the shear flow itself. We report the results of the simulation, and discuss how the saturation amplitude of MRI is determined.

A mechanical comparison of linear and double-looped hung supplemental heavy chain resistance to the back squat: a case study.

PubMed

Neelly, Kurt R; Terry, Joseph G; Morris, Martin J

2010-01-01

A relatively new and scarcely researched technique to increase strength is the use of supplemental heavy chain resistance (SHCR) in conjunction with plate weights to provide variable resistance to free weight exercises. The purpose of this case study was to determine the actual resistance being provided by a double-looped versus a linear hung SHCR to the back squat exercise. The linear technique simply hangs the chain directly from the bar, whereas the double-looped technique uses a smaller chain to adjust the height of the looped chain. In both techniques, as the squat descends, chain weight is unloaded onto the floor, and as the squat ascends, chain weight is progressively loaded back as resistance. One experienced and trained male weight lifter (age = 33 yr; height = 1.83 m; weight = 111.4 kg) served as the subject. Plate weight was set at 84.1 kg, approximately 50% of the subject's 1 repetition maximum. The SHCR was affixed to load cells, sampling at a frequency of 500 Hz, which were affixed to the Olympic bar. Data were collected as the subject completed the back squat under the following conditions: double-looped 1 chain (9.6 kg), double-looped 2 chains (19.2 kg), linear 1 chain, and linear 2 chains. The double-looped SHCR resulted in a 78-89% unloading of the chain weight at the bottom of the squat, whereas the linear hanging SHCR resulted in only a 36-42% unloading. The double-looped technique provided nearly 2 times the variable resistance at the top of the squat compared with the linear hanging technique, showing that attention must be given to the technique used to hang SHCR.

Antifouling composites with self-adaptive controlled release based on an active compound intercalated into layered double hydroxides

NASA Astrophysics Data System (ADS)

Yang, Miaosen; Gu, Lianghua; Yang, Bin; Wang, Li; Sun, Zhiyong; Zheng, Jiyong; Zhang, Jinwei; Hou, Jian; Lin, Cunguo

2017-12-01

This paper reports a novel method to prepare the antifouling composites with properties of self-adaptive controlled release (defined as control the release rate autonomously and adaptively according to the change of environmental conditions) by intercalation of sodium paeonolsilate (PAS) into MgAl and ZnAl layered double hydroxide (LDH) with the molar ratio (M2+/M3+) of 2:1 and 3:1, respectively. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of PAS into the galleries of LDH. The controlled release behavior triggered by temperature for the PAS-LDH composites has been investigated, and the results show that the release rate of all PAS-LDH composites increases as the increase of temperature. However, the MgAl-PAS-LDH composites (Mg2Al-PAS-LDH and Mg3Al-PAS-LDH) exhibit the increased release rate of 0.21 ppm/°C from 15 to 30 °C in 3.5% NaCl solution, more than three times of the ZnAl-PAS-LDH composites (0.06 ppm/°C), owing to the confined microenvironment influenced by metal types in LDH layers. In addition, a possible diffusion-controlled process with surface diffusion, bulk diffusion and heterogeneous flat surface diffusion has been revealed via fitting four kinetic equations. Moreover, to verify the practical application of the PAS-LDH composites, a model coating denoted as Mg2Al-PAS-LDH coating was fabricated. The release result displays that the release rate increases or decreases as temperature altered at 15 and 25 °C alternately, indicating its self-adaptive controlled release behavior with temperature. Moreover, the superior resistance to the settlement of Ulva spores at 15 and 25 °C was observed for the Mg2Al-PAS-LDH coating, as a result of the controllable release of antifoulant. Therefore, this work provides a facile and effective method for the fabrication of antifouling composites with self-adaptive controlled release behavior in response to temperature, which can be used to prolong the lifetime of antifouling coatings.

Mechanisms of heat and mass transfer across a double-diffusive interface

NASA Astrophysics Data System (ADS)

Ko, B. H.; Smith, K. A.

1984-06-01

Flux measurements in an aqueous two-layer double-diffusive system using heat and NaCl confirmed the existence of a regime in which the ratio of the buoyancy fluxes (BFR) of salt and heat is independent of the stability ratio (R = beta(delta C)/alpha(delta T)). Linear analysis showed that the quiescent system can become unstable to small perturbations even when the lower layer is denser than the upper. If R is large, the most unstable mode presents as an oscillatory, antisymmetric pattern.

Effects of instability versus traditional resistance training on strength, power and velocity in untrained men.

PubMed

Maté-Muñoz, José Luis; Monroy, Antonio J Antón; Jodra Jiménez, Pablo; Garnacho-Castaño, Manuel V

2014-09-01

The purpose of this study was compare the effects of a traditional and an instability resistance circuit training program on upper and lower limb strength, power, movement velocity and jumping ability. Thirty-six healthy untrained men were assigned to two experimental groups and a control group. Subjects in the experimental groups performed a resistance circuit training program consisting of traditional exercises (TRT, n = 10) or exercises executed in conditions of instability (using BOSU® and TRX®) (IRT, n = 12). Both programs involved three days per week of training for a total of seven weeks. The following variables were determined before and after training: maximal strength (1RM), average (AV) and peak velocity (PV), average (AP) and peak power (PP), all during bench press (BP) and back squat (BS) exercises, along with squat jump (SJ) height and counter movement jump (CMJ) height. All variables were found to significantly improve (p <0.05) in response to both training programs. Major improvements were observed in SJ height (IRT = 22.1%, TRT = 20.1%), CMJ height (IRT = 17.7%, TRT = 15.2%), 1RM in BS (IRT = 13.03%, TRT = 12.6%), 1RM in BP (IRT = 4.7%, TRT = 4.4%), AP in BS (IRT = 10.5%, TRT = 9.3%), AP in BP (IRT = 2.4%, TRT = 8.1%), PP in BS (IRT=19.42%, TRT = 22.3%), PP in BP (IRT = 7.6%, TRT = 11.5%), AV in BS (IRT = 10.5%, TRT = 9.4%), and PV in BS (IRT = 8.6%, TRT = 4.5%). Despite such improvements no significant differences were detected in the posttraining variables recorded for the two experimental groups. These data indicate that a circuit training program using two instability training devices is as effective in untrained men as a program executed under stable conditions for improving strength (1RM), power, movement velocity and jumping ability. Key PointsSimilar adaptations in terms of gains in strength, power, movement velocity and jumping ability were produced in response to both training programs.Both the stability and instability approaches seem suitable for healthy, physically-active individuals with or with limited experience in resistance training.RPE emerged as a useful tool to monitor exercise intensity during instability strength training.

Effects of Instability Versus Traditional Resistance Training on Strength, Power and Velocity in Untrained Men

PubMed Central

Maté-Muñoz, José Luis; Monroy, Antonio J. Antón; Jodra Jiménez, Pablo; Garnacho-Castaño, Manuel V.

2014-01-01

The purpose of this study was compare the effects of a traditional and an instability resistance circuit training program on upper and lower limb strength, power, movement velocity and jumping ability. Thirty-six healthy untrained men were assigned to two experimental groups and a control group. Subjects in the experimental groups performed a resistance circuit training program consisting of traditional exercises (TRT, n = 10) or exercises executed in conditions of instability (using BOSU® and TRX®) (IRT, n = 12). Both programs involved three days per week of training for a total of seven weeks. The following variables were determined before and after training: maximal strength (1RM), average (AV) and peak velocity (PV), average (AP) and peak power (PP), all during bench press (BP) and back squat (BS) exercises, along with squat jump (SJ) height and counter movement jump (CMJ) height. All variables were found to significantly improve (p <0.05) in response to both training programs. Major improvements were observed in SJ height (IRT = 22.1%, TRT = 20.1%), CMJ height (IRT = 17.7%, TRT = 15.2%), 1RM in BS (IRT = 13.03%, TRT = 12.6%), 1RM in BP (IRT = 4.7%, TRT = 4.4%), AP in BS (IRT = 10.5%, TRT = 9.3%), AP in BP (IRT = 2.4%, TRT = 8.1%), PP in BS (IRT=19.42%, TRT = 22.3%), PP in BP (IRT = 7.6%, TRT = 11.5%), AV in BS (IRT = 10.5%, TRT = 9.4%), and PV in BS (IRT = 8.6%, TRT = 4.5%). Despite such improvements no significant differences were detected in the posttraining variables recorded for the two experimental groups. These data indicate that a circuit training program using two instability training devices is as effective in untrained men as a program executed under stable conditions for improving strength (1RM), power, movement velocity and jumping ability. Key Points Similar adaptations in terms of gains in strength, power, movement velocity and jumping ability were produced in response to both training programs. Both the stability and instability approaches seem suitable for healthy, physically-active individuals with or with limited experience in resistance training. RPE emerged as a useful tool to monitor exercise intensity during instability strength training. PMID:25177170

Quantification of Sheet Resistance in Boron-Diffused Silicon Using Micro-Photoluminescence Spectroscopy at Room Temperature

DOE PAGES

Nguyen, Hieu T.; Johnston, Steve; Paduthol, Appu; ...

2017-09-01

A micro-photoluminescence-based technique is presented, to quantify and map sheet resistances of boron-diffused layers in silicon solar cell precursors with micron-scale spatial resolution at room temperature. The technique utilizes bandgap narrowing effects in the heavily-doped layers, yielding a broader photoluminescence spectrum at the long-wavelength side compared to the spectrum emitted from lightly doped silicon. By choosing an appropriate spectral range as a metric to assess the doping density, the impacts of photon reabsorption on the analysis can be avoided; thus, an accurate characterization of the sheet resistance can be made. This metric is demonstrated to be better representative of themore » sheet resistance than the surface doping density or the total dopant concentration of the diffused layer. The technique is applied to quantify sheet resistances of 12-um-wide diffused fingers in interdigitated back-contact solar cell precursors and large diffused areas. The results are confirmed by both 4-point probe and time-of-flight secondary-ion mass spectrometry measurements. Lastly, the practical limitations associated with extending the proposed technique into an imaging mode are presented and explained.« less

Quantification of Sheet Resistance in Boron-Diffused Silicon Using Micro-Photoluminescence Spectroscopy at Room Temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Hieu T.; Johnston, Steve; Paduthol, Appu

A micro-photoluminescence-based technique is presented, to quantify and map sheet resistances of boron-diffused layers in silicon solar cell precursors with micron-scale spatial resolution at room temperature. The technique utilizes bandgap narrowing effects in the heavily-doped layers, yielding a broader photoluminescence spectrum at the long-wavelength side compared to the spectrum emitted from lightly doped silicon. By choosing an appropriate spectral range as a metric to assess the doping density, the impacts of photon reabsorption on the analysis can be avoided; thus, an accurate characterization of the sheet resistance can be made. This metric is demonstrated to be better representative of themore » sheet resistance than the surface doping density or the total dopant concentration of the diffused layer. The technique is applied to quantify sheet resistances of 12-um-wide diffused fingers in interdigitated back-contact solar cell precursors and large diffused areas. The results are confirmed by both 4-point probe and time-of-flight secondary-ion mass spectrometry measurements. Lastly, the practical limitations associated with extending the proposed technique into an imaging mode are presented and explained.« less

A coupled "AB" system: Rogue waves and modulation instabilities.

PubMed

Wu, C F; Grimshaw, R H J; Chow, K W; Chan, H N

2015-10-01

Rogue waves are unexpectedly large and localized displacements from an equilibrium position or an otherwise calm background. For the nonlinear Schrödinger (NLS) model widely used in fluid mechanics and optics, these waves can occur only when dispersion and nonlinearity are of the same sign, a regime of modulation instability. For coupled NLS equations, rogue waves will arise even if dispersion and nonlinearity are of opposite signs in each component as new regimes of modulation instability will appear in the coupled system. The same phenomenon will be demonstrated here for a coupled "AB" system, a wave-current interaction model describing baroclinic instability processes in geophysical flows. Indeed, the onset of modulation instability correlates precisely with the existence criterion for rogue waves for this system. Transitions from "elevation" rogue waves to "depression" rogue waves are elucidated analytically. The dispersion relation as a polynomial of the fourth order may possess double pairs of complex roots, leading to multiple configurations of rogue waves for a given set of input parameters. For special parameter regimes, the dispersion relation reduces to a cubic polynomial, allowing the existence criterion for rogue waves to be computed explicitly. Numerical tests correlating modulation instability and evolution of rogue waves were conducted.

The Role of Phase Changes in TiO2/Pt/TiO2 Filaments

NASA Astrophysics Data System (ADS)

Bíró, Ferenc; Hajnal, Zoltán; Dücső, Csaba; Bársony, István

2018-04-01

This work analyses the role of phase changes in TiO2/Pt/TiO2 layer stacks for micro-heater application regarding their stability and reliable operation. The polycrystalline Pt layer wrapped in a TiO2 adhesion layer underwent a continuous recrystallisation in a self-heating operation causing a drift in the resistance ( R) versus temperature ( T) performance. Simultaneously, the TiO2 adhesion layer also deteriorates at high temperature by phase changes from amorphous to anatase and rutile crystallite formation, which not only influences the Pt diffusion in different migration phenomena, but also reduces the cross section of the Pt heater wire. Thorough scanning electron microscopy, energy dispersive spectroscopy, cross-sectional transmission electron microscopy (XTEM) and electron beam diffraction analysis of the structures operated at increasing temperature revealed the elemental structural processes leading to the instabilities and the accelerated degradation, resulting in rapid breakdown of the heater wire. Owing to stability and reliability criteria, the conditions for safe operation of these layer structures could be determined.

Tumors overexpressing RNF168 show altered DNA repair and responses to genotoxic treatments, genomic instability and resistance to proteotoxic stress.

PubMed

Chroma, K; Mistrik, M; Moudry, P; Gursky, J; Liptay, M; Strauss, R; Skrott, Z; Vrtel, R; Bartkova, J; Kramara, J; Bartek, J

2017-04-27

Chromatin DNA damage response (DDR) is orchestrated by the E3 ubiquitin ligase ring finger protein 168 (RNF168), resulting in ubiquitin-dependent recruitment of DDR factors and tumor suppressors breast cancer 1 (BRCA1) and p53 binding protein 1 (53BP1). This ubiquitin signaling regulates pathway choice for repair of DNA double-strand breaks (DSB), toxic lesions whose frequency increases during tumorigenesis. Recruitment of 53BP1 curbs DNA end resection, thereby limiting homologous recombination (HR) and directing DSB repair toward error-prone non-homologous end joining (NHEJ). Under cancer-associated ubiquitin starvation conditions reflecting endogenous or treatment-evoked proteotoxic stress, the ubiquitin-dependent accrual of 53BP1 and BRCA1 at the DNA damage sites is attenuated or lost. Challenging this current paradigm, here we identified diverse human cancer cell lines that display 53BP1 recruitment to DSB sites even under proteasome inhibitor-induced proteotoxic stress, that is, under substantial depletion of free ubiquitin. We show that central to this unexpected phenotype is overabundance of RNF168 that enables more efficient exploitation of the residual-free ubiquitin. Cells with elevated RNF168 are more resistant to combined treatment by ionizing radiation and proteasome inhibition, suggesting that such aberrant RNF168-mediated signaling might reflect adaptation to chronic proteotoxic and genotoxic stresses experienced by tumor cells. Moreover, the overabundant RNF168 and the ensuing unorthodox recruitment patterns of 53BP1, RIF1 and REV7 (monitored on laser micro-irradiation-induced DNA damage) shift the DSB repair balance from HR toward NHEJ, a scenario accompanied by enhanced chromosomal instability/micronuclei formation and sensitivity under replication stress-inducing treatments with camptothecin or poly(ADP-ribose) polymerase (PARP) inhibitor. Overall, our data suggest that the deregulated RNF168/53BP1 pathway could promote tumorigenesis by selecting for a more robust, better stress-adapted cancer cell phenotype, through altered DNA repair, fueling genomic instability and tumor heterogeneity. Apart from providing insights into cancer (patho)biology, the elevated RNF168, documented here also by immunohistochemistry on human clinical tumor specimens, may impact responses to standard-of-care and some emerging targeted cancer therapies.

The Kelvin-Helmholtz instability in National Ignition Facility hohlraums as a source of gold-gas mixing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vandenboomgaerde, M.; Bonnefille, M.; Gauthier, P.

Highly resolved radiation-hydrodynamics FCI2 simulations have been performed to model laser experiments on the National Ignition Facility. In these experiments, cylindrical gas-filled hohlraums with gold walls are driven by a 20 ns laser pulse. For the first time, simulations show the appearance of Kelvin-Helmholtz (KH) vortices at the interface between the expanding wall material and the gas fill. In this paper, we determine the mechanisms which generate this instability: the increase of the gas pressure around the expanding gold plasma leads to the aggregation of an over-dense gold layer simultaneously with shear flows. At the surface of this layer, all themore » conditions are met for a KH instability to grow. Later on, as the interface decelerates, the Rayleigh-Taylor instability also comes into play. A potential scenario for the generation of a mixing zone at the gold-gas interface due to the KH instability is presented. Our estimates of the Reynolds number and the plasma diffusion width at the interface support the possibility of such a mix. The key role of the first nanosecond of the laser pulse in the instability occurrence is also underlined.« less

Lessons Learned from Numerical Simulations of Interfacial Instabilities

NASA Astrophysics Data System (ADS)

Cook, Andrew

2015-11-01

Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM) and Kelvin-Helmholtz (KH) instabilities serve as efficient mixing mechanisms in a wide variety of flows, from supernovae to jet engines. Over the past decade, we have used the Miranda code to temporally integrate the multi-component Navier-Stokes equations at spatial resolutions up to 29 billion grid points. The code employs 10th-order compact schemes for spatial derivatives, combined with 4th-order Runge-Kutta time advancement. Some of our major findings are as follows: The rate of growth of a mixing layer is equivalent to the net mass flux through the equi-molar plane. RT growth rates can be significantly reduced by adding shear. RT instability can produce shock waves. The growth rate of RM instability can be predicted from known interfacial perturbations. RM vortex projectiles can far outrun the mixing region. Thermal fluctuations in molecular dynamics simulations can seed instabilities along the braids in KH instability. And finally, enthalpy diffusion is essential in preserving the second law of thermodynamics. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Future prospects of baryon istability search in p-decay and n n(bar) oscillation experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ball, S.J.; Kamyshkov, Y.A.

1996-11-01

These proceedings contain thirty-one papers which review both the theoretical and the experimental status and near future of baryon instability research. Baryon instability is investigated from the vantage point of supersymmetric and unified theories. The interplay between baryogenesis and antimatter is examined. Double beta decay experiments are discussed. The huge Icarus experiment is described with its proton decay capabilities. Neutron-antineutron oscillations investigations are presented, especially efforts with ultra-cold neutrons. Individual papers are indexed separately on the Energy Data Base.

Structure-to-property relationships in fuel cell catalyst supports: Correlation of surface chemistry and morphology with oxidation resistance of carbon blacks

NASA Astrophysics Data System (ADS)

Artyushkova, Kateryna; Pylypenko, Svitlana; Dowlapalli, Madhu; Atanassov, Plamen

2012-09-01

Linking durability of carbon blacks, expressed as their oxidation resistance, used in PEMFCs as catalyst supports, with their chemistry and morphology is an important task towards designing carbon blacks with desired properties. Structure-to-property relationship between surface chemistry determined by X-ray photoelectron spectroscopy (XPS), morphological structure determined by digital image processing of scanning electron microscopy (SEM) images, physical properties, and electrochemical corrosion behavior determined in an air-breathing gas-diffusion electrode is studied for several un-altered and several modified carbon blacks. We are showing that surface chemistry, graphitic content and certain physical characteristics such as Brunauer-Emmett-Teller (BET) surface area and pore volume, determined by nitrogen adsorptions are not sufficient to explain high corrosion instability of types of carbon blacks. Inclusion of morphological characteristics, such as roughness, texture and shape parameters provide for more inclusive description and therefore more complete structure-to-property correlations of corrosion behavior of carbon blacks. This paper presents the first direct statistically-derived structure-to-property relationship, developed by multivariate analysis (MVA) that links chemical and physical structural properties of the carbon blacks to their critical properties as supports for PEMFC catalysts. We have found that balance between electrocatalytic activity and high resistance towards oxidation and corrosion is achieved by balance between amount of graphitic content and surface oxide coverage, smaller overall roughness and, finally, larger amount of big elongated and loose, and, hypothetically, more hydrophobic pores.

THE FATE OF PLANETESIMALS IN TURBULENT DISKS WITH DEAD ZONES. I. THE TURBULENT STIRRING RECIPE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okuzumi, Satoshi; Ormel, Chris W., E-mail: okuzumi@geo.titech.ac.jp

2013-07-01

Turbulence in protoplanetary disks affects planet formation in many ways. While small dust particles are mainly affected by the aerodynamical coupling with turbulent gas velocity fields, planetesimals and larger bodies are more affected by gravitational interaction with gas density fluctuations. For the latter process, a number of numerical simulations have been performed in recent years, but a fully parameter-independent understanding has not been yet established. In this study, we present simple scaling relations for the planetesimal stirring rate in turbulence driven by magnetorotational instability (MRI), taking into account the stabilization of MRI due to ohmic resistivity. We begin with order-of-magnitudemore » estimates of the turbulence-induced gravitational force acting on solid bodies and associated diffusion coefficients for their orbital elements. We then test the predicted scaling relations using the results of recent ohmic-resistive MHD simulations by Gressel et al. We find that these relations successfully explain the simulation results if we properly fix order-of-unity uncertainties within the estimates. We also update the saturation predictor for the density fluctuation amplitude in MRI-driven turbulence originally proposed by Okuzumi and Hirose. Combination of the scaling relations and saturation predictor allows us to know how the turbulent stirring rate of planetesimals depends on disk parameters such as the gas column density, distance from the central star, vertical resistivity distribution, and net vertical magnetic flux. In Paper II, we apply our recipe to planetesimal accretion to discuss its viability in turbulent disks.« less

An axisymmetric non-hydrostatic model for double-diffusive water systems

NASA Astrophysics Data System (ADS)

Hilgersom, Koen; Zijlema, Marcel; van de Giesen, Nick

2018-02-01

The three-dimensional (3-D) modelling of water systems involving double-diffusive processes is challenging due to the large computation times required to solve the flow and transport of constituents. In 3-D systems that approach axisymmetry around a central location, computation times can be reduced by applying a 2-D axisymmetric model set-up. This article applies the Reynolds-averaged Navier-Stokes equations described in cylindrical coordinates and integrates them to guarantee mass and momentum conservation. The discretized equations are presented in a way that a Cartesian finite-volume model can be easily extended to the developed framework, which is demonstrated by the implementation into a non-hydrostatic free-surface flow model. This model employs temperature- and salinity-dependent densities, molecular diffusivities, and kinematic viscosity. One quantitative case study, based on an analytical solution derived for the radial expansion of a dense water layer, and two qualitative case studies demonstrate a good behaviour of the model for seepage inflows with contrasting salinities and temperatures. Four case studies with respect to double-diffusive processes in a stratified water body demonstrate that turbulent flows are not yet correctly modelled near the interfaces and that an advanced turbulence model is required.

Comparative radiation resistance, temperature dependence and performance of diffused junction indium phosphide solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.; Ghandhi, S. K.; Borrego, J. M.

1987-01-01

Indium phosphide solar cells whose p-n junctions were processed by the open tube capped diffusion and by the closed tube uncapped diffusion of sulfur into Czochralski-grown p-type substrates are compared. Differences found in radiation resistance were attributed to the effects of increased base dopant concentration. Both sets of cells showed superior radiation resistance to that of gallium arsenide cells, in agreement with previous results. No correlation was, however, found between the open-circuit voltage and the temperature dependence of the maximum power.

Development and Application of Predictive Tools for MHD Stability Limits in Tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brennan, Dylan; Miller, G. P.

This is a project to develop and apply analytic and computational tools to answer physics questions relevant to the onset of non-ideal magnetohydrodynamic (MHD) instabilities in toroidal magnetic confinement plasmas. The focused goal of the research is to develop predictive tools for these instabilities, including an inner layer solution algorithm, a resistive wall with control coils, and energetic particle effects. The production phase compares studies of instabilities in such systems using analytic techniques, PEST- III and NIMROD. Two important physics puzzles are targeted as guiding thrusts for the analyses. The first is to form an accurate description of the physicsmore » determining whether the resistive wall mode or a tearing mode will appear first as β is increased at low rotation and low error fields in DIII-D. The second is to understand the physical mechanism behind recent NIMROD results indicating strong damping and stabilization from energetic particle effects on linear resistive modes. The work seeks to develop a highly relevant predictive tool for ITER, advance the theoretical description of this physics in general, and analyze these instabilities in experiments such as ASDEX Upgrade, DIII-D, JET, JT-60U and NTSX. The awardee on this grant is the University of Tulsa. The research efforts are supervised principally by Dr. Brennan. Support is included for two graduate students, and a strong collaboration with Dr. John M. Finn of LANL. The work includes several ongoing collaborations with General Atomics, PPPL, and the NIMROD team, among others.« less

Role of Rayleigh numbers on characteristics of double diffusive salt fingers

NASA Astrophysics Data System (ADS)

Rehman, F.; Singh, O. P.

2018-05-01

Double diffusion convection, driven by two constituents of the fluid with different molecular diffusivity, is widely applied in oceanography and large number of other fields like astrophysics, geology, chemistry and metallurgy. In case of ocean, heat (T) and salinity (S) are the two components with varying diffusivity, where heat diffuses hundred times faster than salt. Component (T) stabilizes the system whereas components (S) destabilizes the system with overall density remains stable and forms the rising and sinking fingers known as salt fingers. Recent observations suggest that salt finger characteristics such as growth rates, wavenumber, and fluxes are strongly depending on the Rayleigh numbers as major driving force. In this paper, we corroborate this observation with the help of experiments, numerical simulations and linear theory. An eigenvalue expression for growth rate is derived from the linearized governing equations with explicit dependence on Rayleigh numbers, density stability ratio, Prandtl number and diffusivity ratio. Expressions for fastest growing fingers are also derived as a function various non-dimensional parameter. The predicted results corroborate well with the data reported from the field measurements, experiments and numerical simulations.

Analysis of Jeans instability of optically thick quantum plasma under the effect of modified Ohms law

NASA Astrophysics Data System (ADS)

Pensia, R. K.; Sutar, D. L.; Sharma, S.

2018-05-01

The Jeans instability of self-gravitating optically thick quantum plasma is reanalyzed in the framework of viscosity, black body radiation and modify ohms law. The usual magnetohydrodynamic (MHD) equation is used for the present configuration with black body radiation, viscosity, electrical resistivity and quantum corrections. A general dispersion relation is obtained with the help of linearized perturbation equations. It is found that the quantum correction has stabilizing effect on the system. The instability of system is discussed for various cases as our interest.

Numeric and fluid dynamic representation of tornadic double vortex thunderstorms

NASA Technical Reports Server (NTRS)

Connell, J. R.; Marquart, E. J.; Frost, W.; Boaz, W.

1980-01-01

Current understanding of a double vortex thunderstorm involves a pair of contra-rotating vortices that exists in the dynamic updraft. The pair is believed to be a result of a blocking effect which occurs when a cylindrical thermal updraft of a thunderstorm protrudes into the upper level air and there is a large amount of vertical wind shear between the low level and upper level air layers. A numerical tornado prediction scheme based on the double vortex thunderstorm was developed. The Energy-Shear Index (ESI) is part of the scheme and is calculated from radiosonde measurements. The ESI incorporates parameters representative of thermal instability and blocking effect, and indicates appropriate environments for which the development of double vortex thunderstorms is likely.

Multi-region approach to free-boundary three-dimensional tokamak equilibria and resistive wall instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferraro, N. M.; Jardin, S. C.; Lao, L. L.

Free-boundary 3D tokamak equilibria and resistive wall instabilities are calculated using a new resistive wall model in the two-fluid M3D-C1 code. In this model, the resistive wall and surround- ing vacuum region are included within the computational domain. Our implementation contrasts with the method typically used in fluid codes in which the resistive wall is treated as a boundary condition on the computational domain boundary and has the advantage of maintaining purely local coupling of mesh elements. We use this new capability to simulate perturbed, free-boundary non- axisymmetric equilibria; the linear evolution of resistive wall modes; and the linear andmore » nonlinear evolution of axisymmetric vertical displacement events (VDEs). Calculated growth rates for a resistive wall mode with arbitrary wall thickness are shown to agree well with the analytic theory. Equilibrium and VDE calculations are performed in diverted tokamak geometry, at physically real- istic values of dissipation, and with resistive walls of finite width. Simulations of a VDE disruption extend into the current-quench phase, in which the plasma becomes limited by the first wall, and strong currents are observed to flow in the wall, in the SOL, and from the plasma to the wall.« less

Multi-region approach to free-boundary three-dimensional tokamak equilibria and resistive wall instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferraro, N. M., E-mail: nferraro@pppl.gov; Lao, L. L.; Jardin, S. C.

Free-boundary 3D tokamak equilibria and resistive wall instabilities are calculated using a new resistive wall model in the two-fluid M3D-C1 code. In this model, the resistive wall and surrounding vacuum region are included within the computational domain. This implementation contrasts with the method typically used in fluid codes in which the resistive wall is treated as a boundary condition on the computational domain boundary and has the advantage of maintaining purely local coupling of mesh elements. This new capability is used to simulate perturbed, free-boundary non-axisymmetric equilibria; the linear evolution of resistive wall modes; and the linear and nonlinear evolutionmore » of axisymmetric vertical displacement events (VDEs). Calculated growth rates for a resistive wall mode with arbitrary wall thickness are shown to agree well with the analytic theory. Equilibrium and VDE calculations are performed in diverted tokamak geometry, at physically realistic values of dissipation, and with resistive walls of finite width. Simulations of a VDE disruption extend into the current-quench phase, in which the plasma becomes limited by the first wall, and strong currents are observed to flow in the wall, in the SOL, and from the plasma to the wall.« less

Multi-region approach to free-boundary three-dimensional tokamak equilibria and resistive wall instabilities

DOE PAGES

Ferraro, N. M.; Jardin, S. C.; Lao, L. L.; ...

2016-05-20

Free-boundary 3D tokamak equilibria and resistive wall instabilities are calculated using a new resistive wall model in the two-fluid M3D-C1 code. In this model, the resistive wall and surround- ing vacuum region are included within the computational domain. Our implementation contrasts with the method typically used in fluid codes in which the resistive wall is treated as a boundary condition on the computational domain boundary and has the advantage of maintaining purely local coupling of mesh elements. We use this new capability to simulate perturbed, free-boundary non- axisymmetric equilibria; the linear evolution of resistive wall modes; and the linear andmore » nonlinear evolution of axisymmetric vertical displacement events (VDEs). Calculated growth rates for a resistive wall mode with arbitrary wall thickness are shown to agree well with the analytic theory. Equilibrium and VDE calculations are performed in diverted tokamak geometry, at physically real- istic values of dissipation, and with resistive walls of finite width. Simulations of a VDE disruption extend into the current-quench phase, in which the plasma becomes limited by the first wall, and strong currents are observed to flow in the wall, in the SOL, and from the plasma to the wall.« less

SUSCEPTIBILITY OF RESPIRATORY ISOLATES OF STREPTOCOCCUS PNEUMONIAE ISOLATED FROM CHILDREN HOSPITALIZED IN THE CLINICAL CENTER NIS.

PubMed

Dinić, Marina M; Mladenović Antić, Snezana; Kocić, Branislava; Stanković Dordević, Dobrila; Vrbić, Miodrag; Bogdanović, Milena

2016-01-01

Streptococcus pneumoniae is one of the most common causes of respiratory infections. The aim was to study the susceptibility to antimicrobial agents of respiratory isolates ofStreptococcus pneumoniae obtained from hospitalized children. A total of 190 respiratory pneumococcal isolates obtained from children aged from 0 to 14 years were isolated and identified by using standard microbiological methods. Susceptibility to oxacillin, erythromycin, clindamycin, tetracycline, cotrimoxazole, ofloxacin and rifampicin was tested by disc diffusion method. Minimal inhibitory concentrations for amoxicillin and ceftriaxone were determined by means of E test. The macrolide-resistant phenotype was detected by double disc diffusion test. All tested isolates were susceptible to amoxicillin and ceftriaxone. The minimal amoxicillin concentration inhibiting the growth of 50% of isolates and of 90% of isolates was 0.50 microg/ml and 1.0 microg/ml, respectively and the minimal ceftriaxone concentration inhibiting the growth of 50% of isolates and of 90% of isolates was 0.25 microg/ml and 0.50 microg/ml, respectively. Susceptibility to erythromycin and clindamycin was observed in 21.6% and 29.47% of isolates, respectively. The resistence to macrolides-M phenotype was detected in 10.07% of isolates and constitutive macrolide-lincosamide-streptogramin phenotype (constitutive MLS phenotype) was found in 89.93% of isolates. All tested isolates were susceptible to ofloxacin and rifampicin. Amoxicillin could be the therapy of choice in pediatric practice. The macrolides should not be recommended for the empirical therapy of pneumococcal respiratory tract infection in our local area.

New Layer Thickness Parameterization of Diffusive Convection

NASA Astrophysics Data System (ADS)

Zhou, Sheng-Qi; Lu, Yuan-Zheng; Guo, Shuang-Xi; Song, Xue-Long; Qu, Ling; Cen, Xian-Rong; Fer, Ilker

2017-11-01

Double-diffusion convection is one of the most important non-mechanically driven mixing processes. Its importance has been particular recognized in oceanography, material science, geology, and planetary physics. Double-diffusion occurs in a fluid in which there are gradients of two (or more) properties with different molecular diffusivities and of opposing effects on the vertical density distribution. It has two primary modes: salt finger and diffusive convection. Recently, the importance of diffusive convection has aroused more interest due to its impact to the diapycnal mixing in the interior ocean and the ice and the ice-melting in the Arctic and Antarctic Oceans. In our recent work, we constructed a length scale of energy-containing eddy and proposed a new layer thickness parameterization of diffusive convection by using the laboratory experiment and in situ observations in the lakes and oceans. The new parameterization can well describe the laboratory convecting layer thicknesses (0.01 0.1 m) and those observed in oceans and lakes (0.1 1000 m). This work was supported by China NSF Grants (41476167,41406035 and 41176027), NSF of Guangdong Province, China (2016A030311042) and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA11030302).

Plasma Diffusion in Self-Consistent Fluctuations

NASA Technical Reports Server (NTRS)

Smets, R.; Belmont, G.; Aunai, N.

2012-01-01

The problem of particle diffusion in position space, as a consequence ofeleclromagnetic fluctuations is addressed. Numerical results obtained with a self-consistent hybrid code are presented, and a method to calculate diffusion coefficient in the direction perpendicular to the mean magnetic field is proposed. The diffusion is estimated for two different types of fluctuations. The first type (resuiting from an agyrotropic in itiai setting)is stationary, wide band white noise, and associated to Gaussian probability distribution function for the magnetic fluctuations. The second type (result ing from a Kelvin-Helmholtz instability) is non-stationary, with a power-law spectrum, and a non-Gaussian probabi lity distribution function. The results of the study allow revisiting the question of loading particles of solar wind origin in the Earth magnetosphere.

Dissipation of ionospheric irregularities by wave-particle and collisional interactions

NASA Technical Reports Server (NTRS)

Bernhardt, P. A.; Pongratz, M. B.; Gray, S. P.; Thomsen, M. F.

1982-01-01

The nonlinear dissipation of plasma irregularities aligned parallel to an ambient magnetic field is studied numerically using a model which employs both wave-particle and collisional diffusion. A wave-particle diffusion coefficient derived from a local theory of the universal drift instability is used. This coefficient is effective in regions of nonzero plasma gradients and produces triangular-shaped irregularities with spectra which vary as f to the -4th, where f is the spatial frequency. Collisional diffusion acts rapidly on the vertices of the irregularities to reduce their amplitude. The simultaneous action of the two dissipative processes is more efficient than collisions acting alone. In this model, wave-particle diffusion mimics the forward cascade process of wave-wave coupling.

Surface Nb-ALLOYING on 0.4C-13Cr Stainless Steel: Microstructure and Tribological Behavior

NASA Astrophysics Data System (ADS)

Yu, Shengwang; You, Kai; Liu, Xiaozhen; Zhang, Yihui; Wang, Zhenxia; Liu, Xiaoping

2016-02-01

0.4C-13Cr stainless steel was alloyed with niobium using double glow plasma surface alloying and tribological properties of Nb-alloyed steel such as hardness, friction and wear were measured. Effects of the alloying temperature on microstructure and the tribological behavior of the alloyed steel were investigated compared with untreated steel. Formation mechanisms of Nb-alloyed layers and increased wear resistance were also studied. The result shows that after surface Nb-alloying treatment, the 0.4C-13Cr steel exhibits a diffusion adhesion at the alloyed layer/substrate interface and improved tribological property. The friction coefficient of Nb-alloyed steel is decreased by about 0.3-0.45 and the wear rate after Nb-alloying is only 2-5% of untreated steel.

Migration and head penetration of Vitamin-E diffused cemented polyethylene cup compared to standard cemented cup in total hip arthroplasty: study protocol for a randomised, double-blind, controlled trial (E1 HIP).

PubMed

Sköldenberg, Olof; Rysinska, Agata; Chammout, Ghazi; Salemyr, Mats; Muren, Olle; Bodén, Henrik; Eisler, Thomas

2016-07-07

In vitro, Vitamin-E-diffused, highly cross-linked polyethylene (PE) has been shown to have superior wear resistance and improved mechanical properties when compared to those of standard highly cross-linked PE liners used in total hip arthroplasty (THA). The aim of the study is to evaluate the safety of a new cemented acetabular cup with Vitamin-E-doped PE regarding migration, head penetration and clinical results. In this single-centre, double-blinded, randomised controlled trial, we will include 50 patients with primary hip osteoarthritis scheduled for THA and randomise them in a 1:1 ratio to a cemented cup with either argon gas-sterilised PE (control group) or Vitamin-E-diffused PE (vitamin-e group). All patients and the assessor of the primary outcome will be blinded and the same uncemented stem will be used for all participants. The primary end point will be proximal migration of the cup at 2 years after surgery measured with radiostereometry. Secondary end points include proximal migration at other follow-ups, total migration, femoral head penetration, clinical outcome scores and hip-related complications. Patients will be followed up at 3 months and at 1, 2, 5 and 10 years postoperatively. Results will be analysed using 95% CIs for the effect size. A regression model will also be used to adjust for stratification factors. The ethical committee at Karolinska Institutet has approved the study. The first results from the study will be disseminated to the medical community via presentations and publications in relevant medical journals when the last patient included has been followed up for 2 years. NCT02254980. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

[Effect of inoculum size on sensitivity and specificity of the double-disk synergy test for the detection of wide-spectrum beta-lactamases].

PubMed

Bedenić, B; Boras, A

2001-01-01

The plasmid-mediated extended-spectrum beta-lactamases (ESBL) confer resistance to oxymino-cephalosporins, such as cefotaxime, ceftazidime, and ceftriaxone and to monobactams such as aztreonam. It is well known fact that ESBL producing bacteria exhibit a pronounced inoculum effect against broad spectrum cephalosporins like ceftazidime, cefotaxime, ceftriaxone and cefoperazone. The aim of this investigation was to determine the effect of inoculum size on the sensitivity and specificity of double-disk synergy test (DDST) which is the test most frequently used for detection of ESBLs, in comparison with other two methods (determination of ceftazidime MIC with and without clavulanate and inhibitor potentiated disk-diffusion test) which are seldom used in clinical laboratories. The experiments were performed on a set of K. pneumoniae strains with previously characterized beta-lactamases which comprise: 10 SHV-5 beta-lactamase producing K. pneumoniae, 20 SHV-2 + 1 SHV 2a beta-lactamase producing K. pneumoniae, 7 SHV-12 beta-lactamase producing K. pneumoniae, 39 putative SHV ESBL producing K. pneumoniae and 26 K. pneumoniae isolates highly susceptible to ceftazidime according to Kirby-Bauer disk-diffusion method and thus considered to be ESBL negative. According to the results of this investigation, increase in inoculum size affected more significantly the sensitivity of DDST than of other two methods. The sensitivity of the DDST was lower when a higher inoculum size of 10(8) CFU/ml was applied, in distinction from other two methods (MIC determination and inhibitor potentiated disk-diffusion test) which retained high sensitivity regardless of the density of bacterial suspension. On the other hand, DDST displayed higher specificity compared to other two methods regardless of the inoculum size. This investigation found that DDST is a reliable method but it is important to standardize the inoculum size.

Migration and head penetration of Vitamin-E diffused cemented polyethylene cup compared to standard cemented cup in total hip arthroplasty: study protocol for a randomised, double-blind, controlled trial (E1 HIP)

PubMed Central

Sköldenberg, Olof; Rysinska, Agata; Chammout, Ghazi; Salemyr, Mats; Muren, Olle; Bodén, Henrik; Eisler, Thomas

2016-01-01

Introduction In vitro, Vitamin-E-diffused, highly cross-linked polyethylene (PE) has been shown to have superior wear resistance and improved mechanical properties when compared to those of standard highly cross-linked PE liners used in total hip arthroplasty (THA). The aim of the study is to evaluate the safety of a new cemented acetabular cup with Vitamin-E-doped PE regarding migration, head penetration and clinical results. Methods and analysis In this single-centre, double-blinded, randomised controlled trial, we will include 50 patients with primary hip osteoarthritis scheduled for THA and randomise them in a 1:1 ratio to a cemented cup with either argon gas-sterilised PE (control group) or Vitamin-E-diffused PE (vitamin-e group). All patients and the assessor of the primary outcome will be blinded and the same uncemented stem will be used for all participants. The primary end point will be proximal migration of the cup at 2 years after surgery measured with radiostereometry. Secondary end points include proximal migration at other follow-ups, total migration, femoral head penetration, clinical outcome scores and hip-related complications. Patients will be followed up at 3 months and at 1, 2, 5 and 10 years postoperatively. Results Results will be analysed using 95% CIs for the effect size. A regression model will also be used to adjust for stratification factors. Ethics and dissemination The ethical committee at Karolinska Institutet has approved the study. The first results from the study will be disseminated to the medical community via presentations and publications in relevant medical journals when the last patient included has been followed up for 2 years. Trial registration number NCT02254980. PMID:27388352

Analysis of Thermo-Diffusive Cellular Instabilities in Continuum Combustion Fronts

NASA Astrophysics Data System (ADS)

Azizi, Hossein; Gurevich, Sebastian; Provatas, Nikolas; Department of Physics, Centre Physics of Materials Team

We explore numerically the morphological patterns of thermo-diffusive instabilities in combustion fronts with a continuum solid fuel source, within a range of Lewis numbers, focusing on the cellular regime. Cellular and dendritic instabilities are found at low Lewis numbers. These are studied using a dynamic adaptive mesh refinement technique that allows very large computational domains, thus allowing us to reduce finite size effects that can affect or even preclude the emergence of these patterns. The distinct types of dynamics found in the vicinity of the critical Lewis number. These types of dynamics are classified as ``quasi-linear'' and characterized by low amplitude cells that may be strongly affected by the mode selection mechanism and growth prescribed by the linear theory. Below this range of Lewis number, highly non-linear effects become prominent and large amplitude, complex cellular and seaweed dendritic morphologies emerge. The cellular patterns simulated in this work are similar to those observed in experiments of flame propagation over a bed of nano-aluminum powder burning with a counter-flowing oxidizer conducted by Malchi et al. It is noteworthy that the physical dimension of our computational domain is roughly close to their experimental setup. This work was supported by a Canadian Space Agency Class Grant ''Percolating Reactive Waves in Particulate Suspensions''. We thank Compute Canada for computing resources.

Diffusion Tensor Imaging of Normal-Appearing White Matter as Biomarker for Radiation-Induced Late Delayed Cognitive Decline

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chapman, Christopher H., E-mail: chchap@umich.edu; Nagesh, Vijaya; Sundgren, Pia C.

Purpose: To determine whether early assessment of cerebral white matter degradation can predict late delayed cognitive decline after radiotherapy (RT). Methods and Materials: Ten patients undergoing conformal fractionated brain RT participated in a prospective diffusion tensor magnetic resonance imaging study. Magnetic resonance imaging studies were acquired before RT, at 3 and 6 weeks during RT, and 10, 30, and 78 weeks after starting RT. The diffusivity variables in the parahippocampal cingulum bundle and temporal lobe white matter were computed. A quality-of-life survey and neurocognitive function tests were administered before and after RT at the magnetic resonance imaging follow-up visits. Results:more » In both structures, longitudinal diffusivity ({lambda}{sub Double-Vertical-Line }) decreased and perpendicular diffusivity ({lambda}{sub Up-Tack }) increased after RT, with early changes correlating to later changes (p < .05). The radiation dose correlated with an increase in cingulum {lambda}{sub Up-Tack} at 3 weeks, and patients with >50% of cingula volume receiving >12 Gy had a greater increase in {lambda}{sub Up-Tack} at 3 and 6 weeks (p < .05). The post-RT changes in verbal recall scores correlated linearly with the late changes in cingulum {lambda}{sub Double-Vertical-Line} (30 weeks, p < .02). Using receiver operating characteristic curves, early cingulum {lambda}{sub Double-Vertical-Line} changes predicted for post-RT changes in verbal recall scores (3 and 6 weeks, p < .05). The neurocognitive test scores correlated significantly with the quality-of-life survey results. Conclusions: The correlation between early diffusivity changes in the parahippocampal cingulum and the late decline in verbal recall suggests that diffusion tensor imaging might be useful as a biomarker for predicting late delayed cognitive decline.« less

Effects of radial diffuser hydraulic design on a double-suction centrifugal pump

NASA Astrophysics Data System (ADS)

Hou, H. C.; Zhang, Y. X.; Xu, C.; Zhang, J. Y.; Li, Z. L.

2016-05-01

In order to study effects of radial diffuser on hydraulic performance of crude oil pump, the steady CFD numerical method is applied and one large double-suction oil pump running in long-distance pipeline is considered. The research focuses on analysing the influence of its diffuser vane profile on hydraulic performance of oil pump. The four different types of cylindrical vane have been designed by in-house codes mainly including double arcs (DA), triple arcs (TA), equiangular spiral line (ES) and linear variable angle spiral line (LVS). During design process diffuser vane angles at inlet and outlet are tentatively given within a certain range and then the wrapping angle of the four types of diffuser vanes can be calculated automatically. Under the given inlet and outlet angles, the linear variable angle spiral line profile has the biggest wrapping angle and profile length which is good to delay channel diffusion but bring more friction hydraulic loss. Finally the vane camber line is thickened at the certain uniform thickness distribution and the 3D diffuser models are generated. The whole flow passage of oil pump with different types of diffusers under various flow rate conditions are numerically simulated based on RNG k-ɛ turbulent model and SIMPLEC algorithm. The numerical results show that different types of diffusers can bring about great difference on the hydraulic performance of oil pump, of which the ES profile diffuser with its proper setting angle shows the best hydraulic performance and its inner flow field is improved obviously. Compared with the head data from model sample, all designed diffusers can make a certain improvement on head characteristic. At the large flow rate conditions the hydraulic efficiency increases obviously and the best efficiency point shift to the large flow rate range. The ES profile diffuser embodies the better advantages on pump performance which can be explained theoretically that the diffuser actually acts as a diffusion device and is good to transform the dynamic energy to pressure energy. Then through the hydraulic loss analysis of each pump component for all diffusers, it shows that the impeller takes up the biggest part of the whole loss about 8.19% averagely, the radial diffuser about 3.70% and the volute about 1.65%. The hydraulic loss of impeller is dominant at the large flow rate while the radial diffuser is at the small flow rate. Among all diffusers, the ES profile diffuser generates the least loss and combined to the distribution of velocity vector and turbulent kinetic energy for two kinds of diffusers it also shows that ES profile is fit to apply in radial diffuser. This research can offer a significant reference for the radial diffuser hydraulic design of such centrifugal pumps.

Evaluation of the mass transfer process on thin layer drying of papaya seeds from the perspective of diffusive models

NASA Astrophysics Data System (ADS)

Dotto, Guilherme Luiz; Meili, Lucas; Tanabe, Eduardo Hiromitsu; Chielle, Daniel Padoin; Moreira, Marcos Flávio Pinto

2018-02-01

The mass transfer process that occurs in the thin layer drying of papaya seeds was studied under different conditions. The external mass transfer resistance and the dependence of effective diffusivity ( D EFF ) in relation to the moisture ratio ( \\overline{MR} ) and temperature ( T) were investigated from the perspective of diffusive models. It was verified that the effective diffusivity was affected by the moisture content and temperature. A new correlation was proposed for drying of papaya seeds in order to describe these influences. Regarding the use of diffusive models, the results showed that, at conditions of low drying rates ( T ≤ 70 °C), the external mass transfer resistance, as well as the dependence of the effective diffusivity with respect to the temperature and moisture content should be considered. At high drying rates ( T > 90 °C), the dependence of the effective diffusivity with respect to the temperature and moisture content can be neglected, but the external mass transfer resistance was still considerable in the range of air velocities used in this work.

NMR investigation of the short-chain ionic surfactant-water systems.

PubMed

Popova, M V; Tchernyshev, Y S; Michel, D

2004-02-03

The structure and dynamics of surfactant molecules [CH3(CH2)7COOK] in heavy water solutions were investigated by 1H and 2H NMR. A double-exponential attenuation of the spin-echo amplitude in a Carr-Purcell-Meiboom-Gill experiment was found. We expect correspondence to both bounded and monomeric states. At high concentrations in the NMR self-diffusion measurements also a double-exponential decay of the spin-echo signal versus the square of the dc magnetic gradient was observed. The slow component of the diffusion process is caused by micellar aggregates, while the fast component is the result of the self-diffusion of the monomers through the micelles. The self-diffusion studies indicate that the form of micelles changes with increasing total surfactant concentration. The critical temperature range for self-association is reflected in the 1H transverse relaxation.

Therapeutic Implications for Overcoming Radiation Resistance in Cancer Therapy

PubMed Central

Kim, Byeong Mo; Hong, Yunkyung; Lee, Seunghoon; Liu, Pengda; Lim, Ji Hong; Lee, Yong Heon; Lee, Tae Ho; Chang, Kyu Tae; Hong, Yonggeun

2015-01-01

Ionizing radiation (IR), such as X-rays and gamma (γ)-rays, mediates various forms of cancer cell death such as apoptosis, necrosis, autophagy, mitotic catastrophe, and senescence. Among them, apoptosis and mitotic catastrophe are the main mechanisms of IR action. DNA damage and genomic instability contribute to IR-induced cancer cell death. Although IR therapy may be curative in a number of cancer types, the resistance of cancer cells to radiation remains a major therapeutic problem. In this review, we describe the morphological and molecular aspects of various IR-induced types of cell death. We also discuss cytogenetic variations representative of IR-induced DNA damage and genomic instability. Most importantly, we focus on several pathways and their associated marker proteins responsible for cancer resistance and its therapeutic implications in terms of cancer cell death of various types and characteristics. Finally, we propose radiation-sensitization strategies, such as the modification of fractionation, inflammation, and hypoxia and the combined treatment, that can counteract the resistance of tumors to IR. PMID:26569225

Active stabilization of thin-wall structures under compressive loading

NASA Astrophysics Data System (ADS)

Welham, Jared; Calius, Emilio P.; Chase, J. Geoffrey

2003-08-01

The active suppression of elastic buckling instability has the potential to significantly increase the effective strength of thin-wall structures. Despite all the interest in smart structures, the active suppression of buckling has received comparatively little attention. This paper addresses the effects of embedded actuation on the compression buckling strength of laminated composite plates through analysis and simulation. Numerical models are formulated that include the influence of essential features such as sensor uncertainty and noise, actuator saturation and control architecture on the buckling process. Silicon-based strain sensors and diffuse laser distance sensors are both considered for use in the detection of incipient buckling behavior due to their increased sensitivity. Actuation is provided by paired distributions of piezo-electric material incorporated into both sides of the laminate. Optimal controllers are designed to command the structure to deform in ways that interfere with the development of buckling mode shapes. Commercial software packages are used to solve the resulting non-linear equations, and some of the tradeoffs are enumerated. Overall, the results show that active buckling control can considerably enhance resistance to instability under compressive loads. These buckling load predictions demonstrate the viability of optimal control and piezo-electric actuation for implementing active buckling control. Due to the importance of early detection, the relative effectiveness of active buckling control is shown to be strongly dependent on the performance of the sensing scheme, as well as on the characteristics of the structure.

A study of trends and techniques for space base electronics

NASA Technical Reports Server (NTRS)

Trotter, J. D.; Wade, T. E.; Gassaway, J. D.

1978-01-01

Furnaces and photolithography related equipment were applied to experiments on double layer metal. The double layer metal activity emphasized wet chemistry techniques. By incorporating the following techniques: (1) ultrasonic etching of the vias; (2) premetal clean using a modified buffered hydrogen fluoride; (3) phosphorus doped vapor; and (4) extended sintering, yields of 98 percent were obtained using the standard test pattern. The two dimensional modeling problems have stemmed from, alternately, instability and too much computation time to achieve convergence.

Evaluation of industrial platinum resistance thermometers

NASA Technical Reports Server (NTRS)

Daryabeigi, Kamran; Dillontownes, Lawrence A.; Alderfer, David W.

1987-01-01

The calibration and stability of four surface temperature measuring industrial platinum resistance thermometers for use in the temperature range -120 C to 160 C was investigated. It was found that the calibration formulation of the International Practical Temperature Scale of 1968 provided the most accurate calibration. It was also found that all the resistance thermometers suffered from varying degrees of instability and hysteresis.

Electrochemical performance of microporous and mesoporous activated carbons in neat and diluted 1-ethyl-3-methylimidazolium tetrafluoroborate

NASA Astrophysics Data System (ADS)

Kumagai, Seiji; Hatomi, Masaki; Tashima, Daisuke

2017-03-01

1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIm·BF4), neat and diluted with propylene carbonate to 1 mol L-1, have been employed as electrolytes of electrical double-layer capacitors (EDLCs). The effects of microporosity and mesoporosity in activated carbon (AC) electrodes on the capacitive and resistive performances upon the use of neat and diluted EMIm·BF4 have been explored. In addition to cyclic voltammetry and galvanostatic charge-discharge tests, electrochemical impedance spectroscopy has been performed employing Kang's equivalent circuit model consisting of three resistances, three constant phase elements, and one bounded Warburg impedance. The overall impedance of the EDLC cell was separated into components of intrinsic resistance, bulk electrolyte, diffusion layer, and Helmholtz layer. The specific capacitance and the equivalent series resistance (ESR) of mesoporous AC were found to be highly dependent on the rate of ionic transfer. Lower cell voltage was identified as being responsible for lower specific capacitance and larger ESR of mesoporous AC, which was similarly seen in the neat and diluted EMIm·BF4, and could be alleviated by increasing the cell voltage. The inferior rate performance and the cell-voltage-dependent performance of mesoporous AC, which were more distinctly observed in the neat EMIm·BF4, could be attributed to the lower mobility of EMIm+ and BF4- in mesopores.

The evolution of resistance genes in multi-protein plant resistance systems.

PubMed

Friedman, Aaron R; Baker, Barbara J

2007-12-01

The genomic perspective aids in integrating the analysis of single resistance (R-) genes into a higher order model of complex plant resistance systems. The majority of R-genes encode a class of proteins with nucleotide binding (NB) and leucine-rich repeat (LRR) domains. Several R-proteins act in multi-protein R-complexes that mediate interaction with pathogen effectors to induce resistance signaling. The complexity of these systems seems to have resulted from multiple rounds of plant-pathogen co-evolution. R-gene evolution is thought to be facilitated by the formation of R-gene clusters, which permit sequence exchanges via recombinatorial mispairing and generate high haplotypic diversity. This pattern of evolution may also generate diversity at other loci that contribute to the R-complex. The rate of recombination at R-clusters is not necessarily homogeneous or consistent over evolutionary time: recent evidence suggests that recombination at R-clusters is increased following pathogen infection, suggesting a mechanism that induces temporary genome instability in response to extreme stress. DNA methylation and chromatin modifications may allow this instability to be conditionally regulated and targeted to specific genome regions. Knowledge of natural R-gene evolution may contribute to strategies for artificial evolution of novel resistance specificities.

Antibiotic resistance patterns and occurrence of mecA gene in Staphylococcus intermedius strains of canine origin.

PubMed

Kizerwetter-Swida, M; Chrobak, D; Rzewuska, M; Binek, M

2009-01-01

We have evaluated 102 Staphylococcus intermedius isolates of canine origin for susceptibility to antimicrobial primary agents, i.e. penicillin, amoxicillin, amoxicillin with clavulanic acid, cefuroxime, trimethoprim/sulfonamides, neomycin, streptomycin, gentamicin, norfloxacin, tetracycline, vancomycin, erythromycin and secondary agents, i.e., chloramphenicol, ciprofloxacin, lincomycin, teicoplanin, rifampicin, imipenem, mupirocin. Antimicrobial sensitivity was examined using the disk diffusion method and performed according to NCCLS quidelines. Methicillin resistance was detected using the disk diffusion method with oxacillin, and the occurrence of mecA gene was detected by PCR. Resistance to streptomycin, penicillin, amoxicillin, neomycin, followed by tetracycline was predominant. From 14 mecA-positive strains, 12 were multidrug-resitant, and the remaining two showed atypical susceptibility. One strain resistant to oxacillin in the disc diffusion method was mecA-negative, suggesting a different mechanism of resistance. Our results indicate that the emergence of S. intermedius resistance to methicillin may be underestimated. In case of clinical multidrug-resitant S. intermedius isolates, resistance to methicillin should be considered.

Convective instabilities in traveling fronts of addition polymerization

NASA Technical Reports Server (NTRS)

Pojman, John A.; Jones, Chris E.; Khan, Akhtar M.

1993-01-01

An autocatalytic reaction in an unstirred vessel can support a constant velocity wavefront resulting from the coupling of diffusion to the chemical reaction. A flare front is a common example in which heat is the autocatalytic species that diffuses into unreacted regions stimulating a reaction that produces more heat. Traveling fronts were studied in synthetic polymerization reactions under high pressure by workers in the former USSR. More recently, propagating fronts of methacrylic acid polymerization were studied under ambient conditions, both with video techniques and by NMR.

Study on the effect of Cd-diffusion annealing on the electrical properties of CdZnTe

NASA Astrophysics Data System (ADS)

Wanwan, Li; Zechun, Cao; Bin, Zhang; Feng, Zhan; Hongtao, Liu; Wenbin, Sang; Jiahua, Min; Kang, Sun

2006-06-01

In order to meet the requirements for the device design of radiation detectors, CdZnTe (or Cd 1-xZn xTe) crystals grown by Vertical Bridgman Method often need subsequent annealing to increase their resistivity. The nature of this treatment is a diffusion process. Thus, it is meaningful to relate the change of resistivity to the diffusion parameters. A model correlating resistivity and conduction type of CdZnTe with the main diffusion parameter—diffusion coefficient—is put forward in this paper. Combining the model with the analysis of our experimental data, DCd=1.464×10 -10, 1.085×10 -11 and 4.167×10 -13 cm 2/s are the values of Cd self-diffusion coefficient in Cd 0.9Zn 0.1Te at 1073, 973 and 873 K, respectively. The data coincide closely with the Cd self-diffusion coefficient in CdTe provided by different authors [E.D. Jones, N.M. Stewart, Self-diffusion of cadmium in cadmium telluride, J. Crystal Growth 84 (1987) 289-294; P.M. Borsenberger, D.A. Stevenson, J. Phys. Chem. Solids 29 (1968) 1277; R.C. Whelan, D. Shaw, in: D.G. Thomas (Ed.), II -VI Semiconductor Compounds, Benjamin, New York, 1967, p. 451]. With the data, the effects of annealing time on the change of resistivity and conduction type for Cd 0.9Zn 0.1Te wafers, which are annealed in saturated Cd vapor at 1073, 973 and 873 K, were simulated, and good consistency was found. This work suggests an alternative way to obtain the diffusion coefficient in semiconductor materials and also enables ones to analyze the diffusion process quantitatively and predict the annealing results.

Water masses transform at mid-depths over the Antarctic Continental Slope

NASA Astrophysics Data System (ADS)

Mead Silvester, Jess; Lenn, Yueng-Djern; Polton, Jeffrey; Phillips, Helen E.; Morales Maqueda, Miguel

2017-04-01

The Meridional Overturning Circulation (MOC) controls the oceans' latitudinal heat distribution, helping to regulate the Earth's climate. The Southern Ocean is the primary place where cool, deep waters return to the surface to complete this global circulation. While water mass transformations intrinsic to this process predominantly take place at the surface following upwelling, recent studies implicate vertical mixing in allowing transformation at mid-depths over the Antarctic continental slope. We deployed an EM-Apex float near Elephant Island, north of the Antarctic Peninsula's tip, to profile along the slope and use potential vorticity to diagnose observed instabilities. The float captures direct heat exchange between a lens of Upper Circumpolar Deep Water (UCDW) and surrounding Lower Circumpolar Deep Waters (LCDW) at mid-depths and over the course of several days. Heat fluxes peak across the top and bottom boundaries of the UCDW lens and peak diffusivities across the bottom boundary are associated with shear instability. Estimates of diffusivity from shear-strain finestructure parameterisation and heat fluxes are found to be in reasonable agreement. The two-dimensional Ertel potential vorticity is elevated both inside the UCDW lens and along its bottom boundary, with a strong contribution from the shear term in these regions and instabilities are associated with gravitational and symmetric forcing. Thus, shear instabilities are driving turbulent mixing across the lower boundary between these two water masses, leading to the observed heat exchange and transformation at mid-depths over the Antarctic continental slope. This has implications for our understanding of the rates of upwelling and ocean-atmosphere exchanges of heat and carbon at this critical location.

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

NASA Technical Reports Server (NTRS)

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

1977-01-01

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

Premixed Flames Under Microgravity and Normal Gravity Conditions

NASA Astrophysics Data System (ADS)

Krikunova, Anastasia I.; Son, Eduard E.

2018-03-01

Premixed conical CH4-air flames were studied experimentally and numerically under normal straight, reversed gravity conditions and microgravity. Low-gravity experiments were performed in Drop tower. Classical Bunsen-type burner was used to find out features of gravity influence on the combustion processes. Mixture equivalence ratio was varied from 0.8 to 1.3. Wide range of flow velocity allows to study both laminar and weakly turbulized flames. High-speed flame chemoluminescence video-recording was used as diagnostic. The investigations were performed at atmospheric pressure. As results normalized flame height, laminar flame speed were measured, also features of flame instabilities were shown. Low- and high-frequency flame-instabilities (oscillations) have a various nature as velocity fluctuations, preferential diffusion instability, hydrodynamic and Rayleigh-Taylor ones etc., that was explored and demonstrated.