Science.gov

Sample records for acoustic double layers

  1. Electrostatic supersolitons and double layers at the acoustic speed

    SciTech Connect

    Verheest, Frank; Hellberg, Manfred A.

    2015-01-15

    Supersolitons are characterized by subsidiary extrema on the sides of a typical bipolar electric field signature or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It has been proven that supersolitons may exist in several plasmas having at least three constituent species, but they cannot be found in weakly nonlinear theory. Another recent aspect of pseudopotential theory is that in certain plasma models and parameter regimes solitons and/or double layers can exist at the acoustic speed, having no reductive perturbation counterparts. Importantly, they signal coexistence between solitons having positive and negative polarity, in that one solution can be realized at a time, depending on infinitesimal perturbations from the equilibrium state. Weaving the two strands together, we demonstrate here that one can even find supersolitons and double layers at the acoustic speed, as illustrated using the model of cold positive and negative ions, in the presence of nonthermal electrons following a Cairns distribution. This model has been discussed before, but the existence and properties of supersolitons at the acoustic speed were not established at the time of publication.

  2. Double Layers in Astrophysics

    NASA Technical Reports Server (NTRS)

    Williams, Alton C. (Editor); Moorehead, Tauna W. (Editor)

    1987-01-01

    Topics addressed include: laboratory double layers; ion-acoustic double layers; pumping potential wells; ion phase-space vortices; weak double layers; electric fields and double layers in plasmas; auroral double layers; double layer formation in a plasma; beamed emission from gamma-ray burst source; double layers and extragalactic jets; and electric potential between plasma sheet clouds.

  3. Dust-acoustic double layers - Ion inertial effects

    NASA Technical Reports Server (NTRS)

    Mace, Richard L.; Hellberg, Manfred A.

    1993-01-01

    Space and astrophysical plasmas often comprise a number of massive ion components in addition to a tenuous, negatively charged dust component and an electron component. Stationary electrostatic double layers in a dusty plasma are investigated in a model treating the ion components as Boltzmann-distributed (inertialess) fluids. On comparison with the inertialess theory, one finds considerably reduced double layer existence parameter regimes. Significantly, highly nonlinear double layers are ruled out when ion inertia is incorporated. However, in the restricted parameter regimes in which the inertial theory predicts double layers for small ion/dust mass ratios (about 10 exp -15-10 exp -8) there is good qualitative agreement with inertialess theory. The reasons for these, and other discrepancies and similarities, are discussed.

  4. Weak dust-acoustic double-layers in a polarized dusty plasma

    NASA Astrophysics Data System (ADS)

    Messekher, Abderrahim; Tribeche, Mouloud

    2017-03-01

    The problem of small amplitude dust-acoustic double-layers in a polarized dusty plasma is addressed. Our results show that in such a plasma double-layers structures, the amplitude and nature of which depend sensitively on the plasma parameters, can exist. In particular, it may be noted that as the polarization parameter R increases, the domain of the allowable Mach numbers M enlarges and small values of M are more involved. An increase of R leads to a monotonic decrease of the dust-acoustic double-layers amplitude before levelling-off at a constant value. An increase of M provides qualitatively the same results by with a net shift of the R-values towards lower values. We have then investigated the threshold R_{cr} for the possible onset of rarefactive dust-acoustic double-layers and concluded that only compressive double-layers are admitted.

  5. Time evolution of ion-acoustic double layers in an unmagnetized plasma

    SciTech Connect

    Bharuthram, R.; Momoniat, E.; Mahomed, F.; Singh, S. V.; Islam, M. K.

    2008-08-15

    Ion-acoustic double layers are examined in an unmagnetized, three-component plasma consisting of cold ions and two temperature electrons. Both of the electrons are considered to be Boltzmann distributed and the ions follow the usual fluid dynamical equations. Using the method of characteristics, a time-dependent solution for ion-acoustic double layers is obtained. Results of the findings may have important consequences for the real time satellite observations in the space environment.

  6. Acoustic radiation force on a double-layer microsphere by a Gaussian focused beam

    SciTech Connect

    Wu, Rongrong; Cheng, Kaixuan; Liu, Jiehui; Mao, Yiwei; Gong, Xiufen; Liu, Xiaozhou

    2014-10-14

    A new model for calculating the radiation force on double-layer microsphere is proposed based on the ray acoustics approach. The axial acoustic radiation force resulting from a focused Gaussian beam incident on spherical shells immersed in water is examined theoretically in relation to its thickness and the contents of its double-layer. The attenuation both in the water and inside the sphere is considered in this method, which cannot be ignored while the high frequency ultrasonic is used. Results of numerical calculations are presented for fat and low density polyethylene materials, with the hollow region filled with animal oil, water, or air. These results show how the acoustic impedance and the sound velocity of both layers, together with the thickness of the shell, affect the acoustic radiation force.

  7. Ion-acoustic double-layers in a magnetized plasma with nonthermal electrons

    SciTech Connect

    Rios, L. A.; Galvão, R. M. O.

    2013-11-15

    In the present work we investigate the existence of obliquely propagating ion-acoustic double layers in magnetized two-electron plasmas. The fluid model is used to describe the ion dynamics, and the hot electron population is modeled via a κ distribution function, which has been proved to be appropriate for modeling non-Maxwellian plasmas. A quasineutral condition is assumed to investigate these nonlinear structures, which leads to the formation of double-layers propagating with slow ion-acoustic velocity. The problem is investigated numerically, and the influence of parameters such as nonthermality is discussed.

  8. Ion acoustic solitons/double layers in two-ion plasma revisited

    SciTech Connect

    Lakhina, G. S. Singh, S. V. Kakad, A. P.

    2014-06-15

    Ion acoustic solitons and double layers are studied in a collisionless plasma consisting of cold heavier ion species, a warm lighter ion species, and hot electrons having Boltzmann distributions by Sagdeev pseudo-potential technique. In contrast to the previous results, no double layers and super-solitons are found when both the heavy and lighter ion species are treated as cold. Only the positive potential solitons are found in this case. When the thermal effects of the lighter ion species are included, in addition to the usual ion-acoustic solitons occurring at M > 1 (where the Mach number, M, is defined as the ratio of the speed of the solitary wave and the ion-acoustic speed considering temperature of hot electrons and mass of the heavier ion species), slow ion-acoustic solitons/double layers are found to occur at low Mach number (M < 1). The slow ion-acoustic mode is actually a new ion-ion hybrid acoustic mode which disappears when the normalized number density of lighter ion species tends to 1 (i.e., no heavier species). An interesting property of the new slow ion-acoustic mode is that at low number density of the lighter ion species, only negative potential solitons/double layers are found whereas for increasing densities there is a transition first to positive solitons/double layers, and then only positive solitons. The model can be easily applicable to the dusty plasmas having positively charged dust grains by replacing the heavier ion species by the dust mass and doing a simple normalization to take account of the dust charge.

  9. 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.

  10. Dust acoustic double layers in a magnetized dusty self-gravitating plasma with superthermal particles

    NASA Astrophysics Data System (ADS)

    Sabetkar, Akbar; Dorranian, Davoud

    2016-08-01

    Our prime objective of this paper is to examine the parametric regimes for the existence and polarity of dust acoustic double layers (DADLs) and its solitary structures arising from a magnetized self-gravitating opposite polarity dust-plasma (OPDP) model. The constituents of the OPDP model are two species of positively and negatively charged dust grains, Maxwellian electrons and kappa distributed ions. Contributions of gravitational force only on dust grains are taken into account. For weakly nonlinear analysis, the multiple time scale technique has been used to construct the extended Korteweg-de Vries (E-KdV) and modified Korteweg-de Vries (M-KdV) equations. They pinpoint the evolution of DADLs and solitary structures associated with dust acoustic (DA) mode, respectively. The relevant configurational parameters in our study include the superthermality of ions (κ), obliqueness of propagation (θ), ion concentration (δi), static magnetic field B0 (via ω c p , ω c n ), and self-gravitational field (via γ), as well as the density (μ0), charge (α), and mass (β) ratio of positive to negative dust species. The proposed OPDP model permits positive and negative double layer polarities, while higher order nonlinear equation dictates us only positive polarity solitary structures. The main modification due to an increase in self-gravitational field (via γ) is an enhancement in the spatial width of double layers, yet leaving their amplitude, phase speed, and polarity practically unaffected. With enhanced superthermality and other intrinsic parameters in OPDP model, there is an opposite trend in both amplitude and width of double layers, while the amplitude and the width of solitary waves (via M-KdV equation) undergo the identical behaviors. In particular, the amplitude of solitary waves manifests monotonic behavior for permissible range of obliqueness θ, whereas this scenario is acceptable to only width of double layers. The results are discussed in the context of

  11. Effects of hot electron inertia on electron-acoustic solitons and double layers

    SciTech Connect

    Verheest, Frank; Hellberg, Manfred A.

    2015-07-15

    The propagation of arbitrary amplitude electron-acoustic solitons and double layers is investigated in a plasma containing cold positive ions, cool adiabatic and hot isothermal electrons, with the retention of full inertial effects for all species. For analytical tractability, the resulting Sagdeev pseudopotential is expressed in terms of the hot electron density, rather than the electrostatic potential. The existence domains for Mach numbers and hot electron densities clearly show that both rarefactive and compressive solitons can exist. Soliton limitations come from the cool electron sonic point, followed by the hot electron sonic point, until a range of rarefactive double layers occurs. Increasing the relative cool electron density further yields a switch to compressive double layers, which ends when the model assumptions break down. These qualitative results are but little influenced by variations in compositional parameters. A comparison with a Boltzmann distribution for the hot electrons shows that only the cool electron sonic point limit remains, giving higher maximum Mach numbers but similar densities, and a restricted range in relative hot electron density before the model assumptions are exceeded. The Boltzmann distribution can reproduce neither the double layer solutions nor the switch in rarefactive/compressive character or negative/positive polarity.

  12. Nonlinear ion-acoustic double-layers in electronegative plasmas with electrons featuring Tsallis distribution

    NASA Astrophysics Data System (ADS)

    Ghebache, Siham; Tribeche, Mouloud

    2016-04-01

    Weakly nonlinear ion-acoustic (IA) double-layers (DLs), which accompany electronegative plasmas composed of positive ions, negative ions, and nonextensive electrons are investigated. A generalized Korteweg-de Vries equation with a cubic nonlinearity is derived using a reductive perturbation method. Different types of electronegative plasmas inspired from the experimental studies of Ichiki et al. (2001) are discussed. It is shown that the IA wave phase velocity, in different mixtures of negative and positive ions, decreases as the nonextensive parameter q increases, before levelling-off at a constant value for larger q. Moreover, a relative increase of Q involves an enhancement of the IA phase velocity. Existence domains of either solitary waves or double-layers are then presented and their parametric dependence is determined. Owing to the electron nonextensivity, our present plasma model can admit compressive as well as rarefactive IA-DLs.

  13. Ion acoustic solitary waves and double layers in a plasma with two temperature electrons featuring Tsallis distribution

    SciTech Connect

    Shalini, Saini, N. S.

    2014-10-15

    The propagation properties of large amplitude ion acoustic solitary waves (IASWs) are studied in a plasma containing cold fluid ions and multi-temperature electrons (cool and hot electrons) with nonextensive distribution. Employing Sagdeev pseudopotential method, an energy balance equation has been derived and from the expression for Sagdeev potential function, ion acoustic solitary waves and double layers are investigated numerically. The Mach number (lower and upper limits) for the existence of solitary structures is determined. Positive as well as negative polarity solitary structures are observed. Further, conditions for the existence of ion acoustic double layers (IADLs) are also determined numerically in the form of the critical values of q{sub c}, f and the Mach number (M). It is observed that the nonextensivity of electrons (via q{sub c,h}), concentration of electrons (via f) and temperature ratio of cold to hot electrons (via β) significantly influence the characteristics of ion acoustic solitary waves as well as double layers.

  14. Arbitrary amplitude dust ion acoustic solitons and double layers in the presence of nonthermal positrons and electrons

    NASA Astrophysics Data System (ADS)

    Banerjee, Gadadhar; Maitra, Sarit

    2016-12-01

    Existence of arbitrary amplitude solitons and double layers have been studied in collisionless unmagnetized multicomponent dusty plasmas with nonthermally distributed positrons and electrons by using Sagdeev's pseudopotential method. The linear dispersion relation is obtained for dust ion acoustic wave mode. The present model supports the coexistence of positive potential solitary waves and negative potential solitary waves and double layers. The criterion for the existence of solitary waves and double layers is derived in terms of Mach number limit. The effects of ion temperature and nonthermality of electrons and positrons are studied. Also the effects of positron and dust concentration on the wave propagation are observed.

  15. Role of nonthermal electrons on dust ion acoustic double layer with variable dust charge

    NASA Astrophysics Data System (ADS)

    Borah, Prathana; Gogoi, Deepshikha; Das, Nilakshi

    2016-01-01

    The presence of nonthermal electron may play an important role in the formation of nonlinear structures in plasma. On the other hand, fluctuation of dust charge is an important and unique feature of complex plasma and it gives rise to a dissipative effect in the system leading to the formation of nonlinear structures due to the balance between nonlinearity and dissipation. In this paper, the propagation of nonlinear dust ion acoustic (DIA) wave in unmagnetized collisionless dusty plasma consisting of ions, nonthermal electrons and dust grains with variable negative charge has been investigated using the Sagdeev potential method. The existence domain of rarefactive double layer (DL) in the DIA wave has been investigated for the range of plasma parameters. The real potential has been obtained by numerically solving the Poisson equation and dust charging equation. It is observed that the presence of nonthermal electrons strengthens the DIA DL.

  16. Electro-acoustic solitary waves and double layers in a quantum plasma

    NASA Astrophysics Data System (ADS)

    Dip, P. R.; Hossen, M. A.; Salahuddin, M.; Mamun, A. A.

    2017-02-01

    A meticulous theoretical investigation has carried out to study the properties related to the higher-order nonlinearity of the electro-acoustic waves, specifically ion-acoustic (IA) waves in an unmagnetized, collisionless, quantum electron-positron-ion (EPI) plasma. The plasma system is supposed to be formed of positively charged inertial heavy ions, inertialess electrons and positrons. The reductive perturbation technique is employed to derive the modified Korteweg-de Vries (mK-dV) equation to analyze the solitary waves (SWs), and the standard Gardner (SG) equation to analyze the higher-order SWs as well as double layers (DLs). The basic features (viz. amplitude, width, phase speed, etc.) of the IA SWs and DLs are examined. The comparison between the mK-dV SWs and SG SWs is also made. It is found that the amplitude, width, phase speed, etc. of the IA SWs and DLs are significantly modified by the effects of the both Fermi temperatures as well as pressures and Bohm potentials of electrons and positrons. Our findings may be useful in explaining the physics behind the formation of the IA waves in both astrophysical and laboratory EPI plasmas (viz. white dwarfs, laser-solid matter interaction experiments, etc.).

  17. Ion-acoustic solitons, double layers and supersolitons in a plasma with two ion- and two electron species

    SciTech Connect

    Olivier, C. P. Maharaj, S. K.; Bharuthram, R.

    2015-08-15

    The polarity of ion-acoustic solitons that arise in a plasma with two (same mass, different temperature) ion species and two (different temperature) electron species is investigated. Two different fluid models are compared. The first model treats all species as adiabatic fluids, while the second model treats the ion species as adiabatic, and the electron species as isothermal. Nonlinear structures are analysed via the reductive perturbation analysis and pseudo-potential analysis. Each model supports both slow and fast ion-acoustic solitons, associated with the two (slow and fast) ion-acoustic speeds. The models support both positive and negative polarity solitons associated with the slow ion-acoustic speed. Moreover, results are in good agreement, and both models support positive and negative polarity double layers. For the fast ion-acoustic speed, the first model supports only positive polarity solitons, while the second model supports solitons of both polarity, coexistence of positive and negative polarity solitons, double layers and supersolitons. A novel feature of our analysis is the evaluation of nonlinear structures at critical number densities where polarity changes occur. This analysis shows that solitons that occur at the acoustic speed are neither a necessary nor a sufficient condition for the phenomenon of coexistence. The relationship between the existence regions of supersolitons and soliton polarity is also discussed.

  18. Ion-acoustic solitons, double layers and rogue waves in plasma having superthermal electrons

    NASA Astrophysics Data System (ADS)

    Singh Saini, Nareshpal

    2016-07-01

    Most of the space and astrophysical plasmas contain different type of charged particles with non-Maxwellian velocity distributions (e.g., nonthermal, superthermal, Tsallis ). These distributions are commonly found in the auroral region of the Earth's magnetosphere, planetary magnetosphere, solar and stellar coronas, solar wind, etc. The observations from various satellite missions have confirmed the presence of superthermal particles in space and astrophysical environments. Over the last many years, there have been a much interest in studying the different kind of properties of the electrostatic nonlinear excitations (solitons, double layers, rogue waves etc.) in a multi-component plasmas in the presence of superthermal particles. It has been analyzed that superthermal distributions are more appropriate than Maxwellian distribution for the modeling of space data. It is interesting to study the dynamics of various kinds of solitary waves, Double layers, Shocks etc. in varieties of plasma systems containing different kind of species obeying Lorentzian (kappa-type)/Tsallis distribution. In this talk, I have focused on the study of large amplitude IA solitary structures (bipolar solitary structures, double layers etc.), modulational instability and rogue waves in multicomponent plasmas. The Sagdeev potential method has been employed to setup an energy balance equation, from which we have studied the characteristics of large amplitude solitary waves under the influence of superthermality of charged particles and other plasma parameters. The critical Mach number has been determined, above which solitary structures are observed and its variation with superthermality of electrons and other parameters has also been discussed. Double layers have also been discussed. Multiple scale reductive perturbation method has been employed to derive NLS equation. From the different kind of solutions of this equation, amplitude modulation of envelope solitons and rogue waves have been

  19. Electron acoustic solitary waves and double layers for a magnetized plasma and its relevance with satellite observations

    NASA Astrophysics Data System (ADS)

    Ghosh, Suktisama

    In situ measurements of particles and fields of the Earth’s auroral zone have revealed a reach variety of plasma phenomena on different spatial and temporal scales. One major aspects of them is the bursts of broadband electrostatic noise emissions (BEN) with frequencies from below the lower hybrid frequency (typically tens of Hertz) up to and higher than electron plasma and cyclotron frequencies (typically, a few kilohertz). Many detailed analysis of BEN have been performed using space-borne data from POLAR, FAST, GEOTAIL, and CLUSTER multi-spacecraft missions. It is well understood that the time scale of the high frequency part indicates the involvement of electron dynamics and may be interpreted as a nonlinear evolution electron acoustic instabilities leading to solitary waves and double layers. The study of the generation and propagation of such microstructures is important for understanding the Sun-Earth coupling and the energy dissipation and particle transports across the magnetospheric boundary layers. In the present work, we have delineated the parameter regime for the fully nonlinear solutions of electron acoustic solitary waves adopting the Sagdeev pseudopontial technique. The plasma is assumed to be magnetized and traversed by an electron beam. The ions are assumed to be hotter than electrons (viz., Ti > Te) and obey Boltzmann distribution. It has been observed that both positive and negative amplitude solitary waves may exist. The width-amplitude variation profile for a positive amplitude solution shows increase in the width with increasing amplitude, and the solution eventually terminates to a double layer. The width - amplitude variation profile has been found to agree qualitatively with the Fast satellite observations. On the other hand, the negative amplitude solutions reveal two distinct branches. For the fast moving one (with larger Mach numbers), the width decreases with increasing amplitude and no double layer solutions have been observed for

  20. Dust-ion-acoustic double layers in multi-ion dusty plasma

    NASA Astrophysics Data System (ADS)

    Mamun, A. A.; Deeba, F.

    2015-08-01

    A theoretical investigation has been made on nonplanar (cylindrical and spherical) dust-ionacoustic (DIA) double layers (DLs) in a multi-ion dusty plasma system containing inertial positive and negative ions and arbitrarily charged stationary dust. The dust particles have been considered as arbitrarily (either positively or negatively) charged in order to observe the effects of the dust polarity on the DIA DLs. The ion species were considered to be at different temperatures to observe the effects of the temperatures on that waves. The modified Gardner equation, which has been derived by employing the reductive perturbation method, has been used to analyze time-dependent nonplanar and planar DIA DLs. It has been found that the time evolution of DIA DLs is significantly modified not only by the nonplanar geometry, but also by the polarity, temperature, and mass ratio of the constituent particles. It has been also found that the amplitude of cylindrical DIA DL structures is larger than that of 1D planar ones, but smaller than that of the spherical ones.

  1. Dust-ion-acoustic double layers in multi-ion dusty plasma

    SciTech Connect

    Mamun, A. A.; Deeba, F.

    2015-08-15

    A theoretical investigation has been made on nonplanar (cylindrical and spherical) dust-ionacoustic (DIA) double layers (DLs) in a multi-ion dusty plasma system containing inertial positive and negative ions and arbitrarily charged stationary dust. The dust particles have been considered as arbitrarily (either positively or negatively) charged in order to observe the effects of the dust polarity on the DIA DLs. The ion species were considered to be at different temperatures to observe the effects of the temperatures on that waves. The modified Gardner equation, which has been derived by employing the reductive perturbation method, has been used to analyze time-dependent nonplanar and planar DIA DLs. It has been found that the time evolution of DIA DLs is significantly modified not only by the nonplanar geometry, but also by the polarity, temperature, and mass ratio of the constituent particles. It has been also found that the amplitude of cylindrical DIA DL structures is larger than that of 1D planar ones, but smaller than that of the spherical ones.

  2. Large amplitude dust-acoustic double layers in non-thermal plasmas with positive and negative dust

    SciTech Connect

    Maharaj, S. K.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.; Pillay, S. R.

    2011-11-29

    The existence of large amplitude double layers in a plasma composed of cold negative dust, adiabatic positive dust, non-thermal ions and Boltzmann electrons is investigated using the Sagdeev pseudopotential technique. Both positive potential and negative potential double layers are found to be supported by the model. The variation of the maximum amplitudes of the double layers and corresponding Mach numbers are examined as a function of various plasma parameters. In particular, we investigate to what extent ion non-thermal effects are required for positive potential double layers to occur.

  3. Large amplitude dust-acoustic double layers in non-thermal plasmas with positive and negative dust

    NASA Astrophysics Data System (ADS)

    Maharaj, S. K.; Bharuthram, R.; Singh, S. V.; Pillay, S. R.; Lakhina, G. S.

    2011-11-01

    The existence of large amplitude double layers in a plasma composed of cold negative dust, adiabatic positive dust, non-thermal ions and Boltzmann electrons is investigated using the Sagdeev pseudopotential technique. Both positive potential and negative potential double layers are found to be supported by the model. The variation of the maximum amplitudes of the double layers and corresponding Mach numbers are examined as a function of various plasma parameters. In particular, we investigate to what extent ion non-thermal effects are required for positive potential double layers to occur.

  4. Double-negative acoustic metamaterial.

    PubMed

    Li, Jensen; Chan, C T

    2004-11-01

    We show here the existence of acoustic metamaterial, in which both the effective density and bulk modulus are simultaneously negative, in the true and strict sense of an effective medium. Our double-negative acoustic system is an acoustic analogue of Veselago's medium in electromagnetism, and shares many unique consequences, such as negative refractive index. The double negativity in acoustics is derived from low-frequency resonances, as in the case of electromagnetism, but the negative density and modulus are derived from a single resonance structure as distinct from electromagnetism in which the negative permeability and negative permittivity originates from different resonance mechanisms.

  5. Dust-acoustic Gardner solitons and double layers in dusty plasmas with nonthermally distributed ions of two distinct temperatures

    SciTech Connect

    Tasnim, I.; Mamun, A. A.; Masud, M. M.; Asaduzzaman, M.

    2013-03-15

    A rigorous theoretical investigation has been performed on dust-acoustic (DA) solitary structures in an unmagnetized dusty plasma, consisting of negatively charged mobile dust grains, Boltzmann distributed electrons, and nonthermally distributed ions of two distinct temperatures. The Korteweg-de Vries (K-dV), modified K-dV (mK-dV) and Gardner equations, and their solitary waves (SWs) and double layer (DL) (in case of Gardner equation) solutions are derived by using the reductive perturbation technique. The basic features of the DA Gardner solitons (GSs) and DLs are studied analytically as well as numerically. It has been observed that the GSs significantly differ from K-dV and mK-dV solitons, and only positive potential DLs exist in the system. It is also studied that two-temperature nonthermal ions significantly modify the nature and basic properties of the DA SWs. The present investigation can be very effective for understanding and studying the nonlinear characteristics of the DA waves in laboratory and space dusty plasmas.

  6. Dust-acoustic Gardner solitons and double layers in dusty plasmas with nonthermally distributed ions of two distinct temperatures.

    PubMed

    Tasnim, I; Masud, M M; Asaduzzaman, M; Mamun, A A

    2013-03-01

    A rigorous theoretical investigation has been performed on dust-acoustic (DA) solitary structures in an unmagnetized dusty plasma, consisting of negatively charged mobile dust grains, Boltzmann distributed electrons, and nonthermally distributed ions of two distinct temperatures. The Korteweg-de Vries (K-dV), modified K-dV (mK-dV) and Gardner equations, and their solitary waves (SWs) and double layer (DL) (in case of Gardner equation) solutions are derived by using the reductive perturbation technique. The basic features of the DA Gardner solitons (GSs) and DLs are studied analytically as well as numerically. It has been observed that the GSs significantly differ from K-dV and mK-dV solitons, and only positive potential DLs exist in the system. It is also studied that two-temperature nonthermal ions significantly modify the nature and basic properties of the DA SWs. The present investigation can be very effective for understanding and studying the nonlinear characteristics of the DA waves in laboratory and space dusty plasmas.

  7. Ion-acoustic solitons and double layers in a two-electron temperature plasma with hot isothermal electrons and cold ions

    NASA Astrophysics Data System (ADS)

    Tagare, S. G.

    2000-03-01

    It is found that a two-electron temperature plasma with isothermal electrons and cold ions admits both compressive and rarefactive solitons, as well as compressive and rarefactive double layers (depending on the concentration of low-temperature electrons). In this paper, a Korteweg-de Vries (K-dV) equation and a K-dV-type equation with cubic and fourth-order nonlinearity at the critical density of the low-temperature isothermal electrons are derived to discuss the properties of ion-acoustic solitons in a two-electron temperature plasma. In the vicinity of the critical electron density of low-temperature isothermal electrons, we have derived a K-dV-type equation with mixed nonlinearity, and the solution of this equation will have both compressive and rarefactive double layers for those values of critical electron density of low-temperature electrons for which ion-acoustic solitons do not exist. By using quasipotential analysis, critical Mach numbers M1c and M2c are obtained such that compressive ion-acoustic solitons exist when 1acoustic solitons exist when 1

  8. Dust-acoustic solitary waves and double layers in dusty plasma consisting of cold dust particles and two-temperature isothermal ions

    NASA Astrophysics Data System (ADS)

    Tagare, S. G.

    1997-09-01

    It is found that a dusty plasma with inertial dust fluid and two-temperature isothermal ions admits both compressive and rarefactive solitary waves, as well as compressive and rarefactive double layers (depending on the concentration of low-temperature ions). In this paper, Korteweg-de Vries equation (KdV-type equations) with cubic and fourth-order nonlinearity at the critical density of low-temperature isothermal ions are derived to discuss properties of dust-acoustic solitary waves. In the vicinity of critical density of low-temperature ions, KdV-type equation with mixed nonlinearity is discussed. By using quasipotential analysis, critical Mach numbers M1c and M2c are obtained such that rarefactive dust-acoustic solitons exist when 1acoustic solitons exist when 1

  9. Effects of flat-topped ion distribution and dust temperature on small amplitude dust-acoustic solitary waves and double layers in dusty plasma

    SciTech Connect

    Alinejad, H.; Mamun, A. A.

    2010-12-15

    The combined effects of the flat-topped ion distribution and dust temperature are incorporated in the study of small but finite amplitude dust-acoustic (DA) solitary waves (SWs) as well double layers (DLs) in an unmagnetized dusty plasma. Due to the flat-trapped ions, our plasma model admits only rarefactive localized structures. It is found that the effects of dust temperature and resonant particles significantly modify the criteria for the existence of DA SWs and DLs, as well as significantly modify their basic properties.

  10. Type I intermittency related to the spatiotemporal dynamics of double layers and ion-acoustic instabilities in plasma

    SciTech Connect

    Chiriac, S.; Dimitriu, D. G.; Sanduloviciu, M.

    2007-07-15

    Anodic double layer instabilities occur in low-temperature diffusion filament-type discharge plasma by applying a certain positive bias with respect to the plasma potential to an additional electrode. Periodic nonlinear regimes, characterized by proper dynamics of double layers, are sustained if excitation and ionization rates in front of the electrode reach the value for which current limitation effects appear in the static current-voltage characteristic. It was experimentally shown that under specific experimental conditions these ordered spatiotemporal phenomena can evolve into chaotic states by type I intermittency. This transition was verified by the evolution of time series, fast Fourier transform amplitude plots, three-dimensional reconstructed state spaces, power laws, and flickering phenomena spectrum, as well as by the return map and tangent bifurcation.

  11. Tests on Double Layer Metalization

    NASA Technical Reports Server (NTRS)

    Woo, D. S.

    1983-01-01

    28 page report describes experiments in fabrication of integrated circuits with double-layer metalization. Double-layer metalization requires much less silicon "real estate" and allows more flexibility in placement of circuit elements than does single-layer metalization.

  12. Teaching the Double Layer.

    ERIC Educational Resources Information Center

    Bockris, J. O'M.

    1983-01-01

    Suggests various methods for teaching the double layer in electrochemistry courses. Topics addressed include measuring change in absolute potential difference (PD) at interphase, conventional electrode potential scale, analyzing absolute PD, metal-metal and overlap electron PDs, accumulation of material at interphase, thermodynamics of electrified…

  13. Small amplitude dust ion-acoustic solitary waves and double layers in a dusty plasma with flat-topped electron distribution

    SciTech Connect

    Alinejad, H.; Mamun, A. A.

    2010-12-15

    The properties of small but finite amplitude dust ion-acoustic (DIA) solitary waves (SWs) as well double layers (DLs) in a dusty plasma containing warm adiabatic ions, electrons following flat-topped velocity distribution, and arbitrarily (positively or negatively) charged immobile dust are studied. The effects of ion-temperature, resonant electrons, and dust number density are found to significantly modify the criteria for the existence of the DIA SWs and DLs, as well as significantly modify their basic features. It is also shown that the ion-temperature reduces the possibility for the formation of these localized structures, and that their amplitude decreases (increases) with the increase in the negative (positive) dust number density.

  14. Modified Ion-Acoustic Shock Waves and Double Layers in a Degenerate Electron-Positron-Ion Plasma in Presence of Heavy Negative Ions

    NASA Astrophysics Data System (ADS)

    Hossen, M. A.; Hossen, M. R.; Mamun, A. A.

    2014-12-01

    A general theory for nonlinear propagation of one dimensional modified ion-acoustic waves in an unmagnetized electron-positron-ion (e-p-i) degenerate plasma is investigated. This plasma system is assumed to contain relativistic electron and positron fluids, non-degenerate viscous positive ions, and negatively charged static heavy ions. The modified Burgers and Gardner equations have been derived by employing the reductive perturbation method and analyzed in order to identify the basic features (polarity, width, speed, etc.) of shock and double layer (DL) structures. It is observed that the basic features of these shock and DL structures obtained from this analysis are significantly different from those obtained from the analysis of standard Gardner or Burgers equations. The implications of these results in space and interstellar compact objects (viz. non-rotating white dwarfs, neutron stars, etc.) are also briefly mentioned.

  15. Roles of superthermal electrons and positrons on positron-acoustic solitary waves and double layers in electron-positron-ion plasmas.

    PubMed

    Alam, M S; Uddin, M J; Masud, M M; Mamun, A A

    2014-09-01

    Positron-acoustic (PA) solitary waves (SWs) and double layers (DLs) in four-component plasmas consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated both numerically and analytically by deriving Korteweg-de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with their DLs solutions using the reductive perturbation method. It is examined that depending on the plasma parameters, the K-dV SWs, Gardner SWs, and DLs support either compressive or rarefactive structures, whereas mK-dV SWs support only compressive structure. It is also found that the presence of superthermal (kappa distributed) hot positrons and hot electrons significantly modify the basic features of PA SWs as well as PA DLs. Besides, the critical number density ratio of hot positrons and cold positrons play an important role in the polarity of PA SWs and DLs. The implications of our results in different space as well as laboratory plasma environments are briefly discussed.

  16. Roles of superthermal electrons and positrons on positron-acoustic solitary waves and double layers in electron–positron–ion plasmas

    SciTech Connect

    Alam, M. S.; Uddin, M. J.; Mamun, A. A.; Masud, M. M.

    2014-09-01

    Positron-acoustic (PA) solitary waves (SWs) and double layers (DLs) in four-component plasmas consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated both numerically and analytically by deriving Korteweg–de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with their DLs solutions using the reductive perturbation method. It is examined that depending on the plasma parameters, the K-dV SWs, Gardner SWs, and DLs support either compressive or rarefactive structures, whereas mK-dV SWs support only compressive structure. It is also found that the presence of superthermal (kappa distributed) hot positrons and hot electrons significantly modify the basic features of PA SWs as well as PA DLs. Besides, the critical number density ratio of hot positrons and cold positrons play an important role in the polarity of PA SWs and DLs. The implications of our results in different space as well as laboratory plasma environments are briefly discussed.

  17. Anomalous dc resistivity and double layers in the auroral ionosphere

    SciTech Connect

    Kindel, J.M.; Barnes, C.; Forslund, D.W.

    1980-01-01

    There are at least four candidate instabilities which might account for anomalous dc rereresistivity in the auroral ionosphere. These are: the ion-acoustic instability, the Buneman instability, the ion-cyclotron instability and double layers. Results are reported of computer simulations of these four instabilities which suggest that double layers are most likely to be responsible for sistivity in the auroral zone.

  18. An acoustic double fishnet using Helmholtz resonators.

    PubMed

    Murray, A R J; Summers, I R; Sambles, J R; Hibbins, A P

    2014-09-01

    The acoustic transmission of a closely spaced pair of patterned and perforated rigid plates is explored in air. The structure resembles an acoustic double fishnet design, with each plate modified such that the gap between them acts as an array of Helmholtz resonators. This allows the center frequency of the stop band to be reduced by a factor greater than 2 from the value obtained for the conventional acoustic double fishnet design. Experimental results accord well with the predictions of a finite element model.

  19. Acoustic radiation from single and double ribbed circular cylindrical shells

    NASA Astrophysics Data System (ADS)

    Burroughs, C. B.; Hayek, S. I.; Hallander, J. E.; Bostian, D. A.

    1984-03-01

    Measurements of the acoustic radiation from single and double ribbed circular cylindrical shells were made on the NUSC Transducer Calibration Platform (TCP) in Lake Seneca, NY. Six different types of mechanical drives were used at each of three locations inside the inner shell. Measurements of the shell vibration and acoustic radiation were made with and without outer shells installed around the inner shell structure. For two types of drives, measurements were made with a pressure release layer installed between the inner and outer shell surfaces. Acoustic radiation measurements were made as a function of frequency from 20 to 5,000 Hz and as a function of observation direction at several frequencies for each shell and drive measurement configuration. Measured acoustic radiation data as a function of frequency have been processed. Analysis of the processed data is presented and discussed. It is shown that the location of the drive had a significant effect on the acoustic radiation. The outer shell reduced the acoustic radiation at shell resonant frequencies, but had little effect on other frequencies. The pressure release layer in the double shell had little effect on the acoustic radiation.

  20. Advanced double layer capacitors

    NASA Technical Reports Server (NTRS)

    Sarangapani, S.; Lessner, P.; Forchione, J.; Laconti, A. B.

    1989-01-01

    There is a need for large amounts of power to be delivered rapidly in a number of airborne and space systems. Conventional, portable power sources, such as batteries, are not suited to delivering high peak power pulses. The charge stored at the electrode-electrolyte double layer is, however, much more assessible on a short time scale. Devices exploiting this concept were fabricated using carbon and metal oxides (Pinnacle Research) as the electrodes and sulfuric acid as the electrolyte. The approach reported, replaces the liquid sulfuric acid electrolyte with a solid ionomer electrolyte. The challenge is to form a solid electrode-solid ionomer electrolyte composite which has a high capacitance per geometric area. The approach to maximize contact between the electrode particles and the ionomer was to impregnate the electrode particles using a liquid ionomer solution and to bond the solvent-free structure to a solid ionomer membrane. Ruthenium dioxide is the electrode material used. Three strategies are being pursued to provide for a high area electrode-ionomer contact: mixing of the RuOx with a small volume of ionomer solution followed by filtration to remove the solvent, and impregnation of the ionomer into an already formed RuOx electrode. RuOx powder and electrodes were examined by non-electrochemical techniques. X-ray diffraction has shown that the material is almost pure RuO2. The electrode structure depends on the processing technique used to introduce the Nafion. Impregnated electrodes have Nafion concentrated near the surface. Electrodes prepared by the evaporation method show large aggregates of crystals surrounded by Nafion.

  1. Theory of nonmonotonic double layers

    SciTech Connect

    Kim, K.Y.

    1987-12-01

    A simple graphic method of solving the Vlasov--Poisson system associated with nonlinear eigenvalue conditions for arbitrary potential structures is presented. A general analytic formulation for nonmonotonic double layers is presented and illustrated with some particular closed form solutions. This class of double layers satisfies the time stationary Vlasov--Poisson system while requiring a Sagdeev potential, which is a double-valued function of the physical potential. It follows that any distribution function having a density representation as any integer or noninteger power series of potential can never satisfy the nonmonotonic double-layer boundary conditions. A Korteweg--de Vries-like equation is found showing a relationship among the speed of the nonmonotonic double layer, its scale length, and its degree of asymmetry.

  2. Tunable acoustic double negativity metamaterial.

    PubMed

    Liang, Z; Willatzen, M; Li, J; Christensen, J

    2012-01-01

    Man-made composite materials called "metamaterials" allow for the creation of unusual wave propagation behavior. Acoustic and elastic metamaterials in particular, can pave the way for the full control of sound in realizing cloaks of invisibility, perfect lenses and much more. In this work we design acousto-elastic surface modes that are similar to surface plasmons in metals and on highly conducting surfaces perforated by holes. We combine a structure hosting these modes together with a gap material supporting negative modulus and collectively producing negative dispersion. By analytical techniques and full-wave simulations we attribute the observed behavior to the mass density and bulk modulus being simultaneously negative.

  3. Current driven weak double layers

    NASA Technical Reports Server (NTRS)

    Chanteur, Gerard

    1987-01-01

    Double layers in plasmas can be created by different means. For example, a potential difference forms between two plasmas with different temperatures, in a plasma jet flowing along a converging magnetic field, in a quiescent plasma submitted to an external difference of potential, or in a turbulent plasma carrying an electric charge. The first three cases can be current-free, but not necessarily, although the numerical simulations were made under such conditions for the first two points. Apart from the third case, which is mainly of interest for laboratory experiments, these double layers are good candidates for accelerating the auroral electrons to the few kiloelectron volts observed.

  4. Effect of cooler electrons on a compressive ion acoustic solitary wave in a warm ion plasma — Forbidden regions, double layers, and supersolitons

    SciTech Connect

    Ghosh, S. S.; Sekar Iyengar, A. N.

    2014-08-15

    It is observed that the presence of a minority component of cooler electrons in a three component plasma plays a deterministic role in the evolution of solitary waves, double layers, or the newly discovered structures called supersolitons. The inclusion of the cooler component of electrons in a single electron plasma produces sharp increase in nonlinearity in spite of a decrease in the overall energy of the system. The effect maximizes at certain critical value of the number density of the cooler component (typically 15%–20%) giving rise to a hump in the amplitude variation profile. For larger amplitudes, the hump leads to a forbidden region in the ambient cooler electron concentration which dissociates the overall existence domain of solitary wave solutions in two distinct parameter regime. It is observed that an inclusion of the cooler component of electrons as low as < 1% affects the plasma system significantly resulting in compressive double layers. The solution is further affected by the cold to hot electron temperature ratio. In an adequately hotter bulk plasma (i.e., moderately low cold to hot electron temperature ratio), the parameter domain of compressive double layers is bounded by a sharp discontinuity in the corresponding amplitude variation profile which may lead to supersolitons.

  5. Acoustic Tomography of the Atmospheric Surface Layer

    DTIC Science & Technology

    2014-11-28

    resolution of an ultrasonic anemometer , it was suggested that one consider it is as a small acoustic tomography array and apply appropriate inverse...Fairall, D. Keith Wilson, Ludovic Bariteau. Sonic Anemometer as a Small Acoustic Tomography Array, Boundary-Layer Meteorology, (08 2013): 0. doi...Received Paper 3.00 S. N. Vecherin, V. E. Ostashev, D. K. Wilson, A. Grached. Utilization of an acoustic tomography array as a large sonic anemometer

  6. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable, and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable, and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam, and the beam plasma discharge is ignited.

  7. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam and the 'beam plasma discharge' is ignited.

  8. Double-diffusive layer formation

    NASA Astrophysics Data System (ADS)

    Zaussinger, Florian; Kupka, Friedrich; Hücker, Sebastian; Egbers, Christoph

    2015-04-01

    Double-diffusive convection plays an important role in geo- and astrophysical applications. The special case, where a destabilising temperature gradient counteracts a stabilising solute gradient leads to layering phenomena under certain conditions. Convectively mixed layers sandwiched in diffusive interfaces form a so-called stack. Well-known double-diffusive systems are observed in rift lakes in Africa and even from the coffee drink Latte Macciatto. Stacks of layers are also predicted to occur inside massive stars and inside giant planets. Their dynamics depend on the thermal, the solute and the momentum diffusivities, as well on the ratio of the gradients of the opposing stratifications. Since the layering process cannot be derived from linear stability analysis, the full nonlinear set of equations has to be investigated. Numerical simulations have become feasible for this task, despite the physical processes operate on a vast range of length and time scales, which is challenging for numerical hydrodynamical modelling. The oceanographically relevant case of fresh and salty water is investigated here in further details. The heat and mass transfer is compared with theoretical results and experimental measurements. Additionally, the initial dynamic of layering, the transient behaviour of a stack and the long time evolution are presented using the example of Lake Kivu and the interior of a giant planet.

  9. Acoustic radar investigations of boundary layer phenomena

    NASA Technical Reports Server (NTRS)

    Marks, J. R.

    1974-01-01

    A comparison is made between acoustic radar echoes and conventional meteorological data obtained from the WKY tower, for the purpose of better understanding the relationships between acoustic radar echoes and boundary layer processes. Two thunderstorm outflow cases are presented and compared to both acoustic radar data and Charba's gust front model. The acoustic radar echoes reveal the boundary between warm and cold air and other areas of mixing and strong thermal gradient quite well. The thunderstorm outflow of 27 June 1972 is found to compare with in most respects to Charba's gust front model. The major difference is the complete separation of the head from the main body of cold air, probably caused by erosion of the area behind the head by mixing with the ambient air. Two cases of nocturnal inversions caused by advection of warmer air aloft are presented. It is found that areas of turbulent mixing or strong thermal gradient can be identified quite easily in the acoustic radar record.

  10. Heat generation in double layer capacitors

    NASA Astrophysics Data System (ADS)

    Schiffer, Julia; Linzen, Dirk; Sauer, Dirk Uwe

    Thermal management is a key issue concerning lifetime and performance of double layer capacitors and battery technologies. Double layer capacitor modules for hybrid vehicles are subject to heavy duty cycling conditions and therefore significant heat generation occurs. High temperature causes accelerated aging of the double layer capacitors and hence reduced lifetime. To investigate the thermal behavior of double layer capacitors, thermal measurements during charge/discharge cycles were performed. These measurements show that heat generation in double layer capacitors is the superposition of an irreversible Joule heat generation and a reversible heat generation caused by a change in entropy. A mathematical representation of both parts is provided.

  11. 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.

  12. Double layer -- a particle accelerator in the magnetosphere

    SciTech Connect

    Fu, Xiangrong

    2015-07-16

    Slides present the material under the following topics: Introduction (What is a double layer (DL)? Why is it important? Key unsolved problems); Theory -- time-independent solutions of 1D Vlasov--Poisson system; Particle-in-cell simulations (Current-driven DLs); and Electron acceleration by DL (Betatron acceleration). Key problems include the generation mechanism, stability, and electron acceleration. In summary, recent observations by Van Allen Probes show large number of DLs in the outer radiation belt, associated with enhanced flux of relativistic electrons. Simulations show that ion acoustic double layers can be generated by field-aligned currents. Thermal electrons can gain energy via betatron acceleration in a dipole magnetic field.

  13. Double layers and circuits in astrophysics

    NASA Technical Reports Server (NTRS)

    Alfven, Hannes

    1986-01-01

    As the rate of energy release in a double layer with voltage delta V is P approx I delta V, a double layer must be treated as a part of a circuit which delivers the current I. As neither double layer nor circuit can be derived from magnetofluid models of a plasma, such models are useless for treating energy transfer by means of double layers. They must be replaced by particle models and circuit theory. A simple circuit is suggested which is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object (one example is the double radio sources). It is tentatively suggested in X-ray and Gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). A study of how a number of the most used textbooks in astrophysics treat important concepts like double layers, critical velocity, pinch effects and circuits is made.

  14. Acoustic sounding in the planetary boundary layer

    NASA Technical Reports Server (NTRS)

    Kelly, E. H.

    1974-01-01

    Three case studies are presented involving data from an acoustic radar. The first two cases examine data collected during the passage of a mesoscale cold-air intrusion, probably thunderstorm outflow, and a synoptic-scale cold front. In these studies the radar data are compared to conventional meteorological data obtained from the WKY tower facility for the purpose of radar data interpretation. It is shown that the acoustic radar echoes reveal the boundary between warm and cold air and other areas of turbulent mixing, regions of strong vertical temperature gradients, and areas of weak or no wind shear. The third case study examines the relationship between the nocturnal radiation inversion and the low-level wind maximum or jet in the light of conclusions presented by Blackadar (1957). The low-level jet is seen forming well above the top of the inversion. Sudden rapid growth of the inversion occurs which brings the top of the inversion to a height equal that of the jet. Coincident with the rapid growth of the inversion is a sudden decrease in the intensity of the acoustic radar echoes in the inversion layer. It is suggested that the decrease in echo intensity reveals a decrease in turbulent mixing in the inversion layer as predicted by Blackadar. It is concluded that the acoustic radar can be a valuable tool for study in the lower atmosphere.

  15. Electron temperature differences and double layers

    NASA Technical Reports Server (NTRS)

    Chan, C.; Hershkowitz, N.; Lonngren, K. E.

    1983-01-01

    Electron temperature differences across plasma double layers are studied experimentally. It is shown that the temperature differences across a double layer can be varied and are not a result of thermalization of the bump-on-tail distribution. The implications of these results for electron thermal energy transport in laser-pellet and tandem-mirror experiments are also discussed.

  16. Electric fields and double layers in plasmas

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Thiemann, H.; Schunk, R. W.

    1987-01-01

    Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamical features of the double layers are discussed. These features, as seen in simulations, laboratory experiments, and theory, indicate that double layers and the currents through them undergo slow oscillations which are determined by the ion transit time across an effective length of the system in which double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations were considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields and double layers in an expanding plasma is discussed.

  17. Electric fields and double layers in plasmas

    NASA Astrophysics Data System (ADS)

    Singh, Nagendra; Thiemann, H.; Schunk, R. W.

    1987-05-01

    Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamical features of the double layers are discussed. These features, as seen in simulations, laboratory experiments, and theory, indicate that double layers and the currents through them undergo slow oscillations which are determined by the ion transit time across an effective length of the system in which double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations were considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields and double layers in an expanding plasma is discussed.

  18. Double layers and circuits in astrophysics

    NASA Technical Reports Server (NTRS)

    Alfven, Hannes

    1986-01-01

    A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from earth. Double layers in space should be classified as a new type of celestial object. It is suggested that X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago.

  19. Double layers and circuits in astrophysics

    NASA Technical Reports Server (NTRS)

    Alfven, H.

    1986-01-01

    A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object. It is suggested that X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago.

  20. Acoustic tomography in the atmospheric surface layer

    NASA Astrophysics Data System (ADS)

    Ziemann, A.; Arnold, K.; Raabe, A.

    1999-01-01

    Acoustic tomography is presented as a technique for remote monitoring of meteorological quantities. This method and a special algorithm of analysis can directly produce area-averaged values of meteorological parameters. As a result consistent data will be obtained for validation of numerical atmospheric micro-scale models. Such a measuring system can complement conventional point measurements over different surfaces. The procedure of acoustic tomography uses the horizontal propagation of sound waves in the atmospheric surface layer. Therefore, to provide a general overview of sound propagation under various atmospheric conditions a two-dimensional ray-tracing model according to a modified version of Snell's law is used. The state of the crossed atmosphere can be estimated from measurements of acoustic travel time between sources and receivers at different points. Derivation of area-averaged values of the sound speed and furthermore of air temperature results from the inversion of travel time values for all acoustic paths. Thereby, the applied straight ray two-dimensional tomographic model using SIRT (simultaneous iterative reconstruction technique) is characterised as a method with small computational requirements, satisfactory convergence and stability properties as well as simple handling, especially, during online evaluation.

  1. Dynamical features and electric field strengths of double layers driven by currents. [in auroras

    NASA Technical Reports Server (NTRS)

    Singh, N.; Thiemann, H.; Schunk, R. W.

    1985-01-01

    In recent years, a number of papers have been concerned with 'ion-acoustic' double layers. In the present investigation, results from numerical simulations are presented to show that the shapes and forms of current-driven double layers evolve dynamically with the fluctuations in the current through the plasma. It is shown that double layers with a potential dip can form even without the excitation of ion-acoustic modes. Double layers in two-and one-half-dimensional simulations are discussed, taking into account the simulation technique, the spatial and temporal features of plasma, and the dynamical behavior of the parallel potential distribution. Attention is also given to double layers in one-dimensional simulations, and electrical field strengths predicted by two-and one-half-dimensional simulations.

  2. Reactivity and applications of layered silicates and layered double hydroxides.

    PubMed

    Selvam, Thangaraj; Inayat, Alexandra; Schwieger, Wilhelm

    2014-07-21

    Layered materials, such as layered sodium silicates and layered double hydroxides (LDHs), are well-known for their remarkable adsorption, intercalation and swelling properties. Their tunable interlayers offer an interesting avenue for the fabrication of pillared nanoporous materials, organic-inorganic hybrid materials and catalysts or catalyst supports. This perspective article provides a summary of the reactivity and applications of layered materials including aluminium-free layered sodium silicates (kanemite, ilerite (RUB-18 or octosilicate) and magadiite) and layered double hydroxides (LDHs). Recent developments in the use of layered sodium silicates as precursors for the preparation of various porous, functional and catalytic materials including zeolites, mesoporous materials, pillared layered silicates, organic-inorganic nanocomposites and synthesis of highly dispersed nanoparticles supported on silica are reviewed in detail. Along this perspective, we have attempted to illustrate the reactivity and transformational potential of LDHs in order to deduce the main differences and similarities between these two types of layered materials.

  3. A new hydrodynamic analysis of double layers

    NASA Technical Reports Server (NTRS)

    Hora, Heinrich

    1987-01-01

    A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic (not necessarily static) electric fields and double layers inside of plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser-produced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitous and inverted double layers in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. Results are the rotation of plasmas in magnetic fields and a new second harmonic resonance, explanation of the measured inverted double layers, explanation of the observed density-independent, second harmonics emission from laser-produced plasmas, and a laser acceleration scheme by the very high fields of the double layers.

  4. Acoustics of laminar boundary layers breakdown

    NASA Technical Reports Server (NTRS)

    Wang, Meng

    1994-01-01

    Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.

  5. Electron acceleration in stochastic double layers

    NASA Technical Reports Server (NTRS)

    Lotko, William

    1987-01-01

    Transversely localized double layers evolve randomly in turbulent regions of strongly magnetized plasma carrying current along the magnetic field. Results from numerical simulations and spacecraft observations in the auroral plasma indicate that the parallel electric field in such regions is microscopically intermittent or stochastic. The implications of stochastic double layer fields on electron acceleration will be discussed in terms of a statistical process involving ensemble averages over test particle motion. A Fokker-Planck equation can be derived for the electron phase space density, which depends on the mean and rms amplitudes of the double layers, the mean double layer density, and the initial electron velocity distribution. It is shown that the resulting electron acceleration is very sensitive to the ratio of the initial electron energy to the rms double layer amplitude. When this ratio is large, the acceleration process differs little from that expected in a dc electric field. When it is small, stochastic heating competes with directed acceleration. Evidence for both cases can be found in the auroral ionosphere in association with so-called inverted-V precipitation and collimated edge precipitation.

  6. Multi-ion Double Layers in a Magnetized Plasma

    NASA Astrophysics Data System (ADS)

    Shahmansouri, M.; Alinejad, H.; Tribeche, M.

    2015-11-01

    A theoretical investigation is carried out to study the existence, formation and basic properties of ion acoustic (IA) double layers (DLs) in a magnetized bi-ion plasma consisting of warm/cold ions and Boltzmann distributed electrons. Based on the reductive perturbation technique, an extended Korteweg de-Vries (KdV) equation is derived. The propagation of two possible modes (fast and slow), and their evolution are investigated. The effects of obliqueness, magnitude of the magnetic field, ion concentration, polarity of ions, and ion temperature on the IA DL profile are analyzed, and then the ranges of parameters for which the IA DLs exist are investigated in details.

  7. Shock waves and double layers in electron degenerate dense plasma with viscous ion fluids

    SciTech Connect

    Mamun, A. A.; Zobaer, M. S.

    2014-02-15

    The properties of ion-acoustic shock waves and double layers propagating in a viscous degenerate dense plasma (containing inertial viscous ion fluid, non-relativistic and ultra-relativistic degenerate electron fluid, and negatively charged stationary heavy element) is investigated. A new nonlinear equation (viz. Gardner equation with additional dissipative term) is derived by the reductive perturbation method. The properties of the ion-acoustic shock waves and double layers are examined by the analysis of the shock and double layer solutions of this new equation (we would like to call it “M-Z equation”). It is found that the properties of these shock and double layer structures obtained from this analysis are significantly different from those obtained from the analysis of standard Gardner or Burgers’ equation. The implications of our results to dense plasmas in astrophysical objects (e.g., non-rotating white dwarf stars) are briefly discussed.

  8. Propagating double layers in electronegative plasmas

    SciTech Connect

    Meige, A.; Plihon, N.; Hagelaar, G. J. M.; Boeuf, J.-P.; Chabert, P.; Boswell, R. W.

    2007-05-15

    Double layers have been observed to propagate from the source region to the diffusion chamber of a helicon-type reactor filled up with a low-pressure mixture of Ar/SF{sub 6} [N. Plihon et al., J. Appl. Phys. 98, 023306 (2005)]. In the present paper the most significant and new experimental results are reported. A fully self-consistent hybrid model in which the electron energy distribution function, the electron temperature, and the various source terms are calculated is developed to investigate these propagating double layers. The spontaneous formation of propagating double layers is only observed in the simulation for system in which the localized inductive heating is combined with small diameter chambers. The conditions of formation and the properties of the propagating double layers observed in the simulation are in good agreement with that of the experiment. By correlating the results of the experiment and the simulation, a formation mechanism compatible with ion two-stream instability is proposed.

  9. Double layers and double wells in arbitrary degenerate plasmas

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2016-06-01

    Using the generalized hydrodynamic model, the possibility of variety of large amplitude nonlinear excitations is examined in electron-ion plasma with arbitrary electron degeneracy considering also the ion temperature effect. A new energy-density relation is proposed for plasmas with arbitrary electron degeneracy which reduces to the classical Boltzmann and quantum Thomas-Fermi counterparts in the extreme limits. The pseudopotential method is employed to find the criteria for existence of nonlinear structures such as solitons, periodic nonlinear structures, and double-layers for different cases of adiabatic and isothermal ion fluids for a whole range of normalized electron chemical potential, η0, ranging from dilute classical to completely degenerate electron fluids. It is observed that there is a Mach-speed gap in which no large amplitude localized or periodic nonlinear excitations can propagate in the plasma under consideration. It is further revealed that the plasma under investigation supports propagation of double-wells and double-layers the chemical potential and Mach number ranges of which are studied in terms of other plasma parameters. The Mach number criteria for nonlinear waves are shown to significantly differ for cases of classical with η0 < 0 and quantum with η0 > 0 regimes. It is also shown that the localized structure propagation criteria possess significant dissimilarities for plasmas with adiabatic and isothermal ions. Current research may be generalized to study the nonlinear structures in plasma containing positrons, multiple ions with different charge states, and charged dust grains.

  10. Double layered tailorable advanced blanket insulation

    NASA Technical Reports Server (NTRS)

    Falstrup, D.

    1983-01-01

    An advanced flexible reusable surface insulation material for future space shuttle flights was investigated. A conventional fly shuttle loom with special modifications to weave an integral double layer triangular core fabric from quartz yarn was used. Two types of insulating material were inserted into the cells of the fabric, and a procedure to accomplish this was developed. The program is follow up of a program in which single layer rectangular cell core fabrics are woven and a single type of insulating material was inserted into the cells.

  11. Reversible Heating in Electric Double Layer Capacitors

    NASA Astrophysics Data System (ADS)

    Janssen, Mathijs; van Roij, René

    2017-03-01

    A detailed comparison is made between different viewpoints on reversible heating in electric double layer capacitors. We show in the limit of slow charging that a combined Poisson-Nernst-Planck and heat equation, first studied by d'Entremont and Pilon [J. Power Sources 246, 887 (2014), 10.1016/j.jpowsour.2013.08.024], recovers the temperature changes as predicted by the thermodynamic identity of Janssen et al. [Phys. Rev. Lett. 113, 268501 (2014), 10.1103/PhysRevLett.113.268501], and disagrees with the approximative model of Schiffer et al. [J. Power Sources 160, 765 (2006), 10.1016/j.jpowsour.2005.12.070] that predominates the literature. The thermal response to the adiabatic charging of supercapacitors contains information on electric double layer formation that has remained largely unexplored.

  12. Double layer capacitance of carbon foam electrodes

    SciTech Connect

    Delnick, F.M.; Ingersoll, D.; Firsich, D.

    1993-11-01

    We have evaluated a wide variety of microcellular carbon foams prepared by the controlled pyrolysis and carbonization of several polymers including: polyacrylonitrile (PAN), polymethacrylonitrile (PMAN), resorcinol/formaldehyde (RF), divinylbenzene/methacrylonitrile (DVB), phenolics (furfuryl/alcohol), and cellulose polymers such as Rayon. The porosity may be established by several processes including: Gelation (1-5), phase separation (1-3,5-8), emulsion (1,9,10), aerogel/xerogel formation (1,11,12,13), replication (14) and activation. In this report we present the complex impedance analysis and double layer charging characteristics of electrodes prepared from one of these materials for double layer capacitor applications, namely activated cellulose derived microcellular carbon foam.

  13. Double layer capacitance of carbon foam electrodes

    NASA Astrophysics Data System (ADS)

    Delnick, F. M.; Ingersoll, D.; Firsich, D.

    We have evaluated a wide variety of microcellular carbon foams prepared by the controlled pyrolysis and carbonization of several polymers including: polyacrylonitrile (PAN), polymethacrylonitrile (PMAN), resorcinol/formaldehyde (RF), divinylbenzene/methacrylonitrile (DVB), phenolics (furfuryl/alcohol), and cellulose polymers such as Rayon. The porosity may be established by several processes including: gelation (1-5), phase separation (1-3,5-8), emulsion (1,9,10), aerogel/xerogel formation (1,11,12,13), replication (14), and activation. In this report we present the complex impedance analysis and double layer charging characteristics of electrodes prepared from one of these materials for double layer capacitor applications, namely activated cellulose derived microcellular carbon foam.

  14. Double layers acting as particles accelerators

    SciTech Connect

    Sanduloviciu, M.; Lozneanu, E.

    1995-12-31

    It is shown that self-consistent stable and unstable double layers generated in plasma after a self-organisation process are able to accelerate charged particles. The implication of cosmic double layers (Dls) in the acceleration of electrical charged particles long been advocated by Alfven and his Stockholm school is today disputed by argument that static electric fields associated with Dls are conservative and consequently the line integral of the electric field outside the DL balances the line integral inside it. Related with this dispute we will evidence some, so far not considered, facts which are in our opinion arguments that aurora Dls are able to energize particles. For justifying this assertion we start from recent experimental results concerning the phenomenology of self-consistent Dls whose generation involve beside ionisations the neutrals excitations which are at tile origin of the light phenomena as those observed in auroras.

  15. Reversible Heating in Electric Double Layer Capacitors.

    PubMed

    Janssen, Mathijs; van Roij, René

    2017-03-03

    A detailed comparison is made between different viewpoints on reversible heating in electric double layer capacitors. We show in the limit of slow charging that a combined Poisson-Nernst-Planck and heat equation, first studied by d'Entremont and Pilon [J. Power Sources 246, 887 (2014)JPSODZ0378-775310.1016/j.jpowsour.2013.08.024], recovers the temperature changes as predicted by the thermodynamic identity of Janssen et al. [Phys. Rev. Lett. 113, 268501 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.268501], and disagrees with the approximative model of Schiffer et al. [J. Power Sources 160, 765 (2006)JPSODZ0378-775310.1016/j.jpowsour.2005.12.070] that predominates the literature. The thermal response to the adiabatic charging of supercapacitors contains information on electric double layer formation that has remained largely unexplored.

  16. Plasmons in spatially separated double-layer graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Bagheri, Mehran; Bahrami, Mousa

    2014-05-01

    Motivated by innovative progresses in designing multi-layer graphene nanostructured materials in the laboratory, we theoretically investigate the Dirac plasmon modes of a spatially separated double-layer graphene nanoribbon system, made up of a vertically offset armchair and metallic graphene nanoribbon pair. We find striking features of the collective excitations in this novel Coulomb correlated system, where both nanoribbons are supposed to be either intrinsic (undoped/ungated) or extrinsic (doped/gated). In the former, it is shown the low-energy acoustical and the high-energy optical plasmon modes are tunable only by the inter-ribbon charge separation. In the later, the aforementioned plasmon branches are modified by the added doping factor. As a result, our model could be useful to examine the existence of a linear Landau-undamped low-energy acoustical plasmon mode tuned via the inter-ribbon charge separation as well as doping. This study might also be utilized for devising novel quantum optical waveguides based on the Coulomb coupled graphene nanoribbons.

  17. Plasmons in spatially separated double-layer graphene nanoribbons

    SciTech Connect

    Bagheri, Mehran; Bahrami, Mousa

    2014-05-07

    Motivated by innovative progresses in designing multi-layer graphene nanostructured materials in the laboratory, we theoretically investigate the Dirac plasmon modes of a spatially separated double-layer graphene nanoribbon system, made up of a vertically offset armchair and metallic graphene nanoribbon pair. We find striking features of the collective excitations in this novel Coulomb correlated system, where both nanoribbons are supposed to be either intrinsic (undoped/ungated) or extrinsic (doped/gated). In the former, it is shown the low-energy acoustical and the high-energy optical plasmon modes are tunable only by the inter-ribbon charge separation. In the later, the aforementioned plasmon branches are modified by the added doping factor. As a result, our model could be useful to examine the existence of a linear Landau-undamped low-energy acoustical plasmon mode tuned via the inter-ribbon charge separation as well as doping. This study might also be utilized for devising novel quantum optical waveguides based on the Coulomb coupled graphene nanoribbons.

  18. Spatial and Temporal Variability of Zooplankton Thin Layers: The Effects of Composition and Orientation on Acoustic Detection of Layers

    DTIC Science & Technology

    2007-09-30

    Spatial and Temporal Variability of Zooplankton Thin Layers: The Effects of Composition and Orientation on Acoustic Detection of Layers Carin...physical and biological mechanisms of formation and maintenance of thin layers of zooplankton . Because zooplankton can be strong sound scatterers...acoustic instruments are effective at detecting and describing zooplankton thin layers. Using a combination of instruments (acoustics, image-forming

  19. Spatial and Temporal Variability of Zooplankton Thin Layers: The Effects of Composition and Orientation on Acoustic Detection of Layers

    DTIC Science & Technology

    2006-01-01

    Spatial and Temporal Variability of Zooplankton Thin Layers: The Effects of Composition and Orientation on Acoustic Detection of Layers Carin...physical and biological mechanisms of formation and maintenance of thin layers of zooplankton . Because zooplankton can be strong sound scatterers...acoustic instruments are effective at detecting and describing zooplankton thin layers. Using a combination of instruments (acoustics, image-forming

  20. An acoustic filter based on layered structure.

    PubMed

    Ma, Jianguo; Steer, Michael B; Jiang, Xiaoning

    2015-03-16

    Acoustic filters (AFs) are key components to control wave propagation in multi-frequency systems. We present a design which selectively achieves acoustic filtering with a stop band and passive amplification at the high- and low-frequencies, respectively. Measurement results from the prototypes closely match the design predictions. The AF suppresses the high frequency aliasing echo by 14.5 dB and amplifies the low frequency transmission by 8.0 dB, increasing an axial resolution from 416 to 86 μm in imaging. The AF design approach is proved to be effective in multi-frequency systems.

  1. Ultrasound acoustic metamaterials with double-negative parameters

    NASA Astrophysics Data System (ADS)

    Chen, Huaijun; Li, Hui; Zhai, Shilong; Ding, Changlin; Li, Jiamao; Luo, Chunrong; Zhao, Xiaopeng

    2016-05-01

    We experimentally demonstrate a double-negative acoustic metamaterial (AM) that combines a hollow tube and a split hollow sphere into a structurally simple perforated hollow tube with the ability to generate simultaneous resonances in water. The effective acoustic parameters extracted from the transmission and reflection coefficients confirmed that negative effective mass density and modulus were achieved from 36.68 kHz to 36.96 kHz, and the effective index was also negative in the same frequency range. In addition, further experimental measurements confirmed that the well-designed AM could realize slab focusing phenomenon. With the unique properties, the proposed AM presents potential applications in sub-wavelength imaging and medical ultrasound treatment.

  2. Acoustic scattering reduction using layers of elastic materials

    NASA Astrophysics Data System (ADS)

    Dutrion, Cécile; Simon, Frank

    2017-02-01

    Making an object invisible to acoustic waves could prove useful for military applications or measurements in confined space. Different passive methods have been proposed in recent years to avoid acoustic scattering from rigid obstacles. These techniques are exclusively based on acoustic phenomena, and use for instance multiple resonators or scatterers. This paper examines the possibility of designing an acoustic cloak using a bi-layer elastic cylindrical shell to eliminate the acoustic field scattered from a rigid cylinder hit by plane waves. This field depends on the dimensional and mechanical characteristics of the elastic layers. It is computed by a semi-analytical code modelling the vibrations of the coating under plane wave excitation. Optimization by genetic algorithm is performed to determine the characteristics of a bi-layer material minimizing the scattering. Considering an external fluid consisting of air, realistic configurations of elastic coatings emerge, composed of a thick internal orthotopic layer and a thin external isotropic layer. These coatings are shown to enable scattering reduction at a precise frequency or over a larger frequency band.

  3. Double-Diffusive Layers and Phase Transitions

    NASA Astrophysics Data System (ADS)

    Dude, Sabine; Hansen, Ulrich

    2015-04-01

    Researching the thermal evolution of the Earth's mantle on numerical base is very challenging. During the last decade different approaches are put forward in oder to understand the picture of the today's Earth's mantle. One way is to incorporate all the known features and physics (plate tectonics, phase transitions, CMB-topography, ...) into numerical models and make them as complex (or 'complete') as possible to capture Earth's mantle processes and surface signals. Another way is, to take a step back and look at less complex models which account for single processes and their interaction and evolution. With these 'simpler' models one is able look in detail into the physical processes and dependencies on certain parameters. Since the knowledge of slab stagnation in the transitions zone of the Earth's mantle the question whether the mantle is or at least has been layered to some degree is still under debate. On this basis we address two important features that lead to layered mantle convection and may affect each other and with this the thermal evolution of the mantle. It is commonly known the main mantle mineral olivine pass through various phase changes with depth [1]. Detailed numerical studies had been carried out to ascertain the influence on convective motion and planetary evolution [2]. It is still heavily discussed whether the endothermic phase change at 660km depth can lead an isolated lower mantle. Most of the numerical studies favour a model which has phases of layering that are disrupted by catastrophic events. In the last years double-diffusive convection has also been intensively studied with regard to planetary mantle evolution such as pile formation and core-mantle boundary topography [3]. However, another striking feature still posing open questions are evolving layers self-organised from a previous non layered state. Considering a chemical component that influences the density of a fluid in addition to the temperature leads to dynamical phenomena

  4. Megavolt Parallel Potentials Arising from Double-Layer Streams in the Earth's Outer Radiation Belt

    NASA Astrophysics Data System (ADS)

    Mozer, F. S.; Bale, S. D.; Bonnell, J. W.; Chaston, C. C.; Roth, I.; Wygant, J.

    2013-12-01

    Huge numbers of double layers carrying electric fields parallel to the local magnetic field line have been observed on the Van Allen probes in connection with in situ relativistic electron acceleration in the Earth’s outer radiation belt. For one case with adequate high time resolution data, 7000 double layers were observed in an interval of 1 min to produce a 230 000 V net parallel potential drop crossing the spacecraft. Lower resolution data show that this event lasted for 6 min and that more than 1 000 000 volts of net parallel potential crossed the spacecraft during this time. A double layer traverses the length of a magnetic field line in about 15 s and the orbital motion of the spacecraft perpendicular to the magnetic field was about 700 km during this 6 min interval. Thus, the instantaneous parallel potential along a single magnetic field line was the order of tens of kilovolts. Electrons on the field line might experience many such potential steps in their lifetimes to accelerate them to energies where they serve as the seed population for relativistic acceleration by coherent, large amplitude whistler mode waves. Because the double-layer speed of 3100km/s is the order of the electron acoustic speed (and not the ion acoustic speed) of a 25 eV plasma, the double layers may result from a new electron acoustic mode. Acceleration mechanisms involving double layers may also be important in planetary radiation belts such as Jupiter, Saturn, Uranus, and Neptune, in the solar corona during flares, and in astrophysical objects.

  5. Megavolt parallel potentials arising from double-layer streams in the Earth's outer radiation belt.

    PubMed

    Mozer, F S; Bale, S D; Bonnell, J W; Chaston, C C; Roth, I; Wygant, J

    2013-12-06

    Huge numbers of double layers carrying electric fields parallel to the local magnetic field line have been observed on the Van Allen probes in connection with in situ relativistic electron acceleration in the Earth's outer radiation belt. For one case with adequate high time resolution data, 7000 double layers were observed in an interval of 1 min to produce a 230,000 V net parallel potential drop crossing the spacecraft. Lower resolution data show that this event lasted for 6 min and that more than 1,000,000 volts of net parallel potential crossed the spacecraft during this time. A double layer traverses the length of a magnetic field line in about 15 s and the orbital motion of the spacecraft perpendicular to the magnetic field was about 700 km during this 6 min interval. Thus, the instantaneous parallel potential along a single magnetic field line was the order of tens of kilovolts. Electrons on the field line might experience many such potential steps in their lifetimes to accelerate them to energies where they serve as the seed population for relativistic acceleration by coherent, large amplitude whistler mode waves. Because the double-layer speed of 3100  km/s is the order of the electron acoustic speed (and not the ion acoustic speed) of a 25 eV plasma, the double layers may result from a new electron acoustic mode. Acceleration mechanisms involving double layers may also be important in planetary radiation belts such as Jupiter, Saturn, Uranus, and Neptune, in the solar corona during flares, and in astrophysical objects.

  6. Receptivity of Supersonic Boundary Layers to Acoustic Disturbances

    NASA Technical Reports Server (NTRS)

    Malik, Mujeeb R.; Balakumar, P.

    2005-01-01

    Boundary layer receptivity to two-dimensional slow and fast acoustic waves is investigated by solving Navier-Stokes equations for Mach 4.5 flow over a flat plate with a finite-thickness leading edge. Higher order spatial and temporal schemes are employed to obtain the solution whereby the flat-plate leading edge region is resolved by providing a sufficiently refined grid. The results show that the instability waves are generated in the leading edge region and that the boundary-layer is much more receptive to slow acoustic waves (by almost a factor of 20) as compared to the fast waves. Hence, this leading-edge receptivity mechanism is expected to be more relevant in the transition process for high Mach number flows. The effect of acoustic wave incidence angle is also studied and it is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases by more than a factor of 4 when the incidence angle is increased from 0 to 45 deg. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The effect of leading-edge thickness is also studied and bluntness is found to stabilize the boundary layer. The relative significance of fast acoustic waves is enhanced in the presence of bluntness.

  7. Acoustic contributions of a sound absorbing blanket placed in a double panel structure: absorption versus transmission.

    PubMed

    Doutres, Olivier; Atalla, Noureddine

    2010-08-01

    The objective of this paper is to propose a simple tool to estimate the absorption vs. transmission loss contributions of a multilayered blanket unbounded in a double panel structure and thus guide its optimization. The normal incidence airborne sound transmission loss of the double panel structure, without structure-borne connections, is written in terms of three main contributions; (i) sound transmission loss of the panels, (ii) sound transmission loss of the blanket and (iii) sound absorption due to multiple reflections inside the cavity. The method is applied to four different blankets frequently used in automotive and aeronautic applications: a non-symmetric multilayer made of a screen in sandwich between two porous layers and three symmetric porous layers having different pore geometries. It is shown that the absorption behavior of the blanket controls the acoustic behavior of the treatment at low and medium frequencies and its transmission loss at high frequencies. Acoustic treatment having poor sound absorption behavior can affect the performance of the double panel structure.

  8. Reflection and transmission of acoustic waves from a moving layer

    NASA Technical Reports Server (NTRS)

    Steinmetz, G. G.; Singh, J. J.

    1972-01-01

    The refraction of acoustic waves by a moving medium layer is theoretically treated and the expressions for reflection and transmission coefficients are determined. The moving medium layer velocity is assumed to have a space dependence in one direction. A partitioning of the moving medium layer into constant-velocity sublayers is introduced and the number of sublayers is allowed to increase until the reflection and transmission coefficients converage to their respective values. Numerical results for several sublayer approximations of Poiseuille's flow are presented as functions of the moving layer velocity for several angles of incidence of the acoustic wave. The degenerate case of single constant-velocity layer is also treated, both theoretically and by a numerical analysis.

  9. Large amplitude double layers in a positively charged dusty plasma with nonthermal electrons

    SciTech Connect

    Djebli, M.; Marif, H.

    2009-06-15

    A pseudopotential approach is used to investigate large amplitude dust-acoustic solitary structures for a plasma composed of positively charged dust, cold electrons, and nonthermal hot electrons. Numerical investigation for an adiabatic situation is conducted to examine the existence region of the wave. The negative potential of the double layers is found to be dependent on nonthermal parameters, Mach number, and electrons temperature. A range of the nonthermal parameters values exists for which two possible double layers for the same plasma mix at different Mach numbers and with significant different amplitudes. The present model is used to investigate localized structures in the lower-altitude Earth's ionosphere.

  10. Electric fields and double layers in plasmas

    NASA Astrophysics Data System (ADS)

    Singh, Nagendra; Thiemann, H.; Schunk, R. W.

    1987-05-01

    Various mechanisms for driving double layers (DLs) in plasmas are described, including applied potential drops, currents, contact potentials, and plasma expansions. Somne dynamic features of the DLs are discussed; and it is demonstrated that DLs and the currents through them undergo slow oscillations, determined by the ion transit time across an effective length of the system in which the DLs form. It is shown that a localized potential dip forms at the low potential end of a DL, which interrupts the electron current through it according to the Langmuir criterion whenever the ion flux into the DL is disrupted. Also considered is the generation of electric fields perpendicular to the ambient magnetic field by contact potentials.

  11. Low temperature double-layer capacitors

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J. (Inventor); Smart, Marshall C. (Inventor); West, William C. (Inventor)

    2011-01-01

    Double-layer capacitors capable of operating at extremely low temperatures (e.g., as low as -75.degree. C.) are disclosed. Electrolyte solutions combining a base solvent (e.g., acetonitrile) and a cosolvent are employed to lower the melting point of the base electrolyte. Example cosolvents include methyl formate, ethyl acetate, methyl acetate, propionitrile, butyronitrile, and 1,3-dioxolane. An optimized concentration (e.g., 0.10 M to 0.75 M) of salt, such as tetraethylammonium tetrafluoroborate, is dissolved into the electrolyte solution. In some cases (e.g., 1,3-dioxolane cosolvent) additives, such as 2% by volume triethylamine, may be included in the solvent mixture to prevent polymerization of the solution. Conventional device form factors and structural elements (e.g., porous carbon electrodes and a polyethylene separator) may be employed.

  12. Optical and Electrical Characteristics of Graphene Double Layer Formed by a Double Transfer of Graphene Single Layers.

    PubMed

    Kim, Young Jun; Bae, Gi Yoon; Chun, Sungwoo; Park, Wanjun

    2016-03-01

    We demonstrate formation of double layer graphene by means of a double transfer using two single graphene layers grown by a chemical vapor deposition method. It is observed that shiftiness and broadness in the double-resonance of Raman scattering are much weaker than those of bilayer graphene formed naturally. Transport characteristics examined from transmission line measurements and field effect transistors show the similar behavior with those of single layer graphene. It indicates that interlayer separation, in electrical view, is large enough to avoid correlation between layers for the double layer structure. It is also observed from a transistor with the double layer graphene that molecules adsorpted on two inner graphene surfaces in the double layered structure are isolated and conserved from ambient environment.

  13. Receptivity of Hypersonic Boundary Layers to Acoustic and Vortical Disturbances

    NASA Technical Reports Server (NTRS)

    Balakamar, P.; Kegerise, Michael A.

    2011-01-01

    Boundary layer receptivity to two-dimensional acoustic disturbances at different incidence angles and to vortical disturbances is investigated by solving the Navier-Stokes equations for Mach 6 flow over a 7deg half-angle sharp-tipped wedge and a cone. Higher order spatial and temporal schemes are employed to obtain the solution. The results show that the instability waves are generated in the leading edge region and that the boundary layer is much more receptive to slow acoustic waves as compared to the fast waves. It is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases when the incidence angle is increased from 0 to 30 degrees. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The maximum receptivity is obtained when the wave incident angle is about 20 degrees. Vortical disturbances also generate unstable second modes, however the receptivity coefficients are smaller than that for the acoustic waves. Vortical disturbances first generate the fast acoustic modes and they switch to the slow mode near the continuous spectrum.

  14. Transition from moving to stationary double layers in a single-ended Q machine

    NASA Technical Reports Server (NTRS)

    Song, Bin; Merlino, R. L.; D'Angelo, N.

    1990-01-01

    Large-amplitude (less than about 100 percent) relaxation oscillations in the plasma potential are known to be generated when the cold endplate of a single-ended Q machine is biased positively. These oscillations are associated with double layers that form near the hot plate (plasma source) and travel toward the endplate at about the ion-acoustic velocity. At the endplate they dissolve and then form again near the hot plate, the entire process repeating itself in a regular manner. By admitting a sufficient amount of neutral gas into the system, the moving double layers were slowed down and eventually stopped. The production of stationary double layers requires an ion source on the high-potential side of the double layers. These ions are provided by ionization of the neutral gas by electrons that are accelerated through the double layer. The dependence of the critical neutral gas pressure required for stationary double-layer formation on endplate voltage, magnetic field strength, and neutral atom mass has been examined. These results are discussed in terms of a simple model of ion production and loss, including ion losses across the magnetic field.

  15. Vibro-acoustic modelling of aircraft double-walls with structural links using Statistical Energy Analysis

    NASA Astrophysics Data System (ADS)

    Campolina, Bruno L.

    The prediction of aircraft interior noise involves the vibroacoustic modelling of the fuselage with noise control treatments. This structure is composed of a stiffened metallic or composite panel, lined with a thermal and acoustic insulation layer (glass wool), and structurally connected via vibration isolators to a commercial lining panel (trim). The goal of this work aims at tailoring the noise control treatments taking design constraints such as weight and space optimization into account. For this purpose, a representative aircraft double-wall is modelled using the Statistical Energy Analysis (SEA) method. Laboratory excitations such as diffuse acoustic field and point force are addressed and trends are derived for applications under in-flight conditions, considering turbulent boundary layer excitation. The effect of the porous layer compression is firstly addressed. In aeronautical applications, compression can result from the installation of equipment and cables. It is studied analytically and experimentally, using a single panel and a fibrous uniformly compressed over 100% of its surface. When compression increases, a degradation of the transmission loss up to 5 dB for a 50% compression of the porous thickness is observed mainly in the mid-frequency range (around 800 Hz). However, for realistic cases, the effect should be reduced since the compression rate is lower and compression occurs locally. Then the transmission through structural connections between panels is addressed using a four-pole approach that links the force-velocity pair at each side of the connection. The modelling integrates experimental dynamic stiffness of isolators, derived using an adapted test rig. The structural transmission is then experimentally validated and included in the double-wall SEA model as an equivalent coupling loss factor (CLF) between panels. The tested structures being flat, only axial transmission is addressed. Finally, the dominant sound transmission paths are

  16. Pd/Ni-WO3 anodic double layer gasochromic device

    DOEpatents

    Lee, Se-Hee; Tracy, C. Edwin; Pitts, J. Roland; Liu, Ping

    2004-04-20

    An anodic double layer gasochromic sensor structure for optical detection of hydrogen in improved response time and with improved optical absorption real time constants, comprising: a glass substrate; a tungsten-doped nickel oxide layer coated on the glass substrate; and a palladium layer coated on the tungsten-doped nickel oxide layer.

  17. Coronal electron confinement by double layers

    SciTech Connect

    Li, T. C.; Drake, J. F.; Swisdak, M.

    2013-12-01

    In observations of flare-heated electrons in the solar corona, a longstanding problem is the unexplained prolonged lifetime of the electrons compared to their transit time across the source. This suggests confinement. Recent particle-in-cell (PIC) simulations, which explored the transport of pre-accelerated hot electrons through ambient cold plasma, showed that the formation of a highly localized electrostatic potential drop, in the form of a double layer (DL), significantly inhibited the transport of hot electrons. The effectiveness of confinement by a DL is linked to the strength of the DL as defined by its potential drop. In this work, we investigate the scaling of the DL strength with the hot electron temperature by PIC simulations and find a linear scaling. We demonstrate that the strength is limited by the formation of parallel shocks. Based on this, we analytically determine the maximum DL strength, and also find a linear scaling with the hot electron temperature. The DL strength obtained from the analytic calculation is comparable to that from the simulations. At the maximum strength, the DL is capable of confining a significant fraction of hot electrons in the source.

  18. Discharge rates of porous carbon double layer capacitors

    SciTech Connect

    Eisenmann, E.T.

    1995-10-01

    Double layer capacitors with porous carbon electrodes have very low frequency response limits and correspondingly low charge-discharge rates. Impedance measurements of various commercial double layer capacitors and of carbon electrodes prepared from selected precursor materials were found to yield similar, yet subtly different characteristics. Through modeling with the traditional transmission line equivalent circuit for porous electrodes, a resistive layer can be identified, which forms on carbon films during carbonization and survives the activation procedure. A method for determining the power-to-energy ratio of electrochemical capacitors has been developed. These findings help define new ways for optimizing the properties of double layer capacitors.

  19. Numerical Comparison of Active Acoustic and Structural Noise Control in a Stiffened Double Wall Cylinder

    NASA Technical Reports Server (NTRS)

    Grosveld, Ferdinand W.

    1996-01-01

    The active acoustic and structural noise control characteristics of a double wall cylinder with and without ring stiffeners were numerically evaluated. An exterior monopole was assumed to acoustically excite the outside of the double wall cylinder at an acoustic cavity resonance frequency. Structural modal vibration properties of the inner and outer shells were analyzed by post-processing the results from a finite element analysis. A boundary element approach was used to calculate the acoustic cavity response and the coupled structural-acoustic interaction. In the frequency region of interest, below 500 Hz, all structural resonant modes were found to be acoustically slow and the nonresonant modal response to be dominant. Active sound transmission control was achieved by control forces applied to the inner or outer shell, or acoustic control monopoles placed just outside the inner or outer shell. A least mean square technique was used to minimize the interior sound pressures at the nodes of a data recovery mesh. Results showed that single acoustic control monopoles placed just outside the inner or outer shells resulted in better sound transmission control than six distributed point forces applied to either one of the shells. Adding stiffeners to the double wall structure constrained the modal vibrations of the shells, making the double wall stiffer with associated higher modal frequencies. Active noise control obtained for the stiffened double wall configurations was less than for the unstiffened cylinder. In all cases, the acoustic control monopoles controlled the sound transmission into the interior better than the structural control forces.

  20. Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis.

    PubMed

    Song, Fang; Hu, Xile

    2014-07-17

    The oxygen evolution reaction is a key reaction in water splitting. The common approach in the development of oxygen evolution catalysts is to search for catalytic materials with new and optimized chemical compositions and structures. Here we report an orthogonal approach to improve the activity of catalysts without alternating their compositions or structures. Specifically, liquid phase exfoliation is applied to enhance the oxygen evolution activity of layered double hydroxides. The exfoliated single-layer nanosheets exhibit significantly higher oxygen evolution activity than the corresponding bulk layered double hydroxides in alkaline conditions. The nanosheets from nickel iron and nickel cobalt layered double hydroxides outperform a commercial iridium dioxide catalyst in both activity and stability. The exfoliation creates more active sites and improves the electronic conductivity. This work demonstrates the promising catalytic activity of single-layered double hydroxides for the oxygen evolution reaction.

  1. Challenges facing lithium batteries and electrical double-layer capacitors.

    PubMed

    Choi, Nam-Soon; Chen, Zonghai; Freunberger, Stefan A; Ji, Xiulei; Sun, Yang-Kook; Amine, Khalil; Yushin, Gleb; Nazar, Linda F; Cho, Jaephil; Bruce, Peter G

    2012-10-01

    Energy-storage technologies, including electrical double-layer capacitors and rechargeable batteries, have attracted significant attention for applications in portable electronic devices, electric vehicles, bulk electricity storage at power stations, and "load leveling" of renewable sources, such as solar energy and wind power. Transforming lithium batteries and electric double-layer capacitors requires a step change in the science underpinning these devices, including the discovery of new materials, new electrochemistry, and an increased understanding of the processes on which the devices depend. The Review will consider some of the current scientific issues underpinning lithium batteries and electric double-layer capacitors.

  2. Double-peaked sodium layers at high latitudes

    NASA Technical Reports Server (NTRS)

    Von Zahn, U.; Goldberg, R. A.; Stegman, J.; Witt, G.

    1989-01-01

    Na lidar observations indicate that at high latitudes in summer the neutral Na layer frequently attains a double-peaked structure. The main layer with a maximum near 90 km altitude is supplemented by a secondary, narrow layer near 95 km altitude. Results are presented concerning secondary sodium layers. It appears likely that the formation of secondary Na layers observed frequently above the lidar site is not solely a 'sodium phenomenon', but part of a more comprehensive layering process for metal atoms and ions. Na(+)/Na density ratios close to 0.5 near the peaks of both the main and secondary layers are derived.

  3. Superior coagulation of graphene oxides on nanoscale layered double hydroxides and layered double oxides.

    PubMed

    Zou, Yidong; Wang, Xiangxue; Chen, Zhongshan; Yao, Wen; Ai, Yuejie; Liu, Yunhai; Hayat, Tasawar; Alsaedi, Ahmed; Alharbi, Njud S; Wang, Xiangke

    2016-12-01

    With the development and application of graphene oxides (GO), the potential toxicity and environmental behavior of GO has become one of the most forefront environmental problems. Herein, a novel nanoscale layered double hydroxides (glycerinum-modified nanocrystallined Mg/Al layered double hydroxides, LDH-Gl), layered double oxides (calcined LDH-Gl, LDO-Gl) and metallic oxide (TiO2) were synthesized and applied as superior coagulants for the efficient removal of GO from aqueous solutions. Coagulation of GO as a function of coagulant contents, pH, ionic strength, GO contents, temperature and co-existing ions were studied and compared, and the results showed that the maximum coagulation capacities of GO were LDO-Gl (448.3 mg g(-1)) > TiO2 (365.7 mg g(-1)) > LDH-Gl (339.1 mg g(-1)) at pH 5.5, which were significantly higher than those of bentonite, Al2O3, CaCl2 or other natural materials due to their stronger reaction active and interfacial effect. The presence of SO3(2-) and HCO3(-) inhibited the coagulation of GO on LDH-Gl and LDO-Gl significantly, while other cations (K(+), Mg(2+), Ca(2+), Ni(2+), Al(3+)) or anion (Cl(-)) had slightly effect on GO coagulation. The interaction mechanism of GO coagulation on LDO-Gl and TiO2 might due to the electrostatic interactions and strong surface complexation, while the main driving force of GO coagulation on LDH-Gl might be attributed to electrostatic interaction and hydrogen bond, which were further evidenced by TEM, SEM, FT-IR and XRD analysis. The results of natural environmental simulation showed that LDO-Gl, TiO2 or other kinds of natural metallic oxides could be superior coagulants for the efficient elimination of GO or other toxic nanomaterials from aqueous solutions in real environmental pollution cleanup.

  4. Enhanced intervalley scattering in artificially stacked double-layer graphene

    NASA Astrophysics Data System (ADS)

    Iqbal, M. Z.; Kelekçi, Özgür; Iqbal, M. W.; Jin, Xiaozhan; Hwang, Chanyong; Eom, Jonghwa

    2014-08-01

    We fabricated artificially stacked double-layer graphene by sequentially transferring graphene grown by chemical vapor deposition. The double-layer graphene was characterized by Raman spectroscopy and transport measurements. A weak localization effect was observed for different charge carrier densities and temperatures. The obtained intervalley scattering rate was unusually high compared to normal Bernal-stacked bilayer or single-layer graphene. The sharp point defects, local deformation, or bending of graphene plane required for intervalley scattering from one Dirac cone to another seemed to be enhanced by the artificially stacked graphene layers.

  5. On The Chaotic Dynamics Of Multiple Double Layers In Plasma

    SciTech Connect

    Ivan, L. M.; Chiriac, S. A.; Aflori, M.; Dimitriu, D. G.

    2007-04-23

    When a multiple double layers structure in plasma is driven far from equilibrium, it passes into a chaotic state, characterized by uncorrelated oscillations of the plasma parameters. Two scenarios of transition to chaos were identified: the Feigenbaum scenario (cascade of period doubling bifurcations) and the intermittency scenario.

  6. Layered double hydroxide stability. 1. Relative stabilities of layered double hydroxides and their simple counterparts

    NASA Technical Reports Server (NTRS)

    Boclair, J. W.; Braterman, P. S.

    1999-01-01

    Solutions containing di- and trivalent metal chlorides [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+; M(III) = Al3+, Fe3+] were titrated with NaOH to yield hydrotalcite-like layered double hydroxides (LDH), [[M(II)]1-x[M(III)]x(OH)2][Cl]x yH2O, by way of M(III) hydroxide/hydrous oxide intermediates. Analysis of the resultant titration curves yields nominal solubility constants for the LDH. The corresponding LDH stabilities are in the order Mg < Mn < Co approximately Ni < Zn for M(II) and Al < Fe for M(III). The stability of LDH relative to the separate metal hydroxides/hydrous oxides is discussed.

  7. THz Acoustic Spectroscopy by using Double Quantum Wells and Ultrafast Optical Spectroscopy

    PubMed Central

    Wei, Fan Jun; Yeh, Yu-Hsiang; Sheu, Jinn-Kong; Lin, Kung-Hsuan

    2016-01-01

    GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, but its THz phonon properties have not been experimentally and comprehensively studied. In this report, we demonstrate how to use double quantum wells as a THz acoustic transducer for measuring generated acoustic phonons and deriving a broadband acoustic spectrum with continuous frequencies. We experimentally investigated the sub-THz frequency dependence of acoustic attenuation (i.e., phonon mean-free paths) in GaN, in addition to its physical origins such as anharmonic scattering, defect scattering, and boundary scattering. A new upper limit of attenuation caused by anharmonic scattering, which is lower than previously reported values, was obtained. Our results should be noteworthy for THz acoustic spectroscopy and for gaining a fundamental understanding of heat conduction. PMID:27346494

  8. Acoustic signature reduction using feedback of piezoelectric layers

    NASA Astrophysics Data System (ADS)

    Hamberg, Johan; Malmgren, Anders

    2000-06-01

    The possibilities of using dynamic feedback of piezoelectric layers for controlling the acoustic properties of a surface are investigated. The investigation shows that in principle it is possible to achieve desired properties (e.g. no reflection, artificial transparency or simultaneous transmission and reception of information) using a single piezo-electric layer. The layer then operates both as a sensor and as an actuator. This approach can be described as controlling the boundary conditions of the acoustic field. The study shows that this will work well, also in practice, if the material has an electromechanic coupling factor that is large enough. Explicit controllers for these cases are given. However, for the values of electro-mechanic coupling factors of available materials, the above construction is not suitable for practical purposes, due to non-robustness. Therefore, the possibility of using multiple layers is also investigated. It turns out that a two layer construction can achieve the properties of a single layer with large electro-mechanic coupling factor. For the specific problem of achieving no reflection, an explicit construction of a realistic controller is given. Requirements of robust stability and limited voltage amplitudes imply that low reflection cannot be achieved at low and high frequencies. However for a large frequency interval, it is possible to obtain low reflection. It is shown that both the gain and phase margins are infinite with this controller. Our work makes extensive use of the Redheffer star-product for systematic modeling, analysis and synthesis of the system and the regulator.

  9. Fabrication of double layer optical tissue phantom by spin coating method: mimicking epidermal and dermal layer

    NASA Astrophysics Data System (ADS)

    Park, Jihoon; Bae, Yunjin; Bae, Youngwoo; Kang, Heesung; Lee, Kyoung-Joung; Jung, Byungjo

    2013-02-01

    Methodologies to fabricate a solid optical tissue phantom (OTP) mimicking epidermal thin-layer have been developed for in vitro human skin experiment. However, there are cumbersome and time-consuming efforts in fabrication process such as a custom-made casting and calculation of solvent volume before curing process. In a previous study, we introduced a new methodology based on spin coating method (SCM) which is utilized to fabricate a thin-layer OTP analogous to epidermal thickness. In this study, a double layer solid OTP which has epidermal and dermal layers was fabricated to mimic the morphological and optical similarity of human tissue. The structural characteristic and optical properties of fabricated double layer OTP were measured using optical coherence tomography and inverse adding doubling algorithms, respectively. It is expected that the new methodology based on the SCM may be usefully used in the fabrication of double layer OTP.

  10. Strong double-layer formation by shock waves in nonequilibrium plasmas.

    PubMed

    Bletzinger, P; Ganguly, B N; Garscadden, A

    2003-04-01

    Strong double-layer formation by acoustic shock wave (double layers maintained by the traveling shock front.

  11. Multilabel Image Annotation Based on Double-Layer PLSA Model

    PubMed Central

    Zhang, Jing; Li, Da; Hu, Weiwei; Chen, Zhihua; Yuan, Yubo

    2014-01-01

    Due to the semantic gap between visual features and semantic concepts, automatic image annotation has become a difficult issue in computer vision recently. We propose a new image multilabel annotation method based on double-layer probabilistic latent semantic analysis (PLSA) in this paper. The new double-layer PLSA model is constructed to bridge the low-level visual features and high-level semantic concepts of images for effective image understanding. The low-level features of images are represented as visual words by Bag-of-Words model; latent semantic topics are obtained by the first layer PLSA from two aspects of visual and texture, respectively. Furthermore, we adopt the second layer PLSA to fuse the visual and texture latent semantic topics and achieve a top-layer latent semantic topic. By the double-layer PLSA, the relationships between visual features and semantic concepts of images are established, and we can predict the labels of new images by their low-level features. Experimental results demonstrate that our automatic image annotation model based on double-layer PLSA can achieve promising performance for labeling and outperform previous methods on standard Corel dataset. PMID:24999490

  12. Capacitance of carbon-based electrical double-layer capacitors.

    PubMed

    Ji, Hengxing; Zhao, Xin; Qiao, Zhenhua; Jung, Jeil; Zhu, Yanwu; Lu, Yalin; Zhang, Li Li; MacDonald, Allan H; Ruoff, Rodney S

    2014-01-01

    Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.

  13. Capacitance of carbon-based electrical double-layer capacitors

    NASA Astrophysics Data System (ADS)

    Ji, Hengxing; Zhao, Xin; Qiao, Zhenhua; Jung, Jeil; Zhu, Yanwu; Lu, Yalin; Zhang, Li Li; MacDonald, Allan H.; Ruoff, Rodney S.

    2014-02-01

    Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.

  14. Study of acoustic field modulation in the regenerator by double loudspeakers method.

    PubMed

    Zhou, Lihua; Xie, Xiujuan; Li, Qing

    2011-11-01

    A model to modulate acoustic field in a regenerator of a thermoacoustic system by the double loudspeakers method is presented in this paper. The equations are derived for acoustic field modulation. They represent the relations among acoustic field (complex pressure p(0), complex velocity u(0), and acoustic impedance Z(0)), driving parameters of loudspeakers (voltage amplitude and its phase difference), and operating parameters involved in a matrix H (frequency, temperature of regenerator). The range of acoustic field is adjustable and limited by the maximal driving voltages of loudspeakers according to driving parameters. The range is simulated and analyzed in the amplitude-phase and complex coordinate planes for a given or variable H. The simulated results indicate that the range has its intrinsic characteristics. The expected acoustic field in a regenerator can be obtained feasibly by the modulation.

  15. Gas flows through double-layer membrane of thermomolecular pump

    NASA Astrophysics Data System (ADS)

    Oscar, Friedlander; Yuriy, Nikolskiy; Ivan, Voronich

    2014-12-01

    The results of numerical and experimental modeling of the flows in double-layer permeable membranes are presented. One of the layers, the thick one, is the supporting layer in which the perforation diameter is larger than that in the thin layer. Across one or both layers the temperature differences were created. The calculations of the flows inside the perforated channels and additional drag of the channels in the membrane thick layer were carried out with the Stokes equations and with the kinetic boundary conditions across the membrane thin layer. In the experimental research of the thermomolecular pressure difference the thermoelectric effect (the Peltier effect) was used for creating the temperature difference between the membrane layer surfaces.

  16. Passive hypervelocity boundary layer control using an acoustically absortive surface

    NASA Astrophysics Data System (ADS)

    Rasheed, Adam

    A series of exploratory boundary layer transition experiments was performed on a sharp 5.06 degree half-angle round cone at zero angle-of-attack in the T5 Hypervelocity Shock Tunnel in order to test a novel hypersonic boundary layer control scheme. Recently performed linear stability analyses suggested that transition could be delayed in hypersonic boundary layers by using an ultrasonically absorptive surface that would damp the second mode (Mack mode). The cone used in the experiments was constructed with a smooth surface on half the cone (to serve as a control) and an acoustically absorptive porous surface on the other half. It was instrumented with flush-mounted thermocouples to detect the transition location. Test gases investigated included nitrogen and carbon dioxide at M = 5 with specific reservoir enthalpy ranging from 1.3 MJ/kg to 13.0 MJ/kg and reservoir pressure ranging from 9.0 MPa to 50.0 MPa. Detailed comparisons were performed to insure that previous results obtained in similar boundary layer transition experiments (on a regular smooth surface) were reproduced and the results were extended to examine the effects of the porous surface. These experiments indicated that the porous surface was highly effective in delaying transition provided that the hole size was significantly smaller than the viscous length scale.

  17. A Potential Role of Double Layers on Solar Wind Acceleration

    NASA Astrophysics Data System (ADS)

    Parks, G. K.; McCarthy, M.; Lee, E.; Hong, J.

    2012-12-01

    The distribution function of solar wind (SW) is non-Maxwellian and often includes field-aligned beams. Recently, electrostatic solitary waves (ESW) have been observed in the SW and they have been interpreted as double layers. Taking a cue from Earth's auroral observations that large-scale electric field parallel to magnetic field may be due to many double layers distributed along the geomagnetic field, we have looked at the potential role double layers could play in SW acceleration. This picture would suggest that the halo component of the SW represents a beam that has been accelerated by parallel electric field. The core electrons come from secondaries produced by the beam going through the solar coronal atmosphere. The source of the super-halo component is not known and we speculate that it could represent the field-aligned non-thermal high-energy halo electrons that have been accelerated to ``runaway" energies.

  18. A review of molecular modelling of electric double layer capacitors.

    PubMed

    Burt, Ryan; Birkett, Greg; Zhao, X S

    2014-04-14

    Electric double-layer capacitors are a family of electrochemical energy storage devices that offer a number of advantages, such as high power density and long cyclability. In recent years, research and development of electric double-layer capacitor technology has been growing rapidly, in response to the increasing demand for energy storage devices from emerging industries, such as hybrid and electric vehicles, renewable energy, and smart grid management. The past few years have witnessed a number of significant research breakthroughs in terms of novel electrodes, new electrolytes, and fabrication of devices, thanks to the discovery of innovative materials (e.g. graphene, carbide-derived carbon, and templated carbon) and the availability of advanced experimental and computational tools. However, some experimental observations could not be clearly understood and interpreted due to limitations of traditional theories, some of which were developed more than one hundred years ago. This has led to significant research efforts in computational simulation and modelling, aimed at developing new theories, or improving the existing ones to help interpret experimental results. This review article provides a summary of research progress in molecular modelling of the physical phenomena taking place in electric double-layer capacitors. An introduction to electric double-layer capacitors and their applications, alongside a brief description of electric double layer theories, is presented first. Second, molecular modelling of ion behaviours of various electrolytes interacting with electrodes under different conditions is reviewed. Finally, key conclusions and outlooks are given. Simulations on comparing electric double-layer structure at planar and porous electrode surfaces under equilibrium conditions have revealed significant structural differences between the two electrode types, and porous electrodes have been shown to store charge more efficiently. Accurate electrolyte and

  19. Mass sensitivity of layered shear-horizontal surface acoustic wave devices for sensing applications

    NASA Astrophysics Data System (ADS)

    Kalantar-Zadeh, Kourosh; Trinchi, Adrian; Wlodarski, Wojtek; Holland, Anthony; Galatsis, Kosmas

    2001-11-01

    Layered Surface Acoustic Wave (SAW) devices that allow the propagation of Love mode acoustic waves will be studied in this paper. In these devices, the substrate allows the propagation of Surface Skimming Bulks Waves (SSBWs). By depositing layers, that the speed of Shear Horizontal (SH) acoustic wave propagation is less than that of the substrate, the propagation mode transforms to Love mode. Love mode devices which will be studied in this paper, have SiO2 and ZnO acoustic guiding layers. As Love mode of propagation has no movement of particles component normal to the active sensor surface, they can be employed for the sensing applications in the liquid media.

  20. Double-layered cell transfer technology for bone regeneration

    PubMed Central

    Akazawa, Keiko; Iwasaki, Kengo; Nagata, Mizuki; Yokoyama, Naoki; Ayame, Hirohito; Yamaki, Kazumasa; Tanaka, Yuichi; Honda, Izumi; Morioka, Chikako; Kimura, Tsuyoshi; Komaki, Motohiro; Kishida, Akio; Izumi, Yuichi; Morita, Ikuo

    2016-01-01

    For cell-based medicine, to mimic in vivo cellular localization, various tissue engineering approaches have been studied to obtain a desirable arrangement of cells on scaffold materials. We have developed a novel method of cell manipulation called “cell transfer technology”, enabling the transfer of cultured cells onto scaffold materials, and controlling cell topology. Here we show that using this technique, two different cell types can be transferred onto a scaffold surface as stable double layers or in patterned arrangements. Various combinations of adherent cells were transferred to a scaffold, amniotic membrane, in overlapping bilayers (double-layered cell transfer), and transferred cells showed stability upon deformations of the material including folding and trimming. Transplantation of mesenchymal stem cells from periodontal ligaments (PDLSC) and osteoblasts, using double-layered cell transfer significantly enhanced bone formation, when compared to single cell type transplantation. Our findings suggest that this double-layer cell transfer is useful to produce a cell transplantation material that can bear two cell layers. Moreover, the transplantation of an amniotic membrane with PDLSCs/osteoblasts by cell transfer technology has therapeutic potential for bone defects. We conclude that cell transfer technology provides a novel and unique cell transplantation method for bone regeneration. PMID:27624174

  1. Insights from theory and simulation on the electrical double layer.

    PubMed

    Henderson, Douglas; Boda, Dezso

    2009-05-28

    Despite the fact that our conceptual understanding of the electrical double layer has advanced during the past few decades, the interpretation of experimental and applied work is still largely based on the venerable Poisson-Boltzmann theory of Gouy, Chapman and Stern. This is understandable since this theory is simple and analytic. However, it is not very accurate because the atomic/molecular nature of the ions/solvent and their correlations are ignored. Simulation and some theoretical studies by ourselves and others that have advanced our understanding are discussed. These studies show that the GCS theory predicts a narrow double layer with monotonic profiles. This is not correct. The double layer is wider, and there can be substantial layering that would be even more pronounced if explicit solvent molecules are considered. For many years, experimental studies of the double layer have been directed to the use of electrochemistry as an analytical tool. This is acceptable for analytic chemistry studies. However, the understanding of electrochemical reactions that typically occur at the electrode surface, where simulation and theory indicate that the GCS theory can have substantial errors, requires modern approaches. New, fundamental experimental studies that would lead to deeper insights using more novel systems would be desirable. Further, biophysics is an interesting field. Recent studies of the selectivity of ion channels and of the adsorption of ions in a binding sites of a protein have shown that the linearized GCS theory has substantial errors.

  2. Acoustic Radiation From a Mach 14 Turbulent Boundary Layer

    NASA Technical Reports Server (NTRS)

    Zhang, Chao; Duan, Lian; Choudhari, Meelan M.

    2016-01-01

    Direct numerical simulations (DNS) are used to examine the turbulence statistics and the radiation field generated by a high-speed turbulent boundary layer with a nominal freestream Mach number of 14 and wall temperature of 0:18 times the recovery temperature. The flow conditions fall within the range of nozzle exit conditions of the Arnold Engineering Development Center (AEDC) Hypervelocity Tunnel No. 9 facility. The streamwise domain size is approximately 200 times the boundary-layer thickness at the inlet, with a useful range of Reynolds number corresponding to Re 450 ?? 650. Consistent with previous studies of turbulent boundary layer at high Mach numbers, the weak compressibility hypothesis for turbulent boundary layers remains applicable under this flow condition and the computational results confirm the validity of both the van Driest transformation and Morkovin's scaling. The Reynolds analogy is valid at the surface; the RMS of fluctuations in the surface pressure, wall shear stress, and heat flux is 24%, 53%, and 67% of the surface mean, respectively. The magnitude and dominant frequency of pressure fluctuations are found to vary dramatically within the inner layer (z/delta 0.< or approx. 0.08 or z+ < or approx. 50). The peak of the pre-multiplied frequency spectrum of the pressure fluctuation is f(delta)/U(sub infinity) approx. 2.1 at the surface and shifts to a lower frequency of f(delta)/U(sub infinity) approx. 0.7 in the free stream where the pressure signal is predominantly acoustic. The dominant frequency of the pressure spectrum shows a significant dependence on the freestream Mach number both at the wall and in the free stream.

  3. Double-Capon and double-MUSICAL for arrival separation and observable estimation in an acoustic waveguide

    NASA Astrophysics Data System (ADS)

    Touzé, Grégoire Le; Nicolas, Barbara; Mars, Jérôme I.; Roux, Philippe; Oudompheng, Benoit

    2012-12-01

    Recent developments in shallow water ocean acoustic tomography propose the use of an original configuration composed of two source-receiver vertical arrays and wideband sources. The recording space thus has three dimensions, with two spatial dimensions and the frequency dimension. Using this recording space, it is possible to build a three-dimensional (3D) estimation space that gives access to the three observables associated with the acoustic arrivals: the direction of departure, the direction of arrivals, and the time of arrival. The main interest of this 3D estimation space is its capability for the separation of acoustic arrivals that usually interfere in the recording space, due to multipath propagation. A 3D estimator called double beamforming has already been developed, although it has limited resolution. In this study, the new 3D high-resolution estimators of double Capon and double MUSICAL are proposed to achieve this task. The ocean acoustic tomography configuration allows a single recording realization to estimate the cross-spectral data matrix, which is necessary to build high-resolution estimators. 3D smoothing techniques are thus proposed to increase the rank of the matrix. The estimators developed are validated on real data recorded in an ultrasonic tank, and their detection performances are compared to existing 2D and 3D methods.

  4. A tunable acoustic metamaterial with double-negativity driven by electromagnets

    NASA Astrophysics Data System (ADS)

    Chen, Zhe; Xue, Cheng; Fan, Li; Zhang, Shu-Yi; Li, Xiao-Juan; Zhang, Hui; Ding, Jin

    2016-07-01

    With the advance of the research on acoustic metamaterials, the limits of passive metamaterials have been observed, which prompts the studies concerning actively tunable metamaterials with adjustable characteristic frequency bands. In this work, we present a tunable acoustic metamaterial with double-negativity composed of periodical membranes and side holes, in which the double-negativity pass band can be controlled by an external direct-current voltage. The tension and stiffness of the periodically arranged membranes are actively controlled by electromagnets producing additional stresses, and thus, the transmission and phase velocity of the metamaterial can be adjusted by the driving voltage of the electromagnets. It is demonstrated that a tiny direct-current voltage of 6V can arise a shift of double-negativity pass band by 40% bandwidth, which exhibits that it is an easily controlled and highly tunable acoustic metamaterial, and furthermore, the metamaterial marginally causes electromagnetic interference to the surroundings.

  5. A tunable acoustic metamaterial with double-negativity driven by electromagnets.

    PubMed

    Chen, Zhe; Xue, Cheng; Fan, Li; Zhang, Shu-Yi; Li, Xiao-Juan; Zhang, Hui; Ding, Jin

    2016-07-22

    With the advance of the research on acoustic metamaterials, the limits of passive metamaterials have been observed, which prompts the studies concerning actively tunable metamaterials with adjustable characteristic frequency bands. In this work, we present a tunable acoustic metamaterial with double-negativity composed of periodical membranes and side holes, in which the double-negativity pass band can be controlled by an external direct-current voltage. The tension and stiffness of the periodically arranged membranes are actively controlled by electromagnets producing additional stresses, and thus, the transmission and phase velocity of the metamaterial can be adjusted by the driving voltage of the electromagnets. It is demonstrated that a tiny direct-current voltage of 6V can arise a shift of double-negativity pass band by 40% bandwidth, which exhibits that it is an easily controlled and highly tunable acoustic metamaterial, and furthermore, the metamaterial marginally causes electromagnetic interference to the surroundings.

  6. A tunable acoustic metamaterial with double-negativity driven by electromagnets

    PubMed Central

    Chen, Zhe; Xue, Cheng; Fan, Li; Zhang, Shu-yi; Li, Xiao-juan; Zhang, Hui; Ding, Jin

    2016-01-01

    With the advance of the research on acoustic metamaterials, the limits of passive metamaterials have been observed, which prompts the studies concerning actively tunable metamaterials with adjustable characteristic frequency bands. In this work, we present a tunable acoustic metamaterial with double-negativity composed of periodical membranes and side holes, in which the double-negativity pass band can be controlled by an external direct-current voltage. The tension and stiffness of the periodically arranged membranes are actively controlled by electromagnets producing additional stresses, and thus, the transmission and phase velocity of the metamaterial can be adjusted by the driving voltage of the electromagnets. It is demonstrated that a tiny direct-current voltage of 6V can arise a shift of double-negativity pass band by 40% bandwidth, which exhibits that it is an easily controlled and highly tunable acoustic metamaterial, and furthermore, the metamaterial marginally causes electromagnetic interference to the surroundings. PMID:27443196

  7. Coulomb Drag and Magnetotransport in Graphene Double Layers

    NASA Astrophysics Data System (ADS)

    Tutuc, Emanuel

    2013-03-01

    Graphene double layers, a set of two closely spaced graphene monolayers seperated by an ultra-thin dielectric, represent an interesting electron system to explore correlated electron states. We discuss the fabrication of such samples using a layer-by-layer transfer approach, the electron transport in individual layers at zero and in a high magnetic field, and Coulomb drag measurements. Coulomb drag, probed by flowing a drive current in one layer, and measuring the voltage drop in the opposite layer provides a direct measurement of the electron-electron scattering between the two layers, and can be used to probe the electron system ground state. Coulomb drag in graphene, measured as a function of both layer densities and temperature reveals two distinct regimes: (i) diffusive drag at elevated temperatures, above 50 K, and (ii) mesoscopic fluctuations-dominated drag at low temperatures. A second topic discussed here is a technique that allows a direct measurement of the Fermi energy in an electron system with an accuracy independent of the sample size, using a graphene double layer heterostructure. The underlying principle of the technique is that an interlayer bias applied to bring the top layer to the charge neutrality point is equal to the Fermi energy of the bottom layer, which in effect renders the top graphene layer a resistively detected Kelvin probe. We illustrate this method by measuring the Fermi velocity, Landau level spacing, and Landau level broadening in monolayer graphene. Work done in collaboration with S. Kim, I. Jo, J. Nah, D. Dillen, K. Lee, B. Fallahazad, Z. Yao, and S. K. Banerjee. We thank ONR, NRI, and NSF for support.

  8. Magnetic steering of a helicon double layer thruster

    SciTech Connect

    Charles, C.; Boswell, R. W.; Cox, W.; Laine, R.; MacLellan, P.

    2008-11-17

    The ion beam generated by a helicon double layer has been electrically steered up to 20 deg. off axis by using a solenoid placed normal to the two axial solenoids of the helicon plasma source without significantly changing the beam exhaust velocity.

  9. Double layer formation at the interface of complex plasmas

    SciTech Connect

    Yaroshenko, V. V.; Thoma, M. H.; Thomas, H. M.; Morfill, G. E.

    2008-08-15

    Necessary conditions are formulated for the generation of a double layer at the interface of a complex plasma and a particle-free electron-ion plasma in a weakly collisional discharge. Examples are calculated for realistic observed complex plasmas, and it is shown that situations of both ''smooth'' transitions and 'sharp' transitions can exist. The model can explain the abrupt boundaries observed.

  10. Study of the anode plasma double layer: optogalvanic detectors

    SciTech Connect

    Gurlui, S.; Dimitriu, D.; Strat, M.; Strat, Georgeta

    2006-01-15

    The experimental and theoretical results show that the anode double layer (DL) is a very sensitive plasma formation suitable for fine optogalvanic studies. The obtained results demonstrate that the parameters of the oscillations sustained by a DL (frequency, amplitude) can be used as optogalvanic detectors.

  11. Viscoelastic properties and efficient acoustic damping in confined polymer nano-layers at GHz frequencies

    NASA Astrophysics Data System (ADS)

    Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas

    2016-09-01

    We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids.

  12. Viscoelastic properties and efficient acoustic damping in confined polymer nano-layers at GHz frequencies

    PubMed Central

    Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas

    2016-01-01

    We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids. PMID:27633351

  13. Spatial and Temporal Variability of Zooplankton Thin Layers: The Effects of Composition and Orientation on Acoustic Detection of Layers

    DTIC Science & Technology

    2008-01-01

    Spatial and Temporal Variability of Zooplankton Thin Layers: The Effects of Composition and Orientation...to better understand the physical and biological mechanisms of formation and maintenance of thin layers of zooplankton . Because zooplankton can be...strong sound scatterers, acoustic instruments are effective at detecting and describing zooplankton thin layers. Using a combination of instruments

  14. Anomalous Coulomb drag in bilayer graphene double layers

    NASA Astrophysics Data System (ADS)

    Liu, Xiaomeng; Taniguchi, Takashi; Watanabe, Kenji; Kim, Philip

    Bilayer graphene double-layer structure consists of two layers of bilayer graphene separated by atomically thin hexagonal boron nitride (hBN). With a perfect Fermi surface nesting and strong electron-electron interaction (ECoulomb > Ekinetic), such systems offer exciting platforms to study interaction driven phenomena, such as Coulomb drag and exciton condensation. We fabricate ultra-clean encapsulated bilayer graphene double layers with dry pick-up method. Room temperature drag measurement on our devices shows the sign of drag agree with the typical Fermi liquid behavior. However, at lower temperatures, the sign of drag reversed, indicating a new drag mechanism emerges and dominates. We measure this with different geometry, temperature, bias and gating to investigate the origin of such effect and discuss the implication of the drag sign changes.

  15. Transition Delay in Hypervelocity Boundary Layers By Means of CO2/Acoustic Instability Interaction

    DTIC Science & Technology

    2014-12-16

    AFRL-OSR-VA-TR-2015-0040 TRANSITION DELAY IN HYPERVELOCITY BOUNDARY LAYERS BY MEANS OF CO2 /ACOUSTIC INSTA Joseph Shepherd CALIFORNIA INSTITUTE OF...Delay in Hypervelocity Boundary Layers By Means of CO2 /Acoustic Instability Interaction FA9550-10-1-0491 Shepherd, Joseph E. California Institute of...investigated using the concept of damping Mack’s second mode disturbances by vibrational relaxation of carbon dioxide ( CO2 ) within the boundary layer

  16. Evidence for double acoustic windows in the dolphin, Tursiops truncatus.

    PubMed

    Popov, Vladimir V; Supin, Alexander Ya; Klishin, Vladimir O; Tarakanov, Mikhail B; Pletenko, Mikhail G

    2008-01-01

    In a bottlenose dolphin positions of sound receiving areas on the head surface were determined by comparing the acoustic delays from different sound-source positions. For this investigation, auditory brainstem responses (ABRs) to short tone pips were recorded and their latencies were measured at different sound source positions. After correction for the latency dependence on response amplitude, the difference in ABR latencies was adopted as being the difference of the acoustic delays. These delay differences were used to calculate the position of the sound-receiving point. Measurements were conducted at sound frequencies from 16 to 128 kHz, in half-octave steps. At probe frequencies of 16 and 22.5 kHz, the receiving area was located 21.7-26 cm caudal of the melon tip, which is near the bulla and auditory meatus. At higher probe frequencies, from 32 to 128 kHz, the receiving area was located from 9.3 to 13.1 cm caudal of the melon tip, which corresponds to a proximal part of the lower jaw. Thus, at least two sound-receiving areas (acoustic windows) with different frequency sensitivity were identified.

  17. Nonlinear Surface Transport in the Thin Double-Layer Limit

    NASA Astrophysics Data System (ADS)

    Chu, Kevin; Bazant, Martin

    2006-03-01

    At high applied electric fields, ionic transport within the double layer plays a significant role in the overall response of electrokinetic systems. It is well-known that surface transport processes, including surface electromigration, surface diffusion and surface advection, may impact the strength of electrokinetic phenomena by affecting both the zeta-potential and the magnitude of the tangential electric field. Therefore, it is important to include these effects when formulating the effective boundary conditions for the equations that govern electrokinetic flow outside of the double layer. In this talk, we discuss the application of a general formulation of ``surface conservation laws'' for diffuse boundary layers to derive effective boundary conditions that capture the physics of electrokinetic surface transport. Previous analyses (e.g. Deryagin & Dukhin 1969) are only valid for weak applied fields and are based on a linearization of the concentration and potential about a reference solution, but our results are fully nonlinear and hold at large applied fields as long as the double layer is sufficiently thin. We compare our nonlinear surface transport theory with existing linear analogues and apply it to the canonical problem of induced-charge electro-osmosis around a metal sphere or cylinder in a strong DC field.

  18. Observation of acoustic Dirac-like cone and double zero refractive index

    PubMed Central

    Dubois, Marc; Shi, Chengzhi; Zhu, Xuefeng; Wang, Yuan; Zhang, Xiang

    2017-01-01

    Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre. PMID:28317927

  19. Observation of acoustic Dirac-like cone and double zero refractive index.

    PubMed

    Dubois, Marc; Shi, Chengzhi; Zhu, Xuefeng; Wang, Yuan; Zhang, Xiang

    2017-03-20

    Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre.

  20. Observation of acoustic Dirac-like cone and double zero refractive index

    NASA Astrophysics Data System (ADS)

    Dubois, Marc; Shi, Chengzhi; Zhu, Xuefeng; Wang, Yuan; Zhang, Xiang

    2017-03-01

    Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre.

  1. Reflected wavefronts modulation with acoustic metasurface based on double-split hollow sphere

    NASA Astrophysics Data System (ADS)

    Ding, Changlin; Zhao, Xiaopeng; Chen, Huaijun; Zhai, Shilong; Shen, Fangliang

    2015-08-01

    Metasurfaces with sub-wavelength thickness and planar profile have exhibited abnormal manipulation to waves that could not be realized by traditional materials. Here, we present an acoustic metasurface (AMS) model composed of double-split hollow sphere (DSHS) resonator arrays with the functionality of modulating reflected wavefronts at will. By tailoring the split-hole diameter of DSHS, the AMS can be designed to cover 2 π phase shifts with a step of π/4. The acoustic waves perpendicularly and obliquely incident on the AMS can be reflected at any angle, including anomalous reflection and negative reflection. These anomalous manipulations of the reflected wave are simulated to fulfill the generalized Snell's law by projecting suitable phase gradient. Such AMS provides another path to acoustic applications such as acoustic imaging, cloaking, beam steering devices.

  2. Ordered poly(p-phenylene)/layered double hydroxide ultrathin films with blue luminescence by layer-by-layer assembly.

    PubMed

    Yan, Dongpeng; Lu, Jun; Wei, Min; Han, Jingbin; Ma, Jing; Li, Feng; Evans, David G; Duan, Xue

    2009-01-01

    Lavender layers: A poly(p-phenylene) anionic derivate and exfoliated Mg-Al layered double hydroxide monolayers were assembled into ultrathin films with well-defined blue fluorescence (see picture; the numbers indicate the number of bilayers), long-range order, and high photostability. These films work as multiple quantum-well structures for valence electrons.

  3. Spatial instability of viscous double-layer liquid sheets

    NASA Astrophysics Data System (ADS)

    Ye, Han-Yu; Yang, Li-Jun; Fu, Qing-Fei

    2016-10-01

    This paper investigates the spatial instability of a double-layer viscous liquid sheet moving in a stationary gas medium. A linear stability analysis is conducted and two situations are considered, an inviscid-gas situation and a viscous-gas situation. In the inviscid-gas situation, the basic state of the entire gas phase is stationary and the analytical dispersion relation is derived. Similar to single-layer sheets, the instability of double-layer sheets presents two unstable modes, the sinuous and the varicose modes. However, the result of the base-case double-layer sheet indicates that the cutoff wavenumber of the dispersion curve is larger than that of a single-layer sheet. A decomposition of the growth rate is performed and the result shows that for small wavenumbers, the surface tension of all three interfaces and the aerodynamic forces of both the lower and upper gases contribute significantly to the unstable growth rate. In contrast, for large wavenumbers the major contribution to the unstable growth rate is only the surface tension of the upper interface and the aerodynamic force of the upper gas. In the viscous-gas situation, although the majority of the gas phase is stationary, gas boundary layers exist at the vicinity of the moving liquid sheet, and the stability problem is solved by a spectral collocation method. Compared with the inviscid-gas solution, the growth rate at large wavenumber is significantly suppressed. The decomposition of growth rate indicates that all the aerodynamic and surface tension terms behave consistently throughout the entire unstable wavenumber range. The effects of various parameters are discussed. In addition, the effect of gas viscosity and the gas velocity profile is investigated separately, and the results indicate that both factors affect the maximum growth rate and the dominant wavenumber, although the effect of the gas velocity profile is stronger than that of the gas viscosity.

  4. Observations of double layers in earth's plasma sheet.

    PubMed

    Ergun, R E; Andersson, L; Tao, J; Angelopoulos, V; Bonnell, J; McFadden, J P; Larson, D E; Eriksson, S; Johansson, T; Cully, C M; Newman, D N; Goldman, M V; Roux, A; LeContel, O; Glassmeier, K-H; Baumjohann, W

    2009-04-17

    We report the first direct observations of parallel electric fields (E_{ parallel}) carried by double layers (DLs) in the plasma sheet of Earth's magnetosphere. The DL observations, made by the THEMIS spacecraft, have E_{ parallel} signals that are analogous to those reported in the auroral region. DLs are observed during bursty bulk flow events, in the current sheet, and in plasma sheet boundary layer, all during periods of strong magnetic fluctuations. These observations imply that DLs are a universal process and that strongly nonlinear and kinetic behavior is intrinsic to Earth's plasma sheet.

  5. Electrical power generation by mechanically modulating electrical double layers.

    PubMed

    Moon, Jong Kyun; Jeong, Jaeki; Lee, Dongyun; Pak, Hyuk Kyu

    2013-01-01

    Since Michael Faraday and Joseph Henry made their great discovery of electromagnetic induction, there have been continuous developments in electrical power generation. Most people today get electricity from thermal, hydroelectric, or nuclear power generation systems, which use this electromagnetic induction phenomenon. Here we propose a new method for electrical power generation, without using electromagnetic induction, by mechanically modulating the electrical double layers at the interfacial areas of a water bridge between two conducting plates. We find that when the height of the water bridge is mechanically modulated, the electrical double layer capacitors formed on the two interfacial areas are continuously charged and discharged at different phases from each other, thus generating an AC electric current across the plates. We use a resistor-capacitor circuit model to explain the results of this experiment. This observation could be useful for constructing a micro-fluidic power generation system in the near future.

  6. Effects of double-layer polarization on ion transport.

    PubMed Central

    Hainsworth, A H; Hladky, S B

    1987-01-01

    It has been proposed that changes in ionic strength will alter the shape of current-voltage relations for ion transport across a lipid membrane. To investigate this effect, we measured currents across glyceryl monooleate membranes at applied potentials between 10 and 300 mV using either gramicidin and 1 mM NaCl or valinomycin and 1 mM KCl. A bridge circuit with an integrator as null detector was used to separate the capacitative and ionic components of the current. The changes in the current-voltage relations when ionic strength is varied between 1 and 100 mM are compared with predictions of Gouy-Chapman theory for the effects of these variations on polarization of the electrical diffuse double-layer. Double-layer polarization accounts adequately for the changes observed using membranes made permeable by either gramicidin or valinomycin. PMID:2432953

  7. Development and current status of electric double-layer capacitors

    SciTech Connect

    Morimoto, Takeshi; Hiratsuka, Kazuya; Sanada, Yasuhiro; Kurihara, Kaname

    1995-12-31

    An electric double layer capacitor (EDLC) based on the charge storage at the interface between a high surface area carbon electrode and an electrolyte solution is widely used as maintenance-free power source for IC memories and microcomputers. New applications for electric double-layer capacitors have been proposed in recent years. The popularity of these devices is derived from their high energy density relative to conventional capacitors and their long cycle life and high power density relative to batteries. In this paper a classification and a characteristics of industrially produced Japanese small EDLCs are reviewed. Structure and performance of power capacitors under development as well as materials and performance of industrially produced small capacitors are discussed.

  8. Effects of double-layer polarization on ion transport.

    PubMed

    Hainsworth, A H; Hladky, S B

    1987-01-01

    It has been proposed that changes in ionic strength will alter the shape of current-voltage relations for ion transport across a lipid membrane. To investigate this effect, we measured currents across glyceryl monooleate membranes at applied potentials between 10 and 300 mV using either gramicidin and 1 mM NaCl or valinomycin and 1 mM KCl. A bridge circuit with an integrator as null detector was used to separate the capacitative and ionic components of the current. The changes in the current-voltage relations when ionic strength is varied between 1 and 100 mM are compared with predictions of Gouy-Chapman theory for the effects of these variations on polarization of the electrical diffuse double-layer. Double-layer polarization accounts adequately for the changes observed using membranes made permeable by either gramicidin or valinomycin.

  9. Solitary and double-layer structures in quantum bi-ion plasma

    NASA Astrophysics Data System (ADS)

    Shahmansouri, Mehran; Tribeche, Mouloud

    2016-06-01

    Weak ion-acoustic solitary waves (IASWs) in an unmagnetized quantum plasmas having two-fluid ions and fluid electrons are considered. Using the one-dimensional quantum hydrodynamics model and then the reductive perturbation technique, a generalized form of nonlinear quantum Korteweg-de Vries (KdV) equation governing the dynamics of weak ion acoustic solitary waves is derived. The effects of ion population, warm ion temperature, quantum diffraction, and polarity of ions on the nonlinear properties of these IASWs are analyzed. It is found that our present plasma model may support compressive as well as rarefactive solitary structures. Furthermore, formation and characteristics properties of IA double layers in the present bi-ion plasma model are investigated. The results of this work should be useful and applicable in understanding the wide relevance of nonlinear features of localized electro-acoustic structures in laboratory and space plasma, such as in super-dense astrophysical objects [24] and in the Earth's magnetotail region (Parks [43]. The implications of our results in some space plasma situations are discussed.

  10. Flexible nanoporous tunable electrical double layer biosensors for sweat diagnostics.

    PubMed

    Munje, Rujuta D; Muthukumar, Sriram; Panneer Selvam, Anjan; Prasad, Shalini

    2015-09-30

    An ultra-sensitive and highly specific electrical double layer (EDL) modulated biosensor, using nanoporous flexible substrates for wearable diagnostics is demonstrated with the detection of the stress biomarker cortisol in synthetic and human sweat. Zinc oxide thin film was used as active region in contact with the liquid i.e. synthetic and human sweat containing the biomolecules. Cortisol detection in sweat was accomplished by measuring and quantifying impedance changes due to modulation of the double layer capacitance within the electrical double layer through the application of a low orthogonally directed alternating current (AC) electric field. The EDL formed at the liquid-semiconductor interface was amplified in the presence of the nanoporous flexible substrate allowing for measuring the changes in the alternating current impedance signal due to the antibody-hormone interactions at diagnostically relevant concentrations. High sensitivity of detection of 1 pg/mL or 2.75 pmol cortisol in synthetic sweat and 1 ng/mL in human sweat is demonstrated with these novel biosensors. Specificity in synthetic sweat was demonstrated using a cytokine IL-1β. Cortisol detection in human sweat was demonstrated over a concentration range from 10-200 ng/mL.

  11. Flexible nanoporous tunable electrical double layer biosensors for sweat diagnostics

    NASA Astrophysics Data System (ADS)

    Munje, Rujuta D.; Muthukumar, Sriram; Panneer Selvam, Anjan; Prasad, Shalini

    2015-09-01

    An ultra-sensitive and highly specific electrical double layer (EDL) modulated biosensor, using nanoporous flexible substrates for wearable diagnostics is demonstrated with the detection of the stress biomarker cortisol in synthetic and human sweat. Zinc oxide thin film was used as active region in contact with the liquid i.e. synthetic and human sweat containing the biomolecules. Cortisol detection in sweat was accomplished by measuring and quantifying impedance changes due to modulation of the double layer capacitance within the electrical double layer through the application of a low orthogonally directed alternating current (AC) electric field. The EDL formed at the liquid-semiconductor interface was amplified in the presence of the nanoporous flexible substrate allowing for measuring the changes in the alternating current impedance signal due to the antibody-hormone interactions at diagnostically relevant concentrations. High sensitivity of detection of 1 pg/mL or 2.75 pmol cortisol in synthetic sweat and 1 ng/mL in human sweat is demonstrated with these novel biosensors. Specificity in synthetic sweat was demonstrated using a cytokine IL-1β. Cortisol detection in human sweat was demonstrated over a concentration range from 10-200 ng/mL.

  12. Completed double layer boundary element method for periodic suspensions

    NASA Astrophysics Data System (ADS)

    Fan, X.-J.; Phan-Thien, N.; Zheng, R.

    In this paper, a traction-based boundary element method is formulated and implemented for periodic suspensions. Hydrodynamic interaction of particles at infinity is handled by O'Brien's method (1979), which is suitably modified for the adjoint double layer using the mean field values of the traction and the background flow. After a deflation of the extreme eigenvalue -1 of the adjoint double layer operator, an iterative solution strategy is implemented, which solves for the traction field on the surfaces of a group of near-by particles sequentially. Ewald's summation technique is employed, by expressing the adjoint double layer kernel in two sums, one converges rapidly in real space, and the other, in the reciprocal Fourier space. The implementation is tested on a periodic suspension of spheres and spheroids in simple and elongated face-centred cubic arrays, and proved to be very accurate when compared to established results. New results for the intrinsic viscosities of periodic suspensions of cubes and spheroids from moderate to high volume fractions are reported. Based on the numerical data for suspensions of spheroids, a simple modification of the constitutive equation of Hinch and Leal (1972), which was derived for dilute suspension of spheroids, is reported, allowing the constitutive equation to reasonably fit the numerical data at moderate to high concentrations.

  13. Flexible nanoporous tunable electrical double layer biosensors for sweat diagnostics

    PubMed Central

    Munje, Rujuta D.; Muthukumar, Sriram; Panneer Selvam, Anjan; Prasad, Shalini

    2015-01-01

    An ultra-sensitive and highly specific electrical double layer (EDL) modulated biosensor, using nanoporous flexible substrates for wearable diagnostics is demonstrated with the detection of the stress biomarker cortisol in synthetic and human sweat. Zinc oxide thin film was used as active region in contact with the liquid i.e. synthetic and human sweat containing the biomolecules. Cortisol detection in sweat was accomplished by measuring and quantifying impedance changes due to modulation of the double layer capacitance within the electrical double layer through the application of a low orthogonally directed alternating current (AC) electric field. The EDL formed at the liquid-semiconductor interface was amplified in the presence of the nanoporous flexible substrate allowing for measuring the changes in the alternating current impedance signal due to the antibody-hormone interactions at diagnostically relevant concentrations. High sensitivity of detection of 1 pg/mL or 2.75 pmol cortisol in synthetic sweat and 1 ng/mL in human sweat is demonstrated with these novel biosensors. Specificity in synthetic sweat was demonstrated using a cytokine IL-1β. Cortisol detection in human sweat was demonstrated over a concentration range from 10–200 ng/mL. PMID:26420511

  14. Two-dimensional potential double layers and discrete auroras

    NASA Technical Reports Server (NTRS)

    Kan, J. R.; Lee, L. C.; Akasofu, S.-I.

    1979-01-01

    This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc and with the formation of the inverted V precipitation region. The former is embedded in the latter, and both are associated with field-aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two-dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter solutions are obtained in which the field-aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter solutions are obtained in which the potential drop is confined to a distance on the order of the Debye length. The electric field in the two-dimensional double-layer model is the zeroth-order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first-order field due to current instabilities or turbulences. The maximum potential in the two-dimensional double-layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.

  15. Aerodynamic/acoustic performance of YJ101/double bypass VCE with coannular plug nozzle

    NASA Technical Reports Server (NTRS)

    Vdoviak, J. W.; Knott, P. R.; Ebacker, J. J.

    1981-01-01

    Results of a forward Variable Area Bypass Injector test and a Coannular Nozzle test performed on a YJ101 Double Bypass Variable Cycle Engine are reported. These components are intended for use on a Variable Cycle Engine. The forward Variable Area Bypass Injector test demonstrated the mode shifting capability between single and double bypass operation with less than predicted aerodynamic losses in the bypass duct. The acoustic nozzle test demonstrated that coannular noise suppression was between 4 and 6 PNdB in the aft quadrant. The YJ101 VCE equipped with the forward VABI and the coannular exhaust nozzle performed as predicted with exhaust system aerodynamic losses lower than predicted both in single and double bypass modes. Extensive acoustic data were collected including far field, near field, sound separation/ internal probe measurements as Laser Velocimeter traverses.

  16. Immediate manifestation of acoustic trauma in the auditory cortex is layer specific and cell type dependent

    PubMed Central

    Zelenka, Ondřej; Hromádka, Tomáš; Syka, Josef

    2016-01-01

    Exposure to loud sounds damages the auditory periphery and induces maladaptive changes in central parts of the auditory system. Diminished peripheral afferentation and altered inhibition influence the processing of sounds in the auditory cortex. It is unclear, however, which types of inhibitory interneurons are affected by acoustic trauma. Here we used single-unit electrophysiological recording and two-photon calcium imaging in anesthetized mice to evaluate the effects of acute acoustic trauma (125 dB SPL, white noise, 5 min) on the response properties of neurons in the core auditory cortex. Electrophysiological measurements suggested the selective impact of acoustic trauma on inhibitory interneurons in the auditory cortex. To further investigate which interneuronal types were affected, we used two-photon calcium imaging to record the activity of neurons in cortical layers 2/3 and 4, specifically focusing on parvalbumin-positive (PV+) and somatostatin-positive (SST+) interneurons. Spontaneous and pure-tone-evoked firing rates of SST+ interneurons increased in layer 4 immediately after acoustic trauma and remained almost unchanged in layer 2/3. Furthermore, PV+ interneurons with high best frequencies increased their evoked-to-spontaneous firing rate ratios only in layer 2/3 and did not change in layer 4. Finally, acoustic trauma unmasked low-frequency excitatory inputs only in layer 2/3. Our results demonstrate layer-specific changes in the activity of auditory cortical inhibitory interneurons within minutes after acoustic trauma. PMID:26823513

  17. Interpreting Underwater Acoustic Images of the Upper Ocean Boundary Layer

    ERIC Educational Resources Information Center

    Ulloa, Marco J.

    2007-01-01

    A challenging task in physical studies of the upper ocean using underwater sound is the interpretation of high-resolution acoustic images. This paper covers a number of basic concepts necessary for undergraduate and postgraduate students to identify the most distinctive features of the images, providing a link with the acoustic signatures of…

  18. Intercalation of Layered Silicates, Layered Double Hydroxides, and Lead Iodide: Synthesis, Characterization and Properties.

    NASA Astrophysics Data System (ADS)

    Mehrotra, Vivek

    Layered silicates, layered double hydroxides, and lead iodide are lamellar solids that can incorporate guest species into the galleries between their layers. Various intercalated forms of these layered materials have been synthesized and their properties studied. The dielectric behavior of pristine fluorohectorite, a typical layered silicate, and Zn-Al layered double hydroxide is explained by considering the structural ordering and mobility of the intercalated water molecules, as well as models invoking fractal time processes and fractal structure. Intercalative polymerization of aniline and pyrrole into fluorohectorite leads to a multilayered structure consisting of single polymer chains alternately stacked with the 9.6 A thick silicate layers. The polymer chains are confined to the quasi two-dimensional interlayer space between the rigid host layers. The hybrid films exhibit highly anisotropic properties. The optical, electrical and mechanical behavior is discussed in terms of the molecular confinement of the polymer chains. Ethylenediamine functionalized C _{60} clusters have also been intercalated into fluorohectorite via an ion-exchange procedure. Intercalation results in an improved thermal stability of the functionalized C_{60} clusters. Rutherford backscattering spectrometry has been used to elucidate the mechanism of intercalative ion exchange of silver in muscovite mica, a layered silicate with a layer charge density of 2e per unit cell. It is proposed that ion-exchange progresses by intercalating successive galleries through the edges of the mica layers. Guest-host interactions have been studied in the system aniline-PbI_2. The optical and structural effects of aniline intercalation in lead iodide thin films is discussed. Intercalation leads to a large shift in the optical band gap of PbI_2. The observed change in band gap is not only due to the increased separation between the PbI_2 layers but also because of an electrostatic interaction between the

  19. Gate-Induced Superconductivity in Layered-Material-Based Electric Double Layer Transistors

    NASA Astrophysics Data System (ADS)

    Ye, J. T.; Zhang, Y. J.; Matsuhashi, Y.; Craciun, M. F.; Russo, S.; Kasahara, Y.; Morpurgo, A. F.; Iwasa, Y.

    2012-12-01

    High carrier density part of many materials could be accessed by a variation of the field effect transistor technique: electric double layer transistor. Carrier density regime of n~1014 cm-2 can be easily accessed electrostatically realizing effective doping without chemical modification. In this study, we utilized micro-cleavage on a number of interesting layered materials. And realized high carrier density state and high performance transport on atomically flat surfaces.

  20. Double Layers: Potential Formation and Related Nonlinear Phenomena in Plasmas: Proceedings of the 5th Symposium

    NASA Astrophysics Data System (ADS)

    Iizuka, S.

    1998-02-01

    The Table of Contents for the book is as follows: * PREFACE * INTERNATIONAL SCIENTIFIC COMMITTEE * LOCAL ORGANIZING COMMITTEE AT TOHOKU UNIVERSITY * CHAPTER 1: DOUBLE LAYERS, SHEATHS, AND POTENTIAL STRUCTURES * 1.1 Double Layers * On Fluid Models of Stationary, Acoustic Double Layers (Invited) * Particle Simulation of Double Layer (Invited) * Space-Time Dependence of Non-Steady Double Layers * The Role of Low Energy Electrons for the Generation of Anode Double Layers in Glow Discharges * Arbitrary Amplitude Ion-Acoustic Double Layers in a Dusty Plasma * 1.2 Sheaths * Bounded Plasma Edge Physics as Observed from Simulations in 1D and 2D (Invited) * Control of RF Sheath Structure in RF Diode Discharge * Observation of Density Gradients with Fine Structures and Low Frequency Wave Excitation at the Plasma-Sheath Boundary * Double Sheath Associated with an Electron Emission to a Plasma Containing Negative Ions * Sheath Edge and Floating Potential for Multi-Species Plasmas Including Dust Particles * 1.3 Potential Structures and Oscillations * Potential Structure Formed at a Constriction of a DC He Positive Column and its Coupling with Ionization Wave * Potential Structure in a New RF Magnetron Device with a Hollow Electrode * Potential Disruption in a RF Afterglow Electronegative Plasma * Potential Oscillation in a Strongly Asymmetry RF Discharge Containing Negative Ions * Effects of External Potential Control on Coulomb Dust Behavior * Potential Structure of Carbon Arc Discharge for High-Yield Fullerenes Formation * Control of Axial and Radial Potential Profiles in Tandem Mirrors (Invited) * CHAPTER 2: FIELD-ALIGNED ELECTRIC FIELDS AND RELATED PARTICLE ACCELERATIONS * 2.1 Field-Aligned Potential Formation * Formation of Large Potential Difference in a Plasma Flow along Converging Magnetic Field Lines (Invited) * Presheath Formation in front of an Oblique End-Plate in a Magnetized Sheet Plasma * Plasma Potential Formation Due to ECRH in a Magnetic Well * Electrostatic

  1. Peculiar transmission property of acoustic waves in a one-dimensional layered phononic crystal

    NASA Astrophysics Data System (ADS)

    Zhao, Degang; Wang, Wengang; Liu, Zhengyou; Shi, Jing; Wen, Weijia

    2007-03-01

    In this article, we report both theoretical calculation and experimental observation of acoustic waves abnormally through a one-dimensional layered transmitted phononic crystal at frequencies within the band gap into a material of large acoustic impedance mismatch, with an efficiency as high as unity. The transmission peaks can be interpreted as a result of the interference of acoustic waves reflected from all periodically aligned interfaces. The condition for the appearance of peaks is analyzed in detail and the optimized layer number is given for different configurations.

  2. The acoustic emission of a distributed mode loudspeaker near a porous layer.

    PubMed

    Prokofieva, E Yu; Horoshenkov, Kirill V; Harris, N

    2002-06-01

    Experimental and theoretical modeling of the vibro-acoustic performance of a distributed mode loudspeaker (DML) suggest that their acoustic emission can be significantly affected by the presence of a porous layer. The amplitude of the surface velocity of the panel and the acoustic pressure on the porous surface are reduced largely in the vicinity of structural resonances due to the additional radiation damping and visco-thermal absorption phenomenon in the porous layer. The experimental results suggest that a porous layer between a rigid base and a DML panel can considerably alter its acoustic emission in the near field and in the far field. This is illustrated by a reduction in the level of fluctuations in the emitted acoustic pressure spectra. These fluctuations are normally associated with the interference between the sound emitted by the front surface of the speaker and that emitted from the back. Another contribution comes from the pronounced structural resonances in the surface velocity spectrum. The results of this work suggest that the acoustic boundary conditions near a DML can be modified by the porous layer so that a desired acoustic output can be attained.

  3. Cation ordering and superstructures in natural layered double hydroxides.

    PubMed

    Krivovichev, Sergey V; Yakovenchuk, Victor N; Zolotarev, Andrey A; Ivanyuk, Gregory N; Pakhomovsky, Yakov A

    2010-01-01

    Layered double hydroxides (LDHs) constitute an important group of materials with many applications ranging from catalysis and absorption to carriers for drug delivery, DNA intercalation and carbon dioxide sequestration. The structures of LDHs are based upon double brucite-like hydroxide layers [M(2+)(n)M(3+)(m)(OH)(2(m+n)](m+), where M(2+) = Mg(2+), Fe(2+), Mn(2+), Zn(2+), etc.; M(3+) = Al(3+), Fe(3+), Cr(3+), Mn(3+), etc. Structural features of LDHs such as cation ordering, charge distribution and polytypism have an immediate influence upon their properties. However, all the structural studies on synthetic LDHs deal with powder samples that prevent elucidation of such fine details of structure architecture as formation of superstructures due to cation ordering. In contrast to synthetic materials, natural LDHs are known to form single crystals accessible to single-crystal X-ray diffraction analysis, which provides a unique possibility to investigate 3D cation ordering in LDHs that results in formation of complex superstructures, where 2D cation order is combined with a specific order of layer stacking (polytypism). Therefore LDH minerals provide an indispensable source of structural information for modeling of structures and processes happening in LDHs at the molecular and nanoscale levels.

  4. Shock waves and double layers in a quantum electron-positron-ion plasma

    NASA Astrophysics Data System (ADS)

    Dip, P. R.; Hossen, M. A.; Salahuddin, M.; Mamun, A. A.

    2016-02-01

    The ion-acoustic (IA) shock waves and double layers (DLs) in an unmagnetized, dissipative, quantum electron-positron-ion (EPI) plasma (composed of a viscous heavy ion fluid, Fermi electrons and positrons) have been theoretically investigated. The higher-order Burgers and Gardner equations are derived by employing the reductive perturbation method. The basic features of the IA shock waves and the DLs are identified by analyzing the solutions of both the higher-order Burgers and Gardner equations. The ratio of the Fermi temperature of the positron to that of the electron, the Fermi pressure of electrons and positrons, the viscous force, the plasma particle number densities, etc. are found to change remarkably the basic features (viz. amplitude, width, phase speed, etc.) of the IA waves. The results of our investigation may be helpful in understanding the nonlinear features of localized IA waves propagating in quantum EPI plasmas which are ubiquitous in astrophysical, as well as laboratory, environments.

  5. Decoupling of double-tearing resonant layers by sheared flows

    NASA Astrophysics Data System (ADS)

    Abbott, Stephen; Germaschewski, Kai

    2015-11-01

    Double-tearing modes consist of two resonant, reconnecting layers of the same mode number coupled together by an ideal MHD outer region. Linearly this interaction can result in faster growth as the two layers drive each other. Nonlinearly it may lead to explosive releases of energy, and is a possible driver for off-axis sawtooth crashes in advanced tokamaks. Recent work has shown that differential rotation effects, such as equilibrium sheared flows or diamagnetic drifts, can decouple the DTM layers leaving two drifting, single tearing modes. These isolated tearing layers are slower growing and easier to stabilize. Understanding and producing this decoupling is thus an important element of preventing disruptive DTM activity. In this work we present progress on developing an analytic theory of DTM decoupling. We show that the application of equilibrium sheared flows mixes the symmetric and antisymmetric DTM eigenmode solutions, reducing the growth rate. This representation predicts a linear relationship between the growth rate and the amplitude of differential sheared flow needed to decouple the layers, which we confirm with linear MHD simulations. Through numerical scaling studies we examine the relationship between mode decoupling and the slab-kink mode underlying DTM growth.

  6. Geodesic acoustic mode in anisotropic plasmas using double adiabatic model and gyro-kinetic equation

    SciTech Connect

    Ren, Haijun; Cao, Jintao

    2014-12-15

    Geodesic acoustic mode in anisotropic tokamak plasmas is theoretically analyzed by using double adiabatic model and gyro-kinetic equation. The bi-Maxwellian distribution function for guiding-center ions is assumed to obtain a self-consistent form, yielding pressures satisfying the magnetohydrodynamic (MHD) anisotropic equilibrium condition. The double adiabatic model gives the dispersion relation of geodesic acoustic mode (GAM), which agrees well with the one derived from gyro-kinetic equation. The GAM frequency increases with the ratio of pressures, p{sub ⊥}/p{sub ∥}, and the Landau damping rate is dramatically decreased by p{sub ⊥}/p{sub ∥}. MHD result shows a low-frequency zonal flow existing for all p{sub ⊥}/p{sub ∥}, while according to the kinetic dispersion relation, no low-frequency branch exists for p{sub ⊥}/p{sub ∥}≳ 2.

  7. Energy transmission in a mechanically-linked double-wall structure coupled to an acoustic enclosure

    NASA Astrophysics Data System (ADS)

    Cheng, L.; Li, Y. Y.; Gao, J. X.

    2005-05-01

    The energy transmission in a mechanically linked double-wall structure into an acoustic enclosure is studied in this paper. Based on a fully coupled vibro-acoustic formulation, focus is put on investigating the effect of the air gap and mechanical links between the two panels on the energy transmission and noise insulation properties of such structures. An approximate formula reflecting the gap effect on the lower-order coupled frequencies of the system is proposed. A criterion, based on the ratio between the aerostatic stiffness of the gap cavity and the stiffness of the link, is proposed to predict the dominant transmitting path, with a view to provide guidelines for the design of appropriate control strategies. Numerical results reveal the existence of three distinct zones, within which energy transmission takes place following different mechanisms and transmitting paths. Corresponding effects on noise insulation properties of the double-wall structure are also investigated. .

  8. Langmuir probe measurements of double-layers in a pulsed discharge

    NASA Technical Reports Server (NTRS)

    Levine, J. S.; Crawford, F. W.

    1980-01-01

    Langmuir probe measurements were carried out which confirm the occurrence of double-layers in an argon positive column. Pulsing the discharge current permitted probe measurements to be performed in the presence of the double-layer. Supplementary evidence, obtained from DC and pulsed discharges, indicated that the double-layers formed in the two modes of operation were similar. The double-layers observed were weak and stable; their relation to other classes of double-layers are discussed, and directions for future work are suggested.

  9. Tunable magnetic resonance in double layered metallic structures.

    PubMed

    Zhou, L; Zhu, Y Y

    2011-12-01

    Double layered metallic gratings have been investigated both theoretically and experimentally. The authors have reported that tunable magnetic resonance (MR) can be achieved by modulating the vertical chirped width dh which could be controlled conveniently in the common electron and/or ion beam microfabrications. The linear relationship between MR wavelength and dh has been reported. By introducing the difference of electric and magnetic penetration depth, an analytic formula deduced from a modified LC model has shown good agreement with the simulation results, and an effective width for trapezoidal sandwiched microstructures has been presented. Our results may provide an alternative choice for tunable MR and broad bandwidth of magnetic metamaterials.

  10. Compensation of shear waves in photoacoustic tomography with layered acoustic media

    PubMed Central

    Schoonover, Robert W.; Anastasio, Mark A.

    2012-01-01

    An image reconstruction formula is presented for photoacoustic computed tomography that accounts for conversion between longitudinal and shear waves in a planar-layered acoustic medium. We assume the optical absorber that produces the photoacoustic wave field is embedded in a single fluid layer and any elastic solid layers present are separated by one or more fluid layers. The measurement aperture is assumed to be planar. Computer simulation studies are conducted to demonstrate and investigate the proposed reconstruction formula. PMID:21979514

  11. Compensation of shear waves in photoacoustic tomography with layered acoustic media.

    PubMed

    Schoonover, Robert W; Anastasio, Mark A

    2011-10-01

    An image reconstruction formula is presented for photoacoustic computed tomography that accounts for conversion between longitudinal and shear waves in a planar-layered acoustic medium. We assume the optical absorber that produces the photoacoustic wave field is embedded in a single fluid layer and any elastic solid layers present are separated by one or more fluid layers. The measurement aperture is assumed to be planar. Computer simulation studies are conducted to demonstrate and investigate the proposed reconstruction formula.

  12. Influence of localised double suction on a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Oyewola, O.; Djenidi, L.; Antonia, R. A.

    2007-07-01

    The effects of localised suction applied through a pair of porous wall strips on a turbulent boundary layer have been quantified through the measurements of mean velocity and Reynolds stresses. The results indicate that the use of second strip extends the pseudo-relaminarisation zone but also reduces the overshoot in the longitudinal and normal r.m.s. velocities. While the minimum r.m.s. occurs at x/δo=3.0 (one strip) and x/δo=12 (two strips), the reduction observed for the latter case is larger. Relative to no suction, the turbulence level is modified by suction and the effect is enhanced with double suction. This increased effectiveness reflects the fact that the second strip acts on a boundary layer whose near-wall active motion has been seriously weakened by the first strip.

  13. Buckling instability of circular double-layered graphene sheets.

    PubMed

    Natsuki, Toshiaki; Shi, Jin-Xing; Ni, Qing-Qing

    2012-04-04

    In this paper, we study the buckling properties of circular double-layered graphene sheets (DLGSs), using plate theory. The two graphene layers are modeled as two individual sheets whose interactions are determined by the Lennard-Jones potential of the carbon-carbon bond. An analytical solution of coupled governing equations is proposed for predicting the buckling properties of circular DLGSs. Using the present theoretical approach, the influences of boundary conditions, plate sizes, and buckling-mode shapes on the buckling behaviors are investigated in detail. The buckling stability is significantly affected by the buckling-mode shapes. As a result of van der Waals interactions, the buckling stress of circular DLGSs is much larger for the anti-phase mode than for the in-phase mode.

  14. A novel vibrational energy harvester with electric double layer electrets

    NASA Astrophysics Data System (ADS)

    Ono, S.; Miwa, K.; Iori, J.; Mitsuya, H.; Ishibashi, K.; Sano, C.; Toshiyoshi, H.; Fujita, H.

    2016-11-01

    We propose a new type of vibrational energy harvester with an electric double layer (EDL) electrets. Instead of using any external bias-voltage source or dielectric layer on top of the metal electrode to sustain EDL, we succeed to anchor the ions to polymer network to form the EDL electrets. By changing contact area between the EDL electrets and the electrode, large electric current is generated in the circuit. Owing to extremely large capacitance of the EDL electret, vibrational energy harvesters have the unique capability to leverage the high- density charge accumulation to the electrode and obtained current density becomes as high as 200 μA/cm2 with output voltage of 1V even with low frequency vibrations as low as 1 Hz.

  15. Structural characterisation of a layered double hydroxide nanosheet

    NASA Astrophysics Data System (ADS)

    Funnell, Nicholas P.; Wang, Qiang; Connor, Leigh; Tucker, Matthew G.; O'Hare, Dermot; Goodwin, Andrew L.

    2014-06-01

    We report the atomic-scale structure of a Zn2Al-borate layered double hydroxide (LDH) nanosheet, as determined by reverse Monte Carlo (RMC) modelling of X-ray total scattering data. This study involves the extension of the RMC method to enable structural refinement of two-dimensional nanomaterials. The refined LDH models show the intra-layer geometry in this highly-exfoliated phase to be consistent with that observed in crystalline analogues, with the reciprocal-space scattering data suggesting a disordered arrangement of the Zn2+ and Al3+ cations within the nanosheet. The approach we develop is generalisable and so offers a method of characterising the structures of arbitrary nanosheet phases, including systems that support complex forms of disorder within the nanosheets themselves.We report the atomic-scale structure of a Zn2Al-borate layered double hydroxide (LDH) nanosheet, as determined by reverse Monte Carlo (RMC) modelling of X-ray total scattering data. This study involves the extension of the RMC method to enable structural refinement of two-dimensional nanomaterials. The refined LDH models show the intra-layer geometry in this highly-exfoliated phase to be consistent with that observed in crystalline analogues, with the reciprocal-space scattering data suggesting a disordered arrangement of the Zn2+ and Al3+ cations within the nanosheet. The approach we develop is generalisable and so offers a method of characterising the structures of arbitrary nanosheet phases, including systems that support complex forms of disorder within the nanosheets themselves. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr01265h

  16. Physical properties of fixed-charge layer double hydroxides

    NASA Astrophysics Data System (ADS)

    Hines, D. R.; Solin, S. A.; Costantino, Umberto; Nocchetti, Morena

    2000-05-01

    The physical properties of a series of layer double hydroxides (LDH) of the form [(CO3)0.195(1-x)Cl0.39x(H2O)y]:[Zn0.61Al0.39(OH)2], 0<=x<=1, 0<=y<=(0.4+0.2x) have been studied. The hydration dynamics of these materials indicate that the guest layer water molecules form a hydration ring which defines the height of the solvated, nested Cl anion. The water molecules can tilt around their C2v axis such that the height of the solvated Cl ion is a function of the number of molecules forming the hydration ring. The composition dependence of the basal spacing, determined from x-ray-diffraction powder patterns measured as a function of humidity and temperature for these materials, is a function of both the Cl concentration (x) and the number of guest layer water molecules (y). Distinct basal spacing curves are observed for fully hydrated, partially hydrated, and dehydrated materials. At x=1 the Cl end-member material exhibits a change in stacking sequence from a 3R polytype to a 2H polytype upon dehydration. The dehydrated form of this material also exhibits a (3×3)R30° superlattice ordering of the Cl ions. Due to the nesting of the Cl ion and the active nature of the water molecules, the basal spacing vs x curve for the dehydrated materials is the only curve that can be fit by the discrete finite layer rigidity model. The interlayer rigidity parameter for LDH materials has been determined to be p=4.84+/-0.06 indicating that these materials are stiffer than class-II layered solids but not as stiff as class-III layered solids.

  17. Electrical Power Generation by Mechanically Modulating Electrical Double Layers

    NASA Astrophysics Data System (ADS)

    Pak, Hyuk Kyu; Moon, Jong Kyun

    2014-11-01

    Since Michael Faraday and Joseph Henry made their great discovery of electromagnetic induction, there have been continuous developments in electrical power generation. Most people today get electricity from thermal, hydroelectric, or nuclear power generation systems, which use this electromagnetic induction phenomenon. Here we propose a new method for electrical power generation, without using electromagnetic induction, by mechanically modulating the electrical double layers at the interfacial areas of a water bridge between two conducting plates. We find that when the height of the water bridge is mechanically modulated, the electrical double layer capacitors formed on the two interfacial areas are continuously charged and discharged at different phases from each other, thus generating an AC electric current across the plates. We use a resistor-capacitor circuit model to explain the results of this experiment. This observation could be useful for constructing a micro-fluidic power generation system and for understanding the interfacial charge distribution in solid-liquid interfaces in the near future. This work was supported by Center for Soft and Living Matter through IBS prgram in Korea.

  18. 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.

  19. Biodiesel synthesis using calcined layered double hydroxide catalysts

    SciTech Connect

    Schumaker, J. Link; Crofcheck, Czarena; TAckett, S. Adam; Santillan-Jimenez, Eduardo; Morgan, Tonya; Ji, Yaying; Crocker, Mark; Toops, Todd J

    2008-01-01

    The catalytic properties of calcined Li-Al, Mg-Al and Mg-Fe layered double hydroxides (LDHs) were examined in two transesterification reactions, namely, the reaction of glyceryl tributyrate with methanol, and the reaction of soybean oil with methanol. While the Li-Al catalysts showed high activity in these reactions at the reflux temperature of methanol, the Mg-Fe and Mg-Al catalysts exhibited much lower methyl ester yields. CO2 TPD measurements revealed the presence of sites of weak, medium and strong basicity on both Mg-Al and Li-Al catalysts, the latter showing higher concentrations of medium and strong base sites; by implication, these are the main sites active in transesterification catalyzed by calcined Li-Al LDHs. Maximum activity was observed for the Li-Al catalysts when a calcination temperature of 450-500 aC was applied, corresponding to decomposition of the layered double hydroxide to the mixed oxide without formation of crystalline lithium aluminate phases.

  20. Performance of electric double layer capacitors with polymer gel electrolytes

    SciTech Connect

    Ishikawa, Masashi; Kishino, Takahiro; Katada, Naoji; Morita, Masayuki

    2000-07-01

    Polymer gel electrolytes consisting of poly(vinylidene fluoride) (PVdF), tetraethylammonium tetrafluoroborate (TEABF{sub 4}), and propylene carbonate (PC) as a plasticizer have been investigated for electric double layer capacitors. The PVdF gel electrolytes showed high ionic conductivity (ca. 6 mS/cm at 298 K). To assemble model capacitors with the PVdF gel electrolytes and activated carbon fiber cloth electrodes, a pair of the fixed electrodes was soaked in a precursor solution containing PC, PVdF, and TEABF{sub 4}, followed by evaporation of the PC solvent in a vacuum oven. The resulting gel electrolytes were in good contact with the electrodes. The model capacitors with the PVdF gel electrolytes showed a large value of capacitance and high coulombic efficiency in operation voltage ranges of 1--2 and 1--3 V. It is worth noting that the capacitors with the PVdF electrolytes showed long voltage retention in a self-discharge test. These good characteristics of the gel capacitors were comparable to those of typical double layer capacitors with a liquid organic electrolyte containing PC and TEABF{sub 4}; rather, the voltage retentivity of the PVdF gel capacitors was much superior to that of the capacitors with the organic electrolyte.

  1. SUPPRESSION OF ENERGETIC ELECTRON TRANSPORT IN FLARES BY DOUBLE LAYERS

    SciTech Connect

    Li, T. C.; Drake, J. F.; Swisdak, M.

    2012-09-20

    During flares and coronal mass ejections, energetic electrons from coronal sources typically have very long lifetimes compared to the transit times across the systems, suggesting confinement in the source region. Particle-in-cell simulations are carried out to explore the mechanisms of energetic electron transport from the corona to the chromosphere and possible confinement. We set up an initial system of pre-accelerated hot electrons in contact with ambient cold electrons along the local magnetic field and let it evolve over time. Suppression of transport by a nonlinear, highly localized electrostatic electric field (in the form of a double layer) is observed after a short phase of free-streaming by hot electrons. The double layer (DL) emerges at the contact of the two electron populations. It is driven by an ion-electron streaming instability due to the drift of the back-streaming return current electrons interacting with the ions. The DL grows over time and supports a significant drop in temperature and hence reduces heat flux between the two regions that is sustained for the duration of the simulation. This study shows that transport suppression begins when the energetic electrons start to propagate away from a coronal acceleration site. It also implies confinement of energetic electrons with kinetic energies less than the electrostatic energy of the DL for the DL lifetime, which is much longer than the electron transit time through the source region.

  2. Improving acoustic streaming effects in fluidic systems by matching SU-8 and polydimethylsiloxane layers.

    PubMed

    Catarino, S O; Minas, G; Miranda, J M

    2016-07-01

    This paper reports the use of acoustic waves for promoting and improving streaming in tridimensional polymethylmethacrylate (PMMA) cuvettes of 15mm width×14mm height×2.5mm thickness. The acoustic waves are generated by a 28μm thick poly(vinylidene fluoride) - PVDF - piezoelectric transducer in its β phase, actuated at its resonance frequency: 40MHz. The acoustic transmission properties of two materials - SU-8 and polydimethylsiloxane (PDMS) - were numerically compared. It was concluded that PDMS inhibits, while SU-8 allows, the transmission of the acoustic waves to the propagation medium. Therefore, by simulating the acoustic transmission properties of different materials, it is possible to preview the acoustic behavior in the fluidic system, which allows the optimization of the best layout design, saving costs and time. This work also presents a comparison between numerical and experimental results of acoustic streaming obtained with that β-PVDF transducer in the movement and in the formation of fluid recirculation in tridimensional closed domains. Differences between the numerical and experimental results are credited to the high sensitivity of acoustic streaming to the experimental conditions and to limitations of the numerical method. The reported study contributes for the improvement of simulation models that can be extremely useful for predicting the acoustic effects of new materials in fluidic devices, as well as for optimizing the transducers and matching layers positioning in a fluidic structure.

  3. Structure and dynamics of electrical double layers in organic electrolytes

    SciTech Connect

    Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent; Qiao, Rui; Feng, Guang

    2010-01-01

    The organic electrolyte of tetraethylammonium tetrafluoroborate (TEABF{sub 4}) in the aprotic solvent of acetonitrile (ACN) is widely used in electrochemical systems such as electrochemical capacitors. In this paper, we examine the solvation of TEA{sup +} and BF{sub 4}{sup -} in ACN, and the structure, capacitance, and dynamics of the electrical double layers (EDLs) in the TEABF{sub 4}-ACN electrolyte using molecular dynamics simulations complemented with quantum density functional theory calculations. The solvation of TEA+ and BF4- ions is found to be much weaker than that of small inorganic ions in aqueous solutions, and the ACN molecules in the solvation shell of both types of ions show only weak packing and orientational ordering. These solvation characteristics are caused by the large size, charge delocalization, and irregular shape (in the case of TEA+ cation) of the ions. Near neutral electrodes, the double-layer structure in the organic electrolyte exhibits a rich organization: the solvent shows strong layering and orientational ordering, ions are significantly contact-adsorbed on the electrode, and alternating layers of cations/anions penetrate ca. 1.1 nm into the bulk electrolyte. The significant contact adsorption of ions and the alternating layering of cation/anion are new features found for EDLs in organic electrolytes. These features essentially originate from the fact that van der Waals interactions between organic ions and the electrode are strong and the partial desolvation of these ions occurs easily, as a result of the large size of the organic ions. Near charged electrodes, distinct counter-ion concentration peaks form, and the ion distribution cannot be described by the Helmholtz model or the Helmholtz + Poisson-Boltzmann model. This is because the number of counter-ions adsorbed on the electrode exceeds the number of electrons on the electrode, and the electrode is over-screened in parts of the EDL. The computed capacitances of the EDLs are in

  4. Structure and dynamics of electrical double layers in organic electrolytes.

    PubMed

    Feng, Guang; Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent; Qiao, Rui

    2010-01-01

    The organic electrolyte of tetraethylammonium tetrafluoroborate (TEABF(4)) in the aprotic solvent of acetonitrile (ACN) is widely used in electrochemical systems such as electrochemical capacitors. In this paper, we examine the solvation of TEA(+) and BF(4)(-) in ACN, and the structure, capacitance, and dynamics of the electrical double layers (EDLs) in the TEABF(4-)ACN electrolyte using molecular dynamics simulations complemented with quantum density functional theory calculations. The solvation of TEA(+) and BF(4)(-) ions is found to be much weaker than that of small inorganic ions in aqueous solutions, and the ACN molecules in the solvation shell of both types of ions show only weak packing and orientational ordering. These solvation characteristics are caused by the large size, charge delocalization, and irregular shape (in the case of TEA(+) cation) of the ions. Near neutral electrodes, the double-layer structure in the organic electrolyte exhibits a rich organization: the solvent shows strong layering and orientational ordering, ions are significantly contact-adsorbed on the electrode, and alternating layers of cations/anions penetrate ca. 1.1 nm into the bulk electrolyte. The significant contact adsorption of ions and the alternating layering of cation/anion are new features found for EDLs in organic electrolytes. These features essentially originate from the fact that van der Waals interactions between organic ions and the electrode are strong and the partial desolvation of these ions occurs easily, as a result of the large size of the organic ions. Near charged electrodes, distinct counter-ion concentration peaks form, and the ion distribution cannot be described by the Helmholtz model or the Helmholtz + Poisson-Boltzmann model. This is because the number of counter-ions adsorbed on the electrode exceeds the number of electrons on the electrode, and the electrode is over-screened in parts of the EDL. The computed capacitances of the EDLs are in good

  5. Reflection of an acoustic wave from a bubble layer of finite thickness

    NASA Astrophysics Data System (ADS)

    Gubaidullin, D. A.; Fedorov, Yu. V.

    2016-10-01

    The problem of reflection of an acoustic wave from a two-layer medium containing a layer of bubble liquid is considered. The wave reflectance for a water-water mixture with an air bubble-air mixture is calculated and compared with experimental data. The parameters of the problem at which the reflectance takes extreme values are found and illustrated.

  6. Synthesis and characterization of lawsone-lntercalated Zn-Al-layered double hydroxides.

    PubMed

    Yasin, Yamin; Ismail, Nur Mushirah; Hussein, Mohd Zobir; Aminudin, Norhaniza

    2011-06-01

    A drug-inorganic nanostructured material involving pharmaceutically active compound lawsone intercalated Zn-Al layered double hydroxides (Law-LDHs) with Zn/AI = 4 has been assembled by co-precipitation and ion exchange methods. Powder X-ray diffraction (XRD) and Fourier transform infrared spectra (FTIR) analysis indicate a successful intercalation of lawsone between the layers of layered double hydroxides. It suggests that layered double hydroxides may have application as the basis of a drug delivery system.

  7. Characteristics of Double Tropopause Layers Observed During TORERO

    NASA Astrophysics Data System (ADS)

    Haggerty, J. A.; Mahoney, M. J.; Campos, T. L.; Pierce, B.; Volkamer, R. M.

    2012-12-01

    The existence of double tropopauses is indicated in data collected during the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) experiment in January - February 2012. Airborne remote and in situ measurements from the NSF/NCAR Gulfstream V place tropopause heights at ~12-13 km and ~16-17 km during oceanic flights westward and southward from Antofagasta, Chile. Coastal radiosonde profiles confirm the locations of these tropopause layers. Various measurements define and characterize the transition layer between the upper troposphere and lower stratosphere. The Microwave Temperature Profiler (MTP), a scanning radiometer which measures emitted radiation at three frequencies, provides temperature vertical structure over a layer several kilometers above and below the aircraft with vertical resolution sufficient to resolve the tropopause. Tropopause height as determined from the temperature profile is based on the cold point and lapse rate transitions. In situ measurements of trace gases such as ozone, carbon monoxide, and water vapor also provide distinct signatures at the tropopause, although the aircraft did not always reach sufficient altitudes to detect the second tropopause. Model profiles of temperature and trace gases were also generated by the Real-time Air Quality Modeling System (RAQMS) during TORERO. RAQMS is a global meteorological, chemical and aerosol assimilation/forecasting system that assimilates real-time stratospheric ozone retrievals from the Microwave Limb Sounder (MLS), total column ozone from the Ozone Monitoring Instrument (OMI), and aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS). In this paper, observations of the TORERO double tropopause features as defined by temperature and trace gas profiles are presented and compared to model-defined tropopause properties.

  8. Role of barrier layer on dielectric function of graphene double layer system at finite temperature

    NASA Astrophysics Data System (ADS)

    Patel, Digish K.; Ambavale, Sagar K.; Prajapati, Ketan; Sharma, A. C.

    2016-05-01

    We have theoretically investigated the static dielectric function of graphene double layer system (GDLS) at finite temperatures within the random phase approximation. GDLS has been suspended on a substrate and barrier layer of three different materials; h-BN, Al2O3 and HfO2 has been introduced between two graphene sheets of GDLS. We have reported dependence of the overall dielectric function of GDLS on interlayer distance and the effect of the dielectric environment at finite temperatures. Results show close relation between changing environment and behavior of dielectric constant of GDLS.

  9. Acoustic Radiation from High-Speed Turbulent Boundary Layers in a Tunnel-Like Environment

    NASA Technical Reports Server (NTRS)

    Duan, Lian; Choudhari, Meelan M.; Zhang, Chao

    2015-01-01

    Direct numerical simulation of acoustic radiation from a turbulent boundary layer in a cylindrical domain will be conducted under the flow conditions corresponding to those at the nozzle exit of the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) operated under noisy-flow conditions with a total pressure p(sub t) of 225 kPa and a total temperature of T(sub t) equal to 430 K. Simulations of acoustic radiation from a turbulent boundary layer over a flat surface are used as a reference configuration to illustrate the effects of the cylindrical enclosure. A detailed analysis of acoustic freestream disturbances in the cylindrical domain will be reported in the final paper along with a discussion pertaining to the significance of the flat-plate acoustic simulations and guidelines concerning the modeling of the effects of an axisymmetric tunnel wall on the noise field.

  10. Receptivity of Hypersonic Boundary Layers to Distributed Roughness and Acoustic Disturbances

    NASA Technical Reports Server (NTRS)

    Balakumar, P.

    2013-01-01

    Boundary-layer receptivity and stability of Mach 6 flows over smooth and rough seven-degree half-angle sharp-tipped cones are numerically investigated. The receptivity of the boundary layer to slow acoustic disturbances, fast acoustic disturbances, and vortical disturbances is considered. The effects of three-dimensional isolated roughness on the receptivity and stability are also simulated. The results for the smooth cone show that the instability waves are generated in the leading edge region and that the boundary layer is much more receptive to slow acoustic waves than to the fast acoustic waves. Vortical disturbances also generate unstable second modes, however the receptivity coefficients are smaller than that of the slow acoustic wave. Distributed roughness elements located near the nose region decreased the receptivity of the second mode generated by the slow acoustic wave by a small amount. Roughness elements distributed across the continuous spectrum increased the receptivity of the second mode generated by the slow and fast acoustic waves and the vorticity wave. The largest increase occurred for the vorticity wave. Roughness elements distributed across the synchronization point did not change the receptivity of the second modes generated by the acoustic waves. The receptivity of the second mode generated by the vorticity wave increased in this case, but the increase is lower than that occurred with the roughness elements located across the continuous spectrum. The simulations with an isolated roughness element showed that the second mode waves generated by the acoustic disturbances are not influenced by the small roughness element. Due to the interaction, a three-dimensional wave is generated. However, the amplitude is orders of magnitude smaller than the two-dimensional wave.

  11. Laser Induced Fluorescence Studies of Electrostatic Double Layers in an Expanding Helicon Plasma

    NASA Astrophysics Data System (ADS)

    Carr, Jerry, Jr.

    We report the first evidence of a laboratory double layer (DL) collapsing in the presence of an instability studied by Chakraborty Thakur et al. 1 with the use of time resolved laser induced fluorescence (LIF) studies. Higher time resolution studies then provided the first statistically validated proof of the correlation between the ion acoustic instability and a DL. Time-frequency analysis in the form of time resolved cross power spectra and continuous wavelet transforms were used to provide insight into beam formation. The implications of this work is that in the creation of strong DLs in expanding plasmas for plasma propulsion or other applications may be self-limited through instability growth. Over the past decade, experimental and theoretical studies have demonstrated the formation of stable, electrostatic, current-free double layers (CFDLs) in plasmas with a strong density gradient; typically a result of a divergent magnetic field. In this work, we present evidence for the formation of multiple double layers within a single divergent magnetic field structure. Downstream of the divergent magnetic field, multiple accelerated ion populations are observed through laser induced fluorescence measurements of the ion velocity distribution function. The formation of the multiple double layer structure is a strong function of the neutral gas pressure in the experiment. The similarity of the accelerated ion populations observed in these laboratory experiments to ion populations observed in reconnection outflow regions in the magnetosphere and in numerical simulations is also described. If ion energization during magnetic reconnection also results solely from acceleration in electric fields, these observations imply a prediction that the ion heating, i.e., the broadening of ion velocity distribution functions, reported in magnetic reconnection experiments is more accurately described by a superposition of differently accelerated ion populations. Therefore, the ion

  12. The Unique Characteristics of Double Layered Ejecta Craters on Mars

    NASA Astrophysics Data System (ADS)

    Mouginis-Mark, P. J.; Boyce, J. M.

    2004-12-01

    THEMIS VIS images reveal several unique characteristics of double layered ejecta (DLE) craters on Mars that suggest a strikingly different mode of formation from single layered ejecta (SLE) or multi-layered ejecta (MLE) craters. DLE craters are typically 15 to 25 km in diameter and differ from the other types of Martian craters in the following ways: (1) DLE craters lack secondary craters; (2) ejecta layers of DLE craters lack distal ramparts; (3) flow features within the outer layer of DLE craters suggest a very low emplacement velocity; and (4) radial striations exist only within DLE ejecta, and that these striations cross both the inner and outer ejecta layers. The interior morphology of DLE is also less complex than SLE or MLE layered ejecta craters; DLE craters lack wall terraces and, where present, have only simple central peaks. Previous morphologic analyses of DLE craters proposed that they might have formed in the volatile-rich sediments that are believed to infill areas such as Utopia, Arcadia and Acidalia Planitiae. But our inspection of the THEMIS VIS data set confirms the Viking-based results of Barlow and Perez (JGR-Planets, vol. 108 (E8), doi 10.1029/2002JE002036, 2003) that DLE craters are not uniquely located in the northern plains. We find that DLE craters with nearly identical morphologies also occur within the highlands of Mars, including Hesperia Planum, Icaria Planum, Arabia Terra, Noachis Terra, and Terra Sirenum. A few examples of DLE craters are found at a range of elevations between -5.8 km to +2.7 km relative to the MOLA datum, and within two latitudes belts between 23° to 52° N, and between 29° to 46° S. Thus some other mode of formation apart from impact into volatile-rich sediments of the northern plains needs to be identified. Through our on-going characterization of DLE craters with THEMIS VIS data, we hope to identify the attributes of these craters to help identify their unique mode of formation.

  13. Phase decorrelation, streamwise vortices and acoustic radiation in mixing layers

    NASA Technical Reports Server (NTRS)

    Ho, C. M.; Zohar, Y.; Moser, R. D.; Rogers, M. M.; Lele, S. K.; Buell, J. C.

    1988-01-01

    Several direct numerical simulations were performed and analyzed to study various aspects of the early development of mixing layers. Included are the phase jitter of the large-scale eddies, which was studied using a 2-D spatially-evolving mixing layer simulation; the response of a time developing mixing layer to various spanwise disturbances; and the sound radiation from a 2-D compressible time developing mixing layer.

  14. Biological evaluation of layered double hydroxides as efficient drug vehicles.

    PubMed

    Li, Yan; Liu, Dan; Ai, Hanhua; Chang, Qing; Liu, Dandan; Xia, Ying; Liu, Shuwen; Peng, Nanfang; Xi, Zhuge; Yang, Xu

    2010-03-12

    Recently there has been a rapid expansion of the development of bioinorganic hybrid systems for safe drug delivery. Layered double hydroxides (LDH), a variety of available inorganic matrix, possess great promise for this purpose. In this study, an oxidative stress biomarker system, including measurement of reactive oxygen species, glutathione content, endogenous nitric oxide, carbonyl content in proteins, DNA strand breaks and DNA-protein crosslinks, was designed to evaluate the biocompatibility of different concentrations of nano-Zn/Al-LDH with a Hela cell line. The drug delivery activity of the LDH-folic-acid complex was also assessed. The resulting data clearly demonstrated that nano-LDH could be applied as a relatively safe drug vehicle with good delivery activity, but with the caveat that the effects of high dosages observed here should not be ignored when attempting to maximize therapeutic activity by increasing LDH concentration.

  15. Layered double hydroxides: an attractive material for electrochemical biosensor design.

    PubMed

    Shan, Dan; Cosnier, Serge; Mousty, Christine

    2003-08-01

    Electrochemical biosensors for phenol determination were developed based on the immobilization of polyphenol oxidase (PPO) within two different clay matrixes, one anionic (layered double hydroxide, LDH) and the other cationic (Laponite). The biosensor based on the enzyme immobilized in [Zn-Al-Cl] LDH shows greater sensitivity (7807 mA M(-1) cm(-2)) and maximum current (492 microA cm(-2)). Biosensor characteristics, such as Michaelis-Menten constant, recycling constant, activation energy, and permeability highlight the advantages of LDH matrixes to immobilize PPO. It appears that LDH provides a favorable environment to PPO activity. The best PPO/[Zn-Al-Cl] configuration was used to determine five different phenol derivatives reaching extremely sensitive detection limits (< or = 1 nM).

  16. Hybrid and biohybrid layered double hydroxides for electrochemical analysis.

    PubMed

    Mousty, Christine; Prévot, Vanessa

    2013-04-01

    Layered double hydroxides (LDH) are lamellar materials that have been extensively used as electrode modifiers. Nanostructured organic-inorganic materials can be designed by intercalation of organic or metallic complexes within the interlayer space of these materials or by the formation of composite materials based on biopolymers (alginate or chitosan) or biomolecules, such as enzymes. These hybrid or biohybrid materials have interesting properties applicable in electroanalytical devices. From an exhaustive review of the literature, the relevance of these hybrid and biohybrid LDH materials as electrode materials for electrochemical detection of species with an environmental or health impact is evaluated. The analytical characteristics (sensitivity and detection limit) of LDH-based amperometric sensors or biosensors are scrutinized.

  17. Carbon additives for electrical double layer capacitor electrodes

    NASA Astrophysics Data System (ADS)

    Weingarth, D.; Cericola, D.; Mornaghini, F. C. F.; Hucke, T.; Kötz, R.

    2014-11-01

    Electrochemical double layer capacitors (EDLCs) are inherently high power devices when compared to rechargeable batteries. While capacitance and energy storage ability are mainly increased by optimizing the electrode active material or the electrolyte, the power capability could be improved by including conductive additives in the electrode formulations. This publication deals with the use of four different carbon additives - two carbon blacks and two graphites - in standard activated carbon based EDLC electrodes. The investigations include: (i) physical characterization of carbon powder mixtures such as surface area, press density, and electrical resistivity measurements, and (ii), electrochemical characterization via impedance spectroscopy and cyclic voltammetry of full cells made with electrodes containing 5 wt.% of carbon additive and compared to cells made with pure activated carbon electrodes in organic electrolyte. Improved cell performance was observed in both impedance and cyclic voltammetry responses. The results are discussed considering the main characteristics of the different carbon additives, and important considerations about electrode structure and processability are drawn.

  18. Limiting factors for carbon based chemical double layer capacitors

    NASA Technical Reports Server (NTRS)

    Rose, M. Frank; Johnson, C.; Owens, T.; Stevens, B.

    1993-01-01

    The Chemical Double Layer (CDL) capacitor improves energy storage density dramatically when compared with conventional electrolytic capacitors. When compared to batteries, the CDL Capacitor is much less energy dense; however, the power density is orders of magnitude better. As a result, CDL-battery combinations present an interesting pulse power system with many potential applications. Due to the nature of the CDL it is inherently a low voltage device. The applications of the CDL can be tailored to auxiliary energy and burst mode storages which require fast charge/discharge cycles. Typical of the applications envisioned are power system backup, directed energy weapons concepts, electric automobiles, and electric actuators. In this paper, we will discuss some of the general characteristics of carbon-based CDL technology describing the structure, performance parameters, and methods of construction. Further, analytical and experimental results which define the state of the art are presented and described in terms of impact on applications.

  19. "Thermal Charging" Phenomenon in Electrical Double Layer Capacitors.

    PubMed

    Wang, Jianjian; Feng, Shien-Ping; Yang, Yuan; Hau, Nga Yu; Munro, Mary; Ferreira-Yang, Emerald; Chen, Gang

    2015-09-09

    Electrical double layer capacitors (EDLCs) are usually charged by applying a potential difference across the positive and negative electrodes. In this paper, we demonstrated that EDLCs can be charged by heating. An open circuit voltage of 80-300 mV has been observed by heating the supercapacitor to 65 °C. The charge generated at high temperature can be stored in the device after its returning to the room temperature, thus allowing the lighting up of LEDs by connecting the "thermally charged" supercapacitors in a series. The underlying mechanism is related to a thermo-electrochemical process that enhances the kinetics of Faradaic process at the electrode surface (e.g., surface redox reaction of functional group, or chemical adsorption/desorption of electrolyte ions) at higher temperature. Effects of "thermal charging" times, activation voltage, rate, and times on "thermally charged" voltage are studied and possible mechanisms are discussed.

  20. Layered Double Hydroxide-Based Nanocarriers for Drug Delivery

    PubMed Central

    Bi, Xue; Zhang, Hui; Dou, Liguang

    2014-01-01

    Biocompatible clay materials have attracted particular attention as the efficient drug delivery systems (DDS). In this article, we review developments in the use of layered double hydroxides (LDHs) for controlled drug release and delivery. We show how advances in the ability to synthesize intercalated structures have a significant influence on the development of new applications of these materials. We also show how modification and/or functionalization can lead to new biotechnological and biomedical applications. This review highlights the most recent progresses in research on LDH-based controlled drug delivery systems, focusing mainly on: (i) DDS with cardiovascular drugs as guests; (ii) DDS with anti-inflammatory drugs as guests; and (iii) DDS with anti-cancer drugs as guests. Finally, future prospects for LDH-based drug carriers are also discussed. PMID:24940733

  1. On the dielectric response of complex layered oxides: Mica-type silicates and layered double hydroxides

    NASA Astrophysics Data System (ADS)

    Mehrotra, Vivek; Giannelis, Emmanuel P.

    1992-08-01

    The dielectric properties of mica-type silicates and layered double hydroxides have been studied in the pristine and various intercalated forms in the frequency range 101-107 Hz. A relaxation peak has been observed for the pristine silicate, whereas the pristine layered double hydroxide exhibits an anomalous low-frequency dispersion. The dielectric response is rationalized in terms of structural ordering and fluctuation of charge carriers as well as models invoking fractal time processes and fractal structure. The response is also related to the structure and mobility of the intercalated water molecules. In both pristine hosts, the predominant conduction mechanism is proton hopping between sites generated by a network of intercalated water molecules. Silicate intercalated with the insulating form of polyaniline exhibits an almost frequency-independent response. In the case of conducting polyaniline intercalated silicate, where polarons are the majority charge carriers, an anomalous low-frequency dispersion is observed and the response is typical of a metal-insulator composite. Finally, impedance measurements have been used to calculate the spatial disorder and/or surface irregularity of the host layers, expressed by the fractal dimension ds. The changes observed in ds upon intercalation of high-charge ions are correlated to the stacking disorder of the host layers.

  2. Beam stresses induced by a turbulent boundary layer and simulated with a reverberant acoustic field

    NASA Technical Reports Server (NTRS)

    Schutzenhofer, L. A.

    1981-01-01

    Unsteady pressure fluctuations are a feature of the flow field of an airplane or a space vehicle in atmospheric flight. Undesirable effects of these fluctuations range from internal (cabin) noise to structural fatigue and damage of avionic and ordnance systems. The integrity to withstand these fluctuating loads is established through reverberant room acoustical qualification testing. The purpose of this paper is to develop a methodology of simulating turbulent boundary layer fluctuating pressure loading for a simply supported beam with a reverberant acoustic field. This goal was accomplished using normal mode vibration analysis. The main results were developed in terms of dimensionless quantities such as turbulent boundary layer spectrums, reverberant acoustical field simulation spectrums, and stress response spectrums with parameters: dimensionless fundamental frequency, Mach number, and relative boundary layer displacement thickness.

  3. Acoustic Receptivity of Mach 4.5 Boundary Layer with Leading- Edge Bluntness

    NASA Technical Reports Server (NTRS)

    Malik, Mujeeb R.; Balakumar, Ponnampalam

    2007-01-01

    Boundary layer receptivity to two-dimensional slow and fast acoustic waves is investigated by solving Navier-Stokes equations for Mach 4.5 flow over a flat plate with a finite-thickness leading edge. Higher order spatial and temporal schemes are employed to obtain the solution whereby the flat-plate leading edge region is resolved by providing a sufficiently refined grid. The results show that the instability waves are generated in the leading edge region and that the boundary-layer is much more receptive to slow acoustic waves (by almost a factor of 20) as compared to the fast waves. Hence, this leading-edge receptivity mechanism is expected to be more relevant in the transition process for high Mach number flows where second mode instability is dominant. Computations are performed to investigate the effect of leading-edge thickness and it is found that bluntness tends to stabilize the boundary layer. Furthermore, the relative significance of fast acoustic waves is enhanced in the presence of bluntness. The effect of acoustic wave incidence angle is also studied and it is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases by more than a factor of 4 when the incidence angle is increased from 0 to 45 deg. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle.

  4. Reflection and transmission of acoustical waves from a layer with space-dependent velocity.

    NASA Technical Reports Server (NTRS)

    Steinmetz, G. G.; Singh, J. J.

    1972-01-01

    The refraction of acoustical waves by a moving medium layer is theoretically treated and the reflection and transmission coefficients are determined. The moving-medium-layer velocity is uniform but with a space dependence in one direction. A partitioning of the moving medium layer into constant-velocity sublayers is introduced and numerical results for a three-sublayer approximation of Poiseuille flow are presented. The degenerate case of a single constant-velocity layer is also treated theoretically and numerically. The numerical results show the reflection and transmission coefficients as functions of the peak moving-medium-layer normalized velocity for several angles of incidence.

  5. Acoustic radiation from the submerged circular cylindrical shell treated with active constrained layer damping

    NASA Astrophysics Data System (ADS)

    Yuan, Li-Yun; Xiang, Yu; Lu, Jing; Jiang, Hong-Hua

    2015-12-01

    Based on the transfer matrix method of exploring the circular cylindrical shell treated with active constrained layer damping (i.e., ACLD), combined with the analytical solution of the Helmholtz equation for a point source, a multi-point multipole virtual source simulation method is for the first time proposed for solving the acoustic radiation problem of a submerged ACLD shell. This approach, wherein some virtual point sources are assumed to be evenly distributed on the axial line of the cylindrical shell, and the sound pressure could be written in the form of the sum of the wave functions series with the undetermined coefficients, is demonstrated to be accurate to achieve the radiation acoustic pressure of the pulsating and oscillating spheres respectively. Meanwhile, this approach is proved to be accurate to obtain the radiation acoustic pressure for a stiffened cylindrical shell. Then, the chosen number of the virtual distributed point sources and truncated number of the wave functions series are discussed to achieve the approximate radiation acoustic pressure of an ACLD cylindrical shell. Applying this method, different radiation acoustic pressures of a submerged ACLD cylindrical shell with different boundary conditions, different thickness values of viscoelastic and piezoelectric layer, different feedback gains for the piezoelectric layer and coverage of ACLD are discussed in detail. Results show that a thicker thickness and larger velocity gain for the piezoelectric layer and larger coverage of the ACLD layer can obtain a better damping effect for the whole structure in general. Whereas, laying a thicker viscoelastic layer is not always a better treatment to achieve a better acoustic characteristic. Project supported by the National Natural Science Foundation of China (Grant Nos. 11162001, 11502056, and 51105083), the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2012GXNSFAA053207), the Doctor Foundation of Guangxi

  6. Some dynamical properties of very strong double layers in a triple plasma device

    NASA Technical Reports Server (NTRS)

    Carpenter, T.; Torven, S.

    1987-01-01

    Dynamical properties of very strong double layers seen in a differentially pumped triple plasma device are reported. These double layers are V-shaped. The following findings are discussed: (1) Disruptions in the double layer potential and in the plasma current occur when an inductance is placed in series with the bias supply between the sources in the external circuit. These disruptions, which can be highly periodic, are the result of a negative resistance region. (2) When reactances in the circuit are minimized, the double layer exhibits a jitter motion in position approximately equal to the double layer thickness. (3) When the bias between the sources is rapidly turned on, the initial phase in the double layer formation is the occurrence of a constant electric field for the first few microseconds. First the apparatus used in all of the work is discussed and then each of the three phenomena are considered.

  7. Experimental realization of acoustic metasurface with double-split hollow sphere

    NASA Astrophysics Data System (ADS)

    Ding, Chang-Lin; Wang, Zhen-Ru; Shen, Fang-Liang; Chen, Huai-Jun; Zhai, Shi-Long; Zhao, Xiao-Peng

    2016-03-01

    We experimentally present an acoustic metasurface (AMS) with sub-wavelength thickness based on the meta-molecule consisting of eight different sized double-split hollow spheres (DSHSs). By designing the discontinuous phase profile covered 2π span induced by the DSHSs, the AMS can manipulate the reflected acoustic waves in a way that could not be imitated by natural materials. Both simulations and experiments show that the AMS can realize anomalous reflection, i.e., a normal incident wave can be reflected into an oblique direction. Moreover, the reflection angle can be flexible controlled by mechanically tuning the spatial distance of the DSHSs in the AMS, which is consistent with the generalized Snell's law.

  8. Layered double oxide (LDO) particle containing photoreactive hybrid layers with tunable superhydrophobic and photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Deák, Ágota; Janovák, László; Csapó, Edit; Ungor, Ditta; Pálinkó, István; Puskás, Sándor; Ördög, Tibor; Ricza, Tamás; Dékány, Imre

    2016-12-01

    Inorganic/organic hybrid layers have been prepared having superhydrophobic as well as photoreactive properties. The hybrid thin films with micro- and nanosized dual-scale surface roughness consist of ∼25 μm layered double oxide (LDO) photocatalyst particles and low surface energy poly(perfluorodecyl acrylate) [p(PFDAc)] fluoropolymer binder material. The application of [p(PFDAc)] resulted in the decrease in the surface free energy of the hydrophilic LDO. The structured surface LDO with ∼12% ZnO phase content were synthesized from layer double hydroxide (LDH) spheres. The determined excitation wavelength and the calculated band gap energy values were 386 nm and 3.23 eV, respectively. The hybrid thin films were prepared by a simple spray-coating method, which is a low-cost, fast and scalable film-forming technique. The surface roughness and also the wetting properties of the two-component hybrid layers proved to be finely adjustable by the LDO:fluoropolymer ratio. It was found that at 80-90 wt% LDO content, the thin films with a surface free energy value of ∼12 mJ/m2 displayed superhydrophobic behaviour (Θ > 150°) with satisfactory photocatalytic properties. This means special photoreactive surfaces with superhydrophobic properties instead of the conventional superhydropilic photocatalyst layers. According to the benzoic acid photodegradation test experiments of benzoic acid, the hybrid layers with 80-90 wt% LDO content photooxidized 22-24% of the initial test molecule concentration (0.17 g/L) under UV-A (λmax = 365 nm) illumination.

  9. Vorticity Transport in a Two Layer, Double Gyre Ocean Basin

    NASA Astrophysics Data System (ADS)

    Kaiser, Bryan; Clayson, Carol Anne; Jayne, Steve

    2016-11-01

    The double gyre ocean circulations predicted by strongly frictional, barotropic, linearized ocean models qualitatively agree with the patterns of large scale gyres in the world ocean. However, nonlinear ocean models featuring less intense eddy diffusion parameterization can converge to an infinite number of statistically stationary circulations, depending on the parameterization of dissipation of energy and vorticity. Patterns of vorticity flux and dissipation in a barotropic ocean have been examined previous studies; in this work the inclusion of the first baroclinic mode is examined. The first vertical mode permits the model to be split into two layers, the top approximating the thermocline and the bottom approximating the abyssal circulation. The separation into two layers not only adds realism and but also removes the nonphysical direct restraint of the upper ocean by bottom friction. Steady state circulations for various boundary conditions, sources and sinks of vorticity, and Reynolds numbers are simulated using a parallel pseudo-spectral quasi-geostrophic flow solver and mechanisms of vorticity flux and dissipation are discussed.

  10. Receptivity of Hypersonic Boundary Layers to Distributed Roughness and Acoustic Disturbances

    NASA Technical Reports Server (NTRS)

    Balakumar, Ponnampalam

    2012-01-01

    Boundary-layer receptivity and stability of Mach 6 flow over smooth and rough 7 half-angle sharp-tipped cones are numerically investigated. The receptivity of the boundary layer to slow acoustic disturbances, fast acoustic disturbances, and vortical disturbances are considered. The effects of two-dimensional isolated and distributed roughness on the receptivity and stability are also simulated. The results show that the instability waves are generated in the leading edge region and that the boundary layer is much more receptive to slow acoustic waves than to the fast waves. Vortical disturbances also generate unstable second modes, however the receptivity coefficients are smaller than that of the slow acoustic wave. An isolated two-dimensional roughness element of height h/delta =1/4 did not produce any difference in the receptivity or in the stability of the boundary layer. Distributed roughness elements produced a small decrease in the receptivity coefficient and also stabilized the boundary layer by small amounts.

  11. On The Physical Mechanism At The Origin Of Multiple Double Layers Appearance In Plasma

    SciTech Connect

    Dimitriu, D. G.; Gurlui, S.; Aflori, M.; Ivan, L. M.

    2006-01-15

    Double layer in plasma are nonlinear potential structures consisting of two adjacent layers of positive and negative space charges, respectively. Between these layers a potential jump exists, creating an electric field. A common way to obtain a double layer structure is to positively bias an electrode immersed into stable plasma. Under certain experimental conditions, a more complex structure in form of two or more subsequent double layers was observed, which was called multiple double layers. It appears as several bright and concentric plasma shells attached to the electrode. The successive double layers are located at the abrupt changes of luminosity between two adjacent plasma shells. However, if the electrode is large, the multiple double layers structure appears non-concentrically, as a network of plasma spots, near each other, almost equally distributed on the electrode surface. Each of the plasma spots is confined by an electrical double layer. Here, we will present experimental results on the appearance and dynamics of concentric, as well as non-concentric multiple double layers. The results prove that the same physical mechanism is at the origin of their appearance in plasma. In this mechanism, the electron-neutral impact excitations and ionizations play the key role.

  12. Electrochemical double-layer capacitors based on functionalized graphene

    NASA Astrophysics Data System (ADS)

    Pope, Michael Allan

    Graphene is a promising electrode material for electrochemical double-layer capacitors (EDLCs) used for energy storage due to its high electrical conductivity and theoretical specific surface area. However, the intrinsic capacitance of graphene is known to be low and governed by the electronic side of the interface. Furthermore, graphene tends to aggregate and stack together when processed into thick electrode films. This significantly lowers the ion-accessible specific surface area (SSA). Maximizing both the SSA and the intrinsic capacitance are the main problems addressed in this thesis in an effort to improve the specific capacitance and energy density of EDLCs. In contrast to pristine graphene, functionalized graphene produced by the thermal exfoliation of graphite oxide contains residual functional groups and lattice defects. To study how these properties affect the double-layer capacitance, a model electrode system capable of measuring the intrinsic electrochemical properties of functionalized graphene was developed. To prevent artifacts and uncertainties related to measurements on porous electrodes, the functionalized graphene sheets (FGSs) were assembled as densely tiled monolayers using a Langmuir-Blodgett technique. In this way, charging can be studied in a well-defined 2D geometry. The possibility of measuring and isolating the intrinsic electrochemical properties of FGS monolayers was first demonstrated by comparing capacitance and redox probe measurements carried out on coatings deposited on passivated gold and single crystal graphite substrates. This monolayer system was then used to follow the double-layer capacitance of the FGS/electrolyte interface as the structure and chemistry of graphene was varied by thermal treatments ranging from 300 °C to 2100 °C. Elemental analysis and Raman spectroscopy were used to determine the resulting chemical and structural transformation upon heat treatment. It was demonstrated that intrinsically defective

  13. Asymmetric transmission of acoustic waves in a layer thickness distribution gradient structure using metamaterials

    NASA Astrophysics Data System (ADS)

    Chen, Jung-San; Chang, I.-Ling; Huang, Wan-Ting; Chen, Lien-Wen; Huang, Guan-Hua

    2016-09-01

    This research presents an innovative asymmetric transmission design using alternate layers of water and metamaterial with complex mass density. The directional transmission behavior of acoustic waves is observed numerically inside the composite structure with gradient layer thickness distribution and the rectifying performance of the present design is evaluated. The layer thickness distributions with arithmetic and geometric gradients are considered and the effect of gradient thickness on asymmetric wave propagation is systematically investigated using finite element simulation. The numerical results indicate that the maximum pressure density and transmission through the proposed structure are significantly influenced by the wave propagation direction over a wide range of audible frequencies. Tailoring the thickness of the layered structure enables the manipulation of asymmetric wave propagation within the desired frequency range. In conclusion, the proposed design offers a new possibility for developing directional-dependent acoustic devices.

  14. Acoustic sources in the low Mach number turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Hardin, Jay C.

    1991-01-01

    The sources of sound production in a low Mach number turbulent boundary layer are examined. The sources are shown to be quadrupole in nature and to result from supersonically convecting wave-number components of the fluctuating Reynolds' normal stresses. The primary Tollmien-Schlichting instability of the boundary layer is found to radiate no sound. Analysis of various vortical phenomena suggests that the primary source is the process of formation of horseshoe vortices, with viscous sublayer bursts a possible secondary source.

  15. Large-scale simulations of layered double hydroxide nanocomposite materials

    NASA Astrophysics Data System (ADS)

    Thyveetil, Mary-Ann

    Layered double hydroxides (LDHs) have the ability to intercalate a multitude of anionic species. Atomistic simulation techniques such as molecular dynamics have provided considerable insight into the behaviour of these materials. We review these techniques and recent algorithmic advances which considerably improve the performance of MD applications. In particular, we discuss how the advent of high performance computing and computational grids has allowed us to explore large scale models with considerable ease. Our simulations have been heavily reliant on computational resources on the UK's NGS (National Grid Service), the US TeraGrid and the Distributed European Infrastructure for Supercomputing Applications (DEISA). In order to utilise computational grids we rely on grid middleware to launch, computationally steer and visualise our simulations. We have integrated the RealityGrid steering library into the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) 1 . which has enabled us to perform re mote computational steering and visualisation of molecular dynamics simulations on grid infrastruc tures. We also use the Application Hosting Environment (AHE) 2 in order to launch simulations on remote supercomputing resources and we show that data transfer rates between local clusters and super- computing resources can be considerably enhanced by using optically switched networks. We perform large scale molecular dynamics simulations of MgiAl-LDHs intercalated with either chloride ions or a mixture of DNA and chloride ions. The systems exhibit undulatory modes, which are suppressed in smaller scale simulations, caused by the collective thermal motion of atoms in the LDH layers. Thermal undulations provide elastic properties of the system including the bending modulus, Young's moduli and Poisson's ratios. To explore the interaction between LDHs and DNA. we use molecular dynamics techniques to per form simulations of double stranded, linear and plasmid DNA up

  16. Comparison with Analytical Solution: Generation and Radiation of Acoustic Waves from a 2-D Shear Layer

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.

    2000-01-01

    An acoustic source inside of a 2-D jet excites an instability wave in the shear layer resulting in sound radiating away from the shear layer. Solve the linearized Euler equations to predict the sound radiation outside of the jet. The jet static pressure is assumed to be constant. The jet flow is parallel and symmetric about the x-axis. Use a symmetry boundary condition along the x-axis.

  17. Receptivity and Forced Response to Acoustic Disturbances in High-Speed Boundary Layers

    NASA Technical Reports Server (NTRS)

    Balakumar, P.; King, Rudolph A.; Chou, Amanda; Owens, Lewis R.; Kegerise, Michael A.

    2016-01-01

    Supersonic boundary-layer receptivity to freestream acoustic disturbances is investigated by solving the Navier-Stokes equations for Mach 3.5 flow over a sharp flat plate and a 7-deg half-angle cone. The freestream disturbances are generated from a wavy wall placed at the nozzle wall. The freestream acoustic disturbances radiated by the wavy wall are obtained by solving the linearized Euler equations. The results for the flat plate show that instability modes are generated at all the incident angles ranging from zero to highly oblique. However, the receptivity coefficient decreases by about 20 times when the incident angle increases from zero to a highly oblique angle of 68 degrees. The results for the cone show that no instability modes are generated when the acoustic disturbances impinge the cone obliquely. The results show that the perturbations generated inside the boundary layer by the acoustic disturbances are the response of the boundary layer to the external forcing. The amplitude of the forced disturbances inside the boundary layer are about 2.5 times larger than the incoming field for zero azimuthal wavenumber and they are about 1.5 times for large azimuthal wavenumbers.

  18. Energy distribution of elastically scattered electrons from double layer samples

    NASA Astrophysics Data System (ADS)

    Tőkési, K.; Varga, D.

    2016-02-01

    We present a theoretical description of the spectra of electrons elastically scattered from thin double layered Au-C samples. The analysis is based on the Monte Carlo simulation of the recoil and Doppler effects in reflection and transmission geometries of the scattering at a fixed angle of 44.3 ° and a primary energy of 40 keV. The relativistic correction is taken into account. Besides the experimentally measurable energy distributions the simulations give many partial distributions separately, depending on the number of elastic scatterings (single, and multiple scatterings of different types). Furthermore, we present detailed analytical calculations for the main parameters of the single scattering, taking into account both the ideal scattering geometry, i.e. infinitesimally small angular range, and the effect of the real, finite angular range used in the measurements. We show our results for intensity ratios, peak shifts and broadenings for four cases of measurement geometries and layer thicknesses. While in the peak intensity ratios of gold and carbon for transmission geometries were found to be in good agreement with the results of the single scattering model, especially large deviations were obtained in reflection geometries. The separation of the peaks, depending on the geometry and the thickness, generally smaller, and the peak width generally larger than it can be expected from the nominal values of the primary energy, scattering angle, and mean kinetic energy of the atoms. We also show that the peaks are asymmetric even for the case of the single scattering due to the finite solid angle. Finally, we present a qualitative comparison with the experimental data. We find our resulting energy distribution of elastically scattered electrons to be in good agreement with recent measurements.

  19. Double Layers in Expanding Plasmas and Their Relevance to the Auroral Plasma Processes

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Khazanov, George

    2003-01-01

    When a dense plasma consisting of a cold and a sufficiently warm electron population expands, a rarefaction shock forms [Bezzerides et al., 1978]. In the expansion of the polar wind in the magnetosphere, it has been previously shown that when a sufficiently warm electron population also exists, in addition to the usual cold ionospheric one, a discontinuity forms in the electrostatic potential distribution along the magnetic field lines [Barakat and Schunk, 1984]. Despite the lack of spatial resolution and the assumption of quasi-neutrality in the polar wind models, such discontinuities have been called double layers (DLs). Recently similar discontinuities have been invoked to partly explain the auroral acceleration of electrons and ions in the upward current region [Ergun et al., 2000]. By means of one-dimensional Vlasov simulations of expanding plasmas, for the first time we make here the connection between (1) the rarefaction shocks, (2) the discontinuities in the potential distributions, and (3) DLs. We show that when plasmas expand from opposite directions into a deep density cavity with a potential drop across it and when the plasma on the high-potential side contains hot and cold electron populations, the temporal evolution of the potential and the plasma distribution generates evolving multiple double layers with an ,extended density cavity between them. One of the DLs is the rarefaction-shock (RFS) and it forms by the reflections of the cold electrons coming from the high-potential side; it supports a part of the potential drop approximately determined by the hot electron temperature. The other DLs evolve from charge separations arising either from reflection of ions coming from the low-potential side or stemming from plasma instabilities; they support the rest of the potential drop. The instabilities forming these additional double layers involve electron-ion (e-i) Buneman or ion-ion (i-i) two-stream interactions. The electron-electron two

  20. Fast charging self-powered electric double layer capacitor

    NASA Astrophysics Data System (ADS)

    Parida, Kaushik; Bhavanasi, Venkateswarlu; Kumar, Vipin; Wang, Jiangxin; Lee, Pooi See

    2017-02-01

    Self-powered electrochemical energy storage devices, which store energy upon application of mechanical force, have emerged as a promising technology for the realization of autonomous systems for maintenance-free, independent and multifunctional operations. However, the existing state-of-the-art technology demonstrates slow self-charging due to slow Faradaic reactions and intercalation mechanism. Here, we report a fast self-charging, self-powered electrochemical energy storage device owing to the formation of an electric double layer with fast adsorption and desorption of ions at the carbon nanotube (CNT) electrode upon application of mechanical force. The device charges up to 70 mV from the open-circuit potential, storing a capacitance of 95 μFcm-2 upon application of a mechanical pressure of 70 N at a frequency of 5 Hz. More importantly, it takes less than 10 s to achieve 90% of the increment in the potential (60 mV), which is more than one order of magnitude faster than all of the previously reported self-powered energy storage devices.

  1. Stable electrolyte for high voltage electrochemical double-layer capacitors

    SciTech Connect

    Ruther, Rose E.; Sun, Che -Nan; Holliday, Adam; Cheng, Shiwang; Delnick, Frank M.; Zawodzinski, Thomas A.; Nanda, Jagjit

    2016-12-28

    A simple electrolyte consisting of NaPF6 salt in 1,2-dimethoxyethane (DME) can extend the voltage window of electric double-layer capacitors (EDLCs) to >3.5 V. DME does not passivate carbon electrodes at very negative potentials (near Na/Na+), extending the practical voltage window by about 1.0 V compared to standard, non-aqueous electrolytes based on acetonitrile. The voltage window is demonstrated in two- and three-electrode cells using a combination of electrochemical impedance spectroscopy (EIS), charge-discharge cycling, and measurements of leakage current. DME-based electrolytes cannot match the high conductivity of acetonitrile solutions, but they can satisfy applications that demand high energy density at moderate power. The conductivity of NaPF6 in DME is comparable to commercial lithium-ion battery electrolytes and superior to most ionic liquids. Lastly, factors that limit the voltage window and EDLC energy density are discussed, and strategies to further boost energy density are proposed.

  2. Field-Induced Superconductivity in Electric Double Layer Transistors

    NASA Astrophysics Data System (ADS)

    Ueno, Kazunori; Shimotani, Hidekazu; Yuan, Hongtao; Ye, Jianting; Kawasaki, Masashi; Iwasa, Yoshihiro

    2014-03-01

    Electric field tuning of superconductivity has been a long-standing issue in solid state physics since the invention of the field-effect transistor (FET) in 1960. Owing to limited available carrier density in conventional FET devices, electric-field-induced superconductivity was believed to be possible in principle but impossible in practice. However, in the past several years, this limitation has been overcome by the introduction of an electrochemical concept, and electric-field-induced superconductivity has been realized. In the electric double layer (EDL) formed at the electrochemical interfaces, an extremely high electric field is generated and hence high-density charge carriers sufficient to induce superconductivity exist and are collectively used as a charge accumulation device known as an EDL capacitor. Field-induced superconductivity has been used to establish the relationship between Tc and carrier density and can now be used to search for new superconductors. Here, we review electric-field-induced superconductivity using an FET device, with a particular focus on the latest advances in EDL transistors.

  3. Lubrication approximation in completed double layer boundary element method

    NASA Astrophysics Data System (ADS)

    Nasseri, S.; Phan-Thien, N.; Fan, X.-J.

    This paper reports on the results of the numerical simulation of the motion of solid spherical particles in shear Stokes flows. Using the completed double layer boundary element method (CDLBEM) via distributed computing under Parallel Virtual Machine (PVM), the effective viscosity of suspension has been calculated for a finite number of spheres in a cubic array, or in a random configuration. In the simulation presented here, the short range interactions via lubrication forces are also taken into account, via the range completer in the formulation, whenever the gap between two neighbouring particles is closer than a critical gap. The results for particles in a simple cubic array agree with the results of Nunan and Keller (1984) and Stoksian Dynamics of Brady etal. (1988). To evaluate the lubrication forces between particles in a random configuration, a critical gap of 0.2 of particle's radius is suggested and the results are tested against the experimental data of Thomas (1965) and empirical equation of Krieger-Dougherty (Krieger, 1972). Finally, the quasi-steady trajectories are obtained for time-varying configuration of 125 particles.

  4. Dislocated double-layer metal gratings: an efficient unidirectional coupler.

    PubMed

    Liu, Tianran; Shen, Yang; Shin, Wonseok; Zhu, Qiangzhong; Fan, Shanhui; Jin, Chongjun

    2014-07-09

    We propose theoretically and demonstrate experimentally a dislocated double-layer metal grating structure, which operates as a unidirectional coupler capable of launching surface plasmon polaritons in a desired direction under normal illumination. The structure consists of a slanted dielectric grating sandwiched between two gold gratings. The upper gold grating has a nonzero lateral relative displacement with respect to the lower one. Numerical simulations show that a grating structure with 7 periods can convert 49% of normally incident light into surface plasmons with a contrast ratio of 78 between the powers of the surface plasmons launched in two opposite directions. We explain the unidirectional coupling phenomenon by the dislocation-induced interference of the diffracted waves from the upper and lower gold gratings. Furthermore, we developed a simple and cost-effective technique to fabricate the structure via tilted two-beam interference lithography and subsequent shadow deposition of gold. The experimental results demonstrate a coupling efficiency of 36% and a contrast ratio of 43. The relatively simple periodic nature of our structure lends itself to large-scale low-cost fabrication and simple theoretical analysis. Also, unlike the previous unidirectional couplers based on aperiodic structures, the design parameters of our unidirectional coupler can be determined analytically. Therefore, this structure can be an important component for surface-plasmon-based nanophotonic circuits by providing an efficient interface between free-space and surface plasmon waves.

  5. Stable electrolyte for high voltage electrochemical double-layer capacitors

    DOE PAGES

    Ruther, Rose E.; Sun, Che -Nan; Holliday, Adam; ...

    2016-12-28

    A simple electrolyte consisting of NaPF6 salt in 1,2-dimethoxyethane (DME) can extend the voltage window of electric double-layer capacitors (EDLCs) to >3.5 V. DME does not passivate carbon electrodes at very negative potentials (near Na/Na+), extending the practical voltage window by about 1.0 V compared to standard, non-aqueous electrolytes based on acetonitrile. The voltage window is demonstrated in two- and three-electrode cells using a combination of electrochemical impedance spectroscopy (EIS), charge-discharge cycling, and measurements of leakage current. DME-based electrolytes cannot match the high conductivity of acetonitrile solutions, but they can satisfy applications that demand high energy density at moderate power.more » The conductivity of NaPF6 in DME is comparable to commercial lithium-ion battery electrolytes and superior to most ionic liquids. Lastly, factors that limit the voltage window and EDLC energy density are discussed, and strategies to further boost energy density are proposed.« less

  6. [Sorption of nitrobenzene to anionic surfactant modified layered double hydroxides].

    PubMed

    Xia, Yan; Zhu, Run-Liang; Tao, Qi; Liu, Han-Yang

    2013-01-01

    Sodium dodecyl sulfate (SDS) modified MgAl layered double hydroxides (LDHs) were synthesized at different surfactant concentrations (0.5-2.0 TAEC) by the co-precipitation method. The LDH-DS samples obtained were characterized by powder X-ray diffraction and FT-IR spectroscopy. The results showed that SDS was successfully intercalated into the interlayer of the LDH, and the basal spacing was expanded from 0.80 nm to 3.98 nm. The intercalated SDS was considered consistent with a paraffin bilayers arrangement. The sorption of nitrobenzene on LDH-DS was examined, and the results showed that linear model could fit the sorption isotherms well (R2 > 0.99), which implied a partitioning sorption process. The sorption coefficient of nitrobenzene (K(d)) on LDH-DS was positively related to the DS - loading amount, but the organic carbon content normalized sorption coefficient of nitrobenzene (K(oc)) was shown to remain relatively constant. The sorption thermodynamics results showed that the sorption of nitrobenzene on LDH-DS was an endothermic process, and the increase of entropy was the driving force for the sorption process.

  7. Novel synthesis of layered double hydroxides (LDHs) from zinc hydroxide

    NASA Astrophysics Data System (ADS)

    Meng, Zilin; Zhang, Yihe; Zhang, Qian; Chen, Xue; Liu, Leipeng; Komarneni, Sridhar; Lv, Fengzhu

    2017-02-01

    The most common synthesis methods for layered double hydroxides (LDHs) are co-precipitation and reconstruction, which can have some limitations for application. Here, we report a novel synthesis method for LDHs. We use zinc hydroxide as the precursor to synthesize LDHs phase through a simple transformation process of zinc hydroxide phase. For this transformation process, aluminum can enter into zinc hydroxide and replace zinc quickly to transform it into LDH by creating positive charges in the zinc hydroxide solid phase. The mechanism of LDH formation was through Al3+ reaction first with zinc hydroxide followed by recrystallization of the original structure of zinc hydroxide. Thus, the new process of LDH formation involves a reaction of Al to substitute for Zn and recrystallization leading to LDH and the final pH influences the crystallization of LDHs by this process. In addition, Cr3+ was employed as a trivalent cation for LDH formation to react with zinc hydroxide, which also led to LDH structure.

  8. Methotrexate intercalated ZnAl-layered double hydroxide

    NASA Astrophysics Data System (ADS)

    Chakraborty, Manjusha; Dasgupta, Sudip; Soundrapandian, Chidambaram; Chakraborty, Jui; Ghosh, Swapankumar; Mitra, Manoj K.; Basu, Debabrata

    2011-09-01

    The anticancerous drug methotrexate (MTX) has been intercalated into an ZnAl-layered double hydroxide (LDH) using an anion exchange technique to produce LDH-MTX hybrids having particle sizes in the range of 100-300 nm. X-ray diffraction studies revealed increases in the basal spacings of ZnAl-LDH-MTX hybrid on MTX intercalation. This was corroborated by the transmission electron micrographs, which showed an increase in average interlayer spacing from 8.9 Å in pristine LDH to 21.3 Å in LDH-MTX hybrid. Thermogravimetric analyses showed an increase in the decomposition temperature for the MTX molecule in the LDH-MTX hybrid indicating enhanced thermal stability of the drug molecule in the LDH nanovehicle. The cumulative release profile of MTX from ZnAl-LDH-MTX hybrids in phosphate buffer saline (PBS) at pH 7.4 was successfully sustained for 48 h following Rigter-Peppas model release kinetics via diffusion.

  9. Bionanocomposites based on layered double hydroxides as drug delivery systems

    NASA Astrophysics Data System (ADS)

    Aranda, Pilar; Alcântara, Ana C. S.; Ribeiro, Ligia N. M.; Darder, Margarita; Ruiz-Hitzky, Eduardo

    2012-10-01

    The present work introduces new biohybrid materials involving layered double hydroxides (LDH) and biopolymers to produce bionanocomposites, able to act as effective drug delivery systems (DDS). Ibuprofen (IBU) and 5-aminosalicylic acid (5-ASA) have been chosen as model drugs, being intercalated in a Mg-Al LDH matrix. On the one side, the LDHIBU intercalation compound prepared by ion-exchange reaction was blended with the biopolymers zein, a highly hydrophobic protein, and alginate, a polysaccharide widely applied for encapsulating drugs. On the other side, the LDH- 5-ASA intercalation compound prepared by co-precipitation was assembled to the polysaccharides chitosan and pectin, which show mucoadhesive properties and resistance to acid pH values, respectively. Characterization of the intercalation compounds and the resulting bionanocomposites was carried out by means of different experimental techniques: X-ray diffraction, infrared spectroscopy, chemical and thermal analysis, as well as optical and scanning electron microscopies. Data on the swelling behavior and drug release under different pH conditions are also reported.

  10. Junction conditions in quadratic gravity: thin shells and double layers

    NASA Astrophysics Data System (ADS)

    Reina, Borja; Senovilla, José M. M.; Vera, Raül

    2016-05-01

    The junction conditions for the most general gravitational theory with a Lagrangian containing terms quadratic in the curvature are derived. We include the cases with a possible concentration of matter on the joining hypersurface—termed as thin shells, domain walls or braneworlds in the literature—as well as the proper matching conditions where only finite jumps of the energy-momentum tensor are allowed. In the latter case we prove that the matching conditions are more demanding than in general relativity. In the former case, we show that generically the shells/domain walls are of a new kind because they possess, in addition to the standard energy-momentum tensor, a double layer energy-momentum contribution which actually induces an external energy flux vector and an external scalar pressure/tension on the shell. We prove that all these contributions are necessary to make the entire energy-momentum tensor divergence-free, and we present the field equations satisfied by these energy-momentum quantities. The consequences of all these results are briefly analyzed.

  11. Vertical distribution, composition and migratory patterns of acoustic scattering layers in the Canary Islands

    NASA Astrophysics Data System (ADS)

    Ariza, A.; Landeira, J. M.; Escánez, A.; Wienerroither, R.; Aguilar de Soto, N.; Røstad, A.; Kaartvedt, S.; Hernández-León, S.

    2016-05-01

    Diel vertical migration (DVM) facilitates biogeochemical exchanges between shallow waters and the deep ocean. An effective way of monitoring the migrant biota is by acoustic observations although the interpretation of the scattering layers poses challenges. Here we combine results from acoustic observations at 18 and 38 kHz with limited net sampling in order to unveil the origin of acoustic phenomena around the Canary Islands, subtropical northeast Atlantic Ocean. Trawling data revealed a high diversity of fishes, decapods and cephalopods (152 species), although few dominant species likely were responsible for most of the sound scattering in the region. We identified four different acoustic scattering layers in the mesopelagic realm: (1) at 400-500 m depth, a swimbladder resonance phenomenon at 18 kHz produced by gas-bearing migrant fish such as Vinciguerria spp. and Lobianchia dofleini, (2) at 500-600 m depth, a dense 38 kHz layer resulting primarily from the gas-bearing and non-migrant fish Cyclothone braueri, and to a lesser extent, from fluid-like migrant fauna also inhabiting these depths, (3) between 600 and 800 m depth, a weak signal at both 18 and 38 kHz ascribed either to migrant fish or decapods, and (4) below 800 m depth, a weak non-migrant layer at 18 kHz which was not sampled. All the dielly migrating layers reached the epipelagic zone at night, with the shorter-range migrations moving at 4.6 ± 2.6 cm s - 1 and the long-range ones at 11.5 ± 3.8 cm s - 1. This work reduces uncertainties interpreting standard frequencies in mesopelagic studies, while enhances the potential of acoustics for future research and monitoring of the deep pelagic fauna in the Canary Islands.

  12. Acoustic resonances and sound scattering by a shear layer

    NASA Technical Reports Server (NTRS)

    Koutsoyannis, S. P.; Karamcheti, K.; Galant, D. C.

    1979-01-01

    The energy reflection coefficient is evaluated numerically for plane waves incident on a plane shear layer having a linear velocity profile. The shear layer is found to exhibit no resonances and no Brewster angles. The behavior of the reflection coefficient depends crucially on the parameter tau, a nondimensional measure of the disturbance Strouhal number with respect to the disturbance Mach number in the mean flow direction. For moderate values of tau, the amplified reflection regime degenerates into the total reflection one, whereas in the ordinary reflection regime the variation of the reflection coefficient with tau depends on whether or not the corresponding vortex sheet has a Brewster angle. The results indicate that caution should be exercised in uncritically modeling a finite thickness shear layer by a corresponding vortex sheet.

  13. Acoustic receptivity of compressible boundary layers: Receptivity by way of surface-temperature variations

    NASA Technical Reports Server (NTRS)

    Choudhari, Meelan

    1994-01-01

    The Goldstein-Ruban theory has been extended within the framework of Zavol'skii et al. to study the acoustic receptivity of compressible boundary layers. We consider the receptivity produced in a region of localized, small-amplitude variation in the surface temperature and compare it with the receptivity that is induced through a similar mechanism by a variation in the suction velocity at the surface. It is found that the orientation of the acoustic wave can have a significant impact on the receptivity process, with the maximum receptivity at a given sound-pressure level being produced by upstream oriented acoustic waves. At sufficiently low Mach numbers, the variation of receptivity with the acoustic-wave orientation can be predicted analytically and is the same for both surface suction and surface heating. However, as a result of the acoustic refraction across the mean boundary layer, the above dependence can become rather complex and, also, dependent on the type of surface nonuniformity. The results also suggest that the receptivity caused by temperature nonuniformities may turn out to be more significant than that produced by the mean-flow perturbations associated with strip suction.

  14. Double-layer structure in polar mesospheric clouds observed from SOFIE/AIM

    NASA Astrophysics Data System (ADS)

    Gao, Haiyang; Shepherd, Gordon G.; Tang, Yuanhe; Bu, Lingbing; Wang, Zhen

    2017-02-01

    Double-layer structures in polar mesospheric clouds (PMCs) are observed by using Solar Occultation for Ice Experiment (SOFIE) data between 2007 and 2014. We find 816 and 301 events of double-layer structure with percentages of 10.32 and 7.25 % compared to total PMC events, and the mean distances between two peaks are 3.06 and 2.73 km for the Northern Hemisphere (NH) and Southern Hemisphere (SH) respectively. Double-layer PMCs almost always have less mean ice water content (IWC) than daily IWC during the core of the season, but they are close to each other at the beginning and the end. The result by averaging over all events shows that the particle concentration has obvious double peaks, while the particle radius exhibits an unexpected monotonic increase with decreasing altitude. By further analysis of the background temperature and water vapour residual profiles, we conclude that the lower layer is a reproduced one formed at the bottom of the upper layer. 56.00 and 47.51 % of all double-layer events for the NH and SH respectively have temperature enhancements larger than 2 K locating between their double peaks. The longitudinal anti-correlation between the gravity waves' (GWs') potential energies and occurrence frequencies of double-layer PMCs suggests that the double-layer PMCs tend to form in an environment where the GWs have weaker intensities.

  15. Ion-cyclotron turbulence and diagonal double layers in a magnetospheric plasma

    NASA Technical Reports Server (NTRS)

    Liperovskiy, V. A.; Pudovkin, M. I.; Skuridin, G. A.; Shalimov, S. L.

    1981-01-01

    A survey of current concepts regarding electrostatic ion-cyclotron turbulence (theory and experiment), and regarding inclined double potential layers in the magnetospheric plasma is presented. Anomalous resistance governed by electrostatic ion-cyclotron turbulence, and one-dimensional and two-dimensional models of double electrostatic layers in the magnetospheric plasma are examined.

  16. Illustrating the processability of magnetic layered double hydroxides: layer-by-layer assembly of magnetic ultrathin films.

    PubMed

    Coronado, E; Martí-Gastaldo, C; Navarro-Moratalla, E; Ribera, A; Tatay, S

    2013-05-20

    We report the preparation of single-layer layered double hydroxide (LDH) two-dimensional (2D) nanosheets by exfoliation of highly crystalline NiAl-NO3 LDH. Next, these unilamellar moieties have been incorporated layer-by-layer (LbL) into a poly(sodium 4-styrenesulfonate)/LDH nanosheet multilayer ultrathin film (UTF). Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible light (UV-vis), and X-ray diffraction (XRD) profiles have been used to follow the uniform growth of the UTF. The use of a magnetic LDH as the cationic component of the multilayered architecture enables study of the resulting magnetic properties of the UTFs. Our magnetic data show the appearance of spontaneous magnetization at ∼5 K, thus confirming the effective transfer of the magnetic properties of the bulk LDH to the self-assembled film that displays glassy-like ferromagnetic behavior. The high number of bilayers accessible-more than 80-opens the door for the preparation of more-complex hybrid multifunctional materials that combine magnetism with the physical properties provided by other exfoliable layered inorganic hosts.

  17. A wideband characterization of the acoustic spreading function in the surface layer of the atmosphere

    NASA Astrophysics Data System (ADS)

    Mahon, Mark P.

    2001-07-01

    Acoustic signals propagating in the surface layer (within 100 meters of the earth's surface) of the atmosphere are subjected to refraction and scattering off of turbulent pockets of air, known as eddies. These eddies are postulated to be of varying size with a length-scale directly proportional to the height above the surface and are inherently stochastic. The net effect is a fundamentally dispersive process imparting frequency dependent amplitude and phase variations on the propagating signals. Mathematically, this can be characterized by a spreading function. In addition to the atmospheric effects the acoustic channel will typically possess multiple deterministic propagation paths. In this thesis original experimental work designed to characterize, in a wideband sense, the surface layer spreading function is presented. This is accomplished by analyzing the acoustic channel using communications theory typically employed in the electromagnetic environment. Small- and large-scale acoustic channel fluctuations are characterized simultaneously through signal set design and advanced space-time signal processing techniques. Carefully designed wideband (spread spectrum) signals were used to probe and interact with the channel to provide a mechanism to bound the relevant parameters and classify the type of time and frequency dispersive fading effects. The experimental results demonstrate that the signal design methodology employed facilitates simultaneous parameterization of the time-varying surface layer structures (turbulence) over a spread of time-scales. The signals were collected by an acoustic planar array located approximately 750 meters from the source location. Direction-of-arrival techniques were applied to track the multiple arrival angles over time. This provided a means of tracking the refraction effects imparted onto the acoustic signal by the turbulent atmosphere and discriminating other arrival angles due to ground waves and deterministic paths. The signal

  18. Receptivity of Hypersonic Boundary Layers Due to Acoustic Disturbances over Blunt Cone

    NASA Technical Reports Server (NTRS)

    Kara, K.; Balakumar, P.; Kandil, O. A.

    2007-01-01

    The transition process induced by the interaction of acoustic disturbances in the free-stream with boundary layers over a 5-degree straight cone and a wedge with blunt tips is numerically investigated at a free-stream Mach number of 6.0. To compute the shock and the interaction of shock with the instability waves the Navier-Stokes equations are solved in axisymmetric coordinates. The governing equations are solved using the 5th -order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. After the mean flow field is computed, acoustic disturbances are introduced at the outer boundary of the computational domain and unsteady simulations are performed. Generation and evolution of instability waves and the receptivity of boundary layer to slow and fast acoustic waves are investigated. The mean flow data are compared with the experimental results. The results show that the instability waves are generated near the leading edge and the non-parallel effects are stronger near the nose region for the flow over the cone than that over a wedge. It is also found that the boundary layer is much more receptive to slow acoustic wave (by almost a factor of 67) as compared to the fast wave.

  19. ANGULAR MOMENTUM TRANSPORT BY ACOUSTIC MODES GENERATED IN THE BOUNDARY LAYER. I. HYDRODYNAMICAL THEORY AND SIMULATIONS

    SciTech Connect

    Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M.

    2013-06-10

    The nature of angular momentum transport in the boundary layers of accretion disks has been one of the central and long-standing issues of accretion disk theory. In this work we demonstrate that acoustic waves excited by supersonic shear in the boundary layer serve as an efficient mechanism of mass, momentum, and energy transport at the interface between the disk and the accreting object. We develop the theory of angular momentum transport by acoustic modes in the boundary layer, and support our findings with three-dimensional hydrodynamical simulations, using an isothermal equation of state. Our first major result is the identification of three types of global modes in the boundary layer. We derive dispersion relations for each of these modes that accurately capture the pattern speeds observed in simulations to within a few percent. Second, we show that angular momentum transport in the boundary layer is intrinsically nonlocal, and is driven by radiation of angular momentum away from the boundary layer into both the star and the disk. The picture of angular momentum transport in the boundary layer by waves that can travel large distances before dissipating and redistributing angular momentum and energy to the disk and star is incompatible with the conventional notion of local transport by turbulent stresses. Our results have important implications for semianalytical models that describe the spectral emission from boundary layers.

  20. Boundary-Layer Effects on Acoustic Transmission Through Narrow Slit Cavities

    NASA Astrophysics Data System (ADS)

    Ward, G. P.; Lovelock, R. K.; Murray, A. R. J.; Hibbins, A. P.; Sambles, J. R.; Smith, J. D.

    2015-07-01

    We explore the slit-width dependence of the resonant transmission of sound in air through both a slit array formed of aluminum slats and a single open-ended slit cavity in an aluminum plate. Our experimental results accord well with Lord Rayleigh's theory concerning how thin viscous and thermal boundary layers at a slit's walls affect the acoustic wave across the whole slit cavity. By measuring accurately the frequencies of the Fabry-Perot-like cavity resonances, we find a significant 5% reduction in the effective speed of sound through the slits when an individual viscous boundary layer occupies only 5% of the total slit width. Importantly, this effect is true for any airborne slit cavity, with the reduction being achieved despite the slit width being on a far larger scale than an individual boundary layer's thickness. This work demonstrates that the recent prevalent loss-free treatment of narrow slit cavities within acoustic metamaterials is unrealistic.

  1. Boundary-Layer Effects on Acoustic Transmission Through Narrow Slit Cavities.

    PubMed

    Ward, G P; Lovelock, R K; Murray, A R J; Hibbins, A P; Sambles, J R; Smith, J D

    2015-07-24

    We explore the slit-width dependence of the resonant transmission of sound in air through both a slit array formed of aluminum slats and a single open-ended slit cavity in an aluminum plate. Our experimental results accord well with Lord Rayleigh's theory concerning how thin viscous and thermal boundary layers at a slit's walls affect the acoustic wave across the whole slit cavity. By measuring accurately the frequencies of the Fabry-Perot-like cavity resonances, we find a significant 5% reduction in the effective speed of sound through the slits when an individual viscous boundary layer occupies only 5% of the total slit width. Importantly, this effect is true for any airborne slit cavity, with the reduction being achieved despite the slit width being on a far larger scale than an individual boundary layer's thickness. This work demonstrates that the recent prevalent loss-free treatment of narrow slit cavities within acoustic metamaterials is unrealistic.

  2. Transmission of acoustic waves through mixing layers and 2D isotropic turbulence

    NASA Astrophysics Data System (ADS)

    Juve, D.; Blanc-Benon, P.; Comte-Bellot, G.

    Ray tracing and parabolic equation methods have been used to study the properties of acoustic waves transmitted through turbulent velocity fields. A numerical simulation permits individual realizations of the turbulent field, which then allow, if desired, an ensemble averaging of the fields. Two flows have been considered, 2D isotropic turbulence and a 2D mixing layer. The following complementary aspects are developed: the occurrence of caustics, the reinforced or weakened zones of the acoustic field, the eigenrays between a source and a receiver, and the associated travel times, variances, and scintillation index.

  3. Generation and development of small-amplitude disturbances in a laminar boundary layer in the presence of an acoustic field

    NASA Technical Reports Server (NTRS)

    Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.

    1985-01-01

    A low-turbulence subsonic wind tunnel was used to study the influence of acoustic disturbances on the development of small sinusoidal oscillations (Tollmien-Schlichting waves) which constitute the initial phase of turbulent transition. It is found that acoustic waves propagating opposite to the flow generate vibrations of the model (plate) in the flow. Neither the plate vibrations nor the acoustic field itself have any appreciable influence on the stability of the laminar boundary layer. The influence of an acoustic field on laminar boundary layer disturbances is limited to the generation of Tollmien-Schlichting waves at the leading-edge of the plate.

  4. Highly Efficient Organic Solar Cells Consisting of Double Bulk Heterojunction Layers.

    PubMed

    Huang, Jiang; Wang, Hanyu; Yan, Kangrong; Zhang, Xiaohua; Chen, Hongzheng; Li, Chang-Zhi; Yu, Junsheng

    2017-03-15

    An organic solar cell (OSCs) containing double bulk heterojunction (BHJ) layers, namely, double-BHJ OSCs is constructed via stamp transferring of low bandgap BHJ atop of mediate bandgap active layers. Such devices allow a large gain in photocurrent to be obtained due to enhanced photoharvest, without suffering much from the fill factor drop usually seen in thick-layer-based devices. Overall, double-BHJ OSC with optimal ≈50 nm near-infrared PDPP3T:PC71 BM layer atop of ≈200 nm PTB7-Th:PC71 BM BHJ results in high power conversion efficiencies over 12%.

  5. Layered double hydroxide stability. 2. Formation of Cr(III)-containing layered double hydroxides directly from solution

    NASA Technical Reports Server (NTRS)

    Boclair, J. W.; Braterman, P. S.; Jiang, J.; Lou, S.; Yarberry, F.

    1999-01-01

    Solutions containing divalent metal [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+] chlorides and CrCl3 6H2O were titrated with NaOH to yield, for M(II) = Zn, Co, and Ni, hydrotalcite-like layered double hydroxides (LDHs), [[M(II)]1-z[Cr(III)]z(OH)2][Cl]z yH2O, in a single step, without intermediate formation of chromium hydroxide. Analysis of the resultant titration curves yields solubility constants for these compounds. These are in the order Zn < Ni approximately Co, with a clear preference for formation of the phase with z = 1/3. With Mg2+ as chloride, titration gives a mixture of Cr(OH)3 and Mg(OH)2, but the metal sulfates give Mg2Cr(OH)6 1/2(SO4) by a two-step process. Titrimetric and spectroscopic evidence suggests short-range cation order in the one-step LDH systems.

  6. Semi-analytical model for quasi-double-layer surface electrode ion traps

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Chen, Shuming; Wang, Yaohua

    2016-11-01

    To realize scale quantum processors, the surface-electrode ion trap is an effective scaling approach, including single-layer, double-layer, and quasi-double-layer traps. To calculate critical trap parameters such as the trap center and trap depth, the finite element method (FEM) simulation was widely used, however, it is always time consuming. Moreover, the FEM simulation is also incapable of exhibiting the direct relationship between the geometry dimension and these parameters. To eliminate the problems above, House and Madsen et al. have respectively provided analytic models for single-layer traps and double-layer traps. In this paper, we propose a semi-analytical model for quasi-double-layer traps. This model can be applied to calculate the important parameters above of the ion trap in the trap design process. With this model, we can quickly and precisely find the optimum geometry design for trap electrodes in various cases.

  7. Does the plasma radiate near a Double Layer?

    NASA Astrophysics Data System (ADS)

    Pottelette, Raymond; Berthomier, Matthieu; Pickett, Jolene

    2016-04-01

    Earth is an intense radio source in the kilometer wavelength range. Being a direct consequence of the parallel acceleration processes taking place in the Earth's auroral region, the radiation contains fundamental information on the characteristic spatial and temporal scales of the turbulent accelerating layer. It is now widely assumed that the cyclotron maser instability leads to Auroral Kilometric Radiation (AKR) generation. It has been suggested from the FAST measurements that the AKR results from a so-called horseshoe electron distribution. This distribution is generated when a localized parallel electric field - called Double Layer (DL) - accelerates earthward the electrons that propagate into an increasing magnetic field. The magnetic moment of the electrons is conserved so that their pitch angle is increased. This results in the creation of a horseshoe-like shape for the electron distribution exhibiting large positive velocity gradients in the direction perpendicular to B, thereby providing free energy for the AKR generation which takes place at the local electron gyrofrequency. In these circumstances, the radiation is generated far away (several thousand kilometers) from a DL, because the parallel accelerated electrons need to travel a long distance before forming a horseshoe distribution. From an experimental point of view, it is not an easy task to highlight the presence of DLs, because they are moving transient structures so that high time resolution measurements are needed. A detailed analysis suggests that these large-amplitude parallel electric fields are located inside sharp density gradients at the interface separating the cold, dense ionospheric plasma from the hot, tenuous magnetospheric plasma. We present some FAST observations which illustrate the generation of elementary radiation events in the neighborhood of a DL. The events occur 10 to 20% above the local electron gyrofrequency in association with the presence of nonlinear coherent structures

  8. Development of high energy density electrical double layer capacitors

    NASA Astrophysics Data System (ADS)

    Devarajan, Thamarai selvi

    Electrochemical Double Layer capacitors (EDLCs) have shown themselves as a viable energy storage alternative. EDLCs have high power density, faster charge/discharge, wide operating temperature and long cycle life compared to batteries since it stores charge by physical separation. Despites all their advantages, their low energy density stand as a bottleneck for capacitors. This research aims to increase the energy density of EDLC without compromising the power density. Energy is proportional to the square of cell voltage. Cell voltage is mainly dependent on electrolyte breakdown. Electrolytes also provide ions for charge separation and conduction. Therefore various electrolytes (Solutes and Solvents) which can give high concentration, solubility and decomposition potential were characterized in the first part of the research. In that study, a novel ionic liquid OPBF4 had higher capacitance and comparable voltage window compared to commercial TEABF4 in Acetonitrile. However, the increased polarity of the fixed ring O-atom and the ion-ion interaction in OPBF4 was responsible for lowering its conductivity. Oxygenated ionic compounds with alkyl groups had lower stability due to beta elimination between two electron withdrawing atoms. Volume based thermodynamics and quantum chemical calculations were used to calculate ion size, HOMO/LUMO energies, and free energy changes and establish relationship with capacitance, redox potential and melting points respectively. In addition free energy of fusion was used to predict the melting point. Ion size had correlation with capacitance due to compact double layer formation. Free energy changes did not explain the differences in melting point and predicted dielectric constant was inconsistent with the polarity. This is presumably due to using Van der Waals volume instead of crystal structure volume and insufficient incorporation of polarization term. The HOMO/LUMO energies gave direct relation between oxidation and reduction

  9. Double layer field shaping systems for toroidal plasmas

    DOEpatents

    Ohyabu, Nobuyoshi

    1982-01-01

    Methods and apparatus for plasma generation, confinement and control such as Tokamak plasma systems are described having a two layer field shaping coil system comprising an inner coil layer close to the plasma and an outer coil layer to minimize the current in the inner coil layer.

  10. Acoustic one-way metasurfaces: Asymmetric Phase Modulation of Sound by Subwavelength Layer

    PubMed Central

    Jiang, Xue; Liang, Bin; Zou, Xin-ye; Yang, Jing; Yin, Lei-lei; Yang, Jun; Cheng, Jian-chun

    2016-01-01

    We theoretically design and numerically demonstrate an acoustic one-way metasurface, which is a planar and acoustically subwavelength layer behaving like a nearly-reflectionless surface with arbitrary wave-steering capability for incident wave impinging on one side, while virtually blocking the reversed wave. The underlying mechanism is based on an asymmetric phase modulation by coupling a phase array and a near-zero-index medium. We exemplify a metastructure-based implementation by combining the hybrid metastuctures and labyrinthine structures. Moreover, the performance of the proposed implementation is demonstrated via three distinct phenomena of anomalous refraction, wave splitting and conversion of propagation wave to surface wave. Our findings may offer more possibilities for sound manipulation and improve the application potential of acoustic artificial devices in situations such as ultrasonic imaging and therapy. PMID:27305973

  11. Surface acoustic admittance and absorption of highly porous, layered, fibrous materials

    NASA Astrophysics Data System (ADS)

    Tesar, J. S.; Lambert, R. F.

    1984-06-01

    Some acoustic properties of Kevlar-29 - a fine fibered, layered material is investigated. Kevlar is characterized by very high strength, uniform filaments arranged in a parallel batt where most filaments are random in the x-y plane but ordered as planes in the z direction. For experimental purposes, volume porosity, static flow resistance and mean filament diameter are used to identify the material. To determine the acoustic surface admittance of Kevlar, batts of the material are cut into small pads and placed into a standing wave tube terminated by a rigid brass plug. The attenuation and relative phase shift are recorded at each frequency in the range of 50 to 6000 Hz. Normalized conductance and susceptance are combined to form the acoustic absorption coefficient. The data are compared with theory by plotting the normalized admittance and normal incident absorption coefficient versus cyclic frequency.

  12. Acoustic one-way metasurfaces: Asymmetric Phase Modulation of Sound by Subwavelength Layer

    NASA Astrophysics Data System (ADS)

    Jiang, Xue; Liang, Bin; Zou, Xin-Ye; Yang, Jing; Yin, Lei-Lei; Yang, Jun; Cheng, Jian-Chun

    2016-06-01

    We theoretically design and numerically demonstrate an acoustic one-way metasurface, which is a planar and acoustically subwavelength layer behaving like a nearly-reflectionless surface with arbitrary wave-steering capability for incident wave impinging on one side, while virtually blocking the reversed wave. The underlying mechanism is based on an asymmetric phase modulation by coupling a phase array and a near-zero-index medium. We exemplify a metastructure-based implementation by combining the hybrid metastuctures and labyrinthine structures. Moreover, the performance of the proposed implementation is demonstrated via three distinct phenomena of anomalous refraction, wave splitting and conversion of propagation wave to surface wave. Our findings may offer more possibilities for sound manipulation and improve the application potential of acoustic artificial devices in situations such as ultrasonic imaging and therapy.

  13. Surface acoustic admittance and absorption of highly porous, layered, fibrous materials

    NASA Technical Reports Server (NTRS)

    Tesar, J. S.; Lambert, R. F.

    1984-01-01

    Some acoustic properties of Kevlar-29 - a fine fibered, layered material is investigated. Kevlar is characterized by very high strength, uniform filaments arranged in a parallel batt where most filaments are random in the x-y plane but ordered as planes in the z direction. For experimental purposes, volume porosity, static flow resistance and mean filament diameter are used to identify the material. To determine the acoustic surface admittance of Kevlar, batts of the material are cut into small pads and placed into a standing wave tube terminated by a rigid brass plug. The attenuation and relative phase shift are recorded at each frequency in the range of 50 to 6000 Hz. Normalized conductance and susceptance are combined to form the acoustic absorption coefficient. The data are compared with theory by plotting the normalized admittance and normal incident absorption coefficient versus cyclic frequency.

  14. A theory study of the multiplication characteristics of InP/InGaAs avalanche photodiodes with double multiplication layers and double charge layers

    NASA Astrophysics Data System (ADS)

    Liu, Guipeng; Chen, Wenjie; Liu, Linsheng; Jin, Peng; Tian, Yonghui; Yang, Jianhong

    2016-09-01

    An In0.53Ga0.47As/InP avalanche photodiodes (APD) structure with double multiplication layers and double charge layers has been proposed. The calculated results with considering the dead space effect show that a thin 2nd multiplication layer will reduce the excess noise factor F in this structure for a fixed mean gain . And its performances will reach the best when the 2nd multiplication layer is 0.01 μm, which will reduce the excess noise factor 7% compared to a conventional APD for =10. The effects of 1st and 2nd charge layers on the APD have also been studied in this paper.

  15. A finite difference analysis of the field present behind an acoustically impenetrable two-layer barrier.

    PubMed

    Hurrell, Andrew M

    2008-06-01

    The interaction of an incident sound wave with an acoustically impenetrable two-layer barrier is considered. Of particular interest is the presence of several acoustic wave components in the shadow region of this barrier. A finite difference model capable of simulating this geometry is validated by comparison to the analytical solution for an idealized, hard-soft barrier. A panel comprising a high air-content closed cell foam backed with an elastic (metal) back plate is then examined. The insertion loss of this panel was found to exceed the dynamic range of the measurement system and was thus acoustically impenetrable. Experimental results from such a panel are shown to contain artifacts not present in the diffraction solution, when acoustic waves are incident upon the soft surface. A finite difference analysis of this experimental configuration replicates the presence of the additional field components. Furthermore, the simulated results allow the additional components to be identified as arising from the S(0) and A(0) Lamb modes traveling in the elastic plate. These Lamb mode artifacts are not found to be present in the shadow region when the acoustic waves are incident upon the elastic surface.

  16. Incompressible Modes Excited by Supersonic Shear in Boundary Layers: Acoustic CFS Instability

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail A.

    2017-02-01

    We present an instability for exciting incompressible modes (e.g., gravity or Rossby modes) at the surface of a star accreting through a boundary layer. The instability excites a stellar mode by sourcing an acoustic wave in the disk at the boundary layer, which carries a flux of energy and angular momentum with the opposite sign as the energy and angular momentum density of the stellar mode. We call this instability the acoustic Chandrasekhar–Friedman–Schutz (CFS) instability, because of the direct analogy to the CFS instability for exciting modes on a rotating star by emission of energy in the form of gravitational waves. However, the acoustic CFS instability differs from its gravitational wave counterpart in that the fluid medium in which the acoustic wave propagates (i.e., the accretion disk) typically rotates faster than the star in which the incompressible mode is sourced. For this reason, the instability can operate even for a non-rotating star in the presence of an accretion disk. We discuss applications of our results to high-frequency quasi-periodic oscillations in accreting black hole and neutron star systems and dwarf nova oscillations in cataclysmic variables.

  17. Perfectly matched layer for an elastic parabolic equation model in ocean acoustics

    NASA Astrophysics Data System (ADS)

    Xu, Chuanxiu; Zhang, Haigang; Piao, Shengchun; Yang, Shi'e.; Sun, Sipeng; Tang, Jun

    2017-02-01

    The perfectly matched layer (PML) is an effective technique for truncating unbounded domains with minimal spurious reflections. A fluid parabolic equation (PE) model applying PML technique was previously used to analyze the sound propagation problem in a range-dependent waveguide (Lu and Zhu, 2007). However, Lu and Zhu only considered a standard fluid PE to demonstrate the capability of the PML and did not take improved one-way models into consideration. They applied a [1/1] Padé approximant to the parabolic equation. The higher-order PEs are more accurate than standard ones when a very large angle propagation is considered. As for range-dependent problems, the techniques to handle the vertical interface between adjacent regions are mainly energy conserving and single-scattering. In this paper, the PML technique is generalized to the higher order elastic PE, as is to the higher order fluid PE. The correction of energy conserving is used in range-dependent waveguides. Simulation is made in both acoustic cases and seismo-acoustic cases. Range-independent and range-dependent waveguides are both adopted to test the accuracy and efficiency of this method. The numerical results illustrate that a PML is much more effective than an artificial absorbing layer (ABL) both in acoustic and seismo-acoustic sound propagation modeling.

  18. Acoustic Receptivity of a Blasius Boundary Layer with 2-D and Oblique Surface Waviness

    NASA Technical Reports Server (NTRS)

    King, Rudolph A.; Breuer, Kenneth S.

    2000-01-01

    An experimental investigation was conducted to examine acoustic receptivity and subsequent boundary-layer instability evolution for a Blasius boundary layer formed on a flat plate in the presence of two-dimensional (2-D) and oblique (3-D) surface waviness. The effect of the non-localized surface roughness geometry and acoustic wave amplitude on the receptivity process was explored. The surface roughness had a well defined wavenumber spectrum with fundamental wavenumber k (sub w). A planar downstream traveling acoustic wave was created to temporally excite the flow near the resonance frequency of an unstable eigenmode corresponding to k (sub ts) = k (sub w). The range of acoustic forcing levels, epsilon, and roughness heights, DELTA h, examined resulted in a linear dependence of receptivity coefficients; however, the larger values of the forcing combination epsilon dot DELTA h resulted in subsequent nonlinear development of the Tollmien-Schlichting (T-S) wave. This study provided the first experimental evidence of a marked increase in the receptivity coefficient with increasing obliqueness of the surface waviness in excellent agreement with theory. Detuning of the 2-D and oblique disturbances was investigated by varying the streamwise wall-roughness wavenumber a,, and measuring the T-S response. For the configuration where laminar-to-turbulent breakdown occurred, the breakdown process was found to be dominated by energy at the fundamental and harmonic frequencies, indicative of K-type breakdown.

  19. Enhanced charge separation and oxidation kinetics of BiVO4 photoanode by double layer structure

    NASA Astrophysics Data System (ADS)

    Yang, Lin; Xiong, Yuli; Dong, Hongmei; Peng, Huarong; Zhang, Yunhuai; Xiao, Peng

    2017-03-01

    Monoclinic bismuth vanadate (BiVO4) is a promising semiconductor for photoelectrochemical water splitting. Here, we developed a facile fabrication of BiVO4 double layer photoanode on the fluorine-doped tin oxide substrate by electrodeposition. The BiVO4 double layer photoanode is composed by a dense BiVO4 film as the inner layer and a nanoporous BiVO4 film as the outer layer. Compared to the BiVO4 single layer photoanode, the optimized BiVO4 double layer photoanode produced a much higher photocurrent of 1.15 mA/cm2 at 0.6 V vs. Ag/AgCl under AM 1.5G (100 mW/cm2) illumination. The results of the photoelectric conversion kinetics for different samples revealed that the charge separation and oxidation kinetics efficiencies for the BiVO4 double layer are 47.2% and 51.6% at 0.6 V vs. Ag/AgCl, while the values for BiVO4 single layer are 32.3% and 35.8%, respectively. The improved photoelectrochemical performance for BiVO4 double layer is mainly ascribed to the decrease of defect state at the interface after inserting a dense BiVO4 as an inner layer to prevent the recombination of photogenerated electron-hole pairs.

  20. Approximate nonlinear multi-parameter inversion with single and double scattering seismic wavefields in acoustic media

    NASA Astrophysics Data System (ADS)

    Ouyang, Wei; Mao, Weijian; Li, Wuqun; Zhang, Pan

    2016-11-01

    An approach for approximate direct quadratic nonlinear inversion in two-parameter (density and bulk modulus) heterogeneous acoustic media is being presented and discussed in this paper. The approach consists of two parts: the first is a linear generalized Radon transform (GRT) migration procedure based on the weighted true-amplitude summation of pre-stack seismic scattered data that is adapted to a virtually arbitrary observing system, and the second is a non-iterative quadratic inversion operation, produced from the explicit expression of amplitude radiation pattern that is acting on the migrated data. This ensures the asymptotic inversion can continue to simultaneously locate the discontinuities and reconstruct the size of the discontinuities in the perturbation parameters describing the acoustic media. We identify that the amplitude radiation pattern is the binary quadratic combination of the parameters in the process of formulating nonlinear inverse scattering problems based on second-order Born approximation. The coefficients of the quadratic terms are computed by appropriately handling the double scattering effects. These added quadratic terms provide a better amplitude correction for the parameters inversion. Through numerical tests, we show that for strong perturbations, the errors of the linear inversion are significant and unacceptable. In contrast, the quadratic nonlinear inversion can give fairly accurate inversion results and keep almost the same computational complexity as conventional GRT liner inversion.

  1. Approximate non-linear multiparameter inversion with single and double scattering seismic wavefields in acoustic media

    NASA Astrophysics Data System (ADS)

    Ouyang, Wei; Mao, Weijian; Li, Wuqun; Zhang, Pan

    2017-02-01

    An approach for approximate direct quadratic non-linear inversion in two-parameter (density and bulk modulus) heterogeneous acoustic media is being presented and discussed in this paper. The approach consists of two parts: the first is a linear generalized Radon transform (GRT) migration procedure based on the weighted true-amplitude summation of pre-stack seismic scattered data that is adapted to a virtually arbitrary observing system, and the second is a non-iterative quadratic inversion operation, produced from the explicit expression of amplitude radiation pattern that is acting on the migrated data. This ensures the asymptotic inversion can continue to simultaneously locate the discontinuities and reconstruct the size of the discontinuities in the perturbation parameters describing the acoustic media. We identify that the amplitude radiation pattern is the binary quadratic combination of the parameters in the process of formulating non-linear inverse scattering problems based on second-order Born approximation. The coefficients of the quadratic terms are computed by appropriately handling the double scattering effects. These added quadratic terms provide a better amplitude correction for the parameters inversion. Through numerical tests, we show that for strong perturbations, the errors of the linear inversion are significant and unacceptable. In contrast, the quadratic non-linear inversion can give fairly accurate inversion results and keep almost the same computational complexity as conventional GRT liner inversion.

  2. Double adiabatic theory of driven collisionless geodesic acoustic modes (GAMs) in toroids

    NASA Astrophysics Data System (ADS)

    Hassam, Adil; Kleva, Robert

    2011-10-01

    The GAM is an axisymmetric oscillation of a toroidal magnetically confined plasma, resulting from an interplay between poloidal plasma rotation and perpendicular flux tube compression from the B field gradient. The frequency is super-parallel-sonic, ie, omega ~ (ion thermal speed)/R, greater than the parallel acoustic mode which is lower by a factor of q. Consequently, collisionless geodesic acoustic modes in tokamaks can be described by the Chew-Goldberger-Low double-adiabatic fluid closures. This allows a simpler nonlinear formulation. We use these equations to study driven, collisionless GAMs in tokamaks. The motivation for this study is a proposal by Hallatschek and McKee to drive GAMs on the D3D tokamak at resonance. The drivers in the CGL theory include external magnetic forces to effect flux surface displacements as well as sources to provide modulated non-axisymmetric ion heating. We show that the linear mode frequency from CGL theory agrees with previous kinetic results. Comparisons will be made between different approaches to resonate the mode. Nonlinear effects will be evaluated. A 2D toroidal numerical simulation of driven GAMs is in progress. Work supported by US-DOE.

  3. Double adiabatic theory of driven collisionless geodesic acoustic modes (GAMs) in toroids

    NASA Astrophysics Data System (ADS)

    Hassam, Adil; Kleva, Robert; Sengupta, Wrick

    2012-03-01

    The GAM is an axisymmetric oscillation of a toroidal magnetically confined plasma, resulting from an interplay between poloidal plasma rotation and perpendicular flux tube compression from the B field gradient. The frequency is super-parallel-sonic, ie, φ ˜ (ion thermal speed)/R, greater than the parallel acoustic mode which is lower by a factor of q. Consequently, collisionless geodesic acoustic modes in tokamaks can be described by the Chew-Goldberger-Low double-adiabatic fluid closures. This allows a simpler nonlinear formulation. We use these equations to study driven, collisionless GAMs in tokamaks. The motivation for this study is a proposal by Hallatschek and McKee to drive GAMs on the D3D tokamak at resonance. The drivers in the CGL theory include external magnetic forces to effect flux surface displacements as well as sources to provide modulated non-axisymmetric ion heating. We show that the linear mode frequency from CGL theory agrees with previous kinetic results. Comparisons will be made between different approaches to resonate the mode. Nonlinear effects will be evaluated. Results of a 2D toroidal numerical simulation of driven GAMs are described

  4. Improving Breakdown Behavior by Substrate Bias in a Novel Double Epi-layer Lateral Double Diffused MOS Transistor

    NASA Astrophysics Data System (ADS)

    Li, Qi; Wang, Wei-Dong; Liu, Yun; Wei, Xue-Ming

    2012-02-01

    A new lateral double diffused MOS (LDMOS) transistor with a double epitaxial layer formed by an n-type substrate and a p-type epitaxial layer is reported (DEL LDMOS). The mechanism of the improved breakdown characteristic is that the high electric field around the drain is reduced by substrate reverse bias, which causes the redistribution of the bulk electric field in the drift region, and the vertical blocking voltage is shared by the drain side and the source side. The numerical results indicate that the trade-off between breakdown voltage and on-resistance of the proposed device is improved greatly in comparison to that of the conventional LDMOS.

  5. Design of double layer printed spiral coils for wirelessly-powered biomedical implants.

    PubMed

    Ashoori, Ehsan; Asgarian, Farzad; Sodagar, Amir M; Yoon, Euisik

    2011-01-01

    In this paper employing double layer printed spiral coils (PSCs) is proposed for wireless power transmission in implantable biomedical applications. Detailed modeling of this type of PSCs is presented. Both calculations and measurements of fabricated double layer PSCs indicate that this structure can decrease the size of typical single layer PSCs without any change in the most important parameters of the coils, such as quality factor. Also, it is shown that with equal PSC dimensions and design parameters, double layer PSCs achieve significantly higher inductances and quality factors. Ultimately, a pair of double layer PSCs with a distance of 5 mm in air is used in an inductive link. The power transfer efficiency of this link is about 79.8% with a carrier frequency of 5 MHz and coupling coefficient of 0.189.

  6. Electrochemical Double Layered Capacitor Development and Implementation System

    NASA Astrophysics Data System (ADS)

    Strunk, Gavin P.

    Electrochemical Double Layered Capacitors (EDLC's) are becoming a more popular topic of research for hybrid power systems, especially vehicles. They are known for their high power density, high cycle life, low internal resistance, and wider operating temperature compared to batteries. They are rarely used as a standalone power source; however, because of their lack of energy density compared to batteries and fuel cells. Researchers are now discovering the benefits of using them in hybrid systems. The increased complexity of a hybrid power source presents many challenges. A major drawback of this complexity is the lack of design tools to assist a designer in translating a simulation all the way to a full scale implementation. A full spectrum of tools was designed to assist designers at all stages of implementation including: single cell testing, a multi-cell management system, and a full scale vehicle data acquisition system to monitor performance. First, the full scale vehicle data acquisition is described. The system is isolated from the electric shuttle bus it was tested on to allow the system to be ported to other vehicles and applications. This was done to modularize the system to characterize a wide variety of full scale applications. Next, a single cell test system was designed that allows the designer to characterize cell specifications, as well as, test control and safety systems in a controlled environment. The goal is to ensure safety systems can be thoroughly tested to ensure robustness as the bank is scaled up. This system also includes simulation models that provide examples of using the simulation to predict the behavior of a cell and the test system to validate the results of the simulation. This information is then used by the designer to more effectively design sensor ranges for the bank. Finally, a multi-cell EDLC management system was designed to implement a bank. It incorporates 12 series EDLC cells per control module, and the modular design

  7. Analysis of an existing experiment on the interaction of acoustic waves with a laminar boundary layer

    NASA Technical Reports Server (NTRS)

    Schopper, M. R.

    1982-01-01

    The hot-wire anemometer amplitude data contained in the 1977 report of P. J. Shapiro entitled, ""The Influence of Sound Upon Laminar Boundary'' were reevaluated. Because the low-Reynolds number boundary layer disturbance data were misinterpreted, an effort was made to improve the corresponding disturbance growth rate curves. The data are modeled as the sum of upstream and downstream propagating acoustic waves and a wave representing the Tollmien-Schlichting (TS) wave. The amplitude and phase velocity of the latter wave were then adjusted so that the total signal reasonably matched the amplitude and phase angle hot-wire data along the plate laminar boundary layer. The revised rates show growth occurring further upstream than Shapiro found. It appears that the premature growth is due to the adverse pressure gradient created by the shape of the plate. Basic elements of sound propagation in ducts and the experimental and theoretical acoustic-stability literature are reviewed.

  8. Layer-by-layer assembly of bi-protein/layered double hydroxide ultrathin film and its electrocatalytic behavior for catechol.

    PubMed

    Kong, Xianggui; Rao, Xiuying; Han, Jingbin; Wei, Min; Duan, Xue

    2010-10-15

    This paper reports the fabrication of a bi-protein/layered double hydroxide (LDH) ultrathin film in which hemoglobin (HB) and horseradish peroxidase (HRP) molecules were assembled alternately with LDH nanosheets via the layer-by-layer (LBL) deposition technique, and its electrocatalytic performances for oxidation of catechol were demonstrated. The results of XRD indicate that the HB-HRP/LDH ultrathin film possesses a long range stacking order in the normal direction of the substrate, with the two proteins accommodated in the LDH gallery respectively as monolayer arrangement. SEM images show that the film surface exhibits a continuous and uniform morphology, and AFM reveals the Root-Mean-Square (RMS) roughness of ∼10.2 nm for the film. A stable direct electrochemical redox behavior of the proteins was successfully obtained for the HB-HRP/LDH film modified electrode. In addition, it exhibits remarkable electrocatalytic activity towards oxidation of catechol, based on the synergistic effect of the two proteins. The catechol biosensor in this work displays a wide linear response range (6-170 μM, r=0.999), low detection limit (5 μM), high sensitivity and good reproducibility.

  9. Accretion onto neutron stars with the presence of a double layer

    NASA Technical Reports Server (NTRS)

    Williams, A. C.; Weisskopf, M. C.; Elsner, R. F.; Darbro, W.; Sutherland, P. G.

    1987-01-01

    It is known, from laboratory experiments, that double layers will form in plasmas, usually in the presence of an electric current. It is argued that a double layer may be present in the accretion column of a neutron star in a binary system. It is suggested that the double layer may be the predominant deceleration mechanism for the accreting ions, especially for sources with X-ray luminosities of less than about 10 to the 37th erg/s. Previous models have involved either a collisionless shock or an assumed gradual deceleration of the accreting ions to thermalize the energy of the infalling matter.

  10. Accretion onto neutron stars with the presence of a double layer

    NASA Technical Reports Server (NTRS)

    Williams, A. C.; Weisskopf, M. C.; Elsner, R. F.; Darbro, W.; Sutherland, P. G.

    1986-01-01

    It is known from laboratory experiments that double layers can form in plasmas, usually in the presence of an electric current. It is argued that a double layer may be present in the accretion column of a neutron star in a binary system. It is suggested that the double layer may be the predominant deceleration mechanism for the accreting ions, especially for sources with X-ray luminosities of less than about 10 to the 37th erg/s. Previous models have involved either a collisionless shock or an assumed gradual deceleration of the accreting ions to thermalize the energy of the infalling matter.

  11. Molecular physics of electrical double layers in electrochemical capacitors

    NASA Astrophysics Data System (ADS)

    Feng, Guang

    At present, electrochemical capacitors (ECs) are emerging as a novel type of energy storage devices and have attracted remarkable attention, due to their key characteristics, such as high power density and excellent durability. However, the moderate energy density of ECs restricts their widespread deployment in everyday technology. To surmount this limitation, four strategies are adopted: (1) to reduce the total system mass, (2) to increase the specific surface area of electrodes, (3) to enhance normalized capacitance, and (4) to expand the range of potentials applied on electrodes. The implementation of these approaches critically relies on the fundamental understanding of physical processes underlying the energy storage mechanisms hinging on the electrical double layers (EDLs) in ECs. In this dissertation, to gain the fundamentals of EDLs in ECs, based on the strategies described above, we studied the structure, capacitance, and dynamics of EDLs in different electrolytes near electrodes featuring different pores using atomistic simulations. The pores of electrodes are categorized into macropores, mesopores, and micropores, following the decreasing order of pore size. The chosen electrolytes fall into aqueous electrolytes, organic electrolytes, and ionic liquids (ILs), listed by the increasing order of their decomposition voltages. For the aqueous electrolytes, we explored the water and ion distributions inside electrified micropores (< 2nm) using molecular dynamics (MD) simulations. The results showed that the ion distribution differs qualitatively from that described by classical EDL theories. Based on such exceptional phenomenon, a new sandwich capacitance model was developed to describe the EDLs inside micropores, which is capable of predicting the sharp increase of capacitance that has been experimentally observed in micropores. For the organic electrolytes, we examined the ion solvation and the EDL structure, capacitance, and dynamics in the electrolyte of

  12. Layered Organization in the Coastal Ocean: Acoustical Data Acquisition Analyses and Synthesis

    DTIC Science & Technology

    2009-11-04

    organisms move into the water colum at night, returning to a place they perceive as relatively safe during the day. This can be near the seabed (Kringel... material in thin layers. Those who model the performance of naval systems that use acoustical and optical technologies may wish to consider how...and Special Mission Sensors Division at Patuxent River, MD, NAVSEA’s Naval Undersea Warfare Center in Newport, RI, the Monterey Bay Aquarium

  13. Acoustic characteristics and the design of two-layered soundproof plates

    NASA Astrophysics Data System (ADS)

    Chonan, S.; Kugo, Y.

    1989-03-01

    This paper presents exact solutions for the coincidence frequency and the sound transmission loss of two-layered infinite plates excited by a plane acoustic wave. The problem is studied based on the two-dimensional elasticity theory wih the use of the Lame potential functions . A simple design method for a soundproof sheet with high transmission loss and high coincidence frequency is presented and illustrated with some examples. The results obtained are also compared with those from the thick plate theory.

  14. Calculating acoustical properties of cells: influence of surface topography and liquid layer between cell and substrate.

    PubMed

    Kundu, T; Bereiter-Hahn, J; Hillmann, K

    1992-05-01

    In this paper, a mathematical formulation is presented to compute the V(z) of a tapering layered solid and applying this formulation to the determination of acoustic properties of biological cells and tissues. The formulation is adopted in the simplex inversion algorithm to obtain the acoustic properties of a tapering cell from its V(z) values. The influence of two parameters had been considered: The tapering angle and the presence of a thin liquid layer present between cells and the substratum to which they adhere. Up to a tapering angle less than 10 degrees, it can be safely neglected. However, if a larger angle is neglected, then the acoustic wave velocity in the cell is overestimated. Cell thickness estimation is not affected significantly when the tapering angle is ignored. The calculations of acoustic properties of cells are considerably influenced by the introduction of a thin fluid layer between the solid substratum and the overlying cell, neglecting the presence of at least a very thin layer (20-30 nm), in general, results in a considerable overestimation of sound velocity. The reliability of the data calculated from V(z) values was ascertained using an independent method to determine cell thickness by calculating it from the interference fringe pattern obtained with the reflection-interference light microscope. The shape of the glutaraldehyde-fixed cells was similar to fried eggs. The highest sound velocities were found close to the periphery of the dome-shaped cell center. In the very center and over most of the area of the thin periphery, sound velocity was close to that in saline.

  15. Double sporadic metal layers as observed by colocated Fe and Na lidars at Wuhan, China

    NASA Astrophysics Data System (ADS)

    Wang, Xiaodong; Yi, Fan; Huang, Kaiming

    2017-02-01

    In this paper, we report a set of double sporadic layer events observed by Fe and Na lidars over Wuhan, China. The two sporadic metal layers above normal layer were named as upper and middle sporadic metal layers, respectively. In these events, the upper, middle, and normal Fe layers presented altitude separately. There were nine double sporadic Fe events observed in 163 nights during 2010-2013. Eight of the nine events were observed in summer. The maximum ratios of peak density for upper and middle sporadic Fe layers to normal Fe layer were up to 375% and 225%, respectively. The peak altitudes of upper (middle) sporadic Fe layers were in the range of 102-107 km (95-98.5 km). The double sporadic Fe layers lasted more than 2 h. Interestingly, we found that density enhancement occurred simultaneously in upper, middle, and normal Fe layers on two events. On the nine Fe events, there existed five nights of colocated Na lidar observations. We found that double sporadic Na and Fe layers simultaneously appeared. They presented similar structures, altitudes, and temporal variations in all five compared events. A little different from Fe, the middle sporadic Na layer was not separated from Na main layer maybe for the wide altitude range of Na main layer. The ratios of upper (middle) sporadic Fe and Na peak values were in the range of 6.6-52 (0.57-6.58). While the exact formation mechanism responsible for double sporadic metal layers is still unclear, some possible explanations and corresponding observations are discussed.

  16. Microwave absorption properties of double-layer absorber based on carbonyl iron/barium hexaferrite composites

    NASA Astrophysics Data System (ADS)

    Ren, Xiaohu; Fan, Huiqing; Cheng, Yankui

    2016-05-01

    The microwave absorption properties of BaCo0.4Zn1.6Fe16O27 ferrite and carbonyl iron powder with single-layer and double-layer composite absorbers were investigated based on the electromagnetic transmission line theory in the frequency range from 1 to 14 GHz. XRD was used to characterize the structure of prepared absorbing particles. SEM was used to examine the micromorphology of the particles and composites. The complex permittivity and permeability of composites were measured by using a vector network analyzer. The reflection loss of the single-layer and double-layer absorbers with different thicknesses and orders was investigated. The results show that double-layer absorbers have better microwave absorption properties than single-layer absorbers. The microwave absorption properties of the double-layer structure are influenced by the coupling interactions between the matching and absorption layers. As the pure ferrite used as matching layer and the composite of BF-5CI used as absorption, the minimum RL of absorber can achieve to -55.4 dB and the bandwidth of RL <-10 dB ranged from 5.6 to 10.8 GHz when the thicknesses of matching layer and absorption layer were 0.9 and 1.4 mm, respectively.

  17. Roles of a scatter on boundary-layer instability and acoustic radiation

    NASA Astrophysics Data System (ADS)

    Dong, Ming; Wu, Xuesong

    2015-11-01

    When a boundary-layer instability mode propagates through a region of rapid distortion, the ensuing scattering causes two consequences of physical interest. First, the amplitude of the instability mode may be suppressed or energized. Second, substantial sound wave can be radiated by the boundary-layer instability mode. This paper focuses on this issue by proposing a framework which is called Local Scattering Theory. In this framework, a transmission coefficient, defined as the ratio of the T-S wave amplitude downstream of the scatter to that upstream, is introduced to characterize the effect of a local scatter on boundary-layer instability and transition. The mathematical formulation is based on triple-deck formulism, but in order to accommodate the acoustic far field, the unsteady terms in the upper deck are retained. By computation, the impacts of a steady local suction on flow instability and acoustic radiation are studied. It is found that, (1) a suction slot would suppress the oncoming T-S wave; (2) the acoustic waves radiated by the scattering effect have similar directivities; (3) the intensity of the sound increases with the mass flux when the latter is not too large, and it also increases with the frequency monotonously.

  18. Time-Accurate Simulations and Acoustic Analysis of Slat Free-Shear-Layer. Part 2

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Singer, Bart A.; Lockard, David P.

    2002-01-01

    Unsteady computational simulations of a multi-element, high-lift configuration are performed. Emphasis is placed on accurate spatiotemporal resolution of the free shear layer in the slat-cove region. The excessive dissipative effects of the turbulence model, so prevalent in previous simulations, are circumvented by switching off the turbulence-production term in the slat cove region. The justifications and physical arguments for taking such a step are explained in detail. The removal of this excess damping allows the shear layer to amplify large-scale structures, to achieve a proper non-linear saturation state, and to permit vortex merging. The large-scale disturbances are self-excited, and unlike our prior fully turbulent simulations, no external forcing of the shear layer is required. To obtain the farfield acoustics, the Ffowcs Williams and Hawkings equation is evaluated numerically using the simulated time-accurate flow data. The present comparison between the computed and measured farfield acoustic spectra shows much better agreement for the amplitude and frequency content than past calculations. The effect of the angle-of-attack on the slat's flow features radiated acoustic field are also simulated presented.

  19. Active control of acoustic radiation from laminated cylindrical shells integrated with a piezoelectric layer

    NASA Astrophysics Data System (ADS)

    Cao, Xiongtao; Shi, Lei; Zhang, Xusheng; Jiang, Guohe

    2013-06-01

    Active control of sound radiation from piezoelectric laminated cylindrical shells is theoretically investigated in the wavenumber domain. The governing equations of the smart cylindrical shells are derived by using first-order shear deformation theory. The smart layer is divided into lots of actuator patches, each of which is coated with two very thin electrodes at its inner and outer surfaces. Proportional derivative negative feedback control is applied to the actuator patches and the stiffness of the controlled layer is derived in the wavenumber domain. The equivalent driving forces and moments generated by the piezoelectric layer can produce distinct sound radiation. Large actuator patches cause strong wavenumber conversion and fluctuation of the far-field sound pressure, and do not make any contribution to sound reduction. Nevertheless, suitable small actuator patches induce weak wavenumber conversion and play an important role in the suppression of vibration and acoustic power. The derivative gain of the active control can effectively suppress sound radiation from smart cylindrical shells. The effects of small proportional gain on the sound field can be neglected, but large proportional gain has a great impact on the acoustic radiation of cylindrical shells. The influence of different piezoelectric materials on the acoustic power is described in the numerical results.

  20. Nonlinear scattering of acoustic waves by natural and artificially generated subsurface bubble layers in sea.

    PubMed

    Ostrovsky, Lev A; Sutin, Alexander M; Soustova, Irina A; Matveyev, Alexander L; Potapov, Andrey I; Kluzek, Zigmund

    2003-02-01

    The paper describes nonlinear effects due to a biharmonic acoustic signal scattering from air bubbles in the sea. The results of field experiments in a shallow sea are presented. Two waves radiated at frequencies 30 and 31-37 kHz generated backscattered signals at sum and difference frequencies in a bubble layer. A motorboat propeller was used to generate bubbles with different concentrations at different times, up to the return to the natural subsurface layer. Theoretical consideration is given for these effects. The experimental data are in a reasonably good agreement with theoretical predictions.

  1. Anodic aluminum oxide-epoxy composite acoustic matching layers for ultrasonic transducer application.

    PubMed

    Fang, H J; Chen, Y; Wong, C M; Qiu, W B; Chan, H L W; Dai, J Y; Li, Q; Yan, Q F

    2016-08-01

    The goal of this work is to demonstrate the application of anodic aluminum oxide (AAO) template as matching layer of ultrasonic transducer. Quarter-wavelength acoustic matching layer is known as a vital component in medical ultrasonic transducers to compensate the acoustic impedance mismatch between piezoelectric element and human body. The AAO matching layer is made of anodic aluminum oxide template filled with epoxy resin, i.e. AAO-epoxy 1-3 composite. Using this composite as the first matching layer, a ∼12MHz ultrasonic transducer based on soft lead zirconate titanate piezoelectric ceramic is fabricated, and pulse-echo measurements show that the transducer exhibits very good performance with broad bandwidth of 68% (-6dB) and two-way insertion loss of -22.7dB. Wire phantom ultrasonic image is also used to evaluate the transducer's performance, and the results confirm the process feasibility and merit of AAO-epoxy composite as a new matching material for ultrasonic transducer application. This matching scheme provides a solution to address the problems existing in the conventional 0-3 composite matching layer and suggests another useful application of AAO template.

  2. Double-Layered Matrix of Shellac Wax-Lutrol in Controlled Dual Drug Release.

    PubMed

    Phaechamud, Thawatchai; Choncheewa, Chai-Ek

    2016-12-01

    Double-layered matrix tablets prepared from shellac wax-lutrol were fabricated using a molding technique, and the release of hydrochlorothiazide and propranolol HCl from the inner tablet or outer layer was studied. The simultaneous determination of dual drug release was measured with first derivative UV spectrophotometry. The tablet containing shellac wax as the outer tablet and lutrol as the inner tablet showed more appropriate drug release and the size of the inner layer influenced the rate of drug release. In addition, the aqueous solubility of the drug and the components of the inner tablet or outer layer affected the drug release behavior. Most of the double-layered tablets exhibited the drug-release pattern which fitted well with zero-order kinetic due to the restriction of the release surface. Biphasic drug release pattern was found in the tablet of which the outer layer rapidly eroded. The drug dissolution data from drug-loaded-outer layer could predict the dissolution time for the outer layer of drug-loaded inner part of double-layered matrix tablet. Incorporation of lutrol increased the drug release from shellac wax matrix, and the zero-order release was attained by fabricating it into a double-layered tablet.

  3. Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

    NASA Astrophysics Data System (ADS)

    Favaro, Marco; Jeong, Beomgyun; Ross, Philip N.; Yano, Junko; Hussain, Zahid; Liu, Zhi; Crumlin, Ethan J.

    2016-08-01

    The electrochemical double layer plays a critical role in electrochemical processes. Whilst there have been many theoretical models predicting structural and electrical organization of the electrochemical double layer, the experimental verification of these models has been challenging due to the limitations of available experimental techniques. The induced potential drop in the electrolyte has never been directly observed and verified experimentally, to the best of our knowledge. In this study, we report the direct probing of the potential drop as well as the potential of zero charge by means of ambient pressure X-ray photoelectron spectroscopy performed under polarization conditions. By analyzing the spectra of the solvent (water) and a spectator neutral molecule with numerical simulations of the electric field, we discern the shape of the electrochemical double layer profile. In addition, we determine how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential.

  4. Formation and stability of self-consistent double layer structures in plasma

    SciTech Connect

    Sanduloviciu, M.

    1995-12-31

    The presence of critical values in the current versus voltage characteristic of an electrode immersed in a plasma is used as an argument for the existence of self-consistent (autoorganized) double layers in collisional and collisionless presumed plasmas.

  5. Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

    PubMed Central

    Favaro, Marco; Jeong, Beomgyun; Ross, Philip N.; Yano, Junko; Hussain, Zahid; Liu, Zhi; Crumlin, Ethan J.

    2016-01-01

    The electrochemical double layer plays a critical role in electrochemical processes. Whilst there have been many theoretical models predicting structural and electrical organization of the electrochemical double layer, the experimental verification of these models has been challenging due to the limitations of available experimental techniques. The induced potential drop in the electrolyte has never been directly observed and verified experimentally, to the best of our knowledge. In this study, we report the direct probing of the potential drop as well as the potential of zero charge by means of ambient pressure X-ray photoelectron spectroscopy performed under polarization conditions. By analyzing the spectra of the solvent (water) and a spectator neutral molecule with numerical simulations of the electric field, we discern the shape of the electrochemical double layer profile. In addition, we determine how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential. PMID:27576762

  6. Mesoporous layer-by-layer ordered nanohybrids of layered double hydroxide and layered metal oxide: highly active visible light photocatalysts with improved chemical stability.

    PubMed

    Gunjakar, Jayavant L; Kim, Tae Woo; Kim, Hyo Na; Kim, In Young; Hwang, Seong-Ju

    2011-09-28

    Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O(2) generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn-Cr-layered double hydroxide (Zn-Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn-Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O(2) generation with a rate of ∼1.18 mmol h(-1) g(-1), which is higher than the O(2) production rate (∼0.67 mmol h(-1) g(-1)) by the pristine Zn-Cr-LDH material, that is, one of the most effective visible light photocatalysts for O(2) production, under the same experimental condition. This result highlights an excellent functionality of the Zn-Cr-LDH-layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn-Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical

  7. On the threshold energization of radiation belt electrons by double layers.

    NASA Astrophysics Data System (ADS)

    Dimmock, A. P.; Osmane, A.; Pulkkinen, T. I.

    2014-12-01

    Recent in situ electric field measurements by the Van Allen Probes in the radiation belts have revealed the existence and ubiquitous presence of double layers [Mozer et al. Phys. Rev. Lett., 2013]. Encounters with double layers during 1 minute burst mode intervals were both common and indicative of large cumulative potential drops. With electric fields averaging 20 mV/m, and sometimes reaching as high as 100 mV/m, observed double layers have been suggested as possible accelerators of radiation belt electrons and generators of a seed population of 100 keV. Using a Hamiltonian approach we quantify the energization threshold of electrons interacting with radiation belts' double layers analytically and numerically. We find that double layers with electric field amplitude δE ranging between 10-100 mV/m and spatial scales of the order of few Debye lengths are very efficient in energizing electrons with initial velocities v ≤ vthermal≈3000 km/s to 1 keV levels, but are unable to energize electrons with energies E ≥ 10 keV. Our results therefore indicate that the localized electric field associated with the double layers are unlikely to generate a seed population of 100 keV necessary for a plethora of relativistic acceleration mechanisms and additional transport to higher energetic levels.

  8. The polarization of a nanoparticle surrounded by a thick electric double layer.

    PubMed

    Zhao, Hui; Bau, Haim H

    2009-05-15

    The polarization of a charged, dielectric, nanoparticle enveloped by a thick electric double layer and subjected to a uniform, alternating electric field is studied theoretically with the standard model (the Poisson-Nernst-Planck PNP equations). The dipole coefficient (f) is calculated as a function of the electric field's frequency and the double layer's thickness (lambda(D)). For a weakly charged particle with a small zeta potential zeta, an approximate, analytic expression for the dipole moment coefficient, accurate within O(zeta(2)), is derived. Two processes contribute to the dipole moment: the ion transport in the electric double layer under the action of the electric field and the particle's electrophoretic motion. As the thickness of the electric double layer increases so does the importance of the latter. In contrast to the case of the thin electric double layer, the particle with the thick double layer exhibits only high-frequency dispersion. The theoretical predictions are compared and favorably agree with experimental data, leading one to conclude that the standard, PNP based-model adequately represents the behavior of nanoparticles subject to electric fields.

  9. Thermal analysis of double-layer metal films during femtosecond laser heating

    NASA Astrophysics Data System (ADS)

    Chen, A. M.; Jiang, Y. F.; Sui, L. Z.; Liu, H.; Jin, M. X.; Ding, D. J.

    2011-05-01

    In this paper, the primary interest is the heat effect of the bottom-layer metal on the temperature distribution of the top-layer metal in a double-layer metal structure during femtosecond laser irradiation. The evolution of the surface electron and lattice temperature depends a lot on the thermal parameters of the substrate. The damage threshold can be increased by using a substrate material with high electron-lattice coupling factor. Next, we choose chrome as the bottom-layer material. The results of modeling show that the surface lattice temperature of top-layer gold can be reduced remarkably. For a fixed entire thickness of the double-layer film, there is an optimal proportion of top and bottom layers for which the damage threshold is the highest possible. Also, for increasing the damage threshold, a substrate with higher melting temperature should be chosen.

  10. Non-blind acoustic invisibility by dual layers of homogeneous single-negative media.

    PubMed

    Gao, He; Zhu, Yi-Fan; Fan, Xu-Dong; Liang, Bin; Yang, Jing; Cheng, Jian-Chun

    2017-02-14

    Non-blind invisibility cloaks allowing the concealed object to sense the outside world have great application potentials such as in high-precision sensing or underwater camouflage. However the existing designs based on coordinate transformation techniques need complicated spatially-varying negative index or intricate multi-layered configurations, substantially increasing the difficulty in practical realization. Here we report on the non-blind acoustic invisibility for a circular object in free space with simple distribution of cloak parameters. The mechanism is that, instead of utilizing the transformation acoustics technique, we develop the analytical formulae for fast prediction of the scattering from the object and then use an evolutionary optimization to retrieve the desired cloak parameters for minimizing the scattered field. In this way, it is proven possible to break through the fundamental limit of complementary condition that must be satisfied by the effective parameters of the components in transformation acoustics-based cloaks. Numerical results show that the resulting cloak produces a non-bflind invisibility as perfect as in previous designs, but only needs two layers with homogenous single-negative parameters. With full simplification in parameter distribution and broken symmetry in complementary relationship, our scheme opens new route to free-space non-blind invisibility, taking a significant step towards real-world application of cloaking devices.

  11. Non-blind acoustic invisibility by dual layers of homogeneous single-negative media

    NASA Astrophysics Data System (ADS)

    Gao, He; Zhu, Yi-Fan; Fan, Xu-Dong; Liang, Bin; Yang, Jing; Cheng, Jian-Chun

    2017-02-01

    Non-blind invisibility cloaks allowing the concealed object to sense the outside world have great application potentials such as in high-precision sensing or underwater camouflage. However the existing designs based on coordinate transformation techniques need complicated spatially-varying negative index or intricate multi-layered configurations, substantially increasing the difficulty in practical realization. Here we report on the non-blind acoustic invisibility for a circular object in free space with simple distribution of cloak parameters. The mechanism is that, instead of utilizing the transformation acoustics technique, we develop the analytical formulae for fast prediction of the scattering from the object and then use an evolutionary optimization to retrieve the desired cloak parameters for minimizing the scattered field. In this way, it is proven possible to break through the fundamental limit of complementary condition that must be satisfied by the effective parameters of the components in transformation acoustics-based cloaks. Numerical results show that the resulting cloak produces a non-bflind invisibility as perfect as in previous designs, but only needs two layers with homogenous single-negative parameters. With full simplification in parameter distribution and broken symmetry in complementary relationship, our scheme opens new route to free-space non-blind invisibility, taking a significant step towards real-world application of cloaking devices.

  12. Transition in a Supersonic Boundary-Layer Due to Roughness and Acoustic Disturbances

    NASA Technical Reports Server (NTRS)

    Balakumar, P.

    2003-01-01

    The transition process induced by the interaction of an isolated roughness with acoustic disturbances in the free stream is numerically investigated for a boundary layer over a flat plate with a blunted leading edge at a free stream Mach number of 3.5. The roughness is assumed to be of Gaussian shape and the acoustic disturbances are introduced as boundary condition at the outer field. The governing equations are solved using the 5'h-rder accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third- order total-variation-diminishing (TVD) Runge- Kutta scheme for time integration. The steady field induced by the two and three-dimensional roughness is also computed. The flow field induced by two-dimensional roughness exhibits different characteristics depending on the roughness heights. At small roughness heights the flow passes smoothly over the roughness, at moderate heights the flow separates downstream of the roughness and at larger roughness heights the flow separates upstream and downstream of the roughness. Computations also show that disturbances inside the boundary layer is due to the direct interaction of the acoustic waves and isolated roughness plays a minor role in generating instability waves.

  13. Non-blind acoustic invisibility by dual layers of homogeneous single-negative media

    PubMed Central

    Gao, He; Zhu, Yi-fan; Fan, Xu-dong; Liang, Bin; Yang, Jing; Cheng, Jian-Chun

    2017-01-01

    Non-blind invisibility cloaks allowing the concealed object to sense the outside world have great application potentials such as in high-precision sensing or underwater camouflage. However the existing designs based on coordinate transformation techniques need complicated spatially-varying negative index or intricate multi-layered configurations, substantially increasing the difficulty in practical realization. Here we report on the non-blind acoustic invisibility for a circular object in free space with simple distribution of cloak parameters. The mechanism is that, instead of utilizing the transformation acoustics technique, we develop the analytical formulae for fast prediction of the scattering from the object and then use an evolutionary optimization to retrieve the desired cloak parameters for minimizing the scattered field. In this way, it is proven possible to break through the fundamental limit of complementary condition that must be satisfied by the effective parameters of the components in transformation acoustics-based cloaks. Numerical results show that the resulting cloak produces a non-bflind invisibility as perfect as in previous designs, but only needs two layers with homogenous single-negative parameters. With full simplification in parameter distribution and broken symmetry in complementary relationship, our scheme opens new route to free-space non-blind invisibility, taking a significant step towards real-world application of cloaking devices. PMID:28195227

  14. Receptivity of Hypersonic Boundary Layers to Acoustic and Vortical Disturbances (Invited)

    NASA Technical Reports Server (NTRS)

    Balakumar, P.

    2015-01-01

    Boundary-layer receptivity to two-dimensional acoustic and vortical disturbances for hypersonic flows over two-dimensional and axi-symmetric geometries were numerically investigated. The role of bluntness, wall cooling, and pressure gradients on the receptivity and stability were analyzed and compared with the sharp nose cases. It was found that for flows over sharp nose geometries in adiabatic wall conditions the instability waves are generated in the leading-edge region and that the boundary layer is much more receptive to slow acoustic waves as compared to the fast waves. The computations confirmed the stabilizing effect of nose bluntness and the role of the entropy layer in the delay of boundary layer transition. The receptivity coefficients in flows over blunt bodies are orders of magnitude smaller than that for the sharp cone cases. Wall cooling stabilizes the first mode strongly and destabilizes the second mode. However, the receptivity coefficients are also much smaller compared to the adiabatic case. The adverse pressure gradients increased the unstable second mode regions.

  15. Angular Momentum Transport and Variability in Boundary Layers of Accretion Disks Driven by Global Acoustic Modes

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M.

    2012-11-01

    Disk accretion onto a weakly magnetized central object, e.g., a star, is inevitably accompanied by the formation of a boundary layer near the surface, in which matter slows down from the highly supersonic orbital velocity of the disk to the rotational velocity of the star. We perform high-resolution two-dimensional hydrodynamical simulations in the equatorial plane of an astrophysical boundary layer with the goal of exploring the dynamics of non-axisymmetric structures that form there. We generically find that the supersonic shear in the boundary layer excites non-axisymmetric quasi-stationary acoustic modes that are trapped between the surface of the star and a Lindblad resonance in the disk. These modes rotate in a prograde fashion, are stable for hundreds of orbital periods, and have a pattern speed that is less than and of the order of the rotational velocity at the inner edge of the disk. The origin of these intrinsically global modes is intimately related to the operation of a corotation amplifier in the system. Dissipation of acoustic modes in weak shocks provides a universal mechanism for angular momentum and mass transport even in purely hydrodynamic (i.e., non-magnetized) boundary layers. We discuss the possible implications of these trapped modes for explaining the variability seen in accreting compact objects.

  16. ANGULAR MOMENTUM TRANSPORT AND VARIABILITY IN BOUNDARY LAYERS OF ACCRETION DISKS DRIVEN BY GLOBAL ACOUSTIC MODES

    SciTech Connect

    Belyaev, Mikhail A.; Stone, James M.; Rafikov, Roman R.

    2012-11-20

    Disk accretion onto a weakly magnetized central object, e.g., a star, is inevitably accompanied by the formation of a boundary layer near the surface, in which matter slows down from the highly supersonic orbital velocity of the disk to the rotational velocity of the star. We perform high-resolution two-dimensional hydrodynamical simulations in the equatorial plane of an astrophysical boundary layer with the goal of exploring the dynamics of non-axisymmetric structures that form there. We generically find that the supersonic shear in the boundary layer excites non-axisymmetric quasi-stationary acoustic modes that are trapped between the surface of the star and a Lindblad resonance in the disk. These modes rotate in a prograde fashion, are stable for hundreds of orbital periods, and have a pattern speed that is less than and of the order of the rotational velocity at the inner edge of the disk. The origin of these intrinsically global modes is intimately related to the operation of a corotation amplifier in the system. Dissipation of acoustic modes in weak shocks provides a universal mechanism for angular momentum and mass transport even in purely hydrodynamic (i.e., non-magnetized) boundary layers. We discuss the possible implications of these trapped modes for explaining the variability seen in accreting compact objects.

  17. Viscous effects on the acoustics and stability of a shear layer over an impedance wall

    NASA Astrophysics Data System (ADS)

    Khamis, Doran; Brambley, Edward James

    2017-01-01

    The effect of viscosity and thermal conduction on the acoustics in a shear layer above an impedance wall is investigated numerically and asymptotically by solving the compressible linearised Navier-Stokes equations. It is found that viscothermal effects can be as important as shear, and therefore including shear while neglecting viscothermal effects by solving the linearised Euler equations is questionable. In particular, the damping rate of upstream propagating waves is found to be dramatically under-predicted by the LEE in certain instances. The effects of viscosity on stability are also found to be important. Short wavelength disturbances are stabilised by viscosity, greatly altering the characteristic wavelength and maximum growth rate of instability. For the parameters typical of aeroacoustic simulations considered here, the Reynolds number below which the flow stabilizes ranges from $10^5$ to $10^7$. By assuming a thin but nonzero-thickness boundary layer, asymptotic analysis leads to a system of boundary layer governing equations for the acoustics. This system may be solved numerically to produce an effective impedance boundary condition, applicable at the wall of a uniform inviscid flow, that accounts for both the shear and viscosity within the boundary layer. An alternative asymptotic analysis in the high frequency limit yields a different set of equations with analytic solutions. The acoustic mode shapes and axial wavenumbers from both asymptotic analyses compare well with numerical solutions of the full LNSE. A closed-form effective impedance boundary condition is derived from the high-frequency asymptotics, suitable for application in frequency-domain numerical simulations. Finally, surface waves are considered, and it is shown that a viscous flow over an impedance lining supports a greater number of surface wave modes than an inviscid flow.

  18. Comparison of Numerical Models for Vibro-Acoustic Analysis of Structural Panels in Low Modal Density Range Engaging Air Layers

    NASA Astrophysics Data System (ADS)

    Chimeno-Manguan, M.; Martinz-Calvo, B.; Roibas-Millan, E.; Fajardo, P.; Simon, F.; Lopez-Diez, J.

    2012-07-01

    During launch, satellite and their equipment are subjected to loads of random nature and with a wide frequency range. Their vibro-acoustic response is an important issue to be analysed, for example for folded solar arrays and antennas. The main issue at low modal density is the modelling combinations engaging air layers, structures and external fluid. Depending on the modal density different methodologies, as FEM, BEM and SEA should be considered. This work focuses on the analysis of different combinations of the methodologies previously stated used in order to characterise the vibro-acoustic response of two rectangular sandwich structure panels isolated and engaging an air layer between them under a diffuse acoustic field. Focusing on the modelling of air layers, different models are proposed. To illustrate the phenomenology described and studied, experimental results from an acoustic test on an ARA-MKIII solar array in folded configuration are presented along with numerical results.

  19. Time-Accurate Simulations and Acoustic Analysis of Slat Free-Shear Layer

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Singer, Bart A.; Berkman, Mert E.

    2001-01-01

    A detailed computational aeroacoustic analysis of a high-lift flow field is performed. Time-accurate Reynolds Averaged Navier-Stokes (RANS) computations simulate the free shear layer that originates from the slat cusp. Both unforced and forced cases are studied. Preliminary results show that the shear layer is a good amplifier of disturbances in the low to mid-frequency range. The Ffowcs-Williams and Hawkings equation is solved to determine the acoustic field using the unsteady flow data from the RANS calculations. The noise radiated from the excited shear layer has a spectral shape qualitatively similar to that obtained from measurements in a corresponding experimental study of the high-lift system.

  20. Light-scattering study of the localization of longitudinal acoustic pseudomodes in a buried silica layer

    NASA Astrophysics Data System (ADS)

    Ghislotti, G.; Bottani, C. E.; Mutti, P.; Byloos, C.; Giovannini, L.; Nizzoli, F.

    1995-04-01

    Brillouin light spectroscopy in p-p backscattering geometry is used to study sagittal surface acoustic phonons in silicon on insulator structures formed on a silicon buffer. The experimental spectra show, near the longitudinal threshold of silicon, two peaks whose physical meaning is discussed by comparison with theoretical cross sections. Calculations of Brillouin cross sections were performed, taking into account both the ripple and elastooptic coupling mechanisms. The peaks originate from two pseudomodes: the first is highly localized in the buried SiO2 layer and the second in the top silicon layer. The dependence of the pseudomode localization and cross section intensity with the parallel wave vector and with the thickness of the top silicon layer are discussed.

  1. Topological defects in electric double layers of ionic liquids at carbon interfaces

    DOE PAGES

    Black, Jennifer M.; Okatan, Mahmut Baris; Feng, Guang; ...

    2015-06-07

    The structure and properties of the electrical double layer in ionic liquids is of interest in a wide range of areas including energy storage, catalysis, lubrication, and many more. Theories describing the electrical double layer for ionic liquids have been proposed, however a full molecular level description of the double layer is lacking. To date, studies have been predominantly focused on ion distributions normal to the surface, however the 3D nature of the electrical double layer in ionic liquids requires a full picture of the double layer structure not only normal to the surface, but also in plane. Here wemore » utilize 3D force mapping to probe the in plane structure of an ionic liquid at a graphite interface and report the direct observation of the structure and properties of topological defects. The observation of ion layering at structural defects such as step-edges, reinforced by molecular dynamics simulations, defines the spatial resolution of the method. Observation of defects allows for the establishment of the universality of ionic liquid behavior vs. separation from the carbon surface and to map internal defect structure. In conclusion, these studies offer a universal pathway for probing the internal structure of topological defects in soft condensed matter on the nanometer level in three dimensions.« less

  2. Topological defects in electric double layers of ionic liquids at carbon interfaces

    SciTech Connect

    Black, Jennifer M.; Okatan, Mahmut Baris; Feng, Guang; Cummings, Peter T.; Kalinin, Sergei V.; Balke, Nina

    2015-06-07

    The structure and properties of the electrical double layer in ionic liquids is of interest in a wide range of areas including energy storage, catalysis, lubrication, and many more. Theories describing the electrical double layer for ionic liquids have been proposed, however a full molecular level description of the double layer is lacking. To date, studies have been predominantly focused on ion distributions normal to the surface, however the 3D nature of the electrical double layer in ionic liquids requires a full picture of the double layer structure not only normal to the surface, but also in plane. Here we utilize 3D force mapping to probe the in plane structure of an ionic liquid at a graphite interface and report the direct observation of the structure and properties of topological defects. The observation of ion layering at structural defects such as step-edges, reinforced by molecular dynamics simulations, defines the spatial resolution of the method. Observation of defects allows for the establishment of the universality of ionic liquid behavior vs. separation from the carbon surface and to map internal defect structure. In conclusion, these studies offer a universal pathway for probing the internal structure of topological defects in soft condensed matter on the nanometer level in three dimensions.

  3. Effectiveness of T-shaped acoustic resonators in low-frequency sound transmission control of a finite double-panel partition

    NASA Astrophysics Data System (ADS)

    Li, Deyu; Zhang, Xiao-Hong; Cheng, Li; Yu, Ganghua

    2010-10-01

    Double-panel partitions are widely used for sound insulation purposes. Their insulation efficiency is, however, deteriorated at low frequencies due to the structural and acoustic resonances. To tackle this problem, this paper proposes the use of long T-shaped acoustic resonators in a double-panel partition embedded along the edges. In order to facilitate the design and assess the performance of the structure, a general vibro-acoustic model, characterizing the interaction between the panels, air cavity, and integrated acoustic resonators, is developed. The effectiveness of the technique as well as the optimal locations of the acoustic resonators is examined at various frequencies where the system exhibits different coupling characteristics. The measured optimal locations are also compared with the predicted ones to verify the developed theory. Finally, the performance of the acoustic resonators in broadband sound transmission control is demonstrated.

  4. Surface properties of solids and surface acoustic waves: Application to chemical sensors and layer characterization

    NASA Astrophysics Data System (ADS)

    Krylov, V. V.

    1995-09-01

    A general phenomenological approach is given for the description of mechanical surface properties of solids and their influence on surface acoustic wave propogation. Surface properties under consideration may be changes of the stress distribution in subsurface atomic layers, the presence of adsorbed gas molecules, surface degradation as a result of impacts from an aggressive environment, damage due to mechanical manufacturing or polishing, deposition of thin films or liquid layers, surface corrugations, etc. If the characteristic thickness of the affected layers is much less than the wavelengths of the propagating surface waves, then the effects of all these irregularities can be described by means of non-classical boundary conditions incorporating the integral surface parameters such as surface tension, surface moduli of elasticity and surface mass density. The effect of surface properties on the propagation of Rayleigh surface waves is analysed in comparison with the results of traditional approaches, in particular with Auld's energy perturbation method. One of the important implications of the above-mentioned boudnary conditions is that they are adequate for the description of the effect of rarely distributed adsorbed atoms or molecules. This allows, in particular, to obtain a rigorous theoretical description of chemical sensors using surface acoustic waves and to derive analytical expressions for their sensitivity.

  5. Unipolar Complementary Circuits Using Double Electron Layer Tunneling Tansistors

    SciTech Connect

    Blount, M.A.; Hafich, M.J.; Moon, J.S.; Reno, J.L.; Simmons, J.A.

    1998-10-19

    We demonstrate unipolar complementary circuits consisting of a pair of resonant tunneling transistors based on the gate control of 2D-2D interlayer tunneling, where a single transistor - in addition to exhibiting a welldefined negative-differential-resistance can be operated with either positive or negative transconductance. Details of the device operation are analyzed in terms of the quantum capacitance effect and band-bending in a double quantum well structure, and show good agreement with experiment. Application of resonant tunneling complementary logic is discussed by demonstrating complementary static random access memory using two devices connected in series.

  6. Response of a hypersonic boundary layer to freestream pulse acoustic disturbance.

    PubMed

    Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

    2014-01-01

    The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter.

  7. Response of a Hypersonic Boundary Layer to Freestream Pulse Acoustic Disturbance

    PubMed Central

    Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

    2014-01-01

    The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter. PMID:24737993

  8. A single-layer, planar, optofluidic switch powered by acoustically driven, oscillating microbubbles

    NASA Astrophysics Data System (ADS)

    Huang, Po-Hsun; Ian Lapsley, Michael; Ahmed, Daniel; Chen, Yuchao; Wang, Lin; Jun Huang, Tony

    2012-10-01

    Merging acoustofluidic mixing with optofluidic integration, we have demonstrated a single-layer, planar, optofluidic switch that is driven by acoustically excited oscillating microbubbles. The device was found to have a switching speed of 5 Hz, an insertion loss of 6.02 dB, and an extinction ratio of 28.48 dB. With its simplicity, low fluid consumption, and compatibility with other microfluidic devices, our design could lead to a line of inexpensive, yet effective optical switches for many lab-on-a-chip applications.

  9. A novel unsplit perfectly matched layer for the second-order acoustic wave equation.

    PubMed

    Ma, Youneng; Yu, Jinhua; Wang, Yuanyuan

    2014-08-01

    When solving acoustic field equations by using numerical approximation technique, absorbing boundary conditions (ABCs) are widely used to truncate the simulation to a finite space. The perfectly matched layer (PML) technique has exhibited excellent absorbing efficiency as an ABC for the acoustic wave equation formulated as a first-order system. However, as the PML was originally designed for the first-order equation system, it cannot be applied to the second-order equation system directly. In this article, we aim to extend the unsplit PML to the second-order equation system. We developed an efficient unsplit implementation of PML for the second-order acoustic wave equation based on an auxiliary-differential-equation (ADE) scheme. The proposed method can benefit to the use of PML in simulations based on second-order equations. Compared with the existing PMLs, it has simpler implementation and requires less extra storage. Numerical results from finite-difference time-domain models are provided to illustrate the validity of the approach.

  10. Umbilical Cord Mesenchymal Stem Cells Combined With a Collagenfibrin Double-layered Membrane Accelerates Wound Healing.

    PubMed

    Nan, Wenbin; Liu, Rui; Chen, Hongli; Xu, Zhihao; Chen, Jiannan; Wang, Manman; Yuan, Zhiqing

    2015-05-01

    The aim of this study was to examine the effects of human umbilical cord mesenchymal stem cells (hUCMSCs) in combination with a collagen-fibrin double-layered membrane on wound healing in mice. A collagen-fibrin double-layered membrane was prepared, and the surface properties of the support material were investigated using a scanning electron microscope. Twenty-four mice were prepared for use as full-thickness skin wound models and randomly divided into 3 groups: group A, a control group in which the wounds were bound using a conventional method; group B, a group treated with hUCMSCs combined with a collagen membrane; and group C, a group treated with hUCMSCs combined with a collagen-fibrin double-layered membrane. The postoperative concrescence of the wounds was observed daily to evaluate the effects of the different treatments. Scanning electron microscope observation showed the collagen-fibrin scaffolds exhibited a highly porous and interconnected structure, and wound healing in the double-layered membrane group was better than in groups A or B. Treatment with hUCMSCs combined with a collagen-fibrin double-layered membrane accelerated wound healing.

  11. Conditions for establishing quasistable double layers in the Earth's auroral upward current region

    SciTech Connect

    Main, D. S.; Newman, D. L.; Ergun, R. E.

    2010-12-15

    The strength and stability of simulated double layers at the ionosphere-auroral cavity boundary have been studied as a function of cold ionospheric electron temperature and density. The simulations are performed with an open boundary one-dimensional particle-in- cell (PIC) simulation and are initialized by imposing a density cavity within the simulation domain. The PIC simulation includes H{sup +} and O{sup +} ion beams, a hot H{sup +} background population, cold ionospheric electrons, and a hot electron population. It is shown that a double layer remains quasistable for a variety of initial conditions and plasma parameters. The average potential drop of the double layer is found to increase as the cold electron temperature decreases. However, in terms of cold electron density, the average potential drop of the double layer is found to increase up to some critical cold electron density and decreases above this value. Comparisons with FAST observations are made and agreement is found between simulation results and observations in the shape and width of the double layer. This study helps put a constraint on the plasma conditions in which a DL can be expected to form and remain quasistable.

  12. Double Charged Surface Layers in Lead Halide Perovskite Crystals.

    PubMed

    Sarmah, Smritakshi P; Burlakov, Victor M; Yengel, Emre; Murali, Banavoth; Alarousu, Erkki; El-Zohry, Ahmed M; Yang, Chen; Alias, Mohd S; Zhumekenov, Ayan A; Saidaminov, Makhsud I; Cho, Namchul; Wehbe, Nimer; Mitra, Somak; Ajia, Idris; Dey, Sukumar; Mansour, Ahmed E; Abdelsamie, Maged; Amassian, Aram; Roqan, Iman S; Ooi, Boon S; Goriely, Alain; Bakr, Osman M; Mohammed, Omar F

    2017-03-08

    Understanding defect chemistry, particularly ion migration, and its significant effect on the surface's optical and electronic properties is one of the major challenges impeding the development of hybrid perovskite-based devices. Here, using both experimental and theoretical approaches, we demonstrated that the surface layers of the perovskite crystals may acquire a high concentration of positively charged vacancies with the complementary negatively charged halide ions pushed to the surface. This charge separation near the surface generates an electric field that can induce an increase of optical band gap in the surface layers relative to the bulk. We found that the charge separation, electric field, and the amplitude of shift in the bandgap strongly depend on the halides and organic moieties of perovskite crystals. Our findings reveal the peculiarity of surface effects that are currently limiting the applications of perovskite crystals and more importantly explain their origins, thus enabling viable surface passivation strategies to remediate them.

  13. Computationally efficient parabolic equation solutions to seismo-acoustic problems involving thin or low-shear elastic layers.

    PubMed

    Metzler, Adam M; Collis, Jon M

    2013-04-01

    Shallow-water environments typically include sediments containing thin or low-shear layers. Numerical treatments of these types of layers require finer depth grid spacing than is needed elsewhere in the domain. Thin layers require finer grids to fully sample effects due to elasticity within the layer. As shear wave speeds approach zero, the governing system becomes singular and fine-grid spacing becomes necessary to obtain converged solutions. In this paper, a seismo-acoustic parabolic equation solution is derived utilizing modified difference formulas using Galerkin's method to allow for variable-grid spacing in depth. Propagation results are shown for environments containing thin layers and low-shear layers.

  14. Double-layered ZnO nanostructures for efficient perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Mahmood, Khalid; S. Swain, Bhabani; Amassian, Aram

    2014-11-01

    To date, a single layer of TiO2 or ZnO has been the most successful implementations of any electron transport layer (ETL) in solution-processed perovskite solar cells. In a quest to improve the ETL, we explore a new nanostructured double-layer ZnO film for mesoscopic perovskite-based thin film photovoltaics. This approach yields a maximum power conversion efficiency of 10.35%, which we attribute to the morphology of oxide layer and to faster electron transport. The successful implementation of the low-temperature hydrothermally processed double-layer ZnO film as ETL in perovskite solar cells highlights the opportunities to further improve the efficiencies by focusing on the ETL in this rapidly developing field.

  15. Double-layered ZnO nanostructures for efficient perovskite solar cells.

    PubMed

    Mahmood, Khalid; S Swain, Bhabani; Amassian, Aram

    2014-12-21

    To date, a single layer of TiO2 or ZnO has been the most successful implementations of any electron transport layer (ETL) in solution-processed perovskite solar cells. In a quest to improve the ETL, we explore a new nanostructured double-layer ZnO film for mesoscopic perovskite-based thin film photovoltaics. This approach yields a maximum power conversion efficiency of 10.35%, which we attribute to the morphology of oxide layer and to faster electron transport. The successful implementation of the low-temperature hydrothermally processed double-layer ZnO film as ETL in perovskite solar cells highlights the opportunities to further improve the efficiencies by focusing on the ETL in this rapidly developing field.

  16. Acoustic emission and fatigue damage induced in plasma-sprayed hydroxyapatite coating layers.

    PubMed

    Laonapakul, Teerawat; Otsuka, Yuichi; Nimkerdphol, Achariya Rakngarm; Mutoh, Yoshiharu

    2012-04-01

    In order to improve the adhesive strength of hydroxyapatite (HAp) coatings, grit blasting with Al(2)O(3) powder and then wet blasting with HAp/Ti mixed powders was carried out on a commercially pure Ti (cp-Ti) substrate. Subsequently, an HAp/Ti bond coat layer and HAp top coat layer were deposited by plasma spraying. Fatigue tests of the HAp-coated specimens were carried out under four-point bending. Acoustic emission (AE) signals during the entire fatigue test were monitored to investigate the fatigue cracking behavior of the HAp-coated specimens. The HAp-coated specimens could survive up to 10(7) cycles without spallation of the HAp coating layers at the stress amplitude of 120 MPa. The HAp-coated specimens without HAp/Ti bond coat layer showed shorter fatigue life and easy crack nucleation compared to the HAp-coated specimens with HAp/Ti bond coat layer. The delamination and spallation of the HAp top coat with HAp/Ti bond coat on cp-Ti was not observed until the crack propagated into the cp-Ti during the final fracture stage of the fatigue cycle. Therefore, the HAp/Ti bond coat layer was found to greatly improve the fatigue damage resistance of the HAp coating layer. Three stages of the fatigue failure behavior of the HAp top coat with HAp/Ti bond coat on a cp-Ti substrate can be clearly estimated by the AE monitoring technique. These stages are cracks nucleating and propagating in the coating layer, cracks propagating in the substrate, and cracks propagating unstably to final fracture.

  17. Double-layer anti-reflection coating containing a nanoporous anodic aluminum oxide layer for GaAs solar cells.

    PubMed

    Yang, Tianshu; Wang, Xiaodong; Liu, Wen; Shi, Yanpeng; Yang, Fuhua

    2013-07-29

    Multilayer anti-reflection (AR) coatings can be used to improve the efficiency of Gallium Arsenide (GaAs) solar cells. We propose an alternate method to obtain optical thin films with specified refractive indices, which is using a self-assembled nanoporous anodic aluminum oxide (AAO) template as an optical thin film whose effective refractive index can be tuned by pore-widening. Different kinds of double-layer AR coatings each containing an AAO layer were designed and investigated by finite difference time domain (FDTD) method. We demonstrate that a λ /4n - λ /4n AR coating consisting of a TiO(2) layer and an AAO layer whose effective refractive index is 1.32 realizes a 96.8% light absorption efficiency of the GaAs solar cell under AM1.5 solar spectrum (400 nm-860 nm). We also have concluded some design principles of the double-layer AR coating containing an AAO layer for GaAs solar cells.

  18. Extremely Efficient Liquid Exfoliation and Dispersion of Layered Materials by Unusual Acoustic Cavitation

    PubMed Central

    Han, Joong Tark; Jang, Jeong In; Kim, Haena; Hwang, Jun Yeon; Yoo, Hyung Keun; Woo, Jong Seok; Choi, Sua; Kim, Ho Young; Jeong, Hee Jin; Jeong, Seung Yol; Baeg, Kang-Jun; Cho, Kilwon; Lee, Geon-Woong

    2014-01-01

    Layered materials must be exfoliated and dispersed in solvents for diverse applications. Usually, highly energetic probe sonication may be considered to be an unfavourable method for the less defective exfoliation and dispersion of layered materials. Here we show that judicious use of ultrasonic cavitation can produce exfoliated transition metal dichalcogenide nanosheets extraordinarily dispersed in non-toxic solvent by minimising the sonolysis of solvent molecules. Our method can also lead to produce less defective, large graphene oxide nanosheets from graphite oxide in a short time (within 10 min), which show high electrical conductivity (>20,000 S m−1) of the printed film. This was achieved by adjusting the ultrasonic probe depth to the liquid surface to generate less energetic cavitation (delivered power ~6 W), while maintaining sufficient acoustic shearing (0.73 m s−1) and generating additional microbubbling by aeration at the liquid surface. PMID:24875584

  19. Contactless Monitoring of Conductivity Changes in Vanadium Pentoxide Xerogel Layers Using Surface Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Rimeika, Romualdas; Sereika, Raimundas; Čiplys, Daumantas; Bondarenka, Vladimiras; Sereika, Albertas; Shur, Michael

    The hydrated form of the vanadium pentoxide (V2O5 ·nH2O) deposited by the sol-gel method on the piezoelectric YZ-LiNbO3 substrate has been studied using surface acoustic waves (SAWs). Brush-deposited and spin-coated layers, differing in thickness by an order of magnitude (∼1 μm and ∼0.1 μm, respectively) were studied. The variations with time in the transmitted SAW amplitude and phase during the gel-to-xerogel transition of V2O5 ·nH2O were observed and attributed to the acoustoelectric interaction. The possibilities of using the SAWs for contactless monitoring of the layer sheet conductivity have been demonstrated.

  20. Bulk and surface acoustic waves in solid-fluid Fibonacci layered materials.

    PubMed

    Quotane, I; El Boudouti, E H; Djafari-Rouhani, B; El Hassouani, Y; Velasco, V R

    2015-08-01

    We study theoretically the propagation and localization of acoustic waves in quasi-periodic structures made of solid and fluid layers arranged according to a Fibonacci sequence. We consider two types of structures: either a given Fibonacci sequence or a periodic repetition of a given sequence called Fibonacci superlattice. Various properties of these systems such as: the scaling law and the self-similarity of the transmission spectra or the power law behavior of the measure of the energy spectrum have been highlighted for waves of sagittal polarization in normal and oblique incidence. In addition to the allowed modes which propagate along the system, we study surface modes induced by the surface of the Fibonacci superlattice. In comparison with solid-solid layered structures, the solid-fluid systems exhibit transmission zeros which can break the self-similarity behavior in the transmission spectra for a given sequence or induce additional gaps other than Bragg gaps in a periodic structure.

  1. Receptivity to Roughness, Acoustic, and Vortical Disturbances in Supersonic Boundary Layers Over Swept Wings

    NASA Technical Reports Server (NTRS)

    Balakumar, Ponnampalam; King, Rudolph A.

    2011-01-01

    The receptivity and interaction of stationary and traveling crossflow instability of three-dimensional supersonic boundary layers over a swept biconvex wing with a blunt leading edge are numerically investigated for a freestream Mach number of 3. The steady and unsteady flow fields are obtained by solving the full Navier-Stokes equations. The receptivity of the boundary layer to surface roughness, freestream acoustic waves, and freestream vorticity waves are numerically investigated. The initial amplitudes of the stationary vortices generated by 1 micron roughness elements is about 2000 times larger than the initial amplitudes of the traveling disturbances generated by vortical disturbances. The interaction of stationary and traveling disturbances was investigated by solving the equations with both surface roughness and vortical disturbances. When the initial amplitudes of the stationary disturbances are large compared to the traveling disturbances, the stationary vortex dominates the perturbation field. When the amplitudes are comparable, the traveling vortex prevails and the stationary vortex is suppressed.

  2. SH surface acoustic wave propagation in a cylindrically layered piezomagnetic/piezoelectric structure.

    PubMed

    Du, Jianke; Xian, Kai; Wang, Ji

    2009-01-01

    SH surface acoustic wave (SH-SAW) propagation in a cylindrically layered magneto-electro-elastic structure is investigated analytically, where a piezomagnetic (or piezoelectric) material layer is bonded to a piezoelectric (or piezomagnetic) substrate. By means of transformation, the governing equations of the coupled waves are reduced to Bessel equation and Laplace equation. The boundary conditions imply that the displacements, shear stresses, electric potential, and electric displacements are continuous across the interface between the layer and the substrate together with the traction free at the surface of the layer. The magneto-electrically open and shorted conditions at cylindrical surface are taken to solve the problem. The phase velocity is numerically calculated for different thickness of the layer and wavenumber for piezomagnetic ceramics CoFe(2)O(4) and piezoelectric ceramics BaTiO(3). The effects of magnetic permeability on propagation properties of SH-SAW are discussed in detail. The distributions of displacement, magnetic potential and magneto-electromechanical coupling factor are also figured and discussed.

  3. Application of double-layered skin phantoms for optical flow imaging during laser tattoo treatments

    NASA Astrophysics Data System (ADS)

    Lee, Byeong-il; Song, Woosub; Kim, Hyejin; Kang, Hyun Wook

    2016-05-01

    The feasible application of double-layered skin phantoms was evaluated to identify artificial blood flow with a Doppler optical coherence tomography (DOCT) system for laser tattoo treatments. Polydimethylsiloxane (PDMS) was used to fabricate the artificial phantoms with flow channels embedded. A double-integrating sphere system with an inverse adding-doubling method quantified both the absorption and the reduced scattering coefficients for epidermis and dermis phantoms. Both OCT and caliper measurements confirmed the double-layered phantom structure (epidermis = 136 ± 17 µm vs. dermis = 3.0 ± 0.1 mm). The DOCT method demonstrated that high flow rates were associated with high image contrast, visualizing the position and the shape of the flow channel. Application of the channel-embedded skin phantoms in conjunction with DOCT can be a reliable technique to assess dynamic variations in the blood flow during and after laser tattoo treatments.

  4. Numerical simulation of white double-layer coating with different submicron particles on the spectral reflectance

    NASA Astrophysics Data System (ADS)

    Chai, Jiale; Cheng, Qiang; Si, Mengting; Su, Yang; Zhou, Yifan; Song, Jinlin

    2017-03-01

    The spectral selective coating is becoming more and more popular against solar irradiation not only in keeping the coated objects stay cool but also retain the appearance of the objects by reducing the glare of reflected sunlight. In this work a numerical study is investigated to design the double-layer coating with different submicron particles to achieve better performance both in thermal and aesthetic aspects. By comparison, the performance of double-layer coating with TiO2 and ZnO particles is better than that with single particles. What's more, the particle diameter, volume fraction of particle as well as substrate condition is also investigated. The results show that an optimized double-layer coating with particles should be the one with an appropriate particle diameter, volume fraction and the black substrate.

  5. Characteristics of complex light modulation through an amplitude-phase double-layer spatial light modulator.

    PubMed

    Park, Sungjae; Roh, Jinyoung; Kim, Soobin; Park, Juseong; Kang, Hoon; Hahn, Joonku; Jeon, Youngjin; Park, Shinwoong; Kim, Hwi

    2017-02-20

    The complex modulation characteristics of a light field through an amplitude-phase double-layer spatial light modulator are analyzed based on the wave-optic numerical model, and the structural conditions for the optimal double-layer complex modulation structure are investigated. The relationships of interlayer distance, pixel size, and complex light modulation performance are analyzed. The main finding of this study is that the optimal interlayer distance for the double-layer structure can be found at the Talbot effect condition. For validating the practical usefulness of our findings, a high quality reconstruction of the complex computer-generated holograms and the robustness of the angular tolerance of the complex modulation at the Talbot interlayer distance are numerically demonstrated.

  6. Interfacial double layer mediated electrochemical growth of thin-walled platinum nanotubes

    NASA Astrophysics Data System (ADS)

    Zhang, Liqiu; Kim, Sang Min; Cho, Sanghyun; Jang, Hee-Jeong; Liu, Lichun; Park, Sungho

    2017-01-01

    This work demonstrates that thin-walled platinum nanotubes can be readily synthesized by controlling the interfacial double layer in alumina nanochannels. The gradient distribution of ions in nanochannels enables the creation of Pt nanotubes with walls as thin as 5 nm at the top end when using a solution containing polyvinylpyrrolidone (PVP) and chloroplatinic acid (H2PtCl6) under the influence of an electric potential in nanochannels. The highly efficient formation of thin-walled Pt nanotubes is a result of the concentration gradient of {{{{PtCl}}}6}2- and a thick double layer, which was caused by the low concentration of Pt precursors and the enhanced surface charge density induced by protonated PVP steric adsorption. This well-controlled synthesis reveals that the interfacial double layer is a useful tool to tailor the structure of nanomaterials in a nanoscale space, and holds promise in the construction of more complex functional nanostructures.

  7. Receptivity of Supersonic Boundary Layers Due To Acoustic Disturbances Over Blunt Cones

    NASA Technical Reports Server (NTRS)

    Balakumar, P.

    2007-01-01

    Receptivity and stability of supersonic boundary layers over a 5-degree straight cone with a blunt tip are numerically investigated at a free stream Mach number of 3.5 and at a high Reynolds number of 106/inch. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations using the 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. The linear stability results showed that bluntness has less stabilizing effects on the stability of boundary layers over cones than on flat plates and wedges. The unsteady simulations of the interaction of plane threedimensional acoustic waves with the cone showed that the modulation of wavelength and the generation of instability waves first occurred near the leading edge in the plane where the constant acoustic phase lines are perpendicular to the cone axis. Further downstream, this instability region spreads in the azimuthal direction from this plane.

  8. Intervalley scattering by acoustic phonons in two-dimensional MoS2 revealed by double-resonance Raman spectroscopy.

    PubMed

    Carvalho, Bruno R; Wang, Yuanxi; Mignuzzi, Sandro; Roy, Debdulal; Terrones, Mauricio; Fantini, Cristiano; Crespi, Vincent H; Malard, Leandro M; Pimenta, Marcos A

    2017-03-09

    Double-resonance Raman scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the double-resonance Raman process involves different valleys and phonons in the Brillouin zone, and it has not yet been fully understood. Here we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the double-resonance Raman scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy, and first-principle simulations confirm that such bands arise from distinct acoustic phonons, connecting different valley states. The double-resonance Raman process is affected by the indirect-to-direct bandgap transition, and a comparison of results in monolayer and bulk allows the assignment of each Raman feature near the M or K points of the Brillouin zone. Our work highlights the underlying physics of intervalley scattering of electrons by acoustic phonons, which is essential for valley depolarization in MoS2.

  9. Intervalley scattering by acoustic phonons in two-dimensional MoS2 revealed by double-resonance Raman spectroscopy

    PubMed Central

    Carvalho, Bruno R.; Wang, Yuanxi; Mignuzzi, Sandro; Roy, Debdulal; Terrones, Mauricio; Fantini, Cristiano; Crespi, Vincent H.; Malard, Leandro M.; Pimenta, Marcos A.

    2017-01-01

    Double-resonance Raman scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the double-resonance Raman process involves different valleys and phonons in the Brillouin zone, and it has not yet been fully understood. Here we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the double-resonance Raman scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy, and first-principle simulations confirm that such bands arise from distinct acoustic phonons, connecting different valley states. The double-resonance Raman process is affected by the indirect-to-direct bandgap transition, and a comparison of results in monolayer and bulk allows the assignment of each Raman feature near the M or K points of the Brillouin zone. Our work highlights the underlying physics of intervalley scattering of electrons by acoustic phonons, which is essential for valley depolarization in MoS2. PMID:28276472

  10. Intervalley scattering by acoustic phonons in two-dimensional MoS2 revealed by double-resonance Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Carvalho, Bruno R.; Wang, Yuanxi; Mignuzzi, Sandro; Roy, Debdulal; Terrones, Mauricio; Fantini, Cristiano; Crespi, Vincent H.; Malard, Leandro M.; Pimenta, Marcos A.

    2017-03-01

    Double-resonance Raman scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the double-resonance Raman process involves different valleys and phonons in the Brillouin zone, and it has not yet been fully understood. Here we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the double-resonance Raman scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy, and first-principle simulations confirm that such bands arise from distinct acoustic phonons, connecting different valley states. The double-resonance Raman process is affected by the indirect-to-direct bandgap transition, and a comparison of results in monolayer and bulk allows the assignment of each Raman feature near the M or K points of the Brillouin zone. Our work highlights the underlying physics of intervalley scattering of electrons by acoustic phonons, which is essential for valley depolarization in MoS2.

  11. Improved Performance of Silicon Carbide Detector Using Double Layer Anti Reflection (AR) Coating

    DTIC Science & Technology

    2013-08-01

    chemical vapor deposition (PECVD) technique at 250 °C. Using a double-layer AR coating with a bottom silicon nitride ( Si3N4 ) layer and a top silicon...simulation curve for different combination of Si3N4 and SiO2 films. ........4 Figure 4. Experimental quantum efficiency curves for different AR...layer AR coating (4) consisting of silicon nitride ( Si3N4 ) and SO2 layers. 2. Experimental The 4H-SiC wafer from which the photo detectors were

  12. Acoustics

    NASA Technical Reports Server (NTRS)

    Goodman, Jerry R.; Grosveld, Ferdinand

    2007-01-01

    The acoustics environment in space operations is important to maintain at manageable levels so that the crewperson can remain safe, functional, effective, and reasonably comfortable. High acoustic levels can produce temporary or permanent hearing loss, or cause other physiological symptoms such as auditory pain, headaches, discomfort, strain in the vocal cords, or fatigue. Noise is defined as undesirable sound. Excessive noise may result in psychological effects such as irritability, inability to concentrate, decrease in productivity, annoyance, errors in judgment, and distraction. A noisy environment can also result in the inability to sleep, or sleep well. Elevated noise levels can affect the ability to communicate, understand what is being said, hear what is going on in the environment, degrade crew performance and operations, and create habitability concerns. Superfluous noise emissions can also create the inability to hear alarms or other important auditory cues such as an equipment malfunctioning. Recent space flight experience, evaluations of the requirements in crew habitable areas, and lessons learned (Goodman 2003; Allen and Goodman 2003; Pilkinton 2003; Grosveld et al. 2003) show the importance of maintaining an acceptable acoustics environment. This is best accomplished by having a high-quality set of limits/requirements early in the program, the "designing in" of acoustics in the development of hardware and systems, and by monitoring, testing and verifying the levels to ensure that they are acceptable.

  13. Ion phase-space vortices and their relation to small amplitude double layers

    NASA Technical Reports Server (NTRS)

    Pecseli, Hans L.

    1987-01-01

    The properties of ion phase-space vortices are reviewed with particular attention to their role in the formation of small amplitude double layers in current-carrying plasmas. In a one-dimensional analysis, many such double layers simply add up to produce a large voltage drop. A laboratory experiment is carried out in order to investigate the properties of ion phase-space vortices in three dimensions. Their lifetime is significantly reduced as compared with similar results from one-dimensional numerical simulations of the problem.

  14. Arbitrary amplitude double layers in warm dust kinetic Alfven wave plasmas

    SciTech Connect

    Gogoi, Runmoni; Devi, Nirupama

    2008-07-15

    Large amplitude electrostatic structures associated with low-frequency dust kinetic Alfvenic waves are investigated under the pressure (temperature) gradient indicative of dust dynamics. The set of equations governing the dust dynamics, Boltzmann electrons, ions and Maxwell's equation have been reduced to a single equation known as the Sagdeev potential equation. Parameter ranges for the existence of arbitrary amplitude double layers are observed. Exact analytical expressions for the energy integral is obtained and computed numerically through which sub-Alfvenic arbitrary amplitude rarefactive double layers are found to exist.

  15. Double-layer ion acceleration triggered by ion magnetization in expanding radiofrequency plasma sources

    SciTech Connect

    Takahashi, Kazunori; Charles, Christine; Boswell, Rod W.; Fujiwara, Tamiya

    2010-10-04

    Ion energy distribution functions downstream of the source exit in magnetically expanding low-pressure plasmas are experimentally investigated for four source tube diameters ranging from about 5 to 15 cm. The magnetic-field threshold corresponding to a transition from a simple expanding plasma to a double layer-containing plasma is observed to increase with a decrease in the source tube diameter. The results demonstrate that for the four geometries, the double layer and the accelerated ion beam form when the ion Larmour radius in the source becomes smaller than the source tube radius, i.e., when the ions become magnetized in the source tube.

  16. Auroral-particle precipitation and trapping caused by electrostatic double layers in the ionosphere.

    PubMed

    Albert, R D; Lindstrom, P J

    1970-12-25

    Interpretation of high-resolution angular distribution measurements of the primary auroral electron flux detected by a rocket probe launched into a visible aurora from Fort Churchill in the fall of 1966 leads to the following conclusions. The auroral electron flux is nearly monoenergetic and has a quasi-trapped as well as a precipitating component. The quasi-trapped flux appears to be limited to a region defined by magnetic-mirror points and multiple electrostatic double layers in the ionosphere. The electrostatic field of the double-layer distribution enhances the aurora by lowering the magnetic-mirror points and supplying energy to the primary auroral electrons.

  17. Atomic Layer Deposition Alumina-Passivated Silicon Nanowires: Probing the Transition from Electrochemical Double-Layer Capacitor to Electrolytic Capacitor.

    PubMed

    Gaboriau, Dorian; Boniface, Maxime; Valero, Anthony; Aldakov, Dmitry; Brousse, Thierry; Gentile, Pascal; Sadki, Said

    2017-04-10

    Silicon nanowires were coated by a 1-5 nm thin alumina layer by atomic layer deposition (ALD) in order to replace poorly reproducible and unstable native silicon oxide by a highly conformal passivating alumina layer. The surface coating enabled probing the behavior of symmetric devices using such electrodes in the EMI-TFSI electrolyte, allowing us to attain a large cell voltage up to 6 V in ionic liquid, together with very high cyclability with less than 4% capacitance fade after 10(6) charge/discharge cycles. These results yielded fruitful insights into the transition between an electrochemical double-layer capacitor behavior and an electrolytic capacitor behavior. Ultimately, thin ALD dielectric coatings can be used to obtain hybrid devices exhibiting large cell voltage and excellent cycle life of dielectric capacitors, while retaining energy and power densities close to the ones displayed by supercapacitors.

  18. Expanded graphite—Phenolic resin composites based double layer microwave absorber for X-band applications

    NASA Astrophysics Data System (ADS)

    Gogoi, Jyoti Prasad; Bhattacharyya, Nidhi Saxena

    2014-11-01

    In this investigation, double layer microwave absorbers are designed and developed with paired combination of 5 wt. %, 7 wt. %, 8 wt. %, and 10 wt. % expanded graphite-novolac phenolic resin (EG-NPR) composites, in the frequency range of 8.2-12.4 GHz. The thickness and compositional combination of the two layers constituting the absorber are optimized to achieve minimum value of reflection loss (dB) and a broad microwave absorption bandwidth. Double layer combinations showing -25 dB absorption bandwidth >2 GHz and -30 dB absorption bandwidth >1 GHz are chosen for fabrication. The total thickness of the fabricated double layer microwave absorber is varied from 3 mm to 3.4 mm. Absorption bandwidths at -10 dB, -20 dB, -25 dB and -30 dB are determined for the fabricated structure. The maximum -25 dB and -30 dB absorption bandwidth of 2.47 GHz and 1.77 GHz, respectively, are observed for the double layer structure with (5 wt. %-8 wt. %) EG-NPR composites with total thickness of 3.2 mm, while -10 dB bandwidth covers the entire X-band range.

  19. Oceanic Double-Diffusive Layer Thicknesses in the Presence of Turbulence

    NASA Astrophysics Data System (ADS)

    Shibley, Nicole; Timmermans, Mary-Louise

    2016-11-01

    Double-diffusive stratification in the ocean is characterized by staircase structures consisting of mixed layers separated by high-gradient interfaces in temperature and salinity. Several past studies have examined mechanisms that govern the observed thicknesses of staircase mixed layers. In one formalism, the mixed-layer thickness is set by layer formation that arises when a heat source is applied at the base of water that is stably-stratified in salinity; in another, the equilibrium thickness of mixed layers has been explained as the product of "merging," where thin layers continue to grow until they reach a thickness determined by a criterion relating the ratio of heat flux to salt flux and the density ratio. We extend the above two theories to consider the influence of turbulence on mixed-layer thicknesses. The study has implications for the Arctic Ocean where double-diffusive staircases are widely present, and mixed-layer thicknesses are well-resolved by ocean measurements. Our theoretical framework provides a means to determine turbulent diffusivities (in regions where microstructure measurements are not available) by considering only observations of density ratio, stratification, and layer thicknesses.

  20. Acoustic resonator with Al electrodes on an AlN layer and using a GaAs substrate

    DOEpatents

    Kline, Gerald R.; Lakin, Kenneth M.

    1985-12-03

    A method of fabricating an acoustic wave resonator wherein all processing steps are accomplished from a single side of said substrate. The method involves deposition of a multi-layered Al/AlN structure on a GaAs substrate followed by a series of fabrication steps to define a resonator from said composite. The resulting resonator comprises an AlN layer between two Al layers and another layer of AlN on an exterior of one of said Al layers.

  1. Application of magnetic printing method to hard-disk media with double recording layers

    NASA Astrophysics Data System (ADS)

    Ono, Takuya; Kuboki, Yoshiyuki; Ajishi, Yoshifumi; Saito, Akira

    2003-05-01

    The magnetic printing method, which can duplicate soft magnetic patterns containing digital information such as servosignals formed on a master disk onto recording media, enables signals to be written to hard-disk media having high coercivities above 6000 Oe. We propose the application of the magnetic printing method to a hard-disk medium having double recording layers, one layer of which has high coercivity and is to be printed with digital information. This double recording layer medium is a hard-disk medium that has a magnetic read-only-memory (MROM) layer. In this study, we demonstrated a method for printing to this medium, which has MROM, and discussed the magnetic properties and recording performances of this medium.

  2. Cascading failures coupled model of interdependent double layered public transit network

    NASA Astrophysics Data System (ADS)

    Zhang, Lin; Fu, Bai-Bai; Li, Shu-Bin

    2016-06-01

    Taking urban public transit network as research perspective, this work introduces the influences of adjacent stations on definition of station initial load, the connected edge transit capacity, and the coupled capacity to modify traditional load-capacity cascading failures (CFs) model. Furthermore, we consider the coupled effect of lower layered public transit network on the CFs of upper layered public transit network, and construct CFs coupled model of double layered public transit network with “interdependent relationship”. Finally, taking Jinan city’s public transit network as example, we give the dynamics simulation analysis of CFs under different control parameters based on measurement indicator of station cascading failures ratio (abbreviated as CF) and the scale of time-step cascading failures (abbreviated as TCFl), get the influencing characteristics of various control parameters, and verify the feasibility of CFs coupled model of double layered public transit network.

  3. Influence of intermediate aminodextran layers on the signal response of surface acoustic wave biosensors.

    PubMed

    Länge, Kerstin; Rapp, Michael

    2008-06-15

    Surface acoustic wave (SAW) devices based on horizontally polarized surface shear waves enable direct and label-free detection of proteins in real time. Binding reactions on the sensor surface are detected by determining changes in surface wave velocity caused mainly by mass adsorption or change of viscoelasticity in the sensing layer. Intermediate hydrogel layers have been proven to be useful to immobilize capture molecules or ligands corresponding to the analyte. However, the SAW signal response strongly depends on the morphology of the hydrogel due to different relative changes of its acoustomechanical parameters such as viscoelasticity and density. In this work five aminodextrans (AMD) and one diamino polyethylene glycol (DA-PEG) were used as intermediate hydrogel layers. Sensors with immobilized streptavidin and samples containing biotinylated bovine serum albumin were used to exemplify affinity assays based on immobilized capture molecules for protein detection. The effects of the three-dimensional AMDs and the two-dimensional (2D) DA-PEG on the SAW signal response were investigated. The signal height decreased with increasing molar mass and increasing amount of immobilized AMD. Consequently, thin hydrogel layers are ideal to obtain optimum signal responses in this type of assay, whereas it is not necessarily a 2D hydrogel that gives the best results.

  4. Double layers and plasma-wave resistivity in extragalactic jets - Cavity formation and radio-wave emission

    NASA Technical Reports Server (NTRS)

    Borovsky, Joseph E.

    1987-01-01

    Current driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur in extragalactic jets for estimated values of the carried currents. Strong plasma double layers, however, may exist within self-maintained density cavities. The relativistic double-layer-emitted electron and ion beams drive plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layer-emitted electron beams may also emit polarized radio waves via a collective bremsstrahlung process mediated by electrostatic two-stream instabilities.

  5. Double layers and plasma-wave resistivity in extragalactic jets: Cavity formation and radio-wave emission

    NASA Technical Reports Server (NTRS)

    Borovsky, Joseph E.

    1987-01-01

    For estimated values of the currents carried by extragalactic jets, current-driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur. Strong plasma double layers, however, may exist within self-maintained density cavities, the relativistic double-layer-emitted electron, and ion beams driving plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layer-emitted electron beams may also emit polarized radio waves via a collective bremsstrahlung process mediated by electrostatic two-stream instabilities.

  6. Acoustic emission in a fluid saturated heterogeneous porous layer with application to hydraulic fracture

    SciTech Connect

    Nelson, J.T. . Dept. of Mechanical Engineering Lawrence Berkeley Lab., CA )

    1988-11-01

    A theoretical model for acoustic emission in a vertically heterogeneous porous layer bounded by semi-infinite solid regions is developed using linearized equations of motion for a fluid/solid mixture and a reflectivity method. Green's functions are derived for both point loads and moments. Numerically integrated propagators represent solutions for intermediate heterogeneous layers in the porous region. These are substituted into a global matrix for solution by Gaussian elimination and back-substitution. Fluid partial stress and seismic responses to dislocations associated with fracturing of a layer of rock with a hydraulically conductive fracture network are computed with the model. A constitutive model is developed for representing the fractured rock layer as a porous material, using commonly accepted relationships for moduli. Derivations of density, tortuosity, and sinuosity are provided. The main results of the model application are the prediction of a substantial fluid partial stress response related to a second mode wave for the porous material. The response is observable for relatively large distances, on the order of several tens of meters. The visco-dynamic transition frequency associated with parabolic versus planar fluid velocity distributions across micro-crack apertures is in the low audio or seismic range, in contrast to materials with small pore size, such as porous rocks, for which the transition frequency is ultrasonic. Seismic responses are predicted for receiver locations both in the layer and in the outlying solid regions. In the porous region, the seismic response includes both shear and dilatational wave arrivals and a second-mode arrival. The second-mode arrival is not observable outside of the layer because of its low velocity relative to the dilatational and shear wave propagation velocities of the solid region.

  7. Multiphoton fluorescence microscopic imaging through double-layer turbid tissue media

    NASA Astrophysics Data System (ADS)

    Deng, Xiaoyuan; Gan, Xiaosong; Gu, Min

    2002-04-01

    Image formation in multiphoton fluorescence microscopy through double-layer turbid tissue media is investigated using Monte Carlo simulation. With the help of the concept of the effective point spread function, the relationship of image resolution and signal level to the thickness and scattering properties of the double-layer turbid media under single-, two-, and three-photon excitation is revealed. Results show that for a double-layer turbid medium of a given thickness, small particles in the top layer result in a quicker degradation of signal level than large particles in the top layer. This model is then applied to study the penetration depth of multiphoton fluorescence microscopy through human skin tissue which exhibits a layered structure. It is predicated that using 3p excitation leads to a signal level up to two orders of magnitude higher than that under 2p excitation, while diffraction-limited image resolution can be maintained for skin tissue of thickness up to 500 μm.

  8. Hierarchical Supervisor and Agent Routing Algorithm in LEO/MEO Double-layered Optical Satellite Network

    NASA Astrophysics Data System (ADS)

    Li, Yongjun; Zhao, Shanghong

    2016-09-01

    A novel routing algorithm (Hierarchical Supervisor and Agent Routing Algorithm, HSARA) for LEO/MEO (low earth orbit/medium earth orbit) double-layered optical satellite network is brought forward. The so-called supervisor (MEO satellite) is designed for failure recovery and network management. LEO satellites are grouped according to the virtual managed field of MEO which is different from coverage area of MEO satellite in RF satellite network. In each LEO group, one LEO satellite which has maximal persistent link with its supervisor is called the agent. A LEO group is updated when this optical inter-orbit links between agent LEO satellite and the corresponding MEO satellite supervisor cuts off. In this way, computations of topology changes and LEO group updating can be decreased. Expense of routing is integration of delay and wavelength utilization. HSARA algorithm simulations are implemented and the results are as follows: average network delay of HSARA can reduce 21 ms and 31.2 ms compared with traditional multilayered satellite routing and single-layer LEO satellite respectively; LEO/MEO double-layered optical satellite network can cover polar region which cannot be covered by single-layered LEO satellite and throughput is 1% more than that of single-layered LEO satellite averagely. Therefore, exact global coverage can be achieved with this double-layered optical satellite network.

  9. Perpendicular magnetic tunnel junctions with double barrier and single or synthetic antiferromagnetic storage layer

    SciTech Connect

    Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Prejbeanu, Ioan L.; Dieny, Bernard

    2015-06-21

    The magnetic properties of double tunnel junctions with perpendicular anisotropy were investigated. Two synthetic antiferromagnetic references are used, while the middle storage magnetic layer can be either a single ferromagnetic or a synthetic antiferromagnetic FeCoB-based layer, with a critical thickness as large as 3.0 nm. Among the different achievable magnetic configurations in zero field, those with either antiparallel references, and single ferromagnetic storage layer, or parallel references, and synthetic antiferromagnetic storage layer, are of particular interest since they allow increasing the efficiency of spin transfer torque writing and the thermal stability of the stored information as compared to single tunnel junctions. The latter configuration can be preferred when stray fields would favour a parallel orientation of the reference layers. In this case, the synthetic antiferromagnetic storage layer is also less sensitive to residual stray fields.

  10. Generation and Radiation of Acoustic Waves from a 2-D Shear Layer

    NASA Technical Reports Server (NTRS)

    Agarwal, Anurag; Morris, Philip J.

    2000-01-01

    A parallel numerical simulation of the radiation of sound from an acoustic source inside a 2-D jet is presented in this paper. This basic benchmark problem is used as a test case for scattering problems that are presently being solved by using the Impedance Mismatch Method (IMM). In this technique, a solid body in the domain is represented by setting the acoustic impedance of each medium, encountered by a wave, to a different value. This impedance discrepancy results in reflected and scattered waves with appropriate amplitudes. The great advantage of the use of this method is that no modifications to a simple Cartesian grid need to be made for complicated geometry bodies. Thus, high order finite difference schemes may be applied simply to all parts of the domain. In the IMM, the total perturbation field is split into incident and scattered fields. The incident pressure is assumed to be known and the equivalent sources for the scattered field are associated with the presence of the scattering body (through the impedance mismatch) and the propagation of the incident field through a non-uniform flow. An earlier version of the technique could only handle uniform flow in the vicinity of the source and at the outflow boundary. Scattering problems in non-uniform mean flow are of great practical importance (for example, scattering from a high lift device in a non-uniform mean flow or the effects of a fuselage boundary layer). The solution to this benchmark problem, which has an acoustic wave propagating through a non-uniform mean flow, serves as a test case for the extensions of the IMM technique.

  11. Laser cutting silicon-glass double layer wafer with laser induced thermal-crack propagation

    NASA Astrophysics Data System (ADS)

    Cai, Yecheng; Yang, Lijun; Zhang, Hongzhi; Wang, Yang

    2016-07-01

    This study was aimed at introducing the laser induced thermal-crack propagation (LITP) technology to solve the silicon-glass double layer wafer dicing problems in the packaging procedure of silicon-glass device packaged by WLCSP technology, investigating the feasibility of this idea, and studying the crack propagation process of LITP cutting double layer wafer. In this paper, the physical process of the 1064 nm laser beam interact with the double layer wafer during the cutting process was studied theoretically. A mathematical model consists the volumetric heating source and the surface heating source has been established. The temperature and stress distribution was simulated by using finite element method (FEM) analysis software ABAQUS. The extended finite element method (XFEM) was added to the simulation as the supplementary features to simulate the crack propagation process and the crack propagation profile. The silicon-glass double layer wafer cutting verification experiment under typical parameters was conducted by using the 1064 nm semiconductor laser. The crack propagation profile on the fracture surface was examined by optical microscope and explained from the stress distribution and XFEM status. It was concluded that the quality of the finished fracture surface has been greatly improved, and the experiment results were well supported by the numerical simulation results.

  12. Multiple and configurable optical logic systems based on layered double hydroxides and chromophore assemblies.

    PubMed

    Shi, Wenying; Fu, Yi; Li, Zhixiong; Wei, Min

    2015-01-14

    Multiple and configurable fluorescence logic gates were fabricated via self-assembly of layered double hydroxides and various chromophores. These logic gates were operated by observation of different emissions with the same excitation wavelength, which achieve YES, NOT, AND, INH and INHIBIT logic operations, respectively.

  13. Hierarchical CoNi-Sulfide Nanosheet Arrays Derived from Layered Double Hydroxides toward Efficient Hydrazine Electrooxidation.

    PubMed

    Zhou, Lei; Shao, Mingfei; Zhang, Cong; Zhao, Jingwen; He, Shan; Rao, Deming; Wei, Min; Evans, David G; Duan, Xue

    2017-02-01

    A hierarchical CoNi-sulfide nanosheet array is fabricated via an in situ reduction of CoNi-layered double hydroxide (LDH) nanosheets, then a vulcanization process. The material inherits the morphology of the LDH precursor, consisting of well-distributed CoNi-alloy@CoNi-sulfide nanoparticles with a core-shell structure, and demonstrates promising performance toward hydrazine electrooxidation.

  14. Nb2O5 as a new electron transport layer for double junction polymer solar cells.

    PubMed

    Siddiki, Mahbube K; Venkatesan, Swaminathan; Qiao, Qiquan

    2012-04-14

    Nb(2)O(5) as a new electron transport layer (ETL) was used for double junction polymer solar cells. The Nb(2)O(5) ETL was prepared by spin coating a Nb(2)O(5) sol-gel solution onto the active layer of the optical front subcell. The double junction devices using Nb(2)O(5) ETL exhibit an open circuit voltage (V(oc)) of 1.30 V, which is close to the sum of the s of the individual subcells. The current density-voltage (J-V) simulation showed that the double junction device performance using Nb(2)O(5) as ETL could be significantly increased by reducing the series resistance (R(se)) and matching the current densities of the individual subcells.

  15. Photoacoustic tomography based on the Green's function retrieval with ultrasound interferometry for sample partially behind an acoustically scattering layer

    SciTech Connect

    Yin, Jie; Tao, Chao Cai, Peng; Liu, Xiaojun

    2015-06-08

    Acoustically inhomogeneous mediums with multiple scattering are often the nightmare of photoacoustic tomography. In order to break this limitation, a photoacoustic tomography scheme combining ultrasound interferometry and time reversal is proposed to achieve images in acoustically scattering medium. An ultrasound interferometry is developed to determine the unknown Green's function of strong scattering tissue. Using the determined Greens' function, a time-reversal process is carried out to restore images behind an acoustically inhomogeneous layer from the scattering photoacoustic signals. This method effectively decreases the false contrast, noise, and position deviation of images induced by the multiple scattering. Phantom experiment is carried out to validate the method. Therefore, the proposed method could have potential value in extending the biomedical applications of photoacoustic tomography in acoustically inhomogeneous tissue.

  16. Photoacoustic tomography based on the Green's function retrieval with ultrasound interferometry for sample partially behind an acoustically scattering layer

    NASA Astrophysics Data System (ADS)

    Yin, Jie; Tao, Chao; Cai, Peng; Liu, Xiaojun

    2015-06-01

    Acoustically inhomogeneous mediums with multiple scattering are often the nightmare of photoacoustic tomography. In order to break this limitation, a photoacoustic tomography scheme combining ultrasound interferometry and time reversal is proposed to achieve images in acoustically scattering medium. An ultrasound interferometry is developed to determine the unknown Green's function of strong scattering tissue. Using the determined Greens' function, a time-reversal process is carried out to restore images behind an acoustically inhomogeneous layer from the scattering photoacoustic signals. This method effectively decreases the false contrast, noise, and position deviation of images induced by the multiple scattering. Phantom experiment is carried out to validate the method. Therefore, the proposed method could have potential value in extending the biomedical applications of photoacoustic tomography in acoustically inhomogeneous tissue.

  17. Proposed double-layer target for the generation of high-quality laser-accelerated ion beams.

    PubMed

    Esirkepov, T Zh; Bulanov, S V; Nishihara, K; Tajima, T; Pegoraro, F; Khoroshkov, V S; Mima, K; Daido, H; Kato, Y; Kitagawa, Y; Nagai, K; Sakabe, S

    2002-10-21

    In order to achieve a high-quality, i.e., monoenergetic, intense ion beam, we propose the use of a double-layer target. The first layer, at the target front, consists of high-Z atoms, while the second (rear) layer is a thin coating of low-Z atoms. The generation of high-quality proton beams from the double-layer target, irradiated by an ultraintense laser pulse, is demonstrated with three-dimensional particle-in-cell simulations.

  18. Thin-layer chromatography/laser-induced acoustic desorption/electrospray ionization mass spectrometry.

    PubMed

    Cheng, Sy-Chyi; Huang, Min-Zong; Shiea, Jentaie

    2009-11-15

    The combination of laser-induced acoustic desorption and electrospray ionization mass spectrometry (LIAD/ESI/MS) can be used to rapidly characterize chemical compounds separated on a thin layer chromatography (TLC) plate. We performed LIAD analysis by irradiating the rear side of an aluminum-based TLC plate with a pulsed infrared (IR) laser. To efficiently generate and transfer acoustic and shock waves to ablate the analyte-containing TLC gels, a glass slide was attached to the rear of the TLC plate and the gap between the glass slide and the TLC plate was filled with a viscous solution (glycerol). Although the diameter of the laser spot created on the rear of the TLC plate was approximately 0.35 mm, the ablated areas on the front sides of the silica gel bed and the C(18) reverse-phase gel bed had diameters of approximately 1.3 and 3 mm, respectively. The ablated analyte molecules were ionized in an ESI plume and then detected by an ion trap mass analyzer. This TLC/LIAD/ESI/MS approach allowed the components in mixtures of dye standards, drug standards, and rosemary essential oil to be separated and rapidly characterized.

  19. Surface acoustic wave characterization of optical sol-gel thin layers.

    PubMed

    Fall, Dame; Compoint, François; Duquennoy, Marc; Piombini, Hervé; Ouaftouh, Mohammadi; Jenot, Frédéric; Piwakowski, Bogdan; Belleville, Philippe; Ambard, Chrystel

    2016-05-01

    Controlling the thin film deposition and mechanical properties of materials is a major challenge in several fields of application. We are more particularly interested in the characterization of optical thin layers produced using sol-gel processes to reduce laser-induced damage. The mechanical properties of these coatings must be known to control and maintain optimal performance under various solicitations during their lifetime. It is therefore necessary to have means of characterization adapted to the scale and nature of the deposited materials. In this context, the dispersion of ultrasonic surface waves induced by a micrometric layer was studied on an amorphous substrate (fused silica) coated with a layer of ormosil using a sol-gel process. Our ormosil material is a silica-PDMS mixture with a variable polydimethylsiloxane (PDMS) content. The design and implementation of Surface Acoustic Wave InterDigital Transducers (SAW-IDT) have enabled quasi-monochromatic Rayleigh-type SAW to be generated and the dispersion phenomenon to be studied over a wide frequency range. Young's modulus and Poisson's ratio of coatings were estimated using an inverse method.

  20. Sensitivity comparisons of layered Rayleigh wave and Love wave acoustic devices

    NASA Astrophysics Data System (ADS)

    Pedrick, Michael K.; Tittmann, Bernhard R.

    2007-04-01

    Due to their high sensitivity, layered Surface Acoustic Wave (SAW) devices are ideal for various film characterization and sensor applications. Two prominent wave types realized in these devices are Rayleigh waves consisting of coupled Shear Vertical and Longitudinal displacements and Love waves consisting of Shear Horizontal displacements. Theoretical calculations of sensitivity of SAW devices to pertubations in wave propagation are limited to idealized scenarios. Derivations of sensitivity to mass change in an overlayer are often based on the effect of rigid body motion of the overlayer on the propagation of one of the aforementioned wave types. These devices often utilize polymer overlayers for enhanced sensitivity. The low moduli of such overlayers are not sufficiently stiff to accommodate the rigid body motion assumption. This work presents device modeling based on the Finite Element Method. A coupled-field model allows for a complete description of device operation including displacement profiles, frequency, wave velocity, and insertion loss through the inclusion of transmitting and receiving IDTs. Geometric rotations and coordinate transformations allow for the modeling of different crystal orientations in piezoelectric substrates. The generation of Rayleigh and Love Wave propagation was realized with this model by examining propagation in ST Quartz both normal to and in the direction of the X axis known to support Love Waves and Rayleigh Waves, respectively. Sensitivities of layered SAW devices to pertubations in mass, layer thickness, and mechanical property changes of a Polymethyl methacrylate (PMMA) and SU-8 overlayers were characterized and compared. Experimental validation of these models is presented.

  1. Diffusion barrier performance of novel Ti/TaN double layers for Cu metallization

    NASA Astrophysics Data System (ADS)

    Zhou, Y. M.; He, M. Z.; Xie, Z.

    2014-10-01

    Novel Ti/TaN double layers offering good stability as a barrier against Cu metallization have been made achievable by annealing in vacuum better than 1 × 10-3 Pa. Ti/TaN double layers were formed on SiO2/Si substrates by DC magnetron sputtering and then the properties of Cu/Ti/TaN/SiO2/Si film stacks were studied. It was found that the Ti/TaN double layers provide good diffusion barrier between Cu and SiO2/Si up to 750 °C for 30 min. The XRD, Auger and EDS results show that the Cu-Si compounds like Cu3Si were formed by Cu diffusion through Ti/TaN barrier for the 800 °C annealed samples. It seems that the improved diffusion barrier property of Cu/Ti/TaN/SiO2/Si stack is due to the diffusion of nitrogen along the grain boundaries in Ti layer, which would decrease the defects in Ti film and block the diffusion path for Cu diffusion with increasing annealing temperature. The failure mechanism of Ti/TaN bi-layer is similar to the Cu/TaN/Si metallization system in which Cu atoms diffuse through the grain boundary of barrier and react with silicon to form Cu3Si.

  2. Influence of material parameters on acoustic wave propagation modes in ZnO/Si bi-layered structures.

    PubMed

    Gao, Hui-dong; Zhang, Shu-Yi; Qi, Xue; Wasa, Kiyotaka; Wu, Hao-Dong

    2005-12-01

    The influences of material properties on acoustic wave propagation modes in ZnO/Si bi-layered structures are studied. The transfer matrix method is used to calculate dispersion relations, wave field distributions, and electromechanical coupling coefficients of acoustic wave propagation modes in ZnO/Si bi-layered systems, in which the thickness of the substrate is of the same order of magnitude as the wavelength of the propagating wave modes. The influences of the thin film parameters on the acoustic wave propagation modes and their electromechanical coupling coefficients of the wave modes also are obtained. In addition, some experimental results for characterizing the wave propagation modes and their frequencies have also been obtained, which agree well with the theoretical predictions.

  3. Generation and Radiation of Acoustic Waves from a 2-D Shear Layer using the CE/SE Method

    NASA Technical Reports Server (NTRS)

    Loh, Ching Y.; Wang, Xiao Y.; Chang, Sin-Chung; Jorgenson, Philip C. E.

    2000-01-01

    In the present work, the generation and radiation of acoustic waves from a 2-D shear layer problem is considered. An acoustic source inside of a 2-D jet excites an instability wave in the shear layer, resulting in sound Mach radiation. The numerical solution is obtained by solving the Euler equations using the space time conservation element and solution element (CE/SE) method. Linearization is achieved through choosing a small acoustic source amplitude. The Euler equations are nondimensionalized as instructed in the problem statement. All other conditions are the same except that the Crocco's relation has a slightly different form. In the following, after a brief sketch of the CE/SE method, the numerical results for this problem are presented.

  4. Theoretical Study of Monolayer and Double-Layer Waveguide Love Wave Sensors for Achieving High Sensitivity.

    PubMed

    Li, Shuangming; Wan, Ying; Fan, Chunhai; Su, Yan

    2017-03-22

    Love wave sensors have been widely used for sensing applications. In this work, we introduce the theoretical analysis of the monolayer and double-layer waveguide Love wave sensors. The velocity, particle displacement and energy distribution of Love waves were analyzed. Using the variations of the energy repartition, the sensitivity coefficients of Love wave sensors were calculated. To achieve a higher sensitivity coefficient, a thin gold layer was added as the second waveguide on top of the silicon dioxide (SiO₂) waveguide-based, 36 degree-rotated, Y-cut, X-propagating lithium tantalate (36° YX LiTaO₃) Love wave sensor. The Love wave velocity was significantly reduced by the added gold layer, and the flow of wave energy into the waveguide layer from the substrate was enhanced. By using the double-layer structure, almost a 72-fold enhancement in the sensitivity coefficient was achieved compared to the monolayer structure. Additionally, the thickness of the SiO₂ layer was also reduced with the application of the gold layer, resulting in easier device fabrication. This study allows for the possibility of designing and realizing robust Love wave sensors with high sensitivity and a low limit of detection.

  5. Theoretical Study of Monolayer and Double-Layer Waveguide Love Wave Sensors for Achieving High Sensitivity

    PubMed Central

    Li, Shuangming; Wan, Ying; Fan, Chunhai; Su, Yan

    2017-01-01

    Love wave sensors have been widely used for sensing applications. In this work, we introduce the theoretical analysis of the monolayer and double-layer waveguide Love wave sensors. The velocity, particle displacement and energy distribution of Love waves were analyzed. Using the variations of the energy repartition, the sensitivity coefficients of Love wave sensors were calculated. To achieve a higher sensitivity coefficient, a thin gold layer was added as the second waveguide on top of the silicon dioxide (SiO2) waveguide–based, 36 degree–rotated, Y-cut, X-propagating lithium tantalate (36° YX LiTaO3) Love wave sensor. The Love wave velocity was significantly reduced by the added gold layer, and the flow of wave energy into the waveguide layer from the substrate was enhanced. By using the double-layer structure, almost a 72-fold enhancement in the sensitivity coefficient was achieved compared to the monolayer structure. Additionally, the thickness of the SiO2 layer was also reduced with the application of the gold layer, resulting in easier device fabrication. This study allows for the possibility of designing and realizing robust Love wave sensors with high sensitivity and a low limit of detection. PMID:28327504

  6. Using martian single and double layered ejecta craters to probe subsurface stratigraphy

    NASA Astrophysics Data System (ADS)

    Jones, Eriita; Osinski, Gordon R.

    2015-02-01

    Martian craters with fluidized ejecta - including single-layered, double-layered and multiple-layered craters - have been studied extensively, with their formation generally suggested to require some presence of volatiles in the subsurface. However, experimental reproduction of these morphologies, impact modelling, and the occurrence of layered ejecta in putative volatile poor regions suggests that other factors may also play important roles. A recent extensive catalogue of martian impact craters (Robbins, S.J., Hynek, B.M. [2012a]. J. Geophys. Res. 117, E05004) classifies crater ejecta along with their location, diameters and ejecta extents, potentially providing new information on the links between these morphologies and the subsurface. We utilise this catalogue to examine the regional variation in ejecta mobility, onset diameter and the correlation between ejecta mobility and diameter for single- and double-layered ejecta craters on Mars. A simple regional stratigraphic model is developed to explain the observed trends through the viscosity of the layers within the target. Using this model, the potential relative thickness and burial depths of low viscosity layers in the martian subsurface are hypothesised, and compared to other observations and models of subsurface volatiles and how they have varied throughout time.

  7. Bio-Inspired Aquaporinz Containing Double-Skinned Forward Osmosis Membrane Synthesized through Layer-by-Layer Assembly

    PubMed Central

    Wang, Shuzheng; Cai, Jin; Ding, Wande; Xu, Zhinan; Wang, Zhining

    2015-01-01

    We demonstrated a novel AquaporinZ (AqpZ)-incorporated double-skinned forward osmosis (FO) membrane by layer-by-layer (LbL) assembly strategy. Positively charged poly(ethyleneimine) (PEI) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) were alternately deposited on both the top and bottom surfaces of a hydrolyzed polyacrylonitrile (H-PAN) substrate. Subsequently, an AqpZ-embedded 1,2-dioleloyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dioleoyl-3-trimethylammonium- propane (chloride salt) (DOTAP) supported lipid bilayer (SLB) was formed on PSS-terminated (T-PSS) membrane via vesicle rupture method. The morphology and structure of the biomimetic membranes were characterized by in situ atomic force microscopy (AFM), scanning electron microscope (SEM), Fourier transform infrared spectrometer using the attenuated total reflection technique (ATR-FTIR), and contact angle. Moreover, the FO performance of the resultant membrane was measured by using 2 M MgCl2 solution as draw solution and deionized (DI) water as feed solution, respectively. The membrane with a protein-to-lipid weight ratio (P/L) of 1/50 exhibits 13.2 L/m2h water flux and 3.2 g/m2h reversed flux by using FO mode, as well as 15.6 L/m2h water flux and 3.4 L/m2h reversed flux for PRO mode (the draw solution is placed against the active layer). It was also shown that the SLB layer of the double-skinned FO membrane can increase the surface hydrophilicity and reduce the surface roughness, which leads to an improved anti-fouling performance against humic acid foulant. The current work introduced a new method of fabricating high performance biomimetic FO membrane by combining AqpZ and a double-skinned structure based on LbL assembly. PMID:26266426

  8. Bio-Inspired Aquaporinz Containing Double-Skinned Forward Osmosis Membrane Synthesized through Layer-by-Layer Assembly.

    PubMed

    Wang, Shuzheng; Cai, Jin; Ding, Wande; Xu, Zhinan; Wang, Zhining

    2015-08-10

    We demonstrated a novel AquaporinZ (AqpZ)-incorporated double-skinned forward osmosis (FO) membrane by layer-by-layer (LbL) assembly strategy. Positively charged poly(ethyleneimine) (PEI) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) were alternately deposited on both the top and bottom surfaces of a hydrolyzed polyacrylonitrile (H-PAN) substrate. Subsequently, an AqpZ-embedded 1,2-dioleloyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dioleoyl-3-trimethylammonium- propane (chloride salt) (DOTAP) supported lipid bilayer (SLB) was formed on PSS-terminated (T-PSS) membrane via vesicle rupture method. The morphology and structure of the biomimetic membranes were characterized by in situ atomic force microscopy (AFM), scanning electron microscope (SEM), Fourier transform infrared spectrometer using the attenuated total reflection technique (ATR-FTIR), and contact angle. Moreover, the FO performance of the resultant membrane was measured by using 2 M MgCl2 solution as draw solution and deionized (DI) water as feed solution, respectively. The membrane with a protein-to-lipid weight ratio (P/L) of 1/50 exhibits 13.2 L/m(2)h water flux and 3.2 g/m(2)h reversed flux by using FO mode, as well as 15.6 L/m(2)h water flux and 3.4 L/m(2)h reversed flux for PRO mode (the draw solution is placed against the active layer). It was also shown that the SLB layer of the double-skinned FO membrane can increase the surface hydrophilicity and reduce the surface roughness, which leads to an improved anti-fouling performance against humic acid foulant. The current work introduced a new method of fabricating high performance biomimetic FO membrane by combining AqpZ and a double-skinned structure based on LbL assembly.

  9. A new correlation effect in the Helmholtz and surface potentials of the electrical double layer.

    PubMed

    González-Tovar, Enrique; Jiménez-Angeles, Felipe; Messina, René; Lozada-Cassou, Marcelo

    2004-05-22

    The restricted primitive model of an electrical double layer around a spherical macroparticle is studied by using integral equation theories and Monte Carlo simulations. The resulting theoretical curves for the Helmholtz and surface potentials versus the macroparticle charge show an unexpected positive curvature when the ionic size of uni- and divalent electrolyte species is increased. This is a novel effect that is confirmed here by computer experiments. An explanation of this phenomenon is advanced in terms of the adsorption and layering of the electrolytic species and of the compactness of the diffuse double layer. It is claimed that the interplay between electrostatic and ionic size correlation effects, absent in the classical Poisson-Boltzmann view, is responsible for this singularity.

  10. First steps towards the realization of a double layer perceptron based on organic memristive devices

    NASA Astrophysics Data System (ADS)

    Emelyanov, A. V.; Lapkin, D. A.; Demin, V. A.; Erokhin, V. V.; Battistoni, S.; Baldi, G.; Dimonte, A.; Korovin, A. N.; Iannotta, S.; Kashkarov, P. K.; Kovalchuk, M. V.

    2016-11-01

    Memristors are widely considered as promising elements for the efficient implementation of synaptic weights in artificial neural networks (ANNs) since they are resistors that keep memory of their previous conductive state. Whereas demonstrations of simple neural networks (e.g., a single-layer perceptron) based on memristors already exist, the implementation of more complicated networks is more challenging and has yet to be reported. In this study, we demonstrate linearly nonseparable combinational logic classification (XOR logic task) using a network implemented with CMOS-based neurons and organic memrisitive devices that constitutes the first step toward the realization of a double layer perceptron. We also show numerically the ability of such network to solve a principally analogue task which cannot be realized by digital devices. The obtained results prove the possibility to create a multilayer ANN based on memristive devices that paves the way for designing a more complex network such as the double layer perceptron.

  11. On the existence of Si-C double bonded graphene-like layers

    NASA Astrophysics Data System (ADS)

    Huda, Muhammad N.; Yan, Yanfa; Al-Jassim, Mowafak M.

    2009-09-01

    Upon analyzing an earlier experimental study by density-functional theory we have shown that graphene-like SiC layers can exist. We found that, for a particular stacking sequence, Si dbnd C double bond was responsible for the much larger interlayer distances observed in synthesized multi-walled SiC nanotubes. The Si/C ratios in SiC layers determine the extent of interlayer distances and bonding nature. It has been also shown that for some intermediate ratios of Si:C and/or with other stacking sequences, a collapse of SiC layers to tetrahedrally bonded system is possible. We have argued that these synthesized Si dbnd C double-bonded multi-wall silicon-carbide nanotubes may provide a pathway for future realization of SiC graphene-like materials.

  12. Contact interaction of double-chained surfactant layers on silica: bilayer rupture and capillary bridge formation.

    PubMed

    Barthel, Etienne; Roquigny, Renaud; Serreau, Laurence; Denoyel, Renaud; Clerc-Imperor, Marianne; Drummond, Carlos

    2013-11-26

    The contact between two layers of double-chained C18 surfactants adsorbed on silica has been investigated. Using a custom-made surface forces apparatus with high stiffness, we have studied the process of (1) compression and collapse of the layers and (2) surface separation after layer collapse. A continuum mechanics model accounts for the compression and collapse of the surfactant layers. The layer compressibility and molecular energy of rupture can be inferred directly. When the surfaces are rinsed in deionized water, an intriguing structural force is observed: the resulting attractive interaction induces the diffusion of surfactant to the contact area, with the gradual buildup of a capillary bridge of the pure smectic phase of the surfactant. Models are proposed to analyze the force profile.

  13. Design, fabrication and characterization of a double layer solid oxide fuel cell (DLFC)

    NASA Astrophysics Data System (ADS)

    Wang, Guangjun; Wu, Xiangying; Cai, Yixiao; Ji, Yuan; Yaqub, Azra; Zhu, Bin

    2016-11-01

    A double layer solid oxide fuel cell (DLSOFC) without using the electrolyte (layer) has been designed by integrating advantages of positive electrode material of lithium ion battery(LiNi0.8Co0.15Al0.05O2) and oxygen-permeable membranes material (trace amount cobalt incorporated terbium doped ceria, TDC + Co) based on the semiconductor physics principle. Instead of using an electrolyte layer, the depletion layer between the anode and cathode served as an electronic insulator to block the electrons but to maintain the electrolyte function for ionic transport. Thus the device with two layers can realize the function of SOFC and at the same time avoids the electronic short circuiting problem. Such novel DLFC showed good performance at low temperatures, for instance, a maximum power density of 230 mWcm-2 was achieved at 500 °C. The working principle of the new device is presented.

  14. Experimental investigation of the Marangoni effect on the stability of a double-diffusive layer

    NASA Technical Reports Server (NTRS)

    Tanny, Josef; Chen, Chuan F.

    1994-01-01

    Stability experiments were carried out in 4-cm-thick, salt-stratified fluid layer by heating from below and cooling from above. The bottom boundary was rigid while the top was either free or rigid. The initial solute Rayleigh number varied from 2.5 x 10(exp 6) to 4.6 x 10(exp 7). For the rigid-free case, at initial solute Rayleigh numbers R(sub s) greater than 5.4 x 10(exp 6), thermal Marangoni instabilities were observed to onset along the free surface at a relatively low thermal Rayleigh number, R(sub t). The convection was very weak, and it had almost no effect on the concentration and temperature distributions. Double-diffusive instabilities along the top free surface were observed to onset at a higher R(sub t), with much stronger convection causing changes in the concentration and temperature distributions near the top. At a yet higher R(sub t), double-diffusive convection was observed to onset along the bottom boundary. Fluid motion in the layer then evolved into fully developed thermal convection of a homogeneous fluid without any further increase in the imposed Delta T. For layers with R(sub s) less than 5.4 x 10(exp 6), Marangoni and double-diffusive instabilities onset simultaneously along the free surface first, while double-diffusive instabilities along the bottom wall onset at a higher R(sub t).

  15. Synthesis of Zn–Fe layered double hydroxides via an oxidation process and structural analysis of products

    SciTech Connect

    Morimoto, Kazuya; Tamura, Kenji; Anraku, Sohtaro; Sato, Tsutomu; Suzuki, Masaya; Yamada, Hirohisa

    2015-08-15

    The synthesis of Zn–Fe(III) layered double hydroxides was attempted, employing different pathways using either Fe(II) or Fe(III) species together with Zn as the initial reagents. The product derived from the synthesis employing Fe(II) was found to transition to a Zn–Fe(III) layered double hydroxides phase following oxidation process. In contrast, the product obtained with Fe(III) did not contain a layered double hydroxides phase, but rather consisted of simonkolleite and hydrous ferric oxide. It was determined that the valency of the Fe reagent used in the initial synthesis affected the generation of the layered double hydroxides phase. Fe(II) species have ionic radii and electronegativities similar to those of Zn, and therefore are more likely to form trioctahedral hydroxide layers with Zn species. - Graphical abstract: The synthesis of Zn–Fe(III) layered double hydroxides was attempted, employing different pathways using either Fe(II) or Fe(III) species together with Zn as the initial reagents. - Highlights: • Iron valency affected the generation of Zn–Fe layered double hydroxides. • Zn–Fe layered double hydroxides were successfully synthesized using Fe(II). • Fe(II) species were likely to form trioctahedral hydroxide layers with Zn species.

  16. Cascade of Spatio-Temporal Period-Doubling Bifurcations in Connection with the Appearance and Dynamics of Non-Concentric Multiple Double Layers in Plasma

    SciTech Connect

    Dimitriu, D. G.; Ivan, L. M.

    2008-03-19

    Experimental results are presented that reveal a complex route to chaos in plasma, in which a Feigenbaum scenario (cascade of temporal period-doubling bifurcation) develops simultaneously with a cascade of spatial period-doubling bifurcations, in connection with the appearance of a non-concentric multiple double layers structure. The Feigenbaum scenario is identified in the time series of the oscillations of the current through the plasma conductor.

  17. Catalyzed double layer cathodes for high performance and long life molten carbonate fuel cells

    SciTech Connect

    Bischoff, M.; Jantsch, U.; Rohland, B.

    1996-12-31

    NiO/LiCoO{sub 2} double layer cathodes (DLCs) were prepared with a thin highly active LiCoO{sub 2}-layer by a new double layer tape casting/sintering procedure. The resulting metallic porous precursor plates were mounted into the MCFC and heated up by a special procedure to form LiCoO{sub 2} from air, Co and Li{sub 2}CO{sub 3} in a solid/gas reaction. MCFCs with highly active NiO/LiCoO{sub 2}-DLCs can operate over prolonged periods of time with a Ni-precipitation which is 10% lower than one finds with state of the art NiO cathodes. According to LiCoO{sub 2}-cathodes have theoretical life times of more than 100 000 hours at nonpressurized conditions. MCFCs with new NiO/LiCoO{sub 2} double layer cathodes (DLC) were investigated with regard to variable parameters of their microstructure. From the agglomerate model of the porous MCFC cathode, the dependence of the polarization resistance from the radius of the agglomerates and the inner agglomerate surface area was calculated.

  18. Skin explosion of double-layer conductors in fast-rising high magnetic fields

    SciTech Connect

    Chaikovsky, S. A. Datsko, I. M.; Labetskaya, N. A.; Ratakhin, N. A.

    2014-04-15

    An experiment has been performed to study the electrical explosion of thick cylindrical conductors using the MIG pulsed power generator capable of producing a peak current of 2.5 MA within 100 ns rise time. The experimental goal was to compare the skin explosion of a solid conductor with that of a double-layer conductor whose outer layer had a lower conductivity than the inner one. It has been shown that in magnetic fields of peak induction up to 300 T and average induction rise rate 3 × 10{sup 9} T/s, the double-layer structure of a conductor makes it possible to achieve higher magnetic induction at the conductor surface before it explodes. This can be accounted for, in particular, by the reduction of the ratio of the Joule heat density to the energy density of the magnetic field at the surface of a double-layer conductor due to redistribution of the current density over the conductor cross section.

  19. Skin explosion of double-layer conductors in fast-rising high magnetic fields

    NASA Astrophysics Data System (ADS)

    Chaikovsky, S. A.; Oreshkin, V. I.; Datsko, I. M.; Labetskaya, N. A.; Ratakhin, N. A.

    2014-04-01

    An experiment has been performed to study the electrical explosion of thick cylindrical conductors using the MIG pulsed power generator capable of producing a peak current of 2.5 MA within 100 ns rise time. The experimental goal was to compare the skin explosion of a solid conductor with that of a double-layer conductor whose outer layer had a lower conductivity than the inner one. It has been shown that in magnetic fields of peak induction up to 300 T and average induction rise rate 3 × 109 T/s, the double-layer structure of a conductor makes it possible to achieve higher magnetic induction at the conductor surface before it explodes. This can be accounted for, in particular, by the reduction of the ratio of the Joule heat density to the energy density of the magnetic field at the surface of a double-layer conductor due to redistribution of the current density over the conductor cross section.

  20. Influence of nonelectrostatic ion-ion interactions on double-layer capacitance

    NASA Astrophysics Data System (ADS)

    Zhao, Hui

    2012-11-01

    Recently a Poisson-Helmholtz-Boltzmann (PHB) model [Bohinc , Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.85.031130 85, 031130 (2012)] was developed by accounting for solvent-mediated nonelectrostatic ion-ion interactions. Nonelectrostatic interactions are described by a Yukawa-like pair potential. In the present work, we modify the PHB model by adding steric effects (finite ion size) into the free energy to derive governing equations. The modified PHB model is capable of capturing both ion specificity and ion crowding. This modified model is then employed to study the capacitance of the double layer. More specifically, we focus on the influence of nonelectrostatic ion-ion interactions on charging a double layer near a flat surface in the presence of steric effects. We numerically compute the differential capacitance as a function of the voltage under various conditions. At small voltages and low salt concentrations (dilute solution), we find out that the predictions from the modified PHB model are the same as those from the classical Poisson-Boltzmann theory, indicating that nonelectrostatic ion-ion interactions and steric effects are negligible. At moderate voltages, nonelectrostatic ion-ion interactions play an important role in determining the differential capacitance. Generally speaking, nonelectrostatic interactions decrease the capacitance because of additional nonelectrostatic repulsion among excess counterions inside the double layer. However, increasing the voltage gradually favors steric effects, which induce a condensed layer with crowding of counterions near the electrode. Accordingly, the predictions from the modified PHB model collapse onto those computed by the modified Poisson-Boltzmann theory considering steric effects alone. Finally, theoretical predictions are compared and favorably agree with experimental data, in particular, in concentrated solutions, leading one to conclude that the modified PHB model adequately predicts the diffuse

  1. SPREADING LAYERS IN ACCRETING OBJECTS: ROLE OF ACOUSTIC WAVES FOR ANGULAR MOMENTUM TRANSPORT, MIXING, AND THERMODYNAMICS

    SciTech Connect

    Philippov, Alexander A.; Rafikov, Roman R.; Stone, James M.

    2016-01-20

    Disk accretion at a high rate onto a white dwarf (WD) or a neutron star has been suggested to result in the formation of a spreading layer (SL)—a belt-like structure on the object's surface, in which the accreted matter steadily spreads in the poleward (meridional) direction while spinning down. To assess its basic characteristics, we perform two-dimensional hydrodynamic simulations of supersonic SLs in the relevant morphology with a simple prescription for cooling. We demonstrate that supersonic shear naturally present at the base of the SL inevitably drives sonic instability that gives rise to large-scale acoustic modes governing the evolution of the SL. These modes dominate the transport of momentum and energy, which is intrinsically global and cannot be characterized via some form of local effective viscosity (e.g., α-viscosity). The global nature of the wave-driven transport should have important implications for triggering Type I X-ray bursts in low-mass X-ray binaries. The nonlinear evolution of waves into a system of shocks drives effective rearrangement (sensitively depending on thermodynamical properties of the flow) and deceleration of the SL, which ultimately becomes transonic and susceptible to regular Kelvin–Helmholtz instability. We interpret this evolution in terms of the global structure of the SL and suggest that mixing of the SL material with the underlying stellar fluid should become effective only at intermediate latitudes on the accreting object's surface, where the flow has decelerated appreciably. In the near-equatorial regions the transport is dominated by acoustic waves and mixing is less efficient. We speculate that this latitudinal nonuniformity of mixing in accreting WDs may be linked to the observed bipolar morphology of classical nova ejecta.

  2. Mechanisms governing the interfacial delamination of thermal barrier coating system with double ceramic layers

    NASA Astrophysics Data System (ADS)

    Xu, Rong; Fan, Xueling; Wang, T. J.

    2016-05-01

    A systematic study of factors affecting the interfacial delamination of thermal barrier coating system (TBCs) with double ceramic layers (DCL) is presented. Crack driving forces for delaminations at two weak interfaces are examined. The results show that a thicker outermost ceramic layer can induce dramatic increase in crack driving force and make the interface between two ceramic coatings become more prone to delamination. The behavior is shown to be more prominent in TBCs with stiffer outmost coating. The thickness ratio of two ceramic layers is an important parameter for controlling the failure mechanisms and determining the lifetime of DCL TBCs under inservice condition. By accounting for the influences of thickness ratio of two ceramic layers and interfacial fracture toughnesses of two involved interfaces, the fracture mechanism map of DCL TBCs has been constructed, in which different failure mechanisms are identified. The results quanlitatively agree with the aviliable experimental data.

  3. Micrometer-Thick Graphene Oxide-Layered Double Hydroxide Nacre-Inspired Coatings and Their Properties.

    PubMed

    Yan, You-Xian; Yao, Hong-Bin; Mao, Li-Bo; Asiri, Abdullah M; Alamry, Khalid A; Marwani, Hadi M; Yu, Shu-Hong

    2016-02-10

    Robust, functional, and flame retardant coatings are attractive in various fields such as building construction, food packaging, electronics encapsulation, and so on. Here, strong, colorful, and fire-retardant micrometer-thick hybrid coatings are reported, which can be constructed via an enhanced layer-by-layer assembly of graphene oxide (GO) nanosheets and layered double hydroxide (LDH) nanoplatelets. The fabricated GO-LDH hybrid coatings show uniform nacre-like layered structures that endow them good mechanic properties with Young's modulus of ≈ 18 GPa and hardness of ≈ 0.68 GPa. In addition, the GO-LDH hybrid coatings exhibit nacre-like iridescence and attractive flame retardancy as well due to their well-defined 2D microstructures. This kind of nacre-inspired GO-LDH hybrid thick coatings will be applied in various fields in future due to their high strength and multifunctionalities.

  4. Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric

    PubMed Central

    Ki Min, Bok; Kim, Seong K.; Jun Kim, Seong; Ho Kim, Sung; Kang, Min-A; Park, Chong-Yun; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok

    2015-01-01

    Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer. PMID:26530817

  5. AA stacking, tribological and electronic properties of double-layer graphene with krypton spacer.

    PubMed

    Popov, Andrey M; Lebedeva, Irina V; Knizhnik, Andrey A; Lozovik, Yurii E; Potapkin, Boris V; Poklonski, Nikolai A; Siahlo, Andrei I; Vyrko, Sergey A

    2013-10-21

    Structural, energetic, and tribological characteristics of double-layer graphene with commensurate and incommensurate krypton spacers of nearly monolayer coverage are studied within the van der Waals-corrected density functional theory. It is shown that when the spacer is in the commensurate phase, the graphene layers have the AA stacking. For this phase, the barriers to relative in-plane translational and rotational motion and the shear mode frequency of the graphene layers are calculated. For the incommensurate phase, both of the barriers are found to be negligibly small. A considerable change of tunneling conductance between the graphene layers separated by the commensurate krypton spacer at their relative subangstrom displacement is revealed by the use of the Bardeen method. The possibility of nanoelectromechanical systems based on the studied tribological and electronic properties of the considered heterostructures is discussed.

  6. Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric.

    PubMed

    Ki Min, Bok; Kim, Seong K; Jun Kim, Seong; Ho Kim, Sung; Kang, Min-A; Park, Chong-Yun; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok

    2015-11-04

    Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer.

  7. Double-layer PVDF transducer and V(z) measurement system for measuring leaky Lamb waves in a piezoelectric plate.

    PubMed

    Lee, Yung-Chun; Kuo, Shi Hoa

    2007-03-01

    This paper presents a new experimental measurement method for leaky Lamb waves propagating in a piezoelectric plate immersed in a conductive fluid. The measurement system is a low-frequency version of lens-less acoustic microscopy which has been developed based on a line-focus double-layer PVDF transducer. The transducer and its defocusing measurement system can perform V(z) measurements on a sample plate immersed in a fluid, and therefore can obtain the leaky Lamb wave velocities with high accuracy. An X-cut LiNbO(3) plate is investigated with this experimental measurement system to find out its fluid-loading effects, especially the conductive loading effects by water of various conductivities. Angular dependence of this conductive loading effect along different propagating directions on the X-cut LiNbO(3) plate is measured. It is found out the conductive loading effects are strongly dependent on the piezoelectric coupling factor. Theoretical calculations based on partial wave theory have also been carried out and compared with experimental data. Good agreements have been observed.

  8. Numerical Well Testing Interpretation Model and Applications in Crossflow Double-Layer Reservoirs by Polymer Flooding

    PubMed Central

    Guo, Hui; He, Youwei; Li, Lei; Du, Song; Cheng, Shiqing

    2014-01-01

    This work presents numerical well testing interpretation model and analysis techniques to evaluate formation by using pressure transient data acquired with logging tools in crossflow double-layer reservoirs by polymer flooding. A well testing model is established based on rheology experiments and by considering shear, diffusion, convection, inaccessible pore volume (IPV), permeability reduction, wellbore storage effect, and skin factors. The type curves were then developed based on this model, and parameter sensitivity is analyzed. Our research shows that the type curves have five segments with different flow status: (I) wellbore storage section, (II) intermediate flow section (transient section), (III) mid-radial flow section, (IV) crossflow section (from low permeability layer to high permeability layer), and (V) systematic radial flow section. The polymer flooding field tests prove that our model can accurately determine formation parameters in crossflow double-layer reservoirs by polymer flooding. Moreover, formation damage caused by polymer flooding can also be evaluated by comparison of the interpreted permeability with initial layered permeability before polymer flooding. Comparison of the analysis of numerical solution based on flow mechanism with observed polymer flooding field test data highlights the potential for the application of this interpretation method in formation evaluation and enhanced oil recovery (EOR). PMID:25302335

  9. Numerical well testing interpretation model and applications in crossflow double-layer reservoirs by polymer flooding.

    PubMed

    Yu, Haiyang; Guo, Hui; He, Youwei; Xu, Hainan; Li, Lei; Zhang, Tiantian; Xian, Bo; Du, Song; Cheng, Shiqing

    2014-01-01

    This work presents numerical well testing interpretation model and analysis techniques to evaluate formation by using pressure transient data acquired with logging tools in crossflow double-layer reservoirs by polymer flooding. A well testing model is established based on rheology experiments and by considering shear, diffusion, convection, inaccessible pore volume (IPV), permeability reduction, wellbore storage effect, and skin factors. The type curves were then developed based on this model, and parameter sensitivity is analyzed. Our research shows that the type curves have five segments with different flow status: (I) wellbore storage section, (II) intermediate flow section (transient section), (III) mid-radial flow section, (IV) crossflow section (from low permeability layer to high permeability layer), and (V) systematic radial flow section. The polymer flooding field tests prove that our model can accurately determine formation parameters in crossflow double-layer reservoirs by polymer flooding. Moreover, formation damage caused by polymer flooding can also be evaluated by comparison of the interpreted permeability with initial layered permeability before polymer flooding. Comparison of the analysis of numerical solution based on flow mechanism with observed polymer flooding field test data highlights the potential for the application of this interpretation method in formation evaluation and enhanced oil recovery (EOR).

  10. Synthesis and Characterization of Layered Double Hydroxides Containing Optically Active Transition Metal Ion

    NASA Astrophysics Data System (ADS)

    Tyagi, S. B.; Kharkwal, Aneeta; Nitu; Kharkwal, Mamta; Sharma, Raghunandan

    2017-01-01

    The acetate intercalated layered double hydroxides of Zn and Mn, have been synthesized by chimie douce method. The materials were characterized by XRD, TGA, CHN, IR, XPS, SEM-EDX and UV-visible spectroscopy. The photoluminescence properties was also studied. The optical properties of layered hydroxides are active transition metal ion dependent, particularly d1-10 system plays an important role. Simultaneously the role of host - guest orientation has been considered the basis of photoluminescence. Acetate ion can be exchanged with iodide and sulphate ions. The decomposed product resulted the pure phase Mn doped zinc oxide are also reported.

  11. A hybrid Mg-Al layered double hydroxide/graphene nanostructure obtained via hydrothermal synthesis

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaodong; Cao, Jian-Ping; Zhao, Jun; Hu, Guo-Hua; Dang, Zhi-Min

    2014-06-01

    A hybrid Mg-Al layered double hydroxide/graphene (LDH-GR) material nanostructure has been fabricated by employing the hydrothermal treatment at 140 °C for 10 h. Graphene oxide is simultaneously reduced to graphene during the hydrothermal treatment. The LDH and LDH-GR have high degree of crystallinity and assembled layer structure, which is attributed to electrostatic interaction mechanism. The obtained hybrid nanostructure materials can be used as flame retardant or conductor of electricity and heat due to the combination of different properties arising from graphene and LDH.

  12. Double layer effects in a model of proton discharge on charged electrodes

    PubMed Central

    2014-01-01

    Summary We report first results on double layer effects on proton discharge reactions from aqueous solutions to charged platinum electrodes. We have extended a recently developed combined proton transfer/proton discharge model on the basis of empirical valence bond theory to include specifically adsorbed sodium cations and chloride anions. For each of four studied systems 800–1000 trajectories of a discharging proton were integrated by molecular dynamics simulations until discharge occurred. The results show significant influences of ion presence on the average behavior of protons prior to the discharge event. Rationalization of the observed behavior cannot be based solely on the electrochemical potential (or surface charge) but needs to resort to the molecular details of the double layer structure. PMID:25161833

  13. Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD

    NASA Astrophysics Data System (ADS)

    Vlad, A.; Birjega, R.; Matei, A.; Luculescu, C.; Nedelcea, A.; Dinescu, M.; Zavoianu, R.; Pavel, O. D.

    2015-10-01

    Layered double hydroxides (LDHs) thin films with Mg-Al were deposited using pulsed laser deposition (PLD) technique. We studied the ability of our films to detect copper ions in aqueous solutions. Copper is known to be a common pollutant in water, originating from urban and industrial waste. Clay minerals, including layered double hydroxides (LDHs), can reduce the toxicity of such wastes by adsorbing copper. We report on the uptake of copper ions from aqueous solution on LDH thin films obtained via PLD. The obtained thin films were characterized using X-ray Diffraction, Atomic Force Microscopy, and Scanning Electron Microscopy with Energy Dispersive X-ray analysis. The results in this study indicate that LDHs thin films obtained by PLD have potential as an efficient adsorbent for removing copper from aqueous solution.

  14. Resistivity due to weak double layers - A model for auroral arc thickness

    NASA Technical Reports Server (NTRS)

    Prakash, Manju; Lysak, Robert L.

    1992-01-01

    We have calculated the resistivity due to a sequence of fluctuating weak double layers aligned parallel to the ambient magnetic field line. The average response of an electron drifting through a 1D randomly oriented array of WDLs is studied using a test particle approach. The average is taken over the randomly fluctuating values of the electric field associated with the double layers. Based on our calculations, we estimate that a 350 eV electron energy the thickness of the visual auroral arc is about 2.5 km and that of the auroral fine structure as about 250 m when mapped down to the ionosphere. The significance of our calculations is discussed in the context of magnetosphere-ionosphere coupling.

  15. Molecular simulation of electric double-layer capacitors based on carbon nanotube forests.

    PubMed

    Yang, Lu; Fishbine, Brian H; Migliori, Albert; Pratt, Lawrence R

    2009-09-02

    Described here are the first simulations of electric double-layer capacitors based on carbon nanotube forests modeled fully at a molecular level. The computations determine single-electrode capacitances in the neighborhood of 80 F/g, in agreement with experimental capacitances of electric double-layer capacitors utilizing carbon nanotube forests or carbide-derived carbons as electrode material. The capacitance increases modestly with the decrease of the pore size through radii greater than 1 nm, which is consistent with recent experiments on carbide-derived carbon electrodes. Because the various factors included in these simulations are precisely defined, these simulation data will help to disentangle distinct physical chemical factors that contribute to the performance of these materials, e.g., pore geometry, variable filling of the pores, pseudocapacitance, and electronic characteristics of the nanotubes.

  16. Spatially Resolved Measurements of a Double Layer in an Argon Helicon Plasma

    NASA Astrophysics Data System (ADS)

    Aguirre, Evan; Siddiqui, Umair; McKee, John; Scime, Earl

    2015-11-01

    We report 2-dimensional, spatially resolved observations of a double layer in an expanding helicon plasma. These new measurements investigate the origins of previously observed multiple ion beam populations in the downstream plasma. We use Laser Induced Fluorescence (LIF) to measure the ion velocity distribution functions (IVDFs) of argon ions and neutrals both parallel and perpendicular to the background magnetic field and an rf-compensated Langmuir probe to determine the local plasma potential. These are the first multi-dimensional LIF measurements of ion acceleration in a current-free double layer and were obtained with a recently installed, internal scanning probe system in the HELIX-LEIA experimental facility. This work is supported by US National Science Foundation grant number PHY-1360278.

  17. A double layer model for solar X-ray and microwave pulsations

    NASA Technical Reports Server (NTRS)

    Tapping, K. F.

    1986-01-01

    The wide range of wavelengths over which quasi-periodic pulsations have been observed suggests that the mechanism causing them acts upon the supply of high energy electrons driving the emission processes. A model is described which is based upon the radial shrinkage of a magnetic flux tube. The concentration of the current, along with the reduction in the number of available charge carriers, can rise to a condition where the current demand exceeds the capacity of the thermal electrons. Driven by the large inductance of the external current circuit, an instability takes place in the tube throat, resulting in the formation of a potential double layer, which then accelerates electrons and ions to MeV energies. The double layer can be unstable, collapsing and reforming repeatedly. The resulting pulsed particle beams give rise to pulsating emission which are observed at radio and X-ray wavelengths.

  18. Multianalyte electrochemical biosensor on a monolith electrode by optically scanning the electrical double layer.

    PubMed

    Lee, Seung-Woo; Saraf, Ravi F

    2014-07-15

    Redox on an electrode is an interfacial phenomenon that modulates the charge in the electrical double layer (EDL). A novel instrument, the Scanning Electrometer for Electrical Double-layer (SEED) has been developed to measure multiple enzyme reactions on a monolith electrode due to immunospecific binding with a mixture of respective analytes. SEED quantitatively maps the local redox reaction by scanning a laser on the array of enzyme monolayer spots immobilized on the monolith electrode. SEED measures the change in local charge state of the EDL that abruptly changes due to the redox reaction. The measurement spot size defined by the size of the laser beam is ~10 µm. The SEED signal is linearly proportional to the local redox current density and analyte concentration. The specificity is close to 100%. The SEED readout is compatible with microfluidics platform where the signal degrades less than 2% due to the poly(dimethyl siloxane) (PDMS) body.

  19. Observation of electron hole, double layer, and turbulent heating in a laboratory plasma

    NASA Astrophysics Data System (ADS)

    Tsukishima, T.; Inuzuka, H.

    1990-08-01

    Nonlinear phenomena such as electron hole, double layer, and turbulent heating, which were observed in a linear mirror device, THE NU-II, are reviewed. Observations were carried out with a temporal resolution of 2 ns and a spatial resolution of 1 mm, respectively. Upon applying a voltage difference of the order of 10 kV between two electrodes inserted in the cylindrical plasma at a distance of 67 cm, the nonlinear phenomena evolved consecutively. In particular, a strong current limited double layer was formed, and its lifetime was found to satisfy a simple empirical law. One dimensional computer simulations based on a kinetic code were carried out with boundary conditions close to the experimental ones. The effect of magnetic field was taken into consideration in the simulations.

  20. Structure of an electric double layer containing a 2:2 valency dimer electrolyte

    SciTech Connect

    Silvestre-Alcantara, Whasington; Henderson, Douglas; Wu, Jianzhong; Kaja, Monika; Lamperski, Stanisław; Bhuiyan, Lutful Bari

    2014-12-05

    In this study, the structure of a planar electric double layer formed by a 2:2 valency dimer electrolyte in the vicinity of a uniformly charged planar hard electrode is investigated using density functional theory and Monte Carlo simulations. The dimer electrolyte consists of a mixture of charged divalent dimers and charged divalent monomers in a dielectric continuum. A dimer is constructed by two tangentially tethered rigid spheres, one of which is divalent and positively charged and the other neutral, whereas the monomer is a divalent and negatively charged rigid sphere. The density functional theory reproduces well the simulation results for (i) the singlet distributions of the various ion species with respect to the electrode, and (ii) the mean electrostatic potential. Lastly, comparison with earlier results for a 2:1/1:2 dimer electrolyte shows that the double layer structure is similar when the counterion has the same valency.

  1. Structure of an electric double layer containing a 2:2 valency dimer electrolyte

    DOE PAGES

    Silvestre-Alcantara, Whasington; Henderson, Douglas; Wu, Jianzhong; ...

    2014-12-05

    In this study, the structure of a planar electric double layer formed by a 2:2 valency dimer electrolyte in the vicinity of a uniformly charged planar hard electrode is investigated using density functional theory and Monte Carlo simulations. The dimer electrolyte consists of a mixture of charged divalent dimers and charged divalent monomers in a dielectric continuum. A dimer is constructed by two tangentially tethered rigid spheres, one of which is divalent and positively charged and the other neutral, whereas the monomer is a divalent and negatively charged rigid sphere. The density functional theory reproduces well the simulation results formore » (i) the singlet distributions of the various ion species with respect to the electrode, and (ii) the mean electrostatic potential. Lastly, comparison with earlier results for a 2:1/1:2 dimer electrolyte shows that the double layer structure is similar when the counterion has the same valency.« less

  2. Controlling spin–orbit interaction in a ferromagnetic Fe/Au double layer

    SciTech Connect

    Samarin, Sergey N.; Kostylev, Mikhail; Williams, James F.; Artamonov, Oleg M.; Baraban, Alexander P.; Guagliardo, Paul

    2015-01-26

    Using spin-polarized single- and two-electron spectroscopy, we probe exchange and spin–orbit interaction in a double layer of Fe and Au on W(110) and measure the spin asymmetry of the Bloch spectral density function of the sample. In a 5 ML iron film, the spin-orbit contribution to the measured asymmetry of the (e,2e) spectra was not detectable, whereas a deposition of about 1 ML of gold introduced a substantial spin-orbit component in the measured asymmetry. At the same time, this double layer still exhibits ferromagnetic properties: (i) the spectral density function asymmetry demonstrate imbalance of spin-up and spin-down electron densities in the valence band and (ii) the Stoner excitation asymmetry has almost the same value as in a pure Fe film.

  3. Kinetic model for an auroral double layer that spans many gravitational scale heights

    SciTech Connect

    Robertson, Scott

    2014-12-15

    The electrostatic potential profile and the particle densities of a simplified auroral double layer are found using a relaxation method to solve Poisson's equation in one dimension. The electron and ion distribution functions for the ionosphere and magnetosphere are specified at the boundaries, and the particle densities are found from a collisionless kinetic model. The ion distribution function includes the gravitational potential energy; hence, the unperturbed ionospheric plasma has a density gradient. The plasma potential at the upper boundary is given a large negative value to accelerate electrons downward. The solutions for a wide range of dimensionless parameters show that the double layer forms just above a critical altitude that occurs approximately where the ionospheric density has fallen to the magnetospheric density. Below this altitude, the ionospheric ions are gravitationally confined and have the expected scale height for quasineutral plasma in gravity.

  4. Removal of perchlorate in water by calcined MgAl-CO3 layered double hydroxides.

    PubMed

    Yang, Yiqiong; Gao, Naiyun; Deng, Yang; Yu, Guoping

    2013-04-01

    Perchlorate is widely known as an inorganic endocrine disruptor. In this study, MgAl-CO3 layered double hydroxides with different Mg/Al molar ratios were prepared using a coprecipitation method and followed by a calcination process at a temperature range of 300 to 700 degrees C. Results showed that the best synthesis conditions were a calcination temperature of 550 degrees C and Mg/Al molar ratio of 3. Further, the adsorbent and its adsorption product were characterized by x-ray diffraction, Fourier transform-infrared spectroscopy, and thermogravimetric-differential thermal analysis. The layered double hydroxides structures in the adsorbent were lost during calcination at 550 degrees C but were reconstructed subsequent to adsorption of perchlorate, indicating that the "memory effect" appeared to play an important role in perchlorate adsorption. The perchlorate adsorption pattern was best described by the pseudo-second-order kinetics model, while the Freundlich isotherms appropriately explained perchlorate adsorption data.

  5. Synthesis and properties of Mg{sub 2}Al layered double hydroxides containing 5-fluorouracil

    SciTech Connect

    Wang Zhongliang; Wang Enbo . E-mail: wangenbo@public.cc.jl.cn; Gao Lei; Xu Lin

    2005-03-15

    A pharmaceutically active compound, 5-fluorouracil (5-FU) has been firstly intercalated into layered double hydroxide with the restructure method. Powder X-ray diffraction and spectroscopic analysis indicate that 5-FU molecule is stabilized in the host interlayer by electrostatic interaction and intermolecular interaction, and that the orientation of 5-FU is different when changing the pattern of aging treatment or the swelling agent. The release studies show that a rapid release of the drug during the first 40min is followed by a more sustained one, and that the total amount of drug released from hybrid material into the aqueous solution is almost 87% and 74% at pH 4 and 7, respectively. The studies mentioned above suggest that layered double hydroxide might be used as the basis of a tunable drug delivery carrier.

  6. Density functional study of the electric double layer formed by a high density electrolyte.

    PubMed

    Henderson, Douglas; Lamperski, Stanisław; Jin, Zhehui; Wu, Jianzhong

    2011-11-10

    We use a classical density functional theory (DFT) to study the electric double layer formed by charged hard spheres near a planar charged surface. The DFT predictions are found to be in good agreement with recent computer simulation results. We study the capacitance of the charged hard-sphere system at a range of densities and surface charges and find that the capacitance exhibits a local minimum at low ionic densities and small electrode charge. Although this charging behavior is typical for an aqueous electrolyte solution, the local minimum gradually turns into a maximum as the density of the hard spheres increases. Charged hard spheres at high density provide a reasonable first approximation for ionic liquids. In agreement with experiment, the capacitance of this model ionic liquid double layer has a maximum at small electrode charge density.

  7. Simulation of double layers in a model auroral circuit with nonlinear impedance

    NASA Technical Reports Server (NTRS)

    Smith, R. A.

    1986-01-01

    A reduced circuit description of the U-shaped potential structure of a discrete auroral arc, consisting of the flank transmission line plus parallel-electric-field region, is used to provide the boundary condition for one-dimensional simulations of the double-layer evolution. The model yields asymptotic scalings of the double-layer potential, as a function of an anomalous transport coefficient alpha and of the perpendicular length scale l(a) of the arc. The arc potential phi(DL) scales approximately linearly with alpha, and for alpha fixed phi (DL) about l(a) to the z power. Using parameters appropriate to the auroral zone acceleration region, potentials of phi (DPL) 10 kV scale to projected ionospheric dimensions of about 1 km, with power flows of the order of magnitude of substorm dissipation rates.

  8. Multinuclear in situ magnetic resonance imaging of electrochemical double-layer capacitors.

    PubMed

    Ilott, Andrew J; Trease, Nicole M; Grey, Clare P; Jerschow, Alexej

    2014-08-01

    The last decade has seen an intensified interest in the development and use of electrochemical double-layer capacitors, fuelled by the availability of new electrode materials. The use of nanoporous carbons, in particular, with extremely high surface areas for ion adsorption has enabled the development of working devices with significantly increased capacitances that have become viable alternatives to lithium-ion batteries in certain applications. An understanding of the charge storage mechanism and the ion dynamics inside the nanopores is only just emerging, with the most compelling evidence coming from simulation. Here we present the first in situ magnetic resonance imaging experiments of electrochemical double-layer capacitors. These experiments overcome the limitations of other techniques and give spatially resolved chemical information about the electrolyte ions in real time for a working capacitor of standard geometry. The results provide insight into the predominant capacitive processes occurring at different states of charge and discharge.

  9. A Van der Waals-like theory of plasma double layers

    NASA Technical Reports Server (NTRS)

    Katz, Ira; Davis, V. A.

    1989-01-01

    A theory describing plasma double layers in terms of multiple roots of the charge density expression is presented. The theory presented uses the fact that equilibrium plasmas shield small potential perturbations linearly; for high potentials, the shielding decreases. The approach is analogous to Van der Waals' theory of simple fluids in which inclusion of approximate expressions for both excluded volume and long range attractive forces sufficiently describes the first-order liquid-gas phase transition.

  10. Synthesis of ACECLOFENAC/HYDROXYPROPYL-β-CYCLODEXTRIN Intercalated Layered Double Hydroxides and Controlled Release Properties

    NASA Astrophysics Data System (ADS)

    Li, Shifeng; Shen, Yanming; Liu, Dongbin; Fan, Lihui; Wu, Keke; Xiao, Min

    2013-04-01

    Aceclofenac (AC)/hydroxypropyl-β-cyclodextrin (HP-β-CD) complex intercalated layered double hydroxides (LDHs) have been synthesized by reconstruction method. X-ray diffraction, Fourier transform infrared and thermal gravimetric analyses indicated a successful intercalation of AC/HP-β-CD complex into the LDHs gallery. The AC release properties were also studied in different pH values buffer solution. The results indicate that the AC/HP-β-CD intercalated LDH has a potential application in drug delivery agent.

  11. Novel electric double-layer capacitor with a coaxial fiber structure.

    PubMed

    Chen, Xuli; Qiu, Longbin; Ren, Jing; Guan, Guozhen; Lin, Huijuan; Zhang, Zhitao; Chen, Peining; Wang, Yonggang; Peng, Huisheng

    2013-11-26

    A coaxial electric double-layer capacitor fiber is developed from the aligned carbon nanotube fiber and sheet, which functions as two electrodes with a polymer gel sandwiched between them. The unique coaxial structure enables a rapid transportation of ions between the two electrodes with a high electrochemical performance. These energy storage fibers are also flexible and stretchable, and can be woven into and widely used for electronic textiles.

  12. Formating double layer mechanism by electric charged particle stream in plasma

    NASA Astrophysics Data System (ADS)

    Shan-jun, Ma; Qian-li, Yang; Xiao-qing, Li

    1998-08-01

    In this paper, two-fluid equations have been solved after having considered magnetic field generated by charged particle stream. Finally, the distribution of electric field Ez(z, r) and its growth rate γ in plasma have been obtained. From the expression of Ez(z, r) it can be known that the double layer has been formed. With the increase of disturbance γ will be larger, and finally this will result in the interruption of electric current and occurrence of burst.

  13. Non-mean-field theory of anomalously large double layer capacitance.

    PubMed

    Loth, M S; Skinner, Brian; Shklovskii, B I

    2010-07-01

    Mean-field theories claim that the capacitance of the double layer formed at a metal/ionic conductor interface cannot be larger than that of the Helmholtz capacitor, whose width is equal to the radius of an ion. However, in some experiments the apparent width of the double layer capacitor is substantially smaller. We propose an alternate non-mean-field theory of the ionic double layer to explain such large capacitance values. Our theory allows for the binding of discrete ions to their image charges in the metal, which results in the formation of interface dipoles. We focus primarily on the case where only small cations are mobile and other ions form an oppositely charged background. In this case, at small temperature and zero applied voltage dipoles form a correlated liquid on both contacts. We show that at small voltages the capacitance of the double layer is determined by the transfer of dipoles from one electrode to the other and is therefore limited only by the weak dipole-dipole repulsion between bound ions so that the capacitance is very large. At large voltages the depletion of bound ions from one of the capacitor electrodes triggers a collapse of the capacitance to the much smaller mean-field value, as seen in experimental data. We test our analytical predictions with a Monte Carlo simulation and find good agreement. We further argue that our "one-component plasma" model should work well for strongly asymmetric ion liquids. We believe that this work also suggests an improved theory of pseudocapacitance.

  14. Characteristics and development report for the MC4169 double-layer capacitor assembly

    SciTech Connect

    Clark, N.H.; Baca, W.E.

    1993-09-01

    The MC4169 Double-Layer Capacitor Assembly was developed in response to a request from the B61 Systems organization to provide interim power for the B61 Common JTA Development. The project has been successfully completed, and Lot 1 has been built by MMSC/GEND. Development testing showed that this assembly met all design requirements. This report describes the design configuration, environmental testing, and aging, reliability, and safety studies done to ensure that the design requirements were met.

  15. Ionic Liquids as Electrolytes for Electrochemical Double-Layer Capacitors: Structures that Optimize Specific Energy.

    PubMed

    Mousavi, Maral P S; Wilson, Benjamin E; Kashefolgheta, Sadra; Anderson, Evan L; He, Siyao; Bühlmann, Philippe; Stein, Andreas

    2016-02-10

    Key parameters that influence the specific energy of electrochemical double-layer capacitors (EDLCs) are the double-layer capacitance and the operating potential of the cell. The operating potential of the cell is generally limited by the electrochemical window of the electrolyte solution, that is, the range of applied voltages within which the electrolyte or solvent is not reduced or oxidized. Ionic liquids are of interest as electrolytes for EDLCs because they offer relatively wide potential windows. Here, we provide a systematic study of the influence of the physical properties of ionic liquid electrolytes on the electrochemical stability and electrochemical performance (double-layer capacitance, specific energy) of EDLCs that employ a mesoporous carbon model electrode with uniform, highly interconnected mesopores (3DOm carbon). Several ionic liquids with structurally diverse anions (tetrafluoroborate, trifluoromethanesulfonate, trifluoromethanesulfonimide) and cations (imidazolium, ammonium, pyridinium, piperidinium, and pyrrolidinium) were investigated. We show that the cation size has a significant effect on the electrolyte viscosity and conductivity, as well as the capacitance of EDLCs. Imidazolium- and pyridinium-based ionic liquids provide the highest cell capacitance, and ammonium-based ionic liquids offer potential windows much larger than imidazolium and pyridinium ionic liquids. Increasing the chain length of the alkyl substituents in 1-alkyl-3-methylimidazolium trifluoromethanesulfonimide does not widen the potential window of the ionic liquid. We identified the ionic liquids that maximize the specific energies of EDLCs through the combined effects of their potential windows and the double-layer capacitance. The highest specific energies are obtained with ionic liquid electrolytes that possess moderate electrochemical stability, small ionic volumes, low viscosity, and hence high conductivity, the best performing ionic liquid tested being 1-ethyl-3

  16. Observation of warm, higher energy electrons transiting a double layer in a helicon plasma

    NASA Astrophysics Data System (ADS)

    Sung, Yung-Ta; Li, Yan; Scharer, John

    2015-11-01

    Experimental observations in MadiHeX indicate that fast electrons with substantial density fractions can be created at low helicon operating pressure. Two-temperature electron distributions including a fast (>80 eV) tail are observed in an inductive RF helicon argon plasma double layer at 0.17 mTorr Ar pressure. The fast, untrapped electrons measured downstream of the double layer have a higher temperature of 13 eV than the trapped, upstream electrons with a temperature of 4 eV. The reduction of plasma potential and density observed in the double layer region would require an upstream temperature ten times the measured 4 eV if occurring via Boltzmann ambipolar expansion. Upstream fluctuations of +/- 30% are also observed in the emissive probe measured plasma potential. Sideband frequencies have been observed at +/- 2 kHz of the driven RF frequency of 13.56 MHz, implying a beam instability effect dominantly upstream of the double layer. This can affect ion acceleration and electron temperature distribution in the region. The mechanism behind this has been explored via several plasma diagnostics tools. An RF-compensated Langmuir probe has been used to measure the electron temperatures and densities, which are cross-checked with ADAS, OES and millimeter wave IF. The EEDF in the plasma has also been profiled to understand the acceleration mechanism. A four-grid RPA and an emissive probe have been used to measure the IEDF and plasma potential. The measured IEDF has also been checked with LIF techniques.

  17. Double-Layered PTFE-Covered Nitinol Stents: Experience in 32 Patients with Malignant Esophageal Strictures

    SciTech Connect

    Park, Jung Gu; Jung, Gyoo-Sik Oh, Kyung Seung; Park, Seon-Ja

    2010-08-15

    We evaluated the effectiveness of a double-layered polytetrafluoroethylene (PTFE)-covered nitinol stent in the palliative treatment of malignant esophageal strictures. A double-layered PTFE-covered nitinol stent was designed to reduce the propensity to migration of conventional covered stent. The stent consists of an inner PTFE-covered stent and an outer uncovered nitinol stent tube. With fluoroscopic guidance, the stent was placed in 32 consecutive patients with malignant esophageal strictures. During the follow-up period, the technical and clinical success rates, complications, and cumulative patient survival and stent patency were evaluated. Stent placement was technically successful in all patients, and no procedural complications occurred. After stent placement, the symptoms of 30 patients (94%) showed improvement. During the mean follow-up of 103 days (range, 9-348 days), 11 (34%) of 32 patients developed recurrent symptoms due to tumor overgrowth in five patients (16%), tumor ingrowth owing to detachment of the covering material (PTFE) apart from the stent wire in 3 (9%), mucosal hyperplasia in 2 (6%), and stent migration in 1 (3%). Ten of these 11 patients were treated by means of placing a second covered stent. Thirty patients died, 29 as a result of disease progression and 1 from aspiration pneumonia. The median survival period was 92 days. The median period of primary stent patency was 190 days. The double-layered PTFE-covered nitinol stent seems to be effective for the palliative treatment of malignant esophageal strictures. We believe that the double-layer configuration of this stent can contribute to decreasing the stent's migration rate.

  18. Substituted Quaternary Ammonium Salts Improve Low-Temperature Performance of Double-Layer Capacitors

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J.; Smart, Marshall C.; West, William C.

    2011-01-01

    Double-layer capacitors are unique energy storage devices, capable of supporting large current pulses as well as a very high number of charging and discharging cycles. The performance of doublelayer capacitors is highly dependent on the nature of the electrolyte system used. Many applications, including for electric and fuel cell vehicles, back-up diesel generators, wind generator pitch control back-up power systems, environmental and structural distributed sensors, and spacecraft avionics, can potentially benefit from the use of double-layer capacitors with lower equivalent series resistances (ESRs) over wider temperature limits. Higher ESRs result in decreased power output, which is a particular problem at lower temperatures. Commercially available cells are typically rated for operation down to only 40 C. Previous briefs [for example, Low Temperature Supercapacitors (NPO-44386), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), p. 32, and Supercapacitor Electrolyte Solvents With Liquid Range Below 80 C (NPO-44855), NASA Tech Briefs, Vol. 34, No. 1 (January 2010), p. 44] discussed the use of electrolytes that employed low-melting-point co-solvents to depress the freezing point of traditional acetonitrile-based electrolytes. Using these modified electrolyte formulations can extend the low-temperature operational limit of double-layer capacitors beyond that of commercially available cells. This previous work has shown that although the measured capacitance is relatively insensitive to temperature, the ESR can rise rapidly at low temperatures, due to decreased electrolyte conductance within the pores of the high surface- area carbon electrodes. Most of these advanced electrolyte systems featured tetraethylammonium tetrafluoroborate (TEATFB) as the salt. More recent work at JPL indicates the use of the asymmetric quaternary ammonium salt triethylmethylammonium tetrafluoroborate (TEMATFB) or spiro-(l,l')-bipyrrolidium tetrafluoroborate (SBPBF4) in a 1:1 by volume solvent

  19. Validity of the "thin" and "thick" double-layer assumptions to model streaming currents in porous media

    NASA Astrophysics Data System (ADS)

    Leinov, E.; Jackson, M.

    2012-12-01

    Measurements of the streaming potential component of the spontaneous potential have been used to characterize groundwater flow and subsurface hydraulic properties in numerous studies. Streaming potentials in porous media arise from the electrical double layer which forms at solid-fluid interfaces. The solid surfaces typically become electrically charged, in which case an excess of counter-charge accumulates in the adjacent fluid. If the fluid is induced to flow by an external pressure gradient, then some of the excess charge within the diffuse part of the double layer is transported with the flow, giving rise to a streaming current. Divergence of the streaming current density establishes an electrical potential, termed the streaming potential. Within the diffuse layer, the Poisson-Boltzmann equation is typically used to describe the variation in electrical potential with distance from the solid surface. In many subsurface settings, it is reasonable to assume that the thickness of the diffuse layer is small compared to the pore radius. This is the so-called 'thin double layer assumption', which has been invoked by numerous authors to model streaming potentials in porous media. However, a number of recent papers have proposed a different approach, in which the thickness of the diffuse layer is assumed to be large compared to the pore radius. This is the so-called 'thick double layer assumption' in which the excess charge density within the pore is assumed to be constant and independent of distance from the solid surface. The advantage of both the 'thin' and 'thick' double layer assumptions is that calculation of the streaming current is greatly simplified. However, perhaps surprisingly, the conditions for which these assumptions are valid have not been determined quantitatively, yet they have a significant impact on the interpretation of streaming potential measurements in natural systems. We use a simple capillary tubes to model investigate the validity of the thin

  20. Layered surface acoustic wave devices for film characterization and sensor applications

    NASA Astrophysics Data System (ADS)

    Pedrick, Michael K.

    2007-05-01

    This work has introduced novel applications for Layered Surface Acoustic Wave (SAW) devices along with concepts for enhanced sensitivity via refined modeling techniques. The derivation of Love Wave and Rayleigh wave propagation pertinent to SAW substrates with thin film overlayers was explored. Novel aspects were presented for Finite Element analysis of Layered SAW sensors. This included coordinate transformations of model geometries to coincide with crystallographic orientations known to generate Surface Skimming Bulk Waves (SSBW) and various Rayleigh wave types of propagation in ST Quartz, 90° rotated ST Quartz, and 77° Y rotated Lithium Tantalate. This work has shown for the first time, FEM prediction of SSBW, Generalized SAW and High Velocity SAW waves. Rayleigh damping properties were extended to develop a Finite element model capable of predicting Layered SAW response to glass transition in a polymer film. The ability to monitor localized mechanical behavior in a PMMA film was explored with Love Waves generated by 90° rotated ST Quartz and Shear Vertical (SV)-SAWs generated by 77° Y rotated Lithium Tantalate. Similar trends were found experimentally as compared to the Finite element models. The capability of Love Wave devices for monitoring polymer film curing behavior was investigated. The ability to qualitatively assess the bond quality between film and substrate was also demonstrated based on the characteristics of the transmitted frequency response. The results of these developments have laid the ground work for developing diagnostic tools to better characterize film behavior in practical applications. Several sensor applications for Layered SAW devices were discussed. The Shear Horizontal displacement of the Love Wave device was exploited to demonstrate the capability of such a sensor for ice detection. A clear distinction between air, water, and ice loading was found with Love Waves whereas SV-SAWs were unable to distinguish between liquid and ice

  1. Electrical double layers at shock fronts in glow discharges and afterglows

    SciTech Connect

    Siefert, Nicholas S.

    2010-12-15

    This paper examines the propagation of spark-generated shockwaves (1.0double layer, at the shock front. The double layer balances the flux of charged particles on both sides of the shock front. The double layer voltage drop was measured in the current-carrying discharge using floating probes and compared with previous models. As well, we measured argon 1s{sup 5} metastable-state density and demonstrate that metastable-state neutral species can be compressed across a shock front and approximately predicted using the Rankine-Hugoniot relationship.

  2. Anomalous transport in discrete arcs and simulation of double layers in a model auroral circuit

    NASA Technical Reports Server (NTRS)

    Smith, Robert A.

    1987-01-01

    The evolution and long-time stability of a double layer in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double-layer potential structure. A simple model is presented in which this current re-distribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double-layer potential. The flank charging may be represented as that of a nonlinear transmission. A simplified model circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a 1-d simulation model to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.

  3. Anomalous transport in discrete arcs and simulation of double layers in a model auroral circuit

    NASA Technical Reports Server (NTRS)

    Smith, Robert A.

    1987-01-01

    The evolution and long-time stability of a double layer (DL) in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double layer potential structure. A simple model is presented in which this current redistribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double layer potential. The flank charging may be represented as that of a nonlinear transmission line. A simplified model circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a one-dimensional simulation model to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.

  4. Synthesis, characterization, and efficacy of antituberculosis isoniazid zinc aluminum-layered double hydroxide based nanocomposites.

    PubMed

    Saifullah, Bullo; El Zowalaty, Mohamed Ezzat; Arulselvan, Palanisamy; Fakurazi, Sharida; Webster, Thomas J; Geilich, Benjamin Mahler; Hussein, Mohd Zobir

    2016-01-01

    The chemotherapy for tuberculosis (TB) is complicated by its long-term treatment, its frequent drug dosing, and the adverse effects of anti-TB drugs. In this study, we have developed two nanocomposites (A and B) by intercalating the anti-TB drug isoniazid (INH) into Zn/Al-layered double hydroxides. The average size of the nanocomposites was found to bê164 nm. The efficacy of the Zn/Al-layered double hydroxides intercalated INH against Mycobacterium tuberculosis was increased by approximately three times more than free INH. The nanocomposites were also found to be active against Gram-positive and -negative bacteria. Compared to the free INH, the nanodelivery formulation was determined to be three times more biocompatible with human normal lung fibroblast MRC-5 cells and 3T3 fibroblast cells at a very high concentration of 50 µg/mL for up to 72 hours. The in vitro release of INH from the Zn/Al-layered double hydroxides was found to be sustained in human body-simulated buffer solutions of pH 4.8 and 7.4. This research is a step forward in making the TB chemotherapy patient friendly.

  5. Magnetohydrodynamic effects on a charged colloidal sphere with arbitrary double-layer thickness

    NASA Astrophysics Data System (ADS)

    Hsieh, Tzu H.; Keh, Huan J.

    2010-10-01

    An analytical study is presented for the magnetohydrodynamic (MHD) effects on a translating and rotating colloidal sphere in an arbitrary electrolyte solution prescribed with a general flow field and a uniform magnetic field at a steady state. The electric double layer surrounding the charged particle may have an arbitrary thickness relative to the particle radius. Through the use of a simple perturbation method, the Stokes equations modified with an electric force term, including the Lorentz force contribution, are dealt by using a generalized reciprocal theorem. Using the equilibrium double-layer potential distribution from solving the linearized Poisson-Boltzmann equation, we obtain closed-form formulas for the translational and angular velocities of the spherical particle induced by the MHD effects to the leading order. It is found that the MHD effects on the particle movement associated with the translation and rotation of the particle and the ambient fluid are monotonically increasing functions of κa, where κ is the Debye screening parameter and a is the particle radius. Any pure rotational Stokes flow of the electrolyte solution in the presence of the magnetic field exerts no MHD effect on the particle directly in the case of a very thick double layer (κa →0). The MHD effect caused by the pure straining flow of the electrolyte solution can drive the particle to rotate, but it makes no contribution to the translation of the particle.

  6. Low Temperature Double-layer Capacitors with Improved Energy Density: An Overview of Recent Development Efforts

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J.; West, William C.; Smart, Marshall C.; Korenblit, Yair; Kajdos, Adam; Kvit, Alexander; Jagiello, Jacek; Yushin, Gleb

    2012-01-01

    Electrochemical double-layer capacitors are finding increased use in a wide range of energy storage applications, particularly where high pulse power capabilities are required. Double-layer capacitors store charge at a liquid/solid interface, making them ideal for low temperature power applications, due to the facile kinetic processes associated with the rearrangement of the electrochemical double-layer at these temperatures. Potential low temperature applications include hybrid and electric vehicles, operations in polar regions, high altitude aircraft and aerospace avionics, and distributed environmental and structural health monitoring. State-of-the-art capacitors can typically operate to -40 C, with a subsequent degradation in power performance below room temperature. However, recent efforts focused on advanced electrolyte and electrode systems can enable operation to temperatures as low as -70 C, with capacities similar to room temperature values accompanied by reasonably low equivalent series resistances. This presentation will provide an overview of recent development efforts to extend and improve the wide temperature performance of these devices.

  7. Swelling pressure of a divalent-rich bentonite: Diffuse double-layer theory revisited

    NASA Astrophysics Data System (ADS)

    Schanz, Tom; Tripathy, Snehasis

    2009-05-01

    Physicochemical forces are responsible for the swelling pressure development in saturated bentonites. In this paper, the swelling pressures of several compacted bentonite specimens for a range of dry density of 1.10-1.73 Mg/m3 were measured experimentally. The clay used was a divalent-rich Ca-Mg-bentonite with 12% exchangeable Na+ ions. The theoretical swelling pressure-dry density relationship for the bentonite was determined from the Gouy-Chapman diffuse double-layer theory. A comparison of experimental and theoretical results showed that the experimental swelling pressures are either smaller or greater than their theoretical counterparts within different dry density ranges. It is shown that for dry density of the clay less than about 1.55 Mg/m3, a possible dissociation of ions from the surface of the clay platelets contributed to the diffuse double-layer repulsion. At higher dry densities, the adsorptive forces due to surface and ion hydration dominated the swelling pressures of the clay. A comparison of the modified diffuse double-layer theory equations proposed in the literature to determine the swelling pressures of compacted bentonites and the experimental results for the clay in this study showed that the agreement between the calculated and experimental swelling pressure results is very good for dry densities less than 1.55 Mg/m3, whereas at higher dry densities the use of the equations was found to be limited.

  8. Synthesis, characterization, and efficacy of antituberculosis isoniazid zinc aluminum-layered double hydroxide based nanocomposites

    PubMed Central

    Saifullah, Bullo; El Zowalaty, Mohamed Ezzat; Arulselvan, Palanisamy; Fakurazi, Sharida; Webster, Thomas J; Geilich, Benjamin Mahler; Hussein, Mohd Zobir

    2016-01-01

    The chemotherapy for tuberculosis (TB) is complicated by its long-term treatment, its frequent drug dosing, and the adverse effects of anti-TB drugs. In this study, we have developed two nanocomposites (A and B) by intercalating the anti-TB drug isoniazid (INH) into Zn/Al-layered double hydroxides. The average size of the nanocomposites was found to bê164 nm. The efficacy of the Zn/Al-layered double hydroxides intercalated INH against Mycobacterium tuberculosis was increased by approximately three times more than free INH. The nanocomposites were also found to be active against Gram-positive and -negative bacteria. Compared to the free INH, the nanodelivery formulation was determined to be three times more biocompatible with human normal lung fibroblast MRC-5 cells and 3T3 fibroblast cells at a very high concentration of 50 µg/mL for up to 72 hours. The in vitro release of INH from the Zn/Al-layered double hydroxides was found to be sustained in human body-simulated buffer solutions of pH 4.8 and 7.4. This research is a step forward in making the TB chemotherapy patient friendly. PMID:27486322

  9. Use of electrochemical impedance spectroscopy to determine double-layer capacitance in doped nonpolar liquids.

    PubMed

    Yezer, Benjamin A; Khair, Aditya S; Sides, Paul J; Prieve, Dennis C

    2015-07-01

    Electrochemical impedance spectroscopy in a thin cell (10 μm) was used to infer conductivity, permittivity and the differential double-layer capacitance of solutions of dodecane doped with OLOA 11000 [poly(isobutylene) succinimide] for concentrations of dopant between 0.1% and 10% by weight. All spectra (frequencies between 1 Hz and 100 kHz) were well fit by an equivalent circuit having four elements including a constant-phase element representing the double-layer capacitance. Using Gouy-Chapman theory for small zeta potentials and assuming univalent charge carriers, the double-layer capacitances were converted into charge carrier concentration which was found to be directly proportional to the weight percent of dopant with a 1 wt% solution having 87 carriers/μm(3) (the concentration of either positive or negative charges). This is only 17 ppm of the total monomer concentration calculated from the average molecule weight of the dopant. Dividing the measured conductivities by the charge carrier concentration, we inferred the mobility and hydrodynamic diameters for the charged micelles. The hydrodynamic diameters of carriers were significantly larger than the average diameter of all micelles measured independently by dynamic light scattering. This suggests that only large micelles become charged.

  10. The electric double layer at a metal electrode in pure water

    NASA Astrophysics Data System (ADS)

    Brüesch, Peter; Christen, Thomas

    2004-03-01

    Pure water is a weak electrolyte that dissociates into hydronium ions and hydroxide ions. In contact with a charged electrode a double layer forms for which neither experimental nor theoretical studies exist, in contrast to electrolytes containing extrinsic ions like acids, bases, and solute salts. Starting from a self-consistent solution of the one-dimensional modified Poisson-Boltzmann equation, which takes into account activity coefficients of point-like ions, we explore the properties of the electric double layer by successive incorporation of various correction terms like finite ion size, polarization, image charge, and field dissociation. We also discuss the effect of the usual approximation of an average potential as required for the one-dimensional Poisson-Boltzmann equation, and conclude that the one-dimensional approximation underestimates the ion density. We calculate the electric potential, the ion distributions, the pH-values, the ion-size corrected activity coefficients, and the dissociation constants close to the electric double layer and compare the results for the various model corrections.

  11. Droplet shaped anode double layer and electron sheath formation in magnetically constricted anode

    NASA Astrophysics Data System (ADS)

    Chauhan, S.; Ranjan, M.; Bandyopadhyay, M.; Mukherjee, S.

    2016-01-01

    Anode double layer and droplet shaped fireball are found in a magnetically constricted anode. The disc shaped anode is constricted using permanent magnets. The device has only one anode and vacuum chamber acts as cathode. Plasma is created through glow discharge by applying high voltage between the anode and the cathode. Large size droplet shaped glow is obtained near the anode and is shown to have a double layer structure. Discharge is operated in pressure range from 5 ×10-3 mbar to 5 ×10-2 mbar keeping discharge current between 1 and 10 mA . Typical plasma density obtained near anode is 1 ×1010 cm-3 . The profile of plasma potential clearly shows two distinct regions with potential difference of 15.6 V at the boundary of anode glow. The potential difference is close to the ionization potential of Argon gas, which is used during the experiment. This distinct region is visible as bright anode glow and dark "bulk plasma" fill the chamber. This indicates the presence of the double layer formation. The role of magnetic field is also discussed in the formation of the glow, its shape, and the plasma potential profile.

  12. The capacitance of ionic liquid electric double layer near nanostructured electrodes

    NASA Astrophysics Data System (ADS)

    Park, Yun Sung; Ahn, Myung Mo; Kang, In Seok

    2015-11-01

    The electric double layer capacitors (EDLC) with nanostructured electrodes have attracted much attention of researchers due to their high power density and long life time. Recently, the ionic liquids are used as an electrolyte of EDLC owing to their electrochemical stability. When ionic liquids are used as an electrolyte, the interrelations between the electric double layer of ionic liquids and the nanostructured electrode must be studied. In this study, the EDLC systems with nanostructured electrodes and ionic liquids are simulated by solving the modified Poisson-Boltzmann equation proposed by Bazant, Storey, and Kornyshev with COMSOL Multiphysics. Several electrode geometries including exohedral, endohedral and arrayed shapes with different length scales are simulated. The potential and charge distributions in the normal direction to the electrode surface are analyzed. The capacitance per unit area is obtained and compared to that of flat electrode. The structure determines the space for counter-ion packing and co-ion gathering, thus has crucial effects on electric double layer capacitance. The critical increase of capacitance with nanoscale confined space is observed with low electrode potential. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Grant Number: 2013R1A1A2011956).

  13. Double-channel, frequency-steered acoustic transducer with 2-D imaging capabilities.

    PubMed

    Baravelli, Emanuele; Senesi, Matteo; Ruzzene, Massimo; De Marchi, Luca; Speciale, Nicolò

    2011-07-01

    A frequency-steerable acoustic transducer (FSAT) is employed for imaging of damage in plates through guided wave inspection. The FSAT is a shaped array with a spatial distribution that defines a spiral in wavenumber space. Its resulting frequency-dependent directional properties allow beam steering to be performed by a single two-channel device, which can be used for the imaging of a two-dimensional half-plane. Ad hoc signal processing algorithms are developed and applied to the localization of acoustic sources and scatterers when FSAT arrays are used as part of pitch-catch and pulse-echo configurations. Localization schemes rely on the spectrogram analysis of received signals upon dispersion compensation through frequency warping and the application of the frequency-angle map characteristic of FSAT. The effectiveness of FSAT designs and associated imaging schemes are demonstrated through numerical simulations and experiments. Preliminary experimental validation is performed by forming a discrete array through the points of the measurement grid of a scanning laser Doppler vibrometer. The presented results demonstrate the frequency-dependent directionality of the spiral FSAT and suggest its application for frequency-selective acoustic sensors, for the localization of broadband acoustic events, or for the directional generation of Lamb waves for active interrogation of structural health.

  14. Dichotomy of the electronic structure and superconductivity between single-layer and double-layer FeSe/SrTiO3 films.

    PubMed

    Liu, Xu; Liu, Defa; Zhang, Wenhao; He, Junfeng; Zhao, Lin; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2014-09-23

    The latest discovery of possible high-temperature superconductivity in the single-layer FeSe film grown on a SrTiO3 substrate has generated much attention. Initial work found that, while the single-layer FeSe/SrTiO3 film exhibits a clear signature of superconductivity, the double-layer film shows an insulating behaviour. Such a marked layer-dependent difference is surprising and the underlying origin remains unclear. Here we report a comparative angle-resolved photoemission study between the single-layer and double-layer FeSe/SrTiO3 films annealed in vacuum. We find that, different from the single-layer FeSe/SrTiO3 film, the double-layer FeSe/SrTiO3 film is hard to get doped and remains in the semiconducting/insulating state under an extensive annealing condition. Such a behaviour originates from the much reduced doping efficiency in the bottom FeSe layer of the double-layer FeSe/SrTiO3 film from the FeSe-SrTiO3 interface. These observations provide key insights in understanding the doping mechanism and the origin of superconductivity in the FeSe/SrTiO3 films.

  15. Boosted output performance of triboelectric nanogenerator via electric double layer effect

    NASA Astrophysics Data System (ADS)

    Chun, Jinsung; Ye, Byeong Uk; Lee, Jae Won; Choi, Dukhyun; Kang, Chong-Yun; Kim, Sang-Woo; Wang, Zhong Lin; Baik, Jeong Min

    2016-10-01

    For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Volta's electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm-2 under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed.

  16. Tribological Properties of the Fe-Al-Cr Alloyed Layer by Double Glow Plasma Surface Metallurgy

    NASA Astrophysics Data System (ADS)

    Luo, Xixi; Yao, Zhengjun; Zhang, Pingze; Zhou, Keyin; Wang, Zhangzhong

    2016-09-01

    A Fe-Al-Cr alloyed layer was deposited onto the surface of Q235 low-carbon steel via double glow plasma surface metallurgy (DGPSM) to improve the steel's wear resistance. After the DGPSM treatment, the Fe-Al-Cr alloyed layer grown on the Q235 low-carbon steel was homogeneous and compact and had a thickness of 25 µm. The layer was found to be metallurgically adhered to the substrate. The frictional coefficient and specific wear rate of the sample with a Fe-Al-Cr alloyed layer (treated sample) were both lower than those of the bare substrate (untreated sample) at the measured temperatures (25, 250 and 450 °C). The results indicated that the substrate and the alloyed layer suffered oxidative wear and abrasive wear, respectively, and that the treated samples exhibited much better tribological properties than did the substrate. The formation of Fe2AlCr, Fe3Al(Cr), FeAl(Cr), Fe(Cr) sosoloid and Cr23C6 phases in the alloyed layer dramatically enhanced the wear resistance of the treated sample. In addition, the alloyed layer's oxidation film exhibited a self-healing capacity with lubrication action that also contributed to the improvement of the wear resistance at high temperature. In particular, at 450 °C, the specific wear rate of treated sample was 2.524 × 10-4 mm3/N m, which was only 45.2% of the untreated sample.

  17. Boosted output performance of triboelectric nanogenerator via electric double layer effect

    PubMed Central

    Chun, Jinsung; Ye, Byeong Uk; Lee, Jae Won; Choi, Dukhyun; Kang, Chong-Yun; Kim, Sang-Woo; Wang, Zhong Lin; Baik, Jeong Min

    2016-01-01

    For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Volta's electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm−2 under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed. PMID:27703165

  18. Boosted output performance of triboelectric nanogenerator via electric double layer effect.

    PubMed

    Chun, Jinsung; Ye, Byeong Uk; Lee, Jae Won; Choi, Dukhyun; Kang, Chong-Yun; Kim, Sang-Woo; Wang, Zhong Lin; Baik, Jeong Min

    2016-10-05

    For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Volta's electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm(-2) under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed.

  19. Nitrogen-enriched, double-shelled carbon/layered double hydroxide hollow microspheres for excellent electrochemical performance

    NASA Astrophysics Data System (ADS)

    Xu, Jie; He, Fei; Gai, Shili; Zhang, Shenghuan; Li, Lei; Yang, Piaoping

    2014-08-01

    A unique, double-shelled, hollow, carbon-based composite with enriched nitrogen has been prepared through a facile and versatile synthetic strategy. The hierarchical composite employs the nitrogen-enriched carbon hollow sphere as an interior shell and intercrossed Ni/Al layered double hydroxide (LDH) nanosheets as an exterior shell. The obtained N-C@LDH hollow microspheres (HMS) have high nitrogen enrichment, large specific surface area (337 m2 g-1), and uniform and open mesoporous structure. Taking advantage of these characteristics, the composite exhibits obviously superior capacitive behavior, including high specific capacitance, excellent rate capability and good cycling stability, compared with nitrogen-free carbon@LDH composite and hollow LDH without carbon shell. The composite displays high specific capacitance of 1711.51 F g-1 at a current density of 1 A g-1. In particular, the high specific capacitance can be kept to 997.3 F g-1 at a high current density of 10 A g-1, which still retains 94.97% of the initial specific capacitance after 500 cycles at this high current density. This N-enriched, hollow carbon/LDH composite can be expected to be a promising electrode material for electrochemical capacitors due to its high electrochemical performance.A unique, double-shelled, hollow, carbon-based composite with enriched nitrogen has been prepared through a facile and versatile synthetic strategy. The hierarchical composite employs the nitrogen-enriched carbon hollow sphere as an interior shell and intercrossed Ni/Al layered double hydroxide (LDH) nanosheets as an exterior shell. The obtained N-C@LDH hollow microspheres (HMS) have high nitrogen enrichment, large specific surface area (337 m2 g-1), and uniform and open mesoporous structure. Taking advantage of these characteristics, the composite exhibits obviously superior capacitive behavior, including high specific capacitance, excellent rate capability and good cycling stability, compared with nitrogen

  20. Carbon sequestration monitoring with acoustic double-difference waveform inversion: A case study on SACROC walkaway VSP data

    SciTech Connect

    Huang, Lianjie; Fehler, Michael; Malcolm, Alison; Yang, Di

    2011-01-01

    Geological carbon sequestration involves large-scale injection of carbon dioxide into underground geologic formations and is considered as a potential approach for mitigating global warming. Changes in reservoir properties resulting from the CO{sub 2} injection and migration can be characterized using waveform inversions of time-lapse seismic data. The conventional approach for analysis using waveform tomography is to take the difference of the images obtained using baseline and subsequent time-lapse datasets that are inverted independently. By contrast, double-difference waveform inversion uses timelapse seismic datasets to jointly invert for reservoir changes. We apply this method to a field time-lapse walkaway VSP data set acquired in 2008 and 2009 for monitoring CO{sub 2} injection at an enhanced oil recovery field at SACROC, Texas. The double-difference waveform inversion gives a cleaner and more easily interpreted image of reservoir changes, as compared to that obtained with the conventional scheme. Our results from the applicatoin of acoustic double-difference waveform tomography shows some zones with decreased P-wave velocity within the reservoir due to CO{sub 2} injection and migration.

  1. Double-Layered Lateral Meniscus in an 8-Year-Old Child: Report of a Rare Case

    PubMed Central

    Kubo, Mitsuhiko; Imai, Shinji

    2016-01-01

    Reports of congenital abnormalities of the lateral meniscus include discoid meniscus, accessory meniscus, double-layered meniscus, and ring-shaped meniscus. Particularly, only a few cases of double-layered meniscus have been reported. We report a case of double-layered lateral meniscus, in which an additional semicircular meniscus was observed under the normal lateral meniscus. The accessory hemimeniscus was resected by means of arthroscopic surgery. This case demonstrates an interesting and extremely rare anatomical abnormality of the lateral meniscus. PMID:27833770

  2. Unstacked double-layer templated graphene for high-rate lithium-sulphur batteries.

    PubMed

    Zhao, Meng-Qiang; Zhang, Qiang; Huang, Jia-Qi; Tian, Gui-Li; Nie, Jing-Qi; Peng, Hong-Jie; Wei, Fei

    2014-03-03

    Preventing the stacking of graphene is essential to exploiting its full potential in energy-storage applications. The introduction of spacers into graphene layers always results in a change in the intrinsic properties of graphene and/or induces complexity at the interfaces. Here we show the synthesis of an intrinsically unstacked double-layer templated graphene via template-directed chemical vapour deposition. The as-obtained graphene is composed of two unstacked graphene layers separated by a large amount of mesosized protuberances and can be used for high-power lithium-sulphur batteries with excellent high-rate performance. Even after 1,000 cycles, high reversible capacities of ca. 530 mA h g(-1) and 380 mA h g(-1) are retained at 5 C and 10 C, respectively. This type of double-layer graphene is expected to be an important platform that will enable the investigation of stabilized three-dimensional topological porous systems and demonstrate the potential of unstacked graphene materials for advanced energy storage, environmental protection, nanocomposite and healthcare applications.

  3. Unstacked double-layer templated graphene for high-rate lithium-sulphur batteries

    NASA Astrophysics Data System (ADS)

    Zhao, Meng-Qiang; Zhang, Qiang; Huang, Jia-Qi; Tian, Gui-Li; Nie, Jing-Qi; Peng, Hong-Jie; Wei, Fei

    2014-03-01

    Preventing the stacking of graphene is essential to exploiting its full potential in energy-storage applications. The introduction of spacers into graphene layers always results in a change in the intrinsic properties of graphene and/or induces complexity at the interfaces. Here we show the synthesis of an intrinsically unstacked double-layer templated graphene via template-directed chemical vapour deposition. The as-obtained graphene is composed of two unstacked graphene layers separated by a large amount of mesosized protuberances and can be used for high-power lithium-sulphur batteries with excellent high-rate performance. Even after 1,000 cycles, high reversible capacities of ca. 530 mA h g-1 and 380 mA h g-1 are retained at 5 C and 10 C, respectively. This type of double-layer graphene is expected to be an important platform that will enable the investigation of stabilized three-dimensional topological porous systems and demonstrate the potential of unstacked graphene materials for advanced energy storage, environmental protection, nanocomposite and healthcare applications.

  4. Tungstocobaltate-pillared layered double hydroxides: Preparation, characterization, magnetic and catalytic properties

    SciTech Connect

    Wei Xiaocui; Fu Youzhi; Xu Lin Li Fengyan; Bi Bo; Liu Xizheng

    2008-06-15

    A new polyoxometalate anion-pillared layered double hydroxide (LDH) was prepared by aqueous ion exchange of a Mg-Al LDH precursor in nitrate form with the tungstocobaltate anions [CoW{sub 12}O{sub 40}]{sup 5-}. The physicochemical properties of the product were characterized by the methods of powder X-ray diffraction, elemental analysis, infrared spectroscopy, thermogravimetric analysis and cyclic voltammetry. It was confirmed that [CoW{sub 12}O{sub 40}]{sup 5-} was intercalated between the brucite-type layers of the LDHs without a change in the structure. Magnetic measurement shows the occurrence of antiferromagnetic interactions between the magnetic centers. The investigation of catalytic performance for this sample exhibits high activity for the oxidation of benzaldehyde by hydrogen peroxide. - Graphical abstract: A tungstocobaltate anion [CoW{sub 12}O{sub 40}]{sup 5-} pillared layered double hydroxide (LDH) was prepared by aqueous ion exchange with a Mg-Al LDH precursor in nitrate form, demonstrating that [CoW{sub 12}O{sub 40}]{sup 5-} was intercalated between the brucite-type layers of the LDHs without change in structure. Magnetic measurement shows the occurrence of antiferromagnetic interactions between the magnetic centers. The investigation of catalytic performance for this sample exhibits high activity for the oxidation of benzaldehyde by hydrogen peroxide.

  5. Structural design of a double-layered porous hydrogel for effective mass transport.

    PubMed

    Kim, Hyejeong; Kim, Hyeon Jeong; Huh, Hyung Kyu; Hwang, Hyung Ju; Lee, Sang Joon

    2015-03-01

    Mass transport in porous materials is universal in nature, and its worth attracts great attention in many engineering applications. Plant leaves, which work as natural hydraulic pumps for water uptake, have evolved to have the morphological structure for fast water transport to compensate large water loss by leaf transpiration. In this study, we tried to deduce the advantageous structural features of plant leaves for practical applications. Inspired by the tissue organization of the hydraulic pathways in plant leaves, analogous double-layered porous models were fabricated using agarose hydrogel. Solute transport through the hydrogel models with different thickness ratios of the two layers was experimentally observed. In addition, numerical simulation and theoretical analysis were carried out with varying porosity and thickness ratio to investigate the effect of structural factors on mass transport ability. A simple parametric study was also conducted to examine unveiled relations between structural factors. As a result, the porosity and thickness ratio of the two layers are found to govern the mass transport ability in double-layered porous materials. The hydrogel models with widely dispersed pores at a fixed porosity, i.e., close to a homogeneously porous structure, are mostly turned out to exhibit fast mass transport. The present results would provide a new framework for fundamental design of various porous structures for effective mass transport.

  6. Tris(hydroxymethyl)aminomethane modified layered double hydroxides greatly facilitate polyoxometalate intercalation.

    PubMed

    Chen, Yang; Yan, Dongpeng; Song, Yu-Fei

    2014-10-21

    Polyoxometalate (POM) intercalation to layered double hydroxides (LDHs) has been greatly restricted by the geometry, charge and size of POMs. We report herein, for the first time, the intercalation of Na3[PW12O40]·15H2O into tris(hydroxymethyl)-aminomethane (Tris) modified layered double hydroxides (Tris-LDH-CO3) using an ion exchange method, resulting in the formation of novel intercalated Tris-LDH-PW12 under ambient conditions without the necessity of degassing CO2. Theoretical calculations show the decreased energy and the slightly distorted LDH layer after Tris modification, indicating that the Tris-modified LDH layers greatly facilitate the intercalation of PW12. Further application of Tris-LDH-PW12 for oxygenation of sulfides shows highly efficient and selective catalytic activities under mild conditions. The Tris-LDH-PW12 can be easily recovered and reused for more than 10 times without any obvious decrease of reactivity. This opens a completely new pathway for engineering POM-LDH advanced functional materials.

  7. Investigation of the superconducting proximity effect (SPE) and magnetic dead layers (MDL) in thin film double layers

    NASA Astrophysics Data System (ADS)

    Tateishi, Go

    When a thin superconducting film (S film) is condensed onto a thin normal conducting film (N film), the first layers of the S film loose their superconductivity. This phenomenon is generally called the "superconducting proximity effect (SPE)". As an investigation of SPE we focus on the transition temperature of extremely thin NS double layers in the thin regime. Normal metal is condensed on top of insulating Sb, then Pb is deposited on it in small steps. The transition temperature is plotted in an inverse Tc-reduction 1/Delta T c =1/(Ts - Tc) versus Pb thickness graph. To compare our experimental results with the theoretical prediction, a numerical calculation of the SN double layer is performed by our group using the linear gap equation. As a result, there are large discrepancies between the experimental and theoretical results generally. The results of the NS double layers can be divided into three groups in terms of their discrepancies between experiment and theory.(1) Non-coupling (Tc = 0 K): N= Mg, Ag, Cu, Au. There are large deviations between experiment and theory by a factor to the order of 2.5. (2) Weak coupling (Tc is low (< 2.5 K)) : N=Cd, Zn, Al. Deviation is present, but only by a factor of 1.5. (3) Intermediate coupling (T c is around half of Pb's (≈ 4.5 K)) : N=In, Sn. The experimental results agree with the theory. Next, we examine the detection of the magnetic dead layer (MDL) of Ni thin films in terms of the anomalous Hall effect (AHE) with several non-magnetic metal substrates. In our results, when Ni film is contact with a polyvalent metal substrate film, the sandwich film has around 2 to 3.5 at.lay. of magnetic dead layers. However we have not observed the magnetic dead Ni layers with the alkali and noble metal substrate film. Finally, we revisit the Pb/Ni system to measure the magnetic scattering of Ni with the method of Weak Localization (WL) to compare with the dephasing rate due to the Tc-reduction. In this series, we use only very thin

  8. Internal gravity-shear waves in the atmospheric boundary layer from acoustic remote sensing data

    NASA Astrophysics Data System (ADS)

    Lyulyukin, V. S.; Kallistratova, M. A.; Kouznetsov, R. D.; Kuznetsov, D. D.; Chunchuzov, I. P.; Chirokova, G. Yu.

    2015-03-01

    The year-round continuous remote sounding of the atmospheric boundary layer (ABL) by means of the Doppler acoustic radar (sodar) LATAN-3 has been performed at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, since 2008. A visual analysis of sodar echograms for four years revealed a large number of wavelike patterns in the intensity field of a scattered sound signal. Similar patterns were occasionally identified before in sodar, radar, and lidar sounding data. These patterns in the form of quasi-periodic inclined stripes, or cat's eyes, arise under stable stratification and significant vertical wind shears and result from the loss of the dynamic stability of the flow. In the foreign literature, these patterns, which we call internal gravity-shear waves, are often associated with Kelvin-Helmholtz waves. In the present paper, sodar echograms are classified according to the presence or absence of wavelike patterns, and a statistical analysis of the frequency of their occurrence by the year and season was performed. A relationship between the occurrence of the patterns and wind shear and between the wave length and amplitude was investigated. The criteria for the identification of gravity-shear waves, meteorological conditions of their excitation, and issues related to their observations were discussed.

  9. The role of buffer layers and double windows layers in a solar cell CZTS performances

    NASA Astrophysics Data System (ADS)

    Mebarkia, C.; Dib, D.; Zerfaoui, H.; Belghit, R.

    2016-07-01

    In the overall context of the diversification of the use of natural resources, the use of renewable energy including solar photovoltaic has become increasingly indispensable. As such, the development of a new generation of photovoltaic cells based on CuZnSnS4 (CZTS) looks promising. Cu2ZnSnS4 (CZTS) is a new film absorber, with good physical properties (band gap energy 1.4-1.6 eV with a large absorption coefficient over 104 cm-1). Indeed, the performance of these cells exceeded 30% in recent years. In the present paper, our work based on modeling and numerical simulation, we used SCAPS to study the performance of solar cells based on Cu2ZnSnS4 (CZTS) and thus evaluate the electrical efficiency η for typical structures of n-ZnO:Al / i-ZnO / n-CdS / p-CZTS and n-ITO / n-ZnO:Al / n-CdS /p-CZTS. Furthermore, the influence of the change of CdS by ZnSeand In2S3buffer layer was treated in this paper.

  10. Enhancement of proton acceleration field in laser double-layer target interaction

    SciTech Connect

    Gu, Y. J.; Kong, Q.; Li, X. F.; Yu, Q.; Wang, P. X.; Kawata, S.; Izumiyama, T.; Ma, Y. Y.

    2013-07-15

    A mechanism is proposed to enhance a proton acceleration field in laser plasma interaction. A double-layer plasma with different densities is illuminated by an intense short pulse. Electrons are accelerated to a high energy in the first layer by the wakefield. The electrons accelerated by the laser wakefield induce the enhanced target normal sheath (TNSA) and breakout afterburner (BOA) accelerations through the second layer. The maximum proton energy reaches about 1 GeV, and the total charge with an energy higher than 100 MeV is about several tens of μC/μm. Both the acceleration gradient and laser energy transfer efficiency are higher than those in single-target-based TNSA or BOA. The model has been verified by 2.5D-PIC simulations.

  11. Enhancement of proton acceleration field in laser double-layer target interaction

    NASA Astrophysics Data System (ADS)

    Gu, Y. J.; Kong, Q.; Kawata, S.; Izumiyama, T.; Li, X. F.; Yu, Q.; Wang, P. X.; Ma, Y. Y.

    2013-07-01

    A mechanism is proposed to enhance a proton acceleration field in laser plasma interaction. A double-layer plasma with different densities is illuminated by an intense short pulse. Electrons are accelerated to a high energy in the first layer by the wakefield. The electrons accelerated by the laser wakefield induce the enhanced target normal sheath (TNSA) and breakout afterburner (BOA) accelerations through the second layer. The maximum proton energy reaches about 1 GeV, and the total charge with an energy higher than 100 MeV is about several tens of μC/μm. Both the acceleration gradient and laser energy transfer efficiency are higher than those in single-target-based TNSA or BOA. The model has been verified by 2.5D-PIC simulations.

  12. A double-layer based model of ion confinement in electron cyclotron resonance ion source

    SciTech Connect

    Mascali, D. Neri, L.; Celona, L.; Castro, G.; Gammino, S.; Ciavola, G.; Torrisi, G.; Sorbello, G.

    2014-02-15

    The paper proposes a new model of ion confinement in ECRIS, which can be easily generalized to any magnetic configuration characterized by closed magnetic surfaces. Traditionally, ion confinement in B-min configurations is ascribed to a negative potential dip due to superhot electrons, adiabatically confined by the magneto-static field. However, kinetic simulations including RF heating affected by cavity modes structures indicate that high energy electrons populate just a thin slab overlapping the ECR layer, while their density drops down of more than one order of magnitude outside. Ions, instead, diffuse across the electron layer due to their high collisionality. This is the proper physical condition to establish a double-layer (DL) configuration which self-consistently originates a potential barrier; this “barrier” confines the ions inside the plasma core surrounded by the ECR surface. The paper will describe a simplified ion confinement model based on plasma density non-homogeneity and DL formation.

  13. Double-Layer Magnetic Nanoparticle-Embedded Silica Particles for Efficient Bio-Separation

    PubMed Central

    Kang, Homan; Cho, Hong-Jun; Park, Sung-Jun; Yang, Jin-Kyoung; Kim, Sehoon; Kim, Hyung-Mo; Jun, Bong-Hyun; Lee, Yoon-Sik

    2015-01-01

    Superparamagnetic Fe3O4 nanoparticles (NPs) based nanomaterials have been exploited in various biotechnology fields including biomolecule separation. However, slow accumulation of Fe3O4 NPs by magnets may limit broad applications of Fe3O4 NP-based nanomaterials. In this study, we report fabrication of Fe3O4 NPs double-layered silica nanoparticles (DL MNPs) with a silica core and highly packed Fe3O4 NPs layers. The DL MNPs had a superparamagnetic property and efficient accumulation kinetics under an external magnetic field. Moreover, the magnetic field-exposed DL MNPs show quantitative accumulation, whereas Fe3O4 NPs single-layered silica nanoparticles (SL MNPs) and silica-coated Fe3O4 NPs produced a saturated plateau under full recovery of the NPs. DL MNPs are promising nanomaterials with great potential to separate and analyze biomolecules. PMID:26599084

  14. Double-Layer Magnetic Nanoparticle-Embedded Silica Particles for Efficient Bio-Separation.

    PubMed

    Kyeong, San; Jeong, Cheolhwan; Kang, Homan; Cho, Hong-Jun; Park, Sung-Jun; Yang, Jin-Kyoung; Kim, Sehoon; Kim, Hyung-Mo; Jun, Bong-Hyun; Lee, Yoon-Sik

    2015-01-01

    Superparamagnetic Fe3O4 nanoparticles (NPs) based nanomaterials have been exploited in various biotechnology fields including biomolecule separation. However, slow accumulation of Fe3O4 NPs by magnets may limit broad applications of Fe3O4 NP-based nanomaterials. In this study, we report fabrication of Fe3O4 NPs double-layered silica nanoparticles (DL MNPs) with a silica core and highly packed Fe3O4 NPs layers. The DL MNPs had a superparamagnetic property and efficient accumulation kinetics under an external magnetic field. Moreover, the magnetic field-exposed DL MNPs show quantitative accumulation, whereas Fe3O4 NPs single-layered silica nanoparticles (SL MNPs) and silica-coated Fe3O4 NPs produced a saturated plateau under full recovery of the NPs. DL MNPs are promising nanomaterials with great potential to separate and analyze biomolecules.

  15. Control of boundary layer transition location and plate vibration in the presence of an external acoustic field

    NASA Technical Reports Server (NTRS)

    Maestrello, L.; Grosveld, F. W.

    1991-01-01

    The experiment is aimed at controlling the boundary layer transition location and the plate vibration when excited by a flow and an upstream sound source. Sound has been found to affect the flow at the leading edge and the response of a flexible plate in a boundary layer. Because the sound induces early transition, the panel vibration is acoustically coupled to the turbulent boundary layer by the upstream radiation. Localized surface heating at the leading edge delays the transition location downstream of the flexible plate. The response of the plate excited by a turbulent boundary layer (without sound) shows that the plate is forced to vibrate at different frequencies and with different amplitudes as the flow velocity changes indicating that the plate is driven by the convective waves of the boundary layer. The acoustic disturbances induced by the upstream sound dominate the response of the plate when the boundary layer is either turbulent or laminar. Active vibration control was used to reduce the sound induced displacement amplitude of the plate.

  16. Surface plasmon dispersion engineering via double-metallic AU/AG layers for nitride light-emitting diodes

    DOEpatents

    Tansu, Nelson; Zhao, Hongping; Zhang, Jing; Liu, Guangyu

    2014-04-01

    A double-metallic deposition process is used whereby adjacent layers of different metals are deposited on a substrate. The surface plasmon frequency of a base layer of a first metal is tuned by the surface plasmon frequency of a second layer of a second metal formed thereon. The amount of tuning is dependent upon the thickness of the metallic layers, and thus tuning can be achieved by varying the thicknesses of one or both of the metallic layers. In a preferred embodiment directed to enhanced LED technology in the green spectrum regime, a double-metallic Au/Ag layer comprising a base layer of gold (Au) followed by a second layer of silver (Ag) formed thereon is deposited on top of InGaN/GaN quantum wells (QWs) on a sapphire/GaN substrate.

  17. Observations indicative of rain-induced double diffusion in the ocean surface boundary layer

    NASA Astrophysics Data System (ADS)

    Walesby, K.; Vialard, J.; Minnett, P. J.; Callaghan, A. H.; Ward, B.

    2015-05-01

    Double diffusion can result in the formation of thermohaline staircases, typically observed in the ocean interior. The observations presented here were acquired in the ocean surface boundary layer with the autonomous microstructure Air-Sea Interaction Profiler. An intense rain event (rainfall rates of up to 35 mm/h) resulted in cooler, fresher water (up to 0.15 practical salinity unit (psu) over the upper 7-10 m) overlaying warmer, saltier water, a situation potentially conducive to double-diffusive mixing. Although not as crisp as interfaces in the interior ocean because of elevated background mixing, a total of 303 thermohaline interfaces were detected within and at the base of the fresh layer, with mean changes in temperature (T) and salinity (S) across interfaces of 20 × 10-3∘C and 22 × 10-3 psu, respectively. These results call for new studies to disambiguate whether such interfaces are formed through double-diffusive mixing or shear instabilities and understand any long-term impacts on near-surface stratification.

  18. On the Acousto-Elastic Behaviour of Double-Wall Panels with a Viscothermal Air Layer

    NASA Astrophysics Data System (ADS)

    BASTEN, T. G. H.; VAN DER HOOGT, P. J. M.; SPIERING, R. M. E. J.; TIJDEMAN, H.

    2001-06-01

    In this paper, an analytical two-dimensional model is presented for the acousto-elastic behaviour of double-wall panels with a thin viscothermal air layer. The model for the air is based on the low reduced frequency solution as introduced by Beltman (1998 Ph.D. Thesis, University of Twente; 1999 Journal of Sound and Vibration227, (Part I), 555-586;227 (Part II), 587-609; Beltman et al., 1997 Journal of Sound and Vibration206 , 217-241; 1998 Journal of Sound and Vibration216, 159-185) [1-5] and includes, apart from inertia and compressibility, the effects of viscosity and thermal conductivity. With the analytical model eigenfrequencies were determined and response and transmission calculations were performed. It is shown that high damping coefficients for double-wall panels can be obtained by using the viscous characteristics of the fluid layer. The model makes it possible to conduct parameter analyses very easily and efficiently, which is important for design studies. Furthermore, the model gives exact results for both the vibrational behaviour and the sound transmission characteristics of double-wall panels which can be used to validate numerical codes.

  19. Results from long-term detection of mixing layer height: ceilometer and comparison with Radio-Acoustic Sounding System

    NASA Astrophysics Data System (ADS)

    Schäfer, Klaus; Emeis, Stefan; Jahn, Carsten; Tuma, Michael; Münkel, Christoph; Suppan, Peter

    2012-11-01

    The mixing layer height (MLH) is an important factor which influences exchange processes of ground level emissions. The continuous knowledge of MLH is supporting the understanding of processes directing air quality. If the MLH is located near to the ground, which occurs mainly during winter and night-time, air pollution can be high due to a strongly limited air mass dilution. Since 2006 different methods for long-term continuous remote sensing of mixing layer height (MLH) are operated in Augsburg. The Vaisala ceilometers LD40 and CL31 are used which are eye-safe commercial mini-lidar systems. The ceilometer measurements provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the borders of mixed layers. Special software for these ceilometers provides routine retrievals of lower atmosphere layering from vertical profiles of laser backscatter data. The radiosonde data from the station Oberschleissheim near Munich (about 50 km away from Augsburg city) are also used for MLH determination. The profile behavior of relative humidity (strong decrease) and virtual potential temperature (inversion) of the radiosonde agree mostly well with the MLH indication from ceilometer laser backscatter density gradients. A RASS (Radio-Acoustic Sounding System) from Metek is applied which detects the height of a turbulent layer characterized by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component as well as the vertical temperature profile from the detection of acoustic signal propagation and thus temperature inversions which mark atmospheric layers. These data of RASS measurements are the input for a software-based determination of MLH. A comparison of the results of the remote sensing methods during simultaneous measurements was performed. The information content of the different remote sensing instruments for MLH in dependence from different weather classes was

  20. Capacitance of the double layer formed at the metal/ionic-conductor interface: how large can it be?

    PubMed

    Skinner, Brian; Loth, M S; Shklovskii, B I

    2010-03-26

    The capacitance of the double layer formed at a metal/ionic-conductor interface can be remarkably large, so that the apparent width of the double layer is as small as 0.3 A. Mean-field theories fail to explain such large capacitance. We propose an alternate theory of the ionic double layer which allows for the binding of discrete ions to their image charges in the metal. We show that at small voltages the capacitance of the double layer is limited only by the weak dipole-dipole repulsion between bound ions, and is therefore very large. At large voltages the depletion of bound ions from one of the capacitor electrodes triggers a collapse of the capacitance to the mean-field value.

  1. Synthesis, characterization, and antimicrobial properties of novel double layer nanocomposite electrospun fibers for wound dressing applications

    PubMed Central

    Hassiba, Alaa J; El Zowalaty, Mohamed E; Webster, Thomas J; Abdullah, Aboubakr M; Nasrallah, Gheyath K; Khalil, Khalil Abdelrazek; Luyt, Adriaan S; Elzatahry, Ahmed A

    2017-01-01

    Herein, novel hybrid nanomaterials were developed for wound dressing applications with antimicrobial properties. Electrospinning was used to fabricate a double layer nanocomposite nanofibrous mat consisting of an upper layer of poly(vinyl alcohol) and chitosan loaded with silver nanoparticles (AgNPs) and a lower layer of polyethylene oxide (PEO) or polyvinylpyrrolidone (PVP) nanofibers loaded with chlorhexidine (as an antiseptic). The top layer containing AgNPs, whose purpose was to protect the wound site against environmental germ invasion, was prepared by reducing silver nitrate to its nanoparticulate form through interaction with chitosan. The lower layer, which would be in direct contact with the injured site, contained the antibiotic drug needed to avoid wound infections which would otherwise interfere with the healing process. Initially, the upper layer was electrospun, followed sequentially by electrospinning the second layer, creating a bilayer nanofibrous mat. The morphology of the nanofibrous mats was studied by scanning electron microscopy and transmission electron microscopy, showing successful nanofiber production. X-ray diffraction confirmed the reduction of silver nitrate to AgNPs. Fourier transform infrared spectroscopy showed a successful incorporation of the material used in the produced nanofibrous mats. Thermal studies carried out by thermogravimetric analysis indicated that the PVP–drug-loaded layer had the highest thermal stability in comparison to other fabricated nanofibrous mats. Antimicrobial activities of the as-synthesized nanofibrous mats against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans were determined using disk diffusion method. The results indicated that the PEO–drug-loaded mat had the highest antibacterial activity, warranting further attention for numerous wound-healing applications. PMID:28356737

  2. Fast Response and High Sensitivity ZnO/glass Surface Acoustic Wave Humidity Sensors Using Graphene Oxide Sensing Layer

    PubMed Central

    Xuan, Weipeng; He, Mei; Meng, Nan; He, Xingli; Wang, Wenbo; Chen, Jinkai; Shi, Tianjin; Hasan, Tawfique; Xu, Zhen; Xu, Yang; Luo, J. K.

    2014-01-01

    We report ZnO/glass surface acoustic wave (SAW) humidity sensors with high sensitivity and fast response using graphene oxide sensing layer. The frequency shift of the sensors is exponentially correlated to the humidity change, induced mainly by mass loading effect rather than the complex impedance change of the sensing layer. The SAW sensors show high sensitivity at a broad humidity range from 0.5%RH to 85%RH with < 1 sec rise time. The simple design and excellent stability of our GO-based SAW humidity sensors, complemented with full humidity range measurement, highlights their potential in a wide range of applications. PMID:25425458

  3. Fast Response and High Sensitivity ZnO/glass Surface Acoustic Wave Humidity Sensors Using Graphene Oxide Sensing Layer

    NASA Astrophysics Data System (ADS)

    Xuan, Weipeng; He, Mei; Meng, Nan; He, Xingli; Wang, Wenbo; Chen, Jinkai; Shi, Tianjin; Hasan, Tawfique; Xu, Zhen; Xu, Yang; Luo, J. K.

    2014-11-01

    We report ZnO/glass surface acoustic wave (SAW) humidity sensors with high sensitivity and fast response using graphene oxide sensing layer. The frequency shift of the sensors is exponentially correlated to the humidity change, induced mainly by mass loading effect rather than the complex impedance change of the sensing layer. The SAW sensors show high sensitivity at a broad humidity range from 0.5%RH to 85%RH with < 1 sec rise time. The simple design and excellent stability of our GO-based SAW humidity sensors, complemented with full humidity range measurement, highlights their potential in a wide range of applications.

  4. Fast response and high sensitivity ZnO/glass surface acoustic wave humidity sensors using graphene oxide sensing layer.

    PubMed

    Xuan, Weipeng; He, Mei; Meng, Nan; He, Xingli; Wang, Wenbo; Chen, Jinkai; Shi, Tianjin; Hasan, Tawfique; Xu, Zhen; Xu, Yang; Luo, J K

    2014-11-26

    We report ZnO/glass surface acoustic wave (SAW) humidity sensors with high sensitivity and fast response using graphene oxide sensing layer. The frequency shift of the sensors is exponentially correlated to the humidity change, induced mainly by mass loading effect rather than the complex impedance change of the sensing layer. The SAW sensors show high sensitivity at a broad humidity range from 0.5%RH to 85%RH with < 1 sec rise time. The simple design and excellent stability of our GO-based SAW humidity sensors, complemented with full humidity range measurement, highlights their potential in a wide range of applications.

  5. Spin transport in tantalum studied using magnetic single and double layers

    NASA Astrophysics Data System (ADS)

    Montoya, Eric; Omelchenko, Pavlo; Coutts, Chris; Lee-Hone, Nicholas R.; Hübner, René; Broun, David; Heinrich, Bret; Girt, Erol

    2016-08-01

    We report on spin transport in sputter-grown Ta films measured by ferromagnetic resonance. Spin diffusion length and spin mixing conductance are determined from magnetic damping measurements for a varying thickness of Ta layer 0 ≤dTa≤10 nm. The different boundary conditions of single- and double-magnetic-layer heterostructures Py |Ta and Py |Ta | [Py |Fe ] allow us to significantly narrow down the parameter space and test various models. We show that a common approach of using bulk resistivity value in the analysis yields inconsistent spin diffusion length and spin mixing conductance values for magnetic single- and double-layer structures. X-ray diffraction shows that bulk Ta is a combination of β -Ta and bcc-Ta . However, in the region of significant spin transport, ≲2 nm, there is an intermediate region of growth where the Ta lacks long-range structural order, as observed by transmission electron microscopy. Thickness-dependent resistivity measurements confirm that the bulk and intermediate regions have significantly different resistivity values. We find that the data can be well represented if the intermediate region resistivity value is used in the analysis. Additionally, the data can be fit if resistivity has the measured thickness dependence and spin diffusion length is restricted to be inversely proportional to resistivity. Finally, we rule out a model in which spin diffusion length is a constant, while the resistivity has the measured thickness dependence.

  6. Analytical model of LDMOS with a double step buried oxide layer

    NASA Astrophysics Data System (ADS)

    Yuan, Song; Duan, Baoxing; Cao, Zhen; Guo, Haijun; Yang, Yintang

    2016-09-01

    In this paper, a two-dimensional analytical model is established for the Buried Oxide Double Step Silicon On Insulator structure proposed by the authors. Based on the two-dimensional Poisson equation, the analytic expressions of the surface electric field and potential distributions for the device are achieved. In the BODS (Buried Oxide Double Step Silicon On Insulator) structure, the buried oxide layer thickness changes stepwise along the drift region, and the positive charge in the drift region can be accumulated at the corner of the step. These accumulated charge function as the space charge in the depleted drift region. At the same time, the electric field in the oxide layer also varies with the different drift region thickness. These variations especially the accumulated charge will modulate the surface electric field distribution through the electric field modulation effects, which makes the surface electric field distribution more uniform. As a result, the breakdown voltage of the device is improved by 30% compared with the conventional SOI structure. To verify the accuracy of the analytical model, the device simulation software ISE TCAD is utilized, the analytical values are in good agreement with the simulation results by the simulation software. That means the established two-dimensional analytical model for BODS structure is valid, and it also illustrates the breakdown voltage enhancement by the electric field modulation effect sufficiently. The established analytical models will provide the physical and mathematical basis for further analysis of the new power devices with the patterned buried oxide layer.

  7. Bipolar doping of double-layer graphene vertical heterostructures with hydrogenated boron nitride.

    PubMed

    Liu, Zhun; Wang, Ru-Zhi; Liu, Li-Min; Lau, Woon-Ming; Yan, Hui

    2015-05-07

    Using first-principles calculations, we examined the bipolar doping of double-layer graphene vertical heterostructures, which are constructed by hydrogenated boron nitride (BN) sheets sandwiched into two parallel graphene monolayers. The built-in potential difference in hydrogenated BN breaks the interlayer symmetry, resulting in the p- and n-type doping of two graphene layers at 0.83 and -0.8 eV, respectively. By tuning the interlayer spacing between the graphene and hydrogenated BN, the interfacial dipole and screening charge distribution can be significantly affected, which produces large modulations in band alignments, doping levels and tunnel barriers. Furthermore, we present an analytical model to predicate the doping level as a function of the average interlayer spacing. With large interlayer spacings, the "pillow effect" (Pauli repulsion at the highly charge overlapped interface) is diminished and the calculated Dirac point shifts are in good accordance with our prediction models. Our investigations suggest that this double-layer graphene heterostructures constructed using two-dimensional Janus anisotropic materials offer exciting opportunities for developing novel nanoscale optoelectronic and electronic devices.

  8. Measurements of energetic electrons in a Current-Free Double layer

    NASA Astrophysics Data System (ADS)

    Gulbrandsen, Njaal; Fredriksen, Ashild

    2016-09-01

    In inductively coupled helicon sources, current-free double layers (CFDL) can be formed self-consistently without external current forcing. The CFDLs are evidenced by an ion beam formed as a result of a potential drop between the source and the diffusion chamber. The electrons in the double layer play an important role in balancing the ion beam current, but apart from some observations of electron energy probability functions (EEPFs) by means of Langmuir probes, little information has up to now been obtained about the electron population. By means of an inverted retarding field energy analyzer (RFEA) we have measured for the first time the high-energy part of the electron distribution along the radial direction in the diffusion chamber. In this configuration, the RFEA repeller grid is set to a large positive potential, repelling ions and collecting electrons through the discriminator grid. We find a prominent peak of high-energy electrons up to 60 eV at the footprint of the magnetic field lines emerging from the layer near the wall of the source. This coincides with increased electron temperatures and ion densities at this position. Another small but significant distribution of electrons at energies more than 100 eV are observed within the region of the ion beam itself.

  9. Synthesis of layered double hydroxide nanosheets by coprecipitation using a T-type microchannel reactor

    SciTech Connect

    Pang, Xiujiang; Sun, Meiyu; Ma, Xiuming; Hou, Wanguo

    2014-02-15

    The synthesis of Mg{sub 2}Al–NO{sub 3} layered double hydroxide (LDH) nanosheets by coprecipitation using a T-type microchannel reactor is reported. Aqueous LDH nanosheet dispersions were obtained. The LDH nanosheets were characterized by X-ray diffraction, transmission electron microscopy, atomic force microscopy and particle size analysis, and the transmittance and viscosity of LDH nanosheet dispersions were examined. The two-dimensional LDH nanosheets consisted of 1–2 brucite-like layers and were stable for ca. 16 h at room temperature. In addition, the co-assembly between LDH nanosheets and dodecyl sulfate (DS) anions was carried out, and a DS intercalated LDH nanohybrid was obtained. To the best of our knowledge, this is the first report of LDH nanosheets being directly prepared in bulk aqueous solution. This simple, cheap method can provide naked LDH nanosheets in high quantities, which can be used as building blocks for functional materials. - Graphical abstract: Layered double hydroxide (LDH) nanosheets were synthesized by coprecipitation using a T-type microchannel reactor, and could be used as basic building blocks for LDH-based functional materials. Display Omitted - Highlights: • LDH nanosheets were synthesized by coprecipitation using a T-type microchannel reactor. • Naked LDH nanosheets were dispersed in aqueous media. • LDH nanosheets can be used as building blocks for functional materials.

  10. Heat transfer performance of a novel double-layer mini-channel heat sink

    NASA Astrophysics Data System (ADS)

    Tang, Biao; Zhou, Rui; Bai, Pengfei; Fu, Ting; Lu, Longsheng; Zhou, Guofu

    2017-03-01

    High pressure drop and significant non-uniformity in temperature distribution along the streamwise direction are still challenges to the design of mini-channel heat sink. High density mini-channel arrays with high liquid-wall contact area are usually pursued in a conventional single-layer design of heat sink, which also inevitably brings high pressure drop. A novel double-layer structured heat sink is proposed in this paper. Four heat sinks with various designs in mini-channel density and flow direction were fabricated and studied experimentally on the heat transfer performance. The single factor of heat load does not show obvious effect on the overall thermal resistance of the heat sinks. On the other hand, slight decrease in thermal resistance was found with the increase in heat load at high flow rates. Moreover, a computational fluid dynamics modeling work was conducted. The results indicate that the parallel cross-flow field regulated by the double-layer structure enhances the heat exchange in both horizontal and vertical directions and consequently gives an uniform temperature distribution and high heat transfer efficiency.

  11. Beam focusing from double subwavelength slits surrounded by Ag/SiO2/Ag tri-layer gratings

    NASA Astrophysics Data System (ADS)

    Su, Wei; Zhou, Chong; Zheng, Gaige; Li, Xiangyin

    2016-12-01

    A silver(Ag)/SiO2/Ag tri-layer grating structure with double slits for beam focusing has been proposed. Compared with the metal/dielectric double-layer grating-based structure, the focusing efficiency of our proposed structure can be greatly enhanced. Numerical simulations using the finite-different time-domain (FDTD) method verify that the focal length and deflection angle can be controlled by adjusting the refractive indexes of dielectric mediums in the two slits.

  12. A counter-charge layer in generalized solvents framework for electrical double layers in neat and hybrid ionic liquid electrolytes

    SciTech Connect

    Huang, Jingsong; Feng, Guang; Sumpter, Bobby G; Qiao, Rui; Meunier, Vincent

    2011-01-01

    Room-temperature ionic liquids (RTILs) have received significant attention as electrolytes due to a number of attractive properties such as their wide electrochemical windows. Since electrical double layers (EDLs) are the cornerstone for the applications of RTILs in electrochemical systems such as supercapacitors, it is important to develop an understanding of the structure capacitance relationships for these systems. Here we present a theoretical framework termed counter-charge layer in generalized solvents (CGS) for describing the structure and capacitance of the EDLs in neat RTILs and in RTILs mixed with different mass fractions of organic solvents. Within this framework, an EDL is made up of a counter-charge layer exactly balancing the electrode charge, and of polarized generalized solvents (in the form of layers of ion pairs, each of which has a zero net charge but has a dipole moment the ion pairs thus can be considered as a generalized solvent) consisting of all RTILs inside the system except the counter-ions in the counter-charge layer, together with solvent molecules if present. Several key features of the EDLs that originate from the strong ion ion correlation in RTILs, e.g., overscreening of electrode charge and alternating layering of counter-ions and co-ions, are explicitly incorporated into this framework. We show that the dielectric screening in EDLs is governed predominately by the polarization of generalized solvents (or ion pairs) in the EDL, and the capacitance of an EDL can be related to its microstructure with few a priori assumptions or simplifications. We use this framework to understand two interesting phenomena observed in molecular dynamics simulations of EDLs in a neat IL of 1-butyl-3- methylimidazolium tetrafluoroborate ([BMIM][BF4]) and in a mixture of [BMIM][BF4] and acetonitrile (ACN): (1) the capacitance of the EDLs in the [BMIM][BF4]/ACN mixture increases only slightly when the mass fraction of ACN in the mixture increases from zero

  13. Universal biomimetic preparation and immobilization of layered double hydroxide films and adsorption behavior

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Zhang, Wenpeng; Chen, Zilin

    2017-01-01

    Preparation and immobilization of layered double hydroxides (LDHs) film onto multiple substrates is important and challenging in functional materials fields by date. In this work, a simple and universal polydopamine (PD)-based layer-by-layer assembly strategy was developed for the immobilization of LDHs film onto surfaces such as polypropylene chip, glass slides and metal coins. The surface of substrates was firstly modified by polydopamine functionalization, and then LDHs film was synthesized via urea method and directly immobilized on the PD layer by in situ growing strategy in one step. The PD layer as well as the final LDHs film was characterized by energy dispersive X-ray spectroscopy, scanning electron microscope, infrared spectroscopy, X-ray diffraction pattern and X-ray photoelectron spectra. It has been demonstrated the formation of the dense and homogeneous nanoscaled LDHs film with 400 nm thickness. Adsorption behavior of the fabricated NiAl-LDHs film toward anionic dyes and pharmaceuticals was further assessed. To demonstrate their extensive application, fast and high efficient adsorption of anionic dyes and pharmaceuticals was achieved by NiAl-LDHs-modified polypropylene centrifugal tube.

  14. Double-layer weekly sustained release transdermal patch containing gestodene and ethinylestradiol.

    PubMed

    Gao, Yanli; Liang, Jinying; Liu, Jianping; Xiao, Yan

    2009-07-30

    The combination therapy of gestodene (GEST) and ethinylestradiol (EE) has shown advanced contraception effect and lower side effect. The present study was designed to develop a weekly sustained release matrix type transdermal patch containing GEST and EE using blends of different polymeric combinations. The multiple-layer technique was adopted in order to maintain a steady permeation flux for 7 days. The effects of polymer types, polymer ratios, permeation enhancers, drug loadings and drug ratios in different layers on the skin permeations of the drugs were evaluated using excised mice skin. Polariscope examination was carried out to observe the drug distribution behavior. The formulation with the mixture of polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) (7:1) was found to provide the regular release and propylene glycol (PG) could enhance the permeation fluxes of drugs. Double-layer transdermal drug delivery system (TDDS) could sustain the steady permeation flux of drugs for 7 days when the ratio of drug in drug release layer and drug reservoir layer was 1:4 with the identical total drug amount. The in vitro transdermal permeation fluxes were 0.377 microg/cm(2)/h and 0.092 microg/cm(2)/h, for GEST and EE respectively. The uniformity of dosage units test showed that the distribution of drugs in the matrix was homogeneous, which was further demonstrated by the polariscope result. The developed transdermal delivery system containing GEST and EE could be a promising non-oral contraceptive method.

  15. Molecular modeling of layered double hydroxide intercalated with benzoate, modeling and experiment.

    PubMed

    Kovár, Petr; Pospísil, M; Nocchetti, M; Capková, P; Melánová, Klára

    2007-08-01

    The structure of Zn4Al2 Layered Double Hydroxide intercalated with benzencarboxylate (C6H5COO-) was solved using molecular modeling combined with experiment (X-ray powder diffraction, IR spectroscopy, TG measurements). Molecular modeling revealed the arrangement of guest molecules, layer stacking, water content and water location in the interlayer space of the host structure. Molecular modeling using empirical force field was carried out in Cerius(2) modeling environment. Results of modeling were confronted with experiment that means comparing the calculated and measured diffraction pattern and comparing the calculated water content with the thermogravimetric value. Good agreement has been achieved between calculated and measured basal spacing: d(calc) = 15.3 A and d(exp) = 15.5 A. The number of water molecules per formula unit (6H2O per Zn4Al2(OH)12) obtained by modeling (i.e., corresponding to the energy minimum) agrees with the water content estimated by thermogravimetry. The long axis of guest molecules are almost perpendicular to the LDH layers, anchored to the host layers via COO- groups. Mutual orientation of benzoate ring planes in the interlayer space keeps the parquet arrangement. Water molecules are roughly arranged in planes adjacent to host layers together with COO- groups.

  16. New layered double hydroxides by prepared by the intercalation of gibbsite

    SciTech Connect

    Rees, Jennifer R.; Burden, Chloe S.; Fogg, Andrew M.

    2015-04-15

    New layered double hydroxides (LDHs) with the composition [MAl{sub 4}(OH){sub 12}]Cl{sub 2}·1.5H{sub 2}O (M=Co, Ni) have been prepared by reacting gibbsite, γ-Al(OH){sub 3}, with the appropriate chloride salt in a synthesis in which the water of crystallization is the only solvent present and fully characterized. These LDHs have been shown to undergo facile anion exchange reactions with both organic and inorganic anions at room temperature making them comparable to other LDHs in this respect. Reactions under the same conditions with CuCl{sub 2}·2H{sub 2}O and ZnCl{sub 2} failed to form the desired LDHs but those with nitrate salts did lead to the formation of the previously reported [MAl{sub 4}(OH){sub 12}](NO{sub 3}){sub 2}·1.5H{sub 2}O (M=Co, Ni) compounds. - Graphical abstract: New layered double hydroxides (LDHs) with the composition [MAl{sub 4}(OH){sub 12}]Cl{sub 2}·1.5H{sub 2}O (M=Co, Ni) have been prepared by reacting gibbsite, γ-Al(OH){sub 3}, with the appropriate chloride salt in a synthesis in which no additional solvent is used and fully characterized. These LDHs have been shown to undergo facile anion exchange reactions with both organic and inorganic anions at room temperature. - Highlights: • Synthesis of new layered double hydroxides, [MAl{sub 4}(OH){sub 12}]Cl{sub 2}·1.5H{sub 2}O (M=Co, Ni). • Demonstration of the anion exchange capacity with both organic and inorganic anions. • Demonstration of the generality of the synthesis for LDHs.

  17. Intercalation and controlled release properties of vitamin C intercalated layered double hydroxide

    SciTech Connect

    Gao, Xiaorui; Lei, Lixu; O'Hare, Dermot; Xie, Juan; Gao, Pengran; Chang, Tao

    2013-07-15

    Two drug-inorganic composites involving vitamin C (VC) intercalated in Mg–Al and Mg–Fe layered double hydroxides (LDHs) have been synthesized by the calcination–rehydration (reconstruction) method. Powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), and UV–vis absorption spectroscopy indicate a successful intercalation of VC into the interlayer galleries of the LDH host. Studies of VC release from the LDHs in deionised water and in aqueous CO{sub 3}{sup 2−} solutions imply that Mg{sub 3}Al–VC LDH is a better controlled release system than Mg{sub 3}Fe–VC LDH. Analysis of the release profiles using a number of kinetic models suggests a solution-dependent release mechanism, and a diffusion-controlled deintercalation mechanism in deionised water, but an ion exchange process in CO{sub 3}{sup 2−} solution. - Graphical abstract: Vitamin C anions have been intercalated in the interlayer space of layered double hydroxide and released in CO{sub 3}{sup 2−} solution and deionised water. - Highlights: • Vitamin C intercalated Mg–Al and Mg–Fe layered double hydroxides were prepared. • Release property of vitamin C in aqueous CO{sub 3}{sup 2−} solution is better. • Avrami-Erofe’ev and first-order models provide better fit for release results. • Diffusion-controlled and ion exchange processes occur in deionised water. • An ion exchange process occurs in CO{sub 3}{sup 2−} solution.

  18. A thin layer including a carbon material improves the rate capability of an electric double layer capacitor

    NASA Astrophysics Data System (ADS)

    Sato, Takaya; Marukane, Shoko; Morinaga, Takashi; Uemura, Taichi; Fukumoto, Kunihiro; Yamazaki, Satoshi

    2011-03-01

    We present a new method to improve the rate capability of an electric double layer capacitor (EDLC) using a thin polymer layer having a high concentration of carbon material on a current collector (CLC). A novel thermocuring coating composed of a glycol-chitosan, a pyromellitic acid and a conductive carbon powder can form stable CLC on a metal foil current collector simply by spreading and curing at 160 °C for a couple of minutes. We compared the performance of some demonstration EDLC cells using three kinds of current collector: a conventional aluminum oxide foil for EDLC, an aluminum foil and an aluminum foil with CLC. The cell with the CLC had a much higher rate capability than the cell without CLC. Only the CLC cell was able to discharge at a current density of 500C. This cell shows a slight deterioration in capacity in a high temperature, continuous charging, life test, and the CLC has a suppressing effect on the internal resistance increase of EDLCs. The use of a CLC film current collector is one of the most effective and simple methods for the improvement of EDLC rate performance. In particular, a current collector consisting of aluminum foil coupled with a CLC promises to be a low cost alternative to the aluminum oxide foil commonly used in EDLCs.

  19. Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2

    PubMed Central

    Katase, Takayoshi; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2014-01-01

    A1–xFe2–ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are antiferromagnetic (AFM) insulating phases, and they have extremely high Néel transition temperatures. However, control of carrier doping into the parent AFM insulators has been difficult due to their intrinsic phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2 insulating epitaxial film with an atomically flat surface and examined its electrostatic carrier doping using an electric double-layer transistor (EDLT) structure with an ionic liquid gate. The positive gate voltage gave a conductance modulation of three orders of magnitude at 25 K, and further induced and manipulated a phase transition; i.e., delocalized carrier generation by electrostatic doping is the origin of the phase transition. This is the first demonstration, to the authors' knowledge, of an EDLT using a Mott insulator iron selenide channel and opens a way to explore high Tc superconductivity in iron-based layered materials, where carrier doping by conventional chemical means is difficult. PMID:24591598

  20. Structure and charging kinetics of electrical double layers at large electrode voltage

    SciTech Connect

    Cagle, Clint; Feng, Guang; Qiao, Rui; Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent

    2009-01-01

    The structure and charging kinetics of electrical double layers (EDLs) at interfaces of NaCl solutions and planar electrodes are studied by molecular dynamics (MD) and Poisson Nernst Planck (PNP) simulations. Based on the MD results and prior experimental data, we show that counterion packing in planar EDLs does not reach the steric limit at electrode voltages below 1 V. In addition, we demonstrate that a PNP model, when complemented with a Stern model, can be effectively used to capture the overall charging kinetics. However, the PNP/Stern model can only give a qualitative description of the fine features of the EDL.

  1. Direct thrust measurement of a permanent magnet helicon double layer thruster

    SciTech Connect

    Takahashi, K.; Lafleur, T.; Charles, C.; Alexander, P.; Boswell, R. W.; Perren, M.; Laine, R.; Pottinger, S.; Lappas, V.; Harle, T.; Lamprou, D.

    2011-04-04

    Direct thrust measurements of a permanent magnet helicon double layer thruster have been made using a pendulum thrust balance and a high sensitivity laser displacement sensor. At the low pressures used (0.08 Pa) an ion beam is detected downstream of the thruster exit, and a maximum thrust force of about 3 mN is measured for argon with an rf input power of about 700 W. The measured thrust is proportional to the upstream plasma density and is in good agreement with the theoretical thrust based on the maximum upstream electron pressure.

  2. Post heat treatment effects on double layer metal structures for VLSI applications

    NASA Technical Reports Server (NTRS)

    Wade, T. E.; Trotter, J. D.

    1978-01-01

    The realization of high yield double layer metal systems using wet chemistry processes and the ability to extend yields beyond that attainable with wet chemistry by means of post sintering processes at temperatures below 500 C for potential applications in very large scale integration structures were studied. Yields in excess of 98% and average total contact resistance of less than 150 ohms and 200 ohms were realized for a series of 560 vias of 0.5 X 0.5 mils and 0.2 X 0.2 mils in size, respectively.

  3. Double layers in plasmas; Proceedings of the Conference, Huntsville, AL, Mar. 1986

    NASA Technical Reports Server (NTRS)

    Williams, Alton C. (Editor)

    1987-01-01

    Papers are presented on such topics as double layers (DLs) and plasma-wave resistivity in extragalactic jets; the formation of a DL leading to the critical velocity phenomenon; formation mechanisms of laboratory DLs in triple plasma devices; and linear Vlasov stability in one-dimensional DLs. Consideration is also given to weak DLs in the auroral ionosphere; the dynamical properties of very strong DLs in a triple plasma device; particle simulation of auroral DLs; a muonic X-ray laser assisted by the catalyzed fusion of deuterium and tritium; and the feasbility of measuring the nuclear reaction cross sections at energies of several keV in a target under laser compression.

  4. The Skylab barium plasma injection experiments. II - Evidence for a double layer

    NASA Technical Reports Server (NTRS)

    Wescott, E. M.; Stenbaek-Nielsen, H. C.; Hallinan, T. J.; Davis, T. N.; Peek, H. M.

    1976-01-01

    Television observations of a barium-plasma flux tube extending from near 4500 km to near 10,000 km during a magnetic substorm and dawn-sector auroral display indicated several interesting anomalous events. Beyond 5500 km, there was a rapid increase in brightness accompanied by flux-tube splitting and diffusion, leaving behind a truncated single flux tube. From the orientation of the flux tube compared with theoretical field models, the presence of a substantial field-aligned current sheet is deduced. A suggested explanation of these phenomena is given in terms of a plasma potential double layer.

  5. Experimental and Theoretical Study of Nonlinear Phenomena Related to the Double Layer Dynamics in Plasma

    SciTech Connect

    Niculescu, O.; Dimitriu, D. G.

    2010-08-04

    The periodic current bursts observed in the dynamic current-voltage characteristic of a probe in the presence of a plasma fireball in dynamic state were modeled in the frame of the scale relativity model, based on both the fractal space-time concept and the generalization of Einstein's principle of relativity to scale transformations. The double layer dynamics is described by a set of time-dependent Schroedinger-type equations and the self-structuring is given by means of the negative differential resistance. The obtained experimental and theoretical results are proven to be in very good agreement.

  6. Thin-shell wormholes with a double layer in quadratic F (R ) gravity

    NASA Astrophysics Data System (ADS)

    Eiroa, Ernesto F.; Figueroa Aguirre, Griselda

    2016-08-01

    We present a family of spherically symmetric Lorentzian wormholes in quadratic F (R ) gravity, with a thin shell of matter corresponding to the throat. At each side of the shell, the geometry has a different constant value of the curvature scalar R . The junction conditions determine the equation of state between the pressure and energy density at the throat, where a double layer is also located. We analyze the stability of the configurations under perturbations preserving the spherical symmetry. In particular, we study thin-shell wormholes with mass and charge. We find that there exist values of the parameters for which stable static solutions are possible.

  7. Voltage-tunable terahertz and infrared photodetectors based on double-graphene-layer structures

    SciTech Connect

    Ryzhii, V.; Otsuji, T.; Aleshkin, V. Ya.; Dubinov, A. A.; Ryzhii, M.; Mitin, V.; Shur, M. S.

    2014-04-21

    We propose and theoretically substantiate the concept of terahertz and infrared photodetectors using the resonant radiative transitions between graphene layers (GLs) in double-GL structures. The calculated absorption spectrum and the spectral characteristics of the photodetector responsivity exhibit sharp resonant maxima at the photon energies in a wide range. The resonant maxima can be tuned by the applied voltage. We compare the photodetector responsivity with that of the GL p-i-n photodiodes and quantum-well infrared photodetectors. Weak temperature dependences of the photocurrent and dark current enable the effective operation of the proposed photodetector at room temperature.

  8. Double layer capacitance of porous platinum electrodes in zirconia electrochemical cells

    SciTech Connect

    Robertson, N.L.; Michaels, J.N. )

    1991-05-01

    This paper reports on the capacitance of the double layer at the interface between porous platinum electrodes and yttria-stabilized zirconia measured by potential step chronoampermetry. The capacitance is independent of oxygen partial pressure and electrode potential and increases from 0.2 {mu}F/cm{sup 2} at 555{degrees}C to 1.3 {mu}F/cm{sup 2} at 695{degrees}C. These value are at least an order of magnitude smaller than capacitances extracted from the low-frequency portion of ac impedance spectra. This indicates that the capacitive behavior of platinum electrodes in zirconia cells is dominated by time-dependent faradaic processes.

  9. Effects of mixed discrete surface charges on the electrical double layer.

    PubMed

    Jiménez-Ángeles, Felipe

    2012-08-01

    Adsorption of surface coions and charge reversal are induced at the electrical double layer of a wall charged with positive and negative surface sites next to an electrolyte solution. While for the considered surface charge density these effects are found over a wide range of conditions, they are not observed for the typically employed surface models in equivalent conditions. Important consequences in electrophoresis experiments for different colloids with equal effective surface charge density are foreseen. This study is carried out by means of molecular dynamics simulations.

  10. Anion-exchange membranes derived from quaternized polysulfone and exfoliated layered double hydroxide for fuel cells

    NASA Astrophysics Data System (ADS)

    Liu, Wan; Liang, Na; Peng, Pai; Qu, Rong; Chen, Dongzhi; Zhang, Hongwei

    2017-02-01

    Layered double hydroxides (LDH) are prepared by controlling urea assisted homogeneous precipitation conditions. Morphology and crystallinity of LDHs are confirmed by X-ray diffraction and scanning electron microscope. After LDHs are incorporated into quaternized polysulfone membranes, transmission electron microscope is used to observe the exfoliated morphology of LDH sheets in the membranes. The properties of the nanocomposite membranes, including water uptake, swelling ratio, mechanical property and ionic conductivity are investigated. The nanocomposite membrane containing 5% LDH sheets shows more balanced performances, exhibiting an ionic conductivity of 2.36×10-2 S cm-1 at 60 °C.

  11. Removal of borate by coprecipitation with Mg/Al layered double hydroxide

    NASA Astrophysics Data System (ADS)

    Kurashina, Masashi; Inoue, Tatsuki; Tajima, Chihiro; Kanezaki, Eiji

    2015-03-01

    Borate has been used for various industrial products and excessive dose of boron is harmful to humans. We investigated the removal of borate by direct coprecipitation with Mg/Al layered double hydroxide. In this study, the maximum removal of boron was 90% when Mg 30 mmol and Al 15 mmol at pH = 10 were used for 498 mg/l as B. The boron adsorption isotherms could be fitted to Langmuir model. The calculated constant Ws, saturation limit of boron adsorption, is 25 ± 2 mg/g and it is larger than that of ion exchange reaction (Ws = 15±1 mg/g).

  12. Structure and thermal decomposition of sulfated β-cyclodextrin intercalated in a layered double hydroxide

    NASA Astrophysics Data System (ADS)

    Wang, Ji; Wei, Min; Rao, Guoying; Evans, David G.; Duan, Xue

    2004-01-01

    The sodium salt of hexasulfated β-cyclodextrin has been synthesized and intercalated into a magnesium-aluminum layered double hydroxide by ion exchange. The structure, composition and thermal decomposition behavior of the intercalated material have been studied by variable temperature X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma emission spectroscopy (ICP), and thermal analysis (TG-DTA) and a model for the structure has been proposed. The thermal stability of the intercalated sulfated β-cyclodextrin is significantly enhanced compared with the pure form before intercalation.

  13. Mössbauer and XRD study of intercalated CaFe-layered double hydroxides

    NASA Astrophysics Data System (ADS)

    Sipiczki, Mónika; Kuzmann, Ernő; Pálinkó, István; Homonnay, Zoltán; Sipos, Pál; Kukovecz, Ákos; Kónya, Zoltán

    2014-04-01

    N-containing fully saturated (L-prolinate) or aromatic (indole-2-carboxylate) heterocyclic anions were immobilised in CaFe-layered double hydroxide with the dehydration-rehydration method from aqueous ethanol or acetone. The structure of the resulting organic-inorganic hybrids was characterised mainly with powder X-ray diffraction and 57Fe Mössbauer spectroscopy, and as supplementary analysis scanning electron microscopy, energy dispersive X-ray spectroscopy with elemental mapping and molecular modelling were also applied. It was found that the solvent mixture used for the synthesis caused enormous difference in the interlayer spacings of the obtained inorganic-organic hybrids.

  14. DOUBLE-DIFFUSIVE INSTABILITIES OF A SHEAR-GENERATED MAGNETIC LAYER

    SciTech Connect

    Silvers, Lara J.; Proctor, Michael R. E.; Vasil, Geoffrey M.; Brummell, Nicholas H.

    2009-09-01

    Previous theoretical work has speculated about the existence of double-diffusive magnetic buoyancy instabilities of a dynamically evolving horizontal magnetic layer generated by the interaction of forced vertically sheared velocity and a background vertical magnetic field. Here, we confirm numerically that if the ratio of the magnetic to thermal diffusivities is sufficiently low then such instabilities can indeed exist, even for high Richardson number shear flows. Magnetic buoyancy may therefore occur via this mechanism for parameters that are likely to be relevant to the solar tachocline, where regular magnetic buoyancy instabilities are unlikely.

  15. Efficient deep-blue organic light-emitting diodes using double-emitting layer.

    PubMed

    Seo, Ji Hoon; Seo, Bo Min; Lee, Seok Jae; Lee, Kum Hee; Yoon, Seung Soo; Kim, Young Kwan

    2012-04-01

    Efficient deep-blue organic light-emitting diodes were demonstrated using 1,4-tetranaphthalene doped in double-emitting layers (D-EMLs) consisting of 2-methyl-9,10-di(2-naphthyl)anthracene and 4'-(dinaphthalen-2-yl)-1,1'-binaphthyl as blue hosts. The device with D-EML exhibits good confinement of holes and electrons, as well as a broad recombination zone. The optimized device showed a peak current efficiency of 3.67 cd/A, a peak external quantum efficiency of 3.97%, and Commission Internationale de L'Eclairage coordinates of (0.16, 0.10).

  16. Cobalt-based layered double hydroxides as oxygen evolving electrocatalysts in neutral electrolyte

    NASA Astrophysics Data System (ADS)

    Lin, Hong; Zhang, Ye; Wang, Gang; Li, Jian-Bao

    2012-06-01

    Co-M (M= Co, Ni, Fe, Mn) layered double hydroxides (LDHs) were successfully fabricated by a hexamethylenetetramine (HMT) pyrolysis method. Composite electrodes were made using a self-assembly fashion at inorganic/organic surface binder-free and were used to catalyze oxygen evolution reaction. Water oxidation can take place in neutral electrolyte operating with modest overpotential. The doping of other transitional metal cations affords mix valences and thus more intimate electronic interactions for reversible chemisorption of dioxygen molecules. The application of employing LDH materials in water oxidation process bodes well to facilitate future hydrogen utilization.

  17. A Spherically-Shaped PZT Thin Film Ultrasonic Transducer with an Acoustic Impedance Gradient Matching Layer Based on a Micromachined Periodically Structured Flexible Substrate

    PubMed Central

    Feng, Guo-Hua; Liu, Wei-Fan

    2013-01-01

    This paper presents the microfabrication of an acoustic impedance gradient matching layer on a spherically-shaped piezoelectric ultrasonic transducer. The acoustic matching layer can be designed to achieve higher acoustic energy transmission and operating bandwidth. Also included in this paper are a theoretical analysis of the device design and a micromachining technique to produce the novel transducer. Based on a design of a lead titanium zirconium (PZT) micropillar array, the constructed gradient acoustic matching layer has much better acoustic transmission efficiency within a 20–50 MHz operation range compared to a matching layer with a conventional quarter-wavelength thickness Parylene deposition. To construct the transducer, periodic microcavities are built on a flexible copper sheet, and then the sheet forms a designed curvature with a ball shaping. After PZT slurry deposition, the constructed PZT micropillar array is released onto a curved thin PZT layer. Following Parylene conformal coating on the processed PZT micropillars, the PZT micropillars and the surrounding Parylene comprise a matching layer with gradient acoustic impedance. By using the proposed technique, the fabricated transducer achieves a center frequency of 26 MHz and a −6 dB bandwidth of approximately 65%. PMID:24113683

  18. Acoustic characterization of void distributions across carbon-fiber composite layers

    NASA Astrophysics Data System (ADS)

    Tayong, Rostand B.; Smith, Robert A.; Pinfield, Valerie J.

    2016-02-01

    Carbon Fiber Reinforced Polymer (CFRP) composites are often used as aircraft structural components, mostly due to their superior mechanical properties. In order to improve the efficiency of these structures, it is important to detect and characterize any defects occurring during the manufacturing process, removing the need to mitigate the risk of defects through increased thicknesses of structure. Such defects include porosity, which is well-known to reduce the mechanical performance of composite structures, particularly the inter-laminar shear strength. Previous work by the authors has considered the determination of porosity distributions in a fiber-metal laminate structure [1]. This paper investigates the use of wave-propagation modeling to invert the ultrasonic response and characterize the void distribution within the plies of a CFRP structure. Finite Element (FE) simulations are used to simulate the ultrasonic response of a porous composite laminate to a typical transducer signal. This simulated response is then applied as input data to an inversion method to calculate the distribution of porosity across the layers. The inversion method is a multi-dimensional optimization utilizing an analytical model based on a normal-incidence plane-wave recursive method and appropriate mixture rules to estimate the acoustical properties of the structure, including the effects of plies and porosity. The effect of porosity is defined through an effective wave-number obtained from a scattering model description. Although a single-scattering approach is applied in this initial study, the limitations of the method in terms of the considered porous layer, percentage porosity and void radius are discussed in relation to single- and multiple-scattering methods. A comparison between the properties of the modeled structure and the void distribution obtained from the inversion is discussed. This work supports the general study of the use of ultrasound methods with inversion to

  19. Reciprocity in spatial evolutionary public goods game on double-layered network

    PubMed Central

    Kim, Jinho; Yook, Soon-Hyung; Kim, Yup

    2016-01-01

    Spatial evolutionary games have mainly been studied on a single, isolated network. However, in real world systems, many interaction topologies are not isolated but many different types of networks are inter-connected to each other. In this study, we investigate the spatial evolutionary public goods game (SEPGG) on double-layered random networks (DRN). Based on the mean-field type arguments and numerical simulations, we find that SEPGG on DRN shows very rich interesting phenomena, especially, depending on the size of each layer, intra-connectivity, and inter-connected couplings, the network reciprocity of SEPGG on DRN can be drastically enhanced through the inter-connected coupling. Furthermore, SEPGG on DRN can provide a more general framework which includes the evolutionary dynamics on multiplex networks and inter-connected networks at the same time. PMID:27503801

  20. Tailoring the properties of magnetite nanoparticles clusters by coating with double inorganic layers

    NASA Astrophysics Data System (ADS)

    Petran, Anca; Radu, Teodora; Culic, Bogdan; Turcu, Rodica

    2016-12-01

    New magnetic nanoparticles based on Fe3O4 clusters covered with a double layer of inorganic salts/oxides with high magnetization for incorporation in security materials such as security paper were synthesized. For the inorganic layers ZnO, SiO2 and BaSO4 were used. The microstructure and composition of the products were determined by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). Magnetization measurements on the obtained samples show a straightforward correlation between the saturation magnetization (Ms) and morphology of the samples. The results obtained from color parameter assessment are discussed in relation with the morphology and microstructure of the prepared samples.