NASA Astrophysics Data System (ADS)
Malashetty, M. S.; Basavaraja, D.
The effect of time-periodic temperature/gravity modulation at the onset of convection in a Boussinesq fluid-saturated anisotropic porous medium is investigated by making a linear stability analysis. Brinkman flow model with effective viscosity larger than the viscosity of the fluid is considered to give a more general theoretical result. The perturbation method is applied for computing the critical Rayleigh and wave numbers for small amplitude temperature/gravity modulation. The shift in the critical Rayleigh number is calculated as a function of frequency of the modulation, viscosity ratio, anisotropy parameter and porous parameter. We have shown that it is possible to advance or delay the onset of convection by time-periodic modulation of the wall temperature and to advance convection by gravity modulation. It is also shown that the small anisotropy parameter has a strong influence on the stability of the system. The effect of viscosity ratio, anisotropy parameter, the porous parameter and the Prandtl number is discussed.
Standing Torsional Waves in Fluid-Saturated Porous Circular Cylinder
NASA Astrophysics Data System (ADS)
Solorza, S.; Sahay, P. N.
2002-12-01
For dynamic measurement of elastic constants of a porous material saturated with viscous fluid when resonance-bar technique is applied, one also observes attenuation of the wave field. The current practice is to interpret it in terms of solid-viscosity by assuming a viscoelastic rheology for porous material. The likely mechanisms of attenuation in a fluid saturated porous material are: 1) motion of the fluid with respect to the solid frame and 2) viscous loss within the pore fluid. Therefore, it is appropriate to assume a poroelastic rheology and link the observed attenuation value to fluid properties and permeability. In the framework of poroelastic theory, the explicit formula linking attenuation to the properties of solid and fluid constituents and permeability are not worked out yet. In order to established such a link one has to workout solutions of appropriate boundary value problems in such a framework. Here, we have carried out the solution of boundary value problem associated with torsional oscillation of a finite poroelastic circular cylinder, casted in the framework of volume-averaged theory of poroelasticity. Analysing this solution by a perturbative approach we are able to develop explicit expressions for resonance frequency and attenuation for this mode of vibration. It shows how the attenuation is controlled by the permeability and the fluid properties, and how the resonance frequency drops over its value for the dry porous frame due to the effect of the fluid-mass.
Wave propagation in fluid-saturated porous media
NASA Astrophysics Data System (ADS)
Ren, Jiaxiang
The wave propagation in fluid-saturated porous media is studied by solving the Biot equations, the governing equations for the motion of the porous medium. Methods are devised to solve the Biot equations for different problems and medium models. The problem of the reflection and transmission at an interface is solved by using the eigen-analysis of the Biot equations. The displacement-stress vectors in the media on both sides of the interface are represented by corresponding upgoing and downgoing wave vectors which are then linked by the boundary conditions on the interface. The reflection and transmission coefficients are extracted from the proportionalities between the upgoing and downgoing waves. For an incident fast wave or shear wave, the reflection and transmission coefficients for the reflected and transmitted slow waves are very sensitive to frequency and interface permeability (kappasb{I}); while those for the reflected and transmitted fast waves and shear waves are not, except when incident angles are close to and greater than critical angles. For sandstones, the amplitudes of the reflected and transmitted slow waves could be several percent of the amplitude of the incident fast wave or shear wave. Higher interface permeabilities favor the generation of the slow wave. The slow waves generated at an open interface (kappasb{I}->infty) and a sealed interface (kappasb{I}=0) could be one-order different in amplitude. The reflection and transmission at an interface have been extended to the model composed of multi-layers of porous media. An algorithm based on the compact finite-difference method is developed for 2-D seismic modeling. The compact finite-difference method is used to estimate the spatial derivatives in the Biot equations, with a 6sp{th}-order accuracy. It needs fewer grid intervals to represent a mono-wavelength function than the traditional 2sp{nd}-order central-difference method. Therefore, the algorithm based on the compact finite
Double-diffusive natural convection in a fluid saturated porous cavity with a freely convecting wall
Nithiarasu, P.; Sundararajan, T.; Seetharamu, K.N.
1997-12-01
Double-diffusive natural convection in fluid saturated porous medium has been investigated using a generalized porous medium model. One of the vertical walls of the porous cavity considered is subjected to convective heat and mass transfer conditions. The results show that the flow, heat and mass transfer become sensitive to applied mass transfer coefficient in both the Darcy and non-Darcy flow regimes. It is also observed that the Sherwood number approaches a constant value as the solutal Biot number increases. Double-diffusive natural convection in fluid saturated porous medium is encountered in applications such as food processing, contaminant transport in ground water, and others.
Numerical Analysis of Velocity Dispersion in Multi-Phase Fluid-Saturated Porous Rocks
NASA Astrophysics Data System (ADS)
Chen, Xuehua; Zhong, Wenli; Gao, Gang; Zou, Wen; He, Zhenhua
2017-03-01
Seismic waves are subject to velocity dispersion when they propagate in fluid-saturated porous media. In this work, we explore the velocity dispersion behavior of P- and SV-waves in multi-phase fluid-saturated porous reservoirs while taking into account the effects of multi-phase pore fluids on the effective viscosities that control the wave-induced fluid flow. The effective viscosities associated with the hydrocarbon saturation of a synthetic sandstone reservoir saturated with different pore fluid mixtures are calculated using the Refutas model. We then analyze the frequency-dependent velocity, dispersion variation rate and characteristic frequency for different fluid saturation cases by employing Chapman's dynamic equivalent-medium theory. The results demonstrate that the hydrocarbon proportions and types in multi-phase mixed pore fluids significantly affect the magnitude and characteristic frequencies of velocity dispersion features for both the P- and S-waves. The dispersion anomalies of SV-waves are in general larger than those of the P-waves. This indicates that the velocity dispersion anomalies of SV-waves are equally sensitive to fluid saturation as the P-waves and should not be neglected. The velocities at lower frequencies (e.g., 10 and 100 Hz) within the seismic frequency range show a more remarkable decrease with increasing hydrocarbon proportion than those at higher frequency (1000 Hz). The numerical examples help to improve the understanding of the frequency-dependent AVO inversion from seismic reflection data.
Numerical Analysis of Velocity Dispersion in Multi-Phase Fluid-Saturated Porous Rocks
NASA Astrophysics Data System (ADS)
Chen, Xuehua; Zhong, Wenli; Gao, Gang; Zou, Wen; He, Zhenhua
2016-12-01
Seismic waves are subject to velocity dispersion when they propagate in fluid-saturated porous media. In this work, we explore the velocity dispersion behavior of P- and SV-waves in multi-phase fluid-saturated porous reservoirs while taking into account the effects of multi-phase pore fluids on the effective viscosities that control the wave-induced fluid flow. The effective viscosities associated with the hydrocarbon saturation of a synthetic sandstone reservoir saturated with different pore fluid mixtures are calculated using the Refutas model. We then analyze the frequency-dependent velocity, dispersion variation rate and characteristic frequency for different fluid saturation cases by employing Chapman's dynamic equivalent-medium theory. The results demonstrate that the hydrocarbon proportions and types in multi-phase mixed pore fluids significantly affect the magnitude and characteristic frequencies of velocity dispersion features for both the P- and S-waves. The dispersion anomalies of SV-waves are in general larger than those of the P-waves. This indicates that the velocity dispersion anomalies of SV-waves are equally sensitive to fluid saturation as the P-waves and should not be neglected. The velocities at lower frequencies (e.g., 10 and 100 Hz) within the seismic frequency range show a more remarkable decrease with increasing hydrocarbon proportion than those at higher frequency (1000 Hz). The numerical examples help to improve the understanding of the frequency-dependent AVO inversion from seismic reflection data.
Study of Surface Wave Propagation in Fluid-Saturated Porous Solids.
NASA Astrophysics Data System (ADS)
Azcuaga, Valery Francisco Godinez
1995-01-01
This study addresses the surface wave propagation phenomena on fluid-saturated porous solids. The analytical method for calculation of surface wave velocities (Feng and Johnson, JASA, 74, 906, 1983) is extended to the case of a porous solid saturated with a wetting fluid in contact with a non-wetting fluid, in order to study a material combination suitable for experimental investigation. The analytical method is further extended to the case of a non-wetting fluid/wetting fluid-saturated porous solid interface with an arbitrary finite surface stiffness. These extensions of the analytical method allows to theoretically study surface wave propagation phenomena during the saturation process. A modification to the 2-D space-time reflection Green's function (Feng and Johnson, JASA, 74, 915, 1983) is introduced in order to simulate the behavior of surface wave signals detected during the experimental investigation of surface wave propagation on fluid-saturated porous solids (Nagy, Appl. Phys. Lett., 60, 2735, 1992). This modification, together with the introduction of an excess attenuation for the Rayleigh surface mode, makes it possible to explain the apparent velocity changes observed on the surface wave signals during saturation. Experimental results concerning the propagation of surface waves on an alcohol-saturated porous glass are presented. These experiments were performed at frequencies of 500 and 800 kHz and show the simultaneous propagation of the two surface modes predicted by the extended analytical method. Finally an analysis of the displacements associated with the different surface modes is presented. This analysis reveals that it is possible to favor the generation of the Rayleigh surface mode or of the slow surface mode, simply by changing the type of transducer used in the generation of surface waves. Calculations show that a shear transducer couples more energy into the Rayleigh mode, whereas a longitudinal transducer couples more energy into the slow
NASA Astrophysics Data System (ADS)
Tuck, David M.; Bierck, Barnes R.; Jaffé, Peter R.
1998-06-01
Multiphase flow in porous media is an important research topic. In situ, nondestructive experimental methods for studying multiphase flow are important for improving our understanding and the theory. Rapid changes in fluid saturation, characteristic of immiscible displacement, are difficult to measure accurately using gamma rays due to practical restrictions on source strength. Our objective is to describe a synchrotron radiation technique for rapid, nondestructive saturation measurements of multiple fluids in porous media, and to present a precision and accuracy analysis of the technique. Synchrotron radiation provides a high intensity, inherently collimated photon beam of tunable energy which can yield accurate measurements of fluid saturation in just one second. Measurements were obtained with precision of ±0.01 or better for tetrachloroethylene (PCE) in a 2.5 cm thick glass-bead porous medium using a counting time of 1 s. The normal distribution was shown to provide acceptable confidence limits for PCE saturation changes. Sources of error include heat load on the monochromator, periodic movement of the source beam, and errors in stepping-motor positioning system. Hypodermic needles pushed into the medium to inject PCE changed porosity in a region approximately ±1 mm of the injection point. Improved mass balance between the known and measured PCE injection volumes was obtained when appropriate corrections were applied to calibration values near the injection point.
Manole, D.M.; Lage, J.L.; Antohe, B.V.
1995-12-31
Hadley circulation induced by horizontal and vertical temperature gradients imposed on a fluid saturated porous medium layer is simulated numerically. The flow is assumed to be longitudinal, that is the secondary flow is composed of cells with axes transverse to the direction of the Hadley circulation. Critical (bifurcation) states predicted theoretically via linear stability analysis are verified by the numerical results giving confidence on the accuracy of the method. Several values of horizontal Rayleigh number, Ra{sub h}, and vertical Rayleigh number, Ra{sub v}, are studied. Results indicate that beyond a threshold horizontal Rayleigh number value the flow and temperature fields evolve from subcritical Hadley circulation to a supercritical time periodic flow. The secondary flow emerges in the form of a traveling wave aligned with the main (Hadley) flow direction. This traveling wave is characterized, at supercritical low vertical Rayleigh numbers, by the continuous drifting of two horizontal layers of flow cells that move in opposite directions. As the vertical Rayleigh number increases, the traveling wave becomes characterized by a unique layer of cells drifting in the direction opposite to the applied horizontal temperature gradient. Numerical animation unravels the main features of the transport process. This simplified model is of fundamental and practical importance, for instance, to the study of geothermal activities, underground transport of pollutants, paper processing, crystal growth, building insulation, and gas reservoirs.
Diffusion of high-frequency energy in fluid-saturated porous media
NASA Astrophysics Data System (ADS)
Savin, Eric
2004-05-01
The modern mathematical theory of microlocal analysis shows that the energy associated with the high-frequency solutions of hyperbolic partial differential equations (such as the wave or the Navier equations) satisfy Liouville-type transport equations, or radiative transfer equations for randomly heterogeneous media. For long propagation times the latter can be approached by diffusion equations. Some classical results of the structural acoustics literature about the heat conduction analogy and the statistical energy analysis of structural dynamics at higher frequencies are recovered in this process. The purpose of this communication is to focus on such a diffusive regime for isotropic, fluid-saturated porous media. More specifically, we have derived the diffusion parameters (transport mean-free path and diffusion constant) for such media. Our model considers Biot's equations of poroelasticity, where thermal and viscous effects are modelized by dynamic tortuosity and compressibility with singular memory kernels. The macroscopic bulk modulus and density of the dry solid phase are assumed to be homogeneous random processes, while tortuosity and porosity remain constant.
Yang, Zhixin; Wang, Shaowei; Zhao, Moli; Li, Shucai; Zhang, Qiangyong
2013-01-01
The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer is studied when the fluid and solid phase are not in local thermal equilibrium. The modified Darcy model is used for the momentum equation and a two-field model is used for energy equation each representing the fluid and solid phases separately. The effect of thermal non-equilibrium on the onset of double diffusive convection is discussed. The critical Rayleigh number and the corresponding wave number for the exchange of stability and over-stability are obtained, and the onset criterion for stationary and oscillatory convection is derived analytically and discussed numerically.
NASA Astrophysics Data System (ADS)
Bhadauria, B. S.; Singh, M. K.; Singh, A.; Singh, B. K.; Kiran, P.
2016-12-01
In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.
Seddeek, M A
2006-01-01
Mixed convection flow, heat, and mass transfer about an isothermal vertical flat plate embedded in a fluid-saturated porous medium and the effects of viscous dissipation and thermophoresis in both aiding and opposing flows are analyzed. The similarity solution is used to transform the problem under consideration into a boundary value problem of coupled ordinary differential equations, which are solved numerically by using the shooting method. Numerical computations are carried out for the non-dimensional physical parameter. The results are analyzed for the effect of different physical parameters such as thermophoretic, mixed convection, inertia parameter, buoyancy ratio, and Schmid number on the flow, heat, and mass transfer characteristics. Two cases are considered, one corresponding to the presence of viscous dissipation and the other to the absence of it.
Tsiklauri, David
2002-09-01
It is known that a boundary slip velocity starts to play an important role when the length scale over which the fluid velocity changes approaches the slip length, i.e., when the fluid is highly confined, for example, fluid flow through porous rock or blood vessel capillaries. Zhu and Granick [Phys. Rev. Lett. 87, 096105 (2001)] have recently experimentally established the existence of a boundary slip in a Newtonian liquid. They reported typical values of the slip length of the order of few micrometers. In this light, the effect of introduction of the boundary slip into the theory of propagation of elastic waves in a fluid-saturated porous medium formulated by Biot [J. Acoust. Soc. Am. 28, 179-191 (1956)] is investigated. Namely, the effect of introduction of boundary slip upon the function F(kappa) that measures the deviation from Poiseuille flow friction as a function of frequency parameter kappa is studied. By postulating phenomenological dependence of the slip velocity upon frequency, notable deviations in the domain of intermediate frequencies in the behavior of F(kappa) are introduced with the incorporation of the boundary slip into the model. It is known that F(kappa) crucially enters Biot's equations, which describe dynamics of fluid-saturated porous solid. Thus, consequences of the nonzero boundary slip by calculating the phase velocities and attenuation coefficients of both rotational and dilatational waves with the variation of frequency are investigated. The new model should allow one to fit the experimental seismic data in circumstances when Biot's theory fails, as the introduction of phenomenological dependence of the slip velocity upon frequency, which is based on robust physical arguments, adds an additional degree of freedom to the model. In fact, it predicts higher than the Biot's theory values of attenuation coefficients of the both rotational and dilatational waves in the intermediate frequency domain, which is in qualitative agreement with the
Thermal instability of a fluid-saturated porous medium bounded by thin fluid layers
Pillatsis, G.; Taslim, M.E.; Narusawa, U. )
1987-08-01
A linear stability analysis is performed for a horizontal Darcy porous layer of depth 2d{sub m} sandwiched between two fluid layers of depth d (each) with the top and bottom boundaries being dynamically free and kept at fixed temperatures. The Beavers-Joseph condition is employed as one of the interfacial boundary conditions between the fluid and the porous layer. The critical Rayleigh number and the horizontal wave number for the onset of convective motion depend on the following four dimensional parameters: {cflx d} (= d{sub m}/d, the depth ratio), {delta} (= {radical}K/d{sub m} with K being the permeability of the porous medium) {alpha} (the proportionality constant in the Beavers-Joseph condition), and k/k{sub m} (the thermal conductivity ratio). In order to analyze the effect of these parameters on the stability condition, a set of numerical solutions is obtained in terms of a convergent series for the respective layers, for the case in which the thickness of the porous layer is much greater than that of the fluid layer. A comparison of this study with the previously obtained exact solution for the case of constant heat flux boundaries is made to illustrate quantitative effects of the interfacial and the top/bottom boundaries on the thermal instability of a combined system of porous and fluid layers.
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.
Turbulent flow over a channel with fluid-saturated porous bed
Technology Transfer Automated Retrieval System (TEKTRAN)
The characteristics of fully developed turbulent flow in a hybrid domain channel, which consists of a clear fluid region and a porous bed, are examined numerically using a model based on the macroscopic Reynolds-averaged Navier–Stokes equations. By adopting the classical continuity interface conditi...
(Investigation of ultrasonic wave interactions with fluid-saturated porous rocks)
Adler, L.
1992-01-01
During the last two years we have continued our investigation of ultrasonic wave propagation in fluid-filled porous materials. First, we studied the feasibility of using different surface modes to characterize both synthetic and natural rocks. We introduced a novel experimental technique based on the direct generation of surface waves by edge excitation. We used two low-frequency (100--500 kHz) shear transducers in pitch-catch mode to launch and receive the ultrasonic surface wave. The contact transducers were coupled to the opposite edges of the porous specimens with normal polarization relative to the surface. The same technique was successfully used to generate Rayleigh-type surface modes on the free surface of both dry and water-saturated specimens, as well as Stoneley-type interface modes on the fluid-loaded surfaces of immersed samples. Our main achievement in this area is the realization that, due to surface tension, practically closed-pore boundary conditions can prevail on the free surface of a water-saturated rock for completely open pores. As a result, the velocity of the true surface mode might be much lower than the Rayleigh velocity of the dry skeleton.
[Investigation of ultrasonic wave interactions with fluid-saturated porous rocks]. [Annual report
Adler, L.
1992-07-01
During the last two years we have continued our investigation of ultrasonic wave propagation in fluid-filled porous materials. First, we studied the feasibility of using different surface modes to characterize both synthetic and natural rocks. We introduced a novel experimental technique based on the direct generation of surface waves by edge excitation. We used two low-frequency (100--500 kHz) shear transducers in pitch-catch mode to launch and receive the ultrasonic surface wave. The contact transducers were coupled to the opposite edges of the porous specimens with normal polarization relative to the surface. The same technique was successfully used to generate Rayleigh-type surface modes on the free surface of both dry and water-saturated specimens, as well as Stoneley-type interface modes on the fluid-loaded surfaces of immersed samples. Our main achievement in this area is the realization that, due to surface tension, practically closed-pore boundary conditions can prevail on the free surface of a water-saturated rock for completely open pores. As a result, the velocity of the true surface mode might be much lower than the Rayleigh velocity of the dry skeleton.
Onset of centrifugal convection in a magnetic-fluid-saturated porous medium
NASA Astrophysics Data System (ADS)
Saravanan, S.; Yamaguchi, H.
2005-08-01
This paper concerns the influence of magnetic field on the onset of centrifugal convection in a magnetic-fluid-filled differentially heated porous layer placed in zero-gravity environment by linear stability theory. The axis of rotation of the layer is placed anywhere within its boundaries, which leads to an alternating direction of the centrifugal body force. The critical centrifugal Rayleigh number, the critical wave number, and the eigenfunctions corresponding to two-dimensional flow pattern at the threshold are calculated using a combination of analytical and numerical methods. Results show significant effects even for low magnetic-field strength when the axis location is located near the cold boundary. It is found that the magnetic field has a destabilizing effect and can be suitably adjusted depending on the axis location and particle magnetization to induce more developed convection currents.
NASA Astrophysics Data System (ADS)
Chen, Jui-Sheng; Liu, Chen-Wuing; Lai, Geng-Xin; Ni, Chuen-Fa
2009-06-01
SummaryThe dissolution-induced finger or wormhole patterns in porous medium or fracture rock play a crucial role in a variety of scientific, industrial, and engineering practices. Although previous studies have extensively presented a number of numerical models which couples a system of nonlinear governing equations of porosity change due to mineral dissolution, the conservations of groundwater flow and transport of chemical species to investigate the morphological pattern of a chemical dissolution front within a fluid-saturated porous medium, whereas the mechanical dispersion effect has generally been neglected in the model development. This study addresses the effects of mechanical dispersion on the morphological evolution of a chemical dissolution front for a variety of cases. Mechanical dispersion processes is incorporated with the coupled nonlinear governing equation system so as to rebuild a newly numerical model. The results of numerical simulations demonstrate that mechanical dispersion has pronounced impacts on the morphological pattern of the chemical dissolution front. For single local non-uniformity case, mechanical dispersion reduces the finger length of an unstable single-fingering front or retains the shape of a stable planar front while speeding up the front advancement. In the case of two local non-uniformities, adding mechanical dispersion with different flow conditions can yield one of the following results: (1) the shape of the stable planar front is maintained but its advancement is accelerated; (2) the shape of the unstable single-fingering front is maintained but its length is reduced; (3) the unstable double-fingering front is merged into an unstable single-fingering front; and (4) the shape of the unstable double-fingering front is preserved but its fingering length is reduced. A comparison between the behavior diagrams of dissolution front morphology (with and without considering mechanical dispersion) shows that the double-fingering front
NASA Astrophysics Data System (ADS)
Taleb, A.; BenHamed, H.; Ouarzazi, M. N.; Beji, H.
2016-05-01
We report theoretical and numerical results on bifurcations in thermal instability for a viscoelastic fluid saturating a porous square cavity heated from below. The modified Darcy law based on the Oldroyd-B model was used for modeling the momentum equation. In addition to Rayleigh number ℜ, two more dimensionless parameters are introduced, namely, the relaxation time λ1 and the retardation time λ2. Temporal stability analysis showed that the first bifurcation from the conductive state may be either oscillatory for sufficiently elastic fluids or stationary for weakly elastic fluids. The dynamics associated with the nonlinear interaction between the two kinds of instabilities is first analyzed in the framework of a weakly nonlinear theory. For sufficiently elastic fluids, analytical expressions of the nonlinear threshold above which a second hysteretic bifurcation from oscillatory to stationary convective pattern are derived and found to agree with two-dimensional numerical simulations of the full equations. Computations performed with high Rayleigh number indicated that the system exhibits a third transition from steady single-cell convection to oscillatory multi-cellular flows. Moreover, we found that an intermittent oscillation regime may exist with steady state before the emergence of the secondary Hopf bifurcation. For weakly elastic fluids, we determined a second critical value ℜ2 Osc ( λ 1 , λ 2 ) above which a Hopf bifurcation from steady convective pattern to oscillatory convection occurs. The well known limit of ℜ2 Osc ( λ 1 = 0 , λ 2 = 0 ) = 390 for Newtonian fluids is recovered, while the fluid elasticity is found to delay the onset of the Hopf bifurcation. The major new findings were presented in the form of bifurcation diagrams as functions of viscoelastic parameters for ℜ up to 420.
NASA Astrophysics Data System (ADS)
Kubik, J.; Cieszko, M.
2005-12-01
The compatibility conditions matching macroscopic mechanical fields at the contact surface between a fluid-saturated porous solid and an adjacent bulk fluid are considered. The general form of balance equations at that discontinuity surface are analyzed to obtain the compatibility conditions for the tangent and normal components of the velocity and the stress vector fields. Considerations are based on the procedure similar to that used in the phenomenological thermodynamics for derivation of constitutive relations, where the entropy inequality and the concept of Lagrange multipliers are applied. This procedure made possible to derive the compatibility conditions for the viscous fluid flowing tangentially and perpendicularly to the boundary surface of the porous solid and to formulate the generalized form of the so called slip condition for the fluid velocity field, postulated earlier by Beavers and Joseph, J. Fluid. Mech. 30, 197-207 (1967).
McClure, James E.; Berrill, Mark A.; Gray, William G.; ...
2016-09-02
Here, multiphase flow in porous medium systems is typically modeled using continuum mechanical representations at the macroscale in terms of averaged quantities. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating fluid pressures, fluid saturations, and, in some cases, the interfacial area between the fluid phases, and the Euler characteristic. An unresolved question is whether the inclusion of these additional morphological and topological measures can lead to a non-hysteretic closure relation compared to the hysteretic forms that are used in traditional models, which typically do not include interfacial areas, ormore » the Euler characteristic. We develop a lattice-Boltzmann (LB) simulation approach to investigate the equilibrium states of a two-fluid-phase porous medium system, which include disconnected now- wetting phase features. The proposed approach is applied to a synthetic medium consisting of 1,964 spheres arranged in a random, non-overlapping, close-packed manner, yielding a total of 42,908 different equilibrium points. This information is evaluated using a generalized additive modeling approach to determine if a unique function from this family exists, which can explain the data. The variance of various model estimates is computed, and we conclude that, except for the limiting behavior close to a single fluid regime, capillary pressure can be expressed as a deterministic and non-hysteretic function of fluid saturation, interfacial area between the fluid phases, and the Euler characteristic. This work is unique in the methods employed, the size of the data set, the resolution in space and time, the true equilibrium nature of the data, the parameterizations investigated, and the broad set of functions examined. The conclusion of essentially non-hysteretic behavior provides support for an evolving class of two-fluid-phase flow in porous medium systems models.« less
McClure, James E.; Berrill, Mark A.; Gray, William G.; Miller, Cass T.
2016-09-02
Here, multiphase flow in porous medium systems is typically modeled using continuum mechanical representations at the macroscale in terms of averaged quantities. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating fluid pressures, fluid saturations, and, in some cases, the interfacial area between the fluid phases, and the Euler characteristic. An unresolved question is whether the inclusion of these additional morphological and topological measures can lead to a non-hysteretic closure relation compared to the hysteretic forms that are used in traditional models, which typically do not include interfacial areas, or the Euler characteristic. We develop a lattice-Boltzmann (LB) simulation approach to investigate the equilibrium states of a two-fluid-phase porous medium system, which include disconnected now- wetting phase features. The proposed approach is applied to a synthetic medium consisting of 1,964 spheres arranged in a random, non-overlapping, close-packed manner, yielding a total of 42,908 different equilibrium points. This information is evaluated using a generalized additive modeling approach to determine if a unique function from this family exists, which can explain the data. The variance of various model estimates is computed, and we conclude that, except for the limiting behavior close to a single fluid regime, capillary pressure can be expressed as a deterministic and non-hysteretic function of fluid saturation, interfacial area between the fluid phases, and the Euler characteristic. This work is unique in the methods employed, the size of the data set, the resolution in space and time, the true equilibrium nature of the data, the parameterizations investigated, and the broad set of functions examined. The conclusion of essentially non-hysteretic behavior provides support for an evolving class of two-fluid-phase flow in porous medium systems models.
NASA Astrophysics Data System (ADS)
Pažanin, Igor; Siddheshwar, Pradeep G.
2017-03-01
In this article we investigate the fluid flow through a thin fracture modelled as a fluid-saturated porous medium. We assume that the fracture has constrictions and that the flow is governed by the prescribed pressure drop between the edges of the fracture. The problem is described by the Darcy-Lapwood-Brinkman model acknowledging the Brinkman extension of the Darcy law as well as the flow inertia. Using asymptotic analysis with respect to the thickness of the fracture, we derive the explicit higher-order approximation for the velocity distribution. We make an error analysis to comment on the order of accuracy of the method used and also to provide rigorous justification for the model.
NASA Astrophysics Data System (ADS)
Chandler, Richard N.; Johnson, David Linton
1981-05-01
We have established in a simple and straightforward fashion that the analysis of quasistatic flow in fluid-saturated porous media due to Rice and Cleary is derivable from the low-frequency limit of Biot's slow compressional/diffusive mode. The single material parameter of the problem, the diffusivity, is simply related to the bulk and shear moduli and permeability of the skeletal frame and to the viscous and elastic properties of the constitutive media. Since this common theory treats fluid and solid displacements on an equal footing, it is the most general linearized description of the problem; other treatments are special cases. These latter include the rigid frame approximation used in the petroleum industry and the weak frame approximation used by De Gennes to describe the motion of polymer gels.
NASA Astrophysics Data System (ADS)
Mehta, C. B.; Singh, M.; Kumar, S.
2016-02-01
An investigation is made on the effect of Hall currents on thermal instability of a compressible couple-stress fluid in the presence of a horizontal magnetic field saturated in a porous medium. The analysis is carried out within the framework of the linear stability theory and normal mode technique. A dispersion relation governing the effects of viscoelasticity, Hall currents, compressibility, magnetic field and porous medium is derived. For the stationary convection a couple-stress fluid behaves like an ordinary Newtonian fluid due to the vanishing of the viscoelastic parameter. Compressibility, the magnetic filed and couple-stress parameter have stabilizing effects on the system whereas Hall currents and medium permeability have a destabilizing effect on the system, but in the absence of Hall current couple-stress has a destabilizing effect on the system. It has been observed that oscillatory modes are introduced due to the presence of viscoelasticity, magnetic field porous medium and Hall currents which were non-existent in their absence.
Berryman, J.G.
2009-11-20
Poroelastic analysis usually progresses from assumed knowledge of dry or drained porous media to the predicted behavior of fluid-saturated and undrained porous media. Unfortunately, the experimental situation is often incompatible with these assumptions, especially when field data (from hydrological or oil/gas reservoirs) are involved. The present work considers several different experimental scenarios typified by one in which a set of undrained poroelastic (stiffness) constants has been measured using either ultrasound or seismic wave analysis, while some or all of the dry or drained constants are normally unknown. Drained constants for such a poroelastic system can be deduced for isotropic systems from available data if a complete set of undrained compliance data for the principal stresses are available - together with a few other commonly measured quantities such as porosity, fluid bulk modulus, and grain bulk modulus. Similar results are also developed here for anisotropic systems having up to orthotropic symmetry if the system is granular (i.e., composed of solid grains assembled into a solid matrix, either by a cementation process or by applied stress) and the grains are known to be elastically homogeneous. Finally, the analysis is also fully developed for anisotropic systems with nonhomogeneous (more than one mineral type), but still isotropic, grains - as well as for uniform collections of anisotropic grains as long as their axes of symmetry are either perfectly aligned or perfectly random.
NASA Astrophysics Data System (ADS)
Sunil; Choudhary, Shalu; Mahajan, Amit
2014-06-01
A nonlinear stability threshold for convection in a rotating couple-stress fluid saturating a porous medium with temperature- and pressure-dependent viscosity using a thermal non-equilibrium model is found to be exactly the same as the linear instability boundary. This optimal result is important because it shows that linear theory has completely captured the physics of the onset of convection. The effects of couple-stress fluid parameter F, temperature- and pressure-dependent viscosity Γ, interface heat transfer coefficient H, Taylor number TA, Darcy-Brinkman number D˜a, and porosity modified conductivity ratio γ on the onset of convection have been investigated. Asymptotic analysis for both small and large values of interface heat transfer coefficient H is also presented. An excellent agreement is found between the exact solutions and asymptotic solutions.
NASA Astrophysics Data System (ADS)
Sunil; Choudhary, Shalu; Mahajan, Amit
2013-08-01
A nonlinear stability threshold for rotation in a couple-stress fluid heated from below saturating a porous medium with temperature and pressure dependent viscosity is exactly the same as the linear instability boundary. This optimal result is important because it shows that linearized instability theory has captured completely the physics of the onset of convection. The effects of couple-stress parameter, variable dependent viscosity, medium permeability, Taylor number and Darcy-Brinkman number on the onset of convection are also analysed.
Lifting a large object from an anisotropic porous bed
NASA Astrophysics Data System (ADS)
Karmakar, Timir; Raja Sekhar, G. P.
2016-09-01
An analytical study of two dimensional problem of lifting an object from the top of a fully saturated rigid porous bed is discussed. It is assumed that the porous bed is anisotropic in nature. The flow within the gap region between the object and the porous bed is assumed to be governed by Stokes equation while the flow within the porous bed is governed by Brinkman equation. The breakout phenomenon for different kinds of soil is reported. The effect of mechanical properties like anisotropic permeability, grain diameter size, and porosity on streamlines, velocity, and force is analyzed. Relevant comparison with C. C. Mei, R. W. Yeung, and K. F. Liu ["Lifting a large object from a porous bed," J. Fluid. Mech. 152, 203-215 (1985)] and Y. Chang, L. H. Huang and F. P. Y. Yang ["Two-dimensional lift-up problem for a rigid porous bed," Phys. Fluids, 27, 053101 (2015)] is done.
Goloshubin, Gennady M.; Korneev, Valeri A.
2005-09-06
A method for identifying, imaging and monitoring dry or fluid-saturated underground reservoirs using seismic waves reflected from target porous or fractured layers is set forth. Seismic imaging the porous or fractured layer occurs by low pass filtering of the windowed reflections from the target porous or fractured layers leaving frequencies below low-most corner (or full width at half maximum) of a recorded frequency spectra. Additionally, the ratio of image amplitudes is shown to be approximately proportional to reservoir permeability, viscosity of fluid, and the fluid saturation of the porous or fractured layers.
Goloshubin, Gennady M.; Korneev, Valeri A.
2006-11-14
A method for identifying, imaging and monitoring dry or fluid-saturated underground reservoirs using seismic waves reflected from target porous or fractured layers is set forth. Seismic imaging the porous or fractured layer occurs by low pass filtering of the windowed reflections from the target porous or fractured layers leaving frequencies below low-most corner (or full width at half maximum) of a recorded frequency spectra. Additionally, the ratio of image amplitudes is shown to be approximately proportional to reservoir permeability, viscosity of fluid, and the fluid saturation of the porous or fractured layers.
Stability of Poiseuille flow in a fluid overlying an anisotropic and inhomogeneous porous layer
NASA Astrophysics Data System (ADS)
Deepu, P.; Anand, Prateek; Basu, Saptarshi
2015-08-01
We present the linear stability analysis of horizontal Poiseuille flow in a fluid overlying a porous medium with anisotropic and inhomogeneous permeability. The generalized Darcy model is used to describe the flow in the porous medium with the Beavers-Joseph condition at the interface of the two layers and the eigenvalue problem is solved numerically. The effect of major system parameters on the stability characteristics is addressed in detail. It is shown that the anisotropic and inhomogeneous modulation of the permeability of the underlying porous layer provides an effective means for passive control of the flow stability.
Dissolution in anisotropic porous media: Modelling convection regimes from onset to shutdown
NASA Astrophysics Data System (ADS)
De Paoli, Marco; Zonta, Francesco; Soldati, Alfredo
2017-02-01
In the present study, we use direct numerical simulations to examine the role of non-isotropic permeability on solutal convection in a fluid-saturated porous medium. The dense solute injected from the top boundary is driven downwards by gravity and follows a complex time-dependent dynamics. The process of solute dissolution, which is initially controlled by diffusion, becomes dominated by convection as soon as fingers appear, grow, and interact. The dense solute finally reaches the bottom boundary where, due to the prescribed impermeable boundary, it starts filling the domain so to enter the shutdown stage. We present the entire transient dynamics for large Rayleigh-Darcy numbers, Ra, and non-isotropic permeability. We also try to provide suitable and reliable models to parametrize it. With the conceptual setup presented here, we aim at mimicking the process of liquid CO2 sequestration into geological reservoirs.
Sanya, Arthur S O; Akowanou, Christian; Sanya, Emile A; Degan, Gerard
2014-01-01
The problems of steady film condensation on a vertical surface embedded in a thin porous medium with anisotropic permeability filled with pure saturated vapour are studied analytically by using the Brinkman-Darcy flow model. The principal axes of anisotropic permeability are oriented in a direction that non-coincident with the gravity force. On the basis of the flow permeability tensor due to the anisotropic properties and the Brinkman-Darcy flow model adopted by considering negligible macroscopic and microscopic inertial terms, boundary-layer approximations in the porous liquid film momentum equation is solved analytically. Scale analysis is applied to predict the order-of-magnitudes involved in the boundary layer regime. The first novel contribution in the mathematics consists in the use of the anisotropic permeability tensor inside the expression of the mathematical formulation of the film condensation problem along a vertical surface embedded in a porous medium. The present analytical study reveals that the anisotropic permeability properties have a strong influence on the liquid film thickness, condensate mass flow rate and surface heat transfer rate. The comparison between thin and thick porous media is also presented.
Steady dissolution rate due to convective mixing in anisotropic porous media
NASA Astrophysics Data System (ADS)
Green, Christopher P.; Ennis-King, Jonathan
2014-11-01
Enhanced dissolution of CO2 into a saline aquifer due to convective mixing is an important physical process for the secure long-term storage of significant quantities of CO2. Numerical simulations have previously shown that the dissolution rate of CO2 into reservoir brine will stabilise after a certain time period, with only small oscillations about a long-term average. A theoretical estimate for this average long-term mass flux in an isotropic homogeneous reservoir has previously appeared in the literature. In this paper, an estimate for the steady dissolution rate in anisotropic homogenous porous media is developed using a simple theoretical argument. Detailed numerical simulations confirm that the steady dissolution rate scales as (kvkh) 1 / 2 in an anisotropic homogeneous porous media, where kv and kh are the vertical and horizontal permeabilities, respectively. The scaling is also shown to be appropriate for heterogeneous models where vertical heterogeneity is introduced by including a random distribution of impermeable barriers.
An approximate yield criterion for anisotropic porous media
NASA Astrophysics Data System (ADS)
Keralavarma, Shyam M.; Benzerga, A. Amine
2008-09-01
We derive a new yield function for materials containing spheroidal voids embedded in a perfectly-plastic anisotropic Hill-type matrix. Using approximate limit-analysis and a restricted set of trial velocity fields, analytical yield loci are derived for a hollow, spheroidal volume element containing a confocal spheroidal void. Alternatively, the yield loci are determined through numerical limit-analysis, i.e., employing a larger set of velocity fields. The numerical results are quasi-exact for transversely isotropic materials under axisymmetric loading. We show that an enhanced description of admissible microscopic deformation fields results in a close agreement between analytical and numerical macroscopic yield loci. To cite this article: S.M. Keralavarma, A.A. Benzerga, C. R. Mecanique 336 (2008).
Method of determining interwell oil field fluid saturation distribution
Donaldson, Erle C.; Sutterfield, F. Dexter
1981-01-01
A method of determining the oil and brine saturation distribution in an oil field by taking electrical current and potential measurements among a plurality of open-hole wells geometrically distributed throughout the oil field. Poisson's equation is utilized to develop fluid saturation distributions from the electrical current and potential measurement. Both signal generating equipment and chemical means are used to develop current flow among the several open-hole wells.
Li, Fuping; Li, Jinshan; Xu, Guangsheng; Liu, Gejun; Kou, Hongchao; Zhou, Lian
2015-06-01
Porous titanium with average pore size of 100-650 μm and porosity of 30-70% was fabricated by diffusion bonding of titanium meshes. Pore structure was characterized by Micro-CT scan and SEM. Compressive behavior of porous titanium in the out-of-plane direction was studied. The effect of porosity and pore size on the compressive properties was also discussed based on the deformation mode. The results reveal that the fabrication process can control the porosity precisely. The average pore size of porous titanium can be tailored by adjusting the pore size of titanium meshes. The fabricated porous titanium possesses an anisotropic structure with square pores in the in-plane direction and elongated pores in the out-of-plane direction. The compressive Young's modulus and yield stress are in the range of 1-7.5 GPa and 10-110 MPa, respectively. The dominant compressive deformation mode is buckling of mesh wires, but some uncoordinated buckling is present in porous titanium with lower porosity. Relationship between compressive properties and porosity conforms well to the Gibson-Ashby model. The effect of pore size on compressive properties is fundamentally ascribed to the aspect ratio of titanium meshes. Porous titanium with 60-70% porosity has potential for trabecular bone implant applications.
Shukla, Sourabh; Pasricha, Renu; Sastry, Murali
2009-11-01
Nanostructured metals with hollow interiors are of technological importance due to their unique optoelectronic properties and enhanced surface area. We describe herein, a novel method for the synthesis of anisotropic gold and palladium nanoparticles through a simple galvanic replacement reaction across a semi-permeable dialysis membrane. The control over the reaction kinetics achieved by the presence of membrane enables one to tune the bimetal composition, particle porosity and morphology. Rapid outward diffusion of silver ions generated from the sacrificial silver nanoparticles even at room temperatures prevents the precipitation of high quantities of silver chloride, thereby circumventing the need for product purification. The porous anisotropic nanostructures have potential applications in catalysis, cell imaging and therapeutics.
NASA Astrophysics Data System (ADS)
Degan, Gérard; Sanya, Arthur; Akowanou, Christian
2016-10-01
This work analytically investigates the problem of steady film condensation along a vertical surface embedded in an anisotropic porous medium filled with a dry saturated vapor. The porous medium is anisotropic in permeability whose principal axes are oriented in a direction which is oblique to the gravity vector. On the basis of the generalized Darcy's law and within the boundary layer approximations, similar solutions have been obtained for the temperature and flow patterns in the condensate. Moreover, closed form solutions for the boundary layer thickness and heat transfer rate have been obtained in terms of the governing parameters of the problem.
Simulation of flow of mixtures through anisotropic porous media using a lattice Boltzmann model.
Mendoza, M; Wittel, F K; Herrmann, H J
2010-08-01
We propose a description for transient penetration simulations of miscible and immiscible fluid mixtures into anisotropic porous media, using the lattice Boltzmann (LB) method. Our model incorporates hydrodynamic flow, advection-diffusion, surface tension, and the possibility for global and local viscosity variations to consider various types of hardening fluids. The miscible mixture consists of two fluids, one governed by the hydrodynamic equations and one by advection-diffusion equations. We validate our model on standard problems like Poiseuille flow, the collision of a drop with an impermeable, solid interface and the deformation of the fluid due to surface tension forces. To demonstrate the applicability to complex geometries, we simulate the invasion process of mixtures into wood spruce samples.
Dual-Microstructured Porous, Anisotropic Film for Biomimicking of Endothelial Basement Membrane.
Wang, Zuyong; Teoh, Swee Hin; Hong, Minghui; Luo, Fangfang; Teo, Erin Yiling; Chan, Jerry Kok Yen; Thian, Eng San
2015-06-24
Human endothelial basement membrane (BM) plays a pivotal role in vascular development and homeostasis. Here, a bioresponsive film with dual-microstructured geometries was engineered to mimic the structural roles of the endothelial BM in developing vessels, for vascular tissue engineering (TE) application. Flexible poly(ε-caprolactone) (PCL) thin film was fabricated with microscale anisotropic ridges/grooves and through-holes using a combination of uniaxial thermal stretching and direct laser perforation, respectively. Through optimizing the interhole distance, human mesenchymal stem cells (MSCs) cultured on the PCL film's ridges/grooves obtained an intact cell alignment efficiency. With prolonged culturing for 8 days, these cells formed aligned cell multilayers as found in native tunica media. By coculturing human umbilical vein endothelial cells (HUVECs) on the opposite side of the film, HUVECs were observed to build up transmural interdigitation cell-cell contact with MSCs via the through-holes, leading to a rapid endothelialization on the PCL film surface. Furthermore, vascular tissue construction based on the PCL film showed enhanced bioactivity with an elevated total nitric oxide level as compared to single MSCs or HUVECs culturing and indirect MSCs/HUVECs coculturing systems. These results suggested that the dual-microstructured porous and anisotropic film could simulate the structural roles of endothelial BM for vascular reconstruction, with aligned stromal cell multilayers, rapid endothelialization, and direct cell-cell interaction between the engineered stromal and endothelial components. This study has implications of recapitulating endothelial BM architecture for the de novo design of vascular TE scaffolds.
Calibration of Gurson-type models for porous sheet metals with anisotropic non-quadratic plasticity
NASA Astrophysics Data System (ADS)
Gologanu, M.; Kami, A.; Comsa, D. S.; Banabic, D.
2016-08-01
The growth and coalescence of voids in sheet metals are not only the main active mechanisms in the final stages of fracture in a necking band, but they also contribute to the forming limits via changes in the normal directions to the yield surface. A widely accepted method to include void effects is the development of a Gurson-type model for the appropriate yield criterion, based on an approximate limit analysis of a unit cell containing a single spherical, spheroidal or ellipsoidal void. We have recently [2] obtained dissipation functions and Gurson-type models for porous sheet metals with ellipsoidal voids and anisotropic non-quadratic plasticity, including yield criteria based on linear transformations (Yld91 and Yld2004-18p) and a pure plane stress yield criteria (BBC2005). These Gurson-type models contain several parameters that depend on the void and cell geometries and on the selected yield criterion. Best results are obtained when these key parameters are calibrated via numerical simulations using the same unit cell and a few representative loading conditions. The single most important such loading condition corresponds to a pure hydrostatic macroscopic stress (pure pressure) and the corresponding velocity field found during the solution of the limit analysis problem describes the expansion of the cavity. However, for the case of sheet metals, the condition of plane stress precludes macroscopic stresses with large triaxiality or ratio of mean stress to equivalent stress, including the pure hydrostatic case. Also, pure plane stress yield criteria like BBC2005 must first be extended to 3D stresses before attempting to develop a Gurson-type model and such extensions are purely phenomenological with no due account for the out- of-plane anisotropic properties of the sheet. Therefore, we propose a new calibration method for Gurson- type models that uses only boundary conditions compatible with the plane stress requirement. For each such boundary condition we use
A Computer Program for Consolidation and Dynamic Response Analysis of Fluid-Saturated Media.
1983-06-01
Codes Avail and/or Geotechnical Engineering Report No. 14 Dist I Special The Ohio State University Research Foundation 1314 Kinnear Road, Columbus, Ohio...CONSOLIDATION AND DYNAMIC RESPONSE ANALYSIS OF FLUID-SATURATED MEDIA Ranbir S. Sandhu, B. Aboustit, S. J. Hong and M. S. Hiremath Department of Civil Engineering ...RESPONSE ANALYSIS OF FLUID-SATURATED MEDIA By Ranbir S. Sandhu, B. Aboustit, S. J. Hong and M. S. Hiremath Department of Civil Engineering June 1984 Acce
Mézière, Fabien; Muller, Marie; Bossy, Emmanuel; Derode, Arnaud
2014-07-01
This article quantitatively investigates ultrasound propagation in numerical anisotropic porous media with finite-difference simulations in 3D. The propagation media consist of clusters of ellipsoidal scatterers randomly distributed in water, mimicking the anisotropic structure of cancellous bone. Velocities and attenuation coefficients of the ensemble-averaged transmitted wave (also known as the coherent wave) are measured in various configurations. As in real cancellous bone, one or two longitudinal modes emerge, depending on the micro-structure. The results are confronted with two standard theoretical approaches: Biot's theory, usually invoked in porous media, and the Independent Scattering Approximation (ISA), a classical first-order approach of multiple scattering theory. On the one hand, when only one longitudinal wave is observed, it is found that at porosities higher than 90% the ISA successfully predicts the attenuation coefficient (unlike Biot's theory), as well as the existence of negative dispersion. On the other hand, the ISA is not well suited to study two-wave propagation, unlike Biot's model, at least as far as wave speeds are concerned. No free fitting parameters were used for the application of Biot's theory. Finally we investigate the phase-shift between waves in the fluid and the solid structure, and compare them to Biot's predictions of in-phase and out-of-phase motions.
Earth science: role of fO2 on fluid saturation in oceanic basalt.
Scaillet, Bruno; Pichavant, Michel
2004-07-29
Assessing the conditions under which magmas become fluid-saturated has important bearings on the geochemical modelling of magmas because volatile exsolution may profoundly alter the behaviour of certain trace elements that are strongly partitioned in the coexisting fluid. Saal et al. report primitive melt inclusions from dredged oceanic basalts of the Siqueiros transform fault, from which they derive volatile abundances of the depleted mantle, based on the demonstration that magmas are not fluid-saturated at their eruption depth and so preserve the mantle signature in terms of their volatile contents. However, in their analysis, Saal et al. consider only fluid-melt equilibria, and do not take into account the homogeneous equilibria between fluid species, which, as we show here, may lead to a significant underestimation of the pressure depth of fluid saturation.
Relations between drained and undrained moduli in anisotropic poroelasticity
NASA Astrophysics Data System (ADS)
Loret, Benjamin; Rizzi, Egidio; Zerfa, Zohra
2001-11-01
Although the knowledge of the drained moduli is often assumed to define the material coefficients of elastic fluid-saturated porous media, it is not sufficient. Resorting to the properties of the constituents is possible but may not be satisfactory due to lack of accuracy. On the other hand, the mechanical information contained in the undrained moduli is complementary to that provided by the drained moduli but is also overabundant. The compatibility relations between these two types of moduli are examined for several classes of anisotropic solid skeletons and the information required from the undrained moduli is exactly defined through a spectral analysis of the dyadic difference in tensor compliances. A switch of the results is possible if the undrained moduli are given instead of the drained moduli. An incomplete data set of material coefficients for a transverse isotropic shale is treated as an example. Considerable simplifications arise for a particular form of anisotropy defined by a second order fabric tensor.
Flow and dispersion in anisotropic porous media: A lattice-Boltzmann study
NASA Astrophysics Data System (ADS)
Maggiolo, D.; Picano, F.; Guarnieri, M.
2016-10-01
Given their capability of spreading active chemical species and collecting electricity, porous media made of carbon fibers are extensively used as diffusion layers in energy storage systems, such as redox flow batteries. In spite of this, the dispersion dynamics of species inside porous media is still not well understood and often lends itself to different interpretations. Actually, the microscopic design of efficient porous media, which can potentially and effectively improve the performances of flow batteries, is still an open challenge. The present study aims to investigate the effect of fibrous media micro-structure on dispersion, in particular the effect of fiber orientation on drag and dispersion dynamics. Several lattice-Boltzmann simulations of flows through differently oriented fibrous media coupled with Lagrangian simulations of particle tracers have been performed. Results show that orienting fibers preferentially along the streamwise direction minimizes the drag and maximizes the dispersion, which is the most desirable condition for diffusion layers in flow batteries' applications.
Donius, Amalie E; Liu, Andong; Berglund, Lars A; Wegst, Ulrike G K
2014-09-01
Directionally solidified nanofibrillated cellulose (NFC)-sodium-montmorillonite (MMT) composite aerogels with a honeycomb-like pore structure were compared with non-directionally frozen aerogels with equiaxed pore structure and identical composition and found to have superior functionalities. To explore structure-property correlations, three different aerogel compositions of 3wt% MMT, and 0.4wt%, 0.8wt%, and 1.2wt% NFC, respectively, were tested. Young׳s modulus, compressive strength and toughness were found to increase with increasing NFC content for both architectures. The modulus increased from 25.8kPa to 386kPa for the isotropic and from 2.13MPa to 3.86MPa for the anisotropic aerogels, the compressive yield strength increased from 3.3kPa to 18.0kPa for the isotropic and from 32.3kPa to 52.5kPa for the anisotropic aerogels, and the toughness increased from 6.3kJ/m(3) to 24.1kJ/m(3) for the isotropic and from 22.9kJ/m(3) to 46.2kJ/m(3) for the anisotropic aerogels. The great range of properties, which can be achieved through compositional as well as architectural variations, makes these aerogels highly attractive for a large range of applications, for which either a specific composition, or a particular pore morphology, or both are required. Finally, because NFC is flammable, gasification experiments were performed, which revealed that the inclusion of MMT increased the heat endurance and shape retention functions of the aerogels dramatically up to 800°C while the mechanical properties were retained up to 300°C.
Wang, Yong; Yue, Wenzheng; Zhang, Mo
2016-01-01
The anisotropic transport of thermal neutron in heterogeneous porous media is of great research interests in many fields. In this paper, it is the first time that a new model based on micron X-ray computed tomography (CT) has been proposed to simultaneously consider both the separation of matrix and pore and the distribution of mineral components. We apply the Monte Carlo method to simulate thermal neutrons transporting through the model along different directions, and meanwhile detect those unreacted thermal neutrons by an array detector on the other side of the model. Therefore, the anisotropy of pore structure can be imaged by the amount of received thermal neutrons, due to the difference of rock matrix and pore-filling fluids in the macroscopic reaction cross section (MRCS). The new model has been verified by the consistent between the simulated data and the pore distribution from X-ray CT. The results show that the evaluation of porosity can be affected by the anisotropy of media. Based on the research, a new formula is developed to describe the correlation between the resolution of array detectors and the quality of imaging. The formula can be further used to analyze the critical resolution and the suitable number of thermal neutrons emitted in each simulation. Unconventionally, we find that a higher resolution cannot always lead to a better image. PMID:27271330
NASA Astrophysics Data System (ADS)
Badiey, M.; Yamamoto, T.
1986-01-01
Propogation of acoustic normal modes at excitation frequencies of 50 to 50000 Hz in a shallow stratified ocean overlaying a transverse isotropic poro-elastic sediment bed is modeled. The Biot-Willis stiffness matrix of the poro-elastic anisotropy is defined in terms of physical properties of sediments to model the bed. Propagator matrix method is used to solve the differential equations for the motion stress vectors in both layered sediment and water. The effects of sediment properties on the dispersion and attenuation of acoustic waves are examined numerically. Using the relaxation principle it is observed that the energy loss is maximum at frequency referred to as relaxation frequency of the porous media given by f sub ri = (beta)(nu)/3 pi k (sub si), where beta is the porosity, nu is the kinematic viscosity of the pore fluid and k (sub si) is the anisotropic permeability coefficient. The phase speed of compressional and shear waves in the sediment becomes highly dispersive around this frequency. The sandy bottom's relaxation frequency is the range of several hundred hertz to several kilo hertz. This report presents the derivation of the mathematical expressions used in the model and a complete description of the computer program. Four examples of numerical calculations are provided.
Tunable anisotropic thermal expansion of a porous zinc(II) metal-organic framework.
Grobler, Ilne; Smith, Vincent J; Bhatt, Prashant M; Herbert, Simon A; Barbour, Leonard J
2013-05-01
A novel three-dimensional metal-organic framework (MOF) that displays anisotropic thermal expansion has been prepared and characterized by single-crystal X-ray diffraction (SCD) and thermal analysis. The as-prepared MOF has one-dimensional channels containing guest molecules that can be removed and/or exchanged for other guest molecules in a single-crystal to single-crystal fashion. When the original guest molecules are replaced there is a noticeable effect on the host mechanics, altering the thermal expansion properties of the material. This study of the thermal expansion coefficients of different inclusion complexes of the host MOF involved systematic alteration of guest size, i.e., methanol, ethanol, n-propanol, and isopropanol, showing that fine control over the thermal expansion coefficients can be achieved and that the coefficients can be correlated with the size of the guest. As a proof of concept, this study demonstrates the realizable principle that a single-crystal material with an exchangeable guest component (as opposed to a composite) may be used to achieve a tunable thermal expansion coefficient. In addition, this study demonstrates that greater variance in the absolute dimensions of a crystal can be achieved when one has two variables that affect it, i.e., the host-guest interactions and temperature.
NASA Astrophysics Data System (ADS)
Song, Yongjia; Hu, Hengshan; Rudnicki, John W.
2016-07-01
Grain-scale local fluid flow is an important loss mechanism for attenuating waves in cracked fluid-saturated poroelastic rocks. In this study, a dynamic elastic modulus model is developed to quantify local flow effect on wave attenuation and velocity dispersion in porous isotropic rocks. The Eshelby transform technique, inclusion-based effective medium model (the Mori-Tanaka scheme), fluid dynamics and mass conservation principle are combined to analyze pore-fluid pressure relaxation and its influences on overall elastic properties. The derivation gives fully analytic, frequency-dependent effective bulk and shear moduli of a fluid-saturated porous rock. It is shown that the derived bulk and shear moduli rigorously satisfy the Biot-Gassmann relationship of poroelasticity in the low-frequency limit, while they are consistent with isolated-pore effective medium theory in the high-frequency limit. In particular, a simplified model is proposed to quantify the squirt-flow dispersion for frequencies lower than stiff-pore relaxation frequency. The main advantage of the proposed model over previous models is its ability to predict the dispersion due to squirt flow between pores and cracks with distributed aspect ratio instead of flow in a simply conceptual double-porosity structure. Independent input parameters include pore aspect ratio distribution, fluid bulk modulus and viscosity, and bulk and shear moduli of the solid grain. Physical assumptions made in this model include (1) pores are inter-connected and (2) crack thickness is smaller than the viscous skin depth. This study is restricted to linear elastic, well-consolidated granular rocks.
Preparation of asymmetric porous materials
Coker, Eric N [Albuquerque, NM
2012-08-07
A method for preparing an asymmetric porous material by depositing a porous material film on a flexible substrate, and applying an anisotropic stress to the porous media on the flexible substrate, where the anisotropic stress results from a stress such as an applied mechanical force, a thermal gradient, and an applied voltage, to form an asymmetric porous material.
Joint Inversion of Marine Seismic and CSEM Data for Fluid Saturation Prediction
NASA Astrophysics Data System (ADS)
Hoversten, G. M.; Gasperikova, E.; Chen, J.; Newman, G.
2005-12-01
Recent developments in the application of controlled source marine electromagnetic (CSEM) data in petroleum exploration have brought this technology to the attention of many in exploration and production within the oil and gas industry. These developments are founded on more than two decades of research carried out in academia and at U.S. national laboratories. The commercial availability of CSEM data now makes it possible to consider integrating this new data with existing seismic data in ways that will add considerable value. In particular, the sensitivity of CSEM data to water saturation (Sw), when combined with the spatial and reservoir parameter sensitivity (porosity, Sw, gas saturation [Sg], and oil saturation [So]) of seismic data, can provide enhanced prediction of fluid saturations within existing or prospective reservoirs. There are many ways in which CSEM and seismic data can be combined to estimate reservoir parameters. The possibilities range from what we term cooperative inversion, in which both data sets are used without any formal linkage in the inversion of either, to fully coupled joint inversion, in which both data sets are inverted simultaneously to directly estimate reservoir parameters. Hoversten et al. (2003) present an example of the former, in which crosswell EM and seismic travel-time tomography are used to estimate reservoir parameters using time-lapse changes in shear velocity, electrical conductivity, and acoustic velocity to sequentially strip off the effects of pressure and water saturation before estimating oil and CO2 saturations. Direct reservoir parameter estimation by joint inversion was demonstrated by Hoversten et al. (2004) and Chen et al. (2004), where marine CSEM and AVA data were used in a formal joint inverse to estimate reservoir Sw, So, Sg, and porosity (φ). The formal joint inversion is currently being extended to replace the 1D CSEM solution with full 3D. While the development and testing of more computationally
NASA Astrophysics Data System (ADS)
Schmidt, Max W.; Ulmer, Peter
2004-04-01
Fluid saturated high-pressure experiments often result in strongly zoned experimental charges, this hinders experimentation in chemically homogeneous systems which in turn has serious consequences on equilibration, reaction progress, and (apparent) phase stabilities. In order to overcome these problems, a 600-ton press accommodating either a multianvil or end-loaded piston cylinder module has been mounted in such a way that it can be turned by 180°, thus inverting its position in the gravity field. During turning, hydraulic pressure, heating power, and cooling water remain connected allowing fully controlled pressures and temperatures during experiments. A series of experiments at 13 GPa, 950°C, on a serpentine bulk composition in the MgO-SiO 2-H 2O system demonstrates that continuous turning at a rate of 2 turns/min results in a nearly homogeneous charge composed of phase E + enstatite. The same experiment at static conditions resulted in four mineral zones: quench phase E, enstatite, enstatite + phase E, and phase E + phase A. Phase A disappears in experiments at a turning rate ≥1 turn/min. A static 15-min experiment shows that zonation already forms within this short time span. Placing two short capsules within a single static experiment reveals that the fluid migrates to the hot spot in each capsule and is not gravitationally driven toward the top. The zonation pattern follows isotherms within the capsule, and the degree of zonation increases with temperature gradient (measured as 10 °C within a capsule) and run time. Our preferred interpretation is that Soret diffusion causes a density-stratified fluid within the capsule that does not convect in a static experiment and results in temperature dependant chemical zonation. The aggravation of zonation and appearance of additional phases with run time can be explained with a dissolution-reprecipitation process where the cold spot of the capsule is relatively MgO enriched and the hot spot relatively SiO 2 and H
Koontz, S.L.; Leger, L.J.; Wu, C.; Cross, J.B.; Jurgensen, C.W. |
1994-05-01
Neutral atomic oxygen is the most abundant component of the ionospheric plasma in the low Earth orbit environment (LEO; 200 to 700 kilometers altitude) and can produce significant degradation of some spacecraft materials. In order to produce a more complete understanding of the materials chemistry of atomic oxygen, the chemistry and physics of O-atom interactions with materials were determined in three radically different environments: (1) The Space Shuttle cargo bay in low Earth orbit (the EOIM-3 space flight experiment), (2) a high-velocity neutral atom beam system (HVAB) at Los Alamos National Laboratory (LANL), and (3) a microwave-plasma flowing-discharge system at JSC. The Space Shuttle and the high velocity atom beam systems produce atom-surface collision energies ranging from 0.1 to 7 eV (hyperthermal atoms) under high-vacuum conditions, while the flowing discharge system produces a 0.065 eV surface collision energy at a total pressure of 2 Torr. Data obtained in the three different O-atom environments referred to above show that the rate of O-atom reaction with polymeric materials is strongly dependent on atom kinetic energy, obeying a reactive scattering law which suggests that atom kinetic energy is directly available for overcoming activation barriers in the reaction. General relationships between polymer reactivity with O atoms and polymer composition and molecular structure have been determined. In addition, vacuum ultraviolet photochemical effects have been shown to dominate the reaction of O atoms with fluorocarbon polymers. Finally, studies of the materials chemistry of O atoms have produced results which may be of interest to technologists outside the aerospace industry. Atomic oxygen `spin-off` or `dual use` technologies in the areas of anisotropic etching in microelectronic materials and device processing, as well as surface chemistry engineering of porous solid materials are described.
NASA Technical Reports Server (NTRS)
Koontz, Steve L.; Leger, Lubert J.; Wu, Corina; Cross, Jon B.; Jurgensen, Charles W.
1994-01-01
Neutral atomic oxygen is the most abundant component of the ionospheric plasma in the low Earth orbit environment (LEO; 200 to 700 kilometers altitude) and can produce significant degradation of some spacecraft materials. In order to produce a more complete understanding of the materials chemistry of atomic oxygen, the chemistry and physics of O-atom interactions with materials were determined in three radically different environments: (1) The Space Shuttle cargo bay in low Earth orbit (the EOIM-3 space flight experiment), (2) a high-velocity neutral atom beam system (HVAB) at Los Alamos National Laboratory (LANL), and (3) a microwave-plasma flowing-discharge system at JSC. The Space Shuttle and the high velocity atom beam systems produce atom-surface collision energies ranging from 0.1 to 7 eV (hyperthermal atoms) under high-vacuum conditions, while the flowing discharge system produces a 0.065 eV surface collision energy at a total pressure of 2 Torr. Data obtained in the three different O-atom environments referred to above show that the rate of O-atom reaction with polymeric materials is strongly dependent on atom kinetic energy, obeying a reactive scattering law which suggests that atom kinetic energy is directly available for overcoming activation barriers in the reaction. General relationships between polymer reactivity with O atoms and polymer composition and molecular structure have been determined. In addition, vacuum ultraviolet photochemical effects have been shown to dominate the reaction of O atoms with fluorocarbon polymers. Finally, studies of the materials chemistry of O atoms have produced results which may be of interest to technologists outside the aerospace industry. Atomic oxygen 'spin-off' or 'dual use' technologies in the areas of anisotropic etching in microelectronic materials and device processing, as well as surface chemistry engineering of porous solid materials are described.
A Transverse Dynamic Deflection Model for Thin Plate Made of Saturated Porous Materials
NASA Astrophysics Data System (ADS)
Feng-xi, Zhou; Xiao-lin, Cao
2016-10-01
In this article, a transverse dynamic deflection model is established for thin plate made of saturated porous materials. Based on the Biot's model for fluid-saturated porous media, using the Love-Kirchhoff hypothesis, the governing equations of transverse vibrations of fluid-saturated poroelastic plates are derived in detail, which take the inertial, fluid viscous, mechanical couplings, compressibility of solid, and fluid into account. The free vibration and forced vibration response of a simply supported poroelastic rectangular plate is obtained by Fourier series expansion method. Through numerical examples, the effect of porosity and permeability on the dynamic response, including the natural frequency, amplitude response, and the resonance areas is assessed.
NASA Astrophysics Data System (ADS)
Liu, Zhongxian; Liang, Jianwen; Wu, Chengqing
2016-06-01
Two dimensional diffraction of Rayleigh waves by a fluid-saturated poroelastic alluvial valley of arbitrary shape in a poroelastic half-space is investigated using the method of fundamental solutions (MFS). To satisfy the free surface boundary conditions exactly, Green's functions of compressional (PI and PII) and shear (SV) wave sources buried in a fluid-saturated poroelastic half-space are adopted. Next, the procedure for solving the scattering wave field is presented. It is verified that the MFS is of excellent accuracy and numerical stability. Numerical results illustrate that the dynamic response strongly depends on such factors as the incident frequency, the porosity of alluvium, the boundary drainage condition, and the valley shape. There is a significant difference between the diffraction of Rayleigh waves for the saturated soil case and for the corresponding dry soil case. The wave focusing effect both on the displacement and pore pressure can be observed inside the alluvial valley and the amplification effect seems most obvious in the case of higher porosity and lower frequency. Additionally, special attention should also be paid to the concentration of pore pressure, which is closely related to the site liquefaction in earthquakes.
NASA Astrophysics Data System (ADS)
Cuenca, Jacques; Van der Kelen, Christophe; Göransson, Peter
2014-02-01
This paper proposes an inverse estimation method for the characterisation of the elastic and anelastic properties of the frame of anisotropic open-cell foams used for sound absorption. A model of viscoelasticity based on a fractional differential constitutive equation is used, leading to an augmented Hooke's law in the frequency domain, where the elastic and anelastic phenomena appear as distinctive terms in the stiffness matrix. The parameters of the model are nine orthotropic elastic moduli, three angles of orientation of the material principal directions and three parameters governing the anelastic frequency dependence. The inverse estimation consists in numerically fitting the model on a set of transfer functions extracted from a sample of material. The setup uses a seismic-mass measurement repeated in the three directions of space and is placed in a vacuum chamber in order to remove the air from the pores of the sample. The method allows to reconstruct the full frequency-dependent complex stiffness matrix of the frame of an anisotropic open-cell foam and in particular it provides the frequency of maximum energy dissipation by viscoelastic effects. The characterisation of a melamine foam sample is performed and the relation between the fractional-derivative model and other types of parameterisations of the augmented Hooke's law is discussed.
Cuenca, Jacques Van der Kelen, Christophe; Göransson, Peter
2014-02-28
This paper proposes an inverse estimation method for the characterisation of the elastic and anelastic properties of the frame of anisotropic open-cell foams used for sound absorption. A model of viscoelasticity based on a fractional differential constitutive equation is used, leading to an augmented Hooke's law in the frequency domain, where the elastic and anelastic phenomena appear as distinctive terms in the stiffness matrix. The parameters of the model are nine orthotropic elastic moduli, three angles of orientation of the material principal directions and three parameters governing the anelastic frequency dependence. The inverse estimation consists in numerically fitting the model on a set of transfer functions extracted from a sample of material. The setup uses a seismic-mass measurement repeated in the three directions of space and is placed in a vacuum chamber in order to remove the air from the pores of the sample. The method allows to reconstruct the full frequency-dependent complex stiffness matrix of the frame of an anisotropic open-cell foam and in particular it provides the frequency of maximum energy dissipation by viscoelastic effects. The characterisation of a melamine foam sample is performed and the relation between the fractional-derivative model and other types of parameterisations of the augmented Hooke's law is discussed.
NASA Astrophysics Data System (ADS)
Rubino, J. Germán.; Caspari, Eva; Müller, Tobias M.; Milani, Marco; Barbosa, Nicolás. D.; Holliger, Klaus
2016-09-01
The presence of stiffness contrasts at scales larger than the typical pore sizes but smaller than the predominant seismic wavelengths can produce seismic attenuation and velocity dispersion in fluid-saturated porous rocks. This energy dissipation mechanism is caused by wave-induced fluid pressure diffusion among the different components of the probed geological formations. In many cases, heterogeneities have elongated shapes and preferential orientations, which implies that the overall response of the medium is anisotropic. In this work, we propose a numerical upscaling procedure that permits to quantify seismic attenuation and phase velocity considering fluid pressure diffusion effects as well as generic anisotropy at the sample's scale. The methodology is based on a set of three relaxation tests performed on a 2-D synthetic rock sample representative of the medium of interest. It provides a complex-valued frequency-dependent equivalent stiffness matrix through a least squares procedure. We also derive an approach for computing various poroelastic fields associated with the considered sample in response to the propagation of a seismic wave with arbitrary incidence angle. Using this approach, we provide an energy-based estimation of seismic attenuation. A comprehensive numerical analysis indicates that the methodology is suitable for handling complex media and different levels of overall anisotropy. Comparisons with the energy-based estimations demonstrate that the dynamic-equivalent viscoelastic medium assumption made by the numerical upscaling procedure is reasonable even in the presence of high levels of overall anisotropy. This work also highlights the usefulness of poroelastic fields for the physical interpretation of seismic wave phenomena in strongly heterogeneous and complex media.
NASA Astrophysics Data System (ADS)
Ciz, Radim; Gurevich, Boris
2005-03-01
Spatial heterogeneity of hydrocarbon reservoirs causes significant attenuation and dispersion of seismic waves due to wave-induced flow of the pore fluid between more compliant and less compliant areas. This paper investigates the interaction between a plane elastic wave in a poroelastic medium with a spherical inhomogeneity of another porous material. The behaviour of both the inclusion and the background medium is described by the low-frequency variant of Biot's equations of poroelasticity with the standard boundary conditions at the inclusion surface, and for the inclusion size much smaller than the wavelength of the fast compressional wave. The scattering problem is formulated as a series expansion of displacements expressed in the spherical harmonics. The resulting scattered wavefield consists of the scattered normal compressional and shear waves and Biot's slow wave, which attenuates rapidly with distance from the inclusion and represents the main difference from the elastic case. This study concentrates on the attenuation effects caused by the mode conversion into Biot's slow wave. The solution obtained for Biot's slow wave is well described by the two terms of order n= 0 and n= 2 of the scattering series. The scattering amplitude for the term of order n= 0 is given by a simple expression. The full expression for the term of order n= 2 is very complicated, but can be simplified assuming that the amplitude of the scattered fast (normal) compressional and shear waves are well approximated by the solution of the equivalent elastic problem. This assumption yields a simple approximation for the amplitude of the scattered slow wave, which is accurate for a wide range of material properties and is sufficient for the analysis of the scattering amplitude as a function of frequency. In the low-frequency limit the scattering amplitude of the slow wave scales with ω3/2, and reduces to the asymptotic long-wavelength solution of Berryman (1985), which is valid for
Anisotropic universe with anisotropic sources
Aluri, Pavan K.; Panda, Sukanta; Sharma, Manabendra; Thakur, Snigdha E-mail: sukanta@iiserb.ac.in E-mail: snigdha@iiserb.ac.in
2013-12-01
We analyze the state space of a Bianchi-I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical systems approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Then we repeat the same analysis with a more realistic scenario, adding the isotropic (dust like dark) matter and a cosmological constant (dark energy) to our anisotropic sources, to study their co-evolution. The universe now approaches a de Sitter space asymptotically dominated by the cosmological constant. The cosmic microwave background anisotropy maps due to shear are also generated in this scenario, assuming that the universe contains anisotropic matter along with the usual (dark) matter and vacuum (dark) energy since decoupling. We find that they contribute dominantly to the CMB quadrupole. We also constrain the current level of anisotropy and also search for any cosmic preferred axis present in the data. We use the Union 2 Supernovae data to this extent. An anisotropy axis close to the mirror symmetry axis seen in the cosmic microwave background data from Planck probe is found.
Study of acoustic radiation during air stream filtration through a porous medium
NASA Astrophysics Data System (ADS)
Zaslavskii, Yu. M.; Zaslavskii, V. Yu.
2012-11-01
The paper presents results of laboratory experiments on studying the characteristics of acoustic emission generated by a flow of compressed air, which is filtered by porous pumice samples with and without partial fluid saturation. The construction features of the laboratory setup and details of the experiments are described. Porous samples with dry and partially fluid-filled pores are used. The visual patterns of the acoustic emission spectrum, which occurs under stationary filtration of the compressed air, are presented, and its amplitude-frequency distribution characteristic for different sample porosities and different degrees of their fluid saturation is shown. It is demonstrated that the relaxation times of the emission noise level differ. This is revealed during the sharp elimination of the drop in pressure from such samples, i.e., in the nonstationary filtration mode.
NASA Astrophysics Data System (ADS)
Besedina, A. N.; Vinogradov, E. A.; Gorbunova, E. M.; Kabychenko, N. V.; Svintsov, I. S.; Pigulevskiy, P. I.; Svistun, V. K.; Shcherbina, S. V.
2015-01-01
The first part of this work is dedicated to the response of different-age structures to lunisolar tides, which can be considered as a sounding signal for monitoring the state of fluid-saturated reservoirs. The complex approach to processing the data obtained at the testing sites of the Institute of Geosphere Dynamics of the Russian Academy of Sciences, Institute of Geophysics of the National Academy of Sciences of Ukraine, and KIEV station of the IRIS seismic network is applied for recognizing the tides against the hydrogeological, barometric, and seismic series. The comparative analysis of the experimental and theoretical values of the diurnal and semidiurnal tidal components in the time series of ground displacements is carried out. The tidal variations in the groundwater level are compared with the tidal components revealed in the ground displacement of the different-age structure of the Moscow Basin and Ukrainian Shield, which are parts of the East European artesian region. The differences in the tidal responses of the groundwater level and ground displacement probably suggest that the state of the massif is affected by certain additional factors associated, e.g., with the passage of earthquake-induced seismic waves and the changes in the hydrogeodynamic environment.
Homogenization of two fluid flow in porous media
Daly, K. R.; Roose, T.
2015-01-01
The macroscopic behaviour of air and water in porous media is often approximated using Richards' equation for the fluid saturation and pressure. This equation is parametrized by the hydraulic conductivity and water release curve. In this paper, we use homogenization to derive a general model for saturation and pressure in porous media based on an underlying periodic porous structure. Under an appropriate set of assumptions, i.e. constant gas pressure, this model is shown to reduce to the simpler form of Richards' equation. The starting point for this derivation is the Cahn–Hilliard phase field equation coupled with Stokes equations for fluid flow. This approach allows us, for the first time, to rigorously derive the water release curve and hydraulic conductivities through a series of cell problems. The method captures the hysteresis in the water release curve and ties the macroscopic properties of the porous media with the underlying geometrical and material properties. PMID:27547073
Anisotropic and Hierarchical Porosity in Multifunctional Ceramics
NASA Astrophysics Data System (ADS)
Lichtner, Aaron Zev
The performance of multifunctional porous ceramics is often hindered by the seemingly contradictory effects of porosity on both mechanical and non-structural properties and yet a sufficient body of knowledge linking microstructure to these properties does not exist. Using a combination of tailored anisotropic and hierarchical materials, these disparate effects may be reconciled. In this project, a systematic investigation of the processing, characterization and properties of anisotropic and isotropic hierarchically porous ceramics was conducted. The system chosen was a composite ceramic intended as the cathode for a solid oxide fuel cell (SOFC). Comprehensive processing investigations led to the development of approaches to make hierarchical, anisotropic porous microstructures using directional freeze-casting of well dispersed slurries. The effect of all the important processing parameters was investigated. This resulted in an ability to tailor and control the important microstructural features including the scale of the microstructure, the macropore size and total porosity. Comparable isotropic porous ceramics were also processed using fugitive pore formers. A suite of characterization techniques including x-ray tomography and 3-D sectional scanning electron micrographs (FIB-SEM) was used to characterize and quantify the green and partially sintered microstructures. The effect of sintering temperature on the microstructure was quantified and discrete element simulations (DEM) were used to explain the experimental observations. Finally, the comprehensive mechanical properties, at room temperature, were investigated, experimentally and using DEM, for the different microstructures.
Directional wetting in anisotropic inverse opals.
Phillips, Katherine R; Vogel, Nicolas; Burgess, Ian B; Perry, Carole C; Aizenberg, Joanna
2014-07-01
Porous materials display interesting transport phenomena due to restricted motion of fluids within the nano- to microscale voids. Here, we investigate how liquid wetting in highly ordered inverse opals is affected by anisotropy in pore geometry. We compare samples with different degrees of pore asphericity and find different wetting patterns depending on the pore shape. Highly anisotropic structures are infiltrated more easily than their isotropic counterparts. Further, the wetting of anisotropic inverse opals is directional, with liquids filling from the side more easily. This effect is supported by percolation simulations as well as direct observations of wetting using time-resolved optical microscopy.
Natural thermal convection in fractured porous media
NASA Astrophysics Data System (ADS)
Adler, P. M.; Mezon, C.; Mourzenko, V.; Thovert, J. F.; Antoine, R.; Finizola, A.
2015-12-01
In the crust, fractures/faults can provide preferential pathways for fluid flow or act as barriers preventing the flow across these structures. In hydrothermal systems (usually found in fractured rock masses), these discontinuities may play a critical role at various scales, controlling fluid flows and heat transfer. The thermal convection is numerically computed in 3D fluid satured fractured porous media. Fractures are inserted as discrete objects, randomly distributed over a damaged volume, which is a fraction of the total volume. The fluid is assumed to satisfy Darcy's law in the fractures and in the porous medium with exchanges between them. All simulations were made for Rayleigh numbers (Ra) < 150 (hence, the fluid is in thermal equilibrium with the medium), cubic boxes and closed-top conditions. Checks were performed on an unfractured porous medium and the convection cells do start for the theoretical value of Ra, namely 4p². 2D convection was verified up to Ra=800. The influence of parameters such as fracture aperture (or fracture transmissivity), fracture density and fracture length is studied. Moreover, these models are compared to porous media with the same macroscopic permeability. Preliminary results show that the non-uniqueness associated with initial conditions which makes possible either 2D or 3D convection in porous media (Schubert & Straus 1979) is no longer true for fractured porous media (at least for 50
NASA Astrophysics Data System (ADS)
Huang, Yi-Jyun; Wu, Cheng-Yueh; Hsieh, Bieng-Zih
2016-04-01
Gas hydrates are crystalline compounds in which guest gas molecules are trapped in host lattices of ice crystals. In Taiwan, the significant efforts have recently begun to evaluate the reserves of hydrate because the vast accumulations of gas hydrates had been recognized in southwestern offshore Taiwan. Class-3 type hydrate accumulations are referred to an isolated hydrate layer without an underlying zone of mobile fluids, and the entire hydrate layer may be well within the hydrate stability zone. The depressurization method is a useful dissociation method for gas production from Class-3 hydrate accumulations. The dissociation efficiency is controlled by the responses of hydrate to the propagating pressure disturbance, and the pressure propagation is relating to the amount (or saturation) of the mobile fluid in pore space of the hydrate layer. The purpose of this study is to study the effects of fluid saturation on the gas recovery from a class-3 hydrate accumulation using depressurization method. The case of a class-3 hydrate deposit of Yuan-An Ridge in southwestern offshore Taiwan is studied. The numerical method was used in this study. The reservoir simulator we used to study the dissociation of hydrate and the production of gas was the STARS simulator developed by CMG, which coupled heat transfer, geo-chemical, geo-mechanical, and multiphase fluid flow mechanisms. The study case of Yuan-An Ridge is located in southwestern offshore Taiwan. The hydrate deposit was found by the bottom simulating reflectors (BSRs). The geological structure of the studied hydrate deposit was digitized to build the geological model (grids) of the case. The formation parameters, phase behavior data, rock and fluid properties, and formation's initial conditions were assigned sequentially to grid blocks, and the completion and operation conditions were designed to wellbore blocks to finish the numerical model. The changes of reservoir pressure, temperature, saturation due to the hydrate
NASA Astrophysics Data System (ADS)
Baccheschi, P.; Pastori, M.; Margheriti, L.; Piccinini, D.
2016-03-01
The Abruzzi region is located in the Central Apennines Neogene fold-and-thrust belt and has one of the highest seismogenic potential in Italy, with high and diffuse crustal seismicity related to NE-SW oriented extension. In this study, we investigate the detailed spatial variation in shear wave splitting providing high-resolution anisotropic structure beneath the L'Aquila region. To accomplish this, we performed a systematic analysis of crustal anisotropic parameters: fast polarization direction (ϕ) and delay time (δt). We benefit from the dense coverage of seismic stations operating in the area and from a catalogue of several accurate earthquake locations of the 2009 L'Aquila seismic sequence, related to the Mw 6.1 2009 L'Aquila main shock, to describe in detail the geometry of the anisotropic volume around the active faults that ruptured. The spatial variations both in ϕ and δt suggest a complex anisotropic structure beneath the region caused by a combination of both structural- and stress-induced mechanisms. The average ϕ is NNW-SSE oriented (N141°), showing clear similarity both with the local fault strike and the SHmax. In the central part of the study area fast axes are oriented NW-SE, while moving towards the northeastern and northwestern sectors the fast directions clearly diverge from the general trend of NW-SE and rotate accordingly to the local fault strikes. The above-mentioned fault-parallel ϕ distribution suggests that the observed anisotropy is mostly controlled by the local fault-related structure. Toward the southeast fast directions become orthogonal both to strike of the local mapped faults and to the SHmax. Here, ϕ are predominantly oriented NE-SW; we interpret this orientation as due to the presence of a highly fractured and overpressurized rock volume which should be responsible of the 90° flips in ϕ and the increase in δt. Another possible mechanism for NE-SW orientation of ϕ in the southeastern sector could be ascribed to the
Hayat, Tasawar; Rafiq, Maimona; Ahmad, Bashir
2016-01-01
The objective of present paper is to examine the peristaltic flow of magnetohydrodynamic (MHD) Jeffrey fluid saturating porous space in a channel through rotating frame. Unlike the previous attempts, the flow formulation is based upon modified Darcy's law porous medium effect in Jeffrey fluid situation. In addition the impacts due to Soret and Dufour effects in the radiative peristaltic flow are accounted. Rosseland’s approximation has been utilized for the thermal radiative heat flux. Lubrication approach is implemented for the simplification. Resulting problems are solved for the stream function, temperature and concentration. Graphical results are prepared and analyzed for different parameters of interest entering into the problems. PMID:26808387
NASA Astrophysics Data System (ADS)
Jishi, Fu; Jinchang, Mao; En, Wu; Yongqiang, Jia; Borui, Zhang; Lizhu, Zhang; Guogang, Qin; Yuhua, Zhang; Genshuan, Wui
1994-12-01
An anisotropic EPR signal was observed in porous Si. According to its symmetry and g value, the EPR signal can be attributed to silicon dangling bonds located on the surface of a porous Si skeleton. The evolution of the EPR signal at room temperature in air was measured. The annealing temperature dependence of the EPR and the PL of porous Si in oxygen and the effects of gamma irradiation on the EPR and the PL spectra of porous Si were studied. The changes of the EPR signal and the PL intensity induced in atmosphere by ethyl alcohol and acetone were discovered. The dangling bond is only one of the factors which affect the PL.
Magnetohydrodynamic stability of natural convection in a vertical porous slab
NASA Astrophysics Data System (ADS)
Shankar, B. M.; Kumar, Jai; Shivakumara, I. S.
2017-01-01
The stability of the conduction regime of natural convection in an electrically conducting fluid saturated porous vertical slab is investigated in the presence of a uniform external transverse magnetic field. The flow in the porous medium is described by modified Brinkman-extended Darcy equation with fluid viscosity different from effective viscosity. The boundaries of the vertical porous slab are assumed to be rigid-isothermal and electrically non-conducting. The resulting stability equations are solved numerically using Galerkin method. The critical Grashof number Gc, the critical wave number αc and the critical wave speed cc are computed for a wide range of porous parameter σp, the ratio of effective viscosity to the fluid viscosity Λ, the Prandtl number Pr and the Hartmann number M. Based on these parameters, the stability characteristics of the system are discussed in detail. The presence of advective inertia is to instill instability on the flow in a porous medium and found that the magnetic field, porous parameter and ratio of viscosities have a stabilizing effect on both stationary and oscillatory wave instabilities. Besides, the value of Pr at which transition occurs from stationary to oscillatory mode of instability decreases with increasing M ,σp and Λ .
Numerical solutions for steady thermal convection from a concentrated source in a porous medium
Hickox, C.E.; Watts, H.A.
1980-06-01
Solutions for the steady, axisymmetric velocity and temperature fields associated with a point source of thermal energy in a fluid-saturated porous medium are obtained numerically through use of similarity transformations. The two cases considered are those of a point source located on the lower, insulated boundary of a semi-infinite region and a point source embedded in an infinite region. Numerical results are presented from which complete descriptions of the velocity and temperature fields can be constructed for Rayleigh numbers ranging from 10/sup -3/ to 10/sup 2/.
Study on Two-Phase Flow in Heterogeneous Porous Media by Light Transmission Method
NASA Astrophysics Data System (ADS)
Qiao, W.
2015-12-01
The non-aqueous phase liquid (NAPL) released to the subsurface can form residual ganglia and globules occupying pores and also accumulate and form pools, in which multiphase system forms. Determining transient fluid saturations in a multiphase system is essential to understand the flow characteristics of systems and to perform effective remediation strategies. As a non-destructive and non-invasive laboratory technique utilized for the measurement of liquid saturation in porous media, light transmission is of the lowest cost and safe. Utilization of Coupled Charge Device camera in light transmission systems provides a nearly instantaneous high-density array of spatial measurements over a very large dynamic range. The migration of NAPL and air spariging technique applied to remove NAPL in aquifer systems are typically two-phase flow problem. Because of the natural aquifer normally being heterogeneous, two 2-D sandboxes (Length55cm×width1.3cm×hight45cm) are set up to study the migration of gas and DNAPL in heterogeneous porous media based on light transmission method and its application in two-phase flow. Model D for water/gas system developed by Niemet and Selker (2001) and Model NW-A for water/NAPL system developed by Zhang et al. (2014) are applied for the calculation of fluid saturation in the two experiments, respectively. The gas injection experiments show that the gas moves upward in the irregular channels, piling up beneath the low permeability lenses and starting lateral movement. Bypassing the lenses, the gas moves upward and forms continuous distribution in the top of the sandbox. The faster of gas injects, the wider of gas migration will be. The DNAPL infiltration experiment shows that TCE mainly moves downward as the influence of gravity, stopping vertical infiltration when reaching the low permeability lenses because of its failure to overcome the capillary pressure. Then, TCE accumulates on the surface and starts transverse movement. Bypassing the
Lattice Boltzmann Method for Diffusion-Reaction-Transport Processes in Heterogeneous Porous Media
NASA Astrophysics Data System (ADS)
Xu, You-Sheng; Zhong, Yi-Jun; Huang, Guo-Xiang
2004-07-01
Based on the lattice Boltzmann method and general theory of fluids flowing in porous media, a numerical model is presented for the diffusion-reaction-transport (DRT) processes in porous media. As a test, we simulate a DRT process in a two-dimensional horizontal heterogeneous porous medium. The influence of gravitation in this case can be neglected, and the DRT process can be described by a strongly heterogeneous diagnostic test strip or a thin confined piece of soil with stochastically distributing property in horizontal directions. The results obtained for the relations between reduced fluid saturation S, concentration c1, and concentration c2 are shown by using the visualization computing technique. The computational efficiency and stability of the model are satisfactory.
Mixed Convection Opposing Flow in a Vertical Porous Annulus-Two Temperature Model
NASA Astrophysics Data System (ADS)
Al-Rashed, Abdullah A. AA; J, Salman Ahmed N.; Khaleed, H. M. T.; Yunus Khan, T. M.; NazimAhamed, K. S.
2016-09-01
The opposing flow in a porous medium refers to a condition when the forcing velocity flows in opposite direction to thermal buoyancy obstructing the buoyant force. The present research refers to the effect of opposing flow in a vertical porous annulus embedded with fluid saturated porous medium. The thermal non-equilibrium approach with Darcy modal is considered. The boundary conditions are such that the inner radius is heated with constant temperature Tw the outer radius is maintained at constant temperature Tc. The coupled nonlinear partial differential equations such as momentum equation, energy equation for fluid and energy equation for solid are solved using the finite element method. The opposing flow variation of average Nusselt number with respect to radius ratio Rr, Aspect ratioAr and Radiation parameter Rd for different values of Peclet number Pe are investigated. It is found that the flow behavior is quite different from that of aiding flow.
Anisotropic Artificial Impedance Surfaces
NASA Astrophysics Data System (ADS)
Quarfoth, Ryan Gordon
Anisotropic artificial impedance surfaces are a group of planar materials that can be modeled by the tensor impedance boundary condition. This boundary condition relates the electric and magnetic field components on a surface using a 2x2 tensor. The advantage of using the tensor impedance boundary condition, and by extension anisotropic artificial impedance surfaces, is that the method allows large and complex structures to be modeled quickly and accurately using a planar boundary condition. This thesis presents the theory of anisotropic impedance surfaces and multiple applications. Anisotropic impedance surfaces are a generalization of scalar impedance surfaces. Unlike the scalar version, anisotropic impedance surfaces have material properties that are dependent on the polarization and wave vector of electromagnetic radiation that interacts with the surface. This allows anisotropic impedance surfaces to be used for applications that scalar surfaces cannot achieve. Three of these applications are presented in this thesis. The first is an anisotropic surface wave waveguide which allows propagation in one direction, but passes radiation in the orthogonal direction without reflection. The second application is a surface wave beam shifter which splits a surface wave beam in two directions and reduces the scattering from an object placed on the surface. The third application is a patterned surface which can alter the scattered radiation pattern of a rectangular shape. For each application, anisotropic impedance surfaces are constructed using periodic unit cells. These unit cells are designed to give the desired surface impedance characteristics by modifying a patterned metallic patch on a grounded dielectric substrate. Multiple unit cell geometries are analyzed in order to find the setup with the best performance in terms of impedance characteristics and frequency bandwidth.
Anisotropic Nanoparticles and Anisotropic Surface Chemistry.
Burrows, Nathan D; Vartanian, Ariane M; Abadeer, Nardine S; Grzincic, Elissa M; Jacob, Lisa M; Lin, Wayne; Li, Ji; Dennison, Jordan M; Hinman, Joshua G; Murphy, Catherine J
2016-02-18
Anisotropic nanoparticles are powerful building blocks for materials engineering. Unusual properties emerge with added anisotropy-often to an extraordinary degree-enabling countless new applications. For bottom-up assembly, anisotropy is crucial for programmability; isotropic particles lack directional interactions and can self-assemble only by basic packing rules. Anisotropic particles have long fascinated scientists, and their properties and assembly behavior have been the subjects of many theoretical studies over the years. However, only recently has experiment caught up with theory. We have begun to witness tremendous diversity in the synthesis of nanoparticles with controlled anisotropy. In this Perspective, we highlight the synthetic achievements that have galvanized the field, presenting a comprehensive discussion of the mechanisms and products of both seed-mediated and alternative growth methods. We also address recent breakthroughs and challenges in regiospecific functionalization, which is the next frontier in exploiting nanoparticle anisotropy.
NASA Astrophysics Data System (ADS)
Lam, Wai Sze Tiffany
Optical components made of anisotropic materials, such as crystal polarizers and crystal waveplates, are widely used in many complex optical system, such as display systems, microlithography, biomedical imaging and many other optical systems, and induce more complex aberrations than optical components made of isotropic materials. The goal of this dissertation is to accurately simulate the performance of optical systems with anisotropic materials using polarization ray trace. This work extends the polarization ray tracing calculus to incorporate ray tracing through anisotropic materials, including uniaxial, biaxial and optically active materials. The 3D polarization ray tracing calculus is an invaluable tool for analyzing polarization properties of an optical system. The 3x3 polarization ray tracing P matrix developed for anisotropic ray trace assists tracking the 3D polarization transformations along a ray path with series of surfaces in an optical system. To better represent the anisotropic light-matter interactions, the definition of the P matrix is generalized to incorporate not only the polarization change at a refraction/reflection interface, but also the induced optical phase accumulation as light propagates through the anisotropic medium. This enables realistic modeling of crystalline polarization elements, such as crystal waveplates and crystal polarizers. The wavefront and polarization aberrations of these anisotropic components are more complex than those of isotropic optical components and can be evaluated from the resultant P matrix for each eigen-wavefront as well as for the overall image. One incident ray refracting or reflecting into an anisotropic medium produces two eigenpolarizations or eigenmodes propagating in different directions. The associated ray parameters of these modes necessary for the anisotropic ray trace are described in Chapter 2. The algorithms to calculate the P matrix from these ray parameters are described in Chapter 3 for
Full waveform inversion of seismic waves reflected in a stratified porous medium
NASA Astrophysics Data System (ADS)
De Barros, Louis; Dietrich, Michel; Valette, Bernard
2010-09-01
In reservoir geophysics applications, seismic imaging techniques are expected to provide as much information as possible on fluid-filled reservoir rocks. Since seismograms are, to some degree, sensitive to the mechanical parameters and fluid properties of porous media, inversion methods can be devised to directly estimate these quantities from the waveforms obtained in seismic reflection experiments. An inversion algorithm that uses a generalized least-squares, quasi-Newton approach is described to determine the porosity, permeability, interstitial fluid properties and mechanical parameters of porous media. The proposed algorithm proceeds by iteratively minimizing a misfit function between observed data and synthetic wavefields computed with the Biot theory. Simple models consisting of plane-layered, fluid-saturated and poro-elastic media are considered to demonstrate the concept and evaluate the performance of such a full waveform inversion scheme. Numerical experiments show that, when applied to synthetic data, the inversion procedure can accurately reconstruct the vertical distribution of a single model parameter, if all other parameters are perfectly known. However, the coupling between some of the model parameters does not permit the reconstruction of several model parameters at the same time. To get around this problem, we consider composite parameters defined from the original model properties and from a priori information, such as the fluid saturation rate or the lithology, to reduce the number of unknowns. Another possibility is to apply this inversion algorithm to time-lapse surveys carried out for fluid substitution problems, such as CO2 injection, since in this case only a few parameters may vary as a function of time. We define a two-step differential inversion approach which allows us to reconstruct the fluid saturation rate in reservoir layers, even though the medium properties are poorly known.
Khan, Sami Ullah; Ali, Nasir; Abbas, Zaheer
2015-01-01
An analysis is carried out to study the heat transfer in unsteady two-dimensional boundary layer flow of a magnetohydrodynamics (MHD) second grade fluid over a porous oscillating stretching surface embedded in porous medium. The flow is induced due to infinite elastic sheet which is stretched periodically. With the help of dimensionless variables, the governing flow equations are reduced to a system of non-linear partial differential equations. This system has been solved numerically using the finite difference scheme, in which a coordinate transformation is used to transform the semi-infinite physical space to a bounded computational domain. The influence of the involved parameters on the flow, the temperature distribution, the skin-friction coefficient and the local Nusselt number is shown and discussed in detail. The study reveals that an oscillatory sheet embedded in a fluid-saturated porous medium generates oscillatory motion in the fluid. The amplitude and phase of oscillations depends on the rheology of the fluid as well as on the other parameters coming through imposed boundary conditions, inclusion of body force term and permeability of the porous medium. It is found that amplitude of flow velocity increases with increasing viscoelastic and mass suction/injection parameters. However, it decreases with increasing the strength of the applied magnetic field. Moreover, the temperature of fluid is a decreasing function of viscoelastic parameter, mass suction/injection parameter and Prandtl number.
Khan, Sami Ullah; Ali, Nasir; Abbas, Zaheer
2015-01-01
An analysis is carried out to study the heat transfer in unsteady two-dimensional boundary layer flow of a magnetohydrodynamics (MHD) second grade fluid over a porous oscillating stretching surface embedded in porous medium. The flow is induced due to infinite elastic sheet which is stretched periodically. With the help of dimensionless variables, the governing flow equations are reduced to a system of non-linear partial differential equations. This system has been solved numerically using the finite difference scheme, in which a coordinate transformation is used to transform the semi-infinite physical space to a bounded computational domain. The influence of the involved parameters on the flow, the temperature distribution, the skin-friction coefficient and the local Nusselt number is shown and discussed in detail. The study reveals that an oscillatory sheet embedded in a fluid-saturated porous medium generates oscillatory motion in the fluid. The amplitude and phase of oscillations depends on the rheology of the fluid as well as on the other parameters coming through imposed boundary conditions, inclusion of body force term and permeability of the porous medium. It is found that amplitude of flow velocity increases with increasing viscoelastic and mass suction/injection parameters. However, it decreases with increasing the strength of the applied magnetic field. Moreover, the temperature of fluid is a decreasing function of viscoelastic parameter, mass suction/injection parameter and Prandtl number. PMID:26657931
Nonlinear Behavior Of Saturated Porous Media Under External Impact
NASA Astrophysics Data System (ADS)
Perepechko, Y.
2005-12-01
This paper deals with nonlinear behavior of liquid saturated porous media in gravity filed under external impact. The continuum is assumed to be a two-velocity medium; it consists of a deformable porous matrix (with Maxwell's reology) and a Newtonian liquid that saturates this matrix. The energy dissipation in this model takes place due the interface friction between the solid matrix and saturating liquid, and also through relaxation of inelastic shear stress in the porous matrix. The elaborated nonisothermal mathematical model for this kind of medium is a thermodynamically consistent and closed model. Godunov's explicit difference scheme was used for computer simulation; the method implies numerical simulation for discontinuity decay in flux calculations. As an illustrative example, we consider the formation of dissipation structures in a plain layer of that medium after pulse or periodic impact on the background of liquid filtration through the porous matrix. At the process beginning, one can observe elastic behavior of the porous matrix. Deformation spreading through the saturated porous matrix occurs almost without distortions and produces a channel-shaped zone of stretching with a high porosity. Later on, dissipation processes and reology properties of porous medium causes the diffusion of this channel. We also observe a correlation between the liquid distribution (porosity for the solid matrix) and dilatancy fields; this allows us to restore the dilatancy field from the measured fluid saturation of the medium. This work was supported by the RFBR (Grant No. 04-05-64107), the Presidium of SB RAS (Grant 106), the President's Grants (NSh-2118.2003.5, NSh-1573.2003.5).
Anisotropic contrast optical microscope.
Peev, D; Hofmann, T; Kananizadeh, N; Beeram, S; Rodriguez, E; Wimer, S; Rodenhausen, K B; Herzinger, C M; Kasputis, T; Pfaunmiller, E; Nguyen, A; Korlacki, R; Pannier, A; Li, Y; Schubert, E; Hage, D; Schubert, M
2016-11-01
An optical microscope is described that reveals contrast in the Mueller matrix images of a thin, transparent, or semi-transparent specimen located within an anisotropic object plane (anisotropic filter). The specimen changes the anisotropy of the filter and thereby produces contrast within the Mueller matrix images. Here we use an anisotropic filter composed of a semi-transparent, nanostructured thin film with sub-wavelength thickness placed within the object plane. The sample is illuminated as in common optical microscopy but the light is modulated in its polarization using combinations of linear polarizers and phase plate (compensator) to control and analyze the state of polarization. Direct generalized ellipsometry data analysis approaches permit extraction of fundamental Mueller matrix object plane images dispensing with the need of Fourier expansion methods. Generalized ellipsometry model approaches are used for quantitative image analyses. These images are obtained from sets of multiple images obtained under various polarizer, analyzer, and compensator settings. Up to 16 independent Mueller matrix images can be obtained, while our current setup is limited to 11 images normalized by the unpolarized intensity. We demonstrate the anisotropic contrast optical microscope by measuring lithographically defined micro-patterned anisotropic filters, and we quantify the adsorption of an organic self-assembled monolayer film onto the anisotropic filter. Comparison with an isotropic glass slide demonstrates the image enhancement obtained by our method over microscopy without the use of an anisotropic filter. In our current instrument, we estimate the limit of detection for organic volumetric mass within the object plane of ≈49 fg within ≈7 × 7 μm(2) object surface area. Compared to a quartz crystal microbalance with dissipation instrumentation, where contemporary limits require a total load of ≈500 pg for detection, the instrumentation demonstrated here improves
Anisotropic contrast optical microscope
NASA Astrophysics Data System (ADS)
Peev, D.; Hofmann, T.; Kananizadeh, N.; Beeram, S.; Rodriguez, E.; Wimer, S.; Rodenhausen, K. B.; Herzinger, C. M.; Kasputis, T.; Pfaunmiller, E.; Nguyen, A.; Korlacki, R.; Pannier, A.; Li, Y.; Schubert, E.; Hage, D.; Schubert, M.
2016-11-01
An optical microscope is described that reveals contrast in the Mueller matrix images of a thin, transparent, or semi-transparent specimen located within an anisotropic object plane (anisotropic filter). The specimen changes the anisotropy of the filter and thereby produces contrast within the Mueller matrix images. Here we use an anisotropic filter composed of a semi-transparent, nanostructured thin film with sub-wavelength thickness placed within the object plane. The sample is illuminated as in common optical microscopy but the light is modulated in its polarization using combinations of linear polarizers and phase plate (compensator) to control and analyze the state of polarization. Direct generalized ellipsometry data analysis approaches permit extraction of fundamental Mueller matrix object plane images dispensing with the need of Fourier expansion methods. Generalized ellipsometry model approaches are used for quantitative image analyses. These images are obtained from sets of multiple images obtained under various polarizer, analyzer, and compensator settings. Up to 16 independent Mueller matrix images can be obtained, while our current setup is limited to 11 images normalized by the unpolarized intensity. We demonstrate the anisotropic contrast optical microscope by measuring lithographically defined micro-patterned anisotropic filters, and we quantify the adsorption of an organic self-assembled monolayer film onto the anisotropic filter. Comparison with an isotropic glass slide demonstrates the image enhancement obtained by our method over microscopy without the use of an anisotropic filter. In our current instrument, we estimate the limit of detection for organic volumetric mass within the object plane of ≈49 fg within ≈7 × 7 μm2 object surface area. Compared to a quartz crystal microbalance with dissipation instrumentation, where contemporary limits require a total load of ≈500 pg for detection, the instrumentation demonstrated here improves
Modeling anisotropic flow and heat transport by using mimetic finite differences
NASA Astrophysics Data System (ADS)
Chen, Tao; Clauser, Christoph; Marquart, Gabriele; Willbrand, Karen; Büsing, Henrik
2016-08-01
Modeling anisotropic flow in porous or fractured rock often assumes that the permeability tensor is diagonal, which means that its principle directions are always aligned with the coordinate axes. However, the permeability of a heterogeneous anisotropic medium usually is a full tensor. For overcoming this shortcoming, we use the mimetic finite difference method (mFD) for discretizing the flow equation in a hydrothermal reservoir simulation code, SHEMAT-Suite, which couples this equation with the heat transport equation. We verify SHEMAT-Suite-mFD against analytical solutions of pumping tests, using both diagonal and full permeability tensors. We compare results from three benchmarks for testing the capability of SHEMAT-Suite-mFD to handle anisotropic flow in porous and fractured media. The benchmarks include coupled flow and heat transport problems, three-dimensional problems and flow through a fractured porous medium with full equivalent permeability tensor. It shows firstly that the mimetic finite difference method can model anisotropic flow both in porous and in fractured media accurately and its results are better than those obtained by the multi-point flux approximation method in highly anisotropic models, secondly that the asymmetric permeability tensor can be included and leads to improved results compared the symmetric permeability tensor in the equivalent fracture models, and thirdly that the method can be easily implemented in existing finite volume or finite difference codes, which has been demonstrated successfully for SHEMAT-Suite.
Seismoelectric Phenomena in Fluid-Saturated Sediments
Block, G I; Harris, J G
2005-04-22
Seismoelectric phenomena in sediments arise from acoustic wave-induced fluid motion in the pore space, which perturbs the electrostatic equilibrium of the electric double layer on the grain surfaces. Experimental techniques and the apparatus built to study this electrokinetic (EK) effect are described and outcomes for studies of seismoelectric phenomena in loose glass microspheres and medium-grain sand are presented. By varying the NaCl concentration in the pore fluid, we measured the conductivity dependence of two kinds of EK behavior: (1) the electric fields generated within the samples by the passage of transmitted acoustic waves, and (2) the electromagnetic wave produced at the fluid-sediment interface by the incident acoustic wave. Both phenomena are caused by relative fluid motion in the sediment pores--this feature is characteristic of poroelastic (Biot) media, but not predicted by either viscoelastic fluid or solid models. A model of plane-wave reflection from a fluid-sediment interface using EK-Biot theory leads to theoretical predictions that compare well to the experimental data for both sand and glass microspheres.
Thermal effects in orthotropic porous elastic beams
NASA Astrophysics Data System (ADS)
Iaşan, D.
2009-01-01
This paper is concerned with the linear theory of anisotropic porous elastic bodies. The extension and bending of orthotropic porous elastic cylinders subjected to a plane temperature field is investigated. The work is motivated by the recent interest in the using of the orthotropic porous elastic solid as model for bones and various engineering materials. First, the thermoelastic deformation of inhomogeneous beams whose constitutive coefficients are independent of the axial coordinate is studied. Then, the extension and bending effects in orthotropic cylinders reinforced by longitudinal rods are investigated. The three-dimensional problem is reduced to the study of two-dimensional problems. The method is used to solve the problem of an orthotropic porous circular cylinder with a special kind of inhomogeneity.
Anisotropic eddy viscosity models
NASA Technical Reports Server (NTRS)
Carati, D.; Cabot, W.
1996-01-01
A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry.
Anisotropic resistivity tomography
NASA Astrophysics Data System (ADS)
Herwanger, J. V.; Pain, C. C.; Binley, A.; de Oliveira, C. R. E.; Worthington, M. H.
2004-08-01
Geophysical tomographic techniques have the potential to remotely detect and characterize geological features, such as fractures and spatially varying lithologies, by their response to signals passed through these features. Anisotropic behaviour in many geological materials necessitates the generalization of tomographic methods to include anisotropic material properties in order to attain high-quality images of the subsurface. In this paper, we present a finite element (FE) based direct-current electrical inversion method to reconstruct the conductivity tensor at each node point of a FE mesh from electrical resistance measurements. The inverse problem is formulated as a functional optimization and the non-uniqueness of the electrical inverse problem is overcome by adding penalty terms for structure and anisotropy. We use a modified Levenberg-Marquardt method for the functional optimization and the resulting set of linear equation is solved using pre-conditioned conjugate gradients. The method is tested using both synthetic and field experiments in cross-well geometry. The acquisition geometry for both experiments uses a cross-well experiment at a hard-rock test site in Cornwall, southwest England. Two wells, spaced at 25.7 m, were equipped with electrodes at a 1 m spacing at depths from 21-108 m and data were gathered in pole-pole geometry. The test synthetic model consists of a strongly anisotropic and conductive body underlain by an isotropic resistive formation. Beneath the resistive formation, the model comprises a moderately anisotropic and moderately conductive half-space, intersected by an isotropic conductive layer. This model geometry was derived from the interpretation of a seismic tomogram and available geological logs and the conductivity values are based on observed conductivities. We use the test model to confirm the ability of the inversion scheme to recover the (known) true model. We find that all key features of the model are recovered. However
NASA Astrophysics Data System (ADS)
Pharoah, J. G.; Karan, K.; Sun, W.
This paper reviews the approach taken in the literature to model the effective transport coefficients - mass diffusivity, electrical conductivity, thermal conductivity and hydraulic permeability - of carbon-fibre based porous electrode of polymer electrolyte membrane fuel cells (PEMFCs). It is concluded that current PEMFC model do not account for the inherent anisotropic microstructure of the fibrous electrodes. Simulations using a 2-D PEMFC cathode model show that neglecting the anisotropic nature and associated transport coefficients of the porous electrodes significantly influences both the nature and the magnitude of the model predictions. This emphasizes the need to appropriately characterize the relevant anisotropic properties of the fibrous electrode.
Fractures in anisotropic media
NASA Astrophysics Data System (ADS)
Shao, Siyi
Rocks may be composed of layers and contain fracture sets that cause the hydraulic, mechanical and seismic properties of a rock to be anisotropic. Coexisting fractures and layers in rock give rise to competing mechanisms of anisotropy. For example: (1) at low fracture stiffness, apparent shear-wave anisotropy induced by matrix layering can be masked or enhanced by the presence of a fracture, depending on the fracture orientation with respect to layering, and (2) compressional-wave guided modes generated by parallel fractures can also mask the presence of matrix layerings for particular fracture orientations and fracture specific stiffness. This report focuses on two anisotropic sources that are widely encountered in rock engineering: fractures (mechanical discontinuity) and matrix layering (impedance discontinuity), by investigating: (1) matrix property characterization, i.e., to determine elastic constants in anisotropic solids, (2) interface wave behavior in single-fractured anisotropic media, (3) compressional wave guided modes in parallel-fractured anisotropic media (single fracture orientation) and (4) the elastic response of orthogonal fracture networks. Elastic constants of a medium are required to understand and quantify wave propagation in anisotropic media but are affected by fractures and matrix properties. Experimental observations and analytical analysis demonstrate that behaviors of both fracture interface waves and compressional-wave guided modes for fractures in anisotropic media, are affected by fracture specific stiffness (controlled by external stresses), signal frequency and relative orientation between layerings in the matrix and fractures. A fractured layered medium exhibits: (1) fracture-dominated anisotropy when the fractures are weakly coupled; (2) isotropic behavior when fractures delay waves that are usually fast in a layered medium; and (3) matrix-dominated anisotropy when the fractures are closed and no longer delay the signal. The
Parallel Anisotropic Tetrahedral Adaptation
NASA Technical Reports Server (NTRS)
Park, Michael A.; Darmofal, David L.
2008-01-01
An adaptive method that robustly produces high aspect ratio tetrahedra to a general 3D metric specification without introducing hybrid semi-structured regions is presented. The elemental operators and higher-level logic is described with their respective domain-decomposed parallelizations. An anisotropic tetrahedral grid adaptation scheme is demonstrated for 1000-1 stretching for a simple cube geometry. This form of adaptation is applicable to more complex domain boundaries via a cut-cell approach as demonstrated by a parallel 3D supersonic simulation of a complex fighter aircraft. To avoid the assumptions and approximations required to form a metric to specify adaptation, an approach is introduced that directly evaluates interpolation error. The grid is adapted to reduce and equidistribute this interpolation error calculation without the use of an intervening anisotropic metric. Direct interpolation error adaptation is illustrated for 1D and 3D domains.
Anisotropic Total Variation Filtering
Grasmair, Markus; Lenzen, Frank
2010-12-15
Total variation regularization and anisotropic filtering have been established as standard methods for image denoising because of their ability to detect and keep prominent edges in the data. Both methods, however, introduce artifacts: In the case of anisotropic filtering, the preservation of edges comes at the cost of the creation of additional structures out of noise; total variation regularization, on the other hand, suffers from the stair-casing effect, which leads to gradual contrast changes in homogeneous objects, especially near curved edges and corners. In order to circumvent these drawbacks, we propose to combine the two regularization techniques. To that end we replace the isotropic TV semi-norm by an anisotropic term that mirrors the directional structure of either the noisy original data or the smoothed image. We provide a detailed existence theory for our regularization method by using the concept of relaxation. The numerical examples concluding the paper show that the proposed introduction of an anisotropy to TV regularization indeed leads to improved denoising: the stair-casing effect is reduced while at the same time the creation of artifacts is suppressed.
Textured silicon nitride: processing and anisotropic properties
Zhu, Xinwen; Sakka, Yoshio
2008-01-01
Textured silicon nitride (Si3N4) has been intensively studied over the past 15 years because of its use for achieving its superthermal and mechanical properties. In this review we present the fundamental aspects of the processing and anisotropic properties of textured Si3N4, with emphasis on the anisotropic and abnormal grain growth of β-Si3N4, texture structure and texture analysis, processing methods and anisotropic properties. On the basis of the texturing mechanisms, the processing methods described in this article have been classified into two types: hot-working (HW) and templated grain growth (TGG). The HW method includes the hot-pressing, hot-forging and sinter-forging techniques, and the TGG method includes the cold-pressing, extrusion, tape-casting and strong magnetic field alignment techniques for β-Si3N4 seed crystals. Each processing technique is thoroughly discussed in terms of theoretical models and experimental data, including the texturing mechanisms and the factors affecting texture development. Also, methods of synthesizing the rodlike β-Si3N4 single crystals are presented. Various anisotropic properties of textured Si3N4 and their origins are thoroughly described and discussed, such as hardness, elastic modulus, bending strength, fracture toughness, fracture energy, creep behavior, tribological and wear behavior, erosion behavior, contact damage behavior and thermal conductivity. Models are analyzed to determine the thermal anisotropy by considering the intrinsic thermal anisotropy, degree of orientation and various microstructure factors. Textured porous Si3N4 with a unique microstructure composed of oriented elongated β-Si3N4 and anisotropic pores is also described for the first time, with emphasis on its unique mechanical and thermal-mechanical properties. Moreover, as an important related material, textured α-Sialon is also reviewed, because the presence of elongated α-Sialon grains allows the production of textured α-Sialon using the
Textured silicon nitride: processing and anisotropic properties.
Zhu, Xinwen; Sakka, Yoshio
2008-07-01
Textured silicon nitride (Si3N4) has been intensively studied over the past 15 years because of its use for achieving its superthermal and mechanical properties. In this review we present the fundamental aspects of the processing and anisotropic properties of textured Si3N4, with emphasis on the anisotropic and abnormal grain growth of β-Si3N4, texture structure and texture analysis, processing methods and anisotropic properties. On the basis of the texturing mechanisms, the processing methods described in this article have been classified into two types: hot-working (HW) and templated grain growth (TGG). The HW method includes the hot-pressing, hot-forging and sinter-forging techniques, and the TGG method includes the cold-pressing, extrusion, tape-casting and strong magnetic field alignment techniques for β-Si3N4 seed crystals. Each processing technique is thoroughly discussed in terms of theoretical models and experimental data, including the texturing mechanisms and the factors affecting texture development. Also, methods of synthesizing the rodlike β-Si3N4 single crystals are presented. Various anisotropic properties of textured Si3N4 and their origins are thoroughly described and discussed, such as hardness, elastic modulus, bending strength, fracture toughness, fracture energy, creep behavior, tribological and wear behavior, erosion behavior, contact damage behavior and thermal conductivity. Models are analyzed to determine the thermal anisotropy by considering the intrinsic thermal anisotropy, degree of orientation and various microstructure factors. Textured porous Si3N4 with a unique microstructure composed of oriented elongated β-Si3N4 and anisotropic pores is also described for the first time, with emphasis on its unique mechanical and thermal-mechanical properties. Moreover, as an important related material, textured α-Sialon is also reviewed, because the presence of elongated α-Sialon grains allows the production of textured α-Sialon using the
Brusseau, M.L.; Narter, M.; Schnaar, G.; Marble, J.
2009-06-01
The objective of this study was to quantitatively characterize the impact of porous-medium texture on interfacial area between immiscible organic liquid and water residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of solid and liquid phases in packed columns. The image data were processed to generate quantitative measurements of organic-liquid/water interfacial area and of organic-liquid blob sizes. Ten porous media, comprising a range of median grain sizes, grain-size distributions, and geochemical properties, were used to evaluate the impact of porous-medium texture on interfacial area. The results show that fluid-normalized specific interfacial area (A{sub f}) and maximum specific interfacial area (A{sub m}) correlate very well to inverse median grain diameter. These functionalities were shown to result from a linear relationship between effective organic-liquid blob diameter and median grain diameter. These results provide the basis for a simple method for estimating specific organic-liquid/water interfacial area as a function of fluid saturation for a given porous medium. The availability of a method for which the only parameter needed is the simple-to-measure median grain diameter should be of great utility for a variety of applications.
On the relativistic anisotropic configurations
NASA Astrophysics Data System (ADS)
Shojai, F.; Kohandel, M.; Stepanian, A.
2016-06-01
In this paper we study anisotropic spherical polytropes within the framework of general relativity. Using the anisotropic Tolman-Oppenheimer-Volkov equations, we explore the relativistic anisotropic Lane-Emden equations. We find how the anisotropic pressure affects the boundary conditions of these equations. Also we argue that the behavior of physical quantities near the center of star changes in the presence of anisotropy. For constant density, a class of exact solution is derived with the aid of a new ansatz and its physical properties are discussed.
Bioinspired Strong and Highly Porous Glass Scaffolds.
Fu, Qiang; Saiz, Eduardo; Tomsia, Antoni P
2011-03-22
The quest for more efficient energy-related technologies is driving the development of porous and high-performance structural materials with exceptional mechanical strength. Natural materials achieve their strength through complex hierarchical designs and anisotropic structures that are extremely difficult to replicate synthetically. We emulate nature's design by direct-ink-write assembling of glass scaffolds with a periodic pattern, and controlled sintering of the filaments into anisotropic constructs similar to biological materials. The final product is a porous glass scaffold with a compressive strength (136 MPa) comparable to that of cortical bone and a porosity (60%) comparable to that of trabecular bone. The strength of this porous glass scaffold is ~100 times that of polymer scaffolds and 4-5 times that of ceramic and glass scaffolds with comparable porosities reported elsewhere. The ability to create both porous and strong structures opens a new avenue for fabricating scaffolds for a broad array of applications, including tissue engineering, filtration, lightweight composites, and catalyst support.
Dickakian, G. B.
1985-11-05
An improved process for preparing an optically anisotropic pitch which comprises heating a pitch feed material at a temperature within the range of about 350/sup 0/ C. to 450/sup 0/ C. while passing an inert gas therethrough at a rate of at least 2.5 SCFH/lb of pitch feed material and agitating said pitch feed material at a stirrer rate of from about 500 to 600 rpm to obtain an essentially 100% mesophase pitch product suitable for carbon production.
Anisotropic spinfoam cosmology
NASA Astrophysics Data System (ADS)
Rennert, Julian; Sloan, David
2014-01-01
The dynamics of a homogeneous, anisotropic universe are investigated within the context of spinfoam cosmology. Transition amplitudes are calculated for a graph consisting of a single node and three links—the ‘Daisy graph’—probing the behaviour a classical Bianchi I spacetime. It is shown further how the use of such single node graphs gives rise to a simplification of states such that all orders in the spin expansion can be calculated, indicating that it is the vertex expansion that contains information about quantum dynamics.
Inhomogeneous anisotropic cosmology
Kleban, Matthew; Senatore, Leonardo
2016-10-12
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with “flat” (including toroidal) and “open” (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are “flat” or “open”. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with “flat” or “open” topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
Inhomogeneous anisotropic cosmology
NASA Astrophysics Data System (ADS)
Kleban, Matthew; Senatore, Leonardo
2016-10-01
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with ``flat'' (including toroidal) and ``open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are ``flat'' or ``open''. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with ``flat'' or ``open'' topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
Anisotropic Particles in Turbulence
NASA Astrophysics Data System (ADS)
Voth, Greg A.; Soldati, Alfredo
2017-01-01
Anisotropic particles are common in many industrial and natural turbulent flows. When these particles are small and neutrally buoyant, they follow Lagrangian trajectories while exhibiting rich orientational dynamics from the coupling of their rotation to the velocity gradients of the turbulence field. This system has proven to be a fascinating application of the fundamental properties of velocity gradients in turbulence. When particles are not neutrally buoyant, they experience preferential concentration and very different preferential alignment than neutrally buoyant tracer particles. A vast proportion of the parameter range of anisotropic particles in turbulence is still unexplored, with most existing research focusing on the simple foundational cases of axisymmetric ellipsoids at low concentrations in homogeneous isotropic turbulence and in turbulent channel flow. Numerical simulations and experiments have recently developed a fairly comprehensive picture of alignment and rotation in these cases, and they provide an essential foundation for addressing more complex problems of practical importance. Macroscopic effects of nonspherical particle dynamics include preferential concentration in coherent structures and drag reduction by fiber suspensions. We review the models used to describe nonspherical particle motion, along with numerical and experimental methods for measuring particle dynamics.
Chaotic advection in 2D anisotropic porous media
NASA Astrophysics Data System (ADS)
Varghese, Stephen; Speetjens, Michel; Trieling, Ruben; Toschi, Federico
2015-11-01
Traditional methods for heat recovery from underground geothermal reservoirs employ a static system of injector-producer wells. Recent studies in literature have shown that using a well-devised pumping scheme, through actuation of multiple injector-producer wells, can dramatically enhance production rates due to the increased scalar / heat transport by means of chaotic advection. However the effect of reservoir anisotropy on kinematic mixing and heat transport is unknown and has to be incorporated and studied for practical deployment in the field. As a first step, we numerically investigate the effect of anisotropy (both magnitude and direction) on (chaotic) advection of passive tracers in a time-periodic Darcy flow within a 2D circular domain driven by periodically reoriented diametrically opposite source-sink pairs. Preliminary results indicate that anisotropy has a significant impact on the location, shape and size of coherent structures in the Poincare sections. This implies that the optimal operating parameters (well spacing, time period of well actuation) may vary strongly and must be carefully chosen so as to enhance subsurface transport. This work is part of the research program of the Foundation for Fundamental Research on Matter (FOM), which is part of Netherlands Organisation for Scientific Research (NWO). This research program is co-financed by Shell Global Solutions International B.V.
Anisotropic power-law inflation
Kanno, Sugumi; Soda, Jiro; Watanabe, Masa-aki E-mail: jiro@tap.scphys.kyoto-u.ac.jp
2010-12-01
We study an inflationary scenario in supergravity model with a gauge kinetic function. We find exact anisotropic power-law inflationary solutions when both the potential function for an inflaton and the gauge kinetic function are exponential type. The dynamical system analysis tells us that the anisotropic power-law inflation is an attractor for a large parameter region.
Heterogeneous porous media in hydrology
NASA Astrophysics Data System (ADS)
Ababou, Rachid
In natural geologic formations, flow and transport-related processes are perturbed by multidimensional and anisotropic material heterogeneities of diverse sizes, shapes, and origins (bedding, layering, inclusions, fractures, grains, for example). Heterogeneity tends to disperse and mix transported quantities and may initiate new transfer mechanisms not seen in ideally homogeneous porous media. Effective properties such as conductivity and dispersivity may not be simple averages of locally measured quantities.The special session, “Effective Constitutive Laws for Heterogeneous Porous Media,” convened at AGU's 1992 Fall Meeting in San Francisco, addressed these issue. Over forty-five contributions, both oral and poster, covering a broad range of physical phenomena were presented. The common theme was the macroscale characterization and modeling of flow and flow-related processes in geologic media that are heterogeneous at various scales (from grain size or fracture aperture, up to regional scales). The processes analyzed in the session included coupled hydro-mechanical processes; Darcy-type flow in the saturated, unsaturated, or two-phase regimes; tracer transport, dilution, and dispersion. These processes were studied for either continuous (porous) or discontinuous (fractured) media.
Anisotropic Kepler and anisotropic two fixed centres problems
NASA Astrophysics Data System (ADS)
Maciejewski, Andrzej J.; Przybylska, Maria; Szumiński, Wojciech
2017-02-01
In this paper we show that the anisotropic Kepler problem is dynamically equivalent to a system of two point masses which move in perpendicular lines (or planes) and interact according to Newton's law of universal gravitation. Moreover, we prove that generalised version of anisotropic Kepler problem as well as anisotropic two centres problem are non-integrable. This was achieved thanks to investigation of differential Galois groups of variational equations along certain particular solutions. Properties of these groups yield very strong necessary integrability conditions.
Thermodynamics of anisotropic branes
NASA Astrophysics Data System (ADS)
Ávila, Daniel; Fernández, Daniel; Patiño, Leonardo; Trancanelli, Diego
2016-11-01
We study the thermodynamics of flavor D7-branes embedded in an anisotropic black brane solution of type IIB supergravity. The flavor branes undergo a phase transition between a `Minkowski embedding', in which they lie outside of the horizon, and a `black hole embedding', in which they fall into the horizon. This transition depends on the black hole temperature, its degree of anisotropy, and the mass of the flavor degrees of freedom. It happens either at a critical temperature or at a critical anisotropy. A general lesson we learn from this analysis is that the anisotropy, in this particular realization, induces similar effects as the temperature. In particular, increasing the anisotropy bends the branes more and more into the horizon. Moreover, we observe that the transition becomes smoother for higher anisotropies.
Optical trapping of anisotropic nanocylinder
NASA Astrophysics Data System (ADS)
Bareil, Paul B.; Sheng, Yunlong
2013-09-01
The T-matrix method with the Vector Spherical Wave Function (VSWF) expansions represents some difficulties for computing optical scattering of anisotropic particles. As the divergence of the electric field is nonzero in the anisotropic medium and the VSWFs do not satisfy the anisotropic wave equations one questioned whether the VSWFs are still a suitable basis in the anisotropic medium. We made a systematic and careful review on the vector basis functions and the VSWFs. We found that a field vector in Euclidean space can be decomposed to triplet vectors {L, M, N}, which as non-coplanar. Especially, the vector L is designed to represent non-zero divergence component of the vector solution, so that the VSWF basis is sufficiently general to represent the solutions of the anisotropic wave equation. The mathematical proof can be that when the anisotropic wave equations is solved in the Fourier space, the solution is expanded in the basis of the plan waves with angular spectrum amplitude distributions. The plane waves constitute an orthogonal and complete set for the anisotropic solutions. Furthermore, the plane waves are expanded into the VSWF basis. These two-step expansions are equivalent to the one-step direct expansion of the anisotropic solution to the VSWF basis. We used direct VSWF expansion, along with the point-matching method in the T-matrix, and applied the boundary condition to the normal components displacement field in order to compute the stress and the related forces and torques and to show the mechanism of the optical trap of the anisotropic nano-cylinders.
Vortex dynamics in anisotropic traps
McEndoo, S.; Busch, Th.
2010-07-15
We investigate the dynamics of linear vortex lattices in anisotropic traps in two dimensions and show that the interplay between the rotation and the anisotropy leads to a rich but highly regular dynamics.
Porous to Nonporous Transition in the Morphology of Metal Assisted Etched Silicon Nanowires
NASA Astrophysics Data System (ADS)
Lotty, Olan; Petkov, Nikolay; Georgiev, Yordan M.; Holmes, Justin D.
2012-11-01
A single step metal assisted etching (MAE) process, utilizing metal ion-containing HF solutions in the absence of an external oxidant, has been developed to generate heterostructured Si nanowires with controllable porous (isotropically etched) and non-porous (anisotropically etched) segments. Detailed characterisation of both the porous and non-porous sections of the Si nanowires was provided by transmission electron microscopy studies, enabling the mechanism of nanowire roughening to be ascertained. The versatility of the MAE method for producing heterostructured Si nanowires with varied and controllable textures is discussed in detail.
Actuation performances of anisotropic gels
NASA Astrophysics Data System (ADS)
Nardinocchi, P.; Teresi, L.
2016-12-01
We investigated the actuation performances of anisotropic gels driven by mechanical and chemical stimuli, in terms of both deformation processes and stroke-curves, and distinguished between the fast response of gels before diffusion starts and the asymptotic response attained at the steady state. We also showed as the range of forces that an anisotropic hydrogel can exert when constrained is especially wide; indeed, changing fiber orientation allows us to induce shear as well as transversely isotropic extensions.
Anisotropic assembly and pattern formation
NASA Astrophysics Data System (ADS)
von Brecht, James H.; Uminsky, David T.
2017-01-01
We investigate the role of anisotropy in two classes of individual-based models for self-organization, collective behavior and self-assembly. We accomplish this via first-order dynamical systems of pairwise interacting particles that incorporate anisotropic interactions. At a continuum level, these models represent the natural anisotropic variants of the well-known aggregation equation. We leverage this framework to analyze the impact of anisotropic effects upon the self-assembly of co-dimension one equilibrium structures, such as micelles and vesicles. Our analytical results reveal the regularizing effect of anisotropy, and isolate the contexts in which anisotropic effects are necessary to achieve dynamical stability of co-dimension one structures. Our results therefore place theoretical limits on when anisotropic effects can be safely neglected. We also explore whether anisotropic effects suffice to induce pattern formation in such particle systems. We conclude with brief numerical studies that highlight various aspects of the models we introduce, elucidate their phase structure and partially validate the analysis we provide.
Berryman, J.G.
2010-06-01
The mechanics of vertically layered porous media has some similarities to and some differences from the more typical layered analysis for purely elastic media. Assuming welded solid contact at the solid-solid interfaces implies the usual continuity conditions, which are continuity of the vertical (layering direction) stress components and the horizontal strain components. These conditions are valid for both elastic and poroelastic media. Differences arise through the conditions for the pore pressure and the increment of fluid content in the context of fluid-saturated porous media. The two distinct conditions most often considered between any pair of contiguous layers are: (1) an undrained fluid condition at the interface, meaning that the increment of fluid content is zero (i.e., {delta}{zeta} = 0), or (2) fluid pressure continuity at the interface, implying that the change in fluid pressure is zero across the interface (i.e., {delta}p{sub f} = 0). Depending on the types of measurements being made on the system and the pertinent boundary conditions for these measurements, either (or neither) of these two conditions might be directly pertinent. But these conditions are sufficient nevertheless to be used as thought experiments to determine the expected values of all the poroelastic coefficients. For quasi-static mechanical changes over long time periods, we expect drained conditions to hold, so the pressure must then be continuous. For high frequency wave propagation, the pore-fluid typically acts as if it were undrained (or very nearly so), with vanishing of the fluid increment at the boundaries being appropriate. Poroelastic analysis of both these end-member cases is discussed, and the general equations for a variety of applications to heterogeneous porous media are developed. In particular, effective stress for the fluid permeability of such poroelastic systems is considered; fluid permeabilities characteristic of granular media or tubular pore shapes are treated
Instability of fluid flow over saturated porous medium
NASA Astrophysics Data System (ADS)
Lyubimova, Tatyana; Kolchanova, Ekaterina; Lyubimov, Dmitry
2013-04-01
We investigate the stability of a fluid flow over a saturated porous medium. The problem is of importance due to the applications to washing out of contaminants from the bottom layer of vegetation, whose properties are similar to the properties of porous medium. In the case of porous medium with the relatively high permeability and porosity the flow involves a part of the fluid saturating the porous medium, with the tangential fluid velocity drop occurring because of the resistance of the solid matrix. The drop leads to the instability analogous to Kelvin-Helmholtz one accompanied by the formation of travelling waves. In the present paper we consider a two-layer system consisting of a pure fluid layer and a porous layer saturated by the fluid located underneath. The system is bounded by a rigid surface at the bottom and a non-deformable free surface at the top. It is under the gravity and inclined at a slight angle to the horizontal axis. The boundary conditions at the interface between the fluid and porous layers are the continuity of fluid velocities and the balance of normal and tangential stresses taking into account the resistance of the solid matrix with respect to the fluid flow near the interface [1-2]. The problem is solved in the framework of the Brinkman model applying the classical shooting algorithm with orthogonalization. The stability boundaries of the stationary fluid flow over the saturated porous medium with respect to the small oscillatory perturbations are obtained for the various values of the Darcy number and the ratio of the porous layer thickness to the full thickness of the system d. It was shown that at the d > 0.5 with increasing the porous layer thickness (or with decreasing of the fluid layer thickness) the stability threshold rises. This is because of the fact that the instability is primarily caused by perturbations located in the fluid layer. At the d < 0.5 the reduction of the porous layer thickness leads to the stability threshold
Light propagation through anisotropic turbulence.
Toselli, Italo; Agrawal, Brij; Restaino, Sergio
2011-03-01
A wealth of experimental data has shown that atmospheric turbulence can be anisotropic; in this case, a Kolmogorov spectrum does not describe well the atmospheric turbulence statistics. In this paper, we show a quantitative analysis of anisotropic turbulence by using a non-Kolmogorov power spectrum with an anisotropic coefficient. The spectrum we use does not include the inner and outer scales, it is valid only inside the inertial subrange, and it has a power-law slope that can be different from a Kolmogorov one. Using this power spectrum, in the weak turbulence condition, we analyze the impact of the power-law variations α on the long-term beam spread and scintillation index for several anisotropic coefficient values ς. We consider only horizontal propagation across the turbulence cells, assuming circular symmetry is maintained on the orthogonal plane to the propagation direction. We conclude that the anisotropic coefficient influences both the long-term beam spread and the scintillation index by the factor ς(2-α).
Coefficient adaptive triangulation for strongly anisotropic problems
D`Azevedo, E.F.; Romine, C.H.; Donato, J.M.
1996-01-01
Second order elliptic partial differential equations arise in many important applications, including flow through porous media, heat conduction, the distribution of electrical or magnetic potential. The prototype is the Laplace problem, which in discrete form produces a coefficient matrix that is relatively easy to solve in a regular domain. However, the presence of anisotropy produces a matrix whose condition number is increased, making the resulting linear system more difficult to solve. In this work, we take the anisotropy into account in the discretization by mapping each anisotropic region into a ``stretched`` coordinate space in which the anisotropy is removed. The region is then uniformly triangulated, and the resulting triangulation mapped back to the original space. The effect is to generate long slender triangles that are oriented in the direction of ``preferred flow.`` Slender triangles are generally regarded as numerically undesirable since they tend to cause poor conditioning; however, our triangulation has the effect of producing effective isotropy, thus improving the condition number of the resulting coefficient matrix.
Numerical modeling of anisotropic fiber bundle behavior in oxygenators.
Bhavsar, Sonya S; Schmitz-Rode, Thomas; Steinseifer, Ulrich
2011-11-01
Prediction of flow patterns through oxygenator fiber bundles can allow shape optimization so that efficient gas exchange occurs with minimal thrombus formation and hemolysis. Computational fluid dynamics (CFD) simulations can be used to predict three-dimensional flow velocities and flow distribution from spatially dependent variables and they allow estimations of erythrocyte residence time within the fiber bundle. This study builds upon previous work to develop an accurate numerical model for oxygenators, which would allow for accelerated iterations in oxygenator shape and diffuser plate design optimization. Hollow fiber flow channels were developed to permit experimental calculation of fluid permeability in two directions: main flow along the hollow fiber and perpendicular to the hollow fibers. Commercial software was used to develop three-dimensional CFD models of the experimental flow channels and an anisotropic porous media model for oxygenators from these experimental results. The oxygenator model was used to predict pressure loss throughout the device, visualize blood distribution within the fiber bundle, and estimate erythrocyte residence time within the bundle. Experimental flow channels measurements produced a streamwise permeability of 1.143e(-8) m(2) and transverse permeability of 2.385e(-9) m(2) . These permeabilities, coupled with previous work with volume porosity, were used to develop the numerical model of anisotropic behavior through porous fiber bundles, which indicated a more uniform flow field throughout the oxygenator. Incorporation of known anisotropic fiber bundle behavior in previous numerical models more accurately represents fluid behavior through an oxygenator fiber bundle. CFD coupled with experimental validation can produce a powerful tool for oxygenator design and development.
NASA Astrophysics Data System (ADS)
Aursjø, Olav; Knudsen, Henning Arendt; Flekkøy, Eirik G.; Måløy, Knut Jørgen
2010-08-01
We present a numerical study of the statistical behavior of a two-phase flow in a two-dimensional porous medium subjected to an oscillatory acceleration transverse to the overall direction of flow. A viscous nonwetting fluid is injected into a porous medium filled with a more viscous wetting fluid. During the whole process sinusoidal oscillations of constant amplitude and frequency accelerates the porous medium sideways, perpendicular to the overall direction of flow. The invasion process displays a transient behavior where the saturation of the defending fluid decreases, before it enters a state of irreducible wetting fluid saturation, where there is no net transport of defending fluid toward the outlet of the system. In this state the distribution of sizes of the remaining clusters are observed to obey a power law with an exponential cutoff. The cutoff cluster size is found to be determined by the flow and oscillatory stimulation parameters. This cutoff size is also shown to be directly related to the extracted amount of defending fluid. Specifically, the results show that the oscillatory acceleration of the system leads to potentially a large increase in extracted wetting fluid.
Quantifying solid-fluid interfacial phenomena in porous rocks with proton nuclear magnetic resonance
NASA Astrophysics Data System (ADS)
Schmidt, Ehud J.; Velasco, Katherine K.; Nur, Amos M.
1986-04-01
The three order-of-magnitude variation in the proton nuclear magnetic resonance (NMR) longitudinal relaxation time T1 of water adsorbed on silica surfaces versus that of bulk water makes proton NMR studies of porous materials powerful tools to study the effects of adsorption. Recent theory permits the utilization of this different response to obtain pore space surface-to-volume (S/V) distribution functions by inverting the decay of the z component of magnetization of fully saturated porous rocks; information can likewise be obtained on the fluid distribution at partially saturated conditions. A computer program has been developed to invert the NMR relaxation curves for the S/V distribution function, assuming an isolated pore regime, the ramifications of which are examined. The program has been applied to experimental results from water, porous sandstones, and tight gas sands at various pore fluid saturations and varying electrolyte content. For the fully saturated case, the results show promise in the application of NMR to describing pore space geometries in rock samples with widely varying surface-to-volume ratios. For partially saturated rocks, the results reflect the preferential early draining of the large pores at high water saturations, connectivity percolation phenomena at intermediate saturations, and the dominating role of adsorbed water films at low water saturations. Experiments on rocks saturated with saline solutions disclose the importance of the effects of alteration of the active sites on the rock surfaces as well as the role of electrolytes in modifying the structural properties of bulk solution.
Streaming potential in porous media: 1. Theory of the zeta potential
NASA Astrophysics Data System (ADS)
Revil, A.; Pezard, P. A.; Glover, P. W. J.
1999-09-01
Electrokinetic phenomena are responsible for several electrical properties of fluid-saturated porous materials. Geophysical applications of these phenomena could include the use of streaming potentials for mapping subsurface fluid flow, the study of hydrothermal activity of geothermal areas, and in the context of earthquake prediction and volcanic activity forecasting, for example. The key parameter of electrokinetic phenomena is the ξ potential, which represents roughly the electrical potential at the mineral/water interface. We consider silica-dominated porous materials filled with a binary symmetric 1:1 electrolyte such as NaCl. When in contact with this electrolyte, the silica/water interface gets an excess of charge through chemical reactions. Starting with these chemical reactions, we derive analytical equations for the ξ potential and the specific surface conductance. These equations can be used to predict the variations of these parameters with the pore fluid salinity, temperature, and pH (within a /pH range of 6-8). The input parameters to these equations fall into two categories: (1) mineral/fluid interaction geochemistry (including mineral surface site density and surface equilibrium constants of mineral/fluid reactions), and (2) pore fluid /pH, salinity, and temperature. The ξ potential is shown to increase with increasing temperature and pH and to decrease with increasing salinity. The proposed model is in agreement with available experimental data. The application of this model to electric potentials generated in porous media by fluid flow is explored in the companion paper.
Freeze Tape Casting of Functionally Graded Porous Ceramics
NASA Technical Reports Server (NTRS)
Sofie, Stephen W.
2007-01-01
Freeze tape casting is a means of making preforms of ceramic sheets that, upon subsequent completion of fabrication processing, can have anisotropic and/or functionally graded properties that notably include aligned and graded porosity. Freeze tape casting was developed to enable optimization of the microstructures of porous ceramic components for use as solid oxide electrodes in fuel cells: Through alignment and grading of pores, one can tailor surface areas and diffusion channels for flows of gas and liquid species involved in fuel-cell reactions. Freeze tape casting offers similar benefits for fabrication of optimally porous ceramics for use as catalysts, gas sensors, and filters.
Fluctuation relations for anisotropic systems
NASA Astrophysics Data System (ADS)
Villavicencio-Sanchez, R.; Harris, R. J.; Touchette, H.
2014-02-01
Currents of particles or energy in driven non-equilibrium steady states are known to satisfy certain symmetries, referred to as fluctuation relations, determining the ratio of the probabilities of positive fluctuations to negative ones. A generalization of these fluctuation relations has been proposed recently for extended non-equilibrium systems of dimension greater than one, assuming, crucially, that they are isotropic (Hurtado P. I., Pérez-Espigares C., del Pozo J. J. and Garrido P. L., Proc. Natl. Acad. Sci. U.S.A., 108 (2011) 7704). Here we relax this assumption and derive a fluctuation relation for d-dimensional systems having anisotropic bulk driving rates. We test the validity of this anisotropic fluctuation relation by calculating the particle current fluctuations in the 2d anisotropic zero-range process, using both exact and fluctuating hydrodynamic approaches.
Fabrication, properties, and applications of porous metals with directional pores.
Nakajima, Hideo
2010-01-01
Lotus-type porous metals with aligned long cylindrical pores are fabricated by unidirectional solidification from the melt with a dissolved gas such as hydrogen, nitrogen, or oxygen. The gas atoms can be dissolved into the melt via a pressurized gas atmosphere or thermal decomposition of gaseous compounds. Three types of solidification techniques have been developed: mold casting, continuous zone melting, and continuous casting techniques. The last method is superior from the viewpoint of mass production of lotus metals. The observed anisotropic behaviors of the mechanical properties, sound absorption, and thermal conductivity are inherent to the anisotropic porous structure. In particular, the remarkable anisotropy in the mechanical strength is attributed to the stress concentration around the pores aligned perpendicular to the loading direction. Heat sinks are a promising application of lotus metals due to the high cooling performance with a large heat transfer.
Fabrication, properties, and applications of porous metals with directional pores
NAKAJIMA, Hideo
2010-01-01
Lotus-type porous metals with aligned long cylindrical pores are fabricated by unidirectional solidification from the melt with a dissolved gas such as hydrogen, nitrogen, or oxygen. The gas atoms can be dissolved into the melt via a pressurized gas atmosphere or thermal decomposition of gaseous compounds. Three types of solidification techniques have been developed: mold casting, continuous zone melting, and continuous casting techniques. The last method is superior from the viewpoint of mass production of lotus metals. The observed anisotropic behaviors of the mechanical properties, sound absorption, and thermal conductivity are inherent to the anisotropic porous structure. In particular, the remarkable anisotropy in the mechanical strength is attributed to the stress concentration around the pores aligned perpendicular to the loading direction. Heat sinks are a promising application of lotus metals due to the high cooling performance with a large heat transfer. PMID:21084772
Okada, Kiyoshi; Isobe, Toshihiro; Katsumata, Ken-Ichi; Kameshima, Yoshikazu; Nakajima, Akira; MacKenzie, Kenneth J D
2011-12-01
Porous ceramics with unidirectionally oriented pores have been prepared by various methods such as anodic oxidation, templating using wood, unidirectional solidification, extrusion, etc. The templating method directly replicates the porous microstructure of wood to prepare porous ceramics, whereas the extrusion method mimics the microstructures of tracheids and xylems in trees. These two methods are therefore the main focus of this review as they provide good examples of the preparation of functional porous ceramics with properties replicating nature. The well-oriented cylindrical through-hole pores prepared by the extrusion method using fibers as the pore formers provide excellent permeability together with high mechanical strength. Examples of applications of these porous ceramics are given, including their excellent capillary lift of over 1 m height which could be used to counteract urban heat island phenomena, and other interesting properties arising from anisotropic unidirectional porous structures.
Okada, Kiyoshi; Isobe, Toshihiro; Katsumata, Ken-ichi; Kameshima, Yoshikazu; Nakajima, Akira; MacKenzie, Kenneth J D
2011-01-01
Porous ceramics with unidirectionally oriented pores have been prepared by various methods such as anodic oxidation, templating using wood, unidirectional solidification, extrusion, etc. The templating method directly replicates the porous microstructure of wood to prepare porous ceramics, whereas the extrusion method mimics the microstructures of tracheids and xylems in trees. These two methods are therefore the main focus of this review as they provide good examples of the preparation of functional porous ceramics with properties replicating nature. The well-oriented cylindrical through-hole pores prepared by the extrusion method using fibers as the pore formers provide excellent permeability together with high mechanical strength. Examples of applications of these porous ceramics are given, including their excellent capillary lift of over 1 m height which could be used to counteract urban heat island phenomena, and other interesting properties arising from anisotropic unidirectional porous structures. PMID:27877451
Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C; Wilson, Thomas S; Maitland, Duncan J
2013-02-04
Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use.
BARTON,THOMAS J.; BULL,LUCY M.; KLEMPERER,WALTER G.; LOY,DOUGLAS A.; MCENANEY,BRIAN; MISONO,MAKOTO; MONSON,PETER A.; PEZ,GUIDO; SCHERER,GEORGE W.; VARTULI,JAMES C.; YAGHI,OMAR M.
1999-11-09
Tailoring of porous materials involves not only chemical synthetic techniques for tailoring microscopic properties such as pore size, pore shape, pore connectivity, and pore surface reactivity, but also materials processing techniques for tailoring the meso- and the macroscopic properties of bulk materials in the form of fibers, thin films and monoliths. These issues are addressed in the context of five specific classes of porous materials: oxide molecular sieves, porous coordination solids, porous carbons, sol-gel derived oxides, and porous heteropolyanion salts. Reviews of these specific areas are preceded by a presentation of background material and review of current theoretical approaches to adsorption phenomena. A concluding section outlines current research needs and opportunities.
Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C.; Wilson, Thomas S.; Maitland, Duncan J.
2013-01-01
Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use. PMID:23646038
Yield surfaces for anisotropic plates
NASA Astrophysics Data System (ADS)
Walker, J. D.; Thacker, B. H.
2000-04-01
Aerospace systems are incorporating composite materials into their structures. The composite materials are often anisotropic in mechanical response due to their geometric layout. For many years, the failure surfaces of anisotropic materials were thought to be characterizable by a quadratic function in the stress, referred to as a Tsai-Wu yield surface, or, in a more restrictive form, a Tsai-Hill yield surface. Such a representation does not work for materials that are strong in two directions and weak in one direction, which is the case of most interest since it represents fiber/epoxy composite plates. This paper demonstrates the impossibility of modeling the failure surface with either the Tsai-Wu or Tsai-Hill failure surfaces. A yield surface is presented based on the lemniscate, which is quartic in the stress. This new yield surface addresses the case of strong in two directions and weak in one.
Anisotropic ripple deformation in phosphorene
Kou, Liangzhi; Ma, Yandong; Smith, Sean C.; ...
2015-04-07
Here, two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticitymore » theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.« less
Anisotropic ripple deformation in phosphorene
Kou, Liangzhi; Ma, Yandong; Smith, Sean C.; Chen, Changfeng
2015-04-07
Here, two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS_{2}. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticity theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.
Anisotropic Ripple Deformation in Phosphorene.
Kou, Liangzhi; Ma, Yandong; Smith, Sean C; Chen, Changfeng
2015-05-07
Two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticity theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.
Slotted Antenna with Anisotropic Covering
2015-08-06
08-2015 Publication Slotted Antenna with Anisotropic Covering David A. Tonn et al Naval Under Warfare Center Division, Newport 1176 Howell St...NUWC 300055 Distribution A An antenna includes a tubular, conductive radiator having a longitudinal slot formed therein from a first end of the...conductive radiator to a second end of the conductive radiator. An antenna feed can be joined to the conductive radiator adjacent to and across the slot
Multiscale modeling of turbulent channel flow over porous walls
NASA Astrophysics Data System (ADS)
Yogaraj, Sudhakar; Lacis, Ugis; Bagheri, Shervin
2016-11-01
We perform direct numerical simulations of fully developed turbulent flow through a channel coated with a porous material. The Navier-stokes equations governing the fluid domain and the Darcy equations of the porous medium are coupled using an iterative partitioned scheme. At the interface between the two media, boundary conditions derived using a multiscale homogenization approach are enforced. The main feature of this approach is that the anisotropic micro-structural pore features are directly taken into consideration to derive the constitutive coefficients of the porous media as well as of the interface. The focus of the present work is to study the influence of micro-structure pore geometry on the dynamics of turbulent flows. Detailed turbulence statistics and instantaneous flow field are presented. For comparison, flow through impermeable channel flows are included. Supported by the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant agreement No 708281.
Experimental study of seismic attenuation in partially saturated porous media
NASA Astrophysics Data System (ADS)
Barrière, Julien; Bordes, Clarisse; Sénéchal, Pascale
2010-05-01
Nowadays, it is well admitted that hydrogeological properties of the porous media (porosity, fluid saturation and permeability) can influence seismic properties. In geophysics, the major theory which links hydrogeological and seismic parameters is poroelasticity proposed by Biot (1956). The Biot relaxation process is due to the relative displacement of fluid in comparison to the solid which causes a significant attenuation of seismic waves, notably in unconsolidated medium. In partially saturated medium, pore fluids are considered as a perfect mixture and so called 'effective fluid'. However, in more consolidated rocks, the Biot theory is not sufficient to explain the attenuation level as measured from field seismic and sonic log data. In the last decade, some authors provide new theories to understand the attenuation caused by the interaction of the different fluids. Most experiments are done in the ultrasonic frequency range, where sources of attenuation (like scattering or local fluid flow) are different as in the low frequency range where the wavelength is greater than heterogeneities size. In this way, we propose a forward-looking experiment with the use of a vertical impulsionnal seismic source which have a strong amplitude spectrum ranging from 100Hz to 8kHz. We study three different unconsolidated porous media at atmospheric pressure: fine-grained sand, coarsed-grained sand and coarse gravel. Water content is measured with a calibrated capacitance probe and temperature effects are corrected. Seismic wave propagation is recorded by piezoelectric accelerometers designed for frequencies below 10kHz. The water injection is done by imbibition. We propose to analyse the attenuation in the [100Hz-1.5kHz] frequency range for the studied media with various water saturation levels. The attenuation varies according to the porous medium and the water content and appears more significant at dry condition and at high saturation level. The weak cohesion at dry condition
Yield Surfaces for Anisotropic Plates
NASA Astrophysics Data System (ADS)
Walker, J. D.; Thacker, B. H.
1999-06-01
Modern aerospace systems are incorporating composite materials into their structures. Often, the composite materials are anisotropic in their mechanical response due to the geometric layout of fibers. For many years, the failure surfaces of anisotropic materials were thought to be characterizable by a quadratic function in the stress, often referred to as a Tsai-Wu yield surface, or, in a more restrictive form, a Tsai-Hill yield surface. Such a representation does not work for materials that are strong in two directions and weak in one direction, which, unfortunately, is the case of most interest since it represents most composite plates. This paper demonstrates the impossibility of modeling the failure surface with both the Tsai-Wu and Tsai-Hill failure surfaces. We then present a yield surface based on the lemniscate, which is quartic in the stress. This new yield surface addresses the case of strong in two directions and weak in one. Calculations with a fragment impacting a composite plate modeled with the new yield surface are presented. Modifications of the yield surface are presented to allow, in a limited way, materials that are both anisotropic and have differing strengths in tension and compression.
Viscoacoustic anisotropic full waveform inversion
NASA Astrophysics Data System (ADS)
Qu, Yingming; Li, Zhenchun; Huang, Jianping; Li, Jinli
2017-01-01
A viscoacoustic vertical transverse isotropic (VTI) quasi-differential wave equation, which takes account for both the viscosity and anisotropy of media, is proposed for wavefield simulation in this study. The finite difference method is used to solve the equations, for which the attenuation terms are solved in the wavenumber domain, and all remaining terms in the time-space domain. To stabilize the adjoint wavefield, robust regularization operators are applied to the wave equation to eliminate the high-frequency component of the numerical noise produced during the backward propagation of the viscoacoustic wavefield. Based on these strategies, we derive the corresponding gradient formula and implement a viscoacoustic VTI full waveform inversion (FWI). Numerical tests verify that our proposed viscoacoustic VTI FWI can produce accurate and stable inversion results for viscoacoustic VTI data sets. In addition, we test our method's sensitivity to velocity, Q, and anisotropic parameters. Our results show that the sensitivity to velocity is much higher than that to Q and anisotropic parameters. As such, our proposed method can produce acceptable inversion results as long as the Q and anisotropic parameters are within predefined thresholds.
Optimizing the sensitivity of porous thin film optical sensors
NASA Astrophysics Data System (ADS)
Mackay, Tom G.
2012-10-01
We considered a porous thin film as a platform for optical sensing. It is envisaged that the porous thin filmbecomes infiltrated by a fluid containing an agent to be sensed. The basis for detection of this agent to besensed is provided by changes in the optical properties of the infiltrated porous thin film. Provided that thepore sizes are much smaller than the wavelengths involved, the infiltrated porous thin film may be regardedas a homogenized composite material. Using the well-established Bruggeman homogenization formalism, thesensitivity of such an optical sensor was investigated theoretically. The sensitivity was considered in relation tothe optical properties of the porous thin film and the infiltrating fluid, the porosity of the thin film, and theshape of the pores. For the case of an isotropic dielectric porous thin film of relative permittivity ɛa and anisotropic dielectric fluid of relative permittivity ɛb, the sensitivity was found to be maximized if: (i) the contrast between ɛa and ɛb was maximized; (ii) mid-range values of porosity were used; (iii) the regime 0 < ɛb < 1 with ɛa » 1 pertained, for example; and (iv) pores which have elongated spheroidal shapes were incorporated.
NASA Astrophysics Data System (ADS)
Liang, Dan
Characterization of the structural and optical properties is a subject of significance for nanoporous material research. However, it remains a challenge to find non-destructive methods for investigating the anisotropy of porous thin films with three-dimensional nanostructures. In this thesis, a generalized ellipsometry (GE) analysis approach is employed to study two types of anisotropic nanoporous media: slanted columnar thin films (SCTFs) with polymer infiltration and inverse-SCTF polymeric films. The thesis presents the physical properties obtained from GE analysis, including porosity, columnar shape, principal optical constants, birefringence, etc.. The thesis reports on using a GE analysis approach, combining the homogeneous biaxial layer approach (HBLA) and anisotropic Bruggeman effective medium approximation (AB-EMA), to determine the changes in structural and optical properties of highly porous SCTFs upon polymer infiltration. Via spin-coating, poly(-methyl methacrylate) (PMMA) was infiltrated into the permalloy SCTFs prepared by glancing angle deposition (GLAD). The Mueller matrix GE measurements were conducted on the SCTFs before and after PMMA infiltration. The obtained film thickness and columnar slanting angle show changes due to infiltration which are in good agreement with scanning electron microscopy (SEM) analysis. The method effectively identifies the changes in birefringence and dichroism upon infiltration, and provides constituent fractions consistent with the performed experiments. GE analysis is further utilized to characterize the biaxial optical responses of the porous polymer thin films. The porous polymer films with inverse columnar structure (PMMA iSCTFs) were prepared via infiltrating polymer into the voids of the SCTF templates and selectively removing the columns. The AB-EMA was employed to analyze the GE data of the porous polymer films and SCTF templates to determine the structural and anisotropic optical properties. The structural
Natural convection heat transfer from a horizontal wavy surface in a porous enclosure
Murthy, P.V.S.N.; Kumar, B.V.R.; Singh, P.
1997-02-07
The effect of surface undulations on the natural convection heat transfer from an isothermal surface in a Darcian fluid-saturated porous enclosure has been numerically analyzed using the finite element method on a graded nonuniform mesh system. The flow-driving Rayleigh number Ra together with the geometrical parameters of wave amplitude a, wave phase {phi}, and the number of waves N considered in the horizontal dimension of the cavity are found to influence the flow and heat transfer process in the enclosure. For Ra around 50 and above, the phenomenon of flow separation and reattachment is noticed on the walls of the enclosure. A periodic shift in the reattachment point from the bottom wall to the adjacent walls in the clockwise direction, leading to the manifestation of cycles of unicellular and bicellular clockwise and counterclockwise flows, is observed, with the phase varying between 0{degree} and 350{degree}. The counterflow in the secondary circulation zone is intensified with the increase in the value of Ra. The counterflow on the wavy wall hinders the heat transfer into the system. An increase in either wave amplitude or the number of waves considered per unit length decreases the global heat flux into the system. Only marginal changes in global heat flux are noticed with increasing Ra. On the whole, the comparison of global heat flux results in the wavy wall case with those of the horizontal flat wall case shows that, in a porous enclosure, the wavy wall reduces the heat transfer into the system.
Radiation effect on natural convection over a vertical cylinder embedded in porous media
Yih, K.A.
1999-02-01
Study of buoyancy-induced convection flow and heat transfer in a fluid-saturated porous medium has recently attracted considerable interest because of a number of important energy-related engineering and geophysical applications such as thermal insulation of buildings, geothermal engineering, enhanced recovery of petroleum resources, filtration processes, ground water pollution and sensible heat storage beds. In this paper numerical solutions are presented for the effect of radiation on natural convection about an isothermal vertical cylinder embedded in a saturated porous medium. These partial differential equations are transformed into the nonsimilar boundary layer equations which are solved by an implicit finite-difference method (Keller box method). Numerical results for the dimensionless temperature profiles and the local Nusselt number are presented for the transverse curvature parameter {xi}, conduction-radiation parameter R{sub d} and surface temperature excess ratio H. In general, the local Nusselt number increases as the transverse curvature parameter {xi} increases. Furthermore, decreasing the conduction-radiation parameter R{sub d} and increasing surface temperature excess ratio H augments the local heat transfer rate.
NASA Astrophysics Data System (ADS)
Holst, James R.; Trewin, Abbie; Cooper, Andrew I.
2010-11-01
Most synthetic materials that show molecular-scale porosity consist of one-, two- or three-dimensional networks. Porous metal-organic frameworks in particular have attracted a lot of recent attention. By contrast, discrete molecules tend to pack efficiently in the solid state, leaving as little empty space as possible, which leads to non-porous materials. This Perspective discusses recent developments with discrete organic molecules that are porous in the solid state. Such molecules, which may be either crystalline or amorphous, can be categorized as either intrinsically porous (containing permanent covalent cavities) or extrinsically porous (inefficiently packed). We focus on the possible advantages of organic molecules over inorganic or hybrid systems in terms of molecular solubility, choice of components and functionalities, and structural mobility and responsiveness in non-covalent extended solids. We also highlight the potential for 'undiscovered' porous systems among the large number of cage-like organic molecules that are already known.
Constitutive Equation for Anisotropic Rock
NASA Astrophysics Data System (ADS)
Cazacu, O.
2006-12-01
In many rocks, due to the existence of well-defined fabric elements such as bedding, layering, foliation or lamination planes, or due to the existence of linear structures, anisotropy can be important. The symmetries most frequently encountered are: transverse isotropy and orthotropy. By adopting both theoretical and experimental approaches, many authors have investigated the effect of the presence within the rock of pronounced anisotropic feature on the mechanical behavior in the elastic regime and on strength properties. Fewer attempts however have been made to capture the anisotropy of rocks in the plastic range. In this paper an elastic/viscoplastic non-associated constitutive equation for an initially transversely isotropic material is presented. The model captures the observed dependency of the elastic moduli on the stress state. The limit of the elastic domain is given by an yield function whose expression is a priori unknown and is determined from data. The basic assumption adopted is that the type of anisotropy of the rock does not change during the deformation process. The anisotropy is thus described by a fourth order tensor invariant with respect to any transformation belonging to the symmetry group of the material. This tensor is assumed to be constant: it does not depend on time nor on deformation; A is involved in the expression of the flow rule, of the yield function, and of the failure criterion in the form of a transformed stress tensor. The components of the anisotropic tensor A are determined from the compressive strengths in conjunction with an anisotropic short- term failure The irreversibility is supposed to be due to transient creep, the irreversible stress work per unit volume being considered as hardening parameter. The adequacy of the model is demonstrated by applying it to a stratified sedimentary rock, Tournemire shale.
Signature of anisotropic bubble collisions
Salem, Michael P.
2010-09-15
Our universe may have formed via bubble nucleation in an eternally inflating background. Furthermore, the background may have a compact dimension--the modulus of which tunnels out of a metastable minimum during bubble nucleation--which subsequently grows to become one of our three large spatial dimensions. When in this scenario our bubble universe collides with other ones like it, the collision geometry is constrained by the reduced symmetry of the tunneling instanton. While the regions affected by such bubble collisions still appear (to leading order) as disks in an observer's sky, the centers of these disks all lie on a single great circle, providing a distinct signature of anisotropic bubble nucleation.
Granular Segregation with Anisotropic Particles
NASA Astrophysics Data System (ADS)
Sykes, Tim
2005-11-01
The results from experimental investigations of horizontally vibrated mixtures of anisotropic poppy seeds and long chains of linked spheres will be presented. A critical packing fraction was observed to be required to initiate a transition to segregation. The average size of the resulting patterns was measured and the concentration ratio of the mixtures was varied by changing the number of chains present in the mixtures. A change in the order of the transition, from second to first order with associated hysteresis, was observed as the chain number was reduced. This gave rise to three distinct regions of behaviour: segregated, mixed and a bi-stable state.
Anisotropic inflation from vector impurity
Kanno, Sugumi; Kimura, Masashi; Soda, Jiro; Yokoyama, Shuichiro E-mail: mkimura@sci.osaka-cu.ac.jp E-mail: shu@a.phys.nagoya-u.ac.jp
2008-08-15
We study an inflationary scenario with a vector impurity. We show that the universe undergoes anisotropic inflationary expansion due to a preferred direction determined by the vector. Using the slow roll approximation, we find a formula for determining the anisotropy of the inflationary universe. We discuss possible observable predictions of this scenario. In particular, it is stressed that primordial gravitational waves can be induced from curvature perturbations. Hence, even in low scale inflation, a sizable amount of primordial gravitational waves may be produced during inflation.
Light Propagation through Anisotropic Turbulence
2011-03-01
Kolmogorov stratospheric turbulence on star image motion,” Proc. SPIE 3126, 113–123 (1997). 5. B. E . Stribling, B. M . Welsh, and M . C. Roggemann...746407 (2009). 10. M . Chang, C. O. Font, F. Santiago, Y. Luna, E . Roura, and S. Restaino, “Marine environment optical propagation measure- ments,” Proc...Anisotropic factor as a function of alpha for several zeta values. Toselli et al. Vol. 28, No. 3 / March 2011 / J. Opt. Soc. Am. A 487 14. M . S
Van der Kelen, Christophe; Göransson, Peter
2013-12-01
The flow resistivity tensor, which is the inverse of the viscous permeability tensor, is one of the most important material properties for the acoustic performance of porous materials used in acoustic treatments. Due to the manufacturing processes involved, these porous materials are most often geometrically anisotropic on a microscopic scale, and for demanding applications, there is a need for improved characterization methods. This paper discusses recent refinements of a method for the identification of the anisotropic flow resistivity tensor. The inverse estimation is verified for three fictitious materials with different degrees of anisotropy. Measurements are performed on nine glass wool samples and seven melamine foam samples, and the anisotropic flow resistivity tensors obtained are validated by comparison to measurements performed on uni-directional cylindrical samples, extracted from the same, previously measured cubic samples. The variability of flow resistivity in the batch of material from which the glass wool is extracted is discussed. The results for the melamine foam suggest that there is a relation between the direction of highest flow resistivity, and the rise direction of the material.
Hierarchical Porous Structures
Grote, Christopher John
2016-06-07
Materials Design is often at the forefront of technological innovation. While there has always been a push to generate increasingly low density materials, such as aero or hydrogels, more recently the idea of bicontinuous structures has gone more into play. This review will cover some of the methods and applications for generating both porous, and hierarchically porous structures.
Neeper, D.A.
1994-02-22
Methods are presented for distributing gases throughout the interstices of porous materials and removing volatile substances from the interstices of porous materials. Continuous oscillation of pressures and flows results in increased penetration of the interstices by flowing gases and increased transport of gaseous components out of the interstices. The invention is particularly useful in soil vapor extraction. 10 figures.
Neeper, Donald A.
1994-01-01
Methods for distributing gases throughout the interstices of porous materials and removing volatile substances from the interstices of porous materials. Continuous oscillation of pressures and flows results in increased penetration of the interstices by flowing gases and increased transport of gaseous components out of the interstices. The invention is particularly useful in soil vapor extraction.
NASA Astrophysics Data System (ADS)
Sur, Shouvik; Lee, Sung-Sik
2016-11-01
We study non-Fermi-liquid states that arise at the quantum critical points associated with the spin density wave (SDW) and charge density wave (CDW) transitions in metals with twofold rotational symmetry. We use the dimensional regularization scheme, where a one-dimensional Fermi surface is embedded in (3 -ɛ ) -dimensional momentum space. In three dimensions, quasilocal marginal Fermi liquids arise both at the SDW and CDW critical points: the speed of the collective mode along the ordering wave vector is logarithmically renormalized to zero compared to that of Fermi velocity. Below three dimensions, however, the SDW and CDW critical points exhibit drastically different behaviors. At the SDW critical point, a stable anisotropic non-Fermi-liquid state is realized for small ɛ , where not only time but also different spatial coordinates develop distinct anomalous dimensions. The non-Fermi liquid exhibits an emergent algebraic nesting as the patches of Fermi surface are deformed into a universal power-law shape near the hot spots. Due to the anisotropic scaling, the energy of incoherent spin fluctuations disperse with different power laws in different momentum directions. At the CDW critical point, on the other hand, the perturbative expansion breaks down immediately below three dimensions as the interaction renormalizes the speed of charge fluctuations to zero within a finite renormalization group scale through a two-loop effect. The difference originates from the fact that the vertex correction antiscreens the coupling at the SDW critical point whereas it screens at the CDW critical point.
Discrete vortices on anisotropic lattices
NASA Astrophysics Data System (ADS)
Chen, Gui-Hua; Wang, Hong-Cheng; Chen, Zi-Fa
2015-08-01
We consider the effects of anisotropy on two types of localized states with topological charges equal to 1 in two-dimensional nonlinear lattices, using the discrete nonlinear Schrödinger equation as a paradigm model. We find that on-site-centered vortices with different propagation constants are not globally stable, and that upper and lower boundaries of the propagation constant exist. The region between these two boundaries is the domain outside of which the on-site-centered vortices are unstable. This region decreases in size as the anisotropy parameter is gradually increased. We also consider off-site-centered vortices on anisotropic lattices, which are unstable on this lattice type and either transform into stable quadrupoles or collapse. We find that the transformation of off-sitecentered vortices into quadrupoles, which occurs on anisotropic lattices, cannot occur on isotropic lattices. In the quadrupole case, a propagation-constant region also exists, outside of which the localized states cannot stably exist. The influence of anisotropy on this region is almost identical to its effects on the on-site-centered vortex case.
Postbuckling of laminated anisotropic panels
NASA Technical Reports Server (NTRS)
Jeffrey, Glenda L.
1987-01-01
A two-part study of the buckling and postbuckling of laminated anisotropic plates with bending-extensional coupling is presented. The first part involves the development and application of a modified Rayleigh-Ritz analysis technique. Modifications made to the classical technique can be grouped into three areas. First, known symmetries of anisotropic panels are exploited in the selection of approximation functions. Second, a reduced basis technique based on these same symmetries is applied in the linear range. Finally, geometric boundary conditions are enforced via an exterior penalty function approach, rather than relying on choice of approximation functions to satisfy these boundary conditions. Numerical results are presented for both the linear and nonlinear range, with additional studies made to determine the effect of variation in penalty parameter and number of basis vectors. In the second part, six panels possessing anisotropy and bending-extensional coupling are tested. Detailed comparisons are made between experiment and finite element results in order to gain insight into the postbuckling and failure characteristics of such panels. The panels are constructed using two different lamination sequences, and panels with three different aspect ratios were constructed for each lamination sequence.
Anisotropic water reorientation around ions.
Tielrooij, K J; van der Post, S T; Hunger, J; Bonn, M; Bakker, H J
2011-11-03
We study the reorientation dynamics of water molecules around ions using terahertz dielectric relaxation spectroscopy and polarization-resolved femtosecond infrared pump-probe spectroscopy. The results are discussed in relation to the ion-specific Hofmeister series and the concomitant "structure-making" and "structure-breaking" effects of ions on water. We show that when a dissolved salt consists of a strongly hydrated ion with a weakly hydrated counterion the reorientation of water molecules around the strongly hydrated ion is anisotropic, in the sense that differently charged ions affect reorientation along different molecular axes: cations mainly slow the reorientation dynamics of the water dipole vectors, and anions mainly slow down the reorientation dynamics of the hydroxyl group that points toward the anion. In both cases, motion along only one molecular axis is impeded, so that the hydration shell is best described as semirigid. In this semirigid hydration picture, water molecules in the first hydration shell show anisotropic reorientation, whereas water molecules outside the first hydration shell remain unaffected. The inferred anisotropy in molecular motion explains why terahertz dielectric relaxation spectroscopy, which probes dipolar relaxation, is more sensitive to cation hydration effects while femtosecond infrared pump-probe spectroscopy, which is sensitive to reorientation of hydroxyl groups, is more sensitive to anion hydration effects. We also show that dissolution of CsI-a salt for which both cation and anion are weakly hydrated-has little effect on water reorientation dynamics, with hydration water displaying dynamics that are similar to those in bulk water.
Recent progress in anisotropic hydrodynamics
NASA Astrophysics Data System (ADS)
Strickland, Michael
2017-03-01
The quark-gluon plasma created in a relativistic heavy-ion collisions possesses a sizable pressure anisotropy in the local rest frame at very early times after the initial nuclear impact and this anisotropy only slowly relaxes as the system evolves. In a kinetic theory picture, this translates into the existence of sizable momentum-space anisotropies in the underlying partonic distribution functions, < pL2> ≪ < pT2>. In such cases, it is better to reorganize the hydrodynamical expansion by taking into account momentum-space anisotropies at leading-order in the expansion instead of as a perturbative correction to an isotropic distribution. The resulting anisotropic hydrodynamics framework has been shown to more accurately describe the dynamics of rapidly expanding systems such as the quark-gluon plasma. In this proceedings contribution, I review the basic ideas of anisotropic hydrodynamics, recent progress, and present a few preliminary phenomenological predictions for identified particle spectra and elliptic flow.
Tsuo, Y.S.; Menna, P.; Al-Jassim, M.
1995-08-01
We have studied a novel extrinsic gettering method that utilizes the very large surface areas, produced by porous silicon etch on both front and back surfaces of the silicon wafer, as gettering sites. In this method, a simple and low-cost chemical etching is used to generate the porous silicon layers. Then, a high-flux solar furnace (HFSF) is used to provide high-temperature annealing and the required injection of silicon interstitials. The gettering sites, along with the gettered impurities, can be easily removed at the end the process. The porous silicon removal process consists of oxidizing the porous silicon near the end the gettering process followed by sample immersion in HF acid. Each porous silicon gettering process removes up to about 10 {mu}m of wafer thickness. This gettering process can be repeated so that the desired purity level is obtained.
2-D solution for drying with internal vaporization of anisotropic media
Perre, P.; Passard, J.
1999-01-01
A set of physical assumptions for a straightforward and efficient simulation of the drying of a porous medium submitted to a convective and/or radiative heating is proposed. All of the parameters used are physical (liquid migration coefficient, permeability values along the thickness and the length, thermal conductivity, and external changes), but the relevant geometrical properties (length and thickness of the slab) were also included in the analysis. The 2-D pressure field generated within the medium during the drying process is obtained by using an analytical expression. The treatment of the pressure field, especially for a strongly anisotropic medium, is an important feature of the model, which allows an analytical model for such a complicated porous medium as wood to be used across a wide range of drying conditions. The computer code developed from the proposed formulation permits a complete simulation of the drying process within a few seconds on a personal computer. Different configurations have been tested for both anisotropic (wood) and isotropic (light concrete) porous media. Agreement with the experimental results is reasonable in terms of the observed physical phenomena. For instance, the model highlights dependence of the duration of the first drying rate on both material properties and drying conditions. This new model can be used for a global physical characterization of products by curve fitting and the collated information for the design of dryers.
Characterization of anisotropic acoustic metamaterial slabs
NASA Astrophysics Data System (ADS)
Park, Jun Hyeong; Lee, Hyung Jin; Kim, Yoon Young
2016-01-01
In an anisotropic acoustic metamaterial, the off-diagonal components of its effective mass density tensor should be considered in order to describe the anisotropic behavior produced by arbitrarily shaped inclusions. However, few studies have been carried out to characterize anisotropic acoustic metamaterials. In this paper, we propose a method that uses the non-diagonal effective mass density tensor to determine the behavior of anisotropic acoustic metamaterials. Our method accurately evaluates the effective properties of anisotropic acoustic metamaterials by separately dealing with slabs made of single and multiple unit cells along the thickness direction. To determine the effective properties, the reflection and transmission coefficients of an acoustic metamaterial slab are calculated, and then the wave vectors inside of the slab are determined using these coefficients. The effective material properties are finally determined by utilizing the spatial dispersion relation of the anisotropic acoustic metamaterial. Since the dispersion relation of an anisotropic acoustic metamaterial is explicitly used, its effective properties can be easily determined by only using a limited number of normal and oblique plane wave incidences into a metamaterial slab, unlike existing approaches requiring a large number of wave incidences. The validity of the proposed method is verified by conducting wave simulations for anisotropic acoustic metamaterial slabs with Z-shaped elastic inclusions of tilted principal material axes.
Stability analysis of dissolution-driven convection in porous media
NASA Astrophysics Data System (ADS)
Emami-Meybodi, Hamid
2017-01-01
We study the stability of dissolution-driven convection in the presence of a capillary transition zone and hydrodynamic dispersion in a saturated anisotropic porous medium, where the solute concentration is assumed to decay via a first-order chemical reaction. While the reaction enhances stability by consuming the solute, porous media anisotropy, hydrodynamic dispersion, and capillary transition zone destabilize the diffusive boundary layer that is unstably formed in a gravitational field. We perform linear stability analysis, based on the quasi-steady-state approximation, to assess critical times, critical wavenumbers, and neutral stability curves as a function of anisotropy ratio, dispersivity ratio, dispersion strength, material parameter, Bond number, Damköhler number, and Rayleigh number. The results show that the diffusive boundary layer becomes unstable in anisotropic porous media where both the capillary transition zone and dispersion are considered, even if the geochemical reaction is significantly large. Using direct numerical simulations, based on the finite difference method, we study the nonlinear dynamics of the system by examining dissolution flux, interaction of convective fingers, and flow topology. The results of nonlinear simulations confirm the predictions from the linear stability analysis and reveal that the fingering pattern is significantly influenced by combined effects of reaction, anisotropy, dispersion, and capillarity. Finally, we draw conclusions on implications of our results on carbon dioxide sequestration in deep saline aquifers.
Kim, Hahn; Van Dung Doan; Cho, Woo Jong; Madhav, Miriyala Vijay; Kim, Kwang S.
2014-01-01
Although group (IV–VII) nonmetallic elements do not favor interacting with anionic species, there are counterexamples including the halogen bond. Such binding is known to be related to the charge deficiency because of the adjacent atom's electron withdrawing effect, which creates σ/π-holes at the bond-ends. However, a completely opposite behavior is exhibited by N2 and O2, which have electrostatically positive/negative character around cylindrical-bond-surface/bond-ends. Inspired by this, here we elucidate the unusual features and origin of the anisotropic noncovalent interactions in the ground and excited states of the 2nd and 3rd row elements belonging to groups IV–VII. The anisotropy in charge distributions and van der Waals radii of atoms in such molecular systems are scrutinized. This provides an understanding of their unusual molecular configuration, binding and recognition modes involved in new types of molecular assembling and engineering. This work would lead to the design of intriguing molecular systems exploiting anisotropic noncovalent interactions. PMID:25059645
Anisotropic grid adaptation in LES
NASA Astrophysics Data System (ADS)
Toosi, Siavash; Larsson, Johan
2016-11-01
The modeling errors depend directly on the grid (or filter) spacing in turbulence-resolving simulations (LES, DNS, DES, etc), and are typically at least as significant as the numerical errors. This makes adaptive grid-refinement complicated, since it prevents the estimation of the local error sources through numerical analysis. The present work attempts to address this difficulty with a physics-based error-source indicator that accounts for the anisotropy in the smallest resolved scales, which can thus be used to drive an anisotropic grid-adaptation process. The proposed error indicator is assessed on a sequence of problems, including turbulent channel flow and flows in more complex geometries. The formulation is geometrically general and applicable to complex geometries.
Anisotropic invariance in minisuperspace models
NASA Astrophysics Data System (ADS)
Chagoya, Javier; Sabido, Miguel
2016-06-01
In this paper we introduce invariance under anisotropic transformations to cosmology. This invariance is one of the key ingredients of the theory of quantum gravity at a Lifshitz point put forward by Hořava. We find that this new symmetry in the minisuperspace introduces characteristics to the model that can be relevant in the ultraviolet regime. For example, by canonical quantization we find a Schrödinger-type equation which avoids the problem of frozen time in quantum cosmology. For simple cases we obtain solutions to this quantum equation in a Kantowski-Sachs (KS) minisuperspace. At the classical level, we study KS and Friedmann-Robertson-Walker cosmologies, obtaining modifications to the solutions of general relativity that can be relevant in the early Universe.
Modeling of Anisotropic Inelastic Behavior
Nikkel, D.J.; Nath, D.S.; Brown, A.A.; Casey, J.
2000-02-25
An experimental capability, developed at Lawrence Livermore National Laboratory (LLNL), is being used to study the yield behavior of elastic-plastic materials. The objective of our research is to develop better constitutive equations for polycrystalline metals. We are experimentally determining the multidimensional yield surface of the material, both in its initial state and as it evolves during large inelastic deformations. These experiments provide a more complete picture of material behavior than can be obtained from traditional uniaxial tests. Experimental results show that actual material response can differ significantly from that predicted by simple idealized models. These results are being used to develop improved constitutive models of anisotropic plasticity for use in continuum computer codes.
Anisotropic decomposition of energetic materials
Pravica, Michael; Quine, Zachary; Romano, Edward; Bajar, Sean; Yulga, Brian; Yang Wenge; Hooks, Daniel
2007-12-12
Using a white x-ray synchrotron beam, we have dynamically studied radiation-induced decomposition in single crystalline PETN and TATB. By monitoring the integrated intensity of selected diffraction spots via a CCD x-ray camera as a function of time, we have found that the decomposition rate varies dramatically depending upon the orientation of the crystalline axes relative to polarized x-ray beam and for differing diffracting conditions (spots) within the same crystalline orientation. We suggest that this effect is due to Compton scattering of the polarized x-rays with electron clouds that is dependent upon their relative orientation. This novel effect may yield valuable insight regarding anisotropic detonation sensitivity in energetic materials such as PETN.
Fabricating porous silicon carbide
NASA Technical Reports Server (NTRS)
Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)
1994-01-01
The formation of porous SiC occurs under electrochemical anodization. A sample of SiC is contacted electrically with nickel and placed into an electrochemical cell which cell includes a counter electrode and a reference electrode. The sample is encapsulated so that only a bare semiconductor surface is exposed. The electrochemical cell is filled with an HF electrolyte which dissolves the SiC electrochemically. A potential is applied to the semiconductor and UV light illuminates the surface of the semiconductor. By controlling the light intensity, the potential and the doping level, a porous layer is formed in the semiconductor and thus one produces porous SiC.
Anisotropic microstructure near the sun
NASA Astrophysics Data System (ADS)
Coles, W. A.; Grall, R. R.; Spangler, S. R.; Sakurai, T.; Harmon, J. K.
1996-07-01
Radio scattering observations provide a means of measuring a two-dimensional projection of the three-dimensional spatial spectrum of electron density, i.e., in the plane perpendicular to the line of sight. Earlier observations have shown that the microstructure at scales of the order of 10 km becomes highly field-aligned inside of 10 Rsolar [Armstrong et al., 1990]. Earlier work has also shown that density fluctuations at scales larger than 1000 km have a Kolmogorov spectrum, whereas the smaller scale structure has a flatter spectrum and is considerably enhanced above the Kolmogorov ``background'' [Coles et al., 1991]. Here we present new observations made during 1990 and 1992. These confirm the earlier work, which was restricted to one source on a few days, but they suggest that the anisotropy changes abruptly near 6 Rsolar which was not clear in the earlier data. The axial ratio measurements are shown on Figure 1 below. The new observations were made with a more uniform sampling of the spatial plane. They show that contours of constant correlation are elliptical. This is apparently inconsistent with the spatial correlation of the ISEE-3 magnetic field which shows a ``Maltese Cross'' shape [Matthaeus et al., 1990]. However this inconsistency may be only apparent: the magnetic field and density correlations need not have the same shape; the scale of the magnetic field correlations is at least 4 orders of magnitude larger; they are much further from the sun; and they are point measurements whereas ours are path-integrated. We also made two simultaneous measurements, at 10 Rsolar, of the anisotropy on scales of 200 to 4000 km. Significant anisotropy was seen on the smaller scales, but the larger scale structure was essentially isotropic. This suggests that the process responsible for the anisotropic microstructure is independent of the larger scale isotropic turbulence. It is then tempting to speculate that the damping of this anisotropic process inside of 6 Rsolar
Forced oscillation measurements of seismic attenuation in fluid saturated sandstone
NASA Astrophysics Data System (ADS)
Subramaniyan, Shankar; Quintal, Beatriz; Saenger, Erik H.
2017-02-01
Adopting the method of forced oscillation, attenuation was studied in Fontainebleau sandstone (porosity 10%, permeability 10 mD) at seismic frequencies (1-100 Hz). Confining pressures of 5, 10, and 15 MPa were chosen to simulate reservoir conditions. First, the strain effect on attenuation was investigated in the dry sample for 11 different strains across the range 1 × 10-6-8 × 10-6, at the confining pressure of 5 MPa. The comparison showed that a strain of at least 5 × 10-6 is necessary to obtain a good signal to noise ratio. These results also indicate that nonlinear effects are absent for strains up to 8 × 10-6. For all the confining pressures, attenuation in the dry rock was low, while partial (90%) and full (100%) saturation with water yielded a higher magnitude and frequency dependence of attenuation. The observed high and frequency dependent attenuation was interpreted as being caused by squirt flow.
The Melt Transition in Mature, Fluid-Saturated Gouge
NASA Astrophysics Data System (ADS)
Rempel, A. W.
2006-12-01
Mechanisms that link the evolution of fault strength and temperature during earthquakes have been studied extensively, with accumulating constraints from theoretical, field and laboratory investigations promoting increased confidence in our understanding of the dominant physical interactions. In mature fault zones that have accommodated many large earthquakes and are characterized by gouge layers that greatly exceed the thickness of the ~ mm-scale "principal slip surfaces" in which shear is localized, the thermal pressurization of pore fluids is expected to be particularly important for reducing the fault strength and limiting the extent of shear heating. Nevertheless, for sufficiently large slip distances and reasonable estimates of hydraulic transport properties and other controlling variables, the predicted temperature increases are sometimes able to reach the onset of melting, particularly at mid to lower seismogenic depths (e.g. 10km). Reported field observations of quenched glassy melt products, known as pseudotachylytes, are much more common on young faults, particularly where slip is initiated between coherent rock surfaces, rather than in exhumed mature fault zones, where thermal pressurization is likely to be more important and macroscopic melting appears to be rare. Those pseudotachylyte layers that are recovered from mature fault zones display a range of thicknesses and crystal contents, which indicate that significant shear heating continued long after the onset of melting, with work performed against the viscous resistance of a partially molten slurry. Models that describe the transition to melting in a finite shear zone that is initially saturated with pore fluids are presented with two main conceptual challenges: 1. the energy input for frictional heating is generally assumed to be proportional to the effective stress, which vanishes when macroscopic melt layers are produced and thermodynamic considerations require that the melt pressure balance the normal stress; 2. the typical initial crystal content of a finite shear zone at melt onset almost certainly exceeds the critical solids fraction (~ 50%) that allows for slurry mobilization at a finite effective viscosity and provides the viscous heat source necessary for the melt fraction to increase subsequently. The former consideration motivates a closer examination of the homogenization used to describe the pore pressure, much as the recognized mechanism of "flash-weakening" relies on a parameterized description to account for the effects of localized thermal anomalies at the asperity (μm) scale. The latter consideration suggests both the potential importance of "viscous braking" as a mechanism for transferring slip to adjacent shear zones, and the likely roll of melt onset as a mechanism for extreme localization, requiring slip in a finite zone to actually be accommodated on a series of short-lived effective shear surfaces between adjacent melting gouge particles. Here, we focus on how the melting transition can be placed within the larger context of continuum descriptions for the evolution of fault strength and temperature during earthquakes.
Solidus of carbonated fertile peridotite under fluid-saturated conditions
Falloon, T.J.; Green, D.H. )
1990-03-01
The solidus for a fertile peridotite composition (Hawaiian pyrolite) in the presence of a CO{sub 2}-H{sub 2}O fluid phase has been determined from 10 to 35 kbar. The intersection of the decarbonation reaction (olivine + diopside + CO{sub 2} {l reversible} orthopyroxene + dolomite) with the pyrolite solidus defines the point Q{prime}, located at 22 kbar and 940 C. At pressures less than Q{prime}, the solidus passes through a temperature maximum at kbar, 1060 C. The solidus is coincident with amphibole breakdown at pressures less than 16 kbar. At pressures above Q{prime}, the solidus is defined by the dissolution of crystalline carbonate into a sodic, dolomitic carbonatite melt. The solidus is at a temperature of 925 C at {approximately} 28 kbar. The solidus temperature above the point Q{prime} is similar to the solidus determined for Hawaiian pyrolite-H{sub 2}O-CO{sub 2} for small contents of H{sub 2}O (<0.3 wt%) and CO{sub 2} (<5 wt%), thus indicating that the primary sodic dolomitic carbonatite melt at both solidi has a very low and limited H{sub 2}O solubility. The new data clarify the roles of carbonatite melt, carbonated silicate melt, and H{sub 2}O-rich fluid in mantle conditions that are relatively oxidized (f{sub O{sub 2}} {approximately} MW to FMQ). In particular, a carbonatite melt + garnet lherzolite region is intersected by continental shield geothermal gradients, but such geotherms only intersect regions with carbonated silicate melt if perturbed to higher temperatures (kinked geotherm).
Discrimination of porosity and fluid saturation using seismic velocity analysis
Berryman, James G.
2001-01-01
The method of the invention is employed for determining the state of saturation in a subterranean formation using only seismic velocity measurements (e.g., shear and compressional wave velocity data). Seismic velocity data collected from a region of the formation of like solid material properties can provide relatively accurate partial saturation data derived from a well-defined triangle plotted in a (.rho./.mu., .lambda./.mu.)-plane. When the seismic velocity data are collected over a large region of a formation having both like and unlike materials, the method first distinguishes the like materials by initially plotting the seismic velocity data in a (.rho./.lambda., .mu./.lambda.)-plane to determine regions of the formation having like solid material properties and porosity.
Seismic attenuation: Laboratory measurements in fluid saturated rocks
NASA Astrophysics Data System (ADS)
Subramaniyan, Shankar; Madonna, Claudio; Tisato, Nicola; Saenger, Erik; Quintal, Beatriz
2014-05-01
Seismic wave attenuation could be used as an indicator of reservoir fluids due to its dependence on rock and fluid properties. Over the past 30 years, many laboratory methodologies to study attenuation in rocks have been employed, such as ultrasonic (MHz), resonant bar (kHz) and forced oscillation methods in the low frequency range (0.01-100Hz) (Tisato & Madonna 2012; Madonna & Tisato 2013). Forced oscillation methods have gained prominence over time as the frequency range of measurements correspond to that of field seismic data acquired for oil/gas exploration. These experiments measure attenuation as the phase shift between the applied stress (sinusoidal) and measured strain. Since the magnitudes of measured phase shifts are quite low (Q-1 ~0.01-0.1) and the amplitudes of strain applied to the rock samples are of the order ~10-6 (i.e., similar orders of magnitude to seismic waves), it is challenging. A comparison of such forced oscillation setups will be presented to provide an overview of the various possibilities of design and implementation for future setups. In general, there is a lack of laboratory data and most of the published data are for sandstones. Currently, attenuation measurements are being carried out on carbonate and sandstone samples. We employ the Seismic Wave Attenuation Module (SWAM, Madonna & Tisato 2013) to measure seismic attenuation in these samples for different saturation degrees (90% and 100% water) and under three different confining pressures (5, 10 and 15MPa). Preliminary results from these investigations will be discussed. REFERENCES Madonna, C. & Tisato, N. 2013: A new seismic wave attenuation module to experimentally measure low-frequency attenuation in extensional mode. Geophysical Prospecting, doi: 10.1111/1365-2478.12015. Tisato, N. & Madonna, C. 2012: Attenuation at low seismic frequencies in partially saturated rocks: Measurements and description of a new apparatus. Journal of Applied Geophysics, 86, 44-53.
Finite-volume scheme for anisotropic diffusion
Es, Bram van; Koren, Barry; Blank, Hugo J. de
2016-02-01
In this paper, we apply a special finite-volume scheme, limited to smooth temperature distributions and Cartesian grids, to test the importance of connectivity of the finite volumes. The area of application is nuclear fusion plasma with field line aligned temperature gradients and extreme anisotropy. We apply the scheme to the anisotropic heat-conduction equation, and compare its results with those of existing finite-volume schemes for anisotropic diffusion. Also, we introduce a general model adaptation of the steady diffusion equation for extremely anisotropic diffusion problems with closed field lines.
Shaped beam scattering by an anisotropic particle
NASA Astrophysics Data System (ADS)
Chen, Zhenzhen; Zhang, Huayong; Huang, Zhixiang; Wu, Xianliang
2017-03-01
An exact semi-analytical solution to the electromagnetic scattering from an optically anisotropic particle illuminated by an arbitrarily shaped beam is proposed. The scattered fields and fields within the anisotropic particle are expanded in terms of spherical vector wave functions. The unknown expansion coefficients are determined by using the boundary conditions and the method of moments scheme. For incidence of a Gaussian beam, zero-order Bessel beam and Hertzian electric dipole radiation, numerical results of the normalized differential scattering cross section are given to a uniaxial, gyrotropic anisotropic spheroid and circular cylinder of finite length. The scattering properties are analyzed concisely.
Anisotropic inflation in Gauss-Bonnet gravity
Lahiri, Sayantani
2016-09-19
We study anisotropic inflation with Gauss-Bonnet correction in presence of a massless vector field. In this scenario, exact anisotropic power-law inflation is realized when the inflaton potential, gauge coupling function and the Gauss-Bonnet coupling are exponential functions. We show that anisotropy becomes proportional to two slow-roll parameters of the theory and hence gets enhanced in presence of quadratic curvature corrections. The stability analysis reveals that anisotropic power-law solutions remain stable over a substantially large parameter region.
Gross, Adam F.; Vajo, John J.; Cumberland, Robert W.; Liu, Ping; Salguero, Tina T.
2011-03-22
A porous carbon scaffold with a surface and pores, the porous carbon scaffold containing a primary metal and a secondary metal, where the primary metal is a metal that does not wet the surface of the pores of the carbon scaffold but wets the surface of the secondary metal, and the secondary metal is interspersed between the surface of the pores of the carbon scaffold and the primary metal.
Seismic wave propagation in cracked porous media
NASA Astrophysics Data System (ADS)
Pointer, Tim; Liu, Enru; Hudson, John A.
2000-07-01
The movement of interstitial fluids within a cracked solid can have a significant effect on the properties of seismic waves of long wavelength propagating through the solid. We consider three distinct mechanisms of wave-induced fluid flow: flow through connections between cracks in an otherwise non-porous material, fluid movement within partially saturated cracks, and diffusion from the cracks into a porous matrix material. In each case the cracks may be aligned or randomly oriented, leading, respectively, to anisotropic or isotropic wave speeds and attenuation factors. In general, seismic velocities exhibit behaviour that is intermediate between that of empty cracks and that of isolated liquid-filled cracks if fluid flow is significant. In the range of frequencies for which considerable fluid flow occurs there is high attenuation and dispersion of seismic waves. Fluid flow may be on either a wavelength scale or a local scale depending on the model and whether the cracks are aligned or randomly oriented, resulting in completely different effects on seismic wave propagation. A numerical analysis shows that all models can have an effect over the exploration seismic frequency range.
Gaseous NH3 Confers Porous Pt Nanodendrites Assisted by Halides
Lu, Shuanglong; Eid, Kamel; Li, Weifeng; Cao, Xueqin; Pan, Yue; Guo, Jun; Wang, Liang; Wang, Hongjing; Gu, Hongwei
2016-01-01
Tailoring the morphology of Pt nanocrystals (NCs) is of great concern for their enhancement in catalytic activity and durability. In this article, a novel synthetic strategy is developed to selectively prepare porous dendritic Pt NCs with different structures for oxygen reduction reaction (ORR) assisted by NH3 gas and halides (F−, Cl−, Br−). The NH3 gas plays critical roles on tuning the morphology. Previously, H2 and CO gas are reported to assist the shape control of metallic nanocrystals. This is the first demonstration that NH3 gas assists the Pt anisotropic growth. The halides also play important role in the synthetic strategy to regulate the formation of Pt NCs. As-made porous dendritic Pt NCs, especially when NH4F is used as a regulating reagent, show superior catalytic activity for ORR compared with commercial Pt/C catalyst and other previously reported Pt-based NCs. PMID:27184228
Anisotropic wettability on imprinted hierarchical structures.
Zhang, Fengxiang; Low, Hong Yee
2007-07-03
A series of two-level hierarchical structures on polystyrene (PS) and poly(methyl methacrylate) (PMMA) were fabricated using sequential nanoimprinting lithography (NIL). The hierarchical structures consist of micrometer and sub-micrometer scale grating imprinted with varying orientations. Through water contact angle measurements, these surface hierarchical structures showed a wide range of anisotropic wettabilities on PMMA and PS, with PMMA having an anisotropic wettability from 6 degrees to 54 degrees and PS having an anisotropic wettability from 8 degrees to 32 degrees. At the same time, the water contact angle of PMMA and PS can be tuned to nearly 120 degrees without modifying the surface chemistry. A tunable anisotropic wettability is beneficial for applications where controlling the direction of liquid flow is important, such as in microfluidic devices.
On the anisotropic elastic properties of hydroxyapatite.
NASA Technical Reports Server (NTRS)
Katz, J. L.; Ukraincik, K.
1971-01-01
Experimental measurements of the isotropic elastic moduli on polycrystalline specimens of hydroxyapatite and fluorapatite are compared with elastic constants measured directly from single crystals of fluorapatite in order to derive a set of pseudo single crystal elastic constants for hydroxyapatite. The stiffness coefficients thus derived are given. The anisotropic and isotropic elastic properties are then computed and compared with similar properties derived from experimental observations of the anisotropic behavior of bone.
Phase space analysis in anisotropic optical systems
NASA Technical Reports Server (NTRS)
Rivera, Ana Leonor; Chumakov, Sergey M.; Wolf, Kurt Bernardo
1995-01-01
From the minimal action principle follows the Hamilton equations of evolution for geometric optical rays in anisotropic media. As in classical mechanics of velocity-dependent potentials, the velocity and the canonical momentum are not parallel, but differ by an anisotropy vector potential, similar to that of linear electromagnetism. Descartes' well known diagram for refraction is generalized and a factorization theorem holds for interfaces between two anisotropic media.
Inflation in anisotropic scalar-tensor theories
NASA Technical Reports Server (NTRS)
Pimentel, Luis O.; Stein-Schabes, Jaime
1988-01-01
The existence of an inflationary phase in anisotropic Scalar-Tensor Theories is investigated by means of a conformal transformation that allows us to rewrite these theories as gravity minimally coupled to a scalar field with a nontrivial potential. The explicit form of the potential is then used and the No Hair Theorem concludes that there is an inflationary phase in all open or flat anisotropic spacetimes in these theories. Several examples are constructed where the effect becomes manifest.
NASA Astrophysics Data System (ADS)
Stewart, Robert A.; Shaw, J. M.
2015-09-01
The development and baseline operation of an acoustic view cell for observing fluids, and fluid-fluid and fluid-solid interfaces in porous media over the frequency range of 10-5000 Hz is described. This range includes the industrially relevant frequency range 500-5000 Hz that is not covered by existing devices. Pressure waveforms of arbitrary shape are generated in a 17.46 mm ID by 200 mm and 690.5 mm long glass tubes at flow rates up to 200 ml/min using a syringe pump. Peak-to-peak amplitudes exceeding 80 kPa are readily realized at frequencies from 10 to 5000 Hz in bubble free fluids when actuated with 20 Vpp as exemplified using castor oil. At resonant frequencies, peak-to-peak pressure amplitudes exceeding 500 kPa were obtained (castor oil at 2100 Hz when actuated with 20 Vpp). Impacts of vibration on macroscopic liquid-liquid and liquid-vapour interfaces and interface movement are illustrated. Pressure wave transmission and attenuation in a fluid saturated porous medium, randomly packed 250-330 μm spherical silica beads, is also demonstrated. Attenuation differences and frequency shifts in resonant peaks are used to detect the presence and generation of dispersed micro-bubbles (<180 μm diameter), and bubbles within porous media that are not readily visualized. Envisioned applications include assessment of the impacts of vibration on reaction, mass transfer, and flow/flow pattern outcomes. This knowledge will inform laboratory and pilot scale process studies, where nuisance vibrations may affect the interpretation of process outcomes, and large scale or in situ processes in aquifers or hydrocarbon reservoirs where imposed vibration may be deployed to improve aspects of process performance. Future work will include miscible interface observation and quantitative measurements in the bulk and in porous media where the roles of micro-bubbles comprise subjects of special interest.
Stewart, Robert A; Shaw, J M
2015-09-01
The development and baseline operation of an acoustic view cell for observing fluids, and fluid-fluid and fluid-solid interfaces in porous media over the frequency range of 10-5000 Hz is described. This range includes the industrially relevant frequency range 500-5000 Hz that is not covered by existing devices. Pressure waveforms of arbitrary shape are generated in a 17.46 mm ID by 200 mm and 690.5 mm long glass tubes at flow rates up to 200 ml/min using a syringe pump. Peak-to-peak amplitudes exceeding 80 kPa are readily realized at frequencies from 10 to 5000 Hz in bubble free fluids when actuated with 20 Vpp as exemplified using castor oil. At resonant frequencies, peak-to-peak pressure amplitudes exceeding 500 kPa were obtained (castor oil at 2100 Hz when actuated with 20 Vpp). Impacts of vibration on macroscopic liquid-liquid and liquid-vapour interfaces and interface movement are illustrated. Pressure wave transmission and attenuation in a fluid saturated porous medium, randomly packed 250-330 μm spherical silica beads, is also demonstrated. Attenuation differences and frequency shifts in resonant peaks are used to detect the presence and generation of dispersed micro-bubbles (<180 μm diameter), and bubbles within porous media that are not readily visualized. Envisioned applications include assessment of the impacts of vibration on reaction, mass transfer, and flow/flow pattern outcomes. This knowledge will inform laboratory and pilot scale process studies, where nuisance vibrations may affect the interpretation of process outcomes, and large scale or in situ processes in aquifers or hydrocarbon reservoirs where imposed vibration may be deployed to improve aspects of process performance. Future work will include miscible interface observation and quantitative measurements in the bulk and in porous media where the roles of micro-bubbles comprise subjects of special interest.
NASA Astrophysics Data System (ADS)
Alsabery, A. I.; Chamkha, A. J.; Saleh, H.; Hashim, I.; Chanane, B.
2017-03-01
The effects of finite wall thickness and sinusoidal heating on convection in a nanofluid-saturated local thermal non-equilibrium (LTNE) porous cavity are studied numerically using the finite difference method. The finite thickness vertical wall of the cavity is maintained at a constant temperature and the right wall is heated sinusoidally. The horizontal insulated walls allow no heat transfer to the surrounding. The Darcy law is used along with the Boussinesq approximation for the flow. Water-based nanofluids with Cu nanoparticles are chosen for investigation. The results of this study are obtained for various parameters such as the Rayleigh number, periodicity parameter, nanoparticles volume fraction, thermal conductivity ratio, ratio of wall thickness to its height and the modified conductivity ratio. Explanation for the influence of the various above-mentioned parameters on the streamlines, isotherms, local Nusselt number and the weighted average heat transfer is provided with regards to the thermal conductivities of nanoparticles suspended in the pure fluid and the porous medium. It is shown that the overall heat transfer is significantly increased with the relative non-uniform heating. Further, the convection heat transfer is shown to be inhibited by the presence of the solid wall. The results have possible applications in the heat-storage fluid-saturated porous systems and the applications of the high power heat transfer.
Spin precession in anisotropic media
NASA Astrophysics Data System (ADS)
Raes, B.; Cummings, A. W.; Bonell, F.; Costache, M. V.; Sierra, J. F.; Roche, S.; Valenzuela, S. O.
2017-02-01
We generalize the diffusive model for spin injection and detection in nonlocal spin structures to account for spin precession under an applied magnetic field in an anisotropic medium, for which the spin lifetime is not unique and depends on the spin orientation. We demonstrate that the spin precession (Hanle) line shape is strongly dependent on the degree of anisotropy and on the orientation of the magnetic field. In particular, we show that the anisotropy of the spin lifetime can be extracted from the measured spin signal, after dephasing in an oblique magnetic field, by using an analytical formula with a single fitting parameter. Alternatively, after identifying the fingerprints associated with the anisotropy, we propose a simple scaling of the Hanle line shapes at specific magnetic field orientations that results in a universal curve only in the isotropic case. The deviation from the universal curve can be used as a complementary means of quantifying the anisotropy by direct comparison with the solution of our generalized model. Finally, we applied our model to graphene devices and find that the spin relaxation for graphene on silicon oxide is isotropic within our experimental resolution.
Magnetospheric equilibrium with anisotropic pressure
Cheng, C.Z.
1991-07-01
Self-consistent magnetospheric equilibrium with anisotropic pressure is obtained by employing an iterative metric method for solving the inverse equilibrium equation in an optimal flux coordinate system. A method of determining plasma parallel and perpendicular pressures from either analytic particle distribution or particle distribution measured along the satellite's path is presented. The numerical results of axisymmetric magnetospheric equilibrium including the effects of finite beta, pressure anisotropy, and boundary conditions are presented for a bi-Maxwellian particle distribution. For the isotropic pressure cases, the finite beta effect produces an outward expansion of the constant magnetic flux surfaces in relation to the dipole field lines, and along the magnetic field the toroidal ring current is maximum at the magnetic equator. The effect of pressure anisotropy is found to further expand the flux surfaces outward. Along the magnetic field lines the westward ring current can be peak away from the equator due to an eastward current contribution resulting from pressure anisotropy. As pressure anisotropy increases, the peak westward current can become more singular. The outer boundary flux surface has significant effect on the magnetospheric equilibrium. For the outer flux boundary resembling dayside compressed flux surface due to solar wind pressure, the deformation of the magnetic field can be quite different from that for the outer flux boundary resembling the tail-like surface. 23 refs., 17 figs.
Method of porous diamond deposition on porous silicon
NASA Astrophysics Data System (ADS)
Baranauskas, Vitor; Peterlevitz, Alfredo C.; Chang, Dahge C.; Durrant, Steven F.
2001-12-01
In this paper, we discuss the experimental results of the fabrication of porous diamond/porous silicon and porous diamond structures by chemical vapor deposition of diamond over a skeleton of porous silicon, replicating the porous surface geometry around the Si pores and also creating new porous diamond structures. Scanning electron microscopy (SEM) revealed that the diamond nuclei are deposited on the top of the porous silicon skeleton, forming isolated grains in the first nucleation stages, and then growing like the usual structure of most ceramic materials, making a self-sustained porous diamond structure. Raman spectroscopy revealed that the diamond films are of good quality, close to that of diamond films grown on crystalline silicon.
Tracking interface and common curve dynamics for two-fluid flow in porous media
Mcclure, James E.; Miller, Cass T.; Gray, W. G.; ...
2016-04-29
Pore-scale studies of multiphase flow in porous medium systems can be used to understand transport mechanisms and quantitatively determine closure relations that better incorporate microscale physics into macroscale models. Multiphase flow simulators constructed using the lattice Boltzmann method provide a means to conduct such studies, including both the equilibrium and dynamic aspects. Moving, storing, and analyzing the large state space presents a computational challenge when highly-resolved models are applied. We present an approach to simulate multiphase flow processes in which in-situ analysis is applied to track multiphase flow dynamics at high temporal resolution. We compute a comprehensive set of measuresmore » of the phase distributions and the system dynamics, which can be used to aid fundamental understanding and inform closure relations for macroscale models. The measures computed include microscale point representations and macroscale averages of fluid saturations, the pressure and velocity of the fluid phases, interfacial areas, interfacial curvatures, interface and common curve velocities, interfacial orientation tensors, phase velocities and the contact angle between the fluid-fluid interface and the solid surface. Test cases are studied to validate the approach and illustrate how measures of system state can be obtained and used to inform macroscopic theory.« less
Tracking interface and common curve dynamics for two-fluid flow in porous media
Mcclure, James E.; Miller, Cass T.; Gray, W. G.; Berrill, Mark A.
2016-04-29
Pore-scale studies of multiphase flow in porous medium systems can be used to understand transport mechanisms and quantitatively determine closure relations that better incorporate microscale physics into macroscale models. Multiphase flow simulators constructed using the lattice Boltzmann method provide a means to conduct such studies, including both the equilibrium and dynamic aspects. Moving, storing, and analyzing the large state space presents a computational challenge when highly-resolved models are applied. We present an approach to simulate multiphase flow processes in which in-situ analysis is applied to track multiphase flow dynamics at high temporal resolution. We compute a comprehensive set of measures of the phase distributions and the system dynamics, which can be used to aid fundamental understanding and inform closure relations for macroscale models. The measures computed include microscale point representations and macroscale averages of fluid saturations, the pressure and velocity of the fluid phases, interfacial areas, interfacial curvatures, interface and common curve velocities, interfacial orientation tensors, phase velocities and the contact angle between the fluid-fluid interface and the solid surface. Test cases are studied to validate the approach and illustrate how measures of system state can be obtained and used to inform macroscopic theory.
NASA Astrophysics Data System (ADS)
Miehe, Christian; Mauthe, Steffen; Teichtmeister, Stephan
2015-09-01
This work develops new minimization and saddle point principles for the coupled problem of Darcy-Biot-type fluid transport in porous media at fracture. It shows that the quasi-static problem of elastically deforming, fluid-saturated porous media is related to a minimization principle for the evolution problem. This two-field principle determines the rate of deformation and the fluid mass flux vector. It provides a canonically compact model structure, where the stress equilibrium and the inverse Darcy's law appear as the Euler equations of a variational statement. A Legendre transformation of the dissipation potential relates the minimization principle to a characteristic three field saddle point principle, whose Euler equations determine the evolutions of deformation and fluid content as well as Darcy's law. A further geometric assumption results in modified variational principles for a simplified theory, where the fluid content is linked to the volumetric deformation. The existence of these variational principles underlines inherent symmetries of Darcy-Biot theories of porous media. This can be exploited in the numerical implementation by the construction of time- and space-discrete variational principles, which fully determine the update problems of typical time stepping schemes. Here, the proposed minimization principle for the coupled problem is advantageous with regard to a new unconstrained stable finite element design, while space discretizations of the saddle point principles are constrained by the LBB condition. The variational principles developed provide the most fundamental approach to the discretization of nonlinear fluid-structure interactions, showing symmetric systems in algebraic update procedures. They also provide an excellent starting point for extensions towards more complex problems. This is demonstrated by developing a minimization principle for a phase field description of fracture in fluid-saturated porous media. It is designed for an
Qu, Yongquan; Zhou, Hailong; Duan, Xiangfeng
2011-10-05
In this mini-review, we summarize recent progress in the synthesis, properties and applications of a new type of one-dimensional nanostructures-single crystalline porous silicon nanowires. The growth of porous silicon nanowires starting from both p- and n-type Si wafers with a variety of dopant concentrations can be achieved through either one-step or two-step reactions. The mechanistic studies indicate the dopant concentration of Si wafers, oxidizer concentration, etching time and temperature can affect the morphology of the as-etched silicon nanowires. The porous silicon nanowires are both optically and electronically active and have been explored for potential applications in diverse areas including photocatalysis, lithium ion batteries, gas sensors and drug delivery.
Porous material neutron detector
Diawara, Yacouba [Oak Ridge, TN; Kocsis, Menyhert [Venon, FR
2012-04-10
A neutron detector employs a porous material layer including pores between nanoparticles. The composition of the nanoparticles is selected to cause emission of electrons upon detection of a neutron. The nanoparticles have a maximum dimension that is in the range from 0.1 micron to 1 millimeter, and can be sintered with pores thereamongst. A passing radiation generates electrons at one or more nanoparticles, some of which are scattered into a pore and directed toward a direction opposite to the applied electrical field. These electrons travel through the pore and collide with additional nanoparticles, which generate more electrons. The electrons are amplified in a cascade reaction that occurs along the pores behind the initial detection point. An electron amplification device may be placed behind the porous material layer to further amplify the electrons exiting the porous material layer.
Dynamic flow localization in porous rocks under combined pressure and shear loading
NASA Astrophysics Data System (ADS)
Yarushina, Viktoriya; Podladchikov, Yuri; Simon, Nina
2015-04-01
Flow localization occurs in deforming porous fluid saturated rocks. It exhibits itself as veins, pockmarks on the ocean floor or gas chimneys visible on seismic images from several chalk fields of the Central North Sea and from the Utsira formation at Sleipner in the Norwegian North Sea, which is one of the best documented CO2 storage sites. Porosity waves were repeatedly shown to be a viable mechanism of flow self-localization that does not require the pre-existence of a connected fracture network. Porosity waves result from an instability of the Darcy flow that occurs in porous rocks with time-dependent viscous or viscoelastoplastic rheology. Local fluid overpressure generated by fluid injection or chemical reactions aided by buoyancy force drives upward fluid migration. Viscous deformation delays pressure diffusion thus maintaining local overpressure for considerable periods of time. Development of an under-pressured region just below the over-pressured domain leads to separation of the fluid-filled high-porosity blob from the source and the background flow. The instability organizes the flow into separate vertical channels. Pressure distribution, shape and scaling of these channels are highly sensitive to the rheology of the porous rock. In this contribution, based on a micromechanical approach, we consider the complex rheology of brittle, ductile and transitional regimes of deformation of porous rocks in the presence of combined pressure and shear loading. Accurate description of transitional brittle-ductile deformation is a challenging task due to a large number of microscopic processes involved. We use elastoplastic and viscoplastic analytical solutions for the non-hydrostatic deformation of a singular cavity in the representative volume element in order to deduce expected behavior of the porous rock. The model provides micro-mechanisms for various failure modes (localized and homogeneous) and dilatancy onset. In particular, the model predicts that dilatancy
FLUID TRANSPORT THROUGH POROUS MEDIA
Fluid transport through porous media is a relevant topic to many scientific and engineering fields. Soil scientists, civil engineers, hydrologists and hydrogeologists are concerned with the transport of water, gases and nonaqueous phase liquid contaminants through porous earth m...
Modeling isothermal and non-isothermal flows in porous media
NASA Astrophysics Data System (ADS)
Mohseni Languri, Ehsan
2011-12-01
solutions obtained after applying the stress-continuity and stress-jump boundary conditions are found to work well at low porosities, which is in contradiction with the results achieved earlier by other researchers. The traditional approach of using averaged equations in the regions of sharp gradients in porous media to describe flow and transport is theoretically untenable and perhaps inaccurate. A novel ensemble averaging method is being proposed to test the accuracy of the volume averaged or smoothed description of flows in porous media in the regions of sharp gradients. In the new method, the flow in a certain arrangement of particles (called a realization) is averaged using a small unit cell, much smaller than the REV. Then such an averaged flow variable is further averaged over a whole gamut of randomly-generated particle realizations. First the accuracy of the ensemble averaging method was tested by comparing the permeability of an artificially generated porous medium obtained by the proposed method against the permeability predicted by some established theoretical models of permeability. The proposed method was found to be quite accurate. Later the ensemble average method was applied to the open-channel porous-medium interface region characterized by a sharp gradient in the flow velocities. It was discovered that the volume averaged description of such flows, characterized by the use of the Brinkman equation along with the stress-continuity and stress-jump conditions, is quite accurate for a range of Reynolds numbers. The non-isothermal transport during flow in porous media is examined next. The main focus in this area of research is the thermal dispersion term found in the heat transfer equation for single- and dual-scale porous media. Most of the previous efforts on modeling the heat transfer phenomena in porous media were devoted to isotropic porous media. However, for the anisotropic porous media widely in many industrial applications, not much research on the
Porous block nanofiber composite filters
Ginley, David S.; Curtis, Calvin J.; Miedaner, Alexander; Weiss, Alan J.; Paddock, Arnold
2016-08-09
Porous block nano-fiber composite (110), a filtration system (10) and methods of using the same are disclosed. An exemplary porous block nano-fiber composite (110) includes a porous block (100) having one or more pores (200). The porous block nano-fiber composite (110) also includes a plurality of inorganic nano-fibers (211) formed within at least one of the pores (200).
Tsuo, Y.S.; Menna, P.; Pitts, J.R.
1996-05-01
The authors have studied a novel extrinsic gettering method that uses the large surface areas produced by a porous-silicon etch as gettering sites. The annealing step of the gettering used a high-flux solar furnace. They found that a high density of photons during annealing enhanced the impurity diffusion to the gettering sites. The authors used metallurgical-grade Si (MG-Si) prepared by directional solidification casing as the starting material. They propose to use porous-silicon-gettered MG-Si as a low-cost epitaxial substrate for polycrystalline silicon thin-film growth.
Anisotropic membranes for gas separation
Gollan, Arye Z.
1987-01-01
A gas separation membrane has a dense separating layer about 10,000 Angstroms or less thick and a porous support layer 10 to 400 microns thick that is an integral unit with gradually and continuously decreasing pore size from the base of the support layer to the surface of the thin separating layer and is made from a casting solution comprising ethyl cellulose and ethyl cellulose-based blends, typically greater than 47.5 ethoxyl content ethyl cellulose blended with compatible second polymers, such as nitrocellulose. The polymer content of the casting solution is from about 10% to about 35% by weight of the total solution with up to about 50% of this polymer weight a compatible second polymer to the ethyl cellulose in a volatile solvent such as isopropanol, methylacetate, methanol, ethanol, and acetone. Typical nonsolvents for the casting solutions include water and formamide. The casting solution is cast in air from about zero to 10 seconds to allow the volatile solvent to evaporate and then quenched in a coagulation bath, typically water, at a temperature of 7.degree.-25.degree. C. and then air dried at ambient temperature, typically 10.degree.-30.degree. C.
Anisotropic membranes for gas separation
Gollan, A.Z.
1987-07-21
A gas separation membrane has a dense separating layer about 10,000 Angstroms or less thick and a porous support layer 10 to 400 microns thick that is an integral unit with gradually and continuously decreasing pore size from the base of the support layer to the surface of the thin separating layer and is made from a casting solution comprising ethyl cellulose and ethyl cellulose-based blends, typically greater than 47.5 ethoxyl content ethyl cellulose blended with compatible second polymers, such as nitrocellulose. The polymer content of the casting solution is from about 10% to about 35% by weight of the total solution with up to about 50% of this polymer weight a compatible second polymer to the ethyl cellulose in a volatile solvent such as isopropanol, methylacetate, methanol, ethanol, and acetone. Typical nonsolvents for the casting solutions include water and formamide. The casting solution is cast in air from about zero to 10 seconds to allow the volatile solvent to evaporate and then quenched in a coagulation bath, typically water, at a temperature of 7--25 C and then air dried at ambient temperature, typically 10--30 C. 2 figs.
Anisotropic nanomaterials: structure, growth, assembly, and functions
Sajanlal, Panikkanvalappil R.; Sreeprasad, Theruvakkattil S.; Samal, Akshaya K.; Pradeep, Thalappil
2011-01-01
Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications. PMID:22110867
Anisotropic nanomaterials: structure, growth, assembly, and functions.
Sajanlal, Panikkanvalappil R; Sreeprasad, Theruvakkattil S; Samal, Akshaya K; Pradeep, Thalappil
2011-01-01
Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications.
Matter sourced anisotropic stress for dark energy
NASA Astrophysics Data System (ADS)
Chang, Baorong; Lu, Jianbo; Xu, Lixin
2014-11-01
Usually a dark energy as a perfect fluid is characterized by the ratio of pressure to energy density (w =p /ρ ) and the ratio of their perturbations in its rest frame (cs2=δ p /δ ρ ). However, a dark energy would have other characteristics beyond its equation of state and the effective speed of sound. Here the extra property is the anisotropic stress sourced by matter as a simple extension to the perfect fluid model. At the background level, this anisotropic stress is zero with respect to the cosmological principle, but not at the first-order perturbation. We tested the viability of the existence of this kind of anisotropic stress by using the currently available cosmic observations through the geometrical and dynamical measurements. Using the Markov-chain Monte Carlo method, we found that the upper bounds on the anisotropic stress which enters into the summation of the Newtonian potentials should be of the order O (1 0-3)Δm . We did not find any strong evidence for the existence of this matter-sourced anisotropic stress, even in the 1 σ region.
Quasiparticle anisotropic hydrodynamics for central collisions
NASA Astrophysics Data System (ADS)
Alqahtani, Mubarak; Nopoush, Mohammad; Strickland, Michael
2017-03-01
We use quasiparticle anisotropic hydrodynamics to study an azimuthally symmetric boost-invariant quark-gluon plasma including the effects of both shear and bulk viscosities. In quasiparticle anisotropic hydrodynamics, a single finite-temperature quasiparticle mass is introduced and fit to the lattice data in order to implement a realistic equation of state (EoS). We compare results obtained by using the quasiparticle method with the standard method of imposing the EoS in anisotropic hydrodynamics and viscous hydrodynamics. Using these three methods, we extract the primordial particle spectra, total number of charged particles, and average transverse momentum for various values of the shear viscosity to entropy density ratio η /s . We find that the three methods agree well for small shear viscosity to entropy density ratio η /s , but differ at large η /s , with the standard anisotropic EoS method showing suppressed production at low transverse-momentum compared with the other two methods considered. Finally, we demonstrate explicitly that, when using standard viscous hydrodynamics, the bulk-viscous correction can drive the primordial particle spectra negative at large pT. Such behavior is not seen in either anisotropic hydrodynamics approach, irrespective of the value of η /s .
Landingham, R.L.
1984-03-13
Porous metallic bodies having a substantially uniform pore size of less than about 200 microns and a density of less than about 25 percent theoretical, as well as the method for making them, are disclosed. Group IIA, IIIB, IVB, VB, and rare earth metal hydrides a
NASA Astrophysics Data System (ADS)
Earwaker, L. G.; Farr, J. P. G.; Grzeszczyk, P. E.; Sturland, I.; Keen, J. M.
1985-06-01
Porous silicon, suitable after oxidation for dielectric isolation, has been produced successfully by anodizing silicon in strong HF. The oxidized layer has been shown to have promise in device manufacture, providing high packing densities and radiation hardness. Anodizing has been carried out using both single and double cells, following the effects of current density. HF concentration and silicon resistivity. The resultant porous layers have been characterised with respect to composition and structure. The materials produced differ considerably in lattice strain, composition and reactivities. Prompt radiation analyses 19F(p,αγ), 16O(d,α), 12C(d,p), are useful for monitoring the anodizing procedures and subsequent oxidation: currently, interest centres on the mechanistic information obtained. RBS analysis using α-particles gives a much lower Si response from porous than from bulk silicon. Glancing angle proton recoil analyses reveal considerable quantities of hydrogen in the porous layers. These mutually consistent findings have considerable mechanistic significance; extensive Si-H bonding occurs following a 2 equivalent Faradaic process.
Hydrophobic, Porous Battery Boxes
NASA Technical Reports Server (NTRS)
Bragg, Bobby J.; Casey, John E., Jr.
1995-01-01
Boxes made of porous, hydrophobic polymers developed to contain aqueous potassium hydroxide electrolyte solutions of zinc/air batteries while allowing air to diffuse in as needed for operation. Used on other types of batteries for in-cabin use in which electrolytes aqueous and from which gases generated during operation must be vented without allowing electrolytes to leak out.
Magnetization of anisotropic Type II superconductors
Mints, R.G.
1989-04-10
Peculiarities of magnetization of anisotropic type II superconductors are of considerable interest in view of the discovery of high-T/sub c/ superconductors characterized by strongly asymmetric layered structure. Specifics of the penetration of magnetic flux into an anisotropic type II superconductor were discussed in the literature. This analysis gave the distribution of induction in an isolated vortex, its energy, and critical magnetic field H/sub c1/. However, the magnetization curve of anisotropic superconductors was not considered. This paper deals with the magnetic moment of uniaxial London superconductor in the interval H/sub c1/ /le/ H/sub 0/ << H/sub c2/, where H/sub 0/ is the external magnetic field strength.
Leith diffusion model for homogeneous anisotropic turbulence
Rubinstein, Robert; Clark, Timothy T.; Kurien, Susan
2016-07-19
Here, a proposal for a spectral closure model for homogeneous anisotropic turbulence. The systematic development begins by closing the third-order correlation describing nonlinear interactions by an anisotropic generalization of the Leith diffusion model for isotropic turbulence. The correlation tensor is then decomposed into a tensorially isotropic part, or directional anisotropy, and a trace-free remainder, or polarization anisotropy. The directional and polarization components are then decomposed using irreducible representations of the SO(3) symmetry group. Under the ansatz that the decomposition is truncated at quadratic order, evolution equations are derived for the directional and polarization pieces of the correlation tensor. Here, numerical simulation of the model equations for a freely decaying anisotropic flow illustrate the non-trivial effects of spectral dependencies on the different return-to-isotropy rates of the directional and polarization contributions.
Leith diffusion model for homogeneous anisotropic turbulence
Rubinstein, Robert; Clark, Timothy T.; Kurien, Susan
2016-07-19
Here, a proposal for a spectral closure model for homogeneous anisotropic turbulence. The systematic development begins by closing the third-order correlation describing nonlinear interactions by an anisotropic generalization of the Leith diffusion model for isotropic turbulence. The correlation tensor is then decomposed into a tensorially isotropic part, or directional anisotropy, and a trace-free remainder, or polarization anisotropy. The directional and polarization components are then decomposed using irreducible representations of the SO(3) symmetry group. Under the ansatz that the decomposition is truncated at quadratic order, evolution equations are derived for the directional and polarization pieces of the correlation tensor. Here, numericalmore » simulation of the model equations for a freely decaying anisotropic flow illustrate the non-trivial effects of spectral dependencies on the different return-to-isotropy rates of the directional and polarization contributions.« less
Anisotropic Failure Modeling for HY-100 Steel
NASA Astrophysics Data System (ADS)
Harstad, E. N.; Maudlin, P. J.; McKirgan, J. B.
2004-07-01
HY-100 steel is a material that behaves isotropically in the elastic and plastic region and acts anisotropically in failure. Since HY-100 is a ductile metal, a more gradual failure process is observed as opposed to the nearly instantaneous failure in brittle materials. We extend our elasto-plastic-damage constitutive model by including of a decohesion model to describe material behavior between the onset of failure and fracture. We also develop an anisotropic failure surface to account for directionality in material failure. Both the anisotropic failure and decohesion models have been implemented into a finite element code, where the effects of these models are studied in a uniaxial stress simulations, a plate impact simulations, and a quasistatic notched round bar tensile test simulations.
Gravitational stresses in anisotropic rock masses
Amadei, B.; Savage, W.Z.; Swolfs, H.S.
1987-01-01
This paper presents closed-form solutions for the stress field induced by gravity in anisotropic rock masses. These rocks are assumed to be laterally restrained and are modelled as a homogeneous, orthotropic or transversely isotropic, linearly elastic material. The analysis, constrained by the thermodynamic requirement that strain energy be positive definite, gives the following important result: inclusion of anisotropy broadens the range of permissible values of gravity-induced horizontal stresses. In fact, for some ranges of anisotropic rock properties, it is thermodynamically admissible for gravity-induced horizontal stresses to exceed the vertical stress component; this is not possible for the classical isotropic solution. Specific examples are presented to explore the nature of the gravity-induced stress field in anisotropic rocks and its dependence on the type, degree and orientation of anisotropy with respect to the horizontal ground surface. ?? 1987.
Azimuthally Anisotropic 3D Velocity Continuation
Burnett, William; Fomel, Sergey
2011-01-01
We extend time-domain velocity continuation to the zero-offset 3D azimuthally anisotropic case. Velocity continuation describes how a seismic image changes given a change in migration velocity. This description turns out to be of a wave propagation process, in which images change along a velocity axis. In the anisotropic case, the velocity model is multiparameter. Therefore, anisotropic image propagation is multidimensional. We use a three-parameter slowness model, which is related to azimuthal variations in velocity, as well as their principal directions. This information is useful for fracture and reservoir characterization from seismic data. We provide synthetic diffraction imaging examples to illustratemore » the concept and potential applications of azimuthal velocity continuation and to analyze the impulse response of the 3D velocity continuation operator.« less
Leith diffusion model for homogeneous anisotropic turbulence
NASA Astrophysics Data System (ADS)
Rubinstein, Robert; Clark, Timothy; Kurien, Susan
2016-11-01
A new spectral closure model for homogeneous anisotropic turbulence is proposed. The systematic development begins by closing the third-order correlation describing nonlinear interactions by an anisotropic generalization of the Leith diffusion model for isotropic turbulence. The correlation tensor is then decomposed into a tensorially isotropic part, or directional anisotropy, and a trace-free remainder, or polarization anisotropy. The directional and polarization components are then decomposed using irreducible representations of the SO(3) symmetry group. Under the ansatz that the decomposition is truncated at quadratic order, evolution equations are derived for the directional and polarization pieces of the correlation tensor. Numerical simulation of the model equations for a freely decaying anisotropic flow illustrate the non-trivial effects of spectral dependencies on the different return-to-isotropy rates of the directional and polarization contributions.
Anisotropic Hanle line shape via magnetothermoelectric phenomena
NASA Astrophysics Data System (ADS)
Das, K. S.; Dejene, F. K.; van Wees, B. J.; Vera-Marun, I. J.
2016-11-01
We observe anisotropic Hanle line shape with unequal in-plane and out-of-plane nonlocal signals for spin precession measurements carried out on lateral metallic spin valves with transparent interfaces. The conventional interpretation for this anisotropy corresponds to unequal spin relaxation times for in-plane and out-of-plane spin orientations as for the case of two-dimensional materials like graphene, but it is unexpected in a polycrystalline metallic channel. Systematic measurements as a function of temperature and channel length, combined with both analytical and numerical thermoelectric transport models, demonstrate that the anisotropy in the Hanle line shape is magnetothermal in origin, caused by the anisotropic modulation of the Peltier and Seebeck coefficients of the ferromagnetic electrodes. Our results call for the consideration of such magnetothermoelectric effects in the study of anisotropic spin relaxation.
Foam front propagation in anisotropic oil reservoirs.
Grassia, P; Torres-Ulloa, C; Berres, S; Mas-Hernández, E; Shokri, N
2016-04-01
The pressure-driven growth model is considered, describing the motion of a foam front through an oil reservoir during foam improved oil recovery, foam being formed as gas advances into an initially liquid-filled reservoir. In the model, the foam front is represented by a set of so-called "material points" that track the advance of gas into the liquid-filled region. According to the model, the shape of the foam front is prone to develop concave sharply curved concavities, where the orientation of the front changes rapidly over a small spatial distance: these are referred to as "concave corners". These concave corners need to be propagated differently from the material points on the foam front itself. Typically the corner must move faster than those material points, otherwise spurious numerical artifacts develop in the computed shape of the front. A propagation rule or "speed up" rule is derived for the concave corners, which is shown to be sensitive to the level of anisotropy in the permeability of the reservoir and also sensitive to the orientation of the corners themselves. In particular if a corner in an anisotropic reservoir were to be propagated according to an isotropic speed up rule, this might not be sufficient to suppress spurious numerical artifacts, at least for certain orientations of the corner. On the other hand, systems that are both heterogeneous and anisotropic tend to be well behaved numerically, regardless of whether one uses the isotropic or anisotropic speed up rule for corners. This comes about because, in the heterogeneous and anisotropic case, the orientation of the corner is such that the "correct" anisotropic speed is just very slightly less than the "incorrect" isotropic one. The anisotropic rule does however manage to keep the corner very slightly sharper than the isotropic rule does.
An Anisotropic Multiphysics Model for Intervertebral Disk
Gao, Xin; Zhu, Qiaoqiao; Gu, Weiyong
2016-01-01
Intervertebral disk (IVD) is the largest avascular structure in human body, consisting of three types of charged hydrated soft tissues. Its mechanical behavior is nonlinear and anisotropic, due mainly to nonlinear interactions among different constituents within tissues. In this study, a more realistic anisotropic multiphysics model was developed based on the continuum mixture theory and employed to characterize the couplings of multiple physical fields in the IVD. Numerical simulations demonstrate that this model is capable of systematically predicting the mechanical and electrochemical signals within the disk under various loading conditions, which is essential in understanding the mechanobiology of IVD. PMID:27099402
Optical Activity of Anisotropic Achiral Surfaces
Verbiest, T.; Kauranen, M.; Van Rompaey, Y.; Persoons, A. |
1996-08-01
Anisotropic achiral surfaces respond differently to left- and right-hand circularly polarized light. This occurs when the orientation of the surface with respect to an otherwise achiral experimental setup makes the total geometry chiral. Such optical activity is demonstrated in second-harmonic generation from an anisotropic thin molecular film. The circular-difference response reverses sign as the handedness of the geometry is reversed and vanishes when the setup possesses a mirror plane. The results are explained within the electric-dipole-allowed second-order surface nonlinearity. {copyright} {ital 1996 The American Physical Society.}
On cracking of charged anisotropic polytropes
NASA Astrophysics Data System (ADS)
Azam, M.; Mardan, S. A.
2017-01-01
Recently in [1], the role of electromagnetic field on the cracking of spherical polytropes has been investigated without perturbing charge parameter explicitly. In this study, we have examined the occurrence of cracking of anisotropic spherical polytropes through perturbing parameters like anisotropic pressure, energy density and charge. We consider two different types of polytropes in this study. We discuss the occurrence of cracking in two different ways (i) by perturbing polytropic constant, anisotropy and charge parameter (ii) by perturbing polytropic index, anisotropy and charge parameter for each case. We conclude that cracking appears for a wide range of parameters in both cases. Also, our results are reduced to [2] in the absence of charge.
Inverse moments equilibria for helical anisotropic systems
NASA Astrophysics Data System (ADS)
Cooper, W. A.; Hirshman, S. P.; Depassier, M. C.
1987-11-01
An energy functional is devised for magnetic confinement schemes that have anisotropic plasma pressure. The minimization of this energy functional is demonstrated to reproduce components of the magnetohydrodynamic (MHD) force balance relation in systems with helical symmetry. An iterative steepest descent procedure is applied to the Fourier moments of the inverse magnetic flux coordinates to minimize the total energy and thus generate anisotropic pressure MHD equilibria. Applications to straight ELMO Snaky Torus (NTIS Document No. DE-84002406) configurations that have a magnetic well on the outermost flux surfaces have been obtained.
Raman Tensor Formalism for Optically Anisotropic Crystals.
Kranert, Christian; Sturm, Chris; Schmidt-Grund, Rüdiger; Grundmann, Marius
2016-03-25
We present a formalism for calculating the Raman scattering intensity dependent on the polarization configuration for optically anisotropic crystals. It can be applied to crystals of arbitrary orientation and crystal symmetry measured in normal incidence backscattering geometry. The classical Raman tensor formalism cannot be used for optically anisotropic materials due to birefringence causing the polarization within the crystal to be depth dependent. We show that in the limit of averaging over a sufficiently large scattering depth, the observed Raman intensities converge and can be described by an effective Raman tensor given here. Full agreement with experimental results for uniaxial and biaxial crystals is demonstrated.
Evolution of multidimensional flat anisotropic cosmological models
Beloborodov, A. ); Demianski, M. Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw International Center for Relativistic Astrophysics , Universita di Roma I, La Sapienza, Rome ); Ivanov, P.; Polnarev, A.G. )
1993-07-15
We study the dynamics of a flat multidimensional anisotropic cosmological model filled with an anisotropic fluidlike medium. By an appropriate choice of variables, the dynamical equations reduce to a two-dimensional dynamical system. We present a detailed analysis of the time evolution of this system and the conditions of the existence of spacetime singularities. We investigate the conditions under which violent, exponential, and power-law inflation is possible. We show that dimensional reduction cannot proceed by anti-inflation (rapid contraction of internal space). Our model indicates that it is very difficult to achieve dimensional reduction by classical means.
Differential matrix formalism for depolarizing anisotropic media.
Ossikovski, Razvigor
2011-06-15
Azzam's differential matrix formalism [J. Opt. Soc. Am. 68, 1756 (1978)], originally developed for longitudinally inhomogeneous anisotropic nondepolarizing media, is extended to include depolarizing media. The generalization is physically interpreted in terms of means and uncertainties of the elementary optical properties of the medium, as well as of three anisotropy absorption parameters introduced to describe the depolarization. The formalism results in a particularly simple mathematical procedure for the retrieval of the elementary properties of a generally depolarizing anisotropic medium, assumed to be globally homogeneous, from its experimental Mueller matrix. The approach is illustrated on literature data and the conditions of its validity are identified and discussed.
Modeling of nanostructured porous thermoelastic composites with surface effects
NASA Astrophysics Data System (ADS)
Nasedkin, A. V.; Nasedkina, A. A.; Kornievsky, A. S.
2017-01-01
The paper presents an integrated approach for determination of effective properties of anisotropic porous thermoelastic materials with a nanoscale stochastic porosity structure. This approach includes the effective moduli method for composite me-chanics, the simulation of representative volumes and the finite element method. In order to take into account nanoscale sizes of pores, the Gurtin-Murdoch model of surface stresses and the highly conducting interface model are used at the borders between material and pores. The general methodology for determination of effective properties of porous composites is demonstrated for a two-phase composite with special conditions for stresses and heat flux discontinuities at the phase interfaces. The mathematical statements of boundary value problems and the resulting formulas to determine the complete set of effective constants of the two-phase composites with arbitrary anisotropy and with surface properties are described; the generalized statements are formulated and the finite element approximations are given. It is shown that the homogenization procedures for porous composites with surface effects can be considered as special cases of the corresponding procedures for the two-phase composites with interphase stresses and heat fluxes if the moduli of nanoinclusions are negligibly small. These approaches have been implemented in the finite element package ANSYS for a model of porous material with cubic crystal system for various values of surface moduli, porosity and number of pores. It has been noted that the magnitude of the area of the interphase boundaries has influence on the effective moduli of the porous materials with nanosized structure.
Phase Field Modeling of Directional Fracture in Anisotropic Polycrystals
2015-02-01
ARL-RP-0518 ● FEBRUARY 2015 US Army Research Laboratory Phase Field Modeling of Directional Fracture in Anisotropic Polycrystals...0518 ● FEBRUARY 2015 US Army Research Laboratory Phase Field Modeling of Directional Fracture in Anisotropic Polycrystals by JD Clayton...
NASA Astrophysics Data System (ADS)
Zhang, Kai
Bioactive materials chemically bond to tissues through the development of biologically active apatite. Porous structures in biomaterials are designed to enhance bioactivity, grow artificial tissues and achieve better integration with host tissues in the body. The goal of this research is to design, fabricate and characterize novel porous bioactive materials. 3D ordered macroporous bioactive glasses (3DOM-BGs, pore size: 200--1000 nm) were prepared using a sol-gel process and colloidal crystal templates. 3DOM-BGs are more bioactive and degradable than mesoporous (pore size <50 nm) sol-gel BGs in simulated body fluid (SBF). Apatite formation and 3DOM-BG degradation rates increased with the decrease of soaking ratio. Apatite induction time in SBF increased with 3DOM-BG calcination temperature (600--800°C). Apatite formation and 3DOMBG degradation were slightly enhanced for a phosphate containing composition. Large 3DOM-BG particles formed less apatite and degraded less completely as compared with small particles. An increase in macropore size slowed down 3DOM-BG degradation and apatite formation processes. After heating the converted apatite at a temperature higher than 700°C, highly crystalline hydroxyapatite and a minor tri-calcium phosphate phase formed. 3DOM-BGs have potential applications as bone/periodontal fillers, and drugs and biological factors delivery agents. Anchoring artificial soft tissues (e.g., cartilage) to native bone presents a challenge. Porous polymer/bioactive glass composites are candidate materials for engineering artificial soft tissue/bone interfaces. Porous composites consisting of polymer matrices (e.g., polysulfone, polylactide, and polyurethane) and bioactive glass particles were prepared by polymer phase separation techniques adapted to include ceramic particles. Composites (thickness: 200--500 mum) have asymmetric structures with dense top layers and porous structures beneath. Porous structures consist of large pores (>100 mum) in a
Nonlinear Stability of Convection in a Porous Layer with Solid Partitions
NASA Astrophysics Data System (ADS)
Straughan, B.
2014-07-01
We show that for many classes of convection problem involving a porous layer, or layers, interleaved with finite but non-deformable solid layers, the global nonlinear stability threshold is exactly the same as the linear instability one. The layer(s) of porous material may be of Darcy type, Brinkman type, possess an anisotropic permeability, or even be such that they are of local thermal non-equilibrium type where the fluid and solid matrix constituting the porous material may have different temperatures. The key to the global stability result lies in proving the linear operator attached to the convection problem is a symmetric operator while the nonlinear terms must satisfy appropriate conditions.
MAGNUM2D. Radionuclide Transport Porous Media
Langford, D.W.; Baca, R.G.
1989-03-01
MAGNUM2D was developed to analyze thermally driven fluid motion in the deep basalts below the Paco Basin at the Westinghouse Hanford Site. Has been used in the Basalt Waste Isolation Project to simulate nonisothermal groundwater flow in a heterogeneous anisotropic medium and heat transport in a water/rock system near a high level nuclear waste repository. Allows three representations of the hydrogeologic system: an equivalent porous continuum, a system of discrete, unfilled, and interconnecting fractures separated by impervious rock mass, and a low permeability porous continuum with several discrete, unfilled fractures traversing the medium. The calculations assume local thermodynamic equilibrium between the rock and groundwater, nonisothermal Darcian flow in the continuum portions of the rock, and nonisothermal Poiseuille flow in discrete unfilled fractures. In addition, the code accounts for thermal loading within the elements, zero normal gradient and fixed boundary conditions for both temperature and hydraulic head, and simulation of the temperature and flow independently. The Q2DGEOM preprocessor was developed to generate, modify, plot and verify quadratic two dimensional finite element geometries. The BCGEN preprocessor generates the boundary conditions for head and temperature and ICGEN generates the initial conditions. The GRIDDER postprocessor interpolates nonregularly spaced nodal flow and temperature data onto a regular rectangular grid. CONTOUR plots and labels contour lines for a function of two variables and PARAM plots cross sections and time histories for a function of time and one or two spatial variables. NPRINT generates data tables that display the data along horizontal or vertical cross sections. VELPLT differentiates the hydraulic head and buoyancy data and plots the velocity vectors. The PATH postprocessor plots flow paths and computes the corresponding travel times.
MAGNUM2D. Radionuclide Transport Porous Media
Langford, D.W.; Baca, R.G.
1988-08-01
MAGNUM2D was developed to analyze thermally driven fluid motion in the deep basalts below the Paco Basin at the Westinghouse Hanford Site. Has been used in the Basalt Waste Isolation Project to simulate nonisothermal groundwater flow in a heterogeneous anisotropic medium and heat transport in a water/rock system near a high level nuclear waste repository. Allows three representations of the hydrogeologic system: an equivalent porous continuum, a system of discrete, unfilled, and interconnecting fractures separated by impervious rock mass, and a low permeability porous continuum with several discrete, unfilled fractures traversing the medium. The calculation assumes local thermodynamic equilibrium between the rock and groundwater, nonisothermal Darcian flow in the continuum portions of the rock, and nonisothermal Poiseuille flow in discrete unfilled fractures. In addition, the code accounts for thermal loading within the elements, zero normal gradient and fixed boundary conditions for both temperature and hydraulic head, and simulation of the temperature and flow independently. The Q2DGEOM preprocessor was developed to generate, modify, plot and verify quadratic two dimensional finite element geometries. The BCGEN preprocessor generates the boundary conditions for head and temperature and ICGEN generates the initial conditions. The GRIDDER postprocessor interpolates nonregularly spaced nodal flow and temperature data onto a regular rectangular grid. CONTOUR plots and labels contour lines for a function of two variables and PARAM plots cross sections and time histories for a function of time and one or two spatial variables. NPRINT generates data tables that display the data along horizontal or vertical cross sections. VELPLT differentiates the hydraulic head and buoyancy data and plots the velocity vectors. The PATH postprocessor plots flow paths and computes the corresponding travel times.
An Engineered Anisotropic Nanofilm with Unidirectional Wetting Properties
2010-01-01
ARTICLES PUBLISHED ONLINE: 10 OCTOBER 2010 | DOI: 10.1038/NMAT2864 An engineered anisotropic nanofilm with unidirectional wetting properties Niranjan...body3. Engineering synthetic materials with such anisotropic adhesive properties has led to advances in digitalmicrofluidic devices5,6 andmedicine7,8...The anisotropic wetting properties of existing engineered surfaces are derived either from spatial gradients (for example, temperature, surface
Data-driven imaging in anisotropic media
Volker, Arno; Hunter, Alan
2012-05-17
Anisotropic materials are being used increasingly in high performance industrial applications, particularly in the aeronautical and nuclear industries. Some important examples of these materials are composites, single-crystal and heavy-grained metals. Ultrasonic array imaging in these materials requires exact knowledge of the anisotropic material properties. Without this information, the images can be adversely affected, causing a reduction in defect detection and characterization performance. The imaging operation can be formulated in two consecutive and reciprocal focusing steps, i.e., focusing the sources and then focusing the receivers. Applying just one of these focusing steps yields an interesting intermediate domain. The resulting common focus point gather (CFP-gather) can be interpreted to determine the propagation operator. After focusing the sources, the observed travel-time in the CFP-gather describes the propagation from the focus point to the receivers. If the correct propagation operator is used, the measured travel-times should be the same as the time-reversed focusing operator due to reciprocity. This makes it possible to iteratively update the focusing operator using the data only and allows the material to be imaged without explicit knowledge of the anisotropic material parameters. Furthermore, the determined propagation operator can also be used to invert for the anisotropic medium parameters. This paper details the proposed technique and demonstrates its use on simulated array data from a specimen of Inconel single-crystal alloy commonly used in the aeronautical and nuclear industries.
Vibrations and stresses in layered anisotropic cylinders
NASA Technical Reports Server (NTRS)
Mulholland, G. P.; Gupta, B. P.
1976-01-01
An equation describing the radial displacement in a k layered anisotropic cylinder was obtained. The cylinders are initially unstressed but are subjected to either a time dependent normal stress or a displacement at the external boundaries of the laminate. The solution is obtained by utilizing the Vodicka orthogonalization technique. Numerical examples are given to illustrate the procedure.
Thermal D mesons from anisotropic lattice QCD
NASA Astrophysics Data System (ADS)
Kelly, Aoife; Skullerud, Jon-Ivar
2017-03-01
We present results for correlators and spectral functions of open charm mesons using 2+1 flavours of clover fermions on anisotropic lattices. The D mesons are found to dissociate close to the deconfinement crossover temperature Tc. Our preliminary results suggest a shift in the thermal D meson mass below Tc. Mesons containing strange quarks exhibit smaller thermal modifications than those containing light quarks.
Anisotropic MHD model and some solutions
Kuznetsov, V. D.; Dzhalilov, N. S.
2010-09-15
MHD waves and instabilities in a collisionless anisotropic-pressure plasma are analyzed in an anisotropic MHD model based on the 16-moment approximation, and the results are found to agree well with those obtained in the low-frequency limit of the kinetic model. It is shown that accounting for heat fluxes leads to an asymmetry in the phase velocities of the wave modes with respect to the heat flux direction and also to a strong interaction between the modes, especially between the backward ones (those that propagate in a direction opposite to that of the heat flux). A correct description of the mirror instability is given. The resonant interaction of three backward modes-fast acoustic, fast magnetosonic, and slow acoustic-under the conditions for the onset of the classical firehose instability triggers a new type of instability the growth rate of which is faster than the maximum growth rate of the conventional firehose instability. The results prove that, in contrast to the familiar Chew-Goldberger-Low approximate model, the anisotropic MHD approach provides a correct description of the large-scale dynamics of collisionless anisotropic plasmas (such as solar corona, solar wind, and ionospheric and magnetospheric plasmas).
A generalized anisotropic deformation formulation for geomaterials
NASA Astrophysics Data System (ADS)
Lei, Z.; Rougier, Esteban; Knight, E. E.; Munjiza, A.; Viswanathan, H.
2016-04-01
In this paper, the combined finite-discrete element method (FDEM) has been applied to analyze the deformation of anisotropic geomaterials. In the most general case geomaterials are both non-homogeneous and non-isotropic. With the aim of addressing anisotropic material problems, improved 2D FDEM formulations have been developed. These formulations feature the unified hypo-hyper elastic approach combined with a multiplicative decomposition-based selective integration for volumetric and shear deformation modes. This approach is significantly different from the co-rotational formulations typically encountered in finite element codes. Unlike the co-rotational formulation, the multiplicative decomposition-based formulation naturally decomposes deformation into translation, rotation, plastic stretches, elastic stretches, volumetric stretches, shear stretches, etc. This approach can be implemented for a whole family of finite elements from solids to shells and membranes. This novel 2D FDEM based material formulation was designed in such a way that the anisotropic properties of the solid can be specified in a cell by cell basis, therefore enabling the user to seed these anisotropic properties following any type of spatial variation, for example, following a curvilinear path. In addition, due to the selective integration, there are no problems with volumetric or shear locking with any type of finite element employed.
THEORY OF COMPTON SCATTERING BY ANISOTROPIC ELECTRONS
Poutanen, Juri; Vurm, Indrek E-mail: indrek.vurm@oulu.f
2010-08-15
Compton scattering plays an important role in various astrophysical objects such as accreting black holes and neutron stars, pulsars, relativistic jets, and clusters of galaxies, as well as the early universe. In most of the calculations, it is assumed that the electrons have isotropic angular distribution in some frame. However, there are situations where the anisotropy may be significant due to the bulk motions, or where there is anisotropic cooling by synchrotron radiation or an anisotropic source of seed soft photons. Here we develop an analytical theory of Compton scattering by anisotropic distribution of electrons that can significantly simplify the calculations. Assuming that the electron angular distribution can be represented by a second-order polynomial over the cosine of some angle (dipole and quadrupole anisotropies), we integrate the exact Klein-Nishina cross section over the angles. Exact analytical and approximate formulae valid for any photon and electron energies are derived for the redistribution functions describing Compton scattering of photons with arbitrary angular distribution by anisotropic electrons. The analytical expressions for the corresponding photon scattering cross section on such electrons, as well as the mean energy of scattered photons, its dispersion, and radiation pressure force are also derived. We apply the developed formalism to the accurate calculations of the thermal and kinematic Sunyaev-Zeldovich effects for arbitrary electron distributions.
Porous electrode preparation method
Arons, R.M.; Dusek, J.T.
1983-10-18
A porous sintered plaque is provided with a bimodal porosity that is especially well suited for use as an electrode within a molten carbonate fuel cell. The coarse porosity is sufficient for admitting gases into contact with the reaction surfaces while the fine porosity is wetted with and retains molten electrolyte on the reaction sites. The electrode structure is prepared by providing a very fine powder of such as nickel oxide and blending the powder with a suitable decomposable binder to form a solid mass. The mass is comminuted into agglomerate size particles substantially larger than the fine oxide particles and formed into a cohesive compact for subsequent sintering. Sintering is carried out at sufficient conditions to bind the agglomerates together into a porous structure having both coarse and fine porosity. Where lithiated nickel oxide cathodes are prepared, the sintering conditions can be moderate enough to retain substantial quantities of lithium within the electrode for adequate conductivity. 2 figs.
Strong, Lightweight, Porous Materials
NASA Technical Reports Server (NTRS)
Leventis, Nicholas; Meador, Mary Ann B.; Johnston, James C.; Fabrizio, Eve F.; Ilhan, Ulvi
2007-01-01
A new class of strong, lightweight, porous materials has been invented as an outgrowth of an effort to develop reinforced silica aerogels. The new material, called X-Aerogel is less hygroscopic, but no less porous and of similar density to the corresponding unmodified aerogels. However, the property that sets X-Aerogels apart is their mechanical strength, which can be as much as two and a half orders of magnitude stronger that the unmodified aerogels. X-Aerogels are envisioned to be useful for making extremely lightweight, thermally insulating, structural components, but they may also have applications as electrical insulators, components of laminates, catalyst supports, templates for electrode materials, fuel-cell components, and filter membranes.
Shepodd, Timothy J.
2002-01-01
Highly crosslinked monolithic porous polymer materials for chromatographic applications. By using solvent compositions that provide not only for polymerization of acrylate monomers in such a fashion that a porous polymer network is formed prior to phase separation but also for exchanging the polymerization solvent for a running buffer using electroosmotic flow, the need for high pressure purging is eliminated. The polymer materials have been shown to be an effective capillary electrochromatographic separations medium at lower field strengths than conventional polymer media. Further, because of their highly crosslinked nature these polymer materials are structurally stable in a wide range of organic and aqueous solvents and over a pH range of 2-12.
Wellbore stability analysis in carbonate reservoir considering anisotropic behaviour
NASA Astrophysics Data System (ADS)
Alves, José; Guevara, Nestor; Coelho, Lucia; Baud, Patrick
2010-05-01
Carbonate reservoirs represent a major part of the world oil and gas reserves. In particular, recent discoveries in the pre-salt offshore Brazil place big challenges to exploration and production under high temperatures and pressures (HTHP). During production, the extraction of hydrocarbons reduces pore pressure and thus causes an increase in the effective stress and mechanical compaction in the reservoir. The compactive deformation and failure may be spatially extensive or localized to the vicinity of the wellbore, but in either case the consequences can be economically severe involving surface subsidence, well failure and various production problems. The analysis of wellbore stability and more generally of deformation and failure in carbonate environments hinges upon a relevant constitutive modeling of carbonate rocks over a wide range of porosities, in particular, observed microstructure of samples suggests anisotropic behaviour. In this study, we performed a wellbore stability analysis for a lateral wellbore junction in three dimensions. The complex geometry for the wellbore junction was modeled with tetrahedral finite elements considering a rate independent elastic-plastic isotropic material that presented linear behavior during elastic strain and associated flow rule. A finite element model simulating drilling and production phases were done for field conditions from a deep water reservoir in Campos basin, offshore Brazil. In this context, several scenarios were studied considering true 3D orientation for both in situ stresses and geometry of the wellbore junction itself. We discussed the impact of constitutive modeling, considering anisotropic ductile damage and pressure sensitiveness on the wellbore stability. Parameter values for the analysis were based based on experimental data on two micritic porous carbonates. Series of conventional triaxial experiments were performed at room temperature in dry and wet conditions on samples of Comiso and Tavel
Porous microsphere and its applications
Cai, Yunpeng; Chen, Yinghui; Hong, Xiaoyun; Liu, Zhenguo; Yuan, Weien
2013-01-01
Porous microspheres have drawn great attention in the last two decades for their potential applications in many fields, such as carriers for drugs, absorption and desorption of substances, pulmonary drug delivery, and tissue regeneration. The application of porous microspheres has become a feasible way to address existing problems. In this essay, we give a brief introduction of the porous microsphere, its characteristics, preparation methods, applications, and a brief summary of existing problems and research tendencies. PMID:23515359
Selective formation of porous silicon
NASA Technical Reports Server (NTRS)
Fathauer, Robert W. (Inventor); Jones, Eric W. (Inventor)
1993-01-01
A pattern of porous silicon is produced in the surface of a silicon substrate by forming a pattern of crystal defects in said surface, preferably by applying an ion milling beam through openings in a photoresist layer to the surface, and then exposing said surface to a stain etchant, such as HF:HNO3:H2O. The defected crystal will preferentially etch to form a pattern of porous silicon. When the amorphous content of the porous silicon exceeds 70 percent, the porous silicon pattern emits visible light at room temperature.
Selective formation of porous silicon
NASA Technical Reports Server (NTRS)
Fathauer, Jones (Inventor)
1993-01-01
A pattern of porous silicon is produced in the surface of a silicon substrate by forming a pattern of crystal defects in said surface, preferably by applying an ion milling beam through openings in a photoresist layer to the surface, and then exposing said surface to a stain etchant, such as HF:HNO3:H20. The defected crystal will preferentially etch to form a pattern of porous silicon. When the amorphous content of the porous silicon exceeds 70 percent, the porous silicon pattern emits visible light at room temperature.
Oligonucleotide-Functionalized Anisotropic Gold Nanoparticles
NASA Astrophysics Data System (ADS)
Jones, Matthew Robert
In this thesis, we describe the properties of oligonucleotide-functionalized gold colloids under the unique set of conditions where the particles are geometrically anisotropic and have nanometer-scale dimensions. While nearly two decades of previous work elucidated numerous unexpected and emergent phenomena arising from the combination of inorganic nanoparticles with surface-bound DNA strands, virtually nothing was known about how these properties are altered when the shape of the nanoparticle core is chosen to be non-spherical. In particular, we are interested in understanding, and ultimately controlling, the ways in which these DNA-conjugated anisotropic nanostructures interact when their attraction is governed by programmable DNA hybridization events. Chapter 1 introduces the field of DNA-based materials assembly by discussing how nanoscale building blocks which present rigid, directional interactions can be thought of as possessing artificial versions of the familiar chemical principles of "bonds" and "valency". In chapter 2 we explore the fundamental interparticle binding thermodynamics of DNA-functionalized spherical and anisotropic nanoparticles, which reveals enormous preferences for collective ligand interactions occurring between flat surfaces over those that occur between curved surfaces. Using these insights, chapter 3 demonstrates that when syntheses produce mixtures of different nanoparticle shapes, the tailorable nature of DNA-mediated interparticle association can be used to selectively crystallize and purify the desired anisotropic nanostructure products, leaving spherical impurity particles behind. Chapter 4 leverages the principle that the flat facets of anisotropic particles generate directional DNA-based hybridization interactions to assemble a variety of tailorable nanoparticle superlattices whose symmetry and dimensionality are a direct consequence of the shape of the nanoparticle building block used in their construction. Chapter 5 explores
Mimouni, N.; Chikh, S.; Rahli, O.; Bennacer, R.
2014-07-15
Two-dimensional (2D) and three-dimensional (3D) numerical simulations of double diffusion natural convection in an elongated enclosure filled with a binary fluid saturating a porous medium are carried out in the present work. The Boussinesq approximation is made in the formulation of the problem, and Neumann boundary conditions for temperature and concentration are adopted, respectively, on vertical and horizontal walls of the cavity. The used numerical method is based on the control volume approach, with the third order quadratic upstream interpolation scheme in approximating the advection terms. A semi implicit method algorithm is used to handle the velocity-pressure coupling. To avoid the excessively high computer time inherent to the solution of 3D natural convection problems, full approximation storage with full multigrid method is used to solve the problem. A wide range of the controlling parameters (Rayleigh-Darcy number Ra, lateral aspect ratio Ay, Lewis number Le, and the buoyancy ration N) is investigated. We clearly show that increasing the depth of the cavity (i.e., the lateral aspect ratio) has an important effect on the flow patterns. The 2D perfect parallel flows obtained for small lateral aspect ratio are drastically destabilized by increasing the cavity lateral dimension. This yields a 3D fluid motion with a much more complex flow pattern and the usually considered 2D parallel flow model cannot be applied.
NASA Astrophysics Data System (ADS)
Kim, Min Chan
2014-11-01
To simulate a CO2 sequestration process, some researchers employed a water/propylene glycol (PPG) system which shows a non-monotonic density profile. Motivated by this fact, the stability of the diffusion layer of two miscible fluids saturated in a porous medium is analyzed. For a non-monotonic density profile system, linear stability equations are derived in a global domain, and then transformed into a system of ordinary differential equations in an infinite domain. Initial growth rate analysis is conducted without the quasi-steady state approximation (QSSA) and shows that initially the system is unconditionally stable for the least stable disturbance. For the time evolving case, the ordinary differential equations are solved applying the eigen-analysis and numerical shooting scheme with and without the QSSA. To support these theoretical results, direct numerical simulations are conducted using the Fourier spectral method. The results of theoretical linear stability analyses and numerical simulations validate one another. The present linear and nonlinear analyses show that the water/PPG system is more unstable than the CO2/brine one, and the flow characteristics of these two systems are quite different from each other.
Chiang, Ta-Kuan; Straub, Douglas L.; Dennis, Richard A.
2000-01-01
The present invention involves a porous rigid filter including a plurality of concentric filtration elements having internal flow passages and forming external flow passages there between. The present invention also involves a pressure vessel containing the filter for the removal of particulates from high pressure particulate containing gases, and further involves a method for using the filter to remove such particulates. The present filter has the advantage of requiring fewer filter elements due to the high surface area-to-volume ratio provided by the filter, requires a reduced pressure vessel size, and exhibits enhanced mechanical design properties, improved cleaning properties, configuration options, modularity and ease of fabrication.
Photoactive porous silicon nanopowder.
Meekins, Benjamin H; Lin, Ya-Cheng; Manser, Joseph S; Manukyan, Khachatur; Mukasyan, Alexander S; Kamat, Prashant V; McGinn, Paul J
2013-04-24
Bulk processing of porous silicon nanoparticles (nSi) of 50-300 nm size and surface area of 25-230 m(2)/g has been developed using a combustion synthesis method. nSi exhibits consistent photoresponse to AM 1.5 simulated solar excitation. In confirmation of photoactivity, the films of nSi exhibit prompt bleaching following femtosecond laser pulse excitation resulting from the photoinduced charge separation. Photocurrent generation observed upon AM 1.5 excitation of these films in a photoelectrochemical cell shows strong dependence on the thickness of the intrinsic silica shell that encompasses the nanoparticles and hinders interparticle electron transfer.
Tortuosity of porous particles.
Barrande, M; Bouchet, R; Denoyel, R
2007-12-01
Tortuosity is often used as an adjustable parameter in models of transfer properties through porous media. This parameter, not reducible to classical measured microstructural parameters like specific surface area, porosity, or pore size distribution, reflects the efficiency of percolation paths, which is linked to the topology of the material. The measurement of the effective conductivity of a bed of particles saturated with an electrolyte is a simple way to evaluate tortuosity. Nevertheless, it received only little attention because of the real difficulties in both getting reliable results and interpreting data. Notably, the discrimination between the contribution of interparticle and intraparticle porosities to the tortuosity is not resolved. To our knowledge, there is no model able to fit the experimental data of the tortuosity of a suspension, and a fortiori of a particle bed, in the whole porosity range. Only empirical expressions have been proposed, but they do not allow deriving intratortuosity of a porous particle. For a dilute system, Maxwell's equation predicts the effective conductivity of suspensions of spherical particles as a function of the bulk electrolyte conductivity and of particle conductivity. The intraparticle tortuosity can be derived from the particle conductivity obtained from the Maxwell equation applied to data at infinite dilution of particles. Then, by assuming that the Maxwell equation is a first-order approximation of the conductivity as a function of porosity, we propose an explicit relation of the tortuosity tau of a suspension of porous particles, obtained by conductivity measurement, as tau = tau(epsilon, epsilon(p), tau(p)), where epsilon is the total porosity of the suspension, tau(p) is the intraparticle tortuosity, and epsilon(p) is the particle porosity. This relationship fits the experimental data in the whole porosity range and can be used to determine tau(p) from an experiment at only one porosity. Finally, the obtained
Crosslinked, porous, polyacrylate beads
NASA Technical Reports Server (NTRS)
Rembaum, Alan (Inventor); Yen, Shiao-Ping S. (Inventor); Dreyer, William J. (Inventor)
1977-01-01
Uniformly-shaped, porous, round beads are prepared by the co-polymerization of an acrylic monomer and a cross-linking agent in the presence of 0.05 to 5% by weight of an aqueous soluble polymer such as polyethylene oxide. Cross-linking proceeds at high temperature above about 50.degree. C or at a lower temperature with irradiation. Beads of even shape and even size distribution of less than 2 micron diameter are formed. The beads will find use as adsorbents in chromatography and as markers for studies of cell surface receptors.
Small, porous polyacrylate beads
NASA Technical Reports Server (NTRS)
Rembaum, Alan (Inventor); Yen, Shiao-Ping Siao (Inventor); Dreyer, William J. (Inventor)
1976-01-01
Uniformly-shaped, porous, round beads are prepared by the co-polymerization of an acrylic monomer and a cross-linking agent in the presence of 0.05 to 5% by weight of an aqueous soluble polymer such as polyethylene oxide. Cross-linking proceeds at high temperature above about 50.degree.C or at a lower temperature with irradiation. Beads of even shape and even size distribution of less than 2 micron diameter are formed. The beads will find use as adsorbents in chromatography and as markers for studies of cell surface receptors.
Crosslinked, porous, polyacrylate beads
NASA Technical Reports Server (NTRS)
Rembaum, Alan (Inventor); Yen, Shiao-Ping Siao (Inventor); Dreyer, William J. (Inventor)
1976-01-01
Uniformly-shaped, porous, round beads are prepared by the co-polymerization of an acrylic monomer and a cross-linking agent in the presence of 0.05 to 5% by weight of an aqueous soluble polymer such as polyethylene oxide. Cross-linking proceeds at high temperature above about 50.degree.C or at a lower temperature with irradiation. Beads of even shape and even size distribution of less than 2 micron diameter are formed. The beads will find use as adsorbents in chromatography and as markers for studies of cell surface receptors.
Rainbow metric from quantum gravity: Anisotropic cosmology
NASA Astrophysics Data System (ADS)
Assanioussi, Mehdi; Dapor, Andrea
2017-03-01
In this paper we present a construction of effective cosmological models which describe the propagation of a massive quantum scalar field on a quantum anisotropic cosmological spacetime. Each obtained effective model is represented by a rainbow metric in which particles of distinct momenta propagate on different classical geometries. Our analysis shows that upon certain assumptions and conditions on the parameters determining such anisotropic models, we surprisingly obtain a unique deformation parameter β in the modified dispersion relation of the modes, hence, inducing an isotropic deformation despite the general starting considerations. We then ensure the recovery of the dispersion relation realized in the isotropic case, studied in [M. Assanioussi, A. Dapor, and J. Lewandowski, Phys. Lett. B 751, 302 (2015), 10.1016/j.physletb.2015.10.043], when some proper symmetry constraints are imposed, and we estimate the value of the deformation parameter for this case in loop quantum cosmology context.
Nonminimal coupling in anisotropic teleparallel inflation
NASA Astrophysics Data System (ADS)
Abedi, Habib; Wright, Matthew; Abbassi, Amir M.
2017-03-01
We study an anisotropic inflationary scenario in teleparallel gravity. We consider a model where the inflaton is nonminimally coupled both to torsion and a vector field, which can lead to anisotropic inflation. In the weak-coupling limit, our results coincide with the results obtained in the general relativistic framework. However, in the strong-coupling regime of the Jordan frame, we show that the anisotropy shear to expansion ratio is a constant, and can be much larger than the slow-roll parameter. Applying a conformal transformation we then work in the Einstein frame, which in teleparallel gravity introduces a different form of coupling between the inflaton and torsion. In this frame we show that in the strong coupling regime the anisotropy shear to expansion ratio is a different constant, that can be made suitably small.
Formation of Anisotropic Block Copolymer Gels
NASA Astrophysics Data System (ADS)
Liaw, Chya Yan; Shull, Kenneth; Henderson, Kevin; Joester, Derk
2011-03-01
Anisotropic, fibrillar gels are important in a variety of processes. Biomineralization is one example, where the mineralization process often occurs within a matrix of collagen or chitin fibers that trap the mineral precursors and direct the mineralization process. We wish to replicate this type of behavior within block copolymer gels. Particularly, we are interested in employing gels composed of cylindrical micelles, which are anisotropic and closely mimic biological fibers. Micelle geometry is controlled in our system by manipulating the ratio of molecular weights of the two blocks and by controlling the detailed thermal processing history of the copolymer solutions. Small-Angle X-ray Scattering and Dynamic Light Scattering are used to determine the temperature dependence of the gel formation process. Initial experiments are based on a thermally-reversible alcohol-soluble system, that can be subsequently converted to a water soluble system by hydrolysis of a poly(t-butyl methacrylate) block to a poly (methacrylic acid) block. MRSEC.
Fluctuations in a Primordial Anisotropic ERA
NASA Astrophysics Data System (ADS)
Novello, Mário; de Freitas, Luciane R.
The primordial Universe is treated in terms of a nonperfect fluid configuration endowed with an anisotropic expansion. The deGennes-Landau mechanism of phase transition acts as a very efficient process to provide the elimination of the previous anisotropy and to set the universe in the current isotropic FRW stage. The entropy produced, as a consequence of the phase transition, depends on the strength of the previous shear. We suggest the hypothesis that the germinal perturbations that will grow into the observed system of galaxies occurring in the anisotropic era. We present a model to deal with this idea that provides a power spectrum of fluctuations of the form δ 2k ˜ 1/(a +bk2). We compare this prediction of our model to the current knowledge on the galaxy formation process.
Wireless energy transfer between anisotropic metamaterials shells
Díaz-Rubio, Ana; Carbonell, Jorge; Sánchez-Dehesa, José
2014-06-15
The behavior of strongly coupled Radial Photonic Crystals shells is investigated as a potential alternative to transfer electromagnetic energy wirelessly. These sub-wavelength resonant microstructures, which are based on anisotropic metamaterials, can produce efficient coupling phenomena due to their high quality factor. A configuration of selected constitutive parameters (permittivity and permeability) is analyzed in terms of its resonant characteristics. The coupling to loss ratio between two coupled resonators is calculated as a function of distance, the maximum (in excess of 300) is obtained when the shells are separated by three times their radius. Under practical conditions an 83% of maximum power transfer has been also estimated. -- Highlights: •Anisotropic metamaterial shells exhibit high quality factors and sub-wavelength size. •Exchange of electromagnetic energy between shells with high efficiency is analyzed. •Strong coupling is supported with high wireless transfer efficiency. •End-to-end energy transfer efficiencies higher than 83% can be predicted.
The Impact of Anisotropic Error Correlation Modelling
NASA Technical Reports Server (NTRS)
Swinbank, R.; Riishojgaard, L. P.; Menard, R.
1999-01-01
Most data assimilation systems assume isotropic forecast error correlations, but results from two dimensional Kalman Filter experiments indicate that the correlations can be far from isotropic. In this paper we use a simple two-dimensional data assimilation system, which analyses trace chemical species such as ozone, to assess different approaches to modelling the error correlations. We compare assimilation results using isotropic correlations with results obtained using different approaches to modelling anisotropic correlations: first, using correlations based on the concentrations of the trace chemicals, and secondly using an advective correlation model. We show that these relatively cheap ways of modelling anisotropic correlations give objectively better results than using isotropic correlations. We discuss the possible extension of these approaches to a full 3-D meteorological data assimilation system.
Nonorthogonal polarisation eigenstates in anisotropic cavities
Mamaev, Yu A; Khandokhin, Pavel A
2011-06-30
The Jones matrix method is used to analyse the polarisation eigenmodes of a solid-state laser with an anisotropic Fabry - Perot cavity containing amplitude and phase anisotropic elements. The results demonstrate that, when the axes of these elements do not coincide, the eigenpolarisations become elliptical and nonorthogonal. The ellipticities and azimuths of the polarisation modes and the magnitude and phase of the nonorthogonality parameter are determined as functions of polariser angle at different relationships between the amplitude and phase anisotropies, and the effect is shown to be strongest at a polariser angle of 45{sup 0}. There is critical phase anisotropy, dependent on amplitude anisotropy, at which the magnitude of the nonorthogonality parameter and ellipticity of the polarisation modes approach unity. (resonators)
Anisotropic singularities in modified gravity models
NASA Astrophysics Data System (ADS)
Figueiró, Michele Ferraz; Saa, Alberto
2009-09-01
We show that the common singularities present in generic modified gravity models governed by actions of the type S=∫d4x-gf(R,ϕ,X), with X=-(1)/(2)gab∂aϕ∂bϕ, are essentially the same anisotropic instabilities associated to the hypersurface F(ϕ)=0 in the case of a nonminimal coupling of the type F(ϕ)R, enlightening the physical origin of such singularities that typically arise in rather complex and cumbersome inhomogeneous perturbation analyses. We show, moreover, that such anisotropic instabilities typically give rise to dynamically unavoidable singularities, precluding completely the possibility of having physically viable models for which the hypersurface (∂f)/(∂R)=0 is attained. Some examples are explicitly discussed.
Method of caustics for anisotropic materials
NASA Astrophysics Data System (ADS)
Rossmanith, H. P.
1991-12-01
During the past 25 years the optical method of caustics has matured to a very powerful tool for application in fracture mechanics for the determination of stress intensity factors or the J- integral, in contact mechanics for the determination of contact forces, etc. The technique is applicable to two-dimensional static or dynamic problems and works for any kind of stress- strain relationship. The method displays its full power when employed in conjunction with interactive numerical data reduction and evaluation procedures. Recently, the industrial application of high strength-low weight composite materials has boomed. Application of the method of caustics to anisotropic materials requires the development of the theoretical background. This contribution focuses on the theoretical development of the method of caustics and its applicability to anisotropic materials.
Cosmological signatures of anisotropic spatial curvature
Pereira, Thiago S.; Marugán, Guillermo A. Mena; Carneiro, Saulo E-mail: mena@iem.cfmac.csic.es
2015-07-01
If one is willing to give up the cherished hypothesis of spatial isotropy, many interesting cosmological models can be developed beyond the simple anisotropically expanding scenarios. One interesting possibility is presented by shear-free models in which the anisotropy emerges at the level of the curvature of the homogeneous spatial sections, whereas the expansion is dictated by a single scale factor. We show that such models represent viable alternatives to describe the large-scale structure of the inflationary universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the definition of a complete set of spatial eigenfunctions we compute the two-point correlation function of scalar perturbations in these models. In addition, we show how such scenarios would modify the spectrum of the CMB assuming that the observations take place in a small patch of a universe with anisotropic curvature.
Effect of inflation on anisotropic cosmologies
Jensen, L.G.; Stein-Schabes, J.A.
1986-03-01
The effects of anisotropic cosmologies on inflation are studied. By properly formulating the field equations it is possible to show that any model that undergoes sufficient inflation will become isotropic on scales greater than the horizon today. Furthermore, we shall show that it takes a very long time for anisotropies to become visible in the observable part of the Universe. It is interesting to note that the time scale will be independent of the Bianchi Model and of the initial anisotropy. 6 refs.
Anisotropic cosmological solutions in massive vector theories
NASA Astrophysics Data System (ADS)
Heisenberg, Lavinia; Kase, Ryotaro; Tsujikawa, Shinji
2016-11-01
In beyond-generalized Proca theories including the extension to theories higher than second order, we study the role of a spatial component v of a massive vector field on the anisotropic cosmological background. We show that, as in the case of the isotropic cosmological background, there is no additional ghostly degrees of freedom associated with the Ostrogradski instability. In second-order generalized Proca theories we find the existence of anisotropic solutions on which the ratio between the anisotropic expansion rate Σ and the isotropic expansion rate H remains nearly constant in the radiation-dominated epoch. In the regime where Σ/H is constant, the spatial vector component v works as a dark radiation with the equation of state close to 1/3. During the matter era, the ratio Σ/H decreases with the decrease of v. As long as the conditions |Σ| ll H and v2 ll phi2 are satisfied around the onset of late-time cosmic acceleration, where phi is the temporal vector component, we find that the solutions approach the isotropic de Sitter fixed point (Σ = 0 = v) in accordance with the cosmic no-hair conjecture. In the presence of v and Σ the early evolution of the dark energy equation of state wDE in the radiation era is different from that in the isotropic case, but the approach to the isotropic value wDE(iso) typically occurs at redshifts z much larger than 1. Thus, apart from the existence of dark radiation, the anisotropic cosmological dynamics at low redshifts is similar to that in isotropic generalized Proca theories. In beyond-generalized Proca theories the only consistent solution to avoid the divergence of a determinant of the dynamical system corresponds to v = 0, so Σ always decreases in time.
Anisotropic conducting films for electromagnetic radiation applications
Cavallo, Francesca; Lagally, Max G.; Rojas-Delgado, Richard
2015-06-16
Electronic devices for the generation of electromagnetic radiation are provided. Also provided are methods for using the devices to generate electromagnetic radiation. The radiation sources include an anisotropic electrically conducting thin film that is characterized by a periodically varying charge carrier mobility in the plane of the film. The periodic variation in carrier mobility gives rise to a spatially varying electric field, which produces electromagnetic radiation as charged particles pass through the film.
Anisotropic Thermal Conductivity of Exfoliated Black Phosphorus.
Jang, Hyejin; Wood, Joshua D; Ryder, Christopher R; Hersam, Mark C; Cahill, David G
2015-12-22
The anisotropic thermal conductivity of passivated black phosphorus (BP), a reactive two-dimensional material with strong in-plane anisotropy, is ascertained. The room-temperature thermal conductivity for three crystalline axes of exfoliated BP is measured by time-domain thermo-reflectance. The thermal conductivity along the zigzag direction is ≈2.5 times higher than that of the armchair direction.
Probabilistic Anisotropic Failure Criteria for Composite Materials.
1987-12-01
worksheets were based on Microsoft Excel software. 55 55 ’. 2.’ ..’. -.. ’-,’€’.’’.’ :2.,2..’..’.2.’.’.,’.." ... .2...analytically described the failure cri - terion and probabilistic failure states of a anisotropic composite in a combined stress state. Strength...APPENDIX F RELIABILITY/FAILURE FUNCTION WORKSHEET ........... 76 APPENDIX G PERCENTILE STRENGTH WORKSHEET ....................... 80 LIST OF
Observational signatures of anisotropic inflationary models
Ohashi, Junko; Tsujikawa, Shinji; Soda, Jiro E-mail: jiro@phys.sci.kobe-u.ac.jp
2013-12-01
We study observational signatures of two classes of anisotropic inflationary models in which an inflaton field couples to (i) a vector kinetic term F{sub μν}F{sup μν} and (ii) a two-form kinetic term H{sub μνλ}H{sup μνλ}. We compute the corrections from the anisotropic sources to the power spectrum of gravitational waves as well as the two-point cross correlation between scalar and tensor perturbations. The signs of the anisotropic parameter g{sub *} are different depending on the vector and the two-form models, but the statistical anisotropies generally lead to a suppressed tensor-to-scalar ratio r and a smaller scalar spectral index n{sub s} in both models. In the light of the recent Planck bounds of n{sub s} and r, we place observational constraints on several different inflaton potentials such as those in chaotic and natural inflation in the presence of anisotropic interactions. In the two-form model we also find that there is no cross correlation between scalar and tensor perturbations, while in the vector model the cross correlation does not vanish. The non-linear estimator f{sub NL} of scalar non-Gaussianities in the two-form model is generally smaller than that in the vector model for the same orders of |g{sub *}|, so that the former is easier to be compatible with observational bounds of non-Gaussianities than the latter.
Symmetry analysis for anisotropic field theories
Parra, Lorena; Vergara, J. David
2012-08-24
The purpose of this paper is to study with the help of Noether's theorem the symmetries of anisotropic actions for arbitrary fields which generally depend on higher order spatial derivatives, and to find the corresponding current densities and the Noether charges. We study in particular scale invariance and consider the cases of higher derivative extensions of the scalar field, electrodynamics and Chern-Simons theory.
Perspectives of anisotropic flow measurements at NICA
NASA Astrophysics Data System (ADS)
Korotkikh, V. L.; Lokhtin, I. P.; Malinina, L. V.; Petrushanko, S. V.; Snigirev, A. M.
2016-08-01
High-accuracy and high-luminosity measurements of anisotropic flow for various hadron types over full NICA energy range will provide important constraints on the early dynamics of heavy-ion reactions under the conditions where a first-order quark-hadron phase transition may occur. The statistical reach for elliptic flow measurements at NICA is estimated with HYDJET++ heavy-ion event generator.
Multidimensional reaction rate theory with anisotropic diffusion.
Berezhkovskii, Alexander M; Szabo, Attila; Greives, Nicholas; Zhou, Huan-Xiang
2014-11-28
An analytical expression is derived for the rate constant that describes diffusive transitions between two deep wells of a multidimensional potential. The expression, in contrast to the Kramers-Langer formula for the rate constant, is valid even when the diffusion is highly anisotropic. Our approach is based on a variational principle for the reactive flux and uses a trial function for the splitting probability or commitor. The theoretical result is validated by Brownian dynamics simulations.
Longitudinal fluctuations and decorrelation of anisotropic flow
NASA Astrophysics Data System (ADS)
Pang, Long-Gang; Petersen, Hannah; Qin, Guang-You; Roy, Victor; Wang, Xin-Nian
2016-12-01
We investigate the decorrelation of 2nd and 3rd order anisotropic flow for charged particles in two different pseudo rapidity (η) windows by varying the pseudo rapidity gap, in an event-by-event (3+1)D ideal hydrodynamic model, with fluctuating initial conditions from A Multi-Phase Transport (AMPT) model. We visualize the parton distribution at initial state for Pb+Pb collisions at LHC and Au+Au collisions at RHIC, and demonstrate the longitudinal fluctuations originating from the asymmetry between forward and backward going participants, the fluctuations of the string length and the fluctuations due to finite number of partons at different beam energies. The decorrelation of anisotropic flow of final hadrons with large η gaps is found to originate from the spatial decorrelation along the longitudinal direction in the AMPT initial conditions through hydrodynamic evolution. The agreement between our results and recent CMS data in most centralities suggests that the string-like mechanism of initial parton production in AMPT model captures the initial longitudinal fluctuation that is responsible for the measured decorrelation of anisotropic flow in Pb+Pb collisions at LHC. Our predictions for Au+Au collisions at the highest RHIC energy show stronger longitudinal decorrelation than at LHC, indicating larger longitudinal fluctuations at lower beam energies.
Anisotropic representations for superresolution of hyperspectral data
NASA Astrophysics Data System (ADS)
Bosch, Edward H.; Czaja, Wojciech; Murphy, James M.; Weinberg, Daniel
2015-05-01
We develop a method for superresolution based on anisotropic harmonic analysis. Our ambition is to efficiently increase the resolution of an image without blurring or introducing artifacts, and without integrating additional information, such as sub-pixel shifts of the same image at lower resolutions or multimodal images of the same scene. The approach developed in this article is based on analysis of the directional features present in the image that is to be superesolved. The harmonic analytic technique of shearlets is implemented in order to efficiently capture the directional information present in the image, which is then used to provide smooth, accurate images at higher resolutions. Our algorithm is compared to both a recent anisotropic technique based on frame theory and circulant matrices,1 as well as to the standard superresolution method of bicubic interpolation. We evaluate our algorithm on synthetic test images, as well as a hyperspectral image. Our results indicate the superior performance of anisotropic methods, when compared to standard bicubic interpolation.
Active Damping Using Distributed Anisotropic Actuators
NASA Technical Reports Server (NTRS)
Schiller, Noah H.; Cabell, Randolph H.; Quinones, Juan D.; Wier, Nathan C.
2010-01-01
A helicopter structure experiences substantial high-frequency mechanical excitation from powertrain components such as gearboxes and drive shafts. The resulting structure-borne vibration excites the windows which then radiate sound into the passenger cabin. In many cases the radiated sound power can be reduced by adding damping. This can be accomplished using passive or active approaches. Passive treatments such as constrained layer damping tend to reduce window transparency. Therefore this paper focuses on an active approach utilizing compact decentralized control units distributed around the perimeter of the window. Each control unit consists of a triangularly shaped piezoelectric actuator, a miniature accelerometer, and analog electronics. Earlier work has shown that this type of system can increase damping up to approximately 1 kHz. However at higher frequencies the mismatch between the distributed actuator and the point sensor caused control spillover. This paper describes new anisotropic actuators that can be used to improve the bandwidth of the control system. The anisotropic actuators are composed of piezoelectric material sandwiched between interdigitated electrodes, which enables the application of the electric field in a preferred in-plane direction. When shaped correctly the anisotropic actuators outperform traditional isotropic actuators by reducing the mismatch between the distributed actuator and point sensor at high frequencies. Testing performed on a Plexiglas panel, representative of a helicopter window, shows that the control units can increase damping at low frequencies. However high frequency performance was still limited due to the flexible boundary conditions present on the test structure.
Anisotropic materials appearance analysis using ellipsoidal mirror
NASA Astrophysics Data System (ADS)
Filip, Jiří; Vávra, Radomír.
2015-03-01
Many real-world materials exhibit significant changes in appearance when rotated along a surface normal. The presence of this behavior is often referred to as visual anisotropy. Anisotropic appearance of spatially homogeneous materials is commonly characterized by a four-dimensional BRDF. Unfortunately, due to simplicity most past research has been devoted to three dimensional isotropic BRDFs. In this paper, we introduce an innovative, fast, and inexpensive image-based approach to detect the extent of anisotropy, its main axes and width of corresponding anisotropic highlights. The method does not rely on any moving parts and uses only an off-the-shelf ellipsoidal reflector with a compact camera. We analyze our findings with a material microgeometry scan, and present how results correspond to the microstructure of individual threads in a particular fabric. We show that knowledge of a material's anisotropic behavior can be effectively used in order to design a material-dependent sampling pattern so as the material's BRDF could be measured much more precisely in the same amount of time using a common gonioreflectometer.
Anisotropic hydrodynamics for conformal Gubser flow
NASA Astrophysics Data System (ADS)
Strickland, Michael; Nopoush, Mohammad; Ryblewski, Radoslaw
2016-12-01
In this proceedings contribution, we review the exact solution of the anisotropic hydrodynamics equations for a system subject to Gubser flow. For this purpose, we use the leading-order anisotropic hydrodynamics equations which assume that the distribution function is ellipsoidally symmetric in local-rest-frame momentum. We then prove that the SO(3)q symmetry in de Sitter space constrains the anisotropy tensor to be of spheroidal form with only one independent anisotropy parameter remaining. As a consequence, the exact solution reduces to the problem of solving two coupled non-linear differential equations. We show that, in the limit that the relaxation time goes to zero, one obtains Gubser's ideal hydrodynamic solution and, in the limit that the relaxation time goes to infinity, one obtains the exact free streaming solution obtained originally by Denicol et al. For finite relaxation time, we solve the equations numerically and compare to the exact solution of the relaxation-time-approximation Boltzmann equation subject to Gubser flow. Using this as our standard, we find that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches.
Anisotropic impedance surfaces for enhanced antenna isolation
NASA Astrophysics Data System (ADS)
Miragliotta, Joseph A.; Shrekenhamer, David; Sievenpiper, Daniel F.
2015-09-01
Anisotropic impedance surfaces, which include metasurfaces and high impedance surfaces (HIS), can be designed to control the amplitude and propagation direction of surface electromagnetic waves and are an effective means to enhance the isolation between antennas that share a common ground plane. To date, the majority of metastructures that have been designed for antenna isolation have relied on an isotropic distribution of unit cells that possess a stop band that inhibits the propagation of surface waves between neighboring antennas. A less common approach to isolation has been through the design of a metasurface that enables the re-direction of surface waves away from the location of the antenna structure, which effectively limits the coupling. In this paper, we discuss results from our computational investigation associated with improving antenna isolation through the use of an anisotropic metastructure. Simulated results associated with the isolation performance of two simple, but similar, anisotropic structures are compared to the corresponding results from a broadband magnetic radar absorbing materials (magRAM).
ARTc: Anisotropic reflectivity and transmissivity calculator
NASA Astrophysics Data System (ADS)
Malehmir, Reza; Schmitt, Douglas R.
2016-08-01
While seismic anisotropy is known to exist within the Earth's crust and even deeper, isotropic or even highly symmetric elastic anisotropic assumptions for seismic imaging is an over-simplification which may create artifacts in the image, target mis-positioning and hence flawed interpretation. In this paper, we have developed the ARTc algorithm to solve reflectivity, transmissivity as well as velocity and particle polarization in the most general case of elastic anisotropy. This algorithm is able to provide reflectivity solution from the boundary between two anisotropic slabs with arbitrary symmetry and orientation up to triclinic. To achieve this, the algorithm solves full elastic wave equation to find polarization, slowness and amplitude of all six wave-modes generated from the incident plane-wave and welded interface. In the first step to calculate the reflectivity, the algorithm solves properties of the incident wave such as particle polarization and slowness. After calculation of the direction of generated waves, the algorithm solves their respective slowness and particle polarization. With this information, the algorithm then solves a system of equations incorporating the imposed boundary conditions to arrive at the scattered wave amplitudes, and thus reflectivity and transmissivity. Reflectivity results as well as slowness and polarization are then tested in complex computational anisotropic models to ensure their accuracy and reliability. ARTc is coded in MATLAB ® and bundled with an interactive GUI and bash script to run on single or multi-processor computers.
Anisotropic halo model: implementation and numerical results
NASA Astrophysics Data System (ADS)
Sgró, Mario A.; Paz, Dante J.; Merchán, Manuel
2013-07-01
In the present work, we extend the classic halo model for the large-scale matter distribution including a triaxial model for the halo profiles and their alignments. In particular, we derive general expressions for the halo-matter cross-correlation function. In addition, by numerical integration, we obtain instances of the cross-correlation function depending on the directions given by halo shape axes. These functions are called anisotropic cross-correlations. With the aim of comparing our theoretical results with the simulations, we compute averaged anisotropic correlations in cones with their symmetry axis along each shape direction of the centre halo. From these comparisons we characterize and quantify the alignment of dark matter haloes on the Λcold dark matter context by means of the presented anisotropic halo model. Since our model requires multidimensional integral computation we implement a Monte Carlo method on GPU hardware which allows us to increase the precision of the results and it improves the performance of the computation.
Quasiparticle equation of state for anisotropic hydrodynamics
NASA Astrophysics Data System (ADS)
Alqahtani, Mubarak; Nopoush, Mohammad; Strickland, Michael
2015-11-01
We present a new method for imposing a realistic equation of state in anisotropic hydrodynamics. The method relies on the introduction of a single finite-temperature quasiparticle mass which is fit to lattice data. By taking moments of the Boltzmann equation, we obtain a set of coupled partial differential equations which can be used to describe the 3+1-dimensional (3+1d) spacetime evolution of an anisotropic relativistic system. We then specialize to the case of a 0+1d system undergoing boost-invariant Bjorken expansion and subject to the relaxation-time approximation collisional kernel. Using this setup, we compare results obtained using the new quasiparticle equation of state method with those obtained using the standard method for imposing the equation of state in anisotropic hydrodynamics. We demonstrate that the temperature evolution obtained using the two methods is nearly identical and that there are only small differences in the pressure anisotropy. However, we find that there are significant differences in the evolution of the bulk pressure correction.
Anisotropic Self-Assembly of Nanoparticle Amphiphiles
NASA Astrophysics Data System (ADS)
Kumar, Sanat
2009-03-01
It is easy to understand the self-assembly of particles having anisotropic shapes or interactions, such as Co nanoparticles or proteins, into highly extended structures. However, there is no experimentally established strategy for creating anisotropic structures from common spherical nanoparticles. We demonstrate that spherical nanoparticles, uniformly grafted with macromolecules, robustly self-assemble into a range of anisotropic superstructures when they are dispersed in the corresponding homopolymer matrix. This phenomenon is driven by the microphase separation between the inorganic nanoparticles and the (organic) polymeric chains grafted to their surfaces in a fashion similar to block copolymers. This microphase separation driven particle self-assembly provides a unique means of controlling the global nanoparticle dispersion state in polymer nanocomposites. The relationship between the state of particle dispersion and nanocomposite properties can thus be critically examined, and in particular we focus on the mechanical reinforcement afforded when particles are added to polymers. Grafted nanoparticles are thus versatile building blocks for creating tunable and functional particle superstructures with significant practical applications. With Pinar Akcora, Hongjun Liu, Yu Li, Brian Benicewicz, Linda Schadler, Thanos Panagiotopoulos, Jack Douglas, P. Thiyagarajan and Ralph Colby.
Efficient Anisotropic Filtering of Diffusion Tensor Images
Xu, Qing; Anderson, Adam W.; Gore, John C.; Ding, Zhaohua
2009-01-01
To improve the accuracy of structural and architectural characterization of living tissue with diffusion tensor imaging, an efficient smoothing algorithm is presented for reducing noise in diffusion tensor images. The algorithm is based on anisotropic diffusion filtering, which allows both image detail preservation and noise reduction. However, traditional numerical schemes for anisotropic filtering have the drawback of inefficiency and inaccuracy due to their poor stability and first order time accuracy. To address this, an unconditionally stable and second order time accuracy semi-implicit Craig-Sneyd scheme is adapted in our anisotropic filtering. By using large step size, unconditional stability allows this scheme to take much fewer iterations and thus less computation time than the explicit scheme to achieve a certain degree of smoothing. Second order time accuracy makes the algorithm reduce noise more effectively than a first order scheme with the same total iteration time. Both the efficiency and effectiveness are quantitatively evaluated based on synthetic and in vivo human brain diffusion tensor images, and these tests demonstrate that our algorithm is an efficient and effective tool for denoising diffusion tensor images. PMID:20061113
Post-synthetic Anisotropic Wet-Chemical Etching of Colloidal Sodalite ZIF Crystals
Avci, Civan; Ariñez-Soriano, Javier; Carné-Sánchez, Arnau; Guillerm, Vincent; Carbonell, Carlos; Imaz, Inhar; Maspoch, Daniel
2016-01-01
Controlling the shape of metal-organic framework (MOF) crystals is important for understanding their crystallization and useful for myriad applications. However, despite the many advances in shaping of inorganic nanoparticles, post-synthetic shape control of MOFs and, in general, molecular crystals remains embryonic. Herein we report using a simple wet-chemistry process at room temperature to control the anisotropic etching of colloidal ZIF-8 and ZIF-67 crystals. Our work enables uniform reshaping of these porous materials into unprecedented morphologies, including cubic and tetrahedral crystals, and even hollow boxes, via acid-base reaction and subsequent sequestration of leached metal ions. Etching tests on these ZIFs reveal that etching occurs preferentially in the crystallographic directions richer in metal-ligand bonds; that, among these directions, the etching rate tends to be faster on the crystal surfaces of higher dimensionality; and that the etching can be modulated by adjusting the pH of the etchant solution. PMID:26458081
Post-Synthetic Anisotropic Wet-Chemical Etching of Colloidal Sodalite ZIF Crystals.
Avci, Civan; Ariñez-Soriano, Javier; Carné-Sánchez, Arnau; Guillerm, Vincent; Carbonell, Carlos; Imaz, Inhar; Maspoch, Daniel
2015-11-23
Controlling the shape of metal-organic framework (MOF) crystals is important for understanding their crystallization and useful for myriad applications. However, despite the many advances in shaping of inorganic nanoparticles, post-synthetic shape control of MOFs and, in general, molecular crystals remains embryonic. Herein, we report using a simple wet-chemistry process at room temperature to control the anisotropic etching of colloidal ZIF-8 and ZIF-67 crystals. Our work enables uniform reshaping of these porous materials into unprecedented morphologies, including cubic and tetrahedral crystals, and even hollow boxes, by an acid-base reaction and subsequent sequestration of leached metal ions. Etching tests on these ZIFs reveal that etching occurs preferentially in the crystallographic directions richer in metal-ligand bonds; that, along these directions, the etching rate tends to be faster on the crystal surfaces of higher dimensionality; and that the etching can be modulated by adjusting the pH of the etchant solution.
Shanjani, Yaser; De Croos, J N Amritha; Pilliar, Robert M; Kandel, Rita A; Toyserkani, Ehsan
2010-05-01
Solid freeform fabrication (SFF) enables the fabrication of anatomically shaped porous components required for formation of tissue engineered implants. This article reports on the characterization of a three-dimensional-printing method, as a powder-based SFF technique, to create reproducible porous structures composed of calcium polyphosphate (CPP). CPP powder of 75-150 microm was mixed with 10 wt % polyvinyl alcohol (PVA) polymeric binder, and used in the SFF machine with appropriate settings for powder mesh size. The PVA binder was eliminated during the annealing procedure used to sinter the CPP particles. The porous SFF fabricated components were characterized using scanning electron microscopy, micro-CT scanning, X-ray diffraction, and mercury intrusion porosimetry. In addition, mechanical testing was conducted to determine the compressive strength of the CPP cylinders. The 35 vol % porous structures displayed compressive strength on average of 33.86 MPa, a value 57% higher than CPP of equivalent volume percent porosity made through conventional gravity sintering. Dimensional deviation and shrinkage analysis was conducted to identify anisotropic factors required for dimensional compensation during SFF sample formation and subsequent sintering. Cell culture studies showed that the substrate supported cartilage formation in vitro, which was integrated with the top surface of the porous CPP similar to that observed when chondrocytes were grown on CPP formed by conventional gravity sintering methods as determined histologically and biochemically.
Electroless porous silicon formation applied to fabrication of boron-silica-glass cantilevers
NASA Astrophysics Data System (ADS)
Teva, J.; Davis, Z. J.; Hansen, O.
2010-01-01
This work describes the characterization and optimization of anisotropic formation of porous silicon in large volumes (0.5-1 mm3) of silicon by an electroless wet etching technique. The main goal is to use porous silicon as a sacrificial volume for bulk micromachining processes, especially in cases where etching of the full wafer thickness is needed. The porous silicon volume is formed by a metal-assisted etching in a wet chemical solution composed of hydrogen peroxide (30%), hydrofluoric acid (40%) and ethanol. This paper focuses on optimizing the etching conditions in terms of maximizing the etching rate and reproducibility of the etching. In addition to that, a study of the morphology of the pore that is obtained by this technique is presented. The results from the characterization of the process are applied to the fabrication of boron-silica-glass cantilevers that serve as a platform for bio-chemical sensors. The porous silicon volume is formed in an early step of the fabrication process, allowing easy handling of the wafer during all of the micromachining processes in the process flow. In the final process step, the porous silicon is quickly etched by immersing the wafer in a KOH solution.
Fluid flow in porous media with rough pore-solid interface
NASA Astrophysics Data System (ADS)
Ghanbarian, Behzad; Hunt, Allen G.; Daigle, Hugh
2016-03-01
Quantifying fluid flow through porous media hinges on the description of permeability, a property of considerable importance in many fields ranging from oil and gas exploration to hydrology. A common building block for modeling porous media permeability is consideration of fluid flow through tubes with circular cross section described by Poiseuille's law in which flow discharge is proportional to the fourth power of the tube's radius. In most natural porous media, pores are neither cylindrical nor smooth; they often have an irregular cross section and rough surfaces. This study presents a theoretical scaling of Poiseuille's approximation for flow in pores with irregular rough cross section quantified by a surface fractal dimension Ds2. The flow rate is a function of the average pore radius to the power 2(3-Ds2) instead of 4 in the original Poiseuille's law. Values of Ds2 range from 1 to 2, hence, the power in the modified Poiseuille's approximation varies between 4 and 2, indicating that flow rate decreases as pore surface roughness (and surface fractal dimension Ds2) increases. We also proposed pore length-radius relations for isotropic and anisotropic fractal porous media. The new theoretical derivations are compared with standard approximations and with experimental values of relative permeability. The new approach results in substantially improved prediction of relative permeability of natural porous media relative to the original Poiseuille equation.
NASA Astrophysics Data System (ADS)
Chiogna, Gabriele; Herrera, Paulo
2015-04-01
Several studies have demonstrated how plume deformation induced by flow heterogeneity in porous media can enhance mixing of reactants. This enhancement can have important impact on mixing controlled reactions such a biodegradation of plumes of organic compounds. On the other hand, recent studies have indicated the possibility of observing complex flow topology on groundwater flow that occurs in anisotropic yet homogenous porous media. Moreover, it has been demonstrated that those complex flow topologies can also enhance solute mixing. We study the effect of medium anisotropy on reactive solute transport for the case of a chemical reactor composed of two homogeneous anisotropic layers. We simulate different injection strategies for different chemical reactions that involve two reactants. We demonstrate the effect of the medium anisotropy by analyzing the results of the simulations and identify best strategies for the operation and design of the system to maximize reaction rates. These findings could have potential application in the design of new remediation systems for contaminated groundwater, chemical reactors and other engineering problems that involve flow through porous media.
Large scale anisotropic bias from primordial non-Gaussianity
Baghram, Shant; Firouzjahi, Hassan; Namjoo, Mohammad Hossein E-mail: mh.namjoo@ipm.ir
2013-08-01
In this work we study the large scale structure bias in models of anisotropic inflation. We use the Peak Background Splitting method in Excursion Set Theory to find the scale-dependent bias. We show that the amplitude of the bias is modified by a direction-dependent factor. In the specific anisotropic inflation model which we study, the scale-dependent bias vanishes at leading order when the long wavelength mode in squeezed limit is aligned with the anisotropic direction in the sky. We also extend the scale-dependent bias formulation to the general situations with primordial anisotropy. We find some selection rules indicating that some specific parts of a generic anisotropic bispectrum is picked up by the bias parameter. We argue that the anisotropic bias is mainly sourced by the angle between the anisotropic direction and the long wavelength mode in the squeezed limit.
Comparison of the anisotropic behaviour of undeformed sandstones under dry and saturated conditions
NASA Astrophysics Data System (ADS)
Louis, Laurent; David, Christian; Robion, Philippe
2003-07-01
capturing the nature of the anisotropic behaviour of porous rocks.
NASA Astrophysics Data System (ADS)
Ikeda, Ryusuke
2015-05-01
Motivated by recent experiments on liquid 3He reporting emergence of novel superfluid phases in globally anisotropic aerogels, our previous theory on superfluid 3He in globally anisotropic aerogels is extended to incorporate the effects of anisotropy of the quasiparticle scattering cross section on the strong-coupling (SC) contributions to the Ginzburg-Landau (GL) free energy on the basis of the spin-fluctuation (paramagnon) approach to the SC contributions developed by Brinkman et al. [Phys. Rev. A 10, 2386 (1974), 10.1103/PhysRevA.10.2386]. In the globally isotropic case, impurity effects on the SC correction destabilize the A phase even at higher pressures of about 30 bar and make the B phase the only state in equilibrium, while SC contributions accompanied by a global stretched anisotropy to the GL quartic terms generally tend to broaden the stability region of the A phase compared with that of the B phase. In particular, in contrast to the cases in bulk and in the isotropic aerogel, the SC corrections to the GL quadratic terms are not negligible in the globally anisotropic case but may change the sign of the apparent anisotropy depending on the magnitude of the frequency cutoff of the normal paramagnon propagator. Based on this sign change of the apparent anisotropy, we discuss different strange observations on superfluid 3He in porous media such as the disappearance of the polar superfluid phase at higher pressures seen in nematically ordered aerogels and the absence of B and A phases with planar l ̂ vector in a stretched aerogel.
NASA Astrophysics Data System (ADS)
Vashaee, S.; Marica, F.; Newling, B.; Balcom, B. J.
2015-05-01
Naturally occurring porous media are usually characterized by a distribution of pore sizes. If the material is fluid saturated, the 1H magnetic resonance (MR) signal depends on the pore size, the surface relaxivity and the fluid itself. Measurement of the transverse relaxation time T2 is a well-established technique to characterize material samples by means of MR. T2 distribution measurements, including T2 distribution mapping, are widely employed in clinical applications and in petroleum engineering. T2 distribution measurements are the most basic measurement employed to determine the fluid-matrix properties in MR core analysis. Three methods for T2 distribution mapping, namely spin-echo single point imaging (SE-SPI), DANTE-Z Carr-Purcell-Meiboom-Gill (CPMG) and adiabatic inversion CPMG are compared in terms of spatial resolution, minimum observable T2 and sensitivity. Bulk CPMG measurement is considered to be the gold standard for T2 determination. Bulk measurement of uniform samples is compared to the three spatially resolved measurements. SE-SPI is an imaging method, which measures spatially resolved T2s in samples of interest. A variant is introduced in this work that employs pre-equalized magnetic field gradient waveforms and is therefore able to measure shorter T2s than previously reported. DANTE-Z CPMG and adiabatic inversion CPMG are faster, non-imaging, local T2 distribution measurements. The DANTE-Z pulse train and adiabatic inversion pulse are compared in terms of T1 or T2 relaxation time effects during the RF pulse application, minimum pulse duration, requisite RF pulse power, and inversion profile quality. In addition to experimental comparisons, simulation results are presented.
Grooved organogel surfaces towards anisotropic sliding of water droplets.
Zhang, Pengchao; Liu, Hongliang; Meng, Jingxin; Yang, Gao; Liu, Xueli; Wang, Shutao; Jiang, Lei
2014-05-21
Periodic micro-grooved organogel surfaces can easily realize the anisotropic sliding of water droplets attributing to the formed slippery water/oil/solid interface. Different from the existing anisotropic surfaces, this novel surface provides a versatile candidate for the anisotropic sliding of water droplets and might present a promising way for the easy manipulation of liquid droplets for water collection, liquid-directional transportation, and microfluidics.
Biogenic Cracks in Porous Rock
NASA Astrophysics Data System (ADS)
Hemmerle, A.; Hartung, J.; Hallatschek, O.; Goehring, L.; Herminghaus, S.
2014-12-01
Microorganisms growing on and inside porous rock may fracture it by various processes. Some of the mechanisms of biofouling and bioweathering are today identified and partially understood but most emphasis is on chemical weathering, while mechanical contributions have been neglected. However, as demonstrated by the perseverance of a seed germinating and cracking up a concrete block, the turgor pressure of living organisms can be very significant. Here, we present results of a systematic study of the effects of the mechanical forces of growing microbial populations on the weathering of porous media. We designed a model porous medium made of glass beads held together by polydimethylsiloxane (PDMS), a curable polymer. The rheological properties of the porous medium, whose shape and size are tunable, can be controlled by the ratio of crosslinker to base used in the PDMS (see Fig. 1). Glass and PDMS being inert to most chemicals, we are able to focus on the mechanical processes of biodeterioration, excluding any chemical weathering. Inspired by recent measurements of the high pressure (~0.5 Mpa) exerted by a growing population of yeasts trapped in a microfluidic device, we show that yeast cells can be cultured homogeneously within porous medium until saturation of the porous space. We investigate then the effects of such an inner pressure on the mechanical properties of the sample. Using the same model system, we study also the complex interplay between biofilms and porous media. We focus in particular on the effects of pore size on the penetration of the biofilm within the porous sample, and on the resulting deformations of the matrix, opening new perspectives into the understanding of life in complex geometry. Figure 1. Left : cell culture growing in a model porous medium. The white spheres represent the grains, bonds are displayed in grey, and microbes in green. Right: microscopy picture of glass beads linked by PDMS bridges, scale bar: 100 μm.
Regeneratively Cooled Porous Media Jacket
NASA Technical Reports Server (NTRS)
Mungas, Greg (Inventor); Fisher, David J. (Inventor); London, Adam Pollok (Inventor); Fryer, Jack Merrill (Inventor)
2013-01-01
The fluid and heat transfer theory for regenerative cooling of a rocket combustion chamber with a porous media coolant jacket is presented. This model is used to design a regeneratively cooled rocket or other high temperature engine cooling jacket. Cooling jackets comprising impermeable inner and outer walls, and porous media channels are disclosed. Also disclosed are porous media coolant jackets with additional structures designed to transfer heat directly from the inner wall to the outer wall, and structures designed to direct movement of the coolant fluid from the inner wall to the outer wall. Methods of making such jackets are also disclosed.
Light emission from porous silicon
NASA Astrophysics Data System (ADS)
Penczek, John
The continuous evolution of silicon microelectronics has produced significant gains in electronic information processing. However, greater improvements in performance are expected by utilizing optoelectronic techniques. But these techniques have been severely limited in silicon- based optoelectronics due to the lack of an efficient silicon light emitter. The recent observation of efficient light emission from porous silicon offer a promising opportunity to develop a suitable silicon light source that is compatible with silicon microelectronics. This dissertation examined the porous silicon emission mechanism via photoluminescence, and by a novel device structure for porous silicon emitters. The investigation first examined the correlation between porous silicon formation conditions (and subsequent morphology) with the resulting photoluminescence properties. The quantum confinement theory for porous silicon light emission contends that the morphology changes induced by the different formation conditions determine the optical properties of porous silicon. The photoluminescence spectral shifts measured in this study, in conjunction with TEM analysis and published morphological data, lend support to this theory. However, the photoluminescence spectral broadening was attributed to electronic wavefunction coupling between adjacent silicon nanocrystals. An novel device structure was also investigated in an effort to improve current injection into the porous silicon layer. The selective etching properties of porous silicon were used to create a p-i-n structure with crystalline silicon contacts to the porous silicon layer. The resulting device was found to have unique characteristics, with a negative differential resistance region and current-induced emission that spanned from 400 nm to 5500 nm. The negative differential resistance was correlated to resistive heating effects in the device. A numerical analysis of thermal emission spectra from silicon films, in addition to
Fabrication and characterization of porous silicon nanowires
NASA Astrophysics Data System (ADS)
Jung, Daeyoon; Cho, Soo Gyeong; Moon, Taeho; Sohn, Honglae
2016-01-01
We report the synthesis of porous silicon nanowires through the metalassisted chemical etching of porous silicon in a solution of hydrofluoric acid and hydrogen peroxide. The morphology of porous silicon nanowires was characterized by scanning electron microscopy and transmission electron microscopy. The etch rate of the porous silicon nanowires was faster than that of silicon nanowires, but slower than that of porous silicon. The porous silicon nanowires distributed uniformly on the entire porous silicon layer and the tips of the porous silicon nanowires congregated together. The single crystalline and sponge-like porous structure with the pore diameters of less than 5 nm was confirmed for the porous silicon nanowires. [Figure not available: see fulltext.
Computation of Large Anisotropic Seismic Heterogeneities (CLASH)
NASA Astrophysics Data System (ADS)
Beucler, Éric; Montagner, Jean-Paul
2006-05-01
A general tomographic technique is designed in order (i) to operate in anisotropic media; (ii) to account for the uneven seismic sampling and (iii) to handle massive data sets in a reasonable computing time. One modus operandi to compute a 3-D body wave velocity model relies on surface wave phase velocity measurements. An intermediate step, shared by other approaches, consists in translating, for each period of a given mode branch, the phase velocities integrated along ray paths into local velocity perturbations. To this end, we develop a method, which accounts for the azimuthal anisotropy in its comprehensive form. The weakly non-linear forward problem allows to use a conjugate gradient optimization. The Earth's surface is regularly discretized and the partial derivatives are assigned to the individual grid points. Possible lack of lateral resolution, due to the inescapable uneven ray path coverage, is taken into account through the a priori covariances on parameters with laterally variable correlation lengths. This method allows to efficiently separate the 2ψ and the 4ψ anisotropic effects from the isotropic perturbations. Fundamental mode and overtone phase velocity maps, derived with real Rayleigh wave data sets, are presented and compared with previous maps. The isotropic models concur well with the results of Trampert & Woodhouse. Large 4ψ heterogeneities are located in the tectonically active regions and over the continental lithospheres such as North America, Antarctica or Australia. At various periods, a significant 4ψ signature is correlated with the Hawaii hotspot track. Finally, concurring with the conclusions of Trampert & Woodhouse, our phase velocity maps show that Rayleigh wave data sets do need both 2ψ and 4ψ anisotropic terms.
Harmut Spetzler
2005-11-28
This paper describes the culmination of a research project in which we investigated the complex modulus change in partially fluid saturated porous rocks. The investigation started with simple flow experiments over ''clean'' and ''contaminated'' surfaces, progressed to moduli measurements on partially filled single cracks, to measurements in ''clean'' and ''contaminated'' porous rocks and finally to a feasibility study in the field. For the experiments with the simple geometries we were able to measure fundamental physical properties such as contact angles of the meniscus and time dependent forces required to get the meniscus moving and to keep it moving at various velocities. From the data thus gathered we were able to interpret the complex elastic moduli data we measured in the partially saturated single cracks. While the geometry in real rocks is too complex to make precise calculations we determined that we had indeed identified the mechanisms responsible for the changes in the moduli we had measured. Thus encouraged by the laboratory studies we embarked on a field experiment in the desert of Arizona. The field site allowed for controlled irrigation. Instrumentation for fluid sampling and water penetration were already in place. The porous loosely consolidated rocks at the site were not ideal for finding the effects of the attenuation mechanism we had identified in the lab, but for logistic and cost constraint reasons we chose to field test the idea at that site. Tiltmeters and seismometers were installed and operated nearly continuously for almost 3 years. The field was irrigated with water in the fall of 2003 and with water containing a biosurfactant in the fall of 2004. We have indications that the biosurfactant irrigation has had a notable effect on the tilt data.
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2015-11-16
Theoretical and experimental investigations have shown that the atmospheric turbulence exhibits both anisotropic and non-Kolmogorov properties. In this work, two theoretical atmosphere refractive-index fluctuations spectral models are derived for optical waves propagating through anisotropic non-Kolmogorov atmospheric turbulence. They consider simultaneously the finite turbulence inner and outer scales and the asymmetric property of turbulence eddies in the orthogonal xy-plane throughout the path. Two anisotropy factors which parameterize the asymmetry of turbulence eddies in both horizontal and vertical directions are introduced in the orthogonal xy-plane, so that the circular symmetry assumption of turbulence eddies in the xy-plane is no longer required. Deviations from the classic 11/3 power law behavior in the spectrum model are also allowed by assuming power law value variations between 3 and 4. Based on the derived anisotropic spectral model and the Rytov approximation theory, expressions for the variance of angle of arrival (AOA) fluctuations are derived for optical plane and spherical waves propagating through weak anisotropic non-Kolmogorov turbulence. Calculations are performed to analyze the derived spectral models and the variance of AOA fluctuations.
Chromo-natural model in anisotropic background
Maleknejad, Azadeh; Erfani, Encieh E-mail: eerfani@ipm.ir
2014-03-01
In this work we study the chromo-natural inflation model in the anisotropic setup. Initiating inflation from Bianchi type-I cosmology, we analyze the system thoroughly during the slow-roll inflation, from both analytical and numerical points of view. We show that the isotropic FRW inflation is an attractor of the system. In other words, anisotropies are damped within few e-folds and the chromo-natural model respects the cosmic no-hair conjecture. Furthermore, we demonstrate that in the slow-roll limit, the anisotropies in both chromo-natural and gauge-flation models share the same dynamics.
Anisotropic Tribological Properties of Silicon Carbide
NASA Technical Reports Server (NTRS)
Miyoshi, K.; Buckley, D. H.
1980-01-01
The anisotropic friction, deformation and fracture behavior of single crystal silicon carbide surfaces were investigated in two categories. The categories were called adhesive and abrasive wear processes, respectively. In the adhesive wear process, the adhesion, friction and wear of silicon carbide were markedly dependent on crystallographic orientation. The force to reestablish the shearing fracture of adhesive bond at the interface between silicon carbide and metal was the lowest in the preferred orientation of silicon carbide slip system. The fracturing of silicon carbide occurred near the adhesive bond to metal and it was due to primary cleavages of both prismatic (10(-1)0) and basal (0001) planes.
Local thermodynamics of a magnetized, anisotropic plasma
Hazeltine, R. D.; Mahajan, S. M.; Morrison, P. J.
2013-02-15
An expression for the internal energy of a fluid element in a weakly coupled, magnetized, anisotropic plasma is derived from first principles. The result is a function of entropy, particle density and magnetic field, and as such plays the role of a thermodynamic potential: it determines in principle all thermodynamic properties of the fluid element. In particular it provides equations of state for the magnetized plasma. The derivation uses familiar fluid equations, a few elements of kinetic theory, the MHD version of Faraday's law, and certain familiar stability and regularity conditions.
Laminated anisotropic reinforced plastic plates and shells
NASA Technical Reports Server (NTRS)
Korolev, V. I.
1981-01-01
Basic technical theories and engineering calculation equations for anisotropic plates and shells made of rigid reinforced plastics, mainly laminated fiberglass, are presented and discussed. Solutions are given for many problems of design of structural plates and shells, including curved sections and tanks, as well as two chapters on selection of the optimum materials, are given. Accounting for interlayer shearing and transverse separation, which are new engineering properties, are discussed. Application of the results obtained to thin three ply plates and shells wth a light elastic filler is presented and discussed.
Multichannel image regularization using anisotropic geodesic filtering
Grazzini, Jacopo A
2010-01-01
This paper extends a recent image-dependent regularization approach introduced in aiming at edge-preserving smoothing. For that purpose, geodesic distances equipped with a Riemannian metric need to be estimated in local neighbourhoods. By deriving an appropriate metric from the gradient structure tensor, the associated geodesic paths are constrained to follow salient features in images. Following, we design a generalized anisotropic geodesic filter; incorporating not only a measure of the edge strength, like in the original method, but also further directional information about the image structures. The proposed filter is particularly efficient at smoothing heterogeneous areas while preserving relevant structures in multichannel images.
Creating an anisotropic plasma resistivity with waves
Fisch, N.J.; Boozer, A.H.
1980-05-01
An anisotropic plasma resistivity may be created by preferential heating of electrons traveling in one direction. This can result in a steady-state toroidal current in a tokamak even in the absence of net wave momentum. In fact, at high wave phase velocities, the current associated with the change in resistivity is greater than that associated with net momentum input. An immediate implication is that other waves, such as electron cyclotron waves, may be competitive with lower-hybrid waves as a means for generating current. An analytical expression is derived for the current generated per power dissipated which agrees remarkably well with numerical calculations.
Anisotropic elasticity of experimental colloidal Wigner crystals.
Russell, Emily R; Spaepen, Frans; Weitz, David A
2015-03-01
Colloidal particles interacting via a long-range repulsion can, in contrast to hard-sphere systems, exhibit crystalline ordering at low volume fraction. Here we experimentally investigate the structure and properties of such "colloidal Wigner crystals." We find a body-centered-cubic crystalline phase at volume fractions of ϕ≳15%, which exhibits large fluctuations of individual particles from their average positions. We determine the three independent crystalline elastic constants and find that these crystals are very compliant and highly anisotropic.
Multidimensional Gravitational Model with Anisotropic Pressure
NASA Astrophysics Data System (ADS)
Grigorieva, O. A.; Sharov, G. S.
2013-08-01
We consider the gravitational model with additional spatial dimensions and anisotropic pressure which is nonzero only in these dimensions. Cosmological solutions of the Einstein equations in this model include accelerated expansion of the universe at late stage of its evolution and dynamical compactification of extra dimensions. This model describes observational data for Type Ia supernovae on the level or better than the ΛCDM model. We analyze two equations of state resulting in different predictions for further evolution, but in both variants the acceleration epoch is finite.
Watertight Anisotropic Surface Meshing Using Quadrilateral Patches
NASA Technical Reports Server (NTRS)
Haimes, Robert; Aftosmis, Michael J.
2004-01-01
This paper presents a simple technique for generating anisotropic surface triangulations using unstructured quadrilaterals when the CAD entity can be mapped to a logical rectangle. Watertightness and geometric quality measures are maintained and are consistent with the CAPRI default tessellator. These triangulations can match user specified criteria for chord-height tolerance, neighbor triangle dihedral angle, and maximum triangle side length. This discrete representation has hooks back to the owning geometry and therefore can be used in conjunction with these entities to allow for easy enhancement or modification of the tessellation suitable for grid generation or other downstream applications.
Staggered Fermion Thermodynamics using Anisotropic Lattices
NASA Astrophysics Data System (ADS)
Levkova, L.
2003-05-01
Numerical simulations of full QCD on anisotropic lattices provide a convenient way to study QCD thermodynamics with fixed physics scales and reduced lattice spacing errors. We report results from calculations with 2-flavors of dynamical fermions where all bare parameters and hence the physics scales are kept constant while the temperature is changed in small steps by varying only the number of the time slices. The results from a series of zero-temperature scale setting simulations are used to determine the Karsch coefficients and the equation of state at finite temperatures.
Capillary interactions between anisotropic colloidal particles.
Loudet, J C; Alsayed, A M; Zhang, J; Yodh, A G
2005-01-14
We report on the behavior of micron-sized prolate ellipsoids trapped at an oil-water interface. The particles experience strong, anisotropic, and long-ranged attractive capillary interactions which greatly exceed the thermal energy k(B)T. Depending on surface chemistry, the particles aggregate into open structures or chains. Using video microscopy, we extract the pair interaction potential between ellipsoids and show it exhibits a power law behavior over the length scales probed. Our observations can be explained using recent calculations, if we describe the interfacial ellipsoids as capillary quadrupoles.
Anisotropic fiber alignment in composite structures
Graham, Alan L.; Mondy, Lisa A.; Guell, David C.
1993-01-01
High strength material composite structures are formed with oriented fibers to provide controlled anisotropic fibers. Fibers suspended in non-dilute concentrations (e.g., up to 20 volume percent for fibers having an aspect ratio of 20) in a selected medium are oriented by moving an axially spaced array of elements in the direction of desired fiber alignment. The array elements are generally perpendicular to the desired orientation. The suspension medium may also include sphere-like particles where the resulting material is a ceramic.
Porous substrates filled with nanomaterials
Worsley, Marcus A.; Baumann, Theodore F.; Satcher, Jr., Joe H.; Stadermann, Michael
2014-08-19
A composition comprising: at least one porous carbon monolith, such as a carbon aerogel, comprising internal pores, and at least one nanomaterial, such as carbon nanotubes, disposed uniformly throughout the internal pores. The nanomaterial can be disposed in the middle of the monolith. In addition, a method for making a monolithic solid with both high surface area and good bulk electrical conductivity is provided. A porous substrate having a thickness of 100 microns or more and comprising macropores throughout its thickness is prepared. At least one catalyst is deposited inside the porous substrate. Subsequently, chemical vapor deposition is used to uniformly deposit a nanomaterial in the macropores throughout the thickness of the porous substrate. Applications include electrical energy storage, such as batteries and capacitors, and hydrogen storage.
NASA Astrophysics Data System (ADS)
Ulven, Ole Ivar; Sun, WaiChing
2016-04-01
Fluid transport in a porous medium has important implications for understanding natural geological processes. At a sufficiently large scale, a fluid-saturated porous medium can be regarded as a two-phase continuum, with the fluid constituent flowing in the Darcian regime. Nevertheless, a fluid mediated chemical reaction can in some cases change the permeability of the rock locally: Mineral dissolution can cause increased permeability, whereas mineral precipitation can reduce the permeability. This might trigger a complicated hydro-chemo-mechanical coupling effect that causes channeling of fluids or clogging of the system. If the fluid is injected or produced at a sufficiently high rate, the pressure might increase enough to cause the onset and propagation of fractures. Fractures in return create preferential flow paths that enhance permeability, localize fluid flow and chemical reaction, prevent build-up of pore pressure and cause anisotropy of the hydro-mechanical responses of the effective medium. This leads to a complex coupled process of solid deformation, chemical reaction and fluid transport enhanced by the fracture formation. In this work, we develop a new coupled numerical model to study the complexities of feedback among fluid pressure evolution, fracture formation and permeability changes due to a chemical process in a 2D system. We combine a discrete element model (DEM) previously used to study a volume expanding process[1, 2] with a new fluid transport model based on poroelasticity[3] and a fluid-mediated chemical reaction that changes the permeability of the medium. This provides new insights into the hydro-chemo-mechanical process of a transforming porous medium. References [1] Ulven, O. I., Storheim, H., Austrheim, H., and Malthe-Sørenssen, A. "Fracture Initiation During Volume Increasing Reactions in Rocks and Applications for CO2 Sequestration", Earth Planet. Sc. Lett. 389C, 2014a, pp. 132 - 142, doi:10.1016/j.epsl.2013.12.039. [2] Ulven, O. I
Porous light-emitting compositions
Burrell, Anthony K; McCleskey, Thomas Mark; Jia, Quanxi; Bauer, Eve; Mueller, Alexander H
2012-04-17
Light-emitting devices are prepared by coating a porous substrate using a polymer-assisted deposition process. Solutions of metal precursor and soluble polymers having binding properties for metal precursor were coated onto porous substrates. The coated substrates were heated at high temperatures under a suitable atmosphere. The result was a substrate with a conformal coating that did not substantially block the pores of the substrate.
Porous carbon EOS: numerical analysis
NASA Astrophysics Data System (ADS)
Aliverdiev, A.; Batani, D.; Dezulian, R.; Vinci, T.
2010-10-01
In this paper, we address the problem of direct simulation of laser-driven shock experiments aiming at determining the equation of state (EOS) of carbon using the "relative" impedance mismatch method. In particular, using tabulated carbon EOS (SESAME library, material number 7830), we have found some difficulties in reducing the initial density of the material in simulations with porous carbon. We have therefore calculated a new EOS for porous carbon with a reduced bulk modulus.
Transport of Graphene Oxide through Porous Media
NASA Astrophysics Data System (ADS)
Duster, T. A.; Na, C.; Bolster, D.; Fein, J. B.
2012-12-01
Graphene oxide (GO) is comprised of anisotropic nanosheets decorated with covalently-bonded epoxide, ketone, and hydroxyl functional groups on the basal planes, and carboxylic and phenolic functional groups at the edges. Individual GO nanosheets are generally two to three micrometers in width, with thicknesses depending on the degree of exfoliation and typically ranging from one to approximately 100 nanometers. As a result of this extraordinarily large surface area-to-mass ratio and the presence of numerous proton-active functional groups, GO nanosheets exhibit a tremendous capacity to adsorb metals and other contaminants from aqueous solutions and are thus often suggested for use in in situ remediation efforts. The potential importance of GO nanosheets as an adsorbent in soil and groundwater necessitates a detailed understanding of their mobility in environmental systems, but this topic remains largely unexplored. Hence, the objective of this study was to investigate the transport behavior of GO nanosheets through well-characterized saturated porous media. In this study, we used replicate glass columns packed with two different sand grain sizes, and within each treatment we varied pH (5.5 to 8.5), ionic strength (<0.01 M to 0.1 M), electrolyte composition (Na+ and Ca2+ salts), and GO nanosheet exfoliation extent (few-layered and many-layered) to determine the relative influence of both physical and electrochemical properties on GO nanosheet transport in these systems. The break-through of GO nanosheets from each treatment was continuously monitored using a flow-through quartz cuvette and UV-Vis absorbance at 230 nm. GO nanosheet transport through these systems was then modeled using distinct advection-dispersion equations to establish the relative influence of attachment, deposition, and detachment in the overall transport behavior, and a corresponding retardation coefficient was calculated for each treatment. Break-through curves displayed anomalous transport
Additively manufactured porous tantalum implants.
Wauthle, Ruben; van der Stok, Johan; Amin Yavari, Saber; Van Humbeeck, Jan; Kruth, Jean-Pierre; Zadpoor, Amir Abbas; Weinans, Harrie; Mulier, Michiel; Schrooten, Jan
2015-03-01
The medical device industry's interest in open porous, metallic biomaterials has increased in response to additive manufacturing techniques enabling the production of complex shapes that cannot be produced with conventional techniques. Tantalum is an important metal for medical devices because of its good biocompatibility. In this study selective laser melting technology was used for the first time to manufacture highly porous pure tantalum implants with fully interconnected open pores. The architecture of the porous structure in combination with the material properties of tantalum result in mechanical properties close to those of human bone and allow for bone ingrowth. The bone regeneration performance of the porous tantalum was evaluated in vivo using an orthotopic load-bearing bone defect model in the rat femur. After 12 weeks, substantial bone ingrowth, good quality of the regenerated bone and a strong, functional implant-bone interface connection were observed. Compared to identical porous Ti-6Al-4V structures, laser-melted tantalum shows excellent osteoconductive properties, has a higher normalized fatigue strength and allows for more plastic deformation due to its high ductility. It is therefore concluded that this is a first step towards a new generation of open porous tantalum implants manufactured using selective laser melting.
Anisotropic hydraulic permeability in compressed articular cartilage.
Reynaud, Boris; Quinn, Thomas M
2006-01-01
The extent to which articular cartilage hydraulic permeability is anisotropic is largely unknown, despite its importance for understanding mechanisms of joint lubrication, load bearing, transport phenomena, and mechanotransduction. We developed and applied new techniques for the direct measurement of hydraulic permeability within statically compressed adult bovine cartilage explant disks, dissected such that disk axes were perpendicular to the articular surface. Applied pressure gradients were kept small to minimize flow-induced matrix compaction, and fluid outflows were measured by observation of a meniscus in a glass capillary under a microscope. Explant disk geometry under radially unconfined axial compression was measured by direct microscopic observation. Pressure, flow, and geometry data were input to a finite element model where hydraulic permeabilities in the disk axial and radial directions were determined. At less than 10% static compression, near free-swelling conditions, hydraulic permeability was nearly isotropic, with values corresponding to those of previous studies. With increasing static compression, hydraulic permeability decreased, but the radially directed permeability decreased more dramatically than the axially directed permeability such that strong anisotropy (a 10-fold difference between axial and radial directions) in the hydraulic permeability tensor was evident for static compression of 20-40%. Results correspond well with predictions of a previous microstructurally-based model for effects of tissue mechanical deformations on glycosaminoglycan architecture and cartilage hydraulic permeability. Findings inform understanding of structure-function relationships in cartilage matrix, and suggest several biomechanical roles for compression-induced anisotropic hydraulic permeability in articular cartilage.
Shear waves in acoustic anisotropic media
Grechka, Vladimir; Zhang, Linbin; Rector, James W.
2003-01-02
Acoustic transversely isotropic (TI) media are defined by artificially setting the shear-wave velocity in the direction of symmetry axis, VS0, to zero. Contrary to conventional wisdom that equating VS0 = 0 eliminates shear waves, we demonstrate their presence and examine their properties. Specifically, we show that SV-waves generally have finite nonzero phase and group velocities in acoustic TI media. In fact, these waves have been observed in full waveform modeling, but apparently they were not understood and labeled as numerical artifacts. Acoustic TI media are characterized by extreme, in some sense infinite strength of anisotropy. It makes the following unusual wave phenomena possible: (1) there are propagation directions, where the SV-ray is orthogonal to the corresponding wavefront normal, (2) the SV-wave whose ray propagates along the symmetry axis is polarized parallel to the P-wave propagating in the same direction, (3) P-wave singularities, that is, directions where P- and SV -wave phase velocities coincide might exist in acoustic TI media. We also briefly discuss some aspects of wave propagation in low-symmetry acoustic anisotropic models. Extreme anisotropy in those media creates bizarre phase- and group-velocity surfaces that might bring intellectual delight to an anisotropic guru.
Anisotropic swelling behavior of the cornea.
Matsuura, Toyoaki; Ikeda, Hitoe; Idota, Naokazu; Motokawa, Ryuhei; Hara, Yoshiaki; Annaka, Masahiko
2009-12-24
The phase equilibrium property and structural and dynamical properties of pig cornea were studied by macroscopic observation of swelling behavior, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) under various conditions. It was found that the corneal gel collapses into a compact state isotropically or anisotropically depending on the external conditions. The corneal gel collapses uniformly into a compact state at a temperature above 55 degrees C because of the denaturation of collagen, whereas it collapses along an axis parallel to the optic axis with increasing NaCl concentration. Anisotropic deswelling was also observed during desiccation. SAXS measurements revealed that the periodicity of the collagen fiber of the cornea does not change even at higher NaCl concentration, which indicates that hydration and dehydration resulting from changes in salt concentration simply cause swelling and deswelling of the glycosaminoglycan (GAG), which is located between the regular two-dimensional lattices of collagen fibers, which obliges the change in thickness. From observations of the dynamics of light scattered by the corneal gel, intensity autocorrelation functions that revealed two independent diffusion coefficients were obtained. Divergent behavior in the measured total scattered light intensities and diffusion coefficients with varying temperature was observed. That is, a slowing of the dynamic modes accompanied by increased "static" scattered intensities was observed. This is indicative of the occurrence of a phase transition as a function of temperature.
New formulation of leading order anisotropic hydrodynamics
NASA Astrophysics Data System (ADS)
Tinti, Leonardo
2015-05-01
Anisotropic hydrodynamics is a reorganization of the relativistic hydrodynamics expansion, with the leading order already containing substantial momentum-space anisotropies. The latter are a cause of concern in the traditional viscous hydrodynamics, since large momentum anisotropies generated in ultrarelativistic heavy-ion collisions are not consistent with the hypothesis of small deviations from an isotropic background, i.e., from the local equilibrium distribution. We discuss the leading order of the expansion, presenting a new formulation for the (1+1)- dimensional case, namely, for the longitudinally boost invariant and cylindrically symmetric flow. This new approach is consistent with the well established framework of Israel and Stewart in the close to equilibrium limit (where we expect viscous hydrodynamics to work well). If we consider the (0+1)-dimensional case, that is, transversally homogeneous and longitudinally boost invariant flow, the new form of anisotropic hydrodynamics leads to better agreement with known solutions of the Boltzmann equation than the previous formulations, especially when we consider massive particles.
Building an anisotropic meniscus with zonal variations.
Higashioka, Michael M; Chen, Justin A; Hu, Jerry C; Athanasiou, Kyriacos A
2014-01-01
Toward addressing the difficult problems of knee meniscus regeneration, a self-assembling process has been used to re-create the native morphology and matrix properties. A significant problem in such attempts is the recapitulation of the distinct zones of the meniscus, the inner, more cartilaginous and the outer, more fibrocartilaginous zones. In this study, an anisotropic and zonally variant meniscus was produced by self-assembly of the inner meniscus (100% chondrocytes) followed by cell seeding the outer meniscus (coculture of chondrocytes and meniscus cells). After 4 weeks in culture, the engineered, inner meniscus exhibited a 42% increase in both instantaneous and relaxation moduli and a 62% increase in GAG/DW, as compared to the outer meniscus. In contrast, the circumferential tensile modulus and collagen/DW of the outer zone was 101% and 129% higher, respectively, than the values measured for the inner zone. Furthermore, there was no difference in the radial tensile modulus between the control and zonal engineered menisci, suggesting that the inner and outer zones of the engineered zonal menisci successfully integrated. These data demonstrate that not only can biomechanical and biochemical properties be engineered to differ by the zone, but they can also recapitulate the anisotropic behavior of the knee meniscus.
Radial stability of anisotropic strange quark stars
NASA Astrophysics Data System (ADS)
Arbañil, José D. V.; Malheiro, M.
2016-11-01
The influence of the anisotropy in the equilibrium and stability of strange stars is investigated through the numerical solution of the hydrostatic equilibrium equation and the radial oscillation equation, both modified from their original version to include this effect. The strange matter inside the quark stars is described by the MIT bag model equation of state. For the anisotropy two different kinds of local anisotropic σ = pt-pr are considered, where pt and pr are respectively the tangential and the radial pressure: one that is null at the star's surface defined by pr(R) = 0, and one that is nonnull at the surface, namely, σs = 0 and σs ≠ 0. In the case σs = 0, the maximum mass value and the zero frequency of oscillation are found at the same central energy density, indicating that the maximum mass marks the onset of the instability. For the case σs ≠ 0, we show that the maximum mass point and the zero frequency of oscillation coincide in the same central energy density value only in a sequence of equilibrium configurations with the same value of σs. Thus, the stability star regions are determined always by the condition dM/dρc > 0 only when the tangential pressure is maintained fixed at the star surface's pt(R). These results are also quite important to analyze the stability of other anisotropic compact objects such as neutron stars, boson stars and gravastars.
Anisotropic artificial substrates for microwave applications
NASA Astrophysics Data System (ADS)
Shahvarpour, Attieh
The perfect electromagnetic conductor (PEMC) boundary is a novel fundamental electromagnetic concept. It is a generalized description of the electromagnetic boundary conditions including the perfect electric conductor (PEC) and the perfect magnetic conductor (PMC) and due to its fundamental properties, it has the potential of enabling several electromagnetic applications. However, the PEMC boundaries concept had remained at the theoretical level and has not been practically realized. Therefore, motivated by the importance of this electromagnetic fundamental concept and its potential applications, the first contribution of this thesis is focused on the practical implementation of the PEMC boundaries by exploiting Faraday rotation principle and ground reflection in the ferrite materials which are intrinsically anisotropic. As a result, this thesis reports the first practical approach for the realization of PEMC boundaries. A generalized scattering matrix (GSM) is used for the analysis of the grounded-ferrite PEMC boundaries structure. As an application of the PEMC boundaries, a transverse electromagnetic (TEM) waveguide is experimentally demonstrated using grounded ferrite PMC (as particular case of the PEMC boundaries) side walls. Perfect electromagnetic conductor boundaries may find applications in various types of sensors, reflectors, polarization convertors and polarization-based radio frequency identifiers. Leaky-wave antennas perform as high directivity and frequency beam scanning antennas and as a result they enable applications in radar, point-to-point communications and MIMO systems. The second contribution of this thesis is introducing and analysing a novel broadband and highly directive two-dimensional leaky-wave antenna. This antenna operates differently in the lower and higher frequency ranges. Toward its lower frequencies, it allows full-space conical-beam scanning while at higher frequencies, it provides fixed-beam radiation (at a designable angle
Anisotropic superfluidity in a dipolar Bose gas
Ticknor, Christopher; Wilson, Ryan M; Bohn, John L
2010-11-04
so that the in-plane interaction is anisotropic. By induding repulsive contact interactions to ensure a stable system, we perform direct numeric simulations of an obstacle moving through the system in directions parallel and perpendicular to the tilt of the dipoles. We observe a distinct anisotropic superfluid response in these cases, both for dissipation into quasipartides and topological excitations (vortices), in the form of an anisotropic critical velocity that is larger in the direction of the dipole tilt than in the perpendicular direction. Interestingly, we find that, while the roton displays an anisotropic character, the speed of sound in the systrm is isotropic. Thus, we characterize the DBEC as an fmisotropic superfluid while illuminating the crucial role that the roton plays in this anisotropic behavior.
Optical isotropy at terahertz frequencies using anisotropic metamaterials
NASA Astrophysics Data System (ADS)
Lee, In-Sung; Sohn, Ik-Bu; Kang, Chul; Kee, Chul-Sik; Yang, Jin-Kyu; Lee, Joong Wook
2016-07-01
We demonstrate optically isotropic filters in the terahertz (THz) frequency range using structurally anisotropic metamaterials. The proposed metamaterials with two-dimensional arrangements of anisotropic H-shaped apertures show polarization-independent transmission due to the combined effects of the dipole resonances of resonators and antennas. Our results may offer the potential for the design and realization of versatile THz devices and systems.
Holographic Wilson loops in anisotropic quark-gluon plasma.
NASA Astrophysics Data System (ADS)
Ageev, Dmitry
2016-10-01
The nonequilibrium properties of the anisotropic quark-gluon plasma are condidered from the holographic viewpoint. Lifshitz-like solution is considered as a holographic dual of anisotropic QGP. The black brane formation in such background is considered as a thermalization in dual theory. As a probe of thermalization we consider rectangular spatial Wilson loops with different orientation.
Method for anisotropic etching in the manufacture of semiconductor devices
Koontz, Steven L.; Cross, Jon B.
1993-01-01
Hydrocarbon polymer coatings used in microelectronic manufacturing processes are anisotropically etched by atomic oxygen beams (translational energies of 0.2-20 eV, preferably 1-10 eV). Etching with hyperthermal (kinetic energy>1 eV) oxygen atom species obtains highly anisotropic etching with sharp boundaries between etched and mask-protected areas.
Method for anisotropic etching in the manufacture of semiconductor devices
NASA Technical Reports Server (NTRS)
Koontz, Steven L. (Inventor); Cross, Jon B. (Inventor)
1993-01-01
Hydrocarbon polymer coatings used in microelectronic manufacturing processes are anisotropically etched by hyperthermal atomic oxygen beams (translational energies of 0.2 to 20 eV, preferably 1 to 10 eV). Etching with hyperthermal oxygen atom species obtains highly anisotropic etching with sharp boundaries between etched and mask protected areas.
Effect of supermolecular structure on oil filtration in a porous medium
Gal`tsev, V.E.; Ametov, I.M.; Dzyubenko, E.M.
1995-09-01
The formation of supermolecular structures during the adsorption of a tar-asphaltene fraction on the surface of grains of rock-forming materials in a porous medium was studied. The effect of these structures on the character of oil filtration in a porous medium is established. The filamentary structures formed have a diameter of 20 to 40 {angstrom}, corresponding to the size of asphaltene associates, and exhibit preferred orientation with a tilt in the direction opposite to the direction of flow. Some residual orientation of filaments is retained upon a change in the direction of flow. On the basis of ENDOR data, a model of a spatially anisotropic asphaltene micelle in oil was developed, which explains the observed character of coagulation and the formation of filamentary structures.
Swisdak, M.; Drake, J. F.; Opher, M. E-mail: drake@umd.edu
2013-09-01
The picture of the heliopause (HP)-the boundary between the domains of the Sun and the local interstellar medium (LISM)-as a pristine interface with a large rotation in the magnetic field fails to describe recent Voyager 1 (V1) data. Magnetohydrodynamic (MHD) simulations of the global heliosphere reveal that the rotation angle of the magnetic field across the HP at V1 is small. Particle-in-cell simulations, based on cuts through the MHD model at V1's location, suggest that the sectored region of the heliosheath (HS) produces large-scale magnetic islands that reconnect with the interstellar magnetic field while mixing LISM and HS plasma. Cuts across the simulation reveal multiple, anti-correlated jumps in the number densities of LISM and HS particles, similar to those observed, at the magnetic separatrices. A model is presented, based on both the observations and simulations, of the HP as a porous, multi-layered structure threaded by magnetic fields. This model further suggests that contrary to the conclusions of recent papers, V1 has already crossed the HP.
Zhao, Fu; Landis, Heather R; Skerlos, Steven J
2005-01-01
A methodology for producing a pore-scale, 3D computational model of porous filter permeability is developed that is based on the analysis of 2D images of the filter matrix and first principles. The computationally reconstructed porous filter model retains statistical details of porosity and the spatial correlations of porosity within the filter and can be used to calculate permeability for either isotropic or 1D anisotropic porous filters. In the isotropic case, validation of the methodology was conducted using 0.2 and 0.8 microm ceramic membrane filters,forwhich it is shown that the image-based computational models provide a viable statistical reproduction of actual porosity characteristics. It is also shown that these models can predict water flux directly from first principles with deviations from experimental measurements in the range of experimental error. In the anisotropic case, validation of the methodology was conducted using a natural river sand filter. For this case, it is shown that the methodology yields predictions of filtration velocity that are similar or better than predictions offered by existing filtration models. It was found for the sand filter that the deviation between observation and prediction was mostly due to swelling during the preparation of the sand filter for imaging and can be reduced significantly using alternative methods reported in the literature. On the basis of these results, it is concluded that the computational reconstruction methodology is valid for porous filter modeling, and given that it captures pore-scale details, it has potential application to the investigation of permeability decline underthe influence of pore-scale fouling mechanisms.
Anwar, S.; Cortis, A.; Sukop, M.
2008-10-20
Lattice Boltzmann models simulate solute transport in porous media traversed by conduits. Resulting solute breakthrough curves are fitted with Continuous Time Random Walk models. Porous media are simulated by damping flow inertia and, when the damping is large enough, a Darcy's Law solution instead of the Navier-Stokes solution normally provided by the lattice Boltzmann model is obtained. Anisotropic dispersion is incorporated using a direction-dependent relaxation time. Our particular interest is to simulate transport processes outside the applicability of the standard Advection-Dispersion Equation (ADE) including eddy mixing in conduits. The ADE fails to adequately fit any of these breakthrough curves.
Fabrication of a porous membrane for the gas pre-combustion
NASA Astrophysics Data System (ADS)
Stuermann, Joerg; Boedecker, Andre; Splinter, Alexandra; Benecke, Wolfgang
2003-01-01
This paper presents a micro reactor, which consists of a permeable membrane fabricated by silicon micro machining technology. The fabrication process is a combination of anisotropic silicon etching (wet etching and dry etching) and porous silicon technology. To avoid a reaction chamber with a high dead volume, we have realised a permeable membrane in conjunction with porous silicon to achieve a high surface to volume ratio, impregnated with palladium or platinum. For the activation of the heterogeneous reaction on the surface of the catalytic material a heating element around the permeable membrane, which is thermally decoupled with a porous silicon well of the surrounding bulk material is realised. The gas flows through the membrane and reacts during the passing time. The reaction time for gases depends on the membrane thickness and the active surface of the porous silicon. The application is the integration into a gas analysing system combined with a gas sensor array, a gas chromatographic system, microvalves, and calibration units mounted all on a pneumatic motherboard.
Porous materials with high negative Poisson’s ratios—a mechanism based material design
NASA Astrophysics Data System (ADS)
Kim, Kwangwon; Ju, Jaehyung; Kim, Doo-Man
2013-08-01
In an effort to tailor functional materials with customized anisotropic properties—stiffness and yield strain, we propose porous materials consisting of flexible mesostructures designed from the deformation of a re-entrant auxetic honeycomb and compliant mechanisms. Using an analogy between compliant mechanisms and a cellular material’s deformation, we can tailor the in-plane properties of mesostructures; low stiffness and high strain in one direction and high stiffness and low strain in the other direction. An analytical model is developed to obtain the effective moduli and yield strains of the porous materials by combining the kinematics of a rigid link mechanism and deformation of flexure hinges. A numerical technique is implemented with the analytical model for the nonlinear constitutive relations of the mesostructures and their strain-dependent Poisson’s ratios. A finite element analysis (FEA) is used to validate the analytical and numerical models. The designed moduli and yield strain of porous materials with an aluminum alloy are 2 GPa and 0.28% in one direction and 0.2 MPa and 28% in the other direction. These porous materials with mesostructures have high negative Poisson’s ratios, {\
Constitutive modeling of inelastic anisotropic material response
NASA Technical Reports Server (NTRS)
Stouffer, D. C.
1984-01-01
A constitutive equation was developed to predict the inelastic thermomechanical response of single crystal turbine blades. These equations are essential for developing accurate finite element models of hot section components and contribute significantly to the understanding and prediction of crack initiation and propagation. The method used was limited to unified state variable constitutive equations. Two approaches to developing an anisotropic constitutive equation were reviewed. One approach was to apply the Stouffer-Bodner representation for deformation induced anisotropy to materials with an initial anisotropy such as single crystals. The second approach was to determine the global inelastic strain rate from the contribution of the slip in each of the possible crystallographic slip systems. A three dimensional finite element is being developed with a variable constitutive equation link that can be used for constitutive equation development and to predict the response of an experiment using the actual specimen geometry and loading conditions.
Observable effects of anisotropic bubble nucleation
Blanco-Pillado, Jose J.; Salem, Michael P. E-mail: salem@cosmos.phy.tufts.edu
2010-07-01
Our universe may have formed via bubble nucleation in an eternally-inflating background. Furthermore, the background may have a compact dimension — the modulus of which tunnels out of a metastable minimum during bubble nucleation — which subsequently grows to become one of our three large spatial dimensions. Then the reduced symmetry of the background is equivalent to anisotropic initial conditions in our bubble universe. We compute the inflationary spectrum in such a scenario and, as a first step toward understanding the effects of anisotropy, project it onto spherical harmonics. The resulting spectrum exhibits anomalous multipole correlations, their relative amplitude set by the present curvature parameter, which appear to extend to arbitrarily large multipole moments. This raises the possibility of future detection, if slow-roll inflation does not last too long within our bubble. A full understanding of the observational signal must account for the effects of background anisotropy on photon free streaming, and is left to future work.
GVF-based anisotropic diffusion models.
Yu, Hongchuan; Chua, Chin-Seng
2006-06-01
In this paper, the gradient vector flow fields are introduced in image restoration. Within the context of flow fields, the shock filter, mean curvature flow, and Perona-Malik equation are reformulated. Many advantages over the original models can be obtained; these include numerical stability, large capture range, and high-order derivative estimation. In addition, a fairing process is introduced in the anisotropic diffusion, which contains a fourth-order derivative and is reformulated as the intrinsic Laplacian of curvature under the level set framework. By applying this fairing process, the shape boundaries will become more apparent. In order to overcome numerical errors, the intrinsic Laplacian of curvature is computed from the gradient vector flow fields instead of the observed images.
Anisotropic compact stars in Karmarkar spacetime
NASA Astrophysics Data System (ADS)
Newton Singh, Ksh.; Pant, Neeraj; Govender, M.
2017-01-01
We present a new class of solutions to the Einstein field equations for an anisotropic matter distribution in which the interior space-time obeys the Karmarkar condition. The necessary and sufficient condition required for a spherically symmetric space-time to be of Class One reduces the gravitational behavior of the model to a single metric function. By assuming a physically viable form for the grr metric potential we obtain an exact solution of the Einstein field equations which is free from any singularities and satisfies all the physical criteria. We use this solution to predict the masses and radii of well-known compact objects such as Cen X-3, PSR J0348+0432, PSR B0943+10 and XTE J1739-285.
Anisotropic Absorption of Pure Spin Currents.
Baker, A A; Figueroa, A I; Love, C J; Cavill, S A; Hesjedal, T; van der Laan, G
2016-01-29
Spin transfer in magnetic multilayers offers the possibility of ultrafast, low-power device operation. We report a study of spin pumping in spin valves, demonstrating that a strong anisotropy of spin pumping from the source layer can be induced by an angular dependence of the total Gilbert damping parameter, α, in the spin sink layer. Using lab- and synchrotron-based ferromagnetic resonance, we show that an in-plane variation of damping in a crystalline Co_{50}Fe_{50} layer leads to an anisotropic α in a polycrystalline Ni_{81}Fe_{19} layer. This anisotropy is suppressed above the spin diffusion length in Cr, which is found to be 8 nm, and is independent of static exchange coupling in the spin valve. These results offer a valuable insight into the transmission and absorption of spin currents, and a mechanism by which enhanced spin torques and angular control may be realized for next-generation spintronic devices.
Particle Behavior at Anisotropically Curved Liquid Interfaces
NASA Astrophysics Data System (ADS)
McEnnis, Kathleen; Zeng, Chuan; Davidovitch, Benny; Dinsmore, Anthony; Russell, Thomas
2011-03-01
A particle bound to an anisotropically curved liquid interface, such as a cylinder or catenoid, cannot maintain a constant contact angle without deforming the interface. Theory suggests that the particles will experience a force that depends on the interfacial shape and migrate to minimize the total interfacial energy. To test these predictions, particles were deposited on top of liquid semi-cylinders of ionic liquid or melted polystyrene confined on chemically patterned surfaces. Particles were also deposited on liquid catenoid structures created by placing a melted polymer film under an electric field. The location of the particles on these structures was observed by optical, confocal, and scanning electron microscopy. The implications for the directed assembly of particles and stability of Pickering emulsions are also discussed.
Turbulent Output-Based Anisotropic Adaptation
NASA Technical Reports Server (NTRS)
Park, Michael A.; Carlson, Jan-Renee
2010-01-01
Controlling discretization error is a remaining challenge for computational fluid dynamics simulation. Grid adaptation is applied to reduce estimated discretization error in drag or pressure integral output functions. To enable application to high O(10(exp 7)) Reynolds number turbulent flows, a hybrid approach is utilized that freezes the near-wall boundary layer grids and adapts the grid away from the no slip boundaries. The hybrid approach is not applicable to problems with under resolved initial boundary layer grids, but is a powerful technique for problems with important off-body anisotropic features. Supersonic nozzle plume, turbulent flat plate, and shock-boundary layer interaction examples are presented with comparisons to experimental measurements of pressure and velocity. Adapted grids are produced that resolve off-body features in locations that are not known a priori.
Anisotropic Absorption of Pure Spin Currents
NASA Astrophysics Data System (ADS)
Baker, A. A.; Figueroa, A. I.; Love, C. J.; Cavill, S. A.; Hesjedal, T.; van der Laan, G.
2016-01-01
Spin transfer in magnetic multilayers offers the possibility of ultrafast, low-power device operation. We report a study of spin pumping in spin valves, demonstrating that a strong anisotropy of spin pumping from the source layer can be induced by an angular dependence of the total Gilbert damping parameter, α , in the spin sink layer. Using lab- and synchrotron-based ferromagnetic resonance, we show that an in-plane variation of damping in a crystalline Co50 Fe50 layer leads to an anisotropic α in a polycrystalline Ni81 Fe19 layer. This anisotropy is suppressed above the spin diffusion length in Cr, which is found to be 8 nm, and is independent of static exchange coupling in the spin valve. These results offer a valuable insight into the transmission and absorption of spin currents, and a mechanism by which enhanced spin torques and angular control may be realized for next-generation spintronic devices.
Far field expansion for anisotropic wave equations
NASA Technical Reports Server (NTRS)
Hariharan, S. I.; Hagstrom, Thomas
1989-01-01
A necessary ingredient for the numerical simulation of many time dependent phenomena in acoustics and aerodynamics is the imposition of accurate radiation conditions at artificial boundaries. The asymptotic analysis of propagating waves provides a rational approach to the development of such conditions. A far field asymptotic expansion of solutions of anisotropic wave equations is derived. This generalizes the well known Friedlander expansion for the standard wave operator. The expansion is used to derive a hierarchy of radiation conditions of increasing accuracy. Two numerical experiments are given to illustrate the utility of this approach. The first application is the study of unsteady vortical disturbances impinging on a flat plate; the second is the simulation of inviscid flow past an impulsively started cylinder.
Correlation energy of anisotropic quantum dots
Zhao Yan; Loos, Pierre-Francois; Gill, Peter M. W.
2011-09-15
We study the D-dimensional high-density correlation energy E{sub c} of the singlet ground state of two electrons confined by a harmonic potential with Coulombic repulsion. We allow the harmonic potential to be anisotropic and examine the behavior of E{sub c} as a function of the anisotropy {alpha}{sup -1}. In particular, we are interested in the limit where the anisotropy goes to infinity ({alpha}{yields}0) and the electrons are restricted to a lower-dimensional space. We show that tuning the value of {alpha} from 0 to 1 allows a smooth dimensional interpolation and we demonstrate that the usual model, in which a quantum dot is treated as a two-dimensional system, is inappropriate. Finally, we provide a simple function which reproduces the behavior of E{sub c} over the entire range of {alpha}.
Highly Anisotropic Dirac Fermions in Square Graphynes.
Zhang, L Z; Wang, Z F; Wang, Zhiming M; Du, S X; Gao, H-J; Liu, Feng
2015-08-06
We predict a family of 2D carbon (C) allotropes, square graphynes (S-graphynes) that exhibit highly anisotropic Dirac fermions, using first-principle calculations within density functional theory. They have a square unit-cell containing two sizes of square C rings. The equal-energy contour of their 3D band structure shows a crescent shape, and the Dirac crescent has varying Fermi velocities from 0.6 × 10(5) to 7.2 × 10(5) m/s along different k directions. Near the Fermi level, the Dirac crescent can be nicely expressed by an extended 2D Dirac model Hamiltonian. Furthermore, tight-binding band fitting reveals that the Dirac crescent originates from the next-nearest-neighbor interactions between C atoms. S-graphynes may be used to build new 2D electronic devices taking advantages of their highly directional charge transport.
An Anisotropic Hardening Model for Springback Prediction
Zeng, Danielle; Xia, Z. Cedric
2005-08-05
As more Advanced High-Strength Steels (AHSS) are heavily used for automotive body structures and closures panels, accurate springback prediction for these components becomes more challenging because of their rapid hardening characteristics and ability to sustain even higher stresses. In this paper, a modified Mroz hardening model is proposed to capture realistic Bauschinger effect at reverse loading, such as when material passes through die radii or drawbead during sheet metal forming process. This model accounts for material anisotropic yield surface and nonlinear isotropic/kinematic hardening behavior. Material tension/compression test data are used to accurately represent Bauschinger effect. The effectiveness of the model is demonstrated by comparison of numerical and experimental springback results for a DP600 straight U-channel test.
Anisotropic star on pseudo-spheroidal spacetime
NASA Astrophysics Data System (ADS)
Ratanpal, B. S.; Thomas, V. O.; Pandya, D. M.
2016-02-01
A new class of exact solutions of Einstein's field equations representing anisotropic distribution of matter on pseudo-spheroidal spacetime is obtained. The parameters appearing in the model are restricted through physical requirements of the model. It is found that the models given in the present work is compatible with observational data of a wide variety of compact objects like 4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, PSR J1614-2230, SMC X-4, Cen X-3. A particular model of pulsar PSR J1614-2230 is studied in detail and found that it satisfies all physical requirements needed for physically acceptable model.
Adiabatic theory for anisotropic cold molecule collisions
Pawlak, Mariusz; Shagam, Yuval; Narevicius, Edvardas; Moiseyev, Nimrod
2015-08-21
We developed an adiabatic theory for cold anisotropic collisions between slow atoms and cold molecules. It enables us to investigate the importance of the couplings between the projection states of the rotational motion of the atom about the molecular axis of the diatom. We tested our theory using the recent results from the Penning ionization reaction experiment {sup 4}He(1s2s {sup 3}S) + HD(1s{sup 2}) → {sup 4}He(1s{sup 2}) + HD{sup +}(1s) + e{sup −} [Lavert-Ofir et al., Nat. Chem. 6, 332 (2014)] and demonstrated that the couplings have strong effect on positions of shape resonances. The theory we derived provides cross sections which are in a very good agreement with the experimental findings.
Effects of anisotropic heat conduction on solidification
NASA Technical Reports Server (NTRS)
Weaver, J. A.; Viskanta, R.
1989-01-01
Two-dimensional solidification influenced by anisotropic heat conduction has been considered. The interfacial energy balance was derived to account for the heat transfer in one direction (x or y) depending on the temperature gradient in both the x and y directions. A parametric study was made to determine the effects of the Stefan number, aspect ratio, initial superheat, and thermal conductivity ratios on the solidification rate. Because of the imposed boundary conditions, the interface became skewed and sometimes was not a straight line between the interface position at the upper and lower adiabatic walls (spatially nonlinear along the height). This skewness depends on the thermal conductivity ratio k(yy)/k(yx). The nonlinearity of the interface is influenced by the solidification rate, aspect ratio, and k(yy/k(yx).
Standing shear waves in anisotropic viscoelastic media
NASA Astrophysics Data System (ADS)
Krit, T.; Golubkova, I.; Andreev, V.
2015-10-01
We studied standing shear waves in anisotropic resonator represented by a rectangular parallelepiped (layer) fixed without slipping between two wooden plates of finite mass. The viscoelastic layer with edges of 70 mm × 40 mm × 15 mm was made of a rubber-like polymer plastisol with rubber bands inside. The bands were placed vertical between the top and the bottom plate. Mechanical properties of the plastisol itself were carefully measured previously. It was found that plastisol shows a cubic nonlinear behavior, i.e. the stress-strain curve could be represented as: σ = μɛ + βμɛ3, where ɛ stands for shear strain and σ is an applied shear stress. The value of shear modulus μ depends on frequency and was found to be several kilopascals which is common for such soft solids. Nonlinear parameter β is frequency dependent too and varies in range from tenths to unity at 1-100 Hz frequency range, decreasing with frequency growth. Stretching the rubber bands inside the layer leads to change of elastic properties in resonator. Such effect could be noticed due to frequency response of the resonator. The numerical model of the resonator was based on finite elements method (FEM) and performed in MatLab. The resonator was cut in hundreds of right triangular prisms. Each prism was provided with viscoelastic properties of the layer except for the top prisms provided with the wooden plate properties and the prisms at the site of the rubber bands provided with the rubber properties. The boundary conditions on each prism satisfied the requirements that resonator is inseparable and all its boundaries but bottom are free. The bottom boundary was set to move horizontally with constant acceleration amplitude. It was shown numerically that the resonator shows anisotropic behavior expressed in different frequency response to oscillations applied to a bottom boundary in different directions.
Enhancement of non-resonant dielectric cloaks using anisotropic composites
Takezawa, Akihiro Kitamura, Mitsuru
2014-01-15
Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight- and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite, this may have an advantage in the mass production of cloaking devices.
Acoustic Absorption in Porous Materials
NASA Technical Reports Server (NTRS)
Kuczmarski, Maria A.; Johnston, James C.
2011-01-01
An understanding of both the areas of materials science and acoustics is necessary to successfully develop materials for acoustic absorption applications. This paper presents the basic knowledge and approaches for determining the acoustic performance of porous materials in a manner that will help materials researchers new to this area gain the understanding and skills necessary to make meaningful contributions to this field of study. Beginning with the basics and making as few assumptions as possible, this paper reviews relevant topics in the acoustic performance of porous materials, which are often used to make acoustic bulk absorbers, moving from the physics of sound wave interactions with porous materials to measurement techniques for flow resistivity, characteristic impedance, and wavenumber.
Anisotropic transport in modulation doped quantum well structures
NASA Technical Reports Server (NTRS)
Radulescu, D. C.; Wicks, G. W.; Schaff, W. J.; Calawa, A. R.; Eastman, L. F.
1987-01-01
The degree of anisotropy in the anisotropic electron transport that has been observed in GaAs modulation-doped quantum wells grown by MBE on Al(0.3)Ga(0.7)As is related to the thickness and growth parameters of this substrate, which is grown just prior to the inverted interface. It is presently observed that the inverted interface has an anisotropic roughness which affects the 77 K low field electron transport parallel to the interface, and gives rise to anisotropic electron scattering in the GaAs modulation-doped quantum well.
Vortex liquid crystals in anisotropic type II superconductors.
Carlson, E W; Castro Neto, A H; Campbell, D K
2003-02-28
In an isotropic type II superconductor in a moderate magnetic field, the transition to the normal state occurs by vortex lattice melting. In certain anisotropic cases, the vortices acquire elongated cross sections and interactions. Systems of anisotropic, interacting constituents generally exhibit liquid crystalline phases. We examine the possibility of a two step melting in homogeneous type II superconductors with anisotropic superfluid stiffness from a vortex lattice into first a vortex smectic and then a vortex nematic at high temperature and magnetic field. We find that fluctuations of the ordered phase favor an instability to an intermediate smectic-A in the absence of intrinsic pinning.
Renormalized anisotropic exchange for representing heat assisted magnetic recording media
Jiao, Yipeng; Liu, Zengyuan; Victora, R. H.
2015-05-07
Anisotropic exchange has been incorporated in a description of magnetic recording media near the Curie temperature, as would be found during heat assisted magnetic recording. The new parameters were found using a cost function that minimized the difference between atomistic properties and those of renormalized spin blocks. Interestingly, the anisotropic exchange description at 1.5 nm discretization yields very similar switching and magnetization behavior to that found at 1.2 nm (and below) discretization for the previous isotropic exchange. This suggests that the increased accuracy of anisotropic exchange may also reduce the computational cost during simulation.
Conformal anisotropic mechanics and the Horava dispersion relation
Romero, Juan M.; Cuesta, Vladimir; Garcia, J. Antonio; Vergara, J. David
2010-03-15
In this paper we implement scale anisotropic transformations between space and time in classical mechanics. The resulting system is consistent with the dispersion relation of Horava gravity [P. Horava, Phys. Rev. D 79, 084008 (2009)]. Also, we show that our model is a generalization of the conformal mechanics of Alfaro, Fubini, and Furlan. For an arbitrary dynamical exponent we construct the dynamical symmetries that correspond to the Schroedinger algebra. Furthermore, we obtain the Boltzmann distribution for a gas of free particles compatible with anisotropic scaling transformations and compare our result with the corresponding thermodynamics of the recent anisotropic black branes proposed in the literature.
Anisotropic Nanomechanics of Boron Nitride Nanotubes: Nanostructured "Skin" Effect
NASA Technical Reports Server (NTRS)
Srivastava, Deepak; Menon, Madhu; Cho, KyeongJae
2000-01-01
The stiffness and plasticity of boron nitride nanotubes are investigated using generalized tight-binding molecular dynamics and ab-initio total energy methods. Due to boron-nitride BN bond buckling effects, compressed zigzag BN nanotubes are found to undergo novel anisotropic strain release followed by anisotropic plastic buckling. The strain is preferentially released towards N atoms in the rotated BN bonds. The tubes buckle anisotropically towards only one end when uniaxially compressed from both. A "skin-effect" model of smart nanocomposite materials is proposed which will localize the structural damage towards the 'skin' or surface side of the material.
Luminescence decay of porous silicon
NASA Astrophysics Data System (ADS)
Chen, X.; Uttamchandani, D.; Sander, D.; O'Donnell, K. P.
1993-04-01
The luminescence decay pattern of porous silicon samples prepared by electrochemical etching is characterised experimentally by a non-exponential profile, a strong dependence on temperature and an absence of spectral diffusion. We describe this luminescence as carrier-dopping-assisted recombination. Following the correlation function approach to non-dispersive transport developed by Scher and co-workers [Physics Today 41 (1991) 26], we suggest a simple derivation of analytical functions which accurately describes the anomalous luminescence decay of porous silicon, and show that this model includes exponential and Kohlrausch [Pogg. Ann. Phys. 119 (1863) 352] (stretched-exponential) relaxations as special cases.
Metal recovery from porous materials
Sturcken, Edward F.
1992-01-01
A method for recovering plutonium and other metals from materials by leaching comprising the steps of incinerating the materials to form a porous matrix as the residue of incineration, immersing the matrix into acid in a microwave-transparent pressure vessel, sealing the pressure vessel, and applying microwaves so that the temperature and the pressure in the pressure vessel increase. The acid for recovering plutonium can be a mixture of HBF.sub.4 and HNO.sub.3 and preferably the pressure is increased to at least 100 PSI and the temperature to at least 200.degree. C. The porous material can be pulverized before immersion to further increase the leach rate.
Process of preparing tritiated porous silicon
Tam, S.W.
1997-02-18
A process of preparing tritiated porous silicon is described in which porous silicon is equilibrated with a gaseous vapor containing HT/T{sub 2} gas in a diluent for a time sufficient for tritium in the gas phase to replace hydrogen present in the pore surfaces of the porous silicon. 1 fig.
Anisotropic nature of radially strained metal tubes
NASA Astrophysics Data System (ADS)
Strickland, Julie N.
Metal pipes are sometimes swaged by a metal cone to enlarge them, which increases the strain in the material. The amount of strain is important because it affects the burst and collapse strength. Burst strength is the amount of internal pressure that a pipe can withstand before failure, while collapse strength is the amount of external pressure that a pipe can withstand before failure. If the burst or collapse strengths are exceeded, the pipe may fracture, causing critical failure. Such an event could cost the owners and their customers millions of dollars in clean up, repair, and lost time, in addition to the potential environmental damage. Therefore, a reliable way of estimating the burst and collapse strength of strained pipe is desired and valuable. The sponsor currently rates strained pipes using the properties of raw steel, because those properties are easily measured (for example, yield strength). In the past, the engineers assumed that the metal would be work-hardened when swaged, so that yield strength would increase. However, swaging introduces anisotropic strain, which may decrease the yield strength. This study measured the yield strength of strained material in the transverse and axial direction and compared them to raw material, to determine the amount of anisotropy. This information will be used to more accurately determine burst and collapse ratings for strained pipes. More accurate ratings mean safer products, which will minimize risk for the sponsor's customers. Since the strained metal has a higher yield strength than the raw material, using the raw yield strength to calculate burst and collapse ratings is a conservative method. The metal has even higher yield strength after strain aging, which indicates that the stresses are relieved. Even with the 12% anisotropy in the strained and 9% anisotropy in the strain aged specimens, the raw yield strengths are lower and therefore more conservative. I recommend that the sponsor continue using the raw
Fabrication of anisotropic multifunctional colloidal carriers
NASA Astrophysics Data System (ADS)
Jerri, Huda A.
The field of colloidal assembly has grown tremendously in recent years, although the direct or template-assisted methods used to fabricate complex colloidal constructions from monodisperse micro- and nanoparticles have been generally demonstrated on model materials. In this work, novel core particle syntheses, particle functionalizations and bottom-up assembly techniques are presented to create functional colloidal devices. Using particle lithography, high-information colloidal vectors have been developed and modified with imaging and targeting agents. Localized nanoscale patches have been reliably positioned on microparticles to serve as foundations for further chemical or physical modifications. Site-specific placement of RGD targeting ligands has been achieved in these lithographed patches. Preferential uptake of these targeted vectors by RGD-specific 3T3 fibroblasts was verified using confocal laser scanning microscopy. A transition was made from the functionalization of model imaging core particles to the lithography of colloidal cartridges, in an effort to construct colloidal syringes with specialized, programmable release profiles. A variety of functional, pH-sensitive fluorescent cores were engineered to respond to solution conditions. When triggered, the diverse composite core microparticles and reservoir microcapsules released embedded fluorescent moieties such as dye molecules, and fluorophore-conjugated nanoparticles. The microcapsules, created using layer-by-layer polyelectrolyte deposition on sacrificial templates, were selectively modified with a robust coating. The pH-responsive anisotropic reservoir microcapsules were extremely stable in solution, and exhibited a "Lazarus" functionality of rehydrating to their original state following desiccation. A snapshot of focused-release of core constituents through the lone opening in colloidal monotremes has been obtained by anisotropically-functionalizing degradable cores with barrier shells. Additionally
Borehole Deformation and Failure in Anisotropic Media
NASA Astrophysics Data System (ADS)
Gaede, Oliver; Regenauer-Lieb, Klaus; Lumley, David
2010-05-01
Borehole breakouts develop due to compressive shear failure along the borehole wall and subsequent spalling of near wellbore rock. These compressive shear failures can occur during drilling and lead to a borehole enlargement in the direction of the minimum horizontal stress. In order to investigate the initiation of borehole breakouts in anisotropic media a numerical analysis of the borehole deformation has been performed. The numerical model is based on an extensive geophysical and geomechanical dataset, provided by BHP Billiton Petroleum. This dataset was established during the development and production phase of an oil reservoir on the North West Shelf, Western Australia. The aim of this study is to estimate the severity of the influence of anisotropy on the breakout process. It is proposed that there is a hierarchy among the possible influences on the breakout process: 1. The regional stress field has a first order effect on the borehole breakout direction. 2. This is followed by a preferential fracture direction or anisotropic failure criterion of the medium. 3. And finally the elastic anisotropy of the medium affecting the local stress field around the borehole. A clear separation of these influences through methods of observation is not always trivial. Firstly, the preferential fracture direction and the elastic anisotropy, at least to some degree, are functions of the regional stress field. Secondly, most of the knowledge we have about the regional stress field in relatively aseismic regions is inferred from borehole breakout data. Therefore a numerical simulation is chosen as a method of study. Material properties like elastic anisotropy or failure criterion and even their dependency on the stress field can easily be manipulated. This geophysical and geomechanical data is used to populate the numerical model. The regional stress field is implemented as a boundary condition. The commercial Finite Element package ABAQUS is used to obtain the stress / strain
Anisotropic ionic conductivities in lyotropic supramolecular liquid crystals.
Huang, Youju; Cong, Yuanhua; Li, Junjun; Wang, Daoliang; Zhang, Jingtuo; Xu, Lu; Li, Weili; Li, Liangbin; Pan, Guoqiang; Yang, Chuanlu
2009-12-28
The designed aromatic amide discotic molecule with sulfonic acid groups at its periphery exhibits a hexagonal supramolecular columnar liquid crystalline phase, which leads to the achievement of anisotropic ionic conductivity through macroscopically aligning the ionic channels.
Anisotropic stress and stability in modified gravity models
Saltas, Ippocratis D.; Kunz, Martin
2011-03-15
The existence of anisotropic stress of a purely geometrical origin seems to be a characteristic of higher order gravity models, and has been suggested as a probe to test these models observationally, for example, in weak lensing experiments. In this paper, we seek to find a class of higher order gravity models of f(R,G) type that would give us a zero anisotropic stress and study the consequences for the viability of the actual model. For the special case of a de Sitter background, we identify a subclass of models with the desired property. We also find a direct link between anisotropic stress and the stability of the model as well as the presence of extra degrees of freedom, which seems to be a general feature of higher order gravity models. Particularly, setting the anisotropic stress equal to zero for a de Sitter background leads to a singularity that makes it impossible to reach the de Sitter evolution.
Autofocus imaging: Experimental results in an anisotropic austenitic weld
NASA Astrophysics Data System (ADS)
Zhang, J.; Drinkwater, B. W.; Wilcox, P. D.; Hunter, A.
2012-05-01
The quality of an ultrasonic array image, especially for anisotropic material, depends on accurate information about acoustic properties. Inaccuracy of acoustic properties causes image degradation, e.g., blurring, errors in locating of reflectors and introduction of artifacts. In this paper, for an anisotropic austenitic steel weld, an autofocus imaging technique is presented. The array data from a series of beacons is captured and then used to statistically extract anisotropic weld properties by using a Monte-Carlo inversion approach. The beacon and imaging systems are realized using two separated arrays; one acts as a series of beacons and the other images these beacons. Key to the Monte-Carlo inversion scheme is a fast forward model of wave propagation in the anisotropic weld and this is based on the Dijkstra algorithm. Using this autofocus approach a measured weld map was extracted from an austenitic weld and used to reduce location errors, initially greater than 6mm, to less than 1mm.
An engineered anisotropic nanofilm with unidirectional wetting properties
NASA Astrophysics Data System (ADS)
Malvadkar, Niranjan A.; Hancock, Matthew J.; Sekeroglu, Koray; Dressick, Walter J.; Demirel, Melik C.
2010-12-01
Anisotropic textured surfaces allow water striders to walk on water, butterflies to shed water from their wings and plants to trap insects and pollen. Capturing these natural features in biomimetic surfaces is an active area of research. Here, we report an engineered nanofilm, composed of an array of poly(p-xylylene) nanorods, which demonstrates anisotropic wetting behaviour by means of a pin-release droplet ratchet mechanism. Droplet retention forces in the pin and release directions differ by up to 80μN, which is over ten times greater than the values reported for other engineered anisotropic surfaces. The nanofilm provides a microscale smooth surface on which to transport microlitre droplets, and is also relatively easy to synthesize by a bottom-up vapour-phase technique. An accompanying comprehensive model successfully describes the film's anisotropic wetting behaviour as a function of measurable film morphology parameters.
Reaction profiles in porous electrodes
NASA Astrophysics Data System (ADS)
Katan, T.; Carlen, P. J.
1985-05-01
An experimental program was conducted to ascertain causes of alkaline zinc electrode shape change and to determine the development of reaction profiles within the pores of porous zinc electrodes. Various analog electrochemical cells were operated to isolate and evaluate the individual processes occurring during charge and discharge. It was found that both edge effects and osmosis can be responsible for the shape change phenomenon.
Basser, Peter J.
2008-12-05
The fields of MR in Porous Media and Neuroradiology have largely developed separately during the past two decades with little appreciation of the problems, challenges and methodologies of the other. However, this trend is clearly changing and possibilities for significant cross-fertilization and synergies are now being realized.
Whey drying on porous carriers
Mitura, E.; Kaminski, W.
1996-05-01
Whey is treated very often as a waste which pollutes the natural environment. Whey which is a valuable source of protein, lacrose, vitamins and mineral salts should be utilized completely. The present paper is a proposal of whey drying on porous carriers. It is proved experimentally that the proposed drying method guarantees good product quality.
Metal recovery from porous materials
Sturcken, E.F.
1991-01-01
The present invention relates to recovery of metals. More specifically, the present invention relates to the recovery of plutonium and other metals from porous materials using microwaves. The United States Government has rights in this invention pursuant to Contract No. DE-AC09-89SR18035 between the US Department of Energy and Westinghouse Savannah River Company.
Schwarz alternating methods for anisotropic problems with prolate spheroid boundaries.
Dai, Zhenlong; Du, Qikui; Liu, Baoqing
2016-01-01
The Schwarz alternating algorithm, which is based on natural boundary element method, is constructed for solving the exterior anisotropic problem in the three-dimension domain. The anisotropic problem is transformed into harmonic problem by using the coordinate transformation. Correspondingly, the algorithm is also changed. Continually, we analysis the convergence and the error estimate of the algorithm. Meanwhile, we give the contraction factor for the convergence. Finally, some numerical examples are computed to show the efficiency of this algorithm.
On the electrodynamics of Josephson effect in anisotropic superconductors
Mints, R.G.
1989-01-01
Specificities of Josephson effect electrodynamics in anisotropic superconductors are of considerable interest for the study of high temperature superconductors with strongly anisotropic layered structure. In this paper the authors give the calculation for the tunnel Josephson contact of an isolated vortex, the law of dispersion of its low-amplitude oscillations, the critical field H/sub cl/ for the penetration of magnetic flux, and the maximum current across a rectangular contact.
Anisotropic Bianchi types VIII and IX locally rotationally symmetric cosmologies
Assad, M.J.D.; Soares, I.D.
1983-10-15
We present a class of exact cosmological solutions of Einstein-Maxwell equations, which are anisotropic and spatially homogeneous of Bianchi types VIII and IX, and class IIIb in the Stewart-Ellis classification of locally rotationally symmetric models. If we take the electromagnetic field equal to zero, a class of Bianchi types VIII/IX spatially homogeneous anisotropic cosmological solutions with perfect fluid is obtained.
NASA Astrophysics Data System (ADS)
Wen, Baole
Buoyancy-driven convection in fluid-saturated porous media is a key environmental and technological process, with applications ranging from carbon dioxide storage in terrestrial aquifers to the design of compact heat exchangers. Porous medium convection is also a paradigm for forced-dissipative infinite-dimensional dynamical systems, exhibiting spatiotemporally chaotic dynamics if not "true" turbulence. The objective of this dissertation research is to quantitatively characterize the dynamics and heat transport in two-dimensional horizontal and inclined porous medium convection between isothermal plane parallel boundaries at asymptotically large values of the Rayleigh number Ra by investigating the emergent, quasi-coherent flow. This investigation employs a complement of direct numerical simulations (DNS), secondary stability and dynamical systems theory, and variational analysis. The DNS confirm the remarkable tendency for the interior flow to self-organize into closely-spaced columnar plumes at sufficiently large Ra (up to Ra ≃ 105), with more complex spatiotemporal features being confined to boundary layers near the heated and cooled walls. The relatively simple form of the interior flow motivates investigation of unstable steady and time-periodic convective states at large Ra as a function of the domain aspect ratio L. To gain insight into the development of spatiotemporally chaotic convection, the (secondary) stability of these fully nonlinear states to small-amplitude disturbances is investigated using a spatial Floquet analysis. The results indicate that there exist two distinct modes of instability at large Ra: a bulk instability mode and a wall instability mode. The former usually is excited by long-wavelength disturbances and is generally much weaker than the latter. DNS, strategically initialized to investigate the fully nonlinear evolution of the most dangerous secondary instability modes, suggest that the (long time) mean inter-plume spacing in
Enhanced Raman Scattering on In-plane Anisotropic Layered Materials
Liang, Liangbo; Meunier, Vincent; Sumpter, Bobby G.; ...
2015-11-19
Surface-enhanced Raman scattering (SERS) on two-dimensional (2D) layered materials has provided a unique platform to study the chemical mechanism (CM) of the enhancement due to its natural separation from electromagnetic enhancement. The CM stems from the basic charge interactions between the substrate and molecules. Despite the extensive studies of the energy alignment between 2D materials and molecules, an understanding of how the electronic properties of the substrate are explicitly involved in the charge interaction is still unclear. Lately, a new group of 2D layered materials with anisotropic structure, including orthorhombic black phosphorus (BP) and triclinic rhenium disulphide (ReS2), has attractedmore » great interest due to their unique anisotropic electrical and optical properties. Herein, we report a unique anisotropic Raman enhancement on few-layered BP and ReS2 using copper phthalocyanine (CuPc) molecules as a Raman probe, which is absent on isotropic graphene and h-BN. According to detailed Raman tensor analysis and density functional theory calculations, anisotropic charge interactions due to the anisotropic carrier mobilities of the 2D materials are responsible for the angular dependence of the Raman enhancement. Our findings not only provide new insights into the CM process in SERS, but also open up new avenues for the exploration and application of the electronic properties of anisotropic 2D layered materials.« less
Enhanced Raman Scattering on In-plane Anisotropic Layered Materials
Liang, Liangbo; Meunier, Vincent; Sumpter, Bobby G.; Ling, Xi; Lin, Jingjing; Zhang, Shuqing; Mao, Nannan; Zhang, Na; Tong, Lianming; Zhang, Jin
2015-11-19
Surface-enhanced Raman scattering (SERS) on two-dimensional (2D) layered materials has provided a unique platform to study the chemical mechanism (CM) of the enhancement due to its natural separation from electromagnetic enhancement. The CM stems from the basic charge interactions between the substrate and molecules. Despite the extensive studies of the energy alignment between 2D materials and molecules, an understanding of how the electronic properties of the substrate are explicitly involved in the charge interaction is still unclear. Lately, a new group of 2D layered materials with anisotropic structure, including orthorhombic black phosphorus (BP) and triclinic rhenium disulphide (ReS2), has attracted great interest due to their unique anisotropic electrical and optical properties. Herein, we report a unique anisotropic Raman enhancement on few-layered BP and ReS2 using copper phthalocyanine (CuPc) molecules as a Raman probe, which is absent on isotropic graphene and h-BN. According to detailed Raman tensor analysis and density functional theory calculations, anisotropic charge interactions due to the anisotropic carrier mobilities of the 2D materials are responsible for the angular dependence of the Raman enhancement. Our findings not only provide new insights into the CM process in SERS, but also open up new avenues for the exploration and application of the electronic properties of anisotropic 2D layered materials.
Production and characterization of anisotropic particles from biodegradable materials.
Romanski, Francis S; Winkler, Jennifer S; Riccobene, Ryan C; Tomassone, M Silvina
2012-02-28
In recent years, production and characterization of anisotropic particles has become of interest in a wide range of scientific fields including polymer chemistry, drug delivery, electronics, energy, and nanotechnology. In this work, we demonstrate a novel formulation for production of anisotropic particles via an internal phase separation of biodegradable components. Specifically, binary mixtures of biodegradable polymers poly(lactic-co-glycolic acid), polycaprolactone, and biodegradable lipid Precirol (glyceryl palmitostearate) were dissolved in dichloromethane, emulsified, and prepared into anisotropic particles using a modified solvent evaporation technique. During the slow evaporation process the components self-assembled into anisotropic particles with distinct morphologies. Polymer/polymer formulations resulted in compartmentalized anisotropic heterodimer particles, while polymer/lipid combinations yielded "ice cream cone" shaped particles. It was found that addition of certain active pharmaceuticals resulted in an altered, pox-like segregation at the particle surface of polymer/polymer formulations. The anisotropic nature of the particles was subsequently characterized using optical microscopy, scanning electron microscopy, zeta potential, electrophoresis, and X-ray diffraction. Successful formulations presented here may potentially be employed as multicompartmental drug carriers with staggered drug release rates or alternatively as a colloidal excipient for an arsenal of pharmaceutical applications.
Cosmic anisotropic doomsday in Bianchi type I universes
NASA Astrophysics Data System (ADS)
Cataldo, Mauricio; Cid, Antonella; Labraña, Pedro; Mella, Patricio
2016-11-01
In this paper we study finite time future singularities in anisotropic Bianchi type I models. It is shown that there exist future singularities similar to Big Rip ones (which appear in the framework of phantom Friedmann-Robertson-Walker cosmologies). Specifically, in an ellipsoidal anisotropic scenario or in a fully anisotropic scenario, the three directional and average scale factors may diverge at a finite future time, together with energy densities and anisotropic pressures. We call these singularities "Anisotropic Big Rip Singularities." We show that there also exist Bianchi type I models filled with matter, where one or two directional scale factors may diverge. Another type of future anisotropic singularities is shown to be present in vacuum cosmologies, i.e., Kasner spacetimes. These singularities are induced by the shear scalar, which also blows up at a finite time. We call such a singularity "Vacuum Rip." In this case one directional scale factor blows up, while the other two and average scale factors tend to zero.
Anisotropic emission of neutral atoms: evidence of an anisotropic Rydberg sheath in nanoplasma
NASA Astrophysics Data System (ADS)
Rajeev, R.; Madhu Trivikram, T.; Rishad, K. P. M.; Krishnamurthy, M.
2015-02-01
Intense laser-produced plasma is a complex amalgam of ions, electrons and atoms both in ground and excited states. Little is known about the spatial composition of the excited states that are an integral part of most gaseous or cluster plasma. In cluster-plasma, Rydberg excitations change the charge composition of the ions through charge transfer reactions and shape the angular distributions. Here, we demonstrate a non-invasive technique that reveals the anisotropic Rydberg excited cluster sheath by measuring anisotropy in fast neutral atoms. The sheath is stronger in the direction of light polarization and the enhanced charge transfer by the excited clusters results in larger neutralization.
Anisotropic reflectance from turbid media. I. Theory.
Neuman, Magnus; Edström, Per
2010-05-01
It is shown that the intensity of light reflected from plane-parallel turbid media is anisotropic in all situations encountered in practice. The anisotropy, in the form of higher intensity at large polar angles, increases when the amount of near-surface bulk scattering is increased, which dominates in optically thin and highly absorbing media. The only situation with isotropic intensity is when a non-absorbing infinitely thick medium is illuminated diffusely. This is the only case where the Kubelka-Munk model gives exact results and there exists an exact translation between Kubelka-Munk and general radiative transfer. This also means that a bulk scattering perfect diffusor does not exist. Angle-resolved models are thus crucial for a correct understanding of light scattering in turbid media. The results are derived using simulations and analytical calculations. It is also shown that there exists an optimal angle for directional detection that minimizes the error introduced when using the Kubelka-Munk model to interpret reflectance measurements with diffuse illumination.
Entanglement in the Anisotropic Kondo Necklace Model
NASA Astrophysics Data System (ADS)
Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.
We study the entanglement in the one-dimensional Kondo necklace model with exact diagonalization, calculating the concurrence as a function of the Kondo coupling J and an anisotropy η in the interaction between conduction spins, and we review some results previously obtained in the limiting cases η = 0 and 1. We observe that as J increases, localized and conduction spins get more entangled, while neighboring conduction spins diminish their concurrence; localized spins require a minimum concurrence between conduction spins to be entangled. The anisotropy η diminishes the entanglement for neighboring spins when it increases, driving the system to the Ising limit η = 1 where conduction spins are not entangled. We observe that the concurrence does not give information about the quantum phase transition in the anisotropic Kondo necklace model (between a Kondo singlet and an antiferromagnetic state), but calculating the von Neumann block entropy with the density matrix renormalization group in a chain of 100 sites for the Ising limit indicates that this quantity is useful for locating the quantum critical point.
Discrete solitons and vortices on anisotropic lattices.
Kevrekidis, P G; Frantzeskakis, D J; Carretero-González, R; Malomed, B A; Bishop, A R
2005-10-01
We consider the effects of anisotropy on solitons of various types in two-dimensional nonlinear lattices, using the discrete nonlinear Schrödinger equation as a paradigm model. For fundamental solitons, we develop a variational approximation that predicts that broad quasicontinuum solitons are unstable, while their strongly anisotropic counterparts are stable. By means of numerical methods, it is found that, in the general case, the fundamental solitons and simplest on-site-centered vortex solitons ("vortex crosses") feature enhanced or reduced stability areas, depending on the strength of the anisotropy. More surprising is the effect of anisotropy on the so-called "super-symmetric" intersite-centered vortices ("vortex squares"), with the topological charge equal to the square's size : we predict in an analytical form by means of the Lyapunov-Schmidt theory, and confirm by numerical results, that arbitrarily weak anisotropy results in dramatic changes in the stability and dynamics in comparison with the degenerate, in this case, isotropic, limit.
Zonal flows in tokamaks with anisotropic pressure
Ren, Haijun
2014-04-15
Zonal flows (ZFs) in a tokamak plasma with anisotropic pressure are investigated. The dynamics of perpendicular and parallel pressures are determined by the Chew-Goldberger-Low double equations and low-β condition is adopted, where β is the ratio of plasma pressure to the magnetic field pressure. The dispersion relation is analytically derived and illustrates two branches of ZFs. The low frequency zonal flow (LFZF) branch becomes unstable when χ, the ratio of the perpendicular pressure to the parallel one, is greater than a threshold value χ{sub c}, which is about 3.8. In the stable region, its frequency increases first and then decreases with increasing χ. For χ = 1, the frequency of LFZF agrees well with the experimental observation. For the instability, the growth rate of LFZF increases with χ. The geodesic acoustic mode branch is shown to be always stable with a frequency increasing with χ. The safety factor is shown to diminish the frequencies of both branches or the growth rate of LFZF.
Thermoelectric Figure of Merit in Anisotropic Systems
NASA Astrophysics Data System (ADS)
Bies, W.; Radtke, R. J.; Ehrenreich, H.
1998-03-01
General expressions for the electrical conductivity, thermopower, and electronic thermal conductivity are derived for anisotropic materials including their full tensorial character and properly treating the effects of the sample boundaries. The thermoelectric figure of merit ZT constructed from these quantities is proved to be maximal only when the electric field (in thermoelectric coolers) or thermal gradient (in power generators) is applied along the direction of highest conductivity. Fields applied along directions for which the conductivity tensor is non-diagonal induce transverse electric fields and thermal gradients which may be larger in magnitude than the applied fields. These fields reduce ZT below that expected from anisotropy alone. Numerical results are presented for bulk n-type Bi_2Te3 and quantum well and quantum wire geometries using semiclassical transport theory in the effective mass and relaxation time approximations. The effects of multi-valley conduction and confinement-induced splitting of the valley degeneracy are included. Surprisingly, this model predicts generally that the thermopower and hence ZT are independent of the direction of the applied fields in the limit of vanishing lattice thermal conductivity.
Polar motion under anisotropic random load
NASA Astrophysics Data System (ADS)
Tsurkis, I. Ya.; Kuchai, M. S.; Sinyukhina, S. V.
2014-01-01
The probabilistic approach to the description of the Chandler wobble is expanded to the case of anisotropic random load. The polar motion is treated as a two-dimensional (2D) Markov process—the solution of the Liouville equation—with discrete time. It is shown that with a sufficiently large time step Δ, the polar motion can be considered as an isotropic process irrespective of the particular ratio between the eigenvalues of the diffusion matrix, which characterizes the right-hand side of this equation (random load). The problem of reaching the boundary of the domain [ E min, E max] by the energy of the pole E( t) = x {1/2}+ x {2/2} is considered. With a time step Δ of 1 year and the length of the time series of the observations N = 150, the correction for anisotropy to the total probability P* of a drop by a factor of five in the amplitude of the Chandler wobble A = √ E does not exceed 10-2, and the probability P* is above 0.3 (if the Q-factor of the mantle is below 500). Thus, it is demonstrated that the observed variations in amplitude A( t) can be explained in the context of the probabilistic approach without hypothesizing the isotropy of the random load.
Details of tetrahedral anisotropic mesh adaptation
NASA Astrophysics Data System (ADS)
Jensen, Kristian Ejlebjerg; Gorman, Gerard
2016-04-01
We have implemented tetrahedral anisotropic mesh adaptation using the local operations of coarsening, swapping, refinement and smoothing in MATLAB without the use of any for- N loops, i.e. the script is fully vectorised. In the process of doing so, we have made three observations related to details of the implementation: 1. restricting refinement to a single edge split per element not only simplifies the code, it also improves mesh quality, 2. face to edge swapping is unnecessary, and 3. optimising for the Vassilevski functional tends to give a little higher value for the mean condition number functional than optimising for the condition number functional directly. These observations have been made for a uniform and a radial shock metric field, both starting from a structured mesh in a cube. Finally, we compare two coarsening techniques and demonstrate the importance of applying smoothing in the mesh adaptation loop. The results pertain to a unit cube geometry, but we also show the effect of corners and edges by applying the implementation in a spherical geometry.
Zonal flows in tokamaks with anisotropic pressure
NASA Astrophysics Data System (ADS)
Ren, Haijun
2014-04-01
Zonal flows (ZFs) in a tokamak plasma with anisotropic pressure are investigated. The dynamics of perpendicular and parallel pressures are determined by the Chew-Goldberger-Low double equations and low-β condition is adopted, where β is the ratio of plasma pressure to the magnetic field pressure. The dispersion relation is analytically derived and illustrates two branches of ZFs. The low frequency zonal flow (LFZF) branch becomes unstable when χ, the ratio of the perpendicular pressure to the parallel one, is greater than a threshold value χc, which is about 3.8. In the stable region, its frequency increases first and then decreases with increasing χ. For χ = 1, the frequency of LFZF agrees well with the experimental observation. For the instability, the growth rate of LFZF increases with χ. The geodesic acoustic mode branch is shown to be always stable with a frequency increasing with χ. The safety factor is shown to diminish the frequencies of both branches or the growth rate of LFZF.
Singularity-free anisotropic strange quintessence star
NASA Astrophysics Data System (ADS)
Bhar, Piyali
2015-04-01
Present paper provides a new model of anisotropic strange star corresponding to the exterior Schwarzschild metric. The Einstein field equations have been solved by utilizing the Krori-Barua (KB) ansatz (Krori and Barua in J. Phys. A, Math. Gen. 8:508, 1975) in presence of quintessence field characterized by a parameter ω q with . The obtained solutions are free from central singularity. Our model is potentially stable. The numerical values of mass of the different strange stars SAXJ1808.4-3658(SS1) (radius=7.07 km), 4U1820-30 (radius=10 km), Vela X-12 (radius=9.99 km), PSR J 1614-2230 (radius=10.3 km) obtained from our model is very close to the observational data that confirms the validity of our proposed model. The interior solution is also matched to the exterior Schwarzschild spacetime in presence of thin shell where negative surface pressure is required to hold the thin shell against collapsing.
Colloidal aggregation and dynamics in anisotropic fluids
Mondiot, Frédéric; Botet, Robert; Snabre, Patrick; Mondain-Monval, Olivier; Loudet, Jean-Christophe
2014-01-01
We present experiments and numerical simulations to investigate the collective behavior of submicrometer-sized particles immersed in a nematic micellar solution. We use latex spheres with diameters ranging from 190 to 780 nm and study their aggregation properties due to the interplay of the various colloidal forces at work in the system. We found that the morphology of aggregates strongly depends on the particle size, with evidence for two distinct regimes: the biggest inclusions clump together within minutes into either compact clusters or V-like structures that are completely consistent with attractive elastic interactions. On the contrary, the smallest particles form chains elongated along the nematic axis, within comparable timescales. In this regime, Monte Carlo simulations, based on a modified diffusion-limited cluster aggregation model, strongly suggest that the anisotropic rotational Brownian motion of the clusters combined with short-range depletion interactions dominate the system coarsening; elastic interactions no longer prevail. The simulations reproduce the sharp transition between the two regimes on increasing the particle size. We provide reasonable estimates to interpret our data and propose a likely scenario for colloidal aggregation. These results emphasize the growing importance of the diffusion of species at suboptical-wavelength scales and raise a number of fundamental issues. PMID:24715727
Anisotropic lattice distortions in biogenic aragonite
NASA Astrophysics Data System (ADS)
Pokroy, Boaz; Quintana, John P.; Caspi, El'ad N.; Berner, Alex; Zolotoyabko, Emil
2004-12-01
Composite biogenic materials produced by organisms have a complicated design on a nanometre scale. An outstanding example of organic-inorganic composites is provided by mollusc seashells, whose superior mechanical properties are due to their multi-level crystalline hierarchy and the presence of a small amount (0.1-5 wt%) of organic molecules. The presence of organic molecules, among other characteristics, can influence the coherence length for X-ray scattering in biogenic crystals. Here we show the results of synchrotron high-resolution X-ray powder diffraction measurements in biogenic and non-biogenic (geological) aragonite crystals. On applying the Rietveld refinement procedure to the high-resolution diffraction spectra, we were able to extract the aragonite lattice parameters with an accuracy of 10 p.p.m. As a result, we found anisotropic lattice distortions in biogenic aragonite relative to the geological sample, maximum distortion being 0.1% along the c axis of the orthorhombic unit cell. The organic molecules could be a source of these structural distortions in biogenic crystals. This finding may be important to the general understanding of the biomineralization process and the development of bio-inspired 'smart' materials.
Anisotropic damage effects in masonry walls
NASA Astrophysics Data System (ADS)
Massart, T.; Bouillard, P.; Geers, M. G. D.; Peerlings, R. H. J.
2003-03-01
This paper refers to the characterization of plane masonry behaviour under the assumption of plane stress. Masonry may be seen as a two-phase (bricks and mortar) periodic anisotropic material with complex macroscopic behaviour due to the possible occurrence of cracking in each of the phases. Non-linear constitutive equations have thus to be used in order to realistically represent masonry structures. Most existing macroscopic models defined for such materials are by essence phenomenological. This leads to weakly motivated frameworks and rather complex models, especially if one wants to account for material symmetry evolution due to cracking. The aim of this paper is to identify a simple set of damage mechanics variables for the constituents that could be used in homogenization procedures to infer the overall behaviour of the material from its mesostructural features (geometrical arrangement and mechanical properties of the constituents). Based on unit cell computations, it is shown that scalar damage mesomodels allow to obtain realistic damage patterns encountered in experiments. Results suggest that at the meso-scale, it is possible to use a scalar damage model for the individual phases which naturally leads to the desired anisotropy evolution into the macroscopic descriptions. This macroscopic anisotropy evolution is illustrated using a numerical homogenization procedure to identify the degraded stiffness associated to damage patterns. The influence of variations in the constituent characteristics is also correctly captured as illustrated for some of the loading schemes.
Porous silicon carbide (SIC) semiconductor device
NASA Technical Reports Server (NTRS)
Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)
1996-01-01
Porous silicon carbide is fabricated according to techniques which result in a significant portion of nanocrystallites within the material in a sub 10 nanometer regime. There is described techniques for passivating porous silicon carbide which result in the fabrication of optoelectronic devices which exhibit brighter blue luminescence and exhibit improved qualities. Based on certain of the techniques described porous silicon carbide is used as a sacrificial layer for the patterning of silicon carbide. Porous silicon carbide is then removed from the bulk substrate by oxidation and other methods. The techniques described employ a two-step process which is used to pattern bulk silicon carbide where selected areas of the wafer are then made porous and then the porous layer is subsequently removed. The process to form porous silicon carbide exhibits dopant selectivity and a two-step etching procedure is implemented for silicon carbide multilayers.
NASA Astrophysics Data System (ADS)
Maity, Narottam; Barik, S. P.; Chaudhuri, P. K.
2016-09-01
In this paper, plane wave propagation in a rotating anisotropic material of general nature under the action of a magnetic field of constant magnitude has been investigated. The material is supposed to be porous in nature and contains voids. Following the concept of [Cowin S. C. and Nunziato, J. W. [1983] “Linear elastic materials with voids,” J. Elasticity 13, 125-147.] the governing equations of motion have been written in tensor notation taking account of rotation, magnetic field effect and presence of voids in the medium and the possibility of plane wave propagation has been examined. A number of particular cases have been derived from our general results to match with previously obtained results in this area. Effects of various parameters on the velocity of wave propagation have been presented graphically.
The Interaction of Sound and Shock Waves with Flexible Porous Materials
NASA Astrophysics Data System (ADS)
Abbott, James Fuller
Several topics are studied which illustrate the role of flexibility in determining the acoustical properties of flexible porous materials. A power balance relation is obtained for the flexible porous material which explicitly identifies two loss mechanisms for sound absorption: the losses due to the irreversible deformation of the structure, and those attributed to the viscous drag between the fluid and the structure. The finite flexible porous layer backed by a rigid wall is then considered. Irreversible deformation of the structure is shown to be the dominant loss mechanism for closed layers. Three departures from the basic model-- a porous layer with anisotropic flow resistance and structure factor, periodic structures consisting of porous layers separated by air gaps, and the porous medium in bulk with mean fluid flow--are considered. The reflection of shock waves is also studied, and a quasi-linear theory is developed which reproduces the principal features of experimental results obtained previously by Ingard. The theory assumes that the propagating pulses in the air and structure are linear and the gross, zeroth order motion of the porous layer is modeled by including its energy and momentum in the conservation equations; these equations compare the system just before and just after the reflection of the incident shock from the front surface of the layer. The substantial motion of the layer and its dragging against a constraining boundary (in this case the walls of the shock tube) are found to introduce a dependence of the front reflection coefficient and maximal layer deformation on the peak pressure of the incident shock. Lastly, we address the question of measurement of the complex compressibility K, a key parameter used to describe the dynamics of a given flexible porous material. The standard long-wavelength assumption used to determine K from experimental measurements of the frequency dependent velocity transfer function across a sample is shown to
Advances in design and modeling of porous materials
NASA Astrophysics Data System (ADS)
Ayral, André; Calas-Etienne, Sylvie; Coasne, Benoit; Deratani, André; Evstratov, Alexis; Galarneau, Anne; Grande, Daniel; Hureau, Matthieu; Jobic, Hervé; Morlay, Catherine; Parmentier, Julien; Prelot, Bénédicte; Rossignol, Sylvie; Simon-Masseron, Angélique; Thibault-Starzyk, Frédéric
2015-07-01
This special issue of the European Physical Journal Special Topics is dedicated to selected papers from the symposium "High surface area porous and granular materials" organized in the frame of the conference "Matériaux 2014", held on November 24-28, 2014 in Montpellier, France. Porous materials and granular materials gather a wide variety of heterogeneous, isotropic or anisotropic media made of inorganic, organic or hybrid solid skeletons, with open or closed porosity, and pore sizes ranging from the centimeter scale to the sub-nanometer scale. Their technological and industrial applications cover numerous areas from building and civil engineering to microelectronics, including also metallurgy, chemistry, health, waste water and gas effluent treatment. Many emerging processes related to environmental protection and sustainable development also rely on this class of materials. Their functional properties are related to specific transfer mechanisms (matter, heat, radiation, electrical charge), to pore surface chemistry (exchange, adsorption, heterogeneous catalysis) and to retention inside confined volumes (storage, separation, exchange, controlled release). The development of innovative synthesis, shaping, characterization and modeling approaches enables the design of advanced materials with enhanced functional performance. The papers collected in this special issue offer a good overview of the state-of-the-art and science of these complex media. We would like to thank all the speakers and participants for their contribution to the success of the symposium. We also express our gratitude to the organization committee of "Matériaux 2014". We finally thank the reviewers and the staff of the European Physical Journal Special Topics who made the publication of this special issue possible.
Fingering instability and mixing of a blob in porous media
NASA Astrophysics Data System (ADS)
Pramanik, Satyajit; Mishra, Manoranjan
2016-10-01
The curvature of the unstable part of the miscible interface between a circular blob and the ambient fluid in two-dimensional homogeneous porous media depends on the viscosity of the fluids. The influence of the interface curvature on the fingering instability and mixing of a miscible blob within a rectilinear displacement is investigated numerically. The fluid velocity in porous media is governed by Darcy's law, coupled with a convection-diffusion equation that determines the evolution of the solute concentration controlling the viscosity of the fluids. Numerical simulations are performed using a Fourier pseudospectral method to determine the dynamics of a miscible blob (circular or square). It is shown that for a less viscous circular blob, there exist three different instability regions without any finite R -window for viscous fingering, unlike the case of a more viscous circular blob. Critical blob radius for the onset of instability is smaller for a less viscous blob as compared to its more viscous counterpart. Fingering enhances spreading and mixing of miscible fluids. Hence a less viscous blob mixes with the ambient fluid quicker than the more viscous one. Furthermore, we show that mixing increases with the viscosity contrast for a less viscous blob, while for a more viscous one mixing depends nonmonotonically on the viscosity contrast. For a more viscous blob mixing depends nonmonotonically on the dispersion anisotropy, while it decreases monotonically with the anisotropic dispersion coefficient for a less viscous blob. We also show that the dynamics of a more viscous square blob is qualitatively similar to that of a circular one, except the existence of the lump-shaped instability region in the R -Pe plane. We have shown that the Rayleigh-Taylor instability in a circular blob (heavier or lighter than the ambient fluid) is independent of the interface curvature.
Fracture Interface Waves in an Anisotropic Medium
NASA Astrophysics Data System (ADS)
Pyrak-Nolte, L. J.; Shao, S.; Abell, B.
2011-12-01
The detection of fractures in an anisotropic medium is complicated by discreet modes that are guided or confined by fractures and that travel with velocities close (~92%) to the shear wave velocity. For instance, fractures can mask the presence of textural anisotropy in a rock, and can increase the apparent shear wave velocity anisotropy. In this study, we examine how fracture interface waves affect the interpretation of shear wave velocities for two orthogonal polarizations propagating parallel to the layers. Samples with textural anisotropy measuring 100 x 100 x 100 mm were fabricated from garolite, an epoxy - cloth laminate, with layer thickness on the order of 0.5 mm. Three fracture samples were created with: (1) a fracture oriented parallel to layering, (2) a fracture oriented perpendicular to layering, and (3) two intersecting orthogonal fractures. An intact sample without fractures was used a standard. A seismic array, consisting of source and receiver arrays, was used to perform full waveform measurements. Each array contained two compressional and five shear wave piezoelectric contact transducers with a central frequency of 1 MHz. Shear wave transducers were polarized both perpendicular and parallel to the layering as well as to the fracture. Measurements were made for a range of stresses (0.4 - 4MPa). When the shear wave was polarized parallel to a fracture, the shear wave traveled at the bulk shear velocity respective to the layering. However, when the shear wave was polarized perpendicular to a fracture, the measured velocity ranged between the Rayleigh wave velocity at low stress and the bulk shear wave at high stress. The shear wave velocities perpendicular and parallel to the layering (propagation direction parallel to the layers) were ~1500 m/s and ~1600 m/s, respectively, in the intact sample. However, in the fractured samples, the observed shear wave anisotropy depended on the stress and fracture orientation relative to the layering. When the
Xu, He; Li, Haiyan; Ke, Qinfei; Chang, Jiang
2015-04-29
The development of vascular scaffolds with controlled mechanical properties and stimulatory effects on biological activities of endothelial cells still remains a significant challenge to vascular tissue engineering. In this work, we reported an innovative approach to prepare a new type of vascular scaffolds with anisotropically and heterogeneously aligned patterns using electrospinning technique with unique wire spring templates, and further investigated the structural effects of the patterned electrospun scaffolds on mechanical properties and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs). Results showed that anisotropically aligned patterned nanofibrous structure was obtained by depositing nanofibers on template in a structurally different manner, one part of nanofibers densely deposited on the embossments of wire spring and formed cylindrical-like structures in the transverse direction, while others loosely suspended and aligned along the longitudinal direction, forming a three-dimensional porous microstructure. We further found that such structures could efficiently control the mechanical properties of electrospun vascular scaffolds in both longitudinal and transverse directions by altering the interval distances between the embossments of patterned scaffolds. When HUVECs were cultured on scaffolds with different microstructures, the patterned scaffolds distinctively promoted adhesion of HUVECs at early stage and proliferation during the culture period. Most importantly, cells experienced a large shape change associated with cell cytoskeleton and nuclei remodeling, leading to a stimulatory effect on angiogenesis differentiation of HUVECs by the patterned microstructures of electrospun scaffolds, and the scaffolds with larger distances of intervals showed a higher stimulatory effect. These results suggest that electrospun scaffolds with the anisotropically and heterogeneously aligned patterns, which could efficiently control the
MOSSFRAC: An anisotropic 3D fracture model
Moss, W C; Levatin, J L
2006-08-14
Despite the intense effort for nearly half a century to construct detailed numerical models of plastic flow and plastic damage accumulation, models for describing fracture, an equally important damage mechanism still cannot describe basic fracture phenomena. Typical fracture models set the stress tensor to zero for tensile fracture and set the deviatoric stress tensor to zero for compressive fracture. One consequence is that the simple case of the tensile fracture of a cylinder under combined compressive radial and tensile axial loads is not modeled correctly. The experimental result is a cylinder that can support compressive radial loads, but no axial load, whereas, the typical numerical result is a cylinder with all stresses equal to zero. This incorrect modeling of fracture locally also has a global effect, because material that is fracturing produces stress release waves, which propagate from the fracture and influence the surrounding material. Consequently, it would be useful to have a model that can describe the stress relief and the resulting anisotropy due to fracture. MOSSFRAC is a material model that simulates three-dimensional tensile and shear fracture in initially isotropic elastic-plastic materials, although its framework is also amenable to initially anisotropic materials. It differs from other models by accounting for the effects of cracks on the constitutive response of the material, so that the previously described experiment, as well as complicated fracture scenarios are simulated more accurately. The model is implemented currently in the LLNL hydrocodes DYNA3D, PARADYN, and ALE3D. The purpose of this technical note is to present a complete qualitative description of the model and quantitative descriptions of salient features.
Seismic source theory in stratified anisotropic media
Ben-Menahem, A.; Sena, A.G.
1990-09-10
First, the authors obtain an explicit representation of the spectral elastodynamic Green`s tensor in general homogeneous anisotropic media as a sum of three integrals over the corresponding three slowness surfaces. The multidimensional stationary phase principle is then applied to derive an asymptotic approximation at the far field. In the case of azimuthally isotropic media, they offer an alternative representation of the Green`s tensor and its ensuing displacements fields in the form of an exact Hankel transform over the horizontal wave number variable. The total field is specified here in terms of two potentials: an SH potential and a mixed quasi-transverse/quasi-longitudinal potential, both of which assume the role of two scalar Green`s functions. The availability of the Green`s tensor in analytical form enables one to obtain readily numerical solutions for a wide selection of media and sources. It is shown that the radiation field of an explosion has the following new features: (1) Quasi-transverse waves are created with four and eight lobe patterns; (2) quasi-longitudinal waves are generated for the collatitudinal displacement with four lobe patterns; (3) the energy ratio SV/P may reach the value of 20 for more than 50% of the azimuths in crustal structures such as tuff and shales; and (4) radiation patterns for vertical shear waves are created which are indistinguishable from corresponding waves produced by earthquake faults. The formalism allows the authors to establish a Haskell-type matrix algorithm for a multilayered azimuthally isotropic half-space, which enables them to calculate body waves and surface waves in real-earth crustal models.
Anisotropic surface chemistry of crystalline pharmaceutical solids.
Heng, Jerry Y Y; Bismarck, Alexander; Williams, Daryl R
2006-10-06
The purpose of this study was to establish the link between the wetting behavior of crystalline pharmaceutical solids and the localized surface chemistry. A range of conventional wetting techniques were evaluated and compared with a novel experimental approach: sessile drop contact angle measurements on the individual facets of macroscopic (>1 cm) single crystals. Conventional measurement techniques for determining surface energetics such as capillary rise and sessile drops on powder compacts were found not to provide reliable results. When the macroscopic crystal approach was used, major differences for advancing contact angles, theta(a), of water were observed-as low as 16 degrees on facet (001) and as high as 68 degrees on facet (010) of form I paracetamol. theta(a) trends were in excellent agreement with X-ray photoelectron spectroscopy surface composition and known crystallographic structures, suggesting a direct relationship to the local surface chemistry. Inverse gas chromatography (IGC) was further used to probe the surface properties of milled and unmilled samples, as a function of particle size. IGC experiments confirmed that milling exposes the weakest attachment energy facet, with increasing dominance as particle size is reduced. The weakest attachment energy facet was also found to exhibit the highest theta(a) for water and to be the most hydrophobic facet. This anisotropic wetting behavior was established for a range of crystalline systems: paracetamol polymorphs, aspirin, and ibuprofen racemates. theta(a) was found to be very sensitive to the local surface chemistry. It is proposed that the hydrophilicity/hydrophobicity of facets reflects the presence of functional groups at surfaces to form hydrogen bonds with external molecules.
Resonant Ultrasound Spectroscopy of Anisotropic Shale Samples
NASA Astrophysics Data System (ADS)
Watson, L. M.; van Wijk, K.
2014-12-01
Resonant Ultrasound Spectroscopy (RUS) is a technique that can be used to determine the elastic properties of geological core samples. The resonant frequencies of the sample are measured and the elastic tensor inverted for by the non-linear Levenberg-Marquardt algorithm. It is a non-destructive method that allows the complete elastic tensor to be calculated from a single measurement and can provide important attenuation information. Many crustal rocks are anisotropic and can often be described by a hexagonal model of symmetry, where the sample has a single axis of rotational symmetry with perpendicular isotropic planes. Geological samples are often cylindrical and cut parallel or perpendicular to the layering (termed horizontal or vertical transverse isotropy respectively). The two situations cannot be treated by a single model and have substantially different resonant spectra. We have added functionality to existing forward and inverse codes to account for both situations. It is important to be able to deal with the two subsets of hexagonal symmetry because by using mutually perpendicular samples from the same rock complementary information can be obtained and more accurate results achieved than is possible with a single core. Shale formations consist of thin layered sequences of aligned microscopic clay platelets, which are responsible for the inherent anisotropy of shales, and can be described by a hexagonal symmetry model. RUS is used to determine the complete elastic tensor of two shale samples. When measured using RUS at frequencies on the order of 104 Hz and with time-of-flight methods with a dominant frequency an order of magnitude higher the elastic properties display frequency dispersion.
Metal recovery from porous materials
Sturcken, E.F.
1992-10-13
A method is described for recovering plutonium and other metals from materials by leaching comprising the steps of incinerating the materials to form a porous matrix as the residue of incineration, immersing the matrix into acid in a microwave-transparent pressure vessel, sealing the pressure vessel, and applying microwaves so that the temperature and the pressure in the pressure vessel increase. The acid for recovering plutonium can be a mixture of HBF[sub 4] and HNO[sub 3] and preferably the pressure is increased to at least 100 PSI and the temperature to at least 200 C. The porous material can be pulverized before immersion to further increase the leach rate.
Engineered porous metals for implants
NASA Astrophysics Data System (ADS)
Vamsi Krishna, B.; Xue, Weichang; Bose, Susmita; Bandyopadhyay, Amit
2008-05-01
Interest is significant in patient-specific implants with the possibility of guided tissue regeneration, particularly for load-bearing implants. For such implants to succeed, novel design approaches and fabrication technologies that can achieve balanced mechanical and functional performance in the implants are necessary. This article is focused on porous load-bearing implants with tailored micro-as well as macrostructures using laser-engineered net shaping (LENS™), a solid freeform fabrication or rapid prototyping technique that can be used to manufacture patient-specific implants. This review provides an insight into LENS, some properties of porous metals, and the potential applications of this process to fabricate unitized structures which can eliminate longstanding challenges in load-bearing implants to increase their in-vivo lifetime, such as in a total hip prosthesis.
POROUS WALL, HOLLOW GLASS MICROSPHERES
Sexton, W.
2012-06-30
Hollow Glass Microspheres (HGM) is not a new technology. All one has to do is go to the internet and Google{trademark} HGM. Anyone can buy HGM and they have a wide variety of uses. HGM are usually between 1 to 100 microns in diameter, although their size can range from 100 nanometers to 5 millimeters in diameter. HGM are used as lightweight filler in composite materials such as syntactic foam and lightweight concrete. In 1968 a patent was issued to W. Beck of the 3M{trademark} Company for 'Glass Bubbles Prepared by Reheating Solid Glass Particles'. In 1983 P. Howell was issued a patent for 'Glass Bubbles of Increased Collapse Strength' and in 1988 H. Marshall was issued a patent for 'Glass Microbubbles'. Now Google{trademark}, Porous Wall, Hollow Glass Microspheres (PW-HGMs), the key words here are Porous Wall. Almost every article has its beginning with the research done at the Savannah River National Laboratory (SRNL). The Savannah River Site (SRS) where SRNL is located has a long and successful history of working with hydrogen and its isotopes for national security, energy, waste management and environmental remediation applications. This includes more than 30 years of experience developing, processing, and implementing special ceramics, including glasses for a variety of Department of Energy (DOE) missions. In the case of glasses, SRS and SRNL have been involved in both the science and engineering of vitreous or glass based systems. As a part of this glass experience and expertise, SRNL has developed a number of niches in the glass arena, one of which is the development of porous glass systems for a variety of applications. These porous glass systems include sol gel glasses, which include both xerogels and aerogels, as well as phase separated glass compositions, that can be subsequently treated to produce another unique type of porosity within the glass forms. The porous glasses can increase the surface area compared to 'normal glasses of a 1 to 2 order of
Diffusion in porous crystalline materials.
Krishna, Rajamani
2012-04-21
The design and development of many separation and catalytic process technologies require a proper quantitative description of diffusion of mixtures of guest molecules within porous crystalline materials. This tutorial review presents a unified, phenomenological description of diffusion inside meso- and micro-porous structures. In meso-porous materials, with pore sizes 2 nm < d(p) < 50 nm, there is a central core region where the influence of interactions of the molecules with the pore wall is either small or negligible; meso-pore diffusion is governed by a combination of molecule-molecule and molecule-pore wall interactions. Within micro-pores, with d(p) < 2 nm, the guest molecules are always under the influence of the force field exerted with the wall and we have to reckon with the motion of adsorbed molecules, and there is no "bulk" fluid region. The characteristics and physical significance of the self-, Maxwell-Stefan, and Fick diffusivities are explained with the aid of data obtained either from experiments or molecular dynamics simulations, for a wide variety of structures with different pore sizes and topology. The influence of adsorption thermodynamics, molecular clustering, and segregation on both magnitudes and concentration dependences of the diffusivities is highlighted. In mixture diffusion, correlations in molecular hops have the effect of slowing-down the more mobile species. The need for proper modeling of correlation effects using the Maxwell-Stefan formulation is stressed with the aid of examples of membrane separations and catalytic reactors.
NASA Astrophysics Data System (ADS)
Sarhadi, Fatemeh; Shafiee Afarani, Mahdi; Mohebbi-Kalhori, Davod; Shayesteh, Masoud
2016-04-01
In the present study, porous alumina scaffolds with specific orientation and anisotropic properties are fabricated for application in bone tissue repair. The scaffolds with double shape pores, tubular oriented and isotropic rounded pores, were prepared using alumina and silica as starting materials by the slip casting route. Milled polyurethane foam and silk fibers were applied as replica materials as well. The effect of fiber types and diameter and number of fibers on the microstructure and pore size was studied. Moreover, different characteristics such as porosity, density, orientation, flexural strength and compressive strength of the samples were investigated. Results showed that various fibers with different diameters and numbers led to forming the pores with different pore sizes, microstructure and consequently changes in the physical and mechanical properties. In addition, the simultaneous presence of fibers and particles led to more porous scaffolds. The oriented tiny micro-tube and rounded pores were observed in all porous ceramic scaffolds. Mechanical testing showed an anisotropy in the mechanical behaviors such that higher strengths were observed in the oriented pore direction than that of transverse. With increasing the number and diameter of silk fibers, the scaffolds with a high porosity up to 68 vol% and proper flexural strength were obtained.
Porous titanium scaffolds fabricated using a rapid prototyping and powder metallurgy technique.
Ryan, Garrett E; Pandit, Abhay S; Apatsidis, Dimitrios P
2008-09-01
One of the main issues in orthopaedic implant design is the fabrication of scaffolds that closely mimic the biomechanical properties of the surrounding bone. This research reports on a multi-stage rapid prototyping technique that was successfully developed to produce porous titanium scaffolds with fully interconnected pore networks and reproducible porosity and pore size. The scaffolds' porous characteristics were governed by a sacrificial wax template, fabricated using a commercial 3D-printer. Powder metallurgy processes were employed to generate the titanium scaffolds by filling around the wax template with titanium slurry. In the attempt to optimise the powder metallurgy technique, variations in slurry concentration, compaction pressure and sintering temperature were investigated. By altering the wax design template, pore sizes ranging from 200 to 400 microm were achieved. Scaffolds with porosities of 66.8 +/- 3.6% revealed compression strengths of 104.4+/-22.5 MPa in the axial direction and 23.5 +/- 9.6 MPa in the transverse direction demonstrating their anisotropic nature. Scaffold topography was characterised using scanning electron microscopy and microcomputed tomography. Three-dimensional reconstruction enabled the main architectural parameters such as pore size, interconnecting porosity, level of anisotropy and level of structural disorder to be determined. The titanium scaffolds were compared to their intended designs, as governed by their sacrificial wax templates. Although discrepancies in architectural parameters existed between the intended and the actual scaffolds, overall the results indicate that the porous titanium scaffolds have the properties to be potentially employed in orthopaedic applications.
Capillary-driven, spatially-directed liquid transport on and through thin porous substrates
NASA Astrophysics Data System (ADS)
Chatterjee, Souvick; Sinha Mahapatra, Pallab; Ibrahim, Ali; Ganguly, Ranjan; Megaridis, Constantine; Yu, Lisha; Dodge, Richard
2016-11-01
Thin porous substrates exhibit good wicking properties for liquid distribution. The low cost of such common substrates often makes them useful for point of care biomedical diagnostics. Isotropic and anisotropic liquid transport through porous media has been studied extensively in literature. Moreover, previous research has demonstrated spatially-directed liquid transport on textured surfaces featuring surface-tension confined track. Combining both these features, here we demonstrate and analyze capillary-driven, directional liquid transport both on the surface of, and through, a wettability-patterned, horizontal porous substrate. The vertical (through) penetration is governed by Darcy's law. The horizontal (on surface) transport is driven by the Laplace pressure gradient caused by the geometry of the meniscus on the wettability-confined track. The transport rate on the substrate is found to far exceed the liquid permeation rate through it. Consequently, the penetration resistance can be estimated using a quasi-static approach. Using a semi-analytical model, we analyze the effect of the liquid curvature on the penetration rate of a sessile drop placed on the substrate. The model accounts for the back pressure caused by the liquid on the opposing side. The transport model is validated against the experiments, and the geometry, wettability and substrate porosity parameters causing fastest transport are identified.
Anisotropic Solution Adaptive Unstructured Grid Generation Using AFLR
NASA Technical Reports Server (NTRS)
Marcum, David L.
2007-01-01
An existing volume grid generation procedure, AFLR3, was successfully modified to generate anisotropic tetrahedral elements using a directional metric transformation defined at source nodes. The procedure can be coupled with a solver and an error estimator as part of an overall anisotropic solution adaptation methodology. It is suitable for use with an error estimator based on an adjoint, optimization, sensitivity derivative, or related approach. This offers many advantages, including more efficient point placement along with robust and efficient error estimation. It also serves as a framework for true grid optimization wherein error estimation and computational resources can be used as cost functions to determine the optimal point distribution. Within AFLR3 the metric transformation is implemented using a set of transformation vectors and associated aspect ratios. The modified overall procedure is presented along with details of the anisotropic transformation implementation. Multiple two-and three-dimensional examples are also presented that demonstrate the capability of the modified AFLR procedure to generate anisotropic elements using a set of source nodes with anisotropic transformation metrics. The example cases presented use moderate levels of anisotropy and result in usable element quality. Future testing with various flow solvers and methods for obtaining transformation metric information is needed to determine practical limits and evaluate the efficacy of the overall approach.
Anisotropic diffusion in mesh-free numerical magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Hopkins, Philip F.
2017-04-01
We extend recently developed mesh-free Lagrangian methods for numerical magnetohydrodynamics (MHD) to arbitrary anisotropic diffusion equations, including: passive scalar diffusion, Spitzer-Braginskii conduction and viscosity, cosmic ray diffusion/streaming, anisotropic radiation transport, non-ideal MHD (Ohmic resistivity, ambipolar diffusion, the Hall effect) and turbulent 'eddy diffusion'. We study these as implemented in the code GIZMO for both new meshless finite-volume Godunov schemes (MFM/MFV). We show that the MFM/MFV methods are accurate and stable even with noisy fields and irregular particle arrangements, and recover the correct behaviour even in arbitrarily anisotropic cases. They are competitive with state-of-the-art AMR/moving-mesh methods, and can correctly treat anisotropic diffusion-driven instabilities (e.g. the MTI and HBI, Hall MRI). We also develop a new scheme for stabilizing anisotropic tensor-valued fluxes with high-order gradient estimators and non-linear flux limiters, which is trivially generalized to AMR/moving-mesh codes. We also present applications of some of these improvements for SPH, in the form of a new integral-Godunov SPH formulation that adopts a moving-least squares gradient estimator and introduces a flux-limited Riemann problem between particles.
Weibel Instability Driven by Spatially Anisotropic Density Structures
NASA Astrophysics Data System (ADS)
Tomita, Sara; Ohira, Yutaka
2016-07-01
Observations of afterglows of gamma-ray bursts (GRBs) suggest that post-shock magnetic fields are strongly amplified to about 100 times the shock-compressed value. The Weibel instability appears to play an important role in generating the magnetic field. However, recent simulations of collisionless shocks in homogeneous plasmas show that the magnetic field generated by the Weibel instability rapidly decays. There must be some density fluctuations in interstellar and circumstellar media. The density fluctuations are anisotropically compressed in the downstream region of relativistic shocks. In this paper, we study the Weibel instability in electron-positron plasmas with spatially anisotropic density distributions by means of two-dimensional particle-in-cell simulations. We find that large magnetic fields are maintained for a longer time by the Weibel instability driven by spatially anisotropic density structure. Particles anisotropically escape from the high density region, so that a temperature anisotropy is generated and the Weibel instability becomes unstable. Our simulation results suggest that the Weibel instability driven by an anisotropic density structure can generate sufficiently large magnetic fields and they can cover sufficiently large regions to explain the afterglow emission of GRBs.
What is the Brillouin zone of an anisotropic photonic crystal?
NASA Astrophysics Data System (ADS)
Sivarajah, P.; Maznev, A. A.; Ofori-Okai, B. K.; Nelson, K. A.
2016-02-01
The concept of the Brillouin zone (BZ) in relation to a photonic crystal fabricated in an optically anisotropic material is explored both experimentally and theoretically. In experiment we used femtosecond laser pulses to excite THz polaritons and image their propagation in lithium niobate and lithium tantalate photonic crystal (PhC) slabs. We directly measured the dispersion relation inside PhCs and observed that the lowest band gap expected to form at the BZ boundary forms inside the BZ in the anisotropic lithium niobate PhC. Our analysis shows that in an anisotropic material the BZ—defined as the Wigner-Seitz cell in the reciprocal lattice—is no longer bounded by Bragg planes and thus does not conform to the original definition of the BZ by Brillouin. We construct an alternative Brillouin zone defined by Bragg planes and show its utility in identifying features of the dispersion bands. We show that for an anisotropic two-dimensional PhC without dispersion, the Bragg plane BZ can be constructed by applying the Wigner-Seitz method to a stretched or compressed reciprocal lattice. We also show that in the presence of the dispersion in the underlying material or in a slab waveguide, the Bragg planes are generally represented by curved surfaces rather than planes. The concept of constructing a BZ with Bragg planes should prove useful in understanding the formation of dispersion bands in anisotropic PhCs and in selectively tailoring their optical properties.
Photocatalytic Properties of Porous Silicon Nanowires.
Qu, Yongquan; Zhong, Xing; Li, Yujing; Liao, Lei; Huang, Yu; Duan, Xiangfeng
2010-01-01
Porous silicon nanowires are synthesized through metal assisted wet-chemical etch of highly-doped silicon wafer. The resulted porous silicon nanowires exhibit a large surface area of 337 m(2)·g(-1) and a wide spectrum absorption across the entire ultraviolet, visible and near infrared regime. We further demonstrate that platinum nanoparticles can be loaded onto the surface of the porous silicon nanowires with controlled density. These combined advancements make the porous silicon nanowires an interesting material for photocatalytic applications. We show that the porous silicon nanowires and platinum nanoparticle loaded porous silicon nanowires can be used as effective photocatalysts for photocatalytic degradation of organic dyes and toxic pollutants under visible irradiation, and thus are of significant interest for organic waste treatment and environmental remediation.
Thermally conductive porous element-based recuperators
NASA Technical Reports Server (NTRS)
Du, Jian Hua (Inventor); Chow, Louis C (Inventor); Lin, Yeong-Ren (Inventor); Wu, Wei (Inventor); Kapat, Jayanta (Inventor); Notardonato, William U. (Inventor)
2012-01-01
A heat exchanger includes at least one hot fluid flow channel comprising a first plurality of open cell porous elements having first gaps there between for flowing a hot fluid in a flow direction and at least one cold fluid flow channel comprising a second plurality of open cell porous elements having second gaps therebetween for flowing a cold fluid in a countercurrent flow direction relative to the flow direction. The thermal conductivity of the porous elements is at least 10 W/mK. A separation member is interposed between the hot and cold flow channels for isolating flow paths associated these flow channels. The first and second plurality of porous elements at least partially overlap one another to form a plurality of heat transfer pairs which transfer heat from respective ones of the first porous elements to respective ones of the second porous elements through the separation member.
Porous Carbon Nanoparticle Networks with Tunable Absorbability
Dai, Wei; Kim, Seong Jin; Seong, Won-Kyeong; Kim, Sang Hoon; Lee, Kwang-Ryeol; Kim, Ho-Young; Moon, Myoung-Woon
2013-01-01
Porous carbon materials with high specific surface areas and superhydrophobicity have attracted much research interest due to their potential application in the areas of water filtration, water/oil separation, and oil-spill cleanup. Most reported superhydrophobic porous carbon materials are fabricated by complex processes involving the use of catalysts and high temperatures but with low throughput. Here, we present a facile single-step method for fabricating porous carbon nanoparticle (CNP) networks with selective absorbability for water and oils via the glow discharge of hydrocarbon plasma without a catalyst at room temperature. Porous CNP networks were grown by the continuous deposition of CNPs at a relatively high deposition pressure. By varying the fluorine content, the porous CNP networks exhibited tunable repellence against liquids with various degrees of surface tension. These porous CNP networks could be applied for the separation of not only water/oil mixtures but also mixtures of liquids with different surface tension levels. PMID:23982181
Anisotropic viscoelastic-viscoplastic continuum model for high-density cellulose-based materials
NASA Astrophysics Data System (ADS)
Tjahjanto, D. D.; Girlanda, O.; Östlund, S.
2015-11-01
A continuum material model is developed for simulating the mechanical response of high-density cellulose-based materials subjected to stationary and transient loading. The model is formulated in an infinitesimal strain framework, where the total strain is decomposed into elastic and plastic parts. The model adopts a standard linear viscoelastic solid model expressed in terms of Boltzmann hereditary integral form, which is coupled to a rate-dependent viscoplastic formulation to describe the irreversible plastic part of the overall strain. An anisotropic hardening law with a kinematic effect is particularly adopted in order to capture the complex stress-strain hysteresis typically observed in polymeric materials. In addition, the present model accounts for the effects of material densification associated with through-thickness compression, which are captured using an exponential law typically applied in the continuum description of elasticity in porous media. Material parameters used in the present model are calibrated to the experimental data for high-density (press)boards. The experimental characterization procedures as well as the calibration of the parameters are highlighted. The results of the model simulations are systematically analyzed and validated against the corresponding experimental data. The comparisons show that the predictions of the present model are in very good agreement with the experimental observations for both stationary and transient load cases.
NASA Astrophysics Data System (ADS)
Yoon, Hae-Sung; Lee, Hyun-Taek; Kim, Eun-Seob; Ahn, Sung-Hoon
2017-02-01
Micro- and nanoscale structures are of interest in various engineering fields due to their unique properties, such as hydrophobicity. In particular, micro/nano hierarchical structures have been investigated to promote surface hydrophobicity. Here, aerodynamically focused nanoparticle (AFN) printing was used for direct printing of superhydrophobic patterns. As AFN printing is a room-temperature direct printing technique, printed features have a hierarchical structure of two levels; nanoscale porous surface and microscale-printed patterns in three-dimensional structures. Moreover, because it is an additive fabrication technique, the printed pattern is repairable and can be reconfigured as desired. In this study, silver nanoparticles were used to implement a superhydrophobic pattern with a minimum width of tens of microns. The contact angle of water droplets was measured for various patterns, and the effects of nanoscale porosity and pattern interval were investigated. In addition, patterns were designed and fabricated to have anisotropic superhydrophobicity. The experimental results were analyzed and explained with the classical Wenzel and Cassie-Baxter models.
Kreipke, T C; Niebur, G L
2017-02-02
Trabecular bone is a porous, mineralized tissue found in vertebral bodies, the metaphyses and epiphyses of long bones, and in the irregular and flat shaped bones. The pore space is filled with bone marrow, a highly cellular fluid. Together, the bone and marrow behave as a poroelastic solid. In poroelasticity theory, the permeability is the primary material property that governs the momentum transfer between the solid and fluid constituents. In the linearized theory, the permeability of a material depends on the shape and connectivity of the pores. Developing a model of the relationship between trabecular microarchitecture and permeability could lead to improved simulations of trabecular bone mechanical response, which can be used to investigate bone adaptation, mechanobiological signaling, and progression of diseases such as osteoporosis. This study used finite element models of the trabecular pore space to calculate the complete anisotropic permeability tensor of 12 human and 18 porcine femoral trabecular bone samples. The sensitivity of the simulations to model assumptions and post-processing was analyzed to improve confidence in the result. The orthotropic permeability tensor depended on the fabric tensor, trabecular spacing, and structure model index through a power law relationship. Porosity and fabric alone also provided a reasonable prediction, which may be useful in cases where the image resolution is insufficient to obtain detailed measures of architecture.
NASA Astrophysics Data System (ADS)
Song, Yongjia; Hu, Hengshan; Rudnicki, John W.; Duan, Yunda
2016-09-01
An exact analytical solution is presented for the effective dynamic transverse shear modulus in a heterogeneous fluid-filled porous solid containing cylindrical inclusions. The complex and frequency-dependent properties of the dynamic shear modulus are caused by the physical mechanism of mesoscopic-scale wave-induced fluid flow whose scale is smaller than wavelength but larger than the size of pores. Our model consists of three phases: a long cylindrical inclusion, a cylindrical shell of poroelastic matrix material with different mechanical and/or hydraulic properties than the inclusion and an outer region of effective homogeneous medium of laterally infinite extent. The behavior of both the inclusion and the matrix is described by Biot's consolidation equations, whereas the surrounding effective medium which is used to describe the effective transverse shear properties of the inner poroelastic composite is assumed to be a viscoelastic solid whose complex transverse shear modulus needs to be determined. The determined effective transverse shear modulus is used to quantify the S-wave attenuation and velocity dispersion in heterogeneous fluid-filled poroelastic rocks. The calculation shows the relaxation frequency and relative position of various fluid saturation dispersion curves predicted by this study exhibit very good agreement with those of a previous 2-D finite-element simulation. For the double-porosity model (inclusions having a different solid frame than the matrix but the same pore fluid as the matrix) the effective shear modulus also exhibits a size-dependent characteristic that the relaxation frequency moves to lower frequencies by two orders of magnitude if the radius of the cylindrical poroelastic composite increases by one order of magnitude. For the patchy-saturation model (inclusions having the same solid frame as the matrix but with a different pore fluid from the matrix), the heterogeneity in pore fluid cannot cause any attenuation in the
NASA Astrophysics Data System (ADS)
Ding, Pinbo; Di, Bangrang; Wei, Jianxin; Li, Xiangyang; Deng, Yinghua
2014-02-01
In this study, we analyse the influence of fluid on P- and S-wave anisotropy in a fractured medium. Equivalent medium theories are used to describe the relationship between the fluid properties and the rock physics characteristics in fractured rocks, and P-wave and S-wave velocities and anisotropy are considered to be influenced by fluid saturation. However, these theoretical predictions require experimental measurement results for calibration. A new construction method was used to create synthetic rock samples with controlled fracture parameters. The new construction process provides synthetic rocks that have a more realistic mineral composition, porous structure, cementation and pressure sensitivity than samples used in previous research on fractured media. The synthetic rock samples contain fractures which have a controlled distribution, diameter, thickness and fracture density. In this study, the fracture diameter was about 4 mm, the thickness of fractures was about 0.06 mm, and the fracture density in the two fractured rock samples was about 3.45%. SEM images show well-defined penny-shaped fractures of 4 mm in length and 0.06 mm in width. The rock samples were saturated with air, water and oil, and P- and S-wave velocities were measured in an ultrasonic measurement system. The laboratory measurement results show that the P-wave anisotropy is strongly influenced by saturated fluid, and the P-wave anisotropy parameter, ɛ, has a much larger value in air saturation than in water and oil saturations. The S-wave anisotropy decreases when the samples are saturated with oil, which can be caused by high fluid viscosity. In the direction perpendicular to the fractures (the 0° direction), shear-wave splitting is negligible, and is similar to the blank sample without fractures, as expected. In the direction parallel to the fractures (the 90° direction) shear-wave splitting is significant. The fractured rock samples show significant P- and S-wave anisotropy caused by
Piezoelectric and piezooptic effects in porous silicon
NASA Astrophysics Data System (ADS)
Vinikman-Pinhasi, Shirly; Ribak, Erez N.
2006-03-01
Although silicon is a simple cubic crystal, it can be induced to have a piezoelectric response, by making pores in it and thus spoiling its symmetry. By etching a silicon wafer into porous material, we found that it responds to voltage applied to it, as well as to light. A porous shallow layer on the surface of the wafer induced bimorph bending roughly proportional to the voltage squared. Illuminating the porous patch caused a similar bending.
Anisotropic imaging performance in breast tomosynthesis.
Badano, Aldo; Kyprianou, Iacovos S; Jennings, Robert J; Sempau, Josep
2007-11-01
We describe the anisotropy in imaging performance caused by oblique x-ray incidence in indirect detectors for breast tomosynthesis based on columnar scintillator screens. We use MANTIS, a freely available combined x-ray, electron, and optical Monte Carlo transport package which models the indirect detection processes in columnar screens, interaction by interaction. The code has been previously validated against published optical distributions. In this article, initial validation results are provided concerning the blur for particular designs of phosphor screens for which some details with respect to the columnar geometry are available from scanning electron microscopy. The polyenergetic x-ray spectrum utilized comes from a database of experimental data for three different anode/filter/kVp combinations: Mo/Mo at 28 kVp, Rh/Rh at 28 kVp, and W/Al at 42 kVp. The x-ray spectra were then filtered with breast tissue (3, 4, and 6 cm thickness), compression paddle, and support base, according to the oblique paths determined by the incidence angle. The composition of the breast tissue was 50%/50% adipose/glandular tissue mass ratio. Results are reported on the pulse-height statistics of the light output and on spatial blur, expressed as the response of the detector to a pencil beam with a certain incidence angle. Results suggest that the response is nonsymmetrical and that the resolution properties of a tomosynthesis system vary significantly with the angle of x-ray incidence. In contrast, it is found that the noise due to the variability in the number of light photons detected per primary x-ray interaction changes only a few percent. The anisotropy in the response is not less in screens with absorptive backings while the noise introduced by variations in the depth-dependent light output and optical transport is larger. The results suggest that anisotropic imaging performance across the detector area can be incorporated into reconstruction algorithms for improving the image
Anisotropic shrinkage characteristics of tape cast alumina
NASA Astrophysics Data System (ADS)
Patwardhan, Jaideep Suresh
Dimensional control during sintering is a major issue in ceramics processing to avoid high post-sintering costs associated with machining of the fired ceramic part to desired tolerances and dimensions. Ceramic forming processes such as tape casting, injection molding, and extrusion involve shear of anisotropic particles resulting in preferential alignment of the particles in the green body. This preferential alignment causes directionality in mechanical, electrical, optical, and magnetic properties and most importantly warpage or distortion during sintering. A large effort has been devoted to synthesizing ceramic green bodies with minimal density gradients and uniform packing and modeling the sintering behavior evolution but little effort has been devoted to characterizing orientation of particles and the effect of preferential alignment on sintering shrinkage anisotropy. A systematic study was initiated to study the effect of processing variables such as shear rate, solids loading, temperature, and binder content on aqueous tape cast alumina. Three different alumina systems: A16-SG, Baikowski RC-UFX DBM and RC-LS DBM were investigated. Aqueous tapes of high solids loading alumina (56 vol. %) were tape cast at various speeds and thicknesses and assuming plane Couette flow a shear rate regime of 21--270 s-1 was investigated. Higher shear rates and high solids loading resulted in higher in-plane anisotropy whereas the anisotropy in the thickness direction was higher for low solids loading systems. The anisotropy was found to be fairly constant above a certain critical shear rate (˜100 s-1) irrespective of the temperature and the solids loading and this correlated with the viscosity-shear rate relationship of the cast slips. The higher shrinkage anisotropy in the thickness direction for the low solids loading systems (35 and 45 vol. %) was attributed to the higher amount of organics in the slip required to sustain the suitable viscosity for tape casting and
Bimodal porous gold opals for molecular sensing
NASA Astrophysics Data System (ADS)
Chae, Weon-Sik; Yu, Hyunung; Ham, Sung-Kyoung; Lee, Myung-Jin; Jung, Jin-Seung; Robinson, David B.
2013-11-01
We have fabricated bimodal porous gold skeletons by double-templating routes using poly(styrene) colloidal opals as templates. The fabricated gold skeletons show a bimodal pore-size distribution, with small pores within spheres and large pores between spheres. The templated bimodal porous gold skeletons were applied in Raman scattering experiments to study sensing efficiency for probe molecules. We found that the bimodal porous gold skeletons showed obvious enhancement of Raman scattering signals versus that of the unimodal porous gold which only has interstitial pores of several hundred nanometers.
Foam drainage placed on a porous substrate.
Arjmandi-Tash, O; Kovalchuk, N; Trybala, A; Starov, V
2015-05-14
A model for drainage/imbibition of a foam placed on the top of a porous substrate is presented. The equation of liquid imbibition into the porous substrate is coupled with a foam drainage equation at the foam/porous substrate interface. The deduced dimensionless equations are solved using a finite element method. It was found that the kinetics of foam drainage/imbibition depends on three dimensionless numbers and the initial liquid volume fraction. The result shows that there are three different regimes of the process. Each regime starts after initial rapid decrease of a liquid volume fraction at the foam/porous substrate interface: (i) rapid imbibition: the liquid volume fraction inside the foam at the foam/porous substrate interface remains constant close to a final liquid volume fraction; (ii) intermediate imbibition: the liquid volume fraction at the interface with the porous substrate experiences a peak point and imbibition into the porous substrate is slower as compared with the drainage; (iii) slow imbibition: the liquid volume fraction at the foam/porous substrate interface increases to a maximum limiting value and a free liquid layer is formed between the foam and the porous substrate. However, the free liquid layer disappears after some time. The transition points between these three different drainage/imbibition regimes were delineated by introducing two dimensionless numbers.
Porous media heat transfer for injection molding
Beer, Neil Reginald
2016-05-31
The cooling of injection molded plastic is targeted. Coolant flows into a porous medium disposed within an injection molding component via a porous medium inlet. The porous medium is thermally coupled to a mold cavity configured to receive injected liquid plastic. The porous medium beneficially allows for an increased rate of heat transfer from the injected liquid plastic to the coolant and provides additional structural support over a hollow cooling well. When the temperature of the injected liquid plastic falls below a solidifying temperature threshold, the molded component is ejected and collected.
Transpiration Control Of Aerodynamics Via Porous Surfaces
NASA Technical Reports Server (NTRS)
Banks, Daniel W.; Wood, Richard M.; Bauer, Steven X. S.
1993-01-01
Quasi-active porous surface used to control pressure loading on aerodynamic surface of aircraft or other vehicle, according to proposal. In transpiration control, one makes small additions of pressure and/or mass to cavity beneath surface of porous skin on aerodynamic surface, thereby affecting rate of transpiration through porous surface. Porous skin located on forebody or any other suitable aerodynamic surface, with cavity just below surface. Device based on concept extremely lightweight, mechanically simple, occupies little volume in vehicle, and extremely adaptable.
Dynamic Scaling of Island-size Distribution on Anisotropic Surfaces
NASA Astrophysics Data System (ADS)
Li, Maozhi; Wang, E. G.; Liu, Banggui; Zhang, Zhenyu
2002-03-01
Dynamic scaling of island-size distribution on isotropic and anisotropic surfaces in submonolayer growth is systematically studied using kinetic Monte Carlo simulations. It is found that the island-size distribution in anisotropic submonolayer growth exhibits a general dynamic scaling behavior. An analytic expression is proposed for the scaling function, and is compared with the simulation results. This scaling function not only improves previous results for the isotropic growth (1), but also describes the scaling behavior of the island-size distribution in anisotropic submonolayer growth very well (2). 1. J. G. Amar and F. Family, Phys. Rev. Lett. 74, 2066 (1995). 2. M. Z. Li, E. G. Wang, B. G. Liu, and Z. Y. Zhang, Phys. Rev. Lett. (submitted).
Geodesic acoustic mode in anisotropic plasma with heat flux
NASA Astrophysics Data System (ADS)
Ren, Haijun
2015-10-01
Geodesic acoustic mode (GAM) in an anisotropic tokamak plasma is investigated in fluid approximation. The collisionless anisotropic plasma is described within the 16-momentum magnetohydrodynamic (MHD) fluid closure model, which takes into account not only the pressure anisotropy but also the anisotropic heat flux. It is shown that the GAM frequency agrees better with the kinetic result than the standard Chew-Goldberger-Low (CGL) MHD model. When zeroing the anisotropy, the 16-momentum result is identical with the kinetic one to the order of 1/q2, while the CGL result agrees with the kinetic result only on the leading order. The discrepancies between the results of the CGL fluid model and the kinetic theory are well removed by considering the heat flux effect in the fluid approximation.
A hybrid-stress finite element for linear anisotropic elasticity
NASA Technical Reports Server (NTRS)
Fly, Gerald W.; Oden, J. Tinsley; Pearson, Mark L.
1988-01-01
Standard assumed displacement finite elements with anisotropic material properties perform poorly in complex stress fields such as combined bending and shear and combined bending and torsion. A set of three dimensional hybrid-stress brick elements were developed with fully anisotropic material properties. Both eight-node and twenty-node bricks were developed based on the symmetry group theory of Punch and Atluri. An eight-node brick was also developed using complete polynomials and stress basis functions and reducing the order of the resulting stress parameter matrix by applying equilibrium constraints and stress compatibility constraints. Here the stress compatibility constraints must be formulated assuming anisotropic material properties. The performance of these elements was examined in numerical examples covering a broad range of stress distributions. The stress predictions show significant improvement over the assumed displacement elements but the calculation time is increased.
Anisotropic Smoothing Improves DT-MRI-Based Muscle Fiber Tractography
Buck, Amanda K. W.; Ding, Zhaohua; Elder, Christopher P.; Towse, Theodore F.; Damon, Bruce M.
2015-01-01
Purpose To assess the effect of anisotropic smoothing on fiber tracking measures, including pennation angle, fiber tract length, and fiber tract number in the medial gastrocnemius (MG) muscle in healthy subjects using diffusion-weighted magnetic resonance imaging (DW-MRI). Materials and Methods 3T DW-MRI data were used for muscle fiber tractography in the MG of healthy subjects. Anisotropic smoothing was applied at three levels (5%, 10%, 15%), and pennation angle, tract length, fiber tract number, fractional anisotropy, and principal eigenvector orientation were quantified for each smoothing level. Results Fiber tract length increased with pre-fiber tracking smoothing, and local heterogeneities in fiber direction were reduced. However, pennation angle was not affected by smoothing. Conclusion Modest anisotropic smoothing (10%) improved fiber-tracking results, while preserving structural features. PMID:26010830
Anisotropic Electron Tail Generation during Tearing Mode Magnetic Reconnection
NASA Astrophysics Data System (ADS)
DuBois, Ami M.; Almagri, Abdulgader F.; Anderson, Jay K.; Den Hartog, Daniel J.; Lee, John David; Sarff, John S.
2017-02-01
The first experimental evidence of anisotropic electron energization during magnetic reconnection that favors a direction perpendicular to the guide magnetic field in a toroidal, magnetically confined plasma is reported in this Letter. Magnetic reconnection plays an important role in particle heating, energization, and transport in space and laboratory plasmas. In toroidal devices like the Madison Symmetric Torus, discrete magnetic reconnection events release large amounts of energy from the equilibrium magnetic field. Fast x-ray measurements imply a non-Maxwellian, anisotropic energetic electron tail is formed at the time of reconnection. The tail is well described by a power-law energy dependence. The expected bremsstrahlung from an electron distribution with an anisotropic energetic tail (v⊥>v∥ ) spatially localized in the core region is consistent with x-ray emission measurements. A turbulent process related to tearing fluctuations is the most likely cause for the energetic electron tail formation.
Geodesic acoustic mode in anisotropic plasma with heat flux
Ren, Haijun
2015-10-15
Geodesic acoustic mode (GAM) in an anisotropic tokamak plasma is investigated in fluid approximation. The collisionless anisotropic plasma is described within the 16-momentum magnetohydrodynamic (MHD) fluid closure model, which takes into account not only the pressure anisotropy but also the anisotropic heat flux. It is shown that the GAM frequency agrees better with the kinetic result than the standard Chew-Goldberger-Low (CGL) MHD model. When zeroing the anisotropy, the 16-momentum result is identical with the kinetic one to the order of 1/q{sup 2}, while the CGL result agrees with the kinetic result only on the leading order. The discrepancies between the results of the CGL fluid model and the kinetic theory are well removed by considering the heat flux effect in the fluid approximation.
Hemispherical anisotropic patterns of the Earth’s inner core
Mattesini, Maurizio
2010-01-01
It has been shown that the Earth’s inner core has an axisymmetric anisotropic structure with seismic waves traveling ∼3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth’s core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth’s rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth’s inner core. PMID:20457937
Anomalously large anisotropic magnetoresistance in a perovskite manganite.
Li, Run-Wei; Wang, Huabing; Wang, Xuewen; Yu, X Z; Matsui, Y; Cheng, Zhao-Hua; Shen, Bao-Gen; Plummer, E Ward; Zhang, Jiandi
2009-08-25
The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La(0.69)Ca(0.31)MnO(3), leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a "colossal" AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings.
Hemispherical anisotropic patterns of the Earth's inner core.
Mattesini, Maurizio; Belonoshko, Anatoly B; Buforn, Elisa; Ramírez, María; Simak, Sergei I; Udías, Agustín; Mao, Ho-Kwang; Ahuja, Rajeev
2010-05-25
It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves traveling approximately 3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth's core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth's inner core.
Self-force on dislocation segments in anisotropic crystals.
Fitzgerald, S P; Aubry, S
2010-07-28
A dislocation segment in a crystal experiences a 'self-force', by virtue of the orientation dependence of its elastic energy. If the crystal is elastically isotropic, this force is manifested as a couple acting to rotate the segment toward the lower energy of the pure screw orientation (i.e. acting to align the dislocation line with its Burgers vector). If the crystal is anisotropic, there are additional contributions to the couple, arising from the more complex energy landscape of the lattice itself. These effects can strongly influence the dynamic evolution of dislocation networks, and via their governing role in dislocation multiplication phenomena, control plastic flow in metals. In this paper we develop a model for dislocation self-forces in a general anisotropic crystal, and briefly consider the technologically important example of α-iron, which becomes increasingly anisotropic as the temperature approaches that of the α-γ phase transition at 912 °C.
Anisotropic light scattering of individual sickle red blood cells
NASA Astrophysics Data System (ADS)
Kim, Youngchan; Higgins, John M.; Dasari, Ramachandra R.; Suresh, Subra; Park, YongKeun
2012-04-01
We present the anisotropic light scattering of individual red blood cells (RBCs) from a patient with sickle cell disease (SCD). To measure light scattering spectra along two independent axes of elongated-shaped sickle RBCs with arbitrary orientation, we introduce the anisotropic Fourier transform light scattering (aFTLS) technique and measured both the static and dynamic anisotropic light scattering. We observed strong anisotropy in light scattering patterns of elongated-shaped sickle RBCs along its major axes using static aFTLS. Dynamic aFTLS analysis reveals the significantly altered biophysical properties in individual sickle RBCs. These results provide evidence that effective viscosity and elasticity of sickle RBCs are significantly different from those of the healthy RBCs.
Modeling anisotropic Maxwell-Jüttner distributions: derivation and properties
NASA Astrophysics Data System (ADS)
Livadiotis, George
2016-12-01
In this paper we develop a model for the anisotropic Maxwell-Jüttner distribution and examine its properties. First, we provide the characteristic conditions that the modeling of consistent and well-defined anisotropic Maxwell-Jüttner distributions needs to fulfill. Then, we examine several models, showing their possible advantages and/or failures in accordance to these conditions. We derive a consistent model, and examine its properties and its connection with thermodynamics. We show that the temperature equals the average of the directional temperature-like components, as it holds for the classical, anisotropic Maxwell distribution. We also derive the internal energy and Boltzmann-Gibbs entropy, where we show that both are maximized for zero anisotropy, that is, the isotropic Maxwell-Jüttner distribution.
Measurement of Anisotropic Mechanical Properties of the Tectorial Membrane
NASA Astrophysics Data System (ADS)
Gavara, N.; Chadwick, R. S.
2009-02-01
The tectorial membrane (TM) in the cochlea is an anisotropic tissue with a key role in hearing. The TM's structural andmechanical anisotropy is provided by oriented collagen bundles about 1 micron thick. Here we report the three elastic moduli that characterize the TM, as well as the novel technique used to measure the mechanical properties of an anisotropic material. We have measured mechanical anisotropy by combining Atomic Force Microscopy (AFM) and optical tracking of microspheres. The surface Green's tensor for an incompressible anisotropic material was then used to compute the elastic moduli from imposed forces and the resulting surface deformations. Our results suggest a critical role of TM's strong anisotropy by enhancing the cochlear amplifier.
Vacuum self similar anisotropic cosmologies in F( R)-gravity
NASA Astrophysics Data System (ADS)
Apostolopoulos, Pantelis S.
2017-04-01
The implications from the existence of a proper Homothetic Vector Field on the dynamics of vacuum anisotropic models in F( R) gravitational theory are studied. The fact that every Spatially Homogeneous vacuum model is equivalent, formally, with a "flux"-free anisotropic fluid model in standard gravity and the induced power-law form of the functional F( R) due to self-similarity enable us to close the system of equations. We found some new exact anisotropic solutions that arise as fixed points in the associated dynamical system. The non-existence of Kasner-like (Bianchi type I) solutions in proper F( R)-gravity (i.e. R≠ 0) strengthens the belief that curvature corrections will prevent the shear influence into the past thus permitting an isotropic singularity. We also discuss certain issues regarding the lack of vacuum models of type III, IV, VIIh in comparison with the corresponding results in standard gravity.
Q -factor enhancement in all-dielectric anisotropic nanoresonators
NASA Astrophysics Data System (ADS)
Liu, Wei; Miroshnichenko, Andrey E.; Kivshar, Yuri S.
2016-11-01
It is proposed and demonstrated that the Q factor of optical resonators can be significantly enhanced by introducing an extra anisotropic cladding. We study the optical resonances of all-dielectric core-shell nanoresonators and show that radially anisotropic claddings can be employed to squeeze more energy into the core area, leading to stronger light confinement and thus significant Q -factor enhancement. We further demonstrate that the required homogenous claddings of unusual anisotropy parameters can be realized through all-dielectric multilayered isotropic structures. It is expected that the mechanism we have revealed not only offers extra flexibilities of resonance manipulations for conventional dielectric structures, but also may shed new light onto investigations into unconventional nanostructures consisting of two-dimensional materials that are intrinsically highly anisotropic.
Anisotropic viscoelastic models in large deformation for architectured membranes
NASA Astrophysics Data System (ADS)
Rebouah, Marie; Chagnon, Gregory; Heuillet, Patrick
2016-08-01
Due to the industrial elaboration process, membranes can have an in-plane anisotropic mechanical behaviour. In this paper, anisotropic membranes elaborated with two different materials were developed either by calendering or by inducing a force in one direction during the process. Experimental tests are developed to measure the differences of mechanical behaviour for both materials in different in-plane properties: stiffness, viscoelasticity and stress-softening. A uniaxial formulation is developed, and a homogenisation by means of a sphere unit approach is used to propose a three-dimensional formulation to represent the materials behaviour. An evolution of the mechanical parameters, depending on the direction, is imposed to reproduce the anisotropic behaviour of the materials. Comparison with experimental data highlights very promising results.
Magnetic alignment of plant cell microfibrils and their anisotropic elasticity
NASA Astrophysics Data System (ADS)
Fujimura, Yuu; Sakaida, Hidetaka; Iino, Masaaki
2010-06-01
The magnetic alignment of microfibrils on a single regenerated plant cell surface subjected to magnetic fields and its anisotropic cell surface area expansivity modulus (area modulus) were studied. The magnetic alignment around the equator of the cell (the polar axis parallel to the magnetic field) was confirmed by a 2-dim Fourier analysis of images from a scanning electron microscope, and these were expressed by a theoretical magnetic order parameter for anisotropic relative magnetic permeability of 3×10-27, while the microfibrils near the pole did not show any such magnetic alignment. The magnetic field anisotropically stiffened the cell surface. The stiffness around the equator was greater than that around the pole. The magnetic field dependences of the area modulus agreed with the mechanical model.
Shear-free anisotropic cosmological models in {f (R)} gravity
NASA Astrophysics Data System (ADS)
Abebe, Amare; Momeni, Davood; Myrzakulov, Ratbay
2016-04-01
We study a class of shear-free, homogeneous but anisotropic cosmological models with imperfect matter sources in the context of f( R) gravity. We show that the anisotropic stresses are related to the electric part of the Weyl tensor in such a way that they balance each other. We also show that within the class of orthogonal f( R) models, small perturbations of shear are damped, and that the electric part of the Weyl tensor and the anisotropic stress tensor decay with the expansion as well as the heat flux of the curvature fluid. Specializing in locally rotationally symmetric spacetimes in orthonormal frames, we examine the late-time behaviour of the de Sitter universe in f( R) gravity. For the Starobinsky model of f( R), we study the evolutionary behavior of the Universe by numerically integrating the Friedmann equation, where the initial conditions for the expansion, acceleration and jerk parameters are taken from observational data.
Effects of nonuniform acceptance in anisotropic flow measurements
Selyuzhenkov, Ilya; Voloshin, Sergei
2008-03-15
The applicability of anisotropic flow measurement techniques and their extension for detectors with nonuniform azimuthal acceptance are discussed. Considering anisotropic flow measurements with two and three (mixed harmonic) azimuthal correlations we introduce a set of observables based on the x and y components of the event flow vector. These observables provide independent measures of anisotropic flow and can be used to test the self-consistency of the analysis. Based on these observables we propose a technique that explicitly takes into account the effects of nonuniform detector acceptance. Within this approach the acceptance corrections, as well as parameters that define the method applicability, can be determined directly from experimental data. For practical purposes a brief summary of the method is provided at the end.
Well behaved anisotropic compact star models in general relativity
NASA Astrophysics Data System (ADS)
Jasim, M. K.; Maurya, S. K.; Gupta, Y. K.; Dayanandan, B.
2016-11-01
Anisotropic compact star models have been constructed by assuming a particular form of a metric function e^{λ}. We solved the Einstein field equations for determining the metric function e^{ν}. For this purpose we have assumed a physically valid expression of radial pressure (pr). The obtained anisotropic compact star model is representing the realistic compact objects such as PSR 1937 +21. We have done an extensive study about physical parameters for anisotropic models and found that these parameters are well behaved throughout inside the star. Along with these we have also determined the equation of state for compact star which gives the radial pressure is purely the function of density i.e. pr=f(ρ).
Isotropic and anisotropic bouncing cosmologies in Palatini gravity
Barragan, Carlos; Olmo, Gonzalo J.
2010-10-15
We study isotropic and anisotropic (Bianchi I) cosmologies in Palatini f(R) and f(R,R{sub {mu}{nu}R}{sup {mu}{nu}}) theories of gravity with a perfect fluid and consider the existence of nonsingular bouncing solutions in the early universe. We find that all f(R) models with isotropic bouncing solutions develop shear singularities in the anisotropic case. On the contrary, the simple quadratic model R+aR{sup 2}/R{sub P}+R{sub {mu}{nu}R}{sup {mu}{nu}/}R{sub P} exhibits regular bouncing solutions in both isotropic and anisotropic cases for a wide range of equations of state, including dust (for a<0) and radiation (for arbitrary a). It thus represents a purely gravitational solution to the big bang singularity and anisotropy problems of general relativity without the need for exotic (w>1) sources of matter/energy or extra degrees of freedom.
Dynamics of anisotropic universe in f(G) gravity
NASA Astrophysics Data System (ADS)
Shamir, M. Farasat
2017-04-01
The main objective of this paper is to investigate anisotropic universe in f(G) gravity. Locally rotationally symmetric Bianchi type I cosmological model is considered for this purpose. First, some exact solutions with a well-known form of f(G) model are explored. In particular, two solutions are reported for the analysis. Secondly, we discuss the energy conditions for the model under consideration. The viability of the model is investigated via graphical analysis using the present day values of cosmological parameters. The strong energy condition is violated which shows that anisotropic universe in f(G) gravity supports the phenomenon of expansion of universe.
Anisotropic. cap alpha. -emission of on-line separated isotopes
Wouters, J.; Vandeplassche, D.; van Walle, E.; Severijns, N.; Van Haverbeke, J.; Vanneste, L.
1987-12-10
The technical realization of particle detection at very low temperatures (4K) has made it possible to study for the first time the anisotropic ..cap alpha..-decay of oriented nuclei which have been produced, separated and implanted on line. The measured ..cap alpha..-angular distributions reveal surprising new results on nuclear aspects as well as in solid state physics. The nuclear structure information from these data questions the older ..cap alpha..-decay theoretical interpretation and urges for a reaxamination of the earliest work on anisotropic ..cap alpha..-decay.
Lectin sensitized anisotropic silver nanoparticles for detection of some bacteria.
Gasparyan, Vardan K; Bazukyan, Inga L
2013-03-05
A method of bacteria detection by sensitized anisotropic silver nanoparticles is presented. Anisotropic silver nanoparticles with two bands of surface plasmon resonance (SPR) are prepared and sensitized with potato lectin. These nanoparticles are able to detect three bacterial species: Escherichia coli, Bacillus subtilis and Staphylococcus aureus. The interaction of these bacteria with such nanoparticles induces drastic changes in optical spectra of nanoparticles that are correlated with bacteria titer. The maximal sensitivity is observed for S. aureus (up to 1.5×10(4) mL(-1)).
Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs.
Mannix, Andrew J; Zhou, Xiang-Feng; Kiraly, Brian; Wood, Joshua D; Alducin, Diego; Myers, Benjamin D; Liu, Xiaolong; Fisher, Brandon L; Santiago, Ulises; Guest, Jeffrey R; Yacaman, Miguel Jose; Ponce, Arturo; Oganov, Artem R; Hersam, Mark C; Guisinger, Nathan P
2015-12-18
At the atomic-cluster scale, pure boron is markedly similar to carbon, forming simple planar molecules and cage-like fullerenes. Theoretical studies predict that two-dimensional (2D) boron sheets will adopt an atomic configuration similar to that of boron atomic clusters. We synthesized atomically thin, crystalline 2D boron sheets (i.e., borophene) on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal.
Three-parameter AVO crossplotting in anisotropic media
Chen, H.; Castagna, J.P.; Brown, R.L.; Ramos, A.C.B.
2001-01-01
Amplitude versus offset (AVO) interpretation can be facilitated by crossplotting AVO intercept (A), gradient (B), and curvature (C) terms. However, anisotropy, which exists in the real world, usually complicates AVO analysis. Recognizing anisotropic behavior on AVO crossplots can help avoid AVO interpretation errors. Using a modification to a three-term (A, B, and C) approximation to the exact anisotropic reflection coefficients for transversely isotropic media, we find that anisotropy has a nonlinear effect on an A versus C crossplot yet causes slope changes and differing intercepts on A versus B or C crossplots. Empirical corrections that result in more accurate crossplot interpretation are introduced for specific circumstances.
Stopping power of an electron gas with anisotropic temperature
NASA Astrophysics Data System (ADS)
Khelemelia, O. V.; Kholodov, R. I.
2016-04-01
A general theory of motion of a heavy charged particle in the electron gas with an anisotropic velocity distribution is developed within the quantum-field method. The analytical expressions for the dielectric susceptibility and the stopping power of the electron gas differs in no way from well-known classic formulas in the approximation of large and small velocities. Stopping power of the electron gas with anisotropic temperature in the framework of the quantum-field method is numerically calculated for an arbitrary angle between directions of the motion of the projectile particle and the electron beam. The results of the numerical calculations are compared with the dielectric model approach.
Anisotropic magnetotransport in Dirac-Weyl magnetic junctions
NASA Astrophysics Data System (ADS)
Ominato, Yuya; Kobayashi, Koji; Nomura, Kentaro
2017-02-01
We theoretically study the anisotropic magnetotransport in Dirac-Weyl magnetic junctions where a doped ferromagnetic Weyl semimetal is sandwiched between doped Dirac semimetals. We calculate the conductance using the Landauer formula and find that the system exhibits extraordinarily large anisotropic magnetoresistance (AMR). The AMR depends on the ratio of the Fermi energy to the strength of the exchange interaction. The origin of the AMR is the shift of the Fermi surface in the Weyl semimetal, and the mechanism is completely different from the conventional AMR originating from the spin dependent scattering and the spin-orbit interaction.
Tunable waveguide bends with graphene-based anisotropic metamaterials
NASA Astrophysics Data System (ADS)
Chen, Zhao-xian; Chen, Ze-guo; Ming, Yang; Wu, Ying; Lu, Yan-qing
2016-02-01
We design tunable waveguide bends filled with graphene-based anisotropic metamaterials to achieve a nearly perfect bending effect. The anisotropic properties of the metamaterials can be described by the effective medium theory. The nearly perfect bending effect is demonstrated by finite element simulations of various structures with different bending curvatures and shapes. This effect is attributed to zero effective permittivity along the direction of propagation and matched effective impedance at the interfaces between the bending part and the dielectric waveguides. We envisage that the design will be applicable in the far-infrared and terahertz frequency ranges owing to the tunable dielectric responses of graphene.
Anisotropic diffraction of bulk acoustic wave beams in lithium niobate.
Naumenko, Natalya F; Chizhikov, Sergey I; Molchanov, Vladimir Ya; Yushkov, Konstantin B
2015-12-01
The formalism of planar diffraction tensor was applied to the analysis of anisotropy of bulk acoustic wave diffraction and to build a full map of anisotropic diffractional coefficients for three bulk acoustic wave modes propagating in lithium niobate. For arbitrary propagation direction the diffractional coefficients derived allow estimation of ultrasonic beam divergence in far-field. Analysis of obtained data revealed that the maxima of acousto-optic figure of merit for anisotropic diffraction in the YZ plane correspond to moderate diffractional spreading of the beams exceeding isotropic diffraction 2-3 times.
The traces of anisotropic dark energy in light of Planck
Cardona, Wilmar; Kunz, Martin; Hollenstein, Lukas E-mail: lukas.hollenstein@zhaw.ch
2014-07-01
We study a dark energy model with non-zero anisotropic stress, either linked to the dark energy density or to the dark matter density. We compute approximate solutions that allow to characterise the behaviour of the dark energy model and to assess the stability of the perturbations. We also determine the current limits on such an anisotropic stress from the cosmic microwave background data by the Planck satellite, and derive the corresponding constraints on the modified growth parameters like the growth index, the effective Newton's constant and the gravitational slip.
MHz gravitational waves from short-term anisotropic inflation
Ito, Asuka; Soda, Jiro
2016-04-18
We reveal the universality of short-term anisotropic inflation. As a demonstration, we study inflation with an exponential type gauge kinetic function which is ubiquitous in models obtained by dimensional reduction from higher dimensional fundamental theory. It turns out that an anisotropic inflation universally takes place in the later stage of conventional inflation. Remarkably, we find that primordial gravitational waves with a peak amplitude around 10{sup −26}∼10{sup −27} are copiously produced in high-frequency bands 10 MHz∼100 MHz. If we could detect such gravitational waves in future, we would be able to probe higher dimensional fundamental theory.
An Analysis of Charged Anisotropic Star with de Sitter Spacetime
NASA Astrophysics Data System (ADS)
Das, Kanika; Ali, Nawsad
2016-02-01
We propose a model for charged anisotropic star in de Sitter spacetime. We have taken Krori and Barua (J. Phys. A, Math. Gen. 8, 508, 1975) metric in de Sitter spacetime with non-zero cosmological constant. The model is free from singularity. We incorporate the existence of the cosmological constant on a small scale to study the structure of anisotropic charged star. To solve the Einstein-Maxwell field equations we assume the relation between the radial and transverse pressure as p t - p r = g q( r)2 r 2 (where g is a non-zero positive constant). The physical conditions inside the stellar model are also discussed.
Anisotropic Landau-Lifshitz-Gilbert models of dissipation in qubits
NASA Astrophysics Data System (ADS)
Crowley, Philip J. D.; Green, A. G.
2016-12-01
We derive a microscopic model for dissipative dynamics in a system of mutually interacting qubits coupled to a thermal bath that generalizes the dissipative model of Landau-Lifshitz-Gilbert to the case of anisotropic bath couplings. We show that the dissipation acts to bias the quantum trajectories towards a reduced phase space. This model applies to a system of superconducting flux qubits whose coupling to the environment is necessarily anisotropic. We study the model in the context of the D-Wave computing device and show that the form of environmental coupling in this case produces dynamics that are closely related to several models proposed on phenomenological grounds.
Anisotropic Liquid Microcapsules from Biomimetic Self-Folding Polymer Films.
Zakharchenko, Svetlana; Ionov, Leonid
2015-06-17
We demonstrated a novel approach for the fabrication of anisotropic capsules with liquid content using biomimetic self-folding thermoresponsive polymer films. The behavior of self-folding films is very similar to actuation in plants, where nonhomogenous swelling results in complex movements such as twisting, bending, or folding. This approach allows the design of anisotropic liquid capsules with rodlike and dumbbell-like morphologies. We found that these capsules are able to assemble into different complex structures, such as nematic-like one and 3D network depending on their morphology.
MHz gravitational waves from short-term anisotropic inflation
NASA Astrophysics Data System (ADS)
Ito, Asuka; Soda, Jiro
2016-04-01
We reveal the universality of short-term anisotropic inflation. As a demonstration, we study inflation with an exponential type gauge kinetic function which is ubiquitous in models obtained by dimensional reduction from higher dimensional fundamental theory. It turns out that an anisotropic inflation universally takes place in the later stage of conventional inflation. Remarkably, we find that primordial gravitational waves with a peak amplitude around 10-26~ 10-27 are copiously produced in high-frequency bands 10 MHz~100 MHz. If we could detect such gravitational waves in future, we would be able to probe higher dimensional fundamental theory.
Highly anisotropic effective dielectric functions of silver nanoparticle arrays.
Oates, Thomas W H; Ranjan, Mukesh; Facsko, Stefan; Arwin, Hans
2011-01-31
Variable-angle and Mueller matrix spectroscopic ellipsometry are used to determine the effective dielectric tensors of random and aligned silver nanoparticles and nanorods thin films. Randomly arranged particles are uniaxially anisotropic while aligned particles are biaxially anisotropic, with the anisotropy predominantly at the plasmonic resonances. The strong resonances in nanorod arrays result in the real part of the effective in-plane permittivities being opposite in sign over a significant range in the visible, suggesting the potential to design materials that display tunable negative-refraction. A structural tilt in the particle arrays results in monoclinic dielectric properties.
Anisotropic Second Harmonic Generation at Single Crystal Metal Surfaces.
NASA Astrophysics Data System (ADS)
Kexiang, He.
The work in this thesis comprises a set of experiments designed to study the anisotropic spatial dependence of second harmonic generation (SHG) from the surface of single crystal metals. The anisotropic dependence of reflected SHG from Al_2O_3 Al(111) interface was studied. The isotropic dependence of the SHG signal is used to probe the structural symmetry of the Al_2O_3Al(111) interface. For P- and S-polarized laser light incident at a fixed angle of 45^circ, the intensities of S- and P-polarized components of SHG signal were measured as a function of rotation angle during rotation of the surface about its normal. Anisotropic SHG studies were also performed on high Miller index surface of Al(331) and on a Al surface cut at 22.5^ circ with respect to the Al(111) surface. For the Al(331) surface, the anisotropic dependence of the SHG signal was measured for both the S- and P-polarized signals under both S- and P-polarized laser excitation. The anisotropy of the SHG from Al(331) were fit with theory using the assumption that symmetry is retained for this surface at the metal oxide-metal interface. Existing theory is used to derive the theoretical expressions predicting the anisotropic dependence of SHG from Al(331). The SHG probe was also used to follow pulsed laser annealing (PLA) of the Al_2O_3/Al(111) interface from on a chemically polished Al(111) surface. Using P-polarized pump laser light, the P-polarized SHG signal exhibits three equally spaced, equal intensity maxima during a single complete rotation of Al_2O _3/Al(111) interface about the interface normal. Annealing of the interface is found to occur when the P-polarized 1064nm pump laser light has an incident peak power of 11 times 10 ^6W/cm^2 per pulse. The intensity of the P-polarized 532nm SHG signal generated in reflection from this annealed interface exhibits a reduced anisotropic component in the SHG signal. Measurements of the anisotropic SHG signal from ionized beam deposited Al thin-films on Si(111
Lagrangian and Eulerian statistics in homogeneous, anisotropic flows
NASA Astrophysics Data System (ADS)
Iyer, Kartik; Bonaccorso, Fabio; Toschi, Federico; Biferale, Luca
2016-11-01
We report results from highly resolved direct numerical simulations of anisotropic homogeneous flows using up to 20483 collocations points. We examine a turbulent Kolmogorov flow with randomly correlated phases in order to recover space homogeneity on average. We present Eulerian and Lagrangian measurements concerning the universality of isotropic and anisotropic contributions using a systematic decomposition based on the eigenfunctions of the SO (3) group of rotations in three dimensions. Additionally, we discuss absolute dispersion statistics of particles in flows subjected to different large-scale anisotropies. ERC ADG NewTURB 2013.
Porous Portland Cement Concrete; The State of the Art.
This study investigates the current state of the art relating to the production and use of those porous portland cement concretes that may be...suitable for the construction of porous portland cement friction courses. Porous concretes produced by gap grading or elimination of the fine aggregate...applications discussed include: a no-fines pavement layer, porous portland cement concrete pavements, and porous pavement edge drains or porous hard shoulders
Fluid diffusion in porous silica
NASA Astrophysics Data System (ADS)
McCann, Lowell I.
Fluid motion in porous media has received a great deal of theoretical and experimental attention due to its importance in systems as diverse as ground water aquifers, catalytic processes, and size separation schemes. Often, the motion of interest is the random thermal motion of molecules in a fluid undergoing no net flow. This diffusive motion is particularly important when the size of the pores is nearly the same as the size of the molecules. In this study, fluid diffusion is measured in several varieties of porous silica whose pore structure is determined by the process by which it is made. The samples in this study have porosities (φ, the ratio of the pore volume to the total sample volume) that vary from 0.3 to 0.75 and average pore radii that range from approximately 15 to 120 A. Determining the effect of the pore structure on the diffusion of a liquid in a porous material is complicated by the chemical interactions between the diffusing molecules and the pore surface. In this study, ions in a hydrophilic fluid are used to block the adsorption of the diffusing dye molecules to the hydroxyl groups covering the silica surface. This technique is unlike typical surface treatments of silica in that it does not permanently alter the pore geometry. In this work, fluid diffusion is measured with a transient holographic grating technique where interfering laser beams create a periodic refractive index modulation in the fluid. The diffraction of a third laser off this grating is monitored to determine how quickly the grating relaxes, thereby determining the diffusion coefficient of the molecules in the fluid. Varying the grating periodicity controls the length scale of the diffusion measurement from 1.2 to 100 μm which is much larger than the average pore sizes of the samples. Therefore, over these large scales, we measure 'normal' diffusion, where the mean squared displacement of a diffusing particle varies linearly with time. In one particular type of porous silica
ZnO/porous-Si and TiO{sub 2}/porous-Si nanocomposite nanopillars
Wang, Dong Yan, Yong; Schaaf, Peter; Sharp, Thomas; Schönherr, Sven; Ronning, Carsten; Ji, Ran
2015-01-01
Porous Si nanopillar arrays are used as templates for atomic layer deposition of ZnO and TiO{sub 2}, and thus, ZnO/porous-Si and TiO{sub 2}/porous-Si nanocomposite nanopillars are fabricated. The diffusion of the precursor molecules into the inside of the porous structure occurs via Knudsen diffusion and is strongly limited by the small pore size. The luminescence of the ZnO/porous-Si nanocomposite nanopillars is also investigated, and the optical emission can be changed and even quenched after a strong plasma treatment. Such nanocomposite nanopillars are interesting for photocatalysis and sensors.
Mesoscopic Ni particles and nanowires by pulsed electrodeposition into porous Si
NASA Astrophysics Data System (ADS)
Michelakaki, E.; Valalaki, K.; G. Nassiopoulou, A.
2013-04-01
We report in this article on the formation of mesoscopic Ni particles and filling of continuous Ni nanowires into porous Si layers of thickness in the range of 0.5-4 μm with anisotropic vertical pores of average diameter in the range of 30-45 nm using pulsed electrodeposition from a Ni salt solution. The effect of pulse duration, number of pulses, and total process time on pore filling was investigated for porous Si with different porosities and porous Si layer thicknesses in the above thickness range. Scanning and transmission electron microscopy were used to characterize the samples. It was found that pore filling starts with Ni nucleation and nanoparticle formation at different points of the pore walls along the whole pore length and continues with nanoparticle coalescence to form continuous Ni nanowires that completely fill the pores. The mechanism involved in pore filling is particle nucleation and diffusion-controlled growth of Ni nanoparticles that coalesce to nanowires. From the beginning of the process, a metal film starts to form on the porous Si surface, and its thickness increases with increasing the process time. However, the presence of this film does not impede further pore filling and nanowire formation into the pores. This supports further the diffusion-controlled growth mechanism. Finally, it was demonstrated that full pore filling and continuous Ni nanowire formation were also achieved under direct current electrodeposition, and the results are quite similar to those obtained with pulsed electrodeposition when the same total deposition time is used in both cases.
Mathematical Model of Porous Medium Dynamics
NASA Astrophysics Data System (ADS)
Gerschuk, Peotr; Sapozhnikov, Anatoly
1999-06-01
Semiempirical model describing porous material strains under pulse mechanical and thermal loadings is proposed. Porous medium is considered as continuous one but with special form of pressure dependence upon strain. This model takes into account principal features of porous materials behavior which can be observed when the material is strained in dynamic and static experiments ( non-reversibility of large strains, nonconvexity of loading curve). Elastoplastic properties of porous medium, its damages when it is strained and dynamic fracture are also taken into account. Dispersion of unidirectional motion caused by medium heterogeneity (porousness) is taken into acount by introducing the physical viscosity depending upon pores size. It is supposed that at every moment of time pores are in equilibrium with pressure i.e. kinetic of pores collapse is not taken into account. The model is presented by the system of differential equations connecting pressure and energy of porous medium with its strain. These equations close system of equations of motion and continuity which then is integrated numerically. The proposed model has been tested on carbon materials and porous copper . Results of calculation of these materials shock compressing are in satisfactory agreement with experimental data. Results of calculation of thin plate with porous copper layer collision are given as an illustration.
Thiazolothiazole-linked porous organic polymers
Zhu, Xiang; Tian, Chengcheng; Jin, Tian; Wang, Jitong; Mahurin, Shannon Mark; Mei, Wenwen; Xiong, Yan; Hu, Jun; Feng, Xinliang; Liu, Honglai; Dai, Sheng
2014-10-07
In this study, thiazolothiazole-linked porous organic polymers have been synthesized from a facile catalyst-free condensation reaction between aldehydes and dithiooxamide under solvothermal conditions. The resultant porous frameworks exhibit a highly selective uptake of CO_{2} over N_{2} under ambient conditions.
Thiazolothiazole-linked porous organic polymers
Zhu, Xiang; Tian, Chengcheng; Jin, Tian; ...
2014-10-07
In this study, thiazolothiazole-linked porous organic polymers have been synthesized from a facile catalyst-free condensation reaction between aldehydes and dithiooxamide under solvothermal conditions. The resultant porous frameworks exhibit a highly selective uptake of CO2 over N2 under ambient conditions.
NASA Astrophysics Data System (ADS)
Guo, Xia; Ye, Wei; Sun, Hongyan; Zhang, Qiao; Yang, Jian
2013-11-01
One-dimensional porous metallic nanomaterials have attracted much attention due to their unique shape and hollow structure. Herein, the gold nanorods in a porous shell of an AuAg alloy are synthesized via a dealloying process of the core-shell Au@AuAg nanorods at room temperature. The formation of tiny pores in the shell results in the huge red-shift, sharp decrease and drastic broadening of longitudinal surface plasmon resonance absorption. The continuous removal of silver from the porous nanorods leads to the breakage of tiny pores and leaves a rough surface on the nanorods behind. The rough surface gradually becomes smooth in the subsequent dealloying process. The surface structures of these intermediates are correlated with their absorption spectra and catalytic activities for the catalytic reduction of p-nitrophenol. The porous nanorods show a higher catalytic efficiency than the gold nanorods, the core-shell nanorods and the rough nanorods. The results indicate that the dealloying of anisotropic bimetal nanomaterials not only provides an effective pathway to carve the structures on the nanoscale but also offers numerous opportunities to observe novel optical properties and enhanced catalysis performances.One-dimensional porous metallic nanomaterials have attracted much attention due to their unique shape and hollow structure. Herein, the gold nanorods in a porous shell of an AuAg alloy are synthesized via a dealloying process of the core-shell Au@AuAg nanorods at room temperature. The formation of tiny pores in the shell results in the huge red-shift, sharp decrease and drastic broadening of longitudinal surface plasmon resonance absorption. The continuous removal of silver from the porous nanorods leads to the breakage of tiny pores and leaves a rough surface on the nanorods behind. The rough surface gradually becomes smooth in the subsequent dealloying process. The surface structures of these intermediates are correlated with their absorption spectra and
Mechanics of anisotropic plates and shells - A new look at an old subject
NASA Astrophysics Data System (ADS)
Noor, A. K.
1992-07-01
A number of aspects of the mechanics of anisotropic plates and shells are discussed. The topics covered include computational models of anisotropic plates and shells, consequences of anisotropy on deformation couplings, symmetry types, stress concentrations and edge effects, and importance of transverse shear deformation; recent applications and recent advances in the modeling and analysis of anisotropic plates and shells; and new research directions.
Deformation, fatigue and fracture behavior of two cast anisotropic superalloys
NASA Technical Reports Server (NTRS)
Milligan, Walter W.; Huron, Eric S.; Antolovich, Stephen D.
1987-01-01
Tensile and low cycle fatigue (LCF) tests were conducted on two cast anisotropic superalloys. The effects of temperature, strain rate and stress range were investigated. Deformation behavior was extensively characterized and modeled. LCF and fracture behavior were studied and correlated with deformation behavior.
Symmetry algebra of a generalized anisotropic harmonic oscillator
NASA Technical Reports Server (NTRS)
Castanos, O.; Lopez-Pena, R.
1993-01-01
It is shown that the symmetry Lie algebra of a quantum system with accidental degeneracy can be obtained by means of the Noether's theorem. The procedure is illustrated by considering a generalized anisotropic two dimensional harmonic oscillator, which can have an infinite set of states with the same energy characterized by an u(1,1) Lie algebra.
Quark–gluon plasma phenomenology from anisotropic lattice QCD
Skullerud, Jon-Ivar; Kelly, Aoife; Aarts, Gert; Allton, Chris; Amato, Alessandro; Evans, P. Wynne M.; Hands, Simon; Burnier, Yannis; Giudice, Pietro; Harris, Tim; Ryan, Sinéad M.; Kim, Seyong; Lombardo, Maria Paola; Oktay, Mehmet B.; Rothkopf, Alexander
2016-01-22
The FASTSUM collaboration has been carrying out simulations of N{sub f} = 2 + 1 QCD at nonzero temperature in the fixed-scale approach using anisotropic lattices. Here we present the status of these studies, including recent results for electrical conductivity and charge diffusion, and heavy quarkonium (charm and beauty) physics.
Cluster variation studies of the anisotropic exchange interaction model
NASA Astrophysics Data System (ADS)
King, T. C.; Chen, H. H.
The cluster variation method is applied to study critical properties of the Potts-like ferromagnetic anisotropic exchange interaction model. Phase transition temperatures, order parameter discontinuities and latent heats of the model on the triangular and the fcc lattices are determined by the triangle approximation; and those on the square and the sc lattices are determined by the square approximation.
Mathematical simulation of a steady process of anisotropic filtration
NASA Astrophysics Data System (ADS)
Badriev, I. B.; Banderov, V. V.; Pankratova, O. V.; Shangaraeva, A. I.
2016-11-01
This article discusses the methods of approximate solution of mixed variational inequalities with operators of monotone type. The functional, which is included in this variational inequality, is separable, in other words, it is the sum of a number of nondifferentiable functionals. These variational inequalities appear, in particular, in the description of steady incompressible filtration processes of highly viscous fluids in anisotropic medium.
Propagation characteristics of an extremely anisotropic metamaterial loaded helical guide.
Sharma, Dushyant K; Pathak, Surya K
2016-12-26
In this study, we report slow wave propagation characteristics of an extremely anisotropic metamaterial loaded helical guide (EAMLHG). An analytical expression has been theoretically derived and numerically computed to get exact solutions of all possible guided modes of propagation. Anisotropy is defined in terms of positive longitudinal permittivity (ϵz > 0) and negatives transverse permittivity value (ϵt < 0). The waveguide supports hybrid (HE) mode propagation and possesses characteristics of backward wave (BW) mode, forward wave (FW) mode, zero-group velocity and mode-degeneracy. The large value of effective index of BW mode and mode-degeneracy mechanism leads to slowing and trapping of electromagnetic (EM) wave. Closed-form guided mode energy propagation expressions has been also derived and computed which exhibits zero power flow at mode degeneracy point. A comparative study is also carried out between extremely anisotropic metamaterial helical waveguide (EAMLHG) and conventional extremely anisotropic metamaterial cylindrical guide (EAMCG), which reveals enhanced slow wave behaviour. Engineering feasible design and analysis is also presented by combining alternate disks of silver and glass as an extremely anisotropic medium which exhibits lossy and dispersive properties. This type of waveguide can find applications as a filter, phase shifter, and delay lines in microwave to THz applications and, as an optical buffer in optoelectronics applications.
Noncommutative anisotropic oscillator in a homogeneous magnetic field
NASA Astrophysics Data System (ADS)
Nath, D.; Roy, P.
2017-02-01
We study anisotropic oscillator in the presence of a homogeneous magnetic field and other related systems in the noncommutative plane. Energy values as function of the noncommutative parameter θ and the magnetic field B have been obtained. Some features of the spectrum, for example, formation of energy bands etc. have been examined. The effect of anisotropy on the energy levels has also been discussed.
Hedgehogs in a three-dimensional anisotropic spin system
NASA Astrophysics Data System (ADS)
Jonsson, Thordur
1983-06-01
We study a continuum version of a classical anisotropic spin model in three dimensions with three component spins. We prove the existence of topological defects, called hedgehogs, which are analogous to the vortices in the two-dimensional xy-model and have a logarithmically divergent action. Bounds for the interaction energy of a hedgehog and an antihedgehog are derived.
The role of anisotropic expansion for pulmonary acinar aerosol deposition
Hofemeier, Philipp; Sznitman, Josué
2016-01-01
Lung deformations at the local pulmonary acinar scale are intrinsically anisotropic. Despite progress in imaging modalities, the true heterogeneous nature of acinar expansion during breathing remains controversial, where our understanding of inhaled aerosol deposition still widely emanates from studies under self-similar, isotropic wall motions. Building on recent 3D models of multi-generation acinar networks, we explore in numerical simulations how different hypothesized scenarios of anisotropic expansion influence deposition outcomes of inhaled aerosols in the acinar depths. While the broader range of particles acknowledged to reach the acinar region (dp = 0.005–5.0 μm) are largely unaffected by the details of anisotropic expansion under tidal breathing, our results suggest nevertheless that anisotropy modulates the deposition sites and fractions for a narrow band of sub-micron particles (dp ~ 0.5–0.75 μm), where the fate of aerosols is greatly intertwined with local convective flows. Our findings underscore how intrinsic aerosol motion (i.e. diffusion, sedimentation) undermines the role of anisotropic wall expansion that is often attributed in determining aerosol mixing and acinar deposition. PMID:27614613
Seismic Gradiometry using Ambient Seismic Noise in an Anisotropic Earth
NASA Astrophysics Data System (ADS)
de Ridder, S. A. L.; Curtis, A.
2017-02-01
We introduce a wavefield gradiometry technique to estimate both isotropic and anisotropic local medium characteristics from short recordings of seismic signals by inverting a wave equation. The method exploits the information in the spatial gradients of a seismic wavefield that are calculated using dense deployments of seismic arrays. The application of the method uses the surface wave energy in the ambient seismic field. To estimate isotropic and anisotropic medium properties we invert an elliptically anisotropic wave equation. The spatial derivatives of the recorded wavefield are evaluated by calculating finite differences over nearby recordings, which introduces a systematic anisotropic error. A two step approach corrects this error: finite difference stencils are first calibrated, then the output of the wave-equation inversion is corrected using the linearized impulse response to the inverted velocity anomaly. We test the procedure on ambient seismic noise recorded in a large and dense ocean bottom cable array installed over Ekofisk field. The estimated azimuthal anisotropy forms a circular geometry around the production-induced subsidence bowl. This conforms with results from studies employing controlled sources, and with interferometry correlating long records of seismic noise. Yet in this example, the results where obtained using only a few minutes of ambient seismic noise.
Scale disparity and spectral transfer in anisotropic numerical turbulence
NASA Technical Reports Server (NTRS)
Zhou, YE; Yeung, P. K.; Brasseur, James G.
1994-01-01
To study the effect of cancellations within long-range interactions on local isotropy at the small scales, we calculate explicitly the degree of cancellation in distant interactions in the simulations of Yeung & Brasseur and Yeung, Brasseur & Wang using the single scale disparity parameter 's' developed by Zhou. In the simulations, initially isotropic simulated turbulence was subjected to coherent anisotropic forcing at the large scales and the smallest scales were found to become anisotropic as a consequence of direct large-small scale couplings. We find that the marginally distant interactions in the simulation do not cancel out under summation and that the development of small-scale anisotropy is indeed a direct consequence of the distant triadic group, as argued by Yeung, et. al. A reduction of anisotropy at later times occurs as a result of the isotropizing influences of more local energy-cascading triadic interactions. Nevertheless, the local-to-nonlocal triadic group persists as an isotropizing influence at later times. We find that, whereas long-range interactions, in general, contribute little to net energy transfer into or out of a high wavenumber shell k, the anisotropic transfer of component energy within the shell increases with increasing scale separations. These results are consistent with results by Zhou, and Brasseur & Wei, and suggest that the anisotropizing influences of long range interactions should persist to higher Reynolds numbers. The residual effect of the forced distant group in this low-Reynolds number simulation is found to be forward cascading, on average.