Reply by the author to J. Korringa and R. J. S. Brown

Geophysics ◽  
1984 ◽  
Vol 49 (2) ◽  
pp. 203-203
Author(s):  
James Lange
Keyword(s):  
Dielectric Properties ◽  
Theoretical Model ◽  
Physical Properties ◽  
Porous Materials ◽  
Experimental Model ◽  
Volume Fraction ◽  
Dielectric Material ◽  
Microscopic Structure ◽  
Dielectric Fluids ◽  
Insight Into

An important feature of the dielectric properties of water in porous materials is that it does not behave like many other dielectric fluids of simpler microscopic structure. As a basis for evaluating the deviance of the dielectric properties of water, an experimental model is used in my paper. This experimental model is the volume fraction model and is determined from direct measurement. It involves no theoretical suppositions about the geometry of the composite dielectric material. This approach is taken to illustrate the unique physical properties of water rather than to adopt some theoretical model which depends upon some extraordinary insight into the “approximate” geometry of the composite dielectrics.

scholarly journals ASKAP observations of multiple rapid scintillators reveal a degrees-long plasma filament

2021 ◽  
Vol 502 (3) ◽  
pp. 3294-3311
Author(s):  
Yuanming Wang ◽  
Artem Tuntsov ◽  
Tara Murphy ◽  
Emil Lenc ◽  
Mark Walker ◽  
...  
Keyword(s):  
Physical Properties ◽  
Angular Width ◽  
Scattering Medium ◽  
Central Frequency ◽  
Linear Arrangement ◽  
Plasma Filament ◽  
Kinematic Models ◽  
Tidal Stream ◽  
First Time ◽  
Insight Into

ABSTRACT We present the results from an Australian Square Kilometre Array Pathfinder search for radio variables on timescales of hours. We conducted an untargeted search over a 30 deg2 field, with multiple 10-h observations separated by days to months, at a central frequency of 945 MHz. We discovered six rapid scintillators from 15-min model-subtracted images with sensitivity of $\sim\! 200\, \mu$Jy/beam; two of them are extreme intra-hour variables with modulation indices up to $\sim 40{{\ \rm per\ cent}}$ and timescales as short as tens of minutes. Five of the variables are in a linear arrangement on the sky with angular width ∼1 arcmin and length ∼2 degrees, revealing the existence of a huge plasma filament in front of them. We derived kinematic models of this plasma from the annual modulation of the scintillation rate of our sources, and we estimated its likely physical properties: a distance of ∼4 pc and length of ∼0.1 pc. The characteristics we observe for the scattering screen are incompatible with published suggestions for the origin of intra-hour variability leading us to propose a new picture in which the underlying phenomenon is a cold tidal stream. This is the first time that multiple scintillators have been detected behind the same plasma screen, giving direct insight into the geometry of the scattering medium responsible for enhanced scintillation.

scholarly journals Effect of Terminal Groups on Thermomechanical and Dielectric Properties of Silica–Epoxy Composite Modified by Hyperbranched Polyester

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2451
Author(s):  
Jianwen Zhang ◽  
Dongwei Wang ◽  
Lujia Wang ◽  
Wanwan Zuo ◽  
Lijun Zhou ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Binding Energy ◽  
Epoxy Resin ◽  
Volume Fraction ◽  
Epoxy Composite ◽  
Mean Square Displacement ◽  
Mean Square ◽  
Hyperbranched Polyester ◽  
Free Volume Fraction

To study the effect of hyperbranched polyester with different kinds of terminal groups on the thermomechanical and dielectric properties of silica–epoxy resin composite, a molecular dynamics simulation method was utilized. Pure epoxy resin and four groups of silica–epoxy resin composites were established, where the silica surface was hydrogenated, grafted with silane coupling agents, and grafted with hyperbranched polyester with terminal carboxyl and terminal hydroxyl, respectively. Then the thermal conductivity, glass transition temperature, elastic modulus, dielectric constant, free volume fraction, mean square displacement, hydrogen bonds, and binding energy of the five models were calculated. The results showed that the hyperbranched polyester significantly improved the thermomechanical and dielectric properties of the silica–epoxy composites compared with other surface treatments, and the terminal groups had an obvious effect on the enhancement effect. Among them, epoxy composite modified by the hyperbranched polyester with terminal carboxy exhibited the best thermomechanical properties and lowest dielectric constant. Our analysis of the microstructure found that the two systems grafted with hyperbranched polyester had a smaller free volume fraction (FFV) and mean square displacement (MSD), and the larger number of hydrogen bonds and greater binding energy, indicating that weaker strength of molecular segments motion and stronger interfacial bonding between silica and epoxy resin matrix were the reasons for the enhancement of the thermomechanical and dielectric properties.

Heat Transfer and Crystallization Modeling during Compression Molding of Thermoplastic Composite Parts

2015 ◽  
Vol 651-653 ◽  
pp. 1507-1512 ◽  
Author(s):  
Jalal Faraj ◽  
Baptiste Pignon ◽  
Jean Luc Bailleul ◽  
Nicolas Boyard ◽  
Didier Delaunay ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Volume Fraction ◽  
Thermoplastic Composite ◽  
Large Temperature ◽  
Process Conditions ◽  
Thermoplastic Resin ◽  
Whole Process ◽  
Low Viscosity ◽  
Thermo Physical Properties

We present in this paper, the coupling of heat transfer to the crystallization of composite in a closed mold. The composite is based on thermoplastic resin (low viscosity PA 66) with glass fiber (50% volume fraction). In order to realize this coupling, an accurate characterizationof thermo physical properties in process conditions, especially in the molten and solid state is needed. In addition, theidentification of the parameters of crystallization kinetics is required. Therefore, we present the methods that were used to study the thermo physical properties as the thermal conductivity, heat capacity and the specific volume. Moreover, the kinetic of crystallization was estimated over a large temperature range by using Flash DSC and classical DSC. In order to validate the measurements, the whole process was modeled by finite elements. The model includes the resolution of the strong coupling between the heat transfer and crystallization. Finally, the experimental and numerical results were compared.

Modeling The Microwave Frequency Dielectric Properties of Thermoplastic Composite Materials

1992 ◽  
Vol 269 ◽  
Author(s):  
Mitchell L. Jackson ◽  
Curtis H. Stern
Keyword(s):  
Composite Materials ◽  
Dielectric Properties ◽  
Volume Fraction ◽  
Perturbation Technique ◽  
Resonant Cavity ◽  
Microwave Frequency ◽  
Thermoplastic Composite ◽  
Fiber Volume ◽  
Thermoplastic Matrix ◽  
Rotation Procedure

ABSTRACTMixture models were studied in an effort to predict the microwave frequency permittivities of unidirectional-fiber-reinforced thermoplastic-matrix composite materials as a function of fiber volume fraction, fiber orientation relative to the electric field, and temperature. The permittivities of the constituent fiber and plastic materials were measured using a resonant cavity perturbation technique at 9.4 GHz and at 2.45 GHz. The permittivities of the composite specimens were measured using a reflection cavity technique at 9.4 GHz and at 2.45 GHz. Simple “rule-of-mixtures” models that use the fiber and plastic permittivities have been found to approximate the complex dielectric properties of the composite for varied fiber volume fractions. The permittivities of oriented composites were modeled using a tensor rotation procedure. Composite permittivities were modeled with temperature up to the glass transition temperature of the thermoplastic matrix.

A Yield Criterion of Porous Materials With Anisotropy Caused by Geometry or Distribution of Pores

1991 ◽  
Vol 113 (4) ◽  
pp. 425-429 ◽  
Author(s):  
T. Hisatsune ◽  
T. Tabata ◽  
S. Masaki
Keyword(s):  
Velocity Field ◽  
Porous Materials ◽  
Upper Bound ◽  
Volume Fraction ◽  
Yield Criterion ◽  
Longitudinal Direction ◽  
Axisymmetric Deformation ◽  
The Other ◽  
The Matrix ◽  
Spherical Cells

Axisymmetric deformation of anisotropic porous materials caused by geometry of pores or by distribution of pores is analyzed. Two models of the materials are proposed: one consists of spherical cells each of which has a concentric ellipsoidal pore; and the other consists of ellipsoidal cells each of which has a concentric spherical pore. The velocity field in the matrix is assumed and the upper bound approach is attempted. Yield criteria are expressed as ellipses on the σm σ3 plane which are longer in longitudinal direction with increasing anisotropy and smaller with increasing volume fraction of the pore. Furthermore, the axes rotate about the origin at an angle α from the σm-axis, while the axis for isotropic porous materials is on the σm-axis.

Flow Characteristics of a Powder Lubricant in a Slider Bearing

2001 ◽  
Author(s):  
Manjunath Pappur ◽  
M. M. Khonsari
Keyword(s):  
Slip Velocity ◽  
Thrust Bearing ◽  
Volume Fraction ◽  
Flow Characteristics ◽  
Slider Bearing ◽  
Systematic Development ◽  
Powder Lubrication ◽  
Insight Into ◽  
Theory And Experiment ◽  
Good Agreement

Abstract This paper deals with a systematic development of theory of powder lubrication with the appropriate formalism based on the fundamentals of fluid mechanics. The theory is capable of predicting flow velocity, fluctuation (pseudo-temperature), powder volume fraction, and slip velocity at the boundaries. An extensive set of parametric simulations covering particle size, surface roughness, volumetric flow, load and speed are performed to gain insight into the performance of a powder lubricated thrust bearing. The results of simulations are compared to the published experimental results. Good agreement between the theory and experiment attests to the capability of the model and its potential for design of powder lubricated bearings.

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