Effect of Thermal Conductivity and Thickness of the Walls on the Natural Convection in a Horizontal Viscoelastic Jeffreys Fluid Layer

It is a common practice to use ideal thermal boundary conditions to investigate natural convection. These correspond to very good conducting walls and to very bad conducting walls. In particular, this has been the case in natural convection of viscoelastic fluids. In this paper, these conditions are generalized by taking into account the finite thermal conductivities and thicknesses of the walls in the natural convection of a viscoelastic Jeffreys fluid heated from below. The goal is to present more realistic results related to experimental conditions. The critical Rayleigh number Rc, the frequency of oscillation ωc, and the wavenumber kc have been plotted varying the properties of the walls from the case of very good thermal conductivity to very poor thermal conductivity. In order to understand the convective phenomena, two parameters are fixed and the other one varied among the nondimensional relaxation time F, the relative retardation time E, and the Prandtl number Pr of the viscoelastic fluid. The role of the relative retardation time E on the thermal instability is discussed in detail.

Parameters for Assessing Oil Reservoir Water Flooding Additives

This paper is concerned with deriving parameters for assessing the effectiveness of fluid additives to improve water flooding during enhanced oil recovery. We focus particularly on the use of rheological modifiers, which do not show monotonic behavior with the shear rate within the rock pores. We derive figures of merit based on (1) relative retardation in high and low permeability rock, (2) profile flattening, and (3) injectivity index. Only the last of these provides a measure of water flood profile improvement while maintaining sufficient fluid flow and production levels.

An overdetermined phase-stepping strategy for the capture of high-quality photoelastic data

An overdetermined extension to the phase-stepping approach to digital photoelasticity is described in order to obtain high-quality photoelastic data for use in the examination of contact problems. A framework is adapted from earlier work by Ambirajan and Look and is applied to the generalization of existing phase-stepping strategies and the synthesis of new overdetermined variants on the method. The optimality of these strategies is demonstrated computationally, and the influence of errors in quarter-wave plate orientation and assumed isoclinic angle is explored. Sample experimental results are presented, which demonstrate the excellent performance of the system when used with narrow-bandwidth filters to approximate the use of monochromatic light. When the internal filters integral with the colour camera were used, the results were also of high quality up to a relative retardation of around 4.5 measured on the green channel, but measurements of higher fringe orders were progressively degraded owing to the broad bandwidths of the camera's internal filters.

A Polarizing Microscope for Mapping Birefringent Objects in 3D Space

The traditional polarizing microscope equipped with crossed linear polarizers shows a picture in which the image contrast of a birefringent object depends on both the amount of relative retardation induced by the object and the orientation of its principal axis. For example, if the orientation of the principal axis is parallel to one of the polarizers, then the birefringent object becomes invisible. For best visibility, the principal axis must be oriented at 45° to the polarizers. In addition, the image intensity of the object is proportional to the square of the sine of the relative phase shift between the ordinary and the extraordinary ray passing through the object. The addition of a waveplate as compensator to the optical train provides the opportunity to improve the contrast and measure the relative retardation, but the principal restrictions of orientation dependence and non-linear image contrast remains.

Deltascan, a Light Microscope Imaging System for Examining Birefringent Materials.

DELTASCAN is a new light microscopy imaging system developed and built in the Department of Physics, Oxford, UK. [1] It is able to separate out the contrast seen in a ‘cross-polars’ image into three components, | sin δ | (a function of the optical retardation), φ (the orientation of a section of the optical indicatrix) and Io (the transmittance). These three variables are plotted as separate coded colour images. With the present computer and apparatus the data is collected, processed and the images simultaneously drawn in approximately 40 seconds.DELTASCAN has an optical setup [2] based around a polarising microscope (Figure 5). The intensity through this optical setup can be shown to have the form:I = Io[1 + sin2(ωt−ϕ)sin δ] (1)where ω = frequency of the analyser, φ = orientation of cross section of the indicatrix and, δ = relative retardation which is related to a samples birefringence by δ = 2πΔnL/λ.

Postion angle jumps in pulsar linear polarization

The position angle (PA) behaviour of linear polarization of pulsar emission is simulated after considering the relative retardation between the core and conal components, which are believed to be generated from different emission altitudes. The PA will jump 90° at some points where the complete depolarization occurs.

Texture Development and Anisotropic Photoelastic Properties in Rolled Silver Chloride

Experimental and theoretical studies have been carried out in order to relate elastic anisotropy to optical anisotropy by means of photoelasticity. The fundamentals of anisotropic photoelasticity have been described. Specimens of monocrystalline and polycrystalline silver chloride have been submitted to tensile stress and relative retardation and extinction angles observed in polarized monochromatic light to show conformity to the theories which quantitatively relate the state of stress and optical phenomena. Textures of cold-rolled as well as of recrystallized silver chloride specimens were determined with an X-ray goniometer. Texture determining parameters such as degree of rolling and recrystallisation time and temperature have been varied. Textures found in silver chloride after various processing have been characterized.

Renal cortical interstitium and fluid absorption by peritubular capillaries

Every minute, the cortical peritubular capillaries in a 1-g rat kidney take up more than 0.5 ml tubular reabsorbate. Studies of renal lymph and measurements of pressure in capillaries (Pc) and interstitium (Pi) indicate that normally the protein colloid osmotic pressure of peritubular capillary plasma (COPp) provides the necessary absorptive force, keeping Pi at 2-4 mmHg, i.e., 8-10 mmHg lower than Pc. At reduced COPp, continued delivery of fluid from the tubules automatically raises Pi to maintain capillary fluid uptake. The transient Pi response to sudden exposure of the kidney to subatmospheric pressure shows that such adjustment of forces may take place in only 5 s. Most remarkable, adjustment of forces may take place in only 5 s. Most remarkable, reabsorption continues during protein-free perfusion of the isolated rat kidney, apparently effected by a Pi exceeding Pc. A relative retardation of interstitial uptake of ferritin from plasma in this case suggests fluid reabsorption through both small and large pores in the capillary wall. Collapse of the capillaries is presumably prevented by tight tethering to the capillary wall, giving the narrow interstitium a very low compliance.