An Analytical Method of Electromagnetic Wave Scattering by a Highly Conductive Sphere in a Lossless Medium with Low-Frequency Dipolar Excitation

The current research involves an analytical method of electromagnetic wave scattering by an impenetrable spherical object, which is immerged in an otherwise lossless environment. The highly conducting body is excited by an arbitrarily orientated time-harmonic magnetic dipole that is located at a reasonable remote distance from the sphere and operates at low frequencies for the physical situation under consideration, wherein the wavelength is much bigger than the size of the object. Upon this assumption, the scattering problem is formulated according to expansions of the implicated magnetic and electric fields in terms of positive integer powers of the wave number of the medium, which is linearly associated to the implied frequency. The static Rayleigh zeroth-order case and the initial three dynamic terms provide an excellent approximation for the obtained solution, while terms of higher orders are of minor significance and are neglected, since we work at the low-frequency regime. To this end, Maxwell’s equations reduce to a finite set of interrelated elliptic partial differential equations, each one accompanied by the perfectly electrically conducting boundary conditions on the metal sphere and the necessary limiting behavior as we move towards theoretical infinity, which is in practice very far from the observation domain. The presented analytical technique is based on the introduction of a suitable spherical coordinated system and yields compact fashioned three-dimensional solutions for the scattered components in view of infinite series expansions of spherical harmonic modes. In order to secure the validity and demonstrate the efficiency of this analytical approach, we invoke an example of reducing already known results from the literature to our complete isotropic case.

Effects on a Nearby Bridge of Dismantling Temporary Lining During Excavation of a Shallow-Buried Rectangular Tunnel

It is almost inevitable that when a tunnel is excavated in an urban area, it will pass under an existing bridge. During tunnel excavation, a temporary lining is installed and subsequently removed. However, dismantling temporary lining may affect the stability of a nearby bridge. A numerical model was created and tests were conducted on a large-scale physical model to investigate the effects of dismantling temporary lining on a nearby bridge structure. A novel method of modeling the restraining force at the top of a pier was introduced to make the model more accurate in representing the physical situation. Analysis of the results led to the following conclusions and suggestions. 1. The process of removing temporary lining can have a significant impact on surface settlement and structural deformation of the bridge. 2. The effect of removing the second half temporary lining is greater than that of removing the first half. The key range of the tunnel where this phenomenon is principally observed contains one section of tunnel ahead (i.e., in the direction of tunnel advance) of the bridge span and the two sections to the rear. 3. A 6 m–3 m–6 m mixed dismantling method is recommended for use in the key range, and a rigid cap-connection method is proposed to counteract the considerable effects of dismantling temporary lining.

Unsteady MHD Plane Couette-Poiseuille Flow of Fourth-Grade Fluid with Thermal Radiation, Chemical Reaction and Suction Effects

This study investigates the unsteady MHD flow of a fourth-grade fluid in a horizontal parallel plates channel. The upper plate is oscillating and moving while the bottom plate is stationary. Solutions for momentum, energy and concentration equations are obtained by the He-Laplace scheme. This method was also used by Idowu and Sani [12] and there is agreement with our results. The effect of various flow parameters controlling the physical situation is discussed with the aid of graphs. Significant results from this study show that velocity and temperature fields increase with the increase in the thermal radiation parameter, while velocity and concentric fields decrease with an increase in the chemical reaction parameter. Furthermore, velocity, temperature and concentric fields decrease with an increase in the suction parameter. It is also interesting to note that when S4 = 0, our results will be in complete agreement with Idowu and Sani [12] results. The results of this work are applicable to industrial processes such as polymer extrusion of dye, draining of plastic films etc.

Analysis on physical properties of micropolar nanofluid past a constantly moving porous plate

The computational analysis is presented for boundary layer heat and mass transfer flow of hydro magnetic micropolar nanofluid flow. In the flow model, viscosity of the fluid is taken as temperature-dependent and varies linearly and the other physical properties such as radiative heat flux, the magnetic field, the viscous dissipation, chemical reaction are additionally assumed in the energy equation and spices concentration equation respectively The PDEs representing the fluid flow have been changed into a framework of dimensionless ODEs and explained mathematically through the 4th order R-K and NS shooting technique. Temperature distribution, velocity distribution, micro rotation, and concentration distribution are explored graphically for a series of solid volume fraction (0<ϕ<2) of nano-solid particles. All the findings for various flow parameters agreed perfectly with physical situation of the flow. It is observed that for increasing value of magnetic parameter, the concentration and temperature of the micropolar nano fluid near the boundary layer declines and increasing value of the volume fraction of nano-solid particle ϕ leads to decrease in velocity and micro rotation of the fluid within the boundary layer decreases.

Counterexamples to the Maximum Force Conjecture

Dimensional analysis shows that the speed of light and Newton’s constant of gravitation can be combined to define a quantity F*=c4/GN with the dimensions of force (equivalently, tension). Then in any physical situation we must have Fphysical=fF*, where the quantity f is some dimensionless function of dimensionless parameters. In many physical situations explicit calculation yields f=O(1), and quite often f≤1/4. This has led multiple authors to suggest a (weak or strong) maximum force/maximum tension conjecture. Working within the framework of standard general relativity, we will instead focus on idealized counter-examples to this conjecture, paying particular attention to the extent to which the counter-examples are physically reasonable. The various idealized counter-examples we shall explore strongly suggest that one should not put too much credence into any truly universal maximum force/maximum tension conjecture. Specifically, idealized fluid spheres on the verge of gravitational collapse will generically violate the weak (and strong) maximum force conjectures. If one wishes to retain any truly general notion of “maximum force” then one will have to very carefully specify precisely which forces are to be allowed within the domain of discourse.

Non fourier heat transfer enhancement in power law fluid with mono and hybrid nanoparticles

Several polymers like ethylene glycol exhibit non-Newtonian rheological behavior. Ethylene glycol is a world-widely used engine coolant and therefore, investigation of thermal enhancement by dispersing mono and hybrid nanoparticles in ethylene glycol is worthful. Since ethylene glycol has shear rate-dependent viscosity and it obeys the power-law rheological model. Therefore, based on these facts, the power-law rheological model with thermophysical properties is augmented with basic law of heat transfer in fluid for the modeling of the considered physical situation. $$Mo{S}_{2}$$ M o S 2 are taken as mono-nanoparticles where $$Mo{S}_{2}$$ M o S 2 and $$Si{O}_{2}$$ S i O 2 are taken as hybrid nanoparticles. Comparative study for the enhancement of thermal performance of MoS2 ethylene glycol and $$Mo{S}_{2}$$ M o S 2 −$$Si{O}_{2}$$ S i O 2 – ethylene glycol is done. For energy conservation, non-Fourier’s law of Cattaneo–Christov is used. The power-law fluid becomes more heat generative due to the dispersion of $$Mo{S}_{2}$$ M o S 2 and $$Si{O}_{2}$$ S i O 2 . However, $$Mo{S}_{2}$$ M o S 2 −power-law fluid is less heat generative relative to $$Mo{S}_{2}$$ M o S 2 − $$Si{O}_{2}$$ S i O 2 -nanofluid. Thermal relaxation time is found proportional to the ability of the fluid to restore its thermal equilibrium.

Very Low and High Blood Viscosity are Risk Factors for Internal Flow Choking Causing Asymptomatic Cardiovascular Disease

Herein, we established the proof of the concept of internal flow choking in CVS causing cardiovascular risk through the closed-form analytical, in vitro and in silico methods. An over dose of blood-thinning drug will enhance the Reynolds number, which creates high turbulence level causing an augmented boundary layer blockage factor leading to an early undesirable biofluid/Sanal flow choking at a critical blood-pressure-ratio (BPR). The fact is that in nanoscale vessels when the pressure of fluid increases, average-mean-free-path decreases and thus, the Knudsen number reduces. It leads to the physical situation of no-slip boundary condition with compressible-viscous flow effect. Sanal-flow-choking is a compressible-viscous flow effect establishing a physical condition of the sonic-fluid-throat, at a critical blood pressure ratio (BPR). We concluded that asymptomatic-hemorrhage (AH) and acute-heart-failure (AHF) are transient-events as a result of internal flow-choking in nanoscale and/or large vessels followed by the shock wave creation and transient pressure-overshoot. We concluded that cardiovascular risk could be reduced by simultaneously lessening the blood-viscosity and flow turbulence by increasing thermal-tolerance-level in terms of BHCR and/or by decreasing the blood pressure (BP) ratio.

On Irony in Pride and Prejudice from the Perspective of Pragmatic Presupposition

Presupposition, as a pragmatic concept, plays an important role in discourse construction. Pragmatic presupposition works inside and outside ironic discourse to help maintain cohesion and coherence as well as direction and integrity of it. This paper presents pragmatic analyses on irony selected from Pride and Prejudice with different functions of presuppositions from social standards, collusive agreement, physical situation, and previous circumstances, and hopes to provide a different way of theorizing irony and ironic discourse.

Evaporation and combustion of n-heptane droplets in supersonic combustor

The purpose of the present study is to investigate the combustion of the n-heptane droplet cloud in the supersonic combustor. The finite volume solver is developed to simulate the two-phase reacting compressible flow using single step reaction mechanism as finite rate chemistry. The focus is on the impacts of droplet size and cloud density on the performance of the scramjet. For the considered physical situation, the upper limit of the droplet size is determined to have higher combustion efficiency, and it is shown that the combustion mode is kinetic-controlled for small sizes and is evaporation-controlled for large droplet sizes. The variation of combustor’s exit total pressure and temperature is also investigated for different droplet cloud densities, demonstrating their apparent opposite behavior that must be considered to get optimum propulsion efficiency. In addition, it is illustrated that thermal choking is another criterion which should be avoided by controlling the fuel mass flow rate for intended flight conditions.

Perturbative correction terms to electromagnetic self-force due to metric perturbation: astrophysical and cosmological implications

We consider the equation of motion of a charged particle or a charged compact object in curved space-time, under the reaction of electromagnetic radiation and also consider a physical situation such that the charged particle or compact object emits gravitational radiation, thereby gravitational radiation reaction also acts on it. We investigate the effect of this metric perturbation i.e. the gravitational radiation on the electromagnetic self-force. We show that, besides the interaction terms derived by Zimmerman and Poisson (Phys Rev D 90:084030, 2014), additional perturbative terms are generated, which are linear in metric perturbation and are generated due to perturbation of the electromagnetic self-force by the metric perturbation. We discuss the conditions of significance of these perturbative terms and also the interaction terms with respect to the gravitational self-force in various astrophysical and cosmological cases; such as the motion of charged particles around black holes, some extreme mass-ratio inspirals (EMRIs) involving sufficiently accelerated motion of charged stars (specially neutron stars) or charged stellar mass black holes around supermassive black holes, and motion of charged particles around charged primordial black holes formed in the early Universe etc. We find that in some astrophysical and cosmological cases these perturbative terms can have significant effect in comparison with the gravitational radiation-reaction term.