Rigorous bounds for the complex dielectric constant of a two-component composite

Rigorous bounds are systematically derived for the bulk effective dielectric constant of a two-phase composite material ε_e under various assumptions about the available information. The bounds are drawn for some special cases in the complex ε_e-plane. The question of optimality of the bounds and their connection to solvable microgeometries is discussed. It is shown how linear programming theory can be used to aid in the derivation of these bounds.     

Effective thermal conduction in composite materials

The problem of determining the bounds and/or estimating the effective thermal conductivity (λ _eff) of a composite (multiphase) system given the volume fractions and the conductivities of the components has been investigated. A comparison between the measured data and the results predicted by theoretical models has been made for seven heterogeneous samples. The tested models include those of the effective medium theory (EMT), Hashin and Shtrikman (HS) bounds, and Wiener bounds. These models can be used to characterize macroscopic homogeneous and isotropic multiphase composite materials either by determining the bounds for the effective thermal conductivity and/or by estimating the overall conductivity of the random mixture. It turns out that the most suitable one of these models to estimate λ _eff is the EMT model. This model is a mathematical model based on the homogeneity condition which satisfies the existence of a statistically homogeneous medium that encloses inclusions of different phases. Numerical values of thermal conductivity for the samples that satisfy the homogeneity condition imposed by the effective medium theory are in best agreement with the experimentally measured ones.     

Thermal conduction through loose and granular two-phase materials at normal pressure

The integrated theory derived for the lattice-type dispersions is modified and extended to estimate the effective thermal conductivity of loose and granular two-phase materials at normal pressure assuming an effective continuous media approximation. A comparison of calculated values ofλ _e with the reported experimental results over a wide range of loose and granular two-phase materials shows a good agreement.     

Thermal conduction in a homogeneous two-phase system

Assuming a regular geometry of dispersed phase (λ ₂) an integrated theory for the effective thermal conductivityλ _e of all kind of two-phase materials (including loose materials) is developed. The flux modification is carried out by considering the effective neighbouring interactions in the solution of Poisson’s equation. A comparison of calculatedλ _e values with the reported experimental results over a wide range of two-phase materials shows a good agreement.     

Duality and effective conductivity of random two-phase flat systems

The possible functional forms of the effective conductivity σ_e of randomly inhomogeneous two-phase systems at arbitrary values of concentrations are discussed. Two explicit approximate expressions for effective conductivity are found using a duality relation, a series expansion of σ_e in the inhomogeneity parameter z, and some additional conjectures about the functional form of σ_e. They differ from the effective medium approximation, satisfy all necessary requirements, and reproduce the known formulas for σ_e in the weakly inhomogeneous case. This can also signify that σ_e of the two-phase randomly inhomogeneous systems may be a nonuniversal function, depending on some details of the structure of the random inhomogeneities.     

Effective conductivity for densely packed highly conducting cylinders

We study the effective heat conductivity λ₃ of a periodic square array of nearly touching cylinders of conductivity h, embedded in a matrix material of conductivity 1. We construct a sequence of two-point Padé approximants for the effective conductivity. As the basis for the construction we use the coefficients of the expansions of λ_e at h=1 and h=∞. The two-point Padé approximants form a sequence of rapidly converging upper and lower bounds on the effective conductivity.     

Bounds for Entanglement via an Extension of Strong Subadditivity of Entropy

Let ?? ₁₂ be a bipartite density matrix. We prove lower bounds for the entanglement of formation E_f(?? ₁₂) and the squashed entanglement E_sq(?? ₁₂) in terms of the conditional entropy S ₁₂ ? S ₁ and prove that these bounds are sharp by constructing a new class of states whose entanglements can be computed, and for which the bounds are saturated.     

Experimental constraints on heavy fermions in Higgsless models

Using an effective Lagrangian approach we analyse a generic Higgsless model with composite heavy fermions, transforming as SU(2) _L+R doublets. Assuming that the Standard Model fermions acquire mass through mixing with the new heavy fermions, we constrain the free parameters of the effective Lagrangian studying Flavour Changing Neutral Current processes. In doing so we obtain bounds that can be applied to a wide range of models characterised by the same fermion mixing hypothesis.     

Temperature dependence of effective thermal conductivity and effective thermal diffusivity of Se90In10 bulk chalcogenide glass

Measurement of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of twin pellets of Se₉₀In₁₀ bulk chalcogenide glass has been carried out in the temperature range from 303 to 323 K and cooling from 323 to 303 K using transient plane source (TPS) technique. In the heating process variation of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) is observed. Both quantities are found to be maximum at 313 K, which lies in the vicinity of glass transition temperature (T_g). During the cooling process λ_e and χ_e remain same at all temperatures. Such type of behavior shows thermal hysteresis in this sample, which can be explained on the basis of structural change of the Se₉₀In₁₀ bulk chalcogenide glass.     

Composition dependence of effective thermal conductivity and effective thermal diffusivity of Se100−xInx (x=0, 5, 10, 15 and 20) chalcogenide glasses

Simultaneous measurement of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of twin pallets of Se_100−xIn_x (x=0,5, 10, 15, and 20) glasses, prepared under a load of 5 tons, have been made at room temperature using the Transient Plane Source (TPS) technique. The values of λ_e and χ_e were found to increase initially with the increase of concentration of In in Se-In alloy and had their maximum at 10 at.wt% of indium. For indium concentration beyond 10 at.wt% of the values of effective thermal conductivity and effective thermal diffusivity decrease linearly. This is suggestive of fact that 10 at.wt% of indium can be considered as a critical composition at which the alloy becomes, chemically ordered and maximum thermally stable than other composition. Further addition of indium in selenium decreases the values of λ_e and χ_e. The behaviour is explained on the basis of decrease of localized states and increase in disorderness for higher composition indium.     

Effective diffusivity of solute in multiphase materials with segregation

The effective diffusion coefficient D_eff for solute in a multiphase microstructure in which solute segregation can occur is related to D_eff for an isomorphic microstructure in which no segregation occurs. This permits analytical expressions (approximations, bounds, etc.) and methods of numerical calculation for D_eff that neglect solute segregation to be applied to systems that exhibit segregation. As an example, exact results are obtained for solute diffusion and segregation to grain boundaries in an idealized polycrystalline microstructure.     

Unitarity and approach to scaling at the SPS collider

We use variable-t ₁ bounds on preliminary SPS Collider data to show that these data saturate the unitarity bounds over a wide range oft. The bounds can be used to normalize different sets of data and to estimate reliably a self-consistent set of values for global quantities such as the total and the elastic cross-sections and the forward elastic slope. The approach to scaling is argued to be non-uniform int.     

Can HERA data improve the LEP constraints on the WWV vertex?

The combined results from ep → νWX, ep → eWX, and ep → νγX processes at HERA are used to constrain anomalous three-boson couplings. The effective model for anomalous couplings where there is no light Higgs boson and where interactions responsible for the breakdown of electroweak symmetry are strongly coupled is considered. Bounds on the couplings L _9L and L _9R , which parametrize contributions from the anomalous WWγ (WWZ) vertices, attainable from an analysis of the distributions for the processes in question are presented. The results are compared with the bounds resulting from the LEP I and LEP II data. It is shown that the bounds coming from HERA significantly reduce the parameter region allowed by the analysis of the LEP I and LEP II data.     

Filling of the 3d band of the manganese in GdAl2−xMnxforx < 0.2

X-ray, magnetic, electrical resistivity and ESR studies of GdAl_2?xMn_x compounds were performed. The transition temperatures, effective mass, thermal broadening of resonance linewidth and g-factors were obtained. For low concentration of GdMn₂ in GdAl₂ up to 20%, Mn is nonmagnetic. Increasing of the effective mass and the thermal broadening linewidth ESR with increasing x can be explained by the presence of d-electrons.     

Normal spinel CuCr1.6Sb0.4S4, a new material with a giant magnetoresistance

A giant magnetoresistance, reaching 74% in a magnetic field of 38 T at 3 K, was observed in the CuCr_1.6Sb_0.4S₄ semiconductor spinel. The magnetic properties point to the existence of a magnetic two-phase state in this compound. The giant magnetoresistance was explained by the existence of the magnetic two-phase state due to strong s-d exchange.     

Triple convective flow of micropolar nanofluids in double lid-driven enclosures partially filled with LTNE porous layer under effects of an inclined magnetic field

In this paper, free, forced and Marangoni convective flows within an open enclosure partially filled with a porous medium under impacts of an inclined magnetic field are investigated. The forced convection is due to the movement of the side walls, the free convection induces from the heated part in the bottom wall and the Marangoni convection is a responsible on the thermal interaction at the free surface (top wall). The flow domain is partially heated from below and partially filled by a porous medium. The local thermal non-equilibrium model (LTNEM) is used to represent the thermal field in the porous layer (bottom layer) while the two-phase model is used to simulated the micropolar nanofluid behavior. Two cases based on the direction of the movement of the side walls are considered, namely, assisting flow (downward lid motion) and opposing flow (upward lid motion). Numerical analysis based on the finite volume method is conducted and the obtained are presented in terms of the streamlines, isotherms, angular velocity, and the cup-mixing temperature θ_cup, the bulk-averaged temperature θ_ave and the average Nusselt numbers. The controlling parameters, in this situation, are the Darcy number Da, the Marangoni number Ma, the Nield number H, the vortex viscosity Δ, the Biot number Bi and the Hartmann number Ha. The results revealed that the increase in the Nield number enhances the cup-mixing temperature θ_cupand bulk-averaged temperature θ_ave regardless the direction of the side walls motion. Also, the average Nusselt number is boosted as the Marangoni number is grown.     

Role of magnetism in the formation of a short-range order in an Fe-Ga alloy

The formation of a short-range order in an Fe-Ga bcc alloy has been studied by Monte Carlo simulation with the use of effective interaction potentials calculated within the density functional theory for the ferromagnetic and paramagnetic states. It has been found that the pronounced short-range order of the D0₃ type is formed at Ga concentrations close to the boundary of the two-phase region at T < T _c, whereas no short-range order is observed at T < T _c. The results obtained are in agreement with the experimental X-ray diffraction analysis. The relation of the features of the short-range order in the Fe-Ga alloy to the magnetostriction value has been discussed.     

S-matrix and unitarity bounds for three-channel systems,with application to low-energy photoproduction of pions from nucleons

A parametrization of the S-matrix for three-channel systems is given, where we state explicitly the unitarity bounds on the free parameters. The free parameters are directly related to measurable quantities. The results are applied to low-energy photoproduction of pions from nucleons, and lower bounds for the electric dipole amplitudes E₀₊ for π⁰ production are obtained. These lower bounds follow without using the Fermi-Watson final-state theorem.     

Phase separation of liquid binary mixtures containing metals under pressure

We have measured the pressure variations of the two-phase regions of liquid binary mixtures of metal with metal (LiNaandGaBi), metal with semiconductor (TlSe) and metal with salt (BiBiI₃andBiBiBr₃) up to 28 kbar. It was found that in the mixtures of LiNa and GaBi the two-phase regions enlarge at higher pressures, while in the mixtures of TlSe, BiBiI₃ and BiBiBr₃ the two-phase regions disappear at low pressures.     

Utilization of Fly Ash Nanofluids in Two-phase Closed Thermosyphon for Enhancing Heat Transfer

This study investigates how fly ash nanofluids affect the thermal performance of a two-phase closed thermosyphon at various states of operation. The utilization of nanofluids obtained from X₂O₃-type oxides, such as Al₂O₃, Fe₂O₃, or CuO, on the improvement of two-phase closed thermosyphon performance was reported in a number of studies in the literature. The present study experimentally demonstrated the effect of using a nanofluid obtained from fly ash comprised of various types of metal oxides in varying ratios on improving the performance of a two-phase closed thermosyphon. The fly ash was obtained from the flue gas that was captured in the cyclones of the Yatagan thermal power plant (Turkey). Triton X-100 (Dow Chemical Company) dispersant was used in the study to produce the 0.2% (wt) fly ash/water nanofluid via direct synthesis. A straight copper tube with an inner diameter of 13 mm, outer diameter of 15 mm, and length of 1 m was used as the two-phase closed thermosyphon. The nanofluid filled 33.3% (44.2 ml) of the volume ofthe two-phase closed thermosyphon. Three heating power levels (200, 300, and 400 W) were used in the experiments with three different flow rates of cooling water (5, 7.5, and 10 g/s) used in the condenser for cooling the system. A increase of 26.39% was achieved in the efficiency of the two-phase closed thermosyphon when 4% (wt) fly ash containing nanofluid was used to replace deionized water at a heat load of 200 W and with a cooling water flow rate of 5 g/s.