Penetrative ferroconvection via internal heating in a saturated porous layer with constant heat flux at the lower boundary

A model for penetrative ferroconvection via internal heat generation in a ferrofluid saturated porous layer is explored. The Brinkman-Lapwood extended Darcy equation with fluid viscosity different from effective viscosity is used to describe the flow in the porous medium. The lower boundary of the porous layer is assumed to be rigid- paramagnetic and insulated to temperature perturbations, while at upper stress-free boundary a general convective-radiative exchange condition on perturbed temperature is imposed. The resulting eigenvalue problem is solved numerically using the Galerkin method. It is found that increasing in the dimensionless heat source strength N_s, magnetic number M₁ Darcy number Da and the non-linearity of magnetization parameter M₃ is to hasten, while increase in the ratio of viscosities Λ, Biot number Bi and magnetic susceptibility χ is to delay the onset of ferroconvection. Further, increase in Bi, Da⁻¹ and N_s and decrease in Λ, M₁ and M₃ is to diminish the dimension of convection cells.     

Sol–gel derived nanocrystalline multiferroic BiFeO3 and R (R=Er and Tm) doped therein: Magnetic phase transitions and enhancement of magnetic properties

Nanocrystalline BiFeO₃ and rare earth ion doped BiFeO₃ (Bi_0.9R_0.1FeO₃, R=Er and Tm) were prepared by sol–gel method. Rietveld analysis of the X-ray diffractograms of the samples revealed that small amount of impurity phase of Bi₂Fe₄O₉ was formed together with the desired phase. In the thermal variation of magnetic mass susceptibility (χ_m) of the samples, one sharp transition below T_M (T_M∼100 K, 50 K and 30 K for BiFeO₃, Bi_0.9Er_0.1FeO₃ and Bi_0.9Tm_0.1FeO₃, respectively) was observed, which clearly hint the change of the domination of the ferromagnetic exchange interaction over the usual antiferromagnetic exchange interaction. Also, static magnetization (M) and susceptibility of each doped sample have been drastically enhanced compared to that of BiFeO₃. The values of χ_m and M measured at different temperatures confirmed that the magnetic behavior of the doped systems has been dominated by the paramagnetic/ferromagnetic clusters below ∼T_M. Another phase transition were observed in the χ_m vs. T curve of the samples at relatively higher temperature T_B (∼260 K for BiFeO₃, ∼220 K for Bi_0.9Er_0.1FeO₃ and ∼180 K for Bi_0.9Tm_0.1FeO₃), which may be attributed to the charge ordering transition. Ferroelectric hysteresis loops of the samples observed at 100 Hz confirmed the presence of ferroelectric ordering of the samples. Measured values of dielectric constants at 1 kHz of each sample in presence and absence of magnetic field confirmed a substantial magnetoelectric coupling of all the samples.     

SU(3) lattice Monte Carlo calculation of the glueball mass spectrum

We have calculated the glueball masses of various spins and parities in SU(3) gauge theory. Our first results give m_M(0⁺⁺)=(3.6±0.2)Λ_mom, m_E(0⁺⁺)=(4.3±0.3)Λ_mom, m(0^?+)=(7.2_?0.9^+1.6)Λ_mom, m_M(2⁺⁺)=(8.1±1.1)Λ_mom and m_E(2⁺⁺)=(8.3_?1.0^+1.6)Λ_mom as well as information on the glueball wave functions.     

Effect of Bi2O3 on EPR, optical transmission and DC conductivity of vanadyl doped alkali bismuth borate glasses

Glasses with composition xBi₂O₃·(30−x)M₂O·70B₂O₃ (M=Li, Na) containing 2 mol% V₂O₅ have been prepared over the range 0≤x≤15 (x is in mol%). The electron paramagnetic resonance spectra of VO²⁺ of these glasses have been recorded in the X-band (≈9.3 GHz) at room temperature (RT≈300 K). Spin Hamiltonian parameters, g_∥, g_⊥, A_∥, A_⊥, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. The molecular orbital coefficients, α² and γ², have been calculated by recording the optical transmission spectra. In xBi₂O₃·(30−x)Li₂O·70B₂O₃ glasses there is decrease in the tetragonality of the V⁴⁺O₆ complex for x up to 6 mol% whereas for x≥6 mol%, tetragonality increases. In xBi₂O₃·(30−x)Na₂O·70B₂O₃ glasses there is increase in the tetragonality of the V⁴⁺O₆ complex with increasing x. The 3d_xy orbit expands with increase in Bi₂O₃:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported. The DC conductivity increases with increase in temperature. The order of conductivity is 10⁻⁵ ohm⁻¹ m⁻¹ at low temperature and 10⁻³ ohm⁻¹ m⁻¹ at high temperature. The DC conductivity decreases and the activation energy increases with increase in Bi₂O₃:M₂O ratio.     

Proton decays and neutron oscillations in the rishon model

We analyze proton decays and neutron oscillations in the rishon model. Proton decay is forbidden in lowest order of the compositeness scale Λ_H. In a one-generation rishon model, the leading proton decays violate B?L (e.g., p→νπ⁺). The lifetime is given by τ_p～Λ_H⁸/(U_R²m_p⁷), where U_R～M(W_R) is the mass scale of the right-handed W boson and m_p is the proton mass. For U_R～500 GeV, the obtained limit for the compositeness scale is Λ_H?10⁸ GeV. Neutron oscillations are also proportional to Λ_H⁸ and cannot be detected in the foreseeable future. All of these predictions may depend strongly on the understanding of higher generations of quarks and leptons within the model.     

Effect of Gd addition on the activation energies of Bi-2223 superconductor

We have investigated the effect of addition of Gd in Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃Gd_xO_y superconductor with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared using the standard solid-state reaction method. The activation energies, irreversibility fields (H_irr), upper critical fields (H_c2) and coherence lengths at 0 K (ξ(0)) were calculated from the resistivity versus temperature (R-T) curves under DC magnetic fields up to 7 T. The superconducting transition temperature, T_c, and activation energy, U₀, were found to decrease with increase in Gd concentration and with increase in applied magnetic field. The offset transition temperature of the pure (Gd00) sample without applied magnetic field is 108 K, whereas for Gd05 sample, the offset transition temperature drops to 5 K with 7 T applied magnetic field. The activation energy of the Gd00 sample without applied magnetic field is 34,980 K, and for Gd05 sample with 7 T applied field it is 98 K. H_irr and H_c2 values also decrease with increase in Gd addition. The possible reasons for the observed degradation in microstructural and superconducting properties due to Gd addition were discussed.     

Optical sensing characteristics of the photonic crystal fiber filled with magnetic fluid

A novel photonic crystal fiber sensing theory filled with magnetic fluid is proposed based on the change of the MF refractive index under varied magnetic field. The magnetically induced tuning of the magnetic fluid filled PCF propagation properties were investigated by the full-vector finite element method with a perfectly matched layer. Theoretical calculations show that both the effective refractive index and the effective mode area increase vs. the increased magnetic field, and the PCF filled MF with larger d/Λ is more sensitive to magnetic field. When the wavelength λ = 1550 nm, the duty ratio d/Λ = 0.9, d/Λ = 0.6, the effective refractive indexes increase respectively from 1.598279 to 1.617572, from 1.61948 to 1.632484, and the effective mode areas increase respectively from 3.561115 μm² to 7.052360 μm², from 6.167494 μm² to 37.221998 μm² as the magnetic field changes from 25 Oe to 175 Oe. This scheme provides theoretical foundation to use magnetic field to control light in photonic crystal fiber and also offers a potential method for magnetic field sensing based on the TIR-PCF.     

The glueball mass spectrum in QCD: First results of a lattice Monte Carlo calculation

We perform a variational calculation of the masses of glueballs of various spins and parities in SU(2) gauge theory. The quantum vacuum we use is generated by the lattice Monte Carlo technique. Our first results, obtained on medium sized lattices give m(0⁺) = (3.6 ± 0.35) Λ_mom, m(0^? = (6.0 ± 1.0)Λ_mom, m(2⁺) = (6.5^+1.8_?1.1)Λ_mom, various mass upper bounds and information on glueball wave functions.     

Peristaltically induced transport of a MHD biviscosity fluid in a non-uniform tube

We have analyzed an incompressible flow of electrically conducting biviscosity fluid through an axisymmetric non-uniform tube with a sinusoidal wave under the considerations of long wavelength and low Reynolds number. In our analysis we are taking into account the induced magnetic field. The analytic solution has been obtained from which the axial velocity, the axial induced magnetic field and the axial pressure gradient have been derived. The results for the pressure rise ΔP_λ(t), frictional force per wavelength F_λ(t) and the axial induced magnetic field h_z have been computed numerically and the results were studied for various values of the physical parameters of interest, such as the magnetic Prandtl number p_m, the magnetic field parameter M, the Reynolds number Re, the upper limit apparent viscosity coefficient β, and the time averaged mean flow rate θ.     

Renormalization group and dynamical symmetry breakdown in abelian gauge theories

Generalized renormalization group equations are used to analyze the dynamical mechanism of particle mass generation in terms of the Cornwall-Norton model both with and without cut-off. We look for solutions which contain non-zero physical masses of the two fermions (m₁, m₂) and of one of the vector bosons (μ) when the bare masses m_1Λ, m_2Λ, μ_Λ approach zero. For a theory without cut-off we obtain results which are similar to those of Cornwall. For a theory with cut-off the mass generation mechanism may only occur when a bare coupling constant α_Λ of the A_μ vector boson, which remains massless, exceeds some critical value α_c. In this case the fermion masses turn out to be of the superconductivity type.The model's “memory” of the nature of spontaneous symmetry breaking lim_{m1Λ, m2Λ → 0}m_1Λ/m_2Λ ≠ 1 is an indispensible factor for the vector boson to acquire a mass.     

Bianchi Type-V Cosmology in f(R,T) Gravity with Λ(T)

A new class of cosmological models in f(R,T) modified theories of gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011), where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar R and the trace of the stress-energy tensor T, have been investigated for a specific choice of f(R,T)=f ₁(R)+f ₂(T) by considering time dependent deceleration parameter. The concept of time dependent deceleration parameter (DP) with some proper assumptions yield the average scale factor $a(t) = \sinh^{\frac{1}{n}}(\alpha t)$ , where n and α are positive constants. For 0<n≤1, this generates a class of accelerating models while for n>1, the models of universe exhibit phase transition from early decelerating phase to present accelerating phase which is in good agreement with the results from recent astrophysical observations. Our intention is to reconstruct f(R,T) models inspired by this special law for the deceleration parameter in connection with the theories of modified gravity. In the present study we consider the cosmological constant Λ as a function of the trace of the stress energy-momentum-tensor, and dub such a model “Λ(T) gravity” where we have specified a certain form of Λ(T). Such models may display better uniformity with the cosmological observations. The statefinder diagnostic pair {r,s} parameter has been embraced to characterize different phases of the universe. We also discuss the physical consequences of the derived models.     

Thermal-diffusion and diffusion-thermo effects on combined heat and mass transfer by hydromagnetic three-dimensional free convection over a permeable stretching surface with radiation

The thermal-diffusion and diffusion-thermo effects on the heat and mass transfer characteristics of free convection past a continuously stretching permeable surface in the presence of magnetic field, blowing/suction and radiation are studied. The fluid viscosity is assumed to vary with temperature. The resulting, governing three-dimensional equations are transformed using a similarity transformation and then solved numerically by the shooting method. Comparison with previously published work is performed and full agreement is obtained. A parametric study showing the effects of variable viscosity parameter β, magnetic parameter M, Dufour number Df, Soret number Sr, radiation parameter R and blowing/suction parameter f₀ on the velocity, temperature, and concentration field of a hydrogen-air mixture as a non-chemical reacting fluid pair, as well as the local skin-friction coefficient, the local Nusselt number, and the local Sherwood number is carried out. These are illustrated graphically and in tabular form to depict special features of the solutions.     

Effective field theory for massive gravitons and gravity in theory space

We introduce a technique for restoring general coordinate invariance into theories where it is explicitly broken. This is the analog for gravity of the Callan-Coleman-Wess-Zumino formalism for gauge theories. We use this to elucidate the properties of interacting massless and massive gravitons. For a single graviton with a Planck scale M_Pl and a mass m_g, we find that there is a sensible effective field theory which is valid up to a high-energy cutoff Λ parametrically above m_g. Our methods allow for a transparent understanding of the many peculiarities associated with massive gravitons, among them the need for the Fierz-Pauli form of the Lagrangian, the presence or absence of the van Dam-Veltman-Zakharov discontinuity in general backgrounds, and the onset of non-linear effects and the breakdown of the effective theory at large distances from heavy sources. The natural sizes of all non-linear corrections beyond the Fierz-Pauli term are easily determined. The cutoff scales as Λ∼(m_g⁴M_Pl)^1/5 for the Fierz-Pauli theory, but can be raised to Λ∼(m_g²M_Pl)^1/3 in certain non-linear extensions. Having established that these models make sense as effective theories, there are a number of new avenues for exploration, including model building with gravity in theory space and constructing gravitational dimensions.     

Influence of sample geometry on determination of magnetocaloric effect for Gd60Co30Al10 glassy ribbons using direct and indirect methods

Rare-earth based metallic glasses with high saturation magnetization show a sizeable magnetocaloric effect (MCE) and are subject of extensive research concerning magnetic refrigeration materials. In this work, the magnetic phase transition from paramagnetic to ferromagnetic of Gd₆₀Co₃₀Al₁₀ metallic glass has been characterized and three different methods were applied for the determination of its magnetocaloric specific parameters: (a) direct measurement of the adiabatic temperature change by exposing the material to an adiabatically applied magnetic field; (b) determination of the magnetization M(H,T) and calculation of the temperature dependent magnetic field induced entropy change ΔS_m by application of the Maxwell relation and (c) measuring the total heat capacity C_p(H,T) in zero and non-zero magnetic field. Gd₆₀Co₃₀Al₁₀ glassy ribbons were prepared by melt spinning, a technique that offers very high cooling rates due to the low dimensionality of the sample. Depending on the particular method of measurement, pieces of these glassy ribbons form samples with different appropriate total volume and dimensions. We show that the combination of the pronounced two-dimensionality of the ribbon pieces (aspect ratio ∼100) together with the very high magnetic permeability principally can cause strong internal demagnetizing fields that cannot be neglected when evaluating the intrinsic MCE parameters obtained from different methods.     

Nonmonotonic behavior of magnetoresistance, R(H) hysteresis, and low-temperature heat capacity of the BaPb0.75Bi0.25O3 superconductor in a magnetic field: Possible manifestations of phase separation

The transport properties (R(T) and R(H) dependences at various values of the transport current in magnetic fields up to 65 kOe) and low-temperature heat capacity in magnetic fields up to 90 kOe of the BaPb_0.75Bi_0.25O₃ superconductor (T _C ≈ 11.3 K) are investigated with the goal of clarifying the mechanisms determining the nonmonotonic behavior and hysteresis of its magnetoresistance R(H). The type of R(H) hysteretic dependences for BaPb_0.75Bi_0.25O₃ is analogous to that observed in granular high-T _c superconductors (HTSCs); however, unlike classical HTSC systems, the field width of the magnetoresistance hysteresis loop for polycrystalline BaPb_0.75Bi_0.25O₃ depends on the transport current. This means that although the mechanisms responsible for the magnetoresistance hysteresis (the influence of the magnetic flux trapped in superconducting regions on the effective field in Josephson interlayers) are identical in these objects, the transport current in BaPb_0.75Bi_0.25O₃ may considerably affect the diamagnetic response of the superconductor. A considerable effect of transport current on the field in which the R(H) dependences have a peak and exhibit hysterestic properties is observed. Such a behavior can be adequately interpreted using the model of the spatially inhomogeneous superconductor-insulator state proposed by Gorbatsevich et al. [JETP Lett. 52, 95 (1990)]. The nonmonotonic dependence of quantity C/T (C is the heat capacity) on the magnetic field discovered in the present study also agrees with the conclusions based on this model.     

Local ordered magnetic fields in bismuth dielectrics. 209Bi NQR in Bi4Ge3O12 single crystal

The results of the ²⁰⁹Bi NQR experiments carried out on α-Bi₂O₃, Bi₃O₄Br, Bi₂M₄O₉ (M=Al, Ga), Bi₂Ge₃O₉, and Bi₄Ge₃O₁₂ showed that these compounds are not diamagnets in the conventional sense. The Zeeman perturbed zero-field ²⁰⁹Bi NQR spectra gave an indication that local ordered magnetic fields of the order of 30–200 G exist in these substances comprising neither transition nor rare earth elements. Further aspects of this principally new phenomenon of yet unknown nature were studied by the ²⁰⁹Bi NQR experiments on the Bi₄Ge₃O₁₂ single crystal in external magnetic fields below 500 Oe, applied at various orientations with respect to the crystal axes. The spectral patterns of dramatically increased intensity and multiplicity, caused by the unknown magnetism of the compound, were observed in applied fields and modeled. Based on the results of the modeling, the conclusions were made that at least four magnetically non-equivalent Bi sites characterized by antiferromagnetically ordered local fields of the order of 30 G are present in the Bi₄Ge₃O₁₂ crystal; the intensity increase was interpreted to arise from the change in orientation of the electric field gradient axes at the Bi site upon applying an external magnetic field.     

Majorana masses,photon gas heating and cosmological constraints on neutrinos

Non-vanishing Majorana masses generally lead to flavor-changing neutral currents in the neutrino sector. It is shown that when both right- and left-handed neutrinos have non-vanishing Majorana masses (M_R≠0 and M_L≠0), flavor-changing neutral currents could be as large as flavor-diagonal ones. However, when only right-handed neutrinos have non-vanishing Majorana masses (M_R≠0 but M_L=0), flavor-changing neutral currents are small. If M_R?D (Dirac masses), they are of $\text{O}\text{((}\text{D}\text{M}{}_{\mathrm{<mtext>R</mtext>}}\text{)}{}^2\text{)}$. If M_R?D, they are $\text{?(}\text{m}{}_{\mathrm{<mtext>L</mtext>}}\text{m}{}_{\mathrm{<mtext>H</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, where m_L and m_H are masses of light and heavy neutrinos appearing in a flavor-changing process.By using these results we examine cosmological implications of non-vanishing flavor-changing neutral currents. Heavy neutrinos can decay into three light neutrinos at an appreciable rate by exchanging a Z-boson. It is demonstrated that owing to this decay mode, heavy neutrinos of mass larger than 70 keV but less than 2m_e give rise to no contradiction with the standard big bang cosmology in the most general case.We also show that if there exist heavy neutrinos of mass m_H2m_e, their decay at an early era of the universe induces photon gas heating, which alters Cowsik and McClelland's constraint on light neutrino masses to Σm_L < k · 100 eV with the sum running over all Majorana eigenstates. Here the constant k, representing the heating effect of the photon gas, is restricted by the deuterium abundance of the present universe. For instance, Σm_L < 240 eV for m_H ～ 25 MeV and the present baryon density = 3.4 × 10^?31 g · cm^?3.     

Percolation magnetoresistance in ferromagnetic superconductors

It is shown that the magnetoresistance (as a function of magnetic field H) in polycrystalline magnetic superconductors has the percolation character which is the consequence of the anisotropy of magnetic susceptibility. The magnetoresistance R_m(H), and the upper critical field H_c2(T) of ErRh₄B₄ are evaluated and compared with the experimental data.     

Equation of state and quantal crossover of the XY model in a longitudinal magnetic field

The equation of state of the XY model in a longitudinal (Γ) and transverse field (B) is investigated in the vicinity of a multicritical point (Γ_c, T =0) using the renormalization group method developed recently by the author and K. Walasek. For Γ = Γ_c a quantal crossover behaviour of the form H = M_{R³ψ (z)} is obtained, where H ～ B, M_R denotes the transverse magnetization, z ～ TM_R^?/βq, while ?,β_q are crossover and multicritical exponents, respectively.     

Magnetic properties and magnetocaloric effect of Sr-doped Pr0.7Ca0.3MnO3 compounds

In this work, we pointed out that Sr substitution for Ca leads to modify the magnetic and magnetocaloric properties of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds. Analyzing temperature dependence of magnetization, M(T), proves that the Curie temperature (T_C) increased with increasing Sr content (x); T_C value is found to be 130–260 K for x = 0.0–0.3, respectively. Using the phenomenological model and M(T,H) data measured at several applied magnetic field, the magnetocaloric effect of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds has been investigated through their temperature and magnetic field dependences of magnetic entropy change ΔS_m(T,H) and the change of the specific heat change ΔC_P(T,H). Under an applied magnetic field change of 10 kOe, the maximum value of -ΔS_m is found to be about 3 J/kg·K, and the maximum and minimum values of ΔC_P(T) calculated to be about ±60 J/kg·K for x = 0.3 sample. Additionally, the critical behaviors of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds around their T_C have been also analyzed. Results suggested a coexistence of the ferromagnetic short- and long-range interactions in samples. Moreover, Sr-doping favors establishing the short-range interactions.