Modern Physics Letters B

Anomalous diffusion occurs in many branches of physics. Examples include diffusion in confined nanofilms, Richardson turbulence in the atmosphere, near-surface ocean currents, fracture flow in porous formations and vortex arrays in rotating flows. Classically, anomalous diffusion is characterized by a power law exponent related to the mean-square displacement of a particle or squared separation of pairs of particles: 〈|X(t)|²〉 ~t^γ. The exponent γ is often thought to relate to the fractal dimension of the underlying process. If γ > 1 the flow is super-diffusive, if it equals 1 it is classical, otherwise it is sub-diffusive. In this work we illustrate how time-changed Brownian position processes can be employed to model sub-, super-, and classical diffusion, while time-changed Brownian velocity processes can be used to model super-diffusion alone. Specific examples presented include transport in turbulent fluids and renormalized transport in porous media. Intuitively, a time-changed Brownian process is a classical Brownian motion running with a nonlinear clock (Bm-nlc). The major difference between classical and Bm-nlc is that the time-changed case has nonstationary increments. An important novelty of this approach is that, unlike fractional Brownian motion, the fractal dimension of the process (space filling character) driving anomalous diffusion as modeled by Bm-nlc positions or velocities does not change with the scaling exponent, γ.

Synthesis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and magnetic measurements at low temperature of Ni metallic clusters covered by NiO, Ce₂O₃ and CeO₂, obtained from CeNi₅ powder oxidized in air at different temperatures up to 800°C, are reported. The average crystallite size of Ni core and the thickness of NiO oxide formed at the surface increase with temperature due to recrystallization processes, from 34 nm at 300°C to 77 nm at 800°C and from 9 nm to 19 nm, respectively. Ni metallic component was detected both in XPS valence bands and core levels spectra only after sputtering. The hysteresis loop presents a small shift towards negative magnetic fields which confirms the presence of ferromagnetic Ni/antiferromagnetic NiO interfaces.

The Hamiltonian of a quantum rod with an ellipsoidal boundary is given after a coordinate transformation, which changes the ellipsoidal boundary into a spherical one. We then study the vibrational frequency and the ground state binding energy of the weak-coupling impurity bound magnetopolaron in it. The effects of the aspect ratio of the ellipsoid, the transverse effective confinement lengths, the electron-phonon coupling strength, the magnetic field cyclotron frequency and the Coulomb bound potential are taken into consideration by using linear combination operator method. It is found that the vibrational frequency and the ground state binding energy will increase with increasing Coulomb bound potential and the cyclotron frequency. They are decreasing functions of the aspect ratio of the ellipsoid and the transverse effective confinement lengths, whereas the ground state binding energy is an increasing function of the electron-phonon coupling strength.

By using the Wigner function to evaluate expectation values of any symmetrically order of operator in a classical fashion, we study the quantum fluctuation and the uncertainty relation of mesoscopic RLC circuit at photon-subtracted and photon-added thermo vacuum states. It is found that the fluctuations and the uncertainty relation of both charge and current are linearly related to the photon-subtracted and photon-added number.

First principles studies of structural, elastic, electronic and optical properties of tetragonal CaSiO₃ perovskite under pressure are reported using the pseudopotential plane wave method within the local density approximation (LDA). The calculated equilibrium lattice is in good agreement with the available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. Band structures show that tetragonal CaSiO₃ perovskite is a direct band gap material. In order to understand the optical properties of tetragonal CaSiO₃ perovskite, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 40 eV. This is the first quantitative theoretical prediction of the elastic, electronic and optical properties of tetragonal CaSiO₃ perovskite, and it still awaits experimental confirmation.

Calcium phosphate based biomaterials play important roles in clinical applications. Calcium pyrophosphate (CPP), a kind of calcium phosphate, can be used as a bone substitution material as well as a bone graft. Because of its similarity to inorganic component of bone and teeth it can be used for surface coating of metallic dental and orthopedic implants. In the present study, calcium pyrophosphate dihydrate (CPPD) nanoparticles were synthesized using surfactant mediated approach. Crystalline nature and average crystallite size was studied using Powder XRD. The CPPD nanocrystallites were found to be triclinic from powder XRD. The TEM study indicated that CPPD nanoparticles were in the range of 13 nm to 20 nm. The presence of various bonds was confirmed by FTIR spectroscopy. The amount of water of hydration and the thermal stability was studied by thermogravimetry. The variations of various dielectric parameters with the frequency of applied field in 3.2 kHz to 32 MHz range and within a temperature range from 60°C to 120°C were studied. The formation of other phases such as β-CPP and α-CPP on heating of CPPD at 900°C and 1250°C, respectively, were studied by the Powder XRD. The results are discussed.

Ultrasonic longitudinal velocity measurements between 80 K and 280 K and shear velocity measurements between 80 K and 230 K have been performed in polycrystalline superconducting DyBa₂Cu_3-xZn_xO_7-δ (x = 0, 0.01 and 0.03) and Dy_0.9Ca_0.1Ba₂Cu_3-yZn_yO_7-δ (y = 0.01) samples utilizing the pulsed-echo-overlap technique. A longitudinal anomaly characterized by a step-like slope change was observed at around 240 K for DyBa₂ Cu_3-xZn_xO_7-δ (x = 0) and at 230 K for x=0.01 and 0.03. Zn²⁺ substitution suppressed critical temperature, T_c but did not suppress the step-like anomaly. On the other hand, substitution of Ca²⁺ in Dy_0.9Ca_0.1Ba₂Cu_3-yZn_yO_7-δ (y = 0.01) caused the step-like anomaly to disappear. The step-like anomaly was suggested due to the oxygen-ordering process in Cu–O chains during a phase transition process at low temperatures. Substitution of Zn²⁺ ions in place of Cu was suggested to go into CuO₂ planes and did not interfere with oxygen-ordering in Cu–O chains. This is suggested as the reason why the step-like anomalies were not suppressed in DyBa₂Cu_3-xZn_xO_7-δ (x = 0.01 and 0.03) samples. Disappearance of the step-like anomaly due to Ca²⁺ substitution is probably related to reduction in oxygen content which depletes Cu–O chain sites.