The connection between Ekman and Stewartson layers for a rotating disk

When a disk of finite radius and the surrounding medium rotate coaxially with slightly different angular velocities, a so-called Stewartson layer exists at the edge of the disk. The properties of this layer outside the boundary layer of the disk have been given in a previous publication. In the present paper it is shown how the radial flow of the Ekman boundary layer turns into the axial flow of the Stewartson layer. This happens in a region of which both the radial and axial dimensions are O(E^1/2), where E is the Ekman number.     

Atomic‐Scale Core/Shell Structure Engineering Induces Precise Tensile Strain to Boost Hydrogen Evolution Catalysis

Tuning surface strain is a new strategy for boosting catalytic activity to achieve sustainable energy supplies; however, correlating the surface strain with catalytic performance is scarce because such mechanistic studies strongly require the capability of tailoring surface strain on catalysts as precisely as possible. Herein, a conceptual strategy of precisely tuning tensile surface strain on Co₉S₈/MoS₂ core/shell nanocrystals for boosting the hydrogen evolution reaction (HER) activity by controlling the MoS₂ shell numbers is demonstrated. It is found that the tensile surface strain of Co₉S₈/MoS₂ core/shell nanocrystals can be precisely tuned from 3.5% to 0% by changing the MoS₂ shell layer from 5L to 1L, in which the strained Co₉S₈/1L MoS₂ (3.5%) exhibits the best HER performance with an overpotential of only 97 mV (10 mA cm^?2) and a Tafel slope of 71 mV dec^?1. The density functional theory calculation reveals that the Co₉S₈/1L MoS₂ core/shell nanostructure yields the lowest hydrogen adsorption energy (?E_H) of ?1.03 eV and transition state energy barrier (?E_2H*) of 0.29 eV (MoS₂, ?E_H = ?0.86 eV and ?E_2H* = 0.49 eV), which are the key in boosting HER activity by stabilizing the HER intermediate, seizing H ions, and releasing H₂ gas.     

Source-sink flow in a rotating cylinder

Summary This paper describes the axisymmetric source-sink flow in a rapidly rotating cylinder. Relative fluid motion is induced by the presence of a sink in the bottom corner and a ring source located somewhere in the fluid, at some distance from the solid boundaries. In order to neglect nonlinear effects the volumetric flow rates are assumed to be small, i.e. O(E ^1/2), with E the Ekman number of the flow. The transport from the source to the sink is carried by Ekman layers at the end caps, and a Stewartson layer at the sidewall. At the ring source a free Stewartson layer arises, in which the injected fluid is transported towards the Ekman layers. This Stewartson layer consists of layers of thicknesses E ^1/4 and E ^1/3, which both contribute to the vertical O(E ^1/2) transport. The ring source is enveloped by a ring-shaped region of cross-sectional dimensions O(E ^1/2 × E ^1/2), in which the injected fluid is rearranged before erupting into the E ^1/3 layer. As E ^1/2 E ^1/3, this region appears as an isolated singularity in the E ^1/3 layer; in fact it consists of a combination of an upward and a downward directed source, the strengths of which can be determined by transport arguments. The paper presents an analysis of the E ^1/3-layer structure on the basis of a linear theory; it also describes how the analysis can be extended to the situation in which fluid is injected through an array of sources at different heights.     

Laser-induced surface decomposition of Al2O3 excited in the V-center absorption band

The primary products of desorption from Al₂O₃ surface excited by laser pulses (pulse duration τ∼15 ns; wavelength λ=354 nm, radiant power density P/S<10⁸ W/cm²) in the V-center absorption band were studied by the time-of-flight (TOF) spectroscopy. The TOF spectra show evidence of the desorption of one “ cold” (T ₁=300 K) and two “hot” (T ₂=1000 K, T ₃=4300 K) groups of oxygen molecules with the Maxwell velocity distributions, as well as of the hot Al and O atoms with nonequilibrium energy distributions (E ₁=0.37 eV, E ₂=0.38 eV). A model describing the oxygen desorption as initiated by the electron transitions is suggested, in which escape of the cold O₂ molecules from the surface is related to discharge of the O ₂ ⁻ anions adsorbed on the V-centers, desorption of the hot atoms is attributed to discharge of the surface O⁻ anions, and the appearance of the hot O² molecules is related to the associative desorption of two O⁻ anions localized at the same V-center discharged by a pair of excitons.     

Ultrasonic Velocity Studies of Drug Parvon-spas in Mixed Alcohol–Water Solvent Systems at 25°C

Ultrasonic velocities and densities of the drug Parvon-spas in binary mixtures of water with methanol (MeOH), ethanol (EtOH), and propan-1-ol (1-PrOH) have been measured over the complete solvent composition range at 10 mol% intervals at 25°C. Various acoustic parameters such as the acoustic impedance (Z), adiabatic compressibility (β), intermolecular free length (L_f), relative association (R.A.), molar volume (V_m), and molar sound velocity (R_m) have been calculated. In addition, excess functions, i.e., excess adiabatic compressibility (β^E), excess intermolecular free length (L_f^E), excess molar volume (V^E), excess ultrasonic velocity (U^E), and excess acoustic impedance (Z^E) for these three solvent mixtures in the absence and presence of the drug have been calculated. A different behavior of these parameters in these alcohol systems has been discussed in terms of the length of the alcohol molecule, the molecular volume, as well as inter/intramolecular interactions of these molecules.     

Structural,magnetic, and magnetodielectric correlations in multiferroic Bi5Ti3FeO15

We have investigated the structural, magnetic, magnetodielectric, and magnetoimpedance characteristics of Aurivillius-structured Bi₅Ti₃FeO₁₅ (BTFO) synthesized by a generic solid-state reaction route. Rietveld refinement of X-ray diffraction pattern at room temperature (RT) confirms orthorhombic crystal structure (space group A2₁am). In BTFO, octahedral distortion of the perovskite unit occurs due to antisite defects Fe/Ti in the BO₆ site, which results in the formation of Fe–O clusters. Raman spectra also reveal Ti/FeO6 octahedral distortion due to the vibration of Bi ions in the perovskite layer. Magnetic field-dependent magnetization (M–H) and electric field-dependent polarization (P–E) measurement at RT indicate the existence of multiferroic behavior in BTFO. The M–H hysteresis at 5 K suggests that the non-interacting superparamagnetic state is dominant over the local short-range antiferromagnetic (AFM) ordering. The AFM interaction arises due to the random distribution of antisite defects Fe/Ti causing the distorted Fe–O octahedral unit. These canted spin interact via the Dzyaloshinskii–Moriya (DM) interaction. The superexchange interaction between the Fe–O–Fe ions is stronger than the next-nearest-neighboring Fe–O–O–O–Fe interaction. This happens due to the intermediate fluorite-like layer (Bi₂O₂)²⁺, which opposes the long-range exchange interaction. The negative magnetodielectric (MD) effect is more prominent at low frequency (~?100 Hz) due to the extrinsic contribution. In contrast, in the high-frequency region (>?50 kHz), the intrinsic contribution dominates, which is further ascertained by magnetoimpedance (MI) measurement. The maximum magnitude of the MD effect is found to be?~?0.32% at a magnetic field of 13 kOe at 150 K. Lastly, the ferroelectric characteristic of the sample is obtained from the P–E measurement with a polarization value of 4.35 µC/cm² with an applied electric field of 70 kV/cm.

     

Spin-up and spin-down of a viscous fluid over a heated disk rotating in a vertical plane in the presence of a magnetic field and a buoyancy force

Summary The hydromagnetic spin-up and spin-down of an incompressible electrically conducting fluid on a heated infinite disk rotating in a vertical plane in the presence of a magnetic field and a buoyancy force have been studied. The flow is non-axisymmetric due to the imposition of the buoyancy force. We have considered the situation where there is an initial steady state which is perturbed by suddenly changing the angular velocity of the disk. By using suitable transformations the Navier-Stokes and energy equations with four independent variables (x, y, z, t) are reduced to a system of partial differential equations with two independent variables (,t ^*). Also, these transformations uncouple the momentum and energy equations, resulting in a primary axisymmetric flow with an axial magnetic field, in an energy equation dependent on the primary flow and in a buoyancy induced secondary cross flow dependent on both primary flow and energy.The results indicate that the effect of the step-change in the angular velocity of the disk is more pronounced on the primary flow than on the secondary flow and the temperature field. For both spin-up and spin-down cases the surface shear stress in the non-axial direction normal to gravity for the primary flow and the surface shear stresses for the secondary flow increase with the magnetic parameter, whilst the surface shear stress in the vertical direction and the heat transfer at the surface decrease as the magnetic parameter increases. Also, the secondary flow near the disk dominates the primary flow. We have also developed an asymptotic analysis for large magnetic parameters which complements well the numerical results obtained in the lower magnetic parameter range.     

Nano Titanium Monoxide Crystals and Unusual Superconductivity at 11 K

Nano TiO₂ is investigated intensely due to extraordinary photoelectric performances in photocatalysis, new‐type solar cells, etc., but only very few synthesis and physical properties have been reported on nanostructured TiO or other low valent titanium‐containing oxides. Here, a core–shell nanoparticle made of TiO core covered with a ≈5 nm shell of amorphous TiO_1+x is newly constructed via a controllable reduction method to synthesize nano TiO core and subsequent soft oxidation to form the shell (TiO_1+x). The physical properties measurements of electrical transport and magnetism indicate these TiO@TiO_1+x nanocrystals are a type‐?? superconductor of a recorded T_c^onset = 11 K in the binary Ti–O system. This unusual superconductivity could be attributed to the interfacial effect due to the nearly linear gradient of O/Ti ratio across the outer amorphous layer. This novel synthetic method and enhanced superconductivity could open up possibilities in interface superconductivity of nanostructured composites with well‐controlled interfaces.     

Optical absorption and fluorescence properties of Er3+ in sodium borate glass

Spectroscopic properties of Er³⁺ ions in sodium borate glass have been studied. The indirect and direct optical band gaps (E_opt) and energy level parameters (RacahE ¹, E² and E³), spin-orbit (ξ_4f) and configurational interaction (α)) are evaluated. Spectral intensities for various absorption bands of Er₃₊ doped sodium borate glass are calculated. Using Judd-Ofelt intensity parametersΩ ₂, Ω₄, Ω₆, radiative transition probabilities (A), branching ratios (β) and integrated absorption cross sections (Σ) are reported for certain transitions. The radiative lifetimes (τ_R) for different excited states are estimated. From the fluorescence spectra, the emission cross section (σ_P) for the transition,⁴I_13/2 → ⁴I_15/2 is reported.     

Temperature Dependence of the Volumetric Properties of Binary Mixtures Containing Polyethers and 1-Propanol

Excess molar volumes (V ^E _m ) were measured at 288.15, 298.15, and 308.15 K and atmospheric pressure as a function of composition with a continuous dilution dilatometer for the binary mixtures of 1-propanol [CH₃CH₂CH₂OH] with glymes [CH₃O(CH₂CH₂O) _m CH₃, m=1,2,3, and 4]. With these results and other thermodynamic data from the literature, the following mixing quantities have been reported over the complete range of concentration or at equimolar concentration: , volume expansivity; ^E , excess volume expansivity; (V ^E _m /T) _P , and (H ^E /P) _T at 298.15 K. The Prigogine–Flory–Patterson theory (PFP) of liquid mixtures has been applied to estimate interaction, free-volume, and internal-pressure contributions to V ^E _m and to estimate the different mixing quantities for the mixtures. The calculated values using the PFP theory were then compared at 298.15 K with the experimentally obtained results. The PFP theory predicts excess volume V ^E _m values rather well, while the calculated value of (V ^E _m /T) _P and (H ^E /P) _T by using the Flory theory show general variation with the chain length of the glyme. The (V ^E _m /T) _P and (H ^E /P) _T show deviations between theoretical and experimental values that are slightly larger in systems with lower glyme.     

Study of hydrogenated nanoamorphous silicon(na-Si:H) thin film prepared by RF magnetron sputtering for graded optical band gap (<Emphasis Type="Italic">E</Emphasis><Superscript>opt</Superscript><Subscript>g</Subscript>)

The schematic of the energy band gap figure of the graded optical band gap (E_g^opt) in p-i-n layer in na-Si:H solar cells was given in the paper. The intrinsic hydrogenated nanoamorphous silicon(na-Si:H) thin films with the graded band gap as a function of depth through the films were prepared by varying the processing power, gas pressure, gas composition, and etc., We have carried out a investigation of the relationships between the E_g^opt with the crystallization ratio (Xc) and the E_g^opt with the nanocrystalline grain size (D) in na-Si:H thin films grown by PECVD on glass substrates through XRD, Raman scattering, transmission. The E_g^opt increase with the decreases of the crystallization ratio (Xc) and the nanocrystalline grain size (D). The hydrogen dilution ratio is found to increase basically both the crystallization ratio (Xc) and the nanocrystalline grain size (D). Two relationships in na-Si:H are discussed by the etching effect of atomic hydrogen in the framework of the growth mechanism and the quantum size effect (QSE).     

Thickness dependence of refractive index and optical gap of PMMA layers prepared under electrical field

Optical parameters (refractive index, dispersion energy, optical gap) of polymethylmethacrylate (PMMA) layers prepared by spin coating and modified by electric field have been studied. Refractive index was measured using a refractometer, internal structure was investigated as a structural parameter (E _d) within the One Oscillator Model. Optical gap width (E _g^opt) was assessed using Tauc Approximation from UV-Vis spectra. Surface morphology and roughness was investigated using an AFM. The electric field imposed during preparation of layers increases their refractive index. The highest increase in n (Δn = 0.042) was found for the thinnest PMMA layer (70 nm). Oriented layers have produced higher E _g^opt than non-oriented ones for all studied values of thickness. The electrical field applied at preparation of the oriented layer will not change its surface morphology and roughness.     

Zn/ZnO core/shell nanoparticles synthesized by laser ablation in aqueous environment: Optical and structural characterizations

Zn/ZnO core/shell nanoparticles are synthesized by pulsed laser ablation (PLA) of Zn metal plate in the aqueous environment of sodium dodacyl sulfate (SDS). Solution of nanoparticles is found stable in the colloidal form for a long time, and is characterized by UV-visible absorption, transmission electron microscopy (TEM), photoluminescence (PL) and Raman spectroscopic techniques. UV-visible absorption spectrum has four peaks at 231, 275, 356, and 520 nm, which provides primary information about the synthesis of core-shell and elongated nanoparticles. TEM micrographs reveal that synthesized nanoparticles are monodispersed with three different average sizes and size distributions. Colloidal solution of nanoparticles has significant absorption in the green region, therefore, it absorbs 514·7 nm light of Ar⁺ laser and emits in the blue region centred at 350 and 375 nm, violet at 457 nm and green at 550 nm regions. Raman shift is observed at 300 cm⁻¹ with PL spectrum, which corresponds to ³E_2N and E_3L mode of vibrations of ZnO shell layer. Synthesis mechanism of Zn/ZnO core/shell nanoparticles is discussed.     

Velocity depth profile of granular matter in a horizontal rotating drum

Using MRI velocimetry, we verify that the velocity depth profile of the flowing layer near the axial center of a half-filled 3D drum has the form V _m[1 − (r/r ₀)²]-Ω r, where r is the depth measured from the cylinder center, except very close to the free surface where it lies below the quadratic form. We confirm that this deviation is due in part to particles reaching the surface with large components of their velocity in the azimuthal direction. We used a 3D cylinder with a radial “paddle” placed at approximately the dynamic angle of repose, covering the top third of the flow, so as to null any azimuthal velocity. It was found that the deviation from the quadratic form was reduced by the presence of the paddle when the comparison is made at the same solid body rotation rate, at the same free surface velocity, and with the paddle placed at different positions, so long as it makes good contact with the surface. Thus, we conclude that a quadratic velocity depth profile may be a fundamental property of granular shear flows in this geometry, when the sole effect of the cylinder rotation is to transport the particles from the end of the flow to the beginning without imparting velocity perpendicular to the flow.     

Unsteady motion of a fluid near a disk rotating in a magnetic field

The effect of a magnetic field on the velocity distribution in a fluid close to an unsteadily rotating disk is investigated.Notation r, , and z coordinates in the radial, circular, and axial directions - t time - u, v, and w radial, circular, and axial velocity components - u₀ radial velocity of external potential flux - v₀ circular velocity of the disk - (t) angular velocity of the disk - p pressure - density - v kinematic viscosity - B₀ characteristic of the applied magnetic field - electrical conductivity of fluid - R and Z dimensionless coordinates in the radial and axial directions - =Z/2 dimensionless coordinate - T dimensionless time - U, V, and W radial, circular, and axial components of dimensionless velocity - P dimensionless pressure - a, , and ₀ constants with dimensionality t^–1 - m, n, and positive numbers - k =a constant - = = B ₀ ² / parameter characterizing the magnetic field     

The iCE approach for journal evaluation

Recent research has shown that simple graphical representations of research performance can be obtained using two-dimensional maps based on impact (i) and citations (C). The product of impact and citations leads to an energy term (E). Indeed, using E as the third coordinate, three-dimensional landscape maps can be prepared. In this paper, instead of using the traditional impact factor and total citations received for journal evaluation, Article Influence^TM and Eigenfactor^TM are used as substitutes. Article Influence becomes a measure of quality (i.e. a proxy for impact factor) and Eigenfactor is a proxy for size/quantity (like citations) and taken together, the product is an energy-like term. This can be used to measure the influence/prestige of a journal. It is also possible to propose a p-factor (where p = E ^1/3) as an alternative measure of the prestige or prominence of a journal which plays the equivalent role of the h-index.     

Excess thermodynamic properties of mixtures of alkyl benzoates withn-heptane

The paper reportsh ^E values at 298.15 K andv ^E and values at various temperatures for binary mixtures of propyl or butyl benzoate andn-heptane. The excess Gibbs energy of viscous flow,g ^*E, and the thermodynamic activation properties were calculated from these values. The results are compared with those for similar mixtures and interpreted on the basis of the characteristic dipole-dipole interactions of alkyl esters.Nomenclature A _i Parameters in Eq. (2) - dg ^*E Gibbs free energy of viscous flow (J · mol^–l) - dg Activation free energy (kJ · mol^–1) - K Parameter in Eq. (2) - h Planck constant - h ^E Excess enthalpy (J · mol^–1) - h Activation enthalpy (kJ · mol^–1) - N Avogadro number - R Universal gas constant (J · K^–1 · mol^–1) - s Standard deviation - s Activation entropy (J · K^–1 · mol^–1) - T Temperature (K) - v Molar volume of pure component (m³ · mol^–1) - v ^E Excess volume (m³ · mol^–1) - x _i Mole fraction of componenti Greek Letters Expansion coefficient (K^–1) - Density (kg · m^–1 ) - Viscosity (mPa · s ) - Apparent excess viscosity (mPa · s)     

Effect of sintering temperature on dielectric properties, vibrational modes and crystal structures of Ba[(Ni0.7Zn0.3)1/3Nb2/3]O3 ceramics

The Ba[(Ni_0.7Zn_0.3)_1/3Nb_2/3]O₃ solid solutions were sintered at 1450, 1500, and 1550 °C for 3 h, respectively, by conventional solid-state sintering method, so as to clarify the effect of the sintering temperatures on vibrational modes, crystal structures, and dielectric properties. Ceramics were characterized by X-ray diffraction (XRD), Raman spectroscopy and Fourier transform far-infrared reflection (FTIR) spectroscopy. Space group and crystal symmetry of Pm[`3]m Pm\bar{3}m were determined by XRD. Lattice vibrational spectra, obtained by Raman and FTIR spectroscopy, show the correlation among polar phonon modes, crystal structures, and dielectric properties of Ba[(Ni_0.7Zn_0.3)_1/3Nb_2/3]O₃ ceramics as a function of the sintering temperatures. The results demonstrate that the dielectric constant e_r \varepsilon_{r} reaches a maximum value of 35.713 at 1500 °C and is related to Raman shifts of the A_1g(O) modes and the FWHM values of the E_g(O) modes, the temperature coefficient of the capacitance t_c \tau_{c} , which gradually increases from −6 × 10⁻⁶/°C to 0, is closely related to the Raman shifts of E_g(O) modes, and the dielectric loss values are closely connected with the full width at half-maximum of E_g(O) active modes and the Raman shifts of of the A_1g(O) modes with the increasing temperatures. FTIR shows that the dielectric properties are closely related to the far-infrared phonon modes. Raman and FTIR active modes were indicated according to the group theory.     

Role of Al additions in wear control of nanocrystalline Mo(Si1−xAlx)2 coatings prepared by double cathode glow discharge technique

Abstract

Four kinds of nanocrystalline Mo(Si_1?xAl_x)₂ coatings with differing Al contents are prepared onto a Ti–6Al–4V substrates by a double cathode glow discharge apparatus. The microstructural features of the deposited coatings were characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These coatings are composed of the equiaxed C40–MoSi₂ grains with the average grain size of ～5 nm. Nano-indentation measurements indicated that the hardness H, elastic modulus E and the H/E or H³/E² ratio of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings slightly increase with the increase in Al content. The tribological behaviour of the nanocrystalline Mo(Si_1?xAl_x)₂ coating sliding against a ZrO₂ ceramic ball at room temperature has been compared using a ball-on-disc type tribometer under unlubricated conditions. Experimental results showed that the specific wear rates of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings decrease with increasing Al content and are dramatically reduced by more than 1–2 orders of magnitude over the uncoated Ti–6A1–4V. The enhancement of wear resistance of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings by Al additions is correlated with the increased mechanical properties and the forming oxide layer by tribochemical reactions.     

Growth and characterization of HfO2 high-k gate dielectric films by laser molecular beam epitaxy (LMBE)

The HfO₂ gate dielectric films were fabricated by the laser molecular beam epitaxy (LMBE) technique. High-resolution transmission electron microscopy (HRTEM) observation showed that under optimized condition, there is no detectable SiO₂ interfacial layer in the as-deposited film and a SiO₂ interfacial layer of about 0.4 nm was formed at the Si interface due to the post deposition annealing. Capacitance–voltage (C–V) measurement of the film revealed that the equivalent oxide thickness was about 1.3 nm. Such a film showed very low leakage current density of 1.5 × 10⁻² A cm⁻² at 1 V gate bias from the current–voltage (I–V) analysis. The conduction mechanisms as a function of temperature T and electric field E were also systematically studied.