Rigid Media Research Articles

The microscopic analysis of high forchheimer number flow in porous media

High Forchheimer number flow through a rigid porous medium is numerically analysed by means of the volumetric averaging concept. The microscopic flow mechanisms, which must be known in order to understand the macroscopic flow phenomena, are studied by utilising a periodic diverging-converging representative unit cell (RUC). The detailed information for the microscopic flow field, in association with the locally averaged momentum balance, makes it possible to quantitatively demonstrate that the microscopic inertial phenomenon, which leads to distorted velocity and pressure fields, is the fundamental reason for the onset of nonlinear (non-Darcy) effects as velocity increases. The hydrodynamic definitions for Darcy's law permeabilityk, the inertial coefficientΒ and Forchheimer number Fo are obtained by applying the averaging theorem to the pore level Navier-Stokes equations. Finally, these macroscopic parameters are numerically calculated at various combinations of micro-geometry and flow rate, and graphically correlated with the relevant microscopic parameters.

Jump conditions across strong compaction waves in gas saturated rigid porous media

Based on experimental results and some additional simplifying assumptions, the general macroscopic two-phase equations governing the flow field which is developed in a gas-saturated rigid porous medium domain were simplified to a form which enabled us to develop two analytical models for calculating the jump conditions across a strong compaction wave. Predictions obtained by these two simplified analytical models are compared to the experimental results of Sandusky and Liddiard (1985) and to predictions of another more complicated model which was proposed by Powers et al. (1989). Fairly good to excellent agreements are evident.

The peculiarities of the spectral luminescence properties of N-anthryl-substituted pyridinium cations

Abstract A structureless fluorescence band λ max f ≈ 530 nm) in liquid solution and a fluorescence band with vibrational structure (λ = 376–480 nm) in rigid media (ethanol, 77 K and poly(methyl methacrylate) (PMMA), 296 K) were observed for N -anthryl-substituted pyridinium cations. In liquid solution the long-wave fluorescence is attributed to the biradical structure resulting from the photoinduced electron transfer (PET) from anthracene to the pyridinium ring, and the long-wave, low intensity absorption (and fluorescence excitation) band (λ=465 nm) is attributed to this interfragment PET which is weakly allowed by the torsional vibrations. In rigid media the PET is strongly forbidden (in the strict orthogonal pyridinium-anthracene structure) and radiative deactivation of the anthracene fragment is observed.

Intramolecular excimers and energy migration in polyesters with 2,6-naphthalene dicarboxylic acid units separated by spacers of 1–4 ethylene oxide units

The fluorescence has been measured in dilute solution and in glassy poly(methyl methacrylate) for polyesters of 2,6-naphthalene dicarboxylate and HO(CH 2 CH 2 O) m H, m = 1−4. The model compounds in which the glycol connects two molecules of 2-naphthoate were also studied. Intramolecular energy migration is implied by the anisotropy of the fluorescence in rigid media. The results are consistent with Förster radii of about 12 Å in the model compounds and 14 Å in the polymers, as found previously for a similar series based on HO(CH 2 ) m OH instead of HO(CH 2 CH 2 O) m H.

Modelling and simulation of energy transfer in a saturated flow through a porous medium

Using the continuum theory of mixtures (a generalization of classical continuum mechanics), a model for a local description of the energy transfer in a saturated flow of a newtonian fluid through a rigid porous medium is proposed. It considers the fluid and the porous matrix as continuous constituents of a binary (solid-fluid) mixture. Both constituents coexist superposed in the whole volume of the mixture, so there exist simultaneously at each spatial point two temperatures and two velocities, giving rise to an energy generation and a momentum generation, which provide thermal and dynamical interactions, respectively. The forced convection heat transfer between the fluid and the solid constituents, when the fluid flows past a porous channel bounded by two isothermal parallel plates, is simulated by using a finite difference approach. The effects of some dimensionless parameters, such as β (relating the heat transfer between both constituents to the fluid constituent conduction), γ (relating both constituent's conduction), the aspect ratio, the fluid constituent's Péclet number, and the solid constituent's Nusselt number (at the channel's inlet and outlet) are discussed.

The use of rigid organic microemulsions to fix liquid solutions for Mössbauer studies

Rigid organic microemulsions containing submicroscopic droplets of liquid solutions of tin(IV) chloride in methanol and in ethylene glycol were prepared. In those systems where the walls of the cavities in the microemulsion carried negative charges and the hydrophilic groups of the surfactants and cosurfactants had H-bonding ability, it was shown that the internal surface of the cavities in the microemulsion was covered by a solvent layer separating Mössbauer-active SnCl 4 from this surface. On the other hand, solvated SnCl 4 was bound through the H-bonded solvent cluster to this surface-bound solvent by H bonds, resulting in recoilless γ-ray resonance absorption (Mössbauer effect). Thus, the rigid organic dispersion medium of these microemulsions behaved as a carrier enhancing the Debye-Waller factor for the quasi-liquid phase of the system, resulting in Mössbauer spectra characteristic of SnCl 4 in the bulk solution.

Temperature dependence of the disulfide perturbation to the triplet state of tryptophan

Variability in the temperature dependence of disulfide quenching of the tryptophan phosphorescence of globular proteins in rigid glasses is illustrated with lysozyme and alpha-bungarotoxin. A laser-pulsed phosphorescence study of this short-range interaction with a model indole-disulfide system is described. The perturbation of secondary dibutyl disulfide on the triplet state of the indole moiety in 2-(3-indolyl)ethyl phenyl ketone in rigid media is found to display a bimodal temperature dependence. The quenching rate constant at contact between chromophore and perturber is observed to be temperature independent below 30 K, but to increase with temperature between 30 and 100 K with an activation energy of approximately 200 cm(-1). The results suggest that the underlying quenching interaction involves a photo-induced one-electron transfer from the excited state of indole to the disulfide.

Anomalous absorption of longitudinal acoustic waves by a thin layer of viscous fluid

The existence of anomalous absorption of longitudinal acoustic waves passing obliquely through a narrow slit with viscous fluid is demonstrated. In the frictional contact approximation two cases are treated analytically, viz. when the fluid layer is placed between two identical elastic media and when one medium can be considered as infinitely rigid. Typical layer thickness values corresponding to the absorption maximum are determined. The absorptivity maximum value (up to dozens of percents) is shown to depend only on the wave incidence angle and the ratio of Lamè factors of the elastic media. In the case of an infinitely rigid medium the ratio of the transformation factor at the absorptivity maximum to that in the absence of a layer is found to be a universal constant equal to 0.25.

The Surface Evaporation Problem with Signorini Boundary Condition

The one-dimensional filtration of an incompressible liquid in a homogeneous, isotropic, rigid porous medium is considered. The bottom of the layer is impermeable, whereas on the top surface a Signorini-type boundary condition is imposed. Existence and uniqueness of the weak solution are proved under general conditions. Then some qualitative properties of the solution and its asymptotic behaviour are analyzed. In particular, the characterization of the set $D \equiv \{ {t:u(0,t) = 0} \}$ is discussed.

Optical mode mixing in an isotropic elastic layer

Elastic boundary conditions are shown to emerge naturally from a simple unifying theory describing long-wavelength excitations in bulk semiconductors. Their application to the cases of a freely vibrating layer and to a layer enclosed by an infinitely rigid medium (roughly approximated by a GaAs layer in vacuum and by a GaAs/AlAs quantum well respectively) shows that the disappearance of relevant dilational and shear stresses in the first case and the inhibition of displacement in the second case can only be obtained by s-polarized TO modes without mixing-LO and p-polarized TO modes are forced to mix coherently. It is also necessary for Fuchs-Kliewer interface polaritons to mix with LO modes in order to satisfy elastic boundary conditions. The use of elastic, as distinct from hydrodynamic, boundary conditions brings the continuum model much closer to the predictions of microscopic theory.

Soil Water Diffusivity as Explicitly Dependent on Both Time and Water Content

AbstractReliable experimental data do not always conform with customary soil‐water flow theory for truly rigid porous media. The purpose of this study was to derive a mathematical description capable of accommodating such data. A new mathematical solution was obtained for the absorption of water by an unsaturated horizontal column of soil termed semirigid, but which does not swell in the ordinary sense of a change in bulk density. Nonetheless, the semirigid soil does undergo microlevel rearrangement of its particles, envisaged as introducing an auxiliary dependence on time t into the diffusivity D in addition to the usual dependence on the volumetric water content, θ that is, D = D(θ,t). With product‐form separation of variables introduced at two stages of the solution process, there emerges the new variable λ equal to distance x divided by a new time function [Q(t)]1/2. Subject to modest constraint, Q(t) may be selected to best describe the particular soil in question. Choosing [Q(t)]1/2 = tn with exponent n as a positive constant, thus yielding λ = xt‐n instead of the classical Boltzmann form xt−1/2, the new solution was tested experimentally on a set of published data not conforming to customary flow theory for rigid media. The new solution provided a greatly improved description of these data, with exponent n = 0.46362 instead of 1/2 as for rigid media. The diffusivity function is D(θ,t) = 2nE(θ)t2n‐1, where E(θ) is a diffusivity‐like function of θ alone.

Anomalous absorption of sagittal shear waves by a thin fluid layer

The existence of anomalous absorption of sagittal shear waves passing across a narrow slit with viscous fluid is demonstrated. In the frictional contact approximation, two cases are treated analytically, namely when the fluid layer is placed between two identical elastic media and when one medium can be considered as infinitely rigid. Typical layer thickness values corresponding to the absorption maximum are determined. The absorptivity maximum value (up to dozens of per cent) is shown to depend only in the wave incidence angle and the ratio of Lame factors of the elastic media. For widely spread materials the dependences of the typical layer thickness and absorptivity on the incidence angle are found to have abrupt peak-like maxima which hardly differ in their position. In the case of an infinitely rigid medium the ratio of the transformation factor at the absorptivity maximum to that at the rigid contact of the solids is found to be the universal constant.

Intramolecular electron transfer in rigid media at room temperature

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIntramolecular electron transfer in rigid media at room temperatureWayne E. Jones Jr., Pingyun Chen, and Thomas J. MeyerCite this: J. Am. Chem. Soc. 1992, 114, 1, 387–388Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://doi.org/10.1021/ja00027a073RIGHTS & PERMISSIONSArticle Views181Altmetric-Citations53LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (277 KB) Get e-Alerts Get e-Alerts

Intramolecular energy migration in polyesters from 2,6-naphthalene dicarboxylic acid: polarization of fluorescence in the polymers and in bichromophoric model compounds

The fluorescence has been measured in dilute solution and in glassy poly(methyl methacrylate) for polyesters in which 2,6-naphthalene dicarboxylate is the rigid unit, and (CH 2) m ( m=2–6) is the flexible spacer. Bichromophoric compounds in which the same flexible spacer connects two molecules of 2-naphthoate were also studied. The anisotropy in the rigid medium demonstrates the existence of intramolecular energy migration, which becomes more important as m decreases from 6 to 2. The Förster radius is ∼ 12 A ̊ in the bichromophoric compounds and 14 Å in the polyesters.

Contact perpendicular recording on rigid media

The authors describe integrated head/flexure structures which have an effective mass of about 300 mu g, evidence no indication of head crash, and hold the potential for very low wear of both head and media, when operating in continuous sliding contact at media velocities of 15 m/s or greater. A perpendicular probe type transducer was constructed as an integral part of a thin dielectric flexure. Initial recording performance on two-layer perpendicular media indicates promise for achieving very high linear and track densities, and the extremely small mass facilitates the design of servo systems and actuators capable of substantially reducing track access time.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Flash photolysis of α-naphthil in the temperature range 77 to 320 K

The flash photolysis of α-naphthil was studied in the temperature range 77–320 K. Flash excited α-naphthil produces two triplet conformers and two types of hydrogen-adduct radical in the presence of a hydrogen donor. In isopropanol, one triplet conformer absorbs at 525 nm (triplet I) and the other at 430 nm (triplet II). Triplet I present in the rigid glassy medium, remains in equilibrium with triplet II at the melting point of the soft glass. In fluid medium, only triplet II is present. The enthalpy change for the triplet I to triplet II equilibrium process is 12.4 kJ mol −1. In fluid medium, an equilibrium of the precursors of the two types of radicals can be determined from the relative absorption ratios of radical I at 550 nm and radical II at 460 nm immediately after the laser flash at various temperatures. The equilibrium of the radical precursors requires an enthalpy change of 43.2 kJ mol −1. The equilibria between the two triplet conformers and the two types of radical precursor are not observed in hydrocarbon medium; however, the triplet (530 nm) present in the solid glassy hydrocarbon at low temperature is different from that (440 nm) present in the liquid hydrocarbon. The hydrogen-adduct radicals are generated directly from the excited singlet state when hydrogen donor triethylamine is present in excess. The decay kinetics, stability and reactivity of the different conformers are discussed in the light of the puckered and planar conformations of the α-naphthil molecule.

Flow through isotropic granular porous media

A generalization of the Navier-Stokes equation is developed to include laminar flow through a rigid isotropic granular porous medium of spatially varying permeability. The model is based on a theory of interspersed continua and the mean geometrical properties of an idealized granular porous microstructure. The derived momentum transport equations are applicable to granular porous media over the entire porosity range from zero through unity. No restriction with respect to flow velocity is imposed, except for the assumption of laminar flow within the pores. The results provide useful and versatile equations and substantiate many of the empirical equations currently in use. One of the major advantages of the generalized momentum equation is its adaptability to numerical simulation.

Steric influences on the photoluminescence from copper(I) phenanthrolines in rigid media

Data for a series of copper(I) phenanthrolines in an alcohol glass at 90 K have revealed that substituents in the 2,9-positions of the ligand have a pronounced influence on the energy, intensity, and lifetime of the photoluminescence. All of the complexes exhibit intense metal-to-ligand charge-transfer absorption bands of similar energy in the visible region. However, the absorption maxima and, to an even greater extent, the emission maxima shift to higher energy as bulkier substituents are introduced. At the same time, the emission quantum yieds and lifetimes increase. The results can be understood in terms of contrasting geometric preferences of the ground and excited states involved

Thermally induced 2E decay pathways in chromium(III) complexes

The temperature dependence of 2 E→ 4 A 2 decays has been determined for Cr(III) complexes with varying 4 T 2 − 2 E gaps in several solvents. At sufficiently low temperatures in a rigid medium, the decay is exponential. Nonexponentiality at higher temperatures is strong evidence that 2 E→ 4 T 2 back-transfer is a significant pathway for 2 E depopulation, when photolysis is inhibited by low temperatures or low solvent mobility

Photophysical behavior of double-bridged d7-d7 metal-metal bonded compounds: the crystal structure and the excited- and ground-state electronic spectra of Re2(CO)6(dmpm)2 [dmpm = bis(dimethylphosphino)methane)

Re2(CO)6(dmpm)2 shows photophysical behavior in a rigid medium that differs dramatically from that observed in fluid solution. In a hydrocarbon glass at 77 K, metal-metal bond homolysis is suppressed and an intense phosphorescence is observed. The transient absorption spectrum, which shows only weak transitions to the red of the ground state 1(sigma-sigma asterisk) transition, permits assignment of the emitting state to a 3(sigma-sigma asterisk) transition. The crystal structure of Re2(CO)6(dmpm)2 is also reported. The ground-state electronic structure is discussed relative to the structural data.