Function Of Oscillation Frequency Research Articles

Finite-time Response of Dynamo Mean-field Effects in Magnetorotational Turbulence

Abstract Accretion disk turbulence along with its effect on large-scale magnetic fields plays an important role in understanding disk evolution in general, and the launching of astrophysical jets in particular. Motivated by enabling a comprehensive subgrid description for global long-term simulations of accretions disks, we aim to further characterize the transport coefficients emerging in local simulations of magnetorotational disk turbulence. For the current investigation, we leverage a time-dependent version of the test-field method, which is sensitive to the turbulent electromotive force (EMF) generated as a response to a set of pulsating background fields. We obtain Fourier spectra of the transport coefficients as a function of oscillation frequency. These are well approximated by a simple response function, describing a finite-time buildup of the EMF as a result of a time-variable mean magnetic field. For intermediate timescales (i.e., slightly above the orbital frequency), we observe a significant phase lag of the EMF compared to the causing field. Augmented with our previous result on a nonlocal closure relation in space, and incorporated into a suitable mean-field description that we briefly sketch out here, the new framework will allow us to drop the restrictive assumption of scale separation.

Modeling Local Oscillatory Shear Dynamics of Functionalized Polymer Grafted Nanoparticles

AbstractThis study examines local oscillatory shear dynamics of spherical polymer grafted nanoparticles (PGNs) composed of a rigid nanoparticle core of fixed radius, nm, and coronas of varying number of grafted polymer arms, . The grafted polymer arms are end‐functionalized such that the interacting PGNs form labile bonds when their coronas overlap. The effect of PGN structure on local dynamics is examined by imposing controlled oscillatory displacement on simple systems constructed using three identical interacting PGNs with bonded interactions under mechanical equilibrium. The displacement‐induced bond evolution between PGNs in this system is captured employing a master equation for determining probability of finding n bonds between PGNs as a function of oscillation frequency (). A multi‐component model combined with master equation approach is employed for modeling the effect of varying number of grafted arms ( and 1200) and strain amplitude () on the local shear response of the PGN system. The resulting shear response is analyzed using both linear and non‐linear rheological measures obtained using the Chebyshev polynomial framework. The rheological measures thus obtained are found to vary strongly with the number of grafted arms and strain amplitude.

Carbon dioxide clearance using bubble CPAP with superimposed high-frequency oscillations in a premature infant lung model with abnormal lung mechanics.

High-frequency (HF) oscillatory ventilation has been shown to improve carbon dioxide (CO2 ) clearance in premature infants. In a previous in vitro lung model with normal lung mechanics we demonstrated significantly improved CO2 washout by HF oscillation of bubble continuous positive airway pressure (BCPAP). To examine CO2 clearance in a premature infant lung model with abnormal lung mechanics via measurement of end-tidal CO2 levels (EtCO2 ) while connected to HF oscillated BCPAP. A 40 mL premature infant lung model with either: normal lung mechanics (NLM): compliance 1.0 mL/cm H2 O, airway resistance 56 cm H2 O/(L/s); or abnormal lung mechanics (ALM): compliance 0.5 mL/cm H2 O, airway resistance 136 cm H2 O/(L/s), was connected to BCPAP with HF oscillation at either 4, 6, 8, 10, or 12 Hz. EtCO2 was measured at BCPAPs of 4, 6, and 8 cm H2 O and respiratory rates (RR) of 40, 60, and 80 breaths/min and 6 mL tidal volume. HF oscillation decreased EtCO2 levels at all BCPAPs, RRs, and oscillation frequencies for both lung models. Overall mean ± SD EtCO2 levels decreased (P < .001) from nonoscillated baseline by 19.3 ± 10.2% for NLM vs 14.1 ± 8.8% for ALM. CO2 clearance improved for both lung models (P < .001) as a function of oscillation frequency and RR with greatest effectiveness at 40 to 60 breaths/min and HF at 8 to 12 Hz. In this in vitro premature infant lung model, HF oscillation of BCPAP was associated with improved CO2 clearance as compared with nonoscillated BCPAP for both NLM and ALM. The significant improvement in CO2 clearance in an abnormal lung environment is an important step towards clinical testing of this novel respiratory support modality.

Steady streaming flows in viscoelastic liquids

We discuss experimental investigations on steady streaming flows of dilute and semi-dilute polymer solutions in microfluidic devices. The effect of non-Newtonian behavior on steady streaming for different model fluids is determined by characterizing the evolution of the inner streaming layer as a function of oscillation frequency using particle tracking velocimetry. We find that steady streaming velocity profiles in constant-viscosity elastic liquids are qualitatively similar to those in Newtonian liquids. Steady streaming velocity profiles in elastic liquids with strong shear thinning, however, display two unique features: (i) a non-monotonic evolution of the inner streaming layer with increasing frequency, first growing then decreasing in width, and (ii) a clear asymmetry in the flow profile at high frequencies.

Detection of nonmagnetic metal thin film using magnetic force microscopy

Magnetic force microscopy (MFM) allows detection of stray magnetic fields around magnetic materials and the two-dimensional visualization of these fields. This paper presents a theoretical analysis of the oscillations of an MFM tip above a thin film of nonmagnetic metal. The results show good agreement with experimental data obtained by varying the tip height. The phenomenon analyzed here can be applied as a “metal detector” at the nanometer scale and for contactless measurements of sheet resistivity. The detection sensitivity is obtained as a function of oscillation frequency, thus allowing the determination of the best frequency for the phase-shift measurement. The shift in resonance frequency due to the presence of a nonmagnetic metal is also discussed.

Protruding organic surfaces triggered by in-plane electric fields

Coatings with a dynamic surface topography are of interest for applications in haptics, soft robotics, cell growth in biology, hydro- and air dynamics and tribology. Here we propose a design for creating oscillating surface topographies in thin liquid crystal polymer network coatings under an electric field. By applying an alternating electric field, the coating surface deforms, and pre-designed local corrugations appear. The continuous AC electric field further initiates oscillations superimposed on the formed topographies. This effect is based on microscopic free volume creation. By exciting the liquid crystal network at its resonance frequency, maximum free volume is generated and large surface topographies are formed. Molecular simulation is used to examine this behaviour in microscopic detail as a function of oscillation frequency. Surface topography formation is fast and reversible. Excess free volume is energetically unfavourable, thus the surface topographies disappear within seconds once the electric field is removed.

An Optimal Frequency in Ca2+ Oscillations for Stomatal Closure Is an Emergent Property of Ion Transport in Guard Cells.

Oscillations in cytosolic-free Ca(2+) concentration ([Ca(2+)]i) have been proposed to encode information that controls stomatal closure. [Ca(2+)]i oscillations with a period near 10 min were previously shown to be optimal for stomatal closure in Arabidopsis (Arabidopsis thaliana), but the studies offered no insight into their origins or mechanisms of encoding to validate a role in signaling. We have used a proven systems modeling platform to investigate these [Ca(2+)]i oscillations and analyze their origins in guard cell homeostasis and membrane transport. The model faithfully reproduced differences in stomatal closure as a function of oscillation frequency with an optimum period near 10 min under standard conditions. Analysis showed that this optimum was one of a range of frequencies that accelerated closure, each arising from a balance of transport and the prevailing ion gradients across the plasma membrane and tonoplast. These interactions emerge from the experimentally derived kinetics encoded in the model for each of the relevant transporters, without the need of any additional signaling component. The resulting frequencies are of sufficient duration to permit substantial changes in [Ca(2+)]i and, with the accompanying oscillations in voltage, drive the K(+) and anion efflux for stomatal closure. Thus, the frequency optima arise from emergent interactions of transport across the membrane system of the guard cell. Rather than encoding information for ion flux, these oscillations are a by-product of the transport activities that determine stomatal aperture.

Effect of vapor pressure of grains in formation of planetesimals through the accretion disc

The role of grains in evolution of accretion disc is an important issue in astrophysics. In this paper, we study the effect of vapor pressure of grains in the dead zones of protoplanetary discs. Our study is limited to some particular observed cases in which evaporation of grains would be important and their vapor gas are constrained to an approximately isolated case. Here, we use the Einstein model to investigate the thermodynamics of vapor pressure. The results show that there is a critical temperature as a function of oscillation frequency and binding energy of particles. For temperatures greater than this critical value, the system goes into unstable mode. We show that the dead zone of the disc may reach to enough conditions to condense via instability caused by vapor pressure of grains. This mechanism may play an important role in the formation of planetesimals through protoplanetary disc.

Transport by Oscillatory Flow in Soils with Rate‐Limited Mass Transfer: 1. Theory

Oscillatory flow of fluid in a porous medium can generate a one‐way transport of heat or chemicals if there is a gradient of temperature or chemical concentration and a rate‐limited heat or mass transfer between the moving fluid and an immobile phase. For chemical transport in soils, the immobile phase can occur in stagnant porosity, by sorption, or by dissolution of a vapor in the pore water. As a function of oscillation frequency, the transport rate has a broad peak near the value ωτc = 1, where ω is the angular frequency of oscillation and τc is the characteristic equilibration time of the mobile phase. The transport rate is proportional to the gradient and to the square of the amplitude of periodic fluid displacement. A unique diffusivity derived from the analysis enables prediction of the long‐term transport by a diffusion calculation without fluid flow, thereby providing a tool for estimating the removal of contaminant vapors by passive soil vapor extraction (PSVE). We compared predictions of the analytic theory with numerical simulations of PSVE. The mobile–immobile model is also applicable to transport in other cases of oscillatory flow in porous media, including cyclic motion of water or gas due to tidal aquifers or earth tides.

Dilational rheology of polymer/surfactant mixtures at water/hexane interface

The present work is devoted to the interaction in mixed solutions of the cationic polyelectrolyte PAH and the counter-charged anionic surfactant SDS at the water/oil interface. For this purpose interfacial tension and dilational rheology studies were performed to describe the formation of complexes of PAH and SDS. The dilational elasticity values depend on the concentrations of surfactant and polyelectrolyte and their mixing ratio. As expected the concentration dependence of the dilational elasticities of SDS and PAH-SDS mixtures are similar in the SDS concentration range 10 −5 M till 10 −3 M (at a fixed amount of PAH) and have a maximum which correlates with an observed minimum in the interfacial tension isotherm. The sharp decrease of the dilational elasticity values in a narrow range is presumably due to the destruction of two-dimensional rigid structures and the formation of microaggregates in the interfacial layer. From dilational viscosity measurements as a function of oscillation frequency one can conclude that with increasing surfactant concentration the SDS dominates in the interfacial adsorption layer whereas the polyelectrolyte–surfactant complexes remain in the bulk phase.

Flutter valve improves respiratory mechanics and sputum production in patients with bronchiectasis

Although the application of airway clearance techniques is considered an important component in the treatment of several obstructive pulmonary diseases, there is no scientific evidence supporting the use of Flutter Valve™ in the management of patients with bronchiectasis. Moreover, the consequences of respiratory physiotherapy techniques on respiratory mechanics have not been fully studied. Therefore, we investigated the acute, short-term effects of Flutter Valve™ on respiratory mechanics and sputum production in bronchiectatic patients. EIGHT patients were evaluated in a randomized, blinded, cross-over trial. Impedance at 5 Hz (R5), resistance as a function of oscillation frequency (dR/dF), reactance at 5 Hz (X5), resonant frequency (f(0) ) and integral of reactance between 5 Hz and resonant frequency (AX) were recorded. Flutter Valve™ cleared 8.4 mL more secretions than the Sham Flutter intervention (95% confidence interval [95% CI], 3.4-13.4). There was a higher percentage decrease in R5 (-11.2%; 95% CI, -4.4 to -18.2), dR/dF (-20.8%; 95% CI, -32.4 to -9) and AX (-7.8%; 95% CI, -11.9 to -3.7) under Flutter Valve™. X5 and f(0) variation did not differ between interventions. Flutter Valve™ increases sputum removal during treatment and diminishes total and peripheral airway resistance in hypersecretive patients with bronchiectasis. Impulse oscillometry is a user-friendly tool to evaluate the effects of airway clearance techniques on respiratory mechanics.

Mass transport due to oscillatory flow through a prestressed viscoelastic tube with a retentive and absorptive wall

An asymptotic analysis is presented for the mass transport of a solute due to volume-cycled oscillatory flow in a prestressed and viscoelastic tube with a reactive wall layer (wall retention and absorption). Based on the homogenization technique, the convection–diffusion transport equation is derived for the developed time-mean concentration, containing the effective transport coefficients of advection and dispersion as functions of oscillation frequency, initial stresses, viscoelasticity of the wall, and the two wall reactions. The present model as applied to gas transport in pulmonary airways under high-frequency ventilation is examined in detail, through comparison with a model in the literature. The dispersion coefficient is independent of the wall properties if the tube is tethered. The gas transport rate is found to be enhanced monotonically when either the reversible phase partitioning or its exchange rate increases.

Interpretation of mechanical spectra of carob fibre and oat wholemeal-enriched wheat dough using non-linear regression models

Oscillation and creep shear tests were applied to test the effect of fibre-rich additions – carob fibre (0–5%) and black oat wholemeal (0–20%) – on the rheological properties of wheat flour dough. Interpretation of changes in the values of the storage modulus ( G′) and loss modulus ( G″) and the tangent of the phase angle (tan δ) in the function of oscillation frequency ( f) was performed on the basis of proposed 3-parameter non-linear regression models. The results of creep measurements were analysed using the 6-parameter Burgers model. Increase in the share of the fibre-rich additions caused the G′( f) and G″( f) curves to shift towards higher values, and steeper slope and stronger bending of the shapes of the curves, while the tan δ( f) curve tended to shift towards lower values. The application of carob fibre and oat wholemeal at rates of 2% and 10%, respectively, caused that the ratio of viscous to elastic properties of wheat flour dough was the least dependent on the shear rate ( f). The result of creep tests showed an increase in the instantaneous and retarded moduli of elasticity and the Newtonian viscosity of wheat flour dough with increase in the share of the additions.

Synthesis, Characterization, and Interfacial Properties of an Oligomeric, Cationic Fluorooxetane

The synthesis and characterization of a cationic oligo(fluorooxetane) surfactant with pendant -C4F9 groups are reported. Molecular area demand at saturation was determined to be 55.6 +/- 0.3 angstroms2/molecule and characteristic of an oligomer. The adsorption of the cationic oligo(fluorooxetane) to the air-water interface appears to be diffusion-limited, and dilational rheological properties of the adsorbed molecules are representative of a "soluble" monolayer. Adsorption dynamics have been measured yielding diffusion coefficients that are dependent on concentration and in the 10(-7)-10(-8) cm2/s range. Complex moduli from dilational interfacial rheological measurements as a function of oscillation frequency were well fitted to the Lucassen-van den Tempel equation, providing an estimate of the Gibbs elasticity. The combination of the oligomeric nature of the fluorosurfactant, short perfluoroalkyl chain and its interfacial properties suggests that this synthetic approach is an attractive route to the development of fluorinated surfactants that avoid the environmental concerns of small-molecule, long perfluoroalkyl-chain surfactants.

Transfer function characteristics of bluff-body stabilized, conical V-shaped premixed turbulent propane–air flames

The response of bluff-body stabilized conical V-shaped premixed flames to periodic upstream velocity oscillations was characterized as a function of oscillation frequency, mean flow velocity, and equivalence ratio. The flame heat release response to the imposed velocity oscillations was determined from the CH ∗ chemiluminescence captured by two photomultiplier (PMT) detectors at a wavelength of 430 nm. One of the PMTs viewed flame radiation in a 10-mm horizontal slice, 50 mm above the bluff-body. The second PMT observed the overall flame radiation. The flame transfer function characteristics were determined from the spectral analysis of the velocity and PMT signals. It was found that the flame heat release amplitude response is confined to low-frequency excitation below a Strouhal number of 4. The phase relationship of the transfer function for these turbulent flames was evaluated using the signal from the spatially masked PMT. The transfer function estimate based on these data exhibits second-order characteristics with a phase lag between the velocity and heat release signals. The localized heat-release response contains frequencies that are multiples of the excitation frequency, suggesting splitting and tilting of flame structures as well as some nonlinear effects. Increase of flame equivalence ratio from lean toward stoichiometric resulted in slight amplification of the high-frequency response.

The development of DMA for the detection of amorphous content in pharmaceutical powdered materials

The aim of this short study was to develop a novel method of sample presentation that will allow currently available DMA apparatus designed for the testing of self-supporting materials to detect amorphous content in controlled mixtures of amorphous and crystalline powders. The preparation of amorphous lactose was carried out by spraying drying, using a Büchi mini spray drier. Controlled mixtures of amorphous and crystalline lactose were produced to give eight samples ranging between 2% and 75% (w/w) amorphous content. These powdered mixtures were loaded into the DMA using a novel powder-pocket device, which consisted of folded sheet of stainless steel. The pocket was clamped directly into the DMA using a single cantilever configuration, and subjected to oscillating displacement, forcing horizontal shearing of the powder between the two plates of the pocket. Typical experimental parameters were a dynamic displacement of 0.05 mm with a frequency of 1 Hz and a heating rate of 5 °C/min, from 25 °C to 250 °C. Over the glass transition region of amorphous lactose, the storage modulus decreased rapidly and a peak was observed in the tan δ signal, which are typical DMA responses for self-supporting glassy materials over their glass transition region. In both the storage modulus and tan δ signals, contributions from both plasticized and non-plasticized amorphous lactose were demonstrated. Such an observation was caused by the powder pocket restricting the loss of the 2.5% (w/w) water present in the spray-dried lactose within the time scale of the first heating cycle. The tan δ peak for the non-plasticized amorphous lactose showed Arrhenius behaviour as function of oscillation frequency. The relationship between the increase in the tan δ peak with increasing frequency allowed the determination of an activation energy that was comparable to the literature values for similar compounds. The height of the tan δ peak for the non-plasticized material was directly proportional to the amount of amorphous lactose present in the mixtures. The glass transition response was still detectable in mixtures containing as little as 2% (w/w) amorphous content, however the theoretical limit of detection was higher than that determined for the same mixtures using solution calorimetry. The results demonstrate that the novel powder pocket allows the use of conventional DMA instruments for the analysis of pharmaceutical powders, however the technique requires more development to further reduce its theoretical limit of detection.

Microdisplacement Measurement Using a Liquid-Delay-Line Oscillator

A technique for measuring micromechanical displacement is proposed using a liquid-delay-line oscillator, which consists of two pairs of arch-shaped interdigital transducers (IDTs) on a double-layered substrate composed of an acrylic plate and a piezoelectric ceramic plate, a reflecting plate and a water layer. In the use of the double-layered substrate, the seventh higher-order mode of leaky Lamb wave is favorable for the oscillator construction, because of high phase velocity and large transducer efficiency, while retaining sufficient mechanical strength, compared with the use of an only piezoelectric ceramic plate. The mechanical displacement is evaluated as a function of oscillation frequency, on the basis of the acoustical delay length, linearly dependent on the thickness of the water layer. The present technique is promising for sensing microdisplacement as a precise and convenient method.

Shared dynamics of attentional cost and pattern stability

This paper examines the informational activity devoted by the CNS to couple oscillating limbs in order to sustain and stabilize bimanual coordination patterns. Through a double-task paradigm associating a bimanual coordination task and a reaction time (RT) task, we investigated the relation between the stability of preferred bimanual coordination patterns and the central cost expended by the CNS for their stabilization. Ten participants performed in-phase and anti-phase coordination patterns in a dual task condition (coordination + RT) at several frequencies (0.5, 0.75, 1.0, 1.5, and 2.0 Hz), thereby decreasing the stability of the bimanual patterns. Results showed a U-shaped evolution of pattern stability and attentional cost, as a function of oscillation frequency, exhibiting a minimum value at the same frequency. These findings indicate that central cost and pattern stability covary and may share common, high order dynamics. Moreover, the attentional focus given to the bimanual coordination and the RT task was also manipulated by requiring either shared attention or priority to the coordination task. Such a manipulation led to a tradeoff between pattern stability and RT performance: The more stable the pattern, the more costly it is to stabilize. This suggests that stabilizing a coordination pattern incurs a central cost that depends on its intrinsic stability. Conceptual consequences of these results for understanding the relationship between attention and coordination are drawn, and the mechanisms putatively at work in dual tasks are discussed.

Structure and Viscosity of Grain Boundary in High‐Purity SiAlON Ceramics

Three high‐purity SiAlON materials (Si6−zAlzOzN8−z, z= 1, 2, 3) were characterized with respect to both structure and viscous behavior of internal grain boundaries. Internal friction experiments provided a direct measure of the intrinsic viscosity of grain boundaries and concurrently revealed the occurrence of a grain‐boundary interlocking mechanism that suppressed sliding. A residual glass phase (consisting of aluminum‐rich SiO2) and nanometer‐sized mullite residues were found at glassy triple‐grain junctions of the z= 1 SiAlON. A low‐melting intergranular phase dominated the high‐temperature behavior of this material and caused grain‐boundary sliding at temperatures as low as 1100°C. A quantitative analysis of the grain‐boundary internal friction peak as a function of oscillation frequency indicated an intergranular film viscosity of log η∼ 7.5 Pa · s at 1100°C. Glass‐free grain boundaries were a characteristic of SiAlON materials with z≥ 2, which yielded a significant improvement in refractoriness as compared to the z= 1 SiAlON material. In these materials, relaxation resulting from grain‐boundary sliding was suppressed, and the internal friction curve simply experienced an exponential‐like increase.

Using pseudorandom axial oscillations of concentric cylinders tomeasure the viscoelastic properties of fluids

A pair of concentric cylinders, where the inner cylinder is movedaxially through the outer fixed cylinder, is used to measure the dynamicviscoelastic properties of a fluid which occupies the annulus between them. Amicro-Fourier rheometer is used to cause the inner cylinder to undergo smallamplitude, band-limited pseudorandom oscillations in the axial direction, withsimultaneous measurement of the instantaneous resistance force due to thefluid. The magnitude and phase of the force signal are used to calculate thestorage and loss moduli G'(ω),G''(ω) as functions of oscillationfrequency ω. Tests performed on two types of silicone oil show fairagreement with results conducted with the parallel plate squeezing flowgeometry.