Sinusoidal Time Research Articles

Dynamic Response of Model Lipid Membranes to Ultrasonic Radiation Force

Low-intensity ultrasound can modulate action potential firing in neurons in vitro and in vivo. It has been suggested that this effect is mediated by mechanical interactions of ultrasound with neural cell membranes. We investigated whether these proposed interactions could be reproduced for further study in a synthetic lipid bilayer system. We measured the response of protein-free model membranes to low-intensity ultrasound using electrophysiology and laser Doppler vibrometry. We find that ultrasonic radiation force causes oscillation and displacement of lipid membranes, resulting in small (<1%) changes in membrane area and capacitance. Under voltage-clamp, the changes in capacitance manifest as capacitive currents with an exponentially decaying sinusoidal time course. The membrane oscillation can be modeled as a fluid dynamic response to a step change in pressure caused by ultrasonic radiation force, which disrupts the balance of forces between bilayer tension and hydrostatic pressure. We also investigated the origin of the radiation force acting on the bilayer. Part of the radiation force results from the reflection of the ultrasound from the solution/air interface above the bilayer (an effect that is specific to our experimental configuration) but part appears to reflect a direct interaction of ultrasound with the bilayer, related to either acoustic streaming or scattering of sound by the bilayer. Based on these results, we conclude that synthetic lipid bilayers can be used to study the effects of ultrasound on cell membranes and membrane proteins.

A Novel Radio Interferometric Time Delay Tracking Scheme

This paper presents a novel sinusoidal signal time delay tracking scheme based on radio interferometric for wireless sensor networks. We first design an interference signal composed of two sinusoidals with different frequencies in a transmitter. Then a sinusoidal signal time delay tracking algorithm based on DTFT is also presented. Compared with the source-separated radio interferometric time delay estimation (RITDE) technology, the proposed scheme can directly acquire time delay between two rather than among four receivers. Hence it can be employed directly to the traditional time-difference-of-arrival (TDOA) localization algorithm. Simulation results confirm the efficiency and superior performance of the DTFT-based algorithm as compared to the existing filter-based approaches.

Conjugate heat transfer during oscillatory laminar flow in porous media

Hydrodynamics and conjugate heat transfer in porous media subject to unidirectional-steady state as well as steady-periodic flow conditions were numerically studied. Two-dimensional flows in porous media composed of periodically configured arrays of square cylinders were simulated using a computational fluid dynamics tool, with sinusoidal time variation of inlet and exit boundaries and conjugate heat transfer between the solid and fluid domains. The simulated domain contained seven unit cells, with each unit cell representing a square cylinder. Simulations showed that the end effects did not persist more than two unit cells. Simulations were conducted for flow oscillation frequencies of 0–60Hz, and low and high velocity amplitudes (representing tidal fluid penetration amplitudes of 8 and 2 times the hydraulic diameter, respectively, at inlet) for a 75% porous domain. Using the simulation results, pore-scale volume-average Darcy permeability, Forchheimer coefficient, and Nusselt number associated with the standard volume-average porous media momentum and thermal energy equations were calculated. These parameters were calculated in instantaneous as well as cycle-averaged forms. The Forchheimer coefficient and Nusselt number were significantly different in unidirectional-steady and oscillatory flow conditions. These parameters strongly depend on the flow oscillation frequency and amplitude. Furthermore, significant phase lag occurs among velocity, pressure, temperature and heat transfer processes. The results confirm that unidirectional-steady flow models and correlations are not suitable for applications involving flow oscillations.

Analysis of the electric field produced by power lines using double complex numbers

Purpose – The paper aims to highlight the efficiency of double complex numbers for the complete analysis of the intensity of the electric field produced by power lines.Design/methodology/approach – One set of complex numbers is used to represent all the plane vectors (vector distances) and another set of complex numbers is used to represent all the sinusoidal time varying quantities (electric charges and voltages). The simultaneous representation of vector distances and sinusoidal time varying quantities with complex numbers gives elegant expressions to the electric field vector and simplifies the mathematical relations to a great degree.Findings – General analytical formulas are developed for the direct calculation of all the parameters of the elliptically rotating electric field (rms value, major and minor semi‐axis of the ellipse, angles of the semi‐axes, tracing direction, polarization). The analytical formulas depend on the components of the double complex number.Research limitations/implications – T...

The photo-assisted heat current and its Peltier coefficient in a metal/dot/metal junction

The photo-assisted heat current through a metal/dot/metal junction and its associated Peltier coefficient are computed in the framework of the time-dependent out-of-equilibrium Keldysh formalism in the presence of a dot energy modulation. When the frequency of the modulation is much larger than the amplitude of the modulation, the heat current follows the sinusoidal time evolution of the dot energy. This is no longer the case when the modulation frequency becomes of the order of or smaller than the amplitude of the modulation. To characterize this non-sinusoidal behavior, we have calculated the harmonics of the photo-assisted heat current. The zero-order harmonic can be expressed as an infinite sum of dc heat currents associated with a dot with shifted energies. It exhibits a devil's staircase profile with non-horizontal steps, whereas it is established that the steps are horizontal for the zero-order harmonic of the photo-assisted electric current. This particularity is related to the fact that the dot heat is not a conserved quantity due to energy dissipation within the tunnel barriers.

Rheodynamic Lubrication of an Externally Pressured Thrust Bearing Using Herschel-Bulkley Fluid with Sinusoidal Injection

Lubricants with variable viscosity are assuming greater importance for its application in polymer industry, thermal reactors and in biomechanics. With the bearing operations in machines being subject to high speeds, loads, increasing mechanical shearing forces and continually increasing pressure, there has been an increasing interest to use nonNewtonian fluids characterized by a yield value. Some of them, which fit into this class, are Bingham, Casson and Herchel-Bulkley models. In the present work, the problem of an externally pressurized thrust bearing lubricated with Herschel-Bulkley fluid under the sinusoidal flow rate has been investigated. Herschel-Bulkley fluids are characterized by a yield value, which leads to the formation of rigid core in the flow region. The shape and extent of the core has been determined numerically for various values of the Herschel-Bulkley number, power-law index, amplitude of sinusoidal fluid film and time. Numerical solutions have been obtained for the bearing performances such as pressure distribution and load capacity for different values of the Herschel-Bulkley number, power-law index, amplitude of sinusoidal fluid film and time. The effects of sinusoidal injection of the lubricant and the non-Newtonian characteristics on the bearing performances have been discussed.

Negative index materials and time-harmonic electromagnetic field

Abstract We study the evanescent waveʼs behavior on a device made of a plane interface separating vacuum from a perfect negative index material. The system is described by the macroscopic Maxwellʼs equations with frequency-dependent permittivity and permeability. Assuming that electromagnetic sources with sinusoidal time dependence are switched on at an initial time, we show that, as time increases, evanescent waves result in surface modes at the plane interface. The time dependence of these surface modes is oscillating but not harmonic since their amplitude linearly increases with time. As a consequence, we find that the image of a point source is not a point image. The analysis avoids any ambiguity related with causality and finite energy requirements.

Non-Markovian diffusion over a potential barrier in the presence of periodic time modulation

The diffusive non-Markovian motion over a single-well potential barrier in the presence of a weak sinusoidal time modulation is studied. We found nonmonotonic dependence of the mean escape time from the barrier on a frequency of the periodic modulation that is analogous to the stochastic resonance phenomenon. The resonant increase of diffusion over the barrier occurs at the frequency inversely proportional to the mean first-passage time for the motion in the absence of the time modulation.

Gust wind tunnel study on ballast pick-up by high-speed trains

This paper describes the experimental setup, procedure, and results obtained, concerning the dynamics of a body lying on a floor, attached to a hinge, and exposed to an unsteady flow, which is a model of the initiation of rotational motion of ballast stones due to the wind generated by the passing of a high-speed train. The idea is to obtain experimental data to support the theoretical model developed in Sanz-Andres and Navarro-Medina (J Wind Eng Ind Aerodyn 98, 772–783, (2010), aimed at analyzing the initial phase of the ballast train-induced-wind erosion (BATIWE) phenomenon. The experimental setup is based on an open circuit, closed test section, low-speed wind tunnel, with a new sinusoidal gust generator mechanism concept, designed and built at the IDR/UPM. The tunnel’s main characteristic is the ability to generate a flow with a uniform velocity profile and sinusoidal time fluctuation of the speed. Experimental results and theoretical model predictions are in good agreement.

Active rheology of phospholipid vesicles

Optical tweezers are used to manipulate the shape of artificial dioleoyl-phosphatidylcholine (DOPC) phospholipid vesicles of around 30 μm diameter. Using a time-shared trapping system, a complex of traps drives oscillations of the vesicle equator, with a sinusoidal time dependence and over a range of spatial and temporal frequencies. The mechanical response of the vesicle membrane as a function of the frequency and wavelength of the driving oscillation is monitored. A simple model of the vesicles as spherical elastic membranes immersed in a newtonian fluid, driven by a harmonic trapping potential, describes the experimental data. The bending modulus of the membrane is recovered. The method has potential for future investigation of nonthermally driven systems, where comparison of active and passive rheology can help to distinguish nonthermal forces from equilibrium fluctuations.

An analytical solution of the point kinetics equations with time-variable reactivity by the decomposition method

In this work, we report an analytical solution for the point kinetics equations by the decomposition method, assuming that the reactivity is an arbitrary function of time. The main idea initially consists in the determination of the point kinetics equations solution with constant reactivity by just using the well-known solution results of the first-order system of linear differential equations in matrix form with constant matrix entries. Applying the decomposition method, we are able to transform the point kinetics equations with time-variable reactivity into a set of recursive problems similar to the point kinetics equations with constant reactivity, which can be straightly solved by the mentioned technique. For illustration, we also report simulations for constant, linear and sinusoidal reactivity time functions as well comparisons with results in literature.

Convective heat transfer and thermal dispersion during laminar pulsating flow in porous media

Solid–fluid heat transfer and thermal dispersion during laminar pulsating flow through porous media were numerically studied. Two-dimensional flows in porous media composed of periodically configured arrays of square cylinders were simulated using a computational fluid dynamics tool, with sinusoidal time variation of flow as the inlet boundary condition. Detailed numerical data were obtained for porosities of 0.64–0.84, frequencies of 0–100 Hz, and Reynolds numbers of 70–980, with Reynolds number defined based on the time-average superficial velocity and pore unit-cell dimension. Pore-scale volume-average heat transfer coefficients, and the thermal dispersion term associated with the standard volume-average porous media thermal energy equation were found to be strong functions of porosity, Reynolds number, and most importantly the flow pulsation frequency. Based on the obtained numerical data, empirical correlations were developed for cycle-average pore-scale Nusselt number and the dimensionless thermal dispersion term.

Transient Response of Supported Beams to Moving Forces with Sinusoidal Time Variation

Moving forces are a common loading pattern for flexible beams, found in many applications in both civil and mechanical engineering. These forces give rise to a transient response, the nature of which depends on the time variation of the amplitude of the force and its position along the beam. In addition to the possibility of numerical evaluation, closed form solutions of the beam response are beneficial for their simplicity of use, and because they allow an understanding of the system behavior. On the other hand, these prove to be rather complicated in most cases, and only a limited number of cases are available in the literature. This paper studies the simple but common case of a supported beam loaded by a force with sinusoidal time variation moving at a constant speed. Simple equations are presented for the approximated responses at and away from resonance, and their accuracy is discussed. Transient frequency response functions are also shown. Finally, as an example, the results are applied to an evaluation of the response of a beam footbridge to the action of a walker, and compared to code specifications.

Electron flux during pericyclic reactions in the tunneling limit: Quantum simulation for cyclooctatetraene

Pericyclic rearrangement of cyclooctatetraene proceeds from equivalent sets of two reactants to two products. In the ideal limit of coherent tunneling, these reactants and products may tunnel to each other by ring inversions and by double bond shifting (DBS). We derive simple cosinusoidal or sinusoidal time evolutions of the bond-to-bond electron fluxes and yields during DBS, for the tunneling scenario. These overall yields and fluxes may be decomposed into various contributions for electrons in so called pericyclic, other valence, and core orbitals. Pericyclic orbitals are defined as the subset of valence orbitals which describe the changes of Lewis structures during the pericyclic reaction. The quantum dynamical results are compared with the traditional scheme of fluxes of electrons in pericyclic orbitals, as provided by arrows in Lewis structures.

Identification of linear relationships from noisy data using errors-in-variables models—relevance for reconstruction of past climate from tree-ring and other proxy information

Reliable paleoclimate reconstructions are needed to assess if the recent climatic changes are unusual compared to pre-industrial climate variability. Here, we focus on one important problem in climate reconstructions: Transfer functions relating proxies (predictors) and target climatic quantities (predictands) can be seriously biased when predictand and predictor noise is not adequately accounted for, resulting in biased amplitudes of reconstructed climatic time series. We argue for errors-in-variables models (EVM) for unbiased identification of linear structural relationships between noisy proxies and target climatic quantities by (1) introducing underlying statistical concepts and (2) demonstrating the potential biases of using the EVM approach, the most commonly used direct ordinary least squares (OLS) regression, inverse OLS regression, or the reduced major axis method (‘variance matching’) with a simulation example of artificial noise-disturbed sinusoidal time series. We then develop an alternative strategy for paleoclimate reconstruction from tree-ring and other proxy data, explicitly accounting for the identified problem.

Stability properties of periodically driven overdamped pendula and their implications to physics of semiconductor superlattices and Josephson junctions

We consider the first order differential equation with a sinusoidal nonlinearity and periodic time dependence, that is, the periodically driven overdamped pendulum. The problem is studied in the case that the explicit time dependence has symmetries common to pure ac-driven systems. The only bifurcation that exists in the system is a degenerate pitchfork bifurcation, which describes an exchange of stability between two symmetric nonlinear modes. Using a type of Prüfer transform to a pair of linear differential equations, we derive an approximate condition of the bifurcation. This approximation is in very good agreement with our numerical data. In particular, it works well in the limit of large drive amplitudes and low external frequencies. We demonstrate the usefulness of the theory applying it to the models of pure ac-driven semiconductor superlattices and Josephson junctions. We show how the knowledge of bifurcations in the overdamped pendulum model can be utilized to describe the effects of rectification and amplification of electric fields in these microstructures.

Interferometric imaging of carbon monoxide in comet C/1995 O1 (Hale-Bopp): evidence of a strong rotating jet

Observations of the CO J(1-0) 115 GHz and J(2-1) 230 GHz lines in comet C/1995 O1 (Hale-Bopp) were performed with the IRAM Plateau de Bure interferometer on 11 March, 1997. The observations were conducted in both single-dish (ON-OFF) and interferometric modes with 0.13 km s-1 spectral resolution. Images of CO emission with 1.7 to 3" angular resolution were obtained. The ON-OFF and interferometric spectra show a velocity shift with sinusoidal time variations related to the Hale-Bopp nucleus rotation of 11.35 h. The peak position of the CO images moves perpendicularly to the spin axis direction in the plane of the sky. This suggests the presence of a CO jet, which is active night and day at about the same extent, and is spiralling with nucleus rotation. The high quality of the data allows us to constrain the characteristics of this CO jet. We have developed a 3-D model to interpret the temporal evolution of CO spectra and maps. The CO coma is represented as the combination of an isotropic distribution and a spiralling gas jet, both of nucleus origin. Spectra and visibilities (the direct output of interferometric data) analysis shows that the CO jet comprises ~40% the total CO production and is located at a latitude ~20 degrees North on the nucleus surface. Our inability to reproduce all observational characteristics shows that the real structure of the CO coma is more complex than assumed, especially in the first thousand kilometres from the nucleus. The presence of another moving CO structure, faint but compact and possibly created by an outburst, is identified.

Finite Element AC-Losses Computation in Multi-Layer HTS Cable Using Complex Representation of the Electromagnetic Field

The paper deals with the concept of effective resistivity to use in problems expressed in terms of phasor quantities under a sinusoidal time varying excitation. A single time-harmonic solution with several definitions of the effective electric conductivity is given. The losses in HTS tape and cable are obtained in steady state and the results are validated through Norris formulae.

Viscosity Measurements of Diisodecyl Phthalate Using a Vibrating Wire Instrument Operated In Free Decay Mode: Comparison with Results Obtained with the Forced Mode of Operation

Recently, several authors described measurements of liquid viscosities higher than 100 mPa·s, using the vibrating wire technique in the forced oscillation mode of operation. The use of a vibrating wire instrument to measure increasingly higher viscosities poses experimental difficulties due to the consequent decrease of the quality factor of the resonance. This problem affects both modes of operation: in the steady-state, forced oscillation mode, there is a loss of definition of the resonance curve, and in the transient, free decay mode, there is an increase of the decrement of the sinusoidal time response of the vibrating wire. In the present work, we have measured the viscosity of diisodecyl phthalate (DIDP) at 0.1 MPa with a vibrating wire of nominal radius of 190 μm using the free decay mode of operation. The measurements covered a range of viscosities from (64 to 265) mPa·s. The results agreed with those we have obtained with a vibrating wire instrument operated in the forced mode and with the literature data, within the estimated experimental uncertainty (k = 2) of ± 2 %. The comparisons indicate that the use of the free decay mode of operation does not necessarily imply a significant increase of uncertainty of the viscosity results at moderately high viscosities.

Effect of the days scrolling on the natural convection in an open ended storage silo

The problem of unsteady natural convection heat transfer in a vertical, open ended, porous cylinder heated laterally with a sinusoidal time variation of the temperature has been investigated numerically. The model considered is the classical Darcian flow coupled with the energy equation. In the case of constant wall temperature, two types of chimney flows take place, with and without fluid recirculation. The present problem depends on the filtration Rayleigh number ( Ra), the aspect ratio ( A) and the inlet–outlet conditions ( Bi). For low dimensionless temperature amplitudes ( XA < 0.5) in the sinusoidal time variation, the resulting heat transfer is found to be globally equivalent to the case of constant wall temperature. The observed relative difference between sinusoidal and constant wall temperature is less than 5%. This difference decreases as the Ra is reduced.