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Most industrial process lines involve mixing complex dispersions, which can include non-Newtonian liquids and viscoelastic particles. Knowledge of the parameters of these components may provide a key for understanding how dispersions are formed and how equipment should be designed. One parameter is the shear modulus, which describes the ability of particles to resist mechanical stresses. This parameter may play the main role in the mixing process, when a dispersion is formed by the mechanical influence of a rotor (slice or shear in a rotor-stator mixer). In this work, two methods were chosen for measuring the shear modulus: the evaluation method, based on the Warner-Bratzler cut test, and the oscillatory method. Both methods were used for measuring viscoelastic clusters of particles, and the results were adjusted for the purposes of the comparison. The comparison shows that the shear modulus values obtained from Warner-Bratzler are higher than the values obtained from the oscillatory test for the same conditions. This difference can be explained by differences in the mechanical processes during the experiments. KEYWORDS frequency sweep, shear modulus, viscoelasticity, Warner-Bratzler test, 1 | INTRODUCTION Viscoelastic materials are involved in many processes, for example, mixing, blending, and extrusion. Measurements of the viscoelastic characteristics of these materials are essential for the adjustment of [...]

Superposed mass oscillation that often occurs in a throttled surge tank with a long headrace tunnel is studied. The instant of the worst superposition of mass oscillation in a surge tank is analysed. The analytical formula predicting the worst superposition instant is derived exactly and verified (1) with a numerical solution to the fundamental equations for the surge tank and (2) with a numerical simulation of hydraulic transients in an actual hydropower station. It is shown that the superposed oscillation provides the highest upsurge at the instant that the initial flow rate in the headrace tunnel and initial water level in the surge tank satisfy the judgement formula. The conclusion provides a theoretical and computational basis for the numerical simulation of maximum upsurge in a surge tank. Key words: surge tank, hydropower station, hydraulic transient, critical superposed oscillation, maximum upsurge, theoretical analysis. L'oscillation de masses superposees qui survient souvent dans une cheminee d'equilibre a etranglement associeee a un long canal d'amenee est examinee. Le moment de la pire superposition de l'oscillation de masse dans la cheminee d'equilibre a etranglement est analyse. La formule analytique predisant le moment de pire superposition est deriveee de maniere exacte et verifiee au moyen de (1) une solution numerique aux equations fondamentales pour la cheminee d'equilibre a etranglement et (2) une simulation numerique des transitoires hydrauliques dans une centrale hydroelectrique. Il a ete montre que l'oscillation superposee fournit la plus forte remontee au moment oil le debit initial dans le canal d'amenee et le niveau d'eau initial dans la cheminee d'equilibre a etranglement repondent aux formules de criteres de decision. La conclusion fournit une base theorique et computationnel pour la simulation numerique de la remontee maximale dans une cheminee d'equilibre. Mots-cles: cheminee d'equilibre, station hydroelectrique, transitoire hydraulique, oscillation superposee critique, remontee maximale, analyse theorique. [Traduit par la Redaction], 1. Introduction With the rapid exploitation of hydropower resources in some developing countries in recent years, there have been many hydropower stations under construction or in their design phase. Some [...]

Coherent emission from two or more classical damped oscillators leads to an apparent violation of conservation of energy if the oscillators are assumed to emit independently. To resolve this apparent paradox, it is necessary to include effects related to cooperative decay, wherein each oscillator modifies the damping rate of the other oscillators. We show how these effects are included for two radiating oscillators and for a line of N oscillators. The relation between cooperative decay, optical coherent transients, and superradiance is discussed. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3475686]

An experimental investigation on the formation of dynamic hydraulic jumps in an oscillating rectangular container was performed using a high-resolution, high-speed digital imaging system. The present work investigates driven angular roll oscillations using a state-of-the-art motion simulator and a transparent rectangular container. A hydraulic jump was observed traversing between the walls of the tank when the container was oscillated near the surface-wave resonance frequency based on liquid depth. The hydraulic jump was imaged and its characteristics were measured using image processing software. It was found that the directionally based hydraulic jump formation frequency matches the driven frequency. However, the phase difference between the two is dependent on the ratio of the driven frequency to resonance frequency. Furthermore, the spatial characteristics of the jump are dependent on the amplitude and frequency of the oscillation.

The propulsive force generated by the leading-edge suction of a flapping thin airfoil can be obtained using unsteady aerodynamic notions based on the potential flow theory. Because the potential theory fails to predict the viscous forces, for flapping airfoils, in general there exists a net propulsive force generation. For low Reynolds numbers and for oscillations at low reduced frequencies, however, the viscous forces overcome the propulsive forces to give a net force against the flight direction. In the case of higher Reynolds numbers, flappings with large amplitudes, and high frequencies, the leading-edge suction force generated by the airfoil overcomes the viscous forces. In this study, the critical Reynolds number, the amplitude, and the reduced frequency values that yield the net propulsive force for an oscillating airfoil are predicted with unsteady viscous-inviscid interaction. The airfoil motions are modeled as 1) a thin rigid plate in vertical oscillation, that is, a heaving-plunging motion; 2) a flexibly cambered airfoil whose camber is changing periodically; and 3) the heaving-plunging motion of a flexibly cambered airfoil. The leading-edge suction force for all cases is predicted by means of the well-known Blasius theorem, and the time dependent surface velocity distribution of the airfoil is determined by unsteady aerodynamic considerations. This surface velocity distribution is used as the edge velocity of the unsteady boundary layer to predict the viscous effects. The coefficient of the propulsive force predicted with the present method agrees well with the values given in the literature up to the effective angle of attack at which the dynamic stall takes place.

In this paper, the effects of electromagnetic fields from the frequency band of digital wireless telephones on a superconducting quantum interference device (SQUID) were experimentally investigated. A first-order planar gradiometer based on the double relaxation oscillation SQUID (DROS) was operated without low-frequency magnetic shielding, and was exposed to radiated electromagnetic fields in the frequency range of 300 MHz-2 GHz. The experiments have been performed in a fully anechoic chamber to minimize reflected waves in the chamber. The flux-to-voltage transfer and the field sensitivity of the gradiometer have been observed under the irradiation of fields. Results show that the performance of the gradiometer was significantly affected at a typical power level of the digital wireless telephones for both horizontally and vertically polarized electromagnetic waves. The noise level of the DROS output voltage also increases as the strength of the external fields becomes higher. Index Terms--Biomagnetics, electromagnetic interference, superconducting quantum interference device (SQUID) magnetometers.

A tool for the design of a self-excited oscillation of a desired amplitude and frequency in linear plants by means of the variable structure control is proposed. An approximate approach based on the describing function method is given, which requires that the mechanical plant should be a low-pass filter--the hypothesis that usually holds when the oscillations are relatively fast. The proposed approach is demonstrated via the controller design and experiments on the Furuta pendulum. Index Terms--Frequency domain methods, periodic solution, under-actuated systems, variable structure systems.

The minimum laser energy required to cause sustained harmonic oscillations in a 201-stage ring oscillator varies little with increasing power supply voltage when operating in the subthreshold region. These small changes in threshold laser energy in the subthreshold region suggest that the cross-section curves as a function of power supply voltage remain relatively constant. Simulations show that the minimum pulsewidth required to generate higher-order oscillations decreases as operating voltage increases. Single-event transients are wider when circuits are operating in the subthreshold region than when operating at the nominal power supply voltages. Narrower single-event transients result for strikes on PMOS transistors as compared to those for strikes on NMOS devices in the subthreshold region; the opposite is observed when circuits are operating at the nominal power supply voltages. Index Terms--CMOS circuits, digital circuits, radiation effects, radiation effects in ICs, single-event effects, single event transients.

A direct current (dc) voltage biased II-VI semiconductor multiquantum well structure attached to normal contacts exhibits self-sustained spin-polarized current oscillations if one or more of its wells are doped with Mn. Self-sustained current oscillations are due to repeated triggering of charge dipole domains at the magnetic wells and motion towards the collector. Without magnetic impurities, the only configurations appearing in these structures are stationary. Analysis and numerical solution of a nonlinear spin transport model yield the minimal number of wells and the range of doping density needed to find oscillations, the current-voltage characteristic curve and the main features of stable stationary and time-periodic states. Our study could allow designing the oscillatory spin-polarized current injectors. Index Terms--Diluted magnetic semiconductor superlattices, self-sustained current oscillations, spintronics.

A mechanism to demodulate a two-tone high-frequency oscillation in nonlinear electronic devices due to an external electromagnetic field is investigated. The results of a demodulation are low-frequency disturbances to the internal circuits of electronic devices. A method for the synthesis of nonlinear compensators on the basis of the operational equations of electronic devices is offered for protection against low-frequency noise. The nonlinear operator of the compensator is designed so that a cascade connection of the electronic device and the compensator is described by the linear Volterra functional. As an example, the compensation of nonlinear transformations of a detector at high-frequency oscillation is synthesized with the use of results of measurements. The accuracy of the executed compensation is estimated. Index Terms--Low-frequency noise, nonlinear compensation, nonlinear operator, Volterra polynomial.

This paper presents two different stabilization methods based on the fractional-calculus theory. The first method is proposed via using the fractional differentiator, and the other is constructed based on using the fractional integrator. It has been shown that the proposed techniques can be used to suppress chaotic oscillations in 3-D chaotic systems. To show the practical capability of the methods, some experimental results on the control of chaos in chaotic circuits are presented. Index Terms--Chaos, chaotic circuit, fractional-order controller, stabilization.

The bias oscillation of GaN-based Gunn diodes realized on a n+-GaN substrate is discussed. Findings reveal that GaN Gunn diodes were very stable for pulsewidths up to 70 ns.

A new queue management scheme for reducing queue oscillation at a congested link is presented. Results suggest the capability of the proposed scheme in reducing queue oscillation and in maintaining high utilization with small queue length.

The subsynchronous resonance (SSR) phenomenon may occur when a steam turbine-generator is connected to a long transmission line with series compensation. The main purpose of this work is to verify the capability of the gate-controlled series capacitor (GCSC) to mitigate SSR. For this study the GCSC was tested in conjunction with the IEEE First Benchmark Model. The actual possibility of controlling SSR was verified by digital simulation using the Alternative Transients Program/Electromagnetic Transients Program. As a result it was shown that GCSC can damp SSR even without a specific control. It was also shown that, using a simple controller, SSR as well as electromechanical oscillation can be damped. Index Terms--Controlled series compensation, flexible ac transmission system (FACTS), GCSC, IEEE First Benchmark, subsynchronous resonance (SSR).

When one applies the method of auxiliary sources to scattering problems involving perfect conductors, one first seeks fictitious auxiliary currents located inside the conductor, and then determines the field from these currents. For a simple two-dimensional problem involving an infinite circular cylinder illuminated by an electric current filament, it has recently been shown analytically that it is possible to have divergent auxiliary currents (to make this statement precise, one must properly normalize the currents), together with a convergent field. It was also shown--through numerical investigations--that the aforementioned divergence appears as abnormal, rapid oscillations. In the present paper, we investigate such phenomena in more detail, with particular emphasis on oscillations. For a perfectly conducting ground plane illuminated by an electric current filament, we once again demonstrate the possibility of having divergent, oscillating currents producing a convergent field. We develop an asymptotic formula for the oscillating current values, which sheds light on the nature of the oscillations. We revisit the circular-cylinder problem to develop a similar asymptotic formula. We also discuss roundoff errors, and possible generalizations to scatterers of other shapes. The present study is to a great extent analytical, with the analytical predictions confirmed and supplemented by numerical results. Index Terms--Convergence of numerical methods, Fredholm integral equations, scattering.

Organisms are equipped with regulatory systems that display a variety of dynamical behavior ranging from simple stable steady states, to switching and multistability, to oscillations. Earlier work has shown that oscillations in protein concentrations or gene expression levels are related to the presence of at least one negative feedback loop in the regulatory network. Here, we study the dynamics of a very general class of negative feedback loops. Our main result is that, when a single negative feedback loop dominates the dynamical behavior, the sequence of maxima and minima of the concentrations exhibit a pattern that uniquely identifies the interactions of the loop. This allows us to devise an algorithm to (i) test whether observed oscillating time series are consistent with a single underlying negative feedback loop, and if so, (ii) reconstruct the precise structure of the loop, i.e., the activating/repressing nature of each interaction. This method applies even when some variables are missing from the data set, or if the time series shows transients, like damped oscillations. We illustrate the relevance and the limits of validity of our method with three examples: p53-Mdm2 oscillations, circadian gene expression in cyanobacteria, and cyclic binding of cofactors at the estrogen-sensitive pS2 promoter.

One of the unexplained striking features of tropical convection is the observed statistical self-similarity in clusters, superclusters, and intraseasonal oscillations through complex multiscale processes ranging from the mesoscales to the equatorial synoptic scales to the intraseasonal/planetary scales. Here new multispatialscale, multitime-scale, simplified asymptotic models are derived systematically from the equatorial primitive equations on the range of scales from mesoscale to equatorial synoptic to planetary/ intraseasonal, which provide a useful analytic framework for addressing these issues. New mesoscale equatorial synoptic dynamical (MESD) models and balanced MESD (BMESD) models are developed for the multitime, multispace interaction from mesoscales to equatorial synoptic scales; new multitime versions of the intraseasonal planetary equatorial synoptic dynamics (IPESD) models are developed for multiple spatiotemporal interactions on equatorial synoptic scales and planetary scales. The mathematical character derived below for all these simplified models explicitly demonstrates that the main nonlinear interactions across scales are quasi-linear where eddy flux divergences of momentum and temperature from nonlinear advection from the smaller-scale spatiotemporal flows as well as mean source effects accumulate in time and drive the waves on the successively larger spatiotemporal scales. Furthermore, these processes that transfer energy to the next larger, longer, spatiotemporal scales are self-similar in a suitable sense established here. On the other hand, the larger scales set the environment for this transport through processes such as mean advection of the smaller scales.

The Leybold-Heraeus gravitational torsion balance is commonly used in undergraduate laboratories to measure the gravitational attraction between known masses to find the gravitational constant G. Because the difficult task of data acquisition reduces its usefulness, we have implemented a simple design that minimizes this task and achieves more accurate results. This design features a small car that tracks the oscillating laser with the use of a stepper motor and some simple control circuitry. Step counting yields the location of the reflected laser in time. [DOI: 10.1119/1.2426349]

A model was developed for slow light based on the coherent population oscillation of quantum dots at room temperature. The findings suggest that quantum-dot devices could be potentially used as electrically and optically controllable slow light devices.

Study is presented in which parasitic backward-wave oscillation power is analyzed as a function of interaction length focusing on magnetic field parameters in a generic helix traveling-wave tube (TWT) amplifier in the absence of amplified signal. Results demonstrate that the focusing magnetic field parameters have significant effect on the interaction of the rotating electron beam with the backward wave in the nonlinear regime, as they have in the linear regime.

Periodic oscillations of raindrops falling at terminal velocity in natural rain are visualized for the first time by high-speed imaging. These images show the existence of an oscillation mode with the same frequency as the fundamental harmonic, but with shape different than that predicted by linear theory. These oscillations cause a lateral drift with a speed of approximately 20%-30% of the drop terminal velocity and without a preferred direction. These experimental observations serve as an insightful illustration of the potential benefit of applying high-speed imaging technology to investigate the dynamical microstructure of rainfall at the raindrop scale.

A theoretical investigation of the modification of dynamical properties in a semiconductor laser by a strong injected signal is presented. The results show different relaxation oscillation behaviors for free-running and injected lasers, arising from distinctly different physical processes.

The theory of dynamic force microscopy in air is developed with respect to the application of the Q-control technique. Analytical as well as numerical approaches are applied to solve the equation of motion describing the cantilever dynamics with and without Q-control in the presence of a model tip-sample interaction force.

Two easily implemented methods for generating small amplitude ion-acoustic plasma waves in alkali rf-discharge lamps are demonstrated. The frequency of these waves is proportional to the square root of the rf power driving the lamp, thus suggesting that their examination could provide an easily accessible parameter for monitoring and controlling the lamp's plasma conditions.

The level of arousal in mammals is correlated with metabolic state and specific patterns of cortical neuronal responsivity. In particular, rhythmic transitions between periods of high activity (up phases) and low activity (down phases) vary between wakefulness and deep sleep/anesthesia. Current opinion about changes in cortical response state between sleep and wakefulness is split between neuronal network-mediated mechanisms and neuronal metabolism-related mechanisms. Here, we demonstrate that slow oscillations in network state are a consequence of interactions between both mechanisms. Specifically, recurrent networks of excitatory neurons, whose membrane potential is partly governed by ATP--modulated potassium ([K.sub.ATP]) channels, mediate response-state oscillations via the interaction between excitatory network activity involving slow, kainate receptor-mediated events and the resulting activation of ATP-dependent homeostatic mechanisms. These findings suggest that [K.sub.ATP] channels function as an interface between neuronal metabolic state and network responsivity in mammalian cortex. glutamate | slow-wave oscillation | potassium channel | rhythm

The work described here examines the influence of the equatorial quasi-biennial oscillation (QBO) on the extratropics in a zonally truncated 3D mechanistic stratospheric model. Model results show that the extratropical response to the QBO depends critically on the phase alignment of the QBO with the annual cycle: the signal of extratropical response varies by a factor of 8 between the phase alignment that gives minimum response and that which gives maximum response. Model simulations in which the time and height structure of the QBO are varied suggest that, in this zonally truncated model, the equatorial height of 21-23 km is most influential for the extratropical response and that late autumn/early winter is the time at which the QBO has the most influence over the extratropical circulation. The correlation coefficient between the QBO (measured by zonal wind) and the extratropics (measured by zonal wind or potential temperature) is as high as 0.95. The correlation coefficient is largest for simulations with lower boundary wave forcing weaker than that which gives largest extratropical interannual variability. For stronger extratropical wave forcing, the correlation coefficient is slightly smaller, but the regression coefficient of the linear term in a least squares fit is significantly larger.

This paper studies multiple regimes and low-frequency oscillations in the Northern Hemisphere zonalmean zonal flow in winter, using 55 yr of daily observational data. The probability density function estimated in the phase space spanned by the two leading empirical orthogonal functions exhibits two distinct, statistically significant maxima. The two regimes associated with these maxima describe persistent zonal-flow states that are characterized by meridional displacements of the midlatitude jet, poleward and equatorward of its time-mean position. The geopotential height anomalies of either regime have a pronounced zonally symmetric component, but largest-amplitude anomalies are located over the Atlantic and Pacific Oceans. High-frequency synoptic transients participate in the maintenance of and transitions between these regimes. Significant oscillatory components with periods of 147 and 72 days are identified by spectral analysis of the zonal-flow time series. These oscillations are described by singular spectrum analysis and the multitaper method. The 147-day oscillation involves zonal-flow anomalies that propagate poleward, while the 72-day oscillation only manifests northward propagation in the Atlantic sector. Both modes mainly describe changes in the midlatitude jet position and intensity. In the horizontal plane though, the two modes exhibit synchronous centers of action located over the Atlantic and Pacific Oceans. The two persistent flow regimes are associated with slow phases of either oscillation.

In some cell types, oscillations in the concentration of free intracellular calcium ([[Ca.sup.2+]]) are accompanied by oscillations in the concentration of inositol 1,405-trisphosphate ([I[P.sub.3]]). However, in most cell types it is still an open question as to whether oscillations in [I[P.sub.3]] are necessary for [Ca.sup.2+] oscillations in vivo, or whether they merely follow passively. Using a wide range of models, we show that the response to an artificially applied pulse of I[P.sub.3] can be used to distinguish between these two cases. Hence, we show that muscarinic receptor-mediated, long-period [Ca.sup.2+] oscillations in pancreatic acinar cells depend on [I[P.sub.3]] oscillations, whereas shortperiod [Ca.sup.2+] oscillations in airway smooth muscle do not. mathematical model