Anomalous Behavior of Ultra-Low-Amplitude Capillary Waves. A Glimpse of the Viscoelastic Properties of Interfacial Water?

On the basis of the studies concerning the determination of the surface free energy of Polish coals published earlier analyses of the equilibrium state of three-phase system were carried out. The three-phase systems were: 1) coal - liquid drop - air, 2) coal - water drop -air, 3) coal - water drop - hydrocarbon, 4) coal -hydrocarbon drop - water and 5) coal - air bubble -water. Analysing the measured values of the contact angles in the systems studied the occurrence of a liquid film on the coal surface was taken into account. The surface free energy. of Polish coals results from both dispersion (Ts d) and nondispersion (Ts n) intermolecular interaction. A distinct relationship was found between the dispersion components of the surface free energy and coal ranks.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTThree-Dimensional Mesoscale Self-AssemblyWilhelm T. S. Huck, Joe Tien, and George M. WhitesidesView Author Information Department of Chemistry and Chemical Biology Harvard University, 12 Oxford Street Cambridge, Massachusetts 02138 Cite this: J. Am. Chem. Soc. 1998, 120, 32, 8267–8268Publication Date (Web):July 31, 1998Publication History Received23 April 1998Published online31 July 1998Published inissue 1 August 1998https://doi.org/10.1021/ja981390gCopyright © 1998 American Chemical SocietyRequest reuse permissionsArticle Views1045Altmetric-Citations92LEARN 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 Read OnlinePDF (66 KB) Get e-AlertscloseSUBJECTS:Hydrophilicity,Interfaces,Layers,Liquids,Self organization Get e-Alerts

Numerous cell functions are accompanied by phenotypic changes in viscoelastic properties, and measuring them can help elucidate higher level cellular functions in health and disease. We present a high-throughput, simple and low-cost microfluidic method for quantitatively measuring the elastic (storage) and viscous (loss) modulus of individual cells. Cells are suspended in a high-viscosity fluid and are pumped with high pressure through a 5.8 cm long and 200 µm wide microfluidic channel. The fluid shear stress induces large, ear ellipsoidal cell deformations. In addition, the flow profile in the channel causes the cells to rotate in a tank-treading manner. From the cell deformation and tank treading frequency, we extract the frequency-dependent viscoelastic cell properties based on a theoretical framework developed by R. Roscoe [1] that describes the deformation of a viscoelastic sphere in a viscous fluid under steady laminar flow. We confirm the accuracy of the method using atomic force microscopy-calibrated polyacrylamide beads and cells. Our measurements demonstrate that suspended cells exhibit power-law, soft glassy rheological behavior that is cell-cycle-dependent and mediated by the physical interplay between the actin filament and intermediate filament networks.

The nucleation we discussed in Chapter 7 is about the initiation of condensed phases of cloud and precipitation particles. Our next question is this: Once these particles are initiated, how do they grow and how fast? This is what we will address in the next two chapters. There are two broad categories of particle growth modes: (1) diffusion growth and (2) collision growth. The former refers to the mechanism in which water vapor diffuses toward the surface of a particle, resulting in the increase of the particle’s mass. The latter refers to the collision between two or more particles, which subsequently coalesce together and hence become a larger particle. The latter can mean collisions among water drops, among water drops and ice particles, or among ice particles. The reverse of growth is reduction. Both water drops and ice particles can decrease their size by evaporation and fragmentation. Ice particles can also melt to become liquid and thus reduce their size. Diffusion of water vapor around a spherical water drop When a water drop is suspended in supersaturated air (with respect to the drop), then there will be net deposition of water molecules on the drop surface and the drop grows in size. This is the diffusion growth of water drops. Note that the saturation humidity here should take into account both the curvature and solute effects as discussed in Chapter 5.

Inducing self-motion illusions referred as vection are critical for improving the sensation of walking in virtual environments (VE). Adding viewpoint oscillations to a constant forward velocity in VE is effective for improving vection strength under static conditions. However, the effects of oscillation frequency and amplitude on vection strength under treadmill walking conditions are still unclear. Besides, due to the visuomotor entrainment mechanism, these visual oscillations would affect gait patterns and be detrimental for achieving natural walking if not properly designed. This study was aimed at determining the optimal frequency and amplitude of vertical viewpoint oscillations for improving vection strength and reducing gait constraints. Seven subjects walked on a treadmill while watching a visual scene. The visual scene presented a constant forward velocity equal to the treadmill velocity with different vertical viewpoint oscillations added. Five oscillation patterns with different combinations of frequency and amplitude were tested. Subjects gave verbal ratings of vection strength. The mediolateral (M-L) center of pressure (CoP) complexity was calculated to indicate gait constraints. After the experiment, subjects were asked to give the best and the worst oscillation pattern based on their walking experience. The oscillation frequency and amplitude had strong positive correlations with vection strength. The M-L CoP complexity was reduced under oscillations with low frequency. The medium oscillation amplitude had greater M-L CoP complexity than the small and large amplitude. Besides, subjects preferred those oscillation patterns with large gait complexity. We suggested that the oscillation amplitude with largest M-L CoP complexity should first be chosen to reduce gait constraints. Then, increasing the oscillation frequency to improve vection strength until individual preference or the boundary of motion sickness. These findings provide important guidelines to promote the sensation of natural walking in VE.

It is widely recognized that small amplitude frequency modulation atomic force microscopy probes the derivative of the interaction force between tip and sample. For large amplitudes, however, such a physical connection is currently lacking, although it has been observed that the frequency shift presents a quantity intermediate to the interaction force and energy for certain force laws. Here we prove that these observations are a universal property of large amplitude frequency modulation atomic force microscopy, by establishing that the frequency shift is proportional to the half-fractional integral of the force, regardless of the force law. This finding indicates that frequency modulation atomic force microscopy can be interpreted as a fractional differential operator, where the order of the derivative∕integral is dictated by the oscillation amplitude. We also establish that the measured frequency shift varies systematically from a probe of the force gradient for small oscillation amplitudes, through to the measurement of a quantity intermediate to the force and energy (the half-fractional integral of the force) for large oscillation amplitudes. This has significant implications to measurement sensitivity, since integrating the force will smooth its behavior, while differentiating it will enhance variations. This highlights the importance in choice of oscillation amplitude when wishing to optimize the sensitivity of force spectroscopy measurements to short-range interactions and consequently imaging with the highest possible resolution.

A new integro-differential equation is derived for steady free-surface waves. Numerical solutions of this equation for periodic gravity-capillary waves on a fluid of infinite depth are presented. For the two limiting cases of gravity waves and capillary waves, our results are in excellent agreement with previous calculations. For gravity-capillary waves, detailed calculations are performed near the wave-number at which the classical second-order perturbation solution breaks down. Our calculations yield two solutions in this region, which in the limit of small amplitudes agree with the results obtained by Wilton in 1915; one solution has the small amplitude behaviour of a gravity wave and the other that of a capillary wave, but the numerical results show that at large amplitudes both waves have the characteristics of capillary waves. The calculations also show that the wavenumber range in which two solutions exist increases with increasing wave height.

The formation of sprays from a liquid film on a vibrating surface is used by ultrasonic atomizers for applications ranging from humidification to metal–powder manufacturing. The received opinion in the literature is that droplets are formed periodically from the apexes of an orderly pattern of standing capillary waves, with a wavelength that can be related to vibration frequency by stability analysis. It is described how this assumption may be incorrect in that, after droplet formation commences, the orderliness of the standing–wave pattern is lost due to one or more secondary instability phenomena. These phenomena, which lead to disorderliness, are investigated by using high–speed imaging techniques and a low–frequency vibrating film to model the high–frequency case, because of the difficulty of penetrating clouds of small droplets in the latter case. Different modes of droplet formation are identified and the flow patterns responsible for these modes are discussed. Physical mechanisms are proposed from which it is deduced that only a proportion of standing–wave crests can eject droplets, for a given wall–vibration period, and the identity of these ejecting waves should vary from period to period. The model thus developed demonstrates an apparently random ejection of droplets from one wave cell, even though the model itself is deterministic. The disorder of the capillary waves and the occurrence of several droplet–formation routes are sufficient to explain the range of droplet sizes that is produced by ultrasonic atomization.

Low frequency (O(10 Hz-10 kHz)) vibration excitation of capillary waves has been extensively studied for nearly two centuries. Such waves appear at the excitation frequency or at rational multiples of the excitation frequency through nonlinear coupling as a result of the finite displacement of the wave, most often at one-half the excitation frequency in so-called Faraday waves and twice this frequency in superharmonic waves. Less understood, however, are the dynamics of capillary waves driven by high-frequency vibration (>O(100 kHz)) and small interface length scales, an arrangement ideal for a broad variety of applications, from nebulizers for pulmonary drug delivery to complex nanoparticle synthesis. In the few studies conducted to date, a marked departure from the predictions of classical Faraday wave theory has been shown, with the appearance of broadband capillary wave generation from 100 Hz to the excitation frequency and beyond, without a clear explanation. We show that weak wave turbulence is the dominant mechanism in the behavior of the system, as evident from wave height frequency spectra that closely follow the Rayleigh-Jeans spectral response η ≈ ω(-17/12) as a consequence of a period-halving, weakly turbulent cascade that appears within a 1 mm water drop whether driven by thickness-mode or surface acoustic Rayleigh wave excitation. However, such a cascade is one-way, from low to high frequencies. The mechanism of exciting the cascade with high-frequency acoustic waves is an acoustic streaming-driven turbulent jet in the fluid bulk, driving the fundamental capillary wave resonance through the well-known coupling between bulk flow and surface waves. Unlike capillary waves, turbulent acoustic streaming can exhibit subharmonic cascades from high to low frequencies; here it appears from the excitation frequency all the way to the fundamental modes of the capillary wave at some four orders of magnitude in frequency less than the excitation frequency, enabling the capillary weakly turbulent wave cascade to form from the fundamental capillary wave upward.

This paper reports computational results of forces and wake structure in two-dimensional flow past a circular cylinder forced to vibrate both transversely and inline to a uniform stream, following a figure-eight trajectory. For a flow stream from left to right, we distinguish between a counterclockwise mode and a clockwise mode, if the upper part of the trajectory is traversed counterclockwise or clockwise, respectively. The present computations correspond to a range of transverse oscillation frequencies close to the natural frequency of the Kármán vortex street and several oscillation amplitudes, both for counterclockwise motion and clockwise motion. The nondimensional forces and nondimensional power transfer from the fluid to the body are calculated. The results demonstrate a strong dependence of the forces and power transfer on the direction in which the figure-eight is traversed. In general, counterclockwise motion maintains positive power transfer at higher oscillation amplitudes. Flow visualizations show that the wakes are characterized by the presence of two single (2S) vortex shedding mode at low oscillation amplitudes and can attain more complex structures at higher amplitudes.

In the simplest and original case of study of the Taylor–Couette TC problems, the fluid is contained between a fixed outer cylinder and a concentric inner cylinder which rotates at constant angular velocity. Much of the works done has been concerned on steady rotating cylinder(s) i.e. rotating cylinders with constant velocity and the various transitions that take place as the cylinder(s) velocity (ies) is (are) steadily increased. On this work, we concentrated our attention in the case in which the inner cylinder velocity is not constant, but oscillates harmonically (in time) clockwise and counter-clockwise while the outer cylinder is maintained fixed. Our aim is to attempt to answer the question if the modulation makes the flow more or less stable with respect to the vortices apparition than in the steady case. If the modulation amplitude is large enough to destabilise the circular Couette flow, two classes of axisymmetric Taylor vortex flow are possible: reversing Taylor Vortex Flow (RTVF) and Non-Reversing Taylor Vortex Flow (NRTVF) (Youd et al., 2003; Lopez and Marques, 2002). Our work presents an experimental investigation of the effect of oscillatory Couette-Taylor flow, i.e. both the oscillation frequency and amplitude on the apparition of RTVF and NRTVF by analysing the instantaneous and local mass transfer and wall shear rates evolutions, i.e. the impact of vortices at wall. The vortices may manifest themselves by the presence of time-oscillations of mass transfer and wall shear rates, this generally corresponds to an instability apparition even for steady rotating cylinder. On laminar CT flow, the time-evolution of wall shear rate is linear. It may be presented as a linear function of the angular velocity, i.e. the evolution is steady even if the angular velocity is not steady. At a “critical” frequency and amplitude, the laminar CT flow is disturbed and Taylor vortices appear. Comparing to a steady velocity case, oscillatory flow accelerate the instability apparition, i.e. the critical Taylor number corresponds to the transition is smaller than that of the steady case. For high oscillation amplitudes of the inner cylinder rotation, the mass transfer time-evolution has a sinusoidal evolution with non equal oscillation amplitudes. If the oscillation amplitude is large enough, it can destabilize the laminar Couette flow, Taylor vortices appears. The vortices direction can be deduced from the sign of the instantaneous wall shear rate time evolution.

Extremely large dynamics of axially excited cantilevers

The steady, gravity-driven flow of a liquid film over a topographically structured substrate is investigated. The analysis is based on a model nonlinear equation for the film thickness derived on the basis of long-wave asymptotics. The free-surface shape is expanded in a regular asymptotic expansion in powers of the topography amplitude, and solutions are obtained up to second order. Solutions are constructed for downward steps, upward steps, and rectangular trenches, and the results are compared favorably with numerical solutions of the nonlinear model equation. The results indicate that all of the salient features previously found for film flows over steps and into trenches are captured by the small-step asymptotics, including the capillary ridge formed just above a downward step and oscillations upstream of an upward step. We derive analytical expressions for the period and amplitude of these oscillations. The effect of a normal electric on the film surface shape is also investigated on the assumption that both the film and the medium above the film behave as perfect dielectrics. Again, the small-amplitude asymptotics describe the essential characteristics of the free surface, including oscillations downstream of a downwards step with a quantifiable period and amplitude. It is established analytically and numerically that the amplitude of interfacial oscillations just upstream of a step decreases with an increase of the electric field strength in the case of perfect conductors, but increases to a limiting value for perfect dielectrics. It is found that nonlinear solutions are in excellent agreement with the small-amplitude theory even for relatively large topography amplitudes.

Performance of Flutter® (Axcan Scandipharm Inc, Birmingham, AL), Acapella® (Smiths Medicals Inc, Rockland, MA) and Quake® (Thayer Medical, Tucson, AZ) were compared at similar frequencies and amplitudes of oscillations at nine angles of the device in clearing simulated mucus inside a tracheal model (trachea) oriented at three angles with or without simulated constrictions in airway upstream of trachea. Displacement of 0.4mL of simulated mucus prepared with viscoelastic properties similar to healthy individuals (syrup-like) or patients with COPD (gel-like) using locust bean gum(LBG) solution (0.38g LBG in 100mL water) cross-linked with 3mL or 12mL borax solution (0.02 molar), respectively were measured inside trachea during coughs of 300ms at low cough velocity (15±0.5m/s) generated using a computer controlled solenoid valve. Oscillations were superimposed on cough by connecting the oscillator device to the outlet of the trachea. Frequency and amplitude of oscillations generated by Quake and Acapella and resulting mucus displacement were independent of angle of oscillator, while amplitude of oscillations and resulting mucus displacement generated by Flutter, increased up to 30o upward and 20o downward angles of Flutter from horizontal but decreased significantly thereafter. Displacement with Quake increased significantly with frequencies of oscillations up to 25 Hz and decreased thereafter but increased with amplitudes of oscillations up to 22±4.7 m/s. Quake showed significantly larger displacements than Flutter and Acapella at equal frequencies and amplitudes (p<0.05). Displacements were significantly larger with trachea positioned 30o upwards than horizontal or 20o downwards (p<0.0001). Displacement was the greatest for gel-like mucus than syrup-like (p<0.0001). Airway constrictions upstream resulted in enhanced displacement of mucus (p<0.0001). Mucus clearance can be significantly enhanced by coughing through oscillating positive expiratory devices that generate high amplitude oscillations at moderate frequencies, increasing frontal depths of mucus facing airflow and slightly increasing resistance to airflow in airways in COPD patients.

On the suppression of oscillatory circulation inside an evaporating bi-component drop through acoustic streaming