Constant Drop Research Articles

Actuation Response of Polyacrylate Dielectric Elastomers

Polyacrylate dielectric elastomers have yielded extremely large strain and elastic energy density suggesting that they are useful for many actuator applications. A thorough understanding of the physics underlying the mechanism of the observed response to an electric field can help develop improved actuators. The response is believed to be due to Maxwell stress, a quadratic dependence of the stress upon applied electric field. Based on this supposition, an equation relating the applied voltage to the measured force from an actuator was derived. Experimental data fit with the expected behavior, though there are discrepancies. Further analysis suggests that these arise mostly from imperfect manufacture of the actuators, though there is a small contribution from an explicitly electrostrictive behavior of the acrylic adhesive. Measurements of the dielectric constant of stretched polymer reveal that the dielectric constant drops, when the polymer is strained, indicating the existence of a small electrostrictive effect. Finally, measurements of the electric breakdown field were made. These also show a dependence upon the strain. In the unstrained state the breakdown field is 20 MV/m, which grows to 218 MV/m at 500 500% strain. This large increase could prove to be of importance in actuator design.

Cutaneous absorption and elimination of three acyclic terpenes—in vitro studies

The purpose of the study was to investigate skin absorption and elimination of three acyclic terpenes: citronellol (C), linalool (L) and linalyl acetate (LA). The pure terpenes were applied onto the human skin in vitro, and after 1–4 h, their content in the stratum corneum layers and in the epidermis/dermis was determined using gas chromatography. Similarly, the amounts of terpenes in the skin were analysed during 4 h following 1-h absorption. Good absorption to the all skin layers was demonstrated as soon as after 1 h: the total skin cumulation of L, LA and C was 827, 124 and 954 μg/cm 2, respectively. A self-promoting absorption was observed for L, since the amount of this terpene analysed in the stratum corneum after 1 h was 78.3, rising to 479 μg/cm 2 after 4 h. During the elimination phase, a constant drop in the total amount in the skin was observed only for C, while the total skin content of L and LA did not change, although diffusion from the stratum corneum to epidermis/dermis occurred. The log P values of the terpenes were calculated using three different programs, but generally, neither absorption nor elimination can be directly correlated with the physicochemical parameters, despite of the fact that the least absorption was observed for the most lipophilic LA.

Behaviour of vastus lateralis muscle-tendon during high intensity SSC exercises in vivo.

The interaction between fascicle and tendinous tissue of human vastus lateralis muscle was investigated during varying intensity stretch-shortening cycle (SSC) jumps performed on a sledge apparatus. Eight subjects performed single leg squat (SJ) and drop jumps (DJ) from a constant dropping height but to different rebound heights. The fascicle length of the vastus lateralis muscle (VL) was determined from real-time ultrasonography during the movement. Tendon length changes were calculated by subtracting the horizontal part of the fascicle length from the muscle-tendon unit (MTU) length. Simultaneously, kinematic, kinetic and electromyographic data were recorded from leg muscles. In addition, the in vivo patella tendon force was measured from one subject during the trials. In all DJs, where MTU was stretched prior to shortening, the fascicle and tendinous tissue of the VL also underwent a SSC. The fascicle lengths decreased and the recoil of tendinous tissue increased with increased rebound intensities (P<0.05). The force-velocity curves obtained from the MTU showed the expected force-velocity relationship for SSC activities, demonstrating performance enhancement. However, the increased MTU power during the shortening phase of the movement was due primarily to the enhancement of the tendon compartment. The results of this study show that, at higher rebound intensities, the fascicle is controlled during the braking phase in a distinct manner so that the effective recoil of the tendon is possible during the final push-off phase. In addition, the results suggest that the behaviour of fascicle length change depends on the muscle in question in addition to the movement intensity.

Memory effects in amorphous solids below 20 mK.

At temperatures below 1 K, the capacitance of a glass sample changes due to the application of a dc field in accordance with Burin's dipole gap theory [J. Low Temp. Phys. 100, 309 (1995)]]. However, we now report that below 20 mK, during the first sweep cycle of the dc electric field, the capacitance is smaller by about 10(-5) compared to any subsequent sweep. Despite this overall shift, the field dependence follows the dipole gap predictions. In a subsequent sweep to higher dc fields the dielectric constant drops by about 10(-5) as soon as the applied field is higher than any field previously applied. A picture involving the dynamics of resonant pairs provides a qualitative description of this behavior.

Analysis of two independent methods for retrieving liquid water profiles in spring and summer Arctic boundary clouds

A large number of all‐liquid, nondrizzling stratus clouds (163 hours of measurements) were observed with a dual‐channel microwave radiometer and a colocated 35‐GHz cloud radar during the spring and summer months of the Surface Heat Budget of the Arctic Ocean (SHEBA) project. An algorithm developed by Frisch et al. [1995, 1998] to derive the liquid water content (LWC) is applied to these measurements assuming constant cloud drop number density and cloud drop size distribution breadth with height. A second algorithm developed by Löhnert et al. [2001] is specifically adapted for SHEBA clouds using a priori information from a large eddy simulation (LES) model initialized with summertime SHEBA radiosondes; about 50 soundings during nondrizzling, low‐level, all‐liquid water clouds are used. Using model‐derived drop size distributions, a relationship between simulated radar reflectivity (Z) and model LWC is derived as well as an a priori LWC profile. Once the theoretical error covariance matrix of the Z‐LWC relation is derived and the covariance matrix of the LWC profile is calculated, an optimal estimation method is applied to the SHEBA data. The Frisch et al. and Löhnert et al. methods are also applied to the LES model output, resulting in overall root‐mean‐square differences on the order of 30 to 60%. Both methods are sensitive to the assumed accuracies of the microwave‐radiometer‐derived LWP. When applied to LES model output, the Frisch et al. method shows a LWC overestimation in the lower parts of the cloud. These systematic errors are induced by the assumption of constant cloud number concentration with height.

Evolution of the cosmological constant in effective gravity

In contrast to the phenomenon of nullification of the cosmological constant in the equilibrium vacuum, which is the general property of any quantum vacuum, there are many options in modifying the Einstein equation to allow the cosmological constant to evolve in a non-equilibrium vacuum. An attempt is made to extend the Einstein equation in the direction suggested by the condensed-matter analogy of the quantum vacuum. Different scenarios are found depending on the behavior of and the relation between the relaxation parameters involved, some of these scenarios having been discussed in the literature. One of them reproduces the scenario in which the effective cosmological constant emerges as a constant of integration. The second one describes the situation, when after the cosmological phase transition the cosmological constant drops from zero to the negative value; this scenario describes the relaxation from this big negative value back to zero and then to a small positive value. In the third example the relaxation time is not a constant but depends on matter; this scenario demonstrates that the vacuum energy (or its fraction) can play the role of the cold dark matter.

Contact angle hysteresis on dentin surfaces measured with ADSA on drops and bubbles

Contact angle measurement on biological surfaces is difficult due to substrate hydration, porosity and heterogeneity. The former promotes very low contact angles, and the latter leads to irregular drop shapes and contact angle hysteresis, being meaningful in terms of surface energetics only low rate dynamic contact angles, i.e. the extreme angles corresponding to a slowly advancing and receding contact line. ADSA-CD has been developed to take into account the drop shape irregularity. It requires as input the liquid surface tension and density, the co-ordinates of some contact line points and the drop volume, yielding a mean contact angle. Due to the latter requirement ADSA-CD has been used until now only for static contact angle measurements, i.e. at constant drop volumes. We present an upgrade of the method that permits to control very precisely the drop volume, and to capture simultaneously drop images for contact angle determination, permitting this way to use ADSA-CD for hysteresis measurements. Low contact angles lead to difficulties in their measurement, being the captive bubble technique a known method to overcome this shortcoming. As our system is also capable to measure captive bubble low rate dynamic contact angles, we performed an experimental study with Teflon and bitumen model surfaces, which permits to identify the advancing bubble angles with the receding drop angles. We were therefore able to measure hysteresis on dentin tissue, which has a too low receding drop angle to be measured by ADSA-CD.

The acoustic emission from a nonlinearly oscillating charged drop

A charged drop oscillating in a compressible medium is capable of emitting acoustic waves. According to calculations in the constant drop volume approximation linear in the oscillation amplitude, the most intense acoustic emission corresponds to the dominant mode. An acoustic dipole emission related to the excitation of a translational mode is only revealed by calculations in the second order of smallness with respect to the oscillation amplitude, in the case when two adjacent modes are present in the spectrum of initial deformations.

Predicting the pressure drop across hot gas filter (CTF) installed in a commercial size PFBC system

The 71 MWe PFBC combined cycle power plant at Wakamatsu, Electric Power Development Company (EPDC) (funded by the Ministry of International Trade and Industry (MITI) and the Center of Coal Utilization Japan (CCUJ)) achieved 11,500 h accumulative operation while establishing extremely low dust emission (<1 mg/m3 N) with a hot gas cleaning system combining cyclones and ceramic tube filter (CTF). Two different configurations of cyclones and CTF were examined in Phases 1 and 2, where several coals and domestic limestone as absorbents were used.The pressure drop across the filter (ΔPc) was continuously observed to predict its maximum value (ΔPmax) under operating conditions. The ΔPmax value consisted of irreversible (ΔPbase) and reversible (ΔPown) drops with cleaning as the following equation shows,ΔPmax=ΔPbase+ΔPown=f(facevelocity,gasviscosity,thickness/permeability,dustconcentration)+dΔPc/dt×twhere: dΔPc/dt, mean rate of ΔPc increase during cleaning interval; t, reverse cleaning interval time.The pressure drop across the regenerator (ΔPregenerator) was monitored to calculate the changing face velocity of each compartment according to the Fanning equation. Both pressure drops (ΔPbase and ΔPown) were successfully estimated by the face velocity calculated for both phases. Dust concentration to the filter in both phases was found to improve the predictability of the base line one (ΔPbase).The conditioned filter material was proven to be stable, showing a constant drop depending on the operating condition. The particle size of ashes on the filter must be considered in order to obtain better prediction of the maximum pressure drop in the future.

Dispersion visualization of model fluids in a transparent Couette flow cell

Dispersion mechanisms in model fluid systems of different viscosity ratios were studied in a transparent Couette flow cell. The counter-rotating concentric cylinders were driven by two independent dc motors. Drops of the minor phase were then maintained at a constant position by fixing the inner and outer cylinders’ rotational speeds. The advantage of this new setup is that visualization can be made at high shear rates without any secondary flow effects, usually observed with cone-plate or parallel plates geometry. Constant viscosity viscoelastic drops (Boger fluid) and Newtonian drops [high viscosity polydimethylsiloxane, (PDMS)], deformed at low shear rates in a Newtonian matrix (low viscosity PDMS), oriented along the flow field and drop deformation increased with shear rate, as expected. However, when a critical shear rate (characteristic of the fluid system used) was reached, the deformed drops began to contract in the flow direction. When increasing the shear rate over this critical value, drop contraction was followed by elongation perpendicular to the flow direction, i.e., parallel to the vorticity axis. This elongation increased with shear rate until the final breakup occurred. These deformation and breakup mechanisms were attributed to elastic normal forces present at high deformation rates.

Relationship between coulomb and migration coefficient of chloride ions for concrete in a steady-state chloride migration test

A steady-state chloride migration test with a constant electrical potential drop of 15 V was conducted with a saturated 100 mm diameter × 50 mm long concrete specimen. The migration coefficient of chloride ions for concrete was calculated using the constant flux on the basis of the Nernst–Planck equation. Electrical current was simultaneously monitored throughout the entire period of the migration test. Initial and final coulomb values were separately defined and calculated using the current recorded in non-steady-state and subsequently in steady-state conditions with respect to chloride migration, respectively. A unique relationship existed between the initial coulomb and the migration coefficient depending on the binders of the concrete mixes, that is ordinary Portland cement (OPC) alone, OPC plus fly ash or OPC plus silica fume. However, it appeared that the final coulomb related linearly to the migration coefficient, irrespective of the water:cement ratios, binders and curing periods.

Numerical Analysis of Scattered Power From a Layer of Random Medium Containing Many Particles of High Dielectric Constant - Application To the Detection of a Water Content of Soil- Abstract

This paper shows the scattering cross sections of a random medium which is a simple model of moist soil by analyzing a dense medium radiative transfer equation (DMRT). The parameters in the DMRT, the extinction rate and the scattering coefficient, are calculated by a multiple scattering method called our method in this paper. Our method is valid for particles with high dielectric constant like water drops. Characteristics of the scattering cross section are made clear by changing the fractional volume of water and the incident angle, polarization of incident waves. We discuss the possibility of detection of a water content in this approach by using the characteristics of the scattering cross section.

Electrophoretic Deposition and Characterization of Micrometer‐Scale BaTiO3 Based X7R Dielectric Thick Films

Uniform and relatively dense BaTiO3 thick films of 1–5 μm were prepared by an electrophoretic deposition process using submicrometer BaTiO3 powders (mean particle size: ∼0.2 μm). Two different BaTiO3 powders and solvent media were used to investigate the film quality and thickness control. The surface charge mechanism of BaTiO3 particles was explained according to the observed results. The microstructures were examined by means of SEM. The experimental results show that the thickness could be controlled independently of suspension concentration by keeping a constant applied voltage and a constant current drop in a given suspension. BaTiO3 thick films have good insulation resistance and dielectric properties such as a dielectric constant and a dissipation factor that are compatible with the data from conventional tape‐cast BaTiO3 thin layers.

Styrene Drop Size and Size Distribution in an Aqueous Solution of Poly(vinyl alcohol)

The dispersion of styrene monomer (StM) in an aqueous solution of a poly(vinyl alcohol) (PVA) stabilizer has been studied experimentally. Parameters affecting the initial StM dispersion, such as stirring time, type and concentration of the suspending agent, and the volume fraction of styrene, have been studied in detail and the results compared with existing theories. The transitional time for a dynamic equilibrium to be established in the dispersions was found to be 150 min. When the molecular weight of the PVA increases, the drop size decreases and the StM drops become more stable toward coalescence. With one of the PVAs (PVA-2), the critical PVA concentration, for a constant drop size, was found to be equal to 0.013%, 0.023%, and 0.043% respectively, when the volume fraction of StM correspondingly equaled 0.05, 0.1, and 0.2.

Effects of hexachlorobenzene on phospholipid and porphyrin metabolism in Harderian glands: a time-course study in two strains of rats

Hexachlorobenzene, one of the most persistent environmental pollutants, induces uroporphyria and phospholipid alterations in rat liver. Harderian glands produce a secretion that is rich in lipids and accumulate large amounts of protoporphyrin. The aim of the present study was to determine if hexachlorobenzene administration to rats affects phospholipid and porphyrin metabolisms in Harderian glands and if these effects are strain dependent. For this purpose, a time-course study (2, 3 and 4 weeks of hexachlorobenzene treatment) of phospholipid pattern and porphyrin content was performed comparatively in two strains of rats (Wistar and Chbb THOM) which differ in their susceptibility to develop HCB-induced porphyria. Hexachlorobenzene produced decreases in several phospholipid contents, but no changes in phosphatidylcholine levels. While the sphingomyelin/phosphatidylcholine molar ratio remained essentially constant until the third week in Chbb THOM rats, it showed a constant drop in Wistar rats, suggesting a more pronounced alteration of membrane fluidity in the later strain. In regard to porphyrin metabolism, Wistar rats showed an increase in the porphyrin content of the gland, while Chbb THOM animals showed a decrease. The study revealed that not only are the normal parameters of phospholipid and porphyrin metabolism in rat Harderian glands strain dependent, but the response to hexachlorobenzene is also.

Methodologies for interrill soil erosion studies

Due to wide range of experimental techniques reported in the literature for determining interrill erodibility and soil loss values, meaningful comparisons between experiments often cannot be made. Furthermore, inaccurate concepts are developed because erosion processes are dependent upon methodologies. The purpose of this paper is to discuss problems related to both laboratory and field rainfall simulator experiments. Rainfall simulators cannot duplicate a wide range of rainfall intensities and, at the same time, have similar energies as natural rainstorms, unless several different nozzles are used. Rainfall intensity in most simulators is created by varying the frequency of spray oscillation. This intermittent spray characteristic of most simulators, and the constant drop size characteristic of other simulators, greatly affects results. Erosion pan design for laboratory studies and preparation of soil samples placed in the pans also can influence erosion results. We conclude that standardization of rainfall simulator design and test procedures will allow better comparison of erosion results to be made among researchers.

Determination of the peripheral contact angle of sessile drops on solids from the rate of evaporation

A method was developed to determine the initial peripheral contact angle of sessile drops on solid surfaces from the rate of drop evaporation for the case where 1 < 90°. The constant drop contact radius, the initial weight, and the weight decrease with time should be measured at the ambient temperature for this purpose. When water drops are considered, the relative humidity should also be known. The peripheral contact angle so obtained is regarded as the average of all the various contact angles existing along the circumference of the drop. Thus, each determination yields an average result not unduly influenced by irregularities at a given point on the surface. In addition, the error in personal judgment involved in drawing the tangent to the curved drop profile at the point of contact can be eliminated. The application of this method requires the use of the product of the vapor diffusion coefficient with the vapor pressure at the drop surface temperature. This product can be found experimentally by following the evaporation of fully spherical liquid drops.

Drop Formation at a Two-Phase Nozzle: Part B

The excellent separation performance of columns with structured packings strongly depends on the distributor's quality and this may be utilized only if it is possible to generate a constant drop size and a uniform drop distribution over the cross-section for all loadings. The size of the drops, which are formed at single distributor orifices, may be controlled by an external flow, thus studies of drop formation with a single two-phase nozzle were made. Paper A presents the results of experiments with the liquid system toluene (dispersed) / water and two-phase nozzle. In the paper B the influence of different liquid systems on the drop formation is discussed. The liquid-liquid system butylacetate/ water differs from the system toluene/ water because of its lower interfacial tension.

Drop Formation at a Two-Phase Nozzle: Part A

The excellent separation performance of columns with structured packings strongly depends on the distributor's quality and this may be utilized only if it is possible to generate a constant drop size and a uniform drop distribution over the cross-section for all loadings. The size of the drops, which are formed at single distributor orifices, may be controlled by an external flow, thus studies of drop formation with a single two-phase nozzle were made. Paper A presents the results of experiments with the liquid system toluene (dispersed)/water and two-phase nozzle.

Determination of the Peripheral Contact Angle of Sessile Drops on Solids from the Rate of Drop Evaporation

A method was developed to determine the initial peripheral contact angle of sessile drops on solid surfaces from the rate of drop evaporation by using the published precise data of Rowan et al. The constant drop contact radius throughout this stage of evaporation, the initial weight (or volume), the weight decrease by time, and the experiment temperature should be measured for this purpose. When water drops are considered, the relative humidity should also be known. The drop profile data are not required in the calculations. The peripheral contact angle so obtained may be regarded as the mean of all the various contact angles existing along the circumference of the drop. Thus, each determination yields an average result not unduly influenced by irregularities at a given point on the surface. In addition, the error in personal judgment involved in drawing the tangent to the curved drop profile at the point of contact is eliminated. The application of this method requires the use of the product of the vapor diffusion coefficient of the evaporating liquid with the vapor pressure at the drop surface which can be found directly by experiment by following the evaporation of fully spherical liquid drops. The other alternative method is the measurement of the drop surface temperature in order to find Δpv and then to estimate the product DΔpv.