Drops of biological fluids drying on a hard substrate: Variation of the morphology,weight, temperature,and mechanical properties

The time variation of the morphology, weight, temperature, and integral mechanical properties of drying drops of biological fluids are investigated with the aim of defining more exactly the mechanism of self-organization in the drops. Test fluids in experiments are distilled water, a physiological salt solution (0.9 wt. % NaCl), a solution of bovine serum albumin (BSA) in water, and a solution of BSA (7 wt. %) in the physiological solution. It is shown that the variation of the weight of the drying drops can be described by a sloping straight line with two slightly nonlinear portions at the beginning and at the end of the drying process. The earlier nonlinear portion correlates with a more rapid fall of the temperature, which slows down and stabilizes as a saturated vapor layer forms over the drop. The later nonlinear portion in the drop weight variation is associated with the retardation of water diffusion through the solidifying medium. The temperature variation of the drops is a superposition of endothermal (water evaporation) and exothermal (salt crystallization and gelation) phase transitions. Phase transitions may change the mechanical properties of the drying drops, which can be detected by the method of acoustic impedancemetry.     

Size and Velocity Measurements of Large Drops in Air and in a liquid-liquid two-phase flow by the phase-Doppler technique

Particles comparable in size to or larger than the measurement volume need extra consideration when measured by a phase-Doppler system. The phase of the Doppler burst received when such particles traverse the measurement volume depends not only on the size of the particle but also on its trajectory, since the particle is not uniformly illuminated. This paper presents a strategy for securing correct measurements even under such conditions, taking advantage of the three-detector receiving optics of the Dantec Particle Dynamics Analyzer. The effectiveness of the approach is demonstrated for sizing drops in liquid-gas and liquid-liquid two-phase flows: water drops in air, water drops in FC72 and FC72 drops in water. The combination of water and FC72 is also of interest because the relative refractive index is close to unity. Measurements of drops size were made on a monodisperse stream of drops about 2 mm in diameter, i.e. substantially larger than the measurement volume, and polydisperse distributions of drops ranging in diameter from below 0.2 mm to about 1 mm.     

Generation and interference collapse of distortion-less fs pulses in free space by Fresnel sources

A method of formation of the tightly confined, distortion-free, femtosecond pulses in two dimensions (2D) with the step-like decreasing of intensity after a finite length of propagation in free space is described. The pulses are formed by the Fresnel source of modes corresponding to a 2D hollow waveguide with perfectly reflecting walls (material waveguide). The source reproduces in free space a propagation-invariant pulse confined by the waveguide. Unlike the case of material waveguides, when the pulse goes out from the virtual waveguide formed by the Fresnel source its shape does not change, but the intensity immediately drops down to the near-zero level. It is also shown that there is a limit of the duration of pulse beyond which the step-like decay is not observed.     

Difference in the conditions and characteristics of evaporation of inhomogeneous water drops in a high-temperature gaseous medium

The evaporation of water drops of initial mass 5–15 mg on a stationary graphite substrate, as well as inhomogeneous drops with solitary solid inclusions, during heating by high-temperature combustion products has been investigated experimentally. Experiments have also been carried out with analogous inhomogeneous drops moving through combustion products. The possibility of two mechanisms of phase transformations of inhomogeneous liquid drops has been established. The scales of the effect of the area of the inclusion surface (up to 20%) and the initial mass of water (up to 90%) on the characteristics of the evaporation of inhomogeneous drops have been determined.     

EHD size distribution in pure Ge at pulse optical excitation

The cyclotron resonance (CR) kinetics of free carriers surrounding electron-hole drops (EHD) was investigated in pure Ge (N_D = N_A = 10¹¹cm^?3). We observed the fast decay of the CR amplitude at the long delay time after the excitation pulse [1], that may be connected with intense evaporation of the drops, when the EHD radius has achieved the critical value. The method for investigation of EHD size distribution was proposed for case of pulse excitation. The Gaussian EHD size distribution has been found.     

Dissociation of CO on rounded Pt crystals: III. Influence of high Si contamination on the dissociation activity of {210} and {1195} areas

Measurements on rounded Pt crystals show that in the presence of a high Si contamination the CO dissociation activity of {210} areas drops drastically to zero after about 27% of their adsorption sites (which are identical with their kink sites) are blocked by Si. The drastic decrease is attributed to Pt-silicide formation on {210}. To obtain complete poisoning of {1195} areas, considerably higher contamination levels are required than in the case of {210}.     

Drying and advancing droplets of polymer solutions

In this paper, we report on the competition between evaporation and hydrodynamics for advancing drops of polymer solutions. We thus study advancing drops which are allowed to evaporate. Drying drives the accumulation of polymer at the contact line, whereas the advancing motion tends to homogenize the drop. At high velocity, we experimentally verify classical hydrodynamics predictions. At intermediate velocities, drying dominates and the contact line becomes more viscous than the bulk droplet. In the limiting case of very low velocities, the contact line can be partially pinned on the substrate because of the formation of a glassy defect at the contact line.     

Formation of structures from amorphous metallic nanoparticles by dispersing metal drops continuously charging in an electron beam

The formation of amorphous metal nanoparticles by the method of electrohydrodynamic dispersion is studied. In this method, fine liquid metal drops are generated, charged in an electron beam to an unstable state, and dispersed into nanometer droplets. Rapid cooling of these nanometer droplets results in the formation of amorphous metal nanoparticles. The chief problem in the formation of such particles is that it is difficult to charge molten metal drops to an unstable state, since the bombardment of the drop by an electron beam may cause intense emission of electrons. To overcome this difficulty, the drops are charged by a beam of slow electrons. Charging proceeds in such a way that the electron energy rises with the drop’s charge. It is shown that this method makes it possible to obtain granulated films made up of amorphous metal particles. Copper films with a nanoparticle mean size of 2 nm and a small dimensional variation are prepared.     

Dynamique non-linéaire d'instabilités de surface : gouttes et colonnes liquides formées par ruissellement de films

The destabilization of a thin film by gravity is of central importance in many industrial devices, especially those involved in Thermics (film boiling, heat exchangers). In the simplest case of a liquid film hanging below a solid ceiling, spatial structures are forced by the destabilizing action of gravity (Rayleigh-Taylor instability): one observes regular lattices of pendant drops, that in turn become instable by coalescences and falling of the drops. When the film is supplied with liquid at a constant rate, other flow regimes are observed: periodic emission of drops, formation of regular arrays of liquid columns, liquid sheet. Liquid columns exhibit a collective dynamics that is typical of non-linear systems: modulations of their spatial periodicity, diffusion of the perturbations, self-sustained oscillations, propagation of solitary dilation waves, coalescences and nucleations of the columns, etc.     

Droplet transport and coalescence kinetics in emulsions subjected to acoustic fields

A method to aid the separation of the oil phase from aqueous emulsions using a low-intensity, resonant ultrasonic field has recently been developed. The density and compressibility difference between the dispersed and continuous phases within the emulsion results in a net force on the oil drops that pushes them toward the pressure antinodes of the standing-wave field, where coalescence subsequently occurs. A trajectory model is developed to predict the relative motion of drops subjected to the acoustic field. Such trajectories are sensitive to the physical properties and relative size of interacting drops, the initial configuration of the drops, and acoustic field parameters. Model predictions are validated by comparing experimentally observed trajectories with those predicted by the model. The modeling approach is then extended to determine the temporal evolution of the size of the region surrounding a target drop cleared by coalescence as a function of physical and acoustic field parameters. These results form the basis of a population balance model that attempts to track the size-evolution of a drop population coalescing under the influence of an acoustic field.     

Investigation of the erosion drop fraction for liquid-metalexplosive-emission cathodes

The velocity spectrum of drops emitted by a liquid-metal explosive-emission cathode has been investigated. A relation between the sizes of the drops and their maximum velocities has been found for the velocity range 10³-8×10⁴ cm/s. The relation obtained supports the earlier established mechanism for the emission of drops under the action of high pressures developing in explosive emission centers. The possibilities of an additional acceleration of drops due to the explosion of necks formed on breaking the drops off the cathode surface and at the expense of the kinetic energy of the ions of the expanding cathode plasma have been discussed     

Luminescence lineshape of free excitons and electron-hole drops in Si

We study experimentally and theoretically the lineshape of the TO-LO and TA phonon assisted luminescence of free excitons and electron-hole drops in Si. We show that, in the case of the TA replica, the appropriate electron-phonon matrix element should be taken k-dependent, contrary to previous investigations.     

Self-propelled running droplets on solid substrates driven by chemical reactions

We study chemically driven running droplets on a partially wetting solid substrate by means of coupled evolution equations for the thickness profile of the droplets and the density profile of an adsorbate layer. Two models are introduced corresponding to two qualitatively different types of experiments described in the literature. In both cases an adsorption or desorption reaction underneath the droplets induces a wettability gradient on the substrate and provides the driving force for droplet motion. The difference lies in the behavior of the substrate behind the droplet. In case I the substrate is irreversibly changed whereas in case II it recovers allowing for a periodic droplet movement (as long as the overall system stays far away from equilibrium). Both models allow for a non-saturated and a saturated regime of droplet movement depending on the ratio of the viscous and reactive time scales. In contrast to model I, model II allows for sitting drops at high reaction rate and zero diffusion along the substrate. The transition from running to sitting drops in model II occurs via a super- or subcritical drift-pitchfork bifurcation and may be strongly hysteretic implying a coexistence region of running and sitting drops.     

Diffusion of excitons and electron-hole drops in germanium

Diffusion of excitons and electron-hole drops is investigated in pure germanium, using a time-resolved cyclotron resonance method. The diffusion coefficient of excitons at 4.2 K is obtained to be ≈ 1000 cm²/sec. For electron-hole drops, when excitation is not so high, it is expected to be lower than ≈ 500 cm²/sec at 1.6 K.     

珍珠明目滴眼液中微量钙的共沉淀分离原子吸收光谱分析

采用硝酸锶-碳酸钾共沉淀分离富集珍珠明目滴眼液中的微量钙,用原子吸收分光光度法测定其含量。进样溶液钙浓度在0.0～20.0μg·mL-1范围内与其422.7 nm处的吸光度成良好线性关系,检出限为0.06 μg·mL-1。该法用于珍珠明目滴眼液中钙的测定,具有灵敏、简便、快速、准确、重复性好,平均回收率为97.0%～98.3%,相对标准偏差RSD为0.4%。     

Statistical properties of eigenvalues for an operating quantum computer with static imperfections

We investigate the transition to quantum chaos, induced by static imperfections, for an operating quantum computer that simulates efficiently a dynamical quantum system, the sawtooth map. For the different dynamical regimes of the map, we discuss the quantum chaos border induced by static imperfections by analyzing the statistical properties of the quantum computer eigenvalues. For small imperfection strengths the level spacing statistics is close to the case of quasi-integrable systems while above the border it is described by the random matrix theory. We have found that the border drops exponentially with the number of qubits, both in the ergodic and quasi-integrable dynamical regimes of the map characterized by a complex phase space structure. On the contrary, the regime with integrable map dynamics remains more stable against static imperfections since in this case the border drops only algebraically with the number of qubits. Received 19 June 2002 / Received in final form 30 September 2002 Published online 17 Decembre 2002 RID="a" ID="a"e-mail: dima@irsamc.ups-tlse.fr RID="b" ID="b"UMR 5626 du CNRS     

Dripping to jetting transitions in coflowing liquid streams

A liquid forced through an orifice into an immiscible fluid ultimately breaks into drops due to surface tension. Drop formation can occur right at the orifice in a dripping process. Alternatively, the inner fluid can form a jet, which breaks into drops further downstream. The transition from dripping to jetting is not understood for coflowing fluid streams, unlike the case of drop formation in air. We show that in a coflowing stream this transition can be characterized by a state diagram that depends on the capillary number of the outer fluid and the Weber number of the inner fluid.     

Nonlinear oscillations of an uncharged conducting drop in an external uniform electrostatic field

The problem of nonlinear oscillations of the finite amplitude of an uncharged drop of an ideal incompressible conducting liquid in an external uniform electrostatic field is solved for the first time by analytical asymptotic methods. The problem is solved in an approximation quadratic in amplitude of the initial deformation of the equilibrium shape of the drop and in eccentricity of its equilibrium spheroidal deformation. Compared with the case of nonlinear oscillations of charged drops in the absence of the field, the curvature of the vertices of uncharged drops nonlinearly oscillating in the field is noticeably higher, whereas the number of resonant situations (in the sense of internal resonant interaction of modes) is much smaller.     

On the low-frequency sound scattering in a moving microinhomogeneous medium

The Rayleigh law that governs low-frequency sound attenuation due to the scattering by inhomogeneities in a microinhomogeneous medium is generalized to the case of particles moving in a flow or falling under gravity. Corrections to the scattering’s cross section that adjust the Rayleigh law to the case of a potential flow around inhomogeneities are calculated. It is shown that, when microinhomogeneities are moving in a viscous medium, the characteristics of discrete scatterers may considerably deviate from the Rayleigh law. Based on the data on the velocity and size distribution of falling drops of water in air, refinements are proposed for the laws of low-frequency sound scattering by rain.     

Investigation of evaporation and boiling of liquids

It is shown experimentally that a minimum in the evaporation curve of water drops, a 5% aqueous solution of ethanol, and a 5% aqueous solution of n-butanol, i.e., the maximal evaporation rate of these liquids, is observed at a critical thermal load under boiling. Based on this finding, a method to determine the temperature of onset of the boiling crisis is suggested. It is found that the evaporation stages of drops of a liquid correlate with boiling regimes for this liquid.