98 research outputs found
A bouncing oil droplet in a stratified liquid and its sudden death
Droplets can self-propel when immersed in another liquid in which a
concentration gradient is present. Here we report the experimental and
numerical study of a self-propelling oil droplet in a vertically stratified
ethanol/water mixture: At first, the droplet sinks slowly due to gravity, but
then, before having reached its density matched position, jumps up suddenly.
More remarkably, the droplet bounces repeatedly with an ever increasing jumping
distance, until all of a sudden it stops after about 30 min. We identify the
Marangoni stress at the droplet/liquid interface as responsible for the
jumping: its strength grows exponentially because it pulls down ethanol-rich
liquid, which in turn increases its strength even more. The jumping process can
repeat because gravity restores the system. Finally, the sudden death of the
jumping droplet is also explained. Our findings have demonstrated a type of
prominent droplet bouncing inside a continuous medium with no wall or sharp
interface.Comment: 6 pages, 4 figure
Extremely cold and hot temperatures increase the risk of ischaemic heart disease mortality: epidemiological evidence from China.
OBJECTIVE: To examine the effects of extremely cold and hot temperatures on ischaemic heart disease (IHD) mortality in five cities (Beijing, Tianjin, Shanghai, Wuhan and Guangzhou) in China; and to examine the time relationships between cold and hot temperatures and IHD mortality for each city. DESIGN: A negative binomial regression model combined with a distributed lag non-linear model was used to examine city-specific temperature effects on IHD mortality up to 20 lag days. A meta-analysis was used to pool the cold effects and hot effects across the five cities. PATIENTS: 16 559 IHD deaths were monitored by a sentinel surveillance system in five cities during 2004-2008. RESULTS: The relationships between temperature and IHD mortality were non-linear in all five cities. The minimum-mortality temperatures in northern cities were lower than in southern cities. In Beijing, Tianjin and Guangzhou, the effects of extremely cold temperatures were delayed, while Shanghai and Wuhan had immediate cold effects. The effects of extremely hot temperatures appeared immediately in all the cities except Wuhan. Meta-analysis showed that IHD mortality increased 48% at the 1st percentile of temperature (extremely cold temperature) compared with the 10th percentile, while IHD mortality increased 18% at the 99th percentile of temperature (extremely hot temperature) compared with the 90th percentile. CONCLUSIONS: Results indicate that both extremely cold and hot temperatures increase IHD mortality in China. Each city has its characteristics of heat effects on IHD mortality. The policy for response to climate change should consider local climate-IHD mortality relationships
On the rising and sinking motion of bouncing oil drops in strongly stratified liquids
When an immiscible oil drop is immersed in a stably stratified ethanol-water
mixture, the Marangoni flow on the surface of the drop can experience an
oscillatory instability, so that the drop undergoes a transition from
levitating to bouncing. The onset of the instability and its mechanisms have
been studied previously, yet the bouncing motion of the drop itself, which is a
completely different problem, has not yet been investigated. Here we study how
the bouncing characteristics (jumping height, rising and sinking time) depend
on the control parameters (drop radius, stratification strength, drop
viscosity). We first record experimentally the bouncing trajectories of drops
of different viscosities in different stratifications. Then a simplified
dynamical analysis is performed to get the scaling relations of the jumping
height and the rising and sinking times. The rising and sinking time scales are
found to depend on the drag coefficient of the drop in the stratified
liquid, which is determined empirically for the current parameter space. For
low viscosity (5 cSt) oil drops the results on the drag coefficient match the
ones from the literature. For high viscosity (100 cSt) oil drops the parameter
space had not been explored and the drag coefficients are not readily
available. Numerical simulations are therefore performed to provide external
verification for the drag coefficients, which well match with the experimental
results.Comment: 21 pages, 11 figure
Metabolic profile, bioavailability and toxicokinetics of zearalenone-14-glucoside in rats after oral and intravenous administration by liquid chromatography high-resolution mass spectrometry and tandem mass spectrometry
Zearalenone-14-glucoside (ZEN-14G), a key modified mycotoxin, has attracted a great deal of attention due to the possible conversion to its free form of zearalenone (ZEN) exerting toxicity. In this study, the toxicokinetics of ZEN-14G were investigated in rats after oral and intravenous administration. The plasma concentrations of ZEN-14G and its major five metabolites were quantified using a validated liquid chromatography tandem mass spectrometry (LC-MS/MS) method. The data were analyzed via non-compartmental analysis using software WinNonlin 6.3. The results indicated that ZEN-14G was rapidly hydrolyzed into ZEN in vivo. In addition, the major parameters of ZEN-14G following intravenous administration were: area under the plasma concentration-time curve (AUC), 1.80 h.ng/mL; the apparent volume of distribution (V-Z), 7.25 L/kg; and total body clearance (CL), 5.02 mL/h/kg, respectively. After oral administration, the typical parameters were: AUC, 0.16 h.ng/mL; V-Z, 6.24 mL/kg; and CL, 4.50 mL/h/kg, respectively. The absolute oral bioavailability of ZEN-14G in rats was about 9%, since low levels of ZEN-14G were detected in plasma, which might be attributed to its extensive metabolism. Therefore, liquid chromatography high-resolution mass spectrometry (LC-HRMS) was adopted to clarify the metabolic profile of ZEN-14G in rats' plasma. As a result, eight metabolites were identified in which ZEN-14-glucuronic acid (ZEN-14GlcA) had a large yield from the first time-point and continued accumulating after oral administration, indicating that ZEN-14-glucuronic acid could serve a potential biomarker of ZEN-14G. The obtained outcomes would prompt the accurate safety evaluation of ZEN-14G
Universality in microdroplet nucleation during solvent exchange in Hele-Shaw like channels
Micro and nanodroplets have many important applications such as in drug
delivery, liquid-liquid extraction, nanomaterial synthesis and cosmetics. A
commonly used method to generate a large number of micro or nanodroplets in one
simple step is solvent exchange (also called nanoprecipitation), in which a
good solvent of the droplet phase is displaced by a poor one, generating an
oversaturation pulse that leads to droplet nucleation. Despite its crucial
importance, the droplet growth resulting from the oversaturation pulse in this
ternary system is still poorly understood. We experimentally and theoretically
study this growth in Hele-Shaw like channels by measuring the total volume of
the oil droplets that nucleates out of it. In order to prevent the
oversaturated oil from exiting the channel, we decorated some of the channels
with a porous region in the middle. Solvent exchange is performed with various
solution compositions, flow rates and channel geometries, and the measured
droplets volume is found to increase with the P\'eclet number with an
approximate effective power law . A theoretical model is
developed to account for this finding. With this model we can indeed explain
the scaling, including the prefactor, which can collapse
all data of the "porous" channels onto one universal curve, irrespective of
channel geometry and composition of the mixtures. Our work provides a
macroscopic approach to this bottom-up method of droplet generation and may
guide further studies on oversaturation and nucleation in ternary systems.Comment: Published in Journal of Fluid Mechanics. 16 pages, 6 figure
Convection-dominated dissolution for single and multiple immersed sessile droplets
We numerically investigate both single and multiple droplet dissolution with droplets consisting of less dense liquid dissolving in a denser host liquid. In this situation, buoyancy can lead to convection and thus plays an important role in the dissolution process. The significance of buoyancy is quantified by the Rayleigh number , which is the buoyancy force over the viscous damping force. In this study, spans almost four decades from 0.1 to 400. We focus on how the mass flux, characterized by the Sherwood number , and the flow morphologies depend on. For single droplet dissolution, we first show the transition of the scaling from a constant value to , which confirms the experimental results by Dietrich et al. (J. Fluid Mech., vol. 794, 2016, pp. 45-67). The two distinct regimes, namely the diffusively and the convectively dominated regimes, exhibit different flow morphologies: when , a buoyant plume is clearly visible, which contrasts sharply with the pure diffusion case at low. For multiple droplet dissolution, the well-known shielding effect comes into play at low , so that the dissolution rate is slower as compared to the single droplet case. However, at high , convection becomes more and more dominant so that a collective plume enhances the mass flux, and remarkably the multiple droplets dissolve faster than a single droplet. This has also been found in the experiments by Laghezza et al. (Soft Matt., vol. 12 (26), 2016, pp. 5787-5796). We explain this enhancement by the formation of a single, larger plume rather than several individual plumes. Moreover, there is an optimal at which the enhancement is maximized, because the single plume is narrower at larger , which thus hinders the enhancement. Our findings demonstrate a new mechanism in collective droplet dissolution, which is the merging of the plumes, which leads to non-trivial phenomena, contrasting the shielding effect.</p
Convection-dominated dissolution for single and multiple immersed sessile droplets
We numerically investigate both single and multiple droplet dissolution with
droplets consisting of lighter liquid dissolving in a denser host liquid. The
significance of buoyancy is quantified by the Rayleigh number Ra which is the
buoyancy force over the viscous damping force. In this study, Ra spans almost
four decades from 0.1 to 400. We focus on how the mass flux, characterized by
the Sherwood number Sh, and the flow morphologies depend on Ra. For single
droplet dissolution, we first show the transition of the Sh(Ra) scaling from a
constant value to , which confirms the experimental results by
Dietrich et al. (J. Fluid Mech., vol. 794, 2016, pp. 45--67). The two distinct
regimes, namely the diffusively- and the convectively-dominated regime, exhibit
different flow morphologies: when Ra>=10, a buoyant plume is clearly visible
which contrasts sharply to the pure diffusion case at low Ra. For multiple
droplet dissolution, the well-known shielding effect comes into play at low Ra
so that the dissolution rate is slower as compared to the single droplet case.
However, at high Ra, convection becomes more and more dominant so that a
collective plume enhances the mass flux, and remarkably the multiple droplets
dissolve faster than a single droplet. This has also been found in the
experiments by Laghezza et al. (Soft Matter, vol. 12, 2016, pp. 5787--5796). We
explain this enhancement by the formation of a single, larger plume rather than
several individual plumes. Moreover, there is an optimal Ra at which the
enhancement is maximized, because the single plume is narrower at larger Ra,
which thus hinders the enhancement. Our findings demonstrate a new mechanism in
collective droplet dissolution, which is the merging of the plumes, that leads
to non-trivial phenomena, contrasting the shielding effect.Comment: 18 pages, 11 figures, submitted to JF
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