Effect of Surfactants on the Splashing Dynamics of Drops Impacting Smooth Substrates.

We present the results of a systematic study elucidating the role that dynamic surface tension has on the spreading and splashing dynamics of surfactant-laden droplets during the impact on hydrophobic substrates. Using four different surfactants at various concentrations, we generated a range of solutions whose dynamic surface tension were characterized to submillisecond timescales using maximum bubble-pressure tensiometry. Impact dynamics of these solutions were observed by high-speed imaging with subsequent quantitative image processing to determine the impact parameters (droplet size and speed) and dynamic wetting properties (dynamic contact angle). Droplets were slowly formed by dripping to allow the surfactants to achieve equilibrium at the free surface prior to impact. Our results indicate that while only the fastest surfactants appreciably affect the maximum spreading diameter, the droplet morphology during the initial stages of spreading is different to water for all surfactant solutions studied. Moreover, we show that surfactant-laden droplets splash more easily than pure liquid (water). Based on the association of the splashing ratio to our tensiometry measurements, we are able to predict the effective surface tension acting during splashing. These results suggest that droplet splashing characteristics are primarily defined by the stretching of the equilibrated droplet free surface.

Drop splashing after impact onto immiscible pools of different viscosities.

Droplet impact onto liquid pools is a canonical scenario relevant to numerous natural phenomena and industrial processes. However, despite their ubiquity, multi-fluid systems with the drop and pool consisting of different liquids are far less well understood. Our hypothesis is that the post-impact dynamics greatly depends on the pool-to-droplet viscosity ratioµp/µd, which we explore over a range of six orders of magnitude using a combination of experiments and theoretical approaches (mathematical modelling and direct numerical simulation). Our findings indicate that in this scenario the splashing threshold and the composition of the ejecta sheet are controlled by the viscosity ratio. We uncover that increasing the pool viscosity decreases the splashing threshold for high viscosity pools (µp/µd≳35) when the splash comes from the droplet. By contrast, for low viscosity pools, the splash sheet comes from the pool and increasing the pool viscosity increases the splashing threshold. Surprisingly, there are conditions for which no splashing is observed under the conditions attainable in our laboratory. Furthermore, considering the interface velocity together with asymptotic arguments underlying the generation of the ejecta has allowed us to understand meaningful variations in the pressure during impact and rationalise the observed changes in the splashing threshold.

Cinchona bark and quinine in the Portuguese official pharmacopoeias (1794-2001).

Cinchona bark (bark from plants of the genus Cinchona with antimalarial activity) and its alkaloid quinine were widely used to treat intermittent fevers. This paper aims to quantitatively analyze the presence of Cinchona bark, quinine and other Cinchona bark-derived substances in the Portuguese official pharmacopoeias published between 1794 and 2001. The analysis showed that the Pharmacopêa Portugueza (1876) is the Portuguese official pharmacopeia with the highest percentage of medicines containing Cinchona bark (2.61%). The Farmacopeia Portuguesa IV (1935) is the official pharmacopeia with the highest percentage of quinine-containing medicines (2.34%). Medicines made from Cinchona bark are present in the Portuguese official pharmacopoeias until the Farmacopeia Portuguesa IV (1946). Medicines made from quinine have been present in Portuguese official pharmacopoeias since the Codigo Pharmaceutico Lusitano (1835).

Droplet splashing on curved substrates.

Droplets impacting dry solid substrates often splash above a certain threshold impact velocity. We hypothesise that substrate curvature alters splashing thresholds due to a modification to the lift force acting on the lamella at the point of breakup. We have undertaken high-speed imaging experiments of millimetric droplets impacting convex and concave surfaces to establish splashing thresholds and dynamics across a wide range of substrate geometries and impact conditions. Our findings indicate that the tendency of droplets to splash is proportional to the reciprocal of the substrate's radius of curvature, independent of whether the substrate is convex or concave, with it being harder for droplets to splash on small spheres. Moreover, we consistently parameterise the axisymmetric splashing threshold across all curved substrate geometries via a modification to the well-known splashing ratio. Finally, the splashing dynamics resulting from initial asymmetry between the impacting droplet and curved substrate are also elucidated.

Scientific reports controlling droplet splashing and bouncing by dielectrowetting.

Stopping droplets from bouncing or splashing after impacting a surface is fundamental in preventing cross-contamination, and the spreading of germs and harmful substances. Here we demonstrate that dielectrowetting can be applied to actively control the dynamics of droplet impact. Moreover, we demonstrate that dielectrowetting can be used to prevent droplet bouncing and suppress splashing. In our experiments, the dielectrowetting effect is produced on a flat substrate by two thin interdigitated electrodes connected to an alternating current potential. Our findings show that the strength of the electric potential can affect the dynamic contact angle and regulate the spreading, splashing and receding dynamics at the right time-scales.

The influence of German science on Cinchona and quinine research in Portugal in the second half of the 19th century.

This paper examines the contribution of three Portuguese scientists to Cinchona cultivation in the former Portuguese colonies in the second half of the 19th century, while discussing the importance of their studies in Germany to their professional lives. Portuguese pharmaceutical, medical, and botanical literature from the 19 th and 20 th century was reviewed, as well as books and articles regarding the history of pharmacy and medicine in Portugal. Cinchona bark, source of the antimalarial alkaloid quinine, is obtained from a South American plant, and was an important commodity in the 19th century. Many European nations (including Portugal) tried to acclimatize and cultivate Cinchona plants in their colonies. Pharmacist Joaquim dos Santos e Silva (1842-1906) performed chemical analysis of Cinchona bark samples from the Portuguese colonies in Africa. Forester Bernardino Barros Gomes (1839-1910) wrote a book with practical instructions for Cinchona cultivation and chronicled the history of Cinchona plantations in the British and Dutch colonies. In that work he also encouraged private planters to cultivate Cinchona. Forester Adolpho Frederico Möller (1842-1920), as inspector of the Botanical Garden of Coimbra, managed Cinchona plants' cultivation in the garden's nurseries, which were later sent to the colonies, and answered queries from Cinchona planters. Silva's chemistry studies in Germany were crucial to his career and the work of the three scientists was influenced and guided by their knowledge of German science and scientific culture.

A novel capsule-based smell test fabricated via coaxial dripping.

In this paper, we demonstrate that aromatic oil capsules, produced by dripping droplets, can offer a simple, yet effective, testing tool to aid in the diagnosis of various diseases, in which the loss of smell is a key symptom. These include chronic neurological conditions such as Parkinson's and Alzheimer's diseases, and acute respiratory infections such as that caused by COVID-19. The capsules were fabricated by concentrically dripping oil/alginate droplets, from a coaxial nozzle, into an oppositely charged ionic liquid. This fabrication technique enables full control over the capsule size, the shell thickness and the volume of the encapsulated oil. After formation, liquid capsules were left to dry and form a solid crust surrounding the oil. The prototype test consists of placing a standardized number of capsules between adhesive strips that users crush and pull apart to release the smell. In addition to the fabrication method, a simple mathematical model was developed to predict the volume of encapsulated oil within the capsule in terms of the flow rate ratio and the nozzle size. Tensile tests show that capsule strength is inversely proportional to its size owing to an increase in the shell thickness. By increasing the alginate concentration, the load required to rupture the capsule increases, to the point where capsules are too stiff to be broken by a fingertip grip. Results from a preliminary screening test, within a group of patients with Parkinson's disease, found that smells were detectable using a 'forced choice' paradigm.

Anaphylaxis in an emergency department: a retrospective 10-year study in a tertiary hospital.

Summary: Background. Anaphylaxis is a potentially fatal medical emergency. The frequency of hospital admissions for anaphylaxis seems to be increasing in the recent decades. Objective. Characterize the patients admitted for anaphylaxis to the adult emergency department (ED) of a tertiary care hospital over a 10-year period, discriminating aetiologies, clinical features and therapy administered. Methods. Retrospective, descriptive and inferential study, evaluating age, sex, Manchester triage system, suspected allergen, site of allergen exposure, comorbidities, cofactors, clinical findings and symptoms, treatment and management. Patients admitted between January 2007 and December 2016 were included. Results. Forty-three patients were enrolled: 23 males, mean age 54.3 ± 16.2 years, n = 22 had history of allergic disease. Two patients were triaged as non-urgent. The most frequently suspected causes of anaphylaxis were: drugs (33%, n = 14), Hymenoptera venoms (23%, n = 10), foods (21%, n = 9) and iodinated contrast products (12%, n = 5). Adrenaline was used in 88% of the episodes (n = 38), 55% of which (n = 21) intramuscularly. Mortality was registered in one case. At discharge, adrenaline auto-injector was prescribed in 7% (n = 3) of the patients, and Allergy and Clinical Immunology consultation (ACIC) was requested in 65% of the episodes (n = 28). Statistically significant associations (p minor 0.05) were established: a, anaphylaxis to drugs associated with a low intramuscular adrenaline use and with frequent oxygen therapy; b, anaphylaxis to food associated with intramuscular adrenaline administration; c, anaphylaxis to Hymenoptera venom associated with male sex; and d, anaphylaxis to iodinated contrasts associated with referral to ACIC and with shock. All obese patients developed shock. Conclusions. Anaphylaxis is a life-threatening condition that requires early recognition. Although most patients received adrenaline, administration was not always performed by the recommended route and only a few patients were prescribed adrenaline auto-injector.

Evolution of Gaussian wave packets in capillary jets.

A temporal analysis of the evolution of Gaussian wave packets in cylindrical capillary jets is presented through both a linear two-mode formulation and a one-dimensional nonlinear numerical scheme. These analyses are normally applicable to arbitrary initial conditions but our study focuses on pure-impulsive ones. Linear and nonlinear findings give consistent results in the stages for which the linear theory is valid. The inverse Fourier transforms representing the formal linear solution for the jet shape is both numerically evaluated and approximated by closed formulas. After a transient, these formulas predict an almost Gaussian-shape deformation with (i) a progressive drift of the carrier wave number to that given by the maximum of the Rayleigh dispersion relation, (ii) a progressive increase of its bell width, and (iii) a quasiexponential growth of its amplitude. These parameters agree with those extracted from the fittings of Gaussian wave packets to the numerical simulations. Experimental results are also reported on near-Gaussian pulses perturbing the exit velocity of a 2-mm diameter water jet. The possibility of controlling the breakup location along the jet and other features, such as pinch-off simultaneity, are demonstrated.

A simple levitated-drop tensiometer.

A reliable, simple, and affordable liquid tensiometer is presented in this paper. The instrument consists of 72 ultrasonic transmitters in a tractor beam configuration that levitates small liquid samples (droplets) in air. Under operation, the instrument imparts a pressure instability that causes the droplet to vibrate while still levitating. Droplet oscillations are then detected by a photodiode, and the signal is recorded by an oscilloscope. The frequency of these oscillations is obtained and then used to obtain the effective surface tension of the sample. The instrument operates at the millisecond scale time (t < 12.5 ms), with very small liquid volumes (∼0.5 µl), and the sample is recoverable after testing. The instrument has been experimentally validated with acetone, ethanol, Fluorinert FC-40, water, and whole milk.

Shape of a recoiling liquid filament.

We study the capillary retraction of a Newtonian semi-infinite liquid filament through analytical methods. We derive a long-time asymptotic-state expansion for the filament profile using a one-dimensional free-surface slender cylindrical flow model based on the three-dimensional axisymmetric Navier-Stokes equations. The analysis identifies three distinct length and time scale regions in the retraction domain: a steady filament section, a growing spherical blob, and an intermediate matching zone. We show that liquid filaments naturally develop travelling capillary waves along their surface and a neck behind the blob. We analytically prove that the wavelength of the capillary waves is approximately 3.63 times the filament's radius at the inviscid limit. Additionally, the waves' asymptotic wavelength, decay length, and the minimum neck size are analysed in terms of the Ohnesorge number. Finally, our findings are compared with previous results from the literature and numerical simulations in Basilisk obtaining a good agreement. This analysis provides a full picture of the recoiling process going beyond the classic result of the velocity of retraction found by Taylor and Culick.

The Effect of Surface Roughness on the Contact Line and Splashing Dynamics of Impacting Droplets.

Whether a droplet splashes upon impact onto a solid is known to depend not only on the fluid properties and its speed, but also on the substrate characteristics. Past research has shown that splashing is heavily influenced by the substrate roughness. Indeed, in this manuscript, we demonstrate that splashing is ruled by the surface roughness, the splashing ratio, and the dynamic contact angle. Experiments consist of water and ethanol droplets impacting onto solid substrates with varying degrees of roughness. High speed imaging is used to extract the dynamic contact angle as a function of the spreading speed for these impacting droplets. During the spreading phase, the dynamic contact angle achieves an asymptotic maximum value, which depends on the substrate roughness and the liquid properties. We found that this maximum dynamic contact angle, together with the liquid properties, the ratio of the peak to peak roughness and the surface feature mean width, determines the splashing to no-splashing threshold. In addition, these parameters consistently differentiate the splashing behaviour of impacts onto smooth hydrophilic, hydrophobic and superhydrophobic surfaces.

Role of the Dynamic Contact Angle on Splashing.

In this Letter, we study the splashing behavior of droplets upon impact onto a variety of substrates with different wetting properties, ranging from hydrophilic to superhydrophobic surfaces. In particular, we study the effects of the dynamic contact angle on splashing. The experimental approach uses high-speed imaging and image analysis to recover the apparent contact angle as a function of the spreading speed. Our results show that neither the Capillary number nor the so-called splashing parameter are appropriate to characterize the splashing behavior under these circumstances. However, we show that the maximum dynamic advancing contact angle and the splashing ratio ß adequately characterize the splashing behavior.

Droplet impact dynamics on textiles.

The development of textiles that repel droplets following droplet impact at a high velocity is a common requirement in a number of applications, ranging from waterproof clothing to inkjet printing, yet the underpinning physical mechanisms are not entirely understood. The impact of a droplet on the surface of a textile produces two simultaneous yet separate flows, occurring above and below the surface, and which are associated with the spreading and penetration dynamics. In this paper, we study the temporal evolution of the lateral spreading diameter of a droplet impacting both hydrophobic and hydrophilic textiles. We show that the impact on textiles at short timescales involves no deformation of the droplet shape if the textile's porosity is sufficiently low. We show that the early-stage impact penetration is solely driven by inertia and no lamella is visible. We also show that for hydrophilic textiles, depending on the impact conditions, a droplet can be captured by the textile or penetrate it. We show by balancing the dynamic impact and capillary pressures that the penetration behaviour is governed by a threshold pore size, the liquid characteristics and the droplet diameter. Our conclusions highlight that the ability of a textile to repel water is controlled by the mesh size. Our experiments and analysis were carried out on coated hydrophobic and non-coated hydrophilic textiles with four corresponding mesh sizes, and are in agreement with the previous findings on hydrophobic metallic (copper) meshes.

Controlled cavity collapse: scaling laws of drop formation.

The formation of transient cavities at liquid interfaces occurs in an immense variety of natural processes, among which the bursting of surface bubbles and the impact of a drop on a liquid pool are salient. The collapse of a surface liquid cavity is a well documented natural process that leads to the ejection of a thin and fast jet. Droplets generated through this process can be one order of magnitude smaller than the cavity's aperture, and they are consequently of interest in drop on demand inkjet applications. In this work, the controlled formation and collapse of a liquid cavity is analyzed, and the conditions for minimizing the resulting size and number of ejected drops are determined. The experimental and numerical models are simple and consist of a liquid reservoir, a nozzle plate with the discharge orifice, and a moving piston actuated by single half-sine-shaped pull-mode pulses. The size of the jetted droplet is described by a physical model resulting in a scaling law that is numerically and experimentally validated.

Anaphylaxis in a food allergy outpatient department: one-year review.

Summary: Background. Anaphylaxis is an acute, potentially fatal, multi-organ allergic reac-tion. Our aim was to characterize the population with food induced anaphylaxis followed over a one-year period. Methods. Retrospective analysis of clinical files of patients with food anaphylaxis observed in our food allergy consultation during 2016. Results. Sixty-two patients were included. In the pediatric group, the implicated allergens were cow's milk, egg and fish and in the adults' group, the commonest allergens were nuts and wheat. Allergy to shrimp affected equally children and adults. The most frequent symptoms were urticaria (85.5%), angioedema (64.5%) and dyspnea (62.9%). Cofactors were present in 32.6% of patients, mainly exercise. Asthma and/or rhinitis were the most frequent comorbidities. Conclusion. In accordance to other studies, milk and egg were the most implicated allergens in children. Anaphylaxis in adults reflects the Mediterranean sensitization pattern. Exercise was the most relevant cofactor.

Severe anaphylaxis with cardiac arrest caused by prick test with cefuroxime

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JNKs function as CDK4-activating kinases by phosphorylating CDK4 and p21.

Cyclin D-CDK4/6 are the first cyclin-dependent kinase (CDK) complexes to be activated by mitogenic/oncogenic pathways. They have a central role in the cell multiplication decision and in its deregulation in cancer cells. We identified T172 phosphorylation of CDK4 rather than cyclin D accumulation as the distinctly regulated step determining CDK4 activation. This finding challenges the view that the only identified metazoan CDK-activating kinase, cyclin H-CDK7-Mat1 (CAK), which is constitutively active, is responsible for the activating phosphorylation of all cell cycle CDKs. We previously showed that T172 phosphorylation of CDK4 is conditioned by an adjacent proline (P173), which is not present in CDK6 and CDK1/2. Although CDK7 activity was recently shown to be required for CDK4 activation, we proposed that proline-directed kinases might specifically initiate the activation of CDK4. Here, we report that JNKs, but not ERK1/2 or CAK, can be direct CDK4-activating kinases for cyclin D-CDK4 complexes that are inactivated by p21-mediated stabilization. JNKs and ERK1/2 also phosphorylated p21 at S130 and T57, which might facilitate CDK7-dependent activation of p21-bound CDK4, however, mutation of these sites did not impair the phosphorylation of CDK4 by JNKs. In two selected tumor cells, two different JNK inhibitors inhibited the phosphorylation and activation of cyclin D1-CDK4-p21 but not the activation of cyclin D3-CDK4 that is mainly associated to p27. Specific inhibition by chemical genetics in MEFs confirmed the involvement of JNK2 in cyclin D1-CDK4 activation. Therefore, JNKs could be activating kinases for cyclin D1-CDK4 bound to p21, by independently phosphorylating both CDK4 and p21.

It's Harder to Splash on Soft Solids.

Droplets splash when they impact dry, flat substrates above a critical velocity that depends on parameters such as droplet size, viscosity, and air pressure. By imaging ethanol drops impacting silicone gels of different stiffnesses, we show that substrate stiffness also affects the splashing threshold. Splashing is reduced or even eliminated: droplets on the softest substrates need over 70% more kinetic energy to splash than they do on rigid substrates. We show that this is due to energy losses caused by deformations of soft substrates during the first few microseconds of impact. We find that solids with Young's moduli ≲100 kPa reduce splashing, in agreement with simple scaling arguments. Thus, materials like soft gels and elastomers can be used as simple coatings for effective splash prevention. Soft substrates also serve as a useful system for testing splash-formation theories and sheet-ejection mechanisms, as they allow the characteristics of ejection sheets to be controlled independently of the bulk impact dynamics of droplets.