Oscillatory Motion of Viscoelastic Drops on Slippery Lubricated Surfaces

The introduction of slippery lubricated surfaces allows the investigation of the flow of highly viscous solutions which otherwise will hardly move on standard solid surfaces. Here we present the study of the gravity induced motion of small viscoelastic drops deposited on inclined lubricated surfaces. The viscoelastic fluids exhibit shear thinning and, more importantly, a significant first normal stress difference N1. Despite the homogeneity of the surface and of the fluids, drops of sufficiently high N1 move down with an oscillating instantaneous speed whose frequency is found to be directly proportional to the average speed and inversely to the drop volume. The oscillatory motion is caused by the formation of a bulge at the drop rear that starts rolling around the moving drop.

Vibrio cholerae motility in aquatic and mucus-mimicking environments

Cholera disease is caused by Vibrio cholerae infecting the lining of the small intestine and results in severe diarrhea. V. cholerae ’s swimming motility is known to play a crucial role in pathogenicity and may aid the bacteria in crossing the intestinal mucus barrier to reach sites of infection, but the exact mechanisms are unknown. The cell can be either pushed or pulled by its single polar flagellum, but there is no consensus on the resulting repertoire of motility behaviors. We use high-throughput 3D bacterial tracking to observe V. cholerae swimming in buffer, in viscous solutions of the synthetic polymer PVP, and in mucin solutions that may mimic the host environment. We perform a statistical characterization of its motility behavior on the basis of large 3D trajectory datasets. We find that V. cholerae performs asymmetric run-reverse-flick motility, consisting of a sequence of a forward run, reversal, and a shorter backward run, followed by a turn by approximately 90°, called a flick, preceding the next forward run. Unlike many run-reverse-flick swimmers, V. cholerae ’s backward runs are much shorter than its forward runs, resulting in an increased effective diffusivity. We also find that the swimming speed is not constant, but subject to frequent decreases. The turning frequency in mucin matches that observed in buffer. Run-reverse-flick motility and speed fluctuations are present in all environments studied, suggesting that these behaviors may also occur in natural aquatic habitats as well as the host environment. IMPORTANCE Cholera disease produces vomiting and severe diarrhea and causes approximately 100,000 deaths per year worldwide. The disease is caused by the bacterium Vibrio cholerae colonizing the lining of the small intestine. V. cholerae ’s ability to swim is known to increase its infectivity, but the underlying mechanisms are not known. One possibility is that swimming may aid in crossing the protective mucus barrier that covers the lining of the small intestine. Our work characterizing how V. cholerae swims in environments that mimic properties of the host environment may advance the understanding of how motility contributes to infection.

Vibrio cholerae motility in aquatic and mucus-mimicking environments

Cholera disease is caused by Vibrio cholerae infecting the lining of the small intestine and results in severe diarrhea. V. cholerae's swimming motility is known to play a crucial role in pathogenicity and may aid the bacteria in crossing the intestinal mucus barrier to reach sites of infection, but the exact mechanisms are unknown. The cell can be either pushed or pulled by its single polar flagellum, but there is no consensus on the resulting repertoire of motility behaviors. We use high-throughput 3D bacterial tracking to observe V. cholerae swimming in buffer, in viscous solutions of the synthetic polymer PVP, and in mucin solutions that may mimic the host environment. We perform a statistical characterization of its motility behavior on the basis of large 3D trajectory datasets. We find that V. cholerae performs asymmetric run-reverse-flick motility, consisting of a sequence of a forward run, reversal, and a shorter backward run, followed by a turn by approximately 90°, called a flick, preceding the next forward run. Unlike many run-reverse-flick swimmers, V. cholerae's backward runs are much shorter than its forward runs, resulting in an increased effective diffusivity. We also find that the swimming speed is not constant, but subject to frequent decreases. The turning frequency in mucin matches that observed in buffer. Run-reverse-flick motility and speed fluctuations are present in all environments studied, suggesting that these behaviors may also occur in natural aquatic habitats as well as the host environment.

Self-adaptive and efficient propulsion of Ray sperms at different viscosities enabled by heterogeneous dual helixes

We disclose a peculiar rotational propulsion mechanism of Ray sperms enabled by its unusual heterogeneous dual helixes with a rigid spiral head and a soft tail, named Heterogeneous Dual Helixes (HDH) model for short. Different from the conventional beating propulsion of sperm, the propulsion of Ray sperms is from both the rotational motion of the soft helical tail and the rigid spiral head. Such heterogeneous dual helical propulsion style provides the Ray sperm with high adaptability in viscous solutions along with advantages in linearity, straightness, and bidirectional motion. This HDH model is further corroborated by a miniature swimming robot actuated via a rigid spiral head and a soft tail, which demonstrates similar superiorities over conventional ones in terms of adaptability and efficiency under the same power input. Such findings expand our knowledge on microorganisms’ motion, motivate further studies on natural fertilization, and inspire engineering designs.

Numerical Simulation of Multistage Bimolecular Photoreactions in Liquids: Algorithms and Software

In this paper we consider the tools for numerical simulation of multistage bimolecular photoreactions assisted by diffusive mobility of reactant molecules in viscous solutions. To describe these processes, the differential encounter theory (DET) is extended to account for the coherent dynamics of certain degrees of freedom (for example, electronic spins of reactants and intermediates). The model involves diffusion of reactants in solution and multistage/multichannel physicochemical processes proceeding both at the level of individual molecules and encounter complexes. Algorithms for numerical solution of model equations are proposed, which are related to evaluation of evolution operators. The algorithm for computing the quantum propagator for the density matrix based on the Trotter splitting is presented. A software package for simulation of multistage photoreactions has been developed using the suggested numerical approaches. The structure of the key software components is presented, examples of the program model construction are presented. A software testing has been carried out, showing good correspondence between the numerical results and exact solutions of the model equations in certain particular cases. As an example, a photoreaction with participation of 9,10-dimethylanthracene and 1,3-dicyanobenzene in acetonitrile solution has been considered, and basic procedures for configuring and simulating multistage bimolecular photoprocesses are shown. An importance of coherent description of the electronic spin evolution at the radical stage is shown.

Valorization of Native Soluble and Insoluble Oat Side Streams for Stable Suspensions and Emulsions

Among different cereals, oat is becoming more popular due to its unique composition and health benefits. The increase in oat production is associated with an increase in related side streams, comprising unutilized biomass that is rich in valuable components, such as polysaccharides, proteins, and antioxidants. To valorize such biomass, it is fundamental that side streams enter back into the food production chain, in respect of the circular economy model. Here, we propose the use of soluble and insoluble oat-production side-stream in suspensions and emulsions, avoiding any further extraction, fractionation, and/or chemical derivatization. Our approach further increases the value of these side streams. To this aim, we first studied the effect of thermal and mechanical processes on the behavior and properties of both soluble and insoluble oat side-stream fractions in water and at air/water interface. Then, we characterized the emulsifying and stabilizing abilities of these materials in oil-in-water emulsions. Interestingly, we found that the insoluble fraction was able to form stable suspensions and emulsions after mechanical treatment. The oil droplets in the emulsions were stabilized by anchoring at the surface of the insoluble particles. On the other hand, the soluble fraction formed only stable viscous solutions. Finally, we demonstrated that the two fractions can be combined to increase the storage stability of the resulting emulsion.Our results highlight that oat production side streams can be used as novel bio-based emulsifiers, showing the great potential behind the underutilized cereal-side-stream biomass. Graphical Abstract

Uranium Carbide Fibers with Nano-Grains as Starting Materials for ISOL Targets

This paper presents an experimental study about the preparation, by electrospinning, of uranium carbide fibers with nanometric grain size. Viscous solutions of cellulose acetate and uranyl salts (acetate, acetylacetonate, and formate) on acetic acid and 2,4-pentanedione, adjusted to three different polymer concentrations, 10, 12.5, and 15 weight %, were used for electrospinning. Good quality precursor fibers were obtained from solutions with a 15% cellulose acetate concentration, the best ones being produced from the uranyl acetate solution. As-spun precursor fibers were then decomposed by slow heating until 823 K under argon, resulting in a mixture of nano-grained UO2 and C fibers. A last carboreduction was then carried out under vacuum at 2073 K for 2 h. The final material displayed UC2−y as the major phase, with grain sizes in the 4 nm–10 nm range. UO2+x was still present in moderate concentrations (~30 vol.%). This is due to uncomplete carboreduction that can be explained by the fiber morphology, limiting the effective contact between C and UO2 grains.

Numerical Simulation of Detonation Propagation in Flame Arrestor Applications

A detail numerical study of detonation propagation and interaction with a flame arrestor product was conducted. The simulation domain was based on the detonation flame arrestor validation test setup. The flame arrestor element was modeled as a porous zone using the Forchheimer equation. The coefficients of the Forchheimer equation were determined using experimental data. The Forchheimer equation was incorporated into the governing equations for axisymmetric reactive turbulent flow as a momentum sink. A 21-step elementary reaction mechanism with 10 species was used to model the stoichiometric oxyhydrogen detonation. Different cases of detonation propagation including inviscid, viscous adiabatic, and viscous with heat transfer and a porous zone were studied. A detail discussion of the detonation propagation and effect of the arrestor geometry, the heat transfer and the porous zone are presented. The inviscid numerical model solutions of the detonation propagation parameters are compared to one-dimensional analytical solution for verification. The viscous solutions are qualitatively compared to historical experimental data which shows very similar trend. The effect of the porous media parameters on shock transmission and re-initiation of detonation is presented.

The Trypanosoma brucei subpellicular microtubule array is organized into functionally discrete subdomains defined by microtubule associated proteins

Microtubules are inherently dynamic cytoskeletal polymers whose length and activity can be altered to perform essential functions in eukaryotic cells, such as providing tracks for intracellular trafficking and forming the mitotic spindle. Microtubules can be bundled to create more stable structures that collectively propagate force, such as in the flagellar axoneme, which provides motility. The subpellicular microtubule array of the protist parasite Trypanosoma brucei, the causative agent of African sleeping sickness, is a remarkable example of a highly specialized microtubule bundle, comprising a single microtubule layer that is crosslinked to each other and the plasma membrane. The array microtubules appear to be highly stable and remain intact throughout the cell cycle, but very little is known about the pathways that tune microtubule properties in trypanosomatids. Here, we show that the subpellicular microtubule array is organized into subdomains that consist of differentially localized array-associated proteins. We characterize the localization and function of the array-associated protein PAVE1, which is a component of the inter-microtubule crosslinking fibrils present within the posterior subdomain. PAVE1 functions to stabilize these microtubules to produce the tapered cell posterior. PAVE1 and the newly identified PAVE2 form a complex that binds directly to the microtubule lattice. TbAIR9, which localizes to the entirety of the subpellicular array, is necessary for retaining PAVE1 within the posterior subdomain, and also maintains array-associated proteins in the middle and anterior subdomains of the array. The arrangement of proteins within the array is likely to tune the local properties of the array microtubules and create the asymmetric shape of the cell, which is essential for parasite viability.Author summaryMany parasitic protists use arrays of microtubules that contact the inner leaflet of the plasma membrane, typically known as subpellicular microtubules, to shape their cells into forms that allow them to efficiently infect their hosts. While subpellicular arrays are found in a wide range of parasites, very little is known about how they are assembled and maintained. Trypanosoma brucei, which is the causative agent of human African trypanosomiasis, has an elaborate subpellicular array that produces the helical shape of the parasite, which is essential for its ability to move within crowded and viscous solutions. We have identified a series of proteins that have a range of localization patterns within the array, which suggests that the array is regulated by subdomains of array-associated proteins that may tune the local properties of the microtubules to suit the stresses found at different parts of the cell body. Among these proteins are the first known components of the inter-microtubule crosslinks that are thought to stabilize array microtubules, as well as a potential regulator of the array subdomains. These results establish a foundation to understand how subpellicular arrays are built, shaped, and maintained, which has not previously been appreciated.