Self-shaping of oil droplets via the formation of intermediate rotator phases upon cooling.

Revealing the chemical and physical mechanisms underlying symmetry breaking and shape transformations is key to understanding morphogenesis. If we are to synthesize artificial structures with similar control and complexity to biological systems, we need energy- and material-efficient bottom-up processes to create building blocks of various shapes that can further assemble into hierarchical structures. Lithographic top-down processing allows a high level of structural control in microparticle production but at the expense of limited productivity. Conversely, bottom-up particle syntheses have higher material and energy efficiency, but are more limited in the shapes achievable. Linear hydrocarbons are known to pass through a series of metastable plastic rotator phases before freezing. Here we show that by using appropriate cooling protocols, we can harness these phase transitions to control the deformation of liquid hydrocarbon droplets and then freeze them into solid particles, permanently preserving their shape. Upon cooling, the droplets spontaneously break their shape symmetry several times, morphing through a series of complex regular shapes owing to the internal phase-transition processes. In this way we produce particles including micrometre-sized octahedra, various polygonal platelets, O-shapes, and fibres of submicrometre diameter, which can be selectively frozen into the corresponding solid particles. This mechanism offers insights into achieving complex morphogenesis from a system with a minimal number of molecular components.European Research Council (Grant ID: EMATTER 280078), European networks COST MP 1106 and 1305 and the capacity building project BeyondEverest of the European Commission (Grant ID: 286205)This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nature1618

Fractionation of cellulose nanocrystals : enhancing liquid crystal ordering without promoting gelation

Colloids of electrically charged nanorods can spontaneously develop a fluid yet ordered liquid crystal phase, but this ordering competes with a tendency to form a gel of percolating rods. The threshold for ordering is reduced by increasing the rod aspect ratio, but the percolation threshold is also reduced with this change; hence, prediction of the outcome is nontrivial. Here, we show that by establishing the phase behavior of suspensions of cellulose nanocrystals (CNCs) fractionated according to length, an increased aspect ratio can strongly favor liquid crystallinity without necessarily influencing gelation. Gelation is instead triggered by increasing the counterion concentration until the CNCs lose colloidal stability, triggering linear aggregation, which promotes percolation regardless of the original rod aspect ratio. Our results shine new light on the competition between liquid crystal formation and gelation in nanoparticle suspensions and provide a path for enhanced control of CNC self-organization for applications in photonic crystal paper or advanced composites

International consensus on the most useful physical examination tests used by physiotherapists for patients with headache: A Delphi study

Background: A wide range of physical tests have been published for use in the assessment of musculoskeletal dysfunction in patients with headache. Which tests are used depends on a physiotherapist's clinical and scientific background as there is little guidance on the most clinically useful tests. Objectives: To identify which physical examination tests international experts in physiotherapy consider the most clinically useful for the assessment of patients with headache. Design/methods: Delphi survey with pre-specified procedures based on a systematic search of the literature for physical examination tests proposed for the assessment of musculoskeletal dysfunction in patients with headache. Results: Seventeen experts completed all three rounds of the survey. Fifteen tests were included in round one with eleven additional tests suggested by the experts. Finally eleven physical examination tests were considered clinically useful: manual joint palpation, the cranio-cervical flexion test, the cervical flexion-rotation test, active range of cervical movement, head forward position, trigger point palpation, muscle tests of the shoulder girdle, passive physiological intervertebral movements, reproduction and resolution of headache symptoms, screening of the thoracic spine, and combined movement tests. Conclusions: Eleven tests are suggested as a minimum standard for the physical examination of musculoskeletal dysfunctions in patients with headache

The United States COVID-19 Forecast Hub dataset

Academic researchers, government agencies, industry groups, and individuals have produced forecasts at an unprecedented scale during the COVID-19 pandemic. To leverage these forecasts, the United States Centers for Disease Control and Prevention (CDC) partnered with an academic research lab at the University of Massachusetts Amherst to create the US COVID-19 Forecast Hub. Launched in April 2020, the Forecast Hub is a dataset with point and probabilistic forecasts of incident cases, incident hospitalizations, incident deaths, and cumulative deaths due to COVID-19 at county, state, and national, levels in the United States. Included forecasts represent a variety of modeling approaches, data sources, and assumptions regarding the spread of COVID-19. The goal of this dataset is to establish a standardized and comparable set of short-term forecasts from modeling teams. These data can be used to develop ensemble models, communicate forecasts to the public, create visualizations, compare models, and inform policies regarding COVID-19 mitigation. These open-source data are available via download from GitHub, through an online API, and through R packages

Liquid crystals in aqueous ionic micellar solutions: Interfacial instabilities and optical applications

This thesis presents the properties and applications of various liquid crystal (LC)-aqueous ionic surfactant systems. It begins with the study of micellar solubilization of different LCs in aqueous ionic micellar solutions. The analysis of a few hundred μm-sized LC droplets in either nematic or isotropic state (parent droplets) shows a linear decrease of the droplet size over time. During the entire micellar solubilization process, the material transport across a parent droplet’s surface exists in both directions. Numerous aqueous droplets (daughter droplets) start to appear in the parent droplet due to the transport of surrounding aqueous solution into it. The average size of the aqueous daughter droplets and their number density increase over time. But, no daughter LC droplets form in the surrounding aqueous solution due to the transport of LC molecules from the parent LC droplet into it. However, in special cases, depending on the interfacial tension between the parent droplet and its surrounding aqueous solution, the parent droplet may either expel tiny droplets into the surrounding aqueous medium or transform itself into a filament like structure. Furthermore, the material transfer across a parent droplet’s surface generates convective flows around it. In concentrated aqueous surfactant solutions, the convective flows are strong enough to propel the parent droplet itself. The parent LC droplets become completely solubilized and a clear aqueous solution is produced, provided the weight fraction of the LC in the system is not larger than a few percent. The properties of the equilibrium LC-aqueous systems are investigated through shear and small angle neutron scattering experiments. In the second part, the behavior of the smectic droplets in the aqueous micellar solution is presented. A smectic droplet spontaneously produces smectic filaments at the interface with an aqueous solution, which resemble the myelin figures observed in lyotropic lamellar systems. The three-dimensional structure of the smectic-A filaments is studied with the polarizing optical microscopy and the fluorescence confocal polarizing microscopy. The results show that the LC molecules are oriented perpendicular to the surface of the filament and the layers are wrapped around a central disclination line in a concentric cylindrical fashion. Further, the study on the growth and the stability of the smectic-A filaments shows that the freely floating smectic-A filaments are only transient structures and they either transform into discs or break into small smectic droplets. However, it is possible to stabilize the filaments at least for several months, either by confining them in square capillaries or by photo polymerization. In the last part, the optical applications of the smectic filaments are discussed. In the case of the smectic-A filaments, light guiding through the filaments and Whispering Gallery Mode (WGM) lasing in a plane perpendicular to the filaments are presented. Moreover, it is also shown that smectic-C* filaments act as photonic band-gap waveguides