Ribbon curling via stress relaxation in thin polymer films.

The procedure of curling a ribbon by running it over a sharp blade is commonly used when wrapping presents. Despite its ubiquity, a quantitative explanation of this everyday phenomenon is still lacking. We address this using experiment and theory, examining the dependence of ribbon curvature on blade curvature, the longitudinal load imposed on the ribbon, and the speed of pulling. Experiments in which a ribbon is drawn steadily over a blade under a fixed load show that the ribbon curvature is generated over a restricted range of loads, the curvature/load relationship can be nonmonotonic, and faster pulling (under a constant imposed load) results in less tightly curled ribbons. We develop a theoretical model that captures these features, building on the concept that the ribbon under the imposed deformation undergoes differential plastic stretching across its thickness, resulting in a permanently curved shape. The model identifies factors that optimize curling and clarifies the physical mechanisms underlying the ribbon's nonlinear response to an apparently simple deformation.

A minimal model of elastic instabilities in biological filament bundles.

We present a model of a system of elastic fibres which exhibits complex, coupled, nonlinear deformations via a connecting elastic spring network. This model can capture physically observed deformations such as global buckling, pinching and internal collapse. We explore the transitions between these deformation modes numerically, using an energy minimization approach, highlighting how supported environments, or stiff outer sheath structures, favour internal structural collapse over global deformation. We then derive a novel analytic buckling criterion for the internal collapse of the system, a mode of structural collapse pertinent in many biological filament bundles such as the optic nerve bundle and microtubule bundles involved in cell abscission.

WASP: a software package for correctly characterizing the topological development of ribbon structures.

We introduce the Writhe Application Software Package (WASP) which can be used to characterisze the topology of ribbon structures, the underlying mathematical model of DNA, Biopolymers, superfluid vorticies, elastic ropes and magnetic flux ropes. This characterization is achieved by the general twist-writhe decomposition of both open and closed ribbons, in particular through a quantity termed the polar writhe. We demonstrate how this decomposition is far more natural and straightforward than artificial closure methods commonly utilized in DNA modelling. In particular, we demonstrate how the decomposition of the polar writhe into local and non-local components distinctly characterizes the local helical structure and knotting/linking of the ribbon. This decomposition provides additional information not given by alternative approaches. As example applications, the WASP routines are used to characterise the evolving topology (writhe) of DNA minicircle and open ended plectoneme formation magnetic/optical tweezer simulations, and it is shown that the decomponsition into local and non-local components is particularly important for the detection of plectonemes. Finally it is demonstrated that a number of well known alternative writhe expressions are actually simplifications of the polar writhe measure.

Catastrophic spine injuries in sports.

Catastrophic spine injuries in sports are rare but tragic events. The sports with the highest risk of catastrophic spinal injuries are football, ice hockey, wrestling, diving, skiing and snowboarding, rugby, cheerleading, and baseball. A common mechanism of injury for all at-risk sports is an axial compression force to the top of the head with the neck slightly flexed. We review common mechanisms of injury and prevention strategies for spine injuries in the at-risk sports.

The influence of lens conditioning on signs and symptoms with new hydrogel contact lenses.

BACKGROUND: Daily disposable contact lenses are considered to be the pinnacle of safe contact lens wear, yet it has been suggested that it takes some period of wear for the lens surface to reach optimal compatibility with the ocular surface. This study assesses the influence of brief treatment with a conditioning drop on the ocular response to new contact lenses over a single day of wear. METHODS: The study was a single-masked, paired (contralateral) comparison of the signs and symptoms with wear of new Acuvue 2 contact lenses pretreated with a conditioning agent containing carboxymethylcellulose (carmellose, CMC) against new lenses inserted directly from the blister pack. Sixty-one subjects participated in the study, of whom 59 were considered eligible for data analysis. Subjects were also divided into symptomatic and asymptomatic lens wearers based on their overall comfort level in lens wear. Symptoms and signs were recorded at lens delivery and following eight hours of wear. RESULTS: A set of slitlamp signs, comprising corneal staining (p <0.05), limbal redness (p <0.05), bulbar conjunctival hyperaemia (p <0.05), bulbar conjunctival staining (p <0.01) and palpebral conjunctival redness (p <0.05) showed small but statistically significant (p <0.05) end-of-day mean values in favour of the lens that was conditioned with the rewetting agent. These data were supported by the proportion of subjects showing lower gradings with conditioned lenses versus unconditioned lenses, as follows: corneal staining (35 per cent versus 12 per cent, p <0.05), limbal redness (43 per cent versus 22 per cent, p <0.05), bulbar conjunctival hyperaemia (50 per cent versus 15 per cent, p <0.05), bulbar conjunctival staining (46 per cent versus 30 per cent, p <0.1) and palpebral conjunctival hyperaemia (28 per cent versus 17 per cent, NS). For those subjects reporting symptoms with lens wear (n=12), there was a statistically significant (p <0.05) preference in terms of comfort as a result of preconditioning. CONCLUSIONS: The results of the investigation suggest that use of a conditioning agent can provide a more physiologically suitable environment for a new lens, thereby reducing the clinical signs associated with lens discomfort. The protocol used here, which is based on a statistical paradigm using standard pictorial grading scales, allows high sensitivity in detecting small changes in ocular parameters.

Synthesis and biological evaluation of 16 beta-pyrrolidinosteroidal derivatives.

The synthesis of some steroidal bisquaternary ammonium substances (compounds 10 and 11), and their in vitro and in vivo neuromuscular blocking action are described in this report. The pyrrolidino functionality was incorporated at both the 3-beta and 16-beta positions of the steroid nucleus to study the importance of the interonium distance between the two quaternary ammonium heads. The 16-beta-pyrrolidino monoquaternary derivatives (compounds 14, 15, 16) were also prepared. The 17-beta-acetoxy bisquaternary derivative compound 11 was found to be more potent than d-tubocurarine (CAS 57-94-3) in in vivo studies. The 17-beta-hydroxy bisquaternary derivative, compound 10, and its 16-beta-pyrrolidino monoquaternary partner, compound 15, were found to be less active as compared to d-tubocurarine in in vitro studies. The monoquaternary compounds 14 and 16 were not tested due to their solubility problems. The intermediate substance, compound 12 was selected by the National Cancer Institute (NCI), Bethesda (USA) for investigation for antineoplastic activity but was found to be inactive.

Effects of different formulations on viability and medium-term storage of Metarhizium anisopliae conidia / Efeitos de diferentes formulações na viabilidade e no armazenamento de conídios de Metarhizium anisopliae a médio prazo

O objetivo deste trabalho foi avaliar os efeitos de diferentes formulações na viabilidade de conídios de Metarhizium anisopliae. No experimento 1, a viabilidade de conídios misturados com oito óleos adjuvantes emulsionáveis (OAE), sete espalhantes adesivos, três óleos vegetais e quatro óleos minerais foi avaliada 24h e 48h depois de espalhados sobre o meio de SDA. Formulações que não apresentaram nenhum efeito adverso sobre a viabilidade dos conídios foram utilizadas no experimento sobre armazenamento. No experimento 2, avaliaram-se os efeitos do armazenamento a 10°C e 27°C durante 40 semanas de conídios de M. anisopliae var. acridum formulados em cinco OAE, em um óleo vegetal e em uma mistura de dois óleos minerais, além de conídios puros e secos. No experimento 1, as formulações em óleo não causaram nenhum efeito negativo na germinação dos conídios. Os tratamentos com os óleos adjuvantes Actipron®, Ashlade® e Codacide® proporcionaram níveis de germinação semelhantes aos obtidos com óleos minerais e vegetais, 24h após a incubação. O espalhante Ethoken® C12 foi letal para os conídios. No experimento 2, a viabilidade conidial de uma mesma formulação declinou com o passar do tempo. A viabilidade foi mantida acima de 90% a 10°C em todas os formulantes testados. A formulação com Ashlade® (OAE) proporcionou níveis de germinação semelhantes aos obtidos com a mistura Shellsol e Ondina, a 10°C e 27°C durante 40 semanas. Logo, OAE podem ser usados para formular conídios de M. anisopliae sem nenhum efeito adverso na viabilidade dos mesmos.

The aim of this work was to evaluate the effects of different formulations on the viability of Metarhizium anisopliae conidia. In a first experiment, the viability of conidia mixed with eight emulsifiable adjuvant oils (EAO), seven wetter/spreaders, three vegetable oils and four mineral oils was evaluated 24h and 48h after spreading over SDA medium surface. Some formulations, which did not present any adverse effect on conidial viability in the first 24h of incubation, were recommended for the medium-term storage experiment. In a second experiment, the effects of different formulations on medium-term storage (40 weeks) of M. anisopliae var. acridum conidia were evaluated at 10°C and 27°C. Five EAO, one vegetable oil, a mixture of mineral oils and pure dry conidia were tested. In the experiment 1, the oil formulations did not cause any negative effect on conidial germination. The treatments with the adjuvant oils Actipron®, Ashlade® and Codacide® gave germination levels equal to mineral and vegetable oils after 24h of incubation. The wetter/spreader Ethoken® C12 was lethal to conidia. All tested emulsifiable adjuvant oil-based formulations were compatible to the conidia as the oil-based formulations after 48h of incubation. In the experiment 2, conidial viability within the same formulation declined over time. Conidial viability was maintained above 90% at 10°C in all tested formulants. The conidial suspension with Ashlade® gave equal germination levels to Shellsol plus Ondina, when stored at 10°C and 27°C for 40 weeks. Thus EAO can be used to formulate M. anisopliae conidia without adverse effects on viability.