Nutations in growing plant shoots as a morphoelastic flutter instability.

Growing plant shoots exhibit spontaneous oscillations that Darwin observed, and termed 'circumnutations'. Recently, they have received renewed attention for the design and optimal actuation of bioinspired robotic devices. We discuss a possible interpretation of these spontaneous oscillations as a Hopf-type bifurcation in a growing morphoelastic rod. Using a three-dimensional model and numerical simulations, we analyse the salient features of this flutter-like phenomenon (e.g. the characteristic period of the oscillations) and their dependence on the model details (in particular, the impact of choosing different growth models) finding that, overall, these features are robust with respect to changes in the details of the growth model adopted. This article is part of the theme issue 'Topics in mathematical design of complex materials'.

Crawling motility through the analysis of model locomotors: two case studies.

We study model locomotors on a substrate, which derive their propulsive capabilities from the tangential (viscous or frictional) resistance offered by the substrate. Our aim is to develop new tools and insight for future studies of cellular motility by crawling and of collective bacterial motion. The purely viscous case (worm) is relevant for cellular motility by crawling of individual cells. We re-examine some recent results on snail locomotion in order to assess the role of finely regulated adhesion mechanisms in crawling motility. Our main conclusion is that such regulation, although well documented in several biological systems, is not indispensable to accomplish locomotion driven by internal deformations, provided that the crawler may execute sufficiently large body deformations. Thus, there is no snail theorem. Namely, the crawling analog of the scallop theorem of low Reynolds number hydrodynamics does not hold for snail-like crawlers. The frictional case is obtained by assuming that the viscous coefficient governing tangential resistance forces, which act parallel and in the direction opposite to the velocity of the point to which they are applied, depends on the normal force acting at that point. We combine these surface interactions with inertial effects in order to investigate the mechanisms governing the motility of a bristle-robot. This model locomotor is easily manufactured and has been proposed as an effective tool to replicate and study collective bacterial motility.

All-optical switching based on inverse Raman scattering in liquid-core optical fibers.

We report on a new platform for all-optical switching based on inverse Raman scattering in liquids. Narrowband switching, which could be suitable for wavelength-division-multiplexed applications, is demonstrated using integrated liquid-core optical fiber infiltrated with both neat liquids (CCl(4) and CS(2)) as well as an organic chromophore (ß-carotene) dissolved in CCl(4). Compared to standard glass optical fibers, these liquids have much larger Raman loss coefficients, which help reduce the pump power by at least an order of magnitude. Further improvements can be expected with the development of highly soluble organic compounds possessing large Raman cross sections.

Elastic energies for nematic elastomers.

We discuss several elastic energies for nematic elastomers and their small strain expansions both in the regime of large director rotations, and in the case that director changes are small. We propose two fully non-linear model anisotropic energies and compare the behavior they predict with the currently available experimental evidence.

Optimal strokes for axisymmetric microswimmers.

We present a theory for low-Reynolds-number axisymmetric swimmers and a general strategy for the computation of strokes of maximal efficiency. An explicit equation characterizing optimal strokes is derived, and numerical strategies to obtain solutions are discussed. The merits of this approach are demonstrated by applying it to two concrete examples: the three linked spheres of Najafi and Golestanian and the pushmepullyou of Avron, Kenneth, and Oakmin.

Critical voltages and blocking stresses in nematic gels : dynamics of director rotation for nematic elastomers under electro-mechanical loads.

We present a model of the dynamics of director rotation in nematic gels under combined electro-mechanical loading. Focusing on a model specimen, we describe the critical voltages that must be exceeded to achieve director reorientation, and the blocking stresses that prevent alignment of the nematic director with the applied electric field. The corresponding phase diagram shows that the dynamic thresholds defined above are different from those predicted on the sole basis of energetics. Multistep loading programs are used to explore the energy landscape of our model specimen, showing the existence of multiple local minima under the same voltage and applied stress. This leads us to conclude that hysteresis should be expected in the electro-mechanical response of nematic gels.

Corn fiber oil lowers plasma cholesterol levels and increases cholesterol excretion greater than corn oil and similar to diets containing soy sterols and soy stanols in hamsters.

The aims of this study were to compare the cholesterol-lowering properties of corn fiber oil (CFO) to corn oil (CO), whether the addition of soy stanols or soy sterols to CO at similar levels in CFO would increase CO's cholesterol-lowering properties, and the mechanism(s) of action of these dietary ingredients. Fifty male Golden Syrian hamsters were divided into 5 groups of 10 hamsters each, based on similar plasma total cholesterol (TC) levels. The first group of hamsters was fed a chow-based hypercholesterolemic diet containing either 5% coconut oil + 0.24% cholesterol (coconut oil), 5% CO, 5% CFO, 5% CO + 0.6% soy sterols (sterol), or 5% CO + 0.6% soy stanols (stanol) in place of the coconut oil for 4 weeks. The stanol diet significantly inhibited the elevation of plasma TC compared to all other dietary treatments. Also, the CFO and sterol diets significantly inhibited the elevation of plasma TC compared to the CO and coconut oil diets. The CFO, sterol, and stanol diets significantly inhibited the elevation of plasma non-high density lipoprotein cholesterol compared to the CO and coconut oil diets. The stanol diet significantly inhibited the elevation of plasma high density lipoprotein cholesterol (HDL-C) compared to all other dietary treatments. The sterol diet significantly inhibited the elevation of plasma HDL-C compared to the CO and coconut oil diets, whereas the CFO diet significantly inhibited the elevation of plasma HDL-C compared to the coconut oil diet only. No differences were observed between the CFO and CO for plasma HDL-C. There were no differences observed between groups for plasma triglycerides. The CO and CFO diets had significantly less hepatic TC compared to the coconut oil, sterol, and stanol diets. The CO and CFO diets had significantly less hepatic free cholesterol compared to the sterol and stanol diets but not compared to the coconut oil diet; whereas the coconut oil and sterol diets had significantly less hepatic free cholesterol compared to the stanol diet. The CFO, sterol, and stanol diets excreted significantly more fecal cholesterol compared to the coconut oil and CO diets. In summary, CFO reduces plasma and hepatic cholesterol concentrations and increases fecal cholesterol excretion greater than CO through some other mechanism(s) in addition to increase dietary sterols and stanols-possibly oryzanols.

Single-dose irradiation for the prevention of heterotopic ossification after total hip arthroplasty. A comparison of doses of five hundred and fifty and seven hundred centigray.

One hundred and seven hips (ninety-four patients) that had risk factors associated with the development of heterotopic ossification after total hip arthroplasty were treated with a single dose of radiation after the operation in an attempt to prevent the formation of heterotopic bone. A study was conducted to compare the efficacy of a single dose of 550 centigray (nineteen hips) with that of a single dose of 700 centigray (eighty-eight hips). Heterotopic ossification developed in twelve (63 per cent) of the nineteen hips that were treated with 550 centigray; grades 1, 2, and 3, according to the classification of Brooker et al., developed in four hips each. Two of the patients who received 550 centigray were symptomatic. Heterotopic ossification developed in nine (10 per cent) of the eighty-eight hips that were treated with 700 centigray; the lesion was grade 1 in six, grade 2 in one, and grade 3 in two. None of the patients who received 700 centigray were symptomatic. We concluded that single-dose irradiation consisting of 550 centigray is inadequate for the prevention of heterotopic ossification in high-risk patients after total hip arthroplasty. We recommend a dose of 700 centigray as effective prophylaxis for these patients.

Alcohol use, self-esteem, depression, and suicidality in high school students.

In this study of both high school and college students under 21 years of age, it was found that alcohol use and misuse was positively associated with depression, as expected, but also with self-esteem, opposite to what was expected. It was also found that alcohol use and misuse were associated with depression in college students 21 years of age and older.

Tocainide: a severe adverse reaction.

Tocainide is a primary analog of lidocaine with antiarrhythmic properties used to treat ventricular rhythm disorders. A 76-year-old man with benign paroxysmal premature ventricular contractions was treated with tocainide and developed a generalized maculopapular lupoid eruption, bleeding from the lips and gingivae, vertigo, gross tremors of the extremities, fever, and short-term memory loss, which required hospitalization. The patient recovered slowly over three months with no permanent sequelae after discontinuing the drug and receiving rigorous supportive care. His excellent physical status and absence of concomitant illness contributed to an uneventful recovery. Tocainide is a potent cardioactive drug with a long biological half-life and should be used with caution.