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Objetivo: Caracterizar la práctica y migración de actividad física (AF) en personas activas durante la pandemia de COVID-19. Diseño: Estudio observacional transversal de una encuesta latinoamericana. Escenario: Se aplicó una encuesta online en formato Google Forms entre junio a agosto de 2020 a través de las redes sociales. La encuesta consistió en características generales, del encierro y relacionadas con la AF. Sujetos: Participaron 2134 personas (33,6% hombres), edad media 30,7 ±9,2 años), 95,2% con educación superior, 74% normopeso, 60,8% confinamiento voluntario y 39,2% obligatorio. Resultados: Pre-pandemia hombres realizaban 217,92, y las mujeres 199,78 min/semana, post-pandemia los hombres bajaron a 168.34 y las mujeres a 176.70 min/semana. Los hombres pre pandemia tuvieron una mayor proporción de cumplimiento de la recomendación OMS (77,3% vs 69,4%, p = 0,001). Con respecto a las migraciones del tipo de AF en hombres se observó una reducción de actividades al aire libre, deportes de equipos y aumento de AF el hogar, en mujeres se observa una disminución de actividades al aire libre y deportes en equipos y un aumento en la práctica de clases de fitness, yoga y AF en el hogar. Finalmente, al asociar el cumplimiento de la AF durante el confinamiento esta se asocia a ser mujer y a mayores semanas de confinamiento. Conclusión: Las personas físicamente activas, durante el confinamiento, disminuyeron los minutos de AF, migran a actividades dentro del hogar, mientras que el cumplimiento de la AF se asocia con ser mujer y mayor número de semanas de cuarentena. Abstract. Purpose: The study aims to characterize the practice and migration of physical activity in active people during the COVID-19 pandemic. Design: Cross-sectional observational study of a Latin American survey. Setting: An online survey in Google Forms format was applied between June and July 2020 through social networks. The survey consisted of general characteristics, characteristics of confinement, and characteristics related to physical activity. Subjects: 2134 people participated (33.6% male, the mean age was 30.7 ± 9.2 years), 95.2% with higher education, 74% were normal weight, 60.8% in voluntary lockdown, and 39.2% mandatory lockdown. Results: Pre-pandemic men did 217.92 min/week, and women 199.78 min/week; post-pandemic men declined to 168.34 min/week, and women to 176.70 min/week. Men pre-pandemic, had a higher proportion of compliance the WHO recommendation (77.3% vs 64.9% p =0.001). Regarding, physical activity migrations, men decreased in outside activities, team sports and increase in home physical activity, in women decreased in outside activities, team sports and an increased in fitness classes, yoga and home physical activity. Finally, when associating compliance with physical activity during confinement, it is associated with being a woman and with long weeks of confinement. Conclusion: The physically active people, despite the confinements, remain like this in the four countries evaluated; only changes are observed in the type of physical activity and the frequency of weekly sessions, not affecting their physical condition levels according to self-report.

International audience; Indentation is a standard, widely used technique in mechanical assays and theoretical analysis. It unveils the fundamental modes of deformation and predicts the response of the material under more complex loads. Here we present an experimental setup for testing thin-film materials by studying the lateral indentation of a narrow opening cut into a film, triggering a cascade of buckling events. The force response F is dominated by bending and stretching effects for small displacements and slowly varies with indenter displacement $F\sim d^{2/5}$ , to finally reach a wrinkled state that results in a robust nonlinear asymptotic relation, $F\sim d^4$. Experiments with films of various thicknesses and material properties, and numerical simulations confirm our analysis and help to define an order parameter that accounts for the different response regimes observed in experiments and simulations.

The superiority of many natural surfaces at resisting soft, sticky biofoulants have inspired the integration of dynamic topography with mechanical instability to promote self-cleaning artificial surfaces. The physics behind this novel mechanism is currently limited to elastic biofoulants where surface energy, bending stiffness and topographical wavelength are key factors. However, the viscoelastic nature of many biofoulants causes a complex interplay between these factors with time-dependent characteristics such as material softening and loading rate. Here, we enrich the current elastic theory of topographic de-adhesion using analytical and finite-element models to elucidate the nonlinear, time-dependent interaction of three physical, dimensionless parameters: biofoulant’s stiffness reduction, the product of relaxation time and loading rate, and the critical strain for short-term elastic de-adhesion. Theoretical predictions, in good agreement with numerical simulations, provide insight into tuning these control parameters to optimize surface renewal via topographic de-adhesion in the viscoelastic regime.

Antecedentes: La estenosis de uretra es una entidad urológica que se presenta con relativa frecuencia, siendo una causa común de síntomas urinarios bajos (SUOB) con una prevalencia del 0.6%. En la actualidad existe controversia acerca de la modalidad de energía como factor de riesgo para el desarrollo de estenosis de uretra. Diversos autores han publicado datos contradictorios sobre la estenosis de uretra post resección transuretral de próstata (RTUP). Material y métodos: Se revisaron los expedientes de los pacientes sometidos a RTUP bipolar y monopolar en el Hospital General de Occidente en el período de 1 de enero de 2018 al 31 de diciembre del 2018, se investigó la cantidad de pacientes con presencia de sintomatología urinaria pos-RTUP; determinada por la presencia de sintomatología moderada (>8 puntos) en el cuestionario IPSS (International Prostate Symptom Score) y la determinación de estenosis de uretra mediante uretrograma retrogrado o el registro de haber sido sometidos a uretrotomía interna posterior a la RTUP. El objetivo principal fue determinar la incidencia de estenosis de uretra en pacientes sometidos a RTUP en el Hospital General de Occidente en el periodo comprendido del 1 de enero de 2018 al 31 de diciembre de 2018. Resultados: Se revisaron los expedientes de 113 pacientes, asignados en 2 grupos de pacientes de acuerdo con la modalidad de energía utilizada; energía monopolar (A) 59 pacientes (52.2%) y energía bipolar (B) 54 pacientes (47.8%), se analizaron 16 variables; 8 categóricas y 8 continuas. Se encontró una incidencia de 6.7% de estenosis de uretra en el grupo de energía monopolar y un 5.5% de estenosis de uretra en el grupo de energía bipolar, no se encontró un aumento significativo en la incidencia de estenosis en el grupo de energía bipolar. Conclusiones: Al comparar cada una de las variables de manera aislada, solo la duración de la sonda se asoció de manera estadísticamente significativa (p

Physical activity during childhood and adolescence favors brain development and cognitive functioning, particularly the executive functions. This study aimed to assess potential associations between anthropometric parameters, physical activity, physical fitness, and executive functions among elementary school children returning to school after the COVID-19 lockdown in Chile. School-age male and female participants (n = 90; age, 10–12 years) participated in the study. To determine the association between variables, a multivariable linear regression analysis was performed. Higher fat-related anthropometric indexes were associated with lower working memory, cognitive flexibility, planning, and attention (r = −0.55 to −0.22; p = 0.031 to

There is a close relationship between the development of complex motor skills and executive functions during childhood. This study aimed to analyze the differences in different dimensions of executive functions in children practicing an open-skill sport (handball) and a closed-skill sport (athletics) and controls who did not participate in sports activities after a 12-week intervention period. School-aged male and female subjects (n = 90; mean ± standard deviation = 11.45 ± 0.68 years) participated in a non-randomized controlled study. Data analysis was performed using the STATA V.15 statistical software. The athletics intervention promoted semantic fluency (p = 0.007), whereas handball increased inhibition (p = 0.034). Additionally, physical activity improved in both intervention groups (p = < 0.001), whereas sprint performance improved in the handball group following intervention (p = 0.008), lower body muscular power improved in athletics (p = 0.04), and evidence of improvement in upper body muscular strength was noted in handball (p = 0.037). In turn, an increase in the Physical Activity Questionnaire for older Children score showed an association with the Standard Ten scores of executive functions. In conclusion, compared to controls, both athletics and handball induced meaningful improvements in physical activity and executive functions. However, sport-specific adaptations were noted after athletics (i.e., semantic fluency and lower body muscular power) and handball (i.e., inhibition, sprint, and upper-body muscular strength).

Executive function is among the most affected cognitive dimensions in depression. Physical exercise may improve executive function (e.g., working memory, inhibition, cognitive flexibility), although this is without consensus on adults with depression. Through this systematic review, we aim to elucidate the effects of physical exercise programs on executive functions in adults with depression. The literature search was performed in four relevant electronic databases, combining keywords and medical subject headings, from inception until September 2022. Controlled interventions, involving adults with depression, and reporting working memory, inhibition, and/or cognitive flexibility pre-post-intervention data, were considered includable. Results from meta-analyses included effect size (ES, i.e., Hedges’ g) values reported with 95% confidence intervals (95%CIs), with p set at ≤0.05. Seven studies were included, including 202 men and 457 women (age: 21.0–51.2 years; mild–moderate depression). For working memory, a small favoring effect was observed in the experimental groups compared with controls (ES = 0.33, 95%CI = 0.04–0.61; p = 0.026; I2 = 64.9%). For inhibition, physical exercise had a small favoring non-significant effect compared with controls (ES = 0.28, 95%CI = −0.17–0.74; p = 0.222; I2 = 72.4%). Compared with the control group, physical exercise had a trivial effect on cognitive flexibility (ES = 0.09, 95%CI = −0.21–0.39; p = 0.554; I2 = 68.4%). In conclusion, physical exercise interventions may improve working memory behavioral measures in adults with mild-to-moderate depression when compared with active and passive control conditions. However, the reduced number of available high-quality studies precludes more lucid conclusions.

Physical exercise is a low-cost and easy-to-implement therapeutic option proposed to reduce the negative effect of depression on the executive function cognitive dimension, including working memory, inhibition, and cognitive flexibility. Although a considerable amount of scientific literature on the topic is currently available, the effects of physical exercise interventions on the executive functions in adults with depression remain unclear. The aim of this review protocol is to synthesize the effects of physical exercise interventions on executive functions in adults with depression. Databases including Web of Science, PubMed, Scopus, and EBSCO will be searched for studies by combining keywords and different medical subject headings to identify and evaluate the relevant studies from inception up to September 2022. This study will consider longitudinal studies (duration, ≥3 weeks) with a minimum of one experimental group and pre- and post-intervention measurements involving adults with depression aged 18–65 years. Studies will be included if these reported ≥1 measures of executive function, including dimensions of working memory, inhibition, and cognitive flexibility. The Physiotherapy Evidence Database (PEDro) scale will be used to assess the methodological quality of studies. The DerSimonian and Laird random-effects model will be used for meta-analyses, with effect size (ES, i.e., Hedges’ g) values reported with 95% confidence intervals (95% CIs), and p ≤ 0.05 will indicate statistical significance. The ES values will be calculated for working memory, inhibition, and cognitive flexibility in the experimental and control groups before and after the intervention program. Our results can help professionals and stakeholders in making better evidence-based decisions regarding the implementation of physical exercise programs in adults with depression and providing relevant information to facilitate the functional performance of this population in complex daily tasks where executive functions are essential. No ethical approval is required for this study. PROSPERO registration number: CRD42022358339.

Exercise programs of moderate-to-vigorous intensity have been shown to improve the cognitive performance of older people. However, the specific effects of sports-based exercise programs on cognitive performance, particularly executive functions, remain unclear. Therefore, the purpose of this study is to clarify the effects of sports-based exercise programs on executive functions in older adults using a systematic review and meta-analysis of the scientific literature. A systematic review was conducted between 1 March and 1 July 2022, to look for published scientific evidence that analyzed different sports programs that may have affected executive function in healthy older adults. Longitudinal studies, which assessed the effects of sports interventions on healthy older adults, were identified through a systematic search of the four principal electronic databases: Web of Science, PubMed, Scopus, and EBSCO. A total of nine studies with a total of 398 subjects met the inclusion criteria and were classified based on one or more of the following categories: working memory, inhibition, and cognitive flexibility. The DerSimonian and Laird random-effects model was performed using the Comprehensive Meta-Analysis software to facilitate the analysis of the studies. Statistical significance was set at p ≤ 0.05. In terms of working memory, a small but positive significant effect was noted for the intervention group compared to the control group (effect size (ES) = 0.35, 95% confidence interval (CI) = 0.04–0.67; p = 0.029; I2 = 36.7%); in terms of inhibition, the intervention had a small favoring but no significant effect compared to the control group (ES = 0.20, 95% CI = −0.42–0.84; p = 0.517; I2 = 78.8%); and in terms of cognitive flexibility, the intervention had a small favoring but no significant effect compared to the control group (ES = 0.39, 95% CI = −0.11–0.89; p = 0.131; I2 = 75.5%). Our findings suggest that healthy older adults should be encouraged to participate in sports to improve their working memory; however, more studies are required in this area to reach more robust conclusions. This systematic review was registered with the International Prospective Register of Systematic Reviews (registration number: CRD42022284788).

While important research has been focused on developing surfaces that do not wet, some textures with high-wetting resistance are familiar in other applications in which the opposite is needed. A multivalued surface, common in most fabrics or meshes, allows the invading gas-liquid interface to support relatively high imposed pressures and plays a key role in producing topographic elements that avoid wetting. Here we study experimentally and theoretically the critical pressure needed to move a liquid through a network of pores and show that, for small aperture size, wetting and leaking are typical first-order transitions, with a singular behavior at the omniphobic/omniphilic limit (θc = π/2).

Natural surfaces excel in self-renewal and preventing bio-fouling, while synthetic materials placed in contact with complex fluids quickly foul1,2. We present a novel biophysics-inspired mechanism3,4 for surface renewal using actuating surface topography, generated by wrinkling. We calculate a critical surface curvature, given by an intrinsic characteristic length scale of the fouling layer that accounts for its effective flexural or bending stiffness and adhesion energy, beyond which surface renewal occurs. The effective bending stiffness includes the elasticity and thickness of the fouling patch, but also the boundary layer depth of the imposed wrinkled topography. The analytical scaling laws are validated using finite-element simulations and physical experiments. Our data span over five orders of magnitude in critical curvatures and are well normalized by the analytically calculated scaling. Moreover, our numerics suggests an energy-release mechanism whereby stored elastic energy in the fouling layer drives surface renewal. The strategy is broadly applicable to any surface with tunable topography and fouling layers with elastic response.

The inner surfaces of arteries and veins are naturally anti-thrombogenic, whereas synthetic materials placed in blood contact commonly experience thrombotic deposition that can lead to device failure or clinical complications. Presented here is a bioinspired strategy for self-cleaning anti-thrombotic surfaces using actuating surface topography. As a first test, wrinkled polydimethylsiloxane planar surfaces are constructed that can repeatedly transition between smooth and wrinkled states. When placed in contact with blood, these surfaces display markedly less platelet deposition than control samples. Second, for the specific application of prosthetic vascular grafts, the potential of using pulse pressure, i.e. the continual variation of blood pressure between systole and diastole, to drive topographic actuation was investigated. Soft cylindrical tubes with a luminal surface that transitioned between smooth and wrinkled states were constructed. Upon exposure to blood under continual pressure pulsation, these cylindrical tubes also showed reduced platelet deposition versus control samples under the same fluctuating pressure conditions. In both planar and cylindrical cases, significant reductions in thrombotic deposition were observed, even when the wrinkles had wavelengths of several tens of μm, far larger than individual platelets. We speculate that the observed thrombo-resistance behavior is attributable to a biofilm delamination process in which the bending energy within the biofilm overcomes interfacial adhesion. This novel strategy to reduce thrombotic deposition may be applicable to several types of medical devices placed into the circulatory system, particularly vascular grafts.

The use of implants carries on a series of problems, among them infections, poor biocompatibility, high levels of cytotoxicity, and significant mechanical differences between implants and host organs that promote stress shielding effects. These problems indicate that the materials used to make implants must meet essential requirements and high standards for implantations to be successful. In this work, we present the synthesis, characterization and evaluation of the antibiofilm, mechanical, and thermal properties, and cytotoxic effect of a nanocomposite-based scaffold on polyurethane (PU) and gold nanoparticles (AuNPs) for soft tissue applications. The effect of the quantity of AuNPs on the antibacterial activity of nanocomposite scaffolds was evaluated against Staphylococcus epidermidis and Klebsiella spp., with a resulting 99.99% inhibition of both bacteria using a small quantity of nanoparticles. Cytotoxicity was evaluated with the T10 1/2 test against fibroblast cells. The results demonstrated that porous nanogold/PU scaffolds have no toxic effects on fibroblast cells to the 5 day exposition. With respect to mechanical properties, stress-strain curves showed that the compressive modulus and yield strength of PU scaffolds were significantly enhanced by AuNPs (by at least 10 times). This is due to changes in the arrangement of hard segments of PU, which increase the stiffness of the polymer. Thermogravimetric analysis showed that the degradation onset temperature rises with an increase in the quantity of AuNPs. These properties and characteristics demonstrate that porous nanogold/PU scaffolds are suitable material for use in soft tissue implants.

ANTECEDENTES: los quistes de vesícula seminal son infrecuentes. Se estima una incidencia de 0.005% y se diagnostican con mayor frecuencia de la segunda a la cuarta décadas de la vida. La mayoría de los casos se manifiesta con lesión única, aunque pueden encontrarse múltiples lesiones. La presentación puede ser congénita o adquirida; la primera se asocia con alteraciones del conducto mesonéfrico (conducto de Wolf). En dos terceras partes de los casos se ha descrito agenesia renal ipsilateral (síndrome de Zinner). La forma adquirida se asocia con causas obstructivas, quizá infecciosas.CASO CLÍNICO: paciente masculino de 43 años de edad, que acudió a consulta por síntomas urinarios bajos, de vaciamiento, acompañados de hematoespermia, tenesmo rectal y dolor pélvico.DISCUSIÓN: en pacientes con quistes en la vesícula seminal se han observado formas y grados variables en su manifestación clínica, algunos cursan asintomáticos y otros con síntomas urinarios obstructivos, infecciones urinarias, hematuria, hematoespermia e incluso infertilidad. Cuando los quistes son de mayor tamaño puede haber síntomas gastrointestinales: estreñimiento y tenesmo rectal. Debido a que estos quistes son infrecuentes, no existe consenso actual acerca de la conducta a seguir y el tratamiento. Hoy el tratamiento se reserva para pacientes sintomáticos; diversos artículos proponen el abordaje endoscópico, como la primera opción de tratamiento, considerando a la vesiculoscopia como el patrón de referencia para el tratamiento de los quistes de la vesícula seminal.PALABRAS CLAVE: quiste, vesícula seminal, vesiculoscopia, hematoespermia, quistes genitourinarios.

Fil: Ribba, Laura Gabriela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Fisica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisica de Buenos Aires; Argentina

The buckling and wrinkling of thin films has recently seen a surge of interest among physicists, biologists, mathematicians, and engineers. This activity has been triggered by the growing interest in developing technologies at ever-decreasing scales and the resulting necessity to control the mechanics of tiny structures, as well as by the realization that morphogenetic processes, such as the tissue-shaping instabilities occurring in animal epithelia or plant leaves, often emerge from mechanical instabilities of cell sheets. Although the most basic buckling instability of uniaxially compressed plates was understood by Euler more than two centuries ago, recent experiments on nanometrically thin (ultrathin) films have shown significant deviations from predictions of standard buckling theory. Motivated by this puzzle, we introduce here a theoretical model that allows for a systematic analysis of wrinkling in sheets far from their instability threshold. We focus on the simplest extension of Euler buckling that exhibits wrinkles of finite length—a sheet under axisymmetric tensile loads. The first study of this geometry, which is attributed to Lamé, allows us to construct a phase diagram that demonstrates the dramatic variation of wrinkling patterns from near-threshold to far-from-threshold conditions. Theoretical arguments and comparison to experiments show that the thinner the sheet is, the smaller is the compressive load above which the far-from-threshold regime emerges. This observation emphasizes the relevance of our analysis for nanomechanics applications.

We address the partial wetting of liquid drops on ultrathin solid sheets resting on a deformable foundation. Considering the membrane limit of sheets that can relax compression through wrinkling at negligible energetic cost, we revisit the classical theory for the contact of liquid drops on solids. Our calculations and experiments show that the liquid-solid-vapor contact angle is modified from the Young angle, even though the elastic bulk modulus (E) of the sheet is so large that the ratio between the surface tension γ and E is of molecular size. This finding establishes a new type of “soft capillarity” that stems from the bendability of thin elastic bodies rather than from material softness. We also show that the size of the wrinkle pattern that emerges in the sheet is fully predictable, thus resolving a puzzle noticed in several previous attempts to model “drop-on-a-floating-sheet” experiments, and enabling a reliable usage of this setup for the metrology of ultrathin films.

Polyethylene nanocomposites containing silver nanoparticles with antimicrobial properties were produced via in situ polymerization. The silver nanoparticles were added together with the catalytic system (metallocene catalyst and methylaluminoxane, MAO, as cocatalyst) directly to the reactor. The polymerization activity did not present significant changes with the incorporation of the silver nanoparticles in comparison to the homopolymerization without filler. The effect of various silver nanoparticle contents on silver ion release and antimicrobial efficacy against Escherichia Coli were studied. Nanocomposites containing higher nanosilver concentrations (5 wt.%) showed the highest silver ion release, and after 24 h reached 99.99% of efficacy against the bacteria compared with the neat PE. Transmission electron microscopy (TEM) images showed that the nanospheres were well dispersed throughout the polyethylene matrix.

We study the patterns observed in the vicinity of a Faraday instability, in the limit of a very thin layer of viscous fluid. We numerically solve our previous model [N.O. Rojas et al., Phys. Rev. Lett. 104, 187801 (2010)] and compare our predictions to experiments. Our model captures quantitatively the threshold of instability. The direct simulation of our system permits us to predict the patterns observed in experiments.

We derive a set of non-linear amplitude equations that predicts the presence of nonlinear patterns in a vertically oscillated one dimensional viscous fluid layer.

A piece of paper coiled up in a tube hugs the wall in order to minimize its elastic energy. However, a moment's observation shows that the paper fails to make complete contact near its ends. Here, we show that the detached region in the inner part of the coil touches down the tube wall in an angle that is independent of the system size, thickness and stiffness of the surface. This angle is universal for any coiled sheet whose unstressed state is initially flat. Our results show how the shape and stress distribution for this detached region define the geometry and mechanical equilibrium for the rest of the sheet. In particular, we find scaling relations to describe the structure of the outer part of the coil, in contact with the tube wall, as a function of the number of times the sheet is coiled, N .

When a wound heals, as everyone has observed, it contracts, thickens and wrinkles the neighbouring skin, forming a scar. The morphology of the scar depends on the type of wound; an urgent tracheotomy leads to a very different scar than a carefully planned face lift. The surgical challenges of intrusive procedures such as removal of skin lesions, skin transplantation or grafting, and scar removal are complicated by the complex geometry and stress states in different parts of the body. We show that, for relatively general conditions, the nature of the localisation of the scar is determined by the background tension of the skin which can arrest the formation of wrinkles around a scar. Our physical experiments to simulate this procedure indicate that the region deformed by the defect has a characteristic length scale r * ∼ 1 / τ , where τ is the natural tension of the skin.

We consider two of the simplest problems associated with the packing of a naturally flat thin elastic sheet. Both problems involve packing the sheet into a hollow cylinder; the first considers the partial contact of a cylindrically curved sheet with a cylindrical surface, while the second considers the partial contact of a conically curved sheet with the edge of a cylindrical surface. In each case, we solve the free–boundary problems to determine the shape, response and stability of the confined surfaces. In particular, we show that an exact description of both the cylindrical and conical structures is given by solutions of the Elastica equation, allowing us to present a unified description of a large class of elastic developable surfaces. This includes what is possibly the simplest example of strain localization, occurring at a point and forming one of the constituent elements of a crumpled elastic sheet.

We consider the gravity-induced draping of a 3D object with a naturally flat, isotropic elastic sheet. As the size of the sheet increases, we observe the appearance of new folded structures of increasing complexity that arise because of the competition between elasticity and gravity. We analyze some of the simpler 3D structures by determining their shape and analyzing their response and stability and show that these structures can easily switch between a number of metastable configurations. For more complex draperies, we derive scaling laws for the appearance and disappearance of new length scales. Our results are consistent with commonplace observations of drapes and complement large-scale computations of draping by providing benchmarks. They also yield a qualitative guide to fashion design and virtual reality animation.

Isometric deformations in thin elastic films easily form ridges to connect large flat regions or facets. Depending on the forces applied or the boundary conditions imposed, these ridges can be isometric, with no stretching or "stretching ridges" when bending and stretching are required to relax the elastic energy. Here we study a simple configuration to observe the transition between an isometric ridge to the well-known stretching ridge observed in crumpled films, and obtain the parameters that determine the ridge type. Specifically, we show that the transversal size of a stretching ridge acts as a cutoff length scale: a ridge is isometric if its width is greater than this characteristic length.

We report here a systematic study of the antibacterial behavior of silver nanoparticles coated with fatty acids (oleic: AgNP-O, linoleic: AgNP-L, and palmitic acids: AgNP-P) in water. We have found remarkable differences in their capability to penetrate bacteria cell over a broader range of particle size of ~4–96 nm compared to previously reported work, and a variable toxicity depending on the particles size. Our results indicate that silver nanoparticles stabilized with oleic acid showed clear advantages in antibacterial activity, penetration inside the bacteria cells, cytotoxicity, time effectiveness, efficiency, and stability against light.

We prove that the exact non local equation derived by the present authors for the temporal linear evolution of the surface of a viscous incompressible fluid reduces asymptotically for high viscosity to a second order Mathieu type equation proposed recently by Cerda and Tirapegui. The equation describes a strongly damped pendulum and the conditions of validity of the asymptotic regime are given in terms of the relevant physical parameters.

A crumpled piece of paper is made up of cylindrically curved or nearly planar regions folded along line-like ridges, which themselves pivot about point-like peaks; most of the deformation and energy is focused into these localized objects. Localization of deformation in thin sheets is a diverse phenomenon1,2,3,4,5,6, and is a consequence of the fact7 that bending a thin sheet is energetically more favourable than stretching it. Previous studies8,9,10,11 considered the weakly nonlinear response of peaks and ridges to deformation. Here we report a quantitative description of the shape, response and stability of conical dislocations, the simplest type of topological crumpling deformation. The dislocation consists of a stretched core, in which some of the energy resides, and a peripheral region dominated by bending. We derive scaling laws for the size of the core, characterize the geometry of the dislocation away from the core, and analyse the interaction between two conical dislocations in a simple geometry. Our results show that the initial stages of crumpling (characterized by the large deformation of a few folds) are dominated by bending only. By considering the response of a transversely forced conical dislocation, we show that it is dynamically unstable above a critical load threshold. A similar instability is found for the case of two interacting dislocations, suggesting that a cascade of related instabilities is responsible for the focusing of energy to progressively smaller scales during crumpling.

We derive an exact equation which is nonlocal in time for the linear evolution of the surface of a viscous fluid, and show that this equation becomes local and of second order in an interesting limit. We use our local equation to study Faraday's instability in a strongly dissipative regime and find a new scenario which is the analog of the Rayleigh-Taylor instability. Analytic and numerical calculations are presented for the threshold of the forcing and for the most unstable mode with impressive agreement with experiments and numerical work on the exact Navier-Stokes equations.

Equipe 101 : Nanomagnétisme et électronique de spin; International audience; We report on a method to fabricate laterally modulated Co films using the artificially induced nano-wrinkled surface of a polydimethylsiloxane polymeric film as template. Large area patterning of self-organized parallel wrinkles is formed displaying a submicrometer wavelength. The subsequent deposition of a Co layer on this wavy surface yields a uniaxial magnetic anisotropy imposed by the wrinkles' morphology. Measurement of the remanent magnetization and coercive field as a function of the field angle confirms the uniaxial nature of the anisotropy and reveals a reversal mechanism more complex than pure coherent rotation. The magnetostatic origin of the anisotropy is analyzed.

We study the problem of buckling and postbuckling of a plate under in-plane loads. This system exhibits a complex phase diagram with two distinct regimes: one near the instability for buckling and the other characterized by isometric deformations. Here, we show that the equations of elasticity for this problem can be reduced to the well-known Swift?Hohenberg equation as a leading term in a Galerkin projection. Higher order terms in the expansion are also computed to illustrate the convergence of the analysis.

The wrinkled geometry of thin films is known to vary appreciably as the applied stresses exceed their buckling threshold. Here we derive and analyze a minimal, nonperturbative set of equations that captures the continuous evolution of radial wrinkles in the simplest axisymmetric geometry from threshold to the far-from-threshold limit, where the compressive stress collapses. This description of the growth of wrinkles is different from the traditional post-buckling approach and is expected to be valid for highly bendable sheets. Numerical analysis of our model predicts two surprising results. First, the number of wrinkles scales anomalously with the thickness of the sheet and the exerted load, in apparent contradiction with previous predictions. Second, there exists an invariant quantity that characterizes the mutual variation of the amplitude and number of wrinkles from threshold to the far-from-threshold regime.

Upon release from the anther, pollen grains of angiosperm flowers are exposed to a dry environment and dehydrate. To survive this process, pollen grains possess a variety of physiological and structural adaptations. Perhaps the most striking of these adaptations is the ability of the pollen wall to fold onto itself to prevent further desiccation. Roger P. Wodehouse coined the term harmomegathy for this folding process in recognition of the critical role it plays in the survival of the pollen grain. There is still, however, no quantitative theory that explains how the structure of the pollen wall contributes to harmomegathy. Here we demonstrate that simple geometrical and mechanical principles explain how wall structure guides pollen grains toward distinct folding pathways. We found that the presence of axially elongated apertures of high compliance is critical for achieving a predictable and reversible folding pattern. Moreover, the intricate sculpturing of the wall assists pollen closure by preventing mirror buckling of the surface. These results constitute quantitative structure-function relationships for pollen harmomegathy and provide a framework to elucidate the functional significance of the very diverse pollen morphologies observed in angiosperms.

Thin fluid films can have surprising behavior depending on the boundary conditions enforced, the energy input and the specific Reynolds number of the fluid motion. Here we study the equations of motion for a thin fluid film with a free boundary and its other interface in contact with a solid wall. Although shear dissipation increases for thinner layers and the motion can generally be described in the limit as viscous, inertial modes can always be excited for a sufficiently high input of energy. We derive the minimal set of equations containing inertial effects in this strongly dissipative regime.