Propulsion Mechanisms for Leidenfrost Solids on Ratchets

We propose a model for the propulsion of Leidenfrost solids on ratchets based on viscous drag due to the flow of evaporating vapor. The model assumes pressure-driven flow described by the Navier-Stokes equations and is mainly studied in lubrication approximation. A scaling expression is derived for the dependence of the propulsive force on geometric parameters of the ratchet surface and properties of the sublimating solid. We show that the model results as well as the scaling law compare favorably with experiments and are able to reproduce the experimentally observed scaling with the size of the solid

Trapping Leidenfrost Drops with Crenelations

International audienceDrops placed on very hot solids levitate on a cushion of their own vapor, as discovered by Leidenfrost. This confers to these drops a remarkable mobility, which makes problematic their control and manipulation. Here we show how crenelated surfaces can be used to increase the friction of Leidenfrost drops by a factor on the order of 100, making them decelerate and be trapped on centimetric distances instead of the usual metric ones. We measure and characterize the friction force as a function of the design of the crenelations

The spinning ball spiral

International audienceWe discuss the trajectory of a fast revolving solid ball moving in a fluid of comparable density. As the ball slows down owing to drag, its trajectory follows an exponential spiral as long as the rotation speed remains constant: at the characteristic distance L where the ball speed is significantly affected by the drag, the bending of the trajectory increases, surprisingly. Later, the rotation speed decreases, which makes the ball follow a second kind of spiral, also described in the paper. Finally, the use of these highly curved trajectories is shown to be relevant to sports. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Structural basis of the allergenicity to strawberries due to Fra a 1.02

Strawberry fruits are highly valued due to their flavor, aroma, and benefits for human health. Despite this, 30% of the population with food hypersensitivity also shows adverse reactions to strawberry (Franz-Oberdorf et al, 2016). The FaFra a 1 protein family, homologs of the major birch pollen allergen Bet v 1, is involved in this allergenicity to strawberry. By RNAseq we have identified transcripts for 18 members of the FaFra a 1 family (from 1.01 to 1.18) in strawberry fruits. Although expressed in all tissues analyzed, each family member presents a unique pattern of expression, which suggests functional specialization for each FaFra a 1 protein. FaFra a 1.02 (Fra2 from now on) is the most expressed one in red fruits and is also the most allergenic among the family members tested (Muñoz et al. 2010; Franz- Oberdorf et al, 2016). In order to understand the molecular bases of this allergenicity we crystalized Fra2 and obtained its structure by X-ray diffraction. Fra2 showed a very high structural homology to Bet v 1, and we asked whether the two proteins were recognized by the immune system in a similar way. For this, we generated five different mutant versions of Fra2 in sites described as important for allergenicity in Bet v 1 (Fernandes et al, 2016), and studied their potential allergenicity as well as their crystal structures. Three of the mutants had substitutions in loop 4 (E46R, D48R, E46/48A) and the other two facing the cavity (A141F and Q64W). Compared to Fra2, all the mutants showed a significant reduction in their capacity to be recognized by the serum of patients with allergies to Bet v 1, and their crystal structures revealed conformational changes in the Bet v 1- IgG interaction sites. Together, these results support that Fra2 and Bet v 1 have similar allergenic determinants We hope this research will aid in understanding how human IgGs interact with Fra2 and might help in the development of new cultivars with a lesser allergenic potential.Grants BIO2013-44199R and BES-2014-068723 (MINECO). The authors also acknowledge the support by the Plan Propio from University of Malaga, Campus de Excelencia Internacional de Andalucía

Dexterous Grasping Tasks Generated With an Add-on End Effector of a Haptic Feedback System

The simulation of grasping operations in virtual reality (VR) is required for many applications, especially in the domain of industrial product design, but it is very difficult to achieve without any haptic feedback. Force feedback on the fingers can be provided by a hand exoskeleton, but such a device is very complex, invasive, and costly. In this paper, we present a new device, called HaptiHand, which provides position and force input as well as haptic output for four fingers in a noninvasive way, and is mounted on a standard force-feedback arm. The device incorporates four independent modules, one for each finger, inside an ergonomic shape, allowing the user to generate a wide range of virtual hand configurations to grasp naturally an object. It is also possible to reconfigure the virtual finger positions when holding an object. The paper explains how the device is used to control a virtual hand in order to perform dexterous grasping operations. The structure of the HaptiHand is described through the major technical solutions required and tests of key functions serve as validation process for some key requirements. Also, an effective grasping task illustrates some capabilities of the HaptiHand

Estudo de sistema de refrigeração termoacústica

This work aims to make the experimental study of a thermoacoustic refrigerator in order to observe the essential parameters for its operation. The thermoacoustic refrigeration is a technology which emerged in the 1970s as an alternative solution to classic refrigeration systems that work with steam compression. It has many advantages over traditional technologies in terms of wear, maintenance and pollution and this makes it an economically interesting research topic. There are already many efficient devices in the area of industrial refrigeration for food and natural gas liquefaction and in the area of embedded systems. The operation of such devices consists in converting an acoustic power into a thermal power through the passage of a sound wave throughout a porous structure known as stack. Inside this structure, the gas particles vibrate by effecting a thermodynamic cycle able to recover heat from one side of the stack and supplying it to the other side. Thus, the part is cooling on one side and heating on the other by accumulation of heat. So the goal is to recover the low temperature from the cold side, however this has an influence on the efficiency of the system by heating the cold side. Also cooling the hot side of the machine seems to be a solution to keep a temperature low enough on the cold side. To verify this connection between these two temperatures is the objective of the present study.CEFET/GO - Centro Federal de Educação Tecnológica de GoiásTrabalho de Conclusão de Curso (Graduação)Esse trabalho tem como objetivo fazer o estudo experimental de um refrigerador termoacústico a fim de observar quais são os parâmetros essenciais ao funcionamento deste. A refrigeração termoacústica é uma tecnologia que surgiu nos anos 1970 como uma solução alternativa aos sistemas de refrigeração clássica que funcionam por compressão de vapor. Ela tem muitas vantagens em relação às tecnologias tradicionais em termos de desgaste, manutenção e poluição, o que faz dela um tópico de pesquisa economicamente interessante. Já existem muitos dispositivos eficientes em função na área da refrigeração industrial pela conservação dos produtos e a liquefação de gás natural na saída de poço e na área dos sistemas embarcados. O funcionamento de tais dispositivos consiste em converter uma potência acústica em uma potência térmica graças à passagem de uma onda sonora através de uma estrutura porosa chamada de stack. Dentro dessa peça, as partículas de gás vibram efetuando um ciclo termodinâmico capaz de recuperar o calor de um lado do stack e fornecê-lo ao outro lado. Assim, a peça vai se resfriando de um lado e se aquecendo do outro por acúmulo do calor. Então o objetivo é recuperar a temperatura baixa do lado frio, porém fazer isso tem uma influência sobre a eficiência do sistema por aquecer o lado frio. Daí ventilar o lado quente da máquina parece ser uma solução para manter uma temperatura suficientemente baixa do lado frio. Verificar essa ligação entre essas duas temperaturas é o objetivo do presente estudo

Surgical glues: are they really adhesive?

Objective: The aim of this study is to create a standard test to approve the efficacy of a surgical sealant. An industrial test, the bulge-and-blister test, which is very convenient for measuring adhesion energy, is applied to the surgical field to quantify adhesion of bioadhesives. Methods: Samples were composed of two circular layers of equine pericardium glued by the surgical sealant studied. The sample was fixed to a support with an industrial glue. The support and the bottom layer were perforated in the centre to allow injection of pressurised water. Water was progressively introduced through the hole in the support and the bottom layer to create a blister with constant radius, increasing height and internal pressure during this first step. At a critical pressure, delamination started, the radius and height of the blister increased and the pressure decreased. At this point, the adhesion energy could be determined. The experimental parameters were measured with a pressure sensor and an optical profilometry device for deflection. Results: Adhesion testing was carried out in eight paired equine pericardium samples bonded with a Dermabond® cyanoacrylate glue. The average value of the practical adhesion energy is 2.3Jm−2 with a standard deviation of 1.5Jm−2. Conclusion: Application of the bulge-and-blister test to the surgical field was achieved and allowed a quantification of adhesion of a surgical glue. Such information is essential to compare the different surgical glues presently available. The study of the impact of bonding conditions such as pressure, hygrometry or setting conditions will provide a better understanding of the characteristics of adhesion in the surgical fiel