In the medical field and in soft robotics, flexible devices are required for safe human interaction, while rigid structures are required to withstand the force application and accuracy in motion. ...This paper aims at presenting controllable stiffness mechanisms described in the literature for applications with or without shape-locking performances. A classification of the solutions based on their working principle is proposed. The intrinsic properties of these adaptive structures can be modified to change their mechanical characteristics from a geometrical point of view or equivalent elastic properties (with internal mechanisms or with a change in material properties). These solutions are compared quantitatively, based on selected criteria linked to the medical field as the stiffness range, the activation time and the working conditions. Depending on the application and its requirements, the most suitable solution can be selected following the quantitative comparisons. Several applications of these tunable stiffness structures are proposed and illustrated by examples of the literature.
Liouville theory beyond the cosmological horizon Compère, Geoffrey; Donnay, Laura; Lambert, Pierre-Henry ...
The journal of high energy physics,
03/2015, Volume:
2015, Issue:
3
Journal Article
Peer reviewed
Open access
A
bstract
The dS/CFT correspondence postulates the existence of a Euclidean CFT dual to a suitable gravity theory with Dirichlet boundary conditions asymptotic to de Sitter spacetime. A ...semi-classical model of such a correspondence consists of Einstein gravity with positive cosmological constant and without matter which is dual to Euclidean Liouville theory defined at the future conformal boundary. Here we show that Euclidean Liouville theory is also dual to Einstein gravity with Dirichlet boundary conditions on a fixed timelike slice in the static patch. Intriguingly, the spacetime interpretation of Euclidean Liouville time is the physical time of the static observer. As a prerequisite of this correspondence, we show that the asymptotic symmetry algebra which consists of two copies of the Virasoro algebra extends everywhere into the bulk.
Capillarity in wet granular materials induces cohesion and increases the material strength due to the attractive forces acting on capillary bridges. In the funicular state, water bridges may be not ...only formed between two grains but also binding three or more particles, which breaks the axial symmetry of the liquid bridge. This work presents a fundamental study on capillary forces and rupture behaviours of funicular water bridges between three spherical bodies at equilibrium (or static) configurations. Funicular water clusters are numerically solved by an energy minimization approach. Experimental comparisons are made by measuring capillary forces and these confirm the validity of the numerical solutions. Evolutions of capillary forces and rupture distances are investigated systematically by moving two spheres away from the centre. The fixed water volume condition and the constant mean curvature condition are studied respectively. Comparisons are made between the un-coalesced pendular liquid rings and the coalesced funicular bridge. For a same fixed total water volume, the capillary force is weakened by water bridge coalescence to a funicular bridge when the spheres are packed together, but the situation may vary for different contact angles and inter-particle distances. For the constant mean curvature condition, water bridge coalescence does not alter capillary force significantly when particles are packed closely, but the discrepancy is larger by increasing the gap. Funicular water bridge rupture criteria are also proposed based on the studied configurations. It is observed that in general the transmission from pendular to funicular state extends the rupture distance when it has a relatively high water volume or low air-water pressure difference.
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•Funicular liquid bridges between three spherical particles are numerically solved.•Experimental validation is carried out by measuring capillary force induced by the funicular liquid bridge.•Effects of liquid volume, suction, contact angle and particle separation distance are investigated.•Water bridge coalescence effect (from pendular rings to a funicular cluster) on force and rupture distance is discussed.•Rupture criteria of the studied configuration for liquid volume controlled and constant suction conditions are proposed.
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Flexible instruments, i.e. instruments presenting a great number of degrees of freedom and able to perform snake-like movements when avoiding obstacles, can find a lot of applications in the medical ...field. On the other hand, flexible fluidic actuators, i.e. actuators having a flexible inflatable structure and actuated by fluid, present interesting features regarding medical applications. Therefore, this paper proposes to use these actuators to develop medical flexible instruments.
Firstly, the advantages and drawbacks linked to the use of flexible fluidic actuators are listed and a discussion about the miniaturization of fluidic actuators peripherics (such as valves) is led. Next, a literature review of the existing flexible fluidic actuators is established. It can serve as basis to develop flexible instruments based on these actuators.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The nose of the mammals is responsible for filtering, humidifying, and heating the air before entering the lower respiratory tract. This conditioning avoids, notably, dehydration of the bronchial and ...alveolar mucosa. However, since this conditioning is not perfect, exercising in cold air can induce lung inflammation, both for human and non-human mammals. This work aims to compare the air conditioning in the noses of various mammals during inspiration. We build our study on computational fluid dynamics simulations of the heat exchanges in the lumen of the upper respiratory tract of these mammals. These simulations show that the efficiency of the air conditioning in the nose during inspiration does not relate only to the mass m of the mammal but also to its maximal running speed v. More precisely, the results allow establishing a scaling law relating the efficiency of air conditioning in the nose of mammals to the ratio
. The simulations also correlate the resistance to the flow in the nose to the efficiency of this air conditioning. The obtained scaling law allows predicting the air temperature at the top of the trachea during inspiration for nasal-breathing mammals, and thus notably for humans of various ages.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The RNA helicases DDX5 and DDX17 are members of a large family of highly conserved proteins that are involved in gene-expression regulation; however, their in vivo targets and activities in ...biological processes such as cell differentiation, which requires reprogramming of gene-expression programs at multiple levels, are not well characterized. Here, we uncovered a mechanism by which DDX5 and DDX17 cooperate with heterogeneous nuclear ribonucleoprotein (hnRNP) H/F splicing factors to define epithelial- and myoblast-specific splicing subprograms. We then observed that downregulation of DDX5 and DDX17 protein expression during myogenesis and epithelial-to-mesenchymal transdifferentiation contributes to the switching of splicing programs during these processes. Remarkably, this downregulation is mediated by the production of miRNAs induced upon differentiation in a DDX5/DDX17-dependent manner. Since DDX5 and DDX17 also function as coregulators of master transcriptional regulators of differentiation, we propose to name these proteins “master orchestrators” of differentiation that dynamically orchestrate several layers of gene expression.
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•DDX5/DDX17 and hnRNP H/F regulate splicing by cooperating at GC-rich sequences•DDX5/DDX17 and hnRNP H/F control splicing programs in epithelial cells and myoblasts•A miRNA-mediated negative feedback loop downregulates DDX5/DDX17 in differentiation•DDX5/DDX17 control the expression of master differentiation transcription factors
Dardenne et al. now demonstrate that the multifunctional RNA helicases DDX5 and DDX17 dynamically orchestrate several layers of gene expression during epithelial-to-mesenchymal transition and myogenesis. DDX5 and DDX17 cooperate with heterogeneous nuclear ribonucleoprotein (hnRNP) H/F to control splicing subprograms in epithelial cells and myoblasts. They help to initiate differentiation-specific transcription programs as transcriptional coregulators. These helicases trigger the biogenesis of miRNAs that downregulate DDX5 and DDX17, resulting in splicing switches during differentiation. These data illustrate how different gene-expression steps can be coordinated by single factors during cell differentiation and transcriptome reprogramming.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Fused silica glass is a material with outstanding mechanical, thermal and optical properties. Being a brittle material, it is challenging to shape. In the last decade, the manufacturing of monolithic ...flexible mechanisms in fused silica has evolved with the femtosecond-laser-assisted etching process. However, instrumenting those structures is demanding. To address this obstacle, this article proposes to inscribe a Bragg Grating sensor inside a flexure and interface it with an optical fibre to record the strain using a spectrum analyser. The strain sensitivity of this Bragg Grating sensor is characterized at 1.2 pm/μϵ (1 μϵ = 1 microstrain). Among other applications, deformation sensing can be used to record a force. Its use as a micro-force sensor is estimated. The sensor resolution is limited by our recording equipment to 30 μN over a measurement range above 10 mN. This technology can offer opportunities for surgery applications or others where precision and stability in harsh environments are required.
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Capillary forces are shown to be extremely effective for micro-assembly and pick-and-place processes, especially for their ability to self-align the handled objects. However, in today’s machines, ...micro-objects are submitted to high loads, such as compressions for the electrical testing of the micro-components, or inertial forces coming from the high accelerations of the machines. There, capillary grippers may show some limits. These issues, as well as the difficulty to perform precise visual inspections (due to the tilt of the handled micro-object that can occur after a perturbation, such as the displacement of the gripper), can all be solved by temporarily removing the liquid meniscus. Therefore, we present a novel volume-tuning capillary gripper that provides a solution to these limitations without adding additional significant complexities or changes to the existing pick-and-place machines. A multi-scale prototype was dimensioned and produced by using fast prototyping methods, such as a femtosecond laser-assisted chemical etching process for fused silica. Models bringing a deeper understanding of the subsystems are presented. The proof of concept was extensively tested. Its picking capabilities and enhancements of the handling capabilities during horizontal motions, as well as the repeatability of the tuning of the volume of liquid, are presented.
The rise of soft robotics opens new opportunities in endoscopy and minimally invasive surgery. Pneumatic catheters offer a promising alternative to conventional steerable catheters for safe ...navigation through the natural pathways without tissue injury. In this work, we present an optimized 6 mm diameter two-degree-of-freedom pneumatic actuator, able to bend in every direction and incorporating a 1 mm working channel. A versatile vacuum centrifugal overmolding method capable of producing small geometries with a variety of silicones is described, and meter-long actuators are extruded industrially. An improved method for fiber reinforcement is also presented. The actuator achieves bending more than 180° and curvatures of up to 0.1 mm
−1
. The exerted force remains below 100 mN, and with no rigid parts in the design, it limits the risks of damage on surrounding tissues. The response time of the actuator is below 300 ms and therefore not limited for medical applications. The working space and multi-channel actuation are also experimentally characterized. The focus is on the study of the influence of material stiffness on mechanical performances. As a rule, the softer the material, the better the energy conversion, and the stiffer the material, the larger the force developed at a given curvature. Based on the actuator, a 90 cm long steerable catheter demonstrator carrying an optical fiber is developed, and its potential for endoscopy is demonstrated in a bronchial tree phantom. In conclusion, this work contributes to the development of a toolbox of soft robotic solutions for MIS and endoscopic applications, by validating and characterizing a promising design, describing versatile and scalable fabrication methods, allowing for a better understanding of the influence of material stiffness on the actuator capabilities, and demonstrating the usability of the solution in a potential use-case.
Understanding the processes that govern liver progenitor cell differentiation has important implications for the design of strategies targeting chronic liver diseases, whereby regeneration of liver ...tissue is critical. Although DNA methylation (5mC) and hydroxymethylation (5hmC) are highly dynamic during early embryonic development, less is known about their roles at later stages of differentiation. Using an in vitro model of hepatocyte differentiation, we show here that 5hmC precedes the expression of promoter 1 (P1)-dependent isoforms of HNF4A, a master transcription factor of hepatocyte identity. 5hmC and HNF4A expression from P1 are dependent on ten-eleven translocation (TET) dioxygenases. In turn, the liver pioneer factor FOXA2 is necessary for TET1 binding to the P1 locus. Both FOXA2 and TETs are required for the 5hmC-related switch in HNF4A expression. The epigenetic event identified here may be a key step for the establishment of the hepatocyte program by HNF4A.
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•5hmC marks HNF4A P1 promoter previous to terminal hepatocyte differentiation•TET1-dependent 5hmC is required to activate P1-driven HNF4A expression•Pioneer factor FOXA2 is necessary for TET1 binding to P1 locus•HNF4A promoter switch is reversible upon hepatocyte dedifferentiation
Hepatocyte identity is impaired in various human chronic liver diseases. Methylation and hydroxymethylation dynamically mark the DNA during development. As shown by Hernandez-Vargas and colleagues, discrete changes in these marks also play a role in establishing hepatocyte identity. Specifically, hydroxymethylation of the hepatocyte promoter HNF4A signals a key switch in expression. Because of its reversibility, this switch is susceptible to experimental manipulation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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