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Publications associées (22)

Capsizing due to friction-induced twist in the failure of stopper knots

Pedro Miguel Nunes Pereira de Almeida Reis, Paul Johanns

We investigate the failure mechanism of stopper knots, with a particular focus on the figure -8 knot as a representative example. Stopper knots are widely used in climbing, sailing, racket stringing, and sewing to maintain tension in ropes, strings, or thr ...

Elsevier2024

The strength of surgical knots involves a critical interplay between friction and elastoplasticity

Pedro Miguel Nunes Pereira de Almeida Reis, Paul Johanns, Paul Grandgeorge

Knots are the weakest link in surgical sutures, serving as mechanical ligatures between filaments. Exceeding their safe operational limits can cause fatal complications. The empirical nature of present guidelines calls for a predictive understanding of the ...

AMER ASSOC ADVANCEMENT SCIENCE2023

Mechanics of Physical Knots: From Filaments in Contact to Surgical Suturing

Paul Johanns

In this thesis, we study the mechanics of tight physical knots. Knots are omnipresent in surgery, climbing, and sailing, with disastrous consequences when the filament or the rope fails to perform its function. Even if the importance of mechanical analysis ...

EPFL2023

Computational Exploration of Multistable Elastic Knots

Mark Pauly, Yingying Ren, Michele Vidulis

We present an algorithmic approach to discover, study, and design multistable elastic knots. Elastic knots are physical realizations of closed curves embedded in 3-space. When endowed with the material thickness and bending resistance of a physical wire, t ...

Association for Computing Machinery (ACM)2023

Exploring the inner workings of the clove hitch knot

Pedro Miguel Nunes Pereira de Almeida Reis, Tomohiko Sano, Paul Johanns, Paul Grandgeorge

We perform a combined experimental and computational investigation of the clove hitch knot. We develop a physical model for the clove hitch by tying an elastic rod onto a rigid cylinder. In the experiments, we characterize the mechanical performance, geome ...

ELSEVIER2022

The shapes of physical trefoil knots

Pedro Miguel Nunes Pereira de Almeida Reis, John Maddocks, Paul Johanns, Tomohiko Sano, Paul Grandgeorge

We perform a compare-and-contrast investigation between the equilibrium shapes of physical and ideal trefoil knots, both in closed and open configurations. Ideal knots are purely geometric abstractions for the tightest configuration tied in a perfectly fle ...

2021

Finite Element Modeling of Tight Elastic Knots

Pedro Miguel Nunes Pereira de Almeida Reis, Paul Johanns, Tomohiko Sano, Paul Grandgeorge

We present a methodology to simulate the mechanics of knots in elastic rods using geometrically nonlinear, full three-dimensional (3D) finite element analysis. We focus on the mechanical behavior of knots in tight configurations, for which the full 3D defo ...

2020

Experimenting with knots

Giovanni Dietler

Knots are interesting objects to experiment since their topological properties are combined with mechanical properties, fluid mechanics or dynamical properties like unknotting under the excitation of the thermal energy. Knots play also a role in biology be ...

SPRINGER HEIDELBERG2019

Tuning knot abundance in semiflexible chains with crowders of different sizes: a Monte Carlo study of DNA chains

Giovanni Dietler

We use stochastic simulation techniques to sample the conformational space of linear semiflexible polymers in a crowded medium and study how the knotting properties depend on the crowder size and concentration. The abundance of physical knots in the chains ...

Royal Society of Chemistry2016

Mechanical form-finding of timber fabric structures

Seyed Sina Nabaei

How about fastening a knot? not with ropes... but with timber panels. Timber Fabric Structures (TFS) originate from such an inspiration. An architectural reinterpretation of fabric techniques (mainly braiding) using building scale timber panels to design ...

EPFL2014

Optical-resolution photoacoustic microscopy by use of a multimode fiber

Demetri Psaltis, Christophe Moser, Salma Farahi

We demonstrate Optical-Resolution Photoacoustic Microscopy (OR-PAM), where the optical field is focused and scanned using Digital Phase Conjugation through a multimode fiber. The focus is scanned across the field of view using digital means, and the acoust ...

American Institute of Physics2013

Long knots and maps between operads

Kathryn Hess Bellwald

We identify the space of tangentially straightened long knots in R^m, for m greater than or equal to 4, as the double loops on the space of derived operad maps from the associative operad into a version of the little m-disk operad. This verifies a conjectu ...

Geometry & Topology Publications2012

Fourier Approximation Of Symmetric Ideal Knots

Enforcing a specific symmetry group on a curve, knotted or not, is not trivial using standard interpolations such as polygons or splines. For a prescribed symmetry group we present a symmetrization process based on a Fourier description of a knot. The pres ...

2012

Tightening of DNA knots by supercoiling facilitates their unknotting by type II DNA topoisomerases

Giovanni Dietler, Guillaume Witz

Using numerical simulations, we compare properties of knotted DNA molecules that are either torsionally relaxed or supercoiled. We observe that DNA supercoiling tightens knotted portions of DNA molecules and accentuates the difference in curvature between ...

2011

Computation and visualization of ideal knot shapes

We investigate numerical simulations and visualizations of the problem of tying a knot in a piece of rope. The goal is to use the least possible rope of a fixed, prescribed radius to tie a particular knot, e.g. a trefoil, a figure eight, and so on. The rop ...

EPFL2010

DNA Topology : A Biophysical Study of DNA Rings, Knots, and Catenanes by Means of Atomic Force Microscopy and Numerical Simulations

Guillaume Witz

This thesis explores different aspects of DNA topology through experimental and numerical techniques. Topology is a vast mathematical field, that deals with the spatial properties of objects undergoing continuous deformations, but here it is restricted to ...

EPFL2010

Modélisation mécanique de fils pour la simulation chirurgicale

Lindo Robert Duratti

Minimally Invasive Surgery (MIS) represents one of the major progresses in surgery in the last decade. In general, it is based on the application of small body-cuts through which instruments are inserted into the patient's body allowing the surgeon to carr ...

EPFL2008

Scaling properties of DNA knots studied by atomic force microscopy

Erika Ercolini

The main subject of the present thesis is the experimental study of the scaling properties of DNA knots of different complexities by tapping mode atomic force microscopy (AFM) in air. Homo- or heterogeneous mixture of DNA knot types were deposited onto mic ...

EPFL2008

Fractal dimension and localization of DNA knots

Giovanni Dietler, Paolo De Los Rios, Guillaume Witz, Erika Ercolini

The scaling properties of DNA knots of different complexities were studied by atomic force microscope. Following two different protocols DNA knots are adsorbed onto a mica surface in regimes of (i) strong binding, that induces a kinetic trapping of the thr ...

American Physical Society2007

Simulations of electrophoretic collisions of DNA knots with gel obstacles

Giovanni Dietler, Paolo De Los Rios, Cédric Weber

Gel electrophoresis can be used to separate nicked circular DNA molecules of equal length but forming different knot types. At low electric fields, complex knots drift faster than simpler knots. However, at high electric field the opposite is the case and ...

Institute of Physics2006