Dynamic wrinkling and strengthening of a filament in a viscous fluid

We investigate the wrinkling dynamics of an elastic filament immersed in a viscous fluid submitted to compression at a finite rate with experiments and by combining geometric nonlinearities, elasticity, and slender body theory. The drag induces a dynamic lateral reinforcement of the filament leading to growth of wrinkles that coarsen over time. We discover a new dynamical regime characterized by a timescale with a non-trivial dependence on the loading rate, where the growth of the instability is super-exponential and the wavenumber is an increasing function of the loading rate. We find that this timescale can be interpreted as the characteristic time over which the filament transitions from the extensible to the inextensible regime. In contrast with our analysis with moving boundary conditions, Biot's analysis in the limit of infinitely fast loading leads to rate independent exponential growth and wavelength

Roadmap to the morphological instabilities of a stretched twisted ribbon

We address the mechanics of an elastic ribbon subjected to twist and tensile load. Motivated by the classical work of Green and a recent experiment that discovered a plethora of morphological instabilities, we introduce a comprehensive theoretical framework through which we construct a 4D phase diagram of this basic system, spanned by the exerted twist and tension, as well as the thickness and length of the ribbon. Different types of instabilities appear in various "corners" of this 4D parameter space, and are addressed through distinct types of asymptotic methods. Our theory employs three instruments, whose concerted implementation is necessary to provide an exhaustive study of the various parameter regimes: (i) a covariant form of the F\"oppl-von K\'arm\'an (cFvK) equations to the helicoidal state - necessary to account for the large deflection of the highly-symmetric helicoidal shape from planarity, and the buckling instability of the ribbon in the transverse direction; (ii) a far from threshold (FT) analysis - which describes a state in which a longitudinally-wrinkled zone expands throughout the ribbon and allows it to retain a helicoidal shape with negligible compression; (iii) finally, we introduce an asymptotic isometry equation that characterizes the energetic competition between various types of states through which a twisted ribbon becomes strainless in the singular limit of zero thickness and no tension.Comment: Submitted to Journal of Elasticity, themed issue on ribbons and M\"obius band

Energetics of twisted elastic filament pairs

We investigate the elastic energy stored in a filament pair as a function of applied twist by measuring torque under prescribed end-to-end separation conditions. We show that the torque increases rapidly to a peak with applied twist when the filaments are initially separate, then decreases to a minimum as the filaments cross and come into contact. The torque then increases again while the filaments form a double helix with increasing twist. A nonlinear elasto-geometric model that combines the effect of geometrical nonlinearities with large stretching and self-twist is shown to capture the evolution of the helical geometry, the torque profile, and the stored energy with twist. We find that a large fraction of the total energy is stored in stretching the filaments, which increases with separation distance and applied tension. We find that only a small fraction of energy is stored in the form of bending energy, and that the contribution due to contact energy is negligible. Our study highlights the consequences of stretchablility on filament twisting which is a fundamental topological transformation relevant to making ropes, tying shoelaces, actuating robots, and the physical properties of entangled polymers

Council of Europe annual penal statistics SPACE II: Survey 2015. Persons serving non-custodial sanctions and measures in 2015.

Key points of SPACE II 2015 • The participation rate in the 2015 SPACE II Survey was very satisfying: 47 out of the 52 probation services of the 47 Council of Europe Member States answered the questionnaire. • About 80% of the probation services of the responding countries are placed under the authority of the national Ministry of Justice. This authority is shared with the Prison Administration in around 34% of these cases. • During the year 2015, 1,173,278 persons entered into supervision by the probation services, and 1,130,444 left that supervision. For countries with at least one million inhabitants, this represents an average rate of 227.7 entries and 167.3 exits per 100,000 inhabitants. As a comparison, in 2014, there 220.9 entries per 100,000 inhabitants (+3.07% in 2015) and 165.6 exits per 100,000 inhabitants (+1.02% in 2015). Between 2010 and 2015, the entries into supervision per 100,000 population decreased by 9.3% and the exits decreased by 10.4%. • On 31st December 2015, there were 1,239,426 persons under the supervision or care of the probation services of the responding countries. For countries with at least one million inhabitants, this represents an average rate of 195 per 100,000 inhabitants. As a comparison, on 31st December 2014, the average rate of persons under the supervision or care of the probation services was 196.5 per 100,000 inhabitants (-0.7% in 2015). Between 2010 and 2015, the decrease reached 9.7%. • Non-custodial sanctions and measures are seldom used as an alternative to pre-trial detention: Roughly, only 7.5% of the probation population corresponds to persons placed under supervision before trial. • On average, on 31st December 2015, female probation clients represented 9.8% of the total probation population. The proportion of minors and foreigners was 4.9% and 15.1% respectively. • On average, there are 5.6 probation staff members per 100,000 inhabitants, with great individual variation among the responding countries. • On average, each probation staff member across Europe is in charge of 10.8 pre-sentence reports. • In 24 countries, probation is used for all kind of criminal offences. • The average length of probation for persons sentenced for violence against persons and robbery are 17.5 months and 20.1 months respectively. • The longer length of probation is, on average, 22.8 months, and corresponds to persons sentenced for sexual offences

Les données de police permettent-elles la détection des agresseurs sexuels sériels? Une analyse de la validité concourante de VICLAS

Cette recherche s’intéresse à la capacité du Violent Crime Linkage Analysis System (ViCLAS) à identifier les auteurs sexuels sériels. Pour ce faire, l’étude se focalise sur l’analyse de la validité concourante de l’outil en comparant le pourcentage d’agresseurs sexuels sériels identifié par cet instrument et celui mis en avant par des recherches basées sur des sondages de délinquance autoreportée. Les données utilisées dans cette étude proviennent de la base de données ViCLAS utilisée par les forces de police française. Ces données concernent 3901 cas d’agressions sexuelles extrafamiliales commises entre 1979 et 2013 ainsi que 3500 agresseurs. Les résultats montrent que, parmi les agresseurs de victimes de 15 ans et plus, ViCLAS identifie 5.75 % d’auteurs sériels et que ce pourcentage augmente à 13.5 % pour les agresseurs de victimes de moins de 15 ans. Ces pourcentages sont nettement inférieurs à ceux trouvés par les recherches basées sur des sondages de délinquance autoreportée, ce qui soulève des questionnements sur la validité de ViCLAS