Modeling transitional plane Couette flow

The Galerkin method is used to derive a realistic model of plane Couette flow in terms of partial differential equations governing the space-time dependence of the amplitude of a few cross-stream modes. Numerical simulations show that it reproduces the globally sub-critical behavior typical of this flow. In particular, the statistics of turbulent transients at decay from turbulent to laminar flow displays striking similarities with experimental findings.Comment: 33 pages, 10 figure

Vibrations of cable-suspended rehabilitation robots

Rehabilitation robots help the treatment of diseases by performing cyclic exercises for a long period of time. These exercises must perform movements of the patient's limbs; thus, the robots are required to be flexible and safe. Among rehabilitation robots, cable robots are widely used due to their unique properties, such as being lightweight and the possibility of being equipped with magnetic hooks to improve both safety and ease of use. However, the elasticity and flexibility of cables result in vibrations of the payload and hooks. In this paper, the forced vibrations due to rehabilitation exercises are studied. Since the previous studies of the authors showed a weak coupling between longitudinal and transverse vibrations, a two-cable planar model for the study of transverse vibrations is developed. The model makes it possible to study the forced transverse vibrations due to both cable motion and robot motion. Stiffness and damping of the patient's arm are considered. Results show that the cable system exhibits a simple linear behavior when excited by robot motion and a non-linear behavior when excited by cable motion

Analysis of the Compliance Properties of an Industrial Robot with the Mozzi Axis Approach

In robotic processes, the compliance of the robot arm plays a very important role. In some conditions, for example, in robotic assembly, robot arm compliance can compensate for small position and orientation errors of the end-effector. In other processes, like machining, robot compliance may generate chatter vibrations with an impairment in the quality of the machined surface. In industrial robots, the compliance of the end-effector is chiefly due to joint compliances. In this paper, joint compliances of a serial six-joint industrial robot are identified with a novel modal method making use of specific modes of vibration dominated by the compliance of only one joint. Then, in order to represent the effect of the identified compliances on robot performance in an intuitive and geometric way, a novel kinematic method based on the concept of \u201cMozzi axis\u201d of the end-effector is presented and discusse

Effects of interphase boundary anisotropy on the three-phase growth dynamics in the β(In) – In 2 Bi – γ(Sn) ternary-eutectic system

International audienceWe present an experimental investigation on the effects of the interphase energy anisotropy on the formation of three-phase growth microstructures during directional solidification (DS) of the β(In)-In2Bi-γ(Sn) ternary-eutectic system. Standard DS and rotating directional solidification (RDS) experiments were performed using thin alloy samples with real-time observation. We identified two main types of eutectic grains (EGs): (i) quasi-isotropic EGs within which the solidification dynamics do not exhibit any substantial anisotropy effect, and (ii) anisotropic EGs, within which RDS microstructures exhibit an alternation of locked and unlocked microstructures. EBSD analyses revealed (i) a strong tendency to an alignment of the In2Bi and γ(Sn) crystals (both hexagonal) with respect to the thin-sample walls, and (ii) the existence of special crystal orientation relationships (ORs) between the three solid phases in both quasi-isotropic and anisotropic EGs. We initiate a discussion on the dominating locking effect of the In2Bi-β(In) interphase boundary during quasi steady-state solidification, and the existence of strong crystal selection mechanisms during early nucleation and growth stages

Transition from the Couette-Taylor system to the plane Couette system

We discuss the flow between concentric rotating cylinders in the limit of large radii where the system approaches plane Couette flow. We discuss how in this limit the linear instability that leads to the formation of Taylor vortices is lost and how the character of the transition approaches that of planar shear flows. In particular, a parameter regime is identified where fractal distributions of life times and spatiotemporal intermittency occur. Experiments in this regime should allow to study the characteristics of shear flow turbulence in a closed flow geometry.Comment: 5 pages, 5 figure

Convective and absolute Eckhaus instability leading to modulated waves in a finite box

We report experimental study of the secondary modulational instability of a one-dimensional non-linear traveling wave in a long bounded channel. Two qualitatively different instability regimes involving fronts of spatio-temporal defects are linked to the convective and absolute nature of the instability. Both transitions appear to be subcritical. The spatio-temporal defects control the global mode structure.Comment: 5 pages, 7 figures (ReVTeX 4 and amsmath.sty), final versio

Management of the axilla in breast cancer:\ua0outcome analysis in a series of ductal versus lobular invasive cancers

Introduction: Axillary lymph node dissection (ALND) has been considered essential for the staging of breast cancer (BC). As the impact of tumor biology on clinical outcomes is recognized, a surgical de-escalation approach is being implemented. We performed a retrospective study focused on surgical management of the axilla in invasive lobular carcinoma (ILC) versus invasive ductal carcinoma (IDC). Materials and methods: 1151 newly diagnosed BCs, IDCs (79.6%) or ILCs (20.4%), were selected among patients treated at our Breast Cancer Unit from 2012 to 2018. Tumor characteristics and clinical information were collected and predictors of further metastasis after positive sentinel lymph node biopsy (SLNB) analyzed in relation to disease-free survival (DFS) and overall survival (OS). Results: 27.5% of patients with ILC had 65 3 metastatic lymph nodes at ALND after positive SLNB versus 11.48% of IDCs (p = 0.04). Risk predictors of further metastasis at ALND were the presence of > 2 positive lymph nodes at SLNB (OR = 4.72, 95% CI 1.15\u201319.5 p = 0.03), T3\u2013T4 tumors (OR = 4.93, 95% CI 1.10\u201322.2, p = 0.03) and Non-Luminal BC (OR = 2.74, 95% CI 1.16\u20136.50, p = 0.02). The lobular histotype was not associated with the risk of further metastasis at ALND (OR = 1.62, 95% CI 0.77\u20133.41, p = 0.20). Conclusions: ILC histology is not associated with higher risk of further metastasis at ALND in our analysis. However, surgical management decisions should be taken considering tumor histotype, biology and expected sensitivity to adjuvant therapies

Critical exponents of directed percolation measured in spatiotemporal intermittency

A new experimental system showing a transition to spatiotemporal intermittency is presented. It consists of a ring of hundred oscillating ferrofluidic spikes. Four of five of the measured critical exponents of the system agree with those obtained from a theoretical model of directed percolation.Comment: 7 pages, 12 figures, submitted to PR