93 research outputs found
Oscillations and translation of a free cylinder in a confined flow
An oscillatory instability has been observed experimentally on an horizontal
cylinder free to move and rotate between two parallel vertical walls of
distance H; its characteristics differ both from vortex shedding driven
oscillations and from those of tethered cylinders in the same geometry. The
vertical motion of the cylinder, its rotation about its axis and its transverse
motion across the gap have been investigated as a function of its diameter D,
its density s, of the mean vertical velocity U of the fluid and of its
viscosity. For a blockage ratio D/H above 0.5 and a Reynolds number Re larger
then 14, oscillations of the rolling angle of the cylinder about its axis and
of its transverse coordinate in the gap are observed together with periodic
variations of the vertical velocity. Their frequency f is the same for the
sedimentation of the cylinder in a static fluid (U = 0) and for a non-zero mean
flow (U 6= 0). The Strouhal number St associated to the oscillation varies as
1/Re with : St.Re = 3 0.15. The corresponding period 1/f is then
independent of U and corresponds to a characteristic viscous diffusion time
over a distance ~ D, implying a strong influence of the viscosity. These
characteristics differ from those of vortex shedding and tethered cylinders for
which St is instead roughly constant with Re and higher than here
Influence of confinement on the oscillations of a free cylinder in a viscous flow
We demonstrate and study experimentally two instabilities of a horizontal free cylinder in a vertical viscous Hele-Shaw flow; we show that they depend critically on the confinement of the flow with a different influence of transverse and lateral confinement characterized respectively by the ratios of the diameter (resp. the length) of the cylinder to the gap (resp. the width) of the cell. The onset of the instabilities depends largely on the transverse confinement: for a parameter between 0.4 and 0.6, one observes transverse horizontal oscillations of the cylinder perpendicular to the walls: their frequency is constant with the lateral and transverse confinements at a given cylinder velocity. This instability is shown to be locally two-dimensional and controlled by the local relative velocity between the cylinder and the fluids: it occurs down to Reynolds numbers based on the cell gap â 15, far below the corresponding 2D vortex shedding thresholds (150â250) for fixed cylinders between parallel planes. Above transverse confinements of the order of 0.55, we observe a fluttering motion with periodic oscillations of the tilt angle of the cylinder from the horizontal and of its horizontal position: their frequency decreases strongly as the lateral confinement increases but is independent of the transverse confinement and the cylinder velocity.Fil: Gianorio, Luciano. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Grupo de Medios Porosos; ArgentinaFil: D'angelo, MarĂa VerĂłnica. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Grupo de Medios Porosos; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Cachile, Mario Andres. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Grupo de Medios Porosos; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Hulin, Jean Pierre. Universite Paris Sud; FranciaFil: Auradou, Harold. Universite Paris Sud; Franci
Dispersion enhancement and damping by buoyancy driven flows in 2D networks of capillaries
The influence of a small relative density difference on the displacement of
two miscible liquids is studied experimentally in transparent 2D networks of
micro channels. Both stable displacements in which the denser fluid enters at
the bottom of the cell and displaces the lighter one and unstable displacements
in which the lighter fluid is injected at the bottom and displaces the denser
one are realized. Except at the lowest mean flow velocity U, the average
of the relative concentration satisfies a convection-dispersion
equation. The dispersion coefficient is studied as function of the relative
magnitude of fluid velocity and of the velocity of buoyancy driven fluid
motion. A model is suggested and its applicability to previous results obtained
in 3D media is discussed
Miscible transfer of solute in different model fractures: From random to multiscale wall roughness
Muscle activation during gait in children with Duchenne muscular dystrophy
The aim of this prospective study was to investigate changes in muscle activity during gait in children with Duchenne muscular Dystrophy (DMD). Dynamic surface electromyography recordings (EMGs) of 16 children with DMD and pathological gait were compared with those of 15 control children. The activity of the rectus femoris (RF), vastus lateralis (VL), medial hamstrings (HS), tibialis anterior (TA) and gastrocnemius soleus (GAS) muscles was recorded and analysed quantitatively and qualitatively. The overall muscle activity in the children with DMD was significantly different from that of the control group. Percentage activation amplitudes of RF, HS and TA were greater throughout the gait cycle in the children with DMD and the timing of GAS activity differed from the control children. Significantly greater muscle coactivation was found in the children with DMD. There were no significant differences between sides. Since the motor command is normal in DMD, the hyper-activity and co-contractions likely compensate for gait instability and muscle weakness, however may have negative consequences on the muscles and may increase the energy cost of gait. Simple rehabilitative strategies such as targeted physical therapies may improve stability and thus the pattern of muscle activity
Differential diagnosis of neurodegenerative dementias with the explainable MRI based machine learning algorithm MUQUBIA
Biomarker-based differential diagnosis of the most common forms of dementia is becoming increasingly important. Machine learning (ML) may be able to address this challenge. The aim of this study was to develop and interpret a ML algorithm capable of differentiating Alzheimer's dementia, frontotemporal dementia, dementia with Lewy bodies and cognitively normal control subjects based on sociodemographic, clinical, and magnetic resonance imaging (MRI) variables. 506 subjects from 5 databases were included. MRI images were processed with FreeSurfer, LPA, and TRACULA to obtain brain volumes and thicknesses, white matter lesions and diffusion metrics. MRI metrics were used in conjunction with clinical and demographic data to perform differential diagnosis based on a Support Vector Machine model called MUQUBIA (Multimodal Quantification of Brain whIte matter biomArkers). Age, gender, Clinical Dementia Rating (CDR) Dementia Staging Instrument, and 19 imaging features formed the best set of discriminative features. The predictive model performed with an overall Area Under the Curve of 98%, high overall precision (88%), recall (88%), and F1 scores (88%) in the test group, and good Label Ranking Average Precision score (0.95) in a subset of neuropathologically assessed patients. The results of MUQUBIA were explained by the SHapley Additive exPlanations (SHAP) method. The MUQUBIA algorithm successfully classified various dementias with good performance using cost-effective clinical and MRI information, and with independent validation, has the potential to assist physicians in their clinical diagnosis
The sialyl-glycolipid stage-specific embryonic antigen 4 marks a subpopulation of chemotherapy-resistant breast cancer cells with mesenchymal features
Evaluation of a New Rapid Quantitative D-dimer Assay in Patients with Clinically Suspected Deep Vein Thrombosis
- âŠ