Dynamics of paramagnetic permanent chains and self-assembled clusters under a rapidly rotating magnetic field.

We study experimentally and theoretically the dynamics of permanent paramagnetic chains and mixed clusters formed by permanent paramagnetic chains and paramagnetic particles under the influence of a time-varying magnetic field. First, we examine the dynamics of permanent chains at high frequencies (∼50 to 1000 Hz). These permanent chains exhibit continuous rotational motion with a frequency several orders of magnitude lower than that of the magnetic field.

Immediate postpartum assessment of the anal sphincter by endovaginal ultrasound: An experimental study.

Introduction And Hypothesis: Obstetric anal sphincter injuries are frequently missed and carry a significant risk for the development of anal incontinence. Immediate postpartum endoanal ultrasound increases identification of these injuries but is rarely employed. We hypothesize that endovaginal ultrasound could be a feasible and easily available alternative sonographic tool to improve early diagnosis of anal sphincter tears.

Rotation dynamics and internal structure of self-assembled binary paramagnetic colloidal clusters.

We study experimentally and theoretically the dynamics of two-dimensional self-assembled binary clusters of paramagnetic colloids of two different sizes and magnetic susceptibilities under a time-varying magnetic field. Due to the continuous energy input by the rotating field, these clusters are at a state of dissipative nonequilibrium. Dissipative viscoelastic shear waves traveling around their interface enable the rotation of isotropic binary clusters.

Immediate postpartum assessment of the anal sphincter by endovaginal ultrasound: a new technical approach.

Introduction And Hypothesis: In this study we described a new technical approach to adapt endovaginal ultrasound scanning of the anal sphincter complex to the immediate postpartum period.

Methods: We analyzed the clinical and ultrasonographic examinations of 18 primiparous women presenting deep perineal tears with potential or clearly identified lesions of the anal sphincter. Potential anal sphincter lesion was defined as a second degree perineal tear extending close to the anal sphincter with exposition of its capsule or muscular fibers.

Dissipative non-equilibrium dynamics of self-assembled paramagnetic colloidal clusters.

We study experimentally and theoretically the dynamics of two-dimensional clusters of paramagnetic colloids under a time-varying magnetic field. These self-assembled clusters are a dissipative non-equilibrium system with shared features with aggregates of living matter. We investigate the dynamics of cluster rotation and develop a theoretical model to explain the emergence of collective viscoelastic properties.

Frozen-warmed blastocyst transfer after 6 or 7 days of progesterone administration: impact on live birth rate in hormone replacement therapy cycles.

Objective: To study the difference in live birth rate (LBR) between frozen-warmed blastocyst transfer (FET) on the 6th or the 7th day of progesterone administration in artificially prepared cycles.

Design: Retrospective cohort study.

Setting: Tertiary university-based referral hospital.

More women gynecologists in Belgium: assessment of changes in the workforce-a survey.

Context And Objective: International data highlight the increasing participation of women in the workforce in the medical field and particularly among obstetricians and gynecologists (OB-GYN). Some studies reported a gender difference in work productivity and practice patterns. The aim of this study is to analyze whether disparities exist between male and female OB-GYN in their practices with potential consequences for the organization of the OB-GYN departments.

Ordering of sedimenting paramagnetic colloids in a monolayer.

Sedimentation enables self-assembly of colloidal particles into crystalline structures, as needed for catalysis or photonics applications. Here we combine experiments, theory, and simulations to investigate the equilibrium structure of a colloidal monolayer with tunable interparticle repulsion via an applied external magnetic field. Experimental observations of the equilibrium structure are in excellent agreement with density functional theory.

Resonant reshaping of colloidal clusters on a current carrying wire.

Colloids in confined geometries promise a path towards tailored microscopic superstructures. Yet, a major roadblock is posed by kinetically trapped states that prevent the assemblies from reaching their anticipated shapes. We investigate magnetic colloids trapped on a cylindrical surface of a current carrying wire.

Quantitatively mimicking wet colloidal suspensions with dry granular media.

Athermal two-dimensional granular systems are exposed to external mechanical noise leading to Brownian-like motion. Using tunable repulsive interparticle interaction, it is shown that the same microstructure as that observed in colloidal suspensions can be quantitatively recovered at a macroscopic scale. To that end, experiments on granular and colloidal systems made up of magnetized particles as well as computer simulations are performed and compared.

Rheophysical properties of fluorinated nonionic micellar phases.

Micellar phases can be used as templates for the preparation of mesoporous silica materials. Fluorinated and hydrogenated surfactants can provide a large variety of well-defined micellar structures: spherical and cylindrical micelles as well as more complex structures such as lamellar or sponge phases can be formed in various thermodynamic conditions. However, the preparation of ordered mesoporous materials from these organized media is not always successful for a reason not known at the moment.

Azimuthal instability of the interface in a shear banded flow by direct visual observation.

The stability of the shear banded flow of a Maxwellian fluid is studied from an experimental point of view using rheology and flow visualization with polarized light. We show that the one-layer homogeneous flow cannot sustain shear rates corresponding to the end of the stress plateau. The high shear rate branch is not found and the shear stress oscillates at the end of the plateau.

Strain-induced droplet retraction memory in a pickering emulsion.

We studied the deformation and relaxation of a water droplet covered with polystyrene latex particles (diameter ca. 200 nm) and embedded in an immiscible fluid after a large strain jump. We show that the presence of the solid particles at the droplet interface slows down the retraction kinetics in comparison with a pure water droplet and induces flow singularity not observed with pure water droplets.

Evidence for three-dimensional unstable flows in shear-banding wormlike micelles.

We report on an experimental study of the shear-banding phenomenon in the concentrated wormlike micellar system CTAB at 20wt.% in D2O . Time-resolved velocity profiles are recorded using ultrasonic velocimetry simultaneously to global rheological data.

Yielding and flow in adhesive and nonadhesive concentrated emulsions.

The nonlinear rheological response of soft glassy materials is addressed experimentally by focusing on concentrated emulsions where interdroplet attraction is tuned through varying the surfactant content. Velocity profiles are recorded using ultrasonic velocimetry simultaneously to global rheological data in the Couette geometry. Our data show that nonadhesive and adhesive emulsions have radically different flow behaviors in the vicinity of yielding: while the flow remains homogeneous in the nonadhesive emulsion and the Herschel-Bulkley model for a yield stress fluid describes the data very accurately, the adhesive system displays shear localization and does not follow a simple constitutive equation, suggesting that the mechanisms involved in yielding transitions are not universal.

Spatiotemporal dynamics of wormlike micelles under shear.

Velocity profiles in a wormlike micelle solution (cetyl trimethyl ammonium bromide in D2O) are recorded using ultrasound every 2 s during a startup experiment into the shear-banding regime. The stress relaxation occurs over more than 6 h and corresponds to the very slow nucleation and growth of the high-shear band. Moreover, oscillations of the interface position with a period of about 50 s are observed during the growth process.

Towards local rheology of emulsions under Couette flow using Dynamic Light Scattering.

We present local velocity measurements in emulsions under shear using heterodyne Dynamic Light Scattering. Two emulsions are studied: a dilute system of volume fraction phi = 20% and a concentrated system with phi = 75%. Velocity profiles in both systems clearly show the presence of wall slip.

[Sodium transport in red blood cell membranes in essential arterial hypertension].

Several abnormalities in Na metabolism have been implicated in the pathogenesis of essential hypertension. In addition, recent work by several investigators has showed that some Na transport systems in red cell membranes may be altered in those patients. In order to confirm such abnormalities we evaluated simultaneously four different and clearly defined Na transport systems in red cell membranes: the ouabain sensitive Na pump (P) and the Na-K cotransport (Co) in nystatin loaded cells, the maximal rate of Na-Li countertransport (CTT) in lithium loaded cells and the rate constant of Na passive permeability (pp) in 58 normotensive control subjects with no family history of hypertension (N), 19 normotensive subjects with family history of hypertension (NH) and 34 essential hypertensive patients (HE).

Long-term systemic hypertension in children after successful repair of coarctation of the aorta.

The mechanisms responsible for long-term hypertension in children after successful repair of coarctation of the aorta have not yet been determined. We measured plasma renin activity and aldosterone, adrenalin, and noradrenalin concentrations both under basal conditions and in response to standing and treadmill exercise in 24 normal normotensive children, 16 normotensive postcoarctectomy children, eight hypertensive postcoarctectomy children, and seven children with essential hypertension. Exercise-induced changes in plasma renin activity, aldosterone, adrenalin, and noradrenalin were comparable in the four groups in spite of a significantly greater increase in systolic blood pressure in the children with hypertension.

Small kidney associated with primary vesicoureteral reflux in children. A pathological overhaul.

In this series two quite distinct pathological entities accounted for the small, often deformed, kidney found over a severe primary ureterovesical reflux. One of them is due to dysplastic abnormal metanephric differentiation, and the other is a segmental tubular atrophy with glomerular metamorphosis. In our material there is no evidence to support an inflammatory pathogenesis in these conditions.

Urinary kallikrein in hypertension secondary to hemolytic uremic syndrome: response to diuretic stimulus.

Urinary kallikrein excretion was measured in 43 children, mean age 8 years, who had the hemolytic uremic syndrome (HUS) during the first year of life. Twenty eight were normotensive and fifteen hypertensive. We found no difference in urinary kallikrein excretion between the normotensive and hypertensive groups.