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Biomedical subjects

C Caroli

Publications and source records attributed to C Caroli.

11 recordsLinked to original sources
PubMed2002

Pressure dependence of the sound velocity in a two-dimensional lattice of Hertz-Mindlin balls: mean-field description.

We study the dependence on the external pressure P of the velocities v(L,T) of long wavelength sound waves in a confined two-dimensional hexagonal close-packed lattice of 3D elastic frictional balls interacting via one-sided Hertz-Mindlin contact forces, whose diameters exhibit mild dispersion. The presence of an underlying long range order enables us to build an effective medium description, which incorporates the radial fluctuations of the contact forces acting on a single site. Due to the nonlinearity of Hertz elasticity, self-consistency results in a highly nonlinear differential equation for the "equation of state" linking the effective stiffness of the array with the applied pressure, from which sound velocities are then obtained. The results are in excellent agreement with existing experimental results and simulations in the high- and intermediate-pressure regimes. It emerges from the analysis that the departure of v(L)(P) from the ideal P(1/6) Hertz behavior must be attributed primarily to the fluctuations of the stress field, rather than to the pressure dependence of the number of contacts.

Journal Article↗
PubMed2001

Jamming creep of a frictional interface.

We measure the displacement response of a frictional multicontact interface between identical polymer glasses to a biased shear force oscillation. We evidence the existence, for maximum forces close below the nominal static threshold, of a jamming creep regime governed by an aging-rejuvenation competition acting within the micrometer-sized contacting asperities. The time dependence of the creep process deviates from the standard Rice-Ruina [J. R. Rice and A. L. Ruina, J. Appl. Mech. 50, 343 (1983)] phenomenology at early times; this suggests the possibility of an aging-rejuvenation competition at much smaller scales, within the nanometer-thick adhesive junctions.

Journal Article↗
PubMed2000

Slip pulses at a sheared frictional viscoelastic/nondeformable interface

We study the possibility for a semi-infinite block of linear viscoelastic material, in homogeneous frictional contact with a nondeformable one, to slide under shear via a periodic set of "self-healing pulses," i.e., a set of drifting slip regions separated by stick ones. We show that, contrary to existing experimental indications, such a mode of frictional sliding is impossible for an interface obeying a simple local Coulomb law of solid friction. We then discuss possible physical improvements of the friction model which might open the possibility of such dynamics, among which slip weakening of the friction coefficient, and stress the interest of developing systematic experimental investigations of this question.

Journal Article↗
PubMed2000

Shear response of a frictional interface to a normal load modulation

We study the shear response of a sliding multicontact interface submitted to a harmonically modulated normal load, without loss of contact. We measure, at low velocities (V<100 &mgr;m s(-1)), the average value &Fmacr; of the friction force and the amplitude of its first and second harmonic components. The excitation frequency (f=120 Hz) is chosen much larger than the natural one, associated with the dynamical aging of the interface. We show the following: (i) In agreement with the engineering thumb rule, even a modest modulation induces a substantial decrease of &Fmacr;. (ii) The Rice-Ruina state and rate model, though appropriate to describe the slow frictional dynamics, must be extended when dealing with our "high" frequency regime. That is, the rheology which controls the shear strength must explicitly account not only for the plastic response of the adhesive junctions between load-bearing asperities, but also for the elastic contribution of the asperities bodies. This "elastoplastic" friction model leads to predictions in excellent quantitative agreement with all our experimental data.

Journal Article↗
PubMed1996

[Diastolic left ventricular dysfunction with microvascular angina (Syndrome X)].

Findings on left ventricular function in microvascular angina (syndrome X) are somewhat controversial. Recently, an increased prevalence of insulin resistance and hyperlipoproteinemia has been demonstrated as well as arterial hypertension potentially impairing the left ventricular diastolic function. In an attempt to analyze the diastolic function at rest, we investigated by Doppler echocardiography the transmitral blood flow in 16 patients (51 +/- 8 years). The diastolic data were compared with those of 12 healthy people (50 +/- 6 years) who were matched for age. The patients with microvascular angina revealed a slightly higher systolic blood pressure (134 +/- 18 mm Hg vs 125 +/- 9 mm Hg, n.s.), but imposed by higher left ventricular mass index (92 +/- 18 g/m2 vs 65 +/- 13 g/m2, p < 0.001). There was a trend to an elevated A-wave-peak during transmitral blood flow (61 +/- 14 cm/s vs 50 +/- 9 cm/s). The findings suggest impairment of the left ventricular relaxation before manifestation of left ventricular hypertrophy and hypertension takes place.

Adult↗
PubMed1982

7 alpha-Alkyltestosterone derivatives: synthesis and activity as androgens and as aromatase inhibitors.

The 7 alpha-ethyl,propyl,butyl,3'-t-butoxypropyl,allyl,3'-hydroxypropyl 17-acetate, and 3'-chloropropyl 17-acetate derivatives of testosterone and the 7 alpha-3'-t-butoxypropyl, 3'-hydroxypropyl,3'-acetoxypropyl,3'-bromoacetoxypropyl, 3'-chloropropyl, and 2'-oxo-3'-bromopropyl derivatives of 4-androstene-3,17-dione were synthesized. The testosterone derivatives were found to lose androgenic and anabolic activity rapidly as the size of the group at the 7 position increased. Many of the compounds were tested as inhibitors of aromatase. The 17-keto compounds were more active than the corresponding alcohols and the enzyme was found to tolerate at least the bulk of a hydroxypropyl group at the C-7 alpha position.

Androgens↗