Destabilizing resonances of precessing inertia-gravity waves.

Instabilities in stratified precessing fluid are investigated. We extend the study by Mahalov [Phys. Fluids A 5, 891 (1993)0899-821310.1063/1.858635] in the stably stratified Boussinesq framework, with an external Coriolis force (with rate Ω_{p}) altering the base flow through the distortion of the circular streamlines of the unperturbed axially stratified rotating columns (with constant vorticity 2Ω.) It is shown that the inviscid part of the modified velocity flow (0,Ωr,-2ɛΩrsinφ) and buoyancy with gradient N^{2}(-2ɛcosφ,2ɛsinφ,1) are an exact solution of Boussinesq-Euler equations. Here (r,φ,z) is a cylindrical coordinate system, with ɛ=Ω_{p}/Ω being the Poincaré number and N the Brunt-Väisälä frequency. The base flow is transformed into a Cartesian coordinate system, and the stability of a superimposed perturbation is studied in terms of Fourier (or Kelvin) modes. The resulting Floquet system for the Fourier modes has three parameters: ɛ, N=N/Ω, and µ, which is the angle between the wave vector k and the solid-body rotation axis in the limit ɛ=0. In this limit, there are inertia-gravity waves propagating with frequency ±ω and the resonant cases are those for which 2ω=nΩ, n being an integer. We perform an asymptotic analysis to leading order in ɛ and characterize the destabilizing resonant case of order n=1 (i.e., the subharmonic instability) which exists and for 0≤N<Ω/2. In this range, the subharmonic instability remains the strongest with a maximal growth rate σ_{m}=[ɛ(5sqrt[15]/8)sqrt[1-4N^{2}]/(4-N^{2})]. Stable stratification acts in such a way as to make the subharmonic instability less efficient, so as it disappears for N≥0.5Ω. The destabilizing resonant cases of order n=2,3,4,5 are investigated in detail by numerical computations. The effect of viscosity on these instabilities is briefly addressed assuming the diffusive coefficients (kinematic and thermal) are equal. Likewise, we briefly investigate the case where N^{2}<0 and show that the instability associated to the mode with k_{3}=0 is the strongest.

Spectral energy scaling in precessing turbulence.

We study precessing turbulence, which appears in several geophysical and astrophysical systems, by direct numerical simulations of homogeneous turbulence where precessional instability is triggered due to the imposed background flow. We show that the time development of kinetic energy K occurs in two main phases associated with different flow topologies: (i) an exponential growth characterizing three-dimensional turbulence dynamics and (ii) nonlinear saturation during which K remains almost time independent, the flow becoming quasi-two-dimensional. The latter stage, wherein the development of K remains insensitive to the initial state, shares an important common feature with other quasi-two-dimensional rotating flows such as rotating Rayleigh-Bénard convection, or the large atmospheric scales: in the plane k_{∥}=0, i.e., the plane associated to an infinite wavelength in the direction parallel to the principal rotation axis, the kinetic energy spectrum scales as k_{⊥}^{-3}. We show that this power law is observed for wave numbers ranging between the Zeman "precessional" and "rotational" scales, k_{S}^{-1} and k_{Ω}^{-1}, respectively, at which the associated background shear or inertial timescales are equal to the eddy turnover time. In addition, an inverse cascade develops for (k_{⊥},k)

[What's the optimal time of cesarean section antibiotic prophylaxis, before skin incision or after umbilical cord clamping? A prospective randomized study]. / Quel est le moment optimal de l'antibioprophylaxie pour césarienne élective, avant l'incision cutanée ou après clampage du cordon ombilical ? Étude prospective randomisée.

OBJECTIVES: To compare the effect of antibiotics prophylaxis within 30 mins before skin incision (A) and after umbilical cord clamping (C) on the incidence of postoperative infections in patients undergoing elective caesarean section at Farhat Hached university teaching hospital. MATERIALS AND METHODS: We conducted a randomised clinical trial evaluating 279 patients undergoing elective caesarean section. Patients were randomly assigned a group number that allocated them to either arm of the study. They received the same prophylactic antibiotic (cefazol® 2g) according to their allotment. They were followed up to detect infection up to 30 days postoperatively. The primary outcome was postoperative infection. The data collected were analysed with SPSS version 18.0 using univariate and bivariate analysis. RESULTS: The risk of overall postoperative infection was not significantly lower when prophylaxis was given before skin incision (4.37 % (A) vs 9.85 % (C); P=0.07; OR=0.42 [0.15-1.12]). We also found wound infections to be significantly reduced in the pre-incision group (2.2 % [A] vs 8.45 % [C]; P=0.03; OR=0.24 [0.06-0.88]). However, there was no difference in the endometritis infectious. On the other hand, there was no negative impact on the neonatal features. CONCLUSIONS: Giving prophylactic antibiotics before skin incision reduces risk of postoperative infection, in particular of wound infections.

[Post-cesarean parietal scar characteristics are predictive of pelvic adhesions. A prospective cohort study]. / Les caractéristiques de la cicatrice pariétale de césarienne sont des facteurs prédictifs des adhérences pelviennes. Étude de cohorte prospective.

OBJECTIVE: To investigate whether abdominal scar characteristics could predict the incidence and severity of intra-abdominal adhesions found at repeat cesarean delivery. PATIENTS AND METHODS: Prospective cohort study including 151pregnant women with at least one previous cesarean delivery and who delivered abdominally in the department of obstetrics and gynaecology of Farhat Hached teaching hospital-Sousse-Tunisia, during 6 months. Abdominal scar characteristics were studied. The main outcome measure(s) were the incidence and severity of intra-abdominal adhesions. Statistical analysis was performed using SPSS 18.0. RESULTS: Of 151 women enrolled into this trial, 111 (73.5%) had adhesions, 57 (37.8%) had dense adhesions. Of all the abdominal scar characteristics studied, a depressed scar was associated with an increased incidence of both dense and filmy intra-abdominal adhesions and frozen pelvis if compared of women who did not have a depressed scar (P<10(-4) ; RR=7.6; IC=2.98-19.45). A number of previous cesarean section equal or more than 2 was also correlated with an increased incidence of severe intra-abdominal adhesions and frozen pelvis if compared with women who had only one previous cesarean section (P=0.002; RR=2.53; IC=1.16-5.56). DISCUSSION AND CONCLUSION: A depressed abdominal scar of a previous cesarean delivery and a number of previous cesarean sections are significantly correlated with the incidence and severity of intra-abdominal adhesions.

[Role of deambulation during labour: A prospective randomized study]. / Intérêt de la déambulation au cours du travail obstétrical : étude prospective randomisée de 200 cas.

OBJECTIVE: To assess the effects of ambulation during the first stage of labor on the duration of labor and other maternal and infant outcomes. PATIENTS AND METHODS: A prospective randomized trial conducted from 1st November 2008 to 31st March 2009 at the department of obstetrics and gynecology, CHU Farhat Hached, Sousse, Tunisia. Two hundred mothers with uncomplicated term pregnancies were randomly assigned to one of two groups: first group (100 parturients) authorized to ambulate until 6cm of cervical dilation and a second group (100 parturients) confined to bed in dorsal or lateral recumbence. RESULTS: Upright position reduces significantly (for about 34%) the duration of the first stage of labor (P<0.0001), the pain intensity, the oxytocin consumption (P=0.001), the rate of delivery by cesarean section and of instrumental deliveries. Upright position leads also to a net improvement of the maternal outcome (7% side effects versus 13%) and the fetal outcome (net improvement of the Apgar's score at first and fifth minute, and reduction of a factor 5 of the rate of transfer to the neonatology clinical care unit. CONCLUSION: Our study allowed to confirm the benefits of ambulation on labor progress as well as on the maternal comfort and the maternofetal outcome.