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Experiments to stabilize an unsteady Mach 3 shock wave on a truncated body fitted with a central spike have been conducted in the ONERA R1Ch blowdown wind tunnel. Stabilization was achieved by means of a negative corona discharge created at the tip of the spike. Several runs have been performed, with a freestream unit Reynolds number varying in the range of [0.9[10.sup.7]-3.5[10.sup.7] [m.sup.-1]]. Onboard discharges can be generated using an ac or dc potential between the tip of the spike and the truncated face, similar to the setup of Kuo (Kuo, S., Kalkhoran, I., Bivolaru, D., and Orlick, L., 'Observation of Shock Wave Elimination by a Plasma in a Mach = 2.5 Flow,' Physics of Plasmas, Vol. 7, No. 5, 2000, pp. 1345-1348.). Without discharge, for a certain spike length we observe that, depending on the Reynolds number or the surface state of the spike, the shock front is unsteady or not. In the case of a naturally unsteady shock front, we observe a complete stabilization of the shock when a negative discharge is generated at the spike tip. With positive discharges, the effect is weaker. Both discharges are pulsed, and their input power is less than 1 W. Discharge imaging and current measurements indicate that the negative discharge is a Trichel-pulsed corona discharge, whereas the positive discharge is a streamer discharge. An order-of-magnitude analysis and infrared imaging indicate that continuous volume and surface heating are negligible. To explain the stabilization mechanism, we argue that the pulsed discharge acts as an acoustic source tripping the boundary layer, thus leading to a bypass transition to turbulence.

This paper aims at investigating the effect of discharges generated near steady bow shocks and their possible use for localized heat deposition leading to drag reduction. We report the observation of steady discharges generated in front of a blunted model in a M = 3 supersonic flow. The test model is designed as a pair of coaxial electrodes, and set up in the ONERA R1Ch M = 3 blowdown wind tunnel. A high voltage power supply is used to generate negative discharges. A corona regime, a glow regime, and a filamentary arc regime are observed. The negative corona regime consists of Trichel pulses dissipating less than 200 mW of electrical power. The glow discharge absorbs powers up to 0.5 kW. It displays a strong light emission in the vicinity of the shock front, followed by a darker region downstream of the shock. The drag coefficient is measured and shows no measurable change when a glow discharge is switched on. To explain this and further investigate the effect of localized heat deposition at the shock front, modified Rankine- Hugoniot jump relations are computed, taking into account a volumetric heat source. This allows one to compute a fair estimate of the drag coefficient and shows that drag reduction by localized heating in the shock front is possible. However, it also shows that in our experiment, the plasma thermal power is too small to appreciably reduce the drag, possibly because of the role of the electron impact excitation of N., vibrations, whose fairly long relaxation time could shift downstream the effective gas heating. More generally, the model shows that power-efficient plasma-induced drag reduction requires high plasma heating efficiency.

A study was conducted to characterize an electron-beam-assisted glow discharge device that can determine velocity measurements in hypersonic flows. The device is characterized by two capacitors charged through three resistors and resistor capacitor circuits that promote ground potential for the anode disk. Results showed that the pseudospark device can be utilized in determining the freestream and boundary-layer velocity profiles of hypersonic flows.

Two different high-current pulses were recorded in an experiment to analyze the dynamics behind high-current pulses in the initial or stepped leader phase of lightning and long laboratory sparks at negative polarity. A qualitative model of existing information was quantitatively correlated through computer simulation and used to analyze a lightning strike on an aircraft. Two separate high-current pulses were observed, to obtain a theoretical model that concurred with an electromagnetic equation.

Part II. Presents a study which examined the relevance of crude models based on elementary plasma physics. Stages that comprise the advancing head of a surface spark; Plasma evolution from the advancing boundary between the discharge and the virgin air up to the maximum of the gas temperature; Phenomena that are likely to dominate the glow-to-arc transition for high electronic densities.

Examines the fast propagation of an ionized and thermalized channel in ambient air at atmospheric temperature, using gliding discharges produced over a charged dielectric slab. Details of the experimental arrangements; Description of the basic structure of the discharges and equivalent electric circuit; Improved voltage distribution along negative sparks axis.

Adolescents' access to contraception has improved and indication for their use have been extended beyond pregnancy prevention. For adolescents, this implies the use of hormonal contraception before the accrual of peak bone mass. Sexual hormones, notably estrogens, play a major role in skeletal development, growth and acquisition of maximal bone mass density (BMD). This article will review different contraceptive methods and their impact on BMD, with particular attention to low-dose pills and medroxyprogesterone acetate, both of which seem to alter peak bone mass acquisition. Nevertheless, benefits from appropriate contraception should be weighed against safety concerns, and recommended on an individual basis.