Effects of low O-2 and ageing on spindles and chromosomes in mouse oocytes from pre-antral follicle culture

Hu Y, Betzendahl I, Cortvrindt R, Smitz J, Eichenlaub-Ritter U. Effects of low O-2 and ageing on spindles and chromosomes in mouse oocytes from pre-antral follicle culture. HUMAN REPRODUCTION. 2001;16(4):737-748.To assess their quality, spindles were analysed in mouse oocytes from pre-antral follicle culture. High or low oxygen tension was present during the last 16 or 20 h post human chorionic gonadotrophin (HCG)/epidermal growth factor (EGF) addition. Most oocytes from pre-antral follicle culture possessed typical anastral spindles with flat poles resembling those of ovulated, in-vivo-matured oocytes of sexually mature mice, while denuded oocytes in-vitro matured to metaphase II (MII) formed significantly longer, slender spindles with pointed, narrow poles. Spindles in oocytes from follicle culture were only slightly shorter and less compact at the equator as compared with those of oocytes matured in vivo. Chromosomes were well aligned at the equator in MII oocytes obtained from follicle culture with high oxygen. Maturation rate was significantly reduced by lowering oxygen tension to 5% O-2. Prolonged culture and the presence of only 5% O-2 dramatically increased the percentage of MII oocytes with unaligned chromosomes. These observations indicate that sufficient oxygen supply and time of retrieval after initiation of resumption of maturation by HCG as well as the microenvironment and cell-cell interactions between oocytes and their somatic compartment are critical in affecting the oocyte's capacity to mature to MII, to form a functional spindle, and to align chromosomes correctly

Development of an Iodine Feeding System for Low Power Ion and Hall Effect Thrusters

Iodine is considered as a feasible alternative to xenon to be used as a propellant for electric propulsion systems, thanks to its high density, solid state density and the good propulsive performance. The paper illustrates the results of a development and experimental activity, aimed at producing a controlled iodine feeding system for low power (200 W class) ion and Hall effect thrusters. A prototype has been designed, manufactured and tested. The feeding system mainly consists of a slender, cylindrical reservoir, capable of storing up to 250 g of solid iodine in form of a cartridge, a sublimation assembly, an on/off valve and a thermal throttle. Both the sublimation assembly and the thermal throttle are equipped with heating electrical resistors and Pt100 thermal sensors. The coarse regulation of iodine mass flow rate is made by controlling the sublimation pressure through the temperature of the sublimation assembly; the fine regulation by controlling the thermal throttle temperature. A pair of Gefran 1350 PID is used for temperature control. Seven thermocouples are placed in various positions of the feeding system for a thermal characterization during transient as well as steady state operation. The prototype has been tested in a vacuum chamber at a back-pressure of about 1 Pa. Temperature measurements in seven locations of the system have been made during a complete operation cycle lasting about three hours. Mass flow rates at different sublimation assembly and thermal throttle temperatures have been measured by means of a method based on charcoal chemical traps. The system has proved to be capable of delivering an iodine mass flow rate in a range between 0.5 to 1.5 mg/s with a resolution better than 0.05 mg/s, being the sublimation assembly temperature regulated between 90 and 106 ◦C and the thermal throttle temperature between 100 and 112 ◦C. Electrical power delivered to the feeding system (sublimation assembly, valve, thermal throttle) has been up to 24 W during the heating up of the system starting from room temperature and up to 3 W during the steady state operation

The effect of alternative propellants on the electron drift instability in Hall-effect thrusters: Insight from 2D particle-in-cell simulations

International audienceHall-effect thrusters (HETs) operated with xenon are one of the most commonly used electric propulsion technologies for a wide range of space missions, including drag compensation in low Earth orbit, station-keeping, and orbital insertion, as access to space becomes more affordable. Although anomalous electron transport, the electron drift instability (EDI), and secondary electron emission (SEE) have been studied experimentally and numerically in xenon-based HETs, the impact of alternative propellants is still poorly characterized. In this work, a two-dimensional particle-in-cell/Monte Carlo collision code is used to model the (r – θ) plane of a HET operated separately with four different noble gases: xenon, krypton, argon, and helium. Models for electron induced secondary electron emission (SEE) and dielectric walls are implemented in order to investigate the coupling between the propellant choice and the radial thruster walls. For all conditions and propellants studied, an EDI and enhanced electron cross-field transport are observed. The frequency of the instability, as well as the electron mobility, is compared with analytical expressions from a recently developed kinetic theory. Confirming this theory, it is shown that while the frequency of the EDI depends on the propellant mass, the electron mobility appears to be almost independent of the propellant choice