Calcium ion currents mediating oocyte maturation events

During maturation, the last phase of oogenesis, the oocyte undergoes several changes which prepare it to be ovulated and fertilized. Immature oocytes are arrested in the first meiotic process prophase, that is morphologically identified by a germinal vesicle. The removal of the first meiotic block marks the initiation of maturation. Although a large number of molecules are involved in complex sequences of events, there is evidence that a calcium increase plays a pivotal role in meiosis re-initiation. It is well established that, during this process, calcium is released from the intracellular stores, whereas less is known on the role of external calcium entering the cell through the plasma membrane ion channels. This review is focused on the functional role of calcium currents during oocyte maturation in all the species, from invertebrates to mammals. The emerging role of specific L-type calcium channels will be discussed

Injection locking of excimer lasers

Reliable injection locking of high-power unstable resonator excimer lasers can be achieved with extremely low reference oscillator power. The criteria for injection locking are discussed and experimental results are given

Transform-limited-bandwidth injection locking of an XeF laser

A pulsed Ar-ion laser, operating on the 3511 A line of the doubly ionized species, has been used to injection lock an unstable resonator XeF laser. A single longitudinal mode of the Ar-ion laser was selected with a Fabry-Perot etalon, and the resulting XeF bandwidth was measured to be approx. 50 MHz which is the Fourier-transform limit corresponding to the XeF laser pulse duration of approx. 20 ns. Since the XeF B ..-->.. X emission originates from more than one upper vibrational level, for this pulse duration it was determined that approx. 60% of the total output was available to be locked to the reference oscillator line. The 2 MW output beam was also found to be near (< 1.5 x) diffraction limited

Allocation of Reproductive Effort in Perennial Plants Under Pollen Limitation

International audienceWe find the evolutionarily stable allocation of reproductive effort in both hermaphroditic and dioecious perennial plants. The model focuses on the effect of pollen availability on the allocation of reproductive effort and on sex allocation. The model shows that the effect of pollen limitation depends on the detailed assumptions made about the delivery of pollen to individual plants. We consider two extreme models: the pollen-pool model, which assumes that pollen from different individuals is mixed before being delivered, and the single-donor model, which assumes that pollen delivered to each individual comes from only one pollen donor. In the pollen-pool model, a reduction of pollen availability is equivalent to an overall reduction in fertility, while, in the single-donor model, the results are more complex and depend on the sensitivity of fertility to changes in pollen availability. The results for hermaphroditic and dioecious species are quite similar once the sex ratio of the dioecious species is taken into account

SOME THOUGHTS AND OBSERVATIONS OF PHASE CONJUGATION IN THE ULTRAVIOLET

On rapporte des études de conjugaison de phases en U.V. utilisant les lasers KrF, XeF, et les lasers quadruples Nd : YAG. Les procédés étudiés sont les diffusions Brillouin et Raman stimulées, et le mélange de quatre ondes dégénérées. Dans certains cas des efficacités de conjugaison de phase de plus de 80% sont observées. Les implications et applications de ces phénomènes seront discutées.We report on ultraviolet phase conjugation studies using KrF, XeF, and quadrupled Nd : YAG lasers. Processes studied include stimulated Brillouin scattering, stimulated Raman scattering, and degenerate four-wave mixing. In some cases phase conjugate efficiencies of greater than 80% are observed. Implications and applications of these phenomena will be discussed

Ultraviolet phase conjugation

Diffraction-limited phase conjugate reflection of an injection-locked high-power (approx. 1 MW) ultraviolet excimer laser beam has been demonstrated via stimulated Brillouin scattering. Reflectivities higher than 70% were attained. Limitations as well as coherence and power requirements for image retention are discussed