The 1996-1997 Fading of V651 Monocerotis, the Binary Central Star of the Planetary Nebula NGC 2346
V651 Mon is the binary central star of the bipolar planetary nebula NGC 2346. The star showed the second-ever deep fading in 1996–1997, which was presumably caused by obscuration by a dust cloud in the planetary nebula, as was proposed to explain the 1981–1985 event. The entire duration of the 1996–1997 event was ∼400d, remarkably shorter than the 1981–1985 event, suggesting that the obscuring body was smaller or had a larger tangential velocity. The most remarkable feature in this event was the presence of a sharply defined transient clearing (brightening). From the time-scale of the variation, we propose an upper limit of the projected scale of several times ∼ 10 11 cm of the structure responsible for the brightening. This observation provides the first evidence for a sharply defined,
A comprehensive population synthesis study of post‐common envelope binaries
We apply population synthesis techniques to calculate the present-day population of post-common envelope binaries (PCEBs) for a range of theoretical models describing the common envelope (CE) phase. Adopting the canonical energy budget approach, we consider models where the ejection efficiency α CE is either a constant or a function of the secondary mass. We obtain the envelope binding energy from detailed stellar models of the progenitor primary, with and without the thermal and ionization energy, but we also test a commonly used analytical scaling. We also employ the alternative angular momentum budget approach, known as the γ-algorithm. We find that a constant, global value of α CE >~ 0.1 can adequately account for the observed population of PCEBs with late spectral-type secondaries. However, this prescription fails to reproduce IK Pegasi (IK Peg), which has a secondary with spectral type A8. We can account for IK Peg if we include thermal and ionization energy of the giant's envelope, or if we use the γ-algorithm. However, the γ-algorithm predicts local space densities that are 1 to 2 orders of magnitude greater than estimates from observations. In contrast, the canonical energy budget prescription with an initial mass ratio distribution that 
favours unequal initial mass ratios (n(q i ) ~ 
q -0.99 i ) gives a local space density which is in good agreement with observations, and best reproduces the observed distribution of PCEBs. Finally, all models fail to reproduce the sharp decline for orbital periods, P orb >~ 1 d in the orbital period distribution of observed PCEBs, even if we take into account selection effects against systems with long orbital periods and early spectral-type secondaries.
Time behavior of gas pressure and PD activity in insulation cavities under AC voltage
In the framework of developing defect-based life models (i.e. the life model of partial discharge-induced damage growth from a micro-void in polymer matrix), ageing tests were performed on PE layered specimens with artificial cavities under constant gas pressure and constant gas volume conditions, respectively. Time behavior of the discharge repetition rate and amplitude were recorded and compared under these two conditions. Results show that pressure variation has little influence on PD activities at constant gas volume. Under constant gas pressure, the evolution of gas volume has similar characteristic to the product of discharge amplitude and repetition rate.