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The longitudinal moment pitch-up ahead of the stall angle can decrease the available range of maximum lift coefficient. It has a major influence on take-off and landing performance, and safety of a civil aircraft. Numerical simulation by CFD (Computational Fluid Dynamics) is used to study the longitudinal moment characteristics of a civil aircraft with landing configuration in this paper. Combined with the flowfield post-processing interpolation technology, the reason of longitudinal moment pitch-up is analysed and discussed. According to the research results, the characteristics of longitudinal moment pitch-up are further improved by modification. The relevant research methods and results have some guiding significance for improving the moment characteristics of a civil aircraft.

Both high and low frequency relaxation oscillations have been observed in an argon capacitive discharge connected to a peripheral grounded chamber through a slot with dielectric spacers. The oscillations, observed from time-varying optical emission of the main discharge chamber, show, for example, a high frequency (46 kHz) relaxation oscillation at 100 mTorr, with an absorbed power near the peripheral breakdown, and a low frequency (2.7–3.7 Hz) oscillation, at a higher absorbed power. The high frequency oscillation is found to ignite a plasma in the slot, but usually not in the periphery. The high frequency oscillation is interpreted by using an electromagnetic model of the slot impedance, combined with the circuit analysis of the system including a matching network. The model is further developed by using a parallel connection of variable peripheral capacitance to analyse the low frequency oscillation. The results obtained from the model are in agreement with the experimental observations and indicate that a variety of behaviours are dependent on the matching conditions.

Low-frequency (2.72–3.70Hz) relaxation oscillations at 100 m Torr at higher absorbed power were observed from time-varying optical emission of the main discharge chamber and the periphery. We interpret the low frequency oscillations using an electromagnetic model of the slot impedance with parallel connection variational peripheral capacitance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations, and indicate a variety of behaviours dependent on the matching conditions.

Helium-containing Ti films are prepared using magnetron sputtering in the helium–argon atmosphere. Isochronal annealing at different temperatures for an hour is employed to reveal the behaviour of helium bubble growth. Ion beam analysis is used to measure the retained helium content. Helium can release largely when annealing above 970 K. A thermal helium desorption spectroscopy system is constructed for assessment of the evolution of helium bubbles in the annealed samples by linear heating (0.4 K/s) from room temperature to 1500 K. Also, Doppler broadening measurements of positron annihilation radiation spectrum are performed by using changeable energy positron beam. Bubble coarsening evolves gradually below 680 K, migration and coalescence of small bubbles dominates in the range of 680–970 K, and the Ostwald ripening mechanism enlarges the bubbles with a massive release above 970 K.

Relaxation oscillations due to plasma instabilities at frequencies ranging from a few Hz to tens of kHz have been observed in various types of plasma processing discharges. Relaxation oscillations have been observed in electropositive capacitive discharges between a powered anode and a metallic chamber whose periphery is grounded through a slot with dielectric spacers. The oscillations of time-varying optical emission from the main discharge chamber show, for example, a high-frequency (~ 40?kHz) relaxation oscillation at 13.33Pa, with an absorbed power being nearly the peripheral breakdown power, and a low-frequency (~ 3 Hz) oscillation, with an even higher absorbed power. The high-frequency oscillation is found to ignite plasma in the slot, but usually not in the peripheral chamber. The kilohertz oscillations are modelled using an electromagnetic model of the slot impedance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations, and indicate a variety of behaviours dependent on the matching conditions. In low-pressure inductive discharges, oscillations appear in the transition between low-density capacitively driven and high-density inductively driven discharges when attaching gases such as SF6 and Ar/SF6 mixtures are used. Oscillations of charged particles, plasma potential, and light, at frequencies ranging from a few Hz to tens of kHz, are seen for gas pressures between 0.133 Pa and 13.33 Pa and discharge powers in a range of 75?1200 W. The region of instability increases as the plasma becomes more electronegative, and the frequency of plasma oscillation increases as the power, pressure, and gas flow rate increase. A volume-averaged (global) model of the kilohertz instability has been developed; the results obtained from the model agree well with the experimental observations.

We have observed relaxation oscillations in a capacitive discharge in Ar gas, connected to a peripheral ground chamber. The plasma oscillations observed from time-varying optical emission from the main discharge chamber show, for example, a high frequency (75.37 kHz) relaxation oscillation, at 100 mTorr and 8 W absorbed power, and a low frequency (2.72 Hz) relaxation oscillation, 100 mTorr and 325 W absorbed power. Time-varying optical emission intensity and plasma density are also detected with a Langmuir probe. The theoretical result agrees well with experiments.

The incident angle dependence of secondary electron emission induced by a swift H2+ ion impinging on carbon is studied using the Monte Carlo method combined with the semiempirical theory. The relationships both between the electron emission yield and the project angle and between the statistics and the projectile angle are investigated. The results show that the backward electron emission yield deviates from the inverse cosine law, due to the effect of the valence electrons of H2+. The ratio of the forward electron emission yield to the backward electron emission yield at the inclining incidence is different from that at the normal incidence. The statistical distribution of electron emission is independent of the incident angle. The value of b, the deviation parameter from the Poisson distribution, increases with projectile energy.

The hydrogenation properties of Zr samples with and without an Ni overlayer under various plasma conditions were investigated by means of non-Rutherford backscattering and elastic recoil detection analysis. The theoretical maximum hydrogen capacity, 66.7 at%, could be achieved at a hydrogen absolute pressure of ~2 Pa and a substrate temperature of ~393 K for a plasma irradiation of only 10 min; this was significantly greater than that for gas hydrogenation under the same hydrogen pressure and substrate temperature. It was also found that the C and O contamination on the sample surface strongly influences the hydrogenation, and that the maximum equilibrium hydrogen content drops dramatically with the increasing total contamination. In addition, the influence of the Ni overlayer on the plasma hydrogenation is discussed.

Titanium thin films incorporated with helium are produced by pulsed laser deposition in an electron cyclotron resonance helium plasma environment. Helium is distributed evenly in the film and a relatively high He/Ti atomic ratio (~20%) is obtained from the proton backscattering spectroscopy. This high concentration of helium leads to a surface blistering which is observed by scanning electron microscopy. Laser repetition rate has little influence on film characters. Substrate bias voltage is also changed for the helium incorporating mechanism study, and this is a helium ion implantation process during the film growth. Choosing suitable substrate bias voltage, one can avoid the damage produced by ion implantation, which is always present in general implantation case.

An energy dependence of the axial minimum channeling yield in GexSi1-x/Si(100) Strained-layer superlattice is observed in the energy range of impinging He+ ions from 1.2 to 3.0 MeV. For [100] axial channeling, the measurements are in agreement with what have been known in a single crystal. However, for [110] axial channeling, it is found that the minimum channeling yields increase markedly with the increase of He+ ion energy, which is contrary to the general channeling behaviors in a single crystal. A tentative model is suggested to explain this aberrance.

The backward secondary electron emission yields of MeV ions (H+, He+, He++, Cl, Si, and Cu) impinging on thick carbon and gold targets are studied. The measured results for H+ (1 MeV ≤ E ≤ 5 MeV) on carbon are proportional to the electronic stopping power. Our experimental data and fitting formula of yields for H+ (1 MeV ≤ E ≤ 4.5 MeV) impacting Au are compared with the theoretical expectation. The influence of the collective field and the charge state of ions on the secondary electron emission yield is discussed.