Stark broadening of B IV lines for astrophysical and laboratory plasma research

Stark broadening parameters for 36 multiplets of B IV have been calculated using the semi-classical perturbation formalism. Obtained results have been used to investigate the regularities within spectral series and temperature dependence.     

Stark widths of Ar III spectral lines in the atmospheres of subdwarf B stars

Using semiclassical perturbation approach in impact approximation, we have calculated Stark widths for 32 spectral lines of doubly charged argon (Ar III). Oscillator strengths are calculated using Hartree–Fock method with relativistic correction (HFR) and an atomic model including 17 configurations. Energy levels are taken from NIST database. For perturbing levels for which the corresponding energy does not exist in NIST database, the calculated energies are used. Our widths are compared with the experimental results. The results presented here are of interest for modelling and investigation of stellar atmospheres since argon in different ionization stages is observed in many astrophysical objects. Finally, the importance of Stark broadening mechanism is studied in the atmospheric conditions of sdB stars. Electron impact Stark widths are compared to thermal Doppler widths as a function of temperature and optical depth of atmospheric layers.     

New line profiles of Li–H2 for brown dwarfs

In order to calculate the opacity of a gas it is necessary to consider how its constituent atoms are perturbed by the surrounding medium. This is required both in order to calculate the equation of state, and in order to determine the profiles of the spectrum lines. In this work we report new theoretical Li line profiles perturbed by H₂ and their dependence with temperature.     

Low ionization lines in high luminosity quasars: The calcium triplet

In order to investigate where and how low ionization lines are emitted in quasars we are studying a new collection of spectra of the CaII triplet at λ8498, λ8542, λ8662 observed with the Very Large Telescope (VLT) using the Infrared Spectrometer And Array Camera (ISAAC). Our sample involves luminous quasars at intermediate redshift for which CaII observations are almost nonexistent. We fit the CaII triplet and the OI λ8446 line using the Hβ profile as a model. We derive constraints on the line emitting region from the relative strength of the CaII triplet, OI λ8446 and Hβ.     

Application of novel force control strategies to enhance robotic abrasive belt grinding quality of aero-engine blades

Robotic belt grinding has emerged as a finishing process in recent years for machining components with high surface finish and flexibility.The surface machining consistency, however,is difficult to be guaranteed in such a process.To overcome this problem, a method of hybrid force-position control combined with PI/PD control is proposed to be applied in robotic abrasive belt grinding of complex geometries.Voltage signals are firstly obtained and transformed to force information with signal conditioning methods.Secondly, zero drift and gravity compensation algorithms are presented to calibrate the F/T transducer which is installed on the robot end-effector.Next, a force control strategy combining hybrid force-position control with PI/PD control is introduced to be employed in robotic abrasive belt grinding operations where the force control law is applied to the Z direction of the tool frame and the positon control law is used in the X direction of the tool frame.Then, the accuracy of the F/T transducer and the robotic force control system is analyzed to ensure the stability and reliability of force control in the robotic grinding process.Finally, two typical cases on robotic belt grinding of a test workpiece and an aero-engine blade are conducted to validate the practicality and effectiveness of the force control technology proposed.     

Low Velocity Collisions and the Growth of Planetesimals

The physics of low velocity collisions (5 m/s to 40 m/s) between basalt bodies ranging in size from 1 m to 10 km is studied in an effort to investigate the early phases of planetesimal accretions. To assess the importance of the internal structure of planetesimals on the outcome of the collisions, we model them either as solid spheres or as rubble piles with a filling factor of 0.5. The collisions are simulated using a three dimensional Smooth Particle Hydrodynamics (SPH) code that incorporates the combined effects of material strength and a brittle fragmentation model. This approach allows the determination not only of the mass of the largest fragments surviving the collisions but also their dynamical characteristics. We find that low velocity collisions are for equal incoming kinetic energy per gram of target material considerably more efficient in destroying and dispersing bodies than their high velocity counterparts. Furthermore, planetesimals modeled as rubble piles are found to be characterized by a disruption threshold about 5 times smaller than solid bodies. Both results are a consequence of a more efficient momentum transfer between projectile and fragments in collisions involving bodies of comparable sizes. Size and shape dependent gas drag is shown to provide relative collision velocities between similar meter-sized objects well in excess of the critical disruption threshold of either rubble piles or solid bodies. Unless accretion can proceed avoiding collisions between bodies of similar masses, the relative weakness of bodies in this size range creates a serious bottleneck for planetesimal growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Optical/infrared observations unveiling the formation,nature and evolution of High-Mass X-ray Binaries

In this review I first describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: (i) Be circumstellar disc, (ii) supergiant stellar wind, and (iii) Roche lobe filling supergiants.     

The Solar Quiet Chromosphere—Corona Transition Region

The chromosphere-corona transition region of the Sun enjoys both simplicities of character and complexities of character which result from its very thin geometrical extent. The simplicities derive from the reasonably clear view of the energy balance (both observationally and theoretically), while the complexities derive from both the proximity of the not-so-clearly viewed regions below and above, and the almost certain convolutions and perhaps discontinuities in the three dimensional geometry of the transition sheet. While observational resolution and spectral information has improved greatly in recent years, the problems associated with a single vantage point, the Earth and its environs, have not gone away. To understand the transition region we must resolve structures radially and temporally as well as in the plane of the sky. This revised version was published online in June 2006 with corrections to the Cover Date.     

脉宽调制器中一类振荡器的全面解析结果

用分析法全面讨论脉宽调制器（IC：1842/3/4/5,1842A/3A/4A/5A）中振荡器的振荡特征参数（占空比D和频率f）与外接电阻R和电容C的关系.我们得到以R、C为自变量表达D和f的函数,以D、f为自变量求R、C的函数.并根据这些函数的计算结果绘制描述D、f、R、C（1F）4个参数之间的关系曲线.这些结果,不仅提升了对这类振荡器的认知,而且可供设计时直接引用和参考.     

Soft gamma repeaters

The observational properties of the soft gamma repeaters are reviewed briefly, starting with the time histories and energy spectra of their bursts. The short bursts and giant flares are compared. Their quiescent emission is presented, and the context of the magnetar model is discussed.