Diffusive propagation of fast particles in the presence of a moving shock wave

Based on an analytical model, we determined the temporal dynamics of the spectral shape and spatial distribution of the particles that were impulsively (in time) injected with a specified spectrum in the vicinity of a moving plane shock front. We obtained a condition to determine the influence of the shock front on the particle propagation, where the spatial diffusion coefficient of the particles plays a major role. Diffusive shock acceleration is shown to strongly affect low-energy particles (the intensity maximum coincides spatially with the shock front; hard and soft spectral regions are formed in the spectrum) and weakly affect high-energy particles (the time at which the intensity reaches its maximum is well ahead of the shock arrival time; the spectral shape does not change). In events accompanied by a significant increase in the turbulence level, the influence of the shock front on high-energy particles can change from weak to strong. This change shows up in the spatial distribution and spectral shape of the particles. The dynamics of the particle intensity, calculated with the diffusion coefficients that were determined in accordance with the quasi-linear theory for measured turbulence levels, qualitatively corresponds to the observed solar energetic-particle intensity.     

紫金山天文台4.5-7.5 GHz太阳快速频谱仪图像

运用多种方法，对紫金山天文台4．5—7．5GHz太阳快速频谱仪获得的太阳微波爆发频谱图像进行后续处理，尽可能地去除噪声和干扰，还原爆发事件的本来面目，并突出感兴趣的部分，在MATLAB的平台支持下编写了WINDOWS下的应用软件，取得了较为满意的结果．     

Effective Sensitivity of A Non-uniform Phased Array of Short Dipoles

Short dipoles are a key element in new low frequency array antennas as proposed for LOFAR and other astronomical applications. Unfortunately standard texts on short dipole antennas are based on the effective area and do not lead to an astronomically useful sensitivity formulation in a straightforward manner. The concept of maximum effective area is applied to arrays of short dipoles and allows expressing the sensitivity as the ratio of this area over the effective sky brightness temperature as long as the output noise power is dominated by the antenna input radiation. For both quantities we only need to know the array directivity pattern that includes the mutual coupling effects when the actual loading conditions of the array elements are taken into account. Short dipole elements have a constant directivity pattern for frequencies below resonance, but they exhibit strong complex impedance variations that provide only narrow band performance when power matching is applied as required in transmit applications. However, in receive applications voltage or current sensing can be realized, for example with an active balun. Assisted by the steep increase of the sky brightness with wavelength for frequencies below 300 MHz, this can provide sky noise dominated performance over at least a three to one frequency range. Still the low frequency limit is determined by the amplifier noise contribution and the losses in the antenna and in the dielectric ground surrounding the elements. We show that for a sparse array with the elements non-uniformly distributed according to an exponential shell model, a constant sensitivity can be obtained over a frequency range of at least two octaves. In addition, such a configuration has a factor of six greater sensitivity than a rectangular array for a large part of the frequency band.     

行星状星云NGC 2242的红外辐射

被Zwicky等人列为星系的NGC 2242,后来刘继英等人发现它具有发射特征并认为可能是行星状星云。前原英夫等人用有缝光谱肯定了它是一个行星状星云。我们证认它是IRAS06304+4448。根据IRAS Point Source Catalog所提供的25μm和60μm的辐射流量,我们得到了这一行星状星云的尘埃温度T_d=130K,光学厚度τ_(25μm)=1.98×10~(-7)和尘埃的总质量M_d=1.0×10~(-7)到1.8×10~(-6)M_⊙之间。     

Cyclotron absorption of radio emission within pulsar magnetospheres

Absorption of radio emission through normal cyclotron resonance within pulsar magnetospheres is considered. The optical depth for cyclotron damping is calculated using a plasma distribution with an intrinsically relativistic spread. We argue that such a broad distribution is plausible for pulsar plasmas and that it implies that a class of pulsars that should have cyclotron damping extends to include young pulsars with shorter periods and stronger magnetic fields. There is no obvious observational evidence for disruption of radio pulses, which implies that the optical depth cannot be too large. We propose that cyclotron resonance may cause marginal absorption of radio emission. It is shown that such marginal absorption produces potentially observable asymmetric features for double-peak pulse profiles with wide separation, with one peak tending to be suppressed.