The inner vacuum gap model has become the foundation stone of most theories on pulsar radio emission. The fundamental picture of this model is the sparking, which was conjectured to be induced by magnetic absorption of background gamma photons. However, a question is, can the sparking be triggered in the millisecond pulsars (MSPs) with magnetic fields (B) only about 108 G? We investigate this problem by including the pair production above the inner gap. Under the assumption that the magnetic field is dipolar, our results show the background gamma-ray emission can not be the key factor that triggers the sparking, at least not in MSPs with B - 108 G, if the temperature in the polar cap region is only so high as is observed (< 4 × 106 K). Some other mechanisms are required. 相似文献
This paper has reported the first application of 40Ar/39 Ar dating to orthoclase from Qitianling granite. The resultant plateau ages yielded by three orthoclase specimens 2KL-17, 99LQ-2 and 2KL-31 (Note: The last one was taken from the part of granite which had been attributed to Cailing super-unit of the Indosinian Period by the former researchers) collected from the said granite are (139.57±2.79) Ma, (140.55±2.81) Ma and (144.91±2.90) Ma respectively. The above-mentioned ages represent the closed 40Ar/39 Ar age of the orthoclase. The consistency in age dating results, the similarity in geochemical characteristics and rock textures, and the NW-SE orientation of orthoclase phenocrysts almost throughout the granite, provide evidence for the intimate relationship between the Furong super-unit and the Cailing super-unit that form the main part of the granite, suggesting that they are products of comagmatic conjugate differentiation during the Late Jurassic. This paper also makes a comparison between the Qitianling granite and the Qianlishan granite.
Knowledge of the camera trajectory, which may be determined from the motions between consecutive frames of a video clip, can be used to register images for constructing image mosaics. We discuss a mosaic-based positioning framework for building photo-mosaics and concurrently utilizing them for improved positioning. In this approach, the mosaic is directly exploited in bounding the accumulation of position errors as we integrate the incremental motions of the camera. It is also shown that two earlier closed-form solutions for the estimation of motion directly from spatio-temporal image gradients, as for most gradient-based techniques based on the application of linear(ized) image motion constraint equations, are corrupted with systematic biases. These can be reduced significantly by incorporating the higher-order terms. We propose recursive methods to solve the new nonlinear constraint equations, and investigate the performance of the new solutions in a number of experiments with synthetic and real data 相似文献
The cycling representer algorithm of Xu and Daley (2000) is a weak constraint four-dimensional variational data assimilation algorithm. It was successfully applied to a one-dimensional transport problem and was able to successfully extract the signal from noisy and sparse observations. The algorithm, however, has not previously been applied to a multivariate, multidimensional system with dynamic instability. The algorithm is also very computationally demanding and awaits considerable enhancement in computer power before being practical for operational forecast models. We have two objectives in this paper. The first is to apply the cycling representer algorithm to a two-dimensional, multivariate barotropically unstable linear shallow water system. The second objective is to formulate and test an accelerated representer algorithm that is much more computationally tractable than the cycling representer algorithm itself. A linear shallow water system with a barotropically unstable basic state was used as a test bed to conduct data assimilation experiments. The evolution of a 'neutral' eastward-propagating singular vector was selected as the 'truth', against which all data assimilation experiments were to be evaluated. The results indicated that the cycling representer algorithm was capable of providing satisfying state estimates for a multivariate, multidimensional system. The results from the accelerated representer algorithm were very encouraging because it is sufficiently computationally tractable to be used on present day multi-processor machines for operational applications. 相似文献