A Framework for Realistic and Systematic Multicast Performance Evaluation

Previous multicast research often makes commonly accepted but unverifed assumptions on network topologies and group member distribution in simulation studies. In this paper, we propose a framework to systematically evaluate multicast performance for different protocols. We identify a series of metrics, and carry out extensive simulation studies on these metrics with different topological models and group member distributions for three case studies. Our simulation results indicate that realistic topology and group membership models are crucial to accurate multicast performance evaluation. These results can provide guidance for multicast researchers to perform realistic simulations, and facilitate the design and development of multicast protocols

VLBA 24 and 43 GHz observations of massive binary black hole candidate PKS 1155+251

PKS 1155+251 is a radio-loud quasar source at z=0.203. Observations using very long baseline interferometry (VLBI) at ~2, 5, 8 and 15 GHz show that the structure of the radio source is quite complicated on parsec scales and that the outer hot spots are apparently undergoing a significant contraction. Because these results cannot be fully explained based on the compact symmetric object (CSO) scenario with a radio core located between the northern and southern complexes, we made observations with the Very Long Baseline Array (VLBA) at 24 and 43 GHz to search for compact substructures and alternative interpretations. The results show that the radio core revealed in the previous VLBI observations remains compact with a flat spectrum in our sub-milli-arcsecond--resolution images; the northern lobe emission becomes faint at 24 GHz and is mostly resolving out at 43 GHz; the southern complex is more bright but has been resolved into the brightest southern-end (S1) and jet or tail alike components westwards. Explaining the southern components aligned westward with a standard CSO scenario alone remains a challenge. As for the flatter spectral index of the southern-end component S1 between 24 and 43 GHz in our observations and the significant 15 GHz VLBA flux variability of S1, an alternative scenario is that the southern complex may be powered by a secondary black hole residing at S1. But more sensitive and high-resolution VLBI monitoring is required to discriminate the CSO and the binary black hole scenarios.Comment: 7 pages, 3 figures, accepted by MNRA

Monopole-charged pulsars and relevant issues

The aligned pulsars whose rotation axes and magnetic dipole axes are parallel should be positively charged. The total charge of pulsars is calculated after considering the electromagnetic field in and out the star under a specific condition. The statistical relation between the pulsar's rotation energy loss rate (or the period derivative) and the period may hint that the millisecond radio pulsars with small periods could be low-mass bare strange stars.Comment: 4 pages, 1 figures, and 1 tabl

Compression Behaviour of Natural and Reconstituted Clays

International audienceThe intercept of the log(1+e) - logσv' straight line is introduced to describe the effect of the starting point on the compressibility of natural and reconstituted clays. It is found that when the effective stress exceeds the remoulded yield stress, the compression behaviour of reconstituted clays is controlled solely by the water content at the remoulded yield stress and the liquid limit. Comparison of the compression behaviour of natural and reconstituted clays indicates that their difference in compressibility is caused by soil structure and the difference in water content at the compression starting point. The compression behaviour of natural clays can be classified into three regimes: 1) the pre-yield regime characterised by small compressibility with soil structure restraining the deformation up to the consolidation yield stress; 2) the transitional regime characterised by a gradual loss of soil structure when the effective stress is between the consolidation yield stress and the transitional stress; and 3) the post-transitional regime characterised by the same change law in compression behaviour as reconstituted clays when the effective stress is higher than the transitional stress. For the investigated clays, the transitional stress is 1.0-3.5 times the consolidation yield stress. The compression index varies solely with the void ratio at an effective stress of 1.0 kPa for both natural clays in post-transitional regime and reconstituted clays when the effective stress exceeds the remoulded yield stress, and when compressed in such cases the compression curves of both natural clays and reconstituted clays can be normalised well to a unique line using the void index