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[1] We make a statistical survey of interplanetary (IP) shocks and storm sudden commencements (SSCs) observed between 1995 and 2004. We find that 75% of SSCs are associated with shocks, consistent with previous work. We use this survey to investigate the effect of the interplanetary shock strength and orientation on the SSC rise time. We find that the higher the speed of an IP shock, the less time it takes to sweep by the magnetosphere, and thus the shorter the rise time of the corresponding SSC. The orientation of an IP shock also effects the SSC rise time. Generally speaking, a highly oblique shock causes asymmetric compression of the magnetosphere with respect to the noon-midnight meridian, takes more time to sweep by magnetosphere, and thus results in a longer rise time of the SSC. Citation: Wang, C., C. X. Li, Z. H. Huang, and J. D.Richardson (2006), Effect of interplanetary shock strengths and orientations on storm sudden commencement rise times, Geophys.

The production of large‐scale magnetic fields and associated crustal magnetization in lunar basin‐forming impacts is investigated theoretically. Two‐dimensional numerical models of the partially ionized vapor cloud produced in such impacts show that the low‐density periphery of the cloud expands thermally around the Moon and converges near the antipode in a time of the order of 400 to 500 s for silicate impactor velocities of 15 to 20 km/s. Fields external to the impact plasma cloud are produced by the magnetohydrodynamic interaction of the cloud with ambient magnetic fields and plasmas. For the most typical case in which the Moon is immersed in the solar wind plasma and its embedded magnetic field, an MHD shock wave forms upstream of the cloud periphery separating the shocked solar wind from the free‐stream solar wind. For impacts occurring on the downstream (antisunward) hemisphere, convergence of the impact plasma cloud and associated MHD shock waves occurs on the upstream side and results in a large antipodal field amplification. For impacts occurring on the upstream (sunward) hemisphere, some antipodal field amplification is still expected due to the finite electrical conductivity of the lunar interior (requiring an induced external magnetic field) and the likely presence of some residual plasma in the wake of the impact plasma cloud. During the period of compressed antipodal field amplification, seismic compressional waves from the impact converge at the antipode resulting in transient shock pressures that have been calculated to be as large as 2 GPa (20 kbar). This is near to the range of 50–250 kbar at which stable shock remanent magnetization has been found experimentally to occur in lunar soils. Significant crustal magnetization anomalies antipodal to lunar impact basins are therefore expected, consistent with orbital mapping results. Weaker magnetization observed peripheral to the Imbrium basin may also be explained by shock effects together with compressed ambient fields in a surface boundary layer. Although other processes such as cometary impacts and a former core dynamo may have contributed significantly to the observed paleomagnetism, meteoroid impact plasmas appear capable of explaining a major part of the large‐scale magnetization detected thus far from lunar orbit.

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[1] We perform a statistical survey of geospace magnetic field responses, including the geosynchronous magnetic field and the sudden impulses on the ground, to interplanetary shocks (IP shocks) between 1998 and 2005. The magnitude of the geosynchronous magnetic field (dB z ) responses to IP shocks depends strongly on local time, which peaks near the noon meridian; however, the relative magnitude of the responses depends only weakly on local time. These results are similar to those obtained from the statical study of the responses to solar wind dynamic pressure pulses. However, negative responses (where dB z is negative) were sometimes observed in the nightside of the magnetosphere even though the IP shocks always caused increases in the solar wind dynamic pressure, a new phenomenon not widely reported in the literature. Our analysis shows that $75% of negative responses in the midnight sector are associated with southward interplanetary magnetic field. For a moderately compressed magnetosphere, the amplitude of the geosynchronous response dB z could be determined by the average value of the background local magnetic field. As the magnitude of the upstream solar wind dynamic pressure increases, the rate of response increases correspondingly. The dB z at the geosynchronous orbit near local noon and the amplitude of sudden impulses (dSYM-H) on the ground are highly correlated.

In this paper a robust static-dynamic procedure has been developed. The development extends the capability of the Vulcan software to model the dynamic and static behaviour of steel buildings during both local and global progressive collapse of the structures under fire conditions. The explicit integration method was adopted in the dynamic procedure. This model can be utilized to allow a structural analysis to continue beyond the temporary instabilities which would cause singularities in the full static analyses. The automatic switch between static and dynamic analysis makes the Vulcan a powerful tool to investigate the mechanism of the progressive collapse of the structures generated by the local failure of components. The procedure was validated against several practical cases. Some preliminary studies of the collapse mechanism of steel frame due to columns' failure under fire conditions are also presented. It is concluded that for un-braced frame the lower loading ratio and bigger beam section can give higher failure temperature in which the global structural collapse happens. However, the localised collapse of the frame with the higher loading ratio and smaller beam section can more easily be generated.The bracing system is helpful to prevent the frame from progressive collapse. The higher lateral stiffness of the frame can generate the smaller vertical deformation of the failed column at the restable position. However, the global failure temperature of the frame is not sensitive to the lateral stiffness of the frame.

Residual properties of three-span continuous reinforced concrete slabs subjected to different compartment fires', Engineering Structures.

In this paper a robust non-linear finite element procedure is developed for three-dimensional modelling of reinforced concrete beam-column structures in fire conditions. Because of the changes in material properties and the large deflections experienced in fire, both geometric and NotationThe following symbols are used in this paper: