Spectral evolution of the peculiar Ic Supernova 1998bw

Supernova 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supernovae and probably the first supernova associated with a γ -ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the Anglo-Australian Telescope, the UK Schmidt Telescope and the Siding Springs Observatories 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 d after V -band maximum in comparison with well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from observations of classical Ic supernovae (SNe), we find that the evolution from the photospheric to nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10–50 per cent higher than other SNe and on day 94 emission lines are 45 per cent broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that an additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope.     

A homomorphic model for identifying abrupt abnormalities of landslide forerunners

A homomorphic model is presented for identifying the abnormalities of landslide forerunners from an observation time series. The model developed here is better than previous statistical models because it considers, in the evolution process of the landslide, material degradation or smoothing of the slip plane, groundwater level or pore water pressure fluctuations, and unexplained or random behavior. The identification of abnormalities is made in terms of the confidence interval [−qS, qS], where q is the confidence and S is the output error of the homomorphic model. The case study of the Saleshan landslide in Gansu, China, is presented to illustrate the capability and merit of the homomorphic model.     

Combining the geodetic models of vertical crustal deformation

Different kinds of analytical models of vertical curstal deformation have both advantages and disadvantages, and are appropriate to different deformation patterns. It is difficult to identify which deformation model is most suitable for a particular deformation area. In order to obtain a more precise and reliable analytical result, the combined model based on forecast theory has been approached. As a result, the fitting ability of single models is significantly improved. The combined model still possesses the same important features as the single models, which enable transferal of the derived crustal deformation information, within or even outside the time span of the data coverage, from geodetic sites to any user-specified locations where geodetic data may not exist. Examples are presented of both numerical simulation and a real-life situation, and the results are analysed in detail to demonstrate the efficiency of the proposed methodology. Received: 26 January 1998 / Accepted 14 August 1998     

Symbiodinium (internal transcribed spacer 2) diversity in the coral host Agaricia lamarcki (Cnidaria: Scleractinia) between shallow and mesophotic reefs in the Northern Caribbean (20–70 m)

This study investigated differences in Symbiodinium diversity in the scleractinian coral species Agaricia lamarcki between shallow (20–25 m) and mesophotic (50–70 m) depths in the Northern Caribbean. Corals were sampled in each of four shallow sites (20–25 m; n = 18) and three mesophotic sites (50–70 m; n = 18) from Mona Island (Puerto Rico) and the US Virgin Islands during a mesophotic exploratory cruise and from the La Parguera shelf edge, off Southwestern Puerto Rico. Symbiodinium diversity was assessed using internal transcribed spacer 2 sequences clustered into operational taxonomic units (OTUs). Clustering resulted in eight clade C OTUs and one clade D OTU. Of these, there were three common Symbiodinium OTUs consisting of C3 and D1a.N14 in shallow reefs and C11.N4 in mesophotic reefs. Statistical tests (permutational multivariate analysis of variance and analysis of similarity) showed significant differences between clade C Symbiodinium OTUs in A. lamarcki colonies located at shallow and mesophotic depths, indicating symbiont zonation. Symbiodinium diversity in A. lamarcki from the Northern Caribbean is comparable to previous reports in the Southern Caribbean for this species. This is the first report of the thermal tolerant species Symbiodinium trenchii (D1a) in A. lamarcki.     

Numerical simulation of the fracture process in cutting heterogeneous brittle material

The process of cutting homogeneous soft material has been investigated extensively. However, there are not so many studies on cutting heterogeneous brittle material. In this paper, R‐T^2D (Rock and Tool interaction), based on the rock failure process analysis model, is developed to simulate the fracture process in cutting heterogeneous brittle material. The simulated results reproduce the process involved in the fragmentation of rock or rock‐like material under mechanical tools: the build‐up of the stress field, the formation of the crushed zone, surface chipping, and the formation of the crater and subsurface cracks. Due to the inclusion of heterogeneity in the model, some new features in cutting brittle material are revealed. Firstly, macroscopic cracks sprout at the two edges of the cutter in a tensile mode. Then with the tensile cracks releasing the confining pressure, the rock in the initially high confining pressure zone is compressed into failure and the crushed zone gradually comes into being. The cracked zone near the crushed zone is always available, which makes the boundary of the crushed zone vague. Some cracks propagate to form chipping cracks and some dip into the rock to form subsurface cracks. The chipping cracks are mainly driven to propagate in a tensile mode or a mixed tensile and shear mode, following curvilinear paths, and finally intersect with the free surface to form chips. According to the simulated results, some qualitative and quantitative analyses are performed. It is found that the back rake angle of the cutter has an important effect on the cutting efficiency. Although the quantitative analysis needs more research work, it is not difficult to see the promise that the numerical method holds. It can be utilized to improve our understanding of tool–rock interaction and rock failure mechanisms under the action of mechanical tools, which, in turn, will be useful in assisting the design of fragmentation equipment and fragmentation operations. Copyright © 2002 John Wiley & Sons, Ltd.     

Pulsed gamma rays from Geminga

The pulsed gamma ray spectrum is obtained by analyzing COS-B data of observation no. 14, 39, 54 and 64. We find that the pulsed spectrum differs significantly from that of previous reports in which the pulsed component and steady component are not separated. A clear spectral break of the pulsed spectrum occurs at ~ 100 MeV and the majority of the steady emission is concentrated in the lower energy band. We fit the pulsed spectrum by both the outer gap model and the polar gap model and conclude that only the outer gap model can explain the observed spectrum. Furthermore, the gamma ray spectrum suggests that Geminga is located at a distance ~ 300 pc and is a nearly orthogonal rotator.     

Identification of ice-rafted and other exotic material in deep-sea dredge hauls

It is often difficult to distinguishin situ material from exotic clasts in rock dredge hauls from deep ocean sites. A study of ice-rafted material in the northeast Atlantic Ocean has been undertaken for which a set of criteria has been established for the identification of glacial erratics. These criteria may be divided into two categories. The first is for criteria based on direct evidence visible on individual clasts, for example, striations and faceting. The second is for inferred evidence drawn from complete dredge hauls, for example, variations in the thickness of manganese coatings.     

Structural analysis of FAST reflector supporting system

According to the deformation and movement requirements of the FAST reflector, a multi-purpose analysis, including the load-bearing behavior, deformation, construction costs of the reflector supporting structure and its model, is presented in this paper. The advantages and disadvantages of steel and aluminum alloy structures are also discussed and compared through detailed design calculations under load-bearing capacity and normal working conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Finite layer analysis of the behaviour of a raft on a consolidating soil

A numerical method is developed in this paper for the analysis of the behaviour of a raft resting on a consolidating soil. The response of the raft under an applied loading is determined using the finite layer method for the soil and the finite element method for the raft. By considering deflection compatibility on the contact surface, the distribution of contact pressure is computed at various time steps. The settlement and bending moment in the raft is then evaluated by applying the calculated contact pressure back to the raft. It is shown that, in some cases, the maximum moment in the raft occurs during consolidation and that checking the final moment in the raft by use of elastic theory may not be sufficient.