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There was high prevalence of C-shaped canals in the mandibular second molars of Chinese population. The canal systems varied considerably in their anatomical configuration.

Chlorinated paraffins (CPs) are industrially produced in large quantities in the Liaohe River Basin. Their discharge inevitably causes environmental contamination. However, very limited information is available on their environmental levels and distributions in this typical industrial region. In this study, short chain CPs (SCCPs) were analyzed in sediments, paddy soils, and upland soils from the Liaohe River Basin, with concentrations ranging from 39.8 to 480.3 ng/g dry weight. A decreasing trend in SCCP concentrations was found with increasing distance from the cities, suggesting that local industrial activity was the major source of SCCP contamination. A preliminary sediment inventory of SCCPs indicated approximately 30.82 tonnes of SCCPs residual in the sediments from the Liaohe River. The average discharge of SCCPs was estimated to be about 74.4 mg/tonne industrial wastewater. The congener group profiles showed that the relative abundances of shorter chain and lower chlorinated CP congeners (C 10 −CPs with 5 or 6 chlorine atoms) in soils in rural areas were higher than in sites near cities, which demonstrated that long-range atmospheric transportation could be the major transport pathway. Environmental degradation of SCCPs might occur, where higher chlorinated congeners could dechlorinate to form the lower chlorinated congeners.

The present work examines the mechanism of formation of thermal shock crack patterns in ceramics. An attempt has been made to bridge the gap between theoretical predictions and experimental data. A set of experiments on thin ceramic specimens yielded two-dimensional readings of thermal shock crack patterns with periodical and hierarchical characteristics that vary with the thermal shock temperature. Based on the minimum potential energy principle the finite element method was used for numerical simulations, in which the temperature dependence of the material properties was considered. To overcome the difficulty of a lack of accurate data on the convective heat transfer coefficient at high temperatures, a "semi-inverse method" was developed, which explores a new method for estimating a physical quantity that is difficult to measure using physical quantities, which are relatively easy to measure. The numerical and experimental data were compared and discussed. The obtained numerical results are in good agreement with the experimental data. Furthermore, the numerical simulations can conveniently reproduce the evolution of thermal shock cracks, which is difficult to observe experimentally. In addition, some interesting phenomena related to thermal shock crack pattern evolution were observed. The present theoretical-numerical-experimental study has led to a much improved understanding of the formation and evolution of thermal shock crack patterns in ceramics.

A strengthening mechanism arising from the mineral bridges in the organic matrix layers of nacre (mother of pearl) is presented by studying the structural and mechanical properties of the interfaces in nacre. This mechanism not only increases the average fracture strength of the organic matrix interfaces by about five times, but also effectively arrests the cracks in the organic matrix layers and causes the crack deflection in this biomaterial. The present investigation shows that the main mechanism governing the strength of the organic matrix layers of nacre relies on the mineral bridges rather than the organic matrix. This study provides a guide to the interfacial design of synthetic materials.

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The direct observation of a type of microstructure in the organic matrix layers of nacre was obtained with a transmission electron microscope. The microstructure, which is referred to as mineral bridge in the biomineralization, is nanoscale and randomly distributed in the layers. Statistical analysis gives the distribution laws and characteristics of mineral bridges in the organic matrix layers. The existence of mineral bridges in nacre was confirmed, and it was shown that the microarchitecture of nacre should be described as a "brick-bridge-mortar" arrangement rather than traditional "brick and mortar" one.Nacre, one of several kinds of molluscan hard tissue, is considered as a ceramic composite containing 95 vol% interlocking aragonite platelets staggered in successive laminae and separated by a 5% organic matrix. Since it can give a conceptual guidance to the biomimetic design of synthetic materials, a great deal of attention has been attracted to the microstructure of nacre in recent years. 1-4The traditional model of nacre is considered as a "brick and mortar" (BM) arrangement. It is the unique arrangement that is believed to result in lightweight materials with high mechanical performance.5-8 However, the study of the microstructure of nacre has gained some significant developments in recent years. In particular, Schaffer et al. 9 clearly observed many nanopores in the interlamellar organic matrix sheets of nacre in terms of various microscopic observations and then gave a statistical distribution. Consequently, they supported the model of nacre growth that is based on mineral bridges between successive aragonite platelets. Furthermore, according to their transmission electron microscopy (TEM) micrograph, they stated that "these (gray in the micrograph) may be mineral bridges between the nacre plates, but it is difficult to be certain of this assignment." Here we describe direct observation of mineral bridges in the organic matrix layers of nacre. And by using statistical analysis, we obtain the characteristics and the distribution law of the microstructure. It is interesting that results presented in this paper are consistent with an earlier estimate.

The effect of a negative Poisson ratio is experimentally revealed in the tension deformation of a natural layered ceramic. This effect can increase the volume strain energy per unit volume by 1100% and, simultaneously, decrease the deformation strain energy per unit volume by about 44%, so that it effectively enhances the deformation capacity by about 1 order of magnitude in the tension of the material. The present study also shows that the physical mechanisms producing the effect are attributed to the climbing on one another of the nanostructures in the natural material, which provides a guide to the design of synthetic toughening composites.