Shear transformation zone volume determining ductile–brittle transition of bulk metallic glasses

Three-point bending experiments were performed on as-cast and annealed samples of Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105) bulk metallic glasses over a wide range of temperatures varying from room temperature (293 K) to liquid nitrogen temperature (77 K). The results demonstrated that the free volume decrease due to annealing and/or cryogenic temperature can reduce the propensity for the formation of multiple shear bands and hence deteriorate plastic deformation ability. We clearly observed a sharp ductile-to-brittle transition (DBT), across which microscopic fracture feature transfers from micro-scale vein patterns to nano-scale periodic corrugations. Macroscopically, the corresponding fracture mode changes from ductile shear fracture to brittle tensile fracture. The shear transformation zone volume, taking into account free volume, temperature and strain rate, is proposed to quantitatively characterize the DBT behavior in fracture of metallic glasses.

U-transformation-finite element method in 3-dimensional analysis of orthotropic laminates

For an orthotropic laminate, an equivalent system with doubly cyclic periodicity is introduced. Then a 3-dimensional finite element model for the equivalent system is transformed into the unitary space, where the large finite element matrix equation is decoupled into some small matrix equations. Such a decoupling very efficiently reduces the computational effort. For an orthotropic laminate with four clamped edges, no exact elasticity solution is available, and the deflection values predicted by different methods have a considerable difference each other for a small length-to-thickness ratio. The present predictions are the largest because the present method is a full 3-dimensional finite element analysis without superfluous constraints. Illustrative numerical examples are presented to observe the distributions of stresses through the thickness of the laminates. (C) 2010 Elsevier Ltd. All rights reserved.

Wurtzite-to-tetragonal structure phase transformation and size effect in ZnO nanorods

The deformation of [0001]-oriented ZnO nanorods with hexagonal cross sections under uniaxial tensile loading is analyzed through molecular statistical thermodynamics (MST) simulations. The focus is on the size dependence of mechanical behavior in ZnO nanorods with diameters ranging from 1.95 to 17.5 nm. An irreversible phase transformation from the wurtzite (P6(3)mc space group) structure to a tetragonal structure (P4(2)/mnm space group) occurs during the tensile loading process. Young's modulus before the transformation demonstrates a size dependence consistent with what is observed in experiments. A stronger size dependence of response is seen after the transformation and is attributed to the polycrystalline nature of the transformed structure. A comparison of the MST and molecular dynamics (MD) methods shows that MST is 60 times faster than MD and yields results consistent with the results of MD.

Surface transformation and inversion domain boundaries in gallium nitride nanorods

Phase transformation and subdomain structure in [0001]-oriented gallium nitride (GaN) nanorods of different sizes are studied using molecular dynamics simulations. The analysis concerns the structure of GaN nanorods at 300 K without external loading. Calculations show that a transformation from wurtzite to a tetragonal structure occurs along {0110} lateral surfaces, leading to the formation of a six-sided columnar inversion domain boundary (IDB) in the [0001] direction of the nanorods. This structural configuration is similar to the IDB structure observed experimentally in GaN epitaxial layers. The transformation is significantly dependent on the size of the nanorods.

Hemizygosity for Atm and Brca1 influence the balance between cell transformation and apoptosis

Background: In recent years data from both mouse models and human tumors suggest that loss of one allele of genes involved in DNA repair pathways may play a central role in genomic instability and carcinogenesis. Additionally several examples in mouse models confirmed that loss of one allele of two functionally related genes may have an additive effect on tumor development. To understand some of the mechanisms involved, we examined the role of monoallelic loss or Atm and Brca1 on cell transformation and apoptosis induced by radiation. Methods: Cell transformation and apoptosis were measured in mouse embryo fibroblasts (MEF) and thymocytes respectively. Combinations of wild type and hemizygous genotypes for ATM and BRCA1 were tested in various comparisons. Results: Haploinsufficiency of either ATM or BRCA1 resulted in an increase in the incidence of radiation-induced transformation of MEF and a corresponding decrease in the proportion of thymocytes dying an apoptotic death, compared with cells from wild-type animals. Combined haploinsufficiency for both genes resulted in an even larger effect on apoptosis. Conclusions: Under stress, the efficiency and capacity for DNA repair mediated by the ATM/BRCA1 cell signalling network depends on the expression levels of both proteins.

Phase transformation in the surface region of zirconia and doped zirconia detected by UV Raman spectroscopy

The phase evolution of yttrium oxide and lanthanum oxide doped zirconia (Y2O3-ZrO2 and La2O3-ZrO2, respectively) from their tetragonal to monoclinic phase has been studied using UV Raman spectroscopy, visible Raman spectroscopy and XRD. UV Raman spectroscopy is found to be more sensitive at the surface region while visible Raman spectroscopy and XRD mainly give the bulk information. For Y2O3-ZrO2 and La2O3-ZrO2, the transformation of the bulk phase from the tetragonal to the monoclinic is significantly retarded by the presence of yttrium oxide and lanthanum oxide. However, the tetragonal phase in the surface region is difficult to stabilize, particularly when the stabilizer's content is low. The phase in the surface region can be more effectively stabilized by lanthanum oxide than yttrium oxide even though zirconia seemed to provide more enrichment in the surface region of the La2O3-ZrO2 sample than the Y2O3-ZrO2 sample, based on XPS analysis. The surface structural tension and the enrichment of the ZrO2, component in the surface region of ZrO2-Y2O3 and ZrO2-La2O3 might be the reasons for the striking difference between the phase change in the surface region and the bulk. Accordingly, the stabilized tetragonal surface region can significantly prevent the phase transition from developing into the bulk when the stabilizer's content is high.

The properties and possible transformation path for C12B24N24

The structure and frequencies of C12B24N24 have been calculated by means of an ab initio method. By comparing the average bond energies with C-60, the calculated results predict that the cage C12B24N24 is a stable molecule. The calculated results indicate that the cage molecule C12B24N24 has a relative large HOMO-LUMO energy gap and a low rigidity The structures and stability of six possible isomers of C2B4N4 are used to suggest a possible transformation path from the pentagon CB2N2 to the C12B24N24 materials. (C) 2001 John Wiley & Sons, Inc.

data transformation and attribute subset selection: do they help make differences in software failure prediction?

IEEE, IEEE Comp Soc, Tech Council Software Engn

A data-model fusion approach for upscaling gross ecosystem productivity to the landscape scale based on remote sensing and flux footprint modelling

Chinese Academy of Sciences ; National Science Foundation of China [41071059]; National Key Technology R&D Program of China [2008BAK50B06-02]; National Basic Research Program of China [2010CB950900, 2010CB950704]; Natural Sciences and Engineering Research Council of Canada

China's changing landscape during the 1990s: Large-scale land transformations estimated with satellite data

Land-cover changes in China are being powered by demand for food for its growing population and by the nation's transition from a largely rural society to one in which more than half of its people are expected to live in cities within two decades. Here we use an analysis of remotely sensed data gathered between 1990 and 2000, to map the magnitude and pattern of changes such as the conversion of grasslands and forests to croplands and the loss of croplands to urban expansion. With high-resolution ( 30 m) imagery from Landsat TM for the entire country, we show that between 1990 and 2000 the cropland area increased by 2.99 million hectares and urban areas increased by 0.82 million hectares. In northern China, large areas of woodlands, grasslands and wetlands were converted to croplands, while in southern China large areas of croplands were converted to urban areas. The land-cover products presented here give the Chinese government and international community, for the first time, an unambiguous understanding of the degree to which the nation's landscape is being altered. Documentation of these changes in a reliable and spatially explicit way forms the foundation for management of China's environment over the coming decades.

Landscape change detection of the newly created wetland in Yellow River Delta

Four models are employed in the landscape change detection of the newly created wetland. The models include ones for patch connectivity. ecological diversity, human impact intensity and mean center of land cover. The landscape data of the newly created wetland in Yellow River Delta in 1984, 1991, and 1996 are produced from the unsupervised classification and the supervised classification on the basis of integrating Landsat TM images of the newly created wetland in the four seasons of the each year. The result from operating the models into the data shows that the newly created wetland landscape in Yellow River Delta had a great chance. The driving focus of the change are mainly from natural evolution of the newly created wetland and rapid population growth, especially non-peasant population growth in Yellow River Delta because a considerable amount of oil and gas fields have been found in the Yellow River Delta. For preventing the newly created wetland from more destruction and conserving benign Succession of the ecosystems in the newly created wetland, six measures are suggested on the basis of research results. (C) 2003 Elsevier Science B.V. All rights reserved.

Urban functional structure characteristics and transformation in China

The paper analyzes urban functional structure characteristics of Chinese cities in 1996 using the Nelson method. The manufacturing employment percentage is much higher in metropolitan areas but is decreasing from 1989 to 1996. On the other hand, the weight of science, education, culture, hygiene, finance, insurance and real estate increases. The employment structure changes dramatically. Although the urbanization level of China is lower than that of the USA in 1955, the frequency distribution curve of urban functions is similar. The construction, transportation, commerce, finance, insurance, real estate, science, education, culture, hygiene and administration curves are normal. The mining employment converges on minor cities and the distribution is not normal. The urban function has changed with urban scale. The bigger the cities are, the smaller the manufacture, mining and construction employment weights, and the larger are the science, education, finance, insurance, real estate and administration weights. Commerce and transportation are distributed evenly and the difference is less. From the comparison in three zones of China, the employment percentage of manufacture, finance, insurance and real estate is higher in eastern coastal areas, while the employment percentage of science, education, administration is higher in western areas. (C) 2002 Elsevier Science Ltd. All rights reserved.

Simulated morphological landscape of polymer single crystals by phase-field model

The novel phase field model with the "polymer characteristic" was established based on a nonconserved spatiotemporal Ginzburg-Landau equation (TDGL model A). Especially, we relate the diffusion equation with the crystal growth faces of polymer single crystals. Namely, the diffusion equations are discretized according to the diffusion coefficient of every lattice site in various crystal growth faces and the shape of lattice is selected based on the real proportion of the unit cell dimensions.

Potential Landscape and Flux Framework of Nonequilibrium Networks: Robustness, Dissipation, and Coherence of Biochemical Oscillations

We established a theoretical framework for studying nonequilibrium networks with two distinct natures essential for characterizing the global probabilistic dynamics: the underlying potential landscape and the corresponding curl flux. We applied the idea to a biochemical oscillation network and found that the underlying potential landscape for the oscillation limit cycle has a distinct closed ring valley (Mexican hat-like) shape when the fluctuations are small. This global landscape structure leads to attractions of the system to the ring valley.