Fatigue-life estimation of functionally graded materials using XFEM

The present work deals with the fatigue crack growth simulation of alloy/ceramic functionally graded materials (FGMs) using extended finite element method (XFEM). Various cases of FGM containing multiple inhomogeneities/discontinuities along with either a major edge or a center crack are taken for the purpose of simulation. The fatigue life of the FGM plate is calculated using Paris law of fatigue crack growth under cyclic loading. The effect of multiple inhomogeneities/discontinuities (minor cracks, holes/voids, and inclusions) on the fatigue life of cracked FGM plate is studied in detail. These simulations show that the presence of inhomogeneities/discontinuities in the domain significantly influences the fatigue life of the components.     

Detection of nickel‐induced stress using laser‐induced fluorescence signatures from leaves of wheat seedlings

The continuous increase of heavy metal ions in the environment is imposing serious problems in agricultural yield and increases human health threats through accumulation in the food chain. Various studies have shown that heavy metals influence the metabolic processes and pigment concentrations in leaves, and thus affect the laser induced fluorescence (LIF) spectra. Leaf level in vivo LIF spectra using the 488 nm and 355 nm laser lines, fluorescence induction kinetics (FIK) using the 488 nm laser line, and photosynthetic pigments of the control and nickel treated wheat seedlings were measured. The peak parameters of the blue and UV‐excited spectral bands were calculated by Gaussian curve fitting. The FIK measured at both the chlorophyll (Chl) fluorescence bands was used to evaluate the fluorescence decrease ratio (R _Fd). The variations in R _Fd and fluorescence ratios of intensities, bandwidth and band area, with varying concentrations of nickel, were revealed as promising parameters in determining the health status of wheat seedlings. These leaf level findings can be extended at canopy level in the field using laser based light detection and ranging (LIDAR) systems.     

Dislocation controlled wear in single crystal silicon carbide

For better design and durability of nanoscale devices, it is important to understand deformation in small volumes and in particular how deformation mechanisms can be related to frictional response of an interface in the regime where plasticity is fully developed. Here, we show that when the size of the cutting tool is decreased to the nanometer dimensions, silicon carbide wears in a ductile manner by means of dislocation plasticity. We present different categories of dislocation activity observed for single asperity sliding on SiC as a function of depth of cut and for different sliding directions. For low dislocation density, plastic contribution to frictional energy dissipation is shown to be due to glide of individual dislocations. For high dislocation densities, we present an analytical model to relate shear strength of the sliding interface to subsurface dislocation density. Furthermore, it is shown that a transition from plowing to cutting occurs as function of depth of cut and this transition can be well described by a macroscopic geometry-based model for wear transition.     

Assessing Flood Induced Land-Cover Changes Using Remote Sensing and Fuzzy Approach in Eastern Gujarat (India)

Natural hazards such as flooding can cause changes in land-cover. The present study deals with the changes in land-cover in three worst affected districts (Anand, Vadodara and Kheda) of Gujarat state in India due to severe flood during 2005. The Indian Remote Sensing (IRS) P6 Linear Imaging Self Scanning (LISS) III satellite imageries of pre- and post-flooding periods were used as sources of information for the study area. Three classification approaches (unsupervised ISODATA, supervised Maximum Likelihood Classifier, and fuzzy rule based) were used to extract flood induced land-cover information. Results obtained from the above classification approaches were compared. Soft computing technique such as fuzzy based image classification gave better separability amongst classes as compared to hard classification techniques. The accuracy assessment showed that the fuzzy approach can predict land-cover more accurately than traditional approach and also showed great potential for dealing with mapping of flood induced land-cover. Unsupervised classification results for the period October 2004 to October 2005 revealed decrease in inland water bodies (14.49%) and agricultural area (6.42%) while increase in remaining land-cover. During February 2005 to February 2006, all land-cover classes decreased except agricultural fallow and sparse vegetation. In case of supervised classification, decreasing trend was observed only in case of agricultural area (6.78%) during October 2004 to October 2005. Similarly, during February 2005 to February 2006, increase in coastal water bodies (0.73%) and sparse vegetation (1.7%) was observed where as decreasing trend was noticed in the remaining land-cover classes. In fuzzy based classification, only decrease in agricultural area (7.09%) was observed from October 2004 to October 2005, whereas during February 2005 to February 2006, decrease in area was exhibited in all land-cover classes except coastal water bodies and sparse vegetation. Change detection indicated interchange of areas between inland and coastal water bodies and decrease in agricultural area leading to increase in area of agricultural fallow and sparse vegetation.     

Properties of In-Doped ZnO Films Grown by Metalorganic Chemical Vapor Deposition on GaN(0001) Templates

We investigated the properties of indium-doped zinc oxide layers grown by metalorganic chemical vapor deposition on semi-insulating GaN(0001) templates. Specular and transparent films were grown with n-type carrier concentrations up to 1.82 × 10¹⁹ cm⁻³ as determined by Hall measurements, and all In-doped films had carrier concentrations significantly higher than that of a comparable undoped film. For low In flows, the carrier concentration increased accordingly with trimethyl-indium (TMIn) flow until a maximum carrier concentration of 1.82 × 10¹⁹ cm⁻³ was realized. For higher In flows, the carrier concentration decreased with increasing TMIn flow rate. Sheet resistance as low as 185 Ω/sq was achieved for the In-doped films, which is a significant decrease from that of a comparable undoped ZnO film. Our n-type doping studies show that In is an effective dopant for controlling the n-type conductivity of ZnO.     

Tools for implementing network protocols

This paper describes two software tools—a message manager and a map manager—used to implement network protocols. The tools are provided as part of the x-kernel, an operating system kernel designed to support the construction and composition of protocols. For each tool, we briefly motivate the network task that needs to be done, give a high-level specification of the tool, outline the algorithms and data structures used to implement the tool and give concrete examples of how the tool is used to implement real protocols. We also demonstrate how the tools, even though they are designed for general use, perform efficiently.     

The effect of surface recombination on the frequency-dependentcharacteristics of an ion-implanted GaAs OPFET

The effect of modulation frequency and surface recombination on the characteristics of an ion-implanted GaAs OPFET is determined analytically. The drain-source current is found to decrease with the increase in both modulation frequency and trap center density. The current changes significantly with the trap center density only when the latter is greater than 10²⁰/m². The threshold voltage does not change appreciably with the modulation frequency as in a silicon OPFET. However, the increased in the trap center density causes V_T to increase in the enhancement device and decrease in the depletion device. Further, V_T increases under the normally ON condition and decreases under the normally OFF condition with an increase in the photon absorption coefficient in GaAs. Some anomalous behavior is observed for higher values of the absorption coefficient     

A large-time-stepping scheme for balance equations

A well-balanced, large-time-stepping method for conservation laws with source terms is presented. The numerical method is based on a local reformulation of the balance law as a conservation law with a discontinuous flux function, and the approximate solution of this equation by a front tracking method. This yields an unconditionally stable method which is particularly well suited to calculate stationary states. The viability of this approach is demonstrated by several numerical examples. KHK has been supported in part by an Outstanding Young Investigators Award from the Research Council of Norway.     

A comparative study of YBCO powders prepared by different processes

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.