Ellison A.M.,Harvard University |
Barker Plotkin A.A.,Harvard University |
Khalid S.,Harvard University |
Khalid S.,Islamia College
Forests | Year: 2016
Eastern hemlock (Tsuga canadensis) is a foundation species in eastern North American forests. Because eastern hemlock is a foundation species, it often is assumed that the diversity of associated species is high. However, the herbaceous layer of eastern hemlock stands generally is sparse, species-poor, and lacks unique species or floristic assemblages. The rapidly spreading, nonnative hemlock woolly adelgid (Adelges tusgae) is causing widespread death of eastern hemlock. Loss of individual hemlock trees or whole stands rapidly leads to increases in species richness and cover of shrubs, herbs, graminoids, ferns, and fern-allies. Naively, one could conclude that the loss of eastern hemlock has a net positive effect on biodiversity. What is lost besides hemlock, however, is landscape-scale variability in the structure and composition of the herbaceous layer. In the Harvard Forest Hemlock Removal Experiment, removal of hemlock by either girdling (simulating adelgid infestation) or logging led to a proliferation of early-successional and disturbance-dependent understory species. In other declining hemlock stands, nonnative plant species expand and homogenize the flora. While local richness increases in former eastern hemlock stands, between-site and regional species diversity will be further diminished as this iconic foundation species of eastern North America succumbs to hemlock woolly adelgid. © 2016 by the authors.
Ahmad S.,Islamia College |
Ahmad S.,University of Peshawar |
Iqbal Y.,University of Peshawar
Journal of Ceramic Processing Research | Year: 2016
Clay brick is one of the oldest and commonly used clay products in construction industry in Khyber Pakhtunkhwa (KP) Pakistan. In spite of its widespread use, studies regarding the manufacturing standards and quality of locally made bricks are much less in comparison to those of technologically advanced countries. The aim of the present study was to investigate the chemistry and phase constitution of the raw materials used in local brick kilns. Phase and microstructural analyses of fired bricks from local kilns were performed and compared with those of the laboratory made bricks. X-ray diffraction of raw materials revealed the presence of illite, quartz, clinochlore and albite while calcite was identified as a minor phase in all the investigated samples. Diopside, anorthite and quartz were observed as major phases in the kiln-fired samples, and only diopside and quartz in the laboratory-fired samples. The presence of albite and clinochlore, although in small concentrations, in the kiln-fired samples indicated that the employed temperature was too low to completely dissolve the initial ingredients. Consistent with X-ray diffraction results, semi-quantitative energy dispersive spectroscopy revealed the presence of silicon, aluminum, calcium, magnesium, iron and potassium along with a small amount of sodium in these samples. An increase in firing temperature decreased porosity which resulted in substantial increase in compressive strength and decrease in water absorption. The optimum mechanical properties were achieved at 1000 °C. © 2016, Hanyang University. All rights reserved.
Bouhemadou A.,Ferhat Abbas University Setif |
Khenata R.,University of Mascara |
Bin-Omran S.,King Saud University |
Murtaza G.,Islamia College |
Al-Douri Y.,University Malaysia Perlis
Optical Materials | Year: 2015
We report the results of a detailed first-principles based density functional theory study of the structural, elastic, electronic and optical properties of a recently synthesized layered semiconductor BaGa2P2. The optimized structural parameters are in excellent agreement with the experimental structural findings, which validates the used theoretical method. The single crystal and polycrystalline elastic constants are numerically estimated using the strain-stress method and Voigt-Reuss-Hill approximations. Predicted values of the elastic constants suggest that the considered material is mechanically stable, brittle and very soft material. The three-dimensional surface and its planar projections of Young's modulus are visualized to illustrate the elastic anisotropy. It is found that Young's modulus of BaGa2P2 show strong dependence on the crystallographic directions. Band structure calculation reveals that BaGa2P2 is a direct energy band gap semiconductor. The effective masses of electrons and holes at the minimum of the conduction band and maximum of the valence band are numerically estimated. The density of state, charge density distribution and charge transfers are calculated and analyzed to determine the chemical bonding nature. Dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity and electron-loss energy function spectra are computed for a wide photon energy range up to 20 eV. Calculated optical spectra exhibit a noticeable anisotropy. © 2015 Elsevier B.V. All rights reserved.
Nurul Haque Mollah Md.,The Institute of Statistical Mathematics of Tokyo |
Nurul Haque Mollah Md.,University of Rajshahi |
Sultana N.,Islamia College |
Minami M.,Keio University |
And 2 more authors.
Neural Networks | Year: 2010
This paper discusses a new highly robust learning algorithm for exploring local principal component analysis (PCA) structures in which an observed data follow one of several heterogeneous PCA models. The proposed method is formulated by minimizing β-divergence. It searches a local PCA structure based on an initial location of the shifting parameter and a value for the tuning parameter β. If the initial choice of the shifting parameter belongs to a data cluster, then the proposed method detects the local PCA structure of that data cluster, ignoring data in other clusters as outliers. We discuss the selection procedures for the tuning parameter β and the initial value of the shifting parameter μ in this article. We demonstrate the performance of the proposed method by simulation. Finally, we compare the proposed method with a method based on a finite mixture model. © 2009 Elsevier Ltd. All rights reserved.
Boobalan G.,Annamalai University |
Imran P.K.M.,Islamia College |
Manoharan C.,Annamalai University |
Nagarajan S.,Central University of Tamil Nadu
Journal of Electronic Materials | Year: 2015
Perylene diimides with high photosensitivity and high electron mobility have attracted much attention for use in organic semiconductor devices. In this investigation, thin films of six new perylene tetracarboxylic diimides (PTCDI) were fabricated by spin coating, on glass as substrate, and their optical and electrical properties were studied. The absorption spectra of thin films of PTCDI furnished more informative bands than those of the compounds in solution. The morphology of the thin films was examined by scanning electron microscopy and x-ray diffraction. The absorption spectra and I–V characteristics of the compounds were affected by their molecular structures. HOMO–LUMO band gaps of the films were in the range 1.9–2.0 eV. Band gaps calculated by use of computational methods were comparable with experimental results. © 2015, The Minerals, Metals & Materials Society.