1,759 research outputs found
Tests for covariance matrices, particularly for high dimensional data
Test statistics for sphericity and identity of the covariance matrix are presented, when the data are multivariate normal and the dimension, p, can be larger than the sample size, n. The statistics, derived under very general conditions, follow an approximate normal distribution for large p, also when p >> n. Simulation results, particularly emphasizing the case when p can be much larger than n, show that the proposed statistics are accurate for both size control and power. A discussion of the commonly used assumptions for high dimensional set up is also given, with the conclusions applicable in general as well as in the special case of high dimensional covariance testing
Spatial Distribution of Jack Pine Cones and Those Attacked by Insects
The middle crown and south quadrant of 6-m-tall jack pines, Pinus banksiana Lamb., produced significantly more cones than the rest of the tree. The number of cones attacked by Eucosma monitorana Heinrich was also highest in the middle crown and south quadrant. Laspeyresia toreuta (Grote) attacked the most cones in the middle crown. A positive, linear correlation existed between the number of cones attacked by inseets and cone abundanee per tree, indicating a response of the insect population to inereased food supply
Price-setting for Residential Water: Estimation of Water Demand in Lahore
The Water and Sewerage Agency (WASA) of Lahore is facing soaring demand and rising costs. But while massive investments are made to augment supply, tariffs remain low and are not adjusted in line with growing expenses. This has resulted not only in heavy and increasingly unsustainable reliance on loans and subsidies, but also in consumers undervaluing the resource, resulting in its inefficient utilisation. In this scenario, water tariffs badly need to be reformed. This study explores the potential of a pricing policy to regulate residential water demand in order to achieve the objectives of cost recovery, efficient water use, and equitable allocation of water resources. To this end, a demand function is estimated using household level data about water consumption and socio-economic characteristics of 156 households supplied by WASA, Lahore, for the period 2004-2006. Under block-rate tariffs the price variable is endogenously determined and a system of simultaneous equations emerges, solved here using two-stage least squares method. The estimated model explains 57 percent variation in water demand. The study finds water demand to be inelastic to price and, considering WASA’s exceedingly low tariffs, recommends up to 50 percent increase in the current tariff structure. Further computations show that a 50 percent increase will not endanger lifeline water supply. However, tariff increases may not be felt uniformly across all income groups, and absence of income data remains a limitation of this study. The study also recommends linking the non-volumetric part of tariffs to wealth-determined variables, such as property value and income.Water Demand; Price-setting
1-(2,6-Dichlorobenzoyl)-3-(3-methoxyphenyl)thiourea
The two aromatic rings in the title compound, C15H12Cl2N2O2S, enclose a dihedral angle of 37.49 (6)°. The molecule exists in the solid state in its thione form with typical thiourea C-S and C-O bonds lengths, as well as shortened C-N bonds. An intramolecular N-H...O hydrogen bond stabilizes the molecular conformation. In the crystal, molecules are connected by N-H...O and N-H...S hydrogen bonds, forming chains running along the alpha axis. Key indicators: single-crystal X-ray study; T = 173 K; mean σ (C–C) = 0.002 Å; disorder in main residue; R factor = 0.035; wR factor = 0.087; data-to-parameter ratio = 18.9
1-(3-Chlorophenyl)-3-(2,6-dichlorobenzoyl)thiourea
The structure of the title compound, C14H9Cl3N2OS, is composed of discrete molecules with bond lengths and angles quite typical for thiourea compounds of this class. The plane containing the thiocarbonyl and carbonyl groups subtends dihedral angles of 48.19 (3) and 87.51 (3)° with the planes formed by the 3-chloro and 2,6-dichlorophenyl rings, respectively; the dihedral angle between the two benzene ring planes is 45.32 (3)°. An intramolecular N—H⋯O hydrogen bond stabilizes the molecular conformation and the molecules form intermolecular N—H⋯S and N—H⋯O hydrogen bonds, generating a sheet along the a axis
1-(3-Chlorobenzoyl)-3-(2,3-dimethylphenyl)thiourea
The title molecule, C16H15ClN2OS, exists in the solid state in its thione form with typical thiourea C—S and C—O bonds lengths, as well as shortened C—N bonds. An intramolecular N—H⋯O hydrogen bond stabilizes the molecular conformation and intermolecular N—H⋯S hydrogen bonds link the molecules into centrosymmetric dimers. The dihedral angle between the aromatic rings is 50.18 (5)°
1-(4-Chlorobenzoyl)-3-(2,4,6-trichlorophenyl)thiourea hemihydrate
The asymmetric unit of the title compound, C14H8Cl4N2OS·0.5H2O, contains two independent molecules with different conformations with respect to the aromatic ring planes, and one water molecule. The bond lengths and angles are typical of thiourea compounds of this class. The molecule exists in the solid state in its thione form with typical thiourea C—S and C—O bonds lengths, as well as shortened C—N bonds. The dihedral angles between the two aromatic planes are 66.93 (8) and 60.44 (9)° in the two independent molecules. An intramolecular N—H⋯O hydrogen bond stabilizes the molecular conformation and the crystal packing is characterized by N—H⋯O, O—H⋯S and O—H⋯Cl hydrogen bonds
Molecular-dynamics simulations of stacking-fault-induced dislocation annihilation in pre-strained ultrathin single-crystalline copper films
We report results of large-scale molecular-dynamics (MD) simulations of
dynamic deformation under biaxial tensile strain of pre-strained
single-crystalline nanometer-scale-thick face-centered cubic (fcc) copper
films. Our results show that stacking faults, which are abundantly present in
fcc metals, may play a significant role in the dissociation, cross-slip, and
eventual annihilation of dislocations in small-volume structures of fcc metals.
The underlying mechanisms are mediated by interactions within and between
extended dislocations that lead to annihilation of Shockley partial
dislocations or formation of perfect dislocations. Our findings demonstrate
dislocation starvation in small-volume structures with ultra-thin film
geometry, governed by a mechanism other than dislocation escape to free
surfaces, and underline the significant role of geometry in determining the
mechanical response of metallic small-volume structures.Comment: 28 pages, 3 figure
1-(2,6-Dichlorobenzoyl)-3-(2,3,5,6-tetrachlorophenyl)thiourea trichloromethane hemisolvate
The title compound, C14H6Cl6N2OS·0.5CHCl3, crystallizes with four 1-(2,6-dichlorobenzoyl)-3-(2,3,5,6-tetrachlorophenyl)thiourea molecules and two trichloromethane molecules in the asymmetric unit. The thiourea molecules exist in the solid state in their thione forms with typical thiourea C—S and C—O bonds lengths, as well as shortened C—N bonds. The —NH—C(=S)—NH—C(=O)— plane is almost perpendicular to the benzene ring in each thiourea molecule. Intramolecular N—H⋯O hydrogen bonds stabilize the molecular conformation and intermolecular N—H⋯S hydrogen bonds stabilize the packing arrangement
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