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421.
Anwar Usman Ibrahim Abdul Razak Hoong-Kun Fun Suchada Chantrapromma Yan Zhang Jian-Hua Xu 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(12):1438-1440
In the title compound, C25H19NO4, the indole moiety is not completely planar, the heterocyclic ring being distorted very slightly towards a half-chair conformation. The benzoyl and 4-methoxyphenyl substituents are individually almost planar and are in a bisecting and nearly perpendicular configuration, respectively, with respect to the plane of the indole moiety. The molecular and packing structures in the crystal are stabilized by intramolecular and intermolecular C—H⋯O interactions. 相似文献
422.
Thierry Woignier Juan Primera Anwar Hashmy 《Journal of Sol-Gel Science and Technology》2006,40(2-3):201-207
Volcanic soil comprises weathering products such as allophane, originating from a leaching process of volcanic ashes and glasses.
These soils are interesting in terms of mitigation of the greenhouse effect (C sequestration), because they are known for
accumulating more C than non-volcanic soils. Allophanes are natural amorphous silicates and have physical features very close
to those of synthetic gels. Knowledge of the allophanic soil structure is required to understand the sequestration mechanism.
In this paper, nitrogen adsorption-desorption experiments, measured on allophanic soil samples, show that the hydraulic diameter
(Dh) is shifted towards smaller size while the pore volume (Vp) and specific surface area (S) increase, when the allophane content of the soil increases. We introduce a numerical model
to simulate the structure of this “natural gel”. The algorithm is based on Diffusion-Limited Cluster-Cluster Aggregation in
which larger particles hinder the DLCA. As a function of the relative content of allophane (gel) and larger particles, the
textural properties (Vp, S, Dh) of the different simulated structure are calculated using a simple triangulation method.
Numerical results are in good agreement with experimental data and from the simulated data, we can derive the permeability
evolution as a function of the allophane content. We show that at the scale of the allophanic aggregates the calculated permeability
is low and could be an important parameter to explain the larger C content of allophanic soils. Because of the low allophanic
aggregate permeability, the fluid exchanges and chemical reactions are slow. This gel-allophane analogy and DLCA model allow
proposing a different approach to describe the properties of these peculiar soils. 相似文献
423.
424.
A facile, green, and efficient Fe(III) chloride, one-pot, multicomponent reaction (MCR) for synthesis of 2-aminothiazole-based compounds is reported. Considering the medicinal importance of fused ring 2-aminothiazoles, this process provides an easy route to the synthesis of this class of compound. Detailed mechanism of the reaction has been discussed. 相似文献
425.
The synthesis of chiral pyrrolidinones derived from threonine, making use of a Dieckmann or aldol ring closure, is described. Compounds were found to exhibit antibacterial activity, for which the correlation with various physiochemical parameters was examined. This chiral tetramate scaffold may provide a useful template for fragment-based drug design providing rapid access to novel antibacterial compound libraries. 相似文献
426.
Anwar H Joarder 《International Journal of Mathematical Education in Science & Technology》2013,44(5):772-784
The usual formula for variance depending on rounding off the sample mean lacks precision, especially when computer programs are used for the calculation. The well-known simplification of the total sums of squares does not always give benefit. Since the variance of two observations is easily calculated without the use of a sample mean, and the variance of a sample of n observations is the average of the variances of observations based on n(n-1)/2 distinct subsets of units of size 2 from the sample, it is argued that this sense of pairing may result in precision. Some other forms of variance are presented which provide some insight into it. The contribution of a new observation of variance is highlighted, which is important in sequential sampling. Notions are illustrated with examples. 相似文献
427.
Alireza Heidari O. Anwar Bég Mohammadali Ghorbani 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(2):216-224
Many empirical potential energy functions have been modeled to represent the potential energy function of a diatomic molecule along whole range of internuclear distance coordinate, whereby one can determine certain molecular constants. Here we employ various potential functions such as Morse, Rydberg, Varshni(II), Varshni(III), Varshni(VI), Pöschl-Teller, Hulburt-Hirschfelder, Lippincott, Frost-Musulin, Linnet, and Rosen-Morse, and the Numerov method to solve the nuclear Schrödinger equation for F2, as an example of a homonuclear diatomic molecule. Herewith, the vibrational and vibration-rotation energy levels are obtained and excellent accuracy is achieved. The potential of employing the Numerov method in engineering physics computations is emphasized. 相似文献
428.
Javaid Anwar 《中国物理快报》2010,(3):184-187
In the presence of usual transmission losses, it is shown that phase noise in a four-level laser can be reduced below the Schawlow-Townes limit when lasing levels are coupled to a squeezed vacuum reservoir. The squeezed vacuum coupled to the lasing mode modifies the phase diffusion rate and dominates the contribution from transmission losses. It is predicted to obtain phase stability in the system and phase noise vanishes for larger squeezing. Gain of the laser remains positive under these conditions. 相似文献
429.
Anwar Usman Suchada Chantrapromma Hoong-Kun Fun 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(12):1443-1446
The title compound, 3,5,7-triaza-1-azoniatricyclo[3.3.1.13,7]decane 2,4-dinitrophenolate monohydrate, C6H13N4+·C6H3N2O5−·H2O, the 1:1 hydrate adduct of hexamethylenetetramine (HMT) and 2,4-dinitrophenol, undergoes a temperature phase transition. In the room-temperature phase, the adduct crystallizes in the monoclinic P21/m space group, whereas in the low-temperature phase, the adduct crystallizes in the triclinic P space group. This phase transition is reversible, with the transition temperature at 273 K, and the phase transition is governed by hydrogen bonds and weak interactions. In both these temperature-dependent polymorphs, the crystal structure is alternately layered with sheets of hexamethylenetetramine and sheets of dinitrophenol stacked along the c axis. The hexamethylenetetramine and dinitrophenol moieties are linked by intermolecular hydrogen bonds. The water molecule in the adduct plays an important role, forming O—H⋯O hydrogen bonds which, together with C—H⋯O hydrogen bonds, bridge the adducts into molecular ribbons. Extra hydrogen bonds and weak interactions exist for the low-temperature polymorph and these interconnect the molecular ribbons into a three-dimensional packing structure. Also in these two temperature-dependent polymorphs, dinitrophenol acts as a hydrogen-bond acceptor and HMT acts as a hydrogen-bond donor. 相似文献
430.