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Discrete Units (discrete + unit)
Selected AbstractsSynthesis and X-ray study of the 6-(N -pyrrolyl)purine and thymine derivatives of 1-aminocyclopropane-1-carboxylic acidCHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2004M. Cetina Abstract:, The novel purine and pyrimidine derivatives of 1-aminocyclopropane-1-carboxylic acid 1 and 2 were obtained by alkylation of 6-(N -pyrrolyl)purine and thymine with methyl 1-benzamido-2-chloromethylcyclopropanecarboxylate. X-ray crystal structure analysis shows that the cyclopropane rings in 1 and 2 posses Z -configuration. The cyclopropane ring atoms and attached atoms of the benzamido and methoxycarbonyl moiety of both molecules are disposed perpendicularly to each other. The carbonyl oxygen of the methoxycarbonyl moiety adopts in both compounds a synperiplanar conformation with respect to the midpoint of the distal bond of the cyclopropane ring. The torsion angles , and , for the 1-aminocyclopropane-1-carboxylic acid residue in 1 and 2 correspond to a folded conformation, while the torsion angles , define antiperiplanar conformation. Intermolecular hydrogen bonds connect the molecules of 1 into dimers. Each dimer is hydrogen-bonded with four ethanol molecules, thus forming discrete unit. On the contrary, intermolecular hydrogen bonds link the molecules of 2 generating three-dimensional network. [source] Writing Process and Progress: Where Do We Go from Here?ENGLISH IN EDUCATION, Issue 1 2001Mary Hilton Abstract This article examines the rationale behind the government's methods for raising standards in writing at Key Stage 2. Firstly there is a renewed drive to teach discrete units of sentence grammar. Secondly there is a fresh commitment to shared and guided writing. But, because it is envisaged that these teacher-led sessions will take up at least half of the Literacy Hour two or three times a week, both these aims will lead to a diminution of time for written composition by the children themselves. This is in accordance with new criticisms by NLS policy makers of the model of ,process' embedded in the National Curriculum, particularly the idea of creative pre-writing activities and sustained independent writing. The article goes on to argue that these new measures ignore research on the ways children learn to write and will not lead to a rise in standards. [source] Non-homogeneous infinitely many sites discrete-time model with exact coalescentMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 6 2010Adam Bobrowski Abstract Kingman's coalescent is among the most fertile concepts in mathematical population genetics. However, it only approximates the exact coalescent process associated with the Wright,Fisher model, in which the ancestry of a sample does not have to be a binary tree. The distinction between the approximate and exact coalescent becomes important when population size is small and time has to be measured in discrete units (generations). In the present paper, we explore the exact coalescent, with mutations following the infinitely many sites model. The methods used involve random point processes and generating functionals. This allows obtaining joint distributions of segregating sites in arbitrary intervals or collections of intervals, and generally in arbitrary Borel subsets of two or more chromosomes. Using this framework it is possible to find the moments of the numbers of segregating sites on pairs of chromosomes, as well as the moments of the average of the number of pairwise differences, in the form that is more general than usually. In addition, we demonstrate limit properties of the first two moments under a range of demographic scenarios, including different patterns of population growth. This latter part complements results obtained earlier for Kingman's coalescent. Finally, we discuss various applications, including the analysis of fluctuation experiments, from which mutation rates of biological cells can be inferred. Copyright © 2009 John Wiley & Sons, Ltd. [source] More examples of the 15-crown-5...H2O,M,OH2...15-crown-5 motif, M = Al3+, Cr3+ and Pd2+ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010Maxime A. Siegler Five structures of co-crystals grown from aqueous solutions equimolar in 15-crown-5 (or 15C5) and [M(H2O)6](NO3)n, M = Al3+, Cr3+ and Pd2+, are reported. The hydrogen-bonding patterns in all are similar: metal complexes including the fragment trans -H2O,M,OH2 alternate with 15C5 molecules, to which they are hydrogen bonded, to form stacks. A literature survey shows that this hydrogen-bonding pattern is very common. In each of the two polymorphs of the compound [Al(H2O)6](NO3)3·15C5·4H2O there are two independent cations; one forms hydrogen bonds directly to the 15C5 molecules adjacent in the stack, while the other cation is hydrogen-bonded to two water molecules that act as spacers in the stack. These stacks are then crosslinked by hydrogen bonds formed by the three nitrate counterions and the three lattice water molecules. The hydrogen-bonded stacks in [Cr(H2O)5(NO3)](NO3)2·1.5(15C5)·H2O are discrete rather than infinite; each unit contains two Cr3+ complex cations and three 15C5 molecules. These units are again crosslinked by the uncoordinated nitrate ions and a lattice water molecule. In [Pd(H2O)2(NO3)2]·15C5 the infinite stacks are electrically neutral and are not crosslinked. In [Pd(H2O)2(NO3)2]·2(15C5)·2H2O·2HNO3 a discrete, uncharged unit containing one Pd complex and two 15C5 molecules is `capped off' at either end by a lattice water molecule and an included nitric acid molecule. In all five structures the infinite stacks or discrete units form an array that is at least approximately hexagonal. [source] Dihalodimethyltin(IV) complexes of 2-(pyrazol-1-ylmethyl)pyridineAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2003Pedro Álvarez-Boo Abstract Reaction of dichloro- and dibromodimethyltin(IV) with 2-(pyrazol-1-ylmethyl)pyridine (PMP) afforded [SnMe2Cl2(PMP)] and [SnMe2Br2(PMP)] respectively. The new complexes were characterized by elemental analysis and mass spectrometry and by IR, Raman and NMR (1H, 13C) spectroscopies. Structural studies by X-ray diffraction techniques show that the compounds consist of discrete units with the tin atom octahedrally coordinated to the carbon atoms of the two methyl groups in a trans disposition (SnC = 2.097(5), 2.120(5) Å and 2.110(6), 2.121(6) Å in the chloro and in the bromo compounds respectively), two cis halogen atoms (SnCl = 2.4908(16), 2.5447(17) Å; SnBr = 2.6875(11), 2.7464(9) Å) and the two donor atoms of the ligand (SnN = 2.407(4), 2.471(4) Å and 2.360(5), 2.455(5) Å). In both cases, the SnN(pyridine) bond length is markedly longer than the SnN(pyrazole) distance. Copyright © 2003 John Wiley & Sons, Ltd. [source] Genetic variation of Lates calcarifer in Peninsular Malaysia based on the cytochrome b geneAQUACULTURE RESEARCH, Issue 15 2009M Y Norfatimah Abstract A 312 bp segment of the mitochondrial cytochrome b gene was sequenced from 132 sea bass Lates calcarifer individuals from nine populations across Peninsular Malaysia. Phylogenetic analysis and analysis of molecular variance within and among populations showed no significant geographical structuring. Several populations formed discrete units while others were of mixed populations. The former group suggests a low gene flow among some populations while the latter suggests that widespread translocations have impacted the other wild and cultured local populations. The data from this study have important implications for fishery management, conservation of sea bass stocks and translocation policy for aquaculture and stock enhancement in Peninsular Malaysia. [source] | ||||||||||