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Hexagonal Lattices (hexagonal + lattice)
Selected AbstractsEffect of substrate temperature on the properties of vacuum evaporated indium selenide thin filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2005C. Viswanathan Abstract Thin films of InSe were obtained by thermal evaporation techniques on glass substrates maintained at various temperatures (Tsb = 30°, 400°C). X-ray diffraction analysis showed the occurrence of amorphous to polycrystalline transformation in the films deposited at higher substrate temperature (400°C). The polycrystalline films were found to have a hexagonal lattice. Compositions of these films have been characterized by EDAX and the surface analysis by scanning electron microscopy. Optical properties of the films, investigated by using spectrophotometer transmittance spectra in the wavelength range (300 , 1100 nm), were explained in terms of substrate temperatures. Films formed at room temperature showed an optical band gap (Egopt) 1.56 eV; where as the films formed at 400°C were found to have a Egopt of 1.92 eV. The increase in the value of Egopt with Tsb treatment is interpreted in terms of the density of states model as proposed by Mott and Davis. The analysis of current -Voltage characteristics, based on space charge limited currents (SCLC) measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Periodic spotted patterns in semi-arid vegetation explained by a propagation-inhibition modelJOURNAL OF ECOLOGY, Issue 4 2001P. Couteron Summary 1,Vegetation cover regularly punctuated by spots of bare soil is a frequent feature of certain semi-arid African landscapes, which are also characterized by banded vegetation patterns (i.e. tiger bush). 2,The propagation-inhibition (PI) model suggests that a periodic pattern characterized by a dominant wavelength can theoretically establish itself through a Turing-like spatial instability depending only on a trade-off between facilitative and competitive interactions among plants. Under strictly isotropic conditions, spotted and banded patterns are distinct outcomes of a unique process, whereas anisotropy leads to a banded structure. The model predicts that spotted patterns will have a lower dominant wavelength than bands. 3,We test some outcomes of the PI model against vegetation patterns observable in aerial photographs from West Africa. Two sites with rainfall of c. 500,600 mm year,1 were studied: a 525-ha plain in north-west Burkina Faso and a 300-ha plateau in southern Niger. Digitized photographs were subjected to spectral analysis by Fourier transform in order to quantify vegetation patterns in terms of dominant wavelengths and orientations. 4,Spotted vegetation proved highly periodic. The characteristic range of dominant wavelengths (30,50 m) was similar at two sites more than 500 km apart. The PI model suggests that spots may occur as a hexagonal lattice but there is little evidence of such patterning in the field. A dominant wavelength was far quicker to establish in simulations (c. 102,103 years for annual grasses) than a hexagonal symmetry (c. 105 years), and observed patterns are therefore likely to be far from the asymptotic structure. 5,Elongated and smudged spots that locally became flexuous bands have been observed in southern Niger. This pattern that had a dominant wavelength of 50 m but lacked any dominant orientation can be interpreted as a transition from spots to bands under fairly isotropic conditions. 6,The PI model provides a framework for further investigation of patterns in semi-arid vegetation and may be of a broader ecological application. [source] Investigation of odd,odd nylons based on undecanedioic acid.POLYMER ENGINEERING & SCIENCE, Issue 12 20052: Crystal structures The crystal structures of the odd,odd nylons X 11 (X = 3, 5, 7, 9, and 11) under different conditions, including solution-crystallized samples and melt-crystallized samples, were investigated by wide-angle X-ray diffraction (WAXD) and electron diffraction (ED). For the melt-crystallized samples of the odd,odd nylons under consideration, the strong diffraction at 0.42 nm, which is typical of the hexagonal lattice, was found in the WAXD patterns. As for the solution-crystallized samples, nylon 11 11 presents the monoclinic crystal structure characteristic of the two strong diffractions at about 0.42 and 0.40 nm of the WAXD and ED patterns, while nylons 9 11, 7 11, 5 11, and 3 11 show the hexagonal crystal ones typical of the same diffraction patterns as those of the melt-crystallized samples. The model of hydrogen bonds in crystal structures of the odd,odd nylons under study is discussed. POLYM. ENG. SCI., 45:1673,1679, 2005. © 2005 Society of Plastics Engineers [source] Silver Nanoparticles with Controlled Dispersity and Their Assembly into SuperstructuresADVANCED ENGINEERING MATERIALS, Issue 5 2010Karsten Moh In this paper we report on the influence of particle size distribution, particle substrate interaction, and drying behavior on the self-assembly process using ligand stabilized silver particles. Two-dimensional particle arrays were characterized using transmission electron microscopy and extensive image analysis. The formation of such structures was observed in situ using an environmental scanning electron microscope in WET-STEM mode. The results confirm that a small particle size distribution is crucial for the formation of regular particle patterns with long range order, but also the particle substrate interaction and the particle density have an influence on the degree of ordering. Additionally, we find that separated binary particle assemblies keep the orientation of their two-dimensional hexagonal lattices over alternating domains of small and big particles. This is probably enabled due to the formation of dislocations and a small change of the course of the lattice lines within the respective boundary. [source] Order Distance in Regular Point PatternsGEOGRAPHICAL ANALYSIS, Issue 3 2009Masashi Miyagawa This article examines the kth nearest neighbor distance for three regular point patterns: square, triangular, and hexagonal lattices. The probability density functions of the kth nearest distance and the average kth nearest distances are theoretically derived for k=1, 2, ,, 7. As an application of the kth nearest distance, we consider a facility location problem with closing of facilities. The problem is to find the optimal regular pattern that minimizes the average distance to the nearest open facility. Assuming that facilities are closed independently and at random, we show that the triangular lattice is optimal if at least 68% of facilities are open by comparing the upper and lower bounds of the average distances. El siguiente artículo examina la distancia de los k-vecinos más cercanos en látices cuadrados, triangulares y hexagonales. La funciones de densidad de probabilidad para las distancias k-más próximas y para las k-promedio más próximas son derivadas teóricamente para k=1,2,,7. Con el fin de demostrar una aplicación de la distancia k-más próxima los autores utilizan un ejemplo de localización y clausura de instalaciones. El objetivo es identificar el patrón regular óptimo que minimice la distancia promedio a la instalación abierta más cercana. Bajo el supuesto que las instalaciones cierran independientemente y aleatoriamente, y comparando los límites extremos superiores e inferiores de las distancias promedio, los autores demuestran que el patrón triangular es el óptimo si es que por lo menos 68 por ciento de las instalaciones permanecen abiertas. [source] Zones and sublattices of integral latticesACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2004A. Janner Methods are presented for an analysis of zones and sublattices of integral lattices, whose relevance is revealed by sharp peaks in the frequency distribution of hexagonal and tetragonal lattices, as a function of the axial ratio . Starting from a few examples, zone symmetries, lattice,sublattice relations and integral scaling transformations are derived for hexagonal lattices with axial ratios , , and 1 (the isometric case) and for the related and tetragonal lattices. Sublattices and zones connected by linear rational transformations lead to rational equivalence classes of integral lattices. For properties like the axial ratio and the point-group symmetry (lattice holohedry), rational equivalence can be extended so that also metric tensors differing by an integral factor become equivalent. These two types of equivalence classes are determined for the lattices mentioned above. [source] Crystallization and X-ray diffraction analysis of peroxisomal ,3 -,2 -enoyl-CoA isomerase from Saccharomyces cerevisiaeACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2000Anu M. Mursula The purification, crystallization and X-ray diffraction analysis of Saccharomyces cerevisiae,3 -,2 -enoyl-CoA isomerase is described. ,3 -,2 -Enoyl-CoA isomerase is a member of the hydratase/isomerase protein family and is an auxiliary enzyme required for the ,-oxidation of unsaturated fatty acids. It is a hexameric enzyme consisting of six identical 32,kDa subunits of 280 residues each. In crystallization trials three crystal forms were obtained, with tetragonal and hexagonal lattices. A 2.5,Å data set was collected from the unliganded hexagonal crystals with an Rmerge of 6.6%. The crystal, with unit-cell parameters a = 116.0, b = 116.0, c = 122.9,Å, is likely to have P6322 symmetry. [source] | |||||||||||||