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Cluster Approach (cluster + approach)

Distribution by Scientific Domains

Chemistry	28%

Selected Abstracts

Cluster approach to the Ti2Ni structure type

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2006
D. Rodi
It has been established that the 16(c) first coordination clusters in the Ti2Ni structure type (space group Fd3m) follow icosahedral-face orientational ordering along regular tetrahedron edge directions. The actual crystal structure appears due to the prevalence of the face-centred cubic translational ordering over the cluster assembling. This way, the competition of the `regular' crystal phase and its icosahedral analogue is reconstructed at the atomic level. The model accounts for the markedly different electronic characteristics at the different crystallographic positions obtained by hyperfine interaction measurements, and other curious experimental facts help to create an exact physical definition of the first coordination in the solid state and to distinguish between various structure types on fundamental principles. [source]

Mercury binding on activated carbon

ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2006
Bihter Padak
Abstract Density functional theory has been employed for the modeling of activated carbon (AC) using a fused-benzene ring cluster approach. Oxygen functional groups have been investigated for their promotion of effective elemental mercury binding on AC surface sites. Lactone and carbonyl functional groups yield the highest mercury binding energies. Further, the addition of halogen atoms has been considered to the modeled surface, and has been found to increase the AC's mercury adsorption capacity. The mercury binding energies increase with the addition of the following halogen atoms, F > Cl > Br > I, with the fluorine addition being the most promising halogen for increasing mercury adsorption. © 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source]

Beyond resilients, undercontrollers, and overcontrollers? an extension of personality prototype research

EUROPEAN JOURNAL OF PERSONALITY, Issue 1 2006
Philipp Yorck Herzberg
Prototypes of personality were investigated in two studies. In study I, clusters of Big-Five-based prototypes were examined using a general population sample of 1908 German adults. Convergent evidence suggested the appropriateness of a five-cluster solution, which corresponds to previously identified temperament based prototypes. In study II, the five-cluster solution was cross-validated in a sample of 256 prisoners. Moreover, it was shown that a population-based approach (using discriminant functions derived from study I) was superior over the traditional sample-based cluster approach (using Ward followed by k -means). The authors argue that future typological research can be sufficiently grounded on a five-prototype conception rather than on a three-prototype conception, and suggest a new and flexible assignment procedure. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Magnetic hysteresis loop in antiferromagnetically coupled bilayer structures

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2008
Yan Ma
Abstract The hysteresis behavior of a bilayer film system, in which a hard ferromagnetic layer with larger anisotropy and spin-3/2 couples with a soft ferromagnetic layer with smaller anisotropy and spin-1 antiferromagnetically, is studied by using the Ising model and the linear cluster approach. We calculate the magnetic reversal of the soft magnetic layer at low field while keeping the saturated magnetization state of the hard magnetic layer unperturbed, and find a phenomenon of exchange bias. The influences of anisotropy, intralayer exchange in the soft magnetic layer, and the interlayer exchange on the coercivity and exchange bias in the bilayer film are discussed. It is found that increasing the interlayer coupling can enhance the exchange bias of the system, and the easy plane anisotropy in soft magnetic layers can induce the hysteresis loop moving towards positive field. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Investigations of the g -factors and local phase-transition behavior for Ni3+ ion in the tetragonal phase of RbCaF3 crystal

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2008
Shun-Ru Zhang
Abstract The EPR g factors g, and g, for Ni3+ ion (created by room-temperature X-irradiation of nickel-doped RbCaF3) in the tetragonal phase of RbCaF3 crystal are calculated from the second-order perturbation formulas based on a cluster approach for high-spin 3d7 ions in tetragonal octahedral clusters. The calculated results are in reasonable agreement with the experimental values. The local phase-transition behavior of the Ni3+ impurity center in RbCaF3 is also estimated from the calculation. It is found that the local phase-transition behavior in the Ni3+ center is unlike the intrinsic one in the host crystal (in particular, the fluorine octahedra surrounding the cations change from tetragonal compression in the host crystal to tetragonal elongation in the Ni3+ impurity center). The results are discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The effective-site percolation approach in two dimensions

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2007
G. Paw, owski
Abstract A new Monte Carlo cluster approach to describe the order,order and order,disorder transitions in two-dimensional (2D) correlated systems is presented. It is shown that a phase transition of a physical system can be correctly described in terms of the percolation language of the effective-site approach. In contrast to the well-known bond approaches, the method proposed does not require additional assumptions as to the acceptance of the bonds. The new idea is based on the site approach to elementary ordered plaquettes, leading to the accurate coincidence of percolation and the phase transitions in 2D. Here I present the analysis of the spin-system in the Blume,Capel model and the charged-system in the atomic limit of the extended Hubbard model. In both cases the interpretation of the phase transition is made in terms of the percolation of different types of order. The new method allows precise identification of the pure and mixed phases. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Theoretical and Experimental Study of the Adsorption of Neutral Glycine on Silica from the Gas Phase

CHEMPHYSCHEM, Issue 6 2005
C. Lomenech Dr.
Abstract The adsorption of neutral glycine onto amorphous silica was investigated both theoretically and experimentally. DFT calculations were performed at the BLYP-631++G** level using a cluster approach. Several possible configurations involving the formation of H bonds between glycine and one, two, or three silanol groups (SiOH) were considered. The most favorable bonding of glycine with one silanol group (45 kJ,mol,1) occurs through the COOH moiety, thus forming a cycle in which the CO group is an H-bond acceptor whereas the acidic OH group is an H-bond donor. With two or three silanol groups, additional H bonds are formed between the amine moiety and the silanol groups, which leads to an increased adsorption energy (70 and 80 kJ,mol,1for two and three silanol groups, respectively). Calculated ,CO, ,HNH, and ,HCHvalues are sensitive to the adsorption mode. A bathochromic shift of ,COas compared to the ,COof free glycine (calculated in the 1755,1790 cm,1range) is found for glycine in interaction with silanol(s). The more H bonds are formed between the COOH moiety and silanol groups, the higher the bathochromic shift. For ,HNH, no shift is found for glycine adsorbed on one and two silanol groups (where the amine is either not bound or an H-bond donor), whereas a bathochromic shift is calculated with three silanols when the amine moiety is an H-bond acceptor. Experimental FTIR spectra performed at room temperature for glycine adsorbed at 160,°C on Aerosil amorphous silica exhibit bands at 1371, 1423, 1630, and 1699 cm,1. The experimental/calculated frequencies have their best correspondence for glycine adsorbed on two silanol groups. It is important to note that the forms giving the best correspondence to experimental frequencies are the most stable ones. [source]