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Dispersion Effects (dispersion + effects)
Selected AbstractsConformational analysis of arginine in gas phase,A strategy for scanning the potential energy surface effectivelyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2008Sebastian Schlund Abstract The determination of all possible low-lying energy conformers of flexible molecules is of fundamental interest for various applications. It necessitates a reliable conformational search that is able to detect all important minimum structures and calculates the energies on an adequate level of theory. This work presents a strategy to identify low-energy conformers using arginine as an example by means of a force-field based conformational search in combination with high-level geometry optimizations (RI-MP2/TZVPP+). The methods used for various stages in the conformational search strategy are shown and various pitfalls are discussed. We can show that electronic energies calculated on a DFT level of theory with standard exchange-correlation functionals strongly underestimate the intramolecular stabilization resulting from stacked orientations of the guanidine and carbonyl moiety of arginine due to the deficiency of DFT to describe dispersion effects. In this case by usage of electron correlation methods, low energy conformers comprising stacked arrangements that are counterintuitive become favorable. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] EXTENDED STATISTICAL ANALYSIS OF RANKED DATA FROM BALANCED INCOMPLETE BLOCK AND PAIRED COMPARISON DESIGNSJOURNAL OF SENSORY STUDIES, Issue 4 2000D.J. BEST ABSTRACT The usual Durbin analysis for ranked data obtained from a balanced incomplete block design is extended to allow for (1) dispersion effects, (2) a predetermined ordering of products and (3) more general trends. An application to paired comparison data is given. Calculation of p-values via Monte Carlo simulation is suggested. [source] Determination of the metal ordering in meteoritic (Fe,Ni)3P crystalsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2005O. Moretzki Synchrotron radiation diffraction studies of meteoritic (Fe,Ni)3P crystals have been performed to reveal the ordering of the elements Fe and Ni on the three metal sites M1, M2 and M3 of the unit cell. The , synthesis technique, which is a two-wavelength method using anomalous dispersion effects, was applied. For (Fe,Ni) phosphide crystals with different Fe:Ni ratios extracted from different meteorites, it was found that Ni occupies the M3 site and also partially the M2 site, avoiding the M1 position, whereas the M1 site is preferentially occupied by Fe. In connection with earlier results known from the literature, this metal distribution seems to be characteristic of this compound, and is independent of thermodynamic formation conditions. [source] DC or pulse I(V) measurements to simulate transmission line class E power amplifiersMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2006J. R. Loo-Yau Abstract In FET I(V) nonlinear modeling, the I(V) experimental data are important because they allow one to determine the initial values of the empirical nonlinear model. Pulsed I(V) are preferred over DC measurements because of dispersion phenomena. However, the simulation of a class E PA using I(V) empirical nonlinear model constructed from DC or pulsed measurements to predicts values of PAE, gain, and efficiency are similar. Although this fact can be predictable or evident, because the transistor works in the region where heating and dispersion effects are small, this has not been experimentally demonstrated yet. Therefore the main purpose of this work is to determine whether pulse or DC I(V) measurements are suitable to develop the nonlinear model in order to predict the main features of a transmission line class E PA as Pout, drain efficiency, and PAE. The simulations using both types of data were compared with two experimental transmission line class E PA, designed at 0.8 and 1.9 GHz. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48:1886,1890, 2006; Published online in Wiley InterScience (www.interscience.wiley.com(. DOI 10.1002/mop.21794 [source] Planning and Optimization of a Numerical Control Machine in a Multiple Response CaseQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 5 2006Rossella Berni Abstract This paper focuses on a specific case of experimental planning and optimization in a multiresponse case. Particularly, our attention is dedicated to a numerical control machine and our final goal is to improve this machine's measurement accuracy for a general dental implant. This work substantially aims at addressing two issues: the optimization methods in the presence of more response variables and the related problem of weighting according to the actual importance of these variables. About simultaneous optimization, we suggest an improvement by a new function which takes care of location and dispersion effects. Copyright © 2006 John Wiley & Sons, Ltd. [source] Testing dispersion effects from general unreplicated fractional factorial designsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 4 2001P. C. Wang Abstract Continuous improvement of the quality of industrial products is an essential factor in modern-day manufacturing. The investigation of those factors that affect process mean and process dispersion (standard deviation) is an important step in such improvements. Most often, experiments are executed for such investigations. To detect mean factors, I use the usual analysis of variance on the experimental data. However, there is no unified method to identify dispersion factors. In recent years several methods have been proposed for identifying such factors with two levels. Multilevel factors, especially three-level factors, are common in industrial experiments, but we lack methods for identifying dispersion effects in multilevel factors. In this paper, I develop a method for identifying dispersion effects from general fractional factorial experiments. This method consists of two stages. The first stage involves the identification of mean factors using the performance characteristic as the response. The second stage involves the computation of a dispersion measure and the identification of dispersion factors using the dispersion measure as the response. The sequence for identifying dispersion factors is first to test the significance of the total dispersion effect of a factor, then to test the dispersion contrasts of interest, which is a method similar to the typical post hoc testing procedure in the ANOVA analysis. This familiar approach should be appealing to practitioners. Copyright © 2001 John Wiley & Sons, Ltd. [source] Chirality-induced `forbidden' reflections in X-ray resonant scatteringACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2001V. E. Dmitrienko It is shown that additional Bragg reflections can appear exclusively owing to the local chirality associated with the left,right asymmetric environment of scattering atoms in non-magnetic crystals. The structure amplitude of these reflections depends on the antisymmetric part of a third-rank tensor describing the spatial dispersion effects. It enhances for resonant near-edge scattering through a mixed multipole transition, which includes a dipole,quadrupole contribution. It is shown that this mechanism works even for centrosymmetric crystals, and some realistic examples are considered in detail (,-Fe2O3, LiNbO3etc.). For instance, the interference between the dipole,quadrupole and quadrupole,quadrupole terms may be responsible for the threefold symmetry of the azimuthal dependence of the hhh, h = 2n + 1, reflections observed recently in hematite. [source] Calculation of conformational energies and optical rotation of the most simple chiral alkane,CHIRALITY, Issue 9 2008Stefan Grimme Abstract Quantum chemical calculations have been performed to investigate the conformer distribution of 4-ethyl-4-methyloctane and its optical rotation. With the reference methods MP2 and SCS-MP2, the energies of seven conformers are found within a range of about 1.5 kcal mol,1. It is demonstrated that the relative energies cannot be reliably predicted with conventional GGA or hybrid density functionals, Hartree-Fock, semiempirical AM1, and classical force field (MM3) calculations. An empirical dispersion correction to GGA (PBE-D), hybrid (B3LYP-D), or double hybrid (B2PLYP-D) functionals corrects these errors and results in very good agreement with the reference energies. Optical rotations have been calculated for all seven conformers at the TDDFT(BHLYP/aTZV2P) level. The computed macroscopic rotation is derived from a classical Boltzmann average. The result (1.9,3.2 deg dm,1 (g/mL),1) is very close to the experimental value of 0.2 deg dm,1 (g/mL),1 for the (R)-enantiomer and has the right sign. Because six conformers are significantly populated at room temperature and the rotations of individual conformers differ in sign and magnitude, the calculated average rotation is rather sensitive to the conformer population used. From the electronic structure point of view, this example emphasizes the effect of long-range dispersion effects for the evaluation of population averaged quantities in large molecules. Computations based on free enthalpies are in worse agreement with experiment that is attributed to artefacts of the harmonic approximation used to compute the vibrational entropy terms. Chirality, 2008. © 2008 Wiley-Liss, Inc. [source] | |||||||||||||