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Larger Deviations (larger + deviation)
Selected AbstractsAxisymmetric orbit models of N -body merger remnants: a dependency of reconstructed mass on viewing angleMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007J. Thomas ABSTRACT We model mock observations of collisionless N -body disc,disc mergers with the same axisymmetric orbit superposition program that has been used to model elliptical galaxies in Coma. The remnants sample representatively the shape distribution of disc,disc mergers, including the most extreme cases, like highly prolate, maximally triaxial and dominantly oblate objects. The aim of our study is to better understand how the assumption of axial symmetry affects reconstructed masses and stellar motions of systems which are intrinsically not axisymmetric, whether the axisymmetry assumption then leads to a bias and how such a potential bias can be recognized in models of real galaxies. The mass recovery at the half-light radius depends on viewing angle and intrinsic shape: edge-on views allow to reconstruct total masses with an accuracy between 20 per cent (triaxial/prolate remnants) and 3 per cent (oblate remnant). Masses of highly flattened, face-on systems are underestimated by up to 50 per cent. Deviations in local mass densities can be larger where remnants are strongly triaxial or prolate. Luminous mass-to-light ratios are sensitive to box orbits in the remnants. Box orbits cause the central value of the Gauss,Hermite parameter H4 to vary with viewing angle. Reconstructed luminous mass-to-light ratios, as well as reconstructed central masses, follow this variation. Luminous mass-to-light ratios are always underestimated (up to a factor of 2.5). Respective dark haloes in the models can be overestimated by about the same amount, depending again on viewing angle. Reconstructed velocity anisotropies , depend on viewing angle as well as on the orbital composition of the remnant and are mostly accurate to about ,,= 0.2. Larger deviations can occur towards the centre or the outer regions, respectively. We construct N -body realizations of the Schwarzschild models to discuss chaotic orbits and the virial equilibrium in our models. In this study we explore the extreme limits of axisymmetric models. Apparently flattened, rotating ellipticals of intermediate mass are likely close to both, axial symmetry and edge-on orientation. Our results imply that Schwarzschild models allow a reconstruction of their masses and stellar anisotropies with high accuracy. [source] Intruder state avoidance multireference Møller,Plesset perturbation theoryJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2002Henryk A. Witek Abstract A new perturbation approach is proposed that enhances the low-order, perturbative convergence by modifying the zeroth-order Hamiltonian in a manner that enlarges any small-energy denominators that may otherwise appear in the perturbative expansion. This intruder state avoidance (ISA) method can be used in conjunction with any perturbative approach, but is most applicable to cases where small energy denominators arise from orthogonal-space states,so-called intruder states,that should, under normal circumstances, make a negligible contribution to the target state of interests. This ISA method is used with multireference Møller,Plesset (MRMP) perturbation theory on potential energy curves that are otherwise plagued by singularities when treated with (conventional) MRMP; calculation are performed on the 13, state of O2; and the 21,, 31,, 23,, and 33, states of AgH. This approach is also applied to other calculations where MRMP is influenced by intruder states; calculations are performed on the 3,u state of N2, the 3, state of CO, and the 21A, state of formamide. A number of calculations are also performed to illustrate that this approach has little or no effect on MRMP when intruder states are not present in perturbative calculations; vertical excitation energies are computed for the low-lying states of N2, C2, CO, formamide, and benzene; the adiabatic 1A1,3B1 energy separation in CH2, and the spectroscopic parameters of O2 are also calculated. Vertical excitation energies are also performed on the Q and B bands states of free-base, chlorin, and zinc,chlorin porphyrin, where somewhat larger couplings exists, and,as anticipated,a larger deviation is found between MRMP and ISA-MRMP. © 2002 Wiley Periodicals, Inc. J Comput Chem 10: 957,965, 2002 [source] Accurate prediction of proton chemical shifts.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2001Abstract Forty-five proton chemical shifts in 14 aromatic molecules have been calculated at several levels of theory: Hartree,Fock and density functional theory with several different basis sets, and also second-order Møller,Plesset (MP2) theory. To obtain consistent experimental data, the NMR spectra were remeasured on a 500 MHz spectrometer in CDCl3 solution. A set of 10 molecules without strong electron correlation effects was selected as the parametrization set. The calculated chemical shifts (relative to benzene) of 29 different protons in this set correlate very well with the experiment, and even better after linear regression. For this set, all methods perform roughly equally. The best agreement without linear regression is given by the B3LYP/TZVP method (rms deviation 0.060 ppm), although the best linear fit of the calculated shifts to experimental values is obtained for B3LYP/6-311++G**, with an rms deviation of only 0.037 ppm. Somewhat larger deviations were obtained for the second test set of 4 more difficult molecules: nitrobenzene, azulene, salicylaldehyde, and o -nitroaniline, characterized by strong electron correlation or resonance-assisted intramolecular hydrogen bonding. The results show that it is possible, at a reasonable cost, to calculate relative proton shieldings in a similar chemical environment to high accuracy. Our ultimate goal is to use calculated proton shifts to obtain constraints for local conformations in proteins; this requires a predictive accuracy of 0.1,0.2 ppm. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1887,1895, 2001 [source] Temperature functions of the rate coefficients of net N mineralization in sandy arable soils.JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2004Part II. Abstract The aim of this study was to evaluate experimentally derived temperature functions for the rate coefficients of net N mineralization in sandy arable soils from NW Germany via field measurements. In part I of this paper (Heumann and Böttcher, 2004), different temperature functions for the rate coefficients of a two-pool first-order kinetic equation were derived by long-term laboratory incubations at 3°C to 35°C. In this paper, field net N mineralization during winter of 25 plots was measured in undisturbed soil columns with a diameter of 20,cm to the depth of the Ap horizon. Mean simulated net N mineralization with the most adequate multiple functions corresponded also best with the mean of the measured values despite of an overestimation of about 10%. Distinctly larger deviations under use of other temperature functions (Arrhenius, Q10) were directly related to their deviations from mean, experimentally derived rate coefficients. Simulated net N mineralization in the soil columns was significantly correlated with measured values, regardless of the temperature functions. Yet the goodness of fit was generally relatively low due to the spatial variability of measured net N mineralization within replicate soil columns, although the mean CV (38%) was by far not extraordinary. The pool of slowly mineralizable N contributed considerably to net N mineralization during four to five winter months, on an average 10.0 kg N ha,1, about one third of total simulated N mineralization. Sometimes, it contributed even 21.3 kg N ha,1, which is almost sufficient to reach the EU drinking-water limit for nitrate in these soils. Simulations with widely used functions that were once derived from loess soils overestimated mineralization from pool Nslow in the studied sandy arable soils by a factor of two. Die Temperaturfunktionen der Reaktionskoeffizienten der N-Nettomineralisation in sandigen Ackerböde nII. Überprüfung anhand von Mineralisationsmessungen im Freiland Ziel dieser Untersuchung war die Überprüfung experimentell ermittelter Temperaturfunktionen für die Reaktionskoeffizienten der N-Nettomineralisation in sandigen Ackerböden NW-Deutschlands anhand von Freilandmessungen. In Teil I der Arbeit (Heumann and Böttcher, 2004) wurden verschiedene Temperaturfunktionen für die Reaktionskoeffizienten zweier N-Pools mit Reaktionskinetik erster Ordnung mittels Langzeit-Laborinkubationen bei 3 bis 35°C bestimmt. In diesem Artikel wurde von 25 Plots die winterliche N-Nettomineralisation im Freiland in ungestörten Bodensäulen mit einem Durchmesser von 20,cm bis zur Tiefe des Ap-Horizontes gemessen. Im Mittel gaben die Simulationen mit den am besten passenden, multiplen Funktionen die Messergebnisse auch am besten wieder, trotz einer Überschätzung um etwa 10%. Deutlich größere Abweichungen bei Benutzung anderer Temperaturfunktionen (Arrhenius, Q10) standen in direkter Beziehung zu deren Abweichungen von den mittleren, experimentell ermittelten Reaktionskoeffizienten. Die simulierte N-Nettomineralisation war unabhängig von den Temperaturfunktionen signifikant mit den Messergebnissen korreliert. Jedoch war die Güte der Anpassung im Allgemeinen relativ niedrig aufgrund der räumlichen Variabilität der gemessenen N-Nettomineralisation innerhalb der einzelnen Säulen eines Plots, obwohl der mittlere CV (38%) bei weitem nicht außergewöhnlich war. Der langsam mineralisierbare N-Pool trug beträchtlich zur N-Nettomineralisation innerhalb von vier bis fünf Wintermonaten bei, durchschnittlich 10,0 kg N ha,1, etwa ein Drittel der gesamten simulierten N-Mineralisation. In manchen Böden waren es sogar 21,3 kg N ha,1, was fast ausreicht, um den EU-Trinkwassergrenzwert für Nitrat in diesen Böden zu erreichen. Simulationen mit häufig benutzten Funktionen, die ursprünglich an Lössböden ermittelt wurden, überschätzten die Mineralisation aus dem Pool Nslow in den untersuchten Sandböden um den Faktor zwei. [source] 1H chemical shifts in NMR.MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2005Part 2, Prediction of the 1H chemical shifts of molecules containing the ester group: a modelling, ab initio investigation Abstract The 1H NMR spectra of 24 compounds containing the ester group are given and assigned. These data were used to investigate the effect of the ester group on the 1H chemical shifts in these molecules. These effects were analysed using the CHARGE model, which incorporates the electric field, magnetic anisotropy and steric effects of the functional group for long-range protons together with functions for the calculation of the two- and three-bond effects. The effect of the ester electric field was given by considering the partial atomic charges on the three atoms of the ester group. The anisotropy of the carbonyl group was reproduced with an asymmetric magnetic anisotropy acting at the midpoint of the carbonyl bond with values of ,,parl and ,,perp of 10.1 × 10,30 and ,17.1 × 10,30 cm3 molecule,1. An aromatic ring current (=0.3 times the benzene ring current) was found to be necessary for pyrone but none for maleic anhydride. This result was confirmed by GIAO calculations. The observed 1H chemical shifts in the above compounds were compared with those calculated by CHARGE and the ab initio GIAO method (B3LYP/6,31G**). For the 24 compounds investigated with 150 1H chemical shifts spanning a range of ca 10 ppm, the CHARGE model gave an excellent r.m.s. error (obs , calc) of <0.1 ppm. The GIAO calculations gave a very reasonable r.m.s. error of ca 0.2 ppm although larger deviations of ca 0.5 ppm were observed for protons near to the electronegative atoms. The accurate predictions of the 1H chemical shifts given by the CHARGE model were used in the conformational analysis of the vinyl esters methyl acrylate and methyl crotonate. An illustration of the use of the CHARGE model in the prediction of the 1H spectrum of a complex organic molecule (benzochromen-6-one) is also given. Copyright © 2004 John Wiley & Sons, Ltd. [source] Monetary Policy in the Greenspan Era: A Time Series Analysis of Rules vs.OXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 1 2009Discretion Abstract Relationships between the Federal funds rate, unemployment, inflation and the long-term bond rate are investigated with cointegration techniques. We find a stable long-term relationship between the Federal funds rate, unemployment and the bond rate. This relationship is interpretable as a policy target because deviations are corrected via the Federal funds rate. Deviations of the actual Federal funds rate from the estimated target give simple indications of discretionary monetary policy, and the larger deviations relate to special episodes outside the current information set. A more traditional Taylor-type target, where inflation appears instead of the bond rate, does not seem congruent with the data. [source] Extension to mixtures of two robust hard-sphere equations of state satisfying the ordered close-packed limitTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2001Cyrus Ghotbi Abstract Two new hard-sphere EOS are proposed and tested using the same attractive potential terms used by the SAFT EOS. Generalized expressions for the pair RDF at contact value, the compressibility factor, and the excess chemical potentials have been derived. Extension to mixtures is tested using three mixing rules for multicomponent hard-sphere fluids. The proposed EOS combined with the Santos et al. and the Barrio-Solana mixing rules reproduced the compressibility factors and the excess chemical potentials more accurately than the Boublik-Mansoori-Camahan-Starling-Leland (BMCSL) EOS. However the pair RDF at contact value had larger deviations than those obtained with the BMCSL EOS. The combination of the proposed equations and the Barrio-Solana mixing rule gave an accurate reproduction of the compressibility factor for binary hard-sphere fluids with high diameter ratio even in the low concentration regions of the larger spheres. Deux nouvelles équations d'état de sphères dures sont proposées et vérifiées à l'aide des m,mes termes potentiels attractifs utilisés pour l'équation d'état de SAFT. Des expressions généralisées pour le RDF pair à la valeur de contact, le facteur de compressibilité et les potentiels chimiques d'excès ont été calculées. L'extension à des mélanges est vérifiée à l'aide de trois régies de mélange pour fiuides à sphères dures multi-composants. Les équations d'état proposées, combinées aux règles de mélange de Santos et al. et de Barrio-Solana, reproduisent les facteurs de compressibilité et les potentiels chimiques d'excès de façon plus précise que l'équation d'état de Boublik-Mansoori-Camahan-Starling-Leiand (BMCSL). Cependant, le RDF pair à la valeur de contact a des écarts plus grands que ceux obtenus avec l'équation d'état de BMCSL. La combinaison des équations proposées et la régle de mélange de Barrio-Solana donne une reproduction exacte du facteur de compressibilité pour des fluides de sphères dures binaires ayant un rapport de diamètre important m,me dans les régions de faible concentration de sphères les plus grandes. [source] Bis[S -6-(2,2:6,,2,,-terpyridin-4,-yloxy)hexyl thioacetate]manganese(II) bis(hexafluorophosphate)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Kasper Moth-Poulsen The structure of a manganese(II) complex of terpyridine functionalized with acetylsulfanyl-terminated hexyloxy chains, [Mn(C23H25N3O2S)2](PF6)2, is described. This type of complex is of interest in the study of single-molecule transport properties in open-shell systems. The manganese coordination environment is distorted octahedral but, importantly, with no larger deviations from the idealized geometry than those observed for other metal,terpyridine complexes. The Mn,N bond lengths range from 2.192,(2) to 2.272,(3),Å. The title compound crystallizes with the cation and anions all on general positions, with the hexafluorophosphate anions exhibiting orientational disorder. When compared with other bis-terpyridine complexes, this structure demonstrates that manganese(II) is no more prone to undergo low-symmetry distortions than systems with ligand field stabilization energy contributions. [source] | ||||||||||