Comment: Struggles with Survey Weighting and Regression Modeling

Comment: Struggles with Survey Weighting and Regression Modeling [arXiv:0710.5005]Comment: Published in at http://dx.doi.org/10.1214/088342307000000159 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Quantum chemical studies of carbon-13 equilibrium fractionation in ion–molecule reactions

Ab initio computational quantum chemical methods are used to calculate reduced partition function ratios for all isotopomers of CO, HCO+,HCO+, and HOC+HOC+ involving the nuclides 1H,1H, 2H2H (D), 12C,12C, 13C,13C, 16O,16O, and 18O.18O. The ratios are used to calculate equilibrium constants for the reaction pairs HCO+/CO,HCO+/CO, HOC+/CO,HOC+/CO, and C+/CO.C+/CO. Both simple proton transfers and more complex isotopic variants involving the breaking and reforming of CO bonds are considered. The probable pathways for the HCO+/COHCO+/CO and C+/COC+/CO exchange reactions are explored in detail using high-accuracy quantum chemical calculations. It appears most likely that the HCO+/COHCO+/CO reaction proceeds through exothermic formation of the linear adduct OCHCO+OCHCO+ with D∞hD∞h symmetry. Similarly, the C+/COC+/CO reaction proceeds along a spin-allowed pathway with exothermic formation of the linear adduct COC+COC+ with D∞hD∞h symmetry. An alternate but higher energy spin-allowed pathway for the C+/COC+/CO reaction passes through a transition state with only CsCs symmetry and a locally stable intermediate with C2vC2v symmetry. In the ISM these reactions may proceed by these direct pathways or indirectly through coupled exothermic reaction pairs involving other species to achieve 13C/12C13C/12C isotope exchange. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70679/2/JCPSA6-108-19-8012-1.pd

Forecasting Organic Food Prices: Testing and Evaluating Conditional Predictive Ability

Organic farmers, wholesalers, and retailers need reliable price forecasts to improve their decision- making practices. This paper presents a methodology and protocol to select the best-performing method from several time and frequency domain candidates. Weekly farmgate prices for organic fresh produce are used. Forecasting methods are evaluated on the basis of an aggregate accuracy measure and several out-of-sample predictive ability tests. Combining forecasts to improve on individual forecasts is investigated.Demand and Price Analysis,

Rotational energy dispersions for van der Waals molecular clusters: Analytic descriptions for Rg3, Rg4, and Rg6

We have obtained analytic expressions, parametric in centrifugal displacement coordinates, which provide exact classical descriptions of the rotational energy dispersions, that is, the dependence of the combined rotational and ‘‘electronic’’ (vibrational potential) energies on the rotational angular momenta, for small molecular clusters bound by van der Waals interactions modeled by pairwise additive Lennard‐Jones 6–12 potential energies. The clusters considered consist of three (equilateral triangle), four (tetrahedron), and six (octahedron) units and serve as models for small clusters of rare‐gas atoms such as argon. This work represents an extension of our recently published study of analytic rotational energy dispersions for diatomic molecules bound by harmonic oscillator, Morse, or Lennard‐Jones potentials [J. Mol. Spectrosc. 155, 205 (1992)]. A parallel set of studies were made using an angular momentum‐conserving simulation program. The physical properties of the clusters that are addressed using our results include calculation of quartic and higher‐order spectroscopic constants, location of rotational instabilities, and characterization of the ‘‘cubic’’ anisotropies for the spherical top clusters A4 and A6. Of particular interest is the result that for each of these cluster types the preferred direction of the rotational angular momentum is parallel to a molecular fourfold axis, leading to reduced symmetries of D2d for tetrahedral A4 and D4h for octahedral A6.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70411/2/JCPSA6-99-9-6369-1.pd

Ab initio synthesis of the ozone ultraviolet continuum

Potential energy surfaces for the ground and excited electronic states responsible for the Hartley continuum of ozone are used to obtain quadratic, cubic, and quartic force constants. Vibrational dependence of rotational constants to sixth order is calculated by perturbation theory. The spectroscopic constants enable computation of rovibronic energy levels. Overlap of ground state and excited state perturbed vibrational wave functions yield Franck–Condon factors. Electric dipole allowed rovibronic transitions are generated under the Ir representation. The entire set of results generate the ultraviolet absorption spectrum. It is shown that inclusion of anharmonic terms in the vibrational Hamiltonian has a small effect upon the final spectrum, whereas rotational broadening plays a greater role in achieving agreement with experiment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69598/2/JCPSA6-86-10-5329-1.pd

Erratum: Crystal‐field model study of the xenon hexafluoride molecule. I. Energy levels and molecular geometry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70482/2/JCPSA6-62-5-2013-1.pd

Simple Model of the Dynamic Jahn‐Teller Effect in Six‐Coordinated Copper(II) Complexes

A model potential is assumed for describing the vibrational degrees of freedom associated with the Jahn‐Teller effect in six‐coordinated copper (II) complexes. The pseudorotational limit is characterized by a potential that is constant in the region between two concentric cylinders, but becomes infinite elsewhere. The energy spectrum is obtained for both angular and radial excitations. A square‐well periodic angular potential is applied as a perturbation, yielding a localization of states. The results are used to describe the temperature dependence of the electron spin resonance spectra of copper (II) complexes with emphasis on the system NaCl:Cu(II) containing the hexachlorocuprate (II) complex.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70781/2/JCPSA6-57-2-702-1.pd

A theoretical study of the optical absorption band shape for xenon hexafluoride

The classical Franck–Condon approximation is used together with the Monte Carlo integration technique to calculate the optical absorption band shape arising in xenon hexafluoride from the pseudo‐Jahn–Teller active t1u bending mode. The potential energy function for this mode has the Devonshire form for the hindered rotational motion of a diatomic molecule in a cubic site and is characterized by three parameters. Results are presented using values of these parameters as determined by Pitzer and Bernstein for the 1A1g electronic ground state and as estimated by us from the crystal‐field model of Wang and Lohr for the 1T1u and 3T1u electronic excited states.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71170/2/JCPSA6-67-5-1935-1.pd