Heats of formation of perchloric acid, HClO4_4, and perchloric anhydride, Cl2_2O7_7. Probing the limits of W1 and W2 theory

The heats of formation of HClO$_4$ and Cl$_2$O$_7$ have been determined to chemical accuracy for the first time by means of W1 and W2 theory. These molecules exhibit particularly severe degrees of inner polarization, and as such obtaining a basis-set limit SCF component to the total atomization energy becomes a challenge. (Adding high-exponent $d$ functions to a standard $spd$ basis set has an effect on the order of 100 kcal/mol for Cl$_2$O$_7$.) Wilson's aug-cc-pV(n+d)Z basis sets represent a dramatic improvement over the standard aug-cc-pVnZ basis sets, while the aug-cc-pVnZ+2d1f sequence converges still more rapidly. Jensen's polarization consistent basis sets still require additional high-exponent $d$ functions: for smooth convergence we suggest the \{aug-pc1+3d,aug-pc2+2d,aug-pc3+d,aug-pc4\} sequence. The role of the tight $d$ functions is shown to be an improved description of the Cl (3d) Rydberg orbital, enhancing its ability to receive back-bonding from the oxygen lone pairs. In problematic cases like this (or indeed in general), a single SCF/aug-cc-pV6Z+2d1f calculation may be preferable over empirically motivated extrapolations. Our best estimate heats of formation are $\Delta H^\circ_{f,298}[$HClO$_4$(g)$]=-0.6\pm$1 kcal/mol and $\Delta H^\circ_{f,298}[$Cl$_2$O$_7$(g)$]=65.9\pm$2 kcal/mol, the largest source of uncertainty being our inability to account for post-CCSD(T) correlation effects. While G2 and G3 theory have fairly large errors, G3X theory reproduces both values to within 2 kcal/mol.Comment: J. Mol. Struct. (THEOCHEM), in press (WATOC'05 special issue

A combined cesium-strontium extraction/recovery process

A new solvent extraction process for the simultaneous extraction of cesium and strontium from acidic nitrate media is described. This process uses a solvent formulation comprised of 0.05 M di-t-butylcyclohexano-18-crown-6 (DtBuCH18C6), 0.1 M Crown 100{prime} (a proprietary, cesium-selective derivative of dibenzo-18-crown-6), 1.2 M tributyl phosphate (TBP), and 5% (v/v) lauryl nitrile in an isoparaffinic hydrocarbon diluent. Distribution ratios for cesium and strontium from 4 M nitric acid are 4.13 and 3.46, respectively. A benchtop batch countercurrent extraction experiment indicates that >98% of the cesium and strontium initially present in the feed solution can be removed in only four extraction stages. Through proper choice of extraction and strip conditions, extracted cesium and strontium can be recovered either together or individually

Anharmonic force fields of perchloric acid, HClO4_4, and perchloric anhydride, Cl2_2O7_7. An extreme case of inner polarization

DFT (density functional theory) anharmonic force fields with basis sets near the Kohn-Sham limit have been obtained for perchloric acid, HClO$_4$, and perchloric anhydride, Cl$_2$O$_7$. Calculated fundamental frequencies are in very good agreement with available experimental data. Some reassignments in the vibrational spectra of Cl$_2$O$_7$ are proposed based on our calculations. HClO$_4$ and Cl$_2$O$_7$ are particularly severe examples of the `inner polarization' phenomenon. The polarization consistent basis sets pc-1 and pc-2 (as well as their augmented counterparts) should be supplemented with two (preferably three) and one (preferably two) high-exponent $d$ functions, respectively, on second-row atoms. Complete anharmonic force fields are available as electronic supporting information.Comment: J. Mol. Struct., in press (special issue); Electronic Supporting Information at http://theochem.weizmann.ac.il/web/papers/Cl2O7.htm

Convergence of the critical attractor of dissipative maps: Log-periodic oscillations, fractality and nonextensivity

For a family of logistic-like maps, we investigate the rate of convergence to the critical attractor when an ensemble of initial conditions is uniformly spread over the entire phase space. We found that the phase space volume occupied by the ensemble W(t) depicts a power-law decay with log-periodic oscillations reflecting the multifractal character of the critical attractor. We explore the parametric dependence of the power-law exponent and the amplitude of the log-periodic oscillations with the attractor's fractal dimension governed by the inflexion of the map near its extremal point. Further, we investigate the temporal evolution of W(t) for the circle map whose critical attractor is dense. In this case, we found W(t) to exhibit a rich pattern with a slow logarithmic decay of the lower bounds. These results are discussed in the context of nonextensive Tsallis entropies.Comment: 8 pages and 8 fig

Snacking patterns among Chilean children and adolescents: Is there potential for improvement?

Objective: To examine snacking patterns, food sources and nutrient profiles of snacks in low- and middle-income Chilean children and adolescents. Design: Cross-sectional. Dietary data were collected via 24 h food recalls. We determined the proportion of snackers, snacks per day and energy from top food and beverage groups consumed. We compared the nutrient profile (energy, sodium, total sugars and saturated fat) of snacks v. meals. Setting: South-east region of Chile. Participants: Children and adolescents from two cohorts: the Food Environment Chilean Cohort (n 958, 4-6 years old) and the Growth and Obesity Cohort Study (n 752, 12-14 years old). Results: With a mean of 2·30 (se 0·03) snacks consumed daily, 95·2 % of children and 89·9 % of adolescents reported at least one snacking event. Snacks contributed on average 1506 kJ/d (360 kcal/d) in snacking children and 2218 kJ/d (530 kcal/d) in snacking adolescents (29·0 and 27·4 % daily energy contribution, respectively). Grain-based desserts, salty snacks, other sweets and desserts, dairy foods and cereal-based foods contributed the most energy from snacks in the overall sample. For meals, cereal-based foods, dairy beverages, meat and meat substitutes, oils and fats, and fruits and vegetables were the top energy contributors. Conclusions: Widespread snacking among Chilean youth provides over a quarter of their daily energy and includes foods generally considered high in energy, saturated fat, sodium and/or total sugars. Future research should explore whether snacking behaviours change as the result of Chile's national regulations on food marketing, labelling and school environments

Fermi's golden rule and exponential decay as a RG fixed point

We discuss the decay of unstable states into a quasicontinuum using models of the effective Hamiltonian type. The goal is to show that exponential decay and the golden rule are exact in a suitable scaling limit, and that there is an associated renormalization group (RG) with these properties as a fixed point. The method is inspired by a limit theorem for infinitely divisible distributions in probability theory, where there is a RG with a Cauchy distribution, i.e. a Lorentz line shape, as a fixed point. Our method of solving for the spectrum is well known; it does not involve a perturbation expansion in the interaction, and needs no assumption of a weak interaction. We use random matrices for the interaction, and show that the ensemble fluctuations vanish in the scaling limit. Thus the limit is the same for every model in the ensemble with probability one.Comment: 20 pages, 1 figur

Examining Chile's unique food marketing policy: TV advertising and dietary intake in preschool children, a pre- and post- policy study

Background: The Chilean government implemented the first phase of a comprehensive marketing policy in 2016, restricting child-directed marketing of products high in energy, total sugars, sodium or saturated fat (hereafter “high-in”). Objectives: To examine the role that high-in TV food advertising had in the effect of the policy on consumption of high-in products between 2016 and 2017. Methods: Dietary data were obtained from 24-hour diet recall measured in 2016 (n = 940) and 2017 (n = 853), pre- and post-policy, from a cohort of 4 to 6 years children. Television use was linked to analyses of food advertisements to derive individual-level estimates of exposure to advertising. A multilevel mediation analysis examined direct and indirect effects of the policy through advertising exposure. Results: Children's high-in food consumption and advertising exposure declined significantly from 2016 to 2017 (P <.01). Consumption changes were not significantly mediated by changes in advertising exposure, which might suggest other elements of the Chilean Law potentially driving decreases in consumption to a greater extent than TV ads. Conclusions: Preschoolers' exposure to high-in advertising and consumption of high-in products decreased post-policy. Further research is needed to understand how marketing changes will relate to dietary changes after full implementation of the law and in the long term

TV advertising and dietary intake in adolescents: a pre- and post- study of Chile’s Food Marketing Policy

Background: The first phase of a comprehensive marketing policy was implemented in Chile in 2016. The policy restricted child-directed marketing of foods and beverages considered high in energy, total sugars, sodium or saturated fat (“high-in”). The objective of this study was to examine the role of high-in TV food advertising as a mediator in the association between policy implementation and consumption of high-in foods and beverages between 2016 and 2017. Methods: Dietary data were from 24-hour diet recalls collected in 2016 and 2017 in a cohort of 12–14 y children (n = 721). Television use was assessed concurrently and linked to analyses of food advertisements on broadcast and paid television to derive individual-level estimates of exposure to high-in food advertising. A multilevel mediation analysis examined direct and indirect effects of the policy through advertising exposure. Results: Following the policy implementation, high-in advertising exposure was significantly reduced (p < 0.01). High-in food intake decreased in adolescents with lower levels, but not higher levels, of high-in advertising at baseline. We did not find evidence of mediation by changes in high-in ad exposure. Conclusions: Adolescents’ exposure to high-in TV advertising decreased after the 2016 implementation of the Chilean Food Labeling and Marketing Law. However, evidence that changes in advertisement mediated dietary changes was not found. Further research is needed to understand how marketing changes will relate to dietary changes after full implementation of the law and in the long term

X-ray Diffraction Analysis of γ2 (Sn-Hg) Phase in High Copper Amalgams of Varying Mercury Content

Microstructures of high copper commercial amalgams containing varying amounts of mercury, ranging from 20% above to 25% below recommended values, were primarily investigated by x-ray diffraction. Mechanisms relating to the absence or presence of γ2 (Sn-Hg) phase in these amalgams were discussed in relation to the presence of copper and tin elements in their original alloys. The optimum mercury concentration in some amalgams was determined in order to keep them free of the γ2 (Sn-Hg) phase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66731/2/10.1177_00220345810600021001.pd