Decade fluctuations in the Earth's rate of rotation and long-term librations in polar motion

Summary An investigation into long series of astronomical latitude and time observations is presented in order to analyse their long-term variations. Decade fluctuations in the Earth's rate of rotation and long-term librations in polar motion (secular drift and Markowitz wobble) are discussed. Available data show a good correlation between observed rotational acceleration of the Earth and the motion of the mean pole over periods of about thirty years.     

布朗单极集的性质

本文研究了布朗单极集的性质，得到了布朗单极性的充分条件与必要条件。     

Sunrise and range distribution of meteors

Summary The influence of the sunrise effect on the ionization of the meteor zone has been found from the comparison of meteor echo range distributions obtained by the meteor radars at Springhill (120 000 echoes) and Budrio (7000 echoes) during the activity of the Geminids meteor shower. The position of the maximum of the echo range distribution corresponding to the motion of the shower radiant was found to be shifted to larger distances, as expected from the sunrise effect, independently of different antenna systems of the two equipments.     

反射扩散过程的极集

本文利用Ｄｉｒｉｃｈｌｅｔ型中有产在容度的结论，从几何的观点刻画了反射扩散过程的极集。     

A Review of Potential Use of Amazonian Oils in the Synthesis of Organogels for Cosmetic Application

New strategies for the delivery of bioactives in the deeper layers of the skin have been studied in recent years, using mainly natural ingredients. Among the strategies are organogels as a promising tool to load bioactives with different physicochemical characteristics, using vegetable oils. Studies have shown satisfactory skin permeation, good physicochemical stability mainly due to its three-dimensional structure, and controlled release using vegetable oils and low-molecular-weight organogelators. Within the universe of natural ingredients, vegetable oils, especially those from the Amazon, have a series of benefits and characteristics that make them unique compared to conventional oils. Several studies have shown that the use of Amazonian oils brings a series of benefits to the skin, among which are an emollient, moisturizing, and nourishing effect. This work shows a compilation of the main Amazonian oils and their nutraceutical and physicochemical characteristics together with the minority polar components, related to health benefits, and their possible effects on the synthesis of organogels for cosmetic purposes.     

Comparison of mechanistic models for correlation of activation energies of liquid‐phase addition of carbon‐centered radicals to terminal olefins

The performance of different models for the influence of enthalpy and polar effects on radical additions is compared for the extensive data set from the Fischer group, supplemented by additional data. The best correlations result from the Fischer–Radom (FR) model, but it also contains the largest number of adjustable radical‐dependent parameters not based on physical observables. Updating the literature values of , IP, and EA that are inputs to the FR model led to some deterioration in the quality of the correlations; this is symptomatic of remaining deficiencies in the thermochemical databases. In contrast, the Lalevee–Allonas–Fouassier (LAF) model gives poorer correlation but this is in part compensated because it uses the same inputs but with no adjustable parameters. Hammett‐type models based on polar and radical substituent constants rather than on molecular properties of the reactants perform even more poorly. In all cases, poorer correlation, as judged by increasing sd(ΔE), is accompanied by a systematic bias to over‐predict the lower E values and under‐predict the higher ones. The enthalpy contribution in the FR and LAF models is expressed as a linear Evans–Polanyi dependence of E on ΔH. Replacement by nonlinear Marcus dependences does not significantly improve performance. An attempt to significantly reduce the number of adjustable parameters in the FR model by anchoring them to a base set applicable to all radicals, which is then modulated for spin delocalization based on observable ESR hyperfine constants in the initial and adduct radicals, showed modest success. Copyright © 2008 John Wiley & Sons, Ltd.     

Polar structure of N,N′-dimethylurea crystals

In the crystal structure of N,N′-dimethylurea, there is one molecule in the asymmetric unit, but with two halves related by an axis of pseudosymmetry. All nonhydrogen atoms of each molecule lie on a plane. In the crystal the molecules are held together by hydrogen bonds in the direction of the “a” axis. They form parallel rows with the same sense orientation, so that the crystal has a polar structure.     

Solution of Hadwiger-Levi's Covering Problem for Duals of Cyclic 2k-Polytopes

For a collection C of convex bodies let h(C) be the minimum number m with the property that every element K of C can be covered by m or fewer smaller homothetic copies of K. Denote by C _d ^* the collection of all duals of cyclic d-polytopes, d 2. We show that h(C _2k ^* )=(k +1)2 for any k 2. We also prove the inequalities (d+1) (d+3)/4 h(C _d ^* ) (d+1) 2/2$ for any d 2.