Self-similar vortex reconnection

As shown by Crow in 1970, the evolution of two almost parallel vortex filaments with opposite circulation exhibits a long-wave instability. Ultimately, the symmetric mode increases its amplitude reconnecting both filaments and ending into the formation of an almost periodic structure of vortex rings. This is a universal process, which appears in a wide range of scales: from the vortex trails behind an airplane to a microscopic scale of superfluids and Bose–Einstein condensates. In this paper, I will focus on the vortex reconnection for the latter case by employing Gross–Pitaevskii theory. Essentially, I focus on the well-known laws of interaction and motion of vortex filaments. By means of numerical simulations, as well as theoretically, I show that a self-similar finite-time dynamics manifests near the reconnection time. A self-similar profile is selected showing excellent agreement with numerical simulations.     

Soil δ15N patterns in old-growth forests of southern Chile as integrator for N-cycling

Old-growth forests of southern Chile represent an important reserve of temperate (rain) forests in the world. Wetter and colder forest ecosystems appear to be more efficient in conserving and recycling N such that mostly non-plant available N species are lost, which could be indicated by more depleted δ¹⁵N values of the soil and plants. Hydrological N loss from the old-growth forests in southern Chile occurs mainly via dissolved organic nitrogen and not via dissolved inorganic N. Forest disturbances (e.g. fire, clear-cutting or enhanced N deposition) cause (abrupt) changes in ecosystem N-cycling processes. In this study, we hypothesized that δ¹⁵N signatures of soil profiles under old-growth forests could be used as an integrator for ecosystem N-cycling, and changes of these δ¹⁵N profiles could be valuable to assess ecosystem resilience towards disturbances. Six old-growth forests were selected in the phytogeographical region of the Valdivian rain forest in southern Chile. One of the sites has been partly burned in February 2002. First, we observed that ecosystems with higher mean annual precipitation and lower mean annual temperature were relatively more depleted in ¹⁵N. Secondly, we found that a forest fire caused a 100-fold increase of the nitrate export and induced an enrichment of the soil δ¹⁵N signal in the upper 20 cm.     

A rapid approach for assessment of arsenic exposure by elemental analysis of single strand of hair using laser ablation-inductively coupled plasma-mass spectrometry

Application of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) as a method for identification of arsenic in a single hair strand was investigated. Using a single point ablation method detectability of ⁷⁵As and other two elements (²⁰⁸Pb and ⁶⁴Zn) were evaluated. Arsenic (⁷⁵As) signal is improved with enhanced laser ablation conditions. For the arsenic determination in hair single spots or single linear scans with enhanced laser ablation conditions described in the paper are satisfactory although  800 μm linear scans may be preferable. Arsenic levels in a single strand of hair from individuals who were chronically exposed to arsenic contaminated drinking water from a village in the Atacama Desert in northern Chile were determined by LA-ICP-MS. These results were satisfactorily correlated with total As concentration previously measured by hydride generation (HG)-ICP-MS. The sample throughput is high and it takes  3 min per each hair sample including mounting, focusing and analysis. LA-ICP-MS method can be used for the rapid identification and screening of toxic and nutritionally important elements in hair.     

Symmetry analysis of periodicity and internal torsional conformers around a single bond

A simple formula to predict the number of equivalent conformations upon internal rotation around a single bond is derived. If the separate parts A and B, of a single bonded molecule A-B, possess N_a and N_b symmetry planes that contain the single bond, the number of symmetrical conformations is found to be Z = N_aN_b/J, where J is the number of these planes which are common. The energy potential for internal rotation then has a period of 2π/Z. Unsymmetrical conformations are infinite in number, but are shown to occur in infinite sets, each set with 2N_aN_b/J equivalent conformations. Extension to three-center molecules is also made.     

Fractional sublimation of the β-diketone chelates of the lanthanide and related elements

Various β-diketone chelates of Sc(III), Y(III), Th(IV), U(IV). U(VI), Zr(IV) and the lanthanides have been prepared, characterized and investigated to determine if they were volatile and stable. The ligands employed were acetylacetone(AA), trifluoroacetylacetone(TFAA), hexafluoroacetylacetone(HFAA), and dipivaloyl-methane(DPM). The chelates were sublimed in a fractional vacuum sublimator and the recrystallization temperature zones recorded for individual chelates. None of the lanthanide acetylacetonates arc volatile but the Sc(III), Th(IV), U(IV) and dioxouranium(VI) acetylacetonates are thermally stable and quite volatile below 150° at 1 mm mercury pressure. The lanthanide, Sc(III), Y(III), and dioxouranium(VI) trifluoroacetylacetonates are volatile and can be vacuum-sublimed below 150°, but are thermally unstable; only the Th(IV) chelate is sufficiently stable to be quantitatively recovered by sublimation. The Sc(III), Y(III), Th(IV), and lanthanide hexafluoroacetylacetonates are thermally stable and easily sublimed below 125° in vacua or at atmospheric pressure. All the dipivaloylmethanates studied were thermally stable and volatile and could be quantitatively recovered by vacuum sublimation below 140°.The volatility of the HFAA and DPM lanthanide chelates increased with an increase in atomic weight (a decrease in ionic radii) of the lanthanides. The lack of volatility observed for the lanthanide AA and TFAA chelates is attributed to the fact that only hydrates of the chelates were formed, which decomposed at elevated temperatures in vacuo to form basic polymeric compounds.Separations are proposed for numerous binary mixtures of the β-diketone chelates of the lanthanide and related elements. Recrystallization temperature zones are given for the following binary mixtures which were quantitatively resolved by the fractional sublimation technique; 118-88° for Nd(DPM)₃ and 84-48° for Tm(DPM)₃; 72-49° for Sc(DPM) and 120-88° for Pr(DPM); 128-79° for La(DPM)₃ and 79-47° for Yb(DPM)₃; 70-47° for Th(TFAA)₄ and 116-96° for Gd(TFAA)₃; 52-42° for Th(HFAA)₄ and 120-80° for La(HFAA)₃.