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.     

Deconvolution in microcalorimetry and an application to mass-varying systems

The behaviour of the calorimetric response in continuous injection devices, which are well suited for measurement of excess partial molar enthalpies at different concentrations, is analysed by means of heat transport models. Signal analysis of the thermal response gives the enthalpy values at very low concentrations. We establish an operating routine for the identification of the time-varying device, and a generalized deconvolution procedure to obtain, with high accuracy, the power released in the calorimeter as a function of time. The main features considered are the changes in sensitivity and dynamic properties of the experimental system due to the injection of one component in the mixture. A formal decomposition of the heat transport equations shows that typically time-invariant methods are able to deal with deconvolution in non-invariant systems.     

13C NMR Chemical shifts in bicyclo[2.2.2]octanes—iii: Hydroxy acids and lactones

A number of hydroxybicyclo[2.2.2]octane carboxylic acids and the corresponding delta lactones have been prepared, and the ¹³C NMR spectra show trends that, together with some deuteration experiments, provide a self consistent and unambiguous assignment of the resonance peaks. The effects produced by the substituents and the changes in chemical shifts brought about by the lactonization process are analysed.     

The Physical Tourist

I provide a tour of Madrid, focusing especially on physical institutions that were created during the 19th and 20th centuries.These include the Astronomical Observatory close to the Prado Museum, which itself was conceived as a home for the Royal Academy of Sciences but became instead a world-famous art museum in 1819, leaving the Royal Academy of Sciences without a permanent home until 1866.The Laboratory of Physical Researches was created in 1910, and under the direction of Blas Cabrera (1878–1945), who also held a professorship at the Universidad Central, it fostered most of the Spanish research in physics at the time, in particular the famous spectroscopic researches of Miguel A. Catalán (1894–1957). Nearby were the so-called Transatlantico building and the Students’ Residence where Albert Einstein (1879–1955), for example, lectured in 1923, and which together continue to serve as a major cultural center in Madrid. Later, the physical laboratory was replaced by the National Institute of Physics and Chemistry, which was constructed with funds from the Rockefeller Foundation and inaugurated in 1932. A new University City with its Faculty of Sciences also was constructed on the northwestern outskirts of Madrid, but almost all of its buildings were totally destroyed during the devastating Spanish Civil War of 1936–1939. It was reconstructed after the war and became home, for example, to Spain’s first nuclear reactor, which achieved criticality in 1958.     

Synthesis of two complexes of cadmium(II) iodide with benzenecarbothioamide (BCTA): Crystal and molecular structure of [Cd(BCTA)2I2]

The reaction between CdI₂ and benzenecarbothioamide (BCTA) in ethanol produces crystalline [Cd(BCTA)₂I₂] but in 1,2-dichloroethane it yields [Cd(BCTA)I₂] in powder form. [Cd(BCTA)₂I₂] has been characterized by X-ray crystallography, and both complexes have also been identified by infrared spectra in the solid phase, ¹H NMR, and electrical conductivity studies in solution. The crystals of [Cd(BCTA)₂I₂] are monoclinic, space group P2₁/c, with a = 747.6(1) pm, b = 1958.7(13) pm, c = 1363.6(6) pm, β = 110.307(3)° and Z = 4. Least-squares refinement of the structure based on 4260 observations led to final discrepancy indices of R = 0.043 and R_w = 0.054. The geometry around the cadmium atom is slightly distorted from the tetrahedral. The BCTA is coordinated through the sulphur atom: CdI(1) = 277.2(1) pm, CdI(2) = 272.6(1) pm, CdS(1) = 256.7(3) pm, CdS(2) = 257.5(2) pm. The electrical conductivity studies and NMR and IR spectra are consistent with the structure found for [Cd(BCTA)₂I₂] and suggest a dimeric trans symmetric tetrahedral structure with halogen bridging (C_2h) for [Cd(BCTA)I₂].     

A multi-element serum standard for neutron activation analysis

An annular ²²⁷AcBe isotopic neutron source, containing 6.6-Ci ²²⁷Ac, is described for application in fast and thermal neutron activation analysis, with high accuracy, for major constituents in ores, alloys and industrial concentrates. The characteristics of the neutron output and of the fast, epithermal and thermal flux and flux gradients is described in detail. The determination of manganese in pyrolusite ores and ferro-manganese is compared to results obtained previously with a cylindrical 1-Ci ²²⁶RaBe source. Two new sources of systematic errors have been discovered.     

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.