Isotope effects on resonance cross sections in predissociation/preassociation

Isotope effects on the resonance cross sections of preassociative scattering are explicitly studied for the O₂, OH and OD systems, based on a semiclassical theory similar to Stückelberg's theory of inelastic scattering. It is found that there are significant isotopic differentiations for the systems studied, which may be exploited in the laboratory for selective photodissociations of the molecules.     

Dielectric dispersion in KCl: OH

Dielectric measurements at 9.4 GHz in KCl doped with a concentration of 0.2 at. % OH are reported. The dielectric constant exhibits a relaxational anomaly at temperatures far above that observed in the kilohertz frequency range for the same OH concentration. The results indicate that electric dipole freezing in KCl:OH is governed by a relaxational mechanism.     

Theoretical investigation of clusters of phosphorus and arsenic: fascination and temptation of high symmetries

We present a theoretical study of the energetic and thermodynamic stability of selected phosphorus and arsenic clusters containing 18 to 168 atoms. For this purpose we employ MP2 as well as DFT functionals BP86 and B3LYP with extended basis sets. All procedures predict the family of one-dimensional polymers X18+12n, each with 2n-1 isomers of virtually identical energy, to be more stable than other structures investigated so far. Furthermore, islands of stability result for ring-shaped clusters X24n with Dnd symmetry for n=4 (only for arsenic), 5, 6, and 7. Phosphorus and arsenic show otherwise a very similar behavior. An investigation of basis set effects shows that a doubly polarized triple zeta valence basis (TZVPP) is both necessary and sufficient. In comparison to the reliable spin component scaled MP2 (SCS-MP2) procedure, DFT methods underestimate and MP2 overestimates the stability of larger clusters; the discrepancy increases with the number of atoms. The addition of a long-range dispersion correction to B3LYP energies does not rectify the shortcomings of DFT in comparison with SCS-MP2.     

Time-dependent scaling patterns in high frequency financial data

We measure the influence of different time-scales on the intraday dynamics of financial markets. This is obtained by decomposing financial time series into simple oscillations associated with distinct time-scales. We propose two new time-varying measures of complexity: 1) an amplitude scaling exponent and 2) an entropy-like measure. We apply these measures to intraday, 30-second sampled prices of various stock market indices. Our results reveal intraday trends where different time-horizons contribute with variable relative amplitudes over the course of the trading day. Our findings indicate that the time series we analysed have a non-stationary multifractal nature with predominantly persistent behaviour at the middle of the trading session and anti-persistent behaviour at the opening and at the closing of the session. We demonstrate that these patterns are statistically significant, robust, reproducible and characteristic of each stock market. We argue that any modelling, analytics or trading strategy must take into account these non-stationary intraday scaling patterns.     

A Bibliometric Evaluation of the Top 100 Cited Dimethyl Fumarate Articles

Dimethyl fumarate is a cytoprotective and immunomodulatory drug used in the treatment of multiple sclerosis. We performed a bibliometric study examining the characteristics and trends of the top 100 cited articles that include dimethyl fumarate in the title. On 21 September 2020 we carried out an electronic search in the Web of Science (WOS), seeking articles that include the following terms within the title: dimethyl fumarate, BG-12, or Tecfidera. To focus our investigation on original research, we refined the search to include only articles, early access, others, case report, and clinical trials. We obtained a total of 1115 items, which were cited 7169 times, had a citation density of 6.43 citations/item, and an h-index of 40. Around 2010, there was a jump in the number of published articles per year, rising from 5 articles/year up to 12 articles/year. We sorted all the items by the number of citations and selected the top 100 most cited (T100). The T100 had 4164 citations, with a density of 37 citations/year and contained 16 classic research articles. They were published between 1961 and 2018; the years 2010–2018 amassed nearly 80% of the T100. We noted 17 research areas with articles in the T100. Of these, the number one ranking went to neurosciences/neurology with 39 articles, and chemistry ranked second on the T100 list with 14 items. We noticed that the percentage of articles belonging to different journals changed depending on the time period. Chemistry held the highest number of papers during 1961–2000, while pharmacology andneurosciences/neurology led the 2001–2018 interval. A total of 478 authors from 145 institutions and 25 countries were included in the T100 ranking. The paper by Gold R et al. was the most successful with 14 articles, 1.823 citations and a density of 140.23 citations/year. The biotechnological company Biogen led the T100 list with 20 articles. With 59 published articles, the USA was the leading country in publications. We concluded that this study analyzed the use of and research on dimethyl fumarate from a different perspective, which will allow the readership (expert or not) to understand the relevance of classic and recent literature on this topic.     

Experimental and Theoretical Studies on the Magnetic Anisotropy in Lanthanide(III)‐Centered Fe3Ln Propellers

Compounds [Fe₃Ln(tea)₂(dpm)₆] ( Fe₃Ln ; Ln= Tb–Yb, H₃tea=triethanolamine, Hdpm=dipivaloylmethane) were synthesized as lanthanide(III)‐centered variants of tetrairon(III) single‐molecule magnets (Fe₄) and isolated in crystalline form. Compounds with Ln=Tb–Tm are isomorphous and show crystallographic threefold symmetry. The coordination environment of the rare earth, given by two tea^3? ligands, can be described as a bicapped distorted trigonal prism with D₃ symmetry. Magnetic measurements showed the presence of weak ferromagnetic Fe ??? Ln interactions for derivatives with Tb, Dy, Ho, and Er, and of weak antiferromagnetic or negligible coupling in complexes with Tm and Yb. Alternating current susceptibility measurements showed simple paramagnetic behavior down to 1.8 K and for frequencies reaching 10000 Hz, despite the easy‐axis magnetic anisotropy found in Fe₃Dy , Fe₃Er , and Fe₃Tm by single‐crystal angle‐resolved magnetometry. Relativistic quantum chemistry calculations were performed on Fe₃Ln (Ln=Tb–Tm): the ground J multiplet of Ln³⁺ ion is split by the crystal field to give a ground singlet state for Tb and Tm, and a doublet for Dy, Ho, and Er with a large admixture of m_J states. Gyromagnetic factors result in no predominance of g_z component along the threefold axis, with comparable g_x and g_y values in all compounds. It follows that the environment provided by the tea^3? ligands, though uniaxial, is unsuitable to promote slow magnetic relaxation in Fe₃Ln species.     

Pseudopotential-fragment spectroscopy for organic molecules and carbon allotropes

Following on from a previous work (Punter et al., IJQC 2019, 119, 23), pseudopotential sets are developed and tested for a variety of sp² and sp³ carbon fragments. These fragments contain only one or two explicit protons and electrons, and make use of non-atom-centered potentials. They are tested with density functional theory calculations in a selection of chemical environments in which several physical characteristics, including orbital and first ionization energies, are found to be well reproduced. They are then employed in the reproduction of molecular absorption spectra for large organic molecules and carbon allotropes, and are found to recreate both absorption and electronic circular dichroism spectra to a high accuracy. They are also found significantly to increase the computational efficiency of time dependent density functional theory (TDDFT) calculations in which they are used.