Adatom Defect Induced Spin Polarization of Asymmetric Structures

The spin polarization of carbon nanomaterials is crucial to design spintronic devices. In this paper, the first-principles is used to study the electronic properties of two defect asymmetric structures, Cap-(9, 0)-Def [6, 6] and Cap-(9, 0)-Def [5, 6]. We found that the ground state of Cap-(9, 0)-Def [6, 6] is sextet and the ground state of Cap-(9, 0)-Def [5, 6] is quartet, and the former has a lower energy. In addition, compared with Cap-(9, 0) CNTs, the C adatom on C₃₀ causes spin polarization phenomenon and Cap-(9, 0)-Def [6, 6] has more spin electrons than Cap-(9, 0)-Def [5, 6] structure. Moreover, different adsorb defects reveal different electron accumulation. This finding shows that spin polarization of the asymmetric structure can be adjusted by introducing adatom defects.     

Switch From Pauli-Lowering to LUMO-Lowering Catalysis in Brønsted Acid-Catalyzed Aza-Diels-Alder Reactions

Brønsted acid-catalyzed inverse-electron demand (IED) aza-Diels-Alder reactions between 2-aza-dienes and ethylene were studied using quantum chemical calculations. The computed activation energy systematically decreases as the basic sites of the diene progressively become protonated. Our activation strain and Kohn-Sham molecular orbital analyses traced the origin of this enhanced reactivity to i) “Pauli-lowering catalysis” for mono-protonated 2-aza-dienes due to the induction of an asynchronous, but still concerted, reaction pathway that reduces the Pauli repulsion between the reactants; and ii) “LUMO-lowering catalysis” for multi-protonated 2-aza-dienes due to their highly stabilized LUMO(s) and more concerted synchronous reaction path that facilitates more efficient orbital overlaps in IED interactions. In all, we illustrate how the novel concept of “Pauli-lowering catalysis” can be overruled by the traditional concept of “LUMO-lowering catalysis” when the degree of LUMO stabilization is extreme as in the case of multi-protonated 2-aza-dienes.     

Dual-Metal Electrolytes for Hybrid-Ion Batteries: Synergism or Antagonism?

The construction of hybrid metal-ion batteries faces a plethora of challenges. A critical one is to unveil the solvation/desolvation processes at the molecular level in electrolytes that ensure efficient transfer of several types of charge carriers. This study reports first results on simulations of mixed-ion electrolytes. All combinations of homo- and hetero-binuclear complexes of Li⁺, Na⁺ and Mg²⁺, solvated with varying number of ethylene carbonate (EC) molecules are modeled in non-polar and polar environment by means of first principles calculations and compared to the mononuclear analogues in terms of stability, spatial organization, charge distribution and solvation/desolvation behavior. The used PF₆⁻ counterion is shown to have minor impact on the geometry of the complexes. The desolvation energy penalty of binuclear complexes can be lowered by the fluoride ions, emerging upon the PF₆⁻ decay. These model investigations could be extended to rationalize the solvation structure and ionic mobility in dual-ion electrolytes.     

Recent Progress in the Simulation of Chiral Systems with Real Time Propagation Methods

In this brief review, an overview about recent efforts to simulate the spectroscopic signatures of chiral molecules is given with focus on real time propagation approaches to solve the time-dependent Schrödinger equation. In particular the simulation of electric circular dichroism spectra and vibrational Raman optical activity is discussed. In comparison to linear absorption spectra, where only the response of the electric dipole moment is necessary, the response of the magnetic dipole moment and electric quadrupole moment is more intricate. Issues such as gauge origin dependence, basis set dependence, non-local potentials and the dipole approximation are addressed.     

Effect of relative humidity on current–voltage characteristics of monopolar DC wire-to-plane system

This paper deals with the DC monopolar corona discharge in wire-to-plane geometry under variable humid air conditions. The classical formulas of Townsend commonly used for the current–voltage characteristics were used to determine the various corona parameters for the both polarities of the corona discharge. A circular biased probe has been adapted to the plane and is used to measure the ground plane current density and electric field during the monopolar corona discharge. A new approach to the problem of corona discharge in transmission system has been described in this paper. The effect of varying the humidity and wires diameter is also investigated. The values of the electric field and the current density are maximum beneath the corona wire and decrease when moving away from them and the current–voltage characteristics follow the quadratic Townsend's law. The experimental results show that the monopolar corona discharge is strongly affected by the air humidity. The current density and the electric field are measured and compared with the computed values. The agreement between the calculated values and those obtained experimentally is satisfactory. The per unit electric field and current density are also represented by a unique function.     

Dual-modality and dual-energy gamma ray densitometry of petroleum products using an artificial neural network

The prediction of volume fractions in order to measure the multiphase flow rate is a very important issue and is the key parameter of multi-phase flow meters (MPFMs). Currently, the gamma ray attenuation technique is known as one of the most precise methods for obtaining volume fractions. The gamma ray attenuation technique is based on the mass attenuation coefficient, which is sensitive to density changes; density is sensitive in turn to temperature and pressure fluctuations. Therefore, MPFM efficiency depends strongly on environmental conditions. The conventional solution to this problem is the periodical recalibration of MPFMs, which is a demanding task. In this study, a method based on dual-modality densitometry and artificial intelligence (AI) is presented, which offers the advantage of the measurement of the oil–gas–water volume fractions independent of density changes. For this purpose, several experiments were carried out and used to validate simulated dual modality densitometry results. The reference density point was established at a temperature of 20 °C and pressure of 1 bar. To cover the full range of likely density fluctuations, four additional density sets were defined (at changes of ±4% and ±8% from the reference point). An annular regime with different percentages of oil, gas and water at different densities was simulated. Four features were extracted from the transmission and scattered detectors and were applied to the artificial neural network (ANN) as inputs. The input parameters included the ²⁴¹Am full energy peak, ¹³⁷Cs Compton edge, ¹³⁷Cs full energy peak and total scattered count, and the outputs were the oil and air percentages. A multi-layer perceptron (MLP) neural network was used to predict the volume fraction independent of the oil and water density changes. The obtained results show that the proposed ANN model achieved good agreement with the real data, with an estimated root mean square error (RMSE) of less than 3.     

Shape memory behavior in Fe3Al-modeling and experiments

The Fe₃Al alloy with D0₃ structure exhibits large recoverable strains due to reversible slips. Tension and compression experiments were conducted on single crystals of Fe₃Al, and the onset of slip in forward and reverse directions were obtained utilizing high-resolution digital image correlation technique. The back stress provides the driving force for reversal of deformation upon unloading, resulting in a superelastic phenomenon as in shape memory alloys. Using density functional theory simulations, we obtain the energy barriers (GSFE – generalized stacking fault energy) for {1?1?0}〈1?1?1〉 and {1?1?2}〈1?1?1〉 slips in D0₃ Fe₃Al and the elastic moduli tensor, and undertake anisotropic continuum calculations to obtain the back stress and the frictional stress responsible for reversible slip. We compare the theoretically obtained slip stress magnitudes (friction and back stress) with the experimental measurements disclosing excellent agreement.     

A Multifunctional Photoswitch: 6π Electrocyclization versus ESIPT and Metalation

A terthiazole‐based molecular switch associating 6π electrocyclization, excited state intramolecular proton transfer (ESIPT), and strong metal binding capability was prepared. The photochemical and photophysical properties of this molecule and of the corresponding nickel and copper complexes were thoroughly investigated by steady‐state and ultrafast absorption spectroscopy and rationalized by DFT/TDDFT calculations. The switch behaves as a biphotochrome with time‐dependent photochemical outcome and displays efficient ESIPT‐based fluorescence photoswitching. Both photochemical reactions are suppressed by nickel or copper metalation, and the main factors contributing to the quenching of the electrocyclization are discussed.     

Synthesis of Soluble,Alkyne‐Substituted Trideca‐ and Hexadeca‐Starphenes

Two literature‐known TIPS‐ethynyl‐dibromoacenes were prepared and employed to synthesize cyclotrimers by using Yamamoto coupling conditions. Two large, well‐soluble starphenes were isolated in good yields. Crystallographic characterization verifies the triangular shape and shows significant differences in crystal packing.     

Formation of “Quasi” Contact or Solvent‐separated Ion Pairs in the Local Environment of Probe Molecules Dissolved in Ionic Liquids

The change from “quasi” contact to “quasi” solvent‐separated ion‐pair configuration in the local environment of a probe molecule in ionic liquids depends on the varying interaction strength of the chosen anions. The ion speciation in these Coulomb fluids could be shown by combining infrared spectroscopy, density functional theory calculations, and natural bond orbital analysis using a low‐self‐clustering probe molecule.