Dynamic analysis of multiple cracked Timoshenko beam under moving load–analytical method

When cracks start to surface in the surrounding areas of the structure, they create a local softness zone and influences on the dynamic response of the structure. The beams are more susceptible to shear and flexural cracks because of being subjected to shear and bending stress. In this study, the dynamic response of the single-span and multi-span damped beam under moving load with multi-crack and elastic boundary condition is studied based on Timoshenko’s theory. The Green’s function method is used to calculate the dynamic response of the cracked beam. In addition, the Green’s function method provides a solution for the differential equations. Moreover, the effects of the crack on the essential characteristics of the multi-span beams, especially the natural frequencies, are investigated. In this study, crack by itself is modeled in different situations and its effect on the behavior of the beam is analyzed. Also, the elastically restrained beam is modeled and its effect on the behavior of the beam is assessed. Because of the fact that the Euler–Bernoulli theory is also used in most beams, in this study, the results of the numerical examples are compared with the Euler–Bernoulli theory. Several examples are analyzed for a better understanding of the Timoshenko cracked beam.

Integrating Diphenyl Diselenide and Its Mehg+ Detoxificant Mechanism on a Conceptual DFT Framework

Methylmercury (MeHg+) is an important environmental contaminant and its toxicity is associated with its interaction with selenium (e.g., selenol groups of selenoproteins or HSe−, which is the pivotal metabolite for Se incorporation into selenoproteins). We hypothesized that (PhSe)2 mediated MeHg+ detoxification could be indirectly altered by its open or closed conformation. The two conformations of (PhSe)2 were located on the potential energy surface (PES) computed at ZORA-OPBE-D3(BJ)/ZORA-def2-TZVP level of theory. HPLC analysis indicated that (PhSe)2 did not react with MeHg+, but its reduced intermediate formed a stable complex with MeHg+. The nudged elastic band (NEB) method revealed conformational changes from closed to open state with an H− (2 electrons) transfer from NaBH4, forming a reactant complex-like transition state (TS). The UV-Vis spectrophotometer used in combination with the time-dependent density functional theory (TD-DFT) indicated that the signal of (PhSe)2 at 239 nm was possibly the open conformer’s signal with oscillator strength 0.1 and a π → π * electron transfer character. The experimental band gap energy of (PhSe)2 at 5.20 eV matched to the excitation energy of the open conformation. The local softness (S−) on the selenium atoms almost doubles, as state changes from closed to open. The theoretical results have indicated that the open conformation of (PhSe)2 is likely the one that reacts with NaBH4 to form the PhSeH, which can react with MeHg+.

A QSAR Study on the Persistence of Fungicides in the Environment

The main purpose of this article is to investigate the persistence of fungicides in the environment. QSAR models using four types of reactivity descriptors were constructed to predict the degradation rate constants and examine chemical interactions, to further assess and classify the environmental risks of fungicides. Two major findings emerged. First, the model results show that the degradation in surface water of fungicides is mainly affected by the polarization. The maximum nucleophilic condensed local softness is the most important descriptor. Second, both polarization and chemical potential affect degradation in the soil. The maximum electrophilic condensed local softness is the most important descriptor. The findings not only identified 20 kinds of high ecological risk fungicides, but also showed that phthalimides, sulfamides, and antibiotics are less harmful to the environment because of low persistence and low bioconcentration factors. This approach provides a basis for interpreting chemical interactions between fungicides and environment.

A Local Extension of the Electrophilicity Index Concept

A local measure of the electrophilicity has been recently proposed to analyze the chemical reactivity of several kinds of molecules. In this work a theoretical rationalization of the local extension is proposed following the quantitative definition of the molecular electrophilic power and a variational method for the distribution of the transferred charge. A condensation scheme to atoms or fragments follows from its relation to the Fukui function and the local softness. Differences between these quantities are discussed and they are tested in a model system. The analysis shows that the local electrophilicity is more appropriate to describe differences among a set of substituted molecules.

Revisiting the definition of local hardness and hardness kernel

Local hardness is redefined following similar rules to those of local softness. The new concept describes chemical trends correctly.

Tautomeric transformations and reactivity of isoindole and sila-indole: A computational study

In this work, the tautomeric transformations and reactivity of isoindole and sila-isoindole molecules has been explored using the B3LYP/6-311G(d,p) level of theory in gas and solution phases. These calculations show that isoindole isomer has more stability rather than 1-h-isoindole. There is identical trend in silated species. The frontier molecular orbitals (FMO) and band gap energy calculations were performed at the B3LYP/6-311G(d,p) level in gas and various solvent. Solvent effects have been analyzed by using the self-consistent reaction field (SCRF) method based on polarizable continuum model (PCM) in chloroform, chlorobenzene, dichloromethane and tetrahydrofurane. Thermodynamic parameters calculated at room temperature have been analyzed. Also, electron affinities were computed. Local reactivity descriptors as Fukui functions [Formula: see text] local softness [Formula: see text] and electrophilicity indices [Formula: see text] analyses are performed to find out the reactive sites within molecule. Density functional theory (DFT) calculations were performed to compute nitrogen-14 nuclear quadrupole resonance (NQR) spectroscopy parameters.

Probing the Reactive Center for Site Selective Protonation in a Molecule by the Local Density Functional Descriptors

In this study, the authors have explored the efficacy of the local density functional descriptors like the fukui functions (f), the local softness (s) and the local philicity as probe for the reactive centers and site selectivity of the chemico-physical process of protonation of some molecules having multiple site for protonation, viz CH3NCO (Methyl isocyanate), CH3NCS (methyl isothiocyanate), NH2OH (hydroxyl amine), NH2OCH3 (o-methylhydroxylamine), CH3NHOH (N-methylhydroxylamine), NH2CH2COOH (glycine), CH3CH(NH2)COOH (alanine) and OHCH2CH2NH2 (ethanol amine). The authors have seen in terms of the numerical values of the local descriptors measures the reactivity (nucleophilicity) of a particular atomic site of a donor center towards a proton. In all cases, it can be said that the dynamic chemico-physical process of site selectivity can nicely be correlated in terms of the computed values of the local descriptors. Thus, it is found that the theoretical descriptors of the DFT can be efficiently exploited to study the mechanism of site selectivity in a chemical reaction.