Search

G-quartets are supra-molecular structures that consist of four guanine molecules connected by eight hydrogen bonds. They are additionally stabilized by metal cations. In this contribution, the excited states of G-quartet and its complexes with lithium, sodium and potassium were studied by employing time-dependent density functional theory. The findings indicate that vertical excitations from the optimized ground state involve transitions from several bases, whereas excitations from the optimized lowest excited state include transitions from one base. The charge-transfer character of these states was analyzed. It was shown that the cations are able to modify positions of the maxima of the fluorescence spectra of the complexes. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 451-03-68/2020-14/200146]

Hydrogen transfer from hydroquinone to the methoxy radical was studied using the density functional theory. The energy decomposition technique, interacting quantum atoms, was employed for a detailed investigation of the changes that the bonds of interest go through along the minimum energy path in the vicinity of the transition state. The whole system was divided either into two or three fragments. The two-fragment analysis enabled investigation of the bond that is formed or the one that is cleaved by defining the fragments as reactants and as products, respectively. The three-fragment analysis (the fragments being semiquinone, hydrogen atom and methoxy radical) was used for the simultaneous analysis of the two phenomena, bond cleavage and bond formation. Additionally, it enabled the interaction between the particle that donates the hydrogen atom and the one that accepts it to be investigated. This interaction is characterized by attractive non-classical and repulsive classical interactions. It was demonstrated that the transferring hydrogen atom undergoes the most pronounced energy changes and gives the largest contribution to the deformation energy. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172040]

Metal ion detection rests on host–guest recognition. We propose a theoretical protocol for designing an optimal trap for a desired metal cation. A host for magnesium ions was sought for among derivatives of crown ethers 12-crown-4, 15-crown-5, and 18-crown-6. Mg–crown complexes and their hydrated counterparts with water molecules bound to the cation were optimized using density functional theory. Based on specific geometric criteria, Interacting quantum atoms analysis and density functional theory-based molecular dynamics of Mg–crown complexes immersed in water, crown ethers for optimal accommodation of Mg2+ in aqueous solution were identified. Selectivity of the chosen crowns towards Na+, K+, and Ca2+ ions is addressed. [ABSTRACT FROM AUTHOR]

Condition monitoring has aroused a considerable interest in modern control theory and practice. Nowadays, it is widely used to monitor industrial machinery in order to facilitate predicting failures, enhance schedule maintenance and reduce the probability of downtime in process industry plants, thus saving time and money. In this paper, we will present the basics of condition monitoring based on vibration acquisition, along with an example of such a system implemented in a thermal power plant.

In this paper, a new method for fault detection and isolation of induction motor is proposed, which uses Potential Based Recursive Clustering Algorithm (PBRC). The detection of faults is achieved by analyzing vibration signal, using the adaptive PBRC algorithm for grouping and classification data for identification of the fault or unwanted operating mode of the induction motor. This method allows the detection broken rotor bars, which represents the majority of failures that occur during exploitation.

Introduction. Identification of predictive factors for walking ability with a prosthesis, after lower limb amputation, is very important in order to define patient’s potentials and realistic rehabilitation goals, however challenging they are. Objective. The objective of this study was to investigate whether variables determined at the beginning of rehabilitation process are able to predict walking ability at the end of the treatment using support vector machines (SVMs). Methods. This research was designed as a retrospective clinical case series. The outcome was defined as three-leveled ambulation ability. SVMs were used for predicting model forming. Results. The study included 263 patients, average age 60.82 Ѓ} 9.27 years. In creating SVM models, eleven variables were included: age, gender, cause of amputation, amputation level, period from amputation to prosthetic rehabilitation, Functional Comorbidity Index (FCI), presence of diabetes, presence of a partner, restriction concerning hip or knee extension, residual limb hip extensor strength, and mobility at admission. Six SVM models were created with four, five, six, eight, 10, and 11 variables, respectively. Genetic algorithm was used as an optimization procedure in order to select the best variables for predicting the level of walking ability. The accuracy of these models ranged from 72.5% to 82.5%. Conclusion. By using SVM model with four variables (age, FCI, level of amputation, and mobility at admission) we are able to predict the level of ambulation with a prosthesis in lower limb amputees with high accuracy.

Avobenzone (4-tert-butyl-4’-methoxydibenzoylmethane) is one of the most widely used UVA filters in cosmetic sunscreens. Reactivity of avobenzone is complex and challenging to understand, due to a presence of transient tautomers. In this contribution we study chelated enol, rotamer and keto tautomers of a reduced model of avobenzone which are involved in keto-enol tautomerization. Two thermal tautomerization mechanisms are postulated and their transient structures are discussed. The computed vertical and adiabatic electronic excitation energies of tautomers provide an additional insight into excited state properties of the tautomers. [Projekat Ministarstva nauke Republike Srbije, br. 172040 i br. ON171017]

Expert systems are very suitable for fault detection because they are easy to develop, have capability to reason under uncertainty and the capability to deliver explanations for the solutions provided. In this paper, expert system in domain of energy efficiency and failure detection in process industry is proposed. To design this specific expert system a few different strategies were applied. These strategies were combined in this single unique expert system. The system is tested in one of the subsystems of Victoria Oil plant in Šid, Serbia. Using expert system method for failure detection is shown to be very reliable, fast and robust.

High contact ratio (HCR) gearing is a special kind of the basic involute profile gearing with higher contact ratio, since there are always at least two pairs of teeth in contact. Compared to standard gearings, HCR gearings have greater load capacity, higher resistance and a lower relative noise level. Their main drawbacks are more complicated design than standard involute profiles, greater predisposition for interference, pointed tip thickness and undercut of teeth during production. There is also a larger possibility of some interference or pointed tooth tip occurring. All these issues represent serious design constraints which need to be resolved in the design phase. In this paper, a new method for HCR gearing design is proposed, which uses Generalized Particle Swarm Optimization Algorithm (GPSO) for gearing parameters optimization. This recently introduced global optimization method enables finding of global optimal solution(s), ensuring that all relevant design and function constraints are satisfied.

Stabilization of G-quadruplexes formed in the promoter regions of oncogenes with small molecules is recognized as a convenient method to control oncogenes' overexpression in cancer cells. Due to a huge number of potential G-quadruplex structures in DNA, the success of this method is critically dependent on ligand–quadruplex selectivity. Although external π–π stacking of the ligand to the top G-quartet was extensively exploited in the design of new ligands with aromatic cores, it is believed that symmetric porphyrin derivatives are not capable of specifically interacting with flanking nucleotides. Here, we show that TPyP4, an analogue of TMPyP4, exhibits more pronounced selectivity toward the overhang. To this end, we examined the binding of TMPyP4, TPyP4, TPyAP4, TBP, and TMABP4 to the c-MYC promoter Pu24I G-quadruplex via density functional theory calculations and molecular dynamics based on the classical force field. The ranking of ligand binding energies in the end-stacking binding mode, TMABP4 > TMPyP4 ≈ TPyAP4 > TPyP4≈ TBP, was mainly governed by van der Waals interactions in the binding pocket. TPyP4 was also found to intercalate between the A3 and G2 bases of the overhang and simultaneously stack on two guanine bases of the top G-quartet. The binding affinity for intercalation was stronger than for end-stacking. We propose that the metalation of TPyP4 with a cation whose favored coordination geometry is octahedral might stabilize intercalation over an end-stacking binding mode to a greater extent. [ABSTRACT FROM AUTHOR]

This paper presents the application of some well-known global optimization techniques in optimization of an expert system controlling a ship locking process. Optimization was conducted in order to achieve better results in local distribution of ship arrivals, i.e. lower waiting times for ships and less empty lockages. Particle swarm optimization, artificial bee colony optimization and genetic algorithm were used. The results shown in this paper confirmed that all these procedures show similar results and provide overall improvement of ship lock operation performance, which speaks in favor of their application in similar transportation problem optimization.

In this paper, a case study is presented which demonstrates the efficiency of vibration analysis in induction motor rotor fault detection and diagnosis. Vibration signals of a 3,15 MW induction motor were acquired. The observed motor is specific due to its very low slip, which can cause some difficulties in fault diagnostic process. Employing some of well-known signal processing and analysis techniques, characteristic features in frequency domain were observed. Using the previous experience in fault detection and diagnosis, it is determined that a rotor fault, a broken bar in specific, is present in the motor. Based on this analysis, a general repair of the motor was carried out and the diagnosed fault was confirmed. This way, applying the fault detection and diagnosis in early fault stage, some serious malfunctions and failures were avoided, which resulted in decreased repair costs and undisturbed delivery of heat energy during the heating season.

We performed a theoretical analysis of the structure and vibrational properties of cyclobutane pyrimidine dimer, which is the main product in a photochemical reaction involving two molecules of 1-methylthymine. Thymine is a pyrimidine base that has the highest yield of the dimerization photoproducts. Methylation in position one was chosen because in this position thymine is linked to sugar in DNA. The calculations were performed at the B3LYP/cc-pVTZ level with a Gaussian program package. All molecular geometries were optimized without symmetry constraints in vacuum and D2O. Vibrational frequencies were calculated in the harmonic approximation. It was shown that there are two stable isomers, CPD(cis-syn) and CPD(trans-syn). CPD(trans-syn) is more stable both in vacuum and in D2O. By dissolving these molecules in D2O, both structures become more stable, although the stabilization of the less stable isomer is more pronounced due to its larger dipole moment. Thus, the difference in stability of the two isomers in D2O is almost two times lower than in vacuum. Because of the similarity of the two isomers’ structures, the difference in their vibrational spectra is not pronounced. Within the harmonic approximation, there is only a slight difference in the C=O and C-H stretching region. The difference in the N-H stretching region is more pronounced; in the CPD(cis-syn) molecule the two bonds vibrate separately, whereas in the CPD(trans-syn) the two modes couple, and this coupling results in symmetric and asymmetric N-H stretching. The observation shows that a slight difference in geometry can be reflected in the shape of the infrared spectra. A more detailed analysis of the vibrational properties would involve computation of anharmonic coupling terms, which would enable a more precise determination of the peak positions.

Chlorophylls have been extensively investigated both experimentally and theoretically owing to the fact that they are essential for photosynthesis. We have studied two forms of chlorophyll, chlorophyll a and chlorophyll b, by means of density functional theory. Optimization of S0, S1 and T1 states was performed with the B3-LYP functional. The computed fluorescence lifetimes show good agreement with the available experimental data. The electronic adiabatic energies of S1 and T1 states are 2.09/2.12 and 1.19/1.29 eV for chlorophyll a and chlorophyll b respectively. We discussed the implications of this results on the triplet formation. Also, the calculated vertical ionization potentials shows good agreement with the experimental results. [Projekat Ministarstva nauke Reoublike Srbije, br. 172040]

One of the products of a photochemical reaction induced by UV irradiation of 1-methyltimine dimmer is pyrimidine(6-4)pyrimidone. Due to the low yield of this product, it is difficult to examine its geometry and vibrational spectrum. In this study we used quantum chemical methods to characterize pyrimidine(6-4)pyrimidone structure. Its three conformers were optimized and their structures were compared. Their vibrational frequencies in the harmonic approximation are briefly discussed. It is shown that the most significant changes in the infrared spectra arise from formation of hydrogen bonds. All calculations have been performed both in vacuum and in D2O.

The paper describes the development and implementation of an expert system for fault detection of induction motors. Early detection of induction motors failures may prevent the occurrence of malfunction and ensure timely replacement and servicing. In order to make timely and accurate fault detection an expert system is designed and developed. The expert system is a software system aimed at 'simulating' human-expert knowledge and assistance in making decisions in a particular area. This paper presents a conceptually new type of expert system based on the artificial neural networks. Inputs into the expert system are the results of the algorithms to detect faults based on different physical quantities (current and vibration). The expert system performs analysis of input data and, based on them, it finally defines the type of fault or faults in the case of multiple failures.

In this communication it is shown that the widely held opinion that compact program packages for quantum-mechanical calculations of molecular structure can safely be used as black boxes is completely wrong. In order to illustrate this, the results of computations of equilibrium bond lengths, vibrational frequencies and dissociation energies for all homonuclear diatomic molecules involving the atoms from the first two rows of the Periodic Table, performed using the Gaussian program package are presented. It is demonstrated that the sensible use of the program requires a solid knowledge of quantum chemistry.