Wyniki wyszukiwania - Biblioteka Nauki

1

Theoretical investigation on growth kinetics and thermodynamic properties of pyridine-2-carboxylic acid crystals

100%

Manopradha N. , Rama S. , Gowri S. , Kirubavathi K. , Selvaraju K.

Mechanics and Mechanical Engineering

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2019

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tom Vol. 23, nr 1

23--27

EN

This work illustrates the significance of kinetic parameters of nucleation and thermal decomposition for Pyridine-2-carboxylic acid crystals. In the interest of maximizing the growth condition for the production of single crystals, nucleation parameters such as interfacial energy (σ), volume free energy (ΔGv), critical energy barrier for nucleation (ΔG*), radius of the critical nucleus (r*) and nucleation rate (J) were determined from the classical nucleation theory of solubility-enthalpy relation. The optimized geometry of the compound was computed from the DFTB3LYP gradient calculations employing 6-31G(d,p) basis set and its vibrational frequencies were evaluated. Based on the vibrational analysis, the thermodynamic parameters were obtained and the correlative equations between these thermodynamic properties and variation in temperatures were also reported.

2

Efektywność estymacji parametrów sygnału harmonicznego metodą wielopunktowej interpolowanej DFT

100%

Domańska A. , Grząślewicz P.

Pomiary Automatyka Kontrola

|

2013

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tom R. 59, nr 5

422--424

PL

Artykuł dotyczy zagadnienia estymacji widma sygnałów periodycznych metodą DFT z dodatkowym przetwarzaniem – zastosowaniem okna oraz interpolacją dwu i trzy punktową. Przedstawiono zasadę takiej estymacji w przypadku okna prostokątnego i Hanninga oraz zanalizowano efektywność każdego z wariantów. Przedstawiono interfejs programu, wykonany w celu zobrazowania i śledzenia graficznych i liczbowych wyników estymacji. Program i graficzny interfejs użytkownika mogą mieć zastosowanie w wirtualnym analizatorze widma o podwyższonej dokładności. W artykule tym przedstawiono dwie metody estymacji częstotliwości i amplitudy. Obie metody używały okien Hanninga i prostokątnego. Okazało się metoda trzy punkowej estymacji WMIpDFt osiąga lepsze rezultaty, posługując się kryterium wartości błędu bezwzględnego. Wartości te są mniejsze niż w przypadku stosowania metody estymacji dwu punktowej IpDFT. Jednak użycie prostokątnego okna w trzy punktowej estymacji generuje mniejszy błąd. Dla efektywnej estymacji amplitudy lepszym okazuje się zastosowanie okna Hanninga dla obu metod estymacji. Najmniejszy bezwzględny błąd jest otrzymywany dla estymacji amplitudy z wykorzystaniem dwupunktowej estymacji IpDFT oraz okna Hanninga.

EN

The paper deals with estimation of periodic signal spectra using the DFT method with additional processing (application of time window and two-point and three-point interpolation). The efficiency of esti-mation with the rectangular and Hanning window is analyzed. There is presented a program interface created for tracking graphical and numerical results of estimation. The graphical interface and the simulation program can be used in a high precision spectrum analyzer. In this paper two methods of frequency and amplitude estimation are discussed. Both methods use the Hanning and rectangular window. It turns out that the three-point WMIpDFT method gives better results, using the absolute error value criterion. The values of the absolute error are smaller than those in case of using the two-point IpDFT. However, use of rectangular window in the three-point estimation creates a lower error value. For the effective amplitude estimation it is better to use the Hanning window for both methods. The lowest absolute error value is obtained for the amplitude estimation with use of the two-point IpDFT method with the Hanning window.

3

Cepstrum application in diagnostics of mechanical devices

100%

Kurowski W. , Miranowski K.

Diagnostyka

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2014

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tom Vol. 15, No. 4

21--27

EN

The paper presents one of the methods of digital processing of diagnostic signals such as cepstral analysis and the possibility of its application in the investigations of sources of wave disturbances. In order to solve the problem, simulation and diagnostic research was performed. The simulation experiment consisted in generating different sample signals (by special software) containing known frequency-related information, which aimed at exploring the information generated and presented in the cepstrum characteristics and its reliability. The diagnostic experiment was carried out on an mechanical device – a Ford Transit minivan. The object was a basis for the determination of the possibilities of practical application of the cepstrum characteristics.

PL

W artykule przedstawiono jedną z metod cyfrowego przetwarzania sygnałów diagnostycznych jaką jest analiza cepstralna i możliwość jej zastosowania w diagnostyce urządzeń mechanicznych do badania źródeł zaburzeń. Dla rozwiązania zadania przeprowadzono badania symulacyjne i diagnostyczne. Eksperyment symulacyjny polegał na generowaniu w specjalnym programie różnych sygnałów próbnych, zawierających znane informacje częstotliwościowe, w celu zbadania informacji wytwarzanych i prezentowanych w charakterystyce cepstrum oraz ich wiarygodności. Natomiast eksperyment diagnostyczny, przeprowadzony na rzeczywistym urządzeniu mechanicznym, jakim był mikrobus Ford Transit, stanowił podstawę do określenia możliwości praktycznego zastosowania charakterystyki cepstrum.

4

DFT study of chemical reactivity of free radicals ABTS°+ and DPPH° by Myricetin, Quercetin and Kaempferol

94%

Houngue M. T. A. K. , Doco R. C. , Kpotin G. A. , Kuevi U. A. , Simplice K. , Wilfried K. , Atohoun Y. G. S. , Mensah J.-B.

World Scientific News

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2017

|

tom 90

177-188

EN

Myricetin, quercetin and kaempferol are polyphenols belong to the group of flavonoids. They are known for their many biological activities and particularly their strong ability to trap free radicals that cause nuisance to living organisms. In order to rationalize and compare the antioxidant activities of these molecules, DFT study was conducted in the gas phase, at B3LYP / 6-311G (d, p) and M05-2X / 6-311G (d, p). approximation levels. Calculations carried out relate to electronic affinity EA, ionization energy IP, energy gap (HOMO-LUMO), hardness (η), softness (S), electronegativity (χ), electrophilic index (ω) and energy parameters. Results of various calculations compared to those of trolox, molecule identified in our previous work as reference for study antioxidant properties of bioactive molecules have shown that: The three molecules are good antioxidants and could be effective to fight the oxidative attacks of living organisms; The hydroxyl groups of catechol group and C2 = C3 double bond are determinant for the antioxidant activity of the three molecules; Myricetin is the most antioxidant among the three molecules followed by quercetin; The radical ABTS°+ is more suitable for studying the antioxidant properties of molecules.

5

Nitrogen-doped pyrene as a catalyst for fuel cells

94%

Chudoba A.

World Scientific News

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2017

|

tom 72

52-59

EN

Density functional theory (DFT) was applied to study nitrogen-doped pyrene as an oxygen reduction reaction (ORR) cathode catalyst for fuel cells. Transition states and energy barriers were calculated to predict the catalytic properties of this substance.

6

Investigation on NO2 Catalysis Mechanism in Dimethylnitramine Decomposition Using DFT Method

94%

Xinfeng W. , Yuanjie S. , Chaoyang Z.

Central European Journal of Energetic Materials

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2005

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tom Vol. 2, nr 1

47-54

EN

Dimethylnitramine (DMN) is usually investigated as a model compound for nitramine explosives. In the present study, the reaction of DMN with NO2 molecule and two possible initial channels of unimolecular decomposition of DMN in gas-phase (N-N bond scission and direct HONO elimination) were studied. Critical points on the potential energy surfaces (PES) of all reactions were optimized using the B3LYP density functional method (DFT). The barrier for the N-N bond homolysis is lower about 17 kJ mol-1 than that for the direct HONO elimination. The PES of DMN reaction with NO2 shows that the energy barrier for HONO elimination was descended about 79.3 kJ mol-1 by the catalysis of NO2. As a result, that N-N bond homolysis is the dominative initial channel in the unimolecular decomposition of DMN is supported in theory and NO2 catalysis mechanism in DMN decomposition is presented.

7

DFT Study on Non-reversible Expansion of TATB Crystal

94%

Chaoyang Z. , Yuanjie S. , Xiaodong Z. , Haishan D.

Central European Journal of Energetic Materials

|

2004

|

tom Vol. 1, nr 1

43-49

EN

By using DFT method, changing the six parameters of TATB cell and calculating the total energy corresponding to different volume ratio, this paper concludes that TATB crystal can only extend irreversibly along the c-axis when heated because the point of experiment is unstable thermodynamically and the ratio of non-reversible expansion must be about 2.6-3.7 per cent theoretically.

8

A DFT study on the interaction between europium, uranium and SWCNT

94%

Xie J.-C. , Yong-Jian-Tang , Zhang H.

Open Physics

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2011

|

tom 9

|

nr 3

716-721

EN

We investigate the electronic and band structure for the (8; 0) single-wall carbon nanotube (SWCNT) with a europium (Eu) and a uranium (U) atom outside by using the first-principles method with the density functional theory (DFT). The calculated band structure (BS), total density of state (TDOS), and projected density of state (PDOS) can elucidate the differences between the pure (8; 0) SWCNT and the nuclei outside the SWCNT. The indirect band gaps are obtained when Eu and U atom are put outside the (8; 0) CNT; they are 0.037 eV and 0.036 eV, respectively, which is much smaller than 0.851 eV for pure CNT. Compared with pure (8; 0) SWCNT, the bottom of the conduction band moves down by 0.383 eV and 0.451 eV with the Eu and U outside, and the top of valence band moves up by 0.127 eV and 0.162 eV, respectively. More significantly, the top of the valence band has exceeded the fermi-level. So, a single nucleus changes the semiconductor character of pure nanotube to semi-metal.

9

Elastic constants and analytic bond order potential for atomistic simulations of simple cubic tungsten trioxide

94%

Dendzik Z. , Chrobak D. , Nowak R.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2009

|

tom Vol. 13, No 1-2

93-98

EN

A set of elastic constants was calculated and a parametrization of the potential was derived for simple cubic tungsten trioxide based on an analytical bond-order scheme. It was show that the obtained parametrization provided a good description of interatomic forces and such properties as the lattice constant, the bulk modulus and the elastic constants.

10

Exploring the possibility of high-valent copper in models of copper proteins with a three-histidine copper-binding motif

94%

Anamaria I. , Mot A. , Silaghi-Dumitrescu R.

Open Chemistry

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2012

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tom 10

|

nr 5

1527-1533

EN

An important function of many copper-containing proteins is activation of O2 and subsequent substrate oxidation. The Cu (III) oxidation state is generally considered to be less accessible because of the highly positive Cu (III)/Cu (II) redox potentials with typical amino acid ligands. Here, we employ density functional (DFT) calculations to explore to what extent copper (III) may be accessed in a biologically-relevant coordination environment around a mononuclear copper center, by breaking the oxygen-oxygen bond in a copper-(hydro) peroxide complex. In agreement with previous findings by Solomon and co-workers on copper models with related coordination patterns, the formally high-valent copper complex produced by O-O bond cleavage appears to harbor both oxidizing equivalents on the ligands. The potential energy surface for such a reaction reveals that with the three-histidine binding motif at the copper, O-O bond cleavage is not impossible, but rather disfavored thermodynamically. [...]

11

Ab Initio Study of Structure, Electronic and Magnetic Properties of YFe5 Phase Compound in the DFT Formalism

94%

Gruszka K. , Nabiałek M. , Noga T.

Archives of Metallurgy and Materials

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2016

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tom Vol. 61, iss. 1

369--374

EN

Paper presents results of studies on structural, electronic and magnetic properties of YFe5 compound using density functional theory (DFT) approach. The GGA functional with ultrasoft pseudopotentials were used as implemented in Quantum Espresso software. The structure of YFe5 compound was examined in three different states namely nonmagnetic, antiferromagnetic and ferromagnetic. Also two antiferromagnetic configurations were considered. From the total energy viewpoint the most likely ferromagnetic configuration is favorable. In order to achieve mentioned aims we present projected density of states, electronic band structure and Löwdin population analysis studies results.

12

DFT Calculations of the Structure and Adsorption of HCO3 - Species on the Surface of Al2O3 Catalyst

94%

Gao H. W. , Guo L. , Yan T. X.

Polish Journal of Chemistry

|

2009

|

tom Vol. 83, nr 12

2119-2127

EN

Density functional theory (DFT) calculations have been carried out to study the structure and adsorption of HCO3 - species on Al2O3 catalyst using MPW1PW91 function and the different basis sets of 6-31G, 6-311G, 6-311+G(d), DGDZVP, DGDZVP2, PVQZ, SDD, LANL2DZ, LANL2MB. The geometrical structures and vibration spectra were obtained with DFT methods and compared with the corresponding experimental values. Theoretical calculations show that the calculated IR spectra using MPW1PW91/6-311G, MPW1PW91/SDD and MPW1PW91/LANL2DZ methods are in good agreement with the experimental spectroscopic results.

13

Amplitude value error of periodic signal as a two-dimensional random variable

94%

Purczyński J.

Computer Applications in Electrical Engineering

|

2012

|

tom Vol. 10

29--40

14

Synthesis and pharmacological properties of 3-(2-methyl-furan-3-yl)-4-substituted-Δ2-1,2,4-triazoline-5-thiones

94%

Siwek A. , Wujec M. , Dobosz M. , Jagiełło-Wójtowicz E. , Chodkowska A. , Kleinrok A. , Paneth P.

Open Chemistry

|

2008

|

tom 6

|

nr 1

47-53

EN

By the reaction of 2-methyl-furan-3-carboxylic acid hydrazide with isothiocyanates, 1-[(2-methyl-furan-3-yl)carbonyl]-4-substituted thiosemicarbazides 1 were obtained. Further cyclization with 2% NaOH led to the formation of 3-(2-methyl-furan-3-yl)-4-substituted-Δ2-1,2,4-triazoline-5-thiones 2. The pharmacological effects of 2 on the central nervous system in mice were investigated. Strong antinociceptive properties of the investigated derivatives were observed in a wide range of doses. [...]

15

Charge Localization in Monothiophosphate Monoanions

94%

Rostkowski M. , Paneth P.

Polish Journal of Chemistry

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2007

|

tom Vol. 81, nr 5-6

711-720

EN

We have examined charge distribution between exocyclic oxygen and sulfur atoms in 5,5-dimethyl-1,3,2-dioxaphosphorinan-2-oxy-2-thio monoanion. Our results indicate that while solvent polarity and substituents have minor effect, the presence of a counter- ion results in relative increase of the partial atomic charge on the oxygen atom. Thus it seems that change in the reactivity of this anion observed experimentally can be ascribed to ion pairing in low polarity solvent.

16

How the Bonding Mode in Cyclopentadienylaluminum Complexes Influences the Cp– Ligand Aromaticity

94%

Zachara J. , Madura I. , Kunicki A.

Polish Journal of Chemistry

|

2007

|

tom Vol. 81, nr 5-6

745-755

EN

The substantial influence of floating Cp–Al bond-modes from ni 5(pi) to ni 1(omega) on the Cp– ligand’s aromaticity was discussed basing on the crystal data of organoaluminum complexes and DFT calculations (B3LYP/6-311G**) performed for model compounds. The aromaticity of cyclopentadienyl moiety was characterized by the HOMA index. The spread of HOMA values from 0.8 to –0.5 indicated the electronic structure of the cyclopentadienyl ligand bonded to aluminum center can be regarded as an intermediate between the highly aromatic, uncomplexed cyclopentadienyl anion Cp– and the antiaromatic structure of cyclopentadiene CpH.

17

A Theoretical Study of Chiral Recognition in Bis[amino(phenyl)methanol]chromium(0) Complexes

94%

Zborowski K. , Alkorta I. , Elguero J.

Polish Journal of Chemistry

|

2007

|

tom Vol. 81, nr 5-6

621-629

EN

Atheoretical study of the complexes formed by the chiral -amino--phenylmethanol in the presence and absence of a chromium(0) atom has been carried out. The results indicate that in the presence of chromium, themost stable complex corresponds to that where the two amino(phenyl)-methanol molecules have the same chirality while in the absence of the mentioned atom the preferred one is that with the two molecules with different chirality.

18

pi-Electron Communication Through the Metal Valence Shell –W, Mo and Fe Complexes Containing Maleimidato Moiety

94%

Palusiak M.

Polish Journal of Chemistry

|

2007

|

tom Vol. 81, nr 5-6

903-909

EN

The characterization of carbonyl–metal and maleimidato–metal bonding has been performed using the topological analysis of electron distribution function estimated for molecules of ( 5-C5H5)M(CO)3( 1-N-maleimidato) (M = W, Mo) and ( 5-C5H5)Fe(CO)2( 1-N-maleimidato). The Atoms in Molecules (AIM) approach has been applied for characterization of and -components of the metal–ligand bonds. The -electron communication between trans-placed ligands is present in Wand Mo derivatives. The ellipticity parameter is suggested to be a useful and highly sensitive parameter in the analysis of the metal–ligand bonding

19

Computational characterization of (E)-N-(3-bromo-4-fluorobenzylidene)-4-nitrobenzenamine compound

94%

Premalatha R. , Santhi N.

World Scientific News

|

2017

|

tom 74

121-140

EN

Schiff bases are aldehyde- or ketone-like compounds in which the carbonyl group is replaced by an imine or azomethine group. In this work, (E)-N-(3-bromo-4-fluorobenzylidene)-4-nitrobenzenamine have been synthesized and characterized by IR, 1H and 13C NMR spectral studies. Density functional theory (DFT) has been used to optimize geometrical parameters, atomic charges, vibrational wavenumbers and intensity of vibrational bands. The molecular properties HOMO-LUMO, NBO were calculated using B3LYP/6-311G (d, p) basis set. The polarizability and first order hyperpolariza-bility of the title Compound was calculated and interpreted.

20

Thermodynamic and kinetic properties of scandium (I) ion reacting with SCO in gas phase

94%

Yin P. , Qu R. , Chen H. , Tian Y. , Yin G. , Bao C.

Open Chemistry

|

2008

|

tom 6

|

nr 3

438-442

EN

Theoretical studies on the thermodynamic and kinetic properties of the reactions of scandium (I) ion with the sulfur-transfer reagent SCO via the C-O bond activation pathway have been carried out over the temperature range of 200-1200 K using the DFT/B3LYP method, general statistical thermodynamics, and Eyring transition state theory with Wigner correction. The relevant reactions include reaction 1 1Sc+ + SCO → 1IM1 → 1TS1 → 1IM2 (Step 1) → 1TS2 → 1IM3 → 1ScO+ + 1CS (Step 2), and reaction 2 3Sc+ + SCO → 3IM1 → CP → 1IM2 → 1TS2 → 1IM3 → 1ScO+ +1CS in which the spin multiplicity changes from the triplet state to the singlet state in the crossing region. It was concluded that the order of the equilibrium constants (K) and the reaction rate constants (k) are consistent with that of their corresponding exoergic energies, ΔE, and reaction barriers, respectively. Step 2 of reaction 1 is both thermodynamically and kinetically favored over the whole temperature range. Moreover, both Reaction 1 and reaction 2 are exothermic and spontaneous processes in which their entropy increases, and the magnitudes of their thermodynamic values all decrease with increasing temperature. [...]