Wyniki wyszukiwania - Biblioteka Nauki

1

The dependence of critical temperature on oxygen concentration in YBa2Cu3O6+x in terms of the fragmented chain model

100%

Milic M. , Matic V. , Lazarov N.

Open Physics

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2011

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tom 9

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nr 3

690-697

EN

An extended ASYNNNI model, that beside nearest-neighbour and next-nearest neighbour O-O interactions in the basal plane also includes interactions between the three nearest oxygen atoms, is used to describe the statistics of CuO chain fragmentation and to calculate doping and T c in YBa2Cu3O6+x . Calculations were made by the Monte Carlo method employing the recently proposed charge transfer model that assumes only chains whose length is equal to, or exceeds, a characteristic (critical) length, l cr, can provide holes to the layers and contribute to doping p. The obtained p(x) is then combined with a universal T c versus p relation to yield T c(x) characteristics that correlate remarkably with those reported in recent experiments. The best coordination between theoretical and experimental T c(x) characteristics has been achieved for l cr = 2, implying that only isolated basal plane oxygen atoms (trivial chains) do not contribute holes to CuO2 layers.

2

Phase transformations in locally anharmonic systems. Susceptibility approach to orientational instabilities in molecular solids

100%

Kuchta B. , Luty T.

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1998

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tom Vol. 72, nr 2

426-432

EN

A model of the structural transformation has been discussed, where the local potential is anharmonic but single-welled. Such potential representants a Hamiltonian to model the structural phase transition in charge-transfer molecular crystals A-TCNB (anthracene-tetracyanobenzene). The conditions for the instability and transformation have been found, using the static susceptibility approach, and compared with the variational approximation. The latter method gives a six times lower transition temperature. The fluctuations and entropy are pointed out as the cause of this difference. The exact transition temperature has been calculated by simple Monte Carlo simulations. A comparison with a double-welled case, which models the structural transition in N-TCNB molecular crystal (naphthalene-tetracyanobenzene), has been presented.

3

Acoustically driven charge separation in semiconductor heterostructures sensed by optical spectroscopy techniques

100%

Kuryliuk V. , Podolian A. , Korotchenkov O.

Open Physics

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2010

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tom 8

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nr 1

65-76

EN

We demonstrate a method of using a two-layer sandwich structure, which includes a LiNbO3 plate and a semiconductor heterostructure to create an inhomogeneous stress and piezoelectric harmonic potential in the semiconductor. Both the GaAs/AlGaAs quantum well (QW) structures and SiGe/Si heterostructures are attempted, working with and without using a piezoelectric field in the semiconductor layer. The standing-wave fields generated in the semiconductor and the electron and hole distributions driven by the piezoelectric field are computed by finite element method (FEM) techniques. It is experimentally shown that, in a GaAs/AlxGa1-x As asymmetric double quantum well structure, the resonance enhancement of the narrower QW photoluminescence band is observed, which may be explained by the resonant charge transfer between the wider and narrower QWs. It is also shown that the piezoelectric fields quench the pure LO-phonon lines in the Raman spectra, whereas the coupled LO-phonon-plasmon mode strengthens. Experimental results indicate that the charge separation occurs in the plane of the QWs due to the piezoelectric fields. The recombination of carriers in the SiGe/Si heterostructures can be effectively enhanced by the presence of ultrasonic stress, displaying features consistent with varying electrical activity at dislocations.

4

Ultrafast electron transfer in tetracyanoethylene-benzene charge transfer complex

100%

Jarzęba W. , Tokarczyk B. , Murata S. , Tachiya M.

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1999

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tom Vol. 47, No. 4

347-360

EN

Ultrafast pump-probe transient absorption spectroscopy has been applied to study return electron transfer in the tetracyanoethylene- benzene electron donor-acceptor complex in several polar and non-polar solvents. Ultrafast excitation of the charge transfer band of the complex yields an excited Franck-Condon state, which relaxes to form a contact ion pair. The decay time of the ion pair is, in most cases, longer than the solvation time and is observed on a time scale from 2 picoseconds to 1 ns, depending on the solvent. Using the empirical solvent polarity scale ^vG153 and a conventional non-adiabatic theory of electron transfer, absolute rate constants for the non-radiative return electron transfer can be predicted in different solvents.

5

Real-time probing of elementary charge transfer processes in liquids and solutions

100%

Gauduel Y.

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1999

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tom Vol. 47, No. 4

303-331

EN

With the intensive development of ultrafast spectroscopic methods, the course of elementary reactions may be observable on the time scale of molecular motions. The : femtosecond solution chemistry allows the real-time probing of solvent cage effects during charge transfers. Recent studies devoted to the understanding of electron dynamics in : liquid phase are presented and discussed in the framework of quantum theories on nonequilibrium electronic states. This progress provides guidance for further research works on the microscopic description of reactional processes occurring in complicated many body systems.

6

Spectral studies of some C-60 complexes with TTF-derived donors

88%

Graja A. , Tanatar M. A. , Li Y. L. , Zhu D. B.

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1998

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tom Vol. 72, nr 5

869-876

EN

Electronic and vibrational spectroscopies were applied to the study of the strength of the donor-acceptor interaction and optical properties of the complexes of C-60 with two TTF-derived donors, i.e. bis(methylthio)ethylenedithio-tetrathiafulvalene (C-1TET- TTF) and tetramethyltetraselenafulvalene (TMTSF). The investigations of the single crystalline samples, for various light polarizations and temperatures, were performed. The analysis of all the spectral data shows that the investigated compounds are weak complexes with a neutral ground state.

7

The influence of the phosphorothioate diester bond on the DNA oxidation process

88%

Karwowski B. T.

Open Chemistry

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2015

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tom 13

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nr 1

EN

This study describes the influence of the phosphorothioate internucleotide bond on the deoxyribonucleic acid (DNA) oxidation process. The interaction of an ultraviolet radiation (UVA) with a targeted double-stranded (ds) oligonucleotide, in which one strand contains an antraquinone (AQ) moiety on the 5’-end, may lead to a hole migration process through the double helix. In the end, the migration of theformed radical cation terminates in a suitable place. Usually, this is a guanine-rich sequence. In another experiment, phosphorothioate internucleotide bonds were detected in the bacterial genome as a natural modification. In this study, a polyacrylamide gel electrophoresis (PAGE) autoradiogram analysis of irradiated ds-DNA showed that the oxidation reaction was not inhibited by an isolated guanine. Instead, irrespective of the absence or presence of a phosphorothioate bond, the termination of the ds-DNA oxidation process was predominantly observed on the thymine moieties. Based on the obtained results, it can be concluded that in the discussed case, a hole migration by a hopping mechanism is in competition with an oxidation reaction with a superoxide radical anion. Alternatively, the radical cation migration process is sequence-dependent due to its different ionization potentials. Therefore, the presence of a phosphorothioate internucleotide bond did not change the stability of ds-DNA under UVA irradiation conditions.

8

Kinetics of the reaction of 2,3,5,6-tetrachloro-1,4-benzoquinone with imidazole in acetonitrile and benzene

88%

Dworniczak M. , Przybyszewska M. , Jarczewski A.

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1998

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tom Vol. 72, nr 1

108-112

EN

Nucleophilic vinylic substitution of 2,3,5,6-tetrachloro-1,4-benzoquinone by imidazole in acetonitrile and benzene has been studied spectrophotometrically. The reaction product is the diaminodichlorosubstituted quinone. The values of the activation parameters indicate that there is a considerable charge separation in the transition state. The reaction mechanism is discussed.

9

Dehydration-Induced Charge Transfer in Ni3[Fe(CN)6]2ź15H2Oe T

88%

Liu M. , Bian X. F. , Xia Y. F. , Bao Z. , Xu M. X.

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2009

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tom Vol. 83, nr 10

1729-1735

EN

Molecular magnet nickel(II) hexacyanoferrate(III), powder Ni3[Fe(CN)6]2ź15H2O, was prepared by coprecipitation method. The coprecipitated powder was annealed in vacuum at different temperatures of 80, 100, 120, and 140 graduate C. Water molecules contained in Prussian blue analogues were removed by heating. The effects of dehydration on its charge transfer properties were studied by Fourier-transform infrared and Mössbauer measurements. It was found that the FeIII–CN–NiII state is the major structure in the coprecipitated form, while the FeII–CN–NiIII bond is formed in the annealed samples. The dehydration of NiII ferricyanide above 80°C induces an inner charge transfer from NiII towards FeIII to form the mixed valence system Ni(II) Ni(III) ferri-ferro-cyanide.

10

Matrix infrared spectra of C6H6-HNO3 and C6H6-HONO complexes in solid argon

75%

Krajewska M. , Mielke Z.

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1998

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tom Vol. 72, nr 2

335-346

EN

Infrared spectra of the complex between C6H6 and HNO3, trans-HONO and cis-HONO in solid argon are reported. Nitric acid and both isomers of nitrous acid form stable 1:1 hydrogen bonded complexex in which the OH group of an acid is interacting with the II-electron system of benzene ring. In addition the nitric acid appears to form another 1:1 complex in which both OH and NO2 group interact directly with the benzene ring. In both benzene-nitric acid and benzene-nitrous acid systems the higher order aggregates (C6H6)nHNO3, (C6H6)nHONOn>2 are easily formed.

11

Multi-Pulse Excitation Reveals a Novel Excited State Pathway in a Peryleneimide-Pentaphenylene Dyad

75%

Fron F. , Schweitzer G. , Jacob J. , Müllen K. , Van der Auweraer M.

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2008

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tom Vol. 82, nr 4

701-713

EN

The excited state properties of a peryleneimide-pentaphenylenedyad were in vestigated in detail using pump-probe, single photon timing and three-beam pulsed experiments. Upon excitation with 395 nm pulses ultrafast energy transfer was found to occur from the pentaphenylene to the perylene subunit. In polar solvents this excitation energy transfer is followed by charge transfer from the electron donor pentaphenylene to the electron acceptor perylene. A three-beam femtosecond transient absorption technique revealed the relaxation dynamics of a higher lying singlet state of the peryleneimide subunit to occur on a picoseconds time scale. These results demonstrate the potential use of the threebeam femtosecond technique in manipulating excited states processes.

12

Effect of Vacancies on Electronic and Magnetic Properties of Hydrogen Passivated Graphene Nanoribbons

63%

Haffad S. , Benchallal L. , Lamiri L. , Boubenider F. , Zitoune H. , Kahouadji B. , Samah M.

Acta Physica Polonica A

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2018

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tom 133

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nr 5

1307-1313

EN

Using first-principles calculations we have demonstrated that electronic and magnetic properties of armchair graphene nanoribbons are modified by introducing vacancies defects. The equilibrium geometries, electronic, charge spin density distributions, electronic band structures, and magnetic moments were examined in the presence of vacancies. We have found that introducing vacancies into armchair graphene nanoribbons changes the spatial distribution of neighbor atoms, particularly those located around the vacancies. Our calculations showed that the vacancies have significant effect on the magnetization of armchair graphene nanoribbons. Magnetic moment values and electronic behavior in different configurations depend on the number of vacancies. These results suggest that vacancy defects can be used to modify the electronic and the magnetic properties of armchair graphene nanoribbons.

13

The role of F A1:Ag+ defects in laser light generation and coadsorption of CO and halogen atoms at the KCl and KBr surface sites. First principles calculations

63%

Abdelrazik S. , Shalabi A.

Open Physics

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2007

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tom 5

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nr 4

611-636

EN

FA1:Ag+ color center at the low coordination (100) and (110) surface sites of KCl and KBr thin films play an important role in providing tunable laser oscillation and adsorbatesubstrate interactions. Double-well potentials at this site are investigated using ab initio molecular electronic structure calculations. The calculated Stokes shifted (optical transition bands), opticaloptical conversion efficiencies, the probability of orientational destruction, exciton (energy) transfer and Glasner-Tompkins empirical rule suggest that laser light generation is sensitive to (i) the lattice anion, (ii) the coordination number of surface ions, and (iii) the choice of the basis set centered on the anion vacancy. The adsorbate-substrate interactions were found to be dependent on the electronegativity of the adatom and on the lattice anion. Optimised geometries and the coadsorption of CO and (F, Cl, Br, I) on KCl and KBr (100) crystals are presented. Calculated chemisorption energies for CO on the (halogen atom/defect free sites of KCl and KBr (100) crystals) showed that the coadsorption of halogen atom tends to block other adsorbate-substrate interactions at the nearest neighbour sites. Thus if halogen atom coverage increases, the CO prefers to be adsorbed on the K+ site of the KCl and KBr (100) surfaces and on KBr relative to KCl.

14

Spectrophotometric determination of lisinopril in commercial dosage forms using N-bromosuccinimide and chloranil

51%

Rahman N. , Siddiqui M. R. , Azmi S. N. H.

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2007

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tom Vol. 52, No. 3

465-480

EN

Two simple, fast, sensitive, and economical spectrophotometric methods for quantification of lisinopril in drug formulations have been developed. Method A was based on the reaction between primary amino group of the drug with N-bromosuccinimide in acetone medium giving a yellow-colored product of maximum absorption at 353 nm. Method B was based on the formation of purple-colored charge transfer complex between the drug and chloranil in 1,4-dioxan-acetonitriIe medium. Beer's law was obeyed in the concentration ranges of 10-200 and 24-600 μg mLTwo simple, fast, sensitive, and economical spectrophotometric methods for quantification of lisinopril in drug formulations have been developed. Method A was based on the reaction between primary amino group of the drug with N-bromosuccinimide in acetone medium giving a yellow-colored product of maximum absorption at 353 nm. Method B was based on the formation of purple-colored charge transfer complex between the drug and chloranil in 1,4-dioxan-acetonitriIe medium. Beer's law was obeyed in the concentration ranges of 10-200 and 24-600 ug mL'1 with molar absorptivities of 1.40 x 103 and 7.28 x 102 L-1 mol cm'1 for methods A and B, respectively. Regression analysis yielded the following calibration equations: A = -2.44 x 10-1 + 3.16 x 10-1 C and A = 5.39 x 10-4+ 1.65 x 10-3C for methods A and B, respectively. For both calibration equations correlation coefficients were 0.9999. Intra- and inter-day precisions were lower than 1.60%. The optimum experimental conditions for the proposed methods have been investigated. Methods A and B have been successfully applied to the analysis of lisinopril in drug formulations. The results have been statistically compared to these obtained applying the British pharmacopoeia method with molar absorptivities of 1.40 x 103 and 7.28 x 102 L-1 mol cm-1 for methods A and B, respectively. Regression analysis yielded the following calibration equations: A = -2.44 x 10-1 + 3.16 x 10-1 C and A = 5.39 x 10-4+ 1.65 x 10-3C for methods A and B, respectively. For both calibration equations correlation coefficients were 0.9999. Intra- and inter-day precisions were lower than 1.60%. The optimum experimental conditions for the proposed methods have been investigated. Methods A and B have been successfully applied to the analysis of lisinopril in drug formulations. The results have been statistically compared to these obtained applying the British pharmacopoeia method

PL

Opracowano dwie proste, szybkie, czule i ekonomiczne spektrofotometryczne metody ilościowego oznaczania lizynoprilu w preparatach farmaceutycznych. Metoda A jest oparta na reakcji picrwszorzędowej grupy aminowej leku z N-bromosukcynimidem w acetonie, w wyniku której powstaje żółty produkt wykazujący maksimum absorpcji przy df. fali 353 nm. Metoda B polega na tworzeniu purpurowego kompleksu z przeniesieniem iadunku miedzy lekiem a chloranilem w mieszaninie 1,4-dioksanu i acetonu. Prawo Beer'a było . spełnione w zakresie stężeń 10-200 i 24-600 1.40 x 103; absorpcja molowa wynosiła 1.40 x 103 and 7.28 x 102 L-1 mol cm-1, odpowiednio w przypadku metody A i B, W wyniku analizy regresji otrzymano dwa równania kalibracyjne A =-2,44 x 10-4 + 3,16 x 10-3 C oraz A = 5,39 x10-4 + 1,65 x 10-3 C, odpowiednio dla metody A i B. Obie metody zoptymalizowano i zastosowano z powodzeniem do analizy lizynoprilu w preparatach farmaceutycznych. Otrzymane wyniki porównano z wynikami uzyskanymi według Farmakopei Brytyjskiej.