On the possibility of determining anthracycline antibiotics in aqueous solutions using optical analytical system (biosensor)

We propose a version of the theory describing the circular dichroism spectra of cholesteric liquidcrystal dispersion particles of double-stranded DNA. The basis of the theory is the concept of absorption of electromagnetic waves by large molecular systems. The effect of physical parameters of dispersion particles on their circular dichroism is theoretically determined. It is experimentally demonstrated that circular dichroism can be used as a convenient tool for creating an optical analytical system for the determination of biologically active compounds that interact with DNA molecules.     

Dynamics of the processes of electron-hole recombination and capture of charge carriers in anatase doped with boron, carbon, or nitrogen

The first-principles investigation of the processes of nonradiative recombination of electron-hole pairs and binding of excited charge carriers with impurity atoms in anatase doped with boron, carbon, or nitrogen has been carried out using the perturbation theory method. The perturbation is provided by a dynamically screened electron-electron interaction potential calculated in the random phase approximation. It has been shown that the most probable processes occurring upon doping with boron and carbon are exchange processes in which electrons are bound with the impurity atom, whereas the most probable processes observed upon doping with nitrogen are exchange processes in which holes are bound with the impurity atom. These processes occur within a time interval of shorter than 2 fs. The next in probability are the processes of energy losses by unbound electrons and holes due to the generation of phonons. For the case of nitrogen doping, the time of this process is estimated at approximately 300 fs. For excitons formed in this case, the luminescence photon energy and the binding energy of electrons or holes with the impurity atom are estimated. The agreement between the calculated data and the results of experiments on the photocatalysis proceeding on the surface of N-doped anatase is discussed.     

Effect of irradiation on aqueous dispersions of humic acids and lignin

The influence of electron-beam irradiation on the optical absorption of dilute aqueous solutions of lignin and humic acids has been studied. It has been shown that when the thickness of the irradiated layer of the solution is less than the electron range, preferential enlargement and precipitation of polyphenolic impurities observed. The most profound effect is achieved at doses of 5–15 kGy. When the irradiated-layer thickness is less than the electron range, the radiation-induced coagulation of impurities weakens. This effect can be due to the buildup of uncompensated charge of thermalizing electrons affecting the negatively charged micelles of polyphenolic impurities.     

Vibrational states of the Pt(111)–$$ \left( {\sqrt {3} \times \sqrt {3} } \right) $$ R30°–K surface structure

Vibrational spectrum of the ordered Pt(111)–( ?3 ×?3 ) \left( {\sqrt {3} \times \sqrt {3} } \right) R30°–K surface superstructure formed on the platinum surface with adsorption of 1/3 ML potassium is calculated with the use of the interatomic interaction potentials obtained in the strong bond approximation. Relaxation of the surface, dispersion of the surface phonons, local density of vibrational states, and polarization of phonon modes of adatoms and atoms of the substrate are discussed in the work. The theoretical results obtained agree well with the available experimental data.     

Change in surface states of Ag(111) thin films upon adsorption of a monolayer of PTCDA organic molecules

The change in the electronic structure of silver thin films of different thicknesses with the Ag( 111) orientation due to the interaction with an adsorbed monolayer of ordered organic molecules of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) has been investigated in terms of density functional theory. It has been shown that one of the two surface states of the pure films transforms into an unocc upied interface state due to the interaction so that all the main features of the initial state are retained. The relation of the resulting state to the unoccupied state experimentally observed in the PTCDA/Ag( 111 ) system by scanning tunneling and two-photon photoemi ssion spectroscopy has been discussed.     

Activation energy for diffusion of point defects at the surfaces of F.C.C. metals

The energies for migration of vacancies and adatoms and the adatom formation energy at surfaces with low indices have been calculated for aluminum, nickel, copper, palladium, silver, platinum, and gold using the inserted atom method. We have found the self-diffusion activation energies for the jumpwise diffusion mechanism with participation of both types of surface point defect. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii. Fizika, No. 6, pp. 89–96, June, 1997.     

Ab initio calculation of the lifetime of quasiparticle excitations in transition metals within the framework of the <Emphasis Type="Italic">GW</Emphasis> approximation

This paper reports on the results of ab initio calculations of the lifetimes τ of quasiparticle excitations in cubic d transition metals (V, Nb, Ta, Mo, W, Rh, Ir) within the GW approximation, which represents the self-energy of quasiparticles by the product of the Green’s function and the dynamically screened Coulomb potential. A comparative analysis of the dependences of the lifetime τ(ω) on the excitation energy ω is performed, and the specific features of the dependences τ(ω) in going from metal to metal within a particular group and along the d periods are revealed. It is found that the dependence τ(ω) on the excitation energy differs from the dependence τ ～ ω^?2 obtained within the free-electron model and is primarily determined by the density of d states localized in the vicinity of the Fermi level and by the electron interaction screened by the d electrons.