Isotopic temperature in spallation reactions

The possibility of applying the double-isotope-ratio method for calculating temperature to spallation products formed by high-energy protons is discussed. It is concluded that, at a specific incident-particle energy, spallation is characterized by a single temperature of the formation of products for targets in the mass range 56 ≤ A ≤ 208. No energy dependence of the temperature that was calculated by the double-isotope-ratio method was observed in the energy range 0.3 ≤ E ≤ 300 GeV.     

Fluorescence Study of DNA–Dye Complexes Using One-Photon and Two-Photon Picosecond Excitation

Preliminary results of investigation of one-photon- and two-photon-induced fluorescence of acridine orange (AO), epirubicin (ER), hypericin (HYP), and ethidium bromide (EB) in complexes with DNA are presented. A spectrofluorometer based on a picosecond Nd:YAG laser was used for investigations of two-photon (1064-nm, 1-mJ, 40-ps) and one-photon (532- and 355-nm) dye excitation. The spectra of two-photon-induced fluorescence of dyes and their complexes with DNA as well as the kinetics of dyes' fluorescence intensification during their interactions with DNA in dependence on the biomacromolecule concentration were obtained. The intensities of AO, HYP, and EB fluorescence were increased 2.4, 3.2, and 8 times, respectively, after binding with DNA at two-photon excitation, while at one-photon excitation the corresponding values were 2.5, 3.7, and 10 times. The difference in fluorescence enhancement during DNA–dye complex formation at linear and nonlinear excitation may possibly be associated with the fact that the cross sections of one-photon and two-photon absorption, in general, change unequally during the binding of dyes to organic molecules and bathocromic shift of the electronic transitions. It was shown that the peak of AO fluorescence shifted to a longer wavelength on 10 nm after two-photon excitation at 1064 nm in comparison with one-photon excitation at 532 nm.     

Single-layer antireflection coatings for GaAs solar cells

Optimal parameters of antireflection coatings for GaAs solar cells are simulated and calculated by the optical matrix approach method. It is shown that by using single-layer Ta₂O₅ and ITO antireflection coatings it is possible to reduce essentially the reflectance from the surface of GaAs solar cells.     

Influence of high-spin states on isomeric ratios of nuclear reaction products

The isomeric ratios of some nuclear products of (p, n), (d, 2n), (α, p3n) reactions were analyzed. A comparison of calculation data obtained by using TALYS 1.4 software package with experimental ones shows that the observed significant discrepancies for definite nuclei may be accounted for by the influence of high-spin states on the values of isomeric ratios.     

Influence of frequency modulation of IR femtosecond laser pulse on the generation efficiency of difference frequency radiation

The results of theoretical research and numerical simulation of the generation process of difference frequency radiation by the IR femtosecond laser pulse with the frequency modulation are presented. It is shown that to obtain the maximal generation efficiency of the difference frequency radiation, the instantaneous frequency of the femtosecond IR laser pulse should be the quadratic function of time. The obtained results are independent on the type of nonlinear crystal and can be used to develop and create the pulse source of difference frequency radiation.     

96gTc As an Alternative Gamma-Ray Emitter for Medical Diagnostics

The possibility of employing the isotope ^96gTc as a gamma-ray emitter in medical diagnostics is examined. Corresponding calculations by the TALYS-1.9 revealed that an irradiation of a ⁹⁶Mo target with protons of energy E =12 → 6 MeV at a current of 100 μA for six (eight) hours makes it possible to produce 20 (26) GBq of the isotope ^96gTc. In detecting gamma rays of energy in the range between 770 and 850 keV, the intensity of gamma rays from ^96gTc is close to their intensity for ^99mTc obtained in the reaction ¹⁰⁰Mo(p, n), so that one can use^96gTc as an alternative gamma-ray emitter.

     

Multidimensional mappings in antiferromagnetic models and Lyapunov exponents with the magnetization plateau

We consider the Heisenberg model with two- and three-spin exchange interactions on a recursive ladder in a strong magnetic field. Recurrent relations for branches of the partition function of the Ising model with two- and three-spin exchange interactions are deduced. As a recursive lattice the zigzag ladder is chosen. In the antiferromagnetic case magnetization plateau are observed at low temperatures. Lyapunov exponents for the three-dimensional mapping at low temperatures are calculated. It is shown that for some values of two- and three-spin exchange parameters in the antiferromagnetic case the maximum of the Lyapunov exponent approaches zero.     

Generation of difference-frequency radiation in GaAs in the field of a few-cycle laser pulse in the regime of weakly expressed chromatic dispersion

We derive a system of coupled modified Korteweg-de Vries equations in the approximation of unidirectional waves which describe the evolution of electric fields of mutually-orthogonal linearly polarized laser pulses with duration of several optical oscillations in a nonlinear crystal with quadratic nonlinearity in the regime of weakly expressed chromatic dispersion. An isotropic GaAs crystal is considered as a nonlinear crystal, and the direction of propagation of interacting pulses is assumed to coincide with the normal to the 〈110〉 plane of the crystal. The derived system of equations was solved numerically by the finite difference method. We obtained the dependence of the relative shift of the central wavelength of pumping pulse spectrum on the distance travelled. It is shown that the decrease in the crystal thickness down to values commensurate with the coherence length of difference-frequency radiation leads to an increase in conversion efficiency. In particular, it is shown that the efficiency of difference-frequency generation at 4.1 μm and 10 μm for the 30 fs duration of pumping at 1.98 μm and the 100 MV/m amplitude of the electric field is ?51 dB and ?14 dB, respectively.     

Coherence as ultrashort pulse train generator

Intense, well-controlled regular light pulse trains start to play a crucial role in many fields of physics. We theoretically demonstrate a very simple and robust technique for generating such periodic ultrashort pulses from a continuous probe wave which propagates in a dispersive thermal gas media.     

Nitric Oxide Dioxygenation Reaction by Oxy-Coboglobin Models: In-situ Low-Temperature FTIR Characterization of Coordinated Peroxynitrite

The oxy-cobolglobin models of the general formula (NH(3))Co(Por)(O(2)) (Por = meso-tetra-phenyl and meso-tetra-p-tolylporphyrinato dianions) were constructed by sequential low temperature interaction of NH(3) and dioxygen with microporous layers of Co-porphyrins. At cryogenic temperatures small increments of NO were introduced into the cryostat and the following reactions were monitored by the FTIR and UV-visible spectroscopy during slow warming. Upon warming the layers from 80 to 120 K a set of new IR bands grows with correlating intensities along with the consumption of the ν(O(2)) band. Isotope labeling experiments with (18)O(2), (15)NO and N(18)O along with DFT calculations provides a basis for assigning them to the six-coordinate peroxynitrite complexes (NH(3))Co(Por)(OONO). Over the course of warming the layers from 140 to 170 K these complexes decompose and there are spectral features suggesting the formation of nitrogen dioxide NO(2). Upon keeping the layers at 180-210 K the bands of NO(2) gradually decrease in intensity and the set of new bands grows in the range of 1480, 1270, and 980 cm(-1). These bands have their isotopic counterparts when (15)NO, (18)O(2) and N(18)O are used in the experiments and certainly belong to the 6-coordinate nitrato complexes (NH(3))Co(Por)(η(1)-ONO(2)) demonstrating the ability of oxy coboglobin models to promote the nitric oxide dioxygenation (NOD) reaction similar to oxy-hemes. As in the case of Hb, Mb and model iron-porphyrins, the six-coordinate nitrato complexes are not stable at room temperature and dissociate to give nitrate anion and oxidized cationic complex Co(III)(Por)(NH(3))(1,2).