acta physica slovaca

Abstract: We start by studying the Goldberger-Treiman discrepancy (GTd) D = (2.259 +- 0.591)%. Then we look at the pN s term, with the dimensionless ratio s_N/2m_N=3.35%. Finally we return to predicting (via the quark model) the pN coupling constant, with GTd D -> 0 as m_q -> m_N/3.

Abstract: The photorefractive effect in various crystals of LiNbO3 is investigated in the paper. The experiments were carried out at room temperature by means of set-up for holographic investigation of photorefractive effect. Results of the time dependence of intensity of diffracted beams measurements give information about creation process of the record. Such measurements at high exposures were carried out and their interpretation is presented in the paper. The results of such measurements on samples from different providers indicate the differences among samples with respect to impurities they contain.

Abstract: X-ray diffraction method is applied to study the structure of liquid naphthalene. The main sources of errors are discussed. A numerical analysis is performed of the influence of X-ray data termination on the electron -- density radial -- distribution functions (EDRDF) and on interatomic distances and coordination numbers determined from these functions. The interatomic distances determined from the EDRDF are shown to be practically independent of the termination angle. A strong dependence of coordination numbers on the termination angle, observed by other authors, is confirmed. Structural analysis of liquid naphthalene C10H8 by X-ray monochromatic radiation scattering metod is given. The X-ray measurements were made at 368K for the scattering angle range Q varied from 2° to 60°. The EDRDF maxima at 0.380, 0.455, 0.535, and 0.625 nm correspond to the intermolecular interactions. The integrals over made it possible to determine the value of the mean coordination numbers 1.36, 2.06, 2.37, and 2.76, respectively. A possibility of comparing coordination numbers obtained in different laboratories for liquids is discussed.

Abstract: A reentrant spin glass phase is revealed in the Fe0.7Al0.3 alloy as the temperature is lowered. Our measurements of the DC magnetization in zero field cooled and field cooled of Fe0.7-xRxAl0.3 alloys (with R=Mn or V) showed critical concentrations xc of Mn and V atoms. Above these critical concentrations the alloys no longer exhibit reentrant spin glass behavior. We found for Mn-atoms xc = 0.04 and for V-atoms xc = 0.02. This behavior is attributed to the magnetic nature of these atoms. Also, compared to the V and Mn free alloy (Fe0.7Al0.3) the spin glass temperature Tf is more influenced by the V-atoms.

Abstract: The magnetic properties of the two-dimensional anisotropic Heisenberg model with spin S = 1 are investigated by the Green function method. The Heisenberg model with the exchange anisotropy in the (x,y)-plane and in an external magnetic field H = (H^x,0,0) is considered as a special model of a non-collinear magnetic system. The Hamiltonian for the anisotropic Heisenberg model smoothly interpolates between that of the isotropic Heisenberg model and the Ising model with the variation of the exchange anisotropy parameter. The orientation of the magnetization is determined by the expectation values and of the spin components from which the total magnetization and the orientation angle q are obtained as a function of the temperature and of the transverse magnetic field for various parameters of the exchange anisotropy. We present the results of , , and q obtained within Heisenberg and Ising models.

Abstract: The high/low amplitude anisotropic wave train events (HAE/LAE) in cosmic ray (CR) intensity have been investigated during the period 1991-94 using the Deep River neutron monitoring data. In all, 16 HAE and 13 LAE cases have been studied. An inter-comparison of the first three harmonics during these events has been made so as to understand the basic reason causing the occurrence of these types of events. It has been observed that the phase of diurnal anisotropy shifts towards earlier hours for HAEs; similarly, it shifts towards earlier hour as compared to 18-Hr direction for LAEs. For semi-diurnal anisotropy phase remains statistically the same for both HAE as well as for LAE. Further in case of tri-diurnal anisotropy phase is evenly distributed for both types of events. The interplanetary magnetic field (IMF) and solar wind plasma (SWP) parameters during these events are also investigated. It has also been observed that HAE/LAEs are weakly dependent on solar wind velocity.