Cascade-Exciton Model Analysis of Nucleon-Induced Fission Cross Sections of Lead and Bismuth at Energies from 45 to 500 MeV

An extended version of the Cascade-Exciton Model (CEM) of nuclear reactions is applied to analyze nucleon-induced fission cross sections for Bi-209 and Pb-208 nuclei in the 45-500 MeV energy range. The available data on linear momentum transfer are analyzed as well. The results are compared with analytical approximations resulting from a comparative critical analysis of all available experimental data. Systematic discrepancies between calculations and experimental data are revealed. A modification of the CEM is proposed, which significantly improves the model predictions for projectile energies above 100 MeV.Comment: 38 pages, 16 figures, 7 tables, LaTeX, submitted to Nucl. Sci. En

Detailed Geant4 simulations of the ANITA and ANITA-CUP neutron facilities

Simulations of the ANITA spallation neutron source at The Svedberg Laboratory (TSL) are described. Neutron radiation calculations show close agreement with measurements at both standard and close user positions. Gamma radiation characteristics are also predicted

Разработка математических моделей. Использование методов теории информации при аппроксимации многомерных плотностей распределения наблюдений

Under the decisions of the huge quantity of problems in the different scientifical and technical branchs the used signals are described by models, which must be adequate to real signals. The well-known models are based on the Gauss random processes. However in the real information systems the signals have non-gaussian character and they have to be described by the non-gaussian distributions of momentary values. In this work it is given the analysis of the wide-spread information quantity measures, introduced by Fisher, Shennon, Kulback and Liebrer. Under the mathematical hypothesises verification the similarity criterion was used as the most informative. The Kulback results have the limitations and shortcomings, consist in the single-measure quantities usage and the non-evident presentation of the searched density distribution, what produces the difficulties under these results analysis and usage. The work includes the investigations, carried out on the base of the Lagrange factors methods and eliminate by some degree the above mentioned limitations and shortcomings. The known results for the single-measure distributions were generalized and thus the new results were obtained in relation to the multi-measure case.При решении огромного количества задач в различных областях науки и техники используются сигналы, описываемые с помощью моделей, к которым предъявляются требования адекватности реальным сигналам. Широко известны модели на основе гауссовских случайных процессов. Однако, в реальных информационных системах сигналы носят негауссовский характер и, потому, должны описываться негауссовскими законами распределения мгновенных значений. В настоящей работе дан анализ наиболее распространенных мер количества информации, введенных Фишером, Шенноном, Кульбаком и Лейбрером. При проверке математических гипотез применено отношение правдоподобия как более информативное. Результаты, полученные Кульбаком, имеют ограничения и недостатки, заключающиеся в том, что в исследованиях использовались одномерные величины, а искомая плотность распределения представлена в неявном виде, что затрудняет анализ и использование этих результатов. В работе проведены исследования, на основе метода множителей Лагранжа, в определенной степени устраняющие указанные ограничения и недостатки. Путем обобщения известных результатов для одномерных распределений получены новые результаты, относящиеся к многомерному случаю

Magnetic Properties of the low dimensional spin system (VO)2_2P2_2O7_{7}: ESR and susceptibility

Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)$_2$P$_2$O$_{7}$. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating spin chains. We determine $J$=51 K and $\delta$=0.2. Furthermore we find a spin gap of $\approx 6$meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen below 300 K.Comment: 7 pages, REVTEX, 7 figure

Anisotropic Exchange in LiCuVO4_4 probed by ESR

We investigated the paramagnetic resonance in single crystals of LiCuVO$_4$ with special attention to the angular variation of the absorption spectrum. To explain the large resonance linewidth of the order of 1 kOe, we analyzed the anisotropic exchange interaction in the chains of edge-sharing CuO$_6$ octahedra, taking into account the ring-exchange geometry of the nearest-neighbor coupling via two symmetric rectangular Cu-O bonds. The exchange parameters, which can be estimated from theoretical considerations, nicely agree with the parameters obtained from the angular dependence of the linewidth. The anisotropy of this magnetic ring exchange is found to be much larger than it is usually expected from conventional estimations which neglect the bonding geometry. Hence, the data yield the evidence that in copper oxides with edge-sharing structures the role of the orbital degrees of freedom is strongly enhanced. These findings establish LiCuVO$_4$ as one-dimensional compound at high temperatures. PACS: 76.30.-v, 76.30.Fc, 75.30.EtComment: 18 pages, 6 figure

On Dissipation Rate of Ocean Waves due to White Capping

We calculate the rate of ocean waves energy dissipation due to whitecapping by numerical simulation of deterministic phase resolving model for dynamics of ocean surface. Two independent numerical experiments are performed. First, we solve the $3D$ Hamiltonian equation that includes three- and four-wave interactions. This model is valid for moderate values of surface steepness only, $\mu < 0.09$. Then we solve the exact Euler equation for non-stationary potential flow of an ideal fluid with a free surface in $2D$ geometry. We use the conformal mapping of domain filled with fluid onto the lower half-plane. This model is applicable for arbitrary high levels of steepness. The results of both experiments are close. The whitecapping is the threshold process that takes place if the average steepness $\mu > \mu_{cr} \simeq 0.055$. The rate of energy dissipation grows dramatically with increasing of steepness. Comparison of our results with dissipation functions used in the operational models of wave forecasting shows that these models overestimate the rate of wave dissipation by order of magnitude for typical values of steepness.Comment: 6 pages, 2 figure