5,127 research outputs found
Helicity of convective flows from localized heat source in a rotating layer
Experimental and numerical study of the steady-state cyclonic vortex from
isolated heat source in a rotating fluid layer is described. The structure of
laboratory cyclonic vortex is similar to the typical structure of tropical
cyclones from observational data and numerical modelling including secondary
flows in the boundary layer. Differential characteristics of the flow were
studied by numerical simulation using CFD software FlowVision. Helicity
distribution in rotating fluid layer with localized heat source was analysed.
Two mechanisms which play role in helicity generation are found. The first one
is the strong correlation of cyclonic vortex and intensive upward motion in the
central part of the vessel. The second one is due to large gradients of
velocity on the periphery. The integral helicity in the considered case is
substantial and its relative level is high
Optical spectra, crystal-field parameters, and magnetic susceptibility of the new multiferroic NdFe3(BO3)4
We report high-resolution optical absorption spectra for NdFe3(BO3)4 trigonal
single crystal which is known to exhibit a giant magnetoelectric effect below
the temperature of magnetic ordering TN = 33 K. The analysis of the
temperature-dependent polarized spectra reveals the energies and, in some
cases, symmetries and exchange splittings of Nd3+ 84 Kramers doublets. We
perform crystal-field calculations starting from the exchange-charge model,
obtain a set of six real crystal-field parameters, and calculate wave functions
and magnetic g-factors. In particular, the values g(perpendicular) = 2.385,
g(parallel) = 1.376 were found for the Nd3+ ground-state doublet. We obtain
Bloc=7.88 T and |JFN|= 0.48 K for the values of the local effective magnetic
field at liquid helium temperatures at the Nd3+ site and the Nd - Fe exchange
integral, respectively, using the experimentally measured Nd3+ ground-state
splitting of 8.8 cm-1. To check reliability of our set of crystal field
parameters we model the magnetic susceptibility data from literature. A dimer
containing two nearest-neighbor iron ions in the spiral chain is considered to
partly account for quasi-one-dimensional properties of iron borates, and then
the mean-field approximation is used. The results of calculations with the
exchange parameters for Fe3+ ions Jnn = -6.25 K (intra-chain interactions) and
Jnnn = -1.92 K (inter-chain interactions) obtained from fitting agree well with
the experimental data.Comment: 13 pages, 8 figures, 2 table
Получение пористых полимерных композитов
В данной работе мы экспериментально убедились в целесообразности использования метода прессования форм из композита с примесью NaCl с последующим удалением соли для получения пористой структуры композитов
Effect of culture conditions on viability of mouse and rat embryos developed in vitro
Currently in vitro culture of mouse preimplantation embryos has become a very important technique to investigate different mechanisms of early embryogenesis. However, there is a big difference in the preimplantation development between mammalian species. Despite close relatedness to mice, in vitro cultivation of rat preimplantation embryos is still delicate and needs further investigation and optimizations. In this study we have compared the in vitro developmental potential of mouse and rat embryos cultured at different culture conditions in parallel experiments. Interestingly, mouse zygotes developed in vitro until blastocyst stage even in inadequate medium without any phosphates and with low osmolarity which was formulated especially for cultivation of rat embryos. Rat parthenotes and zygotes developed in M16 medium formulated for mouse embryos only till 2-cell stage and further development is blocked completely at this stage. Moreover, developmental ability of rat embryos in vitro was significantly lower in comparison with mouse even in special rat mR1ECM medium. Mouse and rat embryos at 2-cell stage obtained in vivo developed until blastocyst stages significantly more efficiently compared to zygotes. Culture of mouse zygotes in glass capillaries resulted in a significantly higher rate of morula and blastocyst development compared with dishes. The Well-of-the-Well system resulted in a significant improvement when compared with dishes for the culture of rat zygotes only until morula stage. Reduced oxygen tension increased the developmental rate of rat but not mouse zygotes until blastocyst stage. This study demonstrates that development of early preimplantation embryos is altered by different culture conditions and show strong differences even between two related species such as mice and rats. Therefore, for understanding the fundamental mechanisms of early mammalian development it is very important to use embryos of various species
Mathematical modeling of three-layer beam hydroelastic oscillations
The problem of hydroelastic oscillations of three-layer beam interacting with viscous liquid layer is set up and analytically solved. The problem presents the equation system of a three-layer beam and Navier-Stokes equations. The following boundary conditions are chosen: the no-slip conditions, the conditions for pressure at the edges, the simply supported edges conditions. The problem is solved for the steady-state harmonic regime. The frequency dependent distribution functions of the beam deflection are constructed. The given function allows investigating the resonance hydroelastic oscillations of a three-layer beam, as well as its deflected mode
- …