Numerical modeling of large elastoplastic strains in terms of principal stretches. II. Physical relations,calculation algorithm

The constitutive relations and plastic flow rule are derived from the thermodynamics equations. The known procedures of determining the plastic strain rate value are described. A calculation algorithm is presented that is based on the incremental loading, linearization of the virtual power equation and the projection method. A numerical example is presented.     

Intensification of heat exchange on the convex surface of an annular channel with continuous flow swirling

In this paper, the results of an experimental study concerning average heat transfer in an annular channel with flow swirling by an endless screw and spherical grooves on the convex surface are presented. Also analyzed is the heat and hydraulic efficiency of grooves application under conditions being considered.     

Lithium Depletion in the Sun: A Study of Mixing Based on Hydrodynamical Simulations

Based on radiation hydrodynamics modeling of stellar convection zones, a diffusion scheme has been devised describing the downward penetration of convective motions beyond the Schwarzschild boundary (overshoot) into the radiative interior. This scheme of exponential diffusive overshoot has already been successfully applied to AGB stars. Here we present an application to the Sun in order to determine the time scale and depth extent of this additional mixing, i.e. diffusive overshoot at the base of the convective envelope. We calculated the associated destruction of lithium during the evolution towards and on the main-sequence. We found that the slow-mixing processes induced by the diffusive overshoot may lead to a substantial depletion of lithium during the Sun's main-sequence evolution. This revised version was published online in June 2006 with corrections to the Cover Date.     

High temperature alters the growth reaction of Pottia protonemata.

Under gravistimulation, dark-grown protonemata of Pottia intermedia revealed negative gravitropism with a growth rate of approximately 28 μm·h⁻¹ at room temperature (20 °C). In 7 days, the protonema formed a bundle of vertically oriented filaments. At an elevated temperature (30 °C), bundles of vertically growing filaments were also formed. However, both filament growth rate and amplitude of the gravicurvature were reduced. Red light (RL) irradiation induced a positive phototropism of most apical protonemal cells at 20 °C. In a following period of darkness, approximately two-thirds of such cells began to grow upward again, recovering their negative gravitropism. RL irradiation at the elevated temperature caused a partial increase in the number of protonemal cells with negative phototropism, but the protonemata did not exhibit negative gravitropism after transfer to darkness. The negative gravitropic reaction was renewed only when protonemata were placed at 20 °C. A dramatic decrease in starch amount in protonemal apical cells, which are sensitive to both gravity and light, occurred at the higher temperature. Such a decrease may be one of the reasons for the inhibition of the protonemal gravireaction at the higher temperature. The observation has a bearing on the starch-statolith theory.     

Principles of Invariance in Radiative Transfer

We have reviewed the principle of invariance, its applications and its usefulness for obtaining the radiation field in semi-infinite and finite atmospheres. Various laws of scattering in dispersive media and the consequent radiation field are studied. The H-functions and X- and Y-functions in semi-infinite and finite media respectively are derived in a few cases. The Discrete Space Theory (DST) which is a general form of the Principle of Invariance is described. The method of addition of layers with general properties, is shown to describe all the properties of multiple scattering. A few examples of the application of DST such as polarization, line formation in expanding stellar atmospheres, etc., and a numerical analysis of DST are presented. Other developments in the theory of radiative transfer are briefly described. This revised version was published online in June 2006 with corrections to the Cover Date.     

Multiparametric importance sampling for simulation of radar systems

The performances of the importance sampling (IS) techniques are improved by using multiparametric distortions of the input random processes. The analysis of different constant false-alarm rate (CFAR) algorithms confirms the usefulness of this method. The potential of this new approach is fully exploited if optimization techniques are used to obtain the optimum distortions and to avoid bias in the estimates     

The importance of charged aerosols in the polar mesosphere in connection with Noctilucent Clouds and Polar Mesosphere Summer Echoes

A number of campaigns have been conducted in order to study Polar Mesosphere Summer Echos (PMSE) and Noctilucent Clouds (NLC) in the period 1991–1994. Several sounding rockets have been launched through these layers with measurements being performed on upleg as well as downleg. These include measurements of positive ions and electrons in both ram and wake positions, as well as measurements of charged aerosols in ram on upleg. In this paper we will review these measurements and make a preliminary classification of the data based upon the presence of PMSE and/or NLC. One of the mechanisms responsible for PMSE is the presence of neutral air turbulence in combination with a high Schmidt number. We will briefly discuss this type of echo using in situ rocket data. Differences and similarities of PMSE and NLC as observed both in the Arctic and the Antarctic will be discussed. Observations show that especially PMSE are much more frequent in the Arctic. This may be due to a difference in the water vapour content or the temperature at mesopause heights. Lack of data in the Antarctic makes it difficult to decide which of these two factors are the most important. More measurements, especially co-ordinated in situ and ground-based lidar and radar measurements, are needed to discuss the Arctic and Antarctic similarities and differences in further detail.