The pin power distribution in theVVER-1000 mock-up on the LR-0 research reactor

The pin power density distribution in reactor is an important quantity, necessary for the adequate assessment of fuel conditions and of core structures and pressure vessel radiation embrittlement as well.The paper shows the detailed comparison of calculated and experimentally determined pin by pin power distribution. To verify the reliability of measured data used for comparison with calculated data, the symmetrically located pins were measured. The calculations have been done with deterministic and Monte Carlo approach. The effect of different data libraries used for calculations are discussed as well.     

Synthesis, structural and magnetic properties of nanostructured Ca0.9Gd0.1MnO3 obtained by modified glycine nitrate procedure (MGNP)

Ca_0.9Gd_0.1MnO₃ nanopowders with perovskite type crystal structure were synthesized by modified glycine nitrate procedure. Nanopowders were prepared by combining glycine with metal nitrates and/or metal acetates in their appropriate stoichiometric ratios. Modification of the procedure was performed by partial replacement of nitrates by acetates, in order to control the burn-up reaction. Obtained Ca_0.9Gd_0.1MnO₃ powders were calcinated in the temperature interval from 850 °C to 950 °C for 10 min. Properties such as phase evolution, lattice parameters, chemical composition and magnetic properties were monitored by DTA, X-ray diffraction, SEM/EDS and magnetic measurements. Magnetic measurements performed at the sample with the smallest crystallite size showed that a 10% of Gd³⁺ substituted Ca²⁺ ions changes antiferromagnetic properties of CaMnO₃ by the introduction of ferromagnetic interaction due to a double exchange between Mn³⁺ and Mn⁴⁺ ions. Presence of competing interactions and their randomness lead to a formation of a spin glass state below Neel temperature T_N = 110 K. From the high temperature magnetic susceptibility measurements effective magnetic moment of manganese ions is determined which lies between the values for Mn³⁺ and Mn⁴⁺ ions.     

Shear strength and wettability of active Sn3.5Ag4Ti(Ce,Ga) solder on Al2O3 ceramics

The work deals with the study of wettability of Sn3.5Ag4Ti(Ce,Ga) solder on ceramic material of Al₂O₃. The Sn3.5Ag4Ti(Ce,Ga) solder is used for ultrasonic soldering of metallic and ceramic materials. The microstructure of Sn3.5Ag4Ti(Ce,Ga) solder consists of a tin matrix, where non-uniformly distributed constituents of partially dissolved Ti and uniformly distributed fine needles of Ag–Sn phase were observed. The solder was of heterogeneous composition. X-ray diffraction analysis has revealed the presence of following phases: Ag₃Sn, Ti₆Sn₅, Ti₃Sn. For determination of melting point, the Differential scanning calorimetry analysis (DSC) was performed. Wettability of Sn3.5Ag4Ti(Ce,Ga) solder was determined at temperatures 800, 850 and 900 °C in dependence on wetting time. The best wettability of solder Θ = 46° was achieved at 850 °C/43 min. The experiments with high-temperature activation were performed in vacuum of 10^?4 Pa. On the basis of experience attained by measurement of contact angle, the soldered joints of Al₂O₃/Al₂O₃ and Al₂O₃/metal were fabricated in conditions of high-temperature activation in vacuum at temperature 850 °C/10 min. For comparison, also the joints fabricated in the conditions of ultrasonic activation in the air at temperature 280 °C/1 min were applied. The shear strength of joints of Al₂O₃/Al₂O₃ and Al₂O₃/metal fabricated with Sn3.5Ag4Ti(Ce,Ga) solder varied from 17 to 35 MPa. The shear strength of joints fabricated in vacuum is slightly higher than in the case of joints fabricated by use of power ultrasound.     

Two‐fluid model with interface sharpening

Two‐fluid models are applicable for simulations of all types of two‐phase flows ranging from separated flows with large characteristic interfacial length scales to highly dispersed flows with very small characteristic interfacial length scales. The main drawback of the two‐fluid model, when used for simulations of stratified flows, is the numerical diffusion of the interface. Stratified flows can be easily and more accurately solved with interface tracking methods; however, these methods are limited to the flows, that do not develop into dispersed types of flows. The present paper describes a new approach, where the advantage of the two‐fluid model is combined with the conservative level set method for interface tracking. The advection step of the volume fraction transport equation is followed by the interface sharpening, which preserves the thickness of the interface during the simulation. The proposed two‐fluid model with interface sharpening was found to be more accurate than the existing two‐fluid models. The mixed flow with both: stratified and dispersed flow, is simulated with the coupled model in this paper. In the coupled model, the dispersed two‐fluid model and two‐fluid model with interface sharpening are used locally, depending on the parameter which recognizes the flow regime. Copyright © 2010 John Wiley & Sons, Ltd.     

Force‐Driven Single‐Atom Manipulation on a Low‐Reactive Si Surface for Tip Sharpening

A single atomic manipulation on the delta‐doped B:Si(111)‐()R30° surface using a low temperature dynamic atomic force microscopy based on the Kolibri sensor is investigated. Through a controlled vertical displacement of the probe, a single Si adatom in order to open a vacancy is removed. It is shown that this process is completely reversible, by accurately placing a Si atom back into the vacancy site. In addition, density functional theory simulations are carried out to understand the underlying mechanism of the atomic manipulation in detail. This process also rearranges the atoms at the tip apex, which can be effectively sharpened in this way. Such sharper tips allow for a deeper look into the Si adatom vacancy site. Namely, high‐resolution images of the vacancy showing subsurface Si dangling bond triplets, which surround the substitutional B dopant atom in the first bilayer, are achieved.     

On the solid state heat transport phenomena measurement

The paper deals with theoretical and experimental aspects of lumped capacitance model (LCM) application for the study of heat transport in different materials. Patented construction of the measuring chamber together with special software the fundamental features of which are presented here allows evaluating thermal conductivity k, specific heat capacity c_p and thermal diffusivity α. Obtained results are in relatively very good agreement with those obtained from independent measurement or table values.