Heat Transfer and Crisis Phenomena at the Film Flows of Freon Mixture over Vertical Structured Surfaces

Results on experimental investigation of heat transfer in the liquid films dichlorofluoromethane R21 and dichlorotetrafluoroethane R114 Freon mixture over the vertical tubes are presented. We have studied the film flow over the outer surface of tubes with 50-mm diameter and different configurations: smooth surface, horizontal ribs, and diamond-shape knurling. Heat transfer coefficients were measured under the conditions of evaporation and nucleate boiling together with wave characteristics of the falling film, binary mixture composition, and critical heat fluxes corresponding to dry spots formation. The film Reynolds number at the inlet to the test section was varied from 15 to 250. At evaporation regime the heat transfer coefficient for a smooth surface decreases classically with an increase of Reynolds number. Dependence of heat transfer coefficient on irrigation density for the surface with diamond-shape knurling is similar to dependence for the smooth surface with insignificant heat transfer intensification. The heat transfer coefficients at nucleate boiling for the studied structured surfaces are close to those obtained for the smooth tube. Development of critical phenomena is determined by regularities of dry spots formation typical for evaporation of the wavy liquid film.     

Bionanoelectronics: Bionanoelectronics (Adv. Mater. 7/2011)

Every cell in a living organisms performs a complex array of functions using a vast arsenal of proteins, ion channels, pumps, motors, signaling molecules, and cargo carriers. With all the progress that humankind has made to date in the development of sophisticated machinery and computing capabilities, understanding and communicating with living systems on that level of complexity lags behind. A breakthrough in these capabilities could only come if a way is found to integrate biological components into artificial devices. The central obstacle for this vision of bionanoelectronics is the absence of a versatile interface that facilitates two‐way communication between biological and electronic structures. 1D nanomaterials, such as nanotubes and nanowires, open up the possibility of constructing tight interfaces that could enable such bidirectional flow of information. This report discusses the overall progress in building such interfaces on the level of individual proteins and whole cells and focuses on the latest efforts to create device platforms that integrate membrane proteins, channels, and pumps with nanowire bioelectronics.     

Investigation of bulk metallic glass structure by means of electron irradiation

The sensitivity of radiation effects on structural features in metallic glasses (MG) provides a way of investigating the structure and structural defects of MG through the studies of accumulation and relaxation processes of radiation damages in the glasses. In particular, it is a way to verify the validity of models proposed for the MG structure. Currently, there are two theoretical structural models of MG, based on completely different concepts. On the one hand, the model of random closely packed spheres + free volume approach is based on the idea of “the ultimate disorder”. On the other hand, in the polycluster model the idea of altering and distorted short-range order is used. Each of the models implies fairly different kinds of primary radiation damages, relaxation kinetics, and other properties. We have studied the accumulation and recovery kinetics of radiation defects in ZrTiCuNiBe and ZrTiCuNiAl bulk metallic glasses irradiated with 2.5 MeV electrons at T ～ 80 K. Electrical resistance measurements of the irradiated samples were performed. Dose dependences at ～80 K and the recovery spectrum of irradiation-induced electrical resistance in the 85–300 K temperature range were obtained. The data suggest that the point defects are stable in the metallic glasses, and the defect mobility is a thermally activated process. The results obtained are evidently in accord with the polycluster model of the MG structure.     

Solid-state V NMR and its potentiality in investigation of vanadia systems with paramagnetic centres

In this article we will discuss the potentiality of solid-state ⁵¹V NMR technique to characterize heterogeneous catalysts containing paramagnetic cations located on the surface or incorporated in the bulk of heterogeneous catalysts. ⁵¹V NMR data for a number of 3d and rare earth vanadates, where paramagnetic effects are caused by the presence of paramagnetic cations, are considered. We also summarize results available for vanadium bronzes, where some vanadium is in a paramagnetic V⁴⁺ state, and for some vanadium compounds, where closely spaced paramagnetic centers form diamagnetic pairs. The comprehensive ⁵¹V chemical shift scale (database) for paramagnetic solids was compiled.     

In-vessel corium catcher of a nuclear reactor

A new concept of an in-vessel corium melt catcher is proposed. The lower part of an elongated reactor vessel, which is filled with a sacrificial material of a proper composition, porosity, and arrangement, is used as such a catcher. The concept accounts of the scientific and design experience with the development of the ex-vessel corium catcher for the Tyan’van NPP with VVER-1000 reactors.     

Strong antimicrobial coatings: single-walled carbon nanotubes armored with biopolymers

Large scale biomimetic single-walled carbon nanotube (SWNT) coatings with significant antimicrobial activity, high Young's Modulus, and controlled morphology were fabricated using layer-by-layer assembly. Thickness was controlled within 1.6 nm and SWNT orientation was controlled using a directed air stream. This unique blend of multifunctionality and vertical and lateral control of a bottom-up assembly process is a significant advancement in developing macroscale assemblies with the combined attributes of SWNTs and natural materials.     

Figure of merit enhancement in thermoelectric materials based on γ-Ln0.8Yb0.2S1.5-y (Ln = Gd,Dy) solid solutions

Here we report the study temperature dependencies of the Seebeck coefficient, the electrical resistivity (T = 300–750 K), the total thermal conductivity (T = 300–973 K), and the thermoelectric figure of merit (T = 300–750 K) of ceramic samples of γ-Ln_0.8Yb_0.2S_1.5-y (Ln = Gd, Dy) solid solutions. It was found that Yb³⁺ ions in γ-Ln_0.8Yb_0.2S_1.5-y act as the promoters of higher crystallite nucleation rate during the formation of solid solutions. This results in the sample dispersion increase and the formation of the additional phonon scattering centers (dislocations and strain stresses along the crystallites semi-coherent boundaries). These features of the real structure determined the low value of thermal conductivity of γ-Ln_0.8Yb_0.2S_1.5-y solid solutions. The lowest electrical resistivity 20 μΩ m at 750 K and the thermal conductivity 0.58 W/m K at 973 K, the highest Seebeck coefficient 125 μV/K at 700 K and the maximum thermoelectric efficiency, ZT = 0.60 (at 770 K) were obtained for γ-Dy_0.8Yb_0.2S_1.5-y.     

Formation, stability, and mobility of one-dimensional lipid bilayers on polysilicon nanowires

Curved lipid membranes are ubiquitous in living systems and play an important role in many biological processes. To understand how curvature and lipid composition affect membrane formation and fluidity, we have assembled and studied mixed 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) supported lipid bilayers on amorphous silicon nanowires grown around carbon nanotube cores with controlled wire diameters ranging from 20 to 200 nm. We found that lipid vesicles fused onto nanowire substrates and formed continuous bilayers for all DOPC-DOPE mixtures tested (with the DOPE content of up to 30%). Our measurements demonstrate that nanowire-supported bilayers are mobile, exhibit fast recovery after photobleaching, and have a low concentration of defects. Lipid diffusion coefficients in these high-curvature tubular membranes are comparable to the values reported for flat supported bilayers and increase slightly with decreasing nanowire diameter. A free space diffusion model adequately describes the effect of bilayer curvature on the lipid mobility for nanowire substrates with diameters greater than 50 nm, but shows significant deviations from the experimental values for smaller diameter nanowires.     

Electromodulated reflectance study of self-assembled Ge/Si quantum dots

We perform an electroreflectance spectroscopy of Ge/Si self-assembled quantum dots in the near-infrared and in the mid-infrared spectral range. Up to three optical transitions are observed. The low-energy resonance is proposed to correspond to a band-to-continuum hole transition in the Ge valence band. The other two modulation signals are attributed to the spatially direct transitions between the electrons confined in the L and Δ(4) valleys of the Ge conduction band, and the localized hole states at the Γ point.     

Luminescence of colloidal CdSe/ZnS nanoparticles: high sensitivity to solvent phase transitions

We investigate nanosecond photoluminescence processes in colloidal core/shell CdSe/ZnS nanoparticles dissolved in water and found strong sensitivity of luminescence to the solvent state. Several pronounced changes have been observed in the narrow temperature interval near the water melting point. First of all, the luminescence intensity substantially (approximately 50%) increases near the transition. In a large temperature scale, the energy peak of the photoluminescence decreases with temperature due to temperature dependence of the energy gap. Near the melting point, the peak shows N-type dependence with the maximal changes of approximately 30 meV. The line width increases with temperature and also shows N-type dependence near the melting point. The observed effects are associated with the reconstruction of ligands near the ice/water phase transition.