Experimental verification of heat transfer coefficient for nucleate boiling at sub-atmospheric pressure and small heat fluxes

In this paper we study the influence of sub-atmospheric pressure on nucleate boiling. Sixteen correlations for pool boiling available in literature are gathered and evaluated. Analysis is performed in the pressure range 1–10 kPa and for heat flux densities 10–45 kW/m². Superheats are set between 6.2 and 28.7 K. The results of calculations were compared with experimental values for the same parameters. The experiments were conducted using isolated glass cylinder and water boiling above the copper plate. Results show that low pressure adjust the character of boiling curve—the curve flattened and the natural convection region of boiling is shifted towards higher wall temperature superheats due to the influence of low pressure on the bubble creation and process of its departure. In result, 8 of 16 analyzed correlations were determined as completely invalid in subatmospheric conditions and the remaining set of equations was compared to experimental results. Experimentally obtained values of heat transfer coefficients are between 1 and 2 kW/m²K. With mean absolute deviation (MAD) we have found that the most accurate approximation of heat transfer coefficient is obtained using Mostinski reduced pressure correlation (0.13–0.35 MAD) and Labuntsov correlation (0.12–0.89 MAD).     

Tetra­kis(1‐eth­yl‐1H‐1,2,4‐triazole‐κN4)bis­(nitrato‐κO)copper(II) and bis­(nitrato‐κO)tetra­kis­(1‐prop­yl‐1H‐1,2,4‐triazole‐κN4)copper(II)

The copper(II) environments for tetra­kis­(1‐eth­yl‐1,2,4‐triaz­ole)­dinitratocopper(II), [Cu(NO₃)₂(C₄H₇N₃)₄], and tetrakis­(1‐prop­yl‐1,2,4‐triazole)dinitratocopper(II), [Cu(NO₃)₂(C₅H₉N₃)₄], are distorted square bipyramidal. Both structures are centrosymmetric, with the copper(II) ions located at inversion centers coordinated by four N atoms of four triazole mol­ecules and by two O atoms of two nitrate ions in an elongated octa­hedral geometry. This elongation is a result of the Jahn–Teller effect. The largest distortion is that of the N—Cu—O angles, which differ from 90° by 5.68 (10)° in the eth­yl and 5.59 (8)° in the prop­yl derivative.     

Limit theorems for random walks

We consider a random walk $S_{\tau }$ which is obtained from the simple random walk $S$ by a discrete time version of Bochner’s subordination. We prove that under certain conditions on the subordinator $\tau$ appropriately scaled random walk $S_{\tau }$ converges in the Skorohod space to the symmetric $\alpha$-stable process $B^{\alpha }$. We also prove asymptotic formula for the transition function of $S_{\tau }$ similar to the Pólya’s asymptotic formula for $B^{\alpha }$.     

A study of the interaction between perylene and the TiO2(1 1 0)-(1 × 1) surface-based on XPS, UPS and NEXAFS measurements

The interaction between a semi-large aromatic hydrocarbon compound (perylene) and the TiO₂(1 1 0)-(1 × 1) surface under ultra high vacuum conditions has been probed by X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and near-edge X-ray absorption fine structure (NEXAFS) methods. UPS measurements of the adsorbate system have been compared with an experimental UPS spectrum of perylene in the gas phase and a calculated spectrum obtained by means of density functional theory (DFT) methods. NEXAFS results of perylene molecules adsorbed on TiO₂(1 1 0)-(1 × 1) were compared with data from an α-phase perylene single crystal. A novel analysis of the valence data has been employed to show that no strong chemical interaction takes place between perylene and the TiO₂(1 1 0)-(1 × 1) surface. Furthermore, angle-dependent NEXAFS measurements and the growth curve results suggest that the perylene molecules are oriented flat down onto the TiO₂ substrate due to weak van der Waals interactions.     

Local buckling design problem for topology optimized truss girders

The paper presents practical applying of structural topology optimization algorithm based on the formulation of optimal design with compliance minimization. Problem was presented and discussed for several 2D examples. Analysis of local buckling problem was made for various results obtained by the algorithm and approximated into the truss structures. Real bridge load was considered for girders. Topology based optimal girders were compared to typical truss structure. Relation between rods thicknesses was considered. Stress level including buckling in compressed members was examined. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Internal Architecture and Adsorption Sites of Violet Lander Molecules Assembled on Native and KBr‐Passivated InSb(001) Surfaces

The adsorption of individual Violet Lander molecules self‐assembled on the c(8×2) reconstructed InSb(001) surface in its native form and on the surface passivated with one to three monolayers of KBr is investigated by means of low‐temperature scanning tunneling microscopy (STM). Preferred adsorption sites of the molecules are found on flat terraces as well as at atomic step edges. For molecules immobilized on flat terraces, several different conformations are identified from STM images acquired with submolecular resolution and are explained by the rotation of the 3,5‐di‐tert‐butylphenyl groups around σ bonds, which allows adjustment of the molecular geometry to the anisotropic substrate structure. Formation of ordered molecular chains is found at steps running along substrate reconstruction rows, whereas at the steps oriented perpendicularly no intermolecular ordering is recorded. It is also shown that the molecules deposited at two or more monolayers of the epitaxial KBr spacer do not have any stable adsorption sites recorded with STM. Prospects for the manipulation of single molecules by using the STM tip on highly anisotropic substrates are also explored, and demonstrate the feasibility of controlled lateral displacement in all directions.     

Ionic-like behavior of oppositely charged nanoparticles

Mixtures of oppositely charged nanoparticles of various sizes and charge ratios precipitate only at the point of electroneutrality. This phenomenon-specific to the nanoscale and reminiscent of threshold precipitation of ions-is a consequence of the formation of core-and-shell nanoparticle aggregates, in which the shells are composed of like-charged particles and are stabilized by efficient electrostatic screening.     

Synthesis of quinolines via Friedländer reaction catalyzed by CuBTC metal-organic-framework

Friedl?nder condensation between 2-aminoaryl ketones and different carbonyl compounds, catalyzed by CuBTC was investigated by a combination of various experimental techniques and by density functional theory based modelling. CuBTC exhibiting hard Lewis acid character showed highly improved catalytic activity when compared with other molecular sieves showing high concentraion of Lewis acid sites, e.g. in BEA and (Al)SBA-15. Polysubstituted quinolines were synthesized via a Friedl?nder reaction catalyzed by CuBTC under the solvent-free conditions. High concentration of active sites in CuBTC together with the concerted effect of a pair of adjacent Cu(2+) coordinatively unsaturated active sites are behind a very high quinoline yield reached within a short reaction time. Results reported here make CuBTC a promising catalyst for other Lewis acid-promoted condensations, including those leading to biologically active compounds with a particular relevance for the pharmaceutical industry. The mechanism of a catalyzed Friedl?nder reaction investigated computationally is also reported.