Characteristics investigation on heat transfer growth of sonochemically synthesized ZnO-DW based nanofluids inside square heat exchanger

Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...     

The effect of rapid rotation on a vertical bridgman furnace at large Rayleigh number

In quasi-steady operation, convection currents in a Bridgmandevice, used for producing a semi-conductor crystal, createinhomogeneities that may make the crystal unusable. It has oftenbeen suggested that additional forces due to rotation or magnetismmight be efficacious in reducing the segregation of the elementsof the alloy. It has been found that, over a wide range of rotationrates, there is no improvement in performance due to rotationabout the vertical axis. However, numerical results that havebeen obtained previously (Lee & Pearlstein, J. Crys. Growth240, 2002) indicate that, when effects of centrifugal buoyancyare introduced, a substantial reduction in segregation is achieved.In the work reported here, by contrast, in which we extend previouslarge-Rayleigh-number asymptotic analysis to include centrifugalbuoyancy, we find no improvement in radial segregation, butrather increasing segregation with increasing rotation rate.     

Autoxidation of terpenic aldehydes—II

The influence of steric factors on the autoxidation of aldehydes having tertiary formyl groups has been investigated. These afford nor-derivatives by loss of carbon monoxide, and carboxylic acids. Steric interactions have been shown to affect strongly the ratio between carboxylic acid and nor-derivatives and, in addition, to increase the autoxidation rate. For the first time, formation of formates from aldehydes by autoxidation conditions, has been demonstrated.     

Collective dynamics in molten potassium: an inelastic x-ray scattering study

The high-frequency collective dynamics of molten potassium has been investigated by inelastic x-ray scattering, disclosing an energy/momentum transfer region unreachable by previous inelastic neutron scattering (INS) experiments. We find that a two-step relaxation scenario, similar to that found in other liquid metals, applies to liquid potassium. In particular, we show how the sound velocity determined by INS experiments, exceeding the hydrodynamic value by approximately 30%, is the higher limit of a speedup, located in the momentum region 1 < Q < 3 nm(-1), which marks the departure from the isothermal value. We point out how this phenomenology is the consequence of a microscopic relaxation process that, in turn, can be traced back to the presence of "instantaneous" disorder, rather than to the crossover from a liquid to solidlike response.     

Two new polyhydroxylated sterols from Ruppia maritima

Two new sterols have been isolated from the aquatic plant Ruppia maritima and their structures were established as (24R) ergosta-8,22-diene-3 beta,6 beta,7 alpha-triol (1) and (24R) ergosta-8(14),22-diene-3 beta,6 beta,7 alpha-triol (2) on the basis of spectroscopic analysis.     

Reversal of Clar's Aromatic-Sextet Rule in Ultrashort Single-End-Capped [5,5] Carbon Nanotubes

The three-fold HOMO-LUMO gap oscillation, typical of finite length armchair carbon nanotubes (CNT), has a major effect on the magnetic response of ultrashort, single-end-capped [5,5] carbon nanotubes to a perturbing magnetic field parallel to the main symmetry axis. For the CNT's containing 40, 70, and 100 carbon atoms, for which 100 % of the C=C double bonds can be grouped into aromatic-sextets, i. e., fully or complete Clar networks, large paratropic (antiaromatic) global circulations around the cylindrical axis are predicted at the DFT level of calculation. Local and semi-global diatropic (aromatic) currents of strengths not larger than that of the benzene molecule are determined for a perpendicular perturbing magnetic field. CNTs of intermediate lengths do not display this enhanced antiaromatic response. The paratropic current flow clearly shows that these complete Clar networks can be viewed as stacked cycloparaphenylene belts, each providing a double annulene circuit as a consequence of the quinoidal resonance structure that results from their closure. Paradoxically, the fully aromatic Clar structure itself is responsible for the enhanced global antiaromaticity.     

Enantioselective Synthesis of Phenylpropanetriols

The four stereomer 1-(4-hydroxy-3-methoxy)-phenyl-1,2,3-propanetriols were obtained in about 30% yields starting from ferulic acid by a synthesis based on osmium catalyzed asymmetric dihydroxylation.     

Ergodic to nonergodic transition in liquids with a local order: the case of m-toluidine

The dynamic structure factor of m-toluidine has been measured by inelastic x-ray scattering in the mesoscopic Q range between 1 and 10 nm(-1), where a prepeak is revealed in the static structure factor resulting from the existence of hydrogen bonded, nanometer size clusters. Evidence is given of (i) a square-root cusp in the nonergodicity factor and of (ii) critical nonergodicity parameters which oscillate in phase with the static structure factor. These results demonstrate that local order in a liquid can coexist with the signatures of the ergodic to nonergodic transition predicted by the mode coupling theory for simple, dense liquids.     

Correlation-induced double-plasmon excitation in simple metals studied by inelastic x-ray scattering

We report a new type of peaklike structure observed in the tail of the dynamic structure factor of simple metals, measured by inelastic x-ray scattering. Based on the momentum-transfer dependence of the energy position and the intensity of this structure, it has been unambiguously attributed to intrinsic plasmon-plasmon excitations, an electronic correlation effect that was theoretically predicted by many-body perturbation theory of the homogeneous-electron-gas model beyond the random-phase approximation. This signature appears to be largely unaffected by electron-ion interaction effects. Thus a structure that is primarily caused by correlation effects in the electron gas has been found experimentally in the dynamic structure factor of simple metals.