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.     

Crystallographic parameters in α-UF5 and U2F9 by multiphase refinement of high-resolution neutron powder data

The crystal structures of α-UF₅ and U₂F₉ were refined with high-resolution neutron powder diffraction data from an $\text{α-}\text{UF}{}_5\text{U}{}_2\text{F}{}_9$ mixture. Refinement was achieved by a multiphase Rietveld profile refinement technique. The results are compared with previous X-ray and neutron powder studies.     

Chemical shielding anisotropy of 13C and 15N in acetonitrile

High resolution ¹³C and ¹⁵N NMR spectra have been obtained for powdered CH₃CN. The presence of resolved dipolar structure in the ¹³C spectra permits the conclusion that the symmetry axis of the ¹³C shielding tensor lies along the CN bond direction.     

The structures of fluorides. XV. Neutron diffraction-kubic harmonic profile analysis of the body-centered cubic phase of sulfur hexafluoride at 193°K

Sulfur hexafluoride has a body-centered cubic phase (a = 5.915(3) Å) between its melting point (222.4°K) and 93°K, below which a lower symmetry phase exists. NMR studies show that in both phases there is rapid reorientation of the sulfur hexafluoride molecules. From a neutron diffraction pattern collected at 193°K with λ = 1.086 Å, the data were not satisfied by a model with a spherically symmetrical fluorine density nor by a refinement with conventional ellipsoidal-shaped atoms. The latter gave systematically low S-F distances and abnormally high β_ij thermal factors. Good agreement was obtained by a combination of Kubic Harmonics with full-matrix least-squares analysis of the neutron profile pattern. The refinement was made with one variable Kubic Harmonic coefficient a₂ = 5.94(11), with $\text{R}{}_{\mathrm{w}}\text{= {}\text{∑ w[y}{}_0\text{? (}\text{1}\text{s}\text{)y}{}_{\mathrm{c}}\text{]}{}^2\text{∑ wy}{}_0{}^2\text{}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.079}$ and $\text{χ}{}^2\text{=}\text{∑ w[y}{}_0\text{? (}\text{1}\text{s}\text{)y}{}_{\mathrm{c}}\text{]}{}^2\text{(NO-NV)}\text{= = 1.2}$. Only four least-squares variables were required with 225 observations in the range of one or more hkl reflections to 2θ = 58.3°. AS-F distance of 1.542(4) Å, obtained from the neutron diffraction data, is in good agreement with the reported value of 1.564(10) Å found from electron diffraction measurements of the vapor. The disordered fluorine distribution has broad maxima on the cell edges similar to those found in the plastic cubic phases of MoF₆ and WF₆.     

Collision-Induced dissociations of deprotonated peptides. Dipeptides containing aspartic or glutamic acids

Deprotonated dipeptides, on collisional activation, fragment by the characteristic process NH₂CH(R¹) CONHCH(R²)CO₂^? → NH₂^?C(R¹)CONHCH(R²)CO₂H → ^?NHCH(R²)CO₂H + NH₂C(R¹)?C?O, when R¹ and R² = H or alkyl. However, when one of the constituent amino acids is either aspartic acid or glutamic acid, the standard cleavage becomes minor in comparison with fragmentation through the α-side-chain of Asp or Glu. For example, [Asp-Leu - H]^? and [Leu-Asp - H]^? both fragment principally by loss of water, a fragmentation not normally noted for peptides. In addition, [Leu-Asp - H]^? loses CO₂ and also forms HO₂CCH?CHCO₂^?˙. These fragmentations establish that Asp is the C-terminal amino acid. In contrast, isomeric Glu dipeptides, e.g. [Glu-Ala - H]^? and [Ala-Glu - H]^? undergo similar fragmentation, both competitively losing H₂O and CO₂. Both spectra also contain a product ion at m/z 128, identified as the pyroglutamate anion. Product ion and deuterium-labelling studies have been used in an attempt to elucidate the complex fragmentation mechanisms in these systems.     

Controlled hydrothermal growth of ZnO nanostructures by sequestering the Zn metal ions with the chelating agent EDTA

In the present work, a controlled growth of ZnO nanostructures by manipulating Zn metal ion concentration by the chelating action of ethylene diaminetetra acetic acid in hydrothermal method is studied. EDTA produces metal–chelate complex by the formation of bidentate ligand with Zn²⁺ in the solution and diminishes the reactivity of Zn metal cations. Concentration of EDTA in the mother solution was varied in different ranges like 3, 5 and 10 mM while retaining the zinc metal salt and the NaOH concentration the same. Three different morphologies of wurtzite structured ZnO nanostructures such as nanorods-bunch, separate/discrete uniformly sized hexagonal nanorods and tapered flower petals like shapes are achieved by 3, 5 and 10 mM strengths of EDTA, respectively. The medium concentration 5 mM of EDTA is found to have moderate control over producing ZnO nanostructures of uniform diameter and a high aspect (length to diameter) ratio. An array of vertically aligned free standing ZnO nanorods with uniform spacing is successfully achieved by the addition of 5 mM of EDTA in the mother solution and the same is studied for its fluorescence property at an excitation of 325 nm and it has exhibited a characteristic UV emission of ZnO around 383 nm.     

Phosphine Ligands in the Palladium‐Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP NMR Spectroscopic Study

Novel cis‐1,2‐bis(di‐tert‐butyl‐phosphinomethyl) carbocyclic ligands 6 – 9 have been prepared and the corresponding palladium complexes [Pd(O₃SCH₃)(L‐L)][O₃SCH₃] (L‐ L=diphosphine) 32 – 35 synthesised and characterised by NMR spectroscopy and X‐ray diffraction. These diphosphine ligands give very active catalysts for the palladium‐catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9 , containing four‐ and six‐membered ring backbones giving more active systems. The acid used as co‐catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex [Pd(O₃SCH₃)(L‐ L)][O₃SCH₃], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism.