Vanadium‐Catalyzed Selective Oxidation of Alcohols to Aldehydes and Ketones with tert‐Butyl Hydroperoxide

The oxidation of alcohols to aldehydes and ketones has been described using silica‐supported vanadium(IV ) oxide (V/SiO₂, 1 ) in the presence of tert‐butyl hydroperoxide in tert‐butyl alcohol at ambient temperature with quantitative yields. The procedure is simple, efficient and environmentally benign.     

Alloy Composition and Dendrite Arm Spacing in Al-Si-Cu-Mg-Fe Alloys

Six Al-Si-Cu-Mg-(Fe/Mn) alloys with two levels of each of Cu, Si, and Fe/Mn were cast in the form of quasi-directionally solidified plates. The secondary dendrite arm spacing (SDAS) was measured as a function of the distance from the chill end for each composition and related to the local cooling rate as determined by thermocouples embedded in one of the cast plates. For a given cooling rate, Si has a strong, consistently refining effect on the SDAS per unit of solute content. Cu showed its strongest refining effect at low-Si and high-Fe contents. It is argued that the scale of the SDAS is determined by a combination of five main factors: constitutional undercooling; the fraction of Al-Si eutectic; and the amount, morphology, and distribution of the various intermetallic phases. The first two factors affect the early stages of the dendrite structure and SDAS formation, whereas the ones involving intermetallics affect the dendrite-coarsening mechanisms in the post-eutectic stage. The latter ones are more sensitive to cooling rate than the ones involving solute in solution. The scales of both, SDAS and intermetallics, can be predetermined to a measurable extent through the solute content to best suit particular casting conditions.     

The coating of newtonian liquids onto a rotating roll

The liquid flux picked up by a rotating roll which is partially submerged in a Newtonian liquid, and the variation of the film thickness around the per     

Synthesis and Irreversibility of Oxygen Weight Loss in 80 K YBa2Cu4O8 Superconductor

Synthesis of YBa₂Cu₄O₈ superconductor usually requires oxygen pressure greater than 20 MPa and very long heating schedules at high temperatures. Here we report synthesis of YBa₂Cu₄O₈ superconductor by the standard solid-state reaction between the precursors BaCu₂O₃ and Y₂O₃ in the presence of alkali nitrate. NaNO₃, under ambient O₂ pressure. The resulting sample showed zero resistance at 78 K. The presence of 124 was confirmed by high-resolution X-ray diffraction studies. Irreversibility of oxygen weight loss was studied by thermogravimetric analysis and differential thermal analysis.     

Silica‐Supported Vanadium‐Catalyzed N‐Oxidation of Tertiary Amines with Aqueous Hydrogen Peroxide

A recyclable silica supported vanadium 1 catalyzes the oxidation of tertiray amines to the corresponding N‐oxides with 30% H₂O₂ in high yield.     

The coating of Newtonian liquids onto a roll rotating at low speeds

A theoretical treatment is presented for the prediction of the rate at which a liquid is entrained by a roll which is rotating partially submerged in a Newtonian liquid, and also for the prediction of the variation in the thickness of the film around the roll. The method involves the integration of the momentum equation after neglecting inertia forces in the dynamic meniscus region and the matching of the surface curvature with that derived for the static meniscus region near the liquid surface. The resulting equation allows the prediction of the relationship between a dimensionless film thickness parameter, T, and the capillary number, Ca, as a function of the radius of the roll, the withdrawal angle and the position of the roll periphery. The liquid flux on the roll can also be predicted.     

Large Scale Antenna Arrays with Increasing Antennas in Limited Physical Space

Large Scale multiple input multiple output （MIMO） systems have recently emerged as a promising technology for 5G communications. While they have been shown to offer significant performance benefits in theoretical studies, the large scale MIMO transmitters will have to be deployed in the limited physical space of today＇s base stations （BSs）. Accordingly, this paper examines effects of deploying increasing numbers of antennas in fixed physical space, by reducing the antenna spacing. We focus on the resulting performance of large-scale MIMO transmitters using low complexity closed form precoding techniques. In particular, we investigate the combined effect of reducing the distance between the antenna elements with increasing the number of elements in a fixed transmitter space. This gives rise to two contradicting phenomena： the reduction of spatial diversity due to reducing the separation between antennas and the increase in transmit diversity by increasing the number of elements. To quantify this tradeoff, we investigate densely deployed uniform antenna arrays modelled by detailed electromagnetic simulation. Our results show the somewhat surprising result that, by reducing the separations between theantennas to significantly less than the transmit wavelength to fit more antennas, the resulting system performance improves.     

Cadmium(II)‐Catalyzed C?N Cross‐Coupling of Amines with Aryl Iodides

Cadmium diacetate dihydrate [Cd(OAc)₂⋅2 H₂O] in combination with ethylene glycol catalyzes efficiently the C N cross‐coupling of amines with aryl iodides by a benzyne mechanism. Alkyl, aryl and heterocyclic amines are compatible with this system affording the aminated products in high to excellent yield.