1,6‐Interactions between di­methyl­amino and aldehyde groups in two bi­phenyl derivatives

The title compounds, 2‐(di­methyl­amino)­bi­phenyl‐2′‐carbox­aldehyde, C₁₅H₁₅NO, and 2‐(di­methyl­amino)­bi­phenyl‐2′,6′‐dicarbox­aldehyde, C₁₆H₁₅­NO₂, show similar 1,6‐interactions [N?C=O 2.929 (3) to 3.029 (3) Å] between the di­methyl­amino and aldehyde groups located in the ortho positions of the two rings, which lie at 58.1 (1)–62.4 (1)° to each other.     

Electrical characterisation of AlGaN/GaN heterostructure wafers for high-power HFETs

Undoped 28 nm AlGaN on 1 μm GaN was grown by MOVPE for high power microwave HFETs. Non-destructive methods for rapid characterisation of the layers are described. Double contact mercury probe capacitance voltage measurements gave valuable information on AlGaN layer leakage, thickness and quality, but only gave an estimate of the carrier concentration and pinch-off voltage due to the absence of an ohmic contact to the 2DEG layer. A non-contact resistivity mapping system gave accurate average sheet resistance, but underestimated the cross-wafer variation.     

Cubic arcs in cubic nets

The idea of an arc in a finite plane or block design, and in particular of a maximal arc, is extended to nets. This concept is explored, and in particular 3-arcs in cubic nets are characterized.     

Finite element approximation of a model for phase separation of a multi-component alloy with a concentration-dependent mobility matrix

We consider a model for phase separation of a multi-componentalloy with a concentration-dependent mobility matrix and logarithmicfree energy. In particular we prove that there exists a uniquesolution for sufficiently smooth initial data. Further, we provean error bound for a fully practical piecewise linear finiteelement approximation in one and two space dimensions. Finallynumerical experiments with three components in one space dimensionare presented.     

Double Arrays,Triple Arrays and Balanced Grids

Triple arrays are a class of designs introduced by Agrawal in 1966 for two-way elimination of heterogeneity in experiments. In this paper we investigate their existence and their connection to other classes of designs, including balanced incomplete block designs and balanced grids.AMS Classification:05B05, 05B30     

Solution of the Room square existence problem

We prove that if there is a Room square of side r with a subsquare of side s, then there is a Room square of side 5(r ? s) + s. This enables us to construct a Room square of side 257, thus proving that Room squares exist for all odd positive integer sides except 3 and 5.     

Surface vibrations on face centered cubic metal surfaces: the (111) surfaces

We have studied the dynamics of atom motion at face centered metal (111) surfaces. The interactions between atoms are modelled with central forces and angle bending forces. Results for frequencies and polarizations of surface modes are presented for the following metals: Ag, Al, Au, Cu, Ni, Pd and Pt. In addition, the results obtained for phonon spectral densities are presented for nickel.     

Theory of surface polaritons in n-type silicon in the presence of a DC current

A theoretical investigation has been carried out on the effect of a drift current on surface polaritons in n-type silicon. The current direction is taken to be parallel to the direction of propagation of the surface polaritons. From the dispersion curves, there is evidence that an interaction takes place between the current and the polaritons which gives rise to polariton instability or amplification for certain frequency ranges. These instabilities are believed to be due to the presence of the surface.