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A wideband multibeam antenna for integration in small platforms such as UAVs has been demonstrated. The demonstration was performed on a single facet comprising an 8×4 bowtie antenna elements array and a beamforming network which includes both transmitter and receiver chains and can therefore be used in multifunction systems for EW and communication. The operating frequency band chosen for this demonstrator is 6 - 15 GHz. Due to the modularity of the concept, the demonstrated facet can either be used stand alone or forming a faceted array depending on the required field of coverage and/or platform structure. A compact and lightweight phased array concept for 360o coverage is also discussed.

FeS2 pyrite can incorporate large amounts of arsenic (up to ca. 10 wt%) and hence has a strong impact on the mobility of this toxic metalloid. Focussing on the lowest arsenic concentrations for which the incorporation occurs in solid solution, the substitution mechanisms involved have been investigated by assuming simple incorporation reactions in both oxidising and reducing conditions. The solution energies were calculated by Density Functional Theory (DFT) calculations and we predict that the formation of AsS dianion groups is the most energetically favourable mechanism. The results also suggest that the presence of arsenic will accelerate the dissolution and thus the generation of acid drainage, when the crystal dissolves in oxidising conditions.

Plane-wave density functional calculations are used to investigate the pressure dependence of the geometry and ?-point phonons of FeS2 pyrite up to 150 GPa. The linear response method is employed to calculate the vibrational properties. Raman-active modes are in excellent agreement with the experimental data available up to 50 GPa,1 and we predict the evolution with pressure of the IR-active modes for which no high-pressure spectroscopic data have been reported so far. Over the wide pressure range investigated here, all vibrational frequencies depend nonlinearly on pressure; their pressure dependence is quantified by determining the full set of mode Gru?neisen parameters and their pressure derivatives.

The nature of the metal-ceramic interaction in the Ag/MgO(001) interface is studied using periodic Hartree-Fock calculations with density functional theory a posteriori correlation corrections. Different aspects of the Ag-MgO interaction have been studied by analysis of the electronic properties: total and projected density of states, multipole moments, bond population, and the difference electron density. By linking these properties to the adsorption energy and making a comparative analysis for interfaces with different degrees of coverage and different adsorption models (one- and two-sided adsorption), a detailed description of the Ag-MgO has been acquired., QC 20100525

We have performed periodic Hartree-Fock calculations for OH groups adsorbed on the MgO(001) surface considering different surface coverages. Six types of OH groups are discussed: OH-, OH, H+, H and hydrogen-bonded OH and H. It is found that when both OH and H are present on the surface, the two groups are best described as OH-. We suggest that the highest-frequency fundamental band (similar to3750 cm(-1) in the experimental OH spectrum) is assigned to OH- groups adsorbed on top of Mg2+, while H+ adsorbed on top of O2- give rise to the broader band at similar to3550 cm(-1)., QC 20100525

We present periodic ab initio calculations for ferroelectric NaNO2. The spontaneous polarisation (P-s) has been calculated with three different models based on: (i) point charges; (ii) a multipolar expansion of the charge ;distribution; and (iii) the Berry phase approach. Both the Hartree-Fock and LDA Hamiltonians were employed. Within the Hartree-Fock scheme, at the optimised geometry, we obtain P-s values of 20.3, 13.0 and 16.4 muC cm(-2) with the three models, compared to the experimental value of similar to11.9 muC m(-2). The Berry-phase approach at the Hartree-Fock level gives a value very close to experiment ( namely 12 muC cm(-2)) when the experimental structure is used. At the optimised LDA structure, the LDA P-s values are 16.8, 10.0 and 16.9 muC cm(-2) with models (i)-(iii). The optimised lattice parameters at the Hartree-Fock level are slightly shorter (between 0 and 4%) than those determined experimentally from X-ray-diffraction, while the lattice parameters of the LDA-optimised structure are up to 10% smaller than the experiment. The calculated lattice energies are 679 and 964 kJ mol(-1) at the HF and LDA levels, compared with 729 kJ mol(-1) from the experiment. Charge densities, Mulliken charges and dipole moments are discussed. Finally, we have studied the mechanism for the phase transformation in-between the ferroelectric and paraelectric crystal structures; a rotation of the NO2 group around the c-axis gives the lowest energy barrier., QC 20100525

Periodic ab initio calculations of the O-17 and H-2 quadrupole coupling constants (QCC) and their shifts have been performed for ice VIII and ice IX. Cluster calculations were done for smaller water clusters and chains. The ice Vm crystal structure was op, Addresses: Hermansson K, Univ Uppsala, Angstrom Lab, Box 538, S-75121 Uppsala, Sweden.

Molecular dipole moments, charges, and difference electron densities have been calculated from Hartree-Fock calculations for each individual molecule along geometry-optimized water chains with n=1,...,12,infinity. The complementarity of the three properti, Addresses: Hermansson K, Univ Uppsala, Angstrom Lab, Box 538, S-75121 Uppsala, Sweden. Univ Uppsala, Angstrom Lab, S-75121 Uppsala, Sweden.

This work examines the effect of intermolecular interactions on molecular properties derived from simulated X-ray diffraction data. Model X-ray data are computed from a superposition of ab initio molecular electron densities in the crystal, as well as fr, Addresses: Spackman MA, Univ New England, Div Chem, Armidale, NSW 2351, Australia. Univ New England, Div Chem, Armidale, NSW 2351, Australia. Univ Uppsala, Inst Chem, S-75121 Uppsala, Sweden.

The atomic and electronic structure of the Ag/MgO (1 0 0) and Ag/alpha-Al2O3(0 0 0 1) interfaces are calculated by means of the ab initio Hartree-Fock approach combined with a supercell model. The electronic density distribution and the interface binding energy/equilibrium distance for both interfaces are analyzed. For a complete (1:1) surface coverage of the MgO surface the energetically most favorable adsorption position for the Ag atom is above the O atom. For the Ag/alpha-Al2O3 interface the preferable adsorption positions for the Ag atom are over centers of either large equilateral oxygen triangles (in Al-substituted sites of Al-terminated corundum surface) or isosceles oxygen triangles (over O atoms of a first internal oxygen layer) in O-terminated corundum. This interface is less stable than Ag/MgO (1 O 0), due to a large mismatch between lattice constants of Ag (1 1 1) and alpha-Al2O3 (O O O 1) surfaces as well as the instability of Ag atoms on the Al-terminated corundum surface. (C) 1998 Elsevier Science B.V. All rights reserved.

The total dipole moment of a pair of isolated water molecules that employ a point polarizable dipole is compared with the total dipole moment obtained from MP4 calculations for the same intermolecular orientation and distance. At all reasonable intermolec, Addresses: Alfredsson M, Uppsala Univ, Angstrom Lab, Box 538, SE-75121 Uppsala, Sweden. Uppsala Univ, Angstrom Lab, SE-75121 Uppsala, Sweden. Univ Coll London, Dept Geol Sci, London WC1E 6BT, England. Univ Trent, Ist Nazl Fis Mat, I-38050 Trent, Italy. Un

2D periodic ab initio calculations have been performed for H-2 interacting with a temperature-reconstructed MgO(lll) surface, created from a molecular dynamics (MD) simulation at 300 K. The temperature effects involve both a long-time reconstruction of t, Addresses: Hermansson K, Univ Uppsala, Dept Inorgan Chem, Angstrom Lab, Box 538, S-75121 Uppsala, Sweden. Univ Uppsala, Dept Inorgan Chem, Angstrom Lab, S-75121 Uppsala, Sweden.

Adsorption energies and stretching vibrational frequency shifts for N-2 and HF molecules adsorbed on a LiF(001) surface have been obtained from periodic Hartree-Fock calculations. Surface coverages between 6 and 100% investigated. A one-layer and a three, Addresses: Hermansson K, Univ Uppsala, Angstrom Lab, Box 538, S-75121 Uppsala, Sweden. Univ Uppsala, Angstrom Lab, S-75121 Uppsala, Sweden.