Longitudinal distortion in images reconstructed by reflection holograms

Reflection holograms recorded on photographic materials usually reconstruct an image at a shorter wavelength than that at which they were recorded. As a result, the lateral and longitudinal magnifications of the reconstructed image are not the same and the image appears distorted. It is shown that this distortion can be minimized by a proper choice of the recording geometry. The residual aberrations of the image are discussed.     

Sharpening ofE-plane radiation patterns ofE-plane sectoral horns by metallic grills

Results of an exhaustive experimental study of the effect of conducting grills on theE-plane radiation patterns ofE-plane sectoral horns are presented. It is observed that the grills satisfying certain optimum conditions are capable of focusing the patterns with considerable improvement in beamwidth and directive gain. The impedance conditions are also improved by the presence of the grills. Data for a number of horns operating at a wide range of frequencies are presented.     

Directed assembly of metal-organic cubes from deliberately predesigned molecular building blocks

A novel anionic metal-organic cube (MOC-1), [Ni(8)(HImDC)(12)](8-), has been synthesized by metal-ligand directed assembly of eight tri-connected Ni nodes and twelve doubly deprotonated bis(bidentate) imidazoledicarboxylic acid ligands (HImDC).     

Web Server Performance Modeling

The advent of Web technology has made Web servers core elements of future communication networks. Although the amount of traffic that Web servers must handle has grown explosively during the last decade, the performance limitations and the proper tuning of Web servers are still not well understood. In this paper we present an end-to-end queueing model for the performance of Web servers, encompassing the impacts of client workload characteristics, server harware/software configuration, communication protocols, and interconnect topologies. The model has been implemented in a simulation tool, and performance predictions based on the model are shown to match very well with the performance of a Web server in a test lab environment. The simulation tool forms an excellent basis for development of a Decision Support System for the configuration tuning and sizing of Web servers.     

Physicochemical properties of NaxCoO2 as a cathode for solid state sodium battery

An intercalation compound with composition Na_0.7CoO₂ has been synthesized through different preparative techniques such as solid state reaction, ball milling and sol gel techniques. The investigation reveals that the cathode material with an average particle size of about 500 nm of uniform morphology can be synthesized through sol gel technique. Further, this synthesis technique improves the stoichiometry of the sodium content significantly. The electrical resistivity of these cathode materials is found to be in the range of 4 to 12 mΩ-cm at 300 K. It has been observed that, the resistivity of the cathode material increases with increase in sodium content. The electrochemical cells with the configuration Na | [wt.% 0.3 PEO-0.7 PEG]₆:NaPO₃ |composite cathode material, have shown an open circuit voltage (OCV) value of 2.7 V. The (OCV) of the cells with the cathode prepared by sol-gel and ball milling route has shown a plateau region of about 40 h, when compared to the plateau region of 10 h for the battery with the cathode prepared by solid state reaction. The reduction in the particle size of the cathode material has improved the stability of the electrode electrolyte interface and thereby discharges characteristics.     

Broad-band apochromatic retarders: choice of materials

Apochromatic retarders can be constructed by using a combination of three plates of different birefringent materials with properly chosen thicknesses. However, when dealing with a broad wavelength range, their performance depends very much on the materials chosen. A procedure is presented for optimizing the choice of materials for such a broad-band retarder.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.