Ion-milled waveguide lenses and lens arrays in GaAs

The authors discuss ion-milled planar waveguide lenses in GaAs which exhibit a considerably higher efficiency than that previously reported for those lenses and near diffraction-limited spot size. The authors also report the performance characteristics of these latest lenses, including single lenses and lens array of analog Fresnel, chirp grating, and hybrid types as well as a collimation-Fourier transformation lens-pair, together with the detailed design and fabrication procedures. A simple theoretical model for the lens efficiency is also formulated to assist in the lens design. Ion milling has been shown to be a simple and versatile technique for fabrication of waveguide lenses in GaAs and applicable to any other substrate material. Such ion-milled waveguide lenses should facilitate realization of a variety of monolithically integrated optic device modules and circuits in GaAs and other related substrates with applications to communications, signal processing, and computing     

Selective IR absorption in molecular nanofilms

We have formulated a microscopic theory of optical properties of ultrathin molecular films (nanofilms), i.e. quasi 2D systems parallel to XY planes bounded by two surfaces. Exposure of nanofilms to the external electromagnetic fields has result in creation of excitons - but different than bulk ones. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green’s functions. It has been shown that two types of optical excitations can occur: bulk and surface exciton states. Exciton energy dispersion law shows discrete behavior with non-zero values. Analysis of the dielectric properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. In addition, permittivity shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of both resonance and quantum size effects. Influences of boundary conditions on optical characteristics (through analyses of dynamical absorption coefficient) of these nanostructures were specially and in details explored.     

Pattern nulling in difference pattern by amplitude control

A method of placing nulls in directions of any unwanted radio frequency interference (RFI) sources in the difference pattern of a phased array by controlling the current amplitudes is discussed. Thus one can now achieve pattern nulling in both the sum and difference patterns by amplitude control and can therefore carry out the minimization of RFI noise independently of the maximization of the desired signal. The method therefore provides an efficient alternative approach to the design of adaptive phased arrays.     

Minimisation of mutual coupling effect on doa estimation by using guard elements

The accuracy of the direction-of-arrival (DOA) estimation using a receiving phased array is degraded by the mutual coupling between the antenna elements. It is shown that by putting guard elements on each end of a linear array the DOA estimate error is reduced.     

Optical add-drop multiplexers with low crosstalk

We propose and demonstrate three new optical add-drop multiplexer (OADM) architectures with simple and compact configuration and excellent crosstalk performance. The OADMs use a single multiport optical circulator and either one or two narrow-band fiber Bragg gratings, depending on the crosstalk requirement     

Nonlinear analysis techniques of block masonry walls in nuclear power plants

Concrete masonry walls have been used extensively in nuclear power plants as non-load bearing partitions serving as pipe supports, fire walls, radiation shielding barriers, and similar heavy construction separations. When subjected to earthquake loads, these walls should maintain their structural integrity. However, some of the walls do not meet design requirements based on working stress allowables. Consequently, utilities have used non-linear analysis techniques, such as the arching theory and the energy balance technique, to qualify such walls. This paper presents a critical review of the applicability of non-linear analysis techniques for both unreinforced and reinforced block masonry walls under seismic loading. These techniques are critically assessed in light of the performance of walls from limited available test data. It is concluded that additional test data are needed to justify the use of nonlinear analysis techniques to qualify block walls in nuclear power plants.     

Comparison of llama VH sequences from conventional and heavy chain antibodies

Forty different PCR clones encoding a llama variable heavy chain domain were analysed. The majority of these clones are derived from heavy-chain antibody cDNA in which the entire CH1 exon is absent. It appears from the amino acid within the VHH framework 1 and 3 that all the llama clones belong to the VH III family. However, the individual llama VHH sequences differ more substantially from each other than expected for members of the same family. Several remarkable amino acid substitutions in the framework 2 hinder the proper association of the VL. However, they lay the foundation for the secretion from the endoplasmic reticulum and good solubility behaviour of llama H2 antibodies. The repertoire of the llama VHHs may be extensive due to the presence of a long CDR3-loop, often constrained by a disulfide bridge and the occurrence of H1 and H2 loop conformations not yet encountered in mice or human VHs. The variability plot of the amino acids in the VHH shows that the first hypervariable region coincides with the structural H1 loop in contrast to the situation found in mice and man where the CDR1 and H1 are slightly offset. We propose that the amino acids of the llama H1 loop participate actively in the antigen binding. All these observations are characteristic for the llama VHHs of the homodimeric heavy-chain H2 antibodies, but are not maintained in the llama clones from conventional heterotetrameric H2L2 immunoglobulins.