Spatial Demultiplexing in the sub-millimeter wave band using multlayer free-standing frequency selective surfaces

In this paper, we show that a multilayer freestanding slot array can be designed to give an insertion loss which is significantly lower than the value obtainable from a conventional dielectric backed printed frequency selective surface (FSS). This increase in filter efficiency is highlighted by comparing the performance of two structures designed to provide frequency selective beamsplitting in the quasioptical feed train of a submillimeter wave space borne radiometer. A two layer substrateless FSS providing more than 20 dB of isolation between the bands 316.5â??325.5 GHz and 349.5â??358.5 GHz, gives an insertion loss of 0.6 dB when the filter is orientated at 45 incidence in the TM plane, whereas the loss exhibited by a conventional printed FSS is in excess of 2 dB. A similar frequency response can be obtained in the TE plane, but here a triple screen structure is required and the conductor loss is shown to be comparable to the absorption loss of a dielectric backed FSS. Experimental devices have been fabricated using a precision micromachining technique. Transmission measurements performed in the range 250â??360 GHz are in good agreement with the simulated spectral performance of the individual periodic screens and the two multilayer freestanding FSS structures.

Micromachined 300GHz high Q resonant slot frequency selective surface filter

The design of a low loss quasi-optical beam splitter which is required to provide efficient diplexing of the bands 316.5-325.5 GHz and 349.5-358.5 GHz is presented. To minimise the filter insertion loss, the chosen architecture is a three-layer freestanding array of dipole slot elements. Floquet modal analysis and finite element method computer models are used to establish the geometry of the periodic structure and to predict its spectral response. Two different micromachining approaches have been employed to fabricate close packed arrays of 460 mm long elements in the screens that form the basic building block of the 30mm diameter multilayer frequency selective surface. Comparisons between simulated and measured transmission coefficients for the individual dichroic surfaces are used to determine the accuracy of the computer models and to confirm the suitability of the fabrication methods.

LPCVD of tungsten by selective deposition on silicon

Beta-phase W, selectively grown at 440C had resistivity 20 micro-ohm cm and maximum layer thickness 100nm. Hydrogen passivation proved essential in this process. Higher deposition temperatures resulted in increased layer thickness but incorporated WSi2 and alpha- phase W. Self limiting W grown on polycrystalline and heavily doped silicon yielded reduced thickness. Boron is involved in the WF6 reduction reaction but phosphorus is not and becomes incorporated in the W layer. The paper establishes an optimised and novel CVD process suited to IC contact technology. A funded technology transfer contract with National Semiconductor Greenock (M Fallon) resulted from this work.

Exploring eye movement analysis as a measure of selective visual attention in brain injured individuals

Primary Objective: To investigate the utility of using a new method of assessment for deficits in selective visual attention (SVA). Methods and Procedures: An independent groups design compared six participants with brain injuries with six participants from a non-brain injured control group. The Sensomotoric Instruments Eye Movement system with remote eye-tracking device (eye camera), and 2 sets of eight stimuli were employed to determine if the camera would be a sensitive discriminator of SVA in these groups. Main Outcomes and Results: The attention profile displayed by the brain injured group showed that they were slower, made more errors, were less accurate, and more indecisive than the control group. Conclusions: The utility of eye movement analysis as an assessment method was established, with implications for rehabilitation requiring further development. Key words: selective visual attention, eye movement analysis, brain injury

State-selective one-electron capture by slow state-prepared N2+(P-2) ground-state ions in collisions with hydrogen atoms

The technique of double translational energy spectroscopy.(DTES), recently successfully developed in this laboratory for use with targets of atomic hydrogen, has been used to study one-electron capture by ground-state N2+(2s22p)(2)p(0) ions in collisions with hydrogen atoms at energies within the range 0.8-6.0 keV. Cross sections for the formation of the main excited product channels have been determined. The measurements allow a re-evaluation of our previous TES measurements carried out with N2+ primary beams containing an admixture of metastable N2+(2s2p2)(4)p ions. The main findings of these earlier measurements are confirmed and the DTES measurements now remove any ambiguity in interpretation of the experimental data. While recent theoretical studies correctly predict the two main N+ D-3(0) and P-3(0) product channels, the quantitative agreement with experiment is only partially satisfactory.

The smooth muscle pharmacology of maximakinin, a receptor-selective, bradykinin-related nonadecapeptide from the venom of the Chinese toad, Bombina maxima.

Structural homologues of vertebrate regulatory peptides found in defensive skin secretions of anuran amphibians often display enhanced bioactivity and receptor binding when compared with endogenous mammalian peptide ligands. Maximakinin, a novel N-terminally extended bradykinin (DLPKINRKGPRPPGFSPFR) from the skin venom of a Chinese toad (Bombina maxima), displays such activity enhancement when compared with bradykinin but is additionally highly selective for mammalian arterial smooth muscle bradykinin receptors displaying a 50-fold increase in molar potency in this smooth muscle type. In contrast, a 100-fold decrease in molar potency was observed at bradykinin receptors in intestinal and uterine smooth muscle preparations. Maximakinin has thus evolved as a “smart” defensive weapon in the toad with receptor/tissue selective targeting. Natural selection of amphibian skin venom peptides for antipredator defence, through inter-species delivery by an exogenous secretory mode, produces subtle structural stabilisation modifications that can potentially provide new insights for the design of selectively targeted peptide therapeutics.

Synthesis of Peptidyl Ene Diones: Selective Inactivators of the Cysteine Proteinases

A series of synthetic peptides in which the C-terminal carboxyl grouping (-CO2H) of each has been chemically converted into a variety of ene dione derivatives (-CO-CH CH-CO-X; X -H, -Me, -OBut, - OEt, -OMe, -CO-OMe), have been prepared and tested as inactivators against typical members of the serine and cysteine protease families. For example, the sequences Cbz-Pro-Phe-CH CH-CO-OEt (I) which fulfils the known primary and secondary specificity requirements of the serine protease chymotrypsin, and Cbz-Phe-Ala-CH CH-CO-OEt (II) which represents a general recognition sequence for cysteine proteases such as cathepsins B, L and S, have been tested as putative irreversible inactivators of their respective target proteases. It was found that, whereas II, for example, functioned as a time-dependent, irreversible inactivator of each of the cysteine proteases, I behaved only as a modest competitive reversible inhibitor of chymotrypsin. Within the simple ester sequences Cbz- Phe-Ala-CH CH-CO-R, the rank order of inhibitor effectiveness decreases in the order R -OMe > - OEt >> -OBut. It was also found that the presence of both an unsaturated double bond and an ester (or a-keto ester) moiety were indispensable for obtaining irreversible inactivators. Of the irreversible inactivators synthesized, Cbz-Phe-Ala-CH CHCO- CO-OEt (which contains a highly electrophilic a-keto ester grouping) was found to be the most effective exhibiting, for example, second-order rate constants of approximately 1.7 106/M/min and approximately 4.9 104/M/min against recombinant human cathepsin S and human spleenic cathepsin B, respectively. This initial study thus holds out the promise that this class of inactivator may well be specific for the cysteine protease subclass.