A novel cylindrical TE(2,1) mode converter.

A novel, compact arrangement for Ka-band mode couplers, which convert a rectangular waveguide TE(1,0) to cylindrical waveguide TE(2,1) mode, has been designed, constructed, and tested. The design features a set of longitudinal slots, positioned in regions of negligible current flow for the TE(2,1) mode, allowing its propagation to be preferentially favored, by suppression of the fundamental TE(1,1) mode. Numerical simulations and experimental measurements display good agreement, showing transmission of the intended TE(2,1) mode at levels of better than -5 dB, from a frequency of ∼37.5 to 41 GHz. Subsequent farfield measurements confirm the presence of the TE(2,1) mode, demonstrating good agreement when compared with analytical expectations. Such a device would be an ideal candidate for an application where mode purity, bandwidth, and ease of construction are of primary importance and where the transmission efficiency is of limited concern.

Experimental and theoretical studies of a coaxial free-electron maser based on two-dimensional distributed feedback.

The first operation of a coaxial free-electron maser (FEM) based on two-dimensional (2D) distributed feedback has been recently observed. Analytical and numerical modeling, as well as measurements, of microwave radiation generated by a FEM with a cavity defined by coaxial structures with a 2D periodic perturbation on the inner surfaces of the outer conductor were carried out. The two-mirror cavity was formed with two 2D periodic structures separated by a central smooth section of coaxial waveguide. The FEM was driven by a large diameter (7 cm), high-current (500 A), annular electron beam with electron energy of 475 keV. Studies of the FEM operation have been conducted. It has been demonstrated that by tuning the amplitude of the undulator or guide magnetic field, modes associated with the different band gaps of the 2D structures were excited. The Ka-band FEM generated 15 MW of radiation with a 6% conversion efficiency, in good agreement with theory.

Experimental study of coaxial free-electron maser based on two-dimensional distributed feedback.

The first experimental study of a coaxial free-electron maser (FEM) based on two-dimensional (2D) distributed feedback is presented. A new type of cavity formed with coaxial 2D surface photonic band gap structures was used. The FEM was driven by a large diameter (7 cm), high-current (500 A), annular electron beam of energy 475 keV. By tuning the amplitude of the undulator or guide magnetic field, modes associated with the different band gaps of the 2D structures were excited. The -band coaxial FEM generated 15 MW of radiation with a 6% conversion efficiency, in excellent agreement with theory.

Enhancement of enzyme-activated 1,2-dioxetane chemiluminescence in membrane-based assays.

Processes for enhancing the chemiluminescent signal generated by enzyme-activated 1,2-dioxetanes have been developed for membrane-based assays in which detection is done using a charge-coupled device (CCD) camera or X-ray film. The enhancement is demonstrated using slot-blots of biotinylated lambda DNA in conjunction with an avidin-alkaline phosphatase conjugate. For detection with a CCD camera, the nylon membrane is dried after processing and incubation in dioxetane substrate solution and heated to temperatures of 50 to 80 degrees C during detection. Up to a 100-fold signal increase is obtained using this enhancement process compared to the conventional detection procedure, in which the blot is kept saturated with substrate solution in a sealed plastic bag during detection. For detection with X-ray film, a fivefold increase in signal intensity is realized by drying the membrane before exposure to the film. These enhancement processes greatly reduce the time required for detection in membrane-based assays.

A system for rapid DNA sequencing with fluorescent chain-terminating dideoxynucleotides.

A DNA sequencing system based on the use of a novel set of four chain-terminating dideoxynucleotides, each carrying a different chemically tuned succinylfluorescein dye distinguished by its fluorescent emission is described. Avian myeloblastosis virus reverse transcriptase is used in a modified dideoxy DNA sequencing protocol to produce a complete set of fluorescence-tagged fragments in one reaction mixture. These DNA fragments are resolved by polyacrylamide gel electrophoresis in one sequencing lane and are identified by a fluorescence detection system specifically matched to the emission characteristics of this dye set. A scanning system allows multiple samples to be run simultaneously and computer-based automatic base sequence identifications to be made. The sequence analysis of M13 phage DNA made with this system is described.

A four-pass high resolution spectrometer for the near infrared.

A high resolution Littrow type grating spectrometer designed for four-pass operation in the near ir is described. Using 20-cm gratings, four passed in first and second orders, this instrument achieves a spectral resolution between 0.015 cm(-1) and 0.025 cm(-l) in the l.9-micro to 3.6-micro region. This resolution is up to 40% better than that realized with the same system double passed.