Continuously chirped DFB gratings by specially bent waveguides fortunable lasers

We have implemented and studied a new type of tunable multiple-section semiconductor distributed feedback (DFB) laser using tailored chirped DFB gratings. Arbitrarily and continuously chirped DFB gratings are defined by bent waveguides on homogeneous grating fields with ultrahigh spatial precision. The mathematical bending functions are optimized in this case to provide enlarged wavelength tuning ranges. We present the results of model calculations, the technological device realization and experimental results of the DFB laser characterization e.g. a tuning range of 5.5 nm without wavelength gaps and high side mode suppression ratio     

A soft switching active snubber optimized for IGBT's in singleswitch unity power factor three-phase diode rectifiers

This paper describes a soft switching active snubber for an IGBT operating in a single switch unity power factor three-phase diode rectifier. The soft switching snubber circuit provides zero-voltage turn-off for the main switch. The high turn-off losses of the IGBT due to current tailing are reduced by zero-voltage switching. This allows the circuit to be operated at very high switching frequencies with regulated DC output voltage, high quality input current and unity input power factor. Simulation and experimental results are included     

Arc fusion splices with improved strength (4.8 GPa) approaching thestrength of the fibre

For the first time it has been shown that a median splice strength (4.8 GPa) closely matching that of the fibre can be achieved using a commercial fusion splicer. This is achieved by carefully controlling the stripping process and the environmental conditions     

A rectangular finite element for analysing composite multilayered shallow shells in statics,vibration and buckling

This paper presents a new 32-degree-of-freedom finite element of multilayered composite, moderately thick, shallow shells. The element is a four-node C¹ rectangular element and is built from standard interpolations but with a new kind of kinematics which allows us to exactly ensure the continuity conditions for displacements and stresses at the interfaces between the layers of a laminated structure and the boundary conditions at the upper and lower surfaces of the shell. The transverse shear deformation which is represented by cosine functions is of a higher order and allows us to avoid shear correction factors. The element is evaluated on standard problems and in comparison with exact three-dimensional and analytical solutions for multilayered plates and shells in statics, vibrations and stability.     

Drug resistance of Helicobacter pylori strains isolated from patients with inflammation of stomach mucous membrane and peptic ulcer of stomach and duodenum

Twelve strains of H. pylori were tested. They were isolated from biosamples from 23 patients with stomach inflammation (16 persons) and stomach (3) and duodenum peptic ulcer. By application of solid medium dilution of MIC50 and MIC90-16 antibiotics and antimicrobials were tested. Values of MIC50 and MIC90 for antibiotics from the tetracycline group were, respectively 0.25-0.5 microgram/ml and 0.12-1.0 microgram/ml. Similar results were obtained with macrolide antibiotics. All strains were sensitive to penicillin (MIC 0.03-0.12 microgram/ml, ampicillin (MIC 0.06-0.5 microgram/ml) and amoxicillin and rifampicin (MIC 0.07-0.3 microgram/ml). Ten out of 12 investigated strains were resistant to metronidazole (MIC90 = 30 micrograms/ml). Results of this study may be important for etiotropic treatment of infections with H. pylori.