Tunable wavelength spacing multi-wavelength ring laser using programmable DGD module as intra-cavity filter

A multi-wavelength fibre laser whose channel spacing can be dynamically and continuously tuned is demonstrated experimentally. A novel programmable magneto-optic-based DGD module is used as the intra-cavity optical filter to control the wavelength spacing. Channel spacing tunable from 0.4 to 1.6 nm is achieved.     

Berechnung transienter Ströme in netzgeführten 6-pulsigen Stromrichtern

Übersicht Die Ableitung algebraischer Beziehungen für die Berechnung der transienten Ströme erfolgt mit Hilfe der Laplace-Transformation unter Berücksichtigung allgemeiner Anfangsbedingungen. Die Rücktransfromation wird sowohl für verschiedene als auch für gleiche Pole durchgeführt. Die Bedingungen für das stationäre Verhalten des Schaltkreises werden aufgezeichnet.

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Contents The algebraic equations for the calculation of the nonstationary currents—due to general initial conditions—are derived by applying the standard Laplace transform techniques, evaluating also the solutions for the special case of a double pole. The conditions for directly calculating the stationary currents from the derived equations are outlined.

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Diese Arbeit wurde durch ein Amerika-Stipendium (Wi 253/1) der Deutschen Forschungsgemeinschaft unterstützt.     

Parallel analysis of two analytes in solutions or on surfaces by using a bifunctional aptamer: applications for biosensing and logic gate operations

A bifunctional aptamer that includes two aptamer units for cocaine and adenosine 5'-monophosphate (AMP) is blocked by a nucleic acid to form a hybrid structure with two duplex regions. The blocked bifunctional aptamer assembly is used as a functional structure for the simultaneous sensing of cocaine or AMP. The blocked bifunctional aptamer is dissociated by either of the two analytes, and the readout of the separation of the sensing structure is accomplished by a colorimetric detection, by a released DNAzyme, or by electronic means that use Faradaic impedance spectroscopy or field-effect transistors. In one configuration, the blocked bifunctional aptamer structure is separated by the substrates cocaine or AMP, and the displaced blocker units act as a horseradish peroxidase-mimicking DNAzyme that permits the colorimetric detection of the analytes. In the second system, the blocked bifunctional aptamer hybrid is associated with a Au electrode. The displacement of the aptamer by any of the substrates alters the interfacial electron transfer resistance at the electrode surface, thus providing an electronic signal for the sensing process. In the third configuration, the blocked aptamer hybrid is linked to the gate of a field-effect transistor device. The separation of the complex by means of any of the analytes, cocaine, or AMP alters the gate potential, and this allows the electronic transduction of the sensing process by following the changes in the gate-to-source potentials. The different systems enable not only the simultaneous detection of the two analytes, but they provide a functional assembly that performs a logic gate "OR" operation.     

Zeitverhalten der isothermen Reaktivdestillation beim thermischen Cracken und Desoxygenieren von Rapsöl

Thermal cracking of rapeseed oil under isothermal reactive distillation conditions allows the production of alternative liquid fuels. Temporal changes of the sump phase and the oil condensate show an increased higher heating value due to deoxygenation. The sump phase also shows an increasing thermal stability, accompanied by polymerization and aromatization. This is derived from a changing iodine value, H/C ratio as well as viscosity. The deoxygenation of the oil condensate is confirmed by a decreasing acid value and the reduction of detected carboxylic acids.     

Liposomes labeled with biotin and horseradish peroxidase: a probe for the enhanced amplification of antigen--antibody or oligonucleotide--DNA sensing processes by the precipitation of an insoluble product on electrodes

Liposomes labeled with biotin and the enzyme horseradish peroxidase (HRP) are used as a probe to amplify the sensing of antigen-antibody interactions or oligonucleotide-DNA binding. The HRP-biocatalyzed oxidation of 4-chloro-1-naphthol (1) in the presence of H2O2, and the precipitation of the insoluble product 2 on electrode supports, are used as an amplification route for the sensing processes. The anti-dinitrophenyl antibody (DNP-Ab) is sensed by a dinitrophenyl-L-cysteine antigen monolayer associated with an Au electrode. A biotinylated anti-IgG-antibody (Fc-specific) is linked to the antigen-DNP-Ab complex, and the biotin-labeled HRP-liposomes associate with the assembly through an avidin bridge. The biocatalyzed precipitation of 2 on the electrode increases the electron-transfer resistances at the electrode-solution interface or the electrode resistance itself. The binding events of the different proteins on the electrode and the biocatalyzed precipitation of 2 on the conductive support are followed by Faradaic impedance spectroscopy or constant-current chronopotentiometry. DNP-Ab concentrations as low as 1 x 10(-11) g x mL(-1) can be detected by this method. The labeled liposomes were also used for the amplified detection of DNA 3. The oligonucleotide 4, complementary to a part of the target DNA 3 that is a model nucleic acid sequence for the Tay-Sachs genetic disorder, is assembled on an Au electrode. Hybridization of the analyte 3 followed by the association of the biotin-tagged oligonucleotide 5 yields a three-component double-stranded assembly. Sensing of the analyte 3 is amplified by the association of avidin, the labeled liposomes, and the subsequent biocatalyzed precipitation of 2 on the electrodes. The DNA 3 is detected with a sensitivity that corresponds to 6.5 x 10(-13) M. Faradaic impedance spectroscopy and chronopotentiometry were employed to follow the stepwise assembly of the systems and the electronic transduction of the detection of the analyte DNA 3.     

Adjustable compensation of polarization mode dispersion using ahigh-birefringence nonlinearly chirped fiber Bragg grating

We demonstrate an adjustable polarization-mode-dispersion (PMD) compensator. The device uses a nonlinearly chirped fiber Bragg grating written into a high-birefringence photosensitive fiber. By mechanically stretching the grating, the device generates a time delay between different polarizations that is adjustable from 100 to 320 ps and is tunable over 2.3 nm. We demonstrate tunable PMD compensation of a 10-Gb/s signal that has an initial delay between the two polarization states of 127 or 302 ps     

Bis-Aniline-Crosslinked Enzyme–Metal Nanoparticle Composites on Electrodes for Bioelectronic Applications

The electrical contacting of redox enzymes with electrodes is the most fundamental requirement for the development of amperometric biosensors and biofuel cell elements. We describe a novel method to prepare electrically contacted metallic nanoparticles (NPs) or carbon nanotubes (CNTs)/enzyme hybrid composites on electrodes that act as amperometric biosensors or as the constituents of biofuel cells. Au NPs or Pt NPs were modified with thioaniline electropolymerizable groups, and so were the enzymes glucose oxidase (GOx) or bilirubin oxidase (BOD). Electrochemical polymerization of the thioaniline-functionalized Pt NPs and GOx on a thioaniline monolayer-modified Au surface led to the formation of a bis-aniline-bridged Pt NPs/GOx composite electrode that enabled the analysis of glucose through the electrocatalyzed reduction of H₂O₂. Similarly, a Pt NPs/BOD composite-functionalized electrode showed electrocatalytic activity toward the reduction of O₂ to H₂O. Also, a Au NPs/GOx composite-functionalized electrode revealed direct electrical contacting between the enzyme and the electrode through the electrocatalytic reduction of the bis-aniline bridges, and this enabled the bioelectrocatalytic oxidation and the amperometric sensing of glucose. Finally, a biofuel cell consisting of an anode modified with Nile blue/NAD⁺/alcohol dehydrogenase on carbon nanotubes, and a cathode composed of the bis-aniline-crosslinked Pt NPs/BOD composite was constructed. The biofuel cell operates with a power output corresponding to 200 μW cm^-2.