Coherent FSK transmitter using a negative feedback stabilised semiconductor laser

An electrical negative frequency feedback scheme is applied to a semiconductor laser to improve its direct frequency modulation performance in an FSK transmitter. An error signal caused by imperfect FM response is extracted through heterodyne discrimination detection with a stable master laser and fed back to the FM semiconductor laser.     

Oxygen intake and walking speed before and after total hip replacement

The objective of the study was to evaluate the walking ability and the energy cost of walking in patients before and after total hip replacement. The oxygen intake and the maximum walking speed were measured immediately before and 6 months after operation in 25 patients. Although the oxygen intake did not change significantly in most patients it was decreased in those patients who before surgery had had the worst walking capacity. The average maximum walking speed almost doubled in the 25 patients.     

A graphical tool for parasite genome annotation

A graphical tool to facilitate rapid primary annotation of genomic sequence has been developed. Within a single interface the user can import sequences or database entries, run feature prediction programs and similarity searches, filter results, add additional manually found features and notes, and finally export annotations for database submission. Integrated rule-based feature corroboration and a novel decision support heuristic using ORF orientation, length and base-composition further enhances the efficiency of the annotation process without compromising flexibility. The program has been explicitly tailored to use in protozoan parasite genome projects, but can constitute a useful tool for prokaryote annotation as well. It is successfully being used by our lab in the Trypanosoma cruzi genome project, and can be obtained from the authors upon request.     

Quantifying unfrozen water in frozen soil by high-field 2H NMR

To understand wintertime controls of biogeochemical processes in high latitude soils it is essential to distinguish between direct temperature effects and the effects of changes in water availability mediated by freezing. Efforts to separate these controls are hampered by a lack of adequate methods to determine the proportion of unfrozen water. In this study we present a high-field 2H2O NMR method for quantifying unfrozen water content in frozen soil. The experimental material consisted of the humic layer of a boreal spruce forest soil mixed with varying proportions of quartz sand and humidified with deuterium-enriched water. The relative standard deviation of unfrozen water content (measured as NMR signal integral) was less than 2% for repeated measurements on a given sample and 3.5% among all samples, based on a total of 16 measurements. As compared to 1H NMR, this 2H NMR method was found to be superior for several reasons: it is less sensitive to field inhomogeneity and paramagnetic impurities, it gives a bigger line shape difference between the ice and liquid signal, it shows a sharper response to water fusion, and it excludes the possibility of hydrogen in the organic material interfering with the measurement.     

Improving pulse sequences for 3D diffusion-ordered NMR spectroscopy: 2DJ-IDOSY

An improved pulse sequence for the 3D DOSY experiment 2DJ-DOSY, using diffusion encoding internal to the parent 2DJ spectroscopy sequence (2DJ-IDOSY), is presented. The diffusion-encoding pulses are used to enforce the desired coherence transfer pathway, reducing the minimum experimental time by at least a factor of 4, as compared to existing techniques, and approximately doubling the signal-to-noise ratio for small molecules. The new sequence is demonstrated on a simple mixture and on a complex sample with a high dynamic range (port wine). The principle of internal diffusion encoding can be applied with profit to a range of other 3D DOSY experiments.     

Top-down characterization of nucleic acids modified by structural probes using high-resolution tandem mass spectrometry and automated data interpretation

A top-down approach based on sustained off-resonance irradiation collision-induced dissociation (SORI-CID) has been implemented on an electrospray ionization (ESI) Fourier transform mass spectrometer (FTMS) to characterize nucleic acid substrates modified by structural probes. Solvent accessibility reagents, such as dimethyl sulfate (DMS), 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide metho-p-toluenesulfonate (CMCT), and beta-ethoxy-alpha-ketobutyraldehyde (kethoxal, KT) are widely employed to reveal the position of single- vs double-stranded regions and obtain the footprint of bound proteins onto nucleic acids structures. Established methods require end-labeling of the nucleic acid constructs, probe-specific chemistry to produce strand cleavage at the modified nucleotides, and analysis by polyacrylamide gel electrophoresis to determine the position of the susceptible sites. However, these labor-intensive procedures can be avoided when mass spectrometry is used to identify the probe-induced modifications from their characteristic mass signatures. In particular, ESI-FTMS can be directly employed to monitor the conditions of probe application to avoid excessive alkylation, which could induce unwanted distortion or defolding of the substrate of interest. The sequence position of the covalent modifications can be subsequently obtained from classic tandem techniques, which allow for the analysis of individual target adducts present in complex reaction mixtures with no need for separation techniques. Selection and activation by SORI-CID has been employed to reveal the position of adducts in nucleic acid substrates in excess of 6 kDa. The stability of the different covalent modifications under SORI-CID conditions was investigated. Multiple stages of isolation and activation were employed in MS(n)() experiments to obtain the desired sequence information whenever the adduct stability was not particularly favorable, and SORI-CID induced the facile loss of the modified base. A new program called MS2Links was developed for the automated reduction and interpretation of fragmentation data obtained from modified nucleic acids. Based on an algorithm that searches for plausible isotopic patterns, the data reduction module is capable of discriminating legitimate signals from noise spikes of comparable intensity. The fragment identification module calculates the monoisotopic mass of ion products expected from a certain sequence and user-defined covalent modifications, which are finally matched with the signals selected by the data reduction program. Considering that MS2Links can generate similar fragment libraries for peptides and their covalent conjugates with other peptides or nucleic acids, this program provides an integrated platform for the structural investigation of protein-nucleic acid complexes based on cross-linking strategies and top-down ESI-FTMS.     

Traffic sense--which factors influence the skill to predict the development of traffic scenes?

A study was conducted to evaluate the skill to predict the development of traffic situations. A stop-controlled intersection was filmed over several days, and 12 scenes with varying traffic complexity were selected. In half of the scenes, the traffic rules were violated, in half of the scenes, the rules were observed. A total of 36 participants were asked to watch the scenes and predict how the scene would most likely develop in the 2s after the film was paused. Additionally, the participants rated how certain they were about their prediction, and how complex and dangerous they assessed the scenes to be. With the method used here, experienced drivers were not found to make more correct predictions of situational development, and no difference in skill to predict could be found between genders. Nevertheless, more experienced drivers were more certain in their judgements and evaluated the situations on average as less complex and dangerous than did less experienced drivers. Scenes in which the traffic rules were violated were more difficult to predict correctly. The scenes in which the participants predicted violations were rated as more complex and dangerous. It is concluded that the low-cost method used here is more useful for examining which scenes are generally easy or difficult to predict and how they are experienced subjectively than to investigate differences in performance for different driver categories.     

Evaluations of the stability of sheathless electrospray ionization mass spectrometry emitters using electrochemical techniques

The processes that cause the failure of sheathless electrospray ionization (ESI) emitters, based on different kinds of gold coatings on fused-silica capillaries, are described and explained. The methods chosen for this study include electrochemical methods, ICPMS analysis of the electrolytes used, SEM studies, and electrospray experiments. Generally, the failure occurs by loss of the conductive coating. It is shown that emitters with sputter-coated gold lose their coatings because of mechanical stress caused by the gas evolution accompanying water oxidation or reduction. Emitters with gold coatings on top of adhesion layers of chromium and nickel alloy withstand this mechanical stress and have excellent durability when operating as cathodes. When operating as anodes, the adhesion layer is electrochemically dissolved through the gold film, and the gold film then flakes off. It is shown that the conductive coating behaves as a cathode even in the positive electrospray mode when the magnitude of a superimposed reductive electrophoretic current exceeds that of the oxidative electrospray current. Fairy-dust coatings developed in our laboratory (see Barnidge, D. R.; etal.Anal. Chem. 1999, 71, 4115-4118,) bygluing gold dust onto the emitter, are unaffected by the mechanical stress due to gas evolution. When oxidized, the fairy-dust coatings show an increased surface roughness and decreased conductivities due to the formation of gold oxide. The resistance of this oxide layer is however negligible in comparison with that of the gas phase in ESI. Furthermore, since no flaking and only negligible electrochemical etching of gold was found, practically unlimited emitter lifetimes may be achieved with fairy-dust coatings.