Discrimination between bacterial spore types using time-of-flight mass spectrometry and matrix-free infrared laser desorption and ionization

We demonstrate that molecular ions with mass-to-charge ratios (m/z) ranging from a few hundred to 19 050 can be desorbed from whole bacterial spores using infrared laser desorption and no chemical matrix. We have measured the mass of these ions using time-of-flight mass spectrometry and we observe that different ions are desorbed from spores of Bacillus cereus, Bacillus thuringiensis, Bacillus subtilis, and Bacillus niger. Our results raise the possibility of identifying microorganisms using mass spectrometry without conventional sample preparation techniques such as the addition of a matrix. We have measured the dependence of the ion yield from B. subtilis on desorption wavelength over the range 3.05-3.8 microm, and we observe the best results at 3.05 microm. We have also generated mass spectra from whole spores using 337-nm ultraviolet laser desorption, and we find that these spectra are inferior to spectra generated with infrared desorption. Since aerosol analysis is a natural application for matrix-free desorption, we have measured mass spectra from materials such as ragweed pollen and road dust that are likely to form a background to microbial aerosols. We find that these materials are readily differentiated from bacterial spores.     

The affinity of an oligodeoxynucleotide-peptide conjugate for an RNA hairpin loop depends on stereochemistry at the DNA-peptide junction

Molecular models of an oligodeoxynucleotide-peptide conjugate complexed to an RNA hairpin loop were constructed to assess the effect of stereoisomerism at the point of attachment of the peptide to the oligodeoxynucleotide on the affinity of the conjugate for an RNA target. The peptide portion of the oligodeoxynucleotide-peptide conjugate, (L-lysine)8, was covalently attached to the N-allyl group of (D)- or (L)-aspartic alcohol that was incorporated into the interior of an antisense oligodeoxynucleotide. The stereocenter in the oligodeoxynucleotide interior originates from either (D)- or (L)-aspartic alcohol. The oligodeoxynucleotide portion of the oligodeoxynucleotide-peptide conjugate forms Watson-Crick base pairs with the single-stranded RNA that flanks the RNA hairpin loop. The positively charged peptide makes specific electrostatic contacts with the negatively charged phosphate backbone of the RNA hairpin loop when attached to the N-allyl of (D)-aspartic alcohol but does not have the proper orientation to make these electrostatic contacts when attached to the N-allyl of (L)-aspartic alcohol. This modelling study emphasizes the importance of stereocontrol at the point of branching in synthesizing oligodeoxynucleotide-peptide conjugates for binding of RNA hairpin loops.     

Practical high-impedance fault detection on distribution feeders

Distribution protection systems must balance dependability with security considerations to be practical. This is quite difficult for high-impedance faults. Only highly sensitive algorithms can achieve absolute dependability in detecting very low current faults. This high sensitivity results in a propensity for false tripping, creating a less secure, system and resulting in the potential for decreased service continuity and lower reliability. Researchers at Texas A&M University have balanced fault detection with fault discrimination, resulting in a practical combination of detection algorithms in a commercially viable system. This device has many “intelligent” features, including the ability to analyze and correlate numerous fault characteristics in real time, so that a correct determination of the status of the feeder can be made with a high probability of accuracy. This paper describes the use of multiple algorithms to detect various types of faults and the use of an expert decision maker to decipher incoming data, to determine the status and health of a distribution feeder. Requirements for a practical, secure high-impedance fault relay are also discussed. Finally, Texas A&M has licensed this technology to a commercial partner, which manufactures a device that detects high-impedance faults, in addition to performing numerous other monitoring and protection functions     

An analysis of simultaneous variation in protein structures

The simultaneous substitution of pairs of buried amino acid side chains during divergent evolution has been examined in a set of protein families with known crystal structures. A weak signal is found that shows that amino acid pairs near in space in the folded structure preferentially undergo substitution in a compensatory way. Three different physicochemical types of covariation 'signals' were then examined separately, with consideration given to the evolutionary distance at which different types of compensation occur. Where the compensatory covariation tends towards retaining the combined residue volumes, the signal is significant only at very low evolutionary distances. Where the covariation compensates for changes in the hydrogen bonding, the signal is strongest at intermediate evolutionary distances. Covariations that compensate for charge variations appeared with equal strength at all the evolutionary distances examined. A recipe is suggested for using the weak covariation signal to assemble the predicted secondary structural elements, where the evolutionary distance, covariation type and weighting are considered together with the tertiary structural context (interior or surface) of the residues being examined.      

Characterization of ZrO2-Y2O3 thermal barrier coatings by Raman spectroscopy

Raman spectroscopy is shown to be a useful tool for the observation of phase transitions in Y₂O₃-stabilized ZrO₂ thermal barrier coatings. Data were collected in situ at temperatures up to 1050°C as a function of the Y₂O₃ content. Large hysteresis effects are observed in the phase transition temperatures.     

Fast solution of the linearized Poisson–Boltzmann equation with nonaffine parametrized boundary conditions using the reduced basis method

The code d³f++ developed under the leadership of GRS for simulating 3D flow and solute transport includes an advanced formulation for fracture flow and transport in lower-dimensional elements that has still been in need of qualification. A variety of in-situ experiments in the granitic rock at the Swedish Hard Rock Laboratory Äspö offers an excellent basis for this purpose. Particularly well suited is the work performed in the TRUE Block Scale Project where a hydrostructural model comprising 30 large-scale fractures in a cube-shaped domain with a side length of 200 m has been set up for simulating groundwater flow which in turn forms the basis for reproducing the results of the injection–extraction tracer test “C2”. The present paper deals with modelling 3D flow and solute transport with the code d³f++ as a qualification exercise. The modelling results reveal an excellent representation of the contrasts in flow velocity across the fractures. Also the jumps in tracer concentration along intersecting fractures where waters with different tracer concentrations mix are handled well by the code. Calibration has nevertheless been required in order to achieve a reasonable fit of measured and calculated breakthrough curves.