A method for the determination of the depth distribution of light elements in heavy materials is described. It involves the detection of light elements recoiling under the bombardment by a 35Cl beam. A resolution of 300 Å was achieved for the lithium present in a thin sample. The measures were done with layers of 1016 atoms/cm2 and it is estimated that quantities as small as 1014 atoms/cm2 can be located without much difficulty.

Tests made using electron-beam irradiation for the pretreatment of spruce wood showed that over 90% cellulose present in samples treated with a maximum dose of 2 MGy was converted to sugars by Trichoderma cellulase. The enzymatic hydrolysis of these samples was completed in 24 h, and the sugar solutions produced contained over 88% glucose, the remainder was cellobiose, xylose, and mannose. After irradiation treatment, spruce wood chips were comparable to untreated filter-paper cellulose for enzymatic saccharification. The results suggest that electron beam irradiation is technically feasible as a pretreatment for enzymatic hydrolysis of a softwood.Enzymatic saccharification of cellulose as compared to acid hydrolysis decreases the formation of unwanted by products and is more efficient.' However, for the enzymatic conversion of lignocellulosic biomass to sugars, a pretreatment is required to destroy the lignocellulosic association, to reduce the cellulose crystallinity and to increase the available surface for enzymatic attack. For this purpose, a number of chemical, mechanical, steam, and pressure pretreatments have been studied.24 Many studies have shown that these methods are less effective on softwoods than hardwoods.S.6 More recently, the work carried out by Kumakura and Kaetsu7-'0 has demonstrated the usefulness of irradiation as pretreatment for improving enzymatic hydrolysis of bagasse, chaff, rice straw, sawdust, and wastepaper. This communication describes results of enzymatic hydrolysis of irradiated wood from spruce, a softwood species. MATERIALS AND METHODS Irradiation SourceSpruce wood chips were irradiated with 4-MeV electrons using the Chalk River Electron Test Accelerator." Figure 1 shows a sketch of the continuous-wave linear accelerator, which is capable of producing beams of up to 20 mA. The accelerator is composed of four side-coupled structures operating at 805 MHz, driven in pairs through bridge couplers from two 100 kW klystrons. There are three experimental areas. In line with the accelerator, bremsstrahlung targets are being developed. The electron beam can be brought out into air through a thin window in the 45" beam line where new applications for high power electron beam irradiations can be investigated. Advanced linear accelerator structure designs can be tested in the 90" beam line. Figure 2 shows a sketch of the setup used during the wood chip irradiations. The electron beam was defocussed on the samples with a solenoid lens. The beam current density used was 0.3 pA/cm2. The beam uniformity over the sample area was better than 10%. Samples were maintained at room temperature during the irradiations by cooling the sample container with circulating water. The dose rate was 2 MGy/h. Method of IrradiationThe irradiation dose was obtained from a measurement of the integrated charge. The dose in MGy is given by dE dt D = i o 3 -~where dE/dt is the electron stopping power of the medium (ca. 1.9 MeV cmYg for 4-MeV electrons) and Q

A recently improved sample-sectioning technique allowed us to obtain the entire depth distribution of damage (e.g., cavities) produced by 20-keV 4He+ ions injected into annealed, polycrystalline nickel held at 500 °C. We have also obtained the depth profile of the implanted helium concentration using the elastic recoil detection technique. These experimental depth profiles have been used to test several theoretical predictions for projected range and energy deposition profiles (e.g., based on transport theory or Monte Carlo calculations).

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Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia and its lipopolysaccharides (LPS) have been identified as important adhesins involved in adherence to host cells. To better understand the role of LPS core in the virulence of this organism, the aim of the present study was to identify and clone genes involved in LPS core biosynthesis by complementation with Salmonella enterica serovar Typhimurium mutants (rfaC, rfaD, rfaE and rfaF). Complementation with an A. pleuropneumoniae 4074 genomic library was successful with Salmonella mutant SL1102. This Salmonella deep-rough LPS mutant is defective for the rfaE gene, which is an ADP^heptose synthase. Novobiocin was used to select transformants that had the smooth-LPS type, since Salmonella strains with wild-type smooth-LPS are less permeable, therefore more resistant to hydrophobic antibiotics like novobiocin. We obtained a clone that was able to restore the wild-type smooth-LPS Salmonella phenotype after complementation. The wild-type phenotype was confirmed using phage (Felix-O, P22c.2 and Ffm) susceptibility and SDS^PAGE (sodium dodecyl sulfate^polyacrylamide gel electrophoresis). One of the open reading frames contained in the 3.3-kb insert in the plasmid encoded a 475-amino-acid protein with 71% identity and 85% similarity to the RfaE protein of S. enterica. We then attempted to generate an A. pleuropneumoniae rfaE mutant by gene replacement. The rfaE gene seems essential in A. pleuropneumoniae viability as we were unable to isolate a heptose-less knockout mutant.