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We introduce a new low-loss fast intracavity semiconductor Fabry-Perot saturable absorber operated at anti-resonance both to start and sustain stable mode locking of a cw-pumped Nd:YLF laser. We achieved a 3.3-ps pulse duration at a 220-MHz repetition rate. The average output power was 700 mW with 2 W of cw pump power from a Ti:sapphire laser. At pump powers of less than 1.6 W the laser self-Q switches and produces 4-ps pulses within a 1.4-micros Q-switched pulse at an approximately 150-kHz repetition rate determined by the relaxation oscillation of the Nd:YLF laser. Both modes of operation are stable. In terms of coupled-cavity mode locking, the intra-cavity antiresonant Fabry-Perot saturable absorber corresponds to monolithic resonant passive mode locking.

A methanogenic fluidized bed reactor (FBR) fed with lactate and tetrachloroethene (PCE) was operated for 14 months to study the effect of electron donor and PCE loading on chloroethene dechlorination rates. Lactate was fed continuously at 200 mg/L (2.2 mmol/L), and the influent PCE feed concentration was increased stepwise from 3.5 to 160 µmol/L. Vinyl chloride (VC) and ethene accounted for 80% and 20%, respectively, of the PCE dechlorination. Batch tests with various electron donors showed that H 2 , propionate, and lactate supported dechlorination of PCE, trichloroethene (TCE), cis-dichloroethene (c-DCE), and VC, whereas no dechlorination was observed with acetate or in the absence of an electron donor. Different short-term steady H 2 concentrations were obtained by adjusting the FBR influent lactate feed concentration, and the effect of H 2 concentration on the rate of chloroethene dechlorination was determined. Dechlorination rates for PCE, TCE, c-DCE, and VC showed a Michaelis-Menten relationship with H 2 partial pressure. The half-velocity coefficients for H 2 utilization by dechlorinators ranged from 12 to 28 ppm for the chloroethenes and are at least an order of magnitude lower than values reported for methanogens. This implies that dechlorinating bacteria can out-compete methanogens for H 2 utilization at low H 2 concentration.

To solve or prevent copper pitting problems, it is first necessary to achieve a clearer understanding of copper corrosion theory, parts of which are currently not supported by practical experience. Some current theories of copper pitting are contradicted by practical experience. Although it has been theorized that chloride initiates copper pitting attack, simple experiments show that the presence of chloride ion actually tends to decrease the likelihood that pitting will occur. In contrast, sulfate plays no role in pitting theory, yet sulfate has consistently demonstrated a propensity to initiate and propagate copper pitting. New theories are required to reconcile pitting theory and practical observation in order to allow the rational mitigation of copper pitting problems. In addition, the presence of natural organic matter (NOM) in water supplies prevents or inhibits certain copper corrosion problems. As a result, recent efforts to remove NOM as a means of controlling disinfection by‐products may lead to increased copper corrosion problems.

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Methanosarcina species with a high maximum specific growth rate (l max ) and high half-saturation coefficient (K S ) and Methanosaeta species with a low l max and low K S are the only known aceticlastic methanogens. Because of Methanosaeta's low K S , the low acetate concentrations in conventional, mesophilic anaerobic digestion yield Methanosaeta dominance. However, Methanosarcina absorbs increases in acetate more efficiently and thus promotes more stable digestion. This paper tests the hypothesis that decreasing digester feeding frequencies can increase Methanosarcina predominance. Two acetate-fed reactors were established at a 17-day solids retention time. One reactor was fed hourly, and one was fed once daily. Microscopic and molecular methods were used to verify that the hourly fed reactor enriched for Methanosaeta, while the daily fed reactor enriched for Methanosarcina. Growth and substrate-use kinetics were measured for each reactor. A digester overload condition was simulated, and the Methanosarcina-enriched reactor was found to perform better than the Methanosaeta-enriched reactor. These findings indicate that Methanosarcina dominance can be achieved with infrequent feedings, leading to more stable digestion. Water Environ. Res., 78, 486 (2006).

The anodic film generated in acid electrolytes on high-purity aluminum shows a porous morphology, formed by the packing of approximately hexagonal cells of alumina, containing a centrally located cylindrical pore. Conversely, during anodizing of an AA2024 T3 alloy, the presence of alloying elements, both in solid solution and as second-phase material, influences the filming behavior, with a less regular film morphology developed above the aluminum alloy matrix, and characteristic morphologies generated above and in the zone of influence of second-phase particles. Further, the anodizing behavior of the alloying elements is determined by the applied potential. In this work, the anodizing behavior of AA2024 T3 commercial alloy in sulfuric acid electrolyte has been characterized. Specifically, phenomena related to the oxidation of the second-phase particles have been separated from those associated with the oxidation of the copper-containing aluminum matrix. This has used electrochemical data obtained under potentiostatic and potentiodynamic conditions for the AA2024 T3 alloy, high-purity aluminum, and model Al-Cu alloys, which have been correlated with detailed examination of plan and sectional views of the anodized substrates.