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In open channel systems the phenomenon commonly referred to as clogging is caused by settling and straining of suspended sediment as water moves through the channel bed material, as well as by microbial transport, colonization, and other biological and chemical action. This paper summarizes a threeyear investigation of the clogging process due to accumulation of fine soil particles as it occurs in sedimentladen open channel flow. Significant results include experimental relationships developed between major independent variables i.e., flow velocity, suspended sediment concentration, and suspended sediment particle size distribution and the infiltration reduction occurring through a sand bed filter in the bottom of a recirculating laboratory flume. Factors affecting both magnitude and temporal variation of channel bed infiltration are explained as well as observed differences in the physical nature of the clogged layer developed atop the filter bed. Significant features of sedimentary clogging in open channel flow are also correlated with traditional hydraulic and sediment transport variables and processes. In addition, a dimensional analysis of sedimentary clogging is presented as a focus for future experimental investigation.

ABSTRACTSublethal infection of BALB/c mice with the intracellular bacterial pathogen Listeria monocytogenesleads to the development of antilisterial immunity with concurrent stimulation of major histocompatibility complex (MHC) class Ia- and Ib-restricted CD8+effector T cells. Secondary L. monocytogenesinfection is followed by an accelerated increase in the number of Listeria-specific CD8+cells and rapid clearance of the bacterium from the murine host. Recovery from secondary infection is associated with increased levels of effector cell function, as measured by gamma interferon secretion following coculture of immune cells with L. monocytogenesinfected APCs in vitro, as well as antilisterial cytotoxicity, as measured by effector cell recognition of L. monocytogenes-infected target cells. We assessed the frequency ofL. monocytogenes-specific MHC class I-restricted cells following secondary infection by ELISPOT assays utilizing coculture of immune cells with L. monocytogenes-infected antigen-presenting cells that express MHC class Ia and/or Ib molecules. We found that the antilisterial Qa-1b(MHC class Ib)-restricted effector subset is not detected as an expanded population following secondary infection compared to the frequency of this effector population as measured following recovery from primary infection. This is in contrast to the frequency of antilisterial H2-Kd(MHC class Ia)-restricted effector cells, which following recovery from secondary infection are detected as an expanded population, and appears to undergo a substantial expansion event 3 to 4 days post-secondary infection. These results are consistent with the conclusion that althoughListeria-specific MHC class Ib-restricted effector cells are present following recovery from secondary infection, this subset does not appear to undergo the expansion phase that is detected for the MHC class Ia-restricted effector cell response.

In open channel systems the phenomenon commonly referred to as clogging is caused by settling and straining of suspended sediment as water moves through the channel bed material, as well as by microbial transport, colonization, and other biological and chemical action. This paper summarizes a three‐year investigation of the clogging process due to accumulation of fine soil particles as it occurs in sediment‐laden open channel flow. Significant results include experimental relationships developed between major independent variables (i.e., flow velocity, suspended sediment concentration, and suspended sediment particle size distribution) and the infiltration reduction occurring through a sand bed filter in the bottom of a recirculating laboratory flume. Factors affecting both magnitude and temporal variation of channel bed infiltration are explained as well as observed differences in the physical nature of the clogged layer developed atop the filter bed. Significant features of sedimentary clogging in open channel flow are also correlated with traditional hydraulic and sediment transport variables and processes. In addition, a dimensional analysis of sedimentary clogging is presented as a focus for future experimental investigation.

ABSTRACTListeria monocytogenesis an intracellular bacterial pathogen that elicits a strong cellular immune response following infection and therefore has potential use as a vaccine vector. However, while infections by L. monocytogenesare fairly rare and can readily be controlled by a number of antibiotics, the organism can nevertheless cause meningitis and death, particularly in immunocompromised or pregnant patients. We therefore have endeavored to isolate a highly attenuated strain of this organism for use as a vaccine vector. d-Alanine is required for the synthesis of the mucopeptide component of the cell walls of virtually all bacteria and is found almost exclusively in the microbial world. We have found in L. monocytogenestwo genes that control the synthesis of this compound, an alanine racemase gene (dal) and ad-amino acid aminotransferase gene (dat). By inactivating both genes, we produced an organism that could be grown in the laboratory when supplemented with d-alanine but was unable to grow outside the laboratory, particularly in the cytoplasm of eukaryotic host cells, the natural habitat of this organism during infection. In mice, the double-mutant strain was completely attenuated. Nevertheless, it showed the ability, particularly under conditions of transient suppression of the mutant phenotype, to induce cytotoxic T-lymphocyte responses and to generate protective immunity against lethal challenge by wild-type L. monocytogenesequivalent to that induced by the wild-type organism.

Diffusion and mass flow were important mechanisms of oxygen transport in soil columns intermittently flooded with sewage water. The amount of oxygen entering the soil by mass flow during drainage was 30 to 40% of the total amount entering the soil. Most of the estimated available oxygen was used in the oxidation of NH4+to NO3−. Enough oxygen entered the soil during a 5‐day dry period to oxidize all of the nitrogen applied when the soil was flooded for 6 days with secondary sewage effluent containing 20 mg/liter of NH4‐N at an infiltration rate of 50 cm/day. Application of NH4+in excess of that which could be oxidized during the dry period resulted in a gradual increase in the NH4+concentration of the reclaimed water. An increase in NH4+concentration can be prevented by balancing the NH4‐N applied against the oxygen entered during the dry period. Most of the oxygen entered the columns during the first 3–4 days of the dry period. Thus the amount of oxygen entering the soil can be increased more effectively by increasing the frequency rather than the length of the dry periods. The soil profile remained in a reduced state below the 140‐cm depth during a 10‐day dry period. This showed that NH4+stored below this depth would not be nitrified and that an environment favorable for denitrification was maintained in part of the profile at all times. Anaerobic reactions were as effective as aerobic reactions in reducing the chemical oxygen demand (COD) of sewage water from 50 to 18 mg/liter.