The developmental features of the pancreas are reviewed as a n example of cytodifferentiation and organogenesis. Attention is directed to the regulatory characteristics of the specific proteins synthesized and secreted by the endocrine and exocrine cells. The following topics are discussed: (1) The number of specific protein species and, inferentially, the number of genes involved in differentiated function.( 2 ) The stringent regulation of the concentration of these specific proteins and the probable restriction of their synthesis to exocrine and endocrine cells. (3) The multiphasic pattern of accumulation of these specific proteins during pancreatic development and the synchronized but noncoordinate regulation of individual protein species. Synthetic rates of specific exocrine proteins in uit70 correlate closely with measurements of the accumulation of proteins during development. (4) A model postulating three regulatory transitions. The primary transition (related to organ "determination") denotes the conversion of a "predifferentiated" cell to the "protodifferentiated" state in which low but significant levels of specific proteins are present. The secondary transition is viewed as an amplification of this specific protein synthesis and is associated with typical pancreatic histogenesis. In the third regulatory transition, the synthesis of specific proteins in the "differentiated state" is modulated by diet, or hormonal states, etc. The third regulatory transition may be similar to some types of "enzyme induction" as studied in multicellular systems. (5) The differentiative fidelity in an organotypic culture system; the role of mesenchymal tissue or a particle fraction derived therefrom in supporting the protodifferentiated state and the secondary regulatory transition. (6) The possible mechanisms of the secondary regulatory transition in exocrine cells. Effects of actinomycin D, bromodeoxyuridine, and other mitotic inhibitors suggest the requirement for a critical cell division prior to the loss of proliferative capacity. (7) The synthesis of pro-insulin and insulin during primary and secondary regulatory transitions; the possible interrelationships of endocrine and exocrine cells in pancreas development.Embryological development may be viewed as the formation of cells of different phenotype from common genotypic precursors. Since the basic physiological and morphological features of cells are largely a result of their protein (enzyme) complement, the mechanisms involved in development are reduced largely to the qualitative and quantitative regulation of the proteins of the system. There have been two major lines of investigation contributing to our understanding of the processes involved in embryological development. The f i s t is concerned with the mechanism of "embryonic induction," in which a heterotypic cellular interaction results in a complex series of developmental events usually including alterations in cell proliferation, morphogenesis, and a grossly modified pattern of protein synthesis. T...

In the northern Great Lakes region, limestone sediments deposited some 400 million ybp during the Devonian era have experienced erosion, creating karst features such as caves and sinkholes. The groundwater chemical constituents of the shallow seas that produced these rock formations now contribute to the formation of a unique physical (sharp density gradients), chemical (dissolved oxygen-depleted, sulfate-rich) and biological (microbe-dominated) environment in a submerged sinkhole near Middle Island in freshwater Lake Huron. A variety of methods including aerial photography, physico-chemical mapping, time series measurements, remotely operated vehicle (ROV) survey, diver observations and bathymetric mapping were employed to obtain a preliminary understanding of sinkhole features and to observe physical interactions of the system's groundwater with Lake Huron. High conductivity ground water of relatively constant temperature hugs the sinkhole floor creating a distinct sub-ecosystem within this Great Lakes ecosystem. Extensive photosynthetic purple cyanobacterial benthic mats that characterize the benthos of this shallow sinkhole were strictly limited to the zone of ground water influence.

The relative effectiveness of commercially available road dust suppressants in abating fugitive dust emission and loss of fines from unpaved road surfaces was assessed in a field based research project. The dust suppressants srudied, lignin derivatives and chloride based compounds, were used on unpaved road test sections during the severe dusty months (late spring to fall) of 1993 and 1994 in Colorado. To measure the relative effectiveness of the different dust suppressants, comparative fugitive dust emission srudies were conducted on several unpaved road test sections using the Colorado State Universiry Dustometer, a dust sampling device developed in this research. In addition, total aggregate loss from the surfaces of the test sections was measured. Based upon the prevailing costs, analyses were performed to determined the economics of using the different dust suppressants. The research indicated that the use of the three dust suppressants snrdied reduced fugitive dust emission from the unpaved roadways by 50-70%. The total aggregate losses from the treated test sections were 42-61% less than that of the untreated control test section. The cost savings of retaining aggregare on the treated test sections more than offset the costs of the dust suppressants. resulting in an estimated cost. savings of 3046% over the untreated control test section.

Recent underwater explorations have revealed unique hot spots of biogeochemical activity at several submerged groundwater vents in Lake Huron, the third largest of the Laurentian Great Lakes. Fueled by venting groundwater containing high sulfate and low dissolved oxygen, these underwater ecosystems are characterized by sharp physical and chemical gradients and spectacularly colorful benthic mats that overlie carbon‐rich sediments. Here, typical lake inhabitants such as fish and phytoplankton are replaced by communities dominated by microorganisms: bacteria and archaea that perform unique ecosystem functions. Shallow, sunlit sinkholes are dominated by photosynthetic microorganisms and processes, while food webs in deep aphotic sinkholes are supported primarily by chemosynthesis.

Abstract. The quality of impounded waters often degrades over time because of thermal stratification, sediment oxygen demands, and accumulation of pollutants. Consequently, reservoir releases impact water quality in tailwaters, channels, and other downstream water bodies. Low dissolved oxygen (DO) concentrations in the Cumberland River below Old Hickory dam result from stratification of upstream reservoirs and seasonally low release rates. Operational changes in upstream hydropower reservoirs may be one method to increase DO levels without substantially impacting existing project purposes. A water quality model of the upper Cumberland basin is integrated into an optimal control algorithm to evaluate water quality improvement opportunities through operational modifications. The integrated water quantity/quality model maximizes hydropower revenues, subject to various flow and headwater operational restrictions for satisfying multiple project purposes, as well as maintenance of water quality targets. Optimal daily reservoir release policies are determined for the summer drawdown period which increase DO concentrations under stratification conditions with minimal impact on hydropower production and other project purposes.

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Sampling frequency for a water quality monitoring network is presented, and for illustrative purposes the criterion is applied to the Massachusetts portion of the Connecticut River basin. The proposed frequency criterion is based upon the assumption that the primary objectives of future river quality monitoring networks are the determination of ambient water quality conditions and an assessment of yearly trends rather than detection of stream or effluent standards violations. The sampling frequency criterion is derived as a function of the random variability of the river flow. The criterion is specifically related to the magnitude of the expected half width of the confidence interval of the mean of the random component of the annual statistic‐mean log river flow. The appropriate sampling intervals (at each sampling station within the river basin) are determined by specifying equality of this confidence interval half width, which insures a uniform reliability of the annual statistic.