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Notes: Specific capacity (Q/s) data are usually much more abundant than transmissivity (T) data. Theories which assume uniform transmissivity predict a nearly linear relationship between T and Q/s. However, linear dependence is seldom observed in field studies. Since hydrogeologic studies usually require T data, many hydrogeologists use linear regression analysis of T versus Q/s data to estimate T values where only Q/s data are available. In this paper we use numerical models to investigate the effects of aquifer heterogeneity on the relationship between Q/s and T estimates. The simulations of hydraulic tests in heterogeneous media show that estimates of T derived using Jacob's method tend to their late-time effective value much faster than Q/s values. The latter are found to be more dependent upon local transmissivities near the well. This explains why the regression parameters for T versus Q/s data depend on heterogeneity and the‘lateness’of the test period analyzed. Since this effect is more marked in high T zones than in low T zones, we conclude that natural aquifer heterogeneity can explain the convex deviation from linearity often observed in the field. A further result is that the geometric mean of T estimates, obtained from short and intermediate time pumping tests, seems to systematically underestimate effective T (Teff) of heterogeneous aquifers. In the studied simulation cases, the median of the T values or the arithmetic mean yield better estimates for Teff.

Notes: Cross-hole pumping tests within a subvertical shear zone in granite were interpreted using a geostatistical inverse approach. The objective was to identify flow channels that influence tracer experiments. The spatial correlation structure of transmissivity (T) was unknown. Therefore, a wide variety of geostatistical hypotheses were made for estimating a total of 40 T fields, that honor equally well the pumping tests, the static head measurements, and the point T data. All estimated T fields reveal channels with similar topology and with a preferred horizontal orientation, possibly due to vertical displacements within the subvertical shear zone. This shows that inverse geostatistical modeling of abundant hydraulic measurements can be useful to reveal a coarse heterogeneity structure, even when data are insufficient to identify the geostatistical structure. However, numerical simulations of a field tracer test were highly sensitive to the geostatistical hypotheses. In summary, T fields leading to successful hydraulic data fitting do not necessarily lead to successful transport predictions, even when they appear to reproduce the coarse heterogeneity structure.

Notes: Multipulse dynamic NMR has been employed to study molecular order and dynamics of deuteron (2H) labeled phospholipid membranes. Variation of pulse sequence and pulse separation provides the large number of independent experiments necessary for a proper molecular characterization of the systems. Analysis of these experiments is achieved by employing a density matrix formalism, based on the stochastic Liouville equation. Arbitrary relaxation rates and line shapes of single and multiple quantum transitions are considered.The various 2H NMR experiments of macroscopically unoriented bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), specifically deuterated at the 6- and 14-position of the 2-chain, are faithfully reproduced by the model. Computer simulations provide the orientational distributions and conformations of the hydrocarbon chains and the correlation times of the various motions. In the Lα phase the correlation times τR(parallel) and τR⊥ for chain rotation and chain fluctuation are of the order of 10−8 s, while trans–gauche isomerization occurs significantly faster (τJ∼10−10 s). At the main transition all chain motions slow down abruptly. Further cooling in the Pβ' phase first continuously decreases the motions. However, 10 K below the pretransition (hysteresis), there is another abrupt slow down of the chain dynamics. In the Lβ' phase at T=265 K all three motions occur with correlation times of 10−6 to 10−5 s. Because of higher activation energies, however, intermolecular chain motions freeze out first on the time scale of a particular NMR experiment. Thus, at temperatures T〈210 K, trans–gauche isomerization becomes the dominant process. Detection of this motion is possibleeven at T=168 K, where τJ is of the order of 10−4 s. Arrhenius plots of the various correlation times provide the motional activation energies. Values of 9〈EJ〈14 kJ/mol for trans–gauche isomerization correspond to the local character of this process. As expected, the activation energies for chain rotation (50〈ER(parallel) 〈69 kJ/mol) and chain fluctuation (53〈ER⊥ 〈79 kJ/mol) are substantially higher. The correlation times for methyl group rotation form a continuous straight line on the Arrhenius plot throughout the three phases studied, yielding an activation energy of EJ(CD3) =9.9 kJ/mol. Molecular order of the chains is discussed in terms of two parameters SZZ and SZ′Z′, characterizing the orientational order of the chains as a whole and the conformational order at a particular segment. In the Lα phase the hydrocarbon chains are partially disordered (0.44〈SZZ 〈0.6) and melted, exhibiting segmental order parameters of SZ′Z′ (C-6)∼0.75 and SZ′Z′ (C-13)∼0.35, respectively. As expected, conformational order decreases from the central unit to the terminal one (order gradient). The Pβ' phase exhibits two different chain order parameters of SZZ ∼0.6 and SZZ ∼0.9, indicating heterogeneous chain packing. A unique structural interpretation of this result is not yet possible since the microscopic heterogeneity is compatible with most proposed models. In the Lβ' phase we find SZZ 〉0.95, SZ′Z′ (C-6)〉0.95, and SZ′Z′ (C-13)〉0.9, consistent with highly ordered, fully extended hydrocarbon chains.

Notes: Abstract Bile salts are the major organic solutes in bile and undergo extensive enterohepatic circulation. Hepatocellular bile salt uptake is mediated predominantly by the Na+-taurocholate cotransport proteins Ntcp (rodents) and NTCP (humans) and by the Na+-independent organic anion-transporting polypeptides Oatp1, Oatp2, and Oatp4 (rodents) and OATP-C (humans). After diffusion (bound by intracellular bile salt-binding proteins) to the canalicular membrane, monoanionic bile salts are secreted into bile canaliculi by the bile salt export pump Bsep (rodents) or BSEP (humans). Both belong to the ATP-binding cassette (ABC) transporter superfamily. Dianionic conjugated bile salts are secreted into bile by the multidrug-resistance-associated proteins Mrp2/MRP2. In bile ductules, a minor portion of protonated bile acids and monomeric bile salts are reabsorbed by non-ionic diffusion and the apical sodium-dependent bile salt transporter Asbt/ASBT, transported back into the periductular capillary plexus by Mrp3/MRP3 [and/or a truncated form of Asbt (tAsbt)], and subjected to cholehepatic shunting. The major portion of biliary bile salts is aggregated into mixed micelles and transported into the intestine, where they are reabsorbed by apical Oatp3, the apical sodium-dependent bile salt transporter (ASBT), cytosolic intestinal bile acid-binding protein (IBABP), and basolateral Mrp3/MRP3 and tAsbt. Transcriptional and posttranscriptional regulation of these enterohepatic bile salt transporters is closely related to the regulation of lipid and cholesterol homeostasis. Furthermore, defective expression and function of bile salt transporters have been recognized as important causes for various cholestatic liver diseases.

Notes: : Expansion of the electrical generation system in the Pennsylvania-Jersey-Maryland power pool will impact, and be constrained by, inland water availability. Future interpretations of the Federal Water Pollution Control Act Amendments of 1972 regarding evaporative cooling towers for coastal power plants, offshore siting and energy centers, and the policies and public acceptability of low flow augmentation reservoirs are some of the issues examined in this paper using scenarios generated by the Brookhaven National Laboratory Regional Energy Facility Siting Model (REFS). REFS is a multicommodity, transshipment-location linear programming model used here to allocate power plants among counties in a power pool under a minimization of cost objectives. The solutions are sensitive to the water resources assumptions in the model. For the year 2000, the amount of low flow augmentation allowed in the region's river basins and whether off-shore siting becomes a reality are the two water resources related issues which most affect the scenarios. The results show that decisions regarding specific water problems can have region wide implications for water and nonwater related issues.

Notes: SUMMARY. The influence of exposure time upon macro-invertebrate colonization on modified Hester-Dendy substrate samplers was investigated over a 60-day period. The duration of exposure affected the number of individuals, taxa and community diversity.The numbers of individuals colonizing the samplers reached a maximum after 39 days and then began to decrease, due to the emergence of adult insects. Coefficients of variation for the four replicate samples retrieved each sampling day fluctuated extensively throughout the study. No tendencies toward increasing or decreasing coefficients of variation were noted with increasing time of sampler exposure.The number of taxa colonizing the samplers increased throughout the study period. The community diversity index was calculated for each sampling day and this function tended to increase throughout the same period. This supports the hypothesis that an exposure period of 6 weeks, as recommended by the United States Environmental Protection Agency, may not always provide adequate opportunity for a truly representative community of macro-invertebrates to colonize multiplate samplers.Many of the taxa were collected in quite substantial proportions after periods of absence or extreme sparseness. This is attributed to the growth of periphyton and the collection of other materials that created food and new habitats suitable for the colonization of new taxa.Investigation of the relationship between ‘equitability’ and length of exposure revealed that equitability did not vary like diversity with increased time of exposure.