Specific Conductance Values Research Articles

Taxonomy and ecological distribution of the genus Microspora (Microsporaceae, Chlorophyta) in lotic ecosystems of São Paulo State, southeastern Brazil

Occurence of populations of the genus Microspora was investigated in 172 stream segments, which were sampled from May to October in 1992-1993 and 1996-1997 in six natural regions (parts of biomes or geological areas) of Sao Paulo State, southeastern Brazil. Three species were recognized, distinguished on the basis of shape and size of vegetative cells, H-shaped cell wall pieces and presence of rings in transverse cell walls. M.floccosa had cells with larger diameter (> 9.5 μm) and H-shaped structures clearly discernible throughout the filament lenght. M. quadrata and M. stagnorum had cells with smaller diameter (≤ 9.5 μm), the former with straight inner corners and the latter with rounded inner corners. H-pieces were discernible throughout the filament length in M. quadrata, whereas in M. stagnorum they were more clearly distinguishable at the terminal cells of the filament. In addition, the transverse cell walls of M. stagnorum had reddish to brownish rings. In comparison to macroalgal communities as a whole, the genus Microspora occurred under similar mean values of temperature (19.7 x 19.6 °C, respectively), specific conductance (72 x 69 μS cm -1 ), turbidity (8 x 9 NTU) and pH (6.9 x 6.8) but higher current velocity (48 x 63 cm s -1 ) and lower oxygen saturation (66 x 58 %). Trends for occurrence of individual species were considerably variable around these values. In terms of species occurrence in the regions of Silo Paulo State, the species of Microspora showed a relatively restricted distribution: M. floccosa occurred in only 9 sampling sites of three regions, whereas M. quadrata and M. stagnorum were present in only 3 sites of two regions. The three species were previously reported in boreal, temperate and tropical regions of the world.

Moisture dependence of thermal properties of sheanut kernel

The values of specific heat, thermal conductivity and thermal diffusivity of shea nut kernel were determined and their variation with moisture content investigated. Specific heat was found to be both moisture and temperature dependent. Its value increased linearly with moisture content and temperature in the moisture and temperature range of 3.32–20.70% (db) and 303–363 K, respectively. Thermal conductivity and thermal diffusivity also increased linearly with moisture content in the above moisture range, within the temperature range of 347.5–349.5 K. Regression equations which could be used to reasonably predict the values of these properties at specified moisture content, were established.

X-ray, Electrolytic Conductance, and Dielectric Studies of Bile Salt Micellar Aggregates

Previously, structural models, observed in fibers and crystals, were proposed for sodium deoxycholate (NaDC), glycodeoxycholate (NaGDC), taurodeoxycholate (NaTDC), and taurocholate (NaTC) micellar aggregates, and were verified in aqueous solutions by means of several techniques. Here we report the X-ray analysis of sodium glycocholate (NaGC) fibers, which indicates that NaGC micellar aggregates could be formed by dimers and octamers as in the case of NaTC. Moreover, we present electrolytic conductance and dielectric measurements on NaGDC, NaTC, and NaGC aqueous micellar solutions to verify our micellar aggregate models. Specific conductance values of 0.1 mol dm-3 NaDC, NaTDC, NaGDC, NaTC, and NaGC solutions containing NaCl at concentration ranging from 0 to 0.8 mol dm-3 practically do not depend on the particular bile salt. Comparison with NaCl values shows that bile salt contribution to conductance decreases by increasing NaCl concentration, is nearly zero around the concentration range 0.5−0.6 mol dm-3, and becomes negative at higher concentration. This behavior can be explained if Na+ ions strongly interact with bile salt anions and reinforce their interaction when micellar size increases. Even the inclusion of Na+ and Cl- ions, coming from NaCl, into micellar aggregates cannot be excluded, especially at high ionic strength. NaDC, NaTDC, NaGDC, NaTC, and NaGC present high values of the average electric dipole moment per monomer μ that can be justified by a remarkable hydration of their micellar aggregates. Reasonably, micellar aggregate composition and population change very slightly or do not change at all within the temperature range 15−45 °C, because μ is nearly constant in this interval. Results also suggest that Na+ ions are anchored to anions in dilute solution, thus forming ion pairs in the case of NaTC and NaGC, at least. Dihydroxy and trihydroxy bile salts are characterized by very similar cation−anion interaction strengths, even though their structures are different. The trend of μ, which moderately decreases by increasing bile salt concentration, agrees with our structural models and can be due to coexistence of two structures, at least.

Photopyroelectric thermal wave setup for the absolute measurement of the thermal conductivity of low density gases

A photopyroelectric setup for the accurate absolute measurement of the thermal conductivity of dilute gases is presented. The technique results from a modification of our previously described [Rev. Sci. Instrum. 69, 2452 (1998)] technique for the simultaneous measurement of absolute values of specific heat capacity and thermal conductivity of liquids. Measurement results are presented for different gases at room temperature and at one atmosphere as well as for the dilute Knudsen gas regime at reduced pressure. It is also demonstrated that the setup can be operated as a sensitive pressure gauge with adaptable sensitivity range.

The Distribution of Anurans in Two River Systems of a Coastal Plain Watershed

The Distribution of Anurans in Two River Systems of a Coastal Plain Watershed

Thermal and Chemical Properties of Waldo Lake, Oregon

ABSTRACT Thermal and chemical profiles were obtained periodically in ultraoligotrophic Waldo Lake, Oregon during years 1986 through 1999. Profiling was done on a seasonal basis between May and October. During this period the lake becomes thermally well-stratified. Epilimnetic temperatures peak in August, then rapidly diminish in response to decreasing solar radiation. By October, the lake nears autumnal turnover. During winter, the lake freezes over. The lake features an orthograde oxygen profile, and is well-oxygenated to all depths. The lake is highly dilute, as indicated by extremely low values for specific conductance (2.9–5.2 μmhos cm−1) and alkalinity (0.39–0.71 mg·L−1 as HCO3). pH readings were nearly all less than 7.0. Inorganic phosphorus and nitrogen concentrations were mostly less than the minimum detection limit of 1.0 μg·L−1. Dissolved silica concentrations ranged between 0.12 and 0.34 mg·L−1. TDS concentrations averaged 4.04 mg·L−1, with roughly 10% of all test results reported as 0.000 mg·L−1. The cause of the lake's extreme dilution is uncertain, but a major contributing factor may be the fact that the lake is fed entirely by direct precipitation and runoff, with no rivers or permanent streams entering the lake.

Role of monsoon rain on concentrations and dispersion patterns of metal pollutants in sediments and soils of the Ganga Plain, India

Monsoon rain causes large scale sediment-water movement and reworking of sediments of the Ganga Plain which is one of the largest fluvial systems on Earth. Geomorphology and drainage type combined with sedimentation processes play a substantial role on dispersion and transport patterns of metals bound to sediments and soils. The study area of Kanpur-Unnao industrial region in the Ganga Plain has been divided into five independent geochemical domains on the basis of sediment-geomorphic, hydrological and geochemical characters. The monsoon hydrography and physico-chemical parameters (pH, conductivity) of the river and urban drain waters play a prominent role in regulating the concentrations and behaviour of the metals in the aquatic system of the Ganga Plain. Values of pH and specific electrical conductivity of the river water of the study area decrease whereas those of the urban drain water increase in post-monsoon period. The monsoon rain reduces the contents of Co, C-org, Cr, Fe and Ni and enhances the contents of Cd, Sn and Zn in sediments of post-monsoon period. In soils, it reduces the contents of Al, Co, Fe, Mn and Ni and enhances the contents of Cd, Sn and Zn in the post-monsoon period. These changes in concentrations vary from metal to metal and from one geochemical domain to the other. An increase in the concentrations of few metals in the soils from pre- to post-monsoon periods indicates that these metals were mobilized from the overflooding of metal rich waste-water onto the fields during high water stage and also by reworking of the soils through sheet floods during the monsoon time. Despite the changes in concentrations, metal dispersion patterns in each domain remain similar both in pre- and post-monsoon periods which indicate that the geochemical and sediment-geomorphic processes operating for the metal dispersion and mobilization in sediments are persistent even after large scale sediment-water movement and reworking of the sediments during the monsoon period.

Pulmonary function in children with atrial septal defect before and after heart surgery

ObjectiveTo test the effect of heart disease and heart surgery on lung function.DesignA pulmonary function study of children undergoing surgery for atrial septal defect (ASD).SettingsUniversity hospital.Patients26 children tested before surgery...

Absolute values of specific heat capacity and thermal conductivity of liquids from different modes of operation of a simple photopyroelectric setup

Photothermal techniques offer a nice tool for the determination of changes in thermal parameters of different types of samples. Using a very thin pyroelectric transducer, a very simple and versatile ac calorimeter can be built. The described inverse pyroelectric technique allows high-resolution ac-calorimetric measurements of the temperature dependence of the specific heat capacity. Since measuring frequencies up to a few hertz can be used, which are higher than in most alternative ac-calorimetric setups, noise can be reduced and measuring times shortened. With a small modification of the measurement cell, the determination of absolute specific heat capacity and thermal conductivity values of liquid samples was achieved. Comparison of the frequency response of the system with and without a solid thermal load in the neighborhood of the sample yields data with an accuracy of about 5% and 10% for specific heat capacity and thermal conductivity, respectively. If necessary, absolute values of specific heat capacity and thermal conductivity can also be obtained by making contact between a (solid) thermal load and the liquid. A pure ac-calorimetric operation is then no longer possible, thus restricting this mode of operation to homogeneous or to properly aligned anisotropic liquids.

Wetland hydrology as a function of hydrogeomorphic (HGM) subclass

Characterizing wetland hydrology is key to assessing relative function over a range of wetland types. However, hydrologic data are often lacking. To address this lack of information, we categorized a set of 24 reference wetlands by hydrogeomorphic (HGM) subclass from 1993 to 1995, installed monitoring wells and piezometers, and assessed local water-table levels, pH, and specific conductance by month. Four HGM wetland subclasses were common to central Pennsylvania (riparian depression (n=8), slope (n=7), mainstem floodplain (n=5), and headwater floodplain (n=4)) and formed the basis for our analysis. Median depth to water in the wells differed by HGM subclass. Riparian depressions had the shallowest depth to water (−8 cm) and headwater floodplain wetlands the greatest (−70 cm). Comparisons of the percent occurrence of a piezometric head (from comparisons between paired piezometer and slotted wells) indicated that riparian depressions and slopes had significant ground-water inputs (47 and 48%, respectively), whereas the mainstem floodplain (31%) and headwater floodplain wetlands (23%) were more surface-water-driven systems. Water occurred within the root zone (30 cm) most often for riparian depressions (80% of observations), intermediate for slopes (48%), and least for mainstem floodplains (17%) and headwater floodplains (6%). Headwater floodplain wetlands were never inundated by overbank flow during this study but instead received water from snowmelt and overland flow after rain events. Mainstem floodplain wetlands were inundated by floods during major storm events. The upper 30 cm of soil (i.e., the root zone of plants) was almost continually saturated in riparian depressions, but rarely for both floodplain systems. Slope wetlands were intermediate between riparian depressions and floodplain systems in the amount of time water was present within 30 cm of the ground surface. Riparian depressions and slopes had lower pH than floodplain systems, and pH did not vary significantly by month for any HGM subclass. Floodplain systems (both headwater and mainstem) had greater values of specific conductance than either riparian depressions or slopes; riparian depressions were the only HGM subclass to show seasonality in specific conductance. Factors other than HGM subclass that may have influenced the hydrologic pattern and water quality parameters included bedrock geology, disturbance levels, and watershed attributes.

The Role of SO 2 as an Additive to Organic Li‐Ion Battery Electrolytes

Previous work has shown that the addition of a large amount of sulfur dioxide (∼20 weight percent) promotes the reversible intercalation‐deintercalation of Li ions into graphite in selected nonaqueous electrolytes. These electrolytes were previously considered to be incompatible with graphite negative electrodes because of solvent‐graphite interaction, which led to catastrophic graphite exfoliation of the graphitic structure. We have performed a series of conductivity studies along with electrochemical experiments at varying concentrations. The electrolyte solutions were composed of either or . We found that the specific conductance values of the organic electrolytes containing were increased dramatically. Cyclic voltammetry and Fourier transform infrared measurements show that the use of as an additive to the organic solutions, even at very low levels, offers the advantage of forming fully developed passive films on the graphite electrode at potentials much higher than that of the electrolyte reduction itself. These graphite surface films are composed of mixtures of and solvent reduction products. The reduction products are primarily responsible for the improved characteristics of the Li‐ion cells containing these ‐based electrolytes.

Effect of Watershed Disturbance on Pinelands Stream Vegetation

ZAMPELLA, R. A. AND K. J. LAIDIG (Pinelands Commission, New Lisbon, NJ 08064). Effect of watershed disturbance on Pinelands stream vegetation. J. Torrey Bot. Soc. 124: 52-66. 1997.-We related stream channel and stream bank plant species composition to eighteen site specific and regional environmental variables in the New Jersey Pinelands (Pine Barrens). Canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA) related major patterns in species composition to complex watershed disturbance gradients. There were significant correlations between the first axes of both the CCA and DCA stream site ordinations and agricultural and developed land cover in a drainage area, pH, specific conductance, and channel sediment. There was a clear contrast between stream stations found within relatively undeveloped watersheds and those in highly developed or farmed drainage areas. Surface waters of the undisturbed sites displayed lower pH and specific conductance values compared with waters in the more disturbed watersheds. The most heavily impacted sites supported a unique group of peripheral or exotic plant species that replaced characteristic Pine Barrens species. Overall species richness did not change in response to watershed disturbance. The presence of disturbance indicator species, or species found only at disturbed sites, provided a good measure of watershed disturbance. High between-site variability in the species present at relatively undisturbed stations and the persistence of some species at more recently disturbed sites complicated the identification of sensitive species, or species found only at undisturbed sites. A comparison of the number of species historically found within and outside the Pine Barrens, rather than the presence or absence of particular sensitive species, provided an additional measure of ecological integrity.

Quantitative morphology of physiologically identified and intracellularly labeled neurons from the guinea-pig laterodorsal tegmental nucleus in vitro

Mesopontine cholinergic neurons have been implicated in the initiation and maintenance of rapid eye movement sleep via their efferent connections to the thalamus and the medial pontine reticular formation. As a first step toward understanding how these modulatory neurons integrate synaptic input, we have investigated the dendritic architecture of laterodorsal tegmental nucleus neurons. The principal cells of the guinea-pig laterodorsal tegmental nucleus were identified electrophysiologically in a brain slice preparation, then were intracellularly injected with biocytin and reconstructed using a computer-aided tracing system. The somata were large (27 ± 3 μm; n = 11) and gave rise to an average of 4.8 primary dendrites which, in most cases, emerged from the soma in a pattern that was radially symmetric in the plane of the slice. Primary dendrites had an average of 3.7 endings. A single axon arose from either the soma or a proximal dendrite and exited the nucleus with a medial and/or lateral trajectory. Some axons also gave rise to a local terminal plexus composed of fine fibers bearing numerous punctate swellings that ramified profusely within the neuron's dendritic field. Total dendritic area averaged about 10 5 μm 2, and therefore the average contribution of the soma to the total surface area (20%) was significantly larger than the values reported for many other cell types. Dendritic diameters were non-uniform in three respects. Some processes were sparsely spiny. Most processes were varicose, with the degree of varicosity increasing substantially in secondary and tertiary dendritic segments. There was also a large degree of taper in dendritic processes; those processes with a non-negative taper had an average diameter decrease of 40 ± 25%. Dendritic processes deviated from the criteria necessary for a Rall equivalent cylinder approximation due to non-uniformity in morphotonic path length, failure to conform to the Rall 3/2 branching rule and non-uniformity of dendritic diameter. An analysis was done to assess the impact of dendritic varicosities on the extraction of cable parameters for these cells. Voltage traces were simulated by solving the cable equation for a varicose dendrite and then membrane parameters were recovered using an equivalent cylinder model. Errors in the extracted values of specific membrane conductance and specific membrane capacitance were quite small (≤5%), while larger errors were seen for electrotonic length (≤21%) and intracellular resistivity (≤50%). These data indicate that the principal cells of the laterodorsal tegmental nucleus, while possessing a relatively simple dendritic structure in terms of number and branchiness of dendrites, display a heterogeneity of dendritic process types. Processes range from smooth to markedly varicose, and can be aspiny or sparsely spiny. The possibility that the dendritic varicosities function as sites of either electrical or chemical compartmentalization is discussed. The degree of error resulting from a Rall equivalent cylinder approximation in light of these varicosities indicated that a generalized cable model approach may prove more effective in estimating their cable parameters.

Physicochemical studies of aqueous sodium dodecyl sulphate solutions in pyridine and isomeric picolines

Specific conductance and surface tension values have been reported for aqueous solutions of sodium dodecyl sulphate (SDS) with or without cosolvents, namely, pyridine, α-, β- and γ-picolines at 298.15, 308.15 and 318.15 K. The observed specific conductance data have been utilised to evaluate values of the counter-ion association constant (α) and the limiting equivalent conductance (Λ0) obtained from Onsager's relation. Surface properties, namely surface pressure at the CMC surface excess concentration and minimum area per molecule of surfactant at the air-liquid interface have been obtained from surface tension data. Thermodynamic quantities of micellisation, adsorption at the liquid-air interface and transfer of surfactant molecules from aqueous solution to mixed solvents, evaluated from the CMC data, are reported. While the process of micellisation as well as adsorption at the air-liquid interface are exothermic, transfer of SDS from water to mixed solvent is accompanied by an increase in enthalpy. The observed positive values of Gibb's energy for the transfer of SDS from water to mixed solvent suggests the non-feasibility of such a transfer. The observed data have been interpreted in terms of intermolecular interactions operating between the component molecules in the solution.

Cycloaliphatic Epoxide‐Based Photocured Gelled Electrolytes for Secondary Lithium Battery Applications: Electrochemical Kinetic Studies

Cycloaliphatic epoxide‐based thin gelled films prepared by ultraviolet photocuring were characterized electrochemically. Mixtures of ethylene carbonate and various organic liquids in different volume ratios were used as solvents. General composition of the electrolyte was cycloaliphatic epoxide (being sold under the trade name ENVIBAR by Union Carbide) 10 to 28 weight percent (w/o), polyethylene oxide (200,000 Mw) 4 to 10 w/o, , 6 to 22 w/o, and mixed solvents (of different volume ratios) 80 to 40 w/o. Thin gelled films were formed on lithium (Li) electrodes and subjected to electrochemical studies. Typical values of bulk electrolyte specific conductivity and interfacial resistance obtained from ac impedance and dc measurements at room temperatures are and 3.2 Ω, cm2, respectively. Charge/discharge characteristics of the cells of the type were evaluated. Cathode utilization was only 33% of the total capacity.

Leachate Geochemistry at a Municipal Landfill, Memphis, Tennessee

A leachate plume emanating from the Shelby County Landfill located at Memphis, Tennessee is defined using selected major and trace inorganic constituents. High specific conductance values and elevated concentrations of ammonia, barium, boron, calcium, chloride, dissolved solids, potassium, sodium, and strontium were measured in water samples from wells screened in the alluvial and Memphis aquifers downgradient from or proximal to the landfill. Of these constituents, barium, boron, chloride, and strontium were used in the geochemical model code PHREEQE to estimate the percent leachate component in selected Memphis aquifer samples. Estimates of the leachate component in samples from affected Memphis aquifer wells range from 5 to 37 percent for barium and strontium, the most reliable tracers found during this study.

Reproducible Well‐Purging Procedures and VOC Stabilization Criteria for Ground‐Water Sampling

AbstractRecent research has confirmed that low flow rate purging (i.e., ∼11/min) is a valid technique for 2 (5 cm) diameter monitoring wells with short screened intervals. The use of low flow, dedicated pumping devices for purging and sampling minimizes both the disturbance of stagnant water in the well casing and the potential for mobilization of particulate or colloidal matter which could lead to sampling artifacts. In addition, these techniques allow the use of purging indicator parameters (e.g., dissolved oxygen and specific conductance) to determine when to collect a sample for volatile organic compound (VOC) determinations. Detailed results from a monitoring network in a sand and gravel aquifer contaminated by organochlorine solvents support these findings. Recent publications on monitoring well hydraulic behavior and considerations of mass averaging effects due to pumping also support the use of low flow rate, minimal drawdown purging procedures to achieve reproducible sampling results. The suggested procedure includes documenting purging indicator parameters while purging with dedicated devices at low flow rates with minimal drawdown. This sampling method is less time‐consuming and reduces the need to handle large volumes of purge water since VOC concentrations, 02, and specific conductance values stabilized consistently in less than one bore volume.

Electrical Conductivity of Molten Slags of CaF2+Al2O3 and CaF2+Al2O3+CaO Systems for ESR.

The electrical conductivity of the molten slags of the CaF2+Al2O3 and CaF2+Al2O3+CaO systems for the practical ESR was determined, using the constant-current single pulse technique with three lead-electrodes. All the measurements were carried out under high-purity argon atmosphere, employing a high-purity molybdenum metal crucible with pure iron wire electrodes. The effects of FeO, MnO, MgO, Cr2O3, TiO2, SiO2 and other oxide components and temperature on the conductivity of the slags were examined. The results indicated that in the common concentration ranges for the ESR practice, the specific conductivity values of the slags in these two systems are monotonously increasing with the FeO and MnO contents in the slags following an essentially similar pattern; the additions of MgO, Cr2O3 and TiO2 change also evidently the conductivity but in another roughly similar mode and make it have a maximum value, whilst the influence due to a small amount of SiO2 (≤1.5 mass%) is relatively not large; the conduction of CaF2-based multi-component and complicate liquid slags may be treated as a rate process.

Water Relations and Hydraulic Architecture of a Tropical Tree (Schefflera morototoni)

The water relations and hydraulic architecture of a tropical tree (Schefflera morototoni) and of two temperate species (Acer saccharum and Thuja occidentalis) are reported. Among the water relations parameters measured were leaf and stem water storage capacity, leaf water potential, transpiration, and vulnerability of stems to cavitation and loss of hydraulic conductivity by embolisms. Among the hydraulic architecture parameters measured were hydraulic conductivity per unit pressure gradient, specific conductivity, leaf-specific conductivity, and Huber value. In terms of vulnerability of stems to cavitation, stem and leaf capacitances, and leaf-specific conductivity, all three species followed the same sequence: Schefflera > Acer > Thuja. It is argued here that the high stem capacitance and high leaf-specific conductivity of Schefflera are necessary to compensate for its high vulnerability to cavitation. Extractable water storage per unit leaf area in Schefflera stems is >100 times that of Acer and may permit the species to survive unusually long, dry seasons in Panama. Although Schefflera frequently grows >20 meters, the biggest resistance to water flow in the shoots resides in the leaves.

Riparian zone as a source of phosphorus for a groundwater-dominated lake

Groundwater entering Lake Bysjön in southern Sweden is somewhat higher in specific conductance and up to 20 times higher in phosphate than the mean for the lake. This leads to elevated values of both specific conductance and phosphate in lake water within a 500 m long and several meter wide strip along the shore. In areas not influenced by groundwater inflow, specific conductance and phosphorus content near the shore are close to that of open lake water. High concentrations of phosphate (up to 9 mg/l PO 4-P) in the inflowing groundwater originate from the riparian zone surrounding the lake. It is suggested that, over a long time, this ecotone has accumulated phosphorus and other nutrients that were transported from the adjacent developed areas and arable land. This phosphorus is now entering the lake, probably as a result of increased decomposition of organic matter.