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  • Springer  (73)
  • 1985-1989  (73)
  • 1940-1944
  • 1
    Electronic Resource
    Electronic Resource
    Voltage- and time dependence of apical membrane conductance during current clamp inNecturus gallbladder epithelium (1988)
    Springer
    The journal of membrane biology 103 (1988), S. 191-204 
    Details
    ISSN: 1432-1424
    Keywords: voltage-dependent K+ channel ; TEA+ ; barium ; circuit analysis ; cable analysis ; current-voltage relationship
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effects of short (1 sec) and long (1 min) transepithelial current clamps on membrane voltages and resistances ofNecturus gallbladder were investigated. Transepithelial and cell membrane current-voltage relationships determined from 1-sec clamps revealed that: a) depolarization of the apical membrane voltage (V mc) results in a marked decrease in apical membrane fractional resistance (fR a), whereas hyperpolarization ofV mc results in either no change infR a or a small increase, and b) the voltage-dependent changes infR a are essentially complete within 500 msec. Exposure of the tissue to 5mm TEA+ on the mucosal side caused no significant change in baselineV mc (−69±2 mV) and yet virtually abolished the voltage dependence offR a. A possible interpretation of these results is that two types of K+ channels exist in the apical membrane, with different voltage dependencies and TEA+ sensitivities. Acidification or Ba2+ addition to the mucosal solution also reduced the voltage-dependent changes infR a. The time courses of the changes infR a and in the cable properties of the epithelium were assessed during 1-min transepithelial current clamps (±200 μA/cm2). No secondary change infR a was observed with mucosa-to-serosa currents, but a slow TEA+-sensitive decrease infR a (half-time of seconds) was evident with serosa-to-mucosa currents. Cable analysis experiments demonstrated that the initial (〈500 msec) voltage-dependent decrease infR a is due to a fall in apical membrane resistance. The later decrease infR a is due to changes in both cell membrane resistances attributable to the increase in transcellular current flow resulting from a fall in paracellular conductance. The voltage dependence of the apical membrane conductance is a more significant problem in estimatingfR a than the current-induced effects on the lateral intercellular spaces. In principle, TEA+ can be used to prevent the nonlinear behavior ofR a during measurements of the voltage divider or membrane resistance ratio.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870949
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  • 2
    Electronic Resource
    Electronic Resource
    Dependence of cell membrane conductances on bathing solution HCO 3 − /CO2 inNecturus gallbladder (1988)
    Springer
    The journal of membrane biology 102 (1988), S. 163-174 
    Details
    ISSN: 1432-1424
    Keywords: chloride transport ; equivalent circuit ; cable analysis ; fluid transport ; ouffers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effects of bathing solution HCO 3 − /CO2 concentrations on baseline cell membrane voltages and resistances were measured inNecturus gallbladder epithelium with conventional intracellular microelectrode techniques. Gallbladders were bathed in either low HCO 3 − /CO2 Ringer's solutions (2.4mm HCO 3 − /air or 1mm HEPES/air) or a high HCO 3 − /CO2 Ringer's (10mm HCO 3 − /1% CO2). The principal finding of these studies was that the apical membrane fractional resistance (fR a) was higher in tissues bathed in the 10mm HCO 3 − /CO2 Ringer's, averaging 0.87±0.06, whereasfR a averaged 0.63±0.07 and 0.48±0.08 in 2.4mm HCO 3 − and 1mm HEPES, respectively. Intraepithelial cable analysis was employed to obtain estimates of the individual apical (R a) and basolateral membrane (R b) resistances in tissues bathed in 10mm HCO 3 − /1% CO2 Ringer's. Compared to previous resistance measurements obtained in tissues bathed in a low HCO 3 − /CO2 Ringer's, the higher value offR a was found to be due to both an increase inR a and a decrease inR b. The higher values offR a and lower values ofR b confirm the recent observations of others. To ascertain the pathways responsible for these effects, cell membrane voltages were measured during serosal solution K+ and Cl− substitutions. The results of these studies suggest that an electrodiffusive Cl− transport mechanism exists at the basolateral membrane of tissues bathed in a 10mm HCO 3 − /1% CO2 Ringer's, which can explain in part the fall inR b. The above observations are discussed in terms of a stimulatory effect of solution [HCO 3 − /PCO2 on transepithelial fluid transport, which results in adaptive changes in the conductive properties of the apical and basolateral membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870454
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  • 3
    Electronic Resource
    Electronic Resource
    The origin of mutant cells: mechanisms by whichSaccharomyces cerevisiae produces cells homoplasmic for new mitochondrial mutations (1985)
    Springer
    Current genetics 9 (1985), S. 627-640 
    Details
    ISSN: 1432-0983
    Keywords: Mitochondria ; Mutation ; Yeast ; Selection ; Random drift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Haploid yeast cells have about 50 copies of the mitochondrial genome, and a mutational event is unlikely to affect more than one of these at a time. This raises the question of how such cells, or their progeny, become fixed (homoplasmic) for the mutant alele. We have tested the roles of six hypothetical mechanisms in producing erythromycin-resistant mutant cells: (i) random partitioning of mitochondrial genomes at cell division; (ii) intracellular selection for mtDNA molecules of one genotype; (iii) intracellular random drift of mitochondrial allele frequencies; (iv) intercellular selection for cells of a particular mitochondrial genotype; (v) induction of mitochondrial gene mutations by the antibiotic used to select mutants; and (vi) reduction in the number of mitochondrial genomes per cell by the antibiotic. Our experiments indicate that intracellular selection plays the major role in producing erythromycin-resistant mutant cells in the presence of the antibiotic. In the absence of the antibiotic, the combined effects of random drift and random partitioning are most important in determining the fate of new mutations, most of which are lost rather than fixed. Our experiments provide no evidence for mutation induction or ploidy reduction by erythromycin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00449815
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  • 4
    Electronic Resource
    Electronic Resource
    A method to create simplified versions of existing habitat suitability index (HSI) models (1988)
    Springer
    Environmental management 12 (1988), S. 79-83 
    Details
    ISSN: 1432-1009
    Keywords: Habitat evaluation procedures ; Habitat quality ; Habitat suitability index models ; Impact assessment ; Wildlife management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The habitat evaluation procedures (HEP), developed by the US Fish and Wildlife Service, are widely used in the United States to determine the impacts of major construction projects on fish and wildlife habitats. HEP relies heavily on habitat suitability index (HSI) models that use measurements of important habitat characteristics to rate habitat quality for a species on a scale of 0 (unsuitable) to 1.0 (optimal). This report describes a method to simplify existing HSI models to reduce the time and expense involved in sampling habitat variables. Simplified models for three species produced HSI values within 0.2 of those predicted by the original models 90% of the time. Simplified models are particularly useful for rapid habitat inventories and evaluations, wildlife management, and impact assessments in extensive areas or with limited time and personnel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01867379
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  • 5
    Electronic Resource
    Electronic Resource
    Implementing a Scheme-based parallel processing system (1988)
    Springer
    International journal of parallel programming 17 (1988), S. 367-402 
    Details
    ISSN: 1573-7640
    Keywords: MultiScheme ; parallel Lisp ; implementation ; future construct ; placeholders
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract The Scheme language can be converted into a parallel processing language by adding two new data types (placeholders andweak pairs), two processor synchronization primitives, and a task distribution mechanism. The mechanisms that support task creation, scheduling, and task synchronization are built using these extensions and features already present in the sequential language. Implementing the core of the parallel processing component in Scheme itself provides testbed for a variety of experiments and extensions. MultiScheme, the system resulting from these extensions, supports Halstead's future construct as the simple model for parallelism. By revealing the underlying placeholders on top of which this construct is built, Multischeme supports a variety of additional parallel programming techniques. It supports speculative computation through a simple procedural interface and the automatic garbage collection of tasks. The qlet and qlambda constructs of the QLisp language are also easily implemented in MultiScheme, as are the more familiar fork and join constructs of imperative programming.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01383881
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  • 6
    Electronic Resource
    Electronic Resource
    Temporal variation of mineralogy and petrology in cognate gabbroic enclaves at Arenal volcano, Costa Rica (1989)
    Springer
    Contributions to mineralogy and petrology 103 (1989), S. 110-122 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Gabbroic enclaves ejected during the current eruption phase (A-1) and during the latest prehistoric eruption phase (A-2) of Arenal Volcano show systematic variations in texture, mineralogy and composition as a function of host rock chemistry and timing of eruption. The most differentiated enclaves occur in the more differentiated A-2 lavas. Enclaves in the A-1 volcanics are consistently less evolved. Within the current A-1 eruption, the most mafic enclaves are amphibole-bearing rocks that were erupted during the first 2–3 years of activity (1968–1970). These enclaves occur in the most differentiated A-1 volcanics and are not in equilibrium with their host rocks. They crystallized from a hydrous melt that was slightly more mafic than anything erupted during the current cycle. We interpret the enclaves as sidewall crystallization products of a melt, possibly a high-alumina basalt, that was immediately parental to the A-1 lavas. Enclaves that occur in A-1 rocks erupted after 1970 and all of the A-2 enclaves are amphibole-free and less mafic than the early A-1 enclaves. Their chemistry suggests that they formed during the early to intermediate crystallization of their host lavas. None of the enclaves contain minerals that might have equilibrated with a primary, mantle-derived melt. Geothermometry is consistent with geochemistry, with amphibole-bearing A-1 enclaves yielding the highest pyroxene temperatures (ave. 1090° C) and A-2 enclaves the lowest (ave. 1030° C). Geobarometry suggests mid- to upper crustal depths for the crystallization of all enclaves. The enclaves are cognate and reflect pre-eruptive crystallization of Arenal magmas. They record evolution from a hydrous, basaltic magma to the drier basaltic andesites that characterize the current eruption. Volatiles appear to have been lost due to depressurization during the slow ascent of the magmas through the upper levels of the crust following the initial explosive eruption. Volatile loss and depressurization resulted in the destabilization and the progressive resorption of amphibole. The A-2 lavas may represent the long-term fractionation products of basaltic andesite magmas similar in composition to the A-1 lavas. Anorthitic plagioclase, commonly thought of as a phase stabilized by high Ca/Na and high water pressure, continued to crystallize in a system with relatively low Ca/Na and which had dehydrated and/or depressurized to the point at which amphibole was no longer stable. This suggests that compositional characteristics other than high Ca/Na or high water content may have stabilized the anorthite in the basaltic and basaltic andesite melts at Arenal. We speculate that the high-alumina content of the Arenal magmas may be the stabilizing factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00371368
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  • 7
    Electronic Resource
    Electronic Resource
    31P and 27Al solid-state nuclear magnetic resonance study of taranakite (1989)
    Springer
    Physics and chemistry of minerals 16 (1989), S. 809-816 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract High-resolution 27Al solid-state nuclear magnetic resonance (NMR) spectroscopy indicates that aluminum in taranakite is probably restricted to six-coordinate sites. High-resolution 31P solid-state NMR spectroscopy reveals that phosphate groups exist in two environments in taranakite. The rate of 1H-induced dipolar dephasing of the 31P signals in cross-polarization, magic-angle-spinning NMR spectra of taranakite suggests that one or more oxygens of one of two phosphates are directly protonated. The same experiments suggests that the oxygens of the second form of phosphate are not directly protonated but may be hydrogen-bond receptors. The ratio of protonated phosphate to non-protonated phosphate, as measured from 31P single-pulse excitation, magic-angle-spinning spectra, is approximately one to three.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00209705
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  • 8
    Electronic Resource
    Electronic Resource
    Beckerite (1986)
    Springer
    Physics and chemistry of minerals 13 (1986), S. 411-414 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Beckerite, a minor component of the amber fossil resins of northern Europe, has previously been classified as being mineralogically distinct from common Baltic amber or succinite on the basis of physical properties such as density and chemical properties such as saponification number. We show that beckerite and succinite are spectroscopically identical, according to infrared and carbon-13 nuclear magnetic resonance methods. Following the suggestion of Schubert, we attribute the deviations of beckerite to the presence of low levels of contaminants, such as decomposed wood and insect excrement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00309186
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  • 9
    Electronic Resource
    Electronic Resource
    27Al Solid-state nuclear magnetic resonance study of five-coordinate aluminum in augelite and senegalite (1989)
    Springer
    Physics and chemistry of minerals 16 (1989), S. 817-820 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract This is a report of 27Al magic-angle spinning, nuclear magnetic resonance spectroscopy of 5- and 6-coordinate aluminum in the aluminophosphate minerals augelite and senegalite. We have determined the quadrupolar coupling constants, asymmetry parameters and chemical shifts corrected for quadrupolar-induced shift for both aluminum coordination sites in each mineral. The quadrupolar coupling constants are significantly less in senegalite than in augelite. Structural analysis (viz., longitudinal- and shear-strain of the aluminum coordination polyhedra; coefficient-of-variation for both Al-O bond lengths and 〈O-Al-O bond angles) shows that both 5- and 6-coordinate aluminum sites in senegalite are less distorted than in augelite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00209706
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  • 10
    Electronic Resource
    Electronic Resource
    Residues of chlorinated phenols and phenoxy acid herbicides in the urine of Arkansas children (1989)
    Springer
    Archives of environmental contamination and toxicology 18 (1989), S. 469-474 
    Details
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract Urine samples from 197 Arkansas children were analyzed for eight chlorinated phenols and four chlorinated phenoxy herbicides by using a new procedure that combined gas chromatography with tandem mass spectrometry. With the detection limit of 1 part per billion (ppb), six of these pesticides were detected in more than 10% of the samples. 2,5-Dichlorophenol (a metabolite ofp-dichlorobenzene), and pentachlorophenol were detected in 96% and 100%, respectively, of the children's urine at median concentrations of 9 ppb and 14 ppb, respectively. 2,4,5-Trichlorophenol was detected in 54% of the children's urine at a median concentration of 1 ppb. One trichlorophenol and three other dichlorophenols were found in 3% to 27% of the samples. The herbicide 2,4-dichlorophenoxyacetic acid was observed in 20% of all samples. The concentrations of all analytes are reported as background or reference levels for use in future studies. The finding of 2,5-dichlorophenol as a ubiquitous contaminant merits further study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01055011
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