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  • 1
    ISSN: 1432-0878
    Keywords: Swimbladder ; Teleost ; Cholinergic nerves ; Adrenergic nerves ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The general structure, ultrastructure and innervation of the swimbladder of the smooth toadfish, Tetractenos glaber, were examined with light-microscopic, fluorescence-histochemical, and transmission electron-microscopic techniques. The structure of the swimbladder is similar to that of other euphysoclists. Fluorescence histochemistry showed adrenergic fibres in both the secretory and resorptive areas of the swimbladder. Transmission electron microscopy revealed two morphologically distinct axon profiles type-I profiles containing many small, flattened vesicles; type-II profiles containing both large, granular vesicles and rounded, small clear vesicles in varying proportions. The gas-gland cells and surrounding muscularis mucosae are innervated by both type-I and type-II fibres. Type-I fibres also innervate pre-rete arteries. The rete- and gas-gland capillaries do not appear to be innervated. Arteries running to the resorptive area are innervated by type-I fibres. Both type-I and type-II profiles make contact with the muscularis mucosae in the resorptive area. Only type-I fibres innervate the radial dilator muscle in the oval sphincter region, whereas only type II fibres innervate the circular muscle of the oval sphincter. Type-I fibres took up α-methyl-noradrenaline, and could not be found after pre-treatment with 6-hydroxydopamine. They are, therefore, assumed to be adrenergic. Type-II fibres were tentatively identified, by exclusion, as cholinergic.
    Type of Medium: Electronic Resource
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  • 2
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2017-01-05
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1992
    Description: The work presented in this thesis consists of three parts. The first is a photophysical study of the mechanism of fluorescence quenching by stable nitroxyl radicals, which are becoming an important analytical tool for the study of reactive transients in surface waters (1, 2). In part two, quenching of dissolved organic matter (DOM) fluorescence by nitroxides is employed to investigate the electrostatic propertie~ of DOM in aqueous solution, with the goal of elucidating the apparent ionic strength and pH dependence of metal-fulvic acid binding constants. In part three, the intrinsic optical properties (absorbance, fluorescence, and fluorescence efficiency) of DOM are examined in a coastal region to understand how these properties vary with source. age and sunlight exposure time. Nitroxide-fluorophore adducts were employed to investigate the mechanism by which nitroxyl radicals quench fluorescence (3). Fluorescence quantum yields and lifetimes were measured for a series of adducts, and quenching rates were shown to be quite high (kq≈108-1010 s-1), even at distances of ≈12 Å. Forster or Dexter energy transfer mechanisms are unable to account for the observed rates and lack of solvent dependence in quenching. An excellent correlation is observed between kq and the non-radiative relaxation rate. These results confirm that nitroxyl radicals are very non-selective in their quenching abilities, and suggest that the best analytical probe adducts will include a fluorophore with an appreciable non-radiative relaxation rate. Diffusional quenching by charged and neutral nitroxides was employed to explore the electrostatic properties of fulvic (FA) and humic (HA) acids. Cationic nitroxides were found to be up to 16 times more effective than neutral analogues in quenching the fluorescence of humic materials. This result is attributed to the enhanced coulombic attraction of cations to the anionic FA or HA surface, and is interpreted as an estimate of surface electrostatic potential. Reduction of molecular charge at low pH and shielding of charge at high ionic strength (I) produced diminished enhancements. consistent with this interpretation. The potential was found to be particularly sensitive to ionic strength. suggesting that this electrostatic effect should be of particular importance in transition zones. such as estuaries, where I increases from 〈5 mM to 0.7 M as river water and seawater mix. High molecular weight fractions of HA have a higher apparent surface potential than lower molecular weight fractions. indicating that larger humic molecules may have an enhanced ability to bind metal ions. Optical properties of colored DOM may vary with source and age of the matertal. Absorption spectra can be characterized by their log-linearized slopes (S) as well as by their absolute intensities. The slope, S, is found to be much greater (steeper decrease in absorbance with increasing wavelength) for blue-water samples than for rtverine and coastal samples, indicating that the visible-light absorbing fraction of DOM may be preferentially removed from surface waters. Fluorescence quantum yields were very similar for a wide variety of samples, but do show some minor differences; changes in quantum yield with excitation wavelength within a single sample are an indication of the heterogeneity of the chromophore mixture present in these materials. To better compare fluorescence data, complete excitation/ emission matrix spectra were collected. When normalized to their respective absorbance spectra, these provide a full 'map' of fluorescence quantum efficiency over the entire uv-visible range. This technique is showing promise as a way to identify important spectral regions in these complex chromophore mixtures. DOM isolated on C-18 columns had somewhat different optical charateristics than whole water samples, suggesting selective isolation of absorbing material.
    Keywords: Fluorescence spectroscopy ; Chemical oceanography ; Optical oceanography ; Columbus Iselin (Ship) Cruise ; Knorr (Ship : 1970-) Cruise KN134-12
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
    Format: application/pdf
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We collected samples of dissolved organic matter during Leg 5 of the 1988 RV Knorr Black Sea Expedition (cruise 134-12, July 1988). The study site was located near the centre of the basin (43°5.0' N, 34°00.0' E) in 2,218 m of water. Dissolved oxygen was undetectable (〈5 jxM) below 100m ...
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  • 4
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 5
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 8 (1996), S. 0 
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: In the Epirus region of North-west Greece, spring flows in villages have reduced dramatically over the last few decades, in some cases with serious economic consequences. We argue here that this has resulted from the major reduction of grazing by mountain goats over the same period together with other associated land-use changes. Normally such a contention would be impossible to demonstrate because many different causes could be invoked. However, prior to 1946 culturally homogenous Greek-speaking communities with identical pastoral practices were separated by the closure of the Greek-Albanian border. Changes of spring flow have not occurred on the Albanian side of the border where heavy grazing has continued. In a region such as Greece where pastoralism has continued for thousands of years, the environment had reached an equilibrium with goat grazing. Apart from the reduction of spring flows, other undesirable ecological consequences are occurring.It is also interesting to note that long-term water table changes such as those occurring in Epirus have been attributed to tectonic effects and thought to potentially predict earthquakes. The effect however, may be the result of goats and other livestock ‘leaving’ and not the result of earthquakes ‘coming’.
    Type of Medium: Electronic Resource
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  • 8
    Publication Date: 2012-11-23
    Description: We review recent progress in the stem cell biology of the respiratory system, and discuss its scientific and translational ramifications. Several studies have defined novel stem cells in postnatal lung and airways and implicated their roles in tissue homeostasis and repair. In addition, significant advances in the generation of respiratory epithelium from pluripotent stem cells (PSCs) now provide a novel and powerful platform for understanding lung development, modeling pulmonary diseases, and implementing drug screening. Finally, breakthroughs have been made in the generation of decellularized lung matrices that can serve as a scaffold for repopulation with respiratory cells derived from either postnatal or PSCs. These studies are a critical step forward towards the still distant goal of stem cell-based regenerative medicine for diseases of lung and airways. Recent progress in the identification of lung and airway stem cells and in the generation of respiratory epithelial cells from pluripotent stem cells (PSCs) will have a profound impact on our understanding of human lung development and disease, and on the prospect of regenerative therapy for lung disease.
    Print ISSN: 0265-9247
    Electronic ISSN: 1521-1878
    Topics: Biology , Medicine
    Published by Wiley
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  • 9
    Publication Date: 2013-01-08
    Description: [1]  We evaluate the effect and importance of a ground truth correction for the Moon Mineralogy Mapper (M 3 ) level 2 (reflectance) dataset. This correction is derived from extensive laboratory characterizations of mature feldspathic lunar soils and is designed to improve the accuracy of 1 µm absorption features in M 3 reflectance data. To evaluate the correction, the band strength across a subset of the feldspathic highlands terrane (FHT) is analyzed with M 3 imaging spectroscopy data. Using M 3 reflectance data and derived products, we find significant differences in band strength and shape between M 3 observations collected over identical terrain but under different observational and operational conditions. The ground truth correction minimizes these differences in 1 µm band strengths and also brings the 1 µm band strengths measured with M 3 data into closer agreement with laboratory measurements of lunar soil samples. Although the FHT region studied was found to have very low band strengths, the M 3 ground truth correction results in overall stronger absorption features for all mature soils relative to uncorrected level 2 (reflectance) data for the same region. These differences between M 3 data collected under different operational conditions and the effects of the ground truth correction, while minor in appearance, can have significant implications for interpretations of any regional soil analyses with M 3 data that rely on absolute 1 µm absorption feature strength. The M 3 ground truth correction corrects only wavelengths below ~1500 nm, and comparisons between corrected and uncorrected wavelengths must be done with caution.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2015-02-05
    Description: To forecast rock glacier movements, it is necessary to have dependable information on their internal structures and physical properties. A first attempt to expand our knowledge of a rock glacier in the Swiss Alps involved acquiring ground-based ground-penetrating radar (GPR) data along numerous profiles using different acquisition systems and antennae with different nominal frequencies. Images derived from these ground-based data were inconsistent and unreliable. For our second attempt, we recorded GPR data using a helicopter-mounted system. The helicopter GPR sections were surprisingly good, with consistent images along adjacent and intersecting profiles. Internal shear horizons, ice-rich and ice-poor regions and the bedrock interface were well delineated on the helicopter GPR images. Besides providing excellent-quality images, the helicopter GPR system allowed areas of the rock glacier to be surveyed that would have been difficult or impossible to access for a ground-based study. Because near-surface heterogeneity does not seem to have a major effect on helicopter GPR data acquired across a rugged rock glacier, we suggest that helicopter GPR surveying might be useful for investigating many terrains covered by heterogeneous loose material, including debris avalanches, scree slopes and rockfalls. Copyright © 2015 John Wiley & Sons, Ltd.
    Print ISSN: 1045-6740
    Electronic ISSN: 1099-1530
    Topics: Geography , Geosciences
    Published by Wiley
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