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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 106 (1996), S. 192-198 
    ISSN: 1432-1939
    Keywords: Pollination limitation ; Selection potential ; Seed dispersal ; Microsite limitation ; Fruit production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Will increased fruit and seed production in a severely pollination-limited orchid stimulate population growth? We tested whether safe sites for germination and seedling establishment are limiting for the twig epiphyte, Tolumnia variegata, by manipulating fruit set and monitoring subsequent seedling establishment for two seasons (1991–1992, 1992–1993). In the Cambalache Forest Reserve of Puerto Rico, we established 36 plots along a transect. Each plot consisted of nine trees. A center tree was designated as the site for attaching Tolumnia and manipulating fruit set. The other eight potential host trees were 1–3 and 3–5 m from the center tree in each of the cardinal directions. A 1-m length of stem 1 m from the ground was monitored for recruits on each of the nine trees of 24 fruit-enhanced plots and 12 controls (23 and 13, respectively for the 1992–1993 season). Fruit enhancement plots were divided among two treatments: one-fruit and five-fruit additions for the 1st year and one to five and more than five fruits for the 2nd year. Availability of suitable host species was not limiting. T. variegata showed little specificity for host tree species, good host trees and shrubs were common, and there was no evidence that the orchid had a preference for small branches, despite possessing the entire suite of characteristics thought to respresent “obligate” twig epiphytes. Fruit enhancement increased seed rain and seedling establishment consistently in only the high-fruit treatment plots. Most recruitment occurred near fruiting plants. Over the 2-year period, mortality was 18% for adults and 85.5% for the 1991–1992 cohort of recruits. Net recruitment was positive for both the treatment (average = 1.74) and control plots (average = 0.67). Seedling establishment at our study site was not microsite-limited. If selection for increased pollinator attraction occurs, then an increase in seed output should result in population growth.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0827
    Keywords: Key words: Densitometry — Bone mineral content — Hydroxyapatite — MRI.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. A solid state magnetic resonance imaging technique is used to measure true three-dimensional mineral density of synthetic hydroxyapatite phantoms and specimens of bone ex vivo. The phosphorus-31 free induction decay at 2.0 T magnetic field strength is sampled following application of a short, hard radiofrequency excitation pulse in the presence of a fixed amplitude magnetic field gradient. Multiple gradient directions covering the unit sphere are used in an efficient spherical polar to Cartesian interpolation and Fourier transform projection reconstruction scheme to image the three-dimensional distribution of phosphorus within the specimen. Using 3–6 Gauss/cm magnetic field gradients, a spatial resolution of 0.2 cm over a field of view of 10 cm is achieved in an imaging time of 20–35 minutes. Comparison of solid state magnetic resonance imaging with dual energy X-ray absorptiometry (DXA), gravimetric analysis, and chemical analysis of calcium and phosphorus demonstrates good quantitative accuracy. Direct measurement of bone mineral by solid state magnetic resonance opens up the possibility of imaging variations in mineral composition as well as density. Advantages of the solid state magnetic resonance technique include avoidance of ionizing radiation; direct measurement of a constituent of the mineral without reliance on assumptions about, or models of, tissue composition; the absence of shielding, beam hardening, or multiple scattering artifacts; and its three-dimensional character. Disadvantages include longer measurement times and lower spatial resolution than DXA and computed tomography, and the inability to scan large areas of the body in a single measurement, although spatial resolution is sufficient to resolve cortical from trabecular bone for the purpose of measuring bone mineral density.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1279-8517
    Keywords: Aortic bifurcation ; Vena cava confluence ; Computed tomography ; Ageing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The object of this retrospective study was to determine the sites of abdominal aortic bifurcation and inferior vena cava confluence in relation to age and sex. The study group comprised 180 subjects (90 males and 90 females) divided into 9 groups by age (in decades). The positions of the aortic bifurcation and the inferior vena cava confluence were evaluated by CT, and linear regression models were fitted to the data. The positions of the aortic bifurcation and venous confluence showed a highly significant downward shift with increasing age (p=0.0001). The shift was more pronounced in women. The mean site of the aortic bifurcation for the whole group was at lower L4 (range, upper L3 to upper S1); in males, it was at upper L4 (range, upper L3 to upper L5), and in females at lower L4 (range, upper L3 to upper S1). The mean site of the venous confluence for the whole group was at disc L4-L5 (range, lower L3 to upper S1); in males, it was at disc L4-L5 (range, upper L4 to disc L5-S1), and in females at disc L4-L5 (range, lower L3 to upper S1). Thus, the aorta and the inferior vena cava can extend as low as the level of S1. These data are of relevance in laparoscopic procedures, especially in laparoscopic lumbar discectomy.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1279-8517
    Keywords: Aortic bifurcation ; Vena cava confluence ; Computed tomography ; Ageing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Résumé Le but de cette étude rétrospective était de déterminer la topographie de la bifurcation de l'aorte abdominale et de la confluence cave caudale en fonction de l'âge et du sexe. Le groupe étudié comprenait 180 sujets (90 de sexe masculin et 90 de sexe féminin) divisés en 9 groupes d'âge (9 décennies). Les positions de la bifurcation aortique et de la confluence veineuse cave caudale ont été évaluées par tomodensitométrie, et des modèles de régression linéaire ont été appliqués aux données recueillies. Un déplacement caudal des positions de la bifurcation aortique et de la confluence cave caudale était hautement corrélé à l'âge (p=0.0001). Le déplacement était plus prononcé chez les femmes. La position moyenne de la bifurcation aortique pour le groupe entier était la partie caudale de L4 (extrémités : partie supérieure de L3, partie supérieure de S1) ; chez les sujets de sexe masculin, elle se situait à la partie supérieure de L4 (extrémités : partie supérieure de L3, partie supérieure de L5), et dans le sexe féminin à la partie caudale de L4 (extrémités : partie supérieure de L3, partie supérieure de S1). La situation moyenne de la confluence cave caudale pour le groupe entier était au niveau du disque L4–L5 (extrémités : partie caudale de L3, partie craniale de S1) ; dans le sexe masculin elle se situait en regard du disque L4–L5 (extrémités : partie craniale de L4, disque L5–S1) et dans le sexe féminin au niveau du disque L4–L5 (extrémités : partie caudale de L3, partie craniale de S1). Ainsi, l'aorte et la veine cave caudale peuvent s'étendre aussi bas qu'au niveau de S1. Ces données trouvent leur application dans les procédures laparoscopiques, en particulier dans la discectomie lombaire.
    Notes: Summary The object of this retrospective study was to determine the sites of abdominal aortic bifurcation and inferior vena cava confluence in relation to age and sex. The study group comprised 180 subjects (90 males and 90 females) divided into 9 groups by age (in decades). The positions of the aortic bifurcation and the inferior vena cava confluence were evaluated by CT, and linear regression models were fitted to the data. The positions of the aortic bifurcation and venous confluence showed a highly significant downward shift with increasing age (p=0.0001). The shift was more pronounced in women. The mean site of the aortic bifurcation for the whole group was at lower L4 (range, upper L3 to upper S1); in males, it was at upper L4 (range, upper L3 to upper L5), and in females at lower L4 (range, upper L3 to upper S1). The mean site of the venous confluence for the whole group was at disc L4–L5 (range, lower L3 to upper S1); in males, it was at disc L4–L5 (range, upper L4 to disc L5–S1), and in females at disc L4–L5 (range, lower L3 to upper S1). Thus, the aorta and the inferior vena cava can extend as low as the level of S1. These data are of relevance in laparoscopic procedures, especially in laparoscopic lumbar discectomy.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1279-8517
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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