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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 52 (1991), S. 117-121 
    ISSN: 1432-0649
    Keywords: 42.60D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A colliding pulse mode-locked ring dye laser, pumped by an all-line small frame Ar+ laser has been used to generate stable pulses as short as 49 fs with pulse duration and stability similar to those obtained with the usual configuration where a single line of the pump is used. The effects of cavity alignment on the absorber saturation are presented and explained in terms of an analysis of stability of the ring cavity.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0340-1855
    Keywords: Schlüsselwörter Präzision ; Variationskoeffizient ; DEXA ; Osteoporose ; Polyarthritis ; Key words Precision ; coefficient of variation ; DEXA ; osteoporosis ; rheumatoid arthritis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Precision of osteodensitometric measurements using dual energy X-ray absorptiometry (DEXA) depends on various known factors, such as positioning, aortic calcification or vertebral fractures. The purpose of this study was to investigate the influence of various diseases or bone density on the reproducibility of measurements in the lumbar spine and the proximal femur.  Measurements in the LWS p.a., LWS lat. and at Ward‘s triangle were made in a total of 100 patients. The subjects were repositioned between measurements. In order to be able to determine the influence of various diseases, four groups of 25 patients each were formed: three with the diagnosis osteoarthrosis, osteoporosis and rheumatoid arthritis and one control group. The mean percentual difference and coefficient of variation were calculated as the measure for reproducibility.  Mean percentual differences of 0.18 to 2.6% were found in the four groups at the three measurements sites. After calculation of coefficient of variation, a value between 1.2 and 2.7% was found for LWS p.a., between 7.1 and 15.7% for LWS lat. and between 4.1 and 9.9% at Ward‘s triangle. It was also conspicuous that the difference in coefficient of variation in osteoporosis patients was nearly double that in the control group in all measured areas. Conclusion: Lateral lumbar spinal measurements using DEXA cannot presently be recommended. LWS p.a. measurements and, with limitations, measurements at Ward‘s triangle have good precision and could be used for course documentation of bone density.
    Notes: Zusammenfassung Die Präzision osteodensitometrischer Messungen mit der dual energy X-ray absorptiometry (DEXA) hängt von verschiedenen bekannten Faktoren, wie Lagerung, Aortenverkalkung oder Wirbelkörperfrakturen ab. Ziel der Untersuchung war, den Einfluß verschiedener Erkrankungen bzw. der Knochendichte auf die Reproduzierbarkeit der Messungen an der Lendenwirbelsäule und am Femur zu überprüfen.  Insgesamt wurden 100 Patienten an der LWS p.a., LWS lat. und am Ward‘schen Dreieck doppelt gemessen, wobei zwischen den Messungen neu positioniert wurde. Um den Einfluß unterschiedlicher Erkrankungen festzustellen zu können, wurden zusätzlich 4 Gruppen à 25 Patienten mit den Diagnosen: Arthrose, Osteoporose und chronische Polyarthritis im Vergleich zur Kontrollgruppe gebildet. Als Maß für die Reproduzierbarkeit wurde jeweils die mittlere prozentuale Differenz und der Variationskoeffizient der beiden Messungen berechnet.  In den vier Gruppen ergaben sich an den drei Meßorten mittlere prozentuale Differenzen von 0,18 bis 2,6%. Nach Berechnung der Variationskoeffizienten fand sich für die LWS p.a. ein Wert zwischen 1,2 und 2,7% für die LWS lat. zwischen 7,1 und 15,7% und am Ward‘schen Dreieck zwischen 4,1 und 9,9%. Auffällig war zudem ein nahezu doppelt so hoher Variationskoeffizient der Patienten mit Osteoporose im Vergleich zur Kontrollgruppe an allen gemessenen Regionen. Ergebnis: Die laterale LWS-Messung beim DEXA-Verfahren ist derzeit nicht zu empfehlen. Die LWS p.a.-Messung und mit Einschränkung auch die Messung am Ward‘schen Dreieck können bei guter Präzision zur Verlaufsdokumentation der Knochendichte herangezogen werden.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0649
    Keywords: 42.60D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a multipass femtosecond amplifier pumped by a Nd-YAG laser where the gain medium is given by a variable length dye cell. This system allows amplification factors up to 5 · 106 and output pulse energies of 150 μJ, while restricting the contribution of amplified spontaneous emission to 0.5% of the total output energy, without using any saturable absorber stage. A detailed study of the output pulsewidth as a function of the duration of the input chirped pulse is also presented.
    Type of Medium: Electronic Resource
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