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  • Electronic Resource  (2)
  • 35  (1)
  • CT  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Frequency stability of a mercury ion frequency standard (1981)
    Springer
    Applied physics 24 (1981), S. 107-112 
    Details
    ISSN: 1432-0630
    Keywords: 06.30 F ; 32 ; 35 ; 52-55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Observation with an improved signal-to-noise ratio of the hyperfine resonance pattern of199Hg+ stored in a radiofrequency trap is reported. A frequency control loop which locks the frequency of a 5MHz quartz crystal oscillator to the hyperfine transition of stored mercury ions, close to 40.5 GHz, is described. In this system, pulses delivered by the photomultiplier are processed digitally. Optimal conditions for the interrogation of the hyperfine transition are specified. A fractional frequency stability σy(τ)=3.6×10−11τ−1/2 for 10s〈τ〈3500s has been obtained. This frequency stability is comparble to that of commercially available cesium beam frequency standards. Prospect for improvement by a factor of at least 10 are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00902264
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  • 2
    Electronic Resource
    Electronic Resource
    Postoperative follow-up of juvenile nasopharyngeal angiofibromas: assessment by CT scan and MR imaging (1998)
    Springer
    European radiology 8 (1998), S. 756-764 
    Details
    ISSN: 1432-1084
    Keywords: Key words: Nasopharynx ; neoplasma ; Angiofibroma ; Angiofibroma ; postoperative ; CT ; MR imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The purpose of this study was to assess the radiological findings after surgical removal of juvenile nasopharyngeal angiofibromas (JNA). The postoperative CT and MRI scans of ten patients were reviewed. The cured group included six patients. The non-controlled group included six patients with eight recurrences. Two patients belonged to both groups as they were also followed and cured after surgery for relapse. Four recurrences were asymptomatic and diagnosed by imaging. The imaging patterns were matched to the patients clinical status and endoscopic findings. In the cured group, non-enhanced residual soft tissue masses were seen in all cases. In the non-controlled group, recurrence was always demonstrated on early postoperative CT or MR as a dramatically enhanced mass. The recurrence was located in the lateral or superior aspect of the nasopharynx (n = 3), deep to the fossa of Rosenmuller (n = 4) or out of the nasopharynx (n = 1). In two cases a remaining enhanced mass disappeared spontaneously on iterated examinations. Because of numerous asymptomatic relapses, a radiological workup is recommended four months after surgery, even in patients with normal endoscopy, to rule out posterolateral or extranasopharyngeal recurrences. Spontaneous evolution of residual masses must be appreciated on iterated imaging examinations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003300050468
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    Paper (German National Licenses)
    Fulltext
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