We use a new technique to disseminate microwave reference signals along ordinary optical fiber. The fractional frequency resolution of a link of 86 km in length is 10-17 for a one day integration ...time, a resolution higher than the stability of the best microwave or optical clocks. We use the link to compare the microwave reference and a CO2/OsO4 frequency standard that stabilizes a femtosecond laser frequency comb. This demonstrates a resolution of 3.10-14 at 1 s. An upper value of the instability introduced by the femtosecond laser-based synthesizer is estimated as 1.10-14 at 1 s.
This paper focuses on the development of tools aiming to solve several problems related to the microwave interrogation signal in atomic fountains. We first consider the problem related to cycle ...synchronous phase transients caused by the sequential operation of the atomic fountain. To search for such systematic phase variations deeply buried in the microwave synthesizer phase noise, we have developed a novel triggered-phase transient analyzer capable of processing the microwave signal to extract the phase in a synchronous manner even in the presence of frequency modulation. With this device we check in vivo the LNE-SYRTE fountain's interrogation signals with a resolution approaching 1 microradian. In addition, using this device, we investigate an innovative approach to solve a second problem, namely, the shift caused by microwave leakage in the fountain. Our approach consists of switching off the fountain microwave interrogation signal when atoms are outside the microwave cavity. To do that, we have developed a switch that is almost free of phase transients and is thus able to eliminate the frequency shift caused by microwave leakage without inducing significant phase transients on the interrogation signal.
We use a new technique to disseminate microwave reference signals along ordinary optical fiber. The fractional frequency resolution of a link of 86 km in length is 10(-17) for a one day integration ...time, a resolution higher than the stability of the best microwave or optical clocks. We use the link to compare the microwave reference and a CO2/OsO4 frequency standard that stabilizes a femtosecond laser frequency comb. This demonstrates a resolution of 3 x 10(-14) at 1 s. An upper value of the instability introduced by the femtosecond laser-based synthesizer is estimated as 1 x 10(-14) at 1 s.
We present the construction of an atom interferometer for inertial sensing in microgravity, as part of the I.C.E. (Interferometrie Coherente pour l'Espace) collaboration. On-board laser systems have ...been developed based on fibre-optic components, which are insensitive to mechanical vibrations and acoustic noise, have sub-MHz line width, and remain frequency stabilised for weeks at a time. A compact, transportable vacuum system has been built, and used for laser cooling and magneto-optical trapping. We will use a mixture of quantum degenerate gases, bosonic 87Rb and fermionic 40K, in order to find the optimal conditions for precision and sensitivity of inertial measurements. Microgravity will be realised in parabolic flights lasting up to 20 s in an Airbus. We investigate the experimental limits of our apparatus, and show that the factors limiting the sensitivity of a long-interrogation-time atomic inertial sensor are the phase noise in reference-frequency generation for Raman-pulse atomic beam splitters and acceleration fluctuations during free fall.
BNM-SYRTE fountains: recent results Vian, C.; Rosenbusch, P.; Marion, H. ...
IEEE transactions on instrumentation and measurement,
04/2005, Letnik:
54, Številka:
2
Journal Article
Recenzirano
Recent improvements of Bureau National de Me/spl acute/trologie Syste/spl grave/mes de Re/spl acute/fe/spl acute/rence Temps Espace (BNM-SYRTE) fountains FO1 and FO2 are described. Fractional ...frequency instabilities of 2.9/spl times/10/sup -14//spl tau//sup -1/2/ for FO1 and 1.6/spl times/10/sup -14//spl tau//sup -1/2/ for FO2 have been demonstrated. A preliminary estimate of the systematic frequency shifts gives an uncertainty of /spl plusmn/7.2/spl times/10/sup -16/ for FO1 and /spl plusmn/6.5/spl times/10/sup -16/ for FO2. Furthermore, we present a direct comparison between the two fountains. When a real-time measurement of the collisional shift is included, we observe a stability of the comparison of 5.0/spl times/10/sup -14//spl tau//sup -1/2/ and a frequency difference of /spl delta/=4/spl times/10/sup -16/, well within the combined uncertainties.
In this paper we describe the improved redesign of the microwave frequency synthesizers for Laboratoire National d'Essais-Systemes de Reference Temps-Espace (LNE-SYRTE) atomic fountains. The ...synthesizers use a cryogenic oscillator to generate both Cs and Rb hyperfine frequencies based on a new distribution frequency of 1 GHz. The main metrological features (phase noise, long-term phase stability, and spectral purity) of the synthesizers have been measured in situ connected to an atomic fountain and are compatible with an accuracy goal of 10 -16 for the atomic fountains. The simultaneous test of two different synthesizers on the FO2 atomic fountain at the 10 -16 level also is reported
This prospective, observational study assessed the risk of myocardial infarction among 23,468 HIV-1–infected patients in relation to treatment with combination antiviral medications. The incidence of ...myocardial infarction increased significantly with increasing exposure to combination therapy (adjusted relative rate per year of exposure, 1.26).
The incidence increases with exposure to combination therapy.
Although the benefits of combination antiretroviral therapy have revolutionized the care of patients with human immunodeficiency virus type 1 (HIV-1) infection, increasingly severe treatment-associated metabolic side effects have been observed, among them dyslipidemia, insulin resistance, and overt diabetes mellitus, which are well-known risk factors for cardiovascular disease.
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These side effects may increase the risk of premature myocardial infarction, although direct evidence of such an association is inconsistently reported in the existing literature.
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To address this concern, and as part of an initiative by the European Agency for the Evaluation of Medicinal Products, the Data Collection on Adverse Events . . .
Although an increasing number of noninvasive fibrosis markers are available in HCV-monoinfected patients, data on the performance of these tests in HIV-HCV-coinfected patients are lacking.
To assess ...the diagnostic performance for predicting hepatic fibrosis stage of four simple and inexpensive noninvasive indexes (FIB-4, APRI, Forns, and platelet count) in HIV-HCV-coinfected patients.
Two hundred consecutive HIV-HCV-coinfected patients from the ANRS-CO3 Aquitaine cohort who underwent liver biopsy were studied. Fibrosis stage was assessed according to Metavir scoring system by a single pathologist unaware of the data of the patients. Diagnostic performances were assessed by measuring the areas under the receiver operating characteristic curves (AUROC) and the percentage of patients correctly identified (PCI).
For predicting significant fibrosis (F > or = 2), APRI, Forns index, and FIB-4 had AUROCS of 0.77, 0.75, and 0.79, with 39%, 25%, and 70% of PCI, respectively. For predicting severe fibrosis (F > or = 3), FIB-4 had AUROC of 0.77 with 56% of PCI. For predicting cirrhosis (F4), FIB-4, APRI, and platelet count had AUROCs of 0.80, 0.79, and 0.78, with 59%, 60%, and 76% of PCI, respectively. Overall, diagnostic performances of the different indexes did not differ significantly for both significant fibrosis and cirrhosis.
The use of these noninvasive indexes could save liver biopsies in up to 56-76% of cases for the prediction of severe fibrosis-cirrhosis. However, given the high percentage of misclassified cases for significant fibrosis, such indexes do not appear currently suitable for use in clinical practice in HIV-HCV-coinfected patients.
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