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- Li, W., et al.
(författare)
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Global distribution of whistler-mode chorus waves observed on the THEMIS spacecraft
- 2009
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:9, s. L09104-
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Tidskriftsartikel (refereegranskat)abstract
- Whistler mode chorus waves are receiving increased scientific attention due to their important roles in both acceleration and loss processes of radiation belt electrons. A new global survey of whistler-mode chorus waves is performed using magnetic field filter bank data from the THEMIS spacecraft with 5 probes in near-equatorial orbits. Our results confirm earlier analyses of the strong dependence of wave amplitudes on geomagnetic activity, confinement of nightside emissions to low magnetic latitudes, and extension of dayside emissions to high latitudes. An important new finding is the strong occurrence rate of chorus on the dayside at L > 7, where moderate dayside chorus is present > 10% of the time and can persist even during periods of low geomagnetic activity.
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- Bortnik, J., et al.
(författare)
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An Observation Linking the Origin of Plasmaspheric Hiss to Discrete Chorus Emissions
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 324:5928, s. 775-778
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Tidskriftsartikel (refereegranskat)abstract
- A long-standing problem in the field of space physics has been the origin of plasmaspheric hiss, a naturally occurring electromagnetic wave in the high-density plasmasphere (roughly within 20,000 kilometers of Earth) that is known to remove the high-energy Van Allen Belt electrons that pose a threat to satellites and astronauts. A recent theory tied the origin of plasmaspheric hiss to a seemingly different wave in the outer magnetosphere, but this theory was difficult to test because of a challenging set of observational requirements. Here we report on the experimental verification of the theory, made with a five-satellite NASA mission. This confirmation will allow modeling of plasmaspheric hiss and its effects on the high-energy radiation environment.
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- Cibere, Jolanda, et al.
(författare)
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Association of Biomarkers With Pre-Radiographically Defined and Radiographically Defined Knee Osteoarthritis in a Population-Based Study
- 2009
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Ingår i: Arthritis and Rheumatism. - : Wiley. - 1529-0131 .- 0004-3591. ; 60:5, s. 1372-1380
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Tidskriftsartikel (refereegranskat)abstract
- Objective. To evaluate 10 biomarkers in magnetic resonance imaging (M RI)-determined, pre-radiographically defined osteoarthritis (pre-ROA) and radiographically defined OA (ROA) in a population-based cohort of subjects with symptomatic knee pain. Methods. Two hundred one white subjects with knee pain, ages 40-79 years, were classified into OA subgroups according to MRI-based cartilage (MRC) scores (range 0-4) and Kellgren/Lawrence (K/L) grades of radiographic severity (range 0-4): no OA (MRC score 0, K/L grade <2), pre-ROA (MRC score > 1, K/L grade <2), or ROA (MRC score >= 1, K/L grade >= 2). Urine and serum samples were assessed for levels of the following biomarkers: urinary biomarkers C-telopeptide of type II collagen (uCTX-II), type II and types I and II collagen cleavage neoepitopes (uC2C and uC1,2C, respectively), and N-telopeptide of type I collagen, and serum biomarkers sC1,2C, sC2C, C-propeptide of type II procollagen (sCPII), chondroitin sulfate 846 epitope, cartilage oligomeric matrix protein, and hyaluronic acid. Multicategory logistic regression was performed to evaluate the association of OA subgroup with individual biomarker levels and biomarker ratios, adjusted for age, sex, and body mass index. Results. The risk of ROA versus no OA increased with increasing levels of uCTX-II (odds ratio [OR] 3.12, 95% confidence interval [95% CI] 1.35-7.21), uC2C (OR 2.13, 95% CI 1.04-4.37), and uC1,2C (OR 2.07, 95% CI 1.06-4.04), and was reduced in association with high levels of sCPII (OR 0.53, 95% CI 0.30-0.94). The risk of pre-ROA versus no OA increased with increasing levels of uC2C (OR 2.06, 95% CI 1.05-4.01) and uC1,2C (OR 2.06, 95% CI 1.12-3.77). The ratios of type II collagen degradation markers to collagen synthesis markers were better than individual biomarkers at differentiating the OA subgroups, e.g., the ratio of [uCTX-II] [uC1,2C] to sCPII was associated with a risk of ROA versus no OA of 3.47 (95% CI 1.34-9.03) and a risk of pre-ROA versus no OA of 2.56 (95% CI 1.03-6.40). Conclusion. Different cartilage degradation markers are associated with pre-ROA than are associated with ROA, indicating that their use as diagnostic markers depends on the stage of OA. Biomarker ratios contrasting cartilage degradation with cartilage synthesis are better able to differentiate OA stages compared with levels of the individual markers.
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