39 research outputs found
Does the magnetosphere behave differently on weekends?
International audienceGlobal geomagnetic activity has been suggested to be enhanced during weekends above the weekly average after 1930. Before the 1930s, weekends and weekdays were found to be equally active. This so-called "weekend effect" was suggested to be due to power line harmonic radiation (PLHR) in the VLF range emitted by electric power lines. Since the consumption of electric power is different on weekends and weekdays, leading to different PLHR intensities, this could possibly cause the "weekend effect" in global geomagnetic activity. In the present paper, we reanalyse the suggested "week-end effect" in global geomagnetic activity using the 69-year planetary geomagnetic Ap index and the 131-year antipodal aa index. We conclude that there is no statistically significant "weekend effect" during the interval covered by these geo-magnetic activity indices. Although global geomagnetic activity is slightly enhanced on weekends from the 1930s to the 1980s, the more recent data show rather a relative decrease in global geomagnetic activity on weekends, contrary to the expected increase in the "weekend effect", due to increasing power consumption. Moreover, the weekly distribution is fairly similar in solar wind speed and global geomagnetic activity during the last 35 years, further supporting the view that the "weekend effect" is only a statistical fluctuation
Broadband Meter-Wavelength Observations of Ionospheric Scintillation
Intensity scintillations of cosmic radio sources are used to study
astrophysical plasmas like the ionosphere, the solar wind, and the interstellar
medium. Normally these observations are relatively narrow band. With Low
Frequency Array (LOFAR) technology at the Kilpisj\"arvi Atmospheric Imaging
Receiver Array (KAIRA) station in northern Finland we have observed
scintillations over a 3 octave bandwidth. ``Parabolic arcs'', which were
discovered in interstellar scintillations of pulsars, can provide precise
estimates of the distance and velocity of the scattering plasma. Here we report
the first observations of such arcs in the ionosphere and the first broad-band
observations of arcs anywhere, raising hopes that study of the phenomenon may
similarly improve the analysis of ionospheric scintillations. These
observations were made of the strong natural radio source Cygnus-A and covered
the entire 30-250\,MHz band of KAIRA. Well-defined parabolic arcs were seen
early in the observations, before transit, and disappeared after transit
although scintillations continued to be obvious during the entire observation.
We show that this can be attributed to the structure of Cygnus-A. Initial
results from modeling these scintillation arcs are consistent with simultaneous
ionospheric soundings taken with other instruments, and indicate that
scattering is most likely to be associated more with the topside ionosphere
than the F-region peak altitude. Further modeling and possible extension to
interferometric observations, using international LOFAR stations, are
discussed.Comment: 11 pages, 17 figure
Blood concentrations of the cytokines IL-1beta, IL-6, IL-10, TNF-alpha and IFN-gamma during experimentally induced swine dysentery
Identification of Keratinocyte Growth Factor as a Target of microRNA-155 in Lung Fibroblasts: Implication in Epithelial-Mesenchymal Interactions
International audienceBACKGROUND: Epithelial-mesenchymal interactions are critical in regulating many aspects of vertebrate embryo development, and for the maintenance of homeostatic equilibrium in adult tissues. The interactions between epithelium and mesenchyme are believed to be mediated by paracrine signals such as cytokines and extracellular matrix components secreted from fibroblasts that affect adjacent epithelia. In this study, we sought to identify the repertoire of microRNAs (miRNAs) in normal lung human fibroblasts and their potential regulation by the cytokines TNF-alpha, IL-1beta and TGF-beta. METHODOLOGY/PRINCIPAL FINDINGS: MiR-155 was significantly induced by inflammatory cytokines TNF-alpha and IL-1beta while it was down-regulated by TGF-beta. Ectopic expression of miR-155 in human fibroblasts induced modulation of a large set of genes related to "cell to cell signalling", "cell morphology" and "cellular movement". This was consistent with an induction of caspase-3 activity and with an increase in cell migration in fibroblasts tranfected with miR-155. Using different miRNA bioinformatic target prediction tools, we found a specific enrichment for miR-155 predicted targets among the population of down-regulated transcripts. Among fibroblast-selective targets, one interesting hit was keratinocyte growth factor (KGF, FGF-7), a member of the fibroblast growth factor (FGF) family, which owns two potential binding sites for miR-155 in its 3'-UTR. Luciferase assays experimentally validated that miR-155 can efficiently target KGF 3'-UTR. Site-directed mutagenesis revealed that only one out of the 2 potential sites was truly functional. Functional in vitro assays experimentally validated that miR-155 can efficiently target KGF 3'-UTR. Furthermore, in vivo experiments using a mouse model of lung fibrosis showed that miR-155 expression level was correlated with the degree of lung fibrosis. CONCLUSIONS/SIGNIFICANCE: Our results strongly suggest a physiological function of miR-155 in lung fibroblasts. Altogether, this study implicates this miRNA in the regulation by mesenchymal cells of surrounding lung epithelium, making it a potential key player during tissue injury
Calculation of signal spectrum by means of stochastic inversion
The standard method of calculating the spectrum of a digital signal is based
on the Fourier transform, which gives the amplitude and phase spectra at a
set of equidistant frequencies from signal samples taken at equal intervals.
In this paper a different method based on stochastic inversion is introduced.
It does not imply a fixed sampling rate, and therefore it is useful in
analysing geophysical signals which may be unequally sampled or may have
missing data points. This could not be done by means of Fourier transform
without preliminary interpolation. Another feature of the inversion method is
that it allows unequal frequency steps in the spectrum, although this
property is not needed in practice. The method has a close relation to
methods based on least-squares fitting of sinusoidal functions to the signal.
However, the number of frequency bins is not limited by the number of signal
samples. In Fourier transform this can be achieved by means of additional
zero-valued samples, but no such extra samples are used in this method.
Finally, if the standard deviation of the samples is known, the method is
also able to give error limits to the spectrum. This helps in recognising
signal peaks in noisy spectra
Modelling the effects of the October 1989 solar proton event on mesospheric odd nitrogen using a detailed ion and neutral chemistry model
Methodological influences on F-region peak height trend analyses
Published estimates of the trend in hmF2 using data from ionosondes over the last 30-40 years range from +0.8 to -0.6 km yr(-1) and are subject to the influence of several factors. These are considered here based upon an analysis of two southern hemisphere geomagnetically mid-latitude stations, Argentine Islands and Port Stanley. The influence of the equation used to calculate hmF2 at these stations can result in variations of +/-0.2 km yr(-1); choice of solar proxy has a small influence on the end result, where using E10.7 instead of F10.7 produces changes of -0.04 km yr(-1); neglecting any trends in geomagnetic activity can produce variations of +0.03 to +0.2 km yr(-1) at the two mid-latitude stations considered in this paper; for datasets of 30-40 years length ringing due to long memory processes can produce +/-0.2 km yr(-1) variability; the phase of the 11-year solar cycle, and its harmonics, captured by the datasets can cause variability of +/-0.5 km yr(-1); and the neglect of local time variations in thermospheric wind conditions could result in +0.2 km yr(-1) for analysis which only considers local midday data. The Argentine Islands and Port Stanley datasets show ringing terms that are still converging towards trend results of -0.25 to -0.30 km yr(-1), which are in close agreement with the satellite drag trend estimates
Annual and semiannual variations in the height of the ionospheric F2-layer
Ionosonde data from sixteen stations are used to study the semiannual and annual variations in the height of the ionospheric F2-peak, hmF2. The semiannual variation, which peaks shortly after equinox, has an amplitude of about 8 km at an average level of solar activity (10.7 cm flux = 140 units), both at noon and midnight. The annual variation has an amplitude of about 11 km at northern midlatitudes, peaking in early summer; and is larger at southern stations, where it peaks in late summer. Both annual and semiannual amplitudes increase with increasing solar activity by day, but not at night. The semiannual variation in hmF2 is unrelated to the semiannual variation of the peak electron density NmF2, and is not reproduced by the CTIP and TIME-GCM computational models of the quiet-day thermosphere and ionosphere. The semiannual variation in hmF2 is approximately "isobaric", in that its amplitude corresponds quite well to the semiannual variation in the height of fixed pressure-levels in the thermosphere, as represented by the MSIS empirical model. The annual variation is not "isobaric". The annual mean of hmF2 increases with solar 10.7 cm flux, both by night and by day, on average by about 0.45 km/flux unit, rather smaller than the corresponding increase of height of constant pressure-levels in the MSIS model. The discrepancy may be due to solar-cycle variations of thermospheric winds. Although geomagnetic activity, which affects thermospheric density and temperature and therefore hmF2 also, is greatest at the equinoxes, this seems to account for less than half the semiannual variation of hmF2. The rest may be due to a semiannual variation of tidal and wave energy transmitted to the thermosphere from lower levels in the atmosphere