2,479 research outputs found
On The Determination of MDI High-Degree Mode Frequencies
The characteristic of the solar acoustic spectrum is such that mode lifetimes
get shorter and spatial leaks get closer in frequency as the degree of a mode
increases for a given order. A direct consequence of this property is that
individual p-modes are only resolved at low and intermediate degrees, and that
at high degrees, individual modes blend into ridges. Once modes have blended
into ridges, the power distribution of the ridge defines the ridge central
frequency and it will mask the true underlying mode frequency. An accurate
model of the amplitude of the peaks that contribute to the ridge power
distribution is needed to recover the underlying mode frequency from fitting
the ridge.
We present the results of fitting high degree power ridges (up to l = 900)
computed from several two to three-month-long time-series of full-disk
observations taken with the Michelson Doppler Imager (MDI) on-board the Solar
and Heliospheric Observatory between 1996 and 1999.
We also present a detailed discussion of the modeling of the ridge power
distribution, and the contribution of the various observational and
instrumental effects on the spatial leakage, in the context of the MDI
instrument. We have constructed a physically motivated model (rather than some
ad hoc correction scheme) resulting in a methodology that can produce an
unbiased determination of high-degree modes, once the instrumental
characteristics are well understood.
Finally, we present changes in high degree mode parameters with epoch and
thus solar activity level and discuss their significance.Comment: 59 pages, 38 figures -- High-resolution version at
http://www-sgk.harvard.edu:1080/~sylvain/preprints/ -- Manuscript submitted
to Ap
Evaluation of the presence of the bap gene in Staphylococcus aureus isolates recovered from human and animals species.
International audienceThe implication of biofilm in chronic bacterial infection in many species has triggered an increasing interest in the characterization of genes involved in biofilm formation. The bap gene is a newly identified gene that encodes the biofilm-associated protein, BAP, which is involved in biofilm formation in Staphylococcus aureus. So far the bap gene has only been found in a small proportion of S. aureus strains from bovine mastitis in Spain. In order to study the presence of the bap gene in S. aureus isolates obtained from other species and various locations, a collection of 262 isolates was tested by PCR, using published primers and dot-blot. The results indicated that none of the isolates carried the bap gene suggesting that the prevalence of this gene among S. aureus isolates should be very low
Estimating the effect of rainfall on the surface temperature of a tropical lake
We make use of a unique high-quality, long-term observational
dataset on a tropical lake to assess the effect of rainfall on lake
surface temperature. The lake in question is Lake Kivu, one of the
African Great Lakes, and was selected for its remarkably uniform
climate and availability of multi-year over-lake meteorological
observations. Rain may have a cooling effect on the lake surface by
lowering the near-surface air temperature, by the direct rain heat
flux into the lake, by mixing the lake surface layer through the
flux of kinetic energy and by convective mixing of the lake surface
layer. The potential importance of the rainfall effect is discussed
in terms of both heat flux and kinetic energy flux. To estimate the
rainfall effect on the mean diurnal cycle of lake surface
temperature, the data are binned into categories of daily
rainfall amount. They are further filtered based on comparable
values of daily mean net radiation, which reduces the influence of
radiative-flux differences. Our results indicate that days with
heavy rainfall may experience a reduction in lake surface
temperature of approximately 0.3 K by the end of the day compared to
days with light to moderate rainfall. Overall this study highlights
a new potential control on lake surface temperature and suggests
that further efforts are needed to quantify this effect in other
regions and to include this process in land surface models used
for atmospheric prediction.</p
Future projections of temperature and mixing regime of European temperate lakes
The physical response of lakes to climate warming is regionally
variable and highly dependent on individual lake characteristics, making
generalizations about their development difficult. To qualify the role of
individual lake characteristics in their response to regionally homogeneous
warming, we simulated temperature, ice cover, and mixing in four intensively
studied German lakes of varying morphology and mixing regime with a
one-dimensional lake model. We forced the model with an ensemble of 12
climate projections (RCP4.5) up to 2100. The lakes were projected to warm at
0.10–0.11 ∘C decade−1, which is 75 %–90 % of the
projected air temperature trend. In simulations, surface temperatures
increased strongly in winter and spring, but little or not at all in summer
and autumn. Mean bottom temperatures were projected to increase in all lakes,
with steeper trends in winter and in shallower lakes. Modelled ice thaw and
summer stratification advanced by 1.5–2.2 and 1.4–1.8 days decade−1 respectively, whereas
autumn turnover and winter freeze timing was less sensitive. The projected
summer mixed-layer depth was unaffected by warming but sensitive to changes
in water transparency. By mid-century, the frequency of ice and
stratification-free winters was projected to increase by about 20 %,
making ice cover rare and shifting the two deeper dimictic lakes to a
predominantly monomictic regime. The polymictic lake was unlikely to become
dimictic by the end of the century. A sensitivity analysis predicted that
decreasing transparency would dampen the effect of warming on mean
temperature but amplify its effect on stratification. However, this
interaction was only predicted to occur in clear lakes, and not in the study
lakes at their historical transparency. Not only lake morphology, but also
mixing regime determines how heat is stored and ultimately how lakes respond
to climate warming. Seasonal differences in climate warming rates are thus
important and require more attention.</p
Oscillation frequencies and mode lifetimes in alpha Centauri A
We analyse our recently-published velocity measurements of alpha Cen A
(Butler et al. 2004). After adjusting the weights on a night-by-night basis in
order to optimize the window function to minimize sidelobes, we extract 42
oscillation frequencies with l=0 to 3 and measure the large and small frequency
separations. We give fitted relations to these frequencies that can be compared
with theoretical models and conclude that the observed scatter about these fits
is due to the finite lifetimes of the oscillation modes. We estimate the mode
lifetimes to be 1-2 d, substantially shorter than in the Sun.Comment: Accepted by Ap
Notostraca trackways in Permian playa environments of the Lodève basin (France)
Durante casi veinte años, el Dr Lapeyrie, cirujano en Lodève, ha reunido numerosos fósiles provenientes de la Formación del Salagou de la cuenca pérmica de Lodève. Los mismos incluyen insectos, notostráceos, plantas e icnofósiles. Entre los últimos, hay una multitud de pistas de artrópodos, muy bien preservadas, las cuales fueron recogidas en el techo de secuencias depositadas en alrededores de lagos tipo playa. Experimentos sobre locomoción de artrópodos efectuados con animales actuales sugieren que la mayoría de las pistas estudidas fueron producidas por Notostracos de los cuales se han encontrado algunos millares de restos (caparazónes, apéndices, cuerpos enteros) asignados a Triops cancriformis permiensis y Lepidurus occitaniacus. Todos estos rastros fueron producidos de forma subacuática y corresponden a diferentes eto-morfotipos conocidos en la literatura con el nombre de Acripes para las huellas de locomoción, de Rusophycus para las de descanso y excavación (posiciones horizontales, proclinales y opistoclinales) y de Cruziana para locomoción y excavación activa. Numerosas planchas fósiliferas permiten ver claramente el paso de una actividad a la otra. Esta situación fue registrada en una película con Lepidurus actuales. Se reconocieron los icnotaxones Acribes multiformis nov. isp, Rusophycus eutendorfensis, R. carbonarius, R. versans, R. minutus, R. furcosus, Cruziana problematica, C. pascens y, menos abundantemente, Scoyenia isp. También fueron encontradas numerosas pisadas, destacando la icnofacies Scoyenia, encontrándose solamente en los «overbank settings». Para la Formación del Salagou, éstos corresponden a llanuras de inundación/playas donde las zonas inundadas eran temporales y de poca profundidad, y en las que vivían Notostracos, Insectos, Aracnidos y Concostracos (= Spinicaudata + Laevicaudata), este último grupo conocido solamente por cuerpos-fósiles. Este ambiente de playa distal, desarrollado en un clima árido, ha perdurado durante una gran parte del Pérmico, posiblemente entre el Cisuraliense superior y el Lopingiense inferior
Placental mitochondrial DNA content is associated with childhood intelligence
Background: Developmental processes in the placenta and the fetal brain are shaped by the similar biological signals. Evidence accumulates that adaptive responses of the placenta may influence central nervous system development. We hypothesize that placental mtDNA content at birth is associated with intelligence in childhood. In addition, we investigate if intra-pair differences in mtDNA content are associated with intra-pair differences in intelligence.
Methods: Relative mtDNA content was measured using qPCR in placental tissue of 375 children of the East Flanders Prospective Twin Survey. Intelligence was assessed with the Wechsler Intelligence Scale for Children-Revised (WISC-R) between 8 and 15 years old. We accounted for sex, gestational age, birth weight, birth year, zygosity and chorionicity, cord insertion, age at measurement, indicators of socioeconomic status, smoking during pregnancy, and urban environment.
Results: In multivariable adjusted mixed modelling analysis, each doubling in placental mtDNA content was associated with 2.0 points (95% CI 0.02 to 3.9; p = 0.05) higher total and 2.3 points (95% CI 0.2 to 4.3; p = 0.03) higher performance IQ in childhood. We observed no association between mtDNA content and verbal intelligence. Intra-pair differences in mtDNA content and IQ were significantly (p = 0.01) correlated in monozygotic-monochorionic twin pairs, showing that the twin with the highest mtDNA content was 1.9 times more likely (p = 0.05) to have the highest IQ. This was not observed in dichorionic twin pairs.
Conclusions: We provide the first evidence that placental mtDNA content is associated with childhood intelligence. This emphasizes the importance of placental mitochondrial function during in utero life on fetal brain development with long-lasting consequences
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