1,515 research outputs found
Demographic history and genetic differentiation in apes
SummaryComparisons of genetic variation between humans and great apes are hampered by the fact that we still know little about the demographics and evolutionary history of the latter species [1–4]. In addition, characterizing ape genetic variation is important because they are threatened with extinction, and knowledge about genetic differentiation among groups may guide conservation efforts [5]. We sequenced multiple intergenic autosomal regions totaling 22,400 base pairs (bp) in ten individuals each from western, central, and eastern chimpanzee groups and in nine bonobos, and 16,000 bp in ten Bornean and six Sumatran orangutans. These regions are analyzed together with homologous information from three human populations and gorillas. We find that whereas orangutans have the highest diversity, western chimpanzees have the lowest, and that the demographic histories of most groups differ drastically. Special attention should therefore be paid to sampling strategies and the statistics chosen when comparing levels of variation within and among groups. Finally, we find that the extent of genetic differentiation among “subspecies” of chimpanzees and orangutans is comparable to that seen among human populations, calling the validity of the “subspecies” concept in apes into question
Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare
We analyzed high-cadence sit-and-stare observations acquired with the
Hinode/EIS spectrometer and HXR measurements acquired with RHESSI during an
M-class flare. During the flare impulsive phase, we observe no significant
flows in the cooler Fe XIII line but strong upflows, up to 80-150 km/s, in the
hotter Fe XVI line. The largest Doppler shifts observed in the Fe XVI line were
co-temporal with the sharp intensity peak. The electron density obtained from a
Fe XIII line pair ratio exhibited fast increase (within two minutes) from the
pre-flare level of 5.01x10^(9) cm^(-3) to 3.16x10^(10) cm^(-3) during the flare
peak. The nonthermal energy flux density deposited from the coronal
acceleration site to the lower atmospheric layers during the flare peak was
found to be 1.34x10^(10) erg/s/cm^(2) for a low-energy cut-off that was
estimated to be 16 keV. During the decline flare phase, we found a secondary
intensity and density peak of lower amplitude that was preceded by upflows of
15 km/s that were detected in both lines. The flare was also accompanied by a
filament eruption that was partly captured by the EIS observations. We derived
Doppler velocities of 250-300 km/s for the upflowing filament material.The
spectroscopic results for the flare peak are consistent with the scenario of
explosive chromospheric evaporation, although a comparatively low value of the
nonthermal energy flux density was determined for this phase of the flare. This
outcome is discussed in the context of recent hydrodynamic simulations. It
provides observational evidence that the response of the atmospheric plasma
strongly depends on the properties of the electron beams responsible for the
heating, in particular the steepness of the energy distribution.Comment: 13 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Creating, Visualizing, and Analyzing Dynamic Music Objects in the Browser with the Dymo Designer
Characteristics of long-duration inhibitory postsynaptic potentials in rat neocortical neurons in vitro
1. The characteristics of long-duration inhibitory postsynaptic potentials (l-IPSPs) which are evoked in rat frontal neocortical neurons by local electrical stimulation were investigated with intracellular recordings from anin vitro slice preparation.
2. Stimulation with suprathreshold intensities evoked l-IPSPs with typical durations of 600–900 msec at resting membrane potential. Conductance increases of 15–60% were measured at the peak amplitude of l-IPSPs (150–250 msec poststimulus).
3. The duration of the conductance increases during l-IPSPs displayed a significant voltage dependence, decreasing as the membrance potential was depolarized and increasing with hyperpolarization.
4. The reversal potential of l-IPSPs is significantly altered by reductions in the extracellular potassium concentration. Therefore it is concluded that l-IPSPs in rat neocortical neurons are generated by the activation of a potassium conductance.
5. l-IPSPs exhibit stimulation fatigue. Stimulation with a frequency of 1 Hz produces a complete fatigue of the conductance increases during l-IPSPs after approximately 20 consecutive stimuli. Recovery from this fatigue requires minutes.
6. l-IPSPs are not blocked by bicuculline but are blocked by baclofen
Magnetic helicity and energy budget around large confined and eruptive solar flares
We investigate the coronal magnetic energy and helicity budgets of ten solar
ARs, around the times of large flares. In particular, we are interested in a
possible relation of the derived quantities to the particular type of the
flares that the AR produces, i.e., whether they are associated with a CME or
they are confined. Using an optimization approach, we employ time series of 3D
nonlinear force-free magnetic field models of ten ARs, covering a time span of
several hours around the time of occurrence of large solar flares (GOES class
M1.0 and larger). We subsequently compute the 3D magnetic vector potentials
associated to the model 3D coronal magnetic field using a finite-volume method.
This allows us to correspondingly compute the coronal magnetic energy and
helicity budgets, as well as related (intensive) quantities such as the
relative contribution of free magnetic energy, (energy
ratio), the fraction of non-potential (current-carrying) helicity,
(helicity ratio), and the normalized
current-carrying helicity, . The total
energy and helicity budgets of flare-productive ARs (extensive parameters)
cover a broad range of magnitudes, with no obvious relation to the eruptive
potential of the individual ARs, i.e., whether or not a CME is produced in
association with the flare. The intensive eruptivity proxies,
and , and
, however, seem to be distinctly
different for ARs that produced CME-associated large flares compared to those
which produced confined flares. For the majority of ARs in our sample, we are
able to identify characteristic pre-flare magnitudes of the intensive
quantities, clearly associated to subsequent CME-productivity.Comment: Accepted for publication in A & A journal, 19 pages, and 11 figure
Comparison of force-free coronal magnetic field modeling using vector fields from Hinode and Solar Dynamics Observatory
Photospheric magnetic vector maps from two different instruments are used to
model the nonlinear force-free coronal magnetic field above an active region.
We use vector maps inferred from polarization measurements of the Solar
Dynamics Observatory/Helioseismic and Magnetic Imager (HMI) and the Solar
Optical Telescope Spectropolarimeter (SP) aboard Hinode. Besides basing our
model calculations on HMI data, we use both, SP data of original resolution and
scaled down to the resolution of HMI. This allows us to compare the model
results based on data from different instruments and to investigate how a
binning of high-resolution data effects the model outcome. The resulting 3D
magnetic fields are compared in terms of magnetic energy content and magnetic
topology. We find stronger magnetic fields in the SP data, translating into a
higher total magnetic energy of the SP models. The net Lorentz forces of the
HMI and SP lower boundaries verify their force-free compatibility. We find
substantial differences in the absolute estimates of the magnetic field energy
but similar relative estimates, e.g., the fraction of excess energy and of the
flux shared by distinct areas. The location and extension of neighboring
connectivity domains differs and the SP model fields tend to be higher and more
vertical. Hence, conclusions about the magnetic connectivity based on
force-free field models are to be drawn with caution. We find that the
deviations of the model solution when based on the lower-resolution SP data are
small compared to the differences of the solutions based on data from different
instruments.Comment: 8 pages, 10 figures, APJ, accepte
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