751,211 research outputs found
Atmosphere above a large solar pore
A large solar pore with a granular light bridge was observed on October 15,
2008 with the IBIS spectrometer at the Dunn Solar Telescope and a 69-min long
time series of spectral scans in the lines Ca II 854.2 nm and Fe I 617.3 nm was
obtained. The intensity and Doppler signals in the Ca II line were separated.
This line samples the middle chromosphere in the core and the middle
photosphere in the wings. Although no indication of a penumbra is seen in the
photosphere, an extended filamentary structure, both in intensity and Doppler
signals, is observed in the Ca II line core. An analysis of morphological and
dynamical properties of the structure shows a close similarity to a
superpenumbra of a sunspot with developed penumbra. A special attention is paid
to the light bridge, which is the brightest feature in the pore seen in the Ca
II line centre and shows an enhanced power of chromospheric oscillations at 3-5
mHz. Although the acoustic power flux in the light bridge is five times higher
than in the "quiet" chromosphere, it cannot explain the observed brightness.Comment: 6 pages, 3 figures, accepted in Journal of Physics: Conference Serie
Small-scale chromospheric jets above a sunspot light bridge
High-resolution broadband filtergrams of active region NOAA 11271 in Ca ii H
and G band were obtained with the Solar Optical Telescope on board Hinode to
identify the physical driver responsible for the dynamic and small-scale
chromospheric jets above a sunspot light bridge. We identified the jets in the
Ca images using a semi-automatic routine. The chromospheric jets consist of a
bright, triangular-shaped blob that lies on the light bridge, while the apex of
this blob extends into a spike-like structure that is bright against the dark
umbral background. Most of the jets have apparent lengths of less than 1000 km
and about 30% of them have lengths between 1000-1600 km. They are oriented
within +/-35 deg. to the normal of the light bridge axis. Many of them are
clustered near the central part within a 2 arcsec area. The jets are seen to
move rapidly along the light bridge and most of them cannot be identified in
successive images taken with a 2 min cadence. The jets are primarily located on
one side of the light bridge and are directed into the umbral core. The Stokes
profiles at or close to the location of the blobs on the LB exhibit both a
significant net circular polarization and multiple components, including
opposite-polarity lobes. The magnetic field diverges from the light bridge
towards the umbral cores that it separates. In the photosphere there is a
predominantly uni-directional flow with speeds of 100-150 m/s along the light
bridge which is interrupted by a patch of weak motions that also moves along
the light bridge. The dynamic short-lived jets above the LB seem to be guided
by the magnetic field lines. Reconnection events are a likely trigger for such
phenomenon since they occur at locations where the magnetic field changes
orientation sharply. We find no clear relation between the jets and the
photospheric flow pattern.Comment: Accepted for publication in A&A, 9 pages, 7 figure
Ischemia reperfusion dysfunction changes model-estimated kinetics of myofilament interaction due to inotropic drugs in isolated hearts
BACKGROUND: The phase-space relationship between simultaneously measured myoplasmic [Ca(2+)] and isovolumetric left ventricular pressure (LVP) in guinea pig intact hearts is altered by ischemic and inotropic interventions. Our objective was to mathematically model this phase-space relationship between [Ca(2+)] and LVP with a focus on the changes in cross-bridge kinetics and myofilament Ca(2+ )sensitivity responsible for alterations in Ca(2+)-contraction coupling due to inotropic drugs in the presence and absence of ischemia reperfusion (IR) injury. METHODS: We used a four state computational model to predict LVP using experimentally measured, averaged myoplasmic [Ca(2+)] transients from unpaced, isolated guinea pig hearts as the model input. Values of model parameters were estimated by minimizing the error between experimentally measured LVP and model-predicted LVP. RESULTS: We found that IR injury resulted in reduced myofilament Ca(2+ )sensitivity, and decreased cross-bridge association and dissociation rates. Dopamine (8 μM) reduced myofilament Ca(2+ )sensitivity before, but enhanced it after ischemia while improving cross-bridge kinetics before and after IR injury. Dobutamine (4 μM) reduced myofilament Ca(2+ )sensitivity while improving cross-bridge kinetics before and after ischemia. Digoxin (1 μM) increased myofilament Ca(2+ )sensitivity and cross-bridge kinetics after but not before ischemia. Levosimendan (1 μM) enhanced myofilament Ca(2+ )affinity and cross-bridge kinetics only after ischemia. CONCLUSION: Estimated model parameters reveal mechanistic changes in Ca(2+)-contraction coupling due to IR injury, specifically the inefficient utilization of Ca(2+ )for contractile function with diastolic contracture (increase in resting diastolic LVP). The model parameters also reveal drug-induced improvements in Ca(2+)-contraction coupling before and after IR injury
Following basal stem rot in young oil palm plantings
The PCR primer GanET has previously been shown to be suitable for the specific amplification of DNA from Ganoderma boninense. A DNA extraction and PCR method has been developed that allows for the amplification of the G. boninense DNA from environmental samples of oil palm tissue. The GanET primer reaction was used in conjunction with a palm-sampling programme to investigate the possible infection of young palms through cut frond base surfaces. Ganoderma DNA was detected in frond base material at a greater frequency than would be expected by comparison with current infection levels. Comparisons are made between the height of the frond base infected, the number of frond bases infected, and subsequent development of basal stem rot. The preliminary results suggest that the development of basal stem rot may be more likely to occur when young lower frond bases are infected
Adsorption Sites of Individual Metal Atoms on Ultrathin MgO(100) Films
We use Ca doping during growth of one and two monolayer thick MgO films on
Ag(100) to identify the adsorption sites of individual adatoms with scanning
tunneling microscopy. For this we combine atomic resolution images of the bare
MgO layer with images of the adsorbates and the substitutional Ca atoms taken
at larger tip-sample distance. For Ho atoms, the adsorption sites depend on MgO
thickness. On the monolayer, they are distributed on the O and bridge sites
according to the abundance of those sites, 1/3 and 2/3 respectively. On the MgO
bilayer, Ho atoms populate almost exclusively the O site. A third species
adsorbed on Mg is predicted by density functional theory and can be created by
atomic manipulation. Au atoms adsorb on the bridge sites for both MgO
thicknesses, while Co and Fe atoms prefer the O sites, again for both
thickness.Comment: 8 pages, 9 figures, part of the work presented at the DPG Spring
meeting in Dresden, 201
A Cellular Automaton Model for Bi-Directionnal Traffic
We investigate a cellular automaton (CA) model of traffic on a bi-directional
two-lane road. Our model is an extension of the one-lane CA model of {Nagel and
Schreckenberg 1992}, modified to account for interactions mediated by passing,
and for a distribution of vehicle speeds. We chose values for the various
parameters to approximate the behavior of real traffic. The density-flow
diagram for the bi-directional model is compared to that of a one-lane model,
showing the interaction of the two lanes. Results were also compared to
experimental data, showing close agreement. This model helps bridge the gap
between simplified cellular automata models and the complexity of real-world
traffic.Comment: 4 pages 6 figures. Accepted Phys Rev
Dynamics of the solar atmosphere above a pore with a light bridge
Context: Solar pores are small sunspots lacking a penumbra that have a
prevailing vertical magnetic field component. They can include light bridges at
places with locally reduced magnetic field. Like sunspots, they exhibit a wide
range of oscillatory phenomena.
Aims: A large isolated pore with a light bridge (NOAA 11005) is studied to
obtain characteristics of a chromospheric filamentary structure around the
pore, to analyse oscillations and waves in and around the pore, and to
understand the structure and brightness of the light bridge.
Methods: Spectral imaging observations in the line Ca II 854.2 nm and
complementary spectropolarimetry in Fe I lines, obtained with the DST/IBIS
spectrometer and HINODE/SOT spectropolarimeter, were used to measure
photospheric and chromospheric velocity fields, oscillations, waves, the
magnetic field in the photosphere, and acoustic energy flux and radiative
losses in the chromosphere.
Results: The chromospheric filamentary structure around the pore has all
important characteristics of a superpenumbra: it shows an inverse Evershed
effect and running waves, and has a similar morphology and oscillation
character. The granular structure of the light bridge in the upper photosphere
can be explained by radiative heating. Acoustic waves leaking up from the
photosphere along the inclined magnetic field in the light bridge transfer
enough energy flux to balance the total radiative losses of the light-bridge
chromosphere.
Conclusions: The presence of a penumbra is not a necessary condition for the
formation of a superpenumbra. The light bridge is heated by radiation in the
photosphere and by acoustic waves in the chromosphere.Comment: 14 pages, 14 figures, 3 tables, accepted for publication in
Astrononomy & Astrophysic
Molecular mechanisms of the regulation of ATPase cycle in striated muscle
New data on the molecular mechanism of the regulation of ATPase cycle by troponin-tropomyosin system have been obtained in reconstructed muscle fibers by using the polarized fluorescence technique, which allowed us following the azimuthal movements of tropomyosin, actin subdomain-1 and myosin SH1 helix motor domain during the sequential steps of ATPase cycle. We found that tropomyosin strands "rolling" on thin filament surface from periphery to center at ATPase cycle increases the amplitudes of multistep changes in special arrangement of SH1 helix and subdomain-1 at force generation states. These changes seem to convey to actin monomers and to myosin "lever arm", resulting in enhance of the effectiveness of each cross-bridge work. At high-Ca^2+^ troponin, a shift of tropomyosin strands further to center at strong-binding states increases this effect. At low-Ca^2+^ troponin "freezes" tropomyosin and actin in states typical for weak-binding states, resulting in disturbing the teamwork of actin and myosin
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