935 research outputs found
Coherent control of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As
We report single-color, time resolved magneto-optical measurements in
ferromagnetic semiconductor (Ga,Mn)As. We demonstrate coherent optical control
of the magnetization precession by applying two successive ultrashort laser
pulses. The magnetic field and temperature dependent experiments reveal the
collective Mn-moment nature of the oscillatory part of the time-dependent Kerr
rotation, as well as contributions to the magneto-optical signal that are not
connected with the magnetization dynamics.Comment: 6 pages, 3 figures, accepted in Applied Physics Letter
Trace fossils in the Cretaceous-Eocene flysch of the Sinop-Boyabat Basin, Central Pontides, Turkey
Sixty six ichnotaxa have been recognized in Barremian-Lutetian deep-marine deposits of the Sinop- Boyabat Basin, north-central Turkey, which evolved from a backarc rift into a retroarc foreland, with two episodes of major shallowing. The blackish-grey shales of the Çađlayan Fm (Barremian-Cenomanian) contain low- diversity traces fossils of mobile sediment feeders influenced by low oxygenation. One of the oldest occurrences of Scolicia indicates early adaptation to burrowing in organic-rich mud. The "normal" flysch of the Coniacian- Campanian Yemişliçay Fm bears a low-diversity Nereites ichnofacies influenced by volcanic activity. The Maastrichtian-Late Palaeocene carbonate flysch of the Akveren Fm contains a Nereites ichnofacies of moderate diversity, which is impoverished in the uppermost part, where tempestites indicate marked shallowing. The overlying variegated muddy flysch of the Atbaşý Fm (latest Palaeocene-earliest Eocene) bears an impoverished Nereites ichnofacies, which is attributed to oligotrophy and reduced preservation potential. The sand-rich silici-clastic flysch of the Kusuri Fm (Early-Middle Eocene) bears a high-diversity Nereites ichnofacies, except for the topmost part, where tempestites and littoral bioclastic limestone reflect rapid shallowing due to the tectonic closure of the basin. The turbiditic channel-fill and proximal lobe facies show a reduced trace-fossil diversity, but abundant Ophiomorpha , which is typical of the Ophiomorpha rudis sub-ichnofacies of the Nereites ichnofacies. The high abundance of Ophiomorpha in the Kusuri Fm and its low abundance in the Akveren Fm are related to plant detritus supply. The Kusuri turbiditic system was fed by a large delta, supplying rich plant detritus, whereas the Akveren system was fed by a carbonate ramp that supplied little or no such material. The extension of the Nereites ichnofacies into the tempestite-bearing neritic deposits at the top of both the Akveren and Kusuri formations indicates the capacity of the deep-water ichnofauna to survive in a rapidly-shoaling restricted basin. Only the topmost shoreface sandstones of the Akveren Fm show sporadic Ophiomorpha ? nodosa, a typical shallow-marine trace fossil
Laser-induced Precession of Magnetization in GaMnAs
We report on the photo-induced precession of the ferromagnetically coupled Mn
spins in (Ga,Mn)As, which is observed even with no external magnetic field
applied. We concentrate on various experimental aspects of the time-resolved
magneto-optical Kerr effect (TR-MOKE) technique that can be used to clarify the
origin of the detected signals. We show that the measured data typically
consist of several different contributions, among which only the oscillatory
signal is directly connected with the ferromagnetic order in the sample.Comment: 4 pages, 5 figure
Uncovering hidden modes in RR Lyrae stars
The Kepler space telescope revealed new, unexpected phenomena in RR Lyrae
stars: period doubling and the possible presence of additional modes.
Identifying these modes is complicated because they blend in the rich features
of the Fourier-spectrum. Our hydrodynamic calculations uncovered that a
'hidden' mode, the 9th overtone is involved in the period doubling phenomenon.
The period of the overtone changes by up to 10 per cent compared to the linear
value, indicating a very significant nonlinear period shift caused by its
resonance with the fundamental mode. The observations also revealed weak peaks
that may correspond to the first or second overtones. These additional modes
are often coupled with period doubling. We investigated the possibilities and
occurrences of mutual resonances between the fundamental mode and multiple
overtones in our models. These theoretical findings can help interpreting the
origin and nature of the 'hidden' modes may be found in the high quality light
curves of space observatories.Comment: In proceedings of "20th Stellar Pulsation Conference Series: Impact
of new instrumentation & new insights in stellar pulsations", 5-9 September
2011, Granada, Spai
Stellar impact on disequilibrium chemistry and on observed spectra of hot Jupiter atmospheres
In this work we study the effect of disequilibrium processes on mixing ratio
profiles of neutral species and on the simulated spectra of a hot Jupiter
exoplanet that orbits stars of different spectral types. We also address the
impact of stellar activity that should be present to a different degree in all
stars with convective envelopes. We used the VULCAN chemical kinetic code to
compute number densities of species. The temperature-pressure profile of the
atmosphere was computed with the HELIOS code. We also utilized the -ReX
forward model to predict the spectra of planets in primary and secondary
eclipses. In order to account for the stellar activity we made use of the
observed solar XUV spectrum taken from Virtual Planetary Laboratory (VPL) as a
proxy for an active sun-like star. We find large changes in mixing ratios of
most chemical species in planets orbiting A-type stars that radiate strong XUV
flux inducing a very effective photodissociation. For some species, these
changes can propagate very deep into the planetary atmosphere to pressures of
around 1 bar. To observe disequilibrium chemistry we favor hot Jupiters with
temperatures Teq=1000 K and ultra-hot Jupiters with Teq=3000$ K that also have
temperature inversion in their atmospheres. On the other hand, disequilibrium
calculations predict little changes in spectra of planets with intermediate
temperatures. We also show that stellar activity similar to the one of the
modern Sun drives important changes in mixing ratio profiles of atmospheric
species. However, these changes take place at very high atmospheric altitudes
and thus do not affect predicted spectra. We estimate that the effect of
disequilibrium chemistry in planets orbiting nearby bright stars could be
robustly detected and studied with future missions with spectroscopic
capabilities in infrared such as, e.g., JWST and ARIEL.Comment: 17 pages, 12 figure
Comparison of commercial DNA extraction kits for the detection of bacterial genomic DNA from whole-blood samples using a broad-range PCR
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