20,585 research outputs found
A spatially resolved limb flare on Algol B observed with XMM-Newton
We report XMM-Newton observations of the eclipsing binary Algol A (B8V) and B
(K2III). The XMM-Newton data cover the phase interval 0.35 - 0.58, i.e.,
specifically the time of optical secondary minimum, when the X-ray dark B-type
star occults a major fraction of the X-ray bright K-type star. During the
eclipse a flare was observed with complete light curve coverage. The decay part
of the flare can be well described with an exponential decay law allowing a
rectification of the light curve and a reconstruction of the flaring plasma
region. The flare occurred near the limb of Algol B at a height of about 0.1R
with plasma densities of a few times 10^11 cm^-3 consistent with spectroscopic
density estimates. No eclipse of the quiescent X-ray emission is observed
leading us to the conclusion that the overall coronal filling factor of Algol B
is small.Comment: 8 pages, 7 figures, accepted by A&
Workshop on Geology of the Apollo 17 Landing Site
The topics covered include the following: petrology, lithology, lunar rocks, lunar soil, geochemistry, lunar geology, lunar resources, oxygen production, ilmenite, volcanism, highlands, lunar maria, massifs, impact melts, breccias, lunar crust, Taurus-Littrow, minerals, site selection, regolith, glasses, geomorphology, basalts, tectonics, planetary evolution, anorthosite, titanium oxides, chemical composition, and the Sudbury-Serenitatis analogy
Copepods encounter rates from a model of escape jump behaviour in turbulence
A key ecological parameter for planktonic copepods studies is their
interspecies encounter rate which is driven by their behaviour and is strongly
influenced by turbulence of the surrounding environment. A distinctive feature
of copepods motility is their ability to perform quick displacements, often
dubbed jumps, by means of powerful swimming strokes. Such a reaction has been
associated to an escape behaviour from flow disturbances due to predators or
other external dangers. In the present study, the encounter rate of copepods in
a developed turbulent flow with intensity comparable to the one found in
copepods' habitat is numerically investigated. This is done by means of a
Lagrangian copepod (LC) model that mimics the jump escape reaction behaviour
from localised high-shear rate fluctuations in the turbulent flows. Our
analysis shows that the encounter rate for copepods of typical perception
radius of ~ {\eta}, where {\eta} is the dissipative scale of turbulence, can be
increased by a factor up to ~ 100 compared to the one experienced by passively
transported fluid tracers. Furthermore, we address the effect of introducing in
the LC model a minimal waiting time between consecutive jumps. It is shown that
any encounter-rate enhancement is lost if such time goes beyond the dissipative
time-scale of turbulence, {\tau}_{\eta}. Because typically in the ocean {\eta}
~ 0.001m and {\tau}_{\eta} ~ 1s, this provides stringent constraints on the
turbulent-driven enhancement of encounter-rate due to a purely mechanical
induced escape reaction.Comment: 11 pages, 10 figure
Static and dynamic structure factors in the Haldane phase of the bilinear-biquadratic spin-1
The excitation spectra of the T=0 dynamic structure factors for the spin,
dimer, and trimer fluctuation operators as well as for the newly defined center
fluctuation operator in the one-dimensional S=1 Heisenberg model wi th
isotropic bilinear and biquadratic exchange are
investigated via the recursion method for systems with up to N=18 site s over
the predicted range, , of the topologically ordered
Haldane phase. The four static and dynamic structure factors probe t he
ordering tendencies in the various coupling regimes and the elementary and
composite excitations which dominate the T=0 dynamics. At (VBS point), the dynamically relevant spectra in the invariant
subspaces with total spin are dominated by a branch of magnon
states , by continua of two-magnon scattering states , and by discrete branches of two-magnon bound states with positive
interaction energy . The dimer and trimer spectra at ar e
found to consist of single modes with -independent excitation energies
and , where is
the ground-state energy per site. The basic structure of the dynamically
relevant excitation spectrum remains the same over a substantial parameter
range within the Haldane phase. At the transition to the dimerized phase
(), the two-magnon excitations turn into two-spinon excitations.Comment: 12 pages, 4 Postscript figure
TDC Chip and Readout Driver Developments for COMPASS and LHC-Experiments
A new TDC-chip is under development for the COMPASS experiment at CERN. The
ASIC, which exploits the 0.6 micrometer CMOS sea-of-gate technology, will allow
high resolution time measurements with digitization of 75 ps, and an
unprecedented degree of flexibility accompanied by high rate capability and low
power consumption. Preliminary specifications of this new TDC chip are
presented.
Furthermore a FPGA based readout-driver and buffer-module as an interface
between the front-end of the COMPASS detector systems and an optical S-LINK is
in development. The same module serves also as remote fan-out for the COMPASS
trigger distribution and time synchronization system. This readout-driver
monitors the trigger and data flow to and from front-ends. In addition, a
specific data buffer structure and sophisticated data flow control is used to
pursue local pre-event building. At start-up the module controls all necessary
front-end initializations.Comment: 5 pages, 4 figure
Preliminary data on boulders at station 6, Apollo 17 landing site
A cluster of boulders at Station 6 (Apollo 17 landing site) consists of breccias derived from the North Massif. Three preliminary lithologic units were established, on the basis of photogeologic interpretations; all lithologies identified photogeologically were sampled. Breccia clasts and matrices studied petrographically and chemically fall into two groups by modal mineralogy: (1) low-K Fra Mauro or high basalt composition, consisting of 50-60% modal feldspar, approximately 45% orthopyroxene and 1-7% Fe-Ti oxide; (2) clasts consisting of highland basalt composition, consisting of 70% feldspar, 30% orthopyroxene and olivine and a trace of Fe-Ti oxide
HST FUV C IV observations of the hot DG Tauri jet
Protostellar jets are tightly connected to the accretion process and regulate
the angular momentum balance of accreting star-disk systems. The DG Tau jet is
one of the best-studied protostellar jets and contains plasma with temperatures
ranging over three orders of magnitude within the innermost 50 AU of the jet.
We present new Hubble Space Telescope (HST) far ultraviolet (FUV) long-slit
spectra spatially resolving the C IV emission (T~1e5 K) from the jet for the
first time, and quasi-simultaneous HST observations of optical forbidden
emission lines ([O I], [N II], [S II] and [O III]) and fluorescent H2 lines.
The C IV emission peaks at 42 AU from the stellar position and has a FWHM of 52
AU along the jet. Its deprojected velocity of around 200 km/s decreases
monotonically away from the driving source. In addition, we compare our HST
data with the X-ray emission from the DG Tau jet. We investigate the
requirements to explain the data by an initially hot jet compared to local
heating. Both scenarios indicate a mass loss by the T~1e5 K jet of ~1e-9
Msun/year, i.e., between the values for the lower temperature jet (T~1e4 K) and
the hotter X-ray emitting part (T>1e6 K). However, a simple initially hot wind
requires a large launching region (~1 AU), and we therefore favor local
heating.Comment: 5 pages, 2 figures, accepted by A&A letter
High-energy magnetic excitations in overdoped LaSrCuO studied by neutron and resonant inelastic X-ray scattering
We have performed neutron inelastic scattering and resonant inelastic X-ray
scattering (RIXS) at the Cu- edge to study high-energy magnetic
excitations at energy transfers of more than 100 meV for overdoped
LaSrCuO with ( K) and
(non-superconducting) using identical single crystal samples for the two
techniques. From constant-energy slices of neutron scattering cross-sections,
we have identified magnetic excitations up to ~250 meV for . Although
the width in the momentum direction is large, the peak positions along the (pi,
pi) direction agree with the dispersion relation of the spin-wave in the
non-doped LaCuO (LCO), which is consistent with the previous RIXS
results of cuprate superconductors. Using RIXS at the Cu- edge, we have
measured the dispersion relations of the so-called paramagnon mode along both
(pi, pi) and (pi, 0) directions. Although in both directions the neutron and
RIXS data connect with each other and the paramagnon along (pi, 0) agrees well
with the LCO spin-wave dispersion, the paramagnon in the (pi, pi) direction
probed by RIXS appears to be less dispersive and the excitation energy is lower
than the spin-wave of LCO near (pi/2, pi/2). Thus, our results indicate
consistency between neutron inelastic scattering and RIXS, and elucidate the
entire magnetic excitation in the (pi, pi) direction by the complementary use
of two probes. The polarization dependence of the RIXS profiles indicates that
appreciable charge excitations exist in the same energy range of magnetic
excitations, reflecting the itinerant character of the overdoped sample. A
possible anisotropy in the charge excitation intensity might explain the
apparent differences in the paramagnon dispersion in the (pi, pi) direction as
detected by the X-ray scattering.Comment: 7 pages, 7 figure
X-ray to NIR emission from AA Tauri during the dim state - Occultation of the inner disk and gas-to-dust ratio of the absorber
AA Tau is a well-studied, nearby classical T Tauri star, which is viewed
almost edge-on. A warp in its inner disk periodically eclipses the central
star, causing a clear modulation of its optical light curve. The system
underwent a major dimming event beginning in 2011 caused by an extra absorber,
which is most likely associated with additional disk material in the line of
sight toward the central source. We present new XMM-Newton X-ray, Hubble Space
Telescope FUV, and ground based optical and near-infrared data of the system
obtained in 2013 during the long-lasting dim phase. The line width decrease of
the fluorescent H disk emission shows that the extra absorber is located at
au. Comparison of X-ray absorption () with dust extinction (),
as derived from measurements obtained one inner disk orbit (eight days) after
the X-ray measurement, indicates that the gas-to-dust ratio as probed by the
to ratio of the extra absorber is compatible with the ISM ratio.
Combining both results suggests that the extra absorber, i.e., material at
au, has no significant gas excess in contrast to the elevated
gas-to-dust ratio previously derived for material in the inner region
(au).Comment: 16 pages, 12 figures, accepted by A&
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