3,048 research outputs found
Expedition 306 summary
The overall aim of the North Atlantic paleoceanography study of Integrated Ocean Drilling Program Expedition 306 is to place late Neogene–Quaternary climate proxies in the North Atlantic into a chronology based on a combination of geomagnetic paleointensity, stable isotope, and detrital layer stratigraphies, and in so doing generate integrated North Atlantic millennial-scale stratigraphies for the last few million years. To reach this aim, complete sedimentary sections were drilled by multiple advanced piston coring directly south of the central Atlantic “ice-rafted debris belt” and on the southern Gardar Drift. In addition to the North Atlantic paleoceanography study, a borehole observatory was successfully installed in a new ~180 m deep hole close to Ocean Drilling Program Site 642, consisting of a circulation obviation retrofit kit to seal the borehole from the overlying ocean, a thermistor string, and a data logger to document and monitor bottom water temperature variations through time
Time resolved spectroscopy of dust and gas from extrasolar planetesimals orbiting WD 1145+017
Multiple long and variable transits caused by dust from possibly
disintegrating asteroids were detected in light curves of WD 1145+017. We
present time-resolved spectroscopic observations of this target with QUCAM CCDs
mounted in the Intermediate dispersion Spectrograph and Imaging System at the
4.2-m William Herschel Telescope in two different spectral arms: the blue arm
covering 3800-4025 {\AA} and the red arm covering 7000-7430 {\AA}. When
comparing individual transits in both arms, our observations show with 20
{\sigma} significance an evident colour difference between the in- and
out-of-transit data of the order of 0.05-0.1 mag, where transits are deeper in
the red arm. We also show with > 6 {\sigma} significance that spectral lines in
the blue arm are shallower during transits than out-of-transit. For the
circumstellar lines it also appears that during transits the reduction in
absorption is larger on the red side of the spectral profiles. Our results
confirm previous findings showing the u'-band excess and a decrease in line
absorption during transits. Both can be explained by an opaque body blocking a
fraction of the gas disc causing the absorption, implying that the absorbing
gas is between the white dwarf and the transiting objects. Our results also
demonstrate the capability of EMCCDs to perform high-quality time resolved
spectroscopy of relatively faint targets.Comment: 9 pages, 5 figures. Accepted to MNRA
Enumeration of Stack-Sorting Preimages via a Decomposition Lemma
We give three applications of a recently-proven "Decomposition Lemma," which
allows one to count preimages of certain sets of permutations under West's
stack-sorting map . We first enumerate the permutation class
, finding a new example
of an unbalanced Wilf equivalence. This result is equivalent to the enumeration
of permutations sortable by , where is the bubble
sort map. We then prove that the sets ,
,
and are
counted by the so-called "Boolean-Catalan numbers," settling a conjecture of
the current author and another conjecture of Hossain. This completes the
enumerations of all sets of the form
for
with the exception of the set
. We also find an explicit formula for
, where
is the set of permutations in with descents.
This allows us to prove a conjectured identity involving Catalan numbers and
order ideals in Young's lattice.Comment: 20 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1903.0913
Coupling and induced depinning of magnetic domain walls in adjacent spin valve nanotracks
The magnetostatic interaction between magnetic domain walls (DWs) in adjacent
nanotracks has been shown to produce strong inter-DW coupling and mutual
pinning. In this paper, we have used electrical measurements of adjacent
spin-valve nanotracks to follow the positions of interacting DWs. We show that
the magnetostatic interaction between DWs causes not only mutual pinning, as
observed till now, but that a travelling DW can also induce the depinning of
DWs in near-by tracks. These effects may have great implications for some
proposed high density magnetic devices (e.g. racetrack memory, DW logic
circuits, or DW-based MRAM).Comment: The following article has been accepted by the Journal of Applied
Physic
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