970 research outputs found
Detailed survey of the phase space around Nix and Hydra
We present a detailed survey of the dynamical structure of the phase space
around the new moons of the Pluto - Charon system. The spatial elliptic
restricted three-body problem was used as model and stability maps were created
by chaos indicators. The orbital elements of the moons are in the stable domain
both on the semimajor axis - eccentricity and - inclination spaces. The
structures related to the 4:1 and 6:1 mean motion resonances are clearly
visible on the maps. They do not contain the positions of the moons, confirming
previous studies. We showed the possibility that Nix might be in the 4:1
resonance if its argument of pericenter or longitude of node falls in a certain
range. The results strongly suggest that Hydra is not in the 6:1 resonance for
arbitrary values of the argument of pericenter or longitude of node.Comment: Published in MNRAS. 10 pages, 7 figures, 4 table
Spectroscopy of F
The structure of the weakly-bound F odd-odd nucleus,
produced from Na nuclei, has been investigated at GANIL by means of
the in-beam -ray spectroscopy technique. A single -line is
observed at 657(7) keV in F which has been ascribed to the decay of
the excited J= state to the J=1 ground state. The possible presence of
intruder negative parity states in F is also discussed.Comment: 3 pages, 1 figure, accepted for publication in Physical Review
Core excitations across the neutron shell gap in ²⁰⁷Tl
The single closed-neutron-shell, one proton-hole nucleus 207Tl was populated in deep-inelastic collisions of a 208Pb beam with a 208Pb target. The yrast and near-yrast level scheme has been established up to high excitation energy, comprising an octupol
Possibility of a photometric detection of "exomoons"
We examined which exo-systems contain moons that may be detected in transit.
We numerically modeled transit light curves of Earth-like and giant planets
that cointain moons with 0.005--0.4 Earth-mass. The orbital parameters were
randomly selected, but the entire system fulfilled Hill-stability. We conclude
that the timing effect is caused by two scenarios: the motion of the planet and
the moon around the barycenter. Which one dominates depends on the parameters
of the system. Already planned missions (Kepler, COROT) may be able to detect
the moon in transiting extrasolar Earth-Moon-like systems with a 20%
probability. From our sample of 500 free-designed systems, 8 could be detected
with the photometric accuracy of 0.1 mmag and a 1 minute sampling, and one
contains a stony planet. With ten times better accuracy, 51 detections are
expected. All such systems orbit far from the central star, with the orbital
periods at least 200 and 10 days for the planet and the moon, while they
contain K- and M-dwarf stars. Finally we estimate that a few number of real
detections can be expected by the end of the COROT and the Kepler missions.Comment: 5 pages, 4 figures, accepted by Astronomy and Astrophysic
Combined prompt gamma activation and neutron diffraction analyses of historic metal objects and limestone samples
Two non-destructive neutron techniques have been used for the analysis of archaeological objects, among them English monumental brass plates, Dutch tin-lead spoons, a Roman leaded bronze fibula and several limestone samples. Prompt Gamma Activation Analysis (PGAA) is a non-destructive method for determination of the major and trace element compositions of various archaeological materials.
Time-Of-Flight Neutron Diffraction (TOF-ND), on the other hand, is a non-invasive diagnostic tool for obtaining structural information from ceramic and metal objects. The element information (PGAA) holds the key information for
addressing questions of provenance and authentication, whereas the structure information (TOF-ND) addresses questions of ancient materials and making techniques. Here we present data from those two complementary neutron methods, applied to different types of materials and artefacts, in order to highlight commonalities and
differences
Fundamental Vibrational Transition of CO During the Outburst of EX Lupi in 2008
We report monitoring observations of the T Tauri star EX Lupi during its outburst in 2008 in the CO fundamental
band at 4.6–5.0 μm. The observations were carried out at the Very Large Telescope and the Subaru Telescope at six
epochs from 2008 April to August, covering the plateau of the outburst and the fading phase to a quiescent state.
The line flux of CO emission declines with the visual brightness of the star and the continuum flux at 5 μm, but
composed of two subcomponents that decay with different rates. The narrow-line emission (50 kms^(−1) in FWHM) is
near the systemic velocity of EX Lupi. These emission lines appear exclusively in v =1–0. The line widths translate
to a characteristic orbiting radius of 0.4 AU. The broad-line component (FWZI ~ 150 km s^(−1)) is highly excited up
to v ≤ 6. The line flux of the component decreases faster than the narrow-line emission. Simple modeling of the
line profiles implies that the broad-line emitting gas is orbiting around the star at 0.04–0.4 AU. The excitation state, the decay speed of the line flux, and the line profile indicate that the broad-line emission component is physically distinct from the narrow-line emission component, and more tightly related to the outburst event
Octupole transitions in the 208Pb region
The 208Pb region is characterised by the existence of collective octupole states.
Here we populated such states in 208Pb + 208Pb deep-inelastic reactions. γ-ray angular
distribution measurements were used to infer the octupole character of several E3 transitions.
The octupole character of the 2318 keV 17− → 14+ in 208Pb, 2485 keV 19/2
− → 13/2
+ in
207Pb, 2419 keV 15/2
− → 9/2
+ in 209Pb and 2465 keV 17/2
+ → 11/2
− in 207Tl transitions was
demonstrated for the first time. In addition, shell model calculations were performed using two
different sets of two-body matrix elements. Their predictions were compared with emphasis on
collective octupole states.This work is supported by the Science and Technology Facilities Council
(STFC), UK, US Department of Energy, Office of Nuclear Physics, under Contract No. DEAC02-06CH11357
and DE-FG02-94ER40834, NSF grant PHY-1404442
A low frequency multibeam assessment: Spatial mapping of shallow gas by enhanced penetration and angular response anomaly
This study highlights the potential of using a low frequency multibeam echosounder for detection and visualization of shallow gas occurring several meters beneath the seafloor. The presence of shallow gas was verified in the Bornholm Basin, Baltic Sea, at 80 m water depth with standard geochemical core analysis and hydroacoustic subbottom profiling. Successively, this area was surveyed with a 95 kHz and a 12 kHz multibeam echosounder (MBES). The bathymetric measurements with 12 kHz provided depth values systematically deeper by several meters compared to 95 kHz data. This observation was attributed to enhanced penetration of the low frequency signal energy into soft sediments. Consequently, the subbottom geoacoustic properties contributed highly to the measured backscattered signals. Those appeared up to 17 dB higher inside the shallow gas area compared to reference measurements outside and could be clearly linked to the shallow gas front depth down to 5 meter below seafloor. No elevated backscatter was visible in 95 kHz MBES data, which in turn highlights the superior potential of low frequency MBES to image shallow sub-seafloor features. Small gas pockets could be resolved even on the outer swath (up to 65°). Strongly elevated backscattering from gassy areas occurred at large incidence angles and a high gas sensitivity of the MBES is further supported by an angular response analysis presented in this study. We conclude that the MBES together with subbottom profiling can be used as an efficient tool for spatial subbottom mapping in soft sediment environments
Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes
Two-dimensional materials offer new opportunities for both fundamental
science and technological applications, by exploiting the electron spin. While
graphene is very promising for spin communication due to its extraordinary
electron mobility, the lack of a band gap restricts its prospects for
semiconducting spin devices such as spin diodes and bipolar spin transistors.
The recent emergence of 2D semiconductors could help overcome this basic
challenge. In this letter we report the first important step towards making 2D
semiconductor spin devices. We have fabricated a spin valve based on ultra-thin
(5 nm) semiconducting black phosphorus (bP), and established fundamental spin
properties of this spin channel material which supports all electrical spin
injection, transport, precession and detection up to room temperature (RT).
Inserting a few layers of boron nitride between the ferromagnetic electrodes
and bP alleviates the notorious conductivity mismatch problem and allows
efficient electrical spin injection into an n-type bP. In the non-local spin
valve geometry we measure Hanle spin precession and observe spin relaxation
times as high as 4 ns, with spin relaxation lengths exceeding 6 um. Our
experimental results are in a very good agreement with first-principles
calculations and demonstrate that Elliott-Yafet spin relaxation mechanism is
dominant. We also demonstrate that spin transport in ultra-thin bP depends
strongly on the charge carrier concentration, and can be manipulated by the
electric field effect
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