1,861 research outputs found
Kagom\'{e} ice state in the dipolar spin ice Dy_{2}Ti_{2}O_{7}
We have investigated the kagom\'{e} ice behavior of the dipolar spin-ice
compound Dy_{2}Ti_{2}O_{7} in magnetic field along a [111] direction using
neutron scattering and Monte Carlo simulations. The spin correlations show that
the kagom\'{e} ice behavior predicted for the nearest-neighbor (NN) interacting
model, where the field induces dimensional reduction and spins are frustrated
in each two-dimensional kagom\'{e} lattice, occurs in the dipole interacting
system. The spins freeze at low temperatures within the macroscopically
degenerate ground states of the NN model.Comment: 5 pages, 3 figures, submitted to PR
Stoner gap in the superconducting ferromagnet UGe2
We report the temperature () dependence of ferromagnetic Bragg peak
intensities and dc magnetization of the superconducting ferromagnet UGe2 under
pressure (). We have found that the low- behavior of the uniform
magnetization can be explained by a conventional Stoner model. A functional
analysis of the data produces the following results: The ferromagnetic state
below a critical pressure can be understood as the perfectly polarized state,
in which heavy quasiparticles occupy only majority spin bands. A Stoner gap
decreases monotonically with increasing pressure and increases
linearly with magnetic field. We show that the present analysis based on the
Stoner model is justified by a consistency check, i.e., comparison of density
of states at the Fermi energy deduced from the analysis with observed
electronic specific heat coeffieients. We also argue the influence of the
ferromagnetism on the superconductivity.Comment: 5 pages, 4 figures. to be published in Phys. Rev.
Stabilization of a Fabry-Perot interferometer using a suspension-point interferometer
A suspension-point interferometer (SPI) is an auxiliary interferometer for
active vibration isolation, implemented at the suspension points of the mirrors
of an interferometric gravitational wave detector. We constructed a prototype
Fabry-Perot interferometer equipped with an SPI and observed vibration
isolation in both the spectrum and transfer function. The noise spectrum of the
main interferometer was reduced by 40 dB below 1 Hz. Transfer function
measurements showed that the SPI also produced good vibration suppression above
1 Hz. These results indicate that SPI can improve both the sensitivity and the
stability of the interferometer.Comment: 14 pages, 8 figures; added discussion; to be published in Physics
Letters
The status of DECIGO
DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe. DECIGO will consists of three drag-free spacecraft arranged in an equilateral triangle with 1000 km arm lengths whose relative displacements are measured by a differential Fabry-Perot interferometer, and four units of triangular Fabry-Perot interferometers are arranged on heliocentric orbit around the sun. DECIGO is vary ambitious mission, we plan to launch DECIGO in era of 2030s after precursor satellite mission, B-DECIGO. B-DECIGO is essentially smaller version of DECIGO: B-DECIGO consists of three spacecraft arranged in an triangle with 100 km arm lengths orbiting 2000 km above the surface of the earth. It is hoped that the launch date will be late 2020s for the present
Opportunity to Test non-Newtonian Gravity Using Interferometric Sensors with Dynamic Gravity Field Generators
We present an experimental opportunity for the future to measure possible
violations to Newton's 1/r^2 law in the 0.1-10 meter range using Dynamic
gravity Field Generators (DFG) and taking advantage of the exceptional
sensitivity of modern interferometric techniques. The placement of a DFG in
proximity to one of the interferometer's suspended test masses generates a
change in the local gravitational field that can be measured at a high signal
to noise ratio. The use of multiple DFGs in a null experiment configuration
allows to test composition independent non-Newtonian gravity significantly
beyond the present limits. Advanced and third-generation gravitational-wave
detectors are representing the state-of-the-art in interferometric distance
measurement today, therefore we illustrate the method through their sensitivity
to emphasize the possible scientific reach. Nevertheless, it is expected that
due to the technical details of gravitational-wave detectors, DFGs shall likely
require dedicated custom configured interferometry. However, the sensitivity
measure we derive is a solid baseline indicating that it is feasible to
consider probing orders of magnitude into the pristine parameter well beyond
the present experimental limits significantly cutting into the theoretical
parameter space.Comment: 9 pages, 6 figures; Physical Review D, vol. 84, Issue 8, id. 08200
Severe myoclonic epilepsy in infancy: evolution of seizures
Changes in seizure type of severe myoclonic epilepsy (SME) in infancy were reviewed retrospectively in 14 patients (11 males and 3 females) who were followed-up to the age of 7 years or more. The observation period ranged from 5 to 16 years with a mean of 10 years. During the follow-up, three or four types of seizures were seen per patient, but the pattern of appearance and disappearance of each seizure type varied considerably among the patients. Tonic-clonic convulsion, either generalized or unilateral, was seen most consistently through the entire course, and it continued to the end of follow-up in 11 patients (79%). On the contrary, myoclonic seizure, complex partial seizure, and atypical absence often disappeared and reappeared repeatedly during the course. In SME, seizure symptoms varied widely among patients in comparison with other neurological symptoms, and the most consistent core seizure type was tonic-clonic convulsions
Atomic Carbon and CO Isotope Emission in the Vicinity of DR15
We present observations of the 3P1-3P0 fine structure transition of atomic
carbon [CI], the J=3-2 transition of CO, as well as of the J=1-0 transitions of
13CO and C18O toward DR15, an HII region associated with two mid-infrared dark
clouds (IRDCs). The 13CO and C18O J=1-0 emissions closely follow the dark
patches seen in optical wavelength, showing two self-gravitating molecular
cores with masses of 2000 Msun and 900 Msun, respectively, at the positions of
the catalogued IRDCs.
Our data show a rough spatial correlation between [CI] and 13CO J=1-0. Bright
[CI] emission occurs in relatively cold gas behind the molecular cores, neither
in highly excited gas traced by CO J=3-2 emission nor in HII region/molecular
cloud interface. These results are inconsistent with those predicted by
standard photodissociation region (PDR) models, suggesting an origin for
interstellar atomic carbon unrelated to photodissociation processes.Comment: 11 pages Latex, 6 figures, Accepted for publication in The
Astrophysical Journa
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