13,202 research outputs found
Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure
We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.Comment: 12 pages, 5 figure
Generalized Landau-Pollak Uncertainty Relation
The Landau-Pollak uncertainty relation treats a pair of rank one projection
valued measures and imposes a restriction on their probability distributions.
It gives a nontrivial bound for summation of their maximum values. We give a
generalization of this bound (weak version of the Landau-Pollak uncertainty
relation). Our generalization covers a pair of positive operator valued
measures. A nontrivial but slightly weak inequality that can treat an arbitrary
number of positive operator valued measures is also presented.Comment: Simplified the proofs. To be published in Phys.Rev.
77Se NMR Investigation of the K(x)Fe(2-y)Se(2) High Tc Superconductor (Tc=33K)
We report a comprehensive 77Se NMR study of the structural, magnetic, and
superconducting properties of a single crystalline sample of the newly
discovered FeSe-based high temperature superconductor K(x)Fe(2-y)Se(2) (Tc=33K)
in a broad temperature range up to 290 K. We will compare our results with
those reported for FeSe (Tc=9K) and FeAs-based high Tc systems.Comment: Final versio
The 3-D kinematics of water masers around the semiregular variable RT Virginis
We report observations of water masers around the semiregular variable RT
Virginis (RT Vir), which have been made with the Very Long Baseline Array
(VLBA) of the National Radio Astronomy Observatory (NRAO) at five epochs, each
separated by three weeks of time. We detected about 60 maser features at each
epoch. Overall, 61 features, detected at least twice, were tracked by their
radial velocities and proper motions. The 3-D maser kinematics exhibited a
circumstellar envelope that is expanding roughly spherically with a velocity of
about 8 km/s. Asymmetries in both the spatial and velocity distributions of the
maser features were found in the envelope, but less significant than that found
in other semiregular variables. Systematic radial-velocity drifts of individual
maser features were found with amplitudes of <= 2 km/s/yr. For one maser
feature, we found a quadratic position shift with time along a straight line on
the sky. This apparent motion indicates an acceleration with an amplitude of 33
km/s/yr, implying the passage of a shock wave driven by the stellar pulsation
of RT Vir. The acceleration motion is likely seen only on the sky plane because
of a large velocity gradient formed in the accelerating maser region. We
estimated the distance to RT Vir to be about 220 pc on the basis of both the
statistical parallax and model-fitting methods for the maser kinematics.Comment: 18 pages, 8 figures. Accepted to appear in the Astrophysical Journa
Constraints on the Proper Motion of the Andromeda Galaxy Based on the Survival of Its Satellite M33
A major uncertainty in the dynamical history of the local group of galaxies
originates from the unknown transverse speed of the Andromeda galaxy (M31)
relative to the Milky Way. We show that the recent VLBA measurement of the
proper motion of Andromeda's satellite, M33, severely constrains the possible
values of M31's proper motion. The condition that M33's stellar disk will not
be tidally disrupted by either M31 or the Milky Way over the past 10 billion
years, favors a proper motion amplitude of 100+-20km/s for M31 with the
quadrant of a negative velocity component along Right Ascension and a positive
component along Declination strongly ruled-out. This inference can be tested by
future astrometric measurements with SIM, GAIA, or the SKA. Our results imply
that the dark halos of Andromeda and the Milky Way will pass through each other
within the next 5-10 billion years.Comment: Accepted for publication in Ap
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