2,202 research outputs found
Entropic Inequalities for a Class of Quantum Secret Sharing States
It is well-known that von Neumann entropy is nonmonotonic unlike Shannon
entropy (which is monotonically nondecreasing). Consequently, it is difficult
to relate the entropies of the subsystems of a given quantum state. In this
paper, we show that if we consider quantum secret sharing states arising from a
class of monotone span programs, then we can partially recover the monotonicity
of entropy for the so-called unauthorized sets. Furthermore, we can show for
these quantum states the entropy of the authorized sets is monotonically
nonincreasing.Comment: LaTex, 5 page
Accretion dynamics in the classical T Tauri star V2129 Oph
We analyze the photometric and spectroscopic variability of the classical T
Tauri star V2129 Oph over several rotational cycles to test the dynamical
predictions of magnetospheric accretion models. The photometric variability and
the radial velocity variations in the photospheric lines can be explained by
rotational modulation due to cold spots, while the radial velocity variations
of the He I (5876 \AA) line and the veiling variability are due to hot spot
rotational modulation. The hot and cold spots are located at high latitudes and
about the same phase, but the hot spot is expected to sit at the chromospheric
level, while the cold spot is at the photospheric level. Using the
dipole+octupole magnetic-field configuration previously proposed in the
literature for the system, we compute 3D MHD magnetospheric simulations of the
star-disk system. We use the simulation's density, velocity and scaled
temperature structures as input to a radiative transfer code, from which we
calculate theoretical line profiles at all rotational phases. The theoretical
profiles tend to be narrower than the observed ones, but the qualitative
behavior and the observed rotational modulation of the H\alpha and H\beta
emission lines are well reproduced by the theoretical profiles. The
spectroscopic and photometric variability observed in V2129 Oph support the
general predictions of complex magnetospheric accretion models with
non-axisymmetric, multipolar fields.Comment: Accepted by Astronomy and Astrophysic
Emission-line profile modelling of structured T Tauri magnetospheres
We present hydrogen emission line profile models of magnetospheric accretion
onto Classical T Tauri stars. The models are computed under the Sobolev
approximation using the three-dimensional Monte Carlo radiative-transfer code
TORUS. We have calculated four illustrative models in which the accretion flows
are confined to azimuthal curtains - a geometry predicted by
magneto-hydrodynamical simulations. Properties of the line profile variability
of our models are discussed, with reference to dynamic spectra and
cross-correlation images. We find that some gross characteristics of observed
line profile variability are reproduced by our models, although in general the
level of variability predicted is larger than that observed. We conclude that
this excessive variability probably excludes dynamical simulations that predict
accretion flows with low degrees of axisymmetry.Comment: 14 pages, 12 figures. Published in MNRA
T Tauri stellar magnetic fields: He I measurements
We present measurements of the longitudinal magnetic field in the
circumstellar environment of seven classical T Tauri stars. The measurements
are based on high-resolution circular spectropolarimetry of the He I 5876
emission line, which is thought to form in accretion streams controlled by a
stellar magnetosphere. We detect magnetic fields in BP Tau, DF Tau and DN Tau,
and detect statistically significant fields in GM Aur and RW Aur A at one epoch
but not at others. We detect no field for DG Tau and GG Tau, with the caveat
that these objects were observed at one epoch only. Our measurements for BP Tau
and DF Tau are consistent, both in terms of sign and magnitude, with previous
studies, suggesting that the characteristics of T Tauri magnetospheres are
persistent over several years. We observed the magnetic field of BP Tau to
decline monotonically over three nights, and have detected a peak field of 4kG
in this object, the highest magnetic field yet observed in a T Tauri star. We
combine our observations with results from the literature in order to perform a
statistical analysis of the magnetospheric fields in BP Tau and DF Tau.
Assuming a dipolar field, we determine a polar field of ~3kG and a dipole
offset of 40deg for BP Tau, while DF Tau's field is consistent with a polar
field of ~-4.5kG and a dipole offset of 10deg. We conclude that many classical
T Tauri stars have circumstellar magnetic fields that are both strong enough
and sufficiently globally-ordered to sustain large-scale magnetospheric
accretion flows.Comment: 8 pages, 3 figures. Accepted by MNRAS. Corrected typo
Chiral charge-density-waves
We discovered the chirality of charge density waves (CDW) in 1T-TiSe by
using scanning tunnelling microscopy (STM) and optical ellipsometry. We found
that the CDW intensity becomes , where (i =1, 2, 3) is the amplitude of the tunnelling current
contributed by the CDWs. There were two states, in which the three intensity
peaks of the CDW decrease \textit{clockwise} and \textit{anticlockwise} when we
index each nesting vector in order of intensity in the Fourier transformation
of the STM images. The chirality in CDW results in the three-fold symmetry
breaking. Macroscopically, two-fold symmetry was indeed observed in optical
measurement. We propose the new generalized CDW chirality H_{CDW} \equiv
{\boldmath q_1} \cdot ({\boldmath q_2}\times {\boldmath q_3}), where
{\boldmath q_i} are the nesting vectors, which is independent of the
symmetry of components. The nonzero - the triple-{\boldmath q}
vectors do not exist in an identical plane in the reciprocal space - should
induce a real-space chirality in CDW system.Comment: 12 pages, 4 figure
Development of microwave diagnostic simulator
Two-dimensional simulator models are presented for microwave diagnostics. The models assume the Maxwell wave equation coupled with the equation of plasma current density in a cold magnetized plasma, which can describe propagation, reflection, and cross polarization scattering of the ordinary and extraordinary modes. The effects of waveguide for the microwave launcher and wall boundary of the vacuum vessel are included in the models. The simulations of ultrashort-pulse reflectometry with the use of incident subcyclic ordinary modes in the models are performed to test the problem of density profile reconstruction
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