36,832 research outputs found
Entanglement changing power of two-qubit unitary operations
We consider a two-qubit unitary operation along with arbitrary local unitary
operations acts on a two-qubit pure state, whose entanglement is C_0. We give
the conditions that the final state can be maximally entangled and be
non-entangled. When the final state can not be maximally entangled, we give the
maximal entanglement C_max it can reach. When the final state can not be
non-entangled, we give the minimal entanglement C_min it can reach. We think
C_max and C_min represent the entanglement changing power of two-qubit unitary
operations. According to this power we define an order of gates.Comment: 11 page
Fiber Orientation Estimation Guided by a Deep Network
Diffusion magnetic resonance imaging (dMRI) is currently the only tool for
noninvasively imaging the brain's white matter tracts. The fiber orientation
(FO) is a key feature computed from dMRI for fiber tract reconstruction.
Because the number of FOs in a voxel is usually small, dictionary-based sparse
reconstruction has been used to estimate FOs with a relatively small number of
diffusion gradients. However, accurate FO estimation in regions with complex FO
configurations in the presence of noise can still be challenging. In this work
we explore the use of a deep network for FO estimation in a dictionary-based
framework and propose an algorithm named Fiber Orientation Reconstruction
guided by a Deep Network (FORDN). FORDN consists of two steps. First, we use a
smaller dictionary encoding coarse basis FOs to represent the diffusion
signals. To estimate the mixture fractions of the dictionary atoms (and thus
coarse FOs), a deep network is designed specifically for solving the sparse
reconstruction problem. Here, the smaller dictionary is used to reduce the
computational cost of training. Second, the coarse FOs inform the final FO
estimation, where a larger dictionary encoding dense basis FOs is used and a
weighted l1-norm regularized least squares problem is solved to encourage FOs
that are consistent with the network output. FORDN was evaluated and compared
with state-of-the-art algorithms that estimate FOs using sparse reconstruction
on simulated and real dMRI data, and the results demonstrate the benefit of
using a deep network for FO estimation.Comment: A shorter version is accepted by MICCAI 201
A model of rotating hotspots for 3:2 frequency ratio of HFQPOs in black hole X-ray binaries
We propose a model to explain a puzzling 3:2 frequency ratio of high
frequency quasi-periodic oscillations (HFQPOs) in black hole (BH) X-ray
binaries, GRO J1655-40, GRS 1915+105 and XTE J1550-564. In our model a
non-axisymmetric magnetic coupling (MC) of a rotating black hole (BH) with its
surrounding accretion disc coexists with the Blandford-Znajek (BZ) process. The
upper frequency is fitted by a rotating hotspot near the inner edge of the
disc, which is produced by the energy transferred from the BH to the disc, and
the lower frequency is fitted by another rotating hotspot somewhere away from
the inner edge of the disc, which arises from the screw instability of the
magnetic field on the disc. It turns out that the 3:2 frequency ratio of HFQPOs
in these X-ray binaries could be well fitted to the observational data with a
much narrower range of the BH spin. In addition, the spectral properties of
HFQPOs are discussed. The correlation of HFQPOs with jets from microquasars is
contained naturally in our model.Comment: 8 pages, 4 figures. accepted by MNRA
Domain structure in the monoclinic Pm phase of Pb(Mg1/3Nb2/3)O3 - PbTiO3 single crystals
The domain structure of (1-x)Pb(Mg1/3Nb2/3)O3- xPbTiO3 single crystals with
composition x ~ 0.33 in the range of the morphotropic phase boundary (MPB) was
studied. Based on the analysis of spontaneous strain compatibility and charge
of domain walls, we have established the permissible domain arrangements for
the ferroelectric phases of different symmetry, which are expected to occur in
the range of the MPB. Examination of (001)-oriented unpoled and electrically
poled (along the [001] direction) crystal plates in polarizing microscope
reveals a monophase state with the domain structure compatible with the
structure theoretically predicted for the Mc monoclinic phase (space group Pm),
which was recently discovered in the compositions close to the MPB by x-ray and
neutron diffraction studies. In the unpoled crystal the 180 deg. walls between
the domains whose spontaneous polarization vectors are parallel to the plane of
the crystal plate (i.e. a-domains) are observed. The domain structure of the
poled crystal is predominantly composed of crystallographically prominent Wf
walls parallel to (001) (i.e. the plane of the crystal plate) and inclined S
walls parallel to [110] or [1-10] direction. In poled and unpoled samples the
optical rotatory polarization effect is found, which is related to the
inhomogeneity of the sample resulting from the mixture of domains.Comment: PDF file, 30 pages, 15 figures (3 in color) collected on pp.18-3
Superintegrability on the two dimensional hyperboloid II
This work is devoted to the investigation of the quantum mechanical systems
on the two dimensional hyperboloid which admit separation of variables in at
least two coordinate systems. Here we consider two potentials introduced in a
paper of C.P.Boyer, E.G.Kalnins and P.Winternitz, which haven't yet been
studied. We give an example of an interbasis expansion and work out the
structure of the quadratic algebra generated by the integrals of motion.Comment: 18 pages, LaTex; 1 figure (eps
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