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Mitigation of microbunching instability in x-ray free electron laser linacs
The microbunching instability seeded by small initial density modulation and driven by collective effects can cause significant electron beam quality degradation in next generation x-ray free electron lasers. A method exploiting longitudinal mixing derived from the natural transverse spread of the electron beam through a dispersive bending magnet was proposed to suppress this instability several years ago [Phys. Rev. Lett. 111, 054801 (2013)PRLTAO0031-900710.1103/PhysRevLett.111.054801]. Instead of using bending magnets to introduce the transverse-to-longitudinal coupling, which will lead to an inconvenient deflection of the downstream beam line, in this paper, we propose a scheme to mitigate the microbunching instability by inserting a quadrupole magnet inside a bunch compressor of the accelerator. This results in transverse-to-longitudinal phase space mixing and large slice energy spread that can efficiently mitigate the growth of the microbunching instability through the major accelerator section. Finally, at the exit of the accelerator, a dogleg section is used to restore the emittance and slice energy spread before entering the undulator radiation section. Multiparticle simulations show that the transverse space charge, structure wakefield, and the coherent synchrotron radiation effects will have a relatively small impact on this scheme
Simple parametrization of neutrino mixing matrix
We propose simple forms of neutrino mixing matrix in analogy with the
Wolfenstein parametrization of quark mixing matrix, by adopting the smallest
mixing angle as a measure of expansion parameters with the
tribimaximal pattern as the base matrix. The triminimal parametrization
technique is utilized to expand the mixing matrix under two schemes, i.e., the
standard Chau-Keung (CK) scheme and the original Kobayashi-Maskawa (KM) scheme.
The new parametrizations have their corresponding Wolfenstein-like
parametrizations of quark mixing matrix, and therefore they share the same
intriguing features of the Wolfenstein parametrization. The newly introduced
expansion parameters for neutrinos are connected to the Wolfenstein parameters
for quarks via the quark-lepton complementarity.Comment: 5 pages. Version for publication in PR
Origin of the anapole condition as revealed by a simple expansion beyond the toroidal multipole
Toroidal multipoles are a topic of increasing interest in the nanophotonics
and metamaterials communities. In this paper, we separate out the toroidal
multipole components of multipole expansions in polar coordinates (two- and
three-dimensional) by expanding the Bessel or spherical Bessel functions. We
discuss the formation of the lowest order of magnetic anapoles from the
interaction between the magnetic toroidal dipole and the magnetic dipole. Our
method also reveals that there are higher order current configurations other
than the electric toroidal multipole that have the same radiation
characteristics as the pure electric dipole. Furthermore, we find that the
anapole condition requires that there is a perfect cancellation of all higher
order current configurations
Unified parametrization of quark and lepton mixing matrices in tri-bimaximal pattern
Parametrization of the quark and lepton mixing matrices is the first attempt
to understand the mixing of fermions. In this work, we parameterize the quark
and lepton matrices with the help of quark-lepton complementarity (QLC) in a
tri-bimaximal pattern of lepton mixing matrix. In this way, we combine the
parametrization of the two matrices with each other. We apply this new
parametrization to several physical quantities, and show its simplicity in the
expression of, e.g., the Jarlskog parameter of CP violation.Comment: 12 latex page
Heterogeneous Multi-task Learning for Human Pose Estimation with Deep Convolutional Neural Network
We propose an heterogeneous multi-task learning framework for human pose
estimation from monocular image with deep convolutional neural network. In
particular, we simultaneously learn a pose-joint regressor and a sliding-window
body-part detector in a deep network architecture. We show that including the
body-part detection task helps to regularize the network, directing it to
converge to a good solution. We report competitive and state-of-art results on
several data sets. We also empirically show that the learned neurons in the
middle layer of our network are tuned to localized body parts
Bound State Solutions of Klein-Gordon Equation with the Kratzer Potential
The relativistic problem of spinless particle subject to a Kratzer potential
is analyzed. Bound state solutions for the s-wave are found by separating the
Klein-Gordon equation in two parts, unlike the similar works in the literature,
which provides one to see explicitly the relativistic contributions, if any, to
the solution in the non-relativistic limit.Comment: 6 page
Quark-lepton complementarity revisited
We reexamine the quark-lepton complementarity (QLC) in nine angle-phase
parametrizations with the latest result of a large lepton mixing angle
from the T2K, MINOS and Double Chooz experiments. We find that
there are still two QLC relations satisfied in P1, P4 and P6 parametrizations,
whereas only one QLC relation holds in P2, P3, P5 and P9 parametrizations
separately. We also work out the corresponding reparametrization-invariant
forms of the QLC relations and check the resulting expressions with the
experimental data. The results can be viewed as a check of the validity of the
QLC relations, as well as a new perspective into the issue of seeking for the
connection between quarks and leptons.Comment: 5 Latex pages, 2 tables. Final version for publication in PR
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