27,760 research outputs found
Hydrostatic pressure effects on the static magnetism in Eu(FeCo)As
The effects of hydrostatic pressure on the static magnetism in
Eu(FeCo)As are investigated by complementary
electrical resistivity, ac magnetic susceptibility and single-crystal neutron
diffraction measurements. A specific pressure-temperature phase diagram of
Eu(FeCo)As is established. The structural phase
transition, as well as the spin-density-wave order of Fe sublattice, is
suppressed gradually with increasing pressure and disappears completely above
2.0 GPa. In contrast, the magnetic order of Eu sublattice persists over the
whole investigated pressure range up to 14 GPa, yet displaying a non-monotonic
variation with pressure. With the increase of the hydrostatic pressure, the
magnetic state of Eu evolves from the canted antiferromagnetic structure in the
ground state, via a pure ferromagnetic structure under the intermediate
pressure, finally to a possible "novel" antiferromagnetic structure under the
high pressure. The strong ferromagnetism of Eu coexists with the
pressure-induced superconductivity around 2 GPa. The change of the magnetic
state of Eu in Eu(FeCo)As upon the application
of hydrostatic pressure probably arises from the modification of the indirect
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the Eu moments
tuned by external pressure.Comment: 9 pages, 6 figure
Quantum State Transfer Characterized by Mode Entanglement
We study the quantum state transfer (QST) of a class of tight-bonding Bloch
electron systems with mirror symmetry by considering the mode entanglement.
Some rigorous results are obtained to reveal the intrinsic relationship between
the fidelity of QST and the mirror mode concurrence (MMC), which is defined to
measure the mode entanglement with a certain spatial symmetry and is just the
overlap of a proper wave function with its mirror image. A complementarity is
discovered as the maximum fidelity is accompanied by a minimum of MMC. And at
the instant, which is just half of the characteristic time required to
accomplish a perfect QST, the MMC can reach its maximum value one. A large
class of perfect QST models with a certain spectrum structure are discovered to
support our analytical results.Comment: 6 pages, 3 figures. to appear in PR
Relation between two measures of entanglement in spin-1/2 and spinless fermion quantum chain systems
The concepts of concurrence and mode concurrence are the measures of
entanglement for spin-1/2 and spinless fermion systems respectively. Based on
the Jordan-Wigner transformation, any spin-1/2 system is always associated with
a fermion system (called counterpart system). The comparison of concurrence and
mode concurrence can be made with the aid of the Marshall's sign rule for the
ground states of spin-1/2 and spinless fermion chain systems. We observe
that there exists an inequality between concurrence and mode concurrence for
the ground states of the two corresponding systems. The spin-1/2 XY chain
system and its spinless fermion counterpart as a realistic example is discussed
to demonstrate the analytical results.Comment: 7 pages, no figures, publication version, to appear in PR
Cosmic ray spectral hardening due to dispersion in the source injection spectra
Recent cosmic ray (CR) experiments discovered that the CR spectra experience
a remarkable hardening for rigidity above several hundred GV. We propose that
this is caused by the superposition of the CR energy spectra of many sources
that have a dispersion in the injection spectral indices. Adopting similar
parameters as those of supernova remnants derived from the Fermi -ray
observations, we can reproduce the observational CR spectra of different
species well. This may be interpreted as evidence to support the supernova
remnant origin of CRs below the knee. We further propose that the same
mechanism may explain the "ankle" of the ultra high energy CR spectrum.Comment: 5 pages, 3 figures and 1 table. Updated with the diffusion
propagation model, accepted by Phys. Rev.
Dynamical study of the possible molecular state X(3872) with the s-channel one gluon exchange interaction
The recently observed X(3872) resonance, which is difficult to be assigned a
conventional charmonium state in the quark model, may be interpreted
as a molecular state. Such a molecular state is a hidden flavor four quark
state because of its charmonium-like quantum numbers. The s-channel one gluon
exchange is an interaction which only acts in the hidden flavor multi-quark
system. In this paper, we will study the X(3872) and other similiar hidden
flavor molecular states in a quark model by taking into account of the
s-channel one gluon exchange interaction
FETNet: Feature exchange transformer network for RGB-D object detection
In RGB-D object detection, due to the inherent difference between the RGB and
Depth modalities, it remains challenging to simultaneously leverage sensed photometric and depth information. In this paper, to address this issue, we propose a Feature
Exchange Transformer Network (FETNet), which consists of two well-designed components: the Feature Exchange Module (FEM), and the Multi-modal Vision Transformer
(MViT). Specially, we propose the FEM to exchange part of the channels between RGB
and depth features at each backbone stage, which facilitates the information flow, and
bridges the gap, between the two modalities. Inspired by the success of Vision Transformer (ViT), we develop the variant MViT to effectively fuse multi-modal features and exploit the attention between the RGB and depth features. Different from previous methods developing from specified RGB detection algorithm, our proposal is generic. Extensive experiments prove that, when the proposed modules are integrated into mainstream RGB object detection methods, their RGB-D counterparts can obtain significant performance gains. Moreover, our FETNet surpasses state-of-the-art RGB-D detectors by 7.0% mAP on SUN RGB-D and 1.7% mAP on NYU Depth v2, which also well demonstrates
the effectiveness of the proposed method
Multiuser Scheduler and FDE Design for SC-FDMA MIMO Systems
This paper presents a novel spatial frequency domain packet scheduling and frequency domain equalization (FDE) algorithm for uplink Single Carrier (SC) Frequency Division Multiple Access (FDMA) multiuser MIMO systems. Our analysis model is confined to 3GPP uplink SC-FDMA transmission with Multi-user (MU) Spatial Division Multiplexing (SDM). The results show that the proposed MU-MIMO scheduler in conjunction with the new FDE singificantly increases the maximum achievable rate and improves the bit error rate (BER) performance for the system under consideration
Joint beamforming design for secure RIS-assisted IoT networks
This paper studies secure communication in an internet-of-things (IoT) network, where the confidential signal is sent by an active refracting reconfigurable intelligent surface (RIS)-based transmitter, and a passive reflective RIS is utilized to improve the secrecy performance of users in the presence of multiple eavesdroppers. Specifically, we aim to maximize the weighted sum secrecy rate by jointly designing the power allocation, transmit beamforming (BF) of the refracting RIS, and the phase shifts of the reflective RIS. To solve the non-convex optimization problem, we propose a linearization method to approximate the objective function into a linear form. Then, an alternating optimization (AO) scheme is proposed to jointly optimize the power allocation factors, BF vector and phase shifts, where the first one is found using the Lagrange dual method, while the latter two are obtained by utilizing the penalty dual decomposition method. Moreover, considering the demands of green and secure communications, by applying the Dinkelbach’s method, we extend our proposed scheme to solving a secrecy energy maximization problem. Finally, simulation results demonstrate the effectiveness of the proposed design
Edge and Bulk Transport in the Mixed State of a Type-II Superconductor
By comparing the voltage-current (V-I) curves obtained before and after
cutting a sample of 2H-NbSe2, we separate the bulk and edge contributions to
the transport current at various dissipation levels and derive their respective
V- I curves and critical currents. We find that the edge contribution is
thermally activated across a current dependent surface barrier. By contrast the
bulk V-I curves are linear, as expected from the free flux flow model. The
relative importance of bulk and edge contributions is found to depend on
dissipation level and sample dimensions. We further show that the peak effect
is a sharp bulk phenomenon and that it is broadened by the edge contribution
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