5,290 research outputs found
Binomial Difference Ideal and Toric Difference Variety
In this paper, the concepts of binomial difference ideals and toric
difference varieties are defined and their properties are proved. Two canonical
representations for Laurent binomial difference ideals are given using the
reduced Groebner basis of Z[x]-lattices and regular and coherent difference
ascending chains, respectively. Criteria for a Laurent binomial difference
ideal to be reflexive, prime, well-mixed, perfect, and toric are given in terms
of their support lattices which are Z[x]-lattices. The reflexive, well-mixed,
and perfect closures of a Laurent binomial difference ideal are shown to be
binomial. Four equivalent definitions for toric difference varieties are
presented. Finally, algorithms are given to check whether a given Laurent
binomial difference ideal I is reflexive, prime, well-mixed, perfect, or toric,
and in the negative case, to compute the reflexive, well-mixed, and perfect
closures of I. An algorithm is given to decompose a finitely generated perfect
binomial difference ideal as the intersection of reflexive prime binomial
difference ideals.Comment: 72 page
Design of Reconfigurable Intelligent Surface-Aided Cross-Media Communications
A novel reconfigurable intelligent surface (RIS)-aided hybrid
reflection/transmitter design is proposed for achieving information exchange in
cross-media communications. In pursuit of the balance between energy efficiency
and low-cost implementations, the cloud-management transmission protocol is
adopted in the integrated multi-media system. Specifically, the messages of
devices using heterogeneous propagation media, are firstly transmitted to the
medium-matched AP, with the aid of the RIS-based dual-hop transmission. After
the operation of intermediate frequency conversion, the access point (AP)
uploads the received signals to the cloud for further demodulating and decoding
process. Based on time division multiple access (TDMA), the cloud is able to
distinguish the downlink data transmitted to different devices and transforms
them into the input of the RIS controller via the dedicated control channel.
Thereby, the RIS can passively reflect the incident carrier back into the
original receiver with the exchanged information during the preallocated slots,
following the idea of an index modulation-based transmitter. Moreover, the
iterative optimization algorithm is utilized for optimizing the RIS phase,
transmit rate and time allocation jointly in the delay-constrained cross-media
communication model. Our simulation results demonstrate that the proposed
RIS-based scheme can improve the end-to-end throughput than that of the
AP-based transmission, the equal time allocation, the random and the discrete
phase adjustment benchmarks
Lower Bound of Concurrence Based on Positive Maps
We study the concurrence of arbitrary dimensional bipartite quantum systems.
An explicit analytical lower bound of concurrence is obtained, which detects
entanglement for some quantum states better than some well-known separability
criteria, and improves the lower bounds such as from the PPT, realignment
criteria and the Breuer's entanglement witness.Comment: 8 pages, 1 figur
Probing nuclear symmetry energy at high densities using pion, kaon, eta and photon productions in heavy-ion collisions
The high-density behavior of nuclear symmetry energy is among the most
uncertain properties of dense neutron-rich matter. Its accurate determination
has significant ramifications in understanding not only the reaction dynamics
of heavy-ion reactions especially those induced by radioactive beams but also
many interesting phenomena in astrophysics, such as the explosion mechanism of
supernova and the properties of neutron stars. The heavy-ion physics community
has devoted much effort during the last few years to constrain the high-density
symmetry using various probes. In particular, the pion-/pion+ ratio has been
most extensively studied both theoretically and experimentally. All models have
consistently predicted qualitatively that the pion-/pion+ ratio is a sensitive
probe of the high-density symmetry energy especially with beam energies near
the pion production threshold. However, the predicted values of the pion-/pion+
ratio are still quite model dependent mostly because of the complexity of
modeling pion production and reabsorption dynamics in heavy-ion collisions,
leading to currently still controversial conclusions regarding the high-density
behavior of nuclear symmetry energy from comparing various model calculations
with available experimental data. As more pion-/pion+ data become available and
a deeper understanding about the pion dynamics in heavy-ion reactions is
obtained, more penetrating probes, such as the kaon+/kaon0 ratio, eta meson and
high energy photons are also being investigated or planned at several
facilities. Here, we review some of our recent contributions to the community
effort of constraining the high-density behavior of nuclear symmetry energy in
heavy-ion collisions. In addition, the status of some worldwide experiments for
studying the high-density symmetry energy, including the HIRFL-CSR external
target experiment (CEE) are briefly introduced.Comment: 10 pages, 10 figures, Contribution to the Topical Issue on Nuclear
Symmetry Energy in EPJA Special Volum
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