Heavy ion collisions provide a unique opportunity to study the nature of X(3872) compared with electron-positron and proton-proton (antiproton) collisions. With the abundant charm pairs produced in heavy-ion collisions, the production of multicharm h
adrons and molecules can be enhanced by the combination of charm and anticharm quarks in the medium. We investigate the centrality and momentum dependence of X(3872) in heavy-ion collisions via the Langevin equation and instant coalescence model (LICM). When X(3872) is treated as a compact tetraquark state, the tetraquarks are produced via the coalescence of heavy and light quarks near the quantum chromodynamic (QCD) phase transition due to the restoration of the heavy quark potential at $Trightarrow T_c$. In the molecular scenario, loosely bound X(3872) is produced via the coalescence of $D^0$-$bar D^{*0}$ mesons in a hadronic medium after kinetic freeze-out. The phase space distributions of the charm quarks and D mesons in a bulk medium are studied with the Langevin equation, while the coalescence probability between constituent particles is controlled by the Wigner function, which encodes the internal structure of the formed particle. First, we employ the LICM to explain both $D^0$ and $J/psi$ production as a benchmark. Then, we give predictions regarding X(3872) production. We find that the total yield of tetraquark is several times larger than the molecular production in Pb-Pb collisions. Although the geometric size of the molecule is huge, the coalescence probability is small due to strict constraints on the relative momentum between $D^0$ and $bar D^{*0}$ in the molecular Wigner function, which significantly suppresses the molecular yield.
A water-based switchable frequency selective rasorber with polarization selectivity using the Great Wall structures is presented in this paper. The proposed structure comprises a container containing horizontal and vertical channels enabling dividabl
e injection of water, and a cross-gap FSS. The novelty of the design lies in its switchability among four different operating states by injecting water or not into the water channels. When the container is empty, the structure acts as a polarization-intensive FSS with a -0.42 dB insertion loss passband at 3.75 GHz. When the horizontal channel is filled with water and there is no water in the vertical channel, this structure can be used as an FSR with single polarization selectivity. The FSR with -10 dB absorption band from 6.8 GHz to 18.8 GHz only allows certain polarized electromagnetic (EM) waves to pass at 3.1 GHz with an insertion loss of -0.78 dB, while another polarized EM wave cannot pass. When the container is full of water, the structure operates as an absorber with a reflection band below the absorption band, where neither of polarization EM waves can transmit. Besides, a reconfigurable water-based FSR automatic control system is built to achieve state switching and temperature constancy of the water within the container. Ultimately, a prototype of the presented design is fabricated, simulated and measured to verify the feasibility. This work has potential application in radome design to realize the out-of-band RCS reduction.
Transport and Langevin equations are employed to study hadronic medium effects on charmonium elliptic flows in heavy-ion collisions. In Pb-Pb collisions, the anisotropic energy density of the quark-gluon plasma (QGP) in the transverse plane is transf
ormed into hadron momentum anisotropy after the phase transition. Charmonia with high transverse momentum $p_T$ are produced via the primordial hard process and undergo different degrees of dissociation along different paths in the QGP. They then scatter with light hadrons in the hadron phase. Both contributions to the charmonium elliptic flows are studied at moderate and high transverse momenta. The elliptic flows of the prompt $J/psi$ are found to be considerably enhanced at high transverse momentum when the charmonium diffusion coefficients in the hadronic medium are parametrized through the geometry scale approximation. This hadronic medium effect is negligible for quarkonia with larger mass such as bottomonia.
In this paper, a low radar cross section (RCS) patch antenna based on the 3-bit metasurface composed of linear polarization conversion elements is designed. At first, 3-bit coding metamaterials are constructed by a sequence of eight coded unit cells,
which have a similar cross-polarized reflected amplitude response and gradient reflected phase responses covering 0~2{pi}, respectively. Equivalent circuit models (ECMs) of these unit cells are created to describe their electrical behavior for the two linear incident polarizations at the same time. Then, a patch antenna is integrated on the 3-bit metasurface, of which the elements are placed with a 2-dimensional linear coding sequence. The metal square ring is set around the patch antenna to protect it from the disturbance of metasurface. Both the simulation and experiment results demonstrate that the designed metasurface can primarily reduce the antenna RCS at a broadband, while the antenna performances are not degraded significantly.
Solar arrays are the primary energy source of the satellite. In this paper, a metamaterial absorber for solar arrays with simultaneous high optical transparency and broadband microwave absorption is presented. By tailoring the reflection response of
meta-atoms, 85% absorption performance from 6.8GHz to 18GHz is obtained. In the meantime, by employing transparent substrates, including indium tin oxide (ITO) film and anti-reflection glass, a maximum of 87% light transmittance is achieved. The absorptivity of the proposed metamaterial absorber is simulated and measured experimentally. Light transmittance and the effect of transparent metamaterial absorber on the conversion efficiency of the solar array have also been measured. These results fully demonstrate the reliability of our design for solar arrays, which also meet the requirements of structural strength, atomic oxygen erosion resistance, weight limitation, etc.
