The strong and radiative decays of the low-lying S- and P-wave Λc(b), Σc(b), Ξc(b), Ξc(b)′, and Ωc(b) baryons are systematically studied in a constituent quark model. We find that the radiative decay ...mode Λb0γ could be very useful for us to establish the missing neutral states Σb0 and Σb*0. Our calculation shows that most of those missing λ-mode P-wave singly heavy baryons have a relatively narrow decay width of less than 30 MeV. Their dominant strong and radiative decay channels can be ideal for searching for their signals in future experiments. The Σc(2800) resonance may be assigned to |ΣcP2λ32−⟩ with JP=3/2− or |ΣcP4λ52−⟩ with JP=5/2−. In general, the excitations of |P2λ32−⟩ and |P4λ52−⟩ of the 6F multiplet have similar strong decay properties. In order to identify them, angular distributions of their decays in either strong decay modes or radiative transitions should be needed.
We show that the Pomeron exchanges play a unique role in vector charmonium scatterings. Such a mechanism can provide a natural explanation for the nontrivial structures in the di-J/ψ spectrum ...observed by the LHCb Collaboration. The narrow structure X(6900), as a dynamically generated resonance pole, can arise from the Pomeron exchanges and coupled-channel effects between the J/ψ-J/ψ, J/ψ-ψ(2S) scatterings. A pole structure near the di-J/ψ threshold is also found. Meanwhile, we predict that X(6900) can produce significant threshold enhancement in the J/ψ-ψ(2S) energy spectrum which can be searched for at LHCb.
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•A new method is proposed to calculate the time-varying strain rates.•A modified technique of backstripping is proposed.•Opposite residual subsidence initiated at 28.4 and ...11.6 Ma.•The syn-rift subsidence is deficient and commenced at 28.4 Ma.•Deep mantle upwelling since 28.4 Ma, and decay after 11.6 Ma.
Deep hot mantle upwelling is widely revealed around the Qiongdongnan Basin on the northwestern South China Sea margin. However, when and how it influenced the hyper-extended basin is unclear. To resolve these issues, a detailed analysis of the Cenozoic time-varying residual subsidence derived by subtracting the predicted subsidence from the backstripped subsidence was performed along a new seismic reflection line in the western Qiongdongnan Basin. For the first time, a method is proposed to calculate the time-varying strain rates constrained by the faults growth rates, on basis of which, the predicted basement subsidence is obtained with a basin- and lithosphere-scale coupled finite extension model, and the backstripped subsidence is accurately recovered with a modified technique of backstripping to eliminate the effects of later episodes of rifting on earlier sediment thickness. Results show no residual subsidence in 45–28.4 Ma. But after 28.4 Ma, negative residual subsidence occurred, reached and remained ca. −1000 m during 23–11.6 Ma, and reduced dramatically after 11.6 Ma. In the syn-rift period (45–23 Ma), the residual subsidence is ca. −1000 m, however in the post-rift period (23–0 Ma), it is positive of ca. 300 to 1300 m increasing southeastwards. These results suggest that the syn-rift subsidence deficit commenced at 28.4 Ma, while the post-rift excess subsidence occurred after 11.6 Ma. Combined with previous studies, it is inferred that the opposite residual subsidence in the syn- and post-rift periods with similar large wavelengths (>102 km) and km-scale amplitudes are the results of transient dynamic topography induced by deep mantle upwelling beneath the central QDNB, which started to influence the basin at ca. 28.4 Ma, continued into the Middle Miocene, and decayed at ca. 11.6 Ma. The initial mantle upwelling with significant dynamic uplift had precipitated considerable continental extension and faulting in the Late Oligocene (28.4–23 Ma). After ca. 11.6 Ma, strong mantle upwelling probably occurred beneath the Leizhou–Hainan area to form vast basaltic lava flow.
The discovery of a new superconductor, LaFeAsO1−xFx with a superconducting critical temperatureT,c, of 26 K in 2008, has quickly renewed interest in the exploration of iron‐based superconductors. ...More than 70 new superconductors have been discovered within several months, with the highest Tc of up to 55 K being observed in the SmFeAsO1−x compound. High Tcs have previously only been observed in cuprates; these new iron‐based superconductors have been added as second members of the high‐Tc family. The crystal structure of these compounds contains an almost 2D Fe–As layer formed by FeAs4 tetrahedrons, which can be separated by an oxide or metal layer that provides extra electrons to the Fe–As layer, and the itinerant iron 3d electrons form an antiferromagnetic (AFM) order state in the undoped parent compounds at around 100–200 K. Superconductivity can be induced by carrier doping, which destroys the AFM ground state. In this Review, the most recent findings on and basic experimental facts about this class of high‐Tc materials will be presented, including the various superconducting structures, the synthesis methods, the physical properties of the parent compounds, the doping methods that could produce superconductivity, pressure effects, and the prospects for this new iron‐based high‐Tc family.
A new family of high‐Tc Fe‐based superconductors is reviewed. New findings and basic experimental facts with regard to this class of high‐Tc materials are discussed, including the various superconducting structures, the sample synthesizing methods, the physical properties of the parent compounds, the doping methods that produce superconductivity, the pressure effects, and the future prospects for this new high‐Tc superconductor family.
The strong and radiative decay properties of the low-lying Ωc states are studied in a constituent quark model. We find that the newly observed Ωc states by the LHCb Collaboration can fit well in the ...decay patterns. Thus, their spin parity can possibly be assigned as the following: (i) Ωc(3000) has JP=1/2− and corresponds to the narrow 1P mixed state |1P2λ12−⟩1; its partner |1P2λ12−⟩2 should be a broad state with a width of ∼100 MeV. (ii) Ωc(3050) and Ωc(3066) can be assigned to be two JP=3/2− states, |1P4λ32−⟩ and |1P2λ32−⟩, respectively. (iii) Ωc(3090) can be assigned as the |1P4λ52−⟩ state with JP=5/2−. (iv) Ωc(3119) might correspond to one of the two 2S states of the first radial excitations, i.e., |2S2λλ12+⟩ or |2S4λλ32+⟩.
The Majorana fermion, which is its own antiparticle and obeys non-Abelian statistics, plays a critical role in topological quantum computing. It can be realized as a bound state at zero energy, ...called a Majorana zero mode (MZM), in the vortex core of a topological superconductor, or at the ends of a nanowire when both superconductivity and strong spin orbital coupling are present. A MZM can be detected as a zero-bias conductance peak (ZBCP) in tunneling spectroscopy. However, in practice, clean and robust MZMs have not been realized in the vortices of a superconductor because of contamination from impurity states or other closely packed Caroli–de Gennes-Matricon (CdGM) states, which hampers further manipulations of MZMs. Here, using scanning tunneling spectroscopy, we show that a ZBCP well separated from the other discrete CdGM states exists ubiquitously in the cores of free vortices in the defect-free regions of(Li0.84Fe0.16)OHFeSe, which has a superconducting transition temperature of 42 K. Moreover, a Dirac-cone-type surface state is observed by angle-resolved photoemission spectroscopy, and its topological nature is confirmed by band calculations. The observed ZBCP can naturally be attributed to a MZM arising from the chiral topological surface state of a bulk superconductor. Thus,(Li0.84Fe0.16)OHFeSeprovides an ideal platform for studying MZMs and topological quantum computing.
We revisit the mixing mechanism for pseudoscalar mesons and glueball which is introduced by the axial vector anomaly. We demonstrate that the physical mass of the pseudoscalar glueball does not favor ...to be lower than 1.8 GeV if all the parameters are reasonably constrained. This conclusion, on the one hand, can accommodate the pseudoscalar glueball mass calculated by lattice QCD, and on the other hand, is consistent with the high-statistics analyses at BESIII that all the available measurements do not support the presence of two closely overlapping pseudoscalar states in any exclusive channel. Such a result is in agreement with the recent claim that the slightly shifted peak positions for two possible states η(1405) and η(1475) observed in different channels are actually originated from one single state with the triangle singularity interferences. By resolving this long-standing paradox, one should pay more attention to higher mass region for the purpose of searching for the pseudoscalar glueball candidate.
•The collapse mechanisms of prestressed precast (PC) concrete structure are revealed according to quasi-static pushdown tests.•PC structure presents a different failure mode compared with ...cast-in-place reinforcement concrete (RC) structure.•PC structure has a higher collapse resistant capacity, and RC structure has a perfect ductility under large deformation.•The equivalent restrained stiffness acted at beam ends in the failed span in 1st story is larger than that in 2nd story.•Compared to RC structure, the effect of compressive arch action is reduced in prestressed PC structure, and the effect of tensile catenary action is strengthened.
The prestressed precast concrete frame with dry joints is a novel structural system which has been proved to perform excellently under seismic loads in many researches, but its progressive collapse resistant mechanism need to be investigated further due to the discontinuity of longitudinal bars at joint interface. In this paper, quasi-static pushdown tests were conducted to investigate progressive collapse behavior of three half-scaled plane frame substructures with two stories and two spans under first-story middle column removal scenario. The specimens, including one cast-in-place concrete frame substructure and two prestressed precast concrete frame substructures, were designed according to the same design loads. The test results showed that these two types of frame structures could supply similar vertical resistances in compressive arch action (CAA) stage, while the prestressed precast structure presented a higher bearing capacity in tensile catenary action (TCA) stage, and the load-carrying ability was enhanced with the increase of steel strands area. However, the prestressed precast frame had a smaller failure displacement, which showed a lower ductility. Compared to the cast-in-place concrete frame, the prestressed precast concrete frame showed a distinct failure mode, in which there were almost no obvious cracks in beams, and no plastic hinges formed at beam ends, but a wide through crack appeared at the joint interface. The tension of steel strands decreased the CAA effect in beams, and speeded up the transformation from CAA stage to TCA stage during the progressive collapse process. This phenomenon became prompt with the increase of steel strands area. In terms of the same frame specimen, the peak value of axial compression force of beam in the second story was lower than that in the first story due to distinction of boundary conditions at beam ends in the two stories. However, the strength of steel strands of beams in both stories was fully utilized under large deformation due to a reliable tensile restrained stiffness at beam ends, leading to a similar peak tensile force at TCA stage.
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