Two-photon Rabi-Hubbard and Jaynes-Cummings-Hubbard models: photon pair superradiance, Mott insulator and normal phases

We study the ground state phase diagrams of two-photon Dicke, the one-dimensional Jaynes-Cummings-Hubbard (JCH), and Rabi-Hubbard (RH) models using mean field, perturbation, quantum Monte Carlo (QMC), and density matrix renormalization group (DMRG) methods. We first compare mean field predictions for the phase diagram of the Dicke model with exact QMC results and find excellent agreement. The phase diagram of the JCH model is then shown to exhibit a single Mott insulator lobe with two excitons per site, a superfluid (SF, superradiant) phase and a large region of instability where the Hamiltonian becomes unbounded. Unlike the one-photon model, there are no higher Mott lobes. Also unlike the one-photon case, the SF phases above and below the Mott are surprisingly different: Below the Mott, the SF is that of photon {\it pairs} as opposed to above the Mott where it is SF of simple photons. The mean field phase diagram of the RH model predicts a transition from a normal to a superradiant phase but none is found with QMC.Comment: 14 pages, 14 figure

Nonlinear two-photon Rabi-Hubbard model: superradiance and photon/photon-pair Bose-Einstein condensate

We study the ground state phase diagram of a nonlinear two-photon Rabi-Hubbard (RH) model in one dimension using quantum Monte Carlo (QMC) simulations and density matrix renormalization group (DMRG) calculations. Our model includes a nonlinear photon-photon interaction term. Absent this term, the RH model has only one phase, the normal disordered phase, and suffers from spectral collapse at larger values of the photon-qubit interaction or inter-cavity photon hopping. The photon-photon interaction, no matter how small, stabilizes the system which now exhibits {\it two} quantum phase transitions: Normal phase to {\it photon pair} superfluid (PSF) transition and PSF to single particle superfluid (SPSF). The discrete $Z_4$ symmetry of the Hamiltonian spontaneously breaks in two stages: First it breaks partially as the system enters the PSF and then completely breaks when the system finally enters the SPSF phase. We show detailed numerical results supporting this, and map out the ground state phase diagram.Comment: 9 pages, 11 figure

A Research on the Relationship between Intestinal Flora and Human Longevity

The exploration of human life and health is advancing with the changes of the times. With the growth of age, the occurrence of chronic diseases of human immunity and organ system is frequent, which has a serious impact on human health. Genes, environment and other random factors determine the outcome of longevity, and intestinal flora is considered to be a decisive factor affecting human health and longevity, mainly because of its huge impact on human immunity, growth and development. The study of the relationship between intestinal flora and longevity is beneficial to improve the health status of the elderly and improve the overall life level of human beings, which has great scientific research value. This review will review the role of intestinal flora in longevity

Total Focusing Method for Imaging Defect in CFRP Composite with Anisotropy and Inhomogeneity

Fiber reinforced polymers (FRPs) are increasingly used in thick primary load-bearing structures, while manufacturing and in-service defects occur with a higher chance as the composite thickness increases, which entails the nondestructive detection and evaluation of potential structure defects. This study focuses on the imaging qualities of defects at different depth in thick FRPs via total focusing method (TFM), aiming at determining the optimum imaging strategy for thick FRPs (25 mm for discussion). Dynamic homogenization based on Floquet theory and numerical finite element analysis are performed to interrogate the wave propagation characteristics. The Frequency-dependent time correction method for TFM imaging (F-TFM) is proposed for accurate defect imaging in periodically layered crossply FRP. Finally, the results show that the proposed F-TFM method is able to detect and locate the defects of 2 mm size at all possible depth

Dynamic spin-lattice coupling and nematic fluctuations in NaFeAs

We use inelastic neutron scattering to study acoustic phonons and spin excitations in single crystals of NaFeAs, a parent compound of iron pnictide superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural transition at $T_s\approx 58$ K and a collinear antiferromagnetic (AF) order at $T_N\approx 45$ K. While longitudinal and out-of-plane transverse acoustic phonons behave as expected, the in-plane transverse acoustic phonons reveal considerable softening on cooling to $T_s$, and then harden on approaching $T_N$ before saturating below $T_N$. In addition, we find that spin-spin correlation lengths of low-energy magnetic excitations within the FeAs layer and along the $c$-axis increase dramatically below $T_s$, and show weak anomaly across $T_N$. These results suggest that the electronic nematic phase present in the paramagnetic tetragonal phase is closely associated with dynamic spin-lattice coupling, possibly arising from the one-phonon-two-magnon mechanism

Study on Multisize Effect of Mining Influence of Advance Speed in Steeply Inclined Extrathick Coal Seam

AbstractAiming at the multisize effect of mining in steeply inclined extrathick coal seam, taking the fully mechanized top-coal caving mining in B3+6 coal seam +425 level in the south of Wudong coal mine as the background, this paper studies the mining stress evolution law under the influence of advancing speed, analyzes the mechanical characteristics of coal samples under the mining action of steeply inclined extrathick coal seam, and completes the multisize effect study of mining in steeply inclined extrathick coal seam. The results show that the stress change theory of fully mechanized top-coal caving mining in steeply inclined seam is deduced, and the loading and unloading stress of fully mechanized top-coal caving mining is positively correlated with the advancing speed of the working face. The numerical simulation experiment shows that the ideal advancing condition increases with the advancing speed of the working face, and the cyclic loading and unloading amplitude under the mining stress path increases, the cyclic times decrease, the main influence area increases, and the acting time decreases. The peak value of mining stress, the width of the plastic zone, and its elastic energy under high-speed propulsion are obviously larger. A method of mechanical behavior analysis of coal samples is proposed, which takes the mining stress path of the numerical simulation experiment as the indoor scale loading and unloading stress path of coal samples. The average compressive strength of coal samples under the mining stress path increases with the advancing speed of the working face, and the damage degree of coal samples increases with the advancing speed of different stress paths. The input strain energy of coal cyclic loading and unloading increases with the increase in the advancing speed of the stress path. The input strain energy of the coal sample has obvious linear relationship with the advancing speed of different paths. The research results can be used for reference in the study of multisize effect of mining impact of advancing speed