Under the framework of Taylor series expansion for potential energy, we propose a simple and robust metric, dubbed ``regular residual analysis,'' to measure the fourth-order phonon anharmonicity in crystals. The method is verified by studying the intrinsic strong higher-order anharmonic effects in ${\mathrm{UO}}_{2}$ and ${\mathrm{CeO}}_{2}$. Comparison of the thermal conductivity results, which calculated by the anharmonic lattice dynamics method coupled with the Boltzmann transport equation and the spectral energy density method coupled with ab initio molecular dynamics simulation further validates our analysis. Analysis of the bulk Si and Ge systems confirms that the fourth-order phonon anharmonicity is enhanced and cannot be neglected at high enough temperatures, which agrees with a previous study where the four-phonon scattering was explicitly determined. This metric will facilitate evaluating and interpreting the lattice thermal conductivity of crystals with strong fourth-order phonon anharmonicity.
We discuss the mechanisms of spin–phonon coupling (SPC) in 2D MX3 (M = Fe, Ru; X = Cl, Br, I), and find that the spin induced thermal conductivity variation ranges from −130% to 573%, showing a strong composition effect.
Immune activation plays a significant role in the disease progression of HIV. Microbial products, especially bacterial lipopolysaccharide (LPS), contribute to immune activation. Increasing evidence indicates that T lymphocyte homeostasis disruptions are associated with immune activation. However, the mechanism by which LPS affects disruption of immune response is still not fully understood. Chronically SHIV B’WHU -infected Chinese rhesus macaques received 50 μ g/kg body weight LPS in this study. LPS administration affected the virus/host equilibrium by elevating the levels of viral replication and activating T lymphocytes. LPS induced upregulation of CD8 + naïve T cells and downregulated the number of CD4 + and CD8 + T effector memory cells. The downregulated effector memory cells are associated with a lower frequency of monofunctional and polyfunctional cells, and an upregulated programmed cell death-1 (PD-1) expression on CD4 + and CD8 + T cells was observed in monkeys after LPS stimulation. Our data provide new insights into the function of LPS in the immune activation in SHIV/HIV infection.
Abstract The elderly population infected with HIV-1 is often characterized by the rapid AIDS progression and poor treatment outcome, possibly because of immunosenescence resulting from both HIV infection and aging. However, this hypothesis remains to be fully tested. Here, we studied 6 young and 12 old Chinese rhesus macaques (ChRM) over the course of three months after simian immunodeficiency virus (SIV) SIVmac239 infection. Old ChRM showed a higher risk of accelerated AIDS development than did young macaques, owing to rapidly elevated plasma viral loads and decreased levels of CD4 + T cells. The low frequency of naïve CD4 + T cells before infection was strongly predictive of an increased disease progression, whereas the severe depletion of CD4 + T cells and the rapid proliferation of naïve lymphocytes accelerated the exhaustion of naïve lymphocytes in old ChRM. Moreover, in old ChRM, a robust innate host response with defective regulation was associated with a compensation for naïve T cell depletion and a high level of immune activation. Therefore, we suggest that immunosenescence plays an important role in the accelerated AIDS progression in elderly individuals and that SIV-infected old ChRM may be a favorable model for studying AIDS pathogenesis and researching therapies for elderly AIDS patients.
In this paper, the lattice thermal conductivities of bulk ZnO, GaN, and AlN in the normal-pressure wurtzite phase and high-pressure rocksalt phase at room temperature are investigated by solving the phonon Boltzmann transport equation based on first-principles calculations. The results show that the thermal conductivities of the rocksalt ZnO, GaN, and AlN close to the phase-transition pressure are reduced by 73%, 91%, and 34%, respectively, compared to that of corresponding normal-pressure wurtzite structures. Additionally, the thermal conductivity of wurtzite ZnO and GaN exhibits unexpectedly nonmonotonic dependence on pressure; however, for wurtzite and rocksalt AlN the thermal conductivity increases monotonically with the increase of pressure. Detailed phonon mode analysis reveals that the enhanced lattice anharmonicity is responsible for the depressed thermal conductivity of the rocksalt phase. By evaluating the relative contributions of dominant factors affecting lattice thermal conductivity, we find that the nonmonotonic response of thermal conductivity to pressure in wurtzite ZnO and GaN is attributed to the interplay of group velocity and phonon relaxation time. This study provides quantitative understanding of lattice thermal conductivity of ZnO, GaN, and AlN considering the pressure-induced phase transition and highlights the importance of pressure in manipulating lattice thermal conductivity.
Utilizing high-pressure to modulate optical properties, such as thermoreflectance (dR/dT), over a wide range has received much attention. Nevertheless, how the pressure exerts on the complex dielectric constant and finally on dR/dT remains elusive. Here, we perform a thoroughly experimental and theoretical investigation on dR/dT of Al nano-film from 0 to 25 GPa. The dR/dT values exhibit a sine-like pressure-dependence, with the zero-crossing appearing at around 6 GPa. These special phenomena are well explained from electron transition viewpoints. The first-principles calculations show that the energy difference of parallel bands is enlarged from 1.45 to 2 eV, thereby increasing the threshold for electron transitions. The lifted threshold changes the optical absorption rates of Al and the density of states of the electrons involving interband transitions; finally, the resulting dR/dT exhibits such a pressure-dependent behavior. Our findings provide a deep insight on pressure-induced electronic transitions and photon-electron interactions in metals.
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