Anomalous behavior of the energy gap in the one-dimensional quantum XY model.

We reexamine the well-studied one-dimensional spin-1/2 XY model to reveal its nontrivial energy spectrum, in particular the energy gap between the ground state and the first excited state. In the case of the isotropic XY model, the XX model, the gap behaves very irregularly as a function of the system size at a second order transition point. This is in stark contrast to the usual power-law decay of the gap and is reminiscent of the similar behavior at the first order phase transition in the infinite-range quantum XY model. The gap also shows nontrivial oscillatory behavior for the phase transitions in the anisotropic model in the incommensurate phase. We observe a close relation between this anomalous behavior of the gap and the correlation functions. These results, those for the isotropic case in particular, are important from the viewpoint of quantum annealing where the efficiency of computation is strongly affected by the size dependence of the energy gap.

Tempol intake improves inflammatory status in aged mice.

Oxidative stress is associated with both healthy aging and age-related disease states. In connection with oxidative stress, immunity is also a major component as a result of the chronic, low-grade inflammation associated with the development of tissue aging. Here we show that long-term treatment with the antioxidant tempol extends life-span in mice. Tempol-treated mice exhibited a reduction in mortality at 20 months. Tempol drinking did not have any effect on body weight, amount of visceral adipose tissue, or plasma biochemical parameters in aged mice. Body temperature of aged control mice (which drank only water) was significantly lower than young mice, but this reduction of body temperature was partially restored in aged mice which drank tempol. Plasma thiobarbituric acid-reactive substances and C-reactive protein were significantly increased in the control aged mice compared with young mice, but levels of both were normalized by tempol drinking. One of the endogenous antioxidants, ascorbic acid, was significantly increased in the plasma of mice which consumed tempol. The proportion of CD4 lymphocytes in the blood of aged tempol-treated mice was partially increased in comparison to aged control mice. These results suggest that the reduction of mortality by tempol is due to amelioration of chronic inflammation and improved function of the immune system through antioxidant effects.