Non-Markovian coherence dynamics of driven spin boson model: damped quantum beat or large amplitude coherence oscillation

The dynamics of driven spin boson model is studied analytically by means of the perturbation approach based on a unitary transformation. We gave the analytical expression for the population difference and coherence of the two level system. The results show that in the weak driven case, the population difference present damped coherent oscillation (single or double frequency) and the frequencies depend on the initial state. The coherence exhibit damped oscillation with Rabi frequency. When driven field is strong enough, the population difference exhibit undamped large-amplitude coherent oscillation. The results easily return to the two extreme cases without dissipation or without periodic driven.Comment: 15 pages,5 figure

The Pediatric Obesity Epidemic and the Role of the Corporation: Why Work Conditions and Faith in Meritocracy Matter

The global pediatric obesity epidemic is a “grand challenge” that will reduce quality of life and strain healthcare delivery systems for many years. The root causes and treatments of pediatric obesity are medical and social, requiring cross‐disciplinary collaboration. Research on pediatric obesity spans medicine, molecular biology, public health, and sociology and involves hospitals, clinics, community partners, and schools. However, little attention has been given to how corporations play a role in this nexus of institutions. We make the case for understanding the role of the corporation, beyond that of producer and distributor of unhealthy foods. Specifically, we consider two factors. First, we examine the work conditions that corporations create for parents and how these affect family lifestyle, differentially by socioeconomic status (SES). Second, we expose how the American tendency to “individualize” social problems is reinforced in the corporation. Faith in meritocracy directs attention to individual effort rather than structural constraints. Treating pediatric obesity as remediable by meritorious individual behaviors might obscure root causes and promising approaches based on new medical research

Recommendations for management and research on the fishery of Lake Victoria

This report is based on our experience with the Lake Victoria fishery from 1973 to 1975 while working at the E.A.F.F.R.O. substations in Kisumu and Mwanza. We shall first present management recommendations on three major topics: the on-going inshore artisanal fishery, the proposed offshore trawl fishery, and the possibility of cage culture. These will be followed by specific recommendations for research

Non-Markovian finite-temperature two-time correlation functions of system operators of a pure-dephasing model

We evaluate the non-Markovian finite-temperature two-time correlation functions (CF's) of system operators of a pure-dephasing spin-boson model in two different ways, one by the direct exact operator technique and the other by the recently derived evolution equations, valid to second order in the system-environment interaction Hamiltonian. This pure-dephasing spin-boson model that is exactly solvable has been extensively studied as a simple decoherence model. However, its exact non-Markovian finite-temperature two-time system operator CF's, to our knowledge, have not been presented in the literature. This may be mainly due to the fact, illustrated in this article, that in contrast to the Markovian case, the time evolution of the reduced density matrix of the system (or the reduced quantum master equation) alone is not sufficient to calculate the two-time system operator CF's of non-Markovian open systems. The two-time CF's obtained using the recently derived evolution equations in the weak system-environment coupling case for this non-Markovian pure-dephasing model happen to be the same as those obtained from the exact evaluation. However, these results significantly differ from the non-Markovian two-time CF's obtained by wrongly directly applying the quantum regression theorem (QRT), a useful procedure to calculate the two-time CF's for weak-coupling Markovian open systems. This demonstrates clearly that the recently derived evolution equations generalize correctly the QRT to non-Markovian finite-temperature cases. It is believed that these evolution equations will have applications in many different branches of physics.Comment: To appear in Phys. Rev.