Symmetry-enhanced supertransfer of delocalized quantum states

Coherent hopping of excitation rely on quantum coherence over physically extended states. In this work, we consider simple models to examine the effect of symmetries of delocalized multi-excitation states on the dynamical timescales, including hopping rates, radiative decay, and environmental interactions. While the decoherence (pure dephasing) rate of an extended state over N sites is comparable to that of a non-extended state, superradiance leads to a factor of N enhancement in decay and absorption rates. In addition to superradiance, we illustrate how the multi-excitonic states exhibit `supertransfer' in the far-field regime: hopping from a symmetrized state over N sites to a symmetrized state over M sites at a rate proportional to MN. We argue that such symmetries could play an operational role in physical systems based on the competition between symmetry-enhanced interactions and localized inhomogeneities and environmental interactions that destroy symmetry. As an example, we propose that supertransfer and coherent hopping play a role in recent observations of anomolously long diffusion lengths in nano-engineered assembly of light-harvesting complexes.Comment: 6 page

Geometrical effects on energy transfer in disordered open quantum systems

We explore various design principles for efficient excitation energy transport in complex quantum systems. We investigate energy transfer efficiency in randomly disordered geometries consisting of up to 20 chromophores to explore spatial and spectral properties of small natural/artificial Light-Harvesting Complexes (LHC). We find significant statistical correlations among highly efficient random structures with respect to ground state properties, excitonic energy gaps, multichromophoric spatial connectivity, and path strengths. These correlations can even exist beyond the optimal regime of environment-assisted quantum transport. For random configurations embedded in spatial dimensions of 30 A and 50 A, we observe that the transport efficiency saturates to its maximum value if the systems contain 7 and 14 chromophores respectively. Remarkably, these optimum values coincide with the number of chlorophylls in (Fenna-Matthews-Olson) FMO protein complex and LHC II monomers, respectively, suggesting a potential natural optimization with respect to chromophoric density.Comment: 11 pages, 10 figures. Expanded from the former appendix to arXiv:1104.481

Knowledge about AIDS among medical students in Iran

Young people are among the high risk group who are susceptible to sexually transmitted diseases. Several educational programs are scheduled to raise awareness about risky behaviours and to decrease the rate of the HIV pandemic. This cross sectional study showed that in young medical students, the level of awareness about HIV/AIDS increased during the years of academic education (not significant) and that males have a higher level of awareness than females. Higher awareness is desirable in this group due to their key role in the community

Numerical Evidence for Robustness of Environment-Assisted Quantum Transport

Recent theoretical studies show that decoherence process can enhance transport efficiency in quantum systems. This effect is known as environment-assisted quantum transport (ENAQT). The role of ENAQT in optimal quantum transport is well investigated, however, it is less known how robust ENAQT is with respect to variations in the system or its environment characteristic. Toward answering this question, we simulated excitonic energy transfer in Fenna-Matthews-Olson (FMO) photosynthetic complex. We found that ENAQT is robust with respect to many relevant parameters of environmental interactions and Frenkel-exciton Hamiltonian including reorganization energy, bath frequency cutoff, temperature, and initial excitations, dissipation rate, trapping rate, disorders, and dipole moments orientations. Our study suggests that the ENAQT phenomenon can be exploited in robust design of highly efficient quantum transport systems.Comment: arXiv admin note: substantial text overlap with arXiv:1104.481

Cosmological coincidence problem in interacting dark energy models

An interacting dark energy model with interaction term $Q= \lambda_m H\rho_m+\lambda_dH\rho_d$ is considered. By studying the model near the transition time, in which the system crosses the w=-1 phantom-divide-line, the conditions needed to overcome the coincidence problem is investigated. The phantom model, as a candidate for dark energy, is considered and for two specific examples, the quadratic and exponential phantom potentials, it is shown that it is possible the system crosses the w=-1 line, meanwhile the coincidence problem is alleviated, the two facts that have root in observations.Comment: 15 pages, LaTeX. Some minor explanations are added. To be published in Phys. Rev.

Cooling Effect of the Richtmyer-Meshkov Instability

We provide numerical evidence that the Richtmyer-Meshkov (RM) instability contributes to the cooling of a relativistic fluid. Due to the presence of jet particles traveling throughout the medium, shock waves are generated in the form of Mach cones. The interaction of multiple shock waves can trigger the RM instability, and we have found that this process leads to a down-cooling of the relativistic fluid. To confirm the cooling effect of the instability, shock tube Richtmyer-Meshkov instability simulations are performed. Additionally, in order to provide an experimental observable of the RM instability resulting from the Mach cone interaction, we measure the two particle correlation function and highlight the effects of the interaction. The simulations have been performed with an improved version of the relativistic lattice Boltzmann model, including general equations of state and external forces.Comment: 10 pages, 6 figure