Theoretical studies of the electrochromic response of carotenoids in photosynthetic membranes

Molecular orbital calculations are carried out on a number of carotenoids in the presence of an external charge and a constant electric field. The external charge is used to represent the strong permanent field that is believed to polarize carotenoids in photosynthetic membranes and thus to account for their linear response to the transmembrane potential. Our calculations show that the in vitro leads to in vivo spectral shifts of carotenoids (approximately 25 nm) can be produced by a charge in close proximity to the molecule. The interaction of the induced dipole moment with a constant field accounts for the observed magnitude of the electrochromic response in photosynthetic bacteria. The existence of a second pool of carotenoids that shows a significant (approximately 20 nm) wavelength shift but no electrochromic response can be explained by an external charge positioned near the center of the molecule that affects its absorption maximum while inducing essentially no dipole moment. The spectral shift for this pool is due to the induction of higher multipoles. These also account for discrepancies that arise when one attempts to account quantitatively for available experimental results on carotenoid band shifts in terms of classical electrochromic theory

Energy and Cost Analysis of Cellular Networks Under Co-Channel Interference

In this paper we carry out an energy efficiency and economic cost analysis of different cellular network designs. Our system model considers the co-channel interference, different amounts of available bandwidths and also the reuse of frequencies. The energy efficiency analysis employs a realistic power consumption model, while the economic analysis focus on infrastructure, spectrum licenses, and energy costs. Our results show that from an economic point of view the bandwidth cost and the number of employed base stations can be the most relevant factors to be balanced, while from an energy efficiency analysis it is more interesting to employ larger bandwidths and to balance the reuse of frequencies and the number of base stations. Moreover, although the system design under these two different points of view can be rather different, we also look into scenarios when the most energy efficient system design may also lead to the best economic option

Energy and cost analysis of cellular networks under co-channel interference

In this paper we carry out an energy efficiency and economic cost analysis of different cellular network designs. Our system model considers the co-channel interference, different amounts of available bandwidths and also the reuse of frequencies. The energy efficiency analysis employs a realistic power consumption model, while the economic analysis focus on infrastructure, spectrum licenses, and energy costs. Our results show that from an economic point of view the bandwidth cost and the number of employed base stations can be the most relevant factors to be balanced, while from an energy efficiency analysis it is more interesting to employ larger bandwidths and to balance the reuse of frequencies and the number of base stations. Moreover, although the system design under these two different points of view can be rather different, we also look into scenarios when the most energy efficient system design may also lead to the best economic option

Action Spectroscopy on Dense Samples of Photosynthetic Reaction Centers of Rhodobacter sphaeroides WT Based on Nanosecond Laser-Flash 13C Photo-CIDNP MAS NMR

Photochemically induced dynamic nuclear polarization magic-angle spinning nuclear magnetic resonance (photo-CIDNP MAS NMR) allows for the investigation of the electronic structure of the photochemical machinery of photosynthetic reaction centers (RCs) at atomic resolution. For such experiments, either continuous radiation from white xenon lamps or green laser pulses are applied to optically dense samples. In order to explore their optical properties, optically thick samples of isolated and quinone-removed RCs of the purple bacteria of Rhodobacter sphaeroides wild type are studied by nanosecond laser-flash 13C photo-CIDNP MAS NMR using excitation wavelengths between 720 and 940 nm. Action spectra of both the transient nuclear polarization as well as the nuclear hyperpolarization, remaining in the electronic ground state at the end of the photocycle, are obtained. It is shown that the signal intensity is limited by the amount of accessible RCs and that the different mechanisms of the photo-CIDNP production rely on the same photophysical origin, which is the photocycle induced by one single photon