Energetics of Forced Thermal Ratchet

Molecular motors are known to have the high efficiency of energy transformation in the presence of thermal fluctuation. Motivated by the surprising fact, recent studies of thermal ratchet models are showing how and when work should be extracted from non-equilibrium fluctuations. One of the important finding was brought by Magnasco where he studied the temperature dependence on the fluctuation-induced current in a ratchet (multistable) system and showed that the current can generically be maximized in a finite temperature. The interesting finding has been interpreted that thermal fluctuation is not harmful for the fluctuation-induced work and even facilitates its efficiency. We show, however, this interpretation turns out to be incorrect as soon as we go into the realm of the energetics [Sekimoto,J.Phys.Soc.Jpn.66,1234-1237(1997)]: the efficiency of energy transformation is not maximized at finite temperature, even in the same system that Magnasco considered. The maximum efficiency is realized in the absence of thermal fluctuation. The result presents an open problem whether thermal fluctuation could facilitate the efficiency of energetic transformation from force-fluctuation into work.Comment: 3pages, 4sets of figure

Deep Blue Asymmetrical Streptocyanine Dyes: Synthesis, Spectroscopic Characterizations, and Ion-Specific Cooperative Adsorption at the Surface of TiO₂ Anatase Nanoparticles

Various triflate (TfO^–), tetrafluoroborate (BF₄^–), and perchlorate (ClO₄^–) salts of (<i>E</i>)-9-(3-(4-(diphenylamino)­phenyl)­allylidene)-9<i>H</i>-carbazol-9-ium chromophores, asymmetrical streptocyanine blue dyes, were synthesized, and their structures and photochemical and electrochemical properties were characterized. Displaying a high absorption band in the wavelength range 620–640 nm in acidified benzonitrile, the dyes provide an intense absorption at longer wavelength thanks to their oxidized π-conjugated systems. The π-electronic structure underwent twisting and bending, counteracting the electron-donating/withdrawing induction of its different substituents with a propensity to cancel its dipole moment and HOMO–LUMO charge-transfer coefficient. Zeta potential measurements of colloidal suspensions of sensitized TiO₂ anatase nanoparticles outlined the difference in electric behavior of the organic ionic pairs at the surface of the nanoparticles: The noncoordinating or coordinating characters of the counterions were found governing the molecular density at the surface and the adsorption/desorption kinetics of the ionic pairs. Dye-sensitized solar cell (DSSC) measurements performed with I^–/I₃^– as redox shuttle outlined the availability of the dyes for solar cell sensitization and the conditions for best stability/efficiency of such π-conjugated structures according to the nature of the counterion