A heat pump at a molecular scale controlled by a mechanical force

We show that a mesoscopic system such as Feynman's ratchet may operate as a heat pump, and clarify a underlying physical picture. We consider a system of a particle moving along an asymmetric periodic structure . When put into a contact with two distinct heat baths of equal temperature, the system transfers heat between two baths as the particle is dragged. We examine Onsager relation for the heat flow and the particle flow, and show that the reciprocity coefficient is a product of the characteristic heat and the diffusion constant of the particle. The characteristic heat is the heat transfer between the baths associated with a barrier-overcoming process. Because of the correlation between the heat flow and the particle flow, the system can work as a heat pump when the particle is dragged. This pump is particularly effective at molecular scales where the energy barrier is of the order of the thermal energy.Comment: 7 pages, 5 figures; revise

Hidden heat transfer in equilibrium states implies directed motion in nonequilibrium states

We study a class of heat engines including Feynman's ratchet, which exhibits a directed motion of a particle in nonequilibrium steady states maintained by two heat baths. We measure heat transfer from each heat bath separately, and average them using a careful procedure that reveals the nature of the heat transfer associated with directed steps of the particle. Remarkably we find that steps are associated with nonvanishing heat transfer even in equilibrium, and there is a quantitative relation between this ``hidden heat transfer'' and the directed motion of the particle. This relation is clearly understood in terms of the ``principle of heat transfer enhancement'', which is expected to apply to a large class of highly nonequilibrium systems.Comment: 4 pages, 4 figures; revise

An expression for stationary distribution in nonequilibrium steady state

We study the nonequilibrium steady state realized in a general stochastic system attached to multiple heat baths and/or driven by an external force. Starting from the detailed fluctuation theorem we derive concise and suggestive expressions for the corresponding stationary distribution which are correct up to the second order in thermodynamic forces. The probability of a microstate $\eta$ is proportional to $\exp[{\Phi}(\eta)]$ where ${\Phi}(\eta)=-\sum_k\beta_k\mathcal{E}_k(\eta)$ is the excess entropy change. Here $\mathcal{E}_k(\eta)$ is the difference between two kinds of conditioned path ensemble averages of excess heat transfer from the $k$-th heat bath whose inverse temperature is $\beta_k$. Our expression may be verified experimentally in nonequilibrium states realized, for example, in mesoscopic systems.Comment: 4 pages, 2 figure

Changes in shoot density, biomass and leaf area of Zostera caulescens Miki from Summer to Autumn in Funakoshi Bay of the Sanriku Coast, Japan

The world\u27s longest seagrass, Zostera caulescens Miki, is found in Funakoshi Bay along the Sanriku Coast of Honshu Island, Japan. Our study describes the changes in vertical distribution of shoot density, leaf area index (LAI) and biomass of Z. caulescens from summer (flowering season) to autumn (preparing for overwintering) in Funakoshi Bay. The samples were collected from a 0.5×0.5m quadrat at depths of 4.4m, 10.9m, 13.3m, 14.3m and 15.3m in July, and, for October, at 5.4m, 7.4m, 9.2m, 12.9m, and 15.7m. Above- and below-ground biomass, and flowering and vegetative shoot densities decreased with increasing bottom depth in both summer and autumn seasons except at the shallowest sampling depth, while the maximum above-ground biomass in both seasons was 187.3gDW/m^2 at the depth of 7.4m and 213.5gDW/m^2 at the depth of 10.9m, respectively. Densities of vegetative shoots were greater than those of flowering shoots at each sampling depth in both seasons except a bottom depth of 15.3m in July. The maximum length of flowering shoots in autumn (737cm) was greater than in summer (546cm), and the range of shoot lengths in autumn was wider than in summer. Biomass and densities of vegetative shoots at different depths in autumn were higher than those in summer, and Leaf Area Indices (LAI) of flowering and vegetative shoots at different depths in summer were higher than those in autumn. In addition, the mean LAIs of individual flowering and vegetative shoots in summer were greater than those in autumn as well. These results suggest that Z. caulescens has a higher LAI in summer when there is low seawater transparency and after ripening from summer to autumn, it also makes vegetative shoots in preparation for growth during the next spring