Tsuyoshi Hondou

Unattainability of carnot efficiency in the brownian heat engine

We discuss the reversibility of the Brownian heat engine. We perform an asymptotic analysis of the Kramers equation on a Buttiker-Landauer system and show quantitatively that Carnot efficiency is unattainable even in the fully overdamped limit. The unattainability is attributed to inevitable irreversible heat flow over the temperature boundary.

Thermal noise can facilitate energy conversion by a ratchet system

Molecular motors in biological systems are expected to use ambient fluctuation. In a recent paper [Phys. Rev. Lett. 80, 5251 (1998)], it was shown that the following question was unanswered: Can thermal noise facilitate energy conversion by ratchet system? We consider it using stochastic energetics, and show that there exist systems where thermal noise helps the energy conversion.

Passive Exposure to Mobile Phones: Enhancement of Intensity by Reflection

In a recent Letter [J. Phys. Soc. Jpn. 71 (2002) 432], we reported a preliminary calculation and concluded that public exposure to mobile phones can be enhanced by microwave reflection in public spaces. In this paper, we confirm the significance of microwave reflection reported in our previous Letter by experimental and numerical studies. Furthermore, we show that “hot spots” often emerge in reflective areas, where the local exposure level is much higher than average. Such places include elevators, and we discuss other possible environments including trains, buses, cars, and airplanes. Our results indicate the risk of “passive exposure” to microwaves.

Rising level of public exposure to mobile phones: Accumulation through additivity and reflectivity

A dramatic development occurring in our daily life is the increasing use of mobile equipment including mobile phones and wireless access to the Internet. They enable us to access several types of information more easily than in the past. Simultaneously, the density of mobile users is rapidly increasing. When hundreds of mobile phones emit radiation, their total power is found to be comparable to that of a microwave oven or a satellite broadcasting station. Thus, the question arises: what is the public exposure level in an area with many sources of electromagnetic wave emission? We show that this level can reach the reference level for general public exposure (ICNIRP Guideline) in daily life. This is caused by the fundamental properties of electromagnetic field, namely, reflection and additivity. The level of exposure is found to be much higher than that estimated by the conventional framework of analysis that assumes that the level rapidly decreases with the inverse square distance between the source and ...

Irreversible Operation in a Stalled State of Feynman's Ratchet

We consider the Langevin dynamics which describes the transducer of thermal fluctuation into mechanical work. In the frame of Feynmans ratchet, we prove that irreversiblity is unavoidable in operating the transducer if the system is described by the conventional Langevin equation with two degrees of freedom, where the degrees correspond to two heat baths of different temperatures.

Physical Validity of Assumptions for Public Exposure to Mobile Phones

Inthe Letter, 1) we derived anan alytical formula which estimates the level of public exposure to electromagnetic waves inclosed areas. This is the first study inwhich on e approximately predicts how much the exposure level increases by using two indispensable factors; 1) reflection of the electromagnetic waves at the boundary and 2) additivity of emissions. In their Comment, Kramer et al. claimed that public exposure inclosed areas does not impose additional health risks incomparisonwith those inany other location. Their claim was not toward the analytical derivationof the exposure level, which is the primary result of the Letter. However, we found that the Comment was based on several implicit assumptions which were not relevant to the issue being addressed and thus the claim itself was not valid. Some of the assumptions were based on improper applications of the fundamentals of physics. In this Reply, we will clarify such misunderstandings arising in the Comment through careful consideration of their implicit assumptions. The readers will find the essential issues which should always be taken into account. First, we wish to reconfirm the absolutely essential requirements to deal with issues of public safety. To prevent security holes inpublic safety, on e is required to have a sufficiently deep insight into all the issues concerned, because a one-sided way of looking at things may cause unexpected problems. It would be best to start discussions from the fundamentals of physics which relate to the issues. A confusion between two distinct physical quantities can oftenbe seeninthe studies of exposure, where electro

The effect of a 50-Hz sinusoidal magnetic field on nitric oxide (NO) production by human umbilical vein endothelial cells (HUVECs)

To investigate the effect of magnetic fields on living systems, we analyzed the effect of a 50-Hz, 1-mT sinusoidal magnetic field on nitric oxide (NO) production in human umbilical vein endothelial cells (HUVECs). Statistically significant differences in NO production were identified between exposed and unexposed (sham) cells. This finding confirms previous studies showing that magnetic fields can influence NO production; however, unlike previous studies, our results demonstrate two-way deviation of NO production under the influence of a magnetic field. Thus, in some cases, NO production was higher for the exposed group than the sham group, while in other cases the reverse was true. We suggest that the magnetic field affected the homeostasis of NO levels in a complex manner. Thus, the resulting NO level was dependent on the condition of the cell in each experiment or cells in each experiment were at a different stage in the cell cycle and therefore exhibited a different response when exposed to the magnetic field.

Evaluation of cell viability, DNA single-strand breaks, and nitric oxide production in LPS-stimulated macrophage RAW264 exposed to a 50-Hz magnetic field

Abstract Purpose: Synergistic effects between cellular oxidative stress and magnetic fields may explain the adverse biological effects of 50/60 Hz magnetic fields. To determine whether this hypothesis holds in macrophage RAW264 cells, we measured DNA single-strand breaks (SSB), cell viability, and nitric oxide (NO) production in cells with or without exposure to 0.5-mT, 50-Hz magnetic fields for 24 h and with or without simultaneous stimulation via the bacterial endotoxin, lipopolysaccharide (LPS). Materials and methods: Macrophages stimulated with 10 ng/ml LPS for 1 h were exposed to or not exposed to a magnetic field and were then subjected to (1) the alkaline comet assay to measure SSBs, (2) trypan-blue exclusion assay for cell viability, and (3) measurements of NO for evaluation of oxidative stress. Results: The 50-Hz magnetic field enhanced DNA SSB and decreased cell viability only in the LPS-stimulated macrophages in which NO production was greatly enhanced. The magnetic field alone did not alter NO production. Conclusion: Co-stimulation of the cell with LPS and a 50-Hz magnetic field promoted SSB and lowered cell viability, but these were not mediated by LPS-induced NO production.

Equation of state in a small system: Violation of an assumption of Maxwell's demon

An equation of state for an ideal gas with a small number of particles is studied. The resulting equation is found to differ from that expected in conventional thermodynamics, which is strikingly illustrated when considering the traditional thermodynamic problem of Maxwells demon. We clarify the mechanism of this different feature of thermodynamics arising in small systems.

Self-Annealing Dynamics in a Multistable System

A new type of dynamical behavior of a multistable system is reported. We found that a simple non-equilibrium system can reduce its effective temperature autonomously at a global minimum if the residual frustration at the global minimum is sufficiently small. This highlights an unexpected feature of non-equilibrium multistable systems. 817