Maximum efficiency of solar energy conversion

Owing to the energy scattered or absorbed by the constituents of earth's atmosphere and self‐absorption in the outer layers of the sun, the spectrum of solar flux at earth's surface is different from that of a blackbody. Consequently, the second law of thermodynamics for heat engine cycles operating between thermal reservoirs needs to be revised to determine the maximum conversion efficiency. A thermodynamic model similar to those for multi‐temperature plasmas and non‐isothermal particle‐exchange heat engines is proposed to estimate the maximum conversion efficiency of a mechanical or solid‐state heat engine subject to a radiation flux not having a blackbody spectrum. An example is given to illustrate the calculation of the maximum power that can be converted from a solar flux with considerable gas absorption. Copyright © 2011 John Wiley & Sons, Ltd.     

Ginsenoside‐Free Molecules from Steam‐Dried Ginseng Berry Promote Ethanol Metabolism: An Alternative Choice for an Alcohol Hangover

Ethanol metabolism produces harmful compounds that contribute to liver damage and cause an alcohol hangover. The intermediate metabolite acetaldehyde is responsible for alcohol hangover and CYP2E1‐induced reactive oxygen species damage liver tissues. In this study, we examined whether ginsenoside‐free molecules (GFMs) from steam‐dried ginseng berries promote ethanol metabolism and scavenge free radicals by stimulating primary enzymes (alcohol dehydrogenase, aldehyde dehydrogenase, CYP2E1, and catalase) and antioxidant effects using in vitro and in vivo models. The results revealed that GFM effectively scavenged 2,2‐diphenyl‐1‐picrylhydrazyl hydrate radicals and hydroxyl radicals. Notably, GFM significantly enhanced the expression of primary enzymes within 2 h in HepG2 cells. GFM clearly removed the consumed ethanol and significantly reduced the level of acetaldehyde as well as enhancement of primary gene expression in BALB/c mice. Moreover, GFM successfully protected HepG2 cells from ethanol attack. Of the major components identified in GFM, it was believed that linoleic acid was the most active ingredient. Based on these findings, we conclude that GFM holds promise for use as a new candidate for ethanol metabolism and as an antihangover agent.     

Synthesis and Evaluation of Neuroprotective Selenoflavanones

The physicochemical properties and antioxidant activity of a molecule could be improved by the substitution of an oxygen atom in a molecule with selenium. We synthesized selenoflavanones and flavanones to evaluate their neuroprotective effects. The selenoflavanones showed improved physicochemical properties, suggestive of the ability to pass through the blood-brain barrier (BBB). They showed in vitro antioxidant effects against hydrogen peroxide, and did not result in severe cytotoxicity. Moreover, infarction volumes in a transient ischemia mouse model were significantly reduced by the selenoflavanone treatments.     

Analysis of the root causes of refrigerant-induced noise in refrigerators

Refrigerant-induced noises, which occur irregularly at special thermodynamic cycle conditions, are frequently cited by residential customers who use refrigerators. However, these noises are very difficult to resolve and their root causes cannot usually be exactly identified. In this research, the root causes of the irregular refrigerant-induced noise are estimated through the theories of two-phase flow and bubble dynamics. Also, by using refrigerant-supplying equipment that can continuously supply refrigerant to the test unit at typical cycle conditions, the flow patterns of the evaporator in vertical and horizontal pipes are inspected and their noises are simultaneously measured. Through the observation of the relationship between the flow pattern and the refrigerant-induced noise, the root causes of this irregular refrigerant noise can be identified and verified.     

A CFD study on thermo-acoustic instability of methane/air flames in gas turbine combustor

Thermo-acoustic instability of methane/air flames in an industrial gas-turbine combustor is numerically investigated adopting CFD analysis. The combustor has 37 EV burners through which methane and air are mixed and then injected into the chamber. First, steady fuel/air mixing and flow characteristics established by the burner are investigated by numerical analysis with single burner. And then, based on information on the flow data, the burners are modeled numerically via equivalent swirlers, which facilitates the numerical analysis with the whole combustion system including the chamber and numerous burners. Finally, reactive flow fields within the chamber are investigated numerically by unsteady analysis and thereby, spontaneous instability is simulated. Based on the numerical results, scaling analysis is conducted to find out the instability mechanism in the combustor and the passive control method to suppress the instability is proposed and verified numerically.     

A third-order /spl Sigma//spl Delta/ modulator in 0.18-/spl mu/m CMOS with calibrated mixed-mode integrators

This paper describes a third-order sigma-delta (/spl Sigma//spl Delta/) modulator that is designed and implemented in 0.18-/spl mu/m CMOS process. In order to increase the dynamic range, this modulator takes advantage of mixed-mode integrators that consist of analog and digital integrators. A calibration technique is applied to the digital integrator to mitigate mismatch between analog and digital paths. It is shown that the presented modulator architecture can achieve a 12-dB better dynamic range than conventional structures with the same oversampling ratio (OSR). The experimental prototype chip achieves a 76-dB dynamic range for a 200-kHz signal bandwidth and a 55-dB dynamic range for a 5-MHz signal bandwidth. It dissipates 4 mW from 1.8-V supply voltages and occupies 0.7-mm/sup 2/ silicon area.