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Thermodynamic Processes (thermodynamic + process)

Distribution by Scientific Domains

Chemistry	28%

Selected Abstracts

Self-organized and highly ordered domain structures within swarms of Myxococcus xanthus

CYTOSKELETON, Issue 3 2006
Andrew E. Pelling
Abstract Coordinated group movement (swarming) is a key aspect of Myxococcusxanthus' social behavior. Here we report observation of domain structures formed by multiple cells within large three-dimensional swarming groups grown on amorphous glass substrates, using the atomic force microscope (AFM). Novel analyses revealed that ,90% of the wild type swarms displayed some form of preferential cell alignment. In contrast, cells with mutations in the social and adventurous motility systems displayed a distinct lack of cell alignment. Video microscopy observations of domain features of in vivo swarming M.xanthus cells were also consistent with the AFM data. The results presented here reveal that unique domain formation within swarms of wild type cells is a biologically driven process requiring the social and adventurous motility systems and is not a statistical phenomenon or thermodynamic process arising from liquid crystal behavior. Cell Motil. Cytoskeleton 63, 2006. © 2006 Wiley-Liss, Inc. [source]

Financial and Thermodynamic Equilibrium

ECONOMIC NOTES, Issue 3 2000
Antonio Roma
This paper explores general equilibrium asset pricing implications in a two-period model in which the production side explicitly describes the thermodynamic process unavoidably connected with production. We show that steady state of the production process, i.e. thermodynamic equilibrium, has a one-to-one correspondence with the absence of arbitrage possibilities. This provides an alternative definition of the absence of arbitrage. (J.E.L.: D5, G1, R3) [source]

An examination of exergy destruction in organic Rankine cycles

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2008
P. J. Mago
Abstract The exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113. A detailed roadmap of exergy flow is presented using an exergy wheel, and this visual representation clearly depicts the exergy accounting associated with each thermodynamic process. The analysis indicates that the evaporator accounts for maximum exergy destroyed in the ORC and the process responsible for this is the heat transfer across a finite temperature difference. In addition, the results confirm the thermodynamic superiority of the regenerative ORC over the basic ORC since regenerative heating helps offset a significant amount of exergy destroyed in the evaporator, thereby resulting in a thermodynamically more efficient process. Parameters such as thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This paper also examines the impact of operating parameters such as evaporator pressure and inlet temperature of the hot gases entering the evaporator on ORC performance. It is shown that exergy destruction decreases with increasing evaporator pressure and decreasing turbine inlet temperatures. Finally, the analysis reveals the potential of the exergy topological methodology as a robust technique to identify the magnitude of irreversibilities associated with real thermodynamic processes in practical thermal systems. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Hydrophobic Chemistry in Aqueous Solution: Stabilization and Stereoselective Encapsulation of Phosphonium Guests in a Supramolecular Host

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2004
Julia L. Brumaghim
Abstract Encapsulation of guest molecules inside supramolecular host assemblies provides a way to stabilize reactive species in aqueous solution. The stabilization of reactive phosphonium/ketone adducts of the general formula [R1MeC(OH)PR3]+ by encapsulation as guest molecules within a [Ga4L6]12, tetrahedral metal,ligand assembly is reported; although these cations decompose in aqueous solution, encapsulation inside the hydrophobic cavity of the assembly lengthens their lifetimes considerably, in some cases up to weeks. By varying the phosphane (PMe3, PEt3, PPhMe2, and PPh2Me) and ketone (acetone, methyl ethyl ketone, 1,1,1-trifluoroacetone, and fluoroacetone) which form these adducts, as well as the pD of the solutions, it was determined that the pH of the solution as well as the size and shape of the guest cations play an important role in the stability of these host,guest complexes. Encapsulation of chiral guests in the chiral [Ga4L6]12, assembly results in the formation of diastereomers, as characterized by 1H, 19F, and 31P NMR spectroscopy. Although the [Ga4L6]12, assembly is formed from non-chiral ligands, the assembly itself has ,,,, or ,,,, chirality around the metal centers. Due to the chirality of this assembly, diastereomeric selectivity is observed upon initial guest encapsulation (typical diastereomeric excesses are 30,50%). This initial diastereomeric selectivity decreases over time to reach an equilibrium but does not become 1:1, indicating both kinetic and thermodynamic processes promote selective guest encapsulation. These experiments demonstrate further the applications of nanoscale reaction vessels, self-assembled by design from non-chiral ligands, in providing a chiral and hydrophobic environment for guest molecules in aqueous solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Biomolecular Motor-Powered Self-Assembly of Dissipative Nanocomposite Rings,

ADVANCED MATERIALS, Issue 23 2008
Haiqing Liu
The fundamental mechanisms by which biomolecular motors drive the assembly and disassembly of the composite ring structures are characterized in this study. This system provides an enabling model of how the collective behavior of energy-dissipating and thermodynamic processes may be used to drive the dynamic assembly of nanostructured composites, and provides knowledge for the future development of adaptive, "smart," and reconfigurable materials. [source]

An examination of exergy destruction in organic Rankine cycles

Face-Selective [2]- and [3]Rotaxanes: Kinetic Control of the Threading Direction of Cyclodextrins

CHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2007
Tomoya Oshikiri
Abstract New [2]- and [3]pseudorotaxanes containing ,-cyclodextrin (,-CDs) molecules as rotors and alkyl pyridinium derivatives as axles were prepared by a slipping process. The inclusion behavior of these rotaxanes was investigated by using one- and two-dimensional NMR spectroscopy. The methyl group at the 2-position of the pyridinium moiety at the end of each axle molecule was found to control the rates of threading of the ,-CD onto the axle molecules. ,-CD can approach axle molecules from a particular direction to form inclusion complexes. Axle molecules that contain a 2-methylpyridinium moiety at one end and a bulky stopper at the other end can regulate the direction of approach to give a [2]pseudorotaxane such as 2,b,,-CD. A [3]pseudorotaxane in which two ,-CD molecules are arranged facing in the same direction at two stations of the tetracationic axle molecule was also obtained. These face-selective behaviors are dominated by kinetic processes rather than thermodynamic processes. [source]