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A four-parameter, two degree-of-freedom block-spring model: Effect of the driver velocity (1994)

Brun, Jose L. ; Gomez, Javier B.

Springer

Pure and applied geophysics 143 (1994), S. 633-653

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ISSN: 1420-9136

Keywords: Block-spring models ; chaos ; earthquake patterns

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract We analyze the effect of tectonic plate velocities in the earthquake pattern using a simple mass-spring model of the Burridge and Knopoff type with two blocks and a velocity-weakening friction law. Previous versions of the two-block model assume a steady driver during slip events (limit of zero driver velocity), which, in some cases makes necessary the introduction of artificial parameters to start the numerical integration of the equations of motion at impending slip of any block. Still maintaining the condition of zero driver velocity during slip, we shall introduce a procedure to start the numerical integration without introducing artificial parameters and this will be done by using a linearized version of the equations of motion valid for small velocities and considering nonzero driver velocity. We also introduce a four parameter model in which the driver velocity enters the equations during the whole simulation, and analyze the effect of the new parameter, the driver velocity, in the displacement and time patterns of blocks motion, directly related to earthquake statistics such as coseismic slips and average repeat times.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00879502

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The heat capacity of proteins (1995)

Gómez, Javier ; Hilser, Vincent J. ; Xie, Dong ; [et al.]

New York, NY : Wiley-Blackwell

Proteins: Structure, Function, and Genetics 22 (1995), S. 404-412

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ISSN: 0887-3585

Keywords: protein thermodynamics ; protein folding ; protein stability ; protein thermodynamics ; energetics ; protein design ; Chemistry ; Biochemistry and Biotechnology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: The heat capacity plays a major role in the determination of the energetics of protein folding and molecular recognition. As such, a better understanding of this thermodynamic parameter and its structural origin will provide new insights for the development of better molecular design strategies. In this paper we have analyzed the absolute heat capacity of proteins in different conformations. The results of these studies indicate that three major terms account for the absolute heat capacity of a protein: (1) one term that depends only on the primary or covalent structure of a protein and contains contributions from vibrational frequencies arising from the stretching and bending modes of each valence bond and internal rotations; (2) a term that contains the contributions of noncovalent interactions arising from secondary and tertiary structure; and (3) a term that contains the contributions of hydration. For a typical globular protein in solution the bulk of the heat capacity at 25°C is given by the covalent structure term (close to 85% of the total). The hydration term contributes about 15 and 40% to the total heat capacity of the native and unfolded states, respectively. The contribution of non-covalent structure to the total heat capacity of the native state is positive but very small and does not amount to more than 3% at 25°C. The change in heat capacity upon unfolding is primarily given by the increase in the hydration term (about 95%) and to a much lesser extent by the loss of noncovalent interactions (up to ∼5%). It is demonstrated that a single universal mathematical function can be used to represent the partial molar heat capacity of the native and unfolded states of proteins in solution. This function can be experimentally written in terms of the molecular weight, the polar and apolar solvent accessible surface areas, and the total area buried from the solvent. This unique function accurately predicts the different magnitude and temperature dependences of the heat capacity of both the native and unfolded states, and therefore of the heat capacity changes associated with folding/unfolding transitions. © 1995 Wiley-Liss, Inc.

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