Search PubMed⌕ Search

Biomedical subjects

R F Fox

Publications and source records attributed to R F Fox.

9 recordsLinked to original sources
PubMed2001

Rectified Brownian motion and kinesin motion along microtubules.

The mechanism of rectified Brownian movement is used to analyze measured data for kinesin motion along microtubules. A key component of the mechanism is the diffusive movement of the microtubule binding heads of kinesin during the adenosine triphosphate (ATP) cycle. The first-passage time distribution for this step is analyzed in detail and is shown to be responsible for observed load-velocity profiles. The ATPase activity of the kinesin heads is that of a nucleotide switch and not that of a direct chemomechanical energy converter. Experimental data acquisition, rate constants, and alternative explanations are discussed. The mechanism described in this paper is fundamental to the nanobiology of intracellular processes.

Adenosine Triphosphatases↗
PubMed1997

Stochastic versions of the Hodgkin-Huxley equations.

A Hodgkin-Huxley model algorithm for the numerical simulation of noise in neurons is contracted from a master equation description (cellular automoton) into a Langevin description. This reduction reduces the time required for a simulation by about two orders of magnitude. Earlier work is summarized, condensed, and made explicit to make the algorithm transparent and facilitate applications. Two approximate treatments are reported. An extension of this approach is presented that includes spatial dependence and the propagation of a noisy action potential along an axon.

Axons↗
PubMed1980

The "excess entropy" around nonequilibrium steady states, (deltaS)(ss), is not a Liapunov function.

In a response to my recent paper [Fox, R. F. (1979) Proc. Natl. Acad. Sci. USA 76, 2114-2117], Nicolis and Prigogine [Nicolis, G. & Prigogine, I. (1979) Proc. Natl. Acad. Sci. USA 76, 6060-6061] reasserted that the "excess entropy" around nonequilibrium steady states, (delta(2)S)(ss), is a Liapunov function. A simple, explicit counterexample which invalidates this claim is presented. The existence of an alternative theory possessing a proper Liapunov function for steady states is reviewed.

Journal Article↗
PubMed1979

Irreversible processes at nonequilibrium steady states.

It is shown that a Liapunov criterion exists for the stability of nonequilibrium steady states. This criterion is based upon the fluctuation-dissipation relation, as was first pointed out by Keizer. At steady states, the Liapunov function is constructed from the covariance matrix for the thermodynamic variables. Unlike the situation around equilibrium, at steady states the covariance matrix and the "excess entropy" matrix are not equivalent. The excess entropy, which serves as the Liapunov function around equilibrium, does not work in this capacity at steady states. Keizer's Liapunov function must be viewed as the first correct candidate for a proper Liapunov function for steady states.

Journal Article↗
PubMed1979

The inherited blood factors of some Northern Nigerians.

Results are presented on 147 individuals from northern Nigeria who were tested for the red cell antigens A, A1, B, H, M, N, S, s, He, P1, C, D, Du, E, c, e, Ce, v, Lua, Jka (some for Jkb), Lua, K, Jsa (some for Jsb), Kpa, Rd, Fya and Fyb, and for variants of the serum proteins haptoglobin and transferrin and of the red cell enzymes acid phosphatase, phosphoglucomutase, glucose-6-phosphate dehydrogenase, adenylate kinase, adenosine deaminase, phosphohexose isomerase and lactate dehydrogenase. The results found are of interest as they are among the very few published for this area of Nigeria, but they show little that is unexpected for people living in this region.

Blood Group Antigens↗
PubMed1974

Qualms regarding the range of validity of the glansdorff-prigogine criterion for stability of non-equilibrium States.

Doubt is raised concerning the range of validity of a stability criterion for non-equilibrium states which has been proposed by Glansdorff and Prigogine. In the case of a particular autocatalytic reaction, the stability analysis presented by Glansdorff and Prigogine, and by Eigen and by Katchalsky in their reviews of this problem, does not agree with our analysis, which is based upon exact solution of the relevant rate equations. We also find disagreement between the analysis based upon the Glansdorff-Prigogine criterion and our analysis of a second example which involves non-equilibrium steady states. The situation is quite delicate because seemingly innocent approximations (e.g., the use of specialized conditions in the autocatalytic reaction X + Y right arrow over left arrow 2X discussed in the sequel) may lead to the impression that the scope of validity of the criterion is wider than it actually is. By considering the stability of the equilibrium state, we conclude that the second differential of the entropy, which is at the heart of the Glansdorff-Prigogine criterion, is likely to be relevant for stability questions close to equilibrium only.

Journal Article↗