Biological or social systems--论文代写范文精选

普遍性类优化模型在现实世界的网络中已经观察到。不可分离性的演化网络的拓扑结构和动态显示的事实表示，这是由底层网络的组装决定了它的拓扑结构。然而,在任何情况下这些指数是独一无二的。下面的essay代写范文讲述了这一问题。

Introduction
An essential character of physical systems subject to phase transition is that they belong to particular ‘universality classes’. This means that the exponents of power laws describing behavior at phase transition will be the same for large groups of markedly different systems, with ‘natural’ aggregations representing fundamental class properties. For example, Xenon, binary fluids and β-brass fall in one such class, while Helium 4, Iron, and Nickel fall into another (e.g. Binney, 1986). It is our contention that biological or social systems undergoing phase transition-analogs need not be constrained to such classes, and that ‘universality class tuning’, meaning the strategic alteration of parameters characterizing the renormalization properties of evolutionary punctuation, might well be possible, especially in response to selection pressure or other stressors. 

Here we focus on the tuning of parameters within a single, given, renormalization relation. Clearly, however, wholesale shifts of renormalization properties in response to adaptation pressure must be considered as well, and will be the subject of future analysis. Universality class tuning has been observed in models of ‘real world’ networks. As Albert and Barabasi (2002) put it, “The inseparability of the topology and dynamics of evolving networks is shown by the fact that [the exponents defining universality class] are related by [a] scaling relation..., underlying the fact that a network’s assembly uniquely determines its topology. However, in no case are these exponents unique. They can be tuned continuously...” 

We will extend these results to other phenomena, in particular an information dynamics model of the adaptive mutator mechanism that has been proposed as a means for escaping local optima in fitness landscapes. We explore the model’s implications for understanding both evolutionary process and cancer etiology. The literature on the mutator is vast and growing (see, e.g., Thaler, 1999 and Magnasco and Thaler, 1996). In sum, Thaler (1999) finds “...it is conceivable that the mutagenic effects associated with a cell sensing its environment and history could be as exquisitely regulated as transcription...”. Thus a structured environment may, in a higher iteration which Tenaillon et al. (2001) characterize as ‘second-order selection’, write itself, in a punctuated manner, onto the very internal workings of evolutionary punctuation itself.

This has evident implications for understanding both evolutionary process and cancer tumorigenesis. We begin with a brief review of the information dynamics formalism, describe the ‘tuning’ of evolutionary phase transition, and finally couple selection pressure to the internal structure of renormalization in a ‘natural’ iterated punctuation, producing a mutator. We speculate that internal cellular mechanisms controlling cancers may be actively cognitive, in distinct contrast to evolutionary process which re- flects imposed selection pressures, in the sense of Adami et al. (2000). This cognitive internal process, which includes but transcends Cohen’s (2000) immune cognition, may then itself become linked with the structured system of external selection pressures affecting the mutator, with synergistic impact on a tumorigenesis which we model as a punctuated interpenetration between a process of ‘socio-cellular’ cognition and adaptive clonal responses. Cancer then becomes even more explicitly a complicated disease of human ecology which is likely to respond at the population level only to multifactorial, multiscale strategies including redressing patterns of past and continuing social and economic injustice. Franz Fanon (1966) has made a similar case for ‘behavioral’ and mental disorder, and we have argued that analogous mechanisms entrain immune system function (Wallace, 2002a).

Review of formalism 
Before beginning the formal treatment, we highlight several important points: First, information theory is notorious for providing ‘existence theorems’ whose application is arduous indeed. For example, while the Shannon Coding Theorem implied the possibility of very efficient coding schemes as early as 1949, it took more than forty years for practical ‘turbo codes’ to be created. Our adaptation of the Shannon Source Coding Theorem is unlikely to be less difficult. Second, we are invoking information theory variants of the fundamental asymptotic limit theorems of probability. These are independent of exact mechanism, but constrain the collective behavior of such mechanisms. 

For example, although not all processes involve long sums of individual stochastic variables, those that do, regardless of the individual variable distributions, follow a Normal distribution as a consequence of the Central Limit Theorem. Similarly, the games of chance in a Las Vegas casino are all quite different, but nonetheless the possible success of ‘strategies’ for playing them is strongly and systematically constrained by the Martingale Theorem, regardless of game details. We similarly propose that languages-on-networks and languages-that-interact, as a consequence of the limit theorems of information theory, will be subject to regularities of punctuation and ‘generalized Onsager relations’, regardless of detailed mechanism, as important as the latter may be. Finally, just as we often impose parametric statistics on sometimes questionable experimental situations, relying on the robustness of the Central Limit Theorem to carry us through, we will invoke a similar heuristic approach in our applications of the information theory limit theorems. The essential homology relating information theory to statistical mechanics and nonlinear dynamics has been described elsewhere (Wallace and Wallace, 1998, 1999; Rojdestevnski and Cottam, 2000; Wallace, 2000, 2002a, b), and we truncate the discussion here.

Conclusions
The synergistic effects of structured external stress on both mutation and the selection pressure facing mutated cell clones implies that reductionist magic bullets and ‘life style’ approaches will be largely ineffective for marginalized human populations in the absence of proactive – and likely very intrusive – socioeconomic, political, and related interventions. Cancer plays a multidimensional chess across interacting levels of biological and social organization. To counter cancer, we’ll need to play the same. Only in the full context of such ‘biological control’ can individual-oriented strategies contribute significant impact. ‘Social exposures’ may be far more than incidental cofactors for the development of human cancers: Boyd’s metaphorical aphorism that ‘culture is as much a part of human biology as the enamel on our teeth’ appears literally true at the level of very basic biological mechanisms. A subsequent series of papers will examine hormonal cancers from these perspectives.

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