Taylor Dotson

Cole–Davidson dynamics of simple chain models

Rotational relaxation functions of the end-to-end vector of short, freely jointed and freely rotating chains were determined from molecular dynamics simulations. The associated response functions were obtained from the one-sided Fourier transform of the relaxation functions. The Cole-Davidson function was used to fit the response functions with extensive use being made of Cole-Cole plots in the fitting procedure. For the systems studied, the Cole-Davidson function provided remarkably accurate fits [as compared to the transform of the Kohlrausch-Williams-Watts (KWW) function]. The only appreciable deviations from the simulation results were in the high frequency limit and were due to ballistic or free rotation effects. The accuracy of the Cole-Davidson function appears to be the result of the transition in the time domain from stretched exponential behavior at intermediate time to single exponential behavior at long time. Such a transition can be explained in terms of a distribution of relaxation times with a well-defined longest relaxation time. Since the Cole-Davidson distribution has a sharp cutoff in relaxation time (while the KWW function does not), it makes sense that the Cole-Davidson would provide a better frequency-domain description of the associated response function than the KWW function does.

Rheological complexity in simple chain models.

Dynamical properties of short freely jointed and freely rotating chains are studied using molecular dynamics simulations. These results are combined with those of previous studies, and the degree of rheological complexity of the two models is assessed. New results are based on an improved analysis procedure of the rotational relaxation of the second Legendre polynomials of the end-to-end vector in terms of the Kohlrausch-Williams-Watts (KWW) function. Increased accuracy permits the variation of the KWW stretching exponent beta to be tracked over a wide range of state points. The smoothness of beta as a function of packing fraction eta is a testimony both to the accuracy of the analytical methods and the appropriateness of (eta(0)-eta) as a measure of the distance to the ideal glass transition at eta(0). Relatively direct comparison is made with experiment by viewing beta as a function of the KWW relaxation time tau(KWW). The simulation results are found to be typical of small molecular glass formers. Several manifestations of rheological complexity are considered. First, the proportionality of alpha-relaxation times is explored by the comparison of translational to rotational motion (i.e., the Debye-Stokes-Einstein relation), of motion on different length scales (i.e., the Stokes-Einstein relation), and of rotational motion at intermediate times to that at long time. Second, the range of time-temperature superposition master curve behavior is assessed. Third, the variation of beta across state points is tracked. Although no particulate model of a liquid is rigorously rheologically simple, we find freely jointed chains closely approximated this idealization, while freely rotating chains display distinctly complex dynamical features.

Trial-and-error urbanism: addressing obduracy, uncertainty and complexity in urban planning and design

This article argues that sustainable and communal neighborhoods could be significantly more common in North America if development practices addressed the barriers posed by sociotechnical obduracy and the inevitable limitations of expertise through expanded opportunities for experimentation. In reconceptualizing the problems faced by alternative urbanisms through the lens of science and technology studies, I explore how the intelligent trial-and-error (ITE) framework for governing emerging technologies could be extended to partially address the barriers of obduracy, uncertainty and complexity when pursuing alternative urban designs. An examination of how Baugruppen (cooperative building groups) were integrated into the planning process of Quartier Vauban, Freiburg, is used to illustrate both the potentials and a concrete application of an ITE-like approach. I then discuss some of the barriers to an ITE model of urban planning in North America and recommend further research at the intersection of urban studies and science and technology studies.

Authentic virtual others? The promise of post-modern technologies

While modern technological development has promised the liberation of humanity from the constraints of the natural world: disease, toil, hunger and so on, post-modern technological developments promise a new kind of liberation: the freeing of humanity from the limitations and burdens found in the social world of people. Emerging technologies such as virtual humans and sociable robots exemplify this post-modern promise. This paper aims to explore the potential unintended consequence of such technologies and question the character of the “liberation” they promise. While virtual “other” technologies are being developed under the guise of solving social problems and providing therapeutics, the full effect of their deployment will be much more profound. Developers of virtual others do not aim to create fully intelligent social actors but merely to evoke a sense of social presence. It is notable, however, how easily social presence and attachment are evoked in human beings. The difficulty does not lie in the suspension of disbelief but rather in fighting the unconscious and pre-rational urge to anthropomorphize and imagine objects as social others. As imperfect but highly seductive simulations, virtual others are instances of post-modern hyperreality. Embracing them, I argue, carries the risk of an undesirable shift in the collective conception of authentic sociality. Rather than succumbing to technological somnambulism and naively believing that virtual others can be held at the rational distance necessary to prevent any unwanted reshaping of human social interaction, one should be cautious and critical of what the post-modern promise of technology holds in store for those who pursue it.

Epistemological Luddism: Reinvigorating a Concept for Action in 21st Century Sociotechnical Struggles

ABSTRACT Explicitly dismantling or decommissioning existing sociotechnical systems seems to be unimaginable both within dominant public imaginaries and in academic thought. Indeed, ‘gee whiz’ journalistic narratives regarding emerging technoscience abound as many members of the public appear to eagerly await any new innovation coming out of Silicon Valley. At the same time, most science and technology studies (STS) research focuses on the creation of new technoscience, not its destruction or temporary decommissioning. Yet, lay citizens clearly engage in forms of Luddism: schoolchildren and overworked professionals take digital ‘detoxes’, a number of cities have dismantled their urban highways, and a growing movement of parents have opted their children out of their state’s standardized testing requirements. While all such efforts are rooted in the rejection of a technology, they vary in terms of their resemblance to 19th century English Luddism as well as with respect to Langdon Winner’s concept of epistemological Luddism. How might STS scholars better make sense of 21st century Luddism? This article conceptualizes a number of contemporary examples of technological dismantling with regard to their epistemological and political characteristics. We end with a call for research to better understand lay technological refusal, especially in comparison to elite-driven forms of disruption.