13 research outputs found
Prebiotic Homochirality as a Critical Phenomenon
The development of prebiotic homochirality on early-Earth or another
planetary platform may be viewed as a critical phenomenon. It is shown, in the
context of spatio-temporal polymerization reaction networks, that environmental
effects -- be them temperature surges or other external disruptions -- may
destroy any net chirality previously produced. In order to understand the
emergence of prebiotic homochirality it is important to model the coupling of
polymerization reaction networks to different planetary environments.Comment: 6 Pages, 1 Figure, In Press: Origins of Life and Evolution of
Biosphere
An Extended Model for the Evolution of Prebiotic Homochirality: A Bottom-Up Approach to the Origin of Life
A generalized autocatalytic model for chiral polymerization is investigated
in detail. Apart from enantiomeric cross-inhibition, the model allows for the
autogenic (non-catalytic) formation of left and right-handed monomers from a
substrate with reaction rates and , respectively. The
spatiotemporal evolution of the net chiral asymmetry is studied for models with
several values of the maximum polymer length, N. For N=2, we study the validity
of the adiabatic approximation often cited in the literature. We show that the
approximation obtains the correct equilibrium values of the net chirality, but
fails to reproduce the short time behavior. We show also that the autogenic
term in the full N=2 model behaves as a control parameter in a chiral symmetry-
breaking phase transition leading to full homochirality from racemic initial
conditions. We study the dynamics of the N -> infinity model with symmetric
() autogenic formation, showing that it only achieves
homochirality for , where is an N-dependent
critical value. For we investigate the behavior of
models with several values of N, showing that the net chiral asymmetry grows as
tanh(N). We show that for a given symmetric autogenic reaction rate, the net
chirality and the concentrations of chirally pure polymers increase with the
maximum polymer length in the model. We briefly discuss the consequences of our
results for the development of homochirality in prebiotic Earth and possible
experimental verification of our findings
Punctuated Chirality
Most biomolecules occur in mirror, or chiral, images of each other. However,
life is homochiral: proteins contain almost exclusively levorotatory (L) amino
acids, while only dextrorotatory (R) sugars appear in RNA and DNA. The
mechanism behind this fundamental asymmetry of life remains an open problem.
Coupling the spatiotemporal evolution of a general autocatalytic polymerization
reaction network to external environmental effects, we show through a detailed
statistical analysis that high intensity and long duration events may drive
achiral initial conditions towards chirality. We argue that life's
homochirality resulted from sequential chiral symmetry breaking triggered by
environmental events, thus extending the theory of punctuated equilibrium to
the prebiotic realm. Applying our arguments to other potentially life-bearing
planetary platforms, we predict that a statistically representative sampling
will be racemic on average.Comment: 13 pages, 4 color figures. Final version published in Origins of Life
and Evolution of Biospheres. Typos corrected, figures improved, and a few
definitions and word usage clarifie
The social nature of serial murder: The intersection of gender and modernity
The literature on the aetiology of serial killing has benefited from analyses which offer an alternative perspective to individual/psychological approaches and consider serial murder as a sociological phenomenon. The main argument brought to bear within this body of work identifies the socio-economic and cultural conditions of modernity as enabling and legitimating the motivations and actions of the serial killer. This article interrogates this work from the standpoint of a gendered reading of modernity. Using the Yorkshire Ripper case, it emphasizes how in addition to the political economy, gender relations and masculinity shape the dynamics of serial murder and its representation
DNA charge neutralization by linear polymers. II. Reversible binding.
We model the way in which polymers bind to DNA and neutralize its charged backbone by analyzing the dynamics of the distribution of gaps along the DNA. We generalize existing theory for irreversible binding to construct deterministic models which include polymer removal, movement along the DNA, and allow for binding with overlaps. We show that reversible binding alters the capacity of the DNA for polymers by allowing the rearrangement of polymer positions over a longer time scale than when binding is irreversible. When the polymers do not overlap, allowing reversible binding increases the number of polymers adhered and hence the charge that the DNA can accommodate; in contrast, when overlaps occur, reversible binding reduces the amount of charge neutralized by the polymers
Ureteric stents: investigating flow and encrustation.
Blockages of the ureter, e.g. due to calculi (kidney stones), can result in an increase in renal pelvic pressure. This may be relieved by inserting a stent (essentially a permeable hollow tube). However, a number of complications are associated with stent use. Stents can result in reflux (backflow of urine along the ureter), which will promote recurrent urinary infection and possible renal parenchymal damage. Furthermore, long-term stent use is associated with infection and precipitation of salts from the urine, which can lead to a build-up of crystalline deposits on the stent surface, making stent removal difficult and painful. This paper examines factors governing urine flow in a stented ureter, the implications for reflux, and the processes by which the stent surface encrusts, in particular focusing on the influence of bacterial infection. An interdisciplinary approach is adopted, involving a combination of theoretical investigations and novel experiments