In photoreceptors of a dark adapted eye, the inward flux of sodium and calcium ions in the outer segment is balanced by the outward flux of potassium ions. But in the presence of light the creation of cyclic guanosine monophosphate in the outer segment decreases. Due to low concentration of cG the channels in the outer segment open relatively less and thus the influx of calcium ion decreases, leading finally to hyperpolarization of the photoreceptors. We have analyzed theoretically the effect (...) of oxidizing iron ions on the photoreceptors. In order to explain the effects of iron-induced oxidative stress, the different molecules and ions involved in phototransduction are quantified leading to a differential equation for calculating the electroretinogram a-wave voltage. The theoretical results are compared with published experimental data. In the presence of light, the iron ions could push outward the similarly charged calcium ions resulting in a small increase in the amount of inward calcium flux. Again, the presence of iron ions generates Reactive Oxygen Species, and ROS could attract the calcium ions which also increases the calcium flux. This will result in a reduction in the amplitude and slope of the a-wave voltage in the electroretinogram. These results are parametrized in terms of calcium ion concentrations. As the amplitude of the a-wave shows how much electrical signal is produced, its reduction indicates reduction in the visual signal. Thus, the increase in iron ions could explain the reduction in the electrical signal due to iron-induced oxidative stress. (shrink)

Kant's political thinking is predominantly evaluated in contractarian terms, though recent contributions have also emphasized the natural law influence on him. This paper argues that the assimilation of Kant into either tradition is problematic. An analysis of his account of political obligation cannot ignore the distinctiveness of Kant's general philosophical framework. Two recurrent Kantian themes are crucial to a reconstruction of his political argument. The first is the tension between freedom and causality, or nature. The second is the role of (...) reflective judgment in practical reasoning. The paper analyses Kant's property argument, and his related account of political obligation, from the perspective of these Kantian themes. Kant's ‘antinomy of Right’, formulated in the context of his property argument, is interpreted as a conflict between freedom and nature, and in analogy with the third antinomy of the Critique of Pure Reason. Kant's obscure theorem, the lex permissiva, is central to his ‘solution’ to the antinomy. The theorem is best understood as a reflective practical judgment, through which agents are brought to acknowledge that their obligations of justice towards one another are a direct entailment of their respective claims to property. The connection between property rights and political obligations is thus intrinsic, not extrinsic; the acknowledgement of that connection an act of reflective judgment, not contractual. (shrink)

Aristotle claims man is a political animal and that the polis exists by nature. Taking literally his analogy between the legislator and the craftsman, Aristotle's critics contend that he 'blunders' because the polis is artificial, devised by a legislator/founder and imposed on a people. We defend Aristotle's claims by showing, first, how Aristotle's claim that man is by nature an animal possessing logos -- speech/reason -- grounds his account of the natural development of the polis out of the earliest partnerships (...) (which the critics concede are natural); second, that the person who first brought people together in a polis may well have done so without realizing the scope of his actions; and, finally, that the developmental process is clearly one of praxis (action), not poisis (making, the imposition of a form on matter). Aristotle's claims are evidenced by the Homeric hero Philoctetes, whom one critic takes to disprove Aristotle's theses. (shrink)

Petrovich provides an insightful study on analytic philosophy (AP) with the intention of determining whether this sub-field of philosophy has been operating within what Kuhn calls a normal science framework. Through a citation analysis, Petrovich concludes that AP does not exhibit the sort of pattern that we would expect of a field operating in a normal science phase. I take issue with Petrovich’s way of measuring normal science. I provide some insight into how we might better measure normal science in (...) future studies. (shrink)