Global convergence in systems of differential equations arising from chemical reaction networks

It is shown that certain classes of differential equations arising from the modelling of chemical reaction networks have the following property: the state space is foliated by invariant subspaces each of which contains a unique equilibrium which, in turn, attracts all initial conditions on the associated subspace

The smallest bimolecular mass-action system with a vertical Andronov–Hopf bifurcation

We present a three-dimensional differential equation, which robustly displays a degenerate Andronov–Hopf bifurcation of infinite codimension, leading to a center, i.e., an invariant two-dimensional surface that is filled with periodic orbits surrounding an equilibrium. The system arises from a three-species bimolecular chemical reaction network consisting of four reactions. In fact, it is the only such mass-action system that admits a center via an Andronov–Hopf bifurcation

P matrix properties, injectivity, and stability in chemical reaction systems

In this paper we examine matrices which arise naturally as Jacobians in chemical dynamics. We are particularly interested in when these Jacobians are P matrices (up to a sign change), ensuring certain bounds on their eigenvalues, precluding certain behaviour such as multiple equilibria, and sometimes implying stability. We first explore reaction systems and derive results which provide a deep connection between system structure and the P matrix property. We then examine a class of systems consisting of reactions coupled to an external rate-dependent negative feedback process, and characterise conditions which ensure the P matrix property survives the negative feedback. The techniques presented are applied to examples published in the mathematical and biological literature

Separable Neural Components in the Processing of Black and White Faces

In a study of the neural components of automatic and controlled social evaluation, White participants viewed Black and White faces during event-related functional magnetic resonance imaging. When the faces were presented for 30 ms, activation in the amygdala—a brain region associated with emotion—was greater for Black than for White faces. When the faces were presented for 525 ms, this difference was significantly reduced, and regions of frontal cortex associated with control and regulation showed greater activation for Black than White faces. Furthermore, greater race bias on an indirect behavioral measure was correlated with greater difference in amygdala activation between Black and White faces, and frontal activity predicted a reduction in Black-White differences in amygdala activity from the 30-ms to the 525-ms condition. These results provide evidence for neural distinctions between automatic and more controlled processing of social groups, and suggest that controlled processes may modulate automatic evaluation.Psycholog

Performance on Indirect Measures of Race Evaluation Predicts Amygdala Activation

We used fMRI to explore the neural substrates involved in the unconscious evaluation of Black and White social groups. Specifically, we focused on the amygdala, a subcortical structure known to play a role in emotional learning and evaluation. In Experiment 1, White American subjects observed faces of unfamiliar Black and White males. The strength of amygdala activation to Black-versus-White faces was correlated with two indirect (unconscious) measures of race evaluation (Implicit Association Test [IAT] and potentiated startle), but not with the direct (conscious) expression of race attitudes. In Experiment 2, these patterns were not obtained when the stimulus faces belonged to familiar and positively regarded Black and White individuals. Together, these results suggest that amygdala and behavioral responses to Black-versus-White faces in White subjects reflect cultural evaluations of social groups modified by individual experience.Psycholog

Some considerations concerning the challenge of incorporating social variables into epidemiological models of infectious disease transmission

Incorporation of ‘social’ variables into epidemiological models remains a challenge. Too much detail and models cease to be useful; too little and the very notion of infection —a highly social process in human populations—may be considered with little reference to the social. The French sociologist Emile Durkheim proposed that the scientific study of society required identification and study of ‘social currents.’ Such ‘currents’ are what we might today describe as ‘emergent properties,’ specifiable variables appertaining to individuals and groups, which represent the perspectives of social actors as they experience the environment in which they live their lives. Here we review the ways in which one particular emergent property, hope, relevant to a range of epidemiological situations, might be used in epidemiological modelling of infectious diseases in human populations. We also indicate how such an approach might be extended to include a range of other potential emergent properties to repre

ICTs and ethical consumption: the political and market futures of fair trade

This paper addresses the relationship between information and communication technologies (ICTs) and ethical consumption as part of a cause for the insurance of a sustainable future. It homes in on fair trade as an ethical market, politically progressive cause and, crucially, form of participation where citizens can engage in the formation of an alternative future and the broader issue of food security. An three-dimensional analysis of agencies and uses of digital structures and content is informed by a case study approach, as well as interviews with fair trade activists, and ethically consuming citizens in the British metropolis. Through this, the argument which primarily rises distinguishes between the dimensions of durability (in terms of time and duration) and sustainability (in terms of time, duration and environmental concerns) of engagement in fair trade as a form of participation. Ethical consumption, then, is part of a durable market which has developed despite general market fluctuation, but is still very much bound in traditional physical economic spaces; in other words, ethical consumption has been integrated in the business as usual paradigm. Additionally, ICTs have not challenged the way in which information about ethical consumption is communicated or the spaces in which it is conducted. ICTs have been employed by fair trade activists, but they have not contributed to the development of fair trade as a political or economic project. Over a period of over five decades since the inception of the cause, their use has not significantly altered the way in which citizens engage with fair trade in the alternative or mainstream marketplace

Status boundary enforcement and the categorization of black–white biracials

Individuals who qualify equally for membership in more than one racial group are not judged as belonging equally to both of their parent groups, but instead are seen as belonging more to their lower status parent group. Why? The present paper begins to establish the role of individual differences and social context in hypodescent, the process of assigning multiracials the status of their relatively disadvantaged parent group. Specifically, in two experiments, we found that individual differences in social dominance orientation—a preference for group-based hierarchy and inequality—interacts with perceptions of socioeconomic threat to influence the use of hypodescent in categorizing half-Black, half-White biracial targets. Importantly, this paper begins to establish hypodescent as a “hierarchy-enhancing” social categorization.Psycholog