Adhesion of surfaces via particle adsorption: Exact results for a lattice of fluid columns

We present here exact results for a one-dimensional gas, or fluid, of hard-sphere particles with attractive boundaries. The particles, which can exchange with a bulk reservoir, mediate an interaction between the boundaries. A two-dimensional lattice of such one-dimensional gas `columns' represents a discrete approximation of a three-dimensional gas of particles between two surfaces. The effective particle-mediated interaction potential of the boundaries, or surfaces, is calculated from the grand-canonical partition function of the one-dimensional gas of particles, which is an extension of the well-studied Tonks gas. The effective interaction potential exhibits two minima. The first minimum at boundary contact reflects depletion interactions, while the second minimum at separations close to the particle diameter results from a single adsorbed particle that crosslinks the two boundaries. The second minimum is the global minimum for sufficiently large binding energies of the particles. Interestingly, the effective adhesion energy corresponding to this minimum is maximal at intermediate concentrations of the particles.Comment: to appear in Journal of Statistical Mechanics: Theory and Experimen

Paradigms of Risk, Hazards and Danger

In his 1962 work, The Structure of Scientific Revolutions, Thomas Kuhn defined paradigm as a set of concepts constituting the foundations of a field of science. He presents revolutions as shifts in the existing paradigms and the phrase, paradigm shift, has since entered the language of science and business. Risk is a concern in both fields and this chapter considers the paradigms of risk, and whether they require a shift. Although we avoid negative experiences, often interpreted as resulting from hazards, no common risk management methodology exists. This statement may strike as untrue: after all, safety is a vast field; we analyse hazards and manage risk. Yet is it not a delusion, and is risk management not an attempt to charm reality? Don’t hazards, risk and danger depend on our perception? Perhaps risk can be viewed through the lens of quantum mechanics, existing in a limbo of potential until our actions and interpretations force events and circumstances to assume a danger state. If so, would managing this potential prior to the wave function collapse-inducing observation make any sense? In this chapter we will use the theory of inertia to attempt an answer to the question: is risk management possible

Book Review: Byzantine Military Rhetoric in the Ninth Century. A Translation of the Anonymi Byzantini Rhetorica Militaris, London -New York 2021

Byzantine Military Rhetoric in the Ninth Century. A Translation of the Anonymi Byzantini Rhetorica Militaris, trans. Georgios Theotokis, Dimitrios Sidiropoulos, London – New York 2021

Inertia in Assessing the Possibilities of Economic Development: Limits in Modelling Economies

We cannot transcend our world, our history and time to see ourselves from a broad enough perspective, and so our reasoning is limited by our being in the world. It is easy to draw conclusions a posteriori, analyse historical events and assume that our ancestors were, or should have been, aware of connections which we observe in hindsight. We also find it easy to interpret current affairs, label them and draw conclusions about their future development in accordance with the current theories and our zeitgeist. We are wrong to do so in both situations. Human perception is subject to the laws of inertia. Without realising inertia’s immense influence, we will create models of the world which are distant from reality and short-lived. Players in (what appears to be) the information economy want us to believe that endless progress is possible. States and economic agencies behave as if this were given and no other possibility should be worth serious consideration. Every business and every country present prognoses showing ever-increasing indicators. We want everything to grow: the GDP, our profit margins and sales. Human population continues to grow as well, globally, but is progress the indicator of human population? Is development our destiny

Phase Transitions in Multicomponent String Model

We propose a one-dimensional model of a string decorated with adhesion molecules (stickers) to mimic multicomponent membranes in restricted geometries. The string is bounded by two parallel walls and it interacts with one of them by short range attractive forces while the stickers are attracted by the other wall. The exact solution of the model in the case of infinite wall separation predicts both continuous and discontinuous transitions between phases characterised by low and high concentration of stickers on the string. Our model exhibits also coexistence of these two phases, similarly to models of multicomponent membranes.Comment: letter, 8 pages, 3 figure

Cooperative stabilization of close-contact zones leads to sensitivity and selectivity in T-cell recognition

T cells are sensitive to 1 to 10 foreign-peptide-MHC complexes among a vast majority of self-peptide-MHC complexes, and discriminate selectively between peptide-MHC complexes that differ not much in their binding affinity to T-cell receptors (TCRs). Quantitative models that aim to explain this sensitivity and selectivity largely focus on single TCR/peptide-MHC complexes, but T cell adhesion involves a multitude of different complexes. In this article, we demonstrate in a three-dimensional computational model of T-cell adhesion that the cooperative stabilization of close-contact zones is sensitive to one to three foreign-peptide-MHC complexes and occurs at a rather sharp threshold affinity of these complexes, which implies selectivity. In these close-contact zones with lateral extensions of hundred to several hundred nanometers, few TCR/foreign-peptide-MHC complexes and many TCR/self-peptide-MHC complexes are segregated from LFA-1/ICAM-1 complexes that form at larger membrane separations. Previous high-resolution microscopy experiments indicate that the sensitivity and selectivity in the formation of closed-contact zones reported here are relevant for T-cell recognition, because the stabilization of close-contact zones by foreign, agonist peptide-MHC complexes precedes T-cell signaling and activation in the experiments