133 research outputs found
Relational EPR
We study the EPR-type correlations from the perspective of the relational
interpretation of quantum mechanics. We argue that these correlations do not
entail any form of 'non-locality', when viewed in the context of this
interpretation. The abandonment of strict Einstein realism implied by the
relational stance permits to reconcile quantum mechanics, completeness,
(operationally defined) separability, and locality.Comment: Revised, published versio
Universal Casimir attraction between filaments at the cell scale
The electromagnetic Casimir interaction between dielectric objects immersed
in salted water includes a universal contribution that is not screened by the
solvent and therefore long-ranged. Here, we study the geometry of two parallel
dielectric cylinders. We derive the Casimir free energy by using the scattering
method. We show that its magnitude largely exceeds the thermal energy scale for
a large parameter range. This includes length scales relevant for actin
filaments and microtubules in cells. We show that the Casimir free energy is a
universal function of the geometry, independent of the dielectric response
functions of the cylinders, at all distances of biological interest. While
multiple interactions exist between filaments in cells, this universal
attractive interaction should have an important role in the cohesion of bundles
of parallel filaments.Comment: 15 pages, 9 figures. This paper extends the unpublished short report
arXiv:2304.0600
Membranes by the Numbers
Many of the most important processes in cells take place on and across
membranes. With the rise of an impressive array of powerful quantitative
methods for characterizing these membranes, it is an opportune time to reflect
on the structure and function of membranes from the point of view of biological
numeracy. To that end, in this article, I review the quantitative parameters
that characterize the mechanical, electrical and transport properties of
membranes and carry out a number of corresponding order of magnitude estimates
that help us understand the values of those parameters.Comment: 27 pages, 12 figure
Monsters, Laws of Nature, and Teleology in Late Scholastic Textbooks
In the period of emergence of early modern science, âmonstersâ or individuals with physical congenital anomalies were considered as rare events which required special explanations entailing assumptions about the laws of nature. This concern with monsters was shared by representatives of the new science and Late Scholastic authors of university textbooks. This paper will reconstruct the main theses of the treatment of monsters in Late Scholastic textbooks, by focusing on the question as to how their accounts conceived natureâs regularity and teleology. It shows that they developed a naturalistic teratology in which, in contrast to the naturalistic explanations usually offered by the new science, finality was at central stage. This general point does not impede our noticing that some authors were closer to the views emerging in the Scientific Revolution insofar as they conceived nature as relatively autonomous from God and gave a relevant place to efficient secondary causation. In this connection, this paper suggests that the concept of the laws of nature developed by the new science âas exception-less regularitiesâtransferred to natureâs regularity the âstrongâ character that Late Scholasticism attributed to finality and that the decline of the Late Scholastic view of finality played as an important concomitant factor permitting the transformation of the concept of laws of nature
Membrane-mediated interactions
Interactions mediated by the cell membrane between inclusions, such as
membrane proteins or antimicrobial peptides, play important roles in their
biological activity. They also constitute a fascinating challenge for
physicists, since they test the boundaries of our understanding of
self-assembled lipid membranes, which are remarkable examples of
two-dimensional complex fluids. Inclusions can couple to various degrees of
freedom of the membrane, resulting in different types of interactions. In this
chapter, we review the membrane-mediated interactions that arise from direct
constraints imposed by inclusions on the shape of the membrane. These effects
are generic and do not depend on specific chemical interactions. Hence, they
can be studied using coarse-grained soft matter descriptions. We deal with
long-range membrane-mediated interactions due to the constraints imposed by
inclusions on membrane curvature and on its fluctuations. We also discuss the
shorter-range interactions that arise from the constraints on membrane
thickness imposed by inclusions presenting a hydrophobic mismatch with the
membrane.Comment: 38 pages, 10 figures, pre-submission version. In: Bassereau P., Sens
P. (eds) Physics of Biological Membranes. Springer, Cha
Computing, Design, Art: Reflections on an Innovative Moment in History
The paper is concerned with the role of art and design in the history and philosophy of computing. It offers insights arising from research into a period in the 1960s and 70s, particularly in the UK, when computing became more available to artists and designers, focusing on John Lansdown (1929-1999) and Bruce Archer (1922-2005) in London. Models of computing interacted with conceptualisations of art, design and related creative activities in important ways
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Mathematical analysis of the Escherichia coli chemotaxis signalling pathway
We undertake a detailed mathematical analysis of a recent nonlinear ordinary differential equation (ODE) model describing the chemotactic signalling cascade within an {\it Escherichia coli} cell. The model includes a detailed description of the cell signalling cascade and an average approximation of the receptor activity. A steady-state stability analysis reveals the system exhibits one positive real steady-state which is shown to be asymptotically stable. Given the occurrence of a negative feedback between phosphorylated CheB (CheB-P) and the receptor state, we ask under what conditions, the system may exhibit oscillatory type behaviour. A detailed analysis of parameter space reveals that whilst variation in kinetic rate parameters within known biological limits is unlikely to lead to such behaviour, changes in the total concentration of the signalling proteins does. We postulate that experimentally observed overshoot behaviour can actually be described by damped oscillatory dynamics and consider the relationship between overshoot amplitude, total cell protein concentration and the magnitude of the external ligand stimulus. Model reductions of the full ODE model allow us to understand the link between phosphorylation events and the negative feedback between CheB-P and receptor methylation, as well as elucidate why some mathematical models exhibit overshoot and others do not. Our manuscript closes by discussing intercell variability of total protein concentration as means of ensuring the overall survival of a population as cells are subjected to different environments
The material soul: Strategies for naturalising the soul in an early modern epicurean context
We usually portray the early modern period as one characterised by the âbirth of subjectivityâ with Luther and Descartes as two alternate representatives of this radical break with the past, each ushering in the new era in which âIâ am the locus of judgements about the world. A sub-narrative called âthe mind-body problemâ recounts how Cartesian dualism, responding to the new promise of a mechanistic science of nature, âsplit offâ the world of the soul/mind/self from the world of extended, physical substanceâa split which has preoccupied the philosophy of mind up until the present day. We would like to call attention to a different constellation of textsâneither a robust âtraditionâ nor an isolated âepisodeâ, somewhere in betweenâwhich have in common their indebtedness to, and promotion of an embodied, Epicurean approach to the soul. These texts follow the evocative hint given in Lucretiusâ De rerum natura that âthe soul is to the body as scent is to incenseâ (in an anonymous early modern French version). They neither assert the autonomy of the soul, nor the dualism of body and soul, nor again a sheer physicalism in which âintentionalâ properties are reduced to the basic properties of matter. Rather, to borrow the title of one of these treatises (LâĂme MatĂ©rielle), they seek to articulate the concept of a material soul. We reconstruct the intellectual development of a corporeal, mortal and ultimately material soul, in between medicine, natural philosophy and metaphysics, including discussions of Malebranche and Willis, but focusing primarily on texts including the 1675 Discours anatomiques by the Epicurean physician Guillaume Lamy; the anonymous manuscript from circa 1725 entitled LâĂme MatĂ©rielle, which is essentially a compendium of texts from the later seventeenth century (Malebranche, Bayle) along with excerpts from Lucretius; and materialist writings such Julien Offray de La Mettrieâs LâHomme-Machine (1748), in order to articulate this concept of a âmaterial soulâ with its implications for notions of embodiment, materialism and selfhood
Monsters in early modern philosophy
Monsters as a category seem omnipresent in early modern natural philosophy, in what one might call a âlongâ early modern period stretching from the Renaissance to the late eighteenth century, when the science of teratology emerges. We no longer use this term to refer to developmental anomalies (whether a two-headed calf, an individual suffering from microcephaly or Proteus syndrome) or to âfreak occurrencesâ like Mary Toftâs supposedly giving birth to a litter of rabbits, in Surrey in the early eighteenth-century (Todd 1995). But the term itself has a rich semantic history, coming from the Latin verb monstrare (itself deriving from monere, to remind, warn, advise), âto show,â from which we also get words like âmonitor,â âadmonish,â âmonumentâ and âpremonitionâ; hence there are proverbs like, in French, le monstre est ce qui montre, difficult to render in English: âthe monsters is that which shows.â Scholars have discussed how this âmonstrativeâ dimension of the monster is in fact twofold: on the one hand, and most awkwardly, the monster is an individual who is âpointed at,â who is shown; on the other hand, the monster is a sign, a portent, an omen, and in that sense âshows usâ something (on the complex semantic history of the term across Indo-European languages see Ochsner 2005). The latter dimension persists in naturalized form in the early modern period when authors like Bacon, Fontenelle or William Hunter insist that monsters (or anomalies) can show us something of the workings of Nature
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