Mechanics and mathematicians: George Biddell Airy and the social tensions in constructing time at Parliament, 1845–1860

In mid-Victorian Britain, reconciling elite mathematical expertise with practical mechanical experience presented both engineering and social challenges. Nowhere was this more apparent than in the construction of the Westminster Clock at Britain’s Houses of Parliament. Realizing this scheme engendered the collaboration between Cambridge mathematicians George Biddell Airy and Edmund Beckett Denison, and the clockmaker Edward John Dent. Transforming theoretical mathematical drawings into physical apparatus challenged existing relations between conveyors of privileged scientific knowledge and those with practical experience of what was, and what was not, mechanically possible. My article demonstrates how, within this project, physical models and devices provided material solutions to ambiguities over authority and social disorder in Victorian Britain.

Membrane analogy for multi-material bars under torsion

Prandtl's membrane analogy for the torsion problem of prismatic homogeneous bars is extended to multi-material cross sections. The linear elastic problem is governed by the same equations describing the deformation of an inflated membrane, differently tensioned in regions that correspond to the domains hosting different materials in the bar cross section, in a way proportional to the inverse of the material shear modulus. Multi-connected cross sections correspond to materials with vanishing stiffness inside the holes, implying infinite tension in the corresponding portions of the membrane. To define the interface constrains that allow to apply such a state of prestress to the membrane, a physical apparatus is proposed, which can be numerically modelled with a two-dimensional mesh implementable in commercial finite-element model codes. This approach presents noteworthy advantages with respect to the three-dimensional modelling of the twisted bar.

Ex-Centric Hermeneutics in Stephanus Muller's Nagmusiek

In this review article the author reads Nagmusiek – Stephanus Muller's monumental metafictional biography of South African composer Arnold van Wyk – as an extended allegory on the geopolitics of academic writing. She argues that the book articulates, through its unusual physical apparatus, narratological techniques and metafictional hermeneutic deconcealment, a valuable theory-in-praxis of the aporetics of peripheral writing. In so doing, Muller materializes Walter Mignolo's notion of ‘epistemic delinking’ in radically original and risky ways.

INFORMATION EXTRACTION VERSUS IRREVERSIBILITY IN QUANTUM MEASUREMENT PROCESSES

A quantum measurement process, when non-trivial, is not a closed evolution: the appearance of classical outcomes is usually interpreted as the evidence of some decoherence-like mechanism causing quantum superpositions to degrade into classical mixtures. Such mechanism is due to a net flow of information from the input system (measurement object), through the physical apparatus interacting with the object (measurement probe), into some environment, the latter representing all those degrees of freedom which are not directly accessible by the experimenter. For this reason, the phenomenon of state reduction induced by the measurement process generally entails an irreversible state change. The aim of our contribution is to answer the following questions : how much information a measurement is able to extract? "How much" irreversible is the state reduction due to a particular measurement process? In which way information gain and irreversibility are related?

Physiological Optics and Physical Geometry

ArgumentHermann von Helmholtz’s distinction between “pure intuitive” and “physical” geometry must be counted as the most influential of his many contributions to the philosophy of science. In a series of papers from the 1860s and 70s, Helmholtz argued against Kant’s claim that our knowledge of Euclidean geometry was an a priori condition for empirical knowledge. He claimed that geometrical propositions could be meaningful only if they were taken to concern the behaviors of physical bodies used in measurement, from which it followed that it was posterior to our acquaintance with this behavior. This paper argues that Helmholtz’s understanding of geometry was fundamentally shaped by his work in sense-physiology, above all on the continuum of colors. For in the course of that research, Helmholtz was forced to realize that the color-space had no inherent metrical structure. The latter was a product of axiomatic definitions of color-addition and the empirical results of such additions. Helmholtz’s development of these views is explained with detailed reference to the competing work of the mathematician Hermann Grassmann and that of the young James Clerk Maxwell. It is this separation between 1) essential properties of a continuum, 2) supplementary axioms concerning distance-measurement, and 3) the behaviors of the physical apparatus used to realize the axioms, which is definitive of Helmholtz’s arguments concerning geometry.

Experiments Using Multimodal Virtual Environments in Design for Assembly Analysis

The goal of this work is to investigate whether estimates of ease of part handling and part insertion can be provided by multimodal simulation using virtual environment (VE) technology. The long-term goal is to use this data to extend computer-aided design (CAD) systems in order to evaluate and compare alternate designs using design for assembly analysis. A unified, physically-based model has been developed for modeling dynamic interactions and has been built into a multimodal VE system called the Virtual Environment for Design for Assembly (VEDA). The designer sees a visual representation of objects, hears collision sounds when objects hit each other, and can feel and manipulate the objects through haptic interface devices with force feedback. Currently these models are 2D in order to preserve interactive update rates. Experiments were conducted with human subjects using a two-dimensional peg-in-hole apparatus and a VEDA simulation of the same apparatus. The simulation duplicated as well as possible the weight, shape, size, peg-hole clearance, and fictional characteristics of the physical apparatus. The experiments showed that the multimodal VE is able to replicate experimental results in which increased task completion times correlated with increasing task difficulty (measured as increased friction, increased handling distance, and decreased peg-hole clearance). However, the multimodal VE task completion times are approximately twice those of the physical apparatus completion process. A number of possible factors have been identified, but the effect of these factors has not been quantified.

An Information-Theoretic Method for Revealing System Structure

A generalized version of Shannon's information theory has proven useful in deducing the structure of general systems having many variables. In a system consisting of a human operator interacting with a physical apparatus, the detection of structure will presumably be useful in understanding and modeling the operator's performance. An overview of an information-theoretic technique for detecting system structure is provided.