University of Cambridge

About: University of Cambridge is a education organization based out in Cambridge, United Kingdom. It is known for research contribution in the topics: Population & Galaxy. The organization has 118293 authors who have published 282289 publications receiving 14497093 citations. The organization is also known as: Cambridge University & Cambridge.

Local Convergence of SQP Methods for Mathematical Programs with Equilibrium Constraints

Abstract: Recently, nonlinear programming solvers have been used to solve a range of mathematical programs with equilibrium constraints (MPECs). In particular, sequential quadratic programming (SQP) methods have been very successful. This paper examines the local convergence properties of SQP methods applied to MPECs. SQP is shown to converge superlinearly under reasonable assumptions near a strongly stationary point. A number of examples are presented that show that some of the assumptions are difficult to relax.

Meeting the Contact-Mechanics Challenge

Abstract: This paper summarizes the submissions to a recently announced contact-mechanics modeling challenge. The task was to solve a typical, albeit mathematically fully defined problem on the adhesion between nominally flat surfaces. The surface topography of the rough, rigid substrate, the elastic properties of the indenter, as well as the short-range adhesion between indenter and substrate, were specified so that diverse quantities of interest, e.g., the distribution of interfacial stresses at a given load or the mean gap as a function of load, could be computed and compared to a reference solution. Many different solution strategies were pursued, ranging from traditional asperity-based models via Persson theory and brute-force computational approaches, to real-laboratory experiments and all-atom molecular dynamics simulations of a model, in which the original assignment was scaled down to the atomistic scale. While each submission contained satisfying answers for at least a subset of the posed questions, efficiency, versatility, and accuracy differed between methods, the more precise methods being, in general, computationally more complex. The aim of this paper is to provide both theorists and experimentalists with benchmarks to decide which method is the most appropriate for a particular application and to gauge the errors associated with each one.

Carroll versus Newton and Galilei: two dual non-Einsteinian concepts of time

Abstract: The Carroll group was originally introduced by Levy-Leblond (1965 Ann. Inst. Henri Poincare 3 1) by considering the contraction of the Poincare group as c → 0. In this paper an alternative definition, based on the geometric properties of a non-Minkowskian, non-Galilean but nevertheless boost-invariant, spacetime structure is proposed. A 'duality' with the Galilean limit c → ∞ is established. Our theory is illustrated by Carrollian electromagnetism.

Exact Space-Times in Einstein's General Relativity, by Jerry B. Griffiths and Jiří Podolský. Scope: reference. Level: postgraduate

Abstract: Optical sensors find various applications in all fields of scientific research, instrumentation and practical applications. Optical techniques are widely used in physics, chemistry, biology and medicine. They also have a great impact on today’s technological advances in telecommunications, photolithography on semiconductor chips, particle detection or object tracking to name a few. A book that would provide a summary of all optical sensors and their practical applications would be attractive to many readers across the board. The author’s intent to give an overview on this topic is well suited to meet this goal. This book serves as a good introduction to optical sensors. It covers the basics of light sources, detectors, various optical elements, and goes through some concepts about optical sensors and techniques. Optical sensors may refer to devices for light detection, e.g. CCD or CMOS cameras or PIN photodiodes. The author expands this concept and defines an optical sensor as a system consisting of a light source, a photodetector and optical elements for light delivery. He then describes the basic properties of incoherent and coherent light followed by numerous examples of optical sensors and their applications. Rigorous mathematical treatment, details about experimental arrangements and device architecture are beyond the scope of the book. However, the author provides an extended list of references on any given topic. Some of the references may be unfamiliar to the English speaking audiences. A comprehensive description of many modern optical sensor concepts is provided. The reader will find general coverage on how the humans and insects differ in their vision. The material touches upon the Purkinje effect on the shift of human eye’s spectral sensitivity. The reader will also find an extensive coverage about switches, rain sensors, displacement, velocity and distance measurement concepts, and laser vibrometers. A good discussion on optical techniques for temperature measurement is given. The reader will find examples about pyrometers and microbolometers as well as other thermal sensors used in different wavelength ranges. Microscopy and holography techniques are also discussed among the others. Various interferometric techniques and their applications are provided along with interesting examples. The reader will also find the basic concept of fluorescence detection and its applications. The reader will not find discussion on the state-of-the-art ultrafast techniques, e.g. laser induced fluorescence or four-wavemixing-based methods and their wide range of applications in science and technologies. Concepts and applications in the deep and extreme ultraviolet range, important for the photolithography, are not discussed either. The next editions of the book will hopefully include these important topics. The book is a good start for beginners who want to learn about optical sensors. An experimentalist may use this book as a reference. Engineering undergraduate students may find the material useful to jump start their projects and can use the references provided therein for more in-depth studies. A reader interested in biological applications of optical sensors, e.g. photodynamic therapy or fibre-optic based diagnostic techniques, will not find relevant material in this book. Teachers and general readers may find the material useful in preparing for classroom presentations and for general understanding of the optical sensor principles.

Recent advances in the biomimicry of structural colours

Abstract: Nature has mastered the construction of nanostructures with well-defined macroscopic effects and purposes. Structural colouration is a visible consequence of the particular patterning of a reflecting surface with regular structures at submicron length scales. Structural colours usually appear bright, shiny, iridescent or with a metallic look, as a result of physical processes such as diffraction, interference, or scattering with a typically small dissipative loss. These features have recently attracted much research effort in materials science, chemistry, engineering and physics, in order to understand and produce structural colours. In these early stages of photonics, researchers facing an infinite array of possible colour-producing structures are heavily inspired by the elaborate architectures they find in nature. We review here the recent technological strategies employed to artificially mimic the structural colours found in nature, as well as some of their current and potential applications.