40,237 research outputs found
Electromagnetism in terms of quantum measurements
We consider the question whether electromagnetism can be derived from quantum
physics of measurements. It turns out that this is possible, both for quantum
and classical electromagnetism, if we use more recent innovations such as
smearing of observables and simultaneous measurability. In this way we justify
the use of von Neumann-type measurement models for physical processes.
We apply operational quantum measurement theory to gain insight in
fundamental aspects of quantum physics. Interactions of von Neumann type make
the Heisenberg evolution of observables describable using explicit operator
deformations. In this way one can obtain quantized electromagnetism as a
measurement of a system by another. The relevant deformations (Rieffel
deformations) have a mathematically well-defined "classical" limit which is
indeed classical electromagnetism for our choice of interaction
Assessment of a gas-solid vortex reactor for SO2/NOx adsorption from flue gas
The feasibility of performing the SO2/NOx adsorption process in a gas-solid vortex reactor (GSVR) is examined and compared with the more traditional riser technology. The multiphase reacting flow is modeled using the Eulerian-Eulerian two-fluid model. Models of nonreacting flows were validated using data from a bench-scale experimental setup. The GSVR has the potential to significantly improved heat/mass transfer between phases, as compared to more conventional fluidization technologies. Process intensification opportunities are investigated. The model predicts continuous removal efficiencies greater than 99% for SO2 and approximately 80% for NOx. The gas-solid slip velocity and convective mass transfer coefficient for the riser were 0.2-0.5 and 0.06-0.12 m/s, respectively, whereas the values for the GSVR were 6-7 and 1.0-1.1 m/s, respectively. This order of magnitude increase in the external mass transfer coefficient highlights the potential intensification opportunities provided by the GSVR
A General Theory of Non-equilibrium Dynamics of Lipid-protein Fluid Membranes
We present a general and systematic theory of non-equilibrium dynamics of
multi-component fluid membranes, in general, and membranes containing
transmembrane proteins, in particular. Developed based on a minimal number of
principles of statistical physics and designed to be a meso/macroscopic-scale
effective description, the theory is formulated in terms of a set of equations
of hydrodynamics and linear constitutive relations. As a particular emphasis of
the theory, the equations and the constitutive relations address both the
thermodynamic and the hydrodynamic consequences of the unconventional material
characteristics of lipid-protein membranes and contain proposals as well as
predictions which have not yet been made in already existed work on membrane
hydrodynamics and which may have experimental relevance. The framework
structure of the theory makes possible its applications to a range of
non-equilibrium phenomena in a range of membrane systems, as discussions in the
paper of a few limit cases demonstrate.Comment: 22 pages, 2 figures, minor changes and addition
Covariant and locally Lorentz-invariant varying speed of light theories
We propose definitions for covariance and local Lorentz invariance applicable
when the speed of light is allowed to vary. They have the merit of
retaining only those aspects of the usual definitions which are invariant under
unit transformations, and which can therefore legitimately represent the
outcome of an experiment. We then discuss some possibilities for invariant
actions governing the dynamics of such theories. We consider first the
classical action for matter fields and the effects of a changing upon
quantization. We discover a peculiar form of quantum particle creation due to a
varying . We then study actions governing the dynamics of gravitation and
the speed of light. We find the free, empty-space, no-gravity solution, to be
interpreted as the counterpart of Minkowksi space-time, and highlight its
similarities with Fock-Lorentz space-time. We also find flat-space string-type
solutions, in which near the string core is much higher. We label them
fast-tracks and compare them with gravitational wormholes. We finally discuss
general features of cosmological and black hole solutions, and digress on the
meaning of singularities in these theories.Comment: To be published in Physical Review
Robust Execution of Contact-Rich Motion Plans by Hybrid Force-Velocity Control
In hybrid force-velocity control, the robot can use velocity control in some
directions to follow a trajectory, while performing force control in other
directions to maintain contacts with the environment regardless of positional
errors. We call this way of executing a trajectory hybrid servoing. We propose
an algorithm to compute hybrid force-velocity control actions for hybrid
servoing. We quantify the robustness of a control action and make trade-offs
between different requirements by formulating the control synthesis as
optimization problems. Our method can efficiently compute the dimensions,
directions and magnitudes of force and velocity controls. We demonstrated by
experiments the effectiveness of our method in several contact-rich
manipulation tasks. Link to the video: https://youtu.be/KtSNmvwOenM.Comment: Proceedings of IEEE International Conference on Robotics and
Automation (ICRA2019
Recursive mass matrix factorization and inversion: An operator approach to open- and closed-chain multibody dynamics
This report advances a linear operator approach for analyzing the dynamics of systems of joint-connected rigid bodies.It is established that the mass matrix M for such a system can be factored as M=(I+H phi L)D(I+H phi L) sup T. This yields an immediate inversion M sup -1=(I-H psi L) sup T D sup -1 (I-H psi L), where H and phi are given by known link geometric parameters, and L, psi and D are obtained recursively by a spatial discrete-step Kalman filter and by the corresponding Riccati equation associated with this filter. The factors (I+H phi L) and (I-H psi L) are lower triangular matrices which are inverses of each other, and D is a diagonal matrix. This factorization and inversion of the mass matrix leads to recursive algortihms for forward dynamics based on spatially recursive filtering and smoothing. The primary motivation for advancing the operator approach is to provide a better means to formulate, analyze and understand spatial recursions in multibody dynamics. This is achieved because the linear operator notation allows manipulation of the equations of motion using a very high-level analytical framework (a spatial operator algebra) that is easy to understand and use. Detailed lower-level recursive algorithms can readily be obtained for inspection from the expressions involving spatial operators. The report consists of two main sections. In Part 1, the problem of serial chain manipulators is analyzed and solved. Extensions to a closed-chain system formed by multiple manipulators moving a common task object are contained in Part 2. To retain ease of exposition in the report, only these two types of multibody systems are considered. However, the same methods can be easily applied to arbitrary multibody systems formed by a collection of joint-connected regid bodies
The Holographic Universe
We present a holographic description of four-dimensional single-scalar
inflationary universes in terms of a three-dimensional quantum field theory.
The holographic description correctly reproduces standard inflationary
predictions in their regime of applicability. In the opposite case, wherein
gravity is strongly coupled at early times, we propose a holographic
description in terms of perturbative QFT and present models capable of
satisfying the current observational constraints while exhibiting a
phenomenology distinct from standard inflation. This provides a qualitatively
new method for generating a nearly scale-invariant spectrum of primordial
cosmological perturbations.Comment: 20 pages, 5 figs; extended version of arXiv:0907.5542 including
background material and detailed derivations. To appear in Proceedings of 1st
Mediterranean Conference on Classical and Quantum Gravit
Quantum Spacetime and Algebraic Quantum Field Theory
We review the investigations on the quantum structure of spactime, to be
found at the Planck scale if one takes into account the operational limitations
to localization of events which result from the concurrence of Quantum
Mechanics and General Relativity. We also discuss the different approaches to
(perturbative) Quantum Field Theory on Quantum Spacetime, and some of the
possible cosmological consequences.Comment: 49 pages, 2 figure
Spacetime, General Covariance, Dirac-Bergmann Observables and Non-Inertial Frames
Talk at the 25th Johns Hopkins Workshop "2001: A Relativistic Spacetime
Odyssey", Firenze September 2001.Comment: 23 page
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