8,614 research outputs found
Casimir forces and non-Newtonian gravitation
The search for non-relativistic deviations from Newtonian gravitation can
lead to new phenomena signalling the unification of gravity with the other
fundamental interactions. Various recent theoretical frameworks indicate a
possible window for non-Newtonian forces with gravitational coupling strength
in the micrometre range. The major expected background in the same range is
attributable to the Casimir force or variants of it if dielectric materials,
rather than conducting ones, are considered. Here we review the measurements of
the Casimir force performed so far in the micrometre range and how they
determine constraints on non-Newtonian gravitation, also discussing the
dominant sources of false signals. We also propose a geometry-independent
parameterization of all data in terms of the measurement of the constant c. Any
Casimir force measurement should lead, once all corrections are taken into
account, to a determination of the constant c which, in order to assess the
accuracy of the measurement, can be compared with its more precise value known
through microscopic measurements. Although the last decade of experiments has
resulted in solid demonstrations of the Casimir force, the situation is not
conclusive with respect to being able to discover new physics. Future
experiments and novel phenomenological analysis will be necessary to discover
non-Newtonian forces or to push the window for their possible existence into
regions of the parameter space which theoretically appear unnatural.Comment: Also available at http://www.iop.org/EJ/abstract/1367-2630/8/10/23
Leaking elastic capacitor as model for active matter
VersiĂłn preprintWe introduce the “leaking elastic capacitor” (LEC) model, a nonconservative dynamical system that combines simple electrical and mechanical degrees of freedom. We show that an LEC connected to an external voltage source can be destabilized (Hopf bifurcation) due to positive feedback between the mechanical separation of the plates and their electrical charging. Numerical simulation finds regimes in which the LEC exhibits a limit cycle (regular self-oscillation) or strange attractors (chaos). The LEC acts as an autonomous engine, cyclically performing work at the expense of the constant voltage source. We show that this mechanical work can be used to pump current, generating an electromotive force without any time-varying magnetic flux and in a thermodynamically irreversible way. We consider how this mechanism can sustain electromechanical waves propagating along flexible plates. We argue that the LEC model can offer a qualitatively new and more realistic description of important properties of active systems with electrical double layers in condensed-matter physics, chemistry, and biology.Foundation for Polish Science/[]/FNP/PoloniaGordon and Betty Moore Foundation/[GBMF45130]//Estados UnidosPolish National Agency for Academic Exchange/[PPN/ULM/2019/1/00284]/NAWA/PoloniaUCR::VicerrectorĂa de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de FĂsic
Study of large-signal stability of an inverter-based generator using a Lyapunov function
This document analyses the large-signal stability for an inverter-based generator such as photovoltaic and wind power sources. The objective of this study is to determine the stability region taking into account the electrical and control signal of the generator. The generator uses the concept of the electrostatic machine for the model of the generator. Finally, the applied procedure to find the Lyapunov's function is the Popov method, which not only permits to generate a valid function but also to determine the stability region of the system.Postprint (author's final draft
Trigger, an active release experiment that stimulated auroral particle precipitation and wave emissions
The experiment design, including a description of the diagnostic and chemical release payload, and the general results are given for an auroral process simulation experiment. A drastic increase of the field aligned charged particle flux was observed over the approximate energy range 10 eV to more than 300 keV, starting about 150 ms after the release and lasting about one second. The is evidence of a second particle burst, starting one second after the release and lasting for tens of seconds, and evidence for a periodic train of particle bursts occurring with a 7.7 second period from 40 to 130 seconds after the release. A transient electric field pulse of 200 mv/m appeared just before the particle flux increase started. Electrostatic wave emissions around 2 kHz, as well as a delayed perturbation of the E-region below the plasma cloud were also observed. Some of the particle observations are interpreted in terms of field aligned electrostatic acceleration a few hundred kilometers above the injected plasma cloud. It is suggested that the acceleration electric field was created by an instability driven by field aligned currents originating in the plasma cloud
Exploration of Reaction Pathways and Chemical Transformation Networks
For the investigation of chemical reaction networks, the identification of
all relevant intermediates and elementary reactions is mandatory. Many
algorithmic approaches exist that perform explorations efficiently and
automatedly. These approaches differ in their application range, the level of
completeness of the exploration, as well as the amount of heuristics and human
intervention required. Here, we describe and compare the different approaches
based on these criteria. Future directions leveraging the strengths of chemical
heuristics, human interaction, and physical rigor are discussed.Comment: 48 pages, 4 figure
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