90 research outputs found
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Cyber-Physical Vulnerabilities in Additive Manufacturing Systems
One of the key advantages of additive manufacturing (AM) is its digital thread, which allows
for rapid communication, iteration, and sharing of a design model and its corresponding physical
representation. While this enables a more efficient design process, it also presents opportunities
for cyber-attacks to impact the physical word. In this paper the authors examine potential attack
vectors along the Additive Manufacturing process chain. Specifically, the effects of cyber-physical attacks, and potential means for detecting them, are explored. Based on the results of
this study, recommendations are presented for preventing and detecting cyber-physical attacks on
AM processes.Mechanical Engineerin
Self-organization and optical response of silver nanoparticles dispersed in a dielectric matrix
Abstract. Double ion-beam sputtering has been used to fabricate nanocermet multilayers consisting of silver nanoparticles sandwiched between Si 3 N 4 dielectric layers. The organization of the nanoparticles has been studied in detail by quantitative analysis of transmission electronic microscopy and atomic force microscopy images. Our results show that the nanoparticles deposited on a plane surface present an isotropic macroscopic in-plane organization while their vertical arrangement displays a topology-induced self-organization. The use of faceted alumina substrates with periodic hill-and-valley structures results in the formation of linear chains of silver particles along the valleys. In that case, transmission optical measurements reveal in-plane anisotropy
Deformation and stress of a composite-metal assembly
Compliant structures, e.g. automobile body panel and airplane wing box are widely used. A compliant structure consists of one or more flexible parts, and these parts share the mating features among them. Because of process-induced deformation and part-to-part variations, external forces are applied during the assembly process and the parts are deformed. As a result, the final assembly is pre-stressed and its geometrical shape may deviate from the designed shape. Therefore, the assembly variation and residual stress need to be analysed in order to evaluate the structure performance. In this study, a new approach based on response surface methodology is developed. A number of organised virtual experiments are conducted with the aid of finite element analysis and regression models are fitted to the resulting data. These regression models relate part variations to assembly variation and residual stress. Monte Carlo simulation can be conveniently done using these simple regression models. The effectiveness of this method was illustrated using a composite–metal assembly. It is shown that the method presented in this paper provides a practical and reliable solution to the analysis of compliant structures
Classical Helium Atom with Radiation Reaction
We study a classical model of Helium atom in which, in addition to the
Coulomb forces, the radiation reaction forces are taken into account. This
modification brings in the model a new qualitative feature of a global
character. Indeed, as pointed out by Dirac, in any model of classical
electrodynamics of point particles involving radiation reaction one has to
eliminate, from the a priori conceivable solutions of the problem, those
corresponding to the emission of an infinite amount of energy. We show that the
Dirac prescription solves a problem of inconsistency plaguing all available
models which neglect radiation reaction, namely, the fact that in all such
models most initial data lead to a spontaneous breakdown of the atom. A further
modification is that the system thus acquires a peculiar form of dissipation.
In particular, this makes attractive an invariant manifold of special physical
interest, the zero--dipole manifold, that corresponds to motions in which no
energy is radiated away (in the dipole approximation). We finally study
numerically the invariant measure naturally induced by the time--evolution on
such a manifold, and this corresponds to studying the formation process of the
atom. Indications are given that such a measure may be singular with respect to
that of Lebesgue.Comment: 16 pages, 3 figure
Photo-engineered optoelectronic properties of indium tin oxide via reactive laser annealing
Abstract: Transparent conductive oxides are appealing materials for optoelectronic and plasmonic applications as, amongst other advantages, their properties can be modulated by engineering their defects. Optimisation of this adjustment is, however, a complex design problem. This work examined the modification of the carrier transport properties of sputtered tin-doped indium oxide (ITO) via laser annealing in reactive environments. We relate the optical modifications to the structural, compositional, and electronic properties to elucidate the precise mechanisms behind the reactive laser annealing (ReLA) process. For sufficiently high laser fluence, we reveal an ambient-dependent and purely compositional modulation of the carrier concentration of ITO thin films. Hereby, we demonstrate that ReLA utilises the precise energy delivery of photonic processing to enhance the carrier mobility and finely tune the carrier concentration without significantly affecting the crystal structure. Exploitation of this phenomena may enable one to selectively engineer the optoelectronic properties of ITO, promising an alternative to the exploration of new materials for optoelectronic and photonic applications
Positioning variation modeling for aircraft panels assembly based on elastic deformation theory
Dimensional variation in aircraft panel assembly is one of the most critical issues that affects the aerodynamic performance of aircraft, due to elastic deformation of parts during the positioning and clamping process. This paper proposes an assembly deformation prediction model and a variation propagation model to predict the assembly variation of aircraft panels, and derives consecutive 3-D deformation expressions which explicitly describe the nonlinear behavior of physical interaction occurring in compliant components assembly. An assembly deformation prediction model is derived from equations of statics of elastic beam to calculate the elastic deformation of panel component resulted from positioning error and clamping force. A variation propagation model is used to describe the relationship between local variations and overall assembly variations. Assembly variations of aircraft panels due to positioning error are obtained by solving differential equations of statics and operating spatial transformations of the coordinate. The calculated results show a good prediction of variation in the experiment. The proposed method provides a better understanding of the panel assembly process and creates an analytical foundation for further work on variation control and tolerance optimization
Gravitational waves from single neutron stars: an advanced detector era survey
With the doors beginning to swing open on the new gravitational wave
astronomy, this review provides an up-to-date survey of the most important
physical mechanisms that could lead to emission of potentially detectable
gravitational radiation from isolated and accreting neutron stars. In
particular we discuss the gravitational wave-driven instability and
asteroseismology formalism of the f- and r-modes, the different ways that a
neutron star could form and sustain a non-axisymmetric quadrupolar "mountain"
deformation, the excitation of oscillations during magnetar flares and the
possible gravitational wave signature of pulsar glitches. We focus on progress
made in the recent years in each topic, make a fresh assessment of the
gravitational wave detectability of each mechanism and, finally, highlight key
problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and
Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor
corrections to match published versio
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