1,694 research outputs found
Analytical and experimental study of vibrations in a gear transmission
An analytical simulation of the dynamics of a gear transmission system is presented and compared to experimental results from a gear noise test rig at the NASA Lewis Research Center. The analytical procedure developed couples the dynamic behaviors of the rotor-bearing-gear system with the response of the gearbox structure. The modal synthesis method is used in solving the overall dynamics of the system. Locally each rotor-gear stage is modeled as an individual rotor-bearing system using the matrix transfer technique. The dynamics of each individual rotor are coupled with other rotor stages through the nonlinear gear mesh forces and with the gearbox structure through bearing support systems. The modal characteristics of the gearbox structure are evaluated using the finite element procedure. A variable time steping integration routine is used to calculate the overall time transient behavior of the system in modal coordinates. The global dynamic behavior of the system is expressed in a generalized coordinate system. Transient and steady state vibrations of the gearbox system are presented in the time and frequency domains. The vibration characteristics of a simple single mesh gear noise test rig is modeled. The numerical simulations are compared to experimental data measured under typical operating conditions. The comparison of system natural frequencies, peak vibration amplitudes, and gear mesh frequencies are generally in good agreement
Simulation studies of permeation through two-dimensional ideal polymer networks
We study the diffusion process through an ideal polymer network, using
numerical methods. Polymers are modeled by random walks on the bonds of a
two-dimensional square lattice. Molecules occupy the lattice cells and may jump
to the nearest-neighbor cells, with probability determined by the occupation of
the bond separating the two cells. Subjected to a concentration gradient across
the system, a constant average current flows in the steady state. Its behavior
appears to be a non-trivial function of polymer length, mass density and
temperature, for which we offer qualitative explanations.Comment: 8 pages, 4 figure
Oxidative coupling between C(sp2)-H and C(sp3)-H bonds of indoles and cyclic ethers/cycloalkanes
2015-2016 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Protecting infrastructure networks from cost-based attacks
It has been known that heterogeneous networks are vulnerable to the
intentional removal of a small fraction of highly connected or loaded nodes,
which implies that, to protect a network effectively, a few important nodes
should be allocated with more defense resources than the others. However, if
too many resources are allocated to the few important nodes, the numerous
less-important nodes will be less protected, which, when attacked all together,
still capable of causing a devastating damage. A natural question therefore is
how to efficiently distribute the limited defense resources among the network
nodes such that the network damage is minimized whatever attack strategy the
attacker may take. In this paper, taking into account the factor of attack
cost, we will revisit the problem of network security and search for efficient
network defense against the cost-based attacks. The study shows that, for a
general complex network, there will exist an optimal distribution of the
defense resources, with which the network is well protected from cost-based
attacks. Furthermore, it is found that the configuration of the optimal defense
is dependent on the network parameters. Specifically, network that has a larger
size, sparser connection and more heterogeneous structure will be more
benefited from the defense optimization.Comment: 5 pages, 4 figure
Shining Emitter in a Stable Host: Design of Halide Perovskite Scintillators for X-ray Imaging from Commercial Concept
Halide perovskite (HP) nanocrystals (NCs) have recently shown great potential for X-ray detection and imaging. However, the practical application still has a long way to go with many technical requirements waiting to be fulfilled, including structure optimization, stability enhancement, and cost reduction. A design principle in this beginning stage is urgently needed but still lacking. Herein, with an “emitter-in-matrix” principle refined from commercial scintillators, CsPbBr3@Cs4PbBr6 with emissive CsPbBr3 NCs embedded inside a solid-state Cs4PbBr6 host is subjected to X-ray sensing and imaging. The Cs4PbBr6 matrix not only enhances the attenuation of X-rays but also dramatically improves the stability of CsPbBr3 NCs. A favorable optical design with the Cs4PbBr6 matrix being transparent to the emission from CsPbBr3 NCs enables efficient light output. As a result, stable and sensitive scintillation response to X-ray signals is demonstrated with superior linearity and ultrahigh time resolution. In order to show the huge potential for practical applications, X-ray imaging using a large-area film (360 mm × 240 mm) by the blade-coating technique is carried out to obtain a high-quality image of interior structures invisible to the human eye. In addition to the above advantages in optics, CsPbBr3@Cs4PbBr6 also enjoys facile solution synthesis with large scalability, excellent repeatability, and low cost
Reconstructing phylogenetic level-1 networks from nondense binet and trinet sets
Binets and trinets are phylogenetic networks with two and three leaves, respectively. Here we consider the problem of deciding if there exists a binary level-1 phylogenetic network displaying a given set T of binary binets or trinets over a taxon set X, and constructing such a network whenever it exists. We show that this is NP-hard for trinets but polynomial-time solvable for binets. Moreover, we show that the problem is still polynomial-time solvable for inputs consisting of binets and trinets as long as the cycles in the trinets have size three. Finally, we present an O(3^{|X|} poly(|X|)) time algorithm for general sets of binets and trinets. The latter two algorithms generalise to instances containing level-1 networks with arbitrarily many leaves, and thus provide some of the first supernetwork algorithms for computing networks from a set of rooted 1 phylogenetic networks
Ultra-broadband Light Absorption by a Sawtooth Anisotropic Metamaterial Slab
We present an ultra broadband thin-film infrared absorber made of saw-toothed
anisotropic metamaterial. Absorbtivity of higher than 95% at normal incidence
is supported in a wide range of frequencies, where the full absorption width at
half maximum is about 86%. Such property is retained well at a very wide range
of incident angles too. Light of shorter wavelengths are harvested at upper
parts of the sawteeth of smaller widths, while light of longer wavelengths are
trapped at lower parts of larger tooth widths. This phenomenon is explained by
the slowlight modes in anisotropic metamaterial waveguide. Our study can be
applied in the field of designing photovoltaic devices and thermal emitters.Comment: 12 pages, 4 picture
Measurement of mechanical properties for dense and porous polymer films having a low dielectric constant
Author name used in this publication: C. W. OngAuthor name used in this publication: Chung Loong Choy2000-2001 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Characterization of proton irradiated copolymer thin films for microelectromechanical system applications
Psychological factors and their relation to osteoarthritis pain
We assessed associations between mental health and osteoarthritis (OA) pai
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