| | | | | | 1 | On the diametric compression strength test of brittle spherical particles
2018-05-27 | | Publication date: November–December 2018 Source:European Journal of Mechanics - A/Solids, Volume 72
Author(s): Goran Žagar, Václav Pejchal, Marc Kissling, Andreas Mortensen
Diametric compression testing can be used to measure the hoop strength of spherical particles if one uses platens whose deformation behaviour is tailored in a way that allows the particles to sink sufficiently far into the platens before particle fracture takes place. To obtain the hoop stress of a compressed spherical particle at the moment of failure, and thus interpret the strength tests, an analytical solution derived by Hiramatsu and Oka is generally used. In deriving their analytical equations, Hiramatsu and Oka assumed that the contact stress between the spherical particle and the platens is radial and uniform along two equal diametrically opposed spherical caps. Here we revisit, by means of the finite element method, the mechanics that underlie the diametrical compression of a linear elastic sphere between two parallel and planar elasto-plastic platens. We show that the Hiramatsu and Oka equations give valid hoop stress values only when the contact area between the compressed sphere and the platens is less than roughly $5\text{\%}$ of the equatorial sphere cross-sectional area. At higher contact areas, when the spheres are more deeply embedded in the platen material and the test can be used to measure the particle hoop strength, the Hiramatsu and Oka solution underestimates the hoop stress. By conducting a parametric study, we provide simple expressions that can be used to quickly, yet accurately to within the $\approx 5\text{\%}$, compute the hoop stress of compressed spheres in diametric compression tests as a function of the contact area knowing only two parameters, namely the Poisson's ratio of the material making the sphere and the sphere/platen contact friction coefficient.
| | 2 | Effective bounds for the consistency of differential equations
2018-05-27 | | Publication date: November–December 2018 Source:Journal of Symbolic Computation, Volume 89
Author(s): Richard Gustavson, Omar León Sánchez
One method to determine whether or not a system of partial differential equations is consistent is to attempt to construct a solution using merely the “algebraic data” associated to the system. In technical terms, this translates to the problem of determining the existence of regular realizations of differential kernels via their possible prolongations. In this paper we effectively compute an improved upper bound for the number of prolongations needed to guarantee the existence of such realizations, which ultimately produces solutions to many types of systems of partial differential equations. This bound has several applications, including an improved upper bound for the order of characteristic sets of prime differential ideals. We obtain our upper bound by proving a new result on the growth of the Hilbert–Samuel function, which may be of independent interest.
| | 3 | A novel super-resolution imaging method based on TDI CCD charge transfer and random exposure
2018-05-27 | | Publication date: 1 November 2018 Source:Optics Communications, Volume 426
Author(s): Yun-Hui Li, Xiao-Dong Wang, Zhi Wang
Based on compressed sensing theory and TDI CCD driving mode, a collaborative coding method founded on TDI CCD charge transfer and random exposure is proposed in this paper, which breaks through the limitation of pixel size and achieves the improvement of one-dimensional image resolution. By extending this method, an orthogonal dual detector super-resolution imaging system is established, which realizes the improvement of two-dimensional image resolution. Further, the convex optimization algorithm and the proportional fusion algorithm are proposed as the two-dimensional image fusion algorithm. Theoretical modeling and simulation results demonstrate the effectiveness of the proposed imaging method and system, which provide an innovative approach of system implementation for super-resolution imaging based on compressed sensing theory.
| | 4 | “Long-lived” luminous effects in femtosecond laser filament
2018-05-27 | | Publication date: 1 November 2018 Source:Optics Communications, Volume 426
Author(s): Suyu Li, Anmin Chen, Yuanfei Jiang, Mingxing Jin
Luminous effects like the emission of fluorescence, supercontinuum and terahertz are of great importance in the applications of femtosecond filamentation, which is however short in duration. By carrying out the experiment of femtosecond filamentation in gas flow, we observe the plasma jet induced by femtosecond filament for the first time, indicating that luminous effects still exist long after the termination of femtosecond filamentation. The temporal–spatial measurement of the luminous spectra shows that in air the luminous effect comes from the supercontinuum generated by oxygen, which lasts about 50 $\mathrm{\mu}$s; while in the pure nitrogen, it comes from the nitrogen fluorescence emission, which lasts much longer, reaching several hundred microseconds. Both of them are much longer than the plasma longevity in femtosecond filament in air. This work reveals the “long-lived” luminous effects after femtosecond filamentation and will be helpful to the understanding of femtosecond filamentation in air.
| | 5 | Depth effect on the inertial collapse of cavitation bubble under ultrasound: Special emphasis on the role of the wave attenuation
2018-05-27 | | Publication date: November 2018 Source:Ultrasonics Sonochemistry, Volume 48
Author(s): Nassim Kerabchi, Slimane Merouani, Oualid Hamdaoui
Acoustic cavitation concentrates and releases a very large amount of energy in localized areas, which can be used for many physical and chemical processes. Even though acoustic cavitation has been studied widely for decades in lab-scale sonoreactors, only few studies have been devoted to characterize this event in big-scale sonoreactors, where the liquid depth may have a critical influence on the bubble collapse. The present computational study furnished numerical data about the effect of depth (z = 0–10 m) on acoustic cavitation with special focus on the role of attenuation of the ultrasound wave on the dramatic conditions developed within bubbles at collapse. The used mathematical model takes into account the liquid compressibility, surface tension and viscosity, depth as well as the attenuation of the ultrasound wave with depth. It was found that the maximum bubble temperature (Tmax) and pressure (pmax ) at the collapse diminished considerably with deepening into water up to 10 m with a considerable contribution of the ultrasound wave attenuation in the overall reduction event. The reduction in Tmax and pmax with depth was more pronounced at higher frequency (1000 kHz) and lower temperature (10 °C) in which losses of about up to 72% in Tmax and till 94% in pmax (as compared with values at z = 0) were obtained at z = 10 m. Depending on operating conditions, i.e. frequency, acoustic intensity or liquid temperature, the ultrasound wave attenuation may contribute with up to 47% and 79% in the overall reductive effect of depth toward Tmax and pmax , respectively. These results were discussed, interpreted and used to support some available experimental observations. Finally, the results of the present study may help in designing large-scale sonoreactors through providing data about the effect of one of the missing links between lab-scale sonoreactors and industrial large-scale sonoreactors.
| | 6 | Machine learning-based multi-documents sentiment-oriented summarization using linguistic treatment
2018-05-26 | | Publication date: 1 November 2018 Source:Expert Systems with Applications, Volume 109
Author(s): Asad Abdi, Siti Mariyam Shamsuddin, Shafaatunnur Hasan, Jalil Piran
Sentiment summarization is the process of automatically creating a compressed version of the opinionated information expressed in a text. This paper presents a machine learning-based approach to summarize user's opinion expressed in reviews using: (1) Sentiment knowledge to calculate a sentence sentiment score as one of the features for sentence-level classification. It integrates multiple strategies to tackle the following problems: sentiment shifter, the types of sentences and word coverage limit. (2) Word embedding model, a deep-learning-inspired method to understand meaning and semantic relationships among words and to extract a vector representation for each word. (3) Statistical and linguistic knowledge to determine salient sentences. The proposed method combines several types of features into a unified feature set to design a more accurate classification system (“True”: the extractive reference summary; “False”: otherwise). Thus, to achieve better performance scores, we carried out a performance study of four well-known feature selection techniques and seven of the most famous classifiers to select the most relevant set of features and find an efficient machine learning classifier, respectively. The proposed method is applied to three different datasets and the results show the integration of support vector machine-based classification method and Information Gain (IG) as a feature selection technique can significantly improve the performance and make the method comparable to other existing methods. Furthermore, our method that learns from this unified feature set can obtain better performance than one that learns from a feature subset.
| | 7 | Mobile phone mediated point-of-care testing of HIV p24 antigen through plastic micro-pit array chips
2018-05-26 | | Publication date: 15 October 2018 Source:Sensors and Actuators B: Chemical, Volume 271
Author(s): Fengyun Li, Hongli Li, Zhaoyan Wang, Jing Wu, Wei Wang, Lei Zhou, Qi Xiao, Qiaosheng Pu
Plastic micro-chips with micro-pit array (μPACs) were used for the mobile phone mediated detection of HIV capsid p24 antigen. The μPACs with a size comparable to common test strips were fabricated on transparent cyclic olefin copolymer (COC) sheets to ensure the optical detection and solvent compatibility. An antibody (for p24 antigen) was covalently immobilized onto the inner surface of micro-pits for sandwich immunoassay. The enzyme-catalyzed reaction was imaged by a mobile phone and the captured pictures were sent to a computer (server) for quantitative analysis. Under the optimized condition, detection limits of 190 pg/ml and 650 pg/ml for p24 antigen were attained in buffer and spiked human serum, respectively. Low-cost of μPACs and easy operation combined with wide coverage of mobile phones network all over the world make the proposed method a competent candidate as a diagnostic tool in resource-limited settings. Graphical abstract
| | 8 | Basis adaptive sample efficient polynomial chaos (BASE-PC)
2018-05-26 | | Publication date: 15 October 2018 Source:Journal of Computational Physics, Volume 371
Author(s): Jerrad Hampton, Alireza Doostan
For a large class of orthogonal basis functions, there has been a recent identification of expansion methods for computing accurate, stable approximations of a quantity of interest. This paper presents, within the context of uncertainty quantification, a practical implementation using basis adaptation, and coherence motivated sampling, which under assumptions has satisfying guarantees. This implementation is referred to as Basis Adaptive Sample Efficient Polynomial Chaos (BASE-PC). A key component of this is the use of anisotropic polynomial order which admits evolving global bases for approximation in an efficient manner, leading to consistently stable approximation for a practical class of smooth functionals. This fully adaptive, non-intrusive method, requires no a priori information of the solution, and has satisfying theoretical guarantees of recovery. A key contribution to stability is the use of a presented correction sampling for coherence-optimal sampling in order to improve stability and accuracy within the adaptive basis scheme. Theoretically, the method may dramatically reduce the impact of dimensionality in function approximation, and numerically the method is demonstrated to perform well on problems with dimension up to 1000.
| | 9 | Synthesis and characterization of three new Cd(II) coordination polymers with bidentate flexible ligands: Formation of 3D and 1D structures
2018-05-25 | | Publication date: 5 October 2018 Source:Journal of Molecular Structure, Volume 1169
Author(s): Mehdi Khalaj, Arash Lalegani, Jafar Akbari, Majid Ghazanfarpour-Darjani, Krzysztof Lyczko, Janusz Lipkowski
Three new coordination polymers of {[Cd(bib)3](ClO4)2}n (1), [Cd(μ2-bip)2(N3)2]n (2) and [Cd(μ-bib^{Me})Cl2]n (3) were prepared by using the neutral N-donor ligands 1,4-bis(imidazolyl)butane (bib), 1,3-bis(imidazolyl)propane (bip) and 1,4-bis(2-methylimidazolyl)butane (bib ^{ Me }) and CdX2 (X = ClO4 ^{−}, N3 ^{−} and Cl^{−}). The results of the X-ray measurements demonstrate that in the crystal structure of 1 and 2 the cadmium(II) ion adopts CdN6 octahedral geometry while, in the structure of 3, the metal ion forms CdN2Cl2 tetrahedral geometry. In compound 1, six bib ligands are coordinated to one central cadmium(II) to form an open 3D 2-fold interpenetrating framework of the α-polonium (pcu) type topology, while in compound 2 and 3 the N3 ^{−} or Cl^{−} groups are terminally bonded to the metal center and each linker compound (bip or bib ^{ Me }) acts as bridging ligand connecting two metal ions to form a one-dimensional zig-zag chain. The adjacent 1D chains of complex 2 and 3 are further extended into a non-covalent 2D network structure by CH⋯N and CH⋯Cl intermolecular hydrogen bonds, respectively. The complexes were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. Graphical abstract
| | 10 | Compression of multiple 3D color scenes with experimental recording and reconstruction
2018-05-25 | | Publication date: November 2018 Source:Optics and Lasers in Engineering, Volume 110
Author(s): Sorayda Trejos, John Fredy Barrera Ramirez, Alejandro Velez Zea, Myrian Tebaldi, Roberto Torroba
We present for the first time a method for compression of 3D color scenes with experimental recording and reconstruction, including scene multiplexing. An experimental setup allows separately registering three off-axis Fourier holograms corresponding to the RGB color channels of a 3D scene. Then, the optical field data contained in each hologram is extracted and their phase is retained. The phases associated to each color channel are spatially arranged to get a single phase-only optical field for the experimental full color reconstruction in another optical setup. This process is then further developed to include different 3D color scenes by multiplying the arranged phase-only optical fields corresponding to each scene by complementary binary masks. Three sampled scenes are multiplexed giving a compression in the data volume up to 97.81% in our experiments. The technique used in the context of multiplexing allows a substantial data volume reduction and the appropriate reconstruction of each color scene without cross-talk and in a single step.
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