Search

The aim of this study was to examine the health diagnosis classification method of quadcopter structures with different mixed faults. The loosening of the motor mount, damage to the propeller, and the loosening of the arm mount were the main fault conditions investigated. Data were first acquired under non-fault conditions and the conditions of the three types of fault. Then, the features of the vibration and pulse width modulation signals were extracted by root mean square, standard deviation, and sample entropy. Moreover, the features of the audio signal were extracted by wavelet scattering, which contains time-frequency domain information that provides significant power for classification. In this paper, we propose a simple machine learning method, based on the k-Nearest Neighbor (kNN), not only for classification but also demonstrating the efficacy of the features. To test the limits of accuracy, different configurations of kNN parameters are deployed, in addition to the features. In summary, as a result of the highly efficacious features, despite mixed fault conditions, the accuracy reached 90.73%. This method improves the accuracy of mixed faults’ classification and maintains a certain level of classification effectiveness.

Single-walled carbon nanotubes (SWNTs) exhibit high surface areas and precisely defined pores, making them potentially useful materials for gas adsorption and purification. A thorough understanding of the interactions between adsorbates and SWNTs is therefore critical to predicting adsorption isotherms and selectivities. Metallic (M-) and semiconducting (S-) SWNTs have extremely different polarizabilities that might be expected to significantly affect the adsorption energies of molecules. We experimentally and theoretically show that this expectation is contradicted, for both a long chain molecule (n-heptane) and atoms (Ar, Kr, and Xe). Temperature-programmed desorption experiments are combined with van der Waals corrected density functional theory, examining adsorption on interior and exterior sites of the SWNTs. Our calculations show a clear dependence of the adsorption energy on nanotube diameter but not on whether the tubes are conducting or insulating. We find no significant experimental or theoretical difference in adsorption energies for molecules adsorbed on M- and S-SWNTs having the same diameter. Hence, we conclude that the differences in polarizabilities between M- and S-SWNTs have a negligible influence on gas adsorption for spherical molecules as well as for highly anisotropic molecules such as n-heptane. We expect this conclusion to apply to all types of adsorbed molecules where van der Waals interactions govern the molecular interaction with the SWNT. [ABSTRACT FROM AUTHOR]

The differences in the polarizabilities of metallic (M) and semiconducting (S) single-walled carbon nanotubes (SWNTs) might give rise to differences in adsorption potentials. We show from experiments and van der Waals—corrected density functional theory that the binding energies of Xe adsorbed on M- and S-SWNTs are nearly identical. Temperature programed desorption experiments of Xe on purified M- and S-SWNTs give similar peak temperatures, indicating that desorption kinetics and binding energies are independent of the type of SWNT. Binding energies computed from vdW-corrected density functional theory are in good agreement with experiments. [ABSTRACT FROM AUTHOR]

Fifteen different low molar mass compounds are assessed as CO2solvents based on bubble-point loci on the solvent-rich end (0.6 to 1.0 solvent wt fraction) of the CO2-solvent pressure−composition diagram at 298.15 K. Four of the five best solvents (in descending order of solvent strength on a mass fraction CO2dissolved basis), acetone, methyl acetate, 1,4-dioxane, and 2-methoxyethyl acetate, are oxygen-rich, low molar mass species possessing one or more oxygen atoms in carbonyl, ether, and/or acetate groups that can interact favorably with CO2via Lewis acid/Lewis base interactions. Methanol, a very low molar mass solvent, is comparable to 1,4-dioxane in solvent strength. The remaining solvents, in descending order of solvent strength on a mass basis, include 2-nitropropane, N,N-dimethylacetamide, acetylacetone, 1-nitropropane, iso-octane, 2-(2-butoxyethoxy)ethyl acetate, N-formylmorpholine, propylene carbonate, 2-butoxyethyl acetate, and N-tert-butylformamide. When compared on a molar basis, each of the six best CO2solvents, 2-(2-butoxyethoxy)ethyl acetate, methyl acetate, 2-methoxyethyl acetate, 1,4-dioxane, acetone, and acetyl acetone, is rich in CO2-philic ether or carbonyl oxygen atoms. Methanol, which possesses a CO2-phobic hydroxyl group, is the worst CO2solvent. COSMOtherm accurately predicted the relative solvent strengths of eight of the solvents that contain carbonyl, acetate, ether, and carbonate groups. However, COSMOtherm was not able to predict the correct ordering of solvents possessing hydroxyl, nitro-, amide, secondary amine, and tertiary amine groups. This important failure of the COSMOtherm approach for these molecules is apparently due to problems with the COSMO-RS parametrization. [ABSTRACT FROM AUTHOR]

Among all the 4478 classical isomers of C66, C66( C s:0060) with the lowest number of pentagon–pentagon fusions was predicted to be the most stable isomer, followed by isomers C66( C2 v:0011) and C66( C2:0083). The infrared spectra and aromaticity of the most stable isomers were predicted. The relative stabilities of C66 isomers change with charges or doping of metals. The structures and relative stabilities of the most stable metallofullerenes were delineated and compared with experiment. Sc2@C66( C2:0083) was predicted to be the most stable metallofullerene, although Sc2@C66( C2 v:0011) was observed. Charge-transfer from Sc2 to the fused pentagons and the bonding between these two moieties significantly decrease the strain energies caused by the pair of fused pentagons thereby stabilizing the fullerene cage. [ABSTRACT FROM AUTHOR]

The 3465 classical isomers of C64 fullerene have been investigated by quantum chemical methods PM3, and the most stable isomers have been refined with HCTH/3-21G//SVWN/STO-3G, B3LYP/6-31G(d)//HCTH/3-21G, and B3LYP/6-311G(d)//B3LYP/6-31G(d) level. C64(D2:0003) with the lowest e55 (e55 = 2), the number of pentagon-pentagon fusions, is predicted to be the most stable isomer and it is followed by the C64(Cs:0077) and C64(C2:0103) isomers within relative energy of 20.0 kcal/mol. C64(D2:0003) prevails in a wide temperature range according to energy analysis with entropy contribution at B3LYP/6-31G(d) level. The simulated IR spectra and electronic spectra help to identify different fullerene isomers. All the hexagons in the isomers with e55 = 2 display local aromaticity. The relative stabilities of C64 isomers change with charging in ionic states. Doping also affects the relative stabilities of fullerene isomers as demonstrated by Sc2@C64(D2:0003) and Sc2@C64(Cs:0077). The bonding of Sc atoms with C64 elongates the C&bond;C bond of two adjacent pentagons and enhances the local aromaticity of the fullerene cages. Charging, doping, and derativization can be utilized to isolate C64 isomers through differentiating the electronic and steric effects. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [ABSTRACT FROM AUTHOR]

The 2385 classical isomers and four nonclassical isomers of fullerene C62have been studied by PM3, HCTH/3-21G//SVWN/STO-3G, B3LYP/6-31G(d)//HCTH/3-21G, and B3LYP/6-31G(d)//B3LYP/6-31G(d). The Cs:7mbrisomer, with a chain of four adjacent pentagons surrounding a heptagon, is predicted to be the most stable isomer, followed by C2v:4mbrwhich is 3.15 kcal/mol higher in energy. C2:0032 with three pairs of adjacent pentagons is the most stable isomer in the classical framework. To clarify the relative stabilities of C62isomers at high temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP/6-31G(d) level. Analyses reveal that Cs:7mbrprevails in a wide temperature range. The vibrational frequencies of the five most stable C62fullerene isomers are also predicted at the B3LYP/6-31G(d) level, and the simulated IR spectra show important differences in positions and intensities of the vibrational modes for different isomers. The nucleus-independent chemical shift and the density of states of the three most stable isomers show that the square in C2v:4mbrand the adjacent pentagons in Cs:7mbrand C2:0032 possess high chemical reactivity. In addition, the electronic spectra and second-order hyperpolarizabilities are determined by means of ZINDO and the sum-over-states mode. The intensity-dependent refractive index (−; , , −) at 2.3305 eV of Cs:7mbris very large because of resonance with the external field. The second-order hyperpolarizabilities of the five most stable isomers of C62are predicted to be larger than those of C60. [ABSTRACT FROM AUTHOR]

Stimulated by recent preparation and characterization of the first C58F18fullerene derivative, with a heptagon in the framework (Science, 2005, 309, 278), we have performed systematic density functional studies on the stabilities and electronic properties of two different structures C58X18(A) and C58X18(B), where X H, F, and Cl. The large energy gaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (between 2.64 and 3.45 eV) and the aromatic character (with nucleus independent chemical shifts from −10.0 to −13.9 ppm) of C58X18(A) and C58X18(B) indicate that they possess high stabilities. Further investigations show that the heats of formation of C58X18fullerene derivatives are highly exothermic, suggesting that adding nine X2's releases much of the strain of pure C58fullerene and leads to stabilities of the derivatives. Lower in energy and stronger in aromatic character than C58F18(B), which has been experimentally characterized, C58F18(A) should also be isolated. In addition, C58F18and C58Cl18are predicted to possess large electron affinities, especially for C58F18(B) and C58Cl18(B) with values of 3.00 and 3.06 eV, respectively, even larger than that (2.50 eV) of C60F18. Hence, C58F18and C58Cl18can serve as good electron-acceptors with possible photonic/photovoltaic application. The IR spectra of C58X18are simulated to facilitate identification of different isomers experimentally. In addition, the electronic spectra and second-order hyperpolarizabilities of C58X18are predicted by ZINDO and sum-over-states model. With the addition of 9X2, both the static and frequency-dependent second-order hyperopolarizabilities of C58X18greatly decrease compared to those of C58. [ABSTRACT FROM AUTHOR]

Among all the 4478 classical isomers of C66, C66( C s:0060) with the lowest number of pentagon–pentagon fusions was predicted to be the most stable isomer, followed by isomers C66( C2 v:0011) and C66( C2:0083). The infrared spectra and aromaticity of the most stable isomers were predicted. The relative stabilities of C66 isomers change with charges or doping of metals. The structures and relative stabilities of the most stable metallofullerenes were delineated and compared with experiment. Sc2@C66( C2:0083) was predicted to be the most stable metallofullerene, although Sc2@C66( C2 v:0011) was observed. Charge-transfer from Sc2 to the fused pentagons and the bonding between these two moieties significantly decrease the strain energies caused by the pair of fused pentagons thereby stabilizing the fullerene cage. [ABSTRACT FROM AUTHOR]

The plants of the Trigonostemon sp. genus(Euphorbiaceae family) comprising about 50 species worldwide are mainly distributed in tropical and subtropical Asia, 10 species of which can be found in southern of China. Phytochemical studies on the plants in the genus have demonstrated a large amount of terpenoids and alkaloids. Modern pharmacological studies have demonstrated cytotoxicity, antivirus, antibacterial, anti-inflammation and other pharmacological activities. In this paper, chemical compositions and biological activities of Trigonostemon genus at home and abroad over the past decade were summarized, in order to provide scientific basis for the further development and utilization of Trigonostemon plants.