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61.
Continuous online monitoring of rotating machines is necessary to assess real-time health conditions so as to enable early detection of operation problems and thus reduce the possibility of downtime. Rolling element bearings are crucial parts of many machines and there has been an increasing demand to find effective and reliable health monitoring technique and advanced signal processing to detect and diagnose the size and location of incipient defects. Condition monitoring of rolling element bearings, comprises four main stages which are, statistical analysis, fault diagnostics, defect size calculation, and prognostics. In this paper the effect of defect size, operating speed, and loading conditions on statistical parameters of acoustic emission (AE) signals, using design of experiment method (DOE), have been investigated to select the most sensitive parameters for diagnosing incipient faults and defect growth on rolling element bearings. A modified and effective signal processing algorithm is designed to diagnose localized defects on rolling element bearings components under different operating speeds, loadings, and defect sizes. The algorithm is based on optimizing the ratio of Kurtosis and Shannon entropy to obtain the optimal band pass filter utilizing wavelet packet transform (WPT) and envelope detection. Results show the superiority of the developed algorithm and its effectiveness in extracting bearing characteristic frequencies from the raw acoustic emission signals masked by background noise under different operating conditions. To experimentally measure the defect size on rolling element bearings using acoustic emission technique, the proposed method along with spectrum of squared Hilbert transform are performed under different rotating speeds, loading conditions, and defect sizes to measure the time difference between the double AE impulses. Measurement results show the power of the proposed method for experimentally measuring size of different fault shapes using acoustic emission signals. 相似文献
62.
Iron Oxide Supported on Al2O3 Catalyst for Methane Decomposition Reaction: Effect of MgO Additive and Calcination Temperature 下载免费PDF全文
Ahmed S. Al‐Fatesh Anis H. Fakeeha Ahmed A. Ibrahim Wasim U. Khan H. Atia R. Eckelt Biswajit Chowdhury 《中国化学会会志》2016,63(2):205-212
Production of hydrogen is a challenging task and have significant impact in the recent scenario. The alumina supported iron oxide nanoparticle synthesized using non‐ionic surfactant Triton‐X was found very effective for steady production of hydrogen through methane decomposition reaction. The high surface area, easily reducible catalyst calcined at 500 °C and 800 °C temperature showed steady activity towards methane decomposition reaction. At a higher reaction temperature there was catalyst deactivation. The doping of MgO facilitated particle growth rendering the poor catalytic activity. The TPR study showed that reducibility of TPR was difficult in presence of MgO additive. The formation of Fe? Mg? Al solid solution confirmed by XRD study was found mainly responsible for the lower catalytic activity. The bamboo‐shaped carbon nanotube formed from 20 % Fe/Al2O3 catalyst which is mainly because of the poor wetting property of quasi‐liquid metal and carbon nanotube. 相似文献
63.
A method has been described for the determination of iron from fish otoliths containing high levels of calcium by collision cell technology (CCT) ICP-MS. Iron (Fe) in otolith solutions was quantitatively coprecipitated with small amounts of calcium hydroxide by adding 1.0 M sodium hydroxide solution. The performance of CCT-ICP-MS pressurized with He/H(2) cell gas was investigated on the elimination of Ca-based spectral interferences at m/z 54, 56 and 57. Molecular ion interferences at m/z 54 and 56 were reduced by 2 orders of magnitude. However, the interferences at m/z 57 increased by the same amount in the presence of Ca in solutions owing to the formation of (40)Ca(16) OH(+) through reactions with H(2) in collision cell, indicating that (57)Fe was not suitable for the determination of Fe from otoliths. Results for (56)Fe suffered significantly from interferences of Ca-based molecular ions when the Ca concentration in solution exceeded 100 microg ml(-1), for which matrix-matched calibration was required for accurate determination. CCT with the aid of He/H(2) cell gas proved to be very effective in eliminating the interferences ((40)Ar(14)N(+) and (40)Ca(14)N(+)) at m/z 54. Presence of Ca up to 300 microg ml(-1) had virtually no effect on the ion signals of (54)Fe, which with low background signals, afforded accurate determination of Fe from otoliths by using aqueous external standards. 相似文献
64.
We introduce regular expression constrained sequence alignment as the problem of finding the maximum alignment score between given strings and over all alignments such that in these alignments there exists a segment where some substring of is aligned to some substring of , and both and match a given regular expression R, i.e. where is the regular language described by R. For complexity results we assume, without loss of generality, that . A motivation for the problem is that protein sequences can be aligned in a way that known motifs guide the alignments. We present an time algorithm for the regular expression constrained sequence alignment problem where , and t is the number of states of a nondeterministic finite automaton N that accepts . We use in our algorithm a nondeterministic weighted finite automaton M that we construct from N. M has states where the transition-weights are obtained from the given costs of edit operations, and state-weights correspond to optimum alignment scores we compute using the underlying dynamic programming solution for sequence alignment. If we are given a deterministic finite automaton D accepting with states then our construction creates a deterministic finite automaton with states. In this case, our algorithm takes time. Using results in faster computation than using M when . If we only want to compute the optimum score, the space required by our algorithm is ( if we use a given ). If we also want to compute an optimal alignment then our algorithm uses space ( space if we use a given ) where and are substrings of and , respectively, , and and are aligned together in the optimal alignment that we construct. We also show that our method generalizes for the case of the problem with affine gap penalties, and for finding optimal regular expression constrained local sequence alignments. 相似文献
65.
66.
Four new Hofmann–3-phenylpropylamine (3PPA) type complexes with chemical formulae M(3PPA)2Ni(CN)4 (M = Ni, Co, Cd, and Pd) have been prepared and their vibrational spectra are reported in the region of 4000–60 cm−1. The vibrational bands arising from 3PPA ligand molecule, the polymeric sheet and metal–ligand bands of the compounds are assigned. The thermal behaviour of these complexes is also provided using the DTA and TGA along with the magnetic susceptibility data. The results indicate that the monodentate 3PPA ligand molecule bonds to the metal atom of |M–Ni(CN)4|∞ polymeric layers and hence the compounds are similar in structure to Hofmann-type complexes. 相似文献
67.
Farhat Waqar Saida Jan Bashir Mohammad Muhammad Hakim Shah Alam Wasim Yawar 《中国化学会会志》2009,56(2):335-340
An analytical method has been developed for the preconcentration of rare earth elements (REEs) in seawater for their determination by inductively coupled plasma optical emission spectrometry (ICP‐OES). An indigenously synthesized chelating resin was used for the preconcentration of (REEs) which was based on immobilization of fluorinated β‐diketone group on solid support styrene divinyl benzene. Sample solutions (adjusted to optimized pH) were passed through a polyethylene column packed with 250 mg of the resin. Experimental conditions consisting of pH, sample flow rate, sample volume and eluent concentration were optimized. The established method has been applied for the preconcentration of light, medium and heavy REEs in coastal sea water samples for their subsequent determination by (ICP‐OES). Percentage recoveries of La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb and Lu were ≥ 95%, a preconcentration factor of 200 times, and relative standard deviations < 5% were achieved. 相似文献
68.
Khalida Inayat Noor Mohammad Arif Wasim Ul-Haq 《Applied mathematics and computation》2009,215(2):629-635
In this paper, we define and study some subclasses of analytic functions by using fractional derivative operator. Some interesting properties, coefficients problems and inclusion results of these classes are investigated. It is also shown that these classes are closed under convolution with convex functions and some applications are given. 相似文献
69.
An analytical model is developed to analyze stresses in functionally graded (FGM) curved bars under pure bending. Both elastic and partially plastic stress states are considered. The modulus of elasticity of the bar material is allowed to vary. While the model is outlined, important findings are mentioned. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
70.
Khayat S Hötzl H Geyer S Ali W Knöller K Strauch G 《Isotopes in environmental and health studies》2006,42(3):289-302
Sulphate and chloride concentrations in the shallow Pleistocene aquifer systems in the lower Jordan valley area indicate a general trend of increasing salinity eastward and southward. This study was conducted in one of the important sub-basins feeding the Pleo-Pleistocene aquifer in the Jericho area in the southern part of the valley using S and O isotopes of dissolved sulphate. The results show that sulphate has mainly two contributions to the groundwater. One is the surface seepage, which is present as a salty leachate form with the positive delta34Ssulphate values of primary gypsum in Lisan and Samara formations, and the second is the upwelling saline water which was in contact with a deep secondary gypsum, aragonites and salty rocks and rose up under heavy abstraction with depleted 34S in sulphate and relatively high sulphate and chloride content. The latest was clearly shown in the Arab Project wells to the east that is undergoing a continuous heavy abstraction. The isotopic signatures of S and O in these wells to the east show that this depleted 34S and highly concentrated sulphate might also indicate a dissolved sulphate originating from pyrite oxidation that results from the interaction with a pyrite-rich aquifer, which can well up with salty water under heavy abstraction and is oxidised in the upper aerobic shallow aquifer. 相似文献