1,721,862 research outputs found
Instantaneous reference-free crack detection based on polarization characteristics of piezoelectric materials
No full textA new methodology of guided-wave-based nondestructive testing (NDT) is developed to detect crack damage in a thin metal structure without using prior baseline data or a predetermined decision boundary. In conventional guided-wave-based techniques, damage is often identified by comparing the 'current' data obtained from a potentially damaged condition of a structure with the 'past' baseline data collected at the pristine condition of the structure. However, it has been reported that this type of pattern comparison with the baseline data can lead to increased false alarms due to its susceptibility to varying operational and environmental conditions of the structure. To develop a more robust damage diagnosis technique, a new concept of NDT is conceived so that cracks can be detected even when the system being monitored is subjected to changing operational and environmental conditions. The proposed NDT technique utilizes the polarization characteristics of the piezoelectric wafers attached on both sides of the thin metal structure. Crack formation creates Lamb wave mode conversion due to a sudden change in the thickness of the structure. Then, the proposed technique instantly detects the appearance of the crack by extracting this mode conversion from the measured Lamb waves, and the threshold value from damage classification is also obtained only from the current dataset. Numerical and experimental results are presented to demonstrate the applicability of the proposed technique to instantaneous crack detection.The authors acknowledge the support from the Korea Science
and Engineering Foundation (M20703000015-07N0300-
01510), the Korea Research Foundation (D00462, D0032), and
the US National Science Foundation (CMMI-0529208)
Synthesis and electrode properties of alpha-Fe2O3 from iron phthalocyanine
No full textThe structural evolution of Fe2O3 fine powder synthesized by thermal decomposition of iron phthalocyanine was investigated by X-ray diffraction and Raman spectroscopy. X-ray results indicate that Fe2O3 evolves above 300 degrees C. Raman spectroscopy reveals that it belongs to alpha-Fe2O3. Electrochemical measurements show that only the sample fired at 320 degrees C is of potential interest as an anode in lithium-ion cells, since it displays a recharge capacity of 570 mAh/g in the range of 0.5 to 2.5 V vs. Li. Although the capacity declines during the initial cycles, it becomes stable after ten cycles. (C) 1999 The Electrochemical Society. S1099- 0062( 98) 07- 098- 9. All rights reserved.open1115sciescopu
Improvement of electrochemical properties of LiNi0.5Mn1.5O4 spinel
No full textLiNi0.5Mn1.5O4 material with a spinel structure is prepared by a sol-gel method. The material is initially fired at 850 T and then subjected to a post-reaction annealing at 600 T in order to minimize the nickel deficiency. The elevated firing temperature produces materials with a small surface-area which is beneficial for good capacity retention. Indeed, the spinel LiNi0.5Mn1.5O4 not only shows a good cycle performance, but exhibits an excellent discharge capacity, i.e. 114 mAh g(-1) at 4.66 V plateau and 127 mAh g(-1) in total. Cyclic voltammetry and ac impedance spectroscopy are employed to characterize the reactions of lithium insertion and extraction in the LiNi0.5Mn1.5O4 electrode. Excellent electrochemical performance and low material cost make this compound an attractive cathode for advanced lithium batteries. (C) 2002 Elsevier Science B.V. All rights reserved.X1181sciescopu
Fabrication of Conducting Polymer Films Containing Gold Nanoparticles with Photo-Induced Patterning
No full textA novel Multifunctional nanocomposite (P3OT-AuNPs-CI) consisting of gold nanoparticles coated with the conducting polymer poly(3-octylthiophene) and a molecule containing the cinnamate moiety has been developed. The cinnamate moiety is well-known for its photoreactive properties; that is, it call be rendered reactive through exposure to UV irradiation. Photoreactive cross-linking of this moiety results in aggregation of the AuNPs. In this study, we Introduce a new approach to patterning the conducting polymer by making use of photoreactive gold nanoparticles. We call obtain patterned P3OT-AuNPs-CI thin films by using this fast and facile UV irradiation system. This new nanocomposite not only provides a convenient patterning technique that offers an alternative to conventional lithography for the patterning of conducting polymers, but is also expected to enable the control of the conductivity ill the fabrication of submicro- and microscale electronic devices. We Suggest that this new Multifunctional nanomaterial call be used in the manufacture of microelectronic devices and circuits, solar cells, diodes, and chemical sensors.X111514sciescopu
Understanding a time reversal process in Lamb wave propagation
No full textThis study investigates the time reversal process (TRP) of Lamb wave signals which are transmitted and received by piezoelectric transducers bonded on plate-like structures. A number of previous studies have paid attention to spatial and temporal refocusing capability of an original excitation through the TRP in highly dispersive and complex media. However, when the TRP is applied to Lamb waves in a homogeneous regular waveguide, the refocusing capability is limited due to permanent residual side bands even if the duration of the time reversed signal increases. Based on the reciprocity of elastodynamics and linear piezoelectricity, theoretical interpretation is conducted for the main and residual side bands of the reconstructed signal in the time domain. In particular, the interpretation includes the temporal effect of velocity and amplitude dispersions, the existence of multi-modes, and the reflections from boundaries during the TRP. Then, numerical and experimental tests are conducted to validate the theoretical findings of this paper. Practical issues for the successful implementation of the TRP of Lamb waves are briefly addressed as well. (C) 2009 Elsevier B.V. All rights reserved.This work was supported by Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research
Promotion Fund) (KRF-2008-331-D00590), in which main calculations were performed by using the supercomputing
resource of the Korea Institute of Science and Technology Information (KISTI), and the Radiation Technology Program under
Korea Science and Engineering Foundation (KOSEF) and the Ministry of Science and Technology (M20703000015-07N0300-
01510). The second author would like to acknowledge the graduate fellowship program from Samsung Scholarship in Seoul,
Korea
Continuous fatigue crack monitoring without baseline data
No full textIn order to overcome the susceptibility of conventional non-destructive testing (NDT) techniques to operational and environmental variations, a new damage detection technique that does not require direct comparison with baseline data was previously developed by the authors for detecting a crack in a plate structure. This reference-free technique employs two pairs of collocated lead zirconate titanate transducers (PZTs) placed on both sides of the plate to generate and measure Lamb waves. Then, the existence of mode conversion due to the crack is identified from the Lamb wave signals instantly measured by PZTs. In this study, the effectiveness of the proposed technique is tested using a steel girder specimen. A cyclic loading is applied to the girder resulting in fatigue cracks, and the proposed technique detects the appearance of fatigue damage solely based on the measured Lamb waves at the present stage. Experimental results are presented to demonstrate the applicability of the proposed technique to fatigue crack monitoring, and issues related to PZT installation are discussed.This research is supported by the Radiation Technology
Program under Korea Science and Engineering Foundation
(KOSEF) and the Ministry of Science and Technology
(M20703000015-07N0300-01510) andKorea Research
Foundation Grant funded by the Korean Government
(MOEHRD, Basic Research Promotion Fund)
(KRF-2007-331-D00462). Any opinions, findings and
conclusions or recommendations expressed in this material
are those of the author(s) and do not necessarily reflect
the views of the funding agencies. The authors also
would like to thank Professors Kent A. Harris and Piervincenzo
Rizzo at University of Pittsburgh for designing
the steel girder specimen and conducting fatigue loading
tests
New approach to generalized two-dimensional correlation spectroscopy. II: Eigenvalue manipulation transformation (EMT) for noise suppression
No full textThis paper introduces the concept of eigenvalue manipulating transformation (EMT) of a data matrix for noise suppression in two-dimensional (2D) correlation spectroscopy. The FT-IR spectra of a polystyrene/methyl ethyl ketone/toluene solution mixture during the solvent evaporation process, to which were added a substantial amount of artificial noise, have been analyzed. By uniformly raising the power of a set of eigenvalues, the major eigenvalues become more prominent. As a consequence, minor eigenvectors representing the noise component are no longer strongly represented in the reconstructed data. This EMT operation is similar to the simple truncation of noise-dominated minor factors practiced in standard principal component analysis (PCA), as demonstrated in our preceding paper on PCA-2D correlation spectroscopy. The effect of this new EMT scheme is more gradual, with attractive flexibility to continuously fine-tune the balance between the desired noise reduction effect and the retention of pertinent spectral information.open1135sciescopu
New approach to generalized two-dimensional correlation spectroscopy. III: Eigenvalue (EMT) for spectral selectivity manipulation transformation enhancement
No full textThis paper demonstrates the potential of eigenvalue manipulating transformation (EMT) of a data matrix for spectral selectivity enhancement, especially useful in 2D correlation analysis. The EMT operation aims at the accentuation of select features of the information content of the original data matrix. For example, by uniformly lowering the power of a set of eigenvalues associated with the original data, the smaller eigenvalues become more prominent and the contributions of secondary loadings become amplified. As a direct consequence of the minor factor accentuation by such EMT operations, 2D correlation spectra gain much stronger discriminating power. The selectivity enhancement effect of such manipulation of eigenvalues is much more noticeable on the synchronous 2D correlation spectrum. This improvement for the spectral selectivity of synchronous 2D correlation spectra is potentially very important, as we usually put more emphasis on the interpretation of asynchronous 2D spectra in 2D correlation analysis due to overlaps of synchronous peaks. Such EMT operations tend to exaggerate the information content of minor PCs and reduce that of major PCs. Thus, much more subtle difference of spectral behavior for each component is now highlighted. Surprisingly, asynchronous 2D correlation spectra are found to be much less sensitive to such EMT operations. The result indicates that the distinction of different band responses has already been accomplished effectively by the original asynchronous 2D correlation analysis.open1125sciescopu
RAMAN-SPECTRA OF (LIRBSO4)-LI-6 AND (LIRBSO4)-LI-7
No full textThe polarized Raman spectra of single-crystal (LiRbSO4)-Li-6 and (LiRbSO4)-Li-7 at room temperature are reported. On the basis of these data, symmetry-based band assignments are given for both internal and external optic modes. The translational optic modes of the lithium ion appear in the region between 444 and 364 cm-1. Vibrational coupling interactions are noted between the sulfate ion nu2 and the lithium translational optic modes in the same irreducible representation. Coupling interactions are negligible or small in (LiRbSO4)Li-7, while in (LiRbSO4)-Li-6 the lithium isotope effect shifts the lithium translational modes into more coupling interaction with the sulfate ion nu2 modes.open113sciescopu
Characterization of Raman spectra of size-selected TiO2 nanoparticles by two-dimensional correlation spectroscopy
No full textX1139sciescopuskc
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