共查询到20条相似文献,搜索用时 0 毫秒
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《Infrared Physics & Technology》2002,43(3-5):211-218
This paper describes several experimental investigations of newly developed thermographic NDT techniques based on the transient temperature measurements. Several experimental results of the pulse heating thermographic NDT and the lock-in thermographic NDT are shown. 相似文献
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Detectable defect depth by pulse phase thermography (PPT) is reportedly improved when using phase at low frequency. This study was conducted to identify mechanisms detecting deeper defects by the PPT, and to determine the optimum frequencies for detecting defects with various depths and sizes. One-dimensional and finite element analyses reveal that the optimum frequency decreases continuously with increasing defect depth, and that the amplitude of noise appearing in phase data decreases with decreased frequency. These engender a large signal-to-noise ratio for deep defects in a lower-frequency range. The analytical results were verified by experiments for a polymethylmethacrylate specimen having artificial defects. The experimental results at the optimum frequency demonstrated that defects with up to 5–6 mm depth were detected, which is a significant improvement compared with the reported detectable defect depth of 3.5 mm. 相似文献
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The decay time τ of an optical resonator depends on the special type of resonator (active, passive, homogeneous, inhomogeneous). Starting from a general expression for decay times, some special cases are derived and discussed in detail. It is shown, that the commonly used formulars give only lower or upper limits. These various relations are relevant for high gain laser with low reflectivities. 相似文献
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Iu. Gudyma A. Maksymov C. Enachescu 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(2):167-172
We here focus on the effect of a transition from metastable
high-spin to stable low-spin states in spin-crossover compounds in
contact with heat bath as external realistic (colored) noises.
The systems are described by the way of stochastic methods
using a phenomenological model of photoexcitation and relaxation
in spin-crossover compounds. It is shown that such transitions can
be controlled by a parameter that governs relaxation flow,
intensity of light and noise intensity. 相似文献
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Ralf W. Arndt 《Infrared Physics & Technology》2010,53(4):246-253
A methodical approach for qualitative and quantitative non-destructive testing of near-surface structures in civil engineering (CE) with active thermography is presented. It adopts the non-destructive testing (NDT) method of pulsed phase thermography (PPT) for the special requirements of CE and cultural heritage. The concept might be understood as a square pulse thermography (SPT) in frequency domain or an amplitude-expanded PPT with square pulse heating.After a discussion of the material spanning concept and qualitative results in cultural heritage a new approach for quantitative non-destructive testing (NDT) of near-surface structures in CE with active thermography is introduced and tested by investigations on concrete specimen with artificial defects. It is based on the thermal diffusivity of the material and the characteristic frequency of the first extrema of phase and amplitude contrast and aims at complementing the established approaches for defect depth calculation for measurements with long heating and observation times. It should be easily extendable to other fields of application. 相似文献
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对利用时域多分辨分析(MRTD)方法计算电磁脉冲(EMP)与细线耦合的问题进行了研究。将传统Holland细线算法应用到时域多分辨分析当中,推导出了MRTD方法中对细线结构处理的一种算法,并给出了具体的计算步骤和相关参数的选取方法。计算表明,采用MRTD方法计算细线问题,可以取较大的空间步长,一般可以取到最短工作波长的1/4左右,有效地节约了计算资源;MRTD方法也可以较方便地处理细线位于大地附近的情况,为计算地面铺设较长细线的EMP耦合提供了一种途径。 相似文献
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V. A. Drozdov D. O. Eremenko O. V. Fotina S. Yu. Platonov O. A. Yuminov 《Physics of Atomic Nuclei》2003,66(9):1628-1630
The unified energy dependence of the induced fission times obtained by the crystal blocking technique for heavy nuclei with Z=91–94 in the range of initial excitation energy from 5 to 250 MeV was analyzed. It was demonstrated that, for excitation energies of the investigated heavy fissionable nuclei up to 60–70 MeV, the fission times can be described in the framework of the statistical theory of nuclear reactions taking into account the double-humped structure of the fission barrier and the lifetimes of both classes of excited nuclear states realized in the first and second potential wells. However, for excitation energies above 70 MeV, there is a need to consider the dynamical effects in the fission channel. 相似文献
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Zhi Zeng Jing Zhou Ning Tao Lichun Feng Cunlin Zhang 《Infrared Physics & Technology》2012,55(2-3):200-204
Several methods have been reported in the literature using pulsed thermography for quantitative measurement of defect depth or sample thickness. In this paper, based on the analysis of a theoretical one-dimensional solution of pulsed thermography, we proposed to use the absolute peak slope time (APST) for quantitative measurement of defect depth. APST is the peak slope time of the curve which is obtained by multiplying the original temperature decay with the square root of the corresponding time. The theoretical model shows that APST has linear relation with square of defect depth, which was verified with the experimental results of an aluminum and a steel specimen with six flat-bottom wedges and holes as simulated defects respectively. 相似文献
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Applying multi-electrode-pair pulse TEA CO2 laser to one optical resonance cavity will have several advantages over traditional method, including higher gain, shorter pulse discharge time interval, and in particular, continuous adjustable time interval of multi-pulse laser output can be achieved without high vacuum condition. To improve laser's working stabilization, we proposed new approaches to optimize laser structure design and discharge pulse time interval selection. 相似文献
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A detailed analysis of the population of the N2 vibrational states for the N2 (C
3
II
u,X
1
g
+
) electronic states has been carried out. Quantitative spectral and microwave measurements of vibrational temperatures and electron densities were performed for 2400 MHz non-isothermic pulsed discharges in flowing nitrogen at pressures (60–2700) Pa. From the time dependent peak intensities of the second positive system of N2, the temperature of neutral gas during the h.f. pulses has been determined. 相似文献
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