Single Beam Interferometry of a Thermal Bump: II—Theory

Kuo and Munidasa [1] have reported a method by which a time-dependent optical intensity pattern is produced by the interference of laser light diffracted from a thermally induced bump with the light of the same laser reflected from the plane of the sample on which the bump was induced. In their experiment the thermal bump was induced by a second laser beam which was optically incoherent with the interfering light, but which was intensity modulated at frequencies ranging from the audio to the ultrasonic range. The resulting time-dependent patterns carry information about the thermal and elastic properties of the sample. The purpose of this work is to provide a first-principles calculation of those patterns so that those material properties can be measured with this technique. The starting point of the calculation is the solution to the coupled thermoelastic equations developed by Favro et al. [2–4]. That solution is expressed in terms of the three eigenmodes of the coupled equations: (1) a longitudinal acoustic wave consisting of propagating particle displacements and associated temperature variations arising from the compression and rarefaction of the material; (2) a transverse (shear) wave which consists only of propagating particle displacements and which does not cause any temperature variation as it propagates; and (3) a heavily-damped thermal wave which consists of propagating temperature variations and associated particle displacements arising from the thermal expansion it causes. The combination of surface displacements (i.e. “thermal bump”) resulting from these three kinds of waves when a modulated laser beam is incident on the surface of an opaque solid can be calculated in a straight forward fashion from expressions given in [4]

Parallel Vector Lock-In Thermal Wave IR Video Imaging of Microcracks in Cu Foils Deposited on Polyimide

Recently, the concept of area-wide lock-in detection in infrared video imaging and its application to thermal wave imaging was demonstrated.[1] This technique combines the lock-in detection method with an IR video camera and almost real-time digital image processing to form a parallel vector lock-in thermal wave IR video imaging system. In this method each pixel of an image is processed in the manner similar to the lock-in detection method while the sample is excited (heated) synchronously with a square-wave modulated joule heating. The synchronous detection allows the non-synchronous background radiation to be subtracted from the signal resulting in an enhanced signal-to-noise ratio, thus allowing the signal of interest to be measured even in situations where it is completely masked by noise. The advantage of IR detection (8–12 µm) and high speed data acquisition combined with the area-wide lock-in detection makes this a unique thermal wave imaging technique for non-destructive evaluation. In this paper we report the application of this lock-in thermal wave IR video imaging technique using ac Joule heating to the imaging of microcracks in Cu foils deposited on polyimide substrates. Comparison of the lock-in video images of good and faulty samples are presented

Thermal Wave Imaging of Aircraft Stuructures

In a previous report [1], we introduced the application of thermal wave imaging to adhesion disbonds and corrosion in aircraft. In the present paper, we describe the application of pulse-echo thermal wave imaging to NDT of aging aircraft. The technique uses high-power photographic flash lamps as a heat source and an IR video camera as a detector. The flash lamps launch pulses of heat into the skin of the aircraft and the IR camera images the returning thermal wave reflections from subsurface defects. The system also includes electronic hardware and software for carrying out the time-gated imaging and real time analysis of the defects. It also has the ability to image large areas in short times. The current inspection speed enables the imaging of over 90 feet of a 16″ strip of aircraft per hour. Here we present some examples of airframe defects, both for metal and composite structures

Response of Laser-Induced Thermal Lens Effect at Solid Surface

Recently Kuo et al. [1,2] and Satio et al.[3] presented the surface-thermal lens (STL) technique, this novel photothermal deformation technique has attracted great attention because it is a highly sensitive, noncontact and nondestructive measurement[4–6]. In this technique, a modulated pump beam is focused on the sample surface to produce the surface deformation and a cw probe beam is incident at the deformation region. Differing from the conventional photothermal deformation techniques, the spot size of the probe beam at the sample surface is much larger than the pump beam one. Then the probe beam reflected from the surface produces a diffraction pattern at the detection plane. More recently, STL technique has been successfully applied to study the temperature dependence of the thermal conductivity of semiconductor materials[5], weak absorption of optical thin films[6] and characterization of the solid materials[7,8]. However, the mechanism of STL phenomena has not been completely understood. Most theoretical models took no account of the influence of the air-thermal lens (ATL), although some experiment showed that the air significantly affected the detected diffraction pattern[2]. In addition, it is necessary to characterize frequency responses of signals because the response is used to determine the thermal property of the solid materials[5]

Digital sculpting for historical representation: Neville tomb case study

Despite digital 3-D polygon modelling applications providing a common and powerful tool-set for archaeological, architectural and historical visualisation over recent years, the relatively recent developments in high-resolution sculpting software allow for the possibility to create digital outcomes with a degree of surface fidelity not previously obtainable from the more widely used poly-modelling software packages. Such digital sculpting applications are more commonly applied within the video games and TV/motion picture industries, the intention of this paper is to show how such tools and methodologies together with existing scanned data and some historical knowledge can remediate and re-imagine lost sculptural form. The intended research will focus on an examination and partial re-construction of the tomb of Sir John Neville, 3rd Baron Raby located at Durham Cathedral, County Durham UK

Wide-Area Impact Damage Evaluation with Sonic Infrared Imaging NDE in Advanced Composite Structures

Abstract Sonic Infrared (IR) imaging is a relatively new member in the NDE technology family. This method combines a short pulse of ultrasound excitation, typically a fraction of a second, and infrared imaging. It has been shown its great advantage as a NDE technology to detect defects such as cracks in metal/metal alloy structures. As an imaging technology, Sonic IR is capable of wide area evaluation. Composite materials have been used in broader applications due to its light weight and stiffness. However, composites suffer more to impact than metal structures. Such damage in composites may not present at the surface but severe damage could have occurred in deeper layers. In such case, the structure strength is greatly weakened. We have been studying impact damages in composite structures with Sonic Infrared Imaging, and evaluating how structures affect thermal signatures in defect characterization. In this paper, we will present our study on composite panels containing structures such as doublers and beams or stiffeners, which were subjected to impacts from varying energy projectiles

Broad-line region in NGC 4151 monitored by two decades of reverberation mapping campaigns. I. Evolution of structure and kinematics

We report the results of long-term reverberation mapping (RM) campaigns of the nearby active galactic nuclei (AGN) NGC 4151, spanning from 1994 to 2022, based on archived observations of the FAST Spectrograph Publicly Archived Programs and our new observations with the 2.3m telescope at the Wyoming Infrared Observatory. We reduce and calibrate all the spectra in a consistent way, and derive light curves of the broad H$\beta$ line and 5100\,{\AA} continuum. Continuum light curves are also constructed using public archival photometric data to increase sampling cadences. We subtract the host galaxy contamination using {\it HST} imaging to correct fluxes of the calibrated light curves. Utilizing the long-term archival photometric data, we complete the absolute flux-calibration of the AGN continuum. We find that the H$\beta$ time delays are correlated with the 5100\,{\AA} luminosities as $\tau_{\rm H\beta}\propto L_{5100}^{0.46\pm0.16}$. This is remarkably consistent with Bentz et al. (2013)'s global size-luminosity relationship of AGNs. Moreover, the data sets for five of the seasons allow us to obtain the velocity-resolved delays of the H$\beta$ line, showing diverse structures (outflows, inflows and disks). Combining our results with previous independent measurements, we find the measured dynamics of the H$\beta$ broad-line region (BLR) are possibly related to the long-term trend of the luminosity. There is also a possible additional $\sim$1.86 years time lag between the variation in BLR radius and luminosity. These results suggest that dynamical changes in the BLR may be driven by the effects of radiation pressure.Comment: Accepted for publication in MNRAS; comments welcome

Tourists' consumption and interpretation of sport event imagery

In an era when popular and mass cultures are positioned further up the symbolic hierarchy, sport events are deemed by cities to be a valuable image or branding tools. Event strategies are often justified by their envisaged image effects and the celebrities, iconic structures and media exposure associated with sport events means that they are viewed as being particularly effective for this purpose. This paper evaluates the image effects of strategies deployed by three English cities; Birmingham, Manchester and Sheffield. Each of these cities has used a combination of regular sport fixtures, ‘mega’ sport events and event bids to further their reputations as tourist destinations. Semi-structured interviews with a representative sample of potential tourists were used to provide evidence of the impacts of these initiatives. Despite some participants making connections with traffic chaos and violence, in general sport events appear to have encouraged positive connotations amongst potential tourists, including modernity, progress and vitality. Events seem to be regarded favourably at a cultural level, generating widespread positive meanings even when individual preferences vary. This has positive implications for cities deploying sport events as re-imaging or branding tools

Optimisation of NMR dynamic models I. Minimisation algorithms and their performance within the model-free and Brownian rotational diffusion spaces

The key to obtaining the model-free description of the dynamics of a macromolecule is the optimisation of the model-free and Brownian rotational diffusion parameters using the collected R1, R2 and steady-state NOE relaxation data. The problem of optimising the chi-squared value is often assumed to be trivial, however, the long chain of dependencies required for its calculation complicates the model-free chi-squared space. Convolutions are induced by the Lorentzian form of the spectral density functions, the linear recombinations of certain spectral density values to obtain the relaxation rates, the calculation of the NOE using the ratio of two of these rates, and finally the quadratic form of the chi-squared equation itself. Two major topological features of the model-free space complicate optimisation. The first is a long, shallow valley which commences at infinite correlation times and gradually approaches the minimum. The most severe convolution occurs for motions on two timescales in which the minimum is often located at the end of a long, deep, curved tunnel or multidimensional valley through the space. A large number of optimisation algorithms will be investigated and their performance compared to determine which techniques are suitable for use in model-free analysis. Local optimisation algorithms will be shown to be sufficient for minimisation not only within the model-free space but also for the minimisation of the Brownian rotational diffusion tensor. In addition the performance of the programs Modelfree and Dasha are investigated. A number of model-free optimisation failures were identified: the inability to slide along the limits, the singular matrix failure of the Levenberg–Marquardt minimisation algorithm, the low precision of both programs, and a bug in Modelfree. Significantly, the singular matrix failure of the Levenberg–Marquardt algorithm occurs when internal correlation times are undefined and is greatly amplified in model-free analysis by both the grid search and constraint algorithms. The program relax (http://www.nmr-relax.com) is also presented as a new software package designed for the analysis of macromolecular dynamics through the use of NMR relaxation data and which alleviates all of the problems inherent within model-free analysis