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Metal additive manufacturing differs from traditional manufacturing processes primarily due to repeated heating and cooling cycles that are inherent to the process. Such cycling leads to different thermal signatures and associated heterogeneities in solidification, solid-state transformation, microstructure, and properties of the printed part. There is, therefore, a need to develop methods to compare thermal signatures in a part with reference to part qualification criteria. In this work, we have developed and demonstrated a similarity analysis procedure to meet this need. Thermal signatures are extracted from in-situ infrared (IR) thermography during a part built using a laser powder bed fusion (l-PBF) machine. Layer-wise variations in thermal signature as a function of part geometry were revealed. Ex-situ microstructure characterization was used to validate the results from similarity analysis. Results and analysis confirmed that our similarity analysis is indeed a useful tool for rapid comparison of thermal signatures, i.e., heterogeneity within the part. Similarity analysis was also useful in identification of anomalous thermal signatures. The analysis method paves the way for deploying in-situ monitoring of AM parts for qualification of AM components.

• Studying the thermal and electrical characteristics of individual crystalline silicon cells under different shading levels shows the impact on the module performance. • Advancing the understanding of the impact of partial shading and mismatch on thermal and electrical characteristics of cells, substrings, and modules. • This study improves the interpretation and understanding of thermal images of PV modules operating under varying shading conditions. Variable partial shading was used to analyse the electrical and thermal behaviour of 60 individual cells in an operational crystalline silicon (c-Si) Photovoltaic (PV) module by recording Thermal Infrared (TIR) images concurrently with electrical measurements of individual cells when shading levels between 0 and 100% were applied on one cell. This study investigated the relative changes in each of the individual cells' operational cell voltage and the current of the substring containing the shaded cell. These changes are significant and can give additional insights into the loss of energy production of a module containing a shaded cell. The role of bypass diodes in mitigating these energy losses was also highlighted in this study. The bypass diode gets activated at 40% cell shading level and when the shading level increased from 40- to 100%, the operational voltage and current of the module remain unchanged while that of the shaded cell and substring containing the shaded cell is reduced. The operational temperature of the shaded cell increases to a maximum with an increase in shading level and drops when the substring's bypass diode is activated. As expected, the substring containing the shaded cell tends to operate closer to open-circuit voltage (V OC) as the cells contribute less current than cells in unshaded substrings. The study gives insight into the performance of a c-Si module down to cell level under partial shading on real field conditions and can add value into the operation and TIR imaging of crystalline modules. [ABSTRACT FROM AUTHOR]

Thermal signature reduction in camouflage textiles is a vital requirement to protect soldiers from detection by thermal imaging equipment in low-light conditions. Thermal signature reduction can be achieved by decreasing the surface temperature of the subject by using a low thermally conductive material, such as polycarbonate, which contains bisphenol A. Polycarbonate is a hard type of plastic that generally ends up in dumps and landfills. Accordingly, there is a large amount of polycarbonate waste that needs to be managed to reduce its drawbacks to the environment. Polycarbonate waste has great potential to be used as a material for recycled fibre by the melt spinning method. In this research, polycarbonate roofing-sheet waste was extruded using a 2 mm diameter of spinnerette and a 14 mm barrel diameter in a 265 °C temperature process by using a lab-scale melt spinning machine at various plunger and take-up speeds. The fibres were then inserted into 1 × 1 rib-stitch knitted fabric made by Nm 15 polyacrylic commercial yarns, which were manufactured by a flat knitting machine. The results showed that applying recycled polycarbonate fibre as a fibre insertion in polyacrylic knitted fabric reduced the emitted infrared and thermal signature of the fabric. [ABSTRACT FROM AUTHOR]

The management of thermal emittance always possess challenges in both military and civil domains. The low emissive materials in form of paints offers viable solution for minimising thermal emittance of military objects for camouflage and enhancing infrared reflectivity of roof to reduce cooling loads. Binder apart from pigments is one of the critical components of low emissive paint formulation to decide its ultimate performance. For selection of appropriate resin and binder, a comparative study of five prevalent polymers viz. polyurethane (PU), poly vinyl chloride (PVC), polyethylene (PE), polypropylene (PP) and poly methyl methacrylate (PMMA) has been carried out. Polymeric film of thickness 100µm of each of the polymer is prepared by Elcometer 4340 motorized film applicator. Infrared spectra and thermogravimetric profile have been obtained by Bruker make Tensor 27 FTIR in spectral range 4000 - 600 cm-1 and TGA Q 500. Film formation of PU is excellent and transmission in 3-5 µm is almost 100%. Hence, it may be chosen as binder in low emissive paint for MWIR band. PVC and PMMA among the polymers offer excellent transmission 87-99% in both thermal transmission windows 3-5 µm and 8-12 µm. Thermogravimetric (TG) profile of polymer films evident of thermal stability of PVC, PMMA and PU polymers up to 200 °C. Infrared transmission, TG profile and film formability manifest that both binders-PVC and PMMA are suitable for development of low emissive paints applicable up to temperature 200 °C for both IR transmission windows to evade thermal detectors working for detection of military objects and reducing cooling load in buildings by enhancing reflectivity of roof by application of low emissive paint. [ABSTRACT FROM AUTHOR]

Stress is a normal reaction of the human organism which triggered in situations that require a certain level of activation. This reaction has both positive and negative effects on everyone's life. Therefore, stress management is of vital importance in maintaining the psychological balance of a person. Thermal-based imaging technique is becoming popular among researchers due to its non-contact conductive nature. Moreover, thermal-based imaging has shown promising results in detecting stress in a non-contact and non-invasive manner. Compared to other non-contact stress detection methods such as pupil dilation, keystroke behavior, social media interaction and voice modulation, thermal-based imaging provides better features with clear boundaries and requires no heavy methodology. This paper presented a brief review of previous work on thermal imaging related stress detection in humans. This paper also presented the stages of stress detection based on thermal face signatures such as dataset type, thermal image face detection, feature descriptors and classification performance comparisons are presented. This paper can help future researchers to understand stress detection based on thermal imaging by presenting the popular methods previous researchers use for stress detection based on thermal images. [ABSTRACT FROM AUTHOR]

In this work, the IR thermography has been used to study the steel specimens (DIN 50125 Standard) undergoing the tensile tests. The tensile tests were performed using GUNT® Hamburg Universal Material Tester. The tensile specimens were clamped, and the test force was applied using a hand-operated hydraulic system. A dial gauge measured the elongation of the specimens. The steel specimens were coated with high emissivity paint. Using the WP 300.20 system for data acquisition, the measured values for force and displacement were recorded in a PC. The IR thermographic imaging was performed using the FLIR® T1030sc IR camera and ResearchIR Max software. The tests have revealed that the steel specimens show noticeable thermal signature when undergoing tensile loading.

Photovoltaic (PV) modules installed in the field generate electrical power under different meteorological and operational conditions; therefore, maintenance of the modules is crucial for the longevity of the PV modules. Thermal infrared (TIR) imaging is a widely used monitoring technique for quality checks of PV modules in plants. It is ideally conducted on operational PV modules under steady ambient conditions; however, PV modules operate under dynamic climatic conditions which influence the overall operation of all solar cells and modules. The dynamic nature of thermal signatures was observed on TIR images when monocrystalline PV modules operated under varying electrical loads and irradiance. A change in operating conditions affected the level of current mismatch between cells since at high irradiance of about 1000 watts per square meter (W m-2) and while operating close to short circuit current at reduced load, the PV cells generated a higher current which led to significant current mismatch. This resulted in several abnormally hot cells being identified on TIR images. Under lower irradiance and larger electrical loads, fewer hot cells were observed and cracked cells (identified through Electroluminescence (EL)) appeared as good cells due to minimal current mismatch. The effectiveness of TIR imaging to reveal underperforming defective cells as hot cells depends on the operating conditions and can mislead decision-making when PV module maintenance is carried out. This work gives valuable information which can be of importance in improving the maintenance systems of PV modules when TIR imaging is conducted. [ABSTRACT FROM AUTHOR]

Traditional methods of cadaver detection in outdoor environments include manual ground search, cadaver dogs, and manned aerial reconnaissance during daylight. These methods have limitations; however, a potential low‐cost alternative may be to employ thermal imaging equipment mounted on an unmanned aerial vehicle (UAV) to detect heat emitted by insect and bacterial activity on the decomposing remains. No studies have addressed the influence of wrappings on detection of maggot mass thermal signatures nor assessed thermal detection of smaller body fragments. We addressed these knowledge gaps by utilizing a two‐phase experimental approach to explore thermal detection of carcasses using UAV‐mounted infrared imaging. In Phase 1, pig body fragments were deposited on the surface or shallow buried. In Phase 2, whole pig carcasses were deposited in four conditions: on the surface uncovered, wrapped in plastic or carpet, or buried. Our results demonstrated that observable heat emissions from remains corresponded to peak insect activity during active decay and could be readily detected in uncovered whole carcasses and fragments. Although plastic and carpet wrappings partly impeded detection of insect heat signatures, these materials were clearly detectable themselves because of their contrast to the background ground surface. Thermal signatures of buried partial remains and disturbed gravesoil were also observed; however, the buried whole carcass transitioned to adipocere prior to the decay stage and without any insect colonization or heat signature. These data can inform operational implementation of this technique to complement existing search strategies to offer a robust, low‐cost alternative for use where scene characteristics allow. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (RGO) possesses unique thermal and optical properties. It could act as black body emitter with high-infrared emissivity. RGO could meet wide applications in advanced infrared decoy flares. In this study, RGO nano-sheets were synthesized through the reduction of GO after applying Hummers' method using graphite powder as a precursor. The synthesized RGO owns 10 µm dimensions and 10 nm thicknesses. TEM analysis revealed the amorphous structure of the prepared nano-sheets. XRD diffractogram demonstrated the amorphous RGO structure. Moreover, Raman spectroscopy confirmed the complete reduction of GO into RGO. In addition, decoy flare formulations based on RGO, reactive metal fuels, and fluorocarbon polymer were developed. Additionally, thermal signature was evaluated using Arc-Optics IR spectrometer (1–6 µm) to reference formulation. Our results revealed that nanocomposite flare based on 6 wt % RGO demonstrated superior spectral intensity with an increase in average intensity by 147%. Moreover, advanced radiometric performance with superior relative intensity value (Ɵ) of 0.7 was recorded. To sum up, RGO can act as an excellent source of carbonaceous materials that can strengthen incandescence emission. Surplus magnesium could vaporize and combust with substantial heat output that could promote black body emission. [ABSTRACT FROM AUTHOR]

The unmanned aerial vehicle (UAV) autopilot flight to survey urban rooftop solar panels needs a certain flight altitude at a level that can avoid obstacles such as high-rise buildings, street trees, telegraph poles, etc. For this reason, the autopilot-based thermal imaging has severe data redundancy—namely, that non-solar panel area occupies more than 99% of ground target, causing a serious lack of the thermal markers on solar panels. This study aims to explore the correlations between the thermal signatures of urban rooftop solar panels obtained from a UAV video stream and autopilot-based photomosaic. The thermal signatures of video imaging are strongly correlated (0.89–0.99) to those of autopilot-based photomosaics. Furthermore, the differences in the thermal signatures of solar panels between the video and photomosaic are aligned in the range of noise equivalent differential temperature with a 95% confidence level. The results of this study could serve as a valuable reference for employing video stream-based thermal imaging to urban rooftop solar panels.

Infrared (IR) guided missile is known to cause 90% of aircraft damage. Magnesium/Teflon/Viton (MTV) decoy flares are customized materials, which are capable of yielding thermal signature to interfere with IR guided missile seekers. In this study, the IR-signature of an MTV flare is measured in a jet engine nozzle. The jet engine IR-signature is characterized with two characteristic peaks over the α-band (2–3 µm) and β-band (3–5 µm); this is correlated to black body emission at 690° C. The MTV decoy flare with 65% Mg offers an increase in the average intensity of the α- and β-bands by 21 and 4 times, respectively, to that of the jet engine. Quantification of emitting species in the combustion flame is conducted by using the ICT thermodynamic code. The developed MTV formulation offers the relative intensity ratio of the α- and β-bands equal to 0.96, which is comparable to that of an aircraft (0.7). [ABSTRACT FROM AUTHOR]

Thermal imaging is simply the technique of using the heat given off by an object to produce an image of it or locate it. New thermal imaging frameworks for detection, segmentation and unique feature extraction and similarity measurements for human physiological biometrics recognition have been introduced in literature. The research investigates specialized algorithms that would use the individual's heat signature for human detection, crowd counting and applications that take benefits of this new technology. The highly accurate results obtained by the algorithms presented clearly demonstrate the ability of the thermal infrared systems to extend in application to other thermal imaging based systems.

Super-thermites can offer large amount of energy up to 16736 J/g. Flares based on super-thermites can offer superior thermal signature to countermeasure infrared (IR) guided missile seekers. This study reports on the sustainable fabrication of mono-dispersed Fe2O3 nanoparticles of 3 nm average particle size. Colloidal Fe2O3 nanoparticles were harvested from their synthesis medium and re-dispersed in acetone. Fluorocarbon polymers (teflon and viton) as well as aluminum metal fuel were integrated into Fe2O3/acetone colloid. The colloid mixture was granulated and mold pressed to develop the desired grain. The impact of Fe2O3 nanoparticles on thermal signature was assessed using (FT-MIR 1-6 µm) spectrometer. Flame propagation was investigated by video imaging of combustion wave. Combustion zones were quantified using image analysis. Quantification of flame temperature and main IR emitting species was performed using ICT thermodynamic code (virgin 2008). Nanocomposite flare with 12 wt% Fe2O3 offered an increase in the intensity of β band by 230% to that of reference formulation. The primary reaction zone was extended by 164%. Super-thermite particles not only offered superior spectral performance but also altered the combustion mechanism. [ABSTRACT FROM AUTHOR]

Infrared (IR) guided missiles are real threat; they caused 90% of aircraft damage. Fluorocarbon polymer nanocomposite based on super-thermites can offer superior thermal signature to countermeasure IR guided missile seekers. This study reports on the sustainable fabrication of mono-dispersed colloidal Fe2O3 nanoparticles with 3 nm average particle size. Fe2O3 nanoparticles were dispersed in acetone for subsequent integration in fluorocarbon polymer. The impact of Fe2O3 content on thermal signature was evaluated using (FT-MIR 2-6 μm) spectrophotometer. Nanocomposite polymer with 8 wt% Fe2O3 offered an increase in the average intensity of α (2-3 μm) and β (4-5 μm) bands by 50 and 85% respectively to that of reference formulation. Quantification of stimulated emitting species in the combustion flame was conducted using ICT thermodynamic code. The developed nanothermite particles extended the primary reaction zone by 183%. Full discussions about combustion zones with associated exothermic chemical reactions have been represented. [ABSTRACT FROM AUTHOR]

The increasing risks of border intrusions or attacks on sensitive facilities and the growing availability of surveillance cameras lead to extensive research efforts for robust detection of pedestrians using images. However, the surveillance of borders or sensitive facilities poses many challenges including the need to set up many cameras to cover the whole area of interest, the high bandwidth requirements for data streaming and the high‐processing requirements. Driven by day and night capabilities of the thermal sensors and the distinguished thermal signature of humans, the authors propose a novel and robust method for the detection of pedestrians using thermal images. The method is composed of three steps: a detection which is based on a saliency map in conjunction with a contrast‐enhancement technique, a shape description based on discrete Chebyshev moments and a classification step using a support vector machine classifier. The performance of the method is tested using two different thermal datasets and is compared with the conventional maximally stable extremal regions detector. The obtained results prove the robustness and the superiority of the proposed framework in terms of true and false positives rates and computational costs which make it suitable for low‐performance processing platforms and real‐time applications. [ABSTRACT FROM AUTHOR]

Background. Health-oriented practice is advocated, since 'too much medicine' has led to increased health costs without an increase in health. Conversely, negative iatrogenic outcomes have been reported in both medicine and midwifery care. Recent research has described health-oriented midwifery practice, but little is known about how health-oriented practice can be measured. Aim. This pilot study investigated whether infrared thermal imaging is able to distinguish between health-oriented and clinically-oriented practice. Building upon previous studies that distinguished specific thermal imaging patterns related to specific emotional states, this study attempted to record the specific thermal signatures relating to health-oriented and clinically-oriented practice. Thus it aimed to provide a quantitative definition of health-oriented practice in midwifery consulting sessions. This single case study is the first attempt to assess professionals' health orientation in maternity care. Methods. For this initial purpose two midwives with differing professional orientations were required to enroll in the study. Following consent for participation, the consulting session of a health-oriented midwife was compared to the consulting session of a midwife with a clinical orientation. Both sessions were assessed using thermal imaging and voice recording. Results. Two distinct profiles emerged from the descriptive analysis of the thermal images. While the health-oriented midwife showed significant changes in facial, neck and hand temperature, there were almost no changes in the thermal images taken of the clinically-oriented midwife, both in terms of temperature values and temperature diffusion. Discussion/conclusion. These differences are assumed to be related to the professional orientation of the midwives. To examine these assumptions, further studies on larger samples are needed. [ABSTRACT FROM AUTHOR]

The most effective way to reduce the thermal signature is to reduce the emissivity. The goal of our research is to create the material, which can reduce the thermal signature, and make it interflow with environment. The materials and material compositions concealing the thermal signature of the object were developed using aluminium coatings and conductive metalized fibres, i. e. yarns with stainless steel staples or coated with silver. The analysis of the prepared samples was carried out with equipment consisting of a stand with integrated heating controller imitating the human body. The concealing properties of the samples in the far infrared (FIR) spectral range were evaluated using ThermaCAM Reporter 7.0. The thermal signature analysis of prepared samples demonstrates that respectable results could be obtained using yarns coated with silver and materials coated with aluminium, but the first one is more flexible and preferable for clothing.DOI: http://dx.doi.org/10.5755/j01.ms.19.4.1730

The accurate and efficient prediction of the flow and temperature fields on water surface modulated by internal waves induced by underwater vehicles in a density-stratified ocean can serve as the basis for indirect detection. The disturbance of an underwater object on density-stratified water can be considered as the mixing of two incompressible fluids: freshwater and saltwater. Furthermore, the modulation effect of internal waves on the convergence and divergence of flow field and thermal skin layer is captured at the air–water interface. Therefore, in this study, a CFD solver called "interMixing_skin_Foam" based on OpenFOAM is proposed. It can manage three incompressible fluids, two of which disperse, and the interface between the immiscible fluids (air–water) is captured using the VOF technique. In addition, the energy equation is implemented to investigate the thermal signature variations at the air–water interface. Comparison analysis of experimental results and those obtained from the CFD solver "twoLiquidMixing_skin_Foam" developed in a previous study, wherein only two incompressible fluids were considered, is performed for standard cases in literature. Subsequently, the influence of the air–water interface on the flow and temperature fields is studied for a submerged sphere travelling horizontally in linearly and strongly density-stratified water. • The thermal signature variations of internal waves by underwater target at the air–water interface were investigated. • A solver based on OpenFOAM platform for flow and temperature fields of three incompressible fluids was developed. • The viscosity drag effect, surface tension, and movable free surface have significant influence on thermal signatures. • In strongly density-stratified water, the upper fresh-water layer could suppress the thermal signatures. [ABSTRACT FROM AUTHOR]

[Display omitted] • An in-situ monitoring method and similarity analysis algorithm has been developed as a potential tool for part qualification based on thermal signature comparison in additive manufacturing. • The similarity analysis algorithm combines shape and magnitude similarity in a manner unique to additive manufacturing. • Using similarity analysis, variations in thermal signatures associated with change in part geometry have been demonstrated. • Comparison with microstructure characterized using ex-situ microscopy indicated that similarity analysis correlates well with grain size and microstructure variation within a part. • A proof of concept is also presented to demonstrate similarity analysis to identify anomalous regions corresponding to potential defects in the part. Metal additive manufacturing differs from traditional manufacturing processes primarily due to repeated heating and cooling cycles that are inherent to the process. Such cycling leads to different thermal signatures and associated heterogeneities in solidification, solid-state transformation, microstructure, and properties of the printed part. There is, therefore, a need to develop methods to compare thermal signatures in a part with reference to part qualification criteria. In this work, we have developed and demonstrated a similarity analysis procedure to meet this need. Thermal signatures are extracted from in-situ infrared (IR) thermography during a part built using a laser powder bed fusion (l -PBF) machine. Layer-wise variations in thermal signature as a function of part geometry were revealed. Ex-situ microstructure characterization was used to validate the results from similarity analysis. Results and analysis confirmed that our similarity analysis is indeed a useful tool for rapid comparison of thermal signatures, i.e., heterogeneity within the part. Similarity analysis was also useful in identification of anomalous thermal signatures. The analysis method paves the way for deploying in-situ monitoring of AM parts for qualification of AM components. [ABSTRACT FROM AUTHOR]

Summary Submarine groundwater discharge (SGD) to the Bay of Bengal is an important groundwater discharge process to southern Asia as well as to the global oceans. Water-fluxes in these regions are not very well understood. The present study demonstrates the use of sea-bed porewater temperature as a tracer for delineating seasonal SGD from a shallow coastal aquifer to the Bay of Bengal. Porewater temperature mapping along with chemical profile of porewater column were used to delineate groundwater discharge zones for different seasons in a hydrologic year. While, the temperature profiles were used to evaluate total groundwater discharge (both terrestrial and marine), the salinity and total dissolved solids profiles were used to evaluate the component due to terrestrial (freshwater) discharge. Several springs and seeps were mapped to finger-print the freshwater discharge zones and identify the terrestrial sourced-SGD temperature windows. These zones are also identified to be enriched with algal mats, and hence may indicate the pathways of nutrient–solute discharge that enhance the primary productivity in the marine ecosystem. Assuming vertical flow in the seabed, simulated rates of discharged groundwater provided a good match with measured discharge rates. The porewater fluxes were estimated by applying analytical solutions of the heat conduction–advection equations to the observed vertical temperature profiles. High resolution thermal profiles to identify T-SGD signatures and chemical profiles along mapped transects reveal the nuances of 3-D seasonal hydrodynamics of groundwater–seawater interactions. The calculated vertical porewater fluxes through the seabed ranged from negligible to 2.45 × 10 −2 m 3 /m 2 /d 1 within a zone extending from high tide line to 40 m offshore, and represent the vertical porewater velocity and the average vertical porewater velocity is found as 8.2 × 10 −3 m 3 /m 2 /d 1 . Approximations suggest that in present-day condition, total average annual SGD to Bay of Bengal is about 1.16 × 10 7 m 3 /y. Seasonal estimates suggest that the averages SGD during pre-monsoon and post-monsoon seasons are ranges 0.6–0.8 × 10 7 m 3 /y for pre-monsoon and 0.8–1.5 × 10 7 m 3 /y for post-monsoon, respectively. The findings suggest that monsoonal activity result in a significant porewater displacement from tidal flat sediments by increased groundwater discharge. [ABSTRACT FROM AUTHOR]

We examined groundwater and stream water interaction in the Inbuk stream, Korea, using various approaches including hydrologic, thermal, hydrochemical, and isotopic methods. For this purpose, we installed four piezometers (IYHW1-4) in the streambed at 10 m interval across the stream and at depths of 0.90 to 1.54 m. We monitored water levels and water temperatures every hour using automatic transducers at the piezometers and in the stream (IYSW1) from September 2013 to April 2014. We also analyzed chemical and isotopic compositions for the hyporheic waters, stream water, and nearby groundwater in early September and late November in 2013. The water levels and hydraulic gradients revealed that three (IYHW1, 2, and 4) of the piezometers were in upwelling conditions for most of the monitoring period, except for the earliest short period (considered to be the wet season), whereas one piezometer (IYHW3) showed a reverse behavior, indicating that the gaining was dominant in the dry period. The mean calculated influx to the stream was 3.04 × 10 cm/sec. Observed temperatures of stream water, hyporheic waters, and groundwater also revealed that stream water was downwelling in the early monitoring period (wet season), whereas the groundwater was generally upwelling in most of the resting period, which is consistent with the water level interpretation. Chemical composition analysis indicated that most of the waters were Ca-HCO type for both seasons. However, no distinctive difference between chemical compositions of water without substantial seasonal variation negated any inference on the flow conditions. The mixing ratios computed from oxygen and hydrogen isotopic compositions indicated that losing conditions were dominant in the wet season, whereas gaining conditions prevailed in the dry season. The interpretations of stream water and groundwater interactions based on these different methods are relatively consistent for this study area, indicating that such combined methods will be very useful in enhancing understanding of groundwater and stream water interaction. [ABSTRACT FROM AUTHOR]

Aircraft thermal signature has been modelled by calculating irradiance at ihe observer's spot (detector position) from aircraft elementary surfaces. The elementary surface is a triangle determined by its corner temperatures and the cosine of the angle between the normal surface in the angle centre of gravity and the detector direction. Visibility and overlapping of elementary surfaces are controlled using the perspective transformation of an object into the plane. The mathematical model of aircraft thermal signature also includes the atmosphere influence through the LOWTRAN software.

In Laser Directed Energy Deposition (DED-L) process, based on the particular thermal cycle followed during the laser processing, a wide range of microstructural and dimensional outcomes are envisaged in the end product on account of the interaction of the material or the alloy with the laser. Various parameters can influence the thermal cycle and a direct correlation between the thermal characteristics with the mechanical/metallurgical properties would be helpful to control the process in a better way. Keeping in view of this, the present study is aimed at analyzing thermal signals received from infrared pyrometer and understanding the correlation between thermal signatures, phase prediction data using CALPHAD simulation, microstructure and deposition characteristics. The thermal signatures captured from infrared pyrometer revealed close interrelationship between the input process parameters and the molten pool characteristics, which have a huge influence on the solidification rate vis-à-vis microstructural properties. Total life of melt-pool showed an increase in magnitude from 137 ms to 264 ms with decrease in cooling rates from 3000 °C/s to 1750 °C/s. The grain size increased from 3.48 μm to 7.74 μm with increase in solidification shelf life from 32 ms to 110 ms. The higher solidification shelf life and lower cooling rates also resulted in the larger and the more prominent metal carbide precipitate and intermetallic formations as evident from XRD analysis. Microhardness of the deposits also increased with decrease in solidification shelf life and increase in cooling rates of molten pool. The dimensions of laser deposited tracks were also found to increase with increment in total molten pool lifetime both at increasing laser power and decreasing laser scan peed conditions. • Inconel 625 tracks were deposited at constant power, scan speed and fluence conditions by DED-L. • Shift in solidification shelf life indicated dilution of Fe from SS 304 L substrate. • Increment of solidification shelf life at constant fluence was detected. • Solidification shelf life and cooling rate influenced microstructure and microhardness. • 244 % increase in shelf life led to 122 % increase in grain size at constant scan speed. • Increase in track cross-sectional dimension at constant fluence condition was observed. [ABSTRACT FROM AUTHOR]

Sodium sulfates are well known to be the most damaging salts in building materials and rocks. Unfortunately, the crystallization processes of sodium sulfates are not completely understood. In addition, the metastable heptahydrate has long been neglected in scientific works on salt damage until recently. In this study, we use temperature monitoring and differential scanning calorimetry to detect and identify the crystallization of sodium sulfate hydrates (i.e., mirabilite and heptahydrate) upon cooling/heating a bulk solution. The presence of impurities seems to play a major role in the crystallization sequence and can explain the crystallization of mirabilite and ice close to −10 °C. The crystallization of heptahydrate does not seem to be sensitive to the presence of impurities and does not always occur prior to the crystallization of mirabilite as commonly observed. The heptahydrate and mirabilite show different and characteristic thermal signatures that enable to distinguish each other. The shape, the intensity and the duration of the peak of temperature due to the crystallization depict these differences. Therefore, the thermal signatures can be used in further experimental studies to estimate the role of the different sodium sulfate hydrates involved in the salt weathering of rocks. [ABSTRACT FROM AUTHOR]