Presence Of Temperature Changes Research Articles

Self-referenced robust guided wave based defect detection: Application to woven composite parts of complex shape

The use of a reference state, i.e. a baseline, for data analysis in guided wave based structural health monitoring is limiting the range of applicability of such approaches. This has been largely demonstrated in the literature in the presence of temperature changes but is also true in the presence of other varying environmental and operational conditions, as well as aging effects. This paper presents a novel self-referenced methodology, which is built to be intrinsically robust to the influence of external effects, allegedly including the ones not identified during system design. The method relies on the concept of instantaneous baseline, i.e. the comparison of multiple measurements acquired on structures with a high degree of similarity from a guided wave perspective. The subtlety of the approach is the detection of flaws of small influence on the measurements in the presence of extrinsic and intrinsic variabilities of comparatively larger influence over several similar samples. The method also includes a dimension reduction through the extraction of quantities of interest from the acquired signals, potentially enabling the analysis of several samples with limited data volume. The proposed method is successfully validated on 12 aluminum plates, each with a through-hole crack from 1 to 30mm in length in a laboratory environment with limited external parameters. Next, the approach is tested on 2 woven composite samples of complex shape with up to 7 similar paths from a guided wave perspective. The detection of an added mass is successful over the whole temperature range under consideration (−30°C to 30 °C) for all studied interrogating frequencies (50, 100, and 150 kHz). The proposed methodology performs significantly better than a state of the art imaging algorithm with temperature compensation applied to the same data.

Intrinsically Secure Non-Volatile Memory Using ReRAM Devices

The paper describes a device-level encryption approach for implementing intrinsically secure non-volatile memory (NVM) using resistive RAM (ReRAM). Data is encoded in the ReRAM filament morphology, making it robust to both electrical and optical probing methods. The encoded resistance states are randomized to maximize the entropy of the ReRAM resistance distribution, thus providing robustness to reverse engineering (RE) attacks. Simulations of data encryption and decryption using experimental data from Ru(BE)/ALD-HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (MO)/Zr/W(TE) ReRAM devices reveals an uncorrected bit error rate (BER) < 0.02 and a maximum key entropy of ≈ 17.3 bits per device. A compensation procedure is also developed for maintaining BER in the presence of temperature changes.

Methodology investigation: Impact of crown geometry, crown, abutment and antagonist material and thermal loading on the two-body wear of dental materials

ObjectivesTo investigate the impact of crown geometry, crown/abutment/antagonist material and thermal loading on the two-body wear of dental materials caused by chewing simulation. Materials and methodsFor the crown geometry, crowns (polymethylmethacrylate (PMMA), polyetheretherketone (PEEK) and silicate ceramic (SiO2)) were milled with a flat, steep, or medium cusp inclination (CINC). For the crown/abutment material, crowns (PMMA, PEEK and SiO2) were combined with PMMA, polymer-infiltrated-ceramic-network (PICN), cobalt-chrome alloy (CoCr) and natural teeth (ENAM) abutments. For the antagonist material, antagonists were fabricated from PICN, CAD/CAM resin composite (RECO), steatite (STEA), steel (STL) and ENAM and tested against flat specimens (substrates) made of veneering ceramic (VC). For thermal loading, the duration (30 s, 60 s, 120 s) and presence of temperature changes (37 °C versus 5 °C/55 °C) was varied. Material losses were determined by matching scanned specimens before and after aging (400,000 chewing cycles, 50 N, 1.3 Hz). Martens parameters were determined for the antagonists/substrates. Data were analyzed using Kolmogorov-Smirnov-test, Kruskal-Wallis H, Scheffé-Post-Hoc-tests, pairwise comparisons, Bonferroni correction, one-way ANOVA, Mann-Whitney-U and Spearman rho. ResultsPMMA crowns presented the highest and PEEK the lowest material losses. Flat CINC showed the lowest material losses for PEEK and SiO2 crowns. CoCr and ENAM abutments presented material losses in the same range. Antagonist and cumulative material losses for RECO and ENAM were similar. Thermal loading did not influence material losses. SignificanceCrown geometry influences the crown and antagonists wear, with an increased cusp inclination entailing increased wear. For in vitro set-ups, CoCr abutments and RECO antagonists present valid alternatives to natural teeth. For polymers, in vitro chewing simulations may be performed at a constant temperature (37 °C).

Pain Measurement through Temperature Changes in Children Undergoing Dental Extractions.

Background and Objective. Pain evaluation in children can be a difficult task, since it possesses sensory and affective components that are often hard to discriminate. Infrared thermography has previously been used as a diagnostic tool for pain detection in animals; therefore, the aim of this study was to assess the presence of temperature changes during dental extractions and to evaluate its correlation with heart rate changes as markers of pain and discomfort. Methods. Thermographic changes in the lacrimal caruncle and heart rate measurements were recorded in healthy children scheduled for dental extraction before and during the procedure and compared. Afterwards, correlation between temperature and heart rate was assessed. Results. We found significant differences in temperature and heart rate before the procedure and during the dental extraction (mean difference 4.07°C, p < 0.001, and 18.11 beats per minute, p < 0.001) and no evidence of correlation between both measurements. Conclusion. Thermographic changes in the lacrimal caruncle can be detected in patients who undergo dental extractions. These changes appear to be stable throughout time and to possess very little intersubject variation, thus making them a candidate for a surrogate marker of pain and discomfort. Future studies should be performed to confirm this claim.

Effects of in-plane electric field and temperature change on Young’s modulus of hexagonal boron nitride nanosheets with different chiralities

In the current investigation, the influences of in-plane electric field and temperature change on Young’s modulus of boron nitride nanosheets (BNNs) are studied for both armchair and zigzag chiralities. To this end, the density functional theory (DFT) and quasi-harmonic approximation (QHA) are applied to calculate the total energy of the system. It is found that in the presence of temperature change, by applying the electric field along the zigzag and armchair directions, Young’s modulus of BNNs decreases and increases, respectively. Moreover, it is revealed that the range of variation in Young’s modulus of zigzag BNNs corresponding to different values of electric field is generally lower than that of armchair ones, but the slope of this variation with temperature for zigzag BNNs is more than Armchair ones. Also, it is observed that the rate of variation of Young’s modulus with temperature at lower values is sharper than that at higher temperatures. This behavior can be useful in designing electro-thermo-mechanical nanosensors.

Static and dynamic stability modeling of a capacitive FGM micro-beam in presence of temperature changes

Stability of a functionally graded (FG) micro-beam, based on modified couple stress theory (MCST), subjected to nonlinear electrostatic pressure and thermal changes regarding convection and radiation, is the main purpose of this paper. It is assumed that the functionally graded beam, made of metal and ceramic, follows the volume fraction definition and law of mixtures, and its properties change as an exponential function through its thickness. By changing the ceramic constituent percent of the bottom surface, five different types of the micro-beams are investigated. The static pull-in voltages in presence of temperature changes are obtained by using step-by-step linearization method (SSLM) and, by adapting Runge–Kutta approach, the dynamic pull-in voltages are obtained numerically. Though the temperature distribution through the thickness of FG micro-beam (due to its too small measurement) is considered uniform, owing to the different thermal expansions of layers, temperature changes cause deflection in the micro-beam, and consequently affect pull-in values. Hence the profound effects of different material constituent over the pull-in voltages are illustrated and it is graphically displayed that how in some cases neglecting components of the couple stress leads to inaccurate results.

Nonlinear free vibration of embedded double-walled carbon nanotubes with layerwise boundary conditions

This paper investigates the large-amplitude free vibration of a double-walled carbon nanotube (DWCNT) surrounded by an elastic medium in the presence of temperature change. Based on continuum mechanics, a nonlocal elastic beam model is employed in which nanotubes are coupled together via the van der Waals (vdW) interlayer interactions. The Pasternak foundation model and a nonlinear vdW model are utilized to describe the surrounding elastic medium effect and the vdW interlayer interactions, respectively. DWCNTs with different boundary conditions are analyzed utilizing the Timoshenko beam theory that considers the shear deformation and rotary inertia effects. The governing equations are derived from Hamilton’s principle; the Galerkin method is utilized to discretize the governing equations. The influences of the nonlocal parameter, spring constant, carbon nanotube aspect ratio, and temperature change on the nonlinear free vibration characteristics of a double-walled carbon nanotube with different boundary conditions are thoroughly investigated. It is deduced that the nonlocal parameter, spring constant, and the aspect ratio play significant roles for the value of the nonlinear frequency. Also, the temperature change and the type of boundary conditions have an effect on the nonlinear frequency.

A precise positioning actuator based on feedback-controlled magnetic shape memory alloys

This paper describes a precise positioning system based on magnetic shape memory alloys (MSMAs). This new type of material shows an interesting potential in the area of mechatronics due to its outstanding magnetically-induced strain, which is significantly larger than the one exhibited by other common active materials such as piezoelectric ceramics. However, MSMAs still have not found their way into industrial applications mainly due to their high hysteretic behavior and the strong sensitivity to temperature changes. The aim of this paper is to present the main challenges of using MSMAs for precise positioning systems by means of a simple yet effective experimental prototype. In particular, this paper examines the problem of effectively controlling the device in closed-loop. The performance of an adaptive hysteresis compensator based on the Preisach-like Krasnosel’skii–Pokrovskii model is analyzed and evaluated in the presence of temperature changes. Experiments confirm that the undesirable effects of temperature on the precision of the device can be partially addressed with an adaptive model-based algorithm devised to cope with time-varying nonlinearities.

Computational Modeling of Blood Hydrodynamics and Blockage Formation Phenomena in the Human Cardiovascular System

An international collaborative effort to develop a computational fluid dynamics (CFD) model of the human cardiovascular system (HCVS) has been initiated in 2008. The HCVS model is designed to describe (a) the blood flow hydrodynamics and associated heat transport phenomena, (b) the blood flow interactions with the essential organs, and (c) the vessel blockage formation associated with atherosclerosis and thrombosis. The CFD-HCVS model is being developed as a new specialized software module using as a foundation the CFD code, STAR-CD, that is developed and distributed by CD-adapco, Ltd., a member of the project team. The CFD-HCVS module includes the following components and capabilities. (1) A simplified 3D coarse mesh CFD model of the HCVS, which allows the simulation of hemodynamic transient phenomena. The circulatory system model is closed with porous-media flow components having a hydraulic resistance equivalent to the lumped flow resistance of the smaller vessels, including microcirculation. Both hydrodynamic and thermodynamic phenomena are described, allowing the study of blood flow transients in the presence of temperature changes. (2) Simplified zero-dimensional models of the essential organs (e.g., heart, kidneys, brain, liver, etc.) describing the time-dependent consumption or production of various blood components of interest. The organ models exchange information with the CFD system model through interfaces designed to allow their replacement, in the future, with more complex 3D organ models. (3) Selected sections of the circulatory system can be replaced by realistic 3 fine mesh vessel models allowing the detailed study of the 3D blood flow field and the vascular geometry changes due to blockage formation. (4) Models of local blockage formation due to atherosclerosis and thrombosis. Three HCVS models of increasing complexity have been designed. These models contain 27 vessels, 113 vessels, and 395 vessels. The initial CFD-HCVS model development is based on the medium HCVS model with 113 vessels. A closed circuit CFD model describing the major vessels and containing 0D models of the heart and kidneys has been developed. The CFD-HCVS model includes porous-media models describing the blood flow in the smaller vessels and capillaries. Initial simulations show that the calculated blood flow rates in the vessels modeled are in reasonably good agreement with the corresponding physiological values. A simplified model of thrombosis has also been developed. Current development efforts are focused on the addition of new vessels and 0D organ models and the development of atherosclerosis models. The HCVS model provides a flexible and expandable modeling framework that will allow the researchers from universities, research hospitals and the medical industry to study the impact of a wide range of phenomena associated with diseases of the circulatory system and will help them develop new diagnostics and treatments.

A damage diagnostic imaging algorithm based on the quantitative comparison of Lambwave signals

With the objective of improving the temperature stability of the quantitative comparison ofLamb wave signals captured in different states, a damage diagnostic imaging algorithmintegrated with Shannon-entropy-based interrogation was proposed. It was evaluatedexperimentally by identifying surface damage in a stiffener-reinforced CF/EPquasi-isotropic woven laminate. The variations in Shannon entropy of the reference(without damage) and present (with damage) signals from individual sensing paths werecalibrated as damage signatures and utilized to estimate the probability of the presence ofdamage in the monitoring area enclosed by an active sensor network. The effects oftemperature change on calibration of the damage signatures and estimation of theprobability values for the presence of damage were investigated using a set ofdesynchronized signals. The results demonstrate that the Shannon-entropy-based damagediagnostic imaging algorithm with improved robustness in the presence of temperaturechange has the capability of providing accurate identification of damage in actualenvironments.

Guided Wave Damage Detection in Composite Plates under Temperature Variations

One of the main challenges of guided wave structural damage detection is to find an effective way of compensating temperature changes and to apply it to existing damage detection methods. This article describes a simple method for applying guided waves to the problem of detecting damage in the presence of temperature changes. In order to examine the effectiveness of the presented method, delaminations due to a low-velocity impact on composite plate specimens are detected. The results show that the presented approach can be a potential candidate to detect damage in aircraft structures under the temperature variations.

Temperature Effects on Guided Wave Structural Damage Detection

Guided wave structural damage detection is one of promising candidates for the future aircraft structural health monitoring systems. There are several advantages of guided wave based damage detection: well established theoretical studies, simple sensor devices, large sensing areas, good sensitivity, etc. However, guided wave approaches are still vulnerable to false warnings of detecting damage due to temperature changes of the structures. Therefore, one of main challenges is to find an effective way of compensating temperature changes and to imply it to existing damage detect algorithms. In this paper, a simple method for applying guided waves to the problem of detecting damage in the presence of temperature changes is presented. In order to examine the effectiveness of the presented method, delaminations due to low-velocity impact on composite plate specimens are detected. The results show that the presented approach is simple but useful for detecting structural damage under the temperature variations.

A pressure sensor based upon the transverse loading of a sub-section of an optical fibre Bragg grating

An experimental and theoretical study of locally transverse loaded fibre Bragg gratings (FBGs) for pressure sensing purposes is presented. When a load is applied to a short section of an FBG, a spectral hole is generated in the reflection spectrum, which exhibits a redshift in wavelength as the load is increased. This effect has been modelled using Rouard's method and has been characterized experimentally. Two techniques for analysing the spectrum for pressure measurements at constant temperature are considered, one based on measurement of the wavelength shift of the spectral hole, and the other on measurement of peak reflectivities either side of the hole. Normalized pressure sensitivities of 3.30 ± 7.93 × 10−2 MPa−1 and 4.97 × 10−4 ± 1.37 × 10−5 MPa−1 were obtained for the reflectivity and wavelength measurement, respectively. A pressure resolution of 1.3 kPa, over a range of 745 kPa, was achieved when using a tunable laser of 1 pm wavelength resolution to interrogate the sensor. For pressure measurements in the presence of temperature changes, a technique based on the measurement of the position of the spectral hole within the Bragg envelope is presented. This technique allows the opportunity to discriminate pressure and temperature using a single FBG sensor element.

Solubility product of the hydroxide of U IV: M. A. Stepanov and N. P. Galkin

This paper describes a precise positioning system based on magnetic shape memory alloys (MSMAs). This new type of material shows an interesting potential in the area of mechatronics due to its outstanding magnetically-induced strain, which is significantly larger than the one exhibited by other common active materials such as piezoelectric ceramics. However, MSMAs still have not found their way into industrial applications mainly due to their high hysteretic behavior and the strong sensitivity to temperature changes. The aim of this paper is to present the main challenges of using MSMAs for precise positioning systems by means of a simple yet effective experimental prototype. In particular, this paper examines the problem of effectively controlling the device in closed-loop. The performance of an adaptive hysteresis compensator based on the Preisach-like Krasnosel’skii–Pokrovskii model is analyzed and evaluated in the presence of temperature changes. Experiments confirm that the undesirable effects of temperature on the precision of the device can be partially addressed with an adaptive model-based algorithm devised to cope with time-varying nonlinearities.