•Thermal conductivity of thin films using a periodic pulse excitation waveform.•Bayes minimization technique.•High accuracy with low standard deviation.
The front face photothermal radiometry ...technique has been improved in order to estimate the thermal conductivity of thin films with better accuracy compared to existing techniques. The experimental procedure is based on the front face response to a nanoseconds laser pulse repeated periodically at high frequency, i. e., a Dirac comb waveform. Averaging the thermal response by considering thousands successive pulses allows improving largely the signal noise ratio. The unknown thermal properties and related experimental parameters are identified by minimizing the gap between the measured signal and the theoretical response that accounts with the pulse waveform, the repetition frequency and the detector transfer function. Minimization is first achieved by implementing first a simplex technique that gives an initial set of values to start the Metropolis–Hastings algorithm in a second step. Application of the proposed methodology is done considering amorphous GeTe film deposited on a Si wafer. It is shown that this experimental method as well as the implementation of the Bayes minimization technique allows to identify the thin film intrinsic thermal conductivity with high accuracy considering some uncertainty on the other parameters assumed to be known.
This article presents the results of comparative investigations of thermal parameters of hybrid sol–gel coatings (named TMZ) prepared from tetraethyl orthosilicate and organically modified ...3-methacryloxypropyltrimethoxysilane. The coatings were prepared with the addition of zirconium(IV) tetrapropoxide chelated with methacrylic acid. Two series of samples were investigated: the first series, TMZ-I, TMZ-II and TMZ-III, with different amounts of zirconium, and the second series, TMZ-I/Ce, TMZ-II/Ce and TMZ-III/Ce, with the addition of cerium nitrate. The influence of the amount of zirconium and cerium on the thermal parameters of the sol–gel coatings was next analyzed. Two non-destructive and photothermal techniques were used for this purpose: photothermal radiometry (PTR) and beam deflection spectroscopy (BDS). The thermal diffusivity and conductivity of the coatings were extracted from the frequency experiments and are presented and discussed. The two-layer model was applied to interpret the photothermal spectra. The results obtained using these two techniques are compared and discussed.
We have augmented a recently introduced method for noninvasive analysis of skin structure and composition and applied it to monitoring of dynamical processes in traumatic bruises. The approach ...combines diffuse reflectance spectroscopy in visible spectral range and pulsed photothermal radiometry. Data from both techniques are analyzed simultaneously using a numerical model of light and heat transport in a four-layer model of human skin. Compared to the earlier presented approach, the newly introduced elements include two additional chromophores (
-carotene and bilirubin), individually adjusted thickness of the papillary dermal layer, and analysis of the bruised site using baseline values assessed from intact skin in its vicinity. Analyses of traumatic bruises in three volunteers over a period of 16 days clearly indicate a gradual, yet substantial increase of the dermal blood content and reduction of its oxygenation level in the first days after injury. This is followed by the emergence of bilirubin and relaxation of all model parameters towards the values characteristic for healthy skin approximately two weeks after the injury. The assessed parameter values and time dependences are consistent with existing literature. Thus, the presented methodology offers a viable approach for objective characterization of the bruise healing process.
The aim of the present study was to investigate the ability of operators using The Canary System and DIAGNOdent to detect natural pit and fissure caries under four commonly-used opaque dental ...sealants.
Mixed sound and carious pits/fissures (N = 105) selected from 40 human teeth were randomly assigned (10 teeth/group) to one of four opaque sealant groups (Delton, Embrace WetBond, Helioseal F, UltraSeal XT Plus). Selected pits/fissures sites on occlusal surfaces were scanned with The Canary System and DIAGNOdent, sealed, re-scanned, and subjected to polarized light microscopy to confirm whether the scanned regions were sound or carious. Sensitivities and specificities for each detection method before and after sealant placement were calculated.
The Canary System and DIAGNOdent were able to distinguish between sound and carious tissue beneath opaque sealants with an accuracy of 76% and 59%, respectively.
The Canary System can serve as a clinical tool to aid dental professionals to detect and monitor the status of caries lesions and tooth structure underneath sealant. The increased likelihood of false-positive diagnoses with DIAGNOdent due to intrinsic auto-fluorescence of sealant filler and opacifying agents might limit its usefulness as an aid to detect caries underneath opaque sealants.
The early identification of children who have experienced adversity is critical for the timely delivery of interventions to improve coping and reduce negative consequences. Self-report is the usual ...practice for identifying children with exposure to adversity. However, physiological characteristics that signal the presence of disease or other exposures may provide a more objective identification strategy. This protocol describes a case-control study that assesses whether exposure to adversity is more common in children with tooth enamel anomalies compared to children without such anomalies.
For 150 mother-child pairs from a pediatric dental clinic in Toronto, Canada, maternal interviews will assess the child's adverse and resilience-building experiences. Per child, one (exfoliated or extracted) tooth will be assessed for suspected enamel anomalies. If anomalies are present, the child is a case, and if absent, the child is a control. Tooth assessment modalities will include usual practice for dental exams (visual assessment) and modalities with greater sensitivity to identify anomalies.
If structural changes in children's teeth are associated with exposure to adversity, routine dental exams could provide an opportunity to screen children for experiences of adversity. Affected children could be referred for follow-up.
Al2O3 grown by atomic layer deposition could be proposed as a nonactive layer for back end processes in view of the integration of scaled phase change memory devices. In this paper we report on ...thermal characterization from 50 to 600 °C of amorphous Al2O3 thin films grown on thermally oxidized silicon substrate at a temperature of 100 °C and capped with a 30 nm thick Pt layer. The effects of low temperature deposition and of a post‐deposition rapid thermal annealing process (RTP) on the thermal properties of the films are investigated using a modulated photo‐thermal radiometry technique coupled with post‐annealing morphological characterizations. Degassing process occurring at high temperature greatly affects the film surface quality, though measurements of the films after RTP show that the thermal conductivity of amorphous Al2O3 increases as a function of temperature from 1.8 W K−1 m−1 at 50 °C to 3.3 W K−1 m−1 at 600 °C. At the same time, the value of the thermal boundary resistance at the Pt‐Al2O3 interface decreases from 1.02 × 10−7 K m2 W−1 at 50°C to 4.8 × 10−8 K m2 W−1 at 600 °C.
Al2O3 grown by atomic layer deposition is proposed as a nonactive layer for back end processes in view of the integration of scaled phase change memory devices. It has been measured that the thermal conductivity of amorphous Al2O3 increases from 1.8 W K−1 m−1 at 50 °C to 3.3 W K−1 m−1 at 600 °C.
The objective was to evaluate the ability of photothermal-radiometry and modulated-luminescence (PTR/LUM) to detect non-cavitated approximal caries lesions, including the effect of scanning ...direction.
Thirty human extracted premolars were selected based on micro-computed tomography μ-CT: μ-CT = 0: sound (n = 12), μ-CT = 1: lesions into outer-half of enamel (n = 6), μ-CT = 2: lesions into inner-half of enamel (n = 6), and μ-CT = 3: lesions into outer one-third of dentine (n = 6). Teeth were mounted in a custom-made device to simulate approximal contact. Each tooth was scanned from three directions: buccal, lingual, and occlusal, then repeated 48 h later. Statistical analyses were performed by bootstrap analyses using average and maximum values across all directions. Sensitivity, specificity, area under ROC-curve (AUC), intraclass correlation coefficient (ICC) and correlation with μ-CT were calculated. Sensitivity was further evaluated based on lesion extension.
Using the manufacturer-suggested lesion cut-off, overall sensitivity ranged from 3%–61%, where the maximum value of all measurements (All-max) showed higher sensitivity (61 %) than other measurements except the buccal direction, which was also higher than the lingual and occlusal directions. As μ-CT score increased from μ-CT = 1–3, the sensitivity of All-max also increased from 50 % to 74 %. Specificity was 100 % regardless of direction, and AUC ranged from 0.65 to 0.88. All-max had the highest ICC (0.74). PTR/LUM values showed weak to moderate correlations with μ-CT.
Within the limitations of this in vitro study, PTR/LUM non-cavitated approximal caries lesion detection achieved best individual results from the buccal direction, while using the maximum value from all directions might improve performance.
Non-cavitated approximal caries detection is a challenging procedure. PTR/LUM is a nondestructive, no ionized-radiation caries detection method that can scan from buccal, lingual, and occlusal directions of an approximal surface. PTR/LUM seems suitable to detect deeper non-cavitated approximal caries. The maximum PTR/LUM value from three directions may be optimal.
Pulsed photothermal radiometry (PPTR) allows noninvasive determination of laser-induced temperature depth profiles in optically scattering layered structures. The obtained profiles provide ...information on spatial distribution of selected chromophores such as melanin and hemoglobin in human skin. We apply the described approach to study time evolution of incidental bruises (hematomas) in human subjects. By combining numerical simulations of laser energy deposition in bruised skin with objective fitting of the predicted and measured PPTR signals, we can quantitatively characterize the key processes involved in bruise evolution (i.e., hemoglobin mass diffusion and biochemical decomposition). Simultaneous analysis of PPTR signals obtained at various times post injury provides an insight into the variations of these parameters during the bruise healing process. The presented methodology and results advance our understanding of the bruise evolution and represent an important step toward development of an objective technique for age determination of traumatic bruises in forensic medicine.
This work aimed at thermal transport characterization of high density polyethylene (HDPE) filled with 5 and 50 μm expanded graphite (EG) particles and with 0.4 μm unexpanded graphite (UG) particles. ...Sample platelets were produced by melt mixing followed by compression molding. Thermal conductivity k was determined by combining measurements of density, specific heat capacity and thermal diffusivity, the latter by modulated photothermal radiometry (PTR). Starting from an effective medium approximation model, we derived a linearized expression for the effective k of composites with low particle charge. It explains the unusually high experimental k values (up to four-fold increase) as the effect of strongly non-spherical EG particles (aspect ratio 1/p = 110–290). Larger particle sizes produce higher k enhancement, while the interfacial thermal resistance (Rbd = 2.1⋅10−7 m2⋅K/W) has an opposite effect. The same model is consistent with experimental k for low particle charge HDPE/UG composites. At higher particle charge the model fails due to particle interaction leading to validity break of the effective medium approximation.
► High density polyethylene filled with expanded and unexpanded graphite particles. ► Linearized expression for the effective thermal conductivity of composites. ► Thermal diffusivity measured by modulated laser photothermal radiometry. ► High thermal conductivity due to large and thin expanded graphite flakes. ► Maximum thermal conductivity enhancement if particle size is larger than Kapitza radius.
This study aimed to improve the thermal properties of some biopolymers composites. Two aliphatic polyesters were used as matrix, the polylactic acid (PLA) and the polybutylene succinate (PBS). The ...filler used in the composites was expanded graphite (EG) with three different sizes, 5, 50 and 200 μm. Thermal diffusivities were measured by infrared photothermal radiometry (PTR). Model of effective medium approximation (EMA) was used to study the effect on effective thermal conductivity ke of thermal properties of matrix and fillers, the effect of the interfacial thermal resistance ITR between matrix and fillers or the effect of aspect ratio of fillers. Measurement of particles sizes of fillers before and after preparation process shows the presence of small particles, creating lower thermal conductivities than predicted by EMA model. Filtration of EG before process does not allows to increase ke more than 6% because of mechanical stresses of the process. Finally silane functionalization is used to improve interactions between the fillers and the matrices in order to obtain better thermal conductivities. Mechanical studies on composites are also presented.
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