•It was attempted to quantify the texture of metallic samples by image analysis methods.•By using texture analysis in two spatial and frequency domains, the coarseness of metallic coatings was ...quantified.•Two categories of silver and blue metallic samples were utilized to investigate the effect of the presence of color pigment.•The visual coarseness was evaluated by using Thurstone’s law of comparative.
The industrial need for controlling the quality of metallic coatings for producing efficient and high-quality products makes it necessary to conduct an appearance quantification process. In this study, it had been attempted to present an appropriate algorithm to analyze the coarseness property of the metallic coatings using the image processing technique and texture analysis methods to achieve acceptable correlation with visual perception. For this purpose, we examined metallic silver and metallic blue coatings containing eight grades of aluminum flakes with different size distributions from fine to coarse cases. After capturing the images of samples using a scanner, they were studied using different texture analysis methods including autocorrelation function, distance-dependent edge frequency, gray level co-occurrence matrix (GLCM), Fourier transform and wavelet transform. Visual assessments were performed using a comparative judgment method. The precisions of the applied analysis methods were evaluated based on the correlation between their results and the visual assessment data. According to the obtained data, the autocorrelation function with R-squares of 0.88 and 0.9 for the metallic silver and metallic blue coatings, and also wavelet transform in the vertical channel with R-squares of 0.86 and 0.89 for the same mentioned coatings, respectively, had the best performance in comparison to visual perception. Consequently, it was possible to precisely quantify the coarseness perception of metallic coating using autocorrelation function and the wavelet transform as two feasible texture analysis methods. Moreover, the presence of the blue absorption pigment in the formulation had no significant effect on the performance of these two methods.
A high voltage ratio DC–DC converter is proposed which is comprised of four stages. First, an impedance network along with a switching network have been used to boost the input voltage. The boosted ...voltage waveform is then followed by an isolation transformer to provide another degree of freedom and obtain higher boost ability. Finally, a voltage multiplier rectifier is utilised to rectify the secondary voltage of the transformer. No switching dead-time is required, which increases the reliability of the converter. The proposed converter benefits from the continuous input current. Besides, a comparison with the existing step-up topologies indicates that the number of passive elements and hence the weight and size have been reduced. The operating principles were analysed and the experimental tests on a 260 W prototype reveal that a high efficiency above 91% can be achieved.
The microstructure of grain boundaries (GBs) in the commercial NdFeB-based alloy for permanent magnets has been studied. It is generally accepted that the unique hard magnetic properties of such ...alloys are controlled by the thin layers of a Nd-rich phase in Nd2Fe14B/Nd2Fe14B GBs. These GB layers ensure the magnetic isolation of Nd2Fe14B grains from each other. It is usually supposed that such GB layers contain metallic Nd or Nd-rich intermetallic compounds. However, the commercial NdFeB-based permanent magnets frequently contain a tangible amount of neodymium oxide Nd2O3 at the triple junctions between Nd2Fe14B grains. The goal of this work was to check whether the Nd2Fe14B/Nd2Fe14B GBs could also contain the thin layers of Nd2O3 oxide phase. Indeed, the screening with EELS-based elemental analysis permitted to observe that some of these Nd-rich layers in Nd2Fe14B/Nd2Fe14B GBs contain not only neodymium, but also oxygen. More detailed analysis of such GBs with high-resolution transmission electron microscopy (HR TEM) showed these GB layers are crystalline and have the lattice of neodymium oxide Nd2O3. In turn, the Lorentz micro-magnetic contrast in TEM permitted to observe that the Nd-oxide GB layers prevent the migration of domain walls from one Nd2Fe14B grain to another during remagnetization. This finding proves that the GB oxide layers, similar to those of metallic Nd or Nd-rich intermetallic compounds, can ensure the magnetic isolation between Nd2Fe14B grains needed for high coercivity. Therefore, the GB oxide layers can be used for further development of NdFeB-based permanent magnets.
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•It has been observed that Nd2Fe14B/Nd2Fe14B GBs in the NdFeB-based alloys for permanent magnets can contain Nd2O3 oxide layers.•It has been also shown that Nd2O3 oxide GB layers, similar to GBs with metallic Nd or intermetallic phases, can effectively ensure the magnetic isolation of Nd2Fe14B grains from each other.•Therefore, the GB oxide layers can be used for further development of NdFeB-based permanent magnets.
•Effect of the metallic flakes on optical properties of effect coatings using mathematical descriptions of spectrums such as derivatives of reflectance curves and PC analysis method was ...investigated.•The colorimetric and spectrophotometric changes caused by adding aluminum flakes to the solid base-coat were discussed deeply.•The spectrum derivatives with respect to the wavelength of the spectral reflectance were investigated for metallic samples in comparison to the solid ones.•The basis vectors obtained from PCA method were computed and evaluated for solid and metallic sets and the effect of adding metallic flakes to solid base coats on PC vectors was studied.
Coatings containing aluminum flakes are attractive in terms of appearance in both industry and scientific researches. In the present study, attempts were made to investigate the effect of aluminum flakes presence on the appearance properties of metallic coatings. Therefore, metallic coatings containing three grades of aluminum flakes with different size distributions and solid samples were prepared in nine color centers. In addition to the spectral reflectance and colorimetric values, the derivative of the spectral data with respect to the wavelength and the main components from a Principal Component Analysis on reflectance data of each spectral set were investigated for the prepared solid and metallic samples. The results showed that aluminum flakes in the metallic samples provide more negative values of b* because of higher light scattering of blue wavelengths from the edges and probably rough parts on the surface of the flakes. Depending on the used absorption pigments, aluminum flake size could affect colorimetric variations. The main peak of the spectral derivative, with respect to the wavelength, showed that the intensity and sometimes the wavelength at which the main peak occurred changed for the metallic samples in comparison to the solid ones. Furthermore, more valleys and peaks in the derivative spectrum appeared for the metallic samples, which seem to be a result of interaction between the solid base-coat and the aluminum flakes. Principal Component (PC) analysis showed that although the mean of the spectral curves of the metallic sets have higher values at shorter wavelengths because of the presence of aluminum flakes, the first PC vectors keep the characteristics of the solid set. The main peaks of the other basis vectors shift towards the shorter wavelengths. Moreover, in comparison to the solid set, the significance of the first PC vector decreased and the second one increased which was also influenced by the flake size.
We report new laboratory experiments of a flow accelerating from an initially turbulent state following the opening of a valve, together with large eddy simulations of the experiments and extended ...Stokes first problem solutions for the early stages of the flow. The results show that the transient flow closely resembles an accelerating laminar flow superimposed on the original steady turbulent flow. The primary consequence of the acceleration is the temporal growth of a boundary layer from the wall, gradually leading to a strong instability causing transition. This extends the findings of previous direct numerical simulations of transient flow following a near-step increase in flow rate. In this interpretation, the initial turbulence is not the primary characteristic of the resulting transient flow, but can be regarded as noise, the evolution of which is strongly influenced by the development of the boundary layer. We observe the spontaneous appearance of turbulent spots and discontinuities in the velocity signals in time and space, revealing rich detail of the transition process, including a striking contrast between streamwise and wall-normal fluctuating velocities.
A technique to create a temperature insensitive area on a die using an integrated micro-heater and a phase-locked loop (PLL) configuration is described. The proposed PLL configuration employs thermal ...feedback through the micro-heater to significantly improve the temperature stability of the die area. Two oscillators employed in the PLL act as temperature sensors to detect the ambient temperature variations and command the thermal loop to compensate it. The temperature stability of these oscillators located in the temperature-compensated die area is improved significantly and can provide a stable timing signal needed for the system. Design methodologies and system-level analysis are presented, and a test-chip for proof-of-concept is designed and fabricated using a standard 130 nm CMOS technology. Analysis and experimental results show that micro-heating provides a low pass filtering effect such that the loop filter and charge pump can be eliminated from the PLL system. Test characterization of the realized proof-of-concept chip shows that the temperature stability of the die area can be improved by a factor as large as 50 × for an ambient temperature range of 36–52 °C. It is shown by simulation that this range can be improved by many folds using SOI CMOS instead of bulk CMOS.
•Major features of unsteady flow are identified from DNS results.•Performance of turbulence models are assessed against these features.•Launder and Sharma (1974) 36 and Langtry and Menter’s (2009) ...transition SST are best models.•Chang et al. (1995) 28 is also good but can be unstable sometimes.
The performance of a number of low-Reynolds number turbulence models is evaluated against direct numerical simulations (DNS). All models are applied to an unsteady flow comprising a ramp-type excursion of flow rate inside a closed channel. The flow rate is increased linearly with time from an initial Reynolds number of 9308 (based on hydraulic diameter and bulk velocity) to a final Reynolds number of 29,650. The acceleration rate is varied to cover low, intermediate and high accelerations. It is shown that among the models investigated, the k–ε models of Launder and Sharma (1974) and Chang et al. (1995) 28 and the γ–Reθ transition model of Langtry and Menter (2009) 38 capture well the key flow features of these unsteady turbulent flows. For the cases of low and intermediate acceleration rates, these three models yield predictions of wall shear stress that agree well with the corresponding DNS data. For the case of high acceleration, the γ–Reθ model of Langtry and Menter (2009) 38 and the k–ε model of Launder and Sharma (1974) yield reasonable predictions of wall shear stress.
•Effect of aluminum flake on visual texture and consequently color appearance of metallic coatings was investigated.•Statistical texture analysis methods were applied to quantify texture features of ...metallic coatings.•Correlation between perceptual appearance differences and texture differences was investigated.•Analysis of variation (ANOVA) was applied to find the best texture analysis method.
In this study, the effect of aluminum flake size on the color appearance of metallic coatings has been investigated. To this end, metallic solvent-borne basecoat-clear coat systems with seven different surface textures using different sizes of aluminum flakes were prepared corresponding to nine color centers including blue, yellow, red, green, purple, cyan, orange, greenish yellow and gray. The color changes via texture differences were assessed by visual experiments carried out by 25 observers including 14 women and 11 men using gray scale method and under semi-diffuse illumination conditions. The assessed pairs had the same color center and different visual texture caused by different aluminum flake sizes. Texture analysis was performed using autocorrelation function and fractal dimension on gray scale images of the samples, captured by a scanner, and texture difference for each assessed pair was computed.
The results showed that different aluminum flake size can cause different visual texture and consequently different color appearance. The correlation between perceptual color differences and the texture differences showed that autocorrelation function and fractal dimension have a pretty good performance for quantifying texture feature of the metallic coatings while the texture is caused by aluminum flakes.
Employing an economical and non-destructive method for identifying pigments utilized in artworks is a significant aspect for preserving their antiquity value. One of the non-destructive methods for ...this purpose is spectrophotometry, which is based on the selected absorption of light. Mathematical descriptive methods such as derivatives of the reflectance spectrum, the Kubelka–Munk function and logarithm have been employed for the characterization of the peak features corresponding to the spectrophotometric data. In the present study, the mentioned mathematical descriptive methods were investigated with the aim to characterize the constituents of an Iranian artwork but were not efficient for the samples. Therefore, inverse tangent derivative equation was developed on spectral data for the first time, providing considerable details in the profile of reflectance curves. In the next part, to have a simpler and more practical method it was suggested to use filters made up of pure pigments. By using these filters and placing them on the samples, imaging was done. Then, images of samples with and without filter were evaluated and pure pigments were distinguished. The mentioned methods were also used to identify pigments in a modern Iranian painting specimen. The results confirmed these methods with reliable answers indicating that physical methods (alongside chemical methods) can also be effective in determining the types of pigments.
Background and Objective: One of the most important factors in the success of anterior composite restorations is color stability in different situations in mouth. The aim of this study was to ...evaluate the color stability of four anterior composites in the staining solutions (tea and coffee) and under Ultra-Violette (UV) accelerated aging using spectrophotometer. Methods: This in-vitro study was conducted on 80 samples of four composites (Grandio, G-aenial, Kalore and Estelite Σ quick). Samples were divided into four subgroups (5 samples in each subgroup): immersion in coffee (for 48 hours), tea (for 48 hours), distilled water (as the control group) and exposure to UV for 168 hours. The color of the samples was evaluated by the spectrophotometer before and after the various conditions using the CIE Lab system and color changes (ΔE*ab) were calculated. Findings: In all composites, the maximum and minimum levels of color changes were related to the groups immersed in coffee and distilled water, respectively. The significant color change was observed in all subgroups (ΔE*ab>3.3), except for the control groups and tea-Estelite Σ quick (ΔE*ab=2.79). The highest color change was related to immersion in coffee-Grandio (ΔE*ab=9.084) and the lowest observed in immersion in distilled water-Estelite Σ quick (ΔE*ab=0.836). In coffee immersion subgroups of Grandio and Kalore, higher color change was seen compared to Estelite Σ quick (p=0.02 and p=0.028, respectively). Conclusion: Long-term exposure to tea and coffee and UV accelerated aging leads to clinical color change in Grandio, G-aenial, Kalore and Estelite Σ quick composites.
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