The Effect of Positioning Guide Color on Shade Measurements Using a Clinical Spectrophotometer.

The purpose of this study was to investigate the influence of the color of positioning guides on the CIEL*a*b* color coordinates of ceramic, resin composite and bovine tooth surfaces measured by a clinical spectrophotometer. Positioning guides (n=10) in different colors (translucent, purple, yellow, green and, blue) were made for each surface (ceramic, resin composite and bovine tooth). The CIEL*a*b* color coordinates were measured with the positioning guides and with no positioning guide (control group). The ΔL*, Δa*, Δb*, ΔE*ab, and ΔE00 were calculated between the control group and the different groups. The CIEL*a*b* color coordinates were analyzed by one-way ANOVA followed by the post-hoc Tukey test (α=0.05). Color differences were interpreted using the 50:50% perceptibility and acceptability visual thresholds. Positioning guides with different colors presented significant differences for all surfaces and color coordinates. ΔE*ab, and ΔE00 mean values for all surfaces and positioning guide colors exceeded the acceptability visual thresholds, except for the bovine tooth surface measured with the green positioning guide. The shade measurement was affected by the color of the positioning guides regardless of the surface that was evaluated.

A comparative study of shade-matching performance using intraoral scanner, spectrophotometer, and visual assessment.

This study aimed to explore the clinical applicability of the shade-matching function in intraoral scanners. This study measured the tooth colors of maxillary anterior dentitions of 83 adults using visual matching, a spectrophotometer, and a scanner according to two color systems: VITA Classical (VC) and VITA 3D-Master (V3D). Agreement between each method was assessed by weighted Cohen's kappa coefficient (KW, α = 0.05). For V3D, the overall agreement between the scanner and spectrophotometer (KW = 0.498) was higher than that between the scanner and visual matching (KW = 0.473). Similarly, the agreement between the scanner and spectrophotometer (KW = 0.283) was higher than that between a scanner and visual matching (KW = 0.140) for VC. Regarding tooth position, the highest agreement between the scanner and spectrophotometer was observed on the right central incisor (KW = 0.542) for V3D. Tooth color measurement with a scanner was comparable to that with a spectrophotometer, especially on the central incisors when using the VITA 3D-Master system. A scanner could serve as an alternative to a spectrophotometer for shade selection. However, color matching should still be visually verified.

Development of an affordable light emitting diode spectrophotometer paired with a Python program for calibration and linearity testing and the measurement of uranium(VI).

Uranium (U) is a radiologically and chemically toxic element that occurs naturally in water, soil, and rock at generally low levels. However, anthropogenic uranium can also leach into groundwater sources due to mining, ore refining, and improper nuclear waste management. Over the last few decades, various methods for measuring uranium have emerged; however, most of these techniques require skilled scientists to run samples on expensive instrumentation for detection or require the pretreatment of samples in complex procedures. In this work, a Schiff base ligand (P1) is used to develop a simple spectrophotometric method for measuring the concentration of uranium (VI) with an accurate and affordable light-emitting diode (LED) spectrophotometer. A test for a higher-order polynomial relationship was used to objectively determine the calibration data's linearity. This test was done with a Python program on a Raspberry Pi computer that captured the spectrophotometer's calibration and sample measurement data.

Colourimetric changes experienced in three types of aligners according to the L'Eclairage Commission.

OBJECTIVE: The objective was to compare the colourimetric increment (L*, a*, and b*) of three types of aligners after subjecting them to two stains and to evaluate the initial colourimetric characteristics. METHODS: A total of 120 aligners (40 Invisalign®, 40 Spark®, and 40 QuickSmile®) were immersed in two different agents (distilled water and coffee). Measurements were taken using a spectrophotometer before immersion (T0), after 12 hours (T1), and after 7 days (T2). Colour changes (ΔE*) were evaluated based on the International Commission of L'Eclairage, and subsequently converted to National Bureau of Standards units. The measurement was repeated three times. The intraclass correlation coefficient, one-way ANOVA, Tukey's post hoc test, and the independent t test were used (P ≤ .05). RESULTS: At T0, significant differences were observed for a*: Invisalign® and Spark® tended towards redder tones, whereas Quicksmile® leaned towards greener shades. Regarding b*, all aligners tended towards yellow, with Invisalign® exhibiting the least tendency. No differences were found in water between T1 and T0. In the intervals, T2-T1 and T2-T0, Spark® showed more noticeable changes, whereas for Invisalign® and Quicksmile®, the change was only slight. In coffee, a shift to another colour was detected in T1-T0, T2-T1, and T2-T0 for Invisalign®, whereas for other brands, it was barely noticeable except for T2-T0 in Spark®, where the change was appreciable. In coffee, Invisalign® tended towards darker values (L*), turning redder (a*), and more yellow (b*) in T2-T1 and T2-T0. CONCLUSIONS: Invisalign® aligners initially presented a more reddish and less yellowish colour. In water, after 7 days, a noticeable colour change was found for Spark®. In coffee, a greater loss in brightness and a change to red and yellow were observed after 12 hours and 7 days for Invisalign®. This study highlights the importance of considering the impact of coffee on the colouring of aligners, especially with Invisalign®, which shows more noticeable changes.

MiniRead: A simple and inexpensive do-it-yourself device for multiple analyses of micro-organism growth kinetics.

Fitness in micro-organisms can be proxied by growth parameters on different media and/or temperatures. This is achieved by measuring optical density at 600 nm using a spectrophotometer, which measures the effect of absorbance and side scattering due to turbidity of cells suspensions. However, when growth kinetics must be monitored in many 96-well plates at the same time, buying several 96-channel spectrophotometers is often beyond budgets. The MiniRead device presented here is a simple and inexpensive do-it-yourself 96-well temperature-controlled turbidimeter designed to measure the interception of white light via absorption or side scattering through liquid culture medium. Turbidity is automatically recorded in each well at regular time intervals for up to several days or weeks. Output tabulated text files are recorded into a micro-SD memory card to be easily transferred to a computer. We propose also an R package which allows (1) to compute the nonlinear calibration curves required to convert raw readings into cell concentration values, and (2) to analyze growth kinetics output files to automatically estimate proxies of growth parameters such as lag time, maximum growth rate, or cell concentration at the plateau.

Early detection of plant virus infection using multispectral imaging and spatial-spectral machine learning.

Cassava brown streak disease (CBSD) is an emerging viral disease that can greatly reduce cassava productivity, while causing only mild aerial symptoms that develop late in infection. Early detection of CBSD enables better crop management and intervention. Current techniques require laboratory equipment and are labour intensive and often inaccurate. We have developed a handheld active multispectral imaging (A-MSI) device combined with machine learning for early detection of CBSD in real-time. The principal benefits of A-MSI over passive MSI and conventional camera systems are improved spectral signal-to-noise ratio and temporal repeatability. Information fusion techniques further combine spectral and spatial information to reliably identify features that distinguish healthy cassava from plants with CBSD as early as 28 days post inoculation on a susceptible and a tolerant cultivar. Application of the device has the potential to increase farmers' access to healthy planting materials and reduce losses due to CBSD in Africa. It can also be adapted for sensing other biotic and abiotic stresses in real-world situations where plants are exposed to multiple pest, pathogen and environmental stresses.

The Effect of Coloring Beverages on Color Stability of Hybrid Ceramics with Different Surface Treatments

ABSTRACT Objective To assess the effects of coloring beverages on the color stability of two types of hybrid ceramics with different surface treatments. Material and Methods 180 specimens of two hybrid ceramics (Vita Enamic and Mazic Duro) and a feldspathic ceramic (Vita Mark II) were prepared (n=60 in each group). Half of the discs in each group were glazed while the other was polished. The specimens were then divided into three subgroups and immersed in distilled water, carrot juice, and coffee. The overall color difference (∆E) was calculated based on CIE L*a*b* color space. Data were analyzed using three-way and one-way ANOVA; Tukey's honest significant difference was also done for pairwise comparisons (α=0.05). Results Vita Mark II specimens revealed less overall color changes compared to other groups. The ∆E of the glazed Vita Enamic specimens was greater than polished specimens following immersion in distilled water (p=0.03) and coffee (p=0.001), but it was not significant for carrot juice. The same results were obtained for polished Mazic Duro specimens. Relatively similar amounts of ∆E were recorded in polished and glazed subgroups of Vita Mark II. Conclusion The ∆E of hybrid ceramics was higher than Vita Mark II. Polishing could be recommended for surface treatment of hybrid ceramics instead of glazing, saving time and facilitating the process.

Wearable light spectral sensor optimized for measuring daily α-opic light exposure.

Light has many non-visual effects on human physiology, including alterations in sleep, mood, and alertness. These effects are mainly mediated by photoreceptors containing the photopigment melanopsin, which has a peak sensitivity to short wavelength ('blue') light. Commercially available light sensors are commonly wrist-worn and report photopic illuminance and are calibrated to perceive visual brightness and hence cannot be used to investigate the non-visual impacts of light. In this paper, we report the development of a wearable spectrophotometer designed to be worn as a pendant or affixed to clothing to capture spectral power density data close to eye level in the visible wavelength range 380-780 nm. From this, the relative impact of a given light stimulus can be determined for each photoreceptive input in the human eye by calculating effective illuminances. This device showed high accuracy for all effective illuminances while measuring a range of commonly encountered light sources by calibrating for directional response, dark noise, sensor saturation, non-linearity, stray-light and spectral response. Features of the device include IoT-integration, onboard data storage and processing, Bluetooth Low Energy (BLE) enabled data transfer, and cloud storage in one cohesive unit.

Advanced time-resolved absorption spectroscopy with an ultrashort visible/near IR laser and a multi-channel lock-in detector.

Ultrashort visible-near infrared (NIR) pulse generation and its applications to ultrafast spectroscopy are discussed. Femtosecond pulses of around 800 nm from a Ti:sapphire laser are used as a pump of an optical parametric amplifier (OPA) in a non-collinear configuration to generate ultrashort visible (500-780 nm) pulses and deep-ultraviolet (DUV, 259-282 nm) pulses. The visible-NIR pulses and DUV pulses were compressed to 3.9 fs and 10.4 fs, respectively, and used to elucidate various ultrafast dynamics in condensed matter with a sub-10 fs resolution by pump-probe measurements. We have also developed a 128-channel lock-in amplifier. The combined system of the world-shortest visible pulse from the OPA and the lock-in amplifier with the world-largest channel-number can clarify the sub-10 fs-dynamics in condensed matter. This system clarified structural changes in an excited state, reaction intermediate, and a transition state. This is possible even during molecular vibration and reactions via a real-time-resolved vibronic spectrum, which provides molecular structural change information. Also, ultrafast dynamics in exotic materials like carbon nanotubes, topological insulators, and novel solar battery systems have been clarified. Furthermore, the carrier-envelope phase in the ultrashort pulse has been controlled and measured.

Surface color spectrophotometry in a murine model of steatosis: an accurate technique with potential applicability in liver procurement.

Steatosis is the most important prognostic histologic feature in the setting of liver procurement. The currently utilized diagnostic methods, including gross evaluation and frozen section examination, have important shortcomings. Novel techniques that offer advantages over the current tools could be of significant practical utility. The aim of this study is to evaluate the accuracy of surface color spectrophotometry in the quantitative assessment of steatosis in a murine model of fatty liver. C57BL/6 mice were divided into a control group receiving normal chow (n = 19), and two steatosis groups receiving high-fat diets for up to 20 weeks-mild steatosis (n = 10) and moderate-to-severe steatosis (n = 19). Mouse liver surfaces were scanned with a hand-held spectrophotometer (CM-600D; Konica-Minolta, Osaka, Japan). Spectral reflectance data and color space values (L*a*b*, XYZ, L*c*h*, RBG, and CMYK) were correlated with histopathologic steatosis evaluation by visual estimate, digital image analysis (DIA), as well as biochemical tissue triglyceride measurement. Spectral reflectance and most color space values were very strongly correlated with histologic assessment of total steatosis, with the best predictor being % reflectance at 700 nm (r = 0.91 [0.88-0.94] for visual assessment, r = 0.92 [0.88-0.95] for DIA of H&E slides, r = 0.92 [0.87-0.95] for DIA of oil-red-O stains, and r = 0.78 [0.63-0.87] for biochemical tissue triglyceride measurement, p < 0.0001 for all). Several spectrophotometric parameters were also independently predictive of large droplet steatosis. In conclusion, hepatic steatosis can accurately be assessed using a portable, commercially available hand-held spectrophotometer device. If similarly accurate in human livers, this technique could be utilized as a point-of-care tool for the quantitation of steatosis, which may be especially valuable in assessing livers during deceased donor organ procurement.

Acetylcholinesterase (AChE) Activity in Embryos of Zebrafish.

Acetylcholinesterase (AChE) is a useful biomarker for organophosphate and carbamate pesticides exposure. The inhibition of this enzyme has been associated with neurotoxicity and alterations at higher levels of biological organization, such as behavior and development impairments. In this chapter, we describe the methodologies for analyses of AChE activity in pools of 96 h of embryos of zebrafish (Danio rerio) using a spectrophotometric method adapted to 96-well microtiter plates.

Concentration of heavy metals in UHT dairy milk available in the markets of São Luís, Brazil, and potential health risk to children.

OBJECTIVE: To assess the levels of heavy metals and their antagonists in dairy products available in the markets of São Luís, northeastern Brazil. METHODS: Chemical analysis of the heavy metals copper(Cu), lead(Pb), mercury(Hg), and nickel(Ni) and their antagonists iron(Fe), zinc(Zn), calcium(Ca), selenium(Se), and cobalt(Co) contained in dairy products using inductively coupled plasma optical emission spectrometry (ICP-OES). RESULTS: The main heavy metal observed in dairy products were Hg; Pb; Se and Ni. A significant negative correlation was observed between the concentrations of Cu and Fe (rho = -0.634, p = 0.001), Cu and Zn (rho = -0.794, p = 0.000) in whole milk. A non-significant positive correlation was observed between Pb and Ca (rho = 0.387, p = 0.056), and Hg and Se (rho = 0.055, p = 0.795). CONCLUSIONS: Dairy product brands available in the markets of São Luís could be considered a source of heavy metal contamination (Hg, Pb, Se, Cu, Ni) with weak correlations with their antagonists.

Ocotea daphnifolia: phytochemical investigation, in vitro dual cholinesterase inhibition, and molecular docking studies

This study aimed to evaluate the anticholinesterase activities of extracts and fractions of Ocotea daphnifolia in vitro and characterize its constituents. The effects of hexane, ethyl acetate, and ethanolic extracts on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activity were determined with a spectrophotometry assay. All extracts inhibited cholinesterase activity, and the ethanolic extract (2 mg/mL) exhibited the highest inhibition of both enzymes (99.7% for BuChE and 82.4% for AChE). The ethanolic extract was fractionated by column chromatography resulting in 14 fractions that were also screened for their anticholinesterase effects. Fraction 9 (2 mg/mL) showed the highest activity, inhibiting AChE and BuChE by 71.8% and 90.2%, respectively. This fraction was analyzed by high-performance liquid chromatography high-resolution mass spectrometry which allowed the characterization of seven glycosylated flavonoids (containing kaempferol and quercetin nucleus) and one alkaloid (reticuline). In order to better understand the enzyme-inhibitor interaction of the reticuline toward cholinesterase, molecular modeling studies were performed. Reticuline targeted the catalytic activity site of the enzymes. Ocotea daphnifolia exhibits a dual cholinesterase inhibitory activity and displays the same pattern of intermolecular interactions as described in the literature. The alkaloid reticuline can be considered as an important bioactive constituent of this plant.

Analysis of the qPCR Assay Efficacy as Molecular Diagnostic in Patients with Chemotherapy and/or Antibiotic Therapy

Abstract High sensitivity of qPCR assay can be compromised by the presence of PCR inhibitors in samples analyzed. The aim of this study was to analyze the RT-qPCR assay efficiency considering the RNA quality/quantity and the presence of PCR inhibitors in patients with chemotherapy and/or antibiotic therapy. We analyzed 60 samples using RT-qPCR from individuals suspected of leukemia and 44 samples were quantified by fluorimetry and spectrophotometry. The efficiency of the RT-qPCR assay was evaluated comparing the threshold cycle (Ct) from tested samples and the standard curve. The 260/280 and 260/230 ratios, the presence of PCR inhibitors and the amount of sample (ng) used in the RT-qPCR reaction can be associated with 56.8% (R²=0.56, p<0.05) in the Ct obtained. The decrease of the RT-qPCR efficiency can be explained in 42,8% due to the variation of the 260/280 ratio (R²=0.42,p<0.05). The presence of antibiotics in the blood sample can be associated in 11.3% with the variability of 260/280 ratio (R²=0.11,p<0.05). Presence of chemotherapeutic drugs in the blood sample was not correlated with Ct variation (p=0.17). The spectrophotometer determines a RNA quantification with 2.2 times higher than the fluorimeter (t=2.2, p=0,03) and this difference is correlated with the 260/280 ratio (R²=0.36, p<0.05). Samples with low purity had a reduction in the qPCR efficiency, although we did not observe false results.

Spectrophotometric Analysis of Streptococcus mutans Growth and Biofilm Formation in Saliva and Histatin-5 Relate to pH and Viscosity

ABSTRACT Objective: To analyze the ability of saliva in controlling the growth and the biofilm formation of Streptococcus mutans (S. mutans) as well as the effect of histatin-5 anti-biofilm relate to pH and saliva viscosity. Material and Methods: The S. mutans biofilm assayed by crystal violet 1% and its growth measured by spectrophotometer. The saliva viscosity was analyzed by viscometer, and pH of saliva was measured by pH meter. Results: Based on the optical density values, growth of S. mutans in saliva ranged <300 CFU/mL (0.1 nm) at concentrations of 25%, 12.5% and 6.25% for 24 hours. Whereas at the 48 h and 72 h period of incubation shown an increase in growth of S. mutans ranged 300-600 CFU/mL (0.2-0.36 nm). The inhibitory biofilm formation of S. mutans in saliva was significantly higher at concentrations of 12.5% and 6.25% at 24 h incubation times on a moderate scale, whereas the histatin-5 was effective to inhibit S. mutans biofilm on the 50 and 25 ppm. The saliva possessed a higher inhibitory of biofilm S. mutans than histatin-5 and good level viscosity (0.91-0.92 cP). Conclusion: The saliva was able to control the growth of S. mutans, and histatin-5 can inhibit the biofilm formation S. mutans. Furthermore, the saliva was also able to respond to the pH change with good viscosity of saliva.

Evaluation of Sample Preparation Procedures for Determination of Cr(VI) in Cr2O3 Pigments by Vis Spectrophotometry

Abstract Six sample preparation procedures were evaluated for selective extraction of Cr(VI) from commercial samples of chromium oxide green (Cr2O3) pigments prior to formation of its diphenylcarbazone complex [CrDPCO]- for determination by visible spectrophotometry: (I) water-soluble chromium; (II) EPA method 3060A without Mg2+; (III) EPA method 3060A with Mg2+; (IV) Na3PO4 based extraction; (V) method IRSA16 based on acidic extraction and; (VI) Na2CO3 based extraction. Evaluation of the influence of concomitant Cr(III) ions, time and stability of the [CrDPCO]- complex was investigated. Recoveries of soluble and insoluble Cr(VI) species were 86% and 80%, respectively, using procedure (VI). Direct calibration against aqueous standards prepared in the extraction medium was successful for Cr(VI) in the concentration range 0.05-1.50 μg L-1. Limits of detection and quantitation were 0.3 µg g-1 and 1.0 µg g-1, respectively, for 250 mg subsamples/25 mL. Procedure (VI) was applied to the analysis of four commercial samples of Cr2O3 pigments, three determined to have Cr(VI) within compliance limits below 1.0 µg g-1, but one at 16.6 ± 0.6 µg g-1, prohibiting use of this pigment in cosmetic formulations. This sample was conveniently employed to evaluate the accuracy of the method. The recommended procedure is simple and accurate and has been adopted by Tecpar's laboratory of Parana Institute of Technology (Curitiba, Brazil).

Biofilm dynamics: linking in situ biofilm biomass and metabolic activity measurements in real-time under continuous flow conditions.

The tools used to study biofilms generally involve either destructive, end-point analyses or periodic measurements. The advent of the internet of things (IoT) era allows circumvention of these limitations. Here we introduce and detail the development of the BioSpec; a modular, nondestructive, real-time monitoring system, which accurately and reliably track changes in biofilm biomass over time. The performance of the system was validated using a commercial spectrophotometer and produced comparable results for variations in planktonic and sessile biomass. BioSpec was combined with the previously developed carbon dioxide evolution measurement system (CEMS) to allow simultaneous measurement of biofilm biomass and metabolic activity and revealed a differential response of these interrelated parameters to changing environmental conditions. The application of this system can facilitate a greater understanding of biofilm mass-function relationships and aid in the development of biofilm control strategies.

A Novel Method for Measuring Serum Unbound Bilirubin Levels Using Glucose Oxidase-Peroxidase and Bilirubin-Inducible Fluorescent Protein (UnaG): No Influence of Direct Bilirubin.

The glucose oxidase-peroxidase (GOD-POD) method used to measure serum unbound bilirubin (UB) suffers from direct bilirubin (DB) interference. Using a bilirubin-inducible fluorescent protein from eel muscle (UnaG), a novel GOD-POD-UnaG method for measuring UB was developed. Newborn sera with an indirect bilirubin/albumin (iDB/A) molar ratio of <0.5 were classified into four groups of DB/total serum bilirubin (TB) ratios (<5%, 5-10%, 10-20%, and ≥20%), and the correlation between the UB levels and iDB/A ratio was examined. Linear regression analysis was performed to compare UB values from both methods with the iDB/A ratio from 38 sera samples with DB/TB ratio <5% and 11 samples with DB/TB ratio ≥5%. The correlation coefficient (r) between UB values and the iDB/A ratio for the GOD-POD method was 0.8096 (DB/TB ratio <5%, n = 239), 0.7265 (5-10%, n = 29), 0.7165 (10-20%, n = 17), and 0.4816 (≥20%, n = 16). UB values using the GOD-POD-UnaG method highly correlated with the iDB/A ratio in both <5% and ≥5% DB/TB ratio sera (r = 0.887 and 0.806, respectively), whereas a low correlation (r = 0.428) occurred for ≥5% DB/TB ratio sera using the GOD-POD method. Our GOD-POD-UnaG method can measure UB levels regardless of the presence of DB.

Development of a bio-optical model for the Barents Sea to quantitatively link glider and satellite observations.

A bio-optical model for the Barents Sea is determined from a set of in situ observations of inherent optical properties (IOPs) and associated biogeochemical analyses. The bio-optical model provides a pathway to convert commonly measured parameters from glider-borne sensors (CTD, optical triplet sensor-chlorophyll and CDOM fluorescence, backscattering coefficients) to bulk spectral IOPs (absorption, attenuation and backscattering). IOPs derived from glider observations are subsequently used to estimate remote sensing reflectance spectra that compare well with coincident satellite observations, providing independent validation of the general applicability of the bio-optical model. Various challenges in the generation of a robust bio-optical model involving dealing with partial and limited quantity datasets and the interpretation of data from the optical triplet sensor are discussed. Establishing this quantitative link between glider-borne and satellite-borne data sources is an important step in integrating these data streams and has wide applicability for current and future integrated autonomous observation systems. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Investigation of Volatiles in Cork Samples Using Chromatographic Data and the Superposing Significant Interaction Rules (SSIR) Chemometric Tool.

This study describes a new chemometric tool for the identification of relevant volatile compounds in cork by untargeted headspace solid phase microextraction and gas chromatography mass spectrometry (HS-SPME/GC-MS) analysis. The production process in cork industries commonly includes a washing procedure based on water and temperature cycles in order to reduce off-flavors and decrease the amount of trichloroanisole (TCA) in cork samples. The treatment has been demonstrated to be effective for the designed purpose, but chemical changes in the volatile fraction of the cork sample are produced, which need to be further investigated through the chemometric examination of data obtained from the headspace. Ordinary principal component analysis (PCA) based on the numerical description provided by the chromatographic area of several target compounds was inconclusive. This led us to consider a new tool, which is presented here for the first time for an application in the chromatographic field. The superposing significant interaction rules (SSIR) method is a variable selector which directly analyses the raw internal data coming from the spectrophotometer software and, combined with PCA and discriminant analysis, has been able to separate a group of 56 cork samples into two groups: treated and non-treated. This procedure revealed the presence of two compounds, furfural and 5-methylfurfural, which are increased in the case of treated samples. These compounds explain the sweet notes found in the sensory evaluation of the treated corks. The model that is obtained is robust; the overall sensitivity and specificity are 96% and 100%, respectively. Furthermore, a leave-one-out cross-validation calculation revealed that all of the samples can be correctly classified one at a time if three or more PCA descriptors are considered.