Lambert Law Research Articles

Laser absorption spectroscopy for plasma-assisted thermochemical treatment. Part I.: Applicability of the Beer–Lambert law and interpretation of spectroscopic data

The work is devoted to the development of laser absorption spectroscopy (LAS) of plasma-assisted processes for application under industrial conditions. The interpretation of the LAS measurements was revised by taking into consideration the temperature gradient along the absorption path, which is unavoidable in a reactor for thermochemical treatment. The revision is based on the measurement of , , and molecular lines in an industrial-scale, active screen plasma nitrocarburizing reactor with a steel active screen. It shows that an effective temperature determined from Doppler broadening could be assigned to each measured spectral line. The effective temperature does not only reflect the temperature gradients along the line-of-sight but also the line strength dependence on temperature for the specific spectroscopic transition. Lower limit estimates of the molecular densities are proposed based on the determined effective temperatures under the assumption of a Boltzmann distribution of the population density over the molecular levels at any local volume of the reactor. For a more accurate interpretation of LAS data of plasma-assisted processes, the spatial distribution of the temperature along line-of-sight has to be known and needs to be taken into account to obtain the molecular densities.

ECG augmented pulse oximetry in Atlantic salmon (Salmo salar)—A pilot study

Understanding the tolerance limits of fish is crucial for developing aquaculture operations that ensure good animal welfare. However, there exist little data describing the physiological responses in farmed Atlantic salmon, much because the technological tools for taking such measurements have not existed. Recent advances in electronic implants have enabled concurrent measurement of electrocardiogram (ECG) and photoplethysmograms (PPG) in salmon that can be used for robust estimation of HR and oxygen saturation in arterial blood (i.e., SpO2/pulse oximetry) if appropriate strategies for motion artifact and light scattering compensation can be realized. To enable pulse oximetry for farmed Atlantic salmon (and fish in general), two experiments have been conducted. In Experiment 1, PPGs were obtained from salmon induced to swim at two different water currents under normoxic conditions. By using two water currents, the resulting data provided a foundation for developing methods for motion artifact compensation. Data from this experiment were also used to calculate an average light scattering parameter using the modified Beer–Lambert law, under the assumption that SpO2 was 100% for individual fish. In Experiment 2, fish were placed in a swim tunnel and subjected to hypoxic conditions and corresponding changes in SpO2 were estimated using the motion artifact and light scattering compensation approaches from Experiment 1.Results show that the suggested compensation approaches gives SpO2 estimates within the expected range (95% to 100%) under normoxic conditions. Under hypoxic conditions, changes in SpO2 that coincide with experiment events were observed, demonstrating that PPGs can be used to quantify such changes. The results from this pilot study therefore extend the selection of physiological parameters feasible to measure using electronic implants for Atlantic salmon. In doing so, the scope for physiological measurements is extended such that an improved understanding of physiological responses and tolerances in Atlantic salmon farming can be acquired, and ultimately be used to improve animal welfare in fish production.

UV Spectrophotometric and UPLC assay methods for the determination of Palbociclib in bulk and Tablet Dosage Form

The goal of this study was to create a sensitive and reliable UV-spectrophotometric and reverse phase liquid chromatographic method for determining Palbociclib in bulk and pharmaceutical dosage forms. The current UV approach uses methanol and phosphate buffer as a solvent to evaluate absorption at a maximum wavelength of 220nm. Waters Acquity BEH C18 (2.1 x 50mm, 1.7µm) UPLC column with Empower 2 was used in the UPLC procedure. The mobile phase was made up of 50:50 (v/v) methanol and phosphate buffer.The drug obeyed Beer Lambert's law in the UV technique in the concentration range of 1-70µg/ml with a regression coefficient of 0.999. The linearity level in the UPLC technique was 1-100µg/ml. In the validation investigation, the developed UV and UPLC procedures were successful. For the UPLC and UV methods, the percentage purity of the marketed dosage form of Palbociclib was found to be 98.76 percent and 98.84 percent, respectively. The percent RSD of all validation parameters investigated, as suggested by the ICH recommendations, was determined to be less than 2 in both techniques. The two methods established for determining Palbociclib in bulk and tablet doses were found to be accurate, simple, and validated.

Study of Particle Size Measurement by the Extinction Method in Flame

The laser extinction method (LEM) is particularly suitable for measuring particle sizes in flames because this method, which is based on the Beer–Lambert law, is non-intrusive and easy to implement. In the LEM, the interpretation of the extinction data is usually developed under the assumption that light extinction due to scattering is a result of the superposition of single scattering by individual particles; however, this could be violated for flames with dense concentrations of particles in which multiple scattering could occur. Quantifying the effect of multiple scattering under general conditions is still a formidable problem. In this work, we carried out a series of careful measurements of the laser extinction using standard particles of various known sizes, number densities and optical path lengths, all under the condition that the acceptance angle of the detector was limited to nearly zero. Combined with a four-flux model, we quantitatively analyzed the effect of multiple scattering on the size measurement using the LEM. The results show that the effect of multiple scattering could be ignored when the optical thickness is less than two under strict restrictions on the detector acceptance angle. Guided by this, the size distribution of an alumina (Al2O3) particle sample was measured by the LEM with dual wavelengths. Parameterized distributions were solved with the help of graph plotting, and the results compared well with the measurement from the Malvern particle size analyzer. The same method was then used to measure the particle size distribution in the plume of a solid rocket motor (SRM). The use of an off-axis parabolic mirror in the experimental setup could suppress the jitter of light passing through the SRM plume, and the particle size in the plume of the measured SRM was in the order of microns.

AI-Assisted Disease Monitoring Using Stretchable Polymer-Based Sensors.

Flexible sensors have attracted significant attention for medical applications. Herein, an AI-assisted stretchable polymer-based (AISP) sensor has been developed based on the Beer-Lambert law for disease monitoring and telenursing. Benefiting from the use of superior polymer materials, the AISP sensor features a high tensile strain of up to 100%, durability of >10,000 tests, excellent waterproofness, and no effect of temperature (1.6-60.9 °C). Such advantages support the capability that the AISP can be flexibly pasted on the skin surface as a wearable device for real-time monitoring of multiple physiological parameters. An AISP sensor-based swallowing recognition technique has been proposed with a high accuracy of up to 88.89%. Likewise, it has been expanded to a remote nursing assistance system to meet critical patients' physiological requirements and daily care. The hands-free communication experiment and robot control applications have also been successfully conducted based on the constructed system. Such merits demonstrate its potential as a medical toolkit and indicate promise for intelligent healthcare.

AM–GM Algorithm for Evaluating, Analyzing, and Correcting the Spatial Scaling Bias of the Leaf Area Index

The leaf area index (LAI) is a crucial variable in climate, ecological, and land surface modeling. However, the estimation of the LAI from coarse-resolution remote sensing data can be affected by the spatial scaling bias, which arises from the nonlinearity of retrieval models and the heterogeneity of the land surface. This study provides an algorithm named Arithmetic Mean and Geometric Mean (AM–GM) to correct the spatial scaling bias. It is established based on negative logarithmic functions and avoids second-order stationarity. In this algorithm, relationships are derived between the scaling bias of LAI and the arithmetic and geometric means of directional gap probability for two commonly used remote sensing models, the Beer–Lambert law and a semi-empirical transfer function, respectively. According to the AM–GM algorithm, the expression representing the model nonlinearity is derived and utilized for the analysis of LAI scaling bias. Furthermore, the AM–GM algorithm is simplified by a linear relationship, which is constructed between two quantities related to the directional gap probability between two specific resolutions. Two scenes simulated by the LargE-Scale remote sensing data and image Simulation framework (LESS) model and three sites are used to evaluate the proposed algorithm and analyze the scaling bias of LAI. The validation results show that the AM–GM algorithm provides accurate correction of LAI scaling bias. The analyses based on the AM–GM algorithm demonstrate that the scaling bias of LAI increases with the increase in the LAI value, with stronger surface heterogeneity and coarser spatial resolution. The validation results of the simplified AM–GM algorithm demonstrate that at the Sud-Ouest site, the absolute value of the bias for the estimated LAI decreases from 0.10, 0.22, 0.29, and 0.31 to 0.04, 0.01, 0.04, and 0.05 at 200 m, 500 m, 1000 m, and 1500 m resolutions, respectively. In conclusion, the proposed algorithm is effective in the analysis and correction of the scaling bias for coarse-resolution LAI.

Estimating Three-Dimensional Distribution of Leaf Area Using Airborne LiDAR in Deciduous Broad-Leaved Forest

We examined the performance of airborne light detection and ranging (LiDAR) data obtained in 2011 for leaf area estimation in deciduous broad-leaved forest using the Beer–Lambert law in Takayama, Gifu, Japan. We estimated leaf area index (LAI, allometry-LAI) and vertical leaf area density (LAD) using field survey data by applying allometric equations to estimate leaf-area of trees and a Weibull distribution equation to estimate vertical leaf distribution. We then estimated extinction coefficients (Ke) of LiDAR data for three height layers from the ground to the canopy top using the vertical LAD and vertical laser pulse distribution. The estimated PAI (LiDAR-PAI) using the Beer–Lambert law and Ke, when treating the canopies as three height layers, showed a significant linear relationship with allometry-LAI (p < 0.001). However, LiDAR-PAI when treating the canopies as single layer saturated at a PAI of six. It was similar to the lesser PAI estimation by hemispherical photography or relative photosynthetic photon flux density which treated the canopy as a single layer, compared to LAI measurements by litter traps. It is therefore important to allocate distinct Ke values to each of the multiple height layers for an accurate estimation of PAI and vertical PAD when applying the Beer–Lambert law to airborne LiDAR data.

Developing a Portable Spectrometer to Detect Chemical Contaminants in Irrigation Water

Water pollution is a critical issue since it can severely affect health and the environment. The purpose of the study is to develop a portable spectrometer (ESP32-based spectrometer) to detect chemical contaminants in irrigation water by observing the light absorbance of contaminants. ESP32 and a light sensor (photodiode) were respectively, used as the main controller and detector of the portable spectrometer. It was developed based on optical dispersion and Beer–Lambert law theory. The light absorbance of different types of contaminants was displayed in a Blynk application for real-time monitoring. The samples were also tested using a lab-based spectroscopy method, ultraviolet-visible (UV-Vis) spectrometer. The spectral range of the measurement is from 350 nm to 700 nm and the standard error of the ESP32-based spectrometer is from 0.01 to 0.05. Five water samples were tested, consisting of ammonium nitrate, organic pesticide, zinc oxide and two different reservoirs used for irrigation. The absorption peaks of the ammonium nitrate and organic pesticide are 363 nm and 361 nm, respectively. Zinc oxide shows the absorbance peak at 405 nm, whereas both reservoirs show absorbance peaks lie in the region from 300 nm to 370 nm. Therefore, this study shows that different types of contaminants can absorb light only at specific wavelength regions by considering the concentration of samples. The developed ESP32-based spectrometer can be applied for on-site water quality monitoring as it is portable, light, simple and can be monitored in real time using multiple devices.

One-dimensional physical model for complementary electrochromic device

Eletrochromic devices are electrochemical systems that can undergo the optical modulation in response to an applied electrical stimulus. In order to investigate the electrochromic (EC) process mechanism and predict the electrochromic behavior, this paper proposes a physical model that employs tungsten trioxide (WO3), nickel oxide (NiO) and LiClO4-propylene carbonate (PC) solution. Within electrochromic films, electrolytes can transport lithium ions and anions through porous layers of electrochromic films. At the interfaces between solution and porous layers, lithium-ion intercalation and deintercalation take place. Considering both ion diffusion and electromigration, ion transport kinetics is described by Nernst-Plank equation. The partial differential equations (PDEs) for potential consist of Poisson equations for electrolytes and Ohm’s law for WO3 and NiO films. Moreover, the ion injection behavior at the interface is governed by Frumkin-Butler-Volmer (FBV) equation and potential conditions of the stern layer. Finally, a modified Beer–Lambert law incorporating porosity is proposed to explain the mechanism of transmittance. Under constant step potential conditions, the state variables of multiphysics field can be tracked, and the dynamic process of the transmittance and electrode current can be accurately predicted. This physical model can be applied for parameter design and precise control of ECDs, based on the optimization of device characteristics.

Doe Approach: A Validated Rp -Hplc Method For The Determination Of Dapagliflozin

Background: Dapagliflozin is a competitive inhibitor of sodium / glucose co transporter 2 (SGLT2). It will Inhibiting the reabsorption of filtered glucose in the kidney leads to elevated urinary glucose excretion, thereby lowering blood Method: A new, simple, accurate, rapid, precise, reproducible and cost-effective RP-HPLC method for the quantitative estimation of Dapagliflozin in bulk and pharmaceutical dosage form. The developed RP-HPLC method for the quantitative estimation of Dapagliflozin is based on measurement of absorption at maximum wavelength 254 nm using 0.1% urea: methanol (35:65% v/v) as a solvent. The stock solution for Dapagliflozin was prepared, and subsequent suitable dilution was prepared in mobile phase to obtained standard curve. The standard solution of Dapagliflozin shows absorption maxima at 254 nm. Results: Dapagliflozin will obeys Beers -Lamberts law in the concentration range of 20 - 100μg/ml with regression 0.999 at 254nm.The overall % recovery was found to be 101.59% for Dapagliflozin which reflects that the method was free from the interference of impurities and other impurities, used in bulk and marketed dosage forms. The low value of % RSD was indicative of accuracy and reproducibility of the method. The % RSD for inter-day and intra-day precision was found to be 0.1 for Dapagliflozin respectively which is & it <2% hence proved that method is precise. Conclusion: The results of analysis have been validated as per International Conference on Harmonization (ICH) guidelines. The developed method can be adopted in routine analysis of Dapagliflozin in bulk and tablet dosage form. The Proposed method was found to be rapid, accurate, precise, specific, robust, rugged and economical.

Calculation of surface spectral irradiance using the Geant4 Monte Carlo toolkit

The spectral direct normal irradiance (DNI) of the surface spectral irradiance, with a spectral resolution of 1 nm in the range of 280–1600 nm, and 5 nm in the range of 1600–3000 nm, has been calculated for the first time with the Geant4 Monte Carlo simulation toolkit using the US Standard Atmosphere 1976 model and the reference extraterrestrial solar spectrum SOLAR-ISS. The atmospheric attenuation of DNI has been studied with and without aerosols. In the presence of aerosols corresponding to 10 km visibility, the total solar DNI attenuation can reach about 84% in the UV domain, 56% in the visible domain and 35.08% in the rest of the infrared domain. The Geant4 results have been compared to those calculated by the MYSTIC code of LibRadtran package and the Beer–Lambert law under the same atmospheric conditions. The average relative transmittance difference between Geant4 and MYSTIC is of the order of few percent in the entire solar spectrum. In the case of atmosphere with aerosols corresponding to 23 km visibility, the most important average of the relative difference between Geant4 and MYSTIC transmittances is about 7.5% in the UV domain and stays between 1.19% and, 3.31% in the rest of the spectrum. More importantly, in this last case of the atmosphere, the values of the spectral transmittance of Geant4 remain intermediate between those of MYSTIC and Beer–Lambert law in the entire visible range up to 800 nm.

Boronic Acids and Their Derivatives as Continuous-Flow-Friendly Alkyl Radical Precursors

AbstractSince its recognition as an enabling tool to form challenging C–C and C–heteroatom bonds under mild and sustainable conditions, photoredox catalysis has been in the spotlight within the synthetic community. As a consequence, the interest in developing novel synthetic strategies has spiked together with the need to define suitable technologies to overcome scale-up issues dictated by the Bouguer–Beer–Lambert law. In this context, continuous-flow reactors play a major role in increasing the efficiency of a given photocatalyzed reaction, thus rendering scale-up processes more accessible. In the alkyl radical precursor landscape, boron-based species have begun to play a predominant role. Though the reactivity of trifluoroborates has been deeply investigated, the interest in using other boron species as radical precursors in photocatalyzed reactions has recently arisen. This late exploration lies in the fact that the high oxidation potential of boronic acids (BAs) hinders their possible applications. Nevertheless, to circumvent this issue, a diverse array of activation modes has been developed, exploiting in most cases the inherent Lewis acidity of the boronic acid. The aim of this Account is to highlight our recent contribution to this vibrant field with a focus on broad applicability, selectivity, and scalability via continuous-flow methodology. For the sake of clarity, the Account is discussed under the following sections.1 Introduction2 Why Photochemistry in Flow?2.1 Preliminary Considerations2.2 Batch vs. Flow Photochemical Reactions2.3 Commercially Available Lab-Scale Solutions for Photoflow Chemistry3 Organoboron Compounds3.1 The Evolution of Organoboron Compounds as Radical Precursors in Photoredox Catalysis3.2 Organoboron Compounds in Flow4 Activation of Boronic Acids towards Radical Formation4.1 Giese-Type Addition4.2 Petasis Reaction4.3 Light-Driven Four-Component Reaction4.4 Minisci Reaction5 Conclusion and Future Perspective

GVirtualXray (gVXR): Simulating X-ray radiographs and CT volumes of anthropomorphic phantoms

gVirtualXray (gVXR) is an open-source framework that relies on the Beer–Lambert law to simulate X-ray images in realtime on a graphics processor unit (GPU) using triangular meshes. We produced four Jupyter Notebooks to compare images simulated with gVXR and ground truth image of an anthropomorphic phantom: (i) an X-ray projection generated using a Monte Carlo simulation code, (ii) real digitally reconstructed radiographs (DRRs), (iii) computed tomography (CT) slices, and (iv) a real radiograph acquired with a clinical X-ray imaging system. Image registration was deployed in two Notebooks to align the simulated image on the corresponding ground truth image. We demonstrated that accurate images can be generated in milliseconds with gVirtualXray when scattering can be ignored.

Area under curve and zero order spectrophotometric determination copper complexation with N,N'-cyclohexane-l,2-diylidene-bis(4-methaxybenzoythydrazide)

This paper describes the development of a spectrophotometric for the determination of copper by coupling with ligand (CHMBH). The a maximum absorption at (415nm) .Beer’s Lambert law is obeyed over the concentration ( 4-24 mg/L) limit of detection and limit of quantitation were found to be 0.00338 mg/L and 0.01025 mg/L for the area under curve and 0.1677 mg/L and 0.508 mg/L for zero order method, the high accuracy of both methods was 99.356 % for the area under curve method and 100.087 % for the zero order method respectively. Both methods have applied successfully to determination of copper with (CHMBH).Keywords: Cu(ll), (CHMBH), (AUC), zero order.

Enhanced Schlieren System for In Situ Observation of Dynamic Light–Resin Interactions in Projection-Based Stereolithography Process

Abstract Digital maskless lithography is gaining popularity due to its unique ability to quickly fabricate high-resolution parts without the use of physical masks. By implementing controlled grayscaling and exposure control, it has the potential to replace conventional lithography altogether. However, despite the existence of a theoretical foundation for photopolymerization, observing the voxel growth process in situ is a significant challenge. This difficulty can be attributed to several factors, including the microscopic size of the parts, the low refractive index difference between cured and uncured resin, and the rapid rate of photopolymerization once it crosses a certain threshold. As such, there is a pressing need for a system that can address these issues. To tackle these challenges, the paper proposes a modified Schlieren-based observation system that utilizes confocal magnifying optics to create a virtual screen at the camera's focal plane. This system allows for the visualization of the minute changes in refractive indices made visible by the use of Schlieren optics, specifically the deflection of light by the changing density-induced refractive index gradient. The use of focusing optics provides the system with the flexibility needed to position the virtual screen and implement optical magnification. The researchers employed single-shot binary images with different pixel numbers to fabricate voxels and examine the various factors affecting voxel shape, including chemical composition and energy input. The observed results were then compared against simulations based on Beer–Lambert's law, photopolymerization curve, and Gaussian beam propagation theory. The physical experimental results validated the effectiveness of the proposed observation system. The paper also briefly discusses the application of this system in fabricating microlenses and its advantages over theoretical model-based profile predictions.

Simultaneous Determination of Montelukast Sodium and Loratadine by Eco-Friendly Densitometry and Spectrophotometric Methods.

Recently, the aim of analytical community is to reduce the usage of hazardous chemicals; so eco-friendly, rapid, selective and cost-effective methods were developed for simultaneous determination of montelukast sodium (MKT) and loratadine (LRT). The first method was based on chromatographic separation performed on precoated silica gel 60 GF254 plates with ethyl acetate-ethanol 9: 1 (v/v) as the mobile phase. The developed plates were scanned and quantified at 260nm. The method gives linear correlation over concentration ranges of 0.3-3.6μg/spot and 0.2-4.0μg/spot for MKT and LRT, respectively. It was also successfully applied to analysis of both drugs in their pharmaceutical preparation and human plasma. The other methods are UV-spectrophotometric methods based on smart spectra manipulating to zero order spectrum of each drug. These methods are named response correlation (RC), a-centering and ratio derivative methods. RC and a-centering methods were dependent on the presence of an isosbestic point between the overlapped spectra of both drugs. While ratio derivative method based on manipulation of the ratio spectra of both drugs. The two drugs obey Beer-Lambert law over the concentration ranges of 3.0-30.0μg/mL in the three spectrophotometric methods. Moreover, the greenness of the developed methods is assessed using suitable analytical Eco-Scale and Green Analytical Procedure Index.

Spectral domain isolation of ballistic component in visible light OCT based on random matrix description

Visible light optical coherence tomography (vis-OCT) provides a unique tool for imaging both structure and oxygen metabolism in ophthalmology. Working in visible light bandwidth, it suffers from noises due to strong scattering, especially in the blood. This work established the random matrix (RM) description of vis-OCT’s k-space data as ballistic and multiple scattering components. The eigenvalue density of the hybrid RM follows a low-rank biased Marčenko–Pastur law. The ballistic component can thus be separated out using a generalized likelihood ratio test algorithm. The RM-based method was validated by both the Monte Carlo simulation and ex vivo pure blood phantom study. We further demonstrated that the RM-based method could significantly improve the imaging quality in the human fundus, showing more details of the layered structure than current vis-OCT with ∼23.6% increase of signal-to-noise ratio, measuring the blood oxygen value more accurately, and enabling better structure visualization than the traditional method, a 1.6-fold higher contrast-to-noise ratio in raster scan mode. The isolated ballistic component also fits the Beer–Lambert law better, giving more accurate oxygen saturation in arc scan mode. The RM-based method significantly improves the reconstruction quality in 3D and facilitates clinical diagnostics. As a general framework, random matrix description also provides a new separation strategy to estimate the ballistic component in other spectral domain OCT techniques.

An Experimental Introduction to Colloidal Nanocrystals through InP and InP/ZnS Quantum Dots

Quantum dots are colloidal semiconductor nanocrystals that display size-dependent electronic and optical properties. These materials are a visual demonstration of a quantum-mechanical effect. Here we present a laboratory exercise for undergraduate/Bachelor students as an introduction to colloidal nanocrystals and quantum dots. The students synthesize three sizes of indium phosphide (InP) nanocrystals and perform one core/shell synthesis of indium phosphide cores shelled with zinc sulfide (InP/ZnS). The obtained quantum dots are characterized by quantitative UV–vis, photoluminescence, and 1H NMR spectroscopy. Students are acquainted with several concepts: nanocrystal synthesis, colloids, Beer–Lambert law, quantum confinement, photoluminescence, and surface chemistry. For each concept, background information is provided, rendering this report a comprehensive introduction for students and teachers. Indium phosphide is a safer material to handle in the undergraduate lab compared to cadmium selenide (CdSe), cesium lead bromide (CsPbBr3), or lead sulfide (PbS) nanocrystals.

Synthesis of ZnO Nanoflower Arrays on Patterned Cavity Substrate and Their Application in Methylene Blue Degradation

A novel method was proposed to fabricate a ZnO seed layer with a protrusion and matrix structure, and then ZnO nanorods could be synthesized on it using the hydrothermal method to form ZnO nanoflower arrays (NFAs) easily. A patterned sapphire with a matrix cavity was used as the template, ZnO gel was deposited on the multilayer substrates using spinning coating, and the prepared seed layer with a protrusion and an array-patterned structure was moved to a Si substrate using the lift-off method. Because the ZnO seed layer exhibited a matrix and protrusion structure, ZnO nanorods were grown vertically downwards and formed ZnO NFAs. The XRD patterns resulting from analyses showed that the diffraction peaks of the five growth directions of ZnO NFAs increased as growth time increased. Furthermore, SEM and FIB analyses indicated that the length, width, aspect ratio, and total surface area of ZnO NFAs grown on the transferred seed layer increased as the synthesis time increased. Different ZnO NFAs synthesized for varying synthesis times were used to investigate methylene blue degradation, with the effect of ZnO NFAs on methylene blue degradation determined using the Beer-Lambert law. Our results demonstrate that the effect of ZnO NFAs on methylene blue degradation was enhanced with increasing synthesis time.

Arterial pulsation modulates the optical attenuation coefficient of skin.

Photoplethysmographic (PPG) signals arise from the modulation of light reflectivity on the skin due to changes of physiological origin. Imaging plethysmography (iPPG) is a video-based PPG method that can remotely monitor vital signs in a non-invasive manner. iPPG signals result from skin reflectivity modulation. The origin of such reflectivity modulation is still a subject of debate. Here, we have used optical coherence tomography (OCT) imaging to find whether iPPG signals may result from skin optical properties being directly or indirectly modulated by arterial transmural pressure propagation. The light intensity across the tissue was modeled through a simple exponential decay (Beer-Lambert law) to analyze in vivo the modulation of the optical attenuation coefficient of the skin by arterial pulsation. The OCT transversal images were acquired from a forearm of three subjects in a pilot study. The results show that the optical attenuation coefficient of skin changes at the same frequency as the arterial pulsation due to transmural pressure propagation (local ballistographic effect), but we cannot discard the contribution of global ballistographic effects.