Intensity Of Light Source Research Articles

Luminescent oxygen sensors with highly improved sensitivity based on a porous sensing film with increased oxygen accessibility and photoluminescence

In this study, we present the effects of the morphological modification of an oxygen-sensing film on improving the sensitivity of luminescent oxygen sensors. Pores were made inside the volume and on the external surface of the oxygen-sensing film consisting of platinum(II) octaethylporphyrin (PtOEP) oxygen-sensitive dye embedded in a polystyrene (PS) polymer matrix. The size of the pores with diameters from 300nm to 1μm was controlled through the phase separation of the ternary system of PS, polyethylene glycol (PEG), and chloroform. Photoluminescence (PL) intensity and oxygen accessibility of the oxygen-sensing film were considered the main factors affecting the sensitivity of the sensors. PL intensity was analyzed through the diffused reflectance and absorbance of the oxygen-sensing film. Oxygen accessibility was analyzed based on the Langmuir-Hill absorption theory by considering the sensitivity saturation behaviors of the oxygen-sensing film above the excitation light source intensity of 1000cd/m2. The optimized porous-structured oxygen-sensing film showed 61% higher sensitivity than the solid oxygen-sensing film. According to the measurement results, the sensitivity enhancement in the porous sensing film was significantly more driven by the increase in oxygen accessible sites than the increase in PL intensity. Furthermore, the sensing film with pores only on its external surface and not inside its volume showed 72% enhanced sensitivity relative to the solid sensing film. Therefore, the external surface area of the sensing film affects the sensitivity of the oxygen-sensing film significantly more than the pores inside the volume of the sensing film because the external surface acts as an oxygen diffusion barrier that limits the amount of oxygen that can access the oxygen-sensitive dye embedded in the polymer matrix.

Monte Carlo simulation-based thinning and calculating method for noninvasive blood glucose sensing by near-infrared spectroscopy

Previous results show that the floating reference theory (FRT) is an effective tool to reduce the influence of interference factors on noninvasive blood glucose sensing by near-infrared spectroscopy (NIRS). It is the key to measure the floating reference point (FRP) precisely for the application of FRT. Monte Carlo (MC) simulation has been introduced to quantitatively investigate the effects of positioning errors and light source drifts on measuring FRP. In this article, thinning and calculating method (TCM) is proposed to quantify the positioning error. Meanwhile, the normalization process (NP) is developed to significantly reduce the error induced by light source drift. The results according to TCM show that 7[Formula: see text][Formula: see text]m deviations in positioning can generate about 10.63% relative error in FRP. It is more noticeable that 1% fluctuation in light source intensity may lead to 12.21% relative errors. Gratifyingly, the proposed NP model can effectively reduce the error caused by light source drift. Therefore, the measurement system for FRPs must meet that the positioning error is less than 7[Formula: see text][Formula: see text]m, and the light source drift is kept within 1%. Furthermore, an improvement for measurement system is proposed in order to take advantage of the NP model.

Model independent approach to the single photoelectron calibration of photomultiplier tubes

The accurate calibration of photomultiplier tubes is critical in a wide variety of applications for which it is necessary to know the absolute number of detected photons or precisely determine the resolution of the signal. Conventional calibration methods rely on fitting the photomultiplier response to a low intensity light source with analytical approximations to the single photoelectron distribution. We show that this approach often leads to biased estimates due to an inability to model the full distribution accurately, especially at low charge values. We present a simple statistical method to extract the relevant single photoelectron calibration parameters (first two central moments) without making any assumptions about the underlying single photoelectron distribution. We illustrate the use of this method through the calibration of a Hamamatsu R11410 photomultiplier tube and study the accuracy and precision of the method using Monte Carlo simulations. The method is found to have significantly reduced bias compared to conventional methods and works under a wide range of light intensities, making it suitable for the simultaneous calibration of large arrays of photomultiplier tubes where uniform illumination may not be possible.

Synthesis of sponge-loaded Bi2WO6/ZnFe2O4 magnetic photocatalyst and application in continuous flow photocatalytic reactor

The magnetic photocatalyst Bi2WO6/ZnFe2O4 was loaded on the surface of polyurethane sponge with polyvinyl butyral (PVB) as an immobilizing agent. The as-prepared photocatalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and element mapping. The best operating conditions of the reactor were determined to be 0.10 wt% PVB, mass ratio of sponge to catalyst = 1:1.25, volume ratio of sponge to mixture = 8 g/L and load temperature at 80 °C. The average load rate of the photocatalyst was 56.18%. The photodegradation ratio of tetracycline hydrochloride (TCH, 50 mg/L) was above 98.35% with the load of 5 g/L photocatalyst within 90 min under visible-light irradiation. The best conditions were photocatalyst quantity = 6 g/L, light source intensity = 140000 lux and pollutant concentration = 50 mg/L. The TCH photodegradation ratio reached 91.59%. The addition of PVB increased the fall-off of the photocatalyst and the magnetism of photocatalyst facilitated the recovery. The photocatalyst fall-off rate was 2.53%, and the fall-off part of the powder photocatalyst was adsorbed by magnet, and the recovery rate was 95.13%.

Mexametric and cutometric assessment of the signs of aging of the skin area around the eyes after the use of non-ablative fractional laser, non-ablative radiofrequency and intense pulsed light.

The assessment of the signs of aging within eyes area in cutometric (skin elasticity) and mexametric (discoloration and severity of erythema) examination after the treatment with: non-ablative fractional laser, non-ablative radiofrequency (RF) and intense light source (IPL). This study included 71 patients, aged 33-63 years (the average age was 45.81) with Fitzpatrick skin type II and III. 24 patients received 5 successive treatment sessions with a 1,410-nm non-ablative fractional laser in two-week intervals, 23 patients received 5 successive treatment sessions with a non-ablative RF in one-week intervals and 24 patients received 5 successive treatment sessions with an IPL in two-week intervals. The treatment was performed for the skin in the eye area. The Cutometer and Mexameter (Courage + Khazaka electronic) reference test was used as an objective method for the assessment of skin properties: elasticity, skin pigmentation and erythema. Measurements of skin elasticity were made in three or four sites within eye area. The results of cutometric measurements for R7 showed the improvement in skin elasticity in case of all treatment methods. The largest statistically significant improvement (p < .0001) was observed in case of laser and RF, during treatment sessions, at sites at upper and lower eyelid. The smallest change in skin elasticity for the laser, RF and IPL - p = .017, p = .003 and p = .001, respectively-was observed in a site within the outer corner of the eye. In all sites of measurements and for all methods, the greatest improvement in skin elasticity was demonstrated between the first and second measurement (after 3rd procedures). The majority of the results of mexametric measurements-MEX (melanin level) and ERYT (the severity of erythema) are statistically insignificant. Fractional, non-ablative laser, non-ablation RF and intense light source can be considered as methods significantly affecting elasticity and to a lesser extent erythema and skin pigmentation around the eyes. Fractional non-ablative laser is a method which, in comparison to other methods, has the greatest impact on skin viscoelasticity. These procedures are well tolerated and are associated with a low risk of side effects.

Instrument design and protocol for the study of light controlled processes in aquatic organisms, and its application to examine the effect of infrared light on zebrafish.

The acquisition of reliable data strongly depends on experimental design. When studying the effects of light on processes such as behaviour and physiology it is crucial to maintain all environmental conditions constant apart from the one under study. Furthermore, the precise values of the environmental factors applied during the experiment should be known. Although seemingly obvious, these conditions are often not met when the effects of light are being studied. Here, we document and discuss the wavelengths and light intensities of natural and artificial light sources. We present standardised experimental protocols together with building plans of a custom made instrument designed to accurately control light and temperature for experiments using fresh water or marine species. Infrared light is commonly used for recording behaviour and in electrophysiological experiments although the properties of fish photoreceptors potentially allow detection into the far red. As an example of our experimental procedure we have applied our protocol and instrument to specifically test the impact of infrared light (840 nm) on the zebrafish circadian clock, which controls many aspects of behaviour, physiology and metabolism. We demonstrate that infrared light does not influence the zebrafish circadian clock. Our results help to provide a solid framework for the future study of light dependent processes in aquatic organisms.

A microfluidic device with ion-exchange preconcentration column and photometric detection with Schlieren effect correction

This work describes the construction and evaluation of a microflow analyzer containing a Dowex® 1X8 packed column and LED-based photometric detection with Schlieren effect correction. Flow structures, including a reservoir for the preconcentration column with dimensions 25.0×2.0×1.0mm (l×w×h), were manufactured in a urethane–acrylate resin, and the ion-exchange particles (50–100mesh) were manually packed before sealing the device. Photometric measurements were performed using an integrated flow cell with a 5.0mm optical path by using optical fibers to guide the radiation from a 3.0W RGB LED to the microfluidic device and from the microdevice to a photodiode (OPT-101). It was demonstrated that the Schlieren effect is appropriately corrected by subtracting the signals for two diodes of the RGB LED and, by setting the intensity of light sources before measurements, the discordant response to the effect at different wavelengths is compensated. The preconcentration column was easily and successfully integrated into the microfluidic device without any clogging or leaking of the working solutions, and swelling of the packing particles caused no damage to the sealed structures because of the elastomeric nature of the microfluidic substrate. The application of the proposed device to the determination of nitrite in fresh water provides a linear response (R2=0.99) from 0.05 to 0.20mg NO2−L−1 and an approximate increase in concentration by four fold was estimated when 3.80mL of the sample/standard solutions is percolated through the column, providing recoveries from 96% to 101% for tested samples.

How to Calibrate Your CCD in the Dark? a Precise CCD Calibration Method

Single particle tracking and super-resolution microscopy experiments require good knowledge of CCD pixels’ gains in terms of photoelectrons per ADU (Analog to Digital Unit, output of the CCD camera) registered by the read-out electronics of the CCD camera. This is because the observed CCD output in a given time period produced by light with constant intensity follows, ignoring other noise sources, statistics of photoelectrons produced by incident photons. It is common practice to calibrate the gain of a CCD camera using a constant intensity light source to get the gain in photoelectron per ADU. This procedure requires a stable light source and it is not always possible to achieve a truly uniform and stable illumination. We propose an easier calibration method that uses dark noise as the calibration source for a CCD camera; the method requires that the dark noise level is stable during the calibration data taking. The proposed method works as demonstrated under assumptions that statistics of photoelectrons and thermal electrons follow Poisson distribution and CCD pixel gains in electrons per ADU are the same for the both sources of electrons. We will show that these assumptions are valid and will demonstrate that it is possible to calibrate individual gain of each pixel at ∼1% level or better using real and simulated data. As a byproduct, the proposed calibration method provides properties of individual pixel, not only its gain but also other properties such as linearity in low photon intensity and dark noise level. This information gives assessment of quality of the CCD camera. All the necessary software is developed using freely available software package Octave similar to Matlab. This method might improve the localization of fluorescent molecules in super-resolution and particle tracking measurements.

Charge–Exciton Interaction Rate in Organic Field-Effect Transistors by Means of Transient Photoluminescence Electromodulated Spectroscopy

Organic light-emitting transistors (OLETs) offer a huge potential for the design of highly integrated multifunctional optoelectronic systems and of intense nanoscale light sources, such as the long-searched-for electrically pumped organic laser. In order to fulfill these promises, the efficiency and brightness of the current state-of-the-art devices have to be increased significantly. The dominating quenching process limiting the external quantum efficiency in OLETs is charge–exciton interaction. A comprehensive understanding of this quenching process is therefore of paramount importance. The present article reports a systematic investigation of charge–exciton interaction in organic transistors employing time-resolved photoluminescence electro-modulation (PLEM) spectroscopy on the picosecond time scale. The results show that the injected charges reduce the exciton radiative recombination in two ways: (i) charges may prevent the generation of excitons and (ii) charges activate a further nonradiative channe...

Determination of Hydrogen Sulfide by Wavelength-modulated Diode Laser Absorption Spectroscopy

ABSTRACTRapid, accurate, and sensitive determination of hydrogen sulfide was provided by tunable distributed feedback diode laser absorption spectroscopy. The laser wavelength scanning range covered the strongest absorption band of hydrogen sulfide. The absorption line at 1578 nm was used for analytical measurements. A homemade digital lock-in amplifier was used to demodulate the first and the second harmonic signals. Normalization of the second harmonic by the first harmonic signal provided calibration-free measurements so that interferences from light path, circuitry, and source intensity were minimized. A mass flow controller was used to introduce 0–100 ppm hydrogen sulfide for validating the analytical performance. The results demonstrated the linearity of the normalized harmonic signals with concentration with a correlation coefficient of 0.9995. The response time was approximately 3 s. The detection limit by Allan variance was 45 ppb with an integration time of 35 s. The sensitive hydrogen sulfide sensor is suitable for environmental monitoring with real-time detection.

&lt;em&gt;Dreams are colder than Death&lt;/em&gt; and the Gathering of Black Sociality

While Afro-Pessimist scholars understand blackness under the rubric of the ascendance of the #BlackLivesMatter movement vindicates instead the opposing Afro-Optimist position, which affirms the generative capacity of black social life. Arthur Jafa's essay film Dreams are colder than Death (2013), a meditation on the legacy of Martin Luther King Jr.'s I Have a Dream speech, conducted through interviews with African-American intellectuals and artists, examines this tension. Woven together with lyrical, slow-motion images of unnamed black people, of water, and of cosmological images of deep space, these voices reflect on the ontology of blackness and its relationship to life, death, and the concept of the human. Eventually, through the words of Fred Moten, the film questions the possibility to love black people once blackness is solely understood within the afterlife of slavery. This essay reads the film's edits as passages that effectively perform the very networks of solidarity, grief, and grievance sought by #BlackLivesMatter as the evidence of such love. Through its aesthetic liquidity, i.e., the film's facility to move across scale, from the minute to the cosmological, from the familial to the collective, and the way it disjoins some of the very conditions for black surveillance—voices strategically recorded independently from the image; faces hardly visible because shot against intense light sources—the film claims for blackness the expansiveness that institutes radical networks of black love.

Development of 3D printable formulations containing CNT with enhanced electrical properties

This study demonstrates the feasibility of printing 3D composite objects based on acrylic photocurable formulations containing CNTs, by using an unmodified commercial DLP-printer. In the preliminary investigations, the most suitable formulation was developed. Viscosity and dispersion stability were adjusted by the addition of a reactive diluent to the acrylic formulation. FT-IR analyses in real time and photorheology tests allowed finding the best composition and printing parameters.Printing conditions were adjusted to get 3D structures from formulations with a content up to 0.3 wt % of CNTs. The presence of the filler causes a decrease of the crosslinking density, which could be overcome using higher intensity light sources. Electrical conductivity measurements performed on the printed samples give promising results for the use of the developed formulation for the building of 3D structures with electrical properties.

Self-Referenced Smartphone-Based Nanoplasmonic Imaging Platform for Colorimetric Biochemical Sensing.

Colorimetric sensors usually suffer due to errors from variation in light source intensity, the type of light source, the Bayer filter algorithm, and the sensitivity of the camera to incoming light. Here, we demonstrate a self-referenced portable smartphone-based plasmonic sensing platform integrated with an internal reference sample along with an image processing method to perform colorimetric sensing. Two sensing principles based on unique nanoplasmonics enabled phenomena from a nanostructured plasmonic sensor, named as nanoLCA (nano Lycurgus cup array), were demonstrated here for colorimetric biochemical sensing: liquid refractive index sensing and optical absorbance enhancement sensing. Refractive indices of colorless liquids were measured by simple smartphone imaging and color analysis. Optical absorbance enhancement in the colorimetric biochemical assay was achieved by matching the plasmon resonance wavelength with the chromophore's absorbance peak wavelength. Such a sensing mechanism improved the limit of detection (LoD) by 100 times in a microplate reader format. Compared with a traditional colorimetric assay such as urine testing strips, a smartphone plasmon enhanced colorimetric sensing system provided 30 times improvement in the LoD. The platform was applied for simulated urine testing to precisely identify the samples with higher protein concentration, which showed potential point-of-care and early detection of kidney disease with the smartphone plasmonic resonance sensing system.

Indoor Scene Reconstruction Using Near-Light Photometric Stereo.

We propose a novel framework for photometric stereo (PS) under low-light conditions using uncalibrated near-light illumination. It operates on free-form video sequences captured with a minimalistic and affordable setup. We address issues such as albedo variations, shadowing, perspective projections, and camera noise. Our method uses specular spheres detected with a perspective-correcting Hough transform to robustly triangulate light positions in the presence of outliers via a least-squares approach. Furthermore, we propose an iterative reweighting scheme in combination with an ℓp-norm minimizer to robustly solve the calibrated near-light PS problem. In contrast to other approaches, our framework reconstructs depth, albedo (relative to light source intensity), and normals simultaneously and is demonstrated on synthetic and real-world scenes.

Structural study of light-emitting nanocomposites based on ZnS:Cu deposited by explosive evaporation method on porous anodic Al2O3 matrices

In the work the results of structural studies of nanocomposite systems based on ZnS:Cu (5 at.% and 10 at.%) deposited by explosive evaporation on porous anodic aluminum oxide matrices fulfilled by EXAFS and X-ray phase analysis techniques have been presented. The composites under study are promising for applications in electroluminescent light sources. The results of the studies of emission intensity of light sources depending on frequency and amplitude of exciting field have also been presented.

Centrog Feature Technique for Vehicle Type Recognition at Day and Night Times

This work proposes a feature-based technique to recognize vehicle types within day and night times. Support vector machine (SVM) classifier is applied on image histogram and CENsus Transformed histogRam Oriented Gradient (CENTROG) features in order to classify vehicle types during the day and night. Thermal images were used for the night time experiments. Although thermal images suffer from low image resolution, lack of colour and poor texture information, they offer the advantage of being unaffected by high intensity light sources such as vehicle headlights which tend to render normal images unsuitable for night time image capturing and subsequent analysis. Since contour is useful in shape based categorisation and the most distinctive feature within thermal images, CENTROG is used to capture this feature information and is used within the experiments. The experimental results so obtained were compared with those obtained by employing the CENsus TRansformed hISTogram (CENTRIST). Experimental results revealed that CENTROG offers better recognition accuracies for both day and night times vehicle types recognition.

Theoretical investigations of broadband mid-infrared optical parametric amplification based on a La3Ga5.5Nb0.5O14 crystal.

Recent progress in strong-field physics has stimulated the quest for intense mid-infrared ultrashort light sources. Optical parametric amplification (OPA) is one promising method to build up such sources, however, its development significantly relies on the availability of suitable nonlinear crystals. Here, we introduce a positive uniaxial crystal La3Ga5.5Nb0.5O14 (LGN), which exhibits a favorable set of optical properties for the application in a mid-IR OPA. We theoretically evaluate the performance of LGN as the nonlinear crystal of a mid-infrared OPA, with an emphasis on the bandwidth characteristic. We find that this crystal can support broadband amplifications across its entire mid-infrared transparent region up to 6 μm, outperforming other commonly-used mid-infrared crystals in terms of gain bandwidth. Few-cycle mid-infrared pulses at various wavelengths can be generated from the LGN-based optical parametric chirped-pulse amplifiers.

Quantum optical signatures in strong-field laser physics: Infrared photon counting in high-order-harmonic generation.

We analytically describe the strong-field light-electron interaction using a quantized coherent laser state with arbitrary photon number. We obtain a light-electron wave function which is a closed-form solution of the time-dependent Schrödinger equation (TDSE). This wave function provides information about the quantum optical features of the interaction not accessible by semi-classical theories. With this approach we can reveal the quantum optical properties of high harmonic generation (HHG) process in gases by measuring the photon statistics of the transmitted infrared (IR) laser radiation. This work can lead to novel experiments in high-resolution spectroscopy in extreme-ultraviolet (XUV) and attosecond science without the need to measure the XUV light, while it can pave the way for the development of intense non-classical light sources.

Phototoxic target lipid model of single polycyclic aromatic hydrocarbons.

A phototoxic target lipid model (PTLM) is developed to predict phototoxicity of individual polycyclic aromatic hydrocarbons (PAHs) measured either as median lethal concentration (LC50) or median lethal time (LT50) for a 50% toxic response. The model is able to account for the differences in the physical/chemical properties of PAHs, test species sensitivities, and variations in light source characteristics, intensity, and length of exposure. The PTLM is based on the narcotic target lipid model (NTLM) of PAHs. Both models rely on the assumption that mortality occurs when the toxicant concentration in the target lipid of the organism reaches a threshold concentration. The PTLM is applied to observed LC50s and LT50s for 20 individual PAHs, 15 test species-including arthropods, fishes, amphibians, annelids, mollusks, and algae-exposed to simulated solar and various UV light sources, for exposure times varying from less than 1 h to 100 h, a total of 333 observations. The LC50 concentrations range from less than 0.1 µg/L to greater that 104 µg/L. The model has 2 fitting parameters that are constant and apply to all PAHs and organisms. The root mean square errors of prediction for log(LC50) and log(LT50) are 0.473 and 0.382, respectively. The results indicate that the PTLM can predict the phototoxicity of single PAHs over a wide range of exposure conditions and to organisms with a wide range of sensitivities. Environ Toxicol Chem 2017;36:926-937. © 2016 SETAC.

The Photocatalyzed Aza-Henry Reaction of N-Aryltetrahydroisoquinolines: Comprehensive Mechanism, H•- versus H+-Abstraction, and Background Reactions

The cross-dehydrogenative coupling (CDC) reaction of N-aryltetrahydroisoquinolines (THIQ) is one of the most exploited photocatalytic transformation and a test reaction for an exceptional variety of catalysts. However, its mechanism remained unclear concerning involved intermediates, reactive pathways of the amine radical cation and the influence of oxygen and the light source. Therefore, nuclear magnetic resonance (NMR), electron spin resonance (ESR) and synthetic methods were combined to provide a comprehensive picture of the reaction mechanism using Ru(bpy)3Cl2 as a photocatalyst under aerobic and anaerobic conditions. The reaction profiles and involved intermediates were monitored and analyzed by NMR spectroscopy. Several intermediates contributing to product formation were identified, the iminium ion, the hydroperoxide and dimer of THIQ, and a new ring opened intermediate, cleaved at the benzylic C-N bond. Mechanistic evidence is given that under anaerobic conditions preferentially the α-amino radical is formed by deprotonation, in contrast to the formation of iminium ions via H(•)-abstraction in the presence of oxygen. Further, the light-induced background reaction in the absence of the catalyst was studied in detail, revealing that the product formation rate is correlated to the intensity and wavelength of the light source and that oxygen is essential for an efficient conversion. The reaction rate and efficiency is comparable to previously reported photocatalytic systems, performed under aerobic conditions in combination with intense blue light sources. Thus, the multitude of reaction parameters investigated reveals the preference for hydrogen atom or proton abstraction in photoreactions and allows to assess the influence of experimental conditions on the mechanistic pathways.