Eosin Y is known to be a powerful probe of biological molecules and an efficient photosensitizing agent for the production of singlet molecular oxygen. Under continuous laser excitation, degradation ...through photobleaching is observed in aqueous solutions of eosin Y; this process is driven by the production of singlet oxygen. Optical bleaching in aqueous solutions is known to yield anomalous thermal lens transient signals, which can be evaluated by modeling the relaxation processes that give rise to the generation of heat in the solution. A model describing photobleaching in the thermal lens transient signal is derived and is applied to investigate eosin Y in aqueous solutions at different temperatures. Using this model, quantitative information regarding the molecular diffusion rate, optical bleaching, and fluorescence quantum efficiency is obtained.
Biofuels are an alternative to fossil fuels and can be made from many different raw materials. The use of distinct catalyst and production processes, feedstocks, and types of alcohol results in ...biofuels with different physical and chemical properties. Even though these diverse options for biodiesel production are considered advantageous, they may pose a setback when quality specifications are considered, since different properties are subject to different reactions during usage, storage and handling. In this work, we present a systematic characterization of biodiesels to investigate how accelerated thermal degradation affects fuel properties. Two different types of biodiesel, commercially obtained from distinct feedstocks, were tested. The thermal degradation process was performed by maintaining the temperature of the sample at
140
∘
C
under constant air flux for different times: 0 h, 3 h, 6 h, 9 h, 12 h, 24 h and 36 h. Properties such as density, viscosity, activation energy, volumetric thermal expansion coefficient, gross caloric value, acid value, infrared absorption, and temperature coefficient of the refractive index were used to study the thermal degradation of the biodiesel samples. The results show a significant difference in fuel properties before and after the thermal degradation process suggesting the formation of undesirable compounds. All the properties mentioned above were found to be useful to determine whether a biodiesel sample underwent thermal degradation. Moreover, viscosity and acid value were found to be the most sensitive characteristics to detect the thermal degradation process.
A dual-wavelength on/off-excitation thermal lens technique was used to identify and quantify a laser-induced chemical reaction in ionic aqueous solutions of Fe(II)–TPTZ. On/off modeling was used to ...fit the TL experimental data, which provided the primary effect generated during laser-excitation. The addition of HCl in the solutions reduced the activation barrier; this behavior followed the Arrhenius correlation. The nature of the photo-oxidation of Fe(II)–TPTZ complex is discussed. The results suggest that this technique may contribute to the understanding of the dynamics of complex reactions, which may lead to a more precise determination of the physicochemical properties involved in a photochemical reaction.
We report a theoretical model and experimental results for laser-induced local heating in liquids, and propose a method to detect and quantify the contributions of photochemical and Soret effects in ...several different situations. The time-dependent thermal and mass diffusion equations in the presence and absence of laser excitation are solved. The two effects can produce similar transients for the laser-on refractive index gradient, but very different laser-off behavior. The Soret effect, also called thermal diffusion, and photochemical reaction contributions in photochemically reacting aqueous Cr(VI)-diphenylcarbazide, Eosin Y, and Eosin Y-doped micellar solutions, are decoupled in this work. The extensive use of lasers in various optical techniques suggests that the results may have significance extending from physical-chemical to biological applications.
► Physical properties of optical materials were quantitatively determined using time-resolved Thermal mirror spectrometry. ► The limits of application of the semi-infinite and finite models are ...derived. ► The finite description should be used for samples with thicknesses <1.5mm.
The Thermal mirror technique relies on measuring laser-induced nanoscale surface deformation of a solid sample. The amplitude of the effect is directly dependent on the optical absorption and linear thermal expansion coefficients, and the time evolution depends on the heat diffusion properties of the sample. Measurement of transient signals provide direct access to thermal, optical and mechanical properties of the material. The theoretical models describing this effect can be formulated for very low optical absorbing and for absorbing materials. In addition, the theories describing the effect apply for semi-infinite and finite samples. In this work, we apply the Thermal mirror technique to measure physical properties of optical glasses. The semi-infinite and finite models are used to investigate very low optical absorbing glasses. The thickness limit for which the semi-infinite model retrieves the correct values of the thermal diffusivity and amplitude of the transient is obtained using the finite description. This procedure is also employed on absorbing glasses, and the semi-infinite Beer–Lambert law model is used to analyze the experimental data. The experimental data show the need to use the finite model for samples with very low bulk absorption coefficients and thicknesses L<1.5mm. This analysis helped to establish limit values of thickness for which the semi-infinite model for absorbing materials could be used, L>1.0mm in this case. In addition, the physical properties of the samples were calculated and absolute values derived.
One of the most significant materials in a solar panel is the glass, which provides transparency, UV protection as well as mechanical and chemical resistance. In this work, we describe the production ...of prototypes of four solar modules made using borosilicate, zinc-tellurite, Pr3+ doped zinc-tellurite, and float glass as cover materials. The performance of these prototypes was evaluated under a solar simulator, and a device was developed to monitor all prototypes under real conditions. A comparison between indoor and outdoor measurements shows that outdoor results are fundamental to evaluate the performance of modified solar modules as the ones considered in this study. In addition, we demonstrate the fundamental role played by the refractive index of cover glasses in the performance of the prototypes, and discuss how this feature could be explored to achieve enhanced devices, as well as other benefits that may arise from this field of research.
•Four glasses were used to build prototypes of solar photovoltaic panels.•An affordable tool to monitor the power output of the prototypes is demonstrated.•The performance of these devices during an entire day was measured.•Reflection losses due to the high refractive index of tellurites were quantified.•The development of practical spectral converters is discussed.
The effects of the prior austenite grain sizes in hydrogen embrittlement of Co-containing 18Ni 300 maraging steel were studied employing Slow Strain Rate Testing (SSRT) in 0.6 M NaCl electrolyte ...under simultaneuos cathodic polarization. The material was susceptible to hydrogen embrittlement in all investigated conditions. In addition, the examination of the fractured surface revealed that the presence of hydrogen in steel promotes the formation of quasi-cleavage regions and hydrogen-induced cracks along the grain boundaries. However, the refining of the prior austenite grain allowed an improvement in the HE resistance. Moreover, EBSD analysis showed that intergranular cracks propagated along to grain boundaries orientated to {001} planes parallel to normal direction, whereas they were deflected on {101} and {111} crystallographic planes.
•The control of the prior austenite grain leads to the improvement of the HE resistance.•Intergranular cracks propagated along the grain boundaries orientated to {001} planes.•The cracks were deflected on grain boundaries {110} and {111} crystallographic planes.
During transient brain activation cerebral blood flow (CBF) increases substantially more than cerebral metabolic rate of oxygen consumption (CMRO2) resulting in blood hyperoxygenation, the basis of ...BOLD‐fMRI contrast. Explanations for the high CBF versus CMRO2 slope, termed neurovascular coupling (NVC) constant, focused on maintenance of tissue oxygenation to support mitochondrial ATP production. However, paradoxically the brain has a 3‐fold lower oxygen extraction fraction (OEF) than other organs with high energy requirements, like heart and muscle during exercise. Here, we hypothesize that the NVC constant and the capillary oxygen mass transfer coefficient (which in combination determine OEF) are co‐regulated during activation to maintain simultaneous homeostasis of pH and partial pressure of CO2 and O2 (pCO2 and pO2). To test our hypothesis, we developed an arteriovenous flux balance model for calculating blood and brain pH, pCO2, and pO2 as a function of baseline OEF (OEF0), CBF, CMRO2, and proton production by nonoxidative metabolism coupled to ATP hydrolysis. Our model was validated against published brain arteriovenous difference studies and then used to calculate pH, pCO2, and pO2 in activated human cortex from published calibrated fMRI and PET measurements. In agreement with our hypothesis, calculated pH, pCO2, and pO2 remained close to constant independently of CMRO2 in correspondence to experimental measurements of NVC and OEF0. We also found that the optimum values of the NVC constant and OEF0 that ensure simultaneous homeostasis of pH, pCO2, and pO2 were remarkably similar to their experimental values. Thus, the high NVC constant is overall determined by proton removal by CBF due to increases in nonoxidative glycolysis and glycogenolysis. These findings resolve the paradox of the brain's high CBF yet low OEF during activation, and may contribute to explaining the vulnerability of brain function to reductions in blood flow and capillary density with aging and neurovascular disease.
Our mathematical model shows that the experimental values of cerebral nonoxidative metabolism (Rglyc), neurovascular coupling constant (n), and oxygen extraction fraction (OEF0) are optimized to maintain simultaneous homeostasis of pH and partial pressures of oxygen and carbon dioxide during brain activation, almost independently of cerebral metabolic rate of oxygen (CMRO2). Constraining one variable (among Rglyc, n, and OEF0) to its experimental value uniquely determines the values of the other two variables to be very close to their experimental values, as evidenced by their probability density function (PDF) and corresponding median value and interquartile range (IQR).
This paper presents a review about mercury contamination and human exposure in the Tapajós River basin (Brazil), one of the major tributaries of the Amazon impacted by traditional gold mining from ...the mid 1980s. The most recent review in this region was published more than ten years ago and since then many articles about environment and especially human populations have revealed new aspects of mercury toxicology. Additionally, new biomarkers of mercury exposure and toxicity have been studied in these populations. However, there are still many open, about both mercury's biogeochemical cycle and mercury health risks. Further environmental and human risk research directions are proposed.
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