Experimental Conditions Research Articles

Unsaturation and polar compounds of vegetable oils affect the properties of sunflower wax‐oleogels

AbstractAlthough it is important to understand the factors affecting the physical properties of oleogels for their application in food products, the effects of the kind of oils and components in them are not well understood. Previous studies on the effects of unsaturation and polar compounds of oils on the properties of oleogels reported inconsistent results, presumably, due to different gelling agents, experimental conditions, and different amounts of minor components in oils. In this study, a systematic study was conducted with 12 vegetable oils with and without polar compounds to understand these effects on the properties of 3% and 7% sunflower wax (SW)‐oleogels. In general, oils with higher unsaturation produced oleogels with lower gel strength. Polar compounds in oil negatively affected the gel strength. Melting and crystallization temperatures increased with increasing unsaturation of oil. The platelet shape of SW crystals was almost identical, regardless of the kind of oil. Solid wax content values were similar across the oleogel samples with 12 different oils. This study enlightens several factors affecting the physical properties of SW‐oleogels.Practical Application: This study provides information about the effects of unsaturation of oil and polar compounds in oil on firmness and melting properties of sunflower wax (SW)‐based oleogels. It was found that the firmness of SW‐oleogel can be significantly different (up to 65%) depending on vegetable oils used, and it decreased with increasing unsaturation of oil. It was also found that the firmness of the oleogel can be increased by up to 36% by removing polar compounds in oil. Solid wax content (SWC) of oleogels did show meaningful correlations with the firmness of SW‐oleogels. All the oleogels examined in this study had very similar shapes and sizes of SW crystals. For practical application, the unsaturation of oil and the polar compound content have to be considered when designing oleogels with desired textural properties.

Circadian Rhythms of Body Temperature and Locomotor Activity in Spontaneously Hypertensive Rats under Frequent Changes in Light Conditions.

Changes in lighting accompany modern urbanization trends and can lead to various pathologies based on circadian disturbances. In this study, we assessed the changes in the circadian rhythm of core body temperature (Tcore) and locomotor activity of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) following exposure to different lighting conditions: extended light phase of the day (16 h-8 h, 20 h-4 h, 24 h-0 h), light pollution, monochromatic light, and bright light therapy. The telemetry data was collected after experimental lighting conditions during periods with standard lighting (12 h of light and 12 h of darkness) and was processed using linear and cosinor analysis. The daily rhythms of rats' parameters persisted in accordance with the standard lighting regime. Tcore changes were observed in both groups compared to the initial period: in WKY, a decrease in Tcore during the darkness and an increase during the light; in SHR, the opposite trend, with Tcore increased during the darkness and decreased during the light phase of the day. A relationship between Tcore and activity was observed with weak correlation. WKY exhibited more pronounced signs of adaptive variation and desynchronization compared to SHR, which could be associated with a wider range of functional capabilities of the organism without cardiovascular pathology.

The research on the particle concentration distribution of directed airflow in cleanrooms for operators.

Existing research of non-unidirectional cleanrooms generally suggests that lower-side return air outlets provide better control effect on indoor particle concentration. As a result, there has been relatively less focus on return air outlets. However, installing return air outlets oriented towards operators as particle emission sources can reduce the impact on process layout and improve space utilization, while also provide less impact from upper particle emission sources on the workbench area. To investigate the characteristics of return air outlet for operators (abbreviated as H), this study compared the particle concentration distribution, non-uniformity, and purification efficiency of return air oultet H and the traditional lower-side (abbreviated as L) return air outlets by experiments and CFD simulations. Based on the theory of mass conservation, the expression of required air supply volume under equivalent cleanroom conditions was derived. Under corresponding experimental and simulation conditions, the particle concentration differences range from 2.0% to 12.7% for return air outlet H and from 12.4% to 33.2% for return air outlet L, and these differences gradually decrease with the air exchange rate (ACH) increases. The results show that ACH = 20 is sufficient for cleanliness requirements with return air outlet H when there is one person in the cleanroom, while a higher rate of ACH = 35 is needed when there are two persons. Although lower-side return air outlets have certain potential for reducing particle concentration in the cleanroom, increasing the air exchange rate remains the most effective method to control indoor particle concentration. Compared to the traditional lower-side return air outlet L, the ranges of the non-uniformity coefficients for return air outlet H and L are 0.50 to 0.67 and 0.45 to 0.53, respectively. The average non-uniformity coefficient differs by 11.9%, and there is not a significant difference in uniformity with more than 20 air changes per hour. The use of return air outlets H only requires an additional 11% of air supply volume to achieve the same cleanliness, demonstrating its effectiveness in controlling particle concentration. It is suitable for cleanrooms with higher requirements for workbenches and for cleanrooms with restricted floor usage or requiring flexible layouts. The study also explores the impact of width of return air outlet oriented towards operators as particle emission sources, the results show that the larger-sized outlets facilitate the particle discharge and control the particle distribution inside the room.

The effect of a single cycle of ischemia on bar velocity during bench press exercise

Introduction: The main goal of this study was to investigate the effects of a single cycle of ischemia applied before the bench press exercise on acute bar velocity changes. Materials and Methods: Twelve physically active males participated in the study. The experiment followed a randomized, cross-over design under two testing conditions. The experimental condition involved the application of a single cycle of ischemia (5 minutes; 80% arterial occlusion pressure [AOP]) before the first set of bench press exercise (2 sets at 60% 1RM). The control condition did not use ischemia. The peak and mean bar velocities were measured using a linear position transducer. Results: Two-way repeated measures ANOVA revealed no statistically significant differences in the peak or mean bar velocity between the ischemia and control conditions both during the first and the second set of the bench press exercise. Conclusions: The results of this study indicate that a single cycle of ischemia applied before the bench press exercise did not influence changes in peak or mean bar velocity.

The time validity of Philip's two‐term infiltration equation: An elusive theoretical quantity?

AbstractThe two‐term infiltration equation  is commonly used to determine the sorptivity, , and product, , of the dimensionless multiple and saturated soil hydraulic conductivity from cumulative vertical infiltration measurements (L) at times (T). This reduced form of the quasi‐analytical power series solution of Richardson's equation of Philip enjoys a solid physical underpinning but at the expense of a limited time validity. Using simulated infiltration data, Jaiswal et al. have shown this time validity to equal about 2.5 cm of cumulative infiltration. The goals of this work are twofold. First, we investigate the extent to which cumulative infiltration measurements larger than 2.5 cm bias the estimates of and . Second, we investigate the impact of epistemic errors on the inferred time validities and parameters. Partial infiltration curves up to 2.5 cm of cumulative vertical infiltration improve substantially the agreement between actual and least squares estimates of and . But this only holds if the data generating infiltration process follows Richardson's equation and experimental conditions satisfy assumptions of soil homogeneity and a uniform initial water content. Otherwise, autocorrelated cumulative infiltration residuals will bias the least squares estimates of and . Our findings reiterate and reinvigorate earlier conclusions of Haverkamp et al. and show that epistemic errors deteriorate the physical significance of the coefficients of infiltration functions. As a result, the parameters of infiltration functions cannot simply be used in storm water and vadose zone flow models to forecast runoff and recharge at field and landscape scales unless these predictions are accompanied by realistic uncertainty bounds. We conclude that the time validity of Philip's two‐term equation is an elusive theoretical quantity with arbitrary physical meaning.

Hybrid Organic Polymer/Inorganic Nano-materials for Biomedical Applications: Where we are and Where to go?

Abstract: Hybrid functional materials, composed of inorganic and organic components, are considered versatile platforms whose applications in electronics, optics, mechanics, energy storage, informatics, catalysis, sensors, and medicine field have represented a breakthrough for human well-being. Among hybrid materials, micro/nanostructured hybrid colloidal systems have been widely investigated due to the dramatic enhancement of activity provided by the large surface area exposed at the interfaces with respect to the bulk counterpart. Recently, a growing interest has been in the exploration of novel environmental-friendly and versatile procedures that allow the formulation of hybrid nanostructures through safety procedures and mild experimental conditions. This review aims to provide an introduction to hybrid organic-inorganic materials for biomedical applications in particular nanostructured ones, describing the commonly exploited materials for their fabrication and techniques, advantages, and drawbacks.

Highly nanocrystalline Mg doped ZnFe2O4 powders for rapid and simultaneous adsorption of Lead, Copper, and Cadmium heavy metals ions in synthetic / sea waters

This research aims to investigate the effect of Mg doping on individual and simultaneous adsorption of Pb+2, Cu+2, and Cd+2 heavy metals in aqueous solution and in seawater samples, by Zinc ferrite nanoparticles. The Mg-doped Zinc ferrite nanoparticles are synthesized successfully by the sol-gel route and varying Mg concentrations. TEM, XRD, FTIR, Raman, and XPS characterizations confirm the cubic spinel structure of Zinc ferrite with a semi-spherical shaped nanosized particles (10-15nm) irrespective of Mg doping content. The BET surface area manifests a significant increase within Mg doping (39.3 m2/g) compared with the pure zinc ferrite (28.4 m2/g). Accordingly, Mg-doped Zinc ferrite powders demonstrate considerable adsorption capacities for Pb+2 (143.5mg/g), Cu+2 (117mg/g), and Cd+2 (77mg/g) within 2h under optimized experimental conditions. The prepared nanopowders exhibit high selectivity towards Pb+2 in simultaneous adsorption in aqueous solutions (85mg/g) and real seawater samples. Nonetheless, the selectivity of Pb+2 ions drops dramatically to 25mg/g within real seawater samples due to the strong ionic strength of high-salinity seawater. This study provides insights into the importance of doped spinel ferrite nanoparticles in highly efficient, rapid, and simultaneous adsorption of heavy metals. Besides, it reveals the challenge of performing the adsorption process in real seawater.

Green Synthesis Derived Novel Fe2O3/ZnO Nanocomposite for Efficient Photocatalytic Degradation of Methyl Orange Dye

Introduction: An eco-friendly method was reported for the synthesis of ferric oxide nanoparticles (Fe2O3), zinc oxide nanoparticles (ZnO) and Fe2O3/ZnO nanocomposite using Mangifera indica plant leaf extract as a natural reducing agent. Methods: The synthesized nanomaterials were successfully characterized by X-ray diffraction, UVvisible spectrophotometer, Photoluminescence spectroscopy and Transmission electron microscopy. The obtained XRD spectrums revealed the crystalline nature of synthesized materials and the average diameters of Fe2O3 nanoparticles, ZnO nanoparticles and Fe2O3/ZnO nanocomposite came out to be 11.33 nm, 14.31 nm and 9.80 nm, respectively. The UV-visible absorbance spectra and photoluminescence spectrums confirmed that the Fe2O3/ZnO nanocomposite was visible light active and had excitation peaks in the visible range. Results: The TEM analysis confirmed the composite and semiconductor nature of the synthesized Fe2O3/ZnO nanocomposite. Furthermore, the photocatalytic activity of Fe2O3/ZnO nanocomposite reaches about 91.07% degradation of methyl orange dye within a time period of 150 min at an optimized catalyst dose. Adsorption isotherm and kinetic study were also applied to validate the study. Conclusion:: It was found that there was monolayer adsorption of methyl orange dye molecules on the surface of the synthesized catalyst under optimized experimental conditions and also, the adsorption process follows the pseudo-second-order kinetic model.

Preparation of Ampicillin-derived CQDs and its Application in the Detection of Phenols in Medicinal Materials

Background: In this study, ampicillin sodium fluorescent carbon quantum dots were prepared by one-step hydrothermal method with ampicillin sodium as the carbon source and urea as the nitrogen source. Methods: The structure of CQDs were characterized by UV-Vis and fluorescence spectrophotometer. The pH, reaction time and ionic strength of phenol detected by N-CQDs were optimized. The optimum experimental conditions were 40 μL ampicillin sodium N-CQDs, 2 mL buffer solution with pH 8.0, and the reaction time was 6 min. Results: Through the detection of fluorescence spectrophotometry, p-nitrophenol had obvious fluorescence quenching phenomenon on ampicillin sodium N-CQDs, and the detection limit was 75 nM. It was used in the standard addition experiment of actual samples, and the recovery rates were more than 85%. Conclusion: Therefore, the N-CQDs could be used as fluorescent probe to analyze the content of p-nitrophenol in the actual environment.

Perspective taking reduces the correspondence bias: A systematically replication of Hooper et al. (2015)

Correspondence bias has been extensively described in the scientific literature, along with its harmful consequences to relationships, decision-making, etc. Interventions aiming to reduce correspondence bias or its negative impact have been also offered. In this regard, the present study systematically replicated Hooper et al. (2015) to observe the effect of a brief perspective-taking training based on Relational Frame Theory (RFT-PT) on correspondence bias. Eighty-one participants were randomized into four groups, two experimental groups that underwent training and two control groups that answered a general knowledge questionnaire. To observe the extent of correspondence bias and the effect of training on this phenomenon, all participants were exposed to an experimental condition involving the Attitude Attribution Paradigm consisting of essays in favor of or against meritocracy. This condition demanded that the participant read an essay about meritocracy, supposedly written by a candidate in a selection process, and attribute to the declarant a position in favor or against meritocracy. Attenuation of correspondence bias was observed in the groups that underwent the RFT-PT compared to the control groups, supporting the hypothesis that the opportunity to vary perspectives may decrease correspondence bias. An analysis of correspondence bias in light of the RFT is suggested.

A new approach to the synthesis of CuMoO4 nanoparticles with mechanistic insight into the sunlight-assisted degradation of textile pollutants and antibacterial activity evaluation

CuMoO4 nanoparticles (NPs) were synthesized by a thermal decomposition followed by a precipitation method. Analytical techniques such as SEM, EDS, TEM, XRD, FTIR, UV-visible, PL, and XPS were employed to characterize the structural, optical and photocatalytic properties of CuMoO4. As per XRD analysis, CuMoO4 with different Cu concentrations were consistent, however, their crystallinities were changed. The band gap of CuMoO4 with various concentrations of Cu (0.1, 0.2, and 0.3M) was estimated to be 1.97eV, 1.86eV, and 1.44eV, respectively. The electrical conductivity of 0.3M CuMoO4 NPs was greater than other nanocomposites. Methylene Blue (MB) mineralization in an aqueous medium after 180minutes of exposure to sunlight was investigated to study the photocatalytic activities of all CuMoO4 composites. As per the PL study, the 0.3M CuMoO4 NPs exhibited better photocatalytic efficiency due to their low electron-hole recombination rate. Experimental parameters like the MB concentration, catalyst dosage, and the solution pH were evaluated to optimize the experimental conditions. The in-situ capture analysis proposed a plausible mechanism for the photocatalytic degradation of MB. The two main active species identified for MB degradation were superoxide radical anions and hydroxyl radicals. The repeated photocatalytic MB degradation verified the high level of reusability of 0.3M CuMoO4. The well-diffusion technique was utilized to examine the antibacterial activity of 0.3M CuMoO4 NPs against gram-positive (Salmonella typhi) and gram-negative (Streptococcus mutans) bacterial strains. Optimized CuMoO4 showed excellent promise for application in the field of photocatalysis, electrocatalytic and antibacterial activity.

Experimental and Computational Study of Microhardness Evolution in the HAZ for Al–Cu–Li Alloys

The Laser Beam Welding (LBW) of aluminum alloys has attracted significant interest from industrial sectors, including the shipbuilding, automotive and aeronautics industries, as it expects to contribute to significant cost reduction associated with the production of high-quality welds. To comprehend the behavior of welded structures in regard to their damage tolerance, the application of fracture mechanics serves as the instrumental tool. However, the methods employed overlook the changes in the microstructure within the Heat-Affected Zone (HAZ), which leads to the degradation of the mechanical properties of the material. The purpose of this study is to simulate microhardness evolution in the HAZ of AA2198-T351 LBW. The material represents the latest generation of Al-Cu-Li alloys, which exhibit improved mechanical properties, enhanced damage tolerance behavior, lower density and better corrosion and fatigue crack growth resistance than conventional Al-Cu alloys. In this work, the microhardness profile of LBW AA2198 was measured, and subsequently, through isothermal heat treatments on samples, the microhardness values of the HAZ were replicated. The conditions of the heat treatments (T, t) were selected in line with the thermal cycles that each area of the HAZ experienced during welding. ThermoCalc and DICTRA were employed in order to identify the strengthening precipitates and their evolution (dissolution and coarsening) during the weld thermal cycle. The microstructure of the heat-treated samples was studied employing LOM and TEM, and the strengthening precipitates and their characteristics (volume fraction and size) were defined and correlated to the calculations and the experimental conditions employed during welding. The main conclusion of this study is that it is feasible to imitate the microstructure evolution within the HAZ through the implementation of isothermal heat treatments. This implies that it is possible to fabricate samples for fatigue crack growth tests, enabling the experimental examination of the damage tolerance behavior in welded structures.

Simultaneous reproduction of experimental profiles, fluxes, transport coefficients, and turbulence characteristics via nonlinear gyrokinetic profile predictions in a DIII-D ITER similar shape plasma

Experimental conditions obtained on the DIII-D tokamak in the ITER Similar Shape (ISS) have been compared extensively with nonlinear gyrokinetic simulation using the CGYRO code [Candy et al., J. Comput. Phys. 324, 73–93 (2016)] with comparisons spanning ion and electron heat fluxes, electron and impurity particle transport, and turbulent fluctuation levels and characteristics. Bayesian optimization techniques [Rodriguez-Fernandez et al., Nucl. Fusion 62(7), 076036 (2022)], combined with nonlinear gyrokinetics, have been used to obtain simultaneously Qi, Qe, and Γe flux-matched profiles that are found to be in good agreement with experimental profile measurements. Synthetic diagnostics were used to compare measured beam emission spectroscopy and correlation electron cyclotron emission turbulent fluctuations with nonlinear simulation. Although some disagreements exist, nonlinear simulations are found to be in generally good agreement with measured fluctuation levels, spectral shapes, and measured radial trends in low-k δne/ne and δTe/Te. Low (Li and C) and mid-Z (Ca) impurity transport was also compared with these flux-matched simulations. Fully stripped, low-Z impurities are well reproduced by the gyrokinetic modeling while clear disagreement exists in comparisons with mid-Z impurities. Nonlinear gyrokinetic investigation into the Z dependence of impurity transport in the ISS conditions is also performed, demonstrating clear trends of impurity diffusion with impurity Z (both D∝Z and D∝1/Z) that vary with the radial location studied. These trends are shown to result from the local dominance of ion temperature gradient or ∇n driven trapped electron mode turbulence and may contribute to the disagreement between simulation and experiment in mid-Z impurity transport. The results of this work represent one of the most complete validation studies of the gyrokinetic model performed to date and provide an example of new capabilities for predicting performance in future fusion devices.

The Investigation of Treatment of Pistachio Processing Industrial Wastewater by Electrochemical Methods in Terms of Chemical Oxygen Demand and Total Phenol Removal

<p>This work aims to investigate the efficiency of electrocoagulation (EC) of pistachio processing industrial wastewater (PPIW) using the continuous EC process. The tubular reactor made of stainless steel with an internal diameter of 60 mm was used as a cathode electrode. The effect of some parameters was examined on the removal of chemical oxygen demand (COD) and total phenols (TP) removal efficiency. The influences of the initial pH of wastewater (from 4 to 8), flow rate (from 25 to 125 mL/min), current density (from 7 to 21 mA/cm<sup>2</sup>), and supporting electrolyte type (NaCl, NaNO<sub>3</sub>, and Na<sub>2</sub>SO<sub>4</sub>), supporting electrolyte concentration (from 10 to 100 mg/L NaCl) on removal efficiency were investigated to determine the best experimental conditions. The examination of the physico-chemical parameters during the EC treatment showed that the best removal efficiency was obtained under conditions where the flow rate was 25 mL/min (20 min reaction time), the pH value was 5.2, and the current density was 21 mA/cm<sup>2</sup> has set. Under these experimental conditions, COD and TP removal efficiency were found to be 75% and 97%, respectively, while energy consumption was 18.5 kW h/m<sup>3</sup>. The study results show that the EC can be applied to PPIW pre-treatment.</p>

Effects of Contaminations on Electric Arc Behavior and Occurrence of Defects in Wire Arc Additive Manufacturing of 316L-Si Stainless Steel

Additive Manufacturing is a manufacturing process that consists of obtaining a three-dimensional object from the deposition of material layer by layer, unlike conventional subtractive manufacturing methods. Wire Arc Additive Manufacturing stands out for its high productivity among the Additive Manufacturing technologies for manufacturing metal parts. On the other hand, the excessive heat input promotes increased residual stress levels and the occurrence of defects, such as pores, voids, a lack of fusion, and delamination. These defects result in abnormalities during the process, such as disturbances in electrical responses. Therefore, process monitoring and the detection of defects and failures in manufactured items are of fundamental importance to ensure product quality and certify the high productivity characteristic of this process. Thus, this work aimed to characterize the effects of different contaminations on the electric arc behavior of the Wire Arc Additive Manufacturing process and the occurrence of microscopic defects in thin walls manufactured by this process. To investigate the presence of defects in the metal preforms, experimental conditions were used to promote the appearance of defects, such as the insertion of contaminants. To accomplish the electric arc behavior analysis, voltage and current temporal data were represented through histograms and cyclograms, and the arc stability was assessed based on the Vilarinho index for a short circuit. Effectively, the introduction of contaminants caused electric arc disturbances that led to the appearance of manufacturing defects, such as inclusions and porosities, observed through metallographic characterization. The results confirm that the introduction of contaminations could be identified early in the Wire Arc Additive Manufacturing process through electric arc data analysis.

DeepD3, an open framework for automated quantification of dendritic spines.

Dendritic spines are the seat of most excitatory synapses in the brain, and a cellular structure considered central to learning, memory, and activity-dependent plasticity. The quantification of dendritic spines from light microscopy data is usually performed by humans in a painstaking and error-prone process. We found that human-to-human variability is substantial (inter-rater reliability 82.2±6.4%), raising concerns about the reproducibility of experiments and the validity of using human-annotated 'ground truth' as an evaluation method for computational approaches of spine identification. To address this, we present DeepD3, an open deep learning-based framework to robustly quantify dendritic spines in microscopy data in a fully automated fashion. DeepD3's neural networks have been trained on data from different sources and experimental conditions, annotated and segmented by multiple experts and they offer precise quantification of dendrites and dendritic spines. Importantly, these networks were validated in a number of datasets on varying acquisition modalities, species, anatomical locations and fluorescent indicators. The entire DeepD3 open framework, including the fully segmented training data, a benchmark that multiple experts have annotated, and the DeepD3 model zoo is fully available, addressing the lack of openly available datasets of dendritic spines while offering a ready-to-use, flexible, transparent, and reproducible spine quantification method.

A Study of the Effect of Specific Antibacterial Therapy on the Course of Tuberculous Spondylitis in an Experiment

A Study of the Effect of Specific Antibacterial Therapy on the Course of Tuberculous Spondylitis in an Experiment

Effect of gas content on cavitation nuclei

Cavitation inception originates from nuclei in a liquid. This paper proposes a Gibbs free energy approach that provides a smooth transition from homogeneous to heterogeneous nucleation when gas is present. The impact of gas content on nucleation is explored. It is found that the gas content stabilises nuclei, a phenomenon not present in pure liquid–vapour systems. This reduces the energy barrier over that required to nucleate a vapour bubble. Different gas saturation levels are studied. Gas content can significantly reduce the energy barrier required for nucleation, and under certain circumstances eliminate it. An analytic solution for the critical radius and activation energy is obtained that accounts for gas content. The classical Blake radius is recovered as a limiting case. The hysteresis between incipience and desinence is explained using the asymmetry observed in the critical radii. The solution is used to obtain the initial bubble radius, given a critical pressure condition in cavitation susceptibility meter experiments. The relationship between initial bubble diameter and critical pressure is described by an analytic solution that accounts for gas content. A model for the derivative of the cumulative nuclei histogram with respect to bubble diameter is proposed. An analytic expression is obtained that shows good agreement with decades worth of experimental data compiled by Khoo et al. (Exp. Fluids, vol. 61, issue 2, 2020, pp. 1–20) from ocean to water tunnels. The expression recovers the $-4$ power law that is observed experimentally.

Coupled Stable Isotope Tracing and Sulfamic Acid Reduction (SIT-SAR) Method to Determine the Ammonia and Nitrite Oxidation Rates in Water and Sediments.

Herein, a method was developed to measure the ammonia oxidation rate (Ra) and the nitrite oxidation rate (Rn) of water and sediment samples using a coupled stable isotope tracing and sulfamic acid reduction (SIT-SAR) method. 15NH4+ was used as a tracer to determine the ammonia oxidation rates (Ra) by calculating the concentrations of produced 15NO2- and 15NO3- during incubation, while 15NO2- was used as a tracer to determine the nitrite oxidation rates (Rn) by calculating the increase of 15NO3- during incubation. 15NO2- was chemically reduced to 29N2 with 15 mmol·L-1 sulfamic acid (SA). 15NO3- was first reduced to 15NO2- with a zinc-cadmium reducing agent, and then 15NO2- was subsequently reduced to 29N2 with SA. The produced 29N2 was measured by a membrane inlet mass spectrometer (MIMS). Under optimized experimental conditions, this method provides a sensitive (detection limit: 0.5 μmol·L-1) and precise (relative standard deviation: 4.80% for 15NO2-, 3.82% for 15NO3-) approach to quantify the concentrations of 15NO2- (0.5-150 μmol·L-1) and 15NO3- (0.5-120 μmol·L-1) in water and sediment samples over a wide range of salinities (0-30‰) with excellent calibration curves (R2 ≥ 0.999). This method was a successful application to estuarine water and sediments along the salinity gradient. Overall, the SIT-SAR method provided a rapid, accurate, and cost-effective means to determine Ra and Rn simultaneously.

Upper thermal tolerance and population implications for the Magdalena River stingray Potamotrygon magdalenae.

Knowledge of thermal tolerance limits provides important clues to the capacity of a species to withstand acute and chronic thermal changes. Climate models predict the increase and intensification of events such as heat waves, therefore understanding the upper thermal limits that a species can tolerate has become of utmost importance. We measured the upper thermal tolerance of the endemic Magdalena river stingray Potamotrygon magdalenae acclimated to experimental conditions, and then used critical thermal methodology to find the temperature at which an organism reaches a critical endpoint where locomotory activity becomes disorganized and the animal loses its ability to escape from conditions that will promptly lead to its death. We also describe the behavioral response of individuals to acute thermal stress and infer the possible consequences of temperature increases in the habitats of P. magdalenae populations. There were no significant differences between sexes in temperature tolerance or behavior. The critical thermal maximum (39°C) was 5.9°C above the maximum recorded temperature for the study area. Although P. magdalenae was tolerant to high temperature and currently is not living at its upper thermal limit, its survival in Guarinocito Pond will be threatened if temperatures continue to increase, considering the warming scenarios predicted for tropical regions due to climate change, even including short-term climate phenomena such as El Niño.