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Chemical base flow separation is a widely applied technique in which contributions of groundwater and surface runoff to streamflow are estimated based on the chemical composition of stream water and the two end‐members. This method relies on the assumption that the groundwater end‐member can be accurately defined and remains constant. We simulate solute transport within the aquifer during and after single and multiple river flow events, to show that (1) water adjacent to the river will have a concentration intermediate between that of the river and that of regional groundwater and (2) the concentration of groundwater discharge will approach that of regional groundwater after a flow event but may take many months or years before it reaches it. In applying chemical base flow separation, if the concentration in the river prior to a flow event is used to represent the pre‐event or groundwater end‐member, then the groundwater contribution to streamflow will be overestimated. Alternatively, if the concentration of regional groundwater a sufficient distance from the river is used, then the pre‐event contribution to streamflow will be underestimated. Changes in concentration of groundwater discharge following changes in river stage predicted by a simple model of stream‐aquifer flows show remarkable similarity to changes in river chemistry measured over a 9 month period in the Cockburn River, southeast Australia. If the regional groundwater value was used as the groundwater end‐member, chemical base flow separation techniques would attribute 8% of streamflow to groundwater, as opposed to 25% if the maximum stream flow value was used.

Hydrograph separation procedures aim to separate the baseflow and quickflow components of streamflow. Although widely used, these procedures are considered arbitrary, as they are mostly based on sheer geometrical or mathematical concepts and involve only streamflow data. Because the in-stream chemical concentrations are known to be valuable indicators of the actual flow-generating processes, we propose here a calibration approach for one of the most common hydrograph separation methods: the Recursive Digital Filter (RDF). The proposed approach uses continuous in-stream chloride concentrations, measured at the ORACLE-Orgeval Observatory (France). For this, we combine the RDF method with the chloride solute through the mass balance method (MB) and a multi-objective optimization function. Results show that the calibration approach allows a better estimation of the chemical concentration time series tested at flood event and inter-annual scale.

Static headspace gas chromatography-ion mobility spectrometry (SHS GC-IMS) is a relatively new analytical technique that has considerable potential for analysis of volatile organic compounds (VOCs). In this study, SHS GC-IMS was used for the identification of the major terpene components of various essential oils (EOs). Based on the data obtained from 25 terpene standards and 50 EOs, a database for fingerprint identification of characteristic terpenes and EOs was generated utilizing SHS GC-IMS for authenticity testing of fragrances in foods, cosmetics, and personal care products. This database contains specific normalized IMS drift times and GC retention indices for 50 terpene components of EOs. Initially, the SHS GC-IMS parameters, e.g., drift gas and carrier gas flow rates, drift tube, and column temperatures, were evaluated to determine suitable operating conditions for terpene separation and identification. Gas chromatography-mass spectrometry (GC-MS) was used as a reference method for the identification of terpenes in EOs. The fingerprint pattern based on the normalized IMS drift times and retention indices of 50 terpenes is presented for 50 EOs. The applicability of the method was proven on examples of ten commercially available food, cosmetic, and personal care product samples. The results confirm the suitability of SHS GC-IMS as a powerful analytical technique for direct identification of terpene components in solid and liquid samples without any pretreatment. Graphical abstract Fingerprint pattern identification of terpenes and essential oils using static headspace gas chromatography-ion mobility spectrometry.

Determination of groundwater recharge is a major challenge in areas where rainfall is generally abundant. Variability and uncertainty are inherent in the estimation of recharge, and several methods are therefore recommended for its estimation at a regional level. In this study, we evaluated several methods for estimating recharge: the web GIS-based automated hydrological analysis tool (WHAT), water table fluctuation (WTF), hydrograph analyses, a recession curve displacement method, graphical separation, and empirical formulas. The annual recharge estimated by combining direct recharge and base-flow varied from 84 mm in 2019 to 66.4 mm in 2020. The mean direct recharge was about 44 mm in 2018 and 57.3 mm in 2019, representing about 4% and 5% of the respective rainfall. In 2020, this direct recharge was 43 mm, or about 6% of rainfall, around 25% lower than in 2019. Base-flow separation methods and recession curve displacement generally gave low results, whereas modified empirical formulas gave results close to those of the WTF method and were considered more consistent and reasonable. The regression curve displacement method implemented in the United States geologic survey (USGS) RORA program was found to be unsuitable for the study area. However, the other methods presented more reasonable results and could be used to estimate groundwater recharge in the study area.

A uniform Schiff base network (SNW) film was synthesized in situ in a controllable way through continuous flow of reactants inside the capillary. The properties and application of the as-prepared capillary was investigated in capillary electrochromatography. The effects of reaction monomer concentration and reaction time on coating thickness were studied by SEM. The results show that the reaction condition has a significant influence on the morphology and thickness of the SNW films. The thickness of the film can be controlled by changing the concentration of reaction solution and reaction time. Capillaries coated under different conditions were employed to separate four nucleotides by capillary electrochromatography, which demonstrated significant variation of migration time, peak order, and separation efficiency. Analytes containing nitrogen heterocycle structures, such as nucleotides, methylimidazole isomers, and β-lactam antibiotics, were successfully separated with the prepared open-tubular columns. Under the selected separation conditions, theoretical plate number of four nucleotides is in a range 45,237–104,505 plates·m −1 , and the resolutions are 1.98–8.07. A resolution of 1.75 is obtained for methylimidazole isomers. The nucleotides in a real sample, chicken essence seasoning, were determined using the prepared capillary column with satisfactory recoveries in the range 95 to 105%. Graphical abstract

The substitution of fossil resources by renewable alternatives is a major challenge for our society. Kolbe electrolysis converts carboxylic acids to hydrocarbons, which can be used as base chemicals, specialty chemicals, or fuels. Carboxylic acids may be retrieved from biomass or residues and, in consequence, can be a sustainable feedstock. Since the Kolbe electrolysis has only been investigated in lab scale, this work proposes the first basic engineering design study on process development for a continuously working process. Thermophysical data, including solubility and boiling point, are used to gain insight into requirements on process equipment such as separation processes or process parameters such as operating temperature. Furthermore, Aspen Plus was used to retrieve information on acid base equilibria and azeotropes. The process development for three different feedstocks (acetic acid, valeric acid and lauric acid) was performed. The process design shows that most of the process units are rather straightforward and rely on state of the art technologies. The addition of an alkaline catalyst improves the solubility and deprotonation of the carboxylic acid but on the cost of a possibly lower product selectivity. Elevation of the operating temperature above the Krafft point is necessary for long-chain fatty acids. Kolbe electrolysis can be an interesting technology for future production processes based on carboxylic acids and electricity from sustainable sources.

Documenting how ground- and surface water systems respond to climate change is crucial to understanding water resources, particularly in the U.S. Great Lakes region, where drastic temperature and precipitation changes are observed. This study presents baseflow and baseflow index (BFI) trend analyses for 10 undisturbed watersheds in Michigan using (1) multi-objective optimization (MOO) and (2) modified Mann–Kendall (MK) tests corrected for short-term autocorrelation (STA). Results indicate a variability in mean baseflow (0.09–8.70 m3/s) and BFI (67.9–89.7%) that complicates regional-scale extrapolations of groundwater recharge. Long-term (>60 years) MK trend tests indicate a significant control of total precipitation (P) and snow- to rainfall transitions on baseflow and BFI. In the Lower Peninsula Rifle River watershed, increasing P and a transition from snow- to rainfall has increased baseflow at a lower rate than streamflow; an overall pattern that may contribute to documented flood frequency increases. In the Upper Peninsula Ford River watershed, decreasing P and a transition from rain- to snowfall had no significant effects on baseflow and BFI. Our results highlight the value of an objectively constrained BFI parameter for shorter-term (<50 years) hydrologic trend analysis because of a lower STA susceptibility.

Inhalational anesthesia is supplied through an assisted ventilation system. It is mostly composed of xenon or nitrous oxide, halogenated hydrocarbons (HHCs), and oxygen. In order to reduce costs of the anesthesia compounds, the remaining anesthetics present in exhalation are recycled and reused, in order to minimize the amount of fresh anesthesia. An alkali hydroxide mixture (called soda lime) is employed in order to remove CO2 from the exhalation. However toxic compounds may be formed during the reaction of soda lime with halogenated hydrocarbons. Ionic liquids (ILs) have several advantages such as non-volatility, functionality, high carbon solubility, and low energy requirements for regeneration. In the framework of this research, carbon dioxide removal with ionic liquids has been numerically studied. COMSOL multi-physics finite element software has been applied. It solves the continuity, fluid flow, and diffusion equations. A new algorithm has been developed for calculating the infrared (IR) radiation absorption of CO2. Its absorption coefficient has wavelength-dependent properties. The gaseous absorption coefficient has been calculated by using HITRAN spectral database. It has been found that the CO2 is absorbed almost completely by the 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) ionic liquid after a period of 1000 s. It has been shown that the absorption coefficient of CO2 can be neglected in the interval below 1.565 μm, and then at 1.6 μm, it increases to the same order as that for CO. Thus, it is possible to detect CO2 by applying a laser diode which is capable to transmit IR radiation at a wavelength of 1.6 μm. This time period is a function of the diffusion coefficient of the CO2 in the membrane and in the ionic liquid.

Base oils are produced by refining crude oil or through chemical synthesis. They are a key component of engine oils. With an immense range of carbon numbers and boiling points, analyzing such complex mixtures is very difficult. The need to monitor industrial petroleum processing steps, as well as to identify petrochemical environmental pollutants, drives the search for improved characterization methods. Comprehensive two-dimensional gas chromatography (GC × GC) is one of the best tools for that. The modulator used in GC × GC is responsible for trapping/sampling the first dimension (1D) column analytes, then reinjecting them in the form of narrow bands onto the second dimension (2D) column for further separation. Modulators used today generally fall into two categories, thermal and flow ones. Heater-based thermal modulators trap the 1D column effluent at or above ambient temperatures. Flow-based modulators utilize storage loop(s) to collect the 1D effluent, which is subsequently flushed into the second-dimension column for further separation. A single-stage, consumable-free thermal modulator and a reverse fill/flush flow modulator were compared for the characterization of base oils. Both were evaluated on their ability to achieve separation of several conventional and synthetic engine oils components. A reverse column set, polar 1D and nonpolar 2D, allowed group-type analysis of all classes, including linear, branched, and aromatic species. The results show the ability to achieve a comprehensive separation of specific compound classes and the differentiation of engine oil types and manufacturers. Soft ionization assisted in tentative identification of two alkylated diphenylamines in each sample. The advantages and limitations of both thermal and flow modulation are presented.

In this study, a combined technique of bibliometric and social network analysis was applied on research articles, related to the application of nano-adsorbents for cobalt removal from wastewater, published in Scopus database up to 2020. The results revealed that the first relative research article appeared in the Scopus database in the year 2002. The total output of research articles reached 214 in the year 2020. Published research articles of the years 2014–2020, added up to 83.6% of total articles. King Saud University of Saudi Arabia, Chinese Academy of Science, and LUT University of Finland were found to serve as the gatekeepers who control information flows in the network of the most prolific institutions, while cooperation between China, Saudi Arabia, and United States was also identified. On average, the most prolific authors cooperated with five others, while the top 10 cited publications appeared to represent a sparse and weakly interconnected network of co-authors. Graphene oxide was the most prominent nano-adsorbent among the top 10 cited publications, and their respective co-citations network visualization helped in capturing the value of certain citations to the evolution of the research on the topic, putting thus scientific work impact assessment to a different perspective.