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The higher bioaccessibility of calcium from citrates compared to other salts, often explained by the capacity of hydroxycarboxylates like citrate spontaneously to form supersaturated calcium salt solutions, was analyzed using two models for dissolution of calcium hydrogen phosphate in aqueous sodium hydrogen citrate followed by slow precipitation of calcium citrate hexahydrate after a lag phase. During the dissolution calcium ion activity as measured electrochemically increased to a maximum plateau value for a dissolution time almost independent of initial hydrogen citrate concentration but with a supersaturation degree increasing strongly with increasing hydrogen citrate concentration. The difference in time dependence was analyzed by (i) a model assuming total equilibrium among the dissolved species, and (ii) a kinetic model based on coupled differential rate equations for transformations between involved dissolved species and precipitates using numerical integration. In contrast to model (i), model (ii) could quantify differences in time dependence of the concentration of dissolved species. A major difference was that the concentration of calcium hydrogen citrate follows the dynamics of the total calcium concentration in the equilibrium model, while the concentration decays monotonically towards an equilibrium value in the kinetic model. Calcium hydrogen citrate is concluded to be critical for the precipitation of dissolved calcium with the concentration of calcium hydrogen citrate determining the length of the lag phase and the rate of precipitation. Design of robust supersaturation for functional calcium foods and beverages should accordingly aim of minimizing the concentration of calcium hydrogen citrate.

Crystallization is an important procedure in the production process of separation and purification. Precise control of nucleation kinetics is critical for industrial solution crystallization, particularly in the production of pharmaceuticals such as dipyrone, where product quality is paramount. This study systematically investigates the influence of stirring speed on the metastable zone width (MSZW) and nucleation behavior of dipyrone in a pilot-scale stirred tank. The modified Sangwal’s model is applied to establish a consistent inverse relationship between stirring speed and MSZW. Increasing the stirring speed from 30 rpm to 50 rpm reduces the average MSZW by 12.70%, with the most significant reduction of 15.83% observed at higher saturation temperatures. Higher stirring speeds facilitate the overcoming of nucleation barriers, suppressing supersaturation by 7.98% and 11.70% at saturation temperatures of 333.15 K and 343.15 K, respectively. Nucleation kinetics analysis reveals that the average critical nucleus size increases by 11.74% as the stirring speed rises from 30 rpm to 50 rpm. Conversely, the nucleation rate ( J ) decreases with increasing stirring speed, though the average J is reduced by only 1.72%. From a crystal size perspective, due to shear-induced breakage, the D 32 crystal size at 50 rpm decreases by 5.35% compared to 30 rpm. These findings provide practical guidelines for optimizing stirring-induced nucleation efficiency and crystal size.

Atmospheric aerosols in clean remote oceanic regions contribute significantly to the global albedo through the formation of haze and cloud layers; however, the relative importance of ‘primary’ wind-produced sea-spray over secondary (gas-to-particle conversion) sulphate in forming marine clouds remains unclear. Here we report on marine aerosols (PM 1 ) over the Southern Ocean around Antarctica, in terms of their physical, chemical, and cloud droplet activation properties. Two predominant pristine air masses and aerosol populations were encountered: modified continental Antarctic ( cAA ) comprising predominantly sulphate with minimal sea-salt contribution and maritime Polar ( mP ) comprising sulphate plus sea-salt. We estimate that in cAA air, 75% of the CCN are activated into cloud droplets while in mP air, 37% are activated into droplets, for corresponding peak supersaturation ranges of 0.37–0.45% and 0.19–0.31%, respectively. When realistic marine boundary layer cloud supersaturations are considered (e.g. ~0.2–0.3%), sea-salt CCN contributed 2–13% of the activated nuclei in the cAA air and 8–51% for the marine air for surface-level wind speed < 16 m s −1 . At higher wind speeds, primary marine aerosol can even contribute up to 100% of the activated CCN, for corresponding peak supersaturations as high as 0.32%.

A core feature of covalent organic frameworks (COFs) is crystallinity, but current crystallization processes rely substantially on trial and error, chemical intuition and large-scale screening, which typically require harsh conditions and low levels of supersaturation, hampering the controlled synthesis of single-crystal COFs, particularly on large scales. Here we report a strategy to produce single-crystal imine-linked COFs in aqueous solutions under ambient conditions using amphiphilic amino-acid derivatives with long hydrophobic chains. We propose that these amphiphilic molecules self-assemble into micelles that serve as dynamic barriers to separate monomers in aqueous solution (nodes) and hydrophobic compartments of the micelles (linkers), thereby regulating the polymerization and crystallization processes. Disordered polyimines were obtained in the micelle, which were then converted into crystals in a step-by-step fashion. Five different three-dimensional COFs and a two-dimensional COF were obtained as single crystals on the gram scale, with yields of 92% and above.Covalent organic frameworks (COFs) have remained difficult to grow as single crystals. Now, amphiphilic amino-acid derivatives that assemble in micelles in aqueous solutions have been shown to promote the growth of a variety of imine-bridged COFs into single crystals, in a step-by-step fashion, within their hydrophobic compartment.

Surface tension influences the fraction of atmospheric particles that become cloud droplets. Although surfactants are an important component of aerosol mass, the surface tension of activating aerosol particles is still unresolved, with most climate models assuming activating particles have a surface tension equal to that of water. By studying picoliter droplet coalescence, we demonstrate that surfactants can significantly reduce the surface tension of finite-sized droplets below the value for water, consistent with recent field measurements. Significantly, this surface tension reduction is droplet size-dependent and does not correspond exactly to the macroscopic solution value. A fully independent monolayer partitioning model confirms the observed finite-size-dependent surface tension arises from the high surface-to-volume ratio in finite-sized droplets and enables predictions of aerosol hygroscopic growth. This model, constrained by the laboratory measurements, is consistent with a reduction in critical supersaturation for activation, potentially substantially increasing cloud droplet number concentration and modifying radiative cooling relative to current estimates assuming a water surface tension. The results highlight the need for improved constraints on the identities, properties, and concentrations of atmospheric aerosol surfactants inmultiple environments and are broadly applicable to any discipline where finite volume effects are operative, such as studies of the competition between reaction rates within the bulk and at the surface of confined volumes and explorations of the influence of surfactants on dried particle morphology from spray driers.

Let \\(\\mathrm{ex}(n,H,\\mathcal{F})\\) be the maximum number of copies of \\(H\\) in an \\(n\\)-vertex graph which contains no copy of a graph from \\(\\mathcal{F}\\). Thinking of \\(H\\) and \\(\\mathcal{F}\\) as fixed, we study the asymptotics of \\(\\mathrm{ex}(n,H,\\mathcal{F})\\) in \\(n\\). We say that a rational number \\(r\\) is \\emph{realizable for \\(H\\)} if there exists a finite family \\(\\mathcal{F}\\) such that \\(\\mathrm{ex}(n,H,\\mathcal{F}) = \\Theta(n^r)\\). Using randomized algebraic constructions, Bukh and Conlon showed that every rational between \\(1\\) and \\(2\\) is realizable for \\(K_2\\). We generalize their result to show that every rational between \\(1\\) and \\(t\\) is realizable for \\(K_t\\), for all \\(t \\geq 2\\). We also determine the realizable rationals for stars and note the connection to a related Sidorenko-type supersaturation problem.

Carbon dioxide (CO₂) supersaturation in lakes and rivers worldwide is commonly attributed to terrestrial–aquatic transfers of organic and inorganic carbon (C) and subsequent, in situ aerobic respiration. Methane (CH₄) production and oxidation also contribute CO₂ to freshwaters, yet this remains largely unquantified. Flood pulse lakes and rivers in the tropics are hypothesized to receive large inputs of dissolved CO₂ and CH₄ from floodplains characterized by hypoxia and reducing conditions. We measured stable C isotopes of CO₂ and CH₄, aerobic respiration, and CH₄ production and oxidation during two flood stages in Tonle Sap Lake (Cambodia) to determine whether dissolved CO₂ in this tropical flood pulse ecosystem has a methanogenic origin. Mean CO₂ supersaturation of 11,000 ± 9,000 μatm could not be explained by aerobic respiration alone. 13C depletion of dissolved CO₂ relative to other sources of organic and inorganic C, together with corresponding 13C enrichment of CH₄, suggested extensive CH₄ oxidation. A stable isotope-mixing model shows that the oxidation of 13C depleted CH₄ to CO₂ contributes between 47 and 67% of dissolved CO₂ in Tonle Sap Lake. 13C depletion of dissolved CO₂ was correlated to independently measured rates of CH₄ production and oxidation within the water column and underlying lake sediments. However, mass balance indicates that most of this CH₄ production and oxidation occurs elsewhere, within inundated soils and other floodplain habitats. Seasonal inundation of floodplains is a common feature of tropical freshwaters, where high reported CO₂ supersaturation and atmospheric emissions may be explained in part by coupled CH₄ production and oxidation.

Very small ponds have been omitted from greenhouse gas budgets. Estimates of CO 2 and CH 4 emissions from 427 lakes and ponds show that very small ponds account for 15% of CO 2 and 40% of diffusive CH 4 emissions, but 8.6% of lake and pond area. Inland waters are an important component of the global carbon cycle. Although they contribute to greenhouse gas emissions 1 , 2 , 3 , 4 , 5 , estimates of carbon processing in these waters are uncertain. The global extent of very small ponds, with surface areas of less than 0.001 km 2 , is particularly difficult to map, resulting in their exclusion from greenhouse gas budget estimates. Here we combine estimates of the lake and pond global size distribution, gas exchange rates, and measurements of carbon dioxide and methane concentrations from 427 lakes and ponds ranging in surface area from 2.5 m 2 to 674 km 2 . We estimate that non-running inland waters release 0.583 Pg C yr −1 . Very small ponds comprise 8.6% of lakes and ponds by area globally, but account for 15.1% of CO 2 emissions and 40.6% of diffusive CH 4 emissions. In terms of CO 2 equivalence, the ratio of CO 2 to CH 4 flux increases with surface area, from about 1.5 in very small ponds to about 19 in large lakes. The high fluxes from very small ponds probably result from shallow waters, high sediment and edge to water volume ratios, and frequent mixing. These attributes increase CO 2 and CH 4 supersaturation in the water and limit efficient methane oxidation. We conclude that very small ponds represent an important inland water carbon flux.

Secondary ice production (SIP) plays a key role in the formation of ice particles in tropospheric clouds. Future improvement of the accuracy of weather prediction and climate models relies on a proper description of SIP in numerical simulations. For now, laboratory studies remain a primary tool for developing physically based parameterizations for cloud modeling. Over the past 7 decades, six different SIP-identifying mechanisms have emerged: (1) shattering during droplet freezing, (2) the rime-splintering (Hallett–Mossop) process, (3) fragmentation due to ice–ice collision, (4) ice particle fragmentation due to thermal shock, (5) fragmentation of sublimating ice, and (6) activation of ice-nucleating particles in transient supersaturation around freezing drops. This work presents a critical review of the laboratory studies related to secondary ice production. While some of the six mechanisms have received little research attention, for others contradictory results have been obtained by different research groups. Unfortunately, despite vast investigative efforts, the lack of consistency and the gaps in the accumulated knowledge hinder the development of quantitative descriptions of any of the six SIP mechanisms. The present work aims to identify gaps in our knowledge of SIP as well as to stimulate further laboratory studies focused on obtaining a quantitative description of efficiencies for each SIP mechanism.

Tailoring heat treatments for Laser Powder Bed Fusion (LPBF) processed materials is critical to ensure superior and repeatable material properties for high-end applications. This tailoring requires in-depth understanding of the LPBF-processed material. Therefore, the current study aims at unravelling the threefold interrelationship between the process (LPBF and heat treatment), the microstructure at different scales (macro-, meso-, micro-, and nano-scale), and the macroscopic material properties of AlSi10Mg. A similar solidification trajectory applies at different length scales when comparing the solidification of AlSi10Mg, ranging from mould-casting to rapid solidification (LPBF). The similarity in solidification trajectories triggers the reason why the Brody-Flemings cellular microsegregation solidification model could predict the cellular morphology of the LPBF as-printed microstructure. Where rapid solidification occurs at a much finer scale, the LPBF microstructure exhibits a significant grain refinement and a high degree of silicon (Si) supersaturation. This study has identified the grain refinement and Si supersaturation as critical assets of the as-printed microstructure, playing a vital role in achieving superior mechanical and thermal properties during heat treatment. Next, an electrical conductivity model could accurately predict the Si solute concentration in LPBF-processed and heat-treated AlSi10Mg and allows understanding the microstructural evolution during heat treatment. The LPBF-processed and heat-treated AlSi10Mg conditions (as-built (AB), direct-aged (DA), stress-relieved (SR), preheated (PH)) show an interesting range of superior mechanical properties (tensile strength: 300–450 MPa, elongation: 4–13%) compared to the mould-cast T6 reference condition.