Spatial Variation In Chemical Composition Research Articles

The use of confocal Raman microscopy and microfluidic channels to monitor the location and mobility of β-carotene incorporated in droplet-stabilized oil-in-water emulsions

This study sought to explore the combined use of confocal Raman microscopy and microfluidic channels to probe the location and mobility of hydrophobic antioxidant (β-carotene) incorporated at the interface of food-grade droplet-stabilized emulsions (DSEs).Microfluidic channels were used to isolate emulsion droplets for efficient investigation of antioxidant mobility. This approach proved more conclusive than fixing the sample in agarose, because a single layer of droplets could be obtained. Results also indicated that the migration of β-carotene incorporated in shell droplets of olive oil and trimyristin DSEs to core droplets was minimal and beta-carotene remained mostly localised at the interface even after 3 days of production.This work demonstrates that microfluidic isolation of emulsion droplets combined with confocal Raman microscopy can give new insights into the spatial variation of chemical composition within emulsions.This study revealed that the migration of β-carotene between shell and core was minimal and hence it may be possible to concurrently deliver two incompatible compounds by spatially segregating them between shell and core compartments of DSEs.

A reaction-dissolution strategy for designing solid electrolyte interphases with stable energetics for lithium metal anodes

The spatial variations in chemical composition and transport properties of the interphase formed on reactive metal electrodeposits dictate the stability and reversibility of electrochemical cells that use reactive metals as anodes. Here we report on the influence of carbonate and fluorinated electrolytes infused with ethers as additives on the physical-chemical characteristics and reversibility of metallic lithium (Li) during early stages of electrodeposition and later stages of deep cycling of Li metal anodes. We show that a feasible strategy for achieving and sustaining kinetically enhanced interphases through the cycle life of Li electrodeposits is by simultaneous use of sacrificial electrolyte components that undergo electroreduction to enrich the interphase with fluorinated species in tandem with cleaning electrolyte components that promote dissolution and removal of less desirable carbonaceous compounds. We demonstrate that this approach translates to high electrochemical reversibility during deep cycling of the Li metal anode and improved performance of Li metal batteries. • Rational design of liquid carbonate/fluorinated electrolytes with ether additive • Study of physiochemical characteristics and reversibility of metallic lithium (Li) • Employing reaction-dissolution strategy to enhance reversibility of Li anode • Demonstrating practical Li metal batteries with exceptional performance The rechargeability and stability of lithium metal batteries (LMBs) is affected by the interphase between the lithium metal anode and the electrolyte. Biswal et al. report rational selection of liquid electrolyte components to create, refresh, and sustain a kinetically enhanced interphase on the lithium metal anode through the cycle life of LMBs.

Effect of calcium content on the dissolution rate of dolomites in HCl acid

In previous dissolution studies, dolomite has been commonly assumed to have an ideal composition of CaMg(CO3)2. The objectives of this work are to determine (1) if dolomites composing hydrocarbon reservoir rocks vary in chemical composition, specifically Ca content, and (2) the effect of Ca uptake on the dissolution rate of dolomite in HCl acid. Dolomitic reservoir rocks from different sources were analyzed using several techniques, including: X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and acid solubility. Most dolomites are Fe/Mn poor and nonstoichiometric with 1.02 < nCa <1.13, where nCa is the average number of Ca atoms per formula unit. To quantify the effect of Ca content on the dissolution rate of dolomite, the samples with similar mineral composition and microstructure, but different Ca uptake, were reacted with 21.5 wt% HCl in a rotating disk apparatus (RDA). At 24 °C dolomites with chemical composition Ca1.067Mg0.933(CO3)2 dissolved 1.7 times faster than ones with composition Ca1.015Mg0.985(CO3)2. At 50 °C the difference in the dissolution rates increased 2.2 times. Further increase in temperature decreased the difference in dissolution rates to 1.5 and 1.4 times at 75 and 100 °C, respectively. This non-linear dependence is explained by the shift of the dissolution process from surface reaction rate to predominantly diffusion (mass-transfer) limited. Results also indicate that Ca content in dolomites was not constant along the sampled intervals of the same wells. Since dolomite reactivity depends on calcium content, spatial variation in chemical composition of this mineral should be considered when designing well-stimulation operations. The present study innovatively determines the effect of chemical composition of dolomite on the dissolution rate of this mineral.

The multi‐component Hekla Ö Tephra, Iceland: a complex widespread mid‐Holocene tephra layer

ABSTRACTLarge Plinian eruptions from Hekla volcano, Iceland, produce compositionally zoned tephra used as key markers in tephrochronology. However, spatial variations in chemical composition of a tephra layer may complicate its identification. An example is the 5950–6180 cal a bp Hekla Ö tephra layer, which shows compositional spread from rhyolite, dacite and andesite to basalt. In soil sections north of Hekla, the SiO2 content of the tephra glass reaches 76 wt% in the lowest unit of the Hekla Ö deposit and decreases to 62–63 wt% in the uppermost unit. Intermingled within the whole deposit are basalt tephra grains having 46–47 wt% SiO2. The composition of the basalt glass includes primitive basalt and a more evolved basalt (MgO &gt;6 and &lt;6 wt%, respectively). Together with literature data, the Hekla Ö tephra and the so‐called T‐Tephra/Hekla‐T are most likely from contemporaneous eruptions of different vents on the Hekla volcanic system, forming a single important marker tephra (Hekla ÖT) deposited over 80% of Iceland. Identification is complicated by its spatial compositional heterogeneity, such as systematic decrease in SiO2 content from the east to the west of Hekla volcano. Consequently, an individual tephra layer from a large explosive eruption can have different composition at different locations. © 2020 John Wiley &amp; Sons, Ltd.

Long-term fertilization decreases chemical composition variation of soil humic substance across geographic distances in subtropical China

Many previous research have investigated the spatial distribution of the content of soil organic matter (SOM) and soil humic substance (HS), while few work focused on the chemical composition variation of HS across geographic distance. Paddy soils, collected from different long-term fertilization treatments across a wide geographic area in subtropical China, were used to evaluate the spatial variation of HS chemical composition. The 3-dimensional fluorescence spectroscopy combined with parallel factor analysis was used to evaluate the chemical composition of the soil extractable humic substance (EHS, including humic acid and fulvic acid). Analysis of distance-decay relationship (DDR) was introduced here to study the spatial variation of the chemical compositions of these EHSs. It was found that geographic location impose greater impact on the compositional variation of soil EHS than fertilization practice. Fertilization treatments including NPK (mineral N, P and K fertilizers) and NPKS (NPK fertilizers plus straw return) exhibited significant flattened DDR slopes as compared to CK (no fertilizers), which indicated fertilization (NPK and NPKS) decreased the variation of EHS chemical composition in paddy soils across geographic distance. A positive correlation was found between variations of soil bacterial community and EHS chemical composition, and fertilization (NPK and NPKS) enhanced their relationships. This work demonstrated that although the geographic location mainly dominated the spatial variation of the soil EHS chemical composition across geographic distance, the same long-term fertilization practice could gradually domesticate the paddy soils to display more similar EHS composition.

Chemical composition and hygroscopic properties of aerosol particles over the Aegean Sea

Abstract. The chemical composition and water uptake characteristics of sub-micrometre atmospheric particles over the region of the Aegean Sea were measured between 25 August and 11 September 2011 within the framework of the Aegean-Game campaign. High temporal-resolution measurements of the chemical composition of the particles were conducted using an airborne compact time-of-flight aerosol mass spectrometer (cToF-AMS). These measurements were performed during two flights from the island of Crete to the island of Lemnos and back. A hygroscopic tandem differential mobility analyser (HTDMA) located on the island of Lemnos was used to measure the ability of the particles to take up water. The HTDMA measurements showed that the particles in the dominant mode were internally mixed, having hygroscopic growth factors that ranged from 1.00 to 1.59 when exposed to 85% relative humidity. When the aircraft flew near the ground station on Lemnos, the cToF-AMS measurements showed that the organic volume fraction of the particles ranged from 43 to 56%. These measurements corroborate the range of hygroscopic growth factors measured by the HTDMA during that time. Good closure between HTDMA and cToF-AMS measurements was achieved when assuming that the organic species were less hygroscopic and had an average density that corresponds to aged organic species. Using the results from the closure study, the cToF-AMS measurements were employed to determine vertical profiles of a representative aerosol hygroscopic parameter κmix. Calculated κmix values ranged from 0.19 to 0.84 during the first flight and from 0.22 to 0.80 during the second flight. Air masses of different origin as determined by back trajectory calculations can explain the spatial variation in chemical composition and κmix values of the particles observed in the region.

Radiation damage on sub-cellular scales: beyond DNA

This study investigates a model cell as a target for low-dose radiation using Monte Carlo simulations. Mono-energetic electrons and photons are used with initial energies between 10 and 50 keV, relevant to out-of-field radiotherapy scenarios where modern treatment modalities expose relatively large amounts of healthy tissue to low-dose radiation, and also to microbeam cell irradiation studies which show the importance of the cytoplasm as a radiation target. The relative proportions of number of ionizations and total energy deposit in the nucleus and cytoplasm are calculated. We show that for a macroscopic dose of no more than 1 Gy only a few hundred ionizations occur in the nucleus volume whereas the number of ionizations in the cytoplasm is over a magnitude larger. We find that the cell geometry can have an appreciable effect on the energy deposit in the cell and can cause a nonlinear increase in energy deposit with cytoplasm density. We also show that changing the nucleus volume has negligible effect on the total energy deposit but alters the relative proportion deposited in the nucleus and cytoplasm; the nucleus volume must increase to approximately the same volume as the cytoplasm before the energy deposit in the nucleus matches that in the cytoplasm. Additionally we find that energy deposited by electrons is generally insensitive to spatial variations in chemical composition, which can be attributed to negligible differences in electron stopping power for cytoplasm and nucleus materials. On the other hand, we find that chemical composition can affect energy deposited by photons due to non-negligible differences in attenuation coefficients. These results are of relevance in considering radiation effects in healthy cells, which tend to have smaller nuclei. Our results further show that the cytoplasm and organelles residing therein can be important targets for low-dose radiation damage in healthy cells and warrant investigation as much as the conventional focus of a high-dose radiation DNA target in tumour cells.

Assessment of temporal and spatial variation in chemical composition of groundwater in an unconfined esker aquifer in the cold temperate climate of Northern Finland

Samples of groundwater, surface water, snow and precipitation were collected to identify potential end-members for aquifer recharge in an unconfined esker aquifer connected to nearby surface waters. Concentrations of Ca2 +, Cl−, NO3–N and SiO2 and electrical conductivity were determined in these water samples. Time series, ANOVA followed by HSD test and biplots were used to investigate temporal and spatial variations in surface water and groundwater chemistry. Examination of the spatial and temporal variations in groundwater solutes revealed that water quality was similar in perched groundwater and the main aquifer. The exception was NO3–N concentration, which increased in the perched groundwater with rising groundwater level, indicating a nitrogen source from the overlying airport. In the main aquifer, solute concentrations generally decreased during and immediately after snowmelt periods, indicating the importance of snowmelt input for groundwater quality. Groundwater solute concentrations generally decreased with declining groundwater level. During the spring melt period, the surface water level rise higher than groundwater level and the Cl− concentration in groundwater decreased showing a seasonal surface water intrusion. During the anomalously warm period in winter (T > 0 °C) the solute concentration decreased, implying that groundwater quality may be sensitive to future warming.

Spatial variation of chemical composition and sources of submicron aerosol in Zurich during wintertime using mobile aerosol mass spectrometer data

Abstract. Mobile measurements of PM1 (particulate matter with an aerodynamic diameter &lt;1 μm) chemical composition using a quadrupole aerosol mass spectrometer and a multi-angle absorption photometer were performed using the PSI mobile laboratory during winter 2007/2008 and December 2008 in the metropolitan area of Zurich, Switzerland. Positive matrix factorization (PMF) applied to the organic fraction of PM1 yielded 3 factors: Hydrocarbon-like organic aerosol (HOA) related to traffic emissions; organic aerosol from wood burning for domestic heating purposes (WBOA); and oxygenated organic aerosol (OOA), assigned to secondary organic aerosol formed by oxidation of volatile precursors. The chemical composition of PM1 was assessed for an urban background site and various sites throughout the city. The background site is dominated by secondary inorganic and organic species (57 %), BC, HOA, and WBOA account for 15 %, 6 %, and 12 %, respectively. As for the other sites, HOA is important along major roads (varying between 7 and 14 % of PM1 for different sites within the city, average all sites 8 %), domestic wood burning makes up between 8–15 % of PM1 for different sites within the city (average all sites 10.5 %). OOA makes up the largest fraction of organic aerosol (44 % on average). A new method allows for the separation and quantification of the local fraction of PM1 emitted or rapidly formed in the city, and the fraction of PM1 originating from the urban background. The method is based on simultaneous on-road mobile and stationary background measurements and the correction of small-scale meteorological effects using the ratio of on-road sulfate to stationary sulfate. Especially during thermal inversions over the Swiss plateau, urban background concentrations contribute substantially to particulate number concentrations (between 40 and 80 % depending on meteorological conditions and emissions, 60 % on average) as well as to the mass concentrations of PM1 components measured on road in downtown Zurich (between 30 and 90 %, on average 60 % for black carbon and HOA, and between 90 and 100 % for WBOA, OOA, and the measured inorganic components). The results emphasize, on a scientific level, the advantage of mobile measurements for distinguishing local from regional air pollution research, and on a political level, the importance of regional collaboration for mitigating air pollution issues.

Short-range order in amorphous SiOx by x ray photoelectron spectroscopy

The Si 2p x ray photoelectron spectra of SiOx with a different composition of 0 ≤ x ≤ 2 have been studied experimentally and theoretically. The SiOx films were prepared by low-pressure chemical vapor deposition from SiH4 and N2O source at 750 °C. Neither random bonding nor random mixture models can adequately describe the structure of these compounds. The interpretation of the experimental results is discussed according to a large scale potential fluctuation due to the spatial variation of chemical composition in SiOx.

Compositional Variation of Hydrothermally Altered Volcanic Rocks in Hishikari Gold Epithermal System: A Useful Geochemical Indicator of Gold-Silver Epithermal Mineralization

The hydrothermally altered andesite hosting the Hishikari gold-silver vein deposits in southern Kyushu, Japan, is analyzed with respect to the spatial variation in chemical composition. The (CaO + Na2O) content is found to be inversely correlated with the K2O content as it progresses away from the site of mineralization. It was found that analytical data plotted on a (CaO + Na2O) − K2O diagram cannot be explained only by addition of K+ from the hydrothermal solution to the original rock and release of Ca2+ and Na+ from the original rock (K- alteration). Addition of Ca2+ and Na+ from the hydrothermal solution to the rock and release of K+ from the rock but release of K+, Ca2+, and Na+ to the hydrothermal solution (advanced argillic alteration) is important for causing the wide variations in K2O, CaO, and Na2O contents on the (CaO + Na2O) − K2O diagram. These variations can be explained by superimposed potassic, advanced argillic and calcium alterations. The altered rocks in the Honko-Sanjin area, Yamada area, and Masaki area analyzed by this study are characterized by their intermediate K2O content and variable CaO content, high K2O content and low CaO content, and low K2O content and low CaO content, respectively. The K2O, Na2O and CaO contents and oxygen isotopic composition of altered andesite, in conjunction with the solubility of gold as a thio complex, suggest that both gold deposition and the observed compositional variation of altered andesite are the result of mixing between acidic groundwater and neutral gold-bearing hydrothermal solution. The present results indicate that the compositional variation of hydrothermally altered rocks may represent a useful geochemical indicator of epithermal gold–silver mineralization.

A geochemical transect across a heterogeneous mantle upwelling: Implications for the evolution of the Madeira hotspot in space and time

Young (≤ 3 Ma) lavas from volcanic centers along a 75-km N–S transect from northern Madeira Island to a submarine volcanic field 55 km south of Madeira exhibit distinct spatial geochemical variations. From south to north along this transect, there is a general decrease in Fe(8) (total Fe as FeO normalized to MgO = 8 wt.%), K(8), Pb isotope ratios and Zr/Hf and an increase in Al(8) and Nd isotope ratios, reflecting an increasing contribution of depleted source components to the north. The south to north spatial variations mimic the ca. 6 million year temporal geochemical evolution on Madeira with the isotopic composition of the volcanic rocks becoming progressively more depleted through time. The temporal and spatial variation in chemical composition of lavas is consistent with melt extraction from a heterogeneous blob of upwelling mantle consisting of enriched garnet pyroxenite/eclogite material (recycled hydrothermally altered oceanic crust) in a depleted ultramafic/peridotitic matrix (recycled lower oceanic crust and/or lithospheric mantle). The geochemical transect provides new insights into the spatial heterogeneity of the Madeira plume pulse and confirms models for the temporal evolution of ocean island volcanoes.

Silicon dots/clusters in silicon nitride: photoluminescence and electron spin resonance

Photoluminescence (PL) properties of SiN x (0.51< x<1.3) films are studied. A visible luminescence near the UV region is observed and the PL intensity and peak positions are found to be governed by the excess silicon composition. A large scale potential fluctuation due to the spatial variation of chemical composition in SiN x is proposed to explain these observations. In addition, non-radiative recombination centers (N 3Si·, N 2SiSi·, NSi 2Si·, or Si 3Si·), which have prominent effect on the luminescence intensity, are also studied using electron spin resonance (ESR) measurement. The ESR results suggest that the excess silicon content should not be too high in order to have a strong PL.

Morphology-dependent stimulated Raman scattering imaging. I. Theoretical aspects

Morphology-dependent stimulated Raman scattering is a nonlinear laser Raman spectroscopy that relies on using the cavity modes associated with micron-sized structures to enhance optical signal generation. Since different cavity modes occupy different regions in space, location-specific spectra can be generated. Here we outline the physics behind morphology-dependent stimulated Raman scattering imaging and model the signal generation process. The results show that a simple tailoring of the illumination conditions allows signal from single, but selectable, cavity modes to be generated. Thus, this nonlinear Raman technique can be used to image spatial variations in chemical composition and/or molecular structure within microstructures.

Site-specific adhesion of Staphylococcus epidermidis (RP12) in Ti-Al-V metal systems

Staphylococcus epidermidis (RP12) adhesion patterns were studied on the following titanium (Ti)-aluminium (Al)-vanadium (V) metal systems: (i) microfabricated samples consisting of Ti, AI and V islands deposited onto Ti or V substrata, (ii) pure Ti, AI and V metals, and (ill) medical grade Ti6AI4-V alloy. All of these surfaces were covered with their respective oxides formed upon exposure of the metals to air. Quantitative analysis of the number of cells bound per unit area indicates that S. epidermidis (RP12) exhibits greatest adhesion to pure V surfaces. When exposed to surfaces having controlled spatial variations in chemical composition on the μm scale (microfabricated samples), the bacteria preferentially populate V islands versus Ti or AI substrata. In the case of the biphasic Ti6AI4V alloy, the bacteria tend to adhere to V-rich, mixed phase regions and phase boundaries. These findings demonstrate that enhanced and preferential adhesion of S. epidermidis (RP12) occurs on V surfaces in Ti-AI-V metal systems and suggest that bacterial interactions are influenced by surface oxide composition.

Late Cenozoic basaltic volcanism around the Taiwan Strait, SE China: Product of lithosphere-asthenosphere interaction during continental extension

Late Cenozoic intraplate basaltic volcanism in SE China and Taiwan occurred as a result of lithospheric extension related to the opening of the South China Sea. It was gradually terminated by the compression which propagated westwards from the arc-continent collision in Taiwan since ∼ 12 Ma ago. The basalts show a spatial variation in chemical composition. Their alkalinity, degree of silica undersaturation and abundance of incompatible elements increase whilst Pb isotopic ratios decrease ( 206 Pb 204 Pb from 19.0 to 18.2) progressively away from a NE-trending extension axis in the western Taiwan Strait. Abundant tholeiites were emplaced near the axial zone whereas alkali basalts, basanites and nephelinites took place further away from this axis. Overall, the basalts have Sr-Nd-Pb isotopic systematics similar to those of seamount basalts in the South China Sea which are characterized by a Dupal-type Pb isotopic anomaly. Based on geochemical constraints from the basalts, depth estimates for mantle xenoliths and regional geophysical data, a passive extension model is proposed for the geodynamic evolution of this region. It suggests greatest lithosphere thinning during the Miocene beneath the axial zone. The lithospheric mantle was thermo-mechanically eroded by convective upwelling of the asthenosphere, a process that raised the lithospheric geotherm and resulted in a plum-pudding-type convecting mantle. The spatial chemical and isotopic variation in the basalts can be explained by different degrees of decompression melting of this convecting mantle, corresponding to a change in lithosphere thickness, compounded by various contributions from the continental lithospheric mantle (CLM) -derived plum component. This model, which involves continental extension followed by magma generation via lithosphere-asthenosphere interaction, should be applicable to other areas of Cenozoic rift magmatism around the South China Sea and in the eastern Eurasian continental margin.