Dispersed Clusters Research Articles

Effects of immiscible interface and particle channelization on particle dynamics of oblique oily sand jets

This paper investigates the evolution of oblique sand jets passing through a thin layer of oil and entering stagnant water known as oily sand jets. The jet evolution parameters include the frontal position, the trajectory of particle clusters, the frontal width, the area of oily sand clusters, cloud velocities, and bursting times. Two scaling parameters, known as aspect ratio and particle to nozzle size ratio, were found to control the evolution of oily sand jets. The results show that the ratio of a nozzle to sand particle size can cause particle channelization, which can significantly alter the motion of particle clusters in stagnant water. Moreover, the aspect ratio indicating the correlation between sand mass and nozzle diameter describes the dispersion of particle clusters during the evolution of oily sand jets. The frontal width of the oily sand jet was measured during the experiment, and the results were compared with the width of vertical sand jets in water. The results show that the width of the oblique oily sand jets increased as oily sand jets descended into water. In addition, the frontal width of oily sand jets was found to be greater than the frontal width of vertical sand jets without an oil layer. Experimental observations indicated that the channelization effect is initiated when the nozzle diameter is more than 36 times of mean particle size. The centroid of oily sand jets in the vertical direction increased by 50% due to the channelization effect. A two-stage cluster bursting was observed due to the excess shear stress between the outer boundary of clusters and the ambient water. The bursting stages were called the primary and secondary bursting, and the onset of cluster bursting was extracted for both stages. It was found that the primary and secondary bursting times were longer in experiments without particle channelization. The mean shear stress acting on the oil layer was calculated based on the forces acting on the control volume. Particle channelization was found as the main factor affecting the magnitude of shear stress at the boundary of sand clusters.

Skeletal muscle sympathetic denervation disrupts the neuromuscular junction postterminal organization: A single-cell quantitative approach

The sympathetic nervous system (SNS) regulates skeletal muscle motor innervation and stabilizes the NMJ in health, disease and aging. Previous studies using both chemical (6-hydroxydopamine, 6-OHDA) and microsurgically-induced sympathetic denervation examined the NMJ organization and transmission in the mouse; however, a detailed quantification of the postterminal on larger hindlimb muscles involved in gait mechanics and posture is lacking. The purpose of this study was to determine whether targets of the sympathetic neuron (SN) exhibiting different intrinsic composition such as the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus muscles differ in their response to SN deprivation, and to develop a strategy to accurately quantify the impact of sympathectomy on the NMJ postterminal including those fibers located deeper in the muscle. This approach included muscle fixed ex vivo or through transcardial perfusion in mice treated with 6-OHDA or control ascorbic acid. We measured NMJ postterminal mean terminal total area, number of postterminal fragments, mean fragment area, and mean distance between fragments in free-floating alpha-bungarotoxin-stained in 1038 isolated muscle fibers. We found that muscle fiber sympathetic innervation plays a crucial role in the structural organization of the motorneuron-myofiber synapse postterminal and its deprivation leads to AChR cluster dispersion or shrinking as described in various neuromuscular diseases and aging.

Bio‐Based Piezo‐ and Thermoresistive Photocurable Sensing Materials from Acrylated Epoxidized Soybean Oil

AbstractBio‐based photocurable polymers are increasingly in demand as environmentally friendly materials for advanced applications. Together with functional fillers, these represent a next step for the generation of functional and active smart materials, compatible with additive manufacturing technologies. Herein, acrylated epoxidized soybean oil (AESO) mixed with different amounts of reduced graphene oxide (rGO) up to 6 wt% in order to obtain UV‐curable piezoresistive and thermoresistive materials, is reported. It is shown that the addition of rGO to AESO hinders the curing process, but always maintains double bond conversions higher than 50%. Composites are characterized by a good dispersion of micrometric filler clusters. Further, the thermal stabilities are close to 300 °C and crosslinking degrees are above 1.75 mmol cm–3. The Young modulus of the composites decreases with the addition of the rGO fillers, in particular for the higher filler contents, and electrical conductivities up to 0.13 S m–1 are obtained for the composites with the highest rGO content. UV‐curable composites with piezoresistive and thermoresistive responses suitable for applications are thus obtained, characterized by gauge factors around 26 for deformations up to 2% and maximum thermoresistive sensitivity of S = 0.43, values similar to the values obtained for petroleum‐based materials.

Mesoscale hydrated morphology of perfluorosulfonic acid membranes

AbstractFuel cells are expected to play an important role in global carbon neutralization and future social development with high conversion efficiency and zero emissions. The core of the fuel cell is the proton exchange membrane (PEM). However, the unclear of the proton transport mechanism in PEMs limits the development of membranes with improved performance. Perfluorosulfonic acid (PFSA) membranes are currently the most widely used type of PEM, and exhibit varying proton transport capabilities with various chemical structures. In this study, the hydration morphology of several PFSA membranes was studied using dissipative particle dynamics. The result shows that under low water content the hydrophilic and hydrophobic phases separated and the water clusters are relatively isolated. The increased water content formed hydrophilic channels, while the increase in equivalent weight decreases the water cluster size and improves water dispersion. Aciplex 1128 shows great variation owing to the presence of a long sulfonic acid terminated side chain in water cluster size and dispersion compared with Nafion. The average diffusivity and mean square displacement results showed similar results. These results will promote the development of high performance PEM for fuel cells.

Interaction of n-pentane and n-heptane insoluble asphaltenes in brine with clay and sand

Destabilized asphaltenes cause serious flow assurance problems such as asphaltenes precipitation. This study investigates the impact of clays and salinity on the stability of asphaltenes for five different crude oil samples. First, both n-pentane and n-heptane insoluble fractions of five crude oils were examined under microscope after the interaction with water, brine, and porous media. The porous media was prepared with clay, sand, or sand-clay mixture. A monovalent (NaCl) and a divalent (CaCl2) salts at 0.2% and 4% concentrations were used to prepare the brine solutions. Several systematic microscopic analyses were conducted on the asphaltenes-water and the asphaltenes-brine blends. We have observed that both n-pentane and n-heptane asphaltenes clusters are getting dispersed in water-phase in smaller pieces. This dispersion of asphaltenes clusters form lacework-like structures in the water-phase. The void spaces within these dispersed asphaltenes clusters trap water droplets. This interaction is due to the polar nature of both asphaltenes and water. Further in our systematic analysis, the general trend showed that the polar-polar attraction between water and asphaltenes clusters was disturbed in the presence of dissolved sodium and chlorine ions especially for some oil samples which already contain sodium in its asphaltenes fractions. This phenomenon is observed with the bridge-like formations in the asphaltenes-brine solutions. This indicates that asphaltenes have charged surfaces and the repulsion forces between the surface of the asphaltenes cluster and the dissolved ions in the brine solutions make the asphaltenes cluster align to form a line in the brine solution. The presence of clay in the porous medium reduced the water-asphaltenes or the brine-asphaltenes interaction and resulted in big chunks of asphaltenes-clay mixtures. Our study showed that asphaltenes interact with brine, water, and reservoir fines. Understanding these interactions may help us to mitigate many flow assurance issues such as asphaltenes precipitation and water-in-oil emulsion formation.

Coherent Integration of Organic Gel Polymer Electrolyte and Ambipolar Polyoxometalate Hybrid Nanocomposite Electrode in a Compact High-Performance Supercapacitor.

We report a gel polymer electrolyte (GPE) supercapacitor concept with improved pathways for ion transport, thanks to a facile creation of a coherent continuous distribution of the electrolyte throughout the electrode. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was chosen as the polymer framework for organic electrolytes. A permeating distribution of the GPE into the electrodes, acting both as integrated electrolyte and binder, as well as thin separator, promotes ion diffusion and increases the active electrode–electrolyte interface, which leads to improvements both in capacitance and rate capability. An activation process induced during the first charge–discharge cycles was detected, after which, the charge transfer resistance and Warburg impedance decrease. We found that a GPE thickness of 12 μm led to optimal capacitance and rate capability. A novel hybrid nanocomposite material, formed by the tetraethylammonium salt of the 1 nm-sized phosphomolybdate cluster and activated carbon (AC/TEAPMo12), was shown to improve its capacitive performance with this gel electrolyte arrangement. Due to the homogeneous dispersion of PMo12 clusters, its energy storage process is non-diffusion-controlled. In the symmetric capacitors, the hybrid nanocomposite material can perform redox reactions in both the positive and the negative electrodes in an ambipolar mode. The volumetric capacitance of a symmetric supercapacitor made with the hybrid electrodes increased by 40% compared to a cell with parent AC electrodes. Due to the synergy between permeating GPE and the hybrid electrodes, the GPE hybrid symmetric capacitor delivers three times more energy density at higher power densities and equivalent cycle stability compared with conventional AC symmetric capacitors.

Confining and Highly Dispersing Single Polyoxometalate Clusters in Covalent Organic Frameworks by Covalent Linkages for CO2 Photoreduction.

Single clusters have attracted extensive research interest in the field of catalysis. However, achieving a highly uniform dispersion of a single-cluster catalyst is challenging. In this work, for the first time, we present a versatile strategy for uniformly dispersed polyoxometalates (POMs) in covalent organic frameworks (COFs) through confining POM cluster into the regular nanopores of COF by a covalent linkage. These COF-POM composites combine the properties of light absorption, electron transfer, and suitable catalytic active sites; as a result, they exhibit outstanding catalytic activity in artificial photosynthesis: that is, CO2 photoreduction with H2O as the electron donor. Among them, TCOF-MnMo6 achieved the highest CO yield (37.25 μmol g-1 h-1 with ca. 100% selectivity) in a gas-solid reaction system. Furthermore, a mechanism study based on density functional theory (DFT) calculations demonstrated that the photoinduced electron transfer (PET) process occurs from the COF to the POM, and then CO2 reduction and H2O oxidation occur on the POM and COF, respectively. This work developed a method for a uniform dispersion of POM single clusters into a COF, which also shows the potential of using COF-POM functional materials in the field of photocatalysis.

Genetic divergence and cluster analysis for bulb yield and related traits in garlic (Allium sativum) accessions at Dorze, southern Ethiopia

AbstractDespite the benefits of garlic (Allium sativum L.) in human life, only a little amount of breeding effort has been done so far. The initial stages of a systemic breeding program include the collection and evaluation of genetic variability. As a result, understanding genetic divergence and cluster dispersion between accessions is a great way to improve future crops. This study was aimed to estimate the extent of genetic divergence across 28 Ethiopian garlic accessions using 11 agromorphological traits to identify parent lines for hybridization programs. The experiment was set up with a randomized complete block design with three replicates in Dorze, southern Ethiopia, during the 2017 main harvest season. The cluster analysis revealed the existence of four divergent groups, with the greatest distance among them being between Groups I and IV (D2 = 4.15), and the shortest distance being between Groups I and II (D2 = 2.93). To obtain accessions with high grain yield and early maturing, cross from Clusters I and IV and from III and IV were obtained. Parent material should be produced among clusters rather than within clusters for future hybridization breeding efforts.

High performance magnetorheological fluids: very high magnetization FeCo-Fe3O4 nanoclusters in a ferrofluid carrier.

High magnetization Fe3O4/OA-FeCo/Al2O3 nanocomposite magnetic clusters have been obtained using a modified oil-in-water miniemulsion method. These nanocomposite clusters dispersed in a ferrofluid carrier result in a magnetorheological fluid with improved characteristics. The magnetic clusters have a magnetic core consisting of a mixture of magnetite nanoparticles of about 6 nm average size, stabilized with oleic acid (Fe3O4/OA) and FeCo/Al2O3 particles of about 50 nm average size, compactly packed in the form of spherical clusters with a diameter distribution in the range 100-300 nm and a hydrophilic coating of sodium lauryl sulphate surfactant. The surface chemical composition of the Fe3O4/OA-FeCo/Al2O3 clusters investigated by XPS indicates the presence of the Co2+ and Co3+ oxidation states of cobalt and the components of Fe2+ and Fe3+ characteristic to both an enhanced oxidation state at the surface of the FeCo particles and to the presence of magnetic nanoparticles of spinel structure which are decorating the supporting FeCo. This specific decorating morphology is also indicated by TEM images. Advanced characterization of the Fe3O4/OA-FeCo/Al2O3 magnetic clusters has been performed using Mössbauer spectroscopy and magnetization measurements at various temperatures between 6 K and 200 K. The unexpected formation of Co ferrite decorating nanoparticles was supported by Mössbauer spectroscopy. The dispersion of magnetic clusters in the ferrofluid carrier highly influences the flow properties in the absence of the field (shear thinning for low and moderate shear rates) and especially in applied magnetic field, when significant magnetoviscous effect and shear thinning was observed for the whole range of shear rate values. Detailed analysis of the magnetorheological behavior of the nanocomposite magnetic clusters dispersed in a ferrofluid carrier evidence significantly higher normalized dynamic yield stress values in comparison with the magnetite nanocluster suspensions of the same mass concentration, a promising result for this new type of nanocomposite magnetorheological fluid.

A novel weighted fuzzy c-means based on feature weight learning

In feature weighted fuzzy c-means algorithms, there exist two challenges when the feature weighting techniques are used to improve their performances. On one hand, if the values of feature weights are learnt in advance, and then fixed in the process of clustering, the learnt weights might be lack of flexibility and might not fully reflect their relevance. On the other hand, if the feature weights are adaptively adjusted during the clustering process, the algorithms maybe suffer from bad initialization and lead to incorrect feature weight assignment, thus the performance of the algorithms may degrade the in some conditions. In order to ease these problems, a novel weighted fuzzy c-means based on feature weight learning (FWL-FWCM) is proposed. It is a hybrid of fuzzy weighted c-means (FWCM) algorithm with Improved FWCM (IFWCM) algorithm. FWL-FWCM algorithm first learns feature weights as priori knowledge from the data in advance by minimizing the feature evaluation function using the gradient descent technique, then iteratively optimizes the clustering objective function which integrates the within weighted cluster dispersion with a term of the discrepancy between the weights and the priori knowledge. Experiments conducted on an artificial dataset and real datasets demonstrate the proposed approach outperforms the-state-of-the-art feature weight clustering methods. The convergence property of FWL-FWCM is also presented.

Analysis of the Dispersion of Viscoelastic Clusters in the Industrial Rotor-Stator Equipment

Materials with complex rheology and viscoelasticity may require special equipment for processing, such as for dispergation. Rheological and mechanical data of the material can help with finding the required equipment or designing equipment. For highly viscous and complex material, a rotor-stator mixer can be a good choice for dispergation. Due to the laminar or creeping mechanism of flow inside the equipment, the dispergation mechanism is assumed to be a combination of the shear stress and slicing of the material by the rotor and stator blades. For the validation of the theory, the mechanical properties of the viscose identified in a previous work were used for comparison with the data from the CFD simulation of the rotor-stator mixer. The comparison showed that the rotor-stator device can overcome the complex shear modulus and ultimate strength of the material and homogenize the solution through a combination of the shear stress and slicing. The theory was also confirmed on the process line proposed for homogenization of the specific material. The stability of viscosity during the process of homogenization was measured and used as the main parameter for quality assessment.

Control of Cluster Structures in Catalyst Inks by a Dispersion Medium.

The cluster structure in the catalyst ink of a proton exchange membrane fuel cell determines its performance. The interaction among solvent, ionomer, and catalyst in ink determines the cluster structure and affects the microstructure and surface morphology of the catalyst layer, which is of great significance to improve the conductivity of the catalyst layer to protons, electrons, and water. First, the dissolved state of the main chain and the side chain of the ionomer in solvent was characterized. The results of relative viscosity, ζ-potential, effective proton fraction, and nuclear magnetic resonance (NMR) showed that the alcohol aqueous solution promoted the stretching electrolysis of the main chain and the side chain of the ionomer more than the pure aqueous solvent, making the ionomer clusters smaller. The rheological test of the ink shows that the pure water solvent ink has the largest cluster and the strongest network structure. Under the test conditions, the clusters in the ink can be reconstructed quickly after breakage through viscous shearing. The addition of alcohols will make the clusters in the ink smaller and the network structure brittle. After the clusters and the network structure are damaged, they will slowly recombine and the viscosity in the ink will gradually recover. Ethanol will minimize the clusters in the ink, and the network structure in the ink is the weakest. The effect of the network strength on the cluster structure is weakened by reducing the solid content in the ink. The amplitude scanning test shows that the network structure in the slurry is almost eliminated after reducing the solid content, the storage modulus of ink with water, 50 wt % isopropyl alcohol (IPA), 50 wt % n-propanol (NPA), and 50 wt % ethanol (ET) decreases in turn, as well as the liquid viscosity behavior increases and the cluster particle size in the ink decreases. In conclusion, more dispersed ionomers and alcohol molecules with smaller molecular structures are more conducive to the dispersion of clusters in the ink.

Rotation and Lithium Confirmation of a 500 pc Halo for the Open Cluster NGC 2516*

Abstract Recent analyses of the Gaia data have identified diffuse stellar populations surrounding nearby open clusters. It is important to verify that these “halos,” “tails,” and “strings” are of similar ages and compositions as stars in the denser part of the cluster. We present an analysis of NGC 2516 (≈150 Myr), which has a classical tidal radius of 10 pc and an apparent halo of stars spanning 500 pc (20° on-sky). Combining photometry from Gaia, rotation periods from TESS, and lithium measurements from Gaia-ESO and GALAH, we find that the halo of NGC 2516 is the same age as the cluster’s core. Two-thirds of kinematically selected halo members out to 250 pc from the cluster center have rotation periods consistent with a gyrochronological age of 150 Myr. A comparison sample of field stars shows no such trend. The lithium abundances of stars in the halo are higher than in the field and correlated with the stellar rotation rate and binarity fraction, as has been noted in other young open clusters. Broadly speaking, this work supports a new paradigm wherein the halos of open clusters are often more populous than their cores. We highlight implications for spectroscopic survey targeting, open cluster dispersal, and planet searches around young stars.

Effect of ultrasonication on the size distribution and stability of cellulose nanocrystals in suspension: an asymmetrical flow field-flow fractionation study

Cellulose nanocrystals (CNCs) are bio-based building blocks for sustainable advanced materials with prospective applications in polymer composites, emulsions, electronics, sensors, and biomedical devices. However, their high surface area-to-volume ratio promotes agglomeration, which restrains their performance in size-driven applications, thereby hindering commercial CNC utilization. In this regard, ultrasonication is commonly applied to disperse CNCs in colloidal suspensions; however, ultrasonication methodology is not yet standardized and knowledge of the effects of ultrasound treatments on CNC size distribution is scarce. The major goals of this study were attributed to targeted breakage of CNC agglomerates and clusters by ultrasound. The evolution of particle size distribution and potential de-sulfation by ultrasonication as well as the long-term stability of ultrasonicated CNC suspensions were investigated. Colloidal suspensions of sulfated CNCs were isolated from cotton α-cellulose. Effects of ultrasonication on particle size distribution were determined by asymmetrical flow field-flow fractionation (AF4) coupled with on-line multi-angle light scattering and ultraviolet spectroscopy. These results were complemented with off-line dynamic light scattering. High ultrasound energy densities facilitated cumulative dispersion of CNC clusters. Consequently, the mean rod length decreased logarithmically from 178.1 nm at an ultrasound energy input of 2 kJ g−1 CNC to 141.7 nm (− 20%) at 40 kJ g−1 CNC. Likewise, the hydrodynamic diameter of the particle collective decreased logarithmically from 94.5 to 73.5 nm (− 22%) in the same processing window. While the rod length, below which 95 wt% of the CNCs were found, decreased from 306.5 to 231.8 nm (− 24%) from 2 to 40 kJ g−1 CNC, the shape factor of the main particle fraction ranged from 1.0 to 1.1, which indicated a decreasing number of dimers and clusters in the particle collective. In summary, progressing ultrasonication caused a shift of the particle length distribution to shorter particle lengths and simultaneously induced narrowing of the distribution. The suspension’s electrical conductivity concurrently increased, which has been attributed to faster diffusion of smaller particles and exposure of previously obscured surface charges. Colloidal stability, investigated through electrical AF4 and electrophoretic light scattering, was not affected by ultrasonication and, therefore, indicates no de-sulfation by the applied ultrasound treatment. Occurrence of minor CNC agglomeration at low ultrasound energy densities over the course of 6 months suggest the effect was not unmitigatedly permanent.

Highly Dispersed Pd Clusters Anchored on Nanoporous Cellulose Microspheres as a Highly Efficient Catalyst for the Suzuki Coupling Reaction.

With the depletion of nonrenewable resources such as oil/coal/gas, more and more research studies began to focus on the high-value utilization of residual biomass resources. Herein, for the first time, honeycomb nanoporous microspheres fabricated from renewable biomass resources of cellulose were used as a carrier to fabricate a highly dispersed palladium (Pd) nanocatalyst. Various physicochemical characterizations presented convincing pieces of evidence for the good dispersion of Pd clusters with a mean diameter of 1.6 nm. As the carrier, cellulose microspheres with an interconnected nanoporous structure contributed to the adhesion and dispersion of Pd particles, and their rich hydroxyl groups could fix the Pd particles. Importantly, the cellulose matrix could in situ induce the formation of metallic Pd(0) during calcination without a reductant. The cellulose/Pd catalyst was applied to the Suzuki coupling reaction, which exhibited promising catalytic activity compared to commercial Pd/C and unsupported homogeneous Pd(OAc)2 catalysts, as well as good stability. The utilization of the residual biomass resource to build catalyst materials would be important for the sustainable chemistry.

A Novel Text Ensemble Clustering Based on Weighted Entropy Filtering Model

Text clustering is one of the important technical bases of natural language processing, and ensemble clustering improves the robustness of text clustering. According to the existing research of scholars and experts, the quality and diversity of basic clustering have a great influence on consensus clustering, and it has a particularly significant effect on text clustering. However, there are a few pieces of research aiming at reducing the number of low-quality clustering in ensembles. This paper proposes a novel clustering filtering model based on entropy criteria. The entropy criterion is used to evaluate the uncertainty of each cluster w.r.t. the ensemble. Two indexes are proposed on the basis of the uncertainty of cluster, namely, Clustering Trend Index (CTI) which indicates the contribution of each cluster w.r.t. basic clustering, and Cluster Consistency Index(CCI) which indicates the degree of cluster dispersion in the basic clustering. The proposed clustering filtering model is built on the basis of new weight using two proposed indexes. Thereby, by dropping the low-quality clustering, the percentage of high-quality clustering will increase. A large number of experiments on various real text data sets using optimal thresholds show that the proposed method has greatly improved accuracy and robustness, and is superior to existing ensemble clustering algorithms.

Cover Feature: Double‐Shelled Hollow SiO2@N‐C Nanofiber Boosts the Lithium Storage Performance of [PMo12O40]3− (Chem. Eur. J. 53/2021)

Excellent lithium storage is achieved by the double-shelled hollow PMo12-SiO2@N-C anode material. The outermost N-C shell can improve the electronic conductivity and promote the dispersion of PMo12 clusters. The SiO2 inner shell can efficiently avoid the loss of active components. The hollow structure can buffer the volume expansion and accelerate Li+ diffusion during lithiation/delithiation process. More information can be found in the Full Paper by L. He, W. Chen, Y.-F. Song et al. (DOI: 10.1002/chem.202101638).

Location strategies of spinoff entrants: Implications of clustering and staying close to the parents

The research on agglomeration posits that co-locating in a cluster with industry rivals benefits the firm because of its proximity to resources including suppliers, labor, and knowledge spillover from rivals. Although it’s often assumed that co-location benefits new entrants, more recent research finds that stronger entrants gain less from co-location. Spinoff entrants—the organizational descendants of ongoing established firms—are comparatively stronger entrants because of the product, market, and industry knowledge they inherit from their parents. They may gain less from co-location, because the competitive pressures exerted by their parents and other industry rivals are higher when they are more proximate. For the spinoff entrants that locate farther away, the inheritance from their parents may be portable and thus do not decay with distance. Our paper examines the performance implications of whether spinoff entrants are located inside a cluster and staying close to their parents. Specifically, we conduct an event history analysis estimating the amount of time it takes a spinoff entrant to reach six entrepreneurial milestones. We find that being located inside a cluster and staying close to the parents are beneficial to spinoffs only when the industry has a single dominant cluster, as we observe in the semiconductor industry. When the industry has many clusters widely dispersed across the country, as we observe in the pharmaceutical industry, co-location is associated with worse performance. Our findings suggest that the dispersion of clusters in an industry is one condition where the assumption about new entrants benefiting from co-location is invalid.

Exciting Modes due to the Aberration of Gravitational Waves: Measurability for Extreme-Mass-Ratio Inspirals.

Gravitational waves from a source moving relative to us can suffer from special-relativistic effects such as aberration. The required velocities for these to be significant are on the order of 1000 km s^{-1}. This value corresponds to the velocity dispersion that one finds in clusters of galaxies. Hence, we expect a large number of gravitational-wave sources to have such effects imprinted in their signals. In particular, the signal from a moving source will have its higher modes excited, i.e., (3,3) and beyond. We derive expressions describing this effect and study its measurability for the specific case of a circular, nonspinning extreme-mass-ratio inspiral. We find that the excitation of higher modes by a peculiar velocity of 1000 km s^{-1} is detectable for such inspirals with signal-to-noise ratios of ≳20. Using a Fisher matrix analysis, we show that the velocity of the source can be measured to a precision of just a few percent for a signal-to-noise ratio of 100. If the motion of the source is ignored, parameter estimates could be biased, e.g., the estimated masses of the components through a Doppler shift. Conversely, by including this effect in waveform models, we could measure the velocity dispersion of clusters of galaxies at distances inaccessible to light.

Mechanistic investigation and modeling of Cd immobilization by iron (hydr)oxide-humic acid coprecipitates

A molecular-scale understanding of aqueous metal adsorption onto humic acid-iron (hydr)oxide coprecipitates, and our ability to model these interactions, are lacking. Here, the molecular-scale mechanisms for Cd binding onto iron (hydr)oxide-humic acid (HA) composites were probed using X-ray absorption fine structure (XAFS) spectroscopy and surface complexation modeling (SCM). The immobilization of Cd in (hydr)oxide precipitation systems occurs predominantly through adsorption onto the freshly-formed (hydr)oxide nanoparticles, and SCM calculations suggest a specific surface area of 2400 m2/g available for Cd. The solution and XAFS measurements indicate that HA promotes the precipitation of both Fe clusters and Fe-Cd associations mainly through ligand exchange reactions. Site masking reactions result in a dramatic blockage of functional sites on HA and ~45% migration of the adsorbed Cd to iron (hydr)oxide binding sites at high HA:Fe mass ratios. A composite model that accounts for both site masking between Fe ions and HA and the increase of Fe hydroxyl sites simulate the distribution of Cd in the composites reasonably well. Overall, this study demonstrates that the Fe clusters play an overriding role for heavy metal stabilization in coprecipitation systems, while HA promotes the immobilization of Cd by facilitating the flocculation and dispersion of Fe clusters.