Primary Minimum Research Articles

BIMA 2.0 Progress on ToM Analysis of Contact Binaries: IR Car, V1370 Tau and GY Pup

Abstract The Eclipsing Binaries Minima (BIMA) 2.0 Monitoring Project is a continuation of the previous BIMA program that was initiated by the collaboration of Bosscha Observatory - Lembang, Indonesia and The National Astronomical Research Institute of Thailand (NARIT) in 2012. This project aims to build an open database of eclipsing binary minima and establish each system’s orbital period and its variations in a time of minima (ToM) photometric observation using the Thai Robotic Telescope (TRT) network. In this work, we will present the progress of our monitoring program during 3 ∼ months of observations using TRT with proposal ID TRTC11A_009. We have collected ToM data at least once on 18 samples of contact binary stars and carried out O-C diagram analysis on three selected objects: IR Car, V1370 Tau, and GY Pup. We obtained six, three, and four primary minima on IR Car, V1370 Tau, and GY Pup, respectively. These three objects were chosen due to the lack of ToM data in recent years. We also use the TESS space mission ToM data to increase data coverage. Preliminary results show a significant change in O-C values and indicate mass transfer in this system.

Proximal foundation anchor variations and their correlation with unplanned return to the operating room (UPROR) in children with EOS treated with magnetically controlled growing rods (MCGR).

The evolution of MCGR technique has led to modifications in the configuration of the proximal construct to decrease the incidence of implant-related complications (IRC) and revision surgeries. However, there is no data characterizing the performance of the most used configurations reducing the risk of complications. 487 patients were identified from an international multicenter EOS database. EOS patients, primary dual MCGR, complete radiographs, and minimum of 2-year follow-up. 76 patients had incomplete X-rays, 5 had apical fusions, and 18 had inconclusive complications, leaving 388 patients for review. A digital spine template was created to document UIV; number of levels; number, type, and location of anchors; as well as implant configuration. First available postoperative and latest follow-up radiographs were reviewed by two senior surgeons and two spine fellows. UPROR due to IRC was defined as any change in proximal anchors between the postoperative and final follow-up radiographs. The most common proximal construct configuration: UIV at T2 (50.0%) with 17.5% UPROR, followed by T3 (34.0%) with 12.1% UPROR; number of levels was three (57.1%) with 16.8% UPROR and two (26.0%) with 17.0% UPROR; number of proximal anchors was six (49.9%) with 14.1% UPROR and four (27.0%) with 18.3% UPROR. The most common anchors were all screws (42.0%) with 9.9% UPROR, and all hooks (26.4%) with 31.4% UPROR (P < 0.001). The construct with the lowest rate of UPROR was a UIV at T2, with six anchors (all screws) across three levels (42 cases), with 0% UPROR. Other construct combinations that yielded 0% UPROR rates were UIV of T3, six anchors (all screws) across three levels (25 cases), and a UIV of T3 with six anchors (screws and hooks) across three3 levels (9 cases). Proximal anchor configuration impacts the incidence of UPROR due to IRC in MCGR. UIV at T2 and T3 compared to T4, and the use of all screws or combination of screws and hooks compared to all hooks were associated with a lower UPROR rate. The most common construct configuration was T2 UIV, three levels, six anchors, and all screws. The use of a combination of six anchors (screws or screws and hooks) across three levels with a UIV at T2 or T3 was associated with a lower UPROR rate.Additional research is needed to further evaluate the variables contributing to configuration selection and their association with IRC.

Effect of a nonwoven geotextile on nano-TiO2 transport and retention in aggregated porous media under saturated flow conditions

In this experimental work, the transport and retention of TiO2 nanoparticles (nano-TiO2) through a geotextile-aggregated porous media filtration system at two distinct flow velocities and three ionic strengths (ISs) were investigated. Experimental results showed higher nano-TiO2 recovery in the effluent and less retention when increasing the flow velocities under unfavorable conditions. The surface roughness morphology of the porous media may have a meaningful impact on the attachment of nano-TiO2. The nano-TiO2 deposition increased with IS increasing, which are qualitatively in line with the prediction calculated by the extended Derjaguin−Landau−Verwey−Overbeek (XDLVO) theory. Specially, under unfavorable physicochemical conditions (i.e. 0.1 and 5 mM), nano-TiO2 can be retained on the porous media surface at secondary minima and primary minima. While more deposition of nano-TiO2 may occur at primary minima at the IS of 25 mM (refers to favorable physicochemical conditions). And nano-TiO2 transport pathways became less dispersive and more uniform under high flow rate in the porous media with geotextile. The geotextiles can improve flow homogeneity leading to an enhancement in nano-TiO2 particles removal. Our study showed for the first time that geotextile can be served as an efficient barrier to remove the nano-TiO2 through aggregated porous media. The fitted parameters derived from HYDRUS-1D simulations indicated that both mechanisms of physicochemical attachment and straining occur under the current conditions of this work and they have the same importance in nano-TiO2 retention at column scale.

The detection of polarized X-ray emission from the magnetar 1E 2259+586

ABSTRACT We report on IXPE, NICER, and XMM–Newton observations of the magnetar 1E 2259+586. We find that the source is significantly polarized at about or above 20 per cent for all phases except for the secondary peak where it is more weakly polarized. The polarization degree is strongest during the primary minimum which is also the phase where an absorption feature has been identified previously. The polarization angle of the photons are consistent with a rotating vector model with a mode switch between the primary minimum and the rest of the rotation of the neutron star. We propose a scenario in which the emission at the source is weakly polarized (as in a condensed surface) and, as the radiation passes through a plasma arch, resonant cyclotron scattering off of protons produces the observed polarized radiation. This confirms the magnetar nature of the source with a surface field greater than about 1015 G.

Photometric and spectroscopic properties of the eclipsing system V864 Monocerotis

Abstract We present the orbital period variability and evolutionary status of the W UMa-type binary system V864 Mon from accurately measured fundamental parameters. New BV photometric observations of this system were performed in 2019 January and 2022 January, and the first high-resolution spectroscopic observations were carried out on three nights between 2019 January and March. A total of 29 times of minimum light were collected to examine the behavior of the orbital period. Our analysis of these timings indicates a continuous period increase at a rate of +2.62 × 10−7 d yr−1 over the past 20 years, which can be interpreted as a mass transfer from the less massive primary to the secondary component with a rate of 1.22 × 10−7 M⊙ yr−1. We measured the radial velocities (RVs) for both components, and determined the effective temperature and projected rotational velocity of the more massive secondary star to be Teff,2 = 5450 ± 94 K and v2sin i = 192 ± 40 km s−1, respectively, from the comparison of the observed spectrum at the primary minimum and the theoretical models. The individual masses and radii of both components were determined from a simultaneous analysis of the light and RV curves, which are M1 = 0.34 ± 0.02 M⊙, R1 = 0.69 ± 0.01 R⊙, and M2 = 1.06 ± 0.04 M⊙, R2 = 1.16 ± 0.02 R⊙, respectively. Our results indicate that V864 Mon is a W-subtype of W UMa stars with time-varying spot activity. The positions in the mass-luminosity and mass-radius diagrams indicate that the secondary star belongs to the main-sequence region, while the hotter primary is located beyond the terminal-age main sequence.

Soil organic matter facilitates the transport of microplastic by reducing surface hydrophobicity

Groundwater contamination by microplastic (MP) causes increasing concern about the critical factors that determine MP transport mechanisms in the vadose zone. Strong water repellency of native microplastic surfaces and respective attractive hydrophobic interactions with components of the soil matrix limits its mobility. However, adsorption of dissolved organic matter (DOM) onto microplastic surfaces can potentially make them more hydrophilic, enhancing their mobility. Consequently, the main objective of this study was to systematically determine the effects of DOM on both the surface properties and the mobility of polystyrene microplastic (PSP), and to use the extended DLVO theory (XDLVO) to predict PSP transport behavior with natural DOM for the first time. Breakthrough experiments were conducted in columns filled with quartz sand, through which PSP (1 µm) were percolated at either 0 or 5 mg/L dissolved organic carbon (DOC) derived from beech (Fagus sylvatica) litter at ionic strengths ranging from 0.5 to 2.5 mM CaCl2, since the cation background also affects wettability and mobility. Using sessile drop contact angle and zeta potential measurements, XDLVO interaction energy components including Lewis acid-base energies were approximated. Breakthrough curve analysis confirmed that DOM coming from natural sources strongly enhanced the mobility of PSP in the quartz sand matrix, in particular at higher ionic strength. At 2.5 mM CaCl2, the presence of DOM increased PSP breakthrough from 1 % to 60 %. Consequently, in the absence of DOM, laser microscope images showed much more pronounced formation of microplastic clusters on quartz grain surfaces than at co-percolation of PSP with DOM. This behavior could be clearly predicted with the XLDVO approach, which suggests at 0 mg/L DOC a deep primary energy minimum between individual PSP and between PSP and quartz surfaces. In contrast, repulsive hydrophilic interactions between the surfaces were predicted at 5 mg/L DOC. We conclude that even low concentrations of DOM, as usually found in subsoil, can significantly enhance the mobility of microplastic in soils via rendering the surfaces more hydrophilic. This implies potentially serious repercussions for the spread of this contaminant in the environment.

Simulation and Experimental Analysis of Microalgae and Membrane Surface Interaction

The microalgae-induced membrane system applied in wastewater treatment has attracted attention due to microalgae’s outstanding nutrient fixation capacity and biomass harvesting. However, the fundamental understanding of the interaction of microalgae and membrane surfaces is still limited. This study presents experimental and numerical methods to analyze the attachment of microalgae to the membrane. An atomic force microscope (AFM) analysis confirmed that a polydimethylsiloxane (PDMS) sensor, as a simulated membrane surface, exhibited a rougher surface morphology than a polyurethane (PU) sensor did. The contact angle and adsorption analysis using a quartz crystal microbalance confirmed that the PDMS surface, representing the membrane surface, provided a better attachment affinity than the PU surface for microalgae because of the lower surface tension and stronger hydrophobicity of PDMS. The simulation studies of this work involved the construction of roughly circular-shaped particles to represent microalgae, rough flat surfaces to represent membrane surfaces, and the interaction energy between particles and surfaces based on XDLVO theory. The modeling results of the microalgae adsorption trend are consistent and verified with the experimental results. It was observed that the interfacial energy increased with increasing the size of particles and asperity width of the membrane surface. Contrarily, the predicted interaction energy dropped with elevating the number of asperities and asperity height of the microalgae and membrane. The most influential parameter for controlling interfacial interaction between the simulated microalgae and membrane surface was the asperity height of the membrane; changing the height from 50 nm to 250 nm led to alteration in the primary minimum from −18 kT to −3 kT. Overall, this study predicted that the microalgae attachment depends on the size of the asperities to a great extent and on the number of asperities to a lesser extent. These results provide an insight into the interaction of microalgae and membrane surface, which would provide information on how the performance of microalgae-based membrane systems can be improved.

Risk Prediction of Alzheimer's Disease Conversion in Mild Cognitive Impaired Population Based on Brain Age Estimation.

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases in the world. To reduce the incidence of AD, it's essential to quantify the AD conversion risk of mild cognitive impaired (MCI) individuals. Here, we propose an AD conversion risk estimation system (CRES), which contains an automated MRI feature extractor, brain age estimation (BAE) module, and AD conversion risk estimation module. The CRES is trained on 634 normal controls (NC) from the public IXI and OASIS cohorts, then it is evaluated on 462 subjects (106 NC, 102 stable MCI (sMCI), 124 progressive MCI (pMCI) and 130 AD) from the ADNI dataset. Experimental results show that the MRI derived age gap (AG, chronological age subtracted from the estimated brain age) significantly distinguish NC, sMCI, pMCI and AD groups with p -value =0.000017 . Considering AG as the primary factor, incorporating gender and Minimum Mental State Examination (MMSE) for more robust Cox multi-variate hazard analysis, we concluded that each additional year in AG is associated with 4.57% greater AD conversion risk for the MCI group. Furthermore, a nomogram was drawn to describe MCI conversion risk at the individual level in the next 1 year, 3 years, 5 years and even 8 years from baseline. This work demonstrates that CRES can estimate AG based on MRI data, evaluate AD conversion risk of the MCI subjects, and identify the individuals with high AD conversion risk, which is valuable for effective intervention and diagnosis within an early period.

Distortions of parliamentary amendments to the equitable allocation of federal resources to the PAB.

Analyze the implications of parliamentary amendments (EP) for the model of equitable allocation of resources from the Fixed Primary Care Minimum (PAB-Fixo) to municipalities in the period from 2015 to 2019. A descriptive and exploratory study was conducted on allocating federal resources to the PAB-Fixo and on the increment in the PAB by parliamentary amendment. The municipalities were classified into four groups according to degrees of socioeconomic vulnerability defined by the Ministry of Health for the allocation of PAB-Fixo resources. The transfers from the Ministry by parliamentary amendment were identified. The proportions of municipalities benefiting per group were analyzed by resources allocated from the PAB-Fixo and increment to the minimum by EP. There were reduced resources allocated to the PAB-Fixo (from R$ 6.04 billion to R$ 5.51 billion, -8.8%) and increased increment to PAB by parliamentary amendment (from R$ 95.06 million to R$ 5.58 billion, 5.767%) between 2015 and 2019. The participation of municipalities by the group of those favored by EP was similar to that in the PAB-Fixo. In the proportion of resources for amendments, the municipalities of group I (most vulnerable) had more participation, and those of group IV had less participation if compared to the allocation of the PAB-Fixo. The distribution of resources by the parliamentary amendment did not cover all municipalities, even the most vulnerable ones, i.e., belonging to groups I and II. There was great inequality of resources per capita according to the groups of municipalities. The EP distorted the model of equitable allocation of resources proposed by the Ministry of Health for the PAB-Fixo, by allocating resources in a much more significant proportion to the municipalities of group I and much less to those of group IV, which is in disagreement with this model. Furthermore, this distribution by amendments does not benefit all municipalities, not even the most vulnerable.

Interaction of deformable solid and hollow particles with rough surface morphology in colloidal systems

Hypothesis and backgroundA majority of natural particles have deformable and rough surfaces. Past research indicated a lack of information for a numerical model to simulate the potential non-contact interaction between two deformable particles with uneven surfaces. The simulation of deformable particles is critical to better understanding the interaction of deformable particles in colloidal systems. We hypothesized that numerical models could simulate the deformation process of solid and hollow particles, and the constructed models could predict the impact of deformation on the interaction of rough-surfaced solid or hollow deformable particles. Numerical modelingThis work modeled the deformable solid and hollow particles with rough surface morphologies following a fractal geometry theory. Their non-contact interaction was simulated following the three-stages deformation model. Also, the impacts of surface tension, particle size, and surface roughness on the interaction of the particles were investigated. FindingsIt was observed that the total potential energy of deformable solid and hollow particles followed a similar pattern under different conditions. The difference in the energy profile between solid and hollow particles is that the hollow particles generate a deeper primary minimum, and the energy barrier disappears, indicating that the hollow particles have better attachment affinity. The results show that the increased particle size will strengthen the deformability of deformable solid and hollow particles and their potential interaction, and particle size will be the most influential parameter in affecting the deformability of particles. When the particle size increased from 10 nm to 1000 nm, the deformation region of solid particles was enlarged from 5 nm to 90 nm. Nevertheless, increased surface tension would weaken the deformability of deformable solid and hollow particles, which would significantly reduce particle aggregation. The increase in the fractal dimension would reduce solid and hollow particles' deformability but increase the potential interaction energy. The controversial results could be found by increasing fractal roughness, which would improve the deformability of particles and reduce the interaction energy. The results of this study could be applied for foreseeing the deformation and interaction of deformable particles with potential applications in suspension systems, such as biological cell suspensions.

Coaxing the Eclipsing Binary V367 Cygni out of Its Shell

Spectra that cover 0.63–0.69 μm with a spectral resolution ∼17,000 are presented of the W Serpentis system V367 Cygni. Absorption lines of Fe ii and Si ii that form in a circumsystem shell are prominent features, and the depths of these are stable with time, suggesting that the shell is smoothly distributed and well mixed. Further evidence of uniformity comes from modest radial velocity variations measured in the deepest parts of the shell lines. It is suggested that motions previously attributed to rotation of the shell are instead artifacts of contamination from the donor star spectrum. A donor star spectrum is extracted that is consistent with that of an early to mid-A giant. The depths of metallic lines in the donor spectrum vary with orbital phase, suggesting that spot activity covers a large fraction of the surface of that star. A spectrum of the accretion disk that surrounds the second star is also extracted, and similarities are noted with the emission spectra of Herbig Ae/Be stars. In addition to variations with orbital phase, Hα changes with time over timescales of no more than two orbits. A tentative detection of He i 6678 emission is made near primary minimum, but not at other phases. Finally, projected emission from hot dust in and around V367 Cyg is more or less symmetric and extends over 28″, or 0.09 pc at the distance of the system; V367 Cyg is thus expelling matter into a large volume of the surrounding space.

ISO 8685 compliant contractual ship-loading export facility: bauxite sampling plant process design and equipment selection for chemical sampling

The paper discusses the process design and mass balance for the minimum and maximum design case to illustrate the ISO 8685 compliance of a 2-year-running barge loading payment station sampling plant. The plant samples -100 mm, export quality, bauxite material from a barge-loading conveyor delivering 10 kton/h at 5.4 m/s. The green field operation does not know the Coefficient of Variation or the Size Range Factor as required inputs to calculate the Number of Primary Increments and Minimum Gross Sample Mass required. Therefore, informed assumptions were made given performance data of a neighboring sampling system that is in operation for over a decade. Without the available variation and size factor data the ISO-compliant scheme design could not commence. Where this data is not available for green field projects, it poses a risk that plant designs may not be compliant where variabilities could exceed assumptions on the input parameters. The system is designed for various barge carrying capacities with lot size in mass. Operational quality assurance however requires samples more frequently and therefore sublot periods are 4 hourly time based. ISO 8685 compliance is achieved with sample increments taken at maximum throughputs and barge sizes to determine the time-based interval. At reduced throughputs, the fixed time interval regime results in the minimum ISO requirements to be exceeded and tied in well with client overall quality incentives. Primary sample increments from a tailored cross belt sampler are crushed automatically in the sampling plant to 25 mm and then to 6mm using two stages of double roll crushers. The sample is then subdivided through secondary and tertiary sampling to produce a composite 4-hourly chemical sample. The 4-hourly sublot samples are collected in an ergonomic 4-way carousel with each composite sample representing 1-hour barge loading production— allowing the client quality assurance insights into their blending facility performance.

Radial Potential Energy Functions of Linear Halogen-Bonded Complexes YX···ClF (YX = FB, OC, SC, N2) and the Effects of Substituting X by Second-Row Analogues: Mulliken Inner and Outer Complexes

Energies of linear, halogen-bonded complexes in the isoelectronic series YX···ClF (YX = FB, OC, or N2) are calculated at several levels of theory as a function of the intermolecular distance r(X···Cl) to yield radial potential energy functions. When YX = OC, a secondary minimum is observed corresponding to lengthened and shortened distances r(ClF) and r(CCl), respectively, relative to the primary minimum, suggesting a significant contribution from the Mulliken inner complex structure [O=C–Cl]+···F–. A conventional weak, halogen-bond complex OC···ClF occurs at the primary minimum. For YX = FB, the primary minimum corresponds to the inner complex [F=B–Cl]+···F–, while the outer complex FB···ClF is at the secondary minimum. The effects on the potential energy function of systematic substitution of Y and X by second-row congeners and of reversing the order of X and Y are also investigated. Symmetry-adapted perturbation theory and natural population analyses are applied to further understand the nature of the various halogen-bond interactions.

NEW CMOS PHOTOMETRY AND ARCHIVAL PHOTOGRAPHIC OBSERVATIONS OF THE W UMA STAR V752 CEN: EXTENDING THE O-C RECORD OF PERIOD CHANGES

We present new CMOS Bayer g-band photometry of the southern W UMa star V752 Cen, presenting two new times of primary minimum, and use archival photographic photometry from the Bamberg Sky Survey (mid 1960s) and the Harvard plate collection (∼1890 to 1990) to extend the O-C diagram back in time to ∼1900. Earlier authors have reported a constant period from the earliest published photometry in 1970 to about the year 2000, when a sudden change occurred to an increasing period. The archival photographic record presented here indicates the period was effectively constant back to 1900. Our 2020 data are also consistent with reported period increase. The V752 Cen system is known from earlier work to be a W UMa binary orbiting a lower mass spectroscopic binary. Our preliminary calculations, based on the reported centre-of-mass velocity change of the W UMa binary, suggest the wide orbit may have a period near 245 d, and could give rise to a light-travel time-effect of order 0.02 d. This does not however appear to be consistent with the SuperWASP photometric O-C results. Hence we suggest that considerable uncertainty exists concerning the properties of the wide orbit.

CHROMOSPHERIC ACTIVITY NATURE OF KIC 6044064

This study presents results obtained from the data of KIC 6044064 (KOI 6652). KIC 6044064 was observed by the Kepler Mission for a total of 1384.254 days. 525 minima times were determined, 264 of which were primary minima and the rest were secondary minima. The OPEA model was derived and its parameters were obtained. On the secondary component, there are two different spot bands latitudinally outstretched, consisting of three spots located with a phase interval of 0.33. The average migration period was found to be 623.063±4.870 days (1.71±0.01 years) for the first spot group, while it was 1125.514±7.305 days (3.08±0.02 years) for the second group. The spectral types of the components seem to be G7V+K9V. Their masses and radii were determined to be 0.86Mʘ and 0.89Rʘ for the primary component and 0.54Mʘ and 0.62Rʘ for the secondary component.

Role of nonspherical DLVO and capillary forces in the transport of 2D delaminated Ti3C2Tx MXene in saturated and unsaturated porous media

The transport and retention of two-dimensional (2D) nanomaterials, such as graphene oxide, in porous media have attracted lots of attention. However, previous studies often simplified these 2D colloids as equivalent spheres for numerical simulations, which ignored the influence of particle shape on colloid retention at multiple interfaces. In this study, a novel 2D nanomaterial delaminated Ti3C2Tx (d-Ti3C2Tx) was adopted to fill this knowledge gap. Comprehensive analyses of the 2D colloid retention mechanisms were conducted based on colloid characterization, saturated and unsaturated column experiments, reactive transport modeling, 2D-based DLVO and nonspherical capillary energy simulations. Results show that d-Ti3C2Tx mobility in both saturated and unsaturated conditions enhanced with the increase in pH and decrease in ionic strength. The DLVO interaction energy of d-Ti3C2Tx at the sand-water-interface (SWI) decreased with the orientation angle of the colloidal major axis to the sand surface from 0° to 90°. The primary mechanism under saturated flow conditions was the irreversible attachment in the deep secondary minimum at the SWI with the major axis of d-Ti3C2Tx parallel to the sand surface. The attachment in the primary minimum at 0° was impossible due to the extremely high energy barrier, and the attachment in the primary and secondary minimum at other orientation angles were negligible. d-Ti3C2Tx only experienced repulsive electrostatic force when approaching the air-water-interface (AWI) no matter the particle orientation. The detaching capillary potential energy was 3 orders of magnitude larger than the attractive DLVO interaction energy of the SWI in the secondary minimum at 0°, suggesting that the capillary force-induced irreversible attachment at the AWI was the primary mechanism under unsaturated flow conditions. This study shows that the DLVO and capillary potential energies were significantly dependent on the particle-interface orientation and colloidal shape. A simplification of 2D colloids as spheres is not recommended.

Evidence on enhanced transport and release of silver nanoparticles by colloids in soil due to modification of grain surface morphology and co-transport.

Natural soils have frequently been considered to decrease the mobility of engineered nanoparticles (NPs) in comparison to quartz sand due to the presence of colloids that provide additional retention sites. In contrast, this study demonstrates that the transport and release of silver nanoparticles (AgNPs) in sandy clay loam and loamy sand soils were enhanced in the presence of soil colloids that altered soil grain surface roughness. In particular, we found that the retention of AgNPs in purified soils (colloid-free and acid-treated) was more pronounced than in raw (untreated) soils or soils treated to remove organic matter (H2O2 or 600°C treated). Chemical analysis and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy demonstrated that the grain surfaces of raw and organic matter-removed soils were abundant with metal oxides and colloids compared to purified soil. Column transport and release experimental results, SEM images, and interaction energy calculations revealed that a significant amount of concave locations on purified soils hindered AgNP release by diffusion or ionic strength (IS) reduction due to deep primary energy minima. Conversely, AgNPs that were retained in soils in the presence of soil colloids were more susceptible to release under IS reduction because the primary minimum was shallow on the tops of convex locations created by attached soil colloids. Additionally, a considerable fraction of retained AgNPs in raw soil was released after cation exchange followed by IS reduction, while no release occurred for purified soil under the same conditions. The AgNP release was highly associated with soil colloids and co-transport of AgNPs and soil colloids was observed. Our work is the first to show that the presence of soil colloids can inhibit deposition and facilitate the release and co-transport of NPs in soil by alteration of the soil grain surface morphology and shallow primary minimum interactions.

Colloid Interaction Energies for Surfaces with Steric Effects and Incompressible and/or Compressible Roughness

Colloid aggregation and retention in the presence of macromolecular coatings (e.g., adsorbed polymers, surfactants, proteins, biological exudates, and humic materials) have previously been correlated with electric double layer interactions or repulsive steric interactions, but the underlying causes are not fully resolved. An interaction energy model that accounts for double layer, van der Waals, Born, and steric interactions as well as nanoscale roughness and charge heterogeneity on both surfaces was extended, and theoretical calculations were conducted to address this gap in knowledge. Macromolecular coatings may produce steric interactions in the model, but non-uniform or incomplete surface coverage may also create compressible nanoscale roughness with a charge that is different from the underlying surface. Model results reveal that compressible nanoscale roughness reduces the energy barrier height and the magnitude of the primary minimum at separation distances exterior to the adsorbed organic layer. The depth of the primary minimum initially alters (e.g., increases or decreases) at separation distances smaller than the adsorbed organic coating because of a decrease in the compressible roughness height and an increase in the roughness fraction. However, further decreases in the separation distance create strong steric repulsion that dominates the interaction energy profile and limits the colloid approach distance. Consequently, adsorbed organic coatings on colloids can create shallow primary minimum interactions adjacent to organic coatings that can explain enhanced stability and limited amounts of aggregation and retention that have commonly been observed. The approach outlined in this manuscript provides an improved tool that can be used to design adsorbed organic coatings for specific colloid applications or interpret experimental observations.

Influence of particle size on the aggregation behavior of nanoparticles: Role of structural hydration layer

More and more attention has been paid to the aggregation behavior of nanoparticles, but little research has been done on the effect of particle size. Therefore, this study systematically evaluated the aggregation behavior of nano-silica particles with diameter 130–480 nm at different initial particle concentration, pH, ionic strength, and ionic valence of electrolytes. The modified Smoluchowski theory failed to describe the aggregation kinetics for nano-silica particles with diameters less than 190 nm. Besides, ionic strength, cation species and pH all affected fast aggregation rate coefficients of 130 nm nanoparticles. Through incorporating structural hydration force into the modified Smoluchowski theory, it is found that the reason for all the anomalous aggregation behavior was the different structural hydration layer thickness of nanoparticles with various sizes. The thickness decreased with increasing of particle size, and remained basically unchanged for particles larger than 190 nm. Only when the distance at primary minimum was twice the thickness of structural hydration layer, the structural hydration force dominated, leading to the higher stability of nanoparticles. This study clearly clarified the unique aggregation mechanism of nanoparticles with smaller size, which provided reference for predicting transport and fate of nanoparticles and could help facilitate the evaluation of their environment risks.

Delineating the Relationship between Nanoparticle Attachment Efficiency and Fluid Flow Velocity

The ability to fundamentally describe nanoparticle (NP) transport in the subsurface underpins environmental risk assessment and successful material applications, including advanced remediation and sensing technologies. Despite considerable progress, our understanding of NP deposition behavior remains incomplete as there are conflicting reports regarding the effect of fluid flow velocity on attachment efficiency. To directly address this and more accurately describe NP attachment behavior, we have developed a novel protocol using a quartz crystal microbalance with dissipation monitoring (QCM-D) to separate and individually observe deposition mechanisms (diffusion and sedimentation), providing in situ, real-time information about particle diffusion (from the bulk liquid to solid surface). Through this technique, we have verified that the approaching velocity of NPs via diffusion increases (0.8-6.7 μm/s) with increasing flow velocity (6.1-106.0 μm/s), leading to an increased NP kinetic energy, thus affecting deposition processes. Further, in the presence of a secondary energy minimum associated with organic surface coatings, secondary minimum deposition decreases and primary minimum deposition increases with the flow velocity. NPs deposited at the primary minimum are relatively more resistant to hydrodynamic energies (including detachment associated energies), resulting in an increase of observed attachment efficiencies. Taken together, this work not only describes a novel method to delineate and quantify physical processes underpinning particle behavior but also provides direct measurements regarding key factors defining the relationship(s) of flow velocity and particle attachment. Such insight is valuable for next-generation fate and transport model accuracy, especially under unfavorable attachment regimes, which is a current and critical need for subsurface material applications and implication paradigms.