Silica Glass Beads Research Articles

An experimental setup for studying conduction and radiation heat transfer in a rotary drum

This study presents the development of a novel heating system that aims to bridge the experimental gap for analyzing both radiation and conduction heat transfer in a rotary drum. The experiments were conducted by loading the drum with 4 mm silica glass beads at varying fill levels (10 %, 17.5 %, and 25 %) and rotation rates (2, 5, and 10 RPM), and monitoring the temperature evolution with an infrared camera. Higher fill levels resulted in lower average particle bed temperatures, while rotation rate influenced the contact time between particles and the drum wall and the exposure to radiative heat. A rotation rate of 5 RPM resulted in the highest average bed temperature due to optimal contact and exposure time for conduction and absorption of radiative heat, respectively. Thus, a balance between adequate particle mixing and optimal contact/exposure time is crucial for maximizing heat transfer efficiency in rotary drums exhibiting conduction and radiation.

Investigation of the 106Ru ophthalmic plaque dose distribution in a pseudotumor-contained eye-equivalent phantom by silica glass beads

PurposeTo investigate the 106Ru dose distribution in an intraocular pseudotumor by micro silica glass beads thermo-luminescence dosimeters (TLD). Materials and methodsDosimetry was conducted using Monte Carlo (MC) simulation as well as an experimental setup by employing an in-house eye equivalent phantom. A BEBIG CCA model of 106Ru plaque was used. Bead TLDs were modeled using MCNPX code, choosing water and plexiglass as phantom mediums along with CCA plaque. The deposited energy and electron energy spectra were calculated using *f8 and f4 tallies, respectively. A dedicated eye-equivalent phantom was designed and fabricated by 3D-printing techniques to place glass beads. ResultsAbsorbed dose at the central axis of the CCA plaque by beads TLDs was compared to manufacturer-reported data and simulation results. Maximum, minimum, and mean relative differences of 23%, 7%, and 15% with the manufacturer and 14%, 0%, and 1.6% with the simulation were obtained, respectively. Replacing glass bead material with water resulted in an average relative difference of 33.9% in absorbed energy per mass unit, corresponding to 21% and 44.8% at the first (0.5 mm depth) and last dosimetry points (9.5 mm depth), respectively. It has also been shown that glass beads can shadow each other, leading to a dose reduction of 15%. ConclusionA specific eye equivalent phantom with a pseudotumor was constructed, and silica glass beads were used for dosimetry. The results of the experiment and the MC simulation are in good accord. In the case of 106Ru ophthalmic brachytherapy plaque dosimetry, replacing glass beads material with water led to a mean difference of about 34% as well as shadowing effects. This emphasizes how crucial it is to employ a reliable correction factor in clinical applications.

Reduction in Apparent Permeability Owing to Surface Precipitation of Solutes by Drying Process and Its Effect on Geological Disposal

Disposal tunnels in geological repositories are ventilated continuously for over 50 years until their closure. Under these conditions, an unsaturated zone of mixed liquid and gas phases forms around the tunnels. Moreover, drying is assumed to progress from the host rock to the tunnels. To understand these drying processes, this study investigated the migration and precipitation of solutes via capillary forces during drying in packed columns using silica sand or glass beads as packed layers and X-ray CT analysis. In addition, the apparent permeability of a column packed with silica sand containing precipitation was examined using a flow experiment. The results indicate that the precipitation and accumulation of solutes were significant near the drying surfaces of the columns. The apparent mass transfer coefficient at a relatively early stage of the drying process indicates that the migration rate of solutes depends strongly on the capillary forces during the drying process. Furthermore, the apparent permeability of the columns with precipitation decreased significantly. These indicate that the precipitation and accumulation of solutes with drying in the groundwater reduce the porosity and permeability, and the advection of groundwater around the repository may be suppressed.

Effect of fine particle shot peening on surface friction of stainless steel and ceramic bracket slots

This study aims to compare the static friction of untreated and fine particle shot peening (FPSP) treated stainless steel and ceramic bracket slots. A total of 60 pieces of stainless steel and 60 pieces of ceramic brackets (Roth prescription, 0.022×0.028 in2) were divided into 3 groups: control (n=20), silica glass bead particle surface treatment (n=20) and stainless steel (SUS316L) particle surface treatment (n=20). Ten brackets of each group were combined with 0.019×0.025 in2 orthodontic stainless steel arch wires and were analyzed for static friction. The remaining 10 brackets of each group were tested for slot surface roughness and hardness. The result shows that stainless steel brackets treated with FPSP exhibited lower static friction, with smoother and harder surfaces than the control group (p<0.05). In contrast, treated ceramic brackets showed no difference from the control group in terms of static friction, roughness, and hardness (p>0.05).

A review of micro silica beads in radiation dosimetry applications

A recent development in the field of radiation measurement is the use of silica glass beads as high performance thermoluminescent detectors. The application of using doped silica glass jewellery beads as radiation detectors was first proposed by Jafari in 2014, on the basis that it held the potential to resolve long standing issues in dosimetry, could be cheaply implemented, and had yielded good results in initial experimental work. Today the body of literature concerned with glass bead dosimeters has grown extensively, covering their behaviour in various radiation fields, as well as their handling and storage properties. The purpose of this review is to summarise the results obtained in the literature so far. Paramount among these is the finding that beads could offer excellent performance in radiotherapy applications, particularly due to their small volume (1–3 mm3), measurement reproducibility of less than 3% (k = 2), chemical inertness and low fading rate (10% over the first 30 days after irradiation). The beads are energy independent over the MV photon and MeV electron energy ranges and exhibit good linearity in electron, proton, carbon ion and photon radiation (an R2 of 0.999 having been achieved from 1 cGy to 50 Gy in a 6 MV photon beam) as well as being dose-rate and angular independent. However, significant energy dependence in the lower energy range is apparent (<300 kV), thus careful calibration is required. Irradiation of beads with neutrons has also been studied, the reported results indicate their potential use as high spatial resolution alternatives to the gas detectors presently used in industrial and scientific fields. Published use cases of silica beads have been identified and summarised in this review, these include treatment plan verification, small field dosimetry, SABR audits and kV therapy all of which demonstrating the potential use for silica bead TLDs within Radiotherapy.

Plant Responses on Elective Gels for in Vitro Shoot Multiplication and Root Elongation of Pineapple (Ananas Comosus L.)

The quest for alternative matrices for plant tissue culture is a continuing process. Agar is one of the utmost common coagulating agents in plant in vitro clonal propagation. Pure grade agar has high value price and fear of over manipulation of its resources affected searching for low cost options. Therefore, liquid medium supplement with silica gel, glass beads and sands substratum and agar in two steps of micro propagation (seedling proliferation and root induction) were investigated. The shoot multiplication in the cytokinins hormone of 2.5mg/l BA and 0.5mg/l KN supported by 7g/l agar and alternative matrices has been produced 33.1 shoots and 5.3 shoot length in sands and agar. There is none significant difference among shoot number and shoot length on the agar and sands on shoot multiplication and plant, and there is significant difference in glass beads and silica gel compared with sand/agar in the shoot multiplication, and there is highly significance in shoot length in the matrices of plant support. Pineapple root induced in auxins hormone in vitro culture of plant propagation in half strength MS media, 30g/l sugar, 1mg/l NAA and 7g/l agar. The higher root number in sands 10.6 and followed 10 in silica gel and agar supported matrices. The root length also none significant difference among means treatments in agar, glass beads and sands. However, there is a significance difference with silica gel in root length. These silica gel, glass beads and sands used as agar gels to support and aeration plantlets. Keywords: Elective gels, low cost, shoots multiplication and root elongation. DOI: 10.7176/JBAH/12-7-03 Publication date: April 30 th 2022

Plant Responses on Elective Gels for &amp;lt;i&amp;gt;in vitro&amp;lt;/i&amp;gt; Shoot Multiplication and Root Elongation of Pineapple (&amp;lt;i&amp;gt;Ananas comosus&amp;lt;/i&amp;gt; L.)

The quest for alternative matrices for plant tissue culture is a continuing process. Agar is one of the utmost common coagulating agents in plant <i>in vitro</i> clonal propagation. Pure grade agar has high value price and fear of over manipulation of its resources affected searching for low cost options. Therefore, liquid medium supplement with silica gel, glass beads and sands substratum and agar in two steps of micro propagation (seedling proliferation and root induction) were investigated. The shoot multiplication in the cytokinins hormone of 2.5mg/l BA and 0.5mg/l KN supported by 7g/l agar and alternative matrices has been produced 33.1 shoots and 5.3 shoot length in sands and agar. There is none significant difference among shoot number and shoot length on the agar and sands on shoot multiplication and plant, and there is significant difference in glass beads and silica gel compared with sand/agar in the shoot multiplication, and there is highly significance in shoot length in the matrices of plant support. Pineapple root induced in auxins hormone <i>in vitro</i> culture of plant propagation in half strength MS media, 30g/l sugar, 1mg/l NAA and 7g/l agar. The higher root number in sands 10.6 and followed 10 in silica gel and agar supported matrices. The root length also none significant difference among means treatments in agar, glass beads and sands. However, there is a significance difference with silica gel in root length. These silica gel, glass beads and sands used as agar gels to support and aeration plantlets.

Activity, stability, and binding capacity of β-galactosidase immobilized on electrospun nylon-6 fiber membrane

In this research, we explored various immobilized enzyme support materials, including the novel nylon-6 fiber membrane (NFM), and evaluated the increase in surface area and its effect on enzyme binding potential. We also manipulated incubation and reaction conditions and assessed the subsequent effects on activity and stability of β-galactosidase, with comparisons between various solid support materials and free (dissolved) enzyme. Nylon-6 fiber membranes were created by electrospinning and were compared with other materials as solid supports for enzyme binding. The other materials included polyvinylidene fluoride 5-kDa nanofiltration dairy membranes, nylon-6 pellets, and silica glass beads. Scanning electron microscopy revealed the large surface area of NFM, which correlated with greater enzyme activity compared with the relatively flatter surfaces of the other solid support materials. Enzyme activity was measured spectrophotometrically with the color-changing substrate o-nitrophenyl-β-d-galactopyranoside. Compared with the other solid supports, NFM had greater maximum enzyme binding potential. Across pH conditions ranging from 3.5 to 6.0 (including the optimal pH of 4.0-5.0), enzyme activity was maintained on the membrane-immobilized samples, whereas free enzyme did not maintain activity. Altering the storage temperature (4, 22, and 50°C) affected enzyme stability (i.e., the ability of the enzyme to maintain activity over time) of free and polyvinylidene fluoride membrane samples. However, NFM samples maintained stability across the varying storage temperatures. Increasing the immobilization solution enzyme concentration above the maximum enzyme binding capacity had no significant effect on enzyme stability for membrane-immobilized samples; however, both had lower mean stability than free enzyme by approximately 74%. With further development, β-galactosidase immobilized on NFM or other membranes could be used in continuous processing in the dairy industry for a combination of filtration and lactose hydrolysis-creating products that are reduced in lactose and increased in sweetness, with no requirement for "added sugars" on the nutrition label and no enzyme listed as final product ingredient.

Erosion behavior and failure mechanism of Ti/TiAlN multilayer coatings eroded by silica sand and glass beads

Severe erosion by hard particles is a crucial problem to engine blades when aircraft take off and land in harsh environments, especially for the developed lightweight titanium alloy components. Here, we deposited the Ti/TiAlN multilayer coatings with various cycles on Ti–6Al–4V substrates by a home-made hybrid multisource cathodic arc system. The effects of the silica sand and glass beads on erosion behavior of the coatings were focused. Results showed that the Ti/TiAlN multilayer coatings eroded by the silica sand exhibited the predominant “layer by layer” failure mechanism. In particular, increasing the number of cycles led to the dramatic increase in erosion rate for Ti/TiAlN multilayer coatings, due to the deterioration of their mechanical properties. Different from the silica sand case, however, the erosion rate of the coatings treated by glass beads indicated faint dependence upon the number of cycles, where the coating failure was dominated by the “piece by piece” failure mechanism. Noted that the Ti layers along with the formed interfaces enhanced the erosion resistance of the coatings, although the failure mechanisms were differently eroded by silica sand and glass beads. Meanwhile, the Ti layers and interfaces hindered the propagation of radial cracks and restrained the lateral cracks within one single TiAlN layer.

Plasma‐activated methane partial oxidation reaction to oxygenate platform chemicals over Fe, Mo, Pd and zeolite catalysts

Natural gas from stranded sources is being predominantly flared, and there is a growing demand for new technologies for its utilisation, where electrification, flexibility, and modularity play an important role. Plasma-activated methane partial oxidation reaction was studied in a designed dielectric barrier discharge ionisation reactor unit, producing value-added platform chemicals, namely, methanol, formaldehyde, intermediate formic acid, acetic acid, and paraformaldehyde at ambient temperature and atmospheric pressure. The effects of various process parameters, such as voltage, total convertible gas flow rate, and reagent ratio relationship, were considered. In addition, coupling of the following catalytic materials with plasma was examined: alumina (Al2O3), chabazite, ferrierite, microporous beta zeolite, silica (SiO2) glass beads, ZSM-5 (MFI), Fe on H-ZSM-5 and Al2O3, Mo on H-ZSM-5, TiO2 and SiO2, and Pd on Al2O3. In the liquid product, 21.5% CH3OH, 20.4% CH2O, 0.3% HCOOH, and 2.4% CH3COOH were measured when using pure plasma, and a maximum aggregate yield of the organic oxygenate compounds of 5.21 mol.% was achieved. The usage of shaped silicate surface increased the selectivity towards synthesised oxygen-containing structures, while the application of alumino-silicate mixture constituents reduced it. It was determined that elementary covalently bonded carbon was formed inside pores when pure zeolites were used. Fe- and Pd-based heterogeneous catalysts favoured the complete exothermic combustion of CH4 feedstock reactant species, and the liquid product consisted only of water in the Pd- case. The utilisation of Mo/H-ZSM-5 resulted in a 46% increased yield of formalin. A mechanism for the role of Mo was proposed, where Mo oxidises methanol to formaldehyde and the metal is reoxidised in plasma.

Thermoluminescence measurements of eye-lens dose in a multi-centre stereotactic radiosurgery audit

Stereotactic radiosurgery (SRS), a non-invasive therapeutic technique, seeks delivery of elevated doses of ionizing radiation to precisely defined targets while at the same time preserving surrounding tissue viability. SRS was developed for treatment of various functional abnormalities, extending also to benign and malignant lesions (the latter sometimes referred to as stereotactic body radiation therapy, SBRT). Local tumour control for single and multiple brain metastases at low complication rates is one such outcome. Notable commercial SRS platforms include Gamma Knife and the linac-based systems, Novalis and Cyberknife. Such systems use imaging techniques that include computed tomography (CT) and magnetic resonance imaging (MRI) in localizing SRS targets, down to a small fraction of one mm. With a wide range of platforms for delivery of SRS, greater investigation and standardization is called for. Present work concerns a multi-centre dosimetric audit (20 centres in all), investigating the range of SRS machines and techniques for a single brain metastasis using a series of small dimension detectors (1.55 mm and less) and an anthropomorphic head phantom. With the lens as one of the more radiosensitive tissues, the aim has been to determine the scattered radiation lens dose received during an SRS treatment, as well as the imaging dose received during planning-stage CT-scanning. Custom-designed holders were fabricated to carry three types of thermoluminescence dosimeters: Ge-doped silica fibres, silica glass beads and TLD-100, the latter as a reference dosimeter (being also of larger dimension than the silica-based dosimeters). For reproducible placement of the TLD holders, a bespoke 3D-printed goggle insert was produced for the head phantom. International guidance is to seek reduction in lens dose down to 0.5 Gy. Present results show lens dose values below 0.5 Gy, albeit sometimes to modest degree, there being need to continue to exercise associated due care in SRS planning and delivery.

CO2 hydrogenation reaction over pristine Fe, Co, Ni, Cu and Al2O3 supported Ru: Comparison and determination of the activation energies

Fe, Co, Ni and Cu are the main non-noble industrially significant catalysts in the CO2 and CO gas phase hydrogenation reaction towards hydrocarbons and alcohols. These catalysts are typically supported on metal oxides such as SiO2, TiO2, Al2O3 and ZnO, in order to maximize the activity towards the desired reaction. The role of the supporting material is to stabilize the catalytic nanoparticles and to prevent sintering at the elevated reaction temperatures and pressures. The supporting phase can improve the reaction activity or even have a crucial role in the reaction, as is the case, e.g. for the Methanol synthesis over Cu based catalysts supported on ZnO. Studying the metals without a supporting oxide phase is of great importance for the fundamental understanding of the catalytic activity of the metal phase. Therefore, we investigated the pristine transition metals Fe, Co, Ni and Cu (diluted with silica glass beads to avoid sintering) towards their activity in the CO2 hydrogenation reaction and determined the activation energy. An Al2O3 supported Ruthenium catalyst with 0.5 mass percent of Ru loading was taken as reference system. It was found that Co, Ni and Ru/Al2O3 are mostly active in the Sabatier reaction, while Fe is active in the reverse water gas shift reaction. Cu as pristine metal shows no catalytic activity. C2+ hydrocarbons were formed on Co in low concentrations. For the calculation of the activation energy, the kinetically determined temperature range of the reaction is identified with a high resolution in time by means of a quantitative gas analysis method with an online mass spectrometer. The observation activation energy of the CO2 hydrogenation reaction was determined to be 50 kJ/mol over Fe, 77 kJ/mol over Co, 74 kJ/mol over Ni and 73 kJ/mol over the Ru/Al2O3 catalyst. This indicates similar reaction pathways over Co, Ni and Ru/Al2O3 and a different reaction mechanism on Fe.

A Refined Global Segmentation of X-Ray CT Images for Multi-phase Geomaterials

X-ray computed tomography images of three-phase silica sand and glass bead specimens are analyzed and used to evaluate the segmentation performances of Otsu-, and recursion-based multilevel algorithms. A global image segmentation technique that combines iterative and recursive algorithms, namely a refined statistics-based global segmentation is proposed for segmenting multi-phase granular geomaterials. The performance of the proposed algorithm is tested by segmenting partially saturated silica sand and glass bead specimens. For the tested silica sand specimen, the refined statistics method estimated void ratio and degree of saturation were 0.67 and 39.35%. The estimates for the glass bead specimen yielded 0.64 and 43.49%, respectively. The true void ratio (0.66) and degree of saturation (37.71%) were determined with a user-controlled Image processing software package—Image-Pro. It was found that the proposed method estimated the void ratio and the degree of saturation with 1.52 and 4.35 percent errors for the silica sand and with 15.63 and 0.34 percent errors for the glass bead, respectively. The computational time of the proposed method was found to be shorter than other methods considered. Overall, it is concluded that the proposed technique performed better in segmenting three-phase granular geomaterials.

Critical Influence of Cosolutes and Surfaces on the Assembly of Serpin-Derived Amyloid Fibrils

Many proteins and peptides self-associate into highly ordered and structurally similar amyloid cross-β aggregates. This fibrillation is critically dependent on properties of the protein and the surrounding environment that alter kinetic and thermodynamic equilibria. Here, we report on dominating surface and solution effects on the fibrillogenic behavior and amyloid assembly of the C-36 peptide, a circulating bioactive peptide from the α1-antitrypsin serine protease inhibitor. C-36 converts from an unstructured peptide to mature amyloid twisted-ribbon fibrils over a few hours when incubated on polystyrene plates under physiological conditions through a pathway dominated by surface-enhanced nucleation. In contrast, in plates with nonbinding surfaces, slow bulk nucleation takes precedence over surface catalysis and leads to fibrillar polymorphism. Fibrillation is strongly ion-sensitive, underlining the interplay between hydrophilic and hydrophobic forces in molecular self-assembly. The addition of exogenous surfaces in the form of silica glass beads and polyanionic heparin molecules potently seeds the amyloid conversion process. In particular, heparin acts as an interacting template that rapidly forces β-sheet aggregation of C-36 to distinct amyloid species within minutes and leads to a more homogeneous fibril population according to solid-state NMR analysis. Heparin’s template effect highlights its role in amyloid seeding and homogeneous self-assembly, which applies both in vitro and in vivo, where glycosaminoglycans are strongly associated with amyloid deposits. Our study illustrates the versatile thermodynamic landscape of amyloid formation and highlights how different experimental conditions direct C-36 into distinct macromolecular structures.

Methane Hydrate Formation and Thermal Based Dissociation Behavior in Silica Glass Bead Porous Media

Formation and thermal based dissociation of methane pore space hydrate has been studied at various initial hydrate saturations and heating rates utilizing a 1.3 cm3 glass bead sample pack. Initial ...

Formulation of a physically motivated specific breakage rate parameter for ball milling via the discrete element method

A physically based specific breakage rate parameter of the population balance model for batch dry‐milling is formulated, which explicitly accounts for the impact energy distribution calculated by the discrete element method (DEM). Preliminary DEM simulations of particle impact tests were first performed, which concluded that dissipation energy should be used in contrast to collision energy to accurately define the impact energy distribution. Subsequently, DEM simulations of the motion of spheres representing silica glass beads in a ball mill were performed to determine the specific breakage rate parameter, which was in good agreement with those found experimentally. An analysis of the impact energy distribution, which was only possible within context of the physically motivated specific breakage rate parameter, emphasized the importance of accounting for a threshold impact energy. Without proper assessment of the impact energy distribution, DEM simulations may lead to an erroneous evaluation of milling experiments. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2404–2415, 2014

Transport of Oxidized Multi-Walled Carbon Nanotubes through Silica Based Porous Media: Influences of Aquatic Chemistry, Surface Chemistry, and Natural Organic Matter

This paper provides results from studies of the transport of oxidized multi-walled carbon nanotubes (O-MWCNTs) of varying surface oxygen concentrations under a range of aquatic conditions and through uniform silica glass bead media. In the presence of Na(+), the required ionic strength (IS) for maximum particle attachment efficiency (i.e., the critical deposition concentration, or CDC) increased as the surface oxygen concentration of the O-MWCNTs or pH increased, following qualitative tenets of theories based on electrostatic interactions. In the presence of Ca(2+), CDC values were lower than those with Na(+) present, but were no longer sensitive to surface oxygen content, suggesting that Ca(2+) impacts the interactions between O-MWCNTs and glass beads by mechanisms other than electrostatic alone. The presence of Suwannee River natural organic matter (SRNOM) decreased the attachment efficiency of O-MWCNTs in the presence of either Na(+) or Ca(2+), but with more pronounced effects when Na(+) was present. Nevertheless, low concentrations of SRNOM (<4 mg/L of dissolved organic carbon) were sufficient to mobilize all O-MWCNTs studied at CaCl2 concentrations as high as 10 mM. Overall, this study reveals that NOM content, pH, and cation type show more importance than surface chemistry in affecting O-MWCNTs deposition during transport through silica-based porous media.

Hydrophobic Interactions Increase Attachment of Gum Arabic- and PVP-Coated Ag Nanoparticles to Hydrophobic Surfaces

A fundamental understanding of attachment of surface-coated nanoparticles (NPs) is essential to predict the distribution and potential risks of NPs in the environment. Column deposition studies were used to examine the effect of surface-coating hydrophobicity on NP attachment to collector surfaces in mixtures with varying ratios of octadecylichlorosilane (OTS)-coated (hydrophobic) glass beads and clean silica (hydrophilic) glass beads. Silver nanoparticles (AgNPs) coated with organic coatings of varying hydrophobicity, including citrate, polyvinylpyrrolidone (PVP), and gum arabic (GA), were used. The attachment efficiencies of GA and PVP AgNPs increased by 2- and 4-fold, respectively, for OTS-coated glass beads compared to clean glass beads. Citrate AgNPs showed no substantial change in attachment efficiency for hydrophobic compared to hydrophilic surfaces. The attachment efficiency of PVP-, GA-, and citrate-coated AgNPs to hydrophobic collector surfaces correlated with the relative hydrophobicity of the coatings. The differences in the observed attachment efficiencies among AgNPs could not be explained by classical DLVO, suggesting that hydrophobic interactions between AgNPs and OTS-coated glass beads were responsible for the increase in attachment of surface-coated AgNPs with greater hydrophobicity. This study indicates that the overall attachment efficiency of AgNPs will be influenced by the hydrophobicity of the NP coating and the fraction of hydrophobic surfaces in the environment.

Deposition of Silver Nanoparticles in Geochemically Heterogeneous Porous Media: Predicting Affinity from Surface Composition Analysis

The transport of uncoated silver nanoparticles (AgNPs) in a porous medium composed of silica glass beads modified with a partial coverage of iron oxide (hematite) was studied and compared to that in a porous medium composed of unmodified glass beads (GB). At a pH lower than the point of zero charge (PZC) of hematite, the affinity of AgNPs for a hematite-coated glass bead (FeO-GB) surface was significantly higher than that for an uncoated surface. There was a linear correlation between the average nanoparticle affinity for media composed of mixtures of FeO-GB and GB collectors and the relative composition of those media as quantified by the attachment efficiency over a range of mixing mass ratios of the two types of collectors, so that the average AgNPs affinity for these media is readily predicted from the mass (or surface) weighted average of affinities for each of the surface types. X-ray photoelectron spectroscopy (XPS) was used to quantify the composition of the collector surface as a basis for predicting the affinity between the nanoparticles for a heterogeneous collector surface. A correlation was also observed between the local abundances of AgNPs and FeO on the collector surface.

Water and Oxygen Dependence of Pseudomonas putida Growing in Silica Sand Capillary Fringes

In tests with Hele–Shaw cells containing silica sand, O2 profiles were measured after formation of a capillary fringe (CF) with a nutrient broth, that was inoculated with Pseudomonas putida. After 7 d, the CF became anaerobic up to 2 cm above the water level. Within the next 3 cm at decreasing water saturation, the O2 concentration approached its maximum value. After growth, most P. putida cells were found at the 4‐ to 5‐cm height of the CF, whereas cell densities decreased significantly toward the top of the CF due to water‐limited respiratory activity. This was shown in separate batch experiments by measuring respiration rates of P. putida for defined water saturations. In silica sand (rough surface) or glass beads (smooth surface), respiration of P. putida was significantly reduced at a water saturation of ≤7.5% but was always higher for growth on sand than on glass beads, presumably due to different water bioavailability at the surface. The highest O2 consumption rates of P. putida in both media were measured at 60 to 85% water saturation, which represents the saturated–unsaturated interface region in a CF. To find the minimum required water availability for respiration, batch assays with increasing agar concentrations in LB medium were conducted. The O2 consumption rates of P. putida decreased to zero above an agar concentration of 18% (w/v), equivalent to a water activity &lt;0.978. The results indicate that limited bacterial respiration due to water potential stress would only occur in the top few millimeters of a CF in sand.