OMS-2-Supported Cu Hydroxide-Catalyzed Benzoxazoles Synthesis from Catechols and Amines via Domino Oxidation Process at Room Temperature.

In the presence of manganese oxide octahedral molecular sieve (OMS-2) supported copper hydroxide Cu(OH)x/OMS-2, aerobic synthesis of benzoxazoles from catechols and amines via domino oxidation/cyclization at room temperature is achieved. This heterogeneous benzoxazoles synthesis initiated by the efficient oxidation of catechols over Cu(OH)x/OMS-2 tolerates a variety of substrates, especially amines containing sensitive groups (hydroxyl, cyano, amino, vinyl, ethynyl, ester, and even acetyl groups) and heterocycles, which affords functionalized benzoxazoles in good to excellent yields by employing low catalyst loading (2 mol % Cu). The characterization and plausible catalytic mechanism of Cu(OH)x/OMS-2 are described. The notable features of our catalytic protocol such as the use of air as the benign oxidant and EtOH as the solvent, mild conditions, ease of product separation, being scalable up to the gram level, and superior reusability of catalyst (up to 10 cycles) make it more practical and environmentally friendly for organic synthesis.

Health assessment of an electro-hydraulic servo pump control system for servomotor based on LGA deep neural network.

Due to its advantages of having a high power-to-weight ratio and being energy-efficient, the electro-hydraulic servo pump control system (abbreviated as EHSPCS) is frequently employed in the industrial field, such as the electro-hydraulic servo pump control (EHSPC) servomotor for steam turbine valve regulation control. However, the EHSPCS has strong nonlinearity and time-varying features, and the factors that cause system performance degradation are complex. Once a system failure occurs, it may lead to serious accidents, causing serious casualties and economic losses. To address the above issues, a system health assessment method based on LSTM-GRNN-ANN (LGA) deep neural network is proposed in this paper. Firstly, with oil volume gas content, servo motor air-gap flux density, and system leakage coefficient as the health assessment performance indicators, a health assessment performance index system for the EHSPCS is built, Furthermore, the system performance index threshold is set. Secondly, an LGA deep neural network is constructed by combining LSTM, GRNN and ANN, and a deep neural network based on the LGA is used to create an EHSPCS health assessment model. Subsequently, system feature parameter extraction, algorithm design, and parameter debugging are carried out. Finally, an EHSPCS experimental platform is established, typical system failure simulation experiments are designed, and comparative experimental analysis is conducted. The experimental findings demonstrate that the average accuracy of the system health assessment model based on the LGA deep neural network suggested in this paper is 96.37%, compared to 89.84%, 87.99% for LSTM and GRNN, which validates the accuracy of the system health assessment model based on the LGA deep neural network.

Transport and retention of colloids in porous media: does shape really matter?

The effect of particle shape on its transport and retention in porous media was evaluated by stretching carboxylate-modified fluorescent polystyrene spheres into rod shapes with aspect ratios of 2:1 and 4:1. Quartz crystal microbalance with dissipation (QCM-D) experiments were conducted to measure the deposition rates of spherical and rod-shaped nanoparticles to the collector (poly-l-lysine coated silica sensor) surface under favorable conditions. The spherical particles displayed a significantly higher deposition rate compared with that of the rod-shaped particles. Theoretical analysis based on Smoluchowski-Levich approximation indicated that the rod-shaped particles largely counterbalance the attractive energies due to higher hydrodynamic forces and torques experienced during their transport and rotation. Under unfavorable conditions, the retention of nanoparticles in a microfluidic flow cell packed with glass beads was studied with the use of laser scanning cytometry (LSC). Significantly more attachment was observed for rod-shaped particles than spherical particles, and the attachment rate of the rod-shaped particles showed an increasing trend with the increase in injection volume. Rod-shaped particles were found to be less sensitive to the surface charge heterogeneity change than spherical particles. Increased attachment rate of rod-shaped particles was attributed to surface heterogeneity and possibly enhanced hydrophobicity during the stretching process.

Fecal indicator bacteria transport and deposition in saturated and unsaturated porous media.

Beach sediment and sand are recognized as nonpoint fecal indicator bacteria (FIB) sources capable of causing water quality and health risks for beach-goers. A comprehensive understanding of the key factors and mechanisms governing the migration and exchange of FIB between beach water column and sediment is desired to better predict FIB concentration variations and assess the associated risk. The transport and retention behavior of two model FIB Enterococcus faecalis (E. faecalis) and Escherichia coli (E. coli) was examined using packed-bed columns in both saturated and unsaturated porous media to evaluate FIB migration potentials at conditions simulating the coastal aquatic environment. Additionally, complementary cell characterization techniques were conducted to better understand the migration behaviors of both FIB strains observed in the column experiments. The mobility of the gram-positive species E. faecalis was much more sensitive to solution chemistry and column saturation level than that of the gram-negative species E. coli. Interaction energy calculations suggest that E. faecalis retention was largely governed by the combination of DLVO (Derjaguin-Landau-Verwey-Overbeek) and non-DLVO (most likely hydrophobic and/or polymer bridging) interactions in saturated porous media, while the combination of DLVO and steric interactions controlled the deposition of E. coli cells. The measured surface properties of the two FIB strains supported the distinct bacteria transport behaviors and the differences of the identified mechanisms for each strain. As a result, E. faecalis showed the least affinity to sand in freshwater and appeared to be irreversibly attached in primary energy minima at elevated salt conditions; whereas the retained E. coli cells were reversibly attached and mostly associated with the secondary energy minima at both freshwater and seawater conditions. In unsaturated porous media, E. faecalis cells seemed to prefer to attachment at air/water interface rather than sand surface, while E. coli showed a similar affinity to the two interfaces. It was proposed that the different surface characteristics of the two FIB strains resulted in the distinct transport and retention behavior in porous media. These results highlight the need for FIB management to consider variations in transport behavior between model FIB when assessing water quality and associated risks.

Influence of collector surface composition and water chemistry on the deposition of cerium dioxide nanoparticles: QCM-D and column experiment approaches.

The deposition behavior of cerium dioxide (CeO(2)) nanoparticles (NPs) in dilute NaCl solutions was investigated as a function of collector surface composition, pH, ionic strength, and organic matter (OM). Sensors coated separately with silica, iron oxide, and alumina were applied in quartz crystal microbalance with dissipation (QCM-D) to examine the effect of these mineral phases on CeO(2) deposition in NaCl solution (1-200 mM). Frequency and dissipation shift followed the order: silica > iron oxide > alumina in 10 mM NaCl at pH 4.0. No significant deposition was observed at pH 6.0 and 8.5 on any of the tested sensors. However, ≥ 94.3% of CeO(2) NPs deposited onto Ottawa sand in columns in 10 mM NaCl at pH 6.0 and 8.5. The inconsistency in the different experimental approaches can be mainly attributed to NP aggregation, surface heterogeneity of Ottawa sand, and flow geometry. In QCM-D experiments, the deposition kinetics was found to be qualitatively consistent with the predictions based on the classical colloidal stability theory. The presence of low levels (1-6 mg/L) of Suwannee River humic acid, fulvic acid, alginate, citric acid, and carboxymethyl cellulose greatly enhanced the stability and mobility of CeO(2) NPs in 1 mM NaCl at pH 6.5. The poor correlation between the transport behavior and electrophoretic mobility of CeO(2) NPs implies that the electrosteric effect of OM was involved.

Distinct effects of humic acid on transport and retention of TiO2 rutile nanoparticles in saturated sand columns.

The distinct effects of humic acid (HA, 0-10 mg L(-1)) on the transport of titanium dioxide (rutile) nanoparticles (nTiO(2)) through saturated sand columns were observed under conditions of environmental relevance (ionic strength 3-200 mM NaCl, pH 5.7 and 9.0). Specifically, the transport of nTiO(2) was dramatically enhanced in the presence of HA at pH 5.7, even at a low HA concentration of 1 mg L(-1). The mobility of nTiO(2) was further increased with greater concentrations of HA. In contrast, this enhancement of the nTiO(2) transportability due to the presence of HA was limited at pH 9.0 because of the negligible adsorption of HA onto nTiO(2), regardless of the concentrations of HA examined in this study. The distinct effects can be explained by the adsorption behaviors of HA to nTiO(2) and sand surfaces and the resulting interactions between nTiO(2) and sand surfaces under different conditions, which resulted in a large variation of the nTiO(2) transport and deposition behaviors at various conditions. In addition, theoretical interaction energy calculations and additional elution experiments indicate that the secondary energy minimum played an important role in controlling the nTiO(2) transport and deposition in porous media observed in this study. Moreover, the interaction energy calculations suggest that at pH 5.7, HA affected nTiO(2) transport by increasing the negative surface charge of nTiO(2) at low HA adsorption densities; whereas, combinations of increased electrostatic and steric interactions due to the presence of HA were the main mechanisms of enhanced transportability of nTiO(2) at high HA adsorption densities. Overall, results from this study suggest that natural organic matter and solution pH are likely key factors that govern the stability and mobility of nTiO(2) in the natural aquatic environment.

Transport and retention of TiO2 rutile nanoparticles in saturated porous media under low-ionic-strength conditions: measurements and mechanisms.

The mechanisms governing the transport and retention kinetics of titanium dioxide (TiO(2), rutile) nanoparticle (NP) aggregates were investigated in saturated porous media. Experiments were carried out under a range of well-controlled ionic strength (from DI water up to 1 mM) and ion valence (NaCl vs CaCl(2)) comparable to the low end of environmentally relevant solution chemistry conditions. Solution chemistry was found to have a marked effect on the electrokinetic properties of NP aggregates and the sand and on the resulting extent of NP aggregate transport and retention in the porous media. Comparable transport and retention patterns were observed for NP aggregates in both NaCl and CaCl(2) solutions but at much lower ionic strength with CaCl(2). Transport experimental results showed temporal and spatial variations of NP aggregate deposition in the column. Specifically, the breakthrough curves displayed a transition from blocking to ripening shapes, and the NP retention profiles exhibited a shift of the maximum NP retention segment from the end toward the entrance of the column gradually with increasing ionic strength. Additionally, the deposition rates of the NP aggregates in both KCl and CaCl(2) solutions increased with ionic strength, a trend consistent with traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Upon close examination of the results, it was found that the characteristics of the obtained transport breakthrough curves closely followed the general trends predicted by the DLVO interaction-energy calculations. However, the obtained NP retention profiles were found to deviate severely from the theory. We propose that a NP aggregate reconformation through collision between NP aggregates and sand grains reduced the repulsive interaction energies of NP-NP and NP-sand surfaces, consequently accelerating NP deposition with transport distance and facilitating approaching NP deposition onto NPs that had already been deposited. It is further suggested that TiO(2) NP transport and retention are determined by the combined influence of NP aggregate reconformation associated with solution chemistry, travel distance, and DLVO interactions of the system.

Selectivity-tunable oxidation of tetrahydro-ß-carboline over an OMS-2 composite catalyst: preparation and catalytic performance.

Controlling the reaction selectivity of organic transformations without losing high conversion is always a challenge in catalytic processes. In this work, a H3PO4·12WO3/OMS-2 nanocomposite catalyst ([PW]-OMS-2) was prepared through the oxidation of a Mn(ii) salt with sodium phosphotungstate by KMnO4. Comprehensive characterization indicates that different Mn2+ precursors significantly affected the crystalline phase and morphology of the as-synthesized catalysts and only MnSO4·H2O as the precursor could lead to a cryptomelane phase. Moreover, [PW]-OMS-2 demonstrated excellent catalytic activity toward aerobic oxidative dehydrogenation of tetrahydro-ß-carbolines due to mixed crystalline phases, enhanced surface areas, rich surface oxygen vacancies and labile lattice oxygen species. In particular, ß-carbolines and 3,4-dihydro-ß-carbolines could be obtained from tetrahydro-ß-carbolines with very high selectivity (up to 99%) over [PW]-OMS-2 via tuning the reaction solvent and temperature. Under the present catalytic system, scalable synthesis of a ß-carboline was achieved and the composite catalyst showed good stability and recyclability. This work not only clarified the structure-activity relationship of the catalyst, but also provided a practical pathway to achieve flexible, controllable synthesis of functional N-heterocycles.

Colloidal and bacterial deposition: role of gravity.

The role of gravitational force on the deposition of 0.5, 1.1, and 1.8 mum carboxylate-modified polystyrene latex (CML) microspheres and bacterium Burkholderia cepacia G4g has been evaluated using a parallel plate flow chamber system. This experimental system utilized an inverted and an upright optical microscope attached with image-capturing devices to directly observe and determine the deposition kinetics onto glass surfaces located at the top and bottom of the flow chamber. Deposition kinetics was quantified at 10 mM KCl under electrostatically unfavorable and favorable attachment conditions and at two flow rates (0.06 and 3 mL/min), simulating the range of flow velocities from groundwater to rapid granular filtration. Comparing the particle deposition kinetics on the top and bottom surfaces under identical flowing exposure time, fluid chemistries, and hydrodynamic conditions, results showed that significant differences were observed between the two surfaces, suggesting that gravity was a significant driving force for the initial stages of deposition of particles that were larger than 1 mum size. Simulation results utilizing a particle trajectory model confirmed these experimental observations. This was further supported by additional deposition experiments with 1.1 mum microspheres suspended in a deuterium oxide (D(2)O)/water mixture (heavy water) where the density of colloid and the suspending heavy water were effectively the same. Under this condition, deposition rates were observed to be identical between the top and bottom surfaces. Results from normal and heavy water solutions indicated that the greater deposition of colloidal particles larger than 1 mum on the bottom in normal water solutions is due to gravity. Finally, the experimental results were compared with deposition studies using smaller 0.5 mum colloids as well as some theoretical calculations of expected rates of particle deposition.

Initial colloid deposition on bare and zeolite-coated stainless steel and aluminum: influence of surface roughness.

The impact of surface roughness of bare and zeolite ZSM-5 coated stainless steel and aluminum alloy on colloid deposition has been investigated using a parallel plate flow chamber system in an aqueous environment. The metals were systematically polished to alter the surface roughness from nanoscale to microscale, with the subsequent surface roughness of both the bare and coated surfaces varying from 11.2 to 706 nm. The stainless steel and aluminum alloy surfaces are extensively characterized, both as bare and as coated surfaces. Experimental results suggest that ZSM-5 coating and surface roughness have a pronounced impact on the kinetics of the colloid deposition. The ZSM-5 coating reduced colloid adhesion compared to the corresponding bare metal surface. In general, the greater surface roughness of like samples resulted in higher colloid deposition. Primarily, this is due to greater surface roughness inducing less reduction in the attractive interactions occurring between colloids and collector surfaces. This effect was sensitive to ionic strength and was found to be more pronounced at lower ionic strength conditions. For the most electrostatically unfavorable scenario (ZSM-5 coatings in 1 mM KNO(3)), the enhanced deposition may also be attributed to inherent surface charge heterogeneity of ZSM-5 coatings due to aluminum in the crystalline structure. The two exceptions are ZSM-5 coated mirror-polished stainless steel and the unpolished aluminum surfaces, which are rougher than the other two samples of the same metal type but result in the least deposition. The reasons for these observations are discussed, as well as the effect of surface charge and hydrophobicity on the adhesion. The relative importance of surface roughness versus contributions of electrostatic interactions and hydrophobicity to the colloid deposition is also discussed.

The effect of packing hydrophilization on bacterial attachment and the relationship with the performance of biotrickling filters.

Many bioprocesses depend on the effective formation of a biofilm on a solid support. In the present study, three different surface treatments (sandblasting, pure-O(2) plasma, and He-O(2) plasma treatments) were conducted on polypropylene (PP) Pall rings used as a support in biotrickling filters for air pollution control. The intent was to modify the ring surface and/or electrochemical properties in order to possibly improve cell adhesion, wetting properties, and possibly reduce the start-up time and increase the performance of the biotrickling filters. The surface treatments were found to generally increase the hydrophilicity and the zeta potential of the surfaces. However, the startup and performance of lab-scale biotrickling filters packed with treated Pall rings were not significantly different than the control with untreated rings. Cell and colloid deposition experiments conducted in flow cells showed that the treated surfaces and the hydrodynamic conditions were not favorable for cell deposition indicating that there could be significant opportunities for improving packings used in environmental bioprocess applications.

A novel and effective Ni complex catalyst system for the coupling reactions of carbon dioxide and epoxides.

The coupling of carbon dioxide and mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under a Ni complex catalyst system without using additional organic solvents was achieved in excellent selectivity and TOF.

Silicon impurity release and surface transformation of TiO2 anatase and rutile nanoparticles in water environments.

Surface transformation can affect the stability, reactivity, and toxicity of titanium dioxide (TiO2) nanoparticles (NPs) in water environments. Herein, we investigated the release kinetics of Si impurity frequently introduced during NP synthesis and the resulting effect on TiO2 NP transformation in aqueous solutions. The release of Si increased from 2 h to 19 d at three pHs with the order: pH 11.2 ≥ pH 2.4 > pH 8.2. The Si release process followed parabolic kinetics which is similar to diffusion controlled dissolution of minerals, and the release magnitude followed the order: 10 × 40 nm rutile > 50 nm anatase > 30 × 40 nm rutile. FTIR data indicated preferential dissolving of less polymerized Si species on NP surface. Surface potential and particle size of TiO2 NPs remained almost constant during the 42-day monitoring, implying the unaffected stability and transport of these NPs by the incongruent dissolution of impurities.

Effects of dominant material properties on the stability and transport of TiO2 nanoparticles and carbon nanotubes in aquatic environments: from synthesis to fate.

Recently, increasing studies have focused on the environmental stability, transport, and fate of the anthropogenic nanomaterials in the environment, which contributes to the understanding of the potential risks when released. However, applying nanomaterials from different manufacturers and production methods tends to result in inconsistent experimental data and potentially a biased comparison. The aim of this review is to investigate the dominant material properties that determine the aggregation and deposition behavior of nanomaterials. Herein, we focus on two of the most popular anthropogenic nanomaterials, i.e., titanium dioxide (TiO2) and carbon nanotubes (CNTs). We start from the production methods of nanomaterials of different sources, and then examine their influence on the material properties and surface characteristics. The role of the material properties was carefully analyzed and correlated with the stability and transport in aquatic environments. These two case studies may be extended to other nanomaterials with similar surface properties, which will improve our understanding of the impact and risks of anthropogenic nanomaterials in the environment. This study highlights opportunities to design and produce "green" nanomaterials with less environmental risk and no sacrificing of the novel "nano" properties.

Release of phosphorous impurity from TiO2 anatase and rutile nanoparticles in aquatic environments and its implications.

Phosphorus-bearing materials as an additive have been popularly used in nanomaterial synthesis and the residual phosphorus within the nanoparticles (NPs) can be of an environmental concern. For instance, phosphorus within pristine commercial TiO2 NPs greatly influences the surface charge and aggregation behavior of the host TiO2 in aquatic environments; however, it is unknown whether and how fast phosphorus is released. In this study, we focus on the phosphorus release kinetics from five types of TiO2 NPs (i.e., 5, 10, and 50 nm anatase and 10 × 40, 30 × 40 nm rutile) under the influence of varying solution chemistries. The 50 nm anatase has the highest quantity of P (8.05 g/kg) and most leachable P dissolves within the first 2 h (i.e., 5.01 g/kg), which presents a potential pollutant source of P. Higher pH favors the phosphorus release (release order: pH 11.2 > pH 8.2 > pH 2.4), while variations in the environmentally relevant ionic strengths (0.01 M NaCl + 0.01 M NaHCO3 and 0.04 M NaCl + 0.01 M NaHCO3) and the presence of dissolved natural organic matter (10 mg/L) do not affect release rate greatly. X-ray Absorption Near Edge Structure results suggest that phosphate adsorbed on the pristine 50 nm anatase desorbs, and some dissolved phosphate again re-sorbs as a surface precipitate. The findings from this research may have important environmental implications such as accidental release of TiO2 NPs and other nanomaterials that are synthesized using phosphorus containing chemicals as an ingredient.

[Degradation of beta-naphthol by catalytic wet air oxidation].

A series of MnO(x)/nano-TiO2 catalysts were prepared and their application in degradation of beta-naphthol by catalytic wet air oxidation (CWAO) was investigated. The catalysts preparation conditions, reaction conditions and its stability were tested. The catalysts had been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) measurements. The results showed that the decrease of the COD removal for the degradation of beta-naphthol at high Mn loading was due to the aggregation of the highly dispersed Mn species and the formation of the correlated crystals. The decline of the COD removal at high calcination temperature was probably attributed to the weak electron transfer between Mn2O3 and MnO2 and the formation of the inactive Mn2O3. The COD removal had been falling slightly when the catalyst was used 6 times, and this was likely related to the decrease of the diffraction peaks. The catalyst had a high activity when the Mn loading (mass fraction) was 4% and the calcination temperature was 450 degrees C. The COD removal was up to 96.4% at 110 degrees C and 0.5 MPa with this catalyst. The COD removal of 92.4% could be obtained with the MnO(x)/nano-TiO2 catalyst was recycled 6 times. The Mn leaching at 50, 80, 110 and 150 degrees C were all less than 9.3 mg x L(-1) by means of Atomic Absorption Spectroscopy (AAS). The probable degradation pathway was proposed according to some publications.

Effects of material properties on sedimentation and aggregation of titanium dioxide nanoparticles of anatase and rutile in the aqueous phase.

This study investigated the sedimentation and aggregation kinetics of titanium dioxide (TiO(2)) nanoparticles with varying material properties (i.e., crystallinity, morphology, and chemical composition). Used in the study were various types of commercially available TiO(2) nanoparticles: three spherical anatase (nominal diameters of 5, 10, and 50 nm) and two rutile nanoparticles (10×40 and 30×40 nm). The 50 nm anatase and 10×40 nm rutile showed higher stability in deionized water and 5 mM NaCl solutions at pH 7 than the 5, and 10 nm anatase nanoparticles in sedimentation experiments. In aggregation experiments, critical coagulation concentration values for the 50 nm anatase were the highest, followed by the 10×40 nm rutile and the 5 nm anatase nanoparticles in NaCl and CaCl(2) solutions. The aggregation kinetics was fitted reasonably well with the Derjaguin-Landau-Verwey-Overbeek (DLVO) equations for the TiO(2) nanoparticles tested. Results showed that crystallinity and morphology are not influential factors in determining the stability of TiO(2) nanoparticle suspensions; however, the differences in their chemical compositions, notably, the varying concentrations of impurities (i.e., silicon and phosphorus) in the pristine materials, determined the surface charge and therefore the sedimentation and aggregation of TiO(2) nanoparticles in the aqueous phase.

Initial bacterial deposition on bare and zeolite-coated aluminum alloy and stainless steel.

In this study, the impact of zeolite thin film coatings on bacterial deposition and "biofouling" of surfaces has been investigated in an aqueous environment. The synthesis of two types of zeolite coatings, ZSM-5 coated on aluminum alloy and zeolite A coated on stainless steel, and the characterization of the coated and bare metal surfaces are described. The extent of cell deposition onto the bare and zeolite-coated aluminum alloy and stainless steel surfaces is investigated in a parallel plate flow chamber system under a laminar flow conditions. The initial rates of bacterial transfer to the various surfaces are compared by utilizing a marine bacterium, Halomonas pacifica g, under a range of ionic strength conditions. H. pacifica g deposited onto bare metal surfaces to a greater extent as compared with cells deposited onto the zeolite coatings. The surface properties found to have the most notable effect on attachment are the electrokinetic and hydrophobicity properties of the metal and zeolite-coated surfaces. These results suggest that a combination of two chemical mechanisms-hydrophobic and electrostatic interactions-contribute to the antifouling nature of the zeolite surface. Additional observations on the relative role of the hydrodynamic and physical phenomena are also discussed.

Colloidal deposition on remotely controlled charged micropatterned surfaces in a parallel-plate flow chamber.

This article describes a method to influence colloid deposition by varying the zeta potential at microelectrodes with remotely applied electric potentials. Deposition experiments were conducted in a parallel-plate flow chamber for bulk substrates of glass, indium tin oxide (ITO), and ITO-coated glass microelectrodes in 10 and 60 mM potassium chloride solutions. Colloid deposition was found to be a function of solution chemistry and the small locally delivered electric surface potentials. Electric fields and physical surface heterogeneity can be ruled out as cause of the observed deposition. Results are reported using experimentally determined Sherwood numbers and compared to the predictions of a previously developed patch model. Minor deviations between predicted and experimental Sherwood numbers imply that physical and chemical interactions occur. Specifically, we propose that colloidal particles respond to local variations in surface potential through electrostatic interactions, altering particle streamlines flowing along the surface and ultimately the extent of deposition.