Influence Of Surface Area Research Articles

Equivalent-Design Crack Model for Structural Glass Elements

Analytical determination of safety in glass structures often uses oversimplified resistance criteria or fully probabilistic models which require special software to numerically solve the complex equations. Due to computation cost and remaining uncertainty in these different analytical methods, engineers are often required to perform expensive experimental tests to reliably determine glass-structure safety. As a compromise between the need to accurately model the complex mechanical behavior of glass failure and the need to reduce analytical complexity in calculations, this paper proposes a simple semiprobabilistic failure prediction model for glass structures, called the equivalent-design crack model (EDCM). The EDCM is defined using the basis of linear elastic-fracture mechanics, characterized by a mathematical expression that depends on the probability of failure and the level of surface damage. The proposed model considers the influence of surface area, load time-history and complex stress fields within the structural elements. Experimental results from four-point bending and coaxial double-ring tests show good agreement with analytical results using the proposed EDCM method. Application ofthe EDCM in structural design is also presented.

Functional and clinical outcome of total shoulder arthroplasty with oversized glenoid

The Epoca-Reconstruction-(Reco)®-Glenoid has been developed to treat patients with cuff-tear-arthropathy. The glenoid component of this system has a hemispheric shape that canopies the humeral head. This design is believed to provide a stable fulcrum and restore normal deltoid function. The purpose of this study was to analyse strengths and disadvantages of the Epoca-Reco®-Glenoid in cuff-tear-arthropathy patients. Changes in functional outcome using Constant-Murley-Scoring(CMS), CMS sub-scoring parameters and radiological outcome were analysed. For this purpose, a classification for radiologic lucency was proposed. Diverging results, influencing factors and alternative treatment options have been discussed to analyse weaknesses and enhance future development of this arthroplastic model. 23 patients aged 68 ± 8.4 years with irreparable cuff-tear-arthropathy refractory to physiotherapeutic treatment were treated with Reco-Glenoid Total-Shoulder-Arthroplasty (TSA). Pre-operative standardized evaluations included history, physical examination, radiographs, computer tomography and clinical scorings. The post-operative controls included physical examination with CMS, video documentation and radiological evaluation. After a median follow-up time of 38 ± 18 months, the CMS had been significantly improved (p < 0.001) from (17.4 ± 5.8) to (43.2 ± 19.2) points. Significant improvement in pain, activities of daily life, range of motion (p < 0.001) and power (p = 0.006) was achieved. Significantly, inferior results in functional outcome and higher lucency rates were observed in female patients and in patients treated with small glenoid components. The follow-up rate was 100 %. The semi-constraint reconstruction glenoid prosthesis model in cuff-tear-arthropathy patients significantly improves shoulder function, however, it yields controversial results, with satisfactory results in male and poor results in female patients. Revision rate of the female cohort and loosening of the glenoid component in this short-term follow-up is of concern. Further investigations taking BMD, osteopenic conditions and influence of surface area in smaller individuals into consideration are recommended, to determine whether this is the underlying cause of the inferior results in females.

Influence of Catalyst Porosity on Ethylene Polymerization

The structure and porosity of Cr/silica catalysts has a strong influence on its activity in ethylene polymerization and on the character of the polymer it produces. In this study, silicas of widely varying physical structure were chosen so that the influence of surface area, pore volume, pore diameter, and coalescence could be independently investigated by monitoring the surface activity, the polymer molecular weight (MW), MW distribution, melt flow, and the amount of long-chain branching (LCB). The results are discussed with respect to (1) fragmentation of the silica during polymerization, and (2) egress of polymer from pores inside the resulting fragments. Pores of narrow diameter were found to inhibit polymer egress, resulting in lower surface participation, which in turn raised the molecular weight. Pores of wide diameter were found to produce relatively constant surface participation and polymer molecular weight, but increased the amount of LCB in the polymer. Variations in MW are seen as a function ...

Influence of Surface Area and Geometry of Specimens on Bond Strength in a Microtensile Test: An Analysis by the Three-Dimensional Finite Element Method

This study employed three-dimensional (3D) finite element analysis to investigate the stress distribution patterns in a microtensile test with the goal of evaluating the effects of the bond surface area and geometry on bond strength. Finite element models of six specimens were generated: three stick models and three hourglass models. All models simulated the bond strength between dentin and ceramic. The mechanical properties of the materials-the modulus of elasticity and Poisson's coefficient-were defined according to a literature review. The base of each specimen was considered inserted (constrained area) and possessed nodes with displacements restricted in all directions. A traction load, which was calculated to generate a uniformly distributed stress of 20 N/mm(2) at the bond interface, was applied to the top of the specimen. The distribution pattern of the generated stress was qualitatively and quantitatively measured based on color scales ranging from blue to red, according to the von Mises equivalent stress. Specimens with similar shapes demonstrated similar stress distributions. Ceramic specimens had a higher stress value (30.35 MPa) compared to specimens consisting of resinous cement (23.59 MPa) and dentin (19.77 MPa). At the bond interface, the specimens with square sections demonstrated stress values ranging from 22.00 to 24.20 MPa. For the circular section, the stress values ranged from 23.40 to 27.00 MPa. The maximum stress values determined for the circular and square sections were similar among specimens with the same interface area. At the bond interface, the highest stress values were observed in hourglass-shaped specimens.

Uranium Sorption on Various Forms of Titanium Dioxide – Influence of Surface Area, Surface Charge, and Impurities

Titanium dioxide (TiO(2)) has often served as a model substrate for experimental sorption studies of environmental contaminants. However, various forms of Ti-oxide have been used, and the different sorption properties of these materials have not been thoroughly studied. We investigated uranium sorption on some thoroughly characterized TiO(2) surfaces with particular attention to the influence of surface area, surface charge, and impurities. The sorption of U(VI) differed significantly between samples. Aggressive pretreatment of one material to remove impurities significantly altered the isoelectric point, determined by an electroacoustic method, but did not significantly impact U sorption. Differences in sorption properties between the various TiO(2) materials were related to the crystallographic form, morphology, surface area, and grain size, rather than to surface impurities or surface charge. In-situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopic studies showed that the spectra of the surface species of the TiO(2) samples are not significantly different, suggesting the formation of similar surface complexes. The data provide insights into the effect of different source materials and surface properties on radionuclide sorption.

Influence of Surface Area, Water Level and Adjacent Vegetation on Bat Use of Artificial Water Sources

Reliable natural water sources often are unavailable for bats in semi-arid regions such as the Texas Panhandle. Metal stock tanks commonly are used to supply water to livestock and are used by bats as a water source. It is unknown how surface area, water level and adjacent vegetation influence use of tanks by bats. Infrared video cameras and supplemental infrared lights were used to video tape bat behavior and use of stock tanks in Palo Duro Canyon State Park, Texas. Treatment tanks were set out in pairs approximately 80 m apart in a cross-over design to account for influence of location on use of tanks by bats. Treatments included three sizes of tanks (1.2 m, 1.8 m and 3.0 m in diameter), three levels of cover of adjacent vegetation (no vegetation, light vegetation and heavy vegetation) and two water levels (full and ½ full). The number of bats that passed over 3.0 m and 1.2 m tanks was similar; however, bats drank from large tanks more than small tanks. Passes were similar between the tanks surrounded by light vegetation and tanks with no vegetation, but bats drank more from tanks surrounded by light vegetation. Tanks surrounded by heavy vegetation experienced fewer passes and fewer drinks than tanks without vegetation. Water level had no effect on the number of passes by bats but ½ full tanks were used for drinking less frequently than full tanks. Our research indicates that size of tank, water level in tanks and characteristics of adjacent vegetation influence use of metal livestock tanks by bats. Use of larger tanks, keeping tanks full and managing vegetation around tanks increases use of tanks by bats.

Influence of Surface Area on the Flowability Behaviour of Self-Flow Refractory Castables

Alumina, with high melting point (2050°C), high hardness and mechanical strength, and excellent abrasion resistance, is one of the most common raw materials used in self-flow refractory castables (SFRC) for monolithic linings and is commercially available in various fine to coarse size classes. However, the performance of the refractory lining depends not only on the properties of its ingredients but also on its easy installation (good flowability). The aim of this work was to evaluate the relationship between the flowability index (FI) of fresh castable and the specific surface area (SSA) of its particles, which is mostly determined by the finer particles content. The results obtained showed that, by controlling the proportion between matrix and aggregate, it is possible to control the SSA of the refractory castable and find a mathematical relationship between the specific surface area and the minimum flowability index required to obtain a self-flow refractory castable. It is, thus, possible to optimize the refractory castable size composition and obtain an estimate for FI as a function of SSA. Using a minimum 45 wt.% matrix content in the castable mixture, a SSA value above 2.215 m2/g is obtained, which leads to FI ≥ 80%, the recommended value for self-flow.

The impact of population processes on patterns of species richness: Lessons from elevational gradients

Abstract In the last few years, considerable headway has been made towards understanding patterns of species richness along latitudinal and elevational gradients, mostly by focussing on the influences of surface area, climatic factors, evolutionary history, and stochastic processes. However, the potential impact of population-level processes in determining or modifying patterns of species richness has largely been neglected, partly due to the difficulty of gathering such data for numerous species along geographical or ecological gradients. Based on two empirical examples, I here show that dispersal and the resulting source-sink effects modify patterns of plant species richness along elevation gradients, and that the inclusion or exclusion of such sink populations alters the perception of the diversity patterns and hence our interpretation of them. I argue that population processes should be taken into account when studying patterns of species richness, especially at scales at which dispersal is common in the taxon under consideration.

Role of Surface Area in Oxygen Storage Capacity of Ceria–Zirconia as Soot Combustion Catalyst

Two thermal stable phases, Ce0.75Zr0.25O2 and Ce0.16Zr0.84O2, with different surface area were prepared by coprecipitation. The oxygen storage capacity (OSC) measurements were carried out at 500 °C under both transient (CO–O2 cycle at 0.05, 0.1 and 0.25 Hz) and stationary reaction conditions (CO pulse). In the oxygen storage/release process, the rate-determine step is surface reactions when the specific surface area is lower than 60 m2/g. When the surface area increases further, the influence of surface area is less important. The increased surface area favors diesel soot catalytic combustion via providing more redox sites to activate adsorbed oxygen. Nevertheless, this effect is less important when the specific surface area is larger than 40 m2/g, especially under loose contact condition.

Influence of Surface Area on Charge Transport and Recombination in Dye-Sensitized TiO2 Solar Cells

The dependence of the electron transport and recombination dynamics on the internal surface area of mesoporous nanocrystalline TiO2 films in dye-sensitized solar cells was investigated. The internal surface area was varied by altering the average particle size in the films. The scaling of the photoelectron density and the electron diffusion coefficient at short circuit with internal surface area confirms the results of a recent study (Kopidakis, N.; Neale, N. R.; Zhu, K.; van de Lagemaat, J.; Frank, A. J. Appl. Phys. Lett. 2005, 87, 202106) that transport-limiting traps are located predominately on the surfaces of the particles. The recombination current density was found to increase superlinearly (with an exponent of 1.40 +/- 0.12) with the internal surface area. This result is at odds with the expected linear dependence of the recombination current density on the surface area when only the film thickness is increased. The observed scaling of the recombination current density with surface area is consistent with recombination being transport-limited. Evidence is also presented confirming that photoinjected electrons recombine with redox species in the electrolyte via surface states rather than from the TiO2 conduction band.

Manganese Oxide Catalysts Supported on TiO2, Al2O3, and SiO2: A Comparison for Low-Temperature SCR of NO with NH3

A series of TiO2-, Al2O3-, and SiO2-supported manganese oxide catalysts were prepared, characterized, and catalytically tested for selective catalytic reduction (SCR) of NO with NH3 in the presence of excess oxygen at low temperatures (373−523 K). Various commercial supports were used in this study to find out the influence of surface area, support nature (acidic, basic), and crystalline phase on SCR activity. XRD studies reveal the presence of anatase and rutile phases for titania supports and the existence of γ-alumina in the case of alumina support. Silica support was amorphous. No independent lines corresponding to the crystalline MnO2 were observed on pure anatase and rutile samples. However, the presence of MnO2 was confirmed on other supports by XRD. BET surface area values suggest that specific surface area of the supports was decreased after impregnating with MnO2. The FT-IR and ammonia TPD studies indicate the presence of two types of acid sites on these catalysts, and the acidic strength of the...

The Influences of Surface Area and Circulation Flow Rate of a Flat Plate Solar Water Heater on the Performance of a Solar Driven Adsorptive Desiccant Cooling System

The Influences of Surface Area and Circulation Flow Rate of a Flat Plate Solar Water Heater on the Performance of a Solar Driven Adsorptive Desiccant Cooling System

Methodology for the Immobilization of Enzymes onto Mesoporous Materials

Cytochrome c and xylanase were adsorbed onto two mesoporous materials, SBA-15 (a pure silicate) and MSE (an organosilicate), with very similar physical properties but differing chemical compositions. A methodical order was developed whereby the influences of surface area, pore size, extent of order, particle size, surface potentials, isoelectric points, pH, and ionic strength on immobilization were explored. In silico studies of cytochrome c and xylanase were conducted before any immobilization experiments were carried out in order to select compatible materials and probe the interactions between the adsorbents and the mesoporous silicates. The stabilities of the mesoporous materials at different pH values and their isoelectric points and zeta potentials were determined. Electrostatic attraction dominated protein interactions with SBA-15, while weaker hydrophobic interactions are more prominent with MSE for both cytochrome c and xylanase. The ability of the immobilized protein/enzyme to withstand leaching was measured, and activity tests and thermostability experiments were conducted. Cytochrome c immobilized onto SBA-15 showed resistance to leaching and an enhanced activity compared to free protein. The immobilized cytochrome c was shown to have higher intrinsic activity but lower thermostability than free cytochrome c. From an extensive characterization of the surface properties of the silicates and proteins, we describe a systematic methodology for the adsorption of proteins onto mesoporous silicates. This approach can be utilized in the design of a solid support for any protein.

The Catalytic Effect of Vanadium on the Reactivity of Petroleum Cokes with NO

Petroleum cokes are widely used in cement plants for energy generation. Because of their very low volatile content, the physicochemical processes occurring during their combustion should be mainly controlled by heterogeneous reactions. The reactivities of some petroleum cokes toward NO between 800 and 1000 °C have been characterized through experiments in an entrained flow reactor. These carbonaceous materials exhibit very high reactivities toward NO. Their capacity to reduce NO concentration in the surrounding gas is significant, so that this reaction can have a significant impact in terms of NO emissions resulting from their combustion. The influence of surface area and of the heavy metal content on surface reactivity was tested. As it was the case for carbon−oxygen reaction, the surface measured by mercury porosimetry seems to be a good parameter to calculate surface reaction rate. No correlation was found between calcium or iron content and NO−carbon reaction rate. As for the reaction of petroleum cok...

Talc Functionality as Lubricant: Texture, Mean Diameter, and Specific Surface Area Influence

Talc is widely used as a glidant (flow regulator) for powders. This study highlights the characteristics that confer to talcs new end use properties in improving the lubrication function during compression. We studied the contribution of texture, mean diameter (D50), and specific surface area on the residual die pressure, the ejection pressure, the lubrication index, and the tablet hardness. Different textures were studied: microcrystalline, macrocrystalline, and moderately macrocrystalline talc grade. The compression parameters were improved according to the texture. D50 varies from 0.62 to 15 µm. As D50 decreases, the lubrication performance is improved. Finally, the specific surface area of talcs was studied. This last characteristic of talcs was shown as the most relevant parameter in determining lubrication ability.

Uptake of 64Cu−Oxine by Marine Phytoplankton

Short-term uptake experiments using five phytoplankton species (Synechococcus clone DC2, Amphidinium carterae, Chrysochromulina polylepis, Ditylum brightwelli, and Prorocentrum micans) demonstrated rapid uptake of the lipophilic complex 64Cu−oxine, presumably by diffusion of the complex across the plasma membrane. This passive uptake mechanism was extremely rapid and significantly faster than facilitated uptake by the free metal ion. Measured values of the observed permeability, Pobs, ranged from 0.55 to 18.6 × 10-4 cm s-1, showing only small differences between the various algal species. Removal rate constants, kbio, varied much more widely, 0.009−570 × 10-9 L cell-1 h-1, between the algae, indicating the influence of surface area on the uptake kinetics. Maximum internal Cu levels were reached after approximately 2 h, showing that a major limiting factor in the uptake of Cu from Cu−oxine is the concentration of intracellular Cu binding sites.

SHORT-TERM INFLAMMATORY RESPONSES FOLLOWING INTRATRACHEAL INSTILLATION OF FINE AND ULTRAFINE CARBON BLACK IN RATS

Ultrafine carbon black (ufCB) 14 nm in diameter and fine carbon black (CB) 260 nm in diameter were instilled intratracheally in rats at mass of 125 mug, and the bronchoalveolar lavage (BAL) profile at 6 h was assessed. UfCB generated a 50% neutrophil alveolitis 6 h after intratracheal instillation compared to CB, which showed similar activity to the phosphate-buffered saline (PBS) vehicle control. UfCB instillation also produced a marked increase in lactate dehydrogenase (LDH) levels in BAL fluid, which was associated with increased epithelial permeability measured as total protein. In contrast, CB had much less of an effect in increasing BAL protein. Although both particle types caused a decrease in glutathione (GSH) in lung tissue compared to control, the greatest depletion was seen in ufCB-treated animals. To investigate time response, bronchoalveolar lavage was carried out at 6 h, 24 h, and 7 days after a single 125-mug instillation of ufCB. Neutrophil influx was relatively persistent and was still maintained 7 days later. Tumor necrosis factor (TNF) production by BAL leukocytes increased gradually post instillation, whereas NO production became significantly higher at 24 h after instillation and remained at raised levels up to 7 days. Higher doses of CB caused more inflammation than the ufCB. Thus, in the instillation model, a localized dose of particle over a certain level causes the particle mass to dominate the response, rather than the surface area. In contrast to the effect of CB, which showed a dose-related increasing inflammatory response, ufCB at the highest dose caused less of a neutrophil influx than at the lower dose. Six hours after intratracheal instillation, the threshold dose for neutrophil influx occurred at 50 mug. Calculation of surface area of particles instilled suggested that this was likely to be an overload-inducing dose of particles, as gauged from recent experiments with inhaled particles. In summary, this study provides evidence in a rat instillation model that ufCB has greater ability than CB to produce lung inflammation and oxidant stress at a relatively low dose of 125 mug. At high doses, however, BAL is not a reliable indicator of pulmonary response, since the overall response seems to scale to mass or volume of instilled particulate without an influence of surface area.

Influence of surface area and particle size of dispersed oxide on conductivities of lithium bromide composite electrolytes

Temperature dependent conductivities are reported for composites of LiBr and of LiBr·H 2O with a range of both non-porous and porous dispersed oxides. Enhanced conductivity is observed for both systems with high surface area aluminas. Porous aluminas with similar surface area to enhancing non-porous aluminas give large enhancements despite their much larger elementary particle size. Conductivity enhancements in LiBr·H 2O composites below the temperature characteristic of the α/sB phase transition of LiBr·H 2O prevent the conductivity loss characteristic of that phase at lower temperatures. No simple trend in conductivity enhancement with oxide mole fraction is transferable between oxides. A non-porous silica of similar surface area to enhancing aluminas does not give the same enhancements.

The influence of surface area on the in vitro cytotoxicity of a range of dental materials.

In the toxicity testing of dental materials the quantity of material used may have a profound influence on the biological response obtained. This was investigated in vitro by assessing the cytotoxicity of equal volumes of nine materials in artificial cavities of three different diameters, chosen to cover the range found in vivo. With seven materials there was a significant increase in toxicity with increasing surface area. The pattern of response of different materials within specific groups was fairly uniform. The degree of toxicity of the test materials relative to controls was also investigated. From the data obtained it is apparent that the maximum cavity diameter appropriate for the material under test must be considered when evaluating the toxicity of dental materials.

Influence of surface area and additives on the thermal stability of transition alumina catalyst supports. I: Kinetic data

The influence of surface area and additives on the transformation of transition aluminas into alpha alumina was studied using differential thermal analysis and by measuring the rate of transformation by X-ray diffraction of samples calcined at numerous intervals during a 50 hour period. Four transition alumina samples of different specific surface area ranging from 80 to 130 m 2 g −1 were used. The transformation was found to be facilitated by a high surface area of the initial transition alumina. Initially the surface area decreased very rapidly from its starting value until about 60 m 2 g −1 then more slowly and also linearly with respect to the amount of alpha phase in the sample. The influence of additives was followed by adding Mg 2+, Ca 2+, Ga 3+, In 3+, La 3+, Zr 4+ and Th 4+ cations by the dry impregnation method with nitrate salts. The influence of the method of preparation was determined by using the same procedure for aluminium nitrate. By comparison with pure alumina and in order of increasing effect. In 3+, Ga 3+, Al 3+ and Mg 2+ were found to be accelerators, whereas Zr 4+, Ca 2+, Th 4+ and La 3+ were found to be inhibitors. The influence of adding an ion to different initial aluminas was investigated in the case of Mg 2+.