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1
González-Fonteboa, B., and F. Martínez-Abella. "Hormigones con áridos reciclados: estudio de propiedades de los áridos y de las mezclas." Materiales de Construcción 55, no. 279 (September 30, 2005): 53–66. http://dx.doi.org/10.3989/mc.2005.v55.i279.198.
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Powers, Matthew D., Christopher R. Webster, Kurt S. Pregitzer, and Brian J. Palik. "Spatial dynamics of radial growth and growth efficiency in residualPinus resinosafollowing aggregated retention harvesting." Canadian Journal of Forest Research 39, no. 1 (January 2009): 109–17. http://dx.doi.org/10.1139/x08-162.
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Variable retention harvest systems are encouraged to promote complexity in managed forests, and aggregated retention has been suggested as a means of reducing moisture stress in residual trees. We studied the impacts of within-aggregate position on growth and foliar physiology to better understand the spatial dynamics of residual-tree responses to aggregated retention harvests in even-aged Pinus resinosa Ait. stands. Distance from edge and edge aspect influenced radial growth, volume increment, and growth efficiency, but only edge aspect affected foliar nitrogen content. Spatial variables had no significant relationships with foliar carbon isotope ratios (δ13C). Increases in radial growth, volume increment, and growth efficiency following harvesting were greatest near edges and in the northeastern quadrants of aggregates that received mechanical understory release treatments, and lowest in the southeastern quadrant of aggregates and near aggregate centers. Foliar nitrogen content was highest in the southwestern quadrants of aggregates that received understory release treatments, and lowest in the northwestern quadrants of aggregates. Our results suggest spatial relationships are important determinants of residual-tree responses to aggregated retention harvests.
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Gijsman, AJ, and RJ Thomas. "Aggregate size distribution and stability of an oxisol under legume-based and pure grass pastures in the eastern Colombian savannas." Soil Research 33, no. 1 (1995): 153. http://dx.doi.org/10.1071/sr9950153.
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This study evaluated soil aggregate size distribution and stability of an Oxisol under improved grass-only or grass-legume pastures, established in previously native savanna. Three grass-legume combinations were included at various stocking rates. In all treatments and soil layers, soils were well aggregated, having more than 90% of their weight in macroaggregates (>250 �m). The addition of legumes to pastures did not affect the soil aggregate size distribution, although aggregates showed somewhat more stability against slaking. An increase in stocking rate negatively affected both average aggregate size and aggregate stability. Aggregates showed little or no dispersion of clay particles in any treatment. A positive correlation was found between wet aggregate stability and hot-water extractable carbohydrate concentration, supporting the hypothesis that these carbohydrates equate with plant-derived or microbial polysaccharides which glue soil aggregates together. It is suggested that determination of hot-water extractable carbohydrates may serve as a useful indicator of small differences in aggregate stability, even when these differences are not evident in the stability measurement itself.
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Gadea, J., J. Soriano, A. Martín, P. L. Campos, A. Rodríguez, C. Junco, I. Adán, and V. Calderón. "Reactividad árido-álcali en áridos empleados para hormigón." Materiales de Construcción 60, no. 299 (August 10, 2010): 69–78. http://dx.doi.org/10.3989/mc.2010.48708.
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Alhede, Maria, Melanie Lorenz, Blaine Gabriel Fritz, Peter Østrup Jensen, Hans Christian Ring, Lene Bay, and Thomas Bjarnsholt. "Bacterial aggregate size determines phagocytosis efficiency of polymorphonuclear leukocytes." Medical Microbiology and Immunology 209, no. 6 (September 2, 2020): 669–80. http://dx.doi.org/10.1007/s00430-020-00691-1.
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Abstract The ability of bacteria to aggregate and form biofilms impairs phagocytosis by polymorphonuclear leukocytes (PMNs). The aim of this study was to examine if the size of aggregates is critical for successful phagocytosis and how bacterial biofilms evade phagocytosis. We investigated the live interaction between PMNs and Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and Staphylococcus epidermidis using confocal scanning laser microscopy. Aggregate size significantly affected phagocytosis outcome and larger aggregates were less likely to be phagocytized. Aggregates of S. epidermidis were also less likely to be phagocytized than equally-sized aggregates of the other three species. We found that only aggregates of approx. 5 μm diameter or smaller were consistently phagocytosed. We demonstrate that planktonic and aggregated cells of all four species significantly reduced the viability of PMNs after 4 h of incubation. Our results indicate that larger bacterial aggregates are less likely to be phagocytosed by PMNs and we propose that, if the aggregates become too large, circulating PMNs may not be able to phagocytose them quickly enough, which may lead to chronic infection.
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Alonso, M. M., A. Rodríguez, and F. Puertas. "Viability of the use of construction and demolition waste aggregates in alkali-activated mortars." Materiales de Construcción 68, no. 331 (July 9, 2018): 164. http://dx.doi.org/10.3989/mc.2018.07417.
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This study explores the technological feasibility of using construction and demolition waste (C&DW) as recycled aggregate in alkali activated mortars, ascertaining the mechanical and microstructural behavior. Shrinkage behavior of alkali activated slag mortars (AAS) and fire resistance of alkali activated fly ash (AAFA) incorporating recycled aggregates have been also tested Normalized siliceous sand and two types of recycled concrete aggregates were used in the mixes at different proportions. The findings showed that water demand was higher in mortars prepared with recycled aggregate. Partial replacement (20% - 80/20) of conventional aggregate with the recycled material was also observed to yield mortars with high mechanical strength, although total porosity also rose. Total replaclement, gave worse mechanical performance however. Fire resistance and shrinkage studies conducted indicated that alkaline cement mortars prepared with 80/20 recycled aggregated exhibit acceptable performance.
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Allen, Leah M., John Matyas, Mark Ungrin, David A. Hart, and Arindom Sen. "Serum-Free Culture of Human Mesenchymal Stem Cell Aggregates in Suspension Bioreactors for Tissue Engineering Applications." Stem Cells International 2019 (November 7, 2019): 1–18. http://dx.doi.org/10.1155/2019/4607461.
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Mesenchymal stem cells (MSCs) have the capacity to differentiate towards bone, fat, and cartilage lineages. The most widely used culture and differentiation protocols for MSCs are currently limited by their use of serum-containing media and small-scale static culture vessels. Suspension bioreactors have multiple advantages over static culture vessels (e.g., scalability, control, and mechanical forces). This study sought to compare the formation and culture of 3D aggregates of human synovial fluid MSCs within suspension bioreactors and static microwell plates. It also sought to elucidate the benefits of these techniques in terms of productivity, cell number, and ability to generate aggregates containing extracellular matrix deposition. MSCs in serum-free medium were either (1) inoculated as single cells into suspension bioreactors, (2) aggregated using static microwell plates prior to being inoculated in the bioreactor environment, or (3) aggregated using microwell plates and kept in the static environment. Preformed aggregates that were size-controlled at inoculation had a greater tendency to form large, irregular super aggregates after a few days of suspension culture. The single MSCs inoculated into suspension bioreactors formed a more uniform population of smaller aggregates after a definite culture period of 8 days. Both techniques showed initial deposition of extracellular matrix within the aggregates. When the relationship between aggregate size and ECM deposition was investigated in static culture, midsized aggregates (100-300 cells/aggregate) were found to most consistently maximize sGAG and collagen productivity. Thus, this study presents a 3D tissue culture method, which avoids the clinical drawbacks of serum-containing medium that can easily be scaled for tissue culture applications.
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Tohgi, Hideo, Hiroaki Takahashi, Katsumi Watanabe, Hiroyuki Kuki, and Yoshiaki Shirasawa. "Development of Large Platelet Aggregates from Small Aggregates as Determined by Laser-light Scattering: Effects of Aggregant Concentration and Antiplatelet Medication." Thrombosis and Haemostasis 75, no. 05 (1996): 838–43. http://dx.doi.org/10.1055/s-0038-1650376.
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SummaryParticle-counting methods that employ light scattering (LS) quantify changes in the number of platelet aggregates of different sizes after the application of an aggregating stimulus. Using the LS method, we studied the effects of aggregant concentration, aspirin administration, and ticlopidine administration on aggregate formation and compared the results with those obtained using the conventional optical density (OD) method. Subjects were 47 controls, 31 patients treated with aspirin (330 mg/day), and 37 patients treated with ticlopidine (200 mg/day). Platelet aggregation after stimulation by 0.5, 1.0 or 5.0 μM ADP, or 0.5, 1.0 or 2.0 μg/ml collagen was determined using both methods. Using the LS method, small (9-25 μm), medium (25-50 μm), and large (50-70 μm) aggregates were counted. In patients untreated with antiplatelet medication, greater concentrations of ADP or collagen generated larger aggregates. Generation of small and medium-sized aggregates showed a significant positive correlation with OD levels after stimulation with 0.5 or 1.0 μM ADP, or 0.5 or 1.0 μg/ml collagen. In patients treated with aspirin, the development of small aggregates into large aggregates was inhibited. Thus, the number of small aggregates increased. Inhibition induced by aspirin was more effective against aggregation after stimulation with collagen than with ADP. In patients treated with ticlopidine, small and medium-sized aggregate formation was inhibited after stimulation with low concentrations of ADP or collagen, but was promoted after stimulation with high aggregant concentrations. The capability of the LS method to quantify different sizes of aggregates after stimulation with low concentration agonists may facilitate investigation of the aggregation process, and of how this process is affected by antiplatelet agents.
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Acebrón, Sergio P., Vanesa Fernández-Sáiz, Stefka G. Taneva, Fernando Moro, and Arturo Muga. "DnaJ Recruits DnaK to Protein Aggregates." Journal of Biological Chemistry 283, no. 3 (November 5, 2007): 1381–90. http://dx.doi.org/10.1074/jbc.m706189200.
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Thermal stress might lead to protein aggregation in the cell. Reactivation of protein aggregates depends on Hsp100 and Hsp70 chaperones. We focus in this study on the ability of DnaK, the bacterial representative of the Hsp70 family, to interact with different aggregated model substrates. Our data indicate that DnaK binding to large protein aggregates is mediated by DnaJ, and therefore it depends on its affinity for the cochaperone. Mutations in the structural region of DnaK known as the “latch” decrease the affinity of the chaperone for DnaJ, resulting in a defective activity as protein aggregate-removing agent. As expected, the chaperone activity is recovered when DnaJ concentration is raised to overcome the lower affinity of the mutant for the cochaperone, suggesting that a minimum number of aggregate-bound DnaK molecules is necessary for its efficient reactivation. Our results provide the first experimental evidence of DnaJ-mediated recruiting of ATP-DnaK molecules to the aggregate surface.
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Tang, F. K., M. Cui, Q. Lu, Y. G. Liu, H. Y. Guo, and J. X. Zhou. "Effects of vegetation restoration on the aggregate stability and distribution of aggregate-associated organic carbon in a typical karst gorge region." Solid Earth 7, no. 1 (January 27, 2016): 141–51. http://dx.doi.org/10.5194/se-7-141-2016.
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Abstract. Land use changes have a major impact on soil structure and soil nutrients. The influences of vegetation restoration on aggregate stability and soil carbon storage have been studied extensively, but the distribution of aggregate-associated carbon is not yet understood. The objective of this work was to study the influences of vegetation restoration on aggregate stability and distribution of soil organic carbon (SOC) associated with water-stable aggregates (WSAs) in a karst gorge region. The experiment was carried out in 2012 and included four land use types: bare land (BL), grassland (GL), shrubland (SL), and woodland (WL). Soil samples were collected from the 0–20, 20–40, and 40–60 cm depths, and aggregates were separated by a wet-sieving method. Aggregate stability and aggregated-associated SOC were determined, and the relationships between water-stable aggregation with SOC were examined. The results showed that total SOC and SOC associated with WSAs of various sizes were the highest at a soil depth of 0–20 cm. In addition, the SOC contents of the WSAs increased as the soil aggregate sizes decreased. The SOC contents of the WSAs < 0.25 mm were highest except in the bare land, and the SOC contents of the aggregates < 0.25 mm comprised the majority of the total aggregate SOC contents. The aggregates were dominated by particles with sizes > 5 mm under dry-sieving treatment, while aggregates were predominantly comprised of WSAs < 0.25 mm under wet-sieving treatment. At a soil depth of 0–60 cm, the mean weight diameter (MWD), geometrical mean diameter (GMD), and fractal dimensions (D) of the dry aggregates and water-stable aggregates in the different types of land were ranked, in descending order, as WL > GL > SL > BL. The contents of WSAs > 0.25 mm, MWD, and GMD increased significantly, in that order, and the percentage of aggregate destruction (PAD) and fractal dimensions decreased significantly as the soil aggregate stability improved. SOC contents increased after vegetation restoration, and the average SOC content of WL was 2.35, 1.37, and 1.26 times greater than that in the BL, GL, and SL, respectively. We conclude that woodland and grassland facilitated WSA stability and SOC protection; thus, promoting the natural restoration of vegetation by reducing artificial disturbances could effectively restore the ecology and prevent soil erosion in karst regions.
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Hu, Shu, Yang Liao, Yang Zhang, Xiaoliang Yan, Zhenlu Zhao, Weiqiang Chen, Xin Zhang, et al. "Effect of Thermal Annealing on Conformation of MEH-PPV Chains in Polymer Matrix: Coexistence of H- and J-Aggregates." Polymers 12, no. 8 (August 7, 2020): 1771. http://dx.doi.org/10.3390/polym12081771.
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In diluted solid solution using poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and polymethyl methacrylate (PMMA) or polystyrene (PS), both aggregated and extended conformations could be formed according to the weight ratio. Aggregated conformation in as-cast MEH-PPV/PMMA film presented a J-aggregate-like photoluminescence (PL) emission. After annealing at 160 °C, its PL showed characteristics of both J- and H-aggregates at the same time; however, extended conformation showed an oligomer-like emission, which was not sensitive to either measurement temperature or annealing temperature. Thus, the conformation transition between aggregated and extended is unlikely to happen in MEH-PPV/PMMA blends during thermal annealing. On the contrary, in MEH-PPV/PS blends, extended conformation dominated in as-cast film with oligomer-like emissions; after annealing at 160 °C, both J- and H- aggregate-like PL emissions were observed, indicating the conformation transitioned from extended to aggregated. Therefore, our work may suggest a new method to manipulate photophysical properties of conjugated polymers by combining appropriate host matrix and thermal annealing processes.
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Edwards, D. A., Z. Liu, and R. G. Luthy. "Enhancing Polynuclear Aromatic Uptake into Bulk Solution with Amphiphilic Colloidal Aggregates." Water Science and Technology 26, no. 9-11 (November 1, 1992): 2341–44. http://dx.doi.org/10.2166/wst.1992.0732.
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Aggregated amphiphiles in an aqueous or solid/aqueous system can substantially enhance the uptake of polynuclear aromatic (PNA)compound into a bulk solution. The extent of PNA compound incorporated in an amphiphilic aggregate solution in the absence of solids is linearly dependent on the bulk solution concentration of the aggregated form of the amphiphile. In a system in which solids are in contact with a solution, however, the relationship is nonlinear as a result of the adherence of both amphiphile and PNA compound to the solids. The formation of amphiphile aggregates in the bulk solution of a system containing solids occurs only after a much greater amount of amphiphile has been added to the system than would be required for a similar system containing only solution. The partitioning of PNA compound between the solid, the colloidal amphiphilic aggregates in bulk solution, and the rest of the bulk solution can be characterized with two different partition coefficients and a number of other parameters, all of which are obtainable from independent experiments. The total fraction of PNA compound incorporated into bulk solution can be estimated with a mathematical model. Model results for the uptake of pyrene into a C8PE9.5 aggregate solution are shown plotted with experimental data. The effect of amphiphile aggregates on PNA compound transport in porous media may in some cases be substantial.
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Almirón, Marta A., Mara S. Roset, and Norberto Sanjuan. "The Aggregation of Brucella abortus Occurs Under Microaerobic Conditions and Promotes Desiccation Tolerance and Biofilm Formation." Open Microbiology Journal 7, no. 1 (March 22, 2013): 87–91. http://dx.doi.org/10.2174/1874285801307010087.
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Brucella abortus causes brucellosis mainly in cattle. The infection is transmitted to humans by ingestion of animal products or direct contact with infected material. While the intracellular lifestyle of Brucella is well characterized, its extracellular survival is poorly understood. In nature, bacterial persistence is associated with biofilms, where aggregated cells are protected from adversity. The inability of Brucella abortus to aggregate under aerobiosis and that fact that the replicative niche of Brucella is characterized by microaerobic conditions prompted us to investigate the capacity of this pathogen to aggregate and grow in biofilms under microaerobiotic conditions. The results show that B. abortus aggregates and produces biofilms. The aggregates tolerate desiccation better than planktonic cells do, adhere and displace even in the absence of the lipopolysaccharide-O antigen, flagella, the transcriptional regulator VjbR, or the enzymes that synthesize, transport, and modify cyclic β (1,2) glucan.
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Lutz, Brianna, and Junmin Peng. "Deep Profiling of the Aggregated Proteome in Alzheimer’s Disease: From Pathology to Disease Mechanisms." Proteomes 6, no. 4 (November 12, 2018): 46. http://dx.doi.org/10.3390/proteomes6040046.
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Hallmarks of Alzheimer’s disease (AD), a progressive neurodegenerative disease causing dementia, include protein aggregates such as amyloid beta plaques and tau neurofibrillary tangles in a patient’s brain. Understanding the complete composition and structure of protein aggregates in AD can shed light on the as-yet unidentified underlying mechanisms of AD development and progression. Biochemical isolation of aggregates coupled with mass spectrometry (MS) provides a comprehensive proteomic analysis of aggregates in AD. Dissection of these AD-specific aggregate components, such as U1 small nuclear ribonucleoprotein complex (U1 snRNP), provides novel insights into the deregulation of RNA splicing in the disease. In this review, we summarize the methodologies of laser capture microdissection (LCM) and differential extraction to analyze the aggregated proteomes in AD samples, and discuss the derived novel insights that may contribute to AD pathogenesis.
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Oback, F. C., T. Delaney, J. E. Oliver, M. C. Berg, R. S. F. Lee, and D. N. Wells. "109. AGGREGATING CLONED WITH IN VITRO FERTILISED EMBRYOS RESULTS IN CHIMAERAS AND IMPROVED FETAL SUVIVAL IN CATTLE." Reproduction, Fertility and Development 22, no. 9 (2010): 27. http://dx.doi.org/10.1071/srb10abs109.
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Cloning cattle by somatic cell nuclear transfer (NT) results in low survival and high frequencies of abnormal placentation and fetal development. We postulate that such anomalies may be overcome by complementing NT embryos with in vitro fertilised (IVF) embryos to form chimaeras. The gender and germline composition of chimaeras can be experimentally manipulated. Using embryological methods, we aim to produce chimaeric fetuses that are functionally male and produce sperm derived from the somatic NT embryo. Provided sufficient contribution from the IVF embryo, such chimeras should develop more normally than clones. At the 12- to 16-cell stage, individual male NT embryos were aggregated with female IVF embryos derived from X-sorted sperm. Following aggregation, there were no significant difference in blastocyst development between NT/IVF aggregates and disaggregated and re-aggregated IVF and NT controls (86/183 = 47% v. 77/233 = 33% v. 47/109 = 43%, respectively). Suitable quality embryos were transferred individually into synchronised recipient animals. Pregnancy establishment at Day (D) 35 was not significantly different between aggregate, IVF and NT groups (18/57 = 32% v. 11/45 = 24% v. 6/31 = 19%, respectively). Whilst there was no difference in survival between aggregates and IVF controls to ~D100, aggregates survived significantly better than NT controls (16% v. 18% v. 0%; respectively; P < 0.05). In the aggregate group, 7/8 fetuses recovered were phenotypically male. Using RT-PCR, expression of the female-specific mRNA for Xist was detected in 4/5 liver samples, indicating chimaerism. Despite improved survival to ~D100 compared to NT, 3/7 fetuses in the aggregate group still displayed evidence of abnormalities, such as fetal overgrowth. Further studies will explore alternative aggregation strategies and germline transmission of the NT-derived genome in chimaeras.
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Suzuki, Kazumasa, Yasuaki Tokudome, Hiroshi Tsuda, and Masahide Takahashi. "Morphology control of BiFeO3aggregatesviahydrothermal synthesis." Journal of Applied Crystallography 49, no. 1 (February 1, 2016): 168–74. http://dx.doi.org/10.1107/s1600576715023845.
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The assembly of crystalline building units with specific shape-derived properties into aggregates is often required to broaden their practical applications because the properties of the building units can be fully integrated and used in the aggregates owing to their orientation. Herein, morphology-controlled BiFeO3aggregates composed of oriented crystalline building units were fabricatedviaa hydrothermal process without any additives, and the effects of the supersaturation conditions on the aggregation state were investigated. The supersaturation condition, controlled by varying the KOH concentration, was found to affect the shape of the crystalline building units. For lower supersaturation conditions, the morphology of the aggregates was found to be closely related to the shape of the fundamental building units, and the results indicated that oriented attachment occurred between specific crystal faces of the building units. Under a high supersaturation condition, the morphology of the aggregate did not reflect the shape of the building units and a monodispersed spherical aggregate was obtained. Further, the internal microstructures of the aggregates changed from homogeneous and dense to sparse core and dense shell structures with an increasing supersaturation condition. The formation mechanism of these morphology-controlled aggregates is discussed using microstructure analyses. The present approach to control the morphology of aggregates using the shape of the building units and aggregation kinetics could also be applicable for other microcrystalline aggregated systems in addition to BiFeO3.
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Song, Youtao, Yue-xuan Wu, Giman Jung, Yusuf Tutar, Evan Eisenberg, Lois E. Greene, and Daniel C. Masison. "Role for Hsp70 Chaperone in Saccharomyces cerevisiae Prion Seed Replication." Eukaryotic Cell 4, no. 2 (February 2005): 289–97. http://dx.doi.org/10.1128/ec.4.2.289-297.2005.
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ABSTRACT The Saccharomyces cerevisiae [PSI + ] prion is a misfolded form of Sup35p that propagates as self-replicating cytoplasmic aggregates. Replication is believed to occur through breakage of transmissible [PSI + ] prion particles, or seeds, into more numerous pieces. In [PSI + ] cells, large Sup35p aggregates are formed by coalescence of smaller sodium dodecyl sulfate-insoluble polymers. It is uncertain if polymers or higher-order aggregates or both act as prion seeds. A mutant Hsp70 chaperone, Ssa1-21p, reduces the number of transmissible [PSI + ] seeds per cell by 10-fold but the overall amount of aggregated Sup35p by only two- to threefold. This discrepancy could be explained if, in SSA1-21 cells, [PSI + ] seeds are larger or more of the aggregated Sup35p does not function as a seed. To visualize differences in aggregate size, we constructed a Sup35-green fluorescent protein (GFP) fusion (NGMC) that has normal Sup35p function and can propagate like [PSI + ]. Unlike GFP fusions lacking Sup35p's essential C-terminal domain, NGMC did not form fluorescent foci in log-phase [PSI + ] cells. However, using fluorescence recovery after photobleaching and size fractionation techniques, we find evidence that NGMC is aggregated in these cells. Furthermore, the aggregates were larger in SSA1-21 cells, but the size of NGMC polymers was unchanged. Possibly, NGMC aggregates are bigger in SSA1-21 cells because they contain more polymers. Our data suggest that Ssa1-21p interferes with disruption of large Sup35p aggregates, which lack or have limited capacity to function as seed, into polymers that function more efficiently as [PSI + ] seeds.
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Maisonneuve, Etienne, Laetitia Fraysse, Danielle Moinier, and Sam Dukan. "Existence of Abnormal Protein Aggregates in Healthy Escherichia coli Cells." Journal of Bacteriology 190, no. 3 (November 26, 2007): 887–93. http://dx.doi.org/10.1128/jb.01603-07.
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ABSTRACT Protein aggregation is a phenomenon observed in all organisms and has often been linked with cell disorders. In addition, several groups have reported a virtual absence of protein aggregates in healthy cells. In contrast to previous studies and the expected outcome, we observed aggregated proteins in aerobic exponentially growing and “healthy” Escherichia coli cells. We observed overrepresentation of “aberrant proteins,” as well as substrates of the major conserved chaperone DnaK (Hsp70) and the protease ClpXP (a serine protease), in the aggregates. In addition, the protein aggregates appeared to interact with chaperones known to be involved in the aggregate repair pathway, including ClpB, GroEL, GroES, and DnaK. Finally, we showed that the levels of reactive oxygen species and unfolded or misfolded proteins determine the levels of protein aggregates. Our results led us to speculate that protein aggregates may function as a temporary “trash organelle” for cellular detoxification.
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Doetterl, S., J. T. Cornelis, J. Six, S. Bodé, S. Opfergelt, P. Boeckx, and K. Van Oost. "Soil redistribution and weathering controlling the fate of geochemical and physical carbon stabilization mechanisms in soils of an eroding landscape." Biogeosciences 12, no. 5 (March 4, 2015): 1357–71. http://dx.doi.org/10.5194/bg-12-1357-2015.
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Abstract. The role of eroding landscapes in organic carbon stabilization operating as C sinks or sources has been frequently discussed, but the underlying mechanisms are not fully understood. Our analysis aims to clarify the effects of soil redistribution on physical and biogeochemical soil organic carbon (SOC) stabilization mechanisms along a hillslope transect. The observed mineralogical differences seem partly responsible for the effectiveness of geochemical and physical SOC stabilization mechanisms as the mineral environment along the transect is highly variable and dynamic. The abundance of primary and secondary minerals and the weathering status of the investigated soils differ drastically along this transect. Extractable iron and aluminum components are generally abundant in aggregates, but show no strong correlation to SOC, indicating their importance for aggregate stability but not for SOC retention. We further show that pyrophosphate extractable soil components, especially manganese, play a role in stabilizing SOC within non-aggregated mineral fractions. The abundance of microbial residues and measured 14C ages for aggregated and non-aggregated SOC fractions demonstrate the importance of the combined effect of geochemical and physical protection to stabilize SOC after burial at the depositional site. Mineral alteration and the breakdown of aggregates limit the protection of C by minerals and within aggregates temporally. The 14C ages of buried soil indicate that C in aggregated fractions seems to be preserved more efficiently while C in non-aggregated fractions is released, allowing a re-sequestration of younger C with this fraction. Old 14C ages and at the same time high contents of microbial residues in aggregates suggest either that microorganisms feed on old carbon to build up microbial biomass or that these environments consisting of considerable amounts of old C are proper habitats for microorganisms and preserve their residues. Due to continuous soil weathering and, hence, weakening of protection mechanisms, a potential C sink through soil burial is finally temporally limited.
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Doetterl, S., J. T. Cornelis, J. Six, S. Bodé, S. Opfergelt, P. Boeckx, and K. Van Oost. "Soil redistribution and weathering controlling the fate of geochemical and physical carbon stabilization mechanisms in soils of an eroding landscape." Biogeosciences Discussions 11, no. 11 (November 26, 2014): 16227–68. http://dx.doi.org/10.5194/bgd-11-16227-2014.
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Abstract. It has been suggested that eroding landscapes can form C sinks or sources, but the underlying mechanisms are not fully understood. Our analysis aims to clarify the effects of soil redistribution on physical and biogeochemical soil organic carbon (SOC) stabilization mechanisms along a hillslope transect. The observed mineralogical differences seem partly responsible for the effectiveness of geochemical and physical SOC stabilization mechanisms as the mineral environment along the transect is highly variable and dynamic. The abundance of primary and secondary minerals and the weathering status of the investigated soils differ drastically along this transect. Extractable iron and aluminum components are largely abundant in aggregates, but show no strong correlation to SOC, indicating their importance for aggregate stability but not for SOC retention. We further show that pyrophosphate extractable soil components, especially manganese, play a role in stabilizing SOC within non-aggregated mineral fractions. The abundance of microbial residues and measured 14C ages for aggregated and non-aggregated SOC fractions demonstrate the importance of the combined effect of geochemical and physical protection to stabilize SOC after burial at the depositional site. Mineral alteration and the breakdown of aggregates limit the protection of C by minerals and within aggregates temporally. The 14C ages of buried soil indicate that C in aggregated fractions seem to be preserved more efficiently while C in non-aggregated fractions is released, allowing a re-sequestration of younger C with this fraction. Old 14C ages and at the same time high contents of microbial residues in aggregates suggest that microorganisms either feed on old carbon to build up microbial biomass, or that these environments consisting of considerable amounts of old C are proper habitats for microorganisms and preserve their residues. Due to continuous soil weathering and, hence, weakening of protection mechanisms, a potential C sink through soil burial is finally temporally limited.
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Madsen, Jens, Gunna Christiansen, Lise Giehm, and Daniel Otzen. "Release of Pharmaceutical Peptides in an Aggregated State: Using Fibrillar Polymorphism to Modulate Release Levels." Colloids and Interfaces 3, no. 1 (March 26, 2019): 42. http://dx.doi.org/10.3390/colloids3010042.
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Traditional approaches to achieve sustained delivery of pharmaceutical peptides traditionally use co-excipients (e.g., microspheres and hydrogels). Here, we investigate the release of an amyloidogenic glucagon analogue (3474) from an aggregated state and the influence of surfactants on this process. The formulation of peptide 3474 in dodecyl maltoside (DDM), rhamnolipid (RL), and sophorolipid (SL) led to faster fibrillation. When the aggregates were subjected to multiple cycles of release by repeated resuspension in fresh buffer, the kinetics of the release of soluble peptide 3474 from different surfactant aggregates all followed a simple exponential decay fit, with half-lives of 5–18 min and relatively constant levels of release in each cycle. However, different amounts of peptide are released from different aggregates, ranging from 0.015 mg/mL (3475-buffer) up to 0.03 mg/mL (3474-DDM), with 3474-buffer and 3474-RL in between. In addition to higher release levels, 3474-DDM aggregates showed a different amyloid FTIR structure, compared to 3474-RL and 3474-SL aggregates and a faster rate of degradation by proteinase K. This demonstrates that the stability of organized peptide aggregates can be modulated to achieve differences in release of soluble peptides, thus coupling aggregate polymorphism to differential release profiles. We achieved aggregate polymorphism by the addition of different surfactants, but polymorphism may also be reached through other approaches, including different excipients as well as changes in pH and salinity, providing a versatile handle to control release profiles.
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Suhendra, Suhendra. "Kajian Pengaruh Variasi Material Terhadap Kuat Tekan Beton." Jurnal Civronlit Unbari 3, no. 1 (April 30, 2018): 55. http://dx.doi.org/10.33087/civronlit.v3i1.32.
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Aggregate quality is very influential on the strength of the resulting concrete. Both coarse and fine aggregates have various characteristics identified from laboratory test results. This study aims to examine the use of various aggregates for a quality of concrete. The coarse aggregate and the fine aggregate used are obtained from the nearest location to the work to be performed. The quality of the concrete reviewed is K-125, K-175 and K-225. The coarse aggregates used are 1-2 size (in cm), 2-3 size (in cm) crushed aggregate and coral. The fine aggregates used for each of the coarse aggregates are also different. The results showed that the coral aggregate did not meet the gradations of concrete aggregate. While the fine aggregate does not meet the gradation of concrete aggregate for the three types used. The concrete compressive strength test results show the use of coarse aggregates of 2-3 size of crushed and coarse aggregate of corals giving the average compressive strength value required for all planned concrete strength. While concrete using coarse aggregates of rocks of size 1-2 only meet the specified compressive strength, but does not meet the required compressive strength.Key words: Aggregates, concrete, compressive strength
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Fuller, L. G., and Tee Boon Goh. "Stability-energy relationships and their application to aggregation studies." Canadian Journal of Soil Science 72, no. 4 (November 1, 1992): 453–66. http://dx.doi.org/10.4141/cjss92-038.
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The objective of this study was to develop a method to describe aggregate stability-energy relationships using ultrasonic dispersion and to examine the role played by carbohydrate in soil aggregation. Aggregate size fractions (ASF) from three soils were sonified, and dispersed clay and solubilized carbohydrate measured at energy levels ranging from 0 to 1000 kJ L−1. Study soils included an Orthic Black, Orthic Dark Gray, and Orthic Gray Luvisol, representing the change from a prairie ecosystem to an aspen-forest ecosystem. Ultrasonic dispersion of aggregated clay resulted in characteristic "stability curves" for each ASF which obeyed a first-order decay curve and provided two parameters describing the release of clay from soil aggregates with increasing levels of applied energy: the "stability constant" k and the E1/2 value, which are analogous to a first-order rate constant and half-life, respectively. E1/2 values ranged from 51 to 502 kJ L−1.These values were smallest for the Ae horizon of the Orthic Gray Luvisol and greatest for the macroaggregates of the Ahe horizon of the Orthic Dark Gray. Carbohydrates solubilized upon aggregate destruction generally constituted a minor proportion (10%) of the total ASF carbohydrate, indicating that most of the carbohydrate was strongly adsorbed to surfaces. The development of a stability-energy relationship for aggregates provides a means to study the role of binding agents, such as carbohydrate, in the aggregation process. Key words: Aggregates, ultrasonic dispersion, clay, carbohydrate
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Pierce, Ashley M., S. Marcela Loría-Salazar, W. Patrick Arnott, Grant C. Edwards, Matthieu B. Miller, and Mae S. Gustin. "Aggregated particles caused by instrument artifact." Atmospheric Measurement Techniques 11, no. 4 (April 18, 2018): 2225–37. http://dx.doi.org/10.5194/amt-11-2225-2018.
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Abstract. Previous studies have indicated that superaggregates, clusters of aggregates of soot primary particles, can be formed in large-scale turbulent fires. Due to lower effective densities, higher porosity, and lower aerodynamic diameters, superaggregates may pass through inlets designed to remove particles < 2.5 µm in aerodynamic diameter (PM2.5). Ambient particulate matter samples were collected at Peavine Peak, NV, USA (2515 m) northwest of Reno, NV, USA from June to November 2014. The Teledyne Advanced Pollution Instrumentation (TAPI) 602 BetaPlus particulate monitor was used to collect PM2.5 on two filter types. During this time, aggregated particles > 2.5 µm in aerodynamic diameter were collected on 36 out of 158 sample days. On preliminary analysis, it was thought that these aggregated particles were superaggregates, depositing past PM10 (particles < 10 µm in aerodynamic diameter) pre-impactors and PM2.5 cyclones. However, further analysis revealed that these aggregated particles were dissimilar to superaggregates observed in previous studies, both in morphology and in elemental composition. To determine if the aggregated particles were superaggregates or an instrument artifact, samples were investigated for the presence of certain elements, the occurrence of fires, high relative humidity and wind speeds, as well as the use of generators on site. Samples with aggregated particles, referred to as aggregates, were analyzed using a scanning electron microscope for size and shape and energy dispersive X-ray spectroscopy was used for elemental analysis. It was determined, based on the high amounts of aluminum present in the aggregate samples, that a sampling artifact associated with the sample inlet and prolonged, high wind events was the probable reason for the observed aggregates.
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Roh, Seungjun, Rakhyun Kim, Won-Jun Park, and Hoki Ban. "Environmental Evaluation of Concrete Containing Recycled and By-Product Aggregates Based on Life Cycle Assessment." Applied Sciences 10, no. 21 (October 26, 2020): 7503. http://dx.doi.org/10.3390/app10217503.
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This study aims to compare the potential environmental impact of the manufacture and production of recycled and by-product aggregates based on a life cycle assessment and to evaluate the environmental impact and cost when they are used as aggregates in concrete. To this end, the six potential environmental impacts (i.e., abiotic depletion potential, global warming potential, ozone-layer depletion potential, acidification potential, photochemical ozone creation potential, and eutrophication potential) of the manufacture and production of natural sand, natural gravel, recycled aggregate, slag aggregate, bottom ash aggregate, and waste glass aggregate were compared using information from life cycle inventory databases. Additionally, the environmental impacts and cost were evaluated when these aggregates were used to replace 30% of the fine and coarse aggregates in concrete with a design strength of 24 MPa. The environmental impact of concrete that incorporated slag aggregate as the fine aggregates or bottom ash aggregate as the coarse aggregates were lower than that of concrete that incorporated natural aggregate. However, concrete that incorporated bottom ash aggregate as the fine aggregates demonstrated relatively high environmental impacts. Based on these environmental impacts, the environmental cost was found to range from 5.88 to 8.79 USD/m3.
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Veldhuizen, R. A., J. Marcou, L. J. Yao, L. McCaig, Y. Ito, and J. F. Lewis. "Alveolar surfactant aggregate conversion in ventilated normal and injured rabbits." American Journal of Physiology-Lung Cellular and Molecular Physiology 270, no. 1 (January 1, 1996): L152—L158. http://dx.doi.org/10.1152/ajplung.1996.270.1.l152.
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Alveolar surfactant can be separated into two subtypes; large aggregates and small aggregates. Large aggregates represent the surface active form of surfactant and are the metabolic precursors of small aggregates. Previous studies examined the mechanism by which large aggregates are converted into small aggregates in vitro. We used intratracheal injection of radiolabeled large aggregates in rabbits to probe the aggregate conversion in vivo. After this injection, animals were mechanically ventilated for 60 min. After the animals were killed, the lungs were lavaged, and the percentage of radiolabel present in the small aggregate fraction was determined. Our results showed that ventilation resulted in aggregate conversion and that increases in tidal volume, but not in respiratory rate, correlated with increased conversion. Aggregate conversion in rabbits with acute lung injury correlated significantly with severity of injury. We conclude that a change in surface area (i.e., respiration) is necessary for aggregate conversion in vivo and that the ventilation strategy can affect this conversion. Furthermore, increased aggregate conversion in injured lungs might contribute to increased small-to-large aggregate ratios in these lungs compared with normal lungs.
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NG, CHIU-ON, and CHIANG C. MEI. "Effects of a semipervious lens on soil vapour extraction." Journal of Fluid Mechanics 341 (June 25, 1997): 385–413. http://dx.doi.org/10.1017/s002211209700565x.
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We describe a theory for the removal of volatile organic chemicals from an unsaturated soil stratum consisting of highly porous coarse sand layers sandwiching a thin and semipervious lens. Each soil layer is modelled as a periodic array of spherical aggregates formed by solid grains and immobile water trapped by surface tension. Volatile chemicals are vaporized in the mobile air in pores between aggregates, dissolved in the intra-aggregate water, and adsorbed on the surface of soil grains. Using the effective transport equations derived for the aggregated soils, we consider shallow layers with sharp contrast in physical properties. An asymptotic analysis is developed for an axisymmetric geometry, yielding quasi-one-dimensional governing equations for individual layers. At the leading order the flow and the vapour transport are horizontal in the coarse layers but vertical in the semipervious lens. Numerical results are presented for a simple example to demonstrate the significance of the lens permeability, diffusivity and retardation factor, and the aggregate diffusivity in the coarse layers, on the vapour transport during the stages of contamination and air-venting.
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Yamaguchi, D., W. Suzuki, N. Adachi, S. Akagi, S. Watanabe, and S. Takahashi. "97 CLONED CALF PRODUCTION BY AGGREGATION OF SOMATIC CELL NUCLEAR-TRANSFERRED EMBRYOS." Reproduction, Fertility and Development 19, no. 1 (2007): 166. http://dx.doi.org/10.1071/rdv19n1ab97.
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A low pregnancy rate and high frequency of abortion are observed in bovine somatic cell cloning. It is suggested that one of the factors is the low cell number of nuclear-transferred (NT) embryos at the blastocyst stage compared with that of in vivo-derived embryos. We reported that aggregation of bovine NT embryos can develop to blastocysts with cell numbers that are equivalent to in vivo-derived embryos (Akagi et al. 2005 Reprod. Fertil. Dev. 17, 162 abst). In this study, we examined the in vivo development of aggregates of NT embryos after embryo transfer (ET). Following culture in serum-starved medium for 5 to 7 days, fibroblast cells were used as donor cells for NT. NT was performed as previously described (Akagi et al. 2003 Mol. Reprod. Dev. 66, 264–272). Eight-cell stage embryos on Day 2 or 16- to 32-cell stage embryos on Day 4 were used for embryo aggregation after removal of the zona pellucida. Three NT embryos were placed into the depression in a drop of TCM-199 with 50 µg mL−1 phytohemagglutinin for 20 min, and NT aggregates were then moved into the depression in a drop of IVD-101 (Akagi et al. 2005). On Day 7 after NT, ET was performed nonsurgically. Results are summarized in Table 1. Pregnancy rates obtained with the aggregated NT embryos tended to be high compared with the single NT embryos. All pregnant cows in the single NT embryos and 6 of 8 pregnant cows in the aggregated NT embryos were aborted within 90 days. One cow carrying an aggregate of 3 Day 2 NT embryos went to term, and one carrying an aggregate of 3 Day 4 NT embryos is still pregnant at more than 7 months. These results demonstrate that aggregates of 3 NT embryos can develop to term in cattle. Table 1.In vivo development of aggregated NT embryos
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Shapiro, B. I. "Nanoarchitecture of Aggregates of Polymethine Dyes." Fine Chemical Technologies 14, no. 2 (May 20, 2019): 5–14. http://dx.doi.org/10.32362/2410-6593-2019-14-2-5-14.
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In recent years, the class of polymethine (cyanine) dyes has attracted increasing attention of researchers in the field of nanotechnology due to the structural features of their chromophore system and their tendency to form polymolecular states – dye aggregates. The processes of the formation of aggregates with new optical and electronic properties in aqueous solutions were studied as exemplified by anionic thyatrimethinecyanine dyes. It was shown that the aggregates are formed by a “block” mechanism from dimers. The nanoarchitecture of the aggregates is determined by the type of the alkyl substituent in the meso position of the polymethine chain of the dye. The C2H5 group promotes the formation of long-wavelength J-aggregates with the “brickwork” packing of molecules. The CH3 group promotes the formation of short-wave H-units with the “stepladder” packing of molecules. The formation of spatial isomers – J- and H-aggregates from cis and trans conformations of dye molecules – was established. Inorganic and organic cations, which stabilize highly organized aggregate structures, have a significant effect on the formation of aggregated forms of anionic dyes. Thus, the work presents the author's ideas about a new scientific direction – the nanoarchitecture of aggregates of polymethine dyes.
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Guo, L., S. Li, L. Zhong, L. Guo, L. Wang, F. Zhang, Y. Zhang, and M. Wang. "A study on the effects of the fractal characteristics of aggregates on the mechanical behavior of cemented sand and gravel." Materiales de Construcción 71, no. 342 (May 27, 2021): e250. http://dx.doi.org/10.3989/mc.2021.13020.
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Owing to complex aspects of cemented sand and gravel (CSG), such as included unscreened aggregates, CSG properties differ from those of ordinary concrete. Fractal theory is introduced to study the effects of aggregate characteristics on CSG properties, quantifying aggregate gradation and shape. Numerical simulation and analyses show that: (1) improved aggregate gradation decreases the gradation fractal dimension and increases the CSG peak stress and elastic modulus; (2) more irregularly shaped aggregates increase the shape fractal dimension and decrease the CSG peak stress and elastic modulus; (3) the relationship quantified between aggregate characteristics and CSG mechanical properties provides a theoretical basis for aggregate allocation in engineering design and construction. Mixing artificial aggregates can improve aggregate gradation but reduces CSG performance. Appropriately blending artificial and on-site aggregates achieves optimal CSG performance; in this study, this is attained using 20% artificial aggregates added under standard gradation.
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Xiao, L., Y. Hu, P. Greenwood, and N. J. Kuhn. "The use of a raindrop aggregate destruction device to evaluate sediment and soil organic carbon transport." Geographica Helvetica 70, no. 2 (June 15, 2015): 167–74. http://dx.doi.org/10.5194/gh-70-167-2015.
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Abstract. Raindrop impact and subsequent aggregate breakdown can potentially change the movement behaviour of soil fractions and thus alter their transport distances when compared against non-impacted aggregates. In a given water layer, the transport distances of eroded soil fractions, and thus that of the associated substances across landscapes, such as soil organic carbon (SOC) and phosphorous, are determined by the settling velocities of the eroded soil fractions. However, using mineral size distribution to represent the settling velocities of soil fractions, as often applied in current erosion models, would ignore the potential influence of aggregation on the settling behaviour of soil fractions. The destructive effects of raindrops impacting onto aggregates are also often neglected in current soil erosion models. Therefore, the objective of this study is to develop a proxy method to effectively simulate aggregate breakdown under raindrop impact, and further identify the settling velocity of eroded sediment and the associated SOC. Two agricultural soils with different sandy and silty loam textures were subjected to rainfall using a raindrop aggregate destruction device (RADD). The aggregates sustained after raindrop impact were fractionated by a settling tube into six different classes according to their respective settling velocities. The same mass amount of bulk soil of each soil type was also dispersed and sieved into the same six classes, to form a comparison in size distribution. The SOC content was measured for each settled and dispersed class. Our results show the following: (1) for an aggregated soil, applying dispersed mineral grain size distribution, rather than its actual aggregate distribution, to soil erosion models would lead to a biased estimation on the redistribution of eroded sediment and SOC; (2) the RADD designed in this study effectively captures the effects of raindrop impact on aggregate destruction and is thus able to simulate the quasi-natural sediment spatial redistribution; (3) further RADD tests with more soils under standard rainfall combined with local rainfalls are required to optimize the method.
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Bian, Jiangwei, Wenbing Zhang, Zhenzhong Shen, Song Li, and Zhanglan Chen. "Analysis and optimization of mechanical properties of recycled concrete based on aggregate characteristics." Science and Engineering of Composite Materials 28, no. 1 (January 1, 2021): 516–27. http://dx.doi.org/10.1515/secm-2021-0050.
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Abstract The most significant difference between recycled and natural concretes lies in aggregates. The performance of recycled coarse aggregates directly affects the characteristics of recycled concrete. Therefore, an in-depth study of aggregate characteristics is of great significance for improving the quality of recycled concrete. Based on the coarse aggregate content, maximum aggregate size, and aggregate shape, this study uses experiments, theoretical analysis, and numerical simulation to reveal the impact of aggregate characteristics on the mechanical properties of recycled concrete. In this study, we selected the coarse aggregate content, maximum aggregate size, and the aggregate shape as design variables to establish the regression equations of the peak stress and elastic modulus of recycled concrete using the response surface methodology. The results showed that the peak stress and elastic modulus of recycled concrete reach the best when the coarse aggregate content is 45%, the maximum coarse aggregate size is 16 mm, and the regular round coarse aggregates occupy 75%. Such results provide a theoretical basis for the resource utilization and engineering design of recycled aggregates.
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Iversen, M. H., and H. Ploug. "Ballast minerals and the sinking carbon flux in the ocean: carbon-specific respiration rates and sinking velocities of macroscopic organic aggregates (marine snow)." Biogeosciences Discussions 7, no. 3 (May 7, 2010): 3335–64. http://dx.doi.org/10.5194/bgd-7-3335-2010.
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Abstract. Recent observations have shown that fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and organic carbon fluxes are closely correlated in the bathypelagic zones of the ocean. Hence it has been hypothesized that incorporation of biogenic minerals within marine aggregates could either protect the organic matter from decomposition and/or increase the sinking velocity via ballasting of the aggregates. Here we present the first combined data on size, sinking velocity, carbon-specific respiration rate, and composition measured directly in three aggregate types; Emiliania huxleyi aggregates (carbonate ballasted), Skeletonema costatum aggregates (opal ballasted), and aggregates made from a mix of both E. huxleyi and S. costatum (carbonate and opal ballasted). Overall average carbon-specific respiration rate was ~0.13 d−1 and did not vary with aggregate type and size. Ballasting from carbonate resulted in 2- to 2.5-fold higher sinking velocities than aggregates ballasted by opal. We compiled literature data on carbon-specific respiration rate and sinking velocity measured in aggregate of different composition and sources. Compiled carbon-specific respiration rates (including this study) vary between 0.08 d−1 and 0.20 d−1. Sinking velocity increases with increasing aggregate size within homogeneous sources of aggregates. When compared across different particle and aggregate sources, however, sinking velocity appeared to be independent of particle or aggregate size. The calculated carbon remineralization length scale due to microbial respiration and sinking velocity of mm-large marine aggregates was higher for calcite ballasted aggregates as compared to opal-ballasted aggregates. It varied between 0.0002 m−1 and 0.0030 m−1, and decreased with increasing aggregate size.
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Mazarbhuiya, A. M., H. S. Das, and P. Halder. "The Umov effect in cosmic dust analogue fluffy aggregates." Monthly Notices of the Royal Astronomical Society 502, no. 2 (January 28, 2021): 2536–40. http://dx.doi.org/10.1093/mnras/stab230.
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ABSTRACT We investigate the effect of porosity in the Umov effect for the first time using the aggregate dust model. The Umov effect is an inverse correlation between the reflectivity (or geometric albedo) of an object and the degree of linear polarization of light scattered by it. Three different types of fractal aggregates: ballistic agglomeration (BA), ballistic agglomeration with one migration (BAM1), and ballistic agglomeration with two migrations (BAM2) having porosities 0.87, 0.74, and 0.64, respectively (which have the same characteristic radius ∼1 μm), are considered in our simulations. Using the multisphere T-matrix (mstm) code, maximum positive polarization (Pmax) and geometric albedo (A) are calculated for three different fractal aggregated structures considering amorphous silicate composition. Then Pmax and A are plotted against each other in logarithmic scale that shows a linear inverse correlation and a strong porosity dependence. This study shows that the porosity of the aggregates plays a crucial role in the Umov-law diagram. Further, we explore the effect of aggregate size parameter and the effect of composition in the Umov diagram for particles larger than the wavelength of incident radiation. A systematic study is presented in this paper.
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Haka, Abigail S., Inna Grosheva, Ethan Chiang, Adina R. Buxbaum, Barbara A. Baird, Lynda M. Pierini, and Frederick R. Maxfield. "Macrophages Create an Acidic Extracellular Hydrolytic Compartment to Digest Aggregated Lipoproteins." Molecular Biology of the Cell 20, no. 23 (December 2009): 4932–40. http://dx.doi.org/10.1091/mbc.e09-07-0559.
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A critical event in atherogenesis is the interaction of macrophages with subendothelial lipoproteins. Although most studies model this interaction by incubating macrophages with monomeric lipoproteins, macrophages in vivo encounter lipoproteins that are aggregated. The physical features of the lipoproteins require distinctive mechanisms for their uptake. We show that macrophages create an extracellular, acidic, hydrolytic compartment to carry out digestion of aggregated low-density lipoproteins. We demonstrate delivery of lysosomal contents to these specialized compartments and their acidification by vacuolar ATPase, enabling aggregate catabolism by lysosomal acid hydrolases. We observe transient sealing of portions of the compartments, allowing formation of an “extracellular” proton gradient. An increase in free cholesterol is observed in aggregates contained in these compartments. Thus, cholesteryl ester hydrolysis can occur extracellularly in a specialized compartment, a lysosomal synapse, during the interaction of macrophages with aggregated low-density lipoprotein. A detailed understanding of these processes is essential for developing strategies to prevent atherosclerosis.
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Iversen, M. H., and H. Ploug. "Ballast minerals and the sinking carbon flux in the ocean: carbon-specific respiration rates and sinking velocity of marine snow aggregates." Biogeosciences 7, no. 9 (September 7, 2010): 2613–24. http://dx.doi.org/10.5194/bg-7-2613-2010.
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Abstract. Recent observations have shown that fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and organic carbon fluxes are closely correlated in the bathypelagic zones of the ocean. Hence it has been hypothesized that incorporation of biogenic minerals within marine aggregates could either protect the organic matter from decomposition and/or increase the sinking velocity via ballasting of the aggregates. Here we present the first combined data on size, sinking velocity, carbon-specific respiration rate, and composition measured directly in three aggregate types; Emiliania huxleyi aggregates (carbonate ballasted), Skeletonema costatum aggregates (opal ballasted), and aggregates made from a mix of both E. huxleyi and S. costatum (carbonate and opal ballasted). Overall average carbon-specific respiration rate was ~0.13 d−1 and did not vary with aggregate type and size. Ballasting from carbonate resulted in 2- to 2.5-fold higher sinking velocities than those of aggregates ballasted by opal. We compiled literature data on carbon-specific respiration rate and sinking velocity measured in aggregates of different composition and sources. Compiled carbon-specific respiration rates (including this study) vary between 0.08 d−1 and 0.20 d−1. Sinking velocity increases with increasing aggregate size within homogeneous sources of aggregates. When compared across different particle and aggregate sources, however, sinking velocity appeared to be independent of particle or aggregate size. The carbon-specific respiration rate per meter settled varied between 0.0002 m−1 and 0.0030 m−1, and decreased with increasing aggregate size. It was lower for calcite ballasted aggregates as compared to that of similar sized opal ballasted aggregates.
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Wei, Peng, Yong Chao Zheng, Yu Chen, Yun Sheng Zheng, Hao Peng, and Yan Jun Liu. "Control of Blended Aggregate Gradation for Quality Concrete." Applied Mechanics and Materials 488-489 (January 2014): 304–11. http://dx.doi.org/10.4028/www.scientific.net/amm.488-489.304.
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As quality aggregate resources are exhausting with massive construction development, inferior aggregate resources somehow are the only picks on the jobsite. The negative impact of inferior aggregates on the workability of fresh concrete is becoming pronounced worrisome on the constructability of concrete structures due mainly to their poor gradation. Therefore, intelligent approach must be found to make fresh concrete workable and consistent while using inferior aggregates. In this study, uniform aggregate gradation curve, Aggregate Coarseness Factor (ACF) and Workability Factor (WF) were used to control the gradation of blended aggregates for achieving desirable workability of fresh concrete. Experimental study and engineering practices indicate that uniform aggregate gradation curve cooperating with ACF and WF are reliable tools to control workability of fresh concrete and obtain quality concrete while only poor aggregates available.
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Aoyama, M., D. A. Angers, and A. N'Dayegamiye. "Particulate and mineral-associated organic matter in water-stable aggregates as affected by mineral fertilizer and manure applications." Canadian Journal of Soil Science 79, no. 2 (May 1, 1999): 295–302. http://dx.doi.org/10.4141/s98-049.
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Application of cattle manure generally improves soil structure and organic matter (OM) content. However, changes in forms and location of OM within the aggregate structure are less well known. The effects of long-term (18-yr) applications of cattle manure (20 Mg ha–1 yr−1) and NPK fertilizer on the distribution of particulate and mineral-associated organic matter in water-stable aggregates were investigated in a Le Bras loam (Humic Gleysol). Soil samples from the 0- to 10-cm depth were taken from the untreated control, NPK, manure and NPK + manure treatments. They were separated into four aggregate-size fractions (>1000 µm, 250–1000 µm, 53–250 µm, and <53 µm) by slaking air-dried soil, followed by wet sieving. Particulate (>53 µm) and mineral-associated OM (<53 µm) were separated from water-stable aggregates >53 µm by sieving after mechanical dispersion. After 18 yr, manure increased the OM level of the whole soil and favored formation of slaking-resistant macroaggregates (250–1000 µm). This effect was primarily a result of the OM added by the manure. In contrast, NPK fertilizer did not affect soil OM level or macroaggregation. The increase in OM induced by manure application was observed primarily in macroaggregates, and both as mineral-associated and particulate OM. However, manure did not change OM located in the fraction <53 µm confirming that recently deposited OM preferentially accumulates within the aggregate structure and not in the finely or non-aggregated material. Since previous studies have shown that most of the C in cattle manure is composed of coarse particles, we hypothesize that manure-derived OM first enters the soil primarily as particulate material, then, during decomposition, is transformed within the aggregate structure into mineral-associated material thereby contributing to aggregate stabilization. Key words: Cattle manure, mineral fertilization, particulate organic matter, soil structure
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Le, Hoai Nga, Frank Babick, Klaus Kühn, Minh Tan Nguyen, Michael Stintz, and Gianaurelio Cuniberti. "Impact of ultrasonic dispersion on the photocatalytic activity of titania aggregates." Beilstein Journal of Nanotechnology 6 (December 17, 2015): 2423–30. http://dx.doi.org/10.3762/bjnano.6.250.
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The effectiveness of photocatalytic materials increases with the specific surface area, thus nanoscale photocatalyst particles are preferred. However, such nanomaterials are frequently found in an aggregated state, which may reduce the photocatalytic activity due to internal obscuration and the extended diffusion path of the molecules to be treated. This paper investigates the effect of aggregate size on the photocatalytic activity of pyrogenic titania (Aeroxide® P25, Evonik), which is widely used in fundamental photocatalysis research. Well-defined and reproducible aggregate sizes were achieved by ultrasonic dispersion. The photocatalytic activity was examined by the color removal of methylene blue (MB) with a laboratory-scale setup based on a plug flow reactor (PFR) and planar UV illumination. The process parameters such as flow regime, optical path length and UV intensity are well-defined and can be varied. Our results firstly show that a complete dispersion of the P25 aggregates is not practical. Secondly, the photocatalytic activity is not further increased beyond a certain degree of dispersion, which probably corresponds to a critical size for which UV irradiation can penetrate the aggregate without significant obscuration.
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Choong, Wee Kang, Lau Teck Leong, Choon Seng Sin, and Abdullahi Ali Mohamed. "Effects of Recycled Aggregates on Water-Cement Ratio for Concrete." Applied Mechanics and Materials 423-426 (September 2013): 1010–13. http://dx.doi.org/10.4028/www.scientific.net/amm.423-426.1010.
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Recycled aggregate differs from primary aggregate in that it constitutes of two types of materials: the primary aggregate and the attaching cement mortar. This study was conducted in order to investigate the effects on water-cement ratio for concrete cast with recycled aggregates derived from different origins (hollow blocks & structural concrete elements) and different mixed proportions of recycled aggregate contents. The outcomes of test indicate that higher water cement ratios are required for concrete cast with recycled aggregates as compare to those cast with primary aggregates. Also there appear no obvious relationships or consistencies that can be drawn among types of recycled aggregate.
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GRANT, C. D., B. D. KAY, P. H. GROENEVELT, G. E. KIDD, and G. W. THURTELL. "SPECTRAL ANALYSIS OF MICROPENETROMETER DATA TO CHARACTERIZE SOIL STRUCTURE." Canadian Journal of Soil Science 65, no. 4 (November 1, 1985): 789–804. http://dx.doi.org/10.4141/cjss85-083.
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A micropenetrometer with a diameter similar in magnitude to that of a root is capable of measuring variations in tip resistance over distances as small as 0.1 mm. Measurements at this scale offer the potential of characterizing zones of high resistance to penetration and the frequency of occurrence of zones of low resistance which could be exploited by a growing root. Spectral analysis provides a new approach to characterizing soil structure and has been applied to the micropenetrometer tip resistance profiles obtained from beds of aggregates. Nine different aggregate size ranges were considered; the aggregate diameters varied from less than 0.36 mm to 6.4–12.8 mm. The analyses indicate that larger aggregates are more resistant to penetration. In addition, comparison of variance spectra among several of the aggregate sizes reveals information on the structural make up of soil aggregates, namely that larger aggregates are made up of smaller "component" aggregates which offer higher resistance when they occur in large aggregates than when they occur individually in loose packing. The use of spectral analysis also appears to provide information on the spatial separation of zones of low resistance which correlate with aggregate size if the aggregate diameters are larger than 1.6 mm. Key words: Soil strength, soil resistance to penetration, micropenetrometer, aggregate size
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Yun, Jonghyun, Sanggoo Kang, Amin Darabnoush Tehrani, and Suyun Ham. "Image Analysis and Functional Data Clustering for Random Shape Aggregate Models." Mathematics 8, no. 11 (October 31, 2020): 1903. http://dx.doi.org/10.3390/math8111903.
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This study presents a random shape aggregate model by establishing a functional mixture model for images of aggregate shapes. The mesoscale simulation to consider heterogeneous properties concrete is the highly cost- and time-effective method to predict the mechanical behavior of the concrete. Due to the significance of the design of the mesoscale concrete model, the shape of the aggregate is the most important parameter to obtain a reliable simulation result. We propose image analysis and functional data clustering for random shape aggregate models (IFAM). This novel technique learns the morphological characteristics of aggregates using images of real aggregates as inputs. IFAM provides random aggregates across a broad range of heterogeneous shapes using samples drawn from the estimated functional mixture model as outputs. Our learning algorithm is fully automated and allows flexible learning of the complex characteristics. Therefore, unlike similar studies, IFAM does not require users to perform time-consuming tuning on their model to provide realistic aggregate morphology. Using comparative studies, we demonstrate the random aggregate structures constructed by IFAM achieve close similarities to real aggregates in an inhomogeneous concrete medium. Thanks to our fully data-driven method, users can choose their own libraries of real aggregates for the training of the model and generate random aggregates with high similarities to the target libraries.
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Wang, Enheng, Richard M. Cruse, Xiangwei Chen, and Aaron Daigh. "Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability." Canadian Journal of Soil Science 92, no. 3 (March 2012): 529–36. http://dx.doi.org/10.4141/cjss2010-044.
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Wang, E., Cruse, R. M., Chen, X. and Daigh, A. 2012. Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability. Can. J. Soil Sci. 92: 529–536. Freeze/thaw cycles can affect soil aggregate stability, which in turn impacts wind and water erosion. The objectives of this laboratory study were: (1) to determine the effect of variable freeze/thaw cycles and soil water conditions on aggregate size distribution and stability; and (2) to evaluate differences in aggregate size distribution and stability between disturbed soil and undisturbed soil cores as affected by freeze/thaw cycles and soil water conditions. Surface soil was collected before freezing in late fall of 2009. Aggregates isolated from disturbed soil or intact soil cores were subjected to a factorial combination of 3 gravimetric water content treatments: 0.15 m3 m−3, 0.23 m3 m−3 or 0.30 m3 m−3, and 3 freeze/thaw treatments: 0, 3, or 9 cycles. A freeze/thaw cycle involved soil freezing at –10∘C for 24 h, followed by thawing at 5∘C for 24 h. Most aggregate size classes were affected significantly (P<0.05) by freeze/thaw cycles except for wet-sieved aggregates >5 mm. Dry-sieved aggregates were relatively more sensitive to the freeze/thaw treatment than wet-sieved aggregates. The mean weight diameter (MWD) of dry-sieved aggregates was significantly (P<0.05) greater at 0.30 m3 m−3 than 0.15 m3 m−3 water content, but the opposite trend was observed for MWD of wet aggregates and aggregate stability. There was a significant (P<0.05) response of the MWD in dry-sieved aggregates to the interactive freeze/thaw×water content effect that differed for aggregates obtained from disturbed soil and those in the undisturbed soil core, but not for the MWD of wet-sieved aggregates and aggregate stability.
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Khan, Suhail Mushtaq. "A Study Based upon the Usage Recycled Aggregate to Enhance the Strength Aspects of Conventional Concrete: A Critical Review." International Journal for Research in Applied Science and Engineering Technology 9, no. VI (June 20, 2021): 1567–70. http://dx.doi.org/10.22214/ijraset.2021.35222.
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Recycled aggregates are those crushed cement concrete or asphalt pavement which comes out from the construction debris which is reused in construction. They are made from the reprocessing of materials which have been used in previous constructions. This paper discusses about the study of properties of recycled aggregates from the sources which has already been published. The results are that 100% replacement of natural aggregate by recycled concrete aggregate effect on chloride ions resistance, it plays negative effects on durability of recycled concrete aggregates, and addition of fiber in recycled aggregate concrete mixture gave more effective in the performance of concrete. On experimental study of recycled aggregate, compressive, flexural and split tensile strength of the recycled aggregate were found to be lower than that of the natural aggregate. Use of recycled aggregate in a new concrete production is still limited. Recommendation of introduction of recycled aggregates standard is required for the materials to be used successfully in future. Gaps in literature reviews are also included in this paper.
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LAINÉ, Jean, and Denis LeBEL. "Efficient binding of regulated secretory protein aggregates to membrane phospholipids at acidic pH." Biochemical Journal 338, no. 2 (February 22, 1999): 289–94. http://dx.doi.org/10.1042/bj3380289.
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Some regulated secretory proteins are thought to be targeted to secretory granules through an acidic-dependent aggregation in the trans-Golgi network. In this report we use pancreatic zymogens, a paradigm of regulated proteins, to test this hypothesis, because they qualitatively aggregate upon acidification in vitro. Pig zymogens were found to start to aggregate significantly at pH ∼ 6.0, a pH slightly lower than that at which rat zymogens aggregate, but still compatible with the pH of the cell-sorting compartments. When pig zymogen granule membranes were mixed with the zymogens in the aggregation assay, membranes that normally floated on 1 M sucrose were observed to be pelleted by the aggregating zymogens. Rat membranes were pelleted by pig zymogens and vice versa. Igs, typical constitutively secreted proteins, which needed chemical cross-linking to serve as an aggregated protein control, pelleted membranes almost independently of pH. Corresponding cross-linked zymogen-binding ability and pH dependence was unaffected by the chemical modification. Membranes treated with sodium carbonate, pH 11, or with protease K, were still pelleted by zymogens, suggesting that the aggregated zymogens bound to membrane lipids. This hypothesis was confirmed by the efficient pelleting of unilamellar vesicles composed of granule membrane lipids. Vesicles composed of single classes of phospholipids were also pelleted, but with various efficacies. We conclude that pancreatic zymogen aggregates, formed under the acidic conditions of the secretory pathway sorting compartments, have the capacity to bind firmly to membranes through their phospholipid constituents.
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MAITI, NAKUL C., SHYAMALAVA MAZUMDAR, and N. PERIASAMY. "J- and H-Aggregates of Porphyrins with Surfactants: Fluorescence, Stopped Flow and Electron Microscopy Studies." Journal of Porphyrins and Phthalocyanines 02, no. 05 (October 1998): 369–76. http://dx.doi.org/10.1002/(sici)1099-1409(199807/10)2:4/5<369::aid-jpp92>3.0.co;2-3.
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The interaction of cationic surfactants such as CTAB (cetyl trimethyl ammonium bromide) with tetrakis-(4-sulfonato phenyl) porphine ( H 4 TPPS 2−), a dianion, leads to the formation of two premicellar aggregates of porphyrin when [CTAB] is below CMC (critical micelle concentration) and a micellized monomer when [CTAB] is above CMC. The premicellar aggregates are labeled as J- and H-aggregates because of their characteristic spectroscopic properties. Simple inorganic cations such as K +, Ba 2+, Ca 2+ and Zr 4+ also induce the formation of the J-aggregate but not of the H-aggregate. The formation of the J-aggregate is preceded by kinetic intermediates, while no intermediate was observed prior to the formation of the H-aggregate. The rate of formation of the H-aggregate was faster than that of the J-aggregate. The fluorescence depolarization (anisotropy) properties of the monomer and the H- and J-aggregates were studied and compared. The size and structure of the J-aggregate were examined by transmission electron microscopy (TEM). The structure of the J-aggregate reveals a fiber-like (linear stacking) or domain-like (helical stacking) arrangement of the porphyrin molecules.
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Ahmad, Juraidah, Mohd Yusof Abdul Rahman, and Zainab Mohamed. "Consensus and Source Properties of Malaysian Aggregates for Superior Performing Asphalt Pavements." Scientific Research Journal 5, no. 1 (June 30, 2008): 53. http://dx.doi.org/10.24191/srj.v5i1.5653.
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Aggregates and binder are the two main constituents that make up hot mix asphalt (HMA). Since a wide variety of mineral aggregate is used to produce Hot Mix Asphalt (HMA), proper evaluation of the mineral aggregate properties is important to ensure good performance of asphalt mixture. Unlike Superpave system, Marshall and Hveem method do not incorporate aggregate criteria into their procedures. The Superpave Highway Research Programme (SHRP) modified the Delphi process to include aggregate properties which are divided into two categories; consensus and source. The consensus properties include aggregate angularity, flat and elongated particles and sand equivalent to ensure aggregate quality is sufficient to provide satisfactory HMA performance for all design traffic levels. The source properties are often used to qualify local source of aggregate which include abrasion, deleterious materials and soundness test. In this study, granite aggregates were collected from northern, central and southern region of Peninsular Malaysia. Results of the aggregate testing showed that Malaysian aggregates are durable and of good quality. These aggregates conformed to the criteria as required in the Superpave system, hence suitable for use in the mix design.
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Basu, Susanto, and John G. Fernald. "Aggregate Productivity and the Productivity of Aggregates." International Finance Discussion Paper 1995, no. 532 (December 1995): 1–52. http://dx.doi.org/10.17016/ifdp.1995.532.
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Fernandes, Isabel, Özge Andiç-Çakır, and Doug Hooton. "Assessing aggregates for alkali–aggregate reaction potential." Proceedings of the Institution of Civil Engineers - Construction Materials 169, no. 3 (June 2016): 172–78. http://dx.doi.org/10.1680/jcoma.15.00060.
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Gmachowski, Lech. "Aggregate structure and hydrodynamics of aggregated systems." Colloids and Surfaces A: Physicochemical and Engineering Aspects 255, no. 1-3 (March 2005): 105–10. http://dx.doi.org/10.1016/j.colsurfa.2004.12.028.
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