Academic literature on the topic 'Aggregati stabili'

The amount of bonds between constituting parts of a protein aggregate were determined in wild type (WT) and A53T α-synuclein (αS) oligomers, amyloids and in the complex of thymosin-β4–cytoplasmic domain of stabilin-2 (Tβ4-stabilin CTD). A53T αS aggregates have more extensive βsheet contents reflected by constant regions at low potential barriers in difference (to monomers) melting diagrams (MDs). Energies of the intermolecular interactions and of secondary structures bonds, formed during polymerization, fall into the 5.41 kJ mol−1 ≤ Ea ≤ 5.77 kJ mol−1 range for αS aggregates. Monomers lose more mobile hydration water while forming amyloids than oligomers. Part of the strong mobile hydration water–protein bonds break off and these bonding sites of the protein form intermolecular bonds in the aggregates. The new bonds connect the constituting proteins into aggregates. Amyloid–oligomer difference MD showed an overall more homogeneous solvent accessible surface of A53T αS amyloids. From the comparison of the nominal sum of the MDs of the constituting proteins to the measured MD of the Tβ4-stabilin CTD complex, the number of intermolecular bonds connecting constituent proteins into complex is 20(1) H2O/complex. The energies of these bonds are in the 5.40(3) kJ mol−1 ≤ Ea ≤ 5.70(5) kJ mol−1 range.

Soil aggregates have great effects on soil properties and soil functions. Mulching (organic inputs) has been known as a factor influencing soil aggregate stability. Our study aimed to reveal the causes of the higher stability of soil aggregates under organic mulches. The primary soil characteristics such as organic carbon (Cox), humus quality (E4/E6), potential wettability index (PWI), and aromaticity index (iAR) were determined. The Cox was measured using rapid dichromate oxidation, and E4/E6 was measured using the UV-Vis spectrophotometry. The PWI and iAR were determined according to the intensity of selected bands in diffuse reflectance infrared spectra. Results showed that mulched plots contained higher Cox content in aggregates in comparison with whole soil. This indicates that the carbon was stabilized within the aggregates and sequestrated into the soil. The iAR was significantly higher after using the organic mulches, the aliphatic components of the organic matter thus contribute more to the aggregates stabilization. The PWI of aggregates was found to be higher after applying these mulches than in soil. Organic mulches are therefore able to reduce the wettability of the aggregates and also to protect the aggregate from dispersion with water.

Soil structure is a very important soil property, which influences many processes in the soil. There are many methods for aggregate stability measurement varying in the energy applied in the treatment. The aim of this paper is to compare two aggregate stability measurement methods on a set of reclaimed dumpsite soils. Method proposed by Le Bissonnias (1996) is composed of three tests, which allow distinguishing the particular aggregate breakdown mechanisms. Results can be expressed by a coefficient of vulnerability (Kv). Results of the second method, assessment of water stable aggregates, can be expressed by WSA index. WSA indexes mainly correspond to the results of the first test, which qualify the aggregate breakdown during the fast wetting. A strong statistically significant relationship was found between WSA and Kv for each test. Correlation coefficients were –0.767, –0.806, and –0.741 for linear models. Our conclusion is that results of both methods are comparable.

  The study on the relationship between the soil aggregates stability assessed using water stable aggregate (WSA) index and the selected terrain and soil properties was performed on a morphologically diverse study site in Chernozem soil region of Southern Moravia. Soil analyses and detailed digital elevation model processing were the main methods adopted in the study. The soil structure stability is negatively influenced by the soil material removal from the steep parts of the back-slope and re-deposition of the mineral loess material at the base of the slope. The highest aggregates stability was identified in the upper flat parts of the study plot, undisturbed by erosion processes, and at the concave parts of the back-slope with intensive accumulation of organic matter. Statistical analysis showed a significant dependence of aggregates stability on organic carbon content and plan curvature index.

Soil aggregate instability on unprotected roadside slopes can cause landslide, soil erosion and sedimentation. Different biological and chemical soil stabilizers are used to reinforce the instable slopes. In the present study, straw mulch and Polyacrylamide (PAM) combinations were investigated on a clay soil of road cutslope in campus of Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran. The selected cover treatments were Polyacrylamide (2, 3 and 4 g·m–2) with wheat straw mulch (50, 150 and 250 g·m–2) which was spread by hand to attain 75% groundcover on a 1:1 slope. After the three months, soil sampling was done to determine the changes in aggregate stability of soil. Results showed that the most efficient treatment with respect to mean weight diameter of soil aggregates in dry and wet sieving (MWDdry and MWDwet), aggregate stability index (AS) and aggregate destruction index (DI) was treatment of B (150 g·m–2 wheat straw mulch and 3 g·m–2 Polyacrylamide tackifier) with 34%, 68% and 47% increment in MWDdry, MWDwet and AS, respectively as well as 37% reduction in DI as compared to the bare soil control.<br /><br />

A field experiment was conducted to examine the influence of various organic materials on soil aggregate stability and soil microbiological properties on the Loess Plateau of China. The study involved seven treatments: no fertilizer (CK); inorganic N, P, K fertilizer (NPK); low amount of maize stalks plus NPK (LSNPK); medium amount of maize stalks plus NPK (MSNPK); high amount of maize stalks plus NPK (HSNPK); maize stalk compost plus NPK (CNPK); cattle manure plus NPK (MNPK). The organic fertilizer treatments improved soil aggregate stability and soil microbiological properties compared with CK and NPK treatments. Compared with the NPK treatment, soil treated with LSNPK had a significant increase of 27.1% in 5&ndash;3 mm dry aggregates. The &gt; 5 mm water stable aggregates treated with CNPK increased by 6.5% compared to the NPK. Soil microbial biomass C and N and urease activity were significantly increased in CNPK by 42.0, 54.6 and 19.8%, respectively. The study indicated that the variation trend in the amount of soil aggregate (0.5&ndash;5 mm) for organic fertilizer treatments was similar to the content of soil microbial carbon and nitrogen and soil enzyme activity. Considering the great availability of organic material, especially stalk compost in this region, application of organic materials is recommended to improve soil structure and fertility.

One of the most important binding agents for forming stable aggregates is a soil organic matter (SOM), which can be retained in various size fractions of aggregates. If aggregates are water-resistant, they retain more carbon. Therefore, the aim of this study was to evaluate the stability of aggregates and their ability of carbon sequestration in different soil types and soil management systems in Slovakian vineyards. The highest content of water-stable macro-aggregates (WSA_ma) was determined in Cambisols, and the lowest in Fluvisols. The highest content of WSA_ma (size fraction 0.5&ndash;3 mm) was determined in Chernozems, decreasing within the following sequence: Fluvisols &gt; Leptosols &gt; Cambisols &gt; Luvisols. The soil type had a statistically significant influence on the re-distribution of soil organic matter in size fractions of water-stable aggregates. The highest content of SOM in water-stable aggregates of the vineyards was determined in grassy strips in-between the vineyard rows in comparison to intensively cultivated rows of vineyard. The highest values of carbon sequestration capacity (CSC) in WSA_ma were found in Cambisols &gt; Leptosols and the lowest values of CSC were in Fluvisols. The micro-aggregates represented a significant carbon reservoir for the intensively cultivated soils (rows of vineyard). On the other hand, increasing of macro-aggregates (size fraction 0.5&ndash;3 mm) was characteristic for grassland soils (between the rows of vineyard).

The stability characteristics of soluble nano-sized quinoa protein isolates prepared by different high-pressure homogenization in terms of droplet size and lipid oxidation were studied. Commercial quinoa protein isolates (QPI) were exposed to high-pressure homogenization (HPH) at various pressure (50, 100 and 200 MPa) and pressure cycles (one-cycle and two cycles). The quinoa isolate aggregates were utilized to produce oil-in-water nanoemulsions, which demonstrated the good stabile characteristics for 28 day of storage at 4 oC. While quinoa protein / canola oil nanoemulsions (QPCON) produced with untreated QPI and QPI samples by other HPH treatments were shown a significant increase in terms of droplet size and lipid oxidation in 28 days of storage, QPI samples treated with HPH at 100 MPa for a cycle (100 MPa-1) was found as the most efficient treatment in the stability of protein aggregate sizes and less oxidation level. The sample showed a slight increase from 98 nm to 117 nm for droplet size and from 58 to 102 mmol/kg for lipid oxidation from day 0 to day 28.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting the upper and lower motor neurons causing muscle atrophy and paralysis followed by death. Aggregates containing superoxide dismutase (SOD1) are found as pathological hallmark in diseased ALS patients. Consequently ALS is regarded as a protein misfolding disorder like Alzheimer’s disease and Parkinson’s disease. So far, little is known about the cause and mechanism behind SOD1 aggregation but the inherent property of all polypeptide chains to form stable aggregated structures indicates that the protein misfolding diseases share a common mechanism. Our results show that SOD1 aggregation starts from the globally unfolded state, since fibrillation is fastest at full occupancy of denatured protein induced either by chemical denaturation or mutation. Even so, the fibrillation rate shows a surprisingly weak dependence on the concentration of globally unfolded SOD1 indicating fibril fragmentation as the dominant mechanism for aggregate formation. This is further supported by the observation that the SOD1 sample has to be mechanically agitated for fibrillation to occur.  Interestingly, we observe a similar SOD1 aggregation behaviour in vivo, where the survival times of ALS transgenic mice correlates with mutant stability, and aggregate growth depends weekly on the concentration of unfolded monomer. Additionally, in-cell NMR measurements reveal that in live cells the thermodynamic equilibrium is shifted towards the unfolded state of SOD1, which is also more fully extended than in vitro. This suggests that the globally unfolded aggregation competent protein is more abundant in the crowded environment in vivo than dilute in vitro conditions. Finally, antibody analysis of aggregates from ALS transgenic mice reveals the existence of aggregate strains involving different parts of the protein depending on mutation, which may offer an explanation for the various disease phenotypes observed in ALS. Altogether these findings provide important clues for understanding SOD1 aggregation with implications for ALS, as well as other protein misfolding diseases.

Fort Hood Military Reservation is a 900 km2 military installation located between Killeen, Copperas Cove, and Gatesville in central Texas. It supports two full armored divisions which require year-round, live-fire maneuvers and training (Ft. Hood, 2003). As a result of the constant foot traffic and use of heavy equipment, the soils on the training ranges have become increasingly compacted, eroded, and stripped of vegetation. This study evaluated the impact that selected soil amendments would have on soil aggregation, infiltration, and levels of glomalin. A field study was done on plots located inside Fort Hood on a Nuff silty clay (fine-silty, carbonatic, thermic Udic Calciustoll). The plots were amended with composted dairy manure, inorganic fertilizers, and native grass seed. Aggregate stability was determined using a wet sieving procedure and total glomalin values were quantified using a Bradford assay. Field measurements of infiltration rates were taken using a drip-type rainfall simulator. Aggregate stability exhibited decreased values over time for all treatments but two (Site Prep / No Seed and Site Prep / Compost / Seed). In addition, three treatments changed significantly over time (from before treatment application to after treatment application). These treatments were the Site Prep / Compost / No Seed, No Prep / No Seed, and No Prep / Seed treatments. Levels of glomalin increased significantly over time for all treatments (p-value <0.001). Glomalin was correlated to aggregate stability after treatments were applied (p-value <0.01) but not before (p-value 0.89). In addition, infiltration rates were not related to glomalin (p-value 0.9) or aggregate stability (p-value 0.09). Additional sampling of Fort Hood beyond the plot study demonstrates significant differences in aggregate stability, infiltration rates, and levels of glomalin. Measurements taken from ten sites showed no correlations between aggregate stability, infiltration rates, or glomalin. Organic C was correlated to percent water stable aggregates (%WSA) and levels of glomalin. These results illustrate the relationship between organic C and aggregate stability as well as glomalin levels in maintaining infiltration rates and reducing soil loss by erosion.

The study of aggregation propensity of a monoclonal antibody (mAb) and its sensitivity to applied stresses is believed to correlate with the overall stability of the mAb. As such, the aggregation propensity under various stresses can be used to develop a unique aggregation metric to rank order a panel of mAbs based on their stability. Often in a drug discovery campaign, multiple mAbs may imbue the desired in vivo efficacy, at which point identification of the most developable mAb becomes an important factor to decide on a single candidate for further development. This study focuses on the assessment of the stability of a panel of mAbs, by defining their propensity for aggregation along the native and non-native aggregation pathways. Kosmotrope based solubility evaluates a mAb’s colloidal stability, or propensity for native aggregation, while differential scanning fluorescence reports conformational stability, or propensity for non-native aggregation. By combining the conformational and colloidal stability metrics, an overall aggregation propensity profile can be generated for a mAb. To parse out further information on stability, the mAb panel was exposed to a series of stresses, which mimic stresses a mAb based drug would be exposed to during manufacturing and storage. After exposure to stress, the mAb panel was then monitored for change in apparent colloidal and conformational stability. There was no variation in the stability metrics measured, as a function of stress. However, observed precipitation denoted differential sensitivity to the stresses. Combining observational data with the stability metrics measured, allowed for rank ordering of aggregation propensity, and overall stability.

Contrary to the significant increases of incarceration rates in the United States and England, Canada has maintained relatively stable incarceration rates for the years 1978 2004. However, this overall stability conceals not only bifurcated trends of increasing and decreasing incarceration rates but also significant variation within these trends at the federal, provincial, and territorial sub-levels. As such, this thesis reveals -- on a theoretical level -- that Canada has not entirely resisted the shift towards increasing punitiveness. From a policy perspective, it is suggested that the competing trends must be monitored to avoid exacerbation to the point in which justice is brought into disrepute. This work also raises a methodological question of whether punitiveness is best measured in terms of admissions or counts data.

The effects of biological and physical processes on the aggregate stability of some weakly structured arable and pasture soils were investigated. Preliminary investigations showed significant correlations between soil organic matter and both wet sieving and turbidimetric methods of aggregate stability; the latter method was chosen on grounds of convenience. Scanning electron microscope pictures showed the presence of both fungi and bacteria when soils were incubated. Growth of fungi, estimated by ergosterol measurement, correspond to temporary stability increases, which could be explained by retention of soil particles within the reticulum of fungal hyphae. The effect disappeared as the fungi were destroyed and replaced by bacteria and actinomycetes. Effects caused by fungi were examined separately, using vancomycin to inhibit bacterial growth, and bacterial effects by using cycloheximide to eliminate fungi. Bacterial growth had little direct effect in stabilising soil aggregates; periodate oxidation showed that polysaccharides produced by bacteria are mainly responsible. To examine the contribution of physical processes to increased stability in remoulded soils biological processes were eliminated by sterilisation. Thixotropic changes made a contribution to age hardening in remoulded aggregates similar in magnitude to biological processes. Thixotropic changes were reversible and accompanied by soil strength and metric water potential changes. Polysaccharides did not contribute to thixotropic aging processes. Remoulded soils were subjected to wetting/drying and freezing/thawing cycles. After 3 to 6 cycles the stability of both sterilised and unsteriliserd soils recovered to that of natural aggregates, suggesting a contribution by thixotropy. Repeated weathering cycles decreased the stability of unsterilised, and more so sterilised, field aggregates suggesting that in the former, bond reformation due to biological activity counteracted the destruction caused by wetting/drying and freezing/thawing.

Human platelets aggregated by thrombin (T) under conditions in which the release reaction (RR) occurs to only a small extent can be deaggregated by agents that dissociate 125I-fibrinogen bound to platelets. In contrast, when platelets undergo the RR, they cannot be reading deaggregated even though combinations of inhibitors cause 125I-fibrinogen to dissociate. Therefore, material released from platelet granules seems to stabilize aggregates. T-induced aggregates of washed platelets deficient in fibrinogen or von Willebrand factor cannot be deaggregated readily by deaggregating agents, implying that released fibrinogen or von Willebrand factor do not have a major role in stabilizing aggregates. To examine the role of platelet (δ-granule contents in stabilizing platelet aggregates, aggregation and deaggregation were studied with platelets from patients with (δ- Storage Pool Deficiency (δ- SPD). Platelet aggregation and the release ofβ-TG in response to T (1 U/ml) were similar for platelets from patients and controls. Platelets from patients (but not from controls) could be deaggregated by PGE1 (10 uM) plus chymotrypsin (10 U/ml), with hirudin (5 U/ml) added to block further effects of T. Addition of ADP (20 uM) to the (5-SPD platelets 5 sec after T abolished the ability of this combination of inhibitors to deaggregate the platelets. The addition of serotonin (2 uM) 5 sec after T did not prevent inhibitors from deaggregating δ-SPD platelets. When apyrase was added to normal platelets immediately before they were aggregated by T, the combination of inhibitors readily deaggregated the platelets. Therefore, released ADP may stabilize platelet aggregates through a mechanism that could be independent of released fibrinogen and von Willebrand factor.

Abstract The fate of particulate matter in the ocean is determined in large part by its size and settling rate. Disaggregation, caused by turbulence-induced shear, acts to fracture or erode large particles into slower-settling sub-aggregates and primary particles. The strength and breakup response of organic marine aggregates (i.e. marine snow particles consisting of phytoplankton) is poorly understood, limiting our ability to accurately predict marine particle transport effects on the global carbon cycle. A study was conducted to enable the investigation of disaggregation effects on these organic marine particle aggregates. Due to the fragile nature of the Phytoplankton cells and their resulting aggregates, test facilities that do not rely on external sampling or pumps are required. A novel rolling aggregation tank was developed that can both aggregate phytoplankton cells under varying hydrodynamic conditions and then expose them to calibrated shear forces using laminar oscillating flow. The theory behind the operation of this tank is presented along with the necessary operating conditions to create stable regions within the tank where particle settling effects are minimal but shear is still representative of values expected in the open ocean. Phytoplankton was cultured in the laboratory to create simulated marine snow particles in the open ocean for disaggregation experiments. The procedure to calculate and track the shear-history of each aggregate is described and how the data generated from this facility will be used to quantify disaggregation parameters relevant for population balance modeling is discussed.

Due to unique and tunable optical properties, gold nanoparticles (GNPs) are becoming more widely used in biological and biomedical applications. However, nanoparticles in fluid tend to lose the specific function because of aggregation in the transport process of use. Therefore, it is necessary to investigate the aggregation behavior for having a good understanding of aggregation mechanism and inhibiting GNPs aggregation. A MD simulation in this study was performed to investigate the physical aggregation behavior of GNPs in biological media. By analyzing the aggregation proportion of GNPs in different conditions and the changes in center-to-center distance between GNPs with the time, the effects of the hydrophilic/hydrophobic characteristics of GNPs, velocity of ionic solution, size of GNPs, initial distance between two GNPs, and surface charge were discussed. The simulation results indicate that the aggregation proportion of GNPs with hydrophilic modification is 62.5%, which is less than 87.5% in the model without surface modification, while the final aggregation proportion of GNPs with hydrophobic modification increased to 100%. When the velocity of the NaCl aqueous solution is 0.1 m/s, the final aggregation proportion of GNPs is 87.5%, which is similar with the model without flow velocity. But the final aggregation proportion increased to 100% when the velocity is 1m/s. Under the same conditions, the GNPs of 1 nm diameter aggregated at 0.16 ns, but the GNPs of 1.5 nm and 2 nm diameters aggregated at 0.6 ns and 0.8 ns, respectively. For the GNPs of 1 nm diameter, the GNPs can only get close to each other very slowly when the distance between the surfaces of GNPs is within the range of 0.8–1.2 nm, whereas the GNPs will aggregate quickly when the distance is close enough. GNPs can retain stable by modified with appropriate negative charge. But ions in the solution will weaken this effect.

Ferrohydrodynamics research has been approached predominantly from either numerical or basic experimental techniques. However, to date, these experimental techniques have been limited to ultrasonic point measurements or shadowgraphs due to the opacity of the ferrofluids. As a result, the complete dynamics of many ferrohydrodynamics flows have remained unexplored. In this work, Time Resolved Digital Particle Image Velocimetry (TRDPIV) is employed to fully resolve the dynamic interaction of ferrofluid aggregates with bulk nonmagnetic fluids. This topic is hydrodynamically rich, where shearing between the aggregate and bulk flow develop into the Kelvin-Helmholtz instability. Ferrofluid aggregates are mixed with fluorescent particles in order to enable visualization of the internal flow structure of the aggregate and generate quantitative velocity measurements. The TRDPIV measurements are made in a 15 mm square channel where ferrofluid retained by a 0.5 Tesla permanent magnet is studied as it disperses. The effects of both steady and pulsatile flows are quantified, as are the impact of varying the magnetic field gradients. In both steady and pulsatile flows, a recirculation region is observed within the ferrofluid, driven by the shear layer between the bulk flow and aggregate interface. The interaction of the aggregate with the flow is also governed by the aggregate height relative to that of the test section. Higher, larger aggregates are less stable, and therefore, more likely to be dispersed by the bulk flow. As the aggregate diminishes in size, it is both more stable and is less subject to shearing forces from the flow. Flow pulsatility enriches the dynamics of the flow and generates complex flow structures resulting from interaction between the aggregate and bulk flow. This work is the first to explore the rich spatiotemporal behavior of dispersing ferrofluid aggregates interacting with steady and unsteady bulk flows.

Interest in roller-compacted concrete (RCC) pavement has been increasing because of its low initial cost, construction efficiency, and ability to open to traffic early. Current RCC mixture design methods do not directly consider the aggregate source or optimal cement content. An experimental testing plan was developed to batch RCC mixtures with several aggregate sources, gradations, paste contents, and water-cement (w/c) ratios. Each aggregate blend was compacted in order to determine the intergranular volume of voids. The volume of cement paste was varied to underfill, equifill, and overfill the compacted aggregate voids. Green properties (green strength, green modulus, and softening modulus) were measured on the lab compacted specimens to assess the fresh RCC capacity, stability, and plasticity. Green and hardened properties were then related to the RCC mixture volumetric parameters. Green properties were sensitive to aggregate type and gradation, ratio of voids filled by paste, w/c ratio, and total paste content, which all affected the mixes adhesion and shear resistance. In most cases, high cement contents did not improve green or hardened properties. RCC mixtures containing crushed aggregates achieved maximum green strength and stability with underfilled voids, while RCC with rounded aggregates required overfilling the voids. Workability (Vebe time) measurements were not sensitive unless voids were overfilled and not highly sensitive to w/c ratio.

Pulse proteins are currently being extensively used for the development of various food products. In this work we focused on the utilization of pulse proteins in the development of beverage emulsions. Soluble proteins solution (2.5 wt%), separated from pea protein concentrate (PPC) via centrifugation at 4000×g for 1 minute, was directly used to prepare 5 wt% canola oil-in-water emulsions using high-pressure homogenization. It was hypothesized that soluble protein extracted via mild fractionation would preserve protein functionality and confer better stability to emulsions when compared to original PPC solutions. The emulsions were characterized by measuring the droplet size, zeta potential and creaming velocity. Emulsions were also subjected to environmental stresses including heat treatment, change in pH (2 and 7) and the addition of salt (0.0 M to 1 M). The initial average droplet sizes of pH 7 emulsions were around 300 nm at various salt concentrations, which did not change significantly after 1 week. The pH 2 emulsions initially showed extensive aggregation, with the average droplet and aggregate sizes ranging from 3.0 to 8.8 µm with an increase in salt concentration, which however, decreased significantly to below 1 µm after 1 week, due to breakdown of droplet aggregates over time. Upon heating the emulsions to 90 °C, extensive droplet aggregation was observed in all emulsions leading to emulsion destabilization. To prevent heat-induced emulsion destabilization, soluble protein solution was heated, and the emulsions were made under hot conditions to overcome the problem of protein and droplet aggregation-induced emulsion destabilization. Based on different emulsion characterization tests, it was found that 0.5 M salt-added heated-protein-stabilized emulsion at pH 7 had the highest stability with the lowest average droplet size (below 300 nm). Heat treated soluble pea proteins accompanied with NaCl could serve as a potential high-value emulsifiers for the beverage industry.

The physics of steady and pulsatile flows laden with superparamagnetic nanoparticles in a square channel accumulating under the influence of a 0.5 Tesla permanent magnet are studied by means of focused shadowgraphs. The accumulation physics of these nanoscale particles is explored as functions of the flow type (steady and unsteady) and accumulation type (injected from the top of channel versus bottom of channel). Ferrofluid is accumulated by the steady injection of a streakline that enters the test section upstream of the magnet, where an aggregate forms. The interfacial phenomena resulting from the interaction of the ferrofluid with the bulk flow is resolved using shadowgraph imaging, where a digital camera captures the side view of the aggregate. Ferrofluid aggregate physics is examined both visually in the raw frames as well as by post-processing to determine the aggregate size evolution in time and couple that bulk information with interfacial behavior using the Proper Orthogonal Decomposition (POD). The shadowgraphs show that the aggregate exhibits different regimes based on bulk flow Reynolds number, which is varied between 100 and 1000, based on the mean flow rate. The aggregate exhibits stable behavior at low Reynolds numbers, where it stretches as it grows and minimal decay of the aggregate occurs. At moderate Reynolds numbers above 400, inertial forces dominate the dynamics, and aggregates do not attain the same size and height as in low Reynolds number cases. Therefore, the interaction of the aggregate with the bulk flow is diminished. The accumulation of ferrofluids is positively impacted by increased magnetic field gradients for some Reynolds numbers, while very high or low magnetic field gradients result in smaller, unstable aggregates. This work is the first to study the accumulation of ferrofluid aggregates over such a large parameter space, which reveals many physics that were previously unexplored in ferrohydrodynamics.

We have performed numerical simulation to investigate the restructuring capability of an isolated non-fractal aggregate in simple shear flow. The change in structure of aggregate having different initial packing properties is numerically examined by a Lagrangian approach. Stokesian dynamics is employed as a rigorous method for the calculation of the hydrodynamic interaction, while the inter-particle interaction is estimated by Van der Waals potential. Simulation results show that under the effect of the rotational component and the extensional component of shear flow, the aggregate simultaneously rotates and changes its outer shape and inner connectivity, then it reaches stable state. Correspondingly, the coordination number varies periodically with the rotation and then approaches a stable value different from the initial one. During the progress toward stable state, the relation between coordination number and volume fraction is independent of shear condition but related to the most compact structure that the aggregate is possible to obtain by restructuring. Such behaviors are observed for different aggregates whose initial structure varies from loose to dense. Moreover, at the stable state, the stable structure is strongly dependent on the applied shear stress and the most compact structure rather than the initial configuration.

The paper addresses the state estimation problem for a general class of nonlinear systems. Using an expansion of nonlinear drift dynamics in terms of an aggregate model, the authors analyze the stability of the estimation error equation. Although the treatment is limited to linear feedback, the method results in quadratically stable error dynamics inside a large subset of the state space. The authors tested and verified the proposed approach on the nonlinear dynamics of the rotary pendulum.

Due to instability in the first in vitro period, platelet-aggregometry is usually deliberately postponed until ca. 1 hour after venepuncture (VP) . At that time aggregability is fairly constant for 1 hour or more. Investigation of the period immediately followed VP, hcwever, revealed a high aggregation resistance - measured as the threshold ADP-concentration which the platelets just could resist before they aggregate maximally and irreversibly - which subsequently decreased exponentially with time. This “Transient Aggregation Resistance” (TAR) appeared to be superimposed on a stable, so called Baseline Aggregation Resistance (BAR) .The latter, measurable 60 min or more after VP, yields the “classical” threshold ADP-concentration.Parallel aggregation-studies started 6 min after VP, subsequent studies were performed every 4 min. pH was controlled during storage of PRP at rocmtenperature. Extrapolation of the TAR-curve to t=0 (i.e. time of VP) yields the maximal value:TARmax Coefficients of variation for TARmax-method: 9.4% (n=6) ; intraindividial 15% (n=15, over 3 yrs); interindividual: 51% (n=16,wide range).This TAR-phencmenon which is proven to be caused by a plasma-factor, can be influenced by dietary n-3 fattty acids and can be also inhibited by ASA,suggesting a prostanoid nature. The physiological significance of TAIfoax can be illustrated by the following findings:1. Patients with myocardial infarction, hyperlipoproteinemia, sickle cell anemia (i.e. diseases with a high risk for thrombotic complications) have low TARmax-values. 2.Individuals with “spontaneous platelet aggregation” in vitro,but asymptomatic, have positive TARmax-values. 3.There is a clear,reciproke age-dependency of TARmax It is concluded that a technique is available measuring the effect of circulating,labile platelet-aggregation influencing plasma factor(s). Furthermore, using this technique,it was found that normal fresh plasma contains a labile aggregation-inhibiting factor which is several orders of magnitude more potent than other stabile factors either present in plasma or associated with platelets. This factor is probably of prostanoid nature and might have significance as a reflection of the antithrcmbotic potential of the endothelium.

This report presents a case study for constructing aggregate subgrade improvement (ASI) layers using quarry by-product aggregates (QBA), a quarry mix of large primary crushed rocks (PCR) and sand-sized quarry fines. The construction took place at Larry Power Road in Bourbonnais Township in Kankakee County, Illinois, where the Illinois Department of Transportation placed two QBA mixes. The first mix (QBA_M1) consisted of 45% quarry by-products and 55% railroad ballast–sized 3×1 PCR. The second mix (QBA_M2) consisted of 31% and 69% quarry by-products and PCR, respectively. Two conventional ASI sections were also constructed conforming to Illinois Department of Transportation’s CS02 gradation. All sections consisted of a 9 in. (229 mm) QBA/PCR layer topped with a 3 in. (76 mm) dense-graded capping layer. Laboratory studies preceded the construction to recommend optimum quarry by-product content in the QBA materials and construction practice. The Illinois Center for Transportation research team monitored the quality and uniformity of the construction using nondestructive testing techniques such as dynamic cone penetrometer, lightweight deflectometer, and falling weight deflectometer. The segregation potential was monitored by visual inspection and imaging-based techniques. Short-term field evaluation of the constructed QBA layers, particularly QBA_M2 with a 31% quarry by-product content, showed no evidence of abnormal segregation and did not jeopardize the structural integrity of the QBA ASI layers, which had slightly lower but comparable strength and stiffness profiles to the conventional ASI sections. The use of QBA materials in ASI was field validated as a sustainable construction practice to provide stable pavement foundation layers.

Concentrated flow erosion in rills, pipes, ephermal gullies, and gullies is a major contributor of downstream sedimentation. When rill or gullies form in a landscape, a 3- to 5-fold increase in soil loss commonly occurs. The balance between the erosive power of the flow and the erosion resistance of the bed material determines the rate of concentrated flow erosion. The resistance of the bed material to detachment depends primarily on the magnitude of the interparticle forces or cohesion holding the particles and aggregates together. The effect of soil properties on bed material resistance and concentrated flow erosion was evaluated both in the laboratory and field. Both rill erodibility and critical hydraulic shear were greater when measured in 9.0 m long rills under field conditions compared with laboratory mini-flumes. A greater hydraulic shear was required to initiate erosion in the field compared to the mini-flume because of the greater aggregate and clod size and stability. Once erosion was initiated, however, the rate of erosion as a function of hydraulic shear was greater under field conditions because of the greater potential for slaking upon wetting and the greater soil surface area exposed to hydraulic shear. Erosion tests under controlled laboratory conditions with the mini-flume allowed individual soil variables to be studied. Attempts to relate rill erosion to a group soil properties had limited success. When individual soil properties were isolated and studied separately or grouped separately, some trends were identified. For example, the effect of organic carbon on rill erodibility was high in kaolinitic soils, low in smectitic soils, and intermediate in the soils dominated by illite. Slow prewetting and aging increased the cohesion forces between soil particles and decreased rill erodibility. Quick prewetting increased aggregate slaking and increased erodibility. The magnitude of the effect of aging depended upon soil type. The effect of clay mineralogy was evaluated on sand/clay mixtures with montmorillonite (M), Illite (I), and kaolinite (K) clays. Montmorillonite/sand mixtures were much less erodible than either illite or kaolonite sand mixtures. Na-I and Na-K sand mixtures were more erodible than Ca-I and Ca-K due to increased strength from ionic bonding and suppression of repulsive charges by Ca. Na-M was less erodiblethan Ca-M due to increased surface resulting from the accessibility of internal surfaces due to Na saturation. Erodibility decreased when salt concentration was high enough to cause flocculation. This occurred between 0.001 mole L-1 and 0.01 mole L-1. Measuring rill erodibility in mini-flumes enables the measurement of cohesive forces between particles and enhances our ability to learn more about cohesive forces resisting soil detachment under concentrated water flow.

This report presents findings on the evaluation of foundation layers under concrete pavements in the state of Illinois. It also provides recommendations and scenarios where unbound granular layers can be safely used under concrete pavements as economical and well-performing subbase layers. The current practice and mechanistic design methods for constructing concrete pavements in Illinois was first evaluated, including historical studies that led to the current design procedures and policies. The performance of concrete pavements with unbound granular layers in Illinois were then evaluated, and several case studies of well-performing concrete pavements with granular subbases, high traffic levels, and low distress levels and severity were realized. Next, the practices of surrounding states were evaluated, and several Midwest states, i.e., Wisconsin, Minnesota, Iowa, and Michigan, were found to regularly use unbound granular layers under concrete pavements with no issues. A literature review on the most recent requirements and recommendations for designing granular subbases under concrete pavements was then presented. It is concluded that subbase layers under concrete pavements are mainly used to provide uniform support and prevent pumping. Based on the case study evaluations and literature, a stable, drainable, and durable daylighted granular subbase design is recommended for traffic factors up to 10.0. Stability is ensured by limiting the ratio of gravel-to-sand fractions in the aggregate mix between 1.3 and 1.9. Drainability requirements can be met by limiting the percentage of fines passing the No. 200 sieve (0.075 mm) to 4% and by checking the quality of drainage is at least fair based on the time required to drain 50% of the water. Lastly, a geotextile fabric is recommended for use below the granular subbase for separation to ensure drainability throughout design life.

Behavioral interactions between conspecific animals can be influenced by relatedness and familiarity. To test how kinship and familiarity influenced social behavior in juvenile Eastern Box Turtles (Terrapene carolina), 16 captive-born individuals were reared under semi-natural conditions in four equally sized groups, where each group comprised pairs of siblings and non-siblings. Using separation distance between pairs of turtles in rearing enclosures as a measure of gregariousness, we found no evidence suggesting siblings more frequently interacted with one another compared to non-relatives over the first five months of life. Average pair separation distance decreased during this time but may have been due to turtles aggregating around resources like heat and moist retreat areas as colder temperatures approached. At eight months old, we again measured repeated separation distances between unique pair combinations and similarly found no support for associations being influenced by kinship. Agonistic interactions between individuals were never observed. Based on our results, group housing and rearing of juvenile box turtles did not appear to negatively impact their welfare. Unlike findings for other taxa, our results suggest strategically housing groups of juvenile T. carolina to maintain social stability may not be an important husbandry consideration when planning releases of captive-reared individuals for conservation purposes.

Clavibactermichiganensissubsp. michiganensis(Cmm), the causal agent of bacterial wilt and canker of tomato, is the most destructive bacterial disease of tomato causing substantial economic losses in Israel, the U.S.A. and worldwide. The goal of the project was to unravel the molecular strategies that allow Cmm, a Gram-positive bacterium, to develop a successful infection in tomato. The genome of Cmm contains numerous genes encoding for extracellular serine proteases and cell wall degrading enzymes. The first objective was to elucidate the role of secreted serine proteases in Cmm virulence. Mutants of nine genes encoding serine proteases of 3 different families were tested for their ability to induce wilting, when tomato stems were puncture-inoculated, as compared to blisters formation on leaves, when plants were spray-inoculated. All the mutants showed reduction in wilting and blister formation as compared to the wild type. The chpCmutant displayed the highest reduction, implicating its major role in symptom development. Five mutants of cell wall degrading enzymes and additional genes (i.e. perforin and sortase) caused wilting but were impaired in their ability to form blisters on leaves. These results suggest that Cmm differentially expressed virulence genes according to the site of penetration. Furthermore, we isolated and characterized two Cmmtranscriptional activators, Vatr1 and Vatr2 that regulate the expression of virulence factors, membrane and secreted proteins. The second objective was to determine the effect of bacterial virulence genes on movement of Cmm in tomato plants and identify the routes by which the pathogen contaminates seeds. Using a GFP-labeledCmm we could demonstrate that Cmm extensively colonizes the lumen of xylem vessels and preferentially attaches to spiral secondary wall thickening of the protoxylem and formed biofilm-like structures composed of large bacterial aggregates. Our findings suggest that virulence factors located on the chp/tomAPAI or the plasmids are required for effective movement of the pathogen in tomato and for the formation of cellular aggregates. We constructed a transposon plasmid that can be stably integrated into Cmm chromosome and express GFP, in order to follow movement to the seeds. Field strains from New York that were stably transformed with this construct, could not only access seeds systemically through the xylem, but also externally through tomato fruit lesions, which harbored high intra-and intercellular populations. Active movement and expansion of bacteria into the fruit mesocarp and nearby xylem vessels followed, once the fruit began to ripen. These results highlight the ability of Cmm to invade tomato fruit and seed through multiple entry routes. The third objective was to assess correlation between disease severity and expression levels of Cmm virulence genes and tomato defense genes. The effect of plant age on expression of tomato defense related proteins during Cmm infection was analyzed by qRT-PCR. Five genes out of eleven showed high induction at early stages of infection of plants with 19/20 leaves compared to young plants bearing 7/8 leaves. Previous results showed that Cmm virulence genes were expressed at early stages of infection in young plants compared to older plants. Results of this study suggest that Cmm virulence genes may suppress expression of tomato defense-related genes in young plants allowing effective disease development. The possibility that chpCis involved in suppression of tomato defense genes is currently under investigation by measuring the transcript level of several PR proteins, detected previously in our proteomics study. The fourth objective was to define genome location and stability of virulence genes in Cmm strains. New York isolates were compared to Israeli, Serbian, and NCPPB382 strains. The plasmid profiles of New York isolates were diverse and differed from both Israeli and Serbian strains. PCR analysis indicated that the presence of putative pathogenicity genes varied between isolates and highlighted the ephemeral nature of pathogenicity genes in field populations of Cmm. Results of this project significantly contributed to the understanding of Cmm virulence, its movement within tomato xylem or externally into the seeds, the role of serine proteases in disease development and initiated research on global regulation of Cmm virulence. These results form a basis for developing new strategies to combat wilt and canker disease of tomato.

1.1 Macroeconomic summary Economic recovery has consistently outperformed the technical staff’s expectations following a steep decline in activity in the second quarter of 2020. At the same time, total and core inflation rates have fallen and remain at low levels, suggesting that a significant element of the reactivation of Colombia’s economy has been related to recovery in potential GDP. This would support the technical staff’s diagnosis of weak aggregate demand and ample excess capacity. The most recently available data on 2020 growth suggests a contraction in economic activity of 6.8%, lower than estimates from January’s Monetary Policy Report (-7.2%). High-frequency indicators suggest that economic performance was significantly more dynamic than expected in January, despite mobility restrictions and quarantine measures. This has also come amid declines in total and core inflation, the latter of which was below January projections if controlling for certain relative price changes. This suggests that the unexpected strength of recent growth contains elements of demand, and that excess capacity, while significant, could be lower than previously estimated. Nevertheless, uncertainty over the measurement of excess capacity continues to be unusually high and marked both by variations in the way different economic sectors and spending components have been affected by the pandemic, and by uneven price behavior. The size of excess capacity, and in particular the evolution of the pandemic in forthcoming quarters, constitute substantial risks to the macroeconomic forecast presented in this report. Despite the unexpected strength of the recovery, the technical staff continues to project ample excess capacity that is expected to remain on the forecast horizon, alongside core inflation that will likely remain below the target. Domestic demand remains below 2019 levels amid unusually significant uncertainty over the size of excess capacity in the economy. High national unemployment (14.6% for February 2021) reflects a loose labor market, while observed total and core inflation continue to be below 2%. Inflationary pressures from the exchange rate are expected to continue to be low, with relatively little pass-through on inflation. This would be compatible with a negative output gap. Excess productive capacity and the expectation of core inflation below the 3% target on the forecast horizon provide a basis for an expansive monetary policy posture. The technical staff’s assessment of certain shocks and their expected effects on the economy, as well as the presence of several sources of uncertainty and related assumptions about their potential macroeconomic impacts, remain a feature of this report. The coronavirus pandemic, in particular, continues to affect the public health environment, and the reopening of Colombia’s economy remains incomplete. The technical staff’s assessment is that the COVID-19 shock has affected both aggregate demand and supply, but that the impact on demand has been deeper and more persistent. Given this persistence, the central forecast accounts for a gradual tightening of the output gap in the absence of new waves of contagion, and as vaccination campaigns progress. The central forecast continues to include an expected increase of total and core inflation rates in the second quarter of 2021, alongside the lapse of the temporary price relief measures put in place in 2020. Additional COVID-19 outbreaks (of uncertain duration and intensity) represent a significant risk factor that could affect these projections. Additionally, the forecast continues to include an upward trend in sovereign risk premiums, reflected by higher levels of public debt that in the wake of the pandemic are likely to persist on the forecast horizon, even in the context of a fiscal adjustment. At the same time, the projection accounts for the shortterm effects on private domestic demand from a fiscal adjustment along the lines of the one currently being proposed by the national government. This would be compatible with a gradual recovery of private domestic demand in 2022. The size and characteristics of the fiscal adjustment that is ultimately implemented, as well as the corresponding market response, represent another source of forecast uncertainty. Newly available information offers evidence of the potential for significant changes to the macroeconomic scenario, though without altering the general diagnosis described above. The most recent data on inflation, growth, fiscal policy, and international financial conditions suggests a more dynamic economy than previously expected. However, a third wave of the pandemic has delayed the re-opening of Colombia’s economy and brought with it a deceleration in economic activity. Detailed descriptions of these considerations and subsequent changes to the macroeconomic forecast are presented below. The expected annual decline in GDP (-0.3%) in the first quarter of 2021 appears to have been less pronounced than projected in January (-4.8%). Partial closures in January to address a second wave of COVID-19 appear to have had a less significant negative impact on the economy than previously estimated. This is reflected in figures related to mobility, energy demand, industry and retail sales, foreign trade, commercial transactions from selected banks, and the national statistics agency’s (DANE) economic tracking indicator (ISE). Output is now expected to have declined annually in the first quarter by 0.3%. Private consumption likely continued to recover, registering levels somewhat above those from the previous year, while public consumption likely increased significantly. While a recovery in investment in both housing and in other buildings and structures is expected, overall investment levels in this case likely continued to be low, and gross fixed capital formation is expected to continue to show significant annual declines. Imports likely recovered to again outpace exports, though both are expected to register significant annual declines. Economic activity that outpaced projections, an increase in oil prices and other export products, and an expected increase in public spending this year account for the upward revision to the 2021 growth forecast (from 4.6% with a range between 2% and 6% in January, to 6.0% with a range between 3% and 7% in April). As a result, the output gap is expected to be smaller and to tighten more rapidly than projected in the previous report, though it is still expected to remain in negative territory on the forecast horizon. Wide forecast intervals reflect the fact that the future evolution of the COVID-19 pandemic remains a significant source of uncertainty on these projections. The delay in the recovery of economic activity as a result of the resurgence of COVID-19 in the first quarter appears to have been less significant than projected in the January report. The central forecast scenario expects this improved performance to continue in 2021 alongside increased consumer and business confidence. Low real interest rates and an active credit supply would also support this dynamic, and the overall conditions would be expected to spur a recovery in consumption and investment. Increased growth in public spending and public works based on the national government’s spending plan (Plan Financiero del Gobierno) are other factors to consider. Additionally, an expected recovery in global demand and higher projected prices for oil and coffee would further contribute to improved external revenues and would favor investment, in particular in the oil sector. Given the above, the technical staff’s 2021 growth forecast has been revised upward from 4.6% in January (range from 2% to 6%) to 6.0% in April (range from 3% to 7%). These projections account for the potential for the third wave of COVID-19 to have a larger and more persistent effect on the economy than the previous wave, while also supposing that there will not be any additional significant waves of the pandemic and that mobility restrictions will be relaxed as a result. Economic growth in 2022 is expected to be 3%, with a range between 1% and 5%. This figure would be lower than projected in the January report (3.6% with a range between 2% and 6%), due to a higher base of comparison given the upward revision to expected GDP in 2021. This forecast also takes into account the likely effects on private demand of a fiscal adjustment of the size currently being proposed by the national government, and which would come into effect in 2022. Excess in productive capacity is now expected to be lower than estimated in January but continues to be significant and affected by high levels of uncertainty, as reflected in the wide forecast intervals. The possibility of new waves of the virus (of uncertain intensity and duration) represents a significant downward risk to projected GDP growth, and is signaled by the lower limits of the ranges provided in this report. Inflation (1.51%) and inflation excluding food and regulated items (0.94%) declined in March compared to December, continuing below the 3% target. The decline in inflation in this period was below projections, explained in large part by unanticipated increases in the costs of certain foods (3.92%) and regulated items (1.52%). An increase in international food and shipping prices, increased foreign demand for beef, and specific upward pressures on perishable food supplies appear to explain a lower-than-expected deceleration in the consumer price index (CPI) for foods. An unexpected increase in regulated items prices came amid unanticipated increases in international fuel prices, on some utilities rates, and for regulated education prices. The decline in annual inflation excluding food and regulated items between December and March was in line with projections from January, though this included downward pressure from a significant reduction in telecommunications rates due to the imminent entry of a new operator. When controlling for the effects of this relative price change, inflation excluding food and regulated items exceeds levels forecast in the previous report. Within this indicator of core inflation, the CPI for goods (1.05%) accelerated due to a reversion of the effects of the VAT-free day in November, which was largely accounted for in February, and possibly by the transmission of a recent depreciation of the peso on domestic prices for certain items (electric and household appliances). For their part, services prices decelerated and showed the lowest rate of annual growth (0.89%) among the large consumer baskets in the CPI. Within the services basket, the annual change in rental prices continued to decline, while those services that continue to experience the most significant restrictions on returning to normal operations (tourism, cinemas, nightlife, etc.) continued to register significant price declines. As previously mentioned, telephone rates also fell significantly due to increased competition in the market. Total inflation is expected to continue to be affected by ample excesses in productive capacity for the remainder of 2021 and 2022, though less so than projected in January. As a result, convergence to the inflation target is now expected to be somewhat faster than estimated in the previous report, assuming the absence of significant additional outbreaks of COVID-19. The technical staff’s year-end inflation projections for 2021 and 2022 have increased, suggesting figures around 3% due largely to variation in food and regulated items prices. The projection for inflation excluding food and regulated items also increased, but remains below 3%. Price relief measures on indirect taxes implemented in 2020 are expected to lapse in the second quarter of 2021, generating a one-off effect on prices and temporarily affecting inflation excluding food and regulated items. However, indexation to low levels of past inflation, weak demand, and ample excess productive capacity are expected to keep core inflation below the target, near 2.3% at the end of 2021 (previously 2.1%). The reversion in 2021 of the effects of some price relief measures on utility rates from 2020 should lead to an increase in the CPI for regulated items in the second half of this year. Annual price changes are now expected to be higher than estimated in the January report due to an increased expected path for fuel prices and unanticipated increases in regulated education prices. The projection for the CPI for foods has increased compared to the previous report, taking into account certain factors that were not anticipated in January (a less favorable agricultural cycle, increased pressure from international prices, and transport costs). Given the above, year-end annual inflation for 2021 and 2022 is now expected to be 3% and 2.8%, respectively, which would be above projections from January (2.3% and 2,7%). For its part, expected inflation based on analyst surveys suggests year-end inflation in 2021 and 2022 of 2.8% and 3.1%, respectively. There remains significant uncertainty surrounding the inflation forecasts included in this report due to several factors: 1) the evolution of the pandemic; 2) the difficulty in evaluating the size and persistence of excess productive capacity; 3) the timing and manner in which price relief measures will lapse; and 4) the future behavior of food prices. Projected 2021 growth in foreign demand (4.4% to 5.2%) and the supposed average oil price (USD 53 to USD 61 per Brent benchmark barrel) were both revised upward. An increase in long-term international interest rates has been reflected in a depreciation of the peso and could result in relatively tighter external financial conditions for emerging market economies, including Colombia. Average growth among Colombia’s trade partners was greater than expected in the fourth quarter of 2020. This, together with a sizable fiscal stimulus approved in the United States and the onset of a massive global vaccination campaign, largely explains the projected increase in foreign demand growth in 2021. The resilience of the goods market in the face of global crisis and an expected normalization in international trade are additional factors. These considerations and the expected continuation of a gradual reduction of mobility restrictions abroad suggest that Colombia’s trade partners could grow on average by 5.2% in 2021 and around 3.4% in 2022. The improved prospects for global economic growth have led to an increase in current and expected oil prices. Production interruptions due to a heavy winter, reduced inventories, and increased supply restrictions instituted by producing countries have also contributed to the increase. Meanwhile, market forecasts and recent Federal Reserve pronouncements suggest that the benchmark interest rate in the U.S. will remain stable for the next two years. Nevertheless, a significant increase in public spending in the country has fostered expectations for greater growth and inflation, as well as increased uncertainty over the moment in which a normalization of monetary policy might begin. This has been reflected in an increase in long-term interest rates. In this context, emerging market economies in the region, including Colombia, have registered increases in sovereign risk premiums and long-term domestic interest rates, and a depreciation of local currencies against the dollar. Recent outbreaks of COVID-19 in several of these economies; limits on vaccine supply and the slow pace of immunization campaigns in some countries; a significant increase in public debt; and tensions between the United States and China, among other factors, all add to a high level of uncertainty surrounding interest rate spreads, external financing conditions, and the future performance of risk premiums. The impact that this environment could have on the exchange rate and on domestic financing conditions represent risks to the macroeconomic and monetary policy forecasts. Domestic financial conditions continue to favor recovery in economic activity. The transmission of reductions to the policy interest rate on credit rates has been significant. The banking portfolio continues to recover amid circumstances that have affected both the supply and demand for loans, and in which some credit risks have materialized. Preferential and ordinary commercial interest rates have fallen to a similar degree as the benchmark interest rate. As is generally the case, this transmission has come at a slower pace for consumer credit rates, and has been further delayed in the case of mortgage rates. Commercial credit levels stabilized above pre-pandemic levels in March, following an increase resulting from significant liquidity requirements for businesses in the second quarter of 2020. The consumer credit portfolio continued to recover and has now surpassed February 2020 levels, though overall growth in the portfolio remains low. At the same time, portfolio projections and default indicators have increased, and credit establishment earnings have come down. Despite this, credit disbursements continue to recover and solvency indicators remain well above regulatory minimums. 1.2 Monetary policy decision In its meetings in March and April the BDBR left the benchmark interest rate unchanged at 1.75%.

The Colombian financial system has not suffered major structural disruptions during these months of deep economic contraction and has continued to carry out its basic functions as usual, thus facilitating the economy's response to extreme conditions. This is the result of the soundness of financial institutions at the beginning of the crisis, which was reflected in high liquidity and capital adequacy indicators as well as in the timely response of various authorities. Banco de la República lowered its policy interest rates 250 points to 1.75%, the lowest level since the creation of the new independent bank in 1991, and provided ample temporary and permanent liquidity in both pesos and foreign currency. The Office of the Financial Superintendent of Colombia, in turn, adopted prudential measures to facilitate changes in the conditions for loans in effect and temporary rules for rating and loan-loss provisions. Finally, the national government expanded the transfers as well as the guaranteed credit programs for the economy. The supply of real credit (i.e. discounting inflation) in the economy is 4% higher today than it was 12 months ago with especially marked growth in the housing (5.6%) and commercial (4.7%) loan portfolios (2.3% in consumer and -0.1% in microloans), but there have been significant changes over time. During the first few months of the quarantine, firms increased their demands for liquidity sharply while consumers reduced theirs. Since then, the growth of credit to firms has tended to slow down, while consumer and housing credit has grown. The financial system has responded satisfactorily to the changes in the respective demands of each group or sector and loans may grow at high rates in 2021 if GDP grows at rates close to 4.6% as the technical staff at the Bank expects; but the forecasts are highly uncertain. After the strict quarantine implemented by authorities in Colombia, the turmoil seen in March and early April, which was evident in the sudden reddening of macroeconomic variables on the risk heatmap in Graph A,[1] and the drop in crude oil and coal prices (note the high volatility registered in market risk for the region on Graph A) the local financial markets stabilized relatively quickly. Banco de la República’s credible and sustained policy response played a decisive role in this stabilization in terms of liquidity provision through a sharp expansion of repo operations (and changes in amounts, terms, counterparties, and eligible instruments), the purchases of public and private debt, and the reduction in bank reserve requirements. In this respect, there is now abundant aggregate liquidity and significant improvements in the liquidity position of investment funds. In this context, the main vulnerability factor for financial stability in the short term is still the high degree of uncertainty surrounding loan quality. First, the future trajectory of the number of people infected and deceased by the virus and the possible need for additional health measures is uncertain. For that reason, there is also uncertainty about the path for economic recovery in the short and medium term. Second, the degree to which the current shock will be reflected in loan quality once the risk materializes in banks’ financial statements is uncertain. For the time being, the credit risk heatmap (Graph B) indicates that non-performing and risky loans have not shown major deterioration, but past experience indicates that periods of sharp economic slowdown eventually tend to coincide with rises in non-performing loans: the calculations included in this report suggest that the impact of the recession on credit quality could be significant in the short term. This is particularly worrying since the profitability of credit establishments has been declining in recent months, and this could affect their ability to provide credit to the real sector of the economy. In order to adopt a forward-looking approach to this vulnerability, this Report presents several stress tests that evaluate the resilience of the liquidity and capital adequacy of credit institutions and investment funds in the event of a hypothetical scenario that seeks to simulate an extreme version of current macroeconomic conditions. The results suggest that even though there could be strong impacts on the credit institutions’ volume of credit and profitability under such scenarios, aggregate indicators of total and core capital adequacy will probably remain at levels that are above the regulatory limits over the horizon of a year. At the same time, the exercises highlight the high capacity of the system's liquidity to face adverse scenarios. In compliance with its constitutional objectives and in coordination with the financial system's security network, Banco de la República will continue to closely monitor the outlook for financial stability at this juncture and will make the decisions that are necessary to ensure the proper functioning of the economy, facilitate the flow of sufficient credit and liquidity resources, and further the smooth operation of the payment systems. Juan José Echavarría Governor