Stratification Patterns Research Articles

Impact of long-term fertilization in no-till on the stratification of soil acidity and related parameters

The increasing cost of fuel and machinery used in conventional tillage systems makes no-till management (NT) an enticing alternative for small-grain producers. However, the application of fertilizers to the soil surface under NT has been shown to lead to the stratification of pH and other soil acidity parameters near the soil surface. Despite that, only a few works have reported the soil acidity stratification of the arable layer and were restricted to highly weathered acid soils of the tropics. Therefore, our objective was to quantify soil pH, exchangeable aluminum (AlKCl), aluminum saturation (Al%), soil organic carbon (OC), and cation exchange capacity (CEC) by depth in the topsoils across different levels of nutrient management in three long-term continuous NT wheat studies in the southern Plains of US. Plots were sampled after the winter wheat (Triticum aestivum L.) harvest in the summer of 2019 at sampling depths of 0–15 cm, and 0–2.5, 2.5–5, 5–7.5, 7.5–10, 10–12.5, and 12.5–15 cm. Treatments included an unfertilized check and a combination of increased rates of nitrogen (N) in addition to phosphorus (P) and potassium (K) application across all study locations. It was found that stratification occurred for all soil acidity parameters tested in the study, with higher OC and AlKCl, and lower pH near the soil surface. Patterns of soil pH and OC stratification were generally related to the rate of annual N fertilization. The long-term N fertilization significantly reduced soil pH in the topsoil (0–15 cm) and stratified soil layers, especially at the higher application rates. Regardless of the soil sampling depth, pH decrease was significantly related to the amount of N applied. Also, N fertilization significantly increased AlKCl and Al% but decreased the sum of Ca2++Mg2++K++Na+ both in the whole topsoil or layers. AlKCl and Al% were increased exponentially and linearly with increasing N rate and were for 0–15 cm and stratified layers, respectively. AlKCl was exponentially (inversely) related to soil pH for both sampling methods. Nitrate (NO3) was inversely related to soil pH until up to 21.9 ± 2.6 mg NO3N kg−1. Although not at the same magnitude, non-fertilized plots were likewise stratified for the tested parameters, which indicates other effects of NT on the stratification rather than the fertilizer addition. Overall, the buffer index (BI) was lower if the soil is sampled from 0 to 2.5 cm than 0–15 cm. Attention regarding sampling depth in NT areas is essential for accurate soil attributes monitoring.

THE BRITISH IN THE BAY: OCCUPATIONAL STRESS AND BIOLOGICAL DISPARITIES

THE BRITISH IN THE BAY: OCCUPATIONAL STRESS AND BIOLOGICAL DISPARITIES

Профессиональная стратификация как социальный феномен на региональном рынке труда Хабаровского края

This scientific article studies professional stratification as a social phenomenon in the regional labor market of the Khabarovsk Territory. The author analyzes social stratification, determines its main characteristics and influence on the professional opportunities and prospects of workers in the region. The study is based on a comprehensive data analysis that includes surveys, statistics and economic indicators.The author analyzes various aspects of professional stratification such as the level of education, work experience, professional skills and qualifications, as well as social status and income. He explores the differences in access to high-paying and prestigious jobs, as well as the factors that influence the vertical and horizontal mobility of workers. The author identifies the main trends and patterns of professional stratification in the regional labor market of the Khabarovsk Territory as the result of the study. Recommendations to reduce inequality in access to professional opportunities and improvement in the situation on the labor market in the region are also offered. This article provides valuable information for researchers, practitioners and decision makers in the field of labor relations and social policy.

Numerical investigation of the fluid retention in the tank with a horizontal negatively buoyant jet

The fluid retention in the volume control tank (VCT) will delay the boric concentration of the Reactor Coolant System (RCS) during the boration process in the nuclear power plant. In this work, we studied the fluid retention in the tank with a horizontal negatively buoyant jet employing an experimentally validated computational fluid dynamics (CFD) model. The effects of concentration difference, inlet volume flow rate, nozzle diameter, and Richardson number (Ri) on fluid retention are analyzed to provide insights into the design and operation of VCT and other similar industrial equipment. The results show that there are two typical mixing patterns in the tank, the stratified pattern and the unstratified pattern. A criterion is provided to distinguish the mixing pattern. Increasing the concentration difference/nozzle diameter and decreasing the inlet volume flow can suppress the mixing process inside the tank and consequently weaken fluid retention. The variation of the fluid retention with the Ri is divided into three regimes by two critical numbers. The fluid retention is almost insensitive to the Ri when the number is inferior to the first critical number or exceeds the second critical number. Otherwise, the rise of the Ri inhibits fluid retention. Hence, the Ri is recommended to be maintained above the second critical value to minimize fluid retention in practice.

The structure and diversity of retinal ganglion cells in the masked greenling Hexagrammos octogrammus Pallas, 1814 (Pisces: Scorpaeniformes: Hexagrammidae).

The authors studied the structure and diversity of retinal ganglion cells (GC) in the masked greenling Hexagrammos octogrammus. In vivo labelling with horseradish peroxidase revealed GCs of various structures in retinal wholemounts. A total of 154 cells were camera lucida drawn, and their digital models were generated. Each cell was characterized by 17 structural and topological parameters. Using nine clustering algorithms, a variety of clusterings were obtained. The optimum clustering was found using silhouette analysis. It was based on a set of three variables associated with dendritic field size and dendrite stratification depth in the retina. A total of nine cell types were discovered. A number of non-parametric tests showed significant pair-wise between-cluster differences in at least four parameters with medium and large effect sizes. Three large-field types differed mainly in dendritic field size, total dendrite length, level of dendrite stratification in the retina and position of somata. Six medium- to small-field types differed mainly in the structural complexity of dendritic arbors and level of dendrite arborization. Cells similar and obviously homologous to types 1-4 were identified in many fish species, including teleosts. Potential homologues of type 5 cells were identified in fewer teleost species. Cells similar to types 6-9 in relative dendritic field size and dendrite arborization pattern were also described in several teleostean species. Nonetheless, their homology is more questionable as their stratification patterns do not match so well as they do in large types. Potential functional matches of the GC types were identified in a number of teleostean species. Type 1 and 2 cells probably match spontaneously active units with the large receptive field centre, so-called dimming and lightening detectors; type 4 may be a counterpart of changing contrast detectors with medium receptive field centre size preferring fast-moving stimuli. Type 3 (biplexiform) cells have no obvious functional matches. Probable functional matches of types 6, 8 and 9 belong to ON-centre elements with small receptive fields such as ON-type direction-selective cells, ON-type spot detectors or ON-type spontaneously active units. Type 5 and 7 cells may match ON-OFF type units, in particular, changing contrast detectors or orientation-selective units. Potential functional matches of GC types presently described are involved in a wide spectrum of visual reactions related to adaptation to gradual change in illumination, predator escape, prey detection and capture, habitat selection and social behaviour.

The Banality of Surveillance

Surveillance is a ubiquitous and routine organizational practice. It has a long history as a tool of governance and a tacit right of the state. In the digital age, actors within both public and private institutions increasingly collect data on people and behaviors to classify, sort, and intervene upon people’s lives in ways that are consequential for individual trajectories and patterns of social stratification. Although theoretical scholarship on surveillance is rich, the corpus of empirical work on the subject is more limited, in part due to methodological and data challenges. Fortunately, scholars across a wide range of disciplines are turning their attention to surveillance and finding creative and ambitious strategies for overcoming these data limitations. Future research—particularly that which leverages new sources of data and comparative or experimental designs—may yield new insights about whether and under what conditions technologically mediated surveillance disrupts or ossifies existing inequalities.

Experimental and Prenemilary Numerical Evaluation of Pressure Drops under the Conditions of the Stratified Gas-Liquid Flow in a Horizontal Pipe Filled with Metal Foam

The paper reports the results of experimental tests and numerical simulations related to the pressure drop during two-phase air-water mixture flow through a pipe containing metal foam packing. Aluminium foam with 40 PPI open cells was used in the tests. A horizontal pipe with an internal diameter of 10 mm was used, and the foam only occupied a section of the pipe length equal to 240 mm. In the section of the pipe upwards of the foam, stratified flow pattern was generated, i.e., the most characteristic type for the gas-liquid flow. The results of the experimental research were compared with the values derived on the basis of the empirical method, which was developed for several different metal foams and two-phase systems. The values derived from measurements and calculations were subsequently applied to validate one numerical simulation method that is known to be particularly applicable for two-phase gas-liquid flow through metal foams. As a final result, the phenomena resulting from the presence of foam in the stratified flow through a gas-liquid system, the deficiencies of the methods applied in calculating pressure drops and modeling their values in accordance with the adopted numerical procedure were indicated. All research and modelling were carried out with the purpose of testing the potential of metal foam use in pipes dedicated to heat exchanger design, particularly ones intended to improve energy efficiency.

Detritus‐hosted methanogenesis sustains the methane paradox in an alpine lake

AbstractAccumulation of methane in oxic waters of lakes and the ocean has been widely reported. Despite the importance for the greenhouse gas budget, mechanistic controls of such “methane paradox” remain elusive. Here, we use a combination of CH4 concentration and isotopic (δ13CCH4, δDH2O and δ18OH2O) measurements, plankton incubations and microbial community assessments to demonstrate the existence of the methane paradox in oxygenated waters of a meromictic lake (Lake Cadagno, Switzerland). Following mass dynamics using water isotopes, we exclude the possibility that the accumulation of CH4 at the thermocline results solely from lateral transport. Interannual variability in the magnitude of the methane paradox (between 0.5 and 5 μmol L−1) is associated to stratification patterns, changes in zooplankton biomass and planktonic detritus accumulation along density gradients, as well as fluctuating microbial cell numbers. The links between hydrodynamic conditions, aggregation of planktonic detritus and its microbiome, as well as the accumulation of CH4 in the water column are further supported by high‐resolution echo‐sounder measurements revealing backscatter maxima at the top of the thermocline, where detritus is effectively trapped, and by oxic incubations showing that CH4 is produced in zooplankton detritus (0.046 nmol L−1 to 0.095 CH4 mg dry mass L−1 d−1). Our results also show that detritus‐hosted methanogenesis is stimulated through the addition of methylphosphonate, suggesting that zooplankton‐associated microbiomes exploit organic phosphorus compounds to release CH4. Understanding the variability of the methane paradox in relation to changing hydrodynamics and plankton communities will be crucial to predict the future role of lakes in the global methane budget.

Travelling for public goods, neighborhood effect and spatial stratification

To investigate the spatial stratification of people with heterogeneous incomes, this paper incorporates travelling for public goods and the market friction arising from the minimum area when buying houses into a monocentric model, finding two stratification patterns: mixed stratification wherein people with high and low incomes live in suburbs while middle-income people live in urban areas, and complete stratification in which the wealthy live in urban areas and the poor live in suburbs. When public goods have congestion effect or when the agglomeration effect is small, there is mixed stratification; when the agglomeration effect of public services is large, there is complete stratification. Under mixed stratification, the increase in land supply in the suburbs causes low-income people to move to urban area, while lower commuting costs for suburban residents or increased public services in urban areas causes low-income people to migrate to urban areas. If travelling for public goods is impossible, these policies cause low-income residents to move from urban areas to suburbs.

Relationship of salinity, temperature, pH, and transparency to dissolved oxygen in the Bouregreg estuary (Morocco): First results

Abstract Dissolved oxygen (DO) concentration is an essential indicator for assessment of estuary ecosystems. According to our knowledge, there is no research on the depth profiles of the DO and associated water quality variables of the entire Bouregreg estuary (Morocco). Water samples were collected from three stations at 0.5-m depth intervals during high and low tides (10/11/2021, 20/03/2022, and 02/07/2022). Our study shows that the DO concentrations ranged between 5.5 and 11.8 mg/L and demonstrated an inconsistent stratification pattern. When the tide was high and low in most of the study area, the bottom layer had a higher concentration of DO than the surface layer. There was a relatively high concentration of DO in the bottom layer of the estuary and a relatively low concentration in the surface layer of the estuary due to a high rate of freshwater flow on the surface (the release of Sidi Mohammed Ben Abdellah dam and the existence of estuarine gravitational circulation). Salinity, pH, water temperature, and water transparency ranged from 19.4 to 35.8 ppt, 7.0 to 8.7, 17 to 23 °C, and 16 to 21 cm, respectively, considering the depth profiles in the study area. The study provides scientific support for ecology operation and considerable advances in understanding the ecosystem dynamics of the Bouregreg estuary.

Systemic circulating microRNA landscape in Lynch syndrome.

Circulating microRNAs (c-miRs) are small noncoding RNA molecules that migrate throughout the body and regulate gene expression. Global c-miR expression patterns (c-miRnomes) change with sporadic carcinogenesis and have predictive potential in early detection of cancers. However, there are no studies that have assessed whether c-miRnomes display similar potential in carriers of inherited pathogenic mismatch-repair gene variants (path_MMR), known as Lynch syndrome (LS), who are predisposed to highly increased cancer risk. Using high-throughput sequencing and bioinformatic approaches, we conducted an exploratory analysis to characterize systemic c-miRnomes of path_MMR carriers, sporadic rectal cancer patients and non-LS controls. We showed for the first time that cancer-free path_MMR carriers have a systemic c-miRnome of 40 differentially expressed c-miRs that can distinguish them from non-LS controls. The systemic c-miRnome of cancer-free path_MMR carriers also resembles the systemic c-miRnomes of cancer patients with or without path_MMR. Our pathway analysis linked the found differentially expressed c-miRs to carcinogenesis. A total of 508 putative target genes were identified for 32 out of 40 differentially expressed c-miRs, and 238 of them were enriched in cancer-related pathways. The most enriched c-miR-target genes include well-known oncogenes and tumor suppressor genes such as BCL2, AKT3, PIK3CA, KRAS, NRAS, CDKN1A and PIK3R1. Taken together, our findings suggest that LS and sporadic carcinogenesis share common biological pathways and alterations in these pathways can produce a c-miR signature which can track potential oncogenic stress in cancer-free path_MMR carriers. Therefore, c-miRs hold potential in monitoring the LS risk stratification patterns during clinical surveillance or cancer management.

Functional traits and phylogeny explain snake distribution in the world's largest dry forest ecoregion, the Gran Chaco.

Macroecological studies describe large-scale diversity patterns through analyses of species distribution patterns and allows us to elucidate how species differing in ecology, physical requirements, and life histories are distributed in a multidimensional space. These patterns of distributions can be explained by vegetation, and climatic factors, and are determined by historical and current factors. The continuous accumulation of information on the distribution patterns of species is essential to understand the history and evolution of the biota. In this study, we aimed to identify functional and evolutionary drivers that explain the geographic patterns of vertical stratification. We compiled morphological, ecological, and distribution data of 140 species of Chacoan snakes and constructed null models to map their geographic pattern. We used a range of environmental variables to assess which drivers are influencing these biogeographic patterns. Lastly, we used evolutionary data to build the first map of the phylogenetic regions of Chacoan snakes. We found a latitudinal pattern, with a marked verticality in the snake assemblies in the Chaco. Verticality and long-tailed species richness increased in areas with high stratified habitats and stable temperature. Fossoriality is driven mainly by soil conditions, especially soils with fewer sand particles and less stratified habitat. Phylogenetic regions in the Chaco showed a marked latitudinal pattern, like that observed in the geographic pattern of verticality. The distribution pattern of Chacoan snakes also reflects their evolutionary history, with a marked phylogenetic regionalization.

Computational study of hydrogen injection strategy on the combustion performance of a direct injection rotary engine fueled with natural gas/hydrogen blends

Natural gas/hydrogen blended fuel (NHBF) is considered to be one of the ideal alternative fuels for rotary engine, which can effectively reduce the carbon emission of the rotary engine. The purpose of this paper is to numerically study the influence of hydrogen injection timing (HIT) and hydrogen injection angle (HIA) on mixture formation, flame propagation, and NO emission in the cylinder. In addition, considering that the apex seal leakage (ASL) of rotary engine is difficult to avoid, the NHBF in the cylinder will inevitably leak from the apex seal leakage gap to the adjacent cylinders. Therefore, the NHBF leakage under the action of ASL should be considered. In this paper, a 3D dynamic model of the NHBF rotary engine considering the action of ASL was established. Further, the diffusion and combustion processes of NHBF in the cylinder with different HITs and HIAs were calculated. The results showed that the HIT and HIA can significantly change the flame propagation process by changing the fuel stratification pattern in the cylinder. For improving the combustion efficiency of the engine, the HIA of +45° and HIT of 155°CA (BTDC) adopted by Case:155 + 45 should be set as the hydrogen injection strategy. This is mainly because that for Case: 155 + 45, both natural gas and hydrogen are mainly distributed in the FOC, and the concentration of hydrogen and natural gas near the spark plug is also high. However, the defect of Case:155 + 45 is the significant increase of NO emission.

Connecting the Threads: Stratification Economics and the Political Economy of W.E.B. Du Bois

This analysis expands previous research examining the origins of concepts and theoretical frameworks developed by Stratification Economics (SE) practitioners. Linkages between formulations developed by W.E.B. Du Bois and similar SE constructs are analyzed extending the previous recognition of the relevance of his scholarship for SE. Four specific elements of Du Bois's SE-related scholarship are interrogated: (1) Origins and Parameters of Racial Group Identity; (2) Class Differentiation; (3) Capitalism and Racial Stratification; and (4) Democracy and Racial Stratification. Du Bois's predictions regarding future important economic trends are shown to be relevant for guiding SE analyses of contemporary patterns of racial economic stratification. Reasons why Du Bois's scholarship has received limited attention within the Economics profession are discussed in the context of explaining why formalizing Du Bois's role as a SE progenitor is important for the ongoing development of SE.

In-situ and quantitative imaging of evaporation-induced stratification in binary suspensions

The drying of a multi-component dispersion, such as water-based paint, ink and sunscreen to form a solid film, is a widespread process. Binary colloidal suspensions have proven capable of spontaneous layer formation through size segregation during drying. To design bespoke stratification patterns, a deeper understanding of how these emerge is crucial. Here, we visualize and quantify the spatiotemporally evolving concentration profiles in situ and with high resolution using confocal fluorescence microscopy of custom-designed binary dispersions in a well-defined geometry. Our results conclusively establish two distinct stratification routes, which give rise to three layered structures. A first thin layer develops directly underneath the evaporation front in which large particles are kinetically trapped. At later times, asymmetrical particle interactions lead to the formation of two subsequent layers enriched in small and large particles, respectively. The spatial extent and magnitude of demixing strongly depend on the initial volume fraction. We explain and reproduce the experimental concentration profiles using a theoretical model based on dynamic arrest and higher-order thermodynamic and hydrodynamic interactions. These insights unravel the key mechanisms underlying colloidal auto-stratification in multi-component suspensions, and allow preprogramming of stratification patterns in single-deposition formulations for future applications.

Circulation and Transport Processes during an Extreme Freshwater Discharge Event at the Tagus Estuary

During the winter of 2013, the Tagus estuary was under the influence of intense winds and extreme freshwater discharge that changed its hydrodynamics and, consequently, the salt and heat transport. Moreover, the dynamics of the estuary may change due to climate change which will increase the frequency of heat waves and increase the mean sea level. Therefore, it is of utmost importance to study the impact of the future increase in air temperature and mean sea level under extreme events, such as that in the winter of 2013, to ascertain the foreseen changes in water properties transport within the estuary and near coastal zone. Several scenarios were developed and explored, using the Delft3D model suite, considering the results of the CMIP6 report as forcing conditions. Before the event, the mixing region of the estuary presented well-mixed conditions and its marine area a slight stratification. During the event, the estuary was filled with freshwater and the mixing region migrated toward the coast, leading to lower water temperature values inside the estuary. SLR has a higher impact on the salinity and stratification patterns than the air temperature increase. The response of water temperature is directly related to the increase in air temperature. The estuary mouth and the shallow regions will be more prone to changes than the upstream region of the estuary. The projected changes are directly linked to the future CO2 emissions scenarios, being intensive with the highest emission scenario.

Vertical profile of dissolved oxygen and associated water variables in the Pasur-Rupsha estuary of Bangladesh

Vertical profile of dissolved oxygen (DO) and associated water variables were measured in the head of the Pasur-Rupsha estuary of Bangladesh. Water samples were collected from two stations at 0.60 m depth intervals during high and low tides from July, 2016 to January, 2017. DO concentration was ranged from 6.0 to 8.6 mg/l with maximum two units of variation in the profiles of the stations and demonstrated an inconsistent stratification pattern. The observed stratification pattern was remarkably triggered by a relatively high concentration of DO in the bottom layer than that of the surface layer during both the high and low tides in most of the study periods. High rate of freshwater flow at the surface; existence of estuarine gravitational circulation with 5–15 m depth profile; and lack of consumers in the bottom due to the high deposition of sediment particles were found responsible for the relatively high concentration of DO at bottom and low in surface layer of the estuary. Water temperature, salinity, pH, phytoplankton density and transparency were ranged from 22 to 32 °C, 0–6 ppt, 7.0 to 8.5, 1000–23000 ind/l and 13–17 cm respectively considering the depth profiles in the study periods. Temperature and plankton density were found significantly (P < 0.000) correlated with DO while the pH and salinity did not show any significant (P > 0.3) correlation. The ecosystem process associated with the vertical profile of DO explained in this study will provide considerable advances in understanding the ecosystem dynamics of the Pasur-Rupsha Estuary of Bangladesh.

Part of town as an independent factor: thenorth-forcemerger in Manchester

AbstractThis paper investigates the question of whether, as is often popularly believed, there may be systematic linguistic differences between different neighborhoods within a city by testing the independence of “part of town” as a factor separate from social class in thenorth-forcemerger in Manchester, UK, in a sample of 122 speakers. The phonemic contrast is explored in minimal-pair tests, Cartesian distance, and Pillai scores. In opposition to most dialects of English, thenorth-forcecontrast is still present in Manchester, displaying a pattern of fine social stratification, with lower socioeconomic levels having a stronger distinction. The merger is in progress in the city, but it is slower in north Manchester, showing a significantly greater distinction than the rest of the city, independent of social class. The results indicate a degree of social evaluation of the vowels, with implications for the question of the social meaning of a merger in progress.

Flow Boiling Heat Transfer of Grooved Copper Foam with Open Gap

Introduction. Copper foam material has various advantages. It has been proved effective in enhanced boiling heat transfer, but also increases pump power consumption. Grooved copper foam is a solution to achieve good balance between boiling heat transfer characteristics and pump power consumption. Material and Methods. Grooveless and grooved copper foam in open space was studied. Copper foam specifications comprised the combination of porosities of 70, 80 and 90%, and pore densities of 90 and 110 PPI. The grooved copper foams have two specifications: 11 and 17 grooves. The corresponding rib widths are 2 and 1 mm, with groove depth 2.9 mm and width 0.6 mm. The flow boiling experimental system of copper foam sample includes four parts: a heating water reservoir, pump, a test section, and a data acquisition system. In the test section, liquid water turns into vapor and carries the heat away from a copper block surface, and then vapor condenses into liquid water in the terminal reservoir. Results. Grooved copper foam samples presented significantly higher efficiency than grooveless ones. Grooved copper foams can increase the critical heat flux and heat transfer coefficient, compared with grooveless ones. Seventeen-grooved samples showed more excellent performance than 11-grooved ones. Visual observation disclosed that the stratified flow pattern dominated in moderate and high heat flux for grooved copper foam with open space. Covering vapor mass was more effective to be formed above 17-grooved samples, compared with 11-grooved ones. It indicated more vigorous boiling behavior occurs in 17-grooved sample. Discussion and Conclusion. The number of grooves has a significant impact on boiling heat transfer. Grooved copper foam samples present a significantly higher critical heat flux and heat transfer coefficient. Structural parameters such as porosity and pore density, play a relatively secondly role in heat transfer argumentation. Visual observation shows there exists a cyclic alternation of flow patterns: bubbly flow, annular flow and mass vapor formation for grooved samples. Forming vapor mass is more effective to be formed in 17-grooved samples, compared to 11-grooved ones. It indicates more vigorous boiling behavior occurs in 17-grooved samples.

Using Google Trends Data to Learn More About Survey Participation

As response rates continue to decline, the need to learn more about the survey participation process remains an important task for survey researchers. Search engine data may be one possible source for learning about what information some potential respondents are looking up about a survey when they are making a participation decision. In the present study, we explored the potential of search engine data for learning about survey participation and how it can inform survey design decisions. We drew on freely available Google Trends (GT) data to learn about the use of Google Search with respect to our case study: participation in the Family Research and Demographic Analysis (FReDA) panel survey. Our results showed that some potential respondents were using Google Search to gather information on the FReDA survey. We also showed that the additional data obtained via GT can help survey researchers to discover topics of interest to respondents and geographically stratified search patterns. Moreover, we introduced different approaches for obtaining data via GT, discussed the challenges that come with these data, and closed with practical recommendations on how survey researchers might utilize GT data to learn about survey participation.