Multilevel Sampling Research Articles

MULTILEVEL QUASI-MONTE CARLO FOR INTERVAL ANALYSIS

This paper presents a multilevel quasi-Monte Carlo method for interval analysis, as a computationally efficient method for high-dimensional linear models. Interval analysis typically requires a global optimization procedure to calculate the interval bounds on the output side of a computational model. The main issue of such a procedure is that it requires numerous full-scale model evaluations. Even when simplified approaches such as the vertex method are applied, the required number of model evaluations scales combinatorially with the number of input intervals. This increase in required model evaluations is especially problematic for highly detailed numerical models containing thousands or even millions of degrees of freedom. In the context of probabilistic forward uncertainty propagation, multifidelity techniques such as multilevel quasi-Monte Carlo show great potential to reduce the computational cost. However, their translation to an interval context is not straightforward due to the fundamental differences between interval and probabilistic methods. In this work, we introduce a multilevel quasi-Monte Carlo framework. First, the input intervals are transformed to Cauchy random variables. Then, based on these Cauchy random variables, a multilevel sampling is designed. Finally, the corresponding model responses are post-processed to estimate the intervals on the output quantities with high accuracy. Two numerical examples show that the technique is very efficient for a medium to a high number of input intervals. This is in comparison with traditional propagation approaches for interval analysis and with results well within a predefined tolerance.

Graph Sample and Aggregate-Attention Network for Hyperspectral Image Classification

Graph convolutional network (GCN) has shown potential in hyperspectral image (HSI) classification. However, GCN is a transductive learning method, which is difficult to aggregate the new node. The available GCN-based methods fail to understand the global and contextual information of the graph. To address this deficiency, a novel semisupervised network based on graph sample and aggregate-attention (SAGE-A) for HSIs’ classification is proposed. Different from the GCN-based method, SAGE-A adopts a multilevel graph sample and aggregate (graphSAGE) network, as it can flexibly aggregate the new neighbor node among arbitrarily structured non-Euclidean data and capture long-range contextual relations. Inspired by the convolution neural network (CNN) self-attention mechanism, the proposed network uses the graph attention mechanism to characterize the importance among spatially neighboring regions, so the deep contextual and global information of the graph can be learned automatically by focusing on important spatial targets. Extensive experimental results on different real hyperspectral data sets demonstrate the performances of our proposed method compared with the state-of-the-art methods.

Association of Hypertensive Disorders of Pregnancy (HDP) and tobacco use among women of reproductive age group in India: A secondary data analysis from NFHS-4.

Tobacco use in any form is known to exert several perinatal complications. Through this study, the authors aimed to study the association between tobacco use and Hypertensive Disorders of Pregnancy (HDP) among women (aged 15-49 years) in India. We used data from the National Family Health Survey (NFHS-4, 2015-2016) to study the association between tobacco use and HDP among women of reproductive age (15-49 years) in India. Since the NFHS follows a complex multi-level sampling, sampling weights were used to study the univariate and multivariate associations between the independent and dependent variables. Adjusted odds ratios (AORs) are reported along with 95% Confidence Intervals. A sample of 1,07730 women was included in the analysis. HDP was more likely to be experienced by smokeless and smoking tobacco users (AOR 1.3, 95% CI (1.0-1.6) and AOR 2.7, 95% CI (2.0-3.7), respectively). Women with secondary (AOR 0.7, 95% CI (0.7-0.8)) and higher education (AOR 0.7, 95% CI (0.6-0.8)) were less likely to suffer from HDP as compared to those with no education. Women with daily (AOR 0.7, 95% CI (0.5-0.8)), weekly (AOR 0.8, 95% CI (0.6-0.9)) or occasional AOR 0.7, 95% CI (0.6-0.9)) consumption of fruits were less likely to experience HDP as compared to women with no fruit intake. Healthy diet and lifestyle factors can contribute to reduce the risk of HDP across women. The antenatal check-ups in India should also comprehensively focus on screening and counseling of women against tobacco use.

PENGARUH KEPIMPINAN DAN MODAL SOSIAL ORGANISASI TERHADAP AMALAN KOMUNITI PEMBELAJARAN PROFESIONAL DI SEKOLAH

The high performance of learning organization leadership among head masters is able to strengthen the practice of professional learning community among teachers through the empowerment of organizational social capital. Previous studies have shown that high performing leadership has so far less encouraged the practice of professional learning community because the closeness of organizational social capital is not optimized for that purpose. The purpose of this study was to examine the role of head masters learning organization leadership and organizational social capital on professional learning community practices in schools. This study uses a survey research method involving 476 respondents selected using stratified multi-level cluster sampling method. Meanwhile, the research instruments were adapted from the learning organization leadership questionnaire, the organizational social capital questionnaire and the professional learning community practice benchmark questionnaire. Inferential data were analyzed using Importance-Performance Matrix Analysis (IPMA) procedure through SmartPLS Version 3.2.9 software. The findings of this study indicate that the leadership of learning organizations is at a high level of performance but the importance in improving the level of professional learning community practices in schools is low. While the importance of organizational social capital in improving the level of professional learning community practices in schools is high while its performance is at a low level. Therefore, this study suggests that head masters play a role as leaders of learning organizations in boosting the performance of organizational social capital to ensure the practice of professional learning community among teachers is more robust in their respective schools.

Using virtual microscopy for the development of sampling strategies in quantitative histology and design-based stereology.

Only a fraction of specimens under study are usually selected for quantification in histology. Multilevel sampling or tissue probes, slides and fields of view (FOVs) in the regions of interest (ROIs) are required. In general, all parts of the organs under study should be given the same probability to be taken into account; that is, the sampling should be unbiased on all levels. The objective of our study was to provide an overview of the use of virtual microscopy in the context of developing sampling strategies of FOVs for stereological quantification. We elaborated this idea on 18 examples from multiple fields of histology, including quantification of extracellular matrix and muscle tissue, quantification of organ and tumour microvessels and tumour-infiltrating lymphocytes, assessing osseointegration of bone implants, healing of intestine anastomoses and osteochondral defects, counting brain neurons, counting nuclei in vitro cell cultures and others. We provided practical implications for the most common situations, such as exhaustive sampling of ROIs, sampling ROIs of different sizes, sampling the same ROIs for multiple histological methods, sampling more ROIs with variable intensities or using various objectives, multistage sampling and virtual sampling. Recommendations were provided for pilot studies on systematic uniform random sampling of FOVs as a part of optimizing the efficiency of histological quantification to prevent over- or undersampling. We critically discussed the pros and cons of using virtual sections for sampling FOVs from whole scanned sections. Our review demonstrated that whole slide scans of histological sections facilitate the design of sampling strategies for quantitative histology.

Multiclassification Method of Landslide Risk Assessment in Consideration of Disaster Levels: A Case Study of Xianyang City, Shaanxi Province

Geological disaster risk assessment can quantitatively assess the risk of disasters to hazard-bearing bodies. Visualizing the risk of geological disasters can provide scientific references for regional engineering construction, urban planning, and disaster prevention and mitigation. There are some problems in the current binary classification landslide risk assessment model, such as a single sample type, slow multiclass classification speed, large differences in the number of positive and negative samples, and large errors in classification results. This paper introduces multilevel landslide hazard scale samples, selects multiple types of samples according to the divided multilevel landslide hazard scale grade, and proposes a landslide hazard assessment model based on a multiclass support vector machine (SVM). Due to the objective limitations of the single weighting method, the combined weights are used to determine the vulnerability of the landslide hazard-bearing body, and the analytic hierarchy process (AHP) and entropy method are combined to construct a landslide vulnerability assessment model that considers subjective and objective weights. This paper takes landslide disasters in Xianyang City, Shaanxi Province, as the research object. Based on the landslide hazard assessment model and the landslide vulnerability assessment model, a landslide risk assessment experiment is carried out. It generates the landslide risk assessment zoning map and summarizes the risk characteristics of landslides in various towns. The experimental results verify the feasibility and effectiveness of the proposed model and provide important decision support for decision makers in Xianyang City.

The authority of principals’ technology leadership in empowering teachers’ self-efficacy towards ICT use

<span>The application of information technology and communication (ICT) in education has a significant impact on teachers. Administrators pressure them to use ICT to improve the quality of teaching and to learn in the classroom. However, teachers are still skeptical of the ability to embody pedagogical strategies through the use of ICT. The purpose of this study was to explore the relationship between principals’ technology leadership and teachers’ self-efficacy. The study also determined the dimensions of technology leadership that are predictors to the empowerment of teachers' self-efficacy in using ICT. There are two instruments used, namely NETS-A and TSES. The respondents of the study consisted of 376 teachers in Malaysia. The study was conducted based on a quantitative approach, and respondents were selected through multi-level sampling. The results of the t-test found no significant difference for the gender of teachers on the improvement of self-efficacy. Through correlation testing, there was a moderate relationship between technology leadership and teachers’ self-efficacy. Even so, there is 24% of the influence of technology leadership that affects teachers' self-efficacy. Two contributing dimensions are excellence in professional practice and digital citizenship. In summary, principals can generate a revival of teachers' self -efficacy if they wisely encourage them to use ICT. Principals should be role models to teachers and students in ensuring that the concept of pedagogy in the classroom is always carried out through an ICT approach.</span>

To and fro: The costs and benefits of power fluctuation throughout the day.

Power is a ubiquitous element of organizational relationships. Historically in the organizational and social sciences, power has most commonly been evaluated statically. Although this approach has been beneficial thus far, it may be inconsistent with the realities that most individuals face in organizations. Rather, we suggest that individuals' sense of power changes, even within a given day. Thus, we introduce the concept of power fluctuation to better explain the phenomenon that one's sense of power varies over time. We position power fluctuation as a form of micro role transition and draw from the social distance theory of power to posit that such fluctuation throughout the day has both positive and negative consequences. Specifically, we suggest that daily power fluctuation (day-to-day, within-person variance in power fluctuation) as well as general power fluctuation (person-to-person, between-person variance in power fluctuation) increase perspective taking and contribution to team performance, but those benefits come at an emotional cost (i.e., frustration and emotional exhaustion). The results of our multilevel experience sampling study of 845 matched-responses from 103 employee-coworker dyads largely support our predictions of the manifestation and consequences of power fluctuation. The implications of power fluctuation for theory and practice are discussed. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Painful Diabetic Peripheral Neuropathy Study of Chinese Outpatients (PDNSCOPE): A Multicentre Cross-Sectional Registry Study of Clinical Characteristics and Treatment in Mainland China.

IntroductionThis aim of this study was to delineate current clinical scenarios of painful diabetic peripheral neuropathy (PDN) and associated anxiety and depression among patients in Mainland China, and to report current therapy and clinical practices.MethodsA total of 1547 participants were enrolled in the study between 14 June 2018 and 11 November 2019. Recruitment was conducted using a multilevel sampling method. Participants’ demographics, medical histories, glucose parameters, Douleur Neuropathique 4 Questionnaire (DN4) scores, visual analogue scale (VAS) pain scores, Patient Health Questionnaire 9 (PHQ-9) scores, Generalised Anxiety Disorder 7 (GAD-7) scores and therapies were recorded.ResultsThe male-to-female ratio was 1.09:1 (807:740), and the mean age at onset was 61.28 ± 11.23 years. The mean DN4 score (± standard deviation) was 4.91 ± 1.88. The frequencies of DN4 sub-item phenotypes were: numbness, 81%; tingling, 68.71%; pins and needles, 62.90%; burning, 53.59%; hypoaesthesia to touch, 50.16%; electronic shocks, 43.31%; hypoaesthesia to pinprick, 37.94%; brushing, 37.82%; painful cold, 29.61%; and itching, 25.86%. Age, diabetic duration, depression history, PHQ-9 score and GAD-7 score were identified as risk factors for VAS pain score. Peripheral artery disease (PAD) was a protective factor for VAS pain score. For all participants currently diagnosed with PDN and for those previously diagnosed PDN, fasting blood glucose (FBG) was a risk factor for VAS; there was no association between FBG and VAS pain score for PDN diagnosed within 3 months prior to recruitment. Utilisation rate of opium therapies among enrolled participants was 0.71% , contradiction of first-line guideline recommendation for pain relief accounted for 9.43% (33/350) and contradiction of second-line guideline recommendation for opium dosage form was 0.57% (2/350).ConclusionModerate to severe neuropathic pain in PDN was identified in 73.11% of participants. Age, diabetic duration, depression history, PHQ-9 score, GAD-7 score and FBG were risk factors for VAS pain scores. PAD was protective factor. The majority of pain relief therapies prescribed were in accordance with guidelines.Trial registrationClinicalTrials.gov identifier, NCT03520608, retrospectively registered, 2018-05-11.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40122-021-00281-w.

When Receipt of Gratitude Impacts Work Outcomes via Emotional Regulation amongst Coworkers

Employees engage in emotional regulation not only with customers, but also with coworkers despite the fact that very little is known about emotional labor such as surface and deep acting in coworker relationships. Furthermore, an omission in the literature exists regarding antecedents to emotional regulation. To address these limitations, we suggest how receiving gratitude serves as an antecedent to emotional labor within the underexplored context of coworker exchange relationships. Additionally, the gender of the employee receiving gratitude is an important moderator whereby social norms influencing emotional displays may accentuate the effects on surface acting for women, while strengthening them on deep acting for men. Lastly, we examine downstream consequences for emotional labor that sustain organizations (work withdrawal and work goal progress). We test these assertions with an experiment (Study 1) and two multilevel experience sampling studies (Study 2 and Study 3) and discuss the implications of our findings.

Analysis of Factors Affecting Community on the Use of Non-Cash Payment Tools in Taman District, Sidoarjo Regency

The purpose of the study was to examine the effect of perceived benefits, convenience, trustworthiness, and risk on the use of non-cash payment instruments in Taman Sub-district, Sidoarjo Regency. The Theory Acceptance Model (TAM) is used as the theoretical basis for the research. The research sample is people who transact at Alfamart, Indomaret, McDonald's Geluran, and Alfamidi in Taman sub-district, Sidoarjo district. Multilevel random sampling method. The questionnaires distributed were 100 respondents. The results showed that trust had no effect, while the benefits, convenience, and risk had an effect on noncash payment instruments.

Global and local constrained parallel MRI reconstruction by exploiting dual sparsity and self-consistency

In this study, we introduce global and local constrained reconstruction for highly undersampled magnetic resonance imaging (MRI). This reconstruction not only exploits dual sparsity and self-consistency constraints, but also effectively decouples them regionally and stepwise. Unlike conventional parallel MRI or compressed sensing (CS), we employed multi-level variable-density k-space sampling, wherein the sampling density becomes sparser from the central to the peripheral region (full-shifted lattice R2-M2 undersampling-incoherent pseudo-random undersampling). Furthermore, complementary local k-space model was introduced as a union of wavelet directional filtered signals and its residual for regionally independent reconstruction, in which wavelet subbands are represented in compact frequency partitions. The subbands were partially leaked over neighboring partitions. To further enhance the accuracy of image details and eliminate potential discrepancies resulting from separate regional reconstructions, selfconsistency constrained reconstruction was performed globally over the entire k-space. Simulations and experimental studies demonstrated that the proposed technique substantially outperforms conventional methods in suppressing artifacts and noise with increasing acceleration factors.

Bullying and Its Associated Individual, Peer, Family and School Factors: Evidence from Malaysian National Secondary School Students.

Adolescents involved in bullying can be at risk of developing behavioural problems, physical health problems and suicidal ideation. In view of this, a quantitative research design using a cross-sectional study was conducted to determine the prevalence of bullying and associated individual, peer, family and school factors. The study involved 4469 Malaysian public-school students who made up the response rate of 89.4%. The students were selected using a randomized multilevel sampling method. The study found that 79.1% of student respondents were involved in bullying as perpetrators (14.4%), victims (16.3%), or bully–victims (48.4%). In a multivariate analysis, the individual domain showed a significant association between students’ bullying involvement and age (OR = 1.38; 95% CI 1.12–1.70), gender (OR = 1.73; 95% CI 1.47–0.91), ethnicity (OR = 0.66; 95% CI 0.47–0.91), duration of time spent on social media during the weekends (OR = 1.43; 95% CI 1.09–1.87) and psychological distress level (OR = 2.55; 95% CI 1.94–3.34). In the peer domain, the significantly associated factors were the number of peers (OR = 0.69; 95% CI 0.56–0.86) and frequency of quarrels or fights with peers (OR = 2.12; 95% CI 1.24–3.26). Among the items in the school domain, the significantly associated factors were students being mischievous in classrooms (OR = 1.52; 95% CI 1.06–2.06), student’s affection towards their teachers (OR = 1.53; 95% CI 1.06–2.20), frequency of appraisal from teachers (OR = 1.49; 95% CI 1.16–1.94), frequency of friends being helpful in classrooms (OR = 1.92; 95% CI 1.09–3.38) and frequency of deliberately skipping class (OR = 2.91; 95% CI 2.90–1.72). As a conclusion, the study revealed high levels and widespread bullying involvement among students in Malaysia. As such, timely bullying preventions and interventions are essential, especially in terms of enhancing their mental health capacity, which substantially influences the reduction in the prevalence rates of bullying involvement among students in Malaysia.

Antithetic multilevel sampling method for nonlinear functionals of measure

Let μ∈ P2(Rd), where P2(Rd) denotes the space of square integrable probability measures, and consider a Borel-measurable function Φ:P2(Rd)→R. In this paper we develop an antithetic Monte Carlo estimator (A-MLMC) for Φ(μ), which achieves sharp error bound under mild regularity assumptions. The estimator takes as input the empirical laws μN=1N∑ i=1NδX i, where (a) (Xi)i=1N is a sequence of i.i.d. samples from μ or (b) (Xi)i=1N is a system of interacting particles (diffusions) corresponding to a McKean–Vlasov stochastic differential equation (McKV-SDE). Each case requires a separate analysis. For a mean-field particle system, we also consider the empirical law induced by its Euler discretisation which gives a fully implementable algorithm. As by-products of our analysis, we establish a dimension-independent rate of uniform strong propagation of chaos, as well as an L2 estimate of the antithetic difference for i.i.d. random variables corresponding to general functionals defined on the space of probability measures.

Investigating the Effectiveness of Cognitive-Affective Skills Training on Reduction of Violent Behaviors Tendency among Male High School Students

This study was to investigate the effectiveness of cognitive-emotional skills on the decrease of high school student' tendency to aggressive behaviors. The design of the study was experimental using a pre-test and post-test method with a control group. The population of the study included male students of Hamedan and Tehran studying in 1391-1392. The sampling in the first step was done through multi-level cluster sampling and in the second step, random substitution was used. Also, to increase the assurance coefficient to control the examinees subsidence, twenty students were considered in each group and were assigned to 4 groups by random substitution sampling. Firstly, the Interpersonal Aggressive Questionnaire was administered to the students. Then, 80 students (40 students in each province) were chosen from among those who were upper than the cut point and were randomly assigned to the control and experimental group. The cognitive-emotional skills program were each performed in 10 sessions (each group session took 90 minutes). The tools used in this research were Interpersonal Aggressive Scales (Straus, 1979), Emotional intelligence questionnaire (Bar-On, 1997), Affective control scale (Williams, Chambless, & Ahrens, 1997), and the second version of Rahim organizational conflict scale (Rahim, 1997). The results of Covariance analysis (ANCOVA) indicated that teaching the cognitive-emotional skills to high school students Makes Increase self-awareness skills, anger management, and problem solving. Also, the results of the study indicated that teaching the cognitive-emotional skills have a positive and significant effect on the decrease of students tendency to aggressive behaviors such as verbal aggressive, practical aggressive of the students. However, the results indicated that teaching the cognitive-emotional skills are effective.

Communication Medium Used by Clients and Health Professionals in Accessing and Providing Healthcare in Low Resource Setting: A Descriptive Cross-Sectional Study

Background. There exist continuing challenges with communication medium used during health service provision. These challenges relate to clients and health institution, intra- and interhealth institution communications. This study reviewed the existing healthcare communication medium from the perspectives of clients and health professionals at a tertiary hospital in Ghana. Methods. Cross-sectional design was employed with a multilevel sampling method to select a total of 650 participants consisting of 303 clients, 303 health workers, and 44 hospital directorate managers for the study. A structured survey questionnaire was used to collect data from respondents. Results. Close to ninety percent (89.8%) of staff resort to direct means (face-to-face medium) to communicate among each other. Majority (64.4%) of them also communicated with management through meetings sections. Nearly all healthcare providers (97.4%) communicated with clients through direct means (face-to-face medium). Almost all forms of communication between the hospital management members and the general public were done through letters and official memos. Conclusions. The study revealed blended forms of communication media used by health providers and health service consumers. These differences in medium of communication could amount to possible difficulties such as lack of information and truncation of information flow. Developing a systematic way of information flow using a common information platform will improve access to health services.

Intra-Study Matching Considerations When Using Mixed Methods-Based Research Approaches: A Critical Dialectical Pluralistic Approach

The step of obtaining a sample(s) (i.e., sampling) in mixed methods-based research studies likely represents the least developed step in the research process, with only 21 Scopus-indexed works published on the topic to date. Consequently, the time is rife for mixed methods-based researchers to develop sampling designs that are more TREEful—that is, transparent, rigorous, equitable, and ethical—especially when sampling among/between phases/components. Because, more than the other 13 mixed methods-based research philosophies, critical dialectical pluralism especially is concerned with the welfare of research participants, and because the sampling step is subject to misuse and abuse of participants, the use of a critical dialectical pluralist lens to ensure that mixed methods-based sampling designs are as TREEful as possible has logical appeal. Therefore, in this editorial, we have provided a meta-framework,1 via a critical dialectical pluralism lens, for selecting samples for each of the following four types of relationships among/between phases/components identified by Onwuegbuzie and Collins (2007), namely, identical samples, parallel samples, nested samples, and multilevel samples. This lens has led to the identification of several options for minimizing, or at least reducing, what we refer to as identical sampling bias, parallel sampling bias, nested sampling bias, and multilevel sampling bias such that samples are optimally matched within a single mixed methods-based research study. In the context of mixed methods-based research, matching refers to the process of forming groups to make them as similar as possible with respect to extraneous or confounding factors (e.g., demographic variables [e.g., gender, age]; personality variables [e.g., resilience]; affective variables [e.g., motivation]). In particular, we outline the use of several matching techniques—specifically, exact matching, greedy matching, optimal matching, propensity score matching, subclassification, and magnitude coding—for addressing these different forms of bias. We encourage mixed methods-based researchers to explore using one or more of these matching techniques, whenever appropriate, regardless of their philosophical stance, in order to avoid researcher participants from being misrepresented.

Characterisation of the bacterial microbiota of a landfill-contaminated confined aquifer undergoing intrinsic remediation

Literature on microbiomes of landfill leachate-contaminated aquifers is scarce despite groundwater contaminations from landfills being common globally. In this study, a combination of microbiological techniques was applied to groundwater samples from an aquifer contaminated by a municipal landfill and undergoing intrinsic remediation. Groundwater samples were obtained from three multilevel sampling wells placed along the groundwater flow path in the contaminated aquifer, and additionally from a background well located in a nearby uncontaminated aquifer. The samples were subjected to chemical analysis, microbial culturing and characterisation, cell counting by fluorescence microscopy, and 16S rRNA metabarcoding. Good concordance was realised with the results from the different microbiological techniques. Samples from the uncontaminated aquifer had both lower cell density and lower microbial diversity compared to samples from the contaminated aquifer. Among the wells located in the contaminated aquifer, microbial diversity increased between the well closest to the landfill and the intermediate well but was lower at the most distant well. The majority of the cultured microbes represent taxa frequently recovered from contaminated environments, with 47% belonging to taxa with previously documented bioremediation potential. Multivariate redundancy analysis showed that the microbial composition was most similar in wells located closer to the landfill, although beta diversity analysis indicated a significant difference in microbial composition across the wells. Taken together with the results of cell counting, culture, and metabarcoding, these findings illustrate the effect of landfill leachates on microbial communities.

Field, Laboratory and Modeling Evidence for Strong Attenuation of a Cr(VI) Plume in a Mudstone Aquifer Due to Matrix Diffusion and Reaction Processes.

This study uses a combination of conventional and high resolution field and laboratory methods to investigate processes causing attenuation of a hexavalent chromium (Cr(VI)) plume in sedimentary bedrock at a former industrial facility. Groundwater plume Cr(VI) concentrations decline by more than three orders of magnitude over a 900 m distance down gradient from the site. Internal plume concentrations generally exhibit stable to declining trends due to diffusive and reactive transport in the low permeability matrix as fluxes from the contamination source dissipate due to natural depletion processes and active remediation efforts. The strong attenuation is attributed to diffusion from mobile groundwater in fractures to immobile porewater in the rock matrix, and reactions causing transformation of aqueous Cr(VI) to low-solubility Cr(III) precipitates, confirmed by high spatial resolution rock matrix contaminant concentrations and comparisons with groundwater concentrations from multi-level sampling within the plume. Field characterization data for the fracture network and matrix properties were used to inform 2-D discrete-fracture matrix (DFM) numerical model simulations that quantify attenuation due to diffusion and reaction processes, which show consistency with field datasets, and provide insights regarding future plume conditions. The combination of field, laboratory and modeling evidence demonstrates effects of matrix diffusion and reaction processes causing strong attenuation of a Cr(VI) plume in a sedimentary bedrock aquifer. This approach has important implications for characterization of sites with Cr(VI) contamination for improved site conceptual models and remediation decision-making.

Spatial patterns of Zn, Cd, and Pb isotopic compositions of ground and surface water in mine areas of South Korea reflecting isotopic fractionation during metal attenuation.

As application of multiple metal isotopes can effectively constrain geochemical behavior of contaminants and assess contamination sources and pathways, field-scale studies on the geochemically interlinked fractionation of Zn and Cd isotopes in groundwater are needed. In this study, we collected groundwater samples from multi-level samplers downstream of tailings dumps as well as surface water, ore mineral, precipitate, and tailings samples at the Sambo and Buddeun metallic ore mines in South Korea, and analyzed their Zn, Cd, Pb, and sulfur isotopic compositions. Furthermore, isotopic ratios of ore mineral samples from additional four mines in South Korea (Dangdu, Dongbo, Gomyeong, Samgwang) were compared. A dual isotopic approach using Zn and Cd isotopes was used to assess fractionation processes, and Pb isotopic signatures reflecting their sources were assessed. Increasing trends of δ66Zn and δ114Cd with decreasing Zn and Cd concentrations were observed in groundwater, which was saturated with respect to ZnS (amorphous and sphalerite) and CdS (greenockite). Moreover, for some groundwater samples, δ66Zn showed a positive relationship with δ34SSO4. These results suggest that Zn and Cd are precipitated as sulfide following sulfate reduction. In the plot of δ66Zn against δ114Cd, relatively high and/or increasing δ66Zn in groundwater suggested the effect of fractionation due to sulfide precipitation, while variable and high δ114Cd values suggested the fractionation by adsorption and/or sulfide precipitation, which were based on positive fractionation factors for δ66Zn and δ114Cd during sulfide precipitation and mostly negative and positive fractionation factors for δ66Zn and δ114Cd, respectively, during adsorption. This study shows that the combined use of Zn and Cd isotopes in groundwater can effectively differentiate between adsorption and sulfide precipitation following sulfate reduction in groundwater. Additionally, the 208Pb/206Pb ratios of most water samples reflected those of ore and tailings samples, which verified usefulness of Pb isotopes in water in investigating Pb contamination sources.