University Of Missouri Research Articles

Neutron and gamma radiation effects on thermal storage properties of polyethylene wax

Several nuclear reactors use ice condensers to condense steam in the case of a loss of coolant accident. These ice condensers have many problems that could be alleviated by using another material. The effects of low-dose neutron and gamma radiation on the thermal properties of polyethylene wax (PEW) were investigated for this purpose. PEW was irradiated in the Missouri University of Science and Technology Research Reactor (MSTR), the University of Missouri Cyclotron (MUC) and the University of Missouri Research Reactor (MURR) up to doses equivalent to 10 months in a nuclear power reactor's containment structure. The melting temperature and latent heat of fusion were determined using differential scanning calorimetry (DSC). Changes in the molecular bonds was determined using Raman spectroscopy. It was found that there was not a significant change in the thermal properties nor bonding over the investigated doses. This suggests that organic PCMs could be reliable alternatives to ice in nuclear reactor containment applications. The measured melting peak was found to be significantly wider expected by the suppliers' description. The ramifications of wide melting peaks are discussed in the context of reactor accident analysis and further experiments are suggested.

SNAP for U: Food insecurity and SNAP use among college students, including institution type differences

The objective of this study was to examine food insecurity and knowledge of the Supplemental Nutrition Assistance Program (SNAP), including barriers to and facilitators for enrolling in SNAP among college students in the Midwest. An obser­vational, cross-sectional online survey was admini­stered during Fall 2021 to Spring 2022. Participants included 844 college students from nine higher education institutions across Missouri. Of students who participated, 44.9% reported being food insecure, 67.9% reported knowing what SNAP was, and only 34.3% knew if they were eligible for SNAP. Students at private colleges [unadjusted odds ratio (OR) and 95% confidence interval (CI) = 4.79 (2.45-9.36), p<0.001)], community colleges [OR 3.21 95% CI (2.26-4.56), p<0.001)], technical schools [OR 2.21 95% CI (1.08-4.53), p=0.031], and Historically Black Colleges and Universities (HBCUs) [OR 2.05 95% CI (1.37-3.07)., p<0.001] reported higher odds of food security compared to public institutions. College students reported lack of knowledge of SNAP in general as the main barrier for enrollment and campus assistance as the main facilitator. Food insecurity is highly prevalent in Missouri college students, where SNAP knowl­edge and enrollment barriers persist. Findings sup­port a need for increased attention and resources to target college food insecurity.

Monte Carlo dosimetric analyses on the use of 90Y-IsoPet intratumoral therapy in canine subjects

Objective. To investigate different dosimetric aspects of 90Y-IsoPet™ intratumoral therapy in canine soft tissue sarcomas, model the spatial spread of the gel post-injection, evaluate absorbed dose to clinical target volumes, and assess dose distributions and treatment efficacy. Approach. Six canine cases treated with 90Y-IsoPet™ for soft tissue sarcoma at the Veterinary Health Center, University of Missouri are analyzed in this retrospective study. The dogs received intratumoral IsoPet™ injections, following a grid pattern to achieve a near-uniform dose distribution in the clinical target volume. Two dosimetry methods were performed retrospectively using the Monte Carlo toolkit OpenTOPAS: imaging-based dosimetry obtained from post-injection PET/CT scans, and stylized phantom-based dosimetry modeled from the planned injection points to the gross tumor volume. For the latter, a Gaussian parameter with variable sigma was introduced to reflect the spatial spread of IsoPet™. The two methods were compared using dose-volume histograms (DVHs) and dose homogeneity, allowing an approximation of the closest sigma for the spatial spread of the gel post-injection. In addition, we compared Monte Carlo-based dosimetry with voxel S-value (VSV)-based dosimetry to investigate the dosimetric differences. Main results. Imaging-based dosimetry showed differences between Monte Carlo and VSV calculations in tumor high-density areas with higher self-absorption. Stylized phantom-based dosimetry indicated a more homogeneous target dose with increasing sigma. The sigma approximation of the 90Y-IsoPet™ post-injection gel spread resulted in a median sigma of approximately 0.44 mm across all cases to reproduce the dose heterogeneity observed in Monte Carlo calculations. Significance. The results indicate that dose modeling based on planned injection points can serve as a first-order approximation for the delivered dose in 90Y-IsoPet™ therapy for canine soft tissue sarcomas. The dosimetry evaluation highlights the non-uniformity of absorbed doses despite the gel spread, emphasizing the importance of considering tumor dose heterogeneity in treatment evaluation. Our findings suggest that using Monte Carlo for dose calculation seems more suitable for this type of tumor where high-density areas might play an important role in dosimetry.

Reactive Carbon Capture: Cooperative and Bifunctional Adsorbent-Catalyst Materials and Process Integration for a New Carbon Economy.

ConspectusTo say the least, releasing CO2 into the atmosphere is reaping undue environmental consequences given the ever-present increase in severe global weather events over the past five years. However, it can be argued that-at least in the confines of current technological capabilities-the atmospheric release of CO2 is somewhat unavoidable given that even shifting toward clean energy sources-such as solar, nuclear, wind, battery, or H2 power-incurs an initial carbon requirement by way of manufacturing the very production abilities through which "clean" energy is generated. Even years from now, experts agree that energy production will be diversified and-as the global population continues to drive the growth of global energy consumption-thermal power derived from carbon combustion is likely to remain one intrinsic energetic source, of which CO2 will always be a byproduct. In this context, it is the responsibility of the scientific community to devise improved pathways of carbon management such that (i) the consequences of combustion on the global environment are reduced and (ii) carbon fuels can be leveraged in a sustainable fashion.In this Account, we discuss a pivotal perspective shift on CO2 emissions derived from a considerable breakthrough in material science from our work at Missouri University of Science and Technology. This account details the development of materials which no longer vilify CO2 emissions as a valueless combustion byproduct, instead providing a path for them to become a potential feedstock. In more specific terms, this work details the development of structured, cooperative "bifunctional" materials (BFMs) comprised of (i) a high-temperature adsorbent and (ii) a heterogeneous catalyst that enable single-bed CO2 capture and utilization in oxidative ethane dehydrogenation (ODHE), oxidative propane dehydrogenation (ODHP), and dry methane reforming (DMR) processes. This Account begins with the conceptual development of the BFMs in the powdered state, followed by detailing the first-ever reports of structuring the materials into facile honeycomb contactors by 3D printing. The Account then summarizes the impressive performance of the 3D-printed BFMs, specifically focusing on how their catalysts (metal oxides and perovskites) influence their reactive CO2 capture performances in ODHE, ODHP, and DMR processes. Such promise of CO2-as-fuel offers a glimpse into the future of a diversified energy economy, in which CO2/fuel looping can play an important role. A major factor in achieving this future is, of course, developing an appropriately active catalyst; an account of whose first breakthroughs in material science are detailed herein.

2024 SPE Pioneers of Improved Oil Recovery

Reservoirs present plenty of complexity and mystery. Four oil recovery experts have helped remove some of those mysteries, taming the complex to boost production. From developing preformed particle gels that improve conformance when fractures cause severe channeling to simulating enhanced oil recovery (EOR) processes in the reservoir to identifying the aqueous stability concept to demonstrating the distance polymer solutions can travel without degradation, the four 2024 recipients of the 2024 Improved Oil Recovery (IOR) Pioneer Award have made a “sustained and important contribution to increased oil recovery,” Randy Seright, New Mexico Tech, 2024 Pioneer selection committee chairman and 2008 honoree, told JPT. Seright, four other previous recipients of the recognition, and 2024 SPE IOR Conference General Chairman Tom McCoy evaluated a field of 16 nominees for the lifetime achievement honor and selected four who have throughout their careers “made the most lasting and significant contributions to IOR,” Seright said. “It’s why we are where we are today with respect to IOR.” The 2024 IOR Pioneer recipients who were honored during the biannual IOR conference in Tulsa in April are Baojun Bai, professor of petroleum engineering, who sits in the Lester Birbeck Endowed Chair at Missouri University of Science and Technology (Missouri S&T) in Rolla, Missouri; Mojdeh Delshad, research professor in the Hildebrand Department of Petroleum and Geosystems Engineering at The University of Texas at Austin (UT-Austin); Varadarajan Dwarakanath, team lead for chemical EOR at the Chevron Technology Center in Houston; and Stephane Jouenne, who previously led a TotalEnergies team dedicated to surface and subsurface research topics for polymer flooding and is currently CO2 capture project coordinator at TotalEnergies. “It’s the most prestigious award given out in IOR,” Seright said.

Succeeding in American Government: The Benefits of Supplemental Instruction in Political Science at a Hispanic-Serving Institution

Supplemental instruction (SI) has become ubiquitous on college campuses. Originally developed at the University of Missouri, Kansas City, SI has become a popular pedagogical tool. While ample evidence exists that SI is particularly helpful regarding courses in the natural sciences, less is known about the helpfulness of SI in political science. In this paper, we seek to understand the effect of supplemental instruction in a core political science course, Introduction to American Government. We examine this effect at a community college that is designated as a Hispanic Serving Institution (HSI). Using data from 332 students, across two semesters, we found that participation in SI sessions improved student success outcomes across several indicators, most notably course retention and success. More importantly, we find this improvement among Latinx students as well when further analyzed by race and ethnicity. This is highly relevant given the demographics of the college.

Reimagining the university’s role in the health and well-being of the people it serves

Academic medical centers and university extension programs remain underdeveloped collaborators, despite the complementary objectives between translational science and extension. This case study details the creation of a nationally unique interprofessional organizational structure between the University of Missouri (MU) Office of Extension and Engagement (MU Extension) and the MU School of Medicine to accelerate statewide reach of research and education discoveries using high-touch community health approaches. This article describes specific strategies used to systematically plan for: 1) creation and operation of the new structure, 2) routinization and institutionalizing the work, and 3) sustainability. We further outline challenges and next steps. The development of the backbone organization office of Health Outreach Policy and Education (HOPE) brings together the interprofessional expertise of five units with a common agenda to advance mutually reinforcing activities. HOPE is poised to make significant contributions to amplify MU’s land grant mission, garner additional grant funding, and advance the health of Missourians.

Doing Academia Differently: In Conversation With Neuroatypicality

This special issue originated from a webinar series made possible through a Tri-Continental (3C) Partnership between the University of the Western Cape, the University of Missouri, and Ghent University. These universities organized a series of webinars on the theme “Doing Academia differently: In conversation with neuroatypicality.” The Tri-Continental (3C) Partnership is a trilateral agreement that set out to promote partnership between the three institutions during a time of travel restrictions due to the global pandemic.

Neighborhood Disadvantage, Social Groups, and Adolescent Violence: Assessing Mechanisms in Structural-Cultural Theories

Structural-cultural perspectives link contextual characteristics to interactions with associates who transmit definitions favorable to crime, thus influencing behavior. Drawing on this, we predict that: (1) adolescents in disadvantaged neighborhoods will be more likely to have parents, friends, and schoolmates who hold violent rationalizations, (2) exposure to associates who hold violent rationalizations will increase an adolescent’s own violent rationalizations, and (3) one’s willingness to rationalize violence will be associated with self-reported violent conduct. Using panel data from the University of Missouri – St. Louis Comprehensive School Safety Initiative and structural equation models, our findings indicate that respondents residing in disadvantaged neighborhoods are more likely to be exposed to associates who report a greater willingness to rationalize violence, which in turn predicts an adolescent’s own rationalizations. Further, one’s willingness to rationalize violence is predictive of violent conduct and mediates the effects of associates’ attitudes on self-reported violence.

Short‐term effects of Kernza and alfalfa on microbial communities

AbstractContinuous land disturbance could negatively impact microbial community, but perennial crops can potentially reverse this negativity. The objective of this study was to evaluate the effects of Kernza (Thinopyrum intermedium) and alfalfa (Medicago sativa L.) on soil microbial structure and stress condition using the phospholipid fatty acid profiling. The study was conducted at the Ross Jones Research Farm, University of Missouri and consisted of four treatments: Kernza fertilized, Kernza unfertilized, Kernza and alfalfa intercrop, and alfalfa monocrop with four replications. Treatments were established in September 2021 on 18.3 m × 18.3 m plots. Soils from 0‐ to 5‐cm and 5‐ to 15‐cm depths were sampled in September 2021 (before treatments were placed) and 2022 and analyzed for microbial communities. All microbial communities increased after 1 year with the perennial crops. Since differences were not significant among treatments in 2022, this may lead to positive impacts of perennial crops on microbial communities, irrespective of the crop species and management. Moreover, community structure modifications were also observed with the perennial crops, irrespective of the species and management, as evidenced with changes in bacterial community indices in 2022. While fungi/bacteria ratio increased, Gram‐positive/Gram‐negative bacteria ratio decreased in 2022, suggesting a reduction in microbial stress, which can be attributed to ecological functions of the perennial crops. The study showed improvements in soil microbial biomass and modifications in microbial community structure after 1 year of Kernza and alfalfa. As the system matures, relative benefits of management (fertilization and intercropping) and plant species may be realized.

Adolescent Weapon Carrying Inside and Outside of School: The Impact of Experiences and Perceptions of Violence

This study examined factors that distinguish adolescent weapon carrying in school compared to only in the community. We look at how experiences (offending, victimization, and gang-involvement) and perceptions (school, neighborhood, individual) toward violence are associated with self-reported weapon carrying in these two locations. Data came from two waves of the University of Missouri – St. Louis Comprehensive School Safety Initiative, a longitudinal study on the causes and consequences of school violence. Multinomial logistic regression was used to predict weapon carrying among three mutually exclusive categories: those who do not carry, those who carry only in the community, and those who carry both in school and in the community. We find that victim/offenders are more likely to carry weapons regardless of context, but school weapon carrying is positively associated with fatalism and gang-involvement. One school factor, school commitment, impacted carrying both inside and outside of school. Our results identify unique factors that can reduce adolescent weapon carrying in general and specifically in school.

115 Gene editing: Where are we on campus and where can it go?

Abstract Editing the genome of livestock provides solutions to otherwise intractable problems and can provide a tool to better understand the role of specific proteins during development. The potential benefit for production agriculture is so great that the USDA Agricultural Research Service has invested in 4 positions now located in a research unit at the University of Missouri with a focus currently on swine and poultry. Genome editing can result in introducing alleles from divergent populations or novel alleles to produce animals that have new proteins, modified proteins or animals that no longer produce a protein. Applications of genome editing include improving disease resistance (viral and bacterial), improving digestion, disseminating valuable genetics, improved thermoregulation, changing the body/milk composition, and creating hypoallergenic meat. Changes in these animals will improve animal welfare, animal productivity and the sustainability of animal agriculture. In addition to improving animal agriculture, gene editing has enabled a new understanding of maternal recognition of pregnancy in the pig and a better understanding of molecules involved in growth and development of pigs. With new developments in editing of just somatic cells [somatic cell gene editing (SCGE), rather than germline editing], it will be possible to edit some cells in existing animals and thus change their phenotype. SCGE technologies such as this are being developed via the biomedical community as models to lead to human clinical applications. One such application is to correct cells in the lungs that produce the CFTR protein. Correction of just 10% of the cells in the lungs is estimated to correct the lung symptoms associated with cystic fibrosis. Similar applications in production agriculture might produce animals that have novel phenotypes of an altered carcass composition or better use of nutrients. Application of genetic engineering technologies such as genome editing is limited by biology and the imagination of the investigator.

Leaning Into the Liminal: A Guide for Counselors and Companions (2024). Edited by Timothy L. Carson. ⁠The Liminality Press. ISBN: ‏9798989164004

Liminality is a concept that straddles various domains of thought and practice. In the context of human suffering the concept has much to offer clinical practitioners who work with clients undergoing significant life changes. In Leaning Into the Liminal: A Guide for Counselors and Companions (2024a), editor Dr. Timothy L. Carson facilitates a range of voices exploring the meanings and uses of liminality. Carson is a pastor who completed his doctoral research on liminality and now heads the Liminality Project at the University of Missouri. The concept of liminality is treated in the text as a description of how people move through the disorientating passage from what is known, through unknowing, and into the new. Individuals traverse such passages when they experience key changes in life. Protocols for supporting this movement are a valuable part of the discussions in this book. The book is organised into sections dealing with liminality in clinical practice, recovery from war (including in Ukraine), spiritual direction, and dying. This exploration will be helpful to counsellors, psychotherapists, and practitioners who are unfamiliar with this liminal perspective on human experience. Some of the contributions to the book are tender and intimate in a way that supports a deepening engagement with these essential life transitions.

Registration of ‘S16‐16814R’: A glyphosate‐tolerant, high‐oleic soybean cultivar

AbstractThere is a demand for soybean [Glycine max (L.) Merr.] cultivars with more functional soybean oil for food and industrial applications. Soybean breeding programs have devoted more efforts to developing high‐yielding soybean cultivars with elevated oil content and improved fatty acid profiles. The University of Missouri – Fisher Delta Research, Extension, and Education Center soybean breeding program has developed and released the high‐oleic soybean cultivar ‘S16‐16814R’ (Reg. no. CV‐561, PI 704911). It is a maturity group 4‐late (relative maturity 4.9), glyphosate‐tolerant (Roundup Ready 1) soybean cultivar with high oleic (84.0%) acid content and a reduced linolenic (3.5%) acid content. S16‐16814R is resistant to multiple nematode species, including soybean cyst nematode races 2 (HG Type 1.2.5.7), 3 (HG Type 5.7), and 5 (HG Type 2.5.7); southern root‐knot nematode; and reniform nematode. S16‐16814R was evaluated from 2017 to 2020 in 61 environments across eight southern US states. It averaged 92% of the check mean for yield, indicating competitive yield performance across multiple environments.

Perfect Polar Alignment of Parallel Beloamphiphile Layers: Improved Structural Design Bias Realized in Ferroelectric Crystals of the Novel "Methoxyphenyl Series of Acetophenone Azines".

Invited for the cover of this issue are Harmeet Bhoday, Nathan Knotts, and Rainer Glaser at the Missouri University of Science and Technology. Joe Miner, the university mascot, is a silent and honorary co-author and personifies the spirit of the old west and the determination to succeed (our emphasis). The image depicts one (MeO-Ph, Y)-azine molecule and a model of a perfectly polar stacked bilayer. The floodlight illumination presents a graphic metaphor of second-harmonic generation (frequency doubling) by the crystalline ferroelectric materials. Read the full text of the article at 10.1002/chem.202400182.

Incidence and characterization of aerophagia in dogs using videofluoroscopic swallow studies.

Aerophagia (ingestion of air), is a functional aerodigestive disorder in people. Criteria for diagnosis of aerophagia in dogs are >1/3 of bolus volume containing air or ingested air resulting in gastric distention (>1/3 of end gastric volume). Aerophagia is highlighted during eating and drinking. Videofluoroscopic swallow studies (VFSS) document aerophagia in dogs, but the incidence, clinical signs (CS), and associated disorders are unknown. Identify the incidence of aerophagia, compare CS between dogs with and without aerophagia, and identify associated and predisposing disorders using VFSS. A total of 120 client-owned dogs. Sequential VFSS and associated medical records from dogs presenting to veterinary teaching hospitals at Auburn University and the University of Missouri were retrospectively reviewed. Statistical comparisons were made using Mann-Whitney and chi-squared tests, odds ratios (OR), and multiple logistic regression (P < .05). The incidence (95% confidence interval [CI]) of aerophagia was 40% (31.7-48.9). Dogs with mixed CS (gastrointestinal [GI] and respiratory; P < .001, 58.3%) were more likely to have aerophagia than dogs with exclusively respiratory CS (25%). Aerophagia was significantly more common in brachycephalic dogs (P = .01; 45.8% vs 13.8%), dogs with nonbrachycephalic upper airway obstruction (P < .001; 33.3% vs 4.1%), pathologic penetration and aspiration (P-A) scores (P = .04; 41.6% vs 23.6%), and gagging (P < .001; 25% vs 11.7%). Mixed CS (P = .01), brachycephaly (P < .001), and upper airway obstruction (P < .001) were independent predictors of aerophagia. Aerophagia was common, particularly in dogs with mixed CS. Brachycephalic dogs and dogs with upper airway obstruction are predisposed. Aspiration risk was high, emphasizing overlapping upper aerodigestive pathways.

‘Built on my B(l)ack’: racial capitalism and anti-Blackness in predominantly white institutions of higher education

ABSTRACT This article presents a qualitative analysis of Black student organizers’ experiences of racism at the University of Missouri, where they led a resurgence of campus struggles in 2015. Semi-structured interviews with former student organizers were conducted and, together with archival materials, subject to thematic analysis. Black students faced frequent racist aggression, wherein their presence in campus social and intellectual life was cause for white alarm and aggression. Analyzing experiences and impacts of everyday violence in relation to broader systems of anti-Blackness and racial capitalism, the article identifies educational, psychological, social, spatial, material, and political consequences of campus racism. Several broader impacts of anti-Black racism are delineated, including psychological harm, economic dispossession, and institutional maintenance. The findings illuminate the effects of varied but cohesive instances of anti-Black racism in higher education, making visible repetitive moments of everyday violence that universities both enable and erase.

Experiential Learning in Daylighting Course through Performance Measurements

The main objective of this study is to adapt research studies on performance measurements for daylighting design to education. An experimental course has been introduced in Missouri University of Science and Technology, and the curriculum was developed by including active learning beside the traditional learning environment. The parameters used in the schematic design and design development stages are presented, and the curriculum topics and practical experience are explained in the study. Particularly performance measurements are associated with course assignments. Curriculum results are evaluated qualitatively with assignment results and quantitatively with surveys. Current and emerging metrics are included in lab assignments and results of course assessments show that emerging metrics in daylighting technology and practical experience had attraction over participants. As a result of the evaluation of two sample courses, differences emerge regarding the courses that can be given at undergraduate and graduate levels. These differences are grouped into traditional lecture learning environments and experiential learning environments. The learning outcomes of the course curricula are summarized as gaining the knowledge and skills to communicate technically at the level of design practitioner for the student aiming for undergraduate graduation and at the level of the research community for the student aiming for graduate level.

Unveiling global research trends and hotspots on mitochondria in NAFLD from 2000 to 2023: A bibliometric analysis.

Nonalcoholic fatty liver disease (NAFLD) has garnered significant attention in the past decade as a prevalent chronic liver condition. Despite a growing body of evidence implicating mitochondria in NAFLD development, comprehensive bibliometric analyses within this research domain are scarce. This study aims to provide a thorough overview of the knowledge framework and key research areas related to mitochondria in the context of NAFLD, utilizing bibliometric techniques. A comprehensive search of publications on mitochondria in NAFLD from 2000 to 2023 was conducted using the Web of Science Core Collection database. VOSviewers, CiteSpace, and the R package "bibliometrix" were employed for a precise assessment of the literature. Examining 2530 articles from 77 countries, primarily led by the United States and China, revealed a consistent increase in publications on mitochondria's role in NAFLD. Leading research institutions include the University of Coimbra, the University of Missouri, the Chinese Academy of Sciences, Fudan University, and Shanghai Jiao Tong University. Notably, the International Journal of Molecular Sciences emerged as the most popular journal, and Hepatology was the most frequently cited. With contributions from 14,543 authors, Michael Roden published the highest number of papers, and A. J. Samyal was the most frequently cocited author. Key focus areas include investigating mitochondrial mechanisms impacting NAFLD and developing therapeutic strategies targeting mitochondria. Emerging research hotspots are associated with keywords such as "inflammation," "mitochondrial dysfunction," "autophagy," "obesity," and "insulin resistance." This study, the first comprehensive bibliometric analysis, synthesizes research trends and advancements in the role of mitochondria in NAFLD. Insights derived from this analysis illuminate current frontiers and emerging areas of interest, providing a valuable reference for scholars dedicated to mitochondrial studies.

Effect of shipping on the microbiome of donor mice used to reconstitute germ-free recipients.

The gut microbiota (GM) influences multiple processes during host development and maintenance. To study these events, fecal microbiota transfer (FMT) to germ-free (GF) recipients is often performed. Mouse models of disease are also susceptible to GM-dependent effects, and cryo-repositories often store feces from donated mouse strains. Shipping live mice may affect the GM and result in an inaccurate representation of the baseline GM. We hypothesize that the use of such fecal samples for FMT would transfer shipping-induced changes in the donor GM to GF recipients. To test this, donor mice originating from two suppliers were shipped to the University of Missouri. Fecal samples collected pre- and post-shipping were used to inoculate GF mice. Pre- and post-shipping fecal samples from donors, and fecal and/or cecal contents were collected from recipients at one and two weeks post-FMT. 16S rRNA sequencing revealed supplier-dependent effects of shipping on the donor microbiome. FMT efficiency was independent of shipping timepoint or supplier, resulting in transmission of shipping-induced changes to recipient mice, however the effect of supplier-origin microbiome remained evident. While shipping may cause subtle changes in fecal samples collected for FMT, such effects are inconsistent among supplier-origin GMs and minor in comparison to other biological variables.