Critical Stress Level Research Articles

Avaliação da resiliência térmica de edificações em sobreaquecimento nos cenários presente e de alterações climáticas

Abstract Thermal resilience refers to a building’s capacity to adapt to extreme thermal variations, maintaining a healthy environment for its occupants. This study aims to assess the thermal resilience of a naturally ventilated low-income residential building in overheating conditions within a region of savannah tropical climate. Various indices, including adaptive thermal comfort, Indoor Overheating Degree (IOD) and Exceedance Hours (HE), Heat Index (HI), and Standard Effective Temperature (SET) were calculated in current and climate change scenarios using two models, a standard building (HISp) and a building that incorporates passive bioclimatic strategies (HISe).It was demonstrated that thermal insulation and low absorption strategies significantly contribute to indoor environmental quality, reducing the risk of overheating exposure in all evaluated scenarios. Despite reducing discomfort hours and critical thermal stress levels, the idealized strategies do not provide adequate habitability conditions for the occupants. Overheating will become even more severe in projected future scenarios. Among the two dwellings, HISe demonstrates a superior potential to mitigate the risk of overheating compared to HISp in all the scenarios evaluated.

The role of mineralogical and textural complexity in the damage evolution of brittle rocks.

In brittle rocks, deformation is characterized by the initiation and propagation of cracks at both microscale and mesoscale levels. This study explores how rock texture influences the evolution of cracking networks and progressive rock damage results under uniaxial compression. 3D discrete analyses were employed to identify the critical stresses of three different rock types. Thin sections were prepared from uniaxially loaded core samples at these stresses and crack patterns were captured under a polarizing microscope. The fractal box dimension method was used to quantitatively analyze the crack patterns for each rock type at each stress level. The novelty of this research is revealing the relationship between the development of microcrack patterns and textural properties such as mineral orientation/distribution, interlocking, crystal cleavage/hardness, and the groundmass. Results show that the cracking tendency varies with rock type at each critical stress level. Specifically, diabase exhibited the highest crack intensity, attributed to the interlocking of hard plagioclase and pyroxene crystals. Furthermore, the cleavages in pyroxenes make diabase particularly susceptible to cracking, especially when they are oriented parallel or semi-parallel to the applied load. These findings highlight that rock texture is a crucial factor influencing microcrack development, which should be considered in rock engineering applications.

Experimental and Numerical Indentation Tests to Study the Crack Growth Properties Caused by Various Indenters Under High Temperature

ABSTRACTThis paper investigates the influence of indenter shape and rock texture on the crack growth properties and rock hardness. For this purpose, two different rock specimens such as basalt and marble with various textures were prepared and tested by Vickers indentation hardness device with rhombus indenter shape under two different temperatures of 35°C and 100°C. Concurrent with the experimental test, Vickers indentation simulations have been done on three calibrated rock models with nine different indenter shapes. The tensile strength of marble was 8 MPa, while basalt had a tensile strength of 10.8 MPa. Regarding compressive strength, marble exhibited 71 MPa, whereas basalt had a compressive strength of 153 MPa. Marble and basalt had elastic moduli of 45 and 95 GPa, respectively. The physical loading was applied vertically at a rate of 0.004 mm/min. The rock's texture and temperature significantly impact Vickers indentation hardness. Penetration by the Vickers indenter creates an elastic‐plastic stress field, leading to radial cracks due to exceeding the critical stress level. Ring cracks are caused by bulging of the test material and nested cracks directly under the indentation due to high shear and bending stresses in the region. The indentation shape affected the extent of the damage zone below it, leading to increased crack growth with smaller indentation diameters. The radial fracture number increased when the cross‐section changed from circular to quadrilateral shape. The crack growth and damage zone area increased with higher rock temperature due to increased rock brittleness.

FCC twins and martensites responses of metastable dual-phase high entropy alloy to friction stir processing

Fe50Mn30Co10Cr10 dual-phase high entropy alloy (DP-HEA) has good application prospects in the nuclear and automotive industries due to its strength-ductility synergistic effect. The initial volume fractions of FCC twins and HCP martensites in Fe50Mn30Co10Cr10 HEA affect the relative contribution of transformation-induced plasticity and twinning-induced plasticity to the alloy's strength and ductility under loading conditions. Understanding the relationship between FCC twins and martensites is crucial during the friction stir process (FSP). In this study, the microstructure of Fe50Mn30Co10Cr10 HEA as FSP condition was studied. The HCP phase in the base metal almost completely transformed into the FCC phase during FSP. Both FCC twin and HCP martensite transformations serve to alleviate strain in the FCC matrix. The initiation of FCC twin and martensite formation depends on critical stress levels at different temperatures. Higher strain and coarser grains promote more martensite formation, while finer grains and lower strain impede it, causing FCC twins to occur before HCP martensites during the cooling process of materials in the processed zone. These findings offer insights into controlling the volume fractions of twins and martensites in FSPed DP-HEA, thereby potentially enhancing the mechanical properties of DP-HEA.

Correlation between Malocclusion and Mandibular Fractures: An Experimental Study Comparing Dynamic Finite Element Models and Clinical Case Studies.

Mandibular fractures are very common in maxillofacial trauma surgery. While previous studies have focused on possible risk factors related to post-operative complications, none have tried to identify pre-existing conditions that may increase the risk of mandibular fractures. We hypothesized, through clinical observation, that anatomical conditions involving poor dental contacts, such as malocclusions, may increase the risk of mandibular fractures. This work was subdivided into two parts. In the first part, Digital Imaging and Communications in Medicine (DICOM) data of four healthy patients characterized by different dentoskeletal occlusions (class I, class II, class III, and anterior open bite) have been used to develop four finite element models (FEMs) that accurately reproduce human bone structure. A vertical and lateral impact have been simulated at increasing speed on each model, analyzing the force distribution within the mandibular bone. Both vertical and lateral impact showed higher level of stress at the impact point and in the condylar area in models characterized by malocclusion. Specifically, the class III and the open bite models, at the same speed of impact, had higher values for a longer period, reaching critical stress levels that are correlated with mandibular fracture, while normal occlusion seems to be a protective condition. In the second part of this study, the engineering results were validated through the comparison with a sample of patients previously treated for mandibular fracture. Data from 223 mandibular fractures, due to low-energy injuries, were retrospectively collected to evaluate a possible correlation between pre-existing malocclusion and fracture patterns, considering grade of displacement, numbers of foci, and associated CFI score. Patients were classified, according to their occlusion, into Class I, Class II, Class III, and anterior open bite or poor occlusal contact (POC). Class I patients showed lower frequencies of fracture than class II, III, and open bite or POC patients. Class I was associated with displaced fractures in 16.1% of cases, class II in 47.1%, class III in 48.8% and open bite/POC in 65.2% of cases (p-value < 0.0001). In class I patients we observed a single non-displaced fracture in 51.6% of cases, compared to 12.9% of Class II, 19.5% of Class III and 22.7% of the open bite/POC group. Our analysis shows that class I appears to better dissipate forces applied on the mandible in low-energy injuries. A higher number of dental contacts showed a lower rate of multifocal and displaced fractures, mitigating the effect of direct forces onto the bone. The correlation between clinical data and virtual simulation on FEM models seems to point out that virtual simulation successfully predicts fracture patterns and risk of association with different type of occlusion. Better knowledge of biomechanics and force dissipation on the human body may lead to the development of more effective safety devices, and help select patients to plan medical, orthodontic/dental, and/or surgical intervention to prevent injuries.

Evolutionary mechanisms in the plastic deformation of γ'-Ni3(Al, Ti)-strengthened additively manufactured nickel-based 939 superalloys at intermediate temperatures

Tensile interruption experiments with different strains were conducted on additively fabricated nickel-based Inconel 939 superalloys at 700 ℃ to investigate the evolution of multiple deformation mechanisms. The microstructures of different strain groups captured by transmission electron microscopy (TEM) were analyzed, and it was concluded that a total of four various deformation mechanisms were identified, of which the first to be activated was the Orowan loop bypassing γ', and a tendency of transition from double to single loop was observed. Anti-phase boundary (APB) shearing was subsequently initiated, with a needed critical resolved shear stress level of approximately 195.82 MPa. Stacking faults (SFs) and deformation twinnings (DTs) were observed at higher stress, accompanied by the dissociation of dislocations. In addition, the magnitude of the stacking fault energy of AM 939 superalloys at intermediate temperature was calculated and estimated by matching the experimental phenomena with the critical shear stress.

A local stress criterion to assess the effects of hydrogen embrittlement on the fracture strength of notched tensile specimens

This work addresses the applicability of a local criterion incorporating the coupling of critical stress and a critical hydrogen concentration to predict hydrogen embrittlement effects on the fracture strength of high strength steels using notched round specimens with different notch root radii. The numerical simulations incorporating a relatively simple hydrogen transport model provide strong support for the adoption of a failure criterion in terms of achieving a critical level of tensile stress coupled to the local hydrogen concentration, which, in turn, enable the construction of a failure locus for the degraded material. For the cases analyzed here, construction of such a failure locus based on a critical combination of maximum principal stress and hydrogen concentration enabled predictions of fracture strength for hydrogen-charged tensile specimens which are in very good agreement with experimental data. Overall, the results presented here lend additional support for further developments of a local stress-based criterion to predict hydrogen embrittlement effects on the fracture strength of high strength steels.

Mechanically induced dye-release from polyurea microcapsules in a rubbery adhesive

Especially in the building industry the demand for in situ monitoring concepts of adhesive joints persists. In a new approach, microcapsules filled with special dyes, are added into a rubbery adhesive. Certain stress levels within the adhesive lead to a breakage of the capsules, which release their liquid cores. This results in a detectable colour change and thus, enables non-destructive condition monitoring of the bond. Dye-filled polyurea microcapsules were produced by interfacial polymerization by varying synthesis parameters while their influence on capsule morphology and wall thickness was determined. The morphology and thermal properties of the microcapsules were characterized by scanning electron microscopy and dynamic differential calorimetry, respectively. Subsequently, the method of nanoindentation was used to study the deformation and fracture behaviour of the microcapsules. Finally, it was analysed to what extent the microcapsules break within a polymer matrix, e.g. by critical stress levels or deformations. This development is a new quality assurance method for glass façades.

Assessing Climate-Driven Salinity Intrusion through Water Accounting: A Case Study in Ben Tre Province for More Sustainable Water Management Plans

This scientific paper delves into sustainable water management strategies for Ben Tre Province of the Vietnamese Mekong Delta (VMD) in light of water-infrastructure plans that have been impacted by climate change-induced salinity intrusion. Specifically, we aim to mitigate the effects of salinity intrusion for the province while promoting long-term environmental sustainability. In doing so, a water accounting framework was applied, mostly based on the MIKE11 hydrodynamic modeling and water balance calculations, to determine current and future water stress issues based on two main scenarios of extreme drought year 2016 (baseline) and the future year 2030 under climate change for a medium-low emission scenario (RCP4.5). The study found that salinity intrusion significantly causes severe water stress in the future year 2030 compared to the baseline year 2016, while the existing water management methods are relatively inadequate to control salinity intrusion, leading to over 57% of the area affected by medium to critical water stress levels, although it will go along with planned water infrastructures. Additionally, a system of triple rice cropping converted two rice cropping and upland cropping with 40% water demand cutoff was found to be the most suitable measure for 2030. Particularly, water-saving and water demand reduction should be incorporated into infrastructural planning for sustainable water management. Our study provides valuable insights for policymakers and stakeholders, not only for the province and the VMD, but also other regions facing similar challenges.

Study of the generalized curves of the static and cyclic deformation, damage and fracture

Individual deformation diagrams of all materials on metal, non-metal, or composite base under static and cyclic load link stresses and strains. These diagrams are obtained in standard tensile, compression, torsion or bending tests of laboratory samples with the registration of forces and deformations of their working parts upon loading. The diagram for a single static deformation in the stress-strain coordinates in this case covers both the region of elastic deformations and the region of elastic-plastic deformation, when deformations are localized in the neck of the loaded sample up to the moment of its destruction at a critical stress level. It is shown that linear, fractional-linear and power approximation of the obtained deformation curve are widely used in the description of the obtained deformation diagrams. Direct experiments, the theory of dislocations and the statistical theory of strength confirm the priority of power approximation of considered diagrams. At the same time for all construction materials the generalized deformation diagram in relative coordinates is described by a single power equation with the individual hardening parameter which is determined experimentally or theoretically using the dependences linking data on the module of elasticity, yield stresses, strength, and ultimate plasticity of the material. Diagrams of a cyclic elastoplastic deformation in the form of loops of plastic hysteresis are recorded by analogy with static tension diagrams with «stress – strain» axes of in conditional and true relative values. The generalized deformation diagrams for a single static and cyclic loading form a scientific basis for construction of the generalized fatigue curve on the basis of deformation fracture criterion for a wide range of cycles to failure. An effective solution to the problems of strength and service life for the most complex engineering objects such as nuclear reactors, aircraft, rocket and space systems can be achieved through introduction of generalized deformation and fracture diagrams into consideration and corresponding calculations. Their significance will especially increase in the design and implementation of new unique science-intensive facilities.

Effect of Compressive Loads on the Air-Permeability kT of Concrete

Since long it has been claimed that the departure from linearity of the σ-ε relation for concrete, up to failure under compression, is the result of cracks formation, first along the aggregate-paste interface, which later bridge the aggregates until, at around 75-80% of the maximum load (critical stress level), the matrix cracks become unstable, such that if that load is sustained, fracture will happen after a certain period (due to tertiary creep). This fact has been verified measuring volumetric strains, acoustic emission and ultrasound. The presence, growth and opening of such cracks must have an effect on the permeability of concrete, which was confirmed by water- and gas-permeability tests. The phenomenon was also studied applying a standard NDT method for air-permeability, based on a double-chamber vacuum cell, same as applied in the here reported research. This paper reports results of air-permeability kTof concrete cubes and half-cubes subjected to the following loading conditions: unloaded, sustained loads of 30, 60 and 90% of the ultimate load (measuring kT under the applied static load and the residual value after removing it) and dynamically during a test with monotonically increasing load till failure. The results indicate that a certain degree of damage, reflected in an increase of kT, is noticeably already at a 30% load level, which increases with the level of applied load. The dynamic kTtests were somewhat erratic, possibly, depending on whether the damage happened near or away from the surface where kT was measured.

Quantifying the Rock Damage Intensity Controlled by Mineral Compositions: Insights from Fractal Analyses

Since each rock type represents different deformation characteristics, prediction of the damage beforehand is one of the most fundamental problems of industrial activities and rock engineering studies. Previous studies have predicted the stress–strain behaviors preceding rock failure; however, quantitative analyses of the progressive damage in different rocks under stress have not been accurately presented. This study aims to quantify pre-failure rock damage by investigating the stress-induced microscale cracking process in three different rock types, including diabase, ignimbrite, and marble, representing strong, medium-hard, and weak rock types, respectively. We demonstrate crack intensity at critical stress levels where cracking initiates (σci), propagates (σcd), and where failure occurs (σpeak) based on scanning electron microscope (SEM) images. Furthermore, the progression of rock damage was quantified for each rock type through the fractal analyses of crack patterns on these images. Our results show that the patterns in diabase have the highest fractal dimensions (DB) for all three stress levels. While marble produces the lowest DB value up to σci stress level, it presents greater DB values than those of ignimbrite, starting from the σcd level. This is because rock damage in ignimbrite is controlled by the groundmass, proceeding from such stress level. Rock texture controls the rock stiffness and, hence, the DB values of cracking. The mineral composition is effective on the rock strength, but the textural pattern of the minerals has a first-order control on the rock deformation behavior. Overall, our results provide a better understanding of progressive damage in different rock types, which is crucial in the design of engineering structures.

Invasive frogs show persistent physiological differences to elevation and acclimate to colder temperatures

The coqui frog (Eleutherodactylus coqui) was introduced to the island of Hawai'i in the 1980s and has spread across much of the island. Concern remains that this frog will continue to expand its range and invade higher elevation habitats where much of the island's endemic species are found. We determined whether coqui thermal tolerance and physiology change along Hawai'i’s elevational gradients. We measured physiological responses using a short-term experiment to determine baseline tolerance and physiology by elevation, and a long-term experiment to determine the coqui's ability to acclimate to different temperatures. We collected frogs from low, medium, and high elevations. After both the short and long-term experiments, we measured critical thermal minimum (CTmin), blood glucose, oxidative stress, and corticosterone levels. CTmin was lower in high elevation frogs than low elevation frogs after the short acclimation experiment, signifying that they acclimate to local conditions. After the extended acclimation, CTmin was lower in frogs acclimated to cold temperatures compared to warm-acclimated frogs and no longer varied by elevation. Blood glucose levels were positively correlated with elevation even after the extended acclimation, suggesting glucose may also be related to lower temperatures. Oxidative stress was higher in females than males, and corticosterone was not significantly related to any predictor variables. The extended acclimation experiment showed that coquis can adjust their thermal tolerance to different temperatures over a 3-week period, suggesting the expansion of coqui into higher elevation habitats may still be possible, and they may not be as restricted by cold temperatures as previously thought.

Predictive machine learning approaches for the microstructural behavior of multiphase zirconium alloys

Zirconium alloys are widely used in harsh environments characterized by high temperatures, corrosivity, and radiation exposure. These alloys, which have a hexagonal closed packed (h.c.p.) structure thermo-mechanically degrade, when exposed to severe operating environments due to hydride formation. These hydrides have a different crystalline structure, than the matrix, which results in a multiphase alloy. To accurately model these materials at the relevant physical scale, it is necessary to fully characterize them based on a microstructural fingerprint, which is defined here as a combination of features that include hydride geometry, parent and hydride texture and crystalline structure of these multiphase alloys. Hence, this investigation will develop a reduced order modeling approach, where this microstructural fingerprint is used to predict critical fracture stress levels that are physically consistent with microstructural deformation and fracture modes. Machine Learning (ML) methodologies based on Gaussian Process Regression, random forests, and multilayer perceptrons (MLP) were used to predict material fracture critical stress states. MLPs, or neural networks, had the highest accuracy on held-out test sets across three predetermined strain levels of interest. Hydride orientation, grain orientation or texture, and hydride volume fraction had the greatest effect on critical fracture stress levels and had partial dependencies that were highly significant, and in comparison hydride length and hydride spacing have less effects on fracture stresses. Furthermore, these models were also used accurately predicted material response to nominal applied strains as a function of the microstructural fingerprint.

К вопросу о морфофункциональном статусе детей школьного возраста Нижегородской области в связи с экологическими факторами

Introduction. Morphofunctional (MF) status of school children of Nizhny Novgorod region is analysed in connection with the degree of urbanization and the level of anthropogenic pressure in contrastive ecological clusters with satisfactory (1), comparatively tense (2), tense (3) and critical ecological situation. Material and methods. Over 5 thousand of school children aged 7–17 years, examined in 2010–12, are under discussion. The program includes height, weight, BMI, chest girth, lung vital capacity (VC), systolic and diastolic blood pressure, somatotype according to Shtefko-Ostrovskiy method. Each cluster is characterized by absolute and standardized values of MF indices; significance of differences between means of parameters with continuous variability for separate ecological groups is estimated by using of analysis of variance and Scheffe-tests. Frequency of somatotypes (%) is calculated for each ecological group, Pearson's chi-square criterion is used. Comparative estimation of total somatic dimensions of rural and urban (literary data) children is held. Results. The accelerating influence of modern level of anthropogenic stress (clusters 2 and 3) on indices of transversal body development (weight, BMI, chest girth) and VC of prepubertal (9 years) children irrespective of sex is shown. Decelerating influence of critical stress level (cluster 4) on indices of transversal body development of pubertal children aged 13 years is revealed. No significant differences in frequency of somatotypes in contrastive ecological clusters are fixed. Some gracilization of urban prepubertal boys compared to rural boys is shown. Some macrosomization (height and weight) of urban girls aged 7–13 years combined with modest decrease of chest girth as compared to rural girls is fixed. Up to 16–17 years all described differences are obviously smoothed. Conclusion. The effect of anthropoecological correlations depends on the level of anthropogenic stress, sex and age of examined population and the system of MF indices. Height in our case is less sensitive to the increase of the level of anthropogenic stress. Ecosensitivity of girls is presumably less than boys.

Хладноломкость металлов как структурный многостадийный дислокационный процесс

COLD BRITTLENESS OF METALS AS A STRUCTURAL MULTISTAGE DISLOCATION PROCESS V.M. Chernov1,2 1A.A. Bochvar High-Technology Research Institute of Inorganic Materials, Moscow, Russia. 2National Research Nuclear University MEPhI, Moscow, Russia. E-mail: VMChernov@bochvar.ru. The cold brittleness of metals under conditions "before - during - after" irradiation in nuclear and thermonuclear reactors is considered. The conditions and mechanisms of cold brittleness are determined depending on the type of their crystal lattices, structures, physical and mechanical properties and external influences (temperature, stress, reactor irradiation). The mechanisms of cold brittleness are dislocational and define cold brittleness as a structural multistage process. Stress relaxation at the front of a subcritical crack stops its growth (cold brittleness is not formed). The stacking fault energy of the metal determines the critical level of stress for the beginning of its relaxation by mechanical twinning at the crack front (external stress concentrator). In irradiated metals (cold-brittle “before” irradiation), the temperature range of cold-brittleness expands. "During" irradiation, cold brittleness is not formed.

Cold brittleness of metals as a structural multistage dislocation process

The cold brittleness of metals under conditions &amp;quot;before --- during --- after&amp;quot; irradiation in nuclear and thermonuclear reactors is considered. The conditions and mechanisms of cold brittleness are determined depending on the type of their crystal lattices, structures, physical and mechanical properties and external influences (temperature, stress, reactor irradiation). The mechanisms of cold brittleness are dislocational and define cold brittleness as a structural multistage process. Stress relaxation at the front of a subcritical crack stops its growth (cold brittleness is not formed). The stacking fault energy of the metal determines the critical level of stress for the beginning of its relaxation by mechanical twinning at the crack front (external stress concentrator). In irradiated metals (cold-brittle &amp;quot;before&amp;quot; irradiation), the temperature range of cold-brittleness expands. &amp;quot;During&amp;quot; irradiation, cold brittleness is not formed. Keywords: alloys, steels, low temperatures, reactor irradiation, crack nucleation, brittle fracture, stages, mechanisms.

Numerical Investigation of the Fire Behavior of Storage Rack Systems Protected by Intumescent Coating.

Using a finite element strategy, this study investigates the behavior of beam-to-column connections in storage rack systems exposed to high temperatures. The purpose of this research was to develop moment–rotation (M–θ) curves after painting various structural members with varied configurations in order to evaluate the performance of intumescent-coated beams, uprights, and connectors, which are components of storage rack systems. Within the scope of this work, finite element analyses were carried out in two stages. First, thermal analyses were performed using the transient thermal analysis system of ANSYS Workbench software to estimate the ultimate temperatures of the beam, upright, and connector, which were painted with 1 mm thick paint and exposed to standard (ISO-834) fire. The results were then compared to the Eurocode 3 Part 1.2 with a satisfactory agreement. In the second stage of the analysis, a total of 9 possible alternative models were investigated in the static structural analysis system, reflecting the effect of applying fire protection to the different portions of the rack system. Since the most critical stress level is achieved around the connector tabs, it has been observed that protection of the connector in individual or binary conditions provides higher performance while protection of the beam causes divergent joint behavior. Additionally, comparison of fully protected and unprotected conditions presents an increment of more than 7% on the joint’s ultimate moment capacity and initial stiffness, which is an explicit contribution of the intumescent coating to fire resistance.

On the critical threshold for detonation

This paper considers the stress threshold required to shock an explosive so that it runs to full detonation. At present it is assumed that a reaction zone composes localised burning regions that increase in density as pressure is increased. However, a series of burn rate experiments and investigations into the shock response of explosives indicate a critical stress level at which response changes. The stress at which the theoretical shear strength is exceeded under shock loading is called the Weak Shock Limit. This is the gateway to the strong shock region in which a compression front travels faster than an elastic wave. In this region experiments suggest that the response becomes independent of microstructure and that there is a transition in an energetic crystal's electronic state. This results in pre-explosion conductivity and luminescence, consistent with a reduced bandgap in the homogeneous flow. The rate-limiting steps in explosive decomposition are generally accepted to follow Arrhenius kinetics, and it is hypothesised here that the activation energy then decreases above the weak shock limit. This allows reaction to move from temperature-dependant burn at mesoscale hot spots, to temperature-dependant, homogeneous reaction behind the shock wave. The shock can then quickly build to detonation even through the stress for this transition is an order of magnitude less than the Von Neumann spike pressure. This hypothesis has a range of implications that may be tested in further experiments. If explicitly proven, the weak shock limit will allow the description of the transition to, and propagation of, detonation within continuum codes. It will thus represent a vital quantity to consider for the safe handling of energetic materials.

Forecasting Intra-individual Changes of Affective States Taking into Account Inter-individual Differences Using Intensive Longitudinal Data from a University Student Dropout Study in Math

The longitudinal process that leads to university student dropout in STEM subjects can be described by referring to (a) inter-individual differences (e.g., cognitive abilities) as well as (b) intra-individual changes (e.g., affective states), (c) (unobserved) heterogeneity of trajectories, and d) time-dependent variables. Large dynamic latent variable model frameworks for intensive longitudinal data (ILD) have been proposed which are (partially) capable of simultaneously separating the complex data structures (e.g., DLCA; Asparouhov et al. in Struct Equ Model 24:257–269, 2017; DSEM; Asparouhov et al. in Struct Equ Model 25:359–388, 2018; NDLC-SEM, Kelava and Brandt in Struct Equ Model 26:509–528, 2019). From a methodological perspective, forecasting in dynamic frameworks allowing for real-time inferences on latent or observed variables based on ongoing data collection has not been an extensive research topic. From a practical perspective, there has been no empirical study on student dropout in math that integrates ILD, dynamic frameworks, and forecasting of critical states of the individuals allowing for real-time interventions. In this paper, we show how Bayesian forecasting of multivariate intra-individual variables and time-dependent class membership of individuals (affective states) can be performed in these dynamic frameworks using a Forward Filtering Backward Sampling method. To illustrate our approach, we use an empirical example where we apply the proposed forecasting method to ILD from a large university student dropout study in math with multivariate observations collected over 50 measurement occasions from multiple students (N = 122). More specifically, we forecast emotions and behavior related to dropout. This allows us to predict emerging critical dynamic states (e.g., critical stress levels or pre-decisional states) 8 weeks before the actual dropout occurs.