Systems biology models are typically considered across a spectrum from mechanistic to abstracted description;however, the lines between these forms of modeling are increasingly blurred. Ever-increasing computational p...
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Systems biology models are typically considered across a spectrum from mechanistic to abstracted description;however, the lines between these forms of modeling are increasingly blurred. Ever-increasing computational power is providing novel opportunities for bridging time and length scales. Furthermore, despite biological mechanisms or network topology often ill-defined, the acquisition of high-throughput data leaves modelers with the desire to leverage available measurements. This review surveys modeling tools in which two or more mathematical forms are blended to describe time-dependent processes in a multivariate system. While most commonly manifested as continuous/discrete description, other forms such as mechanistic/inference or deterministic/stochastic hybrid models can be generated. Recent innovations in hybrid modeling methodologies and new applications illustrate advantages for combining model formats to gaining biological systems level insight.
When teaching infants new actions, parents tend to modify their movements. Infants prefer these infant-directed actions (IDAs) over adult-directed actions and learn well from them. Yet, it remains unclear how parents&...
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When teaching infants new actions, parents tend to modify their movements. Infants prefer these infant-directed actions (IDAs) over adult-directed actions and learn well from them. Yet, it remains unclear how parents' action modulations capture infants' attention. Typically, making movements larger than usual is thought to draw attention. Recent findings, however, suggest that parents might exploit movement variability to highlight actions. We hypothesized that variability in movement amplitude rather than higher amplitude is capturing infants' attention during IDAs. Using EEG, we measured 15-month-olds' brain activity while they were observing action demonstrations with normal, high, or variable amplitude movements. Infants' theta power (4-5 Hz) in fronto-central channels was compared between conditions. Frontal theta was significantly higher, indicating stronger attentional engagement, in the variable compared to the other conditions. computational modelling showed that infants' frontal theta power was predicted best by how surprising each movement was. Thus, surprise induced by variability in movements rather than large movements alone engages infants' attention during IDAs. Infants with higher theta power for variable movements were more likely to perform actions successfully and to explore objects novel in the context of the given goal. This highlights the brain mechanisms by which IDAs enhance infants' attention, learning, and exploration.
Objective: We developed a computational model of the effects of sleep deprivation on the vigilance decrement by employing the methods of system dynamics modeling. Background: Situations that require sustained attentio...
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Objective: We developed a computational model of the effects of sleep deprivation on the vigilance decrement by employing the methods of system dynamics modeling. Background: Situations that require sustained attention for a prolonged duration can cause a decline in cognitive performance, the so-called vigilance decrement. One factor that should influence the vigilance decrement is fatigue in the form of sleep deprivation. Method: We employed the methods of system dynamics modeling (numerical-integration techniques for modeling complex feedback systems) to create a computational model of the vigilance decrement. We then simulated the computational effects of sleep deprivation on the behavior of that model, using empirical data obtained from the literature for calibrating such effects. Results: Sleep deprivation of 2 hr over a 14-day period should produce an additional decline of 9% in detection performance over that found with the typical vigilance decrement, whereas 4 hr of sleep deprivation over 14 days should produce an additional decline of 14% in detection performance. Conclusion: With respect to dual-process theory, it is through its deleterious effects on analytical cognition that sleep deprivation should impact the vigilance decrement. Application: Such computational modeling may be advantageous for human-machine teaming by theoretically allowing a future autonomous software agent to anticipate the decline of human performance and compensate accordingly.
Cancer is a life-threatening process that stems from genetic mutations in cells, which leads to the formation of tumors, and is a major cause of deaths in the United States, with secondary metastasis being a major dri...
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Pitting corrosion damage is a major problem affecting material strength and may result in difficult to predict catastrophic failure of metallic material systems and structures. computational models have been developed...
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Pitting corrosion damage is a major problem affecting material strength and may result in difficult to predict catastrophic failure of metallic material systems and structures. computational models have been developed to study and predict the evolution of pitting corrosion with the goal of, in conjunction with experiments, providing insight into pitting processes and their consequences in terms of material reliability. This paper -presents a critical review of the computational models for pitting corrosion. Based on the anodic reaction (dissolution) kinetics at the corrosion front, transport kinetics of ions in the electrolyte inside the pits, and time evolution of the damage (pit growth), these models can be classified into two categories: (1) non-autonomous models that solve a classical transport equation and, separately, solve for the evolution of the pit boundary;and (2) autonomous models like cellular automata, peridynamics, and phase-field models which address the transport, dissolution, and autonomous pit growth in a unified framework. We compare these models with one another and comment on the advantages and disadvantages of each of them. We especially focus on peridynamic and phase-filed models of pitting corrosion. We conclude the paper with a discussion of open areas for future developments.
Objective: To explore the potential of ultrasonic modulation of plateau-potential generating subthalamic nucleus neurons (STN), by modeling their interaction with continuous and pulsed ultrasonic waves. Methods: A com...
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Objective: To explore the potential of ultrasonic modulation of plateau-potential generating subthalamic nucleus neurons (STN), by modeling their interaction with continuous and pulsed ultrasonic waves. Methods: A computational model for ultrasonic stimulation of the STN is created by combining the Otsuka-model with the bilayer sonophore model. The neuronal response to continuous and pulsed ultrasonic waves is computed in parallel for a range of frequencies, duty cycles, pulse repetition frequencies, and intensities. Results: Ultrasonic intensity in continuous-wave stimulation determines the firing pattern of the STN. Three observed spiking modes in order of increasing intensity are low frequency spiking, high frequency spiking with significant spike-frequency and spike-amplitude adaptation, and a silenced mode. Continuous-wave stimulation has little capability to manipulate the saturated spiking rate in the high frequency spiking mode. In contrast, STN firing rates induced by pulsed ultrasound insonication will saturate to the pulse repetition frequency with short latencies, for sufficiently large intensity and repetition frequency. Conclusion: computational results show that the activity of plateau-potential generating STN can be modulated by selection of the stimulus parameters. Low intensities result in repetitive firing, while higher intensities silence the STN. Pulsed ultrasonic stimulation results in a shorter saturation latency and is able to modulate spiking rates. Significance: Stimulation or suppresion of the STN is important in the treatment of Parkinson's disease, e.g., in deep brain stimulation. This explorative study on ultrasonic modulation of the STN, could be a step in the direction of minimally invasive alternatives to conventional deep brain stimulation.
Convective seepage flow plays a key role not only in naturally forming mineral deposits and oil reservoirs, but also in the carbon-dioxide sequestration in fluid-saturated rocks. This paper presents a steady-state num...
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Convective seepage flow plays a key role not only in naturally forming mineral deposits and oil reservoirs, but also in the carbon-dioxide sequestration in fluid-saturated rocks. This paper presents a steady-state numerical solver, which is based on the finite element method (FEM) and progressive asymptotic approach procedure (PAAP), to solve steady-state convective seepage flow problems in fluid-saturated heterogeneous rocks. Although this kind of flow problem is commonly solved by using transient-state numerical solvers, the use of the proposed steady-state numerical solver, which is the main characteristic of this study, can have certain advantages. After the proposed steady-state numerical solver is verified by a benchmark testing problem, for which analytical solutions are available for comparison, it is further applied to simulate steady-state convective seepage flow in the Australia North West Shelf basin, which is composed of naturally-formed heterogeneous porous rocks. Through the simulated numerical results, it can be found that: (1) compared with the analytical solutions of the benchmark testing problem, the use of the steady-state numerical solver can produce correct and accurate numerical simulation results for dealing with convective seepage flow problems in fluid-saturated heterogeneous rocks. (2) The main advantage of using the steady-state numerical solver is to avoid the need of considering initial conditions of the problem, which are commonly difficult to be determined because the convective seepage flow within the upper crust is a past event in geology. (3) In the Australia North West Shelf basin, the convective seepage flow and temperature distribution patterns depend strongly on both the permeability contrast of the faults and the basin geometry (including the layer structures and fault locations) in the computational model.
Citalopram (CIT) is a frequently used modern antidepressant that inhibits selectively serotonin reuptake in the brain. It has a chiral center in its structure and is used in therapy as both racemic mixture and pure en...
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Citalopram (CIT) is a frequently used modern antidepressant that inhibits selectively serotonin reuptake in the brain. It has a chiral center in its structure and is used in therapy as both racemic mixture and pure enantiomer as its pharmacological effect is almost entirely associated with S-CIT. The aim of this study was the development of a simple and rapid capillary electrophoresis (CE) method for the separation and quantification of CIT enantiomers. To establish the optimum chiral selector, several native and derivatized, neutral, and ionized cyclodextrins (CDs) were examined at different pH levels. An experimental design strategy was adopted for method optimization;a fractional factorial design was applied for screening purposes to identify significant experimental factors followed by a face-centered central composite design used for optimization purposes. computational modeling was used to obtain information on the interaction energy and the geometry of the complexes to aid in the understanding of chiral separation mechanism. The best results were obtained when using a 25-mM phosphate buffer at pH 7.0, 3-mM CM-beta-CD as chiral selector, 17.5 degrees C temperature, 15-kV voltage, and 50 mbar/s hydrodynamic injection. The separation time was fast, below 3 min, and the migration order was S-CIT followed by R-CIT. The analytical performance of the method was verified in terms of precision, linearity, accuracy, sensibility, and robustness, and the method was applied for the determination of CIT enantiomers from pharmaceutical preparations.
Post-stroke fatigue (PSF) is prevalent among stroke patients, but its mechanisms are poorly understood. Many patients with PSF experience cognitive difficulties, but studies aiming to identify cognitive correlates of ...
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Post-stroke fatigue (PSF) is prevalent among stroke patients, but its mechanisms are poorly understood. Many patients with PSF experience cognitive difficulties, but studies aiming to identify cognitive correlates of PSF have been largely inconclusive. With the aim of characterizing the relationship between subjective fatigue and attentional function, we collected behavioral data using the attention network test (ANT) and self-reported fatigue scores using the fatigue severity scale (FSS) from 53 stroke patients. In order to evaluate the utility and added value of computational modeling for delineating specific underpinnings of response time (RT) distributions, we fitted a hierarchical drift diffusion model (hDDM) to the ANT data. Results revealed a relationship between fatigue and RT distributions. Specifically, there was a positive interaction between FSS score and elapsed time on RT. Group analyses suggested that patients without PSF increased speed during the course of the session, while patients with PSF did not. In line with the conventional analyses based on observed RT, the best fitting hDD model identified an interaction between elapsed time and fatigue on non-decision time, suggesting an increase in time needed for stimulus encoding and response execution rather than cognitive information processing and evidence accumulation. These novel results demonstrate the significance of considering the sustained nature of effort when defining the cognitive phenotype of PSF, intuitively indicating that the cognitive phenotype of fatigue entails an increased vulnerability to sustained effort, and suggest that the use of computational approaches offers a further characterization of specific processes underlying behavioral differences.
Acute Myocardial Infarction (AMI) is the most common cause of mortality, and cardiac troponin I (cTnI) is the gold standard for AMI diagnosis. Some aptamers have been reported to detect cTnI, but there is rarely any s...
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Acute Myocardial Infarction (AMI) is the most common cause of mortality, and cardiac troponin I (cTnI) is the gold standard for AMI diagnosis. Some aptamers have been reported to detect cTnI, but there is rarely any structural information on their binding with cTnI. There are many studies involving electrochemical aptasensors with methylene blue (MB) as a redox indicator that does not provide any significant new information. Our study, however, involves the computational modeling of the complexes of a documented 40-mer ssDNA-cTnI aptamer with its target and MB. Here, MB was used as a model system to investigate the rather complex interaction modes between small redox molecules and a cTnI-aptamer. Understanding these modes is an important facet in designing electrochemical aptasensors to ascertain the effectiveness of a redox indicator. In our study, docking and molecular dynamics (MD) were used to provide information on the stability, fluctuations, and interaction analysis of the complexes. Based on computational evaluations, we understand how the structure of the cTnI-aptamer steers the MB releasing after inducing cTnI. In order to evaluate the sensing performance of the cTnI-aptamer in the presence of MB experimentally, after covalent immobilization of the 5-amino terminated cTnI-aptamer at a pre-functionalized carboxylated multi-walled carbon nanotube (COOH-MWCNT) glassy carbon electrode, some techniques including spectroscopy and voltammetry were employed.
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