Read by QxMD icon Read

Systems dynamics model

Justin A Lemkul, Alexander D MacKerell
Mg2+ ions are important in biological systems, particularly in stabilizing compact RNA folds. Mg2+ is strongly polarizing, and representing its interactions in heterogeneous environments is a challenge for empirical force field development. To date, the most commonly used force fields in molecular dynamics simulations utilize a pairwise-additive approximation for electrostatic interactions, which cannot account for the significant polarization response in systems containing Mg2+. In the present work, we refine the interactions of Mg2+ with water, Cl- ions, and nucleic acid moieties using a polarizable force field based on the classical Drude oscillator model...
October 19, 2016: Journal of Physical Chemistry. B
Maurice Filo, Fadi Karameh, Mariette Awad
The cochlea is an indispensable preliminary processing stage in auditory perception that employs mechanical frequency-tuning and electrical transduction of incoming sound waves. Cochlear mechanical responses are shown to exhibit active nonlinear spatiotemporal response dynamics (e.g., otoacoustic emission). To model such phenomena, it is often necessary to incorporate cochlear fluid-membrane interactions. This results in both excessively high-order model formulations and computationally intensive solutions that limit their practical use in simulating the model and analyzing its response even for simple single-tone inputs...
October 17, 2016: Biological Cybernetics
John M Frostad, Daniele Tammaro, Luciano Santollani, Simone Bochner de Araujo, Gerald G Fuller
Understanding and enabling the control of the properties of foams is important for a variety of commercial processes and consumer products. In these systems, the role of surface active compounds has been the subject of many investigations using a wide range of techniques. The study of their influence on simplified geometries such as two bubbles in a liquid or a thin film of solution (such as in the well-known Scheludko cell), has yielded important fundamental understanding. Similarly, in this work an interferometric technique is used to study the dynamic evolution of the film formed by a single bubble being pressed against a planar air-liquid interface...
October 18, 2016: Soft Matter
Pablo M Piaggi, Omar Valsson, Michele Parrinello
We study by computer simulation the nucleation of a supersaturated Lennard-Jones vapor into the liquid phase. The large free energy barriers to transition make the time scale of this process impossible to study by ordinary molecular dynamics simulations. Therefore we use a recently developed enhanced sampling method [Valsson and Parrinello, Phys. Rev. Lett.113, 090601 (2014)] based on the variational determination of a bias potential. We differ from previous applications of this method in that the bias is constructed on the basis of the physical model provided by the classical theory of nucleation...
October 18, 2016: Faraday Discussions
Timothy J H Hele, Nandini Ananth
We derive an exact quantum propagator for nonadiabatic dynamics in multi-state systems using the mapping variable representation, where classical-like Cartesian variables are used to represent both continuous nuclear degrees of freedom and discrete electronic states. The resulting Liouvillian is a Moyal series that, when suitably approximated, can allow for the use of classical dynamics to efficiently model large systems. We demonstrate that different truncations of the exact Liouvillian lead to existing approximate semiclassical and mixed quantum-classical methods and we derive an associated error term for each method...
October 18, 2016: Faraday Discussions
Matthew L Paff, Scott L Nuismer, Andrew D Ellington, Ian J Molineux, Ryan H May, James J Bull
BACKGROUND: We propose, model, and implement a novel system of population-level intervention against a virus. One context is a treatment against a chronic infection such as HIV. The underlying principle is a form of virus 'wars' in which a benign, transmissible agent is engineered to protect against infection by and spread of a lethal virus. In our specific case, the protective agent consists of two entities, a benign virus and a gene therapy vector mobilized by the benign virus. RESULTS: Numerical analysis of a mathematical model identified parameter ranges in which adequate, population-wide protection is achieved...
2016: Journal of Biological Engineering
Mamatha Bhat, Peter Ghali, Benoît Dupont, Roy Hilzenrat, Mahmood Tazari, André Roy, Prosanto Chaudhury, Fernando Alvarez, Michel Carrier, Marc Bilodeau
BACKGROUND & AIMS: Patients listed with exception points for Hepatocellular carcinoma (HCC) have been more likely to be transplanted than those listed for chronic liver failure (LF) based on the Model for End-Stage Liver Disease (MELD) score. The aim of this study was to determine outcomes in the 5-year experience of a scoring system designed to reflect heterogeneity of tumor load of patients listed for HCC. METHODS: A novel MELD exception point system based on size and number of HCC was implemented in July 2009...
October 14, 2016: Journal of Hepatology
Qishui Zhong, Fuli Zhong, Jun Cheng, Hui Li, Shouming Zhong
This paper presents a state of charge (SOC) estimation method based on fractional order sliding mode observer (SMO) for lithium-ion batteries. A fractional order RC equivalent circuit model (FORCECM) is firstly constructed to describe the charging and discharging dynamic characteristics of the battery. Then, based on the differential equations of the FORCECM, fractional order SMOs for SOC, polarization voltage and terminal voltage estimation are designed. After that, convergence of the proposed observers is analyzed by Lyapunov's stability theory method...
October 14, 2016: ISA Transactions
Guohua Tao
Accurately describing nuclear motion is crucial in electronically nonadiabatic dynamics simulations. In this work, a coherence-controlled (CC) approach is proposed based on the mapping between the classical state space and the full electronic matrix and that between the decomposed state space and different nuclear dynamics that allows nuclear motion to properly follow either Ehrenfest dynamics in the coherence domain or Born-Oppenheimer-like dynamics in the single-state domain in a consistent manner. This new method is applied to several benchmark models involving nonadiabatic transitions in two-state or three-state systems, and the obtained results are in excellent agreement with exact quantum calculations...
October 17, 2016: Journal of Physical Chemistry Letters
Olga De Castro, Antonietta Di Maio, Mirko Di Febbraro, Gennaro Imparato, Michele Innangi, Errol Véla, Bruno Menale
The Mediterranean coastline is a dynamic and complex system which owes its complexity to its past and present vicissitudes, e.g. complex tectonic history, climatic fluctuations, and prolonged coexistence with human activities. A plant species that is widespread in this habitat is the sea daffodil, Pancratium maritimum (Amaryllidaceae), which is a perennial clonal geophyte of the coastal sands of the Mediterranean and neighbouring areas, well adapted to the stressful conditions of sand dune environments. In this study, an integrated approach was used, combining genetic and environmental data with a niche modelling approach, aimed to investigate: (1) the effect of climate change on the geographic range of this species at different times {past (last inter-glacial, LIG; and last glacial maximum, LGM), present (CURR), near-future (FUT)} and (2) the possible influence of environmental variables on the genetic structure of this species in the current period...
2016: PloS One
Jumpei F Yamagishi, Nen Saito, Kunihiko Kaneko
As cells grow and divide under a given environment, they become crowded and resources are limited, as seen in bacterial biofilms and multicellular aggregates. These cells often show strong interactions through exchanging chemicals, as evident in quorum sensing, to achieve mutualism and division of labor. Here, to achieve stable division of labor, three characteristics are required. First, isogenous cells differentiate into several types. Second, this aggregate of distinct cell types shows better growth than that of isolated cells without interaction and differentiation, by achieving division of labor...
October 2016: PLoS Computational Biology
Xiuhong Cai, Xiang Li, Hong Qi, Fang Wei, Jianyong Chen, Jianwei Shuai
The gating properties of the inositol 1, 4, 5-trisphosphate (IP3) receptor (IP3R) are determined by the binding and unbinding capability of Ca(2+) ions and IP3 messengers. With the patch clamp experiments, the stationary properties have been discussed for Xenopus oocyte type-1 IP3R (Oo-IP3R1), type-3 IP3R (Oo-IP3R3) and Spodoptera frugiperda IP3R (Sf-IP3R). In this paper, in order to provide insights about the relation between the observed gating characteristics and the gating parameters in different IP3Rs, we apply the immune algorithm to fit the parameters of a modified DeYoung-Keizer model...
October 17, 2016: Physical Biology
Kyaw Hpone Myint, Jonathan R Brown, Anne R Shim, Barbara E Wyslouzil, Lisa Michelle Hall
The formation of block copolymer micelles with and without hydrophobic nanoparticles is simulated using dissipative particle dynamics. We use the model developed by Spaeth et al. [J. Chem. Phys. 134, 164902 (2011)], and drive micelle formation by adjusting the interaction parameters linearly over time to represent a rapid change from organic solvent to water. For different concentrations of added nanoparticles, we determine characteristic times for micelle formation and coagulation, and characterize micelles with respect to size, polydispersity, and nanoparticle loading...
October 17, 2016: Journal of Physical Chemistry. B
Ornella Affinito, Giovanni Scala, Domenico Palumbo, Ermanno Florio, Antonella Monticelli, Gennaro Miele, Vittorio Enrico Avvedimento, Alessandro Usiello, Lorenzo Chiariotti, Sergio Cocozza
DNA methylation is often analyzed by reporting the average methylation degree of each cytosine. In this study, we used a single molecule methylation analysis in order to look at the methylation conformation of individual molecules. Using D-aspartate oxidase as a model gene, we performed an in-depth methylation analysis through the developmental stages of three different mouse tissues (brain, lung, and gut), where this gene undergoes opposite methylation destiny. This approach allowed us to track both methylation and demethylation processes at high resolution...
October 17, 2016: Epigenetics: Official Journal of the DNA Methylation Society
Mattias Björnmalm, Matthew Faria, Xi Chen, Jiwei Cui, Frank Caruso
The interaction of engineered particles with biological systems determines their performance in biomedical applications. Although standard static cell cultures remain the norm for in vitro studies, modern models mimicking aspects of the dynamic in vivo environment have been developed. Herein, we investigate fundamental cell-particle interactions under dynamic flow conditions using a simple and self-contained device together with standard multiwell cell culture plates. We engineer two particle systems and evaluate their cell interactions under dynamic flow, and we compare the results to standard static cell cultures...
October 17, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Saeed Izadi, Ramu Anandakrishnan, Alexey V Onufriev
Molecular Dynamics (MD) simulations based on the implicit solvent generalized Born (GB) models can provide significant computational advantages over the traditional explicit solvent simulations. However, the standard GB becomes prohibitively expensive for all-atom simulations of large structures; the model scales poorly, ~n^2, with the number of solute atoms. Here we combine our recently developed Optimal Point Charge Approximation (OPCA) with the Hierarchical Charge Partitioning (HCP) approximation to present an ~n log n multi-scale, yet fully atomistic, GB model (GB-HCPO)...
October 17, 2016: Journal of Chemical Theory and Computation
Alexandros Koutsioubas
Supported lipid bilayers on planar surfaces constitute an archetypical experimental system for the study of biological membranes. The popularity of these ordered molecular layers in the literature, is on one hand related to the simplicity of their preparation using the method of vesicle fusion and on the other hand to their compatibility with a multitude of surface sensitive experimental probes. Neutron reflectivity has proven as an important experimental method for the investigation of such systems with the ability to provide sub-nanometer structural information perpendicular to the supporting plane...
October 17, 2016: Journal of Physical Chemistry. B
Jenny M Pedersen, Yoo-Sik Shim, Vaibhav Hans, Martin B Phillips, Jeffrey M Macdonald, Glenn Walker, Melvin E Andersen, Harvey J Clewell, Miyoung Yoon
Accurate prediction of metabolism is a significant outstanding challenge in toxicology. The best predictions are based on experimental data from in vitro systems using primary hepatocytes. The predictivity of the primary hepatocyte-based culture systems, however, is still limited due to well-known phenotypic instability and rapid decline of metabolic competence within a few hours. Dynamic flow bioreactors for three-dimensional cell cultures are thought to be better at recapitulating tissue microenvironments and show potential to improve in vivo extrapolations of chemical or drug toxicity based on in vitro test results...
2016: Frontiers in Bioengineering and Biotechnology
Rainer Engelken, Farzad Farkhooi, David Hansel, Carl van Vreeswijk, Fred Wolf
Neuronal activity in the central nervous system varies strongly in time and across neuronal populations. It is a longstanding proposal that such fluctuations generically arise from chaotic network dynamics. Various theoretical studies predict that the rich dynamics of rate models operating in the chaotic regime can subserve circuit computation and learning. Neurons in the brain, however, communicate via spikes and it is a theoretical challenge to obtain similar rate fluctuations in networks of spiking neuron models...
2016: F1000Research
Amanda A Koepke, Ira M Longini, M Elizabeth Halloran, Jon Wakefield, Vladimir N Minin
Despite seasonal cholera outbreaks in Bangladesh, little is known about the relationship between environmental conditions and cholera cases. We seek to develop a predictive model for cholera outbreaks in Bangladesh based on environmental predictors. To do this, we estimate the contribution of environmental variables, such as water depth and water temperature, to cholera outbreaks in the context of a disease transmission model. We implement a method which simultaneously accounts for disease dynamics and environmental variables in a Susceptible-Infected-Recovered-Susceptible (SIRS) model...
June 2016: Annals of Applied Statistics
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"