Many models of mutualism have been proposed and studied individually. In this paper, we develop a general class of models of facultative mutualism that covers many of such published models. Using mild assumptions on the growth and self-limiting functions, we establish necessary and sufficient conditions on the boundedness of model solutions and prove the global stability of a unique coexistence equilibrium whenever it exists. These results allow for a greater flexibility in the way each mutualist species can be modelled and avoid the need to analyse any single model of mutualism in isolation. Our generalization also allows each of the mutualists to be subject to a weak Allee effect. Moreover, we find that if one of the interacting species is subject to a strong Allee effect, then the mutualism can overcome it and cause a unique coexistence equilibrium to be globally stable.
- MeSH
- Models, Biological * MeSH
- Population Dynamics MeSH
- Symbiosis * MeSH
- Publication type
- Journal Article MeSH
Layered double hydroxides have been proposed as effective sorbents for As(V), but studies investigating adsorption mechanisms usually lack a comprehensive mechanistic/modeling approach. In this work, we propose coupling surface complexation modeling with various spectroscopic techniques. To this end, a series of batch experiments at different pH values were performed. Kinetic data were well fitted by a pseudo-second order kinetic model, and the equilibrium data were fitted by the Freundlich model. Moreover, the pH-dependent As(V) sorption data were satisfactorily fitted by a diffuse layer model, which described the formation of >SOAsO3H(-) monodentate and >(SO)2AsO2(-) bidentate inner-sphere complexes (">S" represents a crystallographically-bound group on the surface). Additionally, XPS analyses confirmed the adsorption mechanisms. The sorption mechanisms were affected by anion exchange, which was responsible for the formation of outer sphere complexes, as identified by XRD and FTIR analyses. Furthermore, a homogenous distribution of As(V) was determined by HR-TEM with elemental mapping. Using low-temperature Mössbauer spectroscopy on isotope (57)Fe, a slight shift of the hyperfine parameters towards higher values following As(V) sorption was measured, indicating a higher degree of structural disorder. In general, mechanistic adsorption modeling coupled with solid state analyses presents a powerful approach for investigating the adsorption mechanism of As(V) on Mg-Fe LDH or other sorbents.
- MeSH
- Adsorption MeSH
- Arsenates chemistry isolation & purification MeSH
- X-Ray Diffraction MeSH
- Magnesium Hydroxide chemistry MeSH
- Kinetics MeSH
- Hydrogen-Ion Concentration MeSH
- Surface Properties MeSH
- Solutions MeSH
- Spectroscopy, Fourier Transform Infrared MeSH
- Models, Theoretical * MeSH
- Ferric Compounds chemistry MeSH
- Publication type
- Journal Article MeSH
Genome duplication (polyploidy) is a recurrent evolutionary process in plants, often conferring instant reproductive isolation and thus potentially leading to speciation. Outcome of the process is often seen in the field as different cytotypes co-occur in many plant populations. Failure of meiotic reduction during gametogenesis is widely acknowledged to be the main mode of polyploid formation. To get insight into its role in the dynamics of polyploidy generation under natural conditions, and coexistence of several ploidy levels, we developed a general gametic model for diploid-polyploid systems. This model predicts equilibrium ploidy frequencies as functions of several parameters, namely the unreduced gamete proportions and fertilities of higher ploidy plants. We used data on field ploidy frequencies for 39 presumably autopolyploid plant species/populations to infer numerical values of the model parameters (either analytically or using an optimization procedure). With the exception of a few species, the model fit was very high. The estimated proportions of unreduced gametes (median of 0.0089) matched published estimates well. Our results imply that conditions for cytotype coexistence in natural populations are likely to be less restrictive than previously assumed. In addition, rather simple models show sufficiently rich behaviour to explain the prevalence of polyploids among flowering plants.
The input of Stein's model of a single neuron is usually described by using a Poisson process, which is assumed to represent the behaviour of spikes pooled from a large number of presynaptic spike trains. However, such a description of the input is not always appropriate as the variability cannot be separated from the intensity. Therefore, we create and study Stein's model with a more general input, a sum of equilibrium renewal processes. The mean and variance of the membrane potential are derived for this model. Using these formulas and numerical simulations, the model is analyzed to study the influence of the input variability on the properties of the membrane potential and the output spike trains. The generalized Stein's model is compared with the original Stein's model with Poissonian input using the relative difference of variances of membrane potential at steady state and the integral square error of output interspike intervals. Both of the criteria show large differences between the models for input with high variability.
- MeSH
- Humans MeSH
- Membrane Potentials physiology MeSH
- Models, Neurological * MeSH
- Nerve Net physiology MeSH
- Neurons physiology MeSH
- Stochastic Processes MeSH
- Animals MeSH
- Check Tag
- Humans MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Interactions among analyte forms that undergo simultaneous dissociation/protonation and complexation with multiple selectors take the shape of a highly interconnected multi-equilibrium scheme. This makes it difficult to express the effective mobility of the analyte in these systems, which are often encountered in electrophoretical separations, unless a generalized model is introduced. In the first part of this series, we presented the theory of electromigration of a multivalent weakly acidic/basic/amphoteric analyte undergoing complexation with a mixture of an arbitrary number of selectors. In this work we demonstrate the validity of this concept experimentally. The theory leads to three useful perspectives, each of which is closely related to the one originally formulated for simpler systems. If pH, IS and the selector mixture composition are all kept constant, the system is treated as if only a single analyte form interacted with a single selector. If the pH changes at constant IS and mixture composition, the already well-established models of a weakly acidic/basic analyte interacting with a single selector can be employed. Varying the mixture composition at constant IS and pH leads to a situation where virtually a single analyte form interacts with a mixture of selectors. We show how to switch between the three perspectives in practice and confirm that they can be employed interchangeably according to the specific needs by measurements performed in single- and dual-selector systems at a pH where the analyte is fully dissociated, partly dissociated or fully protonated. Weak monoprotic analyte (R-flurbiprofen) and two selectors (native β-cyclodextrin and monovalent positively charged 6-monodeoxy-6-monoamino-β-cyclodextrin) serve as a model system.
A common method for load estimation in biomechanics is the inverse dynamics optimization, where the muscle activation pattern is found by minimizing or maximizing the optimization criterion. It has been shown that various optimization criteria predict remarkably similar muscle activation pattern and intra-articular contact forces during leg motion. The aim of this paper is to study the effect of the choice of optimization criterion on L4/L5 loading during static asymmetric loading. Upright standing with weight in one stretched arm was taken as a representative position. Musculoskeletal model of lumbar spine model was created from CT images of Visible Human Project. Several criteria were tested based on the minimization of muscle forces, muscle stresses, and spinal load. All criteria provide the same level of lumbar spine loading (difference is below 25%), except the criterion of minimum lumbar shear force which predicts unrealistically high spinal load and should not be considered further. Estimated spinal load and predicted muscle force activation pattern are in accordance with the intradiscal pressure measurements and EMG measurements. The L4/L5 spine loads 1312 N, 1674 N, and 1993 N were predicted for mass of weight in hand 2, 5, and 8 kg, respectively using criterion of mininum muscle stress cubed. As the optimization criteria do not considerably affect the spinal load, their choice is not critical in further clinical or ergonomic studies and computationally simpler criterion can be used.
- MeSH
- Models, Anatomic MeSH
- Lumbar Vertebrae physiopathology MeSH
- Biomechanical Phenomena MeSH
- Electromyography MeSH
- Image Interpretation, Computer-Assisted MeSH
- Isometric Contraction physiology MeSH
- Humans MeSH
- Intervertebral Disc physiopathology MeSH
- Tomography, X-Ray Computed MeSH
- Posture physiology MeSH
- Postural Balance MeSH
- Models, Theoretical MeSH
- Weight-Bearing physiology MeSH
- Imaging, Three-Dimensional MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Interaction of dibenzo-18-crown-6 (DBC) with H 3O (+) (HP) in nitrobenzene- d 5 and dichloromethane- d 2 was studied by using (1)H and (13)C NMR spectra and relaxations, FTIR spectra, and quantum chemical DFT calculations. NMR shows that the DBC*HP complex is in a dynamic equilibrium with the reactants, the equilibrium constant K being 0.66 x 10 (3), 1.16 x 10 (4), and 1.03 x 10 (4) L x mol (-1) in CD 2Cl 2, nitrobenzene, and acetonitrile, respectively. The complex appears to have a C 2 v symmetry in NMR, but FTIR combined with DFT normal mode calculations suggest that such high symmetry is only apparent and due to exchange averaging of the structure. FTIR spectra as well as energy-optimized DFT calculations show that the most stable state of the complex in solution is that with three linear hydrogen bonds of HP with one CH 2-O-CH 2 and two Ar-O-Ar oxygen atoms. The structure is similar to that found in solid state but adopts a somewhat different conformation in solution. The dynamics of exchange between bound and free DBC was studied by NMR transverse relaxation. It was found to be too fast to give reproducible results when measured with the ordinary CPMG sequence or its variant DIFTRE removing residual static dipolar interaction, but it could be established by rotating-frame measurements with high intensity of the spin-lock field. The correlation time of exchange was found to be 5.6 x 10 (-6) and 3.8 x 10 (-6) s in dichloromethane and nitrobenzene, respectively. Such fast exchange can be explained by cooperative assistance of present water molecules.
- MeSH
- Models, Chemical MeSH
- Crown Ethers MeSH
- Carbon Isotopes MeSH
- Quantum Theory MeSH
- Magnetic Resonance Spectroscopy methods standards MeSH
- Molecular Structure MeSH
- Onium Compounds MeSH
- Computer Simulation MeSH
- Protons MeSH
- Reference Standards MeSH
- Spectroscopy, Fourier Transform Infrared methods MeSH
- Hydrogen Bonding MeSH
- MeSH
- Acid-Base Equilibrium MeSH
- Adjuvants, Anesthesia MeSH
- Anesthesia, General * MeSH
- Chronobiology Discipline MeSH
- Circadian Rhythm MeSH
- Electrophysiology MeSH
- Models, Animal MeSH
- Myocardium MeSH
- Pentobarbital * administration & dosage therapeutic use MeSH
- Rats, Wistar MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- MeSH
- Acid-Base Equilibrium MeSH
- Anesthetics, Dissociative MeSH
- Autonomic Nervous System drug effects MeSH
- Anesthesia, General * MeSH
- Chronobiology Discipline MeSH
- Circadian Rhythm MeSH
- Electrophysiology MeSH
- Ketamine * administration & dosage therapeutic use MeSH
- Models, Animal MeSH
- Rats, Wistar MeSH
- Heart Rate drug effects MeSH
- Xylazine * administration & dosage therapeutic use MeSH
- Animals MeSH
- Check Tag
- Female MeSH
- Animals MeSH
Rheumatoid arthritis (RA) is a model of multigenic inflammatory disorder in which tumor necrosis factor-alpha (TNF-alpha) plays an important role. Genetic factors may be implicated in the susceptibility to disease initiation as well as in severity of disease course. Elevated levels of TNF-alpha in the plasma and synovial fluid from RA patients may be associated with polymorphisms in the promoter region of the TNF-alpha gene. The aim of this study was to elucidate putative association between the -308 G/A polymorphism in the promoter region of the TNF-alpha gene and susceptibility to onset and severity of RA. A total of 130 RA patients and a control group of 150 healthy subjects with similar age and sex distribution were available for the study. All patients fulfilled the American College of Rheumatology revised criteria for RA. RA patients had a disease duration of at least 2 years. Radiographs of both hands of all RA patients were scored with the Steinbrocker method. There were 15 patients of stage I (nonerosive form) of RA and 114 patients of stages II-IV (erosive form). To assess the RA patient's functional ability, the Health Assessment Questionnaire (HAQ) was used. The -308 G/A promoter polymorphism of the TNF-alpha gene was detected by polymerase chain reaction and restriction fragment length polymorphism analysis. No differences in genotype distribution and allelic frequences of -308 G/A TNF-alpha promoter polymorphism have been found between RA patients and the control group. Significant differences have been observed within the RA group divided according to the radiographic progression of disease based on the Steinbrocker radiographic score and functional ability (HAQ). These results suggest an association of the -308 G/A polymorphism of the TNF-alpha gene with the severity of RA.
- MeSH
- Adult MeSH
- Financing, Organized MeSH
- Gene Frequency MeSH
- Genetic Markers MeSH
- Middle Aged MeSH
- Humans MeSH
- Polymorphism, Restriction Fragment Length MeSH
- Promoter Regions, Genetic MeSH
- Surveys and Questionnaires MeSH
- Arthritis, Rheumatoid diagnosis genetics blood MeSH
- Aged, 80 and over MeSH
- Aged MeSH
- Severity of Illness Index MeSH
- Synovial Fluid metabolism MeSH
- Tumor Necrosis Factor-alpha genetics metabolism MeSH
- Health Status MeSH
- Check Tag
- Adult MeSH
- Middle Aged MeSH
- Humans MeSH
- Male MeSH
- Aged, 80 and over MeSH
- Aged MeSH
- Female MeSH
- Geographicals
- Czech Republic MeSH
