Predicting the relativistic periastron advance of a binary without curving spacetime

Relativistic Newtonian Dynamics, the simple model used previously for predicting accurately the anomalous precession of Mercury, is now applied to predict the periastron advance of a binary. The classical treatment of a binary as a two-body problem is modified to account for the influence of the gravitational potential on spacetime. Without curving spacetime, the model predicts the identical equation for the relativistic periastron advance as the post-Newtonian approximation of general relativity formalism thereby providing further substantiation of this model.Comment: 6 pages, 2 figure

Fast stray field computation on tensor grids

A direct integration algorithm is described to compute the magnetostatic field and energy for given magnetization distributions on not necessarily uniform tensor grids. We use an analytically-based tensor approximation approach for function-related tensors, which reduces calculations to multilinear algebra operations. The algorithm scales with N^(4/3) for N computational cells used and with N^(2/3) (sublinear) when magnetization is given in canonical tensor format. In the final section we confirm our theoretical results concerning computing times and accuracy by means of numerical examples.Comment: 16 pages, 1 figure, submitted to the Journal of Computational Physic

Caffeine vs. carbamazepine as indicators of wastewater pollution in a karst aquifer

This paper presents the analysis of caffeine and carbamazepine transport in the subsurface as a result of wastewater release in the Sorek creek over the outcrops of the carbonate, Yarkon-Taninim, aquifer in Israel. Both caffeine and carbamazepine were used as indicators of sewage contamination in the subsurface. While carbamazepine is considered conservative, caffeine is subject to sorption and degradation. The objective of the study was to quantify differences in their transport under similar conditions in the karst aquifer. Water flow and pollutant transport in a “vadose zone–aquifer” system were simulated by a quasi-3-D dual permeability numerical model. The results of this study show that each of these two pollutants can be considered effective tracers for characterization and assessment of aquifer contamination. Carbamazepine was found to be more suitable for assessing the contamination boundaries, while caffeine can be used as a contaminant tracer only briefly after contamination occurs. In instances where there are low concentrations of carbamazepine which appear as background contamination in an aquifer, caffeine might serve as a better marker for detecting new contamination events, given its temporal nature. The estimated caffeine degradation rate and the distribution coefficient of a linear sorption isotherm were 0.091&thinsp;d−1 and 0.1&thinsp;L&thinsp;kg−1, respectively, which imply a high attenuation capacity. The results of the simulation indicate that by the end of the year most of the carbamazepine mass (approximately 95&thinsp;%) remained in the matrix of the vadose zone, while all of the caffeine was completely degraded a few months after the sewage was discharged.</p

Efficacy of Synaptic Inhibition Depends on Multiple, Dynamically Interacting Mechanisms Implicated in Chloride Homeostasis

Chloride homeostasis is a critical determinant of the strength and robustness of inhibition mediated by GABAA receptors (GABAARs). The impact of changes in steady state Cl− gradient is relatively straightforward to understand, but how dynamic interplay between Cl− influx, diffusion, extrusion and interaction with other ion species affects synaptic signaling remains uncertain. Here we used electrodiffusion modeling to investigate the nonlinear interactions between these processes. Results demonstrate that diffusion is crucial for redistributing intracellular Cl− load on a fast time scale, whereas Cl−extrusion controls steady state levels. Interaction between diffusion and extrusion can result in a somato-dendritic Cl− gradient even when KCC2 is distributed uniformly across the cell. Reducing KCC2 activity led to decreased efficacy of GABAAR-mediated inhibition, but increasing GABAAR input failed to fully compensate for this form of disinhibition because of activity-dependent accumulation of Cl−. Furthermore, if spiking persisted despite the presence of GABAAR input, Cl− accumulation became accelerated because of the large Cl− driving force that occurs during spikes. The resulting positive feedback loop caused catastrophic failure of inhibition. Simulations also revealed other feedback loops, such as competition between Cl− and pH regulation. Several model predictions were tested and confirmed by [Cl−]i imaging experiments. Our study has thus uncovered how Cl− regulation depends on a multiplicity of dynamically interacting mechanisms. Furthermore, the model revealed that enhancing KCC2 activity beyond normal levels did not negatively impact firing frequency or cause overt extracellular K− accumulation, demonstrating that enhancing KCC2 activity is a valid strategy for therapeutic intervention

Kinetic Properties of the Cardiac L-Type Ca(2+) Channel and Its Role in Myocyte Electrophysiology: A Theoretical Investigation

The L-type Ca(2+) channel (Ca(V)1.2) plays an important role in action potential (AP) generation, morphology, and duration (APD) and is the primary source of triggering Ca(2+) for the initiation of Ca(2+)-induced Ca(2+)-release in cardiac myocytes. In this article we present: 1), a detailed kinetic model of Ca(V)1.2, which is incorporated into a model of the ventricular mycoyte where it interacts with a kinetic model of the ryanodine receptor in a restricted subcellular space; 2), evaluation of the contribution of voltage-dependent inactivation (VDI) and Ca(2+)-dependent inactivation (CDI) to total inactivation of Ca(V)1.2; and 3), description of dynamic Ca(V)1.2 and ryanodine receptor channel-state occupancy during the AP. Results are: 1), the Ca(V)1.2 model reproduces experimental single-channel and macroscopic-current data; 2), the model reproduces rate dependence of APD, [Na(+)](i), and the Ca(2+)-transient (CaT), and restitution of APD and CaT during premature stimuli; 3), CDI of Ca(V)1.2 is sensitive to Ca(2+) that enters the subspace through the channel and from SR release. The relative contributions of these Ca(2+) sources to total CDI during the AP vary with time after depolarization, switching from early SR dominance to late Ca(V)1.2 dominance. 4), The relative contribution of CDI to total inactivation of Ca(V)1.2 is greater at negative potentials, when VDI is weak; and 5), loss of VDI due to the Ca(V)1.2 mutation G406R (linked to the Timothy syndrome) results in APD prolongation and increased CaT

Equilibrium and kinetic aspects of protein-DNA recognition.

The specificity of regulatory protein binding to DNA is due to a complementarity between the sequence of reaction centres on the protein and the base pair sequence in the specific DNA site allowing the formation of a number of specific noncovalent bonds between the interacting entities. In the present communication the thermodynamic and kinetic aspects of these interactions are considered. The extent of binding specificity is shown to increase with an increase of the bond stability constants and with an increase in the number of ligand reaction centres. Kinetic analysis is carried out assuming that association process is very fast and that dissociation of nonspecific complexes is a rate-limiting step in the recognition of a specific binding site on DNA. The calculations show that a ligand can recognize its specific binding site on DNA within a reasonably limited time interval if the number of its reaction centres and the corresponding stability constants are strongly limited

The calculation of plasma cell reaction and influence of antigen dose

The injection of sheep red cells and capsular antigen of Pasteurella pestis leads to increase in the absolute and relative number of plasma cells in the draining lymph node and spleen. An equation is proposed which is compatible with the linear relationship which is observed between the logarithm of the antigen dose and the square root of the number of plasma cells. An index of homogeneity is derived from this equation which is related to the number of different antigenic determinants and different antigenic molecules in the immunogen. This index varied in the predicted way when mice were immunized with relatively pure and crude preparations of capsular antigen