An explanatory model to validate the way water activity rules periodic terrace generation in <Emphasis Type="Italic">Proteus mirabilis</Emphasis> swarm

This paper explains the biophysical principles which, according to us, govern the Proteus mirabilis swarm phenomenon. Then, this explanation is translated into a mathematical model, essentially based on partial differential equations. This model is then implemented using numerical methods of the finite volume type in order to make simulations. The simulations show most of the characteristics which are observed in situ and in particular the terrace generation.      

Micromechanical analysis of brain’s diffuse axonal injury

Computational models are important tools which help researchers understand traumatic brain injury (TBI). A mechanistic multi-scale numerical approach is introduced to quantify diffuse axonal injury (DAI), the most important mechanism of TBI, induced by a mechanical insult at micro-scale regions of the white matter or voxels where fiber orientations are the same. Using the mechanical properties of a single axon with a viscoelastic constitutive relation and its functional failure in terms of electrophysiological impairment, a numerical 2D micro-level lattice method is implemented to directly analyze the percentage of injured axons in a voxel containing a bundle of axons all with the same orientation under biaxial stretches. Reference micro-injury maps are then developed with the input parameters based on the principal strain or stretch values and their direction with respect to axons, which provide the percentage of injured axons in the voxel of interest as the output. The methodology is independent of any statistical analyses of the accident data and medical reports to derive probabilistic injury risk curves for DAI. Avoiding a structurally detailed full finite element head model, this study proposes a micro-mechanical approach which considers the anatomical structure of neural axons in the white matter together with their mechanical properties using a numerical lattice method to analyze the brain’s diffuse axonal injury. This work has the potential to help develop safer prevention tools and more effective diagnosis methods for DAI.     

Single pot sequential crystallization-distillation as a new purification procedure

A new purification procedure exploiting the simultaneous presence of a solid, liquid, and gas phase in a low surface area system is proposed and discussed. The assumptions of vanishingly low diffusion coefficients in the solid phase and that of the presence of a single “effective impurity” allow to plan the sequence of operations starting from the knowledge of just the melting and boiling points of the substance to be purified and of those of the “effective impurity”. Examples and results are presented.     

A Comment on Maximum Likelihood Estimation for Finite Mixtures of Distributions

Iterative numerical methods are necessary to find the maximum likelihood estimates for finite mixture distributions. This paper shows that it will often be possible to analytically reduce the number of equations that must ultimately be solved numerically. Such a reduction in dimensionality has not generally been used, or sought after, for mixture distributions. Yet such results are easily derived when each mixture component is assumed to be from the same parametric model within the exponential family.     

Effects of competition and shading in planktonic communities

A model for several algal species which compete both for light and for nutrients, and which are also subject to settling and diffusion, is considered. The settling speeds and diffusion coefficients are assumed to be small, in a sense to be made precise later, and a singular perturbation argument is used. In certain cases vertical segregation of the algal species is observed, and the mechanism for this is interpreted biologically.Supported by the Danish Natural Science Research Council (Grant No. 11-8321)     

Fixation probabilities of additive alleles in diploid populations

The calculation of the survival probability of a selectively advantageous allele is a central part of the quantitative theory of genetic evolution. However, several areas of investigation in population genetics theory, including the generalized neutrality theory, the concept of Muller's ratchet, and the risk of extinction of sexually reproducing populations due to the accumulation of deleterious mutations, rely on the calculation of the survival probability of selectively disadvantageous mutant genes. The calculation of these probabilities in the standard Wright-Fisher model of genetic evolution appears to be intractable, and yet is a key element in the above investigations. In this paper we find bounds for the fixation probability of deleterious and advantageous additive mutants, as well as finding close approximations for these probabilities. In addition, we derive analytical estimates for the relative error of our approximations and compare our results with those from numerical computation. Our results justify the diffusion approximation for the fixation probability of a single mutant.     

Relationship between somatosensory function and the spinothalamocortical pathway in chronic stroke patients

Abstract

Diffusion tensor tractography (DTT) allows for identification and evaluation of the spinothalamic tract and its thalamocortical pathway (STP). We attempted to investigate the relationship between tactile sensation and the STP in chronic stroke patients. We measured fractional anisotropy, mean diffusivity, and tract volume of the STP. The tactile sensation score of the affected side in patients with preserved STP integrity was higher compared with that of patients with an interrupted STP. The remaining volume and integrity of the STP in the affected hemisphere were important factors for tactile sensation of the affected side in chronic patients with intracerebral hemorrhage (ICH).     

Analysis of homodimeric avian and human galectins by two methods based on fluorescence spectroscopy: Different structural alterations upon oxidation and ligand binding

Spectroscopic monitoring is applied to detect structural alterations for homodimeric adhesion/growth-regulatory galectins. Mammalian galectin-1 and the avian ortholog CG-1B, due to their distinct patterns of cysteine positioning, can undergo oxidation. When monitoring tryptophan fluorescence anisotropy comparatively, an indicator of structural changes affecting rotational diffusion, segmental motion and/or fluorescence life time, reductions are seen in both cases upon oxidation. The decrease was especially marked for the human protein, more than 2-fold compared to the avian lectin. Using this approach to analyze binding of lactose, equilibrium and kinetic binding constants of both proteins were similar. This result is corroborated by fluorescence correlation spectroscopy with labeled proteins. Of note, the diffusion constant of CG-1B increased by 5.6% in the presence of lactose, as has been seen for the human protein. When processing the other two homodimeric avian galectins (CG-1A, CG-2) accordingly it was revealed that sequence homology does not translate into identical behavior. The diffusion constant of CG-1A was not affected, a slight decrease (−3.8%) was observed for CG-2. Obviously, alterations induced by oxidation and responses to ligand binding are different between these closely related proteins. Methodologically, the two spectroscopic techniques are proven to be sensitive and robust sensors for detecting intergalectin differences.     

Removing Cancer when it is Correlated with other Causes of Death

This paper presents an identifiability theorem in the theory of dependent competing risks and it applies the result by examining the effect of removing cancer from the United States population when cancer is correlated with the other causes of death. The paper shows how dependence can be modeled with copula functions and it shows that calculating the survival probabilities after cancer is removed is equivalent to solving a system of nonlinear differential equations.