Structures and waves in a nonlinear heat-conducting medium

The paper is an overview of the main contributions of a Bulgarian team of researchers to the problem of finding the possible structures and waves in the open nonlinear heat conducting medium, described by a reaction-diffusion equation. Being posed and actively worked out by the Russian school of A. A. Samarskii and S.P. Kurdyumov since the seventies of the last century, this problem still contains open and challenging questions.Comment: 23 pages, 13 figures, the final publication will appear in Springer Proceedings in Mathematics and Statistics, Numerical Methods for PDEs: Theory, Algorithms and their Application

USE OF INTERNATIONALISMS MOTIVATED BY GREEK ROOT MORPHEME `НАЕМАТ` IN MEDICAL TERMINOLOGY (FIRST COMMUNICATION)

No abstrac

USE OF INTERNATIONALISMS MOTIVATED BY GREEK ROOT MORPHEME `НАЕМАТ` IN MEDICAL TERMINOLOGY (SECOND COMMUNICATION)

No abstrac

Prediction of sanding in subsurface hydrocarbon reservoirs.

Sand production in oil and gas wells can occur if the fluid velocity exceeds a certain value. Due to drilling operations, the mechanical stresses can exceed the load bearing capacity of the rock. As the local stresses exceed certain level, a certain amount of rock is fractured into sand. Then, the sand is carried by the fluid through the wellbore depending on the flow rate. The amount of the solids can be less than a few grams per cubic meter of reservoir fluid or an essential amount. In the later case erosion of the rock and removing sufficient quantities of rock can occur. This can produce subsurface cavities which collapse and destroy the well. When sanding is unavoidable it is necessary to estimate the characteristics of the process. Our aim was to generate a simple one-dimensional local model, which predicts the volume of sanding, the radius and the porosity of the yielded zone. Such model will help the company in the development of complex 3D models

Tinnitus – a manifestation of neurodegenerative diseases

BackgroundTinnitus is a widespread hearing impairment that can be characterized by the perception of sound, such as tone or noise, in the absence of an appropriate external sound source. The cause of tinnitus and mechanism are unclear. The prevalence of tinnitus is higher in people over 60 years of age. Tinnitus is usually a manifestation of а hearing impairment. Symptoms can be acute or chronic. In most cases, tinnitus manifests as an idiopathic condition. In the clinical practice, common factors that affect the psychological and emotional well-being of people with tinnitus are: fear, stress, anxiety and depression, which in turn can cause insomnia, impaired concentration and cognitive dysfunction. Tinnitus is a heterogeneous disorder in terms of its etiology and clinic. Tinnitus is associated with hearing loss, as both symptoms often occur together, though in many clinical cases, people with hearing loss do not develop tinnitus.MethodsWe present а clinical case of a patient diagnosed with a posturographic system, along with a full otoneurological and hearing examinations. Methods of videonystagmography, video head impulse test, subjective visual vertical, audiometry, tympanometry, otoacoustic emissions test, automated auditory brainstem response were used. We provided a dental check-up and an occlusion analysis. Patient filled out questionnaires and signed a written informed consent. The aim of the team was to analyze the manifestation of tinnitus as a precursor of a neurodegenerative disease.Results and discussionFrom the literature review done chronic tinnitus is associated with anatomical brain abnormalities, including decreased cortical gray matter and decreased white matter integrity. There is also a high prevalence of cognitive impairment reported among patients with tinnitus from a clinical point of view. Tinnitus is an independent risk factor for subsequent neurodegenerative disease. There are a number of neurological conditions that can be encountered in the otorhinolaryngological and dental practice. It is important for the dentist to enrich own knowledge of the underlying neurological conditions, as they may affect the provision of dental treatment. Our findings from the examinations executed are consistent with previous studies, which show that diabetes and head injuries can be risk factors for AD and neurodegeneration.ConclusionsFurther research is needed to re-confirm the conclusions of our research and to investigate the pathophysiology of the relationship between tinnitus and the Alzheimer’s disease and tinnitus and the Parkinson’s disease in more depth

Greenhouse gas balance over thaw-freeze cycles in discontinuous zone permafrost

Peat in the discontinuous permafrost zone contains a globally significant reservoir of carbon that has undergone multiple permafrost-thaw cycles since the end of the mid-Holocene (~3700 years before present). Periods of thaw increase C decomposition rates which leads to the release of CO2 and CH4 to the atmosphere creating potential climate feedback. To determine the magnitude and direction of such feedback, we measured CO2 and CH4 emissions and modeled C accumulation rates and radiative fluxes from measurements of two radioactive tracers with differing lifetimes to describe the C balance of the peatland over multiple permafrost-thaw cycles since the initiation of permafrost at the site. At thaw features, the balance between increased primary production and higher CH4 emission stimulated by warmer temperatures and wetter conditions favors C sequestration and enhanced peat accumulation. Flux measurements suggest that frozen plateaus may intermittently (order of years to decades) act as CO2 sources depending on temperature and net ecosystem respiration rates, but modeling results suggest that—despite brief periods of net C loss to the atmosphere at the initiation of thaw—integrated over millennia, these sites have acted as net C sinks via peat accumulation. In greenhouse gas terms, the transition from frozen permafrost to thawed wetland is accompanied by increasing CO2 uptake that is partially offset by increasing CH4 emissions. In the short-term (decadal time scale) the net effect of this transition is likely enhanced warming via increased radiative C emissions, while in the long-term (centuries) net C deposition provides a negative feedback to climate warming

Dynamics of non-equilibrium membrane bud formation

The dynamical response of a lipid membrane to a local perturbation of its molecular symmetry is investigated theoretically. A density asymmetry between the two membrane leaflets is predominantly released by in-plane lipid diffusion or membrane curvature, depending upon the spatial extent of the perturbation. It may result in the formation of non-equilibrium structures (buds), for which a dynamical size selection is observed. A preferred size in the micrometer range is predicted, as a signature of the crossover between membrane and solvent dominated dynamical membrane response.Comment: 7 pages 3 figure

Viscosity of fluid membranes measured from vesicle deformation

Viscosity is a key mechanical property of cell membranes that controls time-dependent processes such as membrane deformation and diffusion of embedded inclusions. Despite its importance, membrane viscosity remains poorly characterized because existing methods rely on complex experimental designs and/or analyses. Here, we describe a facile method to determine the viscosity of bilayer membranes from the transient deformation of giant unilamellar vesicles induced by a uniform electric field. The method is non-invasive, easy to implement, probe-independent, high-throughput, and sensitive enough to discern membrane viscosity of different lipid types, lipid phases, and polymers in a wide range, from 10$^{-8}$ to 10$^{-4}$ Pa.s.m. It enables fast and consistent collection of data that will advance understanding of biomembrane dynamics