scholarly journals Modern perspectives on near-equilibrium analysis of Turing systems

2021 ◽  
Vol 379 (2213) ◽  
Author(s):  
Andrew L. Krause ◽  
Eamonn A. Gaffney ◽  
Philip K. Maini ◽  
Václav Klika
Keyword(s):  
Mathematical Theory ◽  
Diffusion Theory ◽  
Reaction Diffusion ◽  
Equilibrium Analysis ◽  
Open Questions ◽  
Substantial Progress ◽  
Reaction Transport ◽  
Mathematical Techniques ◽  
Underlying Mechanisms ◽  
Made In

In the nearly seven decades since the publication of Alan Turing’s work on morphogenesis, enormous progress has been made in understanding both the mathematical and biological aspects of his proposed reaction–diffusion theory. Some of these developments were nascent in Turing’s paper, and others have been due to new insights from modern mathematical techniques, advances in numerical simulations and extensive biological experiments. Despite such progress, there are still important gaps between theory and experiment, with many examples of biological patterning where the underlying mechanisms are still unclear. Here, we review modern developments in the mathematical theory pioneered by Turing, showing how his approach has been generalized to a range of settings beyond the classical two-species reaction–diffusion framework, including evolving and complex manifolds, systems heterogeneous in space and time, and more general reaction-transport equations. While substantial progress has been made in understanding these more complicated models, there are many remaining challenges that we highlight throughout. We focus on the mathematical theory, and in particular linear stability analysis of ‘trivial’ base states. We emphasize important open questions in developing this theory further, and discuss obstacles in using these techniques to understand biological reality. This article is part of the theme issue ‘Recent progress and open frontiers in Turing’s theory of morphogenesis’.

scholarly journals Rings whose additive endomorphisms are ring endomorphisms

1990 ◽  
Vol 42 (1) ◽  
pp. 145-152 ◽  
Author(s):  
Gary Birkenmeier ◽  
Henry Heatherly
Keyword(s):  
Subdirectly Irreducible ◽  
Finiteness Conditions ◽  
Chain Conditions ◽  
Open Questions ◽  
Open Case ◽  
Ring Endomorphism ◽  
Substantial Progress ◽  
Additive Endomorphism ◽  
Made In

A ring R is said to be an AE-ring if every additive endomorphism is a ring endomorphism. In this paper further steps are made toward solving Sullivan's Problem of characterising these rings. The classification of AE-rings with. R3 ≠ 0 is completed. Complete characterisations are given for AE-rings which are either: (i) subdirectly irreducible, (ii) algebras over fields, or (iii) additively indecomposable. Substantial progress is made in classifying AE-rings which are mixed – the last open case – by imposing various finiteness conditions (chain conditions on special ideals, height restricting conditions). Several open questions are posed.

scholarly journals Metal Abundances in Cool White Dwarfs and the Diffusion Theory

1979 ◽  
Vol 53 ◽  
pp. 165-178
Author(s):  
Gérard Vauclair
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Convection Zone ◽  
Diffusion Theory ◽  
Short Review ◽  
Convective Mixing ◽  
Substantial Progress ◽  
Metal Abundances ◽  
Cool White Dwarfs ◽  
Made In

In this theoretical review about cool white dwarfs, I will restrict myself to the problem of the metallic content in white dwarf outer layers. The first section will be a short review of what we know about the metal abundances. The hottest presently known white dwarf showing metal in its spectrum is the DB GD 40 (Te = 15 000 K). This temperature will be considered here as the hot boundary of the “cool” white dwarfs. Many efforts have been recently devoted to the understanding of these metal abundances. Section 2 will be a summary of recent calculations of diffusion time scales in both hydrogen and helium white dwarfs. It will be seen that diffusion is so efficient in white dwarf conditions that the convection zone which develops in the envelope as the effective temperature decreases along the cooling sequence is never deep enough to bring back to the surface the metals which had previously diffused downwards. A discussion of the carbon white dwarfs, also called λ 4670 stars, will be presented in section 3. Recent calculations show that the convective mixing between a helium envelope and a carbon core would produce λ 4670 composition for only very special conditions and for this reason we believe that this is an improbable explanation for this type of white dwarfs. We clearly need another physical mechanism to compete with diffusion and to maintain an observable amount of metals in some cool white dwarf atmospheres. We discuss in section 4 the competition between diffusion and accretion. This seems a very promising mechanism in spite of the fact that considerable improvements are still needed in the theory of accretion. Substantial progress has to be made in this direction. A few problems related to this model are invoked in the conclusion.

scholarly journals Recent progress understanding pathophysiology and genesis of brain AVM—a narrative review

2021 ◽  
Author(s):  
Hans-Jakob Steiger
Keyword(s):  
Large Degree ◽  
Advanced Imaging ◽  
Genetic Origin ◽  
The Past ◽  
Open Questions ◽  
Brain Avm ◽  
Pubmed Search ◽  
Substantial Progress ◽  
The Individual ◽  
Arterial Aneurysms

AbstractConsiderable progress has been made over the past years to better understand the genetic nature and pathophysiology of brain AVM. For the actual review, a PubMed search was carried out regarding the embryology, inflammation, advanced imaging, and fluid dynamical modeling of brain AVM. Whole-genome sequencing clarified the genetic origin of sporadic and familial AVM to a large degree, although some open questions remain. Advanced MRI and DSA techniques allow for better segmentation of feeding arteries, nidus, and draining veins, as well as the deduction of hemodynamic parameters such as flow and pressure in the individual AVM compartments. Nonetheless, complete modeling of the intranidal flow structure by computed fluid dynamics (CFD) is not possible so far. Substantial progress has been made towards understanding the embryology of brain AVM. In contrast to arterial aneurysms, complete modeling of the intranidal flow and a thorough understanding of the mechanical properties of the AVM nidus are still lacking at the present time.

scholarly journals Translational approaches to understanding metabolic dysfunction and cardiovascular consequences of obstructive sleep apnea

2015 ◽  
Vol 309 (7) ◽  
pp. H1101-H1111 ◽  
Author(s):  
Luciano F. Drager ◽  
Vsevolod Y. Polotsky ◽  
Christopher P. O'Donnell ◽  
Sergio L. Cravo ◽  
Geraldo Lorenzi-Filho ◽  
...  
Keyword(s):  
Obstructive Sleep Apnea ◽  
Cardiovascular Risk ◽  
Sleep Apnea ◽  
Animal Models ◽  
Metabolic Dysfunction ◽  
Significant Progress ◽  
Glucose And Lipid Metabolism ◽  
Obstructive Sleep ◽  
Underlying Mechanisms ◽  
Made In

Obstructive sleep apnea (OSA) is known to be independently associated with several cardiovascular diseases including hypertension, myocardial infarction, and stroke. To determine how OSA can increase cardiovascular risk, animal models have been developed to explore the underlying mechanisms and the cellular and end-organ targets of the predominant pathophysiological disturbance in OSA–intermittent hypoxia. Despite several limitations in translating data from animal models to the clinical arena, significant progress has been made in our understanding of how OSA confers increased cardiovascular risk. It is clear now that the hypoxic stress associated with OSA can elicit a broad spectrum of pathological systemic events including sympathetic activation, systemic inflammation, impaired glucose and lipid metabolism, and endothelial dysfunction, among others. This review provides an update of the basic, clinical, and translational advances in our understanding of the metabolic dysfunction and cardiovascular consequences of OSA and highlights the most recent findings and perspectives in the field.

scholarly journals Pathomechanisms of Oxidative Stress in Inflammatory Bowel Disease and Potential Antioxidant Therapies

2017 ◽  
Vol 2017 ◽  
pp. 1-18 ◽  
Author(s):  
Tian Tian ◽  
Ziling Wang ◽  
Jinhua Zhang
Keyword(s):  
Oxidative Stress ◽  
Inflammatory Bowel Disease ◽  
Bowel Disease ◽  
Defense Mechanisms ◽  
Gastrointestinal Disease ◽  
Mucosal Immune Response ◽  
Stress Signaling ◽  
Substantial Progress ◽  
Inflammatory Bowel ◽  
Underlying Mechanisms

Inflammatory bowel disease (IBD) is a chronic gastrointestinal disease whose incidence has risen worldwide in recent years. Accumulating evidence shows that oxidative stress plays an essential role in the pathogenesis and progression of IBD. This review highlights the generation of reactive oxygen species (ROS) and antioxidant defense mechanisms in the gastrointestinal (GI) tract, the involvement of oxidative stress signaling in the initiation and progression of IBD and its relationships with genetic susceptibility and the mucosal immune response. In addition, potential therapeutic strategies for IBD that target oxidative stress signaling are reviewed and discussed. Though substantial progress has been made in understanding the role of oxidative stress in IBD in humans and experimental animals, the underlying mechanisms are still not well defined. Thus, further studies are needed to validate how oxidative stress signaling is involved in and contributes to the development of IBD.

THE STATUS OF TWO-NEUTRINO AND NEUTRINOLESS DOUBLE BETA DECAY SEARCHES

1993 ◽  
Vol 02 (03) ◽  
pp. 507-546 ◽  
Author(s):  
M.K. MOE
Keyword(s):  
Beta Decay ◽  
Neutrinoless Double Beta Decay ◽  
Double Beta Decay ◽  
Experimental Activity ◽  
The Past ◽  
The Status ◽  
Substantial Progress ◽  
Direct Counting ◽  
Made In

Substantial progress has been made in double beta decay experiments in the past few years, including the beginning of sensitive new searches for neutrinoless double beta decay, and several additional positive detections of the two-neutrino mode by geochemical, radiochemical, and direct-counting techniques. This review discusses the recent experimental activity.

Persistent Questions About The Oxygen Donor In Silicon

1985 ◽  
Vol 59 ◽  
Author(s):  
Michael Stavola
Keyword(s):  
Formation Kinetics ◽  
Oxygen Donor ◽  
Substantial Progress ◽  
Made In

In spite of 30 years of study the most basic questions about the oxygen donor in silicon remain unanswered. There are not accepted models for the structure or formation kinetics. There is not even agreement on what the donor's constituents are. Nonetheless, substantial progress has been made in this field in recent years [1] that narrows model ideas and helps to focus continuing research.

scholarly journals Phosphoinositides regulate force-independent interactions between talin, vinculin, and actin

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Charlotte F Kelley ◽  
Thomas Litschel ◽  
Stephanie Schumacher ◽  
Dirk Dedden ◽  
Petra Schwille ◽  
...  
Keyword(s):  
Network Formation ◽  
Focal Adhesions ◽  
Membrane Composition ◽  
Macromolecular Assemblies ◽  
In Vitro Reconstitution ◽  
Membrane Bound ◽  
Underlying Mechanisms ◽  
Higher Order Networks ◽  
Made In

Focal adhesions (FA) are large macromolecular assemblies which help transmit mechanical forces and regulatory signals between the extracellular matrix and an interacting cell. Two key proteins talin and vinculin connecting integrin to actomyosin networks in the cell. Both proteins bind to F-actin and each other, providing a foundation for network formation within FAs. However, the underlying mechanisms regulating their engagement remain unclear. Here, we report on the results of in vitro reconstitution of talin-vinculin-actin assemblies using synthetic membrane systems. We find that neither talin nor vinculin alone recruit actin filaments to the membrane. In contrast, phosphoinositide-rich membranes recruit and activate talin, and the membrane-bound talin then activates vinculin. Together, the two proteins then link actin to the membrane. Encapsulation of these components within vesicles reorganized actin into higher-order networks. Notably, these observations were made in the absence of applied force, whereby we infer that the initial assembly stage of FAs is force independent. Our findings demonstrate that the local membrane composition plays a key role in controlling the stepwise recruitment, activation, and engagement of proteins within FAs.

scholarly journals Clinical and Neurobiological Aspects of TAO Kinase Family in Neurodevelopmental Disorders

2021 ◽  
Vol 14 ◽  
Author(s):  
Chun Hu ◽  
Pan Feng ◽  
Qian Yang ◽  
Lin Xiao
Keyword(s):  
Neurodevelopmental Disorders ◽  
Basic Research ◽  
Genetic Data ◽  
Review Article ◽  
Biological Processes ◽  
Behavioral Impairment ◽  
Clinical Investigations ◽  
Substantial Progress ◽  
Biochemical Analyses ◽  
Made In

Despite the complexity of neurodevelopmental disorders (NDDs), from their genotype to phenotype, in the last few decades substantial progress has been made in understanding their pathophysiology. Recent accumulating evidence shows the relevance of genetic variants in thousand and one (TAO) kinases as major contributors to several NDDs. Although it is well-known that TAO kinases are a highly conserved family of STE20 kinase and play important roles in multiple biological processes, the emerging roles of TAO kinases in neurodevelopment and NDDs have yet to be intensively discussed. In this review article, we summarize the potential roles of the TAO kinases based on structural and biochemical analyses, present the genetic data from clinical investigations, and assess the mechanistic link between the mutations of TAO kinases, neuropathology, and behavioral impairment in NDDs. We then offer potential perspectives from basic research to clinical therapies, which may contribute to fully understanding how TAO kinases are involved in NDDs.

scholarly journals ASPECTS OF THE DIFFUSION THEORY OF INNOVATIONS AND LOGISTISATION OF AGRICULTURAL INDUSTRY OF UKRAINE

2018 ◽  
pp. 49-56
Author(s):  
Yevhen Nikishyn
Keyword(s):  
Diffusion Of Innovations ◽  
Diffusion Theory ◽  
Reaction Diffusion ◽  
Industrial Complex ◽  
Competitive Advantages ◽  
Agricultural Industry ◽  
Regulatory Factors ◽  
Diffusion Structure ◽  
Cascade Effect ◽  
Separate System

The article is devoted to theoretical aspects of diffusion of innovations, as the conditions of logistics of the agro industrial complex of Ukraine. The concept of innovation-economic niche as a separate system with the potential of making innovations, the development of which creates competitive advantages, is formulated. New types of diffusion are classified on the basis of decision-making mechanisms by innovators. The diffusion models are considered, the descriptions of specific features of the behaviour of the dissemination of innovations in the reaction-diffusion structure are studied and made taking into account the system-regulatory factors. The principle of informational conditionality of economic phenomena as the basis of distribution of diffusion is formulated. The existence of a cascade effect in the diffusion of basic innovations has been determined; the necessity of the accompanying innovations has been substantiated. The causal relationship between the influence of system-regulatory factors on diffusion, the emergence of a cascade effect, the formation of clusters of innovations and the general influence on the Kondratiev cycles have been investigated.

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