Chaotic mixing induced transitions in reaction-diffusion systems

We study the evolution of a localized perturbation in a chemical system with multiple homogeneous steady states, in the presence of stirring by a fluid flow. Two distinct regimes are found as the rate of stirring is varied relative to the rate of the chemical reaction. When the stirring is fast localized perturbations decay towards a spatially homogeneous state. When the stirring is slow (or fast reaction) localized perturbations propagate by advection in form of a filament with a roughly constant width and exponentially increasing length. The width of the filament depends on the stirring rate and reaction rate but is independent of the initial perturbation. We investigate this problem numerically in both closed and open flow systems and explain the results using a one-dimensional "mean-strain" model for the transverse profile of the filament that captures the interplay between the propagation of the reaction-diffusion front and the stretching due to chaotic advection.Comment: to appear in Chaos, special issue on Chaotic Flo

Spontaneous spiking in an autaptic Hodgkin-Huxley set up

The effect of intrinsic channel noise is investigated for the dynamic response of a neuronal cell with a delayed feedback loop. The loop is based on the so-called autapse phenomenon in which dendrites establish not only connections to neighboring cells but as well to its own axon. The biophysical modeling is achieved in terms of a stochastic Hodgkin-Huxley model containing such a built in delayed feedback. The fluctuations stem from intrinsic channel noise, being caused by the stochastic nature of the gating dynamics of ion channels. The influence of the delayed stimulus is systematically analyzed with respect to the coupling parameter and the delay time in terms of the interspike interval histograms and the average interspike interval. The delayed feedback manifests itself in the occurrence of bursting and a rich multimodal interspike interval distribution, exhibiting a delay-induced reduction of the spontaneous spiking activity at characteristic frequencies. Moreover, a specific frequency-locking mechanism is detected for the mean interspike interval.Comment: 8 pages, 10 figure

A systematic review of local vulnerability to climate change: in search of transparency, coherence and comparability

Because vulnerability is a conceptual construct rather than a directly observable phenomenon, most vulnerability assessments measure a set of “vulnerability indicators”. In order to identify the core approaches and range of variation in the field, we conducted a systematic literature review on local vulnerability to climate change. The systematic review entailed an identification of frameworks, concepts, and operationalizations and a transparency assessment of their reporting. Three fully defined relevant frameworks of vulnerability were identified: IPCC, Patterns of Smallholder Vulnerability and Vulnerability as Expected Poverty. Comparative analysis found substantial heterogeneity in frameworks, concepts and operationalizations, making it impossible to identify patterns of climate vulnerability indicators and determinants that have robust empirical support. If research measuring farmers’ vulnerability to climate change is to have any comparability, it needs greater conceptual coherence and empirical validity. We recommend a systematic program of testing and validating vulnerability measures before institutionalizing them in programmatic contexts

Strengthening the food systems governance evidence base: Supporting commensurability of research through a systematic review of methods

This document reports on a systematic review (SR) of food systems governance indicators. This review was undertaken by the CGIAR Research Programme on Climate Change Agriculture and Food Security (CCAFS)-funded 13-member Working Group on Effective Indicators for food systems governance and a review team. The purpose of this technical report is for archival records in line with the principles of full and transparent documentation of systematic reviews. This report is confined to details of the review method and results, with framing and interpretation and implications of results excluded. The latter are published as CCAFS Working Paper no. 167

Autochthony and insecure land tenure : the spatiality of ethnicized hybridity in the periphery of post-conflict Bukavu, DRC

This article analyzes the interaction of the traces of war with institutional hybridity in shaping the use of space in the periphery of Bukavu, in the eastern Democratic Republic of Congo. In peri-urban Bukavu, the urbanization of previously rural areas has created an uncertain mixture of land allocation mechanisms that are not adequately explained by representation in terms of a clash or mixture of statutory and customary law. This hybridity has created uncertainty for both newcomers and early settlers in which the othering and violence required to justify both encroachment on, and the protection of, land are supported by discourses of autochthony. Large parts of peri-urban Bukavu, in particular the area of Kasha, are gradually being balkanized by quasi-voluntary socio-spatial practices of segregation by ethnicities whose existence and salience are constantly, and at times forcibly, re-negotiated. While initially perceived as a safe haven, the city’s periphery is becoming an area of acute insecurity

Sexual selection explains Rensch's rule of allometry for sexual size dimorphism

In 1950, Rensch first described that in groups of related species, sexual size dimorphism is more pronounced in larger species. This widespread and fundamental allometric relationship is now commonly referred to as ‘Rensch's rule’. However, despite numerous recent studies, we still do not have a general explanation for this allometry. Here we report that patterns of allometry in over 5300 bird species demonstrate that Rensch's rule is driven by a correlated evolutionary change in females to directional sexual selection on males. First, in detailed multivariate analysis, the strength of sexual selection was, by far, the strongest predictor of allometry. This was found to be the case even after controlling for numerous potential confounding factors, such as overall size, degree of ornamentation, phylogenetic history and the range and degree of size dimorphism. Second, in groups where sexual selection is stronger in females, allometry consistently goes in the opposite direction to Rensch's rule. Taken together, these results provide the first clear solution to the long-standing evolutionary problem of allometry for sexual size dimorphism: sexual selection causes size dimorphism to correlate with species size

Regulation of the energy sensor AMP-activated protein kinase by antigen receptor and Ca2+ in T lymphocytes

The adenosine monophosphate (AMP)–activated protein kinase (AMPK) has a crucial role in maintaining cellular energy homeostasis. This study shows that human and mouse T lymphocytes express AMPKα1 and that this is rapidly activated in response to triggering of the T cell antigen receptor (TCR). TCR stimulation of AMPK was dependent on the adaptors LAT and SLP76 and could be mimicked by the elevation of intracellular Ca2+ with Ca2+ ionophores or thapsigargin. AMPK activation was also induced by energy stress and depletion of cellular adenosine triphosphate (ATP). However, TCR and Ca2+ stimulation of AMPK required the activity of Ca2+–calmodulin-dependent protein kinase kinases (CaMKKs), whereas AMPK activation induced by increased AMP/ATP ratios did not. These experiments reveal two distinct pathways for the regulation of AMPK in T lymphocytes. The role of AMPK is to promote ATP conservation and production. The rapid activation of AMPK in response to Ca2+ signaling in T lymphocytes thus reveals that TCR triggering is linked to an evolutionally conserved serine kinase that regulates energy metabolism. Moreover, AMPK does not just react to cellular energy depletion but also anticipates it

Cell Delivery: Routing Nanomolar Protein Cargoes to Lipid Raft-Mediated/Caveolar Endocytosis through a Ganglioside GM1-Specific Recognition Tag (Adv. Sci. 4/2020)

In article number 1902621, Tamás A. Martinek and co-workers develop a pentapeptidic tag, which reads the glycan code of ganglioside GM1 and triggers lipid raft-mediated endocytosis, avoiding lysosomal entrapment. This carrier molecule can deliver macromolecular cargoes (e.g., IgG complexes) into live cells with the possibility to escape to the cytosol.Peer reviewe

The UV-Optical Galaxy Color-Magnitude Diagram. I. Basic Properties

We have analyzed the bivariate distribution of galaxies as a function of ultraviolet-optical colors and absolute magnitudes in the local universe. The sample consists of galaxies with redshifts and optical photometry from the Sloan Digital Sky Survey (SDSS) main galaxy sample matched with detections in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands in the Medium Imaging Survey being carried out by the Galaxy Evolution Explorer (GALEX) satellite. In the (NUV − r)_(0.1) versus M_(r,0.1) galaxy color-magnitude diagram, the galaxies separate into two well-defined blue and red sequences. The (NUV − r)_(0.1) color distribution at each M_(r,0.1) is not well fit by the sum of two Gaussians due to an excess of galaxies in between the two sequences. The peaks of both sequences become redder with increasing luminosity, with a distinct blue peak visible up to M_(r,0.1) ~ − 23. The r_(0.1)-band luminosity functions vary systematically with color, with the faint-end slope and characteristic luminosity gradually increasing with color. After correcting for attenuation due to dust, we find that approximately one-quarter of the color variation along the blue sequence is due to dust, with the remainder due to star formation history and metallicity. Finally, we present the distribution of galaxies as a function of specific star formation rate and stellar mass. The specific star formation rates imply that galaxies along the blue sequence progress from low-mass galaxies with star formation rates that increase somewhat with time to more massive galaxies with a more or less constant star formation rate. Above a stellar mass of ~10^(10.5) M_☉, galaxies with low ratios of current to past averaged star formation rate begin to dominate