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"Müller, Michael"
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Global patterns of tropical forest fragmentation
Satellite data and modelling reveal that tropical forest fragments have similar size distributions across continents, and that forest fragmentation is close to a critical point, beyond which fragment numbers will strongly increase.
Forest fragmentation patterns
Agriculture, logging and urban growth have caused unprecedented losses of tropical forest in the past few decades. Franziska Taubert and colleagues examine patterns of tropical forest fragmentation using high-resolution satellite data. They identify 130 million forest fragments across three continental regions, which each have size frequency distributions that are similar, being described by power laws with almost identical exponents. The principles of percolation theory provide one explanation for the observed patterns, and suggest that forest fragmentation is close to a critical threshold, beyond which fragmentation can be expected to accelerate strongly. Numerical modelling supports this hypothesis, suggesting that additional forest loss will strongly increase the total number of forest fragments over the next 50 years. However, the simulations also suggest that reforestation and reductions in deforestation can mitigate this projected increase in fragmentation.
Remote sensing enables the quantification of tropical deforestation with high spatial resolution
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. This in-depth mapping has led to substantial advances in the analysis of continent-wide fragmentation of tropical forests
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. Here we identified approximately 130 million forest fragments in three continents that show surprisingly similar power-law size and perimeter distributions as well as fractal dimensions. Power-law distributions
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have been observed in many natural phenomena
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such as wildfires, landslides and earthquakes. The principles of percolation theory
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provide one explanation for the observed patterns, and suggest that forest fragmentation is close to the critical point of percolation; simulation modelling also supports this hypothesis. The observed patterns emerge not only from random deforestation, which can be described by percolation theory
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, but also from a wide range of deforestation and forest-recovery regimes. Our models predict that additional forest loss will result in a large increase in the total number of forest fragments—at maximum by a factor of 33 over 50 years—as well as a decrease in their size, and that these consequences could be partly mitigated by reforestation and forest protection.
Journal Article
Cortical oscillations support sampling-based computations in spiking neural networks
Being permanently confronted with an uncertain world, brains have faced evolutionary pressure to represent this uncertainty in order to respond appropriately. Often, this requires visiting multiple interpretations of the available information or multiple solutions to an encountered problem. This gives rise to the so-called mixing problem: since all of these “valid” states represent powerful attractors, but between themselves can be very dissimilar, switching between such states can be difficult. We propose that cortical oscillations can be effectively used to overcome this challenge. By acting as an effective temperature, background spiking activity modulates exploration. Rhythmic changes induced by cortical oscillations can then be interpreted as a form of simulated tempering. We provide a rigorous mathematical discussion of this link and study some of its phenomenological implications in computer simulations. This identifies a new computational role of cortical oscillations and connects them to various phenomena in the brain, such as sampling-based probabilistic inference, memory replay, multisensory cue combination, and place cell flickering.
Journal Article
The land of green plums
Set in Romania at the height of Ceausescu's reign of terror, this autobiographical novel tells the story of a group of young students, each of whom has left the impoverished provinces in search of better prospects in the city.
Book
Be Careful in Multimessenger Inference of the Hubble Constant: A Path Forward for Robust Inference
Multimessenger observations of coalescing binary neutron stars (BNSs) using gravitational-wave (GW) and electromagnetic- (EM) wave signals are a direct probe of the expansion history of the Universe and carry the potential to shed light on the disparity between low- and high-redshift measurements of the Hubble constant H 0. To measure the value of H 0 with such observations requires pristine inference of the luminosity distance and the true source redshift with minimal impact from systematics. In this analysis, we carry out joint inference on mock GW signals and their EM afterglows from BNS coalescences and find that the inclination angle inferred from the afterglow light curve and apparent superluminal motion can be precise but need not be accurate and is subject to a systematic uncertainty that could be as large as 1.5σ. This produces a disparity between the EM and GW inferred inclination angles, which if not carefully treated when combining observations can bias the inferred value of H 0. We also find that already small misalignments of 3°–6° between the inherent system inclinations for the GW and EM emission can bias the inference by O(1σ–2σ) if not taken into account. As multimessenger BNS observations are rare, we must make the most out of a small number of events and harness the increased precision while avoiding a reduced accuracy. We demonstrate how to mitigate these potential sources of bias by jointly inferring the mismatch between the GW- and EM-based inclination angles and H 0.
Journal Article
قوة وكالات المخابرات : العملاء والمخبرون من العصور الوسطى إلى الحرب الإلكترونية
في هذا الكتاب، يأخذنا أوفه كلوسمان في رحلة شاملة عبر تطور أجهزة الاستخبارات من بداياتها في العصور الوسطى إلى عصر \"الحرب الإلكترونية\"، مركزا على كيفية تطور دور العملاء والمخبرين عبر الزمن. يبدأ بسرد أنشطة التجسس كفن بدائي مرتبط بالحروب الرومانية والعصور الوسطى، ثم يتناول تشكل أجهزة علاقات المخابرات المنظمة في دول أوروبية حديثة وعصر النهضة، قبل أن يعرض لكيفية تحول السرية والبيروقراطية الاستخباراتية في العالم الحديث خاصة أثناء الحربين العالميتين والحرب الباردة. ويكشف أن استخدام التكنولوجيا (كالإنترنت وكشف الاتصالات المشفرة) قد منح أجهزة مثل CIA وNSA هيمنة غير مسبوقة، وجرى تجاوز مفاهيم الخصوصية والحريات الشخصية إذ باتت القدرة على المراقبة واسعة النطاق، كما رأينا في قضايا تسريبات سنودن، بعد أن توسع النفوذ الاستخباري ليشمل كل زاوية من شبكة الإنترنت العالمية.
BOOK
Gut microbiota facilitates dietary heme-induced epithelial hyperproliferation by opening the mucus barrier in colon
Colorectal cancer risk is associated with diets high in red meat. Heme, the pigment of red meat, induces cytotoxicity of colonic contents and elicits epithelial damage and compensatory hyperproliferation, leading to hyperplasia. Here we explore the possible causal role of the gut microbiota in heme-induced hyperproliferation. To this end, mice were fed a purified control or heme diet (0.5 μmol/g heme) with or without broad-spectrum antibiotics for 14 d. Heme-induced hyperproliferation was shown to depend on the presence of the gut microbiota, because hyperproliferation was completely eliminated by antibiotics, although heme-induced luminal cytotoxicity was sustained in these mice. Colon mucosa transcriptomics revealed that antibiotics block heme-induced differential expression of oncogenes, tumor suppressors, and cell turnover genes, implying that antibiotic treatment prevented the hemedependent cytotoxic micelles to reach the epithelium. Our results indicate that this occurs because antibiotics reinforce the mucus barrier by eliminating sulfide-producing bacteria and mucin-degrading bacteria (e.g.,Akkermansia). Sulfide potently reduces disulfide bonds and can drive mucin denaturation and microbial access to the mucus layer. This reduction results in formation of trisulfides that can be detected in vitro and in vivo. Therefore, trisulfides can serve as a novel marker of colonic mucolysis and thus as a proxy for mucus barrier reduction. In feces, antibiotics drastically decreased trisulfides but increased mucin polymers that can be lysed by sulfide. We conclude that the gut microbiota is required for hemeinduced epithelial hyperproliferation and hyperplasia because of the capacity to reduce mucus barrier function.
Journal Article
Microbial-derived metabolites as a risk factor of age-related cognitive decline and dementia
A consequence of our progressively ageing global population is the increasing prevalence of worldwide age-related cognitive decline and dementia. In the absence of effective therapeutic interventions, identifying risk factors associated with cognitive decline becomes increasingly vital. Novel perspectives suggest that a dynamic bidirectional communication system between the gut, its microbiome, and the central nervous system, commonly referred to as the microbiota-gut-brain axis, may be a contributing factor for cognitive health and disease. However, the exact mechanisms remain undefined. Microbial-derived metabolites produced in the gut can cross the intestinal epithelial barrier, enter systemic circulation and trigger physiological responses both directly and indirectly affecting the central nervous system and its functions. Dysregulation of this system (i.e., dysbiosis) can modulate cytotoxic metabolite production, promote neuroinflammation and negatively impact cognition. In this review, we explore critical connections between microbial-derived metabolites (secondary bile acids, trimethylamine-N-oxide (TMAO), tryptophan derivatives and others) and their influence upon cognitive function and neurodegenerative disorders, with a particular interest in their less-explored role as risk factors of cognitive decline.
Journal Article
Single-dose SARS-CoV-2 vaccinations with either BNT162b2 or AZD1222 induce disparate Th1 responses and IgA production
Background
While vaccination programs against the severe acute respiratory syndrome virus 2 (SARS-CoV-2) are globally ongoing, disparate strategies for the deployment of spike antigen show varying effectiveness.
Methods
In order to explore this phenomenon, we sought to compare the early immune responses against AZD1222 and BNT162b2. SARS-CoV-2 seronegative participants received a single dose of either vaccine and were analyzed for immune cell, effector T cell, and antibody dynamics.
Results
AZD1222 induced transient leukopenia and major changes among innate and adaptive subpopulations. Both vaccines induced spike protein-specific effector T cells which were dominated by type 1 helper T cell responses following AZD1222 vaccination. A significant reduction of anti-inflammatory T cells upon re-stimulation was also restricted to AZD1222 vaccinees. While IgM and IgG were the dominant isotypes elicited by AZD1222, BNT162b2 led to a significant production of IgG and IgA.
Conclusions
Our results suggest that the strategy for spike protein delivery impacts on how and to what extent immune priming against the main SARS-CoV-2 antigen proceeds.
Journal Article