Dark matter as a cancer hazard

We comment on the paper "Dark Matter collisions with the Human Body" by K. Freese and C. Savage (Phys. Lett. B 717, 25 (2012) [arXiv:1204.1339]) and describe a dark matter model for which the results of the previous paper do not quite apply. Within this mirror dark matter model, potentially hazardous objects, mirror micrometeorites, can exist and may lead to diseases triggered by multiple mutations, such as cancer, though with very low probability.Comment: 7 pages, revtex4, some text and references added, version to be published in Physics Letters

Erot spatiaalisissa ja ajallisissa reaktionormeissa kevään ja syksyn fenologisille tapahtumille

For species to stay temporally tuned to their environment, they use cues such as the accumulation of degree-days. The relationships between the timing of a phenological event in a population and its environmental cue can be described by a population-level reaction norm. Variation in reaction norms along environmental gradients may either intensify the envi- ronmental effects on timing (cogradient variation) or attenu- ate the effects (countergradient variation). To resolve spatial and seasonal variation in species’ response, we use a unique dataset of 91 taxa and 178 phenological events observed across a network of 472 monitoring sites, spread across the nations of the former Soviet Union. We show that compared to local rates of advancement of phenological events with the advancement of temperature-related cues (i.e., variation within site over years), spatial variation in reaction normsPeer reviewe

Phenological shifts of abiotic events, producers and consumers across a continent

Ongoing climate change can shift organism phenology in ways that vary depending on species, habitats and climate factors studied. To probe for large-scale patterns in associated phenological change, we use 70,709 observations from six decades of systematic monitoring across the former Union of Soviet Socialist Republics. Among 110 phenological events related to plants, birds, insects, amphibians and fungi, we find a mosaic of change, defying simple predictions of earlier springs, later autumns and stronger changes at higher latitudes and elevations. Site mean temperature emerged as a strong predictor of local phenology, but the magnitude and direction of change varied with trophic level and the relative timing of an event. Beyond temperature-associated variation, we uncover high variation among both sites and years, with some sites being characterized by disproportionately long seasons and others by short ones. Our findings emphasize concerns regarding ecosystem integrity and highlight the difficulty of predicting climate change outcomes. The authors use systematic monitoring across the former USSR to investigate phenological changes across taxa. The long-term mean temperature of a site emerged as a strong predictor of phenological change, with further imprints of trophic level, event timing, site, year and biotic interactions.Peer reviewe

Chronicles of nature calendar, a long-term and large-scale multitaxon database on phenology

We present an extensive, large-scale, long-term and multitaxon database on phenological and climatic variation, involving 506,186 observation dates acquired in 471 localities in Russian Federation, Ukraine, Uzbekistan, Belarus and Kyrgyzstan. The data cover the period 1890-2018, with 96% of the data being from 1960 onwards. The database is rich in plants, birds and climatic events, but also includes insects, amphibians, reptiles and fungi. The database includes multiple events per species, such as the onset days of leaf unfolding and leaf fall for plants, and the days for first spring and last autumn occurrences for birds. The data were acquired using standardized methods by permanent staff of national parks and nature reserves (87% of the data) and members of a phenological observation network (13% of the data). The database is valuable for exploring how species respond in their phenology to climate change. Large-scale analyses of spatial variation in phenological response can help to better predict the consequences of species and community responses to climate change.Peer reviewe

Experimental and computational methods for monitoring of dynamic arterial cellular organization

Suivre la prolifération, la migration et l'organisation cellulaires est important pour comprendre un large éventail de processus, notamment le développement d'organes, la cicatrisation et l'intégration de dispositifs médicaux. Etudier l'interaction entre les cellules et leur environnement promet d'améliorer notre compréhension des diverses pathologies, notamment des maladies cardiovasculaires et du cancer. Dans cette thèse, nous avons développé de nouveaux outils expérimentaux et numériques pour suivre les événements cellulaires majeurs en temps réel. Nous avons commencé par étudier la dynamique de la cicatrisation des cellules endothéliales (CE) en développant un modèle expérimental et un algorithme d'analyse d'image pour quantifier les taux de guérison de la blessure endothéliale en fonction de la rigidité du substrat, de la contrainte de cisaillement sur la surface cellulaire et de la présence de cellules musculaires lisses (CML). Nous avons montré que la guérison est plus rapide sur des substrats rigides que sur des surfaces molles, qu'elle est étonnamment plus lente sous contrainte de cisaillement que dans des conditions sans écoulement, et que les CML aux densités étudiées n'ont pas d'impact significatif sur son efficacité. Nous avons ensuite étudié comment la communication CE-CML pourrait affecter le phénotype des CML et leur activité contractile. En nous basant sur l'approche de polarimétrie de Mueller, nous avons confirmé que les CML remodèlent significativement l'hydrogel de collagène avec un effet plus prononcé en présence de CE. En général, nos résultats suggèrent que l'imagerie polarimétrique de Mueller est en effet un outil approprié pour évaluer l'activité des CML. Enfin, nous avons développé une imitation artérielle "intelligente" avec des capteurs d'impédance. La spectroscopie d'impédance couplée à des outils modernes d'apprentissage automatique nous a permis de prédire l'évolution de la densité cellulaire et de distinguer entre les CE et les CML en nous basant uniquement sur les mesures électriques. À notre connaissance, ce système est le premier exemple de l’artère in vitro "connectée". Nous pensons que notre travail, dans son intégralité, fournit des outils innovants pour suivre en temps réel des événements cellulaires majeurs et dont l’application à la cicatrisation de la couche endothéliale ou à la contractilité des CML montre comment ils peuvent être utilisés pour comprendre la fonction vasculaire.Tracking cellular proliferation, migration, and organization is important for understanding a wide array of processes including organ development, wound healing, and the integration of implantable medical devices. Elucidating how cells interact and remodel their environment promises to enhance our comprehension of various pathologies including cardiovascular disease and cancer. In this thesis, we have developed a number of novel experimental and computational tools to track major cellular events in real time. We began by investigating the dynamics of endothelial cell (EC) wound healing as commonly occurs after an endovascular intervention. To this end, we developed an experimental model and an automated image analysis routine to quantify EC would healing rates as a function of substrate stiffness, wall shear stress, and the presence of smooth muscle cells (SMCs). We showed that EC wound healing is faster on rigid substrates than on soft surfaces, that it is surprisingly slower under shear stress than under no flow conditions, and that SMCs at the densities studied have no significant impact on EC wound healing efficiency. We then investigated how EC-SMC communication might impact SMC phenotype and contractile activity. To this aim we applied Mueller polarimetry approach and confirmed that SMC contraction leads to significant remodeling of the collagen hydrogel with even more pronounced effect in the presence of ECs. In general, our results suggest that Mueller polarimetric imaging is indeed an appropriate tool for assessing SMC activity. The final focus was on the development of a “smart” arterial mimic instrumented with impedance sensors. Impedance spectroscopy coupled with modern machine learning tools allowed us to predict the time evolution of EC and SMC density and to distinguish between ECs and SMCs based solely on the electrical impedance recordings. To our knowledge, this system is the first example of a “connected” arterial mimic. We believe that in its entirety, our work provides innovative tools for real-time dynamic monitoring of important cellular events, while their application to various scenarios including EC wound healing and SMC contractility demonstrate how they can be used to provide valuable insight into vascular function

Expanding Space, Quasars and St. Augustine’s Fireworks

An attempt is made to explain time non-dilation allegedly observed in quasar light curves. The explanation is based on the assumption that quasar black holes are, in some sense, foreign for our Friedmann-Robertson-Walker universe and do not participate in the Hubble flow. Although at first sight such a weird explanation requires unreasonably fine-tuned Big Bang initial conditions, we find a natural justification for it using the Milne cosmological model as an inspiration

Relativity 4-ever?

International audienceThis essay is about superluminal motion. It is generally believed that special relativity prohibits movements faster than the speed of light. It is explained which motion is actually forbidden by special relativity and why. Tachyons are breafly discussed and it is explained that, due to internal instability, tachyon fields cannot be used to transmit information faster than the speed of light. However, as John Stuart Bell remarked, “what is proved by the impossibility proofs is lack of imagination”. Inspired by the Frenkel–Kontorova model of crystal dislocations, we demonstrate the way to overcome the light speed barrier by introducing elvisebrions. Elvisebrions are defined as objects that can exist in the case when some hidden sectors, very weakly interacting with the visible sector, are either not Lorentz invariant, or Lorentz invariant but with different limiting velocities. In this case, elvisebrions can move in a superluminal manner without violating our existing physical models

Radial acceleration relation and dissipative dark matter

International audienceObservations indicate that ordinary matter, the baryons, influence the structural properties of dark matter on galactic scales. One such indication is the radial acceleration relation, which is a tight correlation between the measured gravitational acceleration and that expected from the baryons. We show here that the dark matter density profile that has been motivated by dissipative dark matter models, including mirror dark matter, can reproduce this radial acceleration relation

Mueller polarimetric imaging for fast macroscopic mapping of microscopic collagen matrix remodeling by smooth muscle cells

International audienceSmooth muscle cells (SMCs) are critical players in cardiovascular disease development and undergo complex phenotype switching during disease progression. However, SMC phenotype is difficult to assess and track in co-culture studies. To determine the contractility of SMCs embedded within collagen hydrogels, we performed polarized light imaging and subsequent analysis based on Mueller matrices. Measurements were made both in the absence and presence of endothelial cells (ECs) in order to establish the impact of EC-SMC communication on SMC contractility. The results demonstrated that Mueller polarimetric imaging is indeed an appropriate tool for assessing SMC activity which significantly modifies the hydrogel retardance in the presence of ECs. These findings are consistent with the idea that EC-SMC communication promotes a more contractile SMC phenotype. More broadly, our findings suggest that Mueller polarimetry can be a useful tool for studies of spatial heterogeneities in hydrogel remodeling by SMCs