416 research outputs found
Review of Julia Kristeva, This Incredible Need to Believe.
Julia Kristeva, This Incredible Need to Believe. New York: Columbia University Press, 2009. 136 pp. ISBN 978023114784
Review of Julia Kristeva, This Incredible Need to Believe.
Julia Kristeva, This Incredible Need to Believe. New York: Columbia University Press, 2009. 136 pp. ISBN 978023114784
On shape forming by contractile filaments in the surface of growing tissues
Growing tissues are highly dynamic, and flow on sufficiently long time-scales due to cell proliferation, migration and tissue remodeling. As a consequence, growing tissues can often be approximated as viscous fluids. This means that the shape of microtissues growing in-vitro is governed by their surface stress state, as in fluid droplets. Recent work showed that cells in the near-surface region of fibroblastic or osteoblastic microtissues contract with highly oriented actin filaments, thus making the surface properties highly anisotropic, in contrast to what is expected for an isotropic fluid. Here, we develop a model that includes mechanical anisotropy of the surface generated by contractile fibers and we show that mechanical equilibrium requires contractile filaments to follow geodesic lines on the surface. Constant pressure in the fluid forces these contractile filaments to be along geodesics with a constant normal curvature. We then take this into account to determine equilibrium shapes of rotationally symmetric bodies subjected to anisotropic surface stress states and derive a family of surfaces of revolution. A comparison with recently published shapes of microtissues shows that this theory accurately predicts both the surface shape and the direction of the actin filaments in the surface
Eclipse: Disambiguating Illumination and Materials using Unintended Shadows
Decomposing an object's appearance into representations of its materials and
the surrounding illumination is difficult, even when the object's 3D shape is
known beforehand. This problem is ill-conditioned because diffuse materials
severely blur incoming light, and is ill-posed because diffuse materials under
high-frequency lighting can be indistinguishable from shiny materials under
low-frequency lighting. We show that it is possible to recover precise
materials and illumination -- even from diffuse objects -- by exploiting
unintended shadows, like the ones cast onto an object by the photographer who
moves around it. These shadows are a nuisance in most previous inverse
rendering pipelines, but here we exploit them as signals that improve
conditioning and help resolve material-lighting ambiguities. We present a
method based on differentiable Monte Carlo ray tracing that uses images of an
object to jointly recover its spatially-varying materials, the surrounding
illumination environment, and the shapes of the unseen light occluders who
inadvertently cast shadows upon it.Comment: Project page: https://dorverbin.github.io/eclipse
Mechanics and dynamics of X-chromosome pairing at X inactivation
At the onset of X-chromosome inactivation, the vital process whereby female mammalian cells equalize X products with
respect to males, the X chromosomes are colocalized along their Xic (X-inactivation center) regions. The mechanism
inducing recognition and pairing of the X’s remains, though, elusive. Starting from recent discoveries on the molecular
factors and on the DNA sequences (the so-called "pairing sites") involved, we dissect the mechanical basis of Xic
colocalization by using a statistical physics model. We show that soluble DNA-specific binding molecules, such as those
experimentally identified, can be indeed sufficient to induce the spontaneous colocalization of the homologous
chromosomes but only when their concentration, or chemical affinity, rises above a threshold value as a consequence of a
thermodynamic phase transition. We derive the likelihood of pairing and its probability distribution. Chromosome dynamics
has two stages: an initial independent Brownian diffusion followed, after a characteristic time scale, by recognition and
pairing. Finally, we investigate the effects of DNA deletion/insertions in the region of pairing sites and compare model
predictions to available experimental data
ELENA, a preliminary cost and feasibility study
To produce dense pbar beams at very low energies (100-200 keV), a small decelerator ring could be built and installed between the existing AD ring and the experimental area. Phase-space blowup during deceleration would be compensated by electron cooling in order to obtain final emittances comparable to the 5MeV beam presently delivered by the AD. This report describes preliminary machine parameters and layout of ELENA and also gives an approximate estimate of cost and manpower needs
Principles of meiotic chromosome assembly revealed in S. cerevisiae
During meiotic prophase, chromosomes organise into a series of chromatin loops emanating from a proteinaceous axis, but the mechanisms of assembly remain unclear. Here we use Saccharomyces cerevisiae to explore how this elaborate three-dimensional chromosome organisation is linked to genomic sequence. As cells enter meiosis, we observe that strong cohesin-dependent grid-like Hi-C interaction patterns emerge, reminiscent of mammalian interphase organisation, but with distinct regulation. Meiotic patterns agree with simulations of loop extrusion with growth limited by barriers, in which a heterogeneous population of expanding loops develop along the chromosome. Importantly, CTCF, the factor that imposes similar features in mammalian interphase, is absent in S. cerevisiae, suggesting alternative mechanisms of barrier formation. While grid-like interactions emerge independently of meiotic chromosome synapsis, synapsis itself generates additional compaction that matures differentially according to telomere proximity and chromosome size. Collectively, our results elucidate fundamental principles of chromosome assembly and demonstrate the essential role of cohesin within this evolutionarily conserved process
Identification of storage conditions stabilizing extracellular vesicles pre
Extracellular vesicles (EVs) play a key role in many physiological and pathophysiological processes and hold great potential for therapeutic and diagnostic use. Despite significant advances within the last decade, the key issue of EV storage stability remains unresolved and under investigated. Here, we aimed to identify storage conditions stabilizing EVs and comprehensively compared the impact of various storage buffer formulations at different temperatures on EVs derived from different cellular sources for up to 2 years. EV features including concentration, diameter, surface protein profile and nucleic acid contents were assessed by complementary methods, and engineered EVs containing fluorophores or functionalized surface proteins were utilized to compare cellular uptake and ligand binding. We show that storing EVs in PBS over time leads to drastically reduced recovery particularly for pure EV samples at all temperatures tested, starting already within days. We further report that using PBS as diluent was found to result in severely reduced EV recovery rates already within minutes. Several of the tested new buffer conditions largely prevented the observed effects, the lead candidate being PBS supplemented with human albumin and trehalose (PBS-HAT). We report that PBS-HAT buffer facilitates clearly improved short-term and long-term EV preservation for samples stored at -80°C, stability throughout several freeze-thaw cycles, and drastically improved EV recovery when using a diluent for EV samples for downstream applications
- …