4,181 research outputs found
Line tension and wettability of nanodrops on curved surfaces
In this paper we study the formation of nanodrops on curved surfaces (both
convex and concave) by means of molecular dynamics simulations, where the
particles interact via a Lennard-Jones potential. We find that the contact
angle is not affected by the curvature of the substrate, in agreement with
previous experimental findings. This means that the change in curvature of the
drop in response to the change in curvature of the substrate can be predicted
from simple geometrical considerations, under the assumption that the drop's
shape is a spherical cap, and that the volume remains unchanged through the
curvature. The resulting prediction is in perfect agreement with the simulation
results, for both convex and concave substrates. In addition, we calculate the
line tension, namely by fitting the contact angle for different size drops to
the modified Young equation. We find that the line tension for concave surfaces
is larger than for convex surfaces, while for zero curvature it has a clear
maximum. This feature is found to be correlated with the number of particles in
the first layer of the liquid on the surface
Dimensionality and morphology of particle and bubble clusters in turbulent flow
We conduct numerical experiments to investigate the spatial clustering of
particles and bubbles in simulations of homogeneous and isotropic turbulence.
Varying the Stokes parameter and the densities, striking differences in the
clustering of the particles can be observed. To quantify these visual findings
we use the Kaplan--Yorke dimension. This local scaling analysis shows a
dimension of approximately 1.4 for the light bubble distribution, whereas the
distribution of very heavy particles shows a dimension of approximately 2.4.
However, clearly separate parameter combinations yield the same dimensions. To
overcome this degeneracy and to further develop the understanding of
clustering, we perform a morphological (geometrical and topological) analysis
of the particle distribution. For such an analysis, Minkowski functionals have
been successfully employed in cosmology, in order to quantify the global
geometry and topology of the large-scale distribution of galaxies. In the
context of dispersed multiphase flow, these Minkowski functionals -- being
morphological order parameters -- allow us to discern the filamentary structure
of the light particle distribution from the wall-like distribution of heavy
particles around empty interconnected tunnels.Comment: 12 pages, 8 figure
Small-number statistics near the clustering transition in a compartementalized granular gas
Statistical fluctuations are observed to profoundly influence the clustering behavior of granular material in a vibrated system consisting of two connected compartments. When the number of particles N is sufficiently large sN<300 is sufficientd, the clustering follows the lines of a standard second-order phase transition and a mean-field description works. For smaller N, however, the enhanced influence of statistical fluctuations breaks the mean-field behavior. We quantitatively describe the competition between fluctuations and mean-field behavior sas a function of Nd using a dynamical flux model and molecular dynamics simulations
The clustering morphology of freely rising deformable bubbles
We investigate the clustering morphology of a swarm of freely rising
deformable bubbles. A three-dimensional Vorono\"i analysis enables us to
quantitatively distinguish between two typical clustering configurations:
preferential clustering and a grid-like structure. The bubble data is obtained
from direct numerical simulations (DNS) using the front-tracking method. It is
found that the bubble deformation, represented by the aspect ratio \chi, plays
a significant role in determining which type of clustering is realized: Nearly
spherical bubbles with \chi <~ 1.015 form a grid-like structure, while more
deformed bubbles show preferential clustering. Remarkably, this criteria for
the clustering morphology holds for different diameters of the bubbles, surface
tension, and viscosity of the liquid in the studied parameter regime. The
mechanism of this clustering behavior is connected to the amount of vorticity
generated at the bubble surfaces.Comment: 10 pages, 5 figure
Integrating Philosophy of Science Into Research on Ethical, Legal and Social Issues in the Life Sciences
This paper argues that research on normative issues in the life sciences will benefit from a tighter integration of philosophy of science. We examine research on ethical, legal and social issues in the life sciences (“ELSI”) and discuss three illustrative examples of normative issues that arise in different areas of the life sciences. These examples show that important normative questions are highly dependent on epistemic issues which so far have not been addressed sufficiently in ELSI, RRI and related areas of research. Accordingly, we argue for the integration of research on the epistemic aspects of the relevant areas of science into ELSI research to provide a better basis for addressing normative questions
Differential Signaling Profiles of MC4R Mutations with Three Different Ligands
The melanocortin 4 receptor (MC4R) is a key player in hypothalamic weight regulation and energy expenditure as part of the leptin-melanocortin pathway. Mutations in this G protein coupled receptor (GPCR) are the most common cause for monogenetic obesity, which appears to be mediated by changes in the anorectic action of MC4R via GS-dependent cyclic adenosine-monophosphate (cAMP) signaling as well as other signaling pathways. To study potential bias in the effects of MC4R mutations between the different signaling pathways, we investigated three major MC4R mutations: a GS loss-of-function (S127L) and a GS gain-of-function mutant (H158R), as well as the most common European single nucleotide polymorphism (V103I). We tested signaling of all four major G protein families plus extracellular regulated kinase (ERK) phosphorylation and β-arrestin2 recruitment, using the two endogenous agonists, α- and β-melanocyte stimulating hormone (MSH), along with a synthetic peptide agonist (NDP-α-MSH). The S127L mutation led to a full loss-of-function in all investigated pathways, whereas V103I and H158R were clearly biased towards the Gq/11 pathway when challenged with the endogenous ligands. These results show that MC4R mutations can cause vastly different changes in the various MC4R signaling pathways and highlight the importance of a comprehensive characterization of receptor mutations
Linescan microscopy data to extract diffusion coefficient of a fluorescent species using a commercial confocal microscope
We are grateful to the Max Delbrück Center for Molecular Medicine in the Helmholtz Association for core support and funding. P.A. and M.J.L. would like to acknowledge funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 421152132-SFB1423 subproject C03.We report here on the measurement of the diffusion coefficient of fluorescent species using a commercial microscope possessing a resonant scanner. Sequential linescans with a rate of up to 12 kHz yield a temporal resolution of 83 μs, making the setup amenable to measure diffusion rates over a range covering at least three orders of magnitude, from 100 μm2/s down to 0.1 μm2/s. We share representative data sets covering (i) the diffusion of a dye molecule, observed in media of different viscosities and (ii) the diffusion of a prototypical membrane receptor. The data can be valuable for researchers interested in the rapid diffusion properties of nuclear, cytosolic or membrane bound proteins fused to fluorescent tags.Publisher PDFPeer reviewe
Polarization of Migrating Monocytic Cells Is Independent of PI 3-Kinase Activity
BACKGROUND: Migration of mammalian cells is a complex cell type and environment specific process. Migrating hematopoietic cells assume a rapid amoeboid like movement when exposed to gradients of chemoattractants. The underlying signaling mechanisms remain controversial with respect to localization and distribution of chemotactic receptors within the plasma membrane and the role of PI 3-kinase activity in cell polarization. METHODOLOGY/PRINCIPAL FINDINGS: We present a novel model for the investigation of human leukocyte migration. Monocytic THP-1 cells transfected with the alpha(2A)-adrenoceptor (alpha(2A)AR) display comparable signal transduction responses, such as calcium mobilization, MAP-kinase activation and chemotaxis, to the noradrenaline homologue UK 14'304 as when stimulated with CCL2, which binds to the endogenous chemokine receptor CCR2. Time-lapse video microscopy reveals that chemotactic receptors remain evenly distributed over the plasma membrane and that their internalization is not required for migration. Measurements of intramolecular fluorescence resonance energy transfer (FRET) of alpha(2A)AR-YFP/CFP suggest a uniform activation of the receptors over the entire plasma membrane. Nevertheless, PI 3-kinase activation is confined to the leading edge. When reverting the gradient of chemoattractant by moving the dispensing micropipette, polarized monocytes--in contrast to neutrophils--rapidly flip their polarization axis by developing a new leading edge at the previous posterior side. Flipping of the polarization axis is accompanied by re-localization of PI-3-kinase activity to the new leading edge. However, reversal of the polarization axis occurs in the absence of PI 3-kinase activation. CONCLUSIONS/SIGNIFICANCE: Accumulation and internalization of chemotactic receptors at the leading edge is dispensable for cell migration. Furthermore, uniformly distributed receptors allow the cells to rapidly reorient and adapt to changes in the attractant cue. Polarized monocytes, which display typical amoeboid like motility, can rapidly develop a new leading edge facing the highest chemoattractant concentration at any site of the plasma membrane, including the uropod. The process appears to be independent of PI 3-kinase activity
- …