4,088 research outputs found
Coupling of Active Motion and Advection Shapes Intracellular Cargo Transport
Intracellular cargo transport can arise from passive diffusion, active
motor-driven transport along cytoskeletal filament networks, and passive
advection by fluid flows entrained by such motor/cargo motion. Active and
advective transport are thus intrinsically coupled as related, yet different
representations of the same underlying network structure. A
reaction-advection-diffusion system is used here to show that this coupling
affects the transport and localization of a passive tracer in a confined
geometry. For sufficiently low diffusion, cargo localization to a target zone
is optimized either by low reaction kinetics and decoupling of bound and
unbound states, or by a mostly disordered cytoskeletal network with only weak
directional bias. These generic results may help to rationalize subtle features
of cytoskeletal networks, for example as observed for microtubules in fly
oocytes.Comment: revtex, 5 pages, 5 figures, to appear in PRL (http://prl.aps.org/
Dicke quantum spin glass of atoms and photons
Recent studies of strongly interacting atoms and photons in optical cavities
have rekindled interest in the Dicke model of atomic qubits coupled to discrete
photon cavity modes. We study the multimode Dicke model with variable
atom-photon couplings. We argue that a quantum spin glass phase can appear,
with a random linear combination of the cavity modes superradiant. We compute
atomic and photon spectral response functions across this quantum phase
transition, both of which should be accessible in experiment.Comment: 4 pages, 3 figures, v2: described quantum optics set-up in more
detail; extended discussion on photon correlation functions and experimental
signatures; added reference
Disease spread through animal movements: a static and temporal network analysis of pig trade in Germany
Background: Animal trade plays an important role for the spread of infectious
diseases in livestock populations. As a case study, we consider pig trade in
Germany, where trade actors (agricultural premises) form a complex network. The
central question is how infectious diseases can potentially spread within the
system of trade contacts. We address this question by analyzing the underlying
network of animal movements.
Methodology/Findings: The considered pig trade dataset spans several years
and is analyzed with respect to its potential to spread infectious diseases.
Focusing on measurements of network-topological properties, we avoid the usage
of external parameters, since these properties are independent of specific
pathogens. They are on the contrary of great importance for understanding any
general spreading process on this particular network. We analyze the system
using different network models, which include varying amounts of information:
(i) static network, (ii) network as a time series of uncorrelated snapshots,
(iii) temporal network, where causality is explicitly taken into account.
Findings: Our approach provides a general framework for a
topological-temporal characterization of livestock trade networks. We find that
a static network view captures many relevant aspects of the trade system, and
premises can be classified into two clearly defined risk classes. Moreover, our
results allow for an efficient allocation strategy for intervention measures
using centrality measures. Data on trade volume does barely alter the results
and is therefore of secondary importance. Although a static network description
yields useful results, the temporal resolution of data plays an outstanding
role for an in-depth understanding of spreading processes. This applies in
particular for an accurate calculation of the maximum outbreak size.Comment: main text 33 pages, 17 figures, supporting information 7 pages, 7
figure
Live imaging of whole mouse embryos during gastrulation : migration analyses of epiblast and mesodermal cells
During gastrulation in the mouse embryo, dynamic cell movements including epiblast invagination and mesodermal layer expansion lead to the establishment of the three-layered body plan. The precise details of these movements, however, are sometimes elusive, because of the limitations in live imaging. To overcome this problem, we developed techniques to enable observation of living mouse embryos with digital scanned light sheet microscope (DSLM). The achieved deep and high time-resolution images of GFP-expressing nuclei and following 3D tracking analysis revealed the following findings: (i) Interkinetic nuclear migration (INM) occurs in the epiblast at embryonic day (E)6 and 6.5. (ii) INM-like migration occurs in the E5.5 embryo, when the epiblast is a monolayer and not yet pseudostratified. (iii) Primary driving force for INM at E6.5 is not pressure from neighboring nuclei. (iv) Mesodermal cells migrate not as a sheet but as individual cells without coordination
Ruled Laguerre minimal surfaces
A Laguerre minimal surface is an immersed surface in the Euclidean space
being an extremal of the functional \int (H^2/K - 1) dA. In the present paper,
we prove that the only ruled Laguerre minimal surfaces are up to isometry the
surfaces R(u,v) = (Au, Bu, Cu + D cos 2u) + v (sin u, cos u, 0), where A, B, C,
D are fixed real numbers. To achieve invariance under Laguerre transformations,
we also derive all Laguerre minimal surfaces that are enveloped by a family of
cones. The methodology is based on the isotropic model of Laguerre geometry. In
this model a Laguerre minimal surface enveloped by a family of cones
corresponds to a graph of a biharmonic function carrying a family of isotropic
circles. We classify such functions by showing that the top view of the family
of circles is a pencil.Comment: 28 pages, 9 figures. Minor correction: missed assumption (*) added to
Propositions 1-2 and Theorem 2, missed case (nested circles having nonempty
envelope) added in the proof of Pencil Theorem 4, missed proof that the arcs
cut off by the envelope are disjoint added in the proof of Lemma
Signatures in a Giant Radio Galaxy of a Cosmological Shock Wave at Intersecting Filaments of Galaxies
Sensitive images of low-level, Mpc-sized radio cocoons offer new
opportunities to probe large scale intergalactic gas flows outside clusters of
galaxies. New radio images of high surface brightness sensitivity at
strategically chosen wavelengths of the giant radio galaxy NGC 315 (Mack et al.
1997,1998) reveal significant asymmetries and particularities in the
morphology, radio spectrum and polarization of the ejected radio plasma. We
argue that the combination of these signatures provides a sensitive probe of an
environmental shock wave. Analysis of optical redshifts in NGC 315 vicinity
confirms its location to be near, or at a site of large-scale flow collisions
in the 100 Mpc sized Pisces-Perseus Supercluster region. NGC 315 resides at the
intersection of several galaxy filaments, and its radio plasma serves there as
a `weather station' (Burns 1998) probing the flow of the elusive and previously
invisible IGM gas. If our interpretation is correct, this is the first
indication for a shock wave in flows caused by the cosmological large scale
structure formation, which is located in a filament of galaxies. The
possibility that the putative shock wave is a source of gamma-rays and ultra
high energy cosmic rays is briefly discussed.Comment: accepted by Astrophysical Journal Letters, 4 pages, 3 figures (incl.
2 color), uses emulateapj5.sty (included), aastex.sty (included) and
psfig.st
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