311 research outputs found
Cross-link governed dynamics of biopolymer networks
Cytoskeletal networks of biopolymers are cross-linked by a variety of
proteins. Experiments have shown that dynamic cross-linking with physiological
linker proteins leads to complex stress relaxation and enables network flow at
long times. We present a model for the mechanical properties of transient
networks. By a combination of simulations and analytical techniques we show
that a single microscopic timescale for cross-linker unbinding leads to a broad
spectrum of macroscopic relaxation times, resulting in a weak power-law
dependence of the shear modulus on frequency. By performing rheological
experiments, we demonstrate that our model quantitatively describes the
frequency behavior of actin network cross-linked with -Actinin- over
four decades in frequency.Comment: 4 page
Tuning the mobility of a driven Bose-Einstein condensate via diabatic Floquet bands
We study the response of ultracold atoms to a weak force in the presence of a
temporally strongly modulated optical lattice potential. It is experimentally
demonstrated that the strong ac-driving allows for a tailoring of the mobility
of a dilute atomic Bose-Einstein condensate with the atoms moving ballistically
either along or against the direction of the applied force. Our results are in
agreement with a theoretical analysis of the Floquet spectrum of a model
system, thus revealing the existence of diabatic Floquet bands in the atom's
band spectra and highlighting their role in the non-equilibrium transport of
the atoms
The impact of financialisation on public health in times of COVID-19 and beyond
The substantial literature in political economy and soci- ology has shown that the increasing importance of finan- cial activities (financialisation) exhibits significant effects on many socioeconomic conditions. While these condi- tions are relevant to public health, the dominant focus of the literature has been centred on the impact of financial markets on health services and health-care systems. This paper analyses how the financialisation of non-financial corporations, real estate and pensions can worsen public health through the transformation of workplace and living conditions as well as financially dependent social groups' perception of health risk. Our analysis raises several ques- tions which aim to provide the basis of a future research agenda on the effects of financialisation on public and global health
Coulomb-driven broken-symmetry states in doubly gated suspended bilayer graphene
The non-interacting energy spectrum of graphene and its bilayer counterpart
consists of multiple degeneracies owing to the inherent spin, valley and layer
symmetries. Interactions among charge carriers are expected to spontaneously
break these symmetries, leading to gapped ordered states. In the quantum Hall
regime these states are predicted to be ferromagnetic in nature whereby the
system becomes spin polarized, layer polarized or both. In bilayer graphene,
due to its parabolic dispersion, interaction-induced symmetry breaking is
already expected at zero magnetic field. In this work, the underlying order of
the various broken-symmetry states is investigated in bilayer graphene that is
suspended between top and bottom gate electrodes. By controllably breaking the
spin and sublattice symmetries we are able to deduce the order parameter of the
various quantum Hall ferromagnetic states. At small carrier densities, we
identify for the first time three distinct broken symmetry states, one of which
is consistent with either spontaneously broken time-reversal symmetry or
spontaneously broken rotational symmetry
Interaction-driven (quasi-) insulating ground states of gapped electron-doped bilayer graphene
Bernal bilayer graphene has recently been discovered to exhibit a wide range
of unique ordered phases resulting from interaction-driven effects and
encompassing spin and valley magnetism, correlated insulators, correlated
metals, and superconductivity. This letter reports on a novel family of
correlated phases characterized by spin and valley ordering, observed in
electron-doped bilayer graphene. The novel correlated phases demonstrate an
intriguing non-linear current-bias behavior at ultralow currents that is
sensitive to the onset of the phases and is accompanied by an insulating
temperature dependence, providing strong evidence for the presence of
unconventional charge carrying degrees of freedom originating from ordering.
These characteristics cannot be solely attributed to any of the previously
reported phases, and are qualitatively different from the behavior seen
previously on the hole-doped side. Instead, our observations align with the
presence of charge- or spin-density-waves state that open a gap on a portion of
the Fermi surface or fully gapped Wigner crystals. The resulting new phases,
quasi-insulators in which part of the Fermi surface remains intact or
valley-polarized and valley-unpolarized Wigner crystals, coexist with
previously known Stoner phases, resulting in an exceptionally intricate phase
diagram
Type 1 plasminogen activator inhibitor binds to fibrin via vitronectin
Type 1 plasminogen activator inhibitor (PAI-1), the primary inhibitor of tissue-type plasminogen activator (t-PA), circulates as a complex with the abundant plasma glycoprotein, vitronectin. This interaction stabilizes the inhibitor in its active conformation. In this report, the effects of vitronectin on the interactions of PAI-1 with fibrin clots were studied. Confocal microscopic imaging of platelet-poor plasma clots reveals that essentially all fibrin-associated PAI-1 colocalizes with fibrin-bound vitronectin. Moreover, formation of platelet-poor plasma clots in the presence of polyclonal antibodies specific for vitronectin attenuated the inhibitory effects of PAI-1 on t-PA-mediated fibrinolysis. Addition of vitronectin during clot formation markedly potentiates PAI-1-mediated inhibition of lysis of 125I-labeled fibrin clots by t-PA. This effect is dependent on direct binding interactions of vitronectin with fibrin. There is no significant effect of fibrin-associated vitronectin on fibrinolysis in the absence of PAI-1. The binding of PAI-1 to fibrin clots formed in the absence of vitronectin was characterized by a low affinity (Kd ~ 3.5 μM) and rapid loss of PAI-1 inhibitory activity over time. In contrast, a high affinity and stabilization of PAI-1 activity characterized the cooperative binding of PAI- 1 to fibrin formed in the presence of vitronectin. These findings indicate that plasma PAI-1-vitronectin complexes can be localized to the surface of fibrin clots; by this localization, they may modulate fibrinolysis and clot reorganization
A Model for the Elasticity of Compressed Emulsions
We present a new model to describe the unusual elastic properties of
compressed emulsions. The response of a single droplet under compression is
investigated numerically for different Wigner-Seitz cells. The response is
softer than harmonic, and depends on the coordination number of the droplet.
Using these results, we propose a new effective inter-droplet potential which
is used to determine the elastic response of a monodisperse collection of
disordered droplets as a function of volume fraction. Our results are in
excellent agreement with recent experiments. This suggests that anharmonicity,
together with disorder, are responsible for the quasi-linear increase of
and observed at .Comment: RevTeX with psfig-included figures and a galley macr
Adiabatic creation of coherent superposition states via multiple intermediate states
We consider an adiabatic population transfer process that resembles the well
established stimulated Raman adiabatic passage (STIRAP). In our system, the
states have nonzero angular momentums , therefore, the coupling laser fields
induce transitions among the magnetic sublevels of the states. In particular,
we discuss the possibility of creating coherent superposition states in a
system with coupling pattern and . Initially, the system is in the J=0 state. We show that by two delayed,
overlapping laser pulses it is possible to create any final superposition state
of the magnetic sublevels , , . Moreover, we find that
the relative phases of the applied pulses influence not only the phases of the
final superposition state but the probability amplitudes as well. We show that
if we fix the shape and the time-delay between the pulses, the final state
space can be entirely covered by varying the polarizations and relative phases
of the two pulses. Performing numerical simulations we find that our transfer
process is nearly adiabatic for the whole parameter set.Comment: 7 pages, 10 figure
Probing the tunable multi-cone bandstructure in Bernal bilayer graphene
Controlling the bandstructure of Dirac materials is of wide interest in
current research but has remained an outstanding challenge for systems such as
monolayer graphene. In contrast, Bernal bilayer graphene (BLG) offers a highly
flexible platform for tuning the bandstructure, featuring two distinct regimes.
In one regime, which is well established and widely used, a tunable bandgap is
induced by a large enough transverse displacement field. Another is a gapless
metallic band occurring near charge neutrality and at not too strong fields,
featuring rich 'fine structure' consisting of four linearly-dispersing Dirac
cones with opposite chiralities in each valley and van Hove singularities. Even
though BLG was extensively studied experimentally in the last two decades, the
evidence of this exotic bandstructure is still elusive, likely due to
insufficient energy resolution. Here, rather than probing the bandstructure by
direct spectroscopy, we use Landau levels as markers of the energy dispersion
and carefully analyze the Landau level spectrum in a regime where the cyclotron
orbits of electrons or holes in momentum space are small enough to resolve the
distinct mini Dirac cones. We identify the presence of four distinct Dirac
cones and map out complex topological transitions induced by electric
displacement field. These findings introduce a valuable addition to the toolkit
for graphene electronics
Effect of Coulomb interactions on the physical observables of graphene
We give an update of the situation concerning the effect of electron-electron
interactions on the physics of a neutral graphene system at low energies. We
revise old renormalization group results and the use of 1/N expansion to
address questions of the possible opening of a low-energy gap, and the
magnitude of the graphene fine structure constant. We emphasize the role of
Fermi velocity as the only free parameter determining the transport and
electronic properties of the graphene system and revise its renormalization by
Coulomb interactions in the light of recent experimental evidence.Comment: Proceedings of the Nobel Symposium on graphene 2010, to appear as a
special issue in Physica Script
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