12,781 research outputs found
Crunching Biofilament Rings
We discuss a curious example for the collective mechanical behavior of
coupled non-linear monomer units entrapped in a circular filament. Within a
simple model we elucidate how multistability of monomer units and exponentially
large degeneracy of the filament's ground state emerge as a collective feature
of the closed filament. Surprisingly, increasing the monomer frustration, i.e.,
the bending prestrain within the circular filament, leads to a conformational
softening of the system. The phenomenon, that we term polymorphic crunching, is
discussed and applied to a possible scenario for membrane tube deformation by
switchable dynamin or FtsZ filaments. We find an important role of cooperative
inter-unit interaction for efficient ring induced membrane fission
Radiative corrections to deeply virtual Compton scattering
We discuss possibilities of measurement of deeply virtual Compton scattering
amplitudes via different asymmetries in order to access the underlying skewed
parton distributions. Perturbative one-loop coefficient functions and two-loop
evolution kernels, calculated recently by a tentative use of residual conformal
symmetry of QCD, are used for a model dependent numerical estimation of
scattering amplitudes.Comment: 9 pages LaTeX, 3 figures, czjphyse.cls required Talk given by D.
M\"uller at Inter. Workshop ``PRAHA-Spin99'', Prague, Sept. 6-11, 199
A Role for PPARβ/δ in Tumor Stroma and Tumorigenesis
Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) is a transcription factor that is activated by endogenous fatty acid ligands and by synthetic agonists. Its role in the regulation of skeletal muscle fatty acid catabolism, glucose homeostasis, and cellular differentiation has been established in multiple studies. On the contrary, a role for PPARβ/δ in tumorigenesis is less clear because there are contradictory reports in the literature. However, the majority of these studies have not examined the role of PPARβ/δ in the tumor stroma. Recent evidence suggests that stromal PPARβ/δ regulates tumor endothelial cell proliferation and promotes differentiation leading to the properly orchestrated events required for tumor blood vessel formation. This review briefly summarizes the significance of these studies that may provide clues to help explain the reported discrepancies in the literature regarding the role of PPARβ/δ in tumorigenesis
Rydberg-Atom Quantum Simulation and Chern Number Characterization of a Topological Mott Insulator
In this work we consider a system of spinless fermions with nearest and
next-to-nearest neighbor repulsive Hubbard interactions on a honeycomb lattice,
and propose and analyze a realistic scheme for analog quantum simulation of
this model with cold atoms in a two-dimensional hexagonal optical lattice. To
this end, we first derive the zero-temperature phase diagram of the interacting
model within a mean-field theory treatment. We show that besides a
semi-metallic and a charge-density-wave ordered phase, the system exhibits a
quantum anomalous Hall phase, which is generated dynamically, i.e. purely as a
result of the repulsive fermionic interactions and in the absence of any
external gauge fields. We establish the topological nature of this dynamically
created Mott insulating phase by the numerical calculation of a Chern number.
Based on the knowledge of the mean-field phase diagram, we then discuss in
detail how the interacting Hamiltonian can be engineered effectively by
state-of-the-art experimental techniques for laser-dressing of cold fermionic
ground-state atoms with electronically excited Rydberg states that exhibit
strong dipolar interactions.Comment: Revtex4 file, color figures. Final journal version. References
update
Semiclassical universality of parametric spectral correlations
We consider quantum systems with a chaotic classical limit that depend on an
external parameter, and study correlations between the spectra at different
parameter values. In particular, we consider the parametric spectral form
factor which depends on a scaled parameter difference . For
parameter variations that do not change the symmetry of the system we show by
using semiclassical periodic orbit expansions that the small expansion
of the form factor agrees with Random Matrix Theory for systems with and
without time reversal symmetry.Comment: 18 pages, no figure
Computational study of flow–induced oscillation of a simplified soft palate
Two-dimensional numerical simulations are employed to study fluid structure
interaction soft palate in the pharynx for uniform
inhalation. We take a next step towards a better biomechanical system by modeling the motion of an
inextensible flexible plate. The improved structural model discretized by a low order difference
method permits us to simulate the two-dimensional motion of the flexible plate. The inspiratory
airflow is described by the Navier–Stokes equations for compressible flow solved by a high order
difference method. The explicitly coupled fluid re interaction
model is based on the Arbitrary Lagrangian–Eulerian formulation
Electroweak phase transitions with BSM fermions
We study the impact of additional beyond-the-Standard Model (BSM) fermions, charged under the Standard Model (SM) SU(2) ⊗ U(1) gauge group, on the electroweak phase transition (EWPT) in a 2-Higgs-Doublet-Model (2HDM) of type II. We find that the strength of the EWPT can be enhanced by about 40% compared to the default 2HDM. Therefore, additional light fermions are a useful tool to weaken the tension between increasing mass constraints on BSM scalars and the requirement of additional light scalar degrees of freedom to accommodate a strong first order EWPT. The findings are of particular interest for a variety of (non-minimal) split supersymmetry scenarios which necessarily introduce additional light fermion degrees of freedom
Crowdbreaks: Tracking Health Trends Using Public Social Media Data and Crowdsourcing
In the past decade, tracking health trends using social media data has shown great promise, due to a powerful combination of massive adoption of social media around the world, and increasingly potent hardware and software that enables us to work with these new big data streams. At the same time, many challenging problems have been identified. First, there is often a mismatch between how rapidly online data can change, and how rapidly algorithms are updated, which means that there is limited reusability for algorithms trained on past data as their performance decreases over time. Second, much of the work is focusing on specific issues during a specific past period in time, even though public health institutions would need flexible tools to assess multiple evolving situations in real time. Third, most tools providing such capabilities are proprietary systems with little algorithmic or data transparency, and thus little buy-in from the global public health and research community. Here, we introduce Crowdbreaks, an open platform which allows tracking of health trends by making use of continuous crowdsourced labeling of public social media content. The system is built in a way which automatizes the typical workflow from data collection, filtering, labeling and training of machine learning classifiers and therefore can greatly accelerate the research process in the public health domain. This work describes the technical aspects of the platform, thereby covering the functionalities at its current state and exploring its future use cases and extensions
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