6,484 research outputs found
Coherent regimes of globally coupled dynamical systems
The paper presents a method by which the mean field dynamics of a population
of dynamical systems with parameter diversity and global coupling can be
described in terms of a few macroscopic degrees of freedom. The method applies
to populations of any size and functional form in the region of coherence. It
requires linear variation or a narrow distribution for the dispersed parameter.
Although being an approximation, the method allows us to quantitatively study
the collective regimes that arise as a result of diversity and coupling and to
interpret the transitions among these regimes as bifurcations of the effective
macroscopic degrees of freedom. To illustrate, the phenomenon of oscillator
death and the route to full locking are examined for chaotic oscillators with
time scale mismatch.Comment: 5 pages, 3 figure
Exploiting limited valence patchy particles to understand autocatalytic kinetics
Autocatalysis, i.e., the speeding up of a reaction through the very same molecule which is produced, is common in chemistry, biophysics, and material science. Rate-equation-based approaches are often used to model the time dependence of products, but the key physical mechanisms behind the reaction cannot be properly recognized. Here, we develop a patchy particle model inspired by a bicomponent reactive mixture and endowed with adjustable autocatalytic ability. Such a coarse-grained model captures all general features of an autocatalytic aggregation process that takes place under controlled and realistic conditions, including crowded environments. Simulation reveals that a full understanding of the kinetics involves an unexpected effect that eludes the chemistry of the reaction, and which is crucially related to the presence of an activation barrier. The resulting analytical description can be exported to real systems, as confirmed by experimental data on epoxy-amine polymerizations, solving a long-standing issue in their mechanistic description
Proceedings of Mathsport international 2017 conference
Proceedings of MathSport International 2017 Conference, held in the Botanical Garden of the University of Padua, June 26-28, 2017.
MathSport International organizes biennial conferences dedicated to all topics where mathematics and sport meet.
Topics include: performance measures, optimization of sports performance, statistics and probability models, mathematical and physical models in sports, competitive strategies, statistics and probability match outcome models, optimal tournament design and scheduling, decision support systems, analysis of rules and adjudication, econometrics in sport, analysis of sporting technologies, financial valuation in sport, e-sports (gaming), betting and sports
Multi-scale theoretical approach to X-ray absorption spectra in disordered systems: an application to the study of Zn(II) in water
We develop a multi-scale theoretical approach aimed at calculating from first
principles X-ray absorption spectra of liquid solutions and disordered systems.
We test the method by considering the paradigmatic case of Zn(II) in water
which, besides being relevant in itself, is also of interest for biology. With
the help of classical molecular dynamics simulations we start by producing
bunches of configurations differing for the Zn(II)-water coordination mode.
Different coordination modes are obtained by making use of the so-called dummy
atoms method. From the collected molecular dynamics trajectories, snapshots of
a more manageable subsystem encompassing the metal site and two solvation
layers are cut out. Density functional theory is used to optimize and relax
these reduced system configurations employing a uniform dielectric to mimic the
surrounding bulk liquid water. On the resulting structures, fully quantum
mechanical X-ray absorption spectra calculations are performed by including
core-hole effects and core-level shifts. The proposed approach does not rely on
any guessing or fitting of the force field or of the atomic positions of the
system. The comparison of the theoretically computed spectrum with the
experimental Zn K-edge XANES data unambiguously demonstrates that among the
different a priori possible geometries, Zn(II) in water lives in an octahedral
coordination mode.Comment: 8 pages, 3 figure
A molecular dynamics study of chemical gelation in a patchy particle model
We report event-driven molecular dynamics simulations of the irreversible
gelation of hard ellipsoids of revolution containing several associating
groups, characterizing how the cluster size distribution evolves as a function
of the extent of reaction, both below and above the gel point. We find that in
a very large interval of values of the extent of reaction, parameter-free
mean-field predictions are extremely accurate, providing evidence that in this
model the Ginzburg zone near the gel point, where non-mean field effects are
important, is very limited. We also find that the Flory's hypothesis for the
post-gelation regime properly describes the connectivity of the clusters even
if the long-time limit of the extent of reaction does not reach the fully
reacted state. This study shows that irreversibly aggregating asymmetric
hard-core patchy particles may provide a close realization of the mean-field
model, for which available theoretical predictions may help control the
structure and the connectivity of the gel state. Besides chemical gels, the
model is relevant to network-forming soft materials like systems with
bioselective interactions, functionalized molecules and patchy colloids.Comment: 6 pages, 4 figures, to be published in Soft Matte
Retinoic acid-induced differentiation sensitizes myeloid progenitors cells to ER stress
The clonal expansion of hematopoietic myeloid precursors blocked at different stages of differentiation characterizes the acute myeloid leukemia (AML) phenotype. A subtype of AML, acute promyelocytic leukemia (APL), characterized by the chimeric protein PML-RARα is considered a paradigm of differentiation therapy. In this leukemia subtype the all-trans-retinoic acid (RA)-based treatments are able to induce PML-RARα degradation and leukemic blast terminal differentiation [1-2]. Granulocytic differentiation of APL cells driven by RA triggers a physiological Unfolded Protein Response (UPR), a series of pathways emanating from the ER in case of ER stress, which ensues when higher protein folding activity is required as during differentiation. We show here that, although mild, the ER stress induced by RA is sufficient to render human APL cell lines and primary blasts very sensitive to low doses of Tunicamycin (Tm), an ER stress inducing drug, at doses that are not toxic in the absence of RA. Importantly only human progenitors cells derived from APL patients resulted sensitive to the combined treatment with RA and Tm whereas those obtained from healthy donors were not affected. We also show that the UPR pathway downstream of PERK plays a major protective role against ER stress in differentiating cells and, by using a specific PERK inhibitor, we potentiated the toxic effect of the combination of RA and Tm. In conclusion, our findings identify the ER stress-related pathways as potential targets in the search for novel therapeutic strategies in AML
CMB Polarization Systematics, Cosmological Birefringence and the Gravitational Waves Background
Cosmic Microwave Background experiments must achieve very accurate
calibration of their polarization reference frame to avoid biasing the
cosmological parameters. In particular, a wrong or inaccurate calibration might
mimic the presence of a gravitational wave background, or a signal from
cosmological birefringence, a phenomenon characteristic of several
non-standard, symmetry breaking theories of electrodynamics that allow for
\textit{in vacuo} rotation if the polarization direction of the photon.
Noteworthly, several authors have claimed that the BOOMERanG 2003 (B2K)
published polarized power spectra of the CMB may hint at cosmological
birefringence. Such analyses, however, do not take into account the reported
calibration uncertainties of the BOOMERanG focal plane. We develop a formalism
to include this effect and apply it to the BOOMERanG dataset, finding a
cosmological rotation angle . We also
investigate the expected performances of future space borne experiment, finding
that an overall miscalibration larger then for Planck and
for EPIC, if not properly taken into account, will produce a bias on the
constraints on the cosmological parameters and could misleadingly suggest the
presence of a GW background.Comment: 10 pages, 3 figure
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