1,239 research outputs found
Flocking with discrete symmetry: the 2d Active Ising Model
We study in detail the active Ising model, a stochastic lattice gas where
collective motion emerges from the spontaneous breaking of a discrete symmetry.
On a 2d lattice, active particles undergo a diffusion biased in one of two
possible directions (left and right) and align ferromagnetically their
direction of motion, hence yielding a minimal flocking model with discrete
rotational symmetry. We show that the transition to collective motion amounts
in this model to a bona fide liquid-gas phase transition in the canonical
ensemble. The phase diagram in the density/velocity parameter plane has a
critical point at zero velocity which belongs to the Ising universality class.
In the density/temperature "canonical" ensemble, the usual critical point of
the equilibrium liquid-gas transition is sent to infinite density because the
different symmetries between liquid and gas phases preclude a supercritical
region. We build a continuum theory which reproduces qualitatively the behavior
of the microscopic model. In particular we predict analytically the shapes of
the phase diagrams in the vicinity of the critical points, the binodal and
spinodal densities at coexistence, and the speeds and shapes of the
phase-separated profiles.Comment: 20 pages, 25 figure
Active Brownian Particles and Run-and-Tumble Particles: a Comparative Study
Active Brownian particles (ABPs) and Run-and-Tumble particles (RTPs) both
self-propel at fixed speed along a body-axis that reorients
either through slow angular diffusion (ABPs) or sudden complete randomisation
(RTPs). We compare the physics of these two model systems both at microscopic
and macroscopic scales. Using exact results for their steady-state distribution
in the presence of external potentials, we show that they both admit the same
effective equilibrium regime perturbatively that breaks down for stronger
external potentials, in a model-dependent way. In the presence of collisional
repulsions such particles slow down at high density: their propulsive effort is
unchanged, but their average speed along becomes . A
fruitful avenue is then to construct a mean-field description in which
particles are ghost-like and have no collisions, but swim at a variable speed
that is an explicit function or functional of the density . We give
numerical evidence that the recently shown equivalence of the fluctuating
hydrodynamics of ABPs and RTPs in this case, which we detail here, extends to
microscopic models of ABPs and RTPs interacting with repulsive forces.Comment: 32 pages, 6 figure
Optimal paths on the road network as directed polymers
We analyze the statistics of the shortest and fastest paths on the road
network between randomly sampled end points. To a good approximation, these
optimal paths are found to be directed in that their lengths (at large scales)
are linearly proportional to the absolute distance between them. This motivates
comparisons to universal features of directed polymers in random media. There
are similarities in scalings of fluctuations in length/time and transverse
wanderings, but also important distinctions in the scaling exponents, likely
due to long-range correlations in geographic and man-made features. At short
scales the optimal paths are not directed due to circuitous excursions governed
by a fat-tailed (power-law) probability distribution.Comment: 5 pages, 7 figure
Historic Barns of Iowa State
On March 22, 1858, Governor of Iowa Ralph P. Lowe signed the legislative bill establishing the State Agricultural College and Model Farm. The bill provided for a board of trustees to manage the model farm and college to be developed. Residents of Story and Boone counties presented an attractive proposal to locate the new institution at a site west of Squaw Creek and downtown Ames. The proposal included significant gifts of land and funding to assist in developing the College site. The Story County site was selected by the trustees on June 21, 1859.
The first concern was establishing the model farm specified in the legislation. Priority was given to two buildings. A farmhouse and livestock barn were both considered essential as a beginning, and construction of these two started in 1860
UC-400 Electric Vehicle Team
The KSU Electric Vehicle Team is developing a fully autonomous electric go-kart to compete in the Autonomous Karting Series (AKS). Our team will be making two programs for the kart’s software stack. These programs include a race line optimizer, which can take the centerline of a track and generate a minimum curvature path for it to follow to get around the track faster, as well as a race controller which can switch navigation algorithms automatically based on the current conditions of the race
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