8,594 research outputs found
Simulating the All-Order Hopping Expansion II: Wilson Fermions
We investigate the extension of the Prokof'ev-Svistunov worm algorithm to
Wilson lattice fermions in an external scalar field. We effectively simulate by
Monte Carlo the graphs contributing to the hopping expansion of the two-point
function on a finite lattice to arbitrary order. Tests are conducted for a
constant background field i. e. free fermions at some mass. For the method
introduced here this is expected to be a representative case. Its advantage is
that we know the exact answers and can thus make stringent tests on the
numerics. The approach is formulated in both two and three space-time
dimensions. In D=2 Wilson fermions enjoy special positivity properties and the
simulation is similarly efficient as in the Ising model. In D=3 the method also
works at sufficiently large mass, but there is a hard sign problem in the
present formulation hindering us to take the continuum limit.Comment: 29 pages [12pt], 5 figure
Supersymmetric quantum mechanics on the lattice: III. Simulations and algorithms
In the fermion loop formulation the contributions to the partition function
naturally separate into topological equivalence classes with a definite sign.
This separation forms the basis for an efficient fermion simulation algorithm
using a fluctuating open fermion string. It guarantees sufficient tunnelling
between the topological sectors, and hence provides a solution to the fermion
sign problem affecting systems with broken supersymmetry. Moreover, the
algorithm shows no critical slowing down even in the massless limit and can
hence handle the massless Goldstino mode emerging in the supersymmetry broken
phase. In this paper -- the third in a series of three -- we present the
details of the simulation algorithm and demonstrate its efficiency by means of
a few examples.Comment: 21 pages, 10 figures; typos in text correcte
A Proposal for a Multi-Drive Heterogeneous Modular Pipe- Inspection Micro-Robot
This paper presents the architecture used to develop a micro-robot for narrow pipes inspection. Both the electromechanical design and the control scheme will be described. In pipe environments it is very useful to have a method to retrieve information of the state of the inside part of the pipes in order to detect damages, breaks and holes. Due to the di_erent types of pipes that exists, a modular approach with di_erent types of modules has been chosen in order to be able to adapt to the shape of the pipe and to chose the most appropriate gait. The micro-robot has been designed for narrow pipes, a _eld in which there are not many prototypes. The robot incorporates a camera module for visual inspection and several drive modules for locomotion and turn (helicoidal, inchworm, two degrees of freedom rotation). The control scheme is based on semi-distributed behavior control and is also described. A simulation environment is also presented for prototypes testing
ArchiVISTA: A New Horizon in Providing Access to Visual Records of the National Archives of Canada
published or submitted for publicatio
Recent Developments of World-Line Monte Carlo Methods
World-line quantum Monte Carlo methods are reviewed with an emphasis on
breakthroughs made in recent years. In particular, three algorithms -- the loop
algorithm, the worm algorithm, and the directed-loop algorithm -- for updating
world-line configurations are presented in a unified perspective. Detailed
descriptions of the algorithms in specific cases are also given.Comment: To appear in Journal of Physical Society of Japa
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