20,242 research outputs found
Island formation without attractive interactions
We show that adsorbates on surfaces can form islands even if there are no
attractive interactions. Instead strong repulsion between adsorbates at short
distances can lead to islands, because such islands increase the entropy of the
adsorbates that are not part of the islands. We suggest that this mechanism
cause the observed island formation in O/Pt(111), but it may be important for
many other systems as well.Comment: 11 pages, 4 figure
Outflow boundary conditions for 3D simulations of non-periodic blood flow and pressure fields in deformable arteries
The simulation of blood flow and pressure in arteries requires outflow
boundary conditions that incorporate models of downstream domains. We
previously described a coupled multidomain method to couple analytical models
of the downstream domains with 3D numerical models of the upstream vasculature.
This prior work either included pure resistance boundary conditions or
impedance boundary conditions based on assumed periodicity of the solution.
However, flow and pressure in arteries are not necessarily periodic in time due
to heart rate variability, respiration, complex transitional flow or acute
physiological changes. We present herein an approach for prescribing lumped
parameter outflow boundary conditions that accommodate transient phenomena. We
have applied this method to compute haemodynamic quantities in different
physiologically relevant cardiovascular models, including patient-specific
examples, to study non-periodic flow phenomena often observed in normal
subjects and in patients with acquired or congenital cardiovascular disease.
The relevance of using boundary conditions that accommodate transient phenomena
compared with boundary conditions that assume periodicity of the solution is
discussed
HMC algorithm with multiple time scale integration and mass preconditioning
We describe a new HMC algorithm variant we have recently introduced and
extend the published results by preliminary results of a simulation with a
pseudo scalar mass value of about 300 MeV. This new run confirms our
expectation that simulations with such pseudo scalar mass values become
feasible and affordable with our HMC variant. In addition we discuss
simulations from hot and cold starts at a pseudo scalar mass value of about 300
MeV, which we performed in order to test for possible meta-stabilities.Comment: 6 pages, Talk presented at Lattice 2005 (machines and algorithms
Experiences with OpenMP in tmLQCD
An overview is given of the lessons learned from the introduction of
multi-threading using OpenMP in tmLQCD. In particular, programming style,
performance measurements, cache misses, scaling, thread distribution for hybrid
codes, race conditions, the overlapping of communication and computation and
the measurement and reduction of certain overheads are discussed. Performance
measurements and sampling profiles are given for different implementations of
the hopping matrix computational kernel.Comment: presented at the 31st International Symposium on Lattice Field Theory
(Lattice 2013), 29 July - 3 August 2013, Mainz, German
Graph-Based Shape Analysis Beyond Context-Freeness
We develop a shape analysis for reasoning about relational properties of data
structures. Both the concrete and the abstract domain are represented by
hypergraphs. The analysis is parameterized by user-supplied indexed graph
grammars to guide concretization and abstraction. This novel extension of
context-free graph grammars is powerful enough to model complex data structures
such as balanced binary trees with parent pointers, while preserving most
desirable properties of context-free graph grammars. One strength of our
analysis is that no artifacts apart from grammars are required from the user;
it thus offers a high degree of automation. We implemented our analysis and
successfully applied it to various programs manipulating AVL trees,
(doubly-linked) lists, and combinations of both
SMIL State: an architecture and implementation for adaptive time-based web applications
In this paper we examine adaptive time-based web applications (or presentations). These are interactive presentations where time dictates which parts of the application are presented (providing the major structuring paradigm), and that require interactivity and other dynamic adaptation. We investigate the current technologies available to create such presentations and their shortcomings, and suggest a mechanism for addressing these shortcomings. This mechanism, SMIL State, can be used to add user-defined state to declarative time-based languages such as SMIL or SVG animation, thereby enabling the author to create control flows that are difficult to realize within the temporal containment model of the host languages. In addition, SMIL State can be used as a bridging mechanism between languages, enabling easy integration of external components into the web application. Finally, SMIL State enables richer expressions for content control. This paper defines SMIL State in terms of an introductory example, followed by a detailed specification of the State model. Next, the implementation of this model is discussed. We conclude with a set of potential use cases, including dynamic content adaptation and delayed insertion of custom content such as advertisements. © 2009 Springer Science+Business Media, LLC
Scaling test of quenched Wilson twisted mass QCD at maximal twist
We present the results of an extended scaling test of quenched Wilson twisted
mass QCD. We fix the twist angle by using two definitions of the critical mass,
the first obtained by requiring the vanishing of the pseudoscalar meson mass
m_PS for standard Wilson fermions and the second by requiring restoration of
parity at non-zero value of the twisted mass mu and subsequently extrapolating
to mu=0. Depending on the choice of the critical mass we simulate at values of
beta in [5.7,6.45], for a range of pseudoscalar meson masses 250 MeV < m_PS < 1
GeV and we perform the continuum limit for the pseudoscalar meson decay
constant f_PS and various hadron masses (vector meson m_V, baryon octet m_oct
and baryon decuplet m_dec) at fixed value of r_0 m_PS. For both definitions of
the critical mass, lattice artifacts are consistent with O(a) improvement.
However, with the second definition, large O(a^2) discretization errors present
at small quark mass with the first definition are strongly suppressed. The
results in the continuum limit are in very good agreement with those from the
Alpha and CP-PACS Collaborations.Comment: 6 pages, Talk presented at Lattice 2005, Dublin, 25-30 July 200
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