456 research outputs found
Approximately bisimilar symbolic models for nonlinear control systems
Control systems are usually modeled by differential equations describing how
physical phenomena can be influenced by certain control parameters or inputs.
Although these models are very powerful when dealing with physical phenomena,
they are less suitable to describe software and hardware interfacing the
physical world. For this reason there is a growing interest in describing
control systems through symbolic models that are abstract descriptions of the
continuous dynamics, where each "symbol" corresponds to an "aggregate" of
states in the continuous model. Since these symbolic models are of the same
nature of the models used in computer science to describe software and
hardware, they provide a unified language to study problems of control in which
software and hardware interact with the physical world. Furthermore the use of
symbolic models enables one to leverage techniques from supervisory control and
algorithms from game theory for controller synthesis purposes. In this paper we
show that every incrementally globally asymptotically stable nonlinear control
system is approximately equivalent (bisimilar) to a symbolic model. The
approximation error is a design parameter in the construction of the symbolic
model and can be rendered as small as desired. Furthermore if the state space
of the control system is bounded the obtained symbolic model is finite. For
digital control systems, and under the stronger assumption of incremental
input-to-state stability, symbolic models can be constructed through a suitable
quantization of the inputs.Comment: Corrected typo
Minimal resistance of curves under the single impact assumption
We consider the hollow on the half-plane defined by a function , , and a vertical flow of point particles incident on the hollow. It is assumed that satisfies the so-called single impact condition (SIC): each incident particle is elastically reflected by graph and goes away without hitting the graph of anymore. We solve the problem: find the function minimizing the force of resistance created by the flow. We show that the graph of the minimizer is formed by two arcs of parabolas symmetric to each other with respect to the -axis. Assuming that the resistance of equals 1, we show that the minimal resistance equals . This result completes the previously obtained result [SIAM J. Math. Anal., 46 (2014), pp. 2730--2742] stating in particular that the minimal resistance of a hollow in higher dimensions equals 0.5. We additionally consider a similar problem of minimal resistance, where the hollow in the half-space is defined by a radial function satisfying the SIC, , with , for , and for , and the flow is parallel to the -axis. The minimal resistance is greater than 0.5 (and coincides with 0.6435 when d = 1) and converges to 0.5 as
Prospects for an experiment to measure BR() at the CERN SPS
Precise measurements of the branching ratios for the
decays can provide unique constraints on CKM unitarity and, potentially,
evidence for new physics. It is important to measure both decay modes,
and , since different new
physics models affect the rates for each channel differently. We are
investigating the feasibility of performing a measurement of
BR() using a high-energy secondary neutral beam at the
CERN SPS in a successor experiment to NA62. The planned experiment would reuse
some of the NA62 infrastructure, including possibly the NA48 liquid-krypton
calorimeter. The mean momentum of mesons decaying in the fiducial volume
is 70 GeV; the decay products are boosted forward, so that less demanding
performance is required from the large-angle photon veto detectors. On the
other hand, the layout poses particular challenges for the design of the
small-angle vetoes, which must reject photons from decays escaping
through the beam pipe amidst an intense background from soft photons and
neutrons in the beam. We present some preliminary conclusions from our
feasibility studies, summarizing the design challenges faced and the
sensitivity obtainable for the measurement of BR().Comment: 6 pages, 5 figures. Prepared for the proceedings of the 2016
International Conference on Kaon Physics (KAON 2016), Birmingham, UK, 14-17
September 201
Electroweak Vacuum Stability in light of BICEP2
We consider the effect of a period of inflation with a high energy density
upon the stability of the Higgs potential in the early universe. The recent
measurement of a large tensor-to-scalar ratio, , by the BICEP-2
experiment possibly implies that the energy density during inflation was very
high, comparable with the GUT scale. Given that the standard model Higgs
potential is known to develop an instability at GeV this
means that the resulting large quantum fluctuations of the Higgs field could
destabilize the vacuum during inflation, even if the Higgs field starts at zero
expectation value. We estimate the probability of such a catastrophic
destabilisation given such an inflationary scenario and calculate that for a
Higgs mass of GeV that the top mass must be less than
GeV. We present two possible cures: a direct coupling between the Higgs and the
inflaton and a non-zero temperature from dissipation during inflation.Comment: 5 pages, 4 figures. Typos corrected, results unchanged, matches
version submitted to journa
Precision determination of the top-quark mass
Precision determinations of the top-quark mass require theory predictions
with a well-defined mass parameter in a given renormalization scheme. The
top-quark's running mass in the MSbar scheme can be extracted with good
precision from the total cross section at next-to-next-to-leading order in QCD.
The Monte Carlo top-quark mass parameter measured from comparison to events
with top-quark decay products is not identical with the pole mass. Its
translation to the pole mass scheme introduces an additional uncertainty of the
order of 1 GeV.Comment: Presented at Loops and Legs in Quantum Field Theory 2014, Weimar,
Germany and Large Hadron Collider Physics 2014, New York, US
Modeling and Analysis of Bus Contention for Hardware Accelerators in FPGA SoCs (Artifact)
This artifact provides the means for reproducing the experiments presented in the paper "Modeling and Analysis of Bus Contention for Hardware Accelerators in FPGA SoC". In particular, it provides the means and describes how to replicate the experimental study that has been carried out to evaluate the proposed analysis with synthetic workloads
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