973 research outputs found
Measuring Gaussian rigidity using curved substrates
The Gaussian (saddle splay) rigidity of fluid membranes controls their
equilibrium topology but is notoriously difficult to measure. In lipid
mixtures, typical of living cells, linear interfaces separate liquid ordered
(LO) from liquid disordered (LD) bilayer phases at subcritical temperatures.
Here we consider such membranes supported by curved supports that thereby
control the membrane curvatures. We show how spectral analysis of the
fluctuations of the LO-LD interface provides a novel way of measuring the
difference in Gaussian rigidity between the two phases. We provide a number of
conditions for such interface fluctuations to be both experimentally measurable
and sufficiently sensitive to the value of the Gaussian rigidity, whilst
remaining in the perturbative regime of our analysis.Comment: 5 pages, 3 figures. v2: version accepted for publicatio
Multiplicity of periodic solutions for systems of weakly coupled parametrized second order differential equations
We prove a multiplicity result of periodic solutions for a system of second order differential equations having asymmetric nonlinearities. The proof is based on a recent generalization of the Poincar\ue9\u2013Birkhoff fixed point theorem provided by Fonda and Ure\uf1a
Exponential behavior of a quantum system in a macroscopic medium
An exponential behavior at all times is derived for a solvable dynamical
model in the weak-coupling, macroscopic limit. Some implications for the
quantum measurement problem are discussed, in particular in connection with
dissipation.Comment: 8 pages, report BA-TH/94-17
Quantum Zeno effect in a probed downconversion process
The distorsion of a spontaneous downconvertion process caused by an auxiliary
mode coupled to the idler wave is analyzed. In general, a strong coupling with
the auxiliary mode tends to hinder the downconversion in the nonlinear medium.
On the other hand, provided that the evolution is disturbed by the presence of
a phase mismatch, the coupling may increase the speed of downconversion. These
effects are interpreted as being manifestations of quantum Zeno or anti-Zeno
effects, respectively, and they are understood by using the dressed modes
picture of the device. The possibility of using the coupling as a nontrivial
phase--matching technique is pointed out.Comment: 11 pages, 4 figure
Robust Neural Network RISE Observer Based Fault Diagnostics And Prediction
A novel fault diagnostics and prediction scheme in continuous time is introduced for a class of nonlinear systems. The proposed method uses a novel neural network (NN) based robust integral sign of the error (RISE) observer, or estimator, allowing for semi-global asymptotic stability in the presence of NN approximation errors, disturbances and unmodeled dynamics. This is in comparison to typical results presented in the literature that show only boundedness in the presence of uncertainties. The output of the observer/estimator is compared with that of the nonlinear system and a residual is used for declaring the presence of a fault when the residual exceeds a user defined threshold. The NN weights are tuned online with no offline tuning phase. The output of the RISE observer is utilized for diagnostics. Additionally, a method for time-to-failure (TTF) prediction, a first step in prognostics, is developed by projecting the developed parameter-update law under the assumption that the nonlinear system satisfies a linear-in-the-parameters (LIP) assumption. The TTF method uses known critical values of a system to predict when an estimated parameter will reach a known failure threshold. The performance of the NN/RISE observer system is evaluated on a nonlinear system and a simply supported beam finite element analysis (FEA) simulation based on laboratory experiments. Results show that the proposed method provides as much as 25% increased accuracy while the TTF scheme renders a more accurate prediction. © 2010 IEEE
No classical limit of quantum decay for broad states
Though the classical treatment of spontaneous decay leads to an exponential
decay law, it is well known that this is an approximation of the quantum
mechanical result which is a non-exponential at very small and large times for
narrow states. The non exponential nature at large times is however hard to
establish from experiments. A method to recover the time evolution of unstable
states from a parametrization of the amplitude fitted to data is presented. We
apply the method to a realistic example of a very broad state, the sigma meson
and reveal that an exponential decay is not a valid approximation at any time
for this state. This example derived from experiment, shows the unique nature
of broad resonances
Comparison of analytical functions used to describe topside electron density profiles with satellite data
Electron density models of the ionosphere use different analytical formulations for the electron density vertical
profile in the topside. The present paper compares some single-layer topside analytical descriptions (Chapman,
Epstein, modified Epstein used in the NeQuick model) with experimental topside profiles obtained from measurements
of IK19 and ISIS2 satellites. The limits of height range and shape for each formulation are described
and analyzed and suggestions for the use of multiple layers solution to reproduce experimental results are given
Suppression of Zeno effect for distant detectors
We describe the influence of continuous measurement in a decaying system and
the role of the distance from the detector to the initial location of the
system. The detector is modeled first by a step absorbing potential. For a
close and strong detector, the decay rate of the system is reduced; weaker
detectors do not modify the exponential decay rate but suppress the long-time
deviations above a coupling threshold. Nevertheless, these perturbing effects
of measurement disappear by increasing the distance between the initial state
and the detector, as well as by improving the efficiency of the detector.Comment: 4 pages, 4 figure
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