The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform

P. L. Roney - One of the best experts on this subject based on the ideXlab platform.

  • Theory of spectral line shape. II. Collision Time theory and the line wing
    The Journal of Chemical Physics, 1994
    Co-Authors: P. L. Roney
    Abstract:

    In this second part of a theory on spectral line shapes, applicable to conditions of atmospheric transmission, a means of evaluation of the frequency dependence of the Collision operator is developed. An extension of formal scattering theory relates the off‐the‐energy shell matrix elements of the transition operator to their on‐shell values through an operator Φ which is a function of the energy increment, a Collision Time operator T(E) and a free propagation Time operator T(E). In the spectral line near‐wing application, a first‐order perturbation solution is obtained in terms of Φ as a function of the displacement from the line center. The real and imaginary parts of the (reduced) Fano Collision operator are expressed in terms of shift and width functions and the impact approximation shift Δ(0) and width Γ(0) parameters. In addition, other impact approximation quantities are required which do not play a role in line shape in the impact approximation theory. A preliminary comparison with experiment for the CO2 continuum near 4.3 μm shows excellent agreement. The derived values of the Collision Times are in the expected picosecond range. There also seems to be little temperature dependence for N2–CO2 broadening over a wide range of temperatures.

Riku Jantti - One of the best experts on this subject based on the ideXlab platform.

  • channel ranking based on packet delivery ratio estimation in wireless sensor networks
    Wireless Communications and Networking Conference, 2013
    Co-Authors: Hamidreza Shariatmadari, Aamir Mahmood, Riku Jantti
    Abstract:

    Wireless sensor networks (WSNs) operating in 2.4 GHz unlicensed bands must explore favorable channels in order to mitigate the effects of induced interference by co-existing wireless systems and frequency selective fading. In this context, we develop a packet delivery ratio (PDR) estimation method for channel ranking in WSNs. The PDR, in general, is defined as a function of signal-to-noise ratio (SNR) and signal-to-interferenceplus-noise ratio (SINR) at the sensor and the packet Collision-Time distribution of the sensor link. The Collision-Time distribution depends on the packet size and packet inter-arrival Time distributions of both networks. Under limited channel measurements, the Collision-Time cannot be estimated satisfactorily. In order to bypass the Collision-Time estimation process, the proposed PDR estimation method utilizes signal level, interference and noise characteristics identified by spectrum measurements adjusted to the intended traffic pattern of the sensor link. The proposed method is validated against the empirical PDR using off-the-shelf sensor platform in emulated multi path wireless fading channels. The results reveal that the method is accurate in modeling the empirical PDR with limited channel energy measurements. In addition, we used the estimated PDR as a metric for channel ranking and verified its effectiveness by ranking the available channels to a WSN under interference from multiple WLANs in a real environment.

  • WCNC - Channel ranking based on packet delivery ratio estimation in wireless sensor networks
    2013 IEEE Wireless Communications and Networking Conference (WCNC), 2013
    Co-Authors: Hamidreza Shariatmadari, Aamir Mahmood, Riku Jantti
    Abstract:

    Wireless sensor networks (WSNs) operating in 2.4 GHz unlicensed bands must explore favorable channels in order to mitigate the effects of induced interference by co-existing wireless systems and frequency selective fading. In this context, we develop a packet delivery ratio (PDR) estimation method for channel ranking in WSNs. The PDR, in general, is defined as a function of signal-to-noise ratio (SNR) and signal-to-interferenceplus-noise ratio (SINR) at the sensor and the packet Collision-Time distribution of the sensor link. The Collision-Time distribution depends on the packet size and packet inter-arrival Time distributions of both networks. Under limited channel measurements, the Collision-Time cannot be estimated satisfactorily. In order to bypass the Collision-Time estimation process, the proposed PDR estimation method utilizes signal level, interference and noise characteristics identified by spectrum measurements adjusted to the intended traffic pattern of the sensor link. The proposed method is validated against the empirical PDR using off-the-shelf sensor platform in emulated multi path wireless fading channels. The results reveal that the method is accurate in modeling the empirical PDR with limited channel energy measurements. In addition, we used the estimated PDR as a metric for channel ranking and verified its effectiveness by ranking the available channels to a WSN under interference from multiple WLANs in a real environment.

  • ICC - Stochastic packet Collision modeling in coexisting wireless networks for link quality evaluation
    2013 IEEE International Conference on Communications (ICC), 2013
    Co-Authors: Aamir Mahmood, Hiiseyin Yigitler, Riku Jantti
    Abstract:

    The packet delivery ratio (PDR) performance of a wireless communication network interfered by a coexisting network is determined by the Collision-Time. In this paper, we propose a stochastic Collision-Time model for coexisting wireless networks, and analyze it in particular for coexisting low-rate wireless personal area network (LR-WPAN) and WLAN. Although, the packet Collision-Time of the interfered network is a complex process, as it depends on the packet size and packet inter-arrival Time distributions of both networks, its properties can be inferred by modeling the interference as an alternating renewal process, leading to a stochastic Collision-Time model. The proposed Collision-Time model is utilized to derive the theoretical Collision-Time distributions for periodic, exponential and gamma inter-arrivals. The comparison of the theoretical and simulation based Collision-Time distributions for the studied inter-arrivals suggests that the proposed Collision-Time model can be used for performance analysis of coexisting wireless networks. In order to investigate the effects on the Collision-Time distribution in a realistic multi-terminal WLAN traffic shaped by the CSMA/CA mechanisms, heavy tailed hyper-Erlang and gamma distributions are fitted to an experimental inter-arrival Times data-set. The goodness-of-fit tests of both distributions show that the gamma distributed inter-arrivals model the observed interfering traffic good enough, which allows analytical evaluation of LR-WPAN link quality using the derived Collision-Time model.

J. Szudy - One of the best experts on this subject based on the ideXlab platform.

  • Pressure broadening, shift and asymmetry of the 326.1 nm Cd line perturbed by N2 and CH4
    AIP Conference Proceedings, 2002
    Co-Authors: A. Bielski, J. Szudy, Daniel Lisak, R.s. Trawiński
    Abstract:

    The experimental values of pressure broadening, shift and Collision‐Time asymmetry coefficients of the 326.1 nm 114Cd line perturbed by N2 and by CH4 were determined at perturbing gas pressures between 1 and 350 Torr. All measurements were performed using a Laser Induced Fluorescence (LIF) technique. The experimental coefficients of pressure broadening, shift and Collision‐Time asymmetry were compared with theoretical values calculated from the impact theory assuming van der Waals form of interaction potentials.

  • Line-mixing and Collision-Time asymmetry of spectral line shapes
    Physical Review A, 2001
    Co-Authors: Roman Ciuryło, J. Szudy
    Abstract:

    The quantum-mechanical Baranger-Kolb-Griem theory of pressure broadening is reexamined in order to include both the effects due to overlapping lines and finite duration of Collision. A general line-shape formula is derived which for near wings can be presented as a linear combination of the Lorentzian and dispersion profiles. The asymmetry parameter is expressed by means of evolution operators for the initial and final states. It is shown that in the weak-coupling case only the resultant asymmetry parameter can be approximately given as the sum of parameters describing the asymmetry due to line mixing and finite Collision Time.

John S. Wettlaufer - One of the best experts on this subject based on the ideXlab platform.

  • hertz beyond belief
    Soft Matter, 2014
    Co-Authors: Andong He, John S. Wettlaufer
    Abstract:

    We examine the validity of Hertz's linear elastic theory for central Collisions of spheres using a viscoelastic model. This model explains why Hertz's theory is accurate in predicting the Collision Time and maximum contact area even when 40% of the kinetic energy is lost due to viscous dissipation. The main reason is that both the Collision Time and maximum contact area have a very weak dependence on the impact velocity. Moreover, we show that colliding objects exhibit an apparent size-dependent yield strength, which results from larger objects dissipating less energy at a given impact velocity.

  • hertz beyond belief
    arXiv: Classical Physics, 2013
    Co-Authors: Andong He, John S. Wettlaufer
    Abstract:

    We examine the validity of Hertz's linear elastic theory for central Collisions using a viscoelastic model. This model explains why Hertz's theory is accurate in predicting the Collision Time and maximum contact area even when $40\%$ of the kinetic energy is lost due to viscous dissipation. The main reason is that both the Collision Time and maximum contact area have a very weak dependence on the impact velocity. Moreover, we show that colliding objects exhibit an apparent size dependent yield strength, which results from larger objects dissipating less energy at a given impact velocity.

Remco I. Leine - One of the best experts on this subject based on the ideXlab platform.

  • Experimental Performance Verification of a Synchronization Based State Observer Using Only Collision Time Information
    Volume 8: 30th Conference on Mechanical Vibration and Noise, 2018
    Co-Authors: Pascal V. Preiswerk, Remco I. Leine
    Abstract:

    A state observer that only uses the Collision Time information has recently been developed for linear Time-invariant multibody systems with unilateral constraints. The observer is based on synchronization and makes use of switched geometric unilateral constraints, which generate a unidirectional coupling in a master-slave setup. In presence of uncertainties, such as model inaccuracies or disturbances, an exact reconstruction of the observed state is not possible. As a first step in assessing the robustness of the proposed observer, we present an experimental verification of the observer’s performance. Furthermore, we account for dry friction in the observer design.

  • A synchronization-based state observer for impact oscillators using only Collision Time information
    International Journal of Robust and Nonlinear Control, 2015
    Co-Authors: Michael Baumann, Remco I. Leine
    Abstract:

    Summary We present the design of a state observer for Lagrangian systems subjected to frictionless geometric unilateral constraints. A master–slave synchronization setup is used in which the unidirectional coupling only consists of the information of the impact Time instants. After a brief synchronization phase, the obtained observer replicates the full state of the observed system, independently of the initial conditions and even in the presence of accumulation points (Zeno behavior). The key idea is that the (virtual) observer system is subjected to switched kinematic unilateral constraints such that it may enjoy the property of incremental stability when the impact law is maximal monotone. The main inequality impact laws for hard unilateral constraints, that is, the generalized Poisson's and Newton's impact law, are under mild assumptions maximal monotone, which is a stronger condition than dissipativity. The results are applied to two different examples of mechanical impact oscillators. Copyright © 2015 John Wiley & Sons, Ltd.