The Experts below are selected from a list of 40542 Experts worldwide ranked by ideXlab platform

C Y Zheng - One of the best experts on this subject based on the ideXlab platform.

  • Slow Time Scale magnetic fields driven by fast Time Scale waves in an underdense relativistic vlasov plasma
    Physics of Plasmas, 2001
    Co-Authors: Shaoping Zhu, C Y Zheng
    Abstract:

    Slow-Time-Scale magnetic fields driven by fast-Time-Scale electromagnetic waves or plasma waves are examined from the perspective of the Vlasov–Maxwell equations for a relativistic Vlasov plasma. An equation for Slow-Time-Scale magnetic field is obtained. The field proposed in the present paper is a result of wave–wave beating which drives a solenoidal current. The magnitude of the Slow-Time-Scale magnetic field proposed here can be as high as 20 MG at the critical surface for a laser intensity I=1018 W/cm2 at wavelength λ0=1.05 μm. The predicted magnetic field is observed in two-dimensional particle simulations presented here.

Shaoping Zhu - One of the best experts on this subject based on the ideXlab platform.

Lewis E Kay - One of the best experts on this subject based on the ideXlab platform.

  • an improved 15n relaxation dispersion experiment for the measurement of millisecond Time Scale dynamics in proteins
    Journal of Physical Chemistry B, 2008
    Co-Authors: Flemming D Hansen, Pramodh Vallurupalli, Lewis E Kay
    Abstract:

    A new 15N constant-Time relaxation dispersion pulse scheme for the quantification of millisecond Time-Scale exchange dynamics in proteins is presented. The experiment differs from previously developed sequences in that it includes 1H continuous-wave decoupling during the 15N Carr−Purcell−Meiboom−Gill (CPMG) pulse train that significantly improves the relaxation properties of 15N magnetization, leading to sensitivity gains in experiments. Moreover, it is shown that inclusion of an additional 15N 1800 refocusing pulse (phase cycled ±x) in the center of the CPMG pulse train, consisting of 15Npulses, provides compensation for pulse imperfections beyond the normal CPMG scheme. Relative to existing relaxation-compensated constant-Time relaxation dispersion pulse schemes, νCPMG values that are only half as large can be employed, offering increased sensitivity to Slow Time-Scale exchange processes. The robustness of the methodology is illustrated with applications involving a pair of proteins:  an SH3 domain that...

  • probing Slow Time Scale dynamics at methyl containing side chains in proteins by relaxation dispersion nmr measurements application to methionine residues in a cavity mutant of t4 lysozyme
    Journal of the American Chemical Society, 2001
    Co-Authors: Nikolai R Skrynnikov, Frans A A Mulder, Bin Hon, Frederick W Dahlquist, Lewis E Kay
    Abstract:

    A relaxation dispersion-based NMR experiment is presented for the measurement and quantitation of μs−ms dynamic processes at methyl side-chain positions in proteins. The experiment measures the exchange contribution to the 13C line widths of methyl groups using a constant-Time CPMG scheme. The effects of cross-correlated spin relaxation between dipole−dipole and dipole−CSA interactions as well as the effects of scalar coupling responsible for mixing of magnetization modes during the course of the experiment have been investigated in detail both theoretically and through simulations. It is shown that the complex relaxation properties of the methyl spin system do not complicate extraction of accurate exchange parameters as long as care is taken to ensure that appropriate magnetization modes are interchanged in the middle of the constant-Time CPMG period. An application involving the measurement of relaxation dispersion profiles of methionine residues in a Leu99Ala substitution of T4 lysozyme is presented. A...

M D Fayer - One of the best experts on this subject based on the ideXlab platform.

  • three homeotropically aligned nematic liquid crystals comparison of ultrafast to Slow Time Scale dynamics
    Journal of Chemical Physics, 2006
    Co-Authors: Irene Wang, M D Fayer
    Abstract:

    The dynamics of two nematic liquid crystals, 4-(trans-4′-n-octylcyclohexyl)isothiocyanatobenzene and 4-(4-pentyl-cyclohexyl)-benzonitrile, are investigated as a function of temperature both in the homeotropically aligned nematic phase and in the isotropic phase using optical heterodyne-detected optical Kerr effect experiments, which measures the Time derivative of the polarizability–polarizability-correlation function (orientational relaxation). Data are presented over a Time range of 500fs−70μs for the nematic phase and 500fs to a few hundred nanoseconds for the isotropic phase. The nematic dynamics are compared with a previously studied liquid crystal in the nematic phase. All three liquid crystals have very similar dynamics in the nematic phase that are very different from the isotropic phase. On the Slowest Time Scale (20ns–70μs), a temperature-independent power law, the final power law, t−f with f∼0.5, is observed. On short Time Scales (∼3psto∼1ns), a temperature-dependent intermediate power law is o...

  • comparison of the ultrafast to Slow Time Scale dynamics of three liquid crystals in the isotropic phase
    Journal of Chemical Physics, 2002
    Co-Authors: S D Gottke, Hu Cang, Biman Bagchi, M D Fayer
    Abstract:

    The dynamics of three liquid crystals, 4'(pentyloxy)-4-biphenylcarbonitrile (5-OCB), 4'-pentyl-4-biphenylcarbonitrile (5-CB), and 1-isothiocyanato-(4-propylcyclohexyl)benzene (3-CHBT), are investigated from very short Time (similar to1 ps) to very long Time (>100 ns) as a function of temperature using optical heterodyne detected optical Kerr effect experiments. For all three liquid crystals, the data decay exponentially only on the longest Time Scale (> several ns). The temperature dependence of the long Time Scale exponential decays is described well by the Landau-de Gennes theory of the randomization of pseudonematic domains that exist in the isotropic phase of liquid crystals near the isotropic to nematic phase transition. At short Time, all three liquid crystals display power law decays. Over the full range of Times, the data for all three liquid crystals are fit with a model function that contains a short Time power law. The power law exponents for the three liquid crystals range between 0.63 and 0.76, and the power law exponents are temperature independent over a wide range of temperatures. Integration of the fitting function gives the empirical polarizability-polarizability (orientational) correlation function. A preliminary theoretical treatment of collective motions yields a correlation function that indicates that the data can decay as a power law at short Times. The power law component of the decay reflects intradomain dynamics. (C) 2002 American Institute of Physics.

Prodromos Daoutidis - One of the best experts on this subject based on the ideXlab platform.

  • energy management and load shaping for commercial microgrids coupled with flexible building environment control
    Journal of energy storage, 2018
    Co-Authors: Michael Zachar, Prodromos Daoutidis
    Abstract:

    Abstract This paper explores the load shaping ability of microgrid power systems coupled with flexible operation of HVAC systems for commercial customers. In the proposed framework, this integrated system is treated as a dispatchable power source/sink in order to mitigate the uncertainty and variability imposed on the external utility company. The load shaping required is enabled by the natural flexibility in space heating and cooling, along with dispatchable microgrid resources such as batteries. A hierarchical control approach is formulated for the scheduling and supervisory control of the flexible loads and dispatchable energy units within the microgrid. Stochastic optimization is used for scheduling at the Slow Time Scale to ensure forecasting errors in renewable availability and energy demands can be rejected. Deterministic optimization is used at the fast Time Scale to update dispatch decisions in response to realized conditions. A case study demonstrates that this proposed control approach is able to substantially reduce the uncertainty and variability in energy exchange with the external utility across a variety of commercial load types and in different seasons.

  • model reduction and control in reactor heat exchanger networks
    Journal of Process Control, 2004
    Co-Authors: Michael Baldea, Prodromos Daoutidis
    Abstract:

    Abstract This paper focuses on the dynamics and control of process networks consisting of a reactor connected with an external heat exchanger through a large material recycle stream that acts as an energy carrier. Using singular perturbation arguments, we show that such networks exhibit a dynamic behavior featuring two Time Scales: a fast one, in which the energy balance variables evolve, and a Slow Time Scale that captures the evolution of the terms in the material balance equations. We present a procedure for deriving reduced-order, non-stiff models for the fast and Slow dynamics, and a framework for rational control system design that accounts for the Time Scale separation exhibited by the system dynamics. The theoretical developments are illustrated with an example and numerical simulation results.

  • nonlinear dynamics and control of process systems with recycle
    Journal of Process Control, 2002
    Co-Authors: Aditya Kumar, Prodromos Daoutidis
    Abstract:

    Abstract Process systems with material and energy recycle are well-known to exhibit complex dynamics and to present significant control challenges, due to the feedback interactions induced by the recycle streams. In this paper, we address the dynamic analysis and control of such process systems. Initially, we establish, through an asymptotic analysis, that (i) small recycle flowrates induce a weak coupling among individual processes, whereas (ii) large recycle flowrates induce a Time Scale separation, with the dynamics of individual processes evolving in a fast Time Scale with weak interactions, and the dynamics of the overall system evolving in a Slow Time Scale where these interactions become significant; these Slow dynamics is usually nonlinear and of low order. Motivated by this, we present (i) a model reduction methodology for deriving nonlinear low-order models of the Slow dynamics induced by large recycle streams, and (ii) a controller design framework consisting of properly coordinated controllers in the fast and the Slow Time Scales. The theoretical results are illustrated in a reaction-separation network with a large recycle compared to the throughput.

  • nonlinear dynamics and control of process systems with recycle
    IFAC Proceedings Volumes, 2000
    Co-Authors: Aditya Kumar, Prodromos Daoutidis
    Abstract:

    Abstract Process systems with material and energy recycle are well-known to exhibit complex dynamics and to present significant control challenges, due to the feedback interactions induced by the recycle streams. In this paper, we address the dynamic analysis and control of such process systems. Initially, we establish, through an asymptotic analysis, that i) small recycle flowrates induce a weak coupling among individual processes, whereas ii) large recycle flowrates induce a Time Scale separation, with the dynamics of individual processes evolving in a fast Time Scale with weak interactions, and the dynamics of the overall system evolving in a Slow Time Scale where these interactions become significant; this Slow dynamics is usually nonlinear and of low order. Motivated by this, we present i) a model reduction methodology for deriving nonlinear low-order models of the Slow dynamics induced by large recycle streams, and ii) a controller design framework comprising of properly coordinated controllers in the fast and the Slow Time Scales. The theoretical results are illustrated in a reaction-separation network with a large recycle compared to the throughput.

  • nonlinear model reduction of chemical reaction systems
    American Control Conference, 1999
    Co-Authors: Nishith Vora, Prodromos Daoutidis
    Abstract:

    We consider a broad class of nonisothermal, spatially homogeneous reaction systems, with fast and Slow reactions. The dynamic model of such systems exhibits stiffness (Time-Scale multiplicity) but is not in a standard singularly perturbed form. For such systems, we address the derivation of reduced order nonlinear models of the Slow dynamics, through (i) the identification of algebraic constraints that need to be satisfied in the Slow Time Scale (e.g. reaction equilibrium constraint in the case of fast reversible reactions), and (ii) the derivation of state-space realizations of the resulting differential algebraic system that describes the Slow dynamics.