20,379 research outputs found
Heavy quarkonium in a holographic QCD model
Encouraged by recent developments in AdS/QCD models for light quark system,
we study heavy quarkonium in the framework of the AdS/QCD models. We calculate
the masses of vector meson states using the AdS/QCD models at zero
and at finite temperature. Among the models adopted in this work, we find that
the soft wall model describes the low-lying heavy quark meson states at zero
temperature relatively well. At finite temperature, we observe that once the
bound state is above , its mass will increase with temperature until it
dissociates at a temperature of around . It is shown that the
dissociation temperature is fixed by the infrared cutoff of the models. The
present model serves as a unified non perturbative model to investigate the
properties of bound quarkonium states above .Comment: 9 pages, 1 figure, minor revision, to appear in phys. Rev.
QCD sum rules for the anti-charmed pentaquark
We present a QCD sum rule analysis for the anti-charmed pentaquark state with
and without strangeness. While the sum rules for most of the currents are
either non-convergent or dominated by the continuum, the one for the
non-strange pentaquark current composed of two diquarks and an antiquark, is
convergent and has a structure consistent with a positive parity pentaquark
state after subtracting out the continuum contribution. Arguments are
presented on the similarity between the result of the present analysis and that
based on the constituent quark models, which predict a more stable pentaquark
states when the antiquark is heavy.Comment: 19 pages, 8 figures, REVTex, revised version,new figures added and
references update
Charmonium-hadron interactions from QCD
The heavy quark system is an excellent probe to learn about the QCD dynamics
at finite density. First, we discuss the properties of the and
meson at finite nucleon density. We discuss why their properties should change
at finite density and then introduce an exact QCD relation among these hadron
properties and the energy momentum tensor of the medium. Second, we discuss
attempts to calculate charmonium-hadron total cross section using effective
hadronic models and perturbative QCD. We emphasize a recent calculation, where
the cross section is derived using QCD factorization theorem. We conclude by
discussing some challenges for SIS 200.Comment: 8 pages, Presented at 6th International Conference on Strange Quarks
in Matter: 2001: A Flavorspace Odyssey (SQM2001), Frankfurt, Germany, 25-29
Sep 2001, submitted to J. Phys.
Analysis of decentralized integral controllability for nonlinear systems
This paper extends the concept of decentralized integral controllability to nonlinear process, and presents a steady state sufficient condition by using the singular perturbation theory. A numerical method is provided to facilitate the analysis of the proposed condition and is illustrated using an example of a dual tank level control system. © 2004 Elsevier Ltd. All rights reserved
Control of multivariable Hammerstein systems by using feedforward passivation
This paper presents a new control method for processes which can be described by Hammerstein models. The control design is based on the concept of passive systems. The proposed method is based on feedforward passivation and thus can be applied to nonminimum phase processes and/or processes of high relative degree. A synthesis technique for marginally stable positive real systems has been developed to achieve offset free control. The new control design can be easily implemented by solving a set of linear matrix inequalities. The proposed approach is illustrated using the example of an acid-base pH control problem
Conditions on input disturbance suppression for multivariable nonlinear systems on the basis of feedforward passivity
In this paper, we consider the problem of input disturbance suppression for nonlinear systems based on feedforward passivity. First, we show that integral control can sufficiently suppress a class of slowly variant (including constant) input disturbance and track constant references provided certain closed-loop stability is achieved. Then, sufficient conditions of integral controllability for nonlinear processes are presented. These conditions are further relaxed by using an input and output transformation
A shear spectral sum rule in a non-conformal gravity dual
A sum rule which relates a stress-energy tensor correlator to thermodynamic
functions is examined within the context of a simple non-conformal gravity
dual. Such a sum rule was previously derived using AdS/CFT for conformal
Supersymmetric Yang-Mills theory, but we show that it does
not generalize to the non-conformal theory under consideration. We provide a
generalized sum rule and numerically verify its validity. A useful byproduct of
the calculation is the computation of the spectral density in a strongly
coupled non-conformal theory. Qualitative features of the spectral densities
and implications for lattice measurements of transport coefficients are
discussed.Comment: 13 pages, 3 figures. v5: Typos in Eq. (60) fixed. v4: References
added, matches published version. v3: Minor typographical corrections. v2:
References and some discussion in Appendix A have been added; conclusions
unchange
Calculation of and Couplings in QCD Sum Rules
We calculate the coupling constants, and $, which is also important
in the calculation of the S_{11}(1535) mass itself within the sum rule
approach.Comment: 8 pages (no figure), revte
Calibration of aerodynamic roughness over the Tibetan Plateau with Ensemble Kalman Filter analysed heat flux
Abstract. Aerodynamic roughness height (Zom) is a key parameter required in several land surface hydrological models, since errors in heat flux estimation are largely dependent on optimization of this input. Despite its significance, it remains an uncertain parameter which is not readily determined. This is mostly because of non-linear relationship in Monin-Obukhov similarity (MOS) equations and uncertainty of vertical characteristic of vegetation in a large scale. Previous studies often determined aerodynamic roughness using a minimization of cost function over MOS relationship or linear regression over it, traditional wind profile method, or remotely sensed vegetation index. However, these are complicated procedures that require a high accuracy for several other related parameters embedded in serveral equations including MOS. In order to simplify this procedure and reduce the number of parameters in need, this study suggests a new approach to extract aerodynamic roughness parameter from single or two heat flux measurements analyzed via Ensemble Kalman Filter (EnKF) that affords non-linearity. So far, to our knowledge, no previous study has applied EnKF to aerodynamic roughness estimation, while the majority of data assimilation study have paid attention to updates of other land surface state variables such as soil moisture or land surface temperature. The approach of this study was applied to grassland in semi-arid Tibetan Plateau and maize on moderately wet condition in Italy. It was demonstrated that aerodynamic roughness parameter can be inversely tracked from heat flux EnKF final analysis. The aerodynamic roughness height estimated in this approach was consistent with eddy covariance method and literature value. Through a calibration of this parameter, this adjusted the sensible heat previously overestimated and latent heat flux previously underestimated by the original Surface Energy Balance System (SEBS) model. It was considered that this improved heat flux estimation especially during the summer Monsoon period, based upon a comparison with precipitation and soil moisture field measurement. For an advantage of this approach over other previous methodologies, this approach is useful even when eddy covariance data are absent at a large scale and is time-variant over vegetation growth, as well as is not directly affected by saturation problem of remotely sensed vegetation index
Corrigendum to "Calibration of aerodynamic roughness over the Tibetan Plateau with Ensemble Kalman Filter analysed heat flux" published in Hydrol. Earth Syst. Sci., 16, 4291–4302, 2012
We would like to inform you that there is a mistake in the following sentence on p. 4296 (right column): Because of following relationships Aa = Af + K(D − HAf) ∼= AfKHAf and D = 0, P fHT K = KHP f, then error covariance in Eq. (3-3) is rearranged as followed (Sakov et al., 2008). The correct sentence should read: Because of following relationships Aa = Af + K(D−HAf), D = 0, and P fH T K = KHP f, then error covariance in Eq. (3-3) is rearranged as followed
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