2,820 research outputs found
Geometric Scaling and QCD Dynamics in DIS
DIS data from HERA show a striking regularity as \sigma^{\gamma^* p} is a
function of the ratio \tau=Q^2/Q_s^2(x) only. The scaling function shows a
break at \tau ~ 1, which has been taken as an indication for saturation.
However, besides saturation also the transition between dominance of
k_t-ordered (DGLAP) and k_t-non-ordered (BFKL) evolution contributes to a break
around this value of \tau, as well as the suppression for small Q^2 due to
finite quark masses and confinement. In this paper we use a dipole cascade
model based on Mueller's dipole model, which also includes energy conservation
and pomeron mergins, to investigate the contributions of these different
effects to the scaling behaviour. As a result we predict that the scaling
function for \tau 1 GeV^2 become
available. We also investigate the scaling properties of the charm contribution
and the impact parameter dependence of the saturation scale.Comment: references added, figures 2, 7 and 8 updated v3: reference added,
some misprints correcte
Arnold diffusion in the dynamics of a 4-machine power system undergoing a large fault
We focus on the seemingly complicated dynamics of a four-machine power system which is undergoing a sudden fault. Adopting a Hamiltonian (energy) formulation, we consider the system as an interconnection of (one degree of freedom) subsystems. Under certain configuration (a star network) and parameter values we establish the presence of Arnold diffusion which entails periodic, almost periodic, and complicated nonperiodic dyanmics all simultaneously present; and erratic transfer of energies between the subsystems. In section 1 we introduce the transient stability problem in a mathematical setting and explain what our results mean in the power systems context. Section 2 provides insights into Arnold diffusion and summarizes its mathematical formulation as in [8], [1]. Section 3 gives conditions for which Arnold diffusion arises on certain energy levels of the swing equations. These conditions are verified analytically in the case when all but one subsystem (machine) undergo relatively small oscillations
AC voltage regulation of a bidirectional high-frequency link converter using a deadbeat controller
This paper presents a digital controller for AC voltage regulation of a bidirectional high-frequency link (BHFL) inverter using Deadbeat control. The proposed controller consists of inner current loop, outer voltage loop and a feed-forward controller, which imposes a gain scheduling effect according to the reference signal to compensate the steady-state error of the system. The main property of the proposed controller is that the current- and the voltage-loop controllers have the same structure, and use the same sampling period. This simplifies the design and implementation processes. To improve the overall performance of the system, additional disturbance decoupling networks are employed. This takes into account
the model discretization effect. Therefore, accurate
disturbance decoupling can be achieved, and the system
robustness towards load variations is increased. To avoid
transformer saturation due to low frequency voltage envelopes, an equalized pulse width modulation (PWM)
technique has been introduced. The proposed controller
has been realized using the DS1104 digital signal processor
(DSP) from dSPACE. Its performances have been tested on
a one kVA prototype inverter. Experimental results showed
that the proposed controller has very fast dynamic and good
steady-state responses even under highly nonlinear loads
Diffractive Excitation in DIS and pp Collisions
We have in earlier papers presented an extension of Mueller's dipole cascade
model, which includes subleading effects from energy conservation and running
coupling as well as colour suppressed effects from pomeron loops via a ``dipole
swing''. The model was applied to describe the total cross sections in pp and
gamma*p collisions. In this paper we present a number of improvements of the
model, in particular related to the confinement mechanism. A consistent
treatment of dipole evolution and dipole--dipole interactions is achieved by
replacing the infinite range Coulomb potential by a screened potential, which
further improves the frame-independence of the model. We then apply the model
to elastic scattering and diffractive excitation, where we specifically study
the effects of different sources for fluctuations. In our formalism we can take
into account contributions from all different sources, from the dipole cascade
evolution, the dipole--dipole scattering, from the impact-parameter dependence,
and from the initial photon and proton wavefunctions. Good agreement is
obtained with data from the Tevatron and from HERA, and we also present some
predictions for the LHC.Comment: correction of titl
A hadron model with breaking of spatial homogeneity of vacuum
A possible breaking of spatial homogeneity of vacuum due to the interaction
between quark and Bose-field is analyzed. It is shown that in this case quark
can be in a localized state (like wave packet). Energetic conditions for such a
spontaneous symmetry breaking are found in suggested model. Possible
consequences of such symmetry breaking, in particular, the origin of deep
inelastic processes and quark confinement phenomenon are discussed.Comment: 4 page
LHC Limits on the Top-Higgs in Models with Strong Top-Quark Dynamics
LHC searches for the standard model Higgs Boson in WW or ZZ decay modes place
strong constraints on the top-Higgs state predicted in many models with new
dynamics preferentially affecting top quarks. Such a state couples strongly to
top-quarks, and is therefore produced through gluon fusion at a rate enhanced
relative to the rate for the standard model Higgs boson. A top-Higgs state with
mass less than 300 GeV is excluded at 95% CL if the associated top-pion has a
mass of 150 GeV, and the constraint is even stronger if the mass of the
top-pion state exceeds the top-quark mass or if the top-pion decay constant is
a substantial fraction of the weak scale. These results have significant
implications for theories with strong top dynamics, such as topcolor-assisted
technicolor, top-seesaw models, and certain Higgsless models.Comment: 9 pages, 6 pdf figures included. Updated with 2011 Lepton-Photon
conference Higgs limits. Order of figures reversed, and conclusion slightly
expanded and clarifie
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