5,674 research outputs found
A momentum Space Analysis of the Triple Pomeron Vertex in pQCD
We study properties of the momentum space Triple Pomeron Vertex in
perturbative QCD. Particular attention is given to the collinear limit where
transverse momenta on one side of the vertex are much larger than on the other
side. We also comment on the kernels in nonlinear evolution equations.Comment: Minor misprints corrected. To be published in EPJ
Performance Enhancement of the Flexible Transonic Truss-Braced Wing Aircraft Using Variable-Camber Continuous Trailing-Edge Flaps
Aircraft designers are to a growing extent using vehicle flexibility to optimize performance with objectives such as gust load alleviation and drag minimization. More complex aerodynamically optimized configurations may also require dynamic loads and perhaps eventually flutter suppression. This paper considers an aerodynamically optimized truss-braced wing aircraft designed for a Mach 0.745 cruise. The variable camber continuous trailing edge flap concept with a feedback control system is used to enhance aeroelastic stability. A linearized reduced order aerodynamic model is developed from unsteady Reynolds averaged Navier-Stokes simulations. A static output feedback controller is developed from that model. Closed-loop simulations using the reduced order aerodynamic model show that the controller is effective in stabilizing the vehicle dynamics
Active Flutter Suppression Using Reduced-Order Modeling for Transonic Aeroservoelastic Control Law Development
In this paper, several aerodynamic reduced-order models (ROMs) are generated and coupled with structural models to form aeroelastic ROMs. The aerodynamic ROMs generated here include the effects of control surface motion and are appropriate for use in aeroservoelastic applications. Simple observer-based full-state feedback controllers were designed from these aeroelastic ROMs. Additionally, observer gain matrices were designed from and coupled to the aeroelastic ROMs. Each (linear) observer was then used to estimate the dynamics of a (nonlinear) stand-alone computational fluid-structure dynamics simulation. Then, using the estimated states and the full-state feedback controller, control surface commands were fed back into the computational fluid-structure dynamics simulation to successfully achieve active flutter suppression. The process, as well as some results, are presented in this paper
Reduced Order Modeling for Transonic Aeroservoelastic Control Law Development
As aircraft become more flexible, aeroelastic considerations become increasingly important and complex, particularly for transonic flight where nonlinearities in the flow render linear analysis tools less effective. In order to analyze these aeroelastic interactions between the fluid and the structure efficiently, reduced order models (ROMs) are sometimes generated from and used in place of computational fluid dynamics solutions. In this paper, several aerodynamic ROMs are generated and coupled with structural models to form aeroelastic ROMs. The aerodynamic ROMs generated here include the effects of control surface motion. Hence, the aeroelastic ROMs presented here are appropriate for use in aeroservoelastic applications and are intended to be used for aeroservoelastic control law development. These ROMs are used to simulate a number of test cases with and without control surface involvement. Results show that several of the ROMs generated in the paper are able to predict results similar to solutions of higher-order computational methods
Saturation Effects in Deep Inelastic Scattering at low and its Implications on Diffraction
We present a model based on the concept of saturation for small and
small . With only three parameters we achieve a good description of all Deep
Inelastic Scattering data below . This includes a consistent treatment
of charm and a successful extrapolation into the photoproduction regime. The
same model leads to a roughly constant ratio of diffractive and inclusive cross
section.Comment: 24 pages, 12 figures, Latex-fil
Geometric Scaling in Inclusive Charm Production
We show that the cross section for inclusive charm production exhibits
geometric scaling in a large range of photon virtualities. In the HERA
kinematic domain the saturation momentum stays below the hard
scale , implying charm production probing mostly the color
transparency regime and unitarization effects being almost negligible. We
derive our results considering two saturation models which are able to describe
the DESY ep collider HERA data for the proton structure function at small
values of the Bjorken variable . A striking feature is the scaling on
above saturation limit, corroborating recent
theoretical studies.Comment: 4 pages, 2 figures. Version to be published in Physical Review
Letter
First Report of the Alfalfa Blotch Leafminer (Diptera: Agromyzidae), and Selected Parasites (Hymenoptera: Eulophidae) in Minnesota and Wisconsin, USA
Alfalfa blotch leafminer, Agromyza frontella, has been a serious pest of alfalfa, Medicago sativa, in the northeastern U.S. and in eastern Ontario, Canada. Until recently, the western edge of the A. frontella distribution in the U.S. was limited to eastern Ohio. We document for the first time, the occurrence of A. frontella in Minnesota and Wisconsin. Alfalfa stems damaged by A. frontella, based on adult feeding punctures, obvious blotched leafmining or the presence of larvae, were first found in 3 northern Minnesota counÂties during October, 1994. Infested counties included Lake of the Woods, Cook and Lake, all bordering western Ontario, Canada. In 1995, A. frontella was again found in Cook and Lake counties, where 99-100% of the stems, and 18-35% of the trifoliates/stem, contained larvae or exhibited obvious feeding damage. In 1996, following a more expanded survey, a total of 11 and 5 counties, in Minnesota and Wisconsin, respectively, showed some level of A. frontella feeding damage (stem samples ranged from \u3c5 to 100% infested). Based on additional counties surveyed 11 October, 1996, where A. frontella was not found, we now have a reasonable estimate of the southern edge of the distribution in Minnesota and Wisconsin. A total of 2 and 6 A. frontella adults were identified from sweep-net samples taken from fields with obvious feeding damage during 1995 (Lake Co.) and 1996 (Cook Co,), respectively. Three eulophid (Hymenoptera) parasites were reared from A. frontella-infested alfalfa stems collected during October, 1994 in Cook Co., Minn., including: Diglyphus begini, D. pulchripes, and Diglyphus sp., prob. isaea, all of which are new records. Our hypothesis is that A. frontella moved into Minnesota from Ontario Canada, via alfalfa hay purchased by northern Minnesota growers
A Lattice Formulation of Super Yang-Mills Theories with Exact Supersymmetry
We construct super Yang-Mills theories with extended supersymmetry on
hypercubic lattices of various dimensions keeping one or two supercharges
exactly. Gauge fields are represented by ordinary unitary link variables, and
the exact supercharges are nilpotent up to gauge transformations. Among the
models, we show that the desired continuum theories are obtained without any
fine tuning of parameters for the cases in two-dimensions.Comment: 29 pages, 1 figure, LaTeX, (v2) problem on degenerate vacua
discussed, renormalization arguments modified, (v3) explanations and
references added, published version in JHE
Odderon in the Color Glass Condensate
We discuss the definition and the energy evolution of scattering amplitudes
with -odd ("odderon") quantum numbers within the effective theory for the
Color Glass Condensate (CGC) endowed with the functional, JIMWLK, evolution
equation. We explicitly construct gauge-invariant amplitudes describing
multiple odderon exchanges in the scattering between the CGC and two types of
projectiles: a color--singlet quark--antiquark pair (or `color dipole') and a
system of three quarks in a colorless state. We deduce the energy evolution of
these amplitudes from the general JIMWLK equation, which for this purpose is
recast in a more synthetic form, which is manifestly infrared finite. For the
dipole odderon, we confirm and extend the non--linear evolution equations
recently proposed by Kovchegov, Szymanowski and Wallon, which couple the
evolution of the odderon to that of the pomeron, and predict the rapid
suppression of the odderon exchanges in the saturation regime at high energy.
For the 3--quark system, we focus on the linear regime at relatively low
energy, where our general equations are shown to reduce to the
Bartels--Kwiecinski--Praszalowicz equation. Our gauge--invariant amplitudes,
and the associated evolution equations, stay explicitly outside the M\"obius
representation, which is the Hilbert space where the BFKL Hamiltonian exhibits
holomorphic separability.Comment: 43 pages, 1 figur
The effect of the FIFA 11 prevention programmes on the overall injury rate in football:a systematic review and meta-analysis
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