2,794 research outputs found
CJK-Improved 5 Flavour LO Parton Distributions in the Real Photon
Radiatively generated, LO quark (u,d,s,c,b) and gluon densities in the real,
unpolarized photon, improved in respect to our previous paper, are presented.
We perform three global fits to the F_2^gamma data, using the LO DGLAP
evolution equation. We improve the treatment of the strong coupling running and
used lower values of Lambda_QCD, as we have found that the too high values
adopted in the previous work caused the high chi^2 of the fits. In addition to
the modified FFNS_CJKL model, referred to as FFNS_CJK 1 we analyse a FFNS_CJK 2
model in which we take into account the resolved-photon heavy-quark
contribution. New CJK model with an improved high-x behavior of the
F_2^gamma(x,Q^2) is proposed. Finally, in the case of the CJK model we abandon
the valence sum rule imposed on the VMD input densities. New fits give chi^2
per degree of freedom about 0.25 better than the old results. All features of
the CJKL model, such as the realistic heavy-quark distributions, good
description of the LEP data on the Q^2 dependence of the F_2^gamma and on
F_2,c^gamma are preserved. Moreover we present results of an analysis of the
uncertainties of the CJK parton distributions due to the experimental errors.
It is based on the Hessian method used for the proton and very recently applied
for the photon by one of us. Parton and structure function parametrizations of
the best fits in both FFNS_CJK and CJK approaches are made accessible. For the
CJK model we provide also sets of test parametrizations which allow for
calculation of uncertainties of any physical value depending on the real photon
parton densities.Comment: 27 pages, 14 figures, FORTRAN programs available at
http://www.fuw.edu.pl/~pjank/param.htm
Heavy quark photoproduction at THERA
Measurements of heavy quark production at a possible future facility,
THERA, would provide valuable information on the structure of the photon. QCD
cross-section predictions are made at LO for both charm and beauty production
and their sensitivity to current parametrisations of the photon parton
densities is investigated.Comment: 10 pages, 9 figures. To appear in "The THERA Book",
DESY-LC-REV-2001-062. IFT 2001/
Heavy Quark Production at the TESLA Collider and its Sensitivity to the Gluon Content in Photon
Heavy quark production is studied at the high energy linear e^+e^- collider
(LC) TESLA both in its nominal and Photon Collider (PC) mode. Leading order
cross-sections are calculated for the production of heavy quarks, e^+e^- ->
e^+e^- Q\bar{Q}X, at high transverse momenta. The sensitivity of this process
to the gluon content in the photon is studied.Comment: 16 pages, Latex, 10 ps figures, uses epsfig.sty. IFT 2001/3
Antenna Design for Semi-Passive UHF RFID Transponder with Energy Harvester
A novel microstrip antenna which is dedicated to UHF semi-passive RFID transponders with an energy harvester is presented in this paper. The antenna structure designed and simulated by using Mentor Graphics HyperLynx 3D EM software is described in details. The modeling and simulation results along with comparison with experimental data are analyzed and concluded. The main goal of the project is the need to eliminate a traditional battery form the transponder structure. The energy harvesting block, which is used instead, converts ambient energy (electromagnetic energy of typical radio communication system) into electrical power for internal circuitry. The additional function (gathering extra energy) of the transponder antenna causes the necessity to create new designs in this scope
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Extracting Personal Behavioral Patterns from Geo-Referenced Tweets
This paper presents an exploratory study of the potential of geo-referenced Twitter data for extracting knowledge about significant personal places, behaviors and potential interests of people. The study was done analysing two months’ worth of tweets from residents of the greater Seattle area
The Russia-Ukraine conflict: lessons for europeans from a polish perspective
O corrente conflito russo-ucraniano alterou novamente o destino da Europa do Leste. No entanto, esta crise deve tambĂ©m ser considerada como um fator perturbador da segurança Europeia. Toda a arquitetura da segurança Europeia foi afetada com a instabilidade do flanco oriental do continente. Se este conflito nĂŁo servir como um fator unificador da comunidade transatlântica, poderá ser um prenĂşncio de difĂceis tempos vindouros. Acresce, ainda, que este perigo poder-se-á tornar particularmente grave caso se instale a perceção de que a NATO perdeu a sua credibilidade para dissuadir ameaças e a UniĂŁo Europeia a sua capacidade como potĂŞncia normativa para estimular mudanças no sistema internacional. Inicialmente, este artigo apresenta cinco lições fundamentais que deverĂŁo ser retiradas do conflito russo-ucraniano de forma a conter eventuais desafios e ameaças para a Europa. Posteriormente, serĂŁo abordadas quatro recomendações que constituem uma base para um plano de ação de polĂticas securitárias sĂłlidas e de longo prazo como resposta a este conflito.info:eu-repo/semantics/publishedVersio
Towards a holographic realization of the quarkyonic phase
Large-N_c QCD matter at intermediate baryon density and low temperatures has
been conjectured to be in the so-called quarkyonic phase, i.e., to have a quark
Fermi surface and on top of it a confined spectrum of excitations. It has been
suggested that the presence of the quark Fermi surface leads to a homogeneous
phase with restored chiral symmetry, which is unstable towards creating
condensates breaking both the chiral and translational symmetry. Motivated by
these exotic features, we investigate properties of cold baryonic matter in the
single flavor Sakai-Sugimoto model searching for a holographic realization of
the quarkyonic phase. We use a simplified mean-field description and focus on
the regime of parametrically large baryon densities, of the order of the square
of the 't Hooft coupling, as they turn out to lead to new physical effects
similar to the ones occurring in the quarkyonic phase. One effect, the
appearance of a particular marginally stable mode breaking translational
invariance and linked with the presence of the Chern-Simons term in the flavor
brane Lagrangian, is known to occur in the deconfined phase of the
Sakai-Sugimoto model, but turns out to be absent here. The other, completely
new phenomenon that we, preliminarily, study using strong simplifying
assumptions are density-enhanced interactions of the flavor brane gauge field
with holographically represented baryons. These seem to significantly affect
the spectrum of vector and axial mesons and might lead to approximate chiral
symmetry restoration in the lowest part of the spectrum, where the mesons start
to qualitatively behave like collective excitations of the dense baryonic
medium. We discuss the relevance of these effects for holographic searches of
the quarkyonic phase and conclude with a discussion of various subtleties
involved in constructing a mean-field holographic description of a dense
baryonic medium.Comment: 31 pages, 16 figures; v2: inset plot in Fig. 10 removed, coloring in
Fig. 13 fixed, typos fixed, matches published versio
Hybrid altimeter using a strapdown inertial navigation system
Hybrid radio and barometric altimeter using strapdown inertial navigation syste
Heavy Quark Production at a Linear e^+e^- and Photon Collider and its Sensitivity to the Gluon Content of the Photon
A high energy linear e^+e^- collider (LC) can also be used as a Photon
Collider (PC), using Compton scattering of laser photons on the e^+/e^- beams.
The leading order cross-section for the production of heavy quarks, e^+e^- ->
e^+e^- Q(\bar{Q}) X, at high transverse momenta is calculated for both LC and
PC modes. The sensitivity of this process to the parton distribution
parametrizations of real photons, especially the gluon content, is tested for
both modes.Comment: 8 pages, Latex using epsfig.sty, including 6 postscript figures.
Contribution to Proceedings of the Workshop "Physics Studies for a Future
Linear Collider", Rolf Heuer, Francois Richard and Peter Zerwas Eds., 2000,
DESY 123
Debye mass and heavy quark potential in a PNJL quark plasma
We calculate the Debye mass for the screening of the heavy quark potential in
a plasma of massless quarks coupled to the temporal gluon background governed
by the Polyakov loop potential within the PNJL model in RPA approximation. We
give a physical motivation for a recent phenomenological fit of lattice data by
applying the calculated Debye mass with its suppression in the confined phase
due to the Polyakov-loop to a description of the temperature dependence of the
singlet free energy for QCD with a heavy quark pair at infinite separation. We
compare the result to lattice data.Comment: 6 pages, 1 figure, contribution to Proceedings of the 6th
International Conference on "Critical Point and Onset of Deconfinement", to
appear in Phys. At. Nucl., vol. 7
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