606 research outputs found
Pion form factors with improved infrared factorization
We calculate electromagnetic pion form factors with an analytic model for
which is infrared (IR) finite without invoking a
``freezing'' hypothesis. We show that for the asymptotic pion distribution
amplitude, agrees well with the data, whereas
the IR-enhanced hard contribution to and the soft (nonfactorizing)
part can jointly account for the data.Comment: 12 pages; 3 figures as PS files (1 figure added); modified text;
added references. To appear in Phys. Lett.
Overheating threshold and its effect on time–temperature-transformation diagrams of zirconium based bulk metallic glasses
A pronounced effect of overheating is observed on the crystallization behavior for the three zirconium-based bulk metallic glasses: Zr41.2Ti13.8Cu12.5Ni10Be22.5, Zr57Cu15.4Ni12.6Al10Nb5, and Zr52.5Cu17.9Ni14.6Al10Ti5. A threshold overheating temperature is found for each of the three alloys, above which there is a drastic increase in the undercooling level and the crystallization times. Time–temperature-transformation (TTT) diagrams were measured for the three alloys by overheating above their respective threshold temperatures. The TTT curves for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr57Cu15.4Ni12.6Al10Nb5 are very similar in shape and scale with their respective glass transition temperatures, suggesting that system-specific properties do not play a crucial role in defining crystallization kinetics in these alloys. The critical cooling rates to vitrify the alloys as determined from the TTT curves are about 2 K/s for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and 10 K/s for Zr57Cu15.4Ni12.6Al10Nb5. The measurements were conducted in a high-vacuum electrostatic levitator
Overheating threshold and its effect on time–temperature-transformation diagrams of zirconium based bulk metallic glasses
A pronounced effect of overheating is observed on the crystallization behavior for the three zirconium-based bulk metallic glasses: Zr41.2Ti13.8Cu12.5Ni10Be22.5, Zr57Cu15.4Ni12.6Al10Nb5, and Zr52.5Cu17.9Ni14.6Al10Ti5. A threshold overheating temperature is found for each of the three alloys, above which there is a drastic increase in the undercooling level and the crystallization times. Time–temperature-transformation (TTT) diagrams were measured for the three alloys by overheating above their respective threshold temperatures. The TTT curves for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr57Cu15.4Ni12.6Al10Nb5 are very similar in shape and scale with their respective glass transition temperatures, suggesting that system-specific properties do not play a crucial role in defining crystallization kinetics in these alloys. The critical cooling rates to vitrify the alloys as determined from the TTT curves are about 2 K/s for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and 10 K/s for Zr57Cu15.4Ni12.6Al10Nb5. The measurements were conducted in a high-vacuum electrostatic levitator
Helicity Dependent and Independent Generalized Parton Distributions of the Nucleon in Lattice QCD
A complete description of the nucleon structure in terms of generalized
parton distributions (GPDs) at twist 2 level requires the
measurement/computation of the eight functions H, E, \tilde H, \tilde E, H_T,
E_T, \tilde H_T and \tilde E_T, all depending on the three variables x, \xi and
t. In this talk, we present and discuss our first steps in the framework of
lattice QCD towards this enormous task. Dynamical lattice QCD results for the
lowest three Mellin moments of the helicity dependent and independent GPDs are
shown in terms of their corresponding generalized form factors. Implications
for the transverse coordinate space structure of the nucleon as well as the
orbital angular momentum (OAM) contribution of quarks to the nucleon spin are
discussed in some detail.Comment: 5 pages, 5 figures, Talk presented by Ph.H. at Electron-Nucleus
Scattering VIII, Elba, Italy, June 21-25, 2004; typos corrected, minor change
in wording on p.4&
Hadronic physics with domain-wall valence and improved staggered sea quarks
With the advent of chiral fermion formulations, the simulation of light
valence quarks has finally become realistic for numerical simulations of
lattice QCD. The simulation of light dynamical quarks, however, remains one of
the major challenges and is still an obstacle to realistic simulations. We
attempt to meet this challenge using a hybrid combination of Asqtad sea quarks
and domain-wall valence quarks. Initial results for the proton form factor and
the nucleon axial coupling are presented.Comment: Two Talks presented at Lattice2004(spectrum), LaTex, 6 pages, 6 eps
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Linked and knotted synthetic magnetic fields
We show that the realisation of synthetic magnetic fields via light-matter
coupling in the Lambda-scheme implements a natural geometrical construction of
magnetic fields, namely as the pullback of the area element of the sphere to
Euclidean space via certain maps. For suitable maps, this construction
generates linked and knotted magnetic fields, and the synthetic realisation
amounts to the identification of the map with the ratio of two Rabi frequencies
which represent the coupling of the internal energy levels of an ultracold
atom. We consider examples of maps which can be physically realised in terms of
Rabi frequencies and which lead to linked and knotted synthetic magnetic fields
acting on the neutral atomic gas. We also show that the ground state of the
Bose-Einstein condensate may inherit topological properties of the synthetic
gauge field, with linked and knotted vortex lines appearing in some cases.Comment: 8 pages, 4 figures, supplementary videos attached. Comments welcom
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