40,159 research outputs found
Determination of heat transfer coefficient for hot stamping process
© 2015 The Authors.The selection of the heat transfer coefficient is one of the most important factors that determine the reliability of FE simulation results of a hot stamping process, in which the formed component is held within cold dies until fully quenched. The quenching process could take up to 10. seconds. In order to maximise the production rate, the optimised quenching parameters should be identified to achieve the highest possible quenching rate and to reduce the quenching time. For this purpose, a novel-testing rig for the Gleeble 3800 thermo- mechanical simulator was designed and manufactured, with an advanced control system for temperature and contact pressure. The effect of contact pressure on the heat transfer coefficient was studied. The findings of this research will provide useful guidelines for the selection of the heat transfer coefficient in simulations of hot stamping processes and useful information for the design of hot stamping processes
Lorentz Symmetry and the Internal Structure of the Nucleon
To investigate the internal structure of the nucleon, it is useful to
introduce quantities that do not transform properly under Lorentz symmetry,
such as the four-momentum of the quarks in the nucleon, the amount of the
nucleon spin contributed by quark spin, etc. In this paper, we discuss to what
extent these quantities do provide Lorentz-invariant descriptions of the
nucleon structure.Comment: 6 pages, no figur
Single-Electron Traps: A Quantitative Comparison of Theory and Experiment
We have carried out a coordinated experimental and theoretical study of
single-electron traps based on submicron aluminum islands and aluminum oxide
tunnel junctions. The results of geometrical modeling using a modified version
of MIT's FastCap were used as input data for the general-purpose
single-electron circuit simulator MOSES. The analysis indicates reasonable
quantitative agreement between theory and experiment for those trap
characteristics which are not affected by random offset charges. The observed
differences between theory and experiment (ranging from a few to fifty percent)
can be readily explained by the uncertainty in the exact geometry of the
experimental nanostructures.Comment: 17 pages, 21 figures, RevTex, eps
The box diagram in Yukawa theory
We present a light-front calculation of the box diagram in Yukawa theory. The
covariant box diagram is finite for the case of spin-1/2 constituents
exchanging spin-0 particles. In light-front dynamics, however, individual
time-ordered diagrams are divergent. We analyze the corresponding light-front
singularities and show the equivalence between the light-front and covariant
results by taming the singularities.Comment: 21 pages, 17 figures. submittes to Phys. Rev.
Quark Orbital-Angular-Momentum Distribution in the Nucleon
We introduce gauge-invariant quark and gluon angular momentum distributions
after making a generalization of the angular momentum density operators. From
the quark angular momentum distribution, we define the gauge-invariant and
leading-twist quark {\it orbital} angular momentum distribution . The
latter can be extracted from data on the polarized and unpolarized quark
distributions and the off-forward distribution in the forward limit. We
comment upon the evolution equations obeyed by this as well as other orbital
distributions considered in the literature.Comment: 8 pages, latex, no figures, minor corrections mad
The Exotic (Higher Order L\'evy) Laplacians generate the Markov processes given by distribution derivatives of white noise
The General Theory of Quantum Field Mixing
We present a general theory of mixing for an arbitrary number of fields with
integer or half-integer spin. The time dynamics of the interacting fields is
solved and the Fock space for interacting fields is explicitly constructed. The
unitary inequivalence of the Fock space of base (unmixed) eigenstates and the
physical mixed eigenstates is shown by a straightforward algebraic method for
any number of flavors in boson or fermion statistics. The oscillation formulas
based on the nonperturbative vacuum are derived in a unified general
formulation and then applied to both two and three flavor cases. Especially,
the mixing of spin-1 (vector) mesons and the CKM mixing phenomena in the
Standard Model are discussed emphasizing the nonperturbative vacuum effect in
quantum field theory
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