7,190 research outputs found
Spinodal phase separation in semi-interpenetrating polymer networks - polystyrene-cross-polymethacrylate
Morphology control in semi-interpenetrating polymer networks has been achieved by means of a two-step process, separating morphology formation and polymerization/crosslinking. Phase textures formed during spinodal liquid/liquid demixing of a solution of atactic polystyrene in methacrylate monomers were arrested by thermoreversible gelation of the polymer-rich phase as this phase passed its glass transition temperature. The phase separated structure was permanently stabilized by low-temperature crosslinking ultraviolet (UV) polymerization of the methacrylate monomer, and studied by transmission electron microscopy. Thus, it was directly observed how the initial demixing process depended on the initial viscosity of the polymer solution and the mode of quenching. Arrest of the earliest stage of spinodal demixing resulted in separated domains of 0.05-0.08 m thickness, which were separated by a distance of the spinodal wavelength . A cocontinuous network only developed in a relatively late stage of demixing
Relativistic Quark Spin Coupling Effects in the Nucleon Electromagnetic Form Factors
We investigate the effect of different forms of relativistic spin coupling of
constituent quarks in the nucleon electromagnetic form factors. The
four-dimensional integrations in the two-loop Feynman diagram are reduced to
the null-plane, such that the light-front wave function is introduced in the
computation of the form factors. The neutron charge form factor is very
sensitive to different choices of spin coupling schemes, once its magnetic
moment is fitted to the experimental value. The scalar coupling between two
quarks is preferred by the neutron data, when a reasonable fit of the proton
magnetic momentum is found.Comment: 13 pages, needs axodraw.ps and axodraw.sty for diagrams of Fig.
Three-Fermion Bound States on the Light Front
We investigate the stability of the relativistic three-fermion system with a
zero-range force in the light front form. In particular, introducing an
invariant cut-off, we study the dependence of the bound state on the coupling
strength also for cases where the two-fermion system is unbound. The
relativistic Thomas collapse is discussed by solving the fully coupled integral
equation system. Furthermore, we explicitly investigate the ground state mass
of the three-fermion system and compare to previous simplified calculations.Comment: 23 pages, 6 figure
Report drawn up on behalf of the Committee on Youth, Culture, Education, Information and Sport on the use of languages in the Community, Part A: Motion for a resolution. Working Documents 1984-1985, Document 1-83/84/A, 2 April 1984
Report drawn up on behalf of the Committee on Youth, Culture, Education, Information and Sport on the use of languages in the Community, Part B: Explanatory Statement. Working Documents 1984-1985, Document 1-83/84/B, 2 April 1984
Feynman versus Bakamjian-Thomas in Light Front Dynamics
We compare the Bakamjian-Thomas (BT) formulation of relativistic few-body
systems with light front field theories that maintain closer contact with
Feynman diagrams. We find that Feynman diagrams distinguish Melosh rotations
and other kinematical quantities belonging to various composite subsystem
frames that correspond to different loop integrals. The BT formalism knows only
the rest frame of the whole composite system, where everything is evaluated.Comment: 5 page
Correlation between the reliability of HEMT devices and that of a combined oscillator-amplifier
We evaluate an oscillator-amplifier MMIC submitted to high-temperature operating life time tests. To relate adequately these results with individual components’ results, it is important to realise that failure mechanisms in non-linear MMICs are governed by the maximally instantaneous voltages/currents and hence that comparisons should be conducted at equal instantaneous conditions
Proving Non-Termination via Loop Acceleration
We present the first approach to prove non-termination of integer programs
that is based on loop acceleration. If our technique cannot show
non-termination of a loop, it tries to accelerate it instead in order to find
paths to other non-terminating loops automatically. The prerequisites for our
novel loop acceleration technique generalize a simple yet effective
non-termination criterion. Thus, we can use the same program transformations to
facilitate both non-termination proving and loop acceleration. In particular,
we present a novel invariant inference technique that is tailored to our
approach. An extensive evaluation of our fully automated tool LoAT shows that
it is competitive with the state of the art
Three-quark clusters at finite temperatures and densities
We present a relativistic three-body equation to study correlations in a
medium of finite temperatures and densities. This equation is derived within a
systematic Dyson equation approach and includes the dominant medium effects due
to Pauli blocking and self energy corrections. Relativity is implemented
utilizing the light front form. The equation is solved for a zero-range force
for parameters close to the confinement-deconfinement transition of QCD. We
present correlations between two- and three-particle binding energies and
calculate the three-body Mott transition.Comment: 7 pages, 7 figure
Neutron Charge Radius: Relativistic Effects and the Foldy Term
The neutron charge radius is studied within a light-front model with
different spin coupling schemes and wave functions. The cancellation of the
contributions from the Foldy term and Dirac form factor to the neutron charge
form factor is verified for large nucleon sizes and it is independent of the
detailed form of quark spin coupling and wave function. For the physical
nucleon our results for the contribution of the Dirac form factor to the
neutron radius are insensitive to the form of the wave function while they
strongly depend on the quark spin coupling scheme.Comment: 12 pages, 5 figures, Latex, Int. J. Mod. Phys.
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