200 research outputs found
Austrian higher education institutions' idiosyncrasies and technology transfer system
The aim of this paper is to present the findings of a PhD research (Heinzl, 2007) conducted on the Universities of Applied Sciences in Austria. The research is to establish an idiosyncrasy model for Universities of Applied Sciences in Austria showing the effects of their idiosyncrasies on the ability to successfully conduct technology transfer. Research applied in the study is centred on qualitative methods as major emphasis is placed on theory building. The study pursues a stepwise approach for the establishment of the idiosyncrasy model. In the first step, an initial technology transfer model and list of idiosyncrasies are established based on a synthesis of findings from secondary research. In the second step, these findings are enhanced by the means of empirical research including problem-centred expert interviews, a focus group and participant observation. In the third step, the idiosyncrasies are matched with the factors conducive for technology transfer and focused interviews have been conducted for this purpose. The findings show that idiosyncrasies of Universities of Applied Sciences have remarkable effects on their technology transfer abilities. This paper presents four of the models that emerge from the PhD research: Generic Technology Transfer Model (Section 5.1); Idiosyncrasies Model for the Austrian Universities of Applied Sciences (Section 5.2); Idiosyncrasies-Technology Transfer Effects Model (Section 5.3); Idiosyncrasies-Technology Transfer Cumulated Effects Model (Section 5.3). The primary and secondary research methods employed for this study are: literature survey, focus groups, participant observation, and interviews. The findings of the research contribute to a conceptual design of a technology transfer system which aims to enhance the higher education institutions' technology transfer performance
Effective Actions for the SU(2) Confinement-Deconfinement Phase Transition
We compare different Polyakov loop actions yielding effective descriptions of
finite-temperature SU(2) Yang-Mills theory on the lattice. The actions are
motivated by a simultaneous strong-coupling and character expansion obeying
center symmetry and include both Ising and Ginzburg-Landau type models. To keep
things simple we limit ourselves to nearest-neighbor interactions. Some
truncations involving the most relevant characters are studied within a novel
mean-field approximation. Using inverse Monte-Carlo techniques based on exact
geometrical Schwinger-Dyson equations we determine the effective couplings of
the Polyakov loop actions. Monte-Carlo simulations of these actions reveal that
the mean-field analysis is a fairly good guide to the physics involved. Our
Polyakov loop actions reproduce standard Yang-Mills observables well up to
limitations due to the nearest-neighbor approximation.Comment: 14 pages, 10 figures, v2: typos correcte
A novel approach to light-front perturbation theory
We suggest a possible algorithm to calculate one-loop n-point functions
within a variant of light-front perturbation theory. The key ingredients are
the covariant Passarino-Veltman scheme and a surprising integration formula
that localises Feynman integrals at vanishing longitudinal momentum. The
resulting expressions are generalisations of Weinberg's infinite-momentum
results and are manifestly Lorentz invariant. For n = 2 and 3 we explicitly
show how to relate those to light-front integrals with standard energy
denominators. All expressions are rendered finite by means of transverse
dimensional regularisation.Comment: 10 pages, 5 figure
Effective sigma models and lattice Ward identities
We perform a lattice analysis of the Faddeev-Niemi effective action
conjectured to describe the low-energy sector of SU(2) Yang-Mills theory. To
this end we generate an ensemble of unit vector fields ("color spins") n from
the Wilson action. The ensemble does not show long-range order but exhibits a
mass gap of the order of 1 GeV. From the distribution of color spins we
reconstruct approximate effective actions by means of exact lattice
Schwinger-Dyson and Ward identities ("inverse Monte Carlo"). We show that the
generated ensemble cannot be recovered from a Faddeev-Niemi action, modified in
a minimal way by adding an explicit symmetry-breaking term to avoid the
appearance of Goldstone modes.Comment: 25 pages, 17 figures, JHEP styl
Light-Front Quantisation as an Initial-Boundary Value Problem
In the light front quantisation scheme initial conditions are usually
provided on a single lightlike hyperplane. This, however, is insufficient to
yield a unique solution of the field equations. We investigate under which
additional conditions the problem of solving the field equations becomes well
posed. The consequences for quantisation are studied within a Hamiltonian
formulation by using the method of Faddeev and Jackiw for dealing with
first-order Lagrangians. For the prototype field theory of massive scalar
fields in 1+1 dimensions, we find that initial conditions for fixed light cone
time {\sl and} boundary conditions in the spatial variable are sufficient to
yield a consistent commutator algebra. Data on a second lightlike hyperplane
are not necessary. Hamiltonian and Euler-Lagrange equations of motion become
equivalent; the description of the dynamics remains canonical and simple. In
this way we justify the approach of discretised light cone quantisation.Comment: 26 pages (including figure), tex, figure in latex, TPR 93-
Spontaneous symmetry breaking of (1+1)-dimensional theory in light-front field theory (II)
We discuss spontaneous symmetry breaking of (1+1)-dimensional theory
in light-front field theory using a Tamm-Dancoff truncation. We show that, even
though light-front field theory has a simple vacuum state which is an
eigenstate of the full Hamiltonian, the field can develop a nonzero vacuum
expectation value. This occurs because the zero mode of the field must satisfy
an operator valued constraint equation. In the context of (1+1)-dimensional
theory we present solutions to the constraint equation using a
Tamm-Dancoff truncation to a finite number of particles and modes. We study the
behavior of the zero mode as a function of coupling and Fock space truncation.
The zero mode introduces new interactions into the Hamiltonian which breaks the
symmetry of the theory when the coupling is stronger than the critical
coupling.Comment: 25 page
The Axial Anomaly in D=3+1 Light-Cone QED
We consider -dimensional, Dirac electrons of arbitrary mass,
propagating in the presence of electric and magnetic fields which are both
parallel to the axis. The magnetic field is constant in space and time
whereas the electric field depends arbitrarily upon the light-cone time
parameter . We present an explicit solution to the
Heisenberg equations for the electron field operator in this background. The
electric field results in the creation of electron-positron pairs. We compute
the expectation values of the vector and axial vector currents in the presence
of a state which is free vacuum at . Both current conservation and the
standard result for the axial vector anomaly are verified for the first time
ever in -dimensional light-cone QED. An interesting feature of our
operator solution is the fact that it depends in an essential way upon
operators from the characteristic at , in addition to the usual
dependence upon operators at . This dependence survives even in the
limit of infinite . Ignoring the operators leads to a progressive loss
of unitarity, to the violation of current conservation, to the loss of
renormalizability, and to an incorrect result for the axial vector anomaly.Comment: 31 pages, LaTeX 2 epsilon, no figures, some typoes corrected for
publicatio
Vacuum refractive indices and helicity flip in strong-field QED
Vacuum birefringence is governed by the amplitude for a photon to flip
helicity or polarisation state in an external field. Here we calculate the flip
and non-flip amplitudes in arbitrary plane wave backgrounds, along with the
induced spacetime-dependent refractive indices of the vacuum. We compare the
behaviour of the amplitudes in the low energy and high energy regimes, and
analyse the impact of pulse shape and energy. We also provide the first
lightfront-QED derivation of the coefficients in the Heisenberg-Euler effective
action.Comment: Version 2: additional results added, including discussion of vacuum
refractive indices, analysis of flip and non-flip ampltidues at high-energy,
additional plots, new title. Now 17 pages, 10 figure
Photon polarization in light-by-light scattering: Finite size effects
We derive a simple expression for the photon helicity and polarization-flip probabilities in arbitrary background fields, in the low-energy regime. Taking the background to model a focused laser beam, we study the impact of pulse shape and collision geometry on the probabilities and on ellipticity signals of vacuum birefringence. We find that models which do not account for pulse duration can overestimate all signals in near head-on collisions by up to an order of magnitude. Taking pulse duration into account, the flip probability becomes relatively insensitive to both angular incidence and the fine details of the pulse structure
Noncommutativity from spectral flow
We investigate the transition from second to first order systems. This
transforms configuration space into phase space and hence introduces
noncommutativity in the former. Quantum mechanically, the transition may be
described in terms of spectral flow. Gaps in the energy or mass spectrum may
become large which effectively truncates the available state space. Using both
operator and path integral languages we explicitly discuss examples in quantum
mechanics, (light-front) quantum field theory and string theory.Comment: 31 pages, one Postscript figur
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