6,553 research outputs found
Reconstruction of N=1 supersymmetry from topological symmetry
The scalar and vector topological Yang-Mills symmetries on Calabi-Yau
manifolds geometrically define consistent sectors of Yang-Mills D=4,6 N=1
supersymmetry, which fully determine the supersymmetric actions up to twist.
For a CY_2 manifold, both N=1,D=4 Wess and Zumino and superYang-Mills theory
can be reconstructed in this way. A superpotential can be introduced for the
matter sector, as well as the Fayet-Iliopoulos mechanism. For a CY_3 manifold,
the N=1, D=6 Yang-Mills theory is also obtained, in a twisted form. Putting
these results together with those already known for the D=4,8 N=2 cases, we
conclude that all Yang--Mills supersymmetries with 4, 8 and 16 generators are
determined from topological symmetry on special manifolds.Comment: 13 page
Implementation, demonstration and validation of a user-defined wall-function for direct precipitation fouling in ANSYS Fluent
In a previous paper (Johnsen et al., 2015) and presentation (Johnsen et al.,
2016), we developed and demonstrated a generic modelling framework for the
modelling of direct precipitation fouling from multi-component fluid mixtures
that become super-saturated at the wall. The modelling concept involves the
1-dimensional transport of the fluid species through the turbulent boundary
layer close to the wall. The governing equations include the Reynolds-averaged
(RANS) advection-diffusion equations for each fluid species, and the axial
momentum and energy equations for the fluid mixture. The driving force for the
diffusive transport is the local gradient in the species' chemical potential.
Adsorption mechanisms are not modelled per se, but the time-scale of adsorption
is reflected in the choice of Dirichlet boundary conditions for the depositing
species, at the fluid-solid interface.
In this paper, the modelling framework is implemented as a user-defined
function (UDF) for the CFD software ANSYS Fluent, to act as a wall boundary
condition for mass-transfer to the wall. The subgrid, 1-dimensional formulation
of the model reduces the computational cost associated with resolving the fine
length-scales at which the boundary-layer mass transfer is determined, and
allows for efficient modelling of industry-scale heat exchangers suffering from
fouling.
The current paper describes the modelling framework, and demonstrates and
validates its applicability in a simplified 2D heat exchanger geometry
(experimental and detailed CFD modelling data by P\"a\"akk\"onen et al. (2012,
2016)). By tuning the diffusivity, only, good agreement with the experimental
data and the detailed CFD model was obtained, in terms of area-averaged
deposition rates.Comment: 12th International Conference on CFD in Oil & Gas, Metallurgical and
Process Industries, SINTEF, Trondheim, NORWAY, May 30th - June 1st, 2017, 9
pages, 9 figure
Journal Staff
The aluminum–zinc-vacancy (Al Zn −V Zn ) complex is identified as one of the dominant defects in Al-containing n -type ZnO after electron irradiation at room temperature with energies above 0.8 MeV. The complex is energetically favorable over the isolated V Zn , binding more than 90% of the stable V Zn ’s generated by the irradiation. It acts as a deep acceptor with the (0/− ) energy level located at approximately 1 eV above the valence band. Such a complex is concluded to be a defect of crucial and general importance that limits the n -type doping efficiency by complex formation with donors, thereby literally removing the donors, as well as by charge compensation
Anisotropic thermal expansion and magnetostriction of YNiBC single crystals
We present results of anisotropic thermal expansion and low temperature
magnetostriction measurements on YNiBC single crystals grown by high
temperature flux and floating zone techniques. Quantum oscillations of
magnetostriction were observed at low temperatures for starting at
fields significantly below (). Large irreversible,
longitudinal magnetostriction was seen in both, in-plane and along the c-axis,
directions of the applied magnetic field in the intermediate superconducting
state. Anisotropic uniaxial pressure dependencies of were evaluated using
results of zero field, thermal expansion measurements
Buckling instability in type-II superconductors with strong pinning
We predict a novel buckling instability in the critical state of thin type-II
superconductors with strong pinning. This elastic instability appears in high
perpendicular magnetic fields and may cause an almost periodic series of flux
jumps visible in the magnetization curve. As an illustration we apply the
obtained criteria to a long rectangular strip.Comment: Submitted to Phys. Rev. Let
Quantum theory of successive projective measurements
We show that a quantum state may be represented as the sum of a joint
probability and a complex quantum modification term. The joint probability and
the modification term can both be observed in successive projective
measurements. The complex modification term is a measure of measurement
disturbance. A selective phase rotation is needed to obtain the imaginary part.
This leads to a complex quasiprobability, the Kirkwood distribution. We show
that the Kirkwood distribution contains full information about the state if the
two observables are maximal and complementary. The Kirkwood distribution gives
a new picture of state reduction. In a nonselective measurement, the
modification term vanishes. A selective measurement leads to a quantum state as
a nonnegative conditional probability. We demonstrate the special significance
of the Schwinger basis.Comment: 6 page
Log-periodic route to fractal functions
Log-periodic oscillations have been found to decorate the usual power law
behavior found to describe the approach to a critical point, when the
continuous scale-invariance symmetry is partially broken into a discrete-scale
invariance (DSI) symmetry. We classify the `Weierstrass-type'' solutions of the
renormalization group equation F(x)= g(x)+(1/m)F(g x) into two classes
characterized by the amplitudes A(n) of the power law series expansion. These
two classes are separated by a novel ``critical'' point. Growth processes
(DLA), rupture, earthquake and financial crashes seem to be characterized by
oscillatory or bounded regular microscopic functions g(x) that lead to a slow
power law decay of A(n), giving strong log-periodic amplitudes. In contrast,
the regular function g(x) of statistical physics models with
``ferromagnetic''-type interactions at equibrium involves unbound logarithms of
polynomials of the control variable that lead to a fast exponential decay of
A(n) giving weak log-periodic amplitudes and smoothed observables. These two
classes of behavior can be traced back to the existence or abscence of
``antiferromagnetic'' or ``dipolar''-type interactions which, when present,
make the Green functions non-monotonous oscillatory and favor spatial modulated
patterns.Comment: Latex document of 29 pages + 20 ps figures, addition of a new
demonstration of the source of strong log-periodicity and of a justification
of the general offered classification, update of reference lis
Nonclassicality of Thermal Radiation
It is demonstrated that thermal radiation of small occupation number is
strongly nonclassical. This includes most forms of naturally occurring
radiation. Nonclassicality can be observed as a negative weak value of a
positive observable. It is related to negative values of the Margenau-Hill
quasi-probability distribution.Comment: 3 pages, 3 figure
Topological field theory and physics
Topological Yang-Mills theory with the Belavin-Polyakov-Schwarz-Tyupkin
instanton is solved completely, revealing an underlying multi-link
intersection theory. Link invariants are also shown to survive the coupling to
a certain kind of matter (hyperinstantons). The physical relevance of
topological field theory and its invariants is discovered. By embedding
topological Yang-Mills theory into pure Yang-Mills theory, it is shown that the
topological version TQFT of a quantum field theory QFT allows us to formulate
consistently the perturbative expansion of QFT in the topologically nontrivial
sectors. In particular, TQFT classifies the set of good measures over the
instanton moduli space and solves the inconsistency problems of the previous
approaches. The qualitatively new physical implications are pointed out. Link
numbers in QCD are related to a non abelian analogoue of the Aharonov-Bohm
effect.Comment: 23 pages, 1 figure. Revision: additional explanation
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