88,724 research outputs found
Noncommutativity due to spin
Using the Berezin-Marinov pseudoclassical formulation of spin particle we
propose a classical model of spin noncommutativity. In the nonrelativistic
case, the Poisson brackets between the coordinates are proportional to the spin
angular momentum. The quantization of the model leads to the noncommutativity
with mixed spacial and spin degrees of freedom. A modified Pauli equation,
describing a spin half particle in an external e.m. field is obtained. We show
that nonlocality caused by the spin noncommutativity depends on the spin of the
particle; for spin zero, nonlocality does not appear, for spin half, , etc. In the relativistic case the noncommutative
Dirac equation was derived. For that we introduce a new star product. The
advantage of our model is that in spite of the presence of noncommutativity and
nonlocality, it is Lorentz invariant. Also, in the quasiclassical approximation
it gives noncommutativity with a nilpotent parameter.Comment: 11 pages, references adda
Note on improvement precision of recursive function simulation in floating point standard
An improvement on precision of recursive function simulation in IEEE floating
point standard is presented. It is shown that the average of rounding towards
negative infinite and rounding towards positive infinite yields a better result
than the usual standard rounding to the nearest in the simulation of recursive
functions. In general, the method improves one digit of precision and it has
also been useful to avoid divergence from a correct stationary regime in the
logistic map. Numerical studies are presented to illustrate the method.Comment: DINCON 2017 - Conferencia Brasileira de Dinamica, Controle e
Aplicacoes - Sao Jose do Rio Preto - Brazil. 8 page
Alternative structures and bi-Hamiltonian systems on a Hilbert space
We discuss transformations generated by dynamical quantum systems which are
bi-unitary, i.e. unitary with respect to a pair of Hermitian structures on an
infinite-dimensional complex Hilbert space. We introduce the notion of
Hermitian structures in generic relative position. We provide few necessary and
sufficient conditions for two Hermitian structures to be in generic relative
position to better illustrate the relevance of this notion. The group of
bi-unitary transformations is considered in both the generic and non-generic
case. Finally, we generalize the analysis to real Hilbert spaces and extend to
infinite dimensions results already available in the framework of
finite-dimensional linear bi-Hamiltonian systems.Comment: 11 page
Controlled dephasing of a quantum dot in the Kondo regime
Kondo correlation in a spin polarized quantum dot (QD) results from the
dynamical formation of a spin singlet between the dot's net spin and a Kondo
cloud of electrons in the leads, leading to enhanced coherent transport through
the QD. We demonstrate here significant dephasing of such transport by coupling
the QD and its leads to potential fluctuations in a near by 'potential
detector'. The qualitative dephasing is similar to that of a QD in the Coulomb
Blockade regime in spite of the fact that the mechanism of transport is quite
different. A much stronger than expected suppression of coherent transport is
measured, suggesting that dephasing is induced mostly in the 'Kondo cloud' of
electrons within the leads and not in the QD.Comment: to be published in PR
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An Investigation into the Effect of the Shell on SALM Processed Parts
Shell Assisted Layer Manufacturing (SALM) is a novel process for rapid prototyping/
tooling/ manufacture (RP/RT/RM) which is presently undergoing feasibility studies. SALM is
based on layered manufacturing technology (LMT). Initially it develops the shell (boundaries)
of a selected layer using a technique similar to fused deposition modelling (FDM). The
developed shell is filled with a UV curable resin and is exposed to UV radiation for curing.
This procedure is repeated until the complete part is built. This paper compares and contrasts
properties of parts made using two options available with the SALM technique: building the
part using a soluble shell (FDM support structure material, finally dissolved to recover the
part); or using a polymer material such as ABS that is bonded with the resin whilst making
the part.Mechanical Engineerin
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