3,642 research outputs found
Progress on tilted axis cranking covariant density functional theory for nuclear magnetic and antimagnetic rotation
Magnetic rotation and antimagnetic rotation are exotic rotational phenomena
observed in weakly deformed or near-spherical nuclei, which are
respectivelyinterpreted in terms of the shears mecha-nism and two shearslike
mechanism. Since their observations, magnetic rotation and antimagnetic
rotation phenomena have been mainly investigated in the framework of tilted
axis cranking based on the pairing plus quadrupole model. For the last decades,
the covariant density functional theory and its extension have been proved to
be successful in describing series of nuclear ground-states and excited states
properties, including the binding energies, radii, single-particle spectra,
resonance states, halo phenomena, magnetic moments, magnetic rotation,
low-lying excitations, shape phase transitions, collective rotation and
vibrations, etc. This review will mainly focus on the tilted axis cranking
covariant density functional theory and its application for the magnetic
rotation and antimagnetic rotation phenomena.Comment: 53 pages, 19 figure
Magnetic rotations in 198Pb and 199Pb within covariant density functional theory
Well-known examples of shears bands in the nuclei 198Pb and 199Pb are
investigated within tilted axis cranking relativistic mean-field theory. Energy
spectra, the relation between spin and rotational frequency, deformation
parameters and reduced and transition probabilities are calculated.
The results are in good agreement with available data and with calculations
based on the phenomenological pairing plus-quadrupole-quadrupole tilted-axis
cranking model. It is shown that covariant density functional theory provides a
successful microscopic and fully self-consistent description of magnetic
rotation in the Pb region showing the characteristic properties as the shears
mechanism and relatively large B(M1) transitions decreasing with increasing
spin.Comment: 22 pages, 8 figure
Uniaxial and biaxial soft deformations of nematic elastomers
We give a geometric interpretation of the soft elastic deformation modes of
nematic elastomers, with explicit examples, for both uniaxial and biaxial
nematic order. We show the importance of body rotations in this non-classical
elasticity and how the invariance under rotations of the reference and target
states gives soft elasticity (the Golubovic and Lubensky theorem). The role of
rotations makes the Polar Decomposition Theorem vital for decomposing general
deformations into body rotations and symmetric strains. The role of the square
roots of tensors is discussed in this context and that of finding explicit
forms for soft deformations (the approach of Olmsted).Comment: 10 pages, 10 figures, RevTex, AmsTe
Geometric transformations in octrees using shears
Existent algorithms to perform geometric transformations on octrees
can be classified in two families: inverse transformation and address
computation ones. Those in the inverse transformation family
essentially resample the target octree from the source one, and are
able to cope with all the affine transformations. Those in the address
computation family only deal with translations, but are commonly
accepted as faster than the former ones for they do no intersection
tests, but directly calculate the transformed address of each black
node in the source tree. This work introduces a new translation
algorithm that shows to perform better than previous one when very
small displacements are involved. This property is particularly useful
in applications such as simulation, robotics or computer animation.Postprint (published version
Quantum Transport in Molecular Rings and Chains
We study charge transport driven by deformations in molecular rings and
chains. Level crossings and the associated Longuet-Higgins phase play a central
role in this theory. In molecular rings a vanishing cycle of shears pinching a
gap closure leads, generically, to diverging charge transport around the ring.
We call such behavior homeopathic. In an infinite chain such a cycle leads to
integral charge transport which is independent of the strength of deformation.
In the Jahn-Teller model of a planar molecular ring there is a distinguished
cycle in the space of uniform shears which keeps the molecule in its manifold
of ground states and pinches level crossing. The charge transport in this cycle
gives information on the derivative of the hopping amplitudes.Comment: Final version. 26 pages, 8 fig
Linear hydrodynamics and viscoelasticity of nematic elastomers
We develop a continuum theory of linear viscoelastic response in oriented
monodomain nematic elastomers. The expression for dissipation function is
analogous to the Leslie-Ericksen version of anisotropic nematic viscosity; we
propose the relations between the anisotropic rubber moduli and new viscous
coefficients. A new dimensionless number is introduced, which describes the
relative magnitude of viscous and rubber-elastic torques. In an elastic medium
with an independently mobile internal degree of freedom, the nematic director
with its own relaxation dynamics, the model shows a dramatic decrease in the
dynamic modulus in certain deformation geometries. The degree to which the
storage modulus does not altogether drop to zero is shown to be both dependent
on frequency and to be proportional to the semi-softness, the non-ideality of a
nematic network. We consider the most interesting geometry for the
implementation of the theory, calculating the dynamic response to an imposed
simple shear and making predictions for effective moduli and (exceptionally
high) loss factors.Comment: Latex 2e or PDFlatex (4 EPS or JPG figures) - to appear in
Euro.Phys.J.
Hex Player—a virtual musical controller
In this paper, we describe a playable musical interface for tablets and multi-touch tables. The interface is a generalized keyboard, inspired by the Thummer, and consists of an array of virtual buttons. On a generalized keyboard, any given interval always has the same shape (and therefore fingering); furthermore, the fingering is consistent over a broad range of tunings. Compared to a physical generalized keyboard, a virtual version has some advantages—notably, that the spatial location of the buttons can be transformed by shears and rotations, and their colouring can be changed to reflect their musical function in different scales.
We exploit these flexibilities to facilitate the playing not just of conventional Western scales but also a wide variety of microtonal generalized diatonic scales known as moment of symmetry, or well-formed, scales. A user can choose such a scale, and the buttons are automatically arranged so their spatial height corresponds to their pitch, and buttons an octave apart are always vertically above each other. Furthermore, the most numerous scale steps run along rows, while buttons within the scale are light-coloured, and those outside are dark or removed.
These features can aid beginners; for example, the chosen scale might be the diatonic, in which case the piano’s familiar white and black colouring of the seven diatonic and five chromatic notes is used, but only one scale fingering need ever be learned (unlike a piano where every key needs a different fingering). Alternatively, it can assist advanced composers and musicians seeking to explore the universe of unfamiliar microtonal scales
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