139,803 research outputs found
Conformal Mechanics and the Virasoro Algebra
We demonstrate that any scale-invariant mechanics of one variable exhibits
not only 0+1 conformal symmetry, but also the symmetries of a full Virasoro
algebra. We discuss the implications for the adS/CFT correspondence.Comment: 9 pages, LaTeX. Latest version contains minor clarifications and
change
Energy Controlled Edge Formation for Graphene Nano Ribbons
On the basis of first principles calculations, we report energy estimated to
cut a graphene sheet into nanoribbons of armchair and zigzag configurations.
Our calculations show that the energy required to cut a graphene sheet into
zigzag configuration is higher than that of armchair configuration by an order
of 0.174 eV. Thus, a control over the threshold energy might be helpful in
designing an experiment for cutting a graphene sheet into smooth edged armchair
or zigzag configurations
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First-principles study of crystallographic slip modes in ω-Zr.
We use first-principles density functional theory to study the preferred modes of slip in the high-pressure ω phase of Zr. The generalized stacking fault energy surfaces associated with shearing on nine distinct crystallographic slip modes in the hexagonal ω-Zr crystal are calculated, from which characteristics such as ideal shear stress, the dislocation Burgers vector, and possible accompanying atomic shuffles, are extracted. Comparison of energy barriers and ideal shear stresses suggests that the favorable modes are prismatic 〈c〉, prismatic-II [Formula: see text] and pyramidal-II 〈c + a〉, which are distinct from the ground state hexagonal close packed α phase of Zr. Operation of these three modes can accommodate any deformation state. The relative preferences among the identified slip modes are examined using a mean-field crystal plasticity model and comparing the calculated deformation texture with the measurement. Knowledge of the basic crystallographic modes of slip is critical to understanding and analyzing the plastic deformation behavior of ω-Zr or mixed α-ω phase-Zr
Properties of Phase transitions of a Higher Order
The following is a thermodynamic analysis of a III order (and some aspects of
a IV order) phase transition. Such a transition can occur in a superconductor
if the normal state is a diamagnet. The equation for a phase boundary in an H-T
(H is the magnetic field, T, the temperature) plane is derived. by considering
two possible forms of the gradient energy, it is possible to construct a field
theory which describes a III or a IV order transition and permits a study of
thermal fluctuations and inhomogeneous order parameters.Comment: 13 pages, revtex, no figure
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