4,976 research outputs found
Derivation of the Effective Pion-Nucleon Lagrangian within Heavy Baryon Chiral Perturbation Theory
We develop a method for constructing the Heavy Baryon Chiral Perturbation
Theory Lagrangian (L_{HBChPT}), to a given chiral order, within HBChPT. We work
within SU(2) theory, with only the pion field interacting with the nucleon. The
main difficulties, which are solved, are to develop techniques for implementing
charge conjugation invariance, and for taking the nucleon on shell, both within
the nonrelativistic formalism. We obtain complete lists of independent terms in
L_{HBChPT} through O(q^3) for off- shell nucleons. Then, eliminating
equation-of-motion (eom) terms at the relativistic and nonrelativistic level
(both within HBChPT), we obtain L_{HBCHPT} for on-shell nucleons, through
O(q^3). The extension of the method (to obtain on-shell L_{HBChPT} within
HBChPT) to higher orders is also discussed.Comment: 31 pages, LaTex; original version shortened; 2 new tables and new
material on extending on-shell reduction method within HBChPT to arbitrary
chiral orders, include
A Neural Algorithm of Artistic Style
In fine art, especially painting, humans have mastered the skill to create
unique visual experiences through composing a complex interplay between the
content and style of an image. Thus far the algorithmic basis of this process
is unknown and there exists no artificial system with similar capabilities.
However, in other key areas of visual perception such as object and face
recognition near-human performance was recently demonstrated by a class of
biologically inspired vision models called Deep Neural Networks. Here we
introduce an artificial system based on a Deep Neural Network that creates
artistic images of high perceptual quality. The system uses neural
representations to separate and recombine content and style of arbitrary
images, providing a neural algorithm for the creation of artistic images.
Moreover, in light of the striking similarities between performance-optimised
artificial neural networks and biological vision, our work offers a path
forward to an algorithmic understanding of how humans create and perceive
artistic imagery
Isospin violation in epsilon'
On the basis of a next-to-leading-order calculation in chiral perturbation
theory, the first complete analysis of isospin breaking for direct CP violation
in K^0 -> 2 pi decays is performed. We find a destructive interference between
three different sources of isospin violation in the CP violation parameter
epsilon'. Within the uncertainties of large-N_c estimates for the low-energy
constants, the isospin violating correction for epsilon' is below 15 %.Comment: 4 page
Microcanonical Thermodynamics of First Order Phase Transitions studied in the Potts Model
Phase transitions of first and second order can easily be distinguished in
small systems in the microcanonical ensemble. Configurations of phase
coexistence, which are suppressed in the canonical formulation, carry important
information about the main characteristics of first order phase transitions
like the transition temperature, the latent heat, and the interphase surface
tension. The characterisitc backbending of the micro- canonical caloric
equation of state T(E) (not to be confused with the well known Van der Waals
loops in ordinary thermodynamics) leading to a negative specific heat is
intimatly linked to the interphase surface entropy.Comment: Latex, 4 eps-figures, graphicx.st
The Design of Mechanically Compatible Fasteners for Human Mandible Reconstruction
Mechanically compatible fasteners for use with thin or weakened bone sections in the human mandible are being developed to help reduce large strain discontinuities across the bone/implant interface. Materials being considered for these fasteners are a polyetherertherketone (PEEK) resin with continuous quartz or carbon fiber for the screw. The screws were designed to have a shear strength equivalent to that of compact/trabecular bone and to be used with a conventional nut, nut plate, or an expandable shank/blind nut made of a ceramic filled polymer. Physical and finite element models of the mandible were developed in order to help select the best material fastener design. The models replicate the softer inner core of trabecular bone and the hard outer shell of compact bone. The inner core of the physical model consisted of an expanding foam and the hard outer shell consisted of ceramic particles in an epoxy matrix. This model has some of the cutting and drilling attributes of bone and may be appropriate as an educational tool for surgeons and medical students. The finite element model was exercised to establish boundary conditions consistent with the stress profiles associated with mandible bite forces and muscle loads. Work is continuing to compare stress/strain profiles of a reconstructed mandible with the results from the finite element model. When optimized, these design and fastening techniques may be applicable, not only to other skeletal structures, but to any composite structure
Electromagnetism in nonleptonic weak interactions
We construct a low-energy effective field theory that permits the complete
treatment of isospin-breaking effects in nonleptonic weak interactions to
next-to-leading order. To this end, we enlarge the chiral Lagrangian describing
strong and Delta S=1 weak interactions by including electromagnetic terms with
the photon as additional dynamical degree of freedom. The complete and minimal
list of local terms at next-to-leading order is given. We perform the one-loop
renormalization at the level of the generating functional and specialize to K
-> pi pi decays.Comment: 17 pages, 1 figure; 2 references added, final version for publication
in Nucl. Phys.
<VAP> Green Function in the Resonance Region
We analyse the three-point function of vector, axial-vector and
pseudoscalar currents. In the spirit of large N_C, a resonance dominated Green
function is confronted with the leading high-energy behaviour from the operator
product expansion. The matching is shown to be fully compatible with a chiral
resonance Lagrangian and it allows to determine some of the chiral low-energy
constants of O(p^6).Comment: 13 pages, 2 figures. Published version. Results and conclusions
unchange
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