4,963 research outputs found
Quantum Yang-Mills gravity in flat space-time and effective curved space-time for motions of classical objects
Yang-Mills gravity with translational gauge group T(4) in flat space-time
implies a simple self-coupling of gravitons and a truly conserved
energy-momentum tensor. Its consistency with experiments crucially depends on
an interesting property that an `effective Riemannian metric tensor' emerges in
and only in the geometric-optics limit of the photon and particle wave
equations. We obtain Feynman rules for a coupled graviton-fermion system,
including a general graviton propagator with two gauge parameters and the
interaction of ghost particles. The equation of motion of macroscopic objects,
as an N-body system, is demonstrated as the geometric-optics limit of the
fermion wave equation. We discuss a relativistic Hamilton-Jacobi equation with
an `effective Riemann metric tensor' for the classical particles.Comment: 20 pages, to be published in "The European Physical Journal -
Plus"(2011). The final publication is available at http://www.epj.or
Lack of correlation between constitutive and induced resistance to a herbivore in crucifer plants: real or flawed by experimental methods?
The correlation between constitutive and induced resistance to herbivores in plants has long been of interest to evolutionary biologists, and various approaches to determining levels of resistance have been used in this field of research. In this study, we examined the relationship between constitutive and induced resistance to the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), in 11 closely related species of wild crucifers. We assessed the survival, development, and reproduction of the test insects and calculated their intrinsic rate of increase as an indicator of constitutive and induced resistance for the plants. We used larvae of P. xylostella and jasmonic acid as elicitors of the induced response. We failed to find a correlation between constitutive and induced resistance in these crucifer plants when the induction of resistance was initiated by either herbivory or jasmonic acid application. Analysis of the results suggests that the failure to detect a relationship between the two types of resistance could be caused by flaws in measuring constitutive resistance, which was apparently confounded with induced resistance. We discuss the difficulties and pitfalls in measuring constitutive resistance and ways to improve the methodology in investigating the relationships between constitutive and induced resistance in plant
The role of intermediate layers in the c-axis conductivity of layered superconductors
A simplified model of c axis transport in the high T_c superconductors is
presented. Expressions are found for the c axis optical conductivity, the d.c.
resistivity, and the c axis penetration depth. Within the framework of this
model, the pseudogap in the optical conductivity arises naturally as a result
of the layered band structure of the high T_c materials. We discuss the
occurence of the pseudogap in terms of three parameters: a band gap Delta_{ps},
a temperature dependent scattering rate Gamma(T), and the strength of the
interlayer coupling t_{perp}. We are also able to find analytic expressions for
the d.c. conductivity and the low temperature penetration depth in terms of
these three parameters. This work is an attempt to present a simple, unified
picture of c axis properties in the high T_c cuprates.Comment: 3 pages, 2 figures, Proceedings of Spectroscopies of Novel
Superconductors '97, To be published in J. Phys. Chem. Solid
Applying mesh conformation on shape analysis with missing data
A mesh conformation approach that makes use of deformable generic meshes has been applied to establishing correspondences between 3D shapes with missing data. Given a group of shapes with correspondences, we can build up a statistical shape model by applying principal component analysis (PCA). The conformation at first globally maps the generic mesh to the 3D shape based on manually located corresponding landmarks, and then locally deforms the generic mesh to clone the 3D shape. The local deformation is constrained by minimizing the energy of an elastic model. An algorithm was also embedded in the conformation process to fill missing surface data of the shapes. Using synthetic data, we demonstrate that the conformation preserves the configuration of the generic mesh and hence it helps to establish good correspondences for shape analysis. Case studies of the principal component analysis of shapes were presented to illustrate the successes and advantages of our approach
A Three-Flavor AdS/QCD Model with a Back-Reacted Geometry
A fully back-reaction geometry model of AdS/QCD including the strange quark
is described. We find that with the inclusion of the strange quark the impact
on the metric is very small and the final predictions are changed only
negligibly.Comment: 10 pages, 2 figures; references revised, minor change for caption of
fig
Hund's Rule for Composite Fermions
We consider the ``fractional quantum Hall atom" in the vanishing Zeeman
energy limit, and investigate the validity of Hund's maximum-spin rule for
interacting electrons in various Landau levels. While it is not valid for {\em
electrons} in the lowest Landau level, there are regions of filling factors
where it predicts the ground state spin correctly {\em provided it is applied
to composite fermions}. The composite fermion theory also reveals a
``self-similar" structure in the filling factor range .Comment: 10 pages, revte
Absence of anisotropic universal transport in YBCO
There exists significant in-plane anisotropy between and axis for
various properties in YBCO. However recent thermal conductivity measurement by
Chiao et al. which confirms previous microwave conductivity measurement by
Zhang et al., shows no obvious anisotropy in the context of universal
transport. We give a possible explanation of why the anisotropy is seen in most
properties but not seen in the universal transport.Comment: 4 pages, 4 figure
AdS/QCD Phenomenological Models from a Back-Reacted Geometry
We construct a fully back-reacted holographic dual of a four-dimensional
field theory which exhibits chiral symmetry breaking. Two possible models are
considered by studying the effects of a five-dimensional field, dual to the
operator. One model has smooth geometry at all radii and the other
dynamically generates a cutoff at finite radius. Both of these models satisfy
Einstein's field equations. The second model has only three free parameters, as
in QCD, and we show that this gives phenomenologically consistent results. We
also discuss the possibility that in order to obtain linear confinement from a
back-reacted model it may be necessary to consider the condensate of a
dimension two operator.Comment: 13 pages, 4 figures, Replaced with minor correction
Fractional Quantum Hall States in Low-Zeeman-Energy Limit
We investigate the spectrum of interacting electrons at arbitrary filling
factors in the limit of vanishing Zeeman splitting. The composite fermion
theory successfully explains the low-energy spectrum {\em provided the
composite fermions are treated as hard-core}.Comment: 12 pages, revte
Skyrmion Excitations in Quantum Hall Systems
Using finite size calculations on the surface of a sphere we study the
topological (skyrmion) excitation in quantum Hall system with spin degree of
freedom at filling factors around . In the absence of Zeeman energy, we
find, in systems with one quasi-particle or one quasi-hole, the lowest energy
band consists of states with , where and are the total orbital and
spin angular momentum. These different spin states are almost degenerate in the
thermodynamic limit and their symmetry-breaking ground state is the state with
one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion
size is determined by the interplay of the Zeeman energy and electron-electron
interaction and the skyrmion shrinks to a spin texture of finite size. We have
calculated the energy gap of the system at infinite wave vector limit as a
function of the Zeeman energy and find there are kinks in the energy gap
associated with the shrinking of the size of the skyrmion. breaking ground
state is the state with one skyrmion of infinite size. In the presence of
Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman
energy and electron-electronComment: 4 pages, 5 postscript figures available upon reques
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