6,065 research outputs found
A Model for Granular Texture with Steric Exclusion
We propose a new method to characterize the geometrical texture of a granular
packing at the particle scale including the steric hindrance effect. This
method is based on the assumption of a maximum disorder (entropy) compatible
both with strain-induced anisotropy of the contact network and steric
exclusions. We show that the predicted statistics for the local configurations
is in a fairly agreement with our numerical data.Comment: 9 pages, 5 figure
Sheared force-networks: anisotropies, yielding and geometry
A scenario for yielding of granular matter is presented by considering the
ensemble of force networks for a given contact network and applied shear stress
. As is increased, the probability distribution of contact forces
becomes highly anisotropic, the difference between average contact forces along
minor and major axis grows, and the allowed networks span a shrinking subspace
of all force-networks. Eventually, contacts start to break, and at the yielding
shear stress, the packing becomes effectively isostatic. The size of the
allowed subspace exhibits simple scaling properties, which lead to a prediction
of the yield stress for packings of arbitrary contact number.Comment: 4 pages, 4 figure
The Light-Cone Vacuum in 1+1 Dimensional Super-Yang-Mills Theory
The Discrete Light-Cone Quantization (DLCQ) of a supersymmetric SU(N) gauge
theory in 1+1 dimensions is discussed, with particular emphasis given to the
inclusion of all dynamical zero modes. Interestingly, the notorious `zero-mode
problem' is now tractable because of special supersymmetric cancellations. In
particular, we show that anomalous zero-mode contributions to the currents are
absent, in contrast to what is observed in the non-supersymmetric case. We find
that the supersymmetric partner of the gauge zero mode is the diagonal
component of the fermion zero mode. An analysis of the vacuum structure is
provided and it is shown that the inclusion of zero modes is crucial for
probing the phase properties of the vacua. In particular, we find that the
ground state energy is zero and N-fold degenerate, and thus consistent with
unbroken supersymmetry. We also show that the inclusion of zero modes for the
light-cone supercharges leaves the supersymmetry algebra unchanged. Finally, we
remark that the dependence of the light-cone Fock vacuum in terms of the gauge
zero is unchanged in the presence of matter fields.Comment: REVTEX, 15 page
Bounds on the shear load of cohesionless granular matter
We characterize the force state of shear-loaded granular matter by relating
the macroscopic stress to statistical properties of the force network. The
purely repulsive nature of the interaction between grains naturally provides an
upper bound for the sustainable shear stress, which we analyze using an
optimization procedure inspired by the so-called force network ensemble. We
establish a relation between the maximum possible shear resistance and the
friction coefficient between individual grains, and find that anisotropies of
the contact network (or the fabric tensor) only have a subdominant effect.
These results can be considered the hyperstatic limit of the force network
ensemble and we discuss possible implications for real systems. Finally, we
argue how force anisotropies can be related quantitatively to experimental
measurements of the effective elastic constants.Comment: 17 pages, 6 figures. v2: slightly rearranged, introduction and
discussion rewritte
The general classical solution of the superparticle
The theory of vectors and spinors in 9+1 dimensional spacetime is introduced
in a completely octonionic formalism based on an octonionic representation of
the Clifford algebra \Cl(9,1). The general solution of the classical
equations of motion of the CBS superparticle is given to all orders of the
Grassmann hierarchy. A spinor and a vector are combined into a
Grassmann, octonionic, Jordan matrix in order to construct a superspace
variable to describe the superparticle. The combined Lorentz and supersymmetry
transformations of the fermionic and bosonic variables are expressed in terms
of Jordan products.Comment: 11 pages, REVTe
Rough Surface Effect on Meissner Diamagnetism in Normal-layer of N-S Proximity-Contact System
Rough surface effect on the Meissner diamagnetic current in the normal layer
of proximity contact N-S bi-layer is investigated in the clean limit. The
diamagnetic current and the screening length are calculated by use of
quasi-classical Green's function. We show that the surface roughness has a
sizable effect, even when a normal layer width is large compared with the
coherence length . The effect is as large as that
of the impurity scattering and also as that of the finite reflection at the N-S
interface.Comment: 12 pages, 3 figures. To be published in J. Phys. Soc. Jpn. Vol.71-
Symmetries and observables in topological gravity
After a brief review of topological gravity, we present a superspace approach
to this theory. This formulation allows us to recover in a natural manner
various known results and to gain some insight into the precise relationship
between different approaches to topological gravity. Though the main focus of
our work is on the vielbein formalism, we also discuss the metric approach and
its relationship with the former formalism.Comment: 34 pages; a few explanations added in subsection 2.2.1, published
version of pape
Convergence of the Gaussian Expansion Method in Dimensionally Reduced Yang-Mills Integrals
We advocate a method to improve systematically the self-consistent harmonic
approximation (or the Gaussian approximation), which has been employed
extensively in condensed matter physics and statistical mechanics. We
demonstrate the {\em convergence} of the method in a model obtained from
dimensional reduction of SU() Yang-Mills theory in dimensions. Explicit
calculations have been carried out up to the 7th order in the large-N limit,
and we do observe a clear convergence to Monte Carlo results. For the convergence is already achieved at the 3rd order, which suggests that
the method is particularly useful for studying the IIB matrix model, a
conjectured nonperturbative definition of type IIB superstring theory.Comment: LaTeX, 4 pages, 5 figures; title slightly changed, explanations added
(16 pages, 14 figures), final version published in JHE
Memory of the Unjamming Transition during Cyclic Tiltings of a Granular Pile
Discrete numerical simulations are performed to study the evolution of the
micro-structure and the response of a granular packing during successive
loading-unloading cycles, consisting of quasi-static rotations in the gravity
field between opposite inclination angles. We show that internal variables,
e.g., stress and fabric of the pile, exhibit hysteresis during these cycles due
to the exploration of different metastable configurations. Interestingly, the
hysteretic behaviour of the pile strongly depends on the maximal inclination of
the cycles, giving evidence of the irreversible modifications of the pile state
occurring close to the unjamming transition. More specifically, we show that
for cycles with maximal inclination larger than the repose angle, the weak
contact network carries the memory of the unjamming transition. These results
demonstrate the relevance of a two-phases description -strong and weak contact
networks- for a granular system, as soon as it has approached the unjamming
transition.Comment: 13 pages, 15 figures, soumis \`{a} Phys. Rev.
Partons and Jets at the LHC
I review some issues related to short distance QCD and its relation to the
experimental program of the Large Hadron Collider (LHC) now under construction
in Geneva.Comment: Talk at the conference QCD2002 at IIT Kanpur, India, November 2002.
Ten pages with 12 figure
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