27 research outputs found
Percolation in random environment
We consider bond percolation on the square lattice with perfectly correlated
random probabilities. According to scaling considerations, mapping to a random
walk problem and the results of Monte Carlo simulations the critical behavior
of the system with varying degree of disorder is governed by new, random fixed
points with anisotropic scaling properties. For weaker disorder both the
magnetization and the anisotropy exponents are non-universal, whereas for
strong enough disorder the system scales into an {\it infinite randomness fixed
point} in which the critical exponents are exactly known.Comment: 8 pages, 7 figure
A Dynamical Principle For 3D-4D Interlinkage In Salpeter-like Equations
The half-century old Markov-Yukawa Transversality Principle () which
provides a theoretical rationale for the covariant instantaneous approximation
() that underlies all Salpeter-like equations, is generalized to a
covariant null-plane ansatz (). A common characteristic of both
formulations is an exact 3D-4D interlinkage of BS amplitudes which facilitates
a two-tier description: the 3D form for spectroscopy, and the 4D form for
transition amplitudes as 4D loop integrals. Some basic applications of
on the covariant null plane (quark mass function, vacuum condensates, and decay
constants) are given on the lines of earlier applications to these processes
under .
PACS: 03.65.-w ; 03.65.Co ; 11.10.Qr ; 11.10.St
Keywords: Markov-Yukawa Transversality Principle (); Salpeter-like eqs;
Cov Instantaneity Ansatz (); Cov Null-Plane Ansatz (); 3D-4D
interlinkage; Vertex function; 4D loopsComment: LaTeX file, 25 pages, to be published in Nuclear Phys.
Critical behavior of weakly-disordered anisotropic systems in two dimensions
The critical behavior of two-dimensional (2D) anisotropic systems with weak
quenched disorder described by the so-called generalized Ashkin-Teller model
(GATM) is studied. In the critical region this model is shown to be described
by a multifermion field theory similar to the Gross-Neveu model with a few
independent quartic coupling constants. Renormalization group calculations are
used to obtain the temperature dependence near the critical point of some
thermodynamic quantities and the large distance behavior of the two-spin
correlation function. The equation of state at criticality is also obtained in
this framework. We find that random models described by the GATM belong to the
same universality class as that of the two-dimensional Ising model. The
critical exponent of the correlation length for the 3- and 4-state
random-bond Potts models is also calculated in a 3-loop approximation. We show
that this exponent is given by an apparently convergent series in
(with the central charge of the Potts model) and
that the numerical values of are very close to that of the 2D Ising
model. This work therefore supports the conjecture (valid only approximately
for the 3- and 4-state Potts models) of a superuniversality for the 2D
disordered models with discrete symmetries.Comment: REVTeX, 24 pages, to appear in Phys.Rev.
Untangling the effects of overexploration and overexploitation on organizational performance: The moderating role of environmental dynamism
Because a firm's optimal knowledge search behavior is determined by unique firm and industry conditions, organizational performance should be contingent oil the degree to which a firm's actual level of knowledge search deviates from the optimal level. It is thus hypothesized that deviation from the optimal search, in the form of either overexploitation or overexploration, is detrimental to organizational performance. Furthermore, the negative effect of search deviation oil organizational performance varies with environmental dynamism: that is, overexploitation is expected to become more harmful. whereas overexploration becomes less so with all increase in environmental dynamism. The empirical analyses yield results consistent with these arguments. Implications for research and practice are correspondingly discussed