11,907 research outputs found
Dynamics of modulated and composite aperiodic crystals: the signature of the inner polarization in the neutron coherent inelastic scattering
We compare within an unifying formalism the dynamical properties of modulated
and composite aperiodic (incommensurate) crystals. We discuss the concept of
inner polarization and we define an inner polarization parameter beta that
distinguishes between different acoustic modes of aperiodic crystals. Although
this concept has its limitations, we show that it can be used to extract
valuable information from neutron coherent inelastic scattering experiments.
Within certain conditions, the ratio between the dynamic and the static
structure factors at various Bragg peaks depends on beta. We show how the
knowledge of beta for modes of an unknown structure can be used to decide
whether the structure is composite or modulated. Furthermore, the same
information can be used to predict scattered intensity within unexplored
regions of the reciprocal space, being thus a guide for experiment
The Resistance of Feynman Diagrams and the Percolation Backbone Dimension
We present a new view of Feynman diagrams for the field theory of transport
on percolation clusters. The diagrams for random resistor networks are
interpreted as being resistor networks themselves. This simplifies the field
theory considerably as we demonstrate by calculating the fractal dimension
of the percolation backbone to three loop order. Using renormalization
group methods we obtain , where with
being the spatial dimension and .Comment: 10 pages, 2 figure
Multifractal current distribution in random diode networks
Recently it has been shown analytically that electric currents in a random
diode network are distributed in a multifractal manner [O. Stenull and H. K.
Janssen, Europhys. Lett. 55, 691 (2001)]. In the present work we investigate
the multifractal properties of a random diode network at the critical point by
numerical simulations. We analyze the currents running on a directed
percolation cluster and confirm the field-theoretic predictions for the scaling
behavior of moments of the current distribution. It is pointed out that a
random diode network is a particularly good candidate for a possible
experimental realization of directed percolation.Comment: RevTeX, 4 pages, 5 eps figure
Perverse effects of other-referenced performance goals in an information exchange context
A values-centered leadership model comprised of leader stakeholder and economic values, follower values congruence, and responsible leadership outcomes was tested using data from 122 organizational leaders and 458 of their direct reports. Alleviating same-source bias concerns in leadership survey research, follower ratings of leadership style and follower ratings of values congruence and responsible leadership outcomes were collected from separate sources via the split-sample methodology. Results of structural equation modeling analyses demonstrated that leader stakeholder values predicted transformational leadership, whereas leader economic values were associated with transactional leadership. Follower values congruence was strongly associated with transformational leadership, unrelated to transactional leadership, and partially mediated the relationships between transformational leadership and both follower organizational citizenship behaviors and follower beliefs in the stakeholder view of corporate social responsibility. Implications for responsible leadership and transformational leadership theory, practice, and future research are discussed
Fresh look at randomly branched polymers
We develop a new, dynamical field theory of isotropic randomly branched
polymers, and we use this model in conjunction with the renormalization group
(RG) to study several prominent problems in the physics of these polymers. Our
model provides an alternative vantage point to understand the swollen phase via
dimensional reduction. We reveal a hidden Becchi-Rouet-Stora (BRS) symmetry of
the model that describes the collapse (-)transition to compact
polymer-conformations, and calculate the critical exponents to 2-loop order. It
turns out that the long-standing 1-loop results for these exponents are not
entirely correct. A runaway of the RG flow indicates that the so-called
-transition could be a fluctuation induced first order
transition.Comment: 4 page
Multifractal properties of resistor diode percolation
Focusing on multifractal properties we investigate electric transport on
random resistor diode networks at the phase transition between the
non-percolating and the directed percolating phase. Building on first
principles such as symmetries and relevance we derive a field theoretic
Hamiltonian. Based on this Hamiltonian we determine the multifractal moments of
the current distribution that are governed by a family of critical exponents
. We calculate the family to two-loop order in a
diagrammatic perturbation calculation augmented by renormalization group
methods.Comment: 21 pages, 5 figures, to appear in Phys. Rev.
Transport on Directed Percolation Clusters
We study random lattice networks consisting of resistor like and diode like
bonds. For investigating the transport properties of these random resistor
diode networks we introduce a field theoretic Hamiltonian amenable to
renormalization group analysis. We focus on the average two-port resistance at
the transition from the nonpercolating to the directed percolating phase and
calculate the corresponding resistance exponent to two-loop order.
Moreover, we determine the backbone dimension of directed percolation
clusters to two-loop order. We obtain a scaling relation for that is in
agreement with well known scaling arguments.Comment: 4 page
Disentangling The Effects Of Student Attitudes and Behaviors On Academic Performance
The interplay among motivation, ability, attitudes, behaviors, homework, and learning is unclear from previous research. We analyze data collected from 687 students enrolled in seven economics courses. A model explaining homework and exam scores is estimated, and separate analyses of ability and motivation groups are conducted. We find that motivation and ability explain variation in both homework and exam scores. Attitudes and behaviors, such as procrastination and working with others directly, affect homework score, but not exam score. These effects are not the same within all motivation and ability groups. Given that homework is the strongest predictor of exam score, we conclude that graded homework is beneficial to learning, and attitudes and behaviors related to homework may have an indirect benefit for exam performance. Suggestions are made as to how homework and course design might be managed to help students at different ability and motivational levels maximize learning
Random Resistor-Diode Networks and the Crossover from Isotropic to Directed Percolation
By employing the methods of renormalized field theory we show that the
percolation behavior of random resistor-diode networks near the multicritical
line belongs to the universality class of isotropic percolation. We construct a
mesoscopic model from the general epidemic process by including a relevant
isotropy-breaking perturbation. We present a two-loop calculation of the
crossover exponent . Upon blending the -expansion result with
the exact value for one dimension by a rational approximation, we
obtain for two dimensions . This value is in agreement
with the recent simulations of a two-dimensional random diode network by Inui,
Kakuno, Tretyakov, Komatsu, and Kameoka, who found an order parameter exponent
different from those of isotropic and directed percolation.
Furthermore, we reconsider the theory of the full crossover from isotropic to
directed percolation by Frey, T\"{a}uber, and Schwabl and clear up some minor
shortcomings.Comment: 24 pages, 2 figure
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