6,871 research outputs found
Parallels between the dynamics at the noise-perturbed onset of chaos in logistic maps and the dynamics of glass formation
We develop the characterization of the dynamics at the noise-perturbed edge
of chaos in logistic maps in terms of the quantities normally used to describe
glassy properties in structural glass formers. Following the recognition [Phys.
Lett. \textbf{A 328}, 467 (2004)] that the dynamics at this critical attractor
exhibits analogies with that observed in thermal systems close to
vitrification, we determine the modifications that take place with decreasing
noise amplitude in ensemble and time averaged correlations and in diffusivity.
We corroborate explicitly the occurrence of two-step relaxation, aging with its
characteristic scaling property, and subdiffusion and arrest for this system.
We also discuss features that appear to be specific of the map.Comment: Revised version with substantial improvements. Revtex, 8 pages, 11
figure
Beryllium in the Ultra-Lithium-Deficient,Metal-Poor Halo Dwarf, G186-26
The vast majority of low-metal halo dwarfs show a similar amount of Li; this
has been attributed to the Li that was produced in the Big Bang. However, there
are nine known halo stars with T 5900 K and [Fe/H] 1.0 that are
ultra-Li-deficient. We have looked for Be in the very low metallicity star, G
186-26 at [Fe/H] = 2.71, which is one of the ultra-Li-deficient stars. This
star is also ultra-Be deficient. Relative to Be in the Li-normal stars at
[Fe/H] = 2.7, G 182-26 is down in Be by more than 0.8 dex. Of two potential
causes for the Li-deficiency -- mass-transfer in a pre-blue straggler or extra
rotationally-induced mixing in a star that was initially a very rapid rotator
-- the absence of Be favors the blue-straggler hypothesis, but the rotation
model cannot be ruled-out completely.Comment: Accepted for Ap.J. Letters 10 pages, 4 figure
Spontaneous creation of discrete breathers in Josephson arrays
We report on the experimental generation of discrete breather states
(intrinsic localized modes) in frustrated Josephson arrays. Our experiments
indicate the formation of discrete breathers during the transition from the
static to the dynamic (whirling) system state, induced by a uniform external
current. Moreover, spatially extended resonant states, driven by a uniform
current, are observed to evolve into localized breather states. Experiments
were performed on single Josephson plaquettes as well as open-ended Josephson
ladders with 10 and 20 cells. We interpret the breather formation as the result
of the penetration of vortices into the system.Comment: 5 pages, 5 figure
Constructing the Tree-Level Yang-Mills S-Matrix Using Complex Factorization
A remarkable connection between BCFW recursion relations and constraints on
the S-matrix was made by Benincasa and Cachazo in 0705.4305, who noted that
mutual consistency of different BCFW constructions of four-particle amplitudes
generates non-trivial (but familiar) constraints on three-particle coupling
constants --- these include gauge invariance, the equivalence principle, and
the lack of non-trivial couplings for spins >2. These constraints can also be
derived with weaker assumptions, by demanding the existence of four-point
amplitudes that factorize properly in all unitarity limits with complex
momenta. From this starting point, we show that the BCFW prescription can be
interpreted as an algorithm for fully constructing a tree-level S-matrix, and
that complex factorization of general BCFW amplitudes follows from the
factorization of four-particle amplitudes. The allowed set of BCFW deformations
is identified, formulated entirely as a statement on the three-particle sector,
and using only complex factorization as a guide. Consequently, our analysis
based on the physical consistency of the S-matrix is entirely independent of
field theory. We analyze the case of pure Yang-Mills, and outline a proof for
gravity. For Yang-Mills, we also show that the well-known scaling behavior of
BCFW-deformed amplitudes at large z is a simple consequence of factorization.
For gravity, factorization in certain channels requires asymptotic behavior
~1/z^2.Comment: 35 pages, 6 figure
What type of faculty member interacts with what type of firm? Some reasons for the delocalisation of university-industry interaction
33 pages, 6 tables.While there is significant interest in improving university-industry interaction, literature on the university side has tended not to focus on the characteristics of the personnel involved and has largely ignored the issue that there are differences between types of faculty member in their degrees of interaction. This question is especially relevant at regional level, as those faculty members who do interact with industry may show a preference for firms that are larger and technologically superior to those in the region. Most analysts, though, have tended to focus on the national level, particularly on those countries at the forefront of technological innovation. In the absence of any formal theory, we propose a two-step method to formulate the hypothesis that only selected faculty members interact with selected firms. First, we identify the type of faculty member who interacts with firms. Second, we examine whether this type of faculty member interacts with every type of firm. A test sample is drawn from the Valencian Community of Spain, a region with low absorptive capacity, where firms may show undesirable properties for university interaction. The results allow us to challenge the view that certain individual universities may show a higher propensity for interaction once we take into account differences between the individual characteristics of their faculty members. We also claim that in a region like the Valencian Community, faculty members who usually participate in contracts (male, holding an administrative position) do so mainly with larger firms, but not with firms from their own region, where they find lower technological standards. This partly explains the delocalisation of university-industry interaction.I wish to express my gratitude to the Valencian High Consultancy Council in R&D, for providing the funds to carry out this research.Peer reviewe
Replica Symmetry Breaking in the Random Replicant Model
We study the statistical mechanics of a model describing the coevolution of
species interacting in a random way. We find that at high competition replica
symmetry is broken. We solve the model in the approximation of one step replica
symmetry breaking and we compare our findings with accurate numerical
simulations.Comment: 12 pages, TeX, 5 postscript figures are avalaible upon request,
submitted to Journal of Physics A: Mathematical and Genera
The large scale dynamics of the outer heliosphere and the long-term modulation of galactic cosmic rays
The network of cosmic ray observatories reaching across the heliosphere has given new insight into the process of solar modulation, establishing that the decreases occur principally in the outer heliosphere and are produced by interplanetary flow systems; that the hysteresis effects appear to be produced by changes in the rigidity dependence of the diffusion coefficient and that the predicted effects on the cosmic ray gradients associated with the reversal of the solar magnetic field polarity are not observed
Regulatory networks and connected components of the neutral space
The functioning of a living cell is largely determined by the structure of
its regulatory network, comprising non-linear interactions between regulatory
genes. An important factor for the stability and evolvability of such
regulatory systems is neutrality - typically a large number of alternative
network structures give rise to the necessary dynamics. Here we study the
discretized regulatory dynamics of the yeast cell cycle [Li et al., PNAS, 2004]
and the set of networks capable of reproducing it, which we call functional.
Among these, the empirical yeast wildtype network is close to optimal with
respect to sparse wiring. Under point mutations, which establish or delete
single interactions, the neutral space of functional networks is fragmented
into 4.7 * 10^8 components. One of the smaller ones contains the wildtype
network. On average, functional networks reachable from the wildtype by
mutations are sparser, have higher noise resilience and fewer fixed point
attractors as compared with networks outside of this wildtype component.Comment: 6 pages, 5 figure
Extremely Metal-Poor Stars. VII. The Most Metal-Poor Dwarf, CS 22876-032
We report high-resolution, high-signal-to-noise, observations of the
extremely metal-poor double-lined spectroscopic binary CS 22876-032. The system
has a long period : P = 424.7 0.6 days. It comprises two main sequence
stars having effective temperatures 6300 K and 5600 K, with a ratio of
secondary to primary mass of 0.89 0.04. The metallicity of the system is
[Fe/H] = -3.71 0.11 0.12 (random and systematic errors) -- somewhat
higher than previous estimates. We find [Mg/Fe] = 0.50, typical of values of
less extreme halo material. [Si/Fe], [Ca/Fe], and [Ti/Fe], however, all have
significantly lower values, ~ 0.0-0.1, suggesting that the heavier elements
might have been underproduced relative to Mg in the material from which this
object formed. In the context of the hypothesis that the abundance patterns of
extremely metal-poor stars are driven by individual enrichment events and the
models of Woosley and Weaver (1995), the data for CS 22876-032 are consistent
with its having been enriched by a zero-metallicity supernova of mass 30
M. As the most metal-poor near-main-sequence-turnoff star currently
known, the primary of the system has the potential to strongly constrain the
primordial lithium abundance. We find A(Li) (= log(N(Li)/N(H)) + 12.00) = 2.03
0.07, which is consistent with the finding of Ryan et al. (1999) that for
stars of extremely low metallicity A(Li) is a function of [Fe/H].Comment: 27 pages, 9 figures, accepted for publication in The Astrophysical
Journal, Sept. 1, 2000 issu
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