402 research outputs found
Successful invaders are better defended: The example of Gracilaria vermiculophylla
To evaluate the importance of anti-herbivore resistance for algal invasion success we compared resistance traits among specimens of the red macroalga Gracilaria vermiculophylla from six native populations in Korea and China and eight invasive populations in Europe and Mexico that were maintained under identical conditions in the laboratory. Herbivorous snails both from the native range (Littorina brevicula) and from the invaded range (Littorina littorea) consumed significantly less of seaweed specimens originating from non-native populations. Metabolome profiling revealed that this preference was correlated with an increased woundactivated production of deterring prostaglandins and hydroxyeicosatetraenoic acids. Thus, invasive
populations of G. vermiculophylla are more strongly defended against challenge by herbivores and other biological enemies that cause local tissue or cell disruption and activate oxylipin production.
Anthropogenic distribution of genotypes adapted to resist elevated feeding pressure probably contributed to the invasion success of this species
Extraction of the Spin Glass Correlation Length
The peak of the spin glass relaxation rate, S(t)=d{-M_{TRM}(t,t_w)}/H/{d ln
t}, is directly related to the typical value of the free energy barrier which
can be explored over experimental time scales. A change in magnetic field H
generates an energy E_z={N_s}{X_fc}{H^2} by which the barrier heights are
reduced, where X_{fc} is the field cooled susceptibility per spin, and N_s is
the number of correlated spins. The shift of the peak of S(t) gives E_z,
generating the correlation length, Ksi(t,T), for Cu:Mn 6at.% and
CdCr_{1.7}In_{0.3}S_4. Fits to power law dynamics, Ksi(t,T)\propto
{t}^{\alpha(T)} and activated dynamics Ksi(t,T) \propto {ln t}^{1/psi} compare
well with simulation fits, but possess too small a prefactor for activated
dynamics.Comment: 4 pages, 4 figures. Department of Physics, University of California,
Riverside, California, and Service de Physique de l'Etat Condense, CEA
Saclay, Gif sur Yvette, France. To appear in Phys. Rev. Lett. January 4, 199
Aging in the Relaxor Ferroelectric PMN/PT
The relaxor ferroelectric
(PbMnNbO)(PbTiO), ,
(PMN/PT(90/10)) is found to exhibit several regimes of complicated aging
behavior. Just below the susceptibility peak there is a regime exhibiting
rejuvenation but little memory. At lower temperature, there is a regime with
mainly cumulative aging, expected for simple domain-growth. At still lower
temperature, there is a regime with both rejuvenation and memory, reminiscent
of spin glasses. PMN/PT (88/12) is also found to exhibit some of these aging
regimes. This qualitative aging behavior is reminiscent of that seen in
reentrant ferromagnets, which exhibit a crossover from a domain-growth
ferromagnetic regime into a reentrant spin glass regime at lower temperatures.
These striking parallels suggest a picture of competition in PMN/PT (90/10)
between ferroelectric correlations formed in the domain-growth regime with
glassy correlations formed in the spin glass regime. PMN/PT (90/10) is also
found to exhibit frequency-aging time scaling of the time-dependent part of the
out-of-phase susceptibility for temperatures 260 K and below. The stability of
aging effects to thermal cycles and field perturbations is also reported.Comment: 8 pages RevTeX4, 11 figures; submitted to Phys. Rev.
A Crash Course on Aging
In these lecture notes I describe some of the main theoretical ideas emerged
to explain the aging dynamics. This is meant to be a very short introduction to
aging dynamics and no previous knowledge is assumed. I will go through simple
examples that allow one to grasp the main results and predictions.Comment: Lecture Notes (22 pages) given at "Unifying Concepts in Glass Physics
III", Bangalore (2004); to be published in JSTA
Aging, rejuvenation and memory phenomena in spin glasses
In this paper, we review several important features of the out-of-equilibrium
dynamics of spin glasses. Starting with the simplest experiments, we discuss
the scaling laws used to describe the isothermal aging observed in spin glasses
after a quench down to the low temperature phase. We report in particular new
results on the sub-aging behaviour of spin glasses. We then discuss the
rejuvenation and memory effects observed when a spin glass is submitted to
temperature variations during aging, from the point of view of both energy
landscape pictures and of real space pictures. We highlight the fact that both
approaches point out the necessity of hierarchical processes involved in aging.
Finally, we report an investigation of the effect of small temperature
variations on aging in spin glass samples with various anisotropies which
indicates that this hierarchy depends on the spin anisotropy.Comment: submitted for the Proceedings of Stat Phys 22, Bangalore (India
Aging, rejuvenation and memory effects in Ising and Heisenberg spin glasses
We have compared aging phenomena in the Fe_{0.5}Mn_{0.5}TiO_3 Ising spin
glass and in the CdCr_{1.7}In_{0.3}S_4 Heisenberg-like spin glass by means of
low-frequency ac susceptibility measurements. At constant temperature, aging
obeys the same ` scaling' in both samples as in other systems.
Investigating the effect of temperature variations, we find that the Ising
sample exhibits rejuvenation and memory effects which are qualitatively similar
to those found in other spin glasses, indicating that the existence of these
phenomena does not depend on the dimensionality of the spins. However,
systematic temperature cycling experiments on both samples show important
quantitative differences. In the Ising sample, the contribution of aging at low
temperature to aging at a slightly higher temperature is much larger than
expected from thermal slowing down. This is at variance with the behaviour
observed until now in other spin glasses, which show the opposite trend of a
free-energy barrier growth as the temperature is decreased. We discuss these
results in terms of a strongly renormalized microscopic attempt time for
thermal activation, and estimate the corresponding values of the barrier
exponent introduced in the scaling theories.Comment: 8 pages, including 6 figure
Invasion success of the seaweed Gracilaria vermiculophylla correlates with low palatability
Differences with respect to anti-herbivore defense were investigated in invasive and native populations of the seaweed Gracilaria vermiculophylla. Specimens from 6 native populations in East Asia and from 8 populations invasive in Europe and the Mexican Pacific coast were maintained under identical conditions and offered to herbivorous snails from both the native range (Littorina brevicula) and Europe (L. littorea) in no-choice feeding assays. L. brevicula consumed in total significantly larger amounts of G. vermiculophylla tissue than did L. littorea. Further, both snail species least consumed the seaweed specimens originating from either non-native populations or from populations native to the Korean East Sea/Sea of Japan. The Korean East Sea/Sea of Japan had previously been identified as putative donor region of all the invasive populations of G. vermiculophylla. Thus, populations in the donor region as well as non-native populations in different invaded realms feature an increased capacity to resist feeding pressure. Differences in nutrient content did not account for the observed patterns of consumption, as palatability and carbon to nitrogen (C:N) ratio were not significantly correlated. Thus, mechanical or chemical defenses or the content of feeding cues influenced the behavior of the snails. We suggest that low palatability contributed to the invasion success of the species
Aging in an infinite-range Hamiltonian system of coupled rotators
We analyze numerically the out-of-equilibrium relaxation dynamics of a
long-range Hamiltonian system of fully coupled rotators. For a particular
family of initial conditions, this system is known to enter a particular regime
in which the dynamic behavior does not agree with thermodynamic predictions.
Moreover, there is evidence that in the thermodynamic limit, when
is taken prior to , the system will never attain true equilibrium.
By analyzing the scaling properties of the two-time autocorrelation function we
find that, in that regime, a very complex dynamics unfolds in which {\em aging}
phenomena appear. The scaling law strongly suggests that the system behaves in
a complex way, relaxing towards equilibrium through intricate trajectories. The
present results are obtained for conservative dynamics, where there is no
thermal bath in contact with the system. This is the first time that aging is
observed in such Hamiltonian systems.Comment: Figs. 2-4 modified, minor changes in text. To appear in Phys. Rev.
Numerical Study on Aging Dynamics in the 3D Ising Spin-Glass Model. II. Quasi-Equilibrium Regime of Spin Auto-Correlation Function
Using Monte Carlo simulations, we have studied isothermal aging of
three-dimensional Ising spin-glass model focusing on quasi-equilibrium behavior
of the spin auto-correlation function. Weak violation of the time translational
invariance in the quasi-equilibrium regime is analyzed in terms of {\it
effective stiffness} for droplet excitations in the presence of domain walls.
Within the range of computational time window, we have confirmed that the
effective stiffness follows the expected scaling behavior with respect to the
characteristic length scales associated with droplet excitations and domain
walls, whose growth law has been extracted from our simulated data. Implication
of the results are discussed in relation to experimental works on ac
susceptibilities.Comment: 18 pages, 6 figure
Non-linear sigma model study of magnetic dephasing in a mesoscopic spin glass
We propose a nonlinear sigma model for the description of quantum transport
in a mesoscopic metallic conductor with magnetic impurities frozen in a spin
glass phase. It accounts for the presence of both the corresponding scalar and
magnetic random potentials. In a spin glass, this magnetic random potential is
correlated between different realizations. As the strength of the magnetic
potential is varied, this model describes the crossover between orthogonal and
unitary universality classes of the nonlinear sigma model. We apply this
technique to the calculations of the correlation of conductance between two
frozen spin configurations in terms of dephasing rates for the usual low energy
modes of weak localization theory.Comment: 6 pages, 2 figure
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