622 research outputs found
Variational theory of elastic manifolds with correlated disorder and localization of interacting quantum particles
We apply the gaussian variational method (GVM) to study the equilibrium
statistical mechanics of the two related systems: (i) classical elastic
manifolds, such as flux lattices, in presence of columnar disorder correlated
along the direction (ii) interacting quantum particles in a static
random potential. We find localization by disorder, the localized phase being
described by a replica symmetry broken solution confined to the mode
. For classical systems we compute the correlation function of
relative displacements. In , in the absence of dislocations, the GVM
allows to describes the Bose glass phase. Along the columns the displacements
saturate at a length indicating flux-line localization.
Perpendicularly to the columns long range order is destroyed. We find divergent
tilt modulus and a scaling. Quantum systems
are studied using the analytic continuation from imaginary to real time . We compute the conductivity and find that it behaves at small
frequency as in all dimensions () for
which disorder is relevant. We compute the quantum localization length .
In , where the model also describes interacting fermions in a static
random potential, we find a delocalization transition and obtain analytically
both the low and high frequency behavior of the conductivity for any value of
the interaction. We show that the marginality condition appears as the
condition to obtain the correct physical behavior. Agreement with
renormalization group results is found whenever it can be compared.Comment: 34 pages, REVTeX, no figure
Elastic theory of flux lattices in presence of weak disorder
The effect of disorder on flux lattices at equilibrium is studied
quantitatively in the absence of free dislocations using both the Gaussian
variational method and the renormalization group. Our results for the mean
square relative displacements clarify the nature of the crossovers with
distance. We find three regimes: (i) a short distance regime (``Larkin
regime'') where elasticity holds (ii) an intermediate regime (``Random
Manifold'') where vortices are pinned independently (iii) a large distance,
quasi-ordered regime where the periodicity of the lattice becomes important and
there is universal logarithmic growth of displacements for and
persistence of algebraic quasi-long range translational order. The functional
renormalization group to and the variational method, agree
within on the value of the exponent. In we compute the crossover
function between the three regimes. We discuss the observable signature of this
crossover in decoration experiments and in neutron diffraction experiments on
flux lattices. Qualitative arguments are given suggesting the existence for
weak disorder in of a `` Bragg glass '' phase without free dislocations
and with algebraically divergent Bragg peaks. In both the variational
method and the Cardy-Ostlund renormalization group predict a glassy state below
the same transition temperature , but with different behaviors.
Applications to systems and experiments on magnetic bubbles are
discussed.Comment: 59 pages; RevTeX 3.0; 5 postscript figures uuencode
Particles and fields in fluid turbulence
The understanding of fluid turbulence has considerably progressed in recent
years. The application of the methods of statistical mechanics to the
description of the motion of fluid particles, i.e. to the Lagrangian dynamics,
has led to a new quantitative theory of intermittency in turbulent transport.
The first analytical description of anomalous scaling laws in turbulence has
been obtained. The underlying physical mechanism reveals the role of
statistical integrals of motion in non-equilibrium systems. For turbulent
transport, the statistical conservation laws are hidden in the evolution of
groups of fluid particles and arise from the competition between the expansion
of a group and the change of its geometry. By breaking the scale-invariance
symmetry, the statistically conserved quantities lead to the observed anomalous
scaling of transported fields. Lagrangian methods also shed new light on some
practical issues, such as mixing and turbulent magnetic dynamo.Comment: 165 pages, review article for Rev. Mod. Phy
Predicting range shifts of African apes under global change scenarios
Aim:
Modelling African great ape distribution has until now focused on current or past conditions, while future scenarios remain scarcely explored. Using an ensemble forecasting approach, we predicted changes in taxon-specific distribution under future scenarios of climate, land use and human populations for (1) areas outside protected areas (PAs) only (assuming complete management effectiveness of PAs), (2) the entire study region and (3) interspecies range overlap.
Location:
Tropical Africa.
Methods:
We compiled occurrence data (n = 5,203) on African apes from the IUCN A.P.E.S. database and extracted relevant climate-, habitat- and human-related predictors representing current and future (2050) conditions to predict taxon-specific range change under a best- and a worst-case scenario, using ensemble forecasting.
Results
The predictive performance of the models varied across taxa. Synergistic interactions between predictors are shaping African ape distribution, particularly human-related variables. On average across taxa, a range decline of 50% is expected outside PAs under the best scenario if no dispersal occurs (61% in worst scenario). Otherwise, an 85% range reduction is predicted to occur across study regions (94% worst). However, range gains are predicted outside PAs if dispersal occurs (52% best, 21% worst), with a slight increase in gains expected across study regions (66% best, 24% worst). Moreover, more than half of range losses and gains are predicted to occur outside PAs where interspecific ranges overlap.
Main Conclusions:
Massive range decline is expected by 2050, but range gain is uncertain as African apes will not be able to occupy these new areas immediately due to their limited dispersal capacity, migration lag and ecological constraints. Given that most future range changes are predicted outside PAs, Africa's current PA network is likely to be insufficient for preserving suitable habitats and maintaining connected ape populations. Thus, conservation planners urgently need to integrate land use planning and climate change mitigation measures at all decision-making levels both in range countries and abroad
Altered sensory-weighting mechanisms is observed in adolescents with idiopathic scoliosis
BACKGROUND: Scoliosis is the most common type of spinal deformity. In North American children, adolescent idiopathic scoliosis (AIS) makes up about 90% of all cases of scoliosis. While its prevalence is about 2% to 3% in children aged between 10 to 16 years, girls are more at risk than boys for severe progression with a ratio of 3.6 to 1. The aim of the present study was to test the hypothesis that idiopathic scoliosis interferes with the mechanisms responsible for sensory-reweighting during balance control. METHODS: Eight scoliosis patients (seven female and one male; mean age: 16.4 years) and nine healthy adolescents (average age 16.5 years) participated in the experiment. Visual and ankle proprioceptive information was perturbed (eyes closed and/or tendon vibration) suddenly and then returned to normal (eyes open and/or no tendon vibration). An AMTI force platform was used to compute centre of pressure root mean squared velocity and sway density curve. RESULTS: For the control condition (eyes open and no tendon vibration), adolescent idiopathic scoliosis patients had a greater centre of pressure root mean squared velocity (variability) than control participants. Reintegration of ankle proprioception, when vision was either available or removed, led to an increased centre of pressure velocity variability for the adolescent idiopathic scoliosis patients whereas the control participants reduced their centre of pressure velocity variability. Moreover, in the absence of vision, adolescent idiopathic scoliosis exhibited an increased centre of pressure velocity variability when ankle proprioception was returned to normal (i.e. tendon vibration stopped). The analysis of the sway density plot suggests that adolescent idiopathic scoliosis patients, during sensory reintegration, do not scale appropriately their balance control commands. CONCLUSION: Altogether, the present results demonstrate that idiopathic scoliosis adolescents have difficulty in reweighting sensory inputs following a brief period of sensory deprivation
Space Charge at Nanoscale: Probing Injection and Dynamic Phenomena Under Dark/Light Configurations by Using KPFM and C-AFM
International audienc
Predicting range shifts of African apes under global change scenarios
Aim: Modelling African great ape distribution has until now focused on current or past conditions, while future scenarios remain scarcely explored. Using an ensemble forecasting approach, we predicted changes in taxon-specific distribution under future scenarios of climate, land use and human populations for (1) areas outside protected areas (PAs) only (assuming complete management effectiveness of PAs), (2) the entire study region and (3) interspecies range overlap. Location: Tropical Africa. Methods: We compiled occurrence data (n = 5,203) on African apes from the IUCN A.P.E.S. database and extracted relevant climate-, habitat- and human-related predictors representing current and future (2050) conditions to predict taxon-specific range change under a best- and a worst-case scenario, using ensemble forecasting. Results: The predictive performance of the models varied across taxa. Synergistic interactions between predictors are shaping African ape distribution, particularly human-related variables. On average across taxa, a range decline of 50% is expected outside PAs under the best scenario if no dispersal occurs (61% in worst scenario). Otherwise, an 85% range reduction is predicted to occur across study regions (94% worst). However, range gains are predicted outside PAs if dispersal occurs (52% best, 21% worst), with a slight increase in gains expected across study regions (66% best, 24% worst). Moreover, more than half of range losses and gains are predicted to occur outside PAs where interspecific ranges overlap. Main Conclusions: Massive range decline is expected by 2050, but range gain is uncertain as African apes will not be able to occupy these new areas immediately due to their limited dispersal capacity, migration lag and ecological constraints. Given that most future range changes are predicted outside PAs, Africa\u27s current PA network is likely to be insufficient for preserving suitable habitats and maintaining connected ape populations. Thus, conservation planners urgently need to integrate land use planning and climate change mitigation measures at all decision-making levels both in range countries and abroad
Pathogenic <i>SPTBN1</i> variants cause an autosomal dominant neurodevelopmental syndrome
SPTBN1 encodes ÎČII-spectrin, the ubiquitously expressed ÎČ-spectrin that forms micrometer-scale networks associated with plasma membranes. Mice deficient in neuronal ÎČII-spectrin have defects in cortical organization, developmental delay and behavioral deficiencies. These phenotypes, while less severe, are observed in haploinsufficient animals, suggesting that individuals carrying heterozygous SPTBN1 variants may also show measurable compromise of neural development and function. Here we identify heterozygous SPTBN1 variants in 29 individuals with developmental, language and motor delays; mild to severe intellectual disability; autistic features; seizures; behavioral and movement abnormalities; hypotonia; and variable dysmorphic facial features. We show that these SPTBN1 variants lead to effects that affect ÎČII-spectrin stability, disrupt binding to key molecular partners, and disturb cytoskeleton organization and dynamics. Our studies define SPTBN1 variants as the genetic basis of a neurodevelopmental syndrome, expand the set of spectrinopathies affecting the brain and underscore the critical role of ÎČII-spectrin in the central nervous system
Azospirillum Genomes Reveal Transition of Bacteria from Aquatic to Terrestrial Environments
Fossil records indicate that life appeared in marine environments âŒ3.5 billion years ago (Gyr) and transitioned to terrestrial ecosystems nearly 2.5 Gyr. Sequence analysis suggests that âhydrobacteriaâ and âterrabacteriaâ might have diverged as early as 3 Gyr. Bacteria of the genus Azospirillum are associated with roots of terrestrial plants; however, virtually all their close relatives are aquatic. We obtained genome sequences of two Azospirillum species and analyzed their gene origins. While most Azospirillum house-keeping genes have orthologs in its close aquatic relatives, this lineage has obtained nearly half of its genome from terrestrial organisms. The majority of genes encoding functions critical for association with plants are among horizontally transferred genes. Our results show that transition of some aquatic bacteria to terrestrial habitats occurred much later than the suggested initial divergence of hydro- and terrabacterial clades. The birth of the genus Azospirillum approximately coincided with the emergence of vascular plants on land
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