1,412 research outputs found
Mechanisms of MĂĽller glial cell morphogenesis
MĂĽller Glia (MG), the radial glia cells of the retina, have spectacular morphologies subserving their enormous functional complexity. As early as 1892, the great neuroanatomist Santiago Ramon y Cajal studied the morphological development of MG, defining several steps in their morphogenesis [1, 2]. However, the molecular cues controlling these developmental steps remain poorly understood. As MG have roles to play in every cellular and plexiform layer, this review discusses our current understanding on how MG morphology may be linked to their function, including the developmental mechanisms involved in MG patterning and morphogenesis. Uncovering the mechanisms governing glial morphogenesis, using transcriptomics and imaging, may provide shed new light on the pathophysiology and treatment of human neurological disorders
Correlated disordered interactions on Potts models
Using a weak-disorder scheme and real-space renormalization-group techniques,
we obtain analytical results for the critical behavior of various q-state Potts
models with correlated disordered exchange interactions along d1 of d spatial
dimensions on hierarchical (Migdal-Kadanoff) lattices. Our results indicate
qualitative differences between the cases d-d1=1 (for which we find nonphysical
random fixed points, suggesting the existence of nonperturbative fixed
distributions) and d-d1>1 (for which we do find acceptable perturbartive random
fixed points), in agreement with previous numerical calculations by Andelman
and Aharony. We also rederive a criterion for relevance of correlated disorder,
which generalizes the usual Harris criterion.Comment: 8 pages, 4 figures, to be published in Physical Review
Universality Class of Thermally Diluted Ising Systems at Criticality
The universality class of thermally diluted Ising systems, in which the
realization of the disposition of magnetic atoms and vacancies is taken from
the local distribution of spins in the pure original Ising model at
criticality, is investigated by finite size scaling techniques using the Monte
Carlo method. We find that the critical temperature, the critical exponents and
therefore the universality class of these thermally diluted Ising systems
depart markedly from the ones of short range correlated disordered systems. Our
results agree fairly well with theoretical predictions previously made by
Weinrib and Halperin for systems with long range correlated disorder.Comment: 7 pages, 6 figures, RevTe
The Health Belief Model Applied to Understanding Diabetes Regimen Compliance
Inadequate adherence to prescribed treatment plans is perhaps the most serious obstacle to achieving success ful therapeutic outcomes, and non compliance by diabetic patients is no exception. This is partly based on pa tients' realization that compliance does not necessarily result in lack of illness. A psychosocial framework for under standing patient compliance is the Health Belief Model, which is based upon the value an individual places on the identified goal and the likelihood that compliance will achieve that goal. This Model has been useful to explain noncompliance, to make an "educa tional diagnosis," and for designing compliance-enhancing interventions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68410/2/10.1177_014572178501100108.pd
Dynamic Scaling in Diluted Systems Phase Transitions: Deactivation trough Thermal Dilution
Activated scaling is confirmed to hold in transverse field induced phase
transitions of randomly diluted Ising systems. Quantum Monte Carlo calculations
have been made not just at the percolation threshold but well bellow and above
it including the Griffiths-McCoy phase. A novel deactivation phenomena in the
Griffiths-McCoy phase is observed using a thermal (in contrast to random)
dilution of the system.Comment: 4 pages, 4 figures, RevTe
Generalized contact process on random environments
Spreading from a seed is studied by Monte Carlo simulation on a square
lattice with two types of sites affecting the rates of birth and death. These
systems exhibit a critical transition between survival and extinction. For
time- dependent background, this transition is equivalent to those found in
homogeneous systems (i.e. to directed percolation). For frozen backgrounds, the
appearance of Griffiths phase prevents the accurate analysis of this
transition. For long times in the subcritical region, spreading remains
localized in compact (rather than ramified) patches, and the average number of
occupied sites increases logarithmically in the surviving trials.Comment: 6 pages, 7 figure
He Scattering from Compact Clusters and from Diffusion-Limited Aggregates on Surfaces: Observable Signatures of Structure
The angular intensity distribution of He beams scattered from compact
clusters and from diffusion limited aggregates, epitaxially grown on metal
surfaces, is investigated theoretically. The purpose is twofold: to distinguish
compact cluster structures from diffusion limited aggregates, and to find
observable {\em signatures} that can characterize the compact clusters at the
atomic level of detail. To simplify the collision dynamics, the study is
carried out in the framework of the sudden approximation, which assumes that
momentum changes perpendicular to the surface are large compared with momentum
transfer due to surface corrugation. The diffusion limited aggregates on which
the scattering calculations were done, were generated by kinetic Monte Carlo
simulations. It is demonstrated, by focusing on the example of compact Pt
Heptamers, that signatures of structure of compact clusters may indeed be
extracted from the scattering distribution. These signatures enable both an
experimental distinction between diffusion limited aggregates and compact
clusters, and a determination of the cluster structure. The characteristics
comprising the signatures are, to varying degrees, the Rainbow, Fraunhofer,
specular and constructive interference peaks, all seen in the intensity
distribution. It is also shown, how the distribution of adsorbate heights above
the metal surface can be obtained by an analysis of the specular peak
attenuation. The results contribute to establishing He scattering as a powerful
tool in the investigation of surface disorder and epitaxial growth on surfaces,
alongside with STM.Comment: 41 pages, 16 postscript figures. For more details see
http://www.fh.huji.ac.il/~dan
Universal Critical Behavior of Aperiodic Ferromagnetic Models
We investigate the effects of geometric fluctuations, associated with
aperiodic exchange interactions, on the critical behavior of -state
ferromagnetic Potts models on generalized diamond hierarchical lattices. For
layered exchange interactions according to some two-letter substitutional
sequences, and irrelevant geometric fluctuations, the exact recursion relations
in parameter space display a non-trivial diagonal fixed point that governs the
universal critical behavior. For relevant fluctuations, this fixed point
becomes fully unstable, and we show the apperance of a two-cycle which is
associated with a novel critical behavior. We use scaling arguments to
calculate the critical exponent of the specific heat, which turns out
to be different from the value for the uniform case. We check the scaling
predictions by a direct numerical analysis of the singularity of the
thermodynamic free-energy. The agreement between scaling and direct
calculations is excellent for stronger singularities (large values of ). The
critical exponents do not depend on the strengths of the exchange interactions.Comment: 4 pages, 1 figure (included), RevTeX, submitted to Phys. Rev. E as a
Rapid Communicatio
Excess Spin and the Dynamics of Antiferromagnetic Ferritin
Temperature-dependent magnetization measurements on a series of synthetic
ferritin proteins containing from 100 to 3000 Fe(III) ions are used to
determine the uncompensated moment of these antiferromagnetic particles. The
results are compared with recent theories of macroscopic quantum coherence
which explicitly include the effect of this excess moment. The scaling of the
excess moment with protein size is consistent with a simple model of finite
size effects and sublattice noncompensation.Comment: 4 pages, 3 Postsript figures, 1 table. Submitted to PR
The effect of rare regions on a disordered itinerant quantum antiferromagnet with cubic anisotropy
We study the quantum phase transition of an itinerant antiferromagnet with
cubic anisotropy in the presence of quenched disorder, paying particular
attention to the locally ordered spatial regions that form in the Griffiths
region. We derive an effective action where these rare regions are described in
terms of static annealed disorder. A one loop renormalization group analysis of
the effective action shows that for order parameter dimensions the rare
regions destroy the conventional critical behavior. For order parameter
dimensions the critical behavior is not influenced by the rare regions,
it is described by the conventional dirty cubic fixed point. We also discuss
the influence of the rare regions on the fluctuation-driven first-order
transition in this system.Comment: 6 pages RevTe
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