16,036 research outputs found
From particle segregation to the granular clock
Recently several authors studied the segregation of particles for a system
composed of mono-dispersed inelastic spheres contained in a box divided by a
wall in the middle. The system exhibited a symmetry breaking leading to an
overpopulation of particles in one side of the box. Here we study the
segregation of a mixture of particles composed of inelastic hard spheres and
fluidized by a vibrating wall. Our numerical simulations show a rich
phenomenology: horizontal segregation and periodic behavior. We also propose an
empirical system of ODEs representing the proportion of each type of particles
and the segregation flux of particles. These equations reproduce the major
features observed by the simulations.Comment: 10 page
Phase diagram of a 2D Ising model within a nonextensive approach
In this work we report Monte Carlo simulations of a 2D Ising model, in which
the statistics of the Metropolis algorithm is replaced by the nonextensive one.
We compute the magnetization and show that phase transitions are present for
. A phase diagram (critical temperature vs. the entropic
parameter ) is built and exhibits some interesting features, such as phases
which are governed by the value of the entropic index . It is shown that
such phases favors some energy levels of magnetization states. It is also
showed that the contribution of the Tsallis cutoff is essential to the
existence of phase transitions
The impact of motor symptoms on self-reported anxiety in Parkinson's disease
OBJECTIVE: Anxiety is commonly endorsed in Parkinson's disease (PD) and significantly affects quality of life. The Beck Anxiety Inventory (BAI) is often used but contains items that overlap with common PD motor symptoms (e.g., “hands trembling”). Because of these overlapping items, we hypothesized that PD motor symptoms would significantly affect BAI scores.
METHODS: One hundred non-demented individuals with PD and 74 healthy control participants completed the BAI. PD motor symptoms were assessed by the Unified Parkinson's Disease Rating Scale (UPDRS). Factor analysis of the BAI assessed for a PD motor factor, and further analyses assessed how this factor affected BAI scores.
RESULTS: BAI scores were significantly higher for PD than NC. A five-item PD motor factor correlated with UPDRS observer-rated motor severity and mediated the PD-control difference on BAI total scores. An interaction occurred, whereby removal of the PD motor factor resulted in a significant reduction in BAI scores for PD relative to NC. The correlation between the BAI and UPDRS significantly declined when controlling for the PD motor factor.
CONCLUSIONS: The results indicate that commonly endorsed BAI items may reflect motor symptoms such as tremor instead of, or in addition to, genuine mood symptoms. These findings highlight the importance of considering motor symptoms in the assessment of anxiety in PD and point to the need for selecting anxiety measures that are less subject to contamination by the motor effects of movement disorders.Published versio
Regulation of Synaptic Pumilio Function by an Aggregation-Prone Domain
We identified Pumilio (Pum), a Drosophila translational repressor, in a computational search for metazoan proteins whose activities might be regulated by assembly into ordered aggregates. The search algorithm was based on evolutionary sequence conservation patterns observed for yeast prion proteins, which contain aggregation-prone glutamine/asparagine (Q/N)-rich domains attached to functional domains of normal amino acid composition. We examined aggregation of Pum and its nematode ortholog PUF-9 by expression in yeast. A domain of Pum containing the Q/N-rich sequence, denoted as NQ1, the entire Pum N terminus, and the complete PUF-9 protein localize to macroscopic aggregates (foci) in yeast. NQ1 and PUF-9 can generate the yeast Pin+ trait, which is transmitted by a heritable aggregate. NQ1 also assembles into amyloid fibrils in vitro. In Drosophila, Pum regulates postsynaptic translation at neuromuscular junctions (NMJs). To assess whether NQ1 affects synaptic Pum activity in vivo, we expressed it in muscles. We found that it negatively regulates endogenous Pum, producing gene dosage-dependent pum loss-of-function NMJ phenotypes. NQ1 coexpression also suppresses lethality and NMJ phenotypes caused by overexpression of Pum in muscles. The Q/N block of NQ1 is required for these phenotypic effects. Negative regulation of Pum by NQ1 might be explained by formation of inactive aggregates, but we have been unable to demonstrate that NQ1 aggregates in Drosophila. NQ1 could also regulate Pum by a "dominant-negative" effect, in which it would block Q/N-mediated interactions of Pum with itself or with cofactors required for translational repression
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