863 research outputs found
Opinion dynamics with emergent collective memory: A society shaped by its own past
In order to understand the development of common orientation of opinions in the modern world we propose a model of a society described as a large collection of agents that exchange their expressed opinions under the influence of their mutual interactions and external events. In particular we introduce an interaction bias which results in the emergence of a collective memory such that the society is able to store and recall information coming from several external signals. Our model shows how the inner structure of the society and its future reactions are shaped by its own history. We provide an analytical explanation of such mechanism and we study the features of external influences with higher impact on the society. We show the emergent similarity between the reaction of a society modelled in this way and the Hopfield-like mechanism of information retrieval in Neural Networks
Patch-repetition correlation length in glassy systems
We obtain the patch-repetition entropy Sigma within the Random First Order
Transition theory (RFOT) and for the square plaquette system, a model related
to the dynamical facilitation theory of glassy dynamics. We find that in both
cases the entropy of patches of linear size l, Sigma(l), scales as s_c l^d+A
l^{d-1} down to length-scales of the order of one, where A is a positive
constant, s_c is the configurational entropy density and d the spatial
dimension. In consequence, the only meaningful length that can be defined from
patch-repetition is the cross-over length xi=A/s_c. We relate xi to the typical
length-scales already discussed in the literature and show that it is always of
the order of the largest static length. Our results provide new insights, which
are particularly relevant for RFOT theory, on the possible real space structure
of super-cooled liquids. They suggest that this structure differs from a mosaic
of different patches having roughly the same size.Comment: 6 page
An experimental study of the behaviour of two rockfills accounting for the effects of degree of saturation
Rockfill dams have become more and more recognized for their safety, economy and adaptability to widely varying site conditions. As a contribution to the understanding of the main factors affecting the rockfill behaviour, the paper reports and discusses experimental data on several aspects relevant to the interpretation and analysis of their in-situ response. The experimental programme involved three series of oedometric tests on specimens of two different gravels having the same grading, reconstituted at the same initial relative density. Experimental observations on rockfills compressibility are presented and discussed: attention is paid to the role of degree of saturation (Sr) through the analysis of "driest", "fully saturated"conditions, and the transition from one to the other. Grain crushing tests on dry and saturated soil particles are also reported. Grain size distributions of the specimens, both after compaction and after the oedometer tests, are compared in the paper. The results show that the effect of Sr cannot be overlooked in the mechanical characterization of the material, especially in rockfill/stress conditions prone to crushin
Pharmacological Findings on the Biochemical Bases of Memory Processes: A General View
We have advanced considerably in the past
2 to 3 years in understanding the molecular
mechanisms of consolidation, retrieval, and
extinction of memories, particularly of fear
memory. This advance was mainly due to
pharmacological studies in many laboratories
using localized brain injections of molecularly
specific substances. One area in which significant
advances have been made is in understanding
that many different brain structures are
involved in different memories, and that often
several brain regions are involved in processing
the same memory. These regions can cooperate
or compete with each other, depending on
circumstances that are beginning to be
identified quite clearly. Another aspect in
which major advances were made was retrieval
and post-retrieval events, especially extinction,
pointing to new therapeutic approaches to fearmotivated
mental disorders
Towards an Achievable Performance for the Loop Nests
Numerous code optimization techniques, including loop nest optimizations,
have been developed over the last four decades. Loop optimization techniques
transform loop nests to improve the performance of the code on a target
architecture, including exposing parallelism. Finding and evaluating an
optimal, semantic-preserving sequence of transformations is a complex problem.
The sequence is guided using heuristics and/or analytical models and there is
no way of knowing how close it gets to optimal performance or if there is any
headroom for improvement. This paper makes two contributions. First, it uses a
comparative analysis of loop optimizations/transformations across multiple
compilers to determine how much headroom may exist for each compiler. And
second, it presents an approach to characterize the loop nests based on their
hardware performance counter values and a Machine Learning approach that
predicts which compiler will generate the fastest code for a loop nest. The
prediction is made for both auto-vectorized, serial compilation and for
auto-parallelization. The results show that the headroom for state-of-the-art
compilers ranges from 1.10x to 1.42x for the serial code and from 1.30x to
1.71x for the auto-parallelized code. These results are based on the Machine
Learning predictions.Comment: Accepted at the 31st International Workshop on Languages and
Compilers for Parallel Computing (LCPC 2018
On the convergence of cluster expansions for polymer gases
We compare the different convergence criteria available for cluster
expansions of polymer gases subjected to hard-core exclusions, with emphasis on
polymers defined as finite subsets of a countable set (e.g. contour expansions
and more generally high- and low-temperature expansions). In order of
increasing strength, these criteria are: (i) Dobrushin criterion, obtained by a
simple inductive argument; (ii) Gruber-Kunz criterion obtained through the use
of Kirkwood-Salzburg equations, and (iii) a criterion obtained by two of us via
a direct combinatorial handling of the terms of the expansion. We show that for
subset polymers our sharper criterion can be proven both by a suitable
adaptation of Dobrushin inductive argument and by an alternative --in fact,
more elementary-- handling of the Kirkwood-Salzburg equations. In addition we
show that for general abstract polymers this alternative treatment leads to the
same convergence region as the inductive Dobrushin argument and, furthermore,
to a systematic way to improve bounds on correlations
Cluster expansion for abstract polymer models. New bounds from an old approach
We revisit the classical approach to cluster expansions, based on tree
graphs, and establish a new convergence condition that improves those by
Kotecky-Preiss and Dobrushin, as we show in some examples. The two ingredients
of our approach are: (i) a careful consideration of the Penrose identity for
truncated functions, and (ii) the use of iterated transformations to bound
tree-graph expansions.Comment: 16 pages. This new version, written en reponse to the suggestions of
the referees, includes more detailed introductory sections, a proof of the
generalized Penrose identity and some additional results that follow from our
treatmen
Abstract polymer models with general pair interactions
A convergence criterion of cluster expansion is presented in the case of an
abstract polymer system with general pair interactions (i.e. not necessarily
hard core or repulsive). As a concrete example, the low temperature disordered
phase of the BEG model with infinite range interactions, decaying polynomially
as with , is studied.Comment: 19 pages. Corrected statement for the stability condition (2.3) and
modified section 3.1 of the proof of theorem 1 consistently with (2.3). Added
a reference and modified a sentence at the end of sec. 2.
Inhibition of interleukin-6-induced matrix metalloproteinase-2 expression and invasive ability of lemon peel polyphenol extract in human primary colon cancer cells
Among matrix metalloproteinases (MMPs), MMP-9/2 are key enzymes involved in the proteolysis of extracellular matrices in the inflammatory process and in cancer. Since MMP-9/2 expression levels, activity, and secretion is up-regulated during inflammation in response to pro-inflammatory cytokines, such as interleukin-6 (IL-6), many efforts have been devoted to identifying factors that could inhibit the IL-6-induced MMP-9/2 expression. Up to now, several reports in-dicated that polyphenols from fruits and vegetables are among the major components of health promotion for their antioxidant properties and also for their anti-inflammatory and anti-cancer agents. Among plant derived polyphenols, lemon (Citrus limon) peel extract (LPE) shows anti-cancer properties in various cancer types. In our previous work, we demonstrated that LPE can reduce IL-6-induced migration/invasiveness and MMP-9/2 up-regulation in some gastric cancer cell lines. This study aims to exploit the anti-cancer properties of LPE using an in vitro system model of inflam-mation, consisting of IL-6-exposed human primary colon cancer cells. We first analyzed the effect of LPE on IL-6-induced cell migration and invasiveness by wound healing and Boyden chamber assay, respectively. The MMP-2 mRNA expression levels and gelatinolytic activity in the cell culture media were determined by q-PCR analysis and gelatin zymography, respectively, and finally, the effects of LPE on IL-6-induced JAK2/STAT3 signaling pathways have been investigated by Western blotting analysis. Our results show that LPE is able to inhibit the IL-6-dependent cell migration and invasiveness associated with the up-regulation of MMP-2 expression levels and that these effects are correlated to the STAT3 phosphorylation in human primary T88 and T93 colon cancer cells
Prior learning of relevant non-aversive information is a boundary condition for avoidance memory reconsolidation in the rat hippocampus
Reactivated memories can be modified during reconsolidation, making this process a potential therapeutic target for post-traumatic stress disorder (PTSD), a mental illness characterized by the recurring avoidance of situations that evoke trauma-related fears. However, avoidance memory reconsolidation depends on a set of still loosely defined boundary conditions, limiting the translational value of basic research. In particular, the involvement of the hippocampus in fear-motivated avoidance memory reconsolidation remains controversial. Combining behavioral and electrophysiological analyses in male Wistar rats, we found that previous learning of relevant non-aversive information is essential to elicit the participation of the hippocampus in avoidance memory reconsolidation, which is associated with an increase in theta and gamma oscillations power and cross-frequency coupling in dorsal CA1 during reactivation of the avoidance response. Our results indicate that the hippocampus is involved in memory reconsolidation only when reactivation results in contradictory representations regarding the consequences of avoidance, and suggest that robust nesting of hippocampal theta-gamma rhythms at the time of retrieval is a specific reconsolidation marker.2018-03-1
- …