From caging to rouse dynamics in polymer melts with intramolecular barriers: a critical test of the mode coupling theory

By means of computer simulations and solution of the equations of the mode coupling theory (MCT),we investigate the role of the intramolecular barriers on several dynamic aspects of nonentangled polymers. The investigated dynamic range extends from the caging regime characteristic of glass-formers to the relaxation of the chain Rouse modes. We review our recent work on this question,provide new results, and critically discuss the limitations of the theory. Solutions of the MCT for the structural relaxation reproduce qualitative trends of simulations for weak and moderate barriers. However, a progressive discrepancy is revealed as the limit of stiff chains is approached. This dis-agreement does not seem related with dynamic heterogeneities, which indeed are not enhanced by increasing barrier strength. It is not connected either with the breakdown of the convolution approximation for three-point static correlations, which retains its validity for stiff chains. These findings suggest the need of an improvement of the MCT equations for polymer melts. Concerning the relaxation of the chain degrees of freedom, MCT provides a microscopic basis for time scales from chain reorientation down to the caging regime. It rationalizes, from first principles, the observed deviations from the Rouse model on increasing the barrier strength. These include anomalous scaling of relaxation times, long-time plateaux, and nonmonotonous wavelength dependence of the mode correlators.

Conceptes, notes i comentaris econòmics sobre la incertesa a mode de vocabulari bàsic i quadre síntètic

Gairebé han passat 20 anys d’ençà que vaig començar a reflexionar sobre la incertesa dela mà del Dr. Dídac Ramírez. Vaig presentar una tesi dirigida per ell l’any 2003, he fetarticles, he presentat comunicacions en seminaris i col·loquis. El tema de la incertesa ésmolt ampli; es relaciona amb el coneixement, l'aleatorietat, el caos, l'ètica, la psicologia,etc. En aquests 20 anys, a poc a poc, he anat lligant alguns caps i, en aquests moments,penso que pot tenir interès presentar al seminari IAFI del Departament de Matemàtiquesde la Facultat d’Econòmiques de la UB un esquema amb aquestes idees lligades enforma de vocabulari.Molts dels termes del vocabulari els proposo jo, per la qual cosa no m’he pogut limitar adonar una definició precisa i he necessitat posar explicacions i exemples per tal dejustificar el seu interès.

Fonder un nouveau mode de redistribution des aides sociales sur une philosophie de la personne?

Cet article présente un nouveau modèle de redistribution des aides sociales en France, le mécanisme de "l'allocation personnelle", fondé sur une nouvelle conception des mutuelles auxquelles est assigné un rôle de redistribution. L'enjeu de ce papier est de mettre en avant les fondements philosophiques qui sous-tendent cette nouvelle conception de la redistribution, en particulier la philosophie personnaliste.

Itinéraire clinique en traumatologie, une mode ou un besoin [Clinical pathway in traumatology, a fashion or need?].

A clinical route is defined as a "set of methods and instruments to members of a multidisciplinary and Interprofessional team to agree on the tasks for a specific patient population. This is a program of care to ensure the provision of quality care and efficient realization". The University Hospital is not immune to this phenomenon. In the Department of the musculoskeletal system, a first project of this kind concerns the fracture of the proximal femur in the elderly.

Entre résistance et contestation. La genèse du squat comme mode d'action

Cette contribution vise plusieurs objectifs théoriques : questionner les implicites du concept de répertoire d'action pour proposer une typification des modes d'action, indiquer des pistes pour une analyse conjointe des répertoires instrumentaux et discursifs mis en oeuvre par les organisations, reconsidérer les ruptures historiques mises au jour par Charles Tilly, et enfin réfléchir aux conditions organisationnelles et contextuelles favorisant l'usage de formes d'actions directes. Elle se fonde empiriquement sur l'étude de la genèse d'un mode d'action spécifique, le squat, entre 1880 et 1914, au moyen d'un travail d'archives et d'un travail d'étymologie. On montre notamment que le passage de la « résistance » à la « contestation », dans laquelle prédomine le « revendiqué », suppose une forme particulière de rapport au politique qui, au début de ce siècle, constituait en soi un enjeu de luttes important entre différents groupes.

Oscillations, phase-of-firing coding, and spike timing-dependent plasticity: an efficient learning scheme

Recent experiments have established that information can be encoded in the spike times of neurons relative to the phase of a background oscillation in the local field potential—a phenomenon referred to as “phase-of-firing coding” (PoFC). These firing phase preferences could result from combining an oscillation in the input current with a stimulus-dependent static component that would produce the variations in preferred phase, but it remains unclear whether these phases are an epiphenomenon or really affect neuronal interactions—only then could they have a functional role. Here we show that PoFC has a major impact on downstream learning and decoding with the now well established spike timing-dependent plasticity (STDP). To be precise, we demonstrate with simulations how a single neuron equipped with STDP robustly detects a pattern of input currents automatically encoded in the phases of a subset of its afferents, and repeating at random intervals. Remarkably, learning is possible even when only a small fraction of the afferents (~10%) exhibits PoFC. The ability of STDP to detect repeating patterns had been noted before in continuous activity, but it turns out that oscillations greatly facilitate learning. A benchmark with more conventional rate-based codes demonstrates the superiority of oscillations and PoFC for both STDP-based learning and the speed of decoding: the oscillation partially formats the input spike times, so that they mainly depend on the current input currents, and can be efficiently learned by STDP and then recognized in just one oscillation cycle. This suggests a major functional role for oscillatory brain activity that has been widely reported experimentally.

The long non-coding RNA NEAT1 is increased in IUGR placentas, leading to potential new hypotheses of IUGR origin/development.

INTRODUCTION: Intrauterine Growth Restriction (IUGR) is a multifactorial disease defined by an inability of the fetus to reach its growth potential. IUGR not only increases the risk of neonatal mortality/morbidity, but also the risk of metabolic syndrome during adulthood. Certain placental proteins have been shown to be implicated in IUGR development, such as proteins from the GH/IGF axis and angiogenesis/apoptosis processes. METHODS: Twelve patients with term IUGR pregnancy (birth weight < 10th percentile) and 12 CTRLs were included. mRNA was extracted from the fetal part of the placenta and submitted to a subtraction method (Clontech PCR-Select cDNA Subtraction). RESULTS: One candidate gene identified was the long non-coding RNA NEAT1 (nuclear paraspeckle assembly transcript 1). NEAT1 is the core component of a subnuclear structure called paraspeckle. This structure is responsible for the retention of hyperedited mRNAs in the nucleus. Overall, NEAT1 mRNA expression was 4.14 (±1.16)-fold increased in IUGR vs. CTRL placentas (P = 0.009). NEAT1 was exclusively localized in the nuclei of the villous trophoblasts and was expressed in more nuclei and with greater intensity in IUGR placentas than in CTRLs. PSPC1, one of the three main proteins of the paraspeckle, co-localized with NEAT1 in the villous trophoblasts. The expression of NEAT1_2 mRNA, the long isoform of NEAT1, was only modestly increased in IUGR vs. CTRL placentas. DISCUSSION/CONCLUSION: The increase in NEAT1 and its co-localization with PSPC1 suggests an increase in paraspeckles in IUGR villous trophoblasts. This could lead to an increased retention of important mRNAs in villous trophoblasts nuclei. Given that the villous trophoblasts are crucial for the barrier function of the placenta, this could in part explain placental dysfunction in idiopathic IUGR fetuses.

Structural Insight into the Mode of Action of a Direct Inhibitor of Coregulator Binding to the Thyroid Hormone Receptor.

The development of nuclear hormone receptor antagonists that directly inhibit the association of the receptor with its essential coactivators would allow useful manipulation of nuclear hormone receptor signaling. We previously identified 3-(dibutylamino)-1-(4-hexylphenyl)-propan-1-one (DHPPA), an aromatic β-amino ketone that inhibits coactivator recruitment to thyroid hormone receptor β (TRβ), in a high-throughput screen. Initial evidence suggested that the aromatic β-enone 1-(4-hexylphenyl)-prop-2-en-1-one (HPPE), which alkylates a specific cysteine residue on the TRβ surface, is liberated from DHPPA. Nevertheless, aspects of the mechanism and specificity of action of DHPPA remained unclear. Here, we report an x-ray structure of TRβ with the inhibitor HPPE at 2.3-Å resolution. Unreacted HPPE is located at the interface that normally mediates binding between TRβ and its coactivator. Several lines of evidence, including experiments with TRβ mutants and mass spectroscopic analysis, showed that HPPE specifically alkylates cysteine residue 298 of TRβ, which is located near the activation function-2 pocket. We propose that this covalent adduct formation proceeds through a two-step mechanism: 1) β-elimination to form HPPE; and 2) a covalent bond slowly forms between HPPE and TRβ. DHPPA represents a novel class of potent TRβ antagonist, and its crystal structure suggests new ways to design antagonists that target the assembly of nuclear hormone receptor gene-regulatory complexes and block transcription.

Block structured dynamics and neuronal coding

When certain control parameters of nervous cell models are varied, complex bifurcation structures develop in which the dynamical behaviors available appear classified in blocks, according to criteria of dynamical likelihood. This block structured dynamics may be a clue to understand how activated neurons encode information by firing spike trains of their action potentials.