Validity of Stokes-Einstein Relation in Soft Colloids up to the Glass Transition

We investigate the dynamics of kinetically frozen block copolymer micelles of different softness across a wide range of particle concentrations, from the fluid to the onset of glassy behavior, through a combination of rheology, dynamic light scattering and pulsed field gradient NMR spectroscopy. We additionally perform Brownian dynamics simulations based on an ultrasoft coarse-grained potential, which are found to be in quantitative agreement with experiments, capturing even the very details of dynamic structure factors S(Q, t) on approaching the glass transition. We provide evidence that for these systems the Stokes-Einstein relation holds up to the glass transition; given that it is violated for dense suspensions of hard colloids, our findings suggest that its validity is an intriguing signature of ultrasoft interactions.Comment: 5 pages, 4 figures, Supplementary Information, Accepted to Physical Review Letters (PRL) (2015

End-to-end vector dynamics of nonentangled polymers in lamellar block copolymer melts: The role of junction point motion

By using dielectric spectroscopy, we investigate the chain dynamics of nonentangled polyisoprene (PI) under soft confinement in lamellar domains of block copolymer melts with polydimethylsiloxane (PDMS). The data show a dramatic difference in the end-to-end vector dynamics of the PI blocks as compared not only with that of the corresponding homopolymer PI chains but also with respect to previous results for the same blocks under soft confinement in cylindrical domains. Two contributions to the dielectric normal mode relaxation are detected. The data are analyzed by means of a model including contributions from internal chain modes (accounting for the fastest component) and a slow component attributed to the junction point dynamics. The contribution of the internal chain modes is modeled according to the analysis of the Rouse modes obtained from simulations of a generic bead-spring model for strongly segregated symmetric diblock copolymers. In this way it is shown that the internal chain modes of the blocks have time scales close to those expected from the homopolymer chain independently of the structural details. In contrast, the contribution attributed to the junction point dynamics depends critically on minor structural differences. We interpret these findings as a result of the presence of fast moving defects and/or grain boundaries in the lamellar structures formed by these relatively short, nonentangled diblock copolymers. © 2013 American Chemical Society.We acknowledge the financial support from Projects MAT2012-31088 (Spanish Government) and IT654-13 (Basque Government).Peer Reviewe

Deficient electron microprobe totals: Discussion of potential causes

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Proyecto Vainica: valoración e intervención nutricional e insuficiencia cardiaca

Desde el comienzo del milenio diversos estudios muestran la “paradoja de la obesidad en pacientes con insuficiencia cardiaca”. Existe una epidemiología inversa: la obesidad predispone para desarrollar enfermedades cardiovasculares e insuficiencia cardiaca, pero un índice de masa corporal elevado mejora la supervivencia a dos y cinco años. Esta paradoja se ha extendido con posterioridad, a otras enfermedades de carácter crónico y ha sido un tema controvertido en la comunidad científica. Posteriormente, diversos estudios han ido migrando la orientación, relacionando el pronóstico no con el índice de masa corporal en sí, sino con el estado nutricional y el adelgazamiento no intencionado. De modo que el foco de interés está ahora en el estado nutricional de los pacientes y no en su índice de masa corporal. El peso –y por tanto el índice de masa corporal- es un parámetro cambiante en los pacientes con insuficiencia cardiaca, ya que por la naturaleza de su patología, pueden presentar un volumen hídrico aumentado y son susceptibles a descompensaciones edemo-asciticas. Los episodios de descompensación son habitualmente tratados con diuréticos, con el objetivo de eliminar el exceso de líquido, lo que hace que el peso fluctúe rápidamente, a expensas de la reducción del exceso de volumen hídrico. No existe consenso o marcador universalmente aceptado para definir la malnutrición. Por ello, coexisten múltiples métodos de cribado y valoración nutricional. No destacándose ninguno como “gold estándar”..

Non-nociceptive roles of opioids in the CNS: opioids' effects on neurogenesis, learning, memory and affect.

Mortality due to opioid use has grown to the point where, for the first time in history, opioid-related deaths exceed those caused by car accidents in many states in the United States. Changes in the prescribing of opioids for pain and the illicit use of fentanyl (and derivatives) have contributed to the current epidemic. Less known is the impact of opioids on hippocampal neurogenesis, the functional manipulation of which may improve the deleterious effects of opioid use. We provide new insights into how the dysregulation of neurogenesis by opioids can modify learning and affect, mood and emotions, processes that have been well accepted to motivate addictive behaviours

Investigating anhedonia in a non-conventional species: Do some riding horses Equus caballus display symptoms of depression?

International audienceInvestigating depression-like conditions in animals is methodologically challenging, but potentially important for welfare. Some riding horses display ‘withdrawn’ states of inactivity and low responsiveness that resemble the reduced engagement with the environment shown by certain depressed patients. To assess whether these animals are experiencing a depression-like state, we investigated anhedonia – the loss of pleasure, a key symptom of human depression – in 20 withdrawn and non-withdrawn horses from the same stable. The time horses spent being withdrawn appeared unrelated to age or sex, but correlated with time devoted to stereotypic behaviour, a possible marker of lifetime stress. Comparison with data collected 5 years earlier also revealed that horses scored as withdrawn then remained significantly likely to display the behaviour. We measured sucrose intake, a classic measure of anhedonia never previously applied to horses. Flavoured sugar blocks, novel to these subjects, were mounted in each stall and weighed 3, 8, 24 and 30 h after provision. We predicted that if affected by depression-like states, the most withdrawn horses would consume the least sucrose. This prediction was met (F1,18 = 4.65, two tailed p = 0.04). This pattern could, however, potentially reflect general appetite levels and/or food neophobia. To control for these confounds, hay consumption was measured over 5 days, as were subjects’ latencies to eat a meal scented with a novel odour. Although low hay consumption and long latencies to eat scented food did predict low sucrose consumption, statistically controlling for these confounds did not eliminate the relationship between being withdrawn and consuming less sucrose (although reducing it to a strong trend): F1,15 = 4.28, two-tailed p = 0.056. These data thus suggest long-lasting depression-like states in certain riding horses, which correlate with stereotypic behaviour and are characterised by anhedonia and bouts of ‘withdrawn’ unresponsiveness

Constraining particle acceleration in Sgr A* with simultaneous GRAVITY, Spitzer, NuSTAR, and Chandra observations

High Energy Astrophysic

Nanoscopic Confinement through Self-Assembly: Crystallization within Micellar Cores Exhibits Simple Gibbs-Thomson Behavior

It is well known that liquids confined to small nanoscopic pores and droplets exhibit thermal behavior very different from bulk samples. Less is known about liquids spontaneously confined through self-assembly into micellar structures. Here we demonstrate, using a very well-defined n-alkyl-poly(ethylene oxide) polymer system with a tunable structure, that n-alkane(s) forming 2–3 nm small micellar cores are affected considerably by confinement in the form of melting point depressions. Moreover, comparing the reduction in melting points, ΔTm, determined through volumetric and calorimetric methods with the micellar core radius, Rc, obtained from small-angle x-ray scattering, we find excellent agreement with the well-known Gibbs-Thomson equation, ΔTm∼R−1c. This demonstrates that the reduced size, i.e., the Laplace pressure, is the dominant parameter governing the melting point depression in micellar systems