Fluidization and Active Thinning by Molecular Kinetics in Active Gels

We derive the constitutive equations of an active polar gel from a model for the dynamics of elastic molecules that link polar elements. Molecular binding kinetics induces the fluidization of the material, giving rise to Maxwell viscoelasticity and, provided that detailed balance is broken, to the generation of active stresses. We give explicit expressions for the transport coefficients of active gels in terms of molecular properties, including nonlinear contributions on the departure from equilibrium. In particular, when activity favors linker unbinding, we predict a decrease of viscosity with activity - active thinning - of kinetic origin, which could explain some experimental results on the cell cortex. By bridging the molecular and hydrodynamic scales, our results could help understand the interplay between molecular perturbations and the mechanics of cells and tissues.Comment: 6 pages, 2 figure

Les campanyes de vacunació front al virus de la grip aviària, són eficaces?

Durant les últimes dècades s'han detectat brots de grip aviària causants d'una elevada mortalitat en aus, tant domèstiques com salvatges. La presència de virus de la influença (o grip) aviària d'alta patogenicitat (IAAP) suposa un risc elevat per l'economia i per la sanitat animal i humana. Per intentar prevenir i/o controlar futures epidèmies cal disposar de programes de control i vigilància del virus i de campanyes de vacunació adequades. Un estudi publicat recentment a la revista Clinical and Vaccine Immunology en el que han participat investigadors del Centre de Recerca en Sanitat Animal (CReSA), ha permès avaluar l'èxit de les campanyes de vacunació dutes a terme entre el 2006 i el 2008. Les dades es van recopilar dins un programa coordinat per l'Asociación Ibérica de Zoos y Acuarios i el Ministerio de Medio Ambiente y Medio Rural y Marino per avaluar l'eficàcia de la vacunació.Several avian influenza outbreaks have been reported to be responsible of high mortality in both domestic and wild birds. Highly pathogenic avian influenza (HPAI) viruses are a threat to the economy and animal and human health. Vaccination campaigns, together with good surveillance programs, are an important key to prevent and control future outbreaks. Researchers from Centre de Recerca en Sanitat Animal (CReSA) participated in a study published in Clinical and Vaccine Immunology with the objective to evaluate two vaccination campaigns carried out between 2006 and 2008. Data were collected during a program coordinated by the Iberic Association of Zoos and Aquariums (Asociación Ibérica de Zoos y Acuarios) and the Spanish Government to assess the efficacy of vaccination.Durante las últimas décadas se han detectado brotes de gripe aviar causantes de una elevada mortalidad en aves, tanto domésticas como salvajes. La presencia de virus de la influenza (o gripe) aviar de alta patogenicidad (IAAP) supone un riesgo elevado para la economía y para la sanidad animal y humana. Para intentar prevenir y / o controlar futuras epidemias es necesario disponer de programas de control y vigilancia del virus y de campañas de vacunación adecuadas. Un estudio publicado recientemente en la revista Clinical and Vaccine Immunology en el que han participado investigadores del Centro de Investigación en Sanidad Animal (CReSA), ha permitido evaluar el éxito de las campañas de vacunación llevadas a cabo entre 2006 y 2008. Los datos se recopilaron en un programa coordinado por la Asociación Ibérica de Zoos y Acuarios y el Ministerio de Medio Ambiente y Medio Rural y Marino para evaluar la eficacia de la vacunación

Resposta immunològica a la influença tipus A

Júlia Vergara Alert va defensar al CReSA-UAB el seu treball de tesi doctoral titulat "Immune response to influenza infection and vaccination", dirigit pel Dr. Ayub Darji. El principal objectiu d'aquesta tesi va ser estudiar la resposta immunològica causada per la infecció amb el virus de la influença tipus A (VIA) en models animals, amb l'objectiu final de dissenyar una vacuna front el VIA.Julia Vergara Alert defendió en el CReSA-UAB su trabajo de tesis doctoral titulado "Inmune Response to influenza infection and vaccination", dirigido por el Dr. Ayub Darji. El principal objetivo de esta tesis fue estudiar la respuesta inmunológica causada por la infección con el virus de la influenza tipo A (VIA) en modelos animales, con el objetivo final de diseñar una vacuna frente el VIA

Optimal portfolio choice with predictability in house prices and transaction costs

We generalize the classic Grossman and Laroque (1990) (GL) model of optimal portfolio choice with housing and transaction costs by introducing predictability in house prices. As in the GL model, agents only move to more expensive (cheaper) houses when their wealth-to-housing ratios reach an optimal lower (upper) boundary. However, in our model, these boundaries are time-varying and depend on the dynamics of the expected growth rate of house prices. We find that households moving to a more expensive house in periods of high expected growth in house prices have significantly lower ex-ante wealth-to-housing ratios than those moving in periods of low expected growth. We also find that the share of wealth invested in risky assets is lower during periods of high expected growth in house prices and that it is higher right before moving during periods of low growth. The main implications of the model are robust to tests using household level data from the PSID and SIPP surveys

Fluidization and active thinning by molecular kinetics in active gels

We derive the constitutive equations of an active polar gel from a model for the dynamics of elastic molecules that link polar elements. Molecular binding kinetics induces the fluidization of the material, giving rise to Maxwell viscoelasticity and, provided that detailed balance is broken, to the generation of active stresses. We give explicit expressions for the transport coefficients of active gels in terms of molecular properties, including nonlinear contributions on the departure from equilibrium. In particular, when activity favors linker unbinding, we predict a decrease of viscosity with activity active thinning of kinetic origin, which could explain some experimental results on the cell cortex. By bridging the molecular and hydrodynamic scales, our results could help understand the interplay between molecular perturbations and the mechanics of cells and tissues

Fatty acid composition of the heterotrophic nanoflagellate Paraphysomonas sp. : influence of diet and de novo synthesis

International audienceWe compared the relative importance of dietary factors versus de novo synthesis in determining the polyunsaturated fatty acid (PUFA) composition of the heterotrophic nanoflagellate Paraphysomonas sp. The flagellate was fed with different mutants of the picocyanobacterial strain Synechocystis PCC6803, which differ in their capability to synthesize specific PUFAs. The desA, desB, and desD genes of Synechocystis PCC6803 encode lipid desaturases at the Δ12, Δ15, and Δ6 positions of 18C fatty acids (FAs), respectively. Thus, the use of desA–, desB–, desD–, and desA–/des D– mutants of Synechocystis PCC6803 as food sources permitted us to provide the heterotrophic flagellate with decreasing levels of unsaturated FAs. In each treatment, Paraphysomonas sp. exhibited the same FA composition pattern, i.e. high levels of 16:0 and 18:1, and significant amounts of 18C PUFAs and long-chain PUFAs such as 20:4(n-6), 20:5(n-3), and 22:6(n-3), which indicated that Paraphysomonas sp. is capable of synthesizing these PUFAs de novo. Results also showed that dietary 18C PUFAs seem to be preferentially accumulated in Paraphysomonas sp. lipids. This demonstrates that heterotrophic protists could play a key role in transferring essential compounds from primary producers to metazoan consumers