Microstructural model for cyclic hardening in F-actin networks crosslinked by α-actinin

open2siThe rheology of F-actin networks has attracted a great attention during the last years. In order to gain a complete understanding of the rheological properties of these novel materials, it is necessary the study in a large deformations regime to alter their internal structure. In this sense, Schmoller et al. (2010) showed that the reconstituted networks of F-actin crosslinked with α-actinin unexpectedly harden when they are subjected to a cyclical shear. This observation contradicts the expected Mullins effect observed in most soft materials, such as rubber and living tissues, where a pronounced softening is observed when they are cyclically deformed. We think that the key to understand this stunning effect is the gelation process. To define it, the most relevant constituents are the chemical crosslinks - α-actinin -, the physical crosslinks - introduced by the entanglement of the semiflexible network - and the interaction between them. As a consequence of this interaction, a pre-stressed network emerges and introduces a feedback effect, where the pre-stress also regulates the adhesion energy of the α-actinin, setting the structure in a metastable reference configuration. Therefore, the external loads and the evolvement of the trapped stress drive the microstructural changes during the cyclic loading protocol. In this work, we propose a micromechanical model into the framework of nonlinear continuum mechanics. The mechanics of the F-actin filaments is modelled using the wormlike chain model for semiflexible filaments and the gelation process is modelled as mesoscale dynamics for the α-actinin and physical crosslink. The model has been validated with reported experimental results.López-Menéndez, Horacio; Rodríguez, José FélixLópez Menéndez, Horacio; RODRIGUEZ MATAS, JOSE FELI

Imagen molecular en medicina

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Limitaciones tecnológicas de la tomografía por emisión de positrones (PET) para pequeños animales de laboratorio

La visualización y cuantificación de la función de determinados órganos en animales de laboratorio mediante PET está demostrando ser una herramienta de gran relevancia para la caracterización del fenotipo de animales transgénicos y noqueados, en el estudio de modelos de enfermedades humanas, así como para el descubrimiento y desarrollo de nuevos medicamentos y sondas bioquímicas. Para poder utilizar la PET en animales de laboratorio de un modo análogo al que se aplica en humanos es necesario contemplar el factor de escala en el tamaño del vóxel así como mantener una similar estadística de contaje. En este trabajo se apuntan los problemas que estos requerimientos representan tanto para el diseño técnico de los tomógrafos como para la realización de los experimentos, y desde esta perspectiva se analizan las soluciones tecnológicas más relevantes. Finalmente, se comentan brevemente algunas características de sistemas disponibles hoy comercialmente (microPET y FOCUS, HiDAC, eXplore VISTA, MOSAIC, YAP-(S)PET y rPET)Publicad

Effects of the super bialkali photocathode on the performance characteristics of a position-sensitive depth-of-interaction PET detector module

Proceeding of: IEEE Nuclear Science Symposium Conference. NNS 2008, Dresden, Germany, Oct. 19-25, 2008Super Bialkali (SBA) and Ultra Bialkali (UBA) photocathodes are new technologies that improve the spectral response characteristics of position sensitive PMTs, boosting their quantum efficiency up to 35% and 43% (typ.) respectively [ref Hamamatsu]. Two SBA tubes were introduced into a production line of PET detectors mixed with the regular ones. The detectors were assembled on the same day and by the same operator using the standard factory protocols for detector mounting, calibration and testing. In this work we are reporting our evaluation of the achieved improvement by comparing the spatial and energy resolutions and the depth of-interaction performance of a PET detector modules with DOI capabilities assembled using the regular and the SBA versions of the same PS-PMT. We conclude that the superior performance of the SBA tube may enable the use of arrays with a larger number of crystals of smaller footprint, thus improving the detector intrinsic spatial resolution without degrading the energy resolution or the phoswich discrimination capabilityThis work was supported in part by the CENIT Programme (Ministerio de Industria), CIBER CB07/09/0031, RETIC-RECAVA (Ministerio de Sanidad y Consumo), and TEC2007-64731/TCM (Ministerio de Educación y Ciencia

Modification of the TASMIP x-ray spectral model for the simulation of microfocus x-ray sources

The availability of accurate and simple models for the estimation of x-ray spectra is of great importance for system simulation, optimization, or inclusion of photon energy information into data processing. There is a variety of publicly available tools for estimation of x-ray spectra in radiology and mammography. However, most of these models cannot be used directly for modeling microfocus x-ray sources due to differences in inherent filtration, energy range and/or anode material. For this reason the authors propose in this work a new model for the simulation of microfocus spectra based on existing models for mammography and radiology, modified to compensate for the effects of inherent filtration and energy range.The research was supported by the Innovative Medicines Initiative Joint Undertaking under Grant Agreement No. 115337, which comprises financial contributions from the European Union’s Seventh Framework Programme (FP7/2007-2013) and EFPIA companies’ in kind contribution. This work was also partially funded by the AMIT project (CEN-20101014) from the CDTI-CENIT program, projects TEC2010-21619-C04-01, TEC2011-28972-C02-01, and PI11/00616 from the Spanish Ministerio de Ciencia e Innovación. A. Sisniega is funded by an FPU grant from the Spanish Ministerio de Educación.Publicad

Waking-like Brain Function in Embryos

Background: Experience-dependent plastic changes in the brain underlying complex forms of learning are generally initiated when organisms are awake, and this may limit the earliest developmental time at which learning about external events can take place. It is not known whether waking-like brain function is present prenatally in higher vertebrate (bird or mammal)embryos, or whether embryos have brain circuitry that can selectively turn on a waking-like state in response to salient external sensory stimulation. Results: Combining submillimeter-resolution brain positron emission tomography (PET), structural X-ray computed tomography (CT) of the skeleton for fine-scale embryo aging, and noninvasive behavioral recording of chicken embryos in the egg revealed unexpectedly wide variation in prenatal brain activity, inversely related to behavioral activity, which developed into different sleep-like fetal brain states. Brief prenatal exposure to a salient chicken vocalization (eliciting strong postnatal behavioral responses) increased higher-brain activity significantly more than a spectrally and temporally matching ‘‘nonvocal’’ noise analog. Patterns of correlated activity between the brainstem and higher-brain areas resembling awake, posthatching animals were seen exclusively in chicken-stimulated embryos. Conclusions: Waking-like brain function is present in a latent but inducible state during the final 20% of embryonic life, selectively modulated by context-dependent monitoring circuitry. These data also reveal the developmental emergence of sleep-like behavior and its linkage to metabolic brain states and highlight problems with assigning embryo brain states based on behavioral observations.Fundación BBVA, Cátedra de Biomedicina (Spain)National Science and Engineering Research Council of CanadaCanadian Fund for InnovationScuola Internazionale Superiore di Studi Avanzati (Trieste, Italia)En prens

Full 3D-OSEM reconstruction with compressed response of the system

Proceeding of: Nuclear Science Symposium Conference Record, 2004 IEEE, Rome ,16-22 Oct. 2004Small animal PET scanners require high spatial resolution (< 1 mm) and good sensitivity. To obtain high resolution images, iterative reconstruction methods, like OSEM, applied to image reconstruction in three-dimensional (3D) positron emission tomography (PET), have superior performance over analytical reconstruction algorithms like FBP. However, the high computational cost of iterative methods remains a serious drawback to their development and clinical routine use. The increase in performance of current computers should make iterative image reconstruction fast enough to attain clinical viability. However, dealing with the large number of probability coefficients for the response of the system in high-resolution PET scanners becomes a difficult task that prevents the algorithms from reaching peak performance. Taking into account all possible axial, in-plane and other symmetries, we have reduced the storage needs what allows us to store the whole response of the system in dynamic memory of ordinary industry standard computers, so that the reconstruction algorithm can achieve near peak performance

Corrección de atenuación de imágenes PET usando datos de TAC en el escáner para animales pequeños Argus PET/CT

Actas de: XXVIII Congreso Anual de la Sociedad Española de Ingeniería Biomédica (CASEIB 2010). Madrid, 24-26 de noviembre de 2010.Existen diversos efectos físicos que degradan la calidad de la imagen PET, como por ejemplo la atenuación que sufren los fotones al atravesar el cuerpo en estudio. Este efecto reduce el número de fotones detectados, pero puede corregirse si se dispone de información anatómica del objeto. En este trabajo se describe la corrección de atenuación basada en una imagen TAC para el escáner de animales pequeños Argus PET/CT con imágenes PET reconstruidas con el algoritmo iterativo 3DOSEM.Este trabajo ha sido financiado en parte por el MEC (FPA2007-62216), la UCM (Grupos UCM, 910059), el CPAN (Consolider-Ingenio 2010, CSPD-2007-00042), la red RECAVA-RETIC el proyecto ARTEMIS (S2009/DPI-1802, Fondo Europeo de Desarrollo Regional), el proyecto ENTEPRASE (PSE-300000-2009-5, MICINN. España), por los proyectos del Ministerio de Ciencia e Innovación, TEC2007-64731, TEC 2008-06715-C02-1, la RETIC-RECAVA del Ministerio de Sanidad y Consumo, y el proyecto EU FP7 FMT-XCT-201792.Publicad

Corresponsabilidad familiar : negociación e intercambio en la división del trabajo doméstico

En el presente artículo, mostramos los resultados de una investigación cualitativa realizada en el Principado de Asturias para conocer el reparto de tareas domésticas en las familias asturianas. A través del uso de grupos de discusión, analizamos las actitudes, las preferencias y las creencias que poseen hombres y mujeres acerca de la corresponsabilidad familiar. Además, también analizamos en qué medida están marcadas por el estereotipo de género. Si bien aquí no presentamos, de forma exhaustiva, todas las conclusiones obtenidas, exponemos los resultados referidos a los procesos de negociación que dominan el reparto de funciones y responsabilidades familiares.This paper presents the results of a qualitative research study in the Principality of Asturias on current sharing of domestic tasks in Asturian families. Using focus groups, we show men and women's attitudes, preferences, and beliefs about family shared responsibilities. We also analyze to what extent those attitudes are influenced by gender stereotypes. Although we do not present exhaustively all the findings of the research, we discuss specific conclusions about negotiation and exchange processes that dominate the sharing of domestic labor