Medida de color de películas de pintura

En este estudio se tiene por objetivo fijar límites de alteración cromática para diferentes colores de esmalte para uso exterior; para ello las películas de dichos materiales fueron expuestas a la intemperie y se envejecieron artificialmente en Weather-Ometer. Se establecieron las variaciones de los índices cromáticos, y de luminosidad $latex \Delta$ a, $latex \Delta$ b, $latex \Delta$ L, para distintos períodos empleando un colorímetro Gardner de alta sensibilidad. Se proponen, a los fines de normalización, los valores máximos de variación que deberían admitirse en los índices cromáticos y de luminosidad.The purpose of this work is to establish the limits of the chromatic alterations in the film of synthetic enamels for exterior use. After normal and accelerated weathering, the alterations in the chromatic and lightness indexes $latex \Delta$ a, $latex \Delta$ b, $latex \Delta$ L were periodically recorded by means of an automatic colorimeter. The maximun values admissibles for the different colors are proposed as a contribution to normalization purposes

Estudio de materiales termoplásticos para demarcación de pavimentos

Se estudió en forma comparativa el comportamiento en servicio de materiales termoplásticos que son empleados en señalización vial, buscando correlacionar resultados en servicio con los obtenidos en ensayos de laboratorio. Las experiencias sobre pavimento se realizaron aplicando las muestras tanto sobre asfalto como sobre hormigón. Las franjas se dispusieron en forma perpendicular a la dirección de desplazamiento de los vehículos, y se inspeccionaron periódicamente a lo largo de los 510 días que duró el estudio. Se logró un mejor comportamiento (mejor adhesión) sobre pavimento asfáltico.In a comparative way it was studied the behaviour of some thermoplastic materials of the domestic production, which are used in road demarcation. It is our purpose to correlate the results in service with that obtained in laboratory tests. The experiments on pavements were done applying the samples on asphalt and concrete. The bands were laid out perpendicularly to the sense of the road. They were periodically examined during the 510 days that the study lasted. The best behaviour and adhesion were obtained with thermoplastics applied on asphaltic pavement

Revestimientos exteriores para viviendas económicas: II. Influencia de los parámetros de composición sobre el comportamiento en servicio

Se han modificado, mediante el empleo de diferentes plas- tificantes, las características de productos comerciales que normalmente presentan defectos de cuarteado por exposición al exterior. De esta manera se logra una durabilidad satisfactoria en lapsos superiores a 24 meses. El plastificante más eficiente es una resina poliéster, que se incorpora en presencia de un agente emulsivo. Se observa que su empleo reduce marcadamente la permeabilidad de la película y mejora la resistencia a la intemperie de la misma.The domestic commercial products for this use tested in a previous work usually had cracking deffects. They were modified using different plasticizers. In this way, an outdoor resistance of more than two years was obtained for some of the samples. The most efficient plasticizer is an alkyd resin which is incorporated in the presence of an emulsive agent. The employ of this plasticizer reduces the film permeability markedly and improves its water resistance

CMOS Receiver Front-End Architecture for High-Speed SI-POF Links

This works presents a new CMOS analog front-end for short-reach high-speed optical communications which compensates the limited bandwidth of POF channels and is suitable for the required large area photodetectorf The proposed pseudo-differential architecture, formed by a preamplifier and an equalizer, has been designed in a standard 0.18-μm CMOS process with a 1-V supply voltage targeting gigabit transmission for NRZ modulation. The preamplifier is based on the flipped voltage follower stage to attain a very low input resistance in order to handle the large phodiode capacitance (3 pF). The equalizer can adjust the high-frequency boosting and the gain, to compensate for the variation of the characteristics of the channel due to length of the fiber, connections, etc. causing subtantial changes of the fiber bandwidth. Reliable electrical models are employed for a Mitsubishi GH SI-POF with 10-m to 50-m length and for a S5972 silicon photodiode from Hamamatsu suitable for such a fiber due to its large diameter (0.8 mm) and responsivity at 650 nm (0.44A/W). The bandwidth of the received signal can be enhanced from 100 MHz to 1.4 GHz and from 300 MHz to 1.4 GHz for a 50-m and 10-m POF respectively. The proposed circuit shows a transimpedance of 41.5 dBΩ while the theoretical sensitivity from noise performance is below -7.5 dBm with a BER = 10-12. The power consumption is below 16 mW from 1-V supply voltage. In conclusion it targets 1.25 Gbps through a 1-mm SI-POF up to 50-m length with a commercial Si PIN photodiode

A time-dependent phenomenological model for cell mechano-sensing

Adherent cells normally apply forces as a generic means of sensing and responding to the mechanical nature of their surrounding environment. How these forces vary as a function of the extracellular rigidity is critical to understanding the regulatory functions that drive important phenomena such as wound healing or muscle contraction. In recognition of this fact, experiments have been conducted to understand cell rigidity-sensing properties under known conditions of the extracellular environment, opening new possibilities for modeling this active behaviour. In this work, we provide a physics-based constitutive model taking into account the main structural components of the cell to reproduce its most significant contractile properties such as the traction forces exerted as a function of time and the extracellular stiffness. This model shows how the interplay between the time-dependent response of the acto-myosin contractile system and the elastic response of the cell components determine the mechano-sensing behaviour of single cells

A time-dependent phenomenological model for cell mechano-sensing

Adherent cells normally apply forces as a generic means of sensing and responding to the mechanical nature of their surrounding environment. How these forces vary as a function of the extracellular rigidity is critical to understanding the regulatory functions that drive important phenomena such as wound healing or muscle contraction. In recognition of this fact, experiments have been conducted to understand cell rigidity-sensing properties under known conditions of the extracellular environment, opening new possibilities for modeling this active behaviour. In this work, we provide a physics-based constitutive model taking into account the main structural components of the cell to reproduce its most significant contractile properties such as the traction forces exerted as a function of time and the extracellular stiffness. This model shows how the interplay between the time-dependent response of the acto-myosin contractile system and the elastic response of the cell components determine the mechano-sensing behaviour of single cells

Degradation of extracellular matrix regulates osteoblast migration: A microfluidic-based study

Bone regeneration is strongly dependent on the capacity of cells to move in a 3D microenvironment, where a large cascade of signals is activated. To improve the understanding of this complex process and to advance in the knowledge of the role of each specific signal, it is fundamental to analyze the impact of each factor independently. Microfluidic-based cell culture is an appropriate technology to achieve this objective, because it allows recreating realistic 3D local microenvironments by taking into account the extracellular matrix, cells and chemical gradients in an independent or combined scenario. The main aim of this work is to analyze the impact of extracellular matrix properties and growth factor gradients on 3D osteoblast movement, as well as the role of cell matrix degradation. For that, we used collagen-based hydrogels, with and without crosslinkers, under different chemical gradients, and eventually inhibiting metalloproteinases to tweak matrix degradation. We found that osteoblast''s 3D migratory patterns were affected by the hydrogel properties and the PDGF-BB gradient, although the strongest regulatory factor was determined by the ability of cells to remodel the matrix

Revestimientos exteriores para viviendas económicas: I. Estudio comparativo de productos de la industria nacional

Se ha estudiado, por medio de ensayos en laboratorio .y en servicio, el comportamiento de revestimientos exteriores para viviendas económicas, las que deben cumplir una óptima relación de calidad a costo. Deben poseer carácter decorativo y/o protector adecuados, sin presentar una alteración significativa de los mismos en servicio. El comportamiento al exterior resulta inferior al de buenas pinturas oleorresinosas o al látex, lo cual podrá estar relacionado con una inadecuada selección de los componentes, o de su relación en las formulaciones.The performance of those coatings has been studied by means of laboratory and service trials. They must fulfill a good quality/cost ratio and have to adequate decorative and protective characteristics without showing alterations in service as fading, checking or cracking. Their behaviour in exterior exposure tests is lower than that obtained with some oleoresinous and latex paints of good quality. This fact may be due to an inadequate selection of the components or to their relation in the formulations

Migration of mineral oil aromatic hydrocarbons (MOAH) from cardboard containers to dry food and prediction tool

This research aimed to study the migration of mineral oil aromatic hydrocarbons (MOAH) from primary carton packages to dry foods, using 16 aromatic hydrocarbons as model substances, covering a wide range of molecular masses and chemical structures. Migration experiments were performed using modified polyphenylene oxide as a food simulant and couscous and polenta as dry foods. The migration tests were carried out to simulate storage at room temperature for long periods and in hot food containers as the worst scenario. Multivariate analysis algorithms were applied to correlate and group the migration of model substances, and a partial least squares regression (PLSR) model was built to predict the worst-case migration. The results showed strong correlations in the migration patterns of the model substances, based on their volatility, food matrix, migration time and temperature. Different behaviour between the migration of the most volatile and the heaviest model substances was observed