Corrosión de rodillos conductores en líneas de cincado electrolítico

Los rodillos conductores en líneas continuas de cincado electrolítico en medio ácido de chapa laminada en frío presentan luego de determinado periodo de trabajo un fenómeno de deterioro al cual históricamente se le ha asignado un origen corrosivo-erosivo que modifica el aspecto y la rugosidad de su superficie. Este proceso genera un dibujo o mancha que termina transfiriéndose a la chapa cincada causando un defecto cualitativo no apto para cierto tipo de productos de alta calidad superficial. Este trabajo muestra resultados que permiten comprender la naturaleza de este fenómeno. Se presenta también una nueva herramienta capaz de evaluar la aptitud de los materiales de construcción de estos rodillos desde el punto de vista de su resistencia a la corrosión para este uso específico. Finalmente se proponen aleaciones alternativas para mejorar la respuesta en servicio de los rodillos actuales.Centro de Investigación y Desarrollo en Tecnología de Pintura

Corrosion of Conductor Rolls in an Electrogalvanizing Line

Conductor rolls in continuous cold rolled steel strip horizontal acid electrogalvanizing lines after some period of service suffer a surface deterioration that alters its color, aspect and eventually its roughness what is more deleterious to its good performance. The surface degradation finally produce a pattern on the roll surface that is transferred or copied to the electrogalvanized strip surface originating quality defects that could make some level of rejections in high quality products. This process has been historically thought as an erosion-corrosion one. This work shows some interesting results that help in the understanding of the nature of this specific corrosion mechanism. It is also presented a new method capable of evaluate the corrosion resistance of new materials for construction of conductor rolls for this type of industrial process. Finally a comparison of the corrosion resistance of different alloys using this technique was made.Centro de Investigación y Desarrollo en Tecnología de Pintura

Generación de dendritas en borde de chapa durante el electrocincado en medio ácido

Durante el proceso de electrogalvanizado de chapa de acero para industria automotriz, suelen generarse dendritas en los bordes del material. El desprendimiento de las mismas genera defectos superficiales en la etapa de estampado. Se estudió el efecto de las variables de proceso sobre la generación de dendritas, obteniendo depósitos sobre discos de acero, acoplados a un equipo rotante. El diseño de esta novedoso sistema logra reproducir las condiciones fluido dinámicas y de distribución de corriente encontradas en los bordes de chapa en una línea industrial de electrogalvanizado. La velocidad tangencial en el borde exterior del disco se ajustó a las velocidades relativas entre chapa y fluido utilizadas en la industria. Se analizó el efecto de la densidad de corriente, la temperatura y la rugosidad de los bordes. Ambas variables tienen una gran influencia sobre el tamaño y la morfología de las dendritas generadas.Dendritic growth on strip edges during continuous zinc electroplating of flat steel strip for the automotive industry is a well known problem. They produce surface defects during the stamping process. In this work the effect of the electrolytic process variables on dendrites formation is study. Zinc was electrodeposited on rotating steel discs. This new experimental configuration reproduces the hydrodynamic conditions and the current distribution found on the strip edge in an industrial zinc electroplating line. The tangential velocity of the outer edge of the discs was adjusted the same relative speed between strip and fluid used in the industry. The effect of current density, temperature and edge roughness was evaluated. Both variables have a great influence on the size and morphology of the growth dendrites.Centro de Investigación y Desarrollo en Tecnología de Pintura

Dendritic zinc growth on the edges of flat steel strip during electro galvanizing

Dendritic growth on strip edges during continuous zinc electroplating of flat steel strip for the automotive industry is a wellknown problem. They produce surface defects during the stamping process. In this work the effect of the electrolytic process variables on dendrites formation is studied. Zinc was electrodeposited on rotating steel discs. This new experimental configuration reproduces the hydrodynamic conditions and the current distribution found on the strip edge in an industrial zinc electroplating line. The tangential velocity of the outer edge of the discs was adjusted to a value equal to the relative speed between strip and fluid used in the industry. The effect of current density, temperature and edge roughness was evaluated. All these variables have a great influence on the size and morphology of dendrites.Centro de Investigación y Desarrollo en Tecnología de Pintura

Generación de dendritas en borde de chapa durante el electrocincado en medio ácido

Durante el proceso de electrogalvanizado de chapa de acero para industria automotriz, suelen generarse dendritas en los bordes del material. El desprendimiento de las mismas genera defectos superficiales en la etapa de estampado. Se estudió el efecto de las variables de proceso sobre la generación de dendritas, obteniendo depósitos sobre discos de acero, acoplados a un equipo rotante. El diseño de esta novedoso sistema logra reproducir las condiciones fluido dinámicas y de distribución de corriente encontradas en los bordes de chapa en una línea industrial de electrogalvanizado. La velocidad tangencial en el borde exterior del disco se ajustó a las velocidades relativas entre chapa y fluido utilizadas en la industria. Se analizó el efecto de la densidad de corriente, la temperatura y la rugosidad de los bordes. Ambas variables tienen una gran influencia sobre el tamaño y la morfología de las dendritas generadas.Dendritic growth on strip edges during continuous zinc electroplating of flat steel strip for the automotive industry is a well known problem. They produce surface defects during the stamping process. In this work the effect of the electrolytic process variables on dendrites formation is study. Zinc was electrodeposited on rotating steel discs. This new experimental configuration reproduces the hydrodynamic conditions and the current distribution found on the strip edge in an industrial zinc electroplating line. The tangential velocity of the outer edge of the discs was adjusted the same relative speed between strip and fluid used in the industry. The effect of current density, temperature and edge roughness was evaluated. Both variables have a great influence on the size and morphology of the growth dendrites.Centro de Investigación y Desarrollo en Tecnología de Pintura

Evidence of two-electron tunneling interference in Nb/InAs junctions

The impact of junction transparency in driving phase-coherent charge transfer across diffusive semiconductor-superconductor junctions is demonstrated. We present conductivity data for a set of Nb-InAs junctions differing only in interface transparency. Our experimental findings are analyzed within the quasi-classical Green-function approach and unambiguously show the physical processes giving rise to the observed excess zero-bias conductivity.Comment: 10 pages (RevTex), 4 figures (PostScript), accepted for pubblication in Physical Review

Epstein-Barr virus infection and chronic lymphocytic leukemia: a possible progression factor?

Epstein-Barr virus is pathogenically associated with a well defined group of lymphoid and epithelial tumors in which the virus directly drives transformation of infected cells. Recent evidence however indicates that this virus may infect a subpopulation of tumor cells in patients with chronic lymphocytic leukemia (CLL) and EBV infection has been also associated with Richter transformation in a fraction of cases. We herein review available data suggesting a possible role of EBV as a direct or micro-environmental progression factor in a subset of CLL

Sirt1 carboxyl-domain is an ATP-repressible domain that is transferrable to other proteins

Sirt1 is an NAD(+)-dependent protein deacetylase that regulates many physiological functions, including stress resistance, adipogenesis, cell senescence and energy production. Sirt1 can be activated by energy deprivation, but the mechanism is poorly understood. Here, we report that Sirt1 is negatively regulated by ATP, which binds to the C-terminal domain (CTD) of Sirt1. ATP suppresses Sirt1 activity by impairing the CTD's ability to bind to the deacetylase domain as well as its ability to function as the substrate recruitment site. ATP, but not NAD(+), causes a conformational shift to a less compact structure. Mutations that prevent ATP binding increase Sirt1's ability to promote stress resistance and inhibit adipogenesis under high-ATP conditions. Interestingly, the CTD can be attached to other proteins, thereby converting them into energy-regulated proteins. These discoveries provide insight into how extreme energy deprivation can impact Sirt1 activity and underscore the complex nature of Sirt1 structure and regulation