Base excision repair deficient mice lacking the Aag alkyladenine DNA glycosylase

3-methyladenine (3MeA) DNA glycosylases remove 3MeAs from alkylated DNA to initiate the base excision repair pathway. Here we report the generation of mice deficient in the 3MeA DNA glycosylase encoded by the Aag (Mpg) gene. Alkyladenine DNA glycosylase turns out to be the major DNA glycosylase not only for the cytotoxic 3MeA DNA lesion, but also for the mutagenic 1,N6-ethenoadenine (epsilonA) and hypoxanthine lesions. Aag appears to be the only 3MeA and hypoxanthine DNA glycosylase in liver, testes, kidney, and lung, and the only epsilonA DNA glycosylase in liver, testes, and kidney; another epsilonA DNA glycosylase may be expressed in lung. Although alkyladenine DNA glycosylase has the capacity to remove 8-oxoguanine DNA lesions, it does not appear to be the major glycosylase for 8-oxoguanine repair. Fibroblasts derived from Aag -/- mice are alkylation sensitive, indicating that Aag -/- mice may be similarly sensitive.     

ELAN—A computer model for building energy design

A simplified thermal network model (ELAN) is developed for the assessment of thermal comfort and energy consumption for heating and cooling of a building.

Each zone is modelled by a second order network with two temperature nodes which, for a multizone building, are linked by internal transmission and ventilation.

The model can be solved on an hourly basis. ELAN has the flexibility of large models concerning geometry, number of zones, occupancy pattern, ventilation, plant operation and weather data.     

Plastic zone formation around an arresting crack

We have followed the evolution of strain near the tip of an arresting cleavage crack in a pressure vessel steel using a strain gage technique. The measurements were made using a linear array of strain gages located along the intended crack path and 0.65B (B is the specimen thickness) above this plane. the gages were read using instrumentation capable of resolving strain in time intervals of between 2 and 4 s. The results were obtained in a thick plate, large enough that reflected elastic waves did not contribute significantly to the strain records or crack motion during the time interval of interest.To within the resolution of this technique, the gages did not detect plasticity near the rapidly propagating cleavage crack tip. At the instant of arrest, however, the strain gages detected a plastic zone which increased in intensity over a period of several milliseconds. We have interpreted this increasing intensity as an elastic-plastic boundary emanating from the arresting crack tip and eventually reaching an equilibrium size, i.e., that predicted from the applied stress intensity factor and the static plastic properties. A simple analysis is presented to estimate the velocity of this elastic-plastic boundary from the strain data and results are given for several experiments.

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Résumé En utilisant des jauges de contraintes, on a suivi, dans un acier pour capacités sous pression, l'évolution des déformations près de l'extrémité d'une fissure de clivage en cours d'arrêt. Les mesures ont été faites en recourant à une disposition de jauges en ligne, située le long due parcours obligé de la fissure et à une distance de 0.65 × l'épaisseur de l'éprouvette au-dessus du plan de fissuration. Une instrumentation de lecture des indications des jauges permettait de déceler les variations de déformations toutes les 2 à 4 micro-secondes. Les résultats ont été collationnés pour une tôle forte suffisamment grande pour que les contributions des ondes élastiques à l'enregistrement des déformations ou à la croissance de la fissure durant cet intervalle de temps soient peu significatives.Dans les limites de résolution propres à cette technique, il est apparu que les jauges de contraintes ne décelaient pas de plastification près de l'extrémité de la fissure de clivage en cours de propagation rapide. Cependant, au moment de l'arrêt, les jauges détectent la formation d'une zone plastique, dont la taille s'accroît sur un intervalle de plusieurs millisecondes.On a interprété cette croissance en termes d'une frontière élasto-plastique qui émane de l'extrémité de la fissure lorsqu'elle s'arrête, et qui atteint ensuite un état d'équilibre, tel que celui prédit par le facteur d'intensité de contraintes appliqué, et par les propriétés plastiques du matériau en conditions statiques.On présente une analyse simple en vue d'estimer la vitesse de cette frontière élasto-plastique à partir de données de déformations, et des résultats relatifs à plusieurs essais sont fournis.

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National Institute of Standards and Techonology

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National Institute of Standards and Techonology     

Solidification of thermoviscoelastic melts. Part II: Effects of processing conditions on shrinkage and residual stresses

The solidification of a molten layer of thermoplastic between cooled parallel plates is used to model the mechanics of part shrinkage and the buildup of residual stresses in the injection-molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification, so that this model can be used to assess packing-pressure effects in injection molding. Parametric results are presented on the effects of the mold and melt temperatures, the part thickness, and the packing pressure—the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic—on the in-plane and through-thickness shrinkages, and on residual stresses in plaque-like geometries. The packing pressure is shown to have a significant effect on part shrinkage, but a smaller effect on residual stresses. Packing pressure applied later in the solidification cycle has a larger effect. Mold and melt temperatures are shown to have a much smaller effect. The processing parameters appear to affect the through-thickness shrinkage more than the in-plane shrinkage. While the results are presented in terms of normalized variables based on the properties of bisphenol-A polycarbonate, they can be interpreted for other amorphous thermoplastics such as modified polyphenylene oxide, polyetherimide, and acrylonitrile-butadiene-styrene.     

Source localization by gradient estimation based on Poisson integral

We consider the problem of localizing the source of a diffusion process. The source is supposed to be isotropic, and several sensors, equipped on a vehicle moving without position information, provide pointwise measures of the quantity being emitted. The solution we propose is based on computing the gradient–and higher-order derivatives such as the Hessian–from Poisson integrals: in opposition to other solutions previously proposed, this computation does neither require specific knowledge of the solution of the diffusion process, nor the use of probing signals, but only exploits properties of the PDE describing the diffusion process. The theoretical results are illustrated by simulations.     

A filiform corrosion and potentiodynamic polarisation study of some aluminium alloys

The aim of the present investigation is a combined study of filiform corrosion of aluminium alloys by accelerated exposure tests and potentiodynamic polarisation measurements. The accelerated exposure tests are performed on binary Al-Cu, Al-Mg, Al-Si and Al-Zn model alloys, a ternary Al-MgSi alloy and on the two commercial alloys, AA2024-T351 and AA7075-T651, with variations of composition and surface treatments. The surface treatments cover simple degreasing, chromate and cerium based treatments. A trend of a higher filiform corrosion susceptibility with increasing alloying elements concentrations was observed for all model systems. Furthermore, the filiform corrosion susceptibility varies with the solute atom, in particular Cu was found to have a detrimental effect on the filiform corrosion properties. Both chromating and cerating improve the filiform corrosion resistance of the alloys significantly. To explain the trends observed in the exposure tests, polarisation measurements were performed on the untreated Al-Cu and Al-Zn alloys in bulk anolyte and catholyte solutions which are characteristic for the local anodic and cathodic sites in the filaments on the aluminium substrates. From these measurements a filiform corrosion current, defined as the intercept of the anodic and cathodic curves, can be determined. The present set of experiments shows a correlation between the filiform corrosion properties during accelerated exposure tests and the potentiodynamic polarisation measurements for the Al-Cu alloys. When comparing the results for the Al-Cu and Al-Zn binary alloys it can be concluded that the correlation factor differs significantly with the solute atom and the filiform corrosion current proves to be a non-uniquely discriminating parameter for the filiform corrosion susceptibility of the model alloys. The difference in correlation factor for the Al-Cu and Al-Zn alloys is attributed to differences in the electrochemical behaviour of these alloys with local variations in substrate composition. For the Al-Cu and Al-Zn model alloys the filiform corrosion initiation characteristics are related to the passive range and thus implicitly to the ease of pitting of the alloy. A smaller passive range corresponds to a higher filiform site density for both the Al-Cu and Al-Zn alloys.     

Modification of surface finish produced by hard turning using superfinishing and burnishing operations

In this study the surface finish produced by hard turning of a 41Cr4 low-alloy steel quenched to about 60 HRC hardness, using mixed Al₂O₃-TiC ceramic inserts, was subsequently modified by superfinishing and multipass burnishing operations. In the case of hard turning surfaces were produced by conventional and Wiper cutting tool inserts. The main goal of this study was to examine how additional abrasive and non-removal technological operations change 2D and 3D roughness parameters and enhance service properties of the machined surfaces. It was documented that both superfinishing and burnishing operations allow to obtain smoother surfaces with lower surface roughness and better bearing characteristics.