Pre-Processing of Integral Images for 3-D Displays

This paper seeks to explore a method to accurately correct geometric distortions caused during the capture of three-dimensional (3-D) integral images. Such distortions are rotational and scaling errors which, if not corrected, will cause banding and moire effects on the replayed image. The method for calculating the angle of deviation in the 3-D Integral Images is based on Hough Transform. It allows detection of the angle necessary for correction of the rotational error. Experiments have been conducted on a number of 3-D integral image samples and it has been found that the proposed method produces results with accuracy of 0.05 deg     

Estimation for discrete Markov random fields observed in Gaussiannoise

A finite state Markov random field is observed in Gaussian noise. Changes of measures are defined under which all random variables of the signal are independent and uniformly distributed over the finite state space and all random variables of the observation are independent and N(0,1). The problem of estimating the most likely signal given the observations is treated in a related form by introducing probabilities over the possible signals     

Effect of vegetable and synthetic fibers on mechanical performance and durability of Metakaolin-based mortars

The use of vegetable fibers has regained interest in different fields. In fact, fibers may represent an alternative to traditional fibers incorporated in building materials, such as polypropylene fibers. Sustainable development requires the adoption of ecofriendly and natural materials. In this approach, using vegetable fibers as reinforcement for cementitious materials represents an interesting option for concrete industry. Thus, this article studies mechanical performances and transfer properties of cementitious mortars reinforced with vegetable fibers. The used fibers were Dis (DS), Alfa (AF), Date palm (DP) and Hemp (HE). They were subjected to prior treatment with calcium hydroxide. The results show that reinforced mortars with vegetable fibers represent a better deformation capacity than the control mortar without fibers; the best bending strength was recorded for hemp and date palm mortars; the addition of vegetable fibers leads to thermal conductivity decrease by 15% for a content of 0.1%. However, greater carbonation depths were recorded for vegetable fibers based mixes. These findings, for us, are promising for the use of vegetable fibers in cementitious materials.     

Novel cell architecture for high performance digit-serial computation

A cell architecture for high performance digit-serial computation is presented. The design of this cell is based on the feedforward of the carry digit, which allows a high level of pipelining to increase the throughput rate. This will give designers greater flexibility in finding the best tradeoff between hardware cost and throughput rate. The effect of the number of pipelining levels on the throughput rate and hardware cost are presented.<>     

Effects of calcium nitrate and triisopropanolamine on the setting and strength evolution of Portland cement pastes

The purpose of this work is to study the effect of using some admixtures such as calcium nitrate and triisopropanolamine on the setting and hardening process of cement pastes at 20°C temperature. Tests were performed on specimens cast from various mixtures prepared with two types of cements. The results indicate that calcium nitrate alone acts as a setting accelerator, but has relatively little beneficial effect on the long term period development of mechanical resistances. Regardless of the cement type used, triisopropanolamine used alone performed well as a hardening accelerator at all ages. The combined addition of calcium nitrate and triisopropanolamine produced at very early age significant and promising results with respect to both setting and hardening acceleration. Continuous compressive strength increase was observed with time.     

Combined effect of chemical nature and fineness of mineral powders on Portland cement hydration

This paper focuses on the influence of the chemical nature and the fineness of the fillers on the hydration process and on the compressive strength development. Four different types of fillers are considered in combination with Portland cement: quartzite filler, alumina filler, limestone filler, and silica fume. The study deals with blended mortars having a 0.45 water to powder (cement and filler) ratio with a 10% substitution of cement by filler. Quartzite fillers do not seem to accelerate the hydration process in a significant way. No positive effect is noticed on the strength development either. The presence of a fine inert alumina powder increases the rate of early hydration of Portland cement. The greater the fineness, the faster the rate of hydration heat development. This reactivity leads to an increase in the compressive strength at early age for mortar containing the finest alumina powders. In case of coarse alumina powder, no acceleration effect is obtained. Finely ground limestone (calcite) fillers promote heterogeneous nucleation of hydrates which significantly accelerates hydration. At early age, this also results in an increased mortar compressive strength in comparison with the control mortar. From the obtained results, it is clear that both chemical natures as well as fineness are important with regard to the accelerating effect of the hydration process. With increasing fineness, the accelerating effect increases. For powders with comparable fineness, it is clear that limestone powder has a more significant accelerating effect than silica fume and alumina filler. Quartzite filler seems to have no significant effect.     

Six-bit DPCM video signal processing and implementation using systolic arrays

A novel approach to increase the speed and reduce the hardware requirement of 2-D systolic convolvers for real-time video signal/image processing is proposed. This is achieved by coding video signals/images more efficiently using six-bit 1-D DPCM coding. It is shown that using six-bit differential pulse-code modulation processing results in a 57% improvement in speed and a significant saving in the cost of 2-D systolic convolvers. The effect of quantisation errors on DPCM image convolution is also presented.<>     

Analyse des effets thermiques sur le comportement mécanique des bétons destinés aux revêtements de tunnels

Résumé Le problème de la fissuration des revêtements de tunnels en béton non armé, notamment en l'absence de causes externes est étroitement lié aux caractéristiques physico-chimiques du matériau. La connaissance de la cinétique d'hydratation du béton, à partir d'essais quasi-adiabatiques, nous a permis de déterminer le terme source de l'équation classique de Fourier pour le transfert de la chaleur. La résolution de celle-ci se fait à l'aide du module Texo qui simule d'une manière satisfaisante les champs de températures se développant au cours de la fabrication des pièces en béton. La détermination de ces champs de températures nous a conduit à localiser les zones à fortes élévations de température. A partir d'une loi de comportement thermo-élastique vieillissante, nous déterminons les contraintes qui en résultent. Le résultat, en terme de contraintes, fait appara?tre que la fissuration transversale des revêtements de tunnels en béton non armé est pratiquement inéluctable et surtout qu'elle est traversante. L'ouverture de ces fissures est notamment dépendante de la présence ou non des hors profils géométriques et du dosage en ciment du béton.

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Summary The use of an unreinforced sectional concrete lining in rock excavated tunnels presently appears to be technically and economically appropriate for ensuring good stability and effective operation. However, this type of structure suffers from systematic crack formation. In the absence of external loads, cracking in this type of lining is closely related to the physico-chemical characteristics of the material and to the environment in which this material is ageing. The phenomenon is worsened by conditions particular to tunnels, viz., on the one hand, the strains hindered by the surrounding ground, and on the other the pre-cast invert; also, the presence of geometric overbreaks can lead to variations in the lining thickness. The importance of the heat and hydration gradients resulting from the above phenomena is demonstrated by field tests. Numerical simulations based on laboratory tests let us assess the resulting stresses. (i) Practically unavoidable transverse crack formation can result from the effects of heat. The width of this type of crack and the frequency depend especially on the outer shape and on the proportion of cement in the concrete. (ii) Surface skin cracking can occur, resulting from the effects of hydration. Checks made in the tunnels investigated revealed the cracks expected from our computations. However, these results, in terms of thermal stresses, should not be overestimated especially bearing in mind the numerical model currently used, which does not consider creep effects during the setting and initial hardening of the concrete.