Influence of dentin cavity surface finishing on micro-tensile bond strength of adhesives

The current trend toward minimal-invasive dentistry has introduced innovative techniques for cavity preparation. Chemical vapor deposition (CVD) and laser-irradiation technology have been employed as an alternative to the common use of regular burs in high-speed turbines. Objectives. The purpose of this study was to assess the influence of alternative techniques for cavity preparation on the bonding effectiveness of different adhesives to dentin, and to evaluate the morphological characteristics of dentin prepared with those techniques. Methods. One etch&rinse adhesive (OptiBond FL, Kerr) and three self-etch systems (Adper Prompt L-Pop, 3M ESPE; Clearfil SE Bond, Kuraray; Clearfil S3 Bond, Kuraray) were applied on dentin prepared with a regular bur in a turbine, with a CVD bur in a turbine, with a CVD tip in ultrasound and with an ErCr:YSGG laser. The micro-tensile bond strength (mu TBS) was determined after storage in water for 24 h at 37 degrees C, and morphological evaluation was performed by means of field -emission -gun scanning electron microscopy (Feg-SEM). Results. Feg-SEM evaluation revealed different morphological features on the dentin surface after the usage of both the conventional and alternative techniques for cavity preparation, more specifically regarding smear-layer thickness and surface roughness. CVD bur-cut, CVD ultra-sonoabraded and laser-irradiated dentin resulted in lower mu TBSs than conventionally bur-cut dentin, irrespective of the adhesive employed. Significance. The techniques, such as CVD diamond-bur cutting, CVD diamond ultra-sonoabrasion and laser-irradiation, used for cavity preparation may affect the bonding effectiveness of adhesives to dentin, irrespective of their acidity or approach. (C) 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Reappraisal of the effective elastic thickness for the sub-Andes using 3-D finite element flexural modelling, gravity and geological constraints

P>Estimates of effective elastic thickness (T(e)) for the western portion of the South American Plate using, independently, forward flexural modelling and coherence analysis, suggest different thermomechanical properties for the same continental lithosphere. We present a review of these T(e) estimates and carry out a critical reappraisal using a common methodology of 3-D finite element method to solve a differential equation for the bending of a thin elastic plate. The finite element flexural model incorporates lateral variations of T(e) and the Andes topography as the load. Three T(e) maps for the entire Andes were analysed: Stewart & Watts (1997), Tassara et al. (2007) and Perez-Gussinye et al. (2007). The predicted flexural deformation obtained for each T(e) map was compared with the depth to the base of the foreland basin sequence. Likewise, the gravity effect of flexurally induced crust-mantle deformation was compared with the observed Bouguer gravity. T(e) estimates using forward flexural modelling by Stewart & Watts (1997) better predict the geological and gravity data for most of the Andean system, particularly in the Central Andes, where T(e) ranges from greater than 70 km in the sub-Andes to less than 15 km under the Andes Cordillera. The misfit between the calculated and observed foreland basin subsidence and the gravity anomaly for the Maranon basin in Peru and the Bermejo basin in Argentina, regardless of the assumed T(e) map, may be due to a dynamic topography component associated with the shallow subduction of the Nazca Plate beneath the Andes at these latitudes.

Trophallaxis in Dehydrated Leaf Cutting Colonies of Atta sexdens rubropilosa (Hymenoptera: Formicidae)

Trophallaxis, the transfer of liquid among individuals by oral regurgitation or anal deposition, occurs in many insect groups including ants. The first indication that trophallaxis could occur in leaf cutting ants (Atta sexdens rubropilosa) was made by Autuori in 1942. He reported water collection by this ant species, and highlighted what in those days was an undescribed behavior for this species. In 2005, Da-Silva and Ribeiro presented preliminary results suggesting the existence of trophallaxis in A. sexdens rubropilosa. Here we report on a formal test of the hypothesis of trophallaxis in that species. Our approach was to test ant pairs in which only one individual (Group I) had access to blue-dyed water and the other individual (Group II), a nest-mate, came from a colony dehydrated by offering dry crushed corn for fungal growth. Positive results for trophallaxis were obtained in ants from four colonies and accounted for 33%-46% of all tests in which ants from Group I drank dyed water. These results indicate that trophallaxis occurs in this species.

Colony dehydration and water collection by specialized caste in the leaf-cutting ant Atta sexdens rubropilosa

Social organization enables leaf-cutting ants to keep appropriate micro-ecological nest conditions for the fungus garden (their main food), eggs, larvae and adults. To maintain stability while facing changing conditions, individual ants must perceive destabilising factors and produce a proper behavioral response. We investigated behavioral responses to experimental dehydration in leaf-cutting ants to verify if task specialization exists, and to quantify the ability of ant sub-colonies for water management. Our setup consisted of fourteen sub-colonies, ten of which were randomly assigned to different levels of experimental dehydration with silica gel, whereas the remaining four were controls. The ten experimental sub-colonies were split into two groups, so that five of them had access to water. Diverse ant morphs searched for water in dehydrated colonies, but mainly a caste of small ants collected water after sources had been discovered. Size specialization for water collection was replicable in shorter experiments with three additional colonies. Ants of dehydrated colonies accumulated leaf-fragments on the nest entrance, and covering the fungus garden. Behaviors that may enhance humidity within the nests were common to all dehydration treatments. Water availability increased the life span of dehydrated colonies.

Three-dimensional Reconstruction of Ovaries of Leaf-cutting Ant (Atta sexdens rubropilosa) Queens (Hymenoptera: Formicidae)

In this study, the ovary morphology of newly emerged ant queens of Atta sexdens rubropilosa was studied in whole mount preparations by confocal microscopy. The ovaries are composed of approximately 40 ovarioles, showing non-synchronic oocyte maturation. The terminal filament with clusters of undifferentiated cells was found at the distal end of the ovarioles. Next to this region is the germarium, composed of several elongated cystocytes interconnected by cytoplasmic bridges. The nurse cells (23-28 cells) result from asymmetric mitosis. Cytoskeleton analysis showed F-actin concentrated at the muscle cells of the external tunica and in fusomes inside the ovarioles. Microtubules were concentrated around the nuclei of the nurse and follicular cells. In contrast, the oocytes and the external tunica showed faint staining for tubulin.

On the cutting stock problem under stochastic demand

This paper addresses the one-dimensional cutting stock problem when demand is a random variable. The problem is formulated as a two-stage stochastic nonlinear program with recourse. The first stage decision variables are the number of objects to be cut according to a cutting pattern. The second stage decision variables are the number of holding or backordering items due to the decisions made in the first stage. The problem`s objective is to minimize the total expected cost incurred in both stages, due to waste and holding or backordering penalties. A Simplex-based method with column generation is proposed for solving a linear relaxation of the resulting optimization problem. The proposed method is evaluated by using two well-known measures of uncertainty effects in stochastic programming: the value of stochastic solution-VSS-and the expected value of perfect information-EVPI. The optimal two-stage solution is shown to be more effective than the alternative wait-and-see and expected value approaches, even under small variations in the parameters of the problem.

Heuristics for the one-dimensional cutting stock problem with limited multiple stock lengths

This paper deals with the classical one-dimensional integer cutting stock problem, which consists of cutting a set of available stock lengths in order to produce smaller ordered items. This process is carried out in order to optimize a given objective function (e.g., minimizing waste). Our study deals with a case in which there are several stock lengths available in limited quantities. Moreover, we have focused on problems of low demand. Some heuristic methods are proposed in order to obtain an integer solution and compared with others. The heuristic methods are empirically analyzed by solving a set of randomly generated instances and a set of instances from the literature. Concerning the latter. most of the optimal solutions of these instances are known, therefore it was possible to compare the solutions. The proposed methods presented very small objective function value gaps. (C) 2008 Elsevier Ltd. All rights reserved.

A Lagrangian relaxation approach to a coupled lot-sizing and cutting stock problem

Industrial production processes involving both lot-sizing and cutting stock problems are common in many industrial settings. However, they are usually treated in a separate way, which could lead to costly production plans. In this paper, a coupled mathematical model is formulated and a heuristic method based on Lagrangian relaxation is proposed. Computational results prove its effectiveness. (C) 2009 Elsevier B.V. All rights reserved.

A coupling cutting stock-lot sizing problem in the paper industry

An important production programming problem arises in paper industries coupling multiple machine scheduling with cutting stocks. Concerning machine scheduling: how can the production of the quantity of large rolls of paper of different types be determined. These rolls are cut to meet demand of items. Scheduling that minimizes setups and production costs may produce rolls which may increase waste in the cutting process. On the other hand, the best number of rolls in the point of view of minimizing waste may lead to high setup costs. In this paper, coupled modeling and heuristic methods are proposed. Computational experiments are presented.

Metal location and thickness in a multilayered sheet by measuring K alpha/K beta, L alpha/L beta and L alpha/L gamma X-ray ratios

When a multilayered material is analyzed by means of energy-dispersive X-ray fluorescence analysis, then the X-ray ratios of K alpha/K beta, or L alpha/L beta and L alpha/L gamma, for an element in the multilayered material, depend on the composition and thickness of the layer in which the element is situated, and on the composition and thickness of the superimposed layer (or layers). Multilayered samples are common in archaeometry, for example, in the case of pigment layers in paintings, or in the case of gilded or silvered alloys. The latter situation is examined in detail in the present paper, with a specific reference to pre-Columbian alloys from various museums in the north of Peru. (C) 2009 Elsevier B.V. All rights reserved.

Thickness and Annealing Temperature Effects on the Optical Properties and Surface Morphology of Layer-by-Layer Poly(p-phenyline vinylene) plus Dodecylbenzenesulfonate Films

The fabrication of controlled molecular architectures is essential for organic devices, as is the case of emission of polarized light for the information industry. In this study, we show that optimized conditions can be established to allow layer-by-layer (LbL) films of poly(p-phenylene vinylene) (PPV)+dodecylbenzenesulfonate (DBS) to be obtained with anisotropic properties. Films with five layers and converted at 110 degrees C had a dichroic ratio delta = 2.3 and order parameter r = 34%, as indicated in optical spectroscopy and emission ellipsometry data. This anisotropy was decreased with the number of layers deposited, with delta = 1.0 for a 75-layer LbL PPV + DBS film. The analysis with atomic force microscopy showed the formation of polymer clusters in a random growth process with the normalized height distribution being represented by a Gaussian function. In spite of this randomness in film growth, the self-covariance function pointed to a correlation between clusters, especially for thick films. In summary, the LbL method may be exploited to obtain both anisotropic films with polarized emission and regular, nanostructured surfaces. (c) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 206-213, 2011

Algorithms for two-dimensional cutting stock and strip packing problems using dynamic programming and column generation

We investigate several two-dimensional guillotine cutting stock problems and their variants in which orthogonal rotations are allowed. We first present two dynamic programming based algorithms for the Rectangular Knapsack (RK) problem and its variants in which the patterns must be staged. The first algorithm solves the recurrence formula proposed by Beasley; the second algorithm - for staged patterns - also uses a recurrence formula. We show that if the items are not so small compared to the dimensions of the bin, then these algorithms require polynomial time. Using these algorithms we solved all instances of the RK problem found at the OR-LIBRARY, including one for which no optimal solution was known. We also consider the Two-dimensional Cutting Stock problem. We present a column generation based algorithm for this problem that uses the first algorithm above mentioned to generate the columns. We propose two strategies to tackle the residual instances. We also investigate a variant of this problem where the bins have different sizes. At last, we study the Two-dimensional Strip Packing problem. We also present a column generation based algorithm for this problem that uses the second algorithm above mentioned where staged patterns are imposed. In this case we solve instances for two-, three- and four-staged patterns. We report on some computational experiments with the various algorithms we propose in this paper. The results indicate that these algorithms seem to be suitable for solving real-world instances. We give a detailed description (a pseudo-code) of all the algorithms presented here, so that the reader may easily implement these algorithms. (c) 2007 Elsevier B.V. All rights reserved.