J. M. Ferreira

Effects of continuous-wave CO2 laser on the ultrastructure of human dental enamel

Laser-induced changes in plano-parallel sections were examined by light microscopy (LM) and scanning electron microscopy (SEM), and correlated with ultrastructural changes as observed by transmission electron microscopy (TEM). LM and SEM revealed two different changes--extensive crazing, and crazing and cratering. Rough exposed enamel was commonly found, resulting from lifting off and removal of the top layer of crazed, or crazed and cratered, enamel. The type of induced change was mainly dependent on the energy density used (range approximately 0.8 to approximately 200 J cm-2) and on enamel prism orientation. Lased enamel was also softer than unlased enamel. TEM of both crazed enamel and rough exposed enamel revealed that most crystals generally resembled those of unlased enamel in size and shape, but that inter- and intra-crystalline voids were present in some areas. The crazed and cratered enamel had significant ultrastructural changes: new homogeneous and inhomogeneous crystals of apatite with a different shape and larger size than those of the original, and a loss of prismatic structure. The lack of uniformity of the laser effect on crazed and cratered enamel was shown by variation in crystal packing (from good to poor), variations in crystal size from area to area, and the presence of pockets of poorly packed homogeneous crystals alongside pockets of well-packed inhomogeneous crystals. The crazing, crazing and cratering, rough exposed enamel and the greater number of voids, as well as the relative softness of lased enamel do not indicate an overall ultrastructural improvement. However, the larger apatite crystal size and loss of prismatic structure in crazed and cratered areas may partly explain previous observations of reduced rates of subsurface demineralization in lased enamel.

An analytical study of the transient motion of a dense rigid sphere in an incompressible Newtonian fluid

Abstract A theoretical study of the transient sphere motion (under the influence of gravity) through an incompressible Newtonian fluid subject to an Oseen-type drag relationship has been carried out. Exact closed form expressions for the instantaneous position, velocity and acceleration of the sphere are presented. An analytical expression developed herein also enables the delineation of the “best” sphere-fluid combination for the experimental observations of transient effects and these provide useful guidelines for designing laboratory experiments. However, this study is restricted to dense spheres falling in light liquids when the additional effects arising from the added mass and the Basset forces are negligible. Also, the boundary effects are altogether neglected.

An analytical study of the motion of a sphere rolling down a smooth inclined plane in an incompressible Newtonian fluid

The accelerated motion of a sphere rolling down a smooth inclined plane immersed in a quiescent Newtonian fluid has been investigated theoretically using Jan and Chens drag and added mass coefficient data [C.D. Jan, J.C. Chen, J. Hydraulic Res. 35 (1997) 689]. A modified expression for the drag coefficient was used to obtain an analytical solution to the equations of motion in the inclined plane. Closed form solutions for the instantaneous acceleration, time and distance required by the sphere to reach a given velocity are presented, and the spheres settling velocity is determined. The relationship between the planes angle of inclination and the time and distance required by the sphere to reach 99% of its terminal velocity is also investigated. The analysis reported herein is, however, restricted to dense spheres immersed in light liquids where additional effects arising from the Basset forces can be neglected.

Accelerating motion of a vertically falling sphere in incompressible Newtonian media: an analytical solution

Abstract The transient motion of a sphere falling through a Newtonian fluid has been investigated using a drag of the form given by Abraham/ Wadell, the average accuracy of which was found to be 7.6% for a sphere with Reynolds number Re in the range 0

Dissipative work in thermodynamics

This work explores the concept of dissipative work and shows that such a kind of work is an invariant non-negative quantity. This feature is then used to get a new insight into adiabatic irreversible processes; for instance, why the final temperature in any adiabatic irreversible process is always higher than that attained in a reversible process having the same initial state and equal final pressure or volume. Based on the concept of identical processes, numerical simulations of adiabatic irreversible compression and expansion were performed, enabling a better understanding of differences between configuration and dissipative work. The positive nature of the dissipative work was used to discuss the case where the dissipated energy ends up in the surroundings, while the invariance of such work under a system–surroundings interchange enabled the resulting modification in thermodynamical quantities to be determined. The ideas presented in this study are primarily intended for undergraduate students with a background in thermodynamics, but they may also be of interest to graduate students and teachers.

When an adiabatic irreversible expansion or compression becomes reversible

This paper aims to contribute to a better understanding of the concepts of a reversible process and entropy. For this purpose, an adiabatic irreversible expansion or compression is analysed, by considering that an ideal gas is expanded (compressed), from an initial pressure Pi to a final pressure Pf, by being placed in contact with a set of N work reservoirs with pressures decreasing (increasing) in a geometric or arithmetic progression. The gas entropy change ΔS is evaluated and it is clearly shown that ΔS > 0 for any finite N, but as the number of work reservoirs goes to infinity the entropy change goes to zero, i.e. the process becomes reversible. Additionally, this work draws attention to the work reservoir concept, which is virtually ignored in the literature, and to its analogy with the commonly used heat reservoir concept. Finally, it complements and reinforces an earlier study dealing with irreversible cooling or heating so that the synergy created by the two studies is important from both theoretical and educational standpoints.

Electron microscopic investigation relating the occlusal morphology to the underlying enamel structure of molar teeth of the wombat (Vombatus ursinus)

This investigation relates the occlusal morphology of the continuously growing molars of common wombats (Vombatus ursinus) to the underlying enamel ultrastructure that was investigated using the techniques of light microscopy, scanning electron microscopy, and transmission electron microscopy. The main feature of the occlusal enamel was a prominent ridge, which followed the contour of the dentine‐enamel junction (DEJ). It was found that the occlusal morphology depended upon the orientation of the dentinal and enamel tissues, variations in prism orientation, Hunter‐Schreger bands (HSB), and presence or absence of cleavage. Cleavage of enamel promoted by sheets of parallel prisms occurred along the face between the DEJ and the ridge, whereas on the face between the ridge and the cementum‐enamel junction (CEJ) cleavage was inhibited by HSB. The slope of the latter face was mainly due to a decrease in wear resistance going from the ridge, where prisms were intercepted transversely, toward the CEJ, where they were intercepted obliquely. Occasionally small surface undulations were observed on the face between the ridge and the CEJ. These undulations were found to correspond to gradually decussating enamel regions. The pronounced cleavage of enamel parallel to the face between the DEJ and the ridge played an important role in conferring on the continuously growing molars a distinct property to develop and maintain a self‐sharpening ridge throughout the life of the tooth.

Ampère–Maxwell law for a conducting wire: a topological perspective

The integral form of Ampere–Maxwells law for an arbitrarily-shaped wire is recast from a topological perspective, eliminating the need to use conduction current and displacement current terms to determine the magnetic field circulation around an arbitrarily-shaped loop. A generalized flux of the electric field is defined, enabling Ampere–Maxwells law for magnetic field circulation to be written in a form which parallels that in the absence of conduction current. It is hoped that this work has educational interest since it provides an example of how topology can simplify the formulation of physical laws. The ideas presented herein are primarily intended for undergraduate students of electromagnetism, but may also be of interest to graduate students and teachers.

Standard Blueprints for Interoperability in Factories of the Future (FoF)

Abstract Globalisation has become attractive to small companies, as it has allowed them to enter in new markets and increase their profits. However, they still face some challenges, as larger corporations are also increasing their market share in those new markets, leaving little room for the others to compete. Therefore, SMEs need to join efforts with other SMEs and form consortiums. Still, consortium formation is not without its problems. Some issues arise because the various SMEs in a consortium utilize different systems, different standards, and in the case of international consortiums, there are also language and culture barriers, which cause difficulties in communication. One way to avoid these issues is the creation of a central system, which will relate with the different systems belonging to the various SMEs. This is the aim of the IMAGINE project, which aims to use blueprints as a standard for company, product and process information. This paper presents a proposal for an extension of the Partner and Product Blueprint to be integrated in the IMAGINE platform.

Hydrodynamic behaviour of an ensemble of encapsulated liquid drops in creeping motion: a fluid-mechanic based model for liquid membranes

The free surface cell model is used with the Stokes approximation, to characterize the Newtonian flow of an ensemble of concentric two-phase liquid drops (i.e. globules) in steady, creeping motion through an immiscible continuous liquid phase. The drag on each globule is determined analytically, and its dependence on globule concentration in the ensemble is investigated. Closed form expressions are derived for the stream functions both in the continuous phase and within each globule phase. The effect of globule concentration on streamline patterns and flow velocity is also investigated. The drag and internal circulation patterns are analysed in the limiting situations of a single globule, a rigid sphere ensemble and a fluid sphere ensemble, and their dependence on globule concentration and the other flow parameters is determined.