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Tooth whitening or bleaching is one of the most common dental procedures that optimize the white color of the teeth and minimize the simultaneous damage to the tooth structure. Light can speed up the whitening process with halogen lamps, light-emitting diodes, plasma arc lamps, and lasers. Our results show that combinations of a teeth whitening agent with laser light irradiation with a 0.44 µm blue laser diode or a 1.7 µm near-IR laser diode accelerate the whitening process not only during tooth irradiation but also within two weeks after the procedure.

The main goal of this work was to present spectroscopic and laser characteristics including the wavelength tunability of Er-doped Gd3Ga3Al2O12 (Er:GGAG) crystal. Seven Er:GGAG crystals of various Er/Gd concentrations were investigated. The maximum output peak power of 0.99 W with an absorbed pumping peak power amplitude of 5.22 W for the crystal at 0.55 at.% Er/Gd concentration was researched. The tuning was accomplished using a SiO2 birefringent plate. The laser wavelength was tunable in three eye-safe spectral bands from 1609 to 1650 nm.

In this paper, we consider two models that have been recently developed from a thermodynamic standpoint and that are capable of describing the response of nonlinear viscoelastic fluids. We test the efficacy of both models by comparing their predictions against torsion experiments conducted for asphalt, a material that is notoriously difficult to model. Both the models seem to describe the response adequately, though neither is really very accurate. This should not be surprising as asphalt is a heterogenous material comprising of many components which is being homogenized and modeled as a single constituent viscoelastic fluid.

Classical and temperature‐modulated DSC methods were employed to study aqueous solutions of sucrose in the whole concentration range and the temperature interval of −120°C to 30°C. New interpretati...

Inelastic materials that form dislocation cells on being deformed are modeled as a "constrained-mixture" of plastically hard and soft regions by associating different natural states with these regions. The deformation gradient from the reference configuration to the natural configuration is identified as the plastic deformation tensor and the stress is measured from a changing set of natural configurations. Two sets of natural configurations are introduced: one for the hard phase and the other for the soft phase. The full elastic response of the body is determined by elastic responses from different natural configurations. The energy stored in the dislocation networks is explicitly accounted for in the Helmholtz potential. Within a specialized constitutive set up, the soft phase is assumed to be non-hardening while the hardening response of the hard phase is dependent upon the response of both the hard and soft phases. These special forms are used to model the response of the material that forms cellular structures when subjected to cyclic loading.

The resonance frequency of vibrations of dislocation dipoles in fatigued f.c.c. metals is found rather high, in the range of 100 GHz. Because of high attenuation of ultrasound in the GHz range, the contributions of these self-vibrations to degradation of the dipole structures could be expected only in thin layers.

At the microscale plastically deformed solid behaves as a strongly nonlinear system governed by instability transitions. According to the model proposed for cell forming materials the stored dislocations, mostly in the form of dipolar loops, are arranged into a characteristic pattern of tangles, veins or walls giving rise to strain hardening. Annihilation of stored dislocations in the high density regions changes the wavelength and profile of the pattern. The process tends to reach a steady state, in which the generation and annihilations of stored dislocations are balanced. The geometry of stabilized cell walls derived for single, double and multi slip corresponds well to observed deformation microstructures. However, the dislocation cell formation may be seriously interfered by geometrical instability. The internal bending type instability causes transformation of cell walls into subgrain boundaries or formation of dislocation grids. The second type of geometrical instability triggers strain localization into shear bands or persistent slip bands destroying the original dislocation structure and forming the new one.

Looking at severe plastic deformation experiments, it seems that crystalline materials at yield behave as a special kind of anisotropic, highly viscous fluids flowing through an adjustable crystal lattice space. High viscosity provides a possibility to describe the flow as a quasi-static process, where inertial and other body forces can be neglected. The flow through the lattice space is restricted to preferred crystallographic planes and directions causing anisotropy. In the deformation process the lattice is strained and rotated. The proposed model is based on the rate form of the decomposition rule: the velocity gradient consists of the lattice velocity gradient and the sum of the velocity gradients corresponding to the slip rates of individual slip systems. The proposed crystal plasticity model allowing for large deformations is treated as the flow-adjusted boundary value problem. As a test example we analyze a plastic flow of an single crystal compressed in a channel die. We propose three step algorithm of finite element discretization for a numerical solution in the Arbitrary Lagrangian Eulerian (ALE) configuration.

In comparison with other cereals, rye is produced in smaller quantities, and can be grown in regions with a cooler climate and on soils of lower fertility. In the past, the traditional regions of rye production were central and eastern Europe. In 1990 total world production of rye reached 37 million tonnes. It has increased continuously in the last decade. This trend is quite different from the 1960s when world production dropped from 35 to 31 million tonnes (Bushuk, 1976). During the last 10 years production has increased to 150% of that in 1980 (see Figure 2.1). Figure 2.1 shows that the increase was reached mainly by increasing yields of harvested grain from 1.6 t/ha in 1980 to 2.2 t/ha in 1990. The area harvested also increased, but not so significantly as other characteristics of world rye production.

Ageing of supersaturated solid solution of Al 20 wt % Zn alloy after cyclic deformation results in a preferential precipitation of Zn in regions of higher dislocation density. Characteristic inhomogeneities of the deformation structure revealed by this precipitation image correspond well to the surface relief observed by optical and scanning electron microscopy. The posibility of using the method of precipitation imaging to study spatial arrangement of high and low dislocation density regions in deformed age-hardened alloys is discussed.

It is assumed that the core structure of screw dislocations in the h.c.p. lattice of α-Ti can be described by a sessile splitting on the prism plane and on the first order pyramidal plane simultaneously and that slip can proceed after its transformation into a glissile configuration on the prism plane. The strengthening by interstitial solutes O, N, C is explained by their impeding role in these sessile-glissile transformations. A good agreement between the theoretical temperature dependences of the effective stress for different interstitial content and the experimental values can be reached if the effect of impurities on the stacking fault energies is also taken into account. The similarity between the role of screw dislocations in the low temperature deformation of h.c.p. metals with more slip systems operating and of b.c.c. metals is stressed.

Concepts of loss of stability and spontaneous structuralization are used for a specification of mechanisms of three basic miscroscopic plastic phenomena: excess production of dislocations, dislocation pattern formation, and localization of plastic strain.

For a class of materials for which the principal strain directions always coincide with the principal stress directions one can determine the stress field in an inhomogeneously deformed body from given boundary conditions and a known strain field without knowing the constitutive equations. Each point of the inhomogeneously deformed body contains information such as that derived from an individual homogeneous identification test. The practically important two-dimensional case leads to a problem of solving a linear hyperbolic system where two differential equations describe the principal stress components. The problem can be reduced to that of integration along characteristics.

Low cycle fatigue data are reported for multicrystalline specimens (i.e. polycrystals with a few large grains in the gauge section) of age-hardened AlZn alloy with elliptical G. P. zones. Experiments were carried out at constant strain amplitude, room temperature and frequency 2 Hz. The discussion focused on the role and relative importance of grain boundaries, extrusions and coarse slip bands for crack nucleation and propagation. Precipitation free zones bordering the grain boundaries are the most favoured sites of crack nucleation and early crack growth. The prevailing mechanism of the initial stage of transcrystalline cracking is alternating slip or shear. The large cracks with an extended plastic zone tend to follow the extrusions which are formed at the crack tip after sufficients number of cycles.

The stability of equilibrium configurations of atoms, which represent a dislocation, is studied on a one-dimensional static model of a crystal. The potentialW, which represents the influence of the surrounding crystal lattice on the atoms of the model, is composed of parabolic sections. An expression is derived for Peierls stress and cases are found when this stress is equal to zero.

A system of equations is derived for a simple model of a crystal lattice disturbed by a dislocation. The model is represented by two rows of atoms. The system of equations is analogous to that describing a singular dislocation in the theory of the continuous distribution of crystal imperfections. The method of solving the derived system of equations is given.

The graphical method of solution given in the paper [1] is used to study a pair of dislocations with opposite signs of the Burgers vectors in the Frenkel model of a crystal. The dependence of the force between the dislocations on their mutual distance is determined.

A graphical method is used to determine the static equilibrium configurations of atoms which correspond to a one-dimensional model of a crystal disturbed by a dislocation. The question of the number of equilibrium configurations and their stability with respect to a homogeneous stress is solved and cases of an anomally low Peierls stress are studied.

For a hierarchy of polynomials on the triangle there is derived an algorithm for computing the stiffness matrix of the plate bending element. The algorithm is easy to program and means a considerable saving of the computing time. The same approach can be used for any elliptic equation with constant coefficients.

An attempt is made to develop a theory of inelastic behavior of crystalline materials subjected to arbitrary deformation. The introduced concept of elastic motion leads to a simple decomposition rule: the total velocity gradient is the sum of the elastic velocity gradient and the inelastic velocity gradient. The important role of rotations and relevant constitutive relations is discussed and illustrated by an example of a tensile test of a single crystal. The assumption usual in plasticity that plastic deformation does not change the volume of the body follows in the present theory as a consequence of the second law of thermodynamics and material symmetry.

Changes in the frequency spectrum of the vibrations of a one-dimensional model of a crystal, which is perturbed by dislocations, are determined by the method described in paper [10]. The influence of an external homogeneous stress on the frequency of the local vibrations is qualitatively evaluated.

Relations are derived for the elastic stress field around a linear dislocation in an infinite medium with general anisotropy. The strongly deformed material around the core of the dislocation is cut out in the shape of an elliptic cylinder. The conditions of a free surface are used on the boundary thus formed. The calculation of the field around a crack in a crystal, the model of which was proposed by Fujita in [9], is given as an example.

The study was conducted in two groups of factory apprentices including boys aged 15 to 17 years. The first group consisted of a randomly selected 10% sample of 231 apprentices of the total number of 2,300 boys. The second group included 77 boys with casually found proteinuria. In both groups, the distribution of blood pressure and of the body mass and changes in these indices were followed up over a period of two years. The boys with proteinuria had a significantly higher systolic and diastolic blood pressure and a lower body mass index. Their systolic and diastolic blood pressure was rising more steeply in regression to the body mass. The casual finding of asymptomatic proteinuria in juveniles always calls for a long-term follow-up. It signalizes, inter alia, also the presence of a factor raising blood pressure probably independently of body height and body mass.

In this paper we consider the problem of model checking for well structured Communicating Hierarchical Machines (CHMs), i.e. Finite State Machines with additional features of hierarchy and concurrency. For model checking we follow the automaton theoretic approach, defining an algorithm which solves the problem of model checking without flattening the structure of CHMs.