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From Graphics to Visualization
Published in Alexandru Telea, Data Visualization, 2014
The lighting model in Equation (2.1) is a linear combination of three components: ambient, diffuse, and specular, whose contributions are described by the weighting coefficients camb, cdiff, and cspec, respectively, which are in the range [0, 1]. Ambient lighting is essentially a constant value. This is a rough estimate of the light reflected at the current point that is due to indirect illumination, i.e., light reflected onto the current point by all other objects in the scene. Diffuse lighting, also known as Lambertian reflection, is proportional to the cosine of the angle between the light direction −L and the surface normal n, or the vector dot product − L · n. This models the equal scattering of incoming light in all directions around the surface normal. Diffuse lighting simulates the appearance of plastic-like, matte surfaces, and does not depend on the viewpoint. Finally, specular, or mirror-like, lighting is proportional to the cosine of the angle between the reflected light direction r and view direction v, raised to a specular power α. This models the scattering of the incoming light in directions close to the perfect mirror reflection direction r. Specular lighting simulates the appearance of shiny, or glossy, surfaces, such as polished metal, and is viewpoint-dependent.
Other Topics: From Rugate Filters to Photonic Crystals
Published in H. Angus Macleod, Thin-Film Optical Filters, 2017
One of the early assumptions about the one-dimensional photonic crystal was that it would be completely impossible for it to support a forbidden gap over a range of angles from 0 to 90° or, in optical coating terms, that the reflectance could remain high from normal incidence to an incidence of 90°. No good proof of this assumption appears to exist, and so it is difficult to be certain of its origin. Photonic crystal theory, by analogy with solid-state crystal theory, tends to treat infinite assemblies. It is natural for a photonic crystal theorist, therefore, to be thinking in terms of propagation within the crystal, whereas the thin-film theorist is well aware of restrictions on the number of layers and of the presence of an incident and emergent medium. If propagation is visualized as within the crystal, then it is clear that propagation could laterally be along the layers and not across them, and the resistance to propagation would disappear. Also, it was recognized that there would be a particular propagation direction that would correspond to the Brewster condition between the two materials of the crystal, and this would mean a collapse of the bandgap, or reflecting zone, for p-polarized light. The fact that it is possible, when the incident medium is air, and there is sufficient contrast between the high index and low index of the materials to construct a reflector that, for a limited range of wavelengths, can exhibit high reflectance for both p- and s-polarizations over all angles of incidence from 0 to 90° came, therefore, as a surprise to the photonic crystal community but not to the thin-film community. The effect was called either the omnidirectional reflector [60] or, sometimes, the perfect mirror.
Manipulating Micromachines in a Light Beam
Published in George K. Knopf, Kenji Uchino, Light Driven Micromachines, 2018
As the photons from the sun, or another high intensity light source, strike the sail the momentum is transferred to the absorbing body. Similar to a perfect mirror, if the photons are specularly reflected then the momentum transfer is doubled. The change in photon momentum produces a force on the absorbing—or reflecting body—according to Newton’s second law. The force per unit surface area is called solar radiation pressure (PSRP) and the solar radiation pressure at a distance r from the sun is
The spontaneous emission rate determination of a molecule near a perfect conductive wall
Published in Molecular Physics, 2021
Hossein Falinejad, Maryam Akhgar
In [28], by choosing the mode functions satisfying electromagnetic boundary conditions at the surface of a perfect mirror, the electromagnetic field is quantized and then by using Fermi golden rule, the spontaneous emission rate near the mirror is computed. At the absence of any dissipative boundary surface, or in other words when the dielectric function is real, the mode functions method is a convenient method for quantizingthe electromagnetic field. On the other hand, in Green function approach of field quantization the dielectric function is an arbitrary complex function of frequency and thus the derived field operators can be used at the presence of any kind of boundary surfaces [17,29–37]. In this work, both by using the explicit form of the vector potential operator (quantized in Green Function approach) and also by calculating the required vector potential function tensor components, the spontaneous emission rate of a molecule in vicinity of a conductive wall is evaluated separately. Both methods result the same expression for the spontaneous emission rate which are also in agreement with [28]. In this way, in evaluating the emission rate near a conductive wall, the consistency of the field quantizationapproach and the Green function approaches is shown explicitly.
Cd(II) enantiomers embedding helices from 3D frameworks to 2D layers controlled by shapes of ancillary ligands
Published in Journal of Coordination Chemistry, 2021
Zhong-Xuan Xu, Xu-Ling Bai, Li-Feng Li, Shi-Fei XU
Complexes 1-R and 1-S are 3D pillared-layer frameworks, crystallizing in monoclinic P21 space group with the absolute structural Flack factors of −0.040(16) and −0.060(12), respectively. As shown in Figure 1, 1-R and 1-S are enantiomers with perfect mirror image of each other. For this reason, the structure of 1-R as representative is described below. In 1-R, each asymmetric unit is comprised of two Cd(II) centers, two deprotonated (R)-CBA2- and a 1,4-BMIB ligand. Although two (R)-CBA2- ligands were connected by three Cd(II) ions, they have different coordination modes: the first (R)-CBA2- ligand is κ4-linker, whereas the second (R)-CBA2- ligand is κ5-linker. As a result, a dinuclear [Cd2(CO2)4] cluster is formed according to the coordination modes. In the [Co2(CO2)4] cluster, Cd1 adopted a distorted trigonal bipyramidal geometry to coordinate with four carboxylate O atoms and an imidazole N atom, and Cd2 was octahedral connected by five carboxylate O atoms and an imidazole N atom.
The effect of polishing protocol on surface gloss of different restorative resin composites
Published in Biomaterial Investigations in Dentistry, 2020
Lippo Lassila, Eija Säilynoja, Roosa Prinssi, Pekka K. Vallittu, Sufyan Garoushi
Gloss is an important property and is used primarily as a measure of surface shine [6]. The gloss of a surface may be defined as its degree of approach to a mirror surface. A perfect mirror surface is said to have maximum gloss [6]. It has been suggested that SG can be determined by both the intrinsic characteristics of the RC and the finishing and polishing procedures [7]. Thus, a successful composite restoration requires not only care for restorative material selection, with ideal esthetics and mechanical strength characteristics, but also care with respect to the choice of the finishing and polishing protocol [1,8]. Several finishing and polishing protocols are available on the market, including diamond burs, rubber cups, discs and abrasive pastes [8–10]. Many researchers have studied the polishability of different polishing protocols on the surfaces of various commercial RCs [8–14]. Some studies have indicated that aluminum oxide disks produce smoother surfaces when compared with diamond burs, tungsten carbide drills and rubber cups associated with polishing pastes [11–14]. Usually, the polishing protocols have been evaluated according to the manufacturers’ recommendations. However, the manufacturers rarely support their recommendations with objective investigations that have proven the suggested protocol to be superior to others. Therefore, it would be helpful to compare the clinical polishing protocols with sequences of standardized laboratory-machine polishing protocols to supply quantitative proof for the suggested procedure.