Effect of surface topography on the color of dental porcelain

The objectives of this study were to evaluate the color difference depending on the surface topography of roughness and glazing, and to determine the effects of color measuring geometry and the standard illuminant on the color of a dental porcelain. Disk specimens of A3 shade were fired with commercial dental porcelain for PFM. Specimens were divided into non-polished (ST 1), polished with 200, 400, 1000, 1500-grit SiC papers (ST 2, 3, 4, 5) and glazed (ST 6) groups. After measuring the average surface roughness (Ra), color was determined under the illuminant A and D65 on a spectrophotometer with the specular component excluded (SCE) and included (SCI) geometry. Ra values were significantly influenced by the surface topography. With the SCE, the CIE L* value after glazing was significantly lower than that after polishing. Color differences (E*) measured with the SCE were higher than those with the SCI (2.61–4.66 vs. 0.93–1.57). Therefore the SCE geometry seemed to more accurate protocol for the color measurement of dental porcelain.     

Optics of the average normal cornea from general and canonical representations of its surface topography

Generally, the analysis of corneal topography involves fitting the raw data to a parametric geometric model that includes a regular basis surface, plus some sort of polynomial expansion to adjust the more irregular residual component. So far, these parametric models have been used in their canonical form, ignoring that the observation (keratometric) coordinate system is different from corneal axes of symmetry. Here we propose, instead, to use the canonical form when the topography is referenced to the intrinsic corneal system of coordinates, defined by its principal axes of symmetry. This idea is implemented using the general expression of an ellipsoid to fit the raw data given by the instrument. Then, the position and orientation of the three orthogonal semiaxes of the ellipsoid, which define the intrinsic Cartesian system of coordinates for normal corneas, can be identified by passing to the canonical form, by standard linear algebra. This model has been first validated experimentally obtaining significantly lower values for rms fitting error as compared with previous standard models: spherical, conical, and biconical. The fitting residual was then adjusted by a Zernike polynomial expansion. The topographies of 123 corneas were analyzed obtaining their radii of curvature, conic constants, Zernike coefficients, and the direction and position of the optical axis of the ellipsoid. The results were compared with those obtained using the standard models. The general ellipsoid model provides more negative values for the conic constants and lower apex radii (more prolate shapes) than the standard models applied to the same data. If the data are analyzed using standard models, the resulting mean shape of the cornea is consistent with previous studies, but when using the ellipsoid model we find new interesting features: The mean cornea is a more prolate ellipsoid (apical power 50 D), the direction of the optical axis is about 2.3 degrees nasal, and the residual term shows three Zernike coefficients significantly higher than zero (third-order trefoil and fourth- and sixth-order spherical). These three nonzero Zernike coefficients are responsible for most of the higher-order aberrations of the average cornea. Finally, we propose and implement a simple method for three-dimensional registration of corneal topographies, passing from the general to the canonical form of the ellipsoid.     

Influence of orientation of rough grooves on spectral reflectivity of a surface in the thermal radiation wavelength range

Roughness is one of the principal factors influencing reflectance of a surface that takes place in radiation heat transfer. In the present work, we investigate the influence of the orientation of single-oriented roughness grooves on the directed–directed spectral reflectance of surfaces within the wavelength range of 0.2–20.0 μm. The surfaces have a mean square deviation of the roughness (σ) of 0.2 μm and 2.0 μm and the areas exceed the size of the incident light beam. The angles of reflection are equal to the angles of incidence and are equal to 50° and 70°. The degree of influence of the groove orientation on the reflectance is defined as the ratio of the reflectances of one and the same surface with the grooves oriented parallel and perpendicular to the plane of incidence. In the theoretical investigation, we engage the unidimensionally rough surface model. An experimental study by means of physical modeling was performed: the degree of influence of the groove orientation on the spectral reflection of the surface was estimated, within the investigated wavelength range, according to the degree of influence of the groove orientation on the monochromatic reflectance of the reference ground surfaces within the σ-range of 0.01–4.33 μm on the wavelength 0.405 μm. The studies performed show that the spectral range of the groove orientation influence on the surface reflectance increases with an increase in σ and a decrease in the angle of incidence; the degree of that influence has a maximum the value of which increases with the increase in the angle of incidence. We determine the conditions of agreement of the theory and the experiment.     

Method to determine snow albedo values in the ultraviolet for radiative transfer modeling

For many cases modeled and measured UV global irradiances agree to within +/-5% for cloudless conditions, provided that all relevant parameters for describing the atmosphere and the surface are well known. However, for conditions with snow-covered surfaces this agreement is usually not achievable, because on the one hand the regional albedo, which has to be used in a model, is only rarely available and on the other hand UV irradiance alters with different snow cover of the surface by as much as 50%. Therefore a method is given to determine the regional albedo values for conditions with snow cover by use of a parameterization on the basis of snow depth and snow age, routinely monitored by the weather services. An algorithm is evolved by multiple linear regression between the snow data and snow-albedo values in the UV, which are determined from a best fit of modeled and measured UV irradiances for an alpine site in Europe. The resulting regional albedo values in the case of snow are in the 0.18-0.5 range. Since the constants of the regression depend on the area conditions, they have to be adapted if the method is applied for other sites. Using the algorithm for actual cases with different snow conditions improves the accuracy of modeled UV irradiances considerably. Compared with the use of an average, constant snow albedo, the use of actual albedo values, provided by the algorithm, halves the average deviations between measured and modeled UV global irradiances.     

Method for correcting the wavelength misalignment in measured ultraviolet spectra

A new method for correcting the wavelength misalignment in measured UV spectra is presented. It is based on a comparison between measured irradiances and irradiances computed from a radiative transfer code for a set of given atmospheric and solar conditions (250 < Dobson units < 450, 30 degrees < solar zenith angle < 75 degrees ). Results of tests run with spectra recorded on a clear-sky day by two spectroradiometers in a French UV spectral network station are analyzed. Applying the method once reduces shift to less than 0.05 nm. The smoothing included in the method enables detection of aberrant irradiance values and then completion of an initial quality control of measured spectra. A technique for assessing the instruments' slit function is also presented. The key algorithms needed to build a computer code based on this method are given.     

Retrieval of the ultraviolet effective snow albedo during 1998 winter campaign in the French Alps

A measurement campaign was carried out in February 1998 at Brian?on Station, French Alps (44.9 degrees N, 6.65 degrees E, 1,310 m above sea level) in order to determine the UV effective snow albedo that was retrieved for both erythemal and UV-A irradiances from measurements and modeling enhancement factors. The results are presented for 15 cloudless days with very variable snow cover and a small snowfall in the middle of the campaign. Erythemal irradiance enhancement due to the surface albedo was found to decrease from approximately +15% to +5% with a jump to +22% after the snowfall, whereas UV-A irradiance enhancement decreased from 7% to 5% and increased to 15% after the snowfall. Thesevalues fit to effective surface albedos of 0.4, 0.1, and 0.5 for erythemal, and to effective albedos of 0.25, 0.1, and 0.4 for UV-A irradiances, respectively. An unexpected difference between the effective albedos retrieved in the two wavelength regions can be explained by the difference of the environment contribution.     

Effect of ultraviolet curing wavelength on low-k dielectric material properties and plasma damage resistance

A set of SiCOH low dielectric constant films (low-k) has been deposited by plasma enhanced chemical vapor deposition using variable flow rates of the porogen (sacrificial phase) and matrix precursors. During the deposition, two different substrate temperatures and radio frequency power settings were applied. Next, the deposited films were cured by the UV assisted annealing (UV-cure) using two industrial UV light sources: a monochromatic UV source with intensity maximum at λ = 172 nm (lamp A) and a broadband UV source with intensity spectrum distributed below 200 nm (lamp B). This set of various low-k films has been additionally exposed to NH₃ plasma (used for the CuO_x reduction during Cu/low-k integration) in order to evaluate the effect of the film preparation conditions on the plasma damage resistance of low-k material. Results show that the choice of the UV-curing light source has significant impact on the chemical composition of the low-k material and modifies the porogen removal efficiency and subsequently the material porosity. The 172 nm photons from lamp A induce greater changes to most of the evaluated properties, particularly causing undesired removal of SiCH₃ groups and their replacement with SiH. The softer broadband radiation from lamp B improves the porogen removal efficiency, leaving less porogen residues detected by spectroscopic ellipsometry in UV range. Furthermore, it was found that the degree of bulk hydrophilization (plasma damage) after NH₃ plasma exposure is driven mainly by the film porosity.     

浅海海底地形对吊放声呐探测距离的影响

吊放声呐的探测距离不仅与装备的自身性能和海洋水声环境特性有关,还受海底地形影响.利用射线声学模型,仿真分析了正声速梯度和带有跃变层声速梯度下,不同高度和深度的海底山体和海底盆地(简称:海盆)两种典型地形下的声传播特性.通过声传播特性,得出了不同高度和深度的海底山体和海盆两种典型地形对吊放声呐作用距离的影响.根据声传播特...     

Effect of initial surface topography on the surface status of LY2 aluminum alloy treated by laser shock processing

Samples manufactured by LY2 aluminum (Al) alloy with different initial surface topography were treated by laser shock processing (LSP), and then the surface topographies before and after LSP were carefully investigated with a non-contact optical profiler (NCOP). Moreover, the residual stress and microhardness were also examined. Results showed the following three aspects: (a) Initial surface topography will influence the surface roughness of LY2 when treated by LSP. The values of surface roughness of all the tested samples would tend to be stable after one LSP impact, and there was an ultimate value for the surface roughness after multiple LSP impacts, which was about 0.58 μm. (b) With the increase of initial surface roughness, the compressive residual stress decreased when subjected to one LSP impact. The surface residual stress of all the samples tended to be saturated after three LSP impacts, and the saturated value was nearly equal. (c) With the increase of initial surface roughness, the microhardness of all the samples increased when subjected to one LSP impact.     

Reflective performance of Ir film in vacuum ultraviolet wavelength region

This paper theoretically and experimentally investigates the reflective performance of Ir films in the vacuum ultraviolet wavelength region. Ir reflecting layers of different thicknesses on various substrates are calculated and fabricated by the ion-beam-sputtering technique. Their reflectance in the 115 nm to 140 nm wavelength region was measured continuously by a reflectometer located at the National Synchrotron Radiation Laboratory. The testing results show that the reflectance of Si substrates is quite sensitive to the deposited Ir layer thickness, while the reflectance on a quartz or a BK7 glass substrates is higher. The energy of the sputtering ion beam exerts a significant influence on the reflectance of the layer, and the postannealing can cause a substantial decrease in the reflectance. For normal incidence, the reflectance of an Ir film on BK7 glass can reach as high as 30%.     

Modeling of a crossed-groove cavity in the 8 mm wavelength range

Results are presented of experiments on the scale modeling of a crossed-groove quasioptic cavity. It is demonstrated that high-Q modes can be excited with a ring structure at the mirror and a field maximum at the center of the cavity. Pis’ma Zh. Tekh. Fiz. 24, 69–75 (October 12, 1998)     

Highly absorptive coating for the vacuum ultraviolet range

We have developed new, highly absorptive coatings for the vacuum UV wavelength range. These coatings display two distinct granularity scales: large structures of a 10-100-mum scale form efficient light traps, upon which are superimposed structures of a submicrometer scale. We present results for the total hemispherical reflectivity at normal incidence for 121.6 nm and at a grazing angle incidence for 17.1, 30.4, 58.4, and 121.6 nm. These measurements were made for the new coatings as well as for various coatings in common use. Absorption of the new coatings is in some cases higher than for the best-known coatings and, in contrast to the latter, they are mechanically robust.     

Simple method for antireflection coating ZnSe in the 20 microm wavelength range

We present a simple, inexpensive, and effective method of applying antireflection coatings to zinc selenide windows designed to operate in the thermal infrared wavelength region.     

Influence of binding layer on the reflective performance of a Au film in vacuum ultraviolet wavelength region

We investigate the influence of the binding layer on the reflectance of a Au film in vacuum ultraviolet (VUV) wavelength region theoretically and experimentally. The reflectance of Au films on quartz glass substrates with an approximately 2 nm binding layer of Ti, Cr, and Ir are estimated and fabricated. Their reflectance in the 115-140 nm wavelength region are measured continuously by the reflectometer located in the National Synchroton Radiation Laboratory. The testing results show that the addition of the binding layer indeed greatly enhances the interfacial adhesion of the Au layer to the quartz glass substrate, but it also exerts a considerably adverse impact on the reflectance of the Au layer in VUV wavelength region. In near normal incidence, the reflectance of the Au layer with a 2 nm thick binding layer is less than 20%, approximately 5% lower than those without the binding layer. The material used for the binding layer has little impact on the reflectance if this layer is thin enough.     

Intercomparison of reflectances observed by GOME and SCIAMACHY in the visible wavelength range

We compare the Earth reflectances of the spectrometers Global Ozone Monitoring Experiment (GOME) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) over their overlapping wavelength range (240-800 nm). The goal is to investigate the quality of the radiometric calibration of SCIAMACHY using calibrated GOME data as a reference. However, severe degradation of the GOME instrument in the UV since 2001 prevents it from being a reliable reference below 500 nm. Above 500 nm, GOME is reliable and we find substantial disagreement between GOME and SCIAMACHY, of the order of 15%-20%, which we can attribute completely to the current calibration problems of SCIAMACHY. These numbers are supported by a previous study in which SCIAMACHY was compared with the imager Medium Resolution Imaging Spectrometer (MERIS) onboard the Envisat satellite.     

Development of the surface topography on silica glass due to ion-bombardment

Mechanically polished fused silica surfaces have been bombarded by energetic Ar⁺ ions and the development of surface topography examined by scanning electron microscopy and by transmission electron microscopy of direct carbon replicas in order to study the parameters affecting the surface finish such as charging, angle of ion incidence and rotation of the specimen, A theory based on a simple model of initial surface unevenness on a microscopic scale is proposed to explain the observed surface features due to ion-bombardment.     

Modeling the spatial distribution of surface hoar in complex topography

Buried surface hoar is a well-known weak snowpack layer, often associated with snow avalanches. Knowledge about the spatial distribution of surface hoar is therefore of great importance for avalanche forecasting. We investigate if spatial variations of surface hoar in mountainous terrain can be modeled based on terrain characteristics. Using a detailed radiation balance model, distributed radiation over an ensemble of 1800 simulated topographies, covering a wide range of terrain characteristics, was computed. Light winds and increased relative humidity were assumed to be favorable for surface hoar formation. To describe surface hoar formation, we derived a sky view factor threshold associated with the minimum snow surface cooling necessary for surface hoar formation based on laboratory measurements. To describe surface hoar destruction, as a first approach, we assumed that surface hoar only survives on shaded slopes. Applying two simple thresholds to our spatial radiation modelings, our results show that the spatial distribution of surface hoar is greatly affected by large-scale terrain roughness and sun elevation angle. Spatial correlation ranges for surface hoar, on the order of several hundred meters, were closely related to the typical spacing between mountains. Furthermore, correlation ranges of surface hoar decreased with increasing sun elevation angle. Overall, the modeled spatial patterns of surface hoar were in line with previously published spatial field observations, suggesting that simple terrain parameters can very well be used to describe the predominant surface hoar layer patterns in complex topography.