Height Of Irregularities Research Articles

Side‐wall roughness of deep trenches in 1D and 2D periodic silicon structures fabricated by photoelectrochemical etching

Abstract1D periodic array of trenches and a 2D array of ordered macropores, with trenches, have been fabricated by photoelectrochemical etching (PECE) of n‐Si (100). The roughness of the vertical walls of the deep trenches has been studied in relation to geometric parameters of the structures, etching regime and subsequent treatment in a KOH solution or thermal oxidation. It is shown that the smoothest walls are obtained in structures where the distance between the constituent elements is equal to the characteristic period a dependent on the resistivity of Si. The optimal etching current density for structures of both types is j /jPS = 0.4, where jPS is the critical current density corresponding to the transition from pore formation to electrochemical polishing. An additional smoothing diminished the height of wall irregularities up to ∼25 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spontaneous Formation of Linear Striations and Cell-like Patterns on Dip-Coating Titania Films Prepared from Alkoxide Solutions

Linear striations and cell-like patterns were spontaneously formed on the dip-coating titania films prepared titanium tetraisopropoxide (Ti(OC(3)H(7)(i))(4)) solutions. Such unique patterns on micrometer scale were arranged parallel to the substrate withdrawal direction. The values of R(Z) (10 point height of irregularities) and S (mean spacing of local peaks) of the patterns increased with increasing film thickness depending on the substrate withdrawal speed for dip-coating, the viscosity of the coating solutions, and the distance from the top edge of films. The shape of patterns changed from linear striations to cell-like patterns with increasing viscosity of the coating solutions. Although the heat treatment at 600 degrees C reduced the height (R(Z)) of stripes and cells without the change in spacing (S), the visibility of patterns was enhanced by the increase in refractive index due to the crystallization of films.

Tire wheel assembly and noise-reducing device

Disclosed are a tire wheel assembly and a noise-reducing device whereby cavity resonance sound can be effectively reduced. A noise-reducing device, which includes a shell structure where a rough surface portion having a ten-point height of irregularities (Rz) in a range of 0.1 to 5.0 mm is provided on at least part of a surface, is attached to a wheel rim in a cavity portion of a pneumatic tire, and additionally, a height of the shell structure from a rim sheet is set in a range of 10 to 70% of a cross-sectional height of the tire.

Random laser action in 3‐D ZnO nanostructures

AbstractRoom‐temperature ultraviolet random lasing with low threshold pumping power was successfully achieved by ZnO 3‐D random‐wall nanostructure fabricated on ZnO/SiO2/Si substrate through a thermal chemical reaction and vapor transportation deposition method in a simple horizontal tube furnace from the mixed ZnO and graphite powders. The nanorods grown along c‐axis on the substrate are coalesced to form the 3‐D nano‐wall with 80∼100 nm in wall thickness and irregular height ranging of 95‐250 nm. Mueller matrix spectroscopic ellipsometry reveals that evaluated refractive indices n (E) of ZnO nanowalls are well interpreted by taking account of the ratio between ZnO and void achieved by effective medium theory analysis and isotropic depolarization feature of the designated nanowalls. Random lasing action observed in the wide wavelength range between 375 and 395 nm is realized by coherent amplification of the closed‐loop scattered light inside 3‐D random‐wall nanostructure. It is demonstrated that both transverse electric (TE) and transverse magnetic (TM) modes show the same threshold and pumping power dependent trend, while the intensity of TM lasing is weaker than that of TE due to the different scattering strength originated from the features of the inside of nano wall. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Identification of the state of a wet spouted bed through time‐frequency analysis of pressure fluctuation time series

AbstractThe feasibility of detecting instability in wet spouted beds via pressure fluctuation (PF) time‐series analyses was investigated. Experiments were carried out in a cylindrical Plexiglas column of diameter 150 mm with a conical base of internal angle 60°, an inlet orifice diameter of 25 mm and glass beads of diameter 2.4 mm. Transducers at several axial positions measured PF time series with incremental addition of aqueous sucrose solutions of different concentrations. Liquid addition affected the spouted bed dynamics, causing irregular spouting, increased voidage in the annulus, increased fountain height, irregular annulus height, channelling, agglomeration, and adhesion of particles to the column walls. Autocorrelations indicated the appearance of periodicities in the PF signals with increasing sucrose addition. Dominant peaks in power‐spectral density developed at low frequencies with changing system dynamics. The results indicate that PF signals furnish relevant information on system dynamics, useful for monitoring and control of spouted bed operations such as particle coating and drying of paste‐like materials.

Damage-Free Planarization of 2-Inch 4H-SiC Wafer Using Pt Catalyst Plate and HF Solution

We report a damage-free and efficient planarization process for silicon carbide (SiC) using platinum as a catalyst in hydrofluoric acid (HF) solution. In previous studies, 4H-SiC (0001) on-axis wafers were planarized by this process and an extremely flat surface was obtained. However, electronic device substrates require off-axis wafers. In the present study, 4H-SiC (0001) 8° off-axis Si-face wafers were planarized using a Pt catalyst plate and HF solution. In the first trial using these wafers, the surface roughness worsened and a diagonal pattern was observed by phase-shift interference microscopy. The pattern seemed to have been formed when the Pt plate morphology was transcribed onto the wafer. The removal rate of the 8° off-axis Si-face wafer is much greater than that of the on-axis Si-face wafer. Thus, we concluded that the use of a smoother catalyst plate would be necessary to obtain a smooth 8° off-axis Si-face wafer surface. Improving the Pt plate morphology by hand lapping also improved the surface roughness of the processed wafer as compared with the preprocessed surface. The maximum height of the surface irregularity (peak-to-valley, P-V) and root-mean-square roughness were improved to 0.513 nm and 0.044 nm, respectively, as determined by atomic force microscopy (2×2 μm2).

Wybrane wlasciwosci geometrycznej struktury powierzchni wytworow porowatych otrzymanych z polietylenu

The conditions were found in which the cellular topcoats of energetic and installation cables, fulfilling exploitation requirements (as for cables of trademark "OWY 3 x 1.5mm2 450/750 V"), were obtained by foam extrusion (Fig. 1, 2, 4 and 5). The topcoats were made of two commercial grades of PE-HD polyethylene, produced by Borealis (Table 1). Polyethylene was mixed with blowing agent "Hydrocel 530" in amounts up to 1 wt. %. The effects of blowing agent content on mean density, porosity degree (Table 2) and the roughness parameters of the surface were evaluated. Roughness parameters studied were as follows: mean arithmetic deviation of surface roughness profile (Ra), ten-point height of irregularities (Rz), maximum peak to valley height (Rm) and mean spacing of irregularities (Sm) (Table 3 and 4). Dependence of (Ra) and (Rz) on blowing agent content has been described with regression equations (Table 5). The values of correlation factors obtained (rkw>0.985) confirmed the good agreement of selected mathematical model with experimental data.

Application of the optical method for determining of the RMS roughness of porous glass surfaces

The application of an optical method for characterizing surface roughness is presented. This method was used for an examination of porous glass surfaces. The expressions relating the root mean square rms (σ) of a surface to its specular reflectance at normal incidence are used for σ≪λ, (λ – wavelength). For light of sufficiently long wavelength the decrease in the measured specular reflectance due to the surface roughness depends only on the root mean square (rms) height of the surface irregularities. On the basis of reflectance spectra, one can determine σ for the porous glass surfaces after technological processes. The measured reflectance spectra were compared with calculated ones for which the scattered component of light was taken into account. The parameters rms determined from the optical method are comparable to those obtained from atomic force microscopy examinations.

Verification of significant wave representation method

The significant wave representation method is the simplest method for computing the transformation of significant wave height across-shore. However, many engineers are reluctant to use this method because many researchers have pointed out that the method possibly contains a large estimation error. Nevertheless, Rattanapitikon et al. [Rattanapitikon, W., Karunchintadit, R., Shibayama, T., 2003. Irregular wave height transformation using representative wave approach. Coastal Engineering Journal, JSCE 45(3), 489–510.] showed that the wave representation method could be used to compute the transformation of root mean square wave heights. It may also be possible to use it for computing the significant wave height transformation. Therefore, this study was carried out to examine the possibility of simulating significant wave height transformation across-shore by using the significant wave representation method. Laboratory data from small- and large-scale wave flumes were used to calibrate and examine the models. Six regular wave models were applied directly to irregular waves by using the significant wave height and spectral peak period. The examination showed that three regular wave models (with new coefficients) could be used to compute the significant wave height transformation with very good accuracy. On the strength of both accuracy and simplicity of the three models, a suitable model is recommended for computing the significant wave height transformation. The suitable model was also modified for better predictions. The modified model (with different coefficients) can be used to compute either regular wave height or significant wave height transformation across-shore.

Wear of pantograph collector strips

The overhead conductor system (OCS) could be one of the most economical and feasible engineering solutions to the problem of how to transmit electrical energy to intercity trains (typically at 25 kV AC) or urban/suburban trains (typically at 1.5 kV DC) along open or tunnel routes. However, the consumption of contact wire and collector strips due to wear and tear could impose a severe cost on the railway operator should the interaction between the wear couple formed by the OCS and the pantograph be poor. Following the completion of several OCS improvement projects, this paper examines the factors that might have led to higher than expected consumption of collector strips by analysing statistical data from an operational railway. The observations so far are that irregular contact wire height relative to the rails and high ambient humidity have been identified as two of the many factors that led to the abnormal consumption of collector strips.

KrF Excimer Laser Ablation of Al2O3 and Al2O3–TiC Ceramics

Al2O3–TiC ceramics were processed with KrF excimer laser radiation (248 nm). The surface topography of the ablated Al2O3–TiC exhibits many conelike structures with a diameter of 10 µm and a column height of 30 µm. The surface roughness of Al2O3 at the base end surface is smooth, but the surface projection appears at the lateral face. The maximum height of irregularities (Rmax) of Al2O3–TiC is smaller than that of Al2O3 in the case of 0 to 50 pulses are used. However, the Rmax of Al2O3–TiC is higher than that of Al2O3 when over 50 pulses. Energy-dispersive X-ray spectroscopy (EDX) measurement reveals that the ablated conelike surface is composed of a material with high titanium content. EDX results show that the content of Al2O3 in Al2O3–TiC decreases markedly with an increase in fluence.

Accordant summit heights, summit levels and the origin of the “upper denudation level” in the Serra do Mar (SE-Brazil, São Paulo): A study of hillslope forms and processes

Abstract In southern Sao Paulo the Serra do Mar is characterized by three distinct terrain types: 1) highly dissected areas with closely spaced ridges and accordant summit heights; 2) multiconvex hills; and 3) terrains with highly elevated watershed areas, irregular summit heights, and locally subdued relief. The development of this landscape is considered to be the result of the Cenozoic block-faulting and of the influences that are exerted by the differing lithological and structural setting of block-faulted compartments on weathering and erosion processes. In areas characterized by pronounced accordant summits the close coincidence between hillslope angle and the angle of limiting stability against landsliding points to a close adjustment of hillslope gradients and the mechanical properties of the regolith. The relative height of the hillslopes is functionally related to the spacing of the valleys and the gradient of the hillslopes. In areas with a regular spacing of v-shaped valleys and uniform rocks, this leads to the intersection of valley-side slopes in summits and ridges at a certain elevation. This elevation is determined by the length and steepness of the valley-side slopes. Therefore, the heights of the summits are geometrically constrained and are likely to indicate the upper limit of summit heights or an “upper denudation level” that is adjusted by hillslope processes to the incising streams. Accordant summit heights of this type are poor indicators of formerly more extensive denudation surfaces as it is also likely that they are a result of the long-term adjustment of hillslopes to river incision. The steep mountain flanks of block-faulted compartments on the other hand, comprise regolith-covered hillslopes that are closely adjusted to the maximum stable gradient as well as rock-slopes that are controlled by the rock-mass strength. Their summits are usually not accommodated into uniform summit levels. Highly elevated watershed areas exhibiting a subdued relief are detached from the base level response. On granitoid rocks these areas are often characterized by the rocky hills and domal rock outcrops. However, differences in the elevation of interfluves and summits between rocks of differing resistance and in the elevation of lithologically distinct individual fault-blocks imply that long-term weathering and erosion has transformed and lowered these landscapes. Therefore, these areas cannot be interpreted as a remnant of a pre-uplift topography and it appears to be unlikely that the height of the summits correlates with formerly more widespread planation surfaces in the far hinterland. The studies indicate that concepts such as the parallel retreat of hillslopes cannot account for the observed differences in the landscape. It is suggested that the Serra do Mar is consumed from the Atlantic and the inland side by spatially non-uniform developmental states. These states are determined by local differences in the coupling and distance to the regional base level and sea-level or are due to lithological and structural controls between and within the block-faulted compartments.

Surface electron states produced by a Rayleigh wave

The electronic properties of a semiconductor bounded by an uneven surface representing an infinitely high potential barrier are investigated. The surface irregularities are produced by a Rayleigh acoustic wave. It is shown that, on the boundary of a semiconductor, surface electron states (waves) may arise whose dispersion laws are obtained under the conditions when conduction electrons are located either in or outside the field of the acoustic wave. Existence domains of surface electron states are found that are distinguished by their physical properties. These domains are separated by a band gap whose width is determined by the height of irregularities.

Attenuation of a Stoneley wave and higher Lamb modes due to the scattering by two-dimensional irregularities of the walls of a fluid-filled borehole

Attenuation of Stoneley waves and higher Lamb modes propagating along an irregular surface of a fluid-filled borehole is investigated. This problem generalizes the problem on the attenuation of Rayleigh waves by an irregular surface of an empty borehole [10]. The technique used to evaluate the attenuation coefficient is based on the perturbation method (surface irregularity heights are considered to be small in comparison with the wavelength) and the mean field method. As a result, an expression is obtained for the partial coefficients of the eigenmode attenuation due to the scattering of eigenmodes by the irregularities of the borehole walls into the same or other eigenmodes, as well as into the bulk longitudinal and transverse waves. The frequency-dependent behavior of the partial attenuation coefficients of both Stoneley waves and higher modes is analyzed against the ratio between the irregularity correlation length and the borehole radius for different correlation functions of irregularities.

Modelling dominant height growth and site index curves for rebollo oak (Quercus pyrenaicaWilld.)

A dominant height growth model and a site index model were developed for rebollo oak (Quercus pyrenaica Willd.) in northwest Spain. Data from 147 stem analysis in 90 permanent plots, where rebollo oak was the main species, were used for modelling. The plots were selected from the National Forest Inventory at random in proportion to four biogeoclimatic stratums. Different traditional and generalized algebraic difference equations were tested. The evaluation criteria included qualitative and quantitative examinations and a testing with independent data from another region. The generalized algebraic difference equation of Cieszewski based on Bailey equation showed the best results for the four stratums. An analysis of the height growth patterns among ecological stratums was made in order to study the necessity of different site index curves. Results indicated the validity of a common height growth model for the four stratums. In spite of the irregular height growth pattern observed in rebollo oak, probably due to past management, the model obtained allows us to classify and compare correctly rebollo oak stands growing at different sites.

Distribution of runup heights of the December 26, 2004 tsunami in the Indian Ocean

A massive earthquake with magnitude 9.3 occurred on December 26, 2004 off the northern Sumatra generated huge tsunami waves affected many coastal countries in the Indian Ocean. A number of field surveys have been performed after this tsunami event; in particular, several surveys in the south/east coast of India, Andaman and Nicobar Islands, Sri Lanka, Sumatra, Malaysia, and Thailand have been organized by the Korean Society of Coastal and Ocean Engineers from January to August 2005. Spatial distribution of the tsunami runup is used to analyze the distribution function of the wave heights on different coasts. Theoretical interpretation of this distribution is associated with random coastal bathymetry and coastline led to the log‐normal functions. Observed data also are in a very good agreement with log‐normal distribution confirming the important role of the variable ocean bathymetry in the formation of the irregular wave height distribution along the coasts.

Statistic and coherent properties of scattered light fields for different geometrical parameters of rough surfaces

The relation between the correlation and coherent properties of light fields scattered by rough surfaces and the geometrical parameters of these surfaces is analysed. It is shown that, if the coherence time of illuminating radiation is τc>10ω0 (where ω0 is the central frequency of the emission spectrum), then, by averaging the field intensity scattered by a rough surface over time T>10τc , we can determine the stationary regions and coherent parameters of the scattered field and the conditions imposed on the narrowband and chromatic (spectral) parameters of illuminating radiation. These regions, parameters, and conditions are specified by the following parameters: the coherence length Lc=τcc of illuminating radiation, the transverse size d of the backscattering region of the surface, the depth Ls of the backscattering region, the distance rc from a receiving aperture to the surface, the size dρ of the receiving aperture, the central wavelength λ0=c/ω0 of illuminating radiation, and the root-mean-square deviation σ of the height of irregularities of the surface. The obtained results give the relations between Lc , Ls , and σ at which illuminating radiation behaves as monochromatic, quasi-monochromatic or polychromatic radiation and the scattered field behaves as coherent, partially coherent or incoherent field.

Solitary wave dynamics in shallow water over periodic topography

The problem of long-wave scattering by piecewise-constant periodic topography is studied both for a linear solitary-like wave pulse, and for a weakly nonlinear solitary wave [Korteweg-de Vries (KdV) soliton]. If the characteristic length of the topographic irregularities is larger than the pulse length, the solution of the scattering problem is obtained analytically for a leading wave in the framework of linear shallow-water theory. The wave decrement in the case of the small height of the topographic irregularities is proportional to delta2, where delta is the relative height of the topographic obstacles. An analytical approximate solution is also obtained for the weakly nonlinear problem when the length of the irregularities is larger than the characteristic nonlinear length scale. In this case, the Korteweg-de Vries equation is solved for each piece of constant depth by using the inverse scattering technique; the solutions are matched at each step by using linear shallow-water theory. The weakly nonlinear solitary wave decays more significantly than the linear solitary pulse. Solitary wave dynamics above a random seabed is also discussed, and the results obtained for random topography (including experimental data) are in reasonable agreement with the calculations for piecewise topography.

Cover Picture: Structural Colors in Nature: The Role of Regularity and Irregularity in the Structure (ChemPhysChem 8/2005)

The cover picture shows the mechanism of structural color in the famous Morpho butterflies ranging over Central and South America. Their wings are covered extensively with iridescent scales, on which a lot of ridges bristle with regular projections at both sides. In their Review on page 1442 Kinoshita et al. demonstrate that these regular structures assist the selective reflection of blue light through interference, while their irregular heights give the diffusive light through diffraction. Thus the cooperation of regularity and irregularity generates wavelength‐selective, highly reflective, and spatially diffusive light in the blue region.

Chronoammetry and Chronopotentiometry on Electrodes with a Microrough Surface: Theoretical Consideration

The problem of transient two-dimensional diffusion to a microrough electrode under galvano- and potentiostatic polarization conditions is solved. The effect of the scale and morphology of roughness, as well as the diffusivity on the time dependences of I current and η overpotential is analyzed. Both of them are found to be practically independent of the type of the roughness, while its degree (the microroughness factor f r ) decisively affects the shape of the current- and overpotential-decay curves. At a relatively short polarization when the diffusion front profile repeats the electrode surface relief, the parameters of transient electrochemical methods (the I current in the potentiostatic measurements and the τ1/2 rooted transient time in the galvanostatic ones) linearly depend on the microroughness factor. Upon a relatively long polarization when the diffusion front is noticeably distant from the surface and almost planar, the current and overpotential values fit in with classical equations of chronoammetry and chronopotentiometry, being independent of f r . At a thickness of the diffusion layer comparable to the height of surface irregularities, the current (as well as the rooted transient time) ratio of the microrough to perfectly smooth electrode surface looses its linear dependence on the surface parameters. The time location of this range is chiefly determined by the diffusivity and the mean distance between the microscopic surface irregularities.