Microscopic Irregularities Research Articles

The effect of groove-textured surface on friction and wear and friction-induced vibration and noise

This paper presents an experimental study on the influence of groove-textured surface on tribological behaviors and friction-induced vibration and noise properties. Groove-textured surfaces with different widths and pitches were manufactured on compacted graphite iron materials (brake disc material) by electromachining. The difference between the groove-textured and original smooth surfaces in friction and wear and vibration and noise properties was studied, by using a developed device which is able to synchronously measure and analyze the friction force, vibration acceleration and noise signals in a ball-on-flat reciprocating sliding configuration. It is shown that the squeal generated from the groove-textured surface was more influenced by the dimensional proportion of groove width to pitch, instead independently by groove width or pitch. Groove-textured surfaces with a specific dimensional proportion of groove width to pitch of 1/2, i.e., the width of groove equal to the width of ridge, showed good potential in reducing and suppressing squeal. The groove was the dominant surface component of contact surface topography affecting the generation of squeal compared to the microscopic irregularities of the worn surface. The wave-fluctuations of the friction force caused by counterface ball sliding across the grooves were found to play a crucial role in the squeal generation, which can effectively disturb the self-excited vibration of the friction system and consequently reduce the tendency to squeal.

Propriedades mecânicas e molhabilidade de filmes de zeínas extraídas de glúten de milho

Zeínas são proteínas de reserva do milho (prolaminas), que podem ser extraídas através de solubilização em meio alcoólico. Essas proteínas são altamente hidrofóbicas, com elevado grau de polimerização. Neste estudo, zeínas do tipo a (massa molecular entre 10 e 22 kDa) foram extraídas do glúten do milho e caracterizadas com respeito às suas principais bandas de absorção espectroscópica na região do infravermelho. Blendas de zeínas com ácido oléico (AO) como plastificante foram avaliadas em diversas proporções e filmes processados por casting sobre superfície apolar. Filmes de zeínas sem plastificante mostraram-se inviáveis para manipulação e medidas, mas a adição de 1 e 2% em massa de AO proporcionou um significativo aumento do módulo de elasticidade, segundo análise realizada por DMA. A presença de plastificante introduz também irregularidades superficiais e leva a uma perda das características hidrofóbicas dessas proteínas.

Optical Coherence Tomography Anatomy of the Corneal Endothelial Transplantation Wound

The goal of this study was to prospectively assess the deep lamellar endothelial keratoplasty (DLEK) wound anatomy and its evolution during the 12 months after surgery, using optical coherence tomography (OCT). The eyes of 8 patients (1 eye per patient) who consecutively underwent DLEK for Fuchs dystrophy or pseudophakic bullous keratopathy were prospectively studied before and 1, 3, 6, and 12 months after surgery. The Stratus OCT apparatus (Carl Zeiss Meditec, Dublin, CA) was used to acquire central and radial scans perpendicular to the wound at 3-, 6-, 9-, and 12-o'clock positions. The following parameters were analyzed: central total thickness, posterior donor-recipient edges gap, donor-recipient height mismatch, tissue compression, and graft detachment. A posterior gap was observed in 4 of the 8 DLEK eyes. At 12 months, the mean gap contour, depth, and width were 242 +/- 67, 101 +/- 45, and 87 +/- 29 microm, respectively. A step was documented in all DLEK eyes (average step height 108 +/- 24 microm). A micrograft detachment was observed in one case and tissue compression in another. In all corneas, the mean central corneal thickness returned to normal range and almost normal anatomy with time after surgery. OCT was found to be a very useful tool for DLEK corneal wound architecture analysis. It revealed microscopic wound irregularities and allowed their quantitative follow-up with time.

Effects of surface irregularities on intensity data from laser scanning: an experimental approach.

The results of an experiment carried out with the aim to investigate the role of surface irregularities on the intensity data provided by a terrestrial laser scanner (TLS) survey are reported here. Depending on surface roughness, the interaction between an electromagnetic wave and microscopic irregularities leads to a Lambertian-like diffusive light reflection, allowing the TLS to receive the backscattered component of the signal. The described experiment consists in a series of TLS-based acquisitions of a rotating artificial target specifically conceived in order to highlight the effects on the intensity data due to surface irregularity. This target is articulated in a flat plate and in an irregular surface, whose macro-roughness has a characteristic length with the same order of the spot size. Results point out the different behavior of the plates. The intensity of the signal backscattered by the planar element decreases if the incidence angle increases, whereas the intensity of the signal backscattered by the irregular surface is almost constant if the incidence angle varies. Since the typical surfaces acquired in a geological/geophysical survey are generally irregular, these results imply that the intensity data can be easily used in order to evaluate the reflectance of the material at the considered wavelength, e.g. for pattern recognition purposes.

Chronovoltammetry of the anodic dissolution of Ag-Au alloys in nitrate environments

A theory of quasi-reversible anodic chronovoltammetry of the selective dissolution of a homogeneous A-B alloy controlled by the solid-phase diffusion is proposed. The effects of the equilibrium solid-phase adsorption of the components and the roughness of the electrode surface with either homogeneously or statistically normally distributed microscopic irregularities of diverse kind on the shape of chronovoltammogram (the I A current dependence on the η(t) overpotential) are successively taken into account. An expression for the I A, m current at the voltammogram maximum, which is a generalization of the Randles-Sevik formula, is derived. A technique of estimating the recording-time boundaries of voltammograms, within which the surface roughness effect may be taken into account by simply multiplying the current by the roughness factor f r , is founded. Outside the time interval, the I A,m − ν1/2 dependence (ν is the potential scanning rate), which is criterion for the diffusion kinetics, is shown to be substantially nonlinear. The diffusion-zone parameters (δ thickness and D Ag heterodiffusion coefficient) obtained by processing the experimental data for Ag-Au alloys with a gold content of 15 or 20 at.% with the use of three models discussed are compared.

Microscopic Investigation of the Excitons' Intermolecular Energy Migration in the β Phase of Poly(9,9-dioctylfluorene) by Confocal Laser Spectroscopy

We investigated, by confocal laser spectroscopy, the role of the microscopic morphology on the fluorescence spectra of poly(9,9-dioctylfluorene) (PF8) thin films self-doped by the PF8 β phase. We demonstrate the existence, on the micron scale, of different regions in the films, characterized by locally different fluorescence spectra. We show that the microscopic morphology irregularities lead to locally nonuniform β-phase density resulting in the switching on or off of the intermolecular energy migration within the β-phase excited-state distribution. This effect causes considerable local variation of the fluorescence spectra consisting of a progressive red shift (up to 26 meV) and a line width narrowing from about 70 (similar to the absorption one) down to 52 meV.

Simultaneous occurrence of double micro/macro stress singularities for multiscale crack model

It is rare to find two distinct stress singularities with different order at the same crack tip while the local displacements remained regular. Such a discovery was made when developing a dual scale micro/macro crack model and validated from a closed form asymptotic analytical solution for a micro/macro crack subjected to mixed boundary conditions. The two different orders of the stress singularities are 0.75 and 0.25 for an incompressible material. The existence of multi-singularities with different orders at the crack point is an unexplored area of research. For a sharp notch wedge, multi-stress singularities at the wedge point can prevail and they depend on the notch angle and Poisson’s ratio. Physical implications of such solutions when viewed at the microscopic scale are particularly significant as they tend to suggest that the multiple combinations of geometries and materials can yield so many different combinations of distortional and dilatational effects. No wonder microscopic irregularities seem to be the rule. Discontinuous numerically solutions, however, may or may not correspond to singularities. In view of the recent research emphases on multiscaling, the multiple singularity solution at a point seems to signify the inherent characteristics of micro-defects. They are irregular and defy self-similarity. The double singularity alone implies that a microcrack can extend in two different directions from the same location, known as branching in the very rapid propagation of a macrocrack. At the microscopic scale, double singularity implies the possibility that branching can occur under macroscopic static load. Such a behavior of static branching of microcracks associated with double singularity is being established. A fundamental aspect of this model is the inherent existence of restraining stress from the material that is essential for the microcrack and only sometimes for the macrocrack. As a rule, the microcrack being smaller would react to the material restraint more readily. Such a feature is necessary in the model in addition to the effects of micro/macro material interaction and the macrocrack characteristic length with reference to the macrocrack length. In normalized form, the minimum of three parameters, say μ ∗, σ ∗ and d ∗, would be necessary for the formulation of the dual scale micro/macro crack model. The combined effects of μ ∗ (micro/macro material), σ ∗ (load and restraint) and d ∗ (characteristic length) cannot be over emphasized in multiscale modeling. In the spirit of classical fracture mechanics, a micro/macro crack intensification factor K micro macro is defined and obtained in closed form. It contains three basic parameters μ ∗, d ∗ and σ ∗ being unique to all microcracks while two parameters ϕ 1 and ϕ 2 can be used to describe additional features of the microstructure. More precisely, the specific material microstructure can be modeled by two or more parameters associated with the eigenvalues selected rather than using the constitutive relations in the traditional manner. The asymptotic form of K micro macro is exact such that the case specific nature of microcracking can be distinguished by two constants. The contribution of this work is to establish the potential use of the dual singularity solution. The basic concept of the method applies to other multiscale problems in mechanics and physics.

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.

タングステンカーバイド系溶射皮膜の研削加工に関する研究

This paper discusses the grindability of sprayed coatings of tungsten carbide-based cermet. A sprayed coating exhibits weak interparticle cohesion because it is actually a laminate of fine particles. Nevertheless, sprayed coatings can easily be applied to parts that require the coating of large areas. This experiment compared the grindability of sprayed coatings obtained by high velocity oxygen fuel (HVOF) spraying of thermal spray materials varying in the proportion of tungsten carbide and containing different kinds of binding agents (Co, Ni-Co, Ni, or Ni-Cr). Aresinoid diamond grinding wheel was used to grind the surface of the sprayed coatings. The grinding surfaces tended to be rough because they frequently bore microscopic irregularities caused by partial peeling, cracking, or swelling of the sprayed particles. Of the materials tested, coatings of Co-based binding agents with higher proportions of WC provided better ground surface properties.

Spin fanning configurations in antiferromagnetic layers with a uniaxial anisotropy and torque transfer characteristics from top to bottom spins

Spin configurations along the thickness direction generated in antiferromagnetic (AF) layers with an in-plane uniaxial anisotropy have been calculated by numerical method. It is confirmed that when the bottom-surface anisotropy energy constant is less than 1/4 of 180°-wall energy density, σw, a sudden change or switch of the spin configuration occurs at a critical angle of the top spins when the AF-layer thickness, t, is greater than a critical value, tc. This means that no hysteresis occurs with a rotation of the top spin for t<tc. Spin configurations with a folded or periodic structure which Néel discussed have been revealed to be unstable without microscopic defects or irregularities which pin the spin angle at some depth from the top surface. It is found that when the bottom-surface anisotropy is lower than 1/4σw, the torque sustainable by the top-surface spins does not exceed 1/2σw. It is also found that the effect of top-spin rotation penetrates substantially down as deeply as a few times the 180°-wall thickness. The effect of the AF-easy axis tilting out of the plane has also been studied.

Signal and noise characteristics of thin film media estimated by magnetic force microscopy

An analytical magnetic force microscopy has been applied to investigate the relationship between the media S/N and the microscopic magnetization irregularities of CoCr-alloy longitudinal and single-layer perpendicular media recorded at linear densities up to 450 kFCL. When the S/N is compared between longitudinal and perpendicular media, a 16-nm-thick CoCrPt longitudinal medium shows a little higher S/N than that of a heat-treated 25-nm-thick CoCrTa perpendicular medium. The medium S/N is found to deteriorate with increasing the size and the number of magnetization transition irregularity.

QUANTITATIVE ANALYSIS FOR SHAPE IRREGULARITY OF CERAMIC PARTICLES BASED ON RICHARDSON EFFECT

Quantitative analysis for the shape irregularity of ceramic particles was performed by applying the concept of “Fractal” proposed by B.B. Mandelbrot. Two types of ceramic particles processed by different methods were employed as samples. Silhouette of each particle was repeatedly observed along 3-dimensional Cartesian axes, and then Richardson effect of the configuration of the respective silhouette was normalized by the perimeter. In this normalized Richardson effect, a characteristic aspect concerning the microscopic and macroscopic irregularities of particle shapes was found. The microscopic irregularity was successfully represented by a fractal dimension, whereas the macroscopic one was well evaluated by another parameter of macroscopic shape index introduced in this study.

An investigation of the temporal development of the pseudospark discharge

A study of the different discharge phases of the pseudospark discharge is presented. During the temporal development several modes of the pseudospark discharge are observed leading to a transient, high current, low pressure gas discharge with current densities of the order of 10/sup 4/A/cm/sup 2/ and a forward voltage drop of about 10/sup 2/ volts. Therefore measurements of the discharge current, the total charge transported, the forward voltage drop and the influence of the gas pressure and LRC circuit, from initial phase of discharge until the transient phase to the superdense glow, are reported. Through comparison of experimental results with literature the different types of discharges are characterized. Optical studies of the radially expanding plasma column enable the temporal and spatial location of the discharge plasma. In the high current phase estimations of the temperature on the cathode surface and the solution of the Schottky-Equation show that a constriction of the ion current at microscopic surface irregularities is necessary to sustain the discharge.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Film thickness of die coating agents

Die coating agents are often used during the fabrication of porcelain margins for crowns and fixed partial dentures. These agents seal microscopic irregularities within the stone die and resist abrasion. This investigation measured the film thickness of several die coating agents. A specific reference point was used during the measurement process. The results indicate that there is no significant difference between the die coating agents examined under the conditions of the study. The film thickness measurements ranged between 0.367 μm for Duro Super Glue Material and 2.3 pm for Zap CA material.

On the applicability of a constant phase element (CPE) to the estimation of roughness of solid metal electrodes

The dispersive behaviour observed at rough electrodes can be described by a constant phase element (CPE) of the form Z(ω) = K(jω)−α, where α has a value between 0·5 (porous electrodes) and unity (ideally flat electrodes). It is shown experimentally, that α unequivocally reflects the roughness of solid electrodes and is independent of the electrode material. Using the concept of fractal geometry the parameter α, often denoted only as a fit parameter, is characterized as a purely geometric size. If the rough surface has self-similar scaling characteristics, the CPE is directly related to the so-called fractal dimension D and therefore α can be understood as a measure of microscopic irregularities.

Non-Destructive Detection of Drop Out by a Measurement Tape/Head Contact Condition

With the recent increases in recording density of VCRs, tape/head interface problems have become much more immediate. Magnetic recording characteristics such as dropout are greatly affected by dust and by microscopic irregularities or protrusions on the tape surface. In this paper, we report on the non-destructive detection of dropout using a system which measures the state of tape/head contact. Experiments have shown that stretching of the tape/head spacing was several hundred times the height of protrusions, and that the coefficient of the record/playback spacing loss was 100 dB.

Properties of discrete electrostatic systems

Further to a recent controversy1–5, it is well known that continuous classical electrostatics6,7 is an approximate description which smoothes the ‘microscopic irregularities’7 of discrete systems. Our purpose here is to highlight these microscopic details. We have studied the stability, Coulomb potential energy (W), electrostatic potential (V) and field intensity (E) for several arrangements of N point charges q on and inside the surface of a sphere of radius R (N≤20). As expected, discrete and continuous configurations differ in several respects. The energy form-factor w = W/N2 for a surface-charged sphere ranges from 0.l25q2/R at N = 2 to 0.377 q2/R at N = 20 (the latter value is ∼75% of the continuous limit, 0.5 q2/R). The field intensity inside the sphere is non-zero in the discrete case, but quickly tends, with increasing N, towards the continuous limit (zero). The common practice of treating small-N physical systems as continuous conceals properties that would otherwise be obvious.

Effect of production factors on the surface quality of metal frames for metal-ceramic dental prostheses

1. The surfaces of the different groups of alloys change in different ways during technological processing. With the alloys based on Cr-Ni there is a general tendency to smooth out the sharp protuberances and angles while maintaining the general coefficient for the surface roughness. With alloys based on Cr-Co (KKhS) the surface is “coarsened” during technological processing before deposition of a ceramic. Clearly defined are high peaks of the microscopic irregularities that typify a rough surface with deep craters and abrupt cleavage faces. 2. During the heat treatments the oxide films that form on the surface of specimens for the different alloys differ substantially with respect to strength and thickness. With the alloy KKhS the oxide film obtained is thicker and looser than the oxide film on the surface of frames made from alloys based on Cr-Ni. As a result, the surface of the KKhS alloy after pneumatic-abrasive treatment looks coarser because the “caling” of the oxide film by a jet of corundum takes place at great depth and the phase heterogeneity of the alloy favors the development of abrupt drops in the surface topography. The development of such irregularities in the surface topography causes the appearance of stress concentrators at the metal-to-porcelain interface which may substantially reduce the strength of the metal-ceramic system. With the alloys based on Cr-Ni the possibility that portions of enhanced stress will occur in the transition zone is less than with the alloys based on Cr-Co.

Induction of osteoarthrosis in the guinea pig knee by papain

The main purpose of this investigation was to develop a model for experimental induction of osteoarthrosis. A previously described method using papain was tried on guinea pig knee joints. Eighteen adult guinea pigs were given papain intra-articularly in the right joints; the left joints were used as controls. The animals were killed after 6 hours, 1 week, 2 weeks, 2 months, 4 months, 6 months, 8 months, and 10 months. Specimens of the articular cartilage were removed for histologic and histochemical investigation. Microscopic surface irregularities could be observed in the animals after 6 hours, 1 week, and 2 weeks, and again after 8 and 10 months. Histochemical examination of the sections from the experimental joints indicated a loss and degradation of the sulfated glycosaminoglycans. This loss was evident after 6 hours, 1 week, 2 weeks, and 8 months. The first osteoarthrotic changes were observed macroscopically after 8 months. Radiographic changes in the experimental joints could be observed in all animals killed after 10 months. It was concluded that osteoarthrosis similar to that occurring in humans can be induced by this method.

Performance of low cost solar reflectors for transferring sunlight to a distant collector

Efficiency of reflection and optical transmission to a distant collector is a critical parameter, along with cost per unit area, in the selection of a heliostat design for the Central Collector Solar Electric Plant. Efficient optical transmission is not easily accomplished because of the large distance to be spanned in a multi-MW facility. Depending on heliostat location, the transmission distance may vary from a few hundred to thousands of feet. Design conditions which influence optical transmission over these long distances are: heliostat pointing accuracy; spreading of the reflected solar beam due to the finite size of the Sun's image; beam spreading due to reflector misalignment or waviness; aberration present if curved heliostat reflectors are used and beam spreading due to microscopic irregularities (characteristic length less than 0.1 mm) in the reflective surface. These factors increase in importance as the transmission distance from heliostat to collector increases. Even the most preliminary heliostat design activity requires a detailed evaluation of beam spreading before the most cost effective heliostat concept, or family or concepts depending on transmission distance, can be defined. Data are presented here which will be of value in assessing one of the factors causing beam spreading. An experimental method has been utilized to determine beam spreading due to microscopic surface irregularities prevalent with “mill finished” materials. The test method provides a nearly independent measure of the effect of surface imperfections. Data are presented for five candidate materials and, as reference, an optical quality first surface mirror.