L. V. Vanegas Useche, M. M. Abdel Wahab, and G. A. Parker, “Theoretical model for the free-flight behaviour of the bristles of an oscillatory gutter brush for road sweeping, Proc. XI th Int. Conf. Vibration Engineering, Timisoara (Rumania), Sep. 27- 30 de 2005, pp. 83-90.  E. Rabinowicz, Friction and Wear of Materials, second edition, U.S.A.: John Wiley & Sons, Inc., 1995.  G. G. Adams, S. Müftü, and N. M. Azhar, “A scale- dependent model for multi-asperity contact and friction,” ASME, J. Tribology, vol. 125, pp. 700-708, 2003.
In the same way, authors like García et al , studied the influence of different thermal treatments of quenching and tempering on the microstructure, hardness and tribological behavior of an austenitic steel. The results showed that for without heat treatment, and quenched in air and oil conditions was obtained an increase in the hardness values after of the wear test. In the case of quenched steel in water, the hardness not was obtained. The authors to explain that the increase in the hardness values were consequence of the transformation of austenite to martensite due to the friction force present during the tests. Ulutan et al  studied the coefficientoffriction behavior on the AISI 4140 steel without heat treatment and with quenched in oil, finding that the steel without treatment presented the highest loss of mass. The coefficientoffriction found between the two conditions have practically the same value, however, the values obtained for quenched steel presented lower standard deviation.
This guide presents information to assist in the selection of a method for measuring the frictional proper- ties of materials for a particular application. Requirements for minimum data and a format for presenting these data are suggested. The use of the suggested reporting form will increase the long-term usefulness of the test results within a given laboratory and will facilitate the exchange of test results between labo- ratories. It is hoped that the use of a uniform reporting format will provide the basis for the preparation of handbooks and computerized databases. This guide points out factors that must be considered in con- ducting a valid test for determination of the coefficientoffrictionof a tribosystem, and it encourages the use of a standard reporting format for friction data. The factors that are important for a valid test may not be obvious to non-tribologists, and the friction tests referenced will assist in selecting the apparatus and test technique that is most appropriate to simulate a tribosystem of interest. The tribology literature is replete with friction data that cannot readily be used by others because specifics are not presented on the tribosystem that was used to develop the data. The overall goal of this guide is to provide a reporting format that will enable computer databases to be readily established. These databases can be de searched for material couples and tribosystems fo interest. Their use will significantly reduce the need for each laboratory to do its own testing. Sufficient information on test conditions will be available to determine applicability of the friction data to the engineer’s specific needs.
interesting by their own and by their practical implications. Selected salts are the major constituents of seawater and the parameters obtained by fitting experimental data to Pitzer model can be used to estimate activity coefficients in complex mixtures such as seawater; illustrating how to calculate properties in mixed electrolytes from those in the pure components. On the other hand, acid–base equilibria of organic substances in saline solutions are influenced by the activity coefficientof the neutral species appearing in the equilibria, so this paper can be understood as a previous step to the determination of dissociation constants of TEA in the salts used here and different mixtures, that it is under study in this laboratory.
In general, friction and wear is believed to result from three components: adhesion, ploughing and asperity deformations , several mechanisms have been proposed to explain how material is removed from the surface of WC-Co during sliding test because friction contacting bodies is a complicated phenomenon. The applied load is initially carried by only a few surface asperities, as sliding proceeds, the load is distributed over a large contact area since the surface roughness decreases. As indicated by [5,7,8] and based on the recorded responses from the sliding test, the wear resistance of WC based cemented carbides generally increases with reduced carbide grain size and decrease binder content, and thus, with increases hardness. Fig. 7 shows the values offrictioncoefficient, the 2608 grade have the lowest frictioncoefficient and the highest hardness (Fig 6), it is well know that coarse- grained cermets usually have lower abrasive wear resistance than that of fine or medium grain size and it is clear that the heterogeneity in the particles morphology and the gaps between them is obviously related to the sizes and all this is critical to the wear behavior and coefficientoffriction observed in WC-Co structure. Based on the experiments completed during this test program and the interpretation of the sliding tribological testing, the following is a summary obtained in this investigation:
Figure 4 shows the cross section morphologies of PMMA/CaO coating on UHMWPE used for thickness determination as representative. The micrograph shows a homogenous coating with an average thickness of 107 µm, whereas PMMA coating shows an average thickness of 97 µm. It is important to mention that these coatings did not break after polishing process, which suggests that the coatings exhibit good adhesion to the substrate. Generally, coatings on substrates with different bonding nature can break off due to weak bonding strength  or due to the high stresses between the substrate and the coating . In the case of PMMA-coated UHMWPE, the adhesion results might be related with a good bonding between UHMWPE and PMMA due to formation of covalent bonds.
As the resultant formation of the composite is not only affected by the tool geometries and chosen parameters, but also by the process itself, some other factors have to considered, which may have led to variations within the results. First of all, the channels were filled manually. Even though this was carried out as uniformly as possible, the volume fraction is assumed to vary. Furthermore the touching of the reference point was also carried out manually, which causes variations of the plunging depth. This parameter is also influenced by frictional heating as the tool is elongated by thermal expansion and the tool shoulder plunges in slightly deeper at the end of the joint. Consequently, more powder gets pushed out of the joint by the tool shoulder and the volume fraction decreases at this location. For the analysis of material flow patterns, these errors are not considered as critical but they certainly affect the resistance values in a way, that they can practically all be put into one stray area.
Currently, after appropriate heat treatments, the 6xxx aluminium alloys are used in a variety of applications including aircraft fuselage skins and automobile body panels and bumpers, instead of more expensive 2xxx or 7xxx alloys. The paper presents the results of the residual stress analysis in case ofFriction Stir Processing - FSP of AA6061-T4 plates, 10 mm thickness, demonstrating the process ability to locally modify the base metal properties. The residual stresses, DRX depicted, are correlated with the microstructure and hardness results.
For the purpose of this article, it is convenient to remind that Ref.  obtains Eq. (1) minimizing a ratio of two well-defined times. This minimization is carried out over the set of all the available experimental arrangements (for a two-dimensional cascade) that can support a given operational point defined by steady and homogeneous inlet and outlet profiles (this configuration is called in Ref.  a theoretical flow pattern) in a noisy environment. The Theorem requires as a premise a noisy environment, i.e., it requires the presence of disturbances without specifying the nature (frequency or amplitude) of such disturbances. The required times are the escaping time and the restoring time, which, as it is proved in Ref. , can be calculated by using a model based on the integral form of the conservation equations. The calculation of these times also requires to know two characteristic lengths related to the geometry of the rotor, l and l x . The first characteristic length, l , is the azimuthal length, and the other
dislocations formed during the direct transformation have a unique substruc- ture with leaf-like features. The leaf dislocations are generated during the direct transformation to accommodate the growth of the martensitic plate. However, after the thermal cycle is completed and during the subsequent direct transformation, the leaf dislocations appear to impede the nucleation of the same type of martensitic needle which generated the dislocation in the previous thermocycles. Therefore, the leaf dislocations oppose the nucleation and growth of the martensite and delay these processes. In its turn, the re- sults shown by Pelton et al.  corroborate the generation of dislocations during the thermally induced B2 → B19’ MT and the interaction between the motion of the interphase boundaries and these dislocations. Following Pelton et al., during the first transformations, the growth of the martensite generates shear loops. Next, with the subsequent thermocycles, the moving interfaces act as crystallographic “snowplows” that force the initial shear loops to slip (and cross slip) in a certain crystallographic direction. This mechanism gen- erates sessile bands of dislocations which can lock the interfaces. Another consequence of the generation of dislocations is the increase of both the fric- tional and elastic energy with increasing cycles. The increase of frictional work establishes a link with the already discussed high transformation hys- teresis of the transformations to/from B19’ phase (IMTs) as compared with the athermal transformation paths, see Section 3.5 on page 138.
shoulder. FSP tool characteristics are presented in Table 1. When the rotating pin contacts the surface it rapidly friction heats and softens a small column of metal. The tool shoulder and the length of the entry probe control the penetration depth. When the shoulder contacts the metal surface, its rotation creates additional frictional heat and plasticizes a larger cylindrical metal column around the inserted pin. The shoulder provides a forging force that contains the upward metal flow caused by the tool pin.
DE COLOMBIA a través del Arquitecto Fernando Villada, a quien se le agradece por su gestión. Se dan agradecimientos también a la empresa COLOMBIT de Manizales quien muy gentilmente hizo la donación del panel de fibrocemento para la construcción de la cámara de insonorización. Además, se establece un protocolo para la medición y calculo del NCR. En el caso de la cámara de insonorización, después de analizar las experimentaciones realizadas en este campo se toma como base los modelos implementados por la empresa COLOMBIT S.A.  y el modelo expuesto en el texto Chapman y Hall, The Measurement and Suppresion of Noice, Publishers  y el procedimiento sugerido en Cyril , los cuales se adaptan a los requerimientos deseados para esta investigación de carácter académico. El diseño y construcción de la cámara no se expone en esta publicación en razón a lo extenso y merece un tratamiento independiente .
Reduced models are therefore required to evaluate the sys- tem vibrational response at a much lower computational cost. With this idea in mind, Sinha and Griffin [5, 6] used a simplified mass-spring system to qualitatively analyze the nonlinear friction stabilizing effect of an unstable rotor stage. In this paper, a new, quantitatively accurate simplified model is derived using asymp- totic techniques. In the resulting model the fast linear oscillation of the blades is filtered out, and it describes only the slow time dynamics of the system.
A non-conventional analysis of stoichiometric equilibrium constants versus ionic strength data is carried out. On one hand, Pitzer’s model is easily applied to calculate the salting coefficient and the thermodynamic equilibrium constant of the alkylamines. On the other hand, the mean spherical approximation has the advantage over the Debye–Hückel based theories that it can account for effects produced by species of different sizes. Here, it is applied to predict the dependence of the salting behavior on the size of the alkylamines.
Background: The problem of missing values at the item level is common in studies using educational and psychological tests. The aim of the present work is to explore how the estimation of reliability is affected by missing values. Method: Using real data, we simulated missing values in accordance with a “missing at random mechanism”. Four factors were manipulated with the aim of checking their effect on the estimation of the reliability of the instrument: missing data mechanism, percentage of missing data in the database, sample size, and procedure employed for the treatment of missing values. Results: The results show that the quality of estimations depends on the interaction of various factors. The general tendency is that the estimations are worse when the sample size is small and the percentage of missing values increases. Listwise is the worst procedure for treatment of the missing data in the simulated conditions. Conclusions: It is concluded that with a small percentage of missing values one can obtain estimations that are acceptable from a practical point of view with all the procedures employed, except Listwise.
The ground on which the dam is placed is mafic and ultramafic rocks of the Villa de Cura group. They have been characterised with a Young’s modulus of 20 GPa and a Poisson’s ratio of 0.25. The thermal properties of the ground were assumed to be similar to those of the concrete of the dam. To ensure that the results are conservative in relation with possible concrete cracking, it has been assumed that the ground will not experience any cracking and that the no relative movements take place across the dam-rock interface.
In this paper two measuring systems and two versions of the reflection measuring method are compared. The methods include the Adrienne method for in-situ measurement of the absorption coefficient, and a second method which is basically similar to the first mentioned method, except it uses multiplication of the impulse responses with the ratio between estimated time of arrival of the direct and reflected incoming sound impulse, as used in some commercial acoustic measurement applications such as Easera.
The starting point is to draw a scatter of points on a graph, with one variable on the X-axis and the other variable on the Y-axis; it is customary represent the dependent variable on the vertical axis and independent on the horizontal axis. When studying the relationship between two variables, one can be considered as cause and the other as a result or effect of the other. Call the exogenous or independent variable that causes, the effect is the endogenous variable. The scatter plots or diagrams give an idea of the relationship (if any) between the variables as suggested by the data. The closer the points of a straight line are, the stronger the linear relationship between two variables will be.
If the value of r is 1.0, there is a perfect direct or positive linear (straight-line) relationship. If the value of r is -1.0 indicates a perfect inverse or negative linear relationship, i.e. “y” increases uniformly as “x” decreases, and 1 indicates a perfect direct linear relationship, i.e. “x” and “y” move uniformly together. A value of close to 0 indicates no correlation. Note that correlation can determine that a relationship exists between variables but says nothing about the cause or directional effect.
We use the graph of standardized residuals against estimates typified. If the variance of the residuals is constant, the cloud of points would be concentrated in a band centered at zero and parallel to the x-axis. We note that there is no consistent pattern clearly defined in the data and the residuals fluctuate randomly around the line corresponding to the average of the same and "0" There is, otherwise, good scatter, therefore we can say the error terms are independent.