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Mechanical Models (mechanical + models)
Selected AbstractsViscoelastic and damping characteristics of poly(n -butyl acrylate)-poly(n -butyl methacrylate) semi-IPN latex filmsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2007K. I. Suresh Abstract This article reports the synthesis, characterization, and damping characteristics of semi-interpenetrating (semi-IPN) latex systems composed of poly n -butyl acrylate (PBA) core and poly n -butyl methacrylate (PBMA) shell. The IPN's were prepared by seeded emulsion polymerization using crosslinked PBA seeds with varying crosslinker (m -diisopropenyl benzene) concentration. The polymer weight ratio in the first and second stage polymerization is maintained at 1:1 in all the cases. The particle size determined by dynamic light scattering shows a decrease in the shell thickness with increasing crosslinker concentration of the seed. The mechanical properties, like Shore A hardness of the films, increased from 18 to 65 when the crosslinker concentration is increased from 0 to 4.8,mol%. The dynamic mechanical studies show that the modulus value of the IPN's is below that of non-crosslinked films, and the value depends upon the crosslink density of the seed. Mechanical models, such as the Kerner's model and the Takayanagi's model, were used to explain the variation in the dynamic mechanical properties with the degree of seed crosslinking. The study indicates lower bound (rubbery) behavior for the films with lightly crosslinked cores. The study also shows that, at lower crosslinker concentration enhanced phase separation and better damping properties are achieved but at higher cross linker concentration (>2,mol%) greater interpenetration of the shell monomer to the cores takes place and tough films, with reduced damping properties are formed. Copyright © 2007 John Wiley & Sons, Ltd. [source] A framework for quad/triangle subdivision surface fitting: Application to mechanical objectsCOMPUTER GRAPHICS FORUM, Issue 1 2007Guillaume Lavoué Abstract In this paper we present a new framework for subdivision surface approximation of three-dimensional models represented by polygonal meshes. Our approach, particularly suited for mechanical or Computer Aided Design (CAD) parts, produces a mixed quadrangle-triangle control mesh, optimized in terms of face and vertex numbers while remaining independent of the connectivity of the input mesh. Our algorithm begins with a decomposition of the object into surface patches. The main idea is to approximate the region boundaries first and then the interior data. Thus, for each patch, a first step approximates the boundaries with subdivision curves (associated with control polygons) and creates an initial subdivision surface by linking the boundary control points with respect to the lines of curvature of the target surface. Then, a second step optimizes the initial subdivision surface by iteratively moving control points and enriching regions according to the error distribution. The final control mesh defining the whole model is then created assembling every local subdivision control meshes. This control polyhedron is much more compact than the original mesh and visually represents the same shape after several subdivision steps, hence it is particularly suitable for compression and visualization tasks. Experiments conducted on several mechanical models have proven the coherency and the efficiency of our algorithm, compared with existing methods. [source] Setting up 13C CP/MAS experimentsCONCEPTS IN MAGNETIC RESONANCE, Issue 1 2004R.E. Taylor Abstract The 13C cross-polarization (CP) technique combined with magic angle spinning (MAS) has become one of the more commonly performed solid-state nuclear magnetic resonance (NMR) experiments. The basics of initially setting up the experiment are given and used to illustrate such NMR phenomena as rotational echoes, homogeneous and inhomogeneous interactions, continuous wave 1H decoupling, and coupling of quadrupolar 14N nuclei to 13C nuclei. The polarization transfer from the protons to the carbons is described briefly with the usual thermodynamic and quantum mechanical models. The setup and use of the experiment for routine analyses are discussed. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 22A: 37,49, 2004. [source] Semiclassical path integral theory of a double-well potential in an electric fieldINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2006Theodosios G. Douvropoulos Abstract A recently published methodology based on semiclassical path integral (SCPI) theory was implemented in the case of a model of a double-well potential perturbed by a static electric field, with application to the inversion frequency of NH3. This model was chosen as an idealized case for testing of the present approach, as well as for quantum mechanical models that might be applied in the future. The calculations were concerned with the variation of the frequency of inversion as a function of field strength, F, and of distance, xf (from the symmetric point xo = 0), where the field is "felt." It is found that this variation occurs sharply in very small regions of values of these parameters, and the system switches from internal oscillation to diffusion to the continuum. The fact that the theory is in analytic form allows the extraction of results and conclusions not only at the full SCPI level, but also at the Jeffreys,Wentzel,Kramers,Brillouin (JWKB) level. Comparison shows that the discrepancy sets in as the field strength increases, in accordance with the well-known limitations of the JWKB method regarding its dependence on the degree of variation of the potential as a function of position. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Antinociceptive action of the extract and the flavonoid quercitrin isolated from Bauhinia microstachya leavesJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 10 2005Vinícius M. Gadotti This study examined the antinociceptive effect of Bauhinia microstachya (Leguminosae), a native plant widely distributed in the South of Brazil, in several chemical and mechanical models of pain. The methanolic extract (ME) from B. microstachya (3,30 mg kg,1, i.p.) and the isolated compound quercitrin (1,10 mg kg,1, i.p.), given 30 min earlier, produced a dose-dependent inhibition of acetic-acid-induced visceral pain in mice, with a mean ID50 value (dose necessary to reduce the nociceptive response by 50% relative to the control value) of 7.9 and 2.4 mg kg,1, respectively. The ME of B. microstachya (3,100 mg kg,1, i.p., 30 min earlier) also caused a dose-dependent inhibition of capsaicin-induced pain, with a mean ID50 value of 18.8 mg kg,1. Moreover, the ME (3,100 mg kg,1, i.p., 30 min earlier) produced marked inhibition of both phases of formalin-induced pain, with mean ID50 values for the neurogenic and the inflammatory phases of 30.3 and 17.2 mg kg,1, respectively. In addition, the ME of B. microstachya (3,300 mg kg ,1, i.p., 30 min earlier) inhibited, in a graded manner, the hyperalgesia induced by bradykinin (3.2 ,g/paw), substance P (13.5 ,g/paw), carrageenan (300 ,g/paw), capsaicin (100 ,g/paw) and adrenaline (100ng/paw) in the rat paw, with mean ID50 values of 20.5, 17.9, 101.8, 54.2 and 99.7 mg kg,1, respectively. Taken together, these data demonstrate that ME of B. microstachya elicited a pronounced antinociceptive action against several chemical and mechanical models of pain in mice and rats. The precise mechanism responsible for the antinociceptive effect of the extract still remains unclear, but seems to be partly related to modulation of the release or action of pro-inflammatory mediators involved in the models of pain used. Finally, the flavonoid quercitrin isolated from this plant appears to contribute for the antinociceptive property of the methanolic extract. [source] COMPARISON OF MECHANICAL TESTS FOR EVALUATING TEXTURAL CHANGES IN POTATOES DURING THERMAL SOFTENINGJOURNAL OF TEXTURE STUDIES, Issue 6 2002W. K. SOLOMON ABSTRACT The changes in the texture of cylindrical samples of potato tissues immersed in water at 60, 70, 80 and 90C for up to 80 min were monitored at each temperature in terms of tangent modulus of elasticity in axial and radial compression tests, and elasticity and viscosity parameters in creep and stress relaxation tests. The magnitude of all mechanical test parameters decreased with an increase in heating time and temperature. The creep and stress relaxation responses of individual potato samples were adequately represented by respective mechanical models (R2= 0.94 to 0.99). The mechanical test parameters followed apparent first-order degradation kinetics due to the effect of thermal softening, and the rate constant was used as an index of the sensitivity of a mechanical test. The radial compression test was relatively more sensitive than the axial test. Based on an overall comparison, the parameters from creep and stress relaxation tests were found to be the most sensitive in describing the textural changes during thermal softening of potatoes. [source] Critical buckling load of paper honeycomb under out-of-plane pressure,PACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2005Li-Xin Lu Abstract Two out-of-plane buckling criteria for paper honeycomb are proposed by analysing the structure properties and the collapse mechanism of paper honeycomb: these are based on the peeling strength and ring crush strength of the chipboard wall. Taking into account the orthotropic, initial deflection and large deflection properties of the chipboard wall, the two new mechanical models and the calculation methods are developed to represent the out-of-plane critical load of paper honeycomb. Theoretical calculations and test results show that the models are suitable for describing the collapse mechanism of paper honeycomb. The peeling strength and ring crush strength determine the critical buckling load of paper honeycomb in different stretch phases. The out-of-plane critical buckling load can be predicted when the two models are integrated. Copyright © 2005 John Wiley & Sons, Ltd. [source] Biomechanical models for clinical data analysis of pressure-volume relationship in the human eyeACTA OPHTHALMOLOGICA, Issue 2009S BAUER Purpose To develop mechanical models describing the pressure-volume relationship for the human eye and to compare the results obtained with clinical data in order to find out which mechanical characteristics affect this relationship most significantly. Methods The fibrous coat is treated as a connected elastic shell consisting of two spherical segments with different radii and mechanical characteristics. The dependence of the intraocular pressure on the volume is analyzed using three different models in which the sclera and the cornea are modeled (1) by soft shells; (2) by transversally isotropic shells with small tension modules in the transverse direction; and (3) by 3D elastic solids. The models are studied analytically and numerically, the latter using FEM ANSYS software. Results The results are obtained over a wide range of parameters using all three models. Conclusion The models proposed predict a generally nonlinear relationship between the intraocular pressure and volume. The parameters of both the sclera and the cornea affect this relationship, the role of the sclera being more important. In the first approximation the simple soft shell model is in good agreement with the clinical data. [source] | |||||||||||||