Time-delay effects on the dynamics of Liénard type equation with fast and slow variables

Time-delay effects on the dynamics of Liénard type equation with one fast variable and one slow variable are investigated in the present paper. By using the methods of stability switch and geometric singular perturbation, time-delay-induced complex oscillations and bursting are investigated, and in several case studies, the mechanism of the generation of the complex oscillations and bursting is illuminated. Numerical results demonstrate the validity of the theoretical results.     

Several effects of melt viscosity on the nature ofC p —T data aboveT g for acrylate,methacrylate, and hydrocarbon polymers

Using objective computerized statistical procedures, we have examined high precisionC _p data by DSC reported by Wunderlich and Gaur for a series of alkyl acrylate and methacrylate polymers. Although they claimed the data to be linear inT aboveT _g , our results do not support the linear model. One or two endothermic slope changes are revealed aboveT _g in lowT _f polymers (T _f < 20 °C) and at least one exothermic slope change in highT _f polymers (T _f > 20 °C).T _f is the flow temperature of Ueberreiter. Both the first endotherm and the first exotherm occur near (1.22 ± 0.07)T _g , suggesting aT _ll type phenomenon.T _ll varies as \(1/\bar M_n \) . The first exotherm is associated by us with wetting of the DSC pan by molten polymer on the first heating of particulate highT _f polymers. The rate of wetting, and presumably the magnitude of the exotherm, depends in part on the ratio,γ/η, whereγ is surface tension andη is melt viscosity of the molten polymer. Sinceγ is relatively constant, the molecular weight and temperature dependence for rate of wetting resides inη, which depends on \(\bar M_w \) . For \(\bar M_n > > \bar M_c \) , a second exothermic event caused by sintering, and also controlled by η, may be present. The interactive roles of \(\bar M_n ,\bar M_w ,\bar M_w /\bar M_n \) ;M _c (entanglement molecular weight); particle size, and heating rate onC _p —T behaviour are delineated for the first time. LowT _f hydrocarbon polymers, namely atactic polyalphaolefins,C ₃ ,C ₅ ,C ₆ ; PIB; and dienes, PBD and cis-PI, exhibit single or double endotherms. Other results on highT _f polymers showing exothermic effects, notably PS, PnBMA and polyglycidylmethacrylate are cited.     

Phase evolution of （K,Na）NbO3 powder prepared by high temperature mixing under hydrothermal conditions

（Na, K）NbO3 （KNN） powders were successfully prepared by high temperature mixing method （HTMM） under hydrothermal conditions to study the effect of reaction time on the formation of KNN for three K＋/（K＋ ＋Na＋） ratios of 0.6, 0.7 and 0.8. The products were characterized by X-ray diffraction （XRD）, scanning electron microscope （SEM）, transmission electron microscopy （TEM） and selected area electron diffraction （SAED）, to show the change of phase and morphology of the as-prepared particles with the K＋/（K＋ ＋ Na＋） molar ratio in the solution. Pure Na-rich KNN monoclinic phase and pure K-rich KNN orthorhombic phase could be obtained quickly after mixing the solutions at high temperature when the K＋/（K＋ ＋Na＋） molar ratio was either 0.6 or 0.8. When the K＋/（K＋ ＋Na＋） molar ratio was 0.7, however, the K-rich KNN orthorhombic phase grain formed first, followed by the Na-rich KNN monoclinic phase grain, with the two phases coexisting in the final product.     

Comment on the paper “Magnetohydrodynamic effects on natural convection flow of a nanofluid in the presence of heat source due to solar energy,N. Anbuchezhian,K. Srinivasan,K. Chandrasekaran,R. Kandasamy,Meccanica (2013) 48:307–321”

In the above paper a theoretical investigation of MHD convective flow and heat transfer of an incompressible viscous nanofluid past a porous vertical stretching sheet in the presence of variable stream condition is presented. The governing boundary layer equations are transformed by a Lie symmetry group transformation and the ordinary differential equations are solved numerically using Runge–Kutta Gill method.     

Experimental study to obtain the viscosity of CuO-loaded nanofluid: effects of nanoparticles’ mass fraction,temperature and basefluid’s types to develop a correlation

In this study, the impacts of temperature, nanoparticles mass fraction, and basefluid types were investigated on the dynamic viscosity of CuO-loaded nanofluids. The nanoparticles were dispersed in deionized water, ethanol, and ethylene glycol as basefluids separately and the measurements were performed on samples with nanoparticles loads ranging from 0.005 to 5 wt%, and the temperature range of 25 to 70 °C. TEM analysis were performed on dried nanoparticles and the results showed the average mean diameter of CuO nanoparticles ranged from 10 to 50 nm. The results of DLS analysis confirmed the results of nanoparticles size obtained by TEM analysis in mentioned basefluids and Zeta-Potential tests exhibited the high stability of the nanoparticles in the basefluids environment. The results indicate that by adding tiny amount of CuO nanoparticles to basefluids, relative viscosity of nanofluid increases. By the increase in nanoparticles load higher than 0.1 wt% the effect of both nanoparticles mass fraction and temperature would be more tangible, while for nanoparticles mass fraction lower than 0.1 wt% no significant change in viscosity was observed. In addition, the results declare that viscosity of nanofluid remains constant at various applied shear rates indicating Newtonian behavior of nanofluid at various nanoparticles load and temperature. According to experimental data, it is also evident that with the increase in temperature, the value of relative dynamic viscosity decreases significantly. Also it is concluded that for CuO/ethanol nanofluid, more interfacial interaction is resulted that causes higher relative dynamic viscosity while for CuO/water lower interfacial interaction between nanoparticles surface and water molecules are resulted which leads to the lower values for this parameter. The results of this study implied that with increase the temperature from 25 to 70 °C at the condition where nanoparticles mass fraction was chosen to be 5 wt%, the value of dynamic viscosity of CuO/ethanol, CuO/deionized water, CuO/ethylene glycol declined 69%, 66%, and 65% respectively. Finally, a correlation was proposed for the relative dynamic viscosity of nanofluid based on the CuO nanoparticles mass fraction and temperature of the basefluid and nanoparticles.     

Nonlinear vibrations,bifurcations and chaos of lattice sandwich composite panels on Winkler–Pasternak elastic foundations with thermal effects in supersonic airflow

Meccanica - This paper is devoted to investigate the nonlinear dynamic characteristics of lattice sandwich composite panels resting on Winkler–Pasternak elastic foundations under simultaneous...     

GRADUATE RESEARCH FELLOWSHIPS POSTDOCTORAL RESEARCH FELLOWSHIPS UNDERGRADUATE RESEARCH FELLOWSHIPS——Materials Science and Engineering The University of Tennessee,Knoxville

A number of (1) Ph.D. graduate research fellowships, (2) postdoctoral fellowships, and (3) undergraduate research fellowships are available immediately in the area of neutron-diffraction materials research. Candidates with strong backgrounds in Materials Science, Metallurgy (including Processing, and Mechanical/Physical Behavior), Computational Materials Science, Mechanical/Civil Engineering, Physics, Computer Science and Engineering, or a related field are encouraged to apply. The research activities will focus on the subjects of (1) in-situ neutron-diffraction characterization of mechanical behavior (plasticity, twinning, fatigue, and creep deformation) of advanced ma-     

ACTA MECHANICA SOLIDA SINICA——The Chinese Society of Theoretical and Applied Mechanics Vo1.16,No.1-No.4,2003 CONTENTS

Uneoliventional Gurtin一tyPe variational PrineiPles for firlite deformation elasto- dynalllics ........................................……Luo En,Zllu Huijianl一1A decagonalquasicl’ySta1 with an arc一ShaPed crack……Wdng Xu,Zhong Zhengl一8Propagation of、urfaee aeoustie waves in pre、tressed anisotropie layered Piezo- eleetrie strlle七ures ……Liu,Hua.Kuang Zhenbang,Cai Zhengnlillg认bng Tiejun,、Vang Zikunl一16Gurtin variational PI,121亡iPle and finite element 51仃lulation for dyna…     

A comparative study on design standards of screw conveyors in China,Germany and the USA — Part I: Theoretical calculation and quantitative analysis

Screw conveyors, widely used devices for transporting bulk materials, play an irreplaceable role in the modern industrial system. Despite of their traditional advantages, designers of screw conveyors still heavily rely on their own country’s experiments and standards, which are closely related to empirical data. Therefore, the same conveying task often results in different designs. This work aims to compare the design standards of screw conveyors in China, Germany and the USA. Based on related standards acquired from renowned associations in the three countries, the similarities and particularities of these design guidances are compared. With preforming the geometrical and operational designs for horizontal, slightly inclined and vertical conveyance of three representative bulk solids (barley, lignite, sand), the advantages and disadvantages of these semi-empirical designs are comprehensively presented. Furthermore, the potential influence of empirical coefficients, which are not explicitly documented, are extensively discussed. By analysing all outcomes, the compatibility and applicability of each standard are qualitatively assessed.     

Comment on “The effects of heat transfer on the exergy efficiency of an air-standard Otto cycle” by Hakan Özcan,Heat and Mass Transfer (2011) 47:571–577

In this letter, it is shown that the applied relations in the paper by Hakan Özcan [H. Özcan, The effects of heat transfer on the exergy efficiency of an air-standard Otto cycle, Heat and Mass Transfer (2011) 47:571–577] are erroneous and thus the reported results are invalid. These incorrect relations [Eqs. (8), (9), (10), (14) and (16) of HÖ2011] are replaced by correct ones. Moreover, the obtained results (graphs and tables) are modified based on the correct relations. Finally, to achieve more realistic results, the internal irreversibility described by using the compression and expansion efficiencies is added to the analysis.