A Methodology for Obtaining Material Properties of Polymeric Foam at Elevated Temperatures

A new methodology to characterise the elastic properties of polymeric foam core materials at elevated temperatures is proposed. The focus is to determine reliable values of the tensile and compressive moduli and Poisson’s ratio based on strain data obtained using digital image correlation (DIC). In the paper a detailed coverage of the source of uncertainties in the experimental procedure is provided. The uncertainties include those associated with the load introduction, the measurement and the data processing. The design of the specimens and loading jigs are developed and assessed in terms of the introduction of uniform strain. It is shown that due to the mismatch in stiffness between the jig material and the foam the introduction of a uniform strain through the cross section of the specimens is difficult to obtain. A means for correcting for the non-uniform strain across the specimen cross section is developed. To validate the methodology, tests are firstly conducted at room temperature on Divinycell PVC H100 foam. It is shown that the material is highly anisotropic with a stiffness of 50% less in the plane of the foam sheet compared to the through-thickness direction. It is also shown that because of the compliance of the foam, jig misalignment causes large errors in the measurement, and a means for correcting for this is defined. Tests are then conducted in a temperature controlled chamber at elevated temperatures ranging from 20°C to 90°C. A nonlinear reduction in Young’s modulus is obtained with significant degradation occurring after 70°C. The Poisson’s ratio remains fairly stable at different temperatures. A strong theme in the paper is the accuracy and precision of the DIC data and the factors which introduce scatter in the data, along with the uncertainties that this introduces. Particular attention is paid to the affect of the correlation parameters on the derived strain data.     

Liquid–liquid extraction of neodymium (III) and europium (III) using synergic mixture of furosemide and tribenzylamine in benzyl alcohol

The extraction behavior of Nd(III) and Eu(III) with 0.05 mol dm⁻³ furosemide in benzyl alcohol as single acidic extractant and then with equimolar (0.05 mol dm⁻³) synergic mixture of furosemide as acidic extractant and tribenzylamine as neutral donor in benzyl alcohol has been studied from aqueous solutions of pH 1 to 6. The effect of various parameters and of various cations and anions on the extraction of these metal ions was investigated. The composition of the extracted adducts was determined by slope analysis method that came out to be [(M(FS)₂)⁺ (CH₃COO)⁻] and [M(FS)₃·3TBA] where M = Nd(III) and Eu(III).

     

Peptide‐Directed DNA‐Templated Protein Labelling for The Assembly of a Pseudo‐IgM

The development of methods for conjugation of DNA to proteins is of high relevance for the integration of protein function and DNA structures. Here, we demonstrate that protein‐binding peptides can direct a DNA‐templated reaction, selectively furnishing DNA–protein conjugates with one DNA label. Quantitative conversion of oligonucleotides is achieved at low stoichiometries and the reaction can be performed in complex biological matrixes, such as cell lysates. Further, we have used a star‐like pentameric DNA nanostructure to assemble five DNA–Rituximab conjugates, made by our reported method, into a pseudo‐IgM antibody structure that was subsequently characterized by negative‐stain transmission electron microscopy (nsTEM) analysis.     

Characterization of a magnetic trap by polarization dependent Zeeman spectroscopy

This paper demonstrates a detailed experimental study of our cloverleaf magnetic trap for sodium atoms. By using polarization dependent Zeeman spectroscopy of our atomic beam, passing the magnetic trap region, we have determined important trap parameters such as gradients, their curvatures and corresponding trap frequencies. Experimental findings are compared to theoretical calculations as well as complementary methods of characterizing the trap.     

New limits on coupling of fundamental constants to gravity using 87Sr optical lattice clocks

The 1S0-3P0 clock transition frequency nuSr in neutral 87Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1 x 10(-15) level makes nuSr the best agreed-upon optical atomic frequency. We combine periodic variations in the 87Sr clock frequency with 199Hg+ and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant alpha, electron-proton mass ratio mu, and light quark mass. Furthermore, after 199Hg+, 171Yb+, and H, we add 87Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of alpha and mu.     

Perturbation-based prediction of vibration phase shift along fluid-conveying pipes due to Coriolis forces,nonuniformity, and nonlinearity

This paper investigates the influence of tread conicity variation on hunting dynamical changing features for railway vehicle. Nonlinear contact force between wheels and rail is estimated by Vermeulen–Johnson creep force law. And a piecewise linear function is employed to appropriate the collision between wheel flange and rail. Hunting asymmetrical motions are analyzed by lateral bifurcation behaviors between maximum and minimum of car body lateral displacement. The result shows that the critical speed decreases with the increase in tread conicity, while the speed gap between linear and nonlinear speeds is narrowing. Compared with wheelsets, lateral amplitudes of the bogies are vulnerable to the tread conicity and decrease gradually. Besides, more asymmetrical motions are put into consideration with regard to tread conicity variation. Similarly, one asymmetrical behavior with small amplitude difference originates from the same chaotic attractor at both sides. And small interactive amplitude jumps in two sides at chaotic or periodic occasions are revealed. Distinguishingly, the other new asymmetrical type is found at a certain tread conicity that amplitudes of the hunting motion in positive and reverse directions no longer coincide and go away in opposite directions when the tread conicity increases to a certain value. And this particular asymmetrical motion disappears with further growth of tread conicity.

     

Bifurcation analysis of a smoothed model of a forced impacting beam and comparison with an experiment

A piecewise-linear model with a single degree of freedom is derived from first principles for a driven vertical cantilever beam with a localized mass and symmetric stops. The aim is to show that this model constitutes a considerable step toward developing a vibro-impact model that is able to make qualitative and quantitative predictions of the observed dynamics. The resulting piecewise-linear dynamical system is smoothed by a switching function (nonlinear homotopy). For the chosen smoothing function, it is shown that the smoothing can induce bifurcations in certain parameter regimes. These induced bifurcations disappear when the transition of the switching is sufficiently and increasingly localized as the impact becomes harder. The bifurcation structure of the impact oscillator response is investigated via the one- and two-parameter continuation of periodic orbits in the driving frequency and/or forcing amplitude. The results are in good agreement with experimental measurements.     

Experimental bifurcation analysis of an impact oscillator—Determining stability

We propose and investigate three different methods for assessing stability of dynamical equilibrium states during experimental bifurcation analysis, using a control-based continuation method. The idea is to modify or turn off the control at an equilibrium state and study the resulting behavior. As a proof of concept the three methods are successfully implemented and tested for a harmonically forced impact oscillator with a hardening spring nonlinearity, and controlled by electromagnetic actuators. We show that under certain conditions it is possible to quantify the instability in terms of finite-time Lyapunov exponents. As a special case we study an isolated branch in the bifurcation diagram brought into existence by a 1:3 subharmonic resonance. On this isola it is only possible to determine stability using one of the three methods, which is due to the fact that only this method guarantees that the equilibrium state can be restored after measuring stability.