Incubation time based testing of materials

Some principal features of the behavior of materials subjected to pulsed actions are common for a number of seemingly quite different physical processes, such as dynamic fracture (starting cracks and scabbing), cavitation in liquids, and electrical breakdown in solids. In this paper, we analyze examples illustrating typical dynamic effects inherent in these processes. We propose a unified interpretation for the fracture of solids and liquids and electrical breakdown in insulators using the structural-time approach based on the concept of the fracture incubation time. The examples of different physical processes considered in the paper show the fundamental importance of investigating incubation processes preparing abrupt structural changes (fracture and phase transitions) in continua under intense pulsed actions. The fracture incubation time is evidently a universal basic characteristic of the dynamic strength and must become one of the main material parameters to be experimentally determined (measured).     

Die-swell,splashing drop and a numerical technique for solving the Oldroyd B model for axisymmetric free surface flows

This work deals with the development of a numerical method for simulating viscoelastic axisymmetric free surface flow of an Oldroyd B fluid. A novel formulation is developed for the computation of the non-Newtonian extra-stress components on rigid boundaries and on the symmetry axis. The full free surface stress conditions are employed. The resulting governing equations are solved by finite differences on a Marker-and-cell (MAC) type grid. Validation is provided by simulating a pipe flow problem. The classical die-swell problem is solved and swelling ratios are provided. The height of the splash caused by a falling liquid drop for various Reynolds and Weissenberg numbers is then studied, and the height of the splash is shown to diminish with increasing viscoelasticity.     

Parametric X-rays along the velocity direction of an emitting particle under conditions of the Cherenkov effect

Peculiarities in the parametric X-rays along the velocity direction of a relativistic electron emitting in a regime where the Cherenkov effect is important are considered. It is shown that the emission yield can be increased substantially due to the modification of the anomalous photoabsorption.     

On control of linear spring–mass chains

We consider a finite chain of mass points consecutively linked by linear springs with one of the end points acted upon by an external control force pointing along the chain. Moreover the system is observable by the coordinate of the other end point of the chain. We show that such a system is completely controllable and is completely observable for all choices of the physical parameters.     

A NEW METHOD FOR SEPARATING LONGITUDINAL WAVES IN A LARGE DIAMETER HOPKINSON BAR

This paper outlines various methods for separating fundamental longitudinal waves propagating along a Hopkinson pressure bar. Advantages and disadvantages of the different methods are presented and discussed in detail. A new method is then proposed for separating the fundamental waves in the frequency domain. This new method is based on the assumption that wave propagation can be adequately described by the first mode of the Pochhammer-Chree theory. The method requires two-point strain gauge measurements on the pressure bar. Fourier components of the positive wave at one gauge location are determined either from the corresponding Fourier components of the measured strain histories or from their derivatives. The method also makes use of the derivative of the wave number with respect to the circular frequency of the pressure bar. Important points of the implementation of the technique are described. Numerical accuracy of the proposed method is verified by considering a simple example with analytical solution and by comparing measured data derived from a large diameter Hopkinson pressure bar. The proposed method will find application in dynamic material tests using the split Hopkinson pressure bar technique.     

Electronic states of chromium carbene ions characterized by high-resolution translational energy loss spectroscopy

The electronic states of the unsaturated organometallic carbene CrCH₂⁺ are investigated using high-resolution translational energy loss spectroscopy. The observed energy loss feature (1.05 ±0.2 eV) is in good agreement with theoretical calculations which predict two higher lying states, ⁶B₁, and ⁶A₁ at 0.78 and 0.82 eV respectively, above the ⁴B₁ ground state of CrCH₂⁺.     

CO adsorption on clean and oxidized Al(110)

Electron-energy loss (EELS) spectra and thermal desorption (TDS) traces of carbon monoxide bound to the (100) surface of aluminum are presented. CO chemisorption on clean Al(100) is characterized by vibrational bands at 440 and 2060 cm⁻¹ and by desorption at 125 K. Oxide “islands”, formed by oxidation in O₂ at 575 K, have no observed electronic influence on open metallic areas of the adsorbent but merely block CO adsorption sites.     

Arsenate hydroxyapatite: A physico-chemical and thermodynamic investigation

Arsenate hydroxyapatite, Ca₁₀(AsO₄)₆(OH)₂ (AsHA), was synthesized by precipitation at 100°C, and characterized by X-ray studies, IR spectra, electron microscopy, and thermography (TGA, DTA and DTG). The solubility of AsHA was investigated between temperatures of 308 and 323 K, and in the pH range 4.0–8.0. It exhibited a retrograde solubility. The solubility behaviour can be explained on the basis of the chemical potential and free energy in solution. Standard thermodynamic parameters, ΔH^θ, ΔS^θ and ΔC_p^θ, are reported. The solubility products of AsHA were found to be 4.0 x 10⁻⁹¹, 2.7 x 10⁻⁹¹, 2.1 x 10⁻⁹¹ and 1.2 x 10⁻⁹¹ at temperatures of 3.08, 313, 318 and 323 K, respectively.     

Metal complexes of 1,4,10-trioxa-7,13 -diazacyclopentadecane-N,N'-diacetic acid

The cyclic diaza-crown ether complexone cTOPDA (1,4,10-trioxa-7,13-diaza- cyclopentadecane-N,N'-diacetic acid) has been synthesized and characterized by elemental analysis, titration and NMR spectroscopy. Its ionization constants and the stability constants of its ML and M₂L complexes formed with alkali, alkaline-earth and some transition and representative metals were determined at 25.0±0.1°C and ionic strength 0.10 M (Me₄NNO₃). This ligand forms considerably more stable complexes with the transition metals than the analogous tetraoxa-diaza crown ether complexone cTOODA (1,4,10,13- tetraoxa-7,16-diazacyclooctadecane-N,N'-diacetic acid), but this last ligand favours ions with larger size, particularly K⁺. The cobalt(II) complex of cTOPDA is more stable than the nickel(II) complex, hence the Irving-Williams' order of stability is not obeyed for its transition-metal complexes. These effects are discussed in terms of the size of the cavity of the ligand and of the stereochemical constraints that it may impose.