A numerical model of twin disc test arrangement for the evaluation of railway wheel wear prediction methods

Twin disc tests are commonly used to study wear in railway materials. In this work the implementation of a numerical model of the twin disc arrangement is given, which reproduces the distribution of tangential forces over the contact patch between the two discs. Wear is subsequently calculated by relating the forces and creepage between the two discs using three different wear functions found in the literature. The resulting wear rates are compared with experimental data for discs made of common railway wheel and rail steels. This allows a comparison and assessment of the validity of the different wear algorithms considered

Electron interactions and charge ordering in La2−x_{2-x}Srx_xCuO4_4

We present results of inelastic light scattering experiments on single-crystalline La$_{2-x}$Sr$_{x}$CuO$_4$ in the doping range $0.00 \le x=p \le 0.30$ and Tl$_2$Ba$_2$CuO$_{6+\delta}$ at $p=0.20$ and $p=0.24$. The main emphasis is placed on the response of electronic excitations in the antiferromagnetic phase, in the pseudogap range, in the superconducting state, and in the essentially normal metallic state at $x \ge 0.26$, where no superconductivity could be observed. In most of the cases we compare B$_{1g}$ and B$_{2g}$ spectra which project out electronic properties close to $(\pi,0)$ and $(\pi/2, \pi/2)$, respectively. In the channel of electron-hole excitations we find universal behavior in B$_{2g}$ symmetry as long as the material exhibits superconductivity at low temperature. In contrast, there is a strong doping dependence in B$_{1g}$ symmetry: (i) In the doping range $0.20 \le p \le 0.25$ we observe rapid changes of shape and temperature dependence of the spectra. (ii) In La$_{2-x}$Sr$_{x}$CuO$_4$ new structures appear for $x < 0.13$ which are superposed on the electron-hole continuum. The temperature dependence as well as model calculations support an interpretation in terms of charge-ordering fluctuations. For $x \le 0.05$ the response from fluctuations disappears at B$_{1g}$ and appears at B$_{2g}$ symmetry in full agreement with the orientation change of stripes found by neutron scattering. While, with a grain of salt, the particle-hole continuum is universal for all cuprates the response from fluctuating charge order in the range $0.05 \le p < 0.16$ is so far found only in La$_{2-x}$Sr$_{x}$CuO$_4$. We conclude that La$_{2-x}$Sr$_{x}$CuO$_4$ is close to static charge order and, for this reason, may have a suppressed $T_c$.Comment: 17 pages, 15 figure

Dynamical properties of charged stripes in La(2-x)SrxCuO4

Inelastic light-scattering spectra of underdoped La_2−xSr_xCuO4 single crystals are presented which provide direct evidence of the formation of quasi-one-dimensional charged structures in the two-dimensional CuO2 planes. The stripes manifest themselves in a Drude-like peak at low energies and temperatures. The selection rules allow us to determine the orientation to be along the diagonals at x=0.02 and along the principal axes at x=0.10. The electron-lattice interaction determines the correlation length which turns out to be larger in compound classes with lower superconducting transition temperatures. Temperature is the only scale of the response at different doping levels demonstrating the importance of quantum critical behavior

Phenomenology of the normal state in-plane transport properties of high-TcT_c cuprates

In this article, I review progress towards an understanding of the normal state (in-plane) transport properties of high-$T_c$ cuprates in the light of recent developments in both spectroscopic and transport measurement techniques. Against a backdrop of mounting evidence for anisotropic single-particle lifetimes in cuprate superconductors, new results have emerged that advocate similar momentum dependence in the transport decay rate $\Gamma$({\bf k}). In addition, enhancement of the energy scale (up to the bare bandwidth) over which spectroscopic information on the quasiparticle response can be obtained has led to the discovery of new, unforeseen features that surprisingly, may have a significant bearing on the transport properties at the dc limit. With these two key developments in mind, I consider here whether all the ingredients necessary for a complete phenomenological description of the anomalous normal state transport properties of high-$T_c$ cuprates are now in place.Comment: 31 pages, 10 figure

A study on wear evaluation of railway wheels based on multibody dynamics and wear computation

The wear evolution of railway wheels is a very important issue in railway engineering. In the past, the reprofiling intervals of railway vehicle steel wheels have been scheduled according to designers' experience. Today, more reliable and accurate tools in predicting wheel wear evolution and wheelset lifetime can be used in order to achieve economical and safety benefits. In this work, a computational tool that is able to predict the evolution of the wheel profiles for a given railway system, as a function of the distance run, is presented. The strategy adopted consists of using a commercial multibody software to study the railway dynamic problem and a purpose-built code for managing its pre- and post-processing data in order to compute the wear. The tool is applied here to realistic operation scenarios in order to assess the effect of some service conditions on the wheel wear progression

Pair breaking versus symmetry breaking : origin of the Raman modes in superconducting cuprates

We performed Raman scattering experiments on superconductivity-induced features in Bi2Sr2(Ca1−xYx)Cu2O8+δ (Bi-2212), YBa2Cu3O6+x (Y-123), and Tl2Ba2CuO6+δ (Tl-2201) single crystals. The results in combination with earlier ones enable us to systematically analyze the spectral features in the doping range 0.07⩽p⩽0.24. In B2g (xy) symmetry, we find universal spectra and the maximal gap energy Δ0 to scale with the superconducting transition temperature Tc. The B1g (x2−y2) spectra in all three compounds show an anomalous increase of the intensity toward overdoping. The energy scale of the corresponding peak is neither related to the pairing energy nor to the pseudogap, but possibly stems from a symmetry breaking transition at the onset point of superconductivity at psc2≃0.27

NERAZLIKOVNOST RAZLIKA

Analiziraju se leksikološko-leksikografska polazišta i metodološki postupci u izradi Razlikovnog rječnika srpskog i hrvatskog jezika Vladimira Brodnjaka