A failure study of the railway rail serviced for heavy cargo trains

AbstractIn this case study, a failed railway rail which was used for heavy cargo trains was investigated in order to find out its root cause. The macroscopic beach marks and microscopic fatigue striations were not observed by macro and microscopic observations. The chevron patterns were observed by macro observations. The crack origin was at the tip of chevron patterns. The fan-shaped patterns, cleavage step and the river patterns were observed at the crack origin, which demonstrated the feature of cleavage fracture. The metallurgical structures at the crack origin were pearlite and ferrite networks. The crack is supposed to be initiated from the weaker ferrite networks. Given all of that, the failed railway rail is considered to be caused by overload. It is of great importance to improve the welding technology, and control the load of train in order to prevent similar failure in future

Transient 3D lumped parameter and 3D FE thermal models of a PMASynRM under fault conditions with asymmetric temperature distribution

This paper proposes a novel transient 3D lumped-parameter (LP) thermal model and a 3D finite-element (FE) thermal model of a triple redundant 9-phase permanent magnet-assisted synchronous reluctance machine to predict the asymmetric temperature distribution under various fault conditions. Firstly, the predicted transient and steady-state temperatures are compared between the 3D LP and the 3D FE thermal models under fault conditions with uneven loss distribution. Also, the temperatures predicted by the LP and FE thermal models which account a number of practical issues are comprehensively compared with the test results under healthy and short-circuit fault conditions. The relative merits of the two thermal models are discussed. It is shown that both models have reasonable accuracy in predicting the machine thermal behavior under fault conditions and can be chosen according to the requirements

Influence of electrode distance on heating behaviour associated to radio frequency processing of low moisture foods

Temperature uniformity and heating rate subjected to radio frequency (RF) heating have major impact on the quality of treated low moisture foods. The objective of this paper was to analyse the influence of electrode distance on the heating behaviour of RF on condition that the sample shape, size, and location between the electrodes were defined. Considering peanut butter (PB) and wheat flour (WF) as sample food, a 3D computer simulation model was developed using COMSOL, which was experimentally validated by a RF machine (27.12 MHz, 6 kW). Specifically, the electrode distances were selected as 84, 89, 93, 99 and 89, 93, 98, 103 (mm) for RF heating of PB and WF, respectively. Results showed that the simulated results and experimental data agreed well; the temperature-time histories of the RF heating of PB and WF were approximate straight lines; both the temperature uniformity index and the heating rate decreased with the increase of the electrode distance; the heating rate had a negative logarithmic linear relationship with the electrode distance, which was independent of the types, geometry shapes and sizes of low moisture foods

Phase diagram for morphological transitions of wetting films on chemically structured substrates

Using an interface displacement model we calculate the shapes of thin liquidlike films adsorbed on flat substrates containing a chemical stripe. We determine the entire phase diagram of morphological phase transitions in these films as function of temperature, undersaturation, and stripe widthComment: 15 pages, RevTeX, 7 Figure

Development of an eight-band theory for quantum-dot heterostructures

We derive a nonsymmetrized 8-band effective-mass Hamiltonian for quantum-dot heterostructures (QDHs) in Burt's envelope-function representation. The 8x8 radial Hamiltonian and the boundary conditions for the Schroedinger equation are obtained for spherical QDHs. Boundary conditions for symmetrized and nonsymmetrized radial Hamiltonians are compared with each other and with connection rules that are commonly used to match the wave functions found from the bulk kp Hamiltonians of two adjacent materials. Electron and hole energy spectra in three spherical QDHs: HgS/CdS, InAs/GaAs, and GaAs/AlAs are calculated as a function of the quantum dot radius within the approximate symmetrized and exact nonsymmetrized 8x8 models. The parameters of dissymmetry are shown to influence the energy levels and the wave functions of an electron and a hole and, consequently, the energies of both intraband and interband transitions.Comment: 36 pages, 10 figures, E-mail addresses: [email protected], [email protected]

Euclidean Distances, soft and spectral Clustering on Weighted Graphs

We define a class of Euclidean distances on weighted graphs, enabling to perform thermodynamic soft graph clustering. The class can be constructed form the "raw coordinates" encountered in spectral clustering, and can be extended by means of higher-dimensional embeddings (Schoenberg transformations). Geographical flow data, properly conditioned, illustrate the procedure as well as visualization aspects.Comment: accepted for presentation (and further publication) at the ECML PKDD 2010 conferenc

Radiation-induced oscillatory magnetoresistance as a sensitive probe of the zero-field spin splitting in high mobility GaAs/AlGaAs devices

We suggest an approach for characterizing the zero-field spin splitting of high mobility two-dimensional electron systems, when beats are not readily observable in the Shubnikov-de Haas effect. The zero-field spin splitting and the effective magnetic field seen in the reference frame of the electron is evaluated from a quantitative study of beats observed in radiation-induced magnetoresistance oscillations.Comment: 4 pages, 4 color figure

Phase separation and ferroelectric ordering in charge frustrated LuFe2O4-x

The transmission electron microscopy observations of the charge ordering (CO) which governs the electronic polarization in LuFe2O4-x clearly show the presence of a remarkable phase separation at low temperatures. Two CO ground states are found to adopt the charge modulations of Q1 = (1/3, 1/3, 0) and Q2 = (1/3 + y, 1/3 + y, 3/2), respectively. Our structural study demonstrates that the incommensurately Q2-modulated state is chiefly stable in samples with relatively lower oxygen contents. Data from theoretical simulations of the diffraction suggest that both Q1- and Q2-modulated phases have ferroelectric ordering. The effects of oxygen concentration on the phase separation and electric polarization in this layered system are discussed.Comment: 11 pages, 5 figure

Effects of the field modulation on the Hofstadter's spectrum

We study the effect of spatially modulated magnetic fields on the energy spectrum of a two-dimensional (2D) Bloch electron. Taking into account four kinds of modulated fields and using the method of direct diagonalization of the Hamiltonian matrix, we calculate energy spectra with varying system parameters (i.e., the kind of the modulation, the relative strength of the modulated field to the uniform background field, and the period of the modulation) to elucidate that the energy band structure sensitively depends on such parameters: Inclusion of spatially modulated fields into a uniform field leads occurrence of gap opening, gap closing, band crossing, and band broadening, resulting distinctive energy band structure from the Hofstadter's spectrum. We also discuss the effect of the field modulation on the symmetries appeared in the Hofstadter's spectrum in detail.Comment: 7 pages (in two-column), 10 figures (including 2 tables