Decay of Spin-One Particle into Two Photons in Presence of Uniform External Magnetic Field

Yang's theorem states that an initial J=1 state cannot decay into two photons. Because of this result some reactions relating to elementary particles or atomic transitions can be ruled out. The theorem is not valid in the presence of background electric or magnetic fields. In this work we show that the decay of a J=1 particle into two photons is permitted by Bose symmetry and rotational invariance when the background of the decay process is not pure vacuum but contains an external classical magnetic/electric field. We also discuss constraints on these amplitudes from {\bf CP} invariance.Comment: Tex fil

Failures of welded joints

For a failure at a welded joint, the important factors are : (a) presence of defects in the form of physical discontinuities, (b) a bad microstructure, and (c) residual stresses. A few important examples of bad microstructures leading to failures in stainless steel and alloy steels are presented in the paper. Apart from the references cited in the text, a list of general references are included to help the reader to get a better perspective on the conditions under which the failure of a weld joint takes place

Magnetic NDT for the characterization of industrial materials

Microstructure and residual stresses (RS) are important attributes of an industrial material which determines their various properties. In this paper, first an overview is given on the information available on the relationships of the microstructural parameters and RS on one hand and the parameters related to magnetic hysteresis loop and Barkhausen noise on the other The relevance of the relation¬ships for microstructurel characterisations and RS hr magnetic nondestructive evaluation techniques is discussed. Discussion is also made on the development and the use of sensors for the detec¬tion and assessment of magnetic flux to characterise microstruc¬tures. Two case studies on the use of the techniques in industrial materials and components are presented

Non-Destructive Techniques for Microstructural and Structural Characterisation

The functional quality of a material or a component is influenced by (i) microstructure (ii) flaws (physical discontinuities like cracks, pores,delaminations etc.), and (iii) the presence of stress. Non-destructive evaluation (NDE) techniques are used to control and enhance the quality at various stages of the life cycle of a material or component. In this paper, various NDE techniques are discussed. The techniques mainly discussed are ultrasonics,radiography, X-ray techniques, and acoustic emission. The principles,procedures, advantages, and limitations of each technique, as well as applications in various materials are considered

Amorphization of Vortex Matter and Reentrant Peak Effect in YBa2_2Cu3_3O7−δ_{7-\delta}

The peak effect (PE) has been observed in a twinned crystal of YBa$_2$Cu$_3$O$_{7-\delta}$ for H$\parallel$c in the low field range, close to the zero field superconducting transition temperature (T$_c$(0)) . A sharp depinning transition succeeds the peak temperature T$_p$ of the PE. The PE phenomenon broadens and its internal structure smoothens out as the field is increased or decreased beyond the interval between 250 Oe and 1000 Oe. Moreover, the PE could not be observed above 10 kOe and below 20 Oe. The locus of the T$_p$(H) values shows a reentrant characteristic with a nose like feature located at T$_p$(H)/T$_c$(0)$\approx$0.99 and H$\approx$100 Oe (where the FLL constant a$_0$$\approx$penetration depth $\lambda$). The upper part of the PE curve (0.5 kOe$<$H$<$10 kOe) can be fitted to a melting scenario with the Lindemann number c$_L$$\approx$0.25. The vortex phase diagram near T$_c$(0) determined from the characteristic features of the PE in YBa$_2$Cu$_3$O$_{7-\delta}$(H$\parallel$c) bears close resemblance to that in the 2H-NbSe$_2$ system, in which a reentrant PE had been observed earlier.Comment: 15 pages and 7 figure

Evaporation of alpha particles from 31^31P nucleus

The energy spectra of alpha particles have been measured in coincidence with the evaporation residues for the decay of the compound nucleus $^31$P produced in the reaction $^19$F (96 MeV) + $^12$C. The data have been compared with the predictions of the statistical model code CASCADE. It has been observed that significant deformation effect in the compound nucleus need to be considered in order to explain the shape of the evaporated alpha particle energy spectra.Comment: 4 pages, 3 figures, revtex, epsf styl

Testing Methods for Heat Treated Steel Products

Heat treatment of steels changes the microstructure. For the same chemical composition of a steel, the micro-structural variations is the most important parameter that determines the properties of a component - physical, chemical, mechanical and others. The presence of a wrong or undesirable microstructure reduces the life of a component and often leads to premature failures. Another parameter which is important for component integrity is the presence of physical discontinuity such as cracks which are introduced in the component due to faulty heat treatment which imparts wrong microstructures and residual stresses. The microstructural features have a wide range of dimensions

Double-Well Potential : The WKB Approximation with Phase Loss and Anharmonicity Effect

We derive a general WKB energy splitting formula in a double-well potential by incorporating both phase loss and anharmonicity effect in the usual WKB approximation. A bare application of the phase loss approach to the usual WKB method gives better results only for large separation between two potential minima. In the range of substantial tunneling, however, the phase loss approach with anharmonicity effect considered leads to a great improvement on the accuracy of the WKB approximation.Comment: 14 pages, revtex, 1 figure, will appear at Phys. Rev.