Fracture strength and toughness of ultra high strength TRIP aided steels

The performance of hydrogen embrittlement, fatigue properties and impact toughness of ultra high strength transformation induced plasticity aided steels with bainitic ferrite matrix (TBF steels) has been discussed. Some characteristics and deformation transformation mechanism of the retained austenite has also been discussed. It has been observed that mechanical stability and volume fraction of the interlath retained austenite phase in the TBF steels play an important role in increasing delayed fracture strength, fatigue limit and impact toughness.ArticleMATERIALS SCIENCE AND TECHNOLOGY. 25(9):1108-1117 (2009)journal articl

Spin Hall effect of conserved current: Conditions for a nonzero spin Hall current

We study the spin Hall effect taking into account the impurity scattering effect as general as possible with the focus on the definition of the spin current. The conserved bulk spin current (Shi et al. [Phys. Rev. Lett. 96, 076604 (2006)]) satisfying the continuity equation of spin is considered in addition to the conventional one defined by the symmetric product of the spin and velocity operators. Conditions for non-zero spin Hall current are clarified. In particular, it is found that (i) the spin Hall current is non-zero in the Rashba model with a finite-range impurity potential, and (ii) the spin Hall current vanishes in the cubic Rashba model with a $\delta$-function impurity potential.Comment: 5 pages, minor change from the previous versio

Ellipsoidal Calculus, Singular Perturbations and the State Estimation Problems for Uncertain Systems

One of the basic elements of dynamic modelling of complex systems is the linkage and synchronization of subsystems that develop in different time scales. The relevant techniques applied here are related to a singular perturbation theory for differential systems. A more complicated issue arises for uncertain systems described by differential inclusions, for which an appropriate theory is being developed. In order to make the theory constructive, some further steps are necessary. These are presented in this paper, where a computer-implementable "ellipsoidal" version is given. The results are particularly relevant to the linkage of models related to environmental, demographic and economic problems

Why haven't loose globular clusters collapsed yet?

We report on the discovery of a surprising observed correlation between the slope of the low-mass stellar global mass function (GMF) of globular clusters (GCs) and their central concentration parameter c=log(r_t/r_c), i.e. the logarithmic ratio of tidal and core radii. This result is based on the analysis of a sample of twenty Galactic GCs with solid GMF measurements from deep HST or VLT data. All the high-concentration clusters in the sample have a steep GMF, most likely reflecting their initial mass function. Conversely, low-concentration clusters tend to have a flatter GMF implying that they have lost many stars via evaporation or tidal stripping. No GCs are found with a flat GMF and high central concentration. This finding appears counter-intuitive, since the same two-body relaxation mechanism that causes stars to evaporate and the cluster to eventually dissolve should also lead to higher central density and possibly core-collapse. Therefore, more concentrated clusters should have lost proportionately more stars and have a shallower GMF than low concentration clusters, contrary to what is observed. It is possible that severely depleted GCs have also undergone core collapse and have already recovered a normal radial density profile. It is, however, more likely that GCs with a flat GMF have a much denser and smaller core than suggested by their surface brightness profile and may well be undergoing collapse at present. In either case, we may have so far seriously underestimated the number of post core-collapse clusters and many may be lurking in the Milky Way.Comment: Four pages, one figure, accepted for publication in ApJ Letter

Comments on the classification of orientifolds

The simple current construction of orientifolds based on rational conformal field theories is reviewed. When applied to SO(16) level 1, one can describe all ten-dimensional orientifolds in a unified framework.Comment: 9 pages, Contribution to proceedings of RTN-workshop in Leuven, Belgium, September 200

Effect of suppression of local distortion on magnetic, electrical and thermal transport properties of Cr substituted bi-layer manganite LaSr2_{2}Mn2_{2}O7_{7}

We have investigated magnetic, electrical and thermal transport properties (Seebeck effect and thermal conductivity) of LaSr$_{2}$Mn$_{2-y}$Cr$_{y}$O$_{7}$ polycrystalline samples ($y$=0.1, 0.2, 0.4 and 0.6). The Cr$^{3+}$ substitution for Mn$^{3+}$ sites causes a removal of $d_{x^2-y^2}$ orbital of $e_g$-electron resulting in a volume shrinkage of lattice. Magnetic measurements reveal the appearance of a glassy behavior for Cr-doped samples, accompanied by both a collapse of the A-type antiferromagnetic structure and the growth of ferromagnetic clusters. Cr-doping effect on electrical transport strongly enhances an insulating behavior over a wide range of temperature, while it suppresses a local minimum of thermoelectric power at lower temperatures. The phonon thermal conduction gradually rises with increasing Cr content, which is contradictory to a typical impurity effect on thermal conductivity. We attribute this to a suppression of local lattice distortion through the introduction of Jahn-Teller inactive ions of Cr$^{3+}$.Comment: 8 pages, 9figure

Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide

We have investigated the static and dynamic response of magnetic clusters in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C} $\leq$ 270K and ferromagnetic to canted spin glass state at T_f$$\leq$ 125K is observed