576 research outputs found

    Deviations from Matthiessen rule and resistivity saturation effects in Gd and Fe

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    According to earlier first-principles calculations, the spin-disorder contribution to the resistivity of rare-earth metals in the paramagnetic state is strongly underestimated if Matthiessen's rule is assumed to hold. To understand this discrepancy, the resistivity of paramagnetic Fe and Gd is evaluated by taking into account both spin and phonon disorder. Calculations are performed using the supercell approach within the linear muffin-tin orbital method. Phonon disorder is modeled by introducing random displacements of the atomic nuclei, and the results are compared with the case of fictitious Anderson disorder. In both cases the resistivity shows a nonlinear dependence on the square of the disorder potential, which is interpreted as a resistivity saturation effect. This effect is much stronger in Gd than in Fe. The non-linearity makes the phonon and spin-disorder contributions to the resistivity non-additive, and the standard procedure of extracting the spin-disorder resistivity by extrapolation from high temperatures becomes ambiguous. An "apparent" spin-disorder resistivity obtained through such extrapolation is in much better agreement with experiment compared to the results obtained by considering only spin disorder. By analyzing the spectral function of the paramagnetic Gd in the presence of Anderson disorder, the resistivity saturation is explained by the collapse of a large area of the Fermi surface due to the disorder-induced mixing between the electronic and hole sheets.Comment: 9 pages, 7 figure

    Spectral signatures of thermal spin disorder and excess Mn in half-metallic NiMnSb

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    Effects of thermal spin disorder and excess Mn on the electronic spectrum of half-metallic NiMnSb are studied using first-principles calculations. Temperature-dependent spin disorder, introduced within the vector disordered local moment model, causes the valence band at the Γ\Gamma point to broaden and shift upwards, crossing the Fermi level and thereby closing the half-metallic gap above room temperature. The spectroscopic signatures of excess Mn on the Ni, Sb, and empty sites (MnNi_\mathrm{Ni}, MnSb_\mathrm{Sb}, and MnE_\mathrm{E}) are analyzed. MnNi_\mathrm{Ni} is spectroscopically invisible. The relatively weak coupling of MnSb_\mathrm{Sb} and MnE_\mathrm{E} spins to the host strongly deviates from the Heisenberg model, and the spin of MnE_\mathrm{E} is canted in the ground state. While the half-metallic gap is preserved in the collinear ground state of MnSb_\mathrm{Sb}, thermal spin disorder of the weakly coupled MnSb_\mathrm{Sb} spins destroys it at low temperatures. This property of MnSb_\mathrm{Sb} may be the source of the observed low-temperature transport anomalies.Comment: 5 pages, 7 figures, updated version with minor revisions and an additional figure, accepted in Phys. Rev. B (Rapid Communication

    A COMPARATIVE CLINICAL STUDY ON SHARKARA MISHRITA DUGDA NASYA AND MURCHITA GHRITA NASYA ON ARDHAVABHEDAKA W.S.R. TO MIGRAINE

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    Ardhavabhedaka is one among the 11 types of Shirorogas described in Ayurvedic classical texts. It is a type of headache where pain is localized to one half of the head. It can be correlated with migraine based on the similarity in etiology, pathology, symptoms and treatment principles. This study is conducted with the aim to compare the effect of ‘Sharkara Mishrita Dugdha Nasya’ and ‘Murchita Gritha Nasya’ in the management of Ardhavabhedaka. Two groups of 15 patients each were administered these two types of Nasya drugs for seven days. Patients were assessed on the basis of clinical parameters. Results show good effect on all symptoms of Ardhavabhedaka in both groups but Murchita Ghrita Nasya show better effect than Sharkara Mishrita Dugdha Nasya.Among 15 patients in Group-A, 7 patients (36%) showed good response and among 20 patients in Group-B, 3 patients (16 %) showed good response after the treatment. The response obtained after 28 days of treatment and the study reveals that in Group – B Murchita Ghrita Nasya shows very good response in treating the Ardhavabhedaka. Sharkara acts as Vatapitta hara, Dugdha & Murchita Ghrita acts as Tridoshaghna

    Gossip Codes for Fingerprinting: Construction, Erasure Analysis and Pirate Tracing

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    This work presents two new construction techniques for q-ary Gossip codes from tdesigns and Traceability schemes. These Gossip codes achieve the shortest code length specified in terms of code parameters and can withstand erasures in digital fingerprinting applications. This work presents the construction of embedded Gossip codes for extending an existing Gossip code into a bigger code. It discusses the construction of concatenated codes and realisation of erasure model through concatenated codes.Comment: 28 page
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