This study reports on the effect of annealing on the structural, defect formation and optical characteristics of ZnO nanoparticles (NPs) synthesized via self-combustion reactions. For investigating the effect of annealing, one part of as-synthesized ZnO NPs was kept as such and other two parts were annealed at 450ºC & 700ºC (hereafter referred as ZCA, ZCA450 and ZCA700) for six hours in ambient environment. Rietveld refinement of XRD patterns approved phase pure formation of ZCA, ZCA450 & ZCA700 in the Wurtzite type hexagonal symmetry along with a monotonic increment in the unit cell volume and mean crystallite size with annealing temperature (AT). In the same line, observation of three characteristic Raman modes (2E2H-2E2L, E2 (high) and E1 (LO)) validated hexagonal symmetry of these ZnO NPs. Blue shifting in the E2 (high) and E1 (LO) modes and red shifting in the 2E2H-2E2L mode and, ESR analysis corroborated formation of oxygen and zinc vacancies in these ZnO NPs along with annihilation of surface defects with AT. UV-Vis-NIR data exhibited considerable absorption of light below 500 nm by these ZnO NPs with a maxima noted in the blue color region. The obtained band gap Eg = 2.74 eV for ZCA NPs is found to be higher than ZCA450 (Eg = 2.50 eV) and ZCA700 (Eg = 2.68 eV). Notably, the obtained Eg for these ZnO NPs are considerably lower than the reported values in literature. These ZnO NPs seems to be useful for making UV & blue light protection layers and UV absorbers for sunscreen lotion etc.
An algorithm based on Renormalization Group (RG) to analyze time series forecasting was proposed in cond-mat/0110285. In this paper we explicitly code and test it. We choose in particular some financial time series (stocks, indexes and commodities) with daily data and compute one step ahead forecasts. We then construct some indicators to evaluate performances. The algorithm is supposed to prescribe the future development of the time series by using the self-similarity property intrinsically present in RG approach. This property could be potentially very attractive for the purpose of building winning trading systems. We discuss some relevant points along this direction. Although current performances have to be improved the algorithm seems quite reactive to various combinations of input parameters and different past values sequences. This makes it a potentially good candidate to detect sharp market movements. We finally mention current drawbacks and sketch how to improve them.
In two recent articles (cond-mat/0606177 and arXiv:0804.1615), we have suggested a unified theory of superconductivity based on the real-space spin-parallel electron pairing and superconducting mechanism and have shown that the stable hexagonal and tetragonal vortex lattices (the optimal doping phases) can be expected in the newly discovered LaO{1-x}F{x}FeAs (x0=1/7=0.1428) and SmO{1-x}F{x}FeAs (x0=1/6=0.1667), respectively. In this paper, we present a theoretical study of the effects of hydrostatic and anisotropic pressure on the superconducting transition temperature Tc of the Fe-based layered superconductors based on the above mentioned theory. Our results indicate a strong doping-dependent pressure effects on the Tc of this compound system. Under high hydrostatic pressure, we find that dTc/dP is negative when x>x0 (the so-called overdoped region) and is positive when x 1/6) (arXiv:0804.1582). Furthermore, Tc of both overdoped and underdoped samples shows an increase with uniaxial pressure in the charge stripe direction and a decrease with pressure in the direction perpendicular to the stripes. We suggest that the mechanism responsible for the pressure effect is not specific to the iron-based family and it may also be applicable to other superconducting materials.
This preprint has been withdrawn, as the evidence for persistent currents found with the "infinite-size" DMRG algorithm has not been reproduced with the (presumably more accurate) "finite-size" version of the algorithm (M. Troyer and U. Schollwoeck, private communiation). A much clearer example of long-range order in orbital currents is presented in: J. O. Fjaerestad and J. B. Marston, ``Staggered Orbital Currents in the Half-Filled Two-Leg Ladder,'' cond-mat/0107094.
As a step towards deriving universal amplitude ratios of the superconductive phase transition we calculate the vacuum energy density in the symmetric phase of $\mathrm{O}(N)$-symmetric scalar QED in $D=4\ensuremath{-}\ensuremath{\varepsilon}$ dimensions in an $\ensuremath{\varepsilon}$ expansion using the minimal subtraction scheme commonly denoted by $\overline{\mathrm{MS}}.$ From the diverging parts of the diagrams, we obtain the renormalization constant of the vacuum ${Z}_{v}$ which also contains information on the critical exponent $\ensuremath{\alpha}$ of the specific heat. As a side result, we use an earlier two-loop calculation of the effective potential [H. Kleinert and B. Van den Bossche, cond-mat/0104102] to determine the renormalization constant of the scalar field ${Z}_{\ensuremath{\varphi}}$ up to two loops.
We reply to a comment of Van Enter, Kuelske and Maes (cond-mat/0005176) on our letter "Critical Behavior of the Randomly Spin-Diluted 2-d Ising Model - A Grand Ensemble Approach", Phys. Rev. Lett. {\bf 73}, 2268-2271 (1994).