Multivariate Calibration of Concentrations of C,Mn, Si,Cr, Ni,and Cu in Low-Alloy Steels from Raw Low-Resolution Spectra Obtained By Laser-Induced Breakdown Spectroscopy

Journal of Applied Spectroscopy - Multivariate models were developed on the basis of raw low-resolution LIBS spectra of reference samples of lowalloy steels for calibration of the concentrations of...     

A principal component analysis of transmission spectra of wine distillates

A chemometric method of decomposing multidimensional data into a small-sized space, the principal component method, has been applied to the transmission spectra of vintage Moldovan wine distillates. A sample of 42 distillates aged from four to 7 years from six producers has been used to show the possibility of identifying a producer in a two-dimensional space of principal components describing 94.5% of the data-matrix dispersion. Analysis of the loads into the first two principal components has shown that, in order to measure the optical characteristics of the samples under study using only two wavelengths, it is necessary to select 380 and 540 nm, instead of the standard 420 and 520 nm, to describe the variability of the distillates by one principal component or 370 and 520 nm to describe the variability by two principal components.     

Electronic Structure and Magnetic Properties of Clusters with (μ-1,1-N3) Bridges

Quantum-chemical calculations and a generalized angular overlap model were used to demonstrate that the electronic structure of N^– ₃ anions is favorable for the development of ferromagnetic properties in polynuclear complexes whose structural elements are planar binuclear fragments of the M(N₃)₂M type characterized by a broad range of M–N–M angles (95°–105°). Analysis of the known experimental data points to the correctness of the theoretical views and demonstrates the ferromagnetic stability of complexes of this type to the deviation of the N₃ ligands from the plane of the MN₂M ring.     

Ferromagnetism of Two-Bridge Clusters

A generalized model of angular overlapping was used to analyze the magnetic properties of polynuclear complexes. The structural elements of these complexes contain planar binuclear fragments of the M(LR)₂M type. The maximum ferromagnetism for the monoatomic bridges corresponds to = MLM, which is about 100°. Weak planar interactions between L and R displace the ferromagnetism maximum towards lower , while interactions shift it towards higher . In almost all cases, strong planar interactions (LLR 180°) are responsible for strong antiferromagnetism.     

Optimization of the power ratios of the bidirectional pumping at two wavelengths for erbium-doped fiber amplifiers

The gain and noise factor spectra of erbium-doped fiber amplifiers with pumped according to a copropagating three-level scheme and according to a counterpropagating quasi-two-level scheme in the regime of unsaturated gain in the C band have been simulated numerically. It has been shown that, at the total pump power up to 30 mW and at the optimized power ratio of the copropagating and counterpropagating pumps, the inhomogeneity of the gain in the C band does not exceed 0.25 dB at the noise factor of 4.2–4.7 dB.     

A comparative study of surface‐enhanced Raman scattering from silver‐coated anodic aluminum oxide and porous silicon

Three types of Ag‐coated arrays from porous anodic aluminum oxide (AAO) were prepared and studied as substrates for surface‐enhanced Raman scattering (SERS). They were compared with Ag‐coated porous silicon (PSi) samples. AAO‐based substrates were prepared by the vapor deposition of silver directly onto the surface of porous AAO with different morphologies of the pores, whereas SERS‐active island films on the PSi were prepared by immersion plating. The resulting metallic nanostructures were characterized by UV‐vis absorption spectroscopy and scanning electron microscopy (SEM). Thermal evaporation leads to the formation of granular arrays of Ag nanoparticles on the surface of AAO. SERS activity of the substrates was tested using water‐soluble cationic Zn(II)‐tetrakis (4‐N‐methylpyridyl) porphyrin (ZnTMPyP4) as a probe molecule. The results indicate that all AAO‐based substrates studied here exhibit some degree of SERS activity. Noteworthy, for excitation at 532 nm, signals from AAO‐based substrates were comparable with those from the PSi‐based ones, whereas for 441.6 nm excitation they were about twice higher. The strongest SERS‐enhancement at 441.6 nm excitationwas provided by the AAO substrates with silver deposited on the monolith (originally nonporous) side of AAO. Preferential SERS‐enhancement of the bands ascribed to the vibrations of the N‐methylpyridinium group of ZnTMPyP4 when going to blue excitation was found. Copyright © 2010 John Wiley & Sons, Ltd.