Application of maximum likelihood multivariate curve resolution to noisy data sets

In this work, two different maximum likelihood approaches for multivariate curve resolution based on maximum likelihood principal component analysis (MLPCA) and on weighted alternating least squares (WALS) are compared with the standard multivariate curve resolution alternating least squares (MCR‐ALS) method. To illustrate this comparison, three different experimental data sets are used: the first one is an environmental aerosol source apportionment; the second is a time‐course DNA microarray, and the third one is an ultrafast absorption spectroscopy. Error structures of the first two data sets were heteroscedastic and uncorrelated, and the difference between them was in the existence of missing values in the second case. In the third data set about ultrafast spectroscopy, error correlation between the values at different wavelengths is present. The obtained results confirmed that the resolved component profiles obtained by MLPCA‐MCR‐ALS are practically identical to those obtained by MCR‐WALS and that they can differ from those resolved by ordinary MCR‐ALS, especially in the case of high noise. It is shown that methods that incorporate uncertainty estimations (such as MLPCA‐ALS and MCR‐WALS) can provide more reliable results and better estimated parameters than unweighted approaches (such as MCR‐ALS) in the case of the presence of high amounts of noise. The possible advantage of using MLPCA‐MCR‐ALS over MCR‐WALS is then that the former does not require changing the traditional MCR‐ALS algorithm because MLPCA is only used as a preliminary data pretreatment before MCR analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Preconditioning Newton–Krylov methods in nonconvex large scale optimization

We consider an iterative preconditioning technique for non-convex large scale optimization. First, we refer to the solution of large scale indefinite linear systems by using a Krylov subspace method, and describe the iterative construction of a preconditioner which does not involve matrices products or matrices storage. The set of directions generated by the Krylov subspace method is used, as by product, to provide an approximate inverse preconditioner. Then, we experience our preconditioner within Truncated Newton schemes for large scale unconstrained optimization, where we generalize the truncation rule by Nash–Sofer (Oper. Res. Lett. 9:219–221, 1990) to the indefinite case, too. We use a Krylov subspace method to both approximately solve the Newton equation and to construct the preconditioner to be used at the current outer iteration. An extensive numerical experience shows that the proposed preconditioning strategy, compared with the unpreconditioned strategy and PREQN (Morales and Nocedal in SIAM J. Optim. 10:1079–1096, 2000), may lead to a reduction of the overall inner iterations. Finally, we show that our proposal has some similarities with the Limited Memory Preconditioners (Gratton et al. in SIAM J. Optim. 21:912–935, 2011).     

Radioactivity of honey from northern Poland

This work shows significant variations in the values of ²¹⁰Po in different analyzed Polish voivodeships. Statistical analysis of ²¹⁰Po activity concentrations in honey samples showed significant differences between place of honey collecting, kind of honey and morphological structure of plants from which bees collected nectar.

     

Oxygen self-diffusion in alpha-quartz

We have studied the formation energy of the simplest oxygen defects in alpha-quartz, the oxygen vacancy and interstitial, by an ab initio approach based on density functional theory in the local density approximation. We have determined the formation energies and entropies and the migration paths and energies. From our results we can conclude that oxygen diffuses in quartz by an interstitial mechanism: the interstitial has a dumbbell structure; one of the constitutive atoms jumps towards a neighboring oxygen site. The activation energy amounts to 4.7 eV in the intrinsic regime and 2.8 eV in the extrinsic regime.     

UV‐B and Drought Stress Influenced Growth and Cellular Compounds of Two Cultivars of Phaseolus vulgaris L. (Fabaceae)

Combined enhanced UV‐B radiation and drought may induce different morphological and physiological alterations in plants than either abiotic stress alone. We evaluated morphology, biomass, and primary and secondary metabolism changes in seedlings of two common bean cultivars, IAC Imperador (drought‐resistant) and IAC Milênio. To test the hypothesis that cultivars responded differently to combined stresses in a controlled environment, seedlings of the examined been cultivars were exposed to UV‐B and/or drought treatments for three weeks. The cultivars behaved differently, especially to the drought treatment, suggesting that they use different mechanisms to cope with unfavorable environmental conditions. IAC Imperador showed a stronger protective response, modifying wax composition and primary metabolism, and improving its resistance to UV‐B radiation. For IAC Imperador, the accumulation of cuticular wax and alkane was higher under combined stress but production of primary alcohols was reduced, suggesting a possible fatty acyl switch. Root/shoot length and biomass ratios increased in both cultivars, particularly for the combined stress, indicating a common plant response. We show that these two bean cultivars responded more strongly to UV‐B and combined stress than drought alone as evident in changes to their chemistry and biology. This shows the importance of investigating plant morphological and physiological responses to combined stress.     

Dependence of the Lifetime upon the Excitation Energy and Intramolecular Energy Transfer Rates: The 5D0 EuIII Emission Case

In many Eu^III‐based materials, the presence of an intermediate energy level, such as ligand‐to‐metal charge transfer (LMCT) states or defects, that mediates the energy transfer mechanisms can strongly affect the lifetime of the ⁵D₀ state, mainly at near‐resonance (large transfer rates). We present results for the dependence of the ⁵D₀ lifetime on the excitation wavelength for a wide class of Eu^III‐based compounds: ionic salts, polyoxometalates (POMs), core/shell inorganic nanoparticles (NPs) and nanotubes, coordination polymers, β‐diketonate complexes, organic–inorganic hybrids, macro‐mesocellular foams, functionalized mesoporous silica, and layered double hydroxides (LDHs). This yet unexplained behavior is successfully modelled by a coupled set of rate equations with seven states, in which the wavelength dependence is simulated by varying the intramolecular energy transfer rates. In addition, the simulations of the rate equations for four‐ and three‐level systems show a strong dependence of the emission lifetime upon the excitation wavelength if near‐resonant non‐radiative energy transfer processes are present, indicating that the proposed scheme can be generalized to other trivalent lanthanide ions, as observed for Tb^III/Ce^III. Finally, the proper use of lifetime definition in the presence of energy transfer is emphasized.     

Highly hydrophobic polyfluorinated azo dyes grafted on surfaces

Artificial hydrophobic surfaces have a great potential in a wide range of industrial applications owing to their self-cleaning, anti-fogging and anti-biofouling properties. A family of polyfluorinated reactive azo dyes has been prepared and some of them easily modified and grafted on cotton fabric and glass surfaces obtaining new coloured hydrophobic materials.     

Quasi-TEM mode propagation in twin-wire THz waveguides

We numerically investigate the trade-offs between the dispersion properties,coupling efficiency,and geometrical constraints in dual-wire (twin-lead) terahertz (THz) waveguides.In particular,we show that their inherent linearly polarized quasi-transverse electromagnetic (TEM) modes exist for waveguide transverse dimensions comparable with the wavelength,enabling significant end-fire coupling (>10%) for numericalaperture limited Gaussian beams while supporting a relatively low-dispersion propagation of below 0.5 ps 2 /m,as desired for short-pulse time-domain spectroscopy applications.Starting from the dual-wire structure,we also demonstrate that low-dispersion tapers can be designed to improve coupling efficiency.