Discarding or downweighting high-noise variables in factor analytic models

This work examines the factor analysis of matrices where the proportion of signal and noise is very different in different columns (variables). Such matrices often occur when measuring elemental concentrations in environmental samples. In the strongest variables, the error level may be a few percent. For the weakest variables, the data may consist almost entirely of noise. This paper demonstrates that the proper scaling of weak variables is critical. It is found that if a few weak variables are scaled to too high a weight in the analysis, the errors in computed factors would grow, possibly obscuring the weakest factor(s) by the increased noise level. The mathematical explanation of this phenomenon is explored by means of Givens rotations. It is shown that the customary form of principal component analysis (PCA), based on autoscaling the original data, is generally very ineffective because the scaling of weak variables becomes much too high. Practical advice is given for dealing with noisy data in both PCA and positive matrix factorization (PMF).     

Promotion of photodynamic therapy-induced apoptosis by the mitochondrial protein Smac/DIABLO: dependence on Bax

Photodynamic therapy (PDT) using the second-generation photosensitizer phthalocyanine (Pc) 4 causes mitochondrial damage and induces apoptosis through the release of cytochrome c to the cytosol. Another protein of the mitochondrial intermembrane space, Smac/DIABLO (second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI), is also released to the cytosol in response to apoptotic stimuli and promotes caspase activation by binding IAP. To investigate the possible role of Smac/DIABLO in apoptosis induced by Pc 4-PDT, we transfected Smac/DIABLO (tagged at its C-terminus with green fluorescent protein [GFP]) into MCF-7c3 cells (human breast cancer MCF-7 cells stably transfected with procaspase-3) and DU-145 cells (human prostate cancer cells that express no Bax because of a frameshift insertion mutation). Confocal microscopy showed that recombinant Smac/DIABLO, like cytochrome c, localized to mitochondria and colocalized with MitoTracker Red. Three hours after exposure of MCF-7c3 cells to PDT (200 nM Pc 4 and 150 mJ/cm2 red light), Smac/DIABLO-GFP, as well as cytochrome c, was found largely in the cytosol. In contrast, for DU-145 cells, both Smac/DIABLO-GFP and cytochrome c remained in the mitochondria after PDT. By staining with Hoechst 33,342, typical apoptotic nuclei were observed in MCF-7c3 cells, but not in DU-145 cells, after Pc 4-PDT. These results suggest that the release of Smac/DIABLO from mitochondria may be regulated by a Bax-mediated mechanism and that Smac/DIABLO may cooperate with the cytochrome c-dependent apoptosis pathway. In addition, in MCF-7c3 cells transfected by Smac/DIABLO-GFP, apoptosis induced by Pc 4-PDT was greater than in cells transfected with the GFP vector alone or in untransfected cells, as determined by flow cytometry. Thus, Smac/DIABLO promotes apoptosis after Pc 4-PDT in a Bax-dependent manner and may facilitate the passage of PDT-treated cells through the late steps of apoptosis.     

Towards a Molecular Understanding of Asymmetric Heterogeneous Catalysis: Hydrogenation of 1-Phenyl-1,2-Propanedione1

The present work comprises a detailed investigation of a complex reaction system, revealing features of reaction mechanisms that are general for asymmetric heterogeneous catalysis. Heterogeneous enantioselective hydrogenation of 1-phenyl-1,2-propanedione was studied over cinchonidine modified Pt catalysts producing (R)-1-hydroxy-1-phenylpropanone as the main product with an enantiomeric excess (ee) of 65% at maximum yield, which could be further increased above 90% due to kinetic resolution. The results of kinetic studies in batch and continuous reactors, catalyst screening and characterization results, as well as quantum chemical calculations, are summarized, and pertinent mechanistic aspects are discussed.     

Monitoring the precision of routine analyses by using duplicate determinations

To ensure the reliability of results, analytical laboratories require a continuous qualitycontrol program which must take account of both systematic and random errors. Analyses of reference materials can be used to estimate systematic errors but estimates of random errors (precision) tend to be optimistic, mainly because reference materials cannot be put through the whole analytical process (e.g., primary sampling is often a major source of error). Estimates of precision must be based on routine samples. If duplicate determinations are done on routine samples, the precision can be estimated reliably. Within the optimum concentration range of analytical method (usually starting from 5-10 times the detection limit), the relative standard deviation (s_r can be regarded as being almost constant or independent of concentration. The precision can then be estimated by first calculating the s_r value of each pair of results. Individually, these are not reliable estimates of the true s_r, but they can be regarded as independent measurements of the same s_r and so can be pooled to obtain a more reliable estimate of precision with the number of duplicates as the degrees of freedom. The applicabiilty of the method is tested on soil, rock and ore samples.     

The prediction of mechanical properties of injection moulding parts by vacuum casting

The behaviour of vacuum cast prototypes and injection moulding parts in mechanical tests was compared. The mechanical tests were made using real production parts as references. Distinct correlations were found between vacuum cast prototypes and injection moulding parts. In this light, vacuum cast prototypes can be used for the evaluation of injection moulding products with certain limitations. Vacuum casting is best suited for the evaluation of such mechanical properties of injection moulding products as tensile, flexural and compression strength, while impact strength is the property that is most difficult to evaluate.     

Degradation of viscose fibers during acidic treatment

Novel developments in the fiber sector require additional investigation of their behaviour during the production process. In the core step of the viscose process, cellulose fibres are regenerated in an acidic spinning bath. To investigate the influence of hemicellulose content and temperature on the kinetics of fiber degradation, standard and hemicellose-enriched fibers were treated in the acidic standard spinning bath for time periods up to 292 h. Viscose samples of different hemicellulose content were prepared under standardized conditions and the never dried fibres were subjected to long term degradation in the standard spinning bath at 40, 50 and 60 °C. The changes in the degree of polymerization (DP), molar mass distribution, hemicellulose and the generation of the total organic carbon in the spinning bath were monitored. Further, the changes in crystallinity and the level-off-DP of the fibers were determined to improve the accuracy of the existing degradation model. Changes in morphology of the fibers were monitored by optical microscopy and scanning electron microscopy.     

Electronic energy band structure of the double perovskite Ba2MnWO6

The electronic and magnetic structures of the double perovskite oxide Ba 2MnWO6 (BMW) were determined by employing the density functional theory within the generalized gradient approximation (GGA) + U approach. BMW is considered a prototype double perovskite due to its high degree of B-site ordering and is a good case study for making a comparison between computations and experiments. By adjusting the U-parameter, the electronic energy band structure and magnetic properties, which were consistent with the experimental results, were obtained. These computations revealed that the valence bands are mainly formed from Mn 3d and O 2p states, while the conduction bands are derived from W 5d and O 2p states. The localized bands composed from Mn 3d states are located in the bandgap. The results imply that the formation of polarons in the conduction band initiate the resonance Raman modes observed as a series of equidistant peaks.     

A combined NMR, DFT, and X-ray investigation of some cinchona alkaloid O-ethers

Structures and conformational behavior of several cinchona alkaloid O-ethers in the solid state (X-ray), in solution (NMR and DFT), and in the gas phase (DFT) were investigated. In the crystal, O-phenylcinchonidine adopts the Open(3) conformation similar to cinchonidine, whereas the O-methyl ether derivatives of both cinchonidine and cinchonine are packed in the Closed(1) conformation. Dynamic equilibria in solutions of the alkaloids were revealed by combined experimental-theoretical spin simulation/iteration techniques for the first time. In the (1)H NMR spectra in CDCl3 and toluene-d8 at room temperature, Closed(1) conformation was observed for the O-silyl ethers as a separate set of signals. For O-methyl ether derivatives Closed(1) could be separated only at -30 degrees C in CDCl3 or toluene-d8 and for O-phenylcinchonidine at -70 degrees C in CDCl3/CD2Cl2. The ratio between the Closed(2) and Open(3) conformers was estimated by analyzing the vicinal coupling constant (3)J(H9,H8) at ambient and low temperatures. The observed conformational equilibria of O-(tert-butyldimethylsilyl)cinchonidine in CDCl 3 and toluene-d8 are in good agreement with the theoretically estimated equilibrium populations of the conformations according to Boltzmann statistics. The conformational equilibria of four cinchona alkaloid O-ether solutes in CDCl3 and toluene-d8 are discussed in the light of their relevance to the mechanism of 1-phenyl-1,2-propanedione (PPD) hydrogenation over cinchona alkaloid modified heterogeneous platinum catalysts. It was demonstrated that the conformation found to be abundant in the liquid phase has no direct correlation with the enantioselectivity of the PPD hydrogenation reaction.     

Calculation and optical measurement of laser trapping forces on non-spherical particles

Optical trapping, where microscopic particles are trapped and manipulated by light is a powerful and widespread technique, with the single-beam gradient trap (also known as optical tweezers) in use for a large number of biological and other applications. The forces and torques acting on a trapped particle result from the transfer of momentum and angular momentum from the trapping beam to the particle. Despite the apparent simplicity of a laser trap, with a single particle in a single beam, exact calculation of the optical forces and torques acting on particles is difficult. Calculations can be performed using approximate methods, but are only applicable within their ranges of validity, such as for particles much larger than, or much smaller than, the trapping wavelength, and for spherical isotropic particles. This leaves unfortunate gaps, since wavelength-scale particles are of great practical interest because they are readily and strongly trapped and are used to probe interesting microscopic and macroscopic phenomena, and non-spherical or anisotropic particles, biological, crystalline, or other, due to their frequent occurance in nature, and the possibility of rotating such objects or controlling or sensing their orientation. The systematic application of electromagnetic scattering theory can provide a general theory of laser trapping, and render results missing from existing theory. We present here calculations of force and torque on a trapped particle obtained from this theory and discuss the possible applications, including the optical measurement of the force and torque.