Analysis of cyanobacterial toxins by physicochemical and biochemical methods

Cyanobacteria (blue-green algae) produce a wide range of low molecular weight metabolites that include potent neurotoxins, hepatotoxins, and cytotoxins. The accumulation of such toxins in freshwaters, and in brackish and marine waters presents hazards to human and animal health by a range of exposure routes. A review is presented of developments in the detection and analysis of cyanobacterial toxins, other than bioassays, including application of physicochemical, immunoassays, and enzyme-based methods. Analytical requirements are considered with reference to recently derived guideline levels for the protection of health and to the availability, or otherwise, of purified, quantitative cyanobacterial toxin standards.     

Magnetic Field Effects on Fluorescence Polarization Spectroscopy of Perylene

In the passed decade, great attention has been paid on the study of external magnetic filed effects on chemical reactions and relative phenomena. Our recent previous study show to molecular spectra of some system, such as α-bromonaphthalene in aqueous solution of β-Cyclodextrin, can be modified by external magnetic field effects.     

An analysis of nanoindentation in linearly elastic solids

The conventional method to extract elastic properties in the nanoindentation of linearly elastic solids relies primarily on Sneddon’s solution (1948). The underlying assumptions behind Sneddon’s derivation, namely, (1) an infinitely large incompressible specimen; (2) an infinitely sharp indenter tip, are generally violated in nanoindentation. As such, correction factors are commonly introduced to achieve accurate measurements. However, little is known regarding the relationship between the correction factors and how they affect the overall accuracy. This paper first proposes a criterion for the specimen’s geometry to comply with the first assumption, and modifies Sneddon’s elastic relation to account for the finite tip radius effect. The relationship between the finite tip radius and compressibility of the specimen is then examined and a composite correction factor that involves both factors, derived. The correction factor is found to be a function of indentation depth and a critical depth is derived beyond which, the arbitrary finite tip radius effect is insignificant. Techniques to identify the radius of curvature of the indenter and to decouple the elastic constants (E and ν) for linear elastic materials are proposed. Finally, experimental results on nanoindentation of natural latex are reported and discussed in light of the proposed modified relation and techniques.     

On the decimal numbers base n

This paper focuses on the representation of a proper fraction a/b by a decimal number base n where n is any integer greater than 1. The scope is narrowed to look at only fractions where a, b are positive integers with a<b and b not equal to 0 nor equal to 1. Some relationships were found between b and n, which determine whether the representation will become either finite decimal, pure recurring decimal or mixed decimal base n. Three theorems have been proven to indicate the deciding factors and the relationships. In addition, the length of the finite decimal numbers base n was further explored.     

Silicon photonics: from a microresonator perspective

Silicon photonics leverages the optical, electrical and material properties of silicon and the mature complementary metal‐oxide semiconductor (CMOS) nanofabrication technique to develop on‐chip photonic integration, which has been making significant impacts in various frontiers including next‐generation optical communications networks, on‐chip optical interconnects for high‐speed energy‐efficient computing and biosensing. Among many optical structures fabricated on silicon chips, microresonators due to their high‐Q resonances and small footprints play important roles in various devices including lasers, filters, modulators, switches, routers, delays, detectors and sensors. This paper reviews from a microresonator perspective some of the latest progress in the field, summarizes design considerations in various applications and points out key challenges and potentials.     

Model-based clustering of high-dimensional data: Variable selection versus facet determination

Variable selection is an important problem for cluster analysis of high-dimensional data. It is also a difficult one. The difficulty originates not only from the lack of class information but also the fact that high-dimensional data are often multifaceted and can be meaningfully clustered in multiple ways. In such a case the effort to find one subset of attributes that presumably gives the “best” clustering may be misguided. It makes more sense to identify various facets of a data set (each being based on a subset of attributes), cluster the data along each one, and present the results to the domain experts for appraisal and selection. In this paper, we propose a generalization of the Gaussian mixture models and demonstrate its ability to automatically identify natural facets of data and cluster data along each of those facets simultaneously. We present empirical results to show that facet determination usually leads to better clustering results than variable selection.     

Additive Decomposition of Real Matrices

The orthogonal orbit ${\cal O}(A)$ of an n × n real matrix A is the set of real matrices of the form $P^t \ AP$ where $P^t P = I_n$ . We show that $A/ \| A\|$ is an affine sum of four orthogonal matrices, and note that $A^t$ can always be written as an affine combination of no more than 2 n m 1 matrices in ${\cal O}(A)$ . This improves some recent results of Zhan, and answers some of his questions. Other related results are also discussed.     

Polyelectrolyte complex materials consisting of antibacterial and cell-supporting layers

The characterization of a polyelectrolyte complex material comprised of two biopolymers, a chitosan upper layer and a gellan gum under layer, is reported. It is shown that the upper layer of chitosan with incorporated levofloxacin displays an antibacterial activity, while the under layer of a gellan gum/TiO(2) composite supports the growth of fibroblastic cells.     

Planar optical tweezers using tapered-waveguide junctions

We demonstrate planar optical tweezers using the evanescent field of a silicon nitride tapered-waveguide junction between a singlemode waveguide and a multimode waveguide. Our experiments show that the junction embedded in a fluidic channel holds up to one and two polystyrene particles of sizes of 2.2 μm and 1 μm, respectively. The trapped particles are successively substituted by the incoming particles. Our experiments and numerical modeling reveal that the junction particle trapping depends on particle size and number.     

Simultaneous Determination of Cortisol,Cortisone, and 6β-Hydroxycortisol in Human Urine by UPLC with UV Detector and Application to Determine Diurnal Variations

In the present studies, a simple rapid ultra performance liquid chromatography (UPLC) method with UV detection for the simultaneous determination of cortisol, cortisone and 6β-hydroxycortisol in human urine was developed. The three analytes and the internal standard dexamethasone were separated on a Waters Acquity UPLC-Tunable UV system with an Acquity UPLC BEH C18 column (50 × 2.1 mm ID, 1.7 μm) using a gradient elution of methanol and water (containing 0.01% formic acid) with a run time of 7 min. The method was accurate and precise, over the ranges of 5–200 ng mL⁻¹ for cortisol, and 10–1,000 ng mL⁻¹ for both cortisone and 6β-hydroxycortisol, and showed good linearity (r ² > 0.999). This method was applied for the measurement of cortisol, cortisone and 6β-hydroxycortisol in samples collected over different periods as a tool to assess the activity of CYP3A and 11β-hydroxysteroid dehydrogenase type 2 enzymes.