Continuity of Halfspace Depth Contours and Maximum Depth Estimators: Diagnostics of Depth-Related Methods

Continuity of procedures based on the halfspace (Tukey) depth (location and regression setting) is investigated in the framework of continuity concepts from set-valued analysis. Investigated procedures are depth contours (upper level sets) and maximum depth estimators. Continuity is studied both as the pointwise continuity of data-analytic functions, and the weak continuity of statistical functionals—the latter having relevance for qualitative robustness. After a real-data example, some general criteria and counterexamples are given, as well as positive results holding for “typical” data. Finally, some consequences for diagnostics and practical use of the depth-based techniques are drawn.     

On the preparation of stable poly(2-hydroxyethyl methacrylate) nanoparticles

A comprehensive experimental study of aqueous heterophase homopolymerization of 2-hydroxyetyl methacrylate revealed special conditions that must be fulfilled in order to obtain stable latex particles in the nanometer size range. The results clearly show that the formation and the stability of this kind of hydrophilic latex particle strongly depends on the hydrophobic-hydrophilic properties of both the initiating radicals and the stabilizers. Hydrophobic initiators in combination with sodium alkyl sulfate surfactants of proper chain lengths or ionic surface-active initiators lead to stable latex particles. In the latter case the particles keep their identity and spherical shape even after drying of the aqueous dispersion.     

High-throughput solid-phase permethylation of glycans prior to mass spectrometry

Permethylation of glycans prior to their mass spectrometric determination has now become a time-honored methodology in glycoconjugate analysis due to the advantage of a simultaneous analysis of neutral and acidic glycans as well as enhanced sensitivity and easier tandem mass spectrometry interpretation. While the different solvent extraction-based versions of this method often suffice in different structural studies, they are generally less satisfactory in the quantitative determinations aiming at minor quantities of the analyzed materials. To overcome these difficulties, we recently introduced a solid-phase capillary permethylation technique (Kang et al., Rapid Commun. Mass Spectrom. 2005; 19: 3421) for microscale determination. Here, we describe a very useful high-throughput extension of the solid-phase methodology utilizing spin columns packed with sodium hydroxide beads. This procedure has been thoroughly optimized to match the analytical performance parameters of the previously used capillary technique. As demonstrated with a high-precision glycomic profiling analysis of human blood serum, this methodological improvement offers simplicity and reproducibility, allowing the complete permethylation of 12-18 samples in less than 20 min.     

Structure of low-density nanoporous dielectrics revealed by low-vacuum electron microscopy and small-angle X-ray scattering

Aerogels (AGs) are ultralow-density nanoporous solids that have numerous potential applications. However, as most AGs are strong insulators with poor mechanical properties, direct studies of the complex nanoporous structure of AGs by methods such as atomic force and conventional scanning electron microscopy (SEM) have not proven feasible. Here, we use low-vacuum SEM to image directly the ligament and pore size and shape distributions of representative AGs over a wide range of length scales (approximately 100-105 nm). The structural information obtained is used for unambiguous, real-space interpretation of small-angle X-ray scattering curves for these complex nanoporous systems. Low-vacuum SEM permits imaging of both cross-sections and skin layers of AG monoliths. Images of skin layers reveal the presence of microcracks, which alter the properties of cast monolithic AGs.     

Towards Maintenance‐Free Biosensors for Hundreds of Bind/Release Cycles

A single aptamer bioreceptor layer was formed using a common streptavidin–biotin immobilization strategy and employed for 100–365 bind/release cycles. Chemically induced aptamer unfolding and release of its bound target was accomplished using alkaline solutions with high salt concentrations or deionized (DI) water. The use of DI water scavenged from the ambient atmosphere represents a first step towards maintenance‐free biosensors that do not require the storage of liquid reagents. The aptamer binding affinity was determined by surface plasmon resonance and found to be almost constant over 100–365 bind/release cycles with a variation of less than 5 % relative standard deviation. This reversible operation of biosensors based on immobilized aptamers without storage of liquid reagents introduces a conceptually new perspective in biosensing. Such new biosensing capability will be important for distributed sensor networks, sensors in resource‐limited settings, and wearable sensor applications.     

Development and validation of an HPLC method for determination of ziprasidone and its impurities in pharmaceutical dosage forms

Ziprasidone is known as a novel "atypical" or "second-generation" antipsychotic drug. A sensitive and reproducible method was developed and validated for determination of ziprasidone and its major impurities, which are significantly different in polarity. The separation is performed on a Waters Spherisorb octadecylsilyl 1 column (5.0 microm particle size, 250 x 4.6 mm id) using a gradient with mobile phase A [buffer-acetonitrile (80+20, v/v)] and mobile phase B [buffer-acetonitrile (10+90, v/v)] at a working temperature of 25 degrees C. The buffer was 0.05 M KH2PO4 solution with an addition of 10 mL triethylamine/L solution, adjusted to pH 2.5 with orthophosphoric acid. The flow rate was 1.5 mL/min, and the eluate was monitored at 250 nm using a diode array detector. Optimization of the experimental conditions was performed using partial least squares regression, for which four factors were selected for optimization: buffer concentration, buffer pH, triethylamine concentration, and temperature. The proposed validated method is convenient and reliable for the assay and purity control in both raw materials and dosage forms.     

Microchip electrophoresis of N-glycans on serpentine separation channels with asymmetrically tapered turns

We designed and fabricated microfluidic devices with serpentine separation channels and asymmetrically tapered turns, thus allowing high efficiency separations and minimizing band broadening associated with the “racetrack” effect. We evaluated the performance of these devices by measuring the variation in separation efficiency with separation length, electric field strength, taper ratio of the turns, and number of turns. N‐Glycans derived from ribonuclease B and labeled with 8‐aminopyrene‐1,3,6‐trisulfonic acid were electrophoretically separated on serpentine channels with separation lengths of 11, 18, 22, and 36 cm at electric field strengths from 750 to 1750 V/cm. Separations on the 36‐cm channel produced plate numbers up to 940 000 with an analysis time under 3.1 min, whereas separations on the 22‐cm channel had a shorter analysis time (less than 1.25 min), still with respectable efficiencies (up to 600 000 plates). Turn‐induced dispersion was minimized with taper ratios 2 and 3, whereas having two or four 180° turns along with the separation length did not impact the overall efficiency. The developed device was used to analyze native and desialylated N‐glycans derived from the blood serum of an ovarian cancer patient and a disease‐free individual. Separation efficiencies similar to that achieved with the model glycans from ribonuclease B were attained for these biological samples.     

Oxygen centered radicals in iodine chemical oscillators

The existence of free radicals in iodine-based oscillatory systems has been debated for some time. Recently, we have reported the presence of reactive oxygen species (ROS) in the iodide-peroxide system in acidic medium, which is common to all iodine--based oscillatory systems ( J. Phys. Chem. A 2011 , 115 , 2247--2249 ). In this work, the goal was to identify the ROS produced in this system using an EPR spin trap which can distinguish between hydroxyl (HO(?)) and hydroperoxyl (HOO(?)) radicals. The formation of the hydroperoxyl radical was observed and a possible explanation for the low EPR signal of hydroxyl radical was proposed.     

Reusable components in decision tree induction algorithms

We propose a generic decision tree framework that supports reusable components design. The proposed generic decision tree framework consists of several sub-problems which were recognized by analyzing well-known decision tree induction algorithms, namely ID3, C4.5, CART, CHAID, QUEST, GUIDE, CRUISE, and CTREE. We identified reusable components in these algorithms as well as in several of their partial improvements that can be used as solutions for sub-problems in the generic decision tree framework. The identified components can now be used outside the algorithm they originate from. Combining reusable components allows the replication of original algorithms, their modification but also the creation of new decision tree induction algorithms. Every original algorithm can outperform other algorithms under specific conditions but can also perform poorly when these conditions change. Reusable components allow exchanging of solutions from various algorithms and fast design of new algorithms. We offer a generic framework for component-based algorithms design that enhances understanding, testing and usability of decision tree algorithm parts.