On the fusion of threshold classifiers for categorization and dimensionality reduction

We study ensembles of simple threshold classifiers for the categorization of high-dimensional data of low cardinality and give a compression bound on their prediction risk. Two approaches are utilized to produce such classifiers. One is based on univariate feature selection employing the area under the ROC curve as ranking criterion. The other approach uses a greedy selection strategy. The methods are applied to artificial data, published microarray expression profiles, and highly imbalanced data.     

A monolithic PNGase F enzyme microreactor enabling glycan mass mapping of glycoproteins by mass spectrometry

We demonstrate a simple and rapid single-step method to fabricate an enzyme microreactor incorporating the N-glycosidase PNGase F (peptide-N-glycosidase F) into a porous polymer-based monolith. The monolith is contained in a capillary format, while the enzyme reactor is ready to use within 1 h of preparation. The monomers making up the monolith, including N-acryloxysuccinimide for covalent immobilization of the enzyme, are mixed with PNGase F and introduced into the column by capillary force for polymerization/immobilization. Glycoproteins (ribonuclease B, asialofetuin, alpha1-acid glycoprotein, and ovalbumin) perfused through the PNGase F reactor were shown to be effectively deglycosylated on a time-scale of seconds/low minutes using low nanogram to microgram per microliter concentration (corresponding to a total sample consumption of 0.1-20 microg of a glycoprotein). The reactor enzyme activity was shown to be reproducible for at least 8 weeks when used and stored at room temperature. Evaluation was performed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.     

Cerebral bioimaging of Cu, Fe, Zn, and Mn in the MPTP mouse model of Parkinson’s disease using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been established as a powerful technique for the determination of metal and nonmetal distributions within biological systems with high sensitivity. An imaging LA-ICP-MS technique for Fe, Cu, Zn, and Mn was developed to produce large series of quantitative element maps in native brain sections of mice subchronically intoxicated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP) as a model of Parkinson’s disease. Images were calibrated using matrix-matched laboratory standards. A software solution allowing a precise delineation of anatomical structures was implemented. Coronal brain sections were analyzed crossing the striatum and the substantia nigra, respectively. Animals sacrificed 2 h, 7 d, or 28 d after the last MPTP injection and controls were investigated.     

Nearest neighbor effect on capture cross sections measured in IR phototransients on Si:In

The extrinsic photoconductive decay at T=20–100 K is analyzed in FZ-grown Si: In material after pulsed irradiation by a PbSSe infrared laser (=4 m). Trapping time constants (=10 ns-100 s) are resolved for the prevalent In acceptor (N _In=10¹⁶–10¹⁷ cm^–3) and for additional shallow acceptors B, Al, and the X(In)-center present at low concentrations (N=10¹²–10¹⁴ cm^–3). Hole capture cross sections determined for the acceptor levels show a large scatter over up to 4 orders of magnitude. It is shown that the capture cross section is dependent on all the dopant concentrations present in the sample due to nearest neighbor interaction. Due to the formation of donor-acceptor dipoles, the capture cross section assumes low values. A model calculation of the interaction based on only fundamental parameters of Si is in accordance with the experimental data within the experimental error. The hole capture cross sections for isolated acceptors are _p=1×10^–12, 1×10^–14, 1×10^–13, 2.5×10^–13 cm² for indium, X-center, aluminum, and boron at the temperatures T=95 K, 100 K, 70 K, 45 K, respectively.