Epileptic seizure prediction using hybrid feature selection over multiple intracranial EEG electrode contacts: a report of four patients

Epileptic seizure prediction has steadily evolved from its conception in the 1970s, to proof-of-principle experiments in the late 1980s and 1990s, to its current place as an area of vigorous, clinical and laboratory investigation. As a step toward practical implementation of this technology in humans, we present an individualized method for selecting electroencephalogram (EEG) features and electrode locations for seizure prediction focused on precursors that occur within ten minutes of electrographic seizure onset. This method applies an intelligent genetic search process to EEG signals simultaneously collected from multiple intracranial electrode contacts and multiple quantitative features derived from these signals. The algorithm is trained on a series of baseline and preseizure records and then validated on other, previously unseen data using split sample validation techniques. The performance of this method is demonstrated on multiday recordings obtained from four patients implanted with intracranial electrodes during evaluation for epilepsy surgery. An average probability of prediction (or block sensitivity) of 62.5% was achieved in this group, with an average block false positive (FP) rate of 0.2775 FP predictions/h, corresponding to 90.47% specificity. These findings are presented as an example of a method for training, testing and validating a seizure prediction system on data from individual patients. Given the heterogeneity of epilepsy, it is likely that methods of this type will be required to configure intelligent devices for treating epilepsy to each individual's neurophysiology prior to clinical deployment.     

Force-frequency effect of Y-cut langanite and Y-cut langatate

Most recently, langasite and its isomorphs (LGX) have been advanced as potential substitutes for quartz, owing to their extremely high-quality (Q) factors. At least twice higher Q value of LGX than that of quartz has been reported. High Q translates into potentially greater stability. In order to make such materials practical, the environmental sensitivities must be addressed. One of such sensitivities is the force-frequency effect, which relates the sensitiveness of a resonator to shock and vibration via the third-order (non-Hookean) elastic constants. In this paper, we report measured force-frequency coefficients of a Y-cut langanite (LGN) resonator and a Y-cut langatate (LGT) resonator as a function of the azimuthal angle, which is the angle between the crystalline X-axis of a resonator plate and the direction of in-plane diametric force applied to the periphery of the resonator. It was found that the LGN and the LGT behave like AT-cut quartz in the polarity of the frequency changes and the existence of zero-coefficient angle. The maximum magnitudes of the coefficients of the LGN and the LGT are five and seven times smaller than that of stress-compensated cut (SC-cut) quartz, respectively (or, 7 and 10 times smaller comparing to AT-cut quartz). The coefficients of planar-stress, which represent the superposition of a continuous distribution of periphery stresses, also were obtained as 0.52/spl times/10/sup -15/ m/spl middot/s/N and 0.38/spl times/10/sup -15/ m/spl middot/s/N for the LGN and the LGT, respectively.     

Nucleation of apatite crystals in vitro by self-assembled dentin matrix protein 1

Bones and teeth are biocomposites that require controlled mineral deposition during their self-assembly to form tissues with unique mechanical properties. Acidic extracellular matrix proteins play a pivotal role during biomineral formation. However, the mechanisms of protein-mediated mineral initiation are far from understood. Here we report that dentin matrix protein 1 (DMP1), an acidic protein, can nucleate the formation of hydroxyapatite in vitro in a multistep process that begins by DMP1 binding calcium ions and initiating mineral deposition. The nucleated amorphous calcium phosphate precipitates ripen and nanocrystals form. Subsequently, these expand and coalesce into microscale crystals elongated in the c-axis direction. Characterization of the functional domains in DMP1 demonstrated that intermolecular assembly of acidic clusters into a beta-sheet template was essential for the observed mineral nucleation. Protein-mediated initiation of nanocrystals, as discussed here, might provide a new methodology for constructing nanoscale composites by self-assembly of polypeptides with tailor-made peptide sequences.     

Comparison of modeled and observed astronomical refraction of the setting sun

In this study a ray-tracing model that uses atmospheric data from VIZ and Vaisala RS80 rawinsondes is compared with the observed astronomical refraction presented by the setting Sun as seen from Stony Plain, Alberta, Canada. Photogrammetric measurements taken from photographs of the setting Sun show good agreement with the model for the 14 and 22 December 1998 sunsets. The poorer model results for the 8 December sunset appear to be caused by an obsolete and possibly defective VIZ rawinsonde. The results suggest that the ray-tracing model can produce improved refraction values when compared with the Pulkovo tables [Pulkovo Observatory, Refraction Tables of the Pulkovo Observatory, 5th ed. (Nauka, Leningrad, 1985)]. However, they also indicate that the inverse solution (i.e., extracting the temperature profile from refraction measurements) may produce no improvement on U.S. Standard Atmosphere adjusted to the surface conditions.     

Human cell mutagens in respirable airborne particles from the northeastern United States. 2. Quantification of mutagens and other organic compounds

Few reports have characterized mutagenic compounds in respirable airborne particles (<2.5 micrometers in diameter; PM2.5) collected at different sites on a regional scale (hundreds of km). Previously, we reported differences in the human (h1A1v2) cell mutagenicity of whole and fractionated organic extracts of PM2.5 samples collected in Boston, MA, Rochester, NY, and Quabbin Reservoir, a rural site in western MA. Herein we describe the analysis of mutagens and other organic compounds in these samples. Gas chromatography-mass spectrometry (GC-MS) was used to quantify approximately 150 organic compounds, including 31 known human cell mutagens. Molecular weight (MW) 226-302 amu PAHs were the most important mutagens identified: cyclopenta[cd]pyrene accounted for 1-2% of the measured mutagenicity of the samples, MW 252 PAHs accounted for 4-6%, MW 276-278 PAHs accounted for 2-5%, and MW 302 PAHs accounted for 2-3%. 6H-benzo-[cd]pyren-6-one, a PAH ketone, accounted for 3-5% of the mutagenicity. The same compounds accounted for similar portions of the total attributed mutagenicity in each sample. Mutagen levels were similar in the Boston and Rochester samples, and both were significantly higher than the Quabbin sample. This may explain whythe mutagenicities of the Boston and Rochester samples were higher than the Quabbin sample. The levels of mutagens found in semipolar fractions, however, could not explain why the mutagenicity of semipolar fractions was 2-fold higher in the Rochester sample than in the Boston sample. Known mutagens accounted for only 16-26% of the total mutagenicity of the unfractionated extracts, and only approximately 20% of the mutagenicity of the nonpolar and semipolar fractions. The remaining mutagenicity is likely attributable to other, as-yet unknown, semipolar and polar mutagens, or to interactions among chemical constituents of the samples. These findings are consistent with similar studies performed on airborne particles from Los Angeles and Washington, DC, thus indicating that PAHs, PAH-ketones, and as-yet unidentified polar organic compounds are widely distributed airborne human cell mutagens.     

Measurement of ion swarm distribution functions in miniature low-temperature co-fired ceramic ion mobility spectrometer drift tubes

Measurements of the performance of a miniature, portable 12-mm-diameter, 57-mm-length low-temperature cofired ceramic (LTCC) ion mobility spectrometer drift tube were undertaken to verify models of ion transport and determine the physical shape of the ion "swarms" in the LTCC tube. Simplified two-dimensional Gaussian models of ion swarm shape were fit to measured data to extract geometrical shape parameters. Results indicate that tube-transfer function effects that produce asymmetric ion swarms are minimized in the tube reducing temporal dispersion. Data are presented that illustrate the swarm shape as a function of gate time, electric field magnitude, and total charge in the ion swarm. Characterization and understanding of the ion transport mechanisms and effects that limit the resolution and other performance parameters of miniature IMS drift tubes is essential to the development of practical, robust, portable systems for "first responder" and homeland security missions.     

Extended Nijboer-Zernike approach to aberration and birefringence retrieval in a high-numerical-aperture optical system

The judgment of the imaging quality of an optical system can be carried out by examining its through-focus intensity distribution. It has been shown in a previous paper that a scalar-wave analysis of the imaging process according to the extended Nijboer-Zernike theory allows the retrieval of the complex pupil function of the imaging system, including aberrations as well as transmission variations. However, the applicability of the scalar analysis is limited to systems with a numerical aperture (NA) value of the order of 0.60 or less; beyond these values polarization effects become significant. In this scalar retrieval method, the complex pupil function is represented by means of the coefficients of its expansion in a series involving the Zernike polynomials. This representation is highly efficient, in terms of number and magnitude of the required coefficients, and lends itself quite well to matching procedures in the focal region. This distinguishes the method from the retrieval schemes in the literature, which are normally not based on Zernike-type expansions, and rather rely on point-by-point matching procedures. In a previous paper [J. Opt. Soc. Am. A 20, 2281 (2003)] we have incorporated the extended Nijboer-Zernike approach into the Ignatowsky-Richards/Wolf formalism for the vectorial treatment of optical systems with high NA. In the present paper we further develop this approach by defining an appropriate set of functions that describe the energy density distribution in the focal region. Using this more refined analysis, we establish the set of equations that allow the retrieval of aberrations and birefringence from the intensity point-spread function in the focal volume for high-NA systems. It is shown that one needs four analyses of the intensity distribution in the image volume with different states of polarization in the entrance pupil. Only in this way will it be possible to retrieve the "vectorial" pupil function that includes the effects of birefringence induced by the imaging system. A first numerical test example is presented that illustrates the importance of using the vectorial approach and the correct NA value in the aberration retrieval scheme.     

Highly efficient multiple exciton generation in colloidal PbSe and PbS quantum dots

We report ultra-efficient multiple exciton generation (MEG) for single photon absorption in colloidal PbSe and PbS quantum dots (QDs). We employ transient absorption spectroscopy and present measurement data acquired for both intraband as well as interband probe energies. Quantum yields of 300% indicate the creation, on average, of three excitons per absorbed photon for PbSe QDs at photon energies that are four times the QD energy gap. Results indicate that the threshold photon energy for MEG in QDs is twice the lowest exciton absorption energy. We find that the biexciton effect, which shifts the transition energy for absorption of a second photon, influences the early time transient absorption data and may contribute to a modulation observed when probing near the lowest interband transition. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs, and we also introduce a new model for MEG based on the coherent superposition of multiple excitonic states.     

Impacts of the North Atlantic Oscillation on Scandinavian Hydropower Production and Energy Markets

Dramatic swings in the North Atlantic oscillation (NAO) during the 1990s motivated the authors to build a statistical model of NAO impacts on hydropower production and energy markets in Scandinavia. Variation in the NAO index is shown to explain 55% of the variance of streamflow in Norway and up to 30% of the variance in Norway's hydropower output. It is also possible to identify the influence of NAO anomalies on electricity consumption and prices. Government liberalization allowed a financial market to grow around the international trading of electricity, which in Norway is produced almost entirely from hydropower. The model offers a possible tool for predicting the effects of future NAO movements on hydropower production and energy prices in Scandinavia. The potential influence of skillful climate prediction is discussed.