A direct brain interface based on event-related potentials.

Cross-correlation between a trigger-averaged event-related potential (ERP) template and continuous electrocorticogram was used to detect movement-related ERP's. The accuracy of ERP detection for the five best subjects (of 17 studied), had hit percentages >90% and false positive percentages <10%. These cases were considered appropriate for operation of a direct brain interface.     

Polynomial chaos for simulating random volatilities

In financial mathematics, the fair price of options can be achieved by solutions of parabolic differential equations. The volatility usually enters the model as a constant parameter. However, since this constant has to be estimated with respect to the underlying market, it makes sense to replace the volatility by an according random variable. Consequently, a differential equation with stochastic input occurs, whose solution determines the fair price in the refined model. Corresponding expected values and variances can be computed approximately via a Monte Carlo method. Alternatively, the generalised polynomial chaos yields an efficient approach for calculating the required data. Based on a parabolic equation modelling the fair price of Asian options, the technique is developed and corresponding numerical simulations are presented.     

Bipolar strain hysteresis of poled composites with Nd–Mn-doped PZT fibres

Nd–Mn-doped PZT fibres were produced using the sol–gel process. The PZT was doped with 2 mol% neodymium and an amount of 1.1 mol% or 0.75 mol% manganese. The fibres were investigated with respect to microstructure, composition after sintering and phase content. Strain and polarisation were measured after imbedding the fibres in a polymer matrix.The resulting 1–3-composites were poled with constant electric field. Measurements of strain and polarisation were done using a sinusoidal voltage of high amplitude. Instead of a shifted strain hysteresis (butterfly loop) an asymmetric strain–field relation was observed. The asymmetry depends on the direction of the applied voltage. For the half wave with voltage parallel to former poling voltage the strain curve is linear. For the other half wave the strain curve inflates and there is a region with no change of strain. Possible explanations for the asymmetric strain behaviour are discussed.     

Double-resonance Semiconductor Superlattice Parametric Oscillator for Generation of Subterahertz Radiation

We report on a subterahertz superlattice parametric oscillator that operated simultaneously at two different harmonic frequencies of a microwave pump field. A pump field (frequency near 100 GHz) was coupled to a GaAs/AlAs superlattice in a resonator for the third and the fifth harmonic. The pump field produced a third harmonic field and this together with the pump field created a fifth harmonic field. A theoretical analysis indicates that the nonlinearity, which is based on the dynamics of miniband electrons, should allow for the upconversion of pump radiation of higher frequency into the terahertz frequency range.     

Powder-Route Synthesis and Mechanical Testing of Ultrafine Grain Tungsten Alloys

We report a W-rich alloy (W-7Cr-9Fe, at. pct) produced by high-energy ball milling, with alloying additions that both lower the densification temperature and retard grain growth. The alloy’s consolidation behavior and the resultant compacts’ microstructure and mechanical properties are explored. Under one condition, a 98 pct dense compact with a mean grain size of 130 nm was achieved, and exhibited a hardness of 13.5 GPa, a dynamic uniaxial yield strength of 4.14 GPa in Kolsky bar experiments, and signs of structural shear localization during deformation.     

Quality estimation of subdurally recorded, event-related potentialsbased on signal-to-noise ratio

Our goal is to develop a direct brain interface (DBI) that will provide communication and environmental control to persons who are "locked-in" (or nearly so) as a consequence of brainstem stroke, amyotrophic lateral sclerosis (ALS), or other etiologies. Previously we demonstrated that templates constructed from trigger averaged event-related potentials (ERPs) can be cross-correlated with ongoing electrocorticograms (ECoGs) to detect ERPs associated with the performance of simple motor actions. However, it was difficult to predict a priori which of many candidate ECoG recording site(s) could provide signals that would provide adequate motor action detection. We present here a measure of ERP quality based on an estimate of the signal to noise ratio (SNR) associated with the formation of an ERP template from the performance of consecutive voluntary actions. Detection-theory-based receiver operator characteristics (ROCs) and a database of ECoGs (6000+) recorded from the cortical surface of awake human subjects were used to assess the usefulness of the SNR technique. The SNR method was found to predict the detection efficacy of ERPs when characterized over a wide parameter range, with the majority of ROC curve areas greater than 90%. This method was compared with our previously developed quality measure (the peak-to-baseline ratio) and found to provide significantly better performance (ROC area differences from 4.4% to 13.7%). Thus, the SNR estimate of the ERP is a useful tool to predict the efficacy of ERP templates for cross-correlation-based detection and assist in the selection of viable ERP templates for DBI applications.     

Preparation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) particles in O/W emulsion

In the present paper, we investigate the preparation of polymeric particles based on the biodegradable polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). A new technique for PHBV particle preparation has been developed. This method utilizes the thermoreversible gelation of PHBV in toluene. Particles have been obtained by the secondary dispersion technique in a three-step procedure: (a) preparation of PHBV solution in toluene; (b) preparation of O/W emulsion by ultrasound followed by the gel formation in toluene/PHBV droplets; and (c) toluene extraction. In the present study we investigated the influence of the stabilizer type and its concentration in the aqueous phase, ultrasound power, and PHBV concentration in toluene on the size and stability of the formed droplets as well as the final PHBV particles. It has been found that PEO/PS block copolymers are the best stabilizers for the present system as compared to conventional tensides such as SDS or CTAB. It has been found that PEO/PS block copolymers allow obtaining PHBV particles with a regular shape and controlled dimensions after toluene extraction. The minimal size of the PHBV particles obtained by this technique was ca. 100 nm. The obtained particles exhibit a relatively broad particle size distribution and the particle shape is strongly affected by the block copolymer composition, ultrasound power and the way of toluene extraction.     

Atomistic basis for the plastic yield criterion of metallic glass

Because of their disordered atomic structure, amorphous metals (termed metallic glasses) have fundamentally different deformation mechanisms compared with polycrystalline metals. These different mechanisms give metallic glasses high strength, but the extent to which they affect other macroscopic deformation properties is uncertain. For example, the nature of the plastic-yield criterion is a point of contention, with some studies reporting yield behaviour roughly in line with that of polycrystalline metals, and others indicating strong fundamental differences. In particular, it is unclear whether pressure- or normal stress-dependence needs to be included in the plastic-yield criterion of metallic glasses, and how such a dependence could arise from their disordered structure. In this work we provide an atomic-level explanation for pressure-dependent yield in amorphous metals, based on an elementary unit of deformation. This simple model compares favourably with new atomistic simulations of metallic glasses, as well as existing experimental data.