Focused Ion Beam Nanopatterning for Optoelectronic Device Fabrication

Recent photonic device structures, including distributed Bragg reflectors (DBRs), one-dimensional (1-D) or two-dimensional (2-D) photonic crystals, and surface plasmon devices, often require nanoscale lithography techniques for their device fabrication. Focused ion beam (FIB) etching has been used as a nanolithographic tool for the creation of these nanostructures. We report the use of FIB etching as a lithographic tool that enables sub-100-nm resolution. The FIB patterning of nanoscale holes on an epitaxially grown GaAs layer is characterized. To eliminate redeposition of sputtered materials during FIB patterning, we have developed a process using a dielectric mask and subsequent dry etching. This approach creates patterns with vertical and smooth sidewalls. A thin titanium layer can be deposited on the dielectric layer to avoid surface charging effects during the FIB process. This FIB nanopatterning technique can be applied to fabricate optoelectronic devices, and we show examples of 1-D gratings in optical fibers for sensing applications, photonic crystal vertical cavity lasers, and photonic crystal defect lasers

Loss and index guiding in single mode proton-implanted holey vertical-cavity surface-emitting lasers

Wedge-shaped holes are fabricated in the top mirror of proton-implanted vertical-cavity surface-emitting lasers (VCSELs). A radially symmetric fill factor approach is used to calculate the resulting transverse index profile. To investigate both the index confinement provided by the etched pattern and its effect on optical loss, continuous-wave (CW) and pulsed experiments are performed. Under CW operation, we show proper wedge design leads to improved fundamental-mode output power, decreased threshold, and increased efficiency. We report a significant decrease in threshold under pulsed operation for the etched device compared to an unetched device, indicating a significant reduction in diffraction loss to the fundamental mode due to strong index guiding. Single-mode output is maintained over the entire operating range of the VCSEL due to increased loss for the higher order mode

A Vision-Based Formation Control Framework

We describe a framework for cooperative control of a group of nonholonomic mobile robots that allows us to build complex systems from simple controllers and estimators. The resultant modular approach is attractive because of the potential for reusability. Our approach to composition also guarantees stability and convergence in a wide range of tasks. There are two key features in our approach: 1) a paradigm for switching between simple decentralized controllers that allows for changes in formation; 2) the use of information from a single type of sensor, an omnidirectional camera, for all our controllers. We describe estimators that abstract the sensory information at different levels, enabling both decentralized and centralized cooperative control. Our results include numerical simulations and experiments using a testbed consisting of three nonholonomic robots

Partitioning behavior of trace elements between dacitic melt and plagioclase, orthopyroxene, and clinopyroxene based on laser ablation ICPMS analysis of silicate melt inclusions

Partitioning behavior of Sc, Ti, V, Mn, Sr, Y, Zr, Nb, Ba, La, Nd, Sm, Eu, Gd, Dy, Ho, Yb, Hf, and Pb between dacitic silicate melt and clinopyroxene, orthopyroxene, and plagioclase has been determined based on laser ablation-inductively coupled plasma mass spectrometric (LA-ICPMS) analysis of melt inclusions and the immediately adjacent host mineral. Samples from the 1988 eruption of White Island, New Zealand were selected because petrographic evidence suggests that all three mineral phases are in equilibrium with each other and with the melt inclusions. All three phenocryst types are found as mineral inclusions within each of the other phases, and mineral inclusions often coexist with melt inclusions in growth-zone assemblages. Compositions of melt inclusions do not vary between the different host minerals, suggesting that boundary layer processes did not affect compositions of melt inclusions and that post-trapping modifications have not occurred. Partition coefficients were calculated from the host and melt inclusion compositions and results were compared to published values. All trace elements examined in this study except Sr are incompatible in plagioclase, and all measured trace elements except for Mn are incompatible in orthopyroxene. In clinopyroxene, Sc, V, and Mn are compatible, and Y, Ti, HREE, and the MREE are only slightly incompatible. Most partition coefficients overlap the wide range of values reported in the literature, but the White Island data are consistently at the lower end of the range in published values. Results from the literature obtained using modern microanalytical techniques such as secondary ion mass spectrometry (SIMS) or proton induced X-ray emission spectroscopy (PIXE) also fall at the lower end of the published values, whereas partition coefficients determined from bulk analysis of glass and crystals separated from volcanic rocks typically extend to higher values. Rapid crystal growth-rates, crystal zonation, or the presence of accessory mineral inclusions in phenocrysts likely accounts for the wide range and generally higher partition coefficients obtained using bulk sampling techniques. The results for 3+ cations from this study are consistent with theoretical predictions based on a lattice strain model for site occupancy. The results also confirm that the melt inclusion-mineral (MIM) technique is a reliable method for determining partition coefficients, as long as the melt inclusions have not experienced post-entrapment reequilibration

4.1.1: Neural Network Based Analysis of EEG Signals SPATIO-TEMPORAL FILTERING OF THE EEG VIA NEURAL NETWORK BASED MULTIREFERENCE ADAPTIVE NOISE CANCELLING

Abstract- A system is proposed which enhances transient non-stationarities and, in particular, epileptiform discharges in the EEG. It is based around the technique of multireference adaptive noise cancelling (MRANC) which attenuates the background EEG on a primary channel by using spatial and temporal information from adjacent channels in the multichannel EEG recording. This process has been implemented by means of a 3-layer perceptron artificial neural A. Dutu collection network trained by a backpropagation algorithm. System performance was measured as the percentage increase in signal-to-noise ratio (SNR) of predetermined epileptiform discharges in recorded EEG segments. The results obtained show that, due to the nonlinear nature of the artificial neural network, the improvement in SNR is significant when compared to the performance of MRANC utilising a linear model. MRANC is proposed as the first stage of a neural network based multi-stage system to detect epileptiform discharges in the interictal EEG for the diagnosis of epilepsy. I