Gallium arsenide molecular beam epitaxy: Low temperature and surfactant-mediated

The reflection high-energy electron diffraction (RHEED) specular spot intensity oscillations that were obtained during low-temperature regime and surfactant mediated regime of molecular beam epitaxial (MBE) growth of GaAs is studied and explained using modified stochastic model and a rate equation model, respectively; The dynamics of the physisorbed As layer were introduced into the stochastic model by including the thermally activated processes of chemisorption into and evaporation out of the As physisorbed state. Increased scattering of the RHEED beam due to the higher physisorbed As coverage at 2:1 leads to a factor of 5 decrease in the steady-state amplitude of the RHEED oscillations compared to the 1:1 case. These results are in excellent agreement with the experimental results. A factor in maintaining this growth mode is that arsenic stays in the physisorbed state with lifetimes in the range of 10{dollar}\sp{-3}{dollar} to 10{dollar}\sp{-5}{dollar} seconds and incorporates only when an appropriate configuration of Ga atoms forms on the surface; Beating in the reflection high energy electron diffraction (RHEED) intensity oscillations were observed during molecular beam epitaxial (MBE) growth of GaAs with Sn as a surfactant. A rate equation model of growth was developed to explain this phenomenon by assuming that the GaAs covered by the Sn grows at a faster rate compared to the GaAs not covered by Sn. Assuming that the electron beams reflected from the Sn covered surface and the rest of the surface are incoherent, the results of the dependence of the RHEED oscillations on Sn submonolayer coverages for various Sn coverages were obtained and compared with experimental data and the qualitative agreement is very good. (Abstract shortened by UMI.)

Yield Enhancement of Digital Microfluidics-Based Biochips Using Space Redundancy and Local Reconfiguration

As microfluidics-based biochips become more complex, manufacturing yield will have significant influence on production volume and product cost. We propose an interstitial redundancy approach to enhance the yield of biochips that are based on droplet-based microfluidics. In this design method, spare cells are placed in the interstitial sites within the microfluidic array, and they replace neighboring faulty cells via local reconfiguration. The proposed design method is evaluated using a set of concurrent real-life bioassays.Comment: Submitted on behalf of EDAA (http://www.edaa.com/

Fabrication of Oxide Superconducting Thin Films Using Colloid of Nanoparticles as Precursor

This thesis reports the development of a new approach for the fabrication of superconducting thin films. Among the liquid phase methods of fabricating high temperature superconductors having critical current density about 1 MA/cm2, metalorganic deposition using metal trifluoroacetates (TFA-MOD) is the best known method. In this project, detailed spectroscopic and microscopic analysis was performed at every stage of the TFA-MOD process to understand the evolution of crystalline superconducting film. It was observed that the TFA-MOD has some inherent disadvantages such as long process time, evolution of HF gas and results porosity in films. A new liquid phase process was developed to fabricate superconducting YBCO thin films, which has the potential to overcome the above mentioned drawbacks. This process involves using a precursor, which is a colloidal suspension of Y-Ba-Cu-O nanoparticles of size ~ 20 nm. Precursor films were deposited on LaAlO3 by spin coating or dip coating and heat treated in two stage annealing process to obtain final films. Compared to MOD-TFA processed films, the nanoparticle processed films showed lower porosity and can be grown at faster heating rates. The superconducting transition temperature of nanoparticle processed YBCO films to date is ~ 89 K at R=0. Self-field critical current densities (Jc) of 2 MA/cm2 at 77 K have been achieved

Electromagnetic interventions as a therapeutic approach to spreading depression

Spreading depression (SD) is a slow propagating wave of depolarization that can spread throughout the cortex in the event of brain injury or any general energy failure of the brain. Massive cellular depolarization causes enormous ionic and water shifts and silences synaptic transmission in the affected tissue. Large amounts of energy are required to restore ionic gradients and are not always met. When these energetic demands are not met, brain tissue damage can occur. The exact mechanism behind initiation and propagation of SD are unknown, but a general model is known. It may be possible to prevent or delay the onset of SD using non-invasive electromagnetic techniques. Transcranial magnetic stimulation (TMS), electrical stimulation (ES), and transcranial direct coupled stimulation (tDCS) could be used to decrease neuronal excitability in different ways. In theory, any technique that can reduce cortical excitability could suppress SD initiating or propagating

An experimental study of endwall heat transfer enhancement for flow past staggered non-conducting pin fin arrays

In this work, we study the enhanced endwall heat transfer for flow past non conducting pin fin arrays. The aim is to resolve the controversy over the heat transfer that is taking place from the endwall and the pin surface.Various parameters were studied and results were obtained. Our results are found to be consistent with some of the results that have been previously published. The results were surprisingly found to be dependent on the height of the pin fin

Multidimensional Capacitive Sensing for Robot-Assisted Dressing and Bathing

Robotic assistance presents an opportunity to benefit the lives of many people with physical disabilities, yet accurately sensing the human body and tracking human motion remain difficult for robots. We present a multidimensional capacitive sensing technique that estimates the local pose of a human limb in real time. A key benefit of this sensing method is that it can sense the limb through opaque materials, including fabrics and wet cloth. Our method uses a multielectrode capacitive sensor mounted to a robot's end effector. A neural network model estimates the position of the closest point on a person's limb and the orientation of the limb's central axis relative to the sensor's frame of reference. These pose estimates enable the robot to move its end effector with respect to the limb using feedback control. We demonstrate that a PR2 robot can use this approach with a custom six electrode capacitive sensor to assist with two activities of daily living-dressing and bathing. The robot pulled the sleeve of a hospital gown onto able-bodied participants' right arms, while tracking human motion. When assisting with bathing, the robot moved a soft wet washcloth to follow the contours of able-bodied participants' limbs, cleaning their surfaces. Overall, we found that multidimensional capacitive sensing presents a promising approach for robots to sense and track the human body during assistive tasks that require physical human-robot interaction.Comment: 8 pages, 16 figures, International Conference on Rehabilitation Robotics 201

Macrophage Activation Syndrome as a Complication of Systemic Lupus Erythematosus in an Adult Male

Macrophage activation syndrome (MAS) is a rare life-threatening complication that sometimes occurs in patients with systemic lupus erythematosus (SLE) and other connective tissue diseases. This syndrome is universally fatal without treatment, and therefore, prompt diagnosis and initiation of treatment is of vital importance

An evolutionary algorithmic approach to determine the Nash equilibrium in a duopoly with nonlinearities and constraints

This paper presents an algorithmic approach to obtain the Nash Equilibrium in a duopoly. Analytical solutions to duopolistic competition draw on principles of game theory and require simplifying assumptions such as symmetrical payoff functions, linear demand and linear cost. Such assumptions can reduce the practical use of duopolistic models. In contrast, we use an evolutionary algorithmic approach (EAA) to determine the Nash equilibrium values. This approach has the advantage that it can deal with and find optimum values for duopolistic competition modelled using non-linear functions. In the paper we gradually build up the competitive situation by considering non-linear demand functions, non-linear cost functions, production and environmental constraints, and production in discrete bands. We employ particle swarm optimization with composite particles (PSOCP), a variant of particle swarm optimization, as the evolutionary algorithm. Through the paper we explicitly demonstrate how EAA can solve games with constrained payoff functions that cannot be dealt with by traditional analytical methods. We solve several benchmark problems from the literature and compare the results obtained from EAA with those obtained analytically, demonstrating the resilience and rigor of our EAA solution approach