Oxygen reduction on platinum : an EIS study

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Vita.Includes bibliographical references (p. 197-200).The oxygen reduction reaction (ORR) on platinum over yttria-stabilized zirconia (YSZ) is examined via electrochemical impedance spectroscopy (EIS) for oxygen partial pressures between 10-4 and 1 atm and at temperatures between 475 and 700°C. Use of photolithographic techniques in electrode fabrication renders a precise geometry of the Pt electrodes. Circular electrode design leads to cylindrical symmetry so that models may be applied exactly to the experimental geometry. Interpretation of EIS spectra is carried out by reducing and then extending existing models, and is consistent with the postulate that ORR is rate-limited jointly by two surface chemical processes, namely, sorption/dissociation of molecular O₂ into O[delta]- a over Pt, as well as surface diffusion. Further, the novel experimental design, in conjunction with streamlined analysis techniques, provides accurate surface characterization within the electrochemical environment and allows for a more transparent comparison to relevant literature data. An adsorption coverage isotherm is extracted, and the surface diffusion coefficient is obtained for a number of experimental conditions. Extracted diffusivities fell between 2 x 10-2 and 2 x 10-7 cm2/s, in agreement with literature values for the indicated temperature range.by Theodore Golfinopoulos.S.M

Treatment of adults with attention-deficit/hyperactivity disorder

This review focuses on the treatment of attention deficit hyperactivity disorder (ADHD) in adults. It briefly addresses prevalence, diagnostic and differential diagnostic issues specific to adults. Stimulant medication, non-stimulant medication, and psychosocial treatments are thoroughly reviewed. For each class of medication possible mechanism of action, efficacy and side effects are summarized. Special attention is given to the pharmacological treatment for patients with adult ADHD and various comorbidities. In summary, stimulant medications are most effective and combined medication and psychosocial treatment is the most beneficial treatment option for most adult patients with ADHD

Application of Headspace Solid-Phase Microextraction for Determination of Chloro-Organic Compounds in Sewage Samples

Solid phase microextraction (SPME) has been optimized and applied to the determination of the volatile halogenated compounds (VHCs) and semi-volatile halogenated compounds (SVHCs). Three types of SPME fiber coated with different stationary phases (PDMS–100 μm, CAR/PDMS-75 μm, PDMS/DVB–65 μm) were used to examine their extraction efficiencies for the compounds tested. Experimental parameters such as the selection of SPME coatings, extraction time, and addition of salts were studied. The carboxen-polydimethylsiloxane (CAR/PDMS) fiber appears to be the most suitable for the determination of VHCs. Analytical parameters such as linearity, limit of detection, and precision were also evaluated. Application of ECD detector for the determination of VHCs and SVHCs allows their determination on the low concentration level, ranging from 0.005 to 0.8 μg/L−1. The HS-SPME-GC/ECD procedure gave good analytical precision expressed as relative standard deviation (RSD) (ranged from 5.08% to 8.07%) for a concentration level of 5 μg/L−1 and good linearity (r2 > 0.98) in a wide calibration range. The applied HS-SPME-GC/ECD method was found to be a quick and effective technique for the determination of microtrace amounts of volatile and semi-volatile halogenated compounds in samples containing high amounts of various organic compounds

Altered resting-state network connectivity in stroke patients with and without apraxia of speech

Motor speech disorders, including apraxia of speech (AOS), account for over 50% of the communication disorders following stroke. Given its prevalence and impact, and the need to understand its neural mechanisms, we used resting state functional MRI to examine functional connectivity within a network of regions previously hypothesized as being associated with AOS (bilateral anterior insula (aINS), inferior frontal gyrus (IFG), and ventral premotor cortex (PM)) in a group of 32 left hemisphere stroke patients and 18 healthy, age-matched controls. Two expert clinicians rated severity of AOS, dysarthria and nonverbal oral apraxia of the patients. Fifteen individuals were categorized as AOS and 17 were AOS-absent. Comparison of connectivity in patients with and without AOS demonstrated that AOS patients had reduced connectivity between bilateral PM, and this reduction correlated with the severity of AOS impairment. In addition, AOS patients had negative connectivity between the left PM and right aINS and this effect decreased with increasing severity of non-verbal oral apraxia. These results highlight left PM involvement in AOS, begin to differentiate its neural mechanisms from those of other motor impairments following stroke, and help inform us of the neural mechanisms driving differences in speech motor planning and programming impairment following stroke

Temporal muscle thickness is an independent prognostic marker in patients with progressive glioblastoma: translational imaging analysis of the EORTC 26101 trial

BACKGROUND: Temporal muscle thickness (TMT) was described as surrogate marker of skeletal muscle mass. This study aimed to evaluate the prognostic relevance of TMT in patients with progressive glioblastoma. METHODS: TMT was analyzed on cranial magnetic resonance images of 596 patients with progression of glioblastoma after radio-chemotherapy enrolled in the EORTC 26101 trial. An optimal TMT cutoff for overall survival (OS) and progression free survival (PFS) was defined in the training cohort (n=260, phase 2). Patients were grouped as "below" or "above" the TMT cutoff and associations with OS and PFS were tested using the Cox model adjusted for important risk factors. Findings were validated in a test cohort (n=308, phase 3). RESULTS: An optimal baseline TMT cutoff of 7.2 mm was obtained in the training cohort for both OS and PFS (AUC=0.64). Univariate analyses estimated a hazard ratio (HR) of 0.54 (95% CI: 0.42, 0.70, p<0.0001) for OS and a HR of 0.49 (95% CI: 0.38, 0.64, p<0.0001) for PFS for the comparison of training cohort patients above versus below the TMT cutoff. Similar results were obtained in Cox models adjusted for important risk factors with relevance in the trial for OS (HR of 0.54, 95% CI: 0.41, 0.70, p<0.0001) and PFS (HR of 0.47, 95% CI: 0.36, 0.61, p<0.0001). Results were confirmed in the validation cohort. CONCLUSION: Reduced TMT is an independent negative prognostic parameter in patients with progressive glioblastoma and may help to facilitate patient management by supporting patient stratification for therapeutic interventions or clinical trials

The digital mirror Langmuir probe: Field programmable gate array implementation of real-time Langmuir probe biasing

High bandwidth, high spatial resolution measurements of electron temperature, density, and plasma potential are valuable for resolving turbulence in the boundary plasma of tokamaks. While conventional Langmuir probes can provide such measurements, either their temporal or spatial resolution is limited: the former by the sweep rate necessary for obtaining I-V characteristics and the latter by the need to use multiple electrodes, as is the case in triple and double probe configurations. The Mirror Langmuir Probe (MLP) bias technique overcomes these limitations by rapidly switching the voltage on a single electrode cycling between three bias states, each dynamically optimized for the local plasma conditions. The MLP system on Alcator C-Mod used analog circuitry to perform this function, measuring Te, VF, and Isat at 1.1 MSPS. Recently, a new prototype digital MLP controller has been implemented on a Red Pitaya Field Programmable Gate Array (FPGA) board which reproduces the functionality of the original controller and performs all data acquisition. There is also the potential to provide the plasma parameters externally for use with feedback control systems. The use of FPGA technology means the system is readily customizable at a fraction of the development time and implementation cost. A second Red Pitaya was used to test the MLP by simulating the current response of a physical probe using C-Mod experimental measurements. This project is available as a git repository to facilitate extensibility (e.g., real-time control outputs and more voltage states) and scalability through collaboration

X-point and divertor filament dynamics from Gas Puff Imaging on TCV

A new Gas Puff Imaging (GPI) diagnostic has been installed on the TCV tokamak, providing two-dimensional insights into Scrape-Off-Layer (SOL) turbulence dynamics above, at and below the magnetic X-point. A detailed study in L-mode, attached, lower single-null discharges shows that statistical properties have little poloidal variations, while vast differences are present in the 2D behaviour of intermittent filaments. Strongly elongated filaments, just above the X-point and in the divertor far-SOL, show a good consistency in shape and dynamics with field-line tracing from filaments at the outboard midplane, highlighting their connection. In the near-SOL of the outer divertor leg, shortlived, high frequency and more circular (diameter $\sim$15 sound Larmour radii) filaments are observed. These divertor-localised filaments appear born radially at the position of maximum density and display a radially outward motion with velocity $\approx$400\,m/s that is comparable to radial velocities of upstream-connected filaments. Conversely, in these discharges ($B\times\nabla B$ pointing away from the divertor), these divertor filaments' poloidal velocities differ strongly from those of upstream-connected filaments. The importance of divertor-localised filaments upon radial transport and profile broadening is explored using filament statistics and in-situ kinetic profile measurements along the divertor leg. This provides evidence that these filaments contribute significantly to electron density profile broadening in the divertor.Comment: This is the version of the article before peer review or editing, as submitted by an author to IOPScience Nuclear Fusion. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. 15 pages, 15 figure

The physics mechanisms of the weakly coherent mode in the Alcator C-Mod Tokamak

The weakly coherent mode (WCM) in I-mode has been studied by a six-field two-fluid model based on the Braginskii equations under the BOUT++ framework for the first time. The calculations indicate that a tokamak pedestal exhibiting a WCM is linearly unstable to drift Alfven wave (DAW) instabilities and the resistive ballooning mode. The nonlinear simulation shows promising agreement with the experimental measurements of the WCM. The shape of the density spectral and location of the spectral peak of the dominant toroidal number mode n = 20 agrees with the experimental data from reflectometry. The simulated mode propagates in electron diamagnetic direction is consistent with the results from the magnetic probes in the laboratory frame, a large ratio of particle to heat diffusivity is consistent with the distinctive experimental feature of I-mode, and the value of the simulated χeat the edge is in the range of experimental errors of χefffrom the experiment. The prediction of the WCM shows that free energy is mainly provided by the electron pressure gradient, which gives guidance for pursuing future I-mode studies