Hot-Tail Runaway Seed Landscape during the Thermal Quench in Tokamaks.

Runaway electron populations seeded from the hot tail generated by the rapid cooling in plasma-terminating disruptions are a serious concern for next-step tokamak devices such as ITER. Here, we present a comprehensive treatment of the thermal quench, including the superthermal electron dynamics, heat and particle transport, atomic physics, and radial losses due to magnetic perturbations: processes that are strongly linked and essential for the evaluation of the runaway seed in disruptions mitigated by material injection. We identify limits on the injected impurity density and magnetic perturbation level for which the runaway seed current is acceptable without excessive thermal energy being lost to the wall via particle impact. The consistent modeling of generation and losses shows that runaway beams tend to form near the edge of the plasma, where they could be deconfined via external perturbations.

TiO2/Cu2O/CuO Multi-Nanolayers as Sensors for H2 and Volatile Organic Compounds: An Experimental and Theoretical Investigation.

TiO2/Cu2O/CuO multi-nanolayers highly sensitive toward volatile organic compounds (VOCs) and H2 have been grown in various thicknesses by a cost-effective and reproducible combined spray-sputtering-annealing approach. The ultrathin TiO2 films were deposited by spray pyrolysis on top of sputtered-annealed Cu2O/CuO nanolayers to enhance their gas sensing performance and improve their protection against corrosion at high operating temperatures. The prepared heterostructures were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultraviolet visible (UV-vis) and micro-Raman spectroscopy. The gas sensing properties were measured at several operating temperatures, where the nanolayered sensors with oxide thicknesses between 20 and 30 nm (Cu2O/CuO nanolayers) exhibited a high response and an excellent selectivity to ethanol vapor after thermal annealing the samples at 420 °C. The results obtained at an operating temperature of 350 °C demonstrate that the CuO/Cu2O nanolayers with thicknesses between 20 and 30 nm are sensitive mainly to ethanol vapor, with a response of ∼150. The response changes from ethanol vapors to hydrogen gas as the thickness of the CuO/Cu2O nanolayers changes from 50 to 20 nm. Density functional theory-based calculations were carried out for the geometries of the CuO(1̅11)/Cu2O(111) and TiO2(111)/CuO(1̅11)/Cu2O(111) heterostructures and their sensing mechanism toward alcohols of different chain lengths and molecular hydrogen. The reconstructed hexagonal Cu2O(111) surface and the reconstructed monoclinic CuO(1̅11) and TiO2(111) facets, all of which terminate in an O layer, lead to the lowest surface energies for each isolated material. We studied the formation of the binary and ternary heteroepitaxial interfaces for the surface planes with the best-matching lattices. Despite the impact of the Cu2O(111) substrate in lowering the atomic charges of the CuO(1̅11) adlayer in the binary sensor, we found that it is the different surface structures of the CuO(1̅11)/Cu2O(111) and TiO2(111)/CuO(1̅11)/Cu2O(111) devices that are fundamental in driving the change in the sensitivity response observed experimentally. The experimental data, supported by the computational results, are important in understanding the use of the multi-nanolayered films tested in this work as reliable, accurate, and selective sensor structures for the tracking of gases at low concentrations.

Tuning ZnO Sensors Reactivity toward Volatile Organic Compounds via Ag Doping and Nanoparticle Functionalization.

Nanomaterials for highly selective and sensitive sensors toward specific gas molecules of volatile organic compounds (VOCs) are most important in developing new-generation of detector devices, for example, for biomarkers of diseases as well as for continuous air quality monitoring. Here, we present an innovative preparation approach for engineering sensors, which allow for full control of the dopant concentrations and the nanoparticles functionalization of columnar material surfaces. The main outcome of this powerful design concept lies in fine-tuning the reactivity of the sensor surfaces toward the VOCs of interest. First, nanocolumnar and well-distributed Ag-doped zinc oxide (ZnO:Ag) thin films are synthesized from chemical solution, and, at a second stage, noble nanoparticles of the required size are deposited using a gas aggregation source, ensuring that no percolating paths are formed between them. Typical samples that were investigated are Ag-doped and Ag nanoparticle-functionalized ZnO:Ag nanocolumnar films. The highest responses to VOCs, in particular to (CH3)2CHOH, were obtained at a low operating temperature (250 °C) for the samples synergistically enhanced with dopants and nanoparticles simultaneously. In addition, the response times, particularly the recovery times, are greatly reduced for the fully modified nanocolumnar thin films for a wide range of operating temperatures. The adsorption of propanol, acetone, methane, and hydrogen at various surface sites of the Ag-doped Ag8/ZnO(0001) surface has been examined with the density functional theory (DFT) calculations to understand the preference for organic compounds and to confirm experimental results. The response of the synergistically enhanced sensors to gas molecules containing certain functional groups is in excellent agreement with density functional theory calculations performed in this work too. This new fabrication strategy can underpin the next generation of advanced materials for gas sensing applications and prevent VOC levels that are hazardous to human health and can cause environmental damages.

PdO/PdO2 functionalized ZnO : Pd films for lower operating temperature H2 gas sensing.

Noble metals and their oxide nano-clusters are considered to be the most promising candidates for fabricating advanced H2 gas sensors. Through this work, we propose a novel strategy to grow and modulate the density of PdO/PdO2 nanoparticles uniformly on nanostructured Pd-doped ZnO (ZnO : Pd) films by a one-step solution approach followed by thermal annealing at 650 °C, and thus to detect ppm-level H2 gas in a selective manner. The gas sensing properties of such hybridized materials showed that the PdO-functionalized ZnO samples offer significantly improved H2 gas sensing properties in an operating temperature range of 25-200 °C. The deposition of ZnO : Pd films via a simple synthesis from chemical solutions (SCS) approach with an aqueous bath (at relatively low temperatures, <95 °C) is reported. Furthermore, the functionalization of palladium oxide nanoclusters by a simple but highly effective approach on ZnO : Pd film surfaces was performed and is reported here for the first time. The morphological, structural, vibrational, optical, chemical, and electronic properties were studied in detail and the mixed phases of palladium oxide nanoclusters on the ZnO surface were found. Sensor studies of the ZnO : Pd samples (in the range of 25-350 °C operating temperature) showed good selectivity to H2 gas, especially in the range of higher temperatures (>150 °C, up to 350 °C); however, the PdO/PdO2 mixed phases of the nanocluster-modified surface ZnO : Pd films showed a much better selectivity to H2 gas, even at a lower operating temperature, in the range of 25-150 °C. For such PdO-functionalized ZnO : Pd films, even at room temperature, a gas response of ∼12.7 to 1000 ppm of H2 gas was obtained, without response to any other reducing gases or tested vapors. The large recovery time of the samples at room temperatures (>500 s) can be drastically reduced by applying higher bias voltages. Furthermore, we propose and discuss the gas sensing mechanism for these structures in detail. Our study demonstrates that surface functionalization with PdO/PdO2 mixed phase nanoclusters-nanoparticles (NPs) is much more effective than only the Pd doping of nanostructured ZnO films for selective sensing applications. This approach will pave a new way for the controlled functionalization of PdO/PdO2 nanoclusters on ZnO : Pd surfaces to the exact detection of highly explosive H2 gas under various atmospheres by using solid state gas sensors.

Complex shaped ZnO nano- and microstructure based polymer composites: mechanically stable and environmentally friendly coatings for potential antifouling applications.

Since the prohibition of tributyltin (TBT)-based antifouling paints in 2008, the development of environmentally compatible and commercially realizable alternatives is a crucial issue. Cost effective fabrication of antifouling paints with desired physical and biocompatible features is simultaneously required and recent developments in the direction of inorganic nanomaterials could play a major role. In the present work, a solvent free polymer/particle-composite coating based on two component polythiourethane (PTU) and tetrapodal shaped ZnO (t-ZnO) nano- and microstructures has been synthesized and studied with respect to mechanical, chemical and biocompatibility properties. Furthermore, antifouling tests have been carried out in artificial seawater tanks. Four different PTU/t-ZnO composites with various t-ZnO filling fractions (0 wt%, 1 wt%, 5 wt%, 10 wt%) were prepared and the corresponding tensile, hardness, and pull-off test results revealed that the composite filled with 5 wt% t-ZnO exhibits the strongest mechanical properties. Surface free energy (SFE) studies using contact angle measurements showed that the SFE value decreases with an increase in t-ZnO filler amounts. The influence of t-ZnO on the polymerization reaction was confirmed by Fourier transform infrared-spectroscopy measurements and thermogravimetric analysis. The immersion tests demonstrated that fouling behavior of the PTU/t-ZnO composite with a 1 wt% t-ZnO filler has been decreased in comparison to pure PTU. The composite with a 5 wt% t-ZnO filler showed almost no biofouling.

Long-term outcome after temporal lobe epilepsy surgery in 434 consecutive adult patients.

OBJECT: The aim of this study was to evaluate the long-term efficacy of temporal lobe epilepsy (TLE) surgery and potential risk factors for seizure recurrence after surgery. METHODS: This retrospective study included 434 consecutive adult patients who underwent TLE surgery at Bethel Epilepsy Centre between 1991 and 2002. RESULTS: Hippocampal sclerosis was found in 62% of patients, gliosis in 17.3%, tumors in 20%, and focal cortical dysplasia (FCD) in 6.9%. Based on a Kaplan-Meier analysis, the probability of Engel Class I outcome for the patients overall was 76.2% (95% CI 71-81%) at 6 months, 72.3% (95% CI 68-76%) at 2 years, 71.1% (95% CI 67-75%) at 5 years, 70.8% (95% CI 65-75%) at 10 years, and 69.4% (95% CI 64-74%) at 16 years postoperatively. The likelihood of remaining seizure free after 2 years of freedom from seizures was 90% (95% CI 82-98%) for 16 years. Seizure relapse occurred in all subgroups. Patients with FCD had the highest risk of recurrence (hazard ratio 2.15, 95% CI 0.849-5.545). Predictors of remission were the presence of hippocampal atrophy on preoperative MR imaging and a family history of epilepsy. Predictors of relapse were the presence of bilateral interictal sharp waves and versive seizures. Six-month follow-up electroencephalography predicted relapse in patients with FCD. Short epilepsy duration was predictive of seizure remission in patients with tumors and gliosis; 28.1% of patients were able to discontinue antiepileptic medications without an increased risk of seizure recurrence (hazard ratio 1.05, 95% CI 0.933-1.20). CONCLUSIONS: These findings highlight the role of etiology in prediction of long-term outcome after TLE surgery.

Outcome of extratemporal epilepsy surgery experience of a single center.

OBJECTIVE: Our aim was to determine the surgical outcome in adult patients with intractable extratemporal epilepsy and follow it over time. METHODS: We retrospectively studied the operative outcome in 218 consecutive adult patients with extratemporal lesions who underwent resective surgical treatment for intractable partial epilepsy in the Bethel Epilepsy Center, Bielefeld, Germany, between 1991 and 2005. Patients were divided into three groups according to the 5-year period in which the surgical procedure took place. RESULTS: Group I (1991-1995) consisted of 64 patients. The postoperative Engel Class I outcome was 50% at 6 months, 44.4% at 2 years, and 45.2% at 5 years. Group II (1996-2000) included 91 patients. Engel Class I outcome was 57.1% at 6 months, 53.8% at 2 years, and 53.5% at 5 years. In Group III (2001-2005), there were 63 patients. Engel Class I outcome was 65.1% at 6 months, 61.3% at 2 years, and 60.6% at 5 years. Short duration of epilepsy, surgery before 30 years of age, pathological findings of neoplasm, and well-circumscribed lesions on the preoperative magnetic resonance imaging scan were good prognostic factors. Poor prognostic factors were one or more of the following: psychic aura, generalized tonic-clonic seizure, versive seizure, history of previous surgery, and focal cortical dysplasia. On multivariate analysis, only the presence of well-circumscribed lesions on preoperative magnetic resonance imaging predicted a positive outcome (P = 0.001). CONCLUSION: Our results indicate that extratemporal epilepsy surgery at the Bethel Epilepsy Center has become more effective in the treatment of extratemporal epilepsy patients over the years, ensuring continuous improvement in outcome. This improvement can be attributed mainly to more restrictive patient selection.

Outcome of frontal lobe epilepsy surgery in adults.

Our aim is to investigate seizure outcome and prognostic factors after pure frontal lobe epilepsy (FLE) surgery. We retrospectively studied the operative outcome in 97 consecutive adult patients who underwent resective surgery for intractable partial epilepsy between 1991 and 2005. Based on Kaplan-Meier, the probability of an Engel Class I outcome was found to be 54.6% (95% CI 44-64) at 6 months, 49.5% (95% CI 39.3-59.6) at 2 years, 47% (CI 34-59) at 5 years and 41.9% (CI 23.5-60.3) at 10 years. If the patient was seizure free at 2-year follow-up, the probability of remaining seizure free up to 10 years was 86% (95% CI 76-98). For 13.6% of the patients a running down of seizures could be shown. Factors predictive of poor long-term outcome were incomplete resection, using of subdural grids, IED in follow-up EEG, tonic seizures and an unspecific aura or a postoperative aura. Factors predictive of good long-term outcome were the presence of a well-circumscribed lesion in preoperative MRI, ipsilateral IED in preoperative EEG, surgery before age of 30 and short epilepsy duration prior to surgery. In the multivariate analysis, preoperative well-circumscribed lesion in MRI predicts seizure remission whereas persistent postoperative auras predict seizure relapse. FLE surgery should depend on restrictive patient selection to assure favorable outcome.

Long-term outcome of extratemporal epilepsy surgery among 154 adult patients.

OBJECT: The goal of this study was to evaluate the long-term outcome of patients who underwent extratemporal epilepsy surgery and to assess preoperative prognostic factors associated with seizure outcome. METHODS: This retrospective study included 154 consecutive adult patients who underwent epilepsy surgery at Bethel Epilepsy Centre, Bielefeld, Germany between 1991 and 2001. Seizure outcome was categorized based on the modified Engel classification. Survival statistics were calculated using Kaplan-Meier curves, life tables, and Cox regression models to evaluate the risk factors associated with outcomes. RESULTS: Sixty-one patients (39.6%) underwent frontal resections, 68 (44.1%) had posterior cortex resections, 15 (9.7%) multilobar resections, 6 (3.9%) parietal resections, and 4 (2.6%) occipital resections. The probability of an Engel Class I outcome for the overall patient group was 55.8% (95% confidence interval [CI] 52-58% at 0.5 years), 54.5% (95% CI 50-58%) at 1 year, and 51.1% (95% CI 48-54%) at 14 years. If a patient was in Class I at 2 years postoperatively, the probability of remaining in Class I for 14 years postoperatively was 88% (95% CI 78-98%). Factors predictive of poor long-term outcome after surgery were previous surgery (p = 0.04), tonic-clonic seizures (p = 0.02), and the presence of an auditory aura (p = 0.03). Factors predictive of good long-term outcome were surgery within 5 years after onset (p = 0.015) and preoperative invasive monitoring (p = 0.002). CONCLUSIONS: Extratemporal epilepsy surgery is effective according to findings on long-term follow-up. The outcome at the first 2-year follow-up visit is a reliable predictor of long-term Engel Class I postoperative outcome.