Modeling Micro-Porous Surfaces for Secondary Electron Emission Control to Suppress Multipactor

This work seeks to understand how the topography of a surface can be engineered to control secondary electron emission (SEE) for multipactor suppression. Two unique, semi-empirical models for the secondary electron yield (SEY) of a micro-porous surface are derived and compared. The first model is based on a two-dimensional (2D) pore geometry. The second model is based on a three-dimensional (3D) pore geometry. The SEY of both models is shown to depend on two categories of surface parameters: chemistry and topography. An important parameter in these models is the probability of electron emissions to escape the surface pores. This probability is shown by both models to depend exclusively on the aspect ratio of the pore (the ratio of the pore height to the pore diameter). The increased accuracy of the 3D model (compared to the 2D model) results in lower electron escape probabilities with the greatest reductions occurring for aspect ratios less than two. In order to validate these models, a variety of micro-porous gold surfaces were designed and fabricated using photolithography and electroplating processes. The use of an additive metal-deposition process (instead of the more commonly used subtractive metal-etch process) provided geometrically ideal pores which were necessary to accurately assess the 2D and 3D models. Comparison of the experimentally measured SEY data with model predictions from both the 2D and 3D models illustrates the improved accuracy of the 3D model. For a micro-porous gold surface consisting of pores with aspect ratios of two and a 50% pore density, the 3D model predicts that the maximum total SEY will be one. This provides optimal engineered surface design objectives to pursue for multipactor suppression using gold surfaces

Nanopillar Arrays on Semiconductor Membranes as Electron Emission Amplifiers

A new transmission-type electron multiplier was fabricated from silicon-on-insulator (SOI) material by integrating an array of one dimensional (1D) silicon nanopillars onto a two dimensional (2D) silicon membrane. Primary electrons are injected into the nanopillar-membrane system from the flat surface of the membrane, while electron emission from the other side is probed by an anode. The secondary electron yield (SEY) from nanopillars is found to be about 1.8 times that of plane silicon membrane. This gain in electron number is slightly enhanced by the electric field applied from the anode. Further optimization of the dimensions of nanopillars and membrane and application of field emission promise an even higher gain for detector applications and allow for probing of electronic/mechanical excitations in nanopillar-membrane system excited by incident particles or radiation.Comment: 4 figure

Data reconciliation of immersive heart inspection

IVUS images are complicated medical datasets suffering from some artifacts caused by the data acquisition method of immersive heart inspection. Data reconciliation, which removes tracing and tracking uncertainties of these datasets, is an important step for the medical application of remodeling the arteries in virtual reality to aid diagnosing and treating heart diseases. This paper provides an empirical data reconciliation method, which fuses the features of the coronary longitudinal movement with motion compensation model. It explains the distortion of the data set well and provides a method to analyze and reconcile the dataset

Exocrine and endocrine pancreatic function in patients with pancreatico-jejunostomy or pancreatic duct occlusion after pancreaticoduodenectomy

Pancreatic duct occlusion (PDO) is performed in some centres to avoid complications of pancreaticojejunostomy (PJ) after pancreaticodudodenectomy. The aim of our study was to study the exo- and endocrine pancreatic function, nutritional status and quality of life in patients with a PJ or PDO after a pancreatico-duodenectomy (PD)

Secondary electron emissions and dust charging currents in the nonequilibrium dusty plasma with power-law distributions

We study the secondary electron emissions induced by the impact of electrons on dust grains and the resulting dust charging processes in the nonequilibrium dusty plasma with power-law distributions. We derive new expressions of the secondary emitted electron flux and the dust charging currents that are generalized by the power-law q-distributions, where the nonlinear core functions are numerically studied for the nonextensive parameter q. Our numerical analyses show that the power-law q-distribution of the primary electrons has a significant effect on the secondary emitted electron flux as well as the dust charging currents, and this effect depends strongly on the ratio of the electrostatic potential energy of the primary electrons at the dust grain's surface to the thermodynamic energy, implying that a competition in the dusty plasma between these two energies plays a crucial role in this novel effect.Comment: 16 pages, 6 figures, 32 reference

Potential for CO2 sequestration and enhanced coalbed methane production in the Netherlands

This study investigated the technical and economic feasibility of using CO2 for the enhanced production of coal bed methane (ECBM) in the Netherlands. This concept could lead to both CO2 storage by adsorbing CO2 in deep coal layers that are not suitable for mining, as well as production of methane. For every two molecules of CO2 injected, roughly one molecule of methane is produced. The work included an investigation of the potential CBM reserves in the Dutch underground and the related CO2 storage potential in deep coal layers. The latter was also supported by laboratory experiments on the adsorption capacity of coal. Furthermore, an economic evaluation of ECBM recovery was made by analysing the costs of capturing CO2 from major stationary sources and CO2 transport, modelling the production of ECBM using CO2 injection with reservoir simulations and system analyses to investigate the costs (and it's sensitivities) of gas production. Furthermore, the costs of on-site hydrogen and power production (including on site CO2 removal and injection) were evaluated. CO2 sources in the Netherlands have been inventoried. Annually 3.4 Mtonne CO2 can be captured from chemical installations and transported to sequestration locations at 15 /tonne. Another 55 Mtonne from power generating facilities can be delivered at 40 to 80 /tonne. The technical potential of CBM in the Dutch underground is significant: a maximum reserve of about 60 EJ is stored in coal layers up to a depth of 2000 m. This figure should be compared to the current annual energy consumption of the Netherlands (about 3 EJ) or the known reserves of natural gas in the Netherlands (about 70 EJ in 1994). These reserves are concentrated in four main areas in the Netherlands: Zuid Limburg, the Peel area, the Achterhoek area and Zeeland. The CO2 storage potential could be about 8 Gtonne. This storage potential should be compared to the annual CO2 emissions of the Netherlands: about 180 Mtonne. This means, theoretically, that the total CO2 emissions of the Netherlands could be stored in coal layers for over 40 years and that CBM could meet the total national energy demand of the Netherlands for 20 years. However, it is still uncertain to what extent these reserves can be accessed. With conservative assumptions regarding the potential completion and recovery rate of CBM from coal layers by means of drilling and CO2 injection, as well as by limiting the ECBM recovery to a depth range of 500 -- 1500 metres, the 'proven' reserves could be limited to 0.3 EJ and the 'possible' reserves up to about 3.9 EJ. The accompanying CO2 that can be sequestrated than lays between 54 Mtonne and 0.6 Gtonne. Although those figures are far more modest than the 'theoretical' potential, they are still significant. In case the 'possible' reserves can be accessed, ECBM could supply 5% of the current national energy use on a more than carbon neutral basis for over 25 years. Given the Kyoto targets for 2010, or the national targets for renewable energy, this is a very significant amount. Without any subsidies or carbon taxes, the cost levels for ECBM recovery ranges from 3.5 to 6.5 /GJ methane produced. These costs levels come close to the projected natural gas prices in Europe in a timeframe of 10 to 20 years, which are projected to be between 2.5 and 3.2 /GJ. Inclusion of a carbon tax (or bonus) of 25 /tonne CO2 sequestrated, lowers the price of ECBM to a competitive 1.5 to 4 ?/GJ. The cost level of CO2 sequestration through ECBM is comparable with projected cost levels for CO2 storage in aquifer traps(Steinberg and Cheng 1989) in case the CBM would be sold for current natural gas prices. If the produced CBM is used for electricity or hydrogen production on top of the CBM field, the resulting CO2 can be injected in the coal directly (thereby eliminating CO2 transport costs). CO2 removal from a gas engine or a combined cycle is currently more expensive when compared to CO2 from industrial processes that must be transported to the CBM field. But a (SOFC) fuel cell produces a pure and therefore much cheaper CO2 stream. Although SOFC fuel cells are not fully commercially available and have high capital costs, they could lead to somewhat lower costs of electricity. Without CO2 bonus, on site power generation is more expensive than grid prices for the systems considered. But when a CO2 bonus of 25 /tonne CO2 is assumed, power generation costs are reduced below 3 cent/kWh, which is lower than the current average 3.2 cent/kWh. On the longer term, when SOFC fuel cells could become cheaper, on site power generation could become a (very) attractive alternative. On site (smaller scale) hydrogen production gives similar results. Capital costs for smaller scale on site hydrogen production are relatively high, but with a CO2 bonus of 25 /tonne, hydrogen costs could be lower than current production costs from coal and comparable to production costs from natural gas. Overall, the results of the economic evaluation indicate that CBM by means of enhanced recovery by CO2 injection in deep coal layers can be performed at competitive cost levels when the right system configurations are chosen. A, relatively modest, carbon tax (or 'bonus') of 25 /tonne could easily tick the balance in favour of ECBM recovery in Dutch conditions on short term already. However, a number of important (geo) technical and geological factors play a key role in whether these cost levels can be obtained or not. The dominating factors in the costs are the drilling costs. In case the costs per wellhead appear to be higher than assumed here, the economic performance of the system deteriorates. On the other hand innovations in drilling techniques, gaining more experience with the required drilling methods over time and obtaining 'economies of scale' by drilling relatively large numbers of wells in a short time to exploit larger CBM fields may bring drilling costs (and thus CBM production costs) down considerably. Regarding to the geology, the CBM potential and the actual accessibility of the, theoretical, coal reserves and the predicted presence of producable CBM gas in the coal layers is subject to broad ranges. More detailed surveys of the Dutch underground are needed to reduce uncertainties about CBM gas reserves. This can be obtained by seismic research and obtaining more and better samples of the Dutch underground. Such research is absolutely essential before ECBM is developed in the Netherlands on a significant scale. In conclusion, this study showed that ECBM is likely to become an economically feasible option for the Netherlands on relatively short term. It could at least play a significant (and potentially very large) role in reducing greenhouse gas emission levels for a time period of about 50 years. Although the estimates of energy reserves in the form of CBM are uncertain, they are potentially very significant (varying from 6 -- 60 EJ). The potential CO2 storage capacity is (very) large as well (1-8 Gtonne of CO2). Given the fact that CO2 binds well to the coal matrix, that deep coal layers are unlikely to be accessed for mining or other activities in the future and that CO2 storage with ECBM delivers a clean fossil fuel as a by-product, coal layers may be a preferable CO2 storage medium when compared to (saline) aquifers, empty gas fields or in deep oceans. Therefore, this option deserves further development and study. A mix of more detailed geological surveys combined with getting good quality samples, laboratory experiments, system studies on implementation scenarios and a pilot project (with a special focus on drilling techniques) is recommended

Islet cell cytoplasmic antibody reactivity in midgestational human fetal pancreas

The reactivity of islet cell cytoplasmic antibodies (ICA)-positive and ICA-negative sera of recent onset type 1 diabetic patients was studied in human fetal pancreata of 12-18 weeks' gestation and compared with the reactivity of these sera in adult human control pancreata. The aims of the study were: (1) to observe the presence of ICA staining in human fetal islet cells; (2) to compare endpoint titres (in Juvenile Diabetes Foundation units) of ICA-positive patient sera in fetal pancreata and adult human control pancreata. Ten ICA-positive sera and eight ICA-negative sera from newly diagnosed diabetic patients and four sera from healthy controls were tested on three human adult and eight human fetal pancreata. As in the adult control pancreata. ICA-positive sera reacted to insulin-, glucagon-, and somatostatin-positive cells of fetal pancreata of all gestational ages. This was observed both in single cells and in cells in islet-like cell clusters. Dilution of a reference serum gave similar results in both adult and fetal pancreata. In contrast, the ICA-positive patient sera yielded a striking heterogeneity in fetal as well as in adult pancreata. However, end-point titres between adult and fetal pancreata did not differ significantly (P>0.05). In conclusion, ICA-positive sera from recent onset diabetic patients show that the expression of molecules to which ICA react is present in all islet cells and starts before week 12 of gestation

Antibodies to the Mr 64,000 (64K) protein in islet cell antibody positive non-diabetic individuals indicate high risk for impaired Beta-cell function

A prospective study of a normal childhood population identified 44 islet cell antibody positive individuals. These subjects were typed for HLA DR and DQ alleles and investigated for the presence of antibodies to the Mr 64,000 (64K) islet cell antigen, complement-fixing islet cell antibodies and radiobinding insulin autoantibodies to determine their potency in detecting subjects with impaired Beta-cell function. At initial testing 64K antibodies were found in six of 44 islet cell antibody positive subjects (13.6%). The same sera were also positive for complement-fixing islet cell antibodies and five of them had insulin autoantibodies. During the follow-up at 18 months, islet cell antibodies remained detectable in 50% of the subjects studied. In all six cases who were originally positive, 64K antibodies were persistently detectable, whereas complement-fixing islet cell antibodies became negative in two of six and insulin autoantibodies in one of five individuals. HLA DR4 (p < 0.005) and absence of asparic acid (Asp) at position 57 of the HLA DQ chain (p < 0.05) were significantly increased in subjects with 64K antibodies compared with control subjects. Of 40 individuals tested in the intravenous glucose tolerance test, three had a first phase insulin response below the first percentile of normal control subjects. Two children developed Type 1 (insulin-dependent) diabetes mellitus after 18 and 26 months, respectively. Each of these subjects was non-Asp homozygous and had persistent islet cell and 64K antibodies. We conclude that 64K antibodies, complement-fixing islet cell antibodies and insulin autoantibodies represent sensitive serological markers in assessing high risk for a progression to Type 1 diabetes in islet cell antibody positive non-diabetic individuals

The miswired brain: making connections from neurodevelopment to psychopathology

Developmental neurobiologists have made great progress in elucidating the molecular mechanisms underlying nervous system development. There has been less focus, however, on the consequences when these processes go wrong. As the evidence increases that mutations in neurodevelopmental genes are associated with major psychiatric disorders, defining these consequences assumes paramount importance in elucidating pathogenic mechanisms