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

Firm Size Effects on Venture Capital Syndication: The Role of Resources and Transaction Costs

The present paper examines firm size effects on the decision of venture capital firms to participate in a venture capital investment syndication network. The authors submit that firm size effects in venture capital syndication are dependent on resource acquisition motives and transaction cost considerations. Analysis of 317 venture capital firms in 6 European countries reveals a curve linear relationship between firm size and venture capital syndication participation. We also find positive and negative moderating effects of firm size. The implication of our findings is that there are both advantages and disadvantages in syndicated investment for the smaller and larger venture capitalist.Firm Size;Resource-Based View;Syndication Networks;Transaction Cost Theory;Venture Capital

Nonlinear wave interactions in geochemical modeling

This paper is concerned with the study of the main wave interactions in a system of conservation laws in geochemical modeling. We study the modeling of the chemical complexes on the rock surface. The presence of stable surface complexes affects the relative permeability. We add terms representing surface complexes to the accumulation function in the model presented in \cite{lambert2019nonlinear1}. This addition allows to take into account the interaction of ions with the rock surface in the modeling of the oil recovery by the injection of carbonated water. Compatibility hypotheses with the modeling are made on the coefficients of the system to obtain meaningful solutions. We developed a Riemann solver taking into account the complexity of the interactions and bifurcations of nonlinear waves. Such bifurcations occur at the inflection and resonance surfaces. We present the solution of a generalized eigenvalue problem in a (n+1)-dimensional case, which allows the construction of rarefaction curves. A method to find the discontinuous solutions is also presented. We find the solution path for some examples

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

Why Do European Venture Capital Companies Syndicate?

Financial theory, resource-based theory and access to deal flow are used to explain syndication practices among European venture capital (VC) firms. The desire to share risk and increase portfolio diversification is a more important motive for syndication than the desire to access additional intangible resources or deal flow. Access to resources is, however, more important for non-lead than for lead investors. When resource-based motives are more important, the propensity to syndicate increases. Syndication intensity is higher for young VC firms and for VC firms, specialised in a specific investment stage. Finally, syndication strategies are similar across European countries, but differ from North American strategies

Internationalization Of Management Buyouts

Multivariate statistical analysis is utilized to explore the association between firm strategies, contributions made by venture capitalists and incentives for owners and employees and three exporting variables in a stratified random sample of 147 management buyouts and buyins. Firms focusing upon a diversified product/ service range and/or advertising were significantly more likely to be exporters. Firms focusing upon product/ service quality and financial efficiency and those with high proportions of employees receiving performance related pay were significantly less likely to be exporters. Manufacturing firms and firms focusing upon a diversified product/ service range and/or advertising were significantly more likely to report high percentages of sales exported. Variations in the proportion of sales exported over time were associated with strategies focused upon product/service quality and a diversified product/ service range

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)

Firm Size Effects on Venture Capital Syndication: The Role of Resources and Transaction Costs

The present paper examines firm size effects on the decision of venture capital firms to participate in a venture capital investment syndication network. The authors submit that firm size effects in venture capital syndication are dependent on resource acquisition motives and transaction cost considerations. Analysis of 317 venture capital firms in 6 European countries reveals a curve linear relationship between firm size and venture capital syndication participation. We also find positive and negative moderating effects of firm size. The implication of our findings is that there are both advantages and disadvantages in syndicated investment for the smaller and larger venture capitalist

Dynamic 3D echocardiography in virtual reality

BACKGROUND: This pilot study was performed to evaluate whether virtual reality is applicable for three-dimensional echocardiography and if three-dimensional echocardiographic 'holograms' have the potential to become a clinically useful tool. METHODS: Three-dimensional echocardiographic data sets from 2 normal subjects and from 4 patients with a mitral valve pathological condition were included in the study. The three-dimensional data sets were acquired with the Philips Sonos 7500 echo-system and transferred to the BARCO (Barco N.V., Kortrijk, Belgium) I-space. Ten independent observers assessed the 6 three-dimensional data sets with and without mitral valve pathology. After 10 minutes' instruction in the I-Space, all of the observers could use the virtual pointer that is necessary to create cut planes in the hologram. RESULTS: The 10 independent observers correctly assessed the normal and pathological mitral valve in the holograms (analysis time approximately 10 minutes). CONCLUSION: this report shows that dynamic holographic imaging of three-dimensional echocardiographic data is feasible. However, the applicability and use-fullness of this technology in clinical practice is still limited