Hollow cathodes with BaO impregnated, porous tungsten inserts and tips

The technology of impregnated materials is described and some inherently advantageous characteristics of impregnated cathodes are discussed. Thermionic emission measurements are presented for oxide coated and impregnated cathodes. Five cathode configurations with barium oxide impregnated porous tungsten inserts and/or tips have been fabricated and tested. Reliability, durability, and stability of operation are characterized. One of the cathodes has accumulated over 9000 operational hours, another has been cycled on and off more than 800 times

On Fluxed Instantons and Moduli Stabilisation in IIB Orientifolds and F-theory

We study the superpotential induced by Euclidean D3-brane instantons carrying instanton flux, with special emphasis on its significance for the stabilisation of Kahler moduli and Neveu-Schwarz axions in Type IIB orientifolds. Quite generally, once a chiral observable sector is included in the compactification, arising on intersecting D7-branes with world-volume flux, resulting charged instanton zero modes prevent a class of instantons from participating in moduli stabilisation. We show that instanton flux on Euclidean D3-branes can remove these extra zero modes and helps in reinstating full moduli stabilisation within a geometric regime. We comment also on the F-theoretic description of this effect of alleviating the general tension between moduli stabilisation and chirality. In addition we propose an alternative solution to this problem based on dressing the instantons with charged matter fields which is unique to F-theory and cannot be realised in the weak coupling limit.Comment: 9 pages in 2-column format; v2: refs adde

Optical properties of ion beam textured metals

Copper, silicon, aluminum, titanium and 316 stainless steel were textured by 1000 eV xenon ions from an 8 cm diameter electron bombardment ion source. Simultaneously sputter-deposited tantalum was used to facilitate the development of the surface microstructure. Scanning electron microscopy of the ion textured surfaces revealed two types of microstructure. Copper, silicon, and aluminum developed a cone structure with an average peak-to-peak distance ranging from 1 micron for silicon to 6 microns for aluminum. Titanium and 316 stainless steel developed a serpentine ridge structure. The average peak-to-peak distance for both of these materials was 0.5 micron. Spectral reflectance was measured using an integrating sphere and a holraum reflectometer. Total reflectance for air mass 0 and 2, solar absorptance and total emittance normalized for a 425 K black body were calculated from the reflectance measurements

Status of a five-centimeter-diameter ion thruster technology program

Prototype auxiliary propulsion subsystem with isolated single tank propellant feed system and 5-cm-diameter ion thruste

Meta-Learning for Phonemic Annotation of Corpora

We apply rule induction, classifier combination and meta-learning (stacked classifiers) to the problem of bootstrapping high accuracy automatic annotation of corpora with pronunciation information. The task we address in this paper consists of generating phonemic representations reflecting the Flemish and Dutch pronunciations of a word on the basis of its orthographic representation (which in turn is based on the actual speech recordings). We compare several possible approaches to achieve the text-to-pronunciation mapping task: memory-based learning, transformation-based learning, rule induction, maximum entropy modeling, combination of classifiers in stacked learning, and stacking of meta-learners. We are interested both in optimal accuracy and in obtaining insight into the linguistic regularities involved. As far as accuracy is concerned, an already high accuracy level (93% for Celex and 86% for Fonilex at word level) for single classifiers is boosted significantly with additional error reductions of 31% and 38% respectively using combination of classifiers, and a further 5% using combination of meta-learners, bringing overall word level accuracy to 96% for the Dutch variant and 92% for the Flemish variant. We also show that the application of machine learning methods indeed leads to increased insight into the linguistic regularities determining the variation between the two pronunciation variants studied.Comment: 8 page

Numerical Analysis of a New Mixed Formulation for Eigenvalue Convection-Diffusion Problems

A mixed formulation is proposed and analyzed mathematically for coupled convection-diffusion in heterogeneous medias. Transfer in solid parts driven by pure diffusion is coupled with convection-diffusion transfer in fluid parts. This study is carried out for translation-invariant geometries (general infinite cylinders) and unidirectional flows. This formulation brings to the fore a new convection-diffusion operator, the properties of which are mathematically studied: its symmetry is first shown using a suitable scalar product. It is proved to be self-adjoint with compact resolvent on a simple Hilbert space. Its spectrum is characterized as being composed of a double set of eigenvalues: one converging towards −∞ and the other towards +∞, thus resulting in a nonsectorial operator. The decomposition of the convection-diffusion problem into a generalized eigenvalue problem permits the reduction of the original three-dimensional problem into a two-dimensional one. Despite the operator being nonsectorial, a complete solution on the infinite cylinder, associated to a step change of the wall temperature at the origin, is exhibited with the help of the operator’s two sets of eigenvalues/eigenfunctions. On the computational point of view, a mixed variational formulation is naturally associated to the eigenvalue problem. Numerical illustrations are provided for axisymmetrical situations, the convergence of which is found to be consistent with the numerical discretization

Cold Region Pedestrian Bridge Prototype Maintenance Plan

A Project Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE In CIVIL ENGINEERINGIn recent years there have been several failures of pedestrian bridges in the network of trails maintained by the Municipality of Anchorage (MOA), Parks and Recreation Department, causing the MOA to realize that they need to develop and maintain a bridge maintenance protocol. This project, the Cold Region Pedestrian Bridge Prototype Maintenance Plan, provides a prototype application and platform created to allow the MOA to obtain and utilize information collected by non-engineer workers to report on the condition of various pedestrian bridges (“Prototype Platform”). The Prototype Platform has three major components: the Bridge Inspection Application (BIA), a Bridge Risk Evaluation program (BRE), and the determination of Bridge Risk Categories (BRC). These three components will help the MOA to record bridge condition information, identify safety conditions that need to be addressed, classify the condition of the pedestrian bridges, group them into one of several broad risk categories, and provide the MOA with a way of accessing this information in a more organized manner. This project will provide information about the background of the MOA pedestrian bridges, their importance to the MOA, and prior work done relating to pedestrian bridge inspection approaches. It will also provide detailed information about components of the Prototype Platform, the testing of the components, and recommendations for the future. This project is an overall asset management tool that will help the MOA identify future potential risks on their pedestrian bridge system. The MOA intends to use this data in conjunction with more detailed reports to provide an overall condition assessment for the pedestrian bridges in Anchorage, Alaska. It is understood by all parties that the Prototype Platform is a first step in a broader effort to create a more robust pedestrian bridge maintenance management plan. The fact that the inspection data will be obtained by non-engineer field workers, and is somewhat simplistic and limited as to its content, makes the results from the field inspection data only a place to start. However, given the very real budget constraints and limited resources available to the MOA, the Prototype Platform gives the MOA a way to make meaningful progress in implementing a maintenance protocol. The BIA should be used annually as part of a routine review of pedestrian bridges. However, routine inspections conducted using the application should not replace full inspections and full structural analysis reports that can only be conducted by a professional structural engineer when needed

Wie viel Arbeit macht die Aufzucht von Ökologischen Junghennen? Arbeitwirtschaftlicher Vergleich der konventionellen und ökologischen Aufzucht von Legehennen

Organic pullets are reared with daylight and are not beak-trimmed. Therefore, certain provisions are needed in order to prevent feather-pecking and cannibalism. Respec-tive guidelines are set by the German Organic Associations. It was the goal of this study to investigate whether the higher rearing standards are associated with an increased labour demand compared to conventional rearing systems. Using a ques-tionnaire, data from 32 hen-houses (10 conventional and 6 organic barn systems, 10 conventional and 6 organic aviary systems) about duration and number of working procedures were collected and exemplary models calculated. Total labour demand was between 2.36 and 7.37 worker`s hours/100 pullets. It did not differ between or-ganic and conventional rearing when comparing similar flock sizes, but were partly differently allocated to the different working procedures. On average, organic farms had smaller flocks, and there was a large influence of flock size on labour demand with small houses requiring most labour per hen. Also aviaries were more labour demanding than barn systems, but were usually associated with higher flock sizes. Our results indicate that improved pullet rearing that allows the birds to perform their natural behaviour more completely, does not necessarily cause higher labour re-quirements