Construction experiences with SSC collider dipole magnets atFermilab

Full length and short model SSC (Superconducting Super Collider) 50 mm bore dipoles are being built and tested at Fermilab. The mechanical design of these magnets has been determined from experience with the construction of previous superconducting magnets. Construction experience includes coil fabrication, ground insulation, instrumentation, collaring, and yoke assembly. Fabrication techniques are explained, and construction problems and their solutions are reviewed. The relationship of short to long model construction is discussed     

Electroluminescence from phenylenevinylene-based polymer blends

The electroluminescent behaviour of films of poly(phenylphenylenevinylene) (PPPV), of PPPV blended with polystyrene (PS) and of PS doped with oligo(phenylenevinylene) sandwiched between indium–tin oxide (ITO) and Al contacts has been investigated. Polymer blending increases the relative quantum efficiency by up to two orders of magnitude. Studying the cell performance under application of rectangular voltage pulses as a function of temperature indicates that (i) hole injection at the ITO contact occurs by tunnelling, (ii) tunnel injection of electrons at the cathode is promoted by a space charge field across an interfacial Al₂O₃ layers and (iii) leakage of holes through the cathodic barrier is the main loss mechanism for holes.     

Fiber Coating Concepts for Brittle-Matrix Composites

The current interest in tough, high-temperature materials has motivated fiber coating development for brittle-matrix composites with brittle reinforcements. Such coatings are needed for controlled interface debonding and frictional sliding. The system investigated in this study was sapphire fiber-reinforced alumina. This system is thermochemically stable for severe use conditions, exhibits little thermal expansion mismatch, and utilizes the excellent strength and creep resistance of sapphire reinforcements. Porous oxide and refractory metal coatings which satisfy requirements for toughness improvement in these composites were identified by employing a variety of newly developed mechanical testing techniques for determining the interfacial fracture energies and sliding resistances.     

Importance Sampling Microfacet‐Based BSDFs using the Distribution of Visible Normals

We present a new approach to microfacet‐based BSDF importance sampling. Previously proposed sampling schemes for popular analytic BSDFs typically begin by choosing a microfacet normal at random in a way that is independent of direction of incident light. To sample the full BSDF using these normals requires arbitrarily large sample weights leading to possible fireflies. Additionally, at grazing angles nearly half of the sampled normals face away from the incident ray and must be rejected, making the sampling scheme inefficient. Instead, we show how to use the distribution of visible normals directly to generate samples, where normals are weighted by their projection factor toward the incident direction. In this way, no backfacing normals are sampled and the sample weights contain only the shadowing factor of outgoing rays (and additionally a Fresnel term for conductors). Arbitrarily large sample weights are avoided and variance is reduced. Since the BSDF depends on the microsurface model, we describe our sampling algorithm for two models: the V‐cavity and the Smith models. We demonstrate results for both isotropic and anisotropic rough conductors and dielectrics with Beckmann and GGX distributions.     

Extracting Microfacet‐based BRDF Parameters from Arbitrary Materials with Power Iterations

We introduce a novel fitting procedure that takes as input an arbitrary material, possibly anisotropic, and automatically converts it to a microfacet BRDF. Our algorithm is based on the property that the distribution of microfacets may be retrieved by solving an eigenvector problem that is built solely from backscattering samples. We show that the eigenvector associated to the largest eigenvalue is always the only solution to this problem, and compute it using the power iteration method. This approach is straightforward to implement, much faster to compute, and considerably more robust than solutions based on nonlinear optimizations. In addition, we provide simple conversion procedures of our fits into both Beckmann and GGX roughness parameters, and discuss the advantages of microfacet slope space to make our fits editable. We apply our method to measured materials from two large databases that include anisotropic materials, and demonstrate the benefits of spatially varying roughness on texture mapped geometric models.     

Experiences with large-scale operational trials of ALTO-enhanced P2P filesharing in an intra-ISP scenario

Application Layer Traffic Optimization (ALTO) has recently gained attention in the research and standardisation community as a way for a network operator to guide the peer selection process of distributed applications by providing network layer topology information. In particular P2P applications are expected to gain from ALTO, due to the many connections peers form among each other, often without taking network layer topology information into account. In this paper, we present results of an extensive intra-ISP trial with an ALTO-enhanced P2P filesharing software. In summary, our results show that—depending on the concrete setting and on the distribution of upload capacity in the network—ALTO enables an ISP to save operational costs significantly while not degrading application layer performance noticeably. In addition, based on our experience we are able to give advice to operators on how to save costs with ALTO while not sacrificing application layer performance at all.     

Data access in distributed simulations of multi-agent systems

Distributed simulation has emerged as an important instrument for studying large-scale complex systems. Such systems inherently consist of a large number of components, which operate in a large shared state space interacting with it in highly dynamic and unpredictable ways. Optimising access to the shared state space is crucial for achieving efficient simulation executions. Data accesses may take two forms: locating data according to a set of attribute value ranges (range query) or locating a particular state variable from the given identifier (ID query and update). This paper proposes two alternative routing approaches, namely the address-based approach, which locates data according to their address information, and the range-based approach, whose operation is based on looking up attribute value range information along the paths to the destinations. The two algorithms are discussed and analysed in the context of PDES-MAS, a framework for the distributed simulation of multi-agent systems, which uses a hierarchical infrastructure to manage the shared state space. The paper introduces a generic meta-simulation framework which is used to perform a quantitative comparative analysis of the proposed algorithms under various circumstances.     

Determination of fat in olestra-containing savory snack products by capillary gas chromatography

A quantitative method to determine fat in olestra-containing savory snack products was validated within the AOAC Peer-Verified Methods Program. The method may be used to demonstrate compliance with the guidelines of the U.S. Nutrition Labeling and Education Act for labeling products as "fat free" or "low fat." The method can measure total and saturated fat in savory snacks when present at levels of 0.2-10 g total fat and 0.1-3 g saturated fat per 30 g serving. The method is standardized to measure C6-C24 fatty acids. Extraction of olestra-containing savory snack samples with chloroform-methanol (modified AOAC Official Method 983.23) yields a lipid extract containing the total fat and olestra. The extracted lipid is hydrolyzed by lipase, yielding fatty acids and unreacted olestra. The fatty acids are precipitated as calcium soaps. Olestra is extracted from insoluble soaps with hexane and then discarded. The isolated soaps are converted back into fatty acids with hydrochloric acid and extracted with hexane. The isolated fatty acids are converted to methyl esters with boron trifluoride-methanol and quantitated by capillary gas chromatography using internal standard. Test samples were prepared by blending olestra-containing and full-fat (triglyceride) snacks to obtain 6 levels of spiking (0-10 g total fat added/30 g serving) in potato chips, potato crisps, cheese puffs, and nacho cheese-flavored corn chips. Results were linear (r2 > 0.997) between 0 and 10 g fat/30 g serving for each product matrix. Mean recovery was 101 +/- 6% standard deviation (SD) for total fat and 104 +/- 6% SD for saturated fat. Mean recovery by peer laboratory was 88 +/- 5% SD for total fat and 95 +/- 4% SD for saturated fat in potato chips (0-3 g total fat added/30 g serving). Two sets of 10 replicates of potato chips (0.5 g total fat/30 g serving and 0.16 g saturated fat/30 g serving) and potato crisps (0.5 g total fat/30 g serving and 0.16 g saturated fat/30 g serving) were analyzed by submitting and peer laboratories. Repeatability relative standard deviations ranged from 3.90 to 7.33% for total fat and from 4.01 to 11.53% for saturated fat. Reproducibility relative standard deviations were 7.33% (total fat, potato chips), 7.15% (total fat, potato crisps), 11.36% (saturated fat, potato chips), and 13.50% (saturated fat, potato crisps).