Phonons and spin excitations in the extended t-J model

We consider the effects of spin-phonon coupling within the slave-boson mean-field treatment of the extended t-J model. With no additional assumptions the theory is found to give a semi-quantitative account of the frequency and linewidth anomalies observed for certain phonon modes in Y Ba₂Cu₃O₇ at the superconducting transition. We report also investigations of the role of this coupling in affecting thermodynamic properties and spin dynamics.     

An efficient purification method for detonation nanodiamonds

This article reports the purification process of detonation soot to obtain pure nanodiamond powder. Nanodiamonds are synthesized by detonation using a high explosive mixture composed of trinitrotoluene and hexogen. The detonation of the charge leads to a powder containing nanodiamonds as well as metallic impurities and sp² carbon species. Further, to remove metallic particles, an unusual acidic treatment (hydrofluoric/nitric acids; i.e. fluorinated aqua regia) was set up. To eliminate sp² carbon species such as graphite and amorphous carbon, a thermal oxidation treatment was performed at 420 °C under air in a furnace during several hours. Transmission Electronic Microscopy, Raman spectroscopy, X-ray diffraction and Thermo-Gravimetric Analysis showed that this purification process is very efficient. From TGA measurements, a model of the carbon grain combustion was developed by considering graphitic shells surrounding the nanodiamond particles, and was used to demonstrate that the selective oxidation of graphite was experimentally realistic. Moreover, another model was set up from specific area measurements to evaluate the thickness of the functional groups surrounding the nanodiamonds after the oxidation of sp² carbonaceous species. The treatment described herein was achieved on several tens of grams of product and could be easily adapted to the industrial scale.     

Expressing the equivalence of non‐isothermal and isothermal heat sterilization processes

Currently, the sterility of heat‐processed food and pharmaceuticals is assessed in terms of an F₀ value, based on the equivalence of the heat treatment to an isothermal process at a reference temperature. This F₀ value, however, has a meaning if, and only if, the inactivation kinetics of the targeted spores (or cells) follow a first‐order relationship and the temperature dependence of the D value, the reciprocal of the rate constant, is log‐linear. There is growing evidence that these conditions are not satisfied by many spores, including those of Clostridium botulinum and vegetative cells. Consequently, a replacement for the F₀ value is proposed in the form of a momentary equivalent time at the reference temperature based on the actual survival pattern of the spores, which need not be log‐linear. This equivalent time can be calculated together with the theoretical survival ratio in real time, thus enabling an operator to monitor the lethality of ongoing industrial heat processes. The concept is demonstrated with published survival data of C. botulinum, for which the Weibullian and log‐logistic models served as primary and secondary models, respectively. The safety factor according to the proposed method is in the number of added minutes of processing, beyond the theoretical time needed to reduce the survival ratio of the targeted spores or cells to a level that would produce practical (or commercial) sterility. Copyright © 2006 Society of Chemical Industry     

Sintering of Pt/Al2O3 reforming catalysts: EXAFS study of the behavior of metal particles under oxidizing atmosphere

The effect of an oxidative atmosphere (300 °C) is studied on fresh and sintered unchlorinated naphtha reforming catalysts containing 0.6–1% Pt. The TPR profiles show that only one species is formed using our experimental conditions, regardless of the mean crystallite size of the metal particles. The structural information supplied by EXAFS compared with cuboctahedral particle modeling, implies that such species is a surface platinum oxide, the structure of which is close to that of PtO₂, but largely distorted. This is true whether the catalyst is sintered or not.     

Camera Control in Computer Graphics

Recent progress in modelling, animation and rendering means that rich, high fidelity virtual worlds are found in many interactive graphics applications. However, the viewer's experience of a 3D world is dependent on the nature of the virtual cinematography, in particular, the camera position, orientation and motion in relation to the elements of the scene and the action. Camera control encompasses viewpoint computation, motion planning and editing. We present a range of computer graphics applications and draw on insights from cinematographic practice in identifying their different requirements with regard to camera control. The nature of the camera control problem varies depending on these requirements, which range from augmented manual control (semi‐automatic) in interactive applications, to fully automated approaches. We review the full range of solution techniques from constraint‐based to optimization‐based approaches, and conclude with an examination of occlusion management and expressiveness in the context of declarative approaches to camera control.     

Grounding and ground fault protection of multiple generator installations on medium-voltage industrial and commercial power systems - Part 4: Conclusion and Bibliography Working Group Report

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material.     

Improvement in wear resistance of plasma sprayed yttria stabilized zirconia coating using nanostructured powder

Plasma sprayed yttria stabilized zirconia coatings were prepared using nanostructured and conventional powders with optimized process parameters for the highest deposition efficiency, the smallest porosity and the highest microhardness. The tribological properties of these coatings against 100C6 steel were then tested with a ball-on-disc arrangement. Results showed that although the friction coefficients of the coatings sprayed using the nanostructured powder were slightly different from those of the coatings sprayed using the conventional powder, the former coatings were more wear resistant than the latter coatings. The wear mechanisms of all the coatings were explained in terms of adhesion-induced spallation and micro-fracturing of lamellae. The improvement in wear resistance of the coatings sprayed using the nanostructured powder could be mainly ascribed to the decrease of micrometer-sized defects such as pores and interlamellar and intralamellar cracks in the coatings.     

Effects of grain processing, forage to concentrate ratio, and forage particle size on rumen pH and digestion by dairy cows.

Dietary factors that alter the intake of effective fiber were evaluated for their effects on rumen fermentation, digestion, and milk production using a double 4 x 4 quasi-Latin square design with a 2(3) factorial arrangement of treatments. The dietary factors were extent of barley grain processing, coarse (1.60 mm) or flat (1.36 mm); forage-to-concentrate (F:C) ratio, low (35:65) or high (55:45) (dry matter basis); and forage particle length, long (7.59 mm) or short (6.08 mm). Eight lactating cows with ruminal and duodenal cannulas were offered ad libitum access to a total mixed diet and milked twice daily. Dry matter intake was increased by increasing the extent of grain processing. Mean rumen pH was lower for cows fed flatly rolled barley than for cows fed coarsely rolled barley, whereas F:C ratio or forage particle size had no effect on rumen pH. Rumen pH was not correlated with effective NDF intake but tended to be correlated with digestibility of starch in the rumen. Total tract digestibilities of dry matter, organic matter, starch, and neutral detergent fiber were increased by feeding flatly rolled barley or low F:C ratio diets. Milk yield and milk protein content were higher in cows fed flatly rolled barley or low F:C ratio diets. Milk fat content tended to increase with high F:C ratio or long forage particle length but was reduced by feeding flatly rolled barley. In this study, extent of grain processing and intake of ruminal available starch were the most influential factors affecting milk production. Reducing the ratio of F:C improved total digestion and actual milk production. Forage particle length had minimal impact on digestibility and milk production.     

Use of exogenous fibrolytic enzymes to enhance in vitro fermentation of alfalfa hay and corn silage

Two in vitro experiments were performed to identify promising exogenous fibrolytic enzyme products (EFE) and optimum dose rates (DR) for improving the degradation of alfalfa hay and corn silage. The relationship between enzymatic activity and fermentation responses was examined to identify optimum formulations. In experiment 1, 5 EFE containing mainly endoglucanase and xylanase activities, with different ratios between the 2 activities, were assessed at a DR of 0.7, 1.4, and 2.1 mg/g of DM forage. Milled alfalfa hay or corn silage was incubated in an in vitro batch culture with buffer, ruminal fluid, and EFE. Gas production (GP) was measured during 24 h of incubation, and degradabilities of DM and fiber were measured after terminating the incubation at 24 h. Two (E1 and E3) EFE substantially improved GP and degradation of alfalfa hay and corn silage fiber. The optimum DR of these EFE was 1.4 mg/g of DM for both forages with improvements in NDF degradability up to 20.6% for alfalfa hay and up to 60.3% for corn silage. Whereas added activities of endoglucanase and exoglucanase were positively correlated with improvement in NDF degradability for alfalfa hay and corn silage, there was no relationship between added xylanase activity and NDF degradability. The 2 most promising EFE from experiment 1 were reevaluated in experiment 2, alone and in combination with a high xylanase EFE, to determine whether their effectiveness could be enhanced by decreasing the endoglucanase to xylanase ratio. The 2 EFE improved GP and fiber degradation in a manner similar to that observed in experiment 1, but the combination treatments resulted in no further beneficial effects. Exogenous fibrolytic enzyme products can greatly improve forage utilization, but DR and the activities supplied are critical for achieving this response. Products used with alfalfa hay and corn silage should contain high endoglucanase activity, with an ideal ratio of endoglucanse to xylanase.     

The fate of nitrogen in agroecosystems: An illustration using Canadian estimates

Agroecosystems rely on inputs of nitrogen (N) to sustain productivity. But added N can leak into adjacent environments, affecting the health of other ecosystems and their inhabitants. Worries about global warming have cast further attention on the N cycle in farmlands because farms are a main source of N₂O, and because carbon sequestration, proposed to help reduce CO₂ loads, requires a build-up of N. Our objective was to estimate, as an illustrative example, the net N balance of Canadian agroecosystems in 1996 and then infer some hypotheses about the routes of N loss, their magnitude, and ways of reducing them. We defined agroecosystems as all agricultural lands in Canada including soil to 1 m depth and all biota, except humans. Only net flows of N across those boundaries were counted in our balance – all others represent internal cycling. Based on our estimates, about 2.35 Tg N entered Canadian agroecosystems from biological fixation, fertilizers, and atmospheric deposition (excluding re-deposited NH₃). In the same year, about 1.03 Tg N were exported in crop products and 0.19 Tg were exported in animals and animal products. Consequently, N inputs exceed exports in products by about 1.13 Tg, a surplus that is either accumulating in agroecosystems or lost to the environment. Because potential soil organic matter gains can account for only a small part of the surplus N, most is probably lost to air or groundwater. Our finding, that N losses amount to almost half of N added, concurs with field experiments that show crop recovery of added N in a given year is often not more than 60%. Better management may reduce the fraction lost somewhat but, because N in ecosystems eventually cycles back to N₂, substantive gains in efficiency may not come easily. As well as trying to reduce losses, research might also focus on steering losses directly to N₂, away from more harmful intermediates. If some of the `missing N' can be assimilated into organic matter, agricultural soils in Canada may need little added N to achieve C sequestration targets.