钻头特性的测试设备

介绍了诺丁汉大学研制的一种在实验室测试岩石钻头的钻机，该钻机可以为各种不同的岩石钻头提供严格的测试平台，从而实现在很宽范围的工作条件下最经济地获取实验数据。     

A new electronically tunable phase shifter employing current-controlled current conveyors

A new canonical current-mode (CM) filter topology is presented. It realizes first-order allpass filtering functions using two dual-output current-controlled current conveyors (DO-CCCII) and a single capacitor. The topology gives both inverting and non-inverting types of these filters. Owing to electronically tunability properties of the CCCII, phase response of the circuit can be controlled by an external control current. Realization of the allpass filter imposes no matching condition. All outputs of the filters exhibit high output impedances so that this property makes the circuits very attractive from the viewpoint of cascading in current mode. The theoretical results are verified with PSPICE simulations using a BJT realization of CCCII.     

Relationships between hydration number,water activity and density of aqueous sugar solutions

Hydration numbers (n_h) of simple sugars have been investigated for decades using thermodynamic, spectroscopic as well as molecular modelling techniques. Results were shown to depend on the technique employed. The most reliable values only concern the first hydration shell assuming a maximum oxygen–oxygen distance below 2.8 Å. As concentration increases, sugar–sugar interactions become preponderant and n_h decreases. Assuming that no long range structuring effect is exerted by the solute on water, it is possible to estimate the volume occupied by each of hydration water (with nearly 9% volume contraction) and bulk water from density measurements. Likewise, the volume occupied by non-hydrated sugar molecules in the aqueous medium allows finding for sugar density in the aqueous medium a value comparable to that of solid crystalline form. On the other hand, using the literature values of aqueous sugar solution densities, it was possible to calculate the hydration numbers at different temperatures and concentrations. These values of n_h show a noticeable decrease as temperature is raised and concentration increased. Decrease in n_h can be explained assuming a partial occupation of potential hydration sites (OHs) because of differences in H-bonds lifetimes on the one hand and molecular folding around glycosidic bond on the other.     

Burning of Reactor Grade Plutonium Mixed with Thorium in a Hybrid Reactor

Significant amount of plutonium have been discharged and accumulated from the conventional LWRs and CANDU reactors. Reducing this reactor grade (RG) plutonium is very important because it may be misused and/or released accidentally into the environment. Fusion-fission (hybrid) reactors have strong potential on burning plutonium effectively. This study presents the burning of RG plutonium mixed with thorium in a hybrid reactor for an operation period of 24 months. The effect of various fuel mixtures (98% ThO₂ + 2% RG-PuO₂, 94% ThO₂ + 6% RG-PuO₂ and 90% ThO₂ + 10% RG-PuO₂) and coolants (Flinabe, natural lithium and Li₂₀Sn₈₀) on the reactor’s performance was investigated. Numerical results showed that utilization of RG plutonium in the mixed fuel in such a hybrid reactor not only enhanced the reactor’s performance but also reduced its ²³⁹Pu content significantly.     

Self-aligned nickel, cobalt/tantalum nitride stacked-gate pMOSFETs fabricated with a low temperature process after metal electrode deposition

This letter reports the first replacement (Damascene) metal gate pMOSFETs fabricated with Ni/TaN, Co/TaN stacked electrode, where Ni or Co is in direct contact with the gate SiO/sub 2/, to adjust the electrode metal work function and TaN is used as the filling material for the gate electrode to avoid wet etching and CMP problems. The process is similar to the fabrication of traditional self-aligned polysilicon gate MOSFETs, except that in the back end (after the source/drain implants are activated) a few processing steps are added to replace the polysilicon with metal. Our data show that the Ni or Co/TaN gate electrode has the right work function for the pMOSFETs. The metal gate process can reduce the gate resistivity. Thermal stability of the stacked electrodes is studied and the result is reported in this paper. The damascene process flow bypasses high temperature steps (> 400/spl deg/C)critical for metal gate and hi k materials. This paper demonstrates that a low temperature anneal (300/spl deg/C) can improve the device performance. In this paper, the gate dielectrics is SiO/sub 2/.     

Template-directed synthesis of silica nanotubes for explosive detection

Fluorescent porous organic-inorganic thin films are of interest of explosive detection because of their vapor phase fluorescence quenching property. In this work, we synthesized fluorescent silica nanotubes using a biomineralization process through self-assembled peptidic nanostructures. We designed and synthesized an amyloid-like peptide self-assembling into nanofibers to be used as a template for silica nanotube formation. The amine groups on the peptide nanofibrous system were used for nucleation of silica nanostructures. Silica nanotubes were used to prepare highly porous surfaces, and they were doped with a fluorescent dye by physical adsorption for explosive sensing. These porous surfaces exhibited fast, sensitive, and highly selective fluorescence quenching against nitro-explosive vapors. The materials developed in this work have vast potential in sensing applications due to enhanced surface area.     

A new MILP model proposal in feed formulation and using a hybrid-linear binary PSO (H-LBP) approach for alternative solutions

Large-scale feed factories may have multiple production and storage facilities. Any production facility uses its own available raw materials while performing feed formulation. However, ensuring a reasonable cost is achieved, and the desired quality criteria are met, may require obtaining a certain amount of raw material from other facilities. Selecting a specific amount of raw materials among many raw materials in different facilities requires many combinations to be tried out. Providing solutions, especially when there is a large amount of the raw material, may be costly and take more time. A new mixed-integer linear programming (MILP) model that specifies the type of material and the amount of the material to be selected from external facilities has been proposed in this study. When deterministic methods like MILP are used, only one solution result is obtained. However, when the decision-maker would like to see alternative results, solution constraints can be mitigated and a solution provided within the same or similar time. A new method named hybrid-linear binary PSO (H-LBP) has been proposed in this study for the problems that the decision-maker had limited time for and for which the solution results were required in a shorter time. Continuous particle swarm optimization, which works as a hybrid with linear programming, has been used in this method. The new model proposed in this study was tested on the mixed feeds for sheep, cattle and rabbit species by using both MILP and the proposed H-LBP methods. Raw materials determined by the model were added to the mixture, and the cost in each of the three species was observed to go down. In addition, different alternative solutions at reasonable cost and similar quality were presented to the producer/decision-maker in a shorter time.

     

Tunisian Pistacia atlantica Desf. Extraction Process: Impact on Chemical and Nutritional Characteristics

Plant materials have been used in different fields such as therapeutics, cosmetics, and energy for ages. Several studies have investigated seeds, whether common or not, in order to ensure a better valuation of natural resources. Among these, Pistacia atlantica Desf. has been the subject of several works on its characterization and valorization. Among the current trends in sustainable development and environmental protection, valorizing natural wild plants via green chemistry has become prevalent. One of these plants, Pistacia atlantica Desf., is a tree that grows in arid and semi-arid areas, notably in Tunisia, and produces seeds rich in oil. In this study extracting the oil from its seeds is tried by three methods (supercritical carbon dioxide (CO₂), pressure, and hexane), and the efficiency of these extraction processes is compared in order to obtain the best yield and maximize its valorization in a variety of industrial fields. The obtained oil is found to be rich in polyunsaturated fatty acids, namely linoleic and oleic acids, with a similar acidic composition among all extraction methods. The tocopherol composition of the oil is determined using high performance liquid chromatography. The total polyphenol content is determined using the Folin-Ciocalteu colorimetric analysis method. The results show that the seed oil of Pistacia atlantica Desf. extracted by supercritical CO₂ gives the highest extraction yield (25%) and the lowest acidity and peroxide values with a high degree of oxidation at 232 and 270 nm. This method also gives the highest content of alpha, gamma, and delta tocopherol as well as total phenolic content compared to the other extraction methods. The composition of chlorophylls and carotenes in the seed oil of Pistacia atlantica Desf. is determined. Besides, the analysis of the sterol composition reveals that β-sitosterol is still prevailing. Among all the tested extracts, the supercritical CO₂ extract demonstrates the best antioxidant performance against the tested radicals. The oil extracted by supercritical carbon dioxide (CO₂) is of a higher quality compared to that extracted by pressure and by hexane. Practical applications : The Pistacia atlantica Desf. oil exhibits interesting physicochemical and biological characteristics. The type of extraction affects the quality of the major and minor components in the seeds. However, the supercritical CO₂ method produces a better oil quality with the presence of antioxidants such as tocopherols and polyphenols. In fact, it is found that the oil extracted by the three methods has an important sterolic profile with the predominance of β-sitosterol. According to the classification of vegetable oils, unsaturated fatty acids of atlas pistachio oil can be categorized as oleo linoleic oil, which enhances its nutritional value. Having these characteristics, the use of this oil can be considered in agrifood products.