形变热处理对烧结Cu-Au合金性能与微观组织的影响(英文)

研究Cu-4%Au合金的硬度、显微硬度、导电性和微观组织在形变热处理过程中的变化。在加工硬化后,再对轧制合金在60～350°C温度下退火。由于退火硬化效应,合金的强度增大。结果表明:Cu-Au合金性能在两个阶段都得到改善;合金进行变形量为40%的热轧后,在260°C退火能得到最佳的综合性能。合金的微观组织也在形变热处理过程中发生显著变化。     

The stochastic walk algorithms for point location in pseudo-triangulations

A pseudo-triangulation is a planar subdivision into polygons with three convex vertices, useful for ray shooting, visibility problems and kinetic collision detection. As pseudo-triangulations are quite young, there is a lack of specialized algorithms for them. In this paper, we address the question of location in pseudo-triangulations. We propose two location algorithms based on the so-called stochastic walk and present their experimental results. The class of walk location algorithms is very popular for triangulations, namely in engineering applications, due to simplicity and low memory requirements, in spite of their non-optimality. As far as we know, no walk algorithm specialized on pseudo-triangulations has been developed before.     

Data dissemination in wireless broadcast channels: Network coding versus cooperation

Network coding and cooperative diversity have each extensively been explored in the literature as a means to substantially improve the performance of wireless networks. Yet, little work has been conducted to compare their performance under a common framework. Our goal in this paper is to fill in this gap. Specifically, we consider a single-hop wireless network consisting of a base station and N receivers. We perform an asymptotic analysis, as N → ∞, of the expected delay associated with the broadcasting of a file consisting of K packets. We show that if K is fixed, cooperation outperforms network coding, in the sense that the expected delay is proportional to K (and thus within a constant factor of the optimal delay) in the former case while it grows logarithmically with N in the latter case. On the other hand, if K grows with N at a rate at least as fast as (logN)^r, for r ≫ 1, then we show that the average delay of network coding is also proportional to K and lower than the average delay of cooperation if the packet error probability is smaller than 0.36. Our analytical findings are validated through extensive numerical simulations.     

Polyaniline nanotubes: conditions of formation

The courses of aniline oxidation with ammonium peroxydisulfate in aqueous solutions of strong (sulfuric) and in weak (acetic) acids, followed by temperature and acidity changes, are different. In solutions of sulfuric acid, granular polyaniline (PANI) was produced; in solutions of acetic acid, PANI nanotubes were obtained. The external diameter of the nanotubes was 100–300 nm, the internal cavity 20–100 nm, and the length extended to several micrometres. The morphology of PANI, granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. PANI nanotubes were also produced when aniline was oxidized in the absence of any acid. The bulk conductivity of PANI prepared in solutions of acetic acid was 0.08–0.27 S cm^?1, depending on the acid concentration. Protonated PANI prepared in sulfuric and acetic acids were deprotonated with ammonium hydroxide to obtain PANI bases and the ammonium salt of the protonating acid. FTIR spectroscopy showed the differences in the molecular structure of the PANI bases. Irrespective of whether the polymerization was performed in solutions of sulfuric or acetic acid, PANI had hydrogen sulfate counter‐ions only. The PANI morphology is thus not controlled by the nature of counter‐ions. The acidity of the reaction medium determines the protonation of monomer, oligomer and polymer species. The chemistry of aniline oxidation is likely to be affected especially by the protonation of an intermediate in the pernigraniline form. It is proposed that, in the course of aniline oxidation, pH‐dependent self‐assembly of aniline oligomers predetermines the final PANI morphology. Copyright © 2005 Society of Chemical Industry     

Variable temperature in situ X-ray diffraction study of mechanically activated synthesis of calcium titanate, CaTiO3

The effect of mechanical activation on formation of calcium titanate (CaTiO₃) from calcined mixtures of CaCO₃ and TiO₂ was studied by monitoring the course of this solid-state reaction by variable temperature in situ X-ray diffraction (XRD) experiments, scanning electron microscopy (SEM) and dilatometry. Two equimolar mixtures of powdered CaCO₃ and TiO₂ were prepared: one was mechanically activated by grinding in a high energy vibro-mill. A total of 32 X-ray diffraction data sets for each sample, collected between 30 and 1100 °C, were analyzed by multiphase Rietveld refinement. Quantitative phase analysis and microstructure analysis obtained from X-ray diffraction are correlated to results of scanning electron microscopy and dilatometry. In the non-activated sample, small quantities of the reactants remain in the product until 1100 °C. In the activated sample, the reaction results in pure CaTiO₃ at 920 °C.     

Melt granulation in fluidized bed: a comparative study of spray-on versus in situ procedure

Objective: The aim of this study was to investigate the influence of process parameters, binder content and binder addition method on characteristics of the granules obtained by melt granulation (MG) in fluidized bed.

Methods: Spray-on experiments were performed according to 2³ full factorial design. The effect of binder content, molten binder feed rate, and spray air pressure on granule size and size distribution, granule shape, ?owability and drug release rate was investigated. In the in situ experiments, the influence of binder particle size and binder content was evaluated. Solid-state characterization was performed by means of differential scanning calorimetry, X-ray powder diffraction and Fourier transform infrared spectroscopy.

Results: Size of the granules obtained by spray-on procedure was significantly influenced by binder content and spray air pressure, while the width of particle size distribution was mainly affected by binder feed rate. Spray air pressure showed the most significant influence on granule shape. It was shown that smooth and spherical particles with good flow properties may be obtained by both procedures, spray-on and in situ MG. The results obtained indicated the influence of agglomeration mechanism on granule sphericity, with higher degree of granule sphericity observed when immersion and layering was the dominant mechanism. Paracetamol release from granulates was very rapid, but after compression of the granules into tablets, drug release was considerably slower. Solid-state analysis confirmed that the physical form of the granulate components remained unaffected after the MG process.

Conclusion: The results presented indicate that MG in fluidized bed could be a good alternative to conventional granulation techniques.     

Radon index of a local administrative unit

The determination of radon-prone areas is usually based on indoor radon data and on the prognosis of the occurrence of houses exceeding the action level. However, the sample of houses in the survey must be representative and large enough, which is not easy to fulfill. Despite this, the determination of localities with high radon risk is useful not only for planning of indoor radon surveys, but also mainly for predicting the risk in newly built houses. There exist two more sources of data that can be used when assigning radon-related index to territories: soil gas radon measurements and gamma dose rate maps, both having their own inaccuracies. An attempt has been made to combine Czech indoor radon data, soil gas radon data and gamma dose rate maps for municipalities, where available. The radon-related index has been constructed by means of statistical analysis (linear regression). The equations found can be used for predicting the radon risk of the municipalities where the data sets are not large enough.     

Radon programmes and health marketing

Being aware of negative health effects of radon exposure, many countries aim for the reduction of the radon exposure of their population. The Czech radon programme was commenced >20 y ago. Since then experts have gathered a lot of knowledge, necessary legislation has been enacted, tens of thousands of inhabitants have been offered free measurement and subsidy for the mitigation. Despite the effort, the effectiveness of the radon programme seems to be poor. Newly built houses still exhibit elevated radon concentrations and the number of houses mitigated is very low. Is it possible to enhance the effectivity of radon programme while keeping it on a voluntary basis? One possible way is to employ health marketing that draws together traditional marketing theories and science-based strategies to prevention. The potential of using marketing principles in communication and delivery of radon information will be discussed.     

Cryptanalysis of the Tillich�CZ��mor Hash Function

At CRYPTO ’94, Tillich and Zémor proposed a family of hash functions, based on computing a suitable matrix product in groups of the form SL₂(\mathbbF_2ⁿ)SL_{2}(\mathbb{F}_{2^{n}}). We show how to construct collisions between palindromic bit strings of length 2n+2 for Tillich and Zémor’s construction. The approach also yields collisions for related proposals by Petit et al. from ICECS ’08 and CT-RSA ’09.