Influence of Processing Parameters on the Sintering and Electrical Properties of Pb(Zn1/3Nb2/3)O3-Based Ceramics

Pb(Zn_1/3Nb_2/3)O₃-based ceramics have been prepared by two different processing methods: conventional (PZN-C) and reaction-sintering (PZN-RS). The conventionally prepared PZN-based ceramics densified at lower temperatures (950°C) than the reaction-sintered samples (1100°C), but the perovskite/pyrochlore ratio was always higher in PZN-RS. The presence of a substantial amount of pyrochlore phase in PZN-C ceramics caused a decrease in the electrical properties. The maximum dielectric constant values in PZN-C ceramics were 10%–15% lower than those of PZN-RS, despite a similar average grain size, 7 ± 0.2 μm. The temperature of the maximum of the dielectric constant ( T _max) was lower than that expected from the mixing rule because of the possible formation of Ba–Nb clusters. The higher chemical homogeneity in PZN-RS ceramics is the main reason for the higher dielectric constant, T _max and electromechanical response, as well as for the lower difference between T _max and the depolarization temperature ( T _d) and the lower diffusiveness parameter (δ).     

Soft solution fluorine-free synthesis of anatase nanoparticles with tailored morphology

TiO₂ nanoparticles with tailored morphology have been synthesized under exceptionally soft conditions. The strategy is based on the use of a non-aqueous alcoholic reaction medium in which water traces, coming either from the air (atmospheric water) or from an ethanol–water azeotropic mixture (ethanol 96%), are incorporated in order to accelerate hydrolysis of the Ti–precursor. Moreover, organic surfactants have been used as capping agents so as to tailor crystal growth in certain preferential directions. Combinations of oleic acid and oleylamine, which lead to the formation of another surfactant, dioleamide, are employed instead of fluorine-based compounds, thus increasing the sustainability of the process. As a result, TiO₂ nanostructured hierarchical microspheres and individual nanoparticles with exposed high-energy facets can be obtained at atmospheric pressure and temperatures as low as 78 °C.     

DNA damage detection technique applying time-resolved fluorescence measurements

A novel DNA damage detection technique based on the characteristic fluorescence lifetimes exhibited by Pico-Green-single-stranded DNA and -double-stranded DNA complexes is employed to establish the damage produced on DNA isolated from sheep white blood cells following gamma radiation. This technique, which incorporates key concepts such as alkaline unwinding buffers and higher unwinding rates of damaged DNA compared to undamaged DNA, allows for the differentiation of DNA damage resulting from doses of gamma radiation in the 0-100-Gy range, with the potential of analyzing samples consisting of as little as 10(4) cells. Experiments were carried out using commercial DNA sources as well as DNA isolated from sheep white blood cells, suggesting its potential for use with isolated DNA from virtually any eukaryotic cell.     

LZgrep: a Boyer–Moore string matching tool for Ziv–Lempel compressed text

We present a Boyer–Moore (BM) approach to string matching over LZ78 and LZW compressed text. The idea is to search the text directly in compressed form instead of decompressing and then searching it. We modify the BM approach so as to skip text using the characters explicitly represented in the LZ78/LZW formats, modifying the basic technique where the algorithm can choose which characters to inspect. We present and compare several solutions for single and multipattern searches. We show that our algorithms obtain speedups of up to 50% compared to the simple decompress‐then‐search approach. Finally, we present a public tool, LZgrep, which uses our algorithms to offer grep‐like capabilities directly searching files compressed using Unix's Compress, a LZW compressor. LZgrep can also search files compressed with Unix gzip, using new decompress‐then‐search techniques we develop, which are faster than the current tools. This way, users can always keep their files in compressed form and still search them, uncompressing only when they want to see them. Copyright © 2005 John Wiley & Sons, Ltd.     

Switching class labels to generate classification ensembles

Ensembles that combine the decisions of classifiers generated by using perturbed versions of the training set where the classes of the training examples are randomly switched can produce a significant error reduction, provided that large numbers of units and high class switching rates are used. The classifiers generated by this procedure have statistically uncorrelated errors in the training set. Hence, the ensembles they form exhibit a similar dependence of the training error on ensemble size, independently of the classification problem. In particular, for binary classification problems, the classification performance of the ensemble on the training data can be analysed in terms of a Bernoulli process. Experiments on several UCI datasets demonstrate the improvements in classification accuracy that can be obtained using these class-switching ensembles.     

Searching in metric spaces by spatial approximation

We propose a new data structure to search in metric spaces. A metric space is formed by a collection of objects and a distance function defined among them which satisfies the triangle inequality. The goal is, given a set of objects and a query, retrieve those objects close enough to the query. The complexity measure is the number of distances computed to achieve this goal. Our data structure, called sa-tree (“spatial approximation tree”), is based on approaching the searched objects spatially, that is, getting closer and closer to them, rather than the classic divide-and-conquer approach of other data structures. We analyze our method and show that the number of distance evaluations to search among n objects is sublinear. We show experimentally that the sa-tree is the best existing technique when the metric space is hard to search or the query has low selectivity. These are the most important unsolved cases in real applications. As a practical advantage, our data structure is one of the few that does not need to tune parameters, which makes it appealing for use by non-experts. Edited by R. Sacks-Davis Received: 17 April 2001 / Accepted: 24 January 2002 / Published online: 14 May 2002     

Effective bandwidth estimation and testing for Markov sources

This work addresses the resource sharing problem in broadband communication networks that can guarantee some quality of service (QoS), and develops some results about data source and traffic modelling, especially in aspects of model testing and parameter estimation. The multiplexing of variable bit rate (VBR) sources poses a mathematical and statistical problem: the estimation of the resource requirements of a source or set of sources. The estimation method shall be simple enough to be practically implemented in the connection acceptance control (CAC) function.

In this paper, the VBR video sources are taken as a typical case of variable rate, with real-time constraints. This association of requirements makes the case especially interesting. A Markov model is assumed for the VBR sources. The validity of such models is under research; they seem to be appropriate at least in certain time scales. The model is tested against real video traces. In order to estimate the resource allocation or “channel occupation” of each source, the concept of equivalent bandwidth proposed by Kelly [Notes on effective bandwidth, in: F.P. Kelly, S. Zachary, I.B. Ziedins (Eds.), Stochastic Networks: Theory and Applications, Oxford University Press, Oxford, 1996, pp. 141] is used; it is based on a consistent mathematical theory, and has proven to be robust and useful for technical applications.

A calculation of the equivalent bandwidth of a Markov source, given its parameters, can be found in the literature [IEEE ACM Trans. Networking 1 (4) (1993) 424]. But in fact, one can only estimate model and parameters. In this work, an estimation of the equivalent bandwidth is given, which can be obtained from real data. The convergence and the consistency of the estimation are studied, and practical bounds are found. Illustrative calculations are performed from real video traces that were obtained using a software MPEG coder, developed by the authors. The mathematical and statistical results are valid for whatever phenomenon that can be modelled as a Markov process.     

Detection and Discrimination of Conspecific Scents by the Anguid Slow-Worm Anguis fragilis

We tested the ability of male slow-worms, Anguis fragilis, a limbless anguid lizard with secretive, semifossorial habits, to detect chemical associated with conspecifics by using a T-maze in the laboratory. Male slow-worms discriminated conspecific male and female scent deposits. Males selected the arm with female scent, suggesting that scent deposits may be used to locate potential mates. Also, male slow-worms did not avoid the chemicals of other males, suggesting that they are not territorial. However, males discriminated their own scent from those of other males, and spent more time exploring the arm with other male scent, which suggests that scent marks may bear information that could be used in future intrasexual social contexts. We conclude that discrimination of conspecifics based on scents may be more widespread than previously expected among lizards inhabiting visually restricted environments.