Keyword binding as a method of reducing the length of indexes in library catalogues (based on the experience of Digital Library of Wielkopolska)

This paper presents a relatively simple and cheap method for shortening the subject indexes in library catalogs. The method involves taking a set of several dozen general concepts, characterized by a low semantic awareness barrier. Built around these words are subindexes made up of the words which appear in descriptions containing a particular general concept. The effectiveness of the method was studied by analyzing the content of fragments of subject indexes of the NUKAT central catalog of Polish libraries, the University Library in Poznań and the Library of Congress. Compared with the subject headings language method, this method reduces the length of an index by an average of two-thirds, and makes it significantly easier for readers to navigate the vocabulary used by the cataloger. This method has been developed for the needs of Digital Library of Wielkopolska, and will probably be used in all regional digital libraries in Poland

Keyword binding as a method of reducing the length of indexes in library catalogues (based on the experience of Digital Library of Wielkopolska)

This paper presents a relatively simple and cheap method for shortening the subject indexes in library catalogues. The method involves taking a set of several dozen general concepts, characterized by a low semantic awareness barrier. Built around these words are subindexes made up of the words which appear in descriptions containing a particular general concept. The effectiveness of the method was studied by analyzing the content of fragments of subject indexes of the NUKAT central catalogue of Polish libraries, the University Library in Poznań and the Library of Congress. Compared with the subject headings language method, this method reduces the length of an index by an average of two-thirds, and makes it significantly easier for readers to navigate the vocabulary used by the cataloger. This method has been developed for the needs of Digital Library of Wielkopolska, and will probably be used in all regional digital libraries in Poland.Artykuł przedstawia stosunkowo prostą i tanią metodę skracania indeksów rzeczowych w katalogach bibliotecznych. Polega ona na przyjęciu zestawu kilkudziesięciu pojęć ogólnych - charakteryzujących się niską barierą świadomości semantycznej. Wokół tych słów budowane są subindeksy złożone ze słów występujących w opisach zawierających dane pojęcie ogólne. Skuteczność metody badano, analizując zawartość fragmentów indeksów przedmiotowych centralnego katalogu bibliotek polskich NUKAT, Biblioteki Uniwersyteckiej w Poznaniu i Biblioteki Kongresu. Metoda ta w porównaniu z metodą języka haseł przedmiotowych średnio trzykrotnie skraca długość indeksu i znacznie ułatwia czytelnikowi rozeznanie w użytym przez katalogera słownictwie. Została opracowana dla potrzeb Wielkopolskiej Biblioteki Cyfrowej i prawdopodobnie będzie stosowana we wszystkich regionalnych bibliotekach cyfrowych w Polsce

Keyword binding as a method of reducing the length of indexes in library catalogues (based on the experience of Digital Library of Wielkopolska)

This paper presents a relatively simple and cheap method for shortening the subject indexes in library catalogs. The method involves taking a set of several dozen general concepts, characterized by a low semantic awareness barrier. Built around these words are subindexes made up of the words which appear in descriptions containing a particular general concept. The effectiveness of the method was studied by analyzing the content of fragments of subject indexes of the NUKAT central catalog of Polish libraries, the University Library in Poznań and the Library of Congress. Compared with the subject headings language method, this method reduces the length of an index by an average of two-thirds, and makes it significantly easier for readers to navigate the vocabulary used by the cataloger. This method has been developed for the needs of Digital Library of Wielkopolska, and will probably be used in all regional digital libraries in Poland

Defects and oxide ion migration in the solid oxide fuel cell cathode material LaFeO3

LaFeO3, a mixed ionic electronic conductor, is a promising cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC). Key to understanding the electronic and ion conducting properties is the role of defects. In this study ab initio and static lattice methods have been employed to calculate formation energies of the full range of intrinsic defects—vacancies, interstitials, and antisite defects—under oxygen rich and oxygen poor conditions, to establish which, if any, are likely to occur and the effect these will have on the properties of the material. Under oxygen rich conditions, we find that the defect chemistry favors p-type conductivity, in excellent agreement with experiment, but contrary to previous studies, we find that cation vacancies play a crucial role. In oxygen poor conditions O2– vacancies dominate, leading to n-type conductivity. Finally, static lattice methods and density functional theory were used to calculate activation energies of oxide ion migration through this material. Three pathways were investigated between the two inequivalent oxygen sites, O1 and O2; O2–O2, O1–O2, and O1–O1, with O2–O2 giving the lowest activation energy of 0.58 eV, agreeing well with experimental results and previous computational studies

Computational study of native defects and defect migration in wurtzite AlN: an atomistic approach

We derive an empirical, lattice energy consistent interatomic force field model for wurtzite AlN to predict consistently a wide range of physical and defect properties. Using Mott–Littleton techniques, we calculate formation energies of vacancies and interstitials, which show good agreement with previous ab initio calculations at the edge of the band gap. A novel N3− interstitialcy configuration is proposed to be of lower energy than the octahedral-channel-centred counterpart. With the assistance of the QM/MM method, our potential can predict a VBM level (−7.35 eV) comparable to previous experimental measurements. We further investigate the migration mechanisms and energy barriers of the main intrinsic defects. For the vacancy migration, the axial migration barrier is found to be lower than the basal migration barrier, in contrast to previous calculations. Two interstitialcy migration mechanisms for the interstitial defects are proposed, the “knock-out” mechanism for Al interstitial and the “hand-over” mechanism for N interstitialcy defects. The new force field model proposed here demonstrates that the empirical two-body interatomic potential is still effective for the study of defect properties, electronic states, and other extended systems of III/V semiconductors and further can be employed with QM/MM embedded techniques

Bulk and Surface Contributions to Ionisation Potentials of Metal Oxides

Determining the absolute band edge positions in solid materials is crucial for optimising their performance in wide-ranging applications including photocatalysis and electronic devices. However, obtaining absolute energies is challenging, as seen in CeO2, where experimental measurements show substantial discrepancies in the ionisation potential (IP). Here, we have combined several theoretical approaches, from classical electrostatics to quantum mechanics, to elucidate the bulk and surface contributions to the IP of metal oxides. We have determined a theoretical bulk contribution to the IP of stoichiometric CeO2 of only 5.38 eV, while surface orientation results in intrinsic IP variations from 4.2 eV to 8.2 eV. Highly tuneable IPs were also found in TiO2, ZrO2, and HfO2, in which surface polarisation plays a pivotal role in long-range energy level shifting. Our analysis, in addition to rationalising the observed range of experimental results, provides a firm basis for future interpretations of experimental and computational studies of oxide band structures

Crystal electron binding energy and surface work function control of tin dioxide

The work function of a material is commonly used as an intrinsic reference for band alignment; however, it is notoriously susceptible to extrinsic conditions. Following the classification of Bardeen we calculate values for the bulk binding energy of electrons in rutile-structured SnO2 and the effect of the surface on the work function, thus highlighting the role of the surface in determining the energy levels of a material. Furthermore we demonstrate how, through the use of ultrathin heteroepitaxial oxide layers (SiO2, TiO2, PbO2) at the surface, the work function can be tuned to achieve energy levels commensurate with important technological materials. This approach can be extended from transparent conducting oxides to other semiconducting materials

Heterostructures of GaN with SiC and ZnO enhance carrier stability and separation in framework semiconductors

A computational approach, using the density functional theory, is employed to describe the enhanced electron-hole stability and separation in a novel class of semiconducting composite materials, with the so-called double bubble structural motif, which can be used for photocatalytic applications. We examine the double bubble containing SiC mixed with either GaN or ZnO, as well as related motifs that prove to have low formation energies. We find that a 24-atom SiC sodalite cage inside a 96-atom ZnO cage possesses electronic properties that make this material suitable for solar radiation absorption applications. Surprisingly stable, the inverse structure, with ZnO inside SiC, was found to show a large deformation of the double bubble and a strong localisation of the photo-excited electron charge carriers, with the lowest band gap of ca. 2.15 eV of the composite materials considered. The nanoporous nature of these materials could indicate their suitability for thermoelectric applications

Surface structure and solidification morphology of aluminum nanoclusters

Classical molecular dynamics simulation with embedded atom method potential had been performed to investigate the surface structure and solidification morphology of aluminum nanoclusters Aln (n = 256, 604, 1220 and 2048). It is found that Al cluster surfaces are comprised of (111) and (001) crystal planes. (110) crystal plane is not found on Al cluster surfaces in our simulation. On the surfaces of smaller Al clusters (n = 256 and 604), (111) crystal planes are dominant. On larger Al clusters (n = 1220 and 2048), (111) planes are still dominant but (001) planes can not be neglected. Atomic density on cluster (111)/(001) surface is smaller/larger than the corresponding value on bulk surface. Computational analysis on total surface area and surface energies indicates that the total surface energy of an ideal Al nanocluster has the minimum value when (001) planes occupy 25% of the total surface area. We predict that a melted Al cluster will be a truncated octahedron after equilibrium solidification.Comment: 22 pages, 6 figures, 34 reference