118,284 research outputs found
Towards a fuller understanding of selected molecular compounds
No full textThis work is separated into two distinct sections. The first section deals with the analysis by variable temperature single crystal X-ray diffraction of crystalline molecular materials with novel physical properties. The second section details the electron density analysis of selected crystalline compounds using high resolution, low temperature single crystal X-ray diffraction. Chapter 1 provides introduction to X-ray diffraction outlining the theory this work is based on. Chapter 2 introduces the molecular material studies based on materials containing the bis(ethylenedithio)-tetrathiaftilvalene molecule. The aim of these studies was to achieve a greater understanding of the materials and the changes they undergo when exposed to variations in temperature whilst in the crystalline state. These structural changes observed are very minor but have dramatic effects on the electrical properties of the materials studied. It became apparent that the only way to form a full understanding of these materials was to be able to 'see' the electronic configuration of the materials, not just their gross structure. The field of electron density analysis by X- ray diffraction is now a well documented area. Chapter 4 provides an introduction to the field of electron density analysis. Diffraction experiments were conducted on systems of different complexity to investigate this field and these results are reported in Chapter 5. No electron density analyses have been conducted on the molecular materials studied in Chapter 3 as yet, due to the lack of crystals of suitable quality. It was also noted that to fully categorise the nature of the physical changes occurring in these structures that a diffractometer capable of analysing these samples throughout the temperature range of their physical phenomena was needed. An outline for the development of such a diffractometer is detailed in Chapter 6, 'future works'
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Habitat-correlated seed germination behaviour in populations of wood anemone (Anemone nemorosa L.) from northern Italy
No full textAlthough various aspects of the biology of Anemone nemorosa have been examined, few studies present data on seed germination, and even then information tends to be rather contradictory. A. nemorosa L. is a spring-flowering, woodland geophyte, widely distributed across much of Europe. Germination phenology, including embryo development and radicle and shoot emergence, were investigated in one mountain and three lowland populations from northern Italy. Immediately after harvest, seeds were either sown on agar in the laboratory under simulated seasonal temperatures, or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of dispersal, grew under summer conditions in the laboratory and in the wild. However, seeds did not germinate under continuous summer conditions. Radicle emergence in the field was first recorded at the beginning of autumn, when soil temperatures had dropped to c. 15°C in the case of the three lowland populations, and to c. 10°C at the mountain site. Shoot emergence was delayed under natural conditions until late autumn/early winter, when soil temperatures had dropped to c. 10°C in the lowlands and c. 6°C at the mountain site. In the laboratory, a period of cold stratification was required for shoot emergence, and this requirement was more pronounced in the mountain population. Seeds of the mountain population completed embryo development, radicle emergence and shoot emergence at cooler temperatures compared with the lowland populations. These results suggest that germination in A. nemorosa is highly adapted and finely tuned to local climate. We conclude that seeds of A. nemorosa display deep, simple epicotyl, morphophysiogical dormancy, and this is the first report of such dormancy for the genus Anemone. However, the continuous development and growth of embryos from the time of natural dispersal, and the lack of evidence of developmental arrest under natural conditions, suggests that radicles are non-dormant
Langevin dynamics in constant pressure extended systems
No full textThe advantages of performing Langevin dynamics in extended systems are discussed. A simple Langevin dynamics scheme for producing the canonical ensemble is reviewed, and is then extended to the Hoover ensemble. We show that the resulting equations of motion generate the isobaric–isothermal ensemble. The Parrinello–Rahman ensemble is then discussed and we show that despite the presence of intrinsic probability gradients in this system, a Langevin dynamics approach samples the extended phase space in the correct fashion. The implementation of these methods in the ab initio plane wave density functional theory code CASTEP [M. D. Segall, P. L. D. Lindan, M. J. Probert, C. J. Pickard, P. J. Hasnip, S. J. Clarke, and M. C. Payne, J. Phys.: Condens. Matter 14, 2717 (2003)] is demonstrated
Degree for seed dormancy in Hypericum elodes L. (Hypericaceae) is influenced by local climate and mating type
No full textSquare Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Letter from unknown writer to Jesse L. Boyce
No full textLetter to Jesse L. Boyce from unknown author (possibly Jack) about the investigation into the powder magazine located in the Grand Canyon. Some personal news is included in the letter such as the writer's marriage to the daughter of C.A. Taylor, former Supervisor of Cochise County
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A comparative study of post-dispersal embryo development and germination phenology in populations of Anemone nemorosa L. and A. ranunculoides L. from northern Italy
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