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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Studies and applications of molecular beam epitaxy
No full textSingle crystal Nb samples have been prepared with stepped surfaces to investigate the effect of surface steps on nucleation and growth in molecular beam epitaxy (MBE). Studies of the critical temperature between two-dimensional and three-dimensional growth are completed by means of reflection high energy diffraction. These critical temperatures are observed to depend on the density of surfaces steps as well as the deposition rate. A perturbed step-flow-growth model is formulated and applied to the results to determine a critical cluster size for growth. The analysis reveals that the growth is dominated by mobility changes associated with the formation of adatom pairs, and that the densities of adatoms on the terraces at such critical conditions are typically as low as 10\sp{-3}. Activation energies for surface diffusion and cluster binding energies are determined.In addition to the experiments on growth and nucleation, studies of Dy/Lu superlattices, Dy/Lu and Er/Lu films synthesized by methods of MBE are undertaken. These experiments investigate the effect of epitaxial strain, in particular compression, on the magnetic properties of rare earth metals. The structural and magnetic properties are characterized using x-ray diffraction analysis, bulk magnetization measurement and elastic neutron scattering method. Long range magnetic order is observed in the Dy/Lu superlattices probably owing to an RKKY-like exchange mechanism. The rare earth metal samples exhibit ferromagnetic transitions at temperatures that are very enhanced seen over that seen in bulk. This behavior is the opposite of that reported for Dy/Y and Er/Y samples studied in previous experiments. In these systems the ferromagnetic transition is completely suppressed. The difference is undoubtedly caused by the opposite types of epitaxial strain in these two cases.Made available in DSpace on 2011-05-07T13:27:23Z (GMT). No. of bitstreams: 2
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Previous issue date: 1992Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:54:59Z
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Heavy rare earth superlattices: Epitaxial growth, structure, and magnetic properties
No full textSingle crystal superlattices of heavy rare earth metals with yttrium have been synthesized by methods of molecular beam epitaxy developed in this thesis research. Studies of the growth behavior of hcp rare earth metals on bcc transition metal (110) and (211) surfaces, using electron and x-ray scattering probes, are presented. The structural and magnetic properties of Dy-Y and Er-Y superlattices oriented on the (0002) axis are also characterized using x-ray diffraction analysis, bulk magnetization measurement and elastic neutron scattering method.Epitaxial growth properties of rare earth metals on bcc metal surfaces are anisotropic. Layer-by-layer growth mode is observed for rare earth (0002) planes grown on bcc (110) surfaces. An epitaxial relationship of the Nishiyama-Wasserman type is confirmed for this orientation. Rare earth (1012) planes can be grown tilted on (211) planes of bcc metals. The interface so formed is an asymmetrical coherent tilt boundary. The tilt angles can be predicted by a geometrical model based on the requirement of interfacial coherence with zero long-range strain. One-dimensional pseudomorphism at monolayer coverage, and subsequent dislocation gliding, with a resulting break of surface symmetry for rare earth layers, are also identified. The surface structure of the rare earth (1012) layer is found to be temperature dependent; within a growth temperature window the surface possesses a coherent double-atomic-step structure. Applications of the spontaneous tilt in the synthesis of new magnetic structures including tilted superlattices and atomic chains, are discussed."Long-range magnetic order is observed in Dy-Y and Er-Y superlattices, and is explained in terms of the RKKY exchange mechanism. The primary differences between the magnetic behavior of superlattices and their constituent magnetic components are that ferromagnetic transitions at low temperature are suppressed. This change is caused by lattice ""clamping"" to the substrate, which modifies the available magnetoelastic energy and hence also the magnetic phase diagram."Made available in DSpace on 2011-05-07T12:03:36Z (GMT). No. of bitstreams: 2
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Previous issue date: 1990Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:36:06Z
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Atomic transport mechanisms in irradiated copper(3)-gold alloy
No full textThe properties of radiation-induced defects were investigated by examining the radiation-enhanced diffusion and radiation-induced order-disorder kinetics in the ordered intermetallic alloy Cu\sb3Au.Direct measurements of thermal and radiation-enhanced diffusion on MBE grown Cu\sb3Au films were performed for the first time both above and below the order-disorder transition temperature. Ni and Pd impurity tracers were employed to simulate the diffusion of Cu and Au respectively. Activation enthalpies of diffusion were obtained for the two tracers above and below the ordering temperature. Both diffusion coefficients were found to decrease significantly on ordering, by factors of two and four for thermal and radiation-enhanced diffusion respectively. The results indicate that interstitial atoms do not contribute to atomic transport in irradiated Cu\sb3Au.Radiation-induced order-disorder was studied under He and Ne irradiation. At low temperatures, T 250\sp\circC, the order parameter, S, decayed exponentially with fluence owing to atomic mixing in displacement cascades. At high temperatures, T 300\sp\circC, S quickly reached a steady state indicating a dynamic balance between ordering and disordering processes. The studies revealed the surprising result that the rate of disordering increases strongly with temperature near the transition temperature and that this was due to disordering by vacancy fluxes to sinks.Recovery of order in irradiated and unirradiated systems was also investigated. From measurements of reordering rates in the irradiated and unirradiated system, the defect concentrations in Cu\sb3Au under the He irradiations were obtained for the first time. The results revealed that the vacancy concentration is {\sim}10\sp{-9} and the interstitial concentration is {\sim}10\sp{-4}. The results also suggests that interstitials are clustered and immobile, explaining why they do not contribute to the diffusion process. Using measured defect concentrations from the ordering experiments, D\sb{\rm RED} could be predicted to within a factor of three of the measured values.Made available in DSpace on 2011-05-07T14:21:49Z (GMT). No. of bitstreams: 2
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Previous issue date: 1996Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T15:05:53Z
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Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Novel magnetic behavior in heavy rare earth superlattices
No full textStructural and magnetic properties of heavy rare earth films and superlattices synthesized by molecular beam epitaxy are investigated. Epitaxial films of rare earth metals, and superlattices of rare earths with Y interlayers, are grown along different hcp orientations using novel techniques developed specifically for this thesis research. Interesting growth patterns and surface reconstructions are observed, particularly on the a and b faces of the hcp material. Magnetic behavior is explored by neutron diffraction and SQUID magnetometry experiments.The spatial form of the exchange interaction is explored by probing the dependence of magnetic coherence on crystal growth orientation. The results reveal that Dy/Y and Gd/Y superlattices grown along the a and b axis exhibit weak magnetic coupling between successive magnetic layers, even for nonmagnetic spacers as thin as 20 A. Previous studies of the c-axis materials established that long range magnetic order occurs even through Y spacer layers as thick as 120 A. This measured anisotropy between behavior along the c-axis and perpendicular to it, is over a factor ten in both the coupling strength and the range. The strongly anisotropic coupling behavior is shown to have its origin in nearly 2-dimensional nesting features of the rare earth Fermi surfaces. Nesting along the c-axis gives rise to long range exchange interactions along the c-axis, and the lack of nesting perpendicular to the c-axis leaves a rapid exponential decay of the exchange with spin separation.Magnetic phases of epitaxial Dy films are examined as a function of epitaxial strain, growth orientation, temperature and field. The analysis of the observed anisotropic magnetoelastic behavior reveals the detailed energy balance in the Dy system.The observed spin configurations in thin Gd films show that the magnetocrystalline anisotropy of bulk Gd is substantially modified in the films. This in turn gives insight into the origin of the unusual spin reorientation transition in Gd.Magnetic order in buried monolayers of Gd-Y alloys is studied in order to explore the effects of both the reduced physical dimensions and the modified effective exchange interaction on phase transitions. No long range order occurs in the monolayer system even for nearly full Gd monolayer coverage. A spin-glass transition is observed instead. The zero field susceptibility exhibits a divergence at low temperatures. The analysis of the magnetic states reveals unusual scaling behavior and a dimensionality cross-over in the monolayer system.Made available in DSpace on 2011-05-07T12:19:28Z (GMT). No. of bitstreams: 2
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Previous issue date: 1992Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:39:37Z
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Studies of ordering on surfaces and in superlattices by molecular beam epitaxy
No full textMolecular beam epitaxy, MBE, was used in two different ways to study ordering on atomic scales. In one application the ordering of close packed planes into various stacking sequences was investigated by periodically alternating growth of Ir and Ru to produce single crystal superlattices. In addition, a novel probe of the kinetics by which a surface of Cu\sb3Au re-orders was developed. By growing a disordered layer onto a well ordered surface, the kinetics of ordering in layers of almost arbitrarily small thickness can be studied. By eliminating the need to quench the sample this procedure removes the effects of the re-ordering of the bulk and allows for study at temperatures far below the transition temperature.Single crystal Ir-Ru superlattices have been grown by MBE with their close packed planes perpendicular to the growth direction. The phase diagram which plots structure dependance on the number of Ir monolayers and Ru monolayers in a superlattice has been investigated. The diagram is divided into four regions corresponding to the phases of the superlattices. The types of phases are: bicrystalline, fcc, hcp, and polytype superlattices, determined for each superlattice from qualitative x-ray diffraction features. More detailed computer modeling was also employed. Composition profiles and stacking sequences were determined by means of two distinct x-ray diffraction scans. These simulations make clear that detailed modeling is necessary to fully determine the stacking sequences. The deduction that bicrystal stacking sequences occur has been confirmed.In a conventional experiment, the order-disorder transition of the (111) surface of Cu\sb3Au was studied by means of RHEED intensities. The order parameter was found to go to zero continuously at a temperature equal to that of the discontinuous bulk transition, within experimental uncertainty.A novel kinetic experiment was performed to examine re-ordering of (111) Cu\sb3Au adlayers. It was found that a surface layer re-orders independently on a sublayer frozen by its slower bulk kinetics in its initial disordered state. This re-ordering occurs in two stages. Near the critical temperature it achieves approximately the same degree of order as surfaces under which the subsurface layers have equilibrium order.Made available in DSpace on 2011-05-07T13:58:15Z (GMT). No. of bitstreams: 2
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Previous issue date: 1991Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T15:01:25Z
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Studies of nucleation, coherent tilt and surface phase transitions by molecular beam epitaxy
No full textHigh-quality single crystals and alloys have been synthesized by molecular beam epitaxy (MBE). These crystals were employed to study the nucleation and strain relief processes during epitaxial growth, as well as phenomena of surface order-disorder transformations.Six distinct orientations of high quality hcp titanium single crystals were prepared on freshly grown bcc transition metals on sapphire substrates. Four different nucleation mechanisms were found to select the eventual crystal orientations. In one special case, the growth of tilted Ti (1012) is identified with nucleation at the step-edges rather than on the terraces of the stepped Ta (211) surface.Nucleation and growth of Au on alkali halides also was investigated. It is found that the growth morphology and the critical thickness at which gold clusters coalesce depend strongly on the kinetic factors such as the growth temperature and deposition rate R. It is observed that the critical thickness h\sb{\rm c} is proportional to R\sp{1/6}. The result is explained in terms of phenomenological theory. This led to estimate the activation energy for adatom diffusion of about 0.78 eV, in good agreement with the global behavior described earlier by Yang and Flynn.By preparing epitaxial layers of various hcp metals it has been possible to explore the anelastic behavior required to grow epitaxial crystals with atomic planes which are tilted away from principal low-index planes, explicit requirements for coherent tilt are formulated using the (211) planes of bcc transition metals as templates, as described earlier by Du and Flynn. fcc transition metals have been successfully prepared in the (110) orientation on the same bcc substrates with a predicable and tunable tilt up to 7\sp\circ. The established principles are further adapted to explain the coherent tilt of bcc metals grown on (1012) sapphire substrates.Order-disorder transitions at the (110) surfaces of MBE grown Cu\sb3Au film have been studied using reflection high energy electron diffraction (RHEED). The bulk crystal undergoes a first order transformation at 390\sp\circC. It is observed that the (110) Cu\sb3Au exhibits an apparently continuous order-disorder transition, close to that predicted by mean field theory. This is the first confirmation of earlier mean field treatments of the perturbed order near a crystal surface. The kinetics of the surface ordering process also were monitored by RHEED, after initial deposition of several monolayers of disordered Cu\sb3Au onto the ordered Cu\sb3Au template. The kinetic measurements reveal that the surface ordering occurs in two stages. One, fast process, might correspond to the initial nucleation and growth of ordered domains. The other, slow process, might correspond to the coarsening of the domains. The measured surface activation energies are relatively small compared to the bulk value.Made available in DSpace on 2011-05-07T12:37:29Z (GMT). No. of bitstreams: 2
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Previous issue date: 1992Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:43:29Z
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