| 31. |
- Isaev, E. I., et al.
(författare)
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Phonon related properties of transition metals, their carbides, and nitrides : A first-principles study
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:12
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Forskningsöversikt (refereegranskat)abstract
- Lattice dynamics of body-centered cubic (bcc) V-b-VIb group transition metals (TM), and B1-type monocarbides and mononitrides of IIIb-VIb transition metals are studied by means of first-principles density functional perturbation theory, ultra soft pseudopotentials, and generalized gradient approximation to the exchange-correlation functional. Ground state parameters of transition metals and their compounds are correctly reproduced with the generated ultrasoft pseudopotentials. The calculated phonon spectra of the bcc metals are in excellent agreement with results of inelastic neutron scattering experiments. We show that the superconductivity of transition metal carbides (TMC) and transition metal nitrides (TMN) is related to peculiarities of the phonon spectra, and the anomalies of the spectra are connected to the number of valence electrons in crystals. The calculated electron-phonon interaction constants for TM, TMC, and TMN are in excellent agreement with experimentally determined values. Phonon spectra for a number of monocarbides and mononitrides of transition metals within the cubic NaCl- and hexagonal WC-type structures are predicted. Ideal stoichiometric B1 crystals of ScC, YC, and VC are predicted to be dynamically stable and superconducting materials. We also conclude that YN is a semiconductor.
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| 32. |
- Johansson, Börje
(författare)
-
Diversity and superiority in innovation processes
- 2005
-
Ingår i: MODSIM05. - : Modelling and Simulation Society of Australia and New Zealand Inc. (MSSANZ). - 0975840002 - 9780975840009 ; , s. 1056-1062, s. 1056-1062
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Konferensbidrag (refereegranskat)abstract
- A product group consists of product varieties (phenotypes) that compete for the same customer budget. The paper introduces an approach to identifying separate markets by means of product group (genotype) delineation. The paper contrasts two basic ideas for analysing competition within a product group. The first idea relates to Lancaster's suggestion that every product variety can be identified by its attributes or characteristics (L-model). The second idea relates to the monopolistic-competition model as popularised by Krugman (DS-model). With this latter approach, a product group potentially contains a large set of varieties, where customers as a group have a taste for variety. For each of the two paradigms, the paper presents and compares the process by which novel product varieties are introduced. In the framework of Lancaster, evolution tends to reduce the number of varieties due to development of superior alternatives. The Krugman framework rather predicts an evolution where the number of varieties may increase without limits. The contribution of the paper is to contrast the two perspectives, by comparing the change processes and by assessing the adhering equilibrium solutions. A major question is how these two conflicting perspectives should be interpreted. The paper ends by suggesting a framework that can resolve the conflict between the two perspectives. The L-model provides a theoretical framework for how a separated market can be delineated, whereas the DS-model is more ad hoc in this sense. The prime demarcation aspect is however that in the DS-model diversity of products is generated by customers' taste for variety. This must not be interpreted as a case, in which each customer consumes of all varieties at each point in time. A more reasonable interpretation is that a customer during a time period exercises the taste for variety. In contrast, a customer in the L-model purchases two or several varieties only when there is no product available with the desired combination of attributes. Hence, in the L-model the tendency is towards a smaller set of superior varieties. However, heterogeneity among customers will counteract this tendency and generate product diversity in the L-model. The possibility of a superior product variety for each customer group is inherent in the L-model. One may also observe this phenomenon can associated with so-called technology lock-in effects (Arthur, 1989). In order to understand this, we may consider a product group for which an essential feature is mutual compatibility with other product variants. As some variant gets a large market share, the compatibility aspect will be an important attribute with a decisive role in customers' preference functions. This type of feature is completely absent in the DS-model. In the L-model scale economies explain the dynamics when a superior product increases its market share by replacing established products. Scale economies are the driving force behind competitive exclusion. In the DS-model scale economies provide incentives for firms to develop economies of scope and to continue to expand the number of varieties.
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| 33. |
- Johansson, Börje, et al.
(författare)
-
Regional development and knowledge
- 2019
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Ingår i: Handbook of Regional Growth and Development Theories: Revised and Extended Second Edition. - : Edward Elgar Publishing Ltd.. ; , s. 308-325, s. 308-325
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 34. |
- Karis, O, et al.
(författare)
-
Probing surface states of Cu/Ni thin films using x-ray absorption spectroscopy
- 2001
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:11
-
Tidskriftsartikel (refereegranskat)abstract
- Surface and interface properties of Cu thin films (1–4 monolayers) deposited on Ni(100) have been extracted by means of x-ray absorption spectroscopy and analyzed in combination with ab initio density-functional calculations. An unoccupied Cu surface state is identified in an x-ray absorption spectra and studied as a function of film thickness. Experimental data is supported by calculations of the layer-resolved density of states and the results from this combined theoretical-experimental effort show that the surface state is almost entirely located on the atomic layer closest to the vacuum. Our results also indicate strong hybridization between unoccupied states at the Cu/Ni interface boundary.
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| 35. |
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| 36. |
- Karlsson, Charlie, 1945-, et al.
(författare)
-
Knowledge and Regional Development
- 2009
-
Ingår i: Handbook of Regional Growth and Development Theories. - Cheltenham : Edward Elgar Publishing. - 9781847205063 ; , s. 239-255
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 37. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Exploring monovalent copper compounds with oxygen and hydrogen
- 2012
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:3, s. 686-689
-
Tidskriftsartikel (refereegranskat)abstract
- New important applications of copper metal, e.g., in the areas of hydrogen production, fuel cell operation, and spent nuclear fuel disposal, require accurate knowledge of the physical and chemical properties of stable and metastable copper compounds. Among the copper(I) compounds with oxygen and hydrogen, cuprous oxide Cu(2)O is the only one stable and the best studied. Other such compounds are less known (CuH) or totally unknown (CuOH) due to their instability relative to the oxide. Here we combine quantum-mechanical calculations with experimental studies to search for possible compounds of monovalent copper. Cuprous hydride (CuH) and cuprous hydroxide (CuOH) are proved to exist in solid form. We establish the chemical and physical properties of these compounds, thereby filling the existing gaps in our understanding of hydrogen- and oxygen-related phenomena in Cu metal.
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| 38. |
- Li, Wei, et al.
(författare)
-
Generalized stacking fault energy of gamma-Fe
- 2016
-
Ingår i: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 96:6, s. 524-541
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the generalized stacking fault energy ( [GRAPHICS] -surface) of paramagnetic [GRAPHICS] -Fe as a function of temperature. At static condition, the face-centred cubic (fcc) lattice is thermodynamically unstable with respect to the hexagonal close-packed lattice, resulting in a negative intrinsic stacking fault energy (ISF). However, the unstable stacking fault energy (USF), representing the energy barrier along the [GRAPHICS] -surface connecting the ideal fcc and the intrinsic stacking fault positions, is large and positive. The ISF is calculated to have a strong positive temperature coefficient, while the USF decreases monotonously with temperature. According to the recent plasticity theory, the overall effect of temperature is to move paramagnetic fcc Fe from the stacking fault formation regime ( [GRAPHICS] K) towards maximum twinning ( [GRAPHICS] K) and finally to a dominating full-slip regime ( [GRAPHICS] K). Our predictions are discussed in connection with the available experimental observations.
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| 39. |
- Loa, I, et al.
(författare)
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Lattice Dynamics and Superconductivity in Cerium at High Pressure
- 2012
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 108:4, s. 045502-
-
Tidskriftsartikel (refereegranskat)abstract
- We have measured phonon dispersion relations of the high-pressure phase cerium-oC(4) (alpha phase with the alpha-uranium crystal structure) at 6.5 GPa by using inelastic x-ray scattering. Pronounced phonon anomalies are observed, which are remarkably similar to those of alpha-U. First-principles electronic structure calculations reproduce the anomalies and allow us to identify strong electron-phonon coupling as their origin. At the low-pressure end of its stability range, Ce-oC4 is on the verge of a lattice-dynamical instability and possibly a charge density wave. The superconducting transition temperatures of the fcc, oC4, and mC4 phases of Ce have been calculated, and the superconductivity observed experimentally by Wittig and Probst is attributed to the oC4 phase.
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| 40. |
- Mattesini, M., et al.
(författare)
-
Electronic structure and optical properties of solid C-60
- 2009
-
Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 404:12-13, s. 1776-1780
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and the optical properties of face-centered-cubic C-60 have been investigated by using an all-electron full-potential method. Our ab initio results show that the imaginary dielectric function for high-energy values looks very similar to that of graphite, revealing close electronic structure similarities between the two systems. We have also identified the origin of different peaks in the dielectric function of fullerene by means of the calculated electronic density of states. The computed optical spectrum compares fairly well with the available experimental data for the Vis-UV absorption spectrum of solid C-60.
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