Exchange-correlation potentials for inhomogeneous electron systems in two dimensions from exact diagonalization: comparison with the local-spin-density approximation

We consider electronic exchange and correlation effects in density-functional calculations of two-dimensional systems. Starting from wave function calculations of total energies and electron densities of inhomogeneous model systems, we derive corresponding exchange-correlation potentials and energies. We compare these with predictions of the local-spin-density approximation and discuss its accuracy. Our data will be useful as reference data in testing, comparing and parametrizing exchange and correlation functionals for two-dimensional electronic systems.Comment: Submitted to Physical Review B on January 3, 2012. Second revised version submitted on April 13, 201

Cross-border regional innovation system integration: an analytical framework

The importance of inter-regional cooperation and innovation are widely accepted in the development rhetoric of the European Union. The highlighted importance of both themes in the context of borderlands has recently led to the coining of a new concept, cross-border regional innovation system.However, little attention has been given to the empirical analysis of the concept. This paper suggests a framework for empirically validating the concept by examining the levels of integration between cross-border regions. The outcome is a proposed framework can be operationalized by measurable indicators of cross-border cooperation in a regional innovation system setting. The framework was further tested with illustrative empirical cases that demonstrate its feasibility

Energetics of positron states trapped at vacancies in solids

We report a computational first-principles study of positron trapping at vacancy defects in metals and semiconductors. The main emphasis is on the energetics of the trapping process including the interplay between the positron state and the defect's ionic structure and on the ensuing annihilation characteristics of the trapped state. For vacancies in covalent semiconductors the ion relaxation is a crucial part of the positron trapping process enabling the localization of the positron state. However, positron trapping does not strongly affect the characteristic features of the electronic structure, e.g., the ionization levels change only moderately. Also in the case of metal vacancies the positron-induced ion relaxation has a noticeable effect on the calculated positron lifetime and momentum distribution of annihilating electron-positron pairs.Comment: Submitted to Physical Review B on 17 April 2007. Revised version submitted on 6 July 200

Peer review assessment of originality in tourism journals: critical perspective of key gatekeepers

Originality is an essential element of academic research and the peer review system plays a key gatekeeping role in its acceptance. However, there is no consensus as to the precise definition of the concept, its measurement nor the importance attached to it. Primary data from 26 interviews with editors or editorial board members of top ranking tourism journals inform a discussion of the nuanced understanding of the concept and of how different levels of originality (radical vs. incremental), among other peer review assessment criteria, influence tourism publication. Finally, the main challenges relating to recognising originality in the peer review process are identified leading to recommendations for improvements to how originality is assessed

Modeling the momentum distributions of annihilating electron-positron pairs in solids

Measuring the Doppler broadening of the positron annihilation radiation or the angular correlation between the two annihilation gamma quanta reflects the momentum distribution of electrons seen by positrons in the material.Vacancy-type defects in solids localize positrons and the measured spectra are sensitive to the detailed chemical and geometric environments of the defects. However, the measured information is indirect and when using it in defect identification comparisons with theoretically predicted spectra is indispensable. In this article we present a computational scheme for calculating momentum distributions of electron-positron pairs annihilating in solids. Valence electron states and their interaction with ion cores are described using the all-electron projector augmented-wave method, and atomic orbitals are used to describe the core states. We apply our numerical scheme to selected systems and compare three different enhancement (electron-positron correlation) schemes previously used in the calculation of momentum distributions of annihilating electron-positron pairs within the density-functional theory. We show that the use of a state-dependent enhancement scheme leads to better results than a position-dependent enhancement factor in the case of ratios of Doppler spectra between different systems. Further, we demonstrate the applicability of our scheme for studying vacancy-type defects in metals and semiconductors. Especially we study the effect of forces due to a positron localized at a vacancy-type defect on the ionic relaxations.Comment: Submitted to Physical Review B on September 1 2005. Revised manuscript submitted on November 14 200

High frequency mechanical excitation of a silicon nanostring with piezoelectric aluminum nitride layers

A strong trend for quantum based technologies and applications follows the avenue of combining different platforms to exploit their complementary technological and functional advantages. Micro and nano-mechanical devices are particularly suitable for hybrid integration due to the easiness of fabrication at multi-scales and their pervasive coupling with electrons and photons. Here, we report on a nanomechanical technological platform where a silicon chip is combined with an aluminum nitride layer. Exploiting the AlN piezoelectricity, Surface Acoustic Waves are injected in the Si layer where the material has been localy patterned and etched to form a suspended nanostring. Characterizing the nanostring vertical displacement induced by the SAW, we found an external excitation peak efficiency in excess of 500 pm/V at 1 GHz mechanical frequency. Exploiting the long term expertise in silicon photonic and electronic devices as well as the SAW robustness and versatility, our technological platform represents a strong candidate for hybrid quantum systems

Numerical and experimental verification of a theoretical model of ripple formation in ice growth under supercooled water film flow

Little is known about morphological instability of a solidification front during the crystal growth of a thin film of flowing supercooled liquid with a free surface: for example, the ring-like ripples on the surface of icicles. The length scale of the ripples is nearly 1 cm. Two theoretical models for the ripple formation mechanism have been proposed. However, these models lead to quite different results because of differences in the boundary conditions at the solid-liquid interface and liquid-air surface. The validity of the assumption used in the two models is numerically investigated and some of the theoretical predictions are compared with experiments.Comment: 30 pages, 9 figure

Phonological development of Finnish speaking children at 3;6 and associations to previous and simultaneous lexical ability

Previous studies of Finnish children's phonological development focus mainly on children under 2;0. Earlier findings have suggested that phonological and lexical development are strongly associated at an early age. However, less is known about the longitudinal association. This study describes the phonological skills of Finnish-speaking children at 3;6 and compares them with early lexicon size at 2;0 and lexical ability at 3;6 (N = 67). The children's phonological development was measured using The Finnish Phonology Test. Lexical development was evaluated using the Finnish, long-form version of the Communicative Development Inventory at 2;0 and the Boston naming test at 3;6 At 3;6, all children mastered the vowels and diphthongs fully, and most of the children also mastered the consonants, with the exception of the phonemes/d/and/r/. Phonotactic skills had also been acquired well at this group level, although the word-medial and, especially, word-initial consonant clusters were still challenging. The percentage of phonemes correct was 95. Both paradigmatic and phonotactic skills at 3;6 were significantly associated with lexicon size at 2;0. In addition phonotactic skills correlated with naming ability at 3;6. Lexical development at 2;0 explained 21% of the variance in the phonological development at 3;6, whereas, the explaining value of simultaneous lexical skill was limited (9%). Present findings propose that associations between lexical and phonological skills weaken as phonological skills become more honed.Peer reviewe

Implementing a sectional scheme for early aerosol growth from new particle formation in the Norwegian Earth System Model v2 : comparison to observations and climate impacts

Aerosol-cloud interactions contribute to a large portion of the spread in estimates of climate forcing, climate sensitivity and future projections. An important part of this uncertainty is how much new particle formation (NPF) contributes to cloud condensation nuclei (CCN) and, furthermore, how this changes with changes in anthropogenic emissions. Incorporating NPF and early growth in Earth system models (ESMs) is, however, challenging due to uncertain parameters (e.g. participating vapours), structural issues (numerical description of growth from similar to 1 to similar to 100 nm) and the large scale of an ESM grid compared to the NPF scale. A common approach in ESMs is to represent the particle size distribution by a certain number of log-normal modes. Sectional schemes, on the other hand, in which the size distribution is represented by bins, are considered closer to first principles because they do not make an a priori assumption about the size distribution. In order to improve the representation of early growth, we have implemented a sectional scheme for the smallest particles (5-39.6 nm diameter) in the Norwegian Earth System Model (NorESM), feeding particles into the original aerosol scheme. This is, to our knowledge, the first time such an approach has been tried. We find that including the sectional scheme for early growth improves the aerosol number concentration in the model when comparing against observations, particularly in the 50-100 nm diameter range. Furthermore, we find that the model with the sectional scheme produces much fewer particles than the original scheme in polluted regions, while it produces more in remote regions and the free troposphere, indicating a potential impact on the estimated aerosol forcing. Finally, we analyse the effect on cloud-aerosol interactions and find that the effect of changes in NPF efficiency on clouds is highly heterogeneous in space. While in remote regions, more efficient NPF leads to higher cloud droplet number concentration (CDNC), in polluted regions the opposite is in fact the case.Peer reviewe

Scaling in the correlation energies of two-dimensional artificial atoms

We find an unexpected scaling in the correlation energy of artificial atoms, i.e., harmonically confined two-dimensional quantum dots. The scaling relation is found through extensive numerical examinations including Hartree-Fock, variational quantum Monte Carlo, density-functional, and full configuration-interaction calculations. We show that the correlation energy, i.e., the true ground-state total energy subtracted by the Hartree-Fock total energy, follows a simple function of the Coulomb energy, confimenent strength and, the number of electrons. We find an analytic expression for this function, as well as for the correlation energy per particle and for the ratio between the correlation and total energies. Our tests for independent diffusion Monte Carlo and coupled-cluster results for quantum dots -- including open-shell data -- confirm the generality of the obtained scaling. As the scaling is also well applicable to $\gtrsim$ 100 electrons, our results give interesting prospects for the development of correlation functionals within density-functional theory.Comment: Accepted to Journal of Physics: Condensed Matte