4,986 research outputs found

    Multi-Layer Potfit: An Accurate Potential Representation for Efficient High-Dimensional Quantum Dynamics

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    The multi-layer multi-configuration time-dependent Hartree method (ML-MCTDH) is a highly efficient scheme for studying the dynamics of high-dimensional quantum systems. Its use is greatly facilitated if the Hamiltonian of the system possesses a particular structure through which the multi-dimensional matrix elements can be computed efficiently. In the field of quantum molecular dynamics, the effective interaction between the atoms is often described by potential energy surfaces (PES), and it is necessary to fit such PES into the desired structure. For high-dimensional systems, the current approaches for this fitting process either lead to fits that are too large to be practical, or their accuracy is difficult to predict and control. This article introduces multi-layer Potfit (MLPF), a novel fitting scheme that results in a PES representation in the hierarchical tensor (HT) format. The scheme is based on the hierarchical singular value decomposition, which can yield a near-optimal fit and give strict bounds for the obtained accuracy. Here, a recursive scheme for using the HT-format PES within ML-MCTDH is derived, and theoretical estimates as well as a computational example show that the use of MLPF can reduce the numerical effort for ML-MCTDH by orders of magnitude, compared to the traditionally used Potfit representation of the PES. Moreover, it is shown that MLPF is especially beneficial for high-accuracy PES representations, and it turns out that MLPF leads to computational savings already for comparatively small systems with just four modes.Comment: Copyright (2014) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physic

    ICT loves agglomeration The urban impacts of ICT in the Netherlands

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    Information and Communication Technology (ICT) has had an undeniable impact on our society. Some people argue that technology has projected us onto a new wave of social and cultural change. Nevertheless, despite the growth of technology and the social significance of its applications, we have only a poor grasp of its actual impact on the use of physical space. The key question addressed in this paper is therefore: how will ICT influence the spatial-economic patterns of business activities in the Netherlands? In offering answers to this question, the paper develops a conceptual framework that distinguishes two roles of ICT in spatial-economic development: that of a ‘motor’, enhancing productivity and encourages the development of economic sectors, and that of an ‘enabler’ (of e-work, e-commerce and e-business), which may lead households and firms to adopt a different attitude to space requirements. The paper is based on a thorough survey of the current literature on the subject, the results of a recent survey of ICT’s impact on society, and original empirical research into specific factors such as ICT companies’ location preferences and the willingness of knowledge workers to commute. The paper presents an assessment of the usefulness of these concepts in terms of the Dutch situation, both today and in the future. We conclude that Information and Communication Technology has not yet had a marked visible impact on the use of space. To the contrary, despite predictions neither Dutch companies (particularly those in the ICT sector) nor knowledge workers display any unusual degree of mobility at the local or regional s 2perfect substitute for ‘traditional’ behavioural patterns. Nevertheless, there are clear indications that the ‘spatial order’ of the Netherlands is likely to change. Although it is likely that ICT will consolidate underlying spatial patterns, on the regional aggregate changes are occurring within those patterns. While (inner) cities have traditionally been the breeding ground for new ICT companies, this function has now largely been taken over by the outlying city regions, in which multiple clusters of economic activity are emerging: a process of ‘splintering urbanism’. However, despite this regionalized pattern of deconcentration, the traditional city centres continue to fulfil a number of essential functions. These centres remain the meeting places, and the shopping and entertainment centres for businesses and households (the ‘Consumer City’). In the processes of deconcentration and multimodality, ICT should be seen to play an important facilitating and strengthening role. cale. ICT does not function as a 2perfect substitute for ‘traditional’ behavioural patterns. Nevertheless, there are clear indications that the ‘spatial order’ of the Netherlands is likely to change. Although it is likely that ICT will consolidate underlying spatial patterns, on the regional aggregate changes are occurring within those patterns. While (inner) cities have traditionally been the breeding ground for new ICT companies, this function has now largely been taken over by the outlying city regions, in which multiple clusters of economic activity are emerging: a process of ‘splintering urbanism’. However, despite this regionalized pattern of deconcentration, the traditional city centres continue to fulfil a number of essential functions. These centres remain the meeting places, and the shopping and entertainment centres for businesses and households (the ‘Consumer City’). In the processes of deconcentration and multimodality, ICT should be seen to play an important facilitating and strengthening role.

    The knowledge economy and Dutch cities

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    How can cities and metropolitan regions remain prosperous and competitive in a rapidly changing economy? In our paper we argue that ‘the knowledge economy’ offers perspectives for growth and added value creation. The paper clarifies what elements the knowledge economy actually consists of, how it can be measured in statistical indicators, in which regions and cities in the Netherlands the knowledge economy has its most significant imprints and what statistical association there is between these regions and cities and relatively good economic performance of firms. We test two contrasting hypotheses often heard in the international literature. The current embedding of knowledge externalities in endogenous economic growth theory have led to important contributions that stress the urban character knowledge transmission in particular. The reasoning is that if knowledge spillovers and –externalities are important to growth and innovation, they should be more easily identified in cities where many people are concentrated into a relatively small geographic space so that knowledge can be transmitted between them more easily. Much recent research indeed finds a limited extent of spatial spillovers and a large degree of local clustering. Alternatively, a large body of literature on Western spatial configurations of innovation and high-technology firms predominantly stresses the supposed ‘urban field’ character of firm performance: location and agglomeration aspects do not seem to have a systematic impact on the distribution of innovative and growth inducing activities over space. We test the urban hypothesis using spatial econometric modeling techniques. On the one hand, the fact that a distance squared distance weight matrix in spatial lag estimations fits the performance data best in relation to knowledge economy factors indicates that spatial relations are limited and urban fixed. On the other hand, the significance of several spatial regimes though (especially those of the Randstad core region, the so-called intermediate zone and medium-sized cities) indicates that the urban structure related to the knowledge economy and economic performance is not straightforward hierarchical (largest cities are not the relatively most attached to the knowledge economy). Both hypotheses (urban and non-urban) are too extreme to fit the Dutch situation. We also conclude that the locational attributes of the factor ‘knowledge workers’ are much more significantly related to economic growth and added value (in practically all specifications over regimes and spatial lag estimations) than the R&D-based innovation input factor. This questions Dutch policy initiatives that mainly focus on R&D as stimulator of the ‘knowledge economy’.

    Whole genome sequencing and microsatellite analysis of the Plasmodium falciparum E5 NF54 strain show that the var, rifin and stevor gene families follow Mendelian inheritance

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    Background: Plasmodium falciparum exhibits a high degree of inter-isolate genetic diversity in its variant surface antigen (VSA) families: P. falciparum erythrocyte membrane protein 1, repetitive interspersed family (RIFIN) and subtelomeric variable open reading frame (STEVOR). The role of recombination for the generation of this diversity is a subject of ongoing research. Here the genome of E5, a sibling of the 3D7 genome strain is presented. Short and long read whole genome sequencing (WGS) techniques (Ilumina, Pacific Bioscience) and a set of 84 microsatellites (MS) were employed to characterize the 3D7 and non-3D7 parts of the E5 genome. This is the first time that VSA genes in sibling parasites were analysed with long read sequencing technology. Results: Of the 5733 E5 genes only 278 genes, mostly var and rifin/stevor genes, had no orthologues in the 3D7 genome. WGS and MS analysis revealed that chromosomal crossovers occurred at a rate of 0–3 per chromosome. var, stevor and rifin genes were inherited within the respective non-3D7 or 3D7 chromosomal context. 54 of the 84 MS PCR fragments correctly identified the respective MS as 3D7- or non-3D7 and this correlated with var and rifin/stevor gene inheritance in the adjacent chromosomal regions. E5 had 61 var and 189 rifin/stevor genes. One large non-chromosomal recombination event resulted in a new var gene on chromosome 14. The remainder of the E5 3D7-type subtelomeric and central regions were identical to 3D7. Conclusions: The data show that the rifin/stevor and var gene families represent the most diverse compartments of the P. falciparum genome but that the majority of var genes are inherited without alterations within their respective parental chromosomal context. Furthermore, MS genotyping with 54 MS can successfully distinguish between two sibling progeny of a natural P. falciparum cross and thus can be used to investigate identity by descent in field isolates

    The Exact Wavefunction Factorization of a Vibronic Coupling System

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    We investigate the exact wavefunction as a single product of electronic and nuclear wavefunction for a model conical intersection system. Exact factorized spiky potentials and nodeless nuclear wavefunctions are found. The exact factorized potential preserves the symmetry breaking effect when the coupling mode is present. Additionally the nodeless wavefunctions are found to be closely related to the adiabatic nuclear eigenfunctions. This phenomenon holds even for the regime where the non-adiabatic coupling is relevant, and sheds light on the relation between the exact wavefunction factorization and the adiabatic approximation

    ICT and Productivity - relations and dynamics in a spatial context

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    The strong emergence of ICT in the past decades was accompanied by much research on the potential productivity boosting qualities of ICT: high productivity growth was expected. However, empirical evidence on the productivity impact of ICT stayed behind: the Solow paradox. Since then analytical steps were made by using alternative indicators for both ICT adoption and productivity and including longer time periods, distinctions in types of economic activities and adding micro level and firm specific characteristics like size, age, and intensity of innovation. Moreover, ICT was linked to network relations including externalities. These adaptations led to outcomes in favour of a positive relation between the use of ICT and productivity. However, most convincing in this debate was the finding that the effects of ICT on economic performance should be analysed from a perspective which, besides ICT, includes changes in knowledge and organisations. Knowledge is defined here broadly and includes both codified and tacit knowledge. In this paper we focus on the trinity ‘ICT, knowledge and organization’ and add the regional dimension to this. Based on economic literature our hypothesis is that regions where firms increasingly use ICT show a stronger growth of added value and productivity. This positive relationship is, however, co-determined by changes in the broadly defined knowledge level. The use of ICT by firms is analysed at different levels of urbanism in the Netherlands. Most central is the distinction between the metropolitan Randstad, the intermediate zone and the national periphery. By this regional distinction the debate on the centrifugal and centripetal effects of ICT (the death of distance) is included. The empirical measurement as such is based on the low spatial scale of 496 municipalities.

    What When Space Matters Little For Firm Productivity? A multilevel analysis of localised knowledge externalities

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    This paper contributes to the debate on localized knowledge externalities as potential source for firm productivity gains. We apply multilevel analysis to link firm productivity (and growth) to knowledge intensive spatial contexts in the Netherlands. If localized knowledge externalities are important, then firms are hypothesised to co-locate in order to capitalize on each other's knowledge stocks. We conceptualise the regional knowledge base by three dimensions: local 'research and development' intensity, local 'innovativeness', and the characterization of locations by a ‘knowledge workers’ dimension (based on ICT use, educational level, communicative and creative skills). Controlling for firm's heterogeneity, we find a relatively small spatial effect: regional characteristics contribute for only a few percents to firm productivity. The regional intensity of 'innovation' most significantly contributes to this effect. We do not find a contextual spatial effect for productivity growth. These results suggest that the territorial dimension of knowledge externalities should not be exaggerated.productivity, multilevel analysis, localized knowledge externalities, Netherlands

    Reliability of a Fully Automated Interpretation of

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    Background: Analysis of γ-H2AX foci is a promising approach to evaluate exercise-induced DNA damage. However, baseline levels and day-to-day variability of γ-H2AX foci have not been investigated in healthy subjects at rest. Methods: Blood was taken from eight moderately trained healthy males (29 ± 3 yrs, 1.84 ± 0.03 m, and 85 ± 6 kg) at two separate days (M1/M2) after 24-hour exercise cessation. Number of γ-H2AX foci per 100 lymphocytes (N), number of foci per affected lymphocyte (NAL), percentage of affected lymphocytes (PAL), and diameter (D) of γ-H2AX foci were analyzed (mean ± SD). Differences between M1 and M2 were analyzed using paired t-tests (α = 0.05). Day-to-day variability was evaluated by calculating the coefficients of variation (CV%), bias, and limits of agreement (LoA). Results: There were no statistically significant differences between M1 (N: 7.6 ± 4.4, NAL: 1.2 ± 0.2, PAL: 5.9 ± 2.6%, and D: 0.63 ± 0.07) and M2 (N: 8.4 ± 4.6, NAL: 1.3 ± 0.1, PAL: 6.9 ± 4.2%, and D: 0.66 ± 0.06). CV was calculated to be 98.5% (N), 88.9% (PAL), 11.3% (NAL), and 8.0% (D). Bias (LoA) was 0.75 (-15.2/13.7), -0.02 (-0.36/0.33), -1.0 (-11.9/9.9), and -0.04 (-0.16/0.09), respectively. Conclusions: Background level in healthy subjects is approximately 0.07 to 0.09 γ-H2AX foci/cell. NAL and D are reliable measures

    An antidote for Staphylococcus aureus pneumonia?

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    Methicillin-resistant Staphylococcus aureus (MRSA) is the leading cause of bacterial infections in the United States. Severe invasive MRSA infections, which include pneumonia, are difficult to treat because the bacteria are resistant to antibiotics. A new report now shows that immunization against α-hemolysin (Hla), a cytolytic toxin secreted by most S. aureus strains, protects mice against lethal pneumonia. This finding represents the first successful vaccine strategy for the treatment of staphylococcal pneumonia

    \u27Mid the fields of snowy cotton : (\u27round my dear old southern home)

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    https://digitalcommons.library.umaine.edu/mmb-vp/1025/thumbnail.jp
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