Operators with smooth functional calculi

We introduce a class of (tuples of commuting) unbounded operators on a Banach space, admitting smooth functional calculi, that contains all operators of Helffer-Sj\"ostrand type and is closed under the action of smooth proper mappings. Moreover, the class is closed under tensor product of commuting operators. In general an operator in this class has no resolvent in the usual sense so the spectrum must be defined in terms of the functional calculus. We also consider invariant subspaces and spectral decompositions

Fokus 2015: Die Millenniums-Entwicklungsziele – Magna Charta der Globalisierung? Eine Zwischenbilanz – 5 Jahre nach der UN-Millenniumserklärung. Dokumentation der gleichnamigen Konferenz am 25. Januar 2005 in Berlin

The purpose of this paper is to explore how sustainable competitive advantage is generated in two Swedish best practice companies that successfully exploit logistics as a source for competitive advantage. Using a theoretical framework based on the resource-based view of the firm, this research elaborates on the links between operational and dynamic logistics capabilities and sustainable competitive advantage. The findings conclude that a sustainable competitive advantage is based on a combination of efficient and effective logistics operations and well-functioning, adjusted, in-house-developed IT systems. This operational capability is in turn sustained through five dynamic capabilities: managerial knowledge and presence, cross-functional teamwork, control, learning and supply chain relationships.  This is an electronic version of an article published in:Erik Sandberg and Mats Abrahamsson, Logistics capabilities for sustainable competitive advantage, 2011, International Journal of Logistics, (14), 1, 61-75.International Journal of Logistics is available online at informaworldTM: http://dx.doi.org/10.1080/13675567.2010.551110Copyright: Taylor & Francishttp://www.tandf.co.uk/journals/default.as

STUDY OF THE EFFECTS OF BUILDING DENSITY AND OVERALL SHAPE OF A CITY ON POLLUTANT DISPERSION BY COMBINATION OF WIND TUNNEL EXPERIMENTS AND CFD SIMULATIONS

Despite the improvement made in controlling local air pollution, urban areas are undergoing increasing environmental pressures and poor air quality is one of the major concerns. Recently, much attention has focused on the relationship between urban form and sustainability. There are indications that the density and the overall shape of cities can have implications on street level ventilation and the “compact city” is by many regarded as the most sustainable urban form. In this framework, this paper is devoted to the study of flow and pollutant dispersion from a ground level line source at pedestrian level within different urban configurations. The urban-like configurations vary from the scenario of an urban sprawl to the opposite scenario of a compact city. Wind tunnel experiments and CFD simulations are performed to evaluate pollutant concentrations in each of the idealized city structures. The overall aim is that of assessing and clarifying the effect of city density on atmospheric flow patterns and pollutant dispersion

Characterizing the Heterogeneity of the OpenStreetMap Data and Community

OpenStreetMap (OSM) constitutes an unprecedented, free, geographic information source contributed by millions of individuals, resulting in a database of great volume and heterogeneity. In this study, we characterize the heterogeneity of the entire OSM database and historical archive in the context of big data. We consider all users, geographic elements, and user contributions from an eight-year data archive, at a size of 692 GB. We rely on some nonlinear methods such as power-law statistics and head/tail breaks to uncover and illustrate the underlying scaling properties. All three aspects (users, elements, and contributions) demonstrate striking power laws or heavy-tailed distributions. The heavy-tailed distributions imply that there are far more small elements than large ones, far more inactive users than active ones, and far more lightly edited elements than heavily edited ones. Furthermore, about 500 users in the core group of the OSM are highly networked in terms of collaboration. Keywords: OpenStreetMap, big data, power laws, head/tail breaks, ht-indexComment: 13 pages, 6 figures, and 8 table

Revisiting the ‘Venturi effect’ in passage ventilation between two non-parallel buildings

A recent study conducted by Blocken et al. (Numerical study on the existence of the Venturi effect in passages between perpendicular buildings. Journal of Engineering Mechanics, 2008,134: 1021-1028) challenged the popular view of the existence of the ‘Venturi effect’ in building passages as the wind is exposed to an open boundary. The present research extends the work of Blocken et al. (2008a) into a more general setup with the building orientation varying from 0° to 180° using CFD simulations. Our results reveal that the passage flow is mainly determined by the combination of corner streams. It is also shown that converging passages have a higher wind-blocking effect compared to diverging passages, explained by a lower wind speed and higher drag coefficient. Fluxes on the top plane of the passage volume reverse from outflow to inflow in the cases of α=135°, 150° and 165°. A simple mathematical expression to explain the relationship between the flux ratio and the geometric parameters has been developed to aid wind design in an urban neighborhood. In addition, a converging passage with α=15° is recommended for urban wind design in cold and temperate climates since the passage flow changes smoothly and a relatively lower wind speed is expected compared with that where there are no buildings. While for the high-density urban area in (sub)tropical climates such as Hong Kong where there is a desire for more wind, a diverging passage with α=150° is a better choice to promote ventilation at the pedestrian level

Natural ventilation assessment in typical open an semi-open urban environments under various wind directions

Semi-open street roofs protect pedestrians from intense sunshine and rains. Their effects on natural ventilation of urban canopy layers (UCL) are less understood. This paper investigates two idealized urban models consisting of 4(2×2) or 16(4×4) buildings under a neutral atmospheric condition with parallel (0°) or non-parallel (15°,30°,45°) approaching wind. The aspect ratio (building height (H) / street width (W)) is 1 and building width is B=3H. Computational fluid dynamic (CFD) simulations were first validated by experimental data, confirming that standard k-ε model predicted airflow velocity better than RNG k-ε model, realizable k–ε model and Reynolds stress model. Three ventilation indices were numerically analyzed for ventilation assessment, including flow rates across street roofs and openings to show the mechanisms of air exchange, age of air to display how long external air reaches a place after entering UCL, and purging flow rate to quantify the net UCL ventilation capacity induced by mean flows and turbulence. Five semi-open roof types are studied: Walls being hung above street roofs (coverage ratio λa=100%) at z=1.5H, 1.2H, 1.1H ('Hung1.5H', 'Hung1.2H', 'Hung1.1H' types); Walls partly covering street roofs (λa=80%) at z=H ('Partly-covered' type); Walls fully covering street roofs (λa=100%) at z=H ('Fully-covered' type).They basically obtain worse UCL ventilation than open street roof type due to the decreased roof ventilation. 'Hung1.1H', 'Hung1.2H', 'Hung1.5H' types are better designs than 'Fully-covered' and 'Partly-covered' types. Greater urban size contains larger UCL volume and requires longer time to ventilate. The methodologies and ventilation indices are confirmed effective to quantify UCL ventilation

Meanings of theory : clarifying theory through typification

Developing and evaluating scientific knowledge and its value requires a clear – or at least not too unclear – understanding of what ‘theory’ means. We argue that common definitions of theory are too restrictive, as they do not acknowledge the existence of multiple kinds of scientific knowledge, but largely recognize only one kind as ‘theory’, namely explanatory knowledge. We elaborate a typology that broadens and clarifies the meaning of ‘theory’. Consisting of five basic theory types – explaining, comprehending, ordering, enacting and provoking theories – the typology offers a framework that enables researchers to develop and assess knowledge in more varied ways and for a broader set of purposes than is typically recognized, as well as providing a more level playing field within the academic community

The problematizing review : a counterpoint to Elsbach and Van Knippenberg’s argument for integrative reviews

In this paper we provide a counterpoint to conventional views on integrative reviews in knowledge development, as exemplified by Elsbach and Van Knippenberg (2020). First, we critique their proposed integrative review by identifying and problematizing several key assumptions underlying it, particularly their idea that the integrative review can simply build on existing studies and lead the way to knowledge. Second, based on this critique, we propose as an alternative the problematizing review, which is based on the following four core principles: the ideal of reflexivity, reading more broadly but selectively, not accumulating but problematizing, and the concept that ‘less is more’. In contrast to the integrative review, which regards reviews as a ‘building exercise’, the problematizing review regards reviews as an ‘opening up exercise’ that enables researchers to imagine how to rethink existing literature in ways that generate new and ‘better’ ways of thinking about specific phenomena