Sums over Graphs and Integration over Discrete Groupoids

We show that sums over graphs such as appear in the theory of Feynman diagrams can be seen as integrals over discrete groupoids. From this point of view, basic combinatorial formulas of the theory of Feynman diagrams can be interpreted as pull-back or push-forward formulas for integrals over suitable groupoids.Comment: 27 pages, 4 eps figures; LaTeX2e; uses Xy-Pic. Some ambiguities fixed, and several proofs simplifie

Russian small businesses: entrepreneurship in transition. Exploratory investigation of the factors that pushed and pulled individuals to open their own business in the Krasnodar region of Russia

The purpose of this research was to identify the factors that pushed and pulled individuals to become self-employed in Russia during the post-Soviet Union period. The research methodology adopted in this study was qualitative. The longitudinal multiple case study approach was comprised of in-depth interviews with the founders and co-founders of 26 family businesses in the Krasnodar region of Russia. To summarise particular findings of the present research one push factor and four pull factors have been identified as being the most influential: 1. ‗Unemployment / Restructuring‘ during the transitional period push factor; 2. ‗The Demand for Local Services‘ pull factor; 3. ‗The Development of Entrepreneurial Skills‘ pull factor; 4. The ‗Cultural Changes‘ pull factor; and 5. The ‗Family Relatedness‘ pull factor. This thesis postulates that a contribution to the understanding of the push-pull debate theory can be made through an interpretation of the factors that influence individuals‘ decisions to become self-employed. A significant body of worldwide research currently exists that deals with the concept of the self-employment push-pull debate. There is however no one agreed view on which factors push or pull individuals to become self-employed. An analysis of various literature sources has at times revealed contradictions and inconsistencies within this debate. This observation can be partly explained by the fact that this body of research exists across a diverse range of countries and through time. This thesis highlights the fact that a clear dichotomy of the self-employment push and pull factors may not always be adequate. This analysis highlights that what really matters when identifying the factors that push or pull individuals to become self-employed is how the individuals themselves interpret these factors. Therefore any factor potentially could be considered as being both push and pull depending upon the individual‘s personal interpretation

Smooth K-Theory

We construct an analytic multiplicative model of smooth K-theory. We further introduce the notion of a smooth K-orientation of a proper submersion and define the associated push-forward which satisfies functoriality, compatibility with pull-back diagrams, and projection and bordism formulas. We construct a multiplicative lift of the Chern character from smooth K-theory to smooth rational cohomology and verify that the cohomological version of the Atiyah-Singer index theorem for families lifts to smooth cohomology.Comment: v4 93 pages, version to appear in Asterisque (Bismut 60 proceedings

Robustness of Randomized Rumour Spreading

In this work we consider three well-studied broadcast protocols: Push, Pull and Push&Pull. A key property of all these models, which is also an important reason for their popularity, is that they are presumed to be very robust, since they are simple, randomized, and, crucially, do not utilize explicitly the global structure of the underlying graph. While sporadic results exist, there has been no systematic theoretical treatment quantifying the robustness of these models. Here we investigate this question with respect to two orthogonal aspects: (adversarial) modifications of the underlying graph and message transmission failures. We explore in particular the following notion of Local Resilience: beginning with a graph, we investigate up to which fraction of the edges an adversary has to be allowed to delete at each vertex, so that the protocols need significantly more rounds to broadcast the information. Our main findings establish a separation among the three models. It turns out that Pull is robust with respect to all parameters that we consider. On the other hand, Push may slow down significantly, even if the adversary is allowed to modify the degrees of the vertices by an arbitrarily small positive fraction only. Finally, Push&Pull is robust when no message transmission failures are considered, otherwise it may be slowed down. On the technical side, we develop two novel methods for the analysis of randomized rumour spreading protocols. First, we exploit the notion of self-bounding functions to facilitate significantly the round-based analysis: we show that for any graph the variance of the growth of informed vertices is bounded by its expectation, so that concentration results follow immediately. Second, in order to control adversarial modifications of the graph we make use of a powerful tool from extremal graph theory, namely Szemer\`edi's Regularity Lemma.Comment: version 2: more thorough literature revie

Assessing the UK policies for broadband adoption

Broadband technology has been introduced to the business community and the public as a rapid way of exploiting the Internet. The benefits of its use (fast reliable connections, and always on) have been widely realised and broadband diffusion is one of the items at the top of the agenda for technology related polices of governments worldwide. In this paper an examination of the impact of the UK government’s polices upon broadband adoption is undertaken. Based on institutional theory a consideration of the manipulation of supply push and demand pull forces in the diffusion of broadband is offered. Using primary and secondary data sources, an analysis of the specific institutional actions related to IT diffusion as pursued by the UK government in the case of broadband is provided. Bringing the time dimension into consideration it is revealed that the UK government has shifted its attention from supply push-only strategies to more interventional ones where the demand pull forces are also mobilised. It is believed that this research will assist in the extraction of the “success factors” in government intervention that support the diffusion of technology with a view to render favourable results if applied to other national settings

Intersection of labour and employment market in private further and higher education colleges in the United Kingdom

While past literature identified that the unskilled workers tend to accept nonstandard works, the literature has not explained adequately the reasons for accepting nonstandard work by highly skilled academics. This study addresses this literature gap by examining various reasons for accepting non-standard work by academics in private further and higher education colleges in the United Kingdom. Based on self-determination motivation theory, the study categorizes different reasons according to push factors and pull factors where push factors are the controlled choices and pull factors are autonomous choices. A mixed methodology is employed in this study. The quantitative data are utilized to draw the trends and patterns of nonstandard work in this context, where the qualitative data are used to give an in-depth discussion about the context. Influences of both push and pull factor have been identified as a reason for accepting non-standard contract. However, the links between push factors are stronger than pull factors. We argued that when the push factors become powerful, the pull choice intersects with push factor, and in that situation the pull factors become less important to employees. We also argued that due to strong presence of push factor, the academics in this sector have less control over different aspects of job including wages, training, employment benefits, career progression, and job security

Interplay between Intra- and Intermolecular Charge Transfer in the Optical Excitations of J-Aggregates

In a first-principles study based on density functional theory and many-body perturbation theory, we address the interplay between intra- and intermolecular interactions in a J-aggregate formed by push-pull organic dyes by investigating its electronic and optical properties. We find that the most intense excitation dominating the spectral onset of the aggregate, i.e., the J-band, exhibits a combination of intramolecular charge transfer, coming from the push-pull character of the constituting dyes, and intermolecular charge transfer, due to the dense molecular packing. We also show the presence of a pure intermolecular charge-transfer excitation within the J-band, which is expected to play a relevant role in the emission properties of the J-aggregate. Our results shed light on the microscopic character of optical excitations of J-aggregates and offer new perspectives to further understand the nature of collective excitations in organic semiconductors.Comment: published under ACS Authorchoice licens

Foreign Direct Investment and International Migration to Dutch Cities

This article assesses the push- and pull-factor explanation in Sassen’s theory on migration from newly industrialising countries to cities in OECD countries separately. The former explanation argues that foreign direct investments spawn migration flows to the country where these investments stem from. The pull-factor explanation revolves around demand for low-skilled workers in cities due to the clustering of advanced producer services. It is found that Dutch investment flows indeed function as a push factor for migration to Dutch cities, but that the local settlement of immigrants is not related to the clustering of advanced producer services