The Angular Momentum of Gas in Proto-Galaxies: II -- The Impact of Preheating

We examine the effect of preheating of the intergalactic medium on galaxy formation using cosmological hydrodynamical simulations. By performing simulations both with and without a simple model for preheating, we analyse and compare the angular momentum distributions of the dark matter and the baryons. Preheating unbinds baryons from their dark matter haloes, yielding a baryonic mass fraction that declines with decreasing halo mass. In addition, the spin parameter of the gas is reduced with respect to the case without preheating, while the misalignment between the angular momentum directions of the gas and dark matter increases strongly. The angular momentum distributions of individual haloes reveal that preheating decreases (increases) the mass fraction with low (negative) specific angular momentum. We discuss the implications of these findings for the formation of disk galaxies in a preheated intergalactic medium, and compare our results to the predictions of Maller & Dekel (2002), who propose an alternative interpretation for the origin of the angular momentum of (proto)-galaxies.Comment: 10 pages, 4 figures. Accepted for publication in MNRA

Investigating Managers' Exploration and Exploitation Activities: The Influence of Top-down, Bottom-up, and Horizontal Knowledge Inflows

This paper develops and tests hypotheses on the influence of a manager’s knowledge inflows on this manager’s exploration and exploitation activities. Based on a survey among managers of a leading electronics firm, the findings indicate, as expected, that top-down knowledge inflows of a manager positively relate to the extent to which this manager conducts exploitation activities, while they do not relate to a manager’s exploration activities. Furthermore, as expected, bottom-up and horizontal knowledge inflows of a manager positively relate to this manager’s exploration activities, while they do not relate to a manager’s exploitation activities. We contribute to current literature on exploration and exploitation by focusing on the manager level of analysis, and by adding the importance of knowledge flow configurations to the literature on the impact of organizational factors upon exploration and exploitation

Understanding variation in managers' ambidexterity: Investigating direct and interaction effects of formal structural and personal coordination mechanisms

Previous research focuses on firm and business unit level ambidexterity. Therefore, conceptual and empirically validated understanding about ambidexterity at the individual level of analysis is very scarce. This paper addresses this gap in the literature by investigating managers' ambidexterity, delivering three contributions to theory and empirical research on ambidexterity: first, by proposing three related characteristics of ambidextrous managers; second, by developing a model and associated hypotheses on both the direct and interaction effects of formal structural and personal coordination mechanisms on managers' ambidexterity; and third, by testing the hypotheses based on a sample of 716 business unit level and operational level managers. Findings regarding the formal structural mechanisms indicate that a manager's decision-making authority positively relates to this manager's ambidexterity, whereas formalization of a manager's tasks has no significant relationship with this manager's ambidexterity. Regarding the personal coordination mechanisms, findings indicate that both the participation of a manager in cross-functional interfaces and the connectedness of a manager to other organization members positively relate to this manager's ambidexterity. Furthermore, results show positive interaction effects between the formal structural and personal coordination mechanisms on managers' ambidexterity. The paper's theoretical contributions and empirical results increase our understanding about managers' ambidexterity and about how different types and combinations of coordination mechanisms relate to variation in managers' ambidexterity

The Influence of Managerial and Organizational Determinants of Horizontal Knowledge Exchange on Competence Building and Competence Leveraging

Both in theory as in practice insight is limited about how firms in dynamic environments could organize to manage concurrently both the strategic processes of competence building and competence leveraging. To contribute to this issue, a conceptual framework is developed which considers the ability to exchange knowledge across organization units as a prerequisite for firms to achieve both the goals of competence building and leveraging. The framework shows how several important managerial and organizational determinants, associated with cross-unit knowledge exchange, may stimulate competence-building processes and how they may stimulate competence-leveraging processes. The conceptual framework will be illustrated by two case studies in different contexts of Novartis, one of the leading European life-science companies. These two contexts of respectively ‘organization-enabled’ and ‘web-enabled’ knowledge exchange appear to be complementary. The conceptual framework and cases provide insight into (1) possibilities about how firms could organize to deal with the tension between competence building and leveraging processes, and (2) how managing the determinants of horizontal knowledge exchange can contribute to changing a firm’s actual mixture of competence building/leveraging processes into a more desired strategic mixture

The competitive advantage of nations: the importance of the national environment for strategic management in the EC

Summary: In this paper we investigate the usefulness for strategic management of Porter's framework of analysis of the competitive advantage of nations in particular regarding the importance of the changing national environment within the EC. It appears that Porter's framework - supplemented with contributions from the Industrial Organization field and with special attention to the growing importance of the service sector and the particular characteristics of services - can indeed contribute to our understanding of the importance of the national environment within the EC for strategic management. However, much research has to be done. In this connection, the paper proposes a few key questions for further research

Should management relocate across borders?

As markets and industries become more global, it makes increasing sense for multinationals to shift some or all headquarters functions and resources abroad. However, this is a strategic decision that needs to be weighed carefully

Improved modeling of clinical data with kernel methods

Objective: Despite the rise of high-throughput technologies, clinical data such as age, gender and medical history guide clinical management for most diseases and examinations. To improve clinical management, available patient information should be fully exploited. This requires appropriate modeling of relevant parameters. Methods: When kernel methods are used, traditional kernel functions such as the linear kernel are often applied to the set of clinical parameters. These kernel functions, however, have their disadvantages due to the specific characteristics of clinical data, being a mix of variable types with each variable its own range. We propose a new kernel function specifically adapted to the characteristics of clinical data. Results: The clinical kernel function provides a better representation of patients' similarity by equalizing the influence of all variables and taking into account the range r of the variables. Moreover, it is robust with respect to changes in r. Incorporated in a least squares support vector machine, the new kernel function results in significantly improved diagnosis, prognosis and prediction of therapy response. This is illustrated on four clinical data sets within gynecology, with an average increase in test area under the ROC curve (AUC) of 0.023, 0.021, 0.122 and 0.019, respectively. Moreover, when combining clinical parameters and expression data in three case studies on breast cancer, results improved overall with use of the new kernel function and when considering both data types in a weighted fashion, with a larger weight assigned to the clinical parameters. The increase in AUC with respect to a standard kernel function and/or unweighted data combination was maximum 0.127, 0.042 and 0.118 for the three case studies. Conclusion: For clinical data consisting of variables of different types, the proposed kernel function which takes into account the type and range of each variable - has shown to be a better alternative for linear and non-linear classification problems. (C) 2011 Elsevier B.V. All rights reserved

Inhibition of histone deacetylase 6 (HDAC6) protects against vincristine-induced peripheral neuropathies and inhibits tumor growth

As cancer is becoming more and more a chronic disease, a large proportion of patients is confronted with devastating side effects of certain anti-cancer drugs. The most common neurological complications are painful peripheral neuropathies. Chemotherapeutics that interfere with microtubules, including plant-derived vinca-alkaloids such as vincristine, can cause these chemotherapy-induced peripheral neuropathies (CIPN). Available treatments focus on symptom alleviation and pain reduction rather than prevention of the neuropathy. The aim of this study was to investigate the potential of specific histone deacetylase 6 (HDAC6) inhibitors as a preventive therapy for CIPN using multiple rodent models for vincristine-induced peripheral neuropathies (VIPN). HDAC6 inhibition increased the level of acetylated α-tubulin in tissues of rodents undergoing vincristine-based chemotherapy, which correlates to a reduced severity of the neurological symptoms, both at the electrophysiological and the behavioral level. Mechanistically, disturbances in axonal transport of mitochondria is considered as an important contributing factor in the pathophysiology of VIPN. As vincristine interferes with the polymerization of microtubules, we investigated whether disturbances in axonal transport could contribute to VIPN. We observed that increasing α-tubulin acetylation through HDAC6 inhibition restores vincristine-induced defects of axonal transport in cultured dorsal root ganglion neurons. Finally, we assured that HDAC6-inhibition offers neuroprotection without interfering with the anti-cancer efficacy of vincristine using a mouse model for acute lymphoblastic leukemia. Taken together, our results emphasize the therapeutic potential of HDAC6 inhibitors with beneficial effects both on vincristine-induced neurotoxicity, as well as on tumor proliferation. ispartof: Neurobiology of Disease vol:111 pages:59-69 ispartof: location:United States status: publishe

The shape of the dark matter halo in the early-type galaxy NGC 2974

We present HI observations of the elliptical galaxy NGC 2974, obtained with the Very Large Array. These observations reveal that the previously detected HI disc in this galaxy (Kim et al. 1988) is in fact a ring. By studying the harmonic expansion of the velocity field along the ring, we constrain the elongation of the halo and find that the underlying gravitational potential is consistent with an axisymmetric shape. We construct mass models of NGC 2974 by combining the HI rotation curve with the central kinematics of the ionised gas, obtained with the integral-field spectrograph SAURON. We introduce a new way of correcting the observed velocities of the ionised gas for asymmetric drift, and hereby disentangle the random motions of the gas caused by gravitational interaction from those caused by turbulence. To reproduce the observed flat rotation curve of the HI gas, we need to include a dark halo in our mass models. A pseudo-isothermal sphere provides the best model to fit our data, but we also tested an NFW halo and Modified Newtonian Dynamics (MOND), which fit the data marginally worse. The mass-to-light ratio M/L_I increases in NGC 2974 from 4.3 (M/L_I)sun at one effective radius to 8.5 (M/L_I)sun at 5 Re. This increase of M/L already suggests the presence of dark matter: we find that within 5 Re at least 55 per cent of the total mass is dark.Comment: 17 pages, 20 figures, accepted by MNRA