Simulations of the formation and evolution of isolated dwarf galaxies - II. Angular momentum as a second parameter

We show results based on a large suite of N-Body/SPH simulations of isolated, flat dwarf galaxies, both rotating and non-rotating. The main goal is to investigate possible mechanisms to explain the observed dichotomy in radial stellar metallicity profiles of dwarf galaxies: dwarf irregulars (dIrr) and flat, rotating dwarf ellipticals (dE) generally possess flat metallicity profiles, while rounder and non-rotating dEs show strong negative metallicity gradients. These simulations show that flattening by rotation is key to reproducing the observed characteristics of flat dwarf galaxies, proving particularly efficient in erasing metallicity gradients. We propose a "centrifugal barrier mechanism" as an alternative to the previously suggested "fountain mechanism" for explaining the flat metallicity profiles of dIrrs and flat, rotating dEs. While only flattening the dark-matter halo has little influence, the addition of angular momentum slows down the infall of gas, so that star formation (SF) and the ensuing feedback are less centrally concentrated, occurring galaxy-wide. Additionally, this leads to more continuous SFHs by preventing large-scale oscillations in the SFR ("breathing"), and creates low density holes in the ISM, in agreement with observations of dIrrs. Our general conclusion is that rotation has a significant influence on the evolution and appearance of dwarf galaxies, and we suggest angular momentum as a second parameter (after galaxy mass as the dominant parameter) in dwarf galaxy evolution. Angular momentum differentiates between SF modes, making our fast rotating models qualitatively resemble dIrrs, which does not seem possible without rotation.Comment: Accepted for publication in MNRAS | 19 pages, 20 figures | extra online content available (animations) : on the publisher's website / on the YouTube channel for the astronomy department of the University of Ghent : http://www.youtube.com/user/AstroUGent / YouTube playlist specifically for this article : http://www.youtube.com/user/AstroUGent#grid/user/EFAA5AAE5C5E474

Two Birds, One Stone? Positive Mood Makes Products Seem Less Useful for Multiple-Goal Pursuit

Negotiating the pursuit of multiple goals often requires making difficult trade-offs between goals. In these situations, consumers can benefit from using products that help them pursue several goals at the same time. But do consumers always prefer these multipurpose products? We propose that consumers' incidental mood state alters perceptions of products in a multiple-goals context. Four studies demonstrate that being in a positive mood amplifies perceptions of differences between multiple conflicting goals. As a consequence, consumers are less likely to evaluate multipurpose products as being able to serve multiple distinct goals simultaneously. We conclude by discussing implications of these findings for marketers of multipurpose products

Performance evaluation of portfolio insurance strategies using stochastic dominance criteria

The continuing creation of portfolio insurance applications as well as the mixed research evidence suggests that so far no consensus has been reached about the effectiveness of portfolio insurance. Therefore, this paper provides a performance evaluation of the stop-loss, synthetic put and constant proportion portfolio insurance techniques based on a block-bootstrap simulation. Apart from more traditional performance measures, we consider the Value-at-risk and Expected Shortfall of the strategies, which are more appropriate in an insurance context. An additional performance evaluation is given by means of the stochastic dominance framework where we account for sampling error. A sensitivity analysis is performed in order to examine the impact on performance of a change in a specific decision variable (ceteris paribus). The results indicate that a buy-and-hold strategy does not dominate the portfolio insurance strategies at any stochastic dominance order. Moreover, both for the stop-loss and synthetic put strategy a 100% floor value outperforms lower floor values. For the CPPI strategy we find that a higher CPPI multiple enhances the upward potential of the CPPI strategies, but harms the protection level in return. As regards the optimal rebalancing frequency, daily rebalancing should be preferred for the synthetic put and CPPI strategy, despite the higher transaction costs.Portfolio insurance; Performance evaluation; Stochastic dominance; Block-bootstrap simulation

Role of polymorphonuclear leukocytes in collar-induced intimal thickening in the rabbit carotid artery

Abstract —In this study, the involvement of polymorphonuclear leukocytes (PMNs) in the development of intimal thickening was investigated. A fibromuscular intima was induced by placing a silicone collar around the rabbit carotid artery for 3 days or 2 weeks; the contralateral artery was sham operated. Rabbits received placebo treatments (groups 1 and 3), granulocyte-colony stimulating factor (group 2; G-CSF, 20 μg · kg −1 · d −1 , delivered by subcutaneous osmotic pumps), or an anti-CD18 monoclonal antibody (group 4; 1.5 mg/kg IV). The G-CSF treatment raised the peripheral PMN count 5- to 12-fold but had no effect on intimal thickening on day 3, 12, or 14. A single injection of anti-CD18 prevented PMN extravasation 6 hours after collar implantation without influencing intimal hyperplasia on day 14. Repeated daily administration of anti-CD18 strongly bound to CD18 on peripheral PMNs and inhibited both PMN-dependent plasma extravasation in the skin and accumulation of CD14-immunoreactive leukocytes in the intima and media. However, anti-CD18 did not suppress early intimal thickening or accumulation of α-smooth muscle actin–immunoreactive cells by day 3. It thus appears that the PMN influx in the intima and media evoked by the perivascular collar is of little functional relevance to the subsequent smooth muscle cell migration and intimal thickening in this model. </jats:p

The molecular basis of antithrombin deficiency in Belgian and Dutch families

The molecular basis of hereditary antithrombin (AT) deficiency has been investigated in ten Belgian and three Dutch unrelated kindreds. Eleven of these families had a quantitative or type I AT deficiency. with a history of major venous thromboembolic events in different affected members. In the other two families a qualitative or type I AT deficiency was occasionally diagnosed. DNA studies of the AT gene were performed, using polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) analysis, followed by direct sequencing of the seven exons and intron-exon junction regions. Six novel point mutations were identified: four missense, one nonsense mutation and a single nucleotide deletion near the reactive site, causing a frameshift with premature translation termination. In two kindreds the underlying genetic defect was caused by a whole gene deletion. known as a rare cause of AT deficiency. In these cases, Southern blot and polymorphism analysis of different parts of the AT gene proved useful for diagnosis. In another kindred a partial gene deletion spanning 698 basepairs could precisely be determined to a part of intron 3B and exon 4. In two type I and in both type II AT deficient families a previously reported mutation was identified. In all cases, the affected individuals were heterozygous for the genetic defect