Galois theory and commutators

We prove that the relative commutator with respect to a subvariety of a variety of Omega-groups introduced by the first author can be described in terms of categorical Galois theory. This extends the known correspondence between the Froehlich-Lue and the Janelidze-Kelly notions of central extension. As an example outside the context of Omega-groups we study the reflection of the category of loops to the category of groups where we obtain an interpretation of the associator as a relative commutator.Comment: 14 page

Using backward means to eliminate individual effects from dynamic panels

The within-groups estimator is inconsistent in dynamic panels with fixed T since the sample mean used to eliminate the individual effects from the lagged dependent variable is correlated with the error term. This paper suggests to eliminate individual effects from an AR(1) panel using backward means as an alternative to sample means. Using orthogonal deviations of the lagged dependent variable from its backward mean yields an estimator that is still inconsistent for fixed T but the inconsistency is shown to be negligibly small. A Monte Carlo simulation shows that this alternative estimator has superior small sample properties compared to conventional fixed effects, bias-corrected fixed effects and GMM estimators. Interestingly, it is also consistent for fixed T in the specific cases where (i) T = 2, (ii) the AR parameter is 0 or 1, (iii) the variance of the individual effects is zero

Emotion regulation difficulties related to depression and anxiety : a network approach to model relations among symptoms, positive reappraisal, and repetitive negative thinking

Frequent repetitive negative thinking and infrequent positive reappraisal use are theorized to increase risk for depression and anxiety. Yet, research has studied these regulatory strategies at the disorder level, ignoring the clinical heterogeneity and differential relations among their individual symptoms. In this study, we examined the associations among repetitive negative thinking, positive reappraisal, and individual symptoms of depression and anxiety disorders. Models of regularized partial-correlation networks were estimated using cross-sectional data from 468 participants. Results showed that repetitive negative thinking and positive reappraisal were differentially related to affective, cognitive, and somatic symptoms of depression and anxiety. Moreover, repetitive negative thinking was more central than positive reappraisal with stronger connections to individual symptoms. Finally, repetitive negative thinking was more important than positive reappraisal in connecting clusters of depression and anxiety symptoms. These findings cast light on potential pathways through which repetitive negative thinking and positive reappraisal may operate within depression and anxiety

Choice-based learning : lecture-based or team learning?

This study investigates choice-based learning as a choice between lecture-based or team learning in a large class at a large university in a European country. The study was designed as a between-subjects quasi-experiment where students were allocated their preferred learning approach. Data were collected for eight consecutive years (2008-2016). Based on quantitative and qualitative data, this study investigates the effect of choice-based learning on choice satisfaction, student selection and on student learning outcomes. The results show that team learning has a positive effect on learning outcomes. If students are faced with the choice, the majority select lecture-based learning. Additionally, both student groups are satisfied with their selected learning paths but selected them for specific reasons. Finally, choice-based learning provides job satisfaction for the instructors of both learning paths. These results can re-energize the ongoing discussion on why and how to engage students in learning activities

Effect of β-lactamase inhibitors on in vitro activity of β-lactam antibiotics against Burkholderia cepacia complex species

Background: Bacteria belonging to the Burkholderia cepacia complex (Bcc) are an important cause of chronic respiratory tract infections in cystic fibrosis patients. Intrinsic resistance to a wide range of antimicrobial agents, including a variety of beta-lactam antibiotics, is frequently observed in Bcc strains. Resistance to beta-lactams is most commonly mediated by efflux pumps, alterations in penicillin-binding proteins or the expression of beta-lactamases. beta-lactamase inhibitors are able to restore the in vitro activity of beta-lactam molecules against a variety of Gram-negative species, but the effect of these inhibitors on the activity of beta-lactam treatment against Bcc species is still poorly investigated. Methods: In the present study, the susceptibility of a panel of Bcc strains was determined towards the beta-lactam antibiotics ceftazidime, meropenem, amoxicillin, cefoxitin, cefepime and aztreonam; alone or in combination with a beta-lactamase inhibitor (clavulanic acid, sulbactam, tazobactam and avibactam). Consequently, beta-lactamase activity was determined for active beta-lactam/beta-lactamase inhibitor combinations. Results: Clavulanic acid had no effect on minimum inhibitory concentrations, but addition of sulbactam, tazobactam or avibactam to ceftazidime, amoxicillin, cefoxitin, cefepime or aztreonam leads to increased susceptibility (at least 4-fold MIC-decrease) in some Bcc strains. The effect of beta-lactamase inhibitors on beta-lactamase activity is both strain-and/or antibiotic-dependent, and other mechanisms of beta-lactam resistance (besides production of beta-lactamases) appear to be important. Conclusions: Considerable differences in susceptibility of Bcc strains to beta-lactam antibiotics were observed. Results obtained in the present study suggest that resistance of Bcc strains against beta-lactam antibiotics is mediated by both beta-lactamases and non-beta-lactamase-mediated resistance mechanisms

Some aspects of semi-abelian homology and protoadditive functors

In this note some recent developments in the study of homology in semi-abelian categories are briefly presented. In particular the role of protoadditive functors in the study of Hopf formulae for homology is explained.Comment: 7 page

Protoadditive functors, derived torsion theories and homology

Protoadditive functors are designed to replace additive functors in a non-abelian setting. Their properties are studied, in particular in relationship with torsion theories, Galois theory, homology and factorisation systems. It is shown how a protoadditive torsion-free reflector induces a chain of derived torsion theories in the categories of higher extensions, similar to the Galois structures of higher central extensions previously considered in semi-abelian homological algebra. Such higher central extensions are also studied, with respect to Birkhoff subcategories whose reflector is protoadditive or, more generally, factors through a protoadditive reflector. In this way we obtain simple descriptions of the non-abelian derived functors of the reflectors via higher Hopf formulae. Various examples are considered in the categories of groups, compact groups, internal groupoids in a semi-abelian category, and other ones

Measuring the International Dimension of Output Volatility

This paper studies output fluctuations in a panel of OECD economies with the aim to decompose the evolution in output volatility into domestic and international factors. To this end we use a factor-augmented dynamic panel model with both domestic and international shocks and spillovers between countries through trade linkages. Changes in the volatility of output growth can be due to a time-varying sensitivity to these shocks, changes in the propagation mechanism or shifts in the variances of shocks. We explicitly model cross-sectional dependence in the variance equation by specifying a common factor structure in the volatility of domestic shocks. The results show that while the size of international shocks and spillovers does not decrease in most countries, the volatilities of domestic shocks share a clear common decreasing trend. Hence, the 'Great Moderation' appears to be mainly driven by a decline in the volatility of domestic shocks rather than smaller international shocks