Explorations into the rare earth chemistry of biphenolates and superbulky cyclopentadienyl ligands, and a study of C-F activation by rare earth metals

Angus Shephard studied a range of alternative synthetic methods for accessing valuable rare earth metal complexes. He explored new and previously unused methods of synthesising rare earth biphenolate complexes, superbulky lanthanoid metallocene complexes, and lanthanoid formamidinate and pyrazolate species. His work has provided fundamental insight into the reactivity of free rare earth metals

Des coloriages de pavages super et superbes

II existe une vaste littérature sur le sujet des groupes de couleurs et des coloriages des motifs dans le plan [2, chapitre 8], [6], [8]. II est toutefois étrange qu’aucun de ces travaux ne semble porter directement sur les problèmes du coloriage des pavages comme tel. Plus particulièrernent, bien que les groupes de couleurs soient souvent présentés comme des groupes de symétrie de couleurs des pavages, un examen approfondi révélera que ce ne sont que les motifs des pavés du pavage qui sont considérés; d’autres propriétés essentielles d’un pavage tel que son type topologique et I’adjacence de certaines paires de pavés sont ignorées. Si, par contre, on en tient compte, plusieurs problèmes intéressants (et complexes) se présentent. Le but de cet article est d’aborder quelques-uns de ces problèmes. On s’intéressera plus particulièrement à ce qu’on appelle les super coloriages de pavages isoédriques. (On expliquera ci-dessous les termes essentiels.) Au-delà de I’intérêt mathématique, les super coloriages sont très attrayants d’un point devue esthétique et, à ce titre, ils ont été utilisés par des artistes comme M.C. Escher. En fait dans I’ensemble des collections publiées d’oeuvres d’Escher, tous les coloriages de pavages isoédriques sont super. (On peut consulter, par exemple, [ 1 , Planches E2-E23, E32-E31, E36-E51, E55, E62-E66, E70, E73-E79, E86, E88-E92, E94-E98, E l 02-E109, E116-E119, E124, E127, E128].) Ce fait fut à I’origine du présent article, il est la suite d’une présentation de I’auteur au Escher Symposium de Rome en mars 1985 (un rapport en a été donné dans les Comptes-rendus de cette rencontre [7]). Toutefois, dans I’intérêt du lecteur, on répétera ici la terminologie jugée essentielle et cette présentation sera auto-suffisante. L’auteurtient à exprimer sa reconnaissance à Marjorie Senechal et à Tom Wieting pour hi avoir suggéré les corrections à [6], et, plus particulièrement a Branko Grünbaum pour nos discussions utiles et les commentaires qu’il porta sur les versions préliminaires de cet article, commentaires qui menèrent à plusieurs améliorations.There exists an extensive literature concerning colour groups and the related colourings of the motifs of a plane pattern [2, Chapter 81, [6], [8]. It is strange that none of this work seems to refer directly to the problems of colouring tilings as such. To be more specific, though colour groups are often displayed as the colour symmetry groups of tilings, careful examination will show that it is only the patterns of the tiles in the tilings which are under consideration; other essential properties of a tiling such as its topological type, and the adjacencies of certain pairs of tiles, are ignored. If the latter are taken into account, several interesting (and difficult) problems emerge. It is the purpose of the present paper to consider some of these. In particular, we shall be concerned with what are called super colourings of isohedral tilings. (These words and other essential terminology, will be explained shortly.) Besides being mathematically interesting, super colourings are very attractive from an aesthetic point of view, and have been used by artists such as M.C. Escher. In fact, in the published collections of Escher’s works, all his colourings of isohedral tilings are super. (See, for example, [ l , Plates E2-E23, E32-E31, E36-E51, E55, E62-E66, E70, E73-E79, E86, E88-E92, E94-E98, E102-E109, E l 16-El 19, E 124, E 127, E 1281.) This fact motivated the present paper, which isasequel to the talkgiven bythe authoratthe ExherSymposium in Rome in March 1985, and reported in the Proceedings of that meeting [7]. However, for the convenience of the reader, essential terminology will be repeated here and the presentation will be self-contained. The author wishes to express his gratitude to Marjorie Senechal and Tom Wieting for supplying him with corrections to [6], and, more especially to Branko Grunbaum for helpful discussions and for his comments on preliminary versions of this paper which led to many improvements.Peer Reviewe

Quantum affine Cartan matrices, Poincare series of binary polyhedral groups, and reflection representations

We first review some invariant theoretic results about the finite subgroups of SU(2) in a quick algebraic way by using the McKay correspondence and quantum affine Cartan matrices. By the way it turns out that some parameters (a,b,h;p,q,r) that one usually associates with such a group and hence with a simply-laced Coxeter-Dynkin diagram have a meaningful definition for the non-simply-laced diagrams, too, and as a byproduct we extend Saito's formula for the determinant of the Cartan matrix to all cases. Returning to invariant theory we show that for each irreducible representation i of a binary tetrahedral, octahedral, or icosahedral group one can find a homomorphism into a finite complex reflection group whose defining reflection representation restricts to i.Comment: 19 page

A new structural relaxation pathway of low-density amorphous ice

Low-density amorphous ice (LDA) is involved in critical cosmological processes and has gained prominence as one of the at least two distinct amorphous forms of ice. Despite these accolades, we still have an incomplete understanding of the structural diversity that is encompassed within the LDA state and the dynamic processes that take place upon heating LDA. Heating the high-pressure ice VIII phase at ambient pressure is a remarkable example of temperature-induced amorphisation yielding LDA. We investigate this process in detail using X-ray diffraction and Raman spectroscopy, and show that the LDA obtained from ice VIII is structurally different from the more 'traditional' states of LDA which are approached upon thermal annealing. This new structural relaxation pathway involves an increase of structural order on the intermediate range length scale. In contrast with other LDA materials the local structure is more ordered initially and becomes slightly more disordered upon annealing. We also show that the cascade of phase transitions upon heating ice VIII at ambient pressure includes the formation of ice IX which may be connected with the structural peculiarities of LDA from ice VIII. Overall, this study shows that LDA is a structurally more diverse material than previously appreciated.Comment: 12 pages, 5 figure

Autonomic dysregulation and self‐injurious thoughts and behaviours in children and young people: A systematic review and meta‐analysis

Background: self-injurious thoughts and behaviours (SITBs) have been associated with dysfunction of the Autonomic Nervous System (ANS) in children and young people, suggesting that objective ANS measures may aid assessment of suicide risk, but a systematic synthesis of this literature is currently lacking.Methods: following a pre-registered protocol (PROSPERO CRD42022327605), we conducted a systematic search of PubMed, Medline, Embase, PsycINFO, and Web of Science, for empirical studies published until 10th May 2022 that compared indices of ANS functioning in individuals aged 0–25 years with versus without SITBs, or reported continuous associations between ANS measures and SITBs. Study quality was assessed with the Newcastle-Ottawa Scales. Pooled effect sizes (Hedge's g) were estimated with random-effects meta-analytic models.Results: twenty studies (1979 participants) were included in our systematic review, with 16 included in meta-analyses. Results suggested that SITBs were associated with altered cardiac indices of arousal (g = −0.328, p < 0.001), which was driven by lower heart rate variability in individuals with SITBs (g = −0.375, p = 0.025). Overall results for electrodermal activity were not significant (g = 0.026, p = 0.857), but subgroup analyses showed increased activity in studies of individuals who engaged specifically in non-suicidal self-harm (g = 0.249, p = 0.014) but decreased activity in the remaining studies (g = −0.567, p = 0.004).Conclusions: our systematic review and meta-analysis found evidence of reduced parasympathetic regulation as well as more tentative evidence of altered electrodermal activity in children and young people displaying SITBs. Future longitudinal studies should test the clinical utility of these markers for detecting and monitoring suicide risk

Oscillatory neural networks underlying resting-state, attentional control and social cognition task conditions in children with ASD, ADHD and ASD+ADHD

Autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) are common and impairing neurodevelopmental disorders that frequently co-occur. The neurobiological mechanisms involved in ASD and ADHD are not fully understood. However, alterations in large-scale neural networks have been proposed as core deficits in both ASD and ADHD and may help to disentangle the neurobiological basis of these disorders and their co-occurrence. In this study, we examined similarities and differences in large-scale oscillatory neural networks between boys aged 8-13 years with ASD (n = 19), ADHD (n = 18), ASD + ADHD (n = 29) and typical development (Controls, n = 26). Oscillatory neural networks were computed using graph-theoretical methods from electroencephalographic (EEG) data collected during an eyes-open resting-state and attentional control and social cognition tasks in which we previously reported disorder-specific atypicalities in oscillatory power and event-related potentials (ERPs). We found that children with ASD showed significant hypoconnectivity in large-scale networks during all three task conditions compared to children without ASD. In contrast, children with ADHD showed significant hyperconnectivity in large-scale networks during the attentional control and social cognition tasks, but not during the resting-state, compared to children without ADHD. Children with co-occurring ASD + ADHD did not differ from children with ASD when paired with this group and vice versa when paired with the ADHD group, indicating that these children showed both ASD-like hypoconnectivity and ADHD-like hyperconnectivity. Our findings suggest that ASD and ADHD are associated with distinct alterations in large-scale oscillatory networks, and these atypicalities present together in children with both disorders. These alterations appear to be task-independent in ASD but task-related in ADHD, and may underlie other neurocognitive atypicalities in these disorders. [Abstract copyright: Copyright © 2019 Elsevier Ltd. All rights reserved.

Lyashko-Looijenga morphisms and submaximal factorisations of a Coxeter element

When W is a finite reflection group, the noncrossing partition lattice NCP_W of type W is a rich combinatorial object, extending the notion of noncrossing partitions of an n-gon. A formula (for which the only known proofs are case-by-case) expresses the number of multichains of a given length in NCP_W as a generalised Fuss-Catalan number, depending on the invariant degrees of W. We describe how to understand some specifications of this formula in a case-free way, using an interpretation of the chains of NCP_W as fibers of a Lyashko-Looijenga covering (LL), constructed from the geometry of the discriminant hypersurface of W. We study algebraically the map LL, describing the factorisations of its discriminant and its Jacobian. As byproducts, we generalise a formula stated by K. Saito for real reflection groups, and we deduce new enumeration formulas for certain factorisations of a Coxeter element of W.Comment: 18 pages. Version 2 : corrected typos and improved presentation. Version 3 : corrected typos, added illustrated example. To appear in Journal of Algebraic Combinatoric

Long-term stability of TES satellite radiance measurements

The utilization of Tropospheric Emission Spectrometer (TES) Level 2 (L2) retrieval products for the purpose of assessing long term changes in atmospheric trace gas composition requires knowledge of the overall radiometric stability of the Level 1B (L1B) radiances. The purpose of this study is to evaluate the stability of the radiometric calibration of the TES instrument by analyzing the difference between measured and calculated brightness temperatures in selected window regions of the spectrum. The Global Modeling and Assimilation Office (GMAO) profiles for temperature and water vapor and the Real-Time Global Sea Surface Temperature (RTGSST) are used as input to the Optimal Spectral Sampling (OSS) radiative transfer model to calculate the simulated spectra. The TES reference measurements selected cover a 4-year period of time from mid 2005 through mid 2009 with the selection criteria being; observation latitudes greater than −30° and less than 30°, over ocean, Global Survey mode (nadir view) and retrieved cloud optical depth of less than or equal to 0.01. The TES cloud optical depth retrievals are used only for screening purposes and no effects of clouds on the radiances are included in the forward model. This initial screening results in over 55 000 potential reference spectra spanning the four year period. Presented is a trend analysis of the time series of the residuals (observation minus calculations) in the TES 2B1, 1B2, 2A1, and 1A1 bands, with the standard deviation of the residuals being approximately equal to 0.6 K for bands 2B1, 1B2, 2A1, and 0.9 K for band 1A1. The analysis demonstrates that the trend in the residuals is not significantly different from zero over the 4-year period. This is one method used to demonstrate that the relative radiometric calibration is stable over time, which is very important for any longer term analysis of TES retrieved products (L2), particularly well-mixed species such as carbon dioxide and methane