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Mixing and diffusion in protoplanetary disc chemistry
Full text linkFunding: P.W. acknowledges funding from the European Union H2020-MSCA-ITN-2019 under Grant Agreement no. 860470 (CHAMELEON).We develop a simple iterative scheme to include vertical turbulent mixing and diffusion in PRODIMO thermo-chemical models for protoplanetary discs. The models are carefully checked for convergence towards the time-independent solution of the reaction-diffusion equations, as, for example, used in exoplanet atmosphere models. A series of five TTauri disc models is presented where we vary the mixing parameter αmix from zero to 10−2 and take into account: (a) the radiative transfer feedback of the opacities of icy grains that are mixed upwards; and (b) the feedback of the changing molecular abundances on the gas temperature structure caused by exothermic reactions, and increased line heating and cooling. We see considerable changes in the molecular and ice concentrations in the disc. The most abundant species (H2, CH4, CO, the neutral atoms in higher layers, and the ices in the midplane) are transported both up and down, and at the locations where these abundant chemicals finally decompose, for example by photo processes, the release of reaction products has important consequences for all the other molecules. This generally creates a more active chemistry, with a richer mixture of ionised, atomic, molecular, and ice species, and new chemical pathways that are not relevant in the unmixed case. We discuss the impact on three spectral observations caused by mixing and find that: (i) icy grains can reach the observable disc surface where they cause ice absorption and emission features at IR to far-IR wavelengths; (ii) mixing increases the concentrations of certain neutral molecules observable by mid-IR spectroscopy, in particular OH, HCN, and C2H2; and (iii) mixing can change the optical appearance of CO in ALMA line images and channel maps, where strong mixing would cause the CO molecules to populate the distant midplane.Peer reviewe
Genomic analyses in Drosophila do not support the classic allopatric model of speciation
Full text linkFunding: European Research Council (Grant Number: ModelGenomLand 757648); Natural Environment Research Council (Grant Numbers: NE/L011522/1, NE/V001566/1).The allopatric model of speciation has dominated our understanding of speciation biology and biogeography since the Modern Synthesis. It is uncontroversial because reproductive isolation may readily emerge as a by-product of evolutionary divergence during allopatry unopposed by gene flow. Recent genomic studies have found that gene flow between species is common, but whether allopatric speciation is common has rarely been systematically tested across a continuum of closely related species. Here, we fit a range of demographic models of evolutionary divergence to whole-genome sequence data from 93 pairs of Drosophila species to infer speciation histories and levels of post-divergence gene flow. We find that speciation with gene flow is common, even between currently allopatric pairs of species. Estimates of historical gene flow are not predicted by current range overlap. Whilst evidence for secondary contact is generally limited, a few sympatric pairs showed strong support for a secondary contact model. Our analyses suggest that most speciation processes involve some long-term gene flow, perhaps due to repeated cycles of allopatry and contact, without requiring an extensive allopatric phase.Peer reviewe
Decolonising and depatriarchalising research cultures : a conversation with RAMA, the transnational Latin American women’s audiovisual research network
Full text linkConference panels allow for free-flowing conversation with panellists and the audience. They lead to insights that come through thinking together with people that can bring complementary knowledge to the discussion. Yet these exchanges can also be ephemeral with ideas evaporating as we engage with the next paper or panel discussion. We address this in a search for a lasting contribution to debates in this write up of a panel on women and cinema, for the conference ‘Women and Cinema in Ibero-America: Politics, Histories, Representations, Intersectionality’, at the Universidad Carlos III de Madrid in September 2022. We agreed that the topics and the discussion at our panel were of broad interest and provide food for thought for academics wanting to adopt a decolonial feminist approach. Topics that we discussed included, how to approach archival research in women’s film and video, and how to ‘depatriarchalise’ the archives, and democratise access to them, as fundamental to offering a feminist perspective in archival research; how to challenge a Western androcentric paradigm and auteurist perspectives that too often erase women’s contribution to film cultures; and, how to challenge epistemological barriers that deny women creators voices. In addition, the panel presented a first-hand perspective of eurocentrism and the experience of European academia for a researcher from Brazil and discuss how a decolonial feminist film curator/programmer can be a gate-opener rather than a gate-keeper.Peer reviewe
An active matter model captures spatial dynamics of actomyosin oscillations in larval epithelial cells during Drosophila morphogenesis
No full textFunding: E.D.M. acknowledges funding by the endowed E.N.&M.N. Lindsay PhD studentship. A.B. acknowledges funding by a St Leonard’s College World Leading Scholarship to M.B.&J.K. R.S. acknowledges support from the UK Engineering and Physical Sciences Research Council (Award EP/W023946/1).The apicomedial actomyosin network is crucial for generating mechanical forces in cells. Oscillatory behavior of this contractile network is commonly observed before or during significant morphogenetic events. For instance, during the development of the Drosophila adult abdominal epidermis, larval epithelial cells (LECs) undergo pulsed contractions before being replaced by histoblasts. These contractions involve the formation of contracted regions of concentrated actin and myosin. The emergence and control of pulsed contractions are not fully understood. Here, we combined in vivo 4D microscopy with numerical simulations of an active elastomer model applied to realistic cell geometries and boundary conditions informed by cell polarity to study in vivo subcellular spatial patterns of LEC actomyosin dynamics. The active elastomer model quantitatively reproduced in vivo observations. When compared to rectangular domains, simulations on realistic cell geometries showed systematically better agreement with experiments. We found that cell shape, cell polarity, and organization of the cell’s actomyosin network codetermine spatiotemporal network dynamics both in vivo and in simulations. Furthermore, the model predicted changes to LEC contractile activity under genetic perturbation of the actomyosin network. Our results show that cell geometry, accompanied by boundary conditions which reflect the cells’ polarity, is important to understanding the dynamics of the apicomedial actomyosin network. Moreover, our findings support the notion that spatiotemporal oscillatory behavior of the actomyosin network is an emergent property of the actomyosin network, rather than driven by upstream signaling.Peer reviewe
Complex families in the United Kingdom : mapping children’s diverse family pathways and their correlates from birth to age ten
Full text linkFunding: This research was funded by the Economic and Social Research Council (ESRC; grant number 2460061) facilitated by the Scottish Graduate School of Social Science (SGSSS). Júlia Mikolai’s work was funded by UK Research and Innovation (UKRI) under the UK government’s Horizon Europe funding Guarantee [grant number: EP/Y036441/1].The rise in divorce, cohabitation, non-marital childbearing and multi-partner fertility means that today’s children are more likely to experience less common or less stable family settings compared to previous generations. This may lead to increasing inequalities across the life course. Unlike most existing studies on family change, we investigate family trajectories in the United Kingdom from children’s perspective. We map the family trajectories characterising children’s first ten years of life using multi-channel sequence analysis on data from the UK Household Longitudinal Study, jointly capturing the dynamics of maternal partnership histories and paternal co-residence patterns from the children’s perspective. Multinomial logistic regression is applied to understand the characteristics associated with experiencing different childhood family trajectories. Children experience six typical family trajectories: continuously married; early separation; continuously cohabiting; later separation; early solo motherhood; and a new father. From birth to age ten, over a quarter of children do not continuously live with their two biological parents. Children with lower-educated mothers, mothers in the youngest or oldest groups, who live in urban areas, and belong to certain ethnic groups (White British, Mixed, Caribbean, Black African) tend to experience less common or less stable trajectories. Our elucidation of factors associated with more/less stable childhood family pathways can inform policy decision-making around support for families to mitigate growing short- and long-term inequalities giving rise to children’s diverging destinies.Peer reviewe
Unconventional magnetism and residual entropy in La7Os3O18
Full text linkFunding: The authors acknowledge funding from the Engineering and Physical Sciences Research Council via EP/P024564/1 (AWR), EP/T011130/1 (ASG) as well as the University of St Andrews for a St Leonard's College World-Leading Doctoral Scholarship (ATB), the International Max Planck Research School for Chemistry and Physics of Quantum Materials (MTP), and the EPSRC for characterisation infrastructure via EP/V034138/1, EP/L017008/1, EP/R023751/1, EP/T019298/1 and EP/T031441/1.In this communication we describe the crystal structure and unusual magnetic properties of La7Os3O18, a new layered osmate with structurally discrete (non-corner-sharing) octahedra containing Os5+ with S = 3/2 and strong spin–orbit coupling. Investigations through powder X-ray diffraction, magnetometry and heat capacity measurements demonstrate that the material undergoes an antiferromagnetic ordering transition at TN = 43 ± 1 K, with a further broad overturn in susceptibility at T ≈ 14 K indicating low dimensional short range magnetic ordering. Curie–Weiss fits give an effective moment of µeff = 3.26µB per Os5+ and Weiss constant of θW ≈ −92 K. Heat capacity data reveal that it is the low temperature feature with which the majority of the magnetic entropy is associated. However, between our lowest temperature of 2 K and well above TN we find only approximately half of the expected magnetic entropy to be released. Magnetisation versus field measurements at low temperature reveal a hysteretic metamagnetic transition above 5 T, further indicating that the magnetism below TN is non-trivial in nature.Peer reviewe
Catalytic approaches towards heterocyclic aziridine and aryl ethylamine scaffolds
Full text linkNitrogen-containing heterocyclic scaffolds are prevalent within bioactive molecules and natural products. Of these, aziridine scaffolds represent viable targets, both as bioactive molecules (e.g., as covalent inhibitors) but also as synthetic intermediates within the synthesis of amine-containing molecules. The research described within this thesis details the development of methodologies for the synthesis of heterocyclic aziridine and ethylamine scaffolds.
Despite notable advances, the preparation of complex, α-heterocyclic aziridine variants is particularly challenging, with few examples within the literature. This space is instead dominated by aliphatic and aromatic substituents, presenting a significant gap within the chemical literature. This chapter details the discovery and development of a general method to the diastereoselective synthesis of disubstituted heterocyclic aziridines. Brønsted acid‑catalysis provides access to an intermediate 1,2‑chloroamine, via aza-Michael addition to trisubstituted alkenes. Diastereocontrol of this addition was found to be reliant on trace amounts of acid, and simple SNi allowed access to a variety of cis‑aziridines with complete stereochemical fidelity (up to 20:1 d.r.), which are notoriously inaccessible through alternative synthetic methodologies.
Aryl triazole moieties have also demonstrated widespread applicability within materials science, medicinal chemistry and chemical biology. This chapter details the development of a one-pot, modular reaction which can access 1,4-disubstituted 1,2,3-triazolyl aryl ethylamine scaffolds from styrenes. The methodology employs a single copper catalyst, accessing an aryl aziridine in-situ using metal-nitrene aziridination, which is regioselectively ring-opened by sodium azide, with Cu acting as a Lewis acid. Finally, copper catalysed azide-alkyne cycloaddition (CuAAC) delivers the desired products with high yield. The scope of this transformation was explored, and the method was applied to a variety of pharmaceutically relevant motifs
Raman shifting of XeCl laser radiation
Full text linkA XeCl excimer laser system whose output characteristics are suitable for stimulated Raman wavelength shifting, has been developed and used in single-pass conversion experiments in CH₄ and H₂. The overall system, comprising the laser, Raman focusing optics and Raman cell, has been designed with simplicity and system compactness in mind, suitable for a transportable lidar application.
The XeCl laser is a fast discharge pumped device, driven by a C C transfer circuit with a N₂ filled spark gap switch. Various ultraviolet preionisation schemes and cavity component arrangements, employed during the laser development, are described and compared. A general overview of the basic spark preionisation techniques commonly used in rare gas halide lasers is also presented. Over the course of the development, the available laser output power has been increased by a factor of 100, by methods described. Laser output characteristics relevant to stimulated Raman scattering (SRS), are the emission wavelength (308 nm), the output pulse energy (>100 mJ), pulse duration (~6.5 ns FWHM), peak pulse power (>10⁷ W) and the output beam divergence (4 × 15 mrad). The design for a new laser, using a low inductance cavity geometry and an ‘automatic-integral’ preionisation scheme is described.
The problems of poor laser beam quality and focusability which are inherent in rare gas halide lasers, are overcome by the use of an unstable optical resonator. Experiments with a range of ‘continuously coupled’ unstable resonators, in which the laser output coupler is a simple planoconvex lens, are reported. They show that pulse duration, energy and beam divergence are systematically reduced as the round trip resonator magnification M is increased, with the result that the focal spot area can be up to 2000 times smaller than obtainable with conventional stable cavity optics. Furthermore, these output characteristics are shown to depend not simply on the overall value of M, but also on the individual one way magnifications M₁₂ and M₂₁ in the resonator, between mirrors 1 and 2. The dependence has produced significant experimental differences in resonators with very similar values of M. This new observation is attributed, in part, to the shortness of the laser pulse duration in this device.
Experiments have been performed in high pressure CH₄ and H₂ to find the pumping geometries necessary to achieve SRS. The most unstable of the range of resonators studied, having the least divergent output and the highest beam quality, is shown to be the best configuration for the application. In addition, it is found that pump focal power densities greater than 10¹⁰ W/cm² do not automatically guarantee coherent scattering if they have been produced as a result of tight focusing, and that a relatively long Raman focusing length (≥50 cm) is a more fundamental experimental requirement.
Raman scattering in CH₄ has generated output lines from the first anti Stokes (AS₁) to the fourth Stokes (S₄) order, at wavelengths of 283nm, 338nm, 375nm, 421nm and 480nm. The higher Raman gain in H₂ has produced a wider range of Raman shifted orders, extending from the ultraviolet into the infrared, at wavelengths given by 245nm (AS₂), 273nm, 353nm, 414nm, 500nm, 631nm and 855nm (S₅). The relative abundance of the competing SRS and four wave mixing processes in the Raman cell, which determine the range and distribution of energy within the Raman spectrum, has been varied by reducing the feasibility of angular phase matching in the medium. Increasing the pump beam focal length and the Raman cell pressure has enabled the overall energy conversion efficiency into the S₁ order to be optimised at ~29% in H₂, for a corresponding pump depletion of ~32%. For the most intense region of the XeCl laser pump beam only, these values were measured to be 56% and 60% respectively
Dexterous destriers : the literal and figurative horse as educator in Early Modern France, 1500-1625
No full textThis thesis assesses the role of the horse and horsemanship in the education of the nobility in sixteenth- and early seventeenth-century France through a parallel examination of didactic texts on the topic of horsemanship and its literary representations in contemporaneous canonical texts. Where most studies to date have focused either on actual practice or literary representations, this thesis brings these spheres into dialogue to reveal the extent to which they evolved in tandem, ultimately arguing that this interaction led to horsemanship being viewed as a practice with both physical and intellectual benefits. Chapter 1 focusses on childhood education, situating horsemanship as a fundamental part of noble education through the example of Rabelais’s Gargantua and his wooden horses, where Rabelais portrays horsemanship as a means of exploring physical and linguistic creativity. Chapter 2 transitions to adolescence as it examines Ronsard’s poetry in praise of his riding master, François de Carnavalet, in which the poet draws on the myth of Pegasus and Bellerophon to establish a connection between horsemanship and the poetic arts. Chapter 3 assesses how the same mythical pairing became a literal emblem of equestrian print culture as the printer’s mark of Charles Perier, an image which fuses a literary significance with the physical practice of horsemanship. Chapter 4 examines how the emergent genre of didactic riding manuals, specifically those of Federico Grisone, Salomon de La Broue and Antoine de Pluvinel, employs a narrative approach to riding that solidifies the development of horse and rider as a partnership and encourages self-improvement through discipline. Finally, Chapter 5 reflects on a lifetime of practice through the example of Montaigne, assessing his praise of horsemanship as an aid to improving physical mobility and proposing a kinesic reading of the Essais to explore his conception of riding as an aid to cognition and literary creation
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