The mechanics of Arabidopsis seed germination

Germination is defined as the protrusion of the embryonic radicle through the seed coat layers (endosperm and testa). As the radicle elongates, the testa ruptures, followed by rupture of the endosperm. Arabidopsis seeds exhibit a two-step germination process with sequential rupture of the testa and endosperm. We are interested in exploring the physical process of germination. Whilst much effort has previously been placed on genetic networks, a mathematical approach for furthering the understanding of the physical/mechanical properties of germination has not yet been described. The Mathematics in Plant Sciences Study Group helped us to develop a better understanding of the problem. Several different mathematical models were generated for radicle growth and endosperm stretching. These models were developed on multiscale dimensions – looking at the organ, tissue and cellular levels. The outcomes of the study group have heightened our interest in the mechanical aspects of germination, and we are currently progressing with a grant proposal – a collaboration between the Schools of Biosciences and Engineering at the University of Nottingham, and a group from the Department of Biology at the University of Freiburg, Germany

An electric-field representation of the harmonic XY model

The two-dimensional harmonic XY (HXY) model is a spin model in which the classical spins interact via a piecewise parabolic potential. We argue that the HXY model should be regarded as the canonical classical lattice spin model of phase fluctuations in two-dimensional condensates, as it is the simplest model that guarantees the modular symmetry of the experimental systems. Here we formulate a lattice electric-field representation of the HXY model and contrast this with an analogous representation of the Villain model and the two-dimensional Coulomb gas with a purely rotational auxiliary field. We find that the HXY model is a spin-model analogue of a lattice electric-field model of the Coulomb gas with an auxiliary field, but with a temperature-dependent vacuum (electric) permittivity that encodes the coupling of the spin vortices to their background spin-wave medium. The spin vortices map to the Coulomb charges, while the spin-wave fluctuations correspond to auxiliary-field fluctuations. The coupling explains the striking differences in the high-temperature asymptotes of the specific heats of the HXY model and the Coulomb gas with an auxiliary field. Our results elucidate the propagation of effective long-range interactions throughout the HXY model (whose interactions are purely local) by the lattice electric fields. They also imply that global spin-twist excitations (topological-sector fluctuations) generated by local spin dynamics are ergodically excluded in the low-temperature phase. We discuss the relevance of these results to condensate physics.Comment: 13 pages, 10 figure

Topological-sector fluctuations and ergodicity breaking at the Berezinskii-Kosterlitz-Thouless transition

The Berezinskii-Kosterlitz-Thouless (BKT) phase transition drives the unbinding of topological defects in many two-dimensional systems. In the two-dimensional Coulomb gas, it corresponds to an insulator-conductor transition driven by charge deconfinement. We investigate the global topological properties of this transition, both analytically and by numerical simulation, using a lattice-field description of the two-dimensional Coulomb gas on a torus. The BKT transition is shown to be an ergodicity breaking between the topological sectors of the electric field, which implies a definition of topological order in terms of broken ergodicity. The breakdown of local topological order at the BKT transition leads to the excitation of global topological defects in the electric field, corresponding to different topological sectors. The quantized nature of these classical excitations, and their strict suppression by ergodicity breaking in the low-temperature phase, afford striking global signatures of topological-sector fluctuations at the BKT transition. We discuss how these signatures could be detected in experiments on, for example, magnetic films and cold-atom systems.Comment: 11 pages, 6 figure

Phase order in superfluid helium films

Classic experimental data on helium films are transformed to estimate a finite-size phase order parameter that measures the thermal degradation of the condensate fraction in the two-dimensional superfluid. The order parameter is found to evolve thermally with the exponent $\beta = 3 \pi^2/128$, a characteristic, in analogous magnetic systems, of the Berezinskii-Kosterlitz-Thouless (BKT) phase transition. Universal scaling near the BKT fixed point generates a collapse of experimental data on helium and ferromagnetic films, and implies new experiments and theoretical protocols to explore the phase order. These results give a striking example of experimental finite-size scaling in a critical system that is broadly relevant to two-dimensional Bose fluids.Comment: 6 pages, 2 figure

Every breath you take:new insights into plant and animal oxygen sensing

Responses to hypoxia are regulated by oxygen-dependent degradation of kingdom-specific proteins in animals and plants. Masson et al. (2019) identified and characterized the mammalian counterpart of an oxygen-sensing pathway previously only observed in plants. Alongside other recent findings identifying novel oxygen sensors, this provides new insights into oxygen-sensing origins and mechanisms in eukaryotes.</p

Using Ecological Data as a Foundation for Decision-Making in the USA

Decisions that impact the quality of aquatic systems are being made daily throughout the world based on little or no ecological information (Barbour et al., 2004). Monitoring information, based on scientifically and rigorously tested ecological indicators, is integral to water quality management programs for protecting human health, preserving and restoring ecosystem integrity, and sustaining a viable economy. Under the Clean Water Act of the United States, water quality agencies of the states and tribes are required to conduct monitoring and assessment to address the mandates of the law. However, recent critiques of water monitoring programs have claimed that the United States Environmental Protection Agency (U.S. EPA) and State water quality agencies cannot make statistically valid inferences about water quality and the condition of the Nation's waters, i.e., whether they are improving, degrading or remaining the same; furthermore, we lack data to support management decisions regarding the Nation's aquatic resources. The National Wadeable Streams Assessment Program (WSA) was established in early 2004 to answer the question of what is the status of the Nation's waters, and to maximize partnerships among U.S. EPA, States and Tribes, and other agencies to establish a framework to address issues at state and local scales. Ecological data in any form require some measure of translation to be useable by the environmental manager, i.e., a hierarchy exists in the translation process from basic biological data in its rawest form through a series of manipulations in the analysis phase to reporting of the results and interpretation. This nationally focused program is a step towards ensuring adequate monitoring data exist in the future to assess water quality and make sound watershed management decisions throughout the USA; actions are taken to protect and restore water quality that maximize benefits and minimize costs; and sound science forms the basis of making informed decisions regarding our aquatic resource.Diariamente se están tomando decisiones que inciden en la calidad de los sistemas acuáticos basadas en escasa o ninguna información ecológica (Barbour et al., 2004). La información obtenida en programas de gestión, basada en indicadores cient'ıficos y basados en indicadores ecológicos, se integra en programas de gestión de la calidad del agua para la protección de la salud humana, la preservación o restauración de la integridad de los ecosistemas y el sostenimiento de una economía viable. Por mandato del Acta sobre el Agua Limpia de los Estados Unido, se han creado agencias a nivel de Estados o regiones para realizar programas de estudio y gestión para cumplir el mandato de la ley. No obstante, recientemente han surgido críticas a los programas de gestión señalando que la Agencia de Protección Ambiental de los Estados Unidos (U.S. EPA) y las agencias de calidad del agua estatales no pueden realizar inferencias estadísticamente válidas acerca de la calidad del agua y de la situación de las aguas de la nación, p. e. si estan mejorando, degradando o permanecen igual. Además, no tenemos datos para apoyar las decisiones de gestión en relación con los recursos acuáticos nacionales. El Programa de Estudio de los Ríos Vadeables (WSA) se estableció en 2004 para responder a la pregunta de cual es la situación de las aguas de la nación, y para maximizar la colaboración entre U.S. EPA, y las agencias estatales, locales y similares para realizar un marco de trabajo que permita establecer los objetivos a escalas estatal y local. La información ecológica de cualquier tipo requiere algunas medidas de traducción para que sea utilizable por los gestores ambientales, p. e. existe una jerarquía en el proceso de traslación desde datos biológicos básicos, en su forma poco elaborada, hasta una serie de manipulaciones en la fase de análisis para los informes de resultados y su interpretación. Este programa enfocado a nivel nacional es un paso para asegurar que existen datos adecuados de gestión a través de todo el país. Se están realizando actuaciones para proteger y mejorar la calidad del agua que maximice los beneficios y minimice los costes a la vez que establezcan las bases científicas para tomar decisiones teniendo en cuenta nuestros recursos acuáticos

Virtuous character for the practice of law : research report

The Jubilee Centre’s new report, Virtuous Character for the Practice of Law, sets about trying to examine the place of character and values in the legal profession in Britain. The report draws its findings from a UK focused survey of 966 lawyers and aspiring lawyers at varying stages of their careers. It is one of the largest pieces of research carried out in Britain focusing on issues of character and virtue within a specific industry sector

Comparative Biology of Oxygen Sensing in Plants and Animals

© 2020 Elsevier Inc. Aerobic respiration is essential to almost all eukaryotes and sensing oxygen is a key determinant of survival. Analogous but mechanistically different oxygen-sensing pathways were adopted in plants and metazoan animals, and include ubiquitin-mediated degradation of transcription factors and direct sensing via non-heme iron(Fe2+)-dependent-dioxygenases. Key roles for oxygen sensing have been identified in both groups, with downstream signalling focussed on regulating gene transcription and chromatin modification to control development and stress responses. Components of sensing systems are promising targets for human therapeutic intervention and developing stress-resilient crops. Here, we review current knowledge about the origins, commonalities and differences between oxygen sensing in plants and animals. Holdsworth and Gibbs review the comparative evolution and functions of oxygen-sensing in plants and animals, pathways that are analogous but mechanistically distinct, with essential roles in regulating gene expression and physiology