Obituary| October 31, 2022 ObituaryMarcelle K. Boudagher-Fadel, B.Sc., M.Sc., Ph.D. 1956‐2022 Geoffrey David Price Geoffrey David Price Professor of Mineral Physics, University College London, Gower St., London, WC1E 6BT, UK Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (2022) 52 (4): 197–201. https://doi.org/10.2113/gsjfr.52.4.197 Article history first online: 31 Oct 2022 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Geoffrey David Price; ObituaryMarcelle K. Boudagher-Fadel, B.Sc., M.Sc., Ph.D. 1956‐2022. Journal of Foraminiferal Research 2022;; 52 (4): 197–201. doi: https://doi.org/10.2113/gsjfr.52.4.197 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search View largeDownload slideView largeDownload slide Marcelle BouDagher-Fadel was a Professorial Research Associate at University College London, where she spent her academic life for over 40 years. She was an internationally recognised expert on Larger Benthic and Planktonic Foraminifera. Marcelle's outstanding microscope skills enabled her to identify, at the species level, randomly sectioned fossil foraminifera in rock thin sections, dating from the Holocene to the Carboniferous. Her truly remarkable capability made her a highly sought-after collaborator, and she worked with many research teams around the world. She authored over 200 scientific outputs, perhaps most noteworthy being her two... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

In leadership positions at UCL, we have spent more than a decade seeking to fulfil our university's founding commitment—inspired almost two centuries ago by the utilitarian philosopher Jeremy Bentham—to innovation, accessibility, and relevance for the benefit of humanity. Our guiding principle has been to make our institution and its activities greater than the sum of its parts. To enable us to have most impact in “sustainable human progress,” we have focused our approach on cross-disciplinarity—by which we mean collaboration between experts in different disciplines that transcends subject boundaries—because the problems faced by society cannot be solved by research from one discipline alone. In recent years we have come to understand the boundaries between disciplines to be a subset of the many types of barriers—such as those between communities (disciplinary, academic and otherwise) and between different kinds of activity—that can inhibit the fulfilment of our vision to maximise our public benefit. In order to address crucial challenges—from the local to the global—we need to form collaborations across society that increase our mutual knowledge and engagement. We need to understand how the translation and application of knowledge will change in different settings and according to different practicalities. And we need to better reflect and enhance our role as convenors of different stakeholders to promote greater shared dialogue, co-creation and action.

The superfamily Alveolinoidea is a member of the Order Miliolida, and is comprised of three main families, the Alveolinidae, the Fabulariidae and the Rhapydioninidae. They are examples of Larger Benthic Foraminifera (LBF), which are single cell organisms with specific characteristic endoskeletons. Alveolinoids are found globally from the Cretaceous to present day and are very important biostratigraphic index fossils in shallow-marine carbonates. They are often associated with significant hydrocarbon reservoirs, and exhibit provincialism with characteristic genera often confined to one of the American, Tethyan or Indo-Pacific provinces. Previously, the systematic study of the global interrelationship between the various alveolinoid lineages has not been possible because of the absence of biostratigraphic correlation between the geographically scattered assemblages, and the scarcity of described material from the Indo-Pacific province. Here we use the literature and new material from the Americas, the French Alps, Iran, Tibet, India and SE Asia, coupled with the use the planktonic foraminiferal zonal (PZ) correlation scheme to put forward, for the very first time, a comprehensive, global, systematic analysis of the biostratigraphic, phylogenetic and palaeogeographic evolution of the alveolinoids. The alveolinoids originated in the Cretaceous in the Tethyan province. During a global sea-level low-stand, a westward migration of some alveolinoids species to the Americas occurred in this period, a behaviour also seen in previous studies of contemporaneous orbitolinid LBF. After the K-P event, which saw the extinction of all Cretaceous alveolinoids, rare new forms of alveolinoids evolved again, first in the Americas and later independently in Tethys. As found in previous studies of rotalid LBF, sea-level low-stands in the Paleocene also allowed some alveolinoid forms to migrate, but this time in an eastward direction from the Americas to Tethys, and from Tethys on to the Indo-Pacific. Alveolinoids still exist today ( Borelis and Alveolinella ), the former of which is cosmopolitan, while the latter is restricted to the Indo-Pacific province. Throughout their phylogenetic history alveolinoids characteristically exhibit convergent evolution, with the repeated re-occurrence of certain morphological features. Understanding this propensity to homoplasy is essential in understanding and constructing the phylogenetic relationships within the alveolinoid superfamily.

Members of the Larger Benthic Foraminiferal (LBF) family Orbitolinidae occured from the Cretaceous to the Paleogene, however, they were most diverse during the mid-Cretaceous, and dominated the agglutinated LBF assemblages described from limestones of that period. Various orbitolinid species have been used to zone and date lithologies formed in the shallow, warm waters of the Aptian to the Early Cenomanian, and many, sometimes inaccurate, generic and sub-generic nomenclatures have been proposed to differentiate the often subtle morphological changes that orbitolinids exhibit over time. Until now, it has not been possible to develop an effective global overview of their evolution and environmental development because descriptions of specimens from Asia have been relatively rare. Following our recent study of over 1800 orbitolinid-rich thin sections of material from 13 outcrops of the Langshan Limestone, from the Southern Tibetan Plateau, and from the Barito Basin, South Kalimantan, Indonesia, it has been possible to compare the stratigraphic ranges of these orbitolinids with previously described Tethyan and American forms, based on the use of a planktonic zonal (PZ) scheme, itself tied to the most recent chronostratigraphic scale. This has allowed the reconstruction of the phylogenetic and paleogeographic evolution of the orbitolinids from their Valanginian origin in the Tethys. Although Tethys remained the paleogeographic focus for the orbitolinids, it is inferred here for the first time that a bi-directional paleogeographic migration of some orbitolinid genera occurred from Tethys to the Americas and also to the Western Pacific region. Our observations and dating confirm that global marine regressions in the Aptian were coincident with, and may well have facilitated, these orbitolinid transoceanic migrations. However, migration stopped after rising sea-level in the Early Albian appears to have again isolated these provinces from each other. Tectonic forces associated with the subduction of the Farallon Plate and further sea-level raises led to the opening of the Western Interior Seaway in the North America, which correlates with, and may have been the cause of, the Middle Albian (top of PZ Albian 2) extinction of the American orbitolinids. The extinction of the orbitolinids revealed that the Western Pacific province was split into two sub-provinces, with extinction occurring at the end of the Early Albian (top of PZ Albian 1) in the Northwest Pacific sub-province, and at the end of the Albian (top of PZ Albian 4) in the sub-province that is today South East Asia (on the margins and west of the Wallace Line). The final virtual extinction of the orbitolinids occurred at the end of the Cenomanian in the Tethyan province, which coincides with, and may have been caused by, global anoxic oceanic events that correlate with a near-peak Mesozoic eustatic sea-level high-stand that led to the overall global collapse of the paleotropical reef ecosystem at that time.

The nature of the apparently continuous structural phase transition at 1,049 K in the perovskite-structured, MgSiO3 isomorph, neighborite (NaMgF3), from the orthorhombic (Pbnm) hettotype phase to the cubic (\( Pm\overline{3} m \)) aristotype structure, has been re-investigated using high-resolution, time-of-flight neutron powder diffraction. Using data collected at 1 K intervals close to the nominal phase transition temperature, the temperature dependence of the intensities of superlattice reflections at the M point \( \left( {\frac{2\pi }{a}\left[ {\frac{1}{2},\frac{1}{2},0} \right]} \right) \) and the R point \( \left( {\frac{2\pi }{a}\left[ {\frac{1}{2},\frac{1}{2},\frac{1}{2}} \right]} \right) \) of the pseudocubic Brillouin zone indicate the existence of a new intermediate tetragonal phase in space group P4/mbm, with a narrow phase field extending from ~1,046.5 to ~1,048.5 K, at ambient pressure. Group theoretical analysis shows that the structural transitions identified in this study, Pbnm–P4/mbm, and P4/mbm–\( Pm\overline{3} m \), are permitted to be second order. The observation of the tetragonal phase resolves the longstanding issue of why the high-temperature phase transition, previously identified as Pbnm–\( Pm\overline{3} m \), and which would be expected to be first order under Landau theory, is in fact found to be continuous. Analysis of the pseudocubic shear strain shows it to vary with a critical exponent of 0.5 implying that the phase transition from Pbnm to P4/mbm is tricritical in character. The large librational modes that exist in the MgF6 octahedron at high temperature, and the use of Gaussian probability density functions to describe atomic displacements, result in apparent bond shortening in the Mg–F distances, making mode amplitude determination an unreliable method for determination of the critical exponent from internal coordinates. Crystal structures are reported for the three phases of NaMgF3 at 1,033 K (Pbnm), 1,047 K (P4/mbm) and 1,049 K (\( Pm\overline{3} m \)).

We use an atomistic computer model to calculate the energies of point defects in MgSiO3 perovskite. A magnesium and oxygen Schottky pair defect is predicted to be the lowest energy defect in this structure, while Si Frenkel pair defects are the most difficult to form. The diffusion of oxygen in the perovskite lattice is predicted to occur most readily along <100> of the orthorhombic cell, and to have an activation energy of 452 kJmol−1 for intrinsic diffusion and 81 kJmol−1 for extrinsic diffusion. The predicted activation volume for this process is 1.6 cm3mol−1. All of these values are in excellent agreement with inferred or measured behaviour in other perovskite and related phases. This study lays the foundations for further work aimed at determining the rheological behaviour of silicate perovskites and hence of the Earth's lower mantle

We calculated thermo-elastic properties of pyrope (Mg3Al2Si3O12) at mantle pressures and temperatures using Ab initio molecular dynamic simulation. A third-order Birch-Murnaghan equation at a reference temperature of 2 000 K fits the calculations with bulk modulus, K 0=159.5 GPa, K 0′=4.3, V 0=785.89 Å3, Grüneisen parameter, γ 0=1.15, q=0.80, Anderson Grüneisen parameter δ T =3.76 and thermal expansion, α 0=2.93×10−5 K−1. Referenced to room temperature, where V 0=750.80 Å3, γ 0 and α 0 become 1.11 and 2.47×10−5 K−1. The elastic properties of pyrope are found to be nearly isotropic at transition zone conditions.

We present a general strategy for generating full atomistic models of nanopolycrystalline materials including bulk and thin film. In particular, models for oxide nanoparticles were constructed using simulated amorphisation and crystallisation and used to populate a library of oxide nanoparticles (amorphous and crystalline) with different radii. Nanoparticles were then taken from this library and positioned, within a specific volume, using Monte Carlo techniques, to facilitate a tight-packed structure. The grain size distribution of the polycrystalline material was controlled by selecting particular sized nanoparticles from the library. The (randomly oriented) grains facilitated a polycrystalline oxide, which comprised a network of general grain-boundaries. To help validate the model, gas diffusion through the (polycrystalline) oxide material was then simulated and the activation energy calculated directly. Specifically, we explored He transport in UO2, which is an important material with respect to both civilian and military applications. We found that He transport proceeds much faster through the grain-boundary and grain-junction network compared with intracrystalline UO2 regions, in accord with experiment.

We discuss calculations of the electronic and crystallographic structure at the interfaces of titanium-carbon and tungsten-carbon superlattices. Specifically, we present total energy calculations for an arrangement of atoms designed to allow direct investigation of the competition between the formation of M-C bonds and C-C bonds. We conclude that the equilibrium structure is dominated by C-C bonding and so find that the interface has a graphite-like atomic arrangement rather than a carbide-like arrangement. These total energy calculations have been performed using a recently developed self-consistent linear combination of muffin-tin orbitals electronic structure method. This is a full-potential, all-electron, variation on standard LMTO electronic structure methods and, along with careful self-consistent determination of the parameters involved, allows accurate total energy calculations of the type of low symmetry systems involved in this study.

We present a general strategy for generating full atomistic models of nanopolycrystalline materials including bulk and thin film. In particular, models for oxide nanoparticles were constructed using simulated amorphisation and crystallisation and used to populate a library of oxide nanoparticles (amorphous and crystalline) with different radii. Nanoparticles were then taken from this library and positioned, within a specific volume, using Monte Carlo techniques, to facilitate a tight-packed structure. The grain-size distribution of the polycrystalline material was controlled by selecting particular sized nanoparticles from the library. The (randomly oriented) grains facilitated a polycrystalline oxide, which comprised a network of general grain-boundaries. To help validate the model, gas diffusion through the (polycrystalline) oxide material was then simulated and the activation energy calculated directly. Specifically, we explored He transport in UO(2), which is an important material with respect to both civilian and military applications. We found that He transport proceeds much faster through the grain-boundary and grain-junction network compared with intracrystalline UO(2) regions, in accordance with experiment.

Computer modeling techniques using well-tested potential models to describe the interatomic interactions have been used to study the surface carbonation of the low index surfaces of magnesium and calcium oxides. We begin by studying the {100} surface and related, stepped {310} surface of these model oxides. Our results indicate that carbonation is indeed a favorable process, particularly enhanced by the inclusion of the step on the surface, and proceeds via incorporation into the surface. rather than mono- or bidentate adsorption above the surface. As the amount of surface carbonation is increased, surface energy lowers to a minimum, with calculated vibrational frequencies indicating the formation of a layer of carbonate material. In comparison to water adsorption, the majority of calcium oxide surfaces are predicted to compete favorably, whereas the magnesium equivalents show a greater stability from water. This is particularly apparent for the higher energy, polar {111} surface which forms a very stable hydroxylated surface.

Nanomaterials synthesized from nanobuilding blocks promise size-dependent properties, associated with individual nanoparticles, together with collective properties of ordered arrays. However, one cannot position nanoparticles at specific locations; rather innovative ways of coaxing these particles to self-assemble must be devised. Conversely, model nanoparticles can be placed in any desired position, which enables a systematic enumeration of nanostructure from model nanobuilding blocks. This is desirable because a list of chemically feasible hypothetical structures will help guide the design of strategies leading to their synthesis. Moreover, the models can help characterize nanostructure, calculate (predict) properties, or simulate processes. Here, we start to formulate and use a simulation strategy to generate atomistic models of nanomaterials, which can, potentially, be synthesized from nanobuilding block precursors. Clearly, this represents a formidable task because the number of ways nanoparticles can be arranged into a superlattice is infinite. Nevertheless, numerical tools are available to help build nanoparticle arrays in a systematic way. Here, we exploit the "rules of crystallography" and position nanoparticles, rather than atoms, at crystallographic sites. Specifically, we explore nanoparticle arrays with cubic, tetragonal, and hexagonal symmetries together with primitive, face centered cubic and body centered cubic nanoparticle "packing". We also explore binary nanoparticle superlattices. The resulting nanomaterials, spanning CeO2, Ti-doped CeO2, ZnO, ZnS, MgO, CaO, SrO, and BaO, comprise framework architectures, with cavities interconnected by channels traversing (zero), one, two and three dimensions. The final, fully atomistic models comprise three hierarchical levels of structural complexity: crystal structure, microstructure (i.e., grain boundaries, dislocations), and superlattice structure.

We have used density functional theory to investigate the stability of MgAl 2 O 4 polymorphs under pressure. Our results can reasonably explain the transition sequence of MgAl 2 O 4 polymorphs observed in previous experiments. The spinel phase (stable at ambient conditions) dissociates into periclase and corundum at 14 GPa. With increasing pressure, a phase change from the two oxides to a calcium-ferrite phase occurs, and finally transforms to a calcium-titanate phase at 68 GPa. The calcium-titanate phase is stable up to at least 150 GPa, and we did not observe a stability field for a hexagonal phase or periclase + Rh 2 O 3 (II)-type Al 2 O 3 . The bulk moduli of the phases calculated in this study are in good agreement with those measured in high-pressure experiments. Our results differ from those of a previous study using similar methods. We attribute this inconsistency to an incomplete optimization of a cell shape and ionic positions at high pressures in the previous calculations.

Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK, Bayerisches Geoinstut, Universität Bayreuth, D-95440 Bayreuth, Germany, Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089, USA, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK, ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Chilton, Didcot, Oxon OX11 0QX, UK, Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK, and Materials Science Centre, University of Manchester, Grosvenor Street, Manchester M1 7HS, UK. Correspondence e-mail: ian.wood@ucl.ac.uk

First-principles simulations and high-pressure experiments were used to study the stability of BaCO3 carbonates at high pressures. Witherite, which is orthorhombic and isotypic with CaCO3 aragonite, is stable at ambient conditions. As pressure increases, BaCO3 transforms from witherite to an orthorhombic post-aragonite structure at 8 GPa. The calculated bulk modulus of the post-aragonite structure is 60.7 GPa, which is slightly less than that from experiments. This structure shows an axial anisotropic compressibility and the a axis intersects with the c axis at 70 GPa, which implies that the pressure-induced phase transition reported in previous experimental study is misidentified. Although a pyroxene-like structure is stable in Mg- and Ca-carbonates at pressures >100 GPa, our simulations showed that this structure does not appear in BaCO3.