Search

Your search keyword '"Hill, Adrian A."' showing total 2,391 results
Start Over Author "Hill, Adrian A."
2,391 results on '"Hill, Adrian A."'

1. The Genomic Landscape of Oceania

Author

Quinto-Cortés, Consuelo D., Jonas, Carmina Barberena, Vieyra-Sánchez, Sofía, Oppenheimer, Stephen, González-Buenfil, Ram, Auckland, Kathryn, Robson, Kathryn, Parks, Tom, Moreno-Mayar, J. Víctor, Blanco-Portillo, Javier, Homburger, Julian R., Wojcik, Genevieve L., Severson, Alissa L., Friedlaender, Jonathan S., Friedlaender, Francoise, Allen, Angela, Allen, Stephen, Stoneking, Mark, Hill, Adrian V. S., Aho, George, Koki, George, Pomat, William, Bustamante, Carlos D., Phipps, Maude, Mentzer, Alexander J., Moreno-Estrada, Andrés, and Ioannidis, Alexander G.

Subjects
Quantitative Biology - Populations and Evolution
Abstract

Encompassing regions that were amongst the first inhabited by humans following the out-of-Africa expansion, hosting populations with the highest levels of archaic hominid introgression, and including Pacific islands that are the most isolated inhabited locations on the planet, Oceania has a rich, but understudied, human genomic landscape. Here we describe the first region-wide analysis of genome-wide data from population groups spanning Oceania and its surroundings, from island and peninsular southeast Asia to Papua New Guinea, east across the Pacific through Melanesia, Micronesia, and Polynesia, and west across the Indian Ocean to related island populations in the Andamans and Madagascar. In total we generate and analyze genome-wide data from 981 individuals from 92 different populations, 58 separate islands, and 30 countries, representing the most expansive study of Pacific genetics to date. In each sample we disentangle the Papuan and more recent Austronesian ancestries, which have admixed in various proportions across this region, using ancestry-specific analyses, and characterize the distinct patterns of settlement, migration, and archaic introgression separately in these two ancestries. We also focus on the patterns of clinically relevant genetic variation across Oceania--a landscape rippled with strong founder effects and island-specific genetic drift in allele frequencies--providing an atlas for the development of precision genetic health strategies in this understudied region of the world.

Published
2024

2. High-resolution African HLA resource uncovers HLA-DRB1 expression effects underlying vaccine response.

Author

Mentzer, Alexander, Dilthey, Alexander, Pollard, Martin, Gurdasani, Deepti, Karakoc, Emre, Carstensen, Tommy, Muhwezi, Allan, Cutland, Clare, Diarra, Amidou, da Silva Antunes, Ricardo, Paul, Sinu, Smits, Gaby, Wareing, Susan, Kim, HwaRan, Pomilla, Cristina, Chong, Amanda, Brandt, Debora, Neaves, Samuel, Timpson, Nicolas, Crinklaw, Austin, Lindestam Arlehamn, Cecilia, Rautanen, Anna, Kizito, Dennison, Parks, Tom, Auckland, Kathryn, Elliott, Kate, Mills, Tara, Ewer, Katie, Edwards, Nick, Fatumo, Segun, Webb, Emily, Peacock, Sarah, Jeffery, Katie, van der Klis, Fiona, Kaleebu, Pontiano, Vijayanand, Pandurangan, Peters, Bjorn, Sette, Alessandro, Cereb, Nezih, Sirima, Sodiomon, Madhi, Shabir, Elliott, Alison, McVean, Gil, Hill, Adrian, Sandhu, Manjinder, and Nielsen, Rasmus

Subjects
Humans, HLA-DRB1 Chains, Infant, Black People, Hepatitis B Vaccines, Quantitative Trait Loci, Male, Female, Uganda, Antibody Formation, Pertussis Vaccine, Vaccination, Whooping Cough
Abstract

How human genetic variation contributes to vaccine effectiveness in infants is unclear, and data are limited on these relationships in populations with African ancestries. We undertook genetic analyses of vaccine antibody responses in infants from Uganda (n = 1391), Burkina Faso (n = 353) and South Africa (n = 755), identifying associations between human leukocyte antigen (HLA) and antibody response for five of eight tested antigens spanning pertussis, diphtheria and hepatitis B vaccines. In addition, through HLA typing 1,702 individuals from 11 populations of African ancestry derived predominantly from the 1000 Genomes Project, we constructed an imputation resource, fine-mapping class II HLA-DR and DQ associations explaining up to 10% of antibody response variance in our infant cohorts. We observed differences in the genetic architecture of pertussis antibody response between the cohorts with African ancestries and an independent cohort with European ancestry, but found no in silico evidence of differences in HLA peptide binding affinity or breadth. Using immune cell expression quantitative trait loci datasets derived from African-ancestry samples from the 1000 Genomes Project, we found evidence of differential HLA-DRB1 expression correlating with inferred protection from pertussis following vaccination. This work suggests that HLA-DRB1 expression may play a role in vaccine response and should be considered alongside peptide selection to improve vaccine design.

Published
2024

3. A randomised trial of malaria vaccine R21/Matrix-M™ with and without antimalarial drugs in Thai adults

Author

Hanboonkunupakarn, Borimas, Mukaka, Mavuto, Jittamala, Podjanee, Poovorawan, Kittiyod, Pongsuwan, Pongphaya, Stockdale, Lisa, Provstgaard-Morys, Samuel, Chotivanich, Kesinee, Tarning, Joel, Hoglund, Richard M., Chimjinda, Natenapa, Ewer, Katie, Ramos-Lopez, Fernando, Day, Nicholas P. J., Dondorp, Arjen M., Hill, Adrian V., White, Nicholas J., von Seidlein, Lorenz, and Pukrittayakamee, Sasithon

Published
2024
Full Text
View/download PDF

4. Ancestry-specific analyses of genome-wide data confirm the settlement sequence of Polynesia

Author

Ioannidis, Alexander G., Blanco-Portillo, Javier, Hagelberg, Erika, Rodríguez-Rodríguez, Juan Esteban, Fox, Keolu, Hill, Adrian V. S., Bustamante, Carlos D., Feldman, Marcus W., Mentzer, Alexander J., and Moreno-Estrada, Andrés

Subjects
Quantitative Biology - Populations and Evolution, Quantitative Biology - Genomics
Abstract

By demonstrating the role that historical population replacements and waves of admixture have played around the world, the genetics work of Reich and colleagues has provided a paradigm for understanding human history [Reich et al. 2009; Reich et al. 2012; Patterson et al. 2012]. Although we show in Ioannidis et al. [2021] that the peopling of Polynesia was a range expansion, and not, as suggested by Huang et al. [2022], yet another example of waves of admixture and large-scale gene flow between populations, we believe that our result in this recently settled oceanic expanse is the exception that proves the rule., Comment: 6 pages, 1 figure

Published
2022

6. Mexican Biobank advances population and medical genomics of diverse ancestries

Author

Sohail, Mashaal, Palma-Martínez, María J., Chong, Amanda Y., Quinto-Cortés, Consuelo D., Barberena-Jonas, Carmina, Medina-Muñoz, Santiago G., Ragsdale, Aaron, Delgado-Sánchez, Guadalupe, Cruz-Hervert, Luis Pablo, Ferreyra-Reyes, Leticia, Ferreira-Guerrero, Elizabeth, Mongua-Rodríguez, Norma, Canizales-Quintero, Sergio, Jimenez-Kaufmann, Andrés, Moreno-Macías, Hortensia, Aguilar-Salinas, Carlos A., Auckland, Kathryn, Cortés, Adrián, Acuña-Alonzo, Víctor, Gignoux, Christopher R., Wojcik, Genevieve L., Ioannidis, Alexander G., Fernández-Valverde, Selene L., Hill, Adrian V. S., Tusié-Luna, María Teresa, Mentzer, Alexander J., Novembre, John, García-García, Lourdes, and Moreno-Estrada, Andrés

Published
2023
Full Text
View/download PDF

7. The public health impact and cost-effectiveness of the R21/Matrix-M malaria vaccine: a mathematical modelling study

Author

Schmit, Nora, Topazian, Hillary M, Natama, H Magloire, Bellamy, Duncan, Traoré, Ousmane, Somé, M Athanase, Rouamba, Toussaint, Tahita, Marc Christian, Bonko, Massa dit Achille, Sourabié, Aboubakary, Sorgho, Hermann, Stockdale, Lisa, Provstgaard-Morys, Samuel, Aboagye, Jeremy, Woods, Danielle, Rapi, Katerina, Datoo, Mehreen S, Lopez, Fernando Ramos, Charles, Giovanni D, McCain, Kelly, Ouedraogo, Jean-Bosco, Hamaluba, Mainga, Olotu, Ally, Dicko, Alassane, Tinto, Halidou, Hill, Adrian V S, Ewer, Katie J, Ghani, Azra C, and Winskill, Peter

Published
2024
Full Text
View/download PDF

8. Chemical and biological characterization of vaccine adjuvant QS-21 produced via plant cell culture

Author

Lv, Xiangmin, Martin, Jesse, Hoover, Heather, Joshi, Bishnu, Wilkens, Margaret, Ullisch, David A., Leibold, Thomas, Juchum, John S., Revadkar, Sanket, Kalinovska, Barbara, Keith, Justin, Truby, Adam, Liu, Gui, Sun, Elaine, Haserick, John, DeGnore, Jon, Conolly, Joseph, Hill, Adrian V.S., Baldoni, John, Kensil, Charlotte, Levey, Dan, Spencer, Alexandra J., Gorr, Gilbert, Findeis, Mark, and Tanne, Antoine

Published
2024
Full Text
View/download PDF

9. Safety and efficacy of malaria vaccine candidate R21/Matrix-M in African children: a multicentre, double-blind, randomised, phase 3 trial

Author

Mahamar, Almahamoudou, Sanogo, Koualy, Sidibe, Youssoufa, Diarra, Kalifa, Samassekou, Mamoudou, Attaher, Oumar, Tapily, Amadou, Diallo, Makonon, Dicko, Oumar Mohamed, Kaya, Mahamadou, Maguiraga, Seydina Oumar, Sankare, Yaya, Yalcouye, Hama, Diarra, Soumaila, Niambele, Sidi Mohamed, Thera, Ismaila, Sagara, Issaka, Sylla, Mala, Dolo, Amagana, Misidai, Nsajigwa, Simando, Sylvester, Msami, Hania, Juma, Omary, Gutapaka, Nicolaus, Paul, Rose, Mswata, Sarah, Sasamalo, Ibrahim, Johaness, Kasmir, Sultan, Mwantumu, Alexander, Annastazia, Kimaro, Isaac, Lwanga, Kauye, Mtungwe, Mwajuma, Khamis, Kassim, Rugarabam, Lighton, Kalinga, Wilmina, Mohammed, Mohammed, Kamange, Janeth, Msangi, Jubilate, Mwaijande, Batuli, Mtaka, Ivanny, Mhapa, Matilda, Mlaganile, Tarsis, Mbaga, Thabit, Yerbanga, Rakiswende Serge, Samtouma, Wendkouni, Sienou, Abdoul Aziz, Kabre, Zachari, Ouedraogo, Wendinpui Jedida Muriel, Yarbanga, G Armel Bienvenu, Zongo, Issaka, Savadogo, Hamade, Sanon, Joseph, Compaore, Judicael, Kere, Idrissa, Yoni, Ferdinand Lionel, Sanre, Tewende Martine, Ouattara, Seydou Bienvenu, Provstgaard-Morys, Samuel, Woods, Danielle, Snow, Robert W., Amek, Nyaguara, Ngetsa, Caroline J., Ochola-Oyier, Lynette Isabella, Musyoki, Jennifer, Munene, Marianne, Mumba, Noni, Adetifa, Uche Jane, Muiruri, Charles Mwangi, Mwawaka, Jimmy Shangala, Mwaganyuma, Mwatasa Hussein, Ndichu, Martha Njeri, Weya, Joseph Ochieng, Njogu, Kelvin, Grant, Jane, Webster, Jayne, Lakhkar, Anand, Ido, N. Félix André, Traore, Ousmane, Tahita, Marc Christian, Bonko, Massa dit Achille, Rouamba, Toussaint, Ouedraogo, D. Florence, Soma, Rachidatou, Millogo, Aida, Ouedraogo, Edouard, Sorgho, Faizatou, Konate, Fabé, Valea, Innocent, Datoo, Mehreen S, Dicko, Alassane, Tinto, Halidou, Ouédraogo, Jean-Bosco, Hamaluba, Mainga, Olotu, Ally, Beaumont, Emma, Ramos Lopez, Fernando, Natama, Hamtandi Magloire, Weston, Sophie, Chemba, Mwajuma, Compaore, Yves Daniel, Issiaka, Djibrilla, Salou, Diallo, Some, Athanase M, Omenda, Sharon, Lawrie, Alison, Bejon, Philip, Rao, Harish, Chandramohan, Daniel, Roberts, Rachel, Bharati, Sandesh, Stockdale, Lisa, Gairola, Sunil, Greenwood, Brian M, Ewer, Katie J, Bradley, John, Kulkarni, Prasad S, Shaligram, Umesh, and Hill, Adrian V S

Published
2024
Full Text
View/download PDF

11. Demistify: a large-eddy simulation (LES) and single-column model (SCM) intercomparison of radiation fog

Author

Boutle, Ian, Angevine, Wayne, Bao, Jian-Wen, Bergot, Thierry, Bhattacharya, Ritthik, Bott, Andreas, Ducongé, Leo, Forbes, Richard, Goecke, Tobias, Grell, Evelyn, Hill, Adrian, Igel, Adele L, Kudzotsa, Innocent, Lac, Christine, Maronga, Bjorn, Romakkaniemi, Sami, Schmidli, Juerg, Schwenkel, Johannes, Steeneveld, Gert-Jan, and Vié, Benoît

Subjects
Earth Sciences, Atmospheric Sciences, Astronomical and Space Sciences, Meteorology & Atmospheric Sciences, Atmospheric sciences, Climate change science
Abstract

An intercomparison between 10 single-column (SCM) and 5 large-eddy simulation (LES) models is presented for a radiation fog case study inspired by the Local and Non-local Fog Experiment (LANFEX) field campaign. Seven of the SCMs represent single-column equivalents of operational numerical weather prediction (NWP) models, whilst three are research-grade SCMs designed for fog simulation, and the LESs are designed to reproduce in the best manner currently possible the underlying physical processes governing fog formation. The LES model results are of variable quality and do not provide a consistent baseline against which to compare the NWP models, particularly under high aerosol or cloud droplet number concentration (CDNC) conditions. The main SCM bias appears to be toward the overdevelopment of fog, i.e. fog which is too thick, although the inter-model variability is large. In reality there is a subtle balance between water lost to the surface and water condensed into fog, and the ability of a model to accurately simulate this process strongly determines the quality of its forecast. Some NWP SCMs do not represent fundamental components of this process (e.g. cloud droplet sedimentation) and therefore are naturally hampered in their ability to deliver accurate simulations. Finally, we show that modelled fog development is as sensitive to the shape of the cloud droplet size distribution, a rarely studied or modified part of the microphysical parameterisation, as it is to the underlying aerosol or CDNC.

Published
2022

12. Porting the microphysics model CASIM to GPU and KNL Cray machines

Author

Brown, Nick, Nigay, Alexandr, Weiland, Michèle, Hill, Adrian, and Shipway, Ben

Subjects
Computer Science - Distributed, Parallel, and Cluster Computing
Abstract

CASIM is a microphysics scheme which calculates the interaction between moisture droplets in the atmosphere and forms a critical part of weather and climate modelling codes. However the calculations involved are computationally intensive and so investigating whether CASIM can take advantage of novel hardware architectures and the likely increase in performance this might afford makes sense. In this paper we present work done in porting CASIM to GPUs via the directive driven OpenACC and also modifying CASIM to take advantage of the Knights Landing (KNL) processor using OpenMP. Due to the design, models extracting out specific computational kernels for offload to the GPU proved suboptimal and instead the entire scheme was ported over to the GPU. We consider the suitability and maturity of OpenACC for this approach as well as important optimisations that were identified. Enabling CASIM to take advantage of the KNL was significantly easier, but still required careful experimentation to understand the best design and configuration. The performance of both versions of CASIM, in comparison to the latest generation of CPUs is discussed, before identifying lessons learnt about the suitability of CASIM and other similar models for these architectures. The result of this work are versions of CASIM which show promising performance benefits when utilising both GPUs and KNLs and enable the communities to take advantage of these technologies, in addition to general techniques that can be applied to other similar weather and climate models., Comment: Presented at CUG 2017

Published
2020

13. In-situ data analytics for highly scalable cloud modelling on Cray machines

Author

Brown, Nick, Weiland, Michèle, Hill, Adrian, and Shipway, Ben

Subjects
Computer Science - Distributed, Parallel, and Cluster Computing
Abstract

MONC is a highly scalable modelling tool for the investigation of atmospheric flows, turbulence and cloud microphysics. Typical simulations produce very large amounts of raw data which must then be analysed for scientific investigation. For performance and scalability reasons this analysis and subsequent writing to disk should be performed in-situ on the data as it is generated however one does not wish to pause the computation whilst analysis is carried out. In this paper we present the analytics approach of MONC, where cores of a node are shared between computation and data analytics. By asynchronously sending their data to an analytics core, the computational cores can run continuously without having to pause for data writing or analysis. We describe our IO server framework and analytics workflow, which is highly asynchronous, along with solutions to challenges that this approach raises and the performance implications of some common configuration choices. The result of this work is a highly scalable analytics approach and we illustrate on up to 32768 computational cores of a Cray XC30 that there is minimal performance impact on the runtime when enabling data analytics in MONC and also investigate the performance and suitability of our approach on the KNL., Comment: This is the pre-peer reviewed version of the following article: Leveraging MPI RMA to optimise halo-swapping communications in MONC on Cray machines, which has been published in final form at https://doi.org/10.1002/cpe.4331

Published
2020
Full Text
View/download PDF

14. A directive based hybrid Met Office NERC Cloud model

Author

Brown, Nick, Lepper, Angus, Weiland, Michèle, Hill, Adrian, Shipway, Ben, and Maynard, Chris

Subjects
Computer Science - Distributed, Parallel, and Cluster Computing
Abstract

Large Eddy Simulation is a critical modelling tool for the investigation of atmospheric flows, turbulence and cloud microphysics. The models used by the UK atmospheric research community are homogeneous and the latest model, MONC, is designed to run on substantial HPC systems with very high CPU core counts. In order to future proof these codes it is worth investigating other technologies and architectures which might support the communities running their codes at the exa-scale. In this paper we present a hybrid version of MONC, where the most computationally intensive aspect is offloaded to the GPU while the rest of the functionality runs concurrently on the CPU. Developed using the directive driven OpenACC, we consider the suitability and maturity of this technology to modern Fortran scientific codes as well general software engineering techniques which aid this type of porting work. The performance of our hybrid model at scale is compared against the CPU version before considering other tuning options and making a comparison between the energy usage of the homo- and hetero-geneous versions. The result of this work is a promising hybrid model that shows performance benefits of our approach when the GPU has a significant computational workload which can not only be applied to the MONC model but also other weather and climate simulations in use by the community.

Published
2020
Full Text
View/download PDF

15. A highly scalable Met Office NERC Cloud model

Author

Brown, Nick, Weiland, Michèle, Hill, Adrian, Shipway, Ben, Maynard, Chris, Allen, Thomas, and Rezny, Mike

Subjects
Computer Science - Software Engineering
Abstract

Large Eddy Simulation is a critical modelling tool for scientists investigating atmospheric flows, turbulence and cloud microphysics. Within the UK, the principal LES model used by the atmospheric research community is the Met Office Large Eddy Model (LEM). The LEM was originally developed in the late 1980s using computational techniques and assumptions of the time, which means that the it does not scale beyond 512 cores. In this paper we present the Met Office NERC Cloud model, MONC, which is a re-write of the existing LEM. We discuss the software engineering and architectural decisions made in order to develop a flexible, extensible model which the community can easily customise for their own needs. The scalability of MONC is evaluated, along with numerous additional customisations made to further improve performance at large core counts. The result of this work is a model which delivers to the community significant new scientific modelling capability that takes advantage of the current and future generation HPC machines.

Published
2020

16. Malaria is a cause of iron deficiency in African children

Author

Muriuki, John Muthii, Mentzer, Alexander J, Mitchell, Ruth, Webb, Emily L, Etyang, Anthony O, Kyobutungi, Catherine, Morovat, Alireza, Kimita, Wandia, Ndungu, Francis M, Macharia, Alex W, Ngetsa, Caroline J, Makale, Johnstone, Lule, Swaib A, Musani, Solomon K, Raffield, Laura M, Cutland, Clare L, Sirima, Sodiomon B, Diarra, Amidou, Tiono, Alfred B, Fried, Michal, Gwamaka, Moses, Adu-Afarwuah, Seth, Wirth, James P, Wegmüller, Rita, Madhi, Shabir A, Snow, Robert W, Hill, Adrian VS, Rockett, Kirk A, Sandhu, Manjinder S, Kwiatkowski, Dominic P, Prentice, Andrew M, Byrd, Kendra A, Ndjebayi, Alex, Stewart, Christine P, Engle-Stone, Reina, Green, Tim J, Karakochuk, Crystal D, Suchdev, Parminder S, Bejon, Philip, Duffy, Patrick E, Davey Smith, George, Elliott, Alison M, Williams, Thomas N, and Atkinson, Sarah H

Subjects
Medical Microbiology, Biomedical and Clinical Sciences, Clinical Sciences, Brain Disorders, Pediatric, Infectious Diseases, Malaria, Vector-Borne Diseases, Rare Diseases, Clinical Research, Infection, Good Health and Well Being, Absorption, Physiological, Adolescent, Africa, Child, Child, Preschool, Female, Geography, Hepcidins, Humans, Infant, Iron Deficiencies, Male, Mendelian Randomization Analysis, Sickle Cell Trait, Medical and Health Sciences, Immunology, Biomedical and clinical sciences, Health sciences
Abstract

Malaria and iron deficiency (ID) are common and interrelated public health problems in African children. Observational data suggest that interrupting malaria transmission reduces the prevalence of ID1. To test the hypothesis that malaria might cause ID, we used sickle cell trait (HbAS, rs334 ), a genetic variant that confers specific protection against malaria2, as an instrumental variable in Mendelian randomization analyses. HbAS was associated with a 30% reduction in ID among children living in malaria-endemic countries in Africa (n = 7,453), but not among individuals living in malaria-free areas (n = 3,818). Genetically predicted malaria risk was associated with an odds ratio of 2.65 for ID per unit increase in the log incidence rate of malaria. This suggests that an intervention that halves the risk of malaria episodes would reduce the prevalence of ID in African children by 49%.

Published
2021

17. Safety and immunogenicity of a ChAdOx1 vaccine against Rift Valley fever in UK adults: an open-label, non-randomised, first-in-human phase 1 clinical trial

Author

Jenkin, Daniel, Wright, Daniel, Folegatti, Pedro M, Platt, Abigail, Poulton, Ian, Lawrie, Alison, Tran, Nguyen, Boyd, Amy, Turner, Cheryl, Gitonga, John N, Karanja, Henry K, Mugo, Daisy, Ewer, Katie J, Bowden, Thomas A, Gilbert, Sarah C, Charleston, Bryan, Kaleebu, Pontiano, Hill, Adrian V S, and Warimwe, George M

Published
2023
Full Text
View/download PDF

18. Designing a new spatial light modulator for holographic photostimulation

Author

Shane, Janelle C, McKnight, Douglas J, Hill, Adrian, Taberski, Kevin, and Serati, Steve

Subjects
Physics - Instrumentation and Detectors, Physics - Optics
Abstract

Driven by the demands for speed and field of view in the holographic photostimulation community, we designed, built, and tested a liquid crystal on silicon (LCoS) spatial light modulator (SLM) with a 1536x1536 square pixel array and high-voltage LC drive. We discuss some of the engineering work that made the MacroSLM possible, including the custom FPGA board for handling huge data rates, the large pixel size for minimizing rolloff and crosstalk, and the temperature control to handle heating effects from the high-voltage controls and high-power laser illumination. We also designed an FPGA implementation of the overdrive method for increasing liquid crystal switching speed, allowing us to overcome the significant data bottlenecks that limit frame rates for large arrays. We demonstrate 500 Hz hologram-to-hologram speed at 1064 nm operating wavelength, and discuss the new science that these speeds and array sizes have enabled., Comment: preprint of SPIE San Diego 2019 proceedings paper updated with minor edits including additional references and margin adjustments

Published
2019
Full Text
View/download PDF

20. Efficacy and immunogenicity of R21/Matrix-M vaccine against clinical malaria after 2 years' follow-up in children in Burkina Faso: a phase 1/2b randomised controlled trial

Author

Datoo, Mehreen S, Natama, Hamtandi Magloire, Somé, Athanase, Bellamy, Duncan, Traoré, Ousmane, Rouamba, Toussaint, Tahita, Marc Christian, Ido, N Félix André, Yameogo, Prisca, Valia, Daniel, Millogo, Aida, Ouedraogo, Florence, Soma, Rachidatou, Sawadogo, Seydou, Sorgho, Faizatou, Derra, Karim, Rouamba, Eli, Ramos-Lopez, Fernando, Cairns, Matthew, Provstgaard-Morys, Samuel, Aboagye, Jeremy, Lawrie, Alison, Roberts, Rachel, Valéa, Innocent, Sorgho, Hermann, Williams, Nicola, Glenn, Gregory, Fries, Louis, Reimer, Jenny, Ewer, Katie J, Shaligram, Umesh, Hill, Adrian V S, and Tinto, Halidou

Published
2022
Full Text
View/download PDF

23. Rethinking pathways to the dioecy–polyploidy association: Genera with many dioecious species have fewer polyploids.

Author

Osterman, Wilhelm H. A., Hill, Adrian, Hagan, James G., Whitton, Jeannette, Bacon, Christine D., and Bjorkman, Anne D.

Subjects
*SEXUAL dimorphism, *PLOIDY, *INTERSEXUALITY, *POLYPLOIDY, *POLLINATION, *GENOMES
Abstract

Premise: Numerous studies have found a positive association between dioecy and polyploidy; however, this association presents a theoretical conflict: While polyploids are predicted to benefit from self‐reproduction for successful establishment, dioecious species cannot self‐reproduce. We propose a theoretical framework to resolve this apparent conflict. We hypothesize that the inability of dioecious species to self‐reproduce hinders their establishment as polyploids. We therefore expect that genera with many dioecious species have fewer polyploids, leading to a negative association between polyploidy and dioecy across genera. Methods: We used three publicly available databases to determine ploidy and sexual systems for 131 genera and 546 species. We quantified (1) the relationship between the frequency of polyploid species and the frequency of dioecious species across genera, and (2) the proportion of polyploids with hermaphroditism and dioecy across species, adjusting for phylogenetic history. Results: Across genera, we found a negative relationship between the proportion of polyploids and the proportion of dioecious species, a consistent trend across clades. Across all species, we found that sexual system (dioecious or not) was not associated with polyploidy. Conclusions: Polyploids are rare in genera in which the majority of species are dioecious, consistent with the theory that self‐reproduction favors polyploid establishment. The low frequency of polyploidy among dioecious species indicates the association is not as widespread as previously suggested. Our findings are consistent with previous studies identifying a positive relationship between the two traits, but only if polyploidy promotes a transition to dioecy, and not the reverse. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

24. Paths and timings of the peopling of Polynesia inferred from genomic networks

Author

Ioannidis, Alexander G., Blanco-Portillo, Javier, Sandoval, Karla, Hagelberg, Erika, Barberena-Jonas, Carmina, Hill, Adrian V. S., Rodríguez-Rodríguez, Juan Esteban, Fox, Keolu, Robson, Kathryn, Haoa-Cardinali, Sonia, Quinto-Cortes, Consuelo D., Miquel-Poblete, Juan Francisco, Auckland, Kathryn, Parks, Tom, Sofro, Abdul Salam M., Avila-Arcos, Maria C., and Sockell, Alexandra

Subjects
Polynesia -- Demographic aspects, Polynesians -- Distribution -- Genetic aspects, Company distribution practices, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Polynesia was settled in a series of extraordinary voyages across an ocean spanning one third of the Earth.sup.1, but the sequences of islands settled remain unknown and their timings disputed. Currently, several centuries separate the dates suggested by different archaeological surveys.sup.2-4. Here, using genome-wide data from merely 430 modern individuals from 21 key Pacific island populations and novel ancestry-specific computational analyses, we unravel the detailed genetic history of this vast, dispersed island network. Our reconstruction of the branching Polynesian migration sequence reveals a serial founder expansion, characterized by directional loss of variants, that originated in Samoa and spread first through the Cook Islands (Rarotonga), then to the Society (TÅtaiete ma) Islands (11th century), the western Austral (Tuha'a Pae) Islands and Tuamotu Archipelago (12th century), and finally to the widely separated, but genetically connected, megalithic statue-building cultures of the Marquesas (Te Henua 'Enana) Islands in the north, Raivavae in the south, and Easter Island (Rapa Nui), the easternmost of the Polynesian islands, settled in approximately ad 1200 via Mangareva. Analysis of genomic networks from 430 modern individuals across 21 Pacific island populations reveals the human settlement history of Polynesia., Author(s): Alexander G. Ioannidis [sup.1] [sup.2] , Javier Blanco-Portillo [sup.2] , Karla Sandoval [sup.2] , Erika Hagelberg [sup.3] , Carmina Barberena-Jonas [sup.2] , Adrian V. S. Hill [sup.4] [sup.5] , [...]

Published
2021
Full Text
View/download PDF

25. Reactogenicity and immunogenicity after a late second dose or a third dose of ChAdOx1 nCoV-19 in the UK: a substudy of two randomised controlled trials (COV001 and COV002)

Author

Adlou, Syed, Aley, Robert, Ali, Aabidah, Anslow, Rachel, Baker, Megan, Baker, Phillip, Barrett, Jordan R., Bates, Louise, Beadon, Kirsten, Beckley, Rebecca, Bell, Jonathan, Bellamy, Duncan, Beveridge, Amy, Bissett, Cameron, Blackwell, Luke, Bletchly, Heather, Boyd, Amy, Bridges-Webb, Alice, Brown, Charlie, Byard, Nicholas, Camara, Susana, Cifuentes Gutierrez, Liliana, Collins, Andrea M., Cooper, Rachel, Crocker, Wendy E.M., Darton, Thomas C., Davies, Hannah, Davies, Judith, Demissie, Tesfaye, Di Maso, Claudio, Dinesh, Tanya, Donnellan, Francesca R., Douglas, Alexander D., Drake-Brockman, Rachael, Duncan, Christopher J.A., Elias, Sean C., Emary, Katherine R.W., Ghulam Farooq, Mutjaba, Faust, Saul N., Felle, Sally, Ferreira, Daniela, Ferreira Da Silva, Carla, Finn, Adam, Ford, Karen J., Francis, Emma, Furze, Julie, Fuskova, Michelle, Galiza, Eva, Gibertoni Cruz, Ana, Godfrey, Leila, Goodman, Anna L., Green, Catherine, Green, Christopher A., Greenwood, Nicola, Harrison, Daisy, Hart, Thomas C., Hawkins, Sophia, Heath, Paul T., Hill, Helen, Hillson, Kushalinii, Horsington, Bryn, Hou, Mimi M., Howe, Elizabeth, Howell, Nicola, Joe, Carina, Jones, Elizabeth, Kasanyinga, Mwila, Keen, Jade, Kelly, Sarah, Kerr, David, Khan, Liaquat, Khozoee, Baktash, Kinch, Jasmin, Kinch, Patrick, Koleva, Stanislava, Kwok, Jonathan, Larkworthy, Colin W., Lawrie, Alison M., Lazarus, Rajeka, Lees, Emily A., Li, Grace, Libri, Vincenzo, Lillie, Patrick J., Linder, Aline, Long, Fei, Lopez Ramon, Raquel, Mabbett, Reece, Makinson, Rebecca, Marinou, Spyridoula, Marlow, Emma, Marshall, Julia L., Mazur, Olga, McEwan, Joanne, McGregor, Alastair C., Mokaya, Jolynne, Morey, Ella, Morshead, Gertraud, Morter, Richard, Muller, Jilly, Mweu, Philomena, Noristani, Rabiullah, Owino, Nelly, Polo Peralta Alvarez, Marco, Platt, Abigail, Pollock, Katrina M., Poulton, Ian, Provstgaard-Morys, Samuel, Pulido-Gomez, David, Rajan, Matthew, Ramos Lopez, Fernando, Ritchie, Adam, Roberts, Hannah, Rollier, Christine, Rudiansyah, Indra, Sanders, Katherine, Saunders, Jack E., Seddiqi, Samiullah, Sharpe, Hannah R., Shaw, Robert, Silva-Reyes, Laura, Singh, Nisha, Smith, David J., Smith, Catherine C., Smith, Andrew, Spencer, Alexandra J., Stuart, Arabella S.V., Sutherland, Rebecca, Szigeti, Anna, Tang, Karly, Thomas, Merin, Thomas, Tonia M., Thompson, Amber, Thomson, Emma C., Török, Estée M., Toshner, Mark, Tran, Nguyen, Trivett, Rose, Turnbull, Iain, Turner, Cheryl, Turner, David P.J., Ulaszewska, Marta, Vichos, Iason, Walker, Laura, Watson, Marion E., Whelan, Conor, White, Rachel, Williams, Sarah J., Williams, Christopher J.A., Wright, Daniel, Yao, Andy, Flaxman, Amy, Marchevsky, Natalie G, Jenkin, Daniel, Aboagye, Jeremy, Aley, Parvinder K, Angus, Brian, Belij-Rammerstorfer, Sandra, Bibi, Sagida, Bittaye, Mustapha, Cappuccini, Federica, Cicconi, Paola, Clutterbuck, Elizabeth A, Davies, Sophie, Dejnirattisai, Wanwisa, Dold, Christina, Ewer, Katie J, Folegatti, Pedro M, Fowler, Jamie, Hill, Adrian V S, Kerridge, Simon, Minassian, Angela M, Mongkolsapaya, Juthathip, Mujadidi, Yama F, Plested, Emma, Ramasamy, Maheshi N, Robinson, Hannah, Sanders, Helen, Sheehan, Emma, Smith, Holly, Snape, Matthew D, Song, Rinn, Woods, Danielle, Screaton, Gavin, Gilbert, Sarah C, Voysey, Merryn, Pollard, Andrew J, and Lambe, Teresa

Published
2021
Full Text
View/download PDF

26. Safety and immunogenicity of the ChAdOx1 nCoV-19 (AZD1222) vaccine against SARS-CoV-2 in HIV infection: a single-arm substudy of a phase 2/3 clinical trial

Author

Watson, Marion E.E., Song, Rinn, Cicconi, Paola, Minassian, Angela M., Bibi, Sagida, Kerridge, Simon, Singh, Nisha, Green, Catherine M., Douglas, Alexander D., Lawrie, Alison M., Clutterbuck, Elizabeth A., Frater, John, Ewer, Katie J, Ogbe, Ane, Pace, Mathew, Adele, Sandra, Adland, Emily, Alagaratnam, Jasmini, Aley, Parvinder K, Ali, Mohammad, Ansari, M Azim, Bara, Anna, Bittaye, Mustapha, Broadhead, Samantha, Brown, Anthony, Brown, Helen, Cappuccini, Federica, Cooney, Enya, Dejnirattisai, Wanwisa, Dold, Christina, Fairhead, Cassandra, Fok, Henry, Folegatti, Pedro M, Fowler, Jamie, Gibbs, Charlotte, Goodman, Anna L, Jenkin, Daniel, Jones, Mathew, Makinson, Rebecca, Marchevsky, Natalie G, Mujadidi, Yama F, Nguyen, Hanna, Parolini, Lucia, Petersen, Claire, Plested, Emma, Pollock, Katrina M, Ramasamy, Maheshi N, Rhead, Sarah, Robinson, Hannah, Robinson, Nicola, Rongkard, Patpong, Ryan, Fiona, Serrano, Sonia, Tipoe, Timothy, Voysey, Merryn, Waters, Anele, Zacharopoulou, Panagiota, Barnes, Eleanor, Dunachie, Susanna, Goulder, Philip, Klenerman, Paul, Screaton, Gavin R, Winston, Alan, Hill, Adrian V S, Gilbert, Sarah C, Pollard, Andrew J, Fidler, Sarah, Fox, Julie, and Lambe, Teresa

Published
2021
Full Text
View/download PDF

27. List of contributors

Author

Anagu, Linda Onyeka, primary, Andoh, Nana Efua, additional, Ashfield, Rebecca, additional, Barbosa, Camila R.R., additional, Bettencourt, Paulo J.G., additional, Ceylan, Sebnem Ercelen, additional, Christensen, Dennis, additional, Chukwuanukwu, Rebecca Chinyelu, additional, Corby, George, additional, Ehiaghe, Alfred Friday, additional, Ewer, Katie, additional, Fergusson, Joannah, additional, Gizurarson, Sveinbjorn, additional, Górska, Sabina, additional, Hill, Adrian V.S., additional, Hu, Kefei, additional, Iseghohi, Frances, additional, Lindblad, Erik B., additional, Longet, Stephanie, additional, Luchner, Marina, additional, Marshall, Julia L., additional, Milicic, Anita, additional, Morein, Bror, additional, Mrenoshki, Slavcho, additional, Mukhopadhyay, Ekta, additional, Noé, Andrés, additional, Nwonu, Ezinne Janefrances, additional, Oli, Angus Nnamdi, additional, Razim, Agnieszka, additional, Reinke, Sören, additional, Rowaiye, Adekunle Babajide, additional, Salman, Ahmed M., additional, Thakur, Aneesh, additional, Ugwu, Malachy Chigozie, additional, and Yahemba, Aondona Priscilla, additional

Published
2022
Full Text
View/download PDF

31. Symmetric general linear methods

Author

Butcher, John, Hill, Adrian, and Norton, Terrence

Subjects
Mathematics - Numerical Analysis, 65L05
Abstract

The article considers symmetric general linear methods, a class of numerical time integration methods which, like symmetric Runge--Kutta methods, are applicable to general time--reversible differential equations, not just those derived from separable second--order problems. A definition of time--reversal symmetry is formulated for general linear methods, and criteria are found for the methods to be free of linear parasitism. It is shown that symmetric parasitism--free methods cannot be explicit, but a method of order $4$ is constructed with only one implicit stage. Several characterizations of symmetry are given, and connections are made with $G$--symplecticity. Symmetric methods are shown to be of even order, a suitable symmetric starting method is constructed and shown to be essentially unique. The underlying one--step method is shown to be time--symmetric. Several symmetric methods of order $4$ are constructed and implemented on test problems. The methods are efficient when compared with Runge--Kutta methods of the same order, and invariants of the motion are well--approximated over long time intervals., Comment: 40 pages

Published
2015

32. Hybridization in palms (Arecaceae).

Author

Bacon, Christine D. and Hill, Adrian

Subjects
*PLANT hybridization, *PLANT evolution, *LITERATURE reviews, *SPECIES diversity, *TROPICAL plants, *PALMS, *HYBRID zones
Abstract

Hybridization has significant evolutionary consequences across the Tree of Life. The process of hybridization has played a major role in plant evolution and has contributed to species richness and trait variation. Since morphological traits are partially a product of their environment, there may be a link between hybridization and ecology. Plant hybrid species richness is noted to be higher in harsh environments, and we explore this hypothesis with a keystone tropical plant lineage, palms (Arecaceae). Leveraging a recent literature review of naturally occurring palm hybrids, we developed a method to calculate hybrid frequency, and then tested if there is phylogenetic signal of hybrids using a phylogeny of all palms. Further, we used phylogenetic comparative methods to examine the interaction between hybrid frequency and presence in dry environments, on islands, and the species richness of genera. Phylogenetic generalized least squares models had stronger support than models of random association, indicating phylogenetic signal for the presence of hybrids in dry and island environments. However, all p‐values were >.05 and therefore the correlation was poor between hybridization and the trait frequencies examined. Presence in particular environments are not strongly correlated to hybrid frequency, but phylogenetic signal suggests a role in its distribution in different habitats. Hybridization in palms is not evenly distributed across subfamilies, tribes, subtribes yet plays an important role in palm diversity, nonetheless. Increasing our understanding hybridization in this economically and culturally important plant family is essential, particularly since rates are projected to increase with climate change, reconfiguring the dynamics and distribution of biodiversity. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

33. Safety and immunogenicity of a candidate Middle East respiratory syndrome coronavirus viral-vectored vaccine: a dose-escalation, open-label, non-randomised, uncontrolled, phase 1 trial

Author

Folegatti, Pedro M, Bittaye, Mustapha, Flaxman, Amy, Lopez, Fernando Ramos, Bellamy, Duncan, Kupke, Alexandra, Mair, Catherine, Makinson, Rebecca, Sheridan, Jonathan, Rohde, Cornelius, Halwe, Sandro, Jeong, Yuji, Park, Young-Shin, Kim, Jae-Ouk, Song, Manki, Boyd, Amy, Tran, Nguyen, Silman, Daniel, Poulton, Ian, Datoo, Mehreen, Marshall, Julia, Themistocleous, Yrene, Lawrie, Alison, Roberts, Rachel, Berrie, Eleanor, Becker, Stephan, Lambe, Teresa, Hill, Adrian, Ewer, Katie, and Gilbert, Sarah

Published
2020
Full Text
View/download PDF

36. The evolutionary age-range size relationship is modulated by insularity and dispersal in plants and animals

Author

Alzate, Adriana, primary, Rozzi, Roberto, additional, Velasco, Julian A., additional, Robertson, D. Ross, additional, Zizka, Alexander, additional, Tobias, Joseph A., additional, Hill, Adrian, additional, Bacon, Christine D., additional, Janzen, Thijs, additional, Pellissier, Loïc, additional, van der Plas, Fons, additional, Rosindell, James, additional, and Onstein, Renske E., additional

Published
2023
Full Text
View/download PDF

37. NUMAC: Description of the Nested Unified Model With Aerosols and Chemistry, and Evaluation With KORUS‐AQ Data

Author

Gordon, Hamish, primary, Carslaw, Ken S., additional, Hill, Adrian A., additional, Field, Paul R., additional, Abraham, Nathan Luke, additional, Beyersdorf, Andreas, additional, Corr‐Limoges, Chelsea, additional, Ghosh, Pratapaditya, additional, Hemmings, John, additional, Jones, Anthony C., additional, Sanchez, Claudio, additional, Wang, Xuemei, additional, and Wilkinson, Jonathan, additional

Published
2023
Full Text
View/download PDF

38. A high resolution synchrotron x-ray powder diffraction study of the incommensurate modulation in the martensite phase of Ni2MnGa: Evidence for nearly 7M modulation and phason broadening

Author

Singh, Sanjay, Petricek, V., Rajput, Parasmani, Hill, Adrian H., Suard, E., Barman, S. R., and Pandey, Dhananjai

Subjects
Condensed Matter - Materials Science
Abstract

The modulated structure of the martensite phase of Ni2MnGa is revisited using high resolution synchrotron x-ray powder diffraction (SXRPD) measurements, which reveals higher order satellite reflections up to the 3rd order and phason broadening of the satellite peaks. The structure refinement, using the (3+1) dimensional superspace group approach, shows that the modulated structure of Ni2MnGa can be described by orthorhombic superspace group Immm(00$\gamma$)s00 with lattice parameters a= 4.21861(2) {\AA}, b= 5.54696(3) {\AA}, and c= 4.18763(2) {\AA} and an incommensurate modulation wave vector q= 0.43160(3)c*= (3/7+$\delta$)c*, where $\delta$=0.00303(3) is the degree of incommensuration of the modulated structure. Additional satellite peak broadening, which could not be accounted for in terms of the anisotropic strain broadening based on a lattice parameter distribution , has been modeled in terms of phasons using fourth rank covariant strain tensor representation for incommensurate structures. The simulation of single crystal diffraction patterns from the refined structural parameters unambiguously reveals a rational approximant structure with 7M modulation. The inhomogeneous displacement of different atomic sites on account of incommensurate modulation and the presence of phason broadening clearly rule out the adaptive phase model proposed recently by Kaufmann et al.[1] and suggests that the modulation in Ni2MnGa originates from soft-mode phonons.

Published
2014
Full Text
View/download PDF

42. A single dose of ChAdOx1 Chik vaccine induces neutralizing antibodies against four chikungunya virus lineages in a phase 1 clinical trial

Author

Folegatti, Pedro M., Harrison, Kate, Preciado-Llanes, Lorena, Lopez, Fernando Ramos, Bittaye, Mustapha, Kim, Young Chan, Flaxman, Amy, Bellamy, Duncan, Makinson, Rebecca, Sheridan, Jonathan, Azar, Sasha R., Campos, Rafael Kroon, Tilley, Mark, Tran, Nguyen, Jenkin, Daniel, Poulton, Ian, Lawrie, Alison, Roberts, Rachel, Berrie, Eleanor, Rossi, Shannan L., Hill, Adrian, Ewer, Katie J., and Reyes-Sandoval, Arturo

Published
2021
Full Text
View/download PDF

45. Native American gene flow into Polynesia predating Easter Island settlement

Author

Ioannidis, Alexander G., Blanco-Portillo, Javier, Sandoval, Karla, Hagelberg, Erika, Miquel-Poblete, Juan Francisco, Moreno-Mayar, J. Víctor, Rodríguez-Rodríguez, Juan Esteban, Quinto-Cortés, Consuelo D., Auckland, Kathryn, Parks, Tom, Robson, Kathryn, Hill, Adrian V. S., Avila-Arcos, María C., Sockell, Alexandra, Homburger, Julian R., Wojcik, Genevieve L., Barnes, Kathleen C., Herrera, Luisa, Berríos, Soledad, Acuña, Mónica, Llop, Elena, Eng, Celeste, Huntsman, Scott, Burchard, Esteban G., Gignoux, Christopher R., Cifuentes, Lucía, Verdugo, Ricardo A., Moraga, Mauricio, Mentzer, Alexander J., Bustamante, Carlos D., and Moreno-Estrada, Andrés

Published
2020
Full Text
View/download PDF

47. Nanoscale order in the frustrated mixed conductor La$_{5.4}WO$_{12-\delta}$

Author

Scherb, Tobias, Kimber, Simon A. J., Stephan, Christiane, Henry, Paul F., Schumacher, Gerhard, Just, Justus, Escolastico, Sonia, Serra, Jose M., Seeger, Janka, Hill, Adrian H., and Banhart, John

Subjects
Condensed Matter - Materials Science
Abstract

We report a comprehensive investigation of the average and local structure of La$_{5.4}$WO$_{12-\delta}$, which has excellent mixed proton, electron and oxide ion conduction suitable for device applications. Synchrotron X-ray and neutron powder diffraction show that a cubic fluorite supercell describes the average structure, with highly disordered lanthanum and oxide positions. On average the tungsten sites are six-fold coordinated, and we detect a trace (4.4(2) %) of anti-site disorder. In addition to sharp Bragg reflections, strong diffuse neutron scattering is observed, which hints at short-range order. We consider plausible local configurations, and show that the defect chemistry implies a simple 'chemical exchange' interaction that favours ordered WO6 octahedra. Our local model is confirmed by synchrotron x-ray pair distribution function analysis and EXAFS experiments performed at the La K and W L3-edges. We show that ordered domains of around ca. 3.5 nm are found, implying that mixed conduction in La$_{5.4}$WO$_{12-\delta}$? is associated with a defective glassy-like anion sublattice. The origins of this ground state are proposed to lie in the non-bipartite nature of the fcc lattice and the pairwise interactions which link the orientation of neighbouring octahedral WO6 sites. This 'function through frustration' could provide a means of designing new mixed conductors.

Published
2013

48. Connectivism: Learning Theory of the Future or Vestige of the Past?

Author

Kop, Rita and Hill, Adrian

Abstract

Siemens and Downes initially received increasing attention in the blogosphere in 2005 when they discussed their ideas concerning distributed knowledge. An extended discourse has ensued in and around the status of "connectivism" as a learning theory for the digital age. This has led to a number of questions in relation to existing learning theories. Do they still meet the needs of today's learners, and anticipate the needs of learners of the future? Would a new theory that encompasses new developments in digital technology be more appropriate, and would it be suitable for other aspects of learning, including in the traditional class room, in distance education and e-learning? This paper will highlight current theories of learning and critically analyse connectivism within the context of its predecessors, to establish if it has anything new to offer as a learning theory or as an approach to teaching for the 21st Century. (Contains 1 figure.)

Published
2008

49. Charge order at the frontier between the molecular and solid states in Ba3NaRu2O9

Author

Kimber, Simon A. J., Senn, Mark S., Fratini, Simone, Wu, Hua, Hill, Adrian H., Manuel, Pascal, Attfield, J. Paul, Argyriou, Dimitri N., and Henry, Paul. F.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We show that the valence electrons of Ba3NaRu2O9, which has a quasi-molecular structure, completely crystallize below 210 K. Using an extended Hubbard model, we show that the charge ordering instability results from long-range Coulomb interactions. However, orbital ordering, metal-metal bonding and formation of a partial spin gap enforce the magnitude of the charge separation. The striped charge order and frustrated hcp lattice of Ru2O9 dimers lead to competition with a quasi-degenerate charge-melted phase under photo-excitation at low temperature. Our results establish a broad class of simple metal oxides as models for emergent phenomena at the border between the molecular and solid states., Comment: Minor changes, with supporting information. To appear in Phys. Rev. Lett

Published
2011
Full Text
View/download PDF

50. Spin and Orbital Order of the Vanadium Spinel MgV2O4

Author

Wheeler, Elisa M., Lake, Bella, Islam, A. T. M. Nazmul, Reehuis, Manfred, Steffens, Paul, Guidi, Tatiana, and Hill, Adrian H.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We present a unique study of the frustrated spinel MgV2O4 which possesses highly coupled spin, lattice and orbital degrees of freedom. Using large single-crystal and powder samples, we find a distortion from spinel at room temperature (space group F-43m) which allows for a greater trigonal distortion of the VO6 octahedra and a low temperature space group (I-4m2) that maintains the mirror plane symmetry. The magnetic structure that develops below 42 K consists of antiferromagnetic chains with a strongly reduced moment while inelastic neutron scattering reveals one-dimensional behavior and a single band of excitations. The implications of these results are discussed in terms of various orbital ordering scenarios. We conclude that although spin-orbit coupling must be significant to maintain the mirror plane symmetry, the trigonal distortion is large enough to mix the 3d levels leading to a wave function of mixed real and complex orbitals.

Published
2010
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results