Coleg Gwyddoniaeth a Pheirianneg

  1. 2020
  2. Cyhoeddwyd

    Tides on Other Earths: Implications for Exoplanet and Palaeo-Tidal Simulations

    Blackledge, B., Green, M., Barnes, R. & Way, M., 28 Meh 2020, Yn: Geophysical Research Letters. 47, 12, e2019GL085746.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  3. Cyhoeddwyd

    Ancestral mitogenome capture of the Southeast Asian banded linsang.

    Paijmans, J., Barlow, A., Henneberger, K., Fickel, J., Hofreiter, M. & Foerster, D. W. G., 30 Meh 2020, Yn: PLoS ONE.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  4. Cyhoeddwyd

    Evaluating taxonomic inflation: towards evidence-based species delimitation in Eurasian vipers (Serpentes: Viperinae)

    Freitas, I., Ursenbacher, S., Mebert, K., Zinenko, O., Schweiger, S., Wüster, W., Brito, J. C., Crnobrnja-Isailović, J., Halpern, B., Fahd, S., Santos, X., Pleguezuelos, J. M., Joger, U., Orlov, N., Mizsei, E., Lourdais, O., Zuffi, M. A. L., Strugariu, A., Zamfirescu, Ş. R., Martínez-Solano, Í., Velo-Antón, G., Kaliontzopoulou, A. & Martínez-Freiría, F., 30 Meh 2020, Yn: Amphibia-Reptilia. 41, 3, t. 285-311 27 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  5. Cyhoeddwyd

    Competition influences tree growth, but not mortality, across environmental gradients in Amazonia and tropical Africa

    Rozendaal, D. M. A., Phillips, O. L., Lewis, S. L., Affum-Baffoe, K., Alvarez-Davila, E., Andrade, A., Aragão, L. E. O. C., Araujo-Murakami, A., Baker, T. R., Bánki, O., Brienen, R. J. W., Camargo, J. L. C., Comiskey, J. A., Djuikouo Kamdem, M. N., Fauset, S., Feldpausch, T. R., Killeen, T. J., Laurance, W. F., Laurance, S. G. W., Lovejoy, T., Malhi, Y., Marimon, B. S., Marimon Junior, B.-H., Marshall, A. R., Neill, D. A., Núñez Vargas, P., Pitman, N. C. A., Poorter, L., Reitsma, J., Silveira, M., Sonké, B., Sunderland, T., Taedoumg, H., ter Steege, H., Terborgh, J. W., Umetsu, R. K., van der Heijden, G. M. F., Vilanova, E., Vos, V., White, L. J. T., Willcock, S., Zemagho, L. & Vanderwel, M. C., Gorff 2020, Yn: Ecology. 101, 7, e03052.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  6. Cyhoeddwyd

    Multiple trait dimensions mediate stress gradient effects on plant biomass allocation, with implications for coastal ecosystem services.

    de Battisti, D., Fowler, M. S., Jenkins, S., Skov, M., Bouma, T. J., Neyland, P. J. & Griffin, J., Gorff 2020, Yn: Journal of Ecology. 108, 4, t. 1227-1240

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  7. Cyhoeddwyd

    Ocean warming increases the nitrogen demand and the uptake of organic nitrogen of the globally distributed seagrass Zostera marina

    Alexandre, A., Quinta, R., Hill, P., Jones, D. L. & Santos, R., Gorff 2020, Yn: Functional Ecology. 34, 7, t. 1325-1335 11 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  8. Cyhoeddwyd

    Advanced Gas-cooled reactors technology for enabling molten-salt reactors design - Estimation of coolant impact on neutronic performance

    Margulis, M. & Shwageraus, E., 1 Gorff 2020, Yn: Progress in Nuclear Energy. 125, 103382.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  9. Cyhoeddwyd

    An investigation of the antileishmanial properties of semi-synthetic saponins

    Anderson, O., Beckett, J., Briggs, C. C., Natrass, L. A., Cranston, C. F., Wilkinson, E. J., Owen, J., Williams, R. M., Loukaidis, A., Bouillon, M., Pritchard, D., Lahmann, M., Baird, M. & Denny, P. W., 1 Gorff 2020, Yn: Medicinal Chemistry. 11, 7, t. 833-842

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  10. Cyhoeddwyd

    Critical accumulation of fertilizer-derived uranium in Icelandic grassland Andosol

    Sun, Y., Amelung, W., Gudmundsson, T., Wu, B. & Bol, R., 1 Gorff 2020, Yn: Environmental Sciences Europe. 32, 1, 7 t., 92.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  11. Cyhoeddwyd

    Experimental Demonstrations of Hybrid OFDM-Digital Filter Multiple Access PONs

    Jin, W., Zhong, Z., He, J., Sankoh, A., Giddings, R., Hong, Y., Pierce, I., O'Sullivan, M., Laperle, C., Lee, J., Mariani, G., Durrant, T. & Tang, J., 1 Gorff 2020, Yn: IEEE Photonics Technology Letters. 32, 13, t. 751-754

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  12. Cyhoeddwyd

    Ignoring non‐English‐language studies may bias ecological meta‐analyses

    Konno, K., Akasaka, M., Koshida, C., Katayama, N., Osada, N., Spake, R. & Amano, T., 1 Gorff 2020, Yn: Ecology and Evolution. 10, 13, t. 6373-6384 12 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  13. Cyhoeddwyd

    Insights into aphid prey consumption by ladybirds: Optimising field sampling methods and primer design for High Throughput Sequencing

    Ammann, L., Moorhouse-Gann, R., Bertrand, C., Mestre, L., Cuff, J., Perez Hidalgo, N., Ellison, A., Herzog, F., Entling, M., Albrecht, M. & Symondson, W. O. C., 1 Gorff 2020, Yn: PLoS ONE. 15, 7, e0235054.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  14. Cyhoeddwyd

    Marking the un-markable: visible implant elastomer in wild juvenile snakes

    Major, T., Alkins, D. R., Jeffrey, L. & Wüster, W., 1 Gorff 2020, Yn: Herpetological Journal. 30, 3, t. 173-176 4 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  15. Cyhoeddwyd

    Selection of indicators for assessing and managing the impacts of bottom trawling on seabed habitats

    Hiddink, J. G., Kaiser, M. J., Sciberras, M., McConnaughey, R. A., Mazor, T., Hilborn, R., Collie, J. S., Pitcher, C. R., Parma, A. M., Suuronen, P., Rijnsdorp, A. D. & Jennings, S., 1 Gorff 2020, Yn: Journal of Applied Ecology. 57, 7, t. 1199-1209 11 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  16. Cyhoeddwyd

    Wading through the swamp: what does tropical peatland restoration mean to national-level stakeholders in Indonesia?

    Ward, C., Stringer, L. C., Warren-Thomas, E., Agus, F., Hamer, K., Pettorelli, N., Hariyadi, B., Hodgson, J., Kartika, W. D., Lucey, J., McClean, C., Nurida, N. L., Saad, A. & Hill, J. K., 1 Gorff 2020, Yn: RESTORATION ECOLOGY. 28, 4, t. 817-827

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  17. Cyhoeddwyd

    We use our knowledge of human evolution to explain people’s social and emotional responses to coronavirus for the general public

    Winder, I. C. & Shaw, V., 1 Gorff 2020.

    Allbwn ymchwil: Cyfraniad at gynhadleddMurlenadolygiad gan gymheiriaid

  18. Cyhoeddwyd

    Characteristics of an Iron-Reducing, Moderately Acidophilic Actinobacterium Isolated from Pyritic Mine Waste, and Its Potential Role in Mitigating Mineral Dissolution in Mineral Tailings Deposits

    Nancucheo, I. & Johnson, D. B., 2 Gorff 2020, Yn: Microorganisms . 8, 7, 90.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  19. Cyhoeddwyd

    Impact of the 2018 European heatwave on lake surface water temperature

    Woolway, R. I., Jennings, E. & Carrea, L., 2 Gorff 2020, Yn: INLAND WATERS. 10, 3, t. 322-332

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  20. Cyhoeddwyd

    Relative growth of invasive and indigenous tilapiine cichlid fish in Tanzania

    Bradbeer, S., Ngatunga, B., Turner, G. F. & Genner, M., 2 Gorff 2020, Yn: African Journal of Aquatic Science. 45, 3, t. 378-381 4 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  21. Cyhoeddwyd

    Wastewater-Based Epidemiology: Global Collaborative to Maximize Contributions in the Fight Against COVID-19

    Bivins, A., North, D., Ahmad, A., Ahmed, W., Alm, E., Been, F., Bhattacharya, P., Bijlsma, L., Boehm, A. B., Brown, J., Buttiglieri, G., Calabro, V., Carducci, A., Castiglioni, S., Gurol, Z. C., Chakraborty, S., Costa, F., Curcio, S., de los Reyes, F. L. ,. I., Vela, J. D., Farkas, K., Fernandez-Casi, X., Gerba, C., Gerrity, D., Girones, R., Gonzalez, R., Haramoto, E., Harris, A., Holden, P. A., Islam, M. T., Jones, D. L., Kasprzyk-Hordern, B., Kitajima, M., Kotlarz, N., Kumar, M., Kuroda, K., La Rosa, G., Malpei, F., Mautus, M., McLellan, S. L., Medema, G., Meschke, J. S., Mueller, J., Newton, R. J., Nilsson, D., Noble, R. T., van Nuijs, A., Peccia, J., Perkins, T. A., Pickering, A. J., Rose, J., Sanchez, G., Smith, A., Stadler, L., Stauber, C., Thomas, K., van der Voorn, T., Wigginton, K., Zhu, K. & Bibby, K., 7 Gorff 2020, Yn: Environmental Science and Technology. 54, 13, t. 7754-7757

    Allbwn ymchwil: Cyfraniad at gyfnodolynGolygyddiadadolygiad gan gymheiriaid

  22. Cyhoeddwyd

    What's in the soil?

    Withers, E., 8 Gorff 2020.

    Allbwn ymchwil: Cyfraniad at gynhadleddArall

  23. Cyhoeddwyd

    The earliest domestic cat on the Silk Road

    Haruda, A. F., Miller, A. R. V., Paijmans, J., Barlow, A., Tazhekeyev, A., Bailov, S., Hesse, Y., Preick, M., King, T., Thomas, R., Harke, H. & Arzhantseva, L., 9 Gorff 2020, Yn: Scientific Reports.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  24. Cyhoeddwyd

    Possible control of acute outbreaks of a marine fungal pathogen by nominally herbivorous tropical reef fish

    Neal, B., Honisch, B., Warrender, T., Williams, G. J., Work, T. & Price, N., 12 Gorff 2020, Yn: Oecologia. 193, 3, t. 603-617

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  25. Cyhoeddwyd

    A Clock-gating-based Energy-efficient Scheme for ONUs in Real-time IMDD OFDM-PONs

    Zhang, J., Zhao, J., Huang, H., Ye, N., Giddings, R., Li, Z., Qin, D., Zhang, Q. & Tang, J., 15 Gorff 2020, Yn: Journal of Lightwave Technology. 38, 14, t. 3573-3583

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  26. Cyhoeddwyd

    Characterization Study of Empty Fruit Bunch (EFB) Fibers Reinforcement in Poly(Butylene) Succinate (PBS)/Starch/Glycerol Composite Sheet

    Ayu, R. S., Khalina, A., Harmaen, A. S., Zaman, K., Isma, T., Liu, Q. & Lee, C. H., 15 Gorff 2020, Yn: MDPI Polymers. 12, 1571, t. 1-13 13 t., Polymers 2020, 12, 1571; doi:10.3390/polym12071571.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  27. Cyhoeddwyd

    UV phototransistors based upon spray coated and sputter deposited ZnO TFTs

    Kumar, D., Gomes, T., Alves, N., Fugikawa-Santos, L., Smith, G. C. & Kettle, J., 15 Gorff 2020, Yn: IEEE Sensors Journal. 20, 14, t. 7532 - 7539

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  28. Cyhoeddwyd

    Image-based quanti fication of soil microbial dead zones induced by nitrogen fertilization

    Ruiz, S. A., Fletcher, D. M. M., Boghi, A., Williams, K. A., Duncan, S. J., Scotson, C. P., Petroselli, C., Dias, T. G. S., Chadwick, D. R., Jones, D. L. & Roose, T., 20 Gorff 2020, Yn: Science of the Total Environment. 727, 138197.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  29. Cyhoeddwyd

    Raising the groundwater table in the non -growing season can reduce greenhouse gas emissions and maintain crop productivity in cultivated fen peats

    Wen, Y., Freeman, B., Ma, Q., Evans, C. D., Chadwick, D. R., Zang, H. & Jones, D. L., 20 Gorff 2020, Yn: Journal of Cleaner Production. 262, 121179.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  30. Cyhoeddwyd

    Hemitrygon yemenensis sp. nov., a new species of stingray (Myliobatoidea: Dasyatidae) from the northwestern Indian Ocean

    Moore, A., Last, P. & Naylor, G., 23 Gorff 2020, Yn: Zootaxa. 4819, 2, t. 364-374

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  31. Cyhoeddwyd

    Effects ofAgeratina adenophoraInvasion on the Understory Community and Soil Phosphorus Characteristics of Different Forest Types in Southwest China

    Wu, X., Duan, C., Fu, D., Peng, P., Zhao, L. & Jones, D. L., 25 Gorff 2020, Yn: Forests. 11, 8

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  32. Cyhoeddwyd

    Biologically important artificial light at night on the seafloor

    Davies, T. W., McKee, D., Fishwick, J., Tidau, S. & Smyth, T., 27 Gorff 2020, Yn: Scientific Reports. 10, 1, 12545.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  33. Cyhoeddwyd

    Contrasting effects of climate change on seasonal survival of a hibernating mammal

    Cordes, L., Blumstein, D., Armitage, K., CaraDonna, P., Childs, D., Gerber, B., Martin, J., Oli, M. & Ozgul, A., 28 Gorff 2020, Yn: PNAS. 117, 30, t. 18119-18126 8 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  34. Cyhoeddwyd

    A re-investigation of the mycolic acids of Mycobacterium avium

    Jones, A., Lee, O.Y.-C., Minnikin, D. E., Baird, M. S. & Al Dulayymi, J. R., Awst 2020, Yn: Chemistry and Physics of Lipids. 230, 104928.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  35. Cyhoeddwyd

    Crop residue carbon-to-nitrogen ratio regulates denitrifier N2O production post flooding

    Zhou, W., Jones, D. L., Hu, R., Clark, I. M. & Chadwick, D. R., Awst 2020, Yn: Biology and Fertility of Soils. 56, 6, t. 825-838

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  36. Cyhoeddwyd

    Emerging technologies for the rapid detection of enteric viruses in the aquatic environment

    Farkas, K., Mannion, F., Hillary, L., Malham, S. & Walker, D., Awst 2020, Yn: Current Opinion in Environmental Science & Health. 16, t. 1-6

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  37. Cyhoeddwyd

    Exploring perceptions of marine biosecurity interventions: insights from the commercial marina sector.

    Vye, S., Wynne-Jones, S., Masterson Algar, P. & Jenkins, S., Awst 2020, Yn: Marine Policy. 118, 104027.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  38. Cyhoeddwyd

    Mixed Sand—Mud Bedforms Produced by Transient Turbulent Flows in the Fringe of Submarine Fans: Indicators of Flow Transformation

    Baker, M. L. & Baas, J. H., Awst 2020, Yn: Sedimentology. 67, 5, t. 2645-2671 27 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  39. Cyhoeddwyd

    On the interplay between horizontal resolution and wave drag and their effect on tidal baroclinic mode waves in realistic global ocean simulations

    Buijsman, M. C., Stephenson, G. R., Ansong, J. K., Arbic, B. K., Green, M., Richman, J. G., Shriver, J. F., Vic, C., Wallcraft, A. & Zhao, Z., Awst 2020, Yn: Ocean Modelling. 152, 101656.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  40. Cyhoeddwyd

    Temperature modulates compensatory responses to food limitation at metamorphosis in a marine invertebrate

    Torres, G. & Gimenez Noya, L., Awst 2020, Yn: Functional Ecology. 34, 8, t. 1564-1576

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  41. Cyhoeddwyd

    Tidal range energy resource assessment of the Gulf of California, Mexico

    Mejia-Olivares, C., Haigh, I. D., Angeloudis, A., Lewis, M. & Neill, S., Awst 2020, Yn: Renewable Energy. 155, t. 469-483

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  42. Cyhoeddwyd

    Water mass properties derived from satellite observations in the Barents Sea

    Barton, B., Lique, C. & Lenn, Y.-D., Awst 2020, Yn: Journal of Geophysical Research: Oceans. 125, 8, e2019JC015449.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  43. Cyhoeddwyd

    An Experimental Evaluation of Mixup Regression Forests

    Rodriguez, J., Juez-Gil, M., Arnaiz-Gonzalez, A. & Kuncheva, L., 1 Awst 2020, Yn: Expert Systems with Applications. 151, 113376.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  44. Cyhoeddwyd

    Bioleaching of arsenic-rich cobalt mineral resources, and evidence for concurrent biomineralisation of scorodite during oxidative bio-processing of skutterudite

    Johnson, D. B., Dybowska, A., Schofield, P., Herrington, R., Smith, S. & Santos, A. L., 1 Awst 2020, Yn: Hydrometallurgy. 195, 105395.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  45. Cyhoeddwyd

    Global lake responses to climate change

    Woolway, R. I., Kraemer, B. M., Lenters, J. D., Merchant, C. J., O'Reilly, C. M. & Sharma, S., 1 Awst 2020, Yn: Nature Reviews Earth and Environment. 1, t. 388-403

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  46. Cyhoeddwyd

    Runaway GC evolution in gerbil genomes

    Parcana, R., Hargreaves, A. D., Mulley, J. & Holland, P. W. H., 1 Awst 2020, Yn: Molecular Biology and Evolution. 37, 8, t. 2197-2210 msaa072.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  47. Cyhoeddwyd

    Standardizing Ecosystem Morphological Traits from 3D Information Sources

    Valbuena, R., O'Connor, B., Zellweger, F., Simonson, W., Vihervaara, P., Maltamo, M., Silva, C. A., Almeida, D. R. A., Danks, F., Morsdorf, F., Chirici, G., Lucas, R., Coomes, D. A. & Coops, N. C., 1 Awst 2020, Yn: Trends in Ecology and Evolution. 35, 8, t. 656-667

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygl adolyguadolygiad gan gymheiriaid

  48. Cyhoeddwyd

    Sulfur-enhanced reductive bioprocessing of cobalt-bearing materials for base metals recovery

    Araujo Santos, A. L., Dybowska, A., Schofield, P., Herrington, R. & Johnson, B., 1 Awst 2020, Yn: Hydrometallurgy. 195, 105396.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  49. Cyhoeddwyd

    The spatial ecology of Rajidae from mark-recapture tagging and its implications for assessing fishery interactions and efficacy of Marine Protected Areas

    Simpson, S., Humphries, N. E. & Sims, D. W., 1 Awst 2020, Yn: Fisheries Research. 228, 105569.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  50. Cyhoeddwyd

    Introduced Canadian Eastern grey squirrels: squirrelpox virus surveillance and why nothing matters.

    McInnes, C., Shuttleworth, C., Larsen, K. W., Everest, D. J., Bruemmer, C., Carroll, B., Romeo, C., Sainsbury, A. W., Crawshaw, G., Dubois, S., Gillis, L., Gilray, J. & Percival, A., 3 Awst 2020, Yn: Hystrix-Italian Journal of Mammalogy. 31, t. 95-98

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  51. Cyhoeddwyd

    When nature meets the divine: effect of prohibition regimes on the structure and tree-species composition of sacred forests in Northern Greece

    Marini Govigli, V., Healey, J., Wong, J., Stara, K., Tsiakiris, R. & Halley, J., 7 Awst 2020, Yn: Web Ecology. 20, 2, t. 53-86 48 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid