Ysgol Gwyddorau Amgylcheddol a Naturiol
- Erthygl › Ymchwil › Adolygwyd gan gymheiriaid
- Cyhoeddwyd
Adaptive radiation in Lesser Antillean lizards: molecular phylogenetics and species recognition in the Lesser Antillean dwarf gecko complex, Sphaerodactylus fantasticus.
Thorpe, R. S., Jones, A. G., Malhotra, A. & Surget-Groba, Y., 1 Maw 2008, Yn: Molecular Ecology. 17, 6, t. 1489-1504Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adaptive radiation of cichlid fish.
Turner, G. F., 9 Hyd 2007, Yn: Current Biology. 17, 19, t. R827-R831Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adaptive search in juvenile plaice foraging for aggregated and dispersed prey.
Hill, S., Burrows, M. T. & Hughes, R. N., 1 Tach 2002, Yn: Journal of Fish Biology. 61, 5, t. 1255-1267Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Addition of base cations increases microbial carbon use efficiency and biomass in acidic soils
Horn, E. L., Cooledge, E., Jones, D. L., Hoyle, F. C., Brailsford, F. L. & Murphy, D. V., Hyd 2021, Yn: Soil Biology and Biochemistry. 161, 108392.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Addition of iron to agricultural topsoil and subsoil is not an effective C sequestration strategy
Button, E. S., Chadwick, D. R. & Jones, D. L., 1 Maw 2022, Yn: Geoderma. 409, 115646.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Additional carbon sequestration benefits of grassland diversity restoration.
De Deyn, G. B., Shiel, R. S., Ostle, N. J., McNamara, N. P., Oakley, S., Young, I., Freeman, C., Fenner, N., Quirk, H. & Bardgett, R. D., 1 Meh 2011, Yn: Journal of Applied Ecology. 48, 3, t. 600-608Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Addressing human-tiger conflict using socio-ecological information on tolerance and risk
Struebig, M. J., Linkie, M., Deere, N. J., Martyr, D. J., Milliyanawati, B., Faulkner, S. C., Le Comber, S. C., Mangunjaya, F. M., Leader-Williams, N., McKay, J. E. & St John, F. A. V., 27 Awst 2018, Yn: Nature Communications. 9, 3455.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adenovirus infection: An emerging factor in red squirrel conservation programmes
Everest, D. J., Shuttleworth, C., Stidworthy, M. F., Grierson, S. S., Duff, P. J. & Kenward, R. E., 1 Hyd 2014, Yn: Mammal Review. 44, 3-4, t. 225-233Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adenovirus-associated deaths in red squirrels on Anglesey
Everest, D. J., Shuttleworth, C. & Stidworthy, M. F., 31 Hyd 2008, Yn: The Veterinary record. 163, 14, t. 430Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- E-gyhoeddi cyn argraffu
Adjustable wind selectivity in shearwaters implies knowledge of the foraging landscape
Harris, S., Bishop, C. M., Bond, S., Fernandes, P. G., Guilford, T., Lewin, P. J., Padget, O., Robins, P., Schneider, W., Waggitt, J., Wilmes, S.-B. & Cordes, L., 14 Ion 2025, (E-gyhoeddi cyn argraffu) Yn: Current Biology.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Admixture between ancient lineages, selection, and the formation of sympatric stickleback species-pairs
Dean, L., Magalhaes, I., Foote, A., D'Agostino, D., McGowan, S. & MacColl, A., Tach 2019, Yn: Molecular Biology and Evolution. 36, 11, t. 2481-2497Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adoption of Agroforestry in Northwest Viet Nam: What Roles Do Social and Cultural Norms Play?
Nguyen, M. P., Pagella, T., Catacutan, D. C., Nguyen, T. Q. & Sinclair, F., Ebr 2021, Yn: Forests. 12, 4, 493.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adoption of rice varieties - I. Age of varieties and patterns of variability
Witcombe, J. R., Khadka, K., Puri, R. R., Khanal, N. P., Sapkota, A. & Joshi, K. D., 1 Hyd 2017, Yn: Experimental Agriculture. 53, 4, t. 512-527Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adoption of rice varieties. 2. Accelerating uptake
Witcombe, J. R., Khadka, K., Puri, R. R., Khanal, N. P., Sapkota, A. & Joshi, K. D., 1 Hyd 2017, Yn: Experimental Agriculture. 53, 4, t. 627-643Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adrenergic responses of Antarctic fishes to extreme trauma.
Whiteley, N. M. & Egginton, S., 1 Chwef 2000, Yn: Journal of Physiology. 523, Supplement S, t. 279P-280PAllbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adsorption and desorption dynamics of citric acid anions in soil
Oburger, E., Leitner, D., Jones, D. L., Zygalakis, K. C., Schnepf, A. & Roose, T., 1 Hyd 2011, Yn: European Journal of Soil Science. 62, 5, t. 733-742Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Adult worm tegumental damage and egg-granulomas in praziquantel-resistant and -susceptible Schistosoma mansoni treated in vivo.
Liang, Y. S., Coles, G. C., Dai, J. R., Zhu, Y. C. & Doenhoff, M. J., 1 Rhag 2002, Yn: Journal of Helminthology. 76, 4, t. 327-333Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Advanced Processing of Food Waste Based Digestate for Mitigating Nitrogen Losses in a Winter Wheat Crop
Sanchez Rodriguez, A., Carswell, A. M., Shaw, R., Hunt, J., Saunders, K., Cotton, J., Chadwick, D., Jones, D. L. & Misselbrook, T. H., 17 Gorff 2018, Yn: Frontiers in Sustainable Food Systems.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Advances and Challenges in the Synthesis of Poly(p-phenylene vinylene)-Based Polymers
Blayney, A. J., Perepichka, I. F., Wuld, F. & Perepichka, D. F., 23 Meh 2014, Yn: Israel Journal of Chemistry. 54, 5-6, t. 674-688Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Advances in knowledge of processes in soil–tree–crop interactions in parkland systems in the West African Sahel: A review
Bayala, J., Sanou, J., Teklehaimanot, Z., Quedraogo, S. J., Kalinganire, A., Coe, R. & van Noordwijk, M., 11 Maw 2015, Yn: Agriculture, Ecosystems and Environment. 205, t. 25-35Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Advances in metabarcoding techniques bring us closer to reliable monitoring of the marine benthos
Steyaert, M., Priestley, V., Osborne, O., Herraiz, A., Arnold, R. & Savolainen, V., 1 Tach 2020, Yn: Journal of Applied Ecology. 57, 11, t. 2234–2245Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Aerobic and anaerobic oxidation of hydrogen by acidophilic bacteria
Hedrich, S. & Johnson, D. B., 1 Rhag 2013, Yn: FEMS Microbiology Letters. 349, 1, t. 40-45Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Aerodynamics of tip-reversal upstroke in a revolving pigeon wing
Crandell, K. E. & Tobalske, B. W., Meh 2011, Yn: Journal of Experimental Biology. 214, 11, t. 1867-1873Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
African and Asian leopards are highly differentiated at the genomic level
Paijmans, J., Barlow, A., Becker, M. S., Cahill, J. A., Fickel, J., Forster, D. W. G., Gries, K., Hartmann, S., Havmoller, R. W., Henneberger, K., Kern, C., Kitchener, A. C., Lorenzen, E. D., Mayer, F., O'Brien, S. J., von Seth, J., Sinding, M.-H. S., Spong, G., Uphyrkina, O., Wachter, B., Westbury, M. V., Dalén, L., Bhak, J., Manica, A. & Hofreiter, M., 10 Mai 2021, Yn: Current Biology.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
African cichlid Pseudotropheus spp. males moan to females during foreplay.
Simões, J. M., Fonseca, P. J., Turner, G. F. & Amorim, M. C., 1 Meh 2008, Yn: Journal of Fish Biology. 72, 10, t. 2689-2694Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
African sandalwood (Osyris lanceolata): resource assessment and quality variation among populations in Tanzania.
Mwang'ingo, P. L., Teklehaimanot, Z., Hall, J. B. & Lulandala, L. L., 1 Ion 2003, Yn: Southern African Forestry Journal. 199, t. 77-88Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Against a grey tide: red squirrel conservation on Anglesey
Shuttleworth, C., 2005, Yn: Quarterly Journal of Forestry. 99, t. 213-214Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Age of cichlids: New dates for ancient lake fish radiations
Genner, M. J., Seehausen, O., Lunt, D. H., Joyce, D. A., Shaw, P. W., Carvalho, G. R. & Turner, G. F., 1 Mai 2007, Yn: Molecular Biology and Evolution. 24, 5, t. 1269-1282Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Age-Related Variation in Foraging Behaviour in the Wandering Albatross at South Georgia: No Evidence for Senescence
Froy, H., Lewis, S., Catry, P., Bishop, C. M., Forster, I. P., Fukuda, A., Higuchi, H., Phalan, B., Xavier, J. C., Nussey, D. H. & Phillips, R. A., 9 Ion 2015, Yn: PLoS ONE. 10, 9Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Age-dependent loss of fertility in water-borne sperm of the bryozoan Celleporella hyalina
Manriquez, P. H., Hughes, R. N. & Bishop, J. D., 18 Rhag 2001, Yn: Marine Ecology Progress Series. 224, t. 87-92Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Agricultural land use regulates the fate of soil phosphorus fractions following the reclamation of wetlands
Qin, L., Jiang, M., Freeman, C., Zou, Y., Gao, C., Tian, W. & Wang, G., 10 Maw 2023, Yn: Science of the Total Environment. 863, 160891.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Agriculture and Eutrophication: Where Do We Go from Here?
Withers, P. J., Neal, C., Jarvie, H. P. & Doody, D. G., 2 Medi 2014, Yn: Sustainability. 6, 9, t. 5853-5875Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Agro-Biodiversity Management: Using Indigenous Knowledge to Cope with Climate Change in the Middle-Hills of Nepal
Baul, T. K. & McDonald, M. A., 21 Chwef 2014, Yn: Agricultural Research. 3, 1, t. 41-52Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Agrochemicals interact synergistically to increase bee mortality
Siviter, H., Bailes, E., Martin, C. D., Oliver, T., Koricheva, J., Leadbetter, E. & Brown, M. J. F., 9 Awst 2021, Yn: Nature.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Agroecosystem resilience in response to extreme winter flooding
Harvey, R. J., Chadwick, D. R., Sánchez-Rodríguez, A. R. & Jones, D. L., 1 Gorff 2019, Yn: Agriculture, Ecosystems and Environment. 279, t. 1-13Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Agronomic amendments drive a diversity of real and apparent priming responses within a grassland soil
Brown, R., Reed, E., Chadwick, D., Hill, P. & Jones, D. L., 1 Chwef 2024, Yn: Soil Biology and Biochemistry. 189, 109265.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Agronomic diversity of naked barley (Hordeum vulgare L.): a potential resource for breeding new food barley for Europe
Dickin, E., Steele, K., Edwards-Jones, G. & Wright, D., 1 Maw 2012, Yn: Euphytica. 184, 1, t. 85-99Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Agronomic evaluation and performance of flax varieties for industrial fibre production.
Dimmock, J. P., Bennett, S. J., Wright, D., Edwards-Jones, G. & Harris, I. M., 1 Awst 2005, Yn: Journal of Agricultural Science. 143, 4, t. 299-309Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Airborne DNA reveals predictable spatial and seasonal dynamics of fungi
Abrego, N., Furneaux, B., Hardwick, B., Somervuo, P., Palorinne, I., Aguilar-Trigueros, C. A., Andrew, N. R., Babiy, U. V., Bao, T., Bazzano, G., Bondarchuk, S. N., Bonebrake, T. C., Brennan, G. L., Bret-Harte, S., Bässler, C., Cagnolo, L., Cameron, E. K., Chapurlat, E., Creer, S., D'Acqui, L. P., de Vere, N., Desprez-Loustau, M.-L., Dongmo, M. A. K., Jacobsen, I. B. D., Fisher, B. L., Flores de Jesus, M., Gilbert, G. S., Griffith, G. W., Gritsuk, A. A., Gross, A., Grudd, H., Halme, P., Hanna, R., Hansen, J., Hansen, L. H., Hegbe, A. D. M. T., Hill, S., Hogg, I. D., Hultman, J., Hyde, K. D., Hynson, N. A., Ivanova, N., Karisto, P., Kerdraon, D., Knorre, A., Krisai-Greilhuber, I., Kurhinen, J., Kuzmina, M., Lecomte, N., Lecomte, E., Loaiza, V., Lundin, E., Meire, A., Mešić, A., Miettinen, O., Monkhouse, N., Mortimer, P., Müller, J., Nilsson, R. H., Nonti, P. Y. C., Nordén, J., Nordén, B., Norros, V., Paz, C., Pellikka, P., Pereira, D., Petch, G., Pitkänen, J.-M., Popa, F., Potter, C., Purhonen, J., Pätsi, S., Rafiq, A., Raharinjanahary, D., Rakos, N., Rathnayaka, A. R., Raundrup, K., Rebriev, Y. A., Rikkinen, J., Rogers, H. M. K., Rogovsky, A., Rozhkov, Y., Runnel, K., Saarto, A., Savchenko, A., Schlegel, M., Schmidt, N. M., Seibold, S., Skjøth, C., Stengel, E., Sutyrina, S. V., Syvänperä, I., Tedersoo, L., Timm, J., Tipton, L., Toju, H., Uscka-Perzanowska, M., van der Bank, M., van der Bank, F. H., Vandenbrink, B., Ventura, S., Vignisson, S. R., Wang, X., Weisser, W. W., Wijesinghe, S. N., Wright, S. J., Yang, C., Yorou, N. S., Young, A., Yu, D. W., Zakharov, E. V., Hebert, P. D. N., Roslin, T. & Ovaskainen, O., 25 Gorff 2024, Yn: Nature. 631, 8022, t. 835-842 8 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Alarm call modification by prairie dogs in the presence of juveniles
Wilson-Henjum, G., Job, J., McKenna, M. F., Shannon, G. & Wittemyer, G., Mai 2019, Yn: Ethology. 37, 2, t. 167-174 8 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Albizia zygia, a shade tree for cocoa: the effects of duration of acid scarification and substrate acidity on the germination of seed.
Anim-Kwapong, G. & Teklehaimanot, Z., 1 Ion 2001, Yn: Forests, Trees and Livelihoods. 11, t. 47-55Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Alcalilimnicola halodurans gen. nov., sp nov., an alkaliphilic, moderately halophilic and extremely halotolerant bacterium, isolated from sediments of soda-depositing Lake Natron, East Africa Rift Valley.
Yakimov, M. M., Giuliano, L., Chernikova, T. N., Gentile, G., Abraham, W. R., Lunsdorf, H., Timmis, K. N. & Golyshin, P. N., 1 Tach 2001, Yn: International Journal of Systematic and Evolutionary Microbiology. 51, 6, t. 2133-2143Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Alcanivorax borkumensis gen. nov., sp. nov., a new, hydrocarbon-degrading and surfactant-producing marine bacterium
Yakimov, M. M., Golyshin, P. N., Lang, S., Moore, E. R., Abraham, W. R., Lünsdorf, H. & Timmis, K. N., Ebr 1998, Yn: International journal of systematic bacteriology. 48 Pt 2, t. 339-48 10 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Alcanivorax borkumensis produces an extracellular siderophore in iron-limitation condition maintaining the hydrocarbon-degradation efficiency
Denaro, R., Crisafi, F., Russo, D., Genovese, M., Messina, E., Genovese, L., Carbone, M., Ciavatta, M. L., Ferrer, M., Golyshin, P. & Yakimov, M. M., 1 Hyd 2014, Yn: Marine Genomics. 17, October, t. 43-52Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Alien invasions and livelihoods: Economic benefits of invasive Australian Red Claw crayfish in Jamaica
Pienkowski, T., Williams, S., McLaren, K., Wilson, B. & Hockley, N., 21 Chwef 2015, Yn: Ecological Economics. 112, t. 68-77Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Aligning efficiency benchmarking with sustainable outcomes in the United Kingdom water sector
Walker, N. L., Styles, D., Gallagher, J. & Williams, A. P., 1 Meh 2021, Yn: Journal of Environmental Management. 287, 112317.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Alignment of chevron-shaped molecules for photonic and electronic applications
Ashwell, G. J. & Amiri, M. A., 1 Awst 2002, Yn: Journal of Materials Chemistry. 12, 8, t. 2181-2183Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
All that glitters is not gold: The effect of top-down participation on conservation knowledge, attitudes and institutional trust in a Central Indian tiger reserve
Macura, B., Secco, L., Pisani, E., Pullin, A. & Reyes-García, V., 1 Awst 2016, Yn: Regional Environmental Change. 16, August, t. 125-140Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Alleviation of both water and nutrient limitations is necessary to accelerate ecological restoration of waste rock tips.
Williamson, J. C., Rowe, E. C., Hill, P. W., Nason, M. A., Jones, D. L. & Healey, J. R., Maw 2011, Yn: Restoration Ecology. 19, 2, t. 194-204Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Allometry and Ecology of the Bilaterian Gut Microbiome
Sherrill-Mix, S., McCormick, K., Lauder, A., Bailey, A., Zimmerman, L., Li, Y., Django, J.-B. N., Bertolani, P., Colin, C., Hart, J. A., Hart, T. B., Georgiev, A. V., Sanz, C. M., Morgan, D. B., Atencia, R., Cox, D., Muller, M. N., Sommer, V., Piel, A. K., Stewart, F. A., Speede, S., Roman, J., Wu, G., Taylor, J., Bohm, R., Rose, H. M., Carlson, J., Mjungu, D., Schmidt, P., Gaughan, C., Bushman, J. I., Schmidt, E., Bittinger, K., Collman, R. G., Hahn, B. H. & Bushman, F. D., 27 Maw 2018, Yn: mBio. 9, 2, e00319-18.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid