Ysgol Gwyddorau Amgylcheddol a Naturiol

  1. Cyhoeddwyd

    Chk1 activation requires Rad9 S/TQ-site phosphorylation to promote association with C-terminal BCRT domains of Rad4(TOPBP1).

    Furuya, K., Poitelea, M., Guo, L., Caspari, T. M. & Carr, A. M., 15 Mai 2004, Yn: Genes and Development. 18, (10), t. 1154-1164

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  2. Cyhoeddwyd

    Multiple linker Half-squarylium Dyes for Dye-Sensitized Solar Cells; Are Two Linkers Better than One?

    Furnell, L. W., Kershaw, C. P., Connell, A., Holliman, P. J., Jones, E. W., Furnell, L., Kershaw, C., Davies, M. L., Gwenin, C. D., Pitak, M. B., Coles, S. J. & Cooke, G., 16 Rhag 2014, Yn: Journals of Materials Chemistry A. 3, 6, t. 2883-2894

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  3. Cyhoeddwyd

    Digital imaging to simultaneously study device lifetimes of multiple dye-sensitized solar cells

    Furnell, L., Holliman, P., Connell, A., Jones, E., Hobbs, R., Kershaw, C., Anthony, R., Searle, J., Watson, T. M. & McGetterick, J., 1 Ebr 2017, Yn: Sustainable Energy & Fuels. 2017, 2, t. 362-370

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  4. Cyhoeddwyd

    Photovoltaic product form and importance of colour

    Furnell, L. W., Holliman, P. J., Jones, E. W., Connell, A., Furnell, L. & Davies, M. L., 1 Tach 2014, Yn: Materials Research Innovations. 18, 7, t. 486-489

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  5. Cyhoeddwyd

    ParaHox cluster evolution--hagfish and beyond

    Furlong, R. F. & Mulley, J. F., 25 Hyd 2008, Yn: Zoological Science. 25, 10, t. 955-9 5 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygl adolyguadolygiad gan gymheiriaid

  6. Cyhoeddwyd

    Early-life sibling conflict in Canada jays has lifetime fitness consequences

    Fuirst, M., Strickland, D., Freeman, N. E., Sutton, A. & Norris, D. R., 26 Ebr 2023, Yn: Proceedings of the Royal Society B: Biological Sciences. 290, 1997

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  7. Cyhoeddwyd

    Mono- and ditopic hydroxamate ligands towards discrete and extended network architectures

    Fugu, M. B., Ellaby, R. J., O`Connor, H. M., Pitak, M. B., Klooster, W., Horton, P. N., Coles, S. J., Al-mashhadani, M. H., Brechin, E. K., Perepichka, I. & Jones, L. F., Gorff 2019, Yn: Dalton Transactions. 48, 27, t. 10180-10190

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  8. Cyhoeddwyd

    Seasonal variations in soil microbial communities under different land restoration types in a subtropical mountains region, Southwest China

    Fu, D., Wu, X., Qiu, Q., Duan, C. & Jones, D. L., 1 Medi 2020, Yn: Applied Soil Ecology. 153, 103634.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  9. Cyhoeddwyd

    Response of soil phosphorus fractions and fluxes to different vegetation restoration types in a subtropical mountain ecosystem

    Fu, D., Wu, X., Duan, C., Chadwick, D. R. & Jones, D. L., 1 Hyd 2020, Yn: Catena. 193, 104663.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  10. Cyhoeddwyd

    Land use effects on soil phosphorus behavior characteristics in the eutrophic aquatic-terrestrial ecotone of Dianchi Lake, China

    Fu, D., Xu, Z., Wu, X., Zhao, L., Zhu, A., Duan, C., Chadwick, D. R. & Jones, D. L., 31 Ion 2021, Yn: Soil & Tillage Research. 205, 104793.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  11. Cyhoeddwyd

    The origin and evolution of the Toxicofera reptile venom system.

    Fry, B. G., Sunagar, K., Casewell, N. R., Kochva, E., Roelants, K., Scheib, H., Wüster, W., Vidal, N., Young, B., Burbink, F., Pyron, R. A., Vonk, F. J. & Jackson, T. N. W., Rhag 2015, Venomous Reptiles and Their Toxins: Evolution, Pathophysiology and Biodiscovery. Fry, B. G. (gol.). Oxford: Oxford: OUP, t. 1 31 t.

    Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion CynhadleddPennodadolygiad gan gymheiriaid

  12. 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, 9

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  13. Cyhoeddwyd

    Microscale pollen release and dispersal patterns in flowering grass populations

    Frisk, C. A., Apangu, G. P., Petch, G. M., Creer, S., Hanson, M., Adams-Groom, B. & Skjoth, C. A., 1 Gorff 2023, Yn: Science of the Total Environment. 880, 163345.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  14. Cyhoeddwyd

    Decomposition as a regulator of carbon accretion in mangroves: a review

    Friesen, S., Dunn, C. & Freeman, C., Ebr 2018, Yn: Ecological Engineering. 114, t. 173-178

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  15. Cyhoeddwyd

    Current and future genetic technologies for fisheries and aquaculture: implications for the work of FAO

    Friedman, KJ., Bartley, DM., Rodríguez-Ezpeleta, N., Mair, GC., Ban, N., Beveridge, M., Carolsfeld, J., Carvalho, G., Cowx, I., Dean, G., Glazov, E., Leber, K., Loftus, R., Martinsohn, J., Olesen, I., Soto, E., Van Eenennaam, A. L. & Vigar, JR., 2022. 56 t.

    Allbwn ymchwil: Cyfraniad at gynhadleddPapuradolygiad gan gymheiriaid

  16. Cyhoeddwyd

    Beyond the community in participatory forest management: A governance network perspective

    Friedman, R., Guerrero, R. S., McAllister, R. R. J., Rhodes, J., Santika, T., Budiharta, S., Indrawan, T. P., Hutabarat, J. A., Kusworo, A., Yogaswara, H., Meijaard, E., St John, F. A. V., Struebig, M. J. & Wilson, K. A., 1 Medi 2020, Yn: Land Use Policy. 97, 104738.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  17. Cyhoeddwyd

    Analyzing procedural equity in government-led community-based forest management

    Friedman, R., Rhodes, J., Dean, A., Law, E., Santika, T., Budiharta, S., Hutabarat, J. A., Indrawan, T. P., Kusworo, A., Meijaard, E., St John, F. A. V., Struebig, M. & Wilson, K. A., Medi 2020, Yn: Ecology and Society. 25, 3, 16.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  18. Cyhoeddwyd

    Towards bioremediation of toxic unresolved complex mixtures of hydrocarbons: identification of bacteria capable of rapid degradation of alkyltetralins.

    Frenzel, M., James, P., Burton, S. K., Rowland, S. J. & Lappin-Scott, H. M., 1 Ebr 2009, Yn: Journal of Soils and Sediments. 9, 2, t. 129-136

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  19. Cyhoeddwyd

    Biosensors in bioprocess monitoring and control : Current trends and future prospects

    French, E., Gwenin, C. D., El-Mansi, E. M. (gol.), Bryce, C. F. (gol.), Demain, A. L. (gol.) & Allman, A. R. (gol.), 12 Ion 2012, Fermentation Microbiology and Biotechnology (3rd edition). 2012 gol. CRC Press

    Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion CynhadleddPennod

  20. 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

  21. Cyhoeddwyd

    Evidence for cryptic sex in parthenogenetic stick insects of the genus Timema

    Freitas, S., Parker, D. J., Labédan, M., Dumas, Z. & Schwander, T., 27 Medi 2023, Yn: Proceedings of the Royal Society B: Biological Sciences. 290, 2007, 11 t., 20230404.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  22. Cyhoeddwyd

    Export of organic carbon from peat soils.

    Freeman, C., Evans, C. D., Monteith, D. T., Reynolds, B. & Fenner, N., 23 Awst 2001, Yn: Nature. 412, 6849, t. 785

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  23. Cyhoeddwyd

    Export of dissolved organic carbon from peatlands under elevated carbon dioxide levels.

    Freeman, C., Fenner, N., Ostle, N. J., Kang, H., Dowrick, D. J., Reynolds, B., Lock, M. A., Sleep, D., Hughes, S. & Hudson, J., 8 Gorff 2004, Yn: Nature. 430, 6996, t. 195-198

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  24. Cyhoeddwyd

    Effects of elevated atmospheric CO2 concentrations on soil microorganisms.

    Freeman, C., Kim, S. Y., Lee, S. H. & Kang, H., 1 Rhag 2004, Yn: Journal of Microbiology. 42, 4, t. 267-277

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  25. Cyhoeddwyd

    Peatland geoengineering: an alternative approach to terrestrial carbon sequestration

    Freeman, C., Fenner, N. & Shirsat, A. H., 13 Medi 2012, Yn: Philosophical Transactions of the Royal Society A. 370, 1974, t. 4404-4421

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  26. Cyhoeddwyd

    Contrasted effects of simulated drought on the production and oxidation of methane in a mid-Wales wetland.

    Freeman, C., Nevison, G. B., Kang, H., Hughes, S., Reynolds, B. & Hudson, J. A., 1 Ion 2002, Yn: Soil Biology and Biochemistry. 34, 1, t. 61-67

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  27. Cyhoeddwyd

    An enzymatic 'latch' on a global carbon store;- a shortage of oxygen locks up carbon in peatlands by restraining a single enzyme.

    Freeman, C., Ostle, N. J. & Kang, H., 11 Ion 2001, Yn: Nature. 409, 6817, t. 149

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  28. Cyhoeddwyd

    A regulatory role for phenol oxidase during decomposition in peatlands.

    Freeman, C., Ostle, N., Fenner, N. & Kang, H., 1 Hyd 2004, Yn: Soil Biology and Biochemistry. 36, 10, t. 1663-1667

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  29. Cyhoeddwyd

    Responsible agriculture must adapt to the wetland character of mid-latitude peatlands

    Freeman, B. W. J., Evans, C. D., Musarika, S., Morrison, R., Newman, T. R., Page, S. E., Wiggs, G. F. S., Bell, N. G. A., Styles, D., Wen, Y., Chadwick, D. R. & Jones, D. L., 1 Meh 2022, Yn: Global Change Biology. 28, 12, t. 3795-3811 17 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygl adolyguadolygiad gan gymheiriaid

  30. Cyhoeddwyd

    The use of fluorogenic substrates for measuring enzyme activity in peatlands

    Freeman, C., Liska, G., Ostle, N. J. & Lock, M. A., 1 Awst 1995, Yn: Plant and Soil. 175, 1, t. 147-152

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  31. Cyhoeddwyd

    Provenance and pretreatment effect on seed germination of six provenances of Faidherbia albida (Delile) A. Chev

    Fredrick, C., Muthuri, C., Ngamau, K. & Sinclair, F., Rhag 2017, Yn: Agroforestry Systems. 91, 6, t. 1007-1017

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  32. Cyhoeddwyd

    Provenance variation in seed morphological characteristics, germination and early seedling growth of Faidherbia albida

    Fredrick, C., Muthuri, C., Ngamau, K. & Sinclair, F., Mai 2015, Yn: Journal of Horticulture and Forestry. 7, 5, t. 127-140 14 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  33. Cyhoeddwyd

    Food Access Deficiencies in Sub-saharan Africa: Prevalence and Implications for Agricultural Interventions

    Fraval, S., Hammond, J., Bogard, J. R., Ng'endo, M., van Etten, J., Herrero, M., Oosting, S. J., de Boer, I. J. M., Lannerstad, M., Teufel, N., Lamanna, C., Rosenstock, T. S., Pagella, T., Vanlauwe, B., Dontsop-Nguezet, P. M., Baines, D., Carpena, P., Njingulula, P., Okafor, C., Wichern, J., Ayantunde, A., Bosire, C., Chesterman, S., Kihoro, E., Rao, E. J. O., Skirrow, T., Steinke, J., Stirling, C. M., Yameogo, V. & van Wijk, M. T., 19 Tach 2019, Yn: Frontiers in Sustainable Food Systems. 3, 104.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  34. Cyhoeddwyd

    A multidisciplinary approach in the design of marine protected areas: Integration of science and stakeholder based methods

    Frau, A. R., Possingham, H. P., Edwards-Jones, G., Klein, C. J., Segan, D. & Kaiser, M. J., 24 Tach 2014, Yn: Ocean and Coastal Management. 103, t. 86-93

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  35. Cyhoeddwyd

    Preference classes in society for coastal marine protected areas

    Frau, A., Gibbons, J., Hinz, H., Edwards-Jones, G. & Kaiser, M., 23 Ebr 2019, Yn: PeerJ. PubMed 31065453 .

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  36. Cyhoeddwyd

    Seedling Identification: a Guide to the Tree Species of Mount Cameroon

    Fraser, P. J., Healey, J. & Ndam, N., 1999, Bangor: University of Wales Bangor. 531 t. (SAFS Publication; Rhif 11)

    Allbwn ymchwil: Llyfr/AdroddiadLlyfr

  37. Cyhoeddwyd

    A review of Pinaceae resistance mechanisms against needle and shoot pathogens with a focus on the Dothistroma–Pinus interaction

    Fraser, S., Martin-Garcia, J., Perry, A., Kabir, M. S., Owen, T., Solla, A., Brown, A. V., Bulman, L. S., Barnes, I., Hale, M., Vasconcelos, M. W., Lewis, K. J., Doğmuş-Lehtijarvi, H. T., Markovskaja, S., Woodward, S. & Bradshaw, R. E., Hyd 2016, Yn: Forest Pathology. 46, 5, t. 453-471

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  38. Cyhoeddwyd

    Climate of the Mount Cameroon Region: Long and medium term rainfall, temperature and sunshine data

    Fraser, P., Hall, J. & Healey, J., 1998, University of Wales, Bangor. 56 t.

    Allbwn ymchwil: Llyfr/AdroddiadAdoddiad Arall

  39. Cyhoeddwyd

    Plant succession on the 1922 lava flow of Mount Cameroon

    Fraser, P., Banks, H., Brodie, S., Cheek, M., Dawson, S., Healey, J., Marsden, J., Ndam, N., Nning, J. & McRobb, A., 1999, African Plants: Biodiversity, Taxonomy and Uses: Proceedings of the 1997 AGTFAT Congress, Harare, Zimbabwe. Timberlake, J. & Kativu, S. (gol.). Royal Botanic Gardens, Kew, t. 253-262

    Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion CynhadleddPennodadolygiad gan gymheiriaid

  40. Cyhoeddwyd

    A new black-bellied snake (Pseudoxyrhophiinae: Liophidium) from western Madagascar, with notes on the genus Pararhadinaea.

    Franzen, M., Jones, J. P. G., Raselimanana, A. P., Nagy, Z. T., D'Cruze, N., Glaw, F. & Vences, M., 1 Ion 2009, Yn: Amphibia-Reptilia. 30, 2, t. 173-183

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  41. Cyhoeddwyd

    Aluminium complexation suppresses citrate uptake by acid forest soil microorganisms.

    Fransson, A. M., Vinogradoff, S., Godbold, D. L., Van Hees, P. A. & Jones, D. L., 1 Chwef 2004, Yn: Soil Biology and Biochemistry. 36, 2, t. 353-357

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  42. Cyhoeddwyd

    Phosphatase activity does not limit the microbial use of low molecular weight organic-P substrates in soil.

    Fransson, A. M. & Jones, D. L., 1 Mai 2007, Yn: Soil Biology and Biochemistry. 39, 5, t. 1213-1217

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  43. Cyhoeddwyd

    Geographical Ecology of Dry Forest Tree Communities in the West Indies

    Franklin, J., Andrade, R., Daniels, M. L., Fairbairn, P., Fandino, M. C., Gillespie, T. W., González, G., González, O., Imbert, D., Kapos, V., Kelly, D. L., Marcano-Vega, H., Meléndez-Ackerman, E. J., McLaren, K. P., McDonald, M. A., Ripplinger, J., Rojas-Sandoval, J., Ross, M. S., Ruiz, J., Steadman, D. W., Tanner, E. V. J., Terrill, I. & Vennetier, M., Mai 2018, Yn: Journal of Biogeography. 45, 5, t. 1168-1181

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  44. Cyhoeddwyd

    Hunters and hunting across indigenous and colonist communities at the forest agriculture interface: an ethnozoological study from the Peruvian Amazon

    Francesconi, W., Bax, V., Blundo-Canto, G., Willcock, S., Cuadros, S., Vanegas, M., Quintero, M. & Torres-Vitolas, C. A., 10 Awst 2018, Yn: Journal of Ethnobiology and Ethnomedicine . 14, 22 t., 54.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  45. Cyhoeddwyd

    TaqMan DNA technology confirms likely overestimation of cod (Gadus morhua L.) egg abundance in the Irish Sea: implications for the assessment of the cod stock and mapping of spawning areas using egg-based methods.

    Fox, C. J., Taylor, M. I., Pereyra, R., Villasan, M. I. & Rico, C., 1 Maw 2005, Yn: Molecular Ecology. 14, 3, t. 879-884

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  46. Cyhoeddwyd

    Mapping the spawning grounds of North Sea cod (Gadus morhua) by direct and indirect means.

    Fox, C. J., Taylor, M. I., Dickey-Collas, M., Fossum, P., Kraus, G., Rohlf, N., Munk, P., Van Damme, C. J., Bolle, L. J., Maxwell, D. L. & Wright, P. J., 1 Gorff 2008, Yn: Proceedings of The Royal Society B - Biological Sciences. 275, 1642, t. 1543-1548

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  47. Cyhoeddwyd

    Extraction and characterization of original lignin and hemicelluloses from wheat straw

    Fowler, P. A., Sun, R., Sun, X. F., Sun, R. C., Fowler, P. & Baird, M. S., 23 Chwef 2005, Yn: Journal of Agricultural and Food Chemistry. 53, 4, t. 860-870

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  48. Cyhoeddwyd

    Characteristics of degraded lignins obtained from steam exploded wheat straw.

    Fowler, P. A., Sun, R., Sun, X. F., Xu, F., Sun, R. C., Wang, Y. X., Fowler, P. & Baird, M. S., 1 Tach 2004, Yn: Polymer Degradation and Stability. 86, 2, t. 245-256

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  49. Cyhoeddwyd

    Inhomogeneities in the chemical structure of sugarcane bagasse lignin.

    Fowler, P. A., Sun, R., Sun, J. X., Sun, X. F., Sun, R. C., Fowler, P. & Baird, M. S., 5 Tach 2003, Yn: Journal of Agricultural and Food Chemistry. 51, 23, t. 6719-6725

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  50. Cyhoeddwyd

    Characteristics of degraded hemicellulosic polymers obtained from steam exploded wheat straw.

    Fowler, P. A., Sun, R., Sun, X. F., Xu, F., Sun, R. C., Geng, Z. C., Fowler, P. & Baird, M. S., 7 Ebr 2005, Yn: Carbohydrate Polymers. 60, 1, t. 15-26

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid