Ysgol Gwyddorau Amgylcheddol a Naturiol
- Cyhoeddwyd
Painting the Town Red: Gwynedd red squirrel conservation
Shuttleworth, C., 2015, Shared Experience of Red Squirrel Conservation Practice . Shuttleworth, C. M., Lurz, P. W. W. & Halliwell, E. C. (gol.). European Squirrel Initiative, t. 159-166Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod
- Cyhoeddwyd
Paddy soils have a much higher microbial biomass content than upland soils: A review of the origin, mechanisms, and drivers
Wei, L., Ge, T., Zhu, Z., Ye, R., Penuelas, J., Li, Y., Lynn, T. M., Jones, D. L., Wu, J. & Kuzyakov, Y., 1 Maw 2022, Yn: Agriculture, Ecosystems and Environment. 326Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl adolygu › adolygiad gan gymheiriaid
- Cyhoeddwyd
Packaging choice and coordinated distribution logistics to reduce the environmental footprint of small-scale beer value chains
Morgan, D., Styles, D. & Lane, E., 1 Ebr 2022, Yn: Journal of Environmental Management. 307, 114591.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
PLLA‐Grafted Gelatin Amphiphilic Copolymer and Its Self‐Assembled Nano Carrier for Anticancer Drug Delivery
Beibei, D., Tiantang, F., Jiafeng, L., Qin, Z., Wuyou, Y., Wang, W., Tai, H. & Zhongyong, F., 5 Maw 2019, Yn: Macromolecular Chemistry and Physics. 220, 5, 1800528.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
PCR detection of adenovirus in grey squirrels on Anglesey
Everest, D. J., Grierson, S. S., Stidworthy, M. & Shuttleworth, C., 31 Hyd 2009, Yn: Veterinary Record. 165, t. 482Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Ozone inhibits phloem laoding from a transport pool: compartmental efflux analysis in Pima cotton
Grantz, D. & Farrar, J. F., 1 Ion 2000, Yn: Australian Journal of Plant Physiology. 27, 8-9, t. 859-868Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Ozone impacts on vegetation in a nitrogen enriched and changing climate
Wagg, S. K., Mills, G., Harmens, H., Wagg, S., Sharps, K., Hayes, F., Fowler, D., Sutton, M. & Davies, B., 26 Medi 2015, Yn: Environmental Pollution. 208, Part B, t. 898-908Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Ozone Tolerance Found in Aegilops tauschii and Primary Synthetic Hexaploid Wheat
Brewster, C., Hayes, F. & Fenner, N., 28 Meh 2019, Yn: Plants. 8, 7, 12 t., 195.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxyplasma meridianum gen. nov., sp. nov., an extremely acidophilic organotrophic member of the order Thermoplasmatales
Golyshina, O. V., Lunev, E. A., Distaso, M. A., Bargiela, R., Gaines, M. C., Daum, B., Ferrer, M., Bale, N. J., Koenen, M., Damsté, J. S. S., Yakimov, M. M. & Golyshin, P. N., 27 Awst 2024, Yn: International Journal of Systematic Evolutionary Microbiology. 74, 8Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxidopolyborate chemistry: The self-assembled, templated, synthesis, and an XRD study of a 1-D coordination polymer, [Cu(en){B6O7(OH)(6)}](.)3H(2)O (en=1,2-diaminoethane)
Altahan, M., Beckett, M., Coles, S. J. & Horton, P. N., 1 Tach 2020, Yn: Phosphorus, Sulfur and Silicon and the Related Elements. 195, 11, t. 952-956 5 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxidopolyborate anions templated by transition-metal complex cations: Self-assembled syntheses and structural studies (XRD) of [Co(NH3)(6)](2)[B4O5(OH)(4)](3)center dot 11H(2)O, [Ni(phen)(3)][B7O9(OH)(5)]center dot 9.5H(2)O and [Zn(dac)(2)(H2O)(2)][B7O9(OH)(5)]center dot H2O
Altahan, M., Beckett, M., Coles, S. J. & Horton, P. N., 15 Ion 2020, Yn: Journal of Molecular Structure. 1200, 127071Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxidoborates templated by cationic nickel(II) complexes and self-assembled from B(OH)3
Altahan, M., Beckett, M., Coles, S. J. & Horton, P. N., 31 Awst 2021, Yn: Inorganics. 9, 9, 68.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxidative dissolution of sulfide minerals by defined mixed populations of moderately thermophilic mmicroorganisms
Okibe, N. & Johnson, D. B., 1 Ion 2001, t. 39.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur
- Cyhoeddwyd
Oxidative and reductive bioprocessing of cobalt-containing ores and biomineralisation of cobaltiferous leachates
Smith, S., Grail, B. & Johnson, D. B., Hyd 2015.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxidative and reductive bioprocessing of cobalt bearing ores, and recovery of cobalt minerals via biosulfidogenesis
Smith, S., Grail, B. & Johnson, D. B., Meh 2016, Biohydromet 2016 Proceedings.Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Cyfraniad i Gynhadledd › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxidation of iron, sulfur and arsenic in mine waters and mine wastes: an important role for novel Thiomonas spp.
Coupland, K., Battaglia-Brunet, F., Hallberg, K. B., Dictor, M. C., Garrido, F., Johnson, D. B., Tsezos, M. (Golygydd), Hatzikioseyian, A. (Golygydd) & Remoudaki, E. (Golygydd), 1 Ion 2004, t. 639-646.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur
- Cyhoeddwyd
Oxidation of arsenite by Thiomonas strains and characterization of Thiomonas arsenivorans sp nov.
Battaglia-Brunet, F., Joulian, C., Garrido, F., Dictor, M. C., Morin, D., Coupland, K., Johnson, D. B., Hallberg, K. B. & Baranger, P., 1 Ion 2006, Yn: Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology. 89, 1, t. 99-108Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxalic acid sensors based on sol–gel nanostructured TiO2 films
Morozova, M., Kluson, P., Krysa, J., Gwenin, C. D. & Solcova, O., 1 Ebr 2011, Yn: Journal of Sol-Gel Science and Technology. 58, 1, t. 175-181Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Oxalate and ferricrocin exudation by the extramatrical mycelium of an ectomycorrhizal fungus in symbiosis with Pinus sylvestris.
Van Hees, P. A., Rosling, A., Essen, S., Godbold, D. L., Jones, D. L. & Finlay, R. D., 25 Tach 2005, Yn: New Phytologist. 169, 2, t. 367-377Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Overwintering sites of ladybirds, shieldbugs and allied species in Hertfordshire woodland: how important is aspect?
Gray, J. & Healey, J., 1 Ion 2016, Yn: Transactions of the Hertfordshire Natural History Society. 48, 1, t. 89-98Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl
- Cyhoeddwyd
Overview of the environment research programme project.
Healey, J. R., 12 Meh 2001.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur
- Cyhoeddwyd
Overview of Biomass Energy in Wales, UK
Walmsley, J. D., Jones, D. L. & Healey, J. R., 1 Medi 2006.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur
- Cyhoeddwyd
Overriding water table control on managed peatland greenhouse gas emissions
Evans, C. D., Peacock, M., Baird, A. J., Artz, R. R. E., Burden, A., Callaghan, N., Chapman, P. J., Cooper, H. M., Coyle, M., Craig, E., Cumming, A., Dixon, S., Gauci, V., Grayson, R. P., Helfter, C., Heppell, C. M., Holden, J., Jones, D. L., Kaduk, J., Levy, P., Matthews, R., McNamara, N. P., Misselbrook, T., Oakley, S., Page, S. E., Rayment, M., Ridley, L., Stanley, K. M., Williamson, J. L., Worrall, F. & Morrison, R., 27 Mai 2021, Yn: Nature. 593, t. 548-552Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Overlap not Gap: Understanding the Relationship between Animal Communication and Language with Prototype Theory
Amphaeris, J., Shannon, G. & Tenbrink, T., Meh 2022, Yn: Lingua. 272, 103332.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Over 50 years of behavioural evidence on the magnetic sense in animals: what has been learnt and how?
Schneider, W., Holland, R. & Lindecke, O., Maw 2023, Yn: The European Physical Journal Special Topics. 232, 2, t. 269-278 10 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl adolygu › adolygiad gan gymheiriaid
- Cyhoeddwyd
Outlier SNP markers reveal fine-scale genetic structuring across European hake populations (Merluccius merluccius)
Milano, I., Babbucci, M., Cariani, A., Atanassova, M., Bekkevold, D., Carvalho, G., Espineira, M., Fiorentino, F., Garofalo, G., Geffen, A., Hansen, J. H., Helyar, S. J., Nielsen, E. E., Ogden, R., Patarnello, T., Stagioni, M., Tinti, F. & Bargelloni, L., 18 Tach 2013, Yn: Molecular Ecology. 23, 1, t. 118-135Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Our life companions: The human follicular mite Demodex folliculorum
Perotti, M. A. & Braig, H. R., 30 Tach 2022, Yn: Zoosymposia. 22, t. 29-31Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Origin of the eastern brownsnake, Pseudonaja textilis (Dumeril, Bibron and Dumeril) (Serpentes : Elapidae : Hydrophiinae) in New Guinea: evidence of multiple dispersals from Australia, and comments on the status of Pseudonaja textilis pughi Hoser 2003.
Wuster, W., Williams, D. J., O'Shea, M., Daguerre, R. L., Pook, C. E., Wüster, W., Hayden, C. J., McVay, J. D., Paiva, O., Matainaho, T., Winkel, K. D. & Austin, C. C., 1 Ion 2008, Yn: Zootaxa. 1703, t. 47-61Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Origin and phylogenetic position of the Lesser Antillean species of Bothrops (Serpentes: Viperidae): biogeographical and medical implications.
Wuster, W., Wüster, W., Thorpe, R. S., Salomao, M. G., Thomas, L., Puorto, G., Theakston, R. D. & Warrell, D. A., 1 Ion 2002, Yn: Bulletin of the Natural History Museum London (Zoology). 68, t. 101-106Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Origin and fate of Vanadium in the Hazeltine Creek Catchment following the 2014 Mount Polley mine tailings spill, British Columbia, Canada
Hudson-Edwards, K. A., Byrne, P., Bird, G., Brewer, P. A., Burke, I. T., Jamieson, H. E., Macklin, M. G. & Williams, R. D., 16 Ebr 2019, Yn: Environmental Science and Technology. 53, 8, t. 4088–4098Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Origin and evolution of the South American pitviper fauna: evidence from mitochondrial DNA sequence analysis.
Wuster, W., Wüster, W., Salomao, M. G., Quijada-Mascarenas, J. A., Thorpe, R. S., Campbell, J. A. (Golygydd), Brodie, E. D. (Golygydd), Schuett, G. W. (Golygydd), Hoggren, M. (Golygydd), Douglas, M. E. (Golygydd) & Greene, H. W. (Golygydd), 1 Ion 2002, Biology of the Vipers. 2002 gol. Eagle Mountain Publishing, t. 111-128Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod
- Cyhoeddwyd
Orientation-induced molecular rectification and nonlinear optical properties of a squaraine derivative
Ashwell, G. J., Ewington, J. & Moczko, K., 1 Ion 2005, Yn: Journal of Materials Chemistry. 15, 11, t. 1154-1159Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Orientation and flight behaviour identify the Soprano pipistrelle as a migratory bat species at the Baltic Sea coast
Lindecke, O., Elksne, A., Holland, R., Petersons, G. & Voigt, C. C., 1 Mai 2019, Yn: Journal of Zoology. 308, 1, t. 56-65Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Orientation and Navigation in Bats
Holland, R., 2010, Encyclopedia of Animal Behaviour. Academic Press, Cyfrol 2. t. 177-185 9 t.Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod
- Cyhoeddwyd
Organophosphoryl adducts of tris (pentafluorophenyl) borane; Crystal and molecular structure of B(C6F5)3Ph3PO
Beckett, M. A., Brassington, D. S., Light, M. E. & Hursthouse, M. B., 1 Meh 2001, Yn: Journal of the Chemical Society Dalton Transactions. 11, t. 1768-1772Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organophosphorus Reagents.
Murphy, P. J. (Golygydd), 1 Ion 2004, 2004 gol. Oxford University Press.Allbwn ymchwil: Llyfr/Adroddiad › Llyfr
- Cyhoeddwyd
Organic rectifying junctions from an electron-accepting molecular wire and an electron-donating phthalocyanine
Ashwell, G. J., Tyrrell, W. D., Urasinska, B., Wang, C. S. & Bryce, M. R., 26 Ebr 2006, Yn: Chemical Communications. 15, t. 1640-1642Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic rectifying junctions fabricated by ionic coupling.
Ashwell, G. J., Ewington, J. & Robinson, B. J., 14 Chwef 2006, Yn: Chemical Communications. 6, t. 618-620Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic phosphorus in the terrestrial environment: a perspective on the state of the art and future priorities
George, T. S., Giles, C. D., Menezes-Blackburn, D., Condron, L. M., Gama-Rodrigues, A. C., Jaisi, D., Lang, F., Neal, A. L., Stutter, M. I., Almeida, D. S., Bol, R., Cabugao, K. G., Celi, L., Cotner, J. B., Feng, G., Goll, D. S., Hallama, M., Krueger, J., Plassard, C., Rosling, A., Darch, T., Fraser, T., Giesler, R., Richardson, A. E., Tamburini, F., Shand, C. A., Lumsdon, D. G., Zhang, H., Blackwell, M. S. A., Wearing, C., Mezeli, M. M., Almas, A. R., Audette, Y., Bertrand, I., Beyhaut, E., Boitt, G., Bradshaw, N., Brearley, C. A., Bruulsema, T. W., Ciais, P., Cozzolino, V., Duran, P. C., Mora, M. L., de Menezes, A. B., Dodd, R. J., Dunfield, K., Engl, C., Frazao, J. J., Garland, G., Jimenez, J. L. G., Graca, J., Granger, S. J., Harrison, A. F., Heuck, C., Hou, E. Q., Johnes, P. J., Kaiser, K., Kjaer, H. A., Klumpp, E., Lamb, A. L., Macintosh, K. A., Mackay, E. B., McGrath, J., McIntyre, C., McLaren, T., Meszaros, E., Missong, A., Mooshammer, M., Negron, C. P., Nelson, L. A., Pfahler, V., Poblete-Grant, P., Randall, M., Seguel, A., Seth, K., Smith, A. C., Smits, M. M., Sobarzo, J. A., Spohn, M., Tawaraya, K., Tibbett, M., Voroney, P., Wallander, H., Wang, L., Wasaki, J. & Haygarth, P. M., Meh 2018, Yn: Plant and Soil. 427, 1-2, t. 191-208Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic nitrogen mineralisation in two contrasting agro-ecosystems is unchanged by biochar addition
Dempster, D. N., Jones, D. L. & Murphy, D. V., Mai 2012, Yn: Soil Biology and Biochemistry. 48, t. 47-50Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic mulching promotes soil organic carbon accumulation to deep soil layer in an urban plantation forest
Sun, X., Wang, G., Ma, Q., Liao, J., Wang, D., Guan, Q. & Jones, D. L., 1 Rhag 2021, Yn: Forest Ecosystems. 8, 1Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic mulching masks rhizosphere effects on carbon and nitrogen fractions and enzyme activities in urban greening space
Sun, X., Ye, Y., Guan, Q. & Jones, D. L., 1 Ebr 2021, Yn: Journal of Soils and Sediments. 21, 4, t. 1621-1632Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic carbon stocks in all pools following land cover change in the rainforest of Madagascar.
Mieja , R., Andriamananjara, A., Razafimbelo, T., Hewson, J., Andrisoa, R., Jones, J. P. G., van Meerveld, I., Cameron, A., Ranaivoson, N., Ramifehiarivo, N., Ramboatiana, N., Razafinarivo, R., Ramananantoandro, T., Rasolohery, A., Razafimanantsoa, M., Jourdan, C., Saint-André, L., Rajoelison, G. & Razakamanarivo, H., 2018, Soil Management and Climate Change: Effects on Organic Carbon, Nitrogen Dynamics, and Greenhouse Gas Emissions. Muñoz, M. & Zornoza, R. (gol.). Academic Press, Elsevier, t. 25-37 12 t.Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod
- Cyhoeddwyd
Organic biomolecules bind to phosphate through borate linkages in aqueous solution: a possible role of boron as a phosphorylation chaperone in the prebiotic world
Aydogmus, N., Kose, D. A., Beckett, M. A. & Zumreoglu Karan, B., 11 Meh 2014, Yn: Turkish Journal of Chemistry. 38, t. 617-628Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic and inorganic sulfur and nitrogen uptake by co-existing grassland plant species competing with soil microorganisms
Ma, Q., Xu, M., Liu, M., Cao, X., Hill, P. W., Chadwick, D. R., Wu, L. & Jones, D. L., 1 Mai 2022, Yn: Soil Biology and Biochemistry. 168Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic and elemental elucidation of asphaltene fraction of Nigerian crude oils
Adebiyi, F. M. & Thoss, V., 8 Tach 2013, Yn: Fuel. 118, t. 426-431Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic acids in the rhizosphere - a critical review
Jones, D. L., 30 Awst 1998, Yn: Plant and Soil. 205, 1, t. 25-44Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl adolygu › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic acids alleviate iron chlorosis in chickpea grown on two p-fertilized soils
Sanchez-Rodriguez, A. R., del Campillo, M. C., Torrent, J. & Jones, D., 12 Mai 2014, Yn: Journal of Soil Science and Plant Nutrition. 14, 2, t. 290-301Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Organic acid root-tip tissue concentration in Brachiaria decumbens and Brachiaria ruziziensis
Grundy, S. P., Jones, D. L., Godbold, D. L., Horst, W. W. (Golygydd), Sattelmacher, B. (Golygydd), Schmidhalter, U. (Golygydd), Schubert, S. (Golygydd), Von Wiren, N. (Golygydd), Wittenmayer, L. (Golygydd), Schenk, M. K. (Golygydd), Burkert, A. (Golygydd), Claassen, N. (Golygydd) & Flessa, H. (Golygydd), 1 Ion 2001, Plant nutrition - food security and sustainability of agro-ecosystems through applied and basic research.. 2001 gol. Kluwer Academic Publishers, t. 506-507Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod
- Cyhoeddwyd
Organic acid mediated nutrient extraction efficiency in three calcareous soils.
Khademi, Z., Jones, D. L., Malakouti, M. J., Asadi, F. & Ardebili, M., 31 Maw 2009, Yn: Australian Journal of Soil Research. 47, 2, t. 213-220Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid