Ysgol Gwyddorau Amgylcheddol a Naturiol
- Cyhoeddwyd
Influence of historical climate patterns on streamflow and water demand in Wales, UK
Dallison, R., Patil, S. & Williams, P., 12 Meh 2020, Yn: Water. 12, 6, 1684.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Modelling the impact of climate change on water supply sustainability for the rural Afon Dyfi catchment, mid Wales
Dallison, R. & Patil, S., 8 Ebr 2019.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur › adolygiad gan gymheiriaid
- Cyhoeddwyd
Analysing the historic supply-demand dynamics of public water supply across catchments in Wales, UK
Dallison, R., Patil, S. & Williams, P., 9 Ebr 2018.Allbwn ymchwil: Cyfraniad at gynhadledd › Murlen › adolygiad gan gymheiriaid
- Cyhoeddwyd
Impacts of climate change on future water availability for hydropower and public water supply in Wales, UK
Dallison, R., Patil, S. & Williams, P., 1 Awst 2021, Yn: Journal of Hydrology: Regional Studies. 36, 100866.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Ecology and distribution of neotropical Podocarpaceae
Dalling, J. W., Barkan, P., Bellingham, P. J., Healey, J. R. & Tanner Edmund, V. J., 14 Hyd 2011, Yn: Smithsonian Contributions to Botany. 95, t. 43-56Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Synthesis, structure and spectroscopic properties of a new class of polymerisable nickel dithiolenes
Dalgleish, S., Morrison, C. A., Middlemiss, D. S., Mount, A. R., Collins, A., Pilia, L., Serpe, A., Mercuri, M. L., Roberts-Bleming, S. J., Charlton, A., Deplano, P., Murphy, P. J. & Robertson, N., 1 Ion 2009, Yn: Journal of Materials Chemistry. 19, 34, t. 6194-6200Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
SmI2/water/amine mediates cleavage of allyl ether protected alcohols: Application in carbohydrate synthesis and mechanistic considerations
Dahlen, A., Sundgren, A., Lahmann, M., Oscarson, S. & Hilmersson, G., 30 Hyd 2003, Yn: Organic Letters. 5, 22, t. 4085-4088Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Stratified prokaryote network in the oxic-anoxic transition of a deep-sea halocline
Daffonchio, D., Borin, S., Brusa, T., Brusetti, L., van der Wielen, PWJJ., Bolhuis, H., Yakimov, MM., D'Auria, G., Giuliano, L., Marty, D., Tamburini, C., McGenity, TJ., Hallsworth, JE., Sass, AM., Timmis, KN., Tselepides, A., de Lange, GJ., Hubner, A., Thomson, J., Varnavas, SP., Gasparoni, F., Gerber, HW., Malinverno, E., Corselli, C., Garcin, J., McKew, B., Golyshin, PN., Lampadariou, N., Polymenakou, P., Calore, D., Cenedese, S., Zanon, F. & Hoog, S., 9 Maw 2006, Yn: Nature. 440, 7081, t. 203-207Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
ULIXES, unravelling and exploiting Mediterranean Sea microbial diversity and ecology for xenobiotics' and pollutants' clean up
Daffonchio, D., Mapelli, F., Cherif, A., Malkawi, H. I., Yakimov, M. M., Abdel-Fattah, Y. R., Blaghen, M., Golyshin, P. N., Ferrer, M., Kalogerakis, N., Boon, N., Magagnini, M. & Fava, F., Medi 2012, Yn: Reviews in Environmental Science and Bio/Technology. 11, 3, t. 207-211Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Bioremediation of Southern Mediterranean oil polluted sites comes of age
Daffonchio, D., Ferrer, M., Mapelli, F., Cherif, A., Lafraya, A., Malkawi, H. I., Yakimov, M. M., Abdel-Fattah, Y. R., Blaghen, M., Golyshin, P. N., Kalogerakis, N., Boon, N., Magagnini, M. & Fava, F., 25 Medi 2013, Yn: New Biotechnology. 30, 6, t. 743-748Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Complete mitochondrial genome sequence of a Middle Pleistocene cave bear reconstructed from ultrashort DNA fragments
Dabney, J., Knapp, M., Glocke, I., Gansauge, M. T., Weihmann, A., Nickel, B., Valdiosera, C., Garcia, N., Pääbo, S., Arsuaga, J. L. & Meyer, M., 24 Medi 2013, Yn: Proceedings of the National Academy of Sciences of the United States. 110, 39, t. 15758-15763Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Phylogenetic climatic niche conservatism in sandflies (Diptera: Phlebotominae) and their relatives
D'Agostino, E. R. R., Vivero, R., Romero, L., Bejarano, E., Hurlbert, A. H., Comeault, A. A. & Matute, D. R., 1 Hyd 2022, Yn: Evolution: International Journal of Organic Evolution. 76, 10, t. 2361-2374Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Novel insights into marine fish biodiversity across a pronounced environmental gradient using replicated environmental DNA analyses
Czachur, M. V., Seymour, M., Creer, S. & von der Heyden, S., 1 Ion 2022, Yn: Environmental DNA. 4, 1Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
A method-centric ‘User Manual’ for the mitigation of diffuse water pollution from agriculture
Cuttler, S. P., Newell-Price, J. P., Harris, D., Chadwick, D., Shepherd, M. A., Anthony, S. G. A., Macleod, C. J. A., Haygarth, P. M. & Chambers, B. J., Meh 2016, Yn: Soil Use and Management. 32, S1, t. 162-171Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Correction to: Long-Term Recovery of Microbial Communities in the Boreal Bryosphere Following Fire Disturbance (vol 73, pg 75, 2017)
Cutler, N. A., Arroniz-Crespo, M., Street, L. E., Jones, D. L., Chaput, D. L. & DeLuca, T. H., Chwef 2020, Yn: Microbial Ecology. 79, 2, t. 516-516Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Long-Term Recovery of Microbial Communities in the Boreal Bryosphere Following Fire Disturbance
Cutler, N., Arroniz-Crespo, M., Street, L. E., Jones, D., Chaput, D. L. & DeLuca, T. H., 1 Ion 2017, Yn: Microbial Ecology. 73, 1, t. 75-90Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Soil carbon stocks in tropical forests regulated by base cation effects on fine roots
Cusack, D. F., Markesteijn, L., Condit, R., Lewis, O. T. & Turner, B. L., Ion 2018, Yn: Biochemistry. 137, 1-2, t. 253-266Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Soil carbon stock do not reflect aboveground forest biomass across geological and rainfall gradients: Carbon stocks correspond to soil characteristics
Cusack, D. F., Markesteijn, L. & Turner, B., Rhag 2016.Allbwn ymchwil: Cyfraniad at gynhadledd › Murlen › adolygiad gan gymheiriaid
- Cyhoeddwyd
Eco-hydrological requirements of dune slack vegetation and the implications of climate change
Curreli, A., Wallace, H., Freeman, C., Hollingham, M., Stratford, C., Johnson, H. & Jones, L., 15 Ion 2013, Yn: Science of the Total Environment. 443, t. 910-919Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Effectiveness of a wool based packaging system on the abundance of surface spoilage microorganisms on meat products
Curling, S., Jones, D., Ormondroyd, G. & Williams, A., 2017, Yn: Arab Gulf Journal of Scientific Research. 34, 2/3Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The effect on panel properties of incorporation of reject paper fibre into MDF panels
Curling, S., Stefanowski, B., Laflin, N., Davies, G. & Ormondroyd, G., 2016, Yn: International Wood Products Journal. 7, 3, t. 165-170 6 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Development of a method for the production of hemicellulosic gels from Sitka spruce.
Curling, S. F., Fowler, P. A. & Hill, C. A., 2 Gorff 2007, Yn: Carbohydrate Polymers. 69, 4, t. 673-677Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The kinetics of water vapour sorption: analysis using parallel exponential kinetics model on six malaysian hardwoods.
Curling, S. F., Zaihan, J., Hill, C. A., Curling, S., Hashim, W. S. & Hamdan, H., 1 Ebr 2010, Yn: Journal of Tropical Forest Science. 22, 2, t. 107-117Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
A rapid method for investigating the absorption of formaldehyde from air by wool
Curling, S. F., Loxton, C. & Ormondroyd, G. A., 1 Ebr 2012, Yn: Journal of Materials Science. 47, 7, t. 3248-3251Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Analysis of the water vapour sorption isotherms of thermally modified acacia and sesendok.
Curling, S. F., Jalaludin, Z., Hill, C. A., Xie, Y., Samsi, H. W., Husain, H., Awang, K. & Curling S.F., N. V., 1 Medi 2010, Yn: Wood Material Science and Engineering. 5, 3, t. 1748-0280Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Comparison of the effects of gamma irradiation and steam sterilization on southern pine sapwood.
Curling, S. F., Curling, S. & Winandy, J. E., 1 Ion 2008, Yn: Forest Products Journal. 58, 1-2, t. 87-90Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Development of a laboratory testing concept for whole bio- based wall components against fungal colonisation.
Curling, S., Ormondroyd, G., Mansour, E. & Stefanowski, B., 2015.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur › adolygiad gan gymheiriaid
- Cyhoeddwyd
Comparison of inflammatory and acute-phase responses in the brain and peripheral organs of the ME7 model of prion disease.
Cunningham, C., Wilcockson, D. C., Boche, D. & Perry, V. H., 1 Ebr 2005, Yn: Journal of Virology. 79, 8, t. 5174-5184Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Central and systemic endotoxin challenges exacerbate the local inflammatory response and increase neuronal death during chronic neurodegeneration.
Cunningham, C., Wilcockson, D. C., Campion, S., Lunnon, K. & Perry, V. H., 5 Hyd 2005, Yn: Journal of Neuroscience. 25, 40, t. 9275-9284Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
High aboveground carbon stock of African tropical montane forests
Cuni-Sanchez, A., Sullivan, M. J. P., Platts, P. J., Lewis, S. L., Marchant, R., Imani, G., Hubau, W., Abiem, I., Adhikari, H., Albrecht, T., Altman, J., Amani, C., Aneseyee, A. B., Avitabile, V., Banin, L., Batumike, R., Bauters, M., Beeckman, H., Begne, S. K., Bennett, A. C., Bitariho, R., Boeckx, P., Bogaert, J., Brauning, A., Bulonvu, F., Burgess, N. D., Calders, K., Chapman, C., Chapman, H., Comiskey, J., de Haulleville, T., Decuyper, M., De Vries, B., Dolezal, J., Droissart, V., Ewango, C., Feyera, S., Gebrekristos, A., Gereau, R., Gilpin, M., Hakizimana, D., Hall, J., Hamilton, A., Hardy, O., Hart, T., Heiskanen, J., Hemp, A., Herold, M., Hiltner, U., Horak, D., Kamdem, M-N., Kayijamahe, C., Kenfack, D., Kinyanjui, M. J., Klein, J., Lisingo, J., Lovett, J., Lung, M., Makana, J-R., Malhi, Y., Marshall, A., Martin, E. H., Mitchard, E. T. A., Morel, A., Mukendi, J. T., Muller, T., Nchu, F., Nyirambangutse, B., Okello, J., Peh, K. S. H., Pellikka, P., Phillips, O. L., Plumptre, A., Qie, L., Rovero, F., Sainge, M. N., Schmitt, C. B., Sedlacek, O., Ngute, A. S. K., Sheil, D., Sheleme, D., Simegn, T. Y., Simo-Droissart, M., Sonké, B., Soromessa, T., Sunderland, T., Svoboda, M., Taedoumg, H., Taplin, J., Taylor, D., Thomas, S. C., Timberlake, J., Tuagben, D., Umunay, P., Uzabaho, E., Verbeeck, H., Vleminckx, J., Wallin, G., Wheeler, C., Willcock, S., Woods, J. T. & Zibera, E., 25 Awst 2021, Yn: Nature. 596, 7873, t. 536-542 24 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Early results of ash (Fraxinus excelsior L.) provenance trials at sites in England and Wales.
Cundall, E. P., Cahalan, C. M. & Connolly, T., 1 Medi 2003, Yn: Forestry. 76, 4, t. 385-399Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Carbon and nitrogen recycling from microbial necromass to cope with C:N stoichiometric imbalance by priming
Cui, J., Zhu, Z., Xu, X., Liu, S., Jones, D. L., Kuzyakov, Y., Shibistova, O., Wu, J. & Ge, T., 1 Maw 2020, Yn: Soil Biology and Biochemistry. 142, 107720.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Monitoring SARS-CoV-2 Using Infoveillance, National Reporting Data, and Wastewater in Wales, United Kingdom: Mixed Methods Study
Cuff, J. P., Dighe, S. N., Watson, S. E., Badell-Grau, R. A., Weightman, A. J., Jones, D. L. & Kille, P., 23 Tach 2023, Yn: JMIR infodemiology. 3, e43891.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Development of Gold Coated Superparamagnetic Iron Oxide Nanoparticles for Nitroreductase Delivery
Cude, M. P. & Gwenin, C. D., 1 Ion 2011, Yn: ECS Transactions. 33, 38, t. 79-89Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
He says, she says: ecosystem services and gender among indigenous communities in the Colombian Amazon
Cruz-Garcia, G. S., Cubillos, M. V., Torres-Vitolas, C., Harvey, C. A., Shackleton, C. M., Schreckenberg, K., Willcock, S., Navarrete-Frías, C. & Sachet, E., Meh 2019, Yn: Ecosystem Services. 37, 100921.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
A comparison of satellite remote sensing data fusion methods to map peat swamp forest loss in Sumatra, Indonesia
Crowson, M., Warren-Thomas, E., Hill, J. K., Hariyadi, B., Agus, F., Saad, A., Hamer, K. C., Hodgson, J. A., Kartika, W. D., Lucey, J., McClean, C., Nurida, N. L., Pratiwi, E., Stringer, L. C., Ward, C. & Pettorelli, N., 1 Medi 2019, Yn: Remote Sensing in Ecology and Conservation. 5, 3, t. 247-258Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The genome sequence of the Tawny Mining Bee, Andrena fulva (Müller, 1766)
Crowley, L. M., Mulley, J. F., Lab, U. O. O. A. W. W. G. A., collective, D. T. O. L. B., programme, W. S. I. T. O. L., collective, W. S. I. S. O. DNA. P., collective, T. O. L. C. I. & Consortium, D. T. O. L., 21 Meh 2023, Yn: Wellcome Open Research. 8, 258Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The genome sequence of the hawthorn shieldbug, Acanthosoma haemorrhoidale (Linnaeus, 1758)
Crowley, L. M. & Mulley, J., 5 Gorff 2022, Wellcome Open Research , 7, 178, t. 178 1 t.Allbwn ymchwil: Cyfraniad at gyhoeddiad arbenigol › Erthygl
- Cyhoeddwyd
The genome sequence of Philonthus cognatus (Stephens, 1832) (Coleoptera, Staphylinidae), a rove beetle.
Crowley, L. M., Telfer, M., Geiser, M. & Mulley, J., 13 Ebr 2023, Wellcome Open research, t. 169, (Wellcome open research).Allbwn ymchwil: Papur gweithio › Rhagargraffiad
- Cyhoeddwyd
Good modelling practice.
Crout, N., Kokkonen, T., Jakeman, A. J., Norton, J. P., Newham, L. T., Anderson, R., Assaf, H., Croke, B. F., Gaber, N., Gibbons, J. M., Holzworth, D., Mysiak, J., Reichl, J., Seppelt, R., Wagener, T., Whitfield, P., Voinov, A. A. (gol.), Rizzoli, A. E. (gol.) & Chen, S. H. (gol.), 1 Ion 2009, Environmental modelling: software and decision support: state of the art and new perspectives.. 2009 gol. Elsevier, t. 15-32Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod
- Cyhoeddwyd
The impact of using alternative forages on the nutrient value within slurry and its implications for forage productivity in agricultural systems
Crotty, F. V., Fychan, R., Theobald, V. J., Sanderson, R., Chadwick, D. R. & Marley, C. L., 15 Mai 2014, Yn: PLoS ONE. 9, 5Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Implications of variation in local perception of degradation and restoration processes for implementing land degradation neutrality
Crossland, M., Winowiecki, L., Pagella, T., Hadgu, K. & Sinclair, F., Rhag 2018, Yn: Environmental Development. 28, t. 42-54 12 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Women's Changing Opportunities and Aspirations Amid Male Outmigration: Insights from Makueni County, Kenya
Crossland, M., Paez Valencia, A. M., Pagella, T., Mausch, K., Harris, D., Dilley, L. & Winowiecki, L., Awst 2021, Yn: Journal of Development Research. 33, 4, t. 910-932 23 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The Potential Impact on Farmer Health of Enhanced Export Horticultural Trade between the UK and Uganda.
Cross, P., Edwards, R. T., Nyeko, P. & Edwards-Jones, G., 28 Ebr 2009, Yn: International Journal of Environmental Research and Public Health. 6, 5, t. 1539-1556Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The Shb adaptor protein binds to tyrosine 766 in the FGFR-1 and regulates the Ras/MEK/MAPK pathway via FRS2 phosphorylation in endothelial cells
Cross, M., Cross, M. J., Lu, L., Magnusson, P., Nyqvist, D., Holmqvist, K., Welsh, M. & Claesson-Welsh, L., 1 Awst 2002, Yn: Molecular Biology of the Cell. 13, 8, t. 2881-2893Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The prevalence of non-treatment of sheep scab in Wales and the economic cost to the livestock industry: Final Report.
Cross, P., Edwards-Jones, G., Omed, H. M. & Williams, A. P., 1 Ion 2010, 2010 gol. Unknown.Allbwn ymchwil: Llyfr/Adroddiad › Adroddiad Comisiwn
- Cyhoeddwyd
Eliciting expert opinion on the effectiveness and practicality of interventions in the farm and rural environment to reduce human exposure to Escherichia coli O157
Cross, P., Rigby, D. & Edwards-Jones, G., 1 Ebr 2012, Yn: Epidemiology and Infection. 140, *04), t. 643-654Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Differences in the perceptions of farmers and veterinary surgeons about the efficacy of mitigation strategies for controlling bluetongue.
Cross, P., Williams, A. P. & Edwards-Jones, G., 3 Hyd 2009, Yn: Veterinary Record. 165, 14, t. 397-403Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Angiostatin and endostatin inhabit endothelial cell migration in response to FGF and VEGF without interfering with specific intracellular signal transduction pathways
Cross, M., Eriksson, K., Magnusson, P., Dixelius, J., Claesson-Welsh, L. & Cross, M. J., 11 Chwef 2003, Yn: Febs Letters. 536, 1-3, t. 19-24Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Pesticide hazard trends in orchard fruit production in Great Britain from 1992 to 2008: a time-series analysis
Cross, P., 22 Tach 2012, Yn: Pest Management Science.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid