Coleg Gwyddoniaeth a Pheirianneg

  1. Erthygl › Ymchwil › Adolygwyd gan gymheiriaid
  2. Cyhoeddwyd

    Multiple Views: different meanings and collocated words

    Roberts, J. C., Al-Maneea, H. M. A., Butcher, P., Lew, R., Rees, G., Sharma, N. & Frankenberg-Garcia, A., Meh 2019, Yn: Computer Graphics Forum. 38, 3, t. 79-93 14 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  3. Cyhoeddwyd

    Multiple causation of phylogeographical pattern as revealed by nested clade analysis of the bamboo viper (Trimeresurus stejnegeri) within Taiwan.

    Creer, S., Malhotra, A., Thorpe, R. S. & Chou, W. H., 1 Awst 2001, Yn: Molecular Ecology. 10, 8, t. 1967-1981

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  4. Cyhoeddwyd

    Multiple drivers of decline in the global status of freshwater crayfish (Decapoda: Astacidea)

    Richman, N., Richman, N. I., Bohm, M., Adams, S. B., Alvarez, F., Bergey, E. A., Bunn, J. S., Burnham, Q., Cordeiro, J., Coughran, J., Crandall, K. A., Dawkins, K. L., DiStefano, R. J., Doran, N. E., Edsman, L., Eversole, A. G., Fureder, L., Furse, J. M., Gherardi, F., Hamr, P., Holdich, D. M., Horwitz, P., Johnston, K., Jones, C. M., Jones, J. P., Jones, R. L., Jones, T. G., Kawai, T., Lawler, S., Lopez-Mejia, M., Miller, R. M., Padraza-Lara, C., Reynolds, J. D., Richardson, A. M., Schultz, M. B., Schuster, G. A., Sibley, P. J., Souty-Grosset, C., Taylor, C. A., Thoma, R. F., Walls, J., Walsh, T. S. & Collen, B., 5 Ion 2015, Yn: Philosophical Transactions of the Royal Society B. 370, 1662

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  5. 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

  6. Cyhoeddwyd

    Multiple origins of viviparity, or reversal from viviparity to oviparity? The European common lizard (Zootoca vivipara, Lacertidae) and the evolution of parity.

    Surget-Groba, Y., Heulin, B., Guillaume, C. P., Puky, M., Semenov, D., Orlova, V., Kupriyanova, L., Ghira, I. & Smajda, B., 1 Ion 2006, Yn: Biological Journal of the Linnean Society. 87, 1, t. 1-11

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  7. Cyhoeddwyd

    Multiple paths to aquatic specialisation in four species of Central American Anolis lizards

    Munoz, M. M., Crandell, K. E., Campbell-Staton, S. C., Fenstermacher, K., Frank, H. K., Van Middlesworth, P., Sasa, M., Losos, J. B. & Herrel, A., 26 Gorff 2015, Yn: Journal of Natural History. 49, 27-28, t. 1717-1730

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  8. Cyhoeddwyd

    Multiple stressors facilitate the spread of a non-indigenous bivalve in the Mediterranean Sea

    Mangano, M., Sara, G., Porporato, E. M. D. & Mieszkowska, N., 17 Chwef 2018, Yn: Journal of Biogeography.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  9. 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

  10. Cyhoeddwyd

    Multiplex chaos synchronization in semiconductor lasers with multiple optoelectronic feedbacks

    Shahverdiev, E., Shahverdiev, E. M. & Shore, K. A., 1 Meh 2013, Yn: Optik - International Journal for Light and Electron Optics. 124, 12, t. 1350-1353

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  11. Cyhoeddwyd

    Multisensor Acoustic Tracking of Fish and Seabird Behavior Around Tidal Turbine Structures in Scotland

    Williamson, B. J., Fraser, S., Blondel, P., Bell, P. S., Waggitt, J. J. & Scott, B. E., 17 Ion 2017, Yn: IEEE JOURNAL OF OCEANIC ENGINEERING. 42, 4, t. 948-965

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  12. Cyhoeddwyd

    Multivalent glycoconjugates as anti-pathogenic agents

    Bernardi, A., Jimenez-Barbero, J., Casnati, A., De Castro, C., Darbre, T., Fieschi, F., Finne, J., Funken, H., Jaeger, K-E., Lahmann, M., Lindhorst, T. K., Marradi, M., Messner, P., Molinaro, A., Murphy, P. V., Nativi, C., Oscarson, S., Penades, S., Peri, F., Pieters, R. J., Renaudet, O., Reymond, J-L., Richichi, B., Rojo, J., Sansone, F., Schaeffer, C., Turnbull, W. B., Velasco-Torrijos, T., Vidal, S., Vincent, S., Wennekes, T., Zuilhof, H. & Imberty, A., 2013, Yn: Chemical Society Reviews. 42, 11, t. 4709-4727

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  13. Cyhoeddwyd

    Multivariate Approach for Studying the Degradation of Perovskite Solar Cells.

    Kettle, J., Tyagi, P., David, T. & Stoichkov, V., 15 Tach 2019, Yn: Solar Energy. 193, t. 12-19

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  14. Cyhoeddwyd

    Multivariate statistical methods in Environmental Forensics

    Mudge, S. M., 1 Maw 2007, Yn: Environmental Forensics. 8, 1-2, t. 155-163

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  15. Cyhoeddwyd

    Multiyear trend in reproduction underpins interannual variation in gametogenic development of an Antarctic urchin.

    De Leij, R., Peck, L. S. & Grange, L., 22 Medi 2021, Yn: Scientific Reports. 11, 1, 18868.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  16. Cyhoeddwyd

    Museum DNA reveals a new, potentially extinct species of rinkhals (Serpentes: Elapidae: Hemachatus) from the Eastern Highlands of Zimbabwe

    Major, T., Renk, P., Reissig, J., Paijmans, J., Morris, E., Hofreiter, M., Barlow, A., Broadley, D. G. & Wüster, W., 27 Medi 2023, Yn: PLoS ONE. 18, 9, 19 t., e0291432.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  17. Cyhoeddwyd

    Mutation in a "tesB-like" hydroxyacyl-coenzyme A-specific thioesterase gene causes hyperproduction of extracelluar polyhydroxyalkanoates by Alcanivorax orkumensis SK2.

    Golyshin, P., Sabirova, J. S., Ferrer, M., Lunsdorf, H., Wray, V., Kalscheuer, R., Steinbuchel, A., Timmis, K. N. & Golyshin, P. N., 1 Rhag 2006, Yn: Journal of Bacteriology. 188, 24, t. 8452-8459

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  18. Cyhoeddwyd

    Mutational Meltdown in Primary Endosymbionts: Selection Limits Muller's Ratchet.

    Allen, J. M., Light, J. E., Perotti, M. A., Braig, H. R. & Reed, D. L., 23 Maw 2009, Yn: PLoS ONE. 4, 3, t. e4969

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  19. Cyhoeddwyd

    Mutational analysis of the critical bases involved in activation of the AreR-regulated sigma(54)-dependent promoter in Acinetobacter sp strain ADP1.

    Jones, R. M. & Williams, P. A., 1 Medi 2003, Yn: Applied and Environmental Microbiology. 69, 9, t. 5627-5635

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  20. Cyhoeddwyd

    Mycobacterium alvei (ω-1)-methoxy mycolic acids: Absolute stereochemistry and synthesis

    Alhuwaymil, Z. S., Al-araj, I. Q. M., Dulayymi, A. R. A., Jones, A., Gates, P. J., Valero-Guillén, P. L., Baird, M. S. & Dulayymi, J. R. A., Tach 2020, Yn: Chemistry and Physics of Lipids. 233, 1 t., 104977.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  21. Cyhoeddwyd

    Mycobacterium tuberculosis-associated synthetic mycolates differentially exert immune stimulatory adjuvant activity

    Smet, M., Pollard, C., De Beuckelaer, A., Van Hoecke, L., Beken, S. V., De Koker, S., Al-Dulayymi, J. R., Huygen, K., Verschoor, J., Baird, M. & Grooten, J., 7 Medi 2016, Yn: European Journal of Immunology. 46, t. 2149-2154 6 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  22. Cyhoeddwyd

    Mycolates of Mycobacterium tuberculosis modulate the flow of cholesterol for bacillary proliferation in murine macrophages

    Vermeulen, I., Baird, M., Al-Dulayymi, J., Smet, M., Verschoor, J. & Grooten, J., 1 Ebr 2017, Yn: Journal of Lipid Research. 58, 4, t. 709-718 9 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  23. Cyhoeddwyd

    Mycolyl arabino glycerols from synthetic mycolic acids

    Mohammed, M. O., Baird, M. S. & Al-Dulayymi, J., 16 Ion 2015, Yn: Tetrahedron Letters. 56, 23, t. 3268–3272

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  24. Cyhoeddwyd

    Mycorrhizal hyphal turnover as a dominant process for carbon input into soil organic matter.

    Godbold, D. L., Hoosbeek, M. R., Lukac, M., Cotrufo, M. F., Janssens, I. A., Ceulemans, R., Polle, A., Velthorst, E. J., Scarascia-Mugnozza, G., De Angelis, P., Miglietta, F. & Peressotti, A., 1 Maw 2006, Yn: Plant and Soil. 281, 1-2, t. 15-24

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  25. Cyhoeddwyd

    Mycorrhizas improve the absorption of non-available phosphorus by the green manure Tithonia diversifolia in poor soils

    Scrase, F. M., Sinclair, F. L., Farrar, J. F., Pavinato, P. S. & Jones, D. L., Maw 2019, Yn: Rhizosphere. 9, t. 27-33 7 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  26. Cyhoeddwyd

    Mytilus species under rope culture in Scotland: implications for management.

    Dias, P. J., Bland, M., Shanks, A. M., Beaumont, A. R., Piertney, S. B., Davies, I. M. & Snow, M., 1 Hyd 2009, Yn: Aquaculture International. 17, 5, t. 437-448

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  27. Cyhoeddwyd

    N-15-amino sugar stable isotope probing (N-15-SIP) to trace the assimilation of fertiliser-N by soil bacterial and fungal communities

    Reay, M. K., Charteris, A. F., Jones, D. L. & Evershed, R. P., Tach 2019, Yn: Soil Biology and Biochemistry. 138, 107599.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  28. Cyhoeddwyd

    N-2 Fixation in Feather Mosses is a Sensitive Indicator of N Deposition in Boreal Forests

    Ackermann, K., Zackrisson, O., Rousk, J., Jones, D. L. & DeLuca, T. H., Medi 2012, Yn: Ecosystems. 15, 6, t. 986-998

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  29. Cyhoeddwyd

    N-Acetylglucosaminidase activities in wetlands: a global survey

    Kang, H. J., Freeman, C., Park, S. S. & Chun, J., 1 Ion 2005, Yn: Hydrobiologia. 532, t. 103-110

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  30. Cyhoeddwyd

    N-Fold Cech derived functors and generalised Hopf type formulas.

    Donadze, G., Inassaridze, N. & Porter, T., 1 Awst 2005, Yn: K-Theory. 35, 3-4, t. 341-373

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  31. Cyhoeddwyd

    N-carbamate protected amino acid derived guanidine organocatalysts

    Al-Taie, Z. S., Anderson, J. M., Bischoff, L., Christensen, J., Coles, S. J., Froom, R., Gibbard, M. E., Jones, L. F., de Kleijne, F. F. J., Murphy, P. & Thompson, E., 4 Meh 2021, Yn: Tetrahedron. 89, 132093.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  32. Cyhoeddwyd

    N2 fixation and cycling in Alnus glutinosa, Betula pendula and Fagus sylvatica woodland exposed to free air CO2 enrichment

    Millett, J., Godbold, D., Smith, A. R. & Grant, H., 18 Rhag 2011, Yn: Oecologia. 169, 2, t. 541-52 12 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  33. Cyhoeddwyd

    NH4[Ni(mnt)2.H2O. a new one dimensional Organic ferromagnet

    Allan, M. L., Martens, J. H. F., Coomber, A. T., Friend, R. H., Marsden, I., Marseglia, E. A., Underhill, A. E. & Charlton, A., 1993, Yn: Molecular Crystals and Liquid Crystals. 229, 1, t. 147-152

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  34. Cyhoeddwyd

    NMR study of hydroxy protons of di- and trimannosides, substructures of Man-9

    Hakkarainen, B., Kenne, L., Lahmann, M., Oscarson, S. & Sandstrom, C., 1 Rhag 2007, Yn: Magnetic Resonance in Chemistry. 45, 12, t. 1076-1080

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  35. Cyhoeddwyd

    Naive random subspace ensemble with linear classifiers for real-time classification of fMRI data

    Plumpton, C. O., Kuncheva, L. I., Oosterhof, N. N. & Johnston, S. J., Meh 2012, Yn: Pattern Recognition. 45, 6, t. 2101-2108

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  36. Cyhoeddwyd

    Naja naja Reproduction

    Kuttalam, S. R., Owens, J. B., Das, B., Koley, A. & Santra, V., 2 Mai 2023, Yn: Herpetological Review. 54, 1, t. 141 1 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  37. Cyhoeddwyd

    Nano-Sized and Filterable Bacteria and Archaea: Biodiversity and Function

    Ghuneim, L-A., Jones, D. L., Golyshin, P. & Golyshina, O., 21 Awst 2018, Yn: Frontiers in Microbiology. 9, 1971.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  38. Cyhoeddwyd

    Nanohaloarchaea as beneficiaries of xylan degradation by haloarchaea

    La Cono, V., Messina, E., Reva, O., Smedile, F., La Spada, G., Crisafi, F., Marturano, L., Miguez, N., Ferrer, M., Selivanova, E. A., Golyshina, O., Golyshin, P., Rohde, M., Krupovic, M., Merkel, A. Y., Sorokin, D. Y., Hallsworth, J. E. & Yakimov, M., Medi 2023, Yn: Microbial Biotechnology. 16, 9, t. 1803-1822 20 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  39. Cyhoeddwyd

    Nanosecure: Advanced nanotechnological detection and detoxification of harmful airborne substances for improved public security

    Barrault, J., Bedel, L., Charikane, E., Gunnarsen, L., Gwenin, C. D., Jones, J., Lieberzeit, P., Rowley, A., Soto, T., Thollon, S., Thorstensen, B., Traberg-Borup, S. & Wright, N., 1 Hyd 2013, Yn: L'Actualité Chimique. 378-379, t. 27-34

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  40. Cyhoeddwyd

    Nanotube liquid crystal elastomers: photomechanical response and flexible energy conversion of layered polymer composites

    Campo, E., Fan, X., King, B. C., Loomis, J., Campo, E. M., Hegseth, J., Cohn, R. W., Terentjev, E. & Panchapakesan, B., 5 Medi 2014, Yn: Nanotechnology. 25, 35, t. 355501

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  41. Cyhoeddwyd

    Nanovibration detection based on a microsphere

    Jiang, C., Wang, W., Yan, B., Chen, P., Xu, K., Sun, Y., Cong, Z., Dong, T., Zhou, Y., Wang, Z. & Wang, X., 31 Awst 2022, Yn: Optics Letters. 47, 17, t. 4560-4563

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  42. Cyhoeddwyd

    Narrow-linewidth single-frequency photonicmicrowave generation in optically injected semiconductor lasers with filtered optical feedback

    Xue, C., Ji, S., Wang, A., Jiang, N., Qiu, K. & Hong, Y., 24 Awst 2018, Yn: Optics Letters. 43, 17, t. 4184-4187

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  43. Cyhoeddwyd

    National scale mapping of supply and demand for recreational ecosystem services

    Hooftman, D., Ridding, L., Redhead, J. & Willcock, S., Hyd 2023, Yn: Ecological Indicators. 154, 20 t., 110779.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  44. Cyhoeddwyd

    National-scale remotely sensed lake trophic state from 1984 through 2020

    Meyer, M. F., Topp, S. N., King, T. V., Ladwig, R., Pilla, R. M., Dugan, H. A., Eggleston, J. R., Hampton, S. E., Leech, D. M., Oleksy, I. A., Ross, J. C., Ross, M. R. V., Woolway, R. I., Yang, X., Brousil, M. R., Fickas, K. C., Padowski, J. C., Pollard, A. I., Ren, J. & Zwart, J. A., 16 Ion 2024, Yn: Scientific data. 11, 1, t. 77

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  45. Cyhoeddwyd

    Natural Capital, Ecosystem Services, and Soil Change: Why Soil Science Must Embrace an Ecosystems Approach

    Robinson, D. A., Hockley, N., Dominati, E., Lebron, I., Scow, K. M., Reynolds, B., Emmett, B. A., Keith, A. M., de Jong, L. W., Schjønning, P., Moldrup, P., Jones, S. B. & Tuller, M., 1 Chwef 2012, Yn: Vadose Zone Journal. 11, 1

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  46. Cyhoeddwyd

    Natural History Notes. Naja kaouthia (monocled cobra). Behavior / Spitting.

    Santra, V. & Wüster, W., 1 Meh 2017, Yn: Herpetological Review. 48, 2, t. 455-456 2 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  47. Cyhoeddwyd

    Natural History Notes. Scolecophis atrocinctus (Black-banded Snake). Reproduction / Combat Behaviour

    Chernov, E., Hoffmann, E. P. & Wüster, W., 1 Medi 2020, Yn: Herpetological Review. 51, 3, t. 628-629 2 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  48. Cyhoeddwyd

    Natural History Notes: Crotalus scutulatus (Mohave rattlesnake). Maximum size.

    Mrinalini, N. V., Hicks, J. J. & Wüster, W., 1 Meh 2015, Yn: Herpetological Review. 46, 2, t. 271 1 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  49. Cyhoeddwyd

    Natural bounds on herbivorous coral reef fishes

    Heenan, A., Hoey, A. S., Williams, G. & Williams, I. D., 23 Tach 2016, Yn: Proceedings of the Royal Society B.. 283, 1843

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  50. Cyhoeddwyd

    Natural capital and ecosystem services, developing an appropriate soils framework as a basis for valuation

    Robinson, D. A., Hockley, N., Cooper, D. M., Emmett, B. A., Keith, A. M., Lebron, I., Reynolds, B., Tipping, E., Tye, A. M., Watts, C. W., Whalley, W. R., Black, H. I., Warren, G. P. & Robinson, J. S., 15 Maw 2013, Yn: Soil Biology and Biochemistry. 57, t. 1023-1033

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

  51. Cyhoeddwyd

    Natural carbon stable isotope ratios as indicators of the relative contribution of live and inert diets to growth in larval Senegalese sole (Solea senegalensis).

    Gamboa-Delgado, J., Canavate, J. P., Zerolo, R. & Le Vay, L., 1 Awst 2008, Yn: Aquaculture. 280, 1-4, t. 190-197

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid