Díraonadh

Is éard is díraonadh ann ná iarmhairt trasnaíochta toinne i leith tonnta atá freagrach as leathadh toinne a thagann amach as cró beag (cosúil le fuaimthonn ag teacht amach as callaire fógartha poiblí). Trí dhíraonadh a chasann tonnta thar réada, agus is ar an ábhar seo a bhíonn bandaí caola geala is dorcha ar imeall scátha (frainsí díraonta). Is foinse thánaisteach don tonn iomadaithe é an réad díraonta nó an cró. Cheap an t-eolaí Iodálach Francesco Maria Grimaldi an focal diffractionem, díraonadh (Gaeilge:briseadh as a chéile) agus ba é an chéad duine riamh é a thaifead breathnuithe cruinne ar an bhfeiniméan sa bhliain 1660.^[1]^[2]

San fhisic chlasaiceach, déantar cur síos ar an bhfeiniméan díraonta leis an bprionsabal Huygens-Fresnel a deir gur féidir breathnú ar gach poncfhoinse ar tonnbhráid mar tonnáin tánaisteacha sféarúla.^[3] Bíonn an patrún lúbthachta sainiúil níos suntasaí nuair a thagann tonn ó fhoinse chomhleanúnach (ar nós léasair) ar scoilt/cró atá inchomparáide ó thaobh méide de lena thonnfhad,mar a thaispeántar san íomhá ionsáite..nuair a bhuaileann tonn ó fhoinse chomhleanúnach (cosúil le léasair) scoilt/cró atá inchomparáide ó thaobh méide lena thonnfhad, mar a thaispeántar san íomhá a cuireadh isteach. Tá sé seo mar gheall ar phointí éagsúla (nó trasnaíocht) a chur leis ar an tonnbhráid (nó, gach tonnán) a thaistealaíonn ar chonairí ar faid éagsúla go dtí an dromchla clárúcháin. Má tá oscailtí iolracha a bhfuil leagtha amach go dlúth (m.sh., gríl díraonta), is féidir patrún casta déine éagsúil a bheith mar thoradh air.

Tarlaíonn na héifeachtaí seo freisin nuair a thaistealaíonn tonn solais trí mheán a bhfuil comhéifeacht athraonta éagsúil aige, nó nuair a thaistealaíonn fuaimthonn trí mheán a bhfuil fuaimchoiscis éagsúla aige – díraonann gach tonn,^[4] lena n-áirítear tonnta imtharraingthe, tonnta uisce, agus tonnta leictreamaighnéadacha eile amhail X-ghathanna agus radathonnta. Ina theannta sin, léiríonn meicnic chandamach freisin go bhfuil airíonna cosúil le tonnta ag damhna, agus mar sin go ndéantar díraonadh air (atá intomhaiste ag leibhéil fho-adamhacha go móilíneach). ^[5]

Braitheann an méid díraonta ar mhéid na bearna. Is mó an díraonadh nuair atá méid na bearna cosúil le tonnfhad na toinne. Sa chás seo, nuair a théann na tonnta tríd an mbearna éiríonn siad leathchiorclach.

Déanann na hadaimh atá eagraithe i gcriostail X-ghathanna nó leictreoin nó neodróin a dhíraonadh chun patrúin a tháirgeadh a léiríonn mionstruchtúr an chriostail. I ngreille dhíraonta bíonn na céadta scoilteanna in aghaidh an cheintiméadair, agus is áisiúil í chun léas solais a dheighilt ina chomhdhathanna. Is é díraonadh a chinneann an cumas deiridh díscaoilte in ionstraimí optúla.^[6]

Tagairtí

↑ Francesco Maria Grimaldi, Physico mathesis de lumine, coloribus, et iride, aliisque annexis libri duo (Bologna ("Bonomia"), Italy: Vittorio Bonati, 1665), page 2 Curtha i gcartlann 2016-12-01 ar an Wayback Machine:
Original : Nobis alius quartus modus illuxit, quem nunc proponimus, vocamusque; diffractionem, quia advertimus lumen aliquando diffringi, hoc est partes eius multiplici dissectione separatas per idem tamen medium in diversa ulterius procedere, eo modo, quem mox declarabimus.

Translation : It has illuminated for us another, fourth way, which we now make known and call "diffraction" [i.e., shattering], because we sometimes observe light break up; that is, that parts of the compound [i.e., the beam of light], separated by division, advance farther through the medium but in different [directions], as we will soon show.
↑ Cajori, Florian "A History of Physics in its Elementary Branches, including the evolution of physical laboratories." Curtha i gcartlann 2016-12-01 ar an Wayback Machine MacMillan Company, New York 1899
↑ Wireless Communications: Principles and Practice, Prentice Hall communications engineering and emerging technologies series, T. S. Rappaport, Prentice Hall, 2002 pg 126
↑ "X-Ray Diffraction: A Practical Approach" (as en) (29 June 2013). Springer Science & Business Media.
↑ "Real-time single-molecule imaging of quantum interference" (2012-03-25). Nature Nanotechnology 7 (5): 297–300. doi:10.1038/nnano.2012.34. ISSN 1748-3395. PMID 22447163. Bibcode: 2012NatNa...7..297J.
↑ Hussey, Matt (2011). "Díraonadh". Fréamh an Eolais. Coiscéim. p. 214.

[1] Francesco Maria Grimaldi, Physico mathesis de lumine, coloribus, et iride, aliisque annexis libri duo (Bologna ("Bonomia"), Italy: Vittorio Bonati, 1665), page 2 Curtha i gcartlann 2016-12-01 ar an Wayback Machine:
Original : Nobis alius quartus modus illuxit, quem nunc proponimus, vocamusque; diffractionem, quia advertimus lumen aliquando diffringi, hoc est partes eius multiplici dissectione separatas per idem tamen medium in diversa ulterius procedere, eo modo, quem mox declarabimus.

Translation : It has illuminated for us another, fourth way, which we now make known and call "diffraction" [i.e., shattering], because we sometimes observe light break up; that is, that parts of the compound [i.e., the beam of light], separated by division, advance farther through the medium but in different [directions], as we will soon show.

[2] Cajori, Florian "A History of Physics in its Elementary Branches, including the evolution of physical laboratories." Curtha i gcartlann 2016-12-01 ar an Wayback Machine MacMillan Company, New York 1899

[3] Wireless Communications: Principles and Practice, Prentice Hall communications engineering and emerging technologies series, T. S. Rappaport, Prentice Hall, 2002 pg 126

[4] "X-Ray Diffraction: A Practical Approach" (as en) (29 June 2013). Springer Science & Business Media.

[5] "Real-time single-molecule imaging of quantum interference" (2012-03-25). Nature Nanotechnology 7 (5): 297–300. doi:10.1038/nnano.2012.34. ISSN 1748-3395. PMID 22447163. Bibcode: 2012NatNa...7..297J.

[FreamhanEolais-6] Hussey, Matt (2011). "Díraonadh". Fréamh an Eolais. Coiscéim. p. 214.

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