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三不互扣環

出自維基百科,自由嘅百科全書
三不互扣環
L6a4
交叉數6
Hyperbolic volume7.327724753
棍數9
Conway notation.1
A–B 表示法6Template:Sup sub
ThistlethwaiteL6a4
其他
alternating, hyperbolic

喺數學上,三不互扣環(Borromean rings[a])係三條喺三維空間入面嘅簡單閉曲線。呢三條曲線喺拓撲學上係互相扣埋嘅,冇辦法將佢哋彼此分開;但係,只要將其中任何一條切斷或者拎走,剩低嗰兩條就會即刻變成兩個冇打結、亦冇互相扣住嘅環。

最常見嘅畫法,係將三個圓畫喺同一個平面上,個樣有啲似文氏圖(Venn diagram)。三個圓喺交叉位會輪流一條喺另一條上面、另一條喺下面。其他三條曲線只要喺拓撲學上同呢幅圖入面嘅三條曲線等價,就可以叫做一組博羅米安環。

「博羅米安環」呢個名,係嚟自意大利嘅博羅米奧家族(House of Borromeo)。呢個家族以前將呢種圓環圖案用喺佢哋嘅家族徽章上面。不過,類似博羅米安環嘅圖案其實喺好多唔同文化都有出現,例如北歐人同日本。喺基督教象徵入面,佢亦曾經用嚟代表三位一體;去到現代商業,Ballantine 啤酒亦曾經用博羅米安環做標誌,所以博羅米安環亦有「Ballantine rings」呢個叫法。

現實世界入面,亦有人用互相連住嘅 DNA 或者其他分子,整出真正嘅博羅米安環。物理學上亦有一啲同佢好似嘅現象,例如 Efimov 態同博羅米安原子核(Borromean nuclei)。呢兩種情況都有三個成分互相綁住,但奇怪嘅地方係:任何兩個成分單獨攞出嚟,都唔會互相綁住。

從幾何學角度嚟講,博羅米安環可以用互相扣住嘅橢圓整出嚟;亦可以利用正二十面體嘅頂點,整出由互相連住嘅黃金矩形組成嘅博羅米安環。不過,如果要求三條環都一定要係真正嘅圓,就冇可能喺三維空間入面整到博羅米安環。

另外,有人猜想,只要用任何一條唔係圓形嘅簡單閉曲線,再用佢嘅複製品,都可以整出博羅米安環。

喺結理論(knot theory)入面,可以透過數 Fox n-著色(Fox n-colorings)去證明博羅米安環係互相連結嘅。作為一種鏈結(link),博羅米安環屬於 **Brunnian、交替(alternating)、代數(algebraic)同雙曲(hyperbolic)**鏈結。

喺算術拓撲學(arithmetic topology)入面,有一啲素數三元組亦有同博羅米安環相似嘅「連結」性質。

定義同記號

[編輯]

數學出版物如果要定義博羅米安環,通常都會用鏈結圖(link diagram)嚟表示,即係喺一個平面上畫幾條曲線,再喺佢哋交叉嘅位置加上記號,表示每一個交叉位邊一條曲線、或者曲線嘅邊一部分,係經過另一條嘅上面或者下面。

有咗呢種圖之後,可以將佢變成三維空間入面嘅曲線系統:先將個平面嵌入三維空間,再按照幅圖嘅標示,喺每個交叉位將畫咗嘅曲線拉高或者壓低,令佢經過嵌入咗嘅平面上面或者下面。

最常用嘅博羅米安環圖,係由三個大小相同嘅圓組成。三個圓嘅圓心分別位於一個等邊三角形嘅三個頂點,而且三個圓要畫得夠近,令到佢哋嘅內部有一個共同交集。呢個畫法有啲似文氏圖入面嘅三個圓,亦似用嚟定義勒洛三角形(Reuleaux triangle)嘅三個圓。

沿住每一個圓逐個交叉位睇落去,佢嘅交叉會輪流喺上面同下面[2][3][4]。 亦可以用另一種等價嘅方式去描述三個圓之間嘅上下關係:每一個圓喺佢同第二個圓嘅兩個交叉位,都係行喺對方上面;而去到同第三個圓嘅兩個交叉位,就都係行喺對方下面[5]。

如果可以透過空間嘅連續變形,即係所謂嘅環境同痕變(ambient isotopy),將一個鏈結變成另一個鏈結,就話呢兩個鏈結係等價嘅。因此,「博羅米安環」亦可以指任何一組同呢個標準圖喺呢種意義下等價嘅鏈結[4]。

喺 The Knot Atlas 入面,博羅米安環嘅編號係「L6a4」。呢個記號表示佢係一個有六個交叉位、而且採用交替圖嘅鏈結;喺 Morwen Thistlethwaite 列出嘅所有最多有13個交叉位嘅素鏈結(prime links)之中,佢係五個六交叉位交替鏈結入面嘅第四個[6]。

至於 Dale Rolfsen 喺 1976 年出版嘅《Knots and Links》入面嘅結同鏈結表,亦延續咗 Alexander 同 Briggs 喺1920年代整落嘅較早列表,博羅米安環就用 **Alexander–Briggs 記號「6³₂」**表示。呢個記號即係話,佢係三個六交叉位、三個組成部分嘅鏈結入面,第二個列出嘅鏈結[6][7]。

博羅米安環嘅 Conway 記號「.1」,就係用一個簡化咗嘅方式去描述呢個鏈結嘅標準鏈結圖[8]。

攷

[編輯]
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引用錯誤 喺 <references> 入面定義、名稱為 "notknot" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "ghz" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "ashley" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "brunnian" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "unferth" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "mechbond" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "triangles" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "criticality" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "4arc-rope" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "stoddart" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "crumbrown" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "chartres" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "strange" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "tripod1" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "tripod2" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "gardner" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "glick" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "universal" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "polygonal" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "rare" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "efimov" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "halogen" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "enneagram" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "impossible" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "dna" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "analogies" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "physical" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "nanyes" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "thiolate" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "discord" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "lacan" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "ratcliffe" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "riley" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "dante" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "litcrit" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "nucleus" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "algebraic" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "volume" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "inversive" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "lattice" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "unequal" 嘅 <ref> 標籤喺之前嘅正文冇被使用。引用錯誤 喺 <references> 入面定義、名稱為 "massey" 嘅 <ref> 標籤喺之前嘅正文冇被使用。

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Template:Knot theory

  1. ↑ Pronounced /bɒroʊˈmiːən/[1]
引用錯誤 存在組名為 "lower-alpha" 嘅 <ref> 標籤,但搵唔到對應嘅 標籤。