▁started , ▁the ▁und ist urbed ▁ground ▁temperature ▁must ▁be ▁determined . ▁This ▁can ▁be ▁measured ▁in ▁various ▁ways : ▁e . g ., ▁by ▁temperature ▁log g ings ▁of ▁the ▁bore hole ▁or ▁by ▁meas uring ▁the ▁temperature ▁of ▁the ▁circul ated ▁water ▁through ▁the ▁bore hole ▁without ▁he ating ▁over ▁ 2 0 – 3 0 ▁minutes . ▁The ▁mean ▁fluid ▁temperature ▁corresponds ▁to ▁the ▁und ist urbed ▁mean ▁temperature ▁along ▁the ▁bore hole . ▁The ▁next ▁step ▁is ▁to ▁switch ▁on ▁the ▁he ater ▁and ▁the ▁monitoring ▁system . ▁During ▁the ▁test , ▁the ▁heat ▁transfer ▁into ▁the ▁ground ▁surrounding ▁the ▁bore hole ▁is ▁essentially ▁radial ▁and ▁relatively ▁constant ▁along ▁the ▁bore hole . ▁ ▁References ▁ ▁Category : Ge oth erm al ▁dr illing <0x0A> </s> ▁The ▁China – N orth ▁Korea ▁border ▁is ▁the ▁international ▁border ▁separ ating ▁the ▁People ' s ▁Republic ▁of ▁China ▁( P RC ) ▁and ▁the ▁Democratic ▁People ' s ▁Republic ▁of ▁Korea ▁( N orth ▁Korea ). ▁ ▁Geography ▁ ▁The ▁border ▁is ▁ ▁long . ▁From ▁west ▁to ▁east , ▁the ▁Y alu ▁River , ▁Pa e kt u ▁Mountain , ▁and ▁the ▁T umen ▁River ▁div ides ▁the ▁two ▁countries . ▁ ▁D and ong , ▁in ▁the ▁L ia oning ▁Province ▁of ▁China , ▁on ▁the ▁Y alu ▁River ▁delta , ▁is ▁the ▁largest ▁city ▁on ▁the ▁border . ▁On ▁the ▁other ▁side ▁of ▁the ▁river ▁is ▁the ▁city ▁of ▁S inu iju ▁in ▁North ▁Py ong an ▁Province