( ( Although ( ( in principle ) ( , ( ( the ( HeHg laser ) ) ( can ( be ( operated ( in ( ( ` ( sealed ( tube ( ' fashion ) ) ) ) ( , ( ( as ( a ( practical matter ) ) ) ( , ( ( maintaining ( a connection ) ) ( to ( the ( vacuum system ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ( ( will ( be essential ) ) . ) )
(ROOT (S (SBAR (IN Although) (S (PP (IN in) (NP (NN principle))) (, ,) (NP (DT the) (NNP HeHg) (NN laser)) (VP (MD can) (VP (VB be) (VP (VBN operated) (PP (IN in) (S (NP (`` `) (JJ sealed) (NN tube) ('' ') (NN fashion)) (, ,) (PP (IN as) (NP (DT a) (JJ practical) (NN matter))) (, ,) (VP (VBG maintaining) (NP (DT a) (NN connection)) (PP (TO to) (NP (DT the) (NN vacuum) (NN system))))))))))) (VP (MD will) (VP (VB be) (ADJP (JJ essential)))) (. .)))
Although in principle, the HeHg laser can be operated in 'sealed tube' fashion, as a practical matter, maintaining a connection to the vacuum system will be essential.
(ROOT (S (NP (DT A) (JJ sealed) (, ,) (JJ vacuum-insulated) (NN reaction) (NN flask)) (VP (VBZ approximates) (NP (NP (DT the) (NN condition)) (PP (IN of) (NP (NP (DT a) (VBN isolated) (NN system)) (, ,) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (NP (CC neither) (NP (NN matter)) (CC nor) (NP (NN heat))) (VP (MD can) (VP (VB be) (VP (VBN exchanged) (PP (IN between) (NP (NN system) (CC and) (NNS surroundings)))))))))))) (. .)))
A sealed, vacuum-insulated reaction flask approximates the condition of a isolated system, in which neither matter nor heat can be exchanged between system and surroundings.