The　flame　quenching　ability　of　a　crimped・ribbon　type　arrester　was　discussed． The　quenching　ability　was　evaluated　by　the　minimum　flame　velocity　at　which　the flame　passed　through　the　arrester．The　effect　of　dimensiolls　of　an　aperture　of　arrester　on　the　quenching　ability　were　investigated，and　it　was　shown that　the　ability　could　be　expressed　with　an　equ1valent　diameter　of　an　aperture．Generally，the　ability　increased　with　an arrester　thickness，and　two　different　tendencies　of　the　effect　of　the　thickness　were　observed　depending　on　the　value　o｛an　equivalent　diameter．Especially　for　the　arrester　with　smaller　size　of　equivalent　diameter，the　flame　quenching　ability increased　with　increase　of　the　thlckness　remarkably． The　experimental　chart　or　equation　to　estimate　the　quenching　ability　and　also　the　pressure　drop　were　proposed.

Decision・making　mechanism　is　fulldamental　in　fault　detection．Hypothesis　test　is　applied　to　decision－making　in many　fault　detectiQn　system．Generally，the　settlement　of　hypotheses　is　a　trade－off　problem　and　is　always　difficult. In this　study，the　method　to　settle　hypotheses　based　on　loss　is　considered．Decision・making　process　is evaluated　by　loss concemed　with　false　alam，missed　alam　and　so　on．A　fault　detection　system　using　Wald's　originated　Sequential Probability　Ratio　Test（SPRT）is　supposed　and　the　variation　of　total　loss　by　hypotheses　settlement　is　considered　by Monte　Carlo　simulation．The　followings　are　clarified：（1）A　concrete　process　to　design　hypotheses　is　shown，The optimum　condition　is　determined　based　on　relation　between　hypotheses　and　expected　value　of　the　loss．The　procedure shows　one　method　for　solving　the　practical　problem　on　applying　SPRT　to　fault　detection、（2）By　numerical　considera・tion，the　possibility　is　suggested　to　reduce　several　tens　of　percent　of　Ioss　by　designing　optimum　hypotheses，which depends　on　the　loss　generated　in　each　situation．

We　estimated　the　crystal　structure　of　nitrobenzene　derivative　compomds　without　using　observed　Iattice　constant o「space　group． The　molecular　dynamics　method　which　treats　lattice　constants　as　one　of　the　variables，was　employed　and　calcula－ tions　were　applied　to　nitrobenzene，p-dinitrobenzene　and p-nitroaniline．Good　agreements　were　obtalned　between observed　and　calculated　crystal　structures　in　nitrobenzene　and p-nitrobenzene、The　maximum　tolerance　of　lattice length　between　observed　and　calculated　structure　was　O.28 angstrom　and　that　of　lattice　angle　was　O．10 degree　in p-dinitrobenzene、The　space　group　of　calculated　crystal　structure　also　coincided　with　observed　one・However　the tolerances　of　Iattice　constants　and　Iattice　angles　were　slightly　Iarger　in p-nitroaniline、Because　the　used　potential parameter　in　this　calculation　did　not　reproduce　intermolecular　hydrogen　bond　between　hydrogen　hl　amino　group　and oxygeu　in　nitro　group　very　well．Density　and　heat　of　formation　on　solid　state　were　also　caIculated　from　estimated crystal　structure．