1,980 research outputs found
In-plane Buckling of Rotationally Restrained Heterogeneous Shallow Arches Subjected to a Concentrated Force at the Crown Point
The nonlinear in-plane stability of shallow arches with cross-sectional inhomogeneity is investigated. It is assumed that a central concentrated load is exerted at the crown of the arch and the supports are uniform rotationally restrained pins at the endpoints with constant stiffness. The effects of the springs on the stability is investigated. It is found that such arches may buckle in an antisymmetric bifurcation mode with no strain increment at the moment of the stability loss, and in a symmetric snap-through mode with an increased strain. The effects of the springs are notable on the bucking ranges and also on the critical (buckling) loads. If the spring stiffness is zero we get back the results valid for pinned-pinned arches and as the stiffness of the rotational restraints tends to infinity the results become consistent with those for fixed-fixed arches. The results computed are compared with finite element calculations
Növényvédőszerek fotokatalizált degradációjának vizsgálata
Munkánk fĹ‘ cĂ©lkitűzĂ©se a gyakorlatban is szĂ©les körűen felhasznált növĂ©nyvĂ©dĹ‘szerek fotokatalizált bomlási mechanizmusának megismerĂ©se, a köztitermĂ©kek azonosĂtása Ă©s toxicitásának a vizsgálata. Ez utĂłbbi cĂ©lt mikrobiolĂłgiai modelkĂsĂ©rletekkel valĂłsĂtottuk meg, melynek során reprezentatĂv mikroorganizmusokban a peszticidszármazĂ©kok hatására fellĂ©pĹ‘ gátlĂł hatást vizsgáltuk. FotodegradáciĂłs vizsgálataink a peszticidek döntĹ‘ hányadánál releváns, hiszen fĂ©nyĂ©rzĂ©keny anyagokrĂłl van szĂł.A vizsgálatainkhoz választott tizenkettĹ‘ peszticid kĂ©miai szerkezetĂĽket tekintve öt kĂĽlön csoportba sorolhatĂł, szĂ©les körben alkalmazottak, toxicitásuk ismert, de a termĂ©szetben lejátszĂłdĂł bomlási folyamataikrĂłl nagyon kevĂ©s adat áll rendelkezĂ©sre. Ezen tĂşlmenĹ‘en a fotokatalizált degradáciĂłjuk mechanizmusa, a metabolitok kĂ©miai azonosĂtása, illetve azok biolĂłgiai hatásának elemzĂ©se rendkĂvĂĽl fontos rĂ©szletekkel járult hozzá a peszticidek általános jellemzĂ©sĂ©hez Ă©s alklamazásához. A biolĂłgiai hatás modellezĂ©se cĂ©ljábĂłl mikrobiolĂłgiai modellkĂsĂ©rleteket hajtottunk vĂ©gre reprezentatĂv talajmikrobák tesztfajkĂ©nt törtĂ©nĹ‘ alkalmazásával. Kinetikai vizsgálataink által igazoltuk, hogy az egyes peszticidek degradáciĂłja eltĂ©rĹ‘ kinetikai viszonyok között megy vĂ©gbe.A legfontosabb talajalkotĂł fĂ©mekkel törtĂ©nĹ‘ kölcsönhatást modellezĹ‘ kĂsĂ©rleteink hozzárulnak az alapvegyĂĽletek Ă©s bomlástermĂ©keik viselkedĂ©sĂ©nek ,felvehetĹ‘sĂ©gĂ©nek a megĂ©rtĂ©sĂ©hez. | Major goal of our study was to investigate photolytic degradation of distinctive types of pesticides being frequently applied in practice.A special, immersable UV-light source emitting light of 254 nm effected degradation. Subsequent to the irradiation of the sample the isolation of the degradation products was carried out by column-, and gas-chromatography. Identification of degradation species was implemented by mass spectrometry.Each of the studied 11 distinctive pesticides of definitely different chemical structure exhibited definite liability to undergo photolytic decomposition. The degradation mechanisms of the mentioned pesticedes were entirely revealed, and in each case 5 or 6 major degradation species have been detected. Loss of thiomethyl, alkyloxy, alkyl and chloro groups might be regarded as typical ways of transformation.We observed significant differences in the kinetic behaviour of the investigated pesticides by GC-monitoring. The kinetic curves of photolytic decomposition made it possible to compare photosensibility and reaction mechanisms of the studied pesticides.The research on revealing the exact reaction mechanisms of photolytic degradation of pesticides contributes to the proper understanding of behaviour of pesticides, and points out the possible environmental risk factors and ways of proper application.Interaction of soil-constituent metals and pesticides, as well as decomposition products was also investigated
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