Sound field characteristics of underground railway stations – Effect of interior materials and noise source positions

In the case of most underground railway stations, no acoustical solutions are used to reduce train noise. Because the reflecting features of train noise in an underground station are not known, appropriate methods for controlling these features have yet to be established. The aim of this study was to clarify the sound field characteristics of underground stations by putting a sound source and receiver on the railway track and platform, respectively. The impulse responses for two vacant underground stations were measured to clarify the effects of the interior materials of the station (Comparison I), and the sound source was put in each station and tunnel to clarify the effect of the noise source positions (Comparison II). Results showed that the sound fields were similar between the stations whose lateral walls were covered with either metallic or fire-resistant wooden panels (Comparison I), and that the sound field for the sound sources near or in the tunnel presented a higher strength (G) by 5.1 dB and longer reverberation time (EDT) by 0.7 s compared to the sound source in the station (Comparison II). The sound sources in the tunnel presented strong and long reverberations at around 500 Hz due to the convergence effect of the tunnel. Therefore, this study proposes a platform screen with doors to limit noise transmission into the platform.     

Construction of α-phosphonolactams via rhodium (II)-catalyzed intramolecular C?H insertion reactions

The Rh(II)-catalyzed intramolecular C H insertion reactions of N,N-dialkyl-α-diazo-α-(diethylphosphono)acetamides 2a , f–j in CHCl₃ or ClCH₂CH₂Cl were found to give monocyclic and bicyclic α-phosphono-β-lactams, 3a and 3f–j , in 43–67% yields via regiospecific α-C H insertion of the N-alkyl groups. Similar treatment of N-benzyl-N-isopropyl-α-diazo-α-(diethylphosphono)acetamide ( 2b ) and the corresponding N-isobutyl-N-methylacetamide 2d in ClCH₂CH₂Cl afforded mixtures of β-lactams 3b (35%) and and 3b ′ (16%), β-lactam 3d (47%), and γ-lactam 4d (10%), respectively, each of which is formed by the competitive C H insertion reaction between benzylic and isopropyl α-C H bonds and between methyl α-C H and methine β-C H bonds, respectively. For the formation of β-lactams, the selectivity in the rhodium-mediated C H insertion in ClCH₂CH₂Cl follows the order methyl > methine > benzylic α-C H bond on N-substituents. The N,N-dibutyl-α-diazo homologue 2c and Nα[α-diazo-α-(diethylphosphono)acetyl]-2-methylindoline ( 2k ) exclusively produced γ-lactams 4c (67%) and 4k (81%) via insertion into the methylene β-C H and methyl β-C H bonds. tert-Butyl N-[α-diazo-α-(dibenzylphosphono)acetyl]-piperidine-2-carboxylate ( 2m ) on similar treatment, followed by deprotection of the benzyl ester afforded the 7-phosphono carbacepham 6 in 32% overall yield. Similar Rh(II)-catalyzed cyclization of N-methyl-N[4-benzyloxy-α-(diethylphosphono)-phenyl(diethyl-phosphono)methyl]-α-diazo-acetamide ( 2n ) led to 1-[4′-benzylphenyl(diethylphosphono)methyl] -3-(diethyl-phosphono)azetidin-2-one ( 3n ) in 78% yicld. The phosphono group at C-7 of 3f was converted into the acetylamino group via a four-step reaction. Application of chiral rhodium(II) carboxylates 12a–c to the insertion reactions of 2b , c produced α-phosphono-β-and γ-lactams, 3b and 4c , in 6–24% ee and 25–29% ee, respectively.