In the course of our screening program, the EtOAc extract of Micromonospora sp. A258 from the sponge Haliclona oculata exhibited antimicrobial activity against both gram positive S.aureus ATCC25923 and gram‐negative E.coli ATCC25922, S.enterica ATCC13076. This paper reports the isolation and structural elucidation of eight secondary metabolites including bacilsubteramide A (1), 4,9‐dihydroxy‐3‐isobutyl‐2,3,4,5‐tetrahydrobenzo‐azepin‐1‐one (2), indole‐3‐carboxylic acid (3), N‐acetyltryptamine (4), N‐(4‐hydroxyphenyl)ethyl‐methylbutanamide) (5), N‐phenyl‐acetamide (6), 2‐[(5‐methyl‐1,4‐dioxan‐2‐yl)methoxy]ethanol (7), (2R,3S)‐butane‐2,3‐diol (8) from the culture broth of Micromonospora sp. A258. Their structures were determined by spectroscopic analysis including MS, 1D NMR and 2D NMR, as well as comparison with literature data.
In the current context, an attempt is being made to improve the electrical discharge machining (EDM) process by using powder particles in a suitable combination. To improve the quality of such procedures, the process parameters should be optimized. The present study proposes to utilize Taguchi–Grey relational analysis to discover the optimal combination of process parameters for SKD61 die steel specimens using titanium powder-mixed EDM (PMEDM). Among the machining parameters chosen, the optimal combination of current (3 A), pulse on-time (37 μs), pulse off-time (37 μs), and powder concentration (4 g/L) was determined experimentally. Due to its relevance in spark energy production, peak current is a more significant factor in PMEDM processes. A superior surface topography was obtained with increased microhardness and fewer microfractures over machined specimens with optimal process parameter in PMEDM. The titanium particles can effectively enhance the surface performance measures during PMEDM-based machining owing to tiny craters and pores with better lubrication.
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