Nitroheterocyclic and nitroaromatic compounds constitute an enormous range of chemicals whose potent biological activity has significant human health and environmental implications. The biological activity of nitro-substituted compounds is derived from reductive metabolism of the nitro moiety, a process catalyzed by a variety of nitroreductase activities. Resistance of bacteria to nitro-substituted compounds is believed to result primarily from mutations in genes encoding oxygen-insensitive nitroreductases. We have characterized thenfsA and nfsB genes of a large number of nitrofuran-resistant mutants of Escherichia coli and have correlated mutation with cell extract nitroreductase activity. Our studies demonstrate that first-step resistance to furazolidone or nitrofurazone results from an nfsA mutation, while the increased resistance associated with second-step mutants is a consequence of an nfsB mutation. Inferences made from mutation about the structure-function relationships of NfsA and NfsB are discussed, especially with regard to the identification of flavin mononucleotide binding sites. We show that expression of plasmid-carried nfsA and nfsB genes in resistant mutants restores sensitivity to nitrofurans. Among the 20 first-step and 53 second-step mutants isolated in this study, 65 and 49%, respectively, contained insertion sequence elements innfsA and nfsB. IS1 integrated in both genes, while IS30 and IS186 were found only in nfsA and IS2 and IS5 were observed only in nfsB. Insertion hot spots for IS30 and IS186 are indicated innfsA, and a hot spot for IS5 insertion is evident in nfsB. We discuss potential regional and sequence-specific determinants for insertion sequence element integration in nfsA and nfsB.
In the present investigation, we have reported the fabrication of a low-cost, magnetically separable, solar light active NiFe 2−x Nd x O 4 photocatalyst with different neodymium contents. The synthesized photocatalyst samples were characterized by a combination of various physicochemical techniques such as PXRD, SEM, EDS, FTIR, and UV−vis spectroscopy. It was observed that Nd substitution can greatly enhance absorption in the whole visible region. With an increase in Nd concentration, NiFe 2−x Nd x O 4 samples show a red shift in absorption. Interestingly, Nd substitution into nickel ferrite results in a dramatic conversion of the inert NiFe 2 O 4 into a highly solar light active photocatalyst for the degradation of organic pollutants and also shows excellent recyclability and durability properties. The significant enhancement in photoactivity under solar light irradiation can be ascribed to the reduction of the nickel ferrite band gap by Nd 3+ substitution. Therefore, these unusual properties of NiFe 2−x Nd x O 4 encourage us to extend photocatalytic degradation to another few organic pollutants. This new photocatalyst system, NiFe 2−x Nd x O 4 , can have other potential environmental and energy applications that only need visible light as energy input.
The progress of technology in consumer electronics demand an antenna having a compact size, high gain and bandwidth, and multiple antennas at transmitter and receiver to enhance the channel capacity. Over the last decade, numerous techniques are proposed to improve the performance of the antenna. One such technique is the use of metamaterials (MTMs) in antenna design. MTMs are artificial structures to provide unique electromagnetic properties that are not available in natural materials. The unique properties of these materials allow the design of high-performance antennas, filters, and microwave devices which cannot be obtained using traditional antennas. Loading antenna with the one, two, and three-dimensional MTM structures comprised of a periodic subwavelength unit cell exhibits RLC resonant structures and allows to manipulate electromagnetic waves in the antenna system. These structures offer low resonant frequency compared to the antenna resonant frequency resulting in antenna miniaturization and manipulation of electromagnetic waves helps in enhancing the gain and bandwidth, and achieving circular polarization (CP) of an antenna system. Also, metamaterial loading enhances isolation between the antenna elements in the multiple-input-multiple output (MIMO) system by suppressing the surface waves. In this paper, the electromagnetics of MTM with analytical expressions and its application in antenna design are discussed in detail. The MTM-based antennas are classified into MTM loading, MTM inspired antenna, metasurface loading, and composite right/left hand (CRLH) based antennas. The recent development in MTM inspired antenna and its application in antenna miniaturization, enhancing gain and bandwidth, achieving CP and mutual coupling suppression in MIMO antenna systems are discussed to make it useful for further research. INDEX TERMS Circular Polarization (CP), Metamaterial (MTM), gain, bandwidth, high impedance surface (HIS), mutual coupling, antenna miniaturization, composite right/left hand (CRLH).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.