Facile synthesis of monodispersed 3D hierarchical Fe₃O₄ nanostructures decorated r-GO as the negative electrodes for Li-ion batteries

Kumar, S. Rajesh,Kim, Jong Guk,Viswanathan, C.,Kim, Won Bae,Selvan, R. Kalai,Ponpandian, N. Elsevier 2018 Materials research bulletin Vol.97 No.-

<P><B>Abstract</B></P> <P>One-pot solvothermal process is adopted to develop, 3D hierarchical Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles supported 2D reduced graphene oxide sheets (Fe<SUB>3</SUB>O<SUB>4</SUB>/r-GO) as possible negative electrodes for lithium ion batteries. The synthesis parameters are optimized to prepare agglomeration-free Fe<SUB>3</SUB>O<SUB>4</SUB> nanostructures with uniform size and shape on r-GO. The field emission scanning electron microscopic (FESEM) image reveals that the 3D hierarchical Fe<SUB>3</SUB>O<SUB>4</SUB> nanostructures are uniformly decorated on r-GO. The physicochemical and functional properties of Fe<SUB>3</SUB>O<SUB>4</SUB>/r-GO are systematically investigated using various techniques. The fabricated Fe<SUB>3</SUB>O<SUB>4</SUB>/r-GO electrode delivers an initial discharge capacity of 1221mAhg<SUP>−1</SUP> at a current density of 100mAg<SUP>−1</SUP> and retains the specific capacity of 1560mAhg<SUP>−1</SUP> after 100 cycles. Fe<SUB>3</SUB>O<SUB>4</SUB>/r-GO significantly enhances cyclic performance, when compared with bare Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles due to the uniform distribution of Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles on the graphene sheet with the more number of electrochemically active sites.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Monodispersed Fe<SUB>3</SUB>O<SUB>4</SUB> nanostructures with different shapes synthesized by solvothermal method. </LI> <LI> The fabricated Fe<SUB>3</SUB>O<SUB>4</SUB>/r-GO electrode delivers an initial discharge capacity of 1221mAhg<SUP>−1</SUP> at 100mAhg<SUP>−1</SUP>. </LI> <LI> Fe<SUB>3</SUB>O<SUB>4</SUB>/r-GO significantly enhances the cyclic stability and rate capability than bare Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Influence of corner radius on the near wake structure of a transversely oscillating square cylinder

R. Ajith Kumar,손창현,B. H. Lakshmana Gowda 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.9

The near wake flow field features of transversely oscillating square section cylinders with different corner radii were studied in an attempt to assess the influence of corner radius. The investigation was performed by using particle image velocimetry (PIV) technique in a water channel with a turbulence intensity of 6.5%. Five models were studied with r/B=0, 0.1, 0.2, 0.3 and 0.5 (r is the corner radius and B is the characteristic dimension of the body), and the body oscillation was limited to lock-in condition (at fe/fo=1.0; fe is the excitation frequency and fo is the vortex shedding frequency from a stationary cylinder at the same Re). The corner radius was found to significantly influence the flow features around the bodies. Except for r/B=0.5, for all the other cases of r/B ratios, cycle-to cycle variation in the mode of vortex shedding was observed in the case of oscillating cylinders inducing highly non-linear wake characteristics. Apart from variation in the shedding mode, changes in shedding cycle timing were also observed for sharp and rounded square cylinders. The hgher the r/B ratio, shedding in the near wake was found to be more uniform (lesser variation in shedding cycle timings). Another admissible shedding mechanism is newly identified to operate in the near wake of oscillating cylinders now being called as the ‘passive shedding’ mechanism. Results indicate that increasing the corner radius suppresses the possible instabilities of the cylinder.

A PIV study of the near wake flow features of a square cylinder: influence of corner radius

R. Ajith Kumar,손창현,B. H. Lakshmana Gowda 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2

In this study, the near wake characteristics of transversely oscillating square-section cylinders with different corner radii were investigatedusing the particle image velocimetry (PIV) technique in a water channel with turbulence intensity of 6.5%. Five models with r/B =0, 0.1, 0.2, 0.3, and 0.5, respectively (where r and B represent the corner radius and the characteristic dimension of the body, respectively),were studied, with the body oscillation limited to that under the lock-in condition. Corner radius was found to significantly influence thecharacteristics of the flow around the bodies, both under stationary and oscillating conditions. The results indicate that the Strouhal numberand vortex strength of the flow increase and decrease, respectively, with an increase in the r/B ratio. The spacing between two rows ofvortices (b) as well as that between consecutive vortices in a row (a) was also found to decrease with the increase in the corner radius. The b/a ratio was found to be nearly independent of the r/B ratio and body oscillation.

Effect of oxygen ambient on structural, optical and electrical properties of epitaxial Al-doped ZnO thin films on r-plane sapphire by pulsed laser deposition

Manoj Kumar,최세영,R.M. Mehra 한국물리학회 2009 Current Applied Physics Vol.9 No.4

Al-doped ZnO (ZnO:Al) thin films were grown epitaxially on r-plane sapphire substrate by pulsed laser deposition. Substrate temperature of 400 ℃ and pulsed repetition rate of 5 Hz was kept constant during the deposition. The effect of oxygen ambient pressure from 0.1 to 10 mTorr on structural, optical and electrical properties of the ZnO:Al films were investigated. The lowest resistivity was found to be 2.14 × 10-3 Ω-cm with a carrier concentration of 6.89 × 1019 cm-3 for the film deposited in 1 mTorr of oxygen pressure. ZnO:Al film revealed smoother surface obtained at oxygen ambient pressure of 1 mTorr. The epitaxial relationship between ZnO:Al films and r-plane sapphire was found to be (0001)ZnO // (0112)sapp and [1010]ZnO // [0111]sapp. Photoluminescence spectra of the film grown at the oxygen ambient pressure of 1 mTorr exhibited peak at 3.34 eV, without any deep level. Al-doped ZnO (ZnO:Al) thin films were grown epitaxially on r-plane sapphire substrate by pulsed laser deposition. Substrate temperature of 400 ℃ and pulsed repetition rate of 5 Hz was kept constant during the deposition. The effect of oxygen ambient pressure from 0.1 to 10 mTorr on structural, optical and electrical properties of the ZnO:Al films were investigated. The lowest resistivity was found to be 2.14 × 10-3 Ω-cm with a carrier concentration of 6.89 × 1019 cm-3 for the film deposited in 1 mTorr of oxygen pressure. ZnO:Al film revealed smoother surface obtained at oxygen ambient pressure of 1 mTorr. The epitaxial relationship between ZnO:Al films and r-plane sapphire was found to be (0001)ZnO // (0112)sapp and [1010]ZnO // [0111]sapp. Photoluminescence spectra of the film grown at the oxygen ambient pressure of 1 mTorr exhibited peak at 3.34 eV, without any deep level.

A note on vertex pair sum $k$-zero ring labeling

Antony Sanoj Jerome,K.R. Santhosh Kumar,T.J. Rajesh Kumar 한국전산응용수학회 2024 Journal of applied mathematics & informatics Vol.42 No.2

Let $G=(V,E)$ be a graph with $p$-vertices and $q$-edges and let $R^{\circ}$ be a finite zero ring of order $n$. An injective function $f:V(G)\to \{r_1,r_2,\ldots,r_k\}$, where $r_i\in R^\circ$ is called vertex pair sum $k$-zero ring labeling, if it is possible to label the vertices $x\in V$ with distinct labels from $R^{\circ}$ such that each edge $e=uv$ is labeled with $f(e=uv)=[f(u)+f(v)] \pmod n$ and the edge labels are distinct. A graph admits such labeling is called vertex pair sum $k$-zero ring graph. The minimum value of positive integer $k$ for a graph $G$ which admits a vertex pair sum $k$-zero ring labeling is called the vertex pair sum $k$-zero ring index denoted by $\psi_{pz}(G)$. In this paper, we defined the vertex pair sum $k$-zero ring labeling and applied to some graphs.

Role of p-NiO electron blocking layers in fabrication of (P-N):ZnO/Al:ZnO UV photodiodes

R. Amiruddin,M.C. Santhosh Kumar 한국물리학회 2016 Current Applied Physics Vol.16 No.9

We report the fabrication and characterization of ZnO-based UV photodiodes with p-NiO as an intermediate electron blocking layer (EBL). The n-ZnO and p-ZnO layers are deposited by automated spray pyrolysis technique and NiO layers by r.f.magnetron sputtering. For the realization of p-ZnO, dual acceptor method has been adopted by doping equimolar concentration of group-V elements P and N (0.75 at%) simultaneously in ZnO. The formation of p-type characteristics in ZnO is confirmed by Hall measurement and X-ray photoelectron spectroscopy (XPS) analysis. The n-ZnO is doped with Al (3 at%) in order to improve the electrical properties. The properties of sputtered NiO layers have been investigated under three different deposition temperatures of 300 C, 350 C and 400 C. By analyzing structural and electrical properties, it is revealed that NiO deposited at 350 C possess better crystallinity and electrical properties. The optimum p-ZnO and n-ZnO layers are stacked upon ITO substrates to form ZnO-based p-n junctions. The effect of addition of NiO as an electron blocking layer (EBL) between the p-n junctions is investigated by analyzing the current density-voltage (J-V) and UV photoresponse properties. The fabricated ZnO-based UV photodiodes with NiO EBL exhibits a high photoresponsivity (R) value of 5.53 A/ W with external quantum efficiency (EQE) value of 1.87 103%.

Electrochemical synthesis and surface protection of polypyrrole-CeO₂ nanocomposite coatings on AA2024 alloy

Kumar, A. Madhan,Babu, R. Suresh,Ramakrishna, Suresh,de Barros, Ana L.F. Elsevier 2017 Synthetic metals Vol.234 No.-

<P><B>Abstract</B></P> <P>A facile approach based on electrochemical polymerization was used to synthesize polypyrrole/CeO<SUB>2</SUB> (PPy/CeO<SUB>2</SUB>) nanocomposite on an AA2024 alloy surface. CeO<SUB>2</SUB> nanoparticles (NPs) embedded in the PPy matrix were observed using FESEM micrographs with EDX analysis. IR and UV–vis spectroscopy were used to characterize the synthesized PPy/CeO<SUB>2</SUB> nanocomposite. The Raman spectra reflected the interactions between the π-conjugated structure of PPy and CeO<SUB>2</SUB> NPs. TGA thermograms revealed improved thermal stability of the synthesized nanocomposite and were used to determine the amount of nano ceria incorporated in the PPy matrix. The electrochemical corrosion behavior of the coated alloys in 0.6M NaCl solution was examined through potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) measurements. From these electrochemical studies, a larger shift of E<SUB>corr</SUB> in the positive direction with a high amount of CeO<SUB>2</SUB> in the nanocomposite was obtained, as well as a maximum corrosion protection efficiency of 99.64% by incorporating 3% of CeO<SUB>2</SUB> NPs in the PPy coatings. EIS studies also confirmed the enhanced corrosion protection behavior of PPy/CeO<SUB>2</SUB> coatings with higher R<SUB>ct</SUB>, R<SUB>f</SUB> and lower CPE<SUB>dl</SUB> values compared to those of pure PPy coatings. The results showed that the PPy coatings with CeO<SUB>2</SUB> nanoparticles can be potential coating materials for the corrosion protection of AA2024 alloys substrates.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polypyrrole coatings with nanoceria were prepared through electrochemical route. </LI> <LI> Raman studies confirm the interaction between π-conjugated PPy & nano CeO<SUB>2</SUB>. </LI> <LI> TGA reveals improved thermal stability of the synthesized nanocomposite. </LI> <LI> Uniform distribution of nano CeO<SUB>2</SUB> was confirmed by EDX mapping analysis. </LI> <LI> Corrosion test confirms better surface protection of PPy/Ce than pure PPy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Use of DNA barcoding in wildlife forensics: a study of sambar deer (Rusa unicolor)

Suresh Kumar U,Sanil George,Ratheesh R.V,George Thomas 한국산림과학회 2012 Forest Science And Technology Vol.8 No.4

This paper reports a case in which a wildlife range officer had suspected that some people had killed a sambar deer (Rusa unicolor). Cooked meat and dried skin were seized from the suspects and forwarded to our laboratory for DNA testing to resolve the identity of the animal. Mitochondrial cytochrome C oxidase subunit 1 (CO1) analysis revealed that the cooked meat and skin of the animal were of a sambar deer by comparing the sequences with the reference sequence of R. unicolor generated in our laboratory. The study illuminates the use of barcode sequences and reference databases in wildlife forensic applications.

Biology of Anagyrus kamali (Moursi) (Hymenoptera : Encyrtidae) - A Parasitoid of the Mealybug, Maconellicoccus hirsutus (Green, with a Note on Its Incidence

Katiyar, R.L.,Kumar, Vineet,Manjunath, D.,Sen, A.K.,Shekhar, M.A.,Datta, R.K. Korean Society of Sericultural Science 2000 International Journal of Industrial Entomology Vol.1 No.2

The occurrence of Anagyrus kamali, a solitary endoparasite of the mealybug, Maconellicoccus hirsutus has been reported for the first time from India. The parasitoid was fecund to parasitizing the field population of mealybug to the tune of 10.37 to 42.70% in different months. A comprehensive study on the development of the parasitoid on different stages of mealybug indicated that the parasitoid was able to complete its development in all the stages. Higher parasitism (67.48-78.08%) and more female progeny were observed when 3rd instar nymphs and adult female of the mealybug were exposed to the parasitoid. The biology of A. kamali studied at 25${\pm}1^{\circ}C$ temperature and 60${\pm}$</TEX10% R.H. The parasitoid completes its life cycle in 19.72$\pm$1.12 days. The duration of egg, larva (3 instars) and pupa were 2.67${\pm}$</TEX0.42, 8.80${\pm}$</TEX0.43 and 8.25${\pm}$</TEX0.38 days, respectively. On an average each female of A. kamali laid 39.0${\pm}$</TEX4.53 eggs. It was found to parasitising 8-10 mealybugs and depositing 1-3 eggs per host individual. Observations on adult longevity, parasitizing potential and sex ratio has also been recorded.

Investigation on the Effect of Asymmetric Cyclic Loading on Ratcheting Deformation and Bulk Texture Development in HSLA Steel

Pushpendra Kumar Dwivedi,R. Vinjamuri,S. K. Sahoo,Krishna Dutta 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.8

Ratcheting deformation in association with bulk texture evolution in HSLA steel is studied in this investigation. The cyclicdeformation behaviors and damage modes of the specimens are obtained at room temperature, employing asymmetric stresscontrolledtests under various combinations of mean stress and stress amplitudes. Bulk texture measurements of the specimensare done adopting an X-ray diffraction analysis. The results exhibit an increase in strain accumulation from 0.23 to 30.61%associated with a sharp reduction in ratcheting life from 3320 to 880 cycles by the increment in mean stress/stress amplitude. A continuous cyclic softening until the final failure is observed for all the ratcheting tests. It is noticed that variation of meanstress is more detrimental than stress amplitude in controlling strain accumulation while the effect of stress amplitude is morepronounced than mean stress for the reduction of ratcheting life. The fracture surface morphology indicates typical striationformation in the crack propagation region along with overload failure. The bulk texture studies indicate that there is a transitionbetween ‘ϒ’ fiber and ‘ζ’ fiber during all loading conditions. The texture intensity is increased from 5.71 to 11.68 withprogressive ratcheting strain accumulation. Here also, influence of stress amplitude is more significant than the mean stress.