11 research outputs found
Magnetoelectric CoV2O6—Role of Fe inter-play in Co-based Ising spin chain interactions
No full textCoV2O6, a Brannerite-type material, exists in both monoclinic (α) and triclinic (γ) forms. α- CoV2O6 exhibits quasi-1D ferromagnetic chains of octahedrally-coordinated Co2+ions in the higher spin state. Fe2+ doped α-CoV2O6 (3 mol%) single crystals were synthesized using high temperature melt method. The motivation is to investigate whether disruption of 1D Co2+ ferromagnetic chains by small Fe3+ substitution alters the antiferromagnetic ground state and lead to stronger spin-frustration. In this paper, we report the magnetic and magnetodielectric properties of Fe doped α-CoV2O6 in detail. The strongly anisotropic nature of magnetic and magnetodielectric characteristics were captured well in the data through orientation dependent measurements with H being parallel to a and c axes of the crystal. Relative dielectric permittivity (εr) exhibited sharp peaks coinciding with the plateau edges Hc1 ∼2.2 T and Hc2 ∼4.4 T in the magnetization curves (M-H) for applied H parallel to a-axis. For dielectric measurements under applied H parallel to c-axis, relative dielectric permittivity exhibited sharp peak around Hc2 ∼3.1 T, again coinciding with the M-H behavior. Such closely related magnetic field induced dielectric transitions reflected in both M(H) and εr(H) measurements is a rare phenomenon and representative of strong spin-lattice coupling in this phase
Synthesis, crystal structure and electronic properties of the new iron selenide Ba9Fe4Se16
No full textInternational audienceThe new ternary selenide Ba9Fe4Se16 has been synthesized from the reaction of appropriate amounts of elements at high temperature in a silica sealed tube. The compound crystallizes in the tetragonal space group I41/a with a=10.0068(3) Å and c=35.6415(9) Å, Z=4. It is an isostructural compound to the sulfide α-Ba9Fe4S15, which is a high temperature polymorph of β-Ba9Fe4Se15 that belongs to the indefinitely adaptive phases series Ba3Fe1+xS5, 0≤x≤1. X-ray powder diffraction and TEM analyses of the synthesized compound were used to determine the phase composition and the structure. The crystal structure can be viewed as overlapping sections along the c axis. Those sections are formed by the coordination polyhedra around barium atoms which can be described as trigonal prisms and bidisphenoids. Within the sections formed by barium polyhedra, isolated pairs of edge sharing FeSe4 tetrahedra are found. Magnetic measurements performed on Ba9Fe4Se16 indicate an antiferromagnetic behavior with Néel temperature of ~13 K. Possible influence of air exposure on the magnetic properties is also discussed here. The electric measurements show an insulating behavior below 160 K and the dielectric permittivity and loss tangent at the lowest frequency measured reveal a change of slope very close to TN. However no magneto dielectric effect was evidenced for magnetic fields of up to 3 T. Activation energy, EA=0.18 eV, was extracted from the AC conductivity plot in the temperature range of 160–300 K
Synthesis dependent characteristics of Sr1-xMnxTiO3 (x=0.03, 0.05, 0.07 and 0.09)
No full textSr1-xMnxTiO3 (where x=0.03, 0.05, 0.07 and 0.09) was synthesized via different routes that include solid-state, oxalate precipitation and freeze drying. In oxalate precipitation technique, compositions corresponding to 3 and 5 mol% doping of Mn were monophasic whereas the higher compositions revealed the presence of the secondary phases such as MnO, Mn3O4 etc., as confirmed by high resolution X-ray diffraction (XRD) studies. The decomposition behavior of the precursors prepared using oxalate precipitation method corresponding to the above mentioned compositions was studied. Nanopowders of compositions pertaining to 5 to 9 mol% of Mn doping were obtained using freeze-drying technique. The average crystallite size of these nanopowders was found to be in the 35 to 65 nm range. The microstructural studies carried out on the sintered ceramics, fabricated using powders synthesized by different routes established the fine grained nature ( < 1 mu m) of the one obtained by freeze drying method. Raman scattering studies were carried out in order to complement the observations made from XRD regarding the phase purity. The dielectric properties of the ceramics obtained by different synthesis routes were studied in the 80-300 K temperature range at 100 kHz and the effect of grain size has been discussed. (C) 2012 Elsevier Inc. All rights reserved
Multi-jet propulsion organized by clonal development in a colonial siphonophore
Get PDF© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 6 (2015): 8158, doi:10.1038/ncomms9158.Physonect siphonophores are colonial cnidarians that are pervasive predators in many neritic and oceanic ecosystems. Physonects employ multiple, clonal medusan individuals, termed nectophores, to propel an aggregate colony. Here we show that developmental differences between clonal nectophores of the physonect Nanomia bijuga produce a division of labour in thrust and torque production that controls direction and magnitude of whole-colony swimming. Although smaller and less powerful, the position of young nectophores near the apex of the nectosome allows them to dominate torque production for turning, whereas older, larger and more powerful individuals near the base of the nectosome contribute predominantly to forward thrust production. The patterns we describe offer insight into the biomechanical success of an ecologically important and widespread colonial animal group, but, more broadly, provide basic physical understanding of a natural solution to multi-engine organization that may contribute to the expanding field of underwater-distributed propulsion vehicle design.This work is a product of US National Science Foundation grant OCE-1155084 to K.R.S. and CBET-1511721 to J.H.C., OCE-1061182 to S.P.C. and OCE-1061628 to J.O.D
A ctenophore (comb jelly) employs vortex rebound dynamics and outperforms other gelatinous swimmers
Get PDF© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gemmell, B. J., Colin, S. P., Costello, J. H., & Sutherland, K. R. (2019). A ctenophore (comb jelly) employs vortex rebound dynamics and outperforms other gelatinous swimmers. Royal Society Open Science, 6(3), (2019):181615, doi:10.1098/rsos.181615.Gelatinous zooplankton exhibit a wide range of propulsive swimming modes. One of the most energetically efficient is the rowing behaviour exhibited by many species of schyphomedusae, which employ vortex interactions to achieve this result. Ctenophores (comb jellies) typically use a slow swimming, cilia-based mode of propulsion. However, species within the genus Ocyropsis have developed an additional propulsive strategy of rowing the lobes, which are normally used for feeding, in order to rapidly escape from predators. In this study, we used high-speed digital particle image velocimetry to examine the kinematics and fluid dynamics of this rarely studied propulsive mechanism. This mechanism allows Ocyropsis to achieve size-adjusted speeds that are nearly double those of other large gelatinous swimmers. The investigation of the fluid dynamic basis of this escape mode reveals novel vortex interactions that have not previously been described for other biological propulsion systems. The arrangement of vortices during escape swimming produces a similar configuration and impact as that of the well-studied ‘vortex rebound’ phenomenon which occurs when a vortex ring approaches a solid wall. These results extend our understanding of how animals use vortex–vortex interactions and provide important insights that can inform the bioinspired engineering of propulsion systems.This research was supported by the grants from the National Science Foundation UNS-1511996 and IDBR-1455471 to B.J.G., S.P.C. and J.H.C. as well as OCE-1829945 to B.J.G., S.P.C., J.H.C. and K.R.S
Maneuvering performance in the colonial siphonophore, Nanomia bijuga
Get PDF© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sutherland, K. R., Gemmell, B. J., Colin, S. P., & Costello, J. H. Maneuvering performance in the colonial siphonophore, Nanomia bijuga. Biomimetics, 4(3), (2019): 62, doi:10.3390/biomimetics4030062.The colonial cnidarian, Nanomia bijuga, is highly proficient at moving in three-dimensional space through forward swimming, reverse swimming and turning. We used high speed videography, particle tracking, and particle image velocimetry (PIV) with frame rates up to 6400 s−1 to study the kinematics and fluid mechanics of N. bijuga during turning and reversing. N. bijuga achieved turns with high maneuverability (mean length–specific turning radius, R/L = 0.15 ± 0.10) and agility (mean angular velocity, ω = 104 ± 41 deg. s−1). The maximum angular velocity of N. bijuga, 215 deg. s−1, exceeded that of many vertebrates with more complex body forms and neurocircuitry. Through the combination of rapid nectophore contraction and velum modulation, N. bijuga generated high speed, narrow jets (maximum = 1063 ± 176 mm s−1; 295 nectophore lengths s−1) and thrust vectoring, which enabled high speed reverse swimming (maximum = 134 ± 28 mm s−1; 37 nectophore lengths s−1) that matched previously reported forward swimming speeds. A 1:1 ratio of forward to reverse swimming speed has not been recorded in other swimming organisms. Taken together, the colonial architecture, simple neurocircuitry, and tightly controlled pulsed jets by N. bijuga allow for a diverse repertoire of movements. Considering the further advantages of scalability and redundancy in colonies, N. bijuga is a model system for informing underwater propulsion and navigation of complex environments.This research was funded by the National Science Foundation (NSF) 1829932 and 173764 to K.R.S., NSF 1830015, 1536672, 1511721 to J.H.C., 1455440, 1536688, 1829913 to S.P.C., NSF 1511996 to B.J.G
A Critical Study of the Autobiographical Elements in the Fictional Works of R. K. Narayan
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Existence Criteria and Expressions of the (b, c)-Inverse in Rings and Their Applications
Get PDF[EN] Let R be a ring. Existence criteria for the (b, c)-inverse are given. We present explicit expressions for the (b, c)-inverse by using inner
inverses. We answer the question when the (b, c)-inverse of a ¿ R is an inner inverse of a. As applications, we give a unified theory of some well-known results of the {1, 3}-inverse, the {1, 4}-inverse, the Moore¿Penrose inverse, the group inverse and the core inverse.The first author is grateful to the China Scholarship Council for giving him a scholarship for his further study in Universitat Politecnica de Valencia, Spain.Xu, S.; Benítez López, J. (2018). Existence Criteria and Expressions of the (b, c)-Inverse in Rings and Their Applications. Mediterranean Journal of Mathematics. 15(1). https://doi.org/10.1007/s00009-017-1056-xS151Baksalary, O.M., Trenkler, G.: Core inverse of matrices. Linear Multilinear Algebra 58, 681–697 (2010)Ben-Israel, A., Greville, T.N.E.: Generalized Inverses: Theory and Applications, 2nd edn. Springer, New York (2003)Benítez, J., Boasso, E., Jin, H.W.: On one-sided (B,C)-inverses of arbitrary matrices. Electron. J. Linear Algebra 32, 391–422 (2017). arXiv:1701.09054v1Boasso, E., Kantún-Montiel, G.: The (b,c)-inverses in rings and in the Banach context. Mediterr. J. Math. 14, 112 (2017). https://doi.org/10.1007/s00009-017-0910-1BhaskaraRao, K.R.S.: The Theory of Generalized Inverses over Commutative Rings. Taylor and Francis, London (2002)Campbell, S.L., Meyer, C.D.: Generalized Inverses of Linear Transformations. Pitman, London (1979)Drazin, M.P.: A class of outer generalized inverses. Linear Algebra Appl. 436, 1909–1923 (2012)Drazin, M.P.: Left and right generalized inverses. Linear Algebra Appl. 510, 64–78 (2016)Green, J.A.: On the structure of semigroups. Ann. Math. 54(1), 163–172 (1951)Hartwig, R.E.: Block generalized inverses. Arch. Ration. Mech. Anal. 61, 197–251 (1976)Han, R.Z., Chen, J.L.: Generalized inverses of matrices over rings. Chin. Q. J. Math. 7(4), 40–49 (1992)Ke, Y.Y., Cvetković-Ilić, D.S., Chen, J.L., Višnjić J.: New results on (b,c)-inverses. Linear Multilinear Algebra. https://doi.org/10.1080/03081087.2017.1301362Ke, Y.Y., Višnjić, J., Chen, J.L.: One-sided (b,c)-inverses in rings (2016). arXiv:1607.06230v1Mary, X.: On generalized inverse and Green’s relations. Linear Algebra Appl. 434, 1836–1844 (2011)Mary, X., Patrício, P.: Generalized inverses modulo H in semigroups and rings. Linear Multilinear Algebra 61(8), 1130–1135 (2013)von Neumann, J.: On regular rings. Proc. Natl. Acad. Sci. USA 22(12), 707–713 (1936)Rakić, D.S.: A note on Rao and Mitra’s constrained inverse and Drazin’s (b, c) inverse. Linear Algebra Appl. 523, 102–108 (2017)Rakić, D.S., Dinčić, N.Č., Djordjević, D.S.: Group, Moore–Penrose, core and dual core inverse in rings with involution. Linear Algebra Appl. 463, 115–133 (2014)Rao, C.R., Mitra, S.K.: Generalized inverse of a matrix and its application. In: Proceedings of the Sixth Berkeley Symposium on Mathematics, Statistics and Probability, vol. 1, pp. 601–620. University of California Press, Berkeley (1972)Wei, Y.M.: A characterization and representation of the generalized inverse AT,S(2) and its applications. Linear Algebra Appl. 280, 87–96 (1998)Wang, L., Chen, J.L., Castro-González, N.: Characterizations of the (b,c)-inverse in a ring (2015). arXiv:1507.01446v1Xu, S.Z., Chen, J.L., Zhang, X.X.: New characterizations for core inverses in rings with involution. Front. Math. China 12(1), 231–246 (2017
