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Search Results: 1 - 10 of 461343 matches for " A. Chainani "
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CFD Investigation of Airflow on a Model Radio Control Race Car
Chainani. A,Perera. N
Lecture Notes in Engineering and Computer Science , 2008,
Frustration effects and role of selective exchange coupling for magnetic ordering in the Cairo pentagonal lattice
A. Chainani,K. Sheshadri
Physics , 2014,
Abstract: The Cairo pentagonal lattice, consisting of an irregular pentagonal tiling of magnetic ions on two inequivalent sites (3- and 4-co-ordinated ones), represents a fascinating example for studying geometric frustration effects in two-dimensions. In this work, we investigate the spin $S$ = $1/2$ Cairo pentagonal lattice with respect to selective exchange coupling (which effectively corresponds to a virtual doping of $x$ = $0, 1/6, 1/3$), in a nearest-neighbour antiferromagnetic Ising model. We also develop a simple method to quantify geometric frustration in terms of a frustration index $\phi(\beta,T)$, where $\beta$ = $J/\tilde{J}$, the ratio of the two exchange couplings required by the symmetry of the Cairo lattice. At $T = 0$, the undoped Cairo pentagonal lattice shows antiferromagnetic ordering for $\beta \le \beta_{crit} = 2$, but undergoes a first-order transition to a ferrimagnetic phase for $\beta >$ $\beta_{crit}$. The results show that $\phi(\beta,T = 0)$ tracks the transition in the form of a cusp maximum at $\beta_{crit}$. While both phases show frustration, the obtained magnetic structures reveal that the frustration originates in different bonds for the two phases. The frustration and ferrimagnetic order get quenched by selective exchange coupling, and lead to robust antiferromagnetic ordering for $x$ = 1/6 and 1/3. From mean-field calculations, we determine the temperature-dependent sub-lattice magnetizations for $x$ = $0, 1/6$ and $1/3$. The calculated results are discussed in relation to known experimental results for trivalent Bi$_2$Fe$_4$O$_9$ and mixed valent BiFe$_2$O$_{4.63}$. The study identifies the role of frustration effects, the ratio $\beta$ and selective exchange coupling for stabilizing ferrimagnetic versus anti-ferromagnetic order in the Cairo pentagonal lattice.
Suppression of Magnetic Frustration by Doping in a nearest-neighbour anti-ferromagnetic triangular lattice
K. Sheshadri,A. Chainani
Physics , 2005,
Abstract: Based on experimental observations in A{x}MO{2} (A = Na, Li; M = Co, Ni), a model for suppression of magnetic frustration by electron doping in a nearest-neighbour antiferromagnetic triangular lattice is presented. It is found that frustration can be quantified, as determined by geometry and bond-counting, and its magnitude is a non-monotonic function of $x$. A mean-field calculation provides temperature-dependent magnetization, spin-entropy and heat capacity. Low-doping (x = 0.25, 0.33) results in a highly frustrated regime. A{0.5}MO{2} has strongest order and no frustration, while high doping (x = 0.67, 0.75) leads to low frustration and higher spin-entropy. The results agree with experiments including neutron scattering, spin entropy-driven thermoelectricity and ion ordering.
Analysis and Intervention of Severe Acute Malnutrition in Children at an Urban Public School in Mumbai, India  [PDF]
Esha Chainani
Open Journal of Preventive Medicine (OJPM) , 2018, DOI: 10.4236/ojpm.2018.84013
Abstract: Background: There is a dearth of information regarding trends of malnutrition and weight status in children from rapidly developing economies like India. Objectives: The aim of this study is to analyze the dynamics of malnutrition in a group of school children from India, and then provide interventions for the children that have severe acute malnutrition. Methods: Children that were found to lie between 3 to 4 SD of parameters of BMI, height for age and weight for age were labeled as SAM. Children that were screened for wasting and fell between 2 to 4 SD were also included under the label of SAM. All participants were also given a prototype 1500-calorie diet to follow for the entire duration and 6 weekly sessions were taken for the parents on various topics on nutrition. Results: Quantitative analysis showed a great improvement in weights and heights of severely malnourished children. The average increase in weight of all children that participated in the study was 9.09% and the average increase in height was 1.39%. The weekly sessions given to the parents on various nutrition topics could be the cause of high compliance to the diet given to the children. Conclusion: Malnutrition is still a very big problem in developing countries like India. Basic interventions like an improvement in diet, education about micronutrients and balanced diet, and food-based interventions in severe malnutrition can lead to a great improvement in the health and development status of children.
Role of CDW fluctuations on the spectral function in a metallic CDW system
T. Yokoya,T. Kiss,A. Chainani,S. Shin,K. Yamaya
Physics , 2005,
Abstract: Angle-resolved photoemission spectroscopy of ZrTe3 has been performed from room temperature(T) down to 6 K (across Tcdw = 63K) to study the charge-density-wave (CDW) fluctuation effects in a metallic CDW compound having Fermi surface (FS) sheets with differing dimensionality. While spectra on the 3-dimensional(D) FS show typical Fermi-Dirac function-like T-dependence, those along the quasi 1-D FS show formation of a pseudogap, starting at a much higher T than Tcdw. Simultaneously, a van-Hove singularity consisting of the quasi 1D FS intersecting the 3D FS shows increase of coherence. This demonstrates the role of CDW fluctuations on the spectral function, and relation to the dimensionality of the states, in a metallic CDW system.
Evidence for mass renormalization in LaNiO$"" sub 3_: an in situ soft x-ray photoemission study of epitaxial films
K. Horiba,R. Eguchi,M. Taguchi,A. Chainani,A. Kikkawa,Y. Senba,H. Ohashi,S. Shin
Physics , 2006, DOI: 10.1103/PhysRevB.76.155104
Abstract: We investigate the electronic structure of high-quality single-crystal LaNiO$_3$ (LNO) thin films using in situ photoemission spectroscopy (PES). The in situ high-resolution soft x-ray PES measurements on epitaxial thin films reveal the intrinsic electronic structure of LNO. We find a new sharp feature in the PES spectra crossing the Fermi level, which is derived from the correlated Ni 3$d$ $e_g$ electrons. This feature shows significant enhancement of spectral weight with decreasing temperature. From a detailed analysis of resistivity data, the enhancement of spectral weight is attributed to increasing electron correlations due to antiferromagnetic fluctuations.
Kondo Resonance in PrTi2Al20: Photoemission spectroscopy and single-impurity Anderson model
M. Matsunami,M. Taguchi,A. Chainani,R. Eguchi,M. Oura,A. Sakai,S. Nakatsuji,S. Shin
Physics , 2011, DOI: 10.1103/PhysRevB.84.193101
Abstract: The Kondo resonance at the Fermi level is well-established for the electronic structure of Ce (f1 electron) and Yb (f1 hole) based systems. In this work, we report complementary experimental and theoretical studies on the Kondo resonance in Pr-based f2 system, PrTi2Al20. Using Pr 3d-4f resonant photoemission spectroscopy and single impurity Anderson model (SIAM) calculations including the full multiplets of Pr ions, we show that an f2 system can also give rise to a Kondo resonance at the Fermi level. The Kondo resonance peak is experimentally observed through a final-state-multiplet dependent resonance and is reproduced with properly tuned hybridization strength in SIAM calculations.
Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films
J. Miyawaki,A. Chainani,Y. Takata,M. Mulazzi,M. Oura,Y. Senba,H. Ohashi,S. Shin
Physics , 2009, DOI: 10.1103/PhysRevLett.104.066407
Abstract: Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane and out-of-plane Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films using energy dependent soft x-ray momentum-resolved photoemission spectroscopy. We show that the SS originates in nested regions confined to out-of-plane FSs, which are drastically modified compared to in-plane FSs. From precise reciprocal space maps in successive zones, we obtain the associated real space compressive strain of 1.5+-0.5% along c-axis. An autocorrelation analysis quantifies the incommensurate ordering vector q=(2pi/a)(0,0,~0.86), favoring a SS and consistent with magneto-optic Kerr effect experiments. The results reveal the importance of in-plane and out-of-plane FS mapping for ultrathin films.
Temperature dependent Luttinger surfaces
T. Ito,A. Chainani,T. Haruna,K. Kanai,T. Yokoya,S. Shin,R. Kato
Physics , 2005, DOI: 10.1103/PhysRevLett.95.246402
Abstract: The Luttinger surface of an organic metal (TTF-TCNQ), possessing charge order and spin-charge separation, is investigated using temperature dependent angle-resolved photoemission spectroscopy. The Luttinger surface topology, obtained from momentum distribution curves, changes from quasi-2D(dimensional) to quasi-1D with temperature. The high temperature quasi-2D surface exhibits 4$k_F$ charge-density-wave (CDW) superstructure in the TCNQ derived holon band, in the absence of 2$k_F$ order. Decreasing temperature results in quasi-1D nested 2$k_F$ CDW order in the TCNQ spinon band and in the TTF surface. The results establish the link in momentum-space between charge order and spin-charge separation in a Luttinger liquid.
Layer dependent band dispersion and correlations using tunable Soft X-ray ARPES
N. Kamakura,Y. Takata,T. Tokushima,Y. Harada,A. Chainani,K. Kobayashi,S. Shin
Physics , 2003, DOI: 10.1209/epl/i2004-10052-6
Abstract: Soft X-ray Angle-Resolved Photoemission Spectroscopy is applied to study in-plane band dispersions of Nickel as a function of probing depth. Photon energies between 190 and 780 eV were used to effectively probe up to 3-7 layers. The results show layer dependent band dispersion of the Delta_2 minority-spin band which crosses the Fermi level in 3 or more layers, in contrast to known top 1-2 layers dispersion obtained using ultra-violet rays. The layer dependence corresponds to an increased value of exchange splitting and suggests reduced correlation effects in the bulk compared to the surface.
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