Viability of Noether symmetry of F(R) theory of gravity

Canonization of F(R) theory of gravity to explore Noether symmetry is performed treating R - 6(\frac{\ddot a}{a} + \frac{\dot a^2}{a^2} + \frac{k}{a^2}) = 0 as a constraint of the theory in Robertson-Walker space-time, which implies that R is taken as an auxiliary variable. Although it yields correct field equations, Noether symmetry does not allow linear term in the action, and as such does not produce a viable cosmological model. Here, we show that this technique of exploring Noether symmetry does not allow even a non-linear form of F(R), if the configuration space is enlarged by including a scalar field in addition, or taking anisotropic models into account. Surprisingly enough, it does not reproduce the symmetry that already exists in the literature (A. K. Sanyal, B. Modak, C. Rubano and E. Piedipalumbo, Gen.Relativ.Grav.37, 407 (2005), arXiv:astro-ph/0310610) for scalar tensor theory of gravity in the presence of R^2 term. Thus, R can not be treated as an auxiliary variable and hence Noether symmetry of arbitrary form of F(R) theory of gravity remains obscure. However, there exists in general, a conserved current for F(R) theory of gravity in the presence of a non-minimally coupled scalar-tensor theory (A. K. Sanyal, Phys.Lett.B624, 81 (2005), arXiv:hep-th/0504021 and Mod.Phys.Lett.A25, 2667 (2010), arXiv:0910.2385 [astro-ph.CO]). Here, we briefly expatiate the non-Noether conserved current and cite an example to reveal its importance in finding cosmological solution for such an action, taking F(R) \propto R^{3/2}.Comment: 16 pages, 1 figure. appears in Int J Theoretical Phys (2012

Fluid-fluid phase separation in hard spheres with a bimodal size distribution

The effect of polydispersity on the phase behaviour of hard spheres is examined using a moment projection method. It is found that the Boublik-Mansoori-Carnahan-Starling-Leland equation of state shows a spinodal instability for a bimodal distribution if the large spheres are sufficiently polydisperse, and if there is sufficient disparity in mean size between the small and large spheres. The spinodal instability direction points to the appearance of a very dense phase of large spheres.Comment: 7 pages, 3 figures, moderately REVISED following referees' comments (original was 4 pages, 3 postscript figures

First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors

Employing first principles electronic structure calculations in conjunction with the frozen-magnon method we calculate exchange interactions, spin-wave dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin gapless semiconductor (SGS) compounds Mn$_2$CoAl, Ti$_2$MnAl, Cr$_2$ZnSi, Ti$_2$CoSi and Ti$_2$VAs. We find that their magnetic behavior is similar to the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice exchange interactions play an essential role in the formation of the magnetic ground state and in determining the Curie temperature, $T_\mathrm{c}$. All compounds, except Ti$_2$CoSi possess a ferrimagnetic ground state. Due to the finite energy gap in one spin channel, the exchange interactions decay sharply with the distance, and hence magnetism of these SGSs can be described considering only nearest and next-nearest neighbor exchange interactions. The calculated spin-wave dispersion curves are typical for ferrimagnets and ferromagnets. The spin-wave stiffness constants turn out to be larger than those of the elementary 3$d$-ferromagnets. Calculated exchange parameters are used as input to determine the temperature dependence of the magnetization and $T_\mathrm{c}$ of the SGSs. We find that the $T_\mathrm{c}$ of all compounds is much above the room temperature. The calculated magnetization curve for Mn$_2$CoAl as well as the Curie temperature are in very good agreement with available experimental data. The present study is expected to pave the way for a deeper understanding of the magnetic properties of the inverse-Heusler-based SGSs and enhance the interest in these materials for application in spintronic and magnetoelectronic devices.Comment: Accepted for publ;ication in Physical Review

Transient Monitoring Function based Fault Classifier for Relaying Applications

This paper proposes Transient monitoring function (TMF) based fault classification approach for transmission line protection. The classifier provides accurate results under various system conditions involving fault resistance, inception angle, location and load angle. The transient component during fault is measured by TMF and appropriate logics applied for fault classification. Simulation studies using MATLAB®/SIMULINK™ are carried out for a 400 kV, 50 Hz power system with variable system conditions. Results show that the proposed classifier has high classification accuracy. The method developed has been compared with a fault classification technique based on Discrete Wavelet Transform (DWT). The proposed technique can be implemented for real time protection schemes employing distance relaying

Enteropathogenicity of Plesiomonas Shigelloides

Plesiomonas Shigelloides has been implicated as an aetiological agent in sporadic cases and outbreaks of diarrhoea, and in food poisoning, in various parts of the world. (Schmid, Velaudapillai and Niles, 1954; Osada and Shibata, 1956; Vandepitte et al., 1957; Ueda, Yamasaki and Hori, 1963; Aldova, Rakovsky and Chovanova, 1966; Geizer, Kopecky and Aldova, 1966; Hori et al., 1966; Cooper and Brown, 1968; Pauova and Fukalova, 1968; von Graevenitz and Mensch, 1968; Winton, 1968; Sakazaki et al., 1971; Chatterjee and Neogy, 1972; Sanyal et al., 1972a and b; Zajc-Satler, Dragas and Kumelj, 1972; Bhat, Shantha Kumari and Rajan, 1974; Vandepitte, Makulu and Gatti, 1974; Sanyal, Singh and Sen, 1975; Jandl and Linke, 1976; Tsukamoto et al., 1978). P. shigelloides was isolated in pure culture from stools of patients with diarrhoea of otherwise unexplained origin, and more often from patients than from symptomless persons. Experimental evidence has not, however, been reported in support of its enteropathogenicity, except our preliminary communication on the activity of a few strains in the rabbit ileal-loop model (Saraswathi, Sharma and Sanyal, 1978). The present investigation was undertaken to examine its enterotoxicity and invasiveness

Structure, bonding and magnetism in cobalt clusters

The structural, electronic and magnetic properties of Co$_n$ clusters ($n=2-$20) have been investigated using density functional theory within the pseudopotential plane wave method. An unusual hexagonal growth pattern has been observed in the intermediate size range, $n=15-$20. The cobalt atoms are ferromagnetically ordered and the calculated magnetic moments are found to be higher than that of corresponding hcp bulk value, which are in good agreement with the recent Stern-Gerlach experiments. The average coordination number is found to dominate over the average bond length to determine the effective hybridization and consequently the cluster magnetic moment.Comment: 12 pages and 9 figure

Isotopic and sedimentological clues to productivity change in Late Riphean Sea: a case study from two intracratonic basins of India

Enriched13C/12C ratios with δ13C ~3‰ (w.r.t PDB) of two Late Riphean (~700-610 Ma) intracratonic carbonate successions viz., Bhander Limestone of Vindhyan Basin and Raipur Limestone of Chattisgarh Basin suggest higher organic productivity during this period. This view is supported by sedimentological evidence of higher biohermal growth and consequent increase in depositional relief in the low gradient ramp settings inferred for these basins. Oxygen isotope analysis of these carbonates show distinct segregation between enriched deeper water carbonate mudstone and depleted shallow water stromatolite facies that received fresh water influx. This shows that facies-specific analyses can be useful in understanding the depositional setting of these sediments

Enteropathogenicity of Aeromonas hydrophila and Plesiomonas shigelloides

Aeromonas hydrophila was enteropathogenic in ligated ileal loops of rabbits, causing a fluid accumulation of 14-2.0 ml per cm of gut length. Gut reaction could be produced with an inoculum as low as 104 viable bacteria. There was no difference in the nature of the positive reactions given by strains isolated from diarrhoea1 and non-diarrhoea1 children and adults and from water. Plesiomonas shigelloides, on the other hand, did not cause a significant gut reaction. A. hydrophila multiplied in the ileal loop by about 105 whereas P. shigelloides did so at only 102-3. These experiments on an animal model thus indicated the enteropathogenic nature of A. hydrophila, but no definite conclusion could be drawn from this study on P. shigelloides. We are grateful to Professor Hardas Singh, Head, Department of Microbiology, for his valuable suggestions and encouragement. We acknowledge with thanks the technical assistance of Mr Ram Achal Ram and Mr S. N. Pathak rendered during this study

Enterotoxigenicity of chicken isolates of Campylobacter jejuni in ligated ileal loops of rats

Ligated ileal loops in rats of the Charles-Foster strain, weighing 200-250 g and aged 7-8 months, provided a sensitive and reproducible means of testing the enterotoxigenicity of Campylobacter jejuni. All of 16 chicken isolates caused fluid accumulation comparable to that produced by toxigenic Vibrio cholerae O1, strain 569B. However, 11 of the isolates required one to three consecutive passages through the rat gut before doing so. The amount of fluid produced increased after each passage. Of three culture media tested, brucella broth of pH 6.7 supported the highest degree of enterotoxigenesis. Filtrates of cultures of all 16 chicken isolates in this medium were as effective as viable C. jejuni in producing fluid in ileal loops. The enterotoxin was neutralised completely by cholera antitoxin diluted 1 in 160, indicating its close immunobiological relationship to cholera toxin