Holographic c-theorems in arbitrary dimensions

We re-examine holographic versions of the c-theorem and entanglement entropy in the context of higher curvature gravity and the AdS/CFT correspondence. We select the gravity theories by tuning the gravitational couplings to eliminate non-unitary operators in the boundary theory and demonstrate that all of these theories obey a holographic c-theorem. In cases where the dual CFT is even-dimensional, we show that the quantity that flow is the central charge associated with the A-type trace anomaly. Here, unlike in conventional holographic constructions with Einstein gravity, we are able to distinguish this quantity from other central charges or the leading coefficient in the entropy density of a thermal bath. In general, we are also able to identify this quantity with the coefficient of a universal contribution to the entanglement entropy in a particular construction. Our results suggest that these coefficients appearing in entanglement entropy play the role of central charges in odd-dimensional CFT's. We conjecture a new c-theorem on the space of odd-dimensional field theories, which extends Cardy's proposal for even dimensions. Beyond holography, we were able to show that for any even-dimensional CFT, the universal coefficient appearing the entanglement entropy which we calculate is precisely the A-type central charge.

Characterization and Acceptor Preference of a Soluble Meningococcal Group C Polysialyltransferase

Vaccines against Neisseria meningitidis group C are based on its alpha-2,9-linked polysialic acid capsular polysaccharide. This polysialic acid expressed on the surface of N. meningitidis and in the absence of specific antibody serves to evade host defense mechanisms. The polysialyltransferase (PST) that forms the group C polysialic acid (NmC PST) is located in the cytoplasmic membrane. Until recently, detailed characterization of bacterial polysialyltransferases has been hampered by a lack of availability of soluble enzyme preparations. We have constructed chimeras of the group C polysialyltransferase that catalyzes the formation alpha-2,9-polysialic acid as a soluble enzyme. We used site-directed mutagenesis to determine the region of the enzyme necessary for synthesis of the alpha-2,9 linkage. A chimera of NmB and NmC PSTs containing only amino acids 1 to 107 of the NmB polysialyltransferase catalyzed the synthesis of alpha-2,8-polysialic acid. The NmC polysialyltransferase requires an exogenous acceptor for catalytic activity. While it requires a minimum of a disialylated oligosaccharide to catalyze transfer, it can form high-molecular-weight alpha-2,9-polysialic acid in a nonprocessive fashion when initiated with an alpha-2,8-polysialic acid acceptor. De novo synthesis in vivo requires an endogenous acceptor. We attempted to reconstitute de novo activity of the soluble group C polysialyltransferase with membrane components. We found that an acapsular mutant with a defect in the polysialyltransferase produces outer membrane vesicles containing an acceptor for the alpha-2,9-polysialyltransferase. This acceptor is an amphipathic molecule and can be elongated to produce polysialic acid that is reactive with group C-specific antibody.

Preparation, Structural, and Electrical Studies of Polyaniline/ZnFe2O4 Nanocomposites

Polyaniline/ZnFe2O4 nanocomposites were synthesized by a simple and inexpensive one-step in situ polymerization method in the presence of ZnFe2O4 nanoparticles. The structural, morphological, and electrical properties of the samples were characterized by wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). WAXD and SEM revealed the formation of polyaniline/ZnFe2O4 nanocomposites. Infrared spectroscopy indicated that there was some interaction between the ZnFe2O4 nanoparticles and polyaniline. The dc electrical conductivity measurements were carried in the temperature range of 80 to 300 K. With increase in the doping concentration of ZnFe2O4, the conductivity of the nanocomposites found to be decreasing from 5.15 to 0.92 Scm(-1) and the temperature dependent resistivity follows ln rho(T) similar to T-1/2 behavior. The nanocomposites (80 wt % of ZnFe2O4) show a more negative magnetoresistance compared with that of pure polyaniline (PANI). These results suggest that the interaction between the polymer matrix PANI and zinc nanoparticles take place in these nanocomposites. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2856-2862, 2011

Investigation on the Magnetic Anomaly and the Role of Orbital Moment on the Magnetic Properties of LaMn0.5Co0.5O3

Two distinct ferromagnetic phases are present in LaMn0.5Co0.5O3 for which the spin-only magnetic moment calculated from the high temperature dc susceptibility is found to be unusually high. Such a high moment can only be accounted for by assigning the valence state of the cations to Mn2+-Co4+. This is unrealistic as the earlier report based on X-ray absorption spectroscopy (XAS) has suggested the valence state to be mainly Mn4+-Co2+ with traces of Co3+. Also from our studies using XAS, it is found that the valence state is mainly Mn4+-Co2+. In addition, no notable difference is observed in the minor Co3+ present in both phases. Our results based on X-ray magnetic circular dichroism studies (XMCD) reveal the presence of ``distinct'' high orbital moment associated with Co2+ for both phases. Thus it is found that the distinctness of the orbital moment also plays a vital role in determining the magnetic moment and T-c of both phases of LaMn0.5Co0.5O3. By considering the orbital moment obtained from XMCD, the anomaly in the paramagnetic susceptibility is resolved and thus we are able to assign the valence state to Mn4+-Co2+ configuration. The difference in the magnitude of orbital moment in both phases is believed to be due to the crystal field effects.

Five-level inverter scheme for an open-end winding induction machine with less number of switches

Higher level of inversion is achieved with a less number of switches in the proposed scheme. The scheme proposes a five-level inverter for an open-end winding induction motor which uses only two DC-link rectifiers of voltage rating of Vdc/4, a neutral-point clamped (NPC) three-level inverter and a two-level inverter. Even though the two-level inverter is connected to the high-voltage side, it is always in square-wave operation. Since the two-level inverter is not switching in a pulse width modulated fashion and the magnitude of switching transient is only half compared to the convention three-level NPC inverter, the switching losses and electromagnetic interference is not so high. The scheme is experimentally verified on a 2.5 kW induction machine.

Substrate-dependent structure, microstructure, composition and properties of nanostructured TiN films

Titanium nitride films of a thickness of similar to 1.5 mu m were deposited on amorphous and crystalline substrates by DC reactive magnetron sputtering at ambient temperature with 100% nitrogen in the sputter gas. The growth of nanostructured, i.e. crystalline nano-grain sized, films at ambient temperature is demonstrated. The microstructure of the films grown on crystalline substrates reveals a larger grain size/crystallite size than that of the films deposited on amorphous substrates. Specular reflectance measurements on films deposited on different substrates indicate that the position of the Ti-N 2s band at 2.33 eV is substrate-dependent, indicating substrate-mediated stoichiometry. This clearly demonstrates that not only structure and microstructure, but also chemical composition of the films is substrate-influenced. The films deposited on amorphous substrates display lower hardness and modulus values than the films deposited on crystalline substrates, with the highest value of hardness being 19 GPa on a lanthanum aluminate substrate. (C) 2011 Elsevier Ltd. All rights reserved.

Electrical transport properties of 0.5Li(2)O-0.5M(2)O-2B(2)O(3) (M = Li, Na and K) glasses

Transparent glasses in the system 0.5Li(2)O-0.5M(2)O-2B(2)O(3) (M = Li, Na and K) were fabricated via the conventional melt quenching technique. The amorphous and glassy nature of the samples was confirmed via the X-ray powder diffraction and the differential scanning calorimetry, respectively. The frequency and temperature dependent characteristics of the dielectric relaxation and the electrical conductivity were investigated in the 100 Hz-10 MHz frequency range. The imaginary part of the electric modulus spectra was modeled using an approximate solution of Kohrausch-Williams-Watts relation. The stretching exponent, (3, was found to be temperature independent for 0.5Li(2)O-0.5Na(2)O-2B(2)O(3) (LNBO) glasses. The activation energy associated with DC conduction was found to be higher (1.25 eV) for 0.5Li(2)O-0.5K(2)O-2B(2)O(3) (LKBO) glasses than that of the other glass systems under study. This is attributed to the mixed cation effect. (C) 2011 Elsevier By. All rights reserved.

Study of electrical properties of pulsed excimer laser deposited strontium titanate films

Polycrystalline SrTiO3 films were prepared by pulsed excimer laser ablation on Si and Pt coated Si substrates. Several growth parameters were varied including ablation fluence, pressure, and substrate temperature. The structural studies indicated the presence of [100] and [110] oriented growth after annealing by rapid thermal annealing at 600-degrees-C for 60 s. Deposition at either lower pressures or at higher energy densities encouraged film growth with slightly preferred orientation. The scanning electron microscopy studies showed the absence of any significant particulates on the film surface. Dielectric studies indicated a dielectric constant of 225, a capacitance density of 3.2 fF/mum2, and a charge density of 40 fC/mum for films of 1000 nm thick. The dc conductivity studies on these films suggested a bulk limited space charge conduction in the high field regime, while the low electric fields induced an ohmic conduction. Brief time dependent dielectric breakdown studies on these films, under a field of 250 kV/cm for 2 h, did not exhibit any breakdown, indicating good dielectric strength.

Origin of magnetism and trend in T-c in Cr-based double perovskites: Interplay of two driving mechanisms

Hamiltonian constructed in a first principles manner, we explored the origin of magnetism and the T-c trend in Cr-based double perovskite series, Sr2CrB'O-6 (B' = W/Re/Os). Our study shows that the apparently puzzling T-c trend in Sr2CrB'O-6 (B' = W/Re/Os) series can be understood in terms of the interplay of the hybridization driven mechanism and the superexchange mechanism.

Diurnal variation of atmospheric CO2 concentration and delta C-13 in an urban atmosphere during winter-role of the Nocturnal Boundary Layer

The paper presents the importance of the Nocturnal Boundary Layer in driving the diurnal variability of the atmospheric CO2 mixing ratio and the carbon isotope ratio at ground level from an urban station in India. Our observations are the first of their kind from this region. The atmospheric CO2 mixing ratio and the carbon isotopic ratio were measured for both the morning (05:30-07:30 IST) and afternoon time (16:00-18:00 IST) air samples at 5 m above ground level in Bangalore city, Karnataka State (12 degrees 58' N, 77 degrees 38' E, masl = 920 m) for a 10 day period during the winter of 2008. We observed a change of similar to 7% the in CO2 mixing ratio between the morning and afternoon time air samples. A stable isotope analysis of CO2 from morning samples showed a depletion in the carbon isotope ratio by similar to 2 parts per thousand compared to the afternoon samples. Along with the ground-based measurement of air samples, data of radiosonde measurements were also obtained from the Indian Meteorological Department to identify the vertical atmospheric structure at different time in a day. We proposed the presence or absence of the NBL as a controlling factor for the observed variability in the mixing ratio as well as its isotopic composition. Here we used the Keeling model approach to find out the carbon isotope ratio for the local sources. The local sources have further been characterized as anthropogenic and biological respiration (in %) using a two-component mixing model. We also used a vertical mixing model based on the concept of the mixing of isotopically depleted (carbon isotope) ``polluted air'' (PA) with isotopically enriched ``free atmospheric air'' (FA) above. Using this modeling approach, the contribution of FA at ground level is being estimated for both the morning and afternoon time air samples.

C-13 MAS NMR spectra of cis,cis-mucononitrile in liquid-crystalline media and in the solid state. Orientation of the carbon chemical-shift tensors

The spinning sidebands observed in the C-13 MAS NMR spectra of cis,cis-mucononitrile oriented in liquid-crystalline media and of the neat sample in the solid state are studied. There are differences in the sideband intensity patterns in the two cases. These differences arise because the order parameters which characterize the orientation of the solute in the liquid-crystalline media differ for different axes. It is shown that, in general, the relative intensities of the sidebands contain information on the sign and magnitude of an effective chemical-shift parameter which is a function of the sum of the products of the principal components of the chemical-shift tensor and the corresponding order parameters with respect to the director. A method for obtaining the orientation of the carbon chemical-shift tensor is proposed. The carbon chemical-shift tensors obtained from gauge-including atomic orbital calculations are also presented for comparison. (C) 1996 Academic Press, Inc.

Correlated electronic states of C-60 fragments

We have studied electronic states of various fragments of C-60 within the Pariser-Parr-Pople (PPP) model and have obtained structural, magnetic and spectral properties of these molecules. The fragments studied include corannulene, fluoranthene and pyracylene. Pyracylene is studied using the exact valence bond (VB) approach while fluoranthene and corannulene are studied using a novel restricted CI technique which employs molecular orbitals for constructing the VB functions. The electronic excitations, bond order and ring currents are calculated for these systems. From these studies, the wide range of absorptions in C-60 can be viewed as those localized on pyracylene units or on the corannulene/fluoranthene units. The bond orders and ring currents show the hexagons to be similar to benzene rings. The pentagon-hexagon bonds are also found to be longer than the hexagon-hexagon bonds.

Investigations Of Iron Adducts Of C-60 - Novel Fec60 In The Solid-State With Fe Inside The C-60 Cage

By carrying out contact-arc vaporization of graphite in a partial atmosphere of Fe(CO)5, an iron-adduct with C60 has been obtained. The adduct has been characterized by various techniques including mass spectrometry, Fe-57 Mossbauer spectroscopy and Fe K-EXAFS. Properties of this adduct are compared with those of an adduct prepared by solution method where Fe is clearly outside the cage. Results suggest that FeC60 obtained from the gas phase reaction has the Fe atom in the cage.