Relaxor behaviour in BaBi4Ti4O15 ceramics fabricated using the powders obtained by mechanochemically assisted synthesis route

Mechanochemically activated reactants were found to facilitate the synthesis of fine powders comprising 200-400 nm range crystallites of BaBi4Ti4O15 at a significantly lower temperature (700 A degrees C) than that of solid-state reaction route. Reactants (CaCO3, Bi2O3 and TiO2) in stoichiometric ratio were ball milled for 48 h to obtain homogeneous mixture. The evolution of the BaBi4Ti4O15 phase was systematically followed using X-ray powder diffraction (XRD) technique. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to probe its structural and microstructural details. The electron diffraction studies established the presence of correlated octahedral rotations and associated long-range polar ordering. High-resolution TEM imaging nevertheless revealed structural inhomogeneities leading to intergrowth defects. Dense BaBi4Ti4O15 ceramics with an average grain size of 0.9 mu m were fabricated using mechanochemically assisted synthesized powders at relatively low temperature (1000 A degrees C). The effect of grain size on the dielectric and relaxor behaviour of BaBi4Ti4O15 ceramics was investigated. Fine-grained ceramics (average grain size similar to 0.9 mu m) showed higher diffusion in phase transition, lower temperature of phase transition, lower Vogel-Fulcher freezing temperature and higher activation energy for the polarization reversal than those for coarse-grained ceramics (average grain size similar to 7 mu m) fabricated via the conventional solid-state reaction route.

Temporally distinct roles of ATM and ROS in genotoxic- stress-dependent induction and maintenance of cellular senescence

Cells exposed to genotoxic stress induce cellular senescence through a DNA damage response (DDR) pathway regulated by ATM kinase and reactive oxygen species (ROS). Here, we show that the regulatory roles for ATM kinase and ROS differ during induction and maintenance of cellular senescence. Cells treated with different genotoxic agents were analyzed using specific pathway markers and inhibitors to determine that ATM kinase activation is directly proportional to the dose of the genotoxic stress and that senescence initiation is not dependent on ROS or the p53 status of cells. Cells in which ROS was quenched still activated ATM and initiated the DDR when insulted, and progressed normally to senescence. By contrast, maintenance of a viable senescent state required the presence of ROS as well as activated ATM. Inhibition or removal of either of the components caused cell death in senescent cells, through a deregulated ATM-ROS axis. Overall, our work demonstrates existence of an intricate temporal hierarchy between genotoxic stress, DDR and ROS in cellular senescence. Our model reports the existence of different stages of cellular senescence with distinct regulatory networks.

A model for the classification and survey of clock synchronization protocols in WSNs

Clock synchronization in wireless sensor networks (WSNs) assures that sensor nodes have the same reference clock time. This is necessary not only for various WSN applications but also for many system level protocols for WSNs such as MAC protocols, and protocols for sleep scheduling of sensor nodes. Clock value of a node at a particular instant of time depends on its initial value and the frequency of the crystal oscillator used in the sensor node. The frequency of the crystal oscillator varies from node to node, and may also change over time depending upon many factors like temperature, humidity, etc. As a result, clock values of different sensor nodes diverge from each other and also from the real time clock, and hence, there is a requirement for clock synchronization in WSNs. Consequently, many clock synchronization protocols for WSNs have been proposed in the recent past. These protocols differ from each other considerably, and so, there is a need to understand them using a common platform. Towards this goal, this survey paper categorizes the features of clock synchronization protocols for WSNs into three types, viz, structural features, technical features, and global objective features. Each of these categories has different options to further segregate the features for better understanding. The features of clock synchronization protocols that have been used in this survey include all the features which have been used in existing surveys as well as new features such as how the clock value is propagated, when the clock value is propagated, and when the physical clock is updated, which are required for better understanding of the clock synchronization protocols in WSNs in a systematic way. This paper also gives a brief description of a few basic clock synchronization protocols for WSNs, and shows how these protocols fit into the above classification criteria. In addition, the recent clock synchronization protocols for WSNs, which are based on the above basic clock synchronization protocols, are also given alongside the corresponding basic clock synchronization protocols. Indeed, the proposed model for characterizing the clock synchronization protocols in WSNs can be used not only for analyzing the existing protocols but also for designing new clock synchronization protocols. (C) 2014 Elsevier B.V. All rights reserved.

Calcium Permeable AMPA Receptor-Dependent Long Lasting Plasticity of Intrinsic Excitability in Fast Spiking Interneurons of the Dentate Gyrus Decreases Inhibition in the Granule Cell Layer

The local fast-spiking interneurons (FSINs) are considered to be crucial for the generation, maintenance, and modulation of neuronal network oscillations especially in the gamma frequency band. Gamma frequency oscillations have been associated with different aspects of behavior. But the prolonged effects of gamma frequency synaptic activity on the FSINs remain elusive. Using whole cell current clamp patch recordings, we observed a sustained decrease of intrinsic excitability in the FSINs of the dentate gyrus (DG) following repetitive stimulations of the mossy fibers at 30 Hz (gamma bursts). Surprisingly, the granule cells (GCs) did not express intrinsic plastic changes upon similar synaptic excitation of their apical dendritic inputs. Interestingly, pairing the gamma bursts with membrane hyperpolarization accentuated the plasticity in FSINs following the induction protocol, while the plasticity attenuated following gamma bursts paired with membrane depolarization. Paired pulse ratio measurement of the synaptic responses did not show significant changes during the experiments. However, the induction protocols were accompanied with postsynaptic calcium rise in FSINs. Interestingly, the maximum and the minimum increase occurred during gamma bursts with membrane hyperpolarization and depolarization respectively. Including a selective blocker of calcium-permeable AMPA receptors (CP-AMPARs) in the bath; significantly attenuated the calcium rise and blocked the membrane potential dependence of the calcium rise in the FSINs, suggesting their involvement in the observed phenomenon. Chelation of intracellular calcium, blocking HCN channel conductance or blocking CP-AMPARs during the experiment forbade the long lasting expression of the plasticity. Simultaneous dual patch recordings from FSINs and synaptically connected putative GCs confirmed the decreased inhibition in the GCs accompanying the decreased intrinsic excitability in the FSINs. Experimentally constrained network simulations using NEURON predicted increased spiking in the GC owing to decreased input resistance in the FSIN. We hypothesize that the selective plasticity in the FSINs induced by local network activity may serve to increase information throughput into the downstream hippocampal subfields besides providing neuroprotection to the FSINs. (c) 2014 Wiley Periodicals, Inc.

Effect of Ni-Zr codoping on dielectric and magnetic properties of SrFe12O19 via sol-gel route

Nanocrystalline strontium hexaferrites SrFe12-2x (Ni2+-Zr4+)(x)O-19] nanoparticles were successfully synthesized by sal gel process. For densification the powders were sintered at 950 degrees C/4 h. The sintered samples were characterized by X-ray diffraction (XRD), surface area measurement, and field emission scanning electron microscope (FESEM). The lattice parameter a is almost constant but c increased with x upto 0.8 and then decreased. The frequency dependent complex permittivity (epsilon and epsilon `' and permeability (mu' and mu `') and magnetic properties such as saturation magnetization (M-s), coercive field (H-c) were studied. If is observed that saturation magnetization increased gradually from 57.82 emuig to 67.2 emufg as x increased from 0.2 to 0.4 and then decreased from 672 emufg to 31.63 ernufg for x=1.0. In present study, x=0.4 shows high value of M-s 67.2 emu/g. The real part of permittivity (epsilon') remains constant upto a frequency 1 GHz and increases further with an increase of frequency, a resonance and anti resonance peak was observed above 1 GHz for all the samples. In real part of permeability (mu') the relaxation frequency is observed above 1 GHz for all the samples and it is attributed to the domain wall motion. It is well known that the permeability for polycrystalline ferrites can be described as the superposition of two different magnetizing mechanisms: spin rotation and domain wall motion. These low coercive strontium hexaferrites are suitable for magnetic recording applications in hard disks, floppy disks, video tapes, etc. (C) 2015 Elsevier B.V. All rights reserved.

Implication of a sigma-Methane Complex en Route to Elimination of Methane from a Ruthenium Complex: An Experimental and Theoretical Investigation

The five-coordinated 16-electron complex Ru(Me)(dppe)(2)]OTf] (3) undergoes methane elimination at room temperature to afford the ortho-metalated species (dppe){(C6H5)(C6H4)PCH2CH2P(C6H5)(2)}Ru]OTf] (7). Methane elimination, monitored using NMR spectroscopy, revealed no intermediate throughout the reaction. The NOE between Ru-Me protons and ortho phenyl protons and an agostic interaction trans to the methyl group were found in complex 3 by NMR spectroscopy, which form the basis for three plausible pathways for methane elimination and ortho metalation: pathway I (through spatial interaction), pathway II (through oxidative addition and reductive elimination), and pathway III (through agostic interaction). Methane elimination from complex 3 via pathway I was discounted, since it involves interactions through space and not through bonds. Moreover, the calculated energy barrier for the pathway I transition state was quite high (71.3 kcal/mol), which also indicates that this pathway is very unlikely. Furthermore, no spectroscopic evidence for oxidatively added seven-coordinated Ru(IV) species was found and the computed energy barrier of the transition state for pathway II was moderately high (41.1 kcal/mol), which suggests that this cannot be the right pathway for methane elimination and ortho-metalation of complex 3. On the other hand, indirect evidence in the form of chemical reactions point to the most plausible pathway for methane elimination, pathway III, via the intermediacy of a sigma-CH4 complex that could not be found spectroscopically. DFT calculations at several levels on this pathway showed an initial low-barrier rearrangement through TS1 to a square-pyramidal intermediate wherein methyl and agostic C-H are cis to each other. Migration of hydrogen from agostic C-H and elimination of methane proceed through the transition state TS2, which retains a weak metal-H bonding through most parts of the reaction coordinate. Upon comparison of all three pathways, pathway III was found to be the most likely for methane elimination and ortho-metalation of complex 3.

Piezoelectric properties of individual nanocrystallites of Ba0.85Ca0.15Zr0.1Ti0.9O3 obtained by oxalate precursor route

Nanocrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) powder was synthesized via the complex oxalate precursor route at a relatively low temperature (800 degrees C/5 h). The phase formation temperature of BCZT at nanoscale was confirmed by thermogravimetric (TG), differential thermal analysis (DTA) followed by X-ray powder diffraction (XRD) studies. Fourier transform infrared (FTIR) spectroscopy was carried out to confirm the complete decomposition of oxalate precursor into BCZT phase. The XRD and profile fitting revealed the coexistence of cubic and tetragonal phases and was corroborated by Raman study. Transmission electron microscopy (TEM) carried out on 800 degrees C and 1000 degrees C/5 h heat treated BCZT powder revealed the crystallite size to be in the range of 20-50 nm and 40-200 nm respectively. The optical band gap for BCZT nanocrystalline powder was obtained using Kubelka Munk function and was found to be around 3.12 +/- 0.02 eV and 3.03 +/- 0.02 eV respectively for 800 degrees C (20-50 nm) and 1000 degrees C/5 h (40-200 nm) heat treated samples. The piezoelectric properties were studied for two different crystallite sizes (30 and 70 nm) using a piezoresponse force microscope (PFM). The d(33) coefficients obtained for 30 nm and 70 nm sized crystallites were 4 pm V-1 and 47 pm V-1 respectively. These were superior to that of BaTiO3 nanocrystal (approximate to 50 nm) and promising from a technological/industrial applications viewpoint.

Kinetics of CO oxidation on palladium using microkinetics coupled with reaction route analysis

A plausible microkinetic model has been proposed for the CO oxidation reaction catalysed by palladium (Pd) with the kinetic parameters obtained from the literature. A robust rate expression using the reaction route analysis has been developed for the presented microkinetic scheme and the obtained rate expressions have been validated against the experimental data presented in the literature. A wide range of experimental conditions ranging from single Pd crystals under ultra-high vacuum conditions and impregnated Pd used for fixed bed experiments under atmospheric pressure has been used to validate the reaction mechanism. (C) 2015 Elsevier Ltd. All rights reserved.

Fault Attacks on Pairing-Based Protocols Revisited

Several papers have studied fault attacks on computing a pairing value e(P, Q), where P is a public point and Q is a secret point. In this paper, we observe that these attacks are in fact effective only on a small number of pairing-based protocols, and that too only when the protocols are implemented with specific symmetric pairings. We demonstrate the effectiveness of the fault attacks on a public-key encryption scheme, an identity-based encryption scheme, and an oblivious transfer protocol when implemented with a symmetric pairing derived from a supersingular elliptic curve with embedding degree 2.

Key challenges for the creation and maintenance of specialist protein resources

As the volume of data relating to proteins increases, researchers rely more and more on the analysis of published data, thus increasing the importance of good access to these data that vary from the supplemental material of individual articles, all the way to major reference databases with professional staff and long-term funding. Specialist protein resources fill an important middle ground, providing interactive web interfaces to their databases for a focused topic or family of proteins, using specialized approaches that are not feasible in the major reference databases. Many are labors of love, run by a single lab with little or no dedicated funding and there are many challenges to building and maintaining them. This perspective arose from a meeting of several specialist protein resources and major reference databases held at the Wellcome Trust Genome Campus (Cambridge, UK) on August 11 and 12, 2014. During this meeting some common key challenges involved in creating and maintaining such resources were discussed, along with various approaches to address them. In laying out these challenges, we aim to inform users about how these issues impact our resources and illustrate ways in which our working together could enhance their accuracy, currency, and overall value. Proteins 2015; 83:1005-1013. (c) 2015 The Authors. Proteins: Structure, Function, and Bioinformatics Published by Wiley Periodicals, Inc.

Effect of processing route on phase stability in equiatomic multicomponent Ti20Fe20Ni20Co20Cu20 high entropy alloy

The evolution of microstructure and phase formation in equiatomic Ti20Fe20Ni20Co20Cu20 high entropy alloy synthesised by conventional arc melting followed with suction casting and ball milling with spark plasma sintering route is distinctly different. The cast microstructure exhibits one body centre cubic and two face centre cubic high entropy phases based on titanium, cobalt and copper respectively along with a eutectic containing Ti2Ni type Laves phase. On the contrary, spinodal decomposed microstructure consisting of cobalt and copper solid solution is obtained in the sintered sample. However, long term annealing of cast sample at 950 degrees C reveals a eutectoid transformation with different phases than the cast sample. The aforementioned observations are discussed using CALPHAD thermodynamical approach and available literature.

Non-deterministic transducer models of retransmission protocols over noisy channels

Retransmission protocols such as HDLC and TCP are designed to ensure reliable communication over noisy channels (i.e., channels that can corrupt messages). Thakkar et al. 15] have recently presented an algorithmic verification technique for deterministic streaming string transducer (DSST) models of such protocols. The verification problem is posed as equivalence checking between the specification and protocol DSSTs. In this paper, we argue that more general models need to be obtained using non-deterministic streaming string transducers (NSSTs). However, equivalence checking is undecidable for NSSTs. We present two classes where the models belong to a sub-class of NSSTs for which it is decidable. (C) 2015 Elsevier B.V. All rights reserved.

QoS Performance Analysis of Routing Protocols in Vehicular Ad-hoc Networks

Vehicular Ad-hoc Networks (VANET), is a type of wireless ad-hoc network that aims to provide communication among vehicles. A key characteristic of VANETs is the very high mobility of nodes that result in a frequently changing topology along with the frequent breakage and linkage of the paths among the nodes involved. These characteristics make the Quality of Service (QoS) requirements in VANET a challenging issue. In this paper we characterize the performance available to applications in infrastructureless VANETs in terms of path holding time, path breakage probability and per session throughput as a function of various vehicle densities on road, data traffic rate and number of connections formed among vehicles by making use of table-driven and on-demand routing algorithms. Several QoS constraints in the applications of infrastructureless VANETs are observed in the results obtained.

Combinatorial selection of molecular conformations and supramolecular synthons in quercetin cocrystal landscapes: a route to ternary solids

The crystallization of 28 binary and ternary cocrystals of quercetin with dibasic coformers is analyzed in terms of a combinatorial selection from a solution of preferred molecular conformations and supramolecular synthons. The crystal structures are characterized by distinctive O-H center dot center dot center dot N and O-H center dot center dot center dot O based synthons and are classified as nonporous, porous and helical. Variability in molecular conformation and synthon structure led to an increase in the energetic and structural space around the crystallization event. This space is the crystal structure landscape of the compound and is explored by fine-tuning the experimental conditions of crystallization. In the landscape context, we develop a strategy for the isolation of ternary cocrystals with the use of auxiliary template molecules to reduce the molecular and supramolecular `confusion' that is inherent in a molecule like quercetin. The absence of concomitant polymorphism in this study highlights the selectivity in conformation and synthon choice from the virtual combinatorial library in solution.

Bio-inspired route for the synthesis of spherical shaped MgO:Fe3+ nanoparticles: Structural, photoluminescence and photocatalytic investigation

MgO:Fe3+ (0.1-5 mol%) nanoparticles (NPs) were synthesized via eco-friendly, inexpensive and simple low temperature solution combustion route using Aloe vera gel as fuel. The final products were characterized by SEM, TEM and HRTEM. PXRD data and Rietveld analysis revealed the formation of cubic system. The influence of Fe3+ ion concentration on the structure morphology, UV absorption, PL emission and photocatalytic activity of MgO:Fe3+ NPs were investigated. The yellow emission with CIE chromaticity coordinates (0.44, 0.52) and average correlated color temperature value was found to be 3540 K which corresponds to warm light of NPs. The control of Fe3+. on MgO matrix influences the photocatalytic decolorization of methylene blue (MB) under UV light. The enhanced photocatalytic activity of MgO:Fe3+ (4 mol%) was attributed to dopant concentration, effective crystallite size, textural properties, decreased band gap and capability for reducing the electron hole pair recombination. Further, the trends of inhibitory effect in the presence of different radical scavengers were explored. These findings open up new avenues for the exploration of Fe-doped MgO in eco-friendly water applications and in the process of display devices. (C) 2015 Elsevier B.V. All rights reserved.