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Shiv Nadar University

(SoNS) School of Natural Sciences

There are many electronic and magnetic properties exhibited by complex oxides. Electronic phase separation (EPS) is one of those, the presence of which can be linked to exotic behaviours, such as colossal magnetoresistance, metal-insulator transition and high-temperature superconductivity. A variety of new and unusual electronic phases at the interfaces between complex oxides, in particular between two non-magnetic insulators LaAlO3 and SrTiO 3, have stimulated the oxide community. However, no EPS has been observed in this system despite a theoretical prediction. Here, we report an EPS state at the LaAlO3/SrTiO3 interface, where the interface charges are separated into regions of a quasi-two-dimensional electron gas, a ferromagnetic phase, which persists above room temperature, and a (superconductor like) diamagnetic/paramagnetic phase below 60 K. The EPS is due to the selective occupancy (in the form of 2D-nanoscopic metallic droplets) of interface sub-bands of the nearly degenerate Ti orbital in the SrTiO 3. The observation of this EPS demonstrates the electronic and magnetic phenomena that can emerge at the interface between complex oxides mediated by the Ti orbital. © 2011 Macmillan Publishers Limited. All rights reserved.

World University root node

Physics

Fulltext

Nature Communications

Electronic phase separation at the LaAlO3/SrTiO3 interface

Lateral heterostructure field-effect bipolar transistors (LH-FEBTs) are thin-film transistors that have a distinct heterojunction located roughly midway between the source and drain contacts, with a p-type semiconductor on one side of the junction, and an n-type semiconductor on the other. These devices have potential in display applications but are relatively new to the research community. In this paper, we describe the fabrication of a hybrid LH-FEBT using pentacene and ZnO as the p- and n-type semiconductors, respectively, and describe its unusual bell-shaped electrical transfer characteristics. Using an equivalent circuit approach, we analyse quantitatively how the main features of the current-voltage curves relate to semiconductor properties such as carrier mobility and threshold voltage - information that is essential to the design of such devices. © 2011 Elsevier B.V. All rights reserved.

Organic Electronics

Analysis and modelling of lateral heterostructure field-effect bipolar transistors

In the past decade there has been growing interest in the investigation of plasma bubble (PB), associated irregularities, which often profoundly impact satellite communication and navigation systems and produce ionospheric scintillations. The basic mechanism of generation and development of equatorial spread F (ESF) is the gravitational Rayleigh-Taylor instability. The trans-ionospheric signal scintillation causes considerable communication hazards at a wide range of frequencies and hence is of much practical interest. In the present study we have investigated the effect of geomagnetic storm on the low latitude ionospheric scintillation for the 03 August 2010 storm at Varanasi (25.30°N, 82.99°E), India. © 2011 IEEE.

Life Sciences

2011 30th URSI General Assembly and Scientific Symposium, URSIGASS 2011

Study of equatorial low-latitude ionospheric irregularities during a recent geomagnetic storm of 03 August 2010 using GPS receiver

The “trimpi event” consists of a sudden change in phase and amplitude of the VLF transmitter signal followed by a slow recovery to the initial levels as the ionization decays. We report here preliminary observations of phase and amplitude perturbations (trimpis) on VLF signals propagating in the Earth-ionosphere waveguide. Four VLF transmitter signals are monitored at our low latitude station Varanasi (L = 1.07) using SoftPAL Receiver. This paper deals with the current understanding of lightening discharge associated processes that leads to the changes in the characteristic of the waveguide and thus variation in the received amplitude and/or phase of the VLF transmission signals observed for the period August 25, 2009-December 25, 2009. Occurrence of Trimpi events at low L-values can be interpreted as precipitation of very high energetic electrons which are capable of producing perturbations during daylight, or as evidence of the ‘fast’ Trimpi mechanism which can dominate at low L-value. This wave induced particle precipitation is assumed to occur due to gyroresonance between whistler-mode waves and counter streaming electrons. © 2011 by World Scientific Publishing Co. Pte. Ltd. All rights reserved.

Advances in Geosciences: Volume 27: Solar Terrestrial (ST)

Trimpi events and other amplitude perturbations observed at Varanasi using SoftPAL receiver

Abstract Hypobaric hypoxia is encountered at high altitude. It has a deleterious effect on cognitive functions. An important cause of memory impairment at high altitude is the impairment of neurotransmission. The present study investigates the role of cholinergic markers in hypobaric hypoxia-induced memory impairment. Rats were exposed to hypobaric hypoxia at 6100 m for 7 days in a simulated-decompression chamber. Memory performance was assessed using the Morris water maze task. Cholinergic markers such as acetylcholine, acetylcholinesterase, choline acetyltransferase, α-7-nicotinic acetylcholine receptor and M 1 muscarinic acetylcholine receptor were also evaluated along with neuronal morphology and DNA fragmentation. We found impairment in memory function along with a decrease in acetylcholine levels, increase in acetylcholinesterase activity, down regulation of choline acetyltransferase, α-7-nicotinic acetylcholine receptor and M 1 muscarinic acetylcholine receptor. We also found that cellular damage is associated with a significant increase in DNA fragmentation. However, administration of acetylcholinesterase inhibitors, such as physostigmine and galantamine, resulted in amelioration of the hypobaric hypoxia induced deleterious effects. It improved acetylcholine level, decreased acetylcholinesterase activity and increased the synthesis of acetylcholine by increasing choline acetyltransferase activity. Also, the acetylcholinesterase inhibitors improved neuronal morphology, perhaps by increasing the expression of α-7-nicotinic acetylcholine receptor and by reducing the acetylcholinesterase level in the cortex and the hippocampus. Therefore, our results suggest cholinergic dysfunction is one of the mechanisms involved in hypobaric hypoxia-induced memory impairment and that acetylcholinesterase inhibitors were able to restore cholinergic function and thus improve memory function. © 2011 Elsevier B.V. All rights reserved.

European Journal of Pharmacology

Role of cholinergic markers on memory function of rats exposed to hypobaric hypoxia

A truncated (29 residues from the N-terminus) and N-terminal His-tagged form of SP-0149 from pneumococcal strain ATCC BAA-334 was overexpressed and purified to homogeneity using affinity and gel-filtration chromatography. Diffraction quality crystals were grown at 293 K using the hanging-drop vapour-diffusion technique. X-ray diffraction data were collected to 2.3 {\AA} resolution from a single-crystal that belonged to the orthorhombic space group P2 12 12 1 with the unit-cell parameters a = 54.56, b = 75.61, c = 75.52 {\AA}. The calculated values of the Matthews coefficient assuming one molecule (with calculated molecular weight of 30 400 Da) in the crystal asymmetric unit and the corresponding solvent content were 2.56 {\AA} 3 Da -1 and 52.0%, respectively. {\textcopyright} 2011 International Union of Crystallography All rights reserved.

Acta Crystallographica Section F: Structural Biology and Crystallization Communications

Cloning, overexpression, purification, crystallization and preliminary X-ray studies of SP-0149, the substrate binding protein of an ABC transporter from Streptococcus pneumoniae

A detailed defect energy level map was investigated for heterostructures of 26 unit cells of LaAlO3 on SrTiO3 prepared at a low oxygen partial pressure of 10-6 mbar. The origin is attributed to the presence of dominating oxygen defects in SrTiO3 substrate. Using femtosecond laser spectroscopy, the transient absorption and relaxation times for various transitions were determined. An ultrafast relaxation process of 2-3 ps from the conduction band to the closest defect level and a slower process of 70-92 ps from conduction band to intraband defect level were observed. The results are discussed on the basis of the proposed defect-band diagram. © 2011 American Institute of Physics.

Applied Physics Letters

Static and ultrafast dynamics of defects of SrTiO3 in LaAlO 3 / SrTiO3 heterostructures

The tris-chelate formed by biguanide, H2NC(NH)NHC(NH)NH 2, and Mn(IV) is one of the rarely encountered examples of water-stable mononuclear complexes of this oxidation state. This cation is reduced in aqueous acid by both V(II) and V(III). In contrast to the kinetically straightforward bimolecular reduction by V(II) in 0.5 M HClO4 (k = 7.4 × 103 M-1 s-1 at 22 °C), reductions by excess V(III) yield profiles which are linear (zero-order in MnIV) until the last few percent reaction. Analyses of these composite curves are consistent with the sequences2VIIIk-1k1(VIII)2(VIII) 2+MnIV→k22VIV+MnIIin which reaction is initiated by slow and reversible conversion of VIII to an activated dimeric species (VIII)2 Treatment of data in terms of this sequence yields a value of k1 1.9 × 10-3 M-1 s-1 and a ratio k2/k -1 2 × 106. This activated route for (VIII)2 appears to be preferred over a remarkably slow electron transfer from monomeric V(III) to the Mn(IV) center, reflecting an unusually high barriet to V(III/IV) self-exchange. © 2010 Elsevier B.V. All rights reserved.

Chemistry

Inorganica Chimica Acta

Electron transfer. Part 169 [1]. Delayed reduction of mononuclear manganeses(IV) using vanadium(III)

During the 2009 H1N1 pandemic, many individuals did not seek vaccination immediately but rather decided to "wait and see" until further information was available on vaccination costs. This behaviour implies two sources of strategic interaction: as more individuals become vaccinated, both the perceived vaccination cost and the probability that susceptible individuals become infected decline. Here we analyze the outcome of these two strategic interactions by combining game theory with a disease transmission model during an outbreak of a novel influenza strain. The model exhibits a "wait and see" Nash equilibrium strategy, with vaccine delayers relying on herd immunity and vaccine safety information generated by early vaccinators. This strategic behaviour causes the timing of the epidemic peak to be strongly conserved across a broad range of plausible transmission rates, in contrast to models without such adaptive behaviour. The model exhibits not only feedback mechanisms but also a feed-forward mechanism: a high initial perceived vaccination cost perpetuates high perceived vaccine costs (and lower vaccine coverage) throughout the remainder of the outbreak. This suggests that any effect of risk communication at the start of a pandemic outbreak will be amplified compared to the same amount of risk communication effort distributed throughout the outbreak. © 2011 Elsevier Ltd.

Mathematics

Vaccine

"Wait and see" vaccinating behaviour during a pandemic: A game theoretic analysis

A donor-acceptor polymer semiconductor, PDQT, comprising diketopyrrolopyrrole (DPP) and β-unsubstituted quaterthiophene (QT) for organic thin film transistors (OTFTs) is reported. This polymer forms ordered layer-by-layer lamellar packing with an edge-on orientation in thin films even without thermal annealing. The strong intermolecular interactions arising from the fused aromatic DPP moiety and the DPP-QT donor-acceptor interaction facilitate the spontaneous self-assembly of the polymer chains into close proximity and form a large π-π overlap, which are favorable for intermolecular charge hopping. The well-interconnected crystalline grains form efficient intergranular charge transport pathways. The desirable chemical, electronic, and morphological structures of PDQT bring about high hole mobility of up to 0.97 cm2/(V·s) in OTFTs with polymer thin films annealed at a mild temperature of 100 °C and similarly high mobility of 0.89 cm2/(V·s) for polymer thin films even without thermal annealing. © 2011 American Chemical Society.