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Shiv Nadar University

(SoNS) School of Natural Sciences

Charge transport in copper phthalocyanine (CuPc), partially fluorinated CuPc(F4CuPc), and fluorinated CuPc(F16CuPc) based organic thin film transistors is studied using dual SiO2/ polymethylmethacrylate gate dielectrics. We demonstrate the strong influence of air/moisture induced electron traps on electron transport when the lowest unoccupied molecular orbital is close to the vacuum irrespective of hydroxyl-free dielectrics used in the devices. © 2010 American Institute of Physics.

Physics

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Journal of Applied Physics

Electron transport in copper phthalocyanines

Chemistry

Poly(Lactic Acid): Synthesis, Structures, Properties, Processing, and Applications

Design and Synthesis of Different Types of Poly(Lactic Acid)

Knowledge of the elastic properties of Li-Si alloys as a function of Li concentration is crucial in the development of reliable deformation and fracture mechanics models for Si anodes in Li-ion batteries. Here, we have studied these properties using first-principles calculations for both amorphous and crystalline phases observed during lithiation of Si anodes. In the case of crystalline alloys, we present the anisotropic elastic tensors as well as the homogenized Young's, shear, and bulk moduli and the Poisson's ratios. We find that while these moduli decrease in an approximately linear manner with increasing Li concentration leading to significant elastic softening (by about one order of magnitude) in both crystalline and amorphous systems, the Poisson's ratios remain in the range of 0.05-0.20 and 0.20-0.30 in the case of crystalline and amorphous systems, respectively. Further, for a given Li concentration, we find that the amorphous structures are elastically somewhat softer than their crystalline counterparts, the difference being more significant (about 30-40%) in Li-poor phases. Our results underscore the importance of including the concentration dependence of elastic constants in the analysis of stress and deformation fields during lithiation and de-lithiation of Si anodes. © 2010 Elsevier B.V. All rights reserved.

Journal of Power Sources

Elastic softening of amorphous and crystalline Li-Si Phases with increasing Li concentration: A first-principles study

In this paper, discrete VLF chorus emissions recorded at low latitude ground station Jammu (geomag. Lat. 22° 26/ N, L 1.17) are reported and their characteristics based on complete spectral analysis have been carried out. These discrete chorus emissions are generated during a strong geomagnetic storm period of 2-7 May, 1998. We have computed the sweep rate, repetition period, source region, and drift rate of the individual chorus elements. It is observed that the sweep rate increases with time. To explain the various temporal and spectral features of these emissions, a possible generation mechanism has been presented based on the backward wave oscillator (BWO) regime in the magnetospheric cyclotron maser. On the basis of this model, we have computed some discrete chorus emission parameters as well as magnetospheric parameters relevant to the generation process. A comparison of the computed and observed magnetospheric parameters has been presented. These results show a good agreement with the BWO model. © 2010 IOP Publishing Ltd.

Life Sciences

Journal of Physics: Conference Series

A generation mechanism of chorus emissions using BWO theory

Very low frequency (VLF) hiss emissions were observed for the first time at the Indian Antarctic Station, Maitri (geographic lat. 70°46′S, long. 11°50′E, geomagnetic lat. 66°.03′S, long. 53°.21′E) with the modulating intensity variations. Various spectrograms of modulating VLF hiss emissions clearly show band limited spectra regularly modulating its intensity with almost equal period of the order of few seconds in the frequency range of 9-12.8 kHz. To explain these modulating characteristics of VLF hiss, we propose that the hiss emissions are generated through Doppler-shifted cyclotron interactions near the geomagnetic equator and propagate towards the Earth in the whistlermode. Further, the micropulsations propagating along the geomagnetic field lines could modulate the growth rate of the wave. The growth rates of the waves are also computed.

Current Science

Characteristics of modulating VLF hiss observed at Indian Antarctic Station, Maitri (L = 4.5)

Background. Stem cell factor (SCF) receptor c-Kit is recognized as a key signaling molecule, which transduces signals for the proliferation, differentiation and survival of stem cells. Binding of SCF to its receptor triggers transactivation, leading to the recruitment of kinases and phosphatases to the docking platforms of c-Kit catalytic domain. Tyrosine phosphatase-1 (Shp-1) deactivates/attenuates 'Kit' kinase activity. Whereas, Asp816Val mutation in the Kit activation loop transforms kinase domain to a constitutively activated state (switch off-to-on state), in a ligand-independent manner. This phenomenon completely abrogates negative regulation of Shp-1. To predict the possible molecular basis of interaction between c-Kit and Shp-1, we have performed an in silico protein-protein docking study between crystal structure of activated c-Kit (phosphorylated c-Kit) and full length crystal structure of Shp-2, a close structural counterpart of Shp-1. Findings. Study revealed a stretch of conserved amino acids (Lys818 to Ser821) in the Kit activation domain, which makes decisive H-bonds with N-sh2 and phosphotyrosine binding pocket residues of the phosphatase. These H-bonds may impose an inhibitory steric hindrance to the catalytic domain of c-Kit, there by blocking further interaction of the activation loop molecules with incoming kinases. We have also predicted a phosphotyrosine binding pocket in SH2 domains of Shp-1, which is found to be predominantly closer to a catalytic groove like structure in c-Kit kinase domain. Conclusions. This study predicts that crucial hydrogen bonding between N-sh2 domain of Shp-1 and Kit activation loop can modulate the negative regulation of c-Kit kinase by Shp-1. Thus, this finding is expected to play a significant role in designing suitable gain-of-function c-Kit mutants for inducing conditional proliferation of hematopoietic stem cells. © 2010 Mukhopadhyay et al; licensee BioMed Central Ltd.

BMC Research Notes

The structural insights of stem cell factor receptor (c-Kit) interaction with tyrosine phosphatase-2 (Shp-2): An in silico analysis

Hyperactivation of phosphatidylinositol-3 kinase (PI3K) can occur as a result of somatic mutations in PIK3CA, the gene encoding the p110α subunit of PI3K. The HER2 oncogene is amplified in 25% of all breast cancers and some of these tumors also harbor PIK3CA mutations. We examined mechanisms by which mutant PI3K can enhance transformation and confer resistance to HER2-directed therapies. We introduced the PI3K mutations E545K and H1047R in MCF10A human mammary epithelial cells that also overexpress HER2. Both mutants conferred a gain of function to MCF10A/HER2 cells. Expression of H1047R PI3K, but not E545K PI3K, markedly upregulated the HER3/HER4 ligand heregulin (HRG). HRG siRNA inhibited growth of H1047R but not E545K-expressing cells and synergized with the HER2 inhibitors trastuzumab and lapatinib. The PI3K inhibitor BEZ235 markedly inhibited HRG and pAKT levels and, in combination with lapatinib, completely inhibited growth of cells expressing H1047R PI3K. These observations suggest that PI3K mutants enhance HER2-mediated transformation by amplifying the ligand-induced signaling output of the ErbB network. This also counteracts the full effect of therapeutic inhibitors of HER2. These data also suggest that mammary tumors that contain both HER2 gene amplification and PIK3CA mutations should be treated with a combination of HER2 and PI3K inhibitors. © 2010 Macmillan Publishers Limited All rights reserved.

Oncogene

H1047R phosphatidylinositol 3-kinase mutant enhances HER2-mediated transformation by heregulin production and activation of HER3

A new, solution-processable, low-bandgap, diketopyrrolopyrrole- benzothiadiazole-based, donor-acceptor polymer semiconductor (PDPP-TBT) is reported. This polymer exhibits ambipolar charge transport when used as a single component active semiconductor in OTFTs with balanced hole and electron mobilities of 0.35 cm2 V-1s-1 and 0.40 cm 2 V-1s-1, respectively. This polymer has the potential for ambipolar transistor-based complementary circuits in printed electronics. Copyright © 2010 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Advanced Materials

A low-bandgap diketopyrrolopyrrole-benzothiadiazole-based copolymer for high-mobility ambipolar organic thin-film transistors

We argue that supersymmetric transformation could be applied across the heterojunction formed by joining of two mixed semiconductors. A general framework is described by specifying the structure of ladder operators at the junction for making quantitative estimation of physical quantities. For a particular heterojunction device, we show that an exponential grading inside a nanoscale doped layer is amenable to exact analytical treatment for a class of potentials distorted by the junctions through the solutions of transformed Morse-type potentials. © 2010 Elsevier B.V. All rights reserved.

Physics Letters, Section A: General, Atomic and Solid State Physics

Supersymmetry across nanoscale heterojunction

A novel series of soluble thieno[3,2-b]thiophene (TT) oligomers with alternating TT and bithiophene or fluorene triad architectures have been synthesized for field-effect transistor (FET) applications. Their optical, thermal and electronic properties were investigated using UV-Vis and photoluminescence spectroscopy, thermal gravimetric analysis, and cyclic voltammetry. Compared with α,α′-dihexylsexithiophene (D6HT), these oligomers exhibit blue-shifted absorption spectra, 0.1 eV to 0.3 eV lower than the highest occupied molecular orbital (HOMO) energy levels and accordingly higher ambient stability. Their crystallinity and morphology features of these oligomers were further investigated with X-ray diffraction and atomic force microscopy using vacuum-deposited thin film on Si/SiO2 substrate. Symmetrically structured TT-oligomers including HT2TT, HTTT2, HTTTT and DDFTT exhibit ordered film morphology and promising FET performance with devices fabricated by either vacuum deposition or solution processing techniques. Interestingly, HTTT2 shows interconnected terrace island morphology, which is often observed for pentacene. All p-type transistors show promising performance, with HT2TT demonstrating a hole mobility up to 0.025 cm2V -1s-1 and an on/off current ration ∼1.2 × 103 with vacuum sublimated film deposited on 70 °C substrate. © The Royal Society of Chemistry 2010.