Physics

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We report resistivity, magnetization and 19F NMR results in a polycrystalline sample of SmFeAsO0.86F0.14. The resistivity and magnetization data show a sharp drop at 48 K indicating a superconducting transition. The nuclear spin-lattice rate (1/T1) and spin-spin relaxation rate (1/T2) clearly show the existence of a structural phase transition near 163 K in the sample, which also undergoes a superconducting transition. This finding creates interest in exploring whether this is unique for Sm based systems or is also present in other rare-earth based 1111 superconductors. {\textcopyright} 2013 IOP Publishing Ltd.

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Journal of Physics Condensed Matter

Evidence of a structural phase transition in superconducting SmFeAsO 1-xFx from 19F NMR

We propose a mechanism to obtain the generation of matter in the standard model. We start from the analysis of the T2/ZN shifted orbifold with magnetic flux, which imposes a ZN symmetry on torus. We also consider several orbifolds such as (T2×T2)/ZN, (T2×T2×T2)/ (ZN×ZN') and (T2×T2×T2)/(Z N×ZN'×ZN'). On such orbifolds, we study the behavior of fermions in two different means - the operator formalism and the explicit analysis of wave functions. For an interesting result, it is found that the number of zero-mode fermions is related to N of the ZN symmetry. In other words, the generation of matter relates to the type of orbifolds. Moreover, we find that shifted orbifold models are severely restricted from realizing three generations. For example, the three-generation model on the type of M4×(T2×T2)/ZN is unique. One can also construct other types of three-generation orbifold models with rich flavor structure. Those results may bring us a realistic model with desired Yukawa structure. © 2013 American Physical Society.

Physical Review D - Particles, Fields, Gravitation and Cosmology

Shifted orbifold models with magnetic flux

Vertically aligned few layered graphene (FLGs) nanoflakes were synthesized by microwave plasma deposition for various time durations ranging from 30 to 600 s to yield graphene films of varying morphology, microstructure and areal/edge density. Their intrinsic electrochemical properties were explored using Fe(CN)6 3-/4- and Ru(NH3)6 3+/2+ redox species. All the FLG electrodes demonstrate fast electron transfer kinetics with near ideal ΔEp values of 60-65 mV. Using a relationship between electron transfer rate and edge plane density, an estimation of the edge plane density was carried out which revealed a moderation of edge plane density with increase in growth time. The pristine FLGs also possess excellent electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline solutions. This ORR activity can be further enhanced by exposing the pristine FLGs to nitrogen electron cyclotron resonance plasma. The metal free N-doped FLGs exhibit much higher electrocatalytic activity towards ORR than pristine FLGs with higher durability and selectivity than Pt-based catalysts. The excellent electrochemical performance of N-doped FLGs is explained in terms of enhanced edge plane exposure, high content of pyridinic nitrogen and an increase in the electronic density of states. © 2013 Springer-Verlag Berlin Heidelberg.

Journal of Solid State Electrochemistry

Electrochemical and oxygen reduction properties of pristine and nitrogen-doped few layered graphene nanoflakes (FLGs)

A series of four novel n-type molecules has been synthesized. Unlike previous approaches, the end group of these molecules was fixed and the molecular core was varied. The resulting materials were thoroughly analyzed. Electronic properties were derived from photoemission spectroscopy, optical properties were derived with the help of optical spectroscopy, and the structure of thin films on Au(111) was derived by scanning tunneling microscopy (STM). In addition, prototypical organic field-effect transistors (OFETs) (forming n-channels in OFETs) have been fabricated and tested. The correlation between the device performance of the respective OFETs (i.e., electron mobility) and their electronic as well as structural properties was investigated. It turned out that a combination of beneficial electronic and structural properties provides the best results. These findings are important for the design of new materials for future device applications. © 2013 American Chemical Society.

Journal of Physical Chemistry C

Band gap tunable N-type molecules for organic field effect transistors

Donor-Acceptor-Donor (D-A-D) based conjugated molecules 4,7-bis(5-(4-butoxyphenyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (BOP-TBT) and 4,7-bis(5-(4-trifluoromethyl)phenyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (TFP-TBT) using thiophene-benzothiadiazole-thiophene central core with trifluoromethyl phenyl and butoxyphenyl end capping groups were designed and synthesised via Suzuki coupling. Optical, electrochemical, thermal, and organic field effect transistor (OFET) device properties of BOP-TBT and TFP-TBT were investigated. Both small molecules possess two absorption bands. Optical band gaps were calculated from the absorption cut off to be in the range of 2.06-2.25eV. Cyclic voltammetry indicated reversible oxidation and reduction processes and the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels were calculated to be in the range of 5.15-5.40eV and 3.25-3.62eV, respectively. Upon testing both materials for OFET, trifluoromethylphenyl end capped material (TFP-TBT) shows n-channel behaviour whereas butoxyphenyl end capped material (BOP-TBT) shows p-channel behaviour. Density functional theory calculations correlated with shifting of HOMO-LUMO energy levels with respect to end capping groups. Vacuum processed OFET of these materials have shown highest hole carrier mobility of 0.02cm 2/Vs and electron carrier mobility of 0.004cm2/Vs, respectively using Si/SiO2 substrate. By keeping the central D-A-D segment and just by tuning end capping groups gives both p- and n-channel organic semiconductors which can be prepared in a single step using straightforward synthesis.

Australian Journal of Chemistry

Dithienylbenzothiadiazole-based donor-acceptor organic semiconductors and effect of end capping groups on organic field effect transistor performance

We propose a method based on the Wang-Landau algorithm to numerically generate the spectral densities of random matrix ensembles. The method employs Dyson's log-gas formalism for random matrix eigenvalues and also enables one to simultaneously investigate the thermodynamic properties. This approach is a powerful alternative to the conventionally used Monte Carlo simulations based on the Boltzmann sampling, and is ideally suited for investigating β-ensembles. Copyright © EPLA, 2013.

Random matrix ensembles: Wang-Landau algorithm for spectral densities

We show the bounds on five- and six-dimensional Universal Extra Dimension models from the result of the Higgs boson searches at the Large Hadron Collider and electroweak precision measurement. The latest data released by the ATLAS and the CMS gives the lower bounds on Kaluza-Klein scale which are from 650 GeV to 1350 GeV depending on models from Higgs to diboson/diphoton decay signal. The Higgs production cross section can be enhanced by factor 1.5 in crude estimation, diphoton decay signal is suppressed about 10%. Electroweak precision measurement also gives the lower bounds as from 700 GeV to 1500 GeV. This is a proceedings of the conference "Rencontres de Moriond EW 2013". © EW 2013.

Proceedings of the 48th Rencontres de Moriond - 2013 Electroweak Interactions and Unified Theories, EW 2013

Constraint on universal extra dimensions from scalar boson searches

We examine some nontrivial consequences that emerge from interpreting a position-dependent mass (PDM)-driven Duffing oscillator in the presence of a quartic potential. The propagation dynamics is numerically studied and the sensitivity to the PDM-index is noted. Remarkable transitions from a limit cycle to chaos through period doubling and from a chaotic to a regular motion through intermediate periodic and chaotic routes are demonstrated. © 2013 IOP Publishing Ltd.

Journal of Physics A: Mathematical and Theoretical

Nonlinear dynamics of a position-dependent mass-driven Duffing-type oscillator

In response to the comment of Mustafa (2013 J. Phys. A: Math. Theor. 46 368001) we justify our stand of considering an extended Lagrange equation involving a non-conservative force term when the particle mass varies with position. As has been known for some time, such an extended form not only takes into account the principle of virtual work applied to D'Alembert's principle but yields precisely the form of Newton's equation expected for a particle possessing a position-dependent mass. © 2013 IOP Publishing Ltd.

Reply to Comment on 'Nonlinear dynamics of a position-dependent mass-driven Duffing-type oscillator'

A benzothiadiazole end-capped small molecule 3,6-bis(5-(benzo[c][1,2,5] thiadiazol-4-yl)thiophen-2-yl)-2,5-bis(2-butyloctyl)pyrrolo[3,4-c]pyrrole-1, 4(2H,5H)-dione (BO-DPP-BTZ) using a fused aromatic moiety DPP (at the centre) is designed and synthesized. BO-DPP-BTZ is a donor-acceptor-donor (D-A-D) structure which possesses a band gap of 1.6 eV and exhibits a strong solid state ordering inferred from ∼120 nm red shift of the absorption maxima from solution to thin film. Field-effect transistors utilizing a spin coated thin film of BO-DPP-BTZ as an active layer exhibited a hole mobility of 0.06 cm 2 V-1 s-1. Solution-processed bulk heterojunction organic photovoltaics employing a blend of BO-DPP-BTZ and [70]PCBM demonstrated a power conversion efficiency of 0.9\%. © 2013 the Owner Societies.