Vibrational Spectra and Assignments for the Fundamental Vibrations of Imidazolidine-2-thione and -2-selenone

Infrared spectra of imidazolidine-2-thione (N,N?-ethylenethiourea, ETU) and its N,N?-deuterated (ETU-d2) and S-methylthiouronium iodides have been recorded from 4000 to 30 cm?1. Normal coordinate analyses of ETU and ETU-d2 have been made for all the fundamental frequencies, employing a Urey-Bradley potential function supplemented with valence type constants for the out of plane modes of the planar skeleton. Raman frequencies of ETU from literature have been utilised. The results of the vibrational analyses are discussed in relation to the group frequencies in structurally related molecules and frequency shifts on deuteration and S-methylation. The normal coordinate treatment is also performed for the planar vibrations of imidazolidine-2-selenone (N,N?-ethyleneselenourea, ESU) to propose assignments for ESU and so also to support the assignments of ETU.

Vibrational analysis of 1,3-thiazolidine-2-thione and its selenium analogue

The i.r. spectra of 1,3-thiazolidine-2-thione, ?2-selone and their N-deuteriated derivatives have been investigated in the region between 4000 and 20 cm?1. A complete assignment of the fundamental vibrational frequencies has been made based upon the normal coordinate analysis carried out using a simple Urey�Bradley force field supplemented by the valence force constants for the out-of-plane vibrations of the planar molecular skeleton. The proposed assignments are discussed in relation to the group frequencies in structurally related molecules and in terms of the computed potential energy distributions among the symmetry coordinates.

Out-of-equilibrium microrheology using optical tweezers to probe directional viscoelastic properties under shear

Many wormlike micellar systems exhibit appreciable shear thinning due to shear-induced alignment. As the micelles get aligned introducing directionality in the system, the viscoelastic properties are no longer expected to be isotropic. An optical-tweezers-based active microrheology technique enables us to probe the out-of-equilibrium rheological properties of a wormlike micellar system simultaneously along two orthogonal directions-parallel to the applied shear, as well as perpendicular to it. While the displacements of a trapped bead in response to active drag force carry signature of conventional shear thinning, its spontaneous position fluctuations along the perpendicular direction manifest an orthogonal shear thickening, an effect hitherto unobserved. Copyright (C) EPLA, 2010

On the out of phase appearance of large-scale diffuse magnetic field of the sun with respect to sunspots

We assume the large-scale diffuse magnetic field of the Sun to originate from the poloidal component of a dynamo operating at the base of the convection zone, whereas the sunspots are due to the toroidal component. The evolution of the poloidal component is studied to model the poleward migration of the diffuse field seen on the solar surface and the polar reversal at the time of sunspot maxima (Dikpati and Choudhuri 1994, 1995).

Ultrasonic wave characteristics of a monolayer graphene on silicon substrate

The present work deals with an ultrasonic type of wave propagation characteristics of monolayer graphene on silicon (Si) substrate. An atomistic model of a hybrid lattice involving a hexagonal lattice of graphene and surface atoms of diamond lattice of Si is developed to identify the carbon-silicon bond stiffness. Properties of this hybrid lattice model is then mapped into a nonlocal continuum framework. Equivalent force constant due to Si substrate is obtained by minimizing the total potential energy of the system. For this equilibrium configuration, the nonlocal governing equations are derived to analyze the ultrasonic wave dispersion based on spectral analysis. From the present analysis we show that the silicon substrate affects only the flexural wave mode. The frequency band gap of flexural mode is also significantly affected by this substrate. The results also show that, the silicon substrate adds cushioning effect to the graphene and it makes the graphene more stable. The analysis also show that the frequency bang gap relations of in-plane (longitudinal and lateral) and out-of-plane (flexural) wave modes depends not only on the y-direction wavenumber but also on nonlocal scaling parameter. In the nonlocal analysis, at higher values of the y-directional wavenumber, a decrease in the frequency band gap is observed for all the three fundamental wave modes in the graphene-silicon system. The atoms movement in the graphene due to the wave propagation are also captured for all the tree fundamental wave modes. The results presented in this work are qualitatively different from those obtained based on the local analysis and thus, are important for the development of graphene based nanodevices such as strain sensor, mass and pressure sensors, atomic dust detectors and enhancer of surface image resolution that make use of the ultrasonic wave dispersion properties of graphene. (C) 2011 Elsevier Ltd. All rights reserved.

Structural Transitions of Nitrogen Confined in Slit Graphite Pores

The structure of ordered phases that are formed when nitrogen is confined in slit graphite pores of height h is investigated using Monte Carlo simulations. The pore wall consists of a single-structured graphite sheet. Canonical ensemble simulations are carried out for temperatures ranging from 15 to 70Kwith layer density distributions, in-plane, out-of-plane angular distributions and snapshots evaluated at different temperatures. At each pore height the pore densities are obtained from independent grand ensemble simulations. At the smallest pore height studied (h)7 Å), where a single layer of molecules is accommodated at the center of the pore, the orientations are predominantly wall parallel, forming a biaxially incommensurate herringbone structure.Whentwo or more fluid layers are formed in the slit pore, the orientation of molecules adsorbed next to the wall can exist in either the herringbone or hexagonal phases. In all the multilayered cases studied, with the exception of the h ) 10 Å pore, where both wall layers form a commensurate herringbone structure, the low-temperature wall structures are incommensurate, possessing 6-fold hexagonal symmetry. The presence of the pinwheel structures, which were observed at low temperatures in the h ) 12 Å and h ) 14 Å pores, is determined by the pore height or the proximity and/or density of the adjacent fluid layers when inner layers are present.

Spin-polarized STM spectra of Dirac electrons on the surface of a topological insulator

We provide a theory for the tunneling conductance G(V) of Dirac electrons on the surface of a topological insulator as measured by a spin-polarized scanning tunneling microscope tip for low-bias voltages V. We show that if the in-plane rotational symmetry on the surface of the topological insulator is broken by an external field that does not couple to spin directly (such as an in-plane electric field), G(V) exhibits an unconventional dependence on the direction of the magnetization of the tip, i.e., it acquires a dependence on the azimuthal angle of the magnetization of the tip. We also show that G(V) can be used to measure the magnitude of the local out-of-plane spin orientation of the Dirac electrons on the surface. We explain the role of the Dirac electrons in this unconventional behavior and suggest experiments to test our theory.

Topology Optimization of Micromachined Structures with Surface Micromachining Manufacturing Constraints

Topology optimization methods have been shown to have extensive application in the design of microsystems. However, their utility in practical situations is restricted to predominantly planar configurations due to the limitations of most microfabrication techniques in realizing structures with arbitrary topologies in the direction perpendicular to the substrate. This study addresses the problem of synthesizing optimal topologies in the out-of-plane direction while obeying the constraints imposed by surface micromachining. A new formulation that achieves this by defining a design space that implicitly obeys the manufacturing constraints with a continuous design parameterization is presented in this paper. This is in contrast to including manufacturing cost in the objective function or constraints. The resulting solutions of the new formulation obtained with gradient-based optimization directly provide the photolithographic mask layouts. Two examples that illustrate the approach for the case of stiff structures are included.

Coupled polynomial field approach for elimination of flexure and torsion locking phenomena in the Timoshenko and Euler-Bernoulli curved beam elements

The curvature related locking phenomena in the out-of-plane deformation of Timoshenko and Euler-Bernoulli curved beam elements are demonstrated and a novel approach is proposed to circumvent them. Both flexure and Torsion locking phenomena are noticed in Timoshenko beam and torsion locking phenomenon alone in Euler-Bernoulli beam. Two locking-free curved beam finite element models are developed using coupled polynomial displacement field interpolations to eliminate these locking effects. The coupled polynomial interpolation fields are derived independently for Timoshenko and Euler-Bernoulli beam elements using the governing equations. The presented of penalty terms in the couple displacement fields incorporates the flexure-torsion coupling and flexure-shear coupling effects in an approximate manner and produce no spurious constraints in the extreme geometric limits of flexure, torsion and shear stiffness. the proposed couple polynomial finite element models, as special cases, reduce to the conventional Timoshenko beam element and Euler-Bernoulli beam element, respectively. These models are shown to perform consistently over a wide range of flexure-to-shear (EI/GA) and flexure-to-torsion (EI/GJ) stiffness ratios and are inherently devoid of flexure, torsion and shear locking phenomena. The efficacy, accuracy and reliability of the proposed models to straight and curved beam applications are demonstrated through numerical examples. (C) 2012 Elsevier B.V. All rights reserved.

Role of carrier density and disorder on anisotropic charge transport in polypyrrole

Polypyrrole (PPy) has been synthesized electrochemically on platinum substrate by varying synthesis temperature and dopant concentration. The charge transport in PPy has been investigated as a function of temperature for both in-plane and out-of-plane geometry in a wide temperature range of 5K-300 K. The charge transport showed strong anisotropy and various mechanisms were used to explain the transport. The conductivity ratio, sigma(r) = sigma(300 K)/sigma(5 K) is calculated for each sample to quantify the relative disorder. At all the temperatures, the conductivity values for in-plane transport are found to be more for PPy synthesized at lower temperature, while the behavior is found to be different for out-of-plane transport. The carrier density is found to play a crucial role in case of in-plane transport. An effort has been made to correlate charge transport to morphology by analyzing temperature and frequency dependence of conductivity. Charge transport in lateral direction is found to be dominated by hopping whereas tunneling mechanisms are dominated in vertical direction. Parameters such as density of states at the Fermi level N(E-F)], average hopping distance (R), and average hopping energy (W) have been estimated for each samples in both geometry. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4775405]

Out of equilibrium plasticity dynamics and the annealing of supersolidity in solid He-4

We present a numerical study of a continuum plasticity field coupled to a Ginzburg-Landau model for superfluidity. The results suggest that a supersolid fraction may appear as a long-lived transient during the time evolution of the plasticity field at higher temperatures where both dislocation climb and glide are allowed. Supersolidity, however, vanishes with annealing. As the temperature is decreased, dislocation climb is arrested and any residual supersolidity due to incomplete annealing remains frozen. Our results may provide a resolution of many perplexing issues concerning a variety of experiments on bulk solid He-4.

Modeling of temperature and field-dependent electron mobility in a single-layer graphene sheet

In this paper, we address a physics-based analytical model of electric-field-dependent electron mobility (mu) in a single-layer graphene sheet using the formulation of Landauer and Mc Kelvey's carrier flux approach under finite temperature and quasi-ballistic regime. The energy-dependent, near-elastic scattering rate of in-plane and out-of-plane (flexural) phonons with the electrons are considered to estimate mu over a wide range of temperature. We also demonstrate the variation of mu with carrier concentration as well as the longitudinal electric field. We find that at high electric field (>10(6) Vm(-1)), the mobility falls sharply, exhibiting the scattering between the electrons and flexural phonons. We also note here that under quasi-ballistic transport, the mobility tends to a constant value at low temperature, rather than in between T-2 and T-1 in strongly diffusive regime. Our analytical results agree well with the available experimental data, while the methodologies are put forward to estimate the other carrier-transmission-dependent transport properties.

Solution of Time Dependent Joule Heat Equation for a Graphene Sheet Under Thomson Effect

We address a physics-based solution of joule heating phenomenon in a single-layer graphene (SLG) sheet under the presence of Thomson effect. We demonstrate that the temperature in an isotopically pure (containing only C-12) SLG sheet attains its saturation level quicker than when doped with its isotopes (C-13). From the solution of the joule heating equation, we find that the thermal time constant of the SLG sheet is in the order of tenths of a nanosecond for SLG dimensions of a few micrometers. These results have been formulated using the electron interactions with the inplane and flexural phonons to demonstrate a field-dependent Landauer transmission coefficient. We further develop an analytical model of the SLG specific heat using the quadratic (out of plane) phonon band structure over the room temperature. Additionally, we show that a cooling effect in the SLG sheet can be substantially enhanced with the addition of C-13. The methodologies as discussed in this paper can be put forward to analyze the graphene heat spreader theory.

Vibrational spectra of fluorene, 1-methylfluorene and 1,8-dimethylfluorene

In this paper, we report the gas phase infrared spectra of fluorene and its methylated derivatives using a heated multipass cell and argon as a carrier gas. The observed spectra in the 4000-400 cm(-1) range have been fitted using the modified scaled quantum mechanical force field (SQMFF) calculation with the 6-311G** basis. The advantage of using the modified SQMFF method is that it scales the force constants to find the best fit to the observed spectral lines by minimizing the fitting error. In this way we are able to assign all the observed fundamental bands in the spectra. With consecutive methyl substitutions two sets of bands are found to shift in a systematic way. The set of four aromatic C-H stretching vibrations around 3000 cm(-1) shifts toward lower frequencies while the single most intense aromatic C-H out-of-plane bending mode around 750 cm(-1) shifts toward higher frequencies. The reason for shifting of aromatic C-H stretching frequency toward lower wave numbers with gradual methyl substitution has been attributed to the lengthening of the C-H bonds due to the +I effect of the methyl groups to the ring current as revealed from the calculations. While the unexpected shifting of the aromatic C-H out-of-plane bend toward higher wave numbers with increasing methyl substitution is ascribed to the lowering of the number of adjacent aromatic C-H bonds on the plane of the benzene ring with gradual methyl substitutions. (C) 2013 Elsevier B.V. All rights reserved.

NESP: Nonlinear enhancement and selection of plane for optimal segmentation and recognition of scene word images

In this paper, we report a breakthrough result on the difficult task of segmentation and recognition of coloured text from the word image dataset of ICDAR robust reading competition challenge 2: reading text in scene images. We split the word image into individual colour, gray and lightness planes and enhance the contrast of each of these planes independently by a power-law transform. The discrimination factor of each plane is computed as the maximum between-class variance used in Otsu thresholding. The plane that has maximum discrimination factor is selected for segmentation. The trial version of Omnipage OCR is then used on the binarized words for recognition. Our recognition results on ICDAR 2011 and ICDAR 2003 word datasets are compared with those reported in the literature. As baseline, the images binarized by simple global and local thresholding techniques were also recognized. The word recognition rate obtained by our non-linear enhancement and selection of plance method is 72.8% and 66.2% for ICDAR 2011 and 2003 word datasets, respectively. We have created ground-truth for each image at the pixel level to benchmark these datasets using a toolkit developed by us. The recognition rate of benchmarked images is 86.7% and 83.9% for ICDAR 2011 and 2003 datasets, respectively.