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

Electron spectroscopic investigation of the semiconductor-metal transition in La1-xSrxMnO3

We study the electronic structure of La1-xSrxMnO3+δ, x=0, 0.1, 0.2, 0.3, and 0.4, across the semiconductor-metal transition, using various electron spectroscopy techniques. The negligible intensity seen at EF using ultraviolet photoemission spectroscopy and bremsstrahlung isochromat spectroscopy (BIS) indicate an unusual semiconductor-metal transition observed for x≥0.2, consistent with the resistivity data. The BIS spectra show doped hole states developing about 1.4 eV above EF as a function of x. Auger electron spectroscopy gives an estimate of the intra-atomic Coulomb energy in the O 2p manifold to be about 6.8 eV. The Mn 2p core-level spectrum of LaMnO3, analyzed in terms of a configuration-interaction calculation, gives parameter values of the charge-transfer energy Δ=5.0 eV, the hybridization strength between Mn 3d and O 2p states, t=3.8 eV, and the on-site Coulomb energy in Mn 3d states Udd=4.0 eV, suggesting a mixed character for the ground state of LaMnO3.

Novel photocrosslinkable liquid-crystalline polymers: poly[bis(benzylidene)] esters

A new class of photo-cross-linkable main-chain liquid crystalline polymers (PMCLCPs) containing bis(benzylidene)cycloallranone groups have been synthesized and studied for their liquid crystalline and photochemical properties. The bis(benzylidene)cycloalkanone group in the chain functions both as a mesogen and as a photoreactive center. All of the polymers exhibit a nematic mesophase. Two kinds of photoreactions, namely, photoisomerization and photo-cross-linking, operate in these polymers. Above Tu at the initial stages of irradiation, photoisomerization predominates the cross-linking, which resulta in the disruption of the chromophore aggregates. Below T8, because of the restricted mobility of the chains, only cross-linking takes place. Studies on the model compound, bis(benzylidene)cyclopentanone, confii the above observations and demonstrate further that the cross-linking proceeds by the 2r + 2r cycloaddition reaction of the bis(benzylidene)cycloallranone moieties. The cross-linking rate decreases with increase in the size of the cycloalkanone ring. Heating the solution cast polymer fii results in the ordered aggregation of the chromophores just above TI and also at the crystal to crystal transition temperature, which facilitates the phobcross-linking reactions. In the isotropic phase, the random orientation of the chromophores drastically curtails the cross-linking rata

Thermomechanical behaviour of pin joints subjected to sheet loads

An important problem regarding pin joints in a thermal environment is addressed. The motivation emerges from structural safety requirements in nuclear and aerospace engineering. A two-dimensional model of a smooth, rigid misfit pin in a large isotropic sheet is considered as an abstraction. The sheet is subjected to a biaxial stress system and far-field unidirectional heat flow. The thermoelastic analysis is complex due to non-linear load-dependent contact and separation conditions at the pin-hole interface and the absence of existence and uniqueness theorems for the class of frictionless thermoelastic contact problems. Identification of relevant parameters and appropriate synthesis of thermal and mechanical variables enables the thermomechanical generalization of pin-joint behaviour. This paper then proceeds to explore the possibility of multiple solutions in such problems, especially interface contact configuration.

Thermomechanical generalization of pin joints in finite plates

The understanding of thermoelastic behaviour of joints is significant in order to ensure the integrity of large and complex structures exposed to a thermal environment, particularly in fields such as aerospace and nuclear engineering. Thermomechanical generalization of partial contact behaviour of a pin joint under combined in-plane mechanical loading and on-axis unidirectional heat flow has already been established by the authors for the analytically simpler domains of large plates. This paper successfully extends the on-going investigation to a single pin in a finite rectangular isotropic plate as a two-dimensional abstraction from a practical situation of a multipin fastener joint. The finite element method is used to analyse the joint problem under on-axis thermomechanical loading and unified load-contact relationships are established for a class of loading conditions.

Strong nonlocalization induced by small scale parameter on terahertz flexural wave dispersion characteristics of a monolayer graphene

This paper presents the strong nonlocal scale effect on the flexural wave propagation in a monolayer graphene sheet. The graphene is modeled as an isotropic plate of one atom thick. Nonlocal governing equation of motion is derived and wave propagation analysis is performed using spectral analysis. The present analysis shows that the flexural wave dispersion in graphene obtained by local and nonlocal elasticity theories is quite different. The nonlocal elasticity calculation shows that the wavenumber escapes to infinite at certain frequency and the corresponding wave velocity tends to zero at that frequency indicating localization and stationary behavior. This behavior is captured in the spectrum and dispersion curves. The cut-off frequency of flexural wave not only depend on the axial wavenumber but also on the nonlocal scaling parameter. The effect of axial wavenumber on the wave behavior in graphene is also discussed in the present manuscript. (C) 2010 Elsevier B.V. All rights reserved.

Application of a modified z-cosy experiment for the analysis of spectra of oriented molecules - the spectrum of cis,cis-mucanonitrile

NMR spectra of cis,cis-mucanonitrile oriented in a liquid crystal have been analysed using the connectivity information obtained from a modified Z-COSY experiment which provided crucial clues for the starting parameters for the iterative analysis. The proton spectra with and without C-13 satellites and the C-13 spectra have thus been interpreted. The indirect spin-spin couplings required for the analyses have been obtained from the corresponding isotropic spectra. The H-1-H-1 and C-13-H-1 dipolar couplings so obtained have been utilized to determine the relative internuclear distances. The results indicate that the molecule is planar. (C) 1994 Academic Press, Inc.

Cracks emanating from pin-loaded lugs

Pin-loaded lugs were analysed in the presence of cracks emanating from circular holes. The analysis presents a unified treatment of interference, push or clearance fit pins. Both metallic (isotropic) and composite (orthotropic) plates were dealt with. The finite element model used special singular six-noded quadrilateral elements at the crack tip. The non-linear load contact behaviour at the pin-hole interface was dealt with by an inverse technique. A modified crack closure integral (MCCI) technique was used to evaluate the strain energy release rates (SERRs) and stress intensity factors (SIFs) at the crack tips. Numerical results are presented showing the non-linear variation of SIF with applied stress, and the influence of the amount of interference or clearance and the interfacial friction on SIF.

Finite data performance of MUSIC and minimum norm methods

In the direction of arrival (DOA) estimation problem, we encounter both finite data and insufficient knowledge of array characterization. It is therefore important to study how subspace-based methods perform in such conditions. We analyze the finite data performance of the multiple signal classification (MUSIC) and minimum norm (min. norm) methods in the presence of sensor gain and phase errors, and derive expressions for the mean square error (MSE) in the DOA estimates. These expressions are first derived assuming an arbitrary array and then simplified for the special case of an uniform linear array with isotropic sensors. When they are further simplified for the case of finite data only and sensor errors only, they reduce to the recent results given in [9-12]. Computer simulations are used to verify the closeness between the predicted and simulated values of the MSE.

Magnetism, exchange and crystal field parameters in the orbitally unquenched Ising antiferromagnet FePS3

FePS3 is a layered antiferromagnet (T N=123 K) with a marked Ising anisotropy in magnetic properties. The anisotropy arises from the combined effect of the trigonal distortion from octahedral symmetry and spin-orbit coupling on the orbitally degenerate5 T 2g ground state of the Fe2+ ion. The anisotropic paramagnetic susceptibilities are interpreted in terms of the zero field Hamiltonian, ?=?i [?(L iz 2 ?2)+|?|L i .S i ]?? ij J ij S i .S j . The crystal field trigonal distortion parameter ?, the spin-orbit coupling ? and the isotropic Heisenberg exchange,J ij, were evaluated from an analysis of the high temperature paramagnetic susceptibility data using the Correlated Effective Field (CEF) theory for many-body magnetism developed by Lines. Good agreement with experiment were obtained for ?/k=215.5 K; ?/k=166.5 K;J nn k=27.7 K; andJ nnn k=?2.3 K. Using these values of the crystal field and exchange parameters the CEF predicts aT N=122 K for FePS3, which is remarkably close to the observed value of theT N. The accuracy of the CEF approximation was also ascertained by comparing the calculated susceptibilities in the CEF with the experimental susceptibility for the isotropic Heisenberg layered antiferromagnet MnPS3, for which the high temperature series expansion susceptibility is available.

Orientational Order of Liquid-Crystalline 4-Alkyl-N-(p-cyanophenyl)piperidines by 2H and 13C NMR Spectroscopies

The orientational order of nematic 4-alkyl-N-(4-cyanophenyl) piperidines (I) has been determined from H-2 and C-13 NMR spectra. Molecular-order parameters are derived from the carbon-13 chemical shift of the cyano carbon atom in the nematic and the isotropic phases; the sign of the diamagnetic anisotropy is positive. Deuterium quadrupolar splittings from the partially deuterated piperidine ring of I are then related to various C-D bonds.

Synthesis, Crystal Structure, and Magnetic Properties of a Ferromagnetically Coupled Angular Trinuclear Copper(11) Complex [Cu3(02CMe)4(bpy)s(HzO)](PF)62

The synthesis, X-ray crystal structure, and magnetic properties of an angular trinuclear copper(II) complex [Cu3(O2CMC)4(bpy)3(H2O)](PF6)2 (1), obtained from a reaction of Cu2(O2CMe)4(H2O)2 With 2,2'-bipyridine (bpy) and NH4PF6 in ethanol, are reported. Complex 1 crystallizes in triclinic space group P1BAR with a = 11.529(1) angstrom, b = 12.121(2) angstrom, c = 17.153(2) angstrom, alpha = 82.01(1)-degrees, beta = 79.42(1)-degrees, gamma = 89.62(1)-degrees, and Z = 2. A total of 6928 data with I > 2.5sigma(I) were refined to R = 0.0441 and R(w) = 0.0557. The structure consists of a trinuclear core bridged by four acetate ligands showing different bonding modes. The coordination geometry at each copper is distorted square-pyramidal with a CuN2O2...O chromophore. The Cu...Cu distances are 3.198(1) angstrom, 4.568(1) angstrom, and 6.277(1) angstrom. There are two monoatomic acetate bridges showing Cu-O-Cu angles of 93.1(1) and 97.5(1)-degrees. Magnetic studies in the temperature range 39-297 K show the presence of a strong ferromagnetically coupled dicopper(II) unit (2J = +158 cm-1) and an essentially isolated copper(II) center (2J' = -0.4 cm-1) in 1. The EPR spectra display an axial spectrum giving g(parallel-to) = 2.28 (A(parallel-to) = 160 X 10(-4) cm-1) and g(perpendicular-to) = 2.06 (A(perpendicular-to) = 12 X 10(-4) cm-1) for the normal copper and two intense isotropic signals with g values 2.70 and 1.74 for the strongly coupled copper pair. The structural features of 1 compare well with the first generation models for ascorbate oxidase.

Analysis of a long thick orthotropic circular cylindrical shell panel

An exact three-dimensional elasticity solution has been obtained for an infinitely long, thick transversely isotropic circular cylindrical shell panel, simply supported along the longitudinal edges and subjected to a radial patch load. Using a set of three displacement functions, the boundary value problem is reduced to Bessel's differential equation. Numerical results are presented for different thickness to mean radius ratios and semicentral angles of the shell panel. Classical and first-order shear deformation orthotropic shell theories have been examined in comparison with the present elasticity solution.

Asymptotic and finite element analyses of mode III dynamic crack growth at a ductile-brittle interface

In this work, dynamic crack growth along a ductile-brittle interface under anti-plane strain conditions is studied. The ductile solid is taken to obey the J(2) flow theory of plasticity with linear isotropic strain hardening, while the substrate is assumed to exhibit linear elastic behavior. Firstly, the asymptotic near-tip stress and velocity fields are derived. These fields are assumed to be variable-separable with a power singularity in the radial coordinate centered at the crack tip. The effects of crack speed, strain hardening of the ductile phase and mismatch in elastic moduli of the two phases on the singularity exponent and the angular functions are studied. Secondly, full-field finite element analyses of the problem under small-scale yielding conditions are performed. The validity of the asymptotic fields and their range of dominance are determined by comparing them with the results of the full-field finite element analyses. Finally, theoretical predictions are made of the variations of the dynamic fracture toughness with crack velocity. The influence of the bi-material parameters on the above variation is investigated.

Colloidal dispersions in a liquid crystalline medium

We have prepared stable colloidal suspensions in a lyotropic liquid crystal exhibiting an isotropic-nematic-lamellar phase sequence. Small angle neutron scattering (SANS) and dynamic light scattering (DLS) studies show the existence of attractive interparticle interactions in the nematic phase, which lead to a gas-liquid transition of the particles. The resulting liquid phase is weakly anisotropic. Further, the nematic-lamellar transition of the liquid crystal is found to be accompanied by a liquid-solid transition of the particles.