Nonlinear ac response of anisotropic composites

When a suspension consisting of dielectric particles having nonlinear characteristics is subjected to a sinusoidal (ac) field, the electrical response will in general consist of ac fields at frequencies of the higher-order harmonics. These ac responses will also be anisotropic. In this work, a self-consistent formalism has been employed to compute the induced dipole moment for suspensions in which the suspended particles have nonlinear characteristics, in an attempt to investigate the anisotropy in the ac response. The results showed that the harmonics of the induced dipole moment and the local electric field are both increased as the anisotropy increases for the longitudinal field case, while the harmonics are decreased as the anisotropy increases for the transverse field case. These results are qualitatively understood with the spectral representation. Thus, by measuring the ac responses both parallel and perpendicular to the uniaxial anisotropic axis of the field-induced structures, it is possible to perform a real-time monitoring of the field-induced aggregation process.Comment: 14 pages and 4 eps figure

Gamma prediction models capturing the long term creep shrinkage performance of segmentally-erected prestressed box girder bridges

For creep-sensitive structures like statically in determined large bridges, it is essential to implement an efficient and realistic creep model for example in 3D Finite element considerations. Concrete creep, characterized by the gradual strain growth with time under a unit sustained stress applied at age t’, is generally calculated based on the given compliance function J(t, t’), where t is the current time. For stress level within the designed service strength, the concrete creep is assumed to follow the constitutive law of ageing linear viscoelasticity. In order to systematically study the main influence factors on bridge deflection measurements, which are known to show large scatter, a probabilistic analysis can be performed. Due to the associated computational costs such investigation are limited. The predictions based on these large-scattering basic variables (model inputs) are fraught with uncertainties and accordingly there is interest in alternative prediction models decoupled from complex analytical and numerical models, using measured structural responses. Gamma process considerations are such alternative methods. These approaches are suitable for capturing the structural behavior, like crack formation, bending, and surface strain, as well as previously mentioned long term creep shrinkage performance (can also be captured by traditional inspection and/or monitoring methods). The objective of this contribution is to illustrate the use of gamma process approaches for the prediction of the creep shrinkage performance of complex pre-stressed concrete bridges that incorporates uncertainties and makes predictions in terms of load rating and system-level more reliable with the help of structural health monitoring (SHM) data. The creep-shrinkage response of a statically in determined three span boxgirder bridge extracted (a) from a complex finite-element (FE) model, which is based on the gradual strain growth concrete creep, and (b) from structural health monitoring data, serves for the calibration and verification of the considered gamma process approaches. Finally, The ability of the Gamma process approaches to capture complex creep shrinkage processes in complex statically in determined will be critically examined

Diverse supramolecular structures formed by self-assembling proteins of the B acillus subtilis spore coat

Bacterial spores (endospores), such as those of the pathogens Clostridium difficile and Bacillus anthracis, are uniquely stable cell forms, highly resistant to harsh environmental insults. Bacillus subtilis is the best studied spore-former and we have used it to address the question of how the spore coat is assembled from multiple components to form a robust, protective superstructure. B. subtilis coat proteins (CotY, CotE, CotV and CotW) expressed in Escherichia coli can arrange intracellularly into highly stable macro-structures through processes of self-assembly. Using electron microscopy, we demonstrate the capacity of these proteins to generate ordered one-dimensional fibres, two-dimensional sheets and three-dimensional stacks. In one case (CotY), the high degree of order favours strong, cooperative intracellular disulfide cross-linking. Assemblies of this kind could form exquisitely adapted building blocks for higher-order assembly across all spore-formers. These physically robust arrayed units could also have novel applications in nano-biotechnology processes

Nonlinear alternating current responses of graded materials

When a composite of nonlinear particles suspended in a host medium is subjected to a sinusoidal electric field, the electrical response in the composite will generally consist of alternating current (AC) fields at frequencies of higher-order harmonics. The situation becomes more interesting when the suspended particles are graded, with a spatial variation in the dielectric properties. The local electric field inside the graded particles can be calculated by the differential effective dipole approximation, which agrees very well with a first-principles approach. In this work, a nonlinear differential effective dipole approximation and a perturbation expansion method have been employed to investigate the effect of gradation on the nonlinear AC responses of these composites. The results showed that the fundamental and third-harmonic AC responses are sensitive to the dielectric-constant and/or nonlinear-susceptibility gradation profiles within the particles. Thus, by measuring the AC responses of the graded composites, it is possible to perform a real-time monitoring of the fabrication process of the gradation profiles within the graded particles.Comment: 18 pages, 4 figure

Mesoscopic Effects in the Quantum Hall Regime

We report results of a study of (integer) quantum Hall transitions in a single or multiple Landau levels for non-interacting electrons in disordered two-dimensional systems, obtained by projecting a tight-binding Hamiltonian to corresponding magnetic subbands. In finite-size systems, we find that mesoscopic effects often dominate, leading to apparent non-universal scaling behaviour in higher Landau levels. This is because localization length, which grows exponentially with Landau level index, exceeds the system sizes amenable to numerical study at present. When band mixing between multiple Landau levels is present, mesoscopic effects cause a crossover from a sequence of quantum Hall transitions for weak disorder to classical behaviour for strong disorder. This behaviour may be of relevance to experimentally observed transitions between quantum Hall states and the insulating phase at low magnetic fields.Comment: 13 pages, 6 figures, Proceedings of the International Meeting on Mesoscopic and Disordered Systems, Bangalore December 2000, to appear in Pramana, February 200

Epithelial-mesenchymal transition is associated with increased invasiveness of side population cells from hepatoma SMMC-7721 cells

To study the in vitro invasiveness of side population (SP), cells purified from hepatoma SMMC-7721 cells and the expressions of epithelial-mesenchymal transition (EMT) markers of SP cells and non-SP (NSP) cells, fluorescence-activated cell sorting (FACS) was used to sort SP cells and NSP cells from SMMC-7721 cells. The in vitro invasiveness of both subpopulations was tested by Transwell chamber assay. Quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and western blot were applied to evaluate the expressions of Vimentin, E-cadherin, N-cadherin and Snail in SP cells and NSP cells, respectively. In Transwell invasion assay, the number of SP cells (66.3 ± 7.4) penetrating the basilar membrane was significantly higher than that of NSP cells (27.5 ± 6.5) (P < 0.01). The mRNA expressions of Vimentin, N-cadherin and Snail was significantly increased in SP cells (9.527-fold, 6.834- fold and 8.173-fold, respectively) when compared with that in NSP cells (P < 0.01). In contrast, the decrease of E-cadherin mRNA expression in SP cells (5.353-fold) was markedly higher than that in NSP cells (P<0.01). The protein expressions of E-cadherin, Vimentin, N-cadherin and Snail in SP cells were markedly different from those in NSP cells (0.174 ± 0.014 and 0.935 ± 0.012; 1.117 ± 0.012 and 0.314±0.011; 0.975 ± 0.017 and 0.179 ± 0.013; 0.917 ± 0.014 and 0.202 ± 0.013; P < 0.01). The results suggest that SP cells from hepatoma SMMC-7721 cells are highly invasive in vitro which may be related to the changes in expressions of EMT markers.Key words: SMMC-7721, cancer stem cells, side population cells, invasion, epithelial-mesenchymal transition