Seismic stability of a long unsupported circular tunnel

The stability of a long unsupported circular tunnel (opening) in a cohesive frictional soil has been assessed with the inclusion of pseudo-static horizontal earthquake body forces. The analysis has been performed under plane strain conditions by using upper bound finite element limit analysis in combination with a linear optimization procedure. The results have been presented in the form of a non-dimensional stability number (gamma H-max/c); where H = tunnel cover, c refers to soil cohesion and gamma(max) is the maximum unit weight of soil mass which the tunnel can support without collapse. The results have been obtained for various values of H/D (D = diameter of the tunnel), internal friction angle (phi) of soil, and the horizontal earthquake acceleration coefficient (alpha(h)). The computations reveal that the values of the stability numbers (i) decrease quite significantly with an increase in alpha(h), and (ii) become continuously higher for greater values of H/D and phi. As expected, the failure zones around the periphery of the tunnel becomes always asymmetrical with an inclusion of horizontal seismic body forces. (c) 2012 Elsevier Ltd. All rights reserved.

Regulation of S100A2 expression by TGF-beta-induced MEK/ERK signalling and its role in cell migration/invasion

S100A2, an EF hand calcium-binding protein, is a potential biomarker in several cancers and is also a TGF-beta (transforming growth factor-beta)-regulated gene in melanoma and lung cancer cells. However, the mechanism of S100A2 regulation by TGF-beta and its significance in cancer progression remains largely unknown. In the present study we report the mechanism of S100A2 regulation by TGF-beta and its possible role in TGF-beta-mediated tumour promotion. Characterization of the S100A2 promoter revealed an AP-1 (activator protein-1) element at positions -1161 to -1151 as being the most critical factor for the TGF-beta 1 response. Chromatin immunoprecipitation and electrophoretic mobility-shift assays confirmed the functional binding of the AP-1 complex, predominantly JunB, to the S100A2 promoter in response to TGF-beta 1 in HaCaT keratinocytes. JunB overexpression markedly stimulated the S100A2 promoter which was blocked by the dominant-negative JunB and MEK1 MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase 1] inhibitor, PD98059. Intriguingly, despite the presence of a putative SMAD-binding element, S100A2 regulation by TGF-beta 1 was found to be SMAD3 independent. Interestingly, p53 protein and TGF-beta 1 show synergistic regulation of the S100A2 promoter. Finally, knockdown of S100A2 expression compromised TGF-beta 1-induced cell migration and invasion of Hep3B cells. Together our findings highlight an important link between the TGF-beta 1-induced MAPK and p53 signalling pathways in the regulation of S100A2 expression and pro-tumorigenic actions.

Minimum power consumption for drag reduction on a circular cylinder by tangential surface motion

We investigate the effect of a prescribed tangential velocity on the drag force on a circular cylinder in a spanwise uniform cross flow. Using a combination of theoretical and numerical techniques we make an attempt at determining the optimal tangential velocity profiles which will reduce the drag force acting on the cylindrical body while minimizing the net power consumption characterized through a non-dimensional power loss coefficient (C-PL). A striking conclusion of our analysis is that the tangential velocity associated with the potential flow, which completely suppresses the drag force, is not optimal for both small and large, but finite Reynolds number. When inertial effects are negligible (R e << 1), theoretical analysis based on two-dimensional Oseen equations gives us the optimal tangential velocity profile which leads to energetically efficient drag reduction. Furthermore, in the limit of zero Reynolds number (Re -> 0), minimum power loss is achieved for a tangential velocity profile corresponding to a shear-free perfect slip boundary. At finite Re, results from numerical simulations indicate that perfect slip is not optimum and a further reduction in drag can be achieved for reduced power consumption. A gradual increase in the strength of a tangential velocity which involves only the first reflectionally symmetric mode leads to a monotonic reduction in drag and eventual thrust production. Simulations reveal the existence of an optimal strength for which the power consumption attains a minima. At a Reynolds number of 100, minimum value of the power loss coefficient (C-PL = 0.37) is obtained when the maximum in tangential surface velocity is about one and a half times the free stream uniform velocity corresponding to a percentage drag reduction of approximately 77 %; C-PL = 0.42 and 0.50 for perfect slip and potential flow cases, respectively. Our results suggest that potential flow tangential velocity enables energetically efficient propulsion at all Reynolds numbers but optimal drag reduction only for Re -> infinity. The two-dimensional strategy of reducing drag while minimizing net power consumption is shown to be effective in three dimensions via numerical simulation of flow past an infinite circular cylinder at a Reynolds number of 300. Finally a strategy of reducing drag, suitable for practical implementation and amenable to experimental testing, through piecewise constant tangential velocities distributed along the cylinder periphery is proposed and analysed.

A constant factor approximation algorithm for boxicity of circular arc graphs

Boxicity of a graph G(V, E) is the minimum integer k such that G can be represented as the intersection graph of k-dimensional axis parallel boxes in Rk. Equivalently, it is the minimum number of interval graphs on the vertex set V such that the intersection of their edge sets is E. It is known that boxicity cannot be approximated even for graph classes like bipartite, co-bipartite and split graphs below O(n0.5-ε)-factor, for any ε > 0 in polynomial time unless NP = ZPP. Till date, there is no well known graph class of unbounded boxicity for which even an nε-factor approximation algorithm for computing boxicity is known, for any ε < 1. In this paper, we study the boxicity problem on Circular Arc graphs - intersection graphs of arcs of a circle. We give a (2+ 1/k)-factor polynomial time approximation algorithm for computing the boxicity of any circular arc graph along with a corresponding box representation, where k ≥ 1 is its boxicity. For Normal Circular Arc(NCA) graphs, with an NCA model given, this can be improved to an additive 2-factor approximation algorithm. The time complexity of the algorithms to approximately compute the boxicity is O(mn+n2) in both these cases and in O(mn+kn2) which is at most O(n3) time we also get their corresponding box representations, where n is the number of vertices of the graph and m is its number of edges. The additive 2-factor algorithm directly works for any Proper Circular Arc graph, since computing an NCA model for it can be done in polynomial time.

Asymptotic wavenumber expansions of a strongly orthotropic fluid-filled circular cylindrical shell

In this paper, a suitable nondimensional `orthotropy parameter' is defined and asymptotic expansions are found for the wavenumbers in in vacuo and fluid-filled orthotropic circular cylindrical shells modeled by the Donnell-Mushtari theory. Here, the elastic moduli in the two directions are greatly different; the particular case of E-x >> E-theta is studied in detail, i.e., the elastic modulus in the longitudinal direction is much larger than the elastic modulus in the circumferential direction. These results are compared with the corresponding results for a `slightly orthotropic' shell (E-x approximate to E-theta) and an isotropic shell. The novelty of this presentation lies in obtaining closed-form expansions for the in vacuo and coupled wavenumbers in an orthotropic shell using perturbation methods aiding in a better physical understanding of the problem.

Asymptotic expansions for the structural wavenumbers of isotropic and orthotropic fluid-filled circular cylindrical shells in the intermediate frequency range

We consider wavenumbers in in vacuo and fluid-filled isotropic and orthotropic shells. Using the Donnell-Mushtari (DM) theory we find compact and elegant asymptotic expansions for the wavenumbers in the intermediate frequency range, i.e., around the ring frequency. This frequency range corresponds to the frequencies where there is a rapid change in the values of bending wavenumbers and is found to exist in isotropic and orthotropic shells (in vacua and fluid-filled) for low circumferential orders n only. The same is first identified using the n=0 mode of an orthotropic shell. Following this, using the expression for the intermediate frequency, asymptotic expansions are found for other cases. Here, in order to get compact expansions we consider slight orthotropy (epsilon << 1) and light fluid loading (mu << 1). Thus, the orthotropy parameter epsilon and the fluid loading parameter mu are used as asymptotic parameters along with the non-dimensional thickness parameter beta. The methodology can be extended to any order of epsilon, only the expansions become unwieldy. The expansions are matched with the numerical solutions of the corresponding dispersion relation. The match is found to be good.

Stability of a long unsupported circular tunnel in soils with seismic forces

By using the lower-bound finite element limit analysis, the stability of a long unsupported circular tunnel has been examined with an inclusion of seismic body forces. The numerical results have been presented in terms of a non-dimensional stability number (gamma H/c) which is plotted as a function of horizontal seismic earth pressure coefficient (k (h)) for different combinations of H/D and I center dot; where (1) H is the depth of the crest of the tunnel from ground surface, (2) D is the diameter of the tunnel, (3) k (h) is the earthquake acceleration coefficient and (4) gamma, c and I center dot define unit weight, cohesion and internal friction angle of soil mass, respectively. The stability numbers have been found to decrease continuously with an increase in k (h). With an inclusion of k (h), the plastic zone around the periphery of the tunnel becomes asymmetric. As compared to the results reported in the literature, the present analysis provides a little lower estimate of the stability numbers. The numerical results obtained would be useful for examining the stability of unsupported tunnel under seismic forces.

Numerical simulations of CO2 migration during charnockite genesis

Charnockite is considered to be generated either through the dehydration of granitic magma by CO2 purging or by solid-state dehydration through CO2 metasomatism during granulite facies metamorphism. To understand the extent of dehydration, CO2 migration is quantitatively modeled in silicate melt and metasomatic fluid as a function of temperature, H2O wt%, pressure, basal CO2 flux and dynamic viscosity. Numerical simulations show that CO2 advection through porous and permeable high-grade metamorphic rocks can generate dehydrated patches close to the CO2 flow path, as illustrated by the occurrences of ``incipient charnockites.'' CO2 reaction-front velocity constrained by field observations is 0.69 km/m.y., a reasonable value, which matches well with other studies. On the other hand, temperature, rate of cooling, and basal CO2 flux are the critical parameters affecting CO2 diffusion through a silicate melt. CO2 diffusion through silicate melt can only occur at temperature greater than 840 degrees C and during slow cooling (<= 3.7 x 10(-5) degrees C/yr), features that are typical of magma emplacement in the lower crust. Stalling of CO2 fluxing at similar to 840 degrees C explains why some deep-level plutons contain both hydrous and anhydrous (charnockitic) mineral assemblages. CO2 diffusion through silicate melt is virtually insensitive to pressure. Addition of CO2 basal flux facilitates episodic dehydrated melt migration by generating fracture pathways.

Dynamics of a flexible splitter plate in the wake of a circular cylinder

Rigid splitter plates in the wake of bluff bodies are known to suppress the primary vortex shedding. In the present work, we experimentally study the problem of a flexible splitter plate in the wake of a circular cylinder. In this case, the splitter plate is free to continuously deform along its length due to the fluid forces acting on it; the flexural rigidity (EI) of the plate being an important parameter. Direct visualizations of the splitter plate motions, for very low values of flexural rigidity (EI), indicate periodic traveling wave type deformations of the splitter plate with maximum tip amplitudes of the order of I cylinder diameter. As the Reynolds number based on cylinder diameter is varied, two regimes of periodic splitter plate motions are found that are referred to as mode I and mode II, with a regime of aperiodic motions between them. The frequency of plate motions in both periodic modes is found to be close to the plane cylinder Strouhal number of about 0.2, while the average frequencies in the non-periodic regime are substantially lower. The measured normalized phase speed of the traveling wave for both periodic modes is also close to the convection speed of vortices in the plane cylinder wake. As the flexural rigidity of the plate (EI) is increased, the response of the plate was found to shift to the right when plotted with flow speed or Re. To better capture the effect of varying EI, we define and use a non-dimensional bending stiffness, K*, similar to the ones used in the flag flutter problem, K*=EI/(0.5 rho(UL3)-L-2), where U is the free-stream velocity and L is the splitter plate length. Amplitude data for different EI cases when plotted against this parameter appear to collapse on to a single curve for a given splitter plate length. Measurements of the splitter plate motions for varying splitter plate lengths indicate that plates that are substantially larger than the formation length of the plane cylinder wake have similar responses, while shorter plates show significant differences.

Effect of steady rotation on low Reynolds number vortex shedding behind a circular cylinder

In this paper control of oblique vortex shedding in the wake behind a straight circular cylinder is explored experimentally and computationally. Towards this, steady rotation of the cylinder about its axis is used as a control device. Some limited studies are also performed with a stepped circular cylinder, where at the step the flow is inevitably three-dimensional irrespective of the rotation rate. When there is no rotation, the vortex shedding pattern is three dimensional as described in many previous studies. With a non-zero rotation rate, it is demonstrated experimentally as well as numerically that the shedding pattern becomes more and more two-dimensional. At sufficiently high rotation rates, the vortex shedding is completely suppressed.

Stability of long unsupported twin circular tunnels in soils

The stability of two long unsupported circular parallel tunnels aligned horizontally in fully cohesive and cohesive-frictional soils has been determined. An upper bound limit analysis in combination with finite elements and linear programming is employed to perform the analysis. For different clear spacing (S) between the tunnels, the stability of tunnels is expressed in terms of a non-dimensional stability number (gamma H-max/c); where H is tunnel cover, c refers to soil cohesion, and gamma(max) is maximum unit weight of soil mass which the tunnels can bear without any collapse. The variation of the stability number with tunnels' spacing has been established for different combinations of H/D, m and phi; where D refers to diameter of each tunnel, phi is the internal friction angle of soil and m accounts for the rate at which the cohesion increases linearly with depth. The stability number reduces continuously with a decrease in the spacing between the tunnels. The optimum spacing (S-opt) between the two tunnels required to eliminate the interference effect increases with (i) an increase in H/D and (ii) a decrease in the values of both m and phi. The value of S-opt lies approximately in a range of 1.5D-3.5D with H/D = 1 and 7D-12D with H/D = 7. The results from the analysis compare reasonably well with the different solutions reported in literature. (C) 2013 Elsevier Ltd. All rights reserved.

Computational Study of the Migration of Rhenium from One Enantioface of an Olefin to the Other Facilitated by (C-H)center dot center dot center dot Re Interactions

The migration of a metal atom in a metal olefin complex from one pi face of the olefin to the opposite pi face has been rarely documented. Gladysz and co-workers showed that such a movement is indeed possible in monosubstituted chiral Re olefin complexes, resulting in diastereomerization. Interestingly, this isomerization occurred without dissociation, and on the basis of kinetic isotope effects, the involvement of a trans C-H bond was indicated. Either oxidative addition or an agostic interaction of the vinylic C-H(D) bond with the metal could account for the experimentally observed kinetic isotope effect. In this study we compute the free energy of activation for the migration of Re from one enantioface of the olefin to the other through various pathways. On the basis of DFT calculations at the B3LYP level we show that a trans (C-H)center dot center dot center dot Re interaction and trans C-H oxidative addition provide a nondissociative path for the diastereomerization. The trans (C-H)center dot center dot center dot Re interaction path is computed to be more favorable by 2.3 kcal mol(-1) than the oxidative addition path. While direct experimental evidence was not able to discount the migration of the metal through the formation of a eta(2)-arene complex (conducted tour mechanism), computational results at the B3LYP level show that it is energetically more expensive. Surprisingly, a similar analysis carried out at the M06 level computes a lower energy path for the conducted tour mechanism and is not consistent with the experimental isotope effects observed. Metal-(C-H) interactions and oxidative additions of the metal into C-H bonds are closely separated in energy and might contribute to unusual fluxional processes such as this diastereomerization.

Spectral Migration of Fluorescence in Graphene Oxide Aqueous Dispersions: Evidence for Excited-State Proton Transfer

Aqueous dispersions of graphene oxide (GO) exhibit strong pH-dependent fluorescence in the visible that originates, in part, from the oxygenated functionalities present. Here we examine the spectral migration on nanosecond time-scales of the pH dependent features in the fluorescence spectra. We show, from time-resolved emission spectra (TRES) constructed from the wavelength dependent fluorescence decay curves, that the migration is associated with excited state proton transfer. Both `intramolecular' and `intermolecular' transfer involving the quasi-molecular oxygenated aromatic fragments are observed. As a prerequisite to the time-resolved measurements, we have correlated the changes in the steady state fluorescence spectra with the sequence of dissociation events that occur in GO dispersions at different values of pH.

Asymptotic expansions for wavenumbers in orthotropic fluid-filled circular cylindrical shells for intermediate fluid loading

Coupled wavenumbers in infinite fluid-filled isotropic and orthotropic cylindrical shells are considered. Using the Donnell-Mushtari (DM) theory for thin shells, compact and elegant asymptotic expansions for the wavenumbers are found at an intermediate fluid loading for both the coupled rigid-duct modes (''fluid-originated'') and the coupled structural wavenumbers (''structure-originated modes'') over the entire frequency range where DM theory is valid. The coupled rigid-duct expansions are found to be valid for O(1) orthotropy and for all circumferential orders, whereas the coupled structural wavenumber expansions are valid for small orthotropy and for low circumferential orders. These two above results are then used to derive the expansions for a set of multiple complex roots that display a locking behavior at this intermediate fluid-loading. The expansions are matched with the numerical solutions of the coupled dispersion relation and the match is found to be good over most of the frequency range. (C) 2014 Acoustical Society of America.