Lead Retention by Soils at Field Moisture Contents

The majority of studies pertaining to lead retention by clays and soils have examined the mechanisms, kinetics, and adsorption isotherms using the batch experiment technique that employs solid: water extracts of 1:10 and 1:20. Field soil deposits generally have much lower gravimetric water content ranging between 9 and 45%. Given the wide disparity in the solids: water ratio employed in the batch experiment technique and that prevailing in field deposits, this paper examines the lead retention characteristics of soils at field moisture contents (6%, 13%, and 25%) using artificially lead-contaminated soil specimens. A residually derived (i.e., formed by in-situ weathering of parent rock) red soil was used to prepare the artificially contaminated soil specimens. The impact of variations in clay content on lead retention was examined by diluting the residual soil with various amounts (0 to 60%) of river sand. Soil specimens remolded at 6 and 13% moisture contents produced very stiff to hard soils on compaction, while specimens remolded at 25% moisture content existed in the slurry state. The soil specimens were contaminated with low (30mg/kg) to high (2500mg/kg) concentrations of lead ions by remolding them with 160ppm to 10,000ppm ionic lead solutions. Lead retention by soils at field moisture contents was determined by extracting the lead from the soil using a water leach test. Experimental results showed that the bulk (71 to 99%) of the added lead was retained by the soil in insoluble form at the field moisture content. Correlations between the amount of lead retained and soil/solution parameters indicated that the amounts of Pb retained at field moisture content is a function of the initial Pb addition, total sand content, effective clay porosity, and soil pH.

Safety Assessment of a Masonry Arch Bridge: Field Testing and Simulations

The safety of an in-service brick arch railway bridge is assessed through field testing and finite-element analysis. Different loading test train configurations have been used in the field testing. The response of the bridge in terms of displacements, strains, and accelerations is measured under the ambient and design train traffic loading conditions. Nonlinear fracture mechanics-based finite-element analyses are performed to assess the margin of safety. A parametric study is done to study the effects of tensile strength on the progress of cracking in the arch. Furthermore, a stability analysis to assess collapse of the arch caused by lateral movement at the springing of one of the abutments that is elastically supported is carried out. The margin of safety with respect to cracking and stability failure is computed. Conclusions are drawn with some remarks on the state of the bridge within the framework of the information available and inferred information. DOI: 10.1061/(ASCE)BE.1943-5592.0000338. (C) 2013 American Society of Civil Engineers.

Proactive control of sequential saccades in the human supplementary eye field

Our ability to regulate behavior based on past experience has thus far been examined using single movements. However, natural behavior typically involves a sequence of movements. Here, we examined the effect of previous trial type on the concurrent planning of sequential saccades using a unique paradigm. The task consisted of two trial types: no-shift trials, which implicitly encouraged the concurrent preparation of the second saccade in a subsequent trial; and target-shift trials, which implicitly discouraged the same in the next trial. Using the intersaccadic interval as an index of concurrent planning, we found evidence for context-based preparation of sequential saccades. We also used functional MRI-guided, single-pulse, transcranial magnetic stimulation on human subjects to test the role of the supplementary eye field (SEF) in the proactive control of sequential eye movements. Results showed that (i) stimulating the SEF in the previous trial disrupted the previous trial type-based preparation of the second saccade in the nonstimulated current trial, (ii) stimulating the SEF in the current trial rectified the disruptive effect caused by stimulation in the previous trial, and (iii) stimulating the SEF facilitated the preparation of second saccades based on previous trial type even when the previous trial was not stimulated. Taken together, we show how the human SEF is causally involved in proactive preparation of sequential saccades.

MRT Letter: Experimental Verification of Vectorial Theory to Determine Field at the Geometrical Focus of a Cylindrical Lens

We provide experimental evidence supporting the vectorial theory for determining electric field at and near the geometrical focus of a cylindrical lens. This theory provides precise distribution of field and its polarization effects. Experimental results show a close match (approximate to 95% using (2)-test) with the simulation results (obtained using vectorial theory). Light-sheet generated both at low and high NA cylindrical lens shows the importance of vectorial theory for further development of light-sheet techniques. Potential applications are in planar imaging systems (such as, SPIM, IML-SPIM, imaging cytometry) and spectroscopy. Microsc. Res. Tech. 77:105-109, 2014. (c) 2014 Wiley Periodicals, Inc.

Evaluating shock absorption behavior of small-sized systems under programmable electric field

A simple ball-drop impact tester is developed for studying the dynamic response of hierarchical, complex, small-sized systems and materials. The developed algorithm and set-up have provisions for applying programmable potential difference along the height of a test specimen during an impact loading; this enables us to conduct experiments on various materials and smart structures whose mechanical behavior is sensitive to electric field. The software-hardware system allows not only acquisition of dynamic force-time data at very fast sampling rate (up to 2 x 10(6) samples/s), but also application of a pre-set potential difference (up to +/- 10 V) across a test specimen for a duration determined by feedback from the force-time data. We illustrate the functioning of the set-up by studying the effect of electric field on the energy absorption capability of carbon nanotube foams of 5 x 5 x 1.2 mm(3) size under impact conditions. (C) 2014 AIP Publishing LLC.

Dielectric elastomers: Asymptotically-correct three-dimensional displacement field

Asymptotically-accurate dimensional reduction from three to two dimensions and recovery of 3-D displacement field of non-prestretched dielectric hyperelastic membranes are carried out using the Variational Asymptotic Method (VAM) with moderate strains and very small ratio of the membrane thickness to its shortest wavelength of the deformation along the plate reference surface chosen as the small parameters for asymptotic expansion. Present work incorporates large deformations (displacements and rotations), material nonlinearity (hyperelasticity), and electrical effects. It begins with 3-D nonlinear electroelastic energy and mathematically splits the analysis into a one-dimensional (1-D) through-the-thickness analysis and a 2-D nonlinear plate analysis. Major contribution of this paper is a comprehensive nonlinear through-the-thickness analysis which provides a 2-D energy asymptotically equivalent of the 3-D energy, a 2-D constitutive relation between the 2-D generalized strain and stress tensors for the plate analysis and a set of recovery relations to express the 3-D displacement field. Analytical expressions are derived for warping functions and stiffness coefficients. This is the first attempt to integrate an analytical work on asymptotically-accurate nonlinear electro-elastic constitutive relation for compressible dielectric hyperelastic model with a generalized finite element analysis of plates to provide 3-D displacement fields using VAM. A unified software package `VAMNLM' (Variational Asymptotic Method applied to Non-Linear Material models) was developed to carry out 1-D non-linear analysis (analytical), 2-D non-linear finite element analysis and 3-D recovery analysis. The applicability of the current theory is demonstrated through an actuation test case, for which distribution of 3-D displacements are provided. (C) 2014 Elsevier Ltd. All rights reserved.

Shock tunnel measurements of surface pressures in shock induced separated flow field using MEMS sensor array

Characterized not just by high Mach numbers, but also high flow total enthalpies-often accompanied by dissociation and ionization of flowing gas itself-the experimental simulation of hypersonic flows requires impulse facilities like shock tunnels. However, shock tunnel simulation imposes challenges and restrictions on the flow diagnostics, not just because of the possible extreme flow conditions, but also the short run times-typically around 1 ms. The development, calibration and application of fast response MEMS sensors for surface pressure measurements in IISc hypersonic shock tunnel HST-2, with a typical test time of 600 mu s, for the complex flow field of strong (impinging) shock boundary layer interaction with separation close to the leading edge, is delineated in this paper. For Mach numbers 5.96 (total enthalpy 1.3 MJ kg(-1)) and 8.67 (total enthalpy 1.6 MJ kg(-1)), surface pressures ranging from around 200 Pa to 50 000 Pa, in various regions of the flow field, are measured using the MEMS sensors. The measurements are found to compare well with the measurements using commercial sensors. It was possible to resolve important regions of the flow field involving significant spatial gradients of pressure, with a resolution of 5 data points within 12 mm in each MEMS array, which cannot be achieved with the other commercial sensors. In particular, MEMS sensors enabled the measurement of separation pressure (at Mach 8.67) near the leading edge and the sharply varying pressure in the reattachment zone.