Fundamental structure of steady plastic shock waves in metals

The propagation of steady plane shock waves in metallic materials is considered. Following the constitutive framework adopted by R. J. Clifton [Shock Waves and the Mechanical Properties of Solids, edited by J. J. Burke and V. Weiss (Syracuse University Press, Syracuse, N.Y., 1971), p. 73] for analyzing elastic–plastic transient waves, an analytical solution of the steady state propagation of plastic shocks is proposed. The problem is formulated in a Lagrangian setting appropriate for large deformations. The material response is characterized by a quasistatic tensile (compression) test (providing the isothermal strain hardening law). In addition the elastic response is determined up to second order elastic constants by ultrasonic measurements. Based on this simple information, it is shown that the shock kinetics can be quite well described for moderate shocks in aluminum with stress amplitude up to 10 GPa. Under the later assumption, the elastic response is assumed to be isentropic, and thermomechanical coupling is neglected. The model material considered here is aluminum, but the analysis is general and can be applied to any viscoplastic material subjected to moderate amplitude shocks. Comparisons with experimental data are made for the shock velocity, the particle velocity and the shock structure. The shock structure is obtained by quadrature of a first order differential equation, which provides analytical results under certain simplifying assumptions. The effects of material parameters and loading conditions on the shock kinetics and shock structure are discussed. The shock width is characterized by assuming an overstress formulation for the viscoplastic response. The effects on the shock structure of strain rate sensitivity are analyzed and the rationale for the J. W. Swegle and D. E. Grady [J. Appl. Phys. 58, 692 (1985)] universal scaling law for homogeneous materials is explored. Finally, the ability to deduce information on the viscoplastic response of materials subjected to very high strain rates from shock wave experiments is discussed

Observations of transient high temperature vortical microstructures in solids during adiabatic shear banding

By using a unique infrared high-speed camera especially constructed for recording highly transient temperature fields at the microscale, we are able to reveal the spatial and temporal microstructure within dynamically growing shear bands in metals. It is found that this structure is highly nonuniform and possesses a transient, short range periodicity in the direction of shear band growth in the form of an array of intense "hot spots" reminiscent of the well-known, shear-induced hydrodynamic instabilities in fluids. This is contrary to the prevailing classical view that describes the deformations and the temperatures within shear bands as being essentially one-dimensional fields. These observations are also reminiscent of the nonuniform structure of localized shear regions believed to exist, at an entirely different length scale, in the earth's lower crust and upper mantle

Three-Dimensional Analysis of the Effect of Epidermal Growth Factor on Cell-Cell Adhesion in Epithelial Cell Clusters

The effect that growth factors such as epidermal growth factor (EGF) have on cell-cell adhesion is of interest in the study of cellular processes such as epithelial-mesenchymal transition. Because cell-cell adhesions cannot be measured directly, we use three-dimensional traction force microscopy to measure the tractions applied by clusters of MCF-10A cells to a compliant substrate beneath them before and after stimulating the cells with EGF. To better interpret the results, a finite element model, which simulates a cluster of individual cells adhered to one another and to the substrate with linear springs, is developed to better understand the mechanical interaction between the cells in the experiments. The experiments and simulations show that the cluster of cells acts collectively as a single unit, indicating that cell-cell adhesion remains strong before and after stimulation with EGF. In addition, the experiments and model emphasize the importance of three-dimensional measurements and analysis in these experiments

Competing failure mechanisms in thin films: Application to layer transfer

We investigate the origin of transverse cracks often observed in thin films obtained by the layer transfer technique. During this process, two crystals bonded to each other containing a weak plane produced by ion implantation are heated to let a thin layer of one of the material on the other. The level of stress imposed on the film during the heating phase due to the mismatch of thermal expansion coefficients of the substrate and the film is shown to be the dominent factor in determining the quality of the transferred layer. In particular, it is shown that if the film is submitted to a tensile stress, the microcracks produced by ion implantation are not stable and deviate from the plane of implantation making the layer transfer process impossible. However, if the compressive stress exceeds a threshold value, after layer transfer, the film can buckle and delaminate, leading to transverse cracks induced by bending. As a result, we show that the imposed stress σ_m —- or equivalently the heating temperature -— must be within the range −σ_c<σ_m<0 to produce an intact thin film where σ_c depends on the interfacial fracture energy and the size of defects at the interface between film and substrate

Indian Argo Trajectories and Surface Currents

An important objective of Argo is measurement of ocean circulation. As Argo floats collect salinity/temperature profiles, they also give information on the surface and subsurface currents. Indian National Centre for Ocean Information Services (INCOIS) being a Regional Data Assembly Centre for Indian Argo has so far launched 160 floats in the Indian Ocean to develop the global ocean observation system as a part of international cooperation project and is responsible for real time generation and dissemination of this data. This work is an attempt to extract information on sea surface in application to the Lagrangian part of the Argo floats. This report constitutes two sections. The first section documents the process of operational generation and dissemination of the Argo trajectory data. The second section describes the data product, Surface Currents and its comparison with Simple Ocean Data Assimilation & Drifting buoy currents

Surface winds in the Arabian Sea from MSMR - An empirical approach

Multi-channel Scanning Microwave Radiometer (MSMR) onboard 1RS P4 (Oceansat I) measured Brightness Temperature data of the different bands are found sensitive to the surface and the overlying atmosphere to different degrees. A judicious combination of multi-channel data can provide such oceanic/atmospheric parameters as surface wind speed, sea surface temperature, water vapour in the marine atmosphere, etc. This paper highlights results obtained in relation to surface wind speed. Co-location and concurrence of several ocean data buoys in the Arabian Sea with MSMR observations allowed empirical construction of D-matrix coefficients for surface wind speed. With both MSMR and the Arabian Sea buoys functioning for the period of one and a half year (June, 1999 to December, 2000) without interruptions provided a large database. All channels are found to exhibit moderate sensitivity to surface wind speed. MSMR data in the immediate vicinity (within 150 km) of the buoy locations and within a time window of one hour were used. A multi-channel linear equation for surface wind speed was subsequently derived. The equation was subjected to tests with independent data set for the period January - June 2001 over the Arabian Sea and found to be moderately accurate. The empirical equation is expected to be useful for regional applications over the Arabian Sea and over regions closer to west coasts, which might have been flagged out in the operational geophysical data stream. An interesting subset of data revealed the wind signatures of the May 2001 cyclone in the Arabian Sea

Gurulinga Sangama Worship

Saiva metaphysics, guru worship, Linga worship, confluence worship, and the goal of the soul is to attain godliness. Thirumanthiram, the eighth sutra of Sivagnanabodha refers to the Saarala (Single Point) system. The perfection of the soul, the word Guru is also referred to as the remover of darkness. God will appear as a Guru. Arrogance, karma, and illusion lead to birth. It is God who prevents them. The word Shiva means purity. It is God who purifies the three unclean things. According to perfection in the souls, he will manifest himself as form, incorporeity, and corporeal. Devoted service, godly deeds, meditation, and knowledge are the paths to reaching God. The highest point of spirituality is knowledge. Gurulinga Sangama worship is the simplest way to attain enlightenment. The clergy regarded God as their guru. Gurulinga Sangama worship is a simple means for the soul to be liberated. The Lord himself has come as the Guru of Manickavasagar. He gave knowledge to the Apparadi through his sister. Guru worship is the first way for the soul to reach the end. Guru worship removes the misery of births. Linga worship is the worship of the embodied form of Linga (Here, Linga that is visible to the eyes is invisible to the mind). Confluence worship is the practice of performing worship together with the devotees. Confluence worship is the simplest way to receive god's grace. The confluence worship is explained in the 12 sutras of Thirugnanabodhar. Gurulinga Sangama worship is a state of interconnection with the Lord. When arrogance reduces, the strength of Karma and illusion also diminish. This is the basis of Gurulinga Sangama worship

Population Firm Interaction and the Dynamics of Assimilation Gap

The paper shows that the interaction between population and firm knowledge produces a non-monotonic change in the assimilation gap. The assimilation gap follows a convex curve experiencing an upward slope driven by imitation and the downward slope by knowledge spillovers. Changes in the characteristics of innovation shift its peak across time. The relative advantage and compatibility shift the peak towards the left and the complexity shifts it to the right. The model is tested in a simulated environment and offers insights into the differences in temporal trajectories of the various adopter groups

An Experimental Study on Mesh-and-Fiber Reinforced Cementitious Composites

Development of new composite materials which reduces the large consumption of natural resources is an approach towards sustainability. This study is an attempt to explore the possibility of adding polyolefin fibers (PL-F) in steel mesh reinforced cementitious composites (SMRCC) and conduct low velocity impact tests. For this purpose, test specimens of slab size 250 X 250 X 25 mm (thickness) were cast with steel mesh (3 to 5 layers) and polyolefin fibers (0.5-2.5% of  volume of specimens with 0.5% interval) and compared with control specimens (cast with steel mesh of 3 to 5 layers). Statistical t-tests were employed to find out the paired difference in impact energy absorption capacity between initial impact energy absorption (IIEA) and ultimate impact energy absorption (UIEA). Also, through statistical analysis, it was found that when steel mesh layers were varied keeping fiber percentage constant, and vice-versa, there were significant differences in the energy absorption capacity of cementitious slabs