Ajit Mal

Bio: Ajit Mal is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Lamb waves & Composite laminates. The author has an hindex of 38, co-authored 205 publications receiving 7217 citations. Previous affiliations of Ajit Mal include University of Southern California & California Institute of Technology.

Measurement of thin film interfacial properties using nanosecond laser source

Abstract: A high energy Nd:YAG laser source is used to determine the intrinsic adhesion strength of thin films deposited on substrates. The specimen is designed to convert the thermal energy of the short duration laser pulse to a strong compressive stress on the back face of the substrate. The compressive stress propagates through the layered structure, and upon reflection from the free surface of the film, generates a tensile wave which produces tensile failure of the interface. The stress associated with the interface failure is calculated from a theoretical model of wave propagation through the layered medium. The compressive stress produced by the laser source is determined from a second experiment involving the homogeneous substrate by removing the film. Examples of the applications of the technique in cell biology are presented.

Elastic analysis of a half-plane containing an inclusion and a void using a mixed volume and boundary integral equation method

Abstract: A mixed volume and boundary integral equation method is used to calculate the plane elastostatic field in an isotropic elastic half-plane containing an isotropic or anisotropic inclusion and a void subject to remote loading parallel to a traction-free boundary. A detailed analysis of the stress field is carried out for three different geometries of the problem. It is demonstrated that the method is very accurate and effective for investigating local stresses in an isotropic elastic half-plane containing multiple isotropic or anisotropic inclusions and multiple voids.

Recent Advances in the Application of Leaky Lamb Waves to the Nondestructive Evaluation of Adhesive Bonds

Abstract: In earlier work, the feasibility of applying the Leaky Lamb Wave (LLW) method to the nondestructive evaluation (NDE) of bonded rubber/metal structures was demonstrated. The capability of LLWs to detect and delineate flaws at the bond line was proven, even when the adherends remain in intimate contact. However, variations in adherend properties, surface orientation and thickness can adversely affect detection of bond flaws and assessment of bond quality. In this paper, parameters which degrade both LLW sensitivity and resolution to bond flaws are discussed. Examples of the effects of cold work, thickness change and specimen tilt are presented along with bond flaw detection and characterization results. Also, advances in the theory of bond flaw NDE by LLWs are presented.

Scattering of Love waves by a constriction in the crust

Abstract: A perturbation technique is applied to a study of the propagation of Love waves in a layer of nonuniform thickness lying over a half-space. The layer is assumed to have a plane free surface while the interface protrudes into it in a certain finite region. Love waves are generated by a point source on the free surface of the crust at a distance from the inhomogeneity. A simple but rigorous derivation is given for the scattering of the waves incident at the inhomogeneity. The theory is applicable for any shape of the inhomogeneity. Numerical calculations for the particular case in which the height of the perturbation is constant throughout a finite length indicate mode conversion in the constricted region. There is essentially a phase shift in the same mode; the superposition of the converted modes, however, gives rise to amplitude perturbation in every mode. The results are fairly accurate as long as the height of the inhomogeneity is small in comparison with the wavelength of the incident waves. By suitable interpretation of the results, the theory is extended to include the case in which the area of the perturbed region is large. Although only the scalar problem has been considered, the theory can be extended to treat the vector case without much difficulty.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

An introduction to structural health monitoring

Abstract: This introduction begins with a brief history of SHM technology development. Recent research has begun to recognise that a productive approach to the Structural Health Monitoring (SHM) problem is to regard it as one of statistical pattern recognition (SPR); a paradigm addressing the problem in such a way is described in detail herein as it forms the basis for the organisation of this book. In the process of providing the historical overview and summarising the SPR paradigm, the subsequent chapters in this book are cited in an effort to show how they fit into this overview of SHM. In the conclusions are stated a number of technical challenges that the authors believe must be addressed if SHM is to gain wider acceptance.

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress

Abstract: Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

Silica-Like Malleable Materials from Permanent Organic Networks

Abstract: Permanently cross-linked materials have outstanding mechanical properties and solvent resistance, but they cannot be processed and reshaped once synthesized Non–cross-linked polymers and those with reversible cross-links are processable, but they are soluble We designed epoxy networks that can rearrange their topology by exchange reactions without depolymerization and showed that they are insoluble and processable Unlike organic compounds and polymers whose viscosity varies abruptly near the glass transition, these networks show Arrhenius-like gradual viscosity variations like those of vitreous silica Like silica, the materials can be wrought and welded to make complex objects by local heating without the use of molds The concept of a glass made by reversible topology freezing in epoxy networks can be readily scaled up for applications and generalized to other chemistries

A facile soft-template synthesis of mesoporous polymeric and carbonaceous nanospheres

Abstract: The controlled synthesis of monodisperse nanospheres faces a number of difficulties, such as extensive crosslinking during hydrothermal processes. Here, the authors show a route for the controlled synthesis of mesoporous polymer nanospheres, which can be further converted into carbon nanospheres through carbonization.