Knowledge-based systems

First developed two decades ago, knowledge-based systems have seen widespread application in recent years. While performance has been a strong focus of attention, building such systems has also expanded our conception of a computer program from a black box providing an answer to something capable of explaining its answers, acquiring new knowledge, and transferring knowledge to students. These abilities derive from distinguishing clearly what the program knows from how that knowledge will be used, making it possible to use the same knowledge in different ways.     

Nanoelectromechanical systems

Nanoelectromechanical systems are evolving, with new scientific studies and technical applications emerging. Mechanical devices are shrinking in thickness and width to reduce mass, increase resonant frequency, and lower the force constants of these systems. Advances in the field include improvements in fabrication processes and new methods for actuating and detecting motion at the nanoscale. Lithographic approaches are capable of creating freestanding objects in silicon and other materials, with thickness and lateral dimensions down to about 20 nanometers. Similar processes can make channels or pores of comparable dimensions, approaching the molecular scale. This allows access to a new experimental regime and suggests new applications in sensing and molecular interactions.     

Database systems

Database systems, computer systems that are principally devoted to the management of large amounts of data, are becoming more and more important to the operation of many enterprises. This article surveys the technology of database software and hardware, describing some of the principal issues related to the user's view of data, sharing, concurrent access, security, and integrity.     

Multipolymer systems

Different polymers can be combined to yield a wide variety of composite materials: layered sheets and films, homogeneous and heterogeneous blends, interpenetrating polymer networks, bicomponent fibers, and others. Some properties of a multipolymer material are roughly additive, but synergistic interactions can yield properties and performances superior to those of the individual constituents. Consequently, the use of polymers in combination is a rapidly growing component of polymer materials technology.