Critical Technology Issues Research Articles

Investigations On The Performance Of Ultrasonic Drilling Process With Special Reference To Precision Machining Of Advanced Ceramicsc

Advanced ceramics are assuming an important role in modern industrial technology. The applications and advantages of using advanced ceramics are many.There are several reasons why we should go in for machining of advanced ceramics after their compacting and sintering. These are discussed in this paper. However,precision machining of advanced ceramics must be economical. Critical technological issues to be addressed in cost effective machining of ceramics include design of machine tools, tooling arrangements, improved yield and precision, relationship of part dimensions and finish specifications to functional performance, and on-line inspection.Considering the above Ultrasonic Drilling is an important process used for the precision machining of advanced ceramics. Extensive Studies on tool wear occurring in the ultrasonic machining of advanced ceramics have been carried out. In addition, production accuracy of holes drilled, surface finish obtained and surface integrity aspects in the machining of advanced ceramics have also been investigated. Some specific findings with reference to surface integrity are: (a) There were no cracks or micro-cracks developed during or after ultrasonic machining of advanced ceramics. (b) While machining Hexoloy Alpha Silicon Carbide a recast layer is formed as a result of ultrasonic machining. This is attributed to the viscous heating resulting from high energy impacts during ultrasonic machining. While machining all other types of ceramics no such formation of recast layer was observed, and (c) There is no change in the micro-structure of the advanced ceramics as a result of ultrasonic machining.

Ordered intermetallic alloys: an assessment

Abstract The paper summarizes our present understanding, as established at a recent workshop, of two classes of intermetallic alloys: nickel and iron aluminides, which are currently used by industries; and advanced intermetallic alloys including silicides and Laves-phase alloys, which have a great potential to be developed as new high-temperature structural materials for future industrial use. The workshop emphasized close interaction and co-operation between basic research, applied research, and industrial development, and stressed discussion of critical scientific and technological issues. The current status of these intermetallic alloys was assessed, and the directions for future research and development, as well as emerging opportunities, were identified. The information presented in the text is summarized from the presentations at the workshop, and so no references are given to the published literature. However, an extensive bibliography is appended, in which further details may be found.

Physics design and scaling of recirculating induction accelerators: from benchtop prototypes to drivers

Recirculating induction accelerators (recirculators) have been investigated as possible drivers for inertial fusion energy production because of their potential cost advantage over linear induction accelerators. Point designs were obtained by Barnard et al. (UCRL-LR-108095, 1991; Phys. Fluids B Plasma Phys. 5 (1993), 2698) and many of the critical physics and technology issues that would need to be addressed were detailed. A collaboration (Friedman et al., 32–33 (1996) 235) involving Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory researchers is now developing a small prototype recirculator in order to demonstrate an understanding of nearly all the critical beam dynamics issues that have been raised by Barnard et al. and subsequently. We review the design equations for recirculators (which have been incorporated into a MATHEMATICA-based design code) and demonstrate how, by keeping crucial dimensionless quantities constant, a small prototype recirculator was designed which will simulate the essential beam physics of a driver. We further show how important physical quantities such as the sensitivity to errors of optical elements (in both field strength and placement), insertion-extraction, vacuum requirements and emittance growth scale from small prototype to driver-size accelerator.

Colossal magnetoresistivity in manganese-based perovskites (invited) (abstract)

Magnetoresistivity values of the order of 106% (and in some cases even higher) have been obtained in epitaxial AxB1−xMnO3−y (A=La,Nd; B=Ca,Sr,Ba) thin films grown by pulsed laser deposition. Ferromagnetic resonance experiments suggest a granular-type behavior with conducting ferromagnetic regions (Rcond<10 mΩ cm) in a less conducting matrix (Rinsulazting≳100.Rcond). Ion channeling experiments over a range of temperatures clearly reveal the existence of structural distortion at the peak resistivity temperature TP. Systematic studies of samples prepared under a variety of oxygenation conditions show that the resistivity above TP can be modeled with a single functional form: Rcond≊eΔ/kT, where Δ, the activation energy, is of the order of 50–200 meV. This suggests that these different samples represent the same basic material in a semiconducting matrix, with differing volume fractions of the two components which depends on the processing conditions. These ‘‘colossal’’ values of MR have been obtained at temperatures lower than room temperature and at fields of the order of a few Teslas, both of which are impediments to the development of viable MR sensor and nonvolatile storage technologies. We are therefore addressing the critical scientific and technological issues through a variety of materials integration approaches. Using structural chemistry and lattice matching as fundamental guiding principles, we are growing epitaxial heterostructure superlattices consisting of the CMR oxides interleaved with magnetic perovskites such as La–Sr–Co–O (metallic ferromagnet), rare earth–Fe–O (ferromagnetic insulator). We are also exploring the possibility of using the semiconducting properties of these materials in an all-perovskite field effect transistor device. In this presentation, we will describe our progress to date on these studies to enhance the field and temperature dependence of the MR properties and explore new device architectures that utilize the inherently novel properties of these materials.

Earth Science Computing Conference scheduled

The frontiers of Earth science computing continue to evolve—as does the importance of Earth science in addressing critical national scientific and technological issues, which in part are embodied in the emerging federal High‐Performance Computing and Communications (HPCC) and National Information Infrastructure (NII) initiatives.The Incorporated Research Institutions for Seismology (IRIS) have organized a workshop at the Mesa Lab of the National Center for Atmospheric Research in Boulder, Colo., July 20–22 to plan ambitious and forward‐looking science and facility programs that will take advantage of these very HPCC and NII enterprises.

Removal of Microcontaminants From Surfaces Using a Chemicalfree, Laser-Assisted Process

AbstractThe ability to control and eliminate microcontamination from the manufacturing process is becoming a critical technology issues for such diverse industries as semiconductors, aerospace, and automotive. Current industrial cleaning practices use large amounts of water and chemicals which require disposal. Dry environmentally benign technologies can be alternatives. In this paper, we will look at an alternative technology which consists of deep ultraviolet photons coupled with a flowing inert gas, and compare it to current wet cleaning practices in the semiconductor industry.

Nova Upgrade Program: Ignition and beyond

The Lawrence Livermore National Laboratory (LLNL) Inertial Confinement Fusion (ICF) Program is addressing the critical physics and technology issues directed toward demonstrating and exploiting ignition and propagating burn to high gain with ICF targets for both defense and civilian applications. Nova is the primary U.S. facility employed in the study of the X-ray-driven (indirect drive) approach to ICF. Nova's principal objective is to demonstrate that laser-driven hohlraums can achieve the conditions of driver-target coupling efficiency, driver irradiation symmetry, driver pulseshaping, target preheat, and hydrodynamic stability required by hot-spot ignition and fuel compression to realize a fusion gain.The LLNL ICF Program believes that the next major step in the national ICF Program is the demonstration of ignition and moderate gain (G ≤ 10). Recent theoretical and experimental results show that the ignition drive energy threshold can be reduced significantly by operating indirectly driven targets at radiation temperatures ∼ 1.3–1.6 times higher (thereby achieving higher implosion velocity) than originally proposed for the Laboratory Microfusion Facility (LMF). (Temperatures of ∼ 1.3 times higher have already been demonstrated on Nova.) Specifically, it should be possible to demonstrate ignition and propagating with burn about 1–2 MJ of laser energy as against the 5–10 MJ necessary for the high-yield LMF. LLNL proposes to upgrade the existing Nova facility to 1–2 MJ (2- to 4-ns pulses) and demonstrate ignition and propagating burn to moderate gain with appropriately scaled hydrodynamic equivalents of high-yield targets.Once moderate gain has been demonstrated at 1–2.0 MJ on the Nova Upgrade, investigations into improving, by about 50%, the coupling efficiency between the driver and the capsule could provide gains >20 at about 1 MJ or less. A database for gain below 1-MJ driver energies could lead to a low-capital-cost Engineering Test Facility (ETF) for a first inertial fusion energy engineering reactor. Because the capital cost for both the target chamber and the driver scale with size, there is the opportunity to realize large savings by lowering the required driver energy necessary to demonstrate the technology for a first demonstration power plant. A target gain, G ∼ 25, at a driver energy, ED ∼ 0.75 MJ, would be self-sustaining for a driver efficiency of ∼10% and a thermal-to-electric conversion efficiency of ∼33% and at 12 Hz would generate ∼10 MW of gross electric power. Although the cost of electricity would be high, the combination of low capital cost and early demonstration of reactor technology would be an attractive step in the development of inertial fusion energy.

Interpenetrating Phase Composites

An assessment of the processing and properties of interpenetrating phase composites is presented. Such materials, defined as multiphase composites in which each phase is topologically interconnected throughout the micro‐structure, were the subject of a DOE Basic Energy Sciences sponsored workshop on research needs and opportunities held in July 1989 in Snowmass, Colorado. In place of a report representing the proceeding of the workshop, this paper provides a review of the field in its present, nascent state and identifies some of the critical scientific and technological issues posed by development of this class of material. The emphasis is on processing approaches and properties of interpenetrating phase composites. A list of the participants contributing to the workshop is given.

Panel 3: Critical engineering issues of aneutronic reactor for space, terrestrial, and naval applications

This panel discusses the engineering and technical aspects of aneutronic reactors for aerospace and terrestrial applications.

Urban Water Resources Issues in the 21st Century

The Urban Water Resources Council identifies four critical engineering issues that must be addressed in the 21st century: water supply, storm water management, combined sewer systems, and engineering education. Water supply planning must become part of an integrated water resources-planning process that considers all sources and beneficial uses in allocating a fixed supply to an increasing demand. The interrelationship of groundwater and surface water must be recognized, with programs to replenish these resources being considered in conjunction with water supply. Storm water management must consider the quantity and quality of urban runoff. Storm water systems must be designed so that post-development runoff approximates pre-development runoff, and economical treatment techniques must be invented to retrofit existing drainage systems. Either we must develop cost-effective processes to handle the widely varying ranges of flow and pollutant concentrations from combined sewer systems, or we must create separate systems as we restore infrastructure in the older cities relying on combined sewer systems. In addition to a solid engineering foundation, engineering education must provide training in communication, leadership, people management, and creativity.

Discussion of “ Critical Human Technology Issues for Engineers ” by Kenneth Lesley and Judith Vogt (October, 1985, Vol. 1, No. 4) and “ Harmonizing Organizational and Personal Needs ” by Willy Norup (October, 1985, Vol. 1, No. 4)

Discussion of “ <i>Critical Human Technology Issues for Engineers</i> ” by Kenneth Lesley and Judith Vogt (October, 1985, Vol. 1, No. 4) and “ <i>Harmonizing Organizational and Personal Needs</i> ” by Willy Norup (October, 1985, Vol. 1, No. 4)

Space coherent optical communication systems--An introduction

Critical technology and system issues for space optical heteroydyne communication systems using GaAlAs lasers are discussed. Heterodyne systems offers 10-20 dB better receiver sensitivities and thus smaller telescope sizes for the same laser power than direct detection systems. Based on present state-of-the-art technologies, it is concluded that an efficient optical intersatellite link can be realized with a few years of development.

Critical Human Technology Issues for Engineers

This article identifies the current status of management and team issues including interpersonal relationship skills as viewed by engineers, colleges of engineering, societies of engineering, and employers of engineers. The data was gathered by interviewing members of each sector of the profession and then compiled into general observations. These observations led to a number of specific recommendations. Schools of engineering need to develop within their students an awareness of the business environment by building ties with management departments at the respective schools and with industry. Engineering employers need to continue the engineers' development through the use of mentors and peer groups. Professional societies should provide active forums for the dissemination of management information geared for the practicing engineer, manager, and team member. Finally, a consistent language and applied theory of Human Technology for engineers needs to be developed. Engineers should take the responsibility ...