525 research outputs found
The KASE approach to domain-specific software systems
Designing software systems, like all design activities, is a knowledge-intensive task. Several studies have found that the predominant cause of failures among system designers is lack of knowledge: knowledge about the application domain, knowledge about design schemes, knowledge about design processes, etc. The goal of domain-specific software design systems is to explicitly represent knowledge relevant to a class of applications and use it to partially or completely automate various aspects of the designing systems within that domain. The hope is that this would reduce the intellectual burden on the human designers and lead to more efficient software development. In this paper, we present a domain-specific system built on top of KASE, a knowledge-assisted software engineering environment being developed at the Stanford Knowledge Systems Laboratory. We introduce the main ideas underlying the construction of domain specific systems within KASE, illustrate the application of the idea in the synthesis of a system for tracking aircraft from radar signals, and discuss some of the issues in constructing domain-specific systems
Software design by reusing architectures
Abstraction fosters reuse by providing a class of artifacts that can be instantiated or customized to produce a set of artifacts meeting different specific requirements. It is proposed that significant leverage can be obtained by abstracting software system designs and the design process. The result of such an abstraction is a generic architecture and a set of knowledge-based, customization tools that can be used to instantiate the generic architecture. An approach for designing software systems based on the above idea are described. The approach is illustrated through an implemented example, and the advantages and limitations of the approach are discussed
Electric current control of spin helicity in an itinerant helimagnet
Chirality is breaking of mirror symmetry in matter. In the fields of biology
and chemistry, this is particularly important because some of the essential
molecules in life such as amino acids and DNA have chirality. It is a
long-standing mystery how one of the enantiomers was chosen at the beginning
stage of life. The understanding of the emergence of homochirality under some
conditions is indispensable for the study of the origin of life as well as
pharmaceutical science. The chirality is also emergent in magnetic structures.
The longitudinal helical magnetic structure is the chiral object composed of
magnetic moments, in which the ordered direction of the magnetic moment
spatially rotates in the plane perpendicular to the propagation vector (Fig.
1a). Since the sense of rotation, which is denoted as helicity, is reversed by
any mirror operation, it is corresponding to the chirality. Here we show that
the chirality of a longitudinal helical structure can be controlled by the
magnetic field and electric current owing to the spin-transfer torque
irrelevant to the spin-orbit interaction and probed by electrical magnetochiral
effect, which is sensitive to the chiral symmetry breaking, in an itinerant
helimagnet MnP. This phenomenon is distinct from the multiferroicity in
transverse-type insulating helical magnets, in which the helical plane is
parallel to the propagation vector, because the magnetic structure has polar
symmetry not chiral one. While the combination of the magnetic field and
electric current satisfies the symmetrical rule of external stimulus for the
chirality control, the control with them was not reported for any chiral object
previously. The present result may pave a new route to the control of
chiralities originating from magnetic and atomical arrangements.Comment: 14 pages, 7 figure
Knowledge-based systems in Japan
This report summarizes a study of the state-of-the-art in knowledge-based systems technology in Japan, organized by the Japanese Technology Evaluation Center (JTEC) under the sponsorship of the National Science Foundation and the Advanced Research Projects Agency. The panel visited 19 Japanese sites in March 1992. Based on these site visits plus other interactions with Japanese organizations, both before and after the site visits, the panel prepared a draft final report. JTEC sent the draft to the host organizations for their review. The final report was published in May 1993
High-Temperature Stable Operation of Nanoribbon Field-Effect Transistors
We experimentally demonstrated that nanoribbon field-effect transistors can be used for stable high-temperature applications. The on-current level of the nanoribbon FETs decreases at elevated temperatures due to the degradation of the electron mobility. We propose two methods of compensating for the variation of the current level with the temperature in the range of 25–150°C, involving the application of a suitable (1) positive or (2) negative substrate bias. These two methods were compared by two-dimensional numerical simulations. Although both approaches show constant on-state current saturation characteristics over the proposed temperature range, the latter shows an improvement in the off-state control of up to five orders of magnitude (−5.2 × 10−6)
Induction of lymphokine-activated killer activity in rat splenocyte cultures: The importance of 2-mercaptoethanol and indomethacin
The role of 2-mercaptoethanol and indomethacin in the induction of lymphokine-activated killer (LAK) activity by interleukin-2 (IL-2) in rat splenocyte cultures was investigated. Spleens from 4-month-old male rats of five different strains were tested. Splenocytes were cultured for 3-5 days in the presence of IL-2 (1000 U/ml) and LAK activity was assessed by 4-h51Cr release assays with P815 and YAC-1 cells as targets. LAK activity could be induced by IL-2 in splenocytes from all rat strains, but only when 2-mercaptoethanol was present in the culture medium. Optimal LAK activity was induced when the 2-mercaptoethanol concentration in splenocyte cultures was at least 5 μM. Different rat strains showed differences in levels of in vitro induction of LAK activity. In the presence of 2-mercaptoethanol the level of LAK activity induced by IL-2 was high in BN and Lewis rats, intermediate in Wistar and Wag rats, and low in DZB rats. In the absence of 2-mercaptoethanol no or minimal LAK activity was induced. Furthermore we observed that addition of 50 μm indomethacin to the culture medium in the presence of 2-mercaptoethanol augmented the induction of LAK activity to some extent. In the absence of 2-mercaptoethanol, addition of indomethacin resulted only in low levels or no induction of LAK activity. We conclude that for optimal induction of LAK activity by IL-2 in rat splenocyte cultures 2-mercaptoethanol is essential, while indomethacin can only marginally further improve this induction
- …