Showing papers by "AT&T Labs published in 1990"
05 Feb 1990
TL;DR: The authors present a generalization of the relational model to represent indefinite and maybe kinds of incomplete information and introduce a data structure called M-table which is capable of representing disjunctive/indefinite and maybe facts.
Abstract: The authors present a generalization of the relational model to represent indefinite and maybe kinds of incomplete information. They introduce a data structure called M-table which is capable of representing disjunctive/indefinite and maybe facts. The notion of redundancy in the context of indefinite and maybe information is studied. The information content of an M-table is precisely defined. The relational algebra is then generalized in a semantically correct manner to operate on M-tables. Queries are posed in the same manner as in the conventional relational algebra; however, the user may now expect indefinite as well as maybe answers. >
24 citations
TL;DR: In this article, a mode-locked external-cavity 12.3-mu m InGaAsP diode laser with grating feedback combined with a compressor which is a grating pair containing an internal telescope is discussed.
Abstract: The generation of pulses shorter than 6 ps, tunable from 1.26 to 1.32 mu m, is discussed. The source of these pulses consists of a mode-locked external-cavity 12.3- mu m InGaAsP diode laser with grating feedback combined with a compressor which is a grating pair containing an internal telescope. The dispersion in the compressor can be tuned in both magnitude and sign to optimally compensate the chirp in the mode-locked external cavity laser at each wavelength. >
22 citations
TL;DR: In this paper, 1.55-mu m DFB laser with longitudinal nonuniformity in optical intensity and carrier density is discussed, manifested in soft light-current threshold and varying differential quantum efficiency, blue-shifted static tuning, and free-carrier induced FM response.
Abstract: Static and dynamic characteristics of 1.55- mu m distributed-feedback (DFB) lasers with longitudinal nonuniformity in optical intensity and carrier density are discussed. The nonuniformity is manifested in soft light-current threshold and varying differential quantum efficiency, blue-shifted static tuning, and free-carrier induced FM response. >
13 citations
TL;DR: The author observes that the social fabric of engineering, the support infrastructure of the profession, and the political and economic systems of the world are undergoing shifts that affect what engineering is, how it is accomplished, and what it should do.
Abstract: The author observes that the social fabric of engineering, the support infrastructure of the profession, and the political and economic systems of the world are undergoing shifts that affect what engineering is, how it is accomplished, and what it should do. He asks what these changes mean in terms of the educational system and explores a few of these issues that lie between academia and the industrial environment beyond. He discusses the engineering curriculum as seen from industry, the role of continuing education, research in academia. >
3 citations
TL;DR: In this article, a heterostructure bipolar transistor (HBT) with a base delta -doping of 6*10/sup 14/ cm/sup -2/, near the physical limit of one monolayer (ML) was reported.
Abstract: A heterostructure bipolar transistor (HBT) with a base delta -doping of 6*10/sup 14/ cm/sup -2/, near the physical limit of one monolayer (ML) is reported. The devices exhibits a current gain of 15. The doping confinement of the delta layer is 15 AA. To fabricate the HBT without inducing dopant diffusion or using sensitive etching, a new low-temperature base-contacting procedure (T/sub max/=420 degrees C) which requires no base-emitter etching has been developed. This has the additional benefits of greatly reducing surface recombination and yielding a planar structure.
3 citations
TL;DR: An innovative distributed queue dual bus (DQDB) concept for media access control is the subject of a standardization effort by IEEE Subcommittee 802.6, which has the task of developing a standard to meet metropolitan area network (MAN) requirements.
Abstract: An innovative distributed queue dual bus (DQDB) concept for media access control is the subject of a standardization effort by IEEE Subcommittee 802.6, which has been assigned the task of developing a standard to meet metropolitan area network (MAN) requirements. A unique characteristic of the DQDB standard that differs from the other IEEE 802 (local area network) standards is its intent to support a relatively large set of physical layer interface rates. The viability of the large variety of rates and formats is permitted by physical layer convergence procedures (PLCPs), which provide adaptation functions between a single common DQDB layer and the supported transmission systems. An overview of the dual bus structure of a DQDB subnetwork and background information on the DQDB layer services are provided. The PLCPs are defined in more detail, and the PLCPs for public network transmission systems and customer premises extensions are examined. An example of a stable DQDB subnetwork that experiences a link failure is described. >
3 citations