Mitre Corporation

About: Mitre Corporation is a company organization based out in Bedford, Massachusetts, United States. It is known for research contribution in the topics: Air traffic control & National Airspace System. The organization has 4884 authors who have published 6053 publications receiving 124808 citations. The organization is also known as: Mitre & MITRE.

Minimal realization of discrete linear systems from input-output observations

Abstract: A direct procedure is presented for obtaining a minimal realization of a multiple-input multiple-output linear time-invariant discrete system from observations of the input and output. Discussion is limited to the case of noise-free observations in order to focus attention on the realization procedure and to display the structure of the resulting realization. This known structural form car be used as a check on the realization procedure. Application of the procedure requires knowledge of an upper bound on the minimal system dimension; however, a modification is given to handle the situation where an upper bound is not known. An example is included to show the operation of the procedure.

A framework for simulation-optimization software

Abstract: Research on the optimization of stochastic systems via simulation often centers on the development of algorithms for which global convergence can be guaranteed. On the other hand, commercial software applications that perform optimation via simulation typically employ search heuristics that have been successful in deterministic settings. Such search heuristics give up on global convergence in order to be more generally applicable and to yield rapid progress towards good solutions. Unfortunately, commercial applications do not always formally account for the randomness in simulation responses, meaning that their progress may be no better than a random search if the variability of the outputs is high. In addition, they do not provide statistical guarantees about the "goodness" of the final results. In practice, simulation studies often rely heavily on engineers who, in addition to developing the simulation model and generating the alternatives to be compared, must also perform the statistical analyses off-l...

Linear independence of time-frequency translates

Abstract: . The refinement equation φ(t) = ∑N2 k=N1 ck φ(2t − k) plays a key role in wavelet theory and in subdivision schemes in approximation theory. Viewed as an expression of linear dependence among the time-scale translates |a|1/2φ(at − b) of φ ∈ L2(R), it is natural to ask if there exist similar dependencies among the time-frequency translates e2πibtf(t + a) of f ∈ L2(R). In other words, what is the effect of replacing the group representation of L2(R) induced by the affine group with the corresponding representation induced by the Heisenberg group? This paper proves that there are no nonzero solutions to lattice-type generalizations of the refinement equation to the Heisenberg group. Moreover, it is proved that for each arbitrary finite collection {(ak , bk)}k=1, the set of all functions f ∈ L2(R) such that {e2πibktf(t+ ak)}k=1 is independent is an open, dense subset of L2(R). It is conjectured that this set is all of L2(R) \ {0}.

Web-based simulation: revolution or evolution?

Abstract: The nature of the emerging field of web-based simulation is examined in terms of its relationship to the fundamental aspects of simulation research and practice. The presentation, assuming a form of debate, is based on a panel session held at the first International Conference on Web-Based Modeling and Simulation, which was sponsored by the Society for Computer Simulation during 11-14 January 1998 in San Diego, California. While no clear “winner” is evident in this debate, the issues raised here certainly merit ongoing attention and contemplation.

D‐mannitol, a specific hydroxyl free radical scavenger, reduces the developmental toxicity of hydroxyurea in rabbits

Abstract: Hydroxyurea (HU) is a potent mammalian teratogen. Within 2–4 hours after maternal injection, HU causes 1) a rapid episode of embryonic cell death and 2) profound inhibition of embryonic DNA synthesis. A variety of antioxidants delays the onset of embryonic cell death and reduces the incidence of birth defects. Antioxidants do not block the inhibition of DNA synthesis, indicating that early embryonic cell death is not caused by inhibited DNA synthesis. We have suggested that some HU molecules may react within the embryo to produce H2O2 and subsequent free radicals, including the very reactive hydroxyl free radical. The free radicals could cause the early cell death; antioxidants are believed to terminate the aberrant free radical reactions resulting in lessened developmental toxicity. To investigate whether hydroxyl free radicals cause the early episode of cell death, pregnant New Zealand white rabbits were injected subcutaneously on gestational day 12 with a teratogenic dose of HU (650 mg/kg) in the presence or absence of 550 mg/kg of D–mannitol (Man), a specific scavenger of hydroxyl free radicals. Osmotic control rabbits received HU plus 550 mg/kg of xylose (Xyl, a nonactive aldose). At term, the teratologic effects of HU were ameliorated by Man as evidenced by decreased incidences of the expected limb malformations. Xyl exerted no demonstrable effect on HU teratogenesis. Histological examination of limb buds at 3–8 hours after maternal injection, showed that Man delayed the onset of HU–induced cell death by as much as 4 hours. Xyl had no effect. That Man acts within the embryo was shown by performing intracoelomic injections on alternate implantation sites with Man, Xyl, or saline followed by subcutaneous injection of the pregnant doe with HU. Embryos were harvested 3–8 hours later. Limb buds from saline– and Xyl–injected embryos exhibited the typical pattern of widespread HU–induced cell death at 3–4 hours, whereas Man–injected embryos did not exhibit cell death until 5–8 hours. These results are consistent with those reported for antioxidant–mediated amelioration of HU–induced developmental toxicity and with the hypothesis that hydroxyl free radicals are the proximate reactive species in HU–induced early embryonic cell death. © 1994 Wiley-Liss, Inc.