Learning From Complexity: Effects Of Prior Accidents And Incidents On Airlines' Learning

Using data on accidents and incidents experienced by U.S. commercial airlines from 1983 to 1997, we investigated variation in firm learning by examining whether firms learn more from errors with heterogeneous or homogeneous causes. We measured learning by a reduction in airline accident and incident rates, while controlling for other factors related to accidents and incidents. Our results show that heterogeneity is generally better for learning, as prior heterogeneity in the causes of errors decreases subsequent accident rates, producing a deeper, broader search for causality than simple explanations like >blame the pilot.> The benefits of heterogeneity, however, apply mainly to specialist airlines. Generalist airlines learn, instead, from outside factors such as the experience of others and general improvements in technology. These results suggest a theory of learning across organizational forms: complex forms benefit from simple information, and simple forms benefit from complex information. The implications of our study for learning theories and work on organizational errors are discussed.Business Administratio

Performance of wind turbines in a turbulent atmosphere

The effect of atmospheric turbulence on the power fluctuations of large wind turbines was studied. The significance of spatial non-uniformities of the wind is emphasized. The turbulent wind with correlation in time and space is simulated on the computer by Shinozukas method. The wind turbulence is modelled according to the Davenport spectrum with an exponential spatial correlation function. The rotor aerodynamics is modelled by simple blade element theory. Comparison of the spectrum of power output signal between 1-D and 3-D turbulence, shows the significant power fluctuations centered around the blade passage frequency

Test evaluation of fuel cell catalysts Quarterly report, 15 Feb. - 15 May 1967

Catalytic activity of iron compounds for fuel cell catalyst

Bose-Einstein Correlations and the Equation of State of Nuclear Matter

Within a relativistic hydrodynamic framework, we use four different equations of state of nuclear matter to compare to experimental spectra from CERN/SPS experiments NA44 and NA49. Freeze-out hypersurfaces and Bose-Einstein correlation functions for identical pion pairs are discussed. We find that two-pion Bose-Einstein interferometry measures the relationship between the temperature and the energy density in the equation of state during the late hadronic stage of the fireball expansion. Little sensitivity of the light-hadron data to a quark-gluon plasma phase-transition is seen.Comment: 4 pages, including 4 figures. You can also download a PostScript file of the manuscript from http://p2hp2.lanl.gov/people/schlei/eprint.htm

Baer-Levi semigroups of linear transformations

Given an infinite-dimensional vector space V, we consider the semigroup GS(m,n) of all injective linear transformations of V into itself with defect n, where n is an infinite cardinal less or equal than m, the dimension of V. This is a linear version of the well-known Baer-Levi semigroup BL(p,q) defined on an infinite set X with cardinal p and where q is an infinite cardinal less or equal than p. We show that, although the basic properties of GS(m,n) are the same as those of BL(p,q), the two semigroups are never isomorphic. We also determine all left ideals of GS(m,n) and some of its maximal subsemigroups: in this, we follow previous work on BL(p,q) by Sutov (1966) and Sullivan (1978) as well as Levi and Wood (1984).Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI)

Maximal inverse subsemigroups of the symmetric inverse semigroup on a finite-dimensional vector space

Yang (1999) classified the maximal inverse subsemigroups of all the ideals of the symmetric inverse semigroup $I(X)$ defined on a finite set $X$. Here we do the same for the semigroup $I(V)$ of all one-to-one partial linear transformations of a finite-dimensional vector space. We also show that $I(X)$ is almost never isomorphic to $I(V)$ for any set $X$ and any vector space $V$, and prove that any inverse semigroup can be embedded in some $I(V)$.Fundação para a Ciência e a Tecnologi

Inverse semigroups generated by linear transformations

Suppose X is a set with cardinal p and let q be an infinite cardinal less or equal than p. Let B=BL(p,q) denote the Baer-Levi semigroup defined on X. In 1984, Howie and Marques-Smith showed that, if p=q, then BB^{-1}=I(X), the symmetric inverse semigroup on X, and they described the subsemigroup of I(X) generated by B^{-1}B. In 1994, Lima extended that work to `independence algebras', and thus also to vector spaces. In this paper, we answer the natural question: what happens when p>q? We also show that, in this case, the analogues BB^{-1} for sets and GG^{-1} for vector spaces are never isomorphic, despite their apparent similarities.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI

Probing the Interstellar Medium using HI absorption and emission towards the W3 HII region

HI spectra towards the W3 HII complex are presented and used to probe the Galactic structure and interstellar medium conditions between us and this region. The overall shape of the spectra is consistent with the predictions of the Two-Arm Spiral Shock model wherein the gas found in the -40 km/s to -50 km/s range has been accelerated by some 20 km/s from its rotation curve velocity. Spin temperatures of ~100 K are derived for the Local Arm gas, lower than found in a previous, similar study towards DR 7. For the interarm region, values on the order of 300 K are found, implying a negligible filling factor for the Cold Neutral Medium (<< 1%). Some of the absorbing gas at velocities near -40 km/s is confirmed to be associated with the HII regions.Comment: 23 pages, 6 figures, accepted for publication in the Astronomical Journa

Partial orders on transformation semigroups

In 1986, Kowol and Mitsch studied properties of the so-called 'natural partial order' less than or equal to on T(X), the total transformation semigroup defined on a set X. In particular, they determined when two total transformations are related under this order, and they described the minimal and maximal elements of (T(X), less than or equal to). In this paper, we extend that work to the semigroup P(X) of all partial transformations of X, compare less than or equal to with another 'natural' partial order on P(X), characterise the meet and join of these two orders, and determine the minimal and maximal elements of P(X) with respect to each order.Centro de Matemática da Universidade do Minho.Fundação para a Ciência e a Tecnologia (FCT)