Concordia University

About: Concordia University is a education organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Control theory & Population. The organization has 13565 authors who have published 31084 publications receiving 783525 citations. The organization is also known as: Sir George Williams University & Loyola College, Montreal.

The Absence Culture and Psychological Contract—Who's in Control of Absence?

Abstract: The concepts of absence culture and psychological contract are invoked to explain variations in absence behavior within and between organizations and their subunits. A typology of absence cultures is developed based on the degree of salience of the culture and the level of trust inherent in the psychological contract. An example of an absence culture in transition is provided, and implications for researchers and managers are discussed.

A bank asset and liability management model

Abstract: In managing its assets and liabilities in light of uncertainties in cash flows, cost of funds and return on investments, a bank must determine its optimal trade-off between risk, return and liquidity. In this paper we develop a multiperiod stochastic linear programming model ALM that includes the essential institutional, legal, financial, and bank-related policy considerations, and their uncertainties, yet is computationally tractable for realistically sized problems. A version of the model was developed for the Vancouver City Savings Credit Union for a 5-year planning period. The results indicate that ALM is theoretically and operationally superior to a corresponding deterministic linear programming model, and that the effort required for the implementation of ALM, and its computational requirements, are comparable to those of the deterministic model. Moreover, the qualitative and quantitative characteristics of the solutions are sensitive to the model's stochastic elements, such as the asymmetry of cash flow distributions. We also compare ALM with the stochastic decision tree SDT model developed by S. P. Bradley and D. B. Crane. ALM is computationally more tractable on realistically sized problems than SDT, and simulation results indicate that ALM generates superior policies.

Adaptive variable structure control of a class of nonlinear systems with unknown Prandtl-Ishlinskii hysteresis

Abstract: Control of nonlinear systems preceded by unknown hysteresis nonlinearities is a challenging task and has received increasing attention in recent years due to growing industrial demands involving varied applications. In the literature, many mathematical models have been proposed to describe the hysteresis nonlinearities. The challenge addressed here is how to fuse those hysteresis models with available robust control techniques to have the basic requirement of stability of the system. The purpose of the note is to show such a possibility by using the Prandtl-Ishlinskii (PI) hysteresis model. An adaptive variable structure control approach, serving as an illustration, is fused with the PI model without necessarily constructing a hysteresis inverse. The global stability of the system and tracking a desired trajectory to a certain precision are achieved. Simulation results attained for a nonlinear system are presented to illustrate and further validate the effectiveness of the proposed approach.

Photochemical bromine production implicated in Arctic boundary-layer ozone depletion

Abstract: RECENT measurements1–7 in the Arctic have revealed episodic destruction of boundary-layer ozone from 30–40 parts per 109 by volume (p.p.b.v.) to undetectable levels on a timescale of less than a day, during periods when the boundary layer is very stable. The ozone destruction begins at polar sunrise, continues for the months of March and April, and is strongly associated with levels of filterable bromine which are much greater than during the rest of the year. Here we suggest that sea-salt Br− reaches high concentrations in the snow pack during the long polar night, and is evolved into the atmosphere as Br2at polar sunrise. Ordinarily, gas-phase photochemistry would convert Br2 to HBr or brominated organic compounds with consequently little destruction of boundary-layer ozone. In view of several laboratory experiments8–11, and by analogy with the marine boundary layer12, we propose that the HBr and brominated organic compounds will be scavenged by the ambient aerosols and ice crystals, and that these heterogeneous reactions release Br2 back to the atmosphere. We argue that this cycling of bromine between the aerosol and the gas phase should maintain sufficiently high levels of Br atoms and BrO radicals to destroy ozone, in agreement with observations1–7.