Removing Malmquist bias from linear regressions

Malmquist bias is present in all astronomical surveys where sources are observed above an apparent brightness threshold. Those sources which can be detected at progressively larger distances are progressively more limited to the intrinsically luminous portion of the true distribution. This bias does not distort any of the measurements, but distorts the sample composition. We have developed the first treatment to correct for Malmquist bias in linear regressions of astronomical data. A demonstration of the corrected linear regression that is computed in four steps is presented

Infrared analysis of LMC superbubbles

Researchers are analyzing three superbubbles in the Large Magellanic Cloud (LMC), cataloged by Meaburn (1980) as LMC-1, LMC-4 (a.k.a. Shapley Constellation III), and LMC-5. Superbubbles are the largest infrared sources in the disks of external galaxies. Their expansion requires multiple supernovae from successive generations of star formation. In LMC superbubbles, the grains swept up by shocks and winds represent an interstellar medium (ISM) whose abundances are quite different from the Galaxy. By applying the Dwek (1986) grain model, we can derive the composition and size spectrum of the grains. The inputs to this model are the dust emission in the four Infrared Astronomy Satellite (IRAS) bands and the interstellar radiation field (ISRF) that provides the heating. The first step in the project is to derive the ISRF for star-forming regions on the periphery of superbubbles. Researchers are doing this by combining observations at several wavelengths to determine the energy budget of the region. They will use a UV image to trace the ionizing stellar radiation that escapes, an H alpha image to trace the ionizing stellar radiation that is absorbed by gas, and the four IRAS images to trace the stellar radiation, both ionizing and non-ionizing, that is absorbed by dust. This multi-wavelength approach has the advantages that we do not have to assume the shape of the IMF or the extinction of the source

Cephalon, Inc. Taking Risk Management Theory Seriously

We study a firm that justifies its novel use of equity derivatives as a cash-flow hedging strategy. Our purpose is to understand the challenge of translating risk management theory into managerial action. Cephalon Inc., a biotech firm, bought a large block of call options on its own stock. If the FDA approved the firm's new drug, the firm would have large cash needs, which the options were designed to meet. We analyze this stated rationale for the firm's choice, applying the cash flow hedging concepts articulated by Froot, Scharfstein and Stein (1993). In applying the theory to practice, there are lessons for both managers and theorists. Managers consider deadweight costs of financing and of risk management, whereas theory tends to ignore the latter costs. While theory is driven by costs of external financing, managers must measure these costs to arrive at decisions and this measurement problem is severe. Cephalon's risk management decisions seem motivated as much by fluctuations in the availability and cost of external financing and by accounting considerations as by fluctuations in operating cash flows or desired investment. Finally, even a field-based examination of this strategy cannot reject the conclusion that the transaction was motivated by goals other than risk management.

Accurate Calculation of Hazardous Materials Transport Risks

Cataloged from PDF version of article.We propose two path-selection algorithms for the transport of hazardous materials. The algorithms can deal with link impedances that are path-dependent. This approach is superior to the use of a standard shortest path algorithm, common in the literature and practice, which results in inaccuracies

Matching patient and physician preferences in designing a primary care facility network

Cataloged from PDF version of article.This paper introduces an integer programming model for planning primary care facility networks, which accounts for the interests of different stakeholders while maximizing access to health care. Physician allocation to health-care facilities is explicitly modelled, which allows consideration of physician incentives in the planning phase. An illustrative case study in the Turkish primary care system is presented to show the implications of focusing on patient or physician preferences in the planning phase. A discussion of trade-offs between the different stakeholder preferences and some recommendations for modelling choices to match these preferences are provided. In the context of this case, we found that using an access measure that decays with distance, and incorporating nearest allocation constraints improves performance for all stakeholders. We also show that increasing the number of physicians may have adverse affects on access measures when physician preferences are addressed

Designing emergency response networks for hazardous materials transportation

Cataloged from PDF version of article.Undesirable consequences of dangerous goods incidents can be mitigated by quick arrival of specialized response teams at the accident site. We present a novel methodology to determine the optimal design of a specialized team network so as to maximize its ability to respond to such incidents in a region. We show that this problem can be represented via a maximal arc-covering model.We discuss two formulations for the maximal arc-covering problem, a known one and a new one. Through computational experiments, we establish that the known formulation has excessive computational requirements for large-scale problems, whereas the alternative model constitutes a basis for an efficient heuristic. The methodology is applied to assess the emergency response capability to transport incidents, that involve gasoline, in Quebec and Ontario. We point out the possibility of a significant improvement via relocation of the existing specialized teams, which are currently stationed at the shipment origins. 2005 Elsevier Ltd. All rights reserved

Skin Temperature Analysis and Bias Correction in a Coupled Land-Atmosphere Data Assimilation System

In an initial investigation, remotely sensed surface temperature is assimilated into a coupled atmosphere/land global data assimilation system, with explicit accounting for biases in the model state. In this scheme, an incremental bias correction term is introduced in the model's surface energy budget. In its simplest form, the algorithm estimates and corrects a constant time mean bias for each gridpoint; additional benefits are attained with a refined version of the algorithm which allows for a correction of the mean diurnal cycle. The method is validated against the assimilated observations, as well as independent near-surface air temperature observations. In many regions, not accounting for the diurnal cycle of bias caused degradation of the diurnal amplitude of background model air temperature. Energy fluxes collected through the Coordinated Enhanced Observing Period (CEOP) are used to more closely inspect the surface energy budget. In general, sensible heat flux is improved with the surface temperature assimilation, and two stations show a reduction of bias by as much as 30 Wm(sup -2) Rondonia station in Amazonia, the Bowen ratio changes direction in an improvement related to the temperature assimilation. However, at many stations the monthly latent heat flux bias is slightly increased. These results show the impact of univariate assimilation of surface temperature observations on the surface energy budget, and suggest the need for multivariate land data assimilation. The results also show the need for independent validation data, especially flux stations in varied climate regimes

Designing Personalized Treatment: An Application to Anticoagulation Therapy

In this study, we develop an analytical framework for personalizing the anticoagulation therapy of patients who are taking warfarin. Consistent with medical practice, our treatment design consists of two stages: (i) the initiation stage, modeled using a partially-observable Markov decision process, during which the physician learns through systematic belief updates about the unobservable patient sensitivity to warfarin, and (ii) the maintenance stage, modeled using a Markov decision process, during which the physician relies on his formed belief about patient sensitivity to determine the stable, patient-specific, warfarin dose to prescribe. We develop an expression for belief updates in the POMDP, establish the optimality of the myopic policy for the MDP, and derive conditions for the existence and uniqueness of a myopically optimal dose. We validate our models using a real-life patient data set gathered at the Hematology Clinic of the Jewish General Hospital in Montreal. The proposed analytical framework and case study enable us to develop useful clinical insights, for example, concerning the length of the initiation period and the importance of correctly assessing patient sensitivity

International Trade: The Position of Africa in Global Merchandise Trade

Even though global trade has fluctuated over the years, it has also rapidly increased. However, the structure and pattern of trade vary significantly by-products and regions. Undoubtedly, trade has come with both benefits and daunting challenges to countries involved, especially in African nations, where primary and intermediate merchandise formed a substantial share of exports. Because advanced and newly industrialized economies have better technology and know-how, manufacturing industries, access to finance, and market than Africa, they have a greater market proportion in the world trade. Arguably, African countries have been left in the cold as they struggle to compete with advanced economies. As presented in this chapter, Africa has been struggling to be relevant in the world market. However, its global share of merchandise trade has reduced over the decades. This is partly because the continent has concentrated on the exportation of few primary commodities (i.e., mineral fuels, iron ores, gold, cocoa beans) with volatile prices and demand in the global markets. The frequent global oil crunch other raw products are a wake-up call for a rapid industrialization and diversification for competitiveness in Africa. The World Trade Organization (WTO) has to ensure that defensive trade remedies should not be the next frontier of protectionism. Finally, for trade, growth, and development to be stimulated, African countries should urgently open their markets to expand intra-African trade

On DDO154 and Cold Dark Matter halo profiles

We investigate the claim by Burkert and Silk (1997) that the observed rotation curve of the dwarf irregular galaxy DDO154 cannot be reconciled with the universal CDM halo profile of Navarro, Frenk & White (1996,1997) even when allowance is made for the effect of violent gas outflow events on the structure of the galaxy. By means of N-body simulations we show that under certain conditions it is possible to obtain a reasonable fit to the observed rotation curve without invoking Burkert & Silk's proposed spheroidal MACHO component. We are able to best reproduce the observed decline in the rotation curve by postulating additional hidden disc mass, in an amount that is compatible with disc stability requirements. In the process we improve upon the results of Navarro, Eke & Frenk (1996) on the formation of halo cores by mass loss by using actual haloes from Cold Dark Matter simulations instead of Hernquist (1990) distributions.Comment: LaTeX (mn.sty), 8 pages, 6 figures included; updated to match final version to appear in MNRA