Search results for "Operations Research"
showing 10 items of 1297 documents
Unbiased Estimators and Multilevel Monte Carlo
2018
Multilevel Monte Carlo (MLMC) and unbiased estimators recently proposed by McLeish (Monte Carlo Methods Appl., 2011) and Rhee and Glynn (Oper. Res., 2015) are closely related. This connection is elaborated by presenting a new general class of unbiased estimators, which admits previous debiasing schemes as special cases. New lower variance estimators are proposed, which are stratified versions of earlier unbiased schemes. Under general conditions, essentially when MLMC admits the canonical square root Monte Carlo error rate, the proposed new schemes are shown to be asymptotically as efficient as MLMC, both in terms of variance and cost. The experiments demonstrate that the variance reduction…
Isotonic regression for metallic microstructure data: estimation and testing under order restrictions
2021
Investigating the main determinants of the mechanical performance of metals is not a simple task. Already known physical inspired qualitative relations between 2D microstructure characteristics and 3D mechanical properties can act as the starting point of the investigation. Isotonic regression allows to take into account ordering relations and leads to more efficient and accurate results when the underlying assumptions actually hold. The main goal in this paper is to test order relations in a model inspired by a materials science application. The statistical estimation procedure is described considering three different scenarios according to the knowledge of the variances: known variance ra…
General framework for testing Poisson-Voronoi assumption for real microstructures
2020
Modeling microstructures is an interesting problem not just in Materials Science but also in Mathematics and Statistics. The most basic model for steel microstructure is the Poisson-Voronoi diagram. It has mathematically attractive properties and it has been used in the approximation of single phase steel microstructures. The aim of this paper is to develop methods that can be used to test whether a real steel microstructure can be approximated by such a model. Therefore, a general framework for testing the Poisson-Voronoi assumption based on images of 2D sections of real metals is set out. Following two different approaches, according to the use or not of periodic boundary conditions, thre…
Defining and measuring the network flexibility of humanitarian supply chains: insights from the 2015 Nepal earthquake
2019
International audience; The efficient and effective response to disasters critically depends on humanitarian supply chains (HSCs). HSCs need to be flexible to adapt to uncertainties in needs, infrastructure conditions, and behavior of other organizations. The concept of ‘network flexibility’ is, however, not clearly defined. The lack of an unanimous definition has led to a lack of consistent understanding and comparisons. This paper makes a threefold contribution: first, it defines the concept of network flexibility for HSC in the context of sudden onset disasters. Second, it proposes a framework to measure network flexibility in HSCs. Third, we apply our framework to the 2015 Nepal earthqu…
The General Routing Problem polyhedron: Facets from the RPP and GTSP polyhedra
1998
[EN] In this paper we study the polyhedron associated with the General Routing Problem (GRP). This problem, first introduced by Orloff in 1974, is a generalization of both the Rural Postman Problem (RPP) and the Graphical Traveling Salesman Problem (GTSP) and, thus, is NP -hard. We describe a formulation of the problem such that from every non-trivial facet-inducing inequality for the RPP and GTSP polyhedra, we obtain facet-inducing inequalities for the GRP polyhedron, We describe a new family of facet-inducing inequalities for the GRP, the honeycomb constraints, which seem to be very useful for solving GRP and RPP instances. Finally, new classes of facets obtained by composition of facet-i…
Market entry decisions of US small and medium‐sized software firms
2008
PurposeThe purpose of this paper is to investigate market entry decisions of the US software SMEs by analyzing the impact of the most obvious factors (cultural distance, geographical distance, country risk, and three market size variables) in traditional internationalization theories to target country selection. By investigating the influence of these commonly cited macro‐level factors, this study proposes the best indicator for market entry decisions of the US small and medium‐sized software firms.Design/methodology/approachThis study uses a quantitative research approach applied to a sample of 100 US small and medium‐sized software firms.FindingsEmpirical findings in this study indicate t…
An efficient algorithm for stopping on a sink in a directed graph
2013
Abstract Vertices of an unknown directed graph of order n are revealed one by one in some random permutation. At each point, we know the subgraph induced by the revealed vertices. Our goal is to stop on a sink, a vertex with no out-neighbors. We show that if a sink exists this can be achieved with probability Θ ( 1 / n ) , which is best possible.
Companies’ Selection Methods for Inclusion in Sustainable Indices: A Fuzzy Approach
2017
Sustainability indices handle concepts which are both, of numerical and non-numerical nature. In this context, the use of Fuzzy Logic is highly useful as allows a more faithful representation of reality. Usually these indices follow a three-step process to define sustainable investment universes. First step consists of sustainability assessment. In the second step, assets are rated based on the previously assessed sustainability scores and finally, best assets are selected. This last step relies on the construction of a global score reflecting the performance of the assets in main sustainability dimensions. In this Chapter we are concerned with the third step of the selection process. We re…
Family business internationalization: an insight into opportunities and challenges.
2020
The theme of internationalization in family businesses is a highly topical issue that is increasingly attracting management scholars. This is because, in addition of being a particular type of business (Alcorn, 1982), they play a central role in most economies worldwide. Accounting for 65-80 percent of all the world’s firms, they generate around 70-90 percent of annual global GDP, and are the source of 50-80 percent of new jobs in most countries. Their essence lies in the close bond they have with their founders and above all, in the family’s involvement in the business ownership and management (Franco and Prata, 2019). This bond may prove to be a limit for fuelling internationalization pro…
Success factors of Polish family businesses
2017
This article presents the results of a study carried out among family businesses operating in Poland. It is intended to supplement previously generated knowledge in the area of the operation of family businesses in the specific socio-economic and legal conditions in Poland. The objective was to collate the opinions of entrepreneurs regarding the need for visibility of the family and the family business status in business relations and the marketing activities of enterprises. The data were collected using in-depth interviews with the Polish family business owners. This paper outlines the conclusion of the study with respect to success factors such as: the trust among the family members, flex…