Search results for "Operation"

Group Extensions and Graphs

2016

A classical result of Gaschütz affirms that given a finite A-generated group G and a prime p, there exists a group G# and an epimorphism phi: G# ---> G whose kernel is an elementary abelian p-group which is universal among all groups satisfying this property. This Gaschütz universal extension has also been described in the mathematical literature with the help of the Cayley graph. We give an elementary and self-contained proof of the fact that this description corresponds to the Gaschütz universal extension. Our proof depends on another elementary proof of the Nielsen-Schreier theorem, which states that a subgroup of a free group is free.

The effect of inventory record inaccuracy in information exchange supply chains

2015

Abstract The goal of this paper is to quantify the impact of Inventory Record Inaccuracy on the dynamics of collaborative supply chains, both in terms of operational performance (i.e. order and inventory stability), and customer service level. To do so, we model an Information Exchange Supply Chain under shrinkage errors in the inventory item recording activity of their nodes, present the mathematical formulation of such supply chain model, and conduct a numerical simulation assuming different levels of errors. Results clearly show that Inventory Record Inaccuracy strongly compromises supply chain stability, particularly when moving upwards in the supply chain. Important managerial insights…

Nurse Scheduling Problem: An Integer Programming Model with a Practical Application

2012

We use a binary integer programming model to formulate and solve a nurse scheduling problem (NSP) which maximally satisfies nurse preferences. In a practical application of a VA hospital, besides considering the scheduling of two types of nurses (registered nurses and licensed practical nurses), two other types of employees (nursing assistants and health care techs), one nurse manager, and a clinical nurse leader are also included in our model. Most of these employees are working full-time. In addition, we distinguish the schedule of weekdays and weekends with different requirements and different preferences for employees. Besides the requirements for each shift, we consider requirements fo…

Variable Neighborhood Search for the Vertex Separation Problem

2012

The vertex separation problem belongs to a family of optimization problems in which the objective is to nd the best separator of vertices or edges in a generic graph. This optimization problem is strongly related to other well-known graph problems; such as the Path-Width, the Node Search Number or the Interval Thickness, among others. All of these optimization problems are NP-hard and have practical applications in VLSI, computer language compiler design or graph drawing. Up to know, they have been generally tackled with exact approaches, presenting polynomial-time algorithms to obtain the optimal solution for speci c types of graphs. However, in spite of their practical applications, these…

Analysis of dust exposure during chainsaw forest operations

2017

Abstract: In 1999, the European Union proclaimed hardwood dust carcinogenic based on the classification of the International Agency for Research on Cancer (IARC) issued in 1995. The operational exposure limit (OEL) for inhalable wood dust has been set to 5 mg m-3 by EU directives, though in different countries the OEL ranges from 1 to 5 mg m-3. The objective of this study was to determine the exposure to wood dust of forest workers in chainsaw cutting and processing and suggest possible countermeasures. The study took into consideration different silvicultural treatments (coppice clear cut, conifer thinning, conifer pruning, and sanitary cut) and chainsaw fuel (normal two-stroke gasoline mi…

From the crowd to the market: The role of reward-based crowdfunding performance in attracting professional investors

2017

Abstract We focus on new technology-based entrepreneurial ventures engaging in reward-based crowdfunding and examine the effect of their performance in such funding channel on the likelihood of securing subsequent funding from professional investors. We also study how this effect is influenced by the presence of patents granted for the new product idea and the entrepreneur social capital. Results from a sample of technology projects launched on Kickstarter demonstrate that pledging a higher amount of money in crowdfunding can ignite professional investors’ interest and thus help secure subsequent funding. However, this positive evidence is effective only when complemented by the presence of…

Binary Interaction Parameters, Ternary Systems: Realistic Modeling of Liquid/Liquid Phase Separation

2009

Microphase separation in ternary ABC block copolymers: Ordering control in molten diblock AB copolymers by attaching a short strongly interacting C b…

1997

Some specific features of the microphase separation in molten ternary ABC triblock copolymers (in particular, modifications of the molten AB diblock copolymers by attaching a short third block C strongly incompatible with both A and B blocks) are studied rigorously within the framework of the weak segragation approach. It is shown that via such a modification one can control both the stability as to the microphase separation transition (i.e., the corresponding spinodal temparatures) and the smoothness of such a transition. Two modes of such modifications for every composition are studied in detail:  (i) those resulting in the minimal spinodal temperatures and (ii) those that result in the s…

CO 2 Fixation and Activation by Cu II Complexes of 5,5″‐Terpyridinophane Macrocycles

2007

An aza-terpyridinophane receptor containing the polyamine 4,7,10,13-tetraazahexadecane-1,16-diamine linked through methylene groups to the 5,5″ positions of a terpyridine unit has been prepared and characterized (L). The acid-base behaviour, CuII speciation and ability to form ternary complexes (CuII-L-carbonate) have been explored by potentiometric titrations in 0.15 M NaClO4 and by UV/Vis and paramagnetic NMR spectroscopy. Comparisons are made with a previously reported terpyridinophane containing the polyamine 4,7,10-triazatridecane-1,13-diamine (L1). For this latter receptor, reductive coupling between indigo and carbon dioxide at indigo-modified electrodes produces carboxylated derivat…

Hierarchical Ordering in Ternary Co-Crystals of C60, N-Benzyl Ammonium Resorcinarene Bromide and Solvent Molecules

2014

Co-crystallization of C60 together with an N-benzyl ammonium resorcinarene bromide from toluene:1,2-dichloroethane mixture results in ternary co-crystals where the modulated C60 lattice entraps dimeric resorcinarene assemblies, which, in turn, have 149 and 280 A3 cavities filled with 1,2-dichloroethane molecules.