Maximizing edge-ratio is NP-complete

This is the post-print verison of the Article. The official published version can be accessed from the link below - Copyright @ 2011 ElsevierGiven a graph G and a bipartition of its vertices, the edge-ratio is the minimum for both classes so defined of their number of internal edges divided by their number of cut edges. We prove that maximizing edge-ratio is NP-complete

Sum-of-squares clustering on networks

Finding p prototypes by minimizing the sum of the squared distances from a set of points to its closest prototype is a well-studied problem in clustering, data analysis and continuous location. In this note, this very same problem is addressed assuming, for the first time, that the space of possible prototype locations is a network. We develop some interesting properties of such clustering problem. We also show that optimal cluster prototypes are not necessary located at vertices of the network.Ministerio de Ciencia e InnovaciónJunta de AndalucíaEuropean Regional Development FundSerbian Ministry of Science

LCA of the manufacturing stage of the laboratory belt conveyor

Sprovedena je procena životnog ciklusa malog trakastog transportera. Analizirana je faza proizvodnje sa aspekata uticaja na životnu sredinu i potrošnje energije. Najveći uticaj na životnu sredinu u većini kategorija uticaja za osnovni model kategorija uticaja potiče od proizvodnje niskolegiranih čelika i potrošnje električne energije tokom faze proizvodnje, praćen uticajem transporta. U radu su takođe predloženi načini uštede energije u proizvodnoj praksi uz primenu adekvatnih tehnologija.A cradle-to-gate LCA analysis of a small belt conveyor was conducted. Manufacturing stage was analysed from the aspects of environmental impacts and energy consumption. The biggest environmental impact in majority of baseline impact categories is obtained from low-alloyed steel production and electricity consumption during the manufacturing stage, followed by impact of the transport. Ways for possible energy savings regarding manufacturing practice and technologies were proposed later on

Variable neighbourhood decomposition search for 0-1 mixed integer programs

In this paper we propose a new hybrid heuristic for solving 0-1 mixed integer programs based on the principle of variable neighbourhood decomposition search. It combines variable neighbourhood search with a general-purpose CPLEX MIP solver. We perform systematic hard variable fixing (or diving) following the variable neighbourhood search rules. The variables to be fixed are chosen according to their distance from the corresponding linear relaxation solution values. If there is an improvement, variable neighbourhood descent branching is performed as the local search in the whole solution space. Numerical experiments have proven that exploiting boundary effects in this way considerably improves solution quality. With our approach, we have managed to improve the best known published results for 8 out of 29 instances from a well-known class of very di±cult MIP problems. Moreover, computational results show that our method outperforms the CPLEX MIP solver, as well as three other recent most successful MIP solution methods

Bioaktivne komponente u funkciji oplemenjivanja industrijskog paradajza

Selection of tomato lines for industrial use regarding their nutritional value is a potential that will reflect in the final product obtained from tomato fruits. At the same time, technological process of preparation of tomato juice (100 °C), as well as hot air drying, was studied in order to establish an optimal technological process that is the least disrupting for the natural potential of nutrients contained in fresh fruits. The research was performed on 6 lines and one variety of industrial tomato. The content of vitamin C, vitamin E, lycopene, β-carotene, phenols, flavonoids, dry matter and total antioxidative capacity was studied by applying standard methods for determination of the level of these parameters. Grouping was performed according to traits of average carotenoid content (lycopene, β-carotene), vitamin C, vitamin E, phenols, flavonoids, dry matter and total antioxidative capacity in tomato fruit, by applying PCA. The first two principle components were responsible for 77.18 % of total variability of researched samples. The impact of other five components was low and they were responsible for 22.18 % of the variability. Antioxidative activity was best preserved after finishing, through small losses of lycopene and β-carotene. Losses of vitamin C, vitamin E, phenols and flavonoids during thermal processing were great, mostly in juice, while in dried product, these losses were lower. Nutrient losses were in function of temperature height that the fruits were exposed to during the thermal processing. Genotypes SPRZ and SPSM were marked as the best.Selekcija linija paradajza namenjenog industrijskoj preradi prema osobinama koje definišu njihovu nutritivnu vrednost predstavljaju potencijal koji će se reflektovati u proizvodu dobijenom od plodova paradajza. U isto vreme ispitan je i tehnološki proces pripreme soka paradajza (100 °C) kao i sušenje plodova na toplom vazduhu, kako bi se utvrdio optimalni tehnološki proces koji najmanje narušava prirodni potencijal nutrijenata sadržanih u svežim plodovima. Ispitivanje je sprovedeno na 6 linija i jednoj sorti industrijskog paradajza gde su ispitani sadržaj vitamina C, vitamina E, likopina, β-carotina, fenola, flavonoida, suve materije i ukupni antioksidativni kapacitet, standardnim metodama za utvrđivanje sadržaja ovih parametara. Grupisanje je izvršeno prema osobinama prosečnog sadržaja karetinoida (likopen, β-karoten), vitamina C, vitamina E, fenola, flavonoida, suve materije i ukupnog antioksidatinog kapaciteta u plodu paradajza, pomoću PCA analize. Prve dve principle komponente odgovorne su za 77,18 % ukupne varijabilnosti ispitivanih uzoraka. Uticaj ostalih pet komponenti je mali i one su odgovorne za 22,18 % varijabilnosti. Antioksidativna aktivnost je najbolje očuvana posle dorade kroz male gubitke likopina i β-karotina posle dorade. Gubici vitamina C, vitamina E, fenola, flavonoida pri termičkoj obradi su veliki i to najviše u soku, dok kod sušenog proizvoda ti gubici su nešto manji. Gubici nutrijenata su u funkciji visine temperature kojima su plodovi bili izlagani pri termičkoj obradi. Kao najbolji genotipovi ocenjeni su SPRZ i SPSM

Pooling problem: Alternate formulations and solution methods

Copyright @ 2004 INFORMSThe pooling problem, which is fundamental to the petroleum industry, describes a situation in which products possessing different attribute qualities are mixed in a series of pools in such a way that the attribute qualities of the blended products of the end pools must satisfy given requirements. It is well known that the pooling problem can be modeled through bilinear and nonconvex quadratic programming. In this paper, we investigate how best to apply a new branch-and-cut quadratic programming algorithm to solve the pooling problem. To this effect, we consider two standard models: One is based primarily on flow variables, and the other relies on the proportion. of flows entering pools. A hybrid of these two models is proposed for general pooling problems. Comparison of the computational properties of flow and proportion models is made on several problem instances taken from the literature. Moreover, a simple alternating procedure and a variable neighborhood search heuristic are developed to solve large instances and compared with the well-known method of successive linear programming. Solution of difficult test problems from the literature is substantially accelerated, and larger ones are solved exactly or approximately.This project was funded by Ultramar Canada and Luc Massé. The work of C. Audet was supported by NSERC (Natural Sciences and Engineering Research Council) fellowship PDF-207432-1998 and by CRPC (Center for Research on Parallel Computation). The work of J. Brimberg was supported by NSERC grant #OGP205041. The work of P. Hansen was supported by FCAR(Fonds pour la Formation des Chercheurs et l’Aide à la Recherche) grant #95ER1048, and NSERC grant #GP0105574

Uticaj termičke obrade plodova paradajza na antioksidativnu aktivnost, sadržaj vitamina E, suve materije i ukupnih šećera

The objective of this study was the determination of total antioxidant activity, contents of vitamin E, sugar and total dry matter in fresh and thermally processed (dried and juiced) tomato fruits of different selected tomato lines with the aim to establish the nutritive profile and distinguish superior genotypes in order to obtain high-quality final product with more benefit to human health. Content of vitamin E, total antioxidant activity, dry matter and total sugars, in fresh and dried fruits (dried in parallel hot air dryer at 60 °C, until the final product reached the moisture lower than 10% and in tomato juice pasteurized at 100 °C, for 7 minutes) was studied. Comparative trial with 7 genotypes: one commercial variety (SP-109) and 6 selected high inbreeding generation lines (SPP, SPSM, SPRZ, SPRM-20, S-60 and SPO), was set up. Genotype SPRZ had the highest vitamin E content and total antioxidant capacity, both in fresh fruit and after the treatments. Thermal processing by drying at 60°C and pasteurization of tomato changed the level of total sugar and dry matter content. Total antioxidant activity decreased by drying, comparing to fresh fruit while the level of vitamin E decreased in juice pasteurized at high temperature (100 °C). .Cilj istraživanja je određivanje ukupne antioksidativne aktivnosti, sadržaja vitamina E, sadržaja šećera i ukupne suve materije u svežim i termički obrađenim (sušeni plodovi i sok) plodovima različitih selekcionih linija paradajza, sa ciljem utvrđivanja nutritivnog kvaliteta i izdvajanja superiornih genotipova, čijom preradom bi se dobio kvalitetniji krajnji proizvod sa pozitivnim dejstvom na ljudsko zdravlje. Ispitivani su sadržaj vitamina E, ukupna antioksidativna aktivnost, suva materija, i ukupni sadržaj šećera, kod svežih plodova, sušenih plodova (sušenje toplim vazduhom na 60 °C, do konačne vlage uzorka manje od 10%) i soka paradajza (pasterizacijom na 100 °C, u trajanju od 7 minuta). Izveden je komparativni ogled sa 7 genotipova, jedna komercijalna sorta (SP-109) i 6 selekcionisanih linija (SPP, SPSM, SPRZ, SPRM-20, S-60 I SPO) visokih generacija inbridinga. Termička obrada plodova paradajza (sušenjem na 60 °C) i pravljenjem soka dovodi do promene ukupnog sadržaja šećera i sadržaja ukupne suve materije. Ispitivanjem ukupne antioksidativne aktivnosti utvrđeno je da se ona gubi sušenjem u odnosu na svež plod, a sadržaj vitamina E se smanjio u soku koji je dobijen obradom na višim temperaturama (100 °C). Genotip SPRZ imao je najviše vrednosti za sadržaj vitamina E i ukupan antioksidativni kapacitet kako u svežem stanju tako i nakon primenjene obrade. Izborom superiornih genotipova i akumulacijom nutrijenata kroz oplemenjivačke programe, može se poboljšati kvalitet krajnjeg proizvoda i postići dobijanje prerađevina sa većim pozitivnim uticajem na zdravlje ljudi

Less is more: simplified Nelder-Mead method for large unconstrained optimization

Nelder-Mead method (NM) for solving continuous non-linear optimization problem is probably the most cited and the most used method in the optimization literature and in practical applications, too. It belongs to the direct search methods, those which do not use the first and the second order derivatives. The popularity of NM is based on its simplicity. In this paper we propose even more simple algorithm for larger instances that follows NM idea. We call it Simplified NM (SNM): instead of generating all n + 1 simplex points in Rn, we perform search using just q + 1 vertices, where q is usually much smaller than n. Though the results cannot be better than after performing calculations in n+1 points as in NM, significant speed-up allows to run many times SNM from different starting solutions, usually getting better results than those obtained by NM within the same cpu time. Computational analysis is performed on 10 classical convex and non-convex instances, where the number of variables n can be arbitrarily large. The obtained results show that SNM is more effective than the original NM, confirming that LIMA yields good results when solving a continuous optimization problem

An oil pipeline design problem

Copyright @ 2003 INFORMSWe consider a given set of offshore platforms and onshore wells producing known (or estimated) amounts of oil to be connected to a port. Connections may take place directly between platforms, well sites, and the port, or may go through connection points at given locations. The configuration of the network and sizes of pipes used must be chosen to minimize construction costs. This problem is expressed as a mixed-integer program, and solved both heuristically by Tabu Search and Variable Neighborhood Search methods and exactly by a branch-and-bound method. Two new types of valid inequalities are introduced. Tests are made with data from the South Gabon oil field and randomly generated problems.The work of the first author was supported by NSERC grant #OGP205041. The work of the second author was supported by FCAR (Fonds pour la Formation des Chercheurs et l’Aide à la Recherche) grant #95-ER-1048, and NSERC grant #GP0105574

Način nasleđivanja indeksa oblika lukovice crnog luka (Allium cepa L.)

Onion (Allium cepa L.) is a very important and widespread vegetable crop. Bulb shape index is a very significant biological and commercial trait. Bulb shape impacts the price, processing, resistance to diseases, etc., which is the reason why it is a very important economical trait. Success of the breeding process depends on genetic determination of the traits that were targeted in the selection process. In order to assess the genetic determination of bulb shape index, the trial was set up in the random block system with five replications, with diallel crossing without reciprocals. Bulb shape index in F1 generation was from flat-round to oval shaped. The most common heredity mode of the bulb shape index was superdomination. The highest value of GCA for shape index was found in 'Makoi bronzi', which was the indicator of the best combining abilities. The highest SCA in F1 and F2 generation was found in the hybrid 'Makoi bronzi' x 'AC 101'.Crni luk (Allium cepa L.) je izuzetno važna i široko raspostranjena povrtarska vrsta. Indeks oblika lukovice crnog luka predstavlja veoma značajno biološko i tržišno svojstvo. Oblik lukovica ima uticaja na tržišnu cenu crnog luka, proces dorade, otpotnost na bolesti, itd. Zbog ovoga, indeks oblika se ubraja u važnu ekonomsku osobinu lukovice crnog luka. Genetska determinisanost osobine utiče na uspešnost procesa selekcije. Kako bi utvrdili genetsku determinisanost indeksa oblika lukovice, postavljen je ogled po slučajnom blok sistemu u pet ponavljanja. Primenjen je metod dialelnog ukrštanja bez recipročnog. Posmatrajući hibridne kombinacije Fi generacije može se uočiti da se njihov indeks oblika lukovice kretao od pljosnato-okruglog do ovalnog. Najzastupljeniji način nasleđivanja indeksa oblika lukovice u ovom istraživanju je super dominacija. Najveću vrednost OKS za indeks oblika imala je linija 'Makoi bronzi'. Najvišu vrednost za PKS u F1 i F2 generaciji imao je hibrid dobijen ukrštanjem linije 'Makoi bronzi' x 'AC 101'