98 research outputs found
Recognizing Dart-Free Perfect Graphs
No full textA graph G is called Berge if neither G nor its complement contains a chordless cycle whose length is odd and at least five; what we call a dart is the graph with vertices u, v, w, x, y and edges uv, vw, uy, vy, wy, xy; a graph is called dart-free if it has no induced subgraph isomorphic to the dart. We present a polynomial-time algorithm to recognize dart-free Berge graphs; this algorithm uses as a subroutine the polynomial-time algorithm for recognizing claw-free Berge graphs designed previously by Chvatal and Sbihi
Satisfiability-Based Algorithms for Pseudo-Boolean Optimization Using Gomory Cuts and Search Restarts
No full textA study of waste management policy implications for landfill waste salvagers in the Western Cape
No full textIncludes bibliographical references (leaves 97-104).The aim of this innovative, qualitative research was to explore the factors that led to the Solid Waste Management Department's resolution to prohibit landfill salvaging in the Cape Metropolitan Municipality and the intended and unintended consequences such a decision subsequently had for the landfill waste salvagers. Large numbers of poor, unemployed and illiterate people reside in the Western Cape. The chronic and devastating nature of poverty is forcing thousands of vulnerable people into subsistence waste picking. These people dig through ingrained dirt and filth-ridden mud to extract items that they can use to construct and furnish their homes, to sustain themselves and their dependents, and more importantly, to sell to intermediaries for an income. Although a poorly paid, insecure and unsanitary form of employment, waste salvaging still puts food on the table at the end of the day when all else fails. This novel social development exercise studied what implications the prohibition on landfill salvaging in the Cape Metro has had for an exceedingly marginalized sector of society. This qualitative study mapped out the territory of integrated waste management and the various role players involved. The report explores the drivers for and barriers against landfill salvaging from three different perspectives: policy and planning, management and operations and informal sector waste salvagers. Government policies can sometimes prove to be less than effective in changing the disadvantaged circumstances of vulnerable communities. This research has demonstrated how the Department's decision to ban landfill salvaging has caused an even greater decline in the well-being of a section of the population that is already at risk. The researcher used observation, semi-structured one-on-one interviewing, focus group interviewing and questionnaires as well as conducted a thorough review of waste management policy-related documents and secondary data analysis in this qualitative endeavour. The triangulation of data collection methods helped the researcher interpret how the Department's decision has adversely impacted on the informal sector landfill salvagers and to what extent and helped indicate a possible way out of the subsequent precarious development. The waste salvagers of the Cape Metro are unemployed, experiencing a poorer quality of life and feeling even more socially and economically excluded from the rest of society because of the ban on landfill salvaging. Moreover, they have developed feelings of resentment and anger that have resulted in defiant acts of trespassing and theft. This research has shown that repressive and neglectful policies on landfill salvaging will only be met with significant opposition from the salvagers. Furthermore, given the socio-economic backlog and anticipated population growth in the Province, landfill salvaging will continue to be an important source of revenue for the poor and homeless. It is therefore the researcher's recommendation that landfill salvaging be legitimised and that landfill salvagers be recognized and organized into cooperatives that can provide them with the necessary resources to lobby for better working conditions at the top. Landfill salvaging will persist as long as chronic poverty endures. For this reason, consideration should rather be given as to how to go about formalising and controlling waste recovery at landfill sites to cater for the immediate and most basic needs of the poor. The recommendations brought forth will hopefully influence thinking about waste management policy planning and implementation in general, and be of service to furthering the country's achievement goals of sustainable employment creation and poverty alleviation
Optimizing over the first Chvatal closure
No full textHow difficult is, in practice, to optimize exactly over the first Chvàtal closure of a generic ILP? Which fraction of the integrality gap can be closed this way, e.g., for some hard problems in the MIPLIB library? Does it pay to insist on rank-1 Chvàtal-Gomory inequalities until no such inequality is violated, or one should better follow the usual strategy of generating (mixed-integer) Gomory cuts of any rank from the optimal tableau rows? How effective is this general-purpose approach for solving matching problems, where the first Chvàtal closure coincides with the integer hull? Can this approach be useful as a research (off-line) tool to guess the structure of some relevant classes of inequalities, when a specific combinatorial problem is addressed? In this paper we give, for the first time, concrete answers to the above questions, based on an extensive computational analysis. Our approach is to model the rank-1 Chvàtal-Gomory separation problem, which is known to be NP-hard, through a MIP model, which is then solved through a general-purpose MIP solver. As far as we know, this approach was never implemented and evaluated computationally by previous authors, though it gives a very useful separation tool for general ILP problems. We report the optimal value over the first Chvàtal closure for a set of ILP problems from MIPLIB 3.0. We also report, for the first time, the optimal solution of a very hard instance from MIPIB 2003, namely nsrand-ipx, obtained by using our cut separation procedure to preprocess the original ILP model. Finally, we describe a new class of ATSP facets found with the help of our separation procedure
Electric linear motors
No full textDiplomska naloga obravnava področje električnih linearnih motorjev, s poudar
kom na njihovem principu delovanja, tehnični zasnovi ter praktični uporabi v
industrijskih transportnih sistemih. V uvodnem delu so predstavljene osnovne
lastnosti magnetnega polja in njegova vloga pri generiranju ter usmerjanju sile,
ki je ključna za delovanje linearnih pogonov. Podrobneje so analizirani pojavi,
kot so statična in dinamična magnetna polja, vzdolžno potujoče magnetno polje
ter vpliv feromagnetnih materialov na učinkovitost delovanja.
Osrednji del naloge je namenjen razlagi principov delovanja linearnih asin
hronskih (LAM) in linearnih sinhronskih motorjev (LSM), kjer so podrobno opi
sani ključni sestavni deli sistema, vključno z izmeničnim presmernikom, krmilni
kom gibanja, dajalnikom položaja in ustreznimi algoritmi za regulacijo, kot sta
regulacija orientacije polja (FOC) in neposredna regulacija navora (DTC).
V praktičnem delu naloge je podrobneje predstavljen XTS (angl. extended
transport system) podjetja Beckhoff, ki združuje lastnosti linearnih motorjev z
naprednim krmiljenjem gibanja in omogoča izredno fleksibilnost pri oblikovanju
transportnih poti. Opisani so motorski moduli, tekači in vodilne tračnice ter nji
hova medsebojna interakcija, ki omogoča brezstično premikanje bremen z visoko
natančnostjo. Manjša pozornost je namenjena tudi integraciji sistema v program
sko okolje TwinCAT 3 ter funkcionalnosti brezžične komunikacije neposredno s
posameznim tekačem, ki omogoča brezkontakten prenos energije in podatkov ter
spremeni tekače iz pasivnih enot v aktivne procesne postaje.
Rezultati praktičnega dela na testnem modelu XTS potrjujejo, da napre
dne rešitve linearnih motorjev omogočajo bistveno izboljšanje učinkovitosti, na
tančnosti in fleksibilnosti sodobnih industrijskih procesov. Naloga tako povezuje teoretične osnove elektromagnetizma z uporabo v realnih aplikacijah ter ponuja
vpogled v tehnologije, ki predstavljajo prihodnost industrijske avtomatizacije.The thesis addresses the field of electric linear motors, with an emphasis on their
operating principles, technical design, and practical implementation in industrial
transport systems. The introductory part presents the fundamental properties of
the magnetic field and its role in generating and directing force, which is crucial for
the operation of linear drives. Phenomena such as static and dynamic magnetic
fields, longitudinal traveling magnetic fields, and the influence of ferromagnetic
materials on system performance are analyzed in greater detail.
The central part of the thesis explains the operating principles of linear asyn
chronous motors (LAM) and linear synchronous motors (LSM), with a detailed
description of the key system components, including the inverter, motion con
troller, position encoder, and relevant control algorithms, such as field-oriented
control (FOC) and direct torque control (DTC).
In the practical part of the thesis, the XTS (extended transport system) deve
loped by Beckhoff is presented in detail. XTS combines the advantages of linear
motors with advanced motion control and enables exceptional flexibility in desi
gning transport paths. The thesis describes the motor modules, movers, and guide
rails, along with their mutual interaction, which allows for contactless movement
of loads with high precision. Additional attention is given to the integration of
the system into the TwinCAT 3 software environment and the functionality of
NCT (no cable technology), which enables wireless power and data transmission
directly to individual movers, transforming them from passive transport units
into active mobile processing stations.
The results obtained from testing the XTS system on a practical model confirm that advanced linear motor solutions enable significant improvements in efficiency, precision, and flexibility in modern industrial processes. The thesis therefore connects the theoretical foundations of electromagnetism with real-world applications and provides insight into technologies that represent the future of industrial automation
Lines in bipartite graphs and in 2-metric spaces
No full textThe line generated by two distinct points, x and y, in a finite metric space M=(V,d), is the set of points given by {z is an element of V:d(x,y)=|d(x,z)+d(z,y)|ord(x,y)=|d(x,z)-d(z,y)|}. It is denoted by xy over bar M. A 2-set {x,y} such that xy over bar M=V is called a universal pair and its generated line a universal line. Chen and Chvatal conjectured that in any finite metric space either there is a universal line, or there are at least |V| different (nonuniversal) lines. Chvatal proved that this is indeed the case when the metric space has distances in the set {0,1,2}. Aboulker et al proposed the following strengthenings for Chen and Chvatal conjecture in the context of metric spaces induced by finite graphs: First, the number of lines plus the number of bridges of the graph is at least the number of points. Second, the number of lines plus the number of universal pairs is at least the number of points of the space. In this study, we prove that the first conjecture is true for bipartite graphs different from C4 or K2,3, and that the second conjecture is true for metric spaces with distances in the set {0,1,2}.Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), CONICYT PIA/BASAL: AFB170001.
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), CONICYT FONDECYT: 1180994
Membranove vlastnosti gliovych bunek a jejich uloha v iontove a objemove homeostaze CNS.
No full textSystematic study of the electrophysiological properties of glial cells, astrocytes and oligodendrocytes, began during the sixties, when their possible role in the buffering of K plus, which accumulates in the extracellular space of the central nervous system (CND) during neuronal activity, was first formulated. Even though glial cells and neurons develop from the same type of precursor cell, they have distinct electrophysiological properties, which are determined by the presence of transport protein. It was suggested that transport proteins in glial cells play an important role in various processes in normal nervous tissue, during development as well as during pathological states. Activation of ionic channels and transporters in glial cells takes place during the maintenance of ionic homeostasis, during the regulation of metabolism and the release of hormones, and during communication with surrounding cells. As a result of ionic shifts, the cell volume of glial cells changes, affecting the size and geometry of the extracellular space (ECS), which is the microenvironment of neurons and glial cells. The composition and size of the ECS change dynamically during neuronal activity as well as during pathological states. Following their release, a number of neuroactive substances, including ions, mediators, metabolites and neurotransmitters, diffuse via the ECS to targets distant form their release sites. Glial cells affect the composition and volume of the ECS and therefore also extracellular diffusion, particularly during development, aging and ptahological states such as ischemia, injury, X-irradiation, gliosis, demyelination and often in grafted tissue. Recent studies also indicate that diffusion in the ECS is affected by ECS volume inhomogeneities, which are the result of a more compacted space in certain regions. Besides glial cells, the extracellular matrix also changes ECS geometry and forms diffusion barrier, which may also result in diffusion anisotropy. Glial cells therefore play an important role in extrasynaptic transmission, for example in functions such as vigilance, sleep, depression, chronic pain, LTP, LTD, memory formation and other plastic changes in the CNS. In turn, ECS diffusion parameters affect neuron-glia communication, ionic homeostasis and the movement and/or accumulation of neuroactive substances in the brain. Chvatal, AlexandrSummary and text also in EnglishAvailable from STL, Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi
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