59 research outputs found
Knapsack problem for nilpotent groups
No full textAbstractIn this work we investigate the group version of the well known knapsack problem in the class of nilpotent groups. The main result of this paper is that the knapsack problem is undecidable for any torsion-free group of nilpotency class 2 if the rank of the derived subgroup is at least 316. Also, we extend our result to certain classes of polycyclic groups, linear groups, and nilpotent groups of nilpotency class greater than or equal to 2.</jats:p
Safety mapping of Rannu school bus stops in Elva municipality
No full textKäesolev lõputöö on seotud Transpordiameti poolt läbiviidava kompleksuuringuga, mille fookus on koolibussitransport ja selle ohutus. Lõputöö eesmärgist lähtuvalt kaardistas autor kõik koolibussipeatused Rannu alevikus, analüüsis nende ohutust ning viis läbi küsitlused lastevanemate ja bussijuhtidega. Peale peatuste analüüsimist esitas autor parendusettepanekud ohutuse tõstmiseks.
Lõputöö esimeses ja teises osas keskenduti liiklusohutusele, ühistranspordile ja seal kehtivatele nõuetele. Samuti toodi välja, millised on liikluses kasutatavad bussipeatuste tüübid ning mis tunnused on hea ligipääsetavusega ja ohutul peatusel. Nendes osades leiti vastus esimesele autori poolt püstitatud uurimisküsimusele.
Peatuste ohutuse paremaks ülevaateks koostas autor küsimustikud nii lastevanematele kui ka bussijuhtidele. Lastevanemate küsimustik koosnes 14 ja bussijuhtide oma kaheksast küsimusest, kus oli võimalik lisada avatud vastuseid ja valikvastuseid (Lisa 4, Lisa 5). Lisaküsimused lastevanemate küsimustikus hõlmasid nende lastega seotud faktoreid. Küsimustiku vastuste analüüsis selgus, et paljud lapsevanemad ei ole rahul peatuste tingimustega. Suurimad murekohad olid peatuse tasku puudumine, valgustuste puudumine ja kõrged piirkiirused peatuste alas. Veel lisati, et talvised tingimused muudavad liiklemise eriti ohtlikuks. Bussijuhid lisasid, et ohtlikuks muudavad peatuse kitsad teed, tihe liiklus ja peatuste tasku puudumine. Küsimustikust saadud vastused aitasid autoril täiendada peatuste ohutuse analüüsimist ja parendusettepanekute koostamist. See peatükk aitas osaliselt vastata kolmandale uurimisküsimusele.
Viimases peatükis grupeeris autor peatused lähtuvalt hindamistabeliga saadud skoorist ja tõi välja parendusettepanekud turvalisuse tõstmiseks. Tänu sellele oli võimalik leida läbivaid elemente peatustes ja nende piirkondades, mis mängisid rolli ohutuse tagamisel. Peamisteks soovitusteks olid peatustesse vastava märgistuse lisamine, valgustuse tagamine ja ootekohtade rajamine. Samuti soovitati alandada piirkiirust ja lisada liiklusmärk „Lapsed“ maanteel asuvate peatuste alas. Antud peatükiga leidis autor vastuse neljandale uurimisküsimusele.
Peatuste ohutustaseme hindamiseks koostati hindamistabel kõikide peatuste analüüsimiseks (Lisa 9, Lisa 10). Peatuste analüüsimisel selgus, et umbes pooled said skoori üle keskmise. Suurimad puudused madala tulemusega peatustes olid peatuse märgistuse ja valgustuse puudumine. Samuti muutis peatused ohtlikuks peatuse tasku ja reisijate ootekoha puudumine ning kõrged piirkiirused peatuste alas. Peale kõikide peatuste hindamist ja analüüsi sai autor vastuse teisele ja kolmandale uurimisküsimusele.This dissertation is related to a complex study conducted by Transport Administration, the focus of which is on school bus transport and its safety. For the purpose of this dissertation the author mapped all the school bus stops in Rannu borough, analyzed their safety and surveyed parents and bus drivers. After the analysis the author presented suggestions for improving the level of safety.
The first and second parts of the dissertation focused on road safety, public transport and the requirements which apply. It was also pointed out what types of bus stops are used in traffic and what are the characteristics of a well-accessible and safe bus stop. In these parts, the answer to the first research question posed by the author was found.
For a better overview of the safety of stops, the author prepared questionnaires for both parents and bus drivers. The parents 'questionnaire consisted of 14 and the bus drivers' eight questions, where it was possible to add open-ended and multiple-choice answers (Lisa 4, Lisa 5). Additional questions in the parents' questionnaire included factors related to their children. An analysis of the responses to the questionnaire revealed that many parents were dissatisfied with the conditions of the stops. The main concerns were the lack of a bus turnout, lighting and the high-speed limits in the stop area. It was added that winter conditions make traffic particularly dangerous. Bus drivers added that the narrow roads in the bus stop area, heavy traffic and lack of bus turnouts make stops dangerous. The answers received from the questionnaire helped the author in analyzing the safety of stops and to gather improvement suggestions. This chapter helped to partially answer the third research question.
In the last chapter, the author grouped the stops according to the score obtained with the scoreboard and outlined suggestions for improving safety. This made it possible to find pervasive elements in the stops and their areas that played a role in ensuring safety. The main recommendations were to add appropriate markings to the stops, to provide lighting and to set up waiting areas. It was also suggested that the speed limit be lowered and that the "Children" road sign be added to the roadside stop. In this chapter the author found the answer to the fourth research question.
To assess the safety level of the stops, an evaluation table was prepared to analyze all stops (Lisa 9, Lisa 10). An analysis of the stops revealed that about half scored above average. The biggest shortcomings at low-scoring stops were the lack of stop markings and lighting. The stops were also made dangerous by the lack of a bus turnout and passenger waiting areas, as well as high speed limits in the stop area. After evaluating and analyzing all the stops, the author received an answer to the second and third research questions
Applying lean principles in road transport companies
No full textLean mõtlemist on tootmisvaldkonnas edukalt kasutatud tänaseks juba mitukümmend aastat ning selle kasulikkus on end tõestanud. Samuti on ettevõtteid, kes lean mõtlemist ka teenindussfääris rakendanud ning ka seal on see tõestanud end edukaks. Üsna vähe on aga uuritud lean-i kasutamise võimalusi transpordi- täpsemalt maanteetranspordi valdkonnas. Antud lõputöö keskendubki just maanteetranspordi ja lean-i sobivuse uurimisele. Teema paremaks mõistmiseks algab lõputöö lean mõtlemise kujunemisega. Antakse ülevaade kuidas autotööstuse areng tekitas vajaduse ja võimaluse masstootmiseks. Masstootmine aga ei sobinud universaalselt igale turule, seda mõistsid Jaapani autotootja Toyota insenerid, kes leidsid, et mõningate oluliste muutustega tootmises oleks võimalik luua järjepidev protsesside voog ning pakkuda laia tootevalikut. Sündis Toyota tootmissüsteem, mida hiljem on hakatud nimetama lean tootmiseks. Lean kontseptiooni keskne osa on väärtus, ehk miski, mille eest klient on nõus maksma. Lean jagab tegevused protsessis kolmeks: tegevused, mis lisavad väärtust, tegevused, mis väärtust ei lisa, kuid on vajalikud ning tegevused, mis väärtust üldse ei lisa. Viimaseid nimetatakse ka raiskamiseks, mis tuleb protsessist eemaldada. Järgnevalt tuvastati erinevad raiskamiste liigid logistikas ning uuriti kolme näite põhjal nende olemust, tekkepõhjuseid ning tagajärgi. Nendeks kolmeks näiteks olid Mehhiko külmutatud toiduainete tootja ja jaotaja Sigma Alimentos, S.A. de C.V, Rootsi teadlaste uuring, kus vaadeldi kolme keskmise suurusega transpordifirmat Rootsis ning kahte Šveitsis, ja Iiri odavlennufirma Ryanair Ltd. Nende analüüsimisest selgus, et raiskamiste tekkepõhjusteks on peamiselt ajaga mitte kaasas käimime, ehk vanamoodsate kommunikatsioonivahendite kasutamine, töö topelt tegemine, töö halb organiseerimine ning prognoosimine ja protsessi osapoolte vaheline puudulik koostöö. Töö lõpus jõuti järelduseni, et paljud tuvastatud probleemid ja nendest tulenevad raiskamised on põhjustatud töö ebaefektiivsest korraldusest või halvast organiseerimisest, mis tähendab, et protsesside ümberhindamise ja strateegilise muutmisega on võimalik kogu ahel sujuvamaks ja kiiremaks muuta. Paberkandjate asemel tuleks üle minna täielikult elektroonsele andmevahetusele, mis tähendab, et süsteem viib ise vajalikud andmed kokku, selle asemel, et seda peaks inimene ükshaaval pabereid otsides tegema. Nii säästetakse aega, kulusid administratiivsetele tegevustele ning lisaks säästetakse ka loodust. Tihe infovahetus protsessi osapoolte vahel, nagu saabumistest ja lahkumistest varakult teada andmine hoiaks ära viivituste ja pudelikaelte tekke laadimiste ootamisel terminalialadel. Selle asemel saaksid autojuhid seda aega palju sisukamalt kasutada. Näiteks auto hoolduseks, tankimiseks ning ka korralisteks puhkepeatusteks. Info parem vahetus on aluseks ka laadimisvigade ära hoidmisele. Terminalitöötajatel oleks juba enne auto saabumist teada milline kaup ja millises järjekorras auto peale peaks minema, mis hoiaks ära ümberlaadimise vajaduse ning samuti kaupade omadustest tingitud käitlemisvigade tekke. Kauba laadimisega peaksid tegelema ainult selleks koolitatud inimesed, kes on täpselt teadlikud kuidas ja millises järjekorras erinevaid kaupu tuleks laadida. Töö lõpus pakutakse välja ideaalne transpordiprotsessimudel, mis võtab arvesse lõputöös jõutud järeldusi ning lean mõtlemise seisukohti. See tähendab seda, et kogu protsess kulgeb ühtlase voona ning protsessist on eemaldatud kõik raiskamised, mis eelneva analüüsi käigus tuvastati. Mudeli järgselt peaks tegema igat protsessi vaid ühe korra, näiteks andmete sisestamine. Võimalikult palju kasutatakse infotehnoloogilisi abivahendeid, mis muudavad protsessi maksimaalselt automatiseerituks ning viib inimliku sekkumise vajaduse miinimumini. Selline mudel soodustab ka Just in Time vedusid, mis omakorda annab meeletu konkurentsieelise, sest vedajaid, kes seda nõus tegema on väga vähe. Väga suur roll on ka tihedal infovahetusel ning protsessiosapoolte omavahelisel tihedal koostööl. See tähendab seda, et kõikidele osapooltele on kogu protsessi vältel teada vajalik informatsioon. Seda uurimust on võimalik võtta aluseks edasiste, täpsemate lean maanteetranspordiuuringute puhul. Edasine arengusuund võiks olla näiteks juurutamise maksumuse, säästetud aja ja rahalise kulu arvuliste väärtuste leidmine ja võrdlemine ning tasuvusanalüüsi koostamine. On selge, et selline mudel töötab ainult siis, kui see on täielikult integreeritud ja kõikidele osapooltele ühtselt mõistetav ning vastu võetav. Muuta on vaja kogu transpordisüsteemi, mitte ainult selle ühte osa ja see ongi kõige tõenäolisem takistus, miks tänapäeval lean maanteetransport väga laialdaselt levinud pole.Lean thinking has gained more and more popularity in the past decades. Traditionally it has been used in the field of production, but lately many enterprises from service sector have also started to realize its potential and use its advantages; and have had notable success with it. One field that hasn’t been investigated very thoroughly is road transportation. The purpose of this thesis is to investigate the possibilities of applying those principles in road transportation companies. The goal of this thesis is to map activities that give value to the transportation process and the ones that don’t. Activities that don’t give value are waste, and must be eliminated from the process. The thesis uses three previously conducted attempts of lean usage in the field of transportation as a base for further investigation. Those are: Mexico’s biggest frozen food producer and distributor Sigma Alimentos, S.A. de C.V; research conducted by Swedish researchers, that included three transportation companies from Sweden and two from Switzerland; and lastly Irish budget airline company Ryanair Ltd. Using these as examples, the thesis groups the problems and difficulties they faced as wastes, as classified by Joel Sutherland and Bob Bennett in their 2007 article “The Seven Deadly Wastes of Logistics: Applying Toyota Production System Principles to Create Logistics Value”. The first part of this thesis gives a brief overview of the history and development of lean thinking: how the rise of mass production developed into Toyota Production System or lean production as we know it today. The second part of the thesis explains the main principles of lean, with the main emphasis on value, as the central part of lean thinking. There the author also explains the importance of road transportation in today’s world with an illustrative figure of traditional transportation process. Third part of the thesis summarizes the findings and explains the root causes of those transportation wastes. Author came to conclusion that most of the identified wastes have common root cause, which is inefficient management of work and bad organization. This means that with reevaluation of processes and some strategic changes, it is possible to create better process flow and make the whole chain quicker. The thesis finishes with a suggested “ideal transportation process model”, which has found a solution for all the identified wastes and considers the principles of lean thinking. This means that the whole process is a constant flow. The model is heavily dependent on modern computerized data processing and information exchange between the counterparts of the transportation process. This thesis can be used as a starting point for future researches on lean road transportation. The further investigation directions should be towards investigating the cost of implementing and maintaining a lean transportation model and comparing it to the numerical values of money, time and quality saved. It is clear that this model would only work if it was completely integrated with all the counterparts in the process. For this model to work, the whole transportation process has to be changed, not just part of it
On the complexity of the problem of solving systems of tropical polynomial equations of degree two
No full textIn this paper, we investigate the computational complexity of the problem of solving a one-sided system of equations of degree two of a special form over the max-plus algebra. Also, we consider the asymptotic density of solvable systems of this form. Such systems have appeared during the analysis of some tropical cryptography protocols that were recently suggested. We show how this problem is related to the integer linear programming problem and prove that this problem is NP-complete. We show that the asymptotic density of solvable systems of this form with some restrictions on the coefficients, the number of variables, and the number of equations is 0. As a corollary, we prove that this problem (with some restrictions on the coefficients, the number of variables, and the number of equations) is decidable generically in polynomial time
An attack on a key exchange protocol based on max-times and min-times algebras
No full textIn this paper, we examine one of the public key exchange protocols proposed in [M. I. Durcheva. An application of different dioids in public key cryptography. In AIP Conference Proceedings, vol. 1631, pp 336-343. AIP, 2014] which uses max-times and min-times algebras. We discuss properties of powers of matrices over these algebras and introduce a fast attack on this protocol.
This preprint has not undergone peer review (when applicable) or any post-submission improvements or corrections. The Version of Record of this article is published in Indian Journal of Pure and Applied Mathematics, and is available online at https://doi.org/10.1007/s13226-023-00469-0
On equationally Noetherian predicate structures
No full textIn this paper, we prove a criterion for a predicate structure to beequationally Noetherian.Comment: 13 pages, 4 figures. Published in the journal of Groups, Complexity, Cryptolog
Analysis of four protocols based on tropical circulant matrices
No full textSeveral key exchange protocols based on tropical circulant matrices were proposed in the last two years. In this paper, we show that protocols offered by M. Durcheva [M. I. Durcheva. TrES: Tropical Encryption Scheme Based on Double Key Exchange. In: Eur. J. Inf. Tech. Comp. Sci. 2.4 (2022), pp. 11–17], by B. Amutha and R. Perumal [B. Amutha and R. Perumal. Public key exchange protocols based on tropical lower circulant and anti-circulant matrices. In: AIMS Math. 8.7 (2023), pp. 17307–17334.], and by H. Huang, C. Li, and L. Deng [H. Huang, C. Li, and L. Deng. Public-Key Cryptography Based on Tropical Circular Matrices. In: Appl. Sci. 12.15 (2022), p. 7401] are insecure
How preparation-for-learning with a worked versus an open inventing problem affect subsequent learning processes in pre-service teachers
No full textA worked-out or an open inventing problem with contrasting cases can prepare learners for learning from subsequent instruction differently regarding motivation and cognition. In addition, such activities potentially initiate different learning processes during the subsequent (“future”) learning phase. In this experiment ( N = 45 pre-service teachers), we aimed to replicate effects of earlier studies on learning outcomes and, on this basis, to analyze respective learning processes during the future-learning phase via think-aloud protocols. The inventing group invented criteria to assess learning strategies in learning journals while the worked-example group studied the same problem in a solved version. Afterwards, the pre-service teachers thought aloud during learning in a computer-based learning environment. We did not find substantial motivational differences (interest, self-efficacy), but the worked-example group clearly outperformed their counterparts in transfer ( BF +0 > 313). We found moderate evidence for the hypothesis that their learning processes during the subsequent learning phase was deepened: the example group showed more elaborative processes, more spontaneous application of the canonical, but also of sub-optimal solutions than the inventing group ( BF s around 4), and it tended to focus more on the most relevant learning contents. Explorative analyses suggest that applying canonical solutions to examples is one of the processes explaining why working through the solution leads to higher transfer. In conclusion, a worked-out inventing problem seems to prepare future learning more effectively than an open inventing activity by deepening and focusing subsequent learning processes
Biotic modifiers, environmental modulation and species distribution models
No full textThe ability of species to modulate environmental conditions and resources has long been of interest. In the past three decades the impacts of these biotic modifiers have been investigated as ‘ecosystem engineers’, ‘niche constructors’, ‘facilitators’ and ‘keystone species’. This environmental modulation can vary spatially from extremely local to global, temporally from days to geological time, and taxonomically from a few to a very large number of species. Modulation impacts are pervasive and affect, inter alia, the climate, structural environments, disturbance rates, soils and the atmospheric chemical composition. Biotic modifiers may profoundly transform the projected environmental conditions, and consequently have a significant impact on the predicted occurrence of the focal species in species distribution models (SDMs). This applies especially when these models are projected into different geographical regions or into the future or the past, where these biotic modifiers may be absent, or other biotic modifiers may be present. We show that environmental modulation can be represented in SDMs as additional variables. In some instances it is possible to use the species (e.g. biotic modifiers) in order to reflect the modulation. This would apply particularly to cases where the effect is the result of a single or a small number of species (e.g. elephants transforming woodland to grassland). Where numerous species generate an effect (such as tree species making a forest, or grasses facilitating fire) that modulates the abiotic environment, the effect itself might be a better descriptor for the aggregated action of the numerous species. We refer to this ‘effect’ as the modulator. Much of the information required to incorporate environmental modulation effects in SDMs is already available from remote-sensing data and vegetation models
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