77 research outputs found
Fe in III-V and II-VI semiconductors
No full textMany theoretical and experimental studies deal with the realization of room-temperature ferromagnetism in dilute magnetic semiconductors (DMS). However, a detailed quantitative understanding of the electronic properties of transition metal doped semiconductors has often been neglected. This article points out which issues concerning electronic states and charge transfers need to be considered using Fe as an example. Methods to address these issues are outlined, and a wealth of data on the electronic properties of Fe doped III-V and II-VI compound semiconductors that have been obtained over a few decades is reviewed thoroughly. The review is complemented by new results on the effective-mass-like state consisting of a hole bound to Fe2+ forming a shallow acceptor state. The positions of established Fe3+/2+ and Fe2+/1+ charge transfer levels are summarized and predictions on the positions of further charge transfer levels are made based on the internal reference rule. The Fe3+/4+ level has not been identified unambiguously in any of the studied materials. Detailed term schemes of the observed charge states in tetrahedral and trigonal crystal field symmetry are presented including hyperfine structure, isotope effects and Jahn-Teller effect. Particularly, the radiative transitions Fe3+(4T 1 → 1A1) and Fe2+(5E → 5T2) are analyzed in great detail. An effective-mass-like state [Fe2+, h] consisting of a hole bound to Fe2+ is of great significance for a potential realization of spin-coupling in a DMS. New insights on this shallow acceptor state could be obtained by means of stress dependent and temperature dependent absorption experiments in the mK range. The binding energy and effective Bohr radius were determined for GaN, GaP, InP and GaAs and a weak exchange interaction between the hole and the Fe2+ center was detected. With regard to the Fe 3+ ground state, 6A1, in GaP and InP, the hyperfine structure level Γ8 was found to be above the Γ7 level. All results are discussed with respect to a potential realization of a ferromagnetic spin-coupling in DMSs. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA
Perspective on the Use of Autonomously Flying Taxies in Logistics
No full textAntud lõputöö eesmärk on anda ülevaade õhusõidukitest, mida hakatakse tulevikus kasutama linnasiseseks reisijateveoks ning nende tuleviku perspektiividest. Töös keskendub autor elektrilise toiteallikaga vertikaalse õhkutõusu ja maandumise võimekusega masinatele (eVTOL), mille eesmärk on reisijate vedu linnasiseselt ja mis ideaalis on täisautonoomsed. Uurimismeetoditeks kasutab autor kvalitatiivset uurimismeetodit ja intervjuud alal töötava isikuga. Välja on toodud kolm turuliidrit antud valdkonnast ja nende prototüüpe omavahel võrreldud. Autor tõi välja ka mõned võimalikud kasutuskohad, kus töös uuritavaid õhusõidukeid oleks võimalik rakendada. Läbi viidud intervjuus arutles autor koos intervjueeritavaga õhutaksode tuleviku ja nende turule tulekut pärssivate tegurite alal. Peale intervjuud analüüsis autor selle käigus saadud vastuseid lähemalt ning tõi välja olulisemad eeldused õhusõidukite kasutuselevõtmiseks.The aim of this thesis is to provide an overview of the aircraft that will be used for urban passenger transport in the future as well as their future prospects. The author focuses on electrically powered vertical take-off and landing vehicles (eVTOL), which are designed for inter-city passenger transport and are ideally fully autonomous. The author used qualitative research methods and an interview with a person working in the field. Three market leaders were brought forward and their prototype air taxies compared against each-other. The author also points to some possible use cases for the beforementioned aircraft. In the interview, the author and the interviewee discussed the future of air taxies and the factors currently hindering their entry into the market. After the interview, the answers were analysed and the more important preconditions for air taxi use brought out
Fe-Centers in GaN as Candidates for Spintronics Applications
No full textAbstractThe potential use of Fe doped GaN for spintronics applications requires a complete understanding of the electronic structure of Fe in all of its charge states. To address these issues, a set of 500 µm thick freestanding HVPE grown GaN:Fe crystals with different Fe-concentration levels ranging from 5×1017 to 2×1020 was studied by means of photoluminescence, photoluminescence excitation (PLE) and Fourier transform infrared (FTIR) transmission experiments. The Fe3+/2+ charge transfer (CT) level was determined to be at 2.86 ± 0.01 eV above the valence band maximum considerably lower than the previously reported value of 3.17 ± 0.10 eV. A bound state of the form (Fe2+, hVB) with a binding energy of 50 ± 10 meV has been established as an excited state of Fe3+. FTIR transmission measurements revealed an internal (5E-5T2) transition of Fe2+ around 400 eV which, until now, was believed to be degenerate with the conduction band. Consequently, a second CT band was detected in PLE spectra.</jats:p
Development of ultra-thin tunneling oxides and Si/SiO<sub>2</sub> nanostructures for the application in silicon solar cells
No full textFe-Centers in GaN as Candidates for Spintronics Applications
No full textABSTRACT The potential use of Fe doped GaN for spintronics applications requires a complete understanding of the electronic structure of Fe in all of its charge states. To address these issues, a set of 400 µm thick freestanding HVPE grown GaN:Fe crystals with different Fe-concentration levels ranging from 5×1
Impact of transport connection on Hiiumaa processing industry
No full textHiiumaast peetakse lugu kui heade rekreatiivsete võimalustega saarest, kuid lisaks turismiettevõtetele asuvad seal ka mitmed tööstus ettevõtted, kus tegeletakse peamiselt plasti- ja koostetööde ning puidutööstusega. Lõputöö raames viis autor läbi intervjuud kohalike töötleva tööstuse ettevõtete esindajatega ja valla ekspertidega. Selgitas välja Hiiumaa töötleva tööstuse hetkeolukorra ja kitsaskohad, analüüsis parvlaevaühendust nii saare ja mandri kui ka Hiiumaa ja Saaremaa vahel ning tõi välja uurimistulemuste analüüsid ja ettepanekud. Lõputöös püstitatud uurimisprobleem leidis autori hinnangul lahenduse. Uurimusest selgus, et peamiseks takistuseks Hiiumaa töötleva tööstuse ettevõtetel on oskustööjõu ja nüüdisaegse tehnoloogia kättesaadavus, samuti ka vananev elanikkond ja linnastumine. Tööandjatele on oluline töötajate kättesaadavus, vaba tööjõuressursi olemasolu ja nende kompetentsuse määr. Kõigi ettevõtete esindajatega läbiviidud intervjuudest selgus, et suurimaks konkurentsi pärssivaks teguriks on liiga pikad parvlaevade ooteajad. Hind Heltermaa – Rohuküla liinil ei ole ettevõtete sõnul määrav, kuid aja kulu ja see tõttu ka rahaline kahju on see, mis ettevõtteid mõjutab. Läbiviidud uurimusest selgus, et parvlaevade graafikute kuus põhiväljumist peavad olema nii suvisel kui ka talvisel perioodil samade väljumisaegadega. Samuti peab ühildama bussi- ja parvlaeva graafikud. Parvlaevaühenduse probleemide põhjuseid ja tagajärgi on uuritud ka varasemalt ning uurimuse lõpuks selgus, et suuremalt jaolt parvlaeva liiklusega seotud muudatused on juba sisse viidud. Autor tõi uurimuses välja ka ettevõtete toodete ja teenuste omahinna kallinemise, kuna tööjõupalgad on kasvutrendis ja järjest keerulisem on konkureerida välisturgudega. Saare tööstus toimub keskmise või madala lisandväärtusega tsoonis, kuid selleks, et oma toodetele ja teenustele lisandväärtust juurde anda on vaja tehnoloogiaid ja inimesi. Lisaks selgus uurimusest, et plastitööstuse ettevõtted ei ole kaotanud usku tegeleda Hiiumaal tootmisega ning investeerivad iga aasta uutesse tehnoloogiatesse ja ettevõtte arengusse. Uurimusega seotud kõik osapooled olid seisukohal, et Hiiumaal ei ole keerulisem tegeleda töötleva tööstusega kui mandril. Mõned intervjueeritavad küll tõdesid, et geograafiline paiknemine nõuab mõnevõrra rohkem planeerimist ja arvestamist. Lisaks selgus läbiviidud uurimusest, et veovahendid ei jää väljuvatest parvlaevadest maha tänu piletite eelbroneerimis süsteemile. Piletid broneeritakse aegsasti ning veod planeeritakse pikaajaliselt. Autor leiab, et kindlasti peab tegelema „avaliku teenindamise lepingu alusel teostataval liiniveol sõitja kõrgeim piletihind, sõiduki ja selle haagise piletihinnad ning sõidusoodustused Kuivastu – Virtsu, Rohuküla – Heltermaa ja Sõru – Triigi parvlaevaliinidel” [22] õigusakti muutmisega, et vähendada riski Hiiumaa ettevõtluse jätkusuutlikkusse ja arengusse. See õigusakt vajab autori arvates nüüdisajastamist parvlaeva operaatori teenindustaseme tõstmiseks.Hiiumaa is known as an island with good recreational facilities, however in addition to tourism companies there are several industrial companies that mainly operate within plastics and wood industry and perform assembly work. During the course of the thesis author conducted interviews with representatives of local manufacturing companies and local municipality experts. The author identified the current situation and bottlenecks in the manufacturing industry in Hiiumaa and analyzed the ferry connection between the island and the mainland, as well as between Hiiumaa and Saaremaa, and presented analysis and suggestions based on research results. According to the author, the research problem raised in the thesis found a solution. The study revealed that the main obstacle for companies in the Hiiumaa manufacturing industry is the availability of skilled labor and state-of-the-art technology, as well as the aging population and urbanization. For employers it is important the availability of workforce, of free labor resources and their level of competence. Interviews with all company representatives showed that the most difficult competitive constraints are too long ferry waiting times. According to the companies, the price on the Heltermaa – Rohuküla route is not decisive, but the cost of the time and therefore the financial loss is what affects them. The survey revealed that the six main scheduled ferry departures must be the same for both summer and winter. It is also necessary to combine bus and ferry schedules. The causes and consequences of ferry connection problems have also been investigated earlier - at the end of that study it became clear that most of the changes related to ferry traffic have already been introduced. The author also pointed out the increase in the net cost of companies' products and services as labor wages are growing and it is increasingly difficult to compete with foreign markets. The island's industry takes place in a medium or low value-added zone, but technologies and people are needed to add value to their products and services. In addition, the study revealed that companies in the plastic industry have not lost faith to have their production in Hiiumaa and invest every year in new technologies and business development. All parties involved in the study concluded that it is not harder to deal with manufacturing in Hiiumaa than on the mainland. Some interviewees admitted however, that geographic location requires a little bit more planning and consideration. A study revealed that lorries were not left behind by outgoing ferries due to the ticket pre-booking system. Tickets are booked early and transport has been planned for long-term. The author believes that the following piece of legislation must be amended: ’’the highest fare for a passenger on a regular service under a public service contract, fare and discounts for the vehicle and its trailer on Kuivastu – Virtsu, Rohuküla – Heltermaa and Sõru – Triigi ferry lines’’. This would reduce the risk to Hiiumaa's business sustainability and development. According to the author, this legislation needs to be modernized in order to increase the service level of the ferry operator
Improving the service quality of a sports club on the example of Golden Club Rotermann
No full textLõputöö põhieesmärk oli teenuse kvaliteedi parendamine. Eesmärkide saavutamiseks viidi läbi kvalitatiivne uuring. Tulemuste saamiseks viis autor läbi küsitlus ettevõtte teenust kasutatavate klientide hulgas. Kuna ettevõttes toimub samuti kaupade müük siis vaatas töö autor ka üle selle tarneahela ja otsis sinna parendamisvõimalusi. Töö teoreetilises osas andis autor ülevaate teenuse olemusele ja selle kvaliteediga seonduvale, kuidas kavandada teenust ja millised on trendid tänapäeval teenuseettevõtetel. Lõputöös käsitletakse ka varude teemal, seega on teemadena ka varude juhtimine ning kõik sellega seonduv. Veel kirjeldatakse töös ettevõtet, mille alusel töö tehakse ja tuuakse välja üldised võtmetegurid spordiklubi pidamisel. Töö viimases peatükis analüüsiti läbi küsitluse vastused ja toodi välja parendus ettepanekud, kuidas saaks antud teenust paremaks ja kvaliteetsemaks muuta. Lõputöö tulemusena pakkus autor välja mitu erinevat lahendust ettevõtte teenuse parendamiseks kui ka lahendusi paremaks varude juhtimiseks. Lõputöö küsitluse tulemusena selgusid peamised võtmesõnad, mis klientidel ettevõttele mõeldes pähe tulevad. Kuidas hinnatakse üldiselt teenusekvaliteeti ning mis tasemega on klienditeenindajad. Kuna klienditeenindaja on väga tähtis roll ettevõtte esindamisel siis väga oluline on ettevõtte jaoks, et klienditeenindajad oleksid väga heal tasemel ja klienditeenindjaid oleksid motiveeritud. Küsitluses said hinnata kliendid ka teenuse kõiki protsesse, kui nad teenust kasutavad. Kõige rohkem oli rahulolematust treeningute valiku ja muusika valiku osas. Autor teeb ettepaneku, et mõlemat teemat lähemalt uurida, teha klientide seas küsitlus ja seejärel viia sisse muudatused ning hiljem teha uus uuring, mille pealt vaadata, kas need muudatused on õigustanud ennast või mitte. Samuti käsitleti lõputöös ettevõtte varude haldamist ja nende juhtimist. Kuna praegusel hetkel ei jälgi ettevõtte kõikide toodetega täpselt, mis toodet kui palju müüakse, siis autor soovitab kasutada täpsemaid tootenimetusi kaupade müümisel. Lisaks on autor välja toonud, et ettevõtte hakkaks alles jätma varasemaid toodete ülelugemise tabeleid, et neid võrrelda omavahel varasemaga ning nende põhjal teha paremaid müügiennustusi.The main goal of the thesis was to improve the quality of the service. A qualitative study was conducted to achieve the objectives. In order to obtain the results, the author conducted a survey among the customers using the company's service. As the company also sells goods, the author also reviewed this supply chain and looked for opportunities for improvement. In the theoretical part of the work, the author gave an overview of the nature of the service and its quality, how to design the service and what are the trends of service companies today. The thesis also deals with the topic of inventories, so the topics are also inventory management and related. The work describes the company on the basis of which the work is performed and the general key factors in running a sports club are outlined. In the last chapter of the work, the answers to the survey were analyzed and suggestions for improvement were made, how the given service could be improved. As a result of the work, the author proposed several different solutions to improve the company's service as well as solutions for better inventory management. As a result of the survey, the main keywords that come to mind when thinking of the company became clear. How service quality is assessed in general and at what level are customer service representatives. As the customer service representative plays a very important role in representing the company, it is very important for the company that the customer service representatives are at a very good level and that the customer service representatives are motivated. In the survey, customers were also able to evaluate all the processes of the service when they use the service. There was the greatest dissatisfaction with the choice of training and the choice of music. The author proposes to study both topics in more detail, to conduct a survey among customers and then to make changes, and later to conduct a new study to see if these changes have justified themselves or not. The thesis also dealt with the management of the company's inventories and their management. As the company does not currently track exactly which product is sold, the author recommends using more specific product names when selling goods. In addition, the author has pointed out that the company would keep the previous product recount tables in order to compare them with the previous one and make better sales predictions based on them
How to make the carbon offsets mechanism work in the current phase of the EU ETS?: A model-based analysis
No full textMassively reducing Greenhouse Gas (GHG) emissions is one of the biggest challenges of the 21th century. An important deployment of Renewable Energies (RE) can be a key element in attaining this objective. Setting a (high) carbon price would greatly help as it would send a powerful signal to RE investors that it is time to switch from high-emitting firms to free-emitting ones.Carbon pricing is implemented through the setting of either a carbon tax or an Emissions Trading Scheme (ETS). The European Union (EU) implemented its own ETS, the EU ETS, in 2005. Since then however, it faced low permit prices (partly due to an oversupply of both carbon permits and carbon offset credits), which raises a crucial question: how could the EU ETS and its carbon offsets market be improved to generate higher permit prices, thus promoting RE investment?Two policy measures seem relevant today: implementing a floor price for permits (not examined in this work) and/or modifying the rules of the carbon offset credits market of the EU ETS. This master thesis will focus on offsets policy instruments the EU ETS could implement, drawn from a paper published by Bento et al. (2015), that aim at better designing its carbon offsets market and resulting in a higher permit price. The policy instruments analyzed are: stricter baselines, trade ratios and limits. This work will then discuss the efficiency (in regard to society welfare optimization) of these measures.Electrical Engineering | Sustainable Energy Technolog
Supply Chain Implications Prognosis of the Russia-Ukraine War
No full textLõputöö on koostatud teemal Venemaa-Ukraina sõja mõjuprognoos logistikasektorile. Antud teema puhul on tähtis välja tuua, et lõputöös käsitletud teemad ja allikad on piiritletud kindla aja jooksul alates Venemaa sissetungi algusest Ukrainasse 24. veebruaril kuni 2022. aasta aprillikuu keskpaigani. Autor on lõputöös kasutanud kahest suuremast osast koosnenud uuringut, esiteks on kogutud teiseseid andmeid erinevatest probleemi käsitlevatest allikatest ning teiseks on rakendatud kvalitatiivset uuringut. Töös on kasutatud ka teiste autorite koostatud empiirilisi uuringuid. Kvalitatiivse uuringu käigus on autor läbi viinud intervjuud valitud Eesti logistikaettevõtete esindajatega, selleks, et kaasata lõputöösse lisaks avalikele allikatele ka otsest hinnangut sõjategevusest tingitud sanktsioonide mõjust siinsetele ettevõtetele. Lõputöö on jaotatud viieks suuremaks osaks kus esiteks tõi autor välja globaalsel tasandil esimesed mõjud ja sündmused, mis sõja esimesel perioodil on toimunud, teises peatükis on autor täpsemalt uurinud Ukraina infrastruktuuri ja sadamate töö väljakutseid, kolmandas peatükis viis autor läbi intervjuud Eesti logistikaettevõtete esindajatega, neljandas peatükis on käsitletud tarneahelate riskijuhtimist kriisolukorras ja viies peatükk sisaldab läbivaid järeldusi ja kokkuvõtet.The thesis is on the topic of supply chain implications prognosis of the Russia-Ukraine war. On this topic, it is important to point out that the implications and sources covered in the thesis have been defined for a certain period of time from the beginning of the Russian invasion of Ukraine on February 24 to mid-April 2022. The author has used a study consisting of two major parts in the thesis, firstly, secondary data have been collected from various sources concerning the problem, and secondly, a qualitative study has been applied. Empirical studies by other authors have also been used in this tehsis. In the course of a qualitative study, the author has conducted interviews with representatives of selected Estonian logistics companies in order to include in the thesis, in addition to public sources, a direct assessment of the impact of military sanctions on local companies. The dissertation is divided into five major sections: first, the author outlined the first global influences and events that took place during the first period of the war, the second chapter explored the challenges of Ukrainian infrastructure and port operations, the third chapter consists interviews with Estonian logistics companies, fourth chapter deals with supply chain risk management in crisis situations and fifth, also the last chapter provides cross - sectional conclusions and summaries
Truck drivers’ occupational training on the example of Estonian educators
No full textTranspordi-, logistika- ja tööstusettevõtete üheks jätkusuutlikkuse võtmeelemendiks on transpordi protsessi efektiivsus. Transpordi protsessi efektiivsuse määravad autojuhi teadmised ja oskused tulla toime tööülesannetega. Nende omandamiseks ja parendamiseks tuleb autojuhil läbida pädev ameti- või täiendkoolitus. Lõputöö eesmärgiks on uurida olemasolevat veoautojuhtide ametikoolitussüsteemi Eesti koolitajate näitel ja teha võimalike ettepanekuid olemasoleva süsteemi parendamiseks. Töö käigus käsitleti probleeme, mis tulenevad veoautojuhtide koolitamisest ja mis võivad mõjutada ametikoolituse kvaliteedi taset. Käesolevas lõputöös püstitatud probleem seisneb selles, et tänased veoautojuhi ametikoolituse koolitajad ei täida oma eesmärki koolitada pädevaid autojuhte. Veoautojuhi ametikoolituse protsess lähtub Euroopa Parlamendi ja Nõukogu direktiivist 2003/59/EÜ ja Eesti seadusandlusest. Ametikoolitus koosneb kahest etapis, millest autor keskendus oma töös perioodilistele täiendkoolitustele, tuginedes teoreetilisele taustale ning kasutades kvantitatiivsete ja kvalitatiivsete uurimismeetodite abil kogutud andmeid. Teoreetilise töö osas anti ülevaade Eesti ja Soome Vabariigi veoautojuhi ametikoolituse valdkonnast, käsitleti küsitluse, vaatluse ja intervjuude metoodikat. Tuginedes ekspert hinnangule on lõputöö empiirilises osas läbiviidud Eesti veoautojuhtide seas eriala teadmisi uuriv küsitlus, tutvuti läbi osalusvaatluse Eesti ametikoolitusasutustega ning uuriti läbi intervjuude koolituste lektorite seisukohti. Saadud tulemuste põhjal pakuti välja ettepanekud kolmele erinevale tasandile. Autor on arvamusel, et pakutavad ettepanekud on lähiaastatel teostatavad ning toovad tulevikus kasu nii koolitusasutustele, transpordi-, logistika- ja tööstusettevõtetele ning autojuhtidele läbi pädevate õppejõudude ja efektiivsete õppeprotsesside. Autor pakub välja, et antud ettepanekuid uurida edasi tulevastel diplomandidel.A key element of sustainability in transport, logistics and industrial companies is the efficiency of the transportation process. The efficiency of the transportation process is affected by drivers’ knowledge and skills in coping with the tasks. To acquire and improve them, drivers should attend competent occupational trainings or refresher trainings. Occupational training is required from truck drivers who want to work for salary in the transport sector in the Estonian Republic and abroad. The truck driver’s occupation requires diverse skills and knowledge of the law. The aim of occupational training is to provide truck drivers with competent knowledge to perform their tasks. This final thesis aimed to study the existing occupational training system for truck drivers on the example of educators in Estonia, and make possible suggestions to improve it. The author studied the problems concerning truck drivers’ training, which may affect the level of quality of occupational training. The problem set in the thesis lies in the fact that today educators in occupational training do not fulfil their objective in training proficient drivers. The process of truck drivers’ occupational training is based on the European Parliament and Council Directive 2003/59 / EC and the Estonian legislation. The training consists of two phases, but the author of the thesis focused on periodic refresher trainings, on the basis of the theoretical background and the data collected, when using quantitative and qualitative research methods. The theoretical part of the thesis provided an overview of occupational training of truck drivers in Estonia and Finland, and the methods of survey, observation and interviews were described. Based on an expert assessment, in the empirical part of the thesis, the author carried out a survey among Estonian truck drivers to examine their occupation-based knowledge; through a participatory observation, 45 studied Estonian occupational training institutions; and through interviews investigated lecturers who organise trainings. Based on the results, suggestions were made for three different levels. The author is of the opinion that these suggestions are feasible in the coming years and will bring benefits to training institutions, transport, logistics and industrial businesses, as well as drivers, through competent educators and effective learning processes. The author believes future thesis defenders should further examine the suggestions made
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