Persistent Data Structures for Incremental Join Indices

Join indices are used in relational databases to make join operations faster. Join indices essentially materialise the results of join operations and so accrue maintenance cost, which makes them more suitable for use cases where modifications are rare and joins are performed frequently. To make the maintenance cost lower incrementally updating existing indices is to be preferred. The usage of persistent data structures for the join indices were explored. Motivation for this research was the ability of persistent data structures to construct multiple partially different versions of the same data structure memory efficiently. This is useful, because there can exist different versions of join indices simultaneously due to usage of multi-version concurrency control (MVCC) in a database. The techniques used in Relaxed Radix Balanced Trees (RRB-Trees) persistent data structure were found promising, but none of the popular implementations were found directly suitable for the use case. This exploration was done from the context of a particular proprietary embedded in-memory columnar multidimensional database called FastormDB developed by RELEX Solutions. This focused the research into Java Virtual Machine (JVM) based data structures as the implementation of FastormDB is in Java. Multiple persistent data-structures made for the thesis and ones from Scala, Clojure and Paguro were evaluated with Java Microbenchmark Harness (JMH) and Java Object Layout (JOL) based benchmarks and their results analysed via visualisations

PAPR Constrained Power Allocation for Iterative Frequency Domain Multiuser SIMO Detector

Peak to average power ratio (PAPR) constrained power allocation in single carrier multiuser (MU) single-input multiple-output (SIMO) systems with iterative frequency domain (FD) soft cancelation (SC) minimum mean squared error (MMSE) equalization is considered in this paper. To obtain full benefit of the iterative receiver, its convergence properties need to be taken into account also at the transmitter side. In this paper, we extend the existing results on the area of convergence constrained power allocation (CCPA) to consider the instantaneous PAPR at the transmit antenna of each user. In other words, we will introduce a constraint that PAPR cannot exceed a predetermined threshold. By adding the aforementioned constraint into the CCPA optimization framework, the power efficiency of a power amplifier (PA) can be significantly enhanced by enabling it to operate on its linear operation range. Hence, PAPR constraint is especially beneficial for power limited cell-edge users. In this paper, we will derive the instantaneous PAPR constraint as a function of transmit power allocation. Furthermore, successive convex approximation is derived for the PAPR constrained problem. Numerical results show that the proposed method can achieve the objectives described above.Comment: Presented in IEEE International Conference on Communications (ICC) 201

Implementation strategies in software development - Case XBRL

The main objective of this study is to identify and describe the ways in which companies approach implementing inter-organizational software functionalities into their software products and services and to identify the factors that affect their choice of a software implementation strategy. The study is a descriptive multiple case study that focuses on four companies that are all doing a similar XBRL functionality implementation at the same time. The theoretical framework of the study consists of multiple factors, out of which network effect and path dependence are the most prominent theories that are used to guide the case study design. The reviewed literature categorizes software implementation strategies according to how deeply the new functionality is integrated into existing systems, categorizing software implementations into bolt-on, built-in, and deeply embedded implementation strategies. The findings from the case study indicate support for this kind of categorization in the observed cases, although the categories should be considered to be more of a continuum than set of discrete classes. The results of the case study also indicate that, in the cases that were observed, network effects and path dependence play a role in the software implementation strategy selection but a significant factor in the implementation strategy decisions is also the uncertainty of the future adoption, development, and use of the technology in question. In an inter-organizational context, companies weigh in the perceived benefits of a software implementation against their confidence in the future use of that technology, forming an estimate of the expected value of the future benefit of the software implementation. This expected value will then in turn factor into the software implementation strategy decision and partly contribute to how deeply the company is willing to integrate the functionality into their existing systems

Plaanolattiat

Rakennustyömaitten kireää aikataulua voidaan hallita eri toteutustavoilla. Työn aiheena oli plaanolattiat, joissa otettiin huomioon eri työvaiheet. Tarkoituksena oli poistaa ongelmakohdat ja lisätyöt, joita yleensä tulee eri työvaiheiden aikana. Lisätyöt pidentävät merkittävästi aikatauluja ja tuovat lisäkustannuksia joihin ei ole varauduttu. Plaanolattian tekemisessä on monta työvaihetta, ennen kuin päästään mattoasennukseen ja valmiiseen pintaan. Työssä perehdyin lattiatyön työmaa menetelmiin, työmaatekniikkaan ja aikataulutukseen. Aikataulutus ja se, että aikaa varataan eri työvaiheille riittävästi, on erittäin tärkeää. Työn toteutukseen ja seuraavaan työ vaiheeseen on myös tärkeää perehtyä. Työn tekijöille pidetään aloitus palavereja ja kerrotaan työn tärkeys. Valvotaan tehty työ vaihe vaiheelta. On tärkeää kysyä seuraavan vaiheen työn tekijältä, millaiset aloitusedellytykset pitää olla, että päästään itse työhön. Näin ei tarvitse aloittaa työtä korjaamalla toisten virheitä. Kaikella huolellisella työn toteutuksella ja suunnittelulla saavutettiin annetut tavoitteet. Pieneltäkin asialta tuntuvat työmenetelmät on otettava ajatuksella ja pohdittava seuraamuksia. Jokaisen työvaiheen loppuun saattaminen ja viimeistely luovat onnistuneen lopputuloksen.Tight schedules at construction sites can be maintained with different methods. The subject of this thesis is Plaano-floors with consideration of different work phases. The purpose was to remove problems and additional work which usually appear during different work phases. Additional works delay schedules significantly and bring unexpected extra costs. The construction of Plaano-floors involves many work phases before reaching mat installation and finished surface. In this thesis I looked into work site methods, technique and scheduling. Scheduling and reserving enough time for different work stages is very important. The excecution of the actual work and the next work phase must be considered. Start-up meetings are held for the workers and the importance of the work is discussed. The work must be monitored, phase by phase. It is important to ask the workers of the next stage, what pre-conditions must be in place to start the actual work. This way, the work does not need to start with correcting someone else´s mistakes. All objectives were reached with careful planning and execution of the work. Even small technical aspects and their consequenses must be considered. Proper finishing of every work phase creates a successful result

Pohjatyö positronimikroskooppia varten

Positron annihilation spectroscopy is an efficient method for studying defects, especially vacancies. The resolution of positron microscopy is restricted by the diffusion length of positrons (typically 0.1-0.2 micrometres). In practice, spatial resolutions up to 1 micrometre have been reached. A positron microscope can be used for studying defects in e.g. cracks in metal and optoelectronic components. In this thesis, three existing positron microscopes are reviewed. They all possess a spatial resolution below 5 micrometres with an acceptable count rate. The Munich positron microscope is a pulsed positron beam and is able to measure positron lifetime. It has one remoderation stage for reducing the beam spot size and the spatial resolution of it is 2 micrometres. The positron microscopes in Bonn and Takasaki measure Doppler broadening of annihilation radiation of positrons with resolutions of 1 micrometre and 3.9 micrometres, respectively. They both utilise optical columns of commercial SEMs for focusing the positron beam. The Munich and Bonn positron microscopes can also be used as scanning electron microscopes. Based on the comparison of the existing positron microscopes, the structure of a new positron microscope for the needs of the Aalto positron group is proposed. The structure is based on the Bonn positron microscope with some modifications, such as an additional objective lens below the sample. Some of the modifications require verification of their feasibility. A commercial SEM (ZEISS/Opton, DSM 950), which will be utilised as the optical column of the positron microscope, was initialised and tested. A roadmap for the design and construction of the new positron microscope is outlined.Positroniannihilaatiospektroskopia on herkkä ja tehokas menetelmä hilavirheiden, etenkin vakanssien, tutkimiseen. Positronien diffuusiopituus (tyypillisesti 0.1-0.2 micrometriä) asettaa rajan positronimikroskooppien resoluutiolle. Olemassa olevilla positronimikroskoopeilla on päästy 1 mikrometrin resoluutioon. Positronimikroskooppi soveltuu hilavirheiden tutkimiseen esimerkiksi metallien murtumissa ja optoelektroniikan komponenteissa. Tässä työssä käydään läpi kolmen olemassa olevan positronimikroskoopin rakenne ja toiminta. Kaikkien positronimikroskooppien resoluutio on parempi kuin \SI{5}{\micro \meter} pulssitaajuuden vielä ollessa käyttökelpoinen. Munchenin positronimikroskooppi on pulssitoiminen ja siten pystyy mittaamaan positronien elinaikaa. Se sisältää yhden remoderointi-vaiheen positronisuihkun koon pienentämiseksi ja sen resoluutio on 2 mikrometriä. Bonnin ja Takasakin positronimikroskoopit mittaavat molemmat annihilaatiosäteilyn Doppler-levenemää resoluutioilla 1 (Bonn) ja 3.9 (Takasaki) mikrometriä. Ne käyttävät kaupallisen pyyhkäisyelektronimikroskoopin optista kolumnia positronisuihkun fokusointiin näytteeseen. Munchenin ja Bonnin mikroskoopit pystyvät toimimaan myös pyyhkäisyelektronimikroskooppeina. Olemassa olevien positronimikroskooppien ominaisuuksien ja suorituskykyjen vertailun pohjalta valittiin rakenne ja ominaisuudet Aalto-yliopiston positroniryhmän uutta positronimikroskooppia varten. Lähtökohdaksi valittiin Bonnin positronimikroskooppi, jonka rakenteeseen ehdotettiin muutamia muutoksia, kuten erillisen magneettilinssin lisäämisestä näytteen alle. Ehdotetuista muutoksista osan käyttökelpoisuus vaatii jatkoselvitystä. Työn aikana kaupallinen elektronimikroskooppi (ZEISS/Opton, DSM 950), jota on tarkoitus käyttää positronimikroskoopin optiseksi kolumnina, valmisteltiin käyttökuntoon ja testattiin. Positronimikroskoopin toteuttamiselle hahmoteltiin etenemissuunitelma

Split Ga vacancies : Abundant defects in β-Ga2O3

We have applied positron annihilation spectroscopy to study a wide range of β-Ga2O3bulk crystals and thin films with various doping levels. The Doppler broadening of the 511 keV positron-electron annihilation line exhibits colossal anisotropy compared to other three-dimensional crystalline semiconductors. State-of-the-art theoretical calculations of the positron characteristics in the β-Ga2O3lattice reveal that the positron state is effectively 1-dimensional, giving rise to strong anisotropy. Strongly relaxed split Ga vacancies are found to exhibit even stronger anisotropy and to dominate the positron annihilation signals in almost all experiments. The evidence leads to the conclusion that split Ga vacancies are abundant, with concentration of 1018 cm-3 or more, in β-Ga2O3samples irrespective of conductivity.Peer reviewe