Energy aware software for many-core systems

Many-core systems provide a great potential in application performance with the massively parallel structure. Such systems are currently being integrated into most parts of daily life from high-end server farms to desktop systems, laptops and mobile devices. Yet, these systems are facing increasing challenges such as high temperature causing physical damage, high electrical bills both for servers and individual users, unpleasant noise levels due to active cooling and unrealistic battery drainage in mobile devices; factors caused directly by poor energy efficiency. Power management has traditionally been an area of research providing hardware solutions or runtime power management in the operating system in form of frequency governors. Energy awareness in application software is currently non-existent. This means that applications are not involved in the power management decisions, nor does any interface between the applications and the runtime system to provide such facilities exist. Power management in the operating system is therefore performed purely based on indirect implications of software execution, usually referred to as the workload. It often results in over-allocation of resources, hence power waste. This thesis discusses power management strategies in many-core systems in the form of increasing application software awareness of energy efficiency. The presented approach allows meta-data descriptions in the applications and is manifested in two design recommendations: 1) Energy-aware mapping 2) Energy-aware execution which allow the applications to directly influence the power management decisions. The recommendations eliminate over-allocation of resources and increase the energy efficiency of the computing system. Both recommendations are fully supported in a provided interface in combination with a novel power management runtime system called Bricktop. The work presented in this thesis allows both new- and legacy software to execute with the most energy efficient mapping on a many-core CPU and with the most energy efficient performance level. A set of case study examples demonstrate realworld energy savings in a wide range of applications without performance degradation.

Production of magnesium carbonates from serpentinites for CO2 mineral sequestration : optimisation towards industrial application

Global warming is one of the most alarming problems of this century. Initial scepticism concerning its validity is currently dwarfed by the intensification of extreme weather events whilst the gradual arising level of anthropogenic CO2 is pointed out as its main driver. Most of the greenhouse gas (GHG) emissions come from large point sources (heat and power production and industrial processes) and the continued use of fossil fuels requires quick and effective measures to meet the world’s energy demand whilst (at least) stabilizing CO2 atmospheric levels. The framework known as Carbon Capture and Storage (CCS) – or Carbon Capture Utilization and Storage (CCUS) – comprises a portfolio of technologies applicable to large‐scale GHG sources for preventing CO2 from entering the atmosphere. Amongst them, CO2 capture and mineralisation (CCM) presents the highest potential for CO2 sequestration as the predicted carbon storage capacity (as mineral carbonates) far exceeds the estimated levels of the worldwide identified fossil fuel reserves. The work presented in this thesis aims at taking a step forward to the deployment of an energy/cost effective process for simultaneous capture and storage of CO2 in the form of thermodynamically stable and environmentally friendly solid carbonates. R&D work on the process considered here began in 2007 at Åbo Akademi University in Finland. It involves the processing of magnesium silicate minerals with recyclable ammonium salts for extraction of magnesium at ambient pressure and 400‐440⁰C, followed by aqueous precipitation of magnesium in the form of hydroxide, Mg(OH)2, and finally Mg(OH)2 carbonation in a pressurised fluidized bed reactor at ~510⁰C and ~20 bar PCO2 to produce high purity MgCO3. Rock material taken from the Hitura nickel mine, Finland, and serpentinite collected from Bragança, Portugal, were tested for magnesium extraction with both ammonium sulphate and bisulphate (AS and ABS) for determination of optimal operation parameters, primarily: reaction time, reactor type and presence of moisture. Typical efficiencies range from 50 to 80% of magnesium extraction at 350‐450⁰C. In general ABS performs better than AS showing comparable efficiencies at lower temperature and reaction times. The best experimental results so far obtained include 80% magnesium extraction with ABS at 450⁰C in a laboratory scale rotary kiln and 70% Mg(OH)2 carbonation in the PFB at 500⁰C, 20 bar CO2 pressure for 15 minutes. The extraction reaction with ammonium salts is not at all selective towards magnesium. Other elements like iron, nickel, chromium, copper, etc., are also co‐extracted. Their separation, recovery and valorisation are addressed as well and found to be of great importance. The assessment of the exergetic performance of the process was carried out using Aspen Plus® software and pinch analysis technology. The choice of fluxing agent and its recovery method have a decisive sway in the performance of the process: AS is recovered by crystallisation and in general the whole process requires more exergy (2.48–5.09 GJ/tCO2sequestered) than ABS (2.48–4.47 GJ/tCO2sequestered) when ABS is recovered by thermal decomposition. However, the corrosive nature of molten ABS and operational problems inherent to thermal regeneration of ABS prohibit this route. Regeneration of ABS through addition of H2SO4 to AS (followed by crystallisation) results in an overall negative exergy balance (mainly at the expense of low grade heat) but will flood the system with sulphates. Although the ÅA route is still energy intensive, its performance is comparable to conventional CO2 capture methods using alkanolamine solvents. An energy‐neutral process is dependent on the availability and quality of nearby waste heat and economic viability might be achieved with: magnesium extraction and carbonation levels ≥ 90%, the processing of CO2‐containing flue gases (eliminating the expensive capture step) and production of marketable products.

Offline-tila web-sovelluksissa

Selainpohjaiset sovellukset ovat yleistyneet viimeisen kymmenen vuoden aikana. Samanaikaisesti ympäristö, jossa ihmiset käyttävät sovelluksia, on muuttunut. Nykyään sovelluksia käytetään yhä enenevissä määrin myös mobiililaitteilla, joissa verkkoyhteyden luotettavuus on huomattavasti heikompi kuin työpöytäympäristössä. Verkkoyhteyden toiminta on ehdoton edellytys web- sovelluksen toiminnalle. Kun verkkoyhteyttä ei ole, sovellusta ei useimmiten voi käyttää. Tilanne on käyttäjän kannalta sama myös, jos verkkoyhteyden laatu on hyvin heikko. Tämä uusi käyttöympäristö asettaa web-sovelluksen saavutettavuudelle haasteen, johon sovelluskehittäjien tulisi pystyä vastaamaan uusien teknologioiden avulla ja mahdollisesti sovelluksen arkkitehtuuria muuttamalla. Johdantona aiheeseen kerrotaan mitä hyötyjä offline-tilan tukemisesta on. Selainpohjaiset sovellukset kilpailevat jossain määrin mobiilialustojen natiivisovellusten kanssa. Web-sovelluksia on verrattu natiivisovelluksiin niiltä osin miten ne toimivat offline-tilassa. Pohjustuksena offline-tilan mahdollistavien teknologioiden arvioinnille esitellään Web-sovelluksen arkkitehtuuri yleisellä tasolla. Tässä tutkielmassa on esitelty muutamia offline-tilan asettamia vaatimuksia sovellukselle. Sovelluksen on kyettävä tunnistamaan, onko laitteella internet-yhteyttä. Yhteyden tilan tarkastukseen esitellään muutama vaihtoehto. Käyttäjän luoma tieto on myös tallennettava paikallisesti. Kun käyttäjä luo uutta sisältöä, se pitää tallentaa väliaikaisesti tai pysyvästi selaimeen. Ainakin osa sovelluksessa käsiteltävästä tiedosta pitäisi olla koko ajan saatavilla, käyttäjän internet-yhteyden tilasta riippumatta. Tähän tarkoitukseen selaimissa on nykyään käytettävissä muutamia erityyppisiä tietovarastoja. Kun selain on online-tilassa, sovelluksen tarvitsemat resurssit on tallennettava offline-tilaa varten. Tähän tarkoitukseen on luotu kaksi eri teknologiaa, HTML5 Application cache ja Service worker. Niiden avulla voi toteuttaa selaimen sisäisen välipalvelimen, joka vastaa sovelluksen tekemiin verkkopyyntöihin. Tutkielmassa esitellään näiden teknologioiden toimintaa teknisten määrittelydokumenttien ja verkkoartikkelien pohjalta. Mainittuja teknologoita vertaillaan keskenään toiminnallisten vaatimusten pohjalta. Tutkimuksen perusteella voidaan päätellä, että esitellyillä teknologioilla voidaan toteuttaa offline-tuki web-sovellukseen. Service worker osoittautuu paremmaksi vaihtoehdoksi kuin Application cache toiminnallisuudeltaan.