Maataloustuotteiden pitkän aikavälin tarjontafunktiot

vokKirjasto Aj-

Investigation of abrasion resistance of concrete paving blocks and their suitability for trafficked areas

According to maintenance Engineers of City of Vantaa and Helsinki there has been problems in durability of concrete block pavements in recent years. Concrete block pavers (CBP) have deteriorated fast by wearing down just in 2 to 3 years. These observations have led to believe that the material quality of CBP's have declined during the last twenty years. In the 1980's the use of CBP's was justified by studies, which indicated that concrete block pavers have longer life and better abrasion resistance than asphalt concrete. Objectives of the thesis were to determine what factors affect on abrasion resistance of CBP's and what types of damages occur in concrete block pavements. Research was conducted having in-situ inventory study of damaged pavements and testing abrasion resistance of CBP's in laboratory. Abrasion resistance standard criteria were assessed based on the laboratory tests. In addition, a test area was constructed in Vantaa where construction practices and quality of delivered materials were studied in more detail. Based on the literature survey abrasion resistance of CBP's are particularly affected by cement content, strength of cement, water-cement ratio, granularity, hardness of aggregate and curing time. Standard determines that the abrasion resistance of CBP should be tested with the wide-wheel abrasion test or the Böhme-test. Neither of the tests is applicable to determine the studded tire abrasion resistance. In addition, the weather resistance test, which is used for testing chemical and freeze-thaw resistance, is for the Central European conditions and does not address conditions in Finland. Based on visual inspections of the trafficked areas, the biggest problem with concrete block pavements was peeling of the surface of the CBP. CBP's used in test area decayed only after six months from construction, which is less than is thought. According to manufacturers and maintenance engineers the main cause for this wear was studded tire abrasion aggravated by the maintenance salt and freeze-thaw cycles during winter time. Laboratory tests were carried out by the Böhme apparatus and a Prall apparatus, which is a standard device for testing asphalt concrete's abrasion against studded tires. Most of the CBP samples did poorly on the Prall test and there were large differences among the abrasion values. Only two CBP types passed the lowest abrasion resistance criteria set for asphalt concrete. In Böhme-test, the only CBP type suitable for trafficked areas didn't pass criteria set in the EU-standard. In addtition to CBP's, polymer concrete blocks (PC) were tested. In PC blocks polymer resin serves as a binder instead of cement paste. PC blocks did very well on both tests; the abrasion values of PC blocks were half of the values of the best CBP's. Based on the tests carried out for this work, Prall apparatus is suitable for testing CBP's, but further tests are needed.Betonikiveysten kestävyys ajoneuvoliikenteen alueilla on ollut ongelma viime vuosina. Betonikivet ovat monissa kohteissa kuluneet huonoon kuntoon 2-3 vuodessa. Vantaan kaupungin kokemusten mukaan betonikivien laatu on heikentynyt viimeisten kahdenkymmenen viime vuoden aikana. Vielä 1980-luvulla tutkimusten mukaan betonikivien kulutuskestävyys oli asfalttia parempi ja elinkaari päällystemateriaalina pidempi. Tämän työn tavoitteena oli selvittää, miksi betonikivet eivät kestä ajoneuvoliikenteen alueilla. Työ toteutettiin kirjallisuustutkimuksena ja tekemällä vaurio-inventointi Vantaan ja Helsingin kaupunkien betonikivikohteissa. Laboratoriokokeissa testattiin betonikivien kulutuskestävyyttä ja Prall-kokeen soveltuvuutta betonikivien testaamiseen. Lisäksi työtä varten rakennettiin Vantaalle koekohde, jonka avulla oli tarkoituksena selvittää, kuinka nopeasti betonikivi vaurioituu rakenteessa ollessaan ja seurata betonikiveyksen rakentamisen eri vaiheita. Kirjallisuustutkimuksen perusteella betonikiven kulutuskestävyyteen vaikuttavat erityisesti sementtipitoisuus, sementin lujuus, vesi-sementtisuhde, kiviaineksen kovuus ja rakeisuus sekä jälkihoito. EU-standardin mukaan betonikivien kulutuskestävyys testataan pyöräkulutustestillä tai Böhme-testillä. Testit on tarkoitettu liikenneympäristöön, jossa ei ole nastarengaskulutusta. Lisäksi EU-standardin mukainen säänkestävyystesti, jolla testataan betonikivien kemiallista kestävyyttä ja jäätymis-sulamiskestävyyttä on tarkoitettu Keski-Euroopan oloihin eikä vastaa Suomen oloja. Inventointien perusteella havaittiin, että tyypillinen ja vakavin ongelma oli betonikiven pinnan kuoriutuminen, jopa 2 cm syvyyteen kiven paksuudesta. Työtä varten rakennetun koekohteen betonikivien pinta oli alkanut rapautua jo noin puolen vuoden kuluttua rakentamisesta, mikä on huomattavasti nopeammin kuin on aikaisemmin luultu. Valmistajien ja kunnossapitäjien mukaan suurimpia syitä betonikivien kulumiselle ovat ajoneuvoliikenne, erityisesti nastarengasliikenne, tiesuola sekä veden jäätymis-sulamissyklit. Laboratoriokokeita tehtiin Böhme-testillä. Toiseksi koemenetelmäksi valittiin Prall-koe, joka on standardinmukainen testi asfaltin nastarengaskulutuskestävyyteen. Suurin osa betonikivistä menestyi Prall-kokeessa heikosti ja betonikivien kulutuskestävyydessä oli suuria eroja. Ainoastaan kaksi betonikivityyppiä läpäisi alimman asfaltille asetetun kulumisluokan vaatimukset. Böhme-kokeessa vain yksi ajoneuvoliikenteen alueille tarkoitettu betonikivityyppi ei läpäissyt EU-standardissa asetettuja vaatimuksia. Betonikivien lisäksi testattiin myös uutta polymeerikiveä, jossa sideaineena on sementin sijaan käytetty polymeerihartsia. Polymeerikivet menestyivät molemmissa kokeissa erittäin hyvin, kuluma-arvo oli noin puolet parhaiden betonikivien kuluma-arvosta. Kokeiden perusteella Prall-koe soveltuu betonikivien testaamiseen, mutta tämän varmistamiseksi tarvitaan vielä lisäkokeita

Direct enhancement of nuclear singlet order by dynamic nuclear polarization

Hyperpolarized singlet order is available immediately after dissolution DNP, avoiding need for additional preparation steps. We demonstrate this procedure on a sample of [1,2–13C2]pyruvic aci

Challenges and Governance Solutions for Data Science Services based on Open Data and APIs

Peer reviewe

Improved stability of black silicon detectors using aluminum oxide surface passivation

Publisher Copyright: © 2021 ESA and CNESWe have studied how high-energy electron irradiation (12 MeV, total dose 66 krad(Si)) and long term humidity exposure (75%, 75 °C, 500 hours) influence the induced junction black silicon or planar photodiode characteristics. In our case, the induced junction is formed using n-type silicon and atomic-layer deposited aluminum oxide (Al2O3), which contains a large negative fixed charge. We compare the results with corresponding planar pn-junction detectors passivated with either with silicon dioxide (SiO2) or Al2O3. The results show that the induced junction detectors remain stable as their responsivity remains nearly unaffected during the electron beam irradiation. On the other hand, the SiO2 passivated counterparts that included conventional pn-junction degrade heavily, which is seen as strongly reduced UV response. Similarly, after humidity test the response of the induced junction detector remains unaffected, while the pn-junction detectors passivated with SiO2 degrade significantly, for instance, the response at 200 nm reduces to 50% from the original value. Interestingly, the pn-junction detectors passivated with Al2O3 exhibit no degradation of UV response, indicating that the surface passivation properties of Al2O3 are more stable than SiO2 under the studied conditions. This phenomenon is further confirmed with PC1D simulations suggesting that the UV degradation results from increased surface recombination velocity. To conclude, the results presented here suggest that black silicon photodiodes containing Al2O3-based induced junction are highly promising alternatives for applications that require the best performance and long-term stability under ionizing and humid conditions.Peer reviewe

State of the Practice in Application Programming Interfaces (APIs): A Case Study

Application Programming Interfaces (APIs) have become prevalent in today’s software systems and services. APIs are basically a technical means to realize the co-operation between software systems or services. While there are several guidelines for API development, the actually applied practices and challenges are less clear. To better understand the state of the practice of API development and management in the industry, we conducted a descriptive case study in four Finnish software companies: two consultancy companies developing software for their customers, and two companies developing their software products. As a result, we identified five different usage scenarios for APIs and emphasize that diversity of usage should be taken into account more explicitly especially in research. API development and technical management are well supported by the existing tools and technologies especially available from the cloud technology. This leaves as the main challenge the selection of the right technology from the existing technology stack. Documentation and usability are practical issues to be considered and often less rigorously addressed. However, understanding what kind of API management model to apply for the business context appears as the major challenge. We also suggest considering APIs more clearly a separate concern in the product management with specific practices, such as API roadmapping.Peer reviewe