785 research outputs found
X-ray diffraction studies of VOâ thin films
Abstract. The aim of this work is to investigate the effect of strain in vanadium dioxide (VOâ) thin films. Vanadium dioxide undergoes a metal-insulator transition involving radical changes in the electrical conductivity, and strain is one of the parameters which can influence the transition characteristics. In form of a thin film, vanadium dioxide is subjected to strain which arises from the lattice mismatch between the substrate and the film. To study the effect of strain, a set of vanadium dioxide thin films with thickness from 20 to 240 nm were grown using pulsed laser deposition method, and the structure of the films were characterized using X-ray diffraction. The surface morphology of the thin films was also examined using atomic force microscopy.
In the insulating state, the films were composed of both Mâ and Mâ phases of vanadium dioxide. The transition was observed to be controlled by Mâ phase in films which were thinner than 100 nm and by Mâ phase in thicker films. The presence of Mâ phase was caused by strain. The metal-insulator transition occurred at much wider temperature range in thinner films which were more strained than the thicker films showing more abrupt transitions. The relaxation of the strain in thicker films resulted in misorientation of the crystallites and caused the surface roughness to increase with the film thickness.VOâ ohutkalvojen röntgendiffraktiotutkimuksia. TiivistelmĂ€. TĂ€mĂ€n työn tarkoituksena on tutkia venymĂ€n vaikutusta vanadiinidioksidi (VOâ) ohutkalvoissa. Vanadiinidioksidissa ilmenevĂ€ metalli-eriste transitio aiheuttaa suuria muutoksia aineen sĂ€hkönjohtavuudessa ja venymĂ€n on huomattu vaikuttavan transition ominaisuuksiin. Ohutkalvomuodossa vanadiinidioksidiin kohdistuu venymĂ€, joka aiheutuu kalvon ja substraatin hilavakioiden epĂ€sovituksesta. VenymĂ€stĂ€ aiheutuvien vaikutusten selvittĂ€miseksi eri paksuisia (20â240 nm) vanadiinidioksidi ohutkalvoja valmistettiin pulssilaserkasvatuksella ja niiden rakennetta karakterisoitiin röntgendiffraktiolla. Myös ohutkalvojen pinnanmuotoa tutkittiin atomivoimamikroskopian avulla.
Eristetilassa kalvot koostuivat vanadiinioksidin Mâ ja Mâ faaseista, ja Mâ faasin huomattiin kontrolloivan transitiota kalvoissa, jotka olivat ohuempia kuin 100 nm, kun taas paksuimmissa kalvoissa transitiota kontrolloi Mâ faasi. Mâ faasin mukanaolo johtui venymĂ€stĂ€. Metalli-eriste transitio tapahtui laajemmalla lĂ€mpötila-alueella ohuimmissa kalvoissa, joissa venyminen oli suurempaa kuin paksummissa kalvoissa. Paksuimmissa kalvoissa transitio olikin paljon voimakkaampi. VenymĂ€n relaksoituminen paksuimmissa kalvoissa johti kiteiden kallistumiseen aiheuttaen sen, ettĂ€ pinnan karheus kasvoi kalvon paksuuden mukana
Kinetic Roughening in Slow Combustion of Paper
Results of experiments on the dynamics and kinetic roughening of
one-dimensional slow-combustion fronts in three grades of paper are reported.
Extensive averaging of the data allows a detailed analysis of the spatial and
temporal development of the interface fluctuations. The asymptotic scaling
properties, on long length and time scales, are well described by the
Kardar-Parisi-Zhang (KPZ) equation with short-range, uncorrelated noise. To
obtain a more detailed picture of the strong-coupling fixed point,
characteristic of the KPZ universality class, universal amplitude ratios, and
the universal coupling constant are computed from the data and found to be in
good agreement with theory. Below the spatial and temporal scales at which a
cross-over takes place to the standard KPZ behavior, the fronts display higher
apparent exponents and apparent multiscaling. In this regime the interface
velocities are spatially and temporally correlated, and the distribution of the
magnitudes of the effective noise has a power-law tail. The relation of the
observed short-range behavior and the noise as determined from the local
velocity fluctuations is discussed.Comment: RevTeX v3.1, 13 pages, 12 Postscript figures (uses epsf.sty), 3
tables; submitted to Phys. Rev.
Neuvosto-VenĂ€jĂ€n uhkaan varautuen:Suomen puolustussuunnittelu vuosina 1919â1924
TiivistelmĂ€. Pro gradu -tutkielmassani tarkastelen Suomen puolustussuunnittelua vuosina 1919â1924. SelvitĂ€n työssĂ€ni, mitkĂ€ tahot vaikuttivat Suomen puolustussuunnitteluun ja mitkĂ€ olivat keskeisimmĂ€t sotataidolliset tekijĂ€t. LisĂ€ksi selvitĂ€n puolustussuunnitelmien sisĂ€llön ja niihin kohdistuneen kritiikin vaikutuksineen. Tarkastelen rauhan ajan puolustussuunnittelua, yleisesikunnan roolia sekĂ€ sitĂ€ keinovalikoimaa, jolla varsinainen suunnittelutyö toteutettiin.
Tutkimukseni edustaa laadullista tutkimusta. Keskeisin lÀhderyhmÀ koostuu Kansallisarkistossa sÀilytettÀvistÀ puolustussuunnittelua kÀsittelevistÀ yleisesikunnan asiakirjoista. Muita lÀhderyhmiÀ ovat korkea-arvoisten upseerien muistelmat ja nimikirjanotteet. Analysoin kerÀÀmÀni aineiston aineistolÀhtöisen sisÀllönanalyysin keinoin.
SisĂ€llissodan jĂ€lkeisinĂ€ vuosina Suomessa oli sangen epĂ€vakaat olot ja maan puolustusjĂ€rjestelyt oli turvattava ajankohtaisilla suunnitelmilla. Osoitan tutkielmassani yleisesikunnan pÀÀllikkö kenraaliluutnantti Oscar Enckellin vastanneen Suomen puolustussuunnitelmien laadinnasta vuosina 1919â1924 yleisesikunnan tarjoamin resurssein. Tutkielmassa tarkastellulla ajanjaksolla Suomen puolustusratkaisu saatiin valmiiksi, mutta se ei saavuttanut tĂ€ysin yksimielistĂ€ hyvĂ€ksyntÀÀ sotaneuvostossa. Puolustussuunnittelu oli ensimmĂ€istĂ€ kertaa monen tahon hallinnoima prosessi, jossa tukeuduttiin kansainvĂ€liseen sotataidolliseen tukeen ja sisĂ€iseen opponointiin.
Aineistosta erottui suunnittelutyötÀ tukeneet sotataidolliset tekijÀt: maastontiedustelu, sotapelaaminen, linnoittaminen, kansainvÀlinen sotilaallinen tuki ja suomalaisupseerien ulkomaanopinnot. Suunnitelmista ovat havaittavissa mÀÀrÀvahvuuden, liikkuvaisuuden ja voimansÀÀstöperiaatteen kÀsitteet osana pienen valtion puolustusta.
Suomen puolustussuunnitelmiksi vakiintuivat Karjalankannakselle laaditut VenÀjÀn keskitys 1, 2 ja 3. Ahvenanmaan tilanteen seurauksena Ruotsin uhkaan varauduttiin suunnitelmalla Ruotsin keskitys 1, mutta se jÀi vaille kÀyttöÀ. Tutkielmassani korostuu suomalaisen sotataidon murros: keskijohdon Saksassa koulutetut jÀÀkÀriupseerit haastoivat ajattelullaan korkeimpia sotilasvirkoja hallussaan pitÀneet vanhan vÀen upseerit. LÀpi puolustussuunnittelun rinnalla kulkenut valtataistelu huipentui vuoden 1924 upseerikapinana, jonka seurauksena pÀÀosa VenÀjÀllÀ koulutetuista vanhan vÀen upseereista vÀistyi tehtÀvistÀÀn.
Tutkimustulokseni osoittavat, ettei Suomen puolustussuunnittelua toteutettu ihanteellisissa olosuhteissa laajasta organisaation tarjoamasta tuesta huolimatta. Aineiston perusteella voidaan pÀÀtellĂ€ Suomen puolustussuunnittelun kuitenkin onnistuneen vuosina 1919â1924, sillĂ€ vuonna 1939 pÀÀdyttiin Enckellin suunnitelmaa mukailevaan ratkaisuun
Siirtolaiskeskustelu Pohjois-Pohjanmaalla 1912â1920 paikallisten sanomalehtien antaman kuvan pohjalta
TiivistelmĂ€. Vuosina 1912â1920 kĂ€ytiin Pohjois-Pohjanmaalla sanomalehdissĂ€ intensiivistĂ€ keskustelua siirtolaisista ja siirtolaisuudesta. TĂ€mĂ€n tutkimuksen tavoite oli etsiĂ€ nĂ€issĂ€ keskusteluissa esiintyneitĂ€ erityispiirteitĂ€, sĂ€vyjĂ€ sekĂ€ teemoja.
PÀÀlÀhteinÀ toimivat Pohjois-Pohjanmaalla julkaistut sanomalehdet: Liitto, Kaleva ja Kansan Tahto, joiden kautta Pohjois-Pohjanmaan siirtolaiskeskustelusta saadaan laaja kuva niin aatteellisesti, sosioekonomisesti kuin myös asuinalueen perusteella. NÀistÀ sanomalehdistÀ on kÀyty lÀpi kÀyttÀen erilaisia siirtolaisuuteen liittyviÀ hakusanoja. Hakusanoin tehtyjÀ löydöksiÀ on sen jÀlkeen kÀsitelty media- ja tekstianalyysin keinoin.
Tutkimuksen lopputuloksena voidaan todeta, ettÀ sanomalehdillÀ oli eroja muun muassa siirtolaisiin ja siirtolaisuuteen suhtautumisessa, kÀsittelytapojen teemoissa sekÀ julkaisujen mÀÀrissÀ. ErityispiirteitÀ lehdillÀ olivat esimerkiksi Liiton painotukset maaseutuun ja uskontoon, Kansan Tahdon painotukset ammattiliittoihin ja työvÀenaatteeseen ja Kalevan painotukset raha-asioihin ja isÀnmaallisuuteen
Developing LCA-based benchmarks for sustainable consumption - for and with users
This article presents the development process of a consumer-oriented, illustrative benchmarking tool enabling consumers to use the results of environmental life cycle assessment (LCA) to make informed decisions. Active and environmentally conscious consumers and environmental communicators were identified as key target groups for this type of information. A brochure presenting the benchmarking tool was developed as an participatory, iterative process involving consumer focus groups, stakeholder workshops and questionnaire-based feedback. In addition to learning what works and what does not, detailed suggestions on improved wording and figures were obtained, as well as a wealth of ideas for future applications
Effect of Methyl Group Substitution on the Kinetics of Vinyl Radical + O-2 Reaction
The kinetics of (CH3)(2)CCH + O-2 (1) and (CH3)(2)CCCH3 + O-2 (2) reactions have been measured as a function of temperature (223-600 K) at low pressures (0.4-2 Torr) using a tubular laminar flow reactor coupled to a photoionization mass spectrometer (PIMS). These reactions are important for accurate modeling of unsaturated hydrocarbon combustion. Photolysis of a brominated precursor by a pulsed excimer laser radiation at 248 nm wavelength along the flow reactor axis was used for the production of radicals. The measured bimolecular rate coefficient of reaction 1 shows a negative temperature dependence over the temperature range 223-384 K and becomes temperature independent at higher temperatures. The bimolecular rate coefficient of reaction 2 exhibits a negative temperature dependence throughout the experimental temperature range. The bimolecular rate coefficients of reactions 1 and 2 are expected to be at the high-pressure limit under the current experimental conditions, and the following values are obtained at 298 K: k(1)(298 K) = (4.5 +/- 0.5) x 10(-12) cm(3) s(-1) and k(2)(298 = (8.9 +/- 1.0) x 10(-12) cm(3) s(-1). The observed products for reactions 1 and 2 were CH3COCH3 and CH3 + CH3COCH3, respectively. Substituting both beta-hydrogens in the vinyl radical (CH2CH) with methyl groups decreases the rate coefficient of the CH2CH + O-2 reaction by about 50%. However, the rate coefficient of the triply substituted (CH3)(2)CCCH3 radical reaction with O-2 is almost identical to the CH2CH + O-2 rate coefficient under the covered temperature range.Peer reviewe
Temperature and Pressure Dependence of the Reaction between Ethyl Radical and Molecular Oxygen : Experiments and Master Equation Simulations
Funding Information: We thank Stephen Klippenstein for providing us with the geometries, harmonic frequencies, and relative energies of the stationary points from his recent CH + O publication as well as the state sum for the loose recombination transition state. T.T.P. acknowledges support from the Doctoral Programme in Chemistry and Molecular Sciences of the University of Helsinki and the Magnus Ehrnrooth Foundation for funding. Project K129140 for G.L. was implemented with the support provided by the Ministry of Innovation and Technology of Hungary from the National Research, Development and Innovation Fund, financed under the OTKA funding scheme. T.T.P., E.A.R., and A.J.E. acknowledge support from the Academy of Finland (Grants 325250 and 346374). The authors also acknowledge CSC IT Center for Science in Finland for computational resources. 2 5 ⹠2 Publisher Copyright: © 2023 The Authors.We have used laser-photolysis - photoionization mass-spectrometry to measure the rate coefficient for the reaction between ethyl radical and molecular oxygen as a function of temperature (190-801 K) and pressure (0.2-6 Torr) under pseudo first-order conditions ([He] >> [O2] >> [C2H5 center dot]). Multiple ethyl precursor, photolysis wavelength, reactor material, and coating combinations were used. We reinvestigated the temperature dependence of the title reaction's rate coefficient to resolve inconsistencies in existing data. The current results indicate that some literature values for the rate coefficient may indeed be slightly too large. The experimental work was complemented with master equation simulations. We used the current and some previous rate coefficient measurements to optimize the values of key parameters in the master equation model. After optimization, the model was able to reproduce experimental falloff curves and C2H4 + HO2 center dot yields. We then used the model to perform simulations over wide temperature (200-1500 K) and pressure (10-4-102 bar) ranges and provide the results in PLOG format to facilitate their use in atmospheric and combustion models.Peer reviewe
An experimental and master-equation modeling study of the kinetics of the reaction between resonance-stabilized (CH3)(2)CCHCH2 radical and molecular oxygen
The kinetics of the reaction between resonance-stabilized (CH3)(2)CCHCH2 radical (R) and O-2 has been investigated using photoionization mass spectrometry, and master equation (ME) simulations were performed to support the experimental results. The kinetic measurements of the (CH3)(2)CCHCH2 + O-2 reaction (1) were carried out at low helium bath-gas pressures (0.2-5.7 Torr) and over a wide temperature range (238-660 K). Under low temperature (238-298 K) conditions, the pressure-dependent bimolecular association reaction R + O-2 -> ROO determines kinetics, until at an intermediate temperature range (325-373 K) the ROO adduct becomes thermally unstable and increasingly dissociates back to the reactants with increasing temperature. The initial association of O-2 with (CH3)(2)CCHCH2 radical occurs on two distinct sites: terminal 1(t) and non-terminal 1(nt) sites on R, leading to the barrierless formation of ROO(t) and ROO(nt) adducts, respectively. Important for autoignition modelling of olefinic compounds, bimolecular reaction channels appear to open for the R + O-2 reaction at high temperatures (T > 500 K) and pressure-independent bimolecular rate coefficients of reaction (1) with a weak positive temperature dependence, (2.8-4.6) x 10(-15) cm(3) molecule(-1) s(-1), were measured in the temperature range of 500-660 K. At a temperature of 501 K, a product signal of reaction (1) was observed at m/z = 68, probably originating from isoprene. To explore the reaction mechanism of reaction (1), quantum chemical calculations and ME simulations were performed. According to the ME simulations, without any adjustment to energies, the most important and second most important product channels at the high temperatures are isoprene + HO2 (yield > 91%) and (2R/S)-3-methyl-1,2-epoxybut-3-ene + OH (yield isoprene + HO2 (similar to 2.2 kcal mol(-1)), the ME model was able to reproduce the experimental findings. Modified Arrhenius expressions for the kinetically important reaction channels are enclosed to facilitate the use of current results in combustion models.Peer reviewe
First direct kinetic measurement of i -C4H5 (CH2CHCCH2) + O-2 reaction : Toward quantitative understanding of aromatic ring formation chemistry
The kinetics of the i -C 4 H 5 (buta-1,3-dien-2-yl) radical reaction with molecular oxygen has been measured over a wide temperature range (275-852 K) at low pressures (0.8-3 Torr) in direct, time-resolved experiments. The measurements were performed using a laminar flow reactor coupled to photoionization mass spectrometer (PIMS), and laser photolysis of either chloroprene (2-chlorobuta-1,3-diene) or isoprene was used to produce the resonantly stabilized i -C 4 H 5 radical. Under the experimental conditions, the measured bimolecular rate coefficient of i -C 4 H 5 + O 2 reaction is independent of bath gas density and exhibits weak, negative temperature dependency, and can be described by the expression k 3 = (1.45 +/- 0.05) & times; 10 & minus;12 & times; ( T /298 K) & minus;(0.13 +/- 0.05) cm 3 s & minus;1 . The measured bimolecular rate coefficient is surprisingly fast for a resonantly stabilized radical. Under combustion conditions, the reactions of i -C 4 H 5 radical with ethylene and acetylene are believed to play an important role in forming the first aromatic ring. However, the current measurements show that i C 4 H 5 + O 2 reaction is significantly faster under combustion conditions than previous estimations suggest and, consequently, inhibits the soot forming propensity of i -C 4 H 5 radicals. The bimolecular rate coefficient estimates used for the i -C 4 H 5 + O 2 reaction in recent combustion simulations show significant variation and are up to two orders of magnitude slower than the current, measured value. All estimates, in contrast to our measurements, predict a positive temperature dependency. The observed products for the i -C 4 H 5 + O 2 reaction were formaldehyde and ketene. This is in agreement with the one theoretical study available for i C 4 H 5 + O 2 reaction, which predicts the main bimolecular product channels to be H 2 CO + C 2 H 3 + CO and H 2 CCO + CH 2 CHO. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Peer reviewe
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