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.

Finite-size effects in dynamics of zero-range processes

The finite-size effects prominent in zero-range processes exhibiting a condensation transition are studied by using continuous-time Monte Carlo simulations. We observe that, well above the thermodynamic critical point, both static and dynamic properties display fluid-like behavior up to a density {\rho}c (L), which is the finite-size counterpart of the critical density {\rho}c = {\rho}c (L \rightarrow \infty). We determine this density from the cross-over behavior of the average size of the largest cluster. We then show that several dynamical characteristics undergo a qualitative change at this density. In particular, the size distribution of the largest cluster at the moment of relocation, the persistence properties of the largest cluster and correlations in its motion are studied.Comment: http://pre.aps.org/abstract/PRE/v82/i3/e03111

Island diffusion on metal fcc(100) surfaces

We present Monte Carlo simulations for the size and temperature dependence of the diffusion coefficient of adatom islands on the Cu(100) surface. We show that the scaling exponent for the size dependence is not a constant but a decreasing function of the island size and approaches unity for very large islands. This is due to a crossover from periphery dominated mass transport to a regime where vacancies diffuse inside the island. The effective scaling exponents are in good agreement with theory and experiments.Comment: 13 pages, 2 figures, to be published in Phys. Rev. Let

Biologisten lääkkeiden käyttöönotto ja käyttö Suomessa : Terveydenhuollon käytäntöjä ja näkökulmia

Uusia biologisia lääkkeitä tulee markkinoille koko ajan enemmän, ja niiden kustannukset ovat kasvaneet huomattavasti 2000-luvulla. Näihin lääkkeisiin liittyy useita hoidollisia ja yhteiskunnallisia kysymyksiä muun muassa lääkkeiden tehosta, turvallisuudesta, kohdentamisesta, kustannusvaikuttavuudesta ja hinnasta. Tässä tutkimuksessa selvitettiin biologisten lääkkeiden käyttöönottoon ja käyttöön liittyvää päätöksentekoa. Tutkimus toteutettiin vuosina 2013–2014. Tutkimuksessa haastateltiin reuma- ja syöpälääkäreitä sekä sairaala-apteekkareita eri puolilla Suomea. Lisäksi tarkasteltiin päätöksentekoon liittyviä dokumentteja ja lääkehoidon kustannuksia. Päätettäessä uuden lääkkeen käyttöönotosta arvioidaan sen asemaa sairauden hoidossa. Päätökset tehdään organisaatioissa ja jokapäiväisessä potilastyössä. Kaksikanavainen rahoitusjärjestelmä ohjaa valitsemaan korvattavia avohoitolääkkeitä lääketieteellisesti hyväksytyissä rajoissa. Kaksikanavaisuuteen liittyvät käytännöt koetaan ongelmallisina. Päätöksenteossa voidaan päätyä erilaisiin lopputuloksiin riippuen yksilöistä, organisaatioista ja paikallisista tekijöistä. Yksilöt voivat tulkita olemassa olevaa tietoa eri tavoin. Organisaatioiden linjaukset ja paikalliset tekijät, kuten sairastavuus, hoidon järjestämisen käytännöt ja resurssit, vaikuttavat päätöksenteossa. Vaikka erot päätöksenteossa eivät automaattisesti merkitse huonompia tai parempia hoitotuloksia, nousee tutkimuksen perusteella esille tarve yhtenäisille linjauksille kalliiden lääkehoitojen käytössä. Yhtenäiset linjaukset tukevat yhdenvertaisen hoidon toteutumista. Kalliita lääkkeitä koskeva päätöksenteko on yhdistelmä lääketieteellisiä, yhteiskunnallisia ja arvoihin liittyviä tekijöitä. Päätöksentekoa yhteisistä linjauksista voidaan tukea seuraamalla ja tutkimalla lääkkeiden vaikuttavuutta. Lisäksi päätöksenteossa tarvitaan tietoa eri osapuolten näkökulmista ja intresseistä. Kalliiden lääkehoitojen järkevä käyttö yksilöä hyödyttävällä, yhdenvertaisella ja yhteiskunnallisesti kestävällä tavalla asettaa entistä suuremman haasteen päätöksentekijöille ja väestölle.25,00 euro

Temporal and Spatial Persistence of Combustion Fronts in Paper

The spatial and temporal persistence, or first-return distributions are measured for slow-combustion fronts in paper. The stationary temporal and (perhaps less convincingly) spatial persistence exponents agree with the predictions based on the front dynamics, which asymptotically belongs to the Kardar-Parisi-Zhang universality class. The stationary short-range and the transient behavior of the fronts are non-Markovian, and the observed persistence properties thus do not agree with the predictions based on Markovian theory. This deviation is a consequence of additional time and length scales, related to the crossovers to the asymptotic coarse-grained behavior.Peer reviewe

Diffusion processes and growth on stepped metal surfaces

We study the dynamics of adatoms in a model of vicinal (11m) fcc metal surfaces. We examine the role of different diffusion mechanisms and their implications to surface growth. In particular, we study the effect of steps and kinks on adatom dynamics. We show that the existence of kinks is crucially important for adatom motion along and across steps. Our results are in agreement with recent experiments on Cu(100) and Cu(1,1,19) surfaces. The results also suggest that for some metals exotic diffusion mechanisms may be important for mass transport across the steps.Comment: 3 pages, revtex, complete file available from ftp://rock.helsinki.fi/pub/preprints/tft/ or at http://www.physics.helsinki.fi/tft/tft_preprints.html (to appear in Phys. Rev. B Rapid Comm.

Cluster size distributions in particle systems with asymmetric dynamics

We present exact and asymptotic results for clusters in the one-dimensional totally asymmetric exclusion process (TASEP) with two different dynamics. The expected length of the largest cluster is shown to diverge logarithmically with increasing system size for ordinary TASEP dynamics and as a logarithm divided by a double logarithm for generalized dynamics, where the hopping probability of a particle depends on the size of the cluster it belongs to. The connection with the asymptotic theory of extreme order statistics is discussed in detail. We also consider a related model of interface growth, where the deposited particles are allowed to relax to the local gravitational minimum.Comment: 12 pages, 3 figures, RevTe

Survival in equilibrium step fluctuations

We report the results of analytic and numerical investigations of the time scale of survival or non-zero-crossing probability $S(t)$ in equilibrium step fluctuations described by Langevin equations appropriate for attachment/detachment and edge-diffusion limited kinetics. An exact relation between long-time behaviors of the survival probability and the autocorrelation function is established and numerically verified. $S(t)$ is shown to exhibit simple scaling behavior as a function of system size and sampling time. Our theoretical results are in agreement with those obtained from an analysis of experimental dynamical STM data on step fluctuations on Al/Si(111) and Ag(111) surfaces.Comment: RevTeX, 4 pages, 3 figure

Ising cubes with enhanced surface couplings

Using Monte Carlo techniques, Ising cubes with ferromagnetic nearest-neighbor interactions and enhanced couplings between surface spins are studied. In particular, at the surface transition, the corner magnetization shows non-universal, coupling-dependent critical behavior in the thermodynamic limit. Results on the critical exponent of the corner magnetization are compared to previous findings on two-dimensional Ising models with three intersecting defect lines.Comment: 4 pages, 2 figures included, submitted to Phys. Rev.

Effect of a columnar defect on the shape of slow-combustion fronts

We report experimental results for the behavior of slow-combustion fronts in the presence of a columnar defect with excess or reduced driving, and compare them with those of mean-field theory. We also compare them with simulation results for an analogous problem of driven flow of particles with hard-core repulsion (ASEP) and a single defect bond with a different hopping probability. The difference in the shape of the front profiles for excess vs. reduced driving in the defect, clearly demonstrates the existence of a KPZ-type of nonlinear term in the effective evolution equation for the slow-combustion fronts. We also find that slow-combustion fronts display a faceted form for large enough excess driving, and that there is a corresponding increase then in the average front speed. This increase in the average front speed disappears at a non-zero excess driving in agreement with the simulated behavior of the ASEP model.Comment: 7 pages, 7 figure