Instability and wavelength selection during step flow growth of metal surfaces vicinal to fcc(001)

We study the onset and development of ledge instabilities during growth of vicinal metal surfaces using kinetic Monte Carlo simulations. We observe the formation of periodic patterns at [110] close packed step edges on surfaces vicinal to fcc(001) under realistic molecular beam epitaxy conditions. The corresponding wavelength and its temperature dependence are studied by monitoring the autocorrelation function for step edge position. Simulations suggest that the ledge instability on fcc(1,1,m) vicinal surfaces is controlled by the strong kink Ehrlich-Schwoebel barrier, with the wavelength determined by dimer nucleation at the step edge. Our results are in agreement with recent continuum theoretical predictions, and experiments on Cu(1,1,17) vicinal surfaces.Comment: 4 pages, 4 figures, RevTe

Kinetic Monte Carlo simulations of oscillatory shape evolution for electromigration-driven islands

The shape evolution of two-dimensional islands under electromigration-driven periphery diffusion is studied by kinetic Monte Carlo (KMC) simulations and continuum theory. The energetics of the KMC model is adapted to the Cu(100) surface, and the continuum model is matched to the KMC model by a suitably parametrized choice of the orientation-dependent step stiffness and step atom mobility. At 700 K shape oscillations predicted by continuum theory are quantitatively verified by the KMC simulations, while at 500 K qualitative differences between the two modeling approaches are found.Comment: 7 pages, 6 figure

Eri tuen tasolla opiskelevien oppilaiden hyvinvointiin yhteydessä olevat tekijät etäopetuksessa

Tiivistelmä. Suomi ja koko maailma olivat uuden tilanteen edessä, kun koronapandemia sulki yhteiskunnan kannalta merkittäviä toimintoja keväällä 2020 taudin hillitsemiseksi. Suomessa koulut asetettiin lyhyellä varoitusajalla etäopetukseen ilman valmistautumisaikaa. Myös suurin osa tehostettua tai erityistä tukea saavista oppilaista siirtyi etäopetukseen. Tämän kandidaatintutkielman oli tarkoitus selvittää, mitkä tekijät ovat yhteydessä eri tuen tasoilla opiskelevien oppilaiden hyvinvointiin etäopetuksen aikana. Tutkimus toteutettiin kuvailevana kirjallisuuskatsauksena. Kouluissa on alettu kiinnittää yhä enemmän huomiota oppimisen lisäksi myös oppilaiden hyvinvointiin. Kouluhyvinvointi määritellään neljän ulottuvuuden kautta: koulun olosuhteet, sosiaaliset suhteet, itsensä toteuttamismahdollisuudet sekä terveydentila (Konu, 2002). Myös oppilaan ja opettajan välinen vuorovaikutus on osa oppilaan hyvinvointia. Etäopetuksessa opiskelu tapahtuu erillään kouluympäristöstä ja opettajasta. Etäopetus vaatii oppilaalta suuressa määrin itseohjautuvuuden taitoja ja motivaatiota. Opettajalta opetuksen järjestäminen etäyhteydellä vaatii pedagogista pohdintaa suunnittelun ja toteuttamisen suhteen. Etäopetuksessakin oppilas on oikeutettu opettajan palautteeseen ja tukeen. Oppimisen yleisen, tehostetun tai erityisen tuen tulee olla suunnitelmallista ja muuntautua tarpeen mukaan. Kirjallisuuskatsauksen tulokset osoittavat, että etäopetuksen negatiiviset yhteydet oppilaiden hyvinvointiin liittyivät opetuksen strukturoimattomuuteen, arjen hallinnan puutteisiin sekä negatiivisiin tunteisiin. Elämänlaadun koettiin heikentyneen ystävyyssuhteiden ja muun sosiaalisen elämän ollessa tauolla. Positiiviset yhteydet oppilaiden hyvinvointiin liittyivät vähemmän kuormittavaan arkeen, sosiaalisen paineen ja kiusaamisen puuttumiseen sekä lisääntyneeseen vapaa-aikaan. Oppimisen tuki ei toteutunut riittävästi etäopetuksen aikana, mikä asetti oppilaat eriarvoiseen asemaan. Huoltajien ja perheiden hyvinvointi oli merkittävässä yhteydessä oppilaiden hyvinvointiin. Toisille perheille etäopetusaika oli rauhoittumisen ja lähentymisen aikaa toisten perheiden kokiessa ajan hyvin kuormittavana ja haastavana. Tutkimuksen pohjalta voidaan tehdä johtopäätös, että etäopetuksen yhteydet eri tuen tasolla opiskelevien oppilaiden hyvinvointiin olivat yksilöllisiä, joskin enimmäkseen negatiivisia. Tulevaisuudessa poikkeuksellisissa etäopetustilanteissa tulee kiinnittää huomiota strukturoituun opetukseen, oppimisen tuen riittävään toteutumiseen sekä perheiden hyvinvoinnin tukemiseen.The factors in distance learning connected to the well-being of pupils studying on different levels of learning support. Abstract. Finland along with the whole world were facing a new circumstances when covid-19 pandemic shut down main functions in the society in spring 2020 to inhibit the disease. In Finland schools were placed in distance learning without any time to prepare. Most of the pupils along with the ones who were receiving intensified or special support in their learning transferred to distance learning. The aim of this bachelor’s thesis was to find out which factors in distance learning has connections to the well-being of pupils when studying on different levels of learning support. This thesis has been implemented as a descriptive literature review. In addition to focusing on learning in schools the attention is also more often pointed to the well-being of the pupils. School well-being is defined via four dimensions: circumstances in school, social relationships, possibilities to self-actualization and condition of health. The interaction between the pupil and the teacher is also part of the pupil’s well-being. When studying in distance the pupil is physically apart from the school environment and the teacher. To study in distance pupil needs to have a major amount of self-determination and motivation. As a teacher distance learning needs to be considered pedagogically when planning and implementing it. Also during the distance learning pupil is entitled to have a feedback and support from the teacher. Whether the support in learning is on general, intensified or special level it needs to be planned and adjustable. Based on this literature review, the negative connections that distance learning had on pupil’s well-being were related to unstructured teaching, lack of coping and negative emotions. Quality of life were experienced to decrease because the relationships with friends and other social relations were on a pause. The positive connections that distance learning had on pupil’s well-being were related to a less amount of burden on school days, lacking of social pressure and bullying and increased free time. Support in learning didn’t actualize well enough in distance learning which set the pupils in need of learning support to an unequal status. The well-being of the pupil’s guardians and families had a significant connection to the pupil’s well-being. Other families felt that the period of distance learning was a chance to relax and enjoy the closeness of the family. For the other families the period was challenging. Based on the results of this thesis, as a conclusion it can be stated that connections that distance learning had on the well-being of pupils who are studying on different levels of learning support are individuals, though mostly negative. In the future in similar circumstances, we should pay attention to structured teaching, actualization of learning support in adequate level and supporting the well-being of families

Submonolayer Growth with Anomalously High Island Density in Hyperthermal Deposition

We present a rate equation model for submonolayer island growth under conditions where hyperthermal deposition techniques such as low-energy ion deposition are employed to achieve smooth layer-by-layer growth. By asymptotic analysis, we demonstrate that the model exhibits stationary behavior with well-defined dynamic and growth exponents β and χ, respectively, in the limit of small and high detachment rates. We verify these predictions by using the particle coalescence simulation method. The simulations reveal the existence of a relatively sharp transition regime with an increasing detachment rate of adatoms from high values of the growth exponent β≈1 to much smaller values of β determined by detachment and island diffusion processes. Our numerical results for the island size distribution indicate an anomalously high number of small islands, in agreement with available experimental data.Peer reviewe

Morphology of ledge patterns during step flow growth of metal surfaces vicinal to fcc(001)

The morphological development of step edge patterns in the presence of meandering instability during step flow growth is studied by simulations and numerical integration of a continuum model. It is demonstrated that the kink Ehrlich-Schwoebel barrier responsible for the instability leads to an invariant shape of the step profiles. The step morphologies change with increasing coverage from a somewhat triangular shape to a more flat, invariant steady state form. The average pattern shape extracted from the simulations is shown to be in good agreement with that obtained from numerical integration of the continuum theory.Comment: 4 pages, 4 figures, RevTeX 3, submitted to Phys. Rev.

Meandering instability of curved step edges on growth of a crystalline cone

We study the meandering instability during growth of an isolated nanostructure, a crystalline cone, consisting of concentric circular steps. The onset of the instability is studied analytically within the framework of the standard Burton-Cabrera-Frank model, which is applied to describe step flow growth in circular geometry. We derive the correction to the most unstable wavelength and show that in general it depends on the curvature in a complicated way. Only in the asymptotic limit where the curvature approaches zero the results are shown to reduce to the rectangular case. The results obtained here are of importance in estimating growth regimes for stable nanostructures against step meandering.Comment: 4 pages, 3 figures, RevTe

Panorama of the distal myopathies

Distal myopathies are genetic primary muscle disorders with a prominent weakness at onset in hands and/or feet. The age of onset (from early childhood to adulthood), the distribution of muscle weakness (upper versus lower limbs) and the histological findings (ranging from nonspecific myopathic changes to myofibrillar disarrays and rimmed vacuoles) are extremely variable. However, despite being characterized by a wide clinical and genetic heterogeneity, the distal myopathies are a category of muscular dystrophies: genetic diseases with progressive loss of muscle fibers. Myopathic congenital arthrogryposis is also a form of distal myopathy usually caused by focal amyoplasia. Massive parallel sequencing has further expanded the long list of genes associated with a distal myopathy, and contributed identifying as distal myopathy-causative rare variants in genes more often related with other skeletal or cardiac muscle diseases. Currently, almost 20 genes (ACTN2, CAV3, CRYAB, DNAJB6, DNM2, FLNC, HNRNPA1, HSPB8, KHLH9, LDB3, MATR3, MB, MYOT, PLIN4, TIA1, VCP, NOTCH2NLC, LRP12, GIPS1) have been associated with an autosomal dominant form of distal myopathy. Pathogenic changes in four genes (ADSSL, ANO5, DYSF, GNE) cause an autosomal recessive form; and disease-causing variants in five genes (DES, MYH7, NEB, RYR1 and TTN) result either in a dominant or in a recessive distal myopathy. Finally, a digenic mechanism, underlying a Welander-like form of distal myopathy, has been recently elucidated. Rare pathogenic mutations in SQSTM1, previously identified with a bone disease (Paget disease), unexpectedly cause a distal myopathy when combined with a common polymorphism in TIA1. The present review aims at describing the genetic basis of distal myopathy and at summarizing the clinical features of the different forms described so far. ©2020 Gaetano Conte Academy - Mediterranean Society of Myology, Naples, Italy.Peer reviewe

Competing mechanisms for step meandering in unstable growth

The meander instability of a vicinal surface growing under step flow conditions is studied within a solid-on-solid model. In the absence of edge diffusion the selected meander wavelength agrees quantitatively with the continuum linear stability analysis of Bales and Zangwill [Phys. Rev. B {\bf 41}, 4400 (1990)]. In the presence of edge diffusion a local instability mechanism related to kink rounding barriers dominates, and the meander wavelength is set by one-dimensional nucleation. The long-time behavior of the meander amplitude differs in the two cases, and disagrees with the predictions of a nonlinear step evolution equation [O. Pierre-Louis et al., Phys. Rev. Lett. {\bf 80}, 4221 (1998)]. The variation of the meander wavelength with the deposition flux and with the activation barriers for step adatom detachment and step crossing (the Ehrlich-Schwoebel barrier) is studied in detail. The interpretation of recent experiments on surfaces vicinal to Cu(100) [T. Maroutian et al., Phys. Rev. B {\bf 64}, 165401 (2001)] in the light of our results yields an estimate for the kink barrier at the close packed steps.Comment: 8 pages, 7 .eps figures. Final version. Some errors in chapter V correcte

Evolution of Cu nanoclusters on Cu(100)

Abstract Using molecular dynamics simulations combined with kinetic Monte Carlo methods we have studied the evolution of copper nanoclusters on a copper (100) surface. We have developed a method for relaxing the clusters into a suitable configuration for input into the kinetic Monte Carlo method using molecular dynamics. Using kinetic Monte Carlo methods we have simulated the evolution of clusters with sizes of 22-2045 atoms at temperatures of 220-1020 K. We found that the Cu clusters on the surface will be reduced to one monolayer if given enough time to relax, and that this process shows an Arrhenius behaviour. In this paper we present the relaxation method that we developed and our observations for the evolution of the clusters