Reaction Kinetic Modelling of size selected growth of nanodots

The self-organized growth of nanodots and size selection are studied using reaction kinetic model rate equations. Two independent numerical methods and a mesoscopic continuous model are used to solve and analytically predict the details of the stationary nanodot size distribution. The strongly reversible growth of kinetic origin is studied. The power-law distributions which are common in nature, display scaling of the size distribution with clearly defined scaling exponents. The stochastic simulation results and predictions of continuous model are in good agreement. The self assembly of nanodots, observed in experiments and enabling the industrial use of dots in electronics, arises from the strain in heteroepitaxial growth systems and leads to uniform size distributions. To model the size selection, the size dependent thermodynamical energy of the nanodot is included into the reaction kinetics. The resulting distribution is studied in detail to resolve the overshooting phenomenon in which the mean of the distribution exceeds the thermodynamically favored size. The physical origin of the overshooting is explained as a combination of the reaction kinetics and the thermodynamical energy. The skewness of the size distribution is found from the numerical data, and it is added into the continuous model as a parameter to obtain an analytical estimate of the mean size. The predictions of overshooting are calculated for two different types of growth; the 3D metal nanodots and semiconductor nanodots with double-well thermodynamical energy. The optimal, narrow size distributions are found, and external adatom flux from e.g. an external adatom source or ion beam assisted deposition improves the size selection by driving the size distribution to the narrowest location. Nucleation theory calculations of the thermodynamically stable distributions are performed, and the results are comparable to numerical and modelling results.Tutkimuksen aiheena on metalli- ja puolijohdenanopisteiden itsejärjestäytyvän kasvun mallintaminen. Tarkasteltavat nanorakenteet ovat kooltaan riittävän pieniä kvantti-ilmiöiden esiintymiseen, minkä vuoksi niillä on lukuisia sovelluskohteita mm. optiikassa, elektroniikassa ja lääketieteessä. Sovelluksia varten on tärkeää pystyä tuottamaan tehokkaasti suuria määriä keskenään samankokoisia nanopisteitä. Itsejärjestyminen on lupaava ja edullinen menetelmä, jonka lähtökohtana on heteroepitaksiaalinen kasvu, eli kasvatusalustan ja nanopistemateriaalin hilavakiot eroavat hieman toisistaan. Itsejärjestäytyneiden nanopisteiden stationaarisen kokojakauman yksityiskohtia selvitetään kahdella numeerisella menetelmällä ja ennustetaan analyyttisesti mesoskooppisella jatkumomallilla. Kaikki käytetyt menetelmät perustuvat yksinkertaistettuun reaktiokineettiseen kasvuyhtälömalliin. Koon valikoitumisen mallintamiseksi sisällytetään nanopisteen termodynaaminen, koosta riippuva energia mukaan reaktiokinetiikkaan. Nanopistejakaumaa tutkitaan yksityiskohtaisesti overshooting-ilmiön selvittämiseksi; ilmiössä nanopisteiden kokojakauman keskikohta ylittää termodynaamisesti valikoituvan koon. Kokojakauman paikka ennustetaan kahdelle erilaiselle kasvutilanteelle: 3D metallinanopisteille sekä sellaisille puolijohdenanopisteille, joiden termodynaamisella energialla on kaksi minimiä. Kapein kokojakauma saavutetaan, kun kasvuprosessin aikana pinnalla vapaana liikkuvien atomien vuota suurennetaan ulkoisen atomilähteen tai ionisuihkun avulla. Nukleaatioteorian mukaiset laskelmat nanopisteiden kokojakaumista ovat verrattavissa numeerisiin tuloksiin ja analyyttisen mallin antamiin tuloksiin. Tutkimuksessa käytettyä reaktiokineettistä kasvumallia voidaan siis käyttää itsejärjestäytyneiden nanopisteiden koon ennustamiseen

Predicting Forest Inventory Attributes Using Airborne Laser Scanning, Aerial Imagery, and Harvester Data

The aim of the study was to develop a new method to use tree stem information recorded by harvesters along operative logging in remote sensing-based prediction of forest inventory attributes in mature stands. The reference sample plots were formed from harvester data, using two different tree positions: harvester positions (XYH) in global satellite navigation system and computationally improved harvester head positions (XYHH). Study materials consisted of 158 mature Norway-spruce-dominated stands located in Southern Finland that were clear-cut during 2015–16. Tree attributes were derived from the stem dimensions recorded by the harvester. The forest inventory attributes were compiled for both stands and sample plots generated for stands for four different sample plot sizes (254, 509, 761, and 1018 m2). Prediction models between the harvester-based forest inventory attributes and remote sensing features of sample plots were developed. The stand-level predictions were obtained, and basal-area weighted mean diameter (Dg) and basal-area weighted mean height (Hg) were nearly constant for all model alternatives with relative root-mean-square errors (RMSE) roughly 10–11% and 6–8%, respectively, and minor biases. For basal area (G) and volume (V), using either of the position methods, resulted in roughly similar predictions at best, with approximately 25% relative RMSE and 15% bias. With XYHH positions, the predictions of G and V were nearly independent of the sample plot size within 254–761 m2. Therefore, the harvester-based data can be used as ground truth for remote sensing forest inventory methods. In predicting the forest inventory attributes, it is advisable to utilize harvester head positions (XYHH) and a smallest plot size of 254 m2. Instead, if only harvester positions (XYH) are available, expanding the sample plot size to 761 m2 reaches a similar accuracy to that obtained using XYHH positions, as the larger sample plot moderates the uncertainties when determining the individual tree position

Automated Method for Delineating Harvested Stands Based on Harvester Location Data

The data produced by cut-to-length harvesters provide new large-scale data source for event-based update of national forest stand inventory by Finnish Forest Centre. This study aimed to automate geoprocessing, which generates delineations of operated areas from harvester location data. Automated algorithms were developed and tested with a dataset of 455 harvested objects, recorded during harvestings. In automated stand delineation, the location points are clustered, the stand points are identified and external strip roads are separated. Then, stand polygons are produced. To validate the results, automatic delineations were compared to 57 observed delineations from field measurements and aerial images. A detailed comparison method was developed to study the correspondence. Stand polygonization parameter was adjusted and areal correspondence with 1% error on average was obtained for stands over 0.75 ha. Good stand shape agreement was observed. Overall, the automated method worked well, and the operative stand delineations were found suitable for updating the forest inventory data. To modify the operative stands towards forest inventory stands, a balancing algorithm is introduced to create a solid, unique stand boundary between overlapping stands. This algorithm is beneficial for upkeep of stand networks. In addition, the Global Navigation Satellite System (GNSS) accuracy of the harvesters was examined and estimated numerically

Integrating detailed timber assortments into airborne laser scanning (Als)-based assessments of logging recoveries

The methodology presented here can assist in making timber markets more efficient when assessing the value of harvestable timber stands and the amounts of timber assortments during the planning of harvesting operations. Information on wood quality and timber assortments is essential for wood valuation and procurement planning as varying wood dimensions and qualities may be utilized and refined in different places, including sawmills, plywood mills, pulp mills, heating plants or combined heat and power plants. We investigate here alternative approaches for generating detailed timber assortments for Norway spruce (Picea abies (L.) H.Karst.), Scots pine (Pinus sylvestris L.) and birch (Betula spp.) from airborne laser scanning (ALS) data, aerial images, harvester data and field data. For this purpose, we used 665 circular plots, and logging recovery information recorded from 249 clear-cut stands using cut-to-length harvesters. We estimated timber assortment volumes, economic values and wood paying capabilities (WPC) for each stand in different bucking scenarios, and used the resulting timber assortment estimates to assess logging recoveries. The bucking scenarios were (1) bucking-to-value using maximum sawlog and pulpwood volumes excluding quality (theoretical maximum), and (2) bucking-to-value using sawlog lengths at 30 cm intervals for Norway spruce and Scots pine and veneer logs of lengths 4.7 m, 5.0 m, 6.0 m and 6.7 m for birch, either excluding quality (the usual business practice) or including quality (a novel business practice). The results showed that our procedure can assist in locating stands that are likely to be more valuable and have the desired timber assortment distributions. We conclude that the method can estimate WPC with root mean square errors of 28.7%, 66.0% and 45.7% in Norway spruce, Scots pine and birch, respectively, for sawlogs and 19.3%, 63.7% and 29.5% for pulpwood