Impurity-induced step interactions: a kinetic Monte-Carlo study

A one-dimensional continuum description of growth on vicinal surfaces in the presence of immobile impurities predicts that the impurities can induce step bunching when they suppress the diffusion of adatoms on the surface. In the present communication we verify this prediction by kinetic Monte-Carlo simulations of a two-dimensional solid-on-solid model. We identify the conditions where quasi one-dimensional step flow is stable against island formation or step meandering, and analyse in detail the statistics of the impurity concentration profile. The sign and strength of the impurity-induced step interactions is determined by monitoring the motion of pairs of steps. Assemblies containing up to 20 steps turn out to be unstable towards the emission of single steps. This behavior is traced back to the small value of the effective, impurity-induced attachment asymmetry for adatoms. An analytic estimate for the critical number of steps needed to stabilize a bunch is derived and confirmed by simulations of a one-dimensional model.Comment: 9 pages, 8 figure

Electron-Phonon Interaction in Embedded Semiconductor Nanostructures

The modification of acoustic phonons in semiconductor nanostructures embedded in a host crystal is investigated including corrections due to strain within continuum elasticity theory. Effective elastic constants are calculated employing {\em ab initio} density functional theory. For a spherical InAs quantum dot embedded in GaAs barrier material, the electron-phonon coupling is calculated. Its strength is shown to be suppressed compared to the assumption of bulk phonons

Sulphonated aromatic pollutants: Limits of microbial degradability and potential of phytoremediation

Many synthetic sulphonated aromatic compounds are used as starting material to produce dyes and pigments, or are released as by-products in the effluents of the textile and dye industry. A large number of these chemicals are poorly biodegradable and cannot be eliminated by classical wastewater treatment plants. To limit the impact of these pollutants on the environment, new processes, based on the use of higher plants (constructed wetlands or hydroponic systems), are under development. Detergents and surfactants are essential for both industrial and domestic applications, the most important family being the alkylbenzene sulphonates. Originally, the alkyl side chains were branched and thus recalcitrant to biodegradation. Therefore, they have been replaced by linear alkylbenzene sulphonates. Although more acceptable, present formulations still have adverse environmental and toxic effects. In this context, phytoremediation appears to be a promising approach to remove these compounds from contaminated soils and water

Thermokarst lake monitoring on the Bykovsky Peninsula using high-resolution remote sensing data

Thermokarst lakes are a characteristic element of arctic permafrost regions and an indicator for their rapid landscape changes. Assessing their dynamics contributes to the understanding of driving processes of change, to the evaluation of impacts on landscape characteristics as well as to the estimation of the impact on the permafrost-related carbon budget. Monitoring thermokarst lake dynamics on the Bykovsky Peninsula, consisting of ice-rich Yedoma deposits, using high resolution remote sensing imagery from 1951 to 2016, revealed a long-term tendency towards lake drainage. Approximately 17% of the 1951 lake area was lost due to coastal erosion or the development of drainage networks. In parallel, coastal erosion driven land loss amounts to 2.3% of the peninsula. We find process interconnections between coastal erosion and lake change, as well as lake change dependency on land elevation in a developed alas-yedoma thermokarst relief

Sentinel-1 InSAR measurements of surface elevation changes over yedoma uplands on Sobo-Sise Island, Lena Delta

Yedoma is vulnerable to thawing and degradation under climate warming, which can result in lowering of surface elevations due to thaw subsidence. Quantitative knowledge about elevation changes can help us better understand the freeze-thaw processes of the active layer and yedoma deposits. In this study, we utilize C-band Sentinel-1 InSAR measurements, characterized by frequent sampling, to study the elevation changes over ice-rich yedoma uplands on Sobo-Sise Island, Lena Delta. We observe significant seasonal thaw subsidence during summer months and inter-annual elevation changes from 2016 to 2017. Here, we demonstrate the capability of Sentinel-1 to estimate elevation changes over yedoma uplands. We observe interesting patterns of stronger seasonal thaw subsidence on elevated flat yedoma uplands when compared to surrounding yedoma slopes. Inter-annual analyses from 2016 to 2017 revealed mostly positive surface elevation changes that might be caused by delayed thaw seasonal progression associated with mean annual air temperature fluctuations

Solving simultaneously Dirac and Ricatti equations

We analyse the behaviour of the Dirac equation in $d=1+1$ with Lorentz scalar potential. As the system is known to provide a physical realization of supersymmetric quantum mechanics, we take advantage of the factorization method in order to enlarge the restricted class of solvable problems. To be precise, it suffices to integrate a Ricatti equation to construct one-parameter families of solvable potentials. To illustrate the procedure in a simple but relevant context, we resort to a model which has proved useful in showing the phenomenon of fermion number fractionalization

Hybrid teaching and learning environment in the context of virtual product development

Product development means identifying the needs of different stakeholders, developing a product for them to the point where it is ready for production and use, and documenting it. To manage the complexity of product development, it is becoming increasingly digitalised. As virtual product development is a key area of industry, teaching in this area is an important component of a practice-oriented engineering curriculum. Engineering education constantly requires new teaching and learning formats. The trend is towards a systematic combination of digital teaching materials for self-organised individual and cooperative self-study on the one hand, and in-depth forms of classroom teaching tailored to the needs of students on the other - in short: hybrid forms of teaching and learning. Within the framework of an eTeach impulse project for a hybrid teaching and learning environment for virtual product development, important results have been developed, implemented and evaluated to achieve this goal

Past and present thermokarst lake dynamics in the Yedoma Ice Complex region of North-Eastern Yakutia

Thermokarst lakes are typical components of the yedoma-alas dominated relief in the coastal lowlands of North- Eastern Yakutia and formed as a result of thawing Late Pleistocene ice-rich Yedoma Ice Complex (IC) deposits. The aim of our study is to estimate thermokarst lake area changes from the early Holocene onwards based on RS data. The decrease of thermokarst lake area from the early Holocene, taking into account total alas depression areas, is as much as 81-83 %. Modern climate warming has led to a general trend of thermokarst lake area decrease. Lake drainage occurs mostly on elevated sites with high Yedoma IC fraction while lake area increase is typical for low-lying areas with a small Yedoma IC fraction. The area increase of thermokarst ponds on flat, boggy yedoma surfaces indicates ice wedge degradation in response to rising summer air temperatures and precipitation

Repeat terrestrial LiDAR for permafrost thaw subsidence change detection in North Alaska

The distinguishing feature of permafrost in the Arctic is the presence of a large amount of ice below the earth surface. Thermal degradation and subsequent destabilization of ground ice rich terrain cause thaw subsidence. Because these phenomena are hard to detect, they have received not much attention, despite their potentially global significance through the permafrost carbon feedback and implications for active layer thickness monitoring. Clearly, however, detailed local inventories are required to calibrate regional targeted long and short-term assessments for measuring surface deformation due to permafrost thaw. We analyze time series of repeat terrestrial laser scanning (rLiDAR) for quantification of land surface lowering on a tundra upland in the Teshekpuk Lake Special Area on Alaska´s North Slope. Here, considerable negative surface elevation changes have been detected over two years from 2015 to 2017. Spatial patterns of land elevation changes indicate that ice wedge polygon troughs are particularly prone to subsidence. This highlights the vulnerability of arctic tundra lowlands with ice-rich permafrost close to the surface