Island Dynamics Research Articles

Analysis of feedback control of magnetic islands via rotational field based on Rutherford model

This work uses the Rutherford model for a cylindrical plasma to study the dynamics of magnetic islands under external magnetic perturbations, including both applied rotational magnetic fields and static error magnetic fields. The results show that, in an unstable tearing situation, magnetic islands are completely suppressed by modulating the frequency of the externally applied rotational magnetic field to maintain the phase of the combined external magnetic field to be opposite (or nearly opposite) that of the magnetic islands. The frequency is modulated by using a proportional controller in the simulation, where the frequency of the rotational field is determined by using the island rotation frequency “measured” in the simulation.

Transport, correlations, and chaos in a classical disordered anharmonic chain.

We explore transport properties in a disordered nonlinear chain of classical harmonic oscillators, and thereby identify a regime exhibiting behavior analogous to that seen in quantum many-body-localized systems. Through extensive numerical simulations of this system connected at its ends to heat baths at different temperatures, we computed the heat current and the temperature profile in the nonequilibrium steady state as a function of system size N, disorder strength Δ, and temperature T. The conductivity κ_{N}, obtained for finite length (N), saturates to a value κ_{∞}>0 in the large N limit, for all values of disorder strength Δ and temperature T>0. We show evidence that for any Δ>0 the conductivity goes to zero faster than any power of T in the (T/Δ)→0 limit, and find that the form κ_{∞}∼e^{-B|ln(CΔ/T)|^{3}} fits our data. This form has earlier been suggested by a theory based on the dynamics of multioscillator chaotic islands. The finite-size effect can be κ_{N}<κ_{∞} due to boundary resistance when the bulk conductivity is high (the weak disorder case), or κ_{N}>κ_{∞} due to direct bath-to-bath coupling through bulk localized modes when the bulk is weakly conducting (the strong disorder case). We also present results on equilibrium dynamical correlation functions and on the role of chaos on transport properties. Finally, we explore the differences in the growth and propagation of chaos in the weak and strong chaos regimes by studying the classical version of the out-of-time-ordered commutator.

Climate Change and Extreme Weather Events in the Moscow Agglomeration

Based on monitoring data (surface observation network and satellites) and on the results of climate simulations with the COSMO-CLM and ENVI-MET models, the dynamics of the urban heat island (UHI) and wet/dry island and their 3D structure for the Moscow agglomeration are investigated. It is found that the Moscow UHI is maintained by the anthropogenic heat influx to the urban atmosphere. To some extent, UHI is self-induced due to the feedback mechanism (providing approximately 10% of the effect) between temperature and the downward flux of longwave radiation. The UHI creates a counterclockwise circulation of airflows. The UHI and its circulation system are logically considered a product of self-organization, when a meso-beta scale circulation system is generated under the influence of multiple actions of small (meso-gamma scale) impacts. The UHI is accompanied by the wet/dry island. The domed three-dimensional structure of the islands is disturbed under steady strong winds and is transformed into the plume structure. The interannual trend towards the UHI strengthening is noted. This determines the effect of the warming acceleration related to the global warming and an increase in the discomfort effects in the Moscow urban system. The intense heat waves (1972, 2002, and 2010) which caused catastrophic droughts and wildfires in the European part of Russia are the major factor of vulnerability of the Moscow economy and population. In addition, the influence of the anomalies is amplified by the urban environment.

Discerning the success of sustainable planning: A comparative analysis of urban heat island dynamics in Korean new towns

UHI is an important measure for understanding the urban landscape, especially in terms of thermal agglomeration and disturbance. This research aims to discern the success of sustainability planning by examining and comparing the different characteristics of UHIs through the combination of machine learning and statistical methods. To achieve this, we analyze 4 new towns in Korea, which include two ‘old’ new towns and two ‘recent’ new towns. The key difference between our test towns lies on whether or not the sustainability policies were applied to their development plans. We visualize LST and conduct a k-mean clustering to find and quantify spatial patterning in the resulting UHI measures. We then compare the statistical relations between LST and 6 UHI driven variables across the towns. Using comparative analysis, this research reveals that sustainable development policies have a notable effect on the patterns and intensities of UHI. Urban structures, planned under development policies, including green and blue space ratios, road networks, and housing distributions, were found to affect UHI significantly. We quantifiably confirm that the sustainability policies implemented in planning the ‘recent’ new towns allow the towns to experience less aggravated UHIs than the ‘old’ new towns. However, we also claim a need to develop appropriate, long-term UHI management regulations for the ‘recent’ new towns. This paper provides a solid basis for improving Korean new town planning and managing the environmental issues in urban systems for planners, designers, and decision-makers to establish the sustainable built environment.

Coalescence dynamics of 3D islands on weakly-interacting substrates

We use kinetic Monte Carlo simulations and analytical modelling to study coalescence of three-dimensional (3D) nanoscale faceted silver island pairs on weakly-interacting fcc(111) substrates, with and without concurrent supply of mobile adatoms from the vapor phase. Our simulations show that for vapor flux arrival rates F < 1 monolayer/second (ML/s) coalescence manifests itself by one of the islands absorbing the other via sidewall facet migration. This process is mediated by nucleation and growth of two-dimensional (2D) layers on the island facets, while the supply of mobile atoms increases the nucleation probability and shortens the time required for coalescence completion. When F is increased above 1 ML/s, coalescence is predominantly governed by deposition from the vapor phase and the island pair reaches a compact shape via agglomeration. The crucial role of facets for the coalescence dynamics is further supported by a mean-field thermodynamic description of the nucleation energetics and kinetics. Our findings explain experimental results which show that two-dimensional film growth morphology on weakly-interacting substrates is promoted when the rate of island coalescence is suppressed. The present study also highlights that deviations of experimentally reported film morphological evolutions in weakly-interacting film/substrate systems from predictions based on the sintering and particle growth theories may be understood in light of the effect of deposition flux atoms on the energetics and kinetics of facet-layer nucleation during coalescence.

An Eleven Years Analysis of the Seasonal Dynamics of Urban Heat Island (UHI) Intensity (2004-2014)

An Eleven Years Analysis of the Seasonal Dynamics of Urban Heat Island (UHI) Intensity (2004-2014)

A possible explanation for the enhancement of energetic particles downstream of the heliospheric termination shock

Voyager 2 observations of the energetic particle “time-intensity” profiles from ~1.8 to ~40 MeV show that the flux peaks downstream of the heliospheric termination shock (HTS), which is inconsistent with the predictions of classical diffusive shock acceleration (DSA). Previous studies suggest that shocks are effective in generating downstream magnetic flux ropes, islands or plasmoids. These dynamically interacting small-scale structures can accelerate charged particles statistically through reconnection-related processes. We present a preliminary study of the magnetic field and plasma properties together with the energetic particle data during the V2 crossing of the HTS. We apply a local stochastic acceleration model associated with solar wind magnetic island dynamics to explain the unusual behavior of energetic particles observed in the vicinity of the HTS. An analytic solution for the particle velocity distribution function derived from the Zank et al. statistical transport theory is used to fit the observed particle flux amplification downstream of the HTS. The results show that stochastic acceleration by interacting magnetic islands can successfully predict the observed (i) peaking of particle intensities behind the HTS, instead of at the shock front; (ii) increasing of the particle flux amplification factor with increasing particle energy; and (iii) increase in distance between the particle intensity peak and the HTS with increasing particle energy; This study illustrates the possibility of local acceleration in the inner heliosheath due to the dynamical interaction of magnetic islands.

SPATIO-TEMPORAL STUDY OF BRAHMAPUTRA RIVER ISLANDS (CHARS) FOR AGRICULTURE EXPANSION IN ASSAM, INDIA

Abstract. The present paper aims to understand the spatio-temporal dynamics of the Brahmaputra river islands locally known as chars in Assam for agriculture crop expansion using long term multispectral satellite data and Google Earth Engine. This study also provides information on existing agriculture lands on these chars. For the study Landsat data is analysed to find the long term stable islands (1988–2018) and the present status of these islands for seasonal crop expansion. Validation of results was performed by using high-resolution satellite data. It is found that total area of vegetative chars has increased in past three decades and approximately 146 thousand hectares area of char is stable from past ten years. This study also reveals that the major crop cultivation is in Lower Brahmaputra Valley (LBV). In Upper Brahmaputra Valley (UBV), the crop cultivation is almost negligible compared to the large islands size. It can be inferred that less stable chars which are mostly located in upper Assam has negligible agriculture. It is also observed that at many places in lower Assam, double cropping system is followed. This study can be further extended by including factors like soil type, soil texture, rainfall, socio-economic etc. to study suitability for different crops. Proper facilities and incentives are to be provided to farmers of this region for better food security.

Temporal dynamics of urban heat island correlated with the socio-economic development over the past half-century in Seoul, Korea

Urban heat island (UHI), an iconic consequence of anthropogenic activities and climate condition, affects air pollution, energy use, and health. Therefore, better understanding of the temporal dynamics of UHI is required for sustainable urban planning to mitigate air pollution under a changing climate. Here, we present the evolution of UHI intensity (UHIi) and its controlling factors in the Seoul metropolitan area, Korea, over the last 56 years (1962–2017), which has experienced unique compressed economic growth and urban transformation under monsoon climate. The analysis demonstrated an inverted U-shape long-term variation of UHIi with the progress of urban transformation and economic climate which has not been reported in Asian cities before. Meanwhile, short-term variations in UHIi are related to both diurnal temperature range and duration after rainfall event unlike previous studies, and the UHIi was exacerbated by heat waves. Our findings suggest that the UHIi will exhibit different temporal dynamics with future changes in the monsoon climate, and heat waves in the urban area will be reinforced if current rapid urbanization continues without a shift toward sustainable and equitable development. Asian cities that are likely to face the similar urbanization trajectory and the implications are that urban (re)development strategy considers changes in rainfall magnitude and timing due to monsoon system variation under changing climate and plans to mitigate synergy between heat wave and UHI in this area.

Islands of the upper River Ob: morphometric characteristic, evolution and dynamics

The studied reach of the upper River Ob is quite complicated in the morphological aspect and characterized by very low channel stability and high discharge of sand load. Unconstrained conditions for lateral channel migration promotes active channel deformations not only at long-term scale, but also seasonally. Channel deformations contribute to the transformation of the channel and its morphodynamic type in time. The upper River Ob is intensively used as a water course, so any reorganization of the channel and river islands should be taken into account to support navigation.&#x0D; Morphometric and morphodynamic analysis of the islands made it possible to develop their morphological classification. Morphometric parameters of islands, being associated with the characteristics of the channel itself, are one of the main classification features. Empirical relations were obtained that link the dimensions (Lo, Bo) and shape of islands (Lo/Bo) with the morphodynamic channel type and its stability, the degree of branching of the channel (number of islands no per 1 km of channel length x). The features of island dynamics are also determined by the morphodynamic type of the channel and are associated with the morphometric characteristics of the islands themselves and their position in the channel, which determines the transgressive, regressive and transverse shift or their stable position in time.

Hydrothermal alteration environments and recent dynamics of the Ischia volcanic island (southern Italy): Insights from repeated field, mineralogical and geochemical surveys before and after the 2017 Casamicciola earthquake

This study presents the results of repeated surveys conducted in hydrothermally altered areas on the active volcanic island of Ischia (in the Gulf of Naples, southern Italy). Data were obtained from field work, in situ temperature measurements, X-ray diffraction, optical and scanning electron microscopy, EDS-SEM micro-analysis, infrared spectroscopy and whole-rock geochemistry analyses on samples collected in October 2016, September 2017, March 2018 and November 2018, both prior to and following the damaging seismic event that occurred in August 2017 at Casamicciola. Mineralogical results point to the evolution of acid sulfate zones along the northern and western flanks of a resurgent block located in the central part of the island, in strict relation with endogenous fluid outgassing indicated in the literature. Mineralogy and whole-rock geochemistry of these acid sulfate zones reveal magmatic-hydrothermal environments in association with major structures that enable fluid circulation. It is interpreted that rare coarser alunites within dominant steam-heated and supergene alteration mineral assemblages are associated with environments that are no longer active, but which are supplied by magmatic vapours. In addition, collected data indicate slow endogenous degassing from hydrothermal reservoirs. Data from September 2017 show variations in the sulfate assemblage within the acidic sulfate zone located near the earthquake's epicentre, and acidification and the transitory appearance of alum-(K) is apparent under a nearly unchanged endogenous supply. Meteorological conditions of late summer could, in principle, justify the appearance of alum-(K), but its coexistence with alunogen and soil temperatures refute this possibility. Alum-(K) is interpreted to be the product of alunite decomposition at a local temperature of ca. 100 °C. Assuming a correct space-time relationship between the appearance of alum-(K) and the earthquake, it is thus inferred that mechanical activation by tectonic stress is the possible cause of alunite decomposition.

Coherent X-ray spectroscopy reveals the persistence of island arrangements during layer-by-layer growth

Understanding surface dynamics during epitaxial film growth is key to growing high quality materials with controllable properties. X-ray photon correlation spectroscopy (XPCS) using coherent x-rays opens new opportunities for in situ observation of atomic-scale fluctuation dynamics during crystal growth. Here, we present the first XPCS measurements of 2D island dynamics during homoepitaxial growth in the layer-by-layer mode. Analysis of the results using two-time correlations reveals a new phenomenon - a memory effect in island nucleation sites on successive crystal layers. Simulations indicate that this persistence in the island arrangements arises from communication between islands on different layers via adatoms. With the worldwide advent of new coherent x-ray sources, the XPCS methods pioneered here will be widely applicable to atomic-scale processes on surfaces.

Point island dynamics under fixed rate deposition

In this paper we consider the dynamics of point islands during submonolayer deposition, in which the fragmentation of subcritical size islands is allowed. To understand asymptotics of solutions, we use methods of centre manifold theory, and for globalisation, we employ results from the theories of compartmental systems and of asymptotically autonomous dynamical systems. We also compare our results with those obtained by making the quasi-steady state assumption.

Spatiotemporal Analysis of Land Use/Land Cover and Its Effects on Surface Urban Heat Island Using Landsat Data: A Case Study of Metropolitan City Tehran (1988–2018)

This article summarized the spatiotemporal pattern of land use/land cover (LU/LC) and urban heat island (UHI) dynamics in the Metropolitan city of Tehran between 1988 and 2018. The study showed dynamics of each LU/LC class and their role in influencing the UHI. The impervious surface area expanded by 286.04 (48.27% of total land) and vegetated land was depleted by 42.06 km2 (7.10% of total land) during the period of 1988–2018. The mean land surface temperature (LST) has enlarged by approximately 2–3 °C at the city center and 5–7 °C at the periphery between 1988 and 2018 based on the urban–rural gradient analysis. The lower mean LST was experienced by vegetation land (VL) and water body (WB) by approximately 4–5 °C and 5–7 °C, respectively, and the higher mean LST by open land (OL) by 7–11 °C than other LU/LC classes at all time-points during the time period, 1988–2018. The magnitude of mean LST was calculated based on the main LU/LC categories, where impervious land (IL) recorded the higher temperature difference compared to vegetation land (VL) and water bodies (WB). However, open land (OL) recorded the highest mean LST differences with all the other LU/LC categories. In addition to that, there was an overall negative correlation between LST and the normal difference vegetation index (NDVI). By contrast, there was an overall positive correlation between LST and the normal difference built-up index (NDBI). This article, executed through three decadal change analyses from 1988 to 2018 at 10-year intervals, has made a significant contribution to delineating the long records of change dynamics and could have a great influence on policy making to foster environmental sustainability.

Application of Onsager's variational principle to the dynamics of a solid toroidal island on a substrate

In this paper, we consider the capillarity-driven evolution of a solid toroidal island on a flat rigid substrate, where mass transport is controlled by surface diffusion. This problem is representative of the geometrical complexity associated with the solid-state dewetting of thin films on substrates. We apply Onsager's variational principle to develop a general approach for describing surface diffusion-controlled problems. Based on this approach, we derive a simple, reduced-order model and obtain an analytical expression for the rate of island shrinking and validate this prediction by numerical simulations based on a full, sharp-interface model. We find that the rate of island shrinking is proportional to the material constants B and the surface energy density γ0, and is inversely proportional to the island volume V0. This approach represents a general tool for modeling interface diffusion-controlled morphology evolution.

Initial plant diversification and dispersal event in upper Silurian of the Prague Basin

A relatively rich association of six species of embryophyte plants is known from the upper Silurian of the Prague Basin (Bohemian Massif, Czech Republic). All stratigraphically controlled specimens come from the Neocolonograptus parultimus-Neocolonograptus ultimus Zone of the Přídolí. A new genus and species, Tichavekia grandis Pšenička, Sakala et Kraft, is established. The new combination Aberlemnia bohemica (Schweitzer) Sakala, Pšenička et Kraft, comb. nov. illustrates its Lycophytina affinity. The distribution and taphonomy of these plants in the Prague Basin indicates the proximity of exposed land interpreted to be islands of volcanic origin. Two local associations show primary differences in vegetated areas of the islands and apparent ecological responses of the primitive vascular plants to their habitats. Suitable environments in the coastal zones of volcanic islands in the Prague Basin, which was situated at the outer periphery of a broad Gondwanan shelf, likely represent significant transfer points for an initial dispersion and a first expansion of land plants. Repeated vegetation of the islands is inferred from the discrete distribution of land plants at different stratigraphic levels. These changes are explained partly in context of local changes of the island relief, and partly as responses to global climatic and sea level fluctuations, and fit environmental dynamics of islands of volcanic origin in general. This Initial Plant Diversification and Dispersal Event (IPDDE) is of considerable significance in the evolution of plants documented from the Bohemian Massif.

Spin dynamics of the block orbital-selective Mott phase

Iron-based superconductors display a variety of magnetic phases originating in the competition between electronic, orbital, and spin degrees of freedom. Previous theoretical investigations of the multi-orbital Hubbard model in one-dimension revealed the existence of an orbital-selective Mott phase (OSMP) with block spin order. Recent inelastic neutron scattering (INS) experiments on the BaFe2Se3 ladder compound confirmed the relevance of the block-OSMP. Moreover, the powder INS spectrum revealed an unexpected structure, containing both low-energy acoustic and high-energy optical modes. Here we present the theoretical prediction for the dynamical spin structure factor within a block-OSMP regime using the density-matrix renormalization-group method. In agreement with experiments, we find two dominant features: low-energy dispersive and high-energy dispersionless modes. We argue that the former represents the spin-wave-like dynamics of the block ferromagnetic islands, while the latter is attributed to a novel type of local on-site spin excitations controlled by the Hund coupling.

Identification of typical diurnal patterns for clear-sky climatology of surface urban heat islands

Understanding the diurnal dynamics of surface urban heat islands (SUHIs) is an indispensable step towards their full interpretation at multiple time scales. However, because of the tradeoff between the spatial and temporal resolutions of satellite-derived land surface temperature (LST) data, the climatology, variety, and taxonomy of diurnal SUHI (DSUHI) patterns remain largely unknown for numerous cities with different bioclimates. By combining daily MODIS LST data with a newly developed four-parameter diurnal temperature cycle (DTC) model, we selected 354 Chinese megacities located in different bioclimatic zones to examine the characteristics of the DSUHI descriptors and systematically investigate the prevalent DSUHI temporal patterns.The DSUHI variations demonstrate that both the daily maximum and minimum SUHI intensity (SUHII) can occur during most periods of the day, although these intensities are more likely to occur in the early morning and noon/afternoon. Our results also reveal that both strong SUHIs (SUHII > 3 K) and surface urban cool islands (SUCIs) (SUHII < 0 K) are more prevalent than those identified directly through the four MODIS transits. According to the SUHI dynamics, five typical DSUHI temporal patterns are identified: standard-spoon, weak-spoon, quasi-spoon, inverse-spoon, and straight-line patterns. A gradient was found with spoon-like patterns (DSUHI dynamics typically with a daytime valley and a roughly constant trend or a small peak at night) in North China and inverse-spoon (DSUHI dynamics with a typical daytime peak and a constant trend at night) or straight-line patterns (DSUHI dynamics virtually unchanged all day) in South China. The DSUHI shapes were found to be greatly controlled by the urban-rural contrast in the normalized difference vegetation index (NDVI) and urban geometry. Our results not only advance our understanding of the diurnal climatology of SUHIs but also provide a basis for urban surface heat mitigation by identifying the possible timing of the mitigation requirement.

Parametric investigation of Urban Heat Island dynamics through TEB 1D model for a case study: Assessment of adaptation measures

At present, the urban population has to cope with the effects caused from Urban Heat Island (UHI), poor air quality and increased frequency and/or intensity of extreme weather and climate events. The expected increase of these extremes in areas of the planet and the way to adapt to them has emphasized the need to investigate in detail the climate of the cities. Local vulnerability and risk assessments, supported by using regional climate models at very high resolution, are key to support development and implementation of effective local adaptation measures to make well-adapted and climate-resilient cities, i.e. more sustainable ones. This study aims to provide some quantitative information on the effectiveness of main local adaptation measures to reduce the magnitude of UHI, in terms of temperature and energy fluxes. The investigation was conducted by adopting the TEB 1D model for the Toulouse city case-study. Different urban configurations and adaptation measures have been considered in the model set up. The results confirm that different adaptation measures may reduce the temperature on the town elements during the daylight hours; among the different measures, the green roof prevent the radiative cooling, increasing the roof night temperature and contributing to the night UHI.

The island dynamics model on parallel quadtree grids

We introduce an approach for simulating epitaxial growth by use of an island dynamics model on a forest of quadtree grids, and in a parallel environment. To this end, we use a parallel framework introduced in the context of the level-set method. This framework utilizes: discretizations that achieve a second-order accurate level-set method on non-graded adaptive Cartesian grids for solving the associated free boundary value problem for surface diffusion; and an established library for the partitioning of the grid. We consider the cases with: irreversible aggregation, which amounts to applying Dirichlet boundary conditions at the island boundary; and an asymmetric (Ehrlich–Schwoebel) energy barrier for attachment/detachment of atoms at the island boundary, which entails the use of a Robin boundary condition. We provide the scaling analyses performed on the Stampede supercomputer and numerical examples that illustrate the capability of our methodology to efficiently simulate different aspects of epitaxial growth. The combination of adaptivity and parallelism in our approach enables simulations that are several orders of magnitude faster than those reported in the recent literature and, thus, provides a viable framework for the systematic study of mound formation on crystal surfaces.