Solid phase properties and crystallization in simple model systems

We review theoretical and simulational approaches to the description of equilibrium bulk crystal and interface properties as well as to the nonequilibrium processes of homogeneous and heterogeneous crystal nucleation for the simple model systems of hard spheres and Lennard-Jones particles. For the equilibrium properties of bulk and interfaces, density functional theories employing fundamental measure functionals prove to be a precise and versatile tool, as exemplified with a closer analysis of the hard sphere crystalliquid interface. A detailed understanding of the dynamic process of nucleation in these model systems nevertheless still relies on simulational approaches. We review bulk nucleation and nucleation at structured walls and examine in closer detail the influence of walls with variable strength on nucleation in the Lennard-Jones fluid. We find that a planar crystalline substrate induces the growth of a crystalline film for a large range of lattice spacings and interaction potentials. Only a strongly incommensurate substrate and a very weakly attractive substrate potential lead to crystal growth with a non-zero contact angle

An Automatic Zone Detection System for Safe Landing of UAVs

As the demand increases for the use Unmanned Aerial Vehicles (UAVs) to monitor natural disasters, protecting territories, spraying, vigilance in urban areas, etc., detecting safe landing zones becomes a new area that has gained interest. This paper presents an intelligent system for detecting regions to navigate a UAV when it requires an emergency landing due to technical causes. The proposed system explores the fact that safe regions in images have flat surfaces, which are extracted using the Gabor Transform. This results in images of different orientations. The proposed system then performs histogram operations on different Gabor-oriented images to select pixels that contribute to the highest peak, as Candidate Pixels (CP), for the respective Gabor-oriented images. Next, to group candidate pixels as one region, we explore Markov Chain Codes (MCCs), which estimate the probability of pixels being classified as candidates with neighboring pixels. This process results in Candidate Regions (CRs) detection. For each image of the respective Gabor orientation, including CRs, the proposed system finds a candidate region that has the highest area and considers it as a reference. We then estimate the degree of similarity between the reference CR with corresponding CRs in the respective Gabor-oriented images using a Chi square distance measure. Furthermore, the proposed system chooses the CR which gives the highest similarity to the reference CR to fuse with that reference, which results in the establishment of safe landing zones for the UAV. Experimental results on images from different situations for safe landing detection show that the proposed system outperforms the existing systems. Furthermore, experimental results on relative success rates for different emergency conditions of UAVs show that the proposed intelligent system is effective and useful compared to the existing UAV safe landing systems

A new image size reduction model for an efficient visual sensor network

Image size reduction for energy-efficient transmission without losing quality is critical in Visual Sensor Networks (VSNs). The proposed method finds overlapping regions using camera locations, which eliminate unfocussed regions from the input images. The sharpness for the overlapped regions is estimated to find the Dominant Overlapping Region (DOR). The proposed model partitions further the DOR into sub-DORs according to capacity of the cameras. To reduce noise effects from the sub-DOR, we propose to perform a Median operation, which results in a Compressed Significant Region (CSR). For non-DOR, we obtain Sobel edges, which reduces the size of the images down to ambinary form. The CSR and Sobel edges of the non-DORs are sent by a VSN. Experimental results and a comparative study with the state-of-the-art methods shows that the proposed model outperforms the existing methods in terms of quality, energy consumption and network lifetime

Hard sphere fluids confined between soft repulsive walls: A comparative study using Monte Carlo and density functional methods

Hard-sphere fluids confined between parallel plates a distance $D$ apart are studied for a wide range of packing fractions, including also the onset of crystallization, applying Monte Carlo simulation techniques and density functional theory. The walls repel the hard spheres (of diameter $\sigma$) with a Weeks-Chandler-Andersen (WCA) potential $V_{WCA}(z) = 4 \epsilon [(\sigma_w/z)^{12}-(\sigma_w/z)^6 + 1/4]$, with range $\sigma_w = \sigma/2$. We vary the strength $\epsilon$ over a wide range and the case of simple hard walls is also treated for comparison. By the variation of $\epsilon$ one can change both the surface excess packing fraction and the wall-fluid $(\gamma_{wf})$ and wall-crystal $(\gamma_{wc})$ surface free energies. Several different methods to extract $\gamma_{wf}$ and $\gamma_{wc}$ from Monte Carlo (MC) simulations are implemented, and their accuracy and efficiency is comparatively discussed. The density functional theory (DFT) using Fundamental Measure functionals is found to be quantitatively accurate over a wide range of packing fractions; small deviations between DFT and MC near the fluid to crystal transition need to be studied further. Our results on density profiles near soft walls could be useful to interpret corresponding experiments with suitable colloidal dispersions.Comment: 23 pages, 7 ps, eps figure

Development and analysis of the Soil Water Infiltration Global database

In this paper, we present and analyze a novel global database of soil infiltration measurements, the Soil Water Infiltration Global (SWIG) database. In total, 5023 infiltration curves were collected across all continents in the SWIG database. These data were either provided and quality checked by the scientists who performed the experiments or they were digitized from published articles. Data from 54 different countries were included in the database with major contributions from Iran, China, and the USA. In addition to its extensive geographical coverage, the collected infiltration curves cover research from 1976 to late 2017. Basic information on measurement location and method, soil properties, and land use was gathered along with the infiltration data, making the database valuable for the development of pedotransfer functions (PTFs) for estimating soil hydraulic properties, for the evaluation of infiltration measurement methods, and for developing and validating infiltration models. Soil textural information (clay, silt, and sand content) is available for 3842 out of 5023 infiltration measurements ( ∼ 76%) covering nearly all soil USDA textural classes except for the sandy clay and silt classes. Information on land use is available for 76% of the experimental sites with agricultural land use as the dominant type ( ∼ 40%). We are convinced that the SWIG database will allow for a better parameterization of the infiltration process in land surface models and for testing infiltration models. All collected data and related soil characteristics are provided online in *.xlsx and *.csv formats for reference, and we add a disclaimer that the database is for public domain use only and can be copied freely by referencing it. Supplementary data are available at https://doi.org/10.1594/PANGAEA.885492 (Rahmati et al., 2018). Data quality assessment is strongly advised prior to any use of this database. Finally, we would like to encourage scientists to extend and update the SWIG database by uploading new data to it

Kolloidale harte Kugeln und ihre Grenzflächen in Dichtefunktionaltheorie

The research reported in this thesis addresses necessary equilibrium information for understanding of homogeneous and heterogeneous nucleation in the hard sphere system. Colloidal hard spheres are an intensely studied model system for addressing the nucleation problem. Understanding nucleation requires a precise knowledge about equilibrium crystal structures and free energies. We use classical density functional theory (DFT) of fundamental measure type (FMT) to evaluate the fully minimized crystal density profiles and their interfaces. Results are compared with simulation data and complemented by a cluster expansion approach due to Stillinger which is based on expanding the crystal partition function in terms of the number n of free particles while the remaining particles are pinned at their ideal lattice positions. Finally, dynamical density functional theory (DDFT) as a time dependent extension of static DFT is implemented. Face-centered cubic (fcc), hexagonally close-packed (hcp) and body-centered cubic (bcc) crystals are investigated using fundamental measure theory and results are complemented by results from Stillinger’s approach. Two branches of solutions have been observed for bcc structure corresponding to different width parameters of the density distribution around lattice sites. The free energy of one branch of bcc agrees well with FMT and Stillinger’s approximation truncated at n = 2. A second branch of the bcc solution features rather spread-out density distributions around lattice sites and a large equilibrium vacancy concentration and it is presumably linked to the shear instability of the bcc phase. Within fundamental measure theory and Stillinger approach (n = 2), hcp is more stable than fcc by a free energy per particle of about 10^-3 k_BT. In previous simulation work, the reverse situation has been found which can be rationalized in terms of an effect due to correlated motion of at least 5 particles in the Stillinger picture. At a hard, flat and unstructured substrate, the crystalline phase completely wets the substrate when the fluid density approaches the freezing point. The formed crystal is oriented with close-packed planes parallel to the substrate. Heterogeneous nucleation for the hard sphere fluid at unstructured hard walls has not been found neither in simulation methods nor in DFT approaches. In collaboration with a simulation group, the hard sphere fluid confined between parallel soft plated is studied in search of a variable nonzero contact angle which could allow studying heterogeneous nucleation. The Week-Chandler Andersen (WCA) potential is used as a wall potential with variable wall strength. Two variants of FMT are implemented to evaluate the density distributions and surface tensions of the hard sphere fluid at the wall with different strengths. DFT is found to be quantitatively very accurate over a wide range of packing fraction in comparison with Monte Carlo simulation. For the surface tension, only small deviations between DFT and MC near the fluid-crystal transition are observed. Finally, dynamical density functional theory (DDFT) is implemented for equilibrating the fcc hard sphere crystal and the crystal-liquid interface density profile. DDFT results for fcc are in an excellent agreement with DFT and simulation data. For the crystal-liquid interface tension there is about 4% discrepancy between DDFT and direct minimizations of DFT. This difference is due to the stiffness of the DDFT equation which does not allow us to fully equilibrate the interface density profile.Diese Arbeit addressiert Informationen über das thermische Gleichgewicht in Hartkugelsystemen, die für das Verständnis von homogener und heterogener Keimbildung notwendig sind. Kolloidale harte Kugeln sind ein oft untersuchtes Modellsystem für die Frage der Keimbildung. Das Verständnis der Keimbildung erfordert präzises Wissen der Kristallstrukturen im Gleichgewicht und deren freie Energien. In dieser Arbeit wird klassische Dichtefunktionaltheorie (DFT) in der Form der Fundamentalmaßtheorie (FMT) benutzt, um Dichteprofile im Kristall und an der Grenzfläche durch volle Minimierung zu bestimmen. Die erhaltenen Resultate werden mit Simulationsdaten verglichen und mit Resultaten aus einem Clusterentwicklungszugang nach Stillinger ergänzt. Dieser basiert auf einer Entwicklung der Zustandssumme des Kristalls in der Zahl n von freien Teilchen, während die anderen Teilchen an ihren idealen Gitterpositionen fixiert bleiben. Abschließend wird eine Implementierung von dynamischer Dichtefunktionaltheorie als eine zeitabhängige Erweiterung von DFT diskutiert. Kubisch-flächenzentrierte (fcc), hexagonal-dichtgepackte (hcp) und kubisch-raumzentrierte (bcc) Kristalle werden mit FMT untersucht und mit Resultaten aus Stillingers Zugang ergänzt. Für bcc wurden zwei Lösungszweige gefunden mit entsprechend unterschiedlichen Breiten der Dichteverteilung um einen Gitterplatz. Die freie Energie eines Zweigs stimmt gut mit dem Resultat aus dem Stillinger-Zugang für n=2 überein. Der zweite Lösungszweig zeigt eine verhältnismäßig breite Dichteverteilung um einen Gitterplatz, eine relativ große Leerstellendichte und hat vermutlich eine enge Beziehung mit der bekannten Scherinstabilität der bcc-Phase. Weiterhin ist in FMT und dem Stillinger Zugang (n=2) hcp stabiler als fcc um eine freie Energie pro Teilchen von etwa 10^-3 k_BT. In Simulationen wurde die umgekehrte Situation gefunden, dies kann innerhalb des Stillinger-Zugangs mit der korrellierten Bewegung von mindestens 5 Teilchen erklärt werden. Für Anlagerung an einem harten, flachen und unstrukturierten Substrat ist bekannt, dass die kristalline Phase das Substrat vollständig benetzt, wenn die Dichte der Flüssigkeit der Koexistenzdichte zustrebt. Heterogene Keimbildung im Hartkugel-Fluid an glatten harten Wänden wurde weder in Simulationen oder DFT-Studien gefunden. In Zusammenarbeit mit einer Simulationsgruppe wurde das Hartkugel-Fluid zwischen parallelen weichen Wänden in Hinsicht auf einen von Null verschiedenen Kontaktwinkel untersucht. Dieser würde die Untersuchung von heterogener Keimbildung zulassen. Hierbei wurde das Weeks-Chandler-Anderson-(WCA-)Potential mit variabler Stärke benutzt. Dichteverteilungen an den Wänden und Grenzflächenspannungen wurden mit zwei verschiedenen FMT Funktionalen berechnet. Die DFT-Resultate stimmen quantitativ sehr gut mit Monte-Carlo-Resultaten in einem großen Dichtebereich überein. Für die Oberflächenspannung wurden nur kleine Abweichungen in der Nähe des Flüssig-Kristall-Übergangs gefunden. Abschießend wird eine Implementierung von DDFT für die Equilibrierung von fcc-Kristall- und Grenzflächendichteprofilen diskutiert. Die DDFT-Resultate für fcc stimmen gut mit denen aus DFT und Simulationen gewonnenen überein. Für die Grenzflächenspannung ist eine eta vierprozentige Differenz zwischen DDFT und direkter Minimierung von DFT zu sehen. Diese Differenz ist eine Folge der Steifheit der DDFT-Gleichung, die es nicht erlaubte, das Grenzflächenprofil vollständig zu equilibrieren

Saliency-based bit plane detection for network applications

Transmitting image data without losing significant information is challenging for any network application especially when large color images are transmitted through TCP communication protocol. This is due to network limitations such as buffer overflow, underflow and network traffic flow etc. This paper presents a new method for image size reduction such that the network can transmit data without much loss of information, and hence, quality. The proposed method obtains bit planes for the color input images, which results in eight binary planes. Unlike the existing bit plane based image size reduction methods, which assume that the most significant plane or some other planes contain useful information, the proposed method finds the plane that contains dominant information automatically. For each plane, the proposed method explores the saliency that finds dominant information based on Markov Chain Process and similarity estimation between neighbor pixels. To reduce computational burden, we use Canny edge maps of the saliency of the planes for feature extraction. We propose to explore ring-growing concept for the edge maps to study the spatial distribution of saliency, locally. The proposed method detects the plane based on statistics of saliency distribution. To validate the step of plane detection, we estimate transmission error caused during data transmission through TCP communication protocol for the images at sending and receiving ends. Experimental results on plane detection show that the proposed method is better than the existing methods in terms of detection rate. Our experiments on image transmission through TCP communication protocol show that the proposed method outperforms the existing methods in terms of error estimation and quality analysis. Furthermore, experiments are conducted to analyze packet loss in terms of number of duplicate acknowledgements and retransmission during packets transmission for the color, edge and plane to show that transmitting plane images improves network performance in terms of less number of duplicate acknowledgement, retransmission and time taken in seconds

A scene image classification technique for a ubiquitous visual surveillance system

The concept of smart cities has quickly evolved to improve the quality of life and provide public safety. Smart cities mitigate harmful environmental impacts and offences and bring energy-efficiency, cost saving and mechanisms for better use of resources based on ubiquitous monitoring systems. However, existing visual ubiquitous monitoring systems have only been developed for a specific purpose. As a result, they cannot be used for different scenarios. To overcome this challenge, this paper presents a new ubiquitous visual surveillance mechanism based on classification of scene images. The proposed mechanism supports different applications including Soil, Flood, Air, Plant growth and Garbage monitoring. To classify the scene images of the monitoring systems, we introduce a new technique, which combines edge strength and sharpness to detect focused edge components for Canny and Sobel edges of the input images. For each focused edge component, a patch that merges nearest neighbor components in Canny and Sobel edge images is defined. For each patch, the contribution of the pixels in a cluster given by k-means clustering on edge strength and sharpness is estimated in terms of the percentage of pixels. The same percentage values are considered as a feature vector for classification with the help of a Support Vector Machine (SVM) classifier. Experimental results show that the proposed technique outperforms the state-of-the-art scene categorization methods. Our experimental results demonstrate that the SVM classifier performs better than rule and template-based methods. © 2018, Springer Science+Business Media, LLC, part of Springer Nature