scholarly journals Modelling desert dune fields based on discrete dynamics

2002 ◽  
Vol 7 (1) ◽  
pp. 7-17 ◽  
Author(s):  
Steven R. Bishop ◽  
Hiroshi Momiji ◽  
Ricardo Carretero-González ◽  
Andrew Warren
Keyword(s):  
Spatial Patterns ◽  
Lattice Dynamics ◽  
Sand Dunes ◽  
Mathematical Formulation ◽  
Discrete Dynamics ◽  
Physical Processes ◽  
Dune Field ◽  
Proposed Model ◽  
Dune Migration ◽  
Physical Features

A mathematical formulation is developed to model the dynamics of sand dunes. The physical processes display strong non-linearity that has been taken into account in the model. When assessing the success of such a model in capturing physical features we monitor morphology, dune growth, dune migration and spatial patterns within a dune field. Following recent advances, the proposed model is based on a discrete lattice dynamics approach with new features taken into account which reflect physically observed mechanisms.

The Marine Environment

2017 ◽  
Author(s):  
N. Penny Holliday ◽  
Stephanie Henson
Keyword(s):  
Primary Production ◽  
North Atlantic ◽  
Physical Environment ◽  
Seasonal Cycle ◽  
Physical Processes ◽  
The North ◽  
Basin Scale ◽  
The North Atlantic ◽  
Physical Features ◽  
Growth Distribution

The growth, distribution, and variability of phytoplankton populations in the North Atlantic are primarily controlled by the physical environment. This chapter provides an overview of the regional circulation of the North Atlantic, and an introduction to the key physical features and processes that affect ecosystems, and especially plankton, via the availability of light and nutrients. There is a natural seasonal cycle in primary production driven by physical processes that determine the light and nutrient levels, but the pattern has strong regional variations. The variations are determined by persistent features on the basin scale (e.g. the main currents and mixed layer regimes of the subtropical and subpolar gyres), as well as transient mesoscale features such as eddies and meanders of fronts.

scholarly journals The Sources of Moisture in the Sand Dunes – The Example of the Western Sahara Dune Field

2014 ◽  
Vol 33 (3) ◽  
pp. 199-204 ◽  
Author(s):  
Elwira Żmudzka ◽  
Dariusz Woronko ◽  
Maciej Dłużewski
Keyword(s):  
Surface Layer ◽  
Moisture Content ◽  
Wind Velocity ◽  
Sand Dune ◽  
Sand Dunes ◽  
Shear Velocity ◽  
Meteorological Conditions ◽  
Aeolian Transport ◽  
Western Sahara ◽  
Dune Field

Abstract Climatic and meteorological conditions may limit the aeolian transport within barchans. An explanation of that issue was the main goal of the investigation held in Western Sahara dune fields located around Tarfaya and Laâyoune. Particular attention was paid to the factors causing the moisture content rising of the sand dune surface layer, which could influence the wind threshold shear velocity in the aeolian transport. The wetted surface layer of sand, when receiving moisture from precipitation or suspensions, reduces the aeolian transport, even in case of wind velocity above 4-5 m s-1. Fog and dew condensation does not affect the moisture of deeper sand layers, what occurs after rainfall.

Charged gravastars in f(R,T,RμνTμν) gravity

2021 ◽  
pp. 2150084
Author(s):  
Z. Yousaf ◽  
M. Z. Bhatti
Keyword(s):  
Perfect Fluid ◽  
Energy Momentum Tensor ◽  
Equations Of State ◽  
Mathematical Formulation ◽  
Momentum Tensor ◽  
Spherically Symmetric ◽  
De Sitter ◽  
The Stability ◽  
Physical Features ◽  
Modified Theory

We explore the aspects of the electromagnetism on the stability of gravastar in a particular modified theory, i.e. [Formula: see text] where [Formula: see text], [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of energy–momentum tensor. We assume a spherically symmetric static metric coupled comprising of perfect fluid in the presence of electric charge. The purpose of this paper is to extend the results of [S. Ghosh, F. Rahaman, B. K. Guha and S. Ray, Phys. Lett. B 767 (2017) 380.] to highlight the effects of [Formula: see text] gravity in the formation of charged gravastars. We demonstrated the mathematical formulation, utilizing different equations of state, for the three respective regions (i.e. inner, shell, exterior) of the gravastar. We have matched smoothly the interior de Sitter and the exterior Reissner–Nordström metric at the hypersurface. At the end we extracted few conclusions by working on the physical features of the charged gravastar, mathematically and graphically.

Better estimation of origin–destination matrix using automated intersection movement count data

2015 ◽  
Vol 42 (7) ◽  
pp. 490-502 ◽  
Author(s):  
Hediye Tuydes-Yaman ◽  
Oruc Altintasi ◽  
Nuri Sendil
Keyword(s):  
Measurement Errors ◽  
Programming Model ◽  
A Priori ◽  
Mathematical Formulation ◽  
A Priori Information ◽  
Matrix Estimation ◽  
Flow Estimation ◽  
Proposed Model ◽  
Priori Information ◽  
Link Count

Intersection movements carry more disaggregate information about origin–destination (O–D) flows than link counts in a traffic network. In this paper, a mathematical formulation is presented for O–D matrix estimation using intersection counts, which is based on an existing linear programming model employing link counts. The proposed model estimates static O–D flows for uncongested networks assuming no a priori information on the O–D matrix. Both models were tested in two hypothetical networks previously used in O–D matrix studies to monitor their performances assuming various numbers of count location and measurement errors. Two new measures were proposed to evaluate the model characteristics of O–D flow estimation using traffic counts. While both link count based and intersection count based models performed with the same success under complete data collection assumption, intersection count based formulation estimated the O–D flows more successfully under decreasing number of observation locations. Also, the results of the 30 measurement error scenarios revealed that it performs more robustly than the link count based one; thus, it better estimates the O–D flows.

Volume Element Model for Modeling, Simulation, and Optimization of Parabolic Trough Solar Collectors

2017 ◽  
Author(s):  
Tugba S. Sensoy ◽  
Sam Yang ◽  
Juan C. Ordonez
Keyword(s):  
Heat Transfer ◽  
Differential Equations ◽  
Mathematical Formulation ◽  
Element Model ◽  
Volume Element ◽  
Heat Transfer Fluid ◽  
Solar Collectors ◽  
Parabolic Trough ◽  
Simulation And Optimization ◽  
Proposed Model

In this paper we present a dynamic three-dimensional volume element model (VEM) of a parabolic trough solar collector (PTC) comprising an outer glass cover, annular space, absorber tube, and heat transfer fluid. The spatial domain in the VEM is discretized with lumped control volumes (i.e., volume elements) in cylindrical coordinates according to the predefined collector geometry; therefore, the spatial dependency of the model is taken into account without the need to solve partial differential equations. The proposed model combines principles of thermodynamics and heat transfer, along with empirical heat transfer correlations, to simplify the modeling and expedite the computations. The resulting system of ordinary differential equations is integrated in time, yielding temperature fields which can be visualized and assessed with scientific visualization tools. In addition to the mathematical formulation, we present the model validation using the experimental data provided in the literature, and conduct two simple case studies to investigate the collector performance as a function of annulus pressure for different gases as well as its dynamic behavior throughout a sunny day. The proposed model also exhibits computational advantages over conventional PTC models-the model has been written in Fortran with parallel computing capabilities. In summary, we elaborate the unique features of the proposed model coupled with enhanced computational characteristics, and demonstrate its suitability for future simulation and optimization of parabolic trough solar collectors.

scholarly journals Development of Desertification Indicators for Desertification Monitoring from Landsat Images Using Python Programming

2022 ◽  
Vol 8 (2) ◽  
pp. 99-114
Author(s):  
Lamyaa Gamal EL-Deen Taha ◽  
Manar A. Basheer ◽  
Amany Morsi Mohamed
Keyword(s):  
Sand Dune ◽  
Sand Dunes ◽  
Landsat Images ◽  
Image Differencing ◽  
Layer Stacking ◽  
Southern Side ◽  
Sand Movement ◽  
Dune Migration ◽  
Desertification Assessment ◽  
Python Programming

Nowadays, desertification is one of the most serious environment socioeconomic issues and sand dune advances are a major threat that causes desertification. Wadi El-Rayan is one of the areas facing severe dune migration. Therefore, it's important to monitor desertification and study sand dune migration in this area. Image differencing for the years 2000 (Landsat ETM+) and 2019 (OLI images) and Bi-temporal layer stacking was performed. It was found that image differencing is a superior method to get changes of the study area compared to the visual method (Bi-temporal layer stacking). This research develops a quantitative technique for desertification assessment by developing indicators using Landsat images. Spatial distribution of the movement of sand dunes using some spectral indices (NDVI, BSI, LDI, and LST) was studied and a Python script was developed to calculate these indices. The results show that NDVI and BSI indices are the best indices in the identification and detection of vegetation. It was found that mobile sand dunes on the southern side of the lower Wadi El-Rayan Lake caused filling up of large part of the lower lake. The indices results show that sand movement decreased the size of the lower Wadi El-Rayan Lake and there are reclamation activities in the west of the lower lake. The results show that a good result could be achieved from the developed codes compared to ready-made software (ENVI 5).

scholarly journals Geomorphological characteristics of the sand-dune field of the central Kyparissiakos Gulf

2007 ◽  
Vol 40 (4) ◽  
pp. 1530 ◽  
Author(s):  
Th. Karamousalis ◽  
S. Poulos ◽  
H. Maroukian ◽  
G. Ghionis
Keyword(s):  
Sand Dune ◽  
Sand Dunes ◽  
Fine Sand ◽  
Middle Part ◽  
Alluvial Fan ◽  
Last Glacial Period ◽  
Dune Field ◽  
Natural Processes ◽  
Dune Ridge ◽  
The Last Glacial

Sand dunes are sensitive coastal landforms closely related to the evolution (and/or stability) of the beach zone. The present work refers to the central part of the dune field that lies along the middle part of the shoreline of the Kyparissiakos Gulf. The scope of the present investigation is to reveal the geomorphological and sedimentological characteristics of the sand dune field in association with the natural processes contributing to their formation. On the basis of our findings, the dune field of the central Kyparissiakos Gulf consists of four dune ridges, with heights >4.0 m. Their extent indicates the availability of large quantities of sand and the existence of a rather stable wind field. They consist of well sorted medium to fine sand. The alluvial fan of the Zachareiko torrential river has covered the dune field in the area of its mouth and buried the oldest 4th dune ridge to its south. The development of the dune field is estimated to have taken place during the last 3-4 thousand years subsequently to the completion of the rapid sea level rise at the end of the last glacial period.

scholarly journals Complex Network of Scientific Talent Migration in Discrete Dynamics from 2001 to 2013

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Yinqiu Wang ◽  
Hui Luo ◽  
Yunyan Shi
Keyword(s):  
Complex Network ◽  
Great Majority ◽  
Developed Countries ◽  
Discrete Dynamics ◽  
Unknown Parameters ◽  
Job Opportunities ◽  
Proposed Model ◽  
The Usa ◽  
Scientific Talent ◽  
Migration Network

Scientific talents can make great contributions, including scientific breakthrough innovations and discoveries, and coordinate and guide the actions of many others, propelling the scientific knowledge frontier. We investigate international scientific talent migration from 2001 to 2013 with the quantitative method. The relationship between complex network and international talent migration is introduced. Considering most of talents migrate between some countries with good economy and innovation, the migration network including 37 countries is analysed. The countries are noted by nodes of the migration network, and the migratory flow of talents from one country to another country is viewed as the directed weight edge between the corresponding nodes. The discrete dynamics of talent migration under complex network is proposed. The unknown parameters of the proposed model are identified. The overall situation and time evolution of international talent migration from 2001 to 2013 are given from the discussion on the indicators of complex network. Furthermore, we study the talent migration flows in the view of obstacle factors. It is found that the great majority of talents migrate between developed countries and emerging economies from 2001 to 2013, and this phenomenon becomes more significant. The USA has attracted a great number of talents all over the world, and the country is also the ideal destination for talents who want to live or work in another country for more job opportunities, attractive payment, and better innovation environment. China and India begin to attract talents. Talents emigrate from more and more original countries. It becomes more convenient for talents to immigrate to other countries. The effectiveness of obstructs to migration has become weakening. For immigrating to a certain country, the obstacles have a relationship with the country’s innovation.

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