1,721,070 research outputs found
GeoRadar
No full textIl georadar è una tecnica di prospezione geofisica del suolo non distruttiva, che consiste nella misurazione di alcune proprietà fisiche che possono rivelarne la struttura, la presenza di oggetti sepolti o di varie stratificazioni. La misura si basa sulla generazione di impulsi elettromagnetici che prima vengono diretti e poi riflessi dal suolo. Il segnale riflesso viene ricevuto da un'antenna e quindi interpretato tramite un software che analizza le specifiche caratteristiche del suolo stesso.
Il presente capitolo descrive i principi fisici sui quali si basa la misura,
le caratteristiche degli strumenti utilizzati, i metodi di analisi e interpretazione dei dati. Sono anche presentati alcuni casi studio di applicazione del Georadar
Can molecular dynamics help in understanding dielectric phenomena?
No full textMolecular dynamics (MD) is a modeling technique widely used in material science as well as in chemical physics, biochemistry and biophysics. MD is based on 'first principles', allowing one to compute the physical characteristics of a material, such as density, heat capacity, isothermal compressibility and also the dielectric constant and relaxation, mixing a classical physics approach and statistical mechanics. Although a number of papers exist in the literature concerning the study of the dielectric properties of liquid and solid materials, the MD approach appears to be almost ignored in the electromagnetic aquametry community. We use a rather simple example, a mixture of ethanol and water at various concentrations, to introduce MD as a theoretical tool for investigating the dielectric behavior of more complex moist substances. We show that MD simulations suggest a time-domain model for alcohol-water solutions, consisting in a mixture of a KWW stretched-exponential and a simple exponential, whose validity could be subjected to an experimental verification
Dielectric data analysis: Recovering hidden relaxations by fourth-order derivative spectroscopy
No full textComplex materials exhibit a dielectric behavior that can shed light on their chemophysical structure through a comprehension of the physical mechanisms originating that behavior. For the interpretation of a complex dielectric shape, where multiple relaxations are present (and usually described by semi-empirical functions), a correct interpretation of each simple relaxation is necessary. The separation of often closely overlapped relaxation curves requires the verification of the meaningfulness of such multiple relaxations and to determine their number and relative magnitudes, in other words to resort to a fitting procedure. However, often the physical interpretation of the fitting parameters is not straightforward, and their physical meaning is arguable. The application of even-order derivative spectroscopy is here demonstrated to be able to detect the presence and location of multiple dielectric relaxations, acting on the experimental data without any "a priori" hypothesis
Assessing River Embankment Stability Under Transient Seepage Conditions
No full textAbstractThe evaluation of riverbank stability is a fundamental problem in flood risk management, representing a critical task for engineering practice. Soil heterogeneity together with initial and boundary conditions are among the crucial issues that should be considered to obtain an accurate solution of the problem. Generally, attention and efforts are mostly devoted to the soil characterization, the hydrometric level forecasts and the estimation of the rainfall intensity, while in situ measurements usually receive less attention. Nevertheless, suction and soil water content have a strong influence on the reliability of seepage and stability analyses. A preliminary study aiming at the design of a monitoring system for the measurement of soil moisture and suction in the unsaturated silty soils of a river embankment has been carried out, with the purpose of linking the collected data to the boundary conditions and hence obtaining a more accurate estimate of the riverbank probability of failure. Furthermore, a general outline of the research project, its methodology and application are presented in the paper
Editorial for special section on electromagnetic aquametry
No full textThis special issue of Measurement Science and Technology presents selected contributions from the 11th International Conference on Electromagnetic Wave interaction with Water and Moist Substances (ISEMA) held in Florence, Italy, from 23 to 27 May 2016. The conference was jointly organized by the Institute of Applied Physics of the National Research Council and the Department of Agricultural Sciences of the University of Bologna
Dynamics Solved by the Three-Point Formula: Exact Analytical Results for Rings
No full textIn this paper, we study in the framework of the Gaussian model, the relaxation dynamics, and diffusion process on structures which show a ring-shape geometry. In order to extend the classical connectivity matrix to include interactions between more distant nearest neighbors, we treat the second derivative with respect to position by using the three-point formula. For this new Laplacian matrix, we determine analytical solutions to the eigenvalue problem. The relaxation dynamics is described by the mechanical relaxation moduli and for diffusion we focus on the behavior of the residual concentration at the initial node. Additionally, we investigate the scaling behaviors of the mean squared radius of gyration and of the smallest eigenvalue. To calculate the residual concentration, we consider that initially the whole material is concentrated only in one node and then it spreads over the ring. We compare our results with the ones obtained from the incremental ratio method. We observe that the results of the two methods for the considered quantities are slightly different. At any intermediate time/frequency domain, the results obtained by using the incremental ratio method underestimate the ones obtained by using the three-point formula. This finding can turn important for many applications in polymer systems or in other systems where diffusive motion occurs
Tilmen Höyük: Climate, Soil, Hydrology, and Vegetation
No full textTilmen Höyük is located in the southeastern part of Anatolia, within the so-called
Anatolian corridor. The Amanus mountains to the west of the site form a natural barrier
between the Mediterranean basin and the dry plateaus of inner western Asia. Climate,
soil, and vegetation have been monitored and indexed over a two-year period, both to
analyze the biological and climactic conditions at the site over time, and to begin to formulate a long-term management plan for the conservation of the cultural and natural
heritage
Estimation of thermal instabilities in soils around underground electrical power cables
No full textThe decentralized production of electrical energy from wind requires the installation of more and more underground power cables. From an economic standpoint it is very important to estimate the cables lifetime, which strongly depends on the temperature. A correct estimation of cable temperature requires an accurate description of the heat balance equation around the cable. Most of the models used to assess heat dissipation from cables, however, do not consider that the soil thermal conductivity strongly depends on soil water content and hydraulic dynamics in the vicinity of the cable. The high temperature around the cable induces a water vapor cycle in the soil: liquid water evaporates near the cable, and this vapor condensates in the more distant and colder parts of the soil. Above a critical heat dissipation rate, the soil around the cable dries out and the water vapor cycle breaks down. In this study, we analytically estimated the critical heat dissipation rate as a function of soil type, soil temperature, and water content. We validated the analytical estimation by comparison to a numerical solution of the coupled heat and water vapor transport for various soil types and conditions. The numerical code was validated by simulating a soil drying experiment. The proposed estimation of thermal instabilities in soils could become a powerful tool in the design of underground electrical power cable systems
Numerical simulation of coupled heat, liquid water and water vapor in soils for heat dissipation of underground electrical power cables
No full textThe trend towards renewable energy comes along with a more and more decentralized production of electric energy. As a consequence many countries will have to build hundreds or even thousands of miles of underground transmission lines during the next years. The lifetime of a transmission line system strongly depends on its temperature. Therefore an accurate calculation of the cable temperature is essential for estimating and optimizing the system's lifetime.
The International Electrotechnical Commission and the Institute of Electronics and Electrical Engineers are still employing classic approaches, dating back from the 1950s, that are missing fundamental phenomena involved in heat transport in soils. In recent years several authors [4,37] pointed out that for a proper computation of heat transport in soils, physical processes describing heat, liquid water and vapor transport must be coupled and the respective environmental weather conditions need to be considered.
In this study we present a numerical model of coupled liquid water, vapor and heat flow, to describe heat dissipation from underground cables. At first the model is tested and validated on a downscaled experiment [32], secondly the model is applied on a simplified system to demonstrate the strong relation of the cable temperature on soil water content and finally the model is applied using real weather conditions to demonstrate that small changes in the design of underground transmission line systems can lead to considerable improvements in both average as well as peak-to-peak temperatures
Simulation of root water uptake under consideration of nonequilibrium dynamics in the rhizosphere
No full textThe narrow region of soil around roots, the so-called rhizosphere, defers in its hydraulic properties
from the bulk soil. The rhizosphere hydraulic properties primarily depend on the drying and wetting
rate of mucilage, a polymeric gel exuded by plant roots. Under equilibrium conditions mucilage increases
the water holding capacity. Upon drying mucilage turns hydrophobic and makes the rhizosphere temporarily
water repellent. There are several models of root water uptake, from analytical models of water flow to a
single root to complex numerical models that consider the root architecture. Most of these models, however,
do not account for the specific hydraulic properties of the rhizosphere. Here we describe a single-root
model that includes the altered hydraulic properties of the rhizosphere due to mucilage exudation. We use
the model to reproduce existing experiments reporting unexpected and puzzling hysteresis in the rhizosphere,
which could not be explained under the assumption of homogeneous hydraulic properties. In our
model the hydraulic properties depend on the concentration of mucilage. This enables a continuous transition
from the bulk soil to the root surface. We assumed that: (a) mucilage increases the water holding capacity
in equilibrium conditions, (b) hydrophobicity, swelling and shrinking of mucilage cause a nonequilibrium
relation between water content and water potential and (c) mucilage reduces the mobility of water molecules
in the liquid phase resulting in a lower hydraulic conductivity at a given water content. Our model
reproduces well the experiments and suggests that mucilage softens drought stress in plants during severe
drying events
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