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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
431

Stavební průzkum a hodnocení stavu konstrukce / Building survey and evaluating the state of construction

Kolláriková, Simona January 2021 (has links)
The diploma thesis deals with building survey of the New synagogue in Velké Meziříčí. It is focused on diagnostics of timber structures using non-destructive and semi-destructive testing methods, such as visual inspection, moisture content measurement, penetration depth of a steel pin measurement and endoscopy. The aim of the thesis is to evaluate the condition of the timber structures according to the results of the building survey.
432

Hygrotermálna odozva stavebných konštrukcií / Hygrothermal response of building components

Slávik, Richard January 2019 (has links)
This dissertation thesis is focused on the study of simultaneous transport of heat and moisture in building components. First, the introduction briefly summarises current international state of the art in assessment and evaluation of building components focused on moisture. Besides description of methodological approaches and analysis of differences between them, the approaches are modelled using examples which help to identify their properties and explain the application framework of the methods. These examples do not only illustrate the procedures; they also indicate their limits and identify the pitfalls of models’ application in comparison with each other. Next, the thesis includes basic introduction to material parameters necessary in numerical modelling. Moreover, solutions to questions from the assignment are discussed from the point of view of the theory of heat and moisture transport. To fulfil the thesis’ objectives, theoretical analysis and calculations were implemented. Calculations were carried out not only by well-known methods, but also using an own-developed complex algorithm which implements simultaneous heat and moisture transport modelling based on finite element methods and which allows to implement nonlinear behaviour of material properties. Furthermore, the thesis contains description of and results from two experiments. A brief description of an electronic device developed and used for the experiments is included. Experimental results are confronted with both simplified and advanced theoretical models. At last the thesis concludes with discussion of acquired findings, brief summary of potential contribution of this work to the field of building science and engineering practice, and indication of the directions for further development.
433

Unmanned ground vehicle system to collect soil moisture data

Flynt, Austin Edward 10 December 2021 (has links) (PDF)
With an increased interest in precision agriculture, it is important to identify efficient ways to monitor soil moisture. Soil moisture can be monitored using handheld sensors, but this method is laborious and time consuming. Remote methods, such as radar systems can be used as well, but these methods require ground truth data to verify their accuracy. It becomes clear that to collect this data regularly and reliably, a mobile robotic device is necessary. This thesis proposes to implement mobile robot take soil moisture measurements with less human effort than existing methods while maintaining the same accuracy. This soil moisture data collection system uses an unmanned ground vehicle (UGV) to take measurements with position data. This system uses an actuator inserted soil moisture probe, and a radio frequency identification (RFID) sensing system that uses buried moisture sensing tags. Field testing of both measurement systems showed that the actuator-based system worked reliably.
434

Evaluation of the ERA5-Land dataset for estimation of soil moisture in the permafrost region

van Gent, Alberta January 2023 (has links)
The permafrost region covers a vast area of land surface on the northern hemisphere,storing large amounts of carbon. Unfortunately, climate warming leads to permafrostthaw altering the hydrothermal state of permafrost soils. Due to the remoteness of thepermafrost region, access to field measurements is restricted. Therefore, remotesensing is an asset to study the permafrost region. Since permafrost is a sub-surfacephenomenon it cannot be directly observed from space. However, by using differenttypes of satellites the soil properties of the top soil layer, down to 10 cm depth, can beaccessed. To establish soil properties for the deeper soil layers modelling is required.The ERA5-Land (ERA5L) soil moisture is modelled based on climate reanalysis. Inthis study in-situ soil moisture data from the International Soil Moisture Network(ISMN) is used to evaluate the performance of the ERA5L soil moisture data withinthe permafrost region. The performance of the ERA5L soil moisture is found toperform best in soil layer 1 (0-7 cm depth) and worst in soil layer 3 (28-100 cm depth).For both soil layer 1 and 2 (0-7 and 7-28 cm depth) a moderate correlation(0.309 < R < 0.335) was found between ERA5L and in-situ soil moisture data, in Julyand August. The performance of the ERA5L soil moisture is best in Europe and worstin North-America. Compared to other evaluations of ERA5L soil moisture, within thepermafrost region, this study found a relatively low correlation. Therefore, this studyconcludes that on a global scale the ERA5L soil moisture is not ideal for directlyinforming permafrost research and decision making. However, integrating multisourcedatasets, resampled to a finer spatial resolution, could improve the performance ofERA5L soil moisture model on a global level. Moreover, on a local scale theapplication of a bias correction could also improve the performance of the ERA5L soilmoisture model.
435

Moisture measurements in concrete and characterization using impedance spectroscopy and RC network circuits

Theophanous, Theophanis 08 August 2008 (has links)
The importance of moisture in concrete is unquestionable. However, quantifying the moisture in concrete is very difficult as concrete microstructure water interactions are not well understood. Concrete is a very complex material spanning the range from the atom to the civil infrastructure. It is the medium that controls moisture at the FRP/concrete interface. Concrete is also a composite material at the level of concrete/rebar, aggregate/sand/cement paste and at the hydration product level. Water is vital in concrete microstructure development, properties and concrete durability. A moisture sensor based on the dielectric and resistive properties of cement paste was developed. Impedance spectroscopy techniques are used to explore the moisture behavior in relation to dielectric and resistive properties of the sensors. The sensor capacitive response is frequency dependent and it has been described with a multi-linear curve. Resistance values are related to capacitance through a power Law. Both the capacitance/moisture and capacitance/resistance behaviors were observed in all four cement/sand/aggregate mixtures considered. Although the dielectric constants of water and dry cement paste are not frequency dependent with in the 400 kHz and 10 MHz frequencies considered, the effective dielectric constant of the mixture is frequency dependent Mixing rules cannot predict the effective dielectric constant of the dielectric medium used in the sensors. Impedance analysis indicated also multiple time constants exist within the cement paste. Using the observation from the experimental results in conjunction to the high conductivity of cement pore solution a random R-C network model was developed to explore the impedance behavior of cement paste. / Ph. D.
436

Moisture Content Determination and Temperature Profile Modeling of Flexible Pavement Structures

Diefenderfer, Brian Keith 03 May 2002 (has links)
A majority of the primary roadways in the United States are constructed using hot-mix asphalt (HMA) placed over a granular base material. The strength of this pavement system is strongly influenced by the local environmental conditions. Excessive moisture in a granular base layer can cause that layer to lose its structural contribution by reducing the area over which loading may be distributed. Excessive moisture and fine particles can be transported by hydrostatic pressure to the surface layers, thus reducing the strength of the overlying HMA by contamination. Moisture in the surface HMA layers can cause deterioration through stripping and raveling. In addition, as HMA is a viscoelastic material, it behaves more as a viscous fluid at high temperatures and as an elastic solid at low temperatures. Between these two temperature extremes, a combination of these properties is evident. Thus, understanding the environmental effects on flexible pavements allows better prediction of pavement performance and behavior under different environmental conditions. As part of the ongoing pavement research at the Virginia Smart Road, instrumentation was embedded during construction to monitor pavement response to loading and environment; moisture content of the granular base layers and temperature of the HMA layers were among the responses monitored. The Virginia Smart Road, constructed in Blacksburg, Virginia, is a pavement test facility is approximately 2.5km in length, of which 1.3km is flexible pavement that is divided into 12 sections of approximately 100m each. Each flexible pavement section is comprised of a multi-layer pavement system and possesses a unique structural configuration. The moisture content of aggregate subbase layers was measured utilizing two types of Time-Domain Reflectometry (TDR) probes that differed in their mode of operation. The temperature profile of the pavement was measured using thermocouples. Data for the moisture content determination was collected and results from two probe types were evaluated. In addition, the differences in the moisture content within the aggregate subbase layer due to pavement structural configuration and presence of a moisture barrier were investigated. It was shown that the two TDR probe types gave similar results following a calibration procedure. In addition to effects due to pavement structure and subgrade type, the presence of a moisture barrier appeared to reduce the variability in the moisture content caused by precipitation. Temperature profile data was collected on a continuous basis for the purpose of developing a pavement temperature prediction model. A linear relationship was observed between the temperature given by a thermocouple near the ground surface and the pavement temperature at various depths. Following this, multiple-linear regression models were developed to predict the daily maximum or minimum pavement temperature in the HMA layers regardless of binder type or nominal maximum particle size. In addition, the measured ambient temperature and calculated received daily solar radiation were incorporated into an additional set of models to predict daily pavement temperatures at any location. The predicted temperatures from all developed models were found to be in agreement with in-situ measured temperatures. / Ph. D.
437

The influence of low moisture stress on the gas exchange and thylakoid activity of loblolly pine (pinus taeda) and aleppo pine (pinus halepensis)

Doulis, Andreas G. 08 April 2009 (has links)
The objectives of this study were to determine the influence of sublethal water stress on the physiology of loblolly and Aleppo pine. Gas exchange characteristics, uncoupled thylakoid electron transport capacity, and needle osmotic potentials were measured. Seedlings of both species were watered only when their needle water potential fell below -1.8 and -2.2 MPa respectively (water stress conditioning) or were kept well watered (controls). After 10 weeks of water stress conditioning, both regimes were allowed to dry down. During this period of increasing water stress, photosynthesis in both species was determined at 5 different cuvette CO₂ concentrations (approximately 200, 330, 500, 650, and 800 ppm). With Aleppo pine only, mesophyll resistances and stomatal limitations to gas exchange were estimated. Thylakoids were extracted from both species and their activity was measured in a liquid phase O₂ electrode (Hansatech L<sup>td</sup>) as rate of O₂ consumption. Methyl Viologen (1,1’ -dimethyl -4, 4’- bipyridinium ion ) was included in the reaction medium. Photosynthesis decreased with increasing water stress but fell more slowly in the conditioned seedlings. As water stress increased, total resistance to CO₂ exchange increased for both regimes to a much higher level than explained by stomatal resistance alone. In the conditioned seedlings, resistances increased less precipitously than in controls. Osmotic adjustment as measured with thermocouple psychrometers occurred in both species. Decreases in photosynthesis (both species) and increases in mesophyll resistance (Aleppo pine) were not accompanied by a decrease in whole chain uncoupled electron transport capacity. / Master of Science
438

The effect of moisture gradients on the stiffness and strength of yellow-poplar

Conners, Terrance E. January 1985 (has links)
Wood with a uniform moisture distribution is known to have different mechanical properties compared to wood with a non-uniform moisture distribution. Moisture gradients are likely to develop in full-size members tested in the In-Grade Testing Program and might therefore affect the test results. The purpose of this study was to mathematically model the effect of desorption moisture gradients on the stiffness and strength of yellow-poplar beams. An additional objective was to experimentally determine gradient effects in yellow-poplar beams. Three-dimensional finite-element modeling was employed and several subsidiary models were developed. Among these was a three-parameter segmented model for fitting digitized tension and compression stress-strain curves. Unlike previous models (such as the Ramberg-Osgood model), this model has a linear slope up to the point approximately corresponding to the proportional limit. A methodology was also devised whereby most hardwood and softwood elastic constants can be estimated at any moisture content. Data are required at one moisture content. Equilibrated uniaxial testing was conducted at four moisture contents to acquire data for the finite-element model. It was found that the longitudinal Young's moduli in tension and compression were approximately equal at 6% and 18% moisture content; the compression modulus was greater at 12%, but the tension modulus was greater for green specimens. Intersection points for tension and compression mechanical properties may be different. Tests of small clear yellow-poplar beams indicated that moisture gradients induced at 12% equilibrium moisture content had little effect on the modulus of rupture up to 19% average moisture content. At higher moisture contents, gradient-containing beams were significantly stronger than equilibrated beams when comparisons were made at identical moisture contents. Modulus of elasticity data exhibited a similar trend, although differences between equilibrated and non-equilibrated beams were observed below 19% moisture content. The finite-element program was moderately successful in predicting the effects of moisture gradients on the strength and stiffness of yellow-poplar beams. Computer time and storage constraints limited the accuracy of the solutions. Predicted trends were verified by the experimental data. Modeling of full-size lumber indicated that significant moisture gradients will likely influence the stiffness and strength of higher quality lumber. / Ph. D.
439

Deep learning based soil moisture retrieval using GNSS-R observations from CYGNSS

Nabi, M M 10 May 2024 (has links) (PDF)
The National Aeronautics and Space Administration’s (NASA) Cyclone Global Navigation Satellite System (CYGNSS) mission has grown substantial attention within the land remote sensing community for estimating soil moisture (SM), wind speed, flood extent, and precipitation by using the Global Navigation Satellite System-Reflectometry (GNSS-R) technique. CYGNSS constellation generates important earth surface information called Delay-Doppler Maps (DDMs) from GNSS reflection measurements. Many previous findings considered only designed features from CYGNSS DDMs, such as the peak value of DDMs, whereas the whole DDMs are affected by SM, topography, inundation, and overlying vegetation. This dissertation explores a deep learning approach for estimating SM by leveraging spaceborne GNSS-RDDM observations provided by the CYGNSS constellation along with other remotely sensed geophysical data products. A data-driven approach utilizing convolutional neural networks (CNNs) that is trained jointly with three types of processed DDMs of Analog Power, Effective scattering area, and Bistatic Radar Cross-section (BRCS) with other auxiliary geophysical information such as normalized difference vegetation index (NDVI), elevation, soil properties, and vegetation water content (VWC). The model is trained and evaluated using the Soil Moisture Active Passive (SMAP) mission’s enhanced SM products at a 9km × 9km resolution. The model is also evaluated using in-situ measurements from International Soil Moisture Network (ISMN). The proposed approach is first explored in the Continental United States (CONUS) and then extended for global SM retrieval. The most challenging validation efforts show potential improvement for future spaceborne SM products with high spatial and temporal resolution. In addition, several SM fusion algorithms have been explored in order to combine several CYGNSS-based SM products. The fusion algorithm can help to achieve better estimation performance compared to individual products and keep the properties of individual products.
440

Developments in silicone technology for use in stoma care

Swift, Thomas, Westgate, Gillian E., Van Onselen, J., Lee, S. 15 June 2020 (has links)
Yes / Soft silicone's flexibility, adhesive capacity and non-toxic, non-odourous and hypoallergenic nature have made it an established material for adhesive and protective therapeutic devices. In wound care, silicone is a component of contact layer dressings for superficial wounds and silicone gel sheeting for reducing the risk of scarring, as well as of barriers for incontinence-associated dermatitis. Regarding stoma accessories, silicone is established in barrier films to prevent contact dermatitis, adhesive removers to prevent skin stripping and filler gels to prevent appliance leaks. Until recently, silicone has not been used in stoma appliances flanges, as its hydrophobic nature has not allowed for moisture management to permit trans-epidermal water loss and prevent maceration. Traditional hydrocolloid appliances manage moisture by absorbing water, but this can lead to saturation and moisture-associated skin damage (MASD), as well as increased adhesion and resultant skin tears on removal, known as medical adhesive-related skin injury (MARSI). However, novel silicone compounds have been developed with a distinct evaporation-based mechanism of moisture management. This uses colloidal separation to allow the passage of water vapour at a rate equivalent to normal trans-epidermal water loss. It has been shown to minimise MASD, increase wear time and permit atraumatic removal without the use of adhesive solvents. Trio Healthcare has introduced this technology with a range of silicone-based flange extenders and is working with the University of Bradford Centre for Skin Sciences on prototype silicone-based stoma appliance flanges designed to significantly reduce the incidence of peristomal skin complications, such as MARSI and MASD. It is hoped that this will also increase appliance wear time, reduce costs and improve patient quality of life.

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