269 research outputs found
Challenges in Numerical Modelling of Screw Piles Installation and Vertical Loading Based on Centrifuge Testing
No full textpeer reviewe
In-Situ Determination of Buildings’ Thermo-Physical Characteristics
No full textAccurate determination of building’s critical thermo-physical characteristics such as the walls’ thermal resistance, thermal conductivity, and volumetric heat capacity is essential to indicate effective and efficient energy conservation strategies at building level. In practice, the values of these parameters, which determine not only possible energy savings, but also related costs, are rarely available because the current determination methods are time-and-effort-expensive, and consequently seldom used.This thesis combines theories, simulations, computations, and experiments to develop and improve methods and approaches for determination of a number of buildings’ most important thermophysical characteristics. First, a modification to the existing standard method, “ISO 9869 Average Method” is proposed to measure the walls’ thermal resistance. Two current problems are solved: long measurement duration (weeks) and imprecision. To further shorten the measurement period to a few hours, a new transient in-situ method, Excitation Pulse Method, EPM (Patent No. 2014467), is then developed and tested. This method allows the determination of the walls’ response factors which can be applied directly in dynamic models. More importantly, it is used to extract critical construction information including walls’ thermal resistance, thermal conductivity, volumetric heat capacity, and the possible layer composition. Finally, in an attempt to reduce the hassle, cost, and intrusion associated with locally-conducted experiments, the use of data from smart meters and home automation systems is explored. Building’s global characteristics including heat loss coefficient, global heat capacitance and daily air change rates are accordingly determined.A+BE I Architecture and the Built Environment No 7 (2020)Building Energy Epidemiolog
Quicker measurement of walls' thermal resistance following an extension to ISO 9869 average method
No full textDetermination of the thermo-physical characteristics of the buildings' components is crucial to illustrate their thermal behavior and therefore their energy consumption. Along the same line, accurate determination of the thermal resistance of the building walls falls into one the most important targets. Following the difference between in-lab, and on site thermal performance of walls, in-situ measurements have been highly recommended. The most well-known practice for in-situ measurement of walls' thermal resistance is the Average Method of ISO 9869, using one heat flux meter and two thermocouples. The method, in comparison with other existing methods is quite straight-forward and therefore, is applied widely in large scale. Despite its simplicity, this method usually needs a relatively long time to reach an acceptable result. The current paper deals with a modification to the ISO 9869 method, making it in many situations much quicker than its original state. Through simulation of walls of different typologies, it is shown in which cases the measurement period becomes longer than expected. It is demonstrated how the addition of a heat flux meter to the aforementioned equipment can lead to a much quicker achievement of the thermal resistance, following the rest of the instructions of the standard method.</p
Properties of the triangular excitation pulse and the 3D heat transfer effects in the excitation pulse method
No full textConcerning the high levels of energy consumption in the existing building stock, the necessity for characterization of the building envelop is a well-known issue. Accordingly, numerous methods and practices have been developed and studied to measure the thermal resistance and other thermal characteristics of the walls in-situ. In the current paper, a previously proposed method, the Excitation Pulse Method, EPM, based on the theory of thermal response factors, is further studied and investigated through simulations, to rapidly measure the thermal resistance of existing walls. A prototype is built and introduced to carry out larger number of measurements on site. The triangular pulse's properties such as the relation between its magnitude and its time interval on its corresponding response are investigated. It is shown how changes in time interval can make the method sensitive to the number of residuals and affect its reliability. General constraints and validity domain of the method are studied. In addition, the effect of 3D heat transfer on the performance of the method is further illustrated in light and heavy constructions. It is shown in which cases it is possible to apply the method in-situ and measure the thermal resistance within a couple of hours.</p
A microstructure-based elastoplastic model to describe the behaviour of a compacted clayey silt in isotropic and triaxial compression
No full textThe paper focuses on the hydro-mechanical behaviour of an unsaturated compacted clayey silt, accounting for fabric changes induced by drying-wetting cycles occurring at low-stress levels. The response along isotropic compression and triaxial compression (shear) at constant water content was investigated by laboratory tests on both as compacted and dried-wetted samples. Compaction induces a micro-structural porosity pertinent to clay peds and a macro-structural porosity external to the peds. Drying-wetting cycles decrease the micro-porosity and increase the macro-porosity, which reduces the water retention capacity, increases the compressibility and promotes higher peak strengths with more brittle behaviour during triaxial compression. A coupled double porosity elastic-plastic model was formulated to simulate the experimental results. A non-associated flow rule was defined for the macrostructure, modifying a stress-dilatancy relationship for saturated granular soils to account for the increase in dilatancy with suction observed in the experiments. The average skeleton stress and suction were adopted as stress variables. Consistently with model predictions, the shear strength at critical state is not significantly influenced by the degree of saturation or by the hydraulic history. On the other contrary, the higher peak strength, brittleness and dilatancy of the dried wetted samples are mostly explained by their reduced water retention capacity
Biomechanical regulation of epigenetics and chromatin organization in single living cells
No full textMechanical forces are known to play a key role in regulating various cellular functions that control human development, cancer, disease, and aging. It, however, remains elusive how mechanical cues regulate biochemical mechanisms in the nucleus that control cellular decision-making. These mechanisms include epigenetic modification, chromatin organization, and gene expression. It is, therefore, highly important to investigate force-induced regulation of these mechanisms to better understand human physiology and disease.
In this research, we aim at answering two key questions: one, how mechanical forces regulate epigenetics in tumor repopulating cells (TRCs), and two, how these forces unfold chromatin and induce gene expression in single living cells.
Our findings suggest that mechanical forces play critical roles in regulating nuclear structure and function. Biomechanical cues can propagate deep inside the nucleus and regulate epigenetics, chromatin organization, and gene expression.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2017-05-01The student, Arash Tajik, accepted the attached license on 2015-04-10 at 15:37.The student, Arash Tajik, submitted this Dissertation for approval on 2015-04-10 at 15:45.This Dissertation was approved for publication on 2015-04-13 at 14:33.DSpace SAF Submission Ingestion Package generated from Vireo submission #7818 on 2015-07-22 at 14:24:21Made available in DSpace on 2015-07-22T22:45:14Z (GMT). No. of bitstreams: 2
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Effects of repeated hydraulic loads on microstructure and hydraulic behaviour of a compacted clayey silt
No full textSoils used in earth constructions are mostly unsaturated, and they undergo frequent drying-wetting cycles (repeated hydraulic loads) due to changes in climatic conditions or variations of the ground water level, particularly at shallow depths. After compaction, changes in water content can significantly influence the hydromechanical response of the construction material, which therefore has to be assessed for repeated hydraulic loads. This research investigates the effect of such loads on the microstructure and hydraulic behaviour of a silty soil, typically used in the construction of embankments and dykes, with the aim of providing a better understanding of the consequences of drying-wetting cycles on the response of the material over time. Experimental tests were performed to study the impact of drying-wetting cycles on the water retention, hydraulic conductivity and fabric of compacted specimens. Fabric changes are documented to take place even without significant volumetric strains, promoting an irreversible increase in the hydraulic conductivity and a reduction in the capacity to retain water compared to the as-compacted soil. The fabric changes are interpreted and quantified by means of a hydromechanical model, which accounts for the evolving pore size distribution at different structural levels. The proposed model reproduces quite well the microstructural observations, together with the evolution of the water retention behaviour and of the hydraulic conductivit
Size- and temperature-dependent bending rigidity of graphene using modal analysis
No full textThe bending rigidity of two-dimensional (2D) materials is a key parameter for understanding the mechanics of 2D NEMS devices. The apparent bending rigidity of graphene membranes at macroscopic scale differs from theoretical predictions at micro-scale. This difference is believed to originate from thermally induced dynamic ripples in these atomically thin membranes. In this paper, we perform modal analysis to estimate the effective bending rigidity of graphene membranes from the frequency spectrum of their Brownian motion. Our method is based on fitting the resonance frequencies obtained from the Brownian motion in molecular dynamics simulations, to those obtained from a continuum mechanics model, with bending rigidity and pretension as the fit parameters. In this way, the effective bending rigidity of the membrane and its temperature and size dependence, are extracted, while including the effects of dynamic ripples and thermal fluctuations. The proposed method provides a framework for estimating the macroscopic mechanical properties in other 2D nanostructures at finite temperatures.Dynamics of Micro and Nano SystemsApplied MechanicsQN/Steeneken La
ORIGINAL ARTICLE Biological Standards Survey of Radioactive Materials Concentration in Ilam City Wheat Fields Soil with Gamma Spectrometry 1 Elham Shafiei and Arash Nademi: Biological Standards Survey of Radioactive Materials Concentration in Ilam City Wh
No full textABSTRACT Radionuclide radiation can effect on the human and creature's health. Currently, soil radioactivity levels of Ilam 's wheat champs is not clear. To determine the degree of safety it's necessary to specify the activity levels of the mentioned environment for persons. HPGe detector for measuring consistency of activities and in soil samples taken from wheat was used in Ilam province. 20 soil samples from Ilam provience from wheat fields were collected during Autumn of 2009, spring 0f 2010. From each location of an approximately 10×10 area, 5 sub samples were collected. The sub sample materials were hipandthigh combined and homogenized.In soil samples, the average activity concentrations o
Three essays in public finance
No full textThe first two chapters are on the funding challenges and the value of infrastructure to households and firms. Chapter 1 is titled “Do State Governments Defer Highway Maintenance Expenditures?”. Deferring maintenance expenditures in fiscal downturns can be more costly than accumulating debt or cutting pension contributions. I take advantage of the formulary distribution of Federal highway grants to examine the extent and context of highway maintenance deferral. Since the formula factors used in the apportionment of Federal highway grants are always three years old, I can measure exogenous grant shocks as the difference between this year’s and previous year’s forecast of each state’s future grants. I show that state governments respond to a negative grant shock by cutting highway maintenance expenditures more rapidly than other expenditures. The Impulse Response Functions (IRFs) of maintenance expenditures as a share of total expenditures show that states only partially compensate for the initial cuts in the subsequent periods – deferring maintenance expenditures and accumulating maintenance needs. Furthermore, I find that deferral of maintenance expenditures is more pronounced in election years, which suggests that this inefficient behavior is subject to agency problems.
In Chapter 2, titled “Valuing Public Goods More Generally: The Case of Infrastructure”, David Albouy and I examine the relationship between local public goods, prices, wages, and population in an equilibrium inter-city model. Non-traded production, federal taxes, and imperfect mobility all affect how public goods (or “amenities” more broadly) should be valued from data. Reinterpreting the estimated effects of public infrastructure on prices and wages in Haughwout (2002), we find infrastructure over twice as valuable with our more general model. New estimates based on more years, cities, and datasets indicate stronger wage and positive population effects of infrastructure. These imply higher values of infrastructure to firms, and also to households if moving costs are substantial.
Finally, chapter 3, titled “Imputing Missing Tax Variables for TAXSIM: Nonlinearity Matters”, is a technical paper on improving income tax rate estimates using NBER TAXSIM. Many researchers estimate household income taxes for using the limited house- hold characteristics of survey participants. I show that as a result of missing tax form fields, which are typically entered as zeros, the estimated income taxes are biased. This bias is not only in the form of shifting the distribution of taxes, but also changes the shape of the distribution depending on which tax field is missing. Experimenting with a naively specified linear regression model, the zero-imputed marginal tax estimates are actually performing almost always better than regression-imputed tax outcomes. However, when four TAXSIM variables are simultaneously missing, regression-imputation is outperforming zero-imputation for total taxes. Finally, imputing multiple TAXSIM variables in a replication example shows that the final empirical findings change dramatically.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2019-12-01The student, Arash Mashhadi Farahani, accepted the attached license on 2017-12-02 at 15:21.The student, Arash Mashhadi Farahani, submitted this Dissertation for approval on 2017-12-02 at 15:31.This Dissertation was approved for publication on 2017-12-05 at 08:43.DSpace SAF Submission Ingestion Package generated from Vireo submission #11812 on 2018-03-13 at 09:56:43Made available in DSpace on 2018-03-13T15:25:22Z (GMT). No. of bitstreams: 2
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