Rheological Properties of Modified Crumb Rubber Asphalt Binder and Selecting the Best Modified Binder Using AHP Method

Crumb rubber modifier (CRM) is one of the most popular asphalt binder modifiers due to the economic benefits and desired physical and rheological properties of asphalt binders and asphalt mixes. This research focuses on evaluating the properties of rubber-modified asphalt binders and selecting the best modified binder. The modified binders were produced by blending virgin binders with CRM at various contents of different gradations, and different methods of grinding. CRM made through ambient and cryogenic grinding methods with two gradation sizes were produced and tested. Three different virgin binders from two sources were obtained and used. The Analytic Hierarchy Process (AHP) method was used to determine the best combination of virgin binder and CRM, based on the rheological properties and their importance in Nevada’s construction code. Based on AHP analysis, ambient CRM obtained the highest priority. CRM contents of 10% and 15% were ranked higher than 20% depending on the grade of the virgin binder. Both mesh 20 and 40 CRM sizes were favorable

Toughness, Tenacity and Maximum Initial Strength of Rubber Modified Asphalt Binders

The toughness and tenacity test method, which was developed in the 1980s, is popular for evaluating a polymermodified binder. Several states like Nevada require performing this test to evaluate non-modified binder samples, as well as other types of modified binders. In this regard, a toughness and tenacity test was performed on rubber-modified samples produced from virgin binder PG58-28, PG64-16 and AC-20. In order to take the rubber size, type and content into account, two rubber sizes, mesh #20 and #40, two rubber types, ambient and cryogenic, and three rubber contents, 10%, 15%, and 20% were produced and tested. The results then were compared with polymer-modified and terminally blended rubber-modified samples. The results show improvement in the amount of initial maximum strength, and a decline in the magnitude of elongation, toughness and tenacity for the rubber-modified binder, compared to other types of binders

Numerical Modeling of Suspension and Particle Transport in Thermal Spray Processes

Fine microstructured coatings have attracted many attentions in recent years due to various unique properties such as remarkable wear resistance, enhanced catalytic behavior, and superior thermal insulation. Suspension thermal sprays have been shown to be viable techniques in generating this kind of coatings. In these techniques, suspension which is a combination of a base liquid and fine solid particles is injected into a high-temperature high-velocity jets. After suspension breakup, the evaporation/combustion of base liquid becomes dominant. Then, the remained particles are accelerated and heated up by the gas flow and are deposited on a substrate which results in the generation of dense and well-adhered coatings. Suspension thermal spraying is very complex and many fields such as turbulent flow, multiphase flow, compressible flow, combustion, atomization, suspension properties, and plasma physics are involved in the mentioned technique. In addition, many parameters and mechanisms in this technique are still unknowns. Therefore, both numerical and experimental studies should be performed to obtain a comprehensive understanding of various phenomena in suspension thermal spraying and to improve the coating quality. The main goal of this study is the numerical modeling of suspension thermal sprays. An Eulerian-Lagrangian approach with two-way coupling assumption is presented and suspension droplet evolution in the atmospheric plasma spraying and high velocity oxygen fuel spraying techniques is investigated. In this model, suspension is considered as a multi-component mixture and a predefined droplet distribution is injected into the jet. In this approach, the breakup process is simulated using Taylor Analogy Breakup (TAB), and Kelvin-Helmholtz Rayleigh-Taylor (KHRT) breakup models. After breakup process is complete, the liquid component of suspension droplet evaporates/burns, and the particles/agglomerates are tracked in the domain. In general, the effects of suspension injection velocity, suspension properties, suspension injector location, standoff distance, substrate shape, and gas properties on the coating characteristics can be investigated by this approach. For example, in the case of radial injection of suspension into a plasma plume, it is illustrated that if particles move close to the jet centerline, particle velocity and temperature as well as probability of particle impact on the substrate will increase. The mentioned Eulerian-Lagrangian approach revealed that the breakup phenomenon mainly controls the droplets/particles trajectories, temperatures and velocities. However, the typical TAB and KHRT models ignore liquid/suspension column deformation, and need experimental calibration. To study the breakup process in more details, the effect of nonuniform gaseous crossflow and liquid column perturbations on the primary breakup of liquid jets are investigated. A coupled level set and volume-of-fluid method together with the large eddy simulation turbulence model are used to study the behavior of nonturbulent liquid jets in nonuniform crossflows. It is shown that liquid penetration height is significantly affected by the crossflow nonuniformity. In addition, to investigate the effects of liquid column perturbations on the breakup process, experimental studies are performed using shadowgraphy technique. General correlations for the penetration height, the column breakup point, and the onset of surface breakup are presented. It is found that the liquid column perturbations result in formation of large ligaments very close to the liquid and gas flows interaction point. These ligaments control the droplet size distribution and have significant effects on particle in-flight behavior, and coatings quality. The results of these studies can be used to estimate the spray trajectory in suspension plasma spray process, and to improve the accuracy of TAB and KHRT breakup models

Plasmonic and Ultrafast Optical Response of 2D and 3D Dirac Materials

The fast-evolving field of condensed matter physics is witnessing a rapid development of a new class of materials, called Dirac materials. The low-energy electronic excitation in these materials behaves like massless Dirac particles. These materials exhibit unique optoelectronic properties, and understanding of Dirac quasi-particle dynamics in two and three dimensions is imperative to realizing the potential applications. In this dissertation, we study two prominent Dirac materials that have unique optoelectronic properties: graphene (two-dimensional) and tantalum arsenide (three-dimensional). While the former can be regarded as the father of materials with a symmetry-protected Dirac spectrum, the latter is a more recent example of topology-protected Dirac materials, also known as 3D Weyl semimetals. We employ spectroscopy and ultrafast optical techniques to study plasmons, and the interaction/relaxation dynamics of photo-excited carriers in these materials. More specifically, we study a new class of plasmon resonances in hybrid metal-graphene structures, which is an important step towards practical graphene plasmonic optoelectronic devices. In addition, we investigate the giant nonlinear THz response of graphene plasmons using pump-probe techniques and discuss the physical origin of the plasmon-enhanced nonlinearity. Furthermore, we introduce a novel continuous-wave photomixing spectroscopy technique to investigate the frequency dependence and nonlinearity of hot-electron cooling in graphene. Finally, we explore the relaxation dynamics of photo-excited Weyl fermions in tantalum arsenide via ultrafast optical pump-probe techniques, which shed light on the electron-phonon relaxation processes in this material

Surveying the effective factors in improving high school management from the viewpoints of school administrators and teachers of Urmiah City, Iran

This study intended to survey the effective factors in improving high school management from the viewpoints of school administrators and teachers of Urmiah city, Iran. The method of research was descriptive surveying. We used cross-country method for gathering data by a researcher-made questionnaire, which after the confirmation of content and face validity by experts, the reliability in a sample of 30 using cronbach α, with a correlation coefficient of 93% has been determined. The participants of this study were all secondary school administrators and teachers of Urmiah city, Iran, which were selected out of 1200. We used stratified sampling, because there were 2 groups: school administrators, and teachers. Our sample was 100. The analysis method was descriptive and inferential (t-Test). The results revealed that there was a significant difference between the views of school administrators' and teachers' about the effect of objective targeting, participatory leadership, and participatory decision-making, effective communication with staff and constant evaluation on the improvement of management

Surveying the effective factors in improving high school management from the viewpoints of school administrators and teachers of Urmiah City, Iran

This study intended to survey the effective factors in improving high school management from the viewpoints of school administrators and teachers of Urmiah city, Iran. The method of research was descriptive surveying. We used cross-country method for gathering data by a researcher-made questionnaire, which after the confirmation of content and face validity by experts, the reliability in a sample of 30 using cronbach α, with a correlation coefficient of 93% has been determined. The participants of this study were all secondary school administrators and teachers of Urmiah city, Iran, which were selected out of 1200. We used stratified sampling, because there were 2 groups: school administrators, and teachers. Our sample was 100. The analysis method was descriptive and inferential (t-Test). The results revealed that there was a significant difference between the views of school administrators' and teachers' about the effect of objective targeting, participatory leadership, and participatory decision-making, effective communication with staff and constant evaluation on the improvement of management

Surveying the effective factors in improving high school management from the viewpoints of school administrators and teachers of Urmiah City, Iran

This study intended to survey the effective factors in improving high school management from the viewpoints of school administrators and teachers of Urmiah city, Iran. The method of research was descriptive surveying. We used cross-country method for gathering data by a researcher-made questionnaire, which after the confirmation of content and face validity by experts, the reliability in a sample of 30 using cronbach α, with a correlation coefficient of 93% has been determined. The participants of this study were all secondary school administrators and teachers of Urmiah city, Iran, which were selected out of 1200. We used stratified sampling, because there were 2 groups: school administrators, and teachers. Our sample was 100. The analysis method was descriptive and inferential (t-Test). The results revealed that there was a significant difference between the views of school administrators' and teachers' about the effect of objective targeting, participatory leadership, and participatory decision-making, effective communication with staff and constant evaluation on the improvement of management

A Review of Different Aspects of Applying Asphalt and Bituminous Mixes under a Railway Track

Asphalt is a common material that is used extensively for roadways. Furthermore, bituminous mixes have been used in railways, both as asphalt and as mortar. Different agencies and research institutes have investigated and suggested various applications. These studies indicate the benefits of bituminous material under railways, such as improving a substructure’s stiffness and bearing capacity; enhancing its dynamic characteristics and response, especially under high-speed train loads; waterproofing the subgrade; protecting the top layers against fine contamination. These potential applications can improve the overall track structure performance and lead to minimizing settlement under heavy loads. They can also guarantee an appropriate response under high-speed loads, especially in comparison to a rigid slab track. This review paper documents the literature related to the utilization of asphalt and bituminous mixes in railway tracks. This paper presents a critical review of the research in the application of asphalt and bituminous mixes in railway tracks. Additionally, this paper reviews the design and construction recommendations and procedures for asphalt and bituminous mixes in railway tracks as practiced in different countries. This paper also provides case studies of projects where asphalt and bituminous mixes have been utilized in railway tracks. It is anticipated that this review paper will facilitate (1) the exchange of ideas and innovations in the area of the design and construction of railway tracks and (2) the development of unified standards for the design and construction of railway tracks with asphalt and bituminous mixtures

Low Iris and Anterior Chamber Volume Associated with Deepening after Laser Peripheral Iridotomy in Primary Angle Closure Suspects

Purpose: To evaluate the association between baseline ocular variables and the opening of the anterior chamber angle by laser peripheral iridotomy (LPI) in primary angle closure suspects (PACS) using a new Fourier-domain swept-source anterior segment optical coherence tomography (FD-ASOCT). Method: Sixty-six PACS eyes of 41 individuals were included in this prospective interventional case series. An FD-ASOCT (Casia SS-1000 OCT; Tomey, Nagoya, Japan) was used to measure biometric baseline variables and at one month after the LPI. Paired t-test was used to compare the difference between pre-and post-LPI measurements. Multivariate regression analysis was used to test for an association between baseline iris thickness and volume, anterior chamber depth and volume, and lens vault with a widening of the angle after an LPI. Results: The mean age of participants was 58.6 ± 8.7 years, 682% of whom were female. The angle opening distance, recess area and trabecular iris surface area at 500 microns increased by 48 to 73% (all p<0.001). Lens vault and iris volume did not change. A low anterior chamber volume and low iris volume were associated with angle greater deepening by LPI. Conclusion: Eyes with a shallow anterior chamber and thinner irises are more likely to experience angle opening from an LPI