Use of Warranties on Highway Projects: A Real Option Perspective

Since the introduction of warranty provisions in federal highway jobs, more and more state departments of transportation (DOTs) have considered the use of such provisions to protect their initial investment. This paper describes the pros and cons of warranty contracting in highway construction based on a survey of warranty practices in the United States. In particular, the need for state DOTs to buy a warranty for a well-built project is questioned. As an alternative, this paper introduces the warranty option, which gives the DOT the right to buy a warranty only if it becomes necessary at the end of construction. This option is exercised if the performance on site warrants it. This paper describes the mechanics of the warranty option and its advantages over the conventional warranty. A bid evaluation model is also developed for the warranty option approach.     

A New Recycled Al–Si–Mg Alloy for Sustainable Structural Die Casting Applications

Metallurgical and Materials Transactions A - The use of secondary aluminum for structural components in the automotive industry is limited by the high Fe contents in recycled alloys which often...     

Unveiling the presence of mixed oxidation states of Europium in Li7+δEuxLa3−δZr2−δO12−δ garnet and its impact on the Li-ion conductivity

Recently, lanthanides have been employed by researchers to examine their impact on the structure and properties of Li₇La₃Zr₂O₁₂ (LLZO) garnets. In this regard, we developed Europium oxide (Eu₂O₃) doped LLZO (Li_7+δEu_xLa_3−δZr_2−δO_12−δ) solid electrolyte which demonstrates a cubic phase with the symmetry of Iad (No.230) at room temperature. In this investigation, different concentrations of Eu ranging from 0.1 to 0.6 atoms per formula unit (pfu) were doped into Li₇La₃Zr₂O₁₂ to evaluate the impact of Eu on the stability of the cubic phase and thereby the ionic conductivity. The results unveiled that upon doping Eu³⁺ ions, the Eu²⁺ state is also formed and is then self-doped into the structure in which Rietveld refinement coupled with XPS, EPR, and solid-state NMR suggests that Eu³⁺ ions most probably partially occupy Zr⁴⁺ (16a) site, the Eu²⁺ ions occupy La³⁺ (24d) site, and the Li⁺ ions occupy two different sites (24d and 96h). It was further found that such a site preference induces distortion at LaO₈ polyhedrons opening up the neck for Li-ions diffusion, thereby enhancing the ionic conductivity. Moreover, it was revealed that Li-ions probably hop from 96h to 24d and then to 96h site to generate the Li-ion movement. Overall, by introducing Eu ions into the LLZO structure, an enhanced bulk ionic conductivity of 0.30 × 10⁻³ S/cm at 298 K with a minimum electronic conductivity of 2.547 × 10⁻⁹ S/cm at 298 K was achieved.     

Robustness with dynamic IQCs: An exact state-space characterization of nominal stability with applications to robust estimation

For robustness analysis with integral quadratic constraints, we formulate a new positivity condition on the solution of the corresponding linear matrix inequality which is necessary and sufficient for nominal stability of the underlying system. The application of this technical result is illustrated by a complete solution of the L₂-gain and robust H₂-estimator design problems if the uncertainties are characterized by dynamic integral quadratic constraints.     

On the design considerations of solid-state power amplifiers for satellite communications: A systems perspective

Conventional solid-state power amplifier (SSPA) design approach isolates radio frequency (RF) design from communication theory. In this paper, a unified SSPA design approach is proposed, which optimizes SSPA parameters (bias voltage and input RF signal power) to minimize total DC power consumption while satisfying received SNR constraint specified by the link budget. The effect of SSPA nonlinearity is quantified by the error vector magnitude measured at its output and the corresponding received SNR degradation is analyzed. Using the quantitative metrics for received SNR, it is possible to evaluate highly nonlinear SSPA classes such as Class-B or deep-Class AB, which are normally not considered in conventional SSPA design approach to be used in satellite communication applications.     

Bridging multi-scale approach to consider the effects of local deformations in the analysis of thin-walled members

Thin-walled members that have one dimension relatively large in comparison to the cross-sectional dimensions are usually modelled by using beam-type one-dimensional finite elements. Beam-type elements, however, are based on the assumption of rigid cross-section, thus they only allow considerations associated with the beam axis behaviour such as flexural-, torsional- or lateral-buckling and cannot consider the effects of local deformations such as flange local buckling or distortional buckling. In order to capture the local effects of this type shell-type finite element models can be used. Based on the Bridging multi-scale approach, this study proposes a numerical technique that is able to split the global analysis, which is performed by using simple beam-type elements, from the local analysis which is based on more sophisticated shell-type elements. As a result, the proposed multi-scale method allows the usage of shell elements in a local region to incorporate the local deformation effects on the overall behaviour of thin-walled members without necessitating a shell-type model for the whole member. Comparisons with full shell-type analysis are provided in order to illustrate the efficiency of the method developed herein.     

Wind turbine speed control of a contactless piezoelectric wind energy harvester

ABSTRACT

Wind turbine control is an important task to make the electricity generation secure in terms of energy demand and machine safety. It also yields to control the desired power level and optimized energy because of the assignment of turbine speed. The contactless piezoelectric wind energy harvester (CPWEH) used in this study has three piezoelectric layers located around the shaft with 120 degrees apart and they are buckled by the magnetic force without any physical contact. The superiority of this device is to generate energy for low wind speeds such as 1.5 m/s. However, for high speeds, high total harmonic distortions (THDs) govern the waveforms, thus controlling the turbine speed becomes necessary for optimizing the output power. Encouraged by this, a small low inertia dc generator is coupled with the wind turbine, and the generator terminals are connected to a resistor through a power switch to generate a braking torque that opposes to wind speed direction. By controlling the switch properly, turbine speed is ensured to remain within a certain band, which accordingly prevents the turbine from rotating very fast at damaging wind speeds. Several experiments are performed on the developed CPWEH with/without the presented control scheme which prove the existence of promising performance of our proposal.     

Column solid‐phase extraction of sunset yellow and spectrophotometric determination of its use in powdered beverage and confectionery products

A new and simple solid‐phase extraction method for the determination of trace levels of sunset yellow has been developed on Diaion HP 2MG column system. The adsorbed sunset yellow on the resin was eluted with 3 mL of methanol and determined by UV–Vis spectrophotometry at 484 nm. Various experimental parameters such as pH, amount of sunset yellow, flow rates of sample and eluent solutions, resin amount, sample volumes, etc. were investigated. The influences of some alkali, alkali earth and transition metals on the recoveries of sunset yellow were investigated. The recovery values for sunset yellow were higher than 95%. Preconcentration factor was found as 150. The detection limit (three sigma) of the reagent blank for sunset yellow was 5.2 μg L^?1. The relative standard deviations (RSD) of the procedure were found as 3.9%. The validation of the presented procedure was performed by the method of standard addition. The procedure was successfully applied to the determination of trace levels of sunset yellow in powdered beverage and confectionery products.     

Effects of mixing techniques and dentin moisture conditions on push-out bond strength of ProRoot MTA and Biodentine

Objective: To evaluate the influence of manual and mechanical mixing techniques as well as the effects of moisture on the push-out bond strength of ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK, USA) and Biodentine (Septodont, Saint Maur des Fosses, France) to radicular dentin.

Material and methods: Two hundred and forty dentin discs were assigned into three groups with respect to the moisture condition tested: (1) dry, (2) paper points, (3) wet. The discs were further divided into four subgroups according to the calcium silicate cements (CSCs) and mixing techniques used: (1) ProRoot MTA mixed manually, (2) ProRoot MTA mixed mechanically, (3) Biodentine mixed manually, and (4) Biodentine mixed mechanically. Bond strengths of the cements to root canal dentin were measured using a push-out test setup. The data were statistically analyzed using three-way ANOVA and Bonferroni post hoc test p = 0.05.

Results: The data indicated that the push-out bond strength values were significantly affected by CSCs, mixing techniques, and moisture conditions (p < 0.001). Dry conditions caused a significant decrease in bond strength values for both CSCs (p < 0.001). The mean bond strength of Biodentine was significantly higher than that of ProRoot MTA, regardless of the mixing techniques and moisture conditions (p < 0.001). Mechanical mixing favored bond strength values statistically compared to manual mixing (p < .001).

Conclusion: The mixing techniques and moisture conditions have an effect on the push-out bond strengths of ProRoot MTA and Biodentine. Dry samples and manual mixing of cements deteriorate the push-out bond strengths values.