Search

The present study investigated the durability indices of slag-modified concrete during the self-healing process. For this purpose, slag powder was substituted by 0, 15, 30, and 45% by weight of cement. Then, 28-day moist cured cylindrical specimens were prepared to investigate their autogenous self-healing ability. Two gaps with 100 and 200 microns were created in the specimens, and for re-curing, cracked specimens were exposed to tap water for another 28 days. RCPT, water passing, and electrical resistance tests were employed to evaluate the self-healing progress in the gaps and their durability indices. Moreover, XRD and SEM were utilized to achieve further information about the process of concrete self-healing. Results showed that the slag modified concretes can heal the wide gaps, and the self-healing ability improves by increasing slag substitution. Also, it is proposed that the durability of the self-healed slag modified concretes can be assumed more than that of the sound control concretes under chloride attack. Moreover, XRD and SEM observations revealed that a portion of portlandite was leaked into the curing water during the self-healing process. [ABSTRACT FROM AUTHOR]

Excavation in rock induces the unloading of stress in excavation-disturbed zones and can cause the structural plane to reach shear failure due to the unloading of normal stress. Unloading normal stress tests of a regular sawtooth structural plane were conducted in this study to investigate the influence of the unloading velocities (v) and asperity angles (θ) on mechanical properties and the stability of the structural plane. The average value of normal displacement (Du1) and the shear displacement of unloading (Dsu) gradually increases with an increase in θ and Du1 accounts for 59.70%, 31.81%, and 18.60% of the height of a single asperity under different θ. However, Du2, Ds, and the unloading capacity (Δσn) gradually decreased. Moreover, Ds account for 24.52%, 11.61%, and 7.4% of the length of a single asperity, respectively. With an increase in θ and v, three-dimensional (3D) morphology parameters and normal deformation energy (Un) decreased gradually, indicating that the damage degree of the structural plane increases. The analysis of the evolution of the gap width of the structural plane at the initial point, unloading point, and instability point indicates that the greater the θ or the smaller the v, the lower would be the likelihood for the structural plane to be damaged. Concurrently, its instability is more sudden and the impact tendency is stronger. [ABSTRACT FROM AUTHOR]

Many residential houses in Japan have hip roofs with pitches ranging from 20° to 30°. Recently, roof-mounted photovoltaic (PV) panels have become popular all over the world for environmental conservation. The design of PV systems in Japan is usually based on the Japanese Industrial Standard (JIS) C 8955 (2017). However, the standard does not provide wind force coefficients for PV panels installed near roof edges (up to 0.3 m from the edge) because flow separation at the roof edges causes large up-lift forces on such panels. In this paper, we investigated the wind force coefficients for designing PV panels installed on hip roofs of rectangular and L-shaped low-rise buildings. The roof pitch was set to 25° as a typical value. Rectangular panels were installed almost over the whole roof, including the edge zones. Because the thickness of PV panels and the distance between PV panels and the roof are both as small as several centimeters, it is difficult to make wind tunnel models of PV systems with the same geometric scale as that for buildings. We focused on a numerical simulation using the unsteady Bernoulli equation to estimate the pressures in the space between PV panels and the roof. In the simulation, we used the time histories of wind pressure coefficients on the bare roof, which were measured in a turbulent boundary layer. We propose installing PV panels with small gaps between them along their short sides. The gaps may reduce the wind loads not only on the PV panels but also on the roofing due to pressure equalization. We discuss the optimum gap width from the viewpoint of wind load reduction. [ABSTRACT FROM AUTHOR]

Steel plate shear walls (SPSW) are being increasingly used in steel or concrete structures as lateral load‐resisting systems. Shear buckling is one of the major shortcomings of the SPSW and so to address this issue, buckling‐restrained steel plate shear walls (BRSPSW) have started to appear. Owing to the novel concept of this structural system, this paper aims to investigate the effect of factors influencing the response of BRSPSWs. For this purpose, a parametric study was conducted using ABAQUS software. Based on the results acquired from the hysteretic curves, an increase in the concrete compressive strength does not markedly affect the ductility and energy dissipation capacity. Moreover, it was observed that as the width of the gap between concrete panel and steel plate grows, the energy dissipation and response modification factor are reduced. Besides, the results indicate that as steel strength increases, so energy dissipation increases from 0.7 to 11.7 %. Accordingly, based on a comparison between the rate of improvement in shear capacity arising from an increase in the strength of the concrete panels, frame and steel plate, it is concluded that it would be much more rational to increase the concrete strength so that a high shear capacity can be achieved for the BRSPSW. Lastly, in all models, as the gap width increases from 0 to 20 mm and 20 to 35 mm, ductility decreases by 41 and 30 % respectively. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration and magnetic field complex–assisted techniques have been used in low-speed wire electrical discharge machining (USV-MF complex–assisted WEDM-LS) to improve workpiece surface quality. In this paper, a novel approach, which is based on a three-dimensional successive discharge model, is proposed to investigate the interaction between the workpiece surface forming and the vibration of a wire electrode. The influence of USV-MF complex–assisted technique on workpiece surface forming and vibration of a wire electrode is considered by modifying the parameters in this model. During the simulation, the discharge location, which is determined by the minimum gap width in each step, makes it possible to calculate the vibration of a wire electrode in the successive discharge process. Workpiece surface topographies are obtained at the end of simulation, as well as the vibration responses of the wire electrode and the distribution of discharge locations. The simulation results show that the USV-MF complex–assisted technique can increase the vibration amplitude of the wire electrode by 1.12%. The surface roughness values decrease more than 10% and the distribution uniformity of discharge location increases in the USV-MF complex assisted WEDM-LS process. The simulation results are verified by experiments and simulation error of surface roughness value is less than 5% compared with the experimental results. The analysis shows that the servo feed speed increases more than 50% with surface quality unaltered in the USV-MF complex–assisted WEDM-LS process. [ABSTRACT FROM AUTHOR]

The influence of a nonuniform distribution of the mechanical properties of rolled sheet steel on the shape of a pipe billet in making large-diameter pipes in the 1420 pipe-electric welding unit line is studied. The technique and results of measuring the hardness along the perimeter of the initial 25.8 × 4340 × 12 200 mm rolled sheet of strength class K60 are presented. The hardness of the sheet is maximal in the longitudinal direction at the tail end and is minimal at the center. The height and radius of the crimped edge are measured after crimping. The geometric discrepancy in the billet edges along the length is larger than that across the width by 6%. The horizontal and vertical diameters, the gap width, the edge displacement in height, and the diameters at l = 100 mm from the edge end are measured after step-by-step forming. The dependence of the gap width of the pipe billet after forming on the yield strength of the rolled sheet is determined. [ABSTRACT FROM AUTHOR]

Purpose: Using an optical sensor, to automatically evaluate the marginal seal of restorations placed with 21 adhesive systems of all four adhesive categories in cylindrical cavities of bovine dentin applying different outcome variables, and to evaluate their discriminatory power. Materials and Methods: Twenty-one adhesive systems were evaluated: three 3-step etch-and-rinse systems, three 2-step etch-and-rinse systems, five 2-step self-etching systems, and ten 1-step self-etching systems. All adhesives were applied in cylindrical cavities in bovine dentin together with Tetric Ceram (n=8). In the control group, no adhesive system was used. After 24 h of storage in water at 37°C, the surface was polished with 4000-grit SiC paper, and epoxy resin replicas were produced. An optical sensor (FRT MicroProf) created 100 profiles of the restoration margin, and an algorithm detected gaps and calculated their depths and widths. The following evaluation criteria were used: percentage of specimens without gaps, the percentage of gap-free profiles in relation to all profiles per specimen, mean gap width, mean gap depth, largest gap, modified marginal integrity index MI. The statistical analysis was carried out on log-transformed data for all variables with ANOVA and post-hoc Tukey's test for multiple comparisons. The correlation between the variables was tested with regression analysis, and the pooled data according to the four adhesive categories were compared by applying the Mann-Whitney nonparametric test (p < 0.05). Results: For all the variables that characterized the marginal adaptation, there was a great variation from material to material. In general, the etch-and-rinse adhesive systems demonstrated the best marginal adaptation, followed by the 2-step self-etching and the 1-step self-etching adhesives; the latter showed the highest variability in test results between materials and within the same material. The only exception to this rule was Xeno IV, which showed a marginal adaptation that was comparable to that of the best 3-step etch-and-rinse systems. Except for the variables "largest gap" and "mean gap depth", all the other variables had a similar ability to discriminate between materials. Pooled data according to the four adhesive categories revealed statistically significant differences between the one-step self-etching systems and the other three systems as well as between two-step self-etching and three-step etch-and-rinse systems. Conclusions: With one exception, the one-step self-etching systems yielded the poorest marginal adaptation results and the highest variability between materials and within the same material. Except for the variable "largest gap", the percentage of continuous margin, mean gap width, mean gap depth, and the marginal integrity index MI were closely related to one another and showed -- with the exception of "mean gap depth" -- similar discriminatory power. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the effect of gap width on bone healing around implants placed into simulated extraction socket defects of varying widths in 10 mongrel dogs. All premolars were removed and the alveolar ridges were reduced to a width of 7 mm. Nine weeks later, a total of 80 implants, 10 mm long by 3.3 mm wide, were placed into osteotomy sites prepared to 3 different diameters in the coronal half, simulating extraction sockets. Three experimental sites, with gap sizes of 0.5 mm, 1.0 mm, and 1.4 mm, were created; the control sites had no gap. The depth of each defect was measured at the time of implant placement. All implants were stable at the time of placement. The dogs were euthanized 12 weeks after implant placement, and blocks containing the implants and adjacent bone were submitted for histologic evaluation. Clinically, all control and test sites healed, with complete bone fill in the defect. Percentages of bone-to-implant contact were measured histologically. As the gap widened, the amount of bone-to-implant contact decreased, and the point of the highest bone-to-implant contact shifted apically. These changes were statistically significant (P < .001). No statistically significant differences in bone-to-implant contact were found between the sites when the apical 4 mm of implants were compared. Within the limits of this study, the simulated extraction socket defects healed clinically, with complete bone fill, regardless of the initial gap size. However, the width of the gap at the time of implant placement had a significant impact on the histologic percentage and the height of bone-to-implant contact. [ABSTRACT FROM AUTHOR]

Summary An internal fire whirl can be generated readily in a tall shaft model with appropriate gap width at one corner. Experimental study was carried out to investigate the relationship between the characteristics of an IFW and the corner gap width in a 9‐m‐tall vertical shaft model. The vertical shaft had a 2.1 m by 2.1 m square section with gasoline pool fire of different diameters burning inside. The gap width was varied to investigate its impact on fire whirl characteristics, such as flame development, swirling intensity, flame height, flame temperature, and heat release rate of the gasoline pool fire. Vigorous flame swirling motions were generated when the ratio of the gap width to the shaft section perimeter was within the range 0.16 to 0.21. From the flame streamline angle, it was observed that the swirling component was much stronger than buoyancy component near the bottom of burning region. The swirling component decreased and became roughly the same as buoyancy near the middle. Finally, it diminished to being much weaker than buoyancy near the top of the fire. These observations suggest that the Froude number Fr decreased from a large number to 1, and then continued to decrease to 0. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In micro electrical discharge machining (micro-EDM), the whole discharge process happens in the narrow gap between electrode and workpiece. In this study, the influence of gap width on discharge characteristics was investigated based on the impulse discharge method. With determining the critical breakdown distance firstly, the discharge status under various gap width was classified and analyzed. From the perspective of charged particles in plasma channel and the spark maintenance condition, the reason why two types of spark waveform with different gap voltage exist in micro-EDM was explained. Ignition delay and discharge duration ratio, as two import factors influencing the material removal rate, were also investigated under different gap width. The results indicated that the gap width which is 40 % of critical breakdown distance shows a satisfying performance by the combined consideration of ignition delay and discharge duration ratio under the studied conditions. The morphologies of discharge craters obtained under different gap width were measured and analyzed by atomic force microscope (AFM), which showed that both the diameter and depth of discharge crater are decrescent with the increase of gap width, even under the condition of identical discharge energy. [ABSTRACT FROM AUTHOR]

Results of investigations of the optical properties of Hg 1–x–yCd xDy ySe crystals by the Bridgeman method are presented. Based on independent measurements of the reflection and transmission coefficients with a Nicolet 6700 spectrometer at Т = 300 K for wavelengths 0.9 ≤ λ ≤ 26.6 μm, values of the refractive and absorption indices and of the absorption coefficient are determined for the examined crystals. From the dependences α = f(hν) it is established that direct interband optical transitions are allowed in the crystals, and values of the gap width are determined. The effects of the temperature on the transmission coefficient and on the gap width at Т = 118–297 K are investigated. [ABSTRACT FROM AUTHOR]

The effect of gap width on the stability of non-Newtonian Taylor-Couette flow is studied. The fluid is assumed to follow the pseudo plastic Carreau-Bird model and mixed boundary conditions are imposed. The dynamical system, resulted from Galerkin projection of the conservation of mass and momentum equations, includes additional nonlinear terms in the velocity components originated from the shear-dependent viscosity. It is observed that, depending on the gap width for certain fluid, the base flow loses its radial flow stability to the vortex structure known as Taylor vortices. The emergence of theses vortices corresponds to the onset of a supercritical bifurcation also seen in the flow of a linear fluid. A range of parameters is found in which the combination of shear thinning and gap effect leads to destabilizing the vortex structure indicated as the point of Hopf bifurcation. This is not observed in the Newtonian flow, in which the vortices remain stable regardless of the inertia. Furthermore, upon increase of gap width both the critical Taylor and Hopf bifurcation numbers also increase. The obtained results are in good agreement with the available studies carried out only for certain cases. [ABSTRACT FROM AUTHOR]

Electric and magnetic resonances of split-ring resonators (SRRs) as left-hand materials (LHM) were studied in a free space. Different copper thicknesses were designed to tune the electromagnetic resonance frequencies of SRRs. While the split gap width was varied, double-negative responses in SRRs were investigated in detail. Even both electric and magnetic resonance frequencies became higher as copper thickness was decreased, the electric resonance frequency increased much more higher with the increasing of the split gap width. [ABSTRACT FROM AUTHOR]

Waves and currents are essential elements in the design of an artificial surfing reef (ASR). ASRs are primarily designed to optimize the surfing conditions (i.e., increase the surfability of the incoming waves) possibly in combination with the shoreline protection from erosion. The currents generated by waves breaking on the ASR play an important role in the surfability through the wave-current interaction (WCI). Depending on the design, the WCI may negatively affect the surfability by causing the waves to break prematurely due to the current-induced wave steepening. In addition, wave breaking tends to become more irregular due to the temporal variability of the underlying currents. To mitigate the negative effects of wave breaking induced currents on the surfability, three ASR layouts are examined through detailed laboratory experiments. The layouts differ in the alongshore separation distance between two symmetrical reef sides. The ensuing flow circulations are examined in detail with both in situ current meters and video observations of surface drifters. This is done for regular incident waves, bichromatic incident waves, and irregular incident waves, all with equal energy. A data analysis shows that for a given layout the mean flow patterns for regular, bichromatic, and irregular waves are qualitatively similar, with oblique rip currents exiting at either side of the reef and strong flow circulations onshore of the gap in between the two reef sides. Increasing the separation distance leads to a significant reduction of the obliquely exiting rip currents at the outer sides of the reef, but an increase in the flow circulation onshore of the gap. This has a positive effect on the surfability by reducing the negative effects associated with the WCI on the wave breaking, thus, providing longer rides. [ABSTRACT FROM AUTHOR]

Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are formed by removing the substrate material in a periodic manner. This paper also demonstrates that these structures can serve as a non-destructive characterization tool for materials, a duplexor and frequency selective coupler. The paper presents both experimental results and theoretical simulation based on a commercially available infinite element methodology for comparison. [ABSTRACT FROM AUTHOR]

Objectives: This study was designed to evaluate the effect of gap width and graft placement on bone healing around implants placed in simulated extraction sockets of various widths in four Labrador dogs. Materials and Methods: Five Osseotite® implants per dog were placed in the mandible of four dogs. Two implants were inserted into sites with a 2.37 mm and two with a 1 mm gap present between the implants and bone around the coronal 6 mm of the implants in each dog. For one of each gap sizes, the gap was filled with Bio-Oss®, and the other two with blood alone. A fifth implant was inserted without a gap and used as a control. Ground sections were prepared from biopsies taken at 4 months and histometric measurements of osseointegration and bone between the threads made for the coronal 6 mm. Results: The medians for osseointegration ranged from 5.2 mm for control to 1–2.6 mm for the test modalities. There were significant differences for linear measurements of osseointegration (χ2 18.27; df 4; P=0.0011) and bone area within threads (χ2 23.4; df 4; P=0.0001) between test modalities. Conclusions: The results suggest that the wider the gap around the implants, the less favourable the histological outcome at short time intervals following treatment. They also infer that bone grafting with anorganic bovine bone xenograft seems to lead to a more favourable histological outcome for wider circumferential defects but not for narrower defects. [ABSTRACT FROM AUTHOR]

This study examines the relationship between gap width and the presence of recurrent dental caries subjacent to occlusal margins of amalgam restorations. The study population consisted of 35 adult patients of the university's dental clinic who were having occlusal amalgam restorations removed solely because of defective margins. In this group, an impression was made recording the width of a clinically detected gap between the amalgam restoration and the adjacent enamel cavosurface. Of this study population, 20 teeth with recurrent caries were identified from 18 subjects after restoration removal. Upon removal of the restoration, the presence and location of recurrent dental caries associated with a margin was noted. The mean gap widths of recurrent carious sites and non-carious sites were compared in the same tooth. A difference of 187 μm was found between the mean gap width of the recurrent caries sites and the non-carious sites, with the recurrent caries gaps being wider. A paired t-test based on the differences was calculated (P<0.0001). The results suggest that there is a direct association between gap width and recurrent caries in occlusal margins of amalgam restorations. [ABSTRACT FROM AUTHOR]