Reflection and transmission of normally incident full-vector X waves on planar interfaces

The reflection and transmission of full-vector X waves normally incident on planar half-spaces and slabs are studied. For this purpose, X waves are expanded in terms of weighted vector Bessel beams; this new decomposition and reconstruction method offers a more lucid and intuitive interpretation of the physical phenomena observed upon the reflection or transmission of X waves when compared to the conventional plane-wave decomposition technique. Using the Bessel beam expansion approach, we have characterized changes in the field shape and the intensity distribution of the transmitted and reflected full-vector X waves. We have also identified a novel longitudinal shift, which is observed when a full-vector X wave is transmitted through a dielectric slab under frustrated total reflection condition. The results of our studies presented here are valuable in understanding the behavior of full-vector X waves when they are utilized in practical applications in electromagnetics, optics, and photonics, such as trap and tweezer setups, optical lithography, and immaterial probing.     

Soil-Steel Interaction of Long-Span Box Culverts—Performance during Backfilling

The paper presents the performance of four long-span deep-corrugated steel box culverts with spans of 8- and 14-m during backfilling, as well as comparisons with finite-element modeling and design codes. Two of the culverts were stiffened at the crown arch. The test results show that the stiffening applied on the culverts is quite effective. The crown rises of the respective stiffened culverts were found to be half those of the not-stiffened culverts. The influence of the structure geometry on the soil-passive earth pressure was confirmed, as well as the sensitivity of box culverts to soil loads with increasing spans. The results showed that the influence of the size and shape of the box culverts on the amount of thrusts must be better implemented in the design method. The finite-element analysis results were conservative when live loading was concerned but the crown displacements and thrust during backfilling were underestimated.     

The effect of Fe content in electrodeposited CoFe/Cu multilayers on structural, magnetic and magnetoresistance characterizations

A series of CoFe/Cu multilayers were electrodeposited on Ti substrates from the electrolytes containing their metal ion under potentiostatic control, but the Fe concentration in the electrolytes was changed from 0.0125 M to 0.2 M. The deposition was carried out in a three-electrode cell at room temperature. The deposition of Cu layers was made at a cathode potential of -0.3 V with respect to saturated calomel electrode (SCE), while the ferromagnetic CoFe layers were deposited at -1.5 V versus SCE. The structural studies by X-ray diffraction revealed that the multilayers have face-centered-cubic structure. The magnetic characteristics of the films were investigated using a vibrating sample magnetometer and their easy-axis was found to be in film plane. Magnetoresistance measurements were carried out using the Van der Pauw method at room temperature with magnetic fields up to +/- 12 kOe. All multilayers exhibited giant magnetoresistance (GMR) and the GMR values up to 8% were obtained.     

Mechanical properties of ferrochromium slag in granular layers of flexible pavements

Ferrochromium slag is a waste material obtained from the manufacture of ferrochromium (FeCr). This article reports the results of experiments, aiming to identify the properties of ferrochromium slag when it is used as an artificial aggregate for preparation of granular layers of flexible pavements. The experimental program consisted of two stages: (1) study of the physical and chemical properties of slag; (2) study of the mechanical properties of specimens made with ferrochromium slag and limestone as aggregate. Laboratory prepared cylindrical specimens were tested in repeated load triaxial (RLT) test apparatus, developed at Süleyman Demirel University, Turkey. In addition, particle size analysis, abrasion test, frost resistance, compaction test, California Bearing Ratio (CBR) test and leaching test were performed on the materials prior to RLT testing. The results indicate that the physical and mechanical properties of air-cooled ferrochromium slag are as good or better than those of natural aggregates. Therefore, FeCr slag and SiFeCr slag have potential to be used as a pavement base layer material in applications where crushed limestone aggregate materials are traditionally used.     

Influence of steam curing on the properties of concretes incorporating metakaolin and silica fume

In this paper, influence of steam curing on the compressive strength, ultrasonic pulse velocity, water sorptivity, chloride ion permeability, and electrical resistivity of metakaolin and silica fume blended concretes were investigated. A total of seven mixtures containing various combinations of Portland cement (PC), silica fume (SF), and metakaolin (MK) were produced with 400 kg/m³ of total cementitious materials content and with a constant water/binder ratio of 0.44. For each mixture, concrete samples were either standard-cured in water at 23°C or steam-cured at 70°C maximum temperature over 17 h curing period. Test results revealed that steam curing enhanced the 1-day compressive strength and ultrasonic pulse velocity while leading to reduced long term strength in line with earlier findings. At the end of the water sorptivity, chloride ion permeability, and electrical resistivity tests, it was found that the steam-cured concretes had higher water sorptivity and chloride ion permeability, and lower electrical resistivity values compared to the standard cured specimens. Use of SF and MK as cementitious materials remarkably decreased the water sorptivity and chloride ion permeability of concretes, irrespective of the curing condition.     

Decarburization of TiC in Ni activated sintered W–xTiC (x = 0, 5, 10, 15 wt%) composites and the effects of heat treatment on the microstructural and physical properties

Blended elemental W–xTiC (x = 0, 5, 10, 15 wt%) powders were mechanically alloyed (MA’d) for 30 h in a SPEX Mixer/Mill at room temperature. About 1 wt% Ni was added to each MA’d batch as sintering aid which were further milled for 1 h. MA’d powders were sintered at 1400 °C for 2 h under Ar, H₂ gas flowing conditions and annealed at 1600 °C for 6 h under Ar atmosphere. Microstructural characterizations of as-sintered and annealed samples were conducted using XRD and SEM. XRD patterns of the as-sintered and annealed samples revealed the presence of the matrix W and Ni phases, whereas (Ti_x,W_1−x) solid solution phase came into existence after annealing. In addition to XRD patterns, hot combustion and infrared detection measurements revealed the decarburization of TiC. Relative density values varied between 85.2% and 96.4% after sintering. The density values of sintered samples decreased with increasing TiC content. After annealing, a maximum relative density value of 99.8% was achieved. Vickers microhardness values varied between 5.11 GPa and 10.79 GPa for as-sintered samples and a maximum microhardness value of 8.1 GPa was measured after annealing. Wear resistance of the as-sintered samples increased with increasing TiC content.     

The Hydroloysis of ammonia borane by using Amberlyst-15 supported catalysts for hydrogen generation

Resin catalysts have the advantage of having various properties and long lifetime due to their ability to be regenerated easily, which makes them attractive supports. In this paper, a comparative study was conducted to optimize the dehydrogenation reaction condition using two different types of support materials: alumina (Al₂O₃), and Amberlyst-15 and to improve the catalytic activity as well as preparing an efficient and low-cost system for practical application, ruthenium metal catalyst was incorporated on Amberlyst-15 resin (a sulfonic acid type based upon a styrene-divinylbenzene copolymer) to release H₂ via hydrolytic dehydrogenation of ammonia borane. Using ruthenium (Ru) catalysts based on Amberlyst-15 support material and comparing the results with Al₂O₃ as the common supporting material is considered to be studied for the first time. The effect of temperature (20–50 °C), the initial ammonia borane concentration (0.05–0.5 %wt), and catalyst amount (0.2–0.5 g) on the produced H₂ yield was also investigated. Ru@Amberlyst-15 nanoparticle was discovered to be an effective catalyst for hydrogen evolution via the hydrolysis of ammonia borane with a turnover frequency value (TOF) of 343.3 min^?1, while Ru@Al₂O₃ yielded a TOF of 87.5 min^?1 at the room temperature. Therefore, it can be concluded that the Amberlyst-15 supporting effect on ruthenium metal leads an increase in the hydrogen production rate.     

Hydrogen adsorption on natural and sulphuric acid treated sepiolite and bentonite

In this study, hydrogen (H₂) adsorption on sepiolite and bentonite and those of acid treated forms were studied at 77 K using volumetric apparatus up to 100 kPa. Both clay minerals were treated with 100 ml of 0.5, 1.0, 2.0 and 4.0 M H₂SO₄ solutions at 80 °C for 5 h. Differences in the structures of the sepiolite and bentonite samples before and after the acid treatments were determined by XRD, XRF, TG, DTA and N₂ adsorption methods. The level of H₂ adsorption of original and acid treated sepiolite samples (1.332–2.252 mmol/g) was higher than those of the bentonite samples (0.341–1.003 mmol/g). The variation in the H₂ adsorption capacities during the acid treatment was also discussed.     

Micro milling of titanium alloy Ti-6Al-4V: 3-D finite element modeling for prediction of chip flow and burr formation

Cutting process of titanium alloy Ti-6Al-4V is considered difficult due to chemical affinity between tool and work material, adhesion, built-up edge and burr formation, and tool wear resulting in loss of productivity. Three dimensional (3-D) chip flow together with local field variables such as temperature, elastic/plastic strain, strain-rate and velocity in the shear zones during micro milling process can be predicted using continuum-mechanics based 3-D Finite Element (FE) modelling and simulation of elastic/viscoplastic work material deformations. This paper provides much needed process insight for chip flow, built-up edge and burr formation by using modeling work with experimental validation. Scanning electron microscopic (SEM) observation of the 3-D chip morphology and burrs demonstrate ductile fractured surfaces together with localized instability and failure behaviors. FE simulations are utilized to investigate the effects of micro milling operation i.e. up and down milling and tool edge radius on 3-D chip flow, built-up edge, and 3-D burr formation. Simulated results are compared with measurements of chip morphology, shape, and dimensions together with tool edge condition of built-up edge and chip adhesion yielding to good agreements.