Towards better 3-D reconstructions by combining electron tomography and atom-probe tomography

Scanning transmission electron microscope tomography and atom-probe tomography are both three-dimensional techniques on the nanoscale. We demonstrate here the combination of the techniques by analyzing the very same volume of an Al-Ag alloy specimen. This comparison allows us to directly visualize the theoretically known artifacts of each technique experimentally, providing insight into the optimal parameters to use for reconstructions and assessing the quality of each reconstruction. The combination of the techniques for accurate morphology and compositional information in three dimensions at the nanoscale provides a route for a new level of materials characterization and understanding.     

Reducing the missing wedge: High-resolution dual axis tomography of inorganic materials

Electron tomography is a powerful technique that can probe the three-dimensional (3-D) structure of materials. Recently, this technique has been successfully applied to inorganic materials using Z-contrast imaging in a scanning transmission electron microscope to image nanomaterials in 3-D with a resolution of 1 nm in all three spatial dimensions. However, an artifact intrinsic to this technique limits the amount of information obtainable from any object, namely the missing wedge. One way to circumvent this problem is to acquire data from two perpendicular tilt axes, a technique called "dual axis tomography." This paper presents the first dual axis data at high resolution for inorganic materials, and by studying a CdTe tetrapod sample, demonstrates the increase in information obtained using this technique.     

Scratch adhesion and wear failure characteristics of PVD multilayer CrTi/CrTiN thin film ceramic coating deposited on AA7075-T6 aerospace alloy

This study highlights the scratch adhesion failure characterization and tribo-mechanical properties of physical vapor deposited (Cr, Ti) N coating on AA7075-T6 by using magnetron-sputtering technique. The surface morphology, microstructure and chemical composition of CrTi/CrTiN film were inspected by an optical microscope, scanning electron microscope (SEM) incorporated with energy dispersive X-ray spectroscopy (EDX) in addition to focused ion beam milling. The coating to substrate critical load of about 1261 mN was obtained, by employing coating deposition parameters of; DC power (300 W, RF power (200 W)), temperature (300 °C) and nitrogen flow rate (6%). Failure adhesion characteristics exhibited initial arc-tensile cracking followed by chipping and spallation that led to complete coating failure at L_c3. The tribo-mechanical aspects were evaluated by a pin-on-plate reciprocating testing unit, which showed a lower friction coefficient of 0.36 for CrTiN as compared with 0.43 for AA7075-T6. Subsequently, the wear depth was also reduced from 9.5 to 5.9 μm. It was revealed that the wear mechanism for AA7075-T6 was extensive deformation, abrasion and delamination, while the CrTiN exhibited slightly oxidative abrasive wear mode.     

The economical and international dimensions of the environmental problems,environmental problems in the Black Sea region and the role of the voluntary organizations

Differently than in the past, today environmental problems have local, national and international concern. The environmental problems in the Black Sea region are a good example for this phenomenon. These problems have affected all six countries that have shores with the Black Sea. The current study analyses these problems in detail. It intends to detect potential reasons for problems and provide suggestions to solve these problems by considering the economic dimensions. In addition, the impact of problems on the city life is examined. Also, the roles and importance of voluntary organizations on solving environmental problems are emphasized.     

Shear strength of reinforced concrete beams with stirrups

This study presents alternative shear strength prediction equations for reinforced concrete (RC) beams with stirrups. The shear strength is composed of the contribution of the nominal shear strength provided by stirrups and the nominal shear strength provided by concrete. For the concrete contribution, cracking shear strength values estimated by Arslan’s equations are almost same those obtained with ACI 318 simplified equation in terms of coefficient of variation (COV). However, mean values estimated by ACI 318 tend to be more conservative comparing to the mean values obtained with Arslan’s equations. Thus, for the consideration of concrete contribution to shear strength, Arslan’s equations are used. To obtain the shear strength of RC beams, shear strength provided by stirrups is added to the concrete shear strength estimated by Arslan’s equations. Results of existing 339 beam shear tests are used to investigate how accurate proposed equation estimates the shear strength of RC beams. Furthermore, ACI 318 and TS500 provisions are also compared to the aforementioned test results. It is found that proposed equations for beams with shear span to depth ratios (a/d) between 1.5 and 2.5 are also conservative with a lower COV than ACI 318 and TS500. However, when a/d ratios exceed 2.5 (both normal and high strength concrete beams), ACI 318, TS500 and proposed equations give similar COV value.     

Load transportation by dual arm robot using sliding mode control

In this study, a sliding mode controlled dual arm robotic system was designed. Such multi-arm, collaborative and synchronous robots typically are employed in hazardous situations such as radioactive materials transport explosives disposal and industrial applications. In the present study, a high performance, robust, non-chattering sliding mode controller (SMC) was developed for the purpose of safe load handling, transportation and trajectory realization. First, dynamic equations of robot/load interaction were derived. Then, the robust SMC was designed for the dual arm robotic system. In order to test the robustness of the proposed SMC, parameter variations and external disturbances were introduced to the system. Furthermore, for comparative purposes, the conventional and widely used, PID controller was also applied to the dual arm robot. Significantly, it was found that the SMC made smaller trajectory tracking errors than the PID controller. An overall analysis of the numerical results confirmed that the dual-arm robotic systems with the proposed SMC can safely and effectively be used in hazardous applications.     

An evaluation of the alternative transport fuel policies for Turkey

The search for alternative fuels and new fuel resources is a top priority for Turkey, as is the case in the majority of countries throughout the world. The fuel policies pursued by governmental or civil authorities are of key importance in the success of alternative fuel use, especially for widespread and efficient use. Following the 1973 petroleum crisis, many users in Turkey, especially in transportation sector, searched for alternative fuels and forms of transportation. Gasoline engines were replaced with diesel engines between the mid-1970s and mid-1980s. In addition, natural gas was introduced to the Turkish market for heating in the early 1990s. Liquid petroleum gas was put into use in the mid-1990s, and bio-diesel was introduced into the market for transportation in 2003. However, after long periods of indifference governmental action, guidance and fuel policies were so weak that they did not make sense. Entrepreneurs and users experienced great economical losses and lost confidence in future attempts to search for other possible alternatives. In the present study, we will look at the history of alternative fuel use in the recent past and investigate the alternative engine fuel potential of Turkey, as well as introduce possible future policies based on experience.     

Technoeconomic analysis of electricity generation from wind energy in Kutahya,Turkey

Conventional energy usage has various environmental effects that cause global warming. Renewable energy sources are thus more favorable because they have nearly zero emission. Wind energy, among the various renewable sources, finds increasing usage, concurrent with developing technology. In addition, wind is an infinite energy source. In this study, the electricity-generation ability of Kutahya has been investigated. With this aim, wind data, from the measurement station located on Bunelek Hill, Kutahya, have been collected for a period of 36 months (July 2001–June 2004). From the collected data, the electricity generated has been calculated for different types of wind turbines. The calculations have been based on the electricity requirement of the main campus of the Dumlupinar University. Finally, the economic evaluation has been analyzed using life-cycle cost analysis. For the analysis of the economical aspects, the social and CO₂ costs have also been taken into account.     

Electro-Optics and Band Gap Energies of Nanosilver-Coated TiO_2 Nanotubes on Titanium Metal

TiO_2 nanotubes on Ti metal surface were prepared by the electrochemical anodization method. Then, nanosilver was deposited onto the nanotubes by the electroless dip coating and the anodization. The obtained TiO2 nanotubes were examined by using scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, cyclic voltammetry, and UV–Vis. The electrochemical band gap(E_g~(CV)) of the nanosilver-coated TiO_2 nanotubes prepared by the anodization was found as 1.54 eV. Using the UV–Vis measurements, the optical band gap energy(E_g~(op).) was calculated as 1.51 eV for the Ag/TiO_2 nanotubes obtained by electroless dip coating. The electrical conductivity of the TiO_2 nanotubes also increased from 3.0 9 10-4 to 34.7 S/cm after nano Ag deposition by the anodization method.These Ag/TiO_2 nanotubes with low band gap and high electrical conductivity are desirable for the applications in electronics, Li-ion batteries, and solar cells.