Design and Testing of a Robotic System for mr Image-guided Interventions

The effective integration of robotics together with magnetic resonance (mr) technology is expected to facilitate the real-time guidance of various diagnostic and therapeutic interventions. Specially designed robotic manipulators are required for this purpose, the development of which is a challenging task given the strong magnetic fields and the space limitations that characterize the mr scanning environment. A prototype mr-compatible manipulator is presented, designed to operate inside cylindrical mr scanners. It was developed for the study of minimally invasive diagnostic and therapeutic interventions in the abdominal and thoracic area with real-time mr image guidance. Initial tests were performed inside a high-field clinical mr scanner and included mr-compatibility tests and phantom studies on image-guided targeting.     

Storage of hydrogen in nanostructured carbon materials

Recent developments focusing on novel hydrogen storage media have helped to benchmark nanostructured carbon materials as one of the ongoing strategic research areas in science and technology. In particular, certain microporous carbon powders, carbon nanomaterials, and specifically carbon nanotubes stand to deliver unparalleled performance as the next generation of base materials for storing hydrogen. Accordingly, the main goal of this report is to overview the challenges, distinguishing traits, and apparent contradictions of carbon-based hydrogen storage technologies and to emphasize recently developed nanostructured carbon materials that show potential to store hydrogen by physisorption and/or chemisorption mechanisms. Specifically touched upon are newer material preparation methods as well as experimental and theoretical attempts to elucidate, improve or predict hydrogen storage capacities, sorption–desorption kinetics, microscopic uptake mechanisms and temperature–pressure–loading interrelations in nanostructured carbons, particularly microporous powders and carbon nanotubes.     

Microstructure effects in braze joints formed between Ag/W electrical contacts and Sn-coated Cu using Cu–Ag–P filler metal

Braze joints have been formed between Ag/W electrical contact tips and Sn-coated Cu straps using a Cu–Ag–P-based filler metal by short-cycle direct conductive heating from the Cu strap side. The microstructures of the braze joints have been investigated using a combination of scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, focused ion beam milling, and transmission electron microscopy. The braze joints exhibit regions with two distinct types of microstructures. Type I microstructures contain three micro-constituents: FCC (Ag), FCC (Cu), and a ternary eutectic [(Ag) + (Cu) + Cu₃P]. The difference between the proportions of these phases and those in the baseline filler metal can be accounted for on the basis of P loss due to self-fluxing during the brazing process. Type II microstructures contain mostly (Ag) and (Cu) with a small amount of Cu₃P but no ternary eutectic mixture. Other differences from the Type I regions include a lower P content, incomplete dispersion of the Sn layer, and a refined grain size in the majority (Cu) phase. These effects are accounted for on the basis of local differences in interfacial pressure due to the geometry of the Ag/W contact surface.     

Synthesis and characterization of polypropiolate sodium (PPNa)-Fe3O4 nanocomposite

Polypropiolate sodium (PPNa)-Fe₃O₄ nanocomposites were successfully synthesized by the precipitation of Fe₃O₄ in the presence of sodium polypropiolate and followed by reflux route. Structural, morphological, electrical and magnetic properties evaluation of the nanocomposite were performed by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), vibrating scanning magnetometry (VSM) and conductivity measurements. Crystalline phase was identified as magnetite with an average crystallite size of 7 ± 3 nm as estimated from X-ray line profile fitting. Particle size estimated from TEM, by log-normal fitting, is ∼9 ± 1 nm. FT-IR analysis shows that the binding of PPNa on the surface of iron oxide is through bidentate linkage of carboxyl group. TGA analysis showed the presence of 20% PPNa around 80% magnetic core (Fe₃O₄)…PPNa-Fe₃O₄ nanocomposite show superparamagnetic characteristics at room temperature. It is found that the a.c. conductivity of the nanocomposites obeys the well-known power law of frequency in which it also depends on temperature. Additionally, its d.c. conductivity showed that two operating regions of the activation energy. Both real and imaginary parts of either permittivity exhibit almost the same attitudes which are the indication of the same ability in the stored energy, and dissipation of energy within the PPNa and PPNa-Fe₃O₄ nanocomposites.     

Modulus of elasticity of substandard and normal concretes

Modulus of elasticity is an important parameter used for the structural assessment and retrofitting of concrete structures. In this study, an experimental investigation on the modulus of elasticity of concrete was carried out, the results of which is presented. 60 mixtures were prepared, in which the effects of water/cement ratio, maximum size of the aggregate, aggregate type, and fly ash content were investigated. In order to obtain very low quality concrete, the water/cement ratios were increased to as high as 2.2. Modulus of elasticity of the concretes was obtained according to ASTM C469. Compressive strength and ultrasound pulse velocities of the concretes were also recorded. The experimentally obtained modulus of elasticity values were compared with those calculated by using prediction models given in a selection of codes of practice. Dynamic moduli of elasticity of the concretes were also obtained.     

Catalytic combustion of carbon tetrachloride

The catalytic combustion of carbon tetrachloride (CCl4) by metal oxide catalysts coated on the monolith support was investigated. The prepared catalysts were tested at temperatures between 300 and 800 degrees C and at varying gas hourly space velocity (GHSV) values with an excess air ratio of 3100%. The catalyst, whose composition was 18% Cr2O3, 2% Ce2O3 and 80% gamma-Al2O3, was found to almost completely oxidize CCl4. The operating conditions proposed are 5702 h(-1) for GHSV, 3100% excess air and a temperature slightly higher than 800 degrees C. The reaction rate expression was found to be independent of oxygen partial pressure but strongly dependent on CCl4 partial pressure.     

Bailout forward contracts for edge-to-edge internet services

Despite the huge success of the Internet in providing basic communication services, its economic architecture needs to be upgraded so as to provide end-to-end guaranteed or more reliable services to its customers. Currently, a user or an enterprise that needs end-to-end bandwidth guarantees between two arbitrary points in the Internet for a short period of time has no way of expressing its needs. To allow these much needed basic services, we propose a single-domain edge-to-edge (g2g) dynamic capacity contracting mechanism, where a network customer can enter into a bandwidth contract on a g2g path at a future time, at a predetermined price. For practical and economic viability, such forward contracts must involve a bailout option to account for bandwidth becoming unavailable at service delivery time, and must be priced appropriately to enable Internet Service Providers (ISPs) manage risks in their contracting and investments. Our design allows ISPs to advertise point-to-point different prices for each of their g2g paths instead of the current point-to-anywhere prices, allowing discovery of better end-to-end paths, temporal flexibility and efficiency of bandwidth usage. We compute the risk-neutral prices for these g2g bailout forward contracts (BFCs), taking into account correlations between different contracts due to correlated demand patterns and overlapping paths. We apply this multiple g2g BFC framework on network models with Rocketfuel topologies. We evaluate our contracting mechanism in terms of key network performance metrics like fraction of bailouts, revenue earned by the provider, and adaptability to link failures. We also explore the tradeoffs between complexity of pricing and performance benefits of our BFC mechanism.     

Electrical and tribological properties of a Ni–18%Ru alloy for contact applications

A study of the microstructure, development of contact resistance during oxidation, and abrasive wear behavior for a Ni–18 at.%Ru alloy is presented in this article. It is shown that the alloy can be solutionized and aged, resulting in a fine lamellar mixture of FCC α-Ni and HCP β-Ru phases. Upon oxidation in air for 400 h, the measured contact resistance of the alloy is two orders of magnitude lower than that of pure Ni after 400-h oxidation. This behavior results from the formation of a low-resistivity rutile RuO₂ scale on the β phase lamellae, which gives conducting pathways through the insulating NiO scale that forms on the α phase. After an initial run-in period, the steady-state abrasive wear rate measured for the Ni–Ru alloy is an order of magnitude less than that of pure Ni. Since the micro-cutting and flaking wear mechanisms are the same, the differences in the wear rates are ascribed to the presence of the well-dispersed hard Ru-rich β phase. The combination of a low-resistivity self-healing native oxide scale and good wear properties makes the alloy an excellent candidate for electrical contact applications.     

A production insensitive compact power divider

Power dividers are inevitable components in most microwave systems. Well known topologies like Wilkinson power divider are widely studied in the literature. An “all 50 ohm power divider” is another topology presented in the some works. In this study, an all 50 ohm structure is taken as the basis and a compact-easy to implement modification the power divider is proposed. A sample structure is designed, implemented and measured to prove the topology. The decreased sensitivity to production tolerances is demonstrated by various design modifications. Comparisons with well-known topologies are given for reference.