Effect of stress state on the high temperature workability of AZ31 Mg alloy

The influence of stress state on the high temperature workability of rolled AZ31 Mg alloy was investigated on the basis of a processing map. To construct the processing map, high temperature compression tests were carried out on samples oriented parallel to the rolling direction at various temperatures (25 °C∼450 °C) and strain rates (10⁻³ s⁻¹∼5s⁻¹), and then the results were compared with those of a torsion test. The overall efficiency profiles of both the compression and torsion processing maps were similar to each other, but the index of dissipation efficiency in the torsion was somewhat lower than that in the compression. The microstructure of the compressed specimens revealed much finer grained structure than that of the torsion specimens. Such microstructural differences were attributed to the different tendencies of twin formation and texture evolution depending on the stress state.     

A spectro-microscopic investigation of Fe-Co bimetallic catalysts supported on MgO for the production of thin carbon nanotubes

Fe-Co bimetallic catalysts supported on MgO were studied for the catalytic chemical vapor deposition growth of carbon nanotubes (CNTs). Different wt.% metal loadings were investigated at various deposition temperatures and times. Characterization of the products involved thermal analysis (DTA-TGA), X-ray diffraction, spectroscopy (Raman, UPS, EELS and STS) and microscopy (SEM, TEM and STM) techniques. It was found that the metal content is critical, not only to the yield and the structural quality of the synthesized carbon nanotubes, but it can be also used to tune the desired type of synthesized nanotubes. Lower (2 wt.%) loadings of Fe-Co catalysts favor the formation of single- and/or double-wall CNTs for deposition time and temperature 30 min and 800 °C, respectively. Thermal analysis and Raman measurements showed that these thin CNTs were synthesized at high amounts (CNT-per-catalyst wt.% of more than 100%), exhibiting high graphitization degree with only traces of by-products (mainly amorphous carbon) among them. Microscopy results revealed the formation of CNTs bundles, consisting of individual nanotubes with less than 2 nm outer diameter, while additional energy loss measurements pointed out that the deposited CNTs are mainly single wall. Higher (10 wt.%) Fe-Co loadings resulted to the formation of multi-wall CNTs.     

Friction stir welding between extrusions and laminates

Current market demands drive companies to innovate their production techniques to improve products and simultaneously hold down costs. In the search for solutions aimed at an optimization of production processes, semi-finished products in aluminium alloys very definitely play a significant role. Moreover, the assembly of extruded parts with laminates may result in considerable difficulties, especially in relation to distortions or generated residual stress and process productivity. A solution to these issues may be found in the application of friction stir welding (FSW), characterized by low thermal input and high productivity. The asymmetry of the FSW process determines a different thermal input to the edges of the pieces to be joined. This aspect can be exploited when it is necessary to join pieces characterized by a very different thermal lag, as occurs in the case of joining extruded products and sheeting. This study aims to identify optimal FW parameters, placing particular attention on heat transferred to materials so as to provide an adequate thermal input that will allow for compensation of the different thermal capacity of the pieces in question.     

Shell-and-Tube Minichannel Condenser for Low Refrigerant Charge

The design of an innovative shell-and-tube heat pump condenser using 2 mm ID minichannels is presented. This condenser has been designed aiming at the minimization of the charge, which can be required by safety or environmental restrictions. Nevertheless, minichannels represent also a solution to the high-pressure challenge when using carbon dioxide as a refrigerant. The present prototype was realized for the use with propane in the framework of the European project SHERHPA, concerning the development of heat pumps working with natural fluids. Experimental data for heat transfer and pressure drop are reported in the present paper. The measurements have been obtained using refrigerant R22, which displays a temperature versus pressure saturation curve pretty close to the one of propane. The data have also been compared against a computational procedure for shell-and-tube heat exchangers design. The refrigerant charge has been computed by means of different void fraction correlations, showing that the expected charge is less than half the quantity required by a brazed plate condenser giving the same capacity.     

A reproducing kernel hilbert space approach for q-ball imaging

Diffusion magnetic resonance (MR) imaging has enabled us to reveal the white matter geometry in the living human brain. The Q-ball technique is widely used nowadays to recover the orientational heterogeneity of the intra-voxel fiber architecture. This article proposes to employ the Funk-Radon transform in a Hilbert space with a reproducing kernel derived from the spherical Laplace-Beltrami operator, thus generalizing previous approaches that assume a bandlimited diffusion signal. The function estimation problem is solved within a Tikhonov regularization framework, while a Gaussian process model allows for the selection of the smoothing parameter and the specification of confidence bands. Shortcomings of Q-ball imaging are discussed.     

New inorganic–organic proton conducting membranes based on Nafion and [(ZrO2)·(SiO2)0.67] nanoparticles: Synthesis vibrational studies and conductivity

In this report is described the preparation of six nanocomposite membranes of formula {Nafion/_[(ZrO_2)⋅(SiO_2)0.67]ΨZrO₂}$\{\text{Nafion}/{[(\text{Zr}{\text{O}}_2)\cdot {(\text{Si}{\text{O}}_2)}_{0.67}]}_{{\Psi }_{\text{Zr}{\text{O}}_2}}\}$ with ΨZrO₂${\Psi }_{\text{Zr}{\text{O}}_2}$ ranging from 0 to 1.79 based on Nafion^® and [(ZrO₂)·(SiO₂)_0.67] nanofiller. Morphology investigations carried out by SEM measurements indicate that the composition of membranes is asymmetric. Indeed, with respect to the direction of the films after casting procedure, the top side (A-side) and bottom side (B-side) present a different nanofiller concentration. The concentration of nanofiller increases gradually from A to B side. The membranes present thicknesses ranging from 170 to 350 nm and are studied by FT-IR ATR and micro-Raman measurements.     

The territorial and landscape impacts of photovoltaic systems: Definition of impacts and assessment of the glare risk

The installation and operation of systems that exploit solar energy through photovoltaic conversion, recently promoted in some European countries by new sell-back tariffs, is a relevant transformation of the territory for various reasons (land use, elimination of the existing vegetation, visual impact on the components of the landscape, microclimate change, glare from the reflection of the direct sunlight). The weak energy intensity of the solar source coupled with the low conversion efficiency of the photovoltaic cells, make the physical dimensions of such systems relevant and, with them, also the environmental, territorial and landscape impacts that basically depend on the physical extent of the system. If it is well known that an incentive to the exploitation of renewable sources is one of the features of the policy of land conservation, including the one of the protected areas, at the same time the concerns of local communities and governments about the environmental, territorial and landscape impacts of this technology are increasing rapidly.Given this picture, this work is intended to clarify the territorial impacts of the ground mounted photovoltaic systems. Later, the paper concentrates on a specific impact, which is the assessment of the risk of glare by reflection of direct sunlight from the surfaces of photovoltaic modules. The methodologies that can be used to assess this impact and the outcomes of an evaluation carried out for a 5000 m² PV system currently designed on a hilly territory in Italy are presented.     

Higher Alcohol Synthesis

It has been known for many years that it is possible to produce mixtures of methanol and higher alcohols from synthesis gas by alkali promotion of the methanol synthesis catalysts and by appropriate modification of the reaction conditions [l]. From 1927 to 1945 plants were in operation in the United States and Germany, that were dismantled with the coming of different feedstocks and the necessity of obtaining pure alcohols for chemical use. In the last decade the chemical and petroleum industry has shown a renewed and growing interest in the use of mixtures of methanol and higher aliphatic alcohols. The original goal in the late '70s was mainly to reduce oil dependence by producing synthetic components for gasoline blends. More recently the trend to lead phase-down due to environmental protection has focused the attention on the product performances of such alcohol mixtures as high octane blending stock for gasoline. It has been shown that the addition of higher alcohols to methanol increases the water tolerance in respect to phase separation, reduces the fuel volatility and the vapor lock tendency, and also results in higher volumetric heating values.