614 research outputs found
On high-speed turning of a third-generation gamma titanium aluminide
Gamma titanium aluminides are heat-resistant intermetallic alloys predestined to be employed in components suffering from high mechanical stresses and thermal loads. These materials are regarded as difficult to cut, so this makes process adaptation essential in order to obtain high-quality and defect-free surfaces suitable for aerospace and automotive parts. In this paper, an innovative approach for longitudinal external high-speed turning of a third-generation Ti-45Al-8Nb- 0.2C-0.2B gamma titanium aluminide is presented. The experimental campaign has been executed with different process parameters, tool geometries and lubrication conditions. The results are discussed in terms of surface roughness/integrity, chip morphology, cutting forces and tool wear. Experimental evidence showed that, due to the high cutting speed, the high temperatures reached in the shear zone improve chip formation, so a crack-free surface can be obtained. Furthermore, the use of a cryogenic lubrication system has been identified in order to reduce the huge tool wear, which represents the main drawback when machining gamma titanium aluminides under the chosen process condition
Polyelectrolyte Adsorption
The problem of charged polymer chains (polyelectrolytes) as they adsorb on a
planar surface is addressed theoretically. We review the basic mechanisms and
theory underlying polyelectrolyte adsorption on a single surface in two
situations: adsorption of a single charged chain, and adsorption from a bulk
solution in solvent conditions. The behavior of flexible and
semi-rigid chains is discussed separately and is expressed as function of the
polymer and surface charges, ionic strength of the solution and polymer bulk
concentration. We mainly review mean-field results and briefly comment about
fluctuation effects. The phenomenon of polyelectrolyte adsorption on a planar
surface as presented here is of relevance to the stabilization of colloidal
suspensions. In this respect we also mention calculations of the inter-plate
force between two planar surfaces in presence of polyelectrolyte. Finally, we
comment on the problem of charge overcompensation and its implication to
multi-layers formation of alternating positive and negative polyelectrolytes on
planar surfaces and colloidal particles.Comment: 11 pages, 4 PS figures (Latex/RevTex), submitted to C.R. Acad. Sci
(Paris
Advanced prevention against icing on high voltage power lines
Historical meteorological data indicates, that our weather is becoming more and more extreme. For the
electrical utility operators (Distribution System Operators - DSOs and Transmission System Operators -
TSOs), these changes arise in new operation challenges that need to be addressed. For example, frequent icing
phenomenon affects all the components of the power line by a significant mechanical overload: it endangers
the conductors, the insulators and the towers, as well. The result is often fatal and beside serious failures, it
effects on operators’ decisions. These not only endanger the reliability of electrical grids by the loss of a power
line for weeks or even months, but in general, the safety in the surroundings of the power line. As technology
advances, we will be able to collected, analyses and predict very large databases in the field of meteorology
and electrical engineering. The ability of processing mentioned data, combined with know-how results in the
capacity to operate power lines at their thermal limits during different ambient parameters. This technology
called Dynamic Line Rating (DLR) – is not only a great way to increase the transmission capacity of a given
line, but can also be effectively used to prevent, or even solve icing-related issues. Higher currents result in
higher Joule-heats, that consequently heat the conductors. If limits can be reached or approached, icing can be
prevented. If prevention is not possible, detection and removal of ice layer is necessary. The proper handling
of this icing issues, requires advanced algorithms (expert systems) and reliable measuring equipment. The
combination and synchronization between algorithms, weather service and measuring equipment is the key of
the successful operation. An EU H2020 financed project called FLEXITRANSTORE has just been launched
to develop a cross-country co-operation, with objective to improve anti-icing and de-icing solutions. To
establish and analyse different solutions, the project includes several universities, TSOs and DSOs. To solve
mentioned icing issues Budapest University of Technology and Economics’ (BME) developed an advanced
neural-network based algorithm which use OTLM system. It is planned to install and demonstrate the
capabilities of this new technology on the DSOs grid (Electro Ljubljana - ELJ). Besides the introduction of
DLR and icing, this paper also focuses on the preparation/organisation of co-operation between different
companies and universities
Accelerated hot-carrier cooling in MAPbI3 perovskite by pressure-induced lattice compression
Hot-carrier cooling (HCC) in metal halide perovskites in the high-density
regime is significantly slower compared to conventional semiconductors. This
effect is commonly attributed to a hot-phonon bottleneck but the influence of
the lattice properties on the HCC behaviour is poorly understood. Using
pressure-dependent transient absorption spectroscopy (fs-TAS) we find that at
an excitation density below Mott transition, pressure does not affect the HCC.
On the contrary, above Mott transition, HCC in methylammonium lead iodide
(MAPbI3) is around two times as fast at 0.3 GPa compared to ambient pressure.
Our electron-phonon coupling calculations reveal about two times stronger
electron-phonon coupling for the inorganic cage mode at 0.3 GPa. However, our
experiments reveal that pressure promotes faster HCC only above Mott
transition. Altogether, these findings suggest a change in the nature of
excited carriers in the high-density regime, providing insights on the
electronic behavior of devices operating at such high charge-carrier density
Supercritical phase inversion of starch-poly(e-caprolactone) for tissue engineering applications
In this work, a starch-based polymer, namely a blend of starch-poly(ε-caprolactone) was processed by supercritical assisted phase inversion process. This processing technique has been proposed for the development of 3D structures with potential applications in tissue engineering applications, as scaffolds. The use of carbon dioxide as non-solvent in the phase inversion process leads to the formation of a porous and interconnected structure, dry and free of any residual solvent. Different processing conditions such as pressure (from 80 up to 150 bar) and temperature (45 and 55°C) were studied and the effect on the morphological features of the scaffolds was evaluated by scanning electron microscopy and micro-computed tomography. The mechanical properties of the SPCL scaffolds prepared were also studied. Additionally, in this work, the in vitro biological performance of the scaffolds was studied. Cell adhesion and morphology, viability and proliferation was assessed and the results suggest that the materials prepared are allow cell attachment and promote cell proliferation having thus potential to be used in some for biomedical applications.Ana Rita C. Duarte is grateful for financial support from Fundacao para a Ciencia e Tecnologia through the grant SFRH/BPD/34994/2007
Supercritical fluid technology as a tool to prepare gradient multifunctional architectures towards regeneration of osteochondral injuries
Platelet lysates (PLs) are a natural source of growth factors (GFs) known for its stimulatory role on stem cells which can be obtained after activation of platelets from blood plasma. The possibility to use PLs as growth factor source for tissue healing and regeneration has been pursued following different strategies. Platelet lysates are an enriched pool of growth factors which can be used as either a GFs source or as a three-dimensional (3D) hydrogel. However, most of current PLs-based hydrogels lack stability, exhibiting significant shrinking behavior. This chapter focuses on the application of supercritical fluid technology to develop three-dimensional architectures of PL constructs, crosslinked with genipin. The proposed technology allows in a single step operation the development of mechanically stable porous structures, through chemical crosslinking of the growth factors present in the PL pool, followed by supercritical drying of the samples. Furthermore gradient structures of PL-based structures with bioactive glass are also presented and are described as an interesting approach to the treatment of osteochondral defects.info:eu-repo/semantics/publishedVersio
The effects of the neonicotinoid imiacloprid on gene expression and DNA methylation in the buff-tailed bumblebee Bombus terrestris
Neonicotinoids are effective insecticides used on many important arable and horticultural crops. They are nicotinic acetylcholine receptor agonists which disrupt the function of insect neurons and cause paralysis and death. In addition to direct mortality, there are numerous sublethal effects of low doses of neonicotinoids on bees. We hypothesize that some of these large array of effects could be a consequence of epigenetic changes in bees induced by neonicotinoids. We compared whole methylome (BS-seq) and RNA-seq libraries of the brains of buff-tailed bumblebee Bombus terrestris workers exposed to field-realistic doses of the neonicotinoid imidacloprid to libraries from control workers. We found numerous genes which show differential expression between neonicotinoid-treated bees and control bees, but no differentially methylated cytosines in any context. We found CpG methylation to be focused mainly in exons and associated with highly expressed genes. We discuss the implications of our results for future legislation
The host metabolite D-serine contributes to bacterial niche specificity through gene selection
Escherichia coli comprise a diverse array of both commensals and niche-specific pathotypes. The ability to cause disease results from both carriage of specific virulence factors and regulatory control of these via environmental stimuli. Moreover, host metabolites further refine the response of bacteria to their environment and can dramatically affect the outcome of the host–pathogen interaction. Here, we demonstrate that the host metabolite, D-serine, selectively affects gene expression in E. coli O157:H7. Transcriptomic profiling showed exposure to D-serine results in activation of the SOS response and suppresses expression of the Type 3 Secretion System (T3SS) used to attach to host cells. We also show that concurrent carriage of both the D-serine tolerance locus (dsdCXA) and the locus of enterocyte effacement pathogenicity island encoding a T3SS is extremely rare, a genotype that we attribute to an ‘evolutionary incompatibility’ between the two loci. This study demonstrates the importance of co-operation between both core and pathogenic genetic elements in defining niche specificity
Estimation of changes in the force of infection for intestinal and urogenital schistosomiasis in countries with Schistosomiasis Control Initiative-assisted programmes
The last decade has seen an expansion of national schistosomiasis control programmes in Africa based on large-scale preventative chemotherapy. In many areas this has resulted in considerable reductions in infection and morbidity levels in treated individuals. In this paper, we quantify changes in the force of infection (FOI), defined here as the per (human) host parasite establishment rate, to ascertain the impact on transmission of some of these programmes under the umbrella of the Schistosomiasis Control Initiative (SCI)
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