Mechanical behaviour with temperatures of aluminum matrix composites with CNTs

Aluminum is a very useful structural metal employed in different industrial sectors, in particular it is used in large quantities in automotive, aeronautic and nautical industries. The main reasons of its wide use are: a very good oxidation resistance, excellent ductility, low melting temperature (660 °C) and low density (2.71 g/cm3). However, in order to reduce the emissions and fuel consumption is necessary to reduce the overall weight of vehicles by increasing mechanical properties of the structural material. The improvement of mechanical properties is normally achieved through use of reinforcement in materials, used like matrix, in order to improve some specific characteristics. In this work composites of carbon nanotubes (CNTs) dispersed in aluminum were made. The most difficulties in the preparation of this type of composite are represented by the low wettability between metallic matrix and fillers and the possibility of the oxidation of metal during melting with consequent decreasing of mechanical proprieties. The composite was obtained by three consecutive step: the first one is the functionalization of fillers surface to improve the fillers dispersion, the second one is the dispersion of fillers in the matrix by powder mixing and the third one is the melting and casting of the mix prepared. In particular, fillers used are multi walled carbon nanotubes (MWCNTs) with functionalized surface by treatment with a solfonitric solution. Melting and casting are carried out with the aid of an induction furnace with a controlled atmosphere system and centrifugal casting. Argon is the inert gas used to prevent the oxidation of aluminium during fusion. Young’s modulus was evaluated at different temperature and correlated with the different CNTs percentage. The dispersion rate of fillers and the microstructure of the sample were evaluated by FESEM micrograph

An analytic strategy for data processing of multimode networks

Complex network data structures are considered to capture the richness of social phenomena and real-life data settings. Multipartite networks are an example in which various scenarios are represented by different types of relations, actors, or modes. Within this context, the present contribution aims at discussing an analytic strategy for simplifying multipartite networks in which different sets of nodes are linked. By considering the connection of multimode networks and hypergraphs as theoretical concepts, a three-step procedure is introduced to simplify, normalize, and filter network data structures. Thus, a model-based approach is introduced for derived bipartite weighted networks in order to extract statistically significant links. The usefulness of the strategy is demonstrated in handling two application fields, that is, intranational student mobility in higher education and research collaboration in European framework programs. Finally, both examples are explored using community detection algorithms to determine the presence of groups by mixing up different modes

SERS of cells: What can we learn from cell lysates?

Surface-enhanced Raman spectroscopy (SERS) is a promising and emerging technique to analyze the cellular environment. We developed an alternative, rapid and label-free SERS-based method to get information about the cellular environment by analyzing cells lysates, thus avoiding the need to incorporate nanoparticles into cells. Upon sonicating and filtrating cells, we obtained lysates which, mixed with Au or Ag nanoparticles, yield stable and repeatable SERS spectra, whose overall profile depends on the metal used as substrate, but not on the buffer used for the lysis process. Bands appearing in these spectra were shown to arise mostly from the cytosol and were assigned to adenine, guanine, adenosine and reduced glutathione (GSH). Spectral differences among various cell types also demonstrated that this approach is suitable for cell type identification

Thermochemical characterization of polybenzimidazole with and without nano-ZrO2 for ablative materials application

During the ballistic atmospheric re-entry, a space vehicle has to withstand huge thermo-mechanical solicitations because of its high velocity and the friction with the atmosphere. According to the kind of the re-entry mission, the heat fluxes can be very high (in the order of some MW m−2) ;thus, an adequate thermal protection system is mandatory in order to preserve the structure of the vehicle, the payload and, for manned mission, the crew. Carbon phenolic ablators have been chosen for several missions because they are able to dissipate the incident heat flux very efficiently. Phenolic resin presents satisfying performance but also environmental drawbacks. Thus, a more environmental-friendly solution was conceived: a high-performance thermoplastic material, polybenzimidazole (PBI), was employed instead of phenolic resin. In this work PBI-ablative material samples were manufactured with and without the addition of nano-ZrO2 and tested with an oxyacetylene flame. For comparison, some carbon-phenolic ablators with the same density were manufactured and tested too. Thermogravimetric analysis on PBI samples was carried out at different heating rates, and the obtained TG data were elaborated to evaluate the activation energy of PBI and nano-filled PBI. The thermokinetics results for PBI show an improvement in thermal stability due to the addition of nano-ZrO2, while the oxyacetylene flame test enlightens how PBI ablators are able to overcome the carbon phenolic ablators performance, in particular when modified by the addition of nano-ZrO2

Sulfate geoengineering impact on methane transport and lifetime: results from the Geoengineering Model Intercomparison Project (GeoMIP)

Abstract. Sulfate geoengineering (SG), made by sustained injection of SO2 in the tropical lower stratosphere, may impact the CH4 abundance through several photochemical mechanisms affecting tropospheric OH and hence the methane lifetime. (a) The reflection of incoming solar radiation increases the planetary albedo and cools the surface, with a tropospheric H2O decrease. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O(1D). (c) The extratropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-to-upper troposphere, thus reducing the amount of NOx and O3 production. (d) The tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rate perturbation is highly latitude dependent, producing a stronger meridional component of the Brewer–Dobson circulation. The net effect on tropospheric OH due to the enhanced stratosphere–troposphere exchange may be positive or negative depending on the net result of different superimposed species perturbations (CH4, NOy, O3, SO4) in the extratropical upper troposphere and lower stratosphere (UTLS). In addition, the atmospheric stabilization resulting from the tropospheric cooling and lower stratospheric warming favors an additional decrease of the UTLS extratropical CH4 by lowering the horizontal eddy mixing. Two climate–chemistry coupled models are used to explore the above radiative, chemical and dynamical mechanisms affecting CH4 transport and lifetime (ULAQ-CCM and GEOSCCM). The CH4 lifetime may become significantly longer (by approximately 16 %) with a sustained injection of 8 Tg-SO2 yr−1 starting in the year 2020, which implies an increase of tropospheric CH4 (200 ppbv) and a positive indirect radiative forcing of sulfate geoengineering due to CH4 changes (+0.10 W m−2 in the 2040–2049 decade and +0.15 W m−2 in the 2060–2069 decade)

Shared and Distinctive Ultrastructural Abnormalities Expressed by Megakaryocytes in Bone Marrow and Spleen From Patients With Myelofibrosis

Numerous studies have documented ultrastructural abnormalities in malignant megakaryocytes from bone marrow (BM) of myelofibrosis patients but the morphology of these cells in spleen, an important extramedullary site in this disease, was not investigated as yet. By transmission-electron microscopy, we compared the ultrastructural features of megakaryocytes from BM and spleen of myelofibrosis patients and healthy controls. The number of megakaryocytes was markedly increased in both BM and spleen. However, while most of BM megakaryocytes are immature, those from spleen appear mature with well-developed demarcation membrane systems (DMS) and platelet territories and are surrounded by platelets. In BM megakaryocytes, paucity of DMS is associated with plasma (thick with protrusions) and nuclear (dilated with large pores) membrane abnormalities and presence of numerous glycosomes, suggesting a skewed metabolism toward insoluble polyglucosan accumulation. By contrast, the membranes of the megakaryocytes from the spleen were normal but these cells show mitochondria with reduced crests, suggesting deficient aerobic energy-metabolism. These distinctive morphological features suggest that malignant megakaryocytes from BM and spleen express distinctive metabolic impairments that may play different roles in the pathogenesis of myelofibrosis

Detection of antihydrogen annihilations with a Si-micro-strip and pure CsI detector

In 2002, the ATHENA collaboration reported the creation and detection of cold (~15 K) antihydrogen atoms [1]. The observation was based on the complete reconstruction of antihydrogen annihilations, simultaneous and spatially correlated annihilations of an antiproton and a positron. Annihilation byproducts are measured with a cylindrically symmetric detector system consisting of two layers of double sided Si-micro-strip modules that are surrounded by 16 rows of 12 pure CsI crystals (13 x 17.5 x 17 mm^3). This paper gives a brief overview of the experiment, the detector system, and event reconstruction. Reference 1. M. Amoretti et al., Nature 419, 456 (2002).Comment: 7 pages, 5 figures; Proceedings for the 8th ICATPP Conference on Astroparticle, Particle, Space Physics, Detectors and Medical Physics Applications (Como, Italy October 2003) to be published by World Scientific (style file included

Evidence For The Production Of Slow Antiprotonic Hydrogen In Vacuum

We present evidence showing how antiprotonic hydrogen, the quasistable antiproton-proton (pbar-p) bound system, has been synthesized following the interaction of antiprotons with the hydrogen molecular ion (H2+) in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events, evidence is presented for antiprotonic hydrogen production with sub-eV kinetic energies in states around n=70, and with low angular momenta. The slow antiprotonic hydrogen may be studied using laser spectroscopic techniques.Comment: 5 pages with 4 figures. Published as Phys. Rev. Letters 97, 153401 (2006), in slightly different for

Positron plasma diagnostics and temperature control for antihydrogen production

Production of antihydrogen atoms by mixing antiprotons with a cold, confined, positron plasma depends critically on parameters such as the plasma density and temperature. We discuss non-destructive measurements, based on a novel, real-time analysis of excited, low-order plasma modes, that provide comprehensive characterization of the positron plasma in the ATHENA antihydrogen apparatus. The plasma length, radius, density, and total particle number are obtained. Measurement and control of plasma temperature variations, and the application to antihydrogen production experiments are discussed.Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let